MEMCAL

Gift of the

Panama-Pac if ic Internat
exposition Company

MANUAL

OF

CHEMISTRY.

A GUIDE TO LECTURES AND LABORATORY WORK FOR BEGINNERS

IN CHEMISTRY. A TEXT-BOOK SPECIALLY ADAFfED FOR

STUDENTS OF MEDICINE, PHARMACY, AND

DENTISTRY.

BY

W. J>IMON, PH.D., M.D.,

PROFESSOR OF CHEMISTRY IN THE COLLEGE OF PHYSICIANS AND SURGEONS OF BALTIMORE, AND IN

THE BALTIMORE COLLEGE OF DENTAL SURGERY; EMERITUS PROFESSOR IN THE MARYLAND

COLLEGE OF PHARMACY, DEPARTMENT OF THE UNIVERSITY OF MARYLAND.

AND

DANIEL BASE, PH.D.,

PROFESSOR OF CHEMISTRY IN THE MARYLAND COLLEGE OF PHARMACY, DEPARTMENT OF THE
UNIVERSITY OF MARYLAND, AND OF ANALYTICAL CHEMISTRY IN THE DEPART-
MENT OF MEDICINE, UNIVERSITY OF MARYLAND, BALTIMORE.

TENTH EDITION, THOROUGHLY REVISED.

WITH EIGHTY-TWO ILLUSTRATIONS, ONE COLORED SPECTRA PLATE,

AND

EIGHT COLORED PLATES REPRESENTING SIXTY-FOUR CHEMICAL

REACTIONS.

LEA & FEBIGEK,
PHILADELPHIA AND NEW YORK.
1912.

Copyright, 1912, by
LEA & FEBIGER.

Authority to use for comment the Pharmacopoeia of the United States
of America (Eighth Decennial Revision), in this volume, has been granted
by the Board of Trustees of the United States Pharmacopceial Convention ;
which Board of Trustees is in no way responsible for the accuracy of any
translations of the Official Weights and Measures, or for any statement as
to strength of Official Preparations.

555

PREFACE TO THE TENTH EDITION.

IN this new edition the Manual preserves the plan and characteristics
that have won for it the degree of approval shown in the exhaustion of
the nine previous issues, each in several large printings. Numerous
additions have been made, most of which are of fundamental importance,
and again bring the Manual abreast of modern thought in chemistry to
its date of issue. They embrace articles on the following subjects:
Exothermic and endothermic reactions ; reversible reactions and chemical
equilibrium ; mass action ; extension of the articles on acids and bases ;
thermochemistry;* a new chapter on solution, in which, among other
matters, the solution of gases and Henry's law, freezing-points, boiling-
points and osmotic pressure, Raoult's law and the laws of osmotic pres-
sure are discussed, and the existence of ions foreshadowed ; a new chapter
on the theory of electrolytic dissociation, in which are considered the
origin of the theory, ionic equilibrium, ionization of acids, bases, and
salts, reactions on the ionic basis, activity of acids and bases, hydrolysis
of salts, neutralization, electrolysis and Faraday's laws, etc. ; electrolytic
solution tension of metals ; principle of the storage-battery ; and ionic
explanation of the action of indicators. Ionic relations are discussed in
practically every chapter on acids and the metals, and a number of
compounds have been added to the sections on inorganic and organic
chemistry. Many of these are of medical interest, for example, sodium
cacodylate, atoxyl and salvarsan, phenolphthalein, fluorescein, phenol-
sulphonephthalein.

The section on physiological chemistry has been rewritten and brought
in line with present-day knowledge and theories. A table of inter-
national atomic weights on the 'oxygen = 16 basis has been added to
the U. S. P. table of weights on the hydrogen = 1 basis.

It is hoped that with these alterations and additions the Manual will
fully accomplish its object, viz., to furnish to the student in concise form a
clear presentation of the science, an intelligent discussion of those substances
which are of interest to him, and a trustworthy guide to his work in the
laboratory.

As heretofore, the subject has been divided into seven parts, each one
of which contains so much of the matter under consideration as is believed
to be necessary for a fair understanding of the subject. At the same time
care has been taken to place in the foreground all facts and data which
are of direct interest to, the physician, pharmacist, and dentist.

iii

865

'/

iv PREFACE TO THE TENTH EDITION.

In the first part, treating of chemical physics, the student finds a brief
discussion of those physical conditions of matter which have a close rela-
tionship to chemical phenomena, and also of the principles which lead to
an understanding of many of the instruments, such as the spectroscope,
polariscope, etc., which he uses in his chemical operations.

The second part treats of those principles of chemistry which are the
foundation of the science, and enters briefly into a discussion of theoretical
views regarding the constitution of matter. Though the authors prefer
to present these theories to their classes at the proper times during the
course of lectures, they do not deem it desirable to have them scattered
throughout the work, believing it better to assemble them compactly in
print, so that the student may be able to study them after having acquired
some knowledge of chemical phenomena.

The third and fourth parts are devoted to the consideration of the non-
metallic and metallic elements and their compounds. While the periodic
law furnishes a most admirable basis for a scientific classification of ele-
ments, yet their consideration according to a strict adherence to periodicity
does not seem advisable in this book. For this reason the old classifica-
tion of metals and non-metals, organic and inorganic compounds has been
retained, since experience has shown it to be well adapted for the instruc-
tion of beginners in chemistry.

The fifth part is devoted to analytical chemistry and will serve the
student as a guide in his laboratory work. Qualitative methods are
chiefly considered, but a chapter is added giving official methods for
volumetric determinations.

The sixth part treats of organic chemistry. Though it is impossible to
include within the limits of this text-book an extended consideration of a
branch of chemical science so highly developed, yet it is believed that an
intelligent study of this part will familiarize the student with carbon
compounds sufficiently to give him a clear understanding of their general
character, and a knowledge of the bodies which are most important in
medical science.

The seventh and last part gives the principal facts of physiological
chemistry. Special care has been taken also to introduce here the most
modern methods for chemical examination in clinical diagnosis.

The authors will be grateful for any suggestions looking to the im-
provement of the book.

The authors wish to express here their obligations to G. Howard
White, Jr., M. D., by whom the section on physiological chemistry was
rewritten.

W. S.

D. B.

BALTIMORE, 1912.

CONTENTS.

i.

CHEMICAL PHYSICS.

PAGE

1. Fundamental properties of matter.

Matter — Extension — Solid state — Force — Energy — Crystal-
lization— Liquid and gaseous state — Divisibility — Molecular
theory — Gravitation — Weight — Specific weight — Weight of
gases — Barometer — Surface-action — Adhesion — Capillary at-
traction— Absorption — Diffusion — Osmose — Indestructibility 17-42

2. Heat.

Motion of molecules — Latent heat — Sources of heat — Heat
effects — Thermometers — Absolute zero and absolute tempera-
ture— Mechanical equivalent of heat — Specific heat — Conduc-
tion, Convection, and radiation — Melting, boiling, and evapo-
ration 43-55

3. Light.

Light a form of energy — Reflection — Refraction — Prisms —
Dispersion — The spectroscope — Bright line spectra — Absorp-
tion spectra — Double refraction — Polarization — The polari-
scope — Chemical effects of light 56-68

4. Electricity.

Electricity generated by friction — Conductors and non-
conductors— Duality of Electricity — Induction — Electrical
machines — Static electricity — Magnetism — Electricity gener-
ated by chemical action — Galvanic cells — Current electricity
— Electromotive force — Electric units — Electromagnets —
Electricity generated by magnetism — Voltaic induction — In-
duction coil — Conversion of electric energy into heat, light,
and chemical action — Electric furnace — Electric spark —
Cathode ray — Rontgen rays — Radio-activity 69-86

II.
PRINCIPLES OF CHEMISTRY.

5. Element, compound, chemical affinity, modes of effecting

chemical change.

Decomposition by heat — Elements — Compound substances —
Decomposition by electricity, by light, and by mutual action
of substances upon each other — Physical phenomena accom-
panying chemical action — Chemical or internal energy — Ex-
othermic and endothermic actions — Chemical affinity .... 87-93

6. Laws and theories of chemistry.

Law of the constancy of composition — Law of multiple

(v)

vi CONTENTS.

PAGE

proportions — Combining weights of elements — Atomic theory
— Atomic weight — Atoms and molecules — Chemical symbols —
Formulas of compounds — Law of chemical combinations by
volume — Law of equivalents — Valence or quantivalence . . . 93-104

7. Determination of atomic and molecular weights.

Determination of atomic weights by chemical decomposition,
by means of specific weights of gases or vapors, by means of spe-
cific heat — Determination of molecular weights — Raoult's law 105-110

8. Chemical equations. Types of chemical change. Reversible

actions and chemical equilibrium. Mass action.
Acids, bases, neutralization, salts. Radical. Consti-
tutional formulas ..." 110-124

9. General remarks regarding elements.

Relative importance of different elements — Classification of
elements — Metals and non-metals — Natural groups of elements
— MendelejefF's periodic law — Physical properties of elements
— Allotropic modifications — Relationship between elements
and the compounds formed by their union — Nomenclature —
How to study chemistry 124-133

III.
NON-METALS AND THEIR COMBINATIONS.

Symbols, atomic weights, and derivation of names — Occur-
rence in nature — Time of discovery — Valence 135-136

10. Oxygen.

History — Occurrence in nature — Preparation — Physical and
chemical properties — Combustion — Ozone — Thermo-chemistry 137-144

11. Hydrogen. Water. Hydrogen dioxide.

History — Occurrence in nature — Preparation — Properties —
Nascent state — Water — Mineral waters — Drinking-water — Dis-
tilled water — Analysis and synthesis — Explanation of efflor-
escence and deliquescence — Hydrogen dioxide 144-156

12. Solution.

General remarks — Terms employed — Heat of solution — So-
lution of gases — Henry's law — Freezing-points, boiling-points,
and osmotic pressure of solutions — Raoult's law — Laws of os-
motic pressure 157-164

13. Nitrogen.

Occurrence in nature — Preparation — Properties — Atmo-
spheric air — Argon — Helium — Ammonia — Hydrazine— Hy-
droxylamine — Triazoic acid — Compounds of nitrogen and
oxygen — Nitrogen monoxide— Nitric acid ; tests for it ... 164-177

14. Carbon. Silicon. Boron.

Occurrence in nature — Properties — Diamond — Graphite —
Tests for carbon — Carbon dioxide — Carbonic acid — Tests for
carbonic acid — Carbon monoxide — Carbonyl chloride — Com-
pounds of carbon and hydrogen — Flame — Silicon — Silicic acid

CONTENTS. vii

PAGE

— Carborundum — Boron, boric acid; tests for it — Sodium per-
borate 178-189

15. Theory of electrolytic dissociation, or ionization, etc.

Theory of electrolytic dissociation — Composition of ions —
Ions and atoms not the same — Symbols representing ions —
Ionic equilibrium. Ionization constant — Effects of ionic equi-
librium in chemical reactions — Precipitation — Electrolysis —
Secondary changes in electrolysis — Faraday's laws — Conduc-
tivity— Electromotive force required in electrolysis — Electro-
chemical series of the metals — Acids — Independence of ions —
Analytical reactions or tests — Kinds of ions formed by acids —
Activity or " strength " of acids — Bases — Salts — Acid and basic
salts — Hydrolysis of salts — Neutralization — Heat of neutrali-
zation— Degree of dissociation of common substances .... 189-203

16. Sulphur. Selenium. Tellurium.

Occurrence in nature — Properties — Crude, sublimed, washed,
and precipitated sulphur — Sulphur dioxide — Sulphurous acid ;
tests for it — Sulphur trioxide — Sulphuric acid : its manufac-
ture, properties, and ions — Tests for sulphates — Sulphur acids
— Pyrosulphuric acid — Thiosulphuric acid — Hydrogen sul-
phide ; tests for it — Ions of hydrogen sulphide and its salts —
Use of it in analysis — Carbon disulphide — Selenium — Tellu-
rium— Ionic mechanism of the solution by acids of salts that
are insoluble in water 204-219

17. Phosphorus.

Occurrence in nature — Manufacture, properties, and modi-
fications— Poisonous properties and detection in cases of pois-
oning— Oxides of phosphorus — Hypophosphorous acid ; tests
for it — Phosphorous acid ; tests for it — Metaphosphoric, pyro-
phosphoric, orthophosphoric acids; tests for them — Ions of
phosphoric acid and its salts — Hydrogen phosphide — Phos-
phorus tri- and pentachloride 219-229

18. Chlorine.

Halogens — Occurrence in nature, preparation, and proper-
ties of chlorine— Chlorine water — Hydrochloric acid ; tests for
it — Nitrohydrochloric acid — Compounds of chlorine with oxy-
gen— Hypochlorous acid — Hypochlorites — Solution of chlor-
inated soda— Chloric acid ; tests for it— Perchloric acid . . . 230-238

19. Bromine. Iodine. Fluorine.

Bromine — Hydrobromic acid — Tests for bromides — Hypo-
bromous and bromic acid — Iodine — Hydriodic acid — Tests for
iodine and iodides — lodic acid — Sulphur iodide — Compounds
of iodine with bromine and chlorine — Compounds of nitrogen
with halogens — Fluorine — Hydrofluoric acid 239-245

viii CONTENTS.

IV.

METALS AND THEIR COMBINATIONS.

PAGE

20. General remarks regarding metals.

Derivation of names, symbols, and atomic weights — Melting-
points, specific gravities, time of discovery, valence, occur-
rence in nature, classification, and general properties of metals
— Alloys, their manufacture and properties 217-255

21. Potassium.

General remarks regarding the alkali metals — Occurrence in
nature — Potassium hydroxide, oxide, carbonate, bicarbonate,
percarbonate, nitrate, chlorate, sulphate, sulphite, hypophos-
phite, iodide, bromide — Analytical reactions 255-262

22. Sodium. Lithium. Caesium. Rubidium.

Occurrence in nature — Sodium chloride, hydroxide, perox-
ide, carbonate, bicarbonate, sulphate, sulphite, thiosulphate,
phosphate, nitrate, borate — Analytical reactions — Lithium —
Caesium— Rubidium 262-268

23. Ammonium.

General remarks — Ammonium ion — Ammonium chloride,
carbonate, sulphate, nitrate, phosphate, iodide, bromide, and
sulphide — Analytical reactions — Summary of analytical char-
acters of the alkali-metals 268-272

24. Magnesium.

General remarks — Occurrence in nature — Metallic magne-
sium— Magnesium carbonate, oxide, sulphate, nitride — Re-
marks on tests for metals — Analytical reactions 272-276

25. Calcium. Strontium. Barium. Radium.

General remarks regarding alkaline earths — Occurrence in
nature — Calcium oxide, hydroxide, carbonate, sulphate, phos-
phate, acid phosphate, and hypophosphite — Bone-black and
bone-ash — Chlorinated lime, calcium chloride and bromide —
Sulphurated lime — Calcium carbide — Analytical reactions and
ionic equations for calcium — Barium and strontium ; their salts
and analytical reactions — Radium — Summary of analytical
characters of the alkaline-earth metals 277-285

26. Aluminum. Cerium.

Occurrence in nature — Metallic aluminum — Alum — Alumi-
num hydroxide, oxide, sulphate, and chloride — Ionic equations
— Clay — Glass — Cement — Ultramarine — Analytical reactions
— Cerium — Summary of Analytical characters of the earth-
metals and chromium 285-292

27. Iron.

General remarks regarding the metals of the iron group —
Occurrence in nature — Manufacture of Iron — Properties —
Reduced iron — Ferrous and ferric oxides, hydroxides, and
chlorides — Dialyzed iron — Ferrous iodide, bromide, sulphide,

CONTENTS. ix

PAGE

and sulphate — Ferric sulphate and nitrate — Ferrous carbonate,
phosphate, and hypophosphite — Analytical reactions — Ions of
iron 292-302

28. Manganese. Chromium. Cobalt. Nickel.

[Manganese ; its oxides, sulphate, and hypophosphite — Po-
tassium permanganate — Manganese reactions — Ions of man-
ganese compounds — Chromium — Potassium dichromate —
Chromium trioxide — Ions of chromates and dichromates —
Chromic oxide and hydroxide — Perchromic Acid — Reactions
for chromium compounds — Cobalt and nickel 303-312

29. Zinc. Cadmium.

Occurrence in nature — Metallic zinc — Zinc oxide, chloride,
oxychloride, oxyphosphate, bromide, iodide, carbonate, sul-
phate— Analytical reactions — Ions of zinc — Antidotes — Cad-
mium— Summary of analytical characters of metals of the iron
group 312-318

30. Lead. Copper. Bismuth.

General remarks regarding the metals of the lead group —
Lead — Electrolytic solution tension — Lead oxides — Storage
battery — Lead nitrate, carbonate, iodide — Poisonous proper-
ties of lead — Antidotes — Lead reactions — Copper — Cupric and
' cuprous oxide — Cupric sulphate and carbonate — Ammonio-
copper compounds — Poisonous properties and antidotes —
Copper reactions — Bismuth — Bismuth subnitrate and subcar-
bonate — Bismuth reactions — . . . 318-330

31. Silver. Mercury.

Silver — Silver nitrate — Photography — Silver oxide — Anti-
dotes— Complex silver compounds— Silver reactions — Ions of
silver — Mercury — Amalgams — Mercurous and mercuric ox-
ides, chlorides, iodides, sulphates, nitrates, sulphides — Am-
moniated mercury — Antidotes — Mercury reactions — Ions of
mercury compounds — Summary of analytical characters of
metals of the lead group 330-346

32. Arsenic.

General remarks regarding the metals of the arsenic group
— Arsenic — Arsenous and arsenic oxides and acids — Sodium
arsenate — Lead arsenate — Hydrogen arsenide — Sulphides of
arsenic — Arsenous iodide — Analytical reactions — Ions of ar-
senous and arsenic acids — Preparatory treatment of organic
matter for arsenic analysis — Antidotes , 346-358

33. Antimony. Tin. Gold. Platinum. Iridium. Molybdenum.

Antimony — Trisulphide and pentasulphide of antimony —
Antimonous chloride and oxide — Antidotes — Antimony reac-
tions— Tin — Stannous and stannic hydroxide and chloride —
Metastannic acid — Tin reactions— Gold — Refining gold— Gold
chloride— Platinum — Iridium — Molybdenum — Summary of
analytical characters of metals of the arsenic group 358-369

X CONTENTS.

V.

ANALYTICAL CHEMISTRY.

PAGE

34. Introductory remarks and preliminary examination.

General remarks — Apparatus needed for qualitative analysis
— Reagents needed — General mode of proceeding in qualitative
analysis — Use of reagents — Preliminary examination — Physi-
cal properties — Action on litmus — Heating on platinum foil
Heating on charcoal alone and mixed with sodium carbonate
— Flame-tests — Colored borax-beads — Liquefaction of solid
substances — Table I.: Preliminary examination 371-381

35. Separation of metals into different groups.

General remarks — Group reagents — Acidifying the solution
— Addition of hydrogen sulphide — Separation of the metals of
the arsenic group from those of the lead group — Addition of
ammonium sulphide and ammonium carbonate — Table II. :
Separation of metals into different groups 382-387

36. Separation of the metals of each group.

Table III. : Treatment of the precipitate formed by hydro-
chloric acid — Treatment of the precipitate formed by hydrogen
sulphide — Table IV. : Treatment of that portion of the hydro-
gen sulphide precipitate which is insoluble in ammonium sul-
phide— Table V. : Treatment of that portion of hydrogen
sulphide precipitate which is soluble in ammonium sulphide
— Table VI. : Treatment of the precipitate formed by ammo-
nium hydroxide and sulphide — Table VII. : Treatment of the
precipitate formed by ammonium carbonate — Table VIII. :
Detection of the alkalies and of magnesium 387-390

37. Detection of acids.

General remarks — Detection of acids by means of the action
of strong sulphuric acid — Table IX. : Preliminary examina-
tion for acids — Detection of acids by means of reagents added
to their neutral or acid solution — Table X. : Detection of the
more important acids by means of reagents added to the solu-
tion— Table XI. : Systematically arranged table, showing the
solubility and insolubility of inorganic salts and oxides —
Table XII. : Table of solubility— Special remarks 391-401

38. Methods for quantitative determinations.

General remarks — Gravimetric methods — Volumetric
methods — Standard solutions — Normal solutions — Different
methods of volumetric determination — Indicators and ionic
explanation of their action — Titration — Acidimetry and alka-
limetry— Normal acid and alkali solution — Oxidimetry — Po-
tassium permanganate and dichromate — lodimetry — Solutions
of iodine, sodium thiosulphate, bromine, silver nitrate, sodium
chloride, and potassium sulphocyanate — Gas analysis — Water
analysis 402-432

CONTENTS. xi

PAGE

39. Detection of impurities in official inorganic chemical prep-

arations.

General remarks — Official chemicals and their purity — Tests
as to identity— Qualitative tests for impurities — Quantitative
tests for the limit of impurities 433-437

VI.

CONSIDERATION OF CARBON COMPOUNDS, OR ORGANIC

CHEMISTRY.

40. Introductory remarks. Elementary analysis,

Definition of organic chemistry — Elements entering into or-
ganic compounds — General properties of organic compounds
— Difference in the analysis of organic and inorganic substances
— Qualitative analysis of organic substances — Ultimate or
elementary analysis — Determination of carbon, hydrogen,
oxygen, nitrogen, sulphur, and phosphorus — Determination of
atomic composition from results obtained by elementary
analysis — Empirical and molecular formulas — Rational, con-
stitutional, structural, or graphic formulas 439-448

41. Constitution, decomposition, and classification of organic

compounds.

Radicals or residues — Chains — Homologous series — Sub-
stitution— Derivatives — Isomerism — Metamerism — Polymer-
ism — Stereo-isomerism — Various modes of decomposition —
Action of heat upon organic substances — Dry or destructive
distillation — Action of oxygen upon organic substances —
Combustion — Decay — Fermentation and putrefaction — Anti-
septics, disinfectants, and deodorizers — Action of chlorine, bro-
mine, nitric acid, alkalies, dehydrating and reducing agents
upon organic substances — Classification of organic compounds 448-462

42. Hydrocarbons. Haloid derivatives.

Occurrence in nature — Formation of hydrocarbons — Prop-
erties— Paraffin or methane series — Methane — Ethane — Coal
— Natural gas — Coal-oil, petroleum — Illuminating gas — Coal-
tar — Unsaturated hydrocarbons — Olefines — Ethylene — Amyl-
ene — Acetylene — Halogen derivatives of hydrocarbons —
Methyl chloride— Dichlor- and Tetrachlor-methane— Chloro-
form— Bromoform — lodoform — Ethyl chloride, bromide, and
iodide — Compounds of alkyl radicals with other elements —
Sodium cacodylate 462-478

43. Alcohols.

Constitution of alcohols — Occurrence in nature — Formation
and properties of alcohols — Monatomic normal alcohols —
Methyl alcohol— Ethyl alcohol— Denatured alcohol— Alcoholic
liquors — Wines, beer, spirits — Amyl alcohol — Allyl alcohol —
Glycerin — Glycerin trinitrate — Dynamite — Glycerin-phos-
phoric acid 479-489

xii CONTEXTS.

PAGE

44. Aldehydes. Ketones.

Aldehydes — Formic aldehyde— Formalin — Acetic aldehyde
— Paraldehyde — Trichloraldehyde — Hydrated chloral — Acrylic
aldehyde — Ketones — Acetone — Sulphur derivatives — Sulpho-
nal— Trional— Tetronal 489-496

45. Monobasic fatty acids.

General constitution of organic acids — Occurrence in nature
— Formation of acids— Properties — Fatty acids — Formic acid
— Acetic acid — Vinegar — Reactions for acetates— Acetate of
potassium, sodium, zinc, iron, lead, and copper — Trichlor-
acetic acid— Acetyl chloride — Acetic anhydride — Butyric acid
— Valeric acid and its salts— Stearic acid — Oleic acid — Disso-
ciation of formic acid and its homologues 496-507

46. Polybasic and hydroxy-acids.

Oxalic acid, oxalates, and analytical reactions — Glycolic
acid — Lactic acid — Malic acid — Tartaric acid ; analytical re-
actions— Potassium tartrate— Potassium-sodium tartrate — An-
timony-potassium tartrate— Action of certain organic acids
upon certain metallic oxides — Scale compounds — Citric acid ;
analytical reactions — Citrates 508-518

47. Ethers and esters.

Constitution— Formation of ethers — Occurrence in nature —
General properties — Ethyl ether — Acetic ether — Ethyl nitrite
— Amyl nitrite— Fats and fat oils — Soap — Lanolin 518-527

48. Carbohydrates.

Constitution — Properties — Occurrence in nature — Classifica-
tion — Monosaccharides — Dextrose ; tests for it — Levulose —
Galactose — Inosite — Disaccharides — Cane-sugar — Maltose —
Lactose — Polysaccharides — Starch — Dextrin — Gums — Cellu-
lose—Pyroxylin— Collodion — Glycogen — Glucosides 528-539

49. Compounds containing nitrogen.

Derivatives of nitric acid — Nitro, nitroso, and isonitroso
compounds — Ammonia derivatives — Amines— Poly-amines —
Amino-acids — Amino-acetic and amino-formic acid — Ure-
thanes — Ethyl carbamate — Sarcosine — Cystine — Leucine —
Taurine — Aspartic acid, asparagine — Guanidine— Creatine —
Urea — Ureids— Veronal — Cyanogen compounds — Hydrocyanic
acid — Dissociation of cyanogen compounds — Cyanides of po-
tassium, silver, and mercury— Cyanogen derivatives obtained
from atmospheric nitrogen — Cyanic acid — Metallocyanides —
Potassium ferrocyanide and ferri cyanide— Sodium nitroferri-
cyanide — Nitriles and isocyanides— Iso-sulpho-cyanides —
Myronic acid — Allyl mustard oil 539-557

50. Benzene series. Aromatic compounds.

General remarks — Constitution — Benzene series of hydro-
carbons— Benzene — Toluene — Xylenes — Cymene — Amino com-
pounds of benzene — Aniline — Acetanilide — Sulphanilic acid —
Diphenyl-amine — Meta-phenylene-diamine — Methylene-blue

CONTENTS. xiii

PAGE

— Diazo compounds— Phenyl hydrazine — Atoxyl — Salvarsan —
Hydroxyl derivatives — Phenols — Carbolic acid — Acetphene-
tidin — Trinitro-phenol— Phenolsulphonicacid — Cresols— Creo-
sote— Guaiacol and its compounds — Veratrol — Eugenol — Safrol
—Thymol and the iodide— Resorcinol — Quinol — Pyrogallol —
Phloroglucinol — Aromatic alcohols — Aromatic aldehydes —
Benzaldehyde — Oil of bitter almond— Cinnamic aldehyde —
Vanillin — Cumarin — Acids of the benzene series — Benzoic acid
— Benzoyl chloride — Benzosulphinide — Phthalic acids— Phe-
nolphthalein— Fluorescein, Eosin— Phenolsulphonphthalein—
Salicylic acid— Aspirin— Salicin— Methyl salicylate— Phenyl
salicylate — Gallic and tannic acid — Naphthalene — Naphthol —
Santonin— Pyrrol — Antipyrine— Pyridine — Quinoline — Kai-
rine— Thalline 557-594

51. Terpenes and their derivatives.

Volatile or essential oils— Terpenes — Terebene — Sesquiter-
penes — Rubber — Gutta-percha — Stearoptenes — Camphor —
Cineol — Menthol — Resins — Balsams — Turpentine 594-599

52. Alkaloids.

General remarks— Properties— Assay methods— Antidotes-
Detection— Classification— The pyridine group— Pi perin—
Coniine — Pilocarpine — Nicotine — Sparteine — The tropine
group — Atropine — Homatropine— Hyoscyarnine — Hyoscine —
Cocaine and its substitutes — The quinoline group — Cinchona
alkaloids — Quinine and quinidine— Cinchonine and cinchoni-
dine — Strychnine — Brucine — Veratrine — The isoquinoline
group — Morphine, apomorphine — Codeine — Narcotine, narce-
ine — Meconic acid — Hydrastine, hydrastinine — Berberine —
The xanthine alkaloids — Caffeine — Theobromine — Unclassified
alkaloids — Physostigmine — Aconitine — Colchicine — Pto-
maines ; their formation and properties — Leucomaines . . . 600-621

VII.

PHYSIOLOGICAL CHEMISTRY.

53. Proteins.

Occurrence in nature — General properties — Classification —
Simple proteins — Albumins — Globulins — Glutelins— Prola-
mines or alcohol-soluble proteins — Albuminoids — Histones —
Protamines — Conjugated proteins — Nucleoproteins — Glycopro-
teins — Phosphoproteins — Haemoglobins — Lecithoproteins —
Derived proteins — Proteans— Metaproteins — Coagulated pro-
teins— Proteoses — Peptones — Peptides — Products of proteo-
lysis — Tyrosine — Leucine — Hydrolysis — Enzymes — Pepsin —
Pancreatin 623-639

54. Chemical changes in plants and animals.

Difference between vegetable and animal life — Formation of
organic substances by the plant — Animal food — Digestibility

xiv CONTENTS.

PAGE

— Nutrition — Digestion — Absorption — Respiration — AVaste-
products of animal life — Chemical changes after death . . . 639-649

55. Animal fluids and tissues.

Constituents of the animal body — Blood ; its properties and
composition — Blood-plasma and blood-serum — Blood-pigments
— Fibrin — Hemoglobin — Haematin — Hrematoporphyrin —
Spectroscopic examination — Examination of blood-stains —
Immune bodies of the blood-serum — Lymph — Bone — Teeth —
Hair, nails, etc. — Muscle — Muscle extractives — Creatine and
Creatinine — Xanthine bases — Purine bases — Xanthine and
hypoxanthine — Meat-extracts — The thyroid gland — Brain —
Lecithins— Cholesterin 649-671

56. Digestion. ,

General remarks — Salivary digestion — Saliva, tests for it —
Gastric digestion — Gastric juice, its clinical examination —
Intestinal digestion — Pancreatic secretions — Bile — Biliary pig-
ments, acids, and calculi— Fermentative and putrefactive
changes — Absorption, assimilation — Feces ; their chemical ex-
amination— The liver — Glycogen— Indole — Skatole 672-694

57. Milk.

Properties and composition — Milk-proteins — Casein — Milk-
fat — Butter — Lactose ; tests for it — Changes in milk on stand-
ing— Milk preservatives — Analysis of milk — Human milk —
Modified milk 695-703

58. Urine and its constituents.

Excretion of urine — General properties — Points to be con-
sidered in the analysis of urine — Color — Odor — Volume — Re-
action— Specific gravity — Composition — Normal and patho-
logical constituents — Determination of total solids and inor-
ganic constituents — Nitrogen in the urine — Urea, its reactions
and determination — Ammonia in urine and its determination —
Creatine and creatinine — Uric acid, its tests and determination
— Xanthine bodies — Allan torn — Hippuric acid — Chlorides and
their determination — Phosphoric acid — Sulphur compounds in
urine — Indican — Phenol — Pyrocatechin— Proteins in urine and
tests — Blood and its tests — Carbohydrates and tests — Deter-
mination of dextrose in urine — Laevulose, maltose, lactose, and
pentoses — Glycuronic acid — Acetone, diacetic, and beta-oxy-
butyric acids — Bile — Alkaptonic acids — Diazo-reaction — Func-
tional tests of the kidney — Urinary sediments — Urinary cal-
culi 703-746

APPENDIX.

Table of weights and measures 747

Table of elements 749

Index .... 751

LIST OF ILLUSTRATIONS.

FIG. PAGE

1. The cube 22

2. Regular octahedron 22

3. Quadratic octahedron 23

4. Right-square or quadratic prism 23

5. Rhombic octahedron 23

6. Double six-sided pyramid 23

7. Rhombohedron ." 24

8. Six-sided prism ... 24

9. Monoclinic double pyramid 24

10. Monoclinic prism 24

11. Triclinic prism 25

12. Triclinic octahedron 25

13. 14. Structure of matter 29

15. Dialyzer • . . . . 41

16. Thermometric scales 47

17. Reflection 57

18. Refraction by a parallel plate 58

19. Refraction through a prism ^ 58

20. Prismatic spectrum 59

21. Spectroscope - • • • • 60

22. Direct-vision spectroscope 61

23. Double refraction 63

24. Tourmaline plates 64

25. Undulation in a cord 64

26. Explanatory diagrams of the action of tourmaline plates 65

27. Nicol's prism 66

28. Lippich's polariscope 68

29. Daniell's cell 75

30. Induction coil - . . 79

31. Electric furnace '. 80

32. Longitudinal section of carborundum furnace 81

33. Exterior view of carborundum furnace 81

34. Electrolysis of water 82

35. Apparatus for the decomposition of mercuric oxide 87

36. Diagram of periodic system in spiral form 130

37. Apparatus for generating oxygen 140

38. Apparatus for generating hydrogen 146

39. Apparatus for generating ammonia 168

40. Distillation of nitric acid 175

41. Structure of flame i85

42. Apparatus for making sulphurous acid 207

(xv)

xvi LIST OF ILLUSTRATIONS.

FIG- PAGE

43. Apparatus for detection of phosphorus 223

44-47. Detection of arsenic 353-357

48-52. Apparatus for analytical operations 372, 373

53. Heating of solids in bent glass tube 377

54. Heating on charcoal by means of blowpipe 377

55. Washing and decanting in agate mortar 378

56. Platinum wire for blowpipe experiments v 379

57. 58. Apparatus for generating hydrogen sulphide 384

59. Drying-oven 403

60. Desiccator 404

61. Watch-glass for weighing filters 404

62. Liter flask 405

63. Pipettes 405

64. Mohr's burette and clamp 406

(}•"). Mohr's burette and holder 406

66. Gay Lussac's burette 407

67. Flask for dissolving iron . 419

68. Gas-furnace for organic analysis 444

69. Flasks for fractional distillation 463

70. Liebig's condenser, with flask 484

71. Isomeric salts of tartaric acid 513

72. Absorption-spectra of blood constituents 658

73. Uriuometer 707

74. Doremus' ureometer 714

75. Esbach's albuminometer 727

76. Various forms of uric acid crystals 741

77. Calcium oxalate crystals 742

78. Crystalline phosphates 742

79. Ammonium urate crystals ....... 743

80. Crystals of leucine ^ 743

81. Tyrosine crystals 744

82. Crystals of cystine 744

COLORED PLATES.

PLATE Of Spectra

" I. Compounds of iron, cobalt, and nickel

II. Compounds of manganese and chromium

III. Compounds of copper, lead, and bismuth

IV. Compounds of silver and mercury

V. Compounds of arsenic, antimony, and tin

VI. Reactions of alkaloids ....

VII. Indicators for alkalies and acids .

£t VIII. Physiological reactions ....

. Frontispiece.

facing page 302

" 312

" 326

" " 344

" " 352

" " 602

" 680
« 738

ABBREVIATIONS.

c.c. = Cubic centimeter.

B. P. = Boiling-point.

F. P. = Fusing-pointc

Sp. gr. = Specific gravity.

U. S. P. = United States Pharmacopeia.

(xvii)

PRACTICAL CHEMISTRY,
MEDICAL AND PHARMACEUTICAL,

I.

CHEMICAL PHYSICS.

BOTH sciences, chemistry and physics, have for their object the
study of all substances, or of all varieties of matter, and the changes
which they undergo. When these alterations affect the composition
of matter we have chemical changes, which are considered by chem-
istry ; when the composition is not affected Ve have physical changes,
considered by physics. But whenever chemical changes take place
they are accompanied by physical changes. Indeed, there exists such
a close relation, such a mutual dependency, between these two series
of phenomena that they cannot be studied altogether independently
of one another. Moreover, the chemist uses constantly in his opera-
tions instruments or appliances the construction of which is based on
physical principles. A knowledge of certain parts of physics is
therefore essential for the proper understanding of chemistry. It is
for this reason that a few chapters dealing with certain physical con-
ditions of matter precede the parts on chemistry.

Physics is defined above as the study of those changes in matter which do
not involve an alteration of the composition or constitution of the matter.
The phenomena of light, heat, electricity, magnetism, sound, motion, attrac-
tion, etc., fall within its province. A few examples of physical changes may
help to make the subject clearer. A piece of iron heated sufficiently becomes
luminous, radiates heat, and increases in size. All these are physical changes,
because if the iron be cooled it will be found to be the same in character as
before it was heated. There has been no change in the substance iron. A
body in rapid motion is quite different from the same body at rest, as is evident
if the body hit an individual, yet the nature or composition of the body is not
altered. A wire through which an electric current is passing is different from
2 17

18 CHEMICAL PHYSICS.

one in which there is no current, although the substance of both wires is the
same. Many other examples of physical change might be cited.

Chemistry is the study of those changes in bodies which affect their compo-
sition, and in this respect chemical changes differ from all other kinds of
changes. Another good and broad definition given by the great Russian chem-
ist, Mendelejeff, is the following: Chemistry is concerned with the study of the
homogeneous substances or materials of which all objects of the universe are
made up, with the transformations of these substances into one another, and
with the phenomena which accompany such transformations. When a piece
of paper burns, an ash is left, which is altogether different from the original
paper. Moreover, if proper care be taken to catch the products escaping dur-
ing the burning, water vapor and gases will be found, which are also unlike
the paper. These are new substances and the change is, therefore, a chemical
one. But at the same time several physical changes will be observed, namely,
heat and light.

When a piece of the metal magnesium is ignited, it burns and leaves an ash
entirely different from the metal, being white and brittle. This is a chemical
change, but heat and intense light are observed at the same time, which are
physical changes.

When a piece of marble is heated to redness for some time, a substance
remains on cooling which, although having the same form as the piece o>
marble, is nevertheless entirely different in its composition and properties, anr*
is known as quick-lime. When water is poured upon the latter, great heat is
produced .and the solid lump falls down to a white powder, known as slaked-
lime, whereas marble is not affected by water. By a suitably arranged appa-
ratus it could also be shown tfiat an invisible gas is given off when the marble
is heated.

These illustrations will be sufficient to point out the nature of physical and
chemical changes, and we may proceed now to the discussion of some element-
ary subjects of physics.

1. FUNDAMENTAL PROPERTIES OF MATTER.

Matter is anything that occupies space and may be apprehended
by the aid of our senses. While there are many thousands of various
kinds of matter, possessing widely different properties, yet there are
properties in common which belong to 'every kind of matter, and
these are known as essential or fundamental properties. The funda-
mental properties of matter having a special interest for those study-
ing chemistry are : Extension, Divisibility, Gravitation, Porosity, and
Indestructibility.

Extension. The common property of matter to occupy space is
known as extension. All bodies, without exception, fill a certain
quantity of space ; they all have length, breadth, and thickness.
That portion of matter lying within the surrounding surface of a
body is called its mass; or we may define mass as the quantity of

FUNDAMENTAL PROPERTIES OF MATTER. 19

matter which a body possesses. A body is a definite portion of
matter, such as a knife, a piece of chalk, or a lump of coal. The
term substance is used to designate some particular kind of matter,
possessed of definite qualities, such as gold, water, glass, etc. We
distinguish three different conditions of matter, namely : Solids,
Liquids, and Gases.1 These conditions of matter are known as the
three states of aggregation, and we will now consider the peculiarities
of matter when existing in either of these states.

Solid state. Solids are distinguished by a self-subsistent figure —
i. e., they have a definite size and shape. A solid substance forms
for itself, as it were, a casing in which its smallest particles1 are en-
closed. The questions arise, By what means are these particles con-
nected? How are they kept together? No answer can be given
other than that the particles themselves attract each other to such an
extent that force is necessary to make them alter their relative posi-
tions. We see, consequently, that some form of attraction or at-
tractive power is acting between the particles of a solid mass, and
we call this kind of attraction cohesion, to distinguish it from other
forms of attraction.

Force may be defined as the action of one body upon another
body, or as the action of particles of matter upon other particles
either of the same or of another body. Strictly speaking, we may
say that force is the cause tending to produce, change, or arrest
motion ; or it is any action upon matter changing or tending to change
its form or position. Force is a manifestation of energy, and may
be originated in a variety of ways.

Energy is a universal property of matter ; it is its capacity for
doing work, and is measured by the work it can do. Doing work con-
sists in a transfer of motion, or energy, from the body doing work to
the body on which work is done. Wherever we find matter in motion
we have a certain quantity of energy which may be made to do work.

As examples of different forms of energy we have motion of masses, heat,
light, electricity, chemical changes, etc. Under the influence of the different
forms of energy matter is constantly undergoing change. There are changes
in position, in temperature, in appearance, in the composition of substances,
and in many other directions.

1 It has been shown lately that matter may exist in a fourth state as radiant matter. This
condition will be considered later.

2 It will be shown later that all matter is supposed to consist of smallest particles, which we
call molecules.

20 CHEMICAL PHYSICS.

Energy may be potential (i. e., stored up) or kinetic (i. e., actual). For
instance, potential energy is the energy which we have in a mass held by
the hand, or by a support ; as soon as the support is withdrawn the mass falls,
and in this instance we witness kinetic or actual energy.

Other instances of potential energy are a drawn bow, a wound-up watch-
spring, an elevated tank of water, etc. This potential energy may manifest
itself as kinetic energy by sending an arrow through space, by keeping the
watch in motion, or by rotating a water-wheel. During the conversion of
potential into kinetic energy there is neither gain nor loss ; both are absolutely
alike in quantity.

Crystallization. The external appearance or the figure of solid
bodies is various. It may be an irregular or a natural regular figure.
Of these two forms, only the latter is here of interest, as it includes
all the different crystallized substances.

Crystals are solid substances bounded by plane surfaces symmetri-
cally arranged according to fixed laws. In explaining the formation
of crystals we have to assume that the particles are endowed with the
power of attracting one another in certain directions, thereby building
themselves up into geometrical forms.

The external form of a crystal is only an outward expression of a regular
internal structure. This is shown by the fact that in non-crystalline homo-
geneous bodies such properties as elasticity, hardness, cohesion, transmission
of light, etc., are the same in all directions, while crystallized bodies show dif-
ferences along different directions. A model of glass would not be a crystal,
since the necessary internal structure is absent.

The first condition essential to the formation of crystals is the possi-
bility of free motion of the smallest particles of the matter to be crys-
tallized ; in that case only will they be able to attract each other in
such a way as to assume a regular shape, or form crystals. Particles
of a solid mass can move freely only after they have been transferred
to the liquid or gaseous state. There are two different methods of
liquefaction, viz., by means of heat (melting), or solution in some
suitable agent (dissolving). In the liquid condition thus produced,
the smallest particles can follow their own attraction, and unite to
form crystals on removal of the cause of liquefaction (heat or solvent).

In the great majority of cases the method employed for obtaining crystals
is to dissolve the substance in a liquid, usually water, taking advantage of the
fact that, with very few exceptions, substances are more soluble in hot than in
cold liquids. When such a concentrated hot solution, filtered if necessary to
remove solid matter, is allowed to cool, the particles of the excess of the sub-
stance, beyond what is soluble at the lower temperature, gradually arrange

FUNDAMENTAL PROPERTIES OF MATTER. 21

themselves around certain points as nuclei according to the directions of great-
est cohesion, and thus crystals with regular faces and angles and definite
internal arrangement are built up. The size of the crystals obtained will
depend on several factors, but whatever the size may be, the angles between
the faces and the position of the faces will be the same for every individual
substance. Hence the shape of crystals is a valuable means of identifying
substances. If a concentrated hot solution of a substance be cooled quickly,
and especially if the liquid be disturbed, as by stirring, the crystals will be
small, sometimes almost microscopic in size. But this is often an advantage,
because large crystals are apt to enclose some of the liquid containing the
impurities between the layers. On the large scale, as in industries, enormous
crystals are obtained by the slow cooling of a great volume of solution, for
example, in the case of alum, potassium dichromate, etc. When a substance
is not much more soluble in a hot than in a cold liquid, for example, common
salt in water, the liquid must be removed by allowing it to evaporate, either at
ordinary or at elevated temperature, to obtain a good yield of the substance
in crystal form.

Sometimes sticks, strings, wires, strips of lead, etc., are suspended in the
solutions, to offer starting-points for the formation of crystals and a ready
means for removing the crystals from the liquor. A familiar example is the
string in the center of a stick of rock-candy.

A relatively few substances when heated pass from the solid to the gaseous
state, without undergoing intermediate liquefaction. When the vapor of such
substances comes in contact with cool surfaces, it is deposited in crystals which
sometimes attain to remarkable size and beauty. This process is known as
sublimation and is used in the case of several medicinal agents on the market,
for example, iodine, benzoic acid, ammonium chloride, etc. The words iodine
resublimed, found on labels, and the popular name for mercuric chloride, namely,
corrosive sublimate, refer to the process of sublimation employed in obtaining
these substances.

If two or more (non-isomorphous) substances — for instance, common salt
and Glauber's salt— be dissolved together in water, and the solution be allowed
to crystallize, the attraction of like particles for one another will be readily
noticed by the formation of distinct crystals of common salt alongside of
crystals of Glauber's salt ; neither do the particles of common salt help to
build up a crystal of Glauber's salt, nor the particles of the latter a crystal of
common salt. Advantage is taken of this property in separating (by crystal-
lization) solids from each other, when they are contained in the same solution.

Not all matter can form crystals ; some substances never have been
obtained in a crystallized state, such as starch, gum, glue, etc. A
solid substance showing no crystalline structure whatever is called
amorphous.

Some substances capable of crystallization may be obtained also in
an amorphous state (carbon, sulphur). Other substances are capable
of assuming different crystalline shapes under different conditions.
Thus sulphur, when liquefied by heat, assumes, on cooling, a shape
different from the sulphur crystallized from a solution. One and the

22

CHEMICAL PHYSICS.

same substance under the same conditions always assumes the same
shape. Substances capable of assuming in solidifying two or more
different shapes or conditions, are said to be dimorphous and poly-
morphous, respectively. When substances of different kinds crystallize
in exactly the same form we call them isomorphous (magnesium sul-
phate and zinc sulphate). Also, a crystal of one kind of matter must
have the power of growing in the solution of another kind before
the two kinds of matter are considered isomorphous. If two iso-
morphous substances be contained in one solution, they will crystallize
together, and the crystals be made up of particles of both substances,

Crystal Systems. The study of crystals forms an extensive field, known
as crystallography. The limited scope of this book forbids any detailed study
of crystals, and the reader must be referred to the large works on chemistry or
works on crystallography for such information. But a brief description of the
classification of crystals may not be out of place here.

All crystals are referred to axes or imaginary lines drawn through the cen-
ter. The great variety of forms of crystals depends upon the number and
length of these axes and their relative inclination — that is, the angles at which
they intersect. All crystal forms have been divided into two large groups, the
orthometric and the clinometric, and these have been further subdivided into six
systems. Orthometric refers to the fact that the axes intersect at right angles,
while clinometric means that the axes intersect at oblique angles.

FIG. 1.

FIG. 2.

The cube. Regular octahedron.

The orthometric group includes the following systems :

(1) Kegular system, also known as the monometric, cubic, octahedral, or
tessular system.

The crystals have three axes of equal length and intersecting at right angles.
The fundamental forms of this system are the cube and the octahedron (Figs.
1 and 2). Some substances crystallizing in this system are alum, phosphorus,
arsenic trioxide, diamonds, alkali iodides, chlorides, fluorides, and cyanides,
and many metals and their sulphides.

(2) Quadratic system, also known as the dimetric, square prismatic, or tet-
ragonal system.

FUNDAMENTAL PROPERTIES OF MATTER.

The crystals have three axes intersecting at right angles, two of which are
of equal length and one either longer or shorter than the other two. The fun-
damental forms of this system are the quadratic octahedron (also known as
square-based double pyramid) and the right square prism (Figs. 3 and 4).

FIG. 3. FIG. 4.

Quadratic octahedron. Right-square or quadratic prism.

Some substances crystallizing in this system are potassium ferrocyanide, calo-
mel, nickel sulphate, tin, tin oxide, magnesium sulphate, zinc sulphate.

(3) Rhombic system, also known as the trimetric or right prismatic system.

FIG. 5. FIG. 6.

Rhombic octahedron. Double six-sided pyramid.

The crystals have three unequal axes intersecting at right angles. The fun-
damental form of this system is the rhombic octahedron or right rhombic
double pyramid (Fig. 5). Some substances crystallizing in this system are

24

CHEMICAL PHYSICS.

potassium sulphate and nitrate, resorcin, zinc sulphate, citric acid, iodine,
Rochelle salt, mercuric chloride, barium chloride, tartar emetic, codeine, sali-
cylic acid, piperin, Epsom salt, silver nitrate, ammonium sulphate, cream of
tartar.

(4) Hexagonal or rhombohedral system.

The crystals have four axes, three of which are of equal length, while the
fourth is either longer or shorter than the other three. The three equal axes
are in the same plane and intersect at an angle of 60°, while the fourth axis
intersects these at right angles. The fundamental form is the double six-sided
pyramid. The rhombohedron and regular six-sided prism are modifications
of this system (Figs. 6, 7, and 8). Some substances crystallizing in this system

FIG. 7.

FIG. 8.

i — i • — i

i

j
j

L

<L..,

Rhombohedron.

Six-sided prism.

are sodium nitrate, camphor, graphite, ammonium chloride, ice, calcspar, thy-
mol, metallic bismuth and antimony, arsenic, silicic acid.

The clinometric group includes the following systems :

(5) Monociinic system, also known as the monosymmetric, clinorhombic, or
oblique prismatic system.

The crystals have three unequal axes, two intersecting at oblique angles and
both intersecting the third at right angles. The fundamental forms of this
system are the monoclinic double pyramid or octahedron and the monoclinic
prism (Figs. 9 and 10). Some substances crystallizing in this system are

FIG. 9. FIG. 10.

Monoclinic double pyramid. Monoclinic prism.

ferrous sulphate, borax, lead acetate, cupric acetate, tartaric acid, potassium
chlorate, and sodium acetate, sulphate, thiosulphate, phosphate, and carbonate.
(6) Triclinic system, also known as the asymmetric, clinorhombohedral, or
doubly oblique prismatic system.

FUNDAMENTAL PROPERTIES OF MATTER. 25

The crystals are the most unregular of all, having three unequal axes, all
intersecting at oblique angles. The fundamental forms of this system are the
triclinic prism and the triclinic octahedron or double pyramid (Figs. 11 and
12). Some substances crystallizing in this system are copper sulphate, potas-
sium dichromate, gypsum, boric acid, manganous sulphate.

The pyramidal form is found in all the systems, while the cube is confined
to the regular system, and prisms occur in all but the regular system.

FIG. 11. FIG. 12.

Triclinic prism. Triclinic octahedron.

For some reason or other crystals sometimes grow mainly in one or two
directions and then show forms that are distorted and have little or no resem-
blance to the normal forms of the system to which they belong. Examples of
such forms are the following :

Tabular crystals or flat plates, as potassium chlorate, iodine, etc.

Laminar crystals, thin plates or leaflets, as acetanilid, naphthol, calcium
hypophosphite, etc.

Acicular crystals or needles, as aloin, cinchonidine sulphate, quinine
salts, etc.

Prismatic crystals or prisms, extended chiefly in the direction of the longest
axis, as salicylic acid, santonin, cinchonine sulphate, etc.

The shapes of gems must not be confused with crystal forms. They are the
result of cutting and polishing for the purpose of causing the gem to reflect
more light.

Characteristic properties of solids. Solid substances show a
great variety of properties caused by the differences in the cohesion
of the particles (molecules) composing the substances, and accordingly
we distinguish between hard and soft, brittle, tenacious, malleable,
and ductile substances.

Hardness is that property in virtue of which some bodies resist attempts to
force passage between their particles, or which enables solids to resist the dis-
placement of their particles. Diamond and quartz are extremely hard, while
wax and lead are comparatively soft.

26 CHEMICAL PHYSICS.

Brittleness is that property of solids which causes them to be broken easily
when external force is applied to them. Glass, sulphur, coal, etc., are brittle.

Tenacity is that property in virtue of which solids resist attempts to pull
their particles asunder. Steel is one of the most tenacious substances.

Malleability, possessed by some solids, is the property in virtue of which they
may be hammered or rolled into sheets. Gold is so malleable that it may be
beaten into sheets so thin that it would require about 300,000 laid upon one
another to measure one inch.

Ductility is the property in virtue of which some solids may be drawn into
wire or thin sheets — as, for instance, copper, iron, and platinum.

Liquid state. The characteristic features of liquids are, that they
have no self-subsistent figure; that they consequently require some
vessel to hold them ; and that they present a horizontal surface. While
in a solid substance the smallest particles are held together by cohe-
sion to such an extent that they cannot change their relative position
without force, in a liquid this cohesion acts with much less energy
and permits of a comparatively free motion of the particles; the
repellant and attractive forces nearly balance each other in a liquid.
That cohesion is not altogether suspended in a liquid is shown by the
formation of drops or round globules, which, of course, consist of a
large number of smallest particles. If there were no cohesion at all
between these particles of a liquid, drops could not be formed.

The terms semi-solid and semi-liquid substances are used for bodies occupy-
ing a position intermediate between true solids and fluids; butter, asphalt,
amorphous sulphur, are instances of this kind.

Gaseous state. Matter in the gaseous state has absolutely no
self-subsistent figure. Any quantity of gas in a closed vessel will
fill it completely ; the smallest particles show the highest degree of
mobility and move freely in every direction. Cohesion is entirely sus-
pended in gases ; indeed, there is no attraction between the particles,
but they are in rapid motion and tend to spread out in all directions ;
hence must be retained in a closed vessel. The motion of the par-
ticles causes bombardment on the sides of the vessel, and thus pro-
duces pressure. This characteristic property, possessed by all gases,
is known as elasticity, or, better, as tension, and is so unvarying that
a law1 has been established in relation to it. This law is known
as the Law of Boyle, who discovered it in 1661 ; sometimes it is
referred to as the Law of Mariotte. It may be expressed thus : The
volume of a gas is inversely as the pressure ; the density and elastic
force are directly as the pressure and inversely as the volume.

1 In science, a law or generalization is a brief statement which describes some constant mode
of behavior, or sums up the constant features of a set of phenomena of a like kind.

FUNDAMENTAL PROPERTIES OF MATTER 27

The subject will be clearer from the following considerations : A
gas behaves much like a spring. If we put weights (force) on the
spring it will be compressed — that is, its volume will become less, and
if the weights be gradually removed, the spring will expand. Sim-
ilarly, if we take a metallic tube closed at one end, and fitted with a
piston and handle and containing a certain volume of air, for
example, a bicycle pump, and then press down upon the handle, the
volume of air will become smaller and smaller as the pressure on the
handle is increased. It will be observed also that as the volume
becomes smaller it oifers more and more resistance to compression,
that is, its tension or elastic force becomes greater. Also, since the
amount of material in the original volume of air remains the same
during the experiment, it is plain that when the air is compressed to
a small volume, the amount of material in a unit volume, say 1 cubic
inch, is very much increased ; in other words, the density of the gas is
increased as the pressure is increased. If accurate measurements be
made of the different pressures applied and the corresponding vol-
umes assumed by the air, a constant relationship will be discovered,
such as is expressed in Boyle's Law, stated above. The meaning of
the phrase in the law, the volume of a gas is inversely as the pressure,
is that as the one quantity is increased the other is decreased in just
the same proportion. To illustrate, if a volume of a gas measure 1
cubic foot under a pressure of 10 pounds, and the pressure be
increased to 15 pounds, in other words, || or f times, then the vol-
ume will change from 1 cubic foot to 1 -s- f = f cubic foot. If the
pressure be decreased to say 6 pounds, or -f^ —- f of its original value,
then the volume will become 1 -*- f = f cubic foot, that is, it will
expand.

Such a relation as is expressed in Boyle's Law is known in algebra
as inverse proportion. Since one of the quantities is always decreased
in the same ratio as the other is increased, it follows that the product
of the two quantities thus related must always be the same, that is, a
constant. Hence, another way of expressing Boyle's Law is to say
that the product of the pressure and the corresponding volume of a
definite quantity of a gas is always the same. If V and V1 repre-
sent the volumes of a certain amount of gas, at the corresponding
pressures, P and F, then V X P = V1 X P. In the example
given above, Y == 1 cubic foot, P = 10 pounds, and P1 = 15 pounds,
hence, 1 X 10 = V1 X 15, or V1 == |g- = f cubic foot.

As will be seen later, this law is of great value in all experiments
where results are calculated from measurements of gas volumes.

28 CHEMICAL PHYSICS.

Vapors from liquids and solids at sufficient temperatures above their
points of condensation behave just like gases.

Divisibility. All matter admits of being subdivided into smaller
particles, and this property is called divisibility. The processes by
which we accomplish the comminution of a solid substance may
be of a mechanical nature, such as cutting, crushing, grinding ; but
beside these modes of subdivision we have other agents or causes
by which matter may be divided into smaller particles, and one of
these agents is heat.

Action of heat on matter. Let us take a piece of ice and
convert it, by means of mortar and pestle, into a very fine powder.
When the smallest particle of this finely powdered ice is placed
under the microscope and heat applied, we shall observe that it
becomes liquid, thus proving that it was capable of further sub-
division, that it consisted of smaller particles, which have now by
the action of heat become movable. By further applying heat to the
liquid particle of water we may convert it into a gas or vapor, which
will escape into the air, or which we may collect in an empty flask.
The flask will be filled completely by this water-gas (or steam)
obtained by vaporizing that minute particle of ice-dust. This fact
demonstrates that mechanical comminution does not carry us beyond
a certain degree of subdivision of matter. That is to say, the smallest
fragment of the finest powder still consists of a very large number of
much smaller particles. To the smallest particles which compose
matter the name molecules has been given.

Molecular theory. The expression molecule is derived from the
Latin word molecula — a little mass, and means the smallest particle
of matter that can exist by itself, or into which matter is capable of
being subdivided by physical actions. To explain more fully what is
meant by the expression molecule, we will return to the conversion of
water into steam.

When water boils at the ordinary atmospheric pressure it expands
about 1800 times, or one cubic inch of water yields about 1800 cubic
inches, equal to about one cubic foot of steam. In explaining this
fact we have either to assume that the water, as well as the steam, is
continuous matter (Fig. 13), or that the water consisted of small par-
ticles of a given size, which now exist in the steam again as such,

FUNDAMENTAL PROPERTIES OF MATTER. 29

FIG. 13.

with the only difference that they are more widely separated from
each other (Fig. 14).

FIG. 14.

Of the many proofs which we have of the fact that the latter
assumption is correct, one may be sufficient, viz., that the quantities
of vapor formed by volatile liquids at any certain temperature above
the boiling-point, in close vessels of the same size, are the same, no
matter whether the vessel was entirely empty or contains the vapors
of one, two, or more other substances. For instance : If we place
one cubic inch of water in a flask holding one cubic foot, from which
flask the air has been previously removed, and then heat the flask to
the boiling-point, the cubic inch of water will evaporate, filling the
vessel with steam. Upon now introducing into the flask a second and

30 CHEMICAL PHYSICS.

a third liquid — for instance, alcohol and ether — we find that of each
of these liquids exactly the same quantity will evaporate which would
have evaporated if these liquids had been introduced into the empty
flask.1 This fact is evidence that there must be small particles of
steam which are not in close contact, that there are spaces between
these particles which may be occupied by the particles of a second,
third, or more substances. To these particles of matter we give the
name molecules, and the spaces between them we call intermolecular

We have thus demonstrated the correctness, or, at least, the likeli-
hood, of the so-called molecular theory, but the proof given is but one
of many. Other facts which lead us to accept the theory of the
molecular condition cf matter are : The passage of gases through
solids : for example, of carbon dioxide gas through red-hot iron ; of
water under pressure through gold ; the decrease in a volume of water
when a salt is dissolved in it ; the extreme divisibility of matter as
shown by solution, etc.

Our conception of molecules (though individually by far too small to make
any impression whatever upon our senses) is so perfect that we have formed an
idea of the actual size of these minute particles of matter. Very good reasons
lead us to believe that the diameter of a molecule is equal to about CTnn&rnnnj
of one inch, and that one cubic inch of a gas under ordinary conditions con-
tains about one hundred thousand million million milions of molecules.

These figures at first glance appear to be beyond the limit of human con-
ception, but in order to give some idea of the size of these molecules it may be
mentioned that if a mass of water as large as a pea were to be magnified to the
size of our earth, each molecule being magnified in the same proportion, these
molecules would represent balls of about two inches in diameter.

While molecules consequently are exceedingly small particles, yet they are
not entirely immeasurable ; they are, as Sir W. Thomson says, pieces of matter
of measurable dimensions, with shape, motion, and laws of action, intelligible
subjects of scientific investigation.

Intimately connected with the molecular theory is the Law (more
correctly, the hypothesis) of Avogadro, which may be stated as follows :
All gases or vapors, without exception, contain, in the same volume, the
same number of molecules, provided temperature and pressure are the
same. Or, in other words : Equal volumes of different gases contain,
under equal circumstances, the same number of molecules. The correct-
ness of this law has good mathematical support deduced from the law
of Boyle, many other facts and considerations leading to the same

1 As each gas, in consequence of its tension, exerts a certain pressure, the pressure in the
flask rises with the introduction of every additional gas.

FUNDAMENTAL PROPERTIES OF MATTER. 31

assumption. We shall learn, hereafter, that the law of Avogadro is
one of the greatest importance to the science of chemistry.

Gravitation. Every particle of matter in the universe attracts
every other particle ; consequently, all masses attract each other, and
this attraction is known as gravitation. The action of gravitation
between the thousands of heavenly bodies moving in the universe is
to be considered by astronomy, but some of the phenomena caused
by the mutual attraction of the substances composing the earth are
of importance for our present consideration.

Such phenomena caused by gravitation are the falling of substances,
the flowing of rivers, the resistance which a substance offers on being
lifted or carried. A body thrown up into the air or deprived of its
support will fall back upon the earth. In this case the mutual attrac-
tion between the earth and the substance has caused its fall. It
might appear that in this case the attraction was not mutual, but ex-
erted by the earth only; it has been proved, however, by most exact
experiments, that there is also an attraction of the falling substance
for the earth, but the amount of the force of this attraction is directly
proportional to th.e mass of the bodies, and consequently too insig-
nificant in the above case to be noticed.

The law of gravitation, known as Newton's law, may thus be stated :
All bodies attract each other with a force directly proportional to
their masses and inversely proportional to the squares of their distance
apart. With regard to the earth and bodies upon it at a given place,
the mass of the earth and the distance between the earth and the
bodies remain the same, so that the only thing that varies is the mass
of the bodies. Hence, according to Newton's Law, the force with
which such bodies are attracted to the earth varies directly as their
masses. In other words, if a body A has twice the mass or quan-
tity of matter as a body B, it will be attracted with twice as much
force to the earth as the body B.

Weight is an expression used to denote the quantity of mutual
attraction between the earth and the body weighed. When we weigh
bodies on a balance, we primarily compare two forces, namely, the
pull of the earth on each of the bodies on the pans of the balance,
nevertheless, we can use the balance to measure mass or quantity of
matter. For if two bodies are exactly balanced, that is, " weigh "
the same, we know that the pull of the earth is the same on each, and
since this attraction, as was shown above, is directly proportional to

32 CHEMICAL PHYSICS.

the masses or quantity of matter in the two bodies, the masses must
be equal. That weight and mass are different ideas is evident from
the fact that the force with which a given body is attracted by the
earth varies according to latitude and elevation above the earth, while
the quantity of matter remains the same. But if two bodies weigh
the same in one place, they will do so in any other place. All our
weighing is a comparison with, or measurement by, some standard
weight, such as pound, ounce, gramme, etc.

For scientific purposes the weight of bodies is sometimes deter-
mined invacuo, because it eliminates an error due to the buoyant effect
of atmospheric air. Weight thus determined is called absolute weighty
while by ordinary methods we obtain apparent weight.

"Weights and measures. For scientific purposes the metric or decimal
system of weights and measures is used the world over. This system is used also
for general purposes by practically all except the English-speaking nations.
While metric weights and measures were legalized in the United States and
Great Britain in 1866, unfortunately neither country has as yet enforced their
general adoption. The U. S. Pharmacopoeia, however, uses the metric system
exclusively, and it finds application in all departments of the U. S. govern-
ment, as also for many other purposes. The basis of the metric system is a
quadrant (one-fourth) of the earth's circumference. This divided into ten mil-
lion parts gives a measure of length termed meter (39.37 inches), and this
unit of linear measure is the basis for the measures of extension and of weight.

Subdivisions of all units of metric measure are denoted by prefixes of Latin
numerals — i. e., ^ by deci, ^Q by centi, -^Q by milli ; while multiples are
denoted by prefixes of the Greek numerals — L e., 10 by deka, 100 by hecto, 1000
by kilo.

The unit of measure of capacity is the cubic decimeter called liter (1.0567
U. S. quart), and the unit of weight is the weight of one cubic centimeter of
water at the temperature of its greatest density, 4° C. (39.2° F.), and this unit
is called gramme (15.43-)- grains). One liter of water, equal to 1000 cubic centi-
meters, at its greatest density weighs 1000 grammes or one kilogram. While
gramme is the unit for weights up to a kilogram, the latter is the unit for all
larger weights, and is generally abbreviated to kilo (2.2046 pounds, avoirdupois).

While in our country for commercial purposes the avoirdupois weight is
chiefly used, the apothecaries' weight is employed in this country and Great
Britain in prescription-writing by all who do not use the metric system. The
common link connecting avoirdupois, troy, apothecaries', and Imperial weights
is the grain, which is the same in the four systems. (For table of weights and
measures, see Appendix.)

Specific weight or specific gravity denotes the weight of a body,
as compared with the weight of an equal bulk or equal volume of
another substance, which is taken as a standard or unit. This standard
adopted for all solids and liquids, if not otherwise stated, is water at

FUNDAMENTAL PROPERTIES OF MATTER. 33

a temperature of 25° C. (77° F.) ; that for gases is either atmospheric
air or, more generally, hydrogen at a temperature of 0° C, (32° F.).

Specific weight is generally expressed in numbers which denote how
many times the weight of an equal bulk of water is contained in the
weight of the substance in question. If we say that mercury has a
specific gravity or density of 13.6, or that alcohol has a specific gravity
of 0.79, we mean that equal volumes of water, mercury, and alcohol
represent weights in the proportion of 1, 13.6, and 0.79, or 100, 1360,
and 79.

Since all liquids and solids expand or contract with change of tem-
perature, it is very important to note the temperature in taking the
specific gravity of substances. For example, the specific gravity of
alcohol is less at 25° C. than that at 15° C., because alcohol expands
with rise of temperature. Likewise, at a given temperature, say 25° C.
it is greater when compared with water at 25° C. than when com-
pared with water at 4° C. or 15° C., because a volume of water
weighs less at 25° C. than it does at 15° C. or 4° C. Since the
change in volume of solids with change in temperature is much less
than in the case of liquids, the difference in specific gravity at differ-
ent temperatures is much less noticeable for solids than for liquids.

Density. Density, in physics, is defined as the mass or quantity
of matter in a unit volume of the substance. In the^metric system
the mass of a unit volume of water at 4° C. (39.2° F.) is 1 gramme,
that is, the density of water at 4° C. is unity. At any other temper-
ature the density of water is less than one. It can be seen that when
the specific gravity of a substance is determined by comparison with
water at 4° C., the number expressing this specific gravity is identical
with the number expressing the density of the substance.

When the comparison is made with water at any other temperature
than 4° C., the figures for the specific gravity and the density of a
substance are not identical, although the difference between them is
usually very small.

The specific gravity of solids heavier than water is generally determined by
first weighing the substance in air and then while suspended in water. The
body will be found to weigh less in water because it displaces a volume of water
equal to its own, and loses a weight equal to that of the water displaced. Con-
sequently the relation between the loss in weight and the weight in air is also
the relation between the weights of equal volumes of water and the substance
examined. If, for instance, a body is found to weigh 6 grammes in air and 2
grammes in water, the loss being 4 grammes, then the relation between the
weights of equal volumes of water and the substance is as 4 to 6, or 1 to 1.5;
the latter being the specific gravity of the substance examined.

The specific gravity of a solid soluble in water is determined by weighing it
3

34 CHEMICAL PHYSICS.

first in air, then in a liquid of known specific gravity, but having no solvent
action on the substance. The weight of the solid in air divided by the weight
of the liquid displaced and the quotient then multiplied by the specific gravity
of the liquid employed, gives the specific weight of the substance examined.

The specific gravity of a solid lighter than water is determined by weighing
it first in air, then in water attached to some heavy substance, the weight of
which in water has been ascertained. The two substances combined will weigh
less in water than the heavy solid alone. The difference in weight between the
two weighings in water added to the weight of the light substance in air gives
the weight of water displaced, and this sum, divided into the weight of the
solid in air, gives its specific gravity.

The method of finding the specific gravity of a solid by weighing in a liquid
depends on the Principle of Archimedes, which says : A body immersed in a liquid
loses a part of its weight equal to the weight of the displaced liquid.

The specific gravity of liquids or gases is determined by weighing in suitable
glass flasks equal volumes of the standard substance and the body to be examined.
The weight of the latter divided by the weight of the standard substance gives
the specific gravity.

Small glass flasks suitably arranged for taking the specific gravity of liquids
are known as pycnometers.

A second method by which the specific gravity of liquids may be determined
is by means of the instruments known as hydrometers, or, if made for some
special purposes, as alcoholometers, urinometers, alkalimeters, lactometers, etc.

Hydrometers are instruments generally made of glass tubes,
having a weight at the lower end to maintain them in an upright
position in the fluid to be tested as to specific gravity, and a stem
above, bearing a scale. The principle upon which their construction
depends is the fact that a solid substance when placed in a liquid
heavier than itself displaces a volume of this liquid equal to the
whole weight of the displacing substance. The hydrometer will
consequently sink lower in liquids of lower specific gravity than in
heavier ones, as the instrument has to displace a larger bulk of liquid
in the lighter than in the heavier liquid in order to displace its own
weight.

"Weight of gases. We have so far considered the gravity of solids
and liquids only, and the next question will be : Do gases also possess
weight — are they also attracted by the earth ? The fact that a gas,
when generated or liberated, expands in every direction, might indi-
cate that the molecules of a gas have no weight, are not attracted by
the earth. A few simple experiments will, however, show that gases,
Jike all other substances, have weight. Thus a flask from which the
atmospheric air has been removed will weigh less than the same flask
when filled with atmospheric air or any other gas.

FUNDAMENTAL PROPERTIES OF MATTER. 35

Barometer. A second method by which may be demonstrated
the fact that atmospheric air possesses weight, is by means of the
barometer. The atmosphere is that ocean of gas which encircles the
earth with a layer some 50 or 100 miles in thickness, exerting a con-
siderable pressure upon all substances by its weight. The instru-
ments used for measuring that pressure are known as barometers, and
the most common form of these is the mercury barometer. It may
be constructed by filling with mercury a glass tube closed at one end
(and about three feet long) and then inverting it in a vessel contain-
ing mercury, when it will be found that the mercury no longer fills
the tube to the top,' but only to a height of about 30 inches, leaving
a vacuum above. The column of mercury is maintained at this
height by the pressure of the, atmosphere upon the surface of the
mercury in the vessel ; a column of mercury about 30 inches high
must consequently exert a pressure equal to the pressure of a column
of the atmosphere of the same diameter as that of the mercury
column.

As the weight of a column of mercury, having a base of one square
inch and a height of about 30 inches, is equal to about 15 pounds, a
column of atmosphere having also a base of one square inch must also
weigh 15 pounds. In other words, the atmospheric pressure is equal
to about 15 pounds to the square inch, or about one ton to the square
foot. This enormous pressure is borne without inconvenience by the
animal frame in consequence of the perfect uniformity of the pressure
in every direction.

A barometer may be constructed of other liquids than mercury, but as the
height of the column must always bear an inverse proportion to the density of
the liquid used, the length of the tube required must be greater for lighter
liquids. As water is 13.6 times lighter than mercury, the height of a water
column to balance the atmospheric pressure is 13.6 times 30 inches, or about 34
feet, which would, therefore, be the height of the column of water required.

It is evident that the pressure of the atmosphere is equal to the weight of a
column of mercury, and also that this weight is directly proportional to the
length of the mercury column. Hence, different atmospheric pressures can be
compared in terms of the length of the mercury column of the barometer,
instead of in terms of pounds per square inch. For example, at a pressure of
15 pounds per square inch, the mercury column is about 30 inches, while at a
pressure of 10 pounds per square inch, it is 20 inches. ^ The ratio of the pres-
sures in pounds is 10 : 15 or 2 : 3, and the ratio of the mercury columns is 20 : 30
or 2 : 3, which is the same. This fact is of interest in experiments in which
gas volumes are dealt with, because calculations have to be made involving a
ratio of pressure*, and since this ratio is the same as that of the lengths of the
mercury column corresponding to the pressures, it simplifies matters greatly to
express pressures in terms of the length of a column of mercury.

36 CHEMICAL PHYSICS.

Changes in the atmospheric pressure. The height of the mer-
cury column in a barometer is not the same at all times, but varies
within certain limits. These variations are due to a number of causes
disturbing the density of the atmosphere, and are chiefly atmospheric
currents, temperature, and the amount of moisture contained in the
atmosphere.

As the height and with it the density of the atmosphere diminishes
gradually from the level of the sea upward, the height of the mercury
column will be lower in localities situated at an elevation. This
diminution of pressure is so constant that the barometer is used for
estimating elevations.

Porosity. We have seen that the molecules of any substance are
not in absolute contact, but that there are spaces between them which
we call intermolecular spaces ; the property of matter to have spaces
between the particles composing it is known as porosity.

In the case of solids, these spaces or pores are scmetimes of con-
siderable size, visible even to the naked eye, as, for instance, in
charcoal, while in most cases they cannot be discovered, even by the
microscope. That even apparently very dense substances are porous,
can be demonstrated by the fact that liquids may be pressed through
metallic disks of considerable thickness, that gases may be caused to
pass through plates of metal or stone, that solids dissolve in liquids
without showing a corresponding increase in volume of the solution
thus obtained, and, finally, also by the fact that substances suffer ex-
pansion or contraction in consequence of increased or diminished
heat, or in consequence of mechanical pressure.

Surface. In every-day life the expression "surface" refers to that
part of a substance which is open to our senses, visible and measur-
able ; but from a more scientific point of view, we have also to take
into consideration those surfaces which, in consequence of porosity,
extend to the interior of matter and are invisible to our eyes and
absolutely immeasurable by instruments.

Surface-action. Attraction acts differently under different condi-
tions, and, accordingly, we assign different names to it. We call it
cohesion when it acts between molecules, gravitation when acting
between masses, and surface-action or surface-attraction when the
attraction is exerted either by the visible surface or by that surface
which pervades the whole interior of matter. The phenomena caused

FUNDAMENTAL PROPERTIES OF MATTER. 37

by this surface-action are extremely manifold, and some are of suffi-
cient interest to be taken into consideration.

Adhesion. Most solid substances, when immersed in water,
alcohol, or many other liquids, become moist ; immersed in mercury,
they remain dry. We explain this fact by saying that the surfaces
of most solid substances exert an attraction for the particles of such
liquids as water and alcohol to such an extent that these particles
adhere to the surface of the solids. Such an attraction, however,
does not manifest itself for the particles of mercury. This form of
surface-attraction by which liquids are caused to adhere to solids is
called adhesion.

This adhesion may be noticed also between two plates having plane
surfaces. A drop of water pressed between these plates will cause
them to adhere to each other. The application and use of glue and
mucilage, our methods of writing and painting, the welding together
of pieces of metal, etc., depend on this kind of surface action.

Capillary attraction. While it is the general rule that liquids
in vessels present a horizontal surface, this rule does not hold good
near the sides of the vessel. When the liquids wet the vessel, as in
the case of water in a glass vessel, the surface is somewhat concave
in consequence of the attraction of the glass surface for the particles
of water ; on the contrary, when the liquids do not wet the vessel, as
in the case of mercury in a glass vessel, the surface is somewhat
convex. The smaller the diameter of the vessel holding the liquids,
the more concave or convex will the surface be. If a narrow tube is
placed in a liquid, this surface-action will be more striking, and it
will be found that a liquid wetting the tube will not only have a
completely concave surface, but the level of the liquid stands per-
ceptibly higher in the tube than the level of the liquid outside.
Substances not wetting the tube will show the reverse action, namely,
the surface inside of the tube will be convex, and will be below the
level of the liquid outside.

The attraction of the surface of tubes for liquids, manifesting
itself in the concave shape of the surface and in the elevation of the
liquid near the tube, is known as capillary attraction. Capillary
elevations and depressions depend upon the diameter of the tube,
temperature, and the nature of the liquid. The narrower the tube,
the higher the elevation or the lower the depression ; both are
diminished by increased temperature. Capillary elevations and

38 CHEMICAL PHYSICS.

depressions, all other circumstances being equal, are inversely pro-
portional to the diameters of the tubes.

Defining the phenomena of capillary attraction more scientifically,
we may say that the adhesive force of glass, wood, etc., for water and
most other liquids exceeds the cohesive force acting between the
molecules of these liquids, while in mercury the cohesive force pre-
dominates over the adhesive.

The rise or fall of liquids in capillary tubes is explained thus : There is an
attraction between the particles in the surface of a liquid which causes the
surface to act like a stretched membrane. It requires force to separate the
particles in the surface and this force is spoken of as the surface tension of the
liquid. Proof of this tension is seen in the fact that insects can stand on water
without breaking through, and that an oily needle can float on water although
it is heavier than it. Another principle in physics is that a stretched surface
of a spherical form exerts a force toward the center of curvature of the surface,
and tends to contract toward the center. Illustrations of this are seen in the
fact that drops of liquids assume a spherical form, and that soap bubbles con-
tract when the air in the interior of them is allowed to escape. Now, when a
fine tube is dipped into a liquid that wets it, particles of the liquid are drawn
up by adhesion of the glass, thus causing a curved surface, which, acting like a
membrane, draws up the particles below it by cohesion. The liquid rises until
the weight of the column counterbalances the cohesion between the particles
in the curved surface, that is, the surface tension. Thus we see also why liquids
rise higher in fine tubes than wider ones, since it requires a shorter column
of liquid of greater diameter to equal in weight a longer column of smaller
diameter. Moreover, since surface tension of liquids diminishes as tempera-
ture rises, we see why capillary elevation diminishes as temperature increases.
The same kind of argument will explain why liquids which do not wet a tube,
for example, mercury, will sink in. the tube below the level of the liquid
outside.

Familiar examples of capillary phenomena are the action of lamp-wicks,
the rise of water in wood, sponges, bibulous paper, sand, sugar, and the rise of
sap in the vessels of plants.

Surface-attraction of solids for gases. Any dry solid sub-
stance, carefully weighed, will, after having been exposed to a higher
temperature, show a decrease in weight while yet warm. Upon
cooling, the original weight will be restored. This fact cannot be
explained otherwise than that some substance or substances must
have been expelled by heat, and that this substance or these sub-
stances are reabsorbed on cooling.

This is actually the case, and the substances expelled and reab-
sorbed are the gaseous constituents of the atmospheric air, chiefly the
aqueous vapor.

Every solid substance upon our earth condenses upon its surface

FUNDAMENTAL PROPERTIES OF MATTER. 39

more or less of the gaseous constituents of the atmosphere. This
condensation takes place upon the outer as well as upon the inner
surface. The amount of gas absorbed depends upon the nature of
the gas as well as upon the nature of the absorbing solid. Some of
the so-called porous substances, such as charcoal, generally condense
or absorb larger quantities than solids of a more dense and compact
structure. Heat, as stated above, counteracts this absorbing power.

The absorptive power of charcoal for gases varies with the nature of the
charcoal and the gas absorbed, as will be seen from the following table:

Unit volume of charcoal absorbs —

Boxwood. Cocoanut.

Ammonia gas 90 vols. 172 vols.

Hydrochloric acid gas 85 "

Sulphur dioxide 65 '

Hydrogen sulphide 55 '

Nitrogen monoxide 40 ' 86 vols.

Carbon dioxide 35 ' 68 "

Ethylene gas 35 ' 75 "

Carbon monoxide . 9.42 ' 21 "

Oxygen 9.25 ' 18 "

Nitrogen 7.5 ' 15 "

Hydrogen 1.75 ' 4 "

Pine charcoal has about one-half the absorptive power of boxwood char-
coal. Platinum sponge absorbs about 250 times its volume of oxygen. Other
porous substances, as meerschaum, gypsum, silk, etc., are also very absorbent.

Surface-attraction of solids for liquids or for solids held in
solution. When a mixture of different liquids, or a mixture of
different solids dissolved in a liquid, is brought in contact with or
filtered through a porous solid substance, such as charcoal or bone-
black, it will be found that the surface of the solid substance retains
a certain amount of the liquids or of the solids held in solution, and
that it retains more of one kind than of another.

It is this peculiarity of surface-attraction which is made use of in
purifying drinking-water by allowing it to pass through charcoal.
Bone-black is similarly used for decolorizing sugar-syrup and other
liquids.

Absorbing- power of liquids. In a similar manner as in the
case of solids, liquids also exert an attraction for gases. When a
gas is condensed within the pores or upon the surface of a solid, or
when it is taken up and condensed by a liquid, we call the process
absorption. This absorbing power of different liquids for different
gases varies greatly ; it is facilitated by low temperature and high

40 CHEMICAL PHYSICS.

pressure, and counteracted by high temperature and removal of
pressure. Thus : One volume of water absorbs at ordinary tempera-
ture and pressure about 0.03 volume of oxygen, 1 volume of carbon
dioxide, 30 volumes of sulphur dioxide, and 800 volumes of ammonia.

Diffusion. When a cylindrical glass vessel has been partially
filled with water, and alcohol, which is specifically lighter than
water, is poured upon it, care being taken to prevent a mixing of the
two liquids, so as to form two distinct layers, it will be found that
after a certain lapse of time the two liquids have mixed with each
other, particles of water having entered the alcohol and particles of
alcohol the water, until a uniform mixture of the two liquids has
taken place. Upon repeating the experiment with a layer of water
over a column of solution of common salt, it will again be found that
the two liquids gradually enter one into the other until a uniform
salt solution has been formed.

In a similar manner, two or more gases introduced into a vessel or
a room will readily mix with each other. This gradual passage of
one liquid into another, of a dissolved substance into another liquid,
or of one gas into another gas, is called diffusion.

The rate of diffusion is different for different substances. Saline substances
may be divided into a number of equidiffusive groups. The quantity of a sub-
stance diffused varies also with the temperature. Thus, the rate of diffusion
of hydrochloric acid at 49° C. is 2.18 times that at 15° C. The following table
gives the approximate times of equal diffusion for the substances named :

Hydrochloric acid 1.0 Magnesium sulphate .... 7.0

Sodium chloride 2.3 Albumin 49.0

Sugar 7.0 Caramel 98.0

Magnesium sulphate is one of the least diffusible saline substances, yet it
diffuses 7 times faster than albumin and 14 times faster than caramel.

Diffusion is exhibited also by solids, even at ordinary temperature. Sir "\V.
Roberts- Austen placed gold and lead in contact four years at 18° C., and
found the surfaces united. Gold had penetrated the lead to more than o milli-
meters from the surface, while within 0.75 millimeter from the surface gold
was found at the rate of 1 oz. 6 pwt. per ton, which would be profitable to
extract.

The phenomena of diffusion can be explained only on the theory that matter
is made up of particles or molecules in motion. They are one of the strong
links in the chain of evidence upon which the molecular theory of matter is
founded.

Osmose. Dialysis. This diffusion takes place also when two
liquids are separated by a porous diaphragm, sucb as bladder or
parchment paper, and it is then called osmose, endosmosis, or dialysis.

FUNDAMENTAL PROPERTIES OF MATTER. 41

The apparatus used for dialysis is called a dialyzer (Fig. 1 5), and
consists usually of a glass cylinder, open at one end and closed at the
other by the membrane to be used as the separating medium. This
vessel is placed into another, and
the two liquids are introduced into
the two vessels. If the inner
vessel be filled with a salt solution
and the outer one with pure water,
it will be found that part of the
salt solution passes through the
membrane into the water, whilst
at the same time water passes
over to the salt solution

On subjecting different sub-
stances to this process of dialysis, it has been found that some sub-
stances pass through the membrane with much greater facility or in
larger quantities than others, and that some do not pass through at
all. As a general rule, crystallizable substances pass through more
freely than amorphous substances. Those substances which do not
pass through membranes in the process of dialysis are known as col-
loids, those which diffuse rapidly crystalloids.

Capillary attraction, or, more generally speaking, surface-attrac-
tion, is undoubtedly to some extent the cause of the phenomena of
osmose, the surface of the diaphragm exercising an attraction upon
the liquids.

Diffusion through the membrane will not take place unless the
membrane is in contact with water, and, moreover, its limit will be
reached when the concentration outside is the same as that inside the
dialyzer. Hence, a large quantity of water should be on the outside
and often renewed. Generally, water flows through the membrane
toward the denser liquid, which increases in volume, but alcohol and
ether are exceptions. They act like liquids which are denser than
water. In the case of acids, water flows either into the acids or from
the acids, according as they are more or less dilute. When a dilute
alcohol is kept for a time in a bladder the volume diminishes, but
the alcoholic strength increases. The reason of this is, no doubt,
that the bladder permits the water to pass rather than the alcohol.

An interesting effect of osmosis is seen in the purgative action of
magnesium sulphate. A solution of this salt is not readily absorbed
and causes a flow of water from the intestinal bloodvessels by
osmosis, which, together with the direct stimulating action of the
salt to peristalsis, causes purging action. All strong saline solutions,

42 CHEMICAL PHYSICS.

above 0.7 per cent., abstract liquids from animal tissues when in con-
tact with them.

Diffusion of gases. A diffusion similar to that of liquids takes
place also when two different gases are separated from each other by
some porous substance, such as burned clay, gypsum, and others.

It has been found that specifically lighter gases diffuse with greater rapidity
than the heavier ones. The quantities of two different gases which diffuse
into one another in a given time are, as a general rule, inversely as the square
roots of their specific gravities. Oxygen is sixteen times as heavy as hydrogen ;
when the two gases diffuse, it will be found that four times as much hydrogen
has penetrated into the oxygen as of the latter gas into the hydrogen. This
regularity in the diffusion of gases is expressed in the Law of Graham, thus:
The velocity of the diffusion of any gas is inversely proportional to the square
root of its density.

Indestructibility. All matter is indestructible — i. e., cannot pos-
sibly be destroyed by any means whatever, and this property is known
as indestructibility. Form, shape, appearance, properties, etc., of
matter may be changed in many different ways, but the matter itself
can never be annihilated. Apparently, matter often disappears, as,
for instance, when water evaporates or oil burns; but these apparent
destructions indicate simply a change in the form of matter; in both
cases gases are formed, which become invisible constituents of the
atmospheric air, and can, therefore, not be seen for the time being,
but may be recoudensed or rendered visible in various ways.

Not only is matter indestructible, energy also partakes of this
property. This is expressed in the Law of the conservation of energy,
which says that in a limited system of bodies no gain or loss of
energy is ever observed. But energy may be converted from one
form into some other form. Motion may be converted into heat, and
heat into motion, or this motion into electrical energy and chemical
energy. In fact, all the different forms of energy are convertible one
into the other, theoretically, without loss. This fact is spoken of as
the Law of the correlation of energies.

QUESTIONS. — Define matter, force, and energy. Describe the character-
istic properties of matter in the solid, liquid, and gaseous states. State the dif-
ference between amorphous, crystalline, polymorphous, and isomorphous sub-
stances. State the laws of Boyle and Avogadro. Explain the terms mass and
molecule. What are cohesion, adhesion, and gravitation? Mention instances
of their action. Give a definition of weight and of specific weight. Explain
construction and use of the mercury barometer. Define capillary attraction,
absorption, diffusion, and osmose ; give instances illustrating their action.
What is meant by saying that matter and energy are indestructible?

HEAT. 43

2. HEAT.

Motion of molecules. If we place over a gas-flame a vessel con-
taining a lump of ice of the temperature of 0° C., or 32° F., the ice
melts and becomes converted into water ; but if we measure with a
thermometer the temperature of the water at the moment when the
last particle of ice is melted, we still find it at the freezing-point,
0° C. or 32° F. From the position of the vessel over the flame, as
well as from .the fact that the ice has been liquefied, we know that
the vessel and its contents have absorbed heat. Yet vessel and water
show the same temperature as before. If the heat of the flame is
allowed to continue its action on the ice-cold water, the thermometer
will soon indicate a rapid absorption of heat until the temperature
reaches 100° C. or 212° F. Then the water begins to boil and
escapes in the form of steam, but the temperature remains stationary
until the last particle of water has disappeared.

There must be, consequently, some relation between the state of
aggregation of a substance and that agent which we call heat. It was
the heat which liquefied the ice, it was the heat which converted the
liquid water into steam or gaseous water. Yet the water, having
absorbed considerable heat during the process of melting, shows a
temperature of 0° C. (32° F.), and the steam also having absorbed
large quantities of heat, shows 100° C. (212° F.), the temperature of
boiling water. A certain amount of heat has consequently been lost
or at least hidden. What has become of it?

To answer this we must first examine a little further into the
nature of heat. It is a well-known fact that when two solid bodies
are rubbed together heat is produced. Ice may be melted and water
boiled by friction ; wood may be made to ignite by rubbing it suita-
bly. It is found by accurate experiments that there is an intimate
relation between the amount of heat generated and the amount of
work done to generate it. The amount of heat is always equivalent
to the amount of work expended. This fact is one of the manifesta-
tions of the law known as the law of the correlation of energy.

Many other illustrations of production of heat by the expenditure
of work could be given, and all would point to the conclusion that
heat is associated in some way with the condition of the small parti-
cles of which substances are made up — i. e., the molecules.

It is believed that the molecules of all bodies are in motion.
Those of gases are perfectly free to move in any direction, while in
liquids and solids they are restricted in their motion. In solids the

44 CHEMICAL PHYSICS.

molecules are held rigidly in a fixed position and can vibrate only
back and forth. The molecules thus have a certain energy of motion
which is called kinetic energy, and in liquids and solids an energy of
position also, known as potential energy. This potential energy is
due to the position or molecular arrangement of the particles, and to
make a change in this necessitates the overcoming of the forces
which hold the molecules in place by an expenditure of energy from
some outside source.

Thus it is believed that whenever heat energy is added to a body
it either goes to increasing the motion of molecules — i. e., the kinetic
energy, or to making a change in the relative positions of the mole-
cules— i. e., in their potential energy, or to both.

When the motion of the molecules is increased — i. e, when the
kinetic energy is increased — there is a rise in temperature, which we
can measure by a thermometer. What we call temperature is the
degree or intensity of the sensible heat of a body.

On the other, hand, heat is absorbed whenever solids pass into the
liquid state ; or liquids into the gaseous state. This fact is often
made use of in producing artificial cold. Thus, liquefied ammonia is
employed in the manufacture of ice, the required low temperature
being produced by evaporation of the ammonia. Similarly, the heat
absorbed during the liquefaction of snow or powdered ice by an
admixture of common salt and the liquefaction of the latter through
solution serve for generating a low temperature. The action of the
various freezing-mixtures depends on this principle.

Latent heat. Sometimes heat may be added to a body without
any change of temperature, as above in the case of the melting of ice
and the boiling of water. In such cases it is believed that the heat
added is absorbed in changing the relative arrangement of the mole-
cules, which change must evidently take place in passing from solid
to liquid water and from liquid to gaseous water. This will account
for the apparent loss of heat in melting ice or in boiling water. It
is lost only to our senses, and exists in another form as potential
energy of the molecules ; hence it is called latent heat.

This latent heat is given out again when the molecules return to
their former arrangement. Hence steam in condensing to water, and
water in assuming the solid state, give off large quantities of heat.

Sources of heat. Our principal source of heat is the sun. Other
sources are : The interior of the earth, the high temperature of which
is made manifest by the existence of volcanoes and by the increase of

SEAT. 45

temperature noted in boreholes sunk into the earth's crust ; mechan-
ical actions, as friction and compression ; electric currents ; and, finally,
chemical action, as witnessed in the ordinary processes of combustion
and of animal life.

Up to within a few years ago the principal method for generating heat de-
pended on combustion. Heat generated by electricity is now at our command.
The introduction of the electric furnace has provided means for obtaining much
higher temperatures than formerly. It is through these modern means that
temperatures are produced sufficiently high for the liquefaction or volatilization
of all substances.

On the other hand, during the last few years methods have been invented
for producing very much lower temperatures than formerly. Several gases
which were believed to be permanent can now be liquefied, and even solidified.

Heat Effects. The most familiar changes resulting from the
application of heat, that is, from the absorption of heat energy, are
those affecting the volume, the temperature, and the molecular arrange-
ment or physical state of matter. These changes do not take place
independently, but accompany one another. Chemical changes are
also often produced by application of heat, but these are considered
in chemistry.

Increase of volume by heat. As a general rule^ the volume of
any mass increases with increase in its temperature, but this increase is
not alike for all matter. Gases expand more than liquids, liquids
more than solids, and of the latter the metals more than most other
solid substances. While the expansion of any two or more different
solids or liquids is not alike, gases show a fixed regularity in this
respect, namely, all gases without exception expand or contract
alike when the temperature is raised or lowered an equal number of
degrees.

This expansion or contraction of gases is 0.3665 per cent., or ^ of their
volume at 0° C. for every degree centigrade ; thus 100 volumes of air become
100.3665 volumes when heated from 0° to 1° C., or 136.65 when heated from
0° to 100° C. This regularity in the expansion and contraction of gases is
expressed in the Law of Charles, which says : If the pressure remain constant, the
volume of a gas increases regularly as the temperature increases, and decreases as
the temperature decreases. If heat be applied to a gas confined in a closed ves-
sel and be thus prevented from expanding, the increase of heat will manifest
itself as pressure, which rises with the same regularity as shown for expansion,
viz., 0.3665 per cent, for every degree centigrade.

It often becomes necessary to reduce the volume of a gas measured at any
temperature and at any pressure to the volume it would occupy at 0° C. and
760 mm. pressure, which have been adopted as normal temperature and press-

46 CHEMICAL PHYSICS.

ure. The method for making this calculation is given in the paragraph on
gas-analysis, for which see Index.

In expansion of solids and liquids the heat energy applied is utilized partly
in forcing the molecules farther apart or overcoming cohesion, partly in raising
the temperature or giving the molecules greater motion, and partly in doing
external work, that is, work that the expanding body does in raising a load that
may be resting upon it, or overcoming any force exerted against it. In the
expansion of gases, there being no cohesion between the molecules, the heat
energy is utilized in raising the temperature and in doing work by the gas against
external force.

Expansion is a very important thing which must be taken into account by
constructors, for example, of bridges, railroad beds, etc. Also in very careful
physical measurements, expansion of glass apparatus, solutions, barometers,
etc., must be carefully noted.

Increase in temperature by heat. As was said above, the present
molecular theory of matter regards the molecules as in motion, and
the result of this energy of motion is what we call temperature, or
intensity or degree of heat. Anything that increases this motion of
the molecules, causes a rise of temperature. Our skin is possessed of
nerve structures by which we can judge whether a body is hot or
cold or whether one body is hotter than another, but these are not
delicate enough to make quantitative distinctions between tempera-
tures. For this purpose we make use of instruments called

Thermometers. In these, use is made of the fact that bodies expand
while the temperature rises, and that the expansion is proportional to
rise of temperature. Thermometers, therefore, measure directly only
expansion, and indirectly degrees of heat, but the expansion is used
as a measure of the degree of heat. The most common thermometer
is the mercury thermometer. This instrument may be easily con-
structed by filling a glass tube, having a bulb at the lower end, with
mercury, and heating the tube until the mercury boils and all air has
been expelled, when the tube is sealed. It is then placed in steam
arising from water boiling actively under normal barometric pressure
of 760 millimeters of mercury, and the point to which the mercury
rises is marked B. P. (boiling-point) ; after which it is placed in melting
ice, and the point to which the mercury sinks is marked F. P. (freezing-
point). The distance between the boiling- and freezing-points is then
divided into 100 degrees in the so-called centigrade or Celsius
thermometer, into 80 degrees in the Reaumur thermometer, and into
180 degrees in the Fahrenheit thermometer. The inventor of the
latter instrument, Fahrenheit, commenced counting not from the
freezing-point, but 32 degrees below it, which causes the freezing-

HEAT.

47

point to be at 32°, and the boiling-point at 180 degrees above it, or at
212°. (Fig. 16.) Degrees of temperature below the zero point of
either instrument are designated by — , i. e.y minus.

100

0°

FIG. 16.

....BE—

212

As 100 degrees centigrade are equivalent to 180 degrees Fahrenheit, it follows
that 1 degree C. = 1.8 degree F., or 1 degree F. =
\% degree C. In converting the degrees from one
scale to the other it must be remembered that the
zero point of Fahrenheit is 32 degrees below the
zero on the centigrade scale. Consequently, in
converting the reading on a Fahrenheit scale into
centigrade degrees, 82 degrees must be deducted,
or, vice versa, be added, before the calculation can
be made. In other words, to convert Fahrenheit
into centigrade : Subtract 32 and divide by 1.8 ; to
convert centigrade into Fahrenheit : Multiply by
1.8 and add 32.

Recording or self-registering thermome-
ters. One kind of these instruments is so con-
structed as to show the highest, the other the
lowest temperature to which the thermometer had
been exposed from the time it was last adjusted.
The physician's fever thermometer is a maximum
recording thermometer with a scale ranging usu-
ally from 94° to 112° F. These thermometers
have near the bulb a constriction in the tube
which breaks the column of mercury when it con-
tracts. Consequently the thin column of mercury
retains its position on cooling, but may be forced
back through the constriction into the bulb by
shaking the instrument.

p-p.

32°

Centigrade. Fahrenheit.
Thermometric scales.

Absolute temperature. If differences

of temperature are due to faster or slower motion of molecules, we
can well imagine that there is a limit in both directions. Where the
limit is to be found for rapidity of motion is unknown, but good rea-
sons lead us to believe that we know the point at which molecular
motion ceases.

One of the reasons which lead us to believe in the correctness of
this statement is the Law of Charles, above mentioned. In accord-
ance with this law, it follows that if a mass of air at 0° C. is heated,
its volume is increased -3-7-3- of the original volume for every degree
its temperature is raised. At 273° C. its volume is consequently

48 CHEMICAL PHYSICS.

doubled, and at 546° C. tripled. If a mass of air is cooled below
0° C., its volume is diminished ^^ of its volume for every degree
its temperature is lowered. Consequently, if its volume were to
continue to decrease at that rate until it reached — 273° C., mathe-
matically speaking its volume would become nothing. In fact,
the air long before this low temperature had been reached would
cease to be a gas — would first liquefy, then solidify, and at the tem-
perature of — 273° C. would become a compact mass in which the
molecules were at absolute rest. This point of no heat is called the
absolute zero, and temperature reckoned from this point is called
absolute temperature.

The fraction -^7-3- is called the coefficient of expansion for centigrade
degrees, while ^y is the coefficient of expansion for degrees of
Fahrenheit. The absolute temperature may be found by adding 273
to the reading on a centigrade thermometer, or 459 to the reading on
a Fahrenheit thermometer.

While the temperature of absolute zero may never be obtainable by man,
so much successful work in the field of low temperatures has been done lately
that temperatures within 9 degrees of absolute zero have been observed.

In chemistry and other fields, temperature is often indicated by such phrases
as red heat, white heat, etc. The following table gives approximately the
degrees corresponding to such expressions :

Incipient red heat 525° C. (977° F.).

Dark red heat 700° C. (1292° F.).

Bright red heat 950° C. (1742° F.).

Yellow heat 1100° C. (2012° F.).

Incipient white heat . , 1300° C. (2372° P.).

White heat 1500° C. (2732° F.).

Mechanical equivalent of heat. While thermometers indicate
the intensity of heat, it is often desirable to measure heat quantities.
These determinations are based on the intimate relationship existing
between heat and mechanical or molecular motion, which are capable
of being converted one into the other. Thus, friction produces heat
and heat produces motion in the steam engine. Heat, through its
power to produce motion, can do work, and the amount of work it
can do depends on the quantity of heat.

The unit of heat quantity now universally used in chemical and physiological
work is the calorie. It is the amount of heat consumed in raising 1 kilogram
of water from 0° C. to 1° C. (or, approximately, 1 pound of water 4 degrees of
Fahrenheit). If this amount of heat could all be made to do mechanical work.

HEAT. 49

it would be sufficient to raise. 420 kilograms 1 meter high, or 3000 pounds 1 foot
high — L e., the calorie is equivalent to 420 kilogram-meters, or 3000 foot pounds.
The heat generated by combustion is determined in the laboratory by means of
an apparatus known as the calorimeter. This is generally so constructed that
a definite weight of substance may be burned in a chamber surrounded by cold
water. The rise in temperature of this known quantity of water serves as the
basis for calculation.

Specific heat. Equal weights of different substances require dif-
ferent quantities of heat to raise them to the same temperature. For
instance : The same quantity of heat which is sufficient to raise 1
pound of water from 60° to 70° will raise the temperature of 1
pound of olive oil from 60° to 80°, or that of 2 pounds of olive oil from
60° to 70°. Olive oil consequently requires only one-half of the heat
necessary to raise an equal weight of water the same number of degrees.
As water has been selected as the standard for comparison, we may
say that specific heat is the heat required to raise a certain weight of
a substance a certain number of degrees, compared with the heat
required to raise an equal weight of water the same number of
degrees.

The heat required to raise 1 gramme of water 1 degree centigrade
is usually taken as the unit of comparison. On thus comparing
olive oil, we find its specific heat to be J. If we say the specific
heat of mercury is ^-, we indicate that equal quantities of heat will
be required to raise 1 pound of water or 32 pounds of mercury 1
degree, or that the heat which raises 1 pound of water 1 degree will
raise 1 pound of mercury 32 degrees.

Conduction of heat. When the end of a metallic bar is heated,
a rise in its temperature is soon noticed at a distance from the heated
part. This transfer of heat from some source, for instance from a
flame to a cold substance, is practically a transfer of motion from
more rapidly moving molecules to those moving more slowly. It
may be compared to the motion imparted to a billiard ball at rest or
moving slowly by another ball propelled with greater velocity. The
more rapidly moving ball will lose part of its velocity in imparting
motion to the other ball. Similarly the rapidly moving molecules of
the hot body in transferring motion to molecules moving slowly in
the cold body lose some of their velocity — i. e., the hot body itself
becomes cooler. The expression " cooling off" must never be under-
stood to imply a transfer of cold, but always a removal of heat. In
taking a cold bath, or in applying an ice-bag to a fever patient, we

50 CHEMICAL PHYSICS.

bring about a slower molecular motion in the tissues exposed to the
cold material.

The direct transfer of molecular motion is called conduction of heat,
but in examining various materials we find that they show a great
difference in their power to conduct heat. For instance, if we hold in
a flame the end of a glass rod, it may be made red-hot, while but little
increase of heat will be perceived at the other end. We accordingly
distinguish between good and bad conductors of heat. Gases and
liquids (mercury excepted) are bad conductors, and of the solids
the metals are the best. The following table gives the comparative
heat-conducting power of a number of substances, that of silver being
taken as the standard, and represented by 1 :

Copper . . . .0.96

Iron . . . - . 0.20

Stone .... 0.006
Water 0.002

Glass .... 0.0005

Wool .... 0.00012

Paper .... 0.000094

Air . 0.000049

Convection. On fastening a piece of ice to the bottom of a test-
tube, and filling this with water and holding it over a flame in such
a manner that only the upper portion of the tube is heated, the water
may be made to boil before the ice has been melted. The reason is
that water is a bad conductor of heat. If the flame be applied to the
lower part of the test-tube, the whole mass of water will remain
cold until the ice has melted, and the temperature will then rise
evenly through the mass of water, because the heated lighter par-
ticles will move upward while the colder ones move downward.
Thus ascending and descending currents are produced, equalizing the
temperature. The term convection is applied to this method of con-
veying and distributing heat. Air or gases behave similarly, and
this fact is of practical interest in the construction of chimneys and
in heating and ventilating buildings.

Radiation of heat. A heated body, for instance a ball of red-hot
iron, suspended in the air or in a vacuum will heat objects near by.
If a screen is placed between these objects and the heated body, no
rise in temperature is noticed. Heat is here propagated through
space in straight lines, commonly spoken of as heat rays.

In order to explain these phenomena, as also others closely related
to them, such as those of light and electricity, it has been necessary
to assume the existence of some agent that serves as a means for this
propagation. This hypothetical agent, called ether, is a medium of

HEAT. 51

extreme tenuity and elasticity supposed to be diffused throughout
the universe, and indeed permeating all matter.

Similarly as waves of water are generated by dropping a stone into
it, and as sound waves are produced in air by causing it to vibrate,
so heat waves are produced in the ether whenever it is disturbed by
the rapid molecular motion of a heated body.

While our views regarding the nature of ether are of a hypothetical
character, there can be no doubt of the existence of these heat waves.
Indeed, their length, their velocity, and many other features have
been fully determined ; they obey largely the same laws which have
been established for light waves — i. e., when striking against a body
they are generally reflected, transmitted, diffused, or absorbed. It
is this absorption of heat, as we call it, which causes the heating-
effects through space. It may be compared to the motion that can
be imparted to an object floating on still water. By disturbing the
water, as by dropping a stone into it at a distance from the floating
object, concentric ripples or waves pass from the point where the
water was disturbed, and in striking the floating object cause it to
move. Similarly waves of heat pass from a heated body through
the ether in every direction, and in striking against a body cause its
molecules to move faster — i. e., render it warmer. It is by this
process that heat is transmitted from the sun to the earth.

Change in molecular state. As was pointed out above in the discus-
sion of the nature of heat, it requires energy to bring about a change
in the relative position of the molecules of a substance, which is
called internal work. This is true for solids and liquids, but not for
gases, since there is practically no cohesion between the particles of a
gas, and so no work is required to change the position of the particles.
Several familiar phenomena involve change in the molecular state.

Fusion or melting-. This name is applied to the process by which
a solid passes into the liquid state. When a liquid passes into the solid
state, the process is known as solidification. As a rule, when solids
are heated, they begin to melt at a definite temperature, which is known
as the fusion-point or melting-point. Conversely, when liquids are
cooled, they begin to solidify at a definite temperature, which is iden-
tical with the melting-point of the solid. Moreover, the temperature
remains constant as long as fusion or solidification continues.

Solids that are individuals (not mixtures) and are perfectly pure as
far as they melt without decomposition, have definite or sharp melting-

52 CHEMICAL PHYSICS.

points, which fact is utilized in chemistry extensively for determining
the identity of substances and their purity. A small amount of
impurity in a substance often causes a notable change in its melting-
point and the temperature rises between the beginning and the end of
melting, instead of remaining constant.

Some solids, like wax and paraffin, which are mixtures, do not remain
at the same temperature during fusion, and in such cases the melting-
point is taken as the average of the temperatures at which fusion and
solidification begin.

The determination of the melting-point is carried out by introducing
a column about J inch long of the finely powdered substance into a
capillary glass tube sealed at one end, and attaching this to the bulb
of a thermometer. The latter is then dipped into a liquid of high
boiling-point and the temperature is slowly raised. The instant the
substance melts, the temperature is noted, which is the melting-point,
often abbreviated m.-p.

Latent heat of fusion. This is the number of heat units (calories)
required to make 1 gramme of a substance fuse. Different substances
have different latent heats of fusion, but water (ice) has the greatest.
To melt 1 gramme of ice at 0° C. to water at 0° C. requires 80 calories,
or as. much heat becomes latent as will raise 1 gramme of water from
0° C. to 80° C.

Change of volume by fusion. When any solid fuses, a change in
volume always occurs. Some substances expand during fusion, for
example, bismuth, wax ; others contract, for example, brass, cast-iron,
ice. When a solid floats in its own liquid, this is evidence that it con-
tracts on fusion, because the density of the solid is less than that of its
liquid. When a solid sinks in its own liquid, there is expansion on
fusion.

Evaporation and boiling-. Many liquids, even some solids,
evaporate or assume the gaseous state at nearly all temperatures.
Water and ice, mercury, camphor, and many other substances vapor-
ize at temperatures which are far below their regular boiling-points.
This fact is to be explained by the assumption that during the rapid
vibratory motion of the particles of these masses, some particles are
driven from the surface beyond the sphere to which the surrounding
molecules exert an attraction, and thus intermingle with the mole-
cules of the surrounding air.

HEAT. 53

This evaporation, which takes place at various temperatures and at
the surface only, is not to be confounded with boiling, which is the
rapid conversion of a liquid into a gas at a fixed temperature with
the phenomena of ebullition, due to the formation of gas in the mass
of liquid. Boiling-point may, therefore, be defined as the highest
point to which any liquid can be heated under the normal pressure of
one atmosphere.

A liquid in a closed space evaporates until a definite pressure is
attained by the vapor at a fixed temperature, when the liquid and
vapor remain in equilibrium. When this limit is reached the vapor
is said to be " saturated." If the temperature is increased, more
liquid evaporates and the pressure increases. If the temperature of
a saturated vapor falls, some vapor is condensed to liquid, or if the
pressure is increased, some vapor will also condense to liquid. At a
given temperature a saturated vapor exerts a definite pressure,
which is different for different vapors. Thus, in terms of a column
of mercury, at 20° C. (68° F.), water vapor exerts a pressure of 17
mm., alcohol vapor, 60 mm., and ether vapor, 450 mm.

As a rule, in experiments where gas volumes are measured, the gas is satu-
rated with aqueous vapor, which has to be taken into account in making calcu-
lations. If a volume of gas saturated with water-vapor is measured at atmo-
spheric pressure, the tension of the gas alone is the difference between the
barometric pressure and the tension of the saturated water-vapor at the given
temperature.

Tension of Saturated Water-vapor (Regnault).

Temperature,

Tension

Temperature,

Tensic

Centigrade.

in mm.

Centigrade.

in nan

0°

4.6

16°

13.5

1°

4.9

17°

14.4

2°

5.3

18°

15.4

3°

5.7

19°

16.3

4°

61

20°

17.4

5°

6.5

21°

, 18.5

6°

7.0

22°

19.7

7°

7.5

23°

20.9

8°

8.0

24°

22.2

9°

8.5

25°

23.6

]0°

9.1

26°

, S . . . . 25.0

11°

9.8

27°

26.5

12°

10.4

28°

28.1

13°

11.1

29°

29.8

14°

. . . . 11.9

30°

31.6

15° ...

12.7

Distillation is the conversion of a liquid into a gas, and the con-

54 CHEMICAL PHYSICS.

densation of the gas into a liquid, by causing the gas to pass through
a cooling device or condenser, whereby the heat that was made latent
and is necessary for maintaining the gaseous state, is extracted. Dis-
tillation is usually carried on by boiling the liquid under atmospheric
pressure, but sometimes it is done under reduced pressure by exhaust-
ing the air from the apparatus, and then the liquid boils at a much
lower temperature. Distillation is a very useful process for purify-
ing liquids, as, thereby, non- volatile impurities may be easily removed
from liquids. Moreover, mixtures of liquids having different boiling-
points may be separated approximately into the constituents by dis-
tillation (see Fractional Distillation in Index).

The process of vaporization, known as sublimation, has been men-
tioned under Crystals, page 21.

The determination of the boiling-point is best done in a flask, as
shown in Fig. 69, If inflammable or noxious vapors are likely to
be evolved, they may be condensed to the liquid state by connecting
the exit tube of the flask with a condenser. It is important that the
thermometer should not be immersed in the liquid, but should be
surrounded only by the vapor of the liquid. Heat is applied to the
flask until the liquid assumes a state of active ebullition, and when
vapor is escaping freely and the temperature ceases to rise, the latter
is noted. This is the boiling-point of the liquid at the atmospheric
pressure prevailing at the time.

Pure liquids, under the same pressure, always have the same boil-
ing-points, and this property is very important in chemistry in
judging of the purity of liquids. Impure liquids not only have dif-
ferent boiling-points from the pure substances, but also the tempera-
ture rises during boiling instead of remaining constant.

The boiling-points of different liquids vary widely. Thus, mer-
cury boils at 357° C., water at 100° C., alcohol at 78° C., chloroform
at 61° C., ether at 35° C., oxygen at -182.5° C., hydrogen at
—252.5° C., under standard atmospheric pressure.

Latent heat of vaporization. When a liquid passes to the gas-
eous state, heat energy is absorbed or becomes latent^ and, conversely,
when a vapor is condensed to a liquid, the same heat energy is given
out. If the heat is not added to the liquid from the outside, the heat
is absorbed from the liquid itself during vaporization and its tem-
perature falls. The sensation of cold produced by the evaporation
of water, alcohol, ether, chloroform, etc., from the skin is familiar to
every one. It is by evaporation of moisture from the skin that the

HEAT. 55

temperature of our body is kept normal in heated weather. A thin
glass beaker, containing ether and resting on some water on a glass
plate, may quickly be frozen to the plate by passing a rapid current
of air through the ether.

The number of calories of heat required to vaporize 1 gramme of
any liquid at a given temperature is called its latent heat of vaporiza-
tion. The latent heat of steam at 100° C. is 535.9 calories, that is,
it requires as much heat to convert 1 gramme of water at 100° C.
into steam at 100° C., as would raise 535.9 grammes of water 1° C.
in temperature. Steam has the largest latent heat of all known sub-
stances, hence, its value in warming houses, etc., by the steam-heat-
ing process.

Influence of pressure on state of aggregation. We have seen
that the volume of a substance, and, more especially, of a gas, depends
upon pressure and temperature, an increase of pressure or decrease of
temperature causing the volume to become smaller. We learned also
that liquids may be converted into gases, and that this conversion
takes place at a certain fixed temperature, called the boiling-point.
This point, however, changes with the pressure. An increased pres-
sure will raise, a decreased pressure will lower, the boiling-point.

Thus, water boils at the normal pressure of one atmosphere at 100° C. (212°
F.), but it will boil at a lower temperature on mountains in consequence of the
diminished atmospheric pressure. If the pressure be increased, as, for instance,
in steam-boilers, the boiling-point will be raised. Thus, the boiling-point of
water under a pressure of two atmospheres is at 122° C. (251° F.), of five atmo-
spheres at 153° C. (307° F.), of ten atmospheres at 180° C. (356° F.). A differ-
ence of pressure of 10 millimeters from the normal atmospheric pressure (760
mm.) produces a difference of 0.36° C. in the boiling-point of water, 100° C.

QUESTIONS.— What is the view in regard to the nature of heat? What is
meant by sensible heat and latent heat? What is the law in regard to expan-
sion of gases when heated? Explain the construction of a thermometer and
the principle on which it depends. What Fahrenheit temperature corresponds
to 50° C., to 130° C., to — 40° C.? What Centigrade temperature corresponds
to 167° F., to 311° F., to 14° F. ? What is meant by absolute temperature?
Give a definition of the following : Calorie, specific heat, conduction, convec-
tion, and radiation of heat. Define melting and state how the melting-point is
determined ; define latent heat of fusion. State the difference between evapo-
ration and boiling. What is distillation and sublimation? What is meant by
latent heat of vaporization ? What is the influence of pressure on the boiling-
point of liquids ?

56 CHEMICAL PHYSICS.

3. LIGHT.

Light a form of energy. It has been shown in the preceding
chapter that a heated body sends forth waves through the ether,
which in striking a cooler body cause its molecules to vibrate more
quickly — i. e., heat it to a higher temperature. But an increased
molecular motion may produce other effects than heat, as we may
observe by heating an iron bar, which, when sufficiently hot, will
emit light. That light is different in effect from heat, though both
come from the same hot body, may be observed in the action of
luminously hot bodies on certain chemicals ; for example, the silver
salts, which undergo a change in their chemical composition. The
action of sunlight on photographic plates is an excellent illustration.

The explanation of these phenomena is that ether waves of diverse
characters produce different effects. Thus, the waves coming to us
from the sun may affect the sense of touch, and we call the effect
heat ; they may affect the sense of sight, and we term it light ; or
they may affect the composition of matter, when we speak of it as
chemical action. But in all these results we have simply different
manifestations of some form of radiant energy. Light is that form
of energy which may be appreciated by the organ of vision.

Color. Both heat- and light-producing waves or oscillations are
propagated through ether with the same velocity, viz., at the rate of
300,000 kilometers, or 186,000 miles, per second ; but the waves
differ in regard to length and in the amplitude of vibration. Waves
of a particular limited range of frequency (477,000,000 millions to
699,000,000 millions per second) when falling upon the eye produce
a sensation of light. Of these, the slowest — i. e., the waves with
the least frequency and the greatest wave-length — produce a sensa-
tion of red light ; as the frequency increases, the sensation produced
by them is successively that which is termed orange, yellow, green,
blue, indigo, and violet light.

Ether waves of frequency too limited to be visible are called infra-
red waves ; they have, however, great heating power when falling
upon a substance. On the other hand, there are waves of greater
frequency than those which produce a sensation of violet ; they are
also invisible, but have the power of producing chemical action ; they
are called ultra-violet or actinic waves. There is no inherent difference
between any of the different kinds of waves here mentioned ; indeed,
they all may be produced at the same time by the same body.

In what is called daylight there is a mixture of waves of different
frequencies, affecting our eye simultaneously in such a manner

LIGHT.

57

that none of the specific colors predominates. The reason that even
under the influence of this white light most objects show a distinct
color is not, as might be supposed, an inherent color possession of
these objects, but an effect of the light. Without light all objects
are black — i. <?., without light there is no color. There is a great
diversity in the behavior of different substances toward white light.
It may either be absorbed or reflected, or partly absorbed and partly
reflected. If all be absorbed, black is the result ; if all rays except
the red ones be absorbed, the body appears red, etc.

Not only has the number of wave oscillations per second been
determined, but also their length. The longest waves are those pro-
ducing heat ; the shortest ones are the actinic waves. Between them
are the light waves ranging from 650 millionths of a millimeter in
length for red light, to 442 millionths of a millimeter in length for
violet light.

Light rays. Light travels through homogeneous media, as air,
water, and glass, in straight lines, and a very narrow cylinder of light
is called a ray, beam, or pencil of light. Those bodies which readily
transmit luminous rays are said to be transparent, those not trans-
mitting light are called opaque, while translucent bodies are those
permitting light to pass through them to a limited extent.

A body may be self-luminous, like the sun or a flame ; or it may
be luminous by reflected light, like the moon or any object that is
illuminated by daylight or by any luminous body.

Light of itself is invisible, as can be shown by admitting a sun-
beam through a small hole into a dark room. If the air be free
from dust, the beam is invisible ; but if the eye, or any object upon

which it mav strike, is placed in its path,

~ V.
we are made aware of its presence, not

by seeing the light, but by seeing the ob-
ject which emits it or intercepts it.

Reflection. When a ray of light strikes
a mirror or a polished surface obliquely
we notice that a ray of light is thrown off

or reflected from the mirror. On measuring
,1 , . ,_.. « „. , , .

the angle ^ (Fig. 17) made by the entering
or incident ray CB and a perpendicular NB, and the angle r made
by the reflected ray AB and the perpendicular, they will be found
equal. In other words, in plane mirrors the angle of incidence is
always equal to the angle of reflection.

FIG. 17.

Reflection.

58

CHEMICAL PHYSICS.

Upon this reflection depends the formation of the image seen in mirrors.
If a reflecting surface were an absolutely smooth plane, it would be invisible,
and we would see in it simply the images of other subjects. Most objects are
not bounded by absolutely smooth surfaces, and, consequently, the light which
falls upon them is scattered or diffused, thus rendering them visible in all
directions.

Refraction. While a light ray travels in a straight line through
homogeneous media, the ray is bent when passing from a medium
of one density to that of another density, as from air to glass or to
water. Under these conditions, unless the ray enter perpendicularly,

it is bent out of its course, still moving,
however, in a straight path in the
second medium, but in a different
direction from that in the first. This
bending of rays is known as refrac-
tion. It is refraction which causes a
straight stick, when held obliquely
in clear water, to appear bent at the
point of entering the water.

In Fig. 18, SI represents a ray of
light entering a denser medium — say
a plate of glass — with parallel sides.
Here the ray is bent toward the per-
pendicular N'R ; on leaving the denser medium and re-entering the
air it is again bent, but away from the perpendicular to such an
extent that the rays SI and US' (or rather their extensions) are
parallel to one another.

Refraction through prisms. A prism, in optics, is any trans-
parent medium comprised between two plane surfaces inclined to

Refraction by a parallel plate.

Refraction through a prism.

each other. The intersection of the two planes is called the edge, and

LIGHT.

59

the angle between them is called the refracting angle. Triangular
glass prisms are generally used.

In Fig. 19, ABC is a section of a prism. A is called the summit or
apex, and BC the base. A ray of light, SI, falling upon the prism
will not pass through it in a straight line, SIS', but is bent out of its
course twice, in accordance with the law of refraction, first from
I to I', and then to K. The amount of bending depends on the
angle of the prism, its material, and the angle of incidence of the
ray, shown in i, while r is the angle of refraction. The angle D
represents the angle of deviation.

Dispersion. In Fig. 19, the ray is represented by a single line
throughout. In reality, matters are more complicated, as white
light is made up of rays of different colors, each of which has a dif-
ferent angle of refraction. The result is that when a beam of white
light falls on a prism it does not come through as white light, but
the constituent colors are refracted at different angles, giving rise to a
band of light containing all the colors of the rainbow, viz., red,
orange, yellow, green, blue, indigo, violet ; red being less refracted,
violet most. Such a band of colors is known as the prismatic
spectrum.

In Fig. 20, A represents a ray of light which if unbent would strike
a screen at X, but the prism P intervening the ray is refracted and
at the same time resolved into its constituents, which form the spec-
trum, the colors of which are indicated by the initial letters. This

FIG. 20.

Prismatic spectrum.

spreading out of light, and its separation into different colors, are
called dispersion.

The spectroscope is an instrument that serves for conveniently
observing the spectrum. Differently constructed instruments are

60

CHEMICAL PHYSICS.

employed, of which Fig. 21 represents the single-prism spectroscope,
which is most largely used. It consists of the prism P and of
three telescopes directed toward it. The light is permitted to enter
the tube A through a narrow slit at its distal end, while at the
other end a convex lens, called the collimator, serves to collect the
light into nearly parallel beams. These beams pass through the
prism where the dispersion is brought about, and the spectrum thus
formed is observed at d through the telescope B. Through the third

FIG. 21.

Spectroscope.

tube, C, a fine scale for measurement of the relative position of lines
or colors is reflected to the eye of the observer. This scale is usually
photographed on glass, and when illuminated by a candle or some
other stronger light the image of the scale is directed upon the face
of the prism in such a manner that it is reflected down the axis of
the observing telescope, and is seen above or below the spectrum,
according to the direction given to the axis of the scale tube. The
glass vessel a serves as a container for a liquid to be examined spec-
troscopically.

A second form of spectroscope, known as the direct-vision spec-
troscope, is shown in Fig. 22. It consists of a cylindrical tube
provided with ocular and containing from three to seven prisms,

LIGHT. 61

a draw-tube with adjustable slit, and a collimator lens placed
between them to render the rays parallel. The prisms placed
opposite to one another are made of crown glass and flint glass, re-
spectively. The dispersive power of the latter is nearly double that
of crown glass, while the deviating powers of the two glasses do not
differ much. The result

is that a beam of light Fl°- 22-

entering through the slit
undergoes but little de-
viation from its original

COlirse, while there is Direct-vision spectroscope.

sufficient dispersion be-
tween its colors to produce a spectrum available for spectroscopic
uses. When the luminous flame of a candle, oil, or gas is examined
spectroscopically, it shows a continuous spectrum — i. e., this white
light has been decomposed into its constituents.

Bright line spectra. If into a non-luminous flame of a Bunsen
burner a platinum wire which has been previously dipped into
common salt (sodium chloride) be held, the flame will be colored
yellow, and if it be examined by the spectroscope there will be seen
a bright-yellow line in the yellow part of the spectrum, wrhile no
other colors are visible. In thus examining salts of other metals,
such as potassium, lithium, calcium, etc., by holding in the flame by
means of platinum wire, it will be seen that each one gives a number
of characteristic bands or lines in different parts of the spectrum, the
remaining portion being quite dark. So characteristic are these
spectra of different elements that they furnish a distinctive means
of recognition ; and indeed some elements have been discovered by
this method. These spectra can be seen only when the substance is
heated to a point where volatilization takes place, because gases alone
show the property of giving discontinuous, or bright line, spectra,
and no two gases give the same spectrum.

The reason that luminous flames give a continuous spectrum is
that the luminosity is due to light emitted by particles of solid carbon
floating in the burning gas. This shows that the spectroscope fur-
nishes a reliable means of determining whether light proceeds from
a luminous solid or a luminous gas, as all luminous solids and liquids
give continuous spectra.

Absorption spectra. If the spectroscope is so arranged that a
continuous spectrum is obtained from a strongly luminous flame, or

62 CHEMICAL PHYSICS.

from an electric light, and if then a little sodium chloride be evapo-
rated in the flame of a Bunsen burner that has been placed between
the slit and the luminous flame, it will be seen that the spectrum is
no longer continuous, but that a black line intercepts it, a line hold-
ing precisely the position occupied by the yellow sodium line seen
on a dark background when the luminous flame is removed. In
repeating the experiment with the salts of various metals, we find
like conditions, viz., the discontinuous bright color spectra of indi-
vidual metals are converted into spectra showing black lines in the
continuous spectrum obtained from the luminous flame. (See spectra
on plate facing title page.

From these facts we- may draw the conclusion that the vapors of
different substances absorb precisely the same rays that they are
capable of emitting. Such spectra are called absorption spectra, or
reversed spectra.

Absorption spectra are also of interest because, if white sunlight
be examined with a spectroscope of sufficiently high power, it is found
not to be continuous, but to contain many hundreds of black lines,
called after their discoverer Frauenhofer lines. The more prominent
lines are designated by letters or numbers, as shown in the solar spec-
trum represented on the accompanying plate. On comparing these
lines in the sun spectrum with the positions of lines obtained by known
elements, such as iron, sodium, calcium, etc., it is found that they
correspond exactly to one another. The explanation given is this :
The main body of the sun consists of a highly luminous mass sur-
rounded by an atmosphere of cooler vapor. The luminous body
would give a continuous spectrum, but the rays passing through the
vapors of the sun's atmosphere are partly absorbed, and thus a large
number of black lines are produced. Absorption-spectra are, further-
more, of great interest, because when light passes through certain
liquids, such as blood or a solution of quinine sulphate, dark line
spectra are obtained, sufficiently characteristic to assist in the recog-
nition of these substances.

From what has been said, we learn that we have three kinds of
spectra, viz., continuous spectra, produced by luminous solids or
liquids, and possibly by luminous gases tinder high pressure ; bright
line spectra, produced by luminous vapors ; and absorption spectra,
produced by light that has passed through certain media.

The value of the spectroscope depends on the use made of it in
spectroscopic analysis, as both the bright line spectra and absorption
spectra enable us to determine the nature of many substances, and

LIGHT. 63

to differentiate between elements present not only on our globe, but
in other celestial bodies likewise.

Double refraction. A plate of glass will not interfere with read-
ing printed matter over which the plate is laid. But in trying to
read through several varieties of transparent crystalline substances a

FIG. 23.

Double refraction.

peculiar phenomenon is noticed ; as then each letter will be dupli-
cated, as shown in Fig. 23, where a piece of Iceland spar (crystallized
calcium carbonate) is placed over reading matter.

If a pinhole be made through a card, and the card be placed over a
crystal of Iceland spar and held before the eye toward the light, there
will appear to be two holes, with light shining through each. If
the crystal be made to rotate in a plane parallel with the card, then
one of the holes will appear to remain nearly at rest, while the
other rotates about it. These facts show that a ray of light on enter-
ing the crystal is divided into two parts, one of which obeys the
law of regular refraction, and is called the ordinary ray, while the
other, which does not, is termed the extraordinary ray. This power
of certain substances to refract light rays in two directions is known
as double refraction. .

In all crystals which produce double refraction there is one direc-
tion (in some even two directions) in which an object, looked at
through the crystal, does not appear double. The line through
which double refraction is suspended is called the optic qxis, and is a
line around which the molecules appear to be arranged symmetrically.

Polarization. The semitransparent mineral tourmaline is another
substance refracting double. Two rays, the ordinary and the ex-
traordinary, are formed when a ray of light is passed through a plate

64

CHEMICAL PHYSICS.

of this substance, just as in the case of Iceland spar; but tourmaline
possesses the peculiar property of absorbing the ordinary ray, while
the extraordinary one passes through.

If two plates, cut parallel to the axis of the crystal, are laid upon
each other in a crossed position, as AB in Fig. 24, it is found that

FIG. 24.

Tourmaline plates.

light from the first plate is cut off by the second one, and darkness
results. If one plate be turned round upon the other, it will be
found that the combination is most transparent in two positions dif-
fering by 180 degrees, one of them, ab, being the natural position
which the plates originally occupied in the crystal. The combina-
tion is most opaque in the two positions at right angles with these,
while intermediate positions, such as a'b', show intermediate be-
havior. These facts show that light which has passed through one
such plate is in a peculiar condition. It is said to be plane-polarized.
In order to understand polarization of light, we should bear in
mind that the particles of ether undulate in a variety of planes per-
pendicular to the line of propagation. We assume that in polarized
light the undulations of the ether particles take place in a single
plane. These ether undulations may be compared to those taking
place in a cord fastened at one end and shaken by the hand at the

FIG. 25.

Undulation in a cord.

other end, as in Fig. 25. According to whether we move the hand
horizontally, obliquely, or vertically, the undulations will lie in a
horizontal, oblique, or vertical plane, as represented at A.

LIGHT. 65

If a cardboard, with a long slit in it, be held over the string,
the string will vibrate in one plane only, viz., in that of the slit.
Instead of one cardboard, two or more may be used, and as long as
the slits are in one plane the vibrations will proceed in that plane.
If, however, the slit of one card be set at a right angle to that of
another card placed over the string, then vibrations will no longer
be propagated.

To make the action of the tourmaline plates still more intelligible,
we may compare it to that of a grating, A, Fig. 26, formed of parallel
vertical rods which permit the passage of all vertical planes, as
aa, but intercept that of horizontal planes, cc. As long as the rods

FIG. 26.
A

GH

a

.,,11111

Explanatory diagram of the action of tourmaline plates.

of the gratings A and B are in the same plane, a string may be
made to vibrate through these gratings parallel to the rods, but when
set at a right angle this becomes impossible.

When a ray of light strikes a plate of tourmaline it permits the
passage of those undulations which are parallel with its axis, but it
absorbs those undulations which are in planes at right angles to its
axis. The rays which pass through the plate produce the polarized
light.

Polariscope. As the unaided eye cannot differentiate between
common and polarized light, instruments are constructed by which
the phenomena of polarization can be studied, and these instruments
are known as polariscopes, polarimeters, or, in a special case, sac-
clmrimeters. They all contain some substance, known as a polarizer,
such as tourmaline, Iceland spar, etc., serving as a polarizer of light ;
and a second substance, called an analyzer, for the detection of that
light. In the above experiment with tourmaline plates the first
plate serves as a polarizer and the second as an analyzer.

The material used generally for polarization is Iceland spar, as it
is more transparent than tourmaline. Instead of using plates of
this material, prisms, known as NicoVs prisms, are made by sawing

5

66 CHEMICAL PHYSICS.

through a crystal from one obtuse angle to the other. The two

parts, after their surfaces have
been well polished, are joined
by a transparent cement of
Canada balsam. Fig. 27 rep-
resents a section of this prism.
DB indicates the line where the
crystal has been cut and ce-
mented. A ray of light passing

Nicol's prism. fr°m the °bJect tO thf side AD

is doubly refracted in such a

manner that the ordinary ray on striking the balsam is totally re-
flected to the side AB, and there refracted out of the crystal, while
the extraordinary ray passes on and emerges at the side BC as a
polarized ray. If this ray is now passed into a second NicoPs prism
parallel to the first, as if it were a continuation of the latter, it will
pass through unchanged. If the second prism be turned through an
angle of 90 degrees — that is, if the two prisms be crossed — the ray of
light will be cut off entirely. The ray in the second prism becomes
an ordinary one, and is totally reflected at the layer of balsam
through the side of the prism and is lost, as in the case of the first
prism. In intermediate positions between the crossed and the parallel
ones the extraordinary ray from the first prism is decomposed in the
second one partly into an ordinary and partly into an extraordinary
ray. The former is reflected out of the prism, while the latter goes
through, so that more and more light will pass through as the second
prism is turned so as to approach parallelism to the first. Thus it is
easily seen that a Nicol prism may serve not only to produce polar-
ized light, but also to detect such light.

Polarized light is extensively used in the examination of minerals
and salts, as thin slices of crystals belonging to different crystallo-
graphic systems when brought between two NicoPs prisms show
rings or bands of colors characteristic of the respective systems.

Many organic liquids and solids in solution have a peculiar action
on polarized light. Such substances, for example, are sugars, tar-
taric acid, alkaloids, essential oils, etc. If two NicoPs prisms are
crossed so that no light is emitted, and a solution of sugar, for ex-
ample, is placed in a glass tube between the prisms, light will pass.
The sugar turns the direction of vibrations of the light as it comes
from the first prism, and the effect is the same as if the second prism
had been turned with respect to the first one as described above,

LIGHT. 67

where nothing intervened between the prisms. Substances which
have such an effect on polarized light are said to turn the plane of
polarization, and are called optically active. The amount of this
turning or rotation of the plane of polarization can be measured by
noting to what extent the second prism must be turned to the right
or left to produce the original condition, namely, darkness.

Substances which act in such a manner that the analyzer must be
turned to the right to produce darkness are called dextrorotatory, or
right-handed; while those substances acting in the opposite manner
are called levorotatory , or left-handed. Substances acting in neither
way are called optically inactive.

The degree of rotation varies with the quantity of substance in
solution for a definite length of a column of the latter, and hence is
used to determine the percentage strength, for example, that of sugar
in urine and other liquids. Polariscopes are therefore valuable quan-
titative analytical instruments.

All polariscopes consist essentially of a polarizer and an analyzer,
with a tube between them for containing the substance to be exam-
ined, and a scale for reading the amount of rotation produced, all
carried on a suitable metallic support. In addition to these essential
parts, the polariscopes of different makers are provided with numer-
ous contrivances rendering the instruments more perfect and the
analytical results obtained more accurate.

Plates of crystalline substances, as quartz, have a noteworthy
effect when placed in the path of polarized light between a polarizer
and an analyzer. Not only do they prevent the light from being
entirely shut off when the Nicol prisms are crossed, but they produce
sharply defined appearances, as color tints, alternate lines of light
and darkness, equal or unequal illumination of the two halves of
the field of view, etc. The appearances depend on the particular
arrangement and direction of cutting of the crystalline plates. A
full explanation of the cause of these effects is beyond the scope of
this work.

Fig. 28 shows Lippich's polariscope, used chiefly for sugar solu-
tions. The optical arrangement is shown above the drawing of the
instrument, and consists of a telescope, a-a, the analyzer 6, a station-
ary polarizer, c, a movable polarizer, d, and the condensing lens e ;
/represents a number of diaphragms. The liquid to be examined is
placed in the tube, and the rotatory power of the substance is deter-
mined by turning the polarizer to the right or left, as the case may
require. The amount of turning necessary to establish the same con-

68

CHEMICAL PHYSICS.

ditions existing before the optically active substance was brought
between the prisms is read off on the movable disk, which is pro-

FIG. 28.

a b f

fe dfe

Lippich's polariscope.

vided with a scale. A lamp supplies the illumination by means of
a flame colored yellow by sodium.

Chemical effects of light. The well-known bleaching effect that
sunlight has on many dye-stuffs shows that light has the power to
bring about chemical changes. The art of photography is one of
the practical applications of this principle. Plant-life is dependent
on the light that reaches us from the sun. The storage of many
chemicals in the dark, or in colored glass bottles, is often necessary to
protect them from the decomposing influence of light.

QUESTIONS. — What are our views regarding the nature and propagation of
light? Explain reflection, refraction, and dispersion of light. What is the
prismatic spectrum, and how is it obtained ? Give a full explanation of the
spectroscope and of its use in chemical analysis. Define continuous, bright-
line, and absorption-spectra, and state the conditions under which they are
formed. What is meant by double refraction and by polarization of light?
Mention the essential parts of the polariscope, and the use made of it in chem-
ical analysis. How are the different colors produced under the influence of
white light? What is revealed to us by the Frauenhofer lines in the solar
spectrum? Explain the terms dextrorotatory, levorotatory, and optically
inactive substances.

ELECTRICITY. 69

4. ELECTRICITY.

Electricity generated by friction. When a glass tube is rubbed
with a piece of silk, it will be found to have acquired the property
of attracting light bodies, such as scraps of paper, sawdust, etc.
Moreover, if the tube be brought close to the face, a sensation similar
to that produced by the contact of a cobweb will be experienced.
If a knuckle be held near the tube, a peculiar noise is heard, and
a spark may be seen to pass between the tube and the knuckle.

These phenomena show that the tube has acquired peculiar
properties by friction. It is said to be electrified, and the name
electricity is given to the cause producing these phenomena. The
term electricity is derived from the Greek electron, amber, in which
substance the property of attracting light objects after the applica-
tion of friction was first noticed about twenty-five hundred years ago.

Conductors and non-conductors. Besides glass and amber,
there are many substances, such as sulphur, sealing-wax, hard
rubber, etc., which can be readily electrified by friction. On the
other hand, a bar of metal cannot be electrified unless it be fitted to
a glass rod, a piece of rubber, or to certain other substances, and
held by this handle while being rubbed with flannel. . Moreover, it
can be shown that a piece of glass or sulphur will attract particles
— i. c., becomes electrified — at that spot only where it has been rubbed,
while a tube of metal, fastened to a suitable handle, becomes elec-
trified over the whole surface of the tube. These facts show that
electricity when generated in such bodies as glass, sulphur, and
rubber, remains where it has been produced, while in metals it
immediately spreads over the whole mass.

Bodies of the first kind, such as glass, etc., are said to be non-con-
ductors, while materials such as metals are said to be conductors. A
non7conductor is often called an insulator, and a conductor supported
by a non-conductor is said to be insulated.

The reason that conductors, such as metals, cannot be electrified
by friction unless held by a non-conductor, is that the human body is
a good conductor, and therefore carries off the electricity as quickly
as it is generated.

No substance is absolutely non-conducting, but the difference in
this power possessed by what are termed good conductors and non-
conductors is very great. Of conductors, may be mentioned : All
metals, charcoal, acids, saline solutions, living animals and vege-

70 CHEMICAL PHYSICS.

tables, water, moist earth and stones. Non-conductors are : Shellac,
rubber, resins, sulphur, wax, glass, silk, wool, porcelain, dry paper
and dry air.

Duality of electricity. For a further study of electrical phe-
nomena the simple instrument known as the electric pendulum or
pith -ball electroscope may be used. It consists of a pith-ball sus-
pended by a silk fibre from an insulated support. When an electri-
fied glass rod is brought near the ball, the latter is attracted ; but
as soon as it touches the rod the attraction is changed to repulsion,
which lasts as long as the ball retains the electricity it has acquired
by contact. The same phenomena may be shown by employing any
other electrified body, for example a piece of sealing-wax, sulphur,
etc., in place of the glass rod. If while the pith-ball exhibits re-
pulsion for the glass electrified resin is brought near the ball, it is
attracted by the resin ; and when it is repelled by the resin it is
attracted by the glass. These phenomena clearly show that the
electricity developed on the resin is not of the same kind as that
developed on the glass. They exhibit opposite forces toward any
third electrified body, each attracting what the other repels. They
have accordingly received names which indicate opposition. The
electricity which glass acquires when rubbed with silk is called vitre-
ous or positive, and that which resin acquires by friction with flannel,
resinous or negative electricity.

On repeating the experiment with other substances, it is found
that all electrified bodies behave like either glass or resin. An elec-
trified body is spoken of as being charged with electricity ; the
charge may be either positive or negative. Experiments show
that, whenever electricity of one kind is developed, whether by
friction or other means, an equal quantity of the opposite kind is
simultaneously developed. Thus, in rubbing glass and silk the glass
is charged with positive, the silk with negative electricity. If a
conductor receives two charges of electricity of equal quantity but
opposite kind, it exhibits no trace of electricity, the two charges
having neutralized one another.

The kind of electricity which a body obtains by friction with
another body evidently depends on the nature of the bodies. For
instance, if glass be rubbed with cat's skin the glass becomes charged
with negative, but if rubbed with silk it becomes charged with posi-
tive electricity. In the following " potential series " any one of the
bodies named becomes positively electrified when rubbed with one

ELECTRICITY. 71

of the bodies following, but negatively electrified when rubbed with
one of those which precede it :

1. Cat's skin. 5. Silk. 9. Sealing-wax.

2. Flannel. 6. Human body. 10. Resin.

3. Ivory. 7. Wool. 11. Sulphur.

4. Glass. 8. Metals. 12. Gutta-percha.

When an electrified body is brought to its normal condition it is
said to be discharged. The discharge may take place slowly through
the air, or rapidly by bringing the charged body in contact with the
earth directly or by means of a conductor, such as the human body
or a piece of wire. The discharge may be accompanied by a flash of
light, called a spark.

Induction. A body charged with electricity will exert an influ-
ence upon surrounding unelectrified bodies and destroy the neutral
condition existing in them, attracting to the surface next to the elec-
trified body a charge the opposite to that which it contains. But
while one kind of electricity is drawn toward the original electrified
body, an equal quantity of the opposite kind of electricity is driven
toward the farther extremity of the bodies which are under the influ-
ence of the electrified body. This action exerted by an electrified
body on another body is called induction.

Induction of bodies connected with the earth can last only so long
as they are under the influence of the electrified body, because as
soon as this is removed the induced electricity is immediately carried
off by the earth. But if an insulated body be brought near one that
is electrified, and while under its influence be touched at the end
opposite to the electrified body so as to carry off the electricity there
gathered, then on removing the electrified body the previously neu-
tral body will be found to be electrified with a charge opposite in
character to that of the originally electrified body. This method of
imparting electricity is called charging by induction. Induction
furnishes us the explanation of the attraction and repulsion of light
materials by electrified bodies. A positively excited body decdm-
poses the normal charge present in other bodies, and if sufficiently
light they move toward the excited body, discharging their negative
electricity and becoming charged positively through contact; they
are now repelled, as both bodies are electrified alike.

Electrical machines. Electricity produced by friction or by
induction is called static electricity, or electricity at rest, to differ-

72 CHEMICAL PHYSTCS.

cntiate it from current electricity, or electricity in motion, which will
be considered later. Various machines have been constructed to
generate static electricity. In the older forms of such machines
friction between glass plates or glass cylinders and pads of silk served
as the generating source. In the newer and more powerful forms
of static machines, such as the Toepler-Holtz machines, induction
chiefly is used to generate the electricity.

Nature of Electricity. — The most modern theory of the nature of elec-
tricity teaches that it is a manifestation of some manner of strain set up in the
hypothetical ether. But this theory cannot be discussed to advantage in this
volume. However, the following lines may assist the student in getting an
idea of what electricity is, and how it acts.

It has been stated that energy is a universal property of matter, and that
energy, like matter, can neither be created nor destroyed. But energy, like
matter, can be changed from one form .to another, or from one place to
another. According to whether energy manifests itself in masses, in mole-
cules, or in atoms, we speak of mass energy, molecular energy, and atomic
energy. Mass energy becomes manifest in the attractions due to gravitation,
such as the fall of bodies; in magnetic attractions, as when a magnet attracts
iron ; in electric attractions, as when an electrified body attracts light particles
of matter. Molecular energy manifests itself in heat, in light, in magnetism,
and in electricity. Just what the difference is between the different kinds of
molecular motion that produce in one case heat, in others light or electricity,
has never been discovered. It is supposed to be in the form of undulations
or vibrations, the heat undulations having one form, the electric undulations
another form, so that while both kinds of motion are found in the same body
at the same time, they do not interfere with each other.

Exactly as in the case of heat and light, we have to assume that the propa-
gation of electricity through space takes place in the ether. There is, more-
over, a mutual reaction between the vibratory motion of the molecules and the
undulatory motion of the ether, the vibrations producing the undulations, and
the undulations, in turn, producing the vibrations; just as the vibratory strokes
of an oar produce waves, which in turn may produce vibrations in other oars
resting in the water.

The conclusion, therefore, to which we come in regard to the nature of elec-
tricity is this : Electricity is a manifestation of energy believed to consist in
undulations of the ether and vibrations of the grosser molecules of matter.

We see, then, that electricity is neither energy nor matter, but, like heat,
light, and sound, it is an effect produced by energy on matter. But as the
effect cannot be separated from its cause, it is convenient to speak of it as
electric energy, in the same sense as we speak of mechanical enegy, vital energy,
heat energy, or energy in any other form in which it becomes manifest as asso-
ciated with matter.

To obtain electricity, energy in some other form must be expended, whether
it be the energy of our body expended in rubbing together pieces of glass and
silk, or the energy of chemical action, as in a battery cell, or the potential

ELECTRICITY. 73

energy of coal used in the mechanical working of a dynamo. All methods of
generating electricity bring about a disturbance of the electrical equilibrium
existing under normal conditions in ail matter. Whenever this equilibrium is
disturbed there is a tendency to re-establish it, and it is during the process of
re-establishing the equilibrium that work is done electrically.

One of the principal reasons that electrical phenomena offered great diffi-
culties to the investigator is that the electric undulations taking place in the
ether produce no effect whatever on our senses. Waves of air in striking certain
nerves in the ear produce the sensation of sound ; waves of ether affect certain
other nerves in such a manner as to produce the sensations of heat and light,
but man has no nerves that are affected by electric or magnetic waves — i. e.,
he is magnetically and electrically blind and deaf. The slow development of the
science of electricity was due to this fact.

Magnetism. The native iron ore known as lodestone or mag-
netite (ferrous ferric oxide) has the power of attracting bits of steel
or iron, and also possesses the property of pointing north and south
when suspended by a thread. Pieces of iron may be caused to
acquire the same properties, and all bodies possessing them are called
magnets, while magnetism is the term used to designate the magnetic
condition of matter.

Any bar of steel or iron may be magnetized by drawing over it
lengthwise a magnet ; but while a piece of hard steel will remain
a magnet almost indefinitely, soft iron loses its magnetism very
readily. A pivoted or suspended magnet always places itself in the
direction of the " magnetic meridian'7 of the earth — i.e., nearly
north and south. The end of the magnet pointing north is called
its north pole, the other its south pole. On bringing one pole of a
magnet near a suspended magnet it is found that with magnetism, as
with electricity, like poles repel and unlike poles attract each other.
There exists also magnetic induction, corresponding to induction by
electricity. This can be shown by placing a bar of iron near a
magnet, when it is found that the end of the bar nearest the north
pole is converted into a south pole, and vice versa.

When a magnetized bar is dipped into iron filings, masses of the filings adhere
to the two extremities — i. e., to the two poles — while none are found at the
centre. When a magnetic bar is cut in halves at the non-magnetic centre,
two magnets are produced ; and this cutting into smaller lengths may be con-
tinned indefinitely, with the result that each length, and finally each particle,
possesses two poles and an intermediate neutral zone. This fact, as well as
other considerations, has led to the assumption that each molecule of iron is
a magnet in itself. In ordinary iron these little magnets are not arranged
systematically, while in magnetized iron all the north poles point in one direc-
tion, all the south poles in the opposite direction. Moreover, it is supposed

74 CHEMICAL PHYSICS.

that each magnetic molecule is traversed by a closed electric circuit, which
currents become parallel upon magnetization of ordinary iron. According to
this theory, magnetism is a manifestation of electrical energy.

The shape given to magnets is usually that of a bar or of a horse-
shoe. A bar of soft iron laid over the poles of a horseshoe magnet
is called an armature; it serves to retain the full power of the
magnet.

When fine iron filings are sprinkled on a piece of glass or card-
board which has been placed over a magnet, the filings arrange
themselves in lines radiating from either pole, forming graceful
curves from pole to pole. These lines, called lines of magnetic force,
represent the resultant of the combined action of the two poles, the
space surrounding a magnet as far as its influence extends being
termed its magnetic field. A magnetic needle placed anywhere in
this field follows the lines of magnetic force, always assuming a
position tangent to the magnetic curve.

The explanation given for the fact that the magnetic needle points
north and south is that the earth itself is an immense magnet, pos-
sessing two magnetic poles which are close to the geographical poles.

Electricity generated by chemical action. On placing a strip
of ordinary zinc in diluted sulphuric acid, bubbles of hydrogen gas
are evolved on its surface and the zinc gradually dissolves ; a piece
of platinum placed in the acid is not affected at all. If, however,
strips of zinc and platinum are placed in a vessel containing diluted
acid, on connecting the plates above the liquid by a conductor,
for instance by a piece of copper wire, characteristic changes take
place. First, the evolution of gas stops on the zinc, while bubbles
of hydrogen escape from the surface of the platinum. Next, on
placing the connecting wire near a magnetic needle, this is turned
from its course — i. e., deflected. And again, on cutting the wire and
placing the tongue between the two ends, a metallic taste and a
tingling sensation are perceived. All these phenomena cease as soon
as the connection between the plates is broken, and reappear when
connection is again established.

Undoubtedly something takes place in the wire while the plates
are in the diluted acid. Further investigation shows that during
the action of the acid on the metals electricity is generated, which
travels through the wire, imparting to it characteristic properties.

Galvanic or voltaic cells. In place of zinc, platinum, and sul-

ELECTRICITY. 75

phuric acid, many other materials may be used to bring about the

conditions described in the preceding paragraph ; indeed, electricity

is generated whenever two solids (plates or cylinders are generally

used), conductors themselves and connected by a conductor, are

placed in a liquid that has the power to act chemically on one of the

solids. Any such arrangement is termed

a galvanic or voltaic cell. Here chemical FIG. 29.

action causes the generation of electricity,

resulting in the zinc-platinum cell in the

splitting up of sulphuric acid, H2SO4,

the hydrogen, H2, escaping from the

platinum plate, while the group SO4

combines with the zinc, forming zinc

sulphate, ZnSO4, which dissolves in the

water.

Many combinations are employed in
the different cells for generating elec-
tricity. Fig. 29 represents the Daniell Danieii's ceil.
cell. It consists of the glass jar S, con-
taining a saturated solution of cupric sulphate, in which stands the
copper cylinder C. Inside of this cylinder fits a porous cell, A, con-
taining sulphuric acid, and into this dips the zinc plate. Z.

Chemically pure zinc is scarcely acted on by diluted sulphuric acid ; ordi-
nary zinc contains metallic impurities, and as these are in contact with zinc,
they set up a galvanic action, and thus bring about the chemical changes above
described.

What is believed to take place in any galvanic cell is that the
electrolytic fluid — i. e., the active agent in the liquid state — is split
up into two component parts, called ions, and that these ions, charged
with positive and negative electricity, respectively, unload these
charges on the two plates, while an equalizing effect is brought about
through the connecting wire. In other words, there is a constant
disturbance of the electrical equilibrium through chemical action,
and a tendency to re-establish the equilibrium, which tendency pro-
duces the current.

One of the plates (platinum, in the case cited above) is known
as the positive electrode or anode, while the other one (zinc) is the
negative electrode or cathode of the cell. The same terms are used
also to designate the terminals of the wires leading from the two
plates, which terminals are called also + and — poles.

76 CHEMICAL PHYSICS.

Whenever the plates are connected by the conducting wire elec-
tricity passes from the anode through the wire to the cathode, and
through the liquid back to its point of origin. This continuous
motion is called the electric current, and the different parts through
which the current passes are known as the circuit. Whenever the
connection is broken at any point the circuit is said to be open ;
otherwise it is closed. If the circuit be open, both plates become
charged with positive and negative electricity, respectively ; but as
there is no conductor to carry off these charges, further accumulation
stops, and chemical action ceases until the circuit is again closed.

Whenever two or more galvanic cells are connected so as to use in
one circuit the electricity generated by all the cells, the arrangement
is spoken of as a galvanic battery; at present this term is likewise
applied to a single cell.

Electromotive force. The fact that electricity flows continuously
in a closed circuit containing a galvanic cell shows that the cell has
the power of setting electricity in motion, and this power is desig-
nated as electromotive force (E. M. F.), electrical tension, or potential.
It is the result of the tendency to re-establish equilibrium, and
depends upon the difference in the electrical condition of the two
plates ; the greater this difference the greater the E. M. F.

The action of an electric battery may be compared to a pump sending water
from a reservoir through a pipe to a higher elevation ; the water will return to
its former level with a certain force, depending on the height to which it has
been lifted, and the water while descending can be made to do mechanical
work — turn a wheel or set in motion other machinery. Similarly the cur-
rent of electricity on its return trip can be made to do work, and the quantity
of it depends on the E. M. F. generated by the battery.

Electric units. For obvious reasons, it is desirable to measure the
intensity and quantity of electric currents similarly as heat or other
forms of energy are measured. The three chief units adopted for
such measurements are named, in honor of three great pioneers in
electricity, the ohm, the ampere, and the volt.

It has been stated that we differentiate between conductors and
non-conductors, but even the best conductors offer resistance to the
passage of an electric current. The unit of this resistance is called
the ohm, and represents the resistance to a current in a column of
mercury having a section of 1 square millimeter and a length of
106.28 centimeters, at a temperature of 0° C. For practical pur-

ELECTRICITY. 77

poses, sets of coils, known as resistance coils, having a known resist-
ance, are used for measuring electrical resistance.

An ampere is the unit of quantity of current, which may be deter-
mined by measuring the amount of oxygen and hydrogen liberated
by the current from water within a given time.

The weight of copper deposited electrolytically by the current is used also
as a means of determining its amperage. One ampere of current deposits 1.177
grammes of copper per hour. For practical purposes, instruments known as
amperemeters, or ammeters, are used for measuring amperage; use is made in
these instruments of the fact that a current deflects a magnetic needle, which
is made to move over a dial-face graduated in amperes.

In using electric currents for medical purposes, 1 ampere is often too strong
for the tissues of the body. For this reason the unit is divided into 1000 parts,
each part being designated as a milliampere.

The volt is the unit for electromotive force, and is the pressure
required to maintain a current of 1 ampere through a resistance of
1 ohm.

The relation existing between these three units is expressed in
Ohm's law : The strength of the current is equal to the E. M. F.
divided by the resistance of the current.

The chief diiference between frictional and galvanic electricity is
that the first is of high tension but small in amount, while current
electricity is of low tension but greater in amount.

Electromagnets. When a piece of insulated wire is wound in
spiral form around a bar of soft iron, and an electric current is made
to pass through the wire, the iron becomes a magnet for the time
being, and is then called an electromagnet. If a piece of steel is
treated in the same way, it remains a magnet even after the current
is broken, or after it has been taken from the spiral.

As the strength of an electromagnet is proportional to the strength
of the current and the length of wire wound around it, electromagnets
of very much greater power than ordinary magnets can be made
The position of the north and south poles of the magnet depends on
the direction of the current, a reversion of the latter producing a
reversion of the polarity in the electromagnet. Practical use is made
of the electromagnet in telegraph instruments, in the telephone, the
electric bell, and in many other contrivances.

Electricity generated by magnetism. Not only can magnets be
made by subjecting iron to the influence of electric currents, butj

78 CHEMICAL PHYSICS.

vice versa, electric currents, termed magneto-electric currents, can be
generated by the action of magnets on metallic wires. Indeed, when-
ever a magnet is brought near to, or taken away from, a wire, or is
moved about in its neighborhood ; or if, vice versa, a mass of wire is
moved around a magnet — i. e., whenever metallic wires are made to
pass through a magnetic field — temporary electric currents are always
set up in the wire. These induced currents are the result of the
conversion of mechanical energy — i. e.. the energy required to move
a wire or a magnet — into electrical energy.

Use is made of these facts for the generation of electric currents
by suitably constructed machines, known as magneto-electric machines.
In the smaller ones a permanent horseshoe magnet is used. Between
or in front of its poles revolve two coils of insulated wire with soft
iron cores, known as armatures. During rapid revoluting the soft
iron cores are magnetized while opposite one of the poles of the per-
manent magnet, demagnetized while equidistant from the two poles,
and reversed while passing to the opposite pole. The magnetization
and demagnetization of the iron cores have the same effect on the
coils of wire as if a magnet were suddenly introduced into the coil
and as quickly withdrawn. Thus currents will be induced in the
wire, and they will run in opposite directions as the polarity of the
cores changes with each half revolution. Such currents are known
as alternating currents.

The same principle is made use of in the dynamo-electrical machines
for generating the currents employed for motive power, electric
lighting, etc. Instead of permanent magnets, powerful electro-
magnets are here used, and in place of an armature with two coils
of wire, armatures with many coils are employed. Moreover, an
arrangement known as the commutator is often used to change the
alternating to a direct or continuous current — i. e., the generated
electricity is collected in such a manner that it moves in one direction
continuously.

Electric motors are essentially dynamos in which the action is re-
versed— i. e., electric currents convert iron into electromagnets, which
by successive attraction and repulsion of the iron in the armature
cause its rapid rotation, which motion may be communicated to other
machinery.

Voltaic induction. It has been mentioned that a body charged
with static electricity causes, by induction, an electric disturbance in
all bodies near by. Similarly an electric current passing through

ELECTRICITY.

79

one wire sets up induced currents in neighboring wires. One of the
principal applications made of these induced currents is in the induc-
tion coil, or Ruhmkorf coil, shown diagrammatically in Fig. 30. It
consists of a hollow cylinder covered with a coil of insulated and
relatively coarse wire, P, connected with a battery, B. Over this
first or primary coil is wound another, the secondary coil, S, com-
posed of much longer and finer wire.

FIG. 30.

Induction coil.

While a current passes through the primary wire nothing is noticed
in the secondary wire, but the instant the current is closed an instan-
taneous induced current is set up in the secondary wire in one direc-
tion, and on opening the circuit in the opposite direction. It follows
that it requires a rapid closure and opening of the circuit to generate
electricity in the secondary coil. The opening and closing of the
current are accomplished by the following self-acting arrangement.
In the hollow portion of the primary coil are placed bars of soft iron,
which are magnetized whenever a current passes through the coil.
Near one terminal of the iron bars is a movable metallic hammer, H,
held by a spring in such a position that the current is closed by it.
When the bars are magnetized, they raise the hammer, thereby open-
ing the circuit ; the cessation of the current causes the iron to be de-
magnetized and the hammer falls to its original position, closing the
circuit, and this action continues as long as the current is allowed
to flow. This arrangement, known as a " make and break " con-
trivance, generates, through the very rapid opening and closing of
the primary circuit, in the secondary coil that current which is known
as secondary, induced, interrupted, or/aradic current.

The object of the induction coil is to generate from a battery current of low
E. M. F. induced currents of very high E. M. F. The effectiveness of the

80

CHEMICAL PHYSICS.

induction coil increases with the length of its wire, which in large instruments
is fifty miles and more. While such machines are in operation sparks several
feet in length will pass between the terminals of the secondary coil at A.

Conversion of electrical energy into heat and light. "When-
ever a current passes through a wire (or through any other mass) it
offers more or less resistance, the amount of which depends on the
nature of the material and the thickness of the wire. This resistance
gives rise to the conversion of electrical energy into heat. Practical
use is now extensively made of these heating effects by passing strong
currents through poor conductors, as is done in the heaters used for
heating cars or buildings, in stoves for cooking purposes, in the
vulcanizers used in dental operations, and in electric furnaces. In

M

Electric furnace.

the latter, powerful currents are employed to produce temperatures
unattainable by processes of combustion or by any other means at
our disposal. These furnaces have not only revolutionized many
processes of manufacture, but have led to the discovery of a number
of substances.

The construction of electric furnaces differs widely according to
the use made of them. Fig. 31 represents the vertical section of a
furnace used for the manufacture of aluminum-bronze. The material
to be acted on is contained in a graphite crucible, A, resting on the

ELECTRICITY.

81

metallic plate P, and surrounded by a mass of carbon, C, the whole
being enclosed by the furnace wall M. D is a carbon rod, and acts
as the anode, while connection through the metallic plate is made
with the cathode from below.

Fig. 32 gives a sectional, and Fig. 33 an exterior, view of an elec-
tric furnace used in the manufacture of carborundum. The current

FIG. 32.

Longitudinal section of carborundum furnace.

enters and leaves through the cables which terminate in carbon elec-
trodes fastened in the wall. Between the electrodes is a mass of

FIG. 33.

Exterior view of carborundum furnace.

coke, which, while conducting the current, offers sufficient resistance
to be heated to an extremely high temperature. (For details of the
chemical action see the article on Carborundum.)

The electric arc lamp and the incandescent lamp are well-known examples
of the conversion of electrical energy into light. In the former lamp electricity
6

82

CHEMICAL PHYSICS.

FIG. 34.

of very high electromotive force (1000-3000 volts) passes between terminals of
pencils of hard carbon, which, while infusible, burn away gradually, requiring
an automatically acting contrivance to keep the two pencils at a constant dis-
tance. In the incandescent lamp a filament of carbon, fastened in an exhausted
glass globe, is heated to a white heat by a current of about 50 to 120 volts.

Conversion of electrical energy into chemical action. A highly
important effect of electric currents is their power to cause chemical
decomposition — i. e., the splitting- up of matter into two of its com-
ponent parts. Thus, if the terminals of a battery are placed in a
vessel with acidified water, gas-bubbles rise from
both terminals, and on examination the gases
are found to be hydrogen and oxygen, which
are the constituents of water. In order to col-
lect the gases and measure their volume, the
apparatus shown in Fig. 34 may be used. It
consists of three connected glass tubes, which
are filled with water acidified with sulphuric
acid. The electric current is made to pass
through the liquid from the poles, in this case
preferably pieces of platinum foil fastened to
platinum wire fused in the glass tubes. On
passing a current through the liquid, oxygen
rises from the positive, and hydrogen from the
negative pole. The process of splitting up a
compound body by electricity is called elec-
trolysis ; the bodies undergoing decomposition
are termed electrolytes. The metallic conductors
by which the current enters and leaves a liquid
or gaseous electrolyte are called poles or elec-
trodes, and are designated by the same names
given to the plates in the generating cell — i. e.,
they are called positive ( + ) pole or anode, and negative ( — ) pole
or cathode. The decomposition product appearing at the positive
pole is said to be electronegative, the one appearing at the nega-
tive pole is electropositive.

Electrolysis of water.

Electropositive are :
Hydrogen,
Metals,
Bases and basic radicals.

Electronegative are :
Oxygen,

Halogens (chlorine, etc.),
Acids and acid radicals.

When an electric current passes through a solution of any salt,
this is split up into the base and the acid composing the salt. If

ELECTRICITY. 83

the base be a metal, such as copper, it will be deposited on the elec-
tronegative pole. Use is made of this property in the different
processes of electroplating and electrotyping. Among the metals
requiring the weakest current for their electrolytic precipitation are
copper, silver, gold, and nickel, and these are often precipitated upon
other metals which form the negative pole.

Electrolysis is used also on a large scale for separating metals from
ores, or from one another, and on a small scale for analytical opera-
tions ; it also plays an important part in the work done by the elec-
tric furnace, in which often both the required high temperature and
the decomposing influence are furnished by the electric current.

Discharge through gases. When an electric current of suffi-
ciently high E. M. F. is discharged through a gas, for instance,
through air, the gas is rendered luminous by its passage — i. e., we
have what is called an electric spark, in appearance like that of a flash
of lightning. This spark in many cases exerts chemical action, as,
for instance, when oxygen is converted into ozone, which change will
be considered later.

If the discharge take place in a gas inclosed in a glass globe from
which the gas may be removed by means of an air-pump, it is found
that at a sufficiently reduced pressure the spark ceases and the inte-
rior of the globe assumes a beautiful luminosity, the nature of which
depends on the kind of gas operated on.

By exhausting the air from suitably constructed bulbs or tubes
still further until an almost perfect vacuum is obtained, the electric
discharges passing through this vacuum again show decided changes.
If the cathode of such a vacuum tube be formed of a metallic disk,
while the anode be a straight wire, then on passing the current
through the vacuum tube a pale purplish beam of light radiates from
the face of the disk. This beam is known as the cathode ray ; it has
been shown to consist of streams of portions of matter negatively
charged, and moving with great velocity.

Rontgen rays. During the generation of the cathode rays in the
vacuum tube another kind of rays of a very peculiar character are formed.
They have been called Rontgen rays, after their discoverer, who him-
self named them x-rays. These rays differ from other rays in many
respects ; thus they can pass readily through many kinds of matter
which are opaque to ordinary light ; they cause many substances tg
emit light when they fall upon them ; they affect photographic plates,

84 CHEMICAL PHYSICS.

and have a decided physiological action on various parts of the
human body.

Radio-activity. In 1896 the French scientist Becquerel dis-
covered that the metal uranium and its compounds exert sponta-
neously and continuously a certain influence upon their surroundings.
This influence was found to be due to rays (now called Becquerel
rays) of a peculiar kind. They act upon the photographic plate ; they
pass through black paper and metals ; they render the gases through
which they pass conductors of electricity ; they cannot be reflected or
refracted. Any substance exhibiting the power of sending out such
rays is said to be radio-active. Besides uranium and its compounds
those of thorium were found to possess the same properties.

The subject of radio-activity was next studied by Madam Curie,
who showed that certain minerals (such as pitch-blende) contain-
ing uranium are more radio-active than uranium itself, and in the
course of her investigation demonstrated that in uranium ores are
several substances which show radio-activity to a remarkable extent.

The work, carried yet farther by a number of scientists, has
brought out the following results : Three substances, named polonium,
actinium, and radium, have been obtained from pitch-blende and
show a radio-activity a million times greater than that of uranium
or thorium.

Of these three substances at least one — the radium — has been posi-
tively proven to be an elementary substance of metallic nature form-
ing well-defined salts, such as radium chloride and bromide. Radium
salts show all the previously mentioned properties of Becquerel rays,
but in addition they exhibit some other features.

Thus, radium salts are permanently luminous and render luminous
(or phosphorescent) for a shorter or longer period a great number of
other substances. The most sensitive are barium platinocyanide, zinc
sulphide, diamond, etc. Not only do radium salts impart luminosity
to other substances, but these salts communicate little by little their
radio-active properties to substances in their neighborhood, and these
in turn emit Becquerel rays for some time.

Another startling discovery was made when it was shown that
radium salts develop heat continuously, and consequently are in
themselves warmer than their surroundings. A small flask containing
0.7 gramme of radium bromide shows a temperature of 3° C. higher
than the surrounding air. Calorimetric measurements have shown
that radium bromide evolves enough heat to convert per hour its own

ELECTRICITY. 85

weight of ice into water, or that one gramme of radium bromide will
raise the temperature of 80 grammes of water one degree C. per
hour.

Just as sun rays are made up of heat rays, light rays, and rays of
actinic power, so it has been found that there is a difference in the
rays of a radio-active body. There are at least three kinds, of which
the first group, called alpha rays, possesses remarkable penetrating
power and great photographic energy ; they are not deviated from
their path under the influence of a magnetic field, and resemble the
Rontgen rays in their action. The beta rays produce heat, are devi-
able under the influence of a magnetic field, and resemble cathode
rays. The third group — gamma rays — is easily absorbed.

Of great interest is the physiological action of radium compounds
on the animal system. Radium bromide, even when enclosed in a
wooden or metallic box, brought near the closed eye causes the sensa-
tion of light. While nothing is felt when radium salts are brought
close to our body, yet a strong influence, similar to that of Rontgen
rays, is exerted upon the tissues. This is shown by the fact that days
or weeks after the body had been exposed to radium rays the skin
reddens and, if the exposure was of sufficient duration, sores and
ulcerations will form which require a long time for healing. A sealed
glass tube, containing a little radium bromide, when placed in a bowl
of water with small fishes will cause their death in a few hours.
Attempts are now being made to use radium rays like Rontgen rays
in the treatment of skin diseases, lupus, etc.

When the apparently never-diminishing power of radium to give
out continuously light and heat was discovered, it appeared as if our
views regarding matter and energy were completely upset. A closer
investigation, however, has shown that this apparently unlimited
source of energy may be explained in a way conforming to our pre-
vious views.

What is supposed to take place is this : All radio-active substances
send out with enormous velocity particles, called corpuscles, which are
a thousand times smaller than a hydrogen atom. This substance
which is thrown off, and which Crookes designates the fourth state of
matter, or radiant matte)*, is called emanation. The phenomena of
radio-activity, previously described, are due to these emanations
which cause a bombardment of everything lying in their paths.

The discovery of radiant matter has modified our views regarding
atoms. It is now believed that the atom, as revealed in chemistry, is
a mass of a great number of small corpuscles which have come to a

86 CHEMICAL PHYSICS.

state of stability or equilibrium, in which state they cannot be sepa-
rated by our ordinary chemical operations, and thus appear as single
units or atoms. In radium and in other radio-active bodies these
complexes of corpuscles are in unstable equilibrium and possess
potential energy which has a tendency to diminish in quantity, thus
causing the state of unrest exhibited by radio-active bodies. The
potential energy becomes kinetic in the form of heat, light, etc., and
meantime the complexes are transformed to stable forms which do not
possess radio-activity and which act like the chemical atoms.

This would involve the transformation of one element into a new
element. And that is exactly what has been found to take place in
the case of radium, namely, that the emanation from radium contains
helium. (For the manufacture of radium compounds, see the article
on Radium.)

QUESTIONS. — Name some conductors and non-conductors of electricity, and
explain their behavior in connection with electrical phenomena. What is
meant by positive and negative, and by static and current electricity ? Describe
three methods for generating electricity. Name the three principal units used
in the measurement of electrical currents, and explain the methods employed.
Explain the construction and action of a galvanic cell. What is a permanent
magnet, and what is an electromagnet ? How are they made, and what are their
characteristic properties? Define the following terms: Anode, cathode, circuit,
electric current, induction, and electromotive force. Describe construction of
the electric furnace, and explain its action. How may electricity be used in
the generation of heat, light, mechanical motion, and chemical action?

II.

PRINCIPLES OF CHEMISTRY.

5. ELEMENT, COMPOUND, CHEMICAL AFFINITY, MODES OF
EFFECTING CHEMICAL CHANGE.

HAVING considered some of the subjects of physics, we may now
pass to the field of chemistry. The nature of a chemical change and
the scope of chemistry have already been discussed on page 18. One
of the simplest means of bringing about a change in the composition
of matter is by applying heat. Let us see what may be learned
from the following experiment.

Decomposition by heat. The results of the action- of heat upon
matter have been stated to be : Increased velocity of the motion of
molecules, increase in volume of the substance heated, and in many
cases a conversion of solids into liquids and of these into gases. Be-
sides these results there frequently may be noticed another.

FIG. 35.

Decomposition of mercuric oxide in A ; collection of mercury in B, and of oxygen in C.

To illustrate this action of heat, we will select the red oxide of
mercury, a solid substance which is insoluble in water, almost taste-
, and of a brick-red color. When this oxide of mercury is placed

87

88 PRINCIPLES OF CHEMISTRY.

in a glass tube and heated, it will be found to disappear gradually,
and we might assume that it has been converted into a gas from
which, upon cooling, the red oxide of mercury would be re-obtained.
If the apparatus for heating the oxide of mercury be so constructed
that the escaping gases may be collected and cooled, we shall not find
the red oxide in our receiver, but in its place a colorless gas, while at
the same time globules of metallic mercury will be found deposited
in the cooler parts of the apparatus (Fig. 35).

The action of heat consequently has in this case produced an effect
entirely different from the effects spoken of heretofore. There is no
doubt that the first action of the heat upon the oxide of mercury is
an increased velocity of the motion of its molecules and simulta-
neously an increase of its volume, but afterward a decomposition of
the oxide takes place, and two substances are liberated, each different
from the oxide.

One of these substances is a silvery-wThite, heavy, liquid metal, the
mercury ; the other substance is a colorless, odorless gas, which sup-
ports combustion much more freely than does atmospheric air, and is
known as oxygen.

Elements. We have thus succeeded in proving that red oxide of
mercury may be converted or decomposed by the mere action of heat
into mercury and oxygen. It is but natural to inquire whether it
would be possible further to subdivide the mercury or the oxygen
into two or more new substances of different properties. To this
question, which has been experimentally propounded to Nature over
and over again, we have but one answer, viz. : Oxygen and mercury
are substances incapable of decomposition by any method or means
as yet known to us. They resist the powerful influences of electricity
and heat, even when raised to the highest attainable degrees of in-
tensity, and they issue unchanged from every variety of reaction
hitherto devised with the view of resolving them into simpler forms
of matter.

Therefore we are justified in regarding oxygen and mercury as non-
decomposable or simple substances, in contradistinction to compound
or decomposable substances, such as the red oxide of mercury.

All substances which cannot by any known means be resolved into
simpler forms of matter, are called elements; all substances which
may, by one process or another, be subdivided or decomposed in such
a manner that new substances with new properties are formed, are
called compound substances or compounds.

ELEMENT, COMPOUND, CHEMICAL AFFINITY, ETC. 89

While the number of known compounds exceeds many thousands,
the number of elements is comparatively small, about seventy-six of
these simple substances being known to exist on our earth. And yet
this small number of elements, by combining with each' other in many
different proportions, form all that boundless variety of matter which
we see in nature.

In the case of oxide of mercury heat has evidently caused a weak-
ening of the attractive force which held the two elements, mercury
and oxygen, together, thus permitting them to part company. Such
a change is known as decomposition. But, in other cases, heat
increases the attraction between elements, so that they unite to form
more complex bodies, which would not occur at ordinary tempera-
ture. Such a change is known as combinatioyi . For example, mag-
nesium metal does not unite with the oxygen of the air at ordinary
temperature, but when heated sufficiently, it unites with oxygen
with great vigor. In fact, mercury unites with oxygen when heated
to a temperature a little below its boiling-point, and forms the red
oxide, but if the latter is heated to a higher temperature it is decom-
posed.

The student must not think that elements are obtained in* all cases
of decomposition by heat. In some instances the new products ob-
tained are themselves compounds, while in others an element and a
new compound result. For example, when calcium carbonate is
heated (see page 18), calcium oxide, a solid compound, and carbon
dioxide, a gaseous compound, are obtained. When potassium chlor-
ate, a compound of potassium, chlorine, and oxygen, is heated, the
element oxygen is evolved, while a new compound composed, of po-
tassium and chlorine, and known as potassium chloride, remains as a
solid in the vessel.

The quantity of heat required for decomposition differs widely
according to the nature of the substance. Some substances can be
produced only at a temperature below the freezing-point of water,
a higher temperature causing their decomposition ; other substances
may be decomposed at temperatures between the freezing- and
boiling-points; others again, and to these belong the majority of
inorganic compounds, may be raised to red or white heat before decom-
position sets in; and still another number of compounds have never
yet been decomposed by heat. Theoretically, however, we assume
that all compounds may be decomposed by heat, should it be possible
to raise it to a sufficiently high degree.

90 PRINCIPLES OF CHEMISTRY.

Decomposition by electricity. It has been shown in Chapter 4
that electricity exerts under certain conditions a strong decomposing
influence on many compounds. It was also stated that this process
of decomposition is called electrolysis, while the term electrolyte is
given to the material acted upon. This material must be a conductor
of electricity, and either in the liquid or gaseous state. The electro-
lyte is brought into the liquid state either by melting it if solid or
dissolving it in some other molten medium, or, as is most frequently
the case, by dissolving it in water, which in some cases is rendered
acid or alkaline, before electrolysis is carried out.

Electricity is widely used at the present day in chemical industries
and in quantitative chemical analysis. Some examples of chemicals
obtained thus are metallic sodium and potassium, caustic potash,
chlorine which is converted into bleaching powder, potassium chlor-
ate, aluminum by electrolysis of a solution of aluminum oxide in
molten cryolite, pure copper from the impure product, pure iron,
nitric acid by a powerful electric discharge through air.

Decomposition by light. Another cause of decomposition is, in
many cases, the action of light. The art of photography is based
upon this kind of decomposition. Many substances, easily affected
by light, have to be kept in the dark to prevent them from being
decomposed.

The phenomena of heat, light, and electricity resemble each other in so far
as they are phenomena of motion. Heat is the consequence of the motion of
material particles (molecules) ; light is the consequence of the vibratory motion
of the hypothetical medium ether ; probably the same is true of electricity.

These motions, in being transferred, have, as shown above, frequently the
tendency of splitting up the molecules of compound substances.

Mutual action of substances upon each other. As a general
rule, it may be said that no chemical action takes place between two
substances both of which are in the solid state, because the molecules
do not come in sufficiently close proximity to exchange their parts.
The free motion of the molecules in liquid or gaseous substances
facilitates such a proximity, and consequently chemical action. It is
often sufficient to have but one of the acting substances in the gaseous
or liquid state, while the second one is a solid. By converting two
solids into extremely fine powder and mixing them together thor-
oughly, chemical combination may follow, provided the affinity
between them be sufficiently strong.

ELEMENT, COMPOUND, CHEMICAL AFFINITY, ETC. 91

Physical phenomena accompanying- chemical action. By a
careful observation of all the details in a great variety of chemical
actions, an intimate connection between physics and chemistry be-
comes apparent. A noteworthy fact that stands out prominently is
that in every change in composition, energy in some form is produced
or consumed. In the decomposition of red oxide of mercury, heat
energy is constantly being absorbed and rendered latent as the oxide
separates into the free elements, oxygen and mercury. As soon as
the heat-supply is withdrawn the decomposition ceases. When mag-
nesium burns, that is, unites with oxygen, a great quantity of heat
and intense light is produced, and the action after starting is self-sus-
taining. "We have seen that electric energy is consumed in bringing
about chemical change. On the other hand, chemical action under
proper control can be made to produce electric energy, that is, an
electric current. In some cases the energy of light rays is consumed
in producing chemical change, for example, in photography. De-
composition can be accomplished in certain instances by mechanical
energy, as violent trituration, while, on the other hand, the production
of mechanical energy by chemical action is illustrated by the explo-
sion of gunpowder and movement of muscles.

Chemical or internal energy. Exothermic and endothermic
actions. From the previous discussion, we learn that there must be
another kind of energy stored up in latent form in matter which
under proper conditions is converted into forms of energy with which
we have already become familiar in Section I. on Physics ; namely,
heat, electricity, light, mechanical energy. This form of energy,
which is made manifest during chemical change, is called chemical
or internal energy. Every element and compound should be looked
upon not merely as consisting of certain kinds of matter, but also as
a storehouse of chemical energy. In many chemical changes part of
the internal energy is liberated in forms which can be measured, such
as heat, electricity, etc. This portion is known as free or available
internal energy, and is different in amount according to the nature of
the substances concerned in the chemical change. For example, the
same weight of various articles of food, when undergoing combustion
in the animal body, produces very different amounts of heat, and
therefore these foods have different values as fuels for keeping up the
temperature of the animal body.

Sometimes it is necessary to augment the internal energy of sub-
stances from a supply of energy such as heat, electricity, etc., in order

92 PRINCIPLES OF CHEMISTRY.

to bring about chemical change. Indeed, it has been found that all
chemical changes maybe divided into two classes: (1) those which
take place spontaneously and in which a certain amount of the chem-
ical energy of the substances acting is liberated and converted into
some other forms of energy, which thus become available for use ; (2)
those which do not take place spontaneous! v, but which must be sus-
tained by the addition of energy from without to the substances act-
ing. The energy set free in spontaneous chemical actions usually
appears as heat, and all actions proceeding with liberation of heat
are called exothermic, while those actions which absorb heat are called
endothermic. The study of the energy changes in chemical actions is
very important for a full understanding of such actions. The study
of the heat produced or absorbed in chemical changes constitutes a
subdivision known as Thermochemistry.

Chemical reaction, in its broadest sense, refers to any chemical
change, but is used more especially when the intention is to study
the nature of the substances decomposed or formed. The expression
reagent is applied to those substances used for bringing about such
changes.

Chemical affinity. There must be some cause which enables or
even forces the different elements to unite with each other so as to
form compound bodies. There must be, for instance, a cause which
enables oxygen and mercury to combine and form a red powder.

This cause is to be found in the existence of another form of
attraction which causes the smallest particles of different elements
to unite to form new substances with new properties. This kind of
attractive power is called chemical force or chemical affinity, and
bodies possessing this capacity of uniting with each other are said
to have an affinity for each other.

There is a great difference between chemical attraction and the
various forms of attraction spoken of heretofore. Cohesion simply
holds together the molecules of the same substance, adhesion acts
chiefly between the molecules of solid and liquid substances, gravita-
tion acts between masses. But all these forces do not change the
nature, the external and internal properties of matter ; this is done
when chemical force or affinity is operating, when a chemical change
takes place.

For instance : In a piece of yellow sulphur the molecules are held
together by cohesion, and we can counteract this cohesion by mechan-
ical subdivision, reducing the sulphur to a fine powder ; or by the

LAWS AND THEORIF:S OF CHEMISTRY. 93

application of heat we can further subdivide the sulphur, melt, and
finally volatilize it ; or we can throw a piece of sulphur into the air,
when it will fall back upon the earth in consequence of gravitation ;
or we can dip it into water, when it becomes moist in consequence of
surface-action. Yet in all these cases sulphur remains sulphur.

It is entirely different when sulphur enters into chemical combina-
tion exerting chemical attraction, for instance, when it burns; this
means when it combines with the oxygen of the atmospheric air. In
this case a new substance, a disagreeably smelling gas, a compound of
oxygen and sulphur, is formed.

It is^ consequently a complete change in the properties of matter
which follows the action of true chemical attraction ; we might define
affinity to be a force by which elements unite and new substances are
generated.

It should be noted that affinity does not really explain why chem-
ical union takes place, why an attraction between elements exists.
It is merely a term that has come into use to express a fact that can
be observed ; namely, that elements do unite, but why they do so no
one knows. Likewise no one knows why fhe earth attracts bodies,
although we say it is due to gravitation. This is simply equivalent
to saving that an attractive force exists between the earth and bodies
upon it, a fact which anyone can observe. But no one knows why
this force exists or its nature.

6. LAWS AND THEORIES OF CHEMISTRY.1

Law of the constancy of composition. This law, also known
as the law of definite proportions, was the first ever recognized in
chemical science ; it was discovered toward the close of the 18th
century, and may be stated thus : A definite compound always contains
the same elements in the same proportion; or, in other words, All chemi-
cal compounds are definite in their nature and in their composition.

To make this law perfectly understood, the difference between a
mechanical mixture and a chemical compound must be pointed out.
Two powders, for instance sugar and starch, may be mixed together
very intimately in a mortar, so that it seems impossible for the eye to
discover more than one body. But in looking at this powder with
the aid of a microscope, the particles of sugar as well as those of

1 The subject matters of chapters 6, 7, 8, and 9 are grouped together for convenience. It is
not intended that they should be taken up in lectures or class work at once after chapter 5,
nor in the exact order given here, but each instructor will introduce them in what, to him,
seems the most logical sequence.

94 PRINCIPLES OF CHEMISTRY.

starch may be easily distinguished. The mixture thus produced is n
mechanical mixture of. molecule clusters.

It is somewhat different when two substances, for instance two
metals, are fused together, or when two gases or two liquids (oxygen
and nitrogen, water and alcohol) are mixed together, or when finally
a solid is dissolved in a liquid (sugar in water). In these instances
no separate particles can be discovered even by the microscope. The
mixtures thus produced are mixtures of molecules. Such mixtures
always exhibit properties intermediate between those of their constitu-
ents and in regular gradation according to the quantity of each one
present. The proportions in which substances may be mixed are
variable.

In a true chemical compound the proportions of the constituent
elements admit of no variation whatever ; it is not formed by the
mixing of molecules, but by the combination of molecules; the prop-1
erties of a compound thus formed usually differ very widely from
those of the combining elements.

Powdered iron and powdered sulphur may be mixed together in many
different proportions. If such a mixture be heated until the sulphur becomes
liquid, the two elements, iron and sulphur, combine chemically, but they do so
in one proportion only, 56 parts by weight of iron combining with 32 parts by
weight of sulphur, to form 88 parts of sulphide of iron. If the two substances
are mixed together in any other proportion than the one mentioned, the excess
of one will be left uncornbined.

Law of multiple proportions. While two or more elements
may unite in certain definite proportions to give one definite com-
pound, it does not follow that, under other conditions, they may not
unite in other proportions to give another entirely different com-
pound, but still perfectly definite in its composition. Many such ex-
amples are known in chemistry. Copper unites with oxygen in two
proportions, forming two distinct oxides. Tin does the same. There
are four different compounds of the elements potassium, chlorine, and
oxygen, and nitrogen and oxygen unite in five different ways. In
1804 John Dalton, of England, by a study of such multiple com-
pounds, proposed the law of multiple proportions. He had studied
the composition of two gaseous compounds of carbon and hydrogen,
and found one (olefiant gas) to contain 6 parts of carbon to 1 part of
hydrogen, while the other (marsh gas) contained 6 parts of carbon
to 2 parts of hydrogen. Upon what seems now to be a slight basis,
Dalton put forth his law, which, however, has been verified by every

LAWS AND THEORIES OF CHEMISTRY. 95

exact analysis since his time, and which is one of the most important
foundation-stones upon which the structure of chemical science is
reared. The law of multiple proportions maybe stated thus: If
tiro dements, A and B, are capable of uniting in several proportions,
the quantities of B which combine with a fixed quantity of A bear a
xitnple ratio to each other.

Besides the above illustrations of the law, several other examples
may be mentioned. Sulphur and oxygen unite in two proportions to
form two distinct compounds, one a gas known as sulphur dioxide,
the other a solid known as sulphur trioxide. In these the quantities
of oxygen, united with a fixed weight of sulphur, are in the ratio of

1 : 1 J or 2 : 3. There are two sulphides of iron, known respectively
as ferrous sulphide and pyrite ; in these the weights of sulphur
united with a fixed weight of iron are in the ratio of 1 : 2. The
phrase simple ratio, in the law, means in the ratio of small whole
numbers. This feature of the law is strikingly illustrated in the
case of the four compounds containing potassium, chlorine, and
oxygen, in which the variable weights of oxygen united with fixed
weights of potassium and chlorine are in the ratio of 1:2:3:4;
also in the case of the five compounds of nitrogen and oxygen, in
which the weights of oxygen united with a fixed weight of nitrogen
bear the ratio of 1 : 2 : 3 : 4 : 5.

Combining- weights of elements. The proportions in which any
two elements unite may be expressed by any two figures which stand
in the proper ratio. Thus we may say that water is made up of
hydrogen and oxygen in the proportions by weight of 1 to 8, or

2 to 16, or 5 to 40. Similarly we may state the composition of
ferrous sulphide as 7 parts of iron to 4 parts of sulphur, or 56 parts
of iron to 32 parts of sulphur. Expressing the composition of com-
pounds thus in a random manner, there seems to be no relationship
between the relative quantities with which the different elements
unite with one another. But upon closer inspection of the propor-
tions by weight in which the elements unite, it is found chat they can
be reduced to a system of figures which show a remarkable relation-
ship. It is found, purely from the results of analysis and inde-
pendently of any theory, that a certain figure can be assigned to each
element, which has the remarkable property that it or a simple mul-
tiple of it expresses the relative proportion by weight in which that
element unites with the other elements. Chemists soon became
aware of the fact that hydrogen is the lightest of all known matter

96 PRINCIPLES OF CHEMISTRY.

and also that it enters into union with other elements in the smallest
proportions. Hence in establishing the above-mentioned system of
numbers, one part by weight of hydrogen is taken as the standard of
reference, which offers the advantage that none of the figures is less
than unity. Let us illustrate by a few examples: One part of
hydrogen unites with 35.18 parts of chlorine, 35.18 parts of chlorine
unite with 38.82 parts of potassium, 2 X 38.82 parts of potassium
unite with 15.88 parts of oxygen. But 2x1 parts of hydrogen also
unite with 15.88 parts of oxygen. Also 15.88 parts of oxygen unite
with 64.91 parts of zinc, and 64.91 parts of zinc unite with 2 X 35.18
parts of chlorine. Thus we see that the figures in these instances are
reciprocally related, and the same is true for the figures assigned to
all the other elements. This system of figures is called combining
weights, and has a deep significance, which will appear clearer when
the atomic theory is discussed.

Atomic theory. One of the objects of men of science, besides
experimenting and observing facts and laws, is to determine causes^
that is, to furnish an answer to the question, Why do things take
place as they do? If the senses, even when fortified with delicate
instruments, are not sufficiently refined to perceive the causes,
the philosopher, with the aid of his reasoning faculties, tries to
imagine a cause which will account in the most satisfactory manner
for what he observes. Such an imagined cause is called an hypothe-
sis or theory. For example, to account for the uniform behavior of
all gases as summed up in the Laws of Boyle, Charles, and Avogadro,
it was imagined that the nature of gases is that they are made up of
exceedingly minute particles in motion, acting as elastic bits of
matter and with practically no cohesion between them. This is
known as the kinetic-molecular theory of gases, and from it all the
behaviors of gases can be deduced mathematically. We may never
be able to actually see a gas particle, nevertheless we are willing to
accept that it exists as long as the hypothesis accounts satisfactorily
for what is observed.

There must be some reason for the chemical behavior of the
elements as set forth in the Laws of Definite and Multiple Propor-
tions and the fact that the elements unite in proportions represented
in the system of figures called combining weights. This cause must
lie in the constitution or physical make-up of matter. Reflection
upon the constitution of matter is not peculiar to modern science, for
the ancients had their conceptions, and some (Democritus, Lucretius)

LAWS AND THEORIES OF CHEMISTRY. 97

advocated a theory of atoms. But the views of the ancients were
speculative and had no physical basis resting upon experiments, and
therefore were of no service to science. It was not until 1804 that a
theory or conception of matter was proposed by John Dalton, of
England, that had the merits of being capable of being put to tests
and from which deductions could be made that lent themselves to ex-
perimental verification. Dalton's atomic theory holds that (1) elements
arc made up of inconceivably small particles which are indivisible in
chemical actions and called atoms (from the Greek dro//oc, uncut, or
not yet divided) ; (2) the atoms not only have definite weights, but
the atoms of any one element have the same weight, which is differ-
ent from the weight of the atoms of some other element ; (3) when
the elements unite chemically, the action takes place between the
atoms. If we assume this theory to be correct and argue from it as
a basis, w« can deduce the laws of definite proportions and multiple
proportions. Let us suppose that two certain elements, A and B,
unite, and the union is of the simplest kind possible, that is, in each
instance an atom of A is united with an atom of B. No matter what
the mass of the resulting product may be, whether an ounce, pound,
or ton, the whole chemical action is simply a repetition throughout
the mass of what might be called the unit action, that is, the union
of one atom of A with one atom of B. Hence the ratio between
the weights of the elements in the resulting compound, that is, its
composition, must be the same as the ratio between the weights of
the aton? of A and the atom of B. But the weights of these atoms
arc definite and constant, hence the composition of the compound
must be constant, or, in other words, the compound is an illustration
of the law of definite proportions. By a simple extension of the
above argument, the law of multiple proportions may be deduced.
The theory also accounts for the fact that if two elements are brought
together in other than certain proportions, say 56 parts of iron to 32
parts of sulphur, after union has taken place, part of the one or the
other element is found uncombined. It is easy to see, too, that, if
the theory is correct, the elements ought to combine according to a
system of figures such as were discussed above as combining weights,
for these weights are bound to be proportional to the weight of atoms,
which are definite. The atomic theory has been found in accord with
the facts of chemistry for a century or more, and we are justified in
accepting it, although we cannot prove absolutely the existence of
atoms.

7

'98 PRINCIPLES OF CHEMISTRY.

Atomic weight. If atoms exist, they must have weight, since
they are concrete masses of matter, and all matter is attracted by the
earth. But, of course, it is impossible to weigh single atoms, and we
have no knowledge of the absolute weight of an atom. It is possi-
ble, however, to determine the relative weights of the atoms, that is,
how many times heavier one atom is than another. How this is done
will be briefly indicated in the next chapter. In any process of
weighing, we adopt a unit with which to make a comparison. For
example, in commerce we have a mass of iron which is called a
pound, and we say a body weighs so many times the mass of iron, or
so many pounds. We proceed similarly in the case of atomic
weights. We use the weight of an atom of one element as the unit,
and compare the weight of the atoms of the other elements with it.
The thing to decide is, Which atom shall be chosen as the unit
weight ? As was said in discussing combining weights, hydrogen is
the lightest known substance, and it unites with other elements in the
smallest proportions, hence its atom is chosen as the unit weight.
The figures assigned to the other elements as atomic weights simply
signify how many times heavier those atoms are than the atom of
hydrogen. In other words, the atomic weights are nothing more
than ratios. On the page preceding the Index is a table of the ele-
ments, with symbols and atomic weights.

Atoms and molecules. In Section I, on Physics, we learned that
all matter is made up of exceedingly minute particles, called mole-
cules, and, from a chemical study of matter, we are led to believe
that there is another kind of small particle, the atom. The atoms
unite in chemical action and form the larger masses called molecules.
The molecules of compounds consist of atoms of different kinds.
The elements also, like any kind of matter, consist of molecules,
which evidently must be made up of atoms of the same kind. There
are a few exceptional elements of which the molecule consists of only
one atom, that is, the molecule and atom of these are identical. The
atoms of an element have the power of uniting not only with atoms
of a different kind, but also with themselves, to form molecules of
the element. The present conception as to atoms may be summed
up in the following definition : "Atoms are the indivisible constitu-
ents of molecules. They are the smallest particles of the elements
that take part in chemical reactions, and are, for the greater part, in-
capable of existence in the free state, being generally found in com-
bination with other atoms, either of the same kind 'or of different
kinds" (Remsen).

LAWS AND THEORIES OF CHEMISTRY. 99

We may define molecules as the smallest particles of matter that
can exist in the free state and still retain all the properties of the
substance to which they belong. If we divide the molecule, we
destroy the properties of the substance as we know it in the free state.

Chemical symbols. For reasons to be better understood hereafter,
chemists designate each element by a symbol, and the first or first two
letters of the Latin name of the element have generally been selected.
Thus, the symbol of hydrogen is H, of oxygen O, of mercury Hg
(from hydrargyrum), of sulphur S, etc. These symbols designate,
moreover, not only the elements, but one atom of these elements.
For instance : O not only signifies oxygen, but one atom or 15.88 parts
by weight of oxygen ; and Hg, one atom or 198.5 parts by weight of
mercury.

Symbols or formulas of compounds. By suitable experiments
it is possible for the chemist to determine not only the kinds of ele-
ments in a compound and their proportions, but also how many atoms
are in a molecule of the substance. For the sake of economy of
time and space and to give a better insight into their nature, sub-
stances are represented by formulas, which is a shorthand way of
telling what would require many words. A formula primarily rep-
resents the composition of a molecule, but as any quantity of a sub-
stance is simply the sum of a great multitude of molecules all. alike,
the formula, in a broader sense, stands for the substance itself. Thus
we say HgO is mercuric oxide, although it shows the composition of
a molecule of the oxide, namely, that it consists of one atom of mer-
cury and one atom of oxygen.

The formulas are formed by writing the symbols of the constituent
elements side by side, and the number of atoms of each element,
when more than one atom is present, is represented by a figure below
and to the right of the symbol of the element ; thus H2O means that
a molecule of water consists of two atoms of hydrogen and one atom
of oxygen ; CO2 means that the carbon dioxide molecule consists of
one atom of carbon and two atoms of oxygen. A number placed before
a formula signifies so many molecules, thus 2H2O means two mole-
cules of water. As the formulas represent the size of the molecules,
they are called molecular formulas, and the sum of the atomic weights
of all the atoms composing the molecules is called the molecular
weight, which shows how many times heavier the molecule is than an
atom of hydrogen.

100 PRINCIPLES OF CHEMISTRY.

To establish a molecular formula requires a careful quantitative determina-
tion of the proportions of the constituents of a compound; conversely, if we
know the molecular formula of a compound, we can calculate from it the rela-
tive quantities of the elements, or the percentage composition of the com-
pound. Also, if we know the formula, and the weight of one constituent, we
can calculate the weight of the other constituents, and the total weight of the
compound. Let us consider the red oxide of mercury, which has the molec-
ular formula, HgO. In the molecule there is an atom of mercury weighing
198.5 times as much as an atom of hydrogen, and an atom of oxygen weighing
15.88 times as much as an atom of hydrogen. It is evident that the weights
of the mercury and oxygen in a molecule are to each other as 198.5 : 15.88.
What is true of one molecule must be true of any number of molecules, that
is, of any quantity of oxide of mercury; hence we can conclude that in the
oxide there are 198.5 parts of mercury to every 15.88 parts of oxygen, making
198.5 + 15.88 = 214.38 parts of oxide. To calculate the percentage composi-
tion, or parts per hundred, we use the proportions,

214.38 HgO : 198.5 Hg : : 100 HgO : x Hg and
214.38 HgO : 15.88 O : : 100 HgO : x O.

Of course, in all cases where there are only two constituents, and we find the
per cent, of one, the other need not be calculated.

If we had a quantity of oxide of mercury that we knew contained, say, 30
parts of mercury, and we wanted to know the weight of the oxygen present or
the total weight of oxide, the following proportions would give us the answers:

198.5 Hg : 15.88 O : : 30 Hg : x O.
198.5 Hg : 214.38 HgO : : 30 Hg : x HgO.

We learn from the discussion above that the elements enter into combina-
tion in quantities represented by their atomic weights, or multiples of these,
to produce a quantity of compound represented by the molecular weight.

The law of chemical combination by volume, or the Law of
Gay-Lussac, may be stated as follows : When two or more gaseous
constituents combine chemically to form a gaseous compound, the volumes
of the individual constituents bear a simple relation to the volume of the
product. The law may be divided into two laws, thus : 1. Gases
combine by volume in a simple ratio. 2. The resulting volume of
the compound, when in the form of a gas, bears a simple ratio to the
volumes of the constituents. For instance : 1 volume of hydrogen
combines with 1 volume of chlorine, forming 2 volumes of hydro-
chloric acid gas ; 2 volumes of hydrogen combine with 1 volume of
oxygen, forming 2 volumes of water-vapor ; 3 volumes of hydrogen
combine with 1 volume of nitrogen, forming 2 volumes of ammonia.

If the different combining volumes of the gases mentioned are

LAWS AND THEORIES OF CHPIMISTRY.

101

weighed, it will be found that there exists a simple relation between
these weights and the atomic or molecular weights of the elements.

For instance : Equal volumes of hydrogen and chlorine combine,
and the weights of these volumes are as 1:35.18, which numbers
represent also the atomic weights of the two elements. Two volumes
of hydrogen combine with one volume of oxygen, and the weights of
the volumes are as 1 : 7.94 or 2 : 15.88, the latter being the atomic
weight of oxygen.

2 Vol umes

Hydrochl j oric Acid gas.
W = ! 36.18

2 Vol ; umes

j
Water i -vapor

W = j 17.88

2 Vol j umes
Anna ; onia gas.
W = I 16.93

2 Vol umes
Sulphur ic acid gas.
Weight !=B 97.36

The above diagram shows the simple relation which exists between
combining volumes and atomic and molecular weights. It was,
besides other factors, the discovery of this relation that led to the
adoption of Avogadro's Law, which has been stated. (See Chapter
I., page 30.)

Taking the law of combination by volume and Avogadro's Law as a basis of
argument, we can prove directly in the case of some of the elementary gases
that their molecules consist of more than one atom. One volume of hydrogen
combines with one volume of chlorine to give two volumes of hydrochloric acid
gas. According to Avogadro's Law the volume of hydrogen and chlorine con-
tain the same number of molecules, and the two volumes of product formed
must contain twice as many molecules as does the volume of hydrogen or chlo-

102 PRINCIPLES OF CHEMISTRY.

rine. Hence the molecules of hydrogen and chlorine must be divided to form
part of a product consisting of twice as many molecules, since each molecule of
hydrochloric acid contains some hydrogen and some chlorine. But if the mole-
•cules of hydrogen and chlorine can be divided, they must consist of more than
one atom. Everything that is known about hydrochloric acid justifies the
assumption that its molecule contains one atom each of hydrogen and chlorine.
If this is true, it follows then that the molecule of hydrogen and of chlorine
contains two atoms. The same kind of argument in the case of the union of
hydrogen and oxygen to form water-vapor, leads to the conclusion that the
molecule of oxygen contains at least two atoms. In fact, from various experi-
ments and processes of reasoning, it has been established that the molecule of
nearly all the elements, in the gaseous state, consists of two atoms.

Theory (Law) of equivalents. Valence, or Quantivalence.
When one element replaces another element in a compound, the
quantities of the two elements are said to be equivalent to each other,
and according to the law of equivalents the replacement of elements
one by another takes place always in definite proportions. Formerly
it was believed that the atoms of all elements were equivalent one
with another ; accordingly, atomic weights were frequently designated
as equivalent weights.

This view, however, is not correct, as it ir> found that one atom of
one element frequently displaces two or more atoms of another
element. This fact, as well as other considerations, has led to the
assumption of the quantivalence of atoms. This property will be
understood best by selecting for consideration a few compounds of
different elements with hydrogen.

i. ii. m. iv.

HCl H20 H3N H,C

HBr H2S H3As H4Si

HI H2Se H3P

We see here that Cl, Br, and I combine with H in the proportion
of atom for atom ; O, S, Se combine with H in the proportion of 2
atoms of hydrogen for 1 atom of the other element ; N, As, P com-
bine with 3; C and Si with 4 atoms of hydrogen.

Moreover, it has been found that the compounds mentioned in
column I. are the only ones which can be formed by the union of
the elements Cl, Br, and I with H. They invariably combine in this
proportion only. Other elements show a similar behavior. For
instance, the metal sodium combines with chlorine or bromine in one
proportion only, forming the compound Nad or NaBr.

Looking at columns II., III., and IV., we see that the elements
mentioned there combine with 2, 3, and 4 atoms of hydrogen,
respectively. It is evident, therefore, that there must be some pecu-

LAWS AND THEORIES OF CHEMISTRY. 103

liarity in the power of attraction of different elements toward other
elements, and to this property of the atoms of elements of holding
in combination one, two, three, four, or more atoms of other ele-
ments the name atomicity, quantivalence, or simply valence, has been
given.

According to this theory of the valence of atoms, we distinguish
univalent, bivalent, trivalent, quadrivalent, quinquivalent, sexivalent,
and septivalent elements. All elements which combine with hydro-
gen in the proportion of one atom to one atom are univalent, as, for
instance, Cl, Br, I, F, and all elements which combine with these in
but one proportion, that is, atom with atom, bear the same valence,
or are also univalent, as, for instance, Na, K, Ag, etc.

Those elements which combine with hydrogen or other univalent
elements in the proportion of one atom to two atoms are bivalent,
such as O, S, Se.

Trivalent and quadrivalent elements are those the atoms of which
combine with 3 or 4 atoms of hydrogen, respectively. Figuratively
speaking, we may say that the atoms of univalent elements have but
one, those of bivalent elements two, of trivalent elements three, of
quadrivalent elements four bonds or points of attraction, by means of
which they may attach themselves to other atoms.

Elementary atoms are often named according to their valence :
monads, diads, triads, tetrads, pentads, hexads, and heptads.

To indicate the valence of the elements frequently dots or numbers
are placed above the chemical symbols, thus H1, Ou, Nm, Cmi or Civ.

The bonds are often graphically represented by lines, thus :

H-, -0-, -N-, -0-

It is needless to say that such representations are merely symbolical,
and express the view that atoms have a definite power to combine
with others.

When atoms combine with one another the bonds are said to be
satisfied, and it is graphically expressed thus :

I /

-N-

H— Cl, H— O— H or O , H-N-H or N-H

XH \H

While the valence of some elements is invariably the same under
all circumstances, other elements show a different valence (this means
a different combining power for other atoms) under different condi-

104 PRINCIPLES OF CHEMISTRY.

tions. For instance : Phosphorus combines both with 3 and 5 atoms
of chlorine, forming the compounds PC13 and PC15. As chlorine is
a univalent element, we have to assume that phosphorus has in one
case 3, in another case 5 points of attraction. Many similar instances
are known, and will be spoken of later.

An explanation which is sometimes given in regard to the variability of
the valence of atoms is the assumption that sometimes one or more of the
bonds of an atom unite with other bonds of the same atom. If, for instance,
in the quinquivalent phosphorus atom two bonds unite with one another a
trivalent atom will remain.

It is noticed that the valence of atoms in nearly all cases increases or di-
minishes by two, which could not be otherwise, if the explanation given be
correct. Thus chlorine, the valence of which generally is I., may also have a
valence equal to III., V., or VII., while sulphur shows a valence either of II.,
IV., or VI. Atoms whose valence is even, as in the case of sulphur, are called
artiadu ; those whose valence is expressed in uneven numbers, as chlorine and
phosphorus, are called perissads.

While it is now being assumed that most of the elements possess more than
one valence, in consequence of the assumed power of bonds in the same atom
to saturate one another, in this book will be mentioned chiefly that valence
which the element seems to possess predominantly.

The doctrine of the valence of atoms has modified our views of the
equivalence of atoms. We now say that all atoms of a like valence
are equivalent to each other. The atoms of each univalent element
are equivalent to each other, and so of the atoms of any other valence,
but two atoms of a univalent element are equivalent to one atom of
a bivalent element, or two atoms of a bivalent element to one atom
of a quadrivalent element, etc.

QUESTIONS. — Define a chemical change and state the various modes of
effecting it, with examples. Define element, compound, combination, and
decomposition. About how many elements exist? What is chemical energy?
Define exothermic and endothermic actions. What is chemical affinity and
how does it differ from other forces? State the law of constancy of composi-
tion. What is the distinction between a mixture and a chemical compound?
Give examples of each. State the law of multiple proportions. Give in full
Dalton's atomic theory and show how it accounts for the laws of combination.
What is the relation of atoms to molecules? Define atomic and molecular
weight. What atom is chosen as the unit of atomic weights, and why? What
are chemical symbols and what do they signify? Calculate the per cent, of
oxygen and hydrogen in water, H2O. What weight of carbon dioxide, CO,,
would result from 25 grammes of carbon? What regularity regarding volume
is noticed when gases combine? Define valence. What were considered for-
merly as equivalent quantities, and what are such at present? Mention some
univalent, bivalent, trivalent, and quadrivalent elements. What explanation
is offered for variable valence ?

DETERMINATION OF ATOMIC WEIGHTS. 105

7. DETERMINATION OF ATOMIC AND MOLECULAR WEIGHTS.1

Determination of atomic weights by chemical decomposition.
The great difficulties originally encountered in the determination of
atomic weights cannot well be described here. Consideration will be
given alone to the three principal methods at present in use. These
methods depend either on chemical action or on physical properties.

One of the chemical methods used for the determination of atomic
weights depends upon the determination of the proportions by weight in
which the element, the atomic weight of which is unknown, combines
with an element the atomic weight of which is known. For instance :
If in decomposing a substance we find it to contain in 72 parts by
weight, 16 parts by weight of oxygen2 and 56 parts by weight of
another element, we have a right to assume the atomic weight of this
second element to be 56, provided, however, that the compound is
actually formed by the union of one atom of oxygen and one atom of
the other element. These 56 parts by weight might, however, repre-
sent 2, 3, or more atoms. If 56 represented 2 atoms, the atomic
weight would be but 28 ; if 4 atoms, 14.

As this mode of determination gives no clue to the number of
atoms present in the molecule, the results obtained are liable to be
incorrect. In fact, the atomic weights of a number of elements had
originally been determined incorrectly by using the above or similar
methods, and many of these old atomic weights had to be changed
(generally doubled) in order to obtain the correct numbers.

Thus, in examining water, it was found that it contained 8 parts
by weight of oxygen to 1 part of hydrogen, and the conclusion was
drawn that the atomic weight of oxygen was 8, and that the molecule
of water was formed by the union of one atom of hydrogen and one
atom of oxygen. It will be demonstrated below why we assume to-
day that the atomic weight of oxygen is 16, and that the molecule of
water is composed of 2 atoms of hydrogen and 1 of oxygen.

Another chemical method of determining atomic weights is the
replacement of hydrogen atoms in a known substance by the element
the atomic weight of which is to be determined. For instance : Hy-
drochloric acid is composed of one atom of chlorine weighing 35.2,
and one atom of hydrogen weighing 1, the molecular weight of hy-
drochloric acid being 36.2. If in this acid the hydrogen be replaced
by some other element, for instance by sodium, we are enabled to
determine the atomic weight of sodium by weighing its quantity and

1 The consideration of Chapter 7 should be postponed until the student has become famil-
iar with chemical phenomena generally.

2 For purposes of discussion, whole numbers are often used in place of exact atomic weights
when these contain decimals.

106 PRINCIPLES OF CHEMISTRY.

that of the liberated hydrogen. Suppose that by the action of 36.2
grammes of hydrochloric acid on sodium, 1 gramme of hydrogen
was replaced by 23 grammes of sodium. In that case we would say
that the atomic weight of sodium is equal to 23.

The difficulty which was alluded to above exists also in this mode
of determination of atomic weights, viz., not knowing whether it
was actually one atom of sodium that replaced the one part of hy-
drogen, a doubt is left as to whether or not the determination is correct.

Determination of atomic weights by means of specific weights
of gases or vapors. It has been stated before that equal volumes of
gases contain, under like conditions, the same number of molecules
(no matter how few or many the atoms within the molecules may be),
and that the molecules of elements contain (in most cases) two atoms.
These facts give in themselves the necessary data for the determina-
tion of atomic weights.

For instance: If a certain volume of hydrogen is found to weigh
2 grammes, and an equal volume of some other gaseous element is
found to weigh 71 grammes, then the atomic weight of the latter
element must be 35.5, because 2 and 71 represent the relative weights
of the molecules of the two elements. Each molecule being com-
posed of 2 atoms, these molecular weights have to be divided by 2 in
order to find the atomic weights, which are, consequently, 1 and 35.5
respectively.

In comparing by this method oxygen with hydrogen, it is found
that equal volumes of these gases weigh 32 and 2 respectively, that
the atomic weight of oxygen is consequently 16, and not 8, as deter-
mined by chemical methods.

This mode of determining atomic weights may be applied to all
elements which are gases or which may without decomposition be
converted into gas. There are, however, elements which cannot be
volatilized, and in this case it becomes necessary to determine the
specific gravity of some gaseous compound of the element. The
element carbon itself has never been volatilized, but we know many
of its volatile compounds, and these may be used in the determina-
tion of its atomic weight.

Determination of atomic weights by specific heat. Specific
heat has been stated to be the quantity of heat required to raise the
temperature of a given weight of any substance a given number of
degrees, as compared with the quantity of heat required to raise the
temperature of the same weight of water the same number of degrees.

DETERMINATION OF ATOMIC WEIGHTS. 107

In comparing atomic weights with the numbers expressing the spe-
cific heats, it is found that the higher the atomic weight the lower tHe
specific heat, and the lower the atomic weight the higher the specific
heat. This simple relation may be thus expressed : Atomic weights
are inversely proportional to the specific heats ; or the product of the
atomic weight multiplied by the specific heat is a constant quantity
for the elements examined.

Elements. Specific heat*. Atomic weights. Product of specific heal

(Water = 1 .) X atomic weight.

Lithium, 09408 7 6.59

Sodium, 0.2934 23 6.75

Sulphur, 0 2026 32 6 48

Zinc, 00956 65 6.22

Bromine (solid), 0.0843 79 6.66

Silver, 0.0570 107 6.10

Bismuth, 0.0308 209 644

An examination of this table will show this relation between
atomic weight and specific heat, and also that the product of atomic
weight multiplied by specific heat is equal to about 6.5. The varia-
tions noticed in this constant quantity of about 6.5 may be due to
errors made in the determinations of the specific heats, and subse-
quent determinations may cause a more absolute agreement.

However, the agreement is sufficiently close to justify the deduction
of a law which says : The atoms of all elements have exactly the same
capacity for heat. This law was first recognized by Dulong and Petit
in 1819, and is simply a generalization of the facts stated.

To show more clearly what is meant by saying that all atoms have
the same capacity for heat, we will select three elements to illustrate
this law.

If we take of lithium 7 grammes, of sulphur 32 grammes, of silver
107 grammes, we have of course in these quantities equal numbers of
atoms, because 7, 32, and 107 represent the atomic weights of these
elements. If we expose these stated quantities of the three elements to
the same action of heat, we shall find that the temperature increases
equally for all three substances — that is to say, the same heat will be
required to raise 7 grammes of lithium 1°, which is necessary to raise
either 32 grammes of sulphur or 107 grammes of silver 1°.

The quantity of heat necessary to raise the atom of any element a
certain number of degrees is, consequently, the same. As heat is the
consequence of motion, the result of the facts stated may also be ex-
pressed by saying : It requires the same energy to cause different
atoms to vibrate with such a velocity as to acquire the same tempera-
ture, no matter whether these atoms be light or heavy.

108 PRINCIPLES OF CHEMISTRY.

It is evident that these facts give us another means of determining
atomic weights, by simply dividing 6.5 by the specific heat of the ele-
ment. The specific heat of sulphur, for instance, has been found to be
0.2026. 6.5 divided by this number is 31.6, or nearly 32. Originally
the atomic weight of sulphur had been determined by chemical methods
to be 16, but its specific heat, as well as other properties, has shown
this number to be but one-half of the weight, 32, now adopted.

Tt may be mentioned that elements possess essentially the same
specific heat whether they exist in a free state or are in combination ;
this fact will, in many cases, be of use in the determination of atomic
weights.

Determination of molecular weights. From the statements
made regarding the determination of atomic weights, it is evident
that we may use a number of methods for determining molecular
weights, these methods being to some extent analogous to the former.

Thus we have methods which are based entirely on chemical analysis
or on chemical changes generally. If, for instance, the analysis of a
substance shows of calcium 40 per cent., of carbon 12 per cent., and
of oxygen 48 per cent., we have a right to assume that the molecule is
made up of 1 atom of calcium, 1 atom of carbon, and 3 atoms of
oxygen, as the atomic weights of these elements are 40, 12, and 16
approximately. The molecular weight in this case is 100, and the com-
position is expressed by the formula CaCO3, but the molecular weight
might be 200 and the correct formula Ca2C2O6. There are actually
substances which contain such multiples of atoms, as, for instance, the
compounds C2H2 and C6H6, and as their percentage composition is
identical, analytical methods are insufficient to indicate the number
of atoms contained in these molecules.

The second method, based on Avogadro's law, is applicable to all
substances which are or can be converted into gases or vapors without
decomposition. Since equal volumes of all gases at the same temper-
ature and pressure contain the same number of molecules, the weights
of equal volumes of gases must bear the same ratio to one another as
the weights of the individual molecules. But the weights of mole-
cules are in the same ratio as the molecular weights. Hence we
deduce the following rule from Avogadro's Law : Densities of gases at
the same temperature and pressure are to each other as their molecular
weights. If we know the molecular weight of any gas and its
density, by comparing any other gas with it we can determine its molec-
ular weight. As we have seen, the molecule of hydrogen is known
to contain two atoms, that is, its molecular weight is 2, if we call the

DETERMINATION OF ATOMIC WEIGHTS. 109

weight of its atom 1. Hydrogen is usually chosen for comparison
with other gases. Suppose it is desired to find the molecular weight
of oxygen. One liter of oxygen at 0° C. and 760 mm. of pressure
weighs 1.429 grammes, one liter of hydrogen under the same conditions
weighs 0.08987 gramme. Hence by the proportion,

0.08987:1.429 : : 2:x,

x = 1 .429 X 2 -5- 0.08987 = 31.8,

that is, the molecular weight of oxygen is 31.8, or the molecule is 15.9
times heavier than the molecule of hydrogen.

If we call the density of hydrogen 1, and refer the densities of
other gases to this standard, then the figures indicate how many times
heavier the gases are than hydrogen under like conditions, or, what
comes to the same thing, how many times heavier the molecules of the
gases are than the molecule of hydrogen. Hence, a simple rule for
finding molecular weight is to multiply the density of a gas on the
hydrogen basis by 2.

Conversely, if we know the molecular weights of two gases, and
the density of one of them, we can calculate the density of the other
gas. The density of any gas is equal to the density of hydrogen
multiplied by half the molecular weight of the gas.

A third method, that of Raoult, is based upok the fact that the
freezing-point of a liquid is lowered to the same extent by dissolving
in it compounds in quantities proportional to their molecular weights.
For example : Water begins to solidify at 32° F. (0° C.), but by dis-
solving in it say 4 per cent, of its weight of a salt (the molecular weight
of which is known) the freezing-point is lowered, say 1° C. If, then,
another salt (the molecular weight of which is not known) be dissolved
in water, and it be found that to reduce the freezing-point 1° C. there
must be dissolved a quantity equal to 7 per cent, of the weight of the

QUESTIONS. — What are the three principal methods used for the determina-
tion of atomic weights ? Why are chemical means not always sufficient to
determine atomic weights ? How can the specific gravity of elements in the
gaseous state be used for the determination of atomic weight? Describe a
method of the determination of atomic weight by chemical means. State one
of the reasons why the atomic weight of oxygen has been changed from 8 to 16.
What relation exists between atomic weight and specific heat? State the law
of Dulong and Petit. Suppose the specific heat of an element to be 0.1138,
what will its atomic weight be? Suppose the specific gravity of an elementary
gas to be 14, what will its atomic weight be? Suppose 214.24 grammes of an
element replace 2 grammes of hydrogen in 72.36 grammes of HC1, what will
the atomic weight of the element be?

110 PRINCIPLES OF CHEMISTRY.

water used — then are the molecular weights of the two salts to each
other as is 4 to 7.

In regard to this method of Raoult it should be stated that it is
applicable only to such substances as do not act chemically upon the
solvent used, and that the ratio of the lowering of the freezing-point
is not the same for all substances, but only for members of the same
class of substances.

8. CHEMICAL EQUATIONS. TYPES OF CHEMICAL CHANGE.
REVERSIBLE ACTIONS AND CHEMICAL EQUILIBRIUM.
MASS ACTION. ACIDS, BASES, SALTS. RADICAL. CONSTI-
TUTIONAL FORMULAS.

Chemical equations. We have seen that the composition of sub-
stances can be expressed by symbols or formulas, which show at a
glance the kind of elements and their proportions present in the sub-
stances. Similarly, a method of representing what takes place in a
chemical change concisely and in a way that can be quickly grasped
has been devised. This is done by means of chemical equations.
Such an equation is formed by writing the formulas of the substances
that react on the left of the sign of equality, and connecting them by
the sign +, and the formulas of the products of the reaction on the
right of the sign of equality, also connected by the -f sign. For
example, hydrochloric acid and silver nitrate mutually decompose
each other and give an insoluble white substance, silver chloride and
nitric acid. This may be represented thus, HC1 -f AgNO3 = AgCl
-f HNO3. The + sign should be read and, and the = sign should be
read gives. A chemical equation has nothing in common with an
algebraic one, except its form. It cannot be factored, or in any way
be handled as an algebraic equation. It is simply a statement of facts
learned by experiment. Until we have learned beforehand the com-
position of the substances entering into chemical reaction and also of
the products formed, and the proportions involved, we have no basis
upon which we can legitimately write an equation. The unit of
chemical action is the molecule, and the chemical equations are intended
to show the action taking place between the molecules. Thus, in the
reaction above, one molecule of hydrochloric acid decomposes one
molecule of silver nitrate. We often, however, read an equation in a
broader and less definite manner, thus, in the above case, we say
hydrochloric acid decomposes silver nitrate and gives silver chloride
and nitric acid. When more than one molecule is represented, a
numeral is placed before the symbol. The symbols 2NaCl and Na2Cl2

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. Ill

represent the same number of atoms and the same proportions by
wciuht of the elements, but they are quite different, for NaCl is the
actual size of the molecule, and 2NaCl stands for two molecules, while
Xa.,CU represents a molecule double the size of that of sodium chloride,
Na( -1, as actually known. Often in writing equations, for convenience
we represent elements in the atomic state, while in reality they exist
in the molecular state. The equations are true, however, as far as
proportions are concerned. For example, we represent the union of
hydrogen and oxygen to form water thus, H2 + O = H2O, but to be
in keeping with the fact that molecules of hydrogen and oxygen are
really involved, we should write 2H2 -|- O2 = 2H2O.

Every correct chemical equation is correct mathematically also —
i. e.y the sum of the atoms as well as that of the molecular weights of
the factors equals the sum of the atoms and that of the molecular
weights of the products respectively. For instance : Sodium car-
bonate and calcium chloride form calcium carbonate and sodium
chloride. Expressed in chemical equation we say :

NaaCOs + CaCl2 = CaCO3 + 2NaCl.

Sodium carbonate and calcium chloride are the factors, calcium car-
bonate and sodium chloride the products. Adding together the
molecular weights of the factors and those of the products we find
equal quantities, as follows :

2Na = 45.76
O=11.91

3O = 47.64
105.31

Ca = 39.80
2C1 = 70.36

-f "lioTe

Ca = 39.80
C = 11.91
3O = 47.64

2Na = 45.76
2C1 = 70.36

99.35

+ 316.12

Chemical equations not only are used for representing chemical
changes, but also are the starting-point in all the chemical calcula-
tions in which the quantities of substances entering into chemical
actions, or the quantities of the product formed, are concerned.

The above calculation teaches, for instance, that 105.31 parts by
weight of sodium carbonate are acted upon by 110.16 parts by weight
of calcium chloride, and that 99.35 parts by weight of calcium car-
bonate and 116.12 parts by weight of sodium chloride are formed by
tins action. These data may, of course, be utilized to find how much
calcium chloride may be needed for the decomposition of one pound
or of any other definite weight of sodium carbonate ; or how much
of these two substances may be required to produce one hundred
pounds, or any other definite weight, of calcium carbonate.

While in many cases of chemical decomposition the change which is

112 PRINCIPLES OF CHEMISTRY.

to take place cannot be foretold, but has to be studied experimentally,
there are other chemical changes which can be predicted with certainty.
This is more especially true in the case of the action of acids on
bases and the action of one salt on another salt. This will be easily
seen when the relationship between acids, bases, and salts is under-
stood. Among these classes of compounds the results can usually be
foretold, and there is little difficulty in representing the change by
the proper equation. In doing this it must be borne in mind that
equivalent quantities replace one another; that, for instance, two atoms of a
univalent element are required to replace one atom of a bivalent element,
as, for instance, in the case of the decomposition taking place between
potassium iodide and mercuric chloride, when two molecules of the
first are required to decompose one molecule of the second compound :

K — I rr /Cl TJ- /I K — Cl

K-I + Hg\Cl : Hg\I K-C1
or

2KI + HgCl2 = HgI2 + 2KC1.

Whenever the exchange of atoms takes place between univalent
and trivalent elements, three of the first are required for one of the
second, as in the case of the action of sodium hydroxide on bismuth
chloride :

Na — OH /Cl /OH Na — Cl

Na — OH + Bi— Cl == Bi— OH + Na — Cl
Na — OH \C1 \OH Na — Cl

or

3NaOH + BiCl3 = Bi(OH)3 + 3NaCl.

In the following examples of double decomposition an exchange
takes place between the atoms of metallic elements, or between the
metallic elements and the hydrogen. The student, in completing the
equations, has also to select the correct quantity, i. e., the correct
number of molecules of the factors required for the change. The
interrogation marks indicate that more than one atom or one molecule
of the substance is needed for the reaction.

Na' + H'Cl Cu"SO4 + H/S =

H/S04 -f K'(?) Ba"Cl2 + Na/SO4

Ca" + H'Cl (?) = Na/C03 + H/SO4

Fe" + H/S04 = Bi"'(N03)3 + K'OH (?) =

H'Cl -f Ag'NOg = Ala///(S04)8 + K'OH (?) =r

Ca"Cl2 +Ag'N03(?)= A1/"(S04)S + Ca"(OH)2(?) =

Bi'^CL, + Ag'NOat?) = Fe2"'Cl6 + Ag'NO3 (?) =

Types of chemical change. There are four principal ways in
which chemical actions take place. These may be represented by the

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 113

following equations, in which the letters stand for elements or groups
of elements :

1. A -|- B = AB direct combination or addition.

2. (a) AB = A + B i

(6) ABC = AB -|- C > simple decomposition.
(c) ABC = AC f BCJ

3. AB + C =-- CB + A displacement,

4. AB -f- CD — AD + CB double decomposition or metathesis.

The following concrete examples will serve to illustrate the above
types of change :

1. Mg -f O = MgO.

When magnesium metal is heated to the ignition point it unites
with oxygen of the air, and gives a white ash known as magnesium
oxide.

2. (a) HgO = Hg + O.

Mercuric oxide, when heated to a sufficient temperature, decom-
poses into its elements — mercury and oxygen.

(6) KC1O3 = KC1 + 30.

When potassium chlorate is heated sufficiently high and long it de-
composes into the compound potassium chloride and the element
oxygen.

(c) CaCO3 = CaO + CO2.

When calcium carbonate is heated to redness it is decomposed into
two new compounds — namely, calcium oxide and carbon dioxide.

3. Fe + 2HC1 = FeCl2 + 2H.

When a solution of hydrochloric acid is poured upon some iron, a
brisk evolution of hydrogen gas takes place ; and a new compound,
ferrous chloride, remains in the solution.

Although in a sense there is a displacement of one element by
another in every chemical action between two substances in which
two new substances result, by custom the term displacement is used
in those cases where the element displaced is left in the free or uncom-
bined state.

4. HC1 + AgNO3 == AgCl + HNO3.

When a solution of hydrochloric acid is added to a solution of
silver nitrate, silver chloride is obtained as a white precipitate, and
nitric acid is left in solution. This type of change, known as double
decomposition or metathesis, is one of the most frequently occurring
kinds of chemical change in analysis and chemical industry.

8

114 PRINCIPLES OF CHEMISTRY.

Reversible actions and chemical equilibrium. Experimental study
has shown that in many instances a chemical action, when once started, runs
to completion, that is, continues until the substance, or one of two substances,
undergoing change is used up. For example, when a piece of magnesium is
ignited the action continues until all the metal is used up, or the oxygen in
the supply of air is exhausted. Moreover, this action cannot be reversed, that
is, made to proceed in the opposite manner, no matter how much heat, or what
degree of heat, available in the laboratory, we apply to the magnesium oxide.
In other words, we cannot decompose the latter into magnesium element and.
oxygen by heat alone.

On the other hand, there are many instances in which chemical action,
under a given set of conditions, is not complete, but proceeds to a certain point
beyond which the products formed tend to act in a reverse manner, and repro-
duce the original substance or substances. Such changes are known as revers-
ible actions, and evidently, while the conditions are maintained, the whole
chemical process comes apparently to a standstill. But in the light of the
kinetic-molecular theory of matter it is believed that action is constantly going
on, although there is no progress made in either direction. The forward action
of the system is counterbalanced by the reverse action which proceeds at the
same speed, and thus is produced a condition of seeming rest, or chemical equi-
librium. An example of equilibrium as a result of two equal and opposite
actions is the case of a liquid in a closed container. At a definite temperature,
the space above the liquid is saturated with its vapor which exerts a constant
pressure. Although there is apparent rest, molecules of the liquid are passing
off into the space above it, while vapor molecules are flying back into the
liquid. These opposite actions finally balance each other, and then the system
is in equilibrium. If the conditions are changed, for example, by a rise in
temperature, the equilibrium is disturbed, a readjustment and new equilibrium
follow, in which more vapor molecules exist in the space above the liquid,
and a higher vapor pressure is produced.

Reversible chemical actions are represented by equations which differ from
the ordinary chemical equations, in that the equality sign is replaced by two
oppositely directed arrows, thus :
* AB + CD 7=1 AD -f CB.

Such an equation indicates that the action takes place in two directions, for-
ward and backward, and when equilibrium has been reached as much material
continues to be transformed in one direction as in the reverse direction.

While in many cases the action is reversible, yet it runs far toward comple-
tion in one direction. This condition may be represented by making one of
the arrows heavier than the other, thus :

MN -f PR ;i± MR + PN.

The following is a good example of a reversible chemical change. If finely
divided iron and water vapor be heated in a sealed glass tube so that none of
the products can escape, a state of equilibrium will result, in which four prod-
ucts exist in the tube — namely, iron, iron oxide, water vapor, and hydrogen.

3Fe + 4H2O 7± Fe3O4 -f 8H.
This means that at the equilibrium stage the hydrogen reduces the iron

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 115

oxide reversely as fast as the iron reduces the water vapor ill the forward
direction.

When the experiment is performed in the same manner as above, with iron
oxide and hydrogen sealed in the tube at the equilibrium point, the same kinds
of products exist as in the first case, thus :

Fe3O4 + 8H Til 3Fe + 4H2O.

Evidently a necessary condition for maintaining a chemical equilibrium in
any reversible action is the keeping intact of all the factors taking part. If
one of the products of an action be removed from the field of action as fast as
it is formed, we might reasonably predict that the action would proceed to
completion in the direction made easiest by the removal of such product. This
is exactly what happens, as may be shown in the above instances. When steam
is passed over highly heated iron through an open tube, the action takes place
to completion, thus :

Fe3 + 4H20 = Fe304 + »H.

The hydrogen is swept out of the tube and away from contact with the iron
oxide by the current of steam. The action continues until all the iron is
exhausted.

Conversely, when hydrogen gas is passed over heated iron oxide in an open
tube, the action runs to completion reversely thus :

Fe3O4 + 8H = 3Fe + 4H2O.

The current of hydrogen sweeps the water vapor (steam) out of the tube as fast
as it is produced. The action continues until all the iron oxide is exhausted
by conversion to elementary iron.

If one considered only the first action he would conclude that iron has a
greater affinity for oxygen than hydrogen has, whereas if he considered only
the second action, he would say that hydrogen has a greater affinity for oxygen
than iron has, which apparently is a contradiction. But both conclusions are
correct, depending on circumstances. In fact, in reversible actions affinity
plays a minor part in determining which direction a chemical change will
take, this being controlled in largest measure by the physical conditions of the
experiment, which have nothing to do with affinity. This is admirably shown
by the following example : When common salt (sodium chloride, NaCl) is dis-
solved in 20 per cent, aqueous solution of sulphuric acid (H2SO4), nothing
apparently happens except solution of the salt. Yet a reversible action takes
place, thus :

2NaCl + H2SO4 7=1 Na2SO4 -f 2HC1.

Four products are present in solution in equilibrium. When, however, con-
centrated sulphuric acid, which is about 95 per cent., is -poured upon salt, a
brisk evolution of hydrochloric acid gas takes place, because of the fact that it
is nearly insoluble in concentrated sulphuric acid. One of the factors in the
equilibrium equation above is thus removed from the field of action, which
thus allows the action to go forward nearly to completion and leaves the'im-
pression that the sulphuric acid has a greater affinity for the metal sodium than
has the hydrochloric acid, or, as it is put sometimes in text-books, that sul-
phuric acid is a " stronger " acid than hydrochloric, which, in fact, is not true.

116 PRINCIPLES OF CHEMISTRY.

On the other hand, when hydrochloric acid gas is passed into a saturated
aqueous solution of sodium sulphate until no more is absorbed, nearly all of
the sodium is precipitated as sodium chloride, because the latter is almost
insoluble in concentrated hydrochloric acid solution, and sulphuric acid is
liberated and remains in the solution. In this case one of the factors in the
above equilibrium equation is practically removed from the field of action by
precipitation, thus allowing the reverse action to proceed nearly to completion,
and leaving the impression that hydrochloric acid is a "stronger" acid than
sulphuric.

Mass action. The vigor and extent of a chemical action depends upon
the freedom with which the molecules can clash as well as upon the affinity
between substances. Hence it is found that chemical action is aided far better
in homogeneous mixtures, as when the substances are present in the gaseous
state or in solution. Such physical systems as gas arid solid, gas and liquid,
liquid and solid, solid and solid, offer only limited contact between molecules,
and, therefore, more or less impede chemical change. In homogeneous mix-
tures, in the case of reversible actions, the proportion of the substances changed
chemically is different in different cases. The range extends all the way from
slight change to nearly complete change. But in each individual case the
amount of transformation is found to depend upon the concentration of each
substance as well as upon the affinity between the substances. This is often
called the Law of Mass Action, which may be stated thus : The amount of a
chemical change taking place in a given lime will be dependent upon the molecular
concentration of each substance.

In chemical operations it is usually desirable to obtain one or other of the
products of a chemical change in as large a yield as possible. If the action
employed is a non-reversible one, little difficulty will be experienced in obtain-
ing a full yield. In reversible actions, according to the law of mass action,
the amount of the new product formed can be increased in two ways, either
(1) by increasing the concentration of one or the other of the reacting sub-
stances, or (2) by removing one or the other of the products formed. The
second method — namely, the removal of one of the products of the action, thus
affecting the equilibrium of the system in such a way that the action tends
toward completion — is the more effective way of increasing the yield. This is
most conveniently done by selecting such actions that automatically remove
one of the products of the system in the form of an escaping gas or an insol-
uble body (precipitate1).

As instances of the removal of one of the products, and, therefore, more or
less complete action, may be mentioned the formation of all the hundreds of
insoluble metallic salts which are produced by the action of one salt solution
upon another salt solution, the first solution containing a metal which, with the
acid of the second solution, may form an insoluble compound, which is then
invariably produced as a precipitate. For instance: Calcium carbonate,
CaCO3, is insoluble ; if we bring together two solutions containing a soluble
calcium salt and a soluble carbonate, such as calcium chloride, CaCl2, and
sodium carbonate, Na2CO3, calcium carbonate is precipitated.

1 The term precipitate is used to designate an insoluble substance which separates by chem-
ical action in a liquid, while sediment is applied to the collection of insoluble matter that may
be floating in a liquid, and does not imply chemical action.

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 117

Examples of complete action because of the removal of one of the products
as a gas are: Action of any acid on any carbonate, whereby carbon dioxide
gas is liberated ; action of caustic alkalies, lime or magnesia, on ammonium
salts, whereby ammonia gas is liberated.

Acids. The many compounds formed by the union of elements
are so various in their nature, that no system of classification pro-
posed up to the present time can be called perfect. There are, how-
ever, a few groups or classes of compounds, the properties of which
are so well marked, that a substance belonging to either of them may
be easily recognized. These groups are the acids, bases, and neutral
substances.

The term acid is applied to those compounds of hydrogen with an
electro-negative element or group of elements which are character-
ized by the following properties :

1. The hydrogen present is replaceable by metals, the compound
thus formed being a salt.

2. They change the color of many organic substances. Thus,
litmus, a coloring-matter obtained from certain lichens, is changed
from blue to red.

3. They have (when soluble in water) usually an acid or sour taste.

The great majority of acids are the result of union between water and the
oxides of those elements which are devoid of characteristic metallic properties.
We might, therefore, classify non-metallic elements as acid-forming elements.
There are a few exceptional metals which form a series of oxides, some of
which, when united with water, give acids; for example, chromic acid, H2CrO4,
permanganic acid, HMnO4. The formation of acids from oxides is shown by
the following equations :

SO3 -f H20 = H2SO4.

Sulphur Sulphuric

trioxide. acid.

P205 -f 3H2O : 2H3P04.

Phosphorus Phosphoric

pentoxide. acid.

C02 + H2O = H2C03.

Carbon Carbonic

dioxide. acid.

Evidently in the acids containing oxygen, often called oxyacids, the hydrogen
is derived from the water molecules with which the acidic oxides unite. Those
oxides which unite with water to give acids are called acidic oxides or acid
anhydrides. As was said before, the great majority of acidic oxides are derived
from the non-metals, but there are some oxides of the non-metals which do not
form acids, for example, carbon monoxide, CO, and nitrogen monoxide, N7O.

A few acids contain no oxygen, and these are sometimes called hydracids.
They have no corresponding oxides and are combinations of hydrogen with
non-metallic elements, or groups of elements called radicals. The principal
ones are hvdrochloric acid, HC1, hydrobromic acid, HBr, hydriodic acid, HI,

118 PRINCIPLES OF CHEMISTRY.

hydrofluoric acid, HF, or H2F2, hydrogen sulphide, H2S, hydrocyanic acid,
H(CN>.

However much the acids may differ in certain properties, such as consist-
ency, that is, whether solid, liquid, or gas, solubility in water, degree of acid
taste and action on litmus paper, corrosiveness to organic matter, such as skin,
wood, cloth, etc., they are all alike in one respect, namely, in containing hy-
drogen which is separable from the rest of the molecule, and replaceable by
metals, either by direct action of a metal on the acid, as when zinc acts on a
solution of sulphuric or hydrochloric acid, or in a round-about way. There
seems to be a strong tendency to separation between the hydrogen and the rest
of the molecule of an acid which remains intact as a unit.

According to the number of hydrogen atoms replaceable by metals, we dis-
tinguish monobasic, dibasic, and tribasic acids. Hydrochloric acid, HC1, is a
monobasic ; sulphuric acid, H2SO4, is a dibasic ; phosphoric acid, H3PO4, is a
tribasic acid.

Many of the acids sold in trade, as well as the reagents used in the labora-
tory, are solutions of acids in water. It is customary to call these solutions
by the names given to the acids themselves.

Bases or basic substances show properties which are chemically
opposite to those of acids. As a general rule bases are compounds
of electro-positive elements (metals) with oxygen (oxides) or more
generally with oxygen and hydrogen (hydroxides). Thus, silver
oxide, Ag2O, and sodium hydroxide, NaOH, are basic substances.
Other properties characteristic of bases are :

1. When acted upon by acids, they form salts ; for instance,
when sodium hydroxide and nitric acid are brought together water
and the salt sodium nitrate are formed :

NaOH + HN03 = H2O + NaNO3.

2. They have (when soluble in water) an alkaline reaction, i. e.,
they restore the color of organic substances when previously changed
by acids : for instance, that of litmus, from red to blue.

3. They have (when soluble in water) the taste of lye, or an alka-
line taste.

The term base was originally applied to the metallic oxides, because when
salts of the metals were highly heated they were decomposed, leaving a non-
volatile calx or ash, the oxide of the metal, while the acid radical of the salt
was driven off. Thus the metallic oxides were regarded as the base or stable
groundwork of the salts. In the present-day classification, metallic hydroxides
are called bases, but as the oxides bear such a close relationship to the hy-
droxides, in fact, many of them being converted into hydroxides in contact
with water, many authors also include metallic oxides in the class of bases.
The relationship between metallic oxides and hydroxides is well shown in the
case of quick-lime, calcium oxide. Nearly everyone is familiar with the
process of slaking lime by adding water to quick-lime. The action takes
place thus, CaO + HaO = Ca(OH)2. The slaked lime, Ca(OH)2, is a

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC 119

hydroxide of calcium. The relation might be made more striking by writing
the formula thus, CaO • H2O.

Some oxides do not unite with water to form hydroxides, but, as far as they
are acted upon by acids, they give the same end product (a salt) as the hy-
droxides do, as may be illustrated in the following reactions :

ZnO '+ H2S04 == ZnSO4 + H2O.
Zn(OH)2 + H2SO4 = ZnSO4 + 2H2O.

It should be noted that one of the products that is always formed when an
acid acts on a metallic hydroxide, or oxide, is water. This is shown in the
above reactions.

The hydroxides evidently are compounds derived from water by the re-
placement of part of the hydrogen in the water molecule by metal, thus
leaving the radical, (OH), which is known as hydroxyl, in combination with
metal. Hence, these compounds are called hydroxides. In a few cases hy-
droxides can be obtained by the direct action of the metals on water, the dis-
placed hydrogen escaping as a gas. This seems to be good evidence of the
relationship between the hydroxides and water. Most metals, however, do not
act on water, and their hydroxides are obtained in an indirect way. (See
Remarks on Tests for Metals, in the chapter on Magnesium.)

There are some hydroxides of radicals which can unite with acids just as
the metallic hydroxides do, and these are also classed as basic substances. In
them the radical plays the part of a metal.

Most of the metallic oxides and hydroxides are practically insoluble in
water, and therefore have no appreciable action on litmus paper and no taste.
Hence, alkaline action and taste are not a sure criterion of a basic substance.
But the hydroxides insoluble in water can act on acids and replace their hy-
drogen by metal, just as the soluble hydroxides do.

The hydroxides differ very much in regard to specific properties, such as
solubility in water, color, taste, etc., but there is one feature common to all of
them, namely, the presence of the hydroxyl group, which is responsible for
the class properties upon which such compounds are classified as basic sub-
stances.

It should be noted that there appears to be a tendency to easy separation
between the metal and the hydroxyl radical in the bases, just as there is be-
tween the hydrogen and the acid radical in the case of acids. The significance
of these facts will appear when the Ionic Theory is discussed.

Neutralization is the term applied to the interaction between
acids and bases with the result that both acid and basic properties,
disappear — i. e., are neutralized.

All substances which are acid in character contain hydrogen as
one of their constituents. This hydrogen can readily be replaced by
metals, for instance by magnesium, when hydrogen is liberated.
Not all substances containing hydrogen behave in this manner ; for
example, magnesium does not liberate hydrogen from petroleum,
olive oil, sugar, etc., which all contain hydrogen. Hence the hydro-
gen of acids must be in a peculiar condition. That it is this hydro-

120 PRINCIPLES OF CHEMISTRY.

gen, and the peculiar condition in which it is present, which impart
to acids their peculiar properties, are demonstrated by the fact that the
acid properties disappear as soon as the hydrogen is replaced by a
metal. Thus, the acid characteristics of hydrochloric acid, HC1,
vanish when it is acted on by sodium, or by the basic substance
caustic soda (sodium hydroxide, NaOH), both of which cause a re-
placement of the acid hydrogen by sodium. These actions can be
represented by the equations :

HC1 -f Na NaCl + H.

HC1 + NaOH NaCl -f H2O.

In both cases sodium chloride, NaCl (common salt), is formed, which
possesses neither acid nor basic properties.

Neutral substances. All substances having neither acid nor basic
properties are neutral. Water, for instance, is a neutral substance,
having no acid or alkaline taste, and no action on red or blue litmus.
Many neutral substances, to some extent even water, appear to possess
the characteristic properties of both classes, acids and bases ; of neither
class, however, to a very great extent.

Salts. Salts are acids in which hydrogen has been replaced by
metals or by basic radicals. There are several general methods by
which salts may be obtained :

1. By the action of an acid on a metal. This is illustrated in the
preparation of hydrogen from sulphuric or hydrochloric acid and

zinc or iron.

Zn + H2S04 = ZnS04 + H2.
Fe + 2HC1 = FeCl2 + H2.

2. By the action of an acid on an oxide or hydroxide of a metal.
This is of wider application than the previous method.

ZnO + H2SO4 = ZnSO4 + H20.
MgO + 2HC1 = MgCl2 -f H2O.
NaOH + HC1 = NaCl + H2O.

3. By the action of an acid on a salt of a volatile acid. This finds
most extensive and useful application in the case of carbonates, which
are decomposed by nearly all other acids, and are found ready-formed
in nature or can be easily made.

MgCOs + H.2S04 = MgS04 + H20 + C02.
CaC03 + 2HC1 = CaCl2 + H2O + CO2.

Other volatile acids whose salts are decomposed by acids are sulphur-
ous, nitrous, hydrogen sulphide, hydrocyanic, etc. The manufacture

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 121

of hydrochloric and nitric acids by the aid of concentrated sulphuric
acid is an example of the method, and large quantities of sodium
sulphate are obtained as a by-product for the market.

4. By the action of one salt upon another salt. This method is
chiefly used when one of the products is insoluble or very nearly so,
and is known as precipitation. Usually the insoluble product is the
desired one, but the soluble one may also be isolated. A great many
of the analytical reactions, called tests, fall under this method.
Nearly all carbonates and phosphates are obtained by precipitation.

CaCl2 + Na2CO3 = CaC03 + 2NaCl.
CaCl2 + Na2HPO, = CaHP04 + 2NaCl.

Calcium carbonate and phosphate are precipitated and may be re-
moved.

An example of the use of the method to get the soluble product is
shown by the equation :

CuS04 + BaCl2 = BaS04 + CuCl,.

A solution of copper chloride is obtained by filtering off the barium
sulphate.

In the case of certain salts it is simpler or more economic to
follow special methods, which may be seen under the respective salts.
Some of these salts are ferrous iodide, ammonium iodide, sodium
hypochlorite, iodide, and thiosulphate, potassium permanganate,
dichromate and chlorate, sodium carbonate, mercurous and mercuric
chloride, etc.

According to the number of hydrogen atoms replaced in an acid,
we distinguish normal and acid salts. A normal salt is one formed by
the replacement of all the replaceable hydrogen atoms of an acid.
For instance : Potassium chloride, KC1, potassium sulphate, K2SO4,
potassium phosphate, K3PO4. (As monobasic acids have but one atom
of hydrogen which can be replaced, they form normal salts only.)

Normal salts often have a neutral reaction to litmus, but they may
have an acid or even an alkaline reaction.

It is found that soluble normal salts derived from a weakly ioniz-
ing acid, as carbonic, boric, phosphoric, sulphurous, hypochlorous,
silicic, hydrogen sulphide, and a strongly ionizing base, as sodium
and potassium hydroxide, and some others, have an alkaline reaction,
while those derived from a strongly ionizing acid and a weakly ioniz-
ing base, as the hydroxide of many of the heavy metals, such as
Fe(OH)2, A1(OH)3, Cu(OH)2, etc., have an acid reaction. The reason

122 PRINCIPLES OF CHEMISTRY.

for this is that such salts are partially decomposed or hydrolyzed by
water. Thus, in the case of ferrous sulphate,

FeS04 -f 2H20 = Fe(OH)2 + H2SO4,

the small quantity of free acid formed affects litmus-paper, Fe(OH)2
being neutral. Sodium carbonate is acted on thus :

Na2C03 + H20 = NaHC03 + NaOH,

the free alkali causes litmus to turn blue, while NaHCO3 is neutral.

Acid salts are acids in which there has been replaced only a portion
of their replaceable hydrogen atoms. For instance : KHSO4, K2H PO4,
KH2PO4. While acid salts have generally an acid reaction to litmus,
there are many exceptions to this rule. Indeed, the reaction may be
neutral or even alkaline, as, for instance, in the case of the ordinary
sodium phosphate, Na2HPO4, which is slightly alkaline to litmus.

Basic salts are salts containing a higher proportion of a base than
is necessary for the formation of a normal salt. Instances are basic
mercuric sulphate, HgSO4.(HgO)2, basic lead nitrate, Pb(NO3)2.
Pb(OH)2. According to modern views basic salts are looked upon
as derived from bases by replacement of part of their hydrogen by acid
radicals. In the base lead hydroxide, Pb(OH)2, one of the hydrogen
atoms may be replaced by the radical of nitric acid, when basic lead

nitrate, Pb<TT3' is formed.

In bismuth hydroxide, Bi(OH)3, one, two, or three hydrogen atoms
may be replaced by nitric acid, when the salts Bi(^ /QTT\

and Bi(NO3)3 are formed. The first two compounds are basic salts,
while the third one is the normal salt.

Double salts are salts formed by replacement of hydrogen in an
acid by more than one metal. For instance : Potassium-sodium sul-
phate, KNaSO4.

Residue, radical, or compound radical, are expressions for un-
saturated groups of atoms known to enter as a whole into different
compounds, but having no separate existence. For instance: The
bivalent oxygen combines with two atoms of the univalent hydrogen,
forming the saturated compound H2O, water. If we take from this
H2O one atom of H, there is left the group of atoms HO (generally
written OH), consisting of an atom of oxygen in which but one point
of attraction is actually saturated, the second one not being pro-
vided for.

This group, OH, is a residue or radical, and is known to enter into

CHEMICAL EQUATIONS, TYPES OF CHEMICAL CHANGE, ETC. 123

many compounds ; it is, for instance, a constituent of all the different
hydroxides (formerly called hydrates), such as potassium hydroxide,
KOH, calcium hydroxide, Ca(OH)2, etc.

According to the number of points of attraction left unprovided
for in a radical, we distinguish univalent, bivalent, trivalent, and
quadrivalent radicals.

Carbon is a quadrivalent element forming with the univalent hy-
drogen the saturated compound CH4. By removal of one, two, or
three hydrogen atoms the radicals CH3', CH/', CH'", are formed.

Constitutional or graphic formulas. Though it is impossible
to examine the structure of a molecule by means of a microscope, yet
we may obtain some information of the atomic arrangement within
the molecules by a study of the formation and decomposition which
they undergo under different conditions.

Such investigations lead to the conclusion that molecules are not
merely clusters of atoms held together irregularly, but that the
atoms are arranged systematically and occupy a definite position
within the molecules of each individual substance.

In order to represent figuratively our views regarding the atomic
arrangement the so-called constitutional or graphic formulas are often
used. Thus, while sulphuric acid is represented by the molecular
formula H2SO4, we may assign to it the graphic formula SO/'. (OH)2,
which indicates that sulphuric acid is made up of the bivalent radi-
cal SO2 and of two univalent radicals OH. In order to give a yet
fuller expression of our views regarding the linkage of the atoms, sul-
phuric acid may be graphically represented thus :

O— H

01 vv,

-H

QUESTIONS. — What are chemical equations and how do they serve as a basis
for calculations? Mention the principal types of chemical change, with exam-
ples. Define reversible actions and chemical equilibrium. How may a revers-
ible action be made to run to completion in one direction? Give an example.
What is the law of mass action? Define an acid, and state the general proper?
ties of basic and neutral substances. By what means can they be recognized?
Distinguish between mono-, di-, and tri-basic acids. What are salts and how
are they formed? Define neutral, acid, and double salts. Explain the term
radical or residue.

124 PRINCIPLES OF CHEMISTRY.

In these formulas we show that sulphur exerts the valence of six,
that four of its affinities are saturated by oxygen, while the two re-
maining are attached to two oxygen atoms, the unsaturated affinities
of which are satisfied by hydrogen.

9. GENERAL REMARKS REGARDING ELEMENTS.

Relative importance of different elements. Of the total
number of about seventy-six elements, comparatively few (about
one-fourth) are of great and general importance for the earth, and the
phenomena taking place upon it. These important elements form
the greater part of the mass of the solid portion of the earth, and of
the water and atmosphere, and of all animal and vegetable matter.

Another number of elements are of less importance, because either
they are not found in any large quantity, or do not take any active
or essential part in the formation of organic matter ; yet they are of
interest and importance on account of being used, in their elementary
state or in the form of different compounds, in every-day life for
various purposes.

A third number of elements are found in such minute quantities
in nature that they are almost exclusively of scientific interest. Even
the existence of some elements, the discovery of which has been
claimed, is doubtful.

The elements enumerated in column I. are those of great and gen-
eral interest ; in II. those claiming interest on account of the special
use made of them ; in III. those having scientific interest chiefly.

I. II.

Aluminum Antimony Iridiuin

Calcium Arsenic Lead

Carbon Barium Lithium

Chlorine Bismuth Manganese

Hydrogen Boron Mercury

Iron Bromine Molybdenum

Magnesium Cadmium Nickel

Nitrogen Cerium Platinum

Oxygen Chromium Radium

Phosphorus Cobalt Silver

Potassium Copper Strontium

Silicon Fluorine Tin

Sodium Gold Uranium

Sulphur Iodine Zinc

GENERAL REMARKS REGARDING ELEMENTS. 125
III.

Argon

Neon

Thallium

Beryllium (Glucinum)

Osmium

Thorium

Caesium

Palladium

Thulium

Columbium (Niobium)

Praseodymium

Titanium

Erbium

Rhodium

Tungsten

Gadolinium

Rubidium

Vanadium

Gallium

Ruthenium

Xenon

Germanium

Samarium

Ytterbium

Helium

Scandium

Yttrium

Indium

Selenium

Zirconium

Krypton

Tantalum

Lanthanum

Tellurium

Neodymium

Terbium

Classification of elements may be based upon either physical or
chemical properties, or upon a consideration of both. A natural
classification of all elements is the one dividing them into two groups
of metals and non-rnetals.

Metals are all elements which have that peculiar lustre known as
metallic lustre ; which are good conductors of heat and electricity ;
which, in combination with oxygen, form compounds generally
showing basic properties ; and which are capable of replacing hy-
drogen in acids, thus forming salts.

Non-metals or metalloids are all elements not having the above-
mentioned properties. Their oxides in combination with water gen-
erally have acid properties. In all other respects the chemical and
physical properties of non-metals differ widely. Their number
amounts to 18, the other 58 elements being metals.

Natural groups of elements. Besides classifying all elements
into metals and non-metals, certain members of both classes exhibit
so much resemblance in their properties, that many of them have
been arranged into natural groups. The members of such a natural
group frequently show some connection between atomic weights and
properties.

Chlorine, 35.2 Sulphur, 31.8 Lithium, 7.0 Calcium, 39.8
Bromine, 79.3 Selenium, 78.6 Sodium, 22.9 Strontium, 86.9
Iodine, 125.9 Tellurium, 126.6 Potassium, 38.8 Barium, 136.4

Each three elements mentioned in the above four columns resemble
each other in many respects, forming a natural group. The relation

126 PRINCIPLES OF CHEMISTRY.

between the atomic weights will hardly be suspected by looking at
the figures, but will be noticed at once by adding together the atomic
weights of the first and last elements and dividing this sum by 2,
when the atomic weights (very nearly, at least) of the middle mem-
bers of the series are obtained. Thus :
8S.2 + 125.9 _ go 55 . 31.8 + 126.6 __ 79_2 . 7.0 + 38.8 = 22>g . 39.8 + 136.4 = g8_L

Mendelejeff's periodic law.1 The relationship between atomic
weights and properties has been used for arranging all elements sys-
tematically in such a manner that the existing relation is clearly
pointed out. Of the various schemes proposed, the one arranged by
Mendelejeff may be selected as most suitable to show this relation.

Looking at Mendelejeff's table on page 128 it will be seen that all
the elements are arranged in the order of their atomic weights, and
that the latter increase gradually by only a unit or a few units.
Moreover, the arrangement is such that nine groups and twelve
series are formed. The remarkable features of this classification
may thus be stated : Elements which are more or less closely allied
in their physical and chemical properties are made to stand together
in a group, as may be seen by pointing out a few of the more gen-
erally known instances as found in the groups I., II., and VII., the
first one containing the alkali metals, the second, the metals of the
alkaline earths, the last the halogens.

There is, moreover, to be noticed a periodic repetition in the prop-
erties of the elements arranged in the horizontal lines from left to
right. Leaving out groups 0 and VIII. for the present, we find
that the power of the elements to combine with oxygen atoms
increases regularly from the left to the right, while the power of the
elements to combine with hydrogen atoms increases from the right to
the left, as may be shown by the following instances :

I. II. III. IV. V. VI. VII.

N^O MgO A1203 SiO2 P2O5 SO3 ClaO7

Hydrogen compounds unknown SiH4 PHs SH2 C1H

The oxides on the left show strongly basic properties, as illustrated
by sodium oxide ; these basic properties become weaker in the second,
and still weaker in the third group ; the oxides of the fourth group
show either indifferent, or but slightly acid properties, which latter
increase gradually in the fifth, sixth, and seventh groups.

i The consideration of this law should be postponed until the student has become acquainted
with the larger number of important elements.

GENERAL REMARKS REGARDING ELEMENTS. 127

While some elements show an exception, it may be stated that
most of the elements of group I. are univalent, of II. bivalent, of
III. trivalent, of IV. quadrivalent, of V. quinquivalent, of VI.
sexivalent, and of VII. septivalent.

Properties other than those above mentioned might be enumerated
in order to show the regular gradation which exists between the
members of the various series, but what has been pointed out will
suffice to prove that there exists a regular gradation in. the properties
of the elements belonging to the same series, and that the same change
is repeated in the other series, or that the changes in the properties of
elements are periodic. It is for this reason that a series of elements
is called a period (in reality a small period, in order to distinguish it
from a large period, an explanation of which term will be given
directly).

The 12 series or periods given in the following table show another
highly characteristic feature, which consists in the iact that the corre-
sponding members of the even (2, 4, 6, etc.) periods and of the uneven
(3, 5, 7, etc.) periods resemble each other more closely than the mem-
bers of the even periods resemble those of the uneven periods. Thus
the metals calcium, strontium, and barium, of the even periods, 4, 6,
and 8, resemble each other more closely than they resemble the metals
magnesium, zinc, and cadmium, of the uneven periods, 3, 5, and 7, the
latter metals again resembling each other greatly in many respects.

It is for this reason that in the table the elements belonging to one
group are not placed exactly underneath each other, but are divided
into two lines containing the members of even and uneven periods
separately, whereby the elements resembling each other most are
made to stand together.

In arranging the elements by the method indicated, it was found
that the elements mentioned in group VIII. could not be placed in
any of the 12 small periods, but that they had to be kept separately
in a group by themselves, three of these metals always forming aL
intermediate series following the even periods 4, 6, and 10.

An uneven and even series, together with an intermediate series,
form a large period, the number of elements contained in a complete
large period being, therefore, 8 + 8 + 3 = 19.

An apparently objectionable feature is the incompleteness of the
table, many places being left blank ; but it is this very point which
renders the table so highly interesting and valuable.

Mendelejeff, in arranging his scheme, claimed that the places left
blank belonged to elements not yet discovered, and he predicted not
only the existence of these as yet missing elements, but also described

128

PRINCIPLES OF CHEMISTRY.

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GENERAL REMARKS REGARDING ELEMENTS. 129

their properties. Fortunately his predictions have, in several cases,
been verified, a number of the missing elements having since been
discovered. Among them may be mentioned scandium, gallium, and
ycntianium. These elements not only fitted in the previously blank
spaces by virtue of their atomic weights, but their general properties
also assigned to them the places which they now occupy.

When the table was first arranged it did not show group 0. The
elements forming this group have all been discovered since the year
1894, and their discovery necessitated the addition of an extra group.
In order to avoid renumbering the previously known groups the new
group was designated by zero.

Another graphic representation of the periodic law is obtained by
arranging the elements according to the increase in their atomic
weights on a spiral line, as shown on the diagram (Fig. 36).
From the centre of the spiral extend 20 radii, and in placing the
elements on the intersections of the spiral and a radius three im-
portant facts are noticed, viz. : 1. The distances of the elements
from the centre of the spiral are proportionate (or nearly so) to
their atomic weights. 2. From left to right the elements, arranged
on the diametric lines, follow one another according to the periodic
grouping. 3. The elements belonging to the even series of one of
the groups are on one radius, while the elements belonging to the
uneven series of the same group find their position on the radius
opposite. For example, calcium, strontium, and barium, of the
even series 4, 6, and 8 of group II., are on a radius opposite the
one on which we find magnesium, zinc, and cadmium, of the uneven
series 3, 5, and 7 of group II.

Physical properties of elements. Most elements are, at the
ordinary temperature, solid substances, two are liquids (bromine and
mercury), and of the more important elements five are gases (oxy-
gen, hydrogen, nitrogen, chlorine, and fluorine).

Most, if not all, of the solid elements may be obtained in the crys-
tallized state; a few are amorphous and crystallized, or polymorphous.
The physical properties of many elements in these different states
differ widely. For instance : Carbon is known crystallized as diamond
and graphite, or amorphous as charcoal. The property of elements to
assume such different conditions is called allotropy, and the different
forms of an element are termed allotropic modifications.

Some of the gaseous elements are also capable of existing in allo-
tropic modifications For instance: Oxygen is known as such and as
ozone, the latter differing from the common oxygen both in its physi-
cal and chemical properties. The explanation given for this surprising

130

PRINCIPLES OF CHEMISTRY.

fact, that one and the same element has different properties in certain
modifications, is, that either the molecules or the atoms within the
molecules are arranged differently. Ozone, for instance, has three
atoms of oxygen in the molecule, while the common oxygen molecule
contains but two atoms.

Most of the elements are tasteless and odorless ; a few, however,
have a distinct odor and taste, as, for instance, iodine and bromine.

FIG. 36.

fu~

Diagram of periodic system in spiral form.

Relationship between elements and the compounds formed
by their union. The properties of the compounds formed by the
combination of elements are so various that it is next to impossible
to give any general rule by which they may be indicated. It may

GENERAL REMARKS REGARDING ELEMENTS. 131

be said, however, that nearly all of the gaseous compounds contain
at least one gaseous element, and that solid elements, when combining
with each other, generally form solid substances, rarely liquids, and
never compounds showing the gaseous state at the ordinary tem-
perature.

Nomenclature. The chemical nomenclature of compound sub-
stances has undergone considerable changes within the last twenty-
five years. These changes were made in conformity with our present
views of the constitution of the compounds.

Whenever the syllable ide is used to replace the ending of a non-
metallic element it designates that this element has entered into com-
bination with another element or with a radical. Thus, we speak of
<>x/Vcs, sulphicfos, carbides, chlorides, etc., when referring to compounds
formed by the union of oxygen, sulphur, carbon, or chlorine with
another element or with a radical.

When two elements combine in one proportion only, little difficulty
is experienced in the formation of a name, as, for instance, in iodide
of potassium or potassium iodide, KI, chloride of sodium or sodium
chloride, NaCl.

When two elements combine in more than one proportion, the
syllables, mono, di, tri, tetra, and penta are frequently used to designate
the relative quantity of the elements. For instance : Carbon mon-
oxide, CO, carbon dioxide, CO2, phosphorus tfn'chloride, PC13, nitrogen
t< '//-oxide, N2O4, phosphorus £>entachloride, PC15.

In many cases the syllables ous and ie are used to distinguish the
proportions in which two elements combine ; the syllable ous being
used for the simpler or lower, the syllable ic for the more complex or
higher form of combination. For instance : Phosphorous chloride,
PC13, and phosphoric chloride, PC15; ferrous oxide, FeO, ferric
oxide, Fe2O3.

The syllable sesqui is used occasionally to indicate that a compound
contains one-half more of an element than another compound formed
from the same elements. Thus, ferric chloride, FeCl3, is sometimes
called sesgiiichloride of iron, as it contains one-half more of chlorine
than does ferrous chloride, FeCl2.

The syllables proto or sub and per have also been used as prefixes
to differentiate between compounds formed by the same elements.
For instance, mercurous chloride, HgCl, is called protochloMe or
sw6chloride, while mercuric chloride, HgCl2, is often designated as
jwchloride of mercury.

When two oxides of the same element ending in ous and ic form

132 PRINCIPLES OF CHEMISTRY,

acids (by entering in combination with water), the same syllables are
used to distinguish these acids. Phosphor<n*s oxide, P2O3, forms
phosphoroits acid ; phosphoric oxide, P2O5, forms phosphoric acid.

The salts formed by these acids are distinguished by using the syl-
lables lie and ate. Phosphite of sodium is derived from phosphorous
acid, phosphate of sodium from phosphoric acid. Sulphites and sul-
phates are derived from sulphurous and sulphuric acid, respectively.

When an element forms more than two acids the syllables hypo and
per are often used to designate the nature of these acids, as also that
of their respective salts. Hypo is prefixed to the compound contain-
ing less oxygen than the ous acid ; and per is prefixed to the com-
pound containing more oxygen than the ic acid. For instance, hypo-
chlorous acid, HC1O ; chlorous acid, HC1O2 ; chloric acid, HC1O< ;
perchloric acid, HC1O4. The salts formed from these acids are called
hypochlorites, chlorites, chlorates, and perchlorates.

According to the new nomenclature, the name of the metal precedes
that of the acid or acid radical in an acid. For instance, sodium
phosphite, instead of phosphite of sodium ; potassium sulphate, instead
of sulphate of potassium. The acids themselves are looked upon as
hydrogen salts, and are sometimes named accordingly : hydrogen
nitrate for nitric acid, hydrogen chloride for hydrochloric acid, etc.

When the number of elements and the number of atoms increase in
the molecule, the names become in most cases more complicated. The
rules applied to the formation of such complicated names will be
spoken of later.

How to study chemistry. In studying chemistry, the student
is advised to impress upon his memory five points regarding every
important element or compound. These points are :

1. Occurrence in nature. Whether in free or combined state;
whether in the air, water, or solid part of the earth.

2. Mode of preparation by artificial means.

3. Physical properties. State of aggregation and influence of heat
upon it ; color, odor, taste, solubility, etc.

4. Chemical properties. Atomic and molecular weight ; valence ;
amount of attraction toward other elements or compounds ; acid,
alkaline, or neutral reaction ; reactions by which it may be recog-
nized and distinguished from other substances.

5. Application and use made of it in e very-day life, in the arts,
manufactures, or medicine.

Of the most important elements and compounds, the history

GENERAL REMARKS REGARDING ELEMENTS. 133

their discovery, and, occasionally, some special points of interest,
should be noticed also.

" All students having the facility for working in a chemical labora-
tory are strongly advised to make all those experiments and reactions
which will be mentioned in connection with the different substances
to be considered in this book.

By adopting this mode of studying chemistry the student will soon
acquire a fair knowledge of chemical facts, yet he might know little
of the science of chemistry. In order to acquire this latter knowl-
edge he should study not only facts, but also the relationship existing
between them and between the laws governing the phenomena con-
nected with these facts. It is by this method only that the science
of chemistry can be successfully mastered.

QUESTIONS. — Why are not all the elements of equal importance? State the
physical and chemical properties of metals. How are metals distinguished
from non-metals ? What relation often exists between the atomic weights of
elements belonging to the same group? Explain the term allotropic modifica-
tion. Mention some elements capable of existing in allotropic modifications.
What relation exists between the properties of elements and the properties of
the compounds formed by their union ? In which cases are the syllables mono-,
di-, tri-, tetra-, and penta- used in chemical nomenclature? What use is made
of the syllables ous and ic, ite and ate, in distinguishing compounds from each
other? What are the principal features of the periodic law?

III.

NON-METALS AND THEIR COMBINATIONS.

THE total number of the non-metals is about eighteen ; some of
them, such as selenium, tellurium, argon, helium, and a few others,
are of so little importance that they will be but briefly considered
in this book.

Symbols, atomic weights, and derivation of names.

Boron, B = 10.9. From borax, the substance from which boron was first

obtained.

Bromine, Br = 79.36. From the Greek fip&jios (bromos), stench, in allusion to
the intolerable odor.

Carbon, C = 11.91. From the Latin carbo, coal, which is chiefly carbon.

Chlorine, Cl = 35.18. From the Greek ^Awpdf (chloros), green, in allusion to its
green color.

Fluorine, F = 18.9. From fluorspar, the mineral calcium fluoride, used as flux
(fluo, to flow.)

Hydrogen, H = 1. From the Greek v6up (hudor), water, and -yewdu (gennao),
to generate.

Iodine, I = 125.9. From the Greek lav (ion), violet, referring to the color of

its vapors.

Nitrogen, N = 13.93. From the Greek virpov (nitron), nitre, and -yewdo (gen-

nao), to generate.
Oxygen, O =; 15.88. From the Greek ofvf (oxus), acid, and yevvdu (gennao), .

to generate.
Phosphorus, P = 30.77. From the Greek 0«f (phos), light, and tfpetv (pherein), to

bear.
Silicon, Si = 28.2. From the Latin silex, flint, or silica, the oxide of silicon

Sulphur, S = 31.83. From sal, salt, and nvp (pur), fire, referring to the com-
bustible properties of sulphur.

135

136 NON-METALS AND THEIR COMBINATIONS.

State of aggregation.
Under ordinary conditions the non-metals show the following states:

Gases. Liquids. Solids.

B. P. B. P. F. P. B. P.

Hydrogen, —253° C. Bromine, 64° C. Phosphorus, 44° C. 280° 0.

Oxygen, —183 Iodine, 11 175

Nitrogen, —194 Sulphur, 114 400

Chlorine, - 33 Carbon, | Slightly volatile

Fluorine, — 190 Boron, > in electric

Silicon, ) furnace.

Occurrence in nature.

a. In a free or combined state.

Carbon in coal, organic matter, carbon dioxide, carbonates.
Nitrogen in air, ammonia, nitrates, organic matter.
Oxygen in air, water, organic matter, most minerals.
Sulphur chiefly as sulphates and sulphides.

b. In combination only.
Boron in boric acid and borax.

Bromine in salt wells and sea-water as magnesium bromide, etc.
Chlorine as sodium chloride in sea-water, etc.
Fluorine as calcium fluoride, fluorspar.
Hydrogen in water and organic matter.
Iodine as iodides in sea-water.

Phosphorus as phosphate of calcium, iron, etc., in bones and rocks.
Silicon as silicic acid or silica, and in silicates.

Time of discovery.

Sulphur, ) Long known in the elementary state ; recognized as elements in the

Carbon, / latter part of the eighteenth century.

Phosphorus, 1669, by Brandt, of Germany.

Chlorine, 1774, by Scheele, of Sweden.

Nitrogen, 1772, by Kutherford, of England.

Oxygen, 1773, by Scheele, of Sweden ; 1774, by Priestley, of England.

Hydrogen, 1766, by Cavendish, of England.

Boron, 1808, by Gay-Lussac, of France.

Fluorine, 1810, by Ampere, of France

Iodine, 1812, by Courtois, of France.

Silicon, 1823, by Berzelius, of Sweden.

Valence.1

Univalent. Bivalent. Trivalent or quinquivalent. Quadrivalent.

Hydrogen, Oxygen, Nitrogen, Carbon,

Chlorine, Sulphur. Boron, Silicon.

Bromine, Phosphorus.

Iodine,
Fluorine.

1 The valences here given are the ones generally exerted by the elements, but it will be
shown later that most of the elements may exhibit a valence differing from the ones here
mentioned.

OXYGEN. 137

10. OXYGEN.1

O" = 15.88.

History. Oxygen was discovered in the year 1773 by Scheele, in
Sweden, and one year later by Priestley, in England, independently
of each other ; its true nature was soon afterward recognized by La-
voisier, of France, who gave it the name oxygen, from the two Greek
words, oc^c (oxtis), acid, and ysvvda) (gennao), to produce or generate.
Oxygen means, consequently, generator of acids.

Occurrence in nature. There is no other element on our earth
present in so large a quantity as oxygen. It has been calculated that
not less than about one-third, possibly as much as 45 per cent., of the
total weight of our earth is made up of oxygen ; it is found in a free
or uncombined state in the atmosphere, of which it forms about one-
fifth of the weight. Water contains eight-ninths of its weight of
oxygen, and most of the rocks and different mineral constituents of
our earth contain oxygen in quantities varying from 30 to 50 per
cent. ; finally, it is found as one of the common constituents of most
animal and vegetable matters.

If the unknown interior of our earth should be similar in composition to the
solid crust of mineral constituents which have been analyzed, then the sub-
joined table will give approximately the proportions of those elements present
in the largest quantity.

Oxygen . . .45 parts. Calcium . . .4 parts.

Silicon . . . 28 " Magnesium . . 2 "

Aluminum . 8 " Sodium . . . 2 "

Iron . . . 6 " Potassium . . 2 "

Preparation. The oxides of the so-called noble metals (gold,
silver, mercury, platinum) are by heat easily decomposed into the
metal and oxygen :

HgO= Hg + O;
Ag,0=2Ag + O.

A more economical method of obtaining oxygen is the decomposi-
tion of potassium chlorate, KC1O3, into potassium chloride, KC1,
and oxygen by application of heat :

KC1O3 = KC1 + 3O.

While the above formula represents the final result of the decomposition, it
1 Many instructors prefer to postpone the discussion of the laws of combination, atomic
theory, symbols, and chemical equations until after a few elements and compounds have been
studied as an introduction and foundation. If such a procedure is followed by those who use
this book, the equations in the chapters that may be taken up before the theoretical matters
are presented which make the equations intelligible, should, of course, be omitted. They
are given in each chapter for the sake of completeness and reference.

138 NON-METALS AND THEIR COMBINATIONS.

takes place actually in two stages. At first potassium chlorate gives up but
one-fifth of its total oxygen, forming potassium chloride and perchlorate,
KC104, thus :

5KC1O3 = 3KC1O, + 2KC1 + 3O.

This part of the decomposition takes place at a comparatively low temper-
ature ; after it is complete, the temperature rises considerably and the decom-
position of the perchlorate begins :

KC1O4 = KC1 + 4O.

If the potassium chlorate be mixed with 30-50 per cent, of man-
ganese dioxide, and this mixture be heated, the liberation of oxygen
takes place with greater facility and at a lower temperature than by
heating potassium chlorate alone. Apparently, the manganese dioxide
takes no active part in the decomposition, as its total amount is found
in an unaltered condition after all potassium chlorate has been decom-
posed by heat. A satisfactory explanation regarding this action of
manganese dioxide is yet wanting.

A third method is to heat to redness, in an iron vessel, manganese
dioxide (MnO2), which suffers then a partial decomposition :
3MnO2 = MngO4 -f 2O.

In this case there is liberated but one-third of the total amount of
oxygen present, while two-thirds remain in combination with the
manganese.

Other methods of obtaining oxygen are : Decomposition of water by elec-
tricity, heating of dichromates, nitrates, barium dioxide, and other substances,
which evolve a portion of the oxygen contained in the molecules.

Heating a concentrated solution of bleaching powder with a small quantity
of a cobalt salt (cobaltous chloride) furnishes a liberal supply of oxygen, the
calcium hypochlorite of the bleaching powder being decomposed into calcium
chloride and oxygen :

Ca(ClO)2 = CaCl2 + 2O.

Oxygen may be obtained at the ordinary temperature by adding water to a
mixture of powdered potassium ferricyanide and barium dioxide, and also by
the decomposition of potassium permanganate and hydrogen dioxide in the
presence of dilute sulphuric acid.

A commercial method operated largely in England is Erin's process, which
consists in pumping purified air under pressure over barium oxide contained
in a tube and heated to about 700° C., whereby barium dioxide is formed. The
accumulated nitrogen of the air escapes by a valve from the end of the tube.
When formation of barium dioxide is complete, the air-supply is cut off and
the pump is reversed, thus producing a partial vacuum in the tube. Under
this condition, although the same temperature is maintained as before, the

OXYGEN. 139

barium dioxide decomposes into barium oxide and oxygen, which latter is
pumped away and stored in tanks. Oxygen of about 96 per cent, is obtained.
The changes taking place in the two stages are represented thus :

BaO + O = BaO2;

This process is a good example of the kind of change known as Reversible
Action (see page 114). When the dioxide is exhausted, the process is re-
peated. One kilogram of barium oxide yields about ten liters of oxygen at a
single operation.

The quantity of oxygen liberated from a given quantity of a substance may
be easily calculated from the atomic and molecular weights of the substance
or substances suffering decomposition. For instance : 100 pounds of oxygen
may be obtained from how many pounds of potassium chlorate, or from how
many pounds of manganese dioxide? (See page 100.)

The molecular weight of potassium chlorate is found by adding together
the weights of 1 atom of potassium = 38.86 + 1 atom of chlorine — 35.18 + 3
atoms of oxygen = 47.64; total = 121.68. Every 121.68 parts by weight of
potassium chlorate liberate the weight of 3 atoms, or 47.64 parts by weight, of
oxygen. If 47.64 are obtained from 121.68, 100 are obtained from 255.4.

47.64 : 121.68 : : 100 : x

x = 255.4.

In a similar manner, it will be found that 815.7 pounds of manganese dioxide
are necessary to produce 100 pounds of oxygen. Mn02 = 54.6 -4- 31.76 = 86.36.
3Mn02 = 3 X 86.36 = 259.08. Every 259.08 parts furnish 2 x 15.88 = 31.76
parts of oxygen.

31.76 : 259.08 : : 100 : x

* = 815.7,

The density of a gas is the weight of 1 liter. To find what volume corre-
sponds to a given weight of a gas, divide the weight by the density. The den-
sity of oxygen is 1.429 grammes in 1 liter at 0° C. and 760 mm. pressure.
Hence, under these conditions, 100 grammes of oxygen would measure 100 -*-
1.429 = 69.979 liters. (For method of calculating gas volumes under other than
standard conditions of temperature and pressure, see article on Gas Analysis.)

The densities of gases are generally given in books, but they can be calcu-
lated, if the molecular weights of the gases are known. The relation between
densities and molecular weights of gases is discussed on page 108. The density
of any gas is equal to the density of hydrogen multiplied by one-half the
molecular weight of the gas ; 1 liter of hydrogen at 0° C. and 760 mm. pressure
weighs 0.08987 gramme, the molecular weight of oxygen is 31.76; hence 1 liter
of oxygen weighs 0.08987 X 15.88 = 1.427 grammes.

Experiment 1. Generate oxygen by heating a small quantity (about £
grammes) of potassium chlorate in a dry flask of about 100 c.c. capacity, to
which, by means of a perforated cork, a bent glass tube has been attached,
which leads under the surface of water contained in a dish (Fig. 37). Collect
the gas by placing over the delivery-tube large test-tubes (or other suitable ves-

140

NON-METALS AND THEIR COMBINATIONS.

sels) filled with water. Notice that a strip of wood, a wax candle, or any other
substance which burns in air. burns with greater energy in oxygen, and that
an extinguished taper, on which a spark yet remains, is rekindled when placed
in oxygen gas. Notice, also, the physical properties of the gas. If the decompo-
sition has been too rapid by using too large a flame, the gas will appear cloudy,
due to the dragging over of some of the contents of the flask by it. The cloud
will disappear upon standing.

CAUTION. In all experiments of this kind, where a vessel is filled wiih a hot gas,
the exit tube should be removed from water before removing the flame, to prevent water
from being drawn back into the vessel as the gas cools and contracts.

Experiment 2. In a porcelain crucible held in a pipe-stem triangle, place a
layer of potassium chlorate about J inch deep. Heat moderately at first until

Apparatus for generating oxygen.

frothing ceases, and then gradually to low red heat. Cool and dissolve the
residue in a little water in the crucible, warming to hasten solution. Taste the
solution. Does it taste like common salt (sodium chloride)? Compare with
the taste of potassium chlorate. Pour some of the solution into a test-tube and
add a few drops of a solution of silver nitrate. Do the same with a solution of
common salt. The white clotted substance, known as a precipitate, is silver
chloride, and is given by all soluble chlorides. Also add some silver nitrate
solution to a solution of a little potassium chlorate. Is any precipitate formed?
All chlorates are soluble.

Physical properties. Oxygen is a colorless, inodorous, tasteless
gas, slightly heavier than air. Under a pressure of 50 atmospheres,
and at a temperature of -118° C. (-180.4° F.) it condenses to a
transparent, pale-bluish liquid, which under ordinary atmospheric
pressure boils at -183° C. (-297.4° F.). Its absolute boiling-point,
above which it cannot be condensed to a liquid by any pressure, no
matter how high, is -118° C. (-180.4° F.).

OXYGEN. 141

For practical, including medical, purposes oxygen is sold stored in
strong steel cylinders, the gas being condensed by a pressure, gen-
erally, of 225 pounds to about -fa of its volume.

The temperature above which a gas cannot be liquified by pressure is
known as its critical temperature. The failure of former attempts to liquefy
oxygen and a few other gases was due to the fact that, though an enormous
pressure was used, the gas was not brought to the critical temperature.

Oxygen is but sparingly soluble in water (about 3 volumes in 100
at common temperature). A liter of oxygen under 760 mm. pressure,
and at the temperature of 0° C. (32° F.), weighs 1.429 grammes.

Chemical properties. The principal feature of oxygen is its great
affinity for almost all other elements, both metals and non-metals;
with nearly all of which it combines in a direct manner. The more
important elements with which oxygen does not combine directly are :
Cl, Br, I, F, Au, Ag, and Pt; but even with these it combines in-
directly, excepting F.

The act of combination between other substances and oxygen is
called oxidation, and the products formed, oxides. The large number
of oxides are divided usually into three groups, and distinguished as
basic oxides (sodium oxide, Na2O, calcium oxide, CaO), neutral oxides
(water, H2O, manganese dioxide, MnO2, lead dioxide, PbO2), and
acid-forming or acidic oxides, also called anhydrides (carbon dioxide,
CO2, sulphur trioxide, SO3). Whenever the heat generated by oxida-
tion (or by any other chemical action) is sufficient to cause the emis-
sion of light, the process is called combustion. Oxygen is the chief
supporter of all the ordinary phenomena of combustion. Substances
which burn in atmospheric air burn with greater facility in pure
oxygen. This property is taken advantage of to recognize and dis-
tinguish oxygen from most other gases. Processes of oxidation evolv-
ing no light are called slow combustion. An instance of slow combus-
tion is the combustion of the different organic substances in the living
animal, the oxygen being supplied by respiration.

In some cases the heat generated by the slow combustion of a sub-
stance may raise its temperature sufficiently high to cause ignition,
which is then called spontaneous combustion. Thus, greasy rags or wet
hay, when piled in heaps, may ignite spontaneously, because some oils
and damp hay undergo slow oxidation, which raises the temperature.

For a process of oxidation it is not absolutely necessary that free
oxygen be present. Many substances contain oxygen in such a form
of combination that they part with it easily when brought in contact
with substances having a greater affinity for it. Such substances are

142 NON-METALS AND THEIR COMBINATIONS.

called oxidizing agents, as, for instance, nitric acid, potassium chlorate,
potassium permanganate, etc.

In all combustions we have at least two substances acting chemically upon
one another, which substances are generally spoken of as combustible bodies
and supporters of combustion. Illuminating gas is a combustible substance,
and oxygen a supporter of combustion ; but these terms are only relatively
correct, since oxygen may be caused to burn in illuminating gas, whereby it is
made to assume the position of a combustible substance, while illuminating gas
is the supporter of combustion.

While some substances, such as iron and phosphorus, undergo slow combus-
tion at the ordinary temperature, there is a certain degree of temperature,
characteristic of each substance, at which it inflames. This point is known as
kindling temperature, and varies widely in different substances. Zinc ethyl
ignites at the ordinary temperature, phosphorus at 50° C. (122° F.), sulphur at
about 450° C. (842° F.}, carbon at a red heat, and iron at a white heat. The
heat produced by the combustion is generally higher than the kindling tem-
perature, and it is for this reason that a substance continues to burn until it is
consumed, provided the supply of oxygen be not cut off, and the temperature
be not through some cause lowered below the kindling temperature.

The total amount of heat evolved during the combustion of a substance is
the same as that generated by the same substance when undergoing slow com-
bustion, but the intensity depends upon the time required for the oxidation.
A piece of iron may require years to combine with oxygen, and it may be
burned up in a few minutes ; yet the total heat generated in both cases is the
same, though we can notice and measure it in the first instance by most deli-
cate instruments only, while in the second it is very intense.

While heat is evolved when two or more elements combine chemically, heat
is absorbed when decomposition takes place. In fact, the quantities of heat
evolved and absorbed by combining and decomposing identical quantities of
matter are absolutely alike. Thus, heat is evolved when mercury and oxygen
combine, but the same quantity of heat .is absorbed when the mercuric oxide
thus formed is decomposed into its elements by the action of heat.

Whenever a substance has the power to unite with others, it can do chemical
work ; it possesses chemical energy. Consequently, all combustible substances
can do work ; i. e., by combining with oxygen they evolve heat, which in turn
may be transformed into motion or into some other form of energy.

The chief supply of chemical energy at our disposal is derived from plant-
life. All kinds of wood, and its decomposition-product, coal, possess chemical
energy. This energy is stored up in vegetable matter, because the sun's heat
caused a decomposition of water and carbon dioxide, which substances are the
two chief compounds used in the construction of plant tissue. In burning
vegetable matter the oxygen removed from the water and carbon dioxide by
the action of the sun's rays is taken up again, and heat is evolved.

Ozone is an allotropic modification of oxygen, which is formed
when non-luminous electric discharges pass through atmospheric air
or through oxygen ; when phosphorus, partially covered with water,

OXYGEN. 143

is exposed to air, and also during a number of chemical decomposi-
tions. Ozone differs from ordinary oxygen by possessing a peculiar
odor, by being an even stronger oxidizing agent than common oxygen,
by liberating iodine from potassium iodide, etc. This latter action
may be used for demonstrating the presence of ozone by suspending
in the gas a paper moistened with a solution of potassium iodide and
starch. The iodine, liberated by the ozone, forms with starch a dark-
blue compound. Theoretically, we assume that ozone contains three,
common oxygen but two, atoms in the molecule, which is substan-
tiated by the fact that three volumes suffer a condensation to two
volumes when converted into ozone, which would indicate that three
molecules of oxygen furnish two molecules of ozone, thus :

302 = 203; or 3 [O = O] =2

[A]

Ozone is obtained in a pure condition by passing the impure gas through a
tube cooled by liquid oxygen. It is then a blue liquid which boils at — 110° C.
( — 166° F.), forming a blue gas. Atmospheric air, in which part of the oxygen
has been converted into ozone by the electrical method, is used for bleaching
purposes, purification of starch, resinifying oils, purifying water of germs and
organic matter, etc.

Ozone occurs in small quantities in country air, but is rarely noticed in
cities, where it is decomposed too quickly by the impurities of the atmospheric
air. It has been assumed that ozone acts advantageously, as it has a tendency
to destroy matters which are unwholesome. Too little, however, is known of
the subject to justify a positive opinion in regard to it.

Thermo-chemistry. It is stated in Chapter 5 that the free or available
chemical energy in a chemical change usually appears as heat. This heat can
be measured in calories in an apparatus called a calorimeter (see page 48).
The equations ordinarily used to represent chemical changes do not express
energy changes, but simply what kinds of substances are concerned in the
change, and what new substances are formed. For example, the expression,
2H -}- O = H2O, when translated means that when hydrogen and oxygen unite
water is formed, but it says nothing about the fact that a great amount of chem-
ical energy is liberated as heat. Likewise the expression, HgO = Hg + O,
which means that when mercuric oxide undergoes decomposition (by heat)
mercury and oxygen are formed, says nothing about the fact that during the
change, heat energy is "absorbed and transformed into chemical energy. For
the purpose of showing the energy change involved, use is made of thermal
equations. The amount of heat energy in calories represented in thermal equa-
tions as liberated or absorbed refers to certain weights of the substances in-
volved in the chemical change. These weights are the number of grammes cor-
responding to the chemical symbols of the substances. For instance, the thermal
equation for the formation of water is written, 2H + O = H2O + 67,883 cal.,
which means that when 2 grammes of hydrogen unite with 15.88 grammes of
oxygen to form 17.88 grammes of water (corresponding to the symbol H2O),

144 NON-METALS AND THEIR COMBINATIONS.

67,883 calories of heat are liberated, or enough to raise nearly 68 kilogrammes
of water one degree in temperature. The thermal equation,

HgO = Hg -t O — 30,370.5 cal.,

means that when 214.38 grammes of oxide of mercury (corresponding to HgO)
are decomposed by heat into mercury and oxygen, 30,370.5 calories of heat
are absorbed and converted into chemical energy which is associated with the
elements mercury and oxygen. • The plus sign is used when heat is liberated in
the formation of a compound, and the latter is termed exothermic; while the
minus sign indicates absorption of heat, and the compound is termed endother-
mic. Exothermic compounds are relatively stable, while endothermic ones are
unstable and often explosive. They decompose easily with liberation of heat.

Ozone is endothermic, as heat is absorbed during its formation from oxygen.
When it decomposes heat is liberated. The thermal equation, 2O3 — 3O2 +
64,314 cal., states that when 95.28 grammes of ozone (corresponding to 2O3)
decomposes into ordinary oxygen, 64,314 calories of heat are liberated. The
greater chemical energy of ozone over that of oxygen accounts for its greater
chemical activity as compared with oxygen.

Thermo-chemical measurements are of great importance in several practical
directions; for example, for determining the fuel values of samples of coal,
coke, wood, fuel values of articles of food in the field of physiology, etc.

11. HYDROGEN. WATER. HYDROGEN DIOXIDE.
H = 1. H2O = 17.88. H2O2 = 33.76.

History. Hydrogen was obtained by Paracelsus in the 16th cen-
tury ; its elementary nature was recognized by Cavendish, in 1766.
The name is derived from Mvp (hudor), water, and yewfo (gennao), to
generate, in allusion to the formation of water by the combustion of
hydrogen.

Occurrence in nature. Hydrogen is found chiefly as a component
element of water ; it enters into the composition of most animal and
vegetable substances, and is a constituent of all acids. Small quanti-
ties of free hydrogen are found in the gases produced by the decom-
position of organic matters (as, for instance, in the intestinal gases),
and also in the natural gas escaping from the interior of the earth.

QUESTIONS. — By whom and at what time was oxyge'n discovered? How is
oxygen found in nature? Mention three processes by which oxygen may be
obtained. How much oxygen may be obtained from 490 grammes of potas-
sium chlorate? State the physical and chemical properties of oxygen. Ex-
plain the terms combustion, slow combustion, combustible substance, and sup-
porter of combustion. Mention some oxidizing agents. What is ozone, and
how does it differ from common oxygen? Under what circumstances is ozone
formed? What is thermo-chemistry ? What is a thermal reaction?

HYDROGEN. 145

Preparation. Hydrogen may be obtained by passing an electric
current through water previously acidified with sulphuric acid, by
which it is decomposed into its elements :

H2O = 2H + O.

A second process is the decomposition of water by metals. Some
metals, such as potassium and sodium, decompose water at the ordi-
nary temperature ; while others, iron, for instance, decompose it at a

red heat :

K + H,0 == KOH + H ;
3Fe + 4H20 = FesO4 + 8H.

A very convenient way of liberating hydrogen is the decomposition
of dilute hydrochloric or sulphuric acid by zinc or iron :

Zn + 2HC1 = ZnCl2 + 2H;

Zinc
chloride.

Fe + H2S04 = FeSO, + 2H.
Ferrous
sulphate.

Hydrogen may also be obtained by heating granulated zinc or
aluminum with strong solutions of potassium or sodium hydroxide,
in which case the decomposition is explained thus :

Zn -f 2KOH == K2ZnO2 -f 2H;

Potassium
zincate.

Al + 3NaOH = Na3AlO3 + 3H.

Sodium
aluminate.

Whenever hydrogen is generated, care should be taken to expel all
atmospheric air from the vessel in which the generation takes place,
before the hydrogen is ignited, as otherwise an explosion may result.

Experiment 3. Place a few pieces of granulated zinc (about 10 grammes) in
a flask of about 200 c.c. capacity, which is arranged as shown in Fig. 38. Cover
the zinc with water, and pour upon it through the funnel tube a little sulphuric
acid, adding more when gas ceases to be evolved. Notice the effervescence
around the zinc. Collect the gas in test-tubes over water and ignite it by taking
the test-tube (with mouth downward) to a flame near by. Notice that the first
portions of gas collected, which are a mixture of hydrogen and atmospheric
air, explode when ignited in the test-tube, while the subsequent portions burn
quietly. Pour the contents of one test-tube into another one by allowing the
light hydrogen gas to rise into and replace the air in a test-tube held over the
one filled with hydrogen. Take two test-tubes completely filled with the gas;
hold one mouth upward, the other one mouth downward : notice that from the
first one the gas escapes after a few seconds, while it remains in the second
tube a few minutes, as may be shown by holding the tubes near a flame to
cause ignition.
10

146

NON-METALS AND THEIR COMBINATIONS.

After having ascertained that all atmospheric air has been expelled from the
flask, the gas may be ignited directly at the mouth of the delivery tube, after
moving it out of the water.

Continue to add acid until the zinc is nearly all dissolved, remembering that
the action is not instantaneous and some time should be allowed before the
next addition of acid. Warming the flask will hasten the action, and as long
as small gas-bubbles arise from the zinc, action is not over. Avoid adding too
much acid, but if there is an excess, it may be removed by adding more zinc.
Note the dark particles floating in the liquid and the bad odor of the hydrogen,
which are due to the impurities in the zinc. Finally, filter the solution (by
folding a circle of filter-paper twice at right angles through the center, open-
ing it into a cone, placing in a funnel, wetting with water, and pouring the
solution into it), and evaporate it to about one-third its volume at a tempera-
ture a little below boiling. Set aside a day to cool and crystallize. If no
crystals appear, evaporate further, The crystals are zinc sulphate, the same

FIG. 38.

Apparatus for generating hydrogen.

as is used in medicine. They are an illustration of the formation of a salt by
the action of an add on a metal. Filter the crystals and examine them care-
fully. Expose some to the air for several days. Does any change take place ?
Save the crystals for Experiment 37.

Experiment 4. Pour into a test-tube of not less than 50 c.c. capacity, 5 c.c. of
hydrochloric acid, fill up with water, close the tube with the thumb and set it
inverted into a porcelain dish partly filled with water. Weigh of metallic
zinc 0.04 gramme, and bring it quickly under the mouth of the test-tube, so
that the generated hydrogen rises in the tube. Prepare a second tube in the
same manner, and introduce 0.04 gramme of metallic magnesium. In case the
decomposition of the acids by the metals should proceed too slowly, a little
more acid may be poured into the dishes.

When the metals are completely dissolved it will be seen that the volumes
of hydrogen in the two tubes bear a relation to each other of about 10 to 27.

In order to measure the gas volumes as correctly as the simple apparatus
permits, the tubes should be transferred to a large beaker filled with cold water,

HYDROGEN. 147

bringing the surfaces of the liquids in the test-tube and beaker on a level, and
marking on the outside of the test-tubes (with a file or paper strip) the exact
height of the gas.

After having emptied the test-tubes, they may be filled with water from a
pipette or from a burette to the point which has been marked, and thus the
exact volume of gas generated is ascertained.

Kepeat the operation, using 0.065 gramme of zinc and 0.024 gramme of mag-
nesium. Notice that in this case equal volumes of hydrogen are obtained.
Calculate the weight of hydrogen from the cubic centimetres liberated, and
compare this weight with the weights of zinc and magnesium used. What
relation is there between the weights of the liberated hydrogen and the metala
used, and the atomic weights of these three elements ?

Properties. Hydrogen is a colorless, inodorous, tasteless gas ; it
is the lightest of all known substances, having a specific gravity of
0.0695 as compared with atmospheric air ( = 1). One liter of hydro-
gen at 0° C. (32° F.), and a barometric pressure of 760 mm., weighs
0.08987 gramme, or one gramme occupies a space of 11.127 liters;
100 cubic inches weigh about 2.265 grains.

Hydrogen and helium resist liquefaction more than other gases. Hydro-
gen has been liquefied by causing the gas, cooled to a temperature of
— 205° C. ( — 337° F.), to escape under certain conditions from a vessel in
which it was stored at a pressure of 180 atmospheres. Liquid hydrogen is
clear and colorless ; it has a sp. gr. of 0.07, and boils at — 253° C. (- 423° F.),
under normal atmospheric pressure ; it also has been solidified lately, and the
temperature reached is thought to be about — 256° C. (—428° F.).

In its chemical properties, hydrogen resembles the metals more than
the non-metals ; it burns easily in atmospheric air, or in pure oxygen,
with a non-luminous, colorless, or slightly bluish flame producing
during this process of combustion a higher temperature than can be
obtained by the combustion of an equal weight of any other substance.

Two volumes of hydrogen combine with one volume of oxygen,
forming two volumes of gaseous water, and the formation of water
by the combustion of hydrogen distinguishes it from other gases.

The chemical affinity which hydrogen possesses for oxygen is so
great that it abstracts the oxygen from many oxides. Thus, if
hydrogen at a red heat be passed over the oxides of copper or iron
the metals are set free, while water is formed :
CuO + 2H = H20 + Cu.

This process of abstracting oxygen from an oxide is called reduc-
tion or deoxidation, and substances having the power of accomplish-
ing this result are called reducing or deoxidizing agents. Hydrogen,
consequently, is a reducing agent. .

148 NON-METALS AND THEIR COMBINATIONS.

We thus see that, while in physical properties O and H resemble
one another closely, their chemical properties are practically the re-
verse of each other. Elements which, like the metals, combine readily
with oxygen, do not combine with hydrogen ; and, vice versa, ele-
ments which, like chlorine, combine most readily with hydrogen, will
scarcely combine with oxygen. It will be shown later that, as a
general rule, elements which resemble one another in chemical prop-
erties are not apt to combine with one another, while those differing
widely have great affinity for one another.

Nascent hydrogen. It was stated above that hydrogen is a good reduc-
ing agent, but as far as hydrogen in the free state is concerned reduction takes
place, as a rule, only when heat is employed. There is a condition of hydrogen,
however, in which it is able to reduce many compounds at ordinary tempera-
ture, while free hydrogen has no measurable action on the same. For exam-
ple, the hydrogen liberated during electrolysis of a dilute acid is able to reduce
many compounds present in solution immediately around the pole (cathode) at
which the hydrogen is produced. It also shows different degrees of activity
according to the material of which the pole is made. Similarly, hydrogen
generated by the action of dilute acids on metals has reducing power on sub-
stances immediately surrounding the metals during action, whereas free
hydrogen gas passed through a solution of the same substances or in contact
with them in the dry state has no action. To illustrate : hydrogen gas passed
through a solution of arsenous oxide, As203, has no effect, but if the oxide is
present in a mixture of dilute hydrochloric acid and zinc the hydrogen formed
quickly reduces it to arsine gas, AsH3. This is one of the most delicate tests
for arsenic. The more active condition of hydrogen at the time of its libera-
tion is spoken of as the nascent state. It seems that this increased activity of
hydrogen in contact with the substances that liberate it is an example of con-
tact or catalytic action (see page 154). Good support to this view is the fact
that the efficiency of the nascent hydrogen varies according to the nature of
the material in association with which the hydrogen is produced.

Water, H2O = 17.88. Hydrogen monoxide. Water exists on
our globe in the three states of aggregation. Air at all temperatures
contains water in the gaseous form. Liquid water occurs plentifully
in the oceans, rivers, etc., and also in plants and animals. Seven-
tenths of the human body is water; potatoes contain of it 75 per
cent, and watermelons as much as 94 per cent. Solid water exists
not only as ice and snow, but it also enters into the composition of
many rocks, and is a constituent of many crystals containing water
of crystallization.

Absolutely pure water is not found in nature. The purest natural
water is rain-water collected after the air has been purified from
dust, etc., by previous rain. Comparatively pure water may be

WATER. 149

obtained by melting ice, since, when water containing impurities is
frozen partially, these are mostly left in the uncongeaieu water.

The waters of springs, wells, rivers, etc., differ widely from each
other ; they all contain more or less of substances dissolved by the
water in its course through the atmosphere or through the soil and
rocks. The constituents thus absorbed by the water are either solids
or gases.

Solids generally found in natural waters are common salt (sodium
chloride), gypsum (calcium sulphate), and carbonate of lime (calcium
carbonate) ; frequently found are chlorides and sulphates of potassium
and magnesium, traces of silica and salts of iron. Gases absorbed
by water are constituents of the atmospheric air, chiefly oxygen,
nitrogen, and carbon dioxide. One hundred volumes of water con-
tain about two volumes of nitrogen, one volume of oxygen, and one
volume of carbon dioxide.

Water is said to be hard when it contains so much of salts of cal-
cium and magnesium that the formation of lather by soap is delayed
because these salts form insoluble compounds with the soap. Water
containing but little of inorganic matter is said to be soft.

When the hardness is caused by metallic sulphates or chlorides the
water is called permanently hard, while it is termed temporarily hard
when the metals are present as carbonates, dissolved by carbonic acid.
On boiling such water carbon dioxide escapes, the carbonates of the
metals are precipitated, and the water is rendered soft.

Mineral waters are spring waters containing one or more sub-
stances in such quantities that they impart to the water a peculiar
taste and generally a decided medicinal action. According to the
predominating constituents we distinguish bitter waters, containing
larger quantities of magnesium salts ; iron or chalybeate waters,
containing carbonate or sulphate of iron ; sulphur or hepatic waters,
containing hydrogen sulphide ; effervescent waters, strongly charged
with carbonic acid ; cathartic waters, generally containing sodium or
magnesium sulphate, etc.

Drinking-water. A good drinking-water should be free from
color, odor, and taste ; it should neither be an absolutely pure water,
nor a water containing too much of foreign matter. Water containing
from 2 to 4 parts of total inorganic solids (chiefly carbonate of lime
and common salt) in 10,000 parts of water and about 1 volume of
carbon dioxide in 100 volumes of water, may be said to be a good

150 NON-METALS AND THEIR COMBINATIONS.

drinking-water. There are, however, good drinking-waters which
contain more of total solids than the amount mentioned above.

Most objectionable in drinking-water are organic substances, espe-
cially when derived from animal matter, and more especially when
in a state of decomposition, because such decomposing organic matter
is frequently accompanied by living organisms (germs) which may
cause disease. Boiling of water destroys these germs, and by subse-
quent filtering of the boiled water through sand, charcoal, spongy
iron, etc., an otherwise unwholesome water may be rendered fit for
drinking.

In nature water is rendered free from organic impurities by the
oxidizing power of atmospheric oxygen, which is taken up by the
water and is readily transferred upon organic matter present.

It should be remembered that no filter can remain efficient for any length
of time, as the impurities of the water are retained by the materials used as a
filter, and this may become, therefore, a source of pollution instead of a puri-
fier. By heating to a low red heat the materials used for filtering, these are
cleaned and may be used again. The methods applied to the analysis of
drinking-water will be mentioned later. (See Index.)

Distilled water, Aqua destillata. The process for obtaining
pure water is distillation in a suitable apparatus. From 1000 parts
of water used for distillation, the first 100 parts distilled over should
not be used, as they contain the gaseous constituents. The solids
contained in the water are left in the undistilled portion, which should
not be less than 100 parts.

Composition of water. Until the discovery of oxygen, water
was thought to be a simple substance. In 1781 Cavendish, of Eng-
land, discovered the qualitative composition of water when he
obtained it by causing hydrogen and oxygen to unite. Water was
thus produced synthetically.

The proportion of hydrogen and oxygen in water has been determined
accurately by weighing the oxygen and the water formed by union with hydro-
gen, also by weighing both constituents and the water after union. The results
of the most accurate experiments showed that water contains 11.185 per cent.
of hydrogen and 88.815 per cent, of oxygen, or 2 parts by weight of hydrogen
to 15.88 parts, by weight, of oxygen. It has been ascertained that the mole-
cule of water is made up of two atoms of hydrogen and one atom of oxygen,
H2O. Hence, it follows that the atomic weight of oxygen is 15.88. By vol-
ume, hydrogen and oxygen unite in the proportion of 2 : 1 to form water.

WATER. 151

Analysis and synthesis. These terms refer to two methods of
research in chemistry, accomplished by two kinds of reaction, ana-
lytical and synthetical.

Analysis is that mode of research by which compound substances
are broken up into their elements or into simpler forms of combina-
tion, and analytical reactions are all chemical processes by which the
nature of an element, or of a group of elements, may be recognized.

Synthesis is that method of research by which bodies are made to
unite to produce substances more complex.

Analytical and synthetical methods, or reactions, frequently blend
into one another. This means : A reaction made with the intention
of recognizing a substance, may at the same time produce some com-
pound of interest from a synthetical point of view.

Properties of water. Water is an inodorous, tasteless, and, in
small quantities, colorless liquid. Thick layers of water show a blue
color. On cooling, water contracts until it reaches the temperature
of 4° C. (39.2° F.), at which point it has its greatest density. If
cooled below this temperature it expands and the specific gravity of
ice is somewhat less than that of water. Water is perfectly neutral,
yet it has a tendency to combine with both acid and basic substances.
These compounds are usually called hydroxides (formerly hydrates),
such as NaOH, Ca(OH)2, etc. These compounds are often formed by
direct union of an oxide with water, thus :

CaO + H20 = Ca(OH)2.
SO3 + H2O = SO2(OH)2.

Water is the most common solvent, both in nature and in artificial
processes. As a general rule, solids are dissolved more quickly and
in larger quantities by hot water than by cold, but to this there are
many exceptions. For instance : Common salt is nearly as soluble
in cold as in hot water ; sodium sulphate is most soluble in water of
33° C. (91° F.), and some calcium salts are less soluble in hot than
in cold water.

The term solution is applied to any clear and homogeneous liquid
obtained by causing the transformation of matter from a solid or
gaseous state to the liquid state by means of a liquid called a solvent
or menstruum ; solutions may also be obtained from two liquids, as
when we dissolve oil in ether. A solution is said to be saturated when
the solvent will not take up any more of the substance being dissolved.

Two kinds of solutions are distinguished — viz., simple solutions and complex
or chemical solutions. In the former we have a mere physical change, the mole-

152 , NON-METALS AND THEIR COMBINATIONS.

cules of the dissolved body being present with all their characteristic proper-
ties, and on evaporation the dissolved solid will be re-obtained unchanged.
Instances of this kind are solutions of sugar or table salt and water. (The
breaking down of molecules into ions during simple solution will be considered
later.)

In chemical solutions there takes place a rearrangement of the atoms within
the molecules, both of the solvent and of the substance dissolved. Moreover,
on evaporation of the solution a substance is obtained entirely different from
the one which has been dissolved. Instances of this kind are the dissolving of
sodium in water, when sodium hydroxide is formed ; or the dissolving of zinc
in sulphuric acid, when zinc sulphate is formed. The term emulsion is used
to designate a more or less homogeneous liquid rendered opaque or rnilky by
the suspension in it of finely divided particles of fat, oil, or resin. The milk
of mammalia and the milk-like juice of certain plants are instances of true
emulsions.

Many salts combine with water in crystallizing ; crystallized sodium
sulphate, for instance, contains more than half its weight of water.
This water is called ivater of crystallization, and is expelled generally
at a temperature of 100° C. (212°F.). Some crystallized substances
lose water of crystallization when exposed to the air ; this property is
known as efflorescence. Crystals of sodium carbonate, ferrous sulphate,
etc., effloresce, as is shown by the formation of powder upon the crys-
talline surface. Substances are said to be anhydrous when they are
destitute of water, for instance, when crystals have lost their water
of crystallization or when ether or alcohol have been freed from dis-
solved water. The term anhydride is sometimes used for oxyacids
which have been deprived of all water, so that they are no longer
acids, but oxides. Thus, by removing water from sulphuric acid,
H2SO4, there is left sulphur trioxide, or sulphuric acid anhydride,
SO3. The term deliquescence is applied to the power of certain solid
substances to absorb moisture from the air, thereby becoming damp
or even liquid, as, for instance, potassium hydroxide, calcium chloride,
etc. Such substances are spoken of also as being hygroscopic, and
are used for drying gases.

The term effervescence refers to the escape of a gas from water or
from any other liquid in which the gas was held under pressure or in
which it may be generated ; as, for instance, when an acid is added
to a carbonate, whereupon carbon dioxide escapes with energetic
bubbling.

The explanation of effervescence and deliquescence is found in a well-known
principle of physics. It is well known that liquids will evaporate in a closed
space until the pressure of the vapor is equal to the vapor tension of the liquid,

HYDROGEN DIOXIDE. 153

when equilibrium is established and evaporation of the liquid apparently
ceases. This means that vapor particles fly back into the liquid at the same
rate that liquid particles leave the surface of the liquid to become vapor. If
the vapor pressure in any way becomes greater than the vapor tension of the
liquid, some vapor will be condensed to liquid. On the other hand, if the
vapor pressure is constantly lower than the vapor tension of the liquid, evapo-
ration will go on until no more liquid is left. One way of accomplishing this
is by free exposure of liquids to the atmosphere. Of course the amount of the
vapor pressure varies with the temperature. Now it is found that substances
containing water of crystallization have a vapor tension just as water has.
For example, when a crystal of sodium sulphate (Na2SO4.10H20) is allowed
to rise to the top of a barometer tube at 9° C., it exerts a vapor tension of 5.5
mm. — that is, the pressure of the water vapor given off by the crystal is enough
to depress the mercury column 5.5 mm. Those substances crystallizing with
water which at ordinary temperature exert a vapor tension greater than the
pressure of the water vapor in the atmosphere, are efflorescent and must be
kept in closed containers, just as water must be to prevent loss of water.
When the vapor tension of the substances is about the same or less than the
atmospheric vapor pressure, the substances are stable and need not be carefully
bottled, except to keep them clean. The average pressure of the water vapor
in the atmosphere at 9° C. is about 5 mm. At this temperature crystals of
sodium sulphate have a vapor tension of 5.5 mm. and are efflorescent, while
those of copper sulphate have a vapor tension of 2 mm. and are stable in the
air.

Deliquescent substances are always very soluble in water. A layer of
moisture condenses on these just as it does on all bodies exposed to the atmo-
sphere. In the case of extremely soluble substances, the condensed moisture
forms a thin layer of very concentrated solution upon their surfaces. Concen-
trated solutions have a vapor tension less than that of water, and much less
than the atmospheric vapor pressure. The result is that water vapor continues
to condense from the atmosphere upon the substances until they dissolve and
form solutions so dilute that their correspondingly increased vapor tension bal-
ances the vapor pressure of the moisture in the atmosphere.

0-H
Hydrogen dioxide, Hydrogen peroxide, H2O2, or I • This

O — H

compound may be obtained in aqueous solution from several metallic
dioxides which, when treated with an acid, yield a portion of their
oxygen to water.

Sodium dioxide and barium dioxide are the compounds chiefly
employed in its manufacture, the acid used being either carbonic,
hydrochloric, hydrofluoric, sulphuric, or phosphoric acid. The de-
composition, when sulphuric acid and barium dioxide are used, is
this :

BaO2 + H2SO4 = BaSO4 + H2O2.

154 NON-METALS AND THEIR COMBINATIONS.

In no case is it possible to obtain, as might appear from the
above equation, pure hydrogen dioxide directly, as a considerable
quantity of water has to be present in order to effect the de-
composition. The aqueous solution, if quite pure, can be concen-
trated by evaporation at a temperature not exceeding 60° C. (140°
F.) until it has a strength of 50 per cent. If this be further heated
in vacuo at a gradually increased temperature, a nearly pure hydro-
gen dioxide distils over at a temperature of 85° C. (185° F.).

Pure hydrogen dioxide is a colorless, oily liquid, of a specific
gravity 1.45. It is soluble in water, alcohol, and ether, which latter
extracts it from its aqueous solutions.

Hydrogen dioxide decomposes slowly at ordinary temperature,
more rapidly on exposure to light and at higher temperatures ; at
100° C. the decomposition is often explosively rapid. Many inert
subtances, in powder, cause its decomposition, and it is for this
reason that even dust particles from the air act decomposingly,
especially during evaporation. The presence of very small quanti-
ties of certain substances retards the decomposition. Traces of free
acids, as also boro-glycerin, have been used for this purpose. It has
been found that a very small quantity of acetanilide is an excellent
preservative and it is now added to commercial hydrogen dioxide
solution.

Catalytic action. There are a number of instances in chemistry
where a substance, which apparently undergoes no change itself,
causes by its presence an increase in chemical change in other sub-
stances, or induces a change where, without it, there would be no
chemical action. This is known as catalytic or contact action and
the process is called catalysis. Examples of this action are seen in
the decomposition of hydrogen dioxide by dust particles, or finely
divided platinum, the influence of manganese dioxide on potassium
chlorate in the preparation of oxygen, and the explosion of a mixture
of hydrogen and oxygen when platinum black is introduced into it.

Hydrogen dioxide possesses bleaching, caustic, and antiseptic
properties. It is used as a bleaching agent for hair, wool, teeth, and
other articles, and as an antiseptic in surgical and in dental opera-
tions. It effervesces with pus, as also with saliva, in consequence of
the liberation of oxygen.

Solution of hydrogen dioxide, Aqua hydrogenii dioxidi, should
contain about 3 per cent, by weight, of pure dioxide, corresponding
to about 10 volumes of available oxygen in 1 volume of the solution.

HYDROGEN DIOXIDE. 155

The solution is colorless and without odor, and has a slightly acidu-
lous taste, producing a peculiar sensation and soapy froth in the
mouth. It is liable to deteriorate by age, especially on exposure to
heat and light.

Pyrozone is the trade name under which a 50 per cent, hydrogen peroxide
is sold, but diluted pyrozone also is found in the market.

Glycozone is hydrogen dioxide dissolved in glycerin instead of in water.

Hydrogen dioxide, owing to its instability and tendency to decom-
pose into water and oxygen, is an excellent oxidizing agent. It is
frequently used in preference to other such agen-ts, because by its use
no other products are introduced into solutions than water and oxy-
gen. Toward a few substances, which themselves are unstable and
easily give up oxygen, it also acts as a reducing agent. For example,
silver oxide is reduced to metallic silver thus :

Ag20 + H202 = 2Ag -f 02 + H20.

When hydrogen dioxide decomposes into water and oxygen, heat is liberated.
The thermal equation is —

H2O2 = H2O + O -f 22,926 cal.

that is, when 33.76 grammes of hydrogen dioxide corresponding to the formula,
H202, decomposes, 22,926 calories of heat energy are liberated. This is in
addition to the heat that is produced when the liberated oxygen unites with
other substances. In this way the great activity of hydrogen dioxide as an
oxidizer is accounted for.

Tests 1 for solution of hydrogen dioxide.

(Use the commercial solution after diluting about five times with water.)

1. To a beaker half full of water, add 1 or 2 c.c. of solution of

potassium iodide (see Reagents) and about 2 c.c. of the hydrogen

dioxide solution. Is any yellow color produced ? Then add a few

drops of starch solution (for which, see Index). A deep blue color

is produced by the action of the starch on the iodine liberated from

potassium iodide by the oxidizing action of the hydrogen dioxide :

2KI -f H202 = 2KOH + 21.
The action is more intense if the water is first acidified with 5 or 10

1 Tests are reactions to which a substance may be subjected for the purpose of recognition.
Acids turn blue litmus red, and we call that a test for acids. Carbon dioxide gas gives a
milky appearance to lime-water, which is a test for the gas. Some tests are much more strik-
ing than others, indeed, they are so characteristic that they tell at once the nature of the sub-
stance tested. Such tests might be called decisive, in distinction to others which are only cor-
roborative, and to which several substances may respond.

156 NON-METALS AND THEIR COMBINATIONS.

drops of a dilute acid. This is not a decisive test, since other sub-
stances besides hydrogen dioxide give the same test.

2. To a test-tube half full of water, add in succession, 1 c.c. of the
hydrogen dioxide solution, a few drops of dilute sulphuric acid, and
2 drops of solution of potassium dichromate, and mix. A blue com-
pound, known as perchromic acid, HCrO4, is produced, which fades
after a short time. The color may be made more permanent by
shaking the mixture with ether, which dissolves the compound and
collects on the surface on standing. This is a very delicate and
decisive test.

3. Acidify a few c.c. of the hydrogen dioxide solution with about
2 c.c. of dilute sulphuric acid, and add solution of potassium per-
manganate, a little at a time. The purple color vanishes quickly and
a gas is given off (oxygen). The permanganate is an unstable oxi-
dizing agent, which gives up its oxygen. This unites with oxygen
from the dioxide, and escapes as a gas. The reaction will be under-
stood when the chemistry of manganese is studied. Other substances
also decolorize permanganate.

If a solution is colorless, odorless, practically neutral to litmus-
paper, volatilizes completely upon heating, and responds to the above
tests, especially number 2, it is, without doubt, hydrogen dioxide.

QUESTIONS. — Mention two processes by which hydrogen may be obtained.
Show by symbols the decomposition of water by potassium, and of sulphuric
acid by iron. State the chemical and physical properties of hydrogen. Define
the nascent state. What explanation is offered to account for it? State the
composition of water in parts by weight and by volume. Mention the most
common solid and gaseous constituents of natural waters. How does a mineral
water differ from other waters? Mention some different kinds of mineral
waters and their chief constituents. What are the characteristics of a good
drinking-water ? What are the purest natural waters, and by what process
may chemically pure water be obtained? State composition, mode of manu-
facture, and properties of hydrogen dioxide. What is the explanation of efflo-
rescence and deliquescence ?

SOLUTION. 157

12. SOLUTION.

As stated under Water, the term solution is applied to any homo-
geneous liquid mixture that results when solids, liquids, or gases
an; brought in contact with a liquid and disappear in the liquid.
(There are a few instances of solution of a gas in a solid, and of a
solid in a solid.) Solutions are transparent, and the dissolved mate-
rial is so thoroughly disseminated that its particles cannot be dis-
tinguished by the eye from those of the solvent. Moreover, there is
perfect distribution of the dissolved matter and no tendency for it to
settle. An opalescent or opaque appearance of a liquid is evidence
that there is matter held in suspension, and this matter will settle in
time, or may be filtered out. Dissolved substances cannot be re-
moved by filtration, as they pass through the pores of the paper as
readily as the liquid does.

For the majority of substances there is a limit to the amount that
can be dissolved in a given amount of liquid. This limit ranges
from an almost infinitesimal amount in some cases to a fairly large
quantity in others. Thus, at ordinary temperature, the amount of
ferric oxide that is dissolved by 100 c.c. of pure water is extremely
small, while about 90 grammes of crystallized magnesium sulphate are
dissolved. No substance is absolutely insoluble, but many are so
sparingly soluble that for practical purposes they are considered in-
soluble. In some cases two substances may be mixed in any pro-
portions, for example, water and alcohol. But usually the solubility
of one liquid in another is limited, and when two such liquids are
shaken together they separate after a time into two layers, the liquid
in each layer being saturated with the other liquid. Thus, when ether
and water are shaken together at ordinary temperature they separate
on standing with the lighter (ether) layer on top, and 100 grammes
of water dissolve 2.1 grammes of ether, while 100 grammes of ether
dissolve 11 grammes of water. Pairs of liquids which are only slightly
soluble in each other are known as immiscible solvents, and are often
employed in certain kinds of chemical work for transferring a sub-
stance from one liquid to another. This operation is known as ex-
traction, and depends for its success upon a great difference of solu-
bility of the given substance in the two solvents. The division of a
substance between two immiscible solvents, after thorough shaking
and separation of the liquids, is proportional to its solubility in each
solvent. If a substance is 100 times more soluble in chloroform
than in water, and its aqueous solution is shaken thoroughly with
chloroform, the concentration of the substance in the chloroform

158 NON-METALS AND THEIR COMBINATIONS.

layer will be found 100 times that in the water layer. The process
of extraction must be repeated several times for the complete removal
of a substance from a liquid.

Terms employed. The liquid in which a substance is dissolved
is called the solvent, while the substance, to avoid circumlocution, is
often called the solute. The word strength is frequently used to refer
to the amount of substance in solution, but a more exact term to
employ is concentration. A solution that contains a small quantity,
say 5 grammes of a substance in 100 c.c., is said to have a small con-
centration, or to be dilute. Concentrated solutions contain a relatively
large amount of dissolved substance ; they are often spoken of as very
strong solutions. Concentrating a solution is the removal of part of
the solvent by evaporation. A saturated solution is one that contains
the maximum amount of dissolved substance. This condition may
be attained by long agitation of the liquid with an excess of the sub-
stance. If the latter is a solid, it should be finely divided. The
solubility of a substance is its concentration in saturated solution, and
is expressed in terms of the number of grammes of the substance in 100
grammes of the solvent, or in 100 c.c. of the solution, or of the grammes
of solvent required to dissolve 1 gramme of the substance. The solu-
bility of substances varies with the temperature, being, as a rule, in
the case of solids, much greater at boiling than at ordinary temper-
ature. In most cases, when a hot concentrated solution is allowed
to cool, the excess of material over what corresponds to the solubility
at lower temperature, separates as crystals from the solution (see
Crystals, Chapter 1). But in some instances the excess of material
does not separate from the solution as it cools ; such a solution is
then said to be supersaturated. Crystallization can be induced by
placing in the cool solution a fragment of the same substance as that
in solution. A solution in contact with the solid substance cannot
be more than saturated with respect to that substance. There is an
equilibrium between the solid and the saturated solution. Sulphate,
thiosulphate, and chlorate of sodium have a marked tendency to give
supersaturated solutions, especially if the solutions are freed from all
floating particles by careful filtration.

The solution of certain substances in water takes place with libera-
tion of heat and rise in temperature of the solution, while in other
cases there is an absorption of heat and a fall in temperature. Heat
of solution is the number of calories liberated or absorbed when the
weight of a substance in grammes corresponding to its chemical form-
ula (molecular weight) is dissolved in an unlimited amount of water.

SOLUTION. 159

AVhen 95.35 grammes of sulphuric acid (corresponding to H2SOj are
thus dissolved, 38,880 calories of heat are liberated, or enough heat
to raise over 38 liters of water 1° C. in temperature. When 284.11
grammes of crystallized sodium carbonate (Na2CO3.10H2O) are dis-
solved, 16,038 calories are absorbed, but solution of an equivalent
weight of anhydrous sodium carbonate (Na2CO3), or 105.31 grammes,
liberates 5,598 calories of heat. If a substance absorbs heat during
solution, it develops the same amount of heat when it comes out of
solution as by crystallization. For example, a supersaturated solu-
tion of sodium sulphate, when crystallizing suddenly, produces quite
an appreciable rise in temperature.

Solution of gases. Henry's Law. Gases dissolve in liquids to a vari-
able degree. The range of solubility is quite wide, as may be seen from the
following examples: At 0° C. and 760 mm. pressure, 1 volume of water dissolves
0.02 volume of hydrogen, or nitrogen, 0.04 volume of oxygen, 1.8 volumes of
carbon dioxide, 80 volumes of sulphur dioxide, 550 volumes of hydrochloric
acid gas, and 1050 volumes of ammonia gas.

The solubility of a gas varies with the nature of the solvent; thus, at 0° C.,
a volume of alcohol dissolves twice as much carbon dioxide as the same volume
of water does. It also varies with the temperature, decreasing, as a rule, as the
temperature increases. Thus, 100 volumes of water dissolve about 4 volumes
of oxygen at 0° C., 3 at 20° C., 1.8 at 50° C., and none at 100° C. In many
instances a gas is completely removed from its solution by boiling, but this is
not possible in the case of certain very soluble gases, like hydrochloric acid.
There is in such cases a chemical action, in part at least, between the gas and
the solvent. A 20.2 per cent, aqueous solution of hydrochloric acid distills
unchanged under normal atmospheric pressure.

The solubility of a gas increases with increased pressure on the gas. Com-
mercial aerated water is a good illustration. The water is charged with carbon
dioxide under considerable pressure. When drawn from the container and
exposed to the atmosphere the excess of gas, which cannot remain dissolved
under the diminished pressure, escapes, causing effervescence. Such a solution
is often called soda water. Solutions of gases in liquids fall into two classes :
(1) those from which the gas is completely removed by heat or by decrease of
pressure ; (2) those from which the gas is not thus completely removed. Very
soluble gases give rise to the second class of solutions, in which a complete
chemical and physical independence of the molecules of solvent and gas is
lacking. In solutions of the first class there is a fixed relationship between the
solubility of a gas and pressure, which is known as Henry's Law. It may be
stated thus : The quantity of a gas dissolved by a given quantify of a liquid is pro-
portional to the pressure of the gas. Since the volume of a gas is inversely
proportional to the pressure, another form in which the law may be stated is :
A given quantity of a liquid dissolves the same volume of a gas at all pressures.

In the case of a mixture of gases in contact with a liquid, each gas dissolves
as if it were present alone, and in proportion to its own partial pressure in the
mixture,

160 NON-METALS AND THEIR COMBINATIONS.

Henry's law holds in the case of absorption of gases by saline solutions, if
the gas has no chemical action on the salt in solution, for example, in the
absorption of carbon dioxide, oxygen, or nitrogen, by a solution of sodium
chloride (common salt). When the gas acts chemically on the dissolved salt,
as carbon dioxide does on ordinary sodium phosphate or sodium carbonate,
one portion of the gas is absorbed in accordance with Henry's law, and an
additional portion is absorbed as a result of chemical action and is independent
of pressure.

Freezing-points of solutions. The freezing-point of a solution is always
lower than that of the pure solvent. It is also easily observed, by introducing
small quantities of solutions and pure solvents over the mercury in barometer
tubes, that the vapor tension of the solutions is always less than that of the
pure solvents, no matter what the temperature is. This difference in vapor
tension accounts for the fact that the freezing-point of solutions is depressed.
Theoretical considerations show that freezing (separation of some of the solvent
in the solid state) can take place only at such a temperature at which the solu-
tion and the solid state of the solvent have the same vapor tension, whereby
they are in physical equilibrium and can co-exist permanently (see discussion
under Efflorescence and Deliquescence, p. 152). Since the vapor tension of a
solution is always less than that of the pure solvent, it follows that the freezing-
point of a solution must be lower than that of the pure solvent, in order that
the vapor tension of the solution and of the ice that separates may balance
each other. (On this principle the low temperature of freezing mixtures, such
as snow (or ice) and salt, is explained).

For a description of apparatus and details of method in making determina-
tions of the freezing-points of solutions, the student must be referred to books
on physical chemistry.

For solutions not too concentrated and in which there is no chemical action
between the solvent and the substance dissolved, the following law has been
found to hold : The depression of the freezing-point is directly proportional to the
iveight of dissolved substance in a given amount of the solvent. By calculations
made on the results obtained with dilute solutions, the following law has been
found to hold theoretically for molecular quantities of substances : The molec-
ular weights in grammes of different substances dissolved in 1000 grammes of the
same solvent produce the same depression of the freeezing -point. The depression
thus produced is called the molecular depression constant, and has a different
numerical value for each solvent. For water it is 1.89° C.; for benzene, 4.9° C.,
and for phenol, 7.5° C.

The above law gives a basis for a method of determining molecular weights,
which was first applied extensively by Raoult, and is sometimes called the
cryoscopic method. It is valuable in the case of substances which cannot be
volatilized without decomposition. The molecular weight is calculated from
the equation

D = d X Vv-'

M X g

in which D is the amount of depression in any actual experiment, d the molec-
ular depression constant, W the weight of the substance, M its molecular
weight, and g the weight of the solvent in grammes.

SOLUTION. 161

The above law, often called the law of Eaoult, does not hold in some cases,
especially in those of solutions of acids, bases, and salts in water. For ex-
ample, one molecular weight of sodium chloride, 58.06 grammes, dissolved in
1000 grammes of water, depresses the freezing-point about 3.5° C., or nearly
twice the amount produced by a cane-sugar solution of equivalent concentra-
tion, 1.89° C., which is taken as the molecular depression of normally acting
substances. It is also a noteworthy fact that aqueous solutions of substances
that have abnormal freezing-point depressions are just such as conduct an
electric current, while solutions of substances that give normal depressions do
not conduct a current. The same number of molecules of different substances
in a given amount of solvent produces the same lowering of the freezing-point,
and the molecular weights in grammes contain the same number of molecules.
The fact that the depression of the freezing-point of a solution of the molecular
weight in grammes of sodium chloride in 1000 grammes of water is much
greater than that of a similar solution of cane-sugar, can be accounted for on
the assumption that the number of particles in the sodium chloride solution
must be increased somehow over the number of particles in the sugar solution.
This increase can only take place by a decomposition of the molecule of sodium
chloride, thus,

NaCl •= Na + Cl.

The particles Na and Cl must be different in condition from sodium and chlo-
rine as we know them in the free state, but as far as their effect upon the
freezing-point is concerned they act the same as undecomposed dissolved mole-
cules. This assumption of the decomposition of molecules is applied in the
case of all abnormally acting solutions where the freezing-point depressions
are greater than normal, and will be referred to again farther on under
lonization.

In the field of medicine the determination of the freezing-point of certain
fluids is sometimes carried out in order to learn something of the manner in
which the organs are functioning. Normal blood has a lower freezing-point
than water, the difference is 0.56° C. A greater difference than this indicates
that the kidneys are not properly eliminating the solid waste products from
the blood. The freezing-point depression of normal urine is 1.2°-2.3° C. Of
cows' milk it is 0.55°-0.56° C. A lower depression indicates that the milk has
been tampered with.

Boiling-points of solutions. These are always higher than the boiling-
points of the pure solvents. The boiling-point of any solution is that temper-
ature at which the vapor tension of the solution is equal to the atmospheric
pressure. Since the vapor tension of solutions is less than that of the pure
solvent, it follows that a solution must be heated to a higher temperature than
that at which the pure solvent boils, in order to make its vapor tension equal
to the atmospheric pressure ; in other words, to make it boil. The elevations in
the boiling-points are proportional to the concentrations of the different solutions of
any one substance. The molecular weight in grammes of normally acting sub-
stances, dissolved in 1000 grammes of water, elevates the boiling-point from
100° to 100.52° C. The difference, 0.52°, is called the molecular boiling-point
constant for water. Just as in the case of freezing-points, so here a method
11

162 NON-METALS AND THEIR COMBINATIONS.

of determining molecular weights has been devised, but for a description
of the apparatus and details of working, reference must be made to special
books.

The substances which show abnormalities in the depression of the freezing-
point are also those which give abnormal elevations in the boiling-points of
their solutions. The abnormal behavior is also accounted for by the same ex-
planation, namely, a decomposition of some of the molecules of the dissolved
substance. The deviations from normal behavior are particularly observed in
aqueous solutions.

Osmotic pressure. Soluble substances in contact with a liquid dissolve
and diffuse throughout the liquid until the concentration is uniform in every
part of the solution (see Diffusion, p. 40). In the liquid the substance behaves
somewhat like a gas, in that its molecules tend to spread out and fill the whole
space occupied by the liquid. The cohesion between the molecules of the sub-
stance is overcome and there is freedom of motion, somewhat as in a gas.
Just as a gas exerts a pressure on any partition or membrane that resists the
motion of its molecules, so likewise do the molecules of a substance in solution
exert pressure upon a membrane that prevents their diffusion into a less con-
centrated region of the solution, or into the pure solvent. This pressure is
called osmotic pressure. In the article on Dialysis it is shown that a substance
in aqueous solution on one side of certain kinds of membranes, as bladder or
parchment, will diffuse into pure water on the other side. Osmotic pressure is
exhibited here, but such membranes are not suitable for its study, because the
motion (diffusion) of the molecules of the dissolved substance is not stopped,
but only hindered. It is possible, however, to prepare membranes which are
permeable to the solvent, but impermeable to the dissolved substance. These
are known as semi-permeable membranes, and by their means the phenomena
of osmotic pressure can be studied qualitatively and quantitatively. W.
Pfeffer, a botanist, was the first to successfully construct (1877) an artificial
semi-permeable membrane by causing a precipitate of copper ferrocyanide to
be formed within the walls of a porous unglazed porcelain cup.1 Such cups
are known as osmotic cells. When a solution of any substance, say, cane-sugar,
is placed in the cell and the latter is placed in water, it is observed that water
passes through the cell into the solution, but no sugar passes out into the
water. If the flow of water is unobstructed, it will continue until the solution
is so much diluted that it is practically the same as water. If the accumulation
of water in the cell is obstructed by using a closed cell filled with the solution
and fitted with a manometer, pressure is seen to develop in the cell, due to the
tendency of the water to pass into it, and corresponding to the amount that
would have passed into it had the water not been obstructed. It requires some
hours for this pressure to reach a maximum, and the amount in atmospheres
can be read on the manometer. At the maximum the pressure on the water
within the cell causes it to tend to flow out as fast as the water outside tends
to flow in, thus producing a system in equilibrium. The pressure read on the
manometer is equal to the osmotic pressure of the molecules of the dissolved
substance against the membrane of the cell.

1 It was rather difficult to prepare such membranes until a method was devised by Prof.
H. N. Morse, by which practically flawless osmotic cups can be readily made. See Amer-
Chem. Jour., July, 1905, and later.

SOLUTION. 163

In osmotic cells the pure solvent always passes into the solution, or the sol-
vent passes from a solution of less concentration into one of greater concentra-
tion. This flow can be accounted for on the physical principle of equilibrium,
namely, that in any system capable of movement or adjustment a strain in one
part will cause a movement tending to remove or equalize the strain. A
system of a membrane and a liquid on each side of it can be in equilibrium
only when the osmotic pressure on the two sides of the membrane is the same.
In the case of a semi-permeable membrane, the molecules of the dissolved sub-
stance cannot pass, so the only other way of equalizing osmotic pressure is by
the solvent passing from the exterior of the cell into the solution, until the
osmotic pressure is the same on each side of the membrane. If this passage is
obstructed the tendency still exists, which manifests itself as pressure.

In 1887 van't Hoff deduced from theoretical considerations the laws of
osmotic pressure, which are verified by experiments. These laws are analogous
to the gas laws, and are as follows :

The osmotic pressures of solutions of the same substance are proportional to their
concentrations. This is analogous to Boyle's law for gas pressures, and in gen-
eral is independent of the nature of the solvent. It is illustrated by the
following results :

Grammes of cane-sugar in 1000 grammes of water.. . .

68.4

136.8

171

342

483

972

1215

2446

Osmotic pressure increases in proportion to the absolute temperature. This is
analogous to the law of Charles for gases.

Solutions which at the same temperature have equal osmotic pressure contain
equal numbers of molecules of the dissolved substance in equal volumes. This is
analogous to Avogadro's law for gases.

The osmotic pressure of a substance in solution is the same in value as the gas-
eous pressure which it would exhibit if the same weight of it were contained as a
gas in the same volume at the same temperature. The osmotic pressure of a solution
of the molecular weight in grammes of a substance in one liter of water at 0°
G. is 22 to 23 atmospheres, and the same weight of the substance in gas form
at 0° C., and occupying a liter volume, would have a gas pressure of 22 to 23
atmospheres.

Solutions of different substances having the same osmotic pressure are said
to be is-osmotic or isofonic. It is not an easy matter to carry out measurements
of osmotic pressure except in specially equipped laboratories, but isotonic
solutions can be prepared, nevertheless, by taking advantage of the fact that
such solutions have the same freezing-points, and determination of freezing-
points is a routine task in laboratories. Blood-serum freezes at — 0.56° C.,
which corresponds to an osmotic pressure of about 6.6 atmospheres. A 0.95
per cent, aqueous solution of sodium chloride freezes at — 0.56° C., and, there-
fore, exerts the same osmotic pressure as blood-serum. It is isotonic with
blood-serum. A solution of higher osmotic pressure than that of blood-serum
is called hypertonic, and one of lower pressure is called hypotonic.

164 NON-METALS AND THEIR COMBINATIONS.

In regard to the laws of osmotic pressure, deviations from them are observed
in the case of aqueous solutions of the same substances for which the freezing-
point and boiling-point laws do not hold, namely, acids, bases, and salts.
These always show greater osmotic pressures than those calculated, and than
that shown by cane-sugar, which is a type of normally acting substance. The
deviations are explained by the same assumption that is made to explain devi-
ations from the freezing-point law (see above), namely, decomposition of mole-
cules into a greater number of particles, that is, ions.

13. NITROGEN.
Niii = 14 (13.93).

Occurrence in nature. By far the larger quantity of nitrogen is
found in the atmosphere in a free state. Compounds containing
nitrogen are chiefly the nitrates, ammonia, and many organic sub-
stances.

Preparation. Nitrogen is obtained usually from atmospheric air
by the removal of its oxygen. This may be accomplished by burn-
ing a piece of phosphorus in a confined portion of air, when phos-
phoric oxide, a white solid substance, is formed, while nitrogen is left
in an almost pure state.

Other methods for obtaining nitrogen are by heating a mixture of
potassium nitrite and ammonium chloride dissolved in water :

KNO2 -f NH4C1 = KC1 -f 2H2O + 2N;
or by heating ammonium nitrite in a glass retort :
NH4NO2 = 2H20 + 2N.

Experiment 5. Use an apparatus as shown in Fig. 37, page 140. Place in the
flask about 10 grammes of potassium nitrite and nearly the same amount of
ammonium chloride; add enough water to dissolve the salts, and apply heat,
which is to be carefully regulated from the time the decomposition begins, as

QUESTIONS. — Give a definition of solution and its general characteristics.
What are immiscible solvents and how are they employed? Define dilute,
concentrated, and saturated solutions. What is meant by the solubility of a
substance, and by heat of solution ? What is Henry's law regarding the solu-
tion of gases in liquids? What is the relation between the freezing-points of
solutions and the weights of dissolved substances? What use is made of the
cryoscopic method ? What is osmotic pressure? What is a semi-permeable
membrane? How do the laws of osmotic pressure compare with the gas laws?
What are isotonic, hypertonic, and hypotonic solutions ? What is the expla-
nation of the abnormal behavior shown by solutions of acids, bases, and salts
in their freezing-points, boiling-points, and osmotic pressures?

NITROGEN. 165

the evolution of gas may otherwise become too rapid. Collect the gas, and
notice its properties mentioned below.

Properties. Nitrogen is a colorless, inodorous, tasteless gas;
which, at a temperature of —130° C. (—202° F.) and a pressure of
280 atmospheres, may be condensed to a colorless liquid. It is neither,
like oxygen, a supporter of combustion, nor, like hydrogen, a com-
bustible substance ; in fact, nitrogen is distinguished by having very
little affinity for any other element, and it scarcely enters directly into
combination with any substance. Nitrogen is not poisonous, yet not
being a supporter of combustion it cannot sustain animal life.
Nitrogen is trivalent in some compounds, quinquivalent in others.

Atmospheric air is a mixture of about four-fifths of nitrogen and
one-fifth of oxygen, with small quantities of aqueous vapor, argon,
carbon dioxide, and ammonia, containing frequently also traces of
nitrous or nitric acid, and occasionally hydrogen sulphide, sulphur
dioxide, and hydrocarbons. Besides these gases there are always
suspended in the air solid particles of dust and very minute cells of
either animal or vegetable origin.

100 volumes of atmospheric air contain of

Oxygen 20.60 volumes.

Nitrogen 77.16 "

Argon 0.80 volume.

Carbon dioxide . . . . 0.03-0.04 "
Aqueous vapor .... 0.5 -1.40 "

Ammonia } . traces.

Nitric acid -*

Omitting all minor constituents, the composition of air by volume
is about 79 per cent, of nitrogen and 21 per cent, of oxygen, corre-
sponding in weight to 77 per cent, of nitrogen and 23 per cent, of
oxygen.

That atmospheric air is a mixture and not a compound of oxygen and
nitrogen is shown by the facts that the composition is not absolutely constant,
that the two elements may be mixed in the proper quantities without showing
the least evidence that chemical change has taken place, and that pure water
absorbs from air the two elements in quantities different from those in which
they occur in air.

Humidity, specifically called relative humidity, designates the amount
of aqueous vapor in the atmosphere, compared with that which is
required to saturate it at the respective temperature. When the air
is completely saturated the humidity is expressed at 100; if perfectly

166 NON-METALS AND THEIR COMBINATIONS.

dry, as 0. The instruments used to determine humidity are called
hygrometers.

An analysis of air maybe made by the following method : A graduated glass
tube, containing a measured volume of air, is placed with the open end down-
ward into a dish containing mercury. A small piece of phosphorus is then
introduced and allowed to remain in contact with the air for several hours,
when it gradually combines with the oxygen. The remaining volume of air is
chiefly nitrogen, the loss in volume represents oxygen.

For the determination of carbon dioxide and water, a measured volume of
.air is passed through two U-shaped glass tubes. One of these tubes has previ-
ously been filled with pieces of calcium chloride, the other tube with pieces of
potassium hydroxide, and both tubes have been weighed separately. In pass-
ing the measured air through these tubes the first one will retain all the
moisture, the second one all the carbon dioxide ; the increase in weight of the
tubes at the end of the operation will give the amounts of the two constituents.

That oxygen is found in the atmosphere in a free state is explained
by the fact that all elements having affinity for oxygen have entered
into combination with it, while the excess is left uncombined. Mtro-
gen is found uncombined, because it has so little affinity for other
elements.

Liquefaction of air on a large scale has been made possible by a process
which depends on first subjecting air to a pressure of 2000 pounds to the square
inch and then permitting the compressed gases to escape from a needle-point
orifice. During the expansion of the gas heat is absorbed, i. e., the air as well
as the tubes in which it is contained are cooled off'. The cold thus produced
is used to cool another portion of compressed air, which, on expanding, becomes
colder than the first portion. By repeating the operation a third time the
temperature is brought down to — 191° C. and below, and at this temperature
liquefaction takes place.

Liquefied air is a mobile, slightly bluish liquid which can be kept for some
little time in open vessels— i. e., so long as the temperature of nearly 200° C.
below freezing is maintained by the evaporation of the liquid.

As nitrogen is somewhat more volatile than oxygen, the liquefied air, when
permitted to stand in open vessels, becomes gradually richer in oxygen, so that
finally a liquid is left containing over 80 per cent, of oxygen. Notwithstand-
ing the low temperature of this liquid it acts most energetically as a supporter
of combustion.

Of interest are the changes which are brought about in the physical proper-
ties of different bodies when cooled down to nearly — 200° by immersion in
liquid air. Many malleable metals, many soft or elastic bodies, such as rubber
and paraffin, when subjected to this low temperature, become as brittle as badly
cooled glass ; changes in color, as well as in other properties, take place also.

Argon, mentioned above as a normal constituent of air, is a gaseous element,
discovered in 1894. It may appear strange that a normal constituent of air,
present to the extent of nearly 1 per cent., should have been overlooked for so
many years, although air had been carefully analyzed many hundred times.

NITROGEN. 167

The only explanation that can be offered is the fact that argon has scarcely
any chemical affinity for other elements, and consequently its presence was not
revealed by any of the ordinary reactions used in air analysis. In fact, the
total of argon present had invariably been reported as nitrogen up to the time
of the discovery of the new element.

Helium is another gaseous element discovered in 1895. It occurs absorbed
in a number of rare minerals from which it is expelled by heating. It is also
a constituent of the gases which are disengaged from certain spring waters,
and, in very small quantities, is a constituent of atmospheric air. Both argon
and helium are very inert. Helium has an atomic weight of about 4, while
that of argon is 40. One volume of helium is contained in 245,000 volumes of
air.

Compounds of nitrogen. Nitrogen has very little tendency to
combine directly with other elements, bat it is an easy matter to
obtain compounds of nitrogen. These, however, are all obtained in
indirect ways, being either furnished ready made by processes of nature
or obtained as by-products in manufacturing industries. Conversely,
as a result of the inactivity of nitrogen, most of its compounds are
more or less unstable, either at ordinary or elevated temperatures, or
when brought together with other substances. We have already seen
how easily ammonium nitrite is radically decomposed by heat, and
ammonium nitrate acts in the same way, as will be seen below.

The two principal compounds of nitrogen are ammonia and nitric
acid, and nearly all the others with which we have to do in inorganic
chemistry are derived from these. The valence of nitrogen is 3 in
ammonia, which represents the limit of reduction, while it is 5 in
nitric acid, which is the limit of oxidation of nitrogen.

Ammonia, NH3 — 16.93. This compound is constantly forming
in nature by the decomposition of organic (chiefly animal) matter, such
as meat, urine, blood, etc. It is also obtained during the process of
destructive distillation, which is the heating of non-volatile organic
substances in suitable vessels to such an extent that decomposition
takes place, the generated volatile products being collected in re-
ceivers. The manufacture of illuminating gas is such a process of
destructive distillation ; coal is heated in retorts, and most of the
nitrogen contained in the coal is converted into and liberated as
ammonia gas, which is absorbed in water, through which the gas is
made to pass. This is the source of nearly all the ammonium salts
on the market.

Another method of obtaining ammonia is through decomposition
of ammonium salts by the hydroxides of sodium, potassium, or cal-

168

NON-METALS AND THEIR COMBINATIONS.

cium. Usually ammonium chloride is mixed with calcium hydroxide

and heated, when calcium chloride, water, and ammonia are formed :

2(NH4C1) + Ca(OH)2 = CaCl2 + 2H2O + 21sTH3.

Experiment 6. Mix about equal weights (10 grammes of each) of ammonium
chloride and calcium hydroxide (slaked lime) in a flask of about 200 c.c. capac-
ity, and arranged as in Fig. 39; cover the mixture with water and apply heat.

FIG. 39.

Apparatus for generating amuioiiia.

As long as any atmospheric air remains in the apparatus, bubbles of it will
pass through the water contained in the cylinder; afterward all gas will be
readily and completely absorbed by the water. Notice the odor and alkaline
reaction on litmus of the ammonia water thus obtained. When the gas is
being freely liberated, move the tube upward, as shown in B, and collect the
gas by upward displacement in a cylinder or tube, which when filled with gas
is held mouth downward into water, which will rapidly rise in the tube by
absorption of the gas. Notice that ammonia is not readily combustible, by
applying a flame to the gas escaping from the delivery tube.

Ammonia is a colorless gas, of a very pungent odor, an alkaline
taste, and a strong alkaline reaction. In pure oxygen it burns, form-
ing water and free nitrogen.

By the mere application of a pressure of seven atmospheres or by
intense cold (—40° C., —40° F.), ammonia may be converted into a
liquid, which at —80° C. (—112° F.) forms a solid crystalline mass.
Water, at its freezing-point, dissolves as much as 1050 volumes of
ammonia gas, and at 15° C. (59° F.) still retains 727 volumes of the
gas in solution. This solution contains ammonium hydroxide :
NH3 + H20 = NH4OH.

Certain experimental evidence indicates that only a small propor-
tion of the gas is combined with water to form hydroxide, most of it

NITROGEN. 169

being simply dissolved. By boiling, all the ammonia is finally driven
out of solution.

It has a strong alkaline action on litmus and has basic properties
like those of sodium and potassium hydroxide. It neutralizes acids
forming salts, thus :

NH4OH + HC1 = NH4C1 + H2O.

Ammonia gas also unites with acids directly without elimination of
water. For example, with hydrochloric acid gas, a dense white cloud
of ammonium chloride is formed :

NH3 + HC1 •= NH4C1.

The union of water or hydrochloric acid directly with ammonia is
explained by the increase of valence of the nitrogen atom from 3 to
5. In the hydroxide and all the salts, there is a group of atoms,
(NH4)— , which acts exactly like an atom of metal. It has, therefore,
been called ammonium. This radical and its analytical reactions will
be discussed under Ammonium compounds.

Experiment 7. To about 20 c.c. of dilute ammonia water, add concentrated
hydrochloric acid until litmus-paper is just turned from blue to red by the
liquid. Evaporate to dryness in a porcelain dish over a small flame. Note
appearance of residue and compare its taste with that of the ammonia water,
and dilute hydrochloric acid and also that of ammonium chloride. What is
the residue? This is an example of the formation of a salt by neutralization
of an acid by an alkali.

Ammonia "water, Aqua ammoniae (Spirit of hartshorn). This is
a solution of ammonia gas in water or ammonium hydroxide in water.
The common ammonia water contains 10 per cent, by weight, equal
to 125 volumes of ammonia, and has a specific gravity of 0.958 at
25° C. ; the stronger ammonia water, aqua ammonias fortior, contains
28 per cent., and has a specific gravity of 0.897 at 25° C. Ammonia
water has the odor, taste, and reaction which characterize the gas.

Hydrazine, N2H4 (Diamine], is a compound obtainable from organic com-
pounds by processes which cannot be considered here. It is a colorless gas at
summer heat, readily liquefying at a somewhat lower temperature, and solidi-
fying at the freezing-point of water.

Exposed to the air it takes up oxygen, forming water and nitrogen. In its
chemical properties hydrazine resembles ammonia, forming a hydrate of
the composition N2H4.H2O, and salts with acids, such as N2H4.H2SO4 and
N2H4(HC1)2. The constitution of hydrazine may be represented by the

H\ /H

formula >N — NC

H/ \H

Hydroxylamine, NH2OH. The term amine is used to designate com-

170 NON-METALS AND THEIR COMBINATIONS.

pounds derived from ammonia by replacement of one or more hydrogen atoms
by basic atoms or radicals, and it is in keeping with this terminology that the
compound under consideration is known as hydroxyl-amine, while hydrazine
is termed di-amine.

Hydroxylamine is prepared by the action of nascent hydrogen on nitric acid :

HN03 + 6H = NH2OH -f 2H2O.

The compound is known only in solution ; with acids it forms well-defined
salts, which appear to be ammonium salts in which a hydrogen atom has been
replaced by hydroxyl. The formation of salts may be represented thus :

NH2OH +HN03- NH3OHNOS
NH2OH + HC1 == NH3OHC1

Triazoic acid, N3H (Hydrazoic add). This remarkable substance was first
isolated in 1890 from organic compounds. It is now obtained also from inor-
ganic material by the action of sodium on ammonia, when a compound of
the composition NH2Na is formed, which by treatment with nitrogen monoxide
produces water and sodium triazoate. The latter, by the action of an acid, is
converted into a sodium salt and free triazoic acid. The three steps of the
process may be represented thus :

NH3 + Na = NH2Na + H

NH2Na + N20 = Na — N/ || + H2O

/N /N

2Na-N/ || + H2SO4 = Na2SO4 + 2HN/ |^

Triazoic acid is a colorless gas, possessing a disagreeable odor. It is soluble
in water, and this solution can be distilled, but the operation is dangerous, as
the compound is apt to decompose with explosive violence. When inhaled it
acts as a poison, producing violent headache.

While the three compounds of hydrogen with nitrogen considered above are
of a basic nature, triazoic acid has decidedly acid properties. In fact, it is a
stronger acid than acetic acid, and resembles hydrochloric acid in precipitating
soluble silver and rnercurous salts.

Compounds of nitrogen and oxygen. Five distinct compounds
of nitrogen and oxygen are known. They are named and constituted
as follows :

Composition.

By weight. By volume.

NO NO

Nitrogen monoxide, N2O ... 28 16 2 1

Nitric oxide, NO 28 32 2 2

Nitrogen trioxide, N2O3 ... 28 48 2 3

Nitrogen tetroxide, N2O4 = 2(NO2) . 28 64 24

Nitrogen pentoxide, N2O5 ... 28 80 2 5

The trioxide and pentoxide are called also acid anhydrides, or ni-
trous and nitric anhydride respectively, because they combine with

NITROGEN. 171

water to give nitrous and nitric acid. Conversely, when the acids are
deprived of the elements of water, the respective oxides of nitrogen
are obtained. The monoxide corresponds to hyponitrous acid,
H2N2O2, but does not yield the acid with water. It is, hence, not an
anhydride. All of the oxides are obtained from nitric acid, directly
or indirectly. The last one is formed by abstraction of water from
nitric acid, the others involve reduction of nitric acid or, in reality,
of nitrogen pentoxide.

While our knowledge of the structure of the oxides of nitrogen is unsatis-
factory, the following graphic formulas, in which the valence of nitrogen is
assumed to be either 1, 3, or 5, have been proposed to show the manner in which
the atoms may be linked together :

Nitrogen monoxide, N— O — N or N — N

Nitric oxide, N = O

Nitrogen trioxide, O = N — O — N=Oor

Nitrogen tetroxide,

Nitrogen pentoxide,

Nitrogen tetroxide, at high temperature, has the composition N02, and it is
possible that in NO2, and nitric oxide, NO, the valence of nitrogen is 4 and 2
respectively. The truth is that we have not sufficient knowledge of the struc-
ture of the oxides of nitrogen to make any positive statement as to the valence
of nitrogen in them.

The structure of the nitrogen acids may be represented thus :

N — OH
Hyponitrous acid, N — OH, or possibly II ^

Nitrous acid, O = N — - OH, or N\OH

//O
Nitric acid, °^N — OH, or

Nitrogen tetroxide, at low temperature, has the formula N2O4, but at
elevated temperatures this splits up into 2NO2, to form again N2O4, when
the temperature is decreased. There are many other cases like
chemistry.

172 N OX-METALS AND THEIR COMBINATIONS.

Such a decomposition which proceeds at high temperatures, while at lower ones
the constituents can recombine, is called dissociation.

When electric sparks pass through atmospheric air some ozone is generated
which oxidizes nitrogen, forming first the lower and then also the higher
oxides; these combine with water to form nitrous and nitric acid, which acids
are taken up by the ammonia present in the air, forming the respective
ammonium salts.

Nitrogen monoxide, N2O (sometimes called nitrous oxide ;
also laughing gas). This compound was discovered by Priestley in
1776; its anaesthetic properties were first noticed in 1800 by Sir
Humphry Davy, and it was first used in dentistry by Dr. Horace
Wells, a dentist of Hartford, Conn., in 1844. It may be easily
obtained by heating ammonium nitrate in a flask at a temperature
not exceeding 250° C. (482° F.), when the salt is decomposed into
nitrogen monoxide and water :

NH<NO3 = 2H,O + N3O.

When nitrous oxide is prepared for use as an anesthetic it should
be passed through two wash-bottles containing caustic soda and ferrous
sulphate respectively ; these agents will retain any impurities that may
be formed during the decomposition, especially from an impure salt

Ammonium nitrate to be used for generating pure nitrous oxide should be
completely volatilized when heated on platinum foil ; its solution in water
should not be rendered turbid by silver nitrate, as this would indicate the
presence of chlorides. These latter are objectionable because gaseous com-
pounds of chlorine with the oxides of nitrogen may be formed. If the gas is
prepared as directed above, it can be used with safety.

Impurities found in the gas when not properly made are air, nitric oxide,
chlorine, chloronitrous and chloronitric oxides.

If the gas is stored over water, considerable loss is experienced on account
of the solubility of nitrous oxide in cold water. This loss can be diminished
by using hot water or a concentrated solution of common salt in water, both of
which liquids dissolve less of the gas.

Experiment 8. Use apparatus as represented in Fig. 37, page 140. Place in the
dry flask about 10 grammes of ammonium nitrate, apply heat, collect the gas
in cylinders over water, and verify by experiments and observations the correct-
ness of the statements below regarding the physical and chemical properties
of nitrogen monoxide.

Nitrogen monoxide is a colorless, almost inodorous gas, of dis-
tinctly sweet taste. It supports combustion almost as energetically
as oxygen, but differs from this element by its solubility in cold water,
which absorbs nearly its own volume. Under a pressure of about
50 atmospheres it condenses to a colorless liquid, the boiling-point of
which is at about -90° C. (-130° F.) and the freezing-point at
-102° C. (-151.6° F.).

NITROGEN. 173

When inhaled it causes exhilaration, intoxication, anaesthesia, and,
finally, asphyxia. The gas is used in dentistry as an anesthetic, the
liquefied compound being sold for this purpose in wrought-iron
cylinders. There are two sizes of these cylinders : the smaller con-
tain about one and a half pounds of the liquid, equal to 100 gallons
of gas; the larger size contains about five times that quantity.

Nitric oxide, NO. This is a colorless gas which is formed gener-
ally when nitric acid acts upon metals or upon substances which
deoxidize it. It is capable of combining directly with one or more
atoms of oxygen, thereby forming nitrogen tetroxide, called nitrogen
peroxide, NO2 or N2O4, which is a gas of deep red color and poison-
ous properties. Nitrogen trioxide, N2O3, exists as an indigo-blue
liquid at temperatures below —21° C. (-6° F.); above this tem-
perature it decomposes into NO and NO2.

Experiment 9. Use apparatus as shown in Fig. 38. Put about 20 grammes
of copper or brass turnings into the flask and pour through the funnel tube a
mixture of 30 c.c. concentrated nitric acid and 50 c.c. water. Apply gentle
heat and collect several bottles of gas. ^Note that the gas. in the flask is at
first colored. Why? Remove the cover from a bottle of the gas, and explain
the result. Insert a stick with a flame into another bottle of the gas, and com-
pare with the action of nitrous oxide. If copper is used, filter the solution
after all copper is dissolved, and evaporate to get blue crystals of copper
nitrate. For explanation of the reaction, see below, under Nitric Acid.

Hyponitrous acid, HNO, or possibly H2N202, is a very unstable white,
flaky solid. Neither the acid, nor its salts, the hyponitrifces, are of practical
interest.

Nitrous acid, HNO2, has not been obtained in a pure state, but
exists in solution. Several of its salts, the nitrites, are well known
and are used analytically and otherwise. Nitrous acid very readily
breaks down into water and its anhydride, N2O3, which escapes as
brown fumes from the solution. Hence, the salts of the acid are
decomposed by nearly all other acids. Nitrous acid acts as an oxid-
izing agent toward some substances, being itself reduced to lower
oxides, and as a reducing agent toward others, being then oxidized to
nitric acid. A solution of nitrous acid in water or other acids has a
pale blue color.

Tests for nitrous acid and nitrites.
(Use about a 5 per cent, solution of sodium or potassium nitrite.)
1. To 5 c.c. of the solution, add a little strong sulphuric acid. Note
the colored fumes and effervescence and the bluish color of the liquid.

174 NON-METALS AND THEIR COMBINATIONS.

2. To the same amount of the solution, add some acidified solution
of potassium permanganate, which is decolorized at once. What
becomes of the nitrite ?

3. Carry out the directions of Test 1, under Hydrogen Dioxide,
using a few drops of the nitrite solution in place of the hydrogen
dioxide. Note that the blue color is not developed until an acid is
added. Only free nitrous acid acts on potassium iodide :

HN02 + HI == H20 + NO + I.
This is a very delicate test, but not decisive alone.

4. Dilute 1 drop of the nitrite solution in half a beakerful of
water, add 1 c.c. of meta-phenylene-diamine reagent (see Nitrous Acid,
under Water Analysis, at end of chapter 38). A yellow to dark
brown color is produced, according to the proportion of nitrite. The
test is used only for very small amounts of nitrite.

Test 1 is usually sufficient to recognize a nitrite.

Nitric acid, Acidum nitricum, HNO3 ; NO2OH, = 62.57 (Aqua
fortis). Nitrogen pentoxide, N2O5, a white, solid, unstable compound,
is of scientific interest only. Whjsn brought in contact with water it
readily combines with it, forming nitric acid :

N2O5 + H20 = 2HNO3.

The usual method for obtaining nitric acid is the decomposition of
sodium nitrate by sulphuric acid :

NaNO3 + H2SO4 == HNO3 + HNaSO4;

Sodium
bisulphate.

or

2NaNO3 + H2SO. = 2HNO3 + Na^SO,.

Sodium
sulphate.

At the present time nitric acid is produced also from the atmosphere by
causing the nitrogen and oxygen to unite under the influence of electric dis-
charges. The nitrogen tetroxide formed, when dissolved in water, gives nitric
acid and nitric oxide :

3N02 + H20 == 2HN03 + NO.

The NO unites with oxygen to give N02, which is again dissolved. The com-
mercial success of this method depends upon the cost of electric power. It is
interesting as offering a source of nitrates when the native supply shall have
been exhausted.

Experiment 10. Prepare an apparatus as shown in Fig. 40. Heat in a retort of
about 250-c.c. capacity a mixture of about 50 grammes of potassium nitrate

NITROGEN. 175

and nearly the same weight of sulphuric acid. Nitric acid is evolved and distils
over into the receiver, which is to be kept cool during the operation by pouring
cold water upon it or by surrounding it with pieces of ice. Examine the
properties of nitric acid thus made, and use it for the tests mentioned below.
How much pure nitric acid can be obtained from 50 grammes of potassium
nitrate? Weigh the acid which you obtain in the experiment and compare
this weight with the theoretical quantity.

Nitric acid is an almost colorless, fuming, corrosive liquid, of
a peculiar, somewhat suffocating odor, and a strongly acid reaction.
When exposed to sunlight it assumes a yellow or yellowish-red
color in consequence of its decomposition into nitrogen tetroxide,
water, and oxygen.

Common nitric acid, of a specific gravity 1.403 at 25° C., is com-
posed of 68 per cent, of HNO3 and 32 per cent, of water. The diluted
nitric acid of the U. S. P. is made by mixing ten parts by weight of
the common acid with fifty-eight parts of water, and contains 10 per
cent, of absolute nitric acid ; it has a specific gravity of 1.054 at
25° C.

Fuming nitric add has a brown-red color, due to nitrogen tetroxide,
and emits vapors of the same color. Specific gravity 1.45 to 1 50.

FIG. 40.

Distillation of nitric acid.

Nitric acid is completely volatilized by heat ; it stains animal matter
distinctly yellow and destroys the tissue ; it is a monobasic acid, form-
ing salts called nitrates. These salts are all soluble in water, for
which reason nitric acid cannot be precipitated by any reagent.

176 NON-METALS AND THEIR COMBINATIONS.

Nitric acid is a strong oxidizing agent ; this means that it is capable
of giving off part of its oxygen to substances having affinity for it.

Nitric acid of 68 per cent, has a constant boiling-point and distils un-
changed. A more concentrated acid decomposes in part when distilled,
2HNO3 = 2NO2 4- H20 + O, while a more dilute acid gives off water at first.
In either case, repeated distillation gives a 68 per cent. acid.

The action of nitric acid upon such metals as copper, silver, and many others
involves two changes, viz. : displacement of the hydrogen of the acid by the

metal :

Cu + 2HNO3 = Cu(NO3)2 + 2H;

and the deoxidation of another portion of nitric acid by the liberated hydrogen
while yet in the nascent state. Thus :

HNO3 + 3H = 2H2O + NO.

The liberated nitrogen dioxide, which is colorless, readily absorbs oxygen
from the air, forming red vapors of nitrogen tetroxide.

Another explanation of the chemical action of nitric acid on metals is based
on our knowledge of the fact that nitric acid readily gives up part of its oxygen
to any substance having affinity for it. Therefore, it majjfce assumed that the
first action of the acid on metals 'is their conversion into oxides, which are
immediately changed into nitrates, thus:

2HN03 + 3Cu = 3CuO + H2O + 2NO.
CuO + 2HNO,= Cu(NO3)2 + H2O.

Tests for nitric acid or nitrates.
(Potassium nitrate, KNO3, may be used as a nitrate )

1. Fairly strong nitric acid with copper turnings gives copious red
fumes. Rather dilute acid, however, has not a very marked action,
even when heated, but the action is increased by the addition of some
concentrated sulphuric acid. A nitrate, dry or in solution, has no
action on copper, but addition of concentrated sulphuric acid (to set
free the nitric acid) causes evolution of red fumes.

2. The solution of a nitrate, to which a few small pieces of ferrous
sulphate have been added, will show a reddish-purple or black color-
ation upon pouring a few drops of strong sulphuric acid down the
side of the test-tube, so that it may form a layer at the bottom of the
tube. The black color is due to the formation of an unstable com-
pound of the composition 2FeSO4.NO. Free nitric acid also re-
sponds to this test, which is delicate and very often used.

3. Nitrates deflagrate when heated on charcoal by means of the
blow-pipe flame. The high temperature causes the nitrate to decom-
pose and liberate oxygen, which unites with the charcoal energetically.

NITROGEN. 177

Such action is called dcf (if/ration. Other oxidizing substances act
like nitrates.

4. When a few drops of a solution of 0.1 gramme of diphenylamine
in ;")() c.c. of 10 per cent, sulphuric acid are added to a very dilute
solution of a nitrate, and then some concentrated sulphuric acid is
carefully poured down the side of the test-tube, a deep blue color is
produced at the line of contact.

A similar reaction is also produced by hypochlorites, chlorates,
chromium trioxide, ferric salts, and similar oxidizing agents.

When the test is made with a similar solution of pyrogallic acid
instead of the diphenylamine solution, a deep brown color is
produced.

The tests with diphenylamine and pyrogallic acid show 1 part of nitric
acid in three and ten million parts of water respectively, and are used chiefly
to detect traces of nitric acid in drinking-water. As sulphuric acid may con-
tain nitric acid, the tests should also be made with the sulphuric acid alone in
order to prove its purity.

Tests 1 and 2 are sufficient to identify nitric acid or its salts. Nitrites also
respond to these tests, but they give red fumes by merely adding a dilute acid,
thus differing from nitrates.

Poisonous properties; antidotes. Strong nitric acid is a corrosive,
violent poison. It first stains the tissues with which it comes in contact a
bright-yellow color, and then corrodes them.

As an antidote in cases of poisoning by nitric acid a solution of sodium car-
bonate, or a mixture of magnesia and water, milk of lime, or other alkalies
well diluted may be administered with the view of neutralizing the acid.

QUESTIONS. — State the physical and chemical properties of nitrogen. Men-
tion the principal constituents of atmospheric air and the quantity in which
they are present. By what processes can the four chief constituents of atmo-
spheric air be determined? Mention some decompositions by which ammonia
is generated. Explain the process of making ammonia water. State the
physical and chemical properties of ammonia gas and ammonia water. How
is nitrogen monoxide obtained, and what are its properties? Describe the
process for making nitric acid, and give symbols for decomposition. How
does nitric acid act on animal matter, and what are its properties generally?
Give tests and antidote for nitric acid.
12

178 NON-METALS AND THEIR COMBINATIONS.

14. CARBON. SILICON. BORON.
O = 12 (11.91). Si* = 28.3. B'» = 10.9.

Occurrence in nature. Carbon is a constituent of all organic
matter. In a pure state it is found crystallized as diamond and
graphite, amorphous in a more or less pure condition in the various
kinds of coal, charcoal, boneblack, lampblack, etc. As carbon
dioxide, carbon is found in the air; as carbonic acid, in water; as
carbonates (marble, limestone, etc.), in the solid portion of our earth.

Properties. The three different allotropic modifications of carbon
differ widely from each other in their physical properties.

Diamond is the purest form of carbon, in which it is crystallized in
regular octahedrons, cubes, or in some figure geometrically connected
with these. Diamond is the hardest substance known ; when heated
intensely in the presence of oxygen it burns, forming carbon dioxide.

Graphite, plumbago, or black-lead, is carbon crystallized in short
six-sided prisms ; it is a somewhat rare, dark-gray mineral, having
an almost metallic lustre. It feels soft and greasy between the fingers
and leaves a black mark when drawn over a white surface. It is
used to make lead pencils, and also as a lubricator, in stove polish,
as an admixture with clay used for crucibles, etc.

Amorphous carbon is always a black solid, but the hardness and
specific gravity of the different kinds of amorphous coal differ widely.
Amorphous carbon in the various kinds of coal is the chief agent for
generating heat by combustion. In the form of lamp-black it is used
in printer's ink ; in bone-black it serves for decolorizing sugar syrups
and other liquids.

Neither form of carbon is soluble in any of the common solvents,
but it dissolves to some extent in melted iron. On cooling, under
ordinary conditions, most of the dissolved carbon separates in the
form of graphite ; when cooling takes place under high pressure
small diamond-like crystals may be obtained. By the intense heat
produced by electricity carbon becomes softened and in small quan-
tities also volatilized.

Carbon is a quadrivalent element ; it has little affinity for metals,
though at high temperatures it combines with many, forming com-
pounds, termed carbides. It does not enter into combination with
oxygen at ordinary temperature, but at red heat it combines eagerly
with free or combined oxygen, serving in many cases as a deoxidizing
agent. Compounds of carbon with other non-metallic elements are
mostly formed by indirect processes.

CARBON, SILICON, BORON. 179

Carbon compounds. The chemistry of the carbon compounds is
very extensive and intricate. There are more compounds containing
carbon than the total of all other compounds, and for good reasons
they are ptudied in a subdivision of chemistry, called Organic Chem-
istry. A few simple compounds are taken up in Inorganic Chem-
istry because of their similarity in properties to the other inorganic
compounds. These are the two oxides of carbon, the carbonates,
carbon disulphide, and sometimes the cyanides and sulphocyanates.

Nearly all animal and vegetable substances contain carbon, and
when heated they usually undergo decomposition and char, that is,
leave a residue of black carbon. This is because the other elements
go off first in various combinations, while carbon remains last. But
some of the carbon also passes off as volatile products. If the heat
is high enough and air has access, the carbon finally disappears or, as
is said, the substance burns up. Carbon compounds that are volatile
when heated do not char. For example, alcohol, ether, chloroform,
and many others simply vaporize when heated, although they contain
carbon. Carbon may be shown to be present in such compounds by
burning them in the air (when combustible) under a funnel and draw-
ing the products through lime-water, or by causing the vapors to come
in contact with copper oxide heated to redness in a tube and passing
the products through lime-water. When carbon compounds are
burned up, either in air or by oxidizing agents, as copper oxide, the
carbon passes off as gaseous carbon dioxide, CO2, which unites with
lime-water to form insoluble white calcium carbonate. In fact, this
is the only common gas which acts in this way with lime-water.

When carbon compounds containing non-volatile metals are
charred, the metals remain as carbonates or oxides mixed with the
residue of carbon. Many carbon compounds char when heated with
concentrated sulphuric acid because the acid extracts hydrogen and
oxygen in the proportions to form water, for which it has a powerful
affinity, thus leaving a residue of carbon.

Experiment 11. a. Heat a little starch on charcoal with the blow-pipe
flame. Note that it blackens and burns up completely.

6. Heat a small knifepointful of sugar in a dry test-tube, gradually increas-
ing the temperature. Note the melting, browning condensation of water on
the walls of the tube, odor, and final charring.

c. Heat gradually a little Eochelle salt (K.Na.C4H4O6) in a porcelain cru-
cible held in a triangle. The salt melts, effervesces, evolves inflammable
vapors, and chars. Heat finally to redness, cool, and add some dilute acid.
Any effervescence ? Explain. Make the same experiment with tartaric acid.
Note any difference in results. Note also the odor while heating.

180 NON-METALS AND THEIR COMBINATIONS.

d. Insert a burning stick of wood into a pint bottle or flask, mouth down,
until flame is extinguished ; then remove the stick (is it charred?), pour into
the bottle about 50 c.c. of lime-water and shake it. Explain results.

e. Heat slowly about 2 c.c. concentrated sulphuric acid in a dry test-tube with
a bit of starch, sugar, Rochelle salt, and wood respectively. Describe and
explain the results.

Carbon dioxide, CO2. (Formerly named carbonic acid, or anhy-
drous carbonic acid.) This compound is always formed during the
combustion of carbon or of organic matter ; also during the decay
(slow combustion), fermentation, and putrefaction (process of decom-
position) of organic matter; it is constantly produced in the animal
system, exhaled from the lungs, and given off through the skin.

Many spring waters contain considerable quantities of the gas, a
part of which escapes from the water as it rises to the surface.

By heating, many carbonates are decomposed into oxides of the
metals and carbon dioxide.

Lime-burning is such a process of decomposition :

CaCO3 = CaO -f CO2.
Calcium Calcium
carbonate, oxide.

Another method for the generation of carbon dioxide is the decom-
position of any carbonate by an acid :

CaCO3 + 2HC1 = CaCl2 + H2O + CO2.
Calcium Hydrochloric Calcium
carbonate. acid. chloride.

The reason the action takes place readily and proceeds to completion
is because carbonic acid is only slightly soluble in water and easily
breaks up into water and carbon dioxide gas, which escapes and is
removed from the field of action, thus permitting the decomposition
to be constantly renewed. Almost any acid will liberate carbon di-
oxide from a carbonate. The same principle is involved here as in
the case of the liberation of nitrous acid from nitrites, nitric acid
from nitrates, sulphurous acid from sulphites, or hydrochloric acid
from chlorides. (See Reversible Actions, p. 114.)

Experiment 12. Use apparatus represented in Fig. 38, page 146. Place about
20 grammes of marble, CaCO3, in small pieces (sodium carbonate or any other
carbonate may be used) in the flask, cover it with water, and add hydrochloric
acid through the funnel-tube. The escaping gas may be collected over water,
as in the case of hydrogen, or by downward displacement, i. e., by passing the
delivery-tube to the bottom of a tube or other suitable vessel, when the carbon
dioxide, on account of its being heavier than atmospheric air, gradually dis-
places the latter. This will be shown by examining the contents of the vessel
with a burning taper, which is extinguished as soon as most of the air has
been expelled.

CARBON, SILICON, BO RON. 181

Examine the gas for its high specific gravity by pouring it from one vessel
into another ; for its power of extinguishing flames, by mixing it with an equal
volume of air, which mixture will be found not to support the combustion of
a taper notwithstanding that oxygen is contained in it. Add to one portion of
the collected gas some lime-water, shake it, and notice that it becomes turbid.
Blow air exhaled from the lungs through a glass tube into lime-water, and
notice that it also turns turbid.

Continue to pass the gas through the turbid liquid, and notice that it becomes
clear in consequence of the dissolving action of carbonic acid water on calcium
carbonate. On heating the solution carbon dioxide is expelled and calcium
carbonate is reprecipitated. (So-called " hard " waters often contain calcium
carbonate dissolved by carbonic acid. On heating these hard waters they
become "soft," because the dissolved carbonate is precipitated.)

If marble has been used for the experiment, neutralize the liquid in the flask,
if acid, by adding more marble until action ceases, filter, and evaporate it in a
dish to dry ness. The solid residue is a salt, calcium chloride. Expose some
of it to the air for a long time and note that it absorbs moisture or deliquesces.
What method of salt formation is illustrated by this experiment?

If sodium carbonate has been used, neutralize the liquid by adding acid
or carbonate, as may be required, filter, and evaporate it to dryness. Taste
the residue. What is it ? Taste also sodium carbonate and the acid.

Carbon dioxide is a colorless, odorless gas, having a faintly acid
taste. By a pressure of 38 atmospheres, at a temperature of 0° C.
(32° F.), carbon dioxide is converted into a colorless liquid, which by
intense cold ( — 79° C., — 110° F.) may be converted into a white,
solid, crystalline, snow-like substance. The specific gravity of carbon
dioxide is 1.529 ; it is consequently about one-half heavier than
atmospheric air. One liter at 0° C. and 760 mm. pressure weighs
1.977 grammes.

Cold water absorbs at the ordinary pressure about its own volume
of carbon dioxide, but the solubility is increased one volume for every
increase of one atmosphere in pressure (soda water).

Carbon dioxide is not combustible, and not a supporter of combus-
tion ; on the contrary, it has a decided tendency to extinguish flames,
air containing one-tenth of its volume of carbon dioxide being unable
to support the combustion of a candle. While not poisonous when
taken into the stomach, carbon dioxide acts indirectly as a poison
when inhaled, because it cannot support respiration, and prevents,
moreover, the proper exchange between the carbon dioxide of the
blood and the oxygen of the atmospheric air.

Common atmospheric air contains about 4 volumes of carbon
dioxide in 10,000 of air, or 0.04 per cent. In the process of respira-
tion this air is inhaled, and a portion of the oxygen is absorbed in
the lungs by the blood, which conveys it to the different portions of the

182 NON-METALS AND THEIR COMBINATIONS.

animal body, and receives in exchange for the oxygen a quantity of
carbon dioxide, produced by the union of a former supply of oxygen
with the carbon of the different organs to which the blood is supplied.
The air issuing from the lungs contains this carbon dioxide, in
quantity about 4 volumes in 100 of exhaled air, which is 100 times
more than contained in fresh air.

Exhaled air is, moreover, contaminated by other substances than carbon
dioxide, such as ammonia, hydrocarbons, and most likely traces of other or-
ganic bodies, the true nature of which has not been fully recognized, but which
seem to be directly poisonous. The bad effects experienced in breathing air
which has become contaminated by the exhalations from the lungs, are most
likely due to these unknown bodies. As we have as yet no methods of ascer-
taining the quantity of these poisonous substances present in exhaled air, the
determination of the amount of exhaled carbon dioxide present must serve as
an indicator of the fitness of an air for breathing purposes. As a general rule,
it may be stated that it is not advisable to breathe, for any length of time, air
containing more than 0.1 per cent, of exhaled carbon dioxide; in air contain-
ing 0.5 per cent, most persons are attacked by headache, still larger quantities
produce insensibility, and air containing 8 per cent, of carbon dioxide causes
death in a few minutes.

As exhaled air contains from 3.5 to 4 per cent, of carbon dioxide, it is unfit
to be breathed again.. The total amount of carbon dioxide evolved by the
lungs and skin of a grown person amounts to about 0.7 cubic foot per hour.
Hence the necessity for a constant supply of fresh air by ventilation. This
becomes the more necessary where an additional quantity of carbon dioxide is
supplied by illuminating flames.

Mentioned above are many processes by which carbon dioxide is
constantly produced in nature, and we might assume that the amount
of 0.04 per cent, of carbon dioxide contained in atmospheric air
would gradually increase. This, however, is not the case, because
plants, and more especially all their green parts, are capable of ab-
sorbing carbon dioxide from the air, while at the same time they
liberate oxygen.

This process of vegetable respiration (if we may so call it), which
takes place under the influence of sunlight, is, consequently, the
reverse of that of animal respiration. The animal uses oxygen and
liberates carbon dioxide ; the plant consumes this carbon dioxide and
liberates oxygen.

Carbon dioxide is an acid oxide, which combines with water, form-
ing carbonic acid :

CO2 + H2O = H2CO3.

Carbonic acid, H2CO3, CO(OH)2> is not known in a pure state, but
always diluted with much water, as in all the different natural waters.

CARBON, SILICON, BORON. 183

Carbonic acid is a dibasic, extremely weak acid, the salts of which are
known as carbonates. Many of these carbonates (calcium carbonate,
for instance) are abundantly found in nature. Only the alkali car-
bonates and bicarbonates are soluble in water. Acid carbonates of
some other metals, such as magnesium, calcium, zinc, iron, are also
slightly soluble in water, but these do not exist in the dry state. The
bicarbonates when heated to about 100° C. give up carbon dioxide
and form carbonates :

2NaHCO3 = Na2CO3 -f H2O -f CO^
At high temperatures only alkali carbonates are not decomposed.

Tests. Since nearly all carbonates are insoluble in water, these
are formed as precipitates whenever a solution of an alkali carbonate
(those of potassium, sodium, or ammonium) is added to a solution of
a salt of any other metal. This is a corroborative test for a soluble
carbonate, but the best and decisive test for all carbonates and car-
bonic acid is found in Experiment 12, namely, the liberation of
carbon dioxide and its action on lime-water.

Carbon monoxide, carbonic oxide, CO. While carbon, as a
general rule, is quadrivalent, in this compound it exerts a valence of
2. Carbon monoxide is a colorless, odorless, tasteless, neutral gas,
almost insoluble in water ; it burns with a pale-blue flame, forming
carbon dioxide ; it is very poisonous when inhaled, forming with the
coloring matter of the blood a compound which prevents the absorp-
tion of oxygen. Carbon monoxide is formed when carbon dioxide is
passed over red-hot coal :

C02 + C = 2CO.

The conditions necessary for the formation of carbon monoxide are,
consequently, present in any stove or furnace where coal burns with
an insufficient supply of air. The carbon dioxide formed in the lower
parts of the furnace is decomposed by the coal above. The blue
flames frequently playing over a coal fire are burning carbon mon-
oxide. This gas is formed also by the decomposition of oxalic acid
(and many other organic substances) by sulphuric acid :
H2C2O4 + H2SO4 = H2SO,.H2O + CO2 + CO.

Oxalic Sulphuric

acid. acid.

Carbon monoxide is now manufactured on a large scale by causing the de-
composition of steam by coal heated to red heat. The decomposition takes

place thus:

H20 + C == 2H + CO.

184 NON-METALS AND THEIR COMBINATIONS.

The gas mixture thus obtained, known as water-gas, may be used for heating
purposes directly, but has to be mixed with hydrocarbons when used as an
illuminating agent, for reasons which will be pointed out below when consider-
ing the nature of flames.

Carbonyl chloride, COC12. This is formed when a mixture of carbon
monoxide and chlorine is exposed to sunlight, and, hence, is also known as
phosgene. Commercially it is made by passing a mixture of the two gases over
animal charcoal, which acts as a catalytic agent. Carbonyl chloride is gas-
eous above 8° C., has a suffocating odor, and dissolves readily in benzene.
Water decomposes it at once into carbonic and hydrochloric acids, COC12 +
2H2O = H2C03 H- 2HC1. It is used in making certain synthetic organic
compounds..

Compounds of carbon and hydrogen. There are no other two
elements which are capable of forming so large a number of different
combinations as are carbon and hydrogen. Several hundred of these
hydrocarbons are known, and their consideration belongs to the
domain of organic chemistry.

Two of these hydrocarbons, however, may be briefly mentioned,
as they are of importance in the consideration of common flames.
These compounds are: methane (marsh-gas, fire-damp), CH4; and
efhene (olefiant gas), C2H4.

Both compounds are colorless, almost odorless gases, and both are
products of the destructive distillation of organic substances. De-
structive distillation is the heating of non-volatile organic substances
in such a manner that the oxygen of the atmospheric air has no access,
and to such an extent that the molecules of the organic matter are
split up into simpler compounds. Among the gaseous products
formed by this operation, more or less of the two hydrocarbons
mentioned above is found.

Marsh-gas is formed frequently by the decomposition of organic
matter in the presence of moisture (leaves, etc., in swamps) ; and dur-
ing the formation of coal in the interior of the earth the gas often
gives rise to explosion in coal mines. During these explosions of the
methane (mixed with air and other gases), called fire-damp by the
miners, carbon is converted into carbon dioxide, which the miners
speak of as choke-damp, or after-damp.

Flame is gas in the act of combustion. Of combustible gases,
have been mentioned : hydrogen, carbon monoxide, marsh-gas, and
olefiant gas. These four gases are actually those which are found
chiefly in any of the common flames produced by the combustion o?
organic matter, such as paper, wood, oil, wax, or illuminating gas itself

These gases are generated by destructive distillation, the heat being

CARBON, SILICON, BORON.

185

supplied either by a separate process (manufacture of illuminating
gas by heating wood or coal in retorts), or generated during the
combustion itself.

In burning a candle, for instance, fat is constantly decomposed by
the heat of the flame itself, the generated gases burning continuously
until all fat has been decomposed, and the products of decomposition
have been burned up, i. e., have been converted into carbon dioxide
and water.

An ordinary flame (Fig. 41) consists of three parts or cones. The
inner portion is chiefly unburnt gas ; the second is formed of partially
burnt and burning gas ; the outer cone, showing scarcely any light, is
that part of the flame where complete combustion takes place. The
highest temperature is found between the second and third cone.

The light of a flame is caused by solid particles of carbon heated
to a white heat. The changes that take place in a flame are difficult
to study, but sufficient has been done experimentally to permit the
conclusion to be drawn that the separation of carbon in a flame is due
to dissociation of some of the hydrocarbons, of which ethylene
(ethene) is the most important. It is well known that when ethylene
(C2H4) is heated it yields acetylene (C2H2), which in turn gives carbon
and hydrogen. Evidence that acetylene is present in a gas flame is
furnished by the fact that when a Bunsen flame " strikes
back," that is, burns at the base of the tube so that
incomplete combustion of the gases takes place, a large
quantity of acetylene is formed.

If a sufficient amount of air be previously mixed with
the illuminating gas, as is done in the Bunsen burner, no
separation of carbon takes place, and, therefore, no light
is produced, but a more intense heat is generated. A
similar effect is produced by the aid of the blow-pipe or
by means of the blast lamp, which serve to direct a cur-
rent of air directly into the cone of the flame. The
luminous and non-luminous Bunsen flame, using the
same flow of gas, must produce the same amount of heat
for a definite amount of gas burned, since the end-
products of combustion are the same in both cases.
But the non-luminous flame is much shorter than the
luminous one, and thus the heat is concentrated within a smaller
space, and, therefore, the temperature is much higher than in the
luminous flame.
* The cause of non-luminosity of a flame when air or oxygen is

FIG. 41.

Structure of
flame.

186 NON-METALS AND THEIR COMBINATIONS.

admitted into the interior, as in a Bunsen burner, is difficult to explain.
That it is due to other causes than the presence of the oxygen is shown
bv the fact that nitrogen or carbon dioxide will also destroy luminosity.
The introduction of cold gases into a flame lowers the temperature of
the inner cone, where the dissociation of ethylene takes place. It
seems probable that this lowering of temperature and dilution of the
gases diminish the decomposition of ethylene to such an extent that
not enough carbon is separated to give luminosity.

Silicon or Silicium, Si = 28.3, is found in nature very abundantly as
silicon dioxide, or silica, SiO2 (rock-crystal, quartz, agate, sand), and in the
form of silicates, which are silicic acid in which the hydrogen has been replaced
by metals. Most of our common rocks, such as granite, porphyry, basalt,
feldspar, mica, etc., are such silicates or a mixture of them. Small quantities
of silica are found in spring- waters, as well as in vegetable and animal matters.

Silicon resembles carbon both in its physical and chemical properties. Like
carbon, it is known in the amorphous state, and forms two kinds of crystals,
which resemble graphite and diamond. Like carbon, silicon is quadrivalent,
forming silicon dioxide, Si02, silicic acid, H.2SiO3, silicon hydride, SiH4, silicon
chloride, SiCl4, which compounds are analogous to the corresponding carbon
compounds, C02, H2CO3, CH4, and CC14.

The compounds formed by the union of silicon with hydrogen, chlorine, and
fluorine are gases. The latter compound, silicon fluoride, SiF4, is obtained by
the action of hydrofluoric acid on silica or silicates, thus :

Si03 -f 4HF = SiF4 -f 2H2O.

This reaction is used in the analysis of silicates, which are decomposed and
rendered soluble by the action of hydrofluoric acid.

Silicon fluoride is decomposed by water into silicic acid and hydrofluosilicic
acid, H2SiF6, thus :

3SiF4 + 3H2O = H2Si03 + 2H2SiF6.

Several varieties of silicic acid are known, of which may be mentioned the
normal silicic acid, H4SiO4, and the ordinary silicic acid, H2SiO3, from the latter
of which, by heating, water may be expelled, when silicon dioxide, SiO2, is left.

Tests for silicic acid and silicates.

(Soluble glass or flint may be used.)

1. Silicic acid and most silicates are insoluble in water and acids. By fusing
silicates with about 5 parts of a mixture of the carbonates of sodium and potas-
sium the silicates of these metals (known as soluble glass) are formed. By
dissolving this salt in water and acidifying the solution with hydrochloric acid
a portion of the silica separates as the gelatinous hydroxide.

Complete separation of the silica is accomplished by evaporating the mixt-
ure to complete dryness over a water-bath, and re-dissolving the chlorides of
the metals in water acidulated with hydrochloric acid ; silica remains undis-
solved as a white amorphous powder.

2. Silica or silicates when added to a bead of microcosmic salt (see index)
form on heating before the blowpipe the so-called silica-skeleton.

Silicon carbide, SiO. (Carborundum, Carbon silicide). This compound

CARBON, SILICON, BORON. 187

furnishes a typical illustration of the possibilities of the electric furnace for
manufacturing purposes. Figs. 32 and 33, page 81, give a sectional and an
exterior view of the furnace used. The current enters and leaves the furnace
through cables terminating in carbon electrodes fastened in the wall. Between
them is placed a core of coke, surrounded by a mixture of carbon, sand, and
salt. The current heats the mass to about 3500° C. (6332° F.), when the
carbon combines with both elements of the sand, thus:

Si02 + 3C = 2CO + SiC.

Carborundum forms beautiful, dark-green, iridescent crystals of extreme hard-
ness, in the latter quality being exceeded only by the diamond. It is extensively
used as a polishing agent, gradually replacing emery, to which it is far superior.

Boron, B'" = 10.9, is found in but few localities, either as boric
(boracic) acid or sodium borate (borax). Formerly the total supply
of boron was derived from Italy : large quantities of borax are now
obtained from Nevada and California.

Boron exists as a greenish -brown amorphous powder and also in the form
of hard and often highly lustrous crystals. Boron combines with many of the
non-metals, forming such compounds as boron trichloride, BC13, trifluoride,
BF3, and hydride, BH3. It is one of the few elements which at a high tempera-
ture combine directly with nitrogen, forming nitrogen boride, BN.

Boric acid, Acidum boricum, H3BO3, B(OH)3 = 61.54 (Boracic
acid), is a white, crystalline substance, which is sparingly soluble in
cold water or alcohol, but more soluble in glycerin ; it has but weak
acid properties. When heated to 100° C. (212° F.) it loses water,
and is converted into mdaboric acid, HBO2, which when heated to
160° C. is converted into tetraboric acid, H2B4O7, from which borax,
Na2B4O7 -f 10H2O, is derived. At a white heat boric acid loses all
water, and is converted into boron trioxide, B2O3. From a boiling
solution boric acid readily volatilizes with the steam.

Boric acid is obtained by adding hydrochloric acid to a hot satur-
ated solution of borax, when boric acid separates on cooling. The
chemical change is this :

7 + 2HC1 + 5H2O = 4H3B03 + 2NaCl.

It is rather odd that while the usual form of boric acid in the uncombined
state is the orthoboric acid, H3BO3, salts of this form are hardly known. Salts
of metaboric acid occur, but the best-known salts are derived from tetraboric
acid, and the best representative is the sodium salt, borax. On the other hand,
when the acid is liberated from the salts, it assumes the ortho form. From the
formula of tetraboric acid, it appears that four molecules of the ortho acid com-
bine with elimination of water to form a more complex molecule :

4H3B03 H2B407 + 5H20.

There are other cases of this kind, as will be seen later.

188 NON-METALS AND THEIR COMBINATIONS.

Borax may be looked upon as containing sodium metaborate and boric
oxide, 2NaBO2 + B,O3. When it is heated with basic oxides, these unite with
the excess of B2O3> forming a fused mixed metaborate. This action explains
the use of borax on hot metal surfaces which are to be welded. Some of these
metaborates have distinctive colors. For this reason borax beads are used as
tests for certain metals (see under Sodium Borate).

Boric acid is such a weak acid that its solution has only a slight action on
litmus-paper, and it is displaced from its salts by nearly every other acid. The
borates of the alkali metals only are easily soluble in water, the others being
either insoluble or nearly so. Hence, when a solution of an alkali borate (but
not of free boric acid) is added to a solution of a saltof other metals, a precipitate
is obtained. Alkali borates show a strong alkaline reaction to litmus because
they are partly hydrolyzed in solution to free alkali and boric acid. It will be
?een that boric acid is very much like carbonic acid in behavior.

Boric acid and borax are practically the only compounds of boron that are
used. Both are used in medicine and as preservatives. When powdered they
look much alike, but can be distinguished by the fact that the acid is soluble
in alcohol while borax is not, and that borax has a marked alkaline reaction to
litmus, and when held in a Bunsen flame on platinum wire gives a yellow color,
while free boric acid gives a green color.

Tests for boric acid and borates.

1. When borax is heated on the loop of a platinum wire in a Bunsen
flame it first puffs up very much, and then gradually melts into a
transparent, colorless bead. If the bead is moistened with concen-
trated sulphuric acid and heated again, a green color is produced.
Boric acid also melts into a colorless bead. Note any difference in
color of the flame.

2. Mix in a porcelain dish some borax with 2 c.c. of concentrated
sulphuric acid, add about 10 c.c. of alcohol, and ignite. The flame
has a mantle of green color, which is best seen by alternately extin-
guishing and relighting the alcohol. Eepeat the experiment, omitting
the acid ; no green color is seen. Free boric acid is volatilized with
alcohol, but not its salts.

QUESTIONS.— How is carbon found in nature? State the physical and
chemical properties of carbon in its three allotropic modifications. Mention
three different processes by which carbon dioxide is generated in nature, and
some processes by which it is generated by artificial means. State the physical
and chemical properties of carbon dioxide. Explain the process of respiration
from a chemical point of view. What is the percentage of carbon dioxide in
atmospheric air, and why does its amount not increase ? State the composition
of carbonic acid and of a carbonate. How can they be recognized by analyt-
ical methods? Under what circumstances will carbon monoxide form, and
how does it act when inhaled? What is destructive distillation, and what
gases are generally formed during that process? Explain the structure and
luminosity of flames.

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 189

3. A solution of boric acid, or of a boratc acidulated with dilute
hydrochloric acid, colors a strip of t turmeric paper dark red, which
becomes more intense on drying. The color is changed to bluish black
by dilute ammonia water.

Sodium perborate, NaBO.5.4H.2O. When a mixture of 248 grammes of
boric acid and 78 grammes of sodium peroxide is gradually added to 2 liters of
cold water a crystallized compound is obtained. When the latter in solution is
treated with the proper proportion of an acid, sodium perborate separates. It
is very stable when dry, but in solution it has all the properties of a solution of
hydrogen dioxide. It is a good antiseptic and deodorant, and may be applied
as a dusting-powder or in solution.

15. THEORY OF ELECTROLYTIC DISSOCIATION, OR IONIZATION.
ELECTROLYSIS. DISSOCIATION THEORY APPLIED TO ACIDS,
BASES, SALTS, AND NEUTRALIZATION.

Theory of Electrolytic Dissociation.

It was observed long ago tbat aqueous solutions of certain kinds
of substances, of which cane-sugar is a good type, do not conduct an
electric current, while aqueous solutions of other substances, of which
common salt or hydrochloric acid is a good example, are excellent
conductors of electricity. Moreover, it was also observed that sub-
stances which conduct electricity in aqueous solution do not conduct
when they are dissolved in certain solvents, like benzene, ether, chlo-
roform, etc. This fact evidently points to the conclusion that water
has some peculiar action on some substances whereby they become
possessed of the power to conduct a current. The same kind of
effect is also noticed in regard to chemical behavior. For example,
dry hydrochloric acid gas dissolved in dry benzene neither conducts
electricity nor has an acid reaction on litmus, nor appreciably acts
on zinc, whereas an aqueous solution of the gas conducts well, has a
marked acid reaction on litmus, and attacks zinc vigorously. It appears,
therefore, that hydrochloric acid molecules in aqueous solution must
be in a state different from that when they are dissolved in benzene.
It should be noted that pure water itself is not a conductor, nor are
the other substances when dry, but their solutions in water conduct.
There are a few other liquids which show this property, but to a far
less extent than water does, to which this discussion will be confined.

Substances whose aqueous solutions conduct electricity are known
as electrolytes, those whose solutions do not are called non-electrolytes.
It is found experimentally that acids, bases, and salts are electrolytes,
and it is precisely these substances whose aqueous solutions show

190 NON-METALS AND THEIR COMBINATIONS.

abnormally large values of freezing-point depressions, boiling-point
elevations, and osmotic pressures. In the discussion of the latter
subjects (which see) it is pointed out that the abnormally acting sub-
stances behave as if there are more particles in solution than the
number of molecules corresponding to the weights of the substances
dissolved, which fact can be accounted for only on the supposition
that some molecules are decomposed by the solvent into smaller par-
ticles. Further, since molecules which, like those of sugar, act nor-
mally in regard to freezing-point, boiling-point, and osmotic pressure
phenomena, and thus show no indication of decomposition by the
solvent, do not conduct electricity, it follows that the fragments of
decomposed molecules must be responsible for the ability to conduct
in the case of solutions of electrolytes. In electrolysis (see page 82)
these fragments are the particles that are attracted to the charged
poles, hence the further assumption is made that the fragments (or
ions as they are called) are themselves charged with electricity, be-
cause it is known that electricity attracts only bodies that possess a
charge of electricity. Briefly summed up, then, the THEORY OF
ELECTROLYTIC DISSOCIATION assumes that molecules of electrolytes
when dissolved in water break up to a varying degree into independent
particles charged with electricity, and that the nature and number of
these charged particles determine to a large degree certain physical and
chemical properties of solutions.

This theory was proposed by the Swedish physicist Arrhenius in
lSS7 • its general adoption has been hastened by the work of van't
Hoff, Ostwald, and Nernst.

The dissociation of molecules in solution is also called IONIZATION,
and the electrically charged particles are called ions. These are al-
ways of two kinds, namely, electro-positive ions, or cations, because
they are attracted to the negative pole or cathode during electrolysis,
and electro-negative ions, or anions, because they are attracted to the
positive pole or anode. Since solutions are themselves electrically
neutral, that is, show no charge of electricity as a whole, it follows
that the sum of the electric charges of the positive ions equals the
sum of the charges of the negative ions. The two kinds of ions are
in electrical balance.

Composition of ions. This is learned from a study of the pro-
ducts that are attracted to the anode and cathode, respectively, in
electrolysis, and from the manner in which molecules of electrolytes
exchange their parts or radicals in chemical actions. In molecules

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 191

of acids hydrogen is readily separated in chemical actions from the
rest of the molecule, which is a radical, consisting of a non-metallic
element, or a group of atoms acting as a unit and remaining intact.
In electrolysis, division occurs in the same manner, hydrogen sepa-
rating at the cathode, and acid radical being attracted to the anode.
Salts behave in the same manner as acids in regard to the division
of the molecules, which is only what we should expect, since they
are so closely related to acids. Indeed, some chemists put both in
the same class, regarding acids as salts of hydrogen. Bases in chemical
action and in electrolysis show a division between the metal and
the hydroxyl (OH) radical, the metal going to the cathode, and the
hydroxyl radical to the anode. It appears, then, from the side of
chemical action as well as that of electrolysis that an aqueous solution
of an acid contains positive hydrogen ions and negative acid radical
ions; a solution of a salt contains positive ions of a metal and negative
acid radical ions; and a solution of a base contains positive ions of a
metal and negative hydroxyl ions.

Ions and atoms not the same. The student should note partic-
ularly that a substance in the ionic state is quite different from the
substance in the free state. Simple ions are atoms plus a charge of
electricity, while atoms of free elements are not charged, and this
difference is sufficient to account for the difference of behavior.
Thus, when sodium chloride (NaCl) is dissolved in water, many of
the molecules break up into Na-ions and Cl-ions, but there is tio
chemical action between the water and Na-ions or Cl-ions, whereas
sodium in the free state acts violently on water, and chlorine dissolves
in water with some chemical action and imparts its odor and bleach-
ing properties to the water. A solution of sodium chloride has no
odor or bleaching action.

Symbols representing- ions. Ions are represented by the usual
chemical symbols, with the addition of marks to indicate positive and
negative charges. Thus, Na+, or Na', stands for a positively charged
sodium ion, and Cl~, or Cl', stands for a negatively charged ion of
chlorine. Quantitative experiments in electrolysis show that the
amounts of electricity possessed by ions is proportional to the valence
of the atoms or radicals constituting the ions. If the charge on a
sodium or on a chlorine ion is taken as the unit charge, then the
charge on an ion of a bivalent atom or radical is two units, and is
represented thus, Ca++, or Ca", and SO7~, or SO/'. The ion of
trivalent aluminum is written Al+++, or Al" ', etc.

192 NON-METALS AND THEIR COMBINATIONS.

Ionic equilibrium. The dissociation of molecules into ions must
be considered as a species of chemical change, and, like many others,
it is a reversible action (see page 114). In ordinary dilute solutions
there is always a certain proportion of undissociated molecules which
are in equilibrium with the ions. The degree of dissociation varies
with the concentration of the solution, and of course with the nature
of the dissolved substance, since for the same concentration different
substances vary widely in the amount of dissociation. If the solution
is made more concentrated, as by evaporation, more and more of the
ions unite to form molecules, until finally, when all the solvent is
removed, the dry substance is left entirely in the molecular state. On
the other hand, diluting a solution results in more molecules being
dissociated. Many substances in highly diluted solutions are almost
completely dissociated. The reversible character of dissociation is
represented by reversible ionic equations thus :

HC1 ^ H- -f Cl' ; NaCl ;± Na' + Cl' ; NaOH ;± Na' -f (OH)'.

The first equation means that in any given solution of hydrochloric
acid there is a certain proportion of molecules and a certain propor-
tion of ions. The molecules tend to form ions, but only as fast as
the ions tend to revert to the molecular state, so that an equilibrium
is maintained. By changing the conditions, ions may be forced to
unite to form molecules, or vice versa. In other words, the equilib-
rium may be displaced forward or backward. Likewise for the other
two equations dealing with sodium chloride and sodium hydroxide
respectively.

Theoretical deductions, as well as experimental results, show that
in varying solutions of the same substance there is a constant rela-
tionship, which is expressed thus : The product of the concentration of
the ions divided by the concentration of the undissociated molecules is a
constant quantity (or nearly so in some cases), expressed by a numeral,
and called the IONIZATION CONSTANT. The concentration is ex-
pressed in terms of the number of molecular weights or ion weights
in grammes in a liter of solution. A solution containing one molec-
ular weight or ion weight per liter is taken as unit concentration.

Effect of ionic equilibrium in chemical reactions. Some fa-
miliar results. If in any manner, as by precipitation, one kind of
the ions of a substance is removed from solution, some molecules of
the substance are dissociated to replace the kind of ions removed,
until the balance between ions and molecules, as indicated in the
lonization constant, is restored. This process may go on until all the

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 193

molecules are dissociated. Conversely, if the concentration of one
kind of ion is increased, as by the addition of a substance giving the
same kind of ion — for example, addition of hydrochloric acid to a

solution of sodium chloride (both having a common ion, Cl') the

result is a reunion of some of the ions of the original substance to
form molecules, until the balance between its molecules and all of the
ions of the kinds that it gives satisfies the demands of the ionization
constant. If the solution is saturated in the beginning, and there-
fore contains all the undissociated molecules that it can hold, the for-
mation of an additional number of molecules by union of ions gives
rise to supersaturation and precipitation of some of the substance.
Thus, the addition of hydrochloric acid gas to a saturated solution of
common salt causes a copious precipitate of the salt. Likewise, addi-
tion of some saturated solution of the very soluble sodium chlorate
to one of the less soluble potassium chlorate causes precipitation of
some of the latter salt. The reason the sodium chlorate is not also
reciprocally precipitated is that the additional molecules formed by
union of its ions, Na" and CIO/, are not sufficient to supersaturate the
volume of liquid through which the sodium chlorate is distributed.
The principle just discussed furnishes an explanation of the fact that
is often observed in practical work ; namely, that many substances
are much less soluble in solutions of other substances of similar com-
position than in pure water.

In the case of a solution of a slightly dissociating substance, the
addition of another substance having a common ion with the first
may so far cause a reversal of dissociation of the first substance that
practically only its undissociated molecules exist in the solution, with
an accompanying loss of some of its properties. Thus, in a solution
containing per liter the molecular weight of sodium acetate and the
molecular weight of acetic acid, the latter no longer is able to affect
the indicator methyl-orange, because there are too few hydrogen ions
of the acid left in solution.

Precipitation. When molecules of a substance are dissolved, some
dissociate until a balance is established between ions and molecules, as
represented by the ionization constant. Conversely, when there are
present in a solution two substances which between them produce ions
corresponding to a third substance, some molecules of the third sub-
stance are formed up to the point that corresponds to its ionization
constant. The following ionic equations for a mixture of potassium
chloride and sodium nitrate in solution will illustrate :

13

194 NON-METALS AND THEIR COMBINATIONS.

KC1 ^K- +Cl'j Xaa
NaN03 ^ N0'3 + Na- J

It
KN03

Evidently molecules of four products will be present in this mixture,
and likewise in all similar ones. If all the products are readily solu-
ble and of large dissociating power, and the solution is rather dilute,
there are few undissociated molecules present. The mixture then is
practically a mixture of ions, and nothing can be observed by the
eye to have taken place. But if one of the new products is " insolu-
ble" in water, there are more of its ions present than can be main-
tained in a saturated solution of the same, the excess of ions unite to
form molecules, and the excess of molecules are removed by precipi-
tation. In this way one factor in the equilibrium is removed and the
action runs to completion. This principle is at the basis of all cases
of precipitation in chemical reactions. The precipitation of silver
chloride is a good example, and is represented thus :

It

NaN03 soluble.

A simple equation, in which only the ions are represented, may be
used :

Ag- + NOS' + Na- + Cl' = AgCl 4- Na' 4- NO3'.

The simplest equation of all is one which shows only those ions that
are actually involved in the precipitation, thus :

Ag- 4- Cl' = AgCl.

Reasoning parallel to the above may be applied when one of the
new products formed is a gas with slight solubility in water at ordi-
nary or higher temperatures, or a liquid which is volatile at elevated
temperature. In either case, the new product is removed as fast as
it is formed and the action runs to completion. In the liberation of
ammonia, the ionic equations are :

2XH4C1 ^± 2C1' 4- 2NH4- 1 _

Ca(OH)2 ;± Ca- • 4- 2(OHV / *~ 2^^*^H = 2H2O 4- 2NH3 (gas) undissociated.

It.
CaCl2 soluble.

Or, more simply,

Ca- • 4- 2(OH)' 4- 2NH4- 4- 2C1' == Ca' • +2C1' 4- 2NH4OH.

Ammonium hydroxide is only slightly ionized, and by heating is
easily broken up and driven out of solution as ammonia*gas.

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 195

For the liberation of carbon-dioxide gas the representation is this :

Na2C03 ^± 2Na' + CO/ ' ) ^ „ rn „

H2S04 ^S04" + 2H- /-H2C°3=H20 + C02(gas).

I t
Na2SO4 soluble.

Or simply

2Na- + CO/ ' + 2H- + SO/ ' = 2Na' + SO/ ' + H2CO3.

Carbonic acid is only slightly ionized and very little soluble. Hence
it escapes as fast as it is liberated. This description will serve also
for the liberation of nitrous acid from nitrites.
The formation of nitric acid is represented thus :

it

K2SO4 non-volatile.

Or simply

2K- + 2NO3' + 2H- + SO/' = 2K- + SO/' + 2HNO3.

As concentrated sulphuric acid and dry potassium nitrate are used in
this process, only a relatively small number of ions are present at one
time, but as fast as ions are removed as nitric acid, new ions are
formed to replace them until the operation is completed.

The above discussions on the formation of precipitates, gases, and
volatile liquids, and consequent completion of chemical reactions, is a
presentation in terms of the ionic theory of the same subjects dis-
cussed in a simpler form on p. 114, under Reversible Actions and
Chemical Equilibrium, and furnish an explanation of what is there
stated.

Chemical actions in aqueous solutions are nearly always actions
between ions. Indeed, there are some who claim that chemical action
does not take place except between ions, and the fact that action does
occur is itself evidence of the presence of ions. This is an extreme
view and is not well taken, as there are undoubted examples of action
in solution in which ions do not exist. In the case of acids, bases,
and salts in solution, action is practically always ionic.

Electrolysis.

This name is given to the series of changes that take place when an electric
current is passed through a solution of an electrolyte, and the subject is briefly
discussed on page 82. The process is carried out in an electrolytic cell, which
consists of a suitable vessel holding a solution into which are immersed the
electrodes of the circuit. Fig. 34 illustrates one form of such a cell, which

]96 NON-METALS AND THEIR COMBINATIONS.

is designed to collect gases. The electrodes are made of materials which are
not affected by the products that collect on them. Platinum plates are often
used.

The result of passing a current through a solution of an electrolyte is a
chemical decomposition. The products that appear at the electrodes are always
different. For illustration, one of the simplest cases of electrolysis may be
considered, namely, the decomposition of hydrochloric acid. When the appa-
ratus (Fig. 34) is filled with the concentrated acid and a current is turned on,
hydrogen gas is found to collect and rise into the tube from the cathode or
( — ) electrode, and chlorine gas collects in the other tube from the anode or
(+) electrode. The mechanism of the process is conceived to be as follows :
The solution of the acid contains some ions of hydrogen (H') and of chlorine
(Cl'), the presence of which is entirely independent of the electric current.
These ions, before the current is turned on, are attracted no more in one direc-
tion than in any other. When the current is turned on, one electrode receives
from the battery or dynamo, or whatever the source of electricity, a positive
charge, and the other receives a negative charge, and a constant difference of
voltage or electromotive force is maintained between the electrodes. If the
latter should be connected by a continuous conductor, as a piece of copper wire,
a current would flow from the positive to the negative electrode by their dis-
charge through the wire. But the source of electricity would constantly renew
the charges on the electrodes, and thus a continuous current would be kept up.
When the connecting wire is replaced by hydrochloric acid, the positive elec-
trode attracts the negatively charged chlorine ions and repels the positive
hydrogen ions, while the negative electrode attracts the positive hydrogen ions
and repels the negative chlorine ions. In this way there is a general move-
ment of all positive ions to one electrode, and of all negative ions to the other.
When the ions come in contact with the electrodes, they lose their charges by
neutralizing the charges of opposite kind on the electrodes. The discharged
ions then unite and pass off as molecules of hydrogen and chlorine respect-
ively. The discharged electrodes receive new charges as before, and the pro-
cess is repeated until all of the electrolyte is removed from the solution. The
effect as far as the conduction of the current is concerned is the same as if a
wire connected the electrodes, and the current flowed through a circuit entirely
metallic. In the light of this ionic explanation of electrolysis, we can under-
stand why solutions of substances which do not dissociate into ions like sujrar
do not conduct electricity, and why substances which conduct in aqueous solu-
tion do not conduct in solvents in which they are not dissociated.

Secondary changes in electrolysis. In the electrolysis of hydrochloric

id the products liberated consist of the same elements of which the ions are

constituted, but the majority of cases are not so simple as this one. Many ions

are atomic groups which are not known in the free state, but exist only as ions

solution. When these lose their charges, secondary chemical changes occur

the resulting products accumulate around the electrodes. Thus in the

case^of sulphuric acid, the H' ions become molecules of hydrogen gas, but the

>04 ion when discharged becomes a group not known in the free state It

reacts with water thus : H2O + SO4 = H2SO4 + O. Sulphuric acid accumu-

ound the positive electrode, but is gradually disseminated again through

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 197

the solvent by diffusion. The oxygen escapes and can be collected. The
amount of hydrogen and oxygen liberated are in the same proportion as in
water, and thus we have an explanation of the " decomposition of water by
electrolysis."

When copper sulphate is electrolyzed metallic copper is deposited on the
negative electrode, and sulphuric acid and oxygen collect at the other. In the
case of sodium sulphate the sodium ion when discharged acts on water, result-
ing in the accumulation of sodium hydroxide and hydrogen around the nega-
tive electrode, and as before sulphuric acid and oxygen collect at the positive
electrode.

Faraday's laws of electrolysis, Michael Faraday, of England, was the
first to make a careful quantitative study of electrolysis, and announced the
following two laws:

I. The amount of a substance liberated in an electrolytic cell is proportional to
the quantity of electricity that has passed through it.

II. Chemically equivalent quantities of ions are liberated by the passage of equal
quantities of electricity. Chemically equivalent quantities are determined by
valence. Thus for every divalent ion liberated, two univalent ions are liber-
ated, etc., by the same amount of electricity.

The liberation of 1 gramme of hydrogen requires the passage of 96,540 units
(coulombs) of electricity. A current strength of 1 ampere is such that 1 cou-
lomb of electricity flows through a circuit in 1 second. Hence a current of
1 ampere will require 96,540 seconds (26 hours and 49 minutes) to liberate
1 gramme of hydrogen (nearly 11 liters). A current of 5 amperes would do the
same work in one-fifth of the time.

One coulomb (a current of 1 ampere flowing 1 second) will liberate 0.0000104
gramme of hydrogen, 0.0000828 gramme of oxygen, 0.0003294 gramme of
copper, 0.001118 gramme of silver, etc. These quantities are proportional to
the chemical equivalents, and are called in electrical science, electro-chemical
equivalents.

An instrument constructed for determining the amount of a substance as
silver or copper liberated by a current in a given time, and from this the cur-
rent strength, is called a voltameter (see page 77). Suppose a current flowing
for 1 hour through a voltameter liberates 0.59292 gramme of copper upon the
cathode, the current strength is —

0.59292 gm. copper = i ^

3600 seconds X 0.0003294 elect, chem. equiv. of copper

Conductivity. Every solution of an electrolyte offers a certain resistance
to the flow of the current, which can be measured in ohms (see page 76). If
the resistance is small, the solution offers an easy passage for the current, hence
it is said to have a high conductivity. A solution of great resistance is said to
have a low conductivity. The numerical value for conductivity is the recip-
rocal of the resistance, thus:

Conductivity = —

resistance

In order that results may be compared, conductivity measurements are made
with electrodes 1 cm. apart. The algebraic character used to represent con-

198 NON-METALS AND THEIR COMBINATIONS.

ductivity is Av, which means the conductivity shown by the molecular weight
of the substance in v liters of solution.

The conductivity increases with dilution. This is what we should expect,
since conductivity is proportional to the number of ions, which also increases
with dilution. By measuring the conductivity in a given dilution and also in
very large dilution, it is a simple matter to calculate the degree of ionization
of the substance in the given dilution. This method of study is called the
conductivity method.

Electromotive force required in electrolysis. The amount of work
that can be done by any form of energy depends not merely on the quantity,
but also on the intensity of the energy. Thus, the quantity of steam in a loco-
motive boiler, however large, will not cause the driving-wheels to turn if the
pressure (intensity factor) is not sufficiently large. Likewise, in electrolysis,
different substances require for decomposition currents of different electro-
motive force. If the latter is less than the required minimum, there is no
liberation of ions at the electrodes, that is, no electrolysis. The quantity of
current only controls the amount of material liberated, but the electromotive
force decides whether there will be any decomposition at all. The reason for
the latter fact is that as soon as the electrodes are coated with the products of
electrolysis, a reverse electromotive force and current tend to develop which
oppose the original current. The electrodes are then said to be polarized. To
overcome this polarization current requires a certain minimum electromotive
force in the electrolyzing current. The electromotive force required for a few
common electrolytes are as follows :

Hydriodic acid 0.53 volts.

Silver nitrate 0.7(5 "

Hydrochloric acid 1.41 "

Sulphuric acid 1.92 "

Zinc sulphate . . 2.70 "

Electrochemical series of the metals. If the metals are arranged in
the order of the electromotive force required to liberate them in electrolysis,
we have the following electropositive series :

Electrochemical series of metals.

Potassium Gold

Sodium Platinum

Lithium Palladium

Calcium Silver

Strontium Mercury

Barium Bismuth

Magnesium Antimony

Aluminum Copper

Manganese Arsenic

Zinc Hydrogen
Chromium Lead
Cadmium Tin
Iron Nickel
Cobalt

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 199

The electromotive force required decreases from the potassium end of the
series to the gold end. If the metals are arranged in a series according to the
decreasing intensity of their chemical activity in the free state toward other
substances, the same order is observed as that in the above series. Metals
higher up in the series will displace others following from solutions of their
salts, but not vice versa. All the metals, from potassium to hydrogen, will
displace hydrogen from dilute acids, but those following hydrogen will not.
The metals, down to copper inclusive, will rust in the air. The oxides of the
metals, down to manganese inclusive, cannot be reduced to the metal by heat-
ing in hydrogen, but oxides of cadmium and the metals following can. The
metals down to hydrogen do not occur in the free state in nature.

The non-metals and negative radicals into which they enter (acid radicals)
can also be arranged into a similar electronegative series.

Discociation theory applied to acids, bases, salts, and neutral-
ization.

Acids. A general discussion of acids, bases, and salts is given in Chapter
8. In terms of the ionic theory, acids are substances which give positive hy-
drogen ions in solution, associated with negative ions tbat may be either
simple, as OF, or complex, as SO/', or CO3//. The properties common to all
acids are due to the hydrogen ions ; for example, sour taste, action on litmus,
action on metals with displacement of the hydrogen. The latter action is rep-
resented in the case of zinc by the ionic equation, Zn + 2ET -|- SO/' = Zn** 4-
SO4" + H2. This stands as a type for all acids, and it will be observed that
the action is essentially between the metal and hydrogen ions, and is independ-
ent of the negative ion. The charges on the hydrogen ions are transferred to
the zinc atoms, which then become ionic, and the discharged hydrogen ions
escape as molecules.

The specific properties of the acids in solution are due to the different com-
position of the negative radicals. These radicals are the same whether acids
or their salts are used. When a solution of silver nitrate is added to one of
potassium chloride, a white precipitate of silver chloride is obtained, but when
added to potassium chlorate in solution, no visible change takes place. Both
of these salts contain chlorine, but the first gives the ion CK, and the second
the ion CIO/. In other words, the composition of the negative radicals is
different, which results in a different behavior toward the positive silver ion.
Silver chloride is an insoluble substance and is formed in solutions only when
silver ions and chlorine ions are brought together. Chlorine ions are formed
only from hydrochloric acid or the chlorides. Silver chlorate is a soluble
body, and, therefore, nothing that we can see happens when silver ions and
chlorate ions are brought together in solution.

Independence of ions. The above discussion leads to the conclusion
that the ions of acids are distinct substances with individual physical and
chemical properties. Each kind of ion behaves as if it were alone present in
the solution. This is true of all ions. To illustrate, two instances may be
given that have to do with a physical property, namely, color of salts or acids.
All copper salts of colorless acids have a blue color in dilute solutions. The
blue color is due to the copper ion, and all copper salts that are soluble give

200 NON-METALS AND THEIR COMBINATIONS.

the copper ion. The molecules of copper salts in solution are not blue, as can
be shown by the following experiment: If to a solution of copper chloride
concentrated hydrochloric acid be added, there will be a point at which the
blue changes to a yellowish-green color. The effect of the acid is to reverse
the ionization of the copper chloride so far that the color of the remaining
ions of copper is overbalanced by the color of the molecules of the salt.

Again, permanganic acid in dilute solution is deeply colored, due to the
MnO/ ion (hydrogen ion is colorless). Likewise all its salts in dilute solu-
tions are deeply colored, because they all form the common ion, MnO/. For
equivalent concentrations, the tint of the color is the same in all the solutions.

Analytical reactions or tests. Since acids, bases, and salts ionize, and
chemical actions concern primarily the ions, it is not difficult to see that the
tests made in solutions (wet way) for identifying substances are tests for ions.
Thus, when we test for carbonic acid by lime-water we are testing, not for the
acid H2CO3, but for the ion CO/'. Nevertheless we infer the nature of the
molecules from a study of the reactions of the ions. Since the tests apply to
ions, we have an explanation of the fact that tests for a given ion can be used
in the case of all substances which give that ion in solution, irrespective of the
nature of the other ions. Thus, the silver nitrate test for " chlorine " succeeds
for all chlorides that are soluble. Likewise, the barium chloride test for all
soluble sulphates. It is evident also that two kinds of tests must be made in
the case of each substance, namely, one kind for the positive ion and the other
kind for the negative ion.

Kinds of ions formed by acids. Monobasic acids, as HC1, HNO3, etc.,
can form only one hydrogen ion from each molecule. Dibasic acids, like
H2SO4, form one or two hydrogen ions, according to concentration. In rather
concentrated solution of sulphuric acid the ionization is principally thus:
H2SO4 :± H- + HSO/. The ion HSO/ is an acid, but much less active than
sulphuric. When the acid is highly diluted, further ionization takes place to
a great degree, thus, HSO/ ^± H* -f SO/'. All dibasic acids dissociate in
two stages, like sulphuric. Tribasic acids show a similar behavior.

Activity or "strength" of acids. A proper comparison of acids can
only be made under like conditions of temperature, concentration, etc. For
this purpose like concentration means solutions containing in a given volume
chemically equivalent weights of the respective acids. These are such weights
in grammes as contain the same weight of replaceable hydrogen. For ex-
ample, two molecular weights of HC1 are equivalent to one moleculer weight
of H2SO4. All conditions being equal, the activity of acids is proportional to
the degree of dissociation ; that is, to the concentration of the hydrogen ions.
Those acids that ionize most are the "strongest," and vice versa.

Bases. Bases are substances which give negative hydroxyl (OH) ions in
solution, associated with a positive ion, which is usually metallic, but may be
a group of atoms not containing a metal, as NH4. The properties common to
bases in general when dissolved are due to the hydroxyl ion, for example,
action on litmus, soapy taste, neutralization of acids. Most of the bases are
so sparingly soluble that not enough (OH) ions are present to affect litmus.
Zinc and iron hydroxides are examples of such. In other cases, just enough

THEORY OF ELECTROLYTIC DISSOCIATION, ETC, 201

(OH) ions dissolve to give a faint action on litmus, for example, magnesium
hydroxide. Just as in the case of acids, the activity of bases is proportional
to the degree of ionization. The most active common bases are potassium
and sodium hydroxides, called alkalies, and sometimes caustic alkalies. Their
solutions are called lyes. The hydroxides of barium, strontium, and calcium
are next in activity. Ammonium hydroxide is a rather weak base. The rest
are either sparingly soluble or insoluble.

Salts. The relationship between salts and acids has already been discussed.
As a rule, salts ionize to a considerable degree, and do not show as wide a range in
the degree as do the acids. Non-metals are never found in the positive ion of salts,
except they occur in a composite radical, as NH4. Hence we have no such salts
as nitrogen carbonate, carbon sulphate, or sulphur phosphate. The ions of salts
do not affect litmus, it is only H' and (OH)7 ions that have an effect.

Acid salts. These may be acid, neutral, or alkaline to litmus, depending
on the mode of ionization. An acid salt of a highly ionizing acid shows an
acid reaction in solution, because of the presence of hydrogen ions. For ex-
ample, sodium bisulphate acts thus in solution :

NaHSO4 ±? Na' + HSO/
HSO/ ±?H- 4- SO/

Acid salts of weak acids, like carbonic, phosphoric, boric, etc., may be neutral
or even alkaline, because the remaining hydrogen of the acid does not become
ionic. Sodium bicarbonate is neutral to litmus, because it ionizes thus :

NaHCO3^± Na- + HCO3'.

The ion HCO/ does not furnish sufficient H' ions by further dissociation to
affect litmus.

Basic salts, These are the reverse of acid salts. They are derived from
bases containing more than one (OH) group in the molecule, and the union
with acids is such that not all of the (OH) groups are replaced by acid radical.

/Cl

Thus Mg (OH)2 can form Mg<f QTT which shows the plan of structure of all

basic salts. They are, in nearly all cases, insoluble in water and show slight or
no action on litmus.

Hydrolysis of salts. Some salts, which we would expect from their for-
mulas, such as normal salts, to have a neutral reaction in solution, show a
noticeable acid reaction, while others show an alkaline one. Such salts are
related to an acid or to a base of slight dissociating power, and the cause is
found in the slight ionization of water, which, though extremely minute,
makes itself felt in some cases. The acid reaction of copper sulphate is ex-
plained by the following ionic reaction :

2H20 :±2H' + 2(OH)'
Copper hydroxide dissociates very slightly, being in this respect on a par
with water. As a consequence, some Cu" and (OH)' ions unite to form
molecules of Cu(OH)2. The removal of (OH)' ions of water allows more to
be formed, and more Cu(OH)2 results. This process soon comes to a stop, but
not before enough H' ions have been produced to give the solution an acid re-
action. The molecules of Cu(OH)2 are not precipitated, but remain in solu-
tion. The quantity is too small.

202 NON-METALS AND THEIR COMBINATIONS.

The ionic equation for sodium carbonate which shows marked alkaline reac-

Na2C03 ;± 2Na' + CO/ 1 _^ HCQ ,
H20 ;± (OH)' + H; . /."*

Here a small quantity of (OH)7 ions are produced, which give the solution an
alkaline reaction. This action of water on salts is called hydrolysis. The
changes are usually represented by the simpler reactions :

CuS04 + 2H20 = Cu(OH), + H2S04
Na2C03 + H20 = NaOH + NaHCO.

Soap always shows an alkaline reaction, which is due to hydrolysis. Salts
containing bivalent or trivalent radicals, metallic or acid, are more prone to
undergo hydrolysis than those containing univalent radicals only.

Neutralization. Broadly speaking, the replacement of hydrogen of an acid
by metal is neutralization, but, as shown in the preceding paragraph, certain
salts have an acid or alkaline reaction in solution, and consequently it is
impossible in such instances to produce an exactly neutral solution by bring-
ing the acid and base together in the proportions to form the salt. A great
many salts, however, are neutral, and in these cases it is possible to bring
together the corresponding acids and bases, and have complete reactions and
neutral solutions. In the more restricted sense neutralization refers to such
complete reactions. They can be employed for quantitative determinations
of the acids or bases in solutions. This subject is treated under Acidimetry
and Alkalimetry in the section on Volumetric Analysis.

Neutralization is an example of double decomposition and of a complete
reaction. The interpretation of this is found in the ionic theory. In the
beginning before mixing, there are H* ions which have an acid reaction, and
(OH)' ions which are alkaline. When they are brought together by mixing
the acid and base and the neutral point is established, both H* and (OH)' ions
disappear, as is proved experimentally by conductivity tests. This disappear-
ance results from the fact that water is practically undissociated. and, there-
fore, these ions cannot exist in the same solution, but unite to form molecules
of water. Of course, the metal ions and acid radical ions also unite to some
extent to form molecules, but if the solutions are quite dilute the proportion
of undissociated molecules is negligible.

The ionic equation for the neutralization of sodium hydroxide and nitric
acid serves as a type for all instances :

NaOH ^ Na' + (OH)')
HN03 ;± NO./ + H- / "

It'
NaNO3

As fast as H' and (OH)' unite more. NaOH and HNO3 dissociate, until finally
all is dissociated, and only ions of sodium nitrate and some undissociated mole-
cules of the same are left in the solution at the point of neutrality.
The essential reaction may be shown in the simplified equation :

Na- + (OH)' + H- + N03' = Na' + NO3' -f H2O,

or by the following still simpler equation, which expresses the fact that neu-
tralization is a reaction between H- and (OH)' ions :

THEORY OF ELECTROLYTIC DISSOCIATION, ETC. 203

Heat of neutralization. Heat is produced when an acid and a base neu-
tralize each other. If what is stated above is true, then the heat is due to the
formation of water molecules, and should be the same for all active acids and
bases in dilute solutions. This is exactly what is found by experiment to be
true. The heat of neutralization refers to such weights of acids and bases that
will furnish enough H* and (OH)X ions to form one molecular weight (17.88
gin.) of water, and is nearly 13,600 calories.

Degree of dissociation. The degree of dissociation of electrolytes varies
with the nature of the substance and the concentration of the solution. Usu-
ally it is small in concentrated solutions, and increases rapidly with dilution.
In 62 per cent, nitric acid only about 9 per cent, of the molecules are ionized,
while in the 6.3 per cent, acid about 80 per cent, are ionized. Comparisons
for degree of dissociation must be made with solutions of the same relative con-
centrations. Usually normal solutions at 18° C. are used, except when the
substance is not sufficiently soluble. The following table gives the per cent.
of dissociation in normal solutions1 at 18° C., except when otherwise specified,
of some acids, bases, and salts.

PerCent'

Electrolyte. .. Electrolyte. /,

dissociation. dissociation.

Nitric acid ........... 82 Sodium phosphate, very dilute . . 83

Hydrochloric acid ....... 78.4 Ammonium chloride ...... 74

Sulphuric acid ......... 51 Sodium chloride ........ 67.5

Hydrofluoric acid ...... .7 Potassium nitrate ........ 64

Acetic acid ...... ..... 0.4 Potassium acetate ........ 64

Carbonic acid (^) ....... 0.17 Silver nitrate . . .

,n^ Potassium sulphate ....... 53

Hydrogen sulphide (jg) ..... 0.07 godium acetate ......... 53

Boric acid (^\ ......... 0.01 Sodium bicarbonate ....... 52

. , / n \ A A1 Potassium carbonate , ...... 49

Hydrocyanic acid (1?)) ..... 0.01

Sodium sulphate ........ 44.5

Phosphoric acid (~ at 25° C.) . . .17 Zinc sulphate .......... 24

Potassium hydroxide ...... 77 Zinc chloride .......... 48

Sodium hydroxide ....... 73 Copper sulphate ........ 22

Calcium hydroxide, sat. sol. at 25° C. 90 Mercuric chloride, less than ... 1

Ammonium hydroxide ...... 0.4 Mercuric cyanide ....... minute

Mathematical formulas have been constructed for calculating the degree
of dissociation from the results obtained by four methods of work, namely,
freezing-point, boiling-point, osmotic pressure, and conductivity methods.
The results of calculation all agree. The simplest method in execution is the
conductivity method.

QUESTIONS.— State the theory of electrolytic dissociation or ionization.
Upon what experimental facts does it rest? What is an electrolyte? What
substances are found to be electrolytes ? What is a cation ; an anion ? Write
the ionic equation for the dissociation of sodium chloride in solution. Write
the ionic equation for the precipitation of silver chloride from solution. What
is electrolysis, and how is it explained? How are acids, bases, and salts defined
in terms of the ionic theory ? How is the activity or " strength " of acids and bases
related to dissociation ? How is the fact that some acid salts have an acid action
on litmus, while others are neutral, accounted for.? What is hydrolysis?
1 The concentration of normal solutions is denned in the section on Volumetric Analysis.

204 NON-METALS AND THEIR COMBINATIONS.

16. SULPHUR.
S" = 32 (31.83).

Occurrence in nature. Sulphur is found in the uncombined
state, mixed with earthy matter, in volcanic districts, the chief sup-
ply having been derived until lately from Sicily. Considerable
quantities are now also mined in the United States, chiefly in Louis-
iana, Utah, California, and Nevada. In combination sulphur is widely
diffused in the form of sulphates (gypsum, CaSO4.2H2O), and fre-
quently occurs as sulphides (iron pyrites, FeS2, galena, PbS, cinnabar,
HgS, etc.). Sulphur enters also into organic compounds, being a
normal constituent of all proteids, during the decomposition of which
sulphur is often evolved as hydrogen sulphide, which gas is also a
constituent of some waters.

Properties. Sulphur is a, yellow, brittle, solid substance, having
neither taste nor odor. It is insoluble in water and nearly so in
alcohol ; soluble in benzene, benzin, ether, chloroform, carbon di-
sulphide, oil of turpentine, and fat oils. Sulphur is polymorphous ;
it crystallizes, from a solution in disnlphide of carbon, in octahedrons
with a rhombic base ; when, however, liquefied by heat it crystallizes
in six-sided prisms, and is obtained as a brown, amorphous plastic
substance by pouring melted sulphur into cold water.

Sulphur melts at 115° C. (239° F.) to an amber-colored liquid,
which is fluid as water ; increasing the heat gradually, it becomes
brown and thick, and at about 200° C. (392° F.) it is so tenacious
that it scarcely flows ; when heated still further it again becomes
thin and liquid, and, finally, boils at a temperature of about 440° C.
(824° F.).

In its chemical properties sulphur resembles oxygen, being like
this element generally bivalent, and supporting, when in the form
of vapor, the combustion of many substances, especially the metals.
Many compounds of oxygen and sulphur show an analogous compo-
sition, as, for instance, H2O and H2S, CO2 and CS2, CuO and CuS.
While the valence of sulphur as a general rule is 2, in some com-
pounds it shows a valence of 4 or 6, as in SO2 and SO3.

Crude sulphur is obtained by heating the rock containing sul-
phur sufficiently high to cause the sulphur to melt, and thus to
separate from the earthy matters. As peculiar conditions (great depth
and quicksand) prevented successful working of the sulphur deposits
m Louisiana by the ordinary methods, sulphur is now mined there by
the following ingenious process : Superheated water, forced through
iron pipes to the deposits of sulphur, causes the latter to melt, and this

SULPHUR. 205

liquefied sulphur is raised through other pipes to the surface by means
of compressed air. Crude sulphur generally contains from 2 to 4 per
cent, of earthy impurities.

Sublimed sulphur, Sulphur sublimatum (Flowers of sulphur).
Obtained by heating sulphur to the boiling-point in suitable vessels,
and passing the vapor into large chambers, where it deposits in the
form of a powder, composed of small crystals. Sublimed sulphur,
when melted and poured into round moulds, is known as roll-sulphur
or brimstone.

"Washed sulphur, Sulphur lotum, is sublimed sulphur washed
with a very dilute ammonia water, and then with pure water ; the
object of this treatment being to free the sulphur from all adhering
sulphurous and sulphuric acid, as also from arsenic compounds which
are sometimes present.

Precipitated sulphur, Sulphur prsecipitatum (Milk of sulphur).
Made by boiling one part of calcium hydroxide with two parts of
sulphur and thirty parts of water, filtering the solution, adding to it
dilute hydrochloric acid until nearly neutral, washing and drying the
precipitated sulphur.

By the action of sulphur on calcium hydroxide are formed calcium polysul-
phide, calcium thiosulphate, and water:

3Ca(OH)2 + 12S : : 2CaS5 + CaS2O3 + 3H2O.

On adding hydrochloric acid to the solution, both substances are decom-
posed and sulphur is liberated :

2CaS5 + CaS2O3 + 6HC1 = 3CaCl2 -f- 3H2O + 12S.

While the above equation gives the final result, the decomposition takes
place in stages, thus :

CaS5 -f 2HC1 = CaCl2 + H2S + 4S
CaS2O3 + 2HC1 = CaCl2 + H2S2O8
2H2S + H2S208 = 3H2O + 4S.

Precipitated sulphur differs from sublimed sulphur by being in a more finely
divided state, and by having a much paler yellow, almost white color.

Experiment 13. Mix in a beaker about 10 grammes of powdered sulphur, 20
grammes of slaked lime, and 200 c.c. of water, and boil until the liquid has a
deep brown color. Renew the water that is lost by evaporation occasionally.
Note that the color deepens as boiling is continued. This is due to the poly-
sulphide of calcium, which is colored. Finally, filter into a large flask or
beaker, wash the filter, dilute to about half a liter, and add dilute hydrochloric
acid until the solution is nearly neutral. Note the milk-like appearance of the
liquid. Let the sulphur settle fully, decant the liquid, filter and wash the sulphur,
and let it dry in the air. Compare its appearance with that of lump sulphur.

206 NON-METALS AND THEIR COMBINATIONS.

The following four oxides are known : Sulphur sesquioxide, S2O3 ;
sulphur dioxide, SO2 ; sulphur trioxide, SO3; sulphur heptoxide, S2O7.
The three last named are acid oxides, which, on combining with one
molecule of water, form sulphurous, sulphuric, and persulphuric acid
respectively.

Sulphur dioxide, SO2 = 63.59 (Sulphurous anhydride, improperly
also called sulphurous acid), is formed when sulphur or substances con-
taining it in a combustible form (H2S, CS2, etc.) burn in air. It is
generated also by the action of strong sulphuric acid on many metals
(Cu, Hg, Ag, etc.), or on charcoal :

2H2SO4 + Cu = CuSO4 +-2H2O + SO2.
2H2SO4 + C = CO2 + 2H2O + 2SO2.

Sulphur dioxide is a colorless gas, having a suffocating, disagreeable
odor; it liquefies at a temperature of — 10° C. (14° F.), and solidifies
at — 75 C. ( — 103° F.) ; it is very soluble in water, forming sulphur-
ous acid ; it is a strong, deoxidizing, bleaching, and disinfecting
agent ; when inhaled in a pure state it is poisonous ; when diluted
with air it produces coughing and irritation of the air-passages.

Sulphurous acid, Acidum sulphurosum, H2SO3, SO2.H.OH. This
acid, similar to carbonic acid, is not known in a pure state, but is
believed to exist in aqueous solution, which decomposes into water
and sulphur dioxide when attempts are made to concentrate it. One
volume of cold water absorbs about 40 volumes of sulphur dioxide,
equal to about 11 per cent, by weight. The official acid must contain
not less than 6 per cent, by weight, equal to about 2000 volumes of
gas dissolved in 100 of water. According to the U. S. P. the acid
is made by generating sulphur dioxide from charcoal and sulphuric
acid in a flask, and passing the gas through a wash-bottle containing
water, inta distilled water for absorption.

Experiment 14. Use an apparatus as shown in Fig. 42. Place in the flask
about 20 grammes of charcoal in small pieces, cover it with sulphuric acid,
apply heat, and pass the generated gas first through a small quantity of water
contained in the wash-bottle, and then into pure water, contained in the
cylinder.

The solution, sulphurous acid, may be used for the tests mentioned below ;
when the neutral solution of a sulphite is required, make this by adding solu-
tion of sodium carbonate to a portion of the sulphurous acid until litmus-paper
shows neutral reaction. Examine also the contents of the wash-bottle by
means of the tests given below for sulphuric acid ; most likely some of the
latter will be found. How much carbon and how much H2S04 are required to
make 100 grammes of a 6.4 per cent, sulphurous acid?

SULPHUR.

207

Sulphurous acid is a colorless acid liquid, which has the odor as well as the
disinfecting and bleaching properties of sulphur dioxide; it is completely
volatilized by heat. Sulphurous acid is a dibasic acid, the salts of which are
termed sulphites. Both the acid and its salts are easily oxidized by the air,
and hence almost always give the tests for sulphuric acid. In its chemical be-
havior sulphurous acid is very much like carbonic acid. It is a weak acid,
being displaced from its salts by all acids except carbonic and boric. The sul-
phites of the alkali metals are freely soluble in water, but the normal sulphites of
all other metals are insoluble or nearly so ; hence addition of a solution of an
alkali sulphite to a solution of salts of the other metals causes precipitates. A

FIG. 42.

Apparatus for making sulphurous acid.

few sulphites are soluble in a solution of sulphurous acid, like carbonates, but
are precipitated on boiling. Acid sulphites of the alkali metals can be obtained in
the solid state. These show an acid reaction to litmus, but the normal sul-
phites of these metals have an alkaline reaction, due to hydrolysis by water
into bisulphite and free alkali. All the common sulphites are white.

The ionic equations for the liberation of sulphurous acid from a sulphite,
and the ionization of normal and bisulphites in solution, are ir all respects like
those pertaining to the liberation of carbonic acid and the ionization of normal
and bicarbonate of sodium, which are given on pages 195 and 201. The reason
that bisulphites are slightly acid in solution, and not neutral as bicarbonates
are, is that an appreciable amount of hydrogen ions are formed, thus :

NaHSO3 ^

HS03'
SO3".

The second reaction takes place only to a small degree.

208 NON-METALS AND THEIR COMBINATIONS.

Tests for sulphurous acid and sulphites.
(Sodium sulphite, Na,SO3.7H2O, may be used.)

1. Add sulphur dioxide gas, or a solution of it in water, or a solu-
tion of a sulphite to an acidified solution of potassium permanganate.
The latter is decolorized, due to its giving up oxygen, which oxidizes
the sulphurous acid, thus :

H,S03 + O H2S04.

Make the same experiment with acidified solution of potassium
dichromate. The same kind of change takes place, but the decom-
position products of the dichromate are green. The reaction will be
understood when chromium is studied.

2. Add a few drops of a solution of sulphurous acid or of a sul-
phite to a tube containing some zinc and dilute sulphuric acid
(nascent hydrogen). Hydrogen sulphide is liberated, which can be
detected by the odor, or a piece of filter-paper, wet with solution of
lead acetate, which blackens when held in the mouth of the tube :

H2S03 + 6H H2S + 3H2O.

3. Add to a few drops of the sulphite solution about 2 c.c. of silver
nitrate solution. A white precipitate of silver sulphite is formed,
which darkens on heating, due to reduction to metallic silver :

Ag2S03 + H20 2Ag + H2S04.

Silver sulphite is soluble in an excess of the sulphite solution.

4. A strip of filter-paper, moistened with mercurous nitrate solu-
tion, turns black when suspended in sulphur dioxide, due to reduction
to metallic mercury :

2HgN03 + 2H20 + S02 = 2Hg + H2SO4 + 2HNO3.

Tests 1 and 4, along with the odor of sulphur dioxide, are usually suf-
ficient to recognize sulphurous acid or sulphites.

Sulphur trioxide, SO3 (Sulphuric acid anhydride). This is
a white, silk-like solid substance, having a powerful affinity for
water; it may be obtained by the action of phosphoric oxide on
strong sulphuric acid, or by passing sulphur dioxide and oxygen
together over heated platinum-sponge. It is now made on the large
scale by the latter method for producing fuming sulphuric acid.

Sulphuric acid, Acidum sulphuricum, H2SO4, SO2(OH)2^ 97.35

(0 if of vitriol). There is no other acid, and perhaps no other sub-

SULPHUR. 209

stance, manufactured by chemical action which is so largely used in
chemical operations and in the manufacture of so many of the most
important articles, as is sulphuric acid.

Impure sulphuric acid was known in the eighth century ; in the
fifteenth a purer acid was obtained by heating ferrous sulphate (green
vitriol) in a retort. To the liquid distilling over the name of oil of
vitriol was given, in allusion to its tl.ick or oily appearance and the
green vitriol from which it was obtained. The change is shown in
the following reaction :

4FeSO4 + H2O = 2Fe2O3 + 2SO., + H2SO4.S03.

Sulphuric acid is found in nature in combination with metals as
sulphates. Thus calcium sulphate (gypsum), barium sulphate (heavy-
spar), magnesium sulphate (Epsom salt), and others occur in nature.

Manufacture of sulphuric acid. Sulphuric acid is manufactured
on a very large scale by passing into large leaden chambers simul-
taneously, the vapors of sulphur dioxide (obtained by burning sulphur
or pyrites in furnaces), nitric acid, and steam, a supply of atmospheric
air also being provided for. The most simple explanation that can
be given for the manufacture of sulphuric acid is the fact that sul-
phur dioxide when treated with an oxidizing agent, in the presence
of water, is converted into sulphuric acid :

S02 + O + H2O = H2SO4.

Only a portion of the oxygen necessary for oxidation is derived
from the nitric acid directly ; the larger quantity is obtained from
the atmospheric air, the oxides of nitrogen serving as agents for the
transfer of the atmospheric oxygen.

By the action of nitric acid on sulphur dioxide and steam are formed sul-
phuric acid and nitrogen trioxide :

2SO2 + H2O + 2HNO3 = 2H2SO4 + N2O3.

Nitrogen trioxide next takes up sulphur dioxide, water, and oxygen, forming
a compound called nitrosyl-sulphuric acid :

2SO2 + N2O3 + 2O + H2O = 2(SO2.OH.NO2).

This complex compound is readily decomposed by steam into sulphuric acid
and nitrogen trioxide :

2(SO2.OH.NO2) + H2O = 2H2S04 + N2O3

The nitrogen trioxide again forms nitrosyl-sulphuric acid, which again suffers

decomposition, and so on indefinitely, as long as the constituents necessary for

the changes are supplied. These facts show that a given quantity of nitric acid

will convert an unlimited amount of sulphurous acid into sulphuric acid.

14

210 NON-METALS AND THP:iR COMBINATIONS.

There is, however, an unavoidable loss of small portions of nitric acid, or
oxides of nitrogen, for which reason some nitric acid has to be supplied daily.
It is likely that other chemical changes than the ones mentioned take place
in the acid chamber, but according to modern investigations these are the
principal ones.

The liquid sulphuric acid formed in the lead-chamber collects at
the bottom of the chamber, whence it is drawn oif. In this state it
is known as chamber acid (specific gravity 1.50), and is not pure, but
contains about 36 per cent, of water, and frequently either sulphurous
or nitric acid. By evaporation in shallow leaden pans it is further
concentrated, until it shows a specific gravity of 1.72. When this
point is reached the acid acts upon the lead, wherefore the further
concentration is conducted in vessels of glass or platinum, until a
specific gravity of 1.84 is obtained. This acid contains about 95
per cent, of sulphuric acid ; the remaining 5 per cent, of water can-
not be expelled by heat.

Properties of sulphuric acid. Pure acid has a specific gravity of
1.848 ; it is a colorless liquid, of oily consistence, boiling at 330° C.
(626° F.). When cooled it forms crystals, which melt at 10° C.
(50° F.). When heated to about 160° C. (320° F.), the acid begins
to fume and gives off sulphur trioxide. The 100 per cent, acid
gives off sulphur trioxide, and diluted acid gives off water when
heated, until an acid of 98.33 per cent, is reached, which boils
at the constant temperature of 330° C. It has a great tend-
ency to combine with water, absorbing it readily from atmo-
spheric air. Upon mixing sulphuric acid and water, heat is gen-
erated in consequence of the combination taking place between the
two substances. To the same tendency of sulphuric acid to com-
bine with water must be ascribed its property of destroying
and blackening organic matter. It is due to this decomposing
action of sulphuric acid upon organic matter that traces of the latter
color sulphuric acid dark yellow, brown, and, when present in larger
quantities, almost black. The poisonous caustic properties are due
to the same action. (See Experiments, page 179.)

Sulphuric acid is a very strong dibasic acid, which expels or dis-
places most other acids ; its salts are known- as sulphates.

The sulphuric acid of the U. S. P. should contain not less than
92.5 per cent, of H2SO4, corresponding to a specific gravity of not
V>ss than 1.826 at 25° C.

The diluted sulphuric acid, Acidum mlphuricum dilutum, is a mix-
ture of 100 parts by weight of acid and 825 parts of water, or of

SULPHUR. 211

about 60 c.c. of acid and 900 c.c. of water. This corresponds to 10
per cent, of H2SO4, and a specific gravity of 1.067 at 25° C.

Great care should be taken in diluting concentrated sulphuric acid.
The acid should always be poured slowly into water with constant stir-
ring. It is dangerous to pour the hot acid into water and foolhardy
to pour water into the hot acid. Ignorance or disregard of these rules
may lead to sad consequences.

When diluted sulphuric acid acts on metals, hydrogen is liberated and
escapes as a gas ; but if these same metals are acted on by concentrated sul-
phuric acid, which usually requires heating, other products are formed, such
as sulphur dioxide, hydrogen sulphide, or sulphur. This is due to the fact
that the concentrated acid acts as an oxidizing agent toward the hydrogen that
would otherwise be evolved, and itself is reduced. Certain metals do not act
on dilute sulphuric acid at all, but only on the hot concentrated acid, and
under these conditions hydrogen is never evolved. This is illustrated in the
preparation of sulphur dioxide by heating the concentrated acid with copper.
Other substances, as charcoal, sulphur, etc., that can be oxidized, act in the
same way on the hot, strong acid.

Most sulphates are soluble in water. There are practically only three which
are insoluble in water or dilute acids, namely, barium, strontium, and lead.
Calcium sulphate is slightly soluble in water, and more so in hydrochloric
acid. A solution of it is used as a reagent.

Most sulphates are more or less easily decomposed when heated, but those of
potassium, sodium, lithium, calcium, strontium, and barium can stand red
heat.

Sulphuric acid, like all dibasic acids, has two modes of ionizing according
to concentration (see page 200). In more concentrated solutions, the ions H*
and HSO/ predominate; in dilute solutions, 2H* and SO/X predominate.
Upon diluting a more concentrated solution, HSO/ ions dissociate further,
thus:

±H- + SO/'.

The same thing takes place when SO/7 ions are removed by precipitation,
which has an effect equivalent to diluting the acid.

Tests 1 and 2 below are examples of reversible reactions that run practically
to completion, because of the removal of one of the factors by precipitation,
due to its insolubility (page 114). These tests, like all similar ones that fol-
low, are explained in terms of the ionic theory on pages 193 and 200.

Tests for sulphuric acid and sulphates.

1. When a solution of barium chloride is added to dilute sulphuric
acid, or a solution of any sulphate, a white precipitate of barium
sulphate is obtained, which is insoluble in all dilute acids :

Na2S04 + BaCl2 == BaSO4 + 2NaCl
2Na- + SO/' + Ba" + 2C1' = BaSO4 + 2Na« + 2C1'.

212 NON-METALS AND THEIR COMBINATIONS.

Usually this test alone is sufficient for recognition, as all other
ordinary barium salts are soluble in hydrochloric or nitric acid. It
is very delicate.

2. When a solution of lead nitrate or acetate is employed, a
white precipitate of lead sulphate, PbSO4 is obtained. This is solu-
ble in a solution of ammonium acetate.

3. Grind together in a mortar a knife-pointful of a sulphate, sul-
phur, or any compound containing it, with 5 to 10 times its bulk of
sodium carbonate and about 3 times its bulk of potassium cyanide.
Place the mixture in a hole in a piece of charcoal and heat with the
blow-pipe flame until it is thoroughly fused. The mass now contains
yellowish-brown alkali sulphide (hepar), due to reduction of the sul-
phate by the hot charcoal and potassium cyanide. The sodium car-
bonate serves as &flux, or fusing material.

Remove the mass, place it upon a silver coin, and moisten it with
dilute hydrochloric acid. A black stain of silver sulphide will be
formed. This test is of value in the case of insoluble sulphates and
sulphides.

The above procedure is known as the charcoal reduction test, and is
one of the steps taken in systematic qualitative analysis.

Antidotes. Magnesia, sodium carbonate, chalk, and soap, to neutralize
the acid.

Acids of sulphur. While but four oxides of sulphur exist in the
separate state, there are a large number of acids containing sulphur,
some of which, however, are known only as constituents of the
respective salts. The acids are :

Hyposulphurous acid, H2S2O4. Thiosulphuric acid, H2SaOs.

Sulphurous acid, H2SO3. Dithiouic acid, H2S2O6.

Sulphuric acid, H2SO4. Trithionic acid, H2S3O6.

Pyre-sulphuric acid, H2S2O7. Tetrathionic acid, H2S4O6.

Persulphuric acid, H2S2O8. Pentathionic acid, H2S5O6.

Hydrogen sulphide, H2S.

Pyrosulphuric acid, H2S2O7 (Disulphuric acid, fuming sulphuric
acid, Nordhausen oil of vitriol). This acid is made by passing sulphur
trioxide (obtained by heating ferrous sulphate) into sulphuric acid,
when direct combination takes place :

H2S04 + S03 = H2S207.

It is a thick, highly corrosive liquid, which gives off dense fumes
when exposed to the air, and decomposes readily into sulphur trioxide
and sulphuric acid when heated.

SULPHUR. 213

Thiosulphuric acid, formerly Hyposulphurous acid, H.2S2O3,
SO2.SH.OH, is of interest because some of its salts are used, as, for
instance, sodium thiosulphate, Na2S2O3, the sodium hyposulphite of
commerce. The acid itself is not known in the separate state, since
it decomposes into sulphur and sulphurous acid when attempts are
made to liberate it from its salts.

Sulphuric is the most stable acid of sulphur, and all the others have a tend-
ency to pass to this acid. It is for this reason that both sulphites and thiosul-
phates are good reducing agents. A solution of a thiosulphate, when added
to an acidified solution of potassium permanganate or dichromate, acts in the
same way as a sulphite does. The essential reaction is :

Na2S2O3 + 4O + H2O = Na2S04 + H2S04.

Thiosulphates also react with the halogen elements in the manner shown by
this reaction :

2Na2S2O3 + 21 = Na2S406 + 2NaI,

forming sodium tetrathionate and sodium iodide. This reaction is used for the
quantitative estimation of free iodine and in the preparation of so-called de-
colorized tincture of iodine. It may also be used for removing iodine stains
from the skin or fabrics.

Most of the thiosulphates are soluble in water, those of barium, lead, and
silver being only very sparingly soluble. Alkali thiosulphates have a marked
solvent action on many salts that are insoluble in water, forming double thio-
sulphates. All thiosulphates are decomposed by acids.

Tests for thiosulphates.
(Use about a 5 per cent, solution of sodium thiosulphate. )

1. The solution, upon addition of dilute sulphuric or hydrochloric
acid, liberates sulphur dioxide, while sulphur is precipitated more or
less rapidly, according to the concentration and temperature. The
formation of these two products is characteristic and the test is suffi-
cient for recognition of a thiosulphate. The precipitate of sulphur
distinguishes it from a sulphite.

2. Addition of silver nitrate gives a white precipitate of silver
thiosulphate, Ag2S2O3, which is immediately dissolved if the sodium
thiosulphate is in excess. The precipitate is rather unstable, and
decomposes on standing, and more rapidly on heating, giving black
silver sulphide and sulphuric acid,

Ag2S203 + H20 Ag2S + H2S04.

Addition of solution of lead nitrate or acetate to thiosulphate solution
gives similar results. Most thiosulphates are unstable, like those of
silver and lead.

214 NON-METALS AND THEIR COMBINATIONS.

3. Barium chloride solution gives a white precipitate of barium
thiosulphate, BaS2O3- Calcium chloride, however, gives no precipi-
tate, whereas with a sulphite a precipitate is formed.

Persulplmric acid, H2S208, is obtained by passing an electric current
through sulphuric acid of a specific gravity 1.3 to 1.5. The reaction is
2H2S04 = 2H + H2S208.

The ammonium or potassium salts of this acid are obtained by the electrol-
ysis of saturated solutions of the bisulphates of the metals, thus :
2KHS04 = K2S208 + H2.

Persulphuric acid and its salts act as strong oxidizing agents, liberating,
for instance, chlorine from hydrochloric acid or from chlorides.

Hydrogen sulphide, H2S (Sulphuretted hydrogen). This compound
has been mentioned as being liberated by the decomposition of organic
matter (putrefaction) and as a constituent of some spring waters. It
is formed also during the destructive distillation of organic matter
containing sulphur. The best mode of obtaining it is the decomposi-
tion of metallic sulphides by diluted sulphuric or hydrochloric acid.
Ferrous sulphide is usually selected for decomposition :
FeS + H2SO, = FeS04 + HJ3.

Experiment 15. Use apparatus shown in Fig. 42, page 207. Place about 20
grammes of ferrous sulphide in the flask, cover the pieces with water, and add
sulphuric or hydrochloric acid. Pass a portion of the washed gas into water,
another portion into ammonia water. Use the solutions for the tests mentioned
below. Ignite the gas at the delivery tube and notice that sulphur is deposited
upon the surface of a cold plate held in the flame. Place the apparatus in the
fume chamber during the operation. How much ferrous sulphide is required
to liberate a quantity of hydrogen sulphide sufficient to convert 1000 grammes
of 10 per cent, ammonia water into ammonium sulphide solution? The reac-
tion taking place is this :

2NH3 + H2S = (NHJ2S.

Hydrogen sulphide is a colorless gas, having an exceedingly offen-
sive odor and a disgusting taste. Water absorbs about three volumes
of the gas, and this solution is feebly acid. It is highly combustible
in air, burning with a blue flame, and forming sulphur dioxide and
water. It is directly poisonous when inhaled, its action depending
chiefly on its power of reducing, and combining with, the blood-
coloring matter. Plenty of fresh air, or air containing a very little
chlorine, should be used as an antidote.

Hydrogen sulphide can be driven completely from its aqueous solu-
tion by heating. It is a rather unstable compound, being easily
broken up into its constituents. For this reason it is a good reduc-

SULPHUR. 215

ing agent. For example, sulphur dioxide is reduced by it to sulphur,
but is not affected by free hydrogen gas :

2H2S + SO2 = 2H2O + 38.

It is probable that native sulphur found in volcanic regions is produced
in this way. Because of the instability of the gas, its sulphur often
acts like sulphur in the free state. Thus, the metals from potassium
to silver inclusive in the electrochemical series (see page 198) soon
become tarnished with a layer of sulphide when exposed to the gas :

2Ag + H2S = Ag2S + 2H.

The solution of hydrogen sulphide is slowly affected by oxygen of the
air with precipitation of sulphur, H2S -f O — H2O -f S. Hence,
it does not keep except in full bottles. In solution it is a dibasic
acid of extremely weak character, only 0.07 per cent, of the molecules
being dissociated, mainly according to this equation :

H2S 7± H- + HS'.

The ion HS' also dissociates, but to a less degree even than water :

HS'^±H- + S".

Hydrogen sulphide, like any dibasic acid, can give two kinds of salts,
acid and normal ; for example, sodium hydrosulphide, NaHS, and
sodium sulphide, Na2S. The acid salt is obtained in solution, when
hydrogen sulphide is passed into a solution of sodium hydroxide to
saturation. It has a neutral reaction :

NaOH + H2S = NaHS + H2O.
In solution it dissociates, thus :

NaHS 7± Na- + HS'.

The normal salt, Na2S, does not exist in solution, but can be obtained
in the dry state by adding to the acid salt an amount of alkali equal
to that used in making the same, and evaporating to dry ness :

NaHS 4- NaOH = Na2S -f H2O.

When the dry salt is dissolved in water, it is completely hydrolyzed
into the acid salt and free alkali, and, therefore, has a strong alkaline

reaction :

Na2S + H20 = NaHS + NaOH.

Hydrogen sulphide gas and its solution in water are frequently
used as reagents in analytical chemistry for precipitating and recog-
nizing metals. This use depends on the property of the sulphur to

216 NON-METALS AND THEIR COMBINATIONS.

combine with many metals to form insoluble compounds, the color
of which frequently is very characteristic :

CuS04 + H2S = CuS + H2S04.

The sulphides that are insoluble in water fall approximately into three
groups:

1. Those that are almost completely insoluble in water, such as the sul-
phides of lead, copper, bismuth, silver, mercury, arsenic, antimony, tin, and a
few others. These, moreover, are not dissolved by dilute acids, and hence are
precipitated from solutions of salts of the metals bypassing hydrogen sulphide
into them even when a little free acid is present :

Pb(N03)2 + H2S = PbS + 2HN03,
Lead sulphide.

or Pb" + 2(N03)' + 2H- + S" = PbS + 2H- + 2(NO3)'.

2. Those that are practically insoluble in water, yet more soluble than the
sulphides of group 1, and are dissolved by even very dilute active acids. The
metals iron, cobalt, nickel, manganese, zinc, and a few others form such sul-
phides. Some of these sulphides are so readily soluble in dilute acids that they
are prevented from being precipitated by hydrogen sulphide by the acid that
would be liberated in the reaction (see equation above). In the case of zinc
salts partial precipitation takes place until equilibrium is reached, but if some
free acid is present, no precipitation takes place. To form the sulphides of
this group, a salt of hydrogen sulphide, such as ammonium or sodium sul-
phide, is applied to neutral solutions of the salts of the metals, thus :

FeS04 + (NH4)2S = FeS + (NH4)2SO4,
Iron sulphide.

or Fe" + S04" + 2(NH4)« + S" = FeS + 2(NH4)- -f SO4".

3. Those that are known only in the dry state, and although they are insol-
uble as such in water, yet they dissolve because they are hydrolyzed into solu-
ble products, thus :

2CaS -f 2H20 = Ca(OH)2 + Ca(SH)2.

The sulphides of barium, strontium, and calcium belong to this class. They
cannot be precipitated, either by hydrogen sulphide or ammonium sulphide.
They are generally made from the sulphate by heating with carbon (reduction
to sulphide).

Solutions of normal sulphides, as Na2S, and acid sulphides, as NaHS, or
NH4HS, when used as reagents in precipitation of insoluble sulphides, give
the same results because of the presence of S/x ions, which unite with the ions
of the other metals.

Tests for hydrogen sulphide or sulphides.
1. Hydrogen sulphide or soluble sulphides (ammonium sulphide
may be used) when added to soluble salts of lead, copper, mercury,
etc., give black precipitates of the sulphides of those metals.
^ 2. From insoluble sulphides (ferrous sulphide, FeS, may be used)
liberate the gas by dilute sulphuric or hydrochloric acid, and test as

SULPHUR. 217

above, or suspend a piece of filter-paper, moistened with solution of
lead acetate, in the liberated gas, when the paper turns dark. Some
sulphides, for instance, those of mercury, gold, platinum, as also FeS2,
and a few others, are not decomposed by the acids mentioned, unless
zinc be added.

Carbon disulphide, Carbonei disulphidum, CS2 — 75.57. This
com pound is obtained by passing vapors of sulphur over heated
charcoal. It is a colorless, highly refractive, very volatile, and
inflammable neutral liquid, having a characteristic odor and a sharp,
aromatic taste. It boils at 46° C. (115° F.) ; it is almost insoluble
in water, soluble in alcohol, ether, chloroform, fixed and volatile oils ;
for the latter two it is an excellent solvent, but dissolves, also, many
other substances, such as sulphur, phosphorus, iodine, many alka-
loids, etc.

Selenium, Se, and Tellurium, Te, are but rarely met with. Both elements
show much resemblance to sulphur; both are polymorphous; both combine
with hydrogen, forming H.2Se and H2Te, gaseous compounds having an odor
more disagreeable even than that of H2S. Like sulphur, they form dioxides.
Se02 and TeO2, which combine with water, forming the acids H2SeO3 and
H2Te03, analogous to H2SO3. The acids H2Se04 and H9TeO4, corresponding
to H2SO4, also are known.

Ionic mechanism of the solution by acids of salts that are insol-
uble in water. The operation of dissolving by the aid of an acid, salts that
are insoluble in water is resorted to frequently in general chemical work, and
particularly in chemical analysis. It is a matter of observation, too, that a
salt will dissolve in some acids, but not in others; also that of salts of the same
acid with different metals, some will dissolve in a given acid, while others will
not. Thus zinc sulphide is soluble in dilute hydrochloric acid, but not in
acetic, and the same is true of calcium oxalate and calcium phosphate. Iron
sulphide is soluble in most any dilute acid, but copper sulphide is not appre-
ciably dissolved by the same acids. The student often wonders what the ex-
planation is of such facts as these. The ionic theory gives a physical basis for
accounting for them.

Solution is the converse of precipitation. In the discussion of the latter
subject (see page 193) it is stated that whenever there are more ions of a sub-
stance than a saturated solution of that substance can maintain, the excess of
ions unite to molecules, which separate from solution as a precipitate. The
more insoluble the substance is the smaller is the concentration of molecules
and ions that can be maintained in its saturated solution, and the more com-
plete is the precipitation. Every "insoluble" substance is soluble to some
extent in water, even if only minutely. But many of the so-called insoluble
salts are slightly soluble in water, which is an important factor in accounting
for the solution of salts by acids. Now, water in contact with such a salt be-

218 NON-METALS AND THEIR COMBINATIONS.

comes saturated, that is, it takes up the maximum number of molecules and
ions that it can hold (which, of course, is not large), and these are in equi-
librium. If in any way the concentration of the negative (acid radical) ion is
diminished, more molecules dissociate to keep up the concentration of that
ion, which results in the dissolving of more molecules of the solid salt to keep
up saturation and equilibrium. If the negative ions of the salt are of an acid
that has a slight dissociating power, their concentration will be diminished
when an active (highly dissociating) acid is added to the mixture, thereby
furnishing an abundance of H' ions, with which the negative ions of the salt
unite to form undissociated molecules of the acid. If the concentration of the
negative ions of the salt is greater than that which can be maintained by the
corresponding acid, the salt will dissolve by the addition of an active acid, in
keeping with the principle of equilibrium as involved in the dissociation con-
stant (see page 192). Even an acid of a moderate degree of dissociation may
have its dissociation reversed to such an extent in the presence of an excess
of a highly dissociating acid, like hydrochloric, that it becomes equivalent to
a slightly dissociating acid, and does not maintain as great a concentration of
its negative ion as is maintained by its slightly soluble salts in water. This is
illustrated by the solution of calcium oxalate in excess of hydrochloric acid.
In the case of highly insoluble salts, like barium sulphate, the amount dis-
solved, and consequently the concentration of its ions, is so extremely small
that addition of active acids has very little effect in reducing the concentration
of the negative ion. Hence, extremely little of such a salt is dissolved by
acids. Such salts evidently can be precipitated in an acid medium, whereas
the salts that are dissolved by a given acid cannot be precipitated in the
presence of that acid.

The points just discussed may be given a more concrete form by the consid-
eration of the sulphide of iron and of copper. When dilute hydrochloric acid
is added to iron sulphide, hydrogen sulphide is evolved. The ionic repre-
sentation of the act of solution is the following :

FeS (slightly soluble) ^± Fe' • + S" \ — R s
2HC1 ^± 2Cr + 2H' / "

The negative ion S" coming from the slight amount of FeS dissolved in water
is also the ion of H2S. Hydrogen sulphide dissociates to a less degree than
does FeS ; that is, the concentration of Sx/ that can be maintained by H2S in
solution is less than that which can be maintained by FeS in solution. The
result is that some Sx/ ions unite with H' ions of the hydrochloric acid to
form undissociated molecules of HaS, thus reducing the concentration of S/x
ion. More FeS dissolves to keep up the equilibrium. This is kept up until
all the FeS is dissolved, or until (if FeS is in excess) the HC1 is so much ex-
hausted that the little which remains is in equilibrium with the other products.
As the H,S accumulates, the solution becomes saturated and the excess escapes
as gas.

In the case of copper sulphide, dilute hydrochloric acid has no action. The
ionic reactions would be :

CuS (very slightly soluble) \ ;± Cu' • + S" \ _^ R ~
2HC1 / i± 2C1' + 2H' / *~ 2

PHOSPHORUS. 219

But the concentration of S/x ions maintained by CuS in solution is less than
that maintained by H2S in solution, even in the presence of the excess of H-
ions of the dilute hydrochloric acid, which repress to some extent the disso-
ciation of H2S. Hence, not only is there no solution of the copper sulphide,
but if H2S is passed into an acidified solution of a copper salt, CuS is precipi-
tated. Only a rather concentrated solution of hydrochloric acid will so far
reduce the concentration of Sx/ ions as to allow the copper sulphide to
dissolve.

The subject may be summed up in a general statement, thus : The difficultly
soluble salts of weaker (less ionized) acids are, as a rule, dissolved by solutions
of the stronger (more ionized) acids. Exceptions are salts of extreme insolubility
of stronger acids, and, in a few cases, even of weaker acids.

17. PHOSPHORUS.

pi» = 31 (30.77).

Occurrence in nature. Phosphorus is found in nature chiefly ID
the form of phosphates of calcium (apatite, phosphorite), iron, and
aluminum, which minerals form deposits in some localities, but- occur
also diffused in small quantities through all soils upon which plants
will grow, phosphorus being an essential constituent of the food of
most plants. Through the plants it enters the animal system, where
it is found either in organic compounds, or — and this in by far the
greater quantity — as tricalcium phosphate principally in the bones,
which contain about 60 per cent, of it. From the animal system it
is eliminated chiefly in the urine.

Manufacture of phosphorus. Phosphorus was discovered and
made first in 1669 by Brandt, of Hamburg, Germany, who obtained
it in small quantities by distilling urine previously evaporated and
mixed with sand.

QUESTIONS. — How is sulphur found in nature? Mention of sulphur:
atomic weight, valence, color, odor, taste, solubility, behavior when heated,
and allotropic modifications. State the processes for obtaining sublimed,
washed, and precipitated sulphur. State composition and mode of preparing
sulphur dioxide and sulphurous acid ; what are they used for, and what are
their properties ? Explain the process for the manufacture of sulphuric acid
on a large scale. Mention of sulphuric acid : color, specific gravity, its action
on water and organic substances. Give tests for sulphates and sulphites, sul-
phuric and sulphurous acids. What is the difference between sulphates, sul-
phites, and sulphides? How is hydrogen sulphide formed in nature, and by
what process is it obtained artificially ? What are its properties, and what is
it used for? Mention antidotes in case of poisoning by sulphuric acid and
hydrogen sulphide.

220 NON-METALS AND THEIR COMBINATIONS.

The manufacture of phosphorus to-day depends on the deoxida-
tion of metaphosphoric acid by carbon at a high temperature in
retorts.

The acid is obtained by adding to any suitable tricalcium phophate sulphuric
acid in a quantity sufficient to combine with the total amount of calcium
present. The first action of sulphuric acid upon the phosphate consists in a
removal of only two-thirds of the calcium present, and the formation of an
acid phosphate :

CagCPOJa + 3HaSO4 = CaH4(PO4)2 -f 2CaSO4 + H2SO4.

The nearly insoluble calcium sulphate is separated by filtration, and the
solution of acid phosphate containing free sulphuric acid is evaporated to the
consistency of a syrup, when more calcium sulphate separates and a solution
of nearly pure phosphorig acid is left :

CaH4(PO4)2 + H2SO4 = CaS04 -f 2(H3POJ.

This syrupy phosphoric acid is mixed with coal and heated to a temperature
sufficiently high to expel water and convert the ortho- into meta-phosphoric
acid:

2(H3POJ = 2HPO3 + 2H2O.

The dry solid mixture of this acid and charcoal is now introduced into
retorts and heated to a strong red heat, when the following decomposition
takes place :

2(HP03) + 50 = H20 + SCO + 2P.

The three products formed escape in the form of gases from the retort, and by
passing them through cold water phosphorus is converted into a solid. The
reaction in the retorts is somewhat more complicated than above stated in the
equation, as some gaseous hydrogen phosphide and. a few other products are
formed in small quantities.

Also phosphorus is now made by subjecting to the action of a strong electric
current a mixture of tricalcium phosphate and carbon, when phosphorus is set
free, while calcium carbide and carbonic oxide are formed :

Ca,(PO4)2 + 140 = 2P + 3CaC2 -4- SCO.

Properties of phosphorus. When recently prepared, phos-
phorus is a colorless, translucent, solid substance, which has some-
what the appearance and consistency of bleached wax. In the
course of time, and especially on exposure to light, it becomes by
degrees less translucent, opaque, white, yellow, and finally yellowish-
red. At the freezing-point phosphorus is brittle ; as the temperature
increases it gradually becomes softer, until it fuses at 44° C. (111°F.),
forming a yellowish fluid, which at 290° C. (554° F.) (in the absence
of oxygen) is converted into a colorless vapor. Specific gravity 1.83
at 10° C. (50° F.)

The most characteristic features of phosphorus are its great affinity
for oxygen, and its luminosity, visible in the dark, from which

PHOSPHORUS. 221

latter property its name, signifying " carrier of light," has been
derived. In consequence of its affinity for oxygen, phosphorus has
to be kept under water, as it invariably takes fire when exposed to
the air, the slow oxidation taking place upon the surface of the
phosphorus soon raising it to 50° C. (122° F.) at which temperature
it ignites, burning with a bright white flame, and giving off dense,
white fumes of phosphoric oxide. The luminosity of phosphorus,
due to this slow oxidation, is seen when a piece of it is exposed to
the air, and whitish vapors are emitted which are luminous in the
dark ; at the same time an odor resembling that of garlic is noticed.

Phosphorus is insoluble in water, sparingly soluble in alcohol,
ether, fatty and essential oils, very soluble in chloroform and in
disulphide of carbon, from which solution it separates in the form of
crystals.

Although nitrogen has very weak chemical affinities, while those
of phosphorus are extremely strong, yet there is a close resemblance
in the chemical properties of these two elements. Both are chiefly
either trivalent or quinquivalent; both form compounds corresponding
to one another in composition, as also in properties. Thus we know
the two gaseous compounds NH3 and PH3 ; the oxides N2O3, N2O5,
and P2O3, P2O5. There is also metaphosphoric acid, HPO3, corre-
sponding to nitric acid, HNO3. The chlorides NC13 and PC13 are
known, and many other corresponding features may be pointed out
It will be shown later that nitrogen and phosphorus have a great
resemblance to the metallic elements arsenic and antimony.

Phosphorus not only combines directly with oxygen, but also with
chlorine, bromine, iodine, sulphur, and with many metals, the latter
compounds being known as phosphides.

Phosphorus is trivalent in some compounds, as in PC13, P2O3 ;
quinquivalent in others, as in PC15, P2O6.

The molecules of most elements contain two atoms ; phosphorus is
an exception to this rule, its molecule containing four atoms. The
molecular weight of phosphorus is consequently 4 X 30.77 = 123.08.

Allotropic modifications. Several allotropic modifications of
phosphorus are known, of which the red phosphorus (frequently
called amorphous phosphorus) is the most important. This variety is
obtained by exposing common phosphorus for some time to a tem-
perature of 260° C (500° F.), in an atmosphere of carbon dioxide.
The change takes place rapidly when a higher temperature is used
and pressure is applied. This modified phosphorus is a red powder,
which differs widely from common phosphorus. It is not poisonous.

222 NON-METALS AND THEIR COMBINATIONS.

not luminous, not soluble in the solvents above mentioned, not com-
bustible until it has been heated to about 280° C (536° F.), when it
is reconverted into common phosphorus.

Use of phosphorus. By far the largest quantity of all phos-
phorus (both common and red) is used for matches, which are made
by dipping wooden splints into some combustible substance, as
melted sulphur or paraffin, and then into a paste made by thoroughly
mixing phosphorus with glue in which some oxidizing agent (potas-
sium nitrate or chlorate) has been dissolved.

The so-called " safety matches" contain a mixture of antimony trisulphide,
red lead, and the chlorate and dichromate of potassium. This mixture will not
ignite by simple friction, but does so when drawn across a surface upon which
is a mixture of red phosphorus and antimony pentasulphide.

Pharmaceutical preparations containing phosphorus in the elementary state
are phosphorated oil, pills of phosphorus, and spirit of phosphorus. The second
is official.

Phosphorus is also used for making phosphoric acid and other compounds.

Poisonous properties of phosphorus ; antidotes. Common phosphorus is
extremely poisonous, two kinds of phosphorus-poisoning being distinguished.
They are the acute form, consequent upon the ingestion of a poisonous dose,
and the chronic form affecting the workmen employed in the manufacture of
phosphorus or of lucifer matches.

In cases of poisoning by phosphorus, efforts should be made to eliminate the
poison as rapidly as possible by means of stomach-pump, emetics, or cathartics.
As antidote a one-tenth per cent, solution of potassium permanganate has been
used successfully; it acts by oxidizing the phosphorus, converting it into
ortho-phosphoric acid. Oil of turpentine has also been used as an antidote,
though its action has not been sufficiently explained. Oil or fatty matter
(milk) must not be given, as they act as solvents of the phosphorus, causing its
more ready assimilation.

Detection of phosphorus in cases of poisoning. Use is made of its luminous
properties in detecting phosphorus, when in the elementary state. Organic
matter (contents of stomach, food, etc.) containing phosphorus will often show
this luminosity when agitated in the dark. If this process fails, in consequence
of too small a quantity of the poison, a portion of the matter to be examined
is rendered fluid by the addition of water, slightly acidulated with sulphuric
acid, and placed in a flask, which is connected with a bent glass tube leading
to a Liebig's condenser. The apparatus (Fig. 43) is placed in the dark, and
the flask is heated. If phosphorus be present, a luminous ring will be seen
where the glass tube, leading from the flask, enters the condenser. The heat
should be raised gradually to the boiling-point, the liquid kept boiling for
some time, and the products of distillation collected in a glass vessel. Phos-
phorus volatilizes with the steam, and small globules of it may be found in the
collected fluid. If, however, the quantity of phosphorus in the examined
matter was very small, it may all have become oxidized during the distillation,
and the fluid will then contain phosphorous acid, the tests for which will be
stated below.

PHOSPHORUS. 223

It should be mentioned that the luminosity of phosphorus vapors is dimin-
ished, or even prevented, by vapors of essential oils (oil of turpentine, for
instance), ether, olefiant gas, and a few other substances.

Oxides of phosphorus. Four oxides of phosphorus are known.
They are phosphorus monoxide, P4O, phosphorus trioxidc, P2O3, phos-
phorus tetroxide, P2O4, and phosphorus pentoxide, P2O5. The three
lower oxides are obtained by slow oxidation, or by the burning of
phosphorus in a limited supply of air ; while the pentoxide is formed

FIG. 43.

Apparatus for detection of phosphorus in cases of poisoning.

whenever phosphorus burns under ordinary conditions. The pent-
oxide is a white powder possessing an intense affinity for water,
with which it combines to form phosphoric acid, while the trioxide
with water produces phosphorous acid.

Hypophosphorous acid, Acidum hypophosphorosum, H3PO2,
PO.H2.OH = 65.53. When phosphorus is heated with solution of
potassium, sodium,, or calcium hydroxide, the hypophosphite of these

224 NON-METALS AND THEIR COMBINATIONS.

metals is formed, while gaseous hydrogen phosphide, PH3, is lib-
erated and ignites spontaneously. The action may be represented
thus :

3KOH + 4P + 3H20 = 3KPH2O2 + PH3.
or

3Ca(OH)2 + 8P + 6H2O = 3Ca(PH2O2)2 + 2PH3.

From calcium hypophosphite the acid may be obtained by decom-
posing the salt with oxalic acid, which forms insoluble calcium
oxalate, while hypophosphorous acid remains in solution :

Ca(PH202)2 + H2C204 = CaC204 + 2HPH2O2.

From potassium hypophosphite the acid may be liberated by the
addition of tartaric acid and alcohol, when potassium acid tartrate
forms, which is nearly insoluble in dilute alcohol and may be sepa-
rated by filtration.

Pure hypophosphorous acid is a white crystalline substance, acting
energetically as a deoxidizing agent. Although containing three
atoms of hydrogen, it is a monobasic acid, only one of the hydrogen
atoms being replaceable by metals.

Hypophosphorous acid of the U. S. P. contains 30 per cent, and
the diluted acid 10 per cent, of the pure acid dissolved in water.
Both preparations are colorless acid liquids, which, upon heating, lose
water and are afterward decomposed into phosphoric acid and hydrogen
phosphide, which ignites :

2H3P02 H3P04 + PH3.

Similar to the case of sulphur, the most stable acid of phosphorus is phos-
phoric acid, and the others show a tendency to pass to it. These are, therefore,
easily oxidized and also easily reduced. Thus, hypophosphorous acid is not
only quickly oxidized by the usual oxidizing agents, but even precipitates many
metals from their salts. Hypophosphites, when brought into the presence of
nascent hydrogen, are reduced to phosphine gas, PH3 (compare with sulphites).
All hypophosphites are soluble in water and nearly all are colorless. About
six are used in medicine.

Tests for hypophosphites.

(Use about a 5 per cent, solution of the sodium salt, NaPH2O2.)
1. Heat a small quantity of the dry sodium salt in a porcelain dish
until it ignites. The salt is decomposed into a phosphate and phos-
phine, which burns with a characteristic brilliant light, emitting a
white cloud of oxide of phosphorus. Some red phosphorus is also
formed.

2NaPH202 = Na2HPO, + PH3.
2PH3 + 80 = P205 + 3H20. 2PH3 + 30 = 2P + 3H,O.

PHOSPHORUS. 225

2. Acidify about 5 c.c. of the solution with dilute hydrochloric
acid, and add some mercuric chloride solution. A white precipitate
of mercurous chloride is formed. Above 60° C. and with excess of the
hypophosphite, further reduction to dark metallic mercury takes place.

4HgCl2 + Na.PHA + 2H2O = 4HgCl + H,PO4 + NaCl + 3HC1.
4HgCl + NaPHA + 2H2O == 4Hg + HSPO4 + NaCl + 3HC1.

3. Addition of silver nitrate solution causes a dark precipitate of
metallic silver. In the first instant, a white precipitate of silver hypo-
phosphite is seen, but this is very unstable.

NaPH2Q2 + 4AgN03 + 2H2O == 4Ag + NaH2PO4 + 4HN03.

4. When the solution is added to acidified potassium permanganate
solution, the latter is decolorized. The essential reaction is this,

NaPH202 + 02 = NaH2P04.

Tests 1 and 2 are very distinctive and usually sufficient to recognize
the acid or its salts.

Phosphorous acid, H3PO3, PO.H.(OH)2. This is a dibasic acid
obtained by dissolving phosphorous oxide in water:

PA + 3H20 = 2H3P03.

or still better by the action of water on phosphorus trichloride :
PC13 + 3H2O == H3P03 + 3HC1.

It is a colorless acid liquid, which forms salts known as phos-
phites ; it is a strong deoxidizing agent, easily absorbing oxygen,
forming phosphoric acid.

Tests. Phosphorous acid and its salts give practically the same
reactions as the hypophosphites. The following are the chief dis-
tinctions : Phosphites when added to solutions of calcium, barium, and
strontium salts give precipitates of phosphites of these metals, whereas
hypophosphites do not give a precipitate. Acidified permanganate
solution is decolorized only after some time by phosphites, but imme-
diately by hypophosphites.

Phosphites are of very little importance.

Phosphoric acids. Phosphoric oxide is capable of combining
chemically with one, two, or three molecules of water, forming
thereby three different acids.

P2O5 + H2O = H2P2O6 = 2HPO3 Metaphosphoric acid.
P2O5 -f 2H/) = H4P2O7 Pyrophosphoric acid.

P2O5 + 3H2O = H6P2O8 = 2H3PO4 Orthophosphoric acid.
15

226 NON-METALS AND THEIR COMBINATIONS.

These three acids show different reactions, act differently upon the
animal system, and form different salts.

Metaphosphoric acid, HPO3, PO2OH (Glacial phosphoric, acid).
This acid is always formed when phosphoric oxide is dissolved in
water ; gradually, and more rapidly on heating with water, it absorbs
the latter, forming orthophosphoric acid; by heating the latter to
near a red heat metaphosphoric acid is re-formed.

Metaphosphoric acid is a monobasic acid which forms colorless,
transparent, amorphous masses, readily soluble in water. It coagu-
lates albumin (pyro- and orthophosphoric acids do not) and gives a
white precipitate with ammonio-silver nitrate ; it is not precipitated
by magnesium sulphate in the presence of ammonia and ammonium
chloride. It acts as a poison, while common phosphoric acid is
comparatively harmless.

Pyrophosphoric acid, H4P2O7, P2O3(OH)4. This is a tetra-basic acid
which gives a white precipitate with ammonio-silver nitrate, while orthophos-
phoric acid gives a yellowish precipitate ; it is not precipitated by ammonium
molybdate, and does not coagulate albumin.

Phosphoric acid, Orthophosphoric acid, Acidum phosphoricum,
H3PO4, PO(OH)3 = 97.29 (Common or tribasic phosphoric acid).
Nearly all phosphates found in nature are orthophosphates.

Phosphoric acid may be made by burning phosphorus, dissolving
the phosphoric oxide in water, and boiling for a sufficient length of
time to convert the meta- into orthophosphoric acid.

Experiment 16. Place a piece of phosphorus (about 0.5 gramme), after having
dried it quickly between filter paper, in a small porcelain dish, standing upon
a glass plate ; ignite the phosphorus by touching it with a heated wire, and
place over the dish an inverted large beaker. The white vapors of phosphoric
oxide soon condense into flakes, which fall on the glass plate. Collect the
white mass with a glass rod, 'and dissolve in a few c.c. of water. Use a portion
of the solution for tests of metaphosphoric acid; evaporate the remaining
quantity in a porcelain dish until it becomes syrupy, dilute with water and use
it for making tests for orthophosphoric acid, either as such or after having
neutralized with sodium carbonate. How much phosphorus is needed to make
490 grammes of the U.S. P. 10 per cent, phosphoric acid?

Phosphoric acid is also made by gently heating pieces of phos-
phorus with diluted nitric acid, when the phosphorus is oxidized,
red fumes of nitrogen tetroxide escaping :

3P + 5HNO3 + 2H2O = 3H3PO4 + 5NO.

The liquid is evaporated until the excess of nitric acid has been

PHOSPHORUS. 227

expelled, and enough of water added to obtain an acid which contains
85 per cent, of the pure H3PO4. Specific gravity 1.707 at 25° C.

Diluted phosphoric acid, U. S. P., is made by mixing 100 Gm. of
the 85 per cent, acid with 750 Gm. of water. It contains 10 per cent,
of absolute orthophosphoric acid.

Phosphoric acid, U. S. P., is a colorless, odorless, strongly acid
liquid, which, on evaporation, forms a thick syrupy liquid. This, on
cooling, slowly solidifies in the form of large crystals, which are
highly deliquescent. Heated to a sufficiently high temperature the
acid loses water, being converted successively into pyrophosphoric
and metaphosphoric acid, which is finally volatilized at a low red
heat. It is a tribasic acid, forming three series of salts, namely :

Na3PO4 = Trisodium phosphate.

Na2HPO4 = Disodium hydrogen phosphate.
NaH2PO4 = Sodium dihydrogen phosphate.

If the metal be bivalent, the formulas are thus :

Ca3(PO4)2 = Tricalcium phosphate.
Ca2H2(PO4)2 = Dicalcium orthophosphate.
CaH4(PO4)2 = Monocalcium orthophosphate.

According to the number of hydrogen atoms replaced in the acid,
the salts formed are also termed primary, secondary, and tertiary
phosphates ; KH2PO4 being, for instance, primary potassium phos-
phate ; Na2HPO4 secondary sodium phosphate ; Ag3PO4 tertiary sil-
ver phosphate. All the alkali phosphates, but only primary phos-
phates of the other metals, are soluble in water.

All phosphates insoluble in water are dissolved by nitric, hydrochloric, or
sulphuric acid ; also by acetic acid, except those of lead, aluminum, and ferric
iron. All are soluble in phosphoric acid (forming acid phosphates), except those
of lead, tin, mercury, and bismuth. Primary alkali phosphates are acid to
litmus, but secondary alkali phosphates, although they are acid salts, are alka-
line to litmus because of partial hydrolysis by water into primary phosphate and
free alkali. Tertiary alkali phosphates are decomposed by water into the second-
ary salt and free alkali.

Phosphoric acid belongs to the class of weak acids, and the three hydrogen
atoms in the molecule show very different degrees of dissociation. It dissoci-
ates chiefly according to this equation, H3PO4 ~£. H* + H2PO/. The dihy-
drophosphate ion, H2PO/, dissociates to a small degree into H* and HPO/'
ions, as is shown by the fact that monosodium phosphate has a slightly acid
reaction to litmus, thus :

NaH2PO4 ^ Na* + H2PO/
H2PO4' ^1 H' + HP04/X.

The ion HPO/' is practically not dissociated into H' and PO/' ions, as is

228 NON-METALS AND THEIR COMBINATIONS.

evidenced by the slightly alkaline reaction of disodium phosphate, which dis-
sociates thus,

Na2HP04 i± 2Na- + HPO4".

The alkaline reaction is due to the formation of a slight quantity of free alkali
by the ions of water (hydrolysis) thus,

2Na« + HPO/'l^ Hjpo,
(OH)' + H- /

Na2HPO4 + H20 = NaOH + NaH2PO4,

Trisodium phosphate is completely hydrolyzed in solution into disodium phos-
phate and sodium hydroxide, Na3PO4 + H2O = Na2HPO4 + NaOH.

Tests for phosphoric acid and phosphates.
(Sodium phosphate, Na^HPO^ may be used.)

1. Add to phosphoric acid, or to an aqueous solution of a phos-
phate, a mixture of magnesium sulphate, ammonium chloride, and
ammonia water ; a white crystalline precipitate falls, which is mag-
nesium ammonium phosphate :

H3P04 + MgS04 + 3NH4OH = MgNH4PO4 + (NH4)2SO4 + 3H2O;
Na-jHPO, -f MgS04 + NH4OH = MgNH4PO4 + Na£O4 + H2O.

2. Add to a solution of disodium phosphate, silver nitrate ; a yellow
precipitate of silver phosphate is produced, which is soluble both in
ammonia and nitric acid :

Na,HP04 + 3AgN03 = Ag3PO4 + 2NaNO3 + HN03.

3. Add to phosphoric acid, or to a phosphate dissolved in water
or in nitric acid, an excess of a solution of ammonium molybdate in
dilute nitric acid, and heat gently ; a yellow precipitate of phospho-
molybdate of ammonium, (NH4)3PO4.10MoO3.2H2O, is produced ;
the precipitate is readily soluble in ammonia water. This test is by
far the most delicate, and even traces of phosphoric acid may be
recognized by it ; moreover, it can be used in an acid solution, while
the first two tests cannot. Only a few drops of the solution to be
tested should be used.

4. Add to a solution of a phosphate, calcium or barium chloride ;
a white precipitate of calcium or barium phosphate is produced, which
is soluble in acids.

5. Ferric chloride produces a yellowish-white precipitate of ferric
phosphate, Fe2(PO4)2, thus :

2Na,HP04 + Fe.Cle = Fe2(PO4)2 + 4NaCl + 2HC1.
The liberated hydrochloric acid dissolves some of the precipitate,
which may be avoided by adding previously some sodium acetate ;

PHOSPHORUS. 229

the hydrochloric acid combines with the sodium of the acetate, and
the acetic acid which is set free has no dissolving action upon the
ferric phosphate.

Hydrogen phosphide, PH3 (Phosphoretted hydrogen, phosphine). The forma-
tion of this compound has been mentioned in the paragraph on Hypophos-
phorous acid. It is a colorless, badly smelling, poisonous gas, which, when
generated as directed above, is .spontaneously inflammable. This last-named
property is due to the presence of small quantities of another compound of
phosphorus and hydrogen which has the composition P2H4, and is spontaneously
inflammable, while the compound PH3 is not.

Hydrogen phosphide corresponds to the analogous composition of ammonia,
NH3. While the latter is readily soluble in water and has strong basic prop-
erties, hydrogen phosphide is but sparingly soluble in water and its basic prop-
erties are very weak. However, a few salts, such as the phosphonium chloride,
PH4C1, analogous to ammonium chloride, NH4C1, are known.

There is no scientific evidence whatever for the correctness of the statement,
found in some text-books, that hydrogen phosphide is a product of the putre-
faction of certain organic compounds.

Phosphorus trichloride, PC13. This is a colorless liquid, heavier than
water, boiling at 76° C. Its vapors are very pungent. Water decomposes it
very rapidly into phosphorous and hydrochloric acids, thus, PC13 -f- 3H2O =
HsP03 + 3HC1. For this reason the liquid gives white fumes in moist air.
It can only be obtained by direct union of the elements. This is done by
leading chlorine gas over phosphorus in a retort, when the elements unite with
combustion, and the trichloride distils over into a cold receiver. It is purified
by redistillation in contact with some phosphorus, which removes any penta-
chloride present.

Phosphorus pentachloride, PC15. This consists of pale yellow crystals,
and is obtained by passing chlorine into phosphorus trichloride. It decom-
poses at once in water into phosphoric and hydrochloric acids, PC15 + 4H2O —
H3PO4 -f 5HC1. It fumes strongly in moist air. At 300° C. it is completely
dissociated into trichloride and chlorine. With a small proportion of water it
forms phosphorus oxychloride thus, PC15 + H2O = POC13 + 2HC1. The oxy-
chloride is a colorless liquid that boils at 107.2° C. The pentachloride is often
used in organic chemistry to substitute chlorine for hydroxyl (OH) in compounds.

The bromine compounds of phosphorus, PBr3 and PBr5, are very similar to
the chlorine compounds, and are made in the same way.

QUESTIONS.— In what forms of combination is phosphorus found in na-
ture? Give an outline of the process for manufacturing phosphorus. What
are the symbol, valence, atomic, and molecular weights of phosphorus. State
the chemical and physical properties both of common and red phosphorus.
By what methods may phosphorus be detected in cases of poisoning? What
two oxides of phosphorus are known ; what is their composition, and what
four acids do they form by combining with water? State the official process
for making phosphoric acid, and what are its properties? By what tests may
the three phosphoric acids be recognized and distinguished from phosphorous
acid? What is a phosphide, phosphite, phosphate, and hypophosphite ?
What is glacial phosphoric acid, and in what respect does its action upon the
animal system differ from the action of common phosphoric acid?

230 NON-METALS AND THEIR COMBINATIONS.

18. CHLOEINE.

Cl' = 35 (35.18).

Halogens. The four elements, fluorine, chlorine, bromine, and
iodine, which form a natural group of elements, are known as halogens,
the term meaning producers of salt. The relation shown by the atomic
weights of these four elements has been mentioned in connection with
the consideration of natural groups of elements generally (see page
125). In many other respects a resemblance or relation can be dis-
covered. For instance- : While the haloids as a general rule act as
univalent elements, they all form compounds into which they enter
with a valence of either 3, 5, or 7 ; they combine with hydrogen,
forming the acids HF, HC1, HBr, HI, all of which are colorless
gases, soluble in water ; they combine directly with most metals,
forming fluorides, chlorides, bromides, and iodides. The relative
combining energy lessens as the atomic weight increases ; fluorine
with the lowest atomic weight having the greatest, iodine with the
highest atomic weight the smallest, affinity for other elements. The
first two members of the group are gases, the third (bromine) is a
liquid, the last (iodine) a solid, at ordinary temperature. They all
show a distinct color in the gaseous state, have a disagreeable odor,
and possess disinfecting properties.

Occurrence in nature. Chlorine is found chiefly as sodium
chloride or common salt, NaCI, either dissolved in water (small
quantities in almost every spring water, larger quantities in some
mineral waters, and the principal amount in sea-water), or as solid
deposits in the interior of the earth as rock salt.

Other chlorides, such as those of potassium, magnesium, calcium,
also are found in nature. As common salt, chlorine enters the animal
system, taking there an active part in many of the physiological and
chemical changes.

Preparation of chlorine. Most methods of liberating chlorine
depend on an oxidation of the hydrogen of hydrochloric acid by
suitable oxidizing agents, the hydrogen being converted into water,
while chlorine is set free.

As oxidizing agents, may be used potassium chlorate, potassium
dichromate, potassium permanganate, chromic acid, nitric acid, and
many other substances.

The most common and cheapest mode of obtaining chlorine is to
heat manganese dioxide, usually called black oxide of manganese,

CHLORINE. 231

with hydrochloric acid, or a mixture of manganese dioxide and
sodium chloride with sulphuric acid :

Mn02 + 4HC1 = MnCl2 -f 2H2O + 2C1.

MnO2 + 2NaCl -f 2H2SO4 = MnSO4 -f Na2SO4 -f 2H2O + 2C1.
Chlorine is liberated also by the action of sulphuric or hydrochloric acid on
bleaching-powder, which is a mixture of calcium chloride and calcium hypo-
chlorite :

CaCl2.Ca(ClO)2 -f 2H2SO4 = 2CaSO4 + 2H2O + 401.

Chlorine is now also produced by electrolysis of sodium chloride solution in
suitably constructed apparatus.

Experiment 17. Use apparatus as in Fig. 39, page 168. Conduct operation
in a fume-chamber. Place about 50 grammes of manganese dioxide in coarse
powder in the flask, cover it with hydrochloric acid, shake up well to insure
that no dry powder be left at the bottom of the flask, apply heat, and collect
the gas in dry bottles by downward displacement. Keep the bottles loosely
covered with pieces of stiff paper while filling them. Use the gas for the
following experiments :

a. Fill a test-tube with chlorine, a second test-tube of same size with hydro-
gen ; place them over one another so that the gases mix by diffusion, then
hold them near a flame ; a rapid combustion or explosion ensues.

b. Hold in one of the bottles filled with chlorine a lighted wax candle, and
notice that it continues to burn with liberation of carbon. The hydrogen con-
tained in the wax is in this case the only constituent of the wax which burns,
i. e., combines with chlorine.

c. Moisten a paper with oil of turpentine, C10H16, and drop it into another
bottle filled with the gas ; combustion ensues spontaneously, a black smoke of
carbon being liberated.

d. Drop some finely powdered antimony into another bottle, and notice that
each particle of the metal burns while passing through the gas, forming white
antimonous chloride, SbCls.

e. Pass some chlorine gas into water, and suspend in the chlorine water thus
formed colored flowers or pieces of dyed cotton, and notice that the color fades
and in many cases disappears completely in a few hours.

Properties. Chlorine is a yellowish-green gas, having a disagree-
able taste and an extremely penetrating, suffocating odor, acting
energetically upon the air-passages, producing violent coughing and
inflammation. It is about two and a half times heavier than air,
soluble in water, and convertible into a greenish-yellow liquid by a
pressure of about six atmospheres.

Chemically, the properties of chlorine are well marked, and there
are but few elements which have as strong an affinity for other ele-
ments as chlorine ; it unites with all of them directly, except with
oxygen, nitrogen, and carbon, but even with these it may be made to
combine indirectly. The act of combination between chlorine and
other elements is frequently attended by the evolution of so much

232 NON-METALS AND THEIR COMBINATIONS.

heat that light is produced, or, in other words, combustion takes place.
Thus, hydrogen, phosphorus, and many metals burn easily in chlorine.
The affinity between chlorine and hydrogen is intense, a mixture of
the two gases being highly explosive. Such a mixture, kept in the
dark, will not undergo chemical change, but when ignited, or when
exposed to direct sunlight, combination between the two elements
occurs instantly with an explosion. The affinity of chlorine for
hydrogen is also demonstrated by its property of decomposing water,
ammonia, and many hydrocarbons (compounds of carbon with hydro-
gen), such as oil of turpentine, C10H16, and others :

H20 + 2C1 = 2HC1 -f O.

NH3 + 3C1 = 3HC1 + N.

C10H16 + 16C1 = 16HC1 + IOC.

As shown by these formulas, hydrochloric acid is formed, while
the other elements are set free.

Chlorine is a strong disinfecting, deodorizing, and bleaching agent ;
it acts as such either directly by combining with certain elements of
the coloring or odoriferous matter, or, indirectly, by decomposing
water with liberation of oxygen, which in the nascent state — that is,
at the moment of liberation— has a strong tendency to oxidize other
substances.

It should be noted that perfectly dry chlorine has practically no action on
other substances when also dried. In the absence of all moisture it has no
bleaching action. This inactivity of dry chlorine is exemplified by the fact that
it is now sold in steel cylinders. As ordinarily used, however, it acts readily,
because of the moisture in the atmosphere, and on objects, even if water is not
supplied directly.

Compound solution of chlorine, Liquor chlori compositus (Chlorine
water). Cold water absorbs about two volumes of chlorine, which is equal to
0.4 per cent, by weight. This solution is unstable because the chlorine grad-
ually combines with hydrogen of water, while oxygen is set free. It is for this
reason that the U. S. P. has substituted for ordinary chlorine water the com-
pound solution of chlorine, which is to be freshly made when wanted. It is
prepared by digesting in a large flask potassium chlorate with hydrochloric
acid and then adding water to dissolve the liberated chlorine, as also some
chlorinated products and the potassium chloride which are formed. The
reaction, when complete, is this :

KC103 + 6HC1 == KC1 + 3H2O + 6C1.
Chlorine water is a greenish-yellow liquid, having the odor of chlorine.

Hydrochloric acid, Acidum hydrochloricum, ifCl = 36.18
(Muriatic acid). This acid occurs in the gastric juice of mammalia,

CHLORINE. 233

and has been found in some volcanic gases. One volume of hydrogen
combines with one volume of chlorine to form two volumes of hydro-
chloric acid.

For all practical purposes the acid is obtained by the decomposition
of a chloride by sulphuric acid :

NaCl + H2S04 = HC1 + NaHSO4;
or

2NaCl + H2S04 = 2HC1

Experiment 18. Use apparatus as in Fig. 39, p. 168. Place about 20 grammes
of sodium chloride into the flask (which should be provided with a funnel-tube)
and add about 30 c.c. of concentrated sulphuric acid ; mix well, apply heat, and
pass the gas into water for absorption. If a pure acid be desired, the gas has
to be passed through water contained in a wash-bottle ; apparatus shown in
Fig. 42, page 207, may then be used. Use the acid made for tests mentioned
below. How much of the U. S. P. 31.9 per cent, hydrochloric acid can be
made from 117 pounds of sodium chloride?

The liberation of hydrochloric acid from a chloride by sulphuric acid is an
example of reversible reactions that run to completion because of the removal
of one of the factors that is necessary to maintain an equilibrium (see page
114). The character of the reaction is like that in the case of the liberation
of nitric acid, the ionic features of which are discussed in Chapter 15. The
ionic reaction is this :

NaCl ^± Na* + C1M ^± HC1 — HC1.
H2SO4 ^± HSO/ + H- / dissolved gas.

Hydrochloric acid is a colorless gas, has a sharp, penetrating odor,
and is very irritating when inhaled. It is neither combustible nor
a supporter of combustion, and has great affinity for water, which
property is the cause of the formation of white clouds whenever the gas
comes in contact with the vapors of water, or with moist air ; the white
clouds being formed of minute particles of liquid hydrochloric acid.

While hydrochloric acid is a gas, this name is used also for its
solution in water, one volume of which at ordinary temperature takes
up over 400 volumes of the gas.

The hydrochloric acid of the U. S. P. is an acid containing 31.9
per cent, of HC1. It is a colorless, fuming liquid, having the odor
of the gas, strong acid properties, and a specific gravity of 1.158.
The official diluted hydrochloric acid is made by mixing 100 parts
by weight of the above acid with 219 parts of water. It contains 10
per cent, of HCL

The same antidotes may be used as for nitric acid.

A 20.2 per cent, solution of hydrochloric acid distils unchanged at 110° C.
(230° F.) under 760 mm. pressure. When a more concentrated solution is
heated,, it first loses mainly the gas, and a more dilute solution mainly water

234 NON-METALS AND THEIR COMBINATIONS.

vapor, until 20.2 per cent, is reached, when the residue in the flask passes over
unchanged. Other acids— for example, sulphuric, nitric, hydriodic, hydro-
brornic — show a similar property.

Neither the dry gas (HC1) nor the liquefied gas has any marked acid char-
acter. They do not conduct electricity and have no action on dry litmus-
paper or on zinc, but the presence of water causes strong acid properties to be
developed. This is explained on the Dissociation Theory, which holds that
only hydrogen ions have acid properties. Water is required for the ionization
of HC1, and without it the gas lacks acid character. A solution of the gas in
liquids like benzene and toluene, which have scarcely any ionizing power, has
practically no effect on zinc, which is freely attacked by an aqueous solution
of the gas. The same is true of hydrobromic and hydriodic acids (Chapter
15).

Nearly all chlorides are soluble in water. Of those ordinarily met with
only two are insoluble in water, namely, silver and mercurous chlorides, and
one is difficultly soluble in cold water, but more readily in hot water, namely,
lead chloride.

Tests for hydrochloric acid and chlorides.
(Sodium chloride, NaCl, may be used.)

1. To hydrochloric acid, or to solution of chlorides, add silver
nitrate : a white, curdy precipitate is produced, which is soluble in
ammonia water, even when very dilute, but insoluble in nitric acid :

AgN03 + Nad = AgCl. -f NaNO3.
Ag' + NO/ + Na' + Cl' — AgCl '+ Na' + NO/.

2. Add solution of mercurous salt (mercurous nitrate) : a white
precipitate of mercurous chloride (calomel) is produced, which black-
ens on the addition of ammonia :

HgN03 + NaCl = HgCl + NaNO3.
Hg' + N03' + Na- + Cl' — HgCl + JNV + NO/.

3. Add solution of lead acetate : a white precipitate of lead chloride
is formed, which is soluble in hot, or in much cold water, and is, there-
fore, not formed in dilute solutions. Its composition is PbCl2.

Pb(C2H302)2 + 2NaCl PbCl2 + 2Na(C2H3O2).

Pb" + 2(C,H302)' + 2Na- + 201' - PbCl2 + 2Na' + 2(C2H3O2)'.

4. To a dry chloride add strong sulphuric acid and heat : hydro-
chloric acid gas is evolved, which may be recognized by the odor, or
by its action on silver nitrate, when a drop of the solution on the end
of a glass rod is held in the gas. (The insoluble chlorides of silver,
lead, and mercury do not give this reaction.)

5. Chlorides treated with sulphuric acid and manganese dioxide
evolve chlorine.

Test 1, combined with test 5, is the most decisive proof of hydro-

CHLORINE. 235

chloric acid or chlorides. The others are more corroborative than
decisive.

Nitro-hydrochloric acid, Acidum nitro-hydrochloricum, Aqua
regla (Nitro-muriatic acid). Obtained by mixing 18 c.c. of nitric
acid with 82 c.c. of hydrochloric acid. The two acids act chemically
upon each other, forming chloronitrous gas, chlorine, and water :

HN03 + 3HC1 = NOC1 + 2H2O + 2C1.

The dissolving power of this acid upon gold and platinum depends
on the action of the free chlorine. The action on platinum is repre-
sented by this equation :

2HNO3 + 8HC1 + Pt = H2Pt.Cl6 f 2NOC1 -f 4H2O.

Chloroplatinic acid, H2PtCl6, is in solution. This is used as a test-
solution.

The official diluted nitrohydrochloric acid is made by mixing 182 c.c. of hydro-
chloric acid with 40 c.c. of nitric acid and adding, when effervescence has
ceased, 782 c.c. of water.

Compounds of chlorine -with oxygen. There is no method known
by which to combine chlorine and oxygen directly, all the compounds formed
by the union of these ele%ients being obtained by indirect processes. The
oxides of chlorine are the following:

Chlorine monoxide or hypochlorous oxide, C12O.
Chlorine dioxide, C1Q2.

Chlorine heptoxide, C12O7.

The first two oxides are yellow or brownish-yellow gases ; the third one is a
colorless liquid ; all combine with water, forming hypochlorous, chlorous and
chloric, and perchloric acid, thus :

C12O + H2O = 2HC1O.

2C102 + H20 HC102 + HC103.

C12O7 + H2O 2HC104.

The oxide, C12O5, from which chloric acid, HC1O3, might be formed, is not
known. The chlorine oxides, the acids, and many of their salts are distin-
guished by the great facility with which they decompose, frequently with vio-
lent explosion, for which reason care must be taken in the preparation and
handling of these compounds.

Chlorine acids.

Hypochlorous acid, HC1O. Chloric acid, HC1O8.

Chlorous acid, HC1O2. Perchloric acid, HC1O4.

Hydrochloric acid, HC1.

236 NON-METALS AND THEIR COMBINATIONS.

With the exception of hydrochloric acid, which has been considered,
none of the five acids is of practical interest as such, but many of
the salts of hypochlorous and chloric acids, known as hypochlorites
and chlorates respectively, are of great and general importance.

The constitution of the chlorine acids may be represented by the following
graphic formulas. It is here assumed that chlorine is univalent in hypochlo-
rous, trivalent in chlorous, quinquivalent in chloric, and septivalent in per-
chloric acid :

II II

H — O — Cl, H — O — Cl = 0, H — O — Cl, H — O — Cl = O

O O

Chlorine monoxide, C12O, and Hypochlorous acid, HC1O. When
chlorine is passed over yellow mercuric oxide in a tube, chlorine mon-
oxide is formed, thus,

2HgO + 2C12 = HgO.HgCL, + C12O.

It is a brownish-yellow gas which decomposes with explosion when
heated. One volume of water dissolves 200 volumes of the gas,
giving a yellow solution of hypochlorous acid which has the strong
odor of the chlorine monoxide,

C12O + H2O = 2HC1O.

Hypochlorous acid is also obtained in solution when chlorine gas is
passed into a suspension of mercuric oxide in water, thus,

2HgO + 2C12 + H20 = HgO.HgCl, -f 2HC1O.

The compound known as mercury oxychloride is formed and may be
removed, being insoluble.

Properties. Hypochlorous acid is a feeble (slightly ionizing) mono-
basic acid, which unites with active bases, forming hypochlorites. It
can be obtained only in solution, and keeps only when dilute and
cold. When concentrated it changes gradually to a considerable ex-
tent into chloric and hydrochloric acids, thus,
3HC10 = HC103 + 2HC1.

Warming a solution of the acid, or exposing it to sunlight, causes a
rapid evolution of oxygen,

2HC10 = 2HC1 + 2O.

As a result of this action, the acid is a strong oxidizer. This decom-
position is interesting, as it explains the oxidizing action of chlorine
in the presence of water, and the fact that chlorine water exposed to
bright light does not keep, but gives off oxygen and leaves a solution
of nothing but hydrochloric acid. When chlorine is dissolved, a re-
versible reaction takes place, thus,

C12 + H20 ^± HC1 + HC10.

CHLORINE. 237

Only a slight quantity of hypochlorous acid is formed at one time,
but its decomposition and constant removal in this way allows the
action to go forward to completion. The final result makes it appear
that chlorine decomposes water with direct liberation of oxygen,
which is usually represented by the equation,

C12 + H2O = 2HC1 + O.

Hypochlorites. For practical purposes solutions of free hypochlorous
acid are not made, but the acid is liberated from its salts when wanted. The
hypochlorites are formed by the action of chlorine on the hydroxide of potas-
sium, sodium, calcium, etc., at the ordinary temperature. As stated above,
chlorine with water forms HC1 and HC1O, but the action does not go far,
because these two acids tend to decompose each other in the reverse direction
to produce chlorine. But if they are removed, as by neutralization, action
will be complete, thus,

2C1 -f H2O = HC1 + HC1O

HC1 + NaOH = NaCl + H2O

HC10 + NaOH = NaCIO + H2O.

It will be seen that when hypochlorite is made in this manner there is always
an equivalent amount of a chloride in the mixture. The reaction is generally
written,

2C1 + 2NaOH = NaCl + NaCIO + H2O.

When a hypochlorite is acidified with an active acid, the reverse of the above
reactions takes place, hydrochloric and hypochlorous acids being liberated,
which between them evolve chlorine (see bleaching powder). When a hypo-
chlorite is heated, it decomposes into chlorate and chloride, thus,

SNaCIO = NaClOs + 2NaCl.

Under some conditions a hypochlorite slowly gives off oxygen, leaving a chlo-
ride, but the action may be enormously increased by adding a catalytic agent,
for example, a cobalt salt (see under Oxygen).

Solution of chlorinated soda, Liquor sodae chlorinatse (Solution of
sodium hypochlorite, Labarraque 's solution). This is a solution that yields 2.4
per cent, of available chlorine. It contains chloride and hypochlorite of sodium,
and is made by adding sodium carbonate to a solution of bleaching powder
(calcium hypochlorite), thus precipitating calcium carbonate :

CaCl2 -f Ca(ClO)2 -f 2Na2CO3 = 2CaCO3 -f 2NaCl + 2NaClO.

It is a clear pale greenish liquid, having a faint chlorine-like odor and strong
bleaching properties.

Chloric acid, HC1O3, may be obtained from potassium chlorate b}*
the action of hydrofluosilicic acid ; it is, however, an unstable sub-
stance which will decompose, frequently with a violent explosion.
Chlorates are generally obtained by the action of chlorine on alkali
hydroxides at a temperature of about 100° C. (212° F.).
6KOH + 6C1 as 5KC1 + KC103 + 3H2O.

238 NON-METALS AND THEIR COMBINATIONS.

The explanation of this action is that chlorine first forms a hypo-
chlorite, which, as stated above, decomposes by heating into chlorate
and chloride. The change will be clearer if written in two steps :
6KOH + 6C1 = 3KC1 -f 3KC1O + 3H2O.

3KC10 = 2KC1 + KC103.

In recent years large quantities of chlorates, especially potassium
chlorate, are made by passing an electric current, under proper con-
ditions, through an alkaline solution of potassium chloride.

Perchloric acid, HC1O4. This is a colorless liquid, which, in the pure
state, decomposes, and often explodes spontaneously when kept. A 70
per cent, aqueous solution is stable. Although it contains more oxygen than
the other acids of chlorine, it is the most stable one of all. It can be prepared
by distilling a mixture of potassium perchlorate and concentrated sulphuric
acid in a vacuum. It was seen in the chapter on oxygen that potassium chlor-
ate, when heated, gives the perchlorate, chloride, and oxygen. The perchlor-
ate, being difficultly soluble in water, can be separated easily from the far more
soluble chloride.

Tests for chlorates and hypochlorites.
(Potass, chlorate, KC1O3, and bleaching powder, Ca(ClO)2.CaCl2, may be used.)

1. Chlorates liberate oxygen when heated by themselves.

2. Chlorates liberate chlorine dioxide, C1O2, a deep-yellow explo-
sive gas, on the addition of strong sulphuric acid.

2KC103 + H2S04 = K2S04 + 2HC1O3.
3HC103 = HC104 + H20 + 2C102.

This test should be made only on a quantity about the size of a pea.

3. Chlorates deflagrate when sprinkled on red-hot charcoal.

4. Hypochlorites are strong bleaching agents, and evolve a pecu-
liarly smelling gas (chlorine) on the addition of acid (see page 236).

QUESTIONS. — State the names and general physical and chemical properties
of the four halogens. How is chlorine found in nature, and why does it not
occur in a free state? State the general principle for liberating chlorine from
hydrochloric acid, and explain the action of the latter on manganese dioxide.
Mention of chlorine : its atomic weight, molecular weight, valence, color, odor,
action when inhaled, and solubility in water. How does chlorine act chemi-
cally upon metals, hydrogen, phosphorus, water, ammonia, hydrocarbons, and
coloring matters? Mention two processes for making hydrochloric acid; state
its composition, properties, and tests by which it may be recognized. What is
aqua regia? State the composition of hypochlorous and chloric acids. What
is the difference in the action of chlorine upon a solution of potassium hydrox-
ide at ordinary temperature and at the boiling-point ? How many pounds of
manganese dioxide, and how many of hydrochloric acid gas are required to
liberate 142 pounds of chlorine ?

BROMINE— IODINE- FL UORINE. 239

19. BROMINE— IODINE— FLUORINE.

Bromine, Bro'mum, Br = 79.36. This element is found in sea-
water and many mineral waters, chiefly as magnesium, calcium, and
sodium bromides, which compounds, however, represent in all these
waters a comparatively small percentage of the total quantity of the
different salts present. Most of these salts are separated from the
water by evaporation and crystallization, and the remaining mother-
liquor, containing the bromides, is treated with chlorine, which liber-
ates bromine, the vapors of which are condensed in cooled receivers :

MgBr2 -f 2C1 = MgCl2 + 2Br.

Bromine is at common temperature a heavy, dark reddish-brown
liquid, giving off yellowish-red fumes of an exceedingly suffocating
and irritating odor; it is very volatile, freezes at about — 24° C.
( — 11° F.), and has a specific gravity of 2.99; it is soluble in 33
parts of water, more freely in alcohol, abundantly in ether and bisul-
phide of carbon ; it is a strong disinfectant, and its aqueous solution
is also a bleaching agent ; it acts as a corrosive poison.

Hydrobromic acid, Acldum hydrobromicum, HBr = 8O.36.
This acid cannot well be obtained by the action of concentrated sul-
phuric acid upon bromides, since the hydrobromic acid first formed
becomes readily decomposed with formation of sulphur dioxide and
free bromine. Thus :

2NaBr + H2SO4 = 2HBr + Na2SO4;
2HBr + H2SO4 = 2Br + SO2 + 2H2O.

If, however, dilute sulphuric acid is added to a warm solution of
potassium bromide, potassium sulphate is formed, a portion of which
crystallizes on cooling. From the remaining portion of the salt, the
hydrobromic acid may be separated by distillation.

Hydrobromic acid may also be obtained by the formation of bromide of
phosphorus, PBr5 (the two elements combine directly), and its decomposition

by water :

PBr5 + 4H20 = 5HBr + H3PO4.

In the form of solution this acid may be prepared also by treating bromine
under water with hydrogen sulphide until the brown color of bromine has
entirely disappeared. The reaction is as follows :

lOBr + 2H2S + 4H20 = lOHBr + H2SO, + S.

The liquid is filtered from the sulphur and separated from the sulphuric acid
by distillation,

240 NON-METALS AND THEIR COMBINATIONS.

Hydrobromic acid is, like hydrochloric acid, a colorless gas, of
strong acid properties, easily soluble in water.

Diluted hydrobromic avid, Acidum hydrobromicum dilutum, is a solu-
tion of 10 per cent, of hydrobromic acid in water. It is a colorless,
odorless, acid liquid of the specific gravity 1.076.

Hydrobromic acid acts in nearly all respects like hydrochloric. It is less
stable, and less powerful oxidizing agents will liberate the bromine than are
required to liberate chlorine. Nearly all bromides are soluble in water, the
insoluble ones being those of silver, mercury (ous), and lead. Bromides are
mostly white.

The ionic reactions for bromine compounds are analogous to those for chlo-
rine compounds.

Hypobromous acid, HBrO ; Bromic acid, HBrO3, and their
salts, the hypobromites and bromates, are analogous to the corre-
sponding chlorine compounds, and may be obtained by analogous
processes. Oxides of bromine are not known.

Tests for Bromides.
(Potassium bromide, KBr, may be used.)

1. Silver nitrate produces in solutions of bromides a slightly yel-
lowish-white precipitate of silver bromide, insoluble in nitric acid,
sparingly soluble in ammonia water.

2. Addition of chlorine water, or heating with nitric acid, liberates
bromine, which may be dissolved by shaking with carbon disulphide.
Excess of chlorine oxidizes bromine to colorless bromic acid. Hence,
it must be added cautiously, else a small quantity of bromine will
escape detection. The test is a delicate one.

3. Mucilage of starch added to the liberated bromine is colored
yellow. The starch may be held in the vapor on the end of a rod.

4. A solution of mercurous nitrate, or of lead acetate produces
a white precipitate of mercurous bromide, or lead bromide, both of
which are insoluble in water and dilute acids.

5. Strong sulphuric acid added to a dry bromide liberates hydro-
bromic acid, HBr, a portion of which decomposes with liberation of
yellowish-red vapors of bromine. See explanation above.

Tests 2 and 5 combined with test 1 are decisive and sufficient to
recognize hydrobromic acid and its salts, and to distinguish them
from chlorides.

Iodine, lodum, I = 125.90. Iodine is found in nature in com-
bination with sodium and potassium, in some spring waters and in

BE OMINE- IODINE— FL UOIilNE. 241

sea-water, from which latter it is taken up by sea-plants and many
aquatic animals. Iodine is derived chiefly from the ashes of sea-
weeds known as kelp. By washing these ashes with water, the soluble
constituents are dissolved, the larger quantities of sodium chloride,
sodium and potassium carbonates are removed by evaporation and
crystallization, and from the remaining mother-liquor iodine is ob-
tained by treating the liquor with manganese dioxide and hydro-
chloric (or sulphuric) acid :

2KI -f MnO2 + 2H2SO4 = K^SO^ + MnSO4 + 2H2O -f 21.

The liberated iodine distils, and is collected in cooled receivers.
Sodium nitrate found in Chili contains a small quantity of sodium
iodate, and the mother-liquors, from which the nitrate has been crystal-
lized, contain enough iodate to be employed for the preparation of iodine.

lodins is a bluish-black, crystalline substance of a somewhat
metallic lustre, a distinctive odor, a sharp and acrid taste, and a neu-
tral reaction. Specific gravity 4.948 at 17° C. (62.6° F.). It fuses
at 114° C. (237° F.), and boils at 180° C.(356° F.), being converted
into beautiful purple-violet vapors ; also, it volatilizes in small quanti-
ties at ordinary temperature. It is soluble in about 5000 parts of
water, more soluble in water containing salts, for instance, potassium
iodide ; the official Liquor iodi compositus (LugoPs solution) is a
preparation based on this property. It contains 5 parts of iodine and
10 parts of potassium iodide in 100 parts of aqueous solution. Iodine
is soluble in 10 parts of alcohol, very soluble in ether, disulphide of
carbon, and chloroform. The solution of iodine in alcohol or ether
has a brown, the solution in disulphide of carbon or in chloroform a
violet, color. Iodine stains the skin brown, and when taken inter-
nally acts as an irritant poison.

Tincture of iodine, Tinctura iodi, is a dark reddish-brown solution
of 70 grammes of iodine and 50 grammes of potassium iodide in
enough alcohol to make 1000 c.c. of solution.

The increased solubility of iodine in solutions of iodides, or of
hydriodic acid, is due to the formation of definite compounds by a re-
versible action, thus,

KI + 21 ^± KI3.

The brown color of solutions of iodine in certain solvents, as alcohol,
ether, etc., has been shown to be due to a feeble combination between
one molecule of iodine and one molecule of the solvent. In violet-
colored solutions there is no combination.

Iodine in very small quantity is a constituent of the human body and that
of animals. The greatest portion is found in the thyroid gland, as a complex
16

242 NON-METALS AND THEIR COMBINATIONS.

substance known as tbyro-iodine, which is of great value in certain diseases,
especially cretinism, resulting from deficient development of the thyroid gland.
Bauman discovered (1895) iodine in this gland. The thyroid of sheep, which
in the dried form is official, contains 0.17 per cent, of iodine.

Hydriodic acid, Acidum hydriodicum, HI = 126.9. This is a
colorless gas readily soluble in water ; the solution is unstable, being
easily decomposed with liberation of iodine. It may be obtained by
processes analogous to those mentioned for the preparation of hydro-
bromic acid. The action of hydrogen sulphide upon iodine in the
presence of water is as follows :

H2S + 21 2HI + S.

The official method for making diluted hydriodic acid depends on the decom-
position of an aqueous solution of potassium iodide by an alcoholic solution of
tartaric acid in the presence of a small quantity of potassium hypophosphite,
which acts as a preservative. Upon cooling the mixture to the freezing-point,
acid potassium tartrate separates, while hydriodic acid remains in solution,
which is further diluted until a 10 per cent, acid is obtained. The decomposi-
tion taking place is this :

KI + H2C4H4O6 : KHC4II4O6 -j- HI.

While hydriodic acid itself is not of much importance, many of
its salts, the iodides, are of great interest.

At 0° C. an aqueous solution can be obtained containing as much as 90 per
cent. HI. Nearly all iodides are soluble in water. The insoluble ones are of
silver, mercury, copper (ous). Lead iodide is sparingly soluble.

The ionic reactions for iodine compounds are analogous to those for chlorine
compounds.

Tests for iodine and iodides.

(Any soluble iodide may be used.)

1. Add to solution of an iodide, solution of silver nitrate: a pale-
yellow precipitate of silver iodide, Agl, falls, which is insoluble in
nitric acid, very sparingly soluble in ammonia water, but soluble in
solution of sodium thiosulphate or potassium cyanide. (See Photog-
raphy in Chapter 31, under Silver.)

2. Add lead acetate to a solution of an iodide : a yellow precipi-
tate of lead iodide, PbI2, is produced. When the precipitate is dis-
solved in a large volume (200 c.c.) of boiling water, and the solution
is cooled slowly, beautiful golden spangles are formed.

3. Add mercuric chloride solution to a solution of an iodide : a red
precipitate of mercuric iodide, HgI2, is produced, which is soluble in
solutions of mercuric chloride and potassium iodide. Note that the
corresponding chloride and bromide of mercury are soluble and white.

BR OM1NE— IODINE— FL UORINE. 243

Also make the test with solution of mercurous nitrate. A green-
ish-yellow precipitate of mercurous iodide, Hgl, is obtained. The
corresponding chloride and bromide are white and also insoluble.

4. To the solution of an iodide add some chlorine water, or a few
drops of concentrated nitric acid ; iodine is liberated, which, with
strongly diluted starch solution, gives a blue color. Iodine in com-
bination has no action on starch. Excess of chlorine oxidizes iodine
to colorless iodic acid ; hen.ce, the same precaution must be used as
given in test 2 for bromides.

Traces of iodine may be detected readily by the fine violet color
given to chloroform or carbon disulphide when the liquid is shaken
with them.

5. Add a little concentrated sulphuric acid to a few granules of an
iodide and warm gently. Colorless hydriodic acid gas is liberated,
which causes white fumes with the moisture of the air; also free
iodine, which may be recognized by its violet vapor.

Tests 3 and 4 are usually sufficient to identify iodides or hydriodic
acid.

Iodic acid, HI03. When iodine is dissolved in strong nitric acid, this solu-
tion being then evaporated to dryness and heated to about 200° C. (392° F.)
a white residue remains, which is iodine pentoxide :

61 -f 10HNO3 == 5N2O2 + 5H2O + 3I2O6.
By dissolving this oxide in water, iodic acid is obtained :
IA + H20 = 2HI03.

Iodic acid is a white crystalline substance, very soluble in water. From
iodic acid or from iodates, sulphurous acid and many other reducing agents
liberate iodine.

Hypoiodous acid and its salts are not known. Periodic acid and its salts
can be obtained. These oxygen compounds, in marked contrast to those of
chlorine, are stable. Iodine pentoxide is the only oxide of the element
known.

Sulphur iodide, Sulphuris iodidum, S2I2. When the two elements,
sulphur and iodine, are mixed together in the proportion of their atomic
weights, and this mixture is heated, direct combination takes place. The
fused mass is grayish-black, brittle, has a 'crystalline fracture and a metallic
lustre. It is almost insoluble in water, but soluble in glycerin and in carbon
disulphide.

Compounds of iodine with bromine and chlorine. While the affinity
between the halogens is feeble, yet a few compounds formed by their union are
known ; all of them are unstable, decomposing readily on heating and some
also in contact with water. Of some interest is iodine trichloride, IC13, obtain-
able as an orange, crystalline substance by passing dry chlorine gas over iodine,

244 NON-METALS AND THEIR COMBINATIONS.

when at first iodine monochloride, IC1, and then the trichloride is formed. The
latter has been used as a disinfectant.

Compounds of nitrogen with the halogens. When chlorine or iodine
acts on ammonia the hydrogen of the latter combines with the halogens, while
nitrogen is either set free or also enters into combination with the halogens,
thus:

NH3 + 3C1 = 3HC1 + N,

NH3 + 6C1 == 3HC1 -f NC13.

The compounds NH2C1 and NHC12, as also the corresponding iodine com-
pounds, are known. All these bodies are very unstable ; nitrogen trichloride,
an oily liquid, is one of the most explosive substances known ; nitrogen iodide,
a black powder, also explodes readily.

Fluorine, F = 18.9. This element is found in nature, chiefly as
fluorspar, calcium fluoride, CaF2 ; traces of fluorine occur in many
minerals, in some waters, and also in the enamel of teeth, and in the
bones of mammals. Fluorine was, until 1887, scarcely known in the
elementary state, because all attempts to isolate it were frustrated by
the powerful affinities which this element possesses, and which render
it difficult to obtain any material (from which a vessel may be made)
which is not chemically acted upon, and, therefore, destroyed, by
fluorine. 'The method used now for liberating fluorine depends upon
the decomposition of hydrofluoric acid by a strong current of electricity
in an apparatus constructed of platinum with stoppers of fluorspar.
To prevent too rapid corrosion of the platinum vessels, the decom-
position is accomplished at a temperature below the freezing-point.
Fluorine is a gas of yellowish color, having a highly irritating and
suffocating odor, and possessing affinities stronger than those of any
other element. As a supporter of combustion, fluorine leaves oxygen
far behind ; it combines spontaneously even in the dark and at low
temperature with hydrogen; sulphur, phosphorus, lampblack, and
also many metals ignite readily in fluorine ; even the noble metals,
gold, platinum, and mercury, are converted into fluorides; from
sodium chloride the chlorine is liberated with the formation of
sodium fluoride ; organic substances, such as oil of turpentine, alco-
hol, ether, and even cork ignite spontaneously when brought in
contact with this remarkable element.

Hydrofluoric acid, HF. A colorless gas, very irritating, soluble
in water. It is obtained by the action of sulphuric acid on fluorspar :

CaF2 + H2SO< = 2HF + CaSO4.

Hydrofluoric acid, either in the gaseous state or its, solution in

BROMINE-IODINE-FL UOttINK 245

water, is used for etching on glass. This effect is due to the action of
the acid upon the silica of the glass, which is converted into either
silicon fluoride, SiF4 ; or into hydrofl uosilicic acid, H2SiF6.

Hydrofluoric acid, or strong solutions of it, are powerful antiseptics. In
small quantities the acid is used as an admixture to fermenting liquids, as it
has been found that it does not act upon the principal ferment of yeast, which
causes the decomposition of sugar into alcohol and carbon dioxide, while it
readily destroys a number of objectionable ferments. The yield of alcohol is
thus considerably increased.

Experiment 19, Prepare a glass plate by heating it slightly and covering its
surface with a thin layer of wax or paraffin ; after cooling, scratch some letters
or figures through the wax, thus exposing the glass. Set the plate over a dish
(one made of lead or platinum answers best), in which a few grammes of pow-
dered fluorspar have been mixed with about an equal weight of sulphuric acid,
and set in the open air for a few hours (heating slightly facilitates the action);
upon removing the wax or paraffin, the glass will be found to be etched where
its surface was exposed to the vapors of the acid. This experiment serves also
as the best test for fluorides. (See under Silicon, p. 186.)

QUESTIONS. — How is bromine found in nature? State the physical and
chemical properties of bromine. What is hydrobromic acid, and how can it be
made ? By what tests may bromine and bromides be recognized ? What is the
chief source of iodine? What are the chemical and physical properties of
iodine? What is tincture of iodine, what is its color, and how does it stain
the skin ? Mention reactions by which iodine and iodides may be recognized.
By what element may bromine and iodine be liberated from their compounds?
How is hydrofluoric acid made, and what is it used for?

IV.
METALS AND THEIR COMBINATIONS.

Cobalt,
Copper,

20. GENERAL REMARKS REGARDING METALS.

OF the total number of sixty metallic elements only about one-half
are of sufficient general interest and importance to deserve considera-
tion in this book.

Derivation of names, symbols, and atomic weights.

Aluminum, Al = 26.9. From alum, a salt containing it.
Antimony, Sb = 119.3. From the Greek avrl (anti), against, and raotne, a
(Stibium.) French word for monk, from the fact that some

monks were poisoned by compounds of antimony.
Stibium, from the Greek, orijSi (stibi), the name
for the native sulphide of antimony.
Arsenic, As = 74.4. From the Greek aposvucbv (arsenicon), the name for

the native sulphide of arsenic.

Barium, Ba = 136.4 From the Greek fiapvs (barys), heavy, in allusion to

the high specific gravity of barium sulphate, or
heavy-spar.

From the German wixmuth, an expression used long
ago by the miners in allusion to the variegated
tints of the metal when freshly broken.
From the Greek nadfida (kadmeia) the old name for
calamine (zinc carbonate), with which cadmium
is frequently associated.

Calcium, Ca = 39.8. From the Latin calx, lime, the oxide of calcium.

Chromium, Cr = 51.7. From the Greek XP"/^a (chroma), color, in allusion

to the beautiful colors of all its compounds.
Co = 58.56, From the German Kobold, which means a demon

. inhabiting the mines.

Cu = 63.1. ' From the Latin cuprum, copper, and this from the
Island of Cyprus, where copper was first obtained
by the ancients.
Gold, Au = 195.7. Gold means bright yellow in several old languages.

(Aurum.) The Latin aurum signifies the color of fire.

Iridium, Ir = 191.5. From iris, rainbow, in allusion to the varying tints

of its salt solutions.

Fe = 55.5. Iron probably means metal; the derivation of the
Latin ferrum is not definitely known.

247

Bismuth, Bi = 206.9.

Cadmium, Cd =111.6.

Iron,

248

METALS AND THEIR COMBINATIONS.

Lead, Pb

(Plumbum.)

Lithium, Li

Magnesium, Mg

= 205.35. Both words signify something heavy.

6.98.
24.18.

Manganese, Mn = 54.6.

198.5.

Mercury, Hg

(Hydrargyrum )

Molybdenum, Mo

Nickel, Ni

95.3.

58.3.

Platinum, Pt = 193.3.

Potassium, K — 38.86.
(Kalium.)

Silver, Ag

(Argentum.)

Sodium, Na

(Natrium.)

107.12.

22.88.

Strontium, Sr = 86.94.
118.1.
64.9.

Tin, Sn

(Stannum.)
Zinc, Zn

From the Greek Weiog (litheios), stony.
From Magnesia, a town in Asia Minor, where mag-
nesium carbonate was found as a mineral.
Probably from magnesium, with the compounds of

which it was long confounded.
From Mercury, the messenger of the Greek gods.

Hydrargyrum means liquid silver.
From the Greek n6"kvfi6og (molybdos), lead.
From the old German word nickel, which means

worthless.
Platina is the diminutive of the Spanish word plata,

silver.
From pot-ash ; potassium carbonate being the chief

constituent of the lye of wood-ashes. Kali is the

Arabic word for ashes.
Both words signify white.

From soda-ash, or sod-ash, the ashes of marine plants
which are rich in sodium carbonate Natron is an
old name for natural deposits of sodium carbonate.

From Strontian, a village in Scotland, where stron-
tium carbonate is found.

Both words most likely signify stone.

Most likely from the German zinn or tin, the metals
having been confounded with each other.

Melting-points of metals.

c. F.

Fusible below the f Mercury 40° 40°

boiling-point of -[ Potassium . . . -f 62 -f-144

water, ^ Sodium 97 207

f Lithium ..... 180 356

I Tin 228 443

Cadmium ...... 310 590

Bismuth 260 500

Lead 325 617

Zinc 412 773

Magnesium . . . .700 1292

Antimony .... 425 797

Aluminum . 700 1292

Barium.

Calcium.

Strontium.

Fusible below red
heat,

Fusible
heat,

at red

TIME OF DISCOVERY OF THE METALS.

249

r Silver

Copper

Gold

Cast- iron .

Pure iron,

Infusible below a

Nickel,

red heat.

Cobalt,

Manganese,

Molybdenum, ^

Chromium, J

Platinum, 1

Iridi.um, •»

1020
1100
1200
1150

1868
2012
2192
2102

Highest heat of forge.

| Agglomerate, but do not melt in forge.
Fusible in the oxyhydrogen blowpipe

flame.

Arsenic does not fuse, but volatilizes at a low red heat.

Specific gravities of metals at 15.5° C,

^lithium

Potassium

Sodium

Calcium

Magnesium .

Strontium

Aluminum .

Barium

Arsenic

Antimony

Zinc

Tin

Iron

0.593

0.865

0.972

1.57

1.75

2.54

2.67

4.00

5.88

6.72

6.90

7.29

7.79

Manganese
Molybdenum
Cadmium
Nickel .
Cobalt .
Copper .
Bismuth .
Silver
Lead

Mercury .
Gold

Platinum .
Iridium

800

863

870

870

8.95

896

990

10.50

11.36

1359

19.36

21.50

22.42

Time of discovery of the metals.

Gold,

Silver,

Mercury,

Copper,

Zinc,

Tin,

Iron,

Lead,

Antimony,

Bismuth,

Arsenic,

Cobalt,

Platinum,

Nickel,

Manganese,

Molybdenum,

Chromium,

Iridium,

These metals were known to the ancients, because
either they are found in a metallic state, or can be
obtained by comparatively simple processes from
the oxides.

J

| Latter part of the fifteenth century.

1694, by Schroder.

1733, by Brandt.

1741, by Wood.

1751, by Cronstedt.

1774, by Galm.

1782, by Hjelm.

1797, by Vauquelin.

1804, by Smithson Tennant.

250

METALS AND THEIR COMBINATIONS.

Potassium,

Sodium,

( H

Barium,

. 1807-1808 •]

Calcium,

I

Strontium,

Magnesium, J

Cadmium, 1817, by Stromeyer.

Lithium, 1817, by Arfvedson.

Aluminum, 1828, by Wohler.

Davy discovered methods for the
separation of these metals from
their oxides.

Valence of metals.1

Univalent.

Lithium,

Potassium,

Sodium,

Silver.

Bivalent.

Barium,

Calcium,

Strontium,

Magnesium,

Cadmium,

Zinc,

Copper,

Mercury.

Trivalent.
Aluminum,

Bi, tri, or sexivalent.
Chromium,
Cobalt,
Iron,

Manganese,
Nickel,
Molybdenum.

Bi- and quadrivalent.
Iridium,
Platinum,
Tin.

Tri- and quinquivalent.

Antimony,

Arsenic,
, Bismuth.

Uni- or trivalent.
Gold.

Occurrence in nature.

a. In a free or combined state.

Almost exclusively in the metallic state.

Gold,

Iridium,

Platinum,

Silver,

Mercury,

Bismuth, generally metallic, also as oxide and sulphide.

Copper, rarely metallic ; chiefly as sulphide, oxide, and carbonate

I As metals or sulphides.

Potassium,

Sodium,

Lithium,

6. In combination only.
Chiefly as chlorides or silicates.

1 The valence here given is the one chiefly exerted by the elements, but several compounds
are known in which some of the metals exhibit a yet different valence ; thus copper and mer-
cury seem to be univalent in certain compounds, while some metals exhibiting a valence of
six (iron, chromium, etc.) are also bi- and trivalent.

CLASSIFICATION OF METALS. 251

Barium, as sulphate.

Calcium, \

Strontium, >• As carbonates, sulphates, silicates.

Magnesium, J

Aluminum, in silicates.

Iron, ^

Zinc, [• As oxides, carbonates, sulphide.

Cadmium, J

Arsenic,

Antimony,

Cotit, Chiefly as sulphides.

Nickel,

Molybdenum, J

Chromium, ^

Manganese, >• Chiefly as oxides.

Tin,

Classification of metals.

For the purpose of study, metals may be differently arranged into
groups according to the selection of those properties which are made
the basis for comparison. Thus, the valence alone may serve for
classification, and in that case the arrangement will also largely cor-
respond to the periodic system. The scheme adopted below is based
more especially on the analytical behavior of the metals. While
this classification brings together in many cases those metals belong-
ing to one group of the periodic system, in a few cases the elements
of one periodic group are separated, as for instance in the case of
magnesium, zinc, and cadmium. These elements resemble one
another closely in many respects, and are found together in group
II. of the periodic system, while in a classification based chiefly on
analytical properties these metals are found in different groups.

Light metals. Heavy metals.

Sp. gr. from 0 6 to 4. Sp gr. from 6 to 22.4.

Sulphides soluble in water. Sulphides insoluble in water.

Light metals.

Earth metals. Alkaline earth metals. Alkali-metal.

Al, and many rare metals. Ba, Ca, Sr, (Mg). K, Na, Li, (NH4).

Oxides insoluble. Oxides soluble ; Oxides, carbonates, and

Carbonates insoluble. most salts soluble.

Heavy metals.

Arsenic group. Lead group. Iron group.

As, Sb, Sn, Au, Pt, Mo. Pb, Cu, Bi, Ag, Hg, Cd. Fe, Co, Ni, Mn, Zn, Cr.

— -v — Sulphides soluble in

Sulphides insoluble in dilute acids. dilute acids.

Sulphides soluble in am- Sulphides insoluble in
monium sulphide. ammonium sulphide.

252 METALS AND THEIR COMBINATIONS.

Properties of metals. All metals have a peculiar lustre krrown
as metallic lustre, and all are more or less good conductors of heat
and electricity. The color of most metals is white, grayish, or
bluish-white, or dark gray ; a few metals show a distinct color, as,
for instance, gold (yellow) and copper (red).

At ordinary temperatures metals are solids with the exception of
mercury, all are fusible, and some are so volatile that they may be
distilled. Most, probably all, metals may be obtained in a crystal-
lized condition.

Metals show a wide difference in the properties of malleability, ductility, and
tenacity. Gold is both the most malleable and most ductile metal, while lead
possesses comparatively little of these qualities. In many cases heat increases
or develops malleability and ductility, but diminishes tenacity ; however, the
tenacity of iron, which surpasses that of any other metal, is not lessened by
heating.

The term annealing denotes the process of restoring the malleability and
ductility of some metals after these properties have been diminished, by caus-
ing a change in the molecular structure of the metals through hammering,
rolling, or sudden cooling. Annealing consists in heating the metal and per-
mitting it to cool slowly (in a few cases quickly) in order to allow the cohesive
force to produce the most stable arrangement of the molecules.

Tempering, which term at times is used analogously with annealing, consists
in heating the metal and chilling it suddenly. The result of annealing is the
highest development of softness and in case of some metals the restoration of
cohesiveness ; the object of tempering is the attainment of a certain degree of
hardness and elasticity.

Elasticity, i. e., the power of recovering original form when twisted or bent,
and sonorousness, i. e., the property of yielding a musical sound when struck,
are possessed only by the harder metals, and to a high degree by certain
mixtures of metals.

All metals expand when heated, but the rate, of expansion of the different
metals differs. Within certain limits of temperature the expansion of a metal
occurs uniformly in direct ratio to the increase in temperature. The great
expansibility of zinc is an important property of the metal when used as a die
in dental prosthesis.

Metals do not combine chemically with one another. Their mix-
tures (alloys) still exhibit the* metallic nature in their general physical
characters. It is different, however, when metals combine with non-
metals ; in this case the metallic characters are lost almost invariably.
All metals combine with chlorine, fluorine, and oxygen ; most metals
also with sulphur, bromine, and iodine ; many also with carbon and
phosphorus, forming the respective chlorides, fluorides, oxides, sul-
phides, bromides, iodides, carbides, and phosphides. Metals replace
hydrogen in acids, forming salts.

PROPERTIES OF METALS. 253

The intensity with which metals combine with non-metals or with acids
differs widely. Selecting the combinations with oxygen as a typical instance
we find that the affinity between the alkali metals and the alkaline earth
metals is so intense that these metals cannot be exposed to the atmosphere for
even a few hours without undergoing complete oxidation. It is for this reason
that these metals cannot be used in the metallic state for purposes requiring
constant exposure to air. Other metals, such as iron, will oxidize (rust) slowly
at ordinary temperature or will burn when heated sufficiently high. Yet other
metals retain their metallic lustre in dry or moist air at low or high tempera-
ture. Indeed, the oxides of these metals are decomposed into oxygen and the
respective metal by the mere application of heat. The metals showing this
behavior are often called noble mefals, while all others are designated as base
metals. The noble metals are gold, silver, mercury, platinum, iridium, and a
few other metals related to platinum. (See also page 198.)

Manufacture of metals. Most metals may be obtained from their
oxides by heating the latter with charcoal, the carbon combining with
the oxygen of the oxide, while the metal is liberated :

MO + C = CO + M;
or

2MO + C = CO2 + 2M.

Also hydrogen may be used in some cases as the deoxidizing agent :

MO + 2H = H20 -f M.

Some metals are found in nature chiefly as sulphides, which usually
are converted into oxides (before the metal can be obtained) by roast-
ing. The term roasting, when used in metallurgy, means heating
strongly in an oxidizing atmosphere, when the sulphides are con-
verted into sulphates or oxides, thus :

MS + 4O = MS04; or MS + 3O = MO + SO2.

A few metals are obtained by heating the chloride with metallic
sodium, when sodium chloride is formed, while the other metal is
set free. Electrolysis is also one of the means for obtaining metals
from their compounds.

Recently a generally applicable method of obtaining metals has been devised,
which consists in the action of aluminum powder on the oxides of the metals,
especially of those that have a high fusing-point and form difficultly reducible
oxides. So much heat is developed in these reductions that the method may be
used for welding, for example, the joints between rails.

Alloys are combinations or, more correctly speaking, mixtures of
two or more metals. Whenever mercury is a constituent of an alloy
it is called amalgam. All alloys exhibit metallic nature in their
physical properties— i. e., they have metallic lustre and are more or
less good conductors of heat and electricity.

254 METALS AND THEIR COMBINATIONS.

While alloys are generally looked upon as molecular mixtures, and
not as definite chemical compounds, yet there are many alloys the
properties of which are not intermediate between those of the elements
entering into these alloys, as we should expect if they were mechanical
mixtures. For this reason it is assumed that, in at least some cases,
compounds are formed which, however, are generally dissolved in, or
mixed with, an excess of one of the constituent metals.

On the other hand, there are cases where there is an utter lack of
affinity between the component parts of an alloy. Thus, alloys of
copper and lead, usually termed pot-metal alloys, show particles of the
two metals side by side, when the fractured surface is examined with
the microscope.

Manufacture of alloys. Alloys are generally obtained by fusing the
metals together ; but in order to do it successfully such properties of the com-
ponents as fusibility, specific gravity, proneness to oxidize, etc., should be con-
sidered. As a general rule the metal having the highest fusing-point is melted
first, and to it are added the other metals in the diminishing order of their
fusing- points. Loss or deterioration by oxidation should be guarded against
by covering the surface of the liquid mass with charcoal or with such fluxes as
borax, sodium chloride, or ammonium chloride. The heat should at no time
be higher than is necessary for the liquefaction.

Properties of alloys. Alloys generally are harder and more brittle, but
less ductile and malleable than the constituent metals possessing these qualities
in the highest degree. The union even of two ductile metals may destroy that
property more or less completely, as is shown by the absence of ductility in an
alloy of gold and a small portion of lead. The combination of a brittle and a
ductile metal always yields a brittle alloy.

Tenacity is generally increased. Thus, copper alloyed with 12 per cent, of
tin has its tenacity trippled ; gold, when alloyed with copper, silver, or plat-
inum, has its tensile resistance nearly doubled ; aluminum bronze, an alloy of
copper and aluminum, has a greater tenacity than that of either of the con-
stituent metals.

Certain metals impart to alloys specific properties. Thus, bismuth and
cadmium increase fusibility; tin and lead, both of which are soft metals,
impart hardness and tenacity ; arsenic and antimony produce brittle alloys.

QUESTIONS. — How many metals are known, and about how many are of gen-
eral interest? Mention some metals having very low and some having very
high fusing-points. What range of specific gravities do we find among the
metals ? Mention some univalent and some bivalent metals ; also some which
show a different valence under different conditions. Mention some metals which
are found in nature in an uncombined state; some which are found as oxides,
sulphides, chlorides, and carbonates, respectively. Into what two groups are
the metals divided? State the three groups of light metals. What is a metal ?
What is an alloy, and what is an amalgam ? By what process can most metals
be obtained from their oxides?

POTASSIUM. 255

The fusibility of an alloy is invariably greater than that of its least fusible
constituent, and may be greater than that of its most fusible constituent. Thus
an alloy of 2 parts of tin, 3 of lead, and 5 of bismuth fuses at 91° C., while
tin alone melts at 228°, lead at 325°, and bismuth at 260° C.

The conductivity of alloys for heat and . electricity is less than that of the
pure metals. The color of alloys is generally a modification of the predom-
inating ingredient, but instances are known where the color of alloys has no
relation to its constituents. For instance, German silver is perfectly white
although it contains a considerable portion of red copper.

21. POTASSIUM (KALIUM).

K' = 39 (38.86).

General remarks regarding- alkali-metals. The metals potas-
sium, sodium, lithium (rubidium and caesium) form the group of the
alkali-metals, which, in many respects, show a great resemblance to
each other in chemical and physical properties. For reasons to be
explained hereafter, the compound radical ammonium is usually
classed among the alkali-metals.

The alkali-metals are all univalent; they decompose water at the
ordinary temperature, with liberation of hydrogen; they combine
spontaneously with oxygen and chlorine ; their hydroxides, sulphates,
nitrates, phosphates, carbonates, sulphides, chlorides, iodides, and
nearly all other of their salts are soluble in water ; all these com-
pounds are white, solid substances, most of which are fusible at a
red heat. Of all metals, those of the alkalies are the only ones form-
ing hydroxides and carbonates which are not decomposed by heat.

The metals themselves are of a silver-white color, and extremely
soft; on account of their tendency to combine with oxygen they
must be kept in a liquid, such as coal-oil, which is not acted on by
them, or in an atmosphere of hydrogen.

The metals may be obtained by heating their carbonates with
carbon in iron retorts, the escaping vapors being passed under coal-
oil for condensation of the metal :

K2C03 + 20 = 3CO + 2K.

At present most of the alkali metals are obtained by the electrol-
ysis of the fused hydroxides, the metal and hydrogen being liberated
at the negative, oxygen at the positive pole :
KOH == K 4- H + O.

Occurrence in nature. Potassium is found in nature chiefly as a
double silicate of potassium and aluminum (granite rocks, feldspar,
and other minerals), or as chloride and nitrate. By the gradual dis-
integration of the different granite rocks containing potassium silicate,

256 METALS AND THEIR COMBINATIONS.

this has entered into the soil, whence it is taken up by plants as one
of the necessary constituents of their food.

In the plant potassium enters largely into the combination of
organic compounds, and when the plant is burned ashes are left
containing the potassium, now in the form of carbonate. By ex-
tractincr such ashes with water, the potassium carbonate, along with
small quantities of chlorides and sulphates of potassium and sodium,
is obtained in solution, by the evaporation of which to dryness an
impure article is obtained, known as crude potash. Formerly this
was the chief source of potassium compounds, but about the year
1850 the inexhaustible salt mines of Stassfurt, Germany, were discov-
ered. The salt there mined contains, besides the chlorides and sul-
phates of sodium, magnesium, calcium, and other salts, considerable
quantities of potassium chloride, and the Stassfurt mines at present
are practically the source of all potassium compounds.

Potassium hydroxide, Potassii hydroxidum, KOH == 55.74
(Caustic potash), may be obtained by the action of the metal on water :

K -h H,O = H + KOH

The usual process for making potassium hydroxide is to boil together
a dilute solution of potassium carbonate or bicarbonate and calcium

hydroxide :

K2C03 + Ca(OH)2 = CaC03 + 2KOH.

Large quantities of high-grade potassium hydroxide are now
manufactured directly from the chloride by electrolysis.

Experiment 20. Add gradually 5 grammes of calcium hydroxide (slaked
lime) to a boiling solution of about 5 grammes of potassium carbonate in 50
c.c. of water, and continue to boil until the conversion of potassium carbonate
into hydroxide is complete. This can be shown by filtering off a few drops of
the liquid, and supersaturating with dilute hydrochloric acid, which should not
cause effervescence. Set aside to cool, and when all solids have subsided, pour
off the clear solution of potassium hydroxide, which may be used for Experi-
ment 21 . What quantities of K2CO3 and Ca(OH)2 are required to make one liter
of a 5 per cent, solution of potassium hydroxide ?

Potassium hydroxide is a white, hard, highly deliquescent sub-
stance, soluble in 0.5 part of water and 2 parts of alcohol ; it fuses
at a low red heat, forming an oily liquid, which may be poured into
suitable moulds to form pencils; at a strong red heat it is slowly
volatilized without decomposition; it is strongly alkaline and a
powerful base, readily combining with all acids ; it rapidly destroys
organic tissues, and when taken internally acts as a powerful corrosive,
and most likely otherwise as a poison-

POTASSIUM. 257

Antidotes : dilute acids, vinegar, to form salts ; or fat, oil, or milk, to form soap.
Liquor potassii hydroxidi is a 5 per cent, solution of potassium hydroxide in
water.

Potassium oxide, K2O. This compound can be obtained either
by burning potassium in air and subsequent heating of the product
to a high temperature, or by fusing together potassium hydroxide
and metallic potassium :

2KOH -f 2K = 2K2O + 2H.

Besides this potassium monoxide, corresponding to water in its composition,
two other oxides of the composition K2O2 (corresponding to hydrogen perox-
ide, H2O2) and K2O4 are known. The latter oxide is obtained by the com-
bustion of potassium in oxygen. It is a strong oxidizing agent, and at a high
temperature is decomposed into oxide and oxygen.

Potassium carbonate, Potassii carbonas, K2CO3 = 137.27, is
obtained from wood-ashes in an impure state as described above, or
from the native chloride by the so-called Leblanc process, which will
be described in connection with sodium carbonate. It is also made
by passing carbon dioxide into solution of potassium hydroxide,
obtained by the electrolytic process.

Pure potassium carbonate is obtained by heating the bicarbonate,
which is decomposed as follows :

2KHCO3 = K2CO3 + H2O + CO2.

Potassium carbonate is deliquescent, is soluble in about an equal
weight of water, insoluble in alcohol, and has strong basic and alka-
line properties.

The strong alkaline reaction of potassium and sodium carbonate in solution
is due to hydrolysis of the salts into bicarbonate, which is neutral to litmus and
free alkali. (See pages 122 and 201.)

K2C03 + H20 = KHCO3 + KOH.

Potassium bicarbonate, Potassii bicarbonas, KHCO3 = 99.41.
Obtained by passing carbon dioxide through a strong solution of
potassium carbonate, when the less soluble bicarbonate forms and
separates into crystals :

K2CO3 + H2O + CO2 2KHC03.

Potassium percarbonate, K2C2O6, also exists as a bluish-white powder,
which liberates oxygen when heated, and in dilute acid solution gives off hydro-
gen dioxide. It is obtained by electrolysis of a concentrated solution of potas-
sium carbonate at about —10° C. (14° F.). It is a good oxidizer.
17

258 METALS AND THEIR COMBINATIONS.

Potassium nitrate, Potassii nitras, KNO3 = 100.43 (Niter, Salt-
peter). Potassium and sodium nitrate are found as an incrustation upon
and throughout the soil of certain localities in dry and hot countries,
as, for instance, in Peru, Chile, and India. The formation of these
nitrates is to be explained by the absorption of ammonia by the soil,
where it gradually is oxidized and converted into nitric acid. This
nitrification, i.4.9 the conversion of ammonia into nitric acid, seems to
be due largely to the action of micro-organisms, termed the nitrifying
ferment. The acid after being formed combines with the strongest
base present in the soil. If this base be potash, potassium nitrate
will be formed ; if soda, sodium nitrate ; if lime, calcium nitrate.

Upon the same principle is based the manufacture of niter on a large scale,
which is accomplished by mixing animal refuse matter with earth and lime,
and placing the mixture in heaps under a roof to prevent lixiviation by rain.
By decomposition (putrefaction) of the animal matter ammonia is formed,
Which, by oxidation, is converted into nitric acid, which then combines with
the calcium of the lime, forming calcium nitrate. This is dissolved in water,
and to the solution potassium carbonate (or chloride) is added, when calcium
carbonate (or chloride) and potassium nitrate are formed :

Ca(N03)2 + K2CO3 == 2KN03 + CaCO,.

Large quantities of potassium nitrate are made also by mixing hot concen-
trated solutions of sodium nitrate and potassium chloride, when, on cooling,
potassium nitrate separates in crystals, because it is much less soluble in cold
water than sodium nitrate is. (See page 193.)

NaNO3 + KC1 = KNO3 + NaCl.

Potassium nitrate crystallizes in six-sided prisms ; it is soluble in
about 3.8 parts of cold, and 0.4 part of boiling water. It has a cool-
ing, saline, and pungent taste, and a neutral reaction. When heated
with deoxidizing agents or combustible substances, these are readily
oxidized.

It is this oxidizing power which is made use of in the manufacture
of gunpowder — an intimate mixture of potassium nitrate, sulphur,
and carbon. Upon heating or igniting the gunpowder, the sulphur
and carbon are oxidized, a considerable quantity of various gases
(CO, CO2, N, SO2, etc.) being formed, the sudden generation and
expansion of which cause the explosion.

Potassium chlorate, Potassii chloras, KC1O3 =121.68 (Chlorate
of potash). This salt may be obtained by the action of chlorine on a
boiling solution of potassium hydroxidej as explained on page 237.

A cheaper process for its manufacture is the action of chlorine

POTASSIUM. 259

upon a boiling solution of potassium carbonate, to which calcium
hydroxide has been added :

K2C03 + 6Ca(OH)2 + 12C1 == 2KC1O3 + OaCO3 + 5CaCl2 + 6H2O.

Practically all potassium chlorate is manufactured now by electrol-
ysis of solutions of potassium chloride under proper conditions.

Potassium chlorate crystallizes in white plates of a pearly lustre ;
it is soluble in 16.7 parts of cold, and 1.7 parts of boiling water. It
is even a stronger oxidizing agent than potassium nitrate, for which
reason care must be taken in mixing it with organic matter or other
deoxidizing agents, or with strong acids, which will liberate chloric
acid. When heated by itself, it is decomposed into potassium chloride
and oxygen.

Potassium sulphate, Potassii sulphas, K2SO4 = 173. 04. Ob-
tained by the decomposition of potassium chloride, nitrate, or carbo-
nate, by sulphuric acid :

2KC1 + H2SO4 = 2HC1 + K2SO4;
K2C03 + H2S04 = H20 + C03 + K2S04.

Potassium sulphate exists in small quantities in plants, and in
nearly all animal tissues and fluids, more abundantly in urine.

Potassium hydrogen sulphate, bisulphafe, or potassium acid sulphate, may be
obtained by the action of one molecule of potassium chloride upon one mole-
cule of sulphuric acid :

KC1 + H2SO4 = HC1 -f KHSO4.

Potassium sulphite. Obtained by the decomposition of potassium carbonate
by sulphurous acid :

K3CO3 + H2SOS = H2O + CO2 + K2SOS.

Potassium hypophosphite, Potassii hypophosphis, KPH2O2 =
103.39, may be obtained by decomposing a solution of calcium hypo-
phosphite by potassium carbonate :

Ca(PH2O2)2 + K2CO3 = 2KPH2O2 + CaCO3.

The filtered solution is evaporated at a very gentle heat, stirring
constantly from the time it begins to thicken until a dry, granular
salt is obtained, which is soluble in 0.5 part of cold and 0.3 part of
boiling water.

Potassium iodide, Potassii iodidum, KI = 164.76, is made by
the addition of iodine to a solution of potassium hydroxide until the
dark-brown color no longer disappears :

6KOH + 61 = 5KI + KI03 + 3H2O.

260 METALS AND THEIR COMBINATIONS.

Iodide and iodate of potassium are formed, and may be separated
by crystallization. A better method, however, is to boil to dryness
the liquid containing both salts, and to heat the mass after having
mixed it with some charcoal, in a crucible, when the iodate is con-
verted into iodide :

KIO3 + 30 = KI + SCO.

Experiment 21. Add to a solution of about 3 grammes of potassium hydroxide
in about 25 c.c. of water (or to the solution obtained by making Experiment
20) iodine until the brown color no longer disappears. (How much iodine will
be needed for 3 grammes of KOH?) Evaporate the resulting solution (What
does this solution contain now ?) to dryness, mix the powdered mass with about
10 per cent, of powdered charcoal and heat the mixture in a crucible until
slight deflagration has taken place. Dissolve the cold mass in hot water, filter
and set aside for crystallization ; if too much water has been used for dissolving,
the liquid must be concentrated by evaporation.

Potassium iodide forms colorless, cubical crystals, which are soluble
in 0.5 part of boiling and 0.8 part of cold water, also soluble in 12
parts of alcohol, and 2.5 parts of glycerin. When heated it fuses,
and at a bright-red heat is volatilized without decomposition.

Potassium bromide, Potassii bromidum, KBr = 118.22, may be
obtained in a manner analogous to that given for potassium iodide,
by the action of bromine upon potassium hydroxide, etc.

Or it may be made by the decomposition of a solution of ferrous
bromide by potassium carbonate :

Ferrous carbonate is precipitated, while potassium bromide remains
in solution, from which it is obtained by crystallization.

Potassium salts of interest, which have not yet been mentioned, will be con-
sidered under the head of their respective acids. Some of these salts are
potassium chromate and permanganate, and the salts formed from organic
acids, such as potassium tartrate, acetate, etc.

Tests for potassium.

(Potassium chloride, KC1, or nitrate, KNO3, may be used.)
1. To a solution of any potassium salt add some solution of chloro-
platinic acid. A yellow crystalline precipitate of potassium chloro-
platinate is obtained :

2KN03 + H2PtCl6 = K2PtCl6 + 2HN03;

or 2K- + 2NQ,' + 2H« + PtCl6" = K2PtCl6 + 2H' + 2NQ/ .
This test is not very delicate, as 1 part of the precipitate is soluble in
about 100 parts of water. It is much less soluble in alcohol, which
is usually added to facilitate precipitation.

POTASSIUM. 261

2. To a neutral or slightly acid solution of a potassium salt add solu-
tion of sodium cobaltic nitrite: a yellow precipitate of potassium cobaltic
nitrite, (KNO2)6.Co2(NO2)6 + H2O, is produced. (The reaction is
not influenced by the presence of alkaline earths, earths, or metals of
the iron group, but is not suitable in case of potassium iodide, since
iodine is liberated by the nitrous acid of the cobalt solution, and
interferes with the test.)

3. Add to a concentrated solution of a neutral potassium salt a
freshly prepared strong solution of tartaric acid : a white precipitate
of potassium acid tartrate, KHC4H4O6, is slowly formed. Addition
of alcohol facilitates precipitation.

Tartaric acid, H2.C4H4O6, is dibasic and dissociates chiefly into H*
and HC4H4O/ ions. Potassium ions, K', and HC4H4O6' ions unite
to form the difficultly soluble acid tartrate ;

K- + NO./ -f H- + HC4H4O6' = KHC4H406 + H' + NO,'.

One part of the salt is soluble in about 200 parts of water, but prac-
tically insoluble in alcohol, even when diluted.

4. Potassium compounds color violet the flame of a Bunsen burner
or of alcohol. The presence of sodium, which colors the flame in-
tensely yellow, interferes with this test, as it masks the violet caused
by potassium. The difficulty may be overcome by observing the
flame through a blue glass or through a thin vessel filled with a solu-
tion of indigo. The yellow light is absorbed by the blue medium,
while the violet light passes through and can be recognized.1

With few exceptions, potassium compounds are white, soluble in
water, and not volatile at a low red heat. Of the above tests, the

1 The flame reaction for metals is one of the steps taken in qualitative analysis. For this
purpose the platinum wire should be kept immersed in hydrochloric acid in a test-tube.
When needed, it is cleaned by alternately holding it in the flame and dipping it in the acid,
until no color is given to the flame. The salt best adapted for flame tests is a chloride ; hence
the substance to be tested should be moistened in a dish with hydrochloric acid before intro-
ducing it into the flame on the loop of the wire. Chlorides are readily volatilized. Unless the
substance is volatile, there will be 110 flame reaction.

QUESTIONS. — How is potassium found in nature, and from what sources is
the chief supply of potassium salts obtained ? What color have the salts of the
alkali metals, and which are insoluble ? Mention two processes for making potas-
sium hydroxide, and what are its properties? Show by symbols the conversion
of carbonate into bicarbonate of potassium. Explain the principle of the man-
ufacture of potassium nitrate, and what is the office of the latter in gunpowder?
How is potassium chlorate made, and what are its properties ? Give the proc-
esses for manufacturing iodide and bromide of potassium, both in words and
symbols. State the composition of potassium sulphate and sulphite. How can
they be obtained? Mention tests for potassium compounds. How much iodine
is contained in 33 grammes of potassium iodide?

262 METALS AND THEIR COMBINATIONS.

second is the most delicate. Some other difficultly soluble salts of
potassium arc the picrate, perchlorate and fluosilicate. With the
exception of the acid tartrate (cream of tartar) and the picrate, the
other difficultly soluble salts of potassium are of a kind not usually met
with.

22. SODIUM (NATRIUM).

Nai-=23 (22.88).

Occurrence in nature. Sodium is found very widely diffused in
small quantities through all soils. It occurs in large quantities in
combination with chlorine, as rock-salt, or common salt, which forms
considerable deposits in some regions, or is dissolved in spring waters,
and is by them carried to the rivers, and finally to the ocean, which
contains immense quantities of sodium chloride. It is found, also,
as nitrate, and in double silicates.

Sodium chloride, Sodii chloridum, NaCl — 58.06 (Common salt}.
This is the most important of all sodium compounds, and also is the
material from which the other compounds are directly or indirectly
obtained. Common table-salt frequently contains small quantities
of calcium and magnesium chlorides, the presence of which causes
absorption of moisture, as these compounds are hygroscopic, while
pure sodium chloride is not.

In the animal system, sodium chloride is found in all parts, it
being of great importance in aiding the absorption of albuminoid
substances and the phenomena of osmose; also by furnishing,
through decomposition, the hydrochloric acid of the gastric juice.

Sodium chloride is soluble in 2.8 parts of cold water, and in 2.5
parts of boiling water ; almost insoluble in alcohol ; it crystallizes in
cubes and has a neutral reaction.

Sodium hydroxide, Sodii hydroxidum, NaOH — 39.76 (Caustic
soda), may be obtained by the processes mentioned for potassium
hydroxide, which compound it closely resembles in its chemical and
most of its physical properties.

Experiment 22. Examine the consistency and lustre of sodium metal by
cutting a piece the size of a pea. (Do not get water on it while handling it.
Why ?) Throw small chips of the metal into a little water in a porcelain dish.
When all the metal has disappeared, taste the solution and test its action on
red litmus. Add dilute hydrochloric acid to slight acid reaction and evaporate
to dryness. Taste the residue. What is it ? Explain all that took place and
write reactions.

SODIUM. 263

Sodium peroxide, Na202. is now extensively used as a bleaching and ox-
idi/ing agent. It is a white or yellowish-white powder, readily decomposed by
water into sodium hydroxide and oxygen; when dissolved in a dilute acid,
hydrogen peroxide is formed. It is made by heating sodium in a current of
oxygen. When it is brought in contact with water or dilute acids, great care
must be taken to have a low temperature, else violent action will take place,
with evolution of oxygen.

Sodium carbonate, Na2CO3.10H2O (Washing soda, Sal sodce).
This compound is, of all alkaline substances, the one manufactured in
the largest quantities, being used in the manufacture of many highly
important articles, as, for instance, soap, glass, etc.

Sodium carbonate is made, according to Leblanc's process, from
the chloride by first converting it into sulphate (salt-cake) by the
action of sulphuric acid :

2NaCl + H2S04 == 2HC1 + Na2SO4

The escaping vapors of hydrochloric acid are absorbed in water,
and this liquid acid is used largely in the manufacture of bleaching-
powder. The sodium sulphate is mixed with coal and limestone
(calcium carbonate) and the mixture heated in reverberatory furnaces,
when decomposition takes place, calcium sulphide, sodium carbonate,
and carbonic oxide being formed :

Na2SO4 + 40 + CaCO3 = CaS + Na,CO8 + 4CO

The resulting mass, known as black-ash, is washed with water,
which dissolves the sodium carbonate, while calcium sulphide enters
into combination with calcium oxide, thus forming an insoluble
double compound of oxy-sulphide of calcium.

The liquid obtained by washing the black-ash, when evaporated
to dryness, yields crude sodium carbonate, or " soda ash" ; when this
is dissolved and crystallized it takes up ten molecules of water,
forming the ordinary washing soda.

Sodium carbonate is manufactured also by the so-called ammonia
process, or the Solvay process. This depends on the decomposition
of sodium chloride by ammonium bicarbonate under pressure, when
sodium bicarbonate and ammonium chloride are formed, thus :

NaCl + NH4HCO3 = NH4C1 + NaHCO3.

•

The sodium acid carbonate thus obtained is converted into carbo-
nate by heating :

2NaHCO, == Na2CO3 + H2O + CO2.

The carbon dioxide obtained by this action is caused to act upon
ammonia, liberated from the ammonium chloride, obtained as one of

264 METALS AND THEIR COMBINATIONS.

the products in the first reaction. Ammonium bicarbonate is thus
regenerated and used in a subsequent operation for the decomposition
of common salt.

Sodium carbonate has strong alkaline properties ; it is soluble in
1.6 parts of cold water, and in much less water at higher temper-
atures ; the crystals lose water on exposure to the air, falling into a
white powder; heat facilitates the expulsion of the water of crys-
tallization, and is applied in making the monohydrated sodium car-
bonate, Sodii carbonas monohydras, Na2CO3.H2O = 123.19, which
should contain about 85 per cent, of anhydrous sodium carbonate.

Sodium bicarbonate, Sodii bicarbonas, NaHCO3 = 83.43 (Bak-
ing-soda). Obtained, as stated in the previous paragraph, by the
ammonia-soda process. It can also be made by passing carbon
dioxide over monohydrated sodium carbonate.

Na,CO3.H2O + CO2 = = 2NaHCO3.

It is a white powder, having a cooling, mildly saline taste, and a
slightly alkaline reaction. Soluble in 12 parts of cold water and
insoluble in alcohol. It is decomposed by heat or by hot water into
sodium carbonate, water, and carbon dioxide.

Sodium bicarbonate is a constituent of the various baking-powders, the action
of which depends on the gradual liberation of carbon dioxide in the dough.
This is brought about through a second constituent, generally an acid salt such
as potassium bitartrate or calcium acid phosphate, which decomposes the
bicarbonate.

Sodium sulphate, Sodii sulphas, Na2SO4lOH2O = 319.91 (Glau-
ber's salt). Made, as mentioned above, by the action of sulphuric acid
on sodium chloride, dissolving the salt thus obtained in water, and crys-
tallizing. Large, colorless, transparent crystals, rapidly efflorescing
on exposure to air. Soluble in 2.8 parts of water at 15° C. (59° F.).
in 0.25 part at 34° C. (93° F.), and in 0.47 part of boiling water.

Experiment 23. Dissolve about 10 grammes of crystallized sodium carbonate
in 10 c.c. of hot water, add to this solution dilute sulphuric acid until all effer-
vescence ceases and the reaction on litmus-paper is exactly neutral. Evaporate
to about 20 c.c., and set aside for crystallization. Explain the action taking
place, and state how much H2S04, and how much of the diluted sulphuric
acid, U. S. P., are needed for the decomposition of 10 grammes of crystallized
sodium carbonate.

Sodium sulphite, Sodii sulphis, Na2SO3.7H2O -- = 25O.39.
Sodium bisulphite, Sodii bisulphis, NaHSO3 = 1O3.35. By

SODIUM. 265

saturating a cold solution of sodium carbonate with sulphur dioxide,
sodium bisulphite is formed, and separates in opaque crystals :

Na-jCOg -f 2SO2 + H2O = 2NaHSO3 -f CO2.

If to the sodium bisulphite thus obtained a quantity of sodium car-
bonate be added, equal to that first employed, the normal salt is formed :
2NaHSO3 -(- Na.2CO3 = 2NaaSOs + H2O + CO2.

Sodium thiosulphate, Sodium hyposulphite, Sodii thiosul-
phas, Na2S2O3.5H2O = 246.46. Made by digesting a solution of
sodium sulphite with powdered sulphur, when combination slowly
takes place :

Na2S03 + S : Na2SA-

It is used under the name of " h^po " in photography to dissolve
chloride, bromide, or iodide of silver.

Sodium phosphate, Sodii phosphas, Na2HPO4.12H2O — 355.61,
is made from calcium phosphate by the action of sulphuric acid, which
removes two-thirds of the calcium, forming calcium sulphate, while
acid phosphate of calcium is formed and remains in solution :

Ca3(PO4)2 + 2H2S04 = 2CaSO4 -f CaH4(PO4)2.

The solution is filtered and sodium carbonate added, when calcium
phosphate is precipitated, phosphate of sodium, carbon dioxide, and
water being formed :

CaH4(P04)2 + Na2CO8 = CaHPO4 -f H2O + CO2 -f N^HPO,.

The filtered and evaporated solution yields crystals of sodium
phosphate, which have a slightly alkaline reaction to litmus, but not
to phenol-phthalein.

By exposure of the crystallized sodium phosphate to warm air its water of
crystallization is expelled and the dry salt is Exsiccated sodium phosphate,
Sodii phosphas exsiccatus. This salt, when mixed with the proper quantities
of sodium bicarbonate and tartaric and citric acids, is official under the name
of Effervescent sodium phosphate, Sodii phosphas effervescens.

Experiment 24. Mix thoroughly 30 grammes of bone-ash with 10 c.c. of
sulphuric acid, let stand for some hours, add 20 c.c. of water, and again set
aside for some hours. Mix with 40 c.c. of water, heat to the boiling-point, and
filter. The residue on the filter is chiefly calcium sulphate. To the hot filtrate
of calcium acid phosphate add concentrated solution of sodium carbonate until
a precipitate ceases to form and the liquid is faintly alkaline, filter, evaporate,
and let crystallize.

Sodium pyrophosphate, Sodii pyrophosphas, Na4P2O7.lOH2O =
443.O2. When exsiccated sodium phosphate is heated to a low red

266 METALS AND THEIR COMBINATIONS.

heat it loses water, and is converted into pyrophosphate, which, dis-
solved in hot water and crystallized, forms the official salt. The
chemical change taking place is this :

2(Na2HP04) Na4P207 + H2O.

The normal sodium phosphate, Na3PO4, is known also, but it is not a very
stable compound, being acted upon even by the moisture and carbon dioxide
of the air, with the formation of sodium carbonate and disodium hydrogen
phosphate, thus :

H20 + C02 =

Sodium nitrate, Sodii nitras, NaNO3= 84.45 (Chile saltpeter,
Cubic niter). Found in nature, and is purified by crystallization.
The crystals are transparent, deliquescent, and readily soluble.

Sodium nitrite, Sodii nitris, NaNO2 = 68.57, is formed by heating the nitrate
to a sufficiently high temperature to expel one-third of the oxygen ; or, better,
by treating the fused nitrate with metallic lead, which latter is converted into
oxide. The sodium nitrite which is formed is dissolved and purified by crystal-
lization.

Sodium borate, Sodii boras, Na2B4O7.lOH2O = 379.32 (Borax).
This salt occurs in Clear Lake, Nevada, and in several lakes in Asia.
It is manufactured by adding sodium carbonate to the boric acid
found in Tuscany, Italy. It forms colorless, transparent crystals,
but is sold mostly in the form of a white powder. It is slightly
efflorescent, is soluble in 16 parts of cold, and in 0.5 part of boiling
water ; insoluble in alcohol, but soluble in one part of glycerin at
80° C. (176° F.). When heated, borax puffs up, loses water of
crystallization, and at red heat it melts, forming a colorless liquid
which, on cooling, solidifies to a transparent mass, known as fused
borax, or borax glass. Molten borax has the power to combine with
metallic oxides, forming double borates, some of which have a char-
acteristic color, for which reason borax is used in blow-pipe analysis.
Borax has antiseptic properties, preventing the decomposition of some
organic substances.

A solution of borax is alkaline and has no action on carbonates or bicarbon-
ates, but if an equal volume of glycerin is added to the solution, it becomes
strongly acid and decomposes carbonates and bicarbonates with effervescence.
This behavior has an important bearing in prescription writing. On diluting
the glycerin mixture strongly with water, the alkaline reaction returns.

Other sodium salts which are official are sodium hypophosphite,
NaPH2O2 + H2O; bromide, NaBr; iodide, Nal ; chlorate, NaClO3.

SODIUM. 267

These salts may be obtained by processes analogous to those given
for the corresponding potassium compounds.

Sodium compounds are nearly all white and are not volatile at or
below a red heat.

Tests for sodium.

(Sodium chloride, NaCl, may be used.)

1. As all salts of sodium are soluble in water, we cannot precipi-
tate this metal in the form of a compound by any of the common
reagents. (Potassium antimoniate precipitates neutral solution of
sodium salts, but this test is not reliable.)

2. The chief reaction for sodium is the flame-test, compounds of
sodium imparting to a colorless flame a yellow color, which is very
intense. A crystal of potassium dichromate appears colorless, and a
paper coated with red mercuric iodide appears white when illuminated
by the yellow sodium flame. (The spectroscope shows a characteristic
yellow line.)

As practically all substances contain a trace of some sodium com-
pound, and give a momentary sodium flame, the yellow flame can only
be used to judge the presence of an actual sodium compound when
it persists for a long time.

Lithium, Li = 6.98. Found in nature in combination with silicic acid in
a few rare minerals or as a chloride in some spring waters. Of inorganic
salts, lithium bromide and carbonate are official. Hydroxide, carbonate, and
phosphate of lithium are much less soluble than the corresponding com-
pounds of potassium and sodium. Sodium phosphate added to a strong solu-
tion of a lithium salt produces, on boiling, a white precipitate of lithium
phosphate, Li3PO4. Lithium compounds color the flame a beautiful crimson
or carmine-red.

LiOH is soluble in 14.5 parts of water at 20° C., Li2CO3 in 75 parts at 20° C.,
and 140 parts of boiling water, Li3PO4 in 2540 parts of plain water and 3920
parts of ammoniacal water.

Caesium, Cs, and Rubidium, Rb, occur widely distributed, but only in
small quantities, and generally in company with potassium, which they resem-

QUESTIONS. — What is the composition of common salt ; how is it found in
nature, and what is it used for? Describe Leblanc's and the Solvay process
for manufacturing sodium carbonate on a large scale. How much water is in
100 pounds of the crystallized sodium carbonate ? What is Glauber salt, and
how is it made ? State the composition of disodium hydrogen phosphate, and
how is it prepared from calcium phosphate? What difference exists between
sodium carbonate and bicarbonate both in regard to physical and chemical
properties? Give the composition of sodium thiosulphate; what is it used for?
Which sodium salts are. soluble, and which are insoluble? How does sodium
and how does lithium color the flame? Which lithium salts are official?

268 METALS AND THEIR COMBINATIONS.

ble closely. Kubidium occurs in carnallite of the Stassfurt beds, and is obtained
as rubidium alum, from the mother-liquors after the potassium chloride is
crystallized out. Csesium takes fire in air at the ordinary temperature, and it
is the most electropositive of all metals. Kubidium takes fire in air and decom-
poses water with greater energy than does potassium, the hydroxide formed,
Rb(OH), having even stronger basic properties than potassium hydroxide.
Both rubidium and caesium have a marked power of forming double salts. All
the salts are white and soluble in water. Probably the one most often used
medicinally is ccesium-rubidium-ammonium bromide, (CsEb)Br2.3NH4Br. Rubid-
ium bromide, RbBr, and iodide, Rbl, have been recommended as substitutes for
the corresponding potassium salts. Cesium bromide, CsBr, has also been used.

23. AMMONIUM.
NH^IS (17.93).

General remarks. The salts of ammonium show so much resem-
blance, both in their physical and chemical properties, to those of the
alkali-metals, that they may be studied most conveniently at this
place.

The compound radical NH4 acts in these ammonium salts very
much like one atom of an alkali-metal, and, therefore, frequently has
been looked upon as a compound metal. The physical metallic prop-
erties (lustre, etc.) of ammonium cannot be fully demonstrated, as it
is not capable of existing in a separate or free state. There is known,
however, an alloy of ammonium and mercury, which may be obtained
by dissolving potassium in mercury, and adding to the potassium-
amalgam thus formed, a strong solution of ammonium chloride, when
potassium chloride and ammonium-amalgam are formed. The latter
is a soft, spongy, metallic-looking substance, which readily decomposes
into mercury, ammonia, and hydrogen :

HgK + NH4C1 = KC1 + NH4Hg;
NH4Hg = NH3 + H + Hg.

The source of all ammonium compounds is ammonia NH3, or am-
monium hydroxide, NH4OH, both of which have been considered
heretofore.

A solution of ammonia has much weaker basic properties than a solution
of sodium or potassium hydroxide has. In a normal solution (about 1.7 per
cent.) only about 0.4 per cent, of the ammonia molecules are dissociated into
NH4- and (OH)/ ions. There is much free NH3, besides the NH4OH which
results from union of NH3 with water. It is only the ionized portion of the
NH4OH which shows basic properties.

The ionic equation for the neutralization of ammonia water with an acid is
this:

NH4-,-f OH' + H- + d' -> NH4- + Cl' + H2O.
As fast as (OH)7 and H' ions unite to form water, more NH4OH dissociates

AMMONIUM. 269

and more NH3 unites with water to form NH4OH until the reaction is com-
plete. All ammonium salts are highly dissociated in dilute solutions.

The reverse of the above action, namely, the liberation of ammonia from its
salts by an alkali, is discussed from the ionic point of view on page 194.

Ammonium chloride, Ammonii chloridum, NH4C1~ 53.11 (Sal-
ammoniac). Obtained by saturating the "ammoniacal liquor" of the
gas-works with hydrochloric acid, evaporating to dryness, and puri-
fying the crude article by sublimation.

Pure ammonium chloride either is a white, crystalline powder, or
occurs in the form of long, fibrous crystals, which are tough and
flexible ; it has a cooling, saline taste ; is soluble in 2 parts of cold,
and in 1 part of boiling water; and, like all ammonium compounds,
is completely volatilized by heat.

Carbamic acid, CO.NH2.OH. This acid may be looked upon as carbonic
acid, CO.(OH)2, in which one of the hydroxyl groups is replaced by NH^ The
ammonium salt of this acid, CO.NH.2.ONH4, is formed when dry ammonia gas
and dry carbon dioxide are brought together, direct combination taking place,

thus:

NH2
CO2 + 2NH3 = CO(

\ONH4

Ammonium carbonate, Ammonii carbonas, NH4HCO3.NH4
NH2CO2 = 156. Ol (Ammonium sesquicarbonate, sal volatile, Preston
salt). Commercial ammonium carbonate is not the normal salt, but,
as shown by the above formula, a combination of acid ammonium
carbonate with ammonium carbamate. It is obtained by sublimation
of a mixture of ammonium chloride and calcium carbonate, when
calcium chloride is formed, ammonia gas and water escape, and am-
monium carbonate condenses in the cooler part of the apparatus :

2CaC03 + 4NH4C1 = NH4HCO3 NH4NH2CO2 + 2CaCl2 + H2O + NH3.

Ammonium carbonate thus obtained forms white, translucent masses, losing
both ammonia and carbon dioxide on exposure to the air, becoming opaque,
and finally converted into a white powder of acid ammonium carbonate.

NH4HCO3 NH4NH2CO2 = NH4HCO3 + 2NH3 -f CO2.

When commercial ammonium carbonate is dissolved in water the carbamate
unites with one molecule of water, forming normal ammonium carbonate.

NH4NH2CO2 + H2O = (NH4)2C08.

A solution of the common ammonium carbonate in water is, consequently, a
liquid containing both acid and normal carbonate of ammonium ; by the addi-
tion of some ammonia water the acid carbonate is converted into the normal
salt. The solution thus obtained is used frequently as a reagent.

The Aromatic spirit of ammonia is a solution of normal ammonium carbonate
in diluted alcohol to which some essential oils have been added.

270 METALS AND THEIR COMBINATIONS.

Ammonium sulphate, (NH4)2SO4, Ammonium nitrate, NH4NO3,
and Ammonium phosphate, (NH4)2HPO4, may be obtained by the
addition of the respective acids to ammonia water or ammonium
carbonate :

H2S04 + 2NH4OH = (NH4)2S04 -f 2H2O.
HNO3 + NH4OH = NH4NO3 -f H2O.
H3P04 + 2NH4OH = (NH4)2HP04 + 2H2O.
H2S04 -f (NH4)2C03 = (NH4)2S04 + H2O + COa.

Ammonium iodide, Ammonii iodidum, NH4I, and Ammonium
bromide, Ammonii bromidum, NH4Br, may be obtained by mixing
together strong solutions of potassium iodide (or bromide) and am-
monium sulphate, and adding alcohol, which precipitates the potas-
sium sulphate formed ; by evaporation of the solution the ammonium
iodide (or bromide) is obtained :

2KI + (NH4)2SO4 = 2NH4I -f K2SO4;
2KBr + (NH4)2S04 = 2NH4Br

Another mode of preparing these compounds is by the decomposi-
tion of ferrous bromide (or iodide) by ammonium hydroxide :
FeBr2 + 2NH4OH = 2NH4Br + Fe(OH)2.

Ammonium iodide is the principal constituent of the Decolorized
tincture of iodine.

Ammonium hydrogen sulphide, NH4SH (Ammonium hydro-
sulphide, Ammonium sulphydrate). Obtained by passing hydrogen
sulphide through ammonia water until this is saturated :

H2S + NH4OH = NH4SH 4- H2O.

The solution thus obtained is, when recently prepared, a colorless
liquid, having the odor of both ammonia and of hydrogen sulphide ;
when exposed to the air it soon assumes a yellow color. This behavior
is characteristic of the soluble hydrosulphides in general, and is due
to the liberation of sulphur by oxidation, thus :

NH4SH + O = NH4OH + S.

The sulphur combines with undecomposed hydrosulphide, forming
polysulphides, which are yellow. The normal sulphide, (NH4)2S, can
be obtained in the solid state, but it quickly loses half of its ammonia
and forms hydrosulphide. In solution it is almost completely hydro-
lyzed, thus :

(NH4)2S + H20 ^± NH4OH + NH4SH.
A mixture corresponding to the normal sulphide is obtained by add-

AMMONIUM. 271

ing to a solution of the hydrosulphide, prepared as above, an equiva-
lent amount of ammonia water.

These solutions can easily be freed from the sulphide by boiling. Both sub-
stances, the ammonium hydrogen sulphide and ammonium sulphide, are valu-
able reagents, frequently used for precipitation of certain heavy metals, or for
dissolving certain metallic sulphides. (See under Hydrogen Sulphide.).

Tests for ammonium compounds.

(Ammonium chloride, NH4C1, may be used.)

1. Ammonium salts give the same form of precipitates as potas-
sium with solution of platinic chloride, sodium cobaltic nitrite, and
tartaric acid (see tests for potassium).

2. All compounds of ammonium are volatilized below or at a low
red heat, either with or without decomposition (see preparation of
nitrogen and nitrogen monoxide in chapter on Nitrogen). If the
acid constituent of the salt is volatile and not decomposed by heat,
the salt volatilizes without decomposition.

Heat with a small flame a little ammonium chloride in a covered
porcelain crucible. The salt sublimes upon the sides and cover of
the crucible.

3. The best test and one which is sufficient for recognition of any
ammonium compound is to heat a mixture of it and slaked lime or
strong alkali in a tube. Ammonia gas is liberated, which may be
recognized by its odor and action on red litmus-paper, and by causing
dense white fumes when a rod, moistened with strong hydrochloric
acid, is held in the mouth of the tube.

All commonly occurring ammonium salts are colorless, soluble in
water, and odorless, with the exception of the carbonate and sulphide.
Traces of ammonium compounds are detected by Nessler's

QUESTIONS. — What is ammonium, and why is it classed with the alkali-
metals? Is ammonium known in a separate state? What is ammonium-
amalgam, how is it obtained, and what are its properties? What is the source
of ammonium compounds? State the composition, mode of preparation, and
properties of sal ammoniac. How is ammonium carbonate manufactured, and
what difference exists between the solid article and its solution ? State the
composition of ammonium sulphide and of ammonium hydrogen sulphide ;
how are they made, and what are they used for? By what process may ammo-
nium sulphate, nitrate, and phosphate be obtained from ammonium hydroxide
or ammonium carbonate, and what chemical change takes place ? How does
heat act upon ammonium compounds? Give analytical reactions for ammo-
nium salts.

272

METALS 'AND THEIR COMBINATIONS.

solution (see Index), which causes a reddish-brown precipitate or
coloration. (See under Water Analysis, end of chapter 38.)

Summary of analytical characters of the alkali-metals.

Potassium.

/Sodium.

Lithium.

Ammonium.

Sodium cobaltic nitrite . .
Platinic chloride ....
Sodium bitartrate . . .
Sodium phosphate . . .

Sodium hydroxide . . .
Action of heat ....

Yellow pre-
cipitate.
Yellow pre-
cipitate.
White preci-
pitate.

Yellow pre-
cipitate.
Yellow pre-
cipitate.
White preci-
pitate.

White preci-
pitate in cone,
solution on
boiling.

Ammonia
gas.
Volatile.

Fusible.
Violet.

Fusible.
Yellow.

Fusible.
Crimson.

24. MAGNESIUM.
Mg11 = 24.18.

General remarks. Magnesium occupies a position intermediate
between the alkali metals and the alkaline earths. To some extent
it resembles also the heavy metal zinc, with which it has in common
the volatility of the chloride, the solubility of the sulphate, and the
isomorphism of several of its compounds with the analogously con-
stituted compounds of zinc.

Occurrence in nature. Magnesium is widely diffused in nature,
and several of its compounds are found in large quantities. It occurs
as chloride and sulphate in many spring waters and in the salt-mines
at Stassfurt; as carbonate in the mineral magnesite; as double car-
bonate of magnesium and calcium in the mineral dolomite (magnesian
limestone), which forms entire mountains ; as silicate of magnesium
in the minerals serpentine, meerschaum, tale, asbestos, soapstone, etc.

Metallic magnesium may be obtained by the decomposition of
magnesium chloride by sodium ; but is now made in large quantities
by electrolysis of the molten double chloride of magnesium and
potassium, MgCl2.KCl. The furnace used for the operation is shown
in Fig. 31, page 80.

Magnesium is an almost silver-white metal, losing its lustre rap-
idly in moist air by oxidation of the surface. It decomposes hot

MAGNESIUM. 273

water with liberation of hydrogen ; and when heated to a red
heat burns with a brilliant bluish-white light, which is extensively
used for photographic purposes.

Magnesium carbonate, Magnesii carbonas. Approximately :
(MgC03)4.Mg(OH)2.5H,0 == 482.26 (Magnesia alba). The normal
magnesium carbonate, MgCO3, is found in nature, but the official
preparation contains carbonate, hydroxide, and water. It is ob-
tained by boiling a solution of magnesium sulphate with solution
of sodium carbonate, when the carbonate is precipitated, some carbon
dioxide evolved, and sodium sulphate remains in solution:

5MgSO4 + SN^COg + 6H2O == (MgCO3)4 Mg(OH)2 5H2O + 5Na2SO4 + CO3.

By filtering, washing, and drying the precipitate, it is obtained in
the form of a white, light powder.

Experiment 25. Dissolve 10 grammes of magnesium sulphate in hot water
and add a concentrated solution of sodium carbonate until no more precipitate
is formed. Collect the precipitated magnesium carbonate on a filter and dry it
at a low temperature. (How much crystallized sodium carbonate is needed
for the decomposition of 10 grammes of crystallized magnesium sulphate?)
Notice that the dried precipitate evolves carbon dioxide when heated with
acids.

Magnesium oxide, Mag-nesii oxidum, MgO — 40.O6 (Calcined
magnesia), is obtained by heating light magnesium carbonate in a
crucible to a full red heat, when all carbon dioxide and water are
expelled :

(MgC03)4.Mg(OH)2.5H2O = 5MgO -f 4CO2 + 6H2O.

It is a very light, amorphous, white, almost tasteless powder, which
absorbs moisture and carbon dioxide gradually from the air; in con-
tact with water it forms the hydroxide Mg(OH)2, which is almost
insoluble in water, requiring of the latter over 50,000 parts for solu-
tion. Milk of magnesia is the hydroxide suspended in water (1 part
in about 15).

Heavy magnesium oxide, magnesii oxidum ponderosum, differs from the com-
mon or light magnesia, not in its chemical composition, but merely in its
physical condition, being denser and heavier.

Experiment 26. Place 1 gramme of magnesium carbonate, obtained in per-
forming Experiment 25, into a weighed crucible and heat to redness, or until
by further heating no more loss in weight ensues. Treat the residue with
dilute hydrochloric acid and notice that no evolution of carbon dioxide takes
place. What is the calculated loss in weight of magnesium carbonate when
converted into oxide, and how does this correspond with the actual loss deter-
mined by the experiment?
18

274 NON-METALS AND THEIR COMBINATIONS.

Magnesium sulphate, Magnesii sulphas, MgSO4.7H2O = 244.69
(Epsom salt), is obtained from spring waters, from the mineral
Kieserite, MgSOrH2O, and by decomposition of the native carbonate
by sulphuric acid :

MgC03 + H2SO4 = MgS04 + C02 + H2O.

It forms colorless crystals, which have a cooling, saline, and bitter
taste, a neutral reaction, and are easily soluble in water.

Effervescent magnesium sulphate, Magnesii sulphas efferves-
cens, is a granular mixture of magnesium sulphate, sodium bicarbonate, tar-
taric and citric acids, in proper proportions. It contains what is equal to 50
per cent, of crystallized magnesium sulphate, and, like all effervescent salts,
gives off carbonic acid when dissolved, which makes it more palatable.

Magnesium nitride, Mg3N2, is obtained as a yellow, porous mass by
heating magnesium to red heat in nitrogen. With water it forms magnesium
hydroxide and ammonia, thus :

Mg3N2 + 6H20 = 3Mg(OH)2 + 2NH3,

Remarks on tests for metals. Many of the tests for magnesium
and the metals to follow have already been before us when discuss-
ing the acids. They involve reactions of double decomposition, re-
sulting in the formation of an insoluble product. The solubilities of
the different classes of salts, such as chlorides, carbonates, sulphates,
etc., have been stated under the various acids, and the student, by
keeping these facts in mind, will be able to anticipate many of the
tests enumerated under the metals. Some of these are not distinctive
at all, but simply corroborative, because two or more metals may re-
spond to the same test. For example, to obtain a white precipitate
on adding a solution of sodium carbonate or phosphate to a solution
of a substance is no more a test for magnesium than for calcium,
strontium, barium, or any other metal whose carbonate or phosphate is
white and insoluble in water. In cases where distinctive tests are
lacking, a systematic procedure of elimination is followed. This is
known as qualitative analysis.

The solubilities of the classes of salts and the different methods
of producing salts have been mentioned, and something has been
said in this respect about the two classes of compounds of metals
known as oxides and hydroxides. In regard to solubility in water,
the oxides and hydroxides are very much alike : that is, if a hydrox-
ide is soluble, the corresponding oxide is also soluble, and vice versa.
The hydroxides of the common metals that are soluble in water are
those of potassium, sodium, lithium, barium, strontium, and the hypo-

M AGNES fUM. 275

thetical metal, ammonium. Calcium hydroxide is slightly soluble,
less than calcium sulphate, but sufficiently soluble to be employed as
a reagent. Hydroxides of the other metals are either insoluble or so
little soluble as to be classed insoluble. These are obtained as pre-
cipitates by adding a soluble hydroxide (usually of sodium, potas-
sium, or ammonium) to a salt of the metals whose hydroxides are in-
soluble. The principle involved here is the same as in the case of
precipitation of insoluble carbonates, namely, bringing together in
solution constituents which by their union can form insoluble prod-
ucts and thus be eliminated from the solution, thereby allowing the
reaction to go on to completion. This reaction is given as a test under
many of the metals.

Ammonium hydroxide acts, in general, like the alkalies, but
toward certain metals it shows a marked difference. For example,
calcium hydroxide is precipitated from fairly concentrated solutions
of calcium salts by the alkalies, but not by ammonia water. This is
explained by the ionic or dissociation theory by the fact that ammo-
nium hydroxide is only slightly dissociated. According to this
theory, practically all reactions in aqueous solutions take place be-
tween ions (see page 195). The alkalies are largely dissociated into
metal ions and (OH) ions, which latter unite with the metal ions of
the other metals to form the slightly ionized and insoluble hydrox-
ides. Now ammonium hydroxide is only slightly ionized — in fact,
to a less extent than calcium hydroxide — so that only a small amount
of calcium hydroxide is formed, which remains in solution, because
somewhat soluble. The presence of this calcium hydroxide in solu-
tion prevents further ionization of the ammonium hydroxide to such
an extent that it ceases to act as an alkali or soluble hydroxide. In
fact, the slight ionization of ammonium hydroxide accounts for the
reverse action, namely, the liberation of ammonia from its salts by
the action of calcium hydroxide.

In the presence of ammonium salts, ammonium hydroxide ionizes
only to a very slight extent, so that it loses almost all the character
of a hydroxide as far as precipitating other metallic hydroxides is
concerned, only the extremely insoluble ones being precipitated.
This accounts for the fact that magnesium hydroxide is not precipi-
tated by ammonia water when ammonium salts are present. The
magnesium hydroxide, although being nearly insoluble, is sufficiently
soluble and ionizable not to be precipitated by ammonia water under
these conditions. Alkalies, on the other hand, precipitate magnesium
hydroxide copiously, because they are almost completely ionized in

276 METALS AND THEIR COMBINATIONS.

dilute solutions, and thus act as strong bases, as we say. Ammonium
carbonate behaves very much like ammonia water toward magnesium
and some other metals.

Hydroxides of nearly all metals, when heated sufficiently, lose
water and give the oxide. Many oxides are prepared in this way.
Only a few oxides unite with water to form a hydroxide. One of the
best examples of this is the process of slaking lime. Oxides may
also be obtained by heating carbonates or nitrates, or directly from
the metals. The method followed in any particular case is deter-
mined by the properties of the metal, the question of economy, etc.

Tests for magnesium.
(Use the reagent solution of magnesium sulphate. )

1. The addition of an alkali carbonate solution causes a white pre-
cipitate of basic magnesium carbonate (see Experiment 25).

2. Add to the solution some caustic alkali : a white precipitate of
magnesium hydroxide, Mg(OH)2, is formed, insoluble in excess of alkali.

Mg" + SO/' + 2Na' + 2(OH)' = Mg(OH), + 2Na' + SO/'.

3. Add to the solution ammonia water or ammonium carbonate :
part of the magnesium is precipitated as hydroxide or carbonate.
The latter is increased on heating. If an equal volume of ammo-
nium chloride solution is previously added, no precipitate is obtained
(for explanation, see Remarks on Tests above).

4. To the solution add an equal volume of solution of ammonium
chloride and some ammonia water. The mixture should be clear.
Then add sodium phosphate solution : a white, finely crystalline pre-
cipitate of the double salt, ammonium magnesium phosphate, is pro-
duced, which increases by shaking (see reactions under test 1 for
phosphoric acid). This is a delicate and decisive test for magnesium,
when other metals which resemble it are eliminated. This is easily
done by adding to a solution some chloride, sulphide, and carbonate
of ammonium, which will remove by precipitation all metals except
magnesium and alkali metals.

QUESTIONS. — How is magnesium found in nature? By what process is
metallic magnesium obtained? Give the physical and chemical properties of
magnesium. State two methods by which magnesium oxide can be obtained.
What is calcined magnesia? State the composition and properties of the
official magnesium carbonate, and how it is made. What is Epsom salt, and
how is it obtained? Which compounds of magnesium are insoluble? Give
tests for magnesium compounds. How can the presence of magnesium be
demonstrated in a mixture of magnesium sulphate and sodium sulphate ?

CALCIUM. 277

25. CALCIUM. STRONTIUM. BARIUM.
Ca" = 40 (39.81 ). Sr" = 86.94. Ba" = 136.4.

General remarks regarding the metals of the alkaline earths.

The three metals, calcium, barium, and strontium, form the second
group of light metals. Similar to the alkali-metals, they decompose
water at the ordinary temperature with liberation of hydrogen; their
separation in the elementary state is even more difficult than that of
the alkali-metals.

They differ from the latter by forming insoluble carbonates and
phosphates (those of the alkalies are soluble), from the earths by
their soluble hydroxides (those of the earths are insoluble), and from
all heavy metals by the solubility of their sulphides (those of heavy
metals are insoluble). ' The sulphates are either insoluble (barium)
or sparingly soluble (strontium and calcium). The hydroxides and
carbonates are decomposed by heat, water or carbon dioxide being
expelled and the oxides formed. In case of calcium carbonate this
decomposition takes place easily, while the carbonates of barium
and strontium require a much higher temperature. They are bivalent
elements.

Occurrence in nature. Calcium is one of the most abundantly
occurring elements. As carbonate (CaCO3) it is found in the form
of calc-spar, limestone, chalk, marble, shells of eggs and mollusca,
etc., or, as acid carbonate, dissolved in water. The sulphate is found
as gypsum or alabaster, CaSO42H2O; the phosphate, Ca3(PO4)2, in
the different phosphatic rocks (apatite, etc.) ; the fluoride, CaF2, as
fluor-spar; the chloride, CaCl2, in some waters, and the silicate in
many rocks. It enters the vegetable and animal system in various
forms of combination, chiefly, however, as phosphate and sulphate.

Calcium oxide, Lime, Calx, CaO = 55.68 (Quick-lime, Burned
lime), is obtained on a large scale by the common process of lime-
burning, which is the heating of limestone or any other calcium car-
bonate to about 800° C. (1472° F.), in furnaces termed lime-kilns.
On a small scale decomposition may be accomplished in a suitable
crucible over a blowpipe flame :

CaCO3 = CaO + CO2.

The pieces of oxide thus formed retain the shape and size of the
carbonate used for decomposition.

Lime is a white, odorless, amorphous, infusible substance, of alka-

278 METALS AND THEIR COMBINATIONS.

line taste and reaction; exposed to the air it gradually absorbs
acid among acids, and is used directly or indirectly in many branches
of chemical manufacture.

Calcium hydroxide, Calcium hydrate, Ca(OH)2 (Slaked lime).
When water is sprinkled upon pieces of calcium oxide, the two sub-
stances combine chemically, liberating much heat; the pieces swell
up, and are converted gradually into a dry, white powder, which is
the slaked lime. When this is mixed with water, the so-called milk
of lime is formed.

Freshly slacked lime, made into a thin paste with water and mixed with 3
to 4 times as much sand as lime used, forms the ordinary mortar, employed for
building purposes. The hardening of mortar is due first to loss of water, fol-
lowed by a gradual conversion of calcium hydroxide into carbonate. In the
course of years calcium silicate is also formed.

Lime-water, Liquor calcis (Solution of lime). This is a sat-
urated solution of calcium hydroxide in water : 10,000 parts of the
latter dissolving about 15 to 17 parts of hydroxide. In making
lime-water, 1 part of calcium oxide is slaked and agitated occasionally
during half an hour with 30 parts of water. The mixture is then
allowed to settle, and the liquid, containing besides calcium hydroxide
the salts of the alkali-metals which may have been present in the
lime, is decanted and thrown away. To the calcium hydroxide left,
and thus purified, 300 parts of water are added and occasionally
shaken in a well -stoppered bottle, from which the clear liquid may
be poured off for use.

Lime-water is a colorless, odorless liquid, having a feebly caustic
taste and an alkaline reaction. When heated to boiling it becomes
turbid by precipitation of calcium hydroxide (or perhaps oxide) which
re-dissolves when the liquid is cooled. Carbon dioxide causes a pre-
cipitation of calcium carbonate, soluble in an excess of carbonic acid.

Experiment 27. Make lime-water according to directions given above.

Calcium carbonate, Calcii carbonas praecipitatus, CaCO3 =
99.35. Precipitated calcium carbonate is obtained as a white, taste-
less, neutral, impalpable powder by mixing solutions of calcium
chloride and sodium carbonate:

CaCl2 + Na^CO, = 2NaCl + CaCO3.

CALCIUM. 279

Experiment 28. Add to about 10 grammes of marble (calcium carbonate), in
small pieces, hydrochloric acid as long as effervescence takes place ; filter the
solution of calcium chloride thus obtained and add to it solution of sodium
carbonate as long as a precipitate is formed, collect the precipitate on a filter,
wash and dry it.

Dried calcium sulphate, Calcii sulphas exsiccatus, CaSO4 =;
135.15 (Dried gypsum, Plaster-of-Paris, Calcined plaster). It has
been mentioned above that the mineral gypsum is native calcium
sulphate in combination with 2 molecules of water of crystallization,
By heating to about 115° C. (239° F.) about three-fourths of this
water is expelled, and a nearly anhydrous sulphate formed. This
article readily recombines with water, becoming a hard mass, for
which reason it is used for making moulds and casts, and in surgery.
If the gypsum is heated to a higher temperature than the one men-
tioned, all water is expelled, and the product thus obtained combines
with water but very slowly.

Precipitated calcium phosphate, Calcii phosphas preecipitatus,
Cas(p04)2 = 307.98 (Phosphate of lime). By dissolving bone-ash
(bone from which all organic matter has been expelled hy heat) in
hydrochloric acid, and precipitating the solution with ammonia water
there is obtained calcium phosphate, which contains traces of calcium
fluoride and magnesium phosphate.

A pure article is made by precipitating a solution of calcium
chloride by sodium phosphate and ammonia :

2Na2HPO4 + 3CaCl2 + 2NH4OH = Ca3(PO4)2 + 4NaCl + 2NH4C1 + 2H2O.

It is a white, tasteless, amorphous powder, insoluble in cold water,
soluble in hydrochloric or nitric acids.

Superphosphate, or acid phosphate of lime. Among the inorganic sub-
stances which serve as plant-food, calcium phosphate is a highly important
one. As this compound is found usually in very small quantities as a con-
stituent of the soil, and as this small quantity is soon removed by the various
crops taken from a cultivated soil, it becomes necessary to replace it in order
to enable the plant to grow and to form seeds.

For this purpose the various phosphatic rocks (chiefly calcium phosphate)
are converted into commercial fertilizers, which is accomplished by the addi-
tion of sulphuric acid to the ground rock. The sulphuric acid removes from
the tricalcium phosphate one or two atoms of calcium, forming mono- or
dicalcium phosphate and calcium sulphate. The mixture of these substances,
containing also the impurities originally present in the phosphatic rocks, is
sold as acid phosphate or superphosphate.

Bone-black and bone-ash. Phosphates enter the animal system
in the various kinds of food, and are to be found in every tissue and

280 METALS AND THEIR COMBINATIONS.

fluid, but most abundantly in the bones and teeth. Bones contain
about 30 per cent, of organic and 70 per cent, of inorganic matter,
most of which is tricalcium phosphate. When bones are burned until
all the organic matter has been destroyed and volatilized, the result-
ing product is known as bone-ash. If, however, the bones are sub-
jected to the process of destructive distillation (heating with exclusion
of air), the organic matter suffers decomposition, many volatile
products escape, and most of the non-volatile carbon remains mixed
with the inorganic portion of the bones, which substance is known
as bone-black or animal charcoal, carbo animalis. It contains about
85 per cent, of inorganic matter, the balance being chiefly carbon.

Calcium hypophosphite, Calcii hypophosphis, Ca(PH2O2)2 =
168.86. Obtained by heating pieces of phosphorus with milk of lime
until hydrogen phosphide ceases to escape. From the filtered liquid
the excess of lime is removed by carbon dioxide, and the clear liquid
evaporated to dryness. (Great care must be taken during the whole
of the operation, which is somewhat dangerous on account of the
inflammable and explosive nature of the compounds.)

8P + 6H2O + 3[Ca(OH)2] = 3[Ca(PH2O2)2] + 2PH3.

Calcium hypophosphite is generally met with as a white, crystal-
line powder with a pearly lustre ; it is soluble in 6 parts of water
and has a neutral reaction to litmus.

Calcium chloride, Calcii chloridum, CaCl2 = 11O.16, and
Calcium bromide, Calcii bromidum, CaBr2 = 198.52, may both
be obtained by dissolving calcium carbonate in hydrochloric acid or
hydrobromic acid, until the acids are neutralized. Both salts are
highly deliquescent.

Chlorinated lime, Calx chlorinata (Bleaching -powder, incorrectly
called Chloride of lime\ This is chiefly a mixture (according to some,
a compound) of calcium chloride with calcium hypochlorite, and is
manufactured on a very large scale by the action of chlorine upon
calcium hydroxide :

2Ca(OH)2 + 4C1 = 2H20 + Ca(ClO)2 + CaCl2.
Calcium hydroxide. Chlorinated lime.

Bleaching-powder is a white powder, having a feeble chlorine-like
odor ; exposed to the air it becomes damp from absorption of moist-
ure, undergoing decomposition at the same time; with dilute acids it

CALCIUM. 281

evolves chlorine, of which it should contain not less than 30 per cent,
in available form. The action of hydrochloric acid takes place thus:

Ca(ClO), -f 2HC1 = CaCl2 + 2HC1O;
2HC10 -f 2HC1 = 2H2O + 4C1.

Bleaching-powder is a powerful disinfecting and bleaching agent.

Sulphurated lime, Calx sulphurata, is a mixture of calcium sulphide and
sulphate, obtained by heating to redness in a crucible a mixture of dried cal-
cium sulphate, starch, and charcoal until the contents have lost their black
color. By the deoxidizing action of the coal and starch the larger portion of
the calcium sulphate is converted into sulphide.

Calcium carbide, C.2Ca, is manufactured on a large scale by heating in
an electric furnace a mixture of lime and coal, or coal-tar. The combined
action of the high temperature and of the electric current causes this decompo*
sition to take place :

CaO + 30 = CaC2 + CO.

Calcium carbide thus made is not pure; it forms gray or brown masses of
extreme hardness ; it is used extensively for generating acetylene gas, C2H8, which
is evolved when calcium carbide acts on water :

C2Ca + H2O = C2H2 -f- CaO.

Tests for calcium.
(The reagent solution of calcium chloride, CaCl^ may be used.)

1. Add to solution of a calcium salt, the carbonate of either potas-
sium, sodium, or ammonium : a white precipitate of calcium carbon-
ate, CaCO3, is produced. Try the test also on solution of calcium
sulphate and lime-water.

2. Add sodium phosphate to neutral solution of a calcium salt : a
white precipitate of calcium phosphate, CaHPO4, is produced.

3. Add ammonium (or potassium) oxalate to solution of a calcium
salt : a white precipitate of calcium oxalate, CaC2O4, is produced,
which is insoluble in acetic, soluble in hydrochloric acid. Try the test
also on solution of calcium sulphate and lime-water.

4. Sulphuric acid or soluble sulphates produce a white precipitate
of calcium sulphate, CaSO4, in concentrated, but not in dilute solu-
tions of a calcium salt. Try the test also on lime-water.

5. Add potassium or sodium hydroxide : a white precipitate of
calcium hydroxide, Ca(OH)2, is produced in concentrated, but not in
diluted solutions. Ammonia water gives no precipitate. (See Remarks
on Tests, page 274.)

6. Volatile compounds of calcium impart a reddish-yellow color to
the Bunsen flame. Non-volatile compounds, as the oxide, carbonate,
phosphate, etc., have scarcely any effect on the flame. (Try it.) These

282 METALS AND THEIR COMBINATIONS.

should first be moistened with strong hydrochloric acid to convert
them to the volatile chloride before introducing into the flame. (See
note to test 4 for potassium.)

Test 3, done in dilute solution, combined with tests 4 and 6, is
decisive for recognizing calcium compounds. The oxide, carbonate,
and phosphate may be dissolved by dilute hydrochloric acid for tests.
The phosphate solution cannot be neutralized without precipitation,
but if left weakly acid and considerably diluted test 3 can be applied.

The above tests are examples of more or less complete reactions, due to the
formation of insoluble or sparingly soluble substances, and their removal from
the field of action by precipitation (see pages 116 and 193). The ionic equa-
tions in the tests are as follows :

Test 1. Ca" -f 2C1' + 2Na' + CO3" = CaCO3 + 2Na" + 2C1';
Ca" + SO/' + 2Na' + CO3" = CaCO3 + 2Na' + SO/';
Ca" + 2(OH)' + 2Na- + CO3" - CaCO3 + 2Na' + 2(OH)'.

Test 2. Ca" + 2C1' + 2Na' + HPO4" = CaHPO4 + 2Na- + 2C1';
Test 3. Ca" + 2C1' + 2NH4'+ C,O4" = CaC2O4 + 2NH4- -f- 2C1'.
The equations for sulphate and hydroxide of calcium are similar (see test 1).
Test 4. Ca" + 2C1' + 2H- + SO/' = CaSO4 + 2H- 4- 2C1';
Test 5. Ca" + 2C1' + 2Na« + 2(OH)7 = Ca(OH)2 + 2Na« -f- 2C1'.

The ionic equations in the tests for strontium and barium are like those for
calcium.

Strontium, Sr" = 86.94. Found in a few localities in the minerals
strontianite, SrCO3, and celestite, SrSO4. Its compounds resemble
those of calcium and barium. The oxide, SrO, cannot be obtained
easily by heating the carbonate, as this is much more stable than
calcium carbonate. It may, however, be readily prepared by heating
the nitrate. The hydroxide, Sr(OH)2, is formed when the oxide is
brought in contact with water; it is more soluble than calcium
hydroxide.

Strontium nitrate, Sr(NO3)2, Strontium chloride, SrCl2, Strontium
bromide, SrBr2, and Strontium iodide, SrI2, may be obtained by dis-
solving the carbonate in the respective acids. The nitrate is used
extensively for pyrotechnic purposes, as strontium imparts a beau-
tiful red color to flames ; the bromide and iodide are official.

Tests for strontium.

(Use about a 5 per cent, solution of strontium nitrate.)

1 . The reactions of strontium with soluble carbonates, oxalates, and
phosphates are analogous to those of calcium.

STRONTIUM. 283

2. Add calcium sulphate solution : a white precipitate of strontium
sulphate, SrSO4, is formed after a few minutes. This test shows that
the sulphate is less soluble than calcium sulphate.

3. Add dilute sulphuric acid or a solution of a sulphate : a white
precipitate forms at once in concentrated, after a while in dilute,
solutions.

4. Add potassium chromate solution : a pale-yellow precipitate of
strontium chromate, SrCrO4, is formed, which is soluble in acetic acid
and in hydrochloric acid. (Potassium dichromate causes no precipi-
tation.)

5. Volatile strontium compounds color the Bunsen flame crimson
(see remarks in test 6 for calcium.) The color appears at the moment
when the substance is first introduced into the flame, whereby the color
can be seen, even in the presence of barium. Lithium is the only
other metal which gives a similar flame, but strontium may be dis-
tinguished from it by test 3 applied in somewhat dilute solution.

Tests 2 and 3 combined with 5 give conclusive proof of strontium
compounds. Insoluble compounds are treated as directed under tests
for calcium.

Barium, Ba11 = 136.4. Occurs in nature chiefly as sulphate in
barite or heavy spar, BaSO4, but also as carbonate in witherite, BaCO3.
Barium and its compounds resemble closely those of calcium and
strontium.

Barium chloride, BaCl2 + 2H2O, is prepared by dissolving the
carbonate in hydrochloric acid. It crystallizes in prismatic plates,
and is used as a valuable reagent.

Barium dioxide or peroxide, BaO2, is made by heating the oxide to
a dark -red heat in the air or in oxygen. When heated above the tem-
perature at which it is formed, decomposition into oxide and oxygen
takes place. This power to absorb oxygen from air and to give it up
again at a higher temperature has been used as a method of preparing
oxygen on the large scale. Unfortunately, the barium oxide cannot
be used for an unlimited number of operations, as it loses the power
to absorb oxygen after it has been heated several times. The use
made of barium dioxide in preparing hydrogen dioxide has been
mentioned before.

Barium dioxide is a heavy, grayish-white, amorphous powder,
almost insoluble in water, with which, however, it forms a hydroxide,
and to which it imparts an alkaline reaction.

284 METALS AND THEIR COMBINATIONS.

Barium oxide, BaO, is made by heating barium nitrate, Ba(N03)2, which
itself is made by dissolving barium carbonate in nitric acid.

Barium salts are poisonous ; antidotes are sodium and magnesium sulphates.

Tests for barium.
(Use the reagent solution of barium chloride.)

1. The reactions of barium salts with soluble carbonates, oxalates,
and phosphates are analogous to those of solutions of calcium salts.

2. Add dilute sulphuric acid or solution of a sulphate : a white
precipitate of barium sulphate, BaSO4, is produced immediately, even
in dilute solutions. The precipitate is insoluble in all diluted acids.

3. Add calcium sulphate solution : a white precipitate, insoluble in
all diluted acids, is formed immediately (compare with test 2 under
Strontium).

4. Add potassium chromate or dichromate solution : a pale-yellow
precipitate of barium chromate, BaCrO4, is formed, insoluble in acetic
acid, but soluble in hydrochloric or nitric acid.

5. Volatile barium compounds color a Buusen flame yellowish
green (see remarks under test 6 for calcium).

Tests 3, 4, and 5 give conclusive proof of barium. Insoluble com-
pounds are treated as directed under tests for calcium.

Radium, Ha = 223.3, This element, discovered in 1899, has been men-
tioned in the article on radio-activity, page 85. While radium is closely
related to barium it has not been found in the native barium compounds, except
when they occur associated with uranium as in pitch-blende, an ore from which
uranium compounds are extracted. This ore contains, however, but 0.1 gramme
of radium in 1000 kilograms, which is equal to 0.00001 per cent. The residue
left, after the uranium has been eliminated, contains from 2 to 3 times as much
radium as the original ore. From 1000 kilograms of this residue 10 to 15 kilo-
grams of radiferous barium salt (chloride or bromide) are extracted, and from

QUESTIONS. — Which metals form the group of the alkaline earths, and in
what respect do their compounds differ from those of the alkali-metals? How
is calcium found in nature? What is burned lime; from what, and by what
process is it made, and how does water act on it? What is lime-water; how
is it made, and what are its properties? Mention some varieties of calcium
carbonate as found in nature, and how is it obtained by an artificial process
from the chloride ? What is Plaster-of-Paris, and what is gypsum ; what are
they used for? State composition and mode of manufacturing bleaching-
powder ; what are its properties, and how do acids act upon it ? What is bone-
black, bone-ash, acid phosphate, and precipitated tricalcium phosphate ? How
are they made? Give tests for barium, calcium, and strontium ; how can they
be distinguished from each other ? Which compounds of barium and stron-
tium are of interest, and what are they used for?

ALUMINUM.

285

this the radium salt is prepared by repeated fractional crystallization. The
small yield of radium obtained after long and tedious operations make it the
most costly material of the day.

Both the chloride and bromide of radium are white, crystalline substances
turning grayish in the course of time. Lack of a liberal supply of radium has
so far prevented a closer study of its chemical behavior.

Summary of analytical characters of the alkaline earth-metals.

Magnesium.

Calcium.

Strontium.

Barium.

Yellow pre-

Yellow pre-

cipitate.
Yellow pre-

cipitate.
White pre-

cipitate.
White pre-

Ammonium carbonate . .

White preci-
pitate soluble
in NH4C1.
\Vhite pre-

White pre-
cipitate.

cipitate form-
ing slowly
White pre-
cipitate.

cipitate form-
ing at once.
White pre-
cipitate.

Ammonium oxalate . . .
Sodium phosphate . . .

cipitate
No precipi
tate unless
very con-
centrated
White pre-
cipitate.

White pre-
cipitate in
dilute
solution
White pre-
cipitate.
Yello wish-

White pre-
cipitate in
strong
solution.
White pre-
cipitate.
Eed

White pre-
cipitate in
strong
solution.
White pre-
cipitate
Yellowish-

One part of hydroxide is
soluble in

One part of sulphate is
soluble in

50,000 parts
of water.

1.5 parts of

red.

666 parts of
water.

400 parts of

50 parts of
water.

8000 parts of

green.

28.6 parts of
water.

400,000 parts

water.

water.

water.

of water.

26. ALUMINUM.

Aliu 27 (26.9).

Aluminum is the representative of the metals of the earths proper ;
all other members of this class are found in nature in very small
quantities, and are chiefly of scientific interest, with the exception of
cerium, which furnishes an official preparation.

Occurrence in nature. Aluminum is found almost exclusively
in the solid mineral portion of the earth ; rarely more than traces of
aluminum compounds are found dissolved in water, and the occur-
rence of aluminum in the animal organism seems to be purely
accidental.

By far the largest quantity of aluminum is found in combination

286 METALS AND THEIR COMBINATIONS.

with silicic acid in the various silicated rocks forming the greater
mass of our earth, such as feldspar, slate, basalt, granite, mica, horn-
blende, etc., or in the various modifications of clay formed by their
decomposition.

The minerals known as corundum, ruby, sapphire, and emery, are
aluminum oxide in a crystallized state, and more or less colored by
traces of other substances.

Metallic aluminum may be obtained by the decomposition of
aluminum chloride by metallic sodium :

A1C13 + 3Na — SNaCl -f Al.

It is now manufactured by the electrolysis of aluminum and sodium
fluoride, or of other aluminum compounds.

Aluminum is an almost silver- white metal of a very low specific
gravity (2.67) ; it is capable of assuming a high polish, and for this
reason is used for ornamental articles ; it is very ductile and malleable
and ranks with silver in hardness, as also in its power of conducting
heat and electricity.

Aluminum is not oxidized to any great extent in dry or moist air
nor is it affected by hydrogen sulphide. It is not readily acted on by
nitric or sulphuric acid, but easily dissolves in hydrochloric acid and
in solutions of the alkali hydroxides.

Aluminum forms alloys with nearly all metals, lead being an exception.
The hardness and elasticity of tin is increased by addition of aluminum ;
readily obtainable alloys with zinc are used as solders for aluminum. A small
quantity of aluminum added to wrought iron so increases its fusibility that it
may be poured as easily as cast iron. Largely used is aluminum-bronze, an alloy
resembling gold and composed of 10 parts of aluminum with 90 of copper.

Aluminum would be an ideal base for artificial dentures, were it not that
the corrosive action of alkaline fluids upon it limits its use.

Aluminum is trivalent, and the composition of the chloride and
hydroxide is therefore given as A1C13 and Al(OH), respectively.

Alum is the general name for a group of isomorphous double sul-
phates containing an atom each of a univaletit and a trivalent metal,
combined in crystallizing with 12 molecules of water. The general
formula of an alum is consequently MiMiii(SO4)2.12H2O. Mi repre-
sents in this case a univalent, Miu a trivalent metal.

Alums known are, for instance :

Ammonium-aluminum sulphate, NH4A1(SO4)2.12H2O.
Potassium-chromium sulphate, KCr(SO4)2.12H2O.
Ammonium-ferric sulphate, NH4Fe(SO4)8.12H8O.

ALUMINUM. 287

The official alum, (i/iimen, is the potassium alum, KA1(SO4)2.12H2O
= 471.02, a white salt crystallizing in large octahedrons, soluble in
10 parts of cold and 0.3 part of boiling water; this solution has an
acid reaction and a sweetish astringent taste.

Alum is manufactured on a large scale by decomposing certain
kinds of clay (aluminum silicates) by sulphuric acid, when aluminum
sulphate is formed, to the solution of which potassium or ammonium
sulphate is added, when, on evaporation, potassium or ammonium
alum crystallizes.

Dried alum; Alumen exsiccatum, KA1(SO4)2 = 256.46 (Burnt
alum). This is common alum, from which the water of crystallization
has been expelled by heat. It is a white powder, dissolving very
slowly in cold, but quickly in boiling water.

Aluminum hydroxide, Alumini hydroxidum, A1(OH)3 = 77.54.
Obtained by adding ammonia water or solution of sodium carbonate
to solution of alum, when aluminum hydroxide is precipitated in the
form of a highly gelatinous substance, which, after being well washed,
is dried at a temperature not exceeding 40° C. (104° F.).

2KA1(SO4)2 + 6NH4OH = K2SO4 + 3(NH4)2SO4 + 2A1(OH)3;
2KA1(SO4)2 + 3Na2CO3 + 3H2O = K2SO4 + 3Na2SO4 + 3CO2 + 2A1(OH)S.

When aluminum hydroxide is heated, water is expelled and the
oxide is left, which is often termed alumina.

The usual decomposition between a soluble carbonate and any soluble salt
(provided decomposition takes place at all) is the formation of an insoluble
carbonate ; according to this rule, the addition of a soluble carbonate to alum
should produce aluminum carbonate. The basic properties of aluminum
oxide, however, are so weak that it is not capable of uniting with so weak an
acid as carbonic acid, and it is for this reason that the decomposition takes
place as shown by the above formula, with liberation of carbon dioxide,
while the hydroxide is formed. (Other metals, the oxides of which have weak
basic properties, show similar reactions, as, for instance, chromium, and iron in
the ferric salts.)

The weak basic properties of aluminum are shown also by the fact that alu-
minum sulphate, chloride, and nitrate, and even alum itself, have an acid
reaction, while the corresponding salts of the alkalies or alkaline earths are
neutral.

Aluminum salts in solution give the ion Al*'% which forms insoluble
compounds with hydroxyl ion (OH)7, carbonate ion COg", phosphate ion
PO/X/, sulphide ion S/x, etc. The carbonate and sulphide are hydrolyzed
with elimination of CO2 and H2S respectively. Aluminum hydroxide has
such weak basic properties that it actually shows an acid character toward the

288 METALS AND THEIR COMBINATIONS.

active bases, and is dissolved by them to form compounds called aluminates.
This means that A1(OH)3 has two modes of ionization, namely,
A1(OH)3^± Al— f 3(OH)';
Al(OH), ;± A10/" + 3H-.

The first mode takes place mainly, and in the presence of acids, salts are
formed thus :

Al- -f- 3(OH)' -f 3H- + 3C1' = Al- + 3C1' + 3H2O.

The second mode of ionization takes place to a less extent, but in the presence
of excess of alkalies action results thus :

A10S"' -f 3H- + SNa- + 3(OH)' = A1O3' " -f 3Na' + 3H,O.
These reactions are generally written thus :

A1(OH)3 + 3HC1 = A1C13 + 3H2O;
A1(OH)3 -f 3NaOH = Na3AlO3 + 3H2O.

The compounds of the form Na3AlO3, called aluminates, are largely hydrolyzed
by water into NaOH and A1(OH)3. Hence, an excess of alkali is required to
dissolve the aluminum hydroxide. Ammonium hydroxide is too weak a base
to unite with it.

Aluminum hydroxide, in common with many other substances, as hydroxide
of iron, chromium, tin, tannic acid, etc., has the power of uniting with dyes and
forming colored compounds which adhere firmly to cotton and linen fabrics.
Such substances are called mordants (meaning biting), and without their use it
is impossible to dye cotton and linen permanently with most dyes. The insoluble
compounds of dyes with mordants are called lakes. When aluminum hy-
droxide is to be the mordant, the fabric is immersed in a hot solution of alum,
aluminum sulphate or acetate, or sodium aluminate, by which some aluminum
hydroxide, formed by hydrolysis of the compounds, is taken up by the fibres
of the fabric. The latter is then boiled in water containing the dye, which
unites with the mordant in the fibres, to form an insoluble permanent color.

Experiment 29. Dissolve 10 grammes of sodium carbonate in 100 c.c. of
water, heat it to boiling, and add to it, with constant stirring, a hot solution,
made by dissolving 10 grammes of alum in 100 c.c. of water. Wash the pre-
cipitate first by decantation, and then upon a filter, until the washings are not
rendered turbid by barium chloride. Dry a portion of the precipitate at a low
temperature, and use as aluminum hydroxide. Mix a small quantity of the
wet precipitate with a decoction of logwood (made by boiling about 0.2
grammes of logwood with 50 c.c. of water), agitate for a few minutes, and
filter. Notice that the red color of the solution has entirely disappeared, or
nearly so, in consequence of the combination of the aluminum hydroxide
and coloring matter.

Aluminum sulphate, Alumini sulphas, A12(SO4)3.16H2O =
625.93. A white crystalline powder, soluble in about its weight
_of water, obtained by dissolving the oxide or hydroxide in sulphuric
acid and evaporating the solution to dryness over a water-bath.

2A1(OH)3 + 3H2S04 == A1.2(S04), + 6H2O.

ALUMINUM. 289

Aluminum chloride, A1C13. This compound is of interest on account of
being the salt from which the metal was formerly obtained. Most chlorides
may be formed by dissolving the metal, its oxide, hydroxide, or carbonate in
hydrochloric acid. Accordingly aluminum chloride may be obtained in
solution :

A1(OH)3 + 3HC1 = A1C13 + 3H2O.

On evaporating the solution to dryness, however, and heating the dry mass
further with the view of expelling all water, decomposition takes place, hydro-
chloric acid escapes, and aluminum oxide is left:

2A1CL, + 3H2O = A1203 -f 6HC1.

Aluminum chloride, consequently, cannot be obtained in a pure state (free
from water) by this process, but it may be made by exposing to the action of
chlorine a heated mixture of aluminum oxide and carbon. Neither carbon
nor chlorine alone causes decomposition of the aluminum oxide, but by the
united efforts of these two substances decomposition is accomplished :

A12O3 f 3C + GC1 = 3CO + 2A1CL,.

Clay is the name applied to a large class of mineral substances,
differing considerably in composition, but possessing in common the
two characteristic features of plasticity and the predominance of
aluminum silicate in combination with water. A white clay, known as
kaolin, consists chiefly of a silicate of the composition

The various kinds of clay have been formed in the course of time from such
double silicates as feldspar and others, by a process which is partly of a
mechanical, partly of a chemical nature, and consists chiefly in the disintegra-
tion of rocks and a removal of potassium and sodium by the chemical action of
carbonic acid, water, and other agents.

The various kinds of clay are used in the manufacture of bricks, earthenware,
stoneware, porcelain, etc. The process of burning these substances accom-
plishes the hardening by expelling water which is present in the clay. Pure
clay is white ; the red color of the common varieties is due to the presence of
ferric oxide. For china or porcelain, clay is used containing silicates of the
alkalies which, in burning, melt, causing the production of a more homoge-
neous mass, while in common earthenware the pores, produced by expelling
the moisture, remain unfilled.

Glass is similar in composition to the better varieties of porcelain.
All varieties of glass are mixtures of fusible, insoluble silicates, made
by fusing silicic acid (white sand) with different metallic oxides or
carbonates, the silicic acid combining chemically with the metals.
Sodium and calcium are the chief metals in common glass, though
potassium, lead, and others also are frequently used. Color is im-
parted to the glass by the addition of certain metallic oxides, which

19

290 METALS AND THEIR COMBINATIONS.

have a coloring effect, as. for instance, manganese violet, cobalt blue,
chromium green, etc.

Cement or hydraulic mortar is the name given to a finely powdered
mineral, consisting chiefly of basic silicates of lime and alumina, and having
the power of forming an insoluble solid mass when mixed with water. Some
native limestones, containing also magnesium carbonate and aluminum silicate,
furnish cement after being heated to expel water and carbon dioxide. Other
cements are made by burning mixtures of limestone and clay of a suitable com-
position. The slag of iron furnaces also furnishes the material for cement.

Ultramarine is a beautiful blue substance, found in nature as the mineral
" lapis lazuli" which was highly valued by artists as a color before the dis-
covery of the artificial process for manufacturing it.

Ultramarine is now manufactured on a very large scale by heating a mix-
ture of clay, sodium sulphate and carbonate, sulphur, and charcoal in large
crucibles, when decomposition takes place and the beautiful blue compound
is obtained. As neither of the substances used in the manufacture has a ten-
dency to form colored compounds, the formation of this blue ultramarine is
rather surprising, and the true chemical constitution of it is yet unknown.

Ultramarine is insoluble in water and is decomposed by acids with libera-
tion of hydrogen sulphide, which shows the presence of sodium sulphide. A
green ultramarine is now also manufactured. The approximate formula of the
blue compound is Na2S2.4NaAlSiO4.

Tests for aluminum.
(Use about a 5 percent, solution of alum or aluminum sulphate.)

1. To the solution add solution of potassium or sodium hydroxide :
a faintly bluish-white gelatinous precipitate of aluminum hydroxide,
A1(OH)3, is produced. The physical appearance of the precipitate is
characteristic. It is soluble in excess of the alkali, forming an
al-uminate, thus :

A1(OH)3 + 3NaOH = Al(ONa)3 + 3H2O.

This shows that A1(OH)3 has weak acid character toward strong alka-
lies. It is reprecipitated on adding ammonium chloride and heating.
Aluminum hydroxide is soluble in acids, even acetic acid.

2. To the solution add ammonia water : the same precipitate as
above is obtained, but it is insoluble in an excess of the reagent (dif-
ference from zinc) and also in ammonium chloride solution (difference
from magnesium).

3. A solution of a carbonate produces the same precipitate as
above, with liberation of carbon dioxide, not very noticeable in dilute
solutions (see explanation in text).

ALUMINUM. 291

4. Solution of ammonium sulphide produces the same precipitate,
with generation of hydrogen sulphide :

A12(S04)3 + 3(NH4)2S + 6H20 = 2A1(OH), + 3(NH4)2SO4 + 3H2S.

5. Solution of sodium phosphate produces a white precipitate of
aluminum phosphate, A1PO4.4H2O, soluble in mineral acids, but not
acetic, and in fixed alkalies (difference from iron).

6. Heat a dry aluminum salt on charcoal strongly with the blow-
pipe flame. The residue is aluminum oxide, which, when moistened
with solution of cobalt nitrate and again heated, gives a blue com-
pound, cobalt aluminate.

Test 1 combined with Tests 5 and 6 are conclusive. evidence of the
presence of aluminum. The salts are white, have a sweetish, astringent
taste, are acid to litmus, and decomposed by heat, leaving a residue
of oxide.

Cerium, Ce = 141. This element occurs in nature sparingly in a few rare
minerals, chiefly as silicate in cerite. In its general deportment cerium resem-
bles aluminum. Cerous solutions give with either ammonium sulphide or
ammonium and sodium hydroxide, a white precipitate of cerous hydroxide,
Ce2(OH)6. Ammonium oxalate forms a white precipitate of cerium oxalate,
ceriioxalas, Ce2(C204)310H2O, which is the only official cerium preparation.
Cerium oxalate is a white, granular powder, insoluble in water and alcohol,
but soluble in hydrochloric acid. Exposed to a red heat it is decomposed and
converted into reddish-yellow eerie oxide. If this oxide, or the residue obtained
by heating any cerium salt to red heat, is dissolved in concentrated sulphuric
acid, and a crystal of strychnine added, a deep blue color appears, which
changes first to purple and then to red. The official cerium oxalate contains
also a small quantity of the oxalates of didymiuin, lanthanum, and other rare
earths.

Monazite sand, found in North Carolina and elsewhere, contains, besides
cerite. the silicates or oxides or phosphates of other earth metals, especially
of zirconium, erbium, and thorium. It is chiefly the oxide of thorium which is
used in the mantle of the Welsbach incandescent burner, on account of the
bright white light which this oxide emits at a comparatively low temperature.

QUESTIONS. — Mention some varieties of crystallized aluminum oxide found
in nature and some silicates containing it. Give the general formula of an
alum, and mention some alums. Which alum is official, how is it made, what
are its properties, and what is it used for? What is dried alum, and how does
it differ from common alum? How is aluminum chloride made, and how ia
the metal obtained from it? State the properties of aluminum. What change
takes place when ammonium hydroxide, and what change when sodium car-
bonate is added to a solution of alum ? What is the composition of earthen-
ware, porcelain, and glass ; how and from what materials are they manufac-
tured? What is ultramarine ? Give tests for aluminum compounds.

292

METALS AND THEIR COMBINATIONS.

Summary of analytical characters of the earth-metals and

chromium.

Aluminum,

Cerium.

Chromium.

Ammonium sulphide .

White precipitate.

White precipitate.

Green precipitate.

Potassium hydroxide .
Ammonia water . . .

White precipitate.
Soluble in KOH.
Not re-precipitated
by boiling.
White precipitate.

WThite precipitate.
Insoluble in KOH

White precipitate.

Green precipitate.
Soluble in KOH.
Re-precipitated
by boiling.
Green precipitate.

Ammonium carbonate

White precipitate.

White precipitate.

Green precipitate.

27. IRON. (Ferrum.)
Fe» = 55.5.

General remarks regarding- the metals of the iron group. The
six metals (Fe, Co, Ni, Mn, Cr, Zn) belonging to this group are distin-
guished by forming sulphides (chromium excepted) which are insolu-
ble in water, but soluble in dilute mineral acids; they are, conse-
quently, not precipitated from their neutral or acid solutions by
hydrogen sulphide, but by ammonium sulphide as sulphides
(chromium as hydroxide); their oxides, hydroxides, carbonates,
phosphates, and sulphides are insoluble; their chlorides, iodides,
bromides, sulphates, and nitrates are soluble in water.

With the exception of zinc, these metals are magnetic ; they de-
compose water at a red heat, the oxide being formed and hydrogen
liberated; in dilute hydrochloric or sulphuric acid they dissolve
with formation of chlorides or sulphates respectively, and liberation
of hydrogen.

Zinc is constantly bivalent, nickel is usually bivalent, but trivalent
in a few compounds, cobalt is bi- and trivalent, iron and chromium
are bi-, tri-, and sexivalent, manganese is bi-, tri-, sexi-, and septiva-
lenf. All the metals, except zinc, form several oxides, the higher
ones of which have acid character, as iron trioxide, chromium tri-
oxide, manganese trioxide and heptoxide.

Occurrence in nature. Among all the heavy metals, iron is both
the most useful and the most widely and abundantly diffused in
nature. It is found, though usually in but small quantities, in nearly
all forms of rock, clay, sand, and earth ; its presence in these being

IRON. 293

indicated generally by their color (red, reddish-brown, or yellowish-
red), as iron is the most common of all natural, inorganic coloring
agents. It is found also, though in small quantities, in plants, and
in somewhat larger proportions in the animal system, chiefly in the
blood. In the metallic state iron is scarcely ever found, except in
the meteorites or metallic masses which fall occasionally upon our
earth out of space.

The chief compounds of iron found in nature are :

Hematite, ferric oxide, Fe2O3.

Magnetic iron ore, ferrous-ferric oxide, FeO.Fe2O9.

Spathic iron ore, ferrous carbonate, FeCOs.

Iron pyrites, bisulphide of iron, FeS2.

The carbonate and sulphate are found sometimes in spring waters,
which, when containing considerable quantities of iron, are called
chalybeate waters. Finally, iron is a constituent of some organic
substances which are of importance in the animal system.

Manufacture of iron. There is no other metal manufactured in
such immense quantities as iron, the use of which in thousands of
different tools, machines, and appliances is highly characteristic of
our present age. Iron is manufactured from the above-named oxides
or the carbonate by heating them with coke and limestone in large
blast furnaces, which have a somewhat cylindrical shape, and are
constantly fed from above with a mixture of the substances named,
while hot air is forced into the furnace through suitable apertures
near its hearth. The chemical change which takes place in the upper
and less heated part of the furnace is a deoxidation of the iron oxide

by the carbon :

Fe2O3 + 30 == SCO -f 2Fe

The heat necessary for this decomposition and fusion of the re-
duced iron is produced by the combustion of the fuel, maintained by
the oxygen of the air blown into the furnace. At the same time the
lime and other bases combine with the silica contained in the ore,
forming a fusible glass, called cinder or slag. The iron and slag
collect at the bottom of the furnace, where they separate by gravity,
and are run off every few hours.

Iron thus obtained is known as cast-iron, or pig-iron, and is not
pure, but always contains, besides silicon (also sulphur, phosphorus,
and various metals), a quantity of carbon varying from 2 to 5 per
cent. It is the quantity of this carbon and its condition which im-
parts to the different kinds of iron different properties. Steel contains

294 METALS AND THEIR COMBINATIONS.

from 0.16 to 2 per cent,, wrought- or bar-iron but very small quanti-
ties, of carbon. Wrought-iron is made from cast-iron by the process
known as puddling, which is a burning-out of the carbon by oxida-
tion, accomplished by agitating the molten mass in the presence of
an oxidizing flame. Steel is made either from cast-iron by partially
removing the carbon, or from wrought-iron by recombining it with
carbon — i. e., by agitating together molten wrought- and cast-iron in
proper proportions.

Properties. The high position which iron occupies among the useful metals
is due to a combination of valuable properties not found in any other metal.
Although possessing nearly twice as great a tenacity or strength as any of the
other metals commonly used in the metallic state, it is yet one of the lightest,
its specific gravity being about 7.7. Though being when cold the least yield-
ing or malleable of the metals in common use, its ductility when heated is such
that it admits of being rolled into the thinnest sheets and drawn into the finest
wire, the strength of which is so great that a wire of one-tenth of an inch in
diameter is capable of sustaining TOO pounds. Finally, iron is, with the ex-
ception of platinum, the least fusible of all the useful metals.

For certain articles, such as armor plate, rock breakers, lathe tools, etc., steel
is hardened by alloying it with small quantities of certain other metals, chiefly
with chromium, nickel, or manganese.

Iron is little affected by dry air, but is readily acted upon by moist air, when
ferric oxide and ferric hydroxide (rust) are formed.

Hardening and tempering steel. Steel contains carbon both in the ele-
mentary state as graphite, and chemically combined as iron carbide. Within
certain limits the tenacity of the metal, and its hardness after having been
heated and suddenly cooled, bear a direct ratio to the amount of combined
carbon. The more of the latter is present the harder is the steel and vice versd.

If steel be heated to redness and suddenly chilled it has attained its maxi-
mum hardness; if, however, it be permitted to cool slowly after heating, it
becomes soft. Any degree of hardness between these extremes can be obtained
by the process known as tempering or " letting down." It consists in carefully
reheating the previously hardened metal to a certain temperature and then
plunging it into cold water. To the experienced worker the required temper-
ature is indicated by a series of colors appearing successively on the surface of
the steel. These colors are due to a gradually thickening film of iron oxides
while the iron softens. The colors pass successively from pale yellow through
several shades of darker yellow to brown, purple, blue, and bluish black. The
highest temperature gives the least hardness and vice versd.

In hardening steel, prior to tempering, care should be taken not to injure
the metal by overheating, which causes oxidation of the carbon and blisters the
metallic surface, rendering a fine temper impossible. In tempering small
instruments a coating of some material, such as soap, is necessary to prevent
oxidation as far as possible.

Elasticity and tenacity desired for specific purposes, as in the case of springs,
is imparted to steel by hammering. This causes a condensation of the particles

IRON. 295

and the conversion of the crystalline structure to a fibrous condition, in which
state steel is more elastic, tougher, and of greater tensile strength.

Iron forms two series of compounds, distinguished as ferrous and
ferric compounds ; in the former, iron is bivalent, in the latter,
apparently trivalent. Almost all ferrous compounds show a tendency
to pass into ferric compounds when exposed to the air, or more readily
when treated with oxidizing agents, such as nitric acid, chlorine, etc.
As the reaction of iron in ferrous and ferric compounds diifers con-
siderably, they must be studied separately. Ferrous oxide and
hydroxide are more strongly basic than ferric oxide and hy-
droxide.

Reduced iron, Ferrum reductum. This is metallic iron, obtained
as a very fine, grayish-black, lustreless powder by passing hydrogen
gas (purified and dried by passing it through sulphuric acid) over
ferric oxide, heated in a glass tube :

FeA + 6H = 3H20 + 2Fe.

The official article should have at least 90 per cent, of metallic
iron.

Ferrous oxide, FeO (Monoxide or suboxide of iron). This com-
pound is little known in the separate state, as it has (like most ferrous
compounds) a great tendency to absorb oxygen from the air. The
ferrous hydroxide, Fe(OH)2, may be obtained by the addition of any
alkaline hydroxide to the solution of any ferrous salt, when a white
precipitate is produced which rapidly turns bluish -green, dark-gray,
black, and finally brown, in consequence of absorption of oxygen
(see Plate I., 2) :

FeSO4 + 2NH.OH = (NH4)2SO4 + Fe(OH)2;
2Fe(OH)2 + O + H20 = Fe2(OH)6.

The precipitation of ferrous hydroxide is not complete, some iron
always remaining in solution.

Ferrous oxide is a strong base, uniting with acids to form salts,
which have usually a palo-groen color.

Ferric oxide, Fe2O3. A reddish-brown powder, which may be
obtained by heating ferric hydroxide to expel water :

2Fe(OH)3 = Fe2O3 + 3K.O.
It is a feeble base ; its salts show usually a brown color.

296 METALS AND THEIR COMBINATIONS.

In the preparation of fuming sulphuric acid (which see) by heating ferrous
sulphate there is left a residue of ferric oxide, known as rouge, which is used
as a red pigment and as a polishing powder.

4FeS04 + H20 = 2Fe,O, + H2S04.SO3 4- 2SO2.

A specially fine variety of rouge for polishing is manufactured by heating
ferrous oxalate, FeC2O4, in contact with the air.

Ferric hydroxide, Ferri hydroxidum, Fe(OH)3 = 106.14, Is
obtained by precipitation of ferric sulphate or ferric chloride by am-
monium or sodium hydroxide (see Plate I., 3) :

Fe2(S04)3 + 6NH4OH = 3[(NH4)2SOJ -f 2Fe(OH)3.

Precipitation is complete, no iron remaining in solution as in the
case of ferrous salts.

Ferric hydroxide is a reddish-brown powder, sometimes used as
an antidote in arsenic poisoning ; for this purpose it is not used in
the dry state, but after having been freshly precipitated and washed,
it is mixed with water, and this mixture used.

Ferric hydroxide with magnesium oxide, U. S. P., is a mixture freshly made,
when called for, by adding magnesia to a solution of ferric sulphate, when
magnesium sulphate and ferric hydroxide are formed; the two substances are
not separated from each other, the mixture being intended for immediate
administration as an antidote in cases of arsenic poisoning.

Ferrous-ferric oxide, FeO.Fe2O3 (Magnetic oxide). This com-
pound, which shows strong magnetic properties, has been mentioned
above as one of the iron ores, and is known as loadstone. It has a
metallic lustre and iron-black color, and is produced artificially by
the combustion of iron in oxygen, or in the hydrated state by the
addition of ammonium hydroxide to a mixture of solutions of ferrous
and ferric salts.

Iron trioxide, FeO3. Not known in a separate state, but in com-
bination with alkalies. In these compounds, called ferrates, FeO3
acts as an acid oxide, analogous to chromium trioxide, CrO3, in chro-
mates. The composition of potassium ferrate is K2FeO4.

Ferrous Chloride, FeCl2 (Protochloride of iron), is obtained as a
pale-green solution by dissolving iron in hydrochloric acid :
Fe + 2HC1 = FeCl2 + 2H.

The anhydrous salt cannot be obtained by evaporation of the solu-
tion, as it decomposes ; but it may be made by heating iron in a cur-

IKON. 297

rent of dry hydrochloric acid gas. The solution and salt absorb
oxygen very readily :

3FeCl2 -f O = FeO + 2FeCl3.

Ferric chloride, Perri chloridum, FeClr6H2O =268.32 (Chlo-
ride, sesqui-chloride, or perchloride of iron), is obtained by adding to
the solution of ferrous chloride (obtained as mentioned above) hydro-
chloric and nitric acids in sufficient quantities, and applying heat
until complete oxidation has taken place. The nitric acid oxidizes
the hydrogen of the hydrochloric acid to water, while the chlorine
combines with the ferrous chloride, nitrogen dioxide being formed
also :

3FeCl2 + HNO8 + 3HC1 = 3FeCls + 2H2O + NO.

By sufficient evaporation of the solution, ferric chloride is obtained
as a crystalline mass of an orange-yellow color; it is very deli-
quescent, has an acid reaction, and a strongly styptic taste. The
water of crystallization cannot be expelled by heat, because heat
decomposes the salt, free hydrochloric acid and ferric oxide being
formed.

Experiment 30. Dissolve by the aid of heat 1 gramme of fine iron wire in
about 4 c.c. of hydrochloric acid, previously diluted with 2 c.c. of water.
Filter the warm solution of ferrous chloride, mix it with 2 c.c. of hydrochloric
acid, and add to it slowly and gradually about 0.6 c.c. of nitric acid. Evap-
orate in a fume chamber as long as red vapors escape ; then test a few drops
with potassium ferricyanide, which should not give a blue precipitate ; if it
does, the solution has to be heated with a little more nitric acid until the con-
version into ferric chloride is complete and the potassium ferricyanide pro-
duces no precipitate. Ferric chloride thus obtained may be mixed with 4 c.c.
of hot water and set aside, when it forms a solid mass of FeCl3.6H2O. How
much FeCl2, how much FeCl3, and how much FeCl3.6H2O can be obtained
from 1 gramme of iron?

Solution of ferric chloride, Liquor ferri chloridi. This is a
solution in water, containing 29 per cent, of the anhydrous ferric
chloride. It is a reddish-brown liquid of specific gravity 1.315, hav-
ing the taste and reaction of the dry salt. This solution, mixed with
alcohol in the proportion of 35 to 65 parts by volume, and left stand-
ing in a closed vessel for at least three months, forms the tincture of
ferric chloride, Tinctura ferri chloridi. By the action of the alcohol
on ferric chloride this is reduced to the ferrous state, while at the
same time a number of other compounds are formed, imparting to the
liquid an ethereal odor.

Solutions of ferric salts usually have a brown color and show an acid reac-
tion. This is due to the partial hydrolysis of the salts, forming ferric hydroxide

298 METALS AND THEIR COMBINATIONS.

and free acid. Addition of acid, by preventing hydrolysis, renders the solu-
tions colorless or nearly so. Hydrolysis is increased by heating the solutions,
hence hot ferric solutions have a deeper color than cold ones.

Ferrous salts are much less hydrolyzed than ferric salts, as ferrous iron is a
stronger base than ferric iron. They also are not as acid to litmus as the
ferric salts.

Dialyzed iron is an aqueous solution of about 5 per cent, of ferric hydrox-
ide with some ferric chloride. It is made by slowly adding ammonium hy-
droxide to a solution of ferric chloride as long as the precipitate of ferric
hydroxide formed is redissolved in the ferric chloride solution, on shaking
violently. The clear solution thus obtained is placed in a dialyzer floating in
water which latter is renewed every day until it shows no reaction with silver
nitrate. The ammonium chloride passes through the membrane of the dialyzer
into the water, while all iroir as hydroxide with some chloride, is left in
solution.

The combination of an oxide or hydroxide with a normal salt is called
usually a basic salt or oxy-salt ; dialyzed iron is a highly basic oxychloride
of iron.

Ferrous iodide, Fel^ and Ferrous bromide, FeBr2, may both be
obtained by the action of iodine and bromine, respectively, on iron filings,
when combination takes place. Both salts are unstable, absorbing oxygen
from the air very readily.

Experiment 31. Cover some fine iron wire with water, heat gently, and add
iodine in fragments as long as the red color of iodine disappears. Notice that
the iron is dissolved gradually, the result of the reaction being the formation
of a pale-green solution of ferrous iodide.

Ferrous sulphide, FeS. Easily obtained as a black, brittle mass,
by heating iron filings with sulphur, when the elements combine. It
is used chiefly for liberating hydrogen sulphide, by the addition of
sulphuric acid. Iron combines with sulphur in several proportions;
some of these iron sulphides are found in nature.

Ferrous sulphate, Ferri sulphas, FeSO4.7H2O = 276.O1 (Sul-
phate of iron, Green vitriol, Copperas). Obtained by dissolving iron
in dilute sulphuric acid, evaporating, and crystallizing :
Fe + H2S04 = 2H + FeSO4.

Also obtained as a by-product in some branches of chemical indus-
try, and by heap-roasting of the native iron sulphide :

FeS2 + 60 = FeS04 + SO2.

Ferrous sulphate crystallizes in large, bluish-green prisms ; it is
soluble in water, insoluble in alcohol. Exposed to the air, it loses
water of crystallization and absorbs oxygen.

IKON. 299

The exsiccated ferrous sulphate, U. S. P., is made by expelling
nearly all the water of crystallization by heating to 100° C. (212° F.) ;
the granulated (precipitated) ferrous sulphate is made by quickly
cooling a hot saturated solution of ferrous sulphate, slightly acidu-
lated with sulphuric acid, while stirring, when ferrous sulphate sepa-
rates as a crystalline powder, which is filtered, washed with alcohol,
and dried.

Experiment 32. In a flask put 10 c.c. of concentrated sulphuric acid diluted
with 40 c.c. of water, add iron wire, card teeth, or nails, in portions, until the
acid is exhausted, as seen by the cessation of effervescence. Gently heating
facilitates the action at the end. Note the bad odor of the hydrogen, due to
impurities, and the dark flakes of carbon in the solution. Finally, filter the
hot solution and set it aside to crystallize. If crystals do not form, evaporate
further.

Ferrous sulphate readily forms double salts with alkali sulphates, which are
not efflorescent, and in the dry state are less readily oxidized than ferrous sul-
phate. When a hot, strong solution of 1 part of ammonium sulphate is added
to a similar solution of 2 parts of crystals of ferrous sulphate, on cooling, a
salt with the composition, (NHJ2SO4.FeSO4.6H.20, separates (Mohr's salt).
This is often used when a stable ferrous salt is wanted.

Ferric sulphate, Fe2(SO4)3. The solution of this salt, Liquor ferri
tersulphatis, is made by adding sulphuric and nitric acids to a solution
of ferrous sulphate and heating :

6FeS04 + 3H2S04 + 2HNO3 = 3[Fe2(SO4)3] + 2NO + 4H2O.

The action of nitric acid is similar to that described above under
ferric chloride. The hydrogen of the sulphuric acid is oxidized, and
the radical SO4 unites with the ferrous sulphate, nitrogen dioxide
being liberated.

Experiment 33. Dissolve several crystals of ferrous sulphate in about 20 c.c.
of water, add about 5 c.c. of dilute sulphuric acid. Warm the solution and
add concentrated nitric acid, in drops, until the dark color first produced sud-
denly turns to reddish-brown. Note the red fumes of oxide of nitrogen
escaping. The dark color is due to the union of nitric oxide, NO (see reaction
above), with unoxidized ferrous sulphate (see test 2 for nitric acid). Heat the
solution to expel oxide of nitrogen and excess of nitric acid. Dilute a few
drops and test with ferricyanide, as in Experiment 30.

Solution of ferric sulphate is used in the preparation of Ferric
ammonium sulphate, Ferri et ammonii sulphas, FeNH4(SO4)2.12H2O
(iron alum, or ammonio-ferric alum), which is made by mixing a solu-
tion of ferric sulphate with ammonium sulphate and crystallizing.
The salt has a pale violet color and is readily soluble in water.

300 METALS AND THEIR COMBINATIONS.

Solution of ferric subsulphate, Liquor ferri subsulphatis
(Mouses solution). This is a solution similar to the preceding, but
contains less sulphuric acid, and is, therefore, looked upon as a basic
ferric sulphate, of the doubtful composition 5[Fe2(SO4)3].Fe2(OH)6.

Ferrous carbonate, PeCO3. Occurs in nature; maybe obtained
by mixing solutions of ferrous sulphate and sodium carbonate or
bicarbonate :

FeS04 + 2NaHC03 = NaJSO, -f FeCO3 + CO2 + H2O.

The precipitate is first nearly white, but soon assumes a gray color
from oxidation. The saccharated ferrous carbonate, U. S. P., is made
by mixing the washed precipitate with sugar, and drying. The
sugar prevents, to some extent, rapid oxidation. The preparation
contains 15 per cent, of ferrous carbonate.

Ferric carbonate does not exist, the affinity between the feeble ferric
oxide and the weak carbonic acid not being sufficient to unite them
chemically.

Ferrous phosphate, Fe3(PO4)2. When sodium phosphate is
added to solution of ferrous sulphate, a precipitate of the composi-
tion FeHPO4 is formed :

NajHPO^ + FeSO4 = FeHPO4 + Na.jSO4.

If, however, sodium acetate is added, a precipitate of the composi-
tion Fe3(PO4)2 is formed :

3FeSO4 + 2N02HPO4 = Fe3(PO4)2 + 2Na2SO4 -f H2SO4.

The sulphuric acid liberated, as shown in this formula, decomposes
the sodium acetate, forming sodium sulphate and free acetic acid.
Ferrous phosphate is a slate-colored powder, absorbing oxygen
readily, becoming darker in color.

Ferric phosphate, FePO4, may be obtained from ferric chloride
solution by precipitation with an alkali phosphate. The Soluble ferric
phosphate and the Soluble ferric pyrophosphate of the U. S. P., are
scale compounds. (See index.)

Ferric hypophosphite, Ferri hypophosphis, Fe(H2PO2)3 =
249.09 (Hypophosphite of iron). It is obtained by adding a solution
of sodium hypophosphite to a solution of ferric chloride or sulphate,
free from excess of acid. The precipitate is filtered, washed, and dried.
It is a grayish-white powder, slightly soluble in water, soluble in
hydrochloric acid, in hypophosphorous acid, and in a warm, concen-
trated solution of an alkali citrate.

IRON.

301

Tests for iron.

1. Ammonium sul-
phide.

2. Hydrogen sul-
phide.

3. Ammonium, so-
dium, or potas-
sium hydroxide

4. Ammonium, so-
dium, or potas-
sium carbonate.

5. Alkali phosphates

or arsenates

6. Potassium ferro-

cyanide.

K4Fe(CN)6.

7. Potassium ferri-

cyanide.

K6Fe2(CN)12.

8. Tannic acid.

9 Potassium sul-
phocyanate.
KCNS.

Ferrous salts.

(Use FeSO4.)

Black precipitate of ferrous
sulphide (Plate I., 1).
FeSO4 + (NH4)2S =
(NH4)2SO4 + FeS.

No change, except sometimes
a slight black discoloration,
due to the formation of a
trace of FeS. .

White precipitate of ferrous
hydroxide soon turning
green, black, and brown.
Precipitation not complete
(Plate I., 2).

2NaCl+ Fe(OH)2.

White precipitate of ferrous
carbonate, soon turning
darker.

FeCl2 + Na2CO8 =
2NaCl 4- FeCO3.

Almost white precipitate, soon
turning darker.

Almost white precipitate,
K2Fe[Fe(CN)6], soon turning
blue by absorption of oxygen
(Plate I., 4).

Blue precipitate of ferrous ferri-

cyanide, or Turnbull's blue.

3FeCl2 + K6Fe2(CN)12 =

6KC1 + Fe8Fea(CN)lr

No change, provided oxidation
of the ferrous salt has not
taken place.

As above.

Ferric taltt.

(UseFeCl,.)

Black precipitate of ferrous sul-
phide mixed with sulphur.
2FeCl3 + 3[(NH4)2S]=
6NH4C1 + 2FeS + S.

Ferric salts are converted into
ferrous salts with precipita-
tion of sulphur.

2FeCl.2 + 2HCl-f S..

Keddish-brown precipitate of
ferric hydroxide. Precipita-
tion is complete (Plate I., 3).
3(NH4OH) =
Fe(OH)3:

Reddish-brown precipitate of
ferric hydroxide, with libera-
tion of carbon dioxide (Plate
I., 3).

2FeCl3 -f 3Na2CO3 + 3H,O -
GNaCl + 2Fe(OH)8 + 3CO2.

A yellowish-white precipitate
is produced.

Dark-blue precipitate of ferric
ferrocyanide, or Prussian blue.
Decomposed by alkalies ; in-
soluble in acids (Plate I., 5).
3[K4Fe(CN)6] =
Fe43[Fe(CN)fl].

No precipitate is produced, but
the liquid is darkened to a
greenish-brown hue.

A dark greenish-black precipi-
tate of ferric tannate is pro-
duced.

Deep blood-red solution of fer-
ric sulphocyanate, Fe(CNS)3
(Plate I., 6).

302 METALS AND THEIR COMBINATIONS.

Remarks to tests. In test 1 iron in the ferric state is too weakly
basic to form ferric sulphide, but in the ferrous state it is a stronger
base, so that the ferric sulphide breaks down at the moment of forma-
tion to ferrous sulphide and sulphur. If ferrous iron were as weakly
basic as aluminum and chromium, no precipitate of sulphide would
be obtained.

In test 2 no precipitate is formed, because of the acid that would
be set free by the reaction. Ferric salts are easily reduced to ferrous
salts, and vice versa. H2S is a good reducing agent, and, when acting
as such, always gives a precipitate of milk of sulphur, which easily
passes through filter-paper and causes annoyance in the course of
qualitative analysis.

In test 4 the weak basic character of ferric iron and the resem-
blance to aluminum and chromium is again shown.

Tests 6, 7, 8, and 9 are not only delicate and decisive, but permit
iron in either state to be detected in the presence of the other.

Ferrous compounds form the divalent ion Fe", which is pale-green, and
ferric compounds form the trivalent ion Fe*", which is nearly colorless. The
ionic reactions for the tests for iron are of the same form as those given under
the tests for calcium. In test 2, the reduction of ferric to ferrous salt by H2S
is expressed by the ionic equation :

2Fe'" + 6C1' + 2H- + S" = 2Fe" + 2H* + 6C1' + S.
Each of the iron ions loses a charge of electricity and the sulphur ion loses
its two charges, which mutually neutralize each other, and elementary sulphur
is precipitated. The reduction with ammonium sulphide is represented by a
similar equation.

The formation of ferric from ferrous chloride is expressed thus :

Fe" + 2CP + Cl = Fe- + 3C1'.

The iron ion assumes another positive charge, becoming trivalent ion, and the
chlorine atom assumes a negative charge, becoming chlorine ion. A similar
equation holds in the case of the sulphate.

QUESTIONS — Which metals belong to the " iron group," and what are their
general properties? How is iron found in nature, and what compounds are
used in its manufacture ? Describe the process for manufacturing iron on a
large scale, and state the difference between cast-iron, wrought-iron, steel, and
reduced iron. State the composition and mode of preparation of ferrous and
ferric hydroxides. What are their properties? Describe in words and chem-
ical symbols the process for making ferric chloride. What is tincture of chlo-
ride of iron? How are ferrous iodide and bromide made? State the proper-
ties of ferrous sulphate. Under what other names is it known, and how is it
made? What change takes place when soluble carbonates are added to soluble
ferrous and ferric salts? Mention agents by which ferrous compounds may be
converted into ferric compounds, and these into ferrous compounds. Explain
the chemical changes taking place. Mention tests for ferrous and ferric com-
pounds.

IRON. COBALT. NICKEL,

PLATE I.

Ferrous sulphide, precipitated from
ferrous solutions by ammonium sulphide.

Ferrous hydroxide, passing into
ferric hydroxide. Ferrous solutions precipi-
tated by alkali hydroxides.

Ferric hydroxide, precipitated from
ferric solutions by alkali hydroxides.

Ferrous solutions, precipitated by
potassium ferrocyanide.

Ferric solutions, precipitated by

potassium ferrocyanide, or, Ferrous

solutions precipitated by potassium
ferricyanide.

Ferric solutions, treated with alkali
sulphocyanates.

Cobaltous carbonate, precipitated
from cobaltous solutions by sodium
carbonate.

8

Nickelous carbonate, precipitated
from nickelous solutions by sodium
carbonate.

A ftoen &Co LM Babuiion. . ltd

MANGANESE-CHROMIUM— COBALT-NICKEL. 303

28. MANGANESE— CHROMIUM— COBALT— MCKEL.

Manganese, Mn = 54.6. The principal ore is the dioxide (black
oxide of manganese, pyrolusite), MnOj, which is always accompanied
by iron compounds. Other forms occurring in nature are braunite,
MnfO3, hausmannite, Mn^O^, and manganese spar, MnCO3. In small
quantities it is a constituent of many minerals.

Metallic manganese resembles iron in its physical and chemical
properties, and may be obtained by reducing the carbonate with
charcoal. Manganese is darker in color than iron, considerably
harder, and somewhat more easily oxidized. Alloys of iron and
manganese (20 to 80 per cent.), known as ferro-manganese, are used
in the arts.

Oxides of manganese. Six oxides are known. MnO3 and
Mn2O7 have been obtained in the free state, but they are very unsta-
ble, and are known best through their compounds :

Manganoos oxide (monoxide or protoxide), MnO.

Manganous manganic oxide, MnOMn,0^ = Mn^O^

Manganic oxide (sesquioxide), MiijQj.

Manganese dioxide (binoxide, peroxide, black oxide), MnOr

Manganese trioxide, MnQ,.

Manganese heptoxide, Mn,Oj.

The chemical behavior of these oxides varies with the degree of oxidation,
or, in other words, with the valence of the manganese. MnO is strongly basic ;
Mn,Oj is weakly basic; MnOj has feebly acidic character; MnOs is more
strongly acidic, being the anhydride of manganic acid, HjMnO4, which is
known only in its salts ; MnsOT is the anhydride of permanganic acid, which
is known in aqueous solution, and has strong acid character.

The only stable salts of manganese are the manganou.* salts, derived from
manganons oxide, MnO, in which the valence of manganese is 2. When any
oxide of manganese (or compounds of those oxides which are unstable in the
free state) is heated with an acid, a manganous salt is obtained. In this action
the oxides higher than MnO give off oxygen, or oxidize the excess of acid (see
action of hydrochloric acid on MnOj). The decomposition of potassium per-
manganate, which has been used hitherto as an oxidizer, may now be explained.
In dilute sulphuric acid solution permanganic acid is liberated thus :

2KMn04 + H,SO4 = K,SO4 + 2HMnO4.

The acid is stable enough when nothing else is present that can be oxidized,
but if such a substance is added the permanganic acid breaks down to mangan-
ous oxide and oxygen :

2HMnO4 = HSO + MnA,
Mn,O, = 5O + 2MnO,

2MnO + 2HjSO4 = 2MnSO4 + 2H,O.

The manganous oxide is dissolved by the acid to form the colorless manganous

304 METALS AND THEIR COMBINATIONS.

sulphate, MnSO4. The oxygen does not escape, but goes to the reducing com-
pound. Conversely, when oxygen is forcibly added to any of the lower oxides
in the presence of alkalies, the MnO3 state of oxidation is attained, that is,
salts of manganic acid, or manganates, are produced, as K2MnO4, from which
the more stable permanganates are readily obtained (see below).

While manganous salts are stable and do not absorb oxygen like ferrous
salts, manganous hydroxide and carbonate readily absorb oxygen and turn
dark, resembling in this respect iron.

Manganous oxide is a greenish-gray powder obtainable by heating
the carbonate ; or as a nearly white hydroxide by precipitating a
manganous salt by sodium hydroxide. It is a strong base, saturating
acids completely, and forming salts which have generally a rose
color or a pale reddish tint.

Manganese dioxide, MnO2, is by far the most important com-
pound of manganese found in nature, as it is largely used for gener-
ating chlorine and oxygen, as described in former chapters.

Precipitated manganese dioxide, Mangani dioxidum praecipitatum,
MnO.j — 86.36, is obtained by pouring a mixture of ammonia water and
hydrogen peroxide into a solution of manganese sulphate, when manganese
dioxide mixed with some oxide is precipitated as a heavy, black powder :

MnS04 + 2NH4OH + H2O2 = (NH4)aSO4 + 2H2O -f MnO2.

Experiment 34. Mix 10 c.c. of 5 per cent, ammonia water with 10 c.c. of
1.5 per cent, hydrogen dioxide solution, and pour slowly while stirring into
20 c.c. of a 5 per cent, solution of manganous sulphate. Let the mixture
stand for one hour, stirring frequently. Then filter and wash thoroughly with
hot water, let drain, and dry. Heat some of the precipitate with hydrochloric
acid in a test-tube and explain the result.

Manganese sulphate, Mangani sulphas, MnSO4.4H2O = 221.47,
maybe obtained by dissolving the oxide or dioxide in sulphuric acid ;
in the latter case oxygen is evolved :

MnO2 + H,SO4 = MnSO4 -f H2O -f O.

As manganese dioxide generally contains iron oxide, the solution contains
sulphates of both metals. By evaporating to dryness and strongly igniting,
the iron salt is decomposed. The ignited mass is now lixiviated with water,
and the filtered solution evaporated for Crystallization.

It is an almost colorless, or pale rose-colored substance, isomorphous with
the sulphates of magnesium and zinc ; it is easily soluble in water.

Manganese hypophosphite, Mangani hypophosphis, Mn(PH202)2.H,0

= 201.54, may be made by mixing a solution of 1 part of calcium hypo-
phosphite with a solution of 1.31 parts of manganous sulphate, allowing

MANGANESE— CHROMIUM-COBALT-NICKEL. 305

the precipitate of calcium sulphate to settle, and evaporating the filtrate to
dryness. It is a pink crystalline powder, permanent in the air, and soluble in
6.6 parts of water. Its chief use is as a constituent of compound syrup of

hypophosphites.

Potassium permanganate, Potassii permanganas, KMnO4 =
156.98. Whenever a compound (any oxide or salt) of manganese is
fused with alkali carbonates (or hydroxides) and alkali nitrates (or
chlorates) the manganese is converted into manganic acid, which
combines with the alkali, forming potassium (or sodium) manganate:
3MnOa -f 3K8CO8 + KC1O3 = 3K2MnO4 + 3CO? + KC1.

The fused mass has a dark-green color, and when dissolved in
water* gives a dark emerald-green solution, from which, by evapora-
tion, green crystals of potassium manganate may be obtained.

The green solution is decomposed easily by any acid (or even by
water in large quantity) into a red solution of potassium perman-
ganate and a precipitate of manganese dioxide.

3K2Mn04 + 2H2SO4 = MnO2 + 2K2SO4 + 2KMnO4 + 2H2O.

By evaporation and crystallization potassium permanganate is ob-
tained in slender, prismatic crystals, of a dark- purple color, and a
somewhat metallic lustre. The solution in water has a deep purple,
or, when highly diluted, a pink color (Plate II., 1). It is a power-
ful oxidizing agent, and an excellent disinfectant, both properties
being due to the facility with which a portion of the oxygen is given
off to any substance which has affinity for it. If the oxidation
takes place in the absence of an acid, a lower oxide of manganese is
formed, which separates as an insoluble substance. If an acid is
present, both the potassium and manganese combine with it, forming
salts, thus :

2(KMnO4) 4- 6HC1 + x = 2KC1 + 2MnCl2 + 3H2O -f xO5.

x represents here any substance capable of combining with oxygen
while in solution.

Experiment 35. Heat in an iron crucible a mixture of 2 grammes man-
ganese dioxide, 2 grammes potassium hydroxide, and 1 gramme potassium
chlorate, until the fused mass has turned dark-green. Dissolve the cooled
mass with water, filter the green solution of potassium manganate, and pass
carbon dioxide through it until it has assumed a purple color, showing that
the conversion into permanganate is complete. Notice that the acidified solu-
tion is readily decolorized by ferrous salts and other deoxidizing agents.

Permanganic acid, HMn04, can now be obtained in solution by electrol-
20

306 METALS AND THEIR COMBINATIONS.

ysis of potassium permanganate. It has the color of the potassium salt, is
stable, and from it the permanganates of other metals may be made.

Tests for manganese.
(A 5 per cent, solution of manganous sulphate may be used.)

1. Ammonium sulphide produces a yellowish-pink or flesh-colored
precipitate of hydrated inanganous sulphide, MnS.H2O, soluble in
acetic and in mineral acids (Plate II., 2).

2. Ammonium (or sodium) hydroxide produces a white precipi-
tate of manganous hydroxide, which soon darkens by absorption
of oxygen (Plate II., 3) and dissolves in oxalic acid with a rose-red
color. The presence of ammonium salts prevents the precipitation of
manganous hydroxide by ammonia-water (see test 2 for magnesium).

3. Sodium (or potassium) carbonate produces a nearly white pre-
cipitate of manganous carbonate, which oxidizes to brown manganic
hydroxide.

4. Any compound of manganese heated on platinum foil with a
mixture of sodium carbonate and nitrate forms a bluish-green mass,
giving a green solution in water, which turns red on addition of an
acid. (See explanation above.)

5. Manganese compounds fused with borax on a platinum wire
give a violet color to the borax bead. Only a very small quantity of
the manganese compound should be used.

6. Heat a trace of manganese compound (not the dioxide) with about
5 c.c. of dilute nitric acid and a small knife-pointful of red oxide of
lead (minium) to boiling, dilute with water, and let stand to settle.
A reddish-purple color of permanganic acid will be seen. This is a
very delicate test.

Tests 4, 5, and 6 are the most decisive for manganese compounds.
Test 2 is also characteristic. Permanganate is usually recognized by
its color and action on reducing agents. Manganese salts are neu-
tral and colorless, or light red to pink.

The most common ions of manganese are the divalent Mn' • ions of the man-
ganous salts, and the univalent permanganate ions MnO/, which are purple
(see page 200). The divalent manganate ions MnO/x, which are green, exist
only in neutral or alkaline solutions. In acid solutions they pass into MnO/
ions. The ionic equations in the tests above for manganous ions, Mn' * are
similar to those given under the tests for calcium.

Chromium, Cr = 51.7. Found in nature almost exclusively as
chromite, or chrome-iron ore, FeO.Cr2O3, a mineral analogous in
composition to magnetic iron ore, FeO.Fe?O?. The name chromium.

MA NGANESE— CHROMIUM-COB A LT- NICKEL. 307

from the Greek %po>/jLa (chroma), color, was given to this metal on
account of the beautiful colors of its different compounds, none of
which is colorless. Chromium forms two basic oxides, Chromous
oxide, CrO, the salts of which are, however, very unstable, and chromic
oxide or chromium sesquiozide, Cr2O8, and an acid oxide, chromium
trioxide, CrO8, the combinations and reactions of which have to be
studied separately. While chromium is closely allied to aluminum
and iron on one side, it also shows a resemblance to sulphur, as indi-
cated by the trioxide, CrO3, and the acid, H2CrO4, which are analogous
to SO3 and H2SO4. Moreover, the barium and lead salts of chromic
and sulphuric acids are both insoluble in water.

Metallic chromium is used in small proportion as an admixture to steel to
which it imparts great hardness.

Potassium dichromate, Potassii dichromas, K2Cr2O7 = 292.28
(Bichromate or red chr ornate of potash). This salt is by far the most
important of all chromium compounds, and is the source from which
they are obtained.

Potassium dichromate is manufactured on a large scale by expos-
ing a mixture of the finely ground chrome-iron ore with potassium
carbonate and calcium hydroxide to the heat of an oxidizing flame
in a reverberatory furnace, when both constituents of the ore become
oxidized, ferric oxide and chromic acid being formed, the latter
combining with the potassium, forming normal potassium chromate,
K2Cr04.

2(FeOCr203) + 4K2CO3 + 7O = Fe2O3 + 4CO2 + 4(K2CrOJ.

By treating the furnaced mass with water a yellow solution of
potassium chromate is obtained, which, upon the addition of sul-
phuric acid, is decomposed into potassium dichromate and potassium

sulphate :

2(K2CrO4) + H2SO4 = K2Cr2O7 + K2SO4 + H2O.

The two salts may be separated by crystallization. Potassium
dichromate forms large, orange-red, transparent crystals, which are
easily soluble in water; heated by itself oxygen is evolved, heated
with hydrochloric acid chlorine is liberated, heated with organic
matter or reducing agents these are oxidized.

Sodium dichromate, Na2Cr2O7.2H2O (Bichromate of soda), is manufac-
tured by a process analogous to that used for potassium dichromate. The
crystallized compound resembles the potassium salt, but dissolves in less than
its own weight of water. The crystals being deliquescent, a granulated anhy-
drous salt which is but slightly hygroscopic, is also manufactured, and has
largely replaced the use of potassium dichromate.

308 METALS AND THEIR COMBINATIONS.

Chromium trioxide, Chromii trioxidum, CrO3 = 99.34 (Chromic
acid, Chromic anhydride), is prepared by adding sulphuric acid to a
saturated solution of potassium dichromate, when chromium trioxide
separates in crystals :

K20207 -f H2S04 = K2S04 + H20 + 2CrO3.

Thus prepared, it forms deep purplish-red, needle-shaped crystals,
which are deliquescent, and very soluble in water; it is destructive
to animal and vegetable matter, and one of the strongest oxidizing
agents ; the solution in water has strong acid properties, but neither
chromic nor dichromic acid are known in a pure state as an aqueous
solution of chromium trioxide, on concentration breaks up into the
oxide and water.

Experiment 36. Dissolve a few grammes of potassium dichromate in water
and add to 4 volumes of the cold saturated solution 5 volumes of strong sul-
phuric acid ; chromium trioxide separates on cooling. Collect the crystals on
asbestos, wash them with a little nitric acid, and dry them by passing warm
dry air through a tube in which they have been placed for this purpose.

Chromates and dichromates, When chromium trioxide is dissolved in
water, dichromic acid is mainly formed thus :

200. + H20 = H2Cr207,

which gives the ions 2H* and Cr2O7". The Cr2O7x/ ion is yellowish red in
color. There is, however, a slight amount of chromic acid formed, thus :

Ci03 + H20 = H2CrO4,

which gives the ions 2H' and CrO4". The ion CrO4" is yellow. Chromic acid
is known through its salts, the chromates, which give the ion, CrO/'.

Potassium and sodium chromate in solution show a basic reaction which is
not due to any weak acid character of chromic acid, but to the fact that chro-
mates have a great tendency to pass to salts of dichromic acid. They are de-
composed to some extent by water, thus :

2K2CrO4 + H20 == K2Cr2O7 + 2KOH.

If an acid, even a weak one, is added to the solution, the decomposition be-
comes practically complete by the removal of the KOH by union with the
acid. The color changes from yellow to red, and, upon concentration, the
rather moderately soluble dichromate crystallizes out in the case of the potas-
sium salt. Potassium dichromate is almost neutral in reaction ; it is, therefore,
not an acid chromate. In fact acid chromates are not known in which respect
chromic acid diners from sulphuric acid. The acid salt of the composition,
KHCr04, which we would expect to be formed by acidifying a solution of the
chromate, changes at once into the salt of dichromic acid, thus :
2KHCr04 = K2Cr207 -f H2O.

Although potassium dichromate contains no acid hydrogen, it acts essen-
tially like an acid salt toward alkalies. When potassium hydroxide is added

MANGANESE-CHROMIUM—COBALT-NICKEL. 309

to the dichromate the solution turns yellow, and upon evaporation a salt of
the composition, K2CrO4, is obtained. The reason for this is the fact that,
although the dichromate dissociates in the main into 2K' and Cr.,0/' ions, it
also dissociates to a slight extent, thus :

K2Cr207 + H2O ^± 2K- + 2H- + 2CrO4".
As alkali is added, the hydrogen ions are neutralized, thus :
2K- + 2(OH)' + 2H- = 2K- + 2H2O.

To keep up the equilibrium, more H* ions and CrO/' ions are formed from the
dichromate, the H* ions react with more alkali, etc., until by this process the
dichromate is practically all converted into chromate. This change is usually
represented by the simple equation :

K.2Cr207 -f- 2KOH =r 21^010, + H2O.

Many chromates, for example, those of barium, lead, silver, mercury, etc., are
insoluble in water and are obtained by precipitation. The ionic reaction in
the case of barium will serve to illustrate the other cases :

2K- -f Cr04" + Ba- * + 2C1' = BaCiO4 + 2K> + 2C1'.

The same precipitates result when a solution of a dichromate is used, because
it contains some CrO/' ions, and as fast as these are removed by precipitation,
others are produced to take their place in the system. But the precipitation
of the metal as chromate is not complete, as so.me dichromate of the metal re-
mains in solution, because of the acid that is liberated in the reaction. The
essential change is represented by the simple equation :

K2Cr2O7 -f 2BaCl2 + H2O = 2BaCrO4 + 2KC1 + 2HC1.

This reaction is analogous to that between barium chloride and potassium
bisulphate :

KHS04 + BaCl2 = BaSO4 + KC1 + HC1,

with the difference that barium sulphate is so difficultly soluble, even in acids,
that precipitation is practically complete, whereas the chromates are more
easily soluble in acids, and precipitation therefore is only partial.

Chromic oxide, Cr2O3 (Sesquioxide of chromium), is obtained by
heating potassium dichromate with sulphur, when potassium sulphate
and chromic oxide are formed :

K3Cr2O7 -1- S = K2S04 + Cr2O3.

By washing the heated mass with water, the chromic oxide is left
as a green powder, which is used as a green color, especially in the manu-
facture of painted glass and porcelain. Prepared by this method at
high temperature the oxide is insoluble in acids, but when obtained
in the form of its hydroxide by precipitation it is soluble in acids
forming the chromic salts. It is, therefore, a basic oxide.

310 METALS AND THEIR COMBINATIONS.

Chromic hydroxide, Cr(OH)3. A solution of potassium dichro-
rnate may be deoxidized by the action of hydrogen sulphide, sul-
phurous acid, alcohol, or any other deoxidizing agent, in the presence
of sulphuric or hydrochloric acid :

K2Cr207 + 4H2S04 + 3H2S = K2SO4 -f 7H2O + 3S + Cr2(SO4)3.

As shown by this formula, the sulphates of potassium and chro-
mium are formed and remain in solution, while sulphur is precipi-
tated, the hydrogen of the hydrogen sulphide having been oxidized
and converted into water.

By adding ammonium hydroxide to the solution thus obtained,
chromic hydroxide is precipitated as a bluish-green gelatinous sub-
stance :

Cra(S(Vs + 6NH4OH = 3(NH4)2SO4 -f 2Cr(OH)3.

By dissolving this hydroxide in the different acids, the various
salts, such as chloride, CrCl3, sulphate, etc., are obtained. Chromic
sulphate, similar to aluminum sulphate, combines with potassium or
ammonium sulphate and water, forming chrome alum, KCr(SO4)2.
12H2O; it is a purple salt, and is isomorphous with other alums.

Perchromic acid, H2Cr2O8. This acid is of interest because it is analogous
to persulphuric acid, H2S2O8, and is formed in the test for hydrogen dioxide.
The ethereal solution is obtained when an acidified saturated aqueous solution
of potassium dichromate is shaken with ether and just sufficient hydrogen
dioxide solution to give an intense blue color. Excess of hydrogen dioxide
must be avoided. The ethereal solution is much more permanent than an
aqueous solution of the acid. When it is cooled to — 20° C. (—4° F.) and
treated with metallic potassium, a purplish-black precipitate of potassium per-
chromate, K2Cr,,O8, is formed. This is stable only at low temperature, decom-
posing at ordinary temperature into oxygen and potassium chromate. Several
other salts have been prepared ; they are all very unstable.

The chemical conduct of chromium, according to the degree of oxidation or
the valence of the metal, is like that of manganese. Chromous salts, corres-
ponding to the oxide CrO, are known, but, like ferrous salts, they are very
readily oxidized and pass to the stable chromic salts, corresponding to the oxide
Cr2O3. The chromates and the acid, derived from the oxide CrO3, although
stable when alone in solution, readily give up oxygen in acid solutions to
reducing agents, just like permanganates, and the chromium gives salts of the
lower oxide, Cr2O8, which are green :

K2Cr207 + H2S04 = K2S04 + H2Cr207,

H2Cr2O7 ^ H2O + 2CrO3 ; 2Cr03 = Cr2O3 + 3O,
Cr203 + 3H2S04 = 02(S04)3 + 3H2O.

MANGA NESE- CJIR OMIUM- COB A LT- NICK EL . 311

Tests for chromium.

a. Of chromates.

(Use the reagent solution of potassium chromate, K2CrO4.)
.1. Hydrogen sulphide added to an acidified warm solution of a
chromate changes the red color into green with precipitation of sulphur.
The solution now contains chromium in the basic form. (See explana-
tion above.) (Plate II., 4.) The conversion of a chromate to a
chromium salt is more readily accomplished by heating the chromic
solution with alcohol and hydrochloric acid; the alcohol is partly
oxidized, being converted into aldehyde, which has a peculiar but
pleasant odor.

2. Soluble lead salts produce a yellow precipitate of lead chromate
(chrome yellow), PbCrO4, insoluble in acetic, soluble in hydrochloric
acid and in sodium hydroxide (Plate II., 6) :

K2CrO4 + Pb(NO3)2 = PbCrO4 + 2KNO3.

3. Barium chloride produces a pale yellow precipitate of barium
chromate, BaCrO4 ; insoluble in sodium hydroxide.

4. Silver nitrate produces a dark-red precipitate of silver chromate,
Ag2Cr04 (Plate II., 7). '

5. Mercurous nitrate produces a red precipitate of mercurous chro-
mate, Hg2CrO4 (Plate II., 8).

6. On pouring a layer of ether upon a solution of hydrogen
dioxide, adding a few drops of potassium dichromate solution, a
little sulphuric acid, and shaking, the ether assumes a blue color, due
to the formation of unstable perchromic acid. A very delicate test.

b. Of salts of chromium.
(Use a 5 per cent, solution of chrome-alum, or chromic chloride, CrCl3.)

7. To the solution add ammonium hydroxide or ammonium sul-
phide : in both cases the green hydroxide of chromium, Cr(OH)3, is
precipitated (Plate II., 5). Compare with aluminum.

2CrCl3 + 3(NH4)2S + 6H,O = 6NH4C1 + 3H2S + 2Cr(OH)3.

8. Potassium or sodium hydroxide causes a similar green precipi-
tate of chromic hydroxide, which is soluble in an excess of the
reagent, but is re-precipitated on boiling for a few minutes.

Ammonia water causes precipitation of chromic hydroxide, but
the precipitate is nearly insoluble in excess of the reagent.

312 METALS AND THEIR COMBINATIONS.

c. Of chromium in any form.

9. Compounds of chromium, when mixed with sodium (or potas-
sium) carbonate and nitrate, give, when heated upon platinum foil or
in a crucible, a yellow mass of the alkali chromate.

10. Compounds of chromium impart a green color to the borax
bead. Use only a very small quantity of the chromium compound.

Chromium salts have a green or violet to purple color. Solutions
of the violet salts turn green when heated. They are acid to litmus,
due to hydrolysis in solution. Chromates are all red or yellow, and
mostly insoluble in water. The color of a chromate is noticeable in
very dilute solution (made with the aid of an acid in the case of in-
soluble salts).

Cobalt and Nickel, Co =58.56, Ni = 58.3. These two metals show much
resemblance to each other in their chemical and physical properties, and occur
in nature often associated with each other as sulphides or arsenides.

Both metals are nearly silver-white ; the salts of cobalt show generally a red,
those of nickel a green color. The solutions of both metals give a black pre-
cipitate of the respective sulphides on the addition of ammonium sulphide.
Ammonium hydroxide produces in solutions of cobalt a blue, in solutions of
nickel a green precipitate of the hydroxides, both of which are soluble in an
excess of the reagent ; potassium or sodium hydroxide produces similar pre-
cipitates, which are insoluble in an excess. Sodium carbonate produces in
solutions of cobalt a violet, and in solutions of nickel a green precipitate of the
respective carbonates. (Plate I., 7 and 8.)

Cobalt is used chiefly when in a state of combination (for coloring glass blue) ;
nickel when in the metallic state. (German silver is an alloy of nickel, copper,
and zinc.)

29. ZINC.
Zn» == 64.9.

Occurrence in nature. Zinc is found chiefly either as sulphide
(zinc-blende), ZnS, or as carbonate (calamine), ZnCO3 ; it occurs also
as silicate, H2Zn2SiO5, and as oxide in combination with the oxides
of iron or manganese.

QUESTIONS.— How is manganese found in nature? Mention the different
oxides of manganese. What is the dioxide used for ? What is the color of
manganese salts, of manganates, and of permanganates? How is potassium
permanganate made; what are its properties, and what is it used for? Give
tests for manganese. State composition and properties of potassium dichro-
mate. How is chromium trioxide made ; what are its properties ; what is it
used for ; and under what other name is it known ? By what process may
chromium sesquioxide be converted into chromates ? What is the composition
of the oxide and hydroxide of chromium, and how are they made? Mention
tests for chromates and chromium salts.

MANGANESE. CHROMIUM.

PLATE II.

Potassium permanganate solution,
more or less saturated. Boraxbead colored
by manganese.

Manganous sulphide, precipitated
from manganous solutions by ammonium
sulphide.

Manganous hydroxide, passing into
the higher oxides. Manganous solution*
precipitated by alkali hydroxides.

Potassium dichromate solution de-
oxidized by reducing agents.

Chromic hydroxide, precipitated
from chromic solutions by alkali hydrox-
ides.

Lead chromate, precipitated from
soluble cbromates by lead acetate.

Silver chromate, precipitated from
neutral chromates by silver nitrate.

Mercurous chromate, precipitated
from neutral chromates by mercurous bolu-
tious.

, I.,rli tiolniuorf, . IM

ZINC. 313

Metallic Zinc is obtained by heating in retorts the oxide or
carbonate mixed with charcoal, when decomposition takes place.
The liberated metal is vaporized, and distils into suitable receivers,
where it solidifies.

Zinc is a bluish-white metal, which slowly tarnishes in the air,
becoming coated with a film of oxide and carbonate ; it has a crys-
talline structure and is, under ordinary circumstances, brittle ; when
heated to about 130°-150°C. (260°-302° F.) 'it is malleable, and
may be rolled or hammered without fracture. Zinc thus treated
retains this malleability when cold ; the sheet-zinc of commerce is
thus made. When zinc is further heated to about 300° C. (572° F.),
it loses its malleability and becomes so brittle that it may be pow-
dered ; at 410° C. (760° F.) it fuses, and at a bright- red heat it
boils, volatilizes, and, if air be not excluded, burns with a splendid
greenish -white light, generating the oxide.

Zinc is used by itself in the metallic state or fused together with
other metals (German silver and brass contain it) ; galvanized iron
is iron coated with metallic zinc.

Zinc combines- with mercury forming a crystalline amalgam of the compo-
sition Zn2Hg. As a constituent of dental amalgam alloys zinc hastens the
setting, aids in controlling shrinkage and to some extent prevents discoloration.
While zinc unites with tin in all proportions forming excellent alloys for dental
dies, it is not suitable for alloying with lead.

Zinc is a bivalent metal, forming but one oxide and one series of
salts, most of which have a white color,

As has been pointed out in Chapter 24, zinc bears a close chemical relation-
ship to magnesium, and both these metals resemble cadmium in their chemical
properties. In fact,, the three elements magnesium, zinc, and cadmium form a
natural group similar to that of the alkali metals or the alkaline earth metals.

Zinc oxide, Zinci oxiduni, ZnO = 80.78 (Flores zinci, Zinc-white),
may be obtained by burning the metal, but if made for medicinal
purposes, by heating the carbonate, when carbon dioxide and water
escape and the oxide is left :

3[Zn(OH)2J.2ZnCO3 = 5ZnO -f 2CO2 + 3H2O.

It is an amorphous, white, tasteless powder, insoluble in water,
soluble in acids; when strongly heated it turns yellow, but on
cooling resumes the white color.

Zinc hydroxide, Zn(OH)2, is obtained by precipitating zinc salts
with the hydroxide of sodium or ammonium ; the precipitate, how-
ever, is soluble in an excess of either of the alkali hydroxides.

314 METALS AND THEIR COMBINATIONS.

Zinc chloride, Zinci chloridum, ZnCl2= 135.26. Made by dis-
solving zinc or zinc carbonate in hydrochloric acid and evaporating
the solution to dryness :

Zn + 2HC1 = ZnCl2 + 2H.

It is met with either as a white crystalline powder, or in white
opaque pieces ; it is very deliquescent and easily soluble in water
and alcohol; it combines readily with albuminoid substances; it
fuses at about 115°C. (239° F.), and is volatilized, with partial
decomposition, at a higher temperature.

Liquor zinci chloridi, U. S. P., is an aqueous solution of zinc chloride, con-
taining 50 per cent, of the salt.

Zinc oxychloride is used extensively for dental purposes, and is made by
mixing zinc oxide with a strong solution of zinc chloride. At first a plastic
mass forms, which rapidly hardens. The proportions in which the two sub-
stances are mixed differ widely, the weights corresponding all the way from 3
to 9 molecules of zinc oxide for each molecule of zinc chloride. Whether or
to what extent the oxychloride of zinc is a true chemical compound is not
known.

Zinc oxyphosphate is a preparation used similarly to the oxychloride. It
is made by mixing zinc oxide with phosphoric acid. The acid used is either
ortho- or metaphosphoric acid, or a mixture of both. In all cases a zinc phos-
phate is formed, but as the quantity of zinc oxide used is larger than needed
for saturating the acid completely, the mass as used by dentists is generally a
mixture of zinc phosphate with zinc oxide.

Zinc bromide, Zinci bromidum, ZnBr2 = 223.62. Obtained
analogously to the chloride by dissolving zinc in hydrobromic acid ;
it is a white powder, resembling the chloride in its properties.

Zinc iodide, Zinci iodidum, ZnI2 = 316.7. The two elements
zinc and iodine combine readily when heated with water ; the color-
less solution when evaporated to dryness yields a powder whose
physical properties resemble those of the chloride.

Zinc carbonate, Zinci carbonas prsecipitatus, 2ZnCO3.3Zn(OH)2
(Precipitated carbonate of zinc). Solutions of equal quantities of zinc
sulphate and sodium carbonate are mixed and boiled, when a white pre-
cipitate is formed, which is a mixture of the carbonate and hydroxide
of zinc, corresponding more or less to the formula given above.
5ZnSO4 + 5Na2CO3 + 3H2O = 3CO2 + 5Na2SO4 -f 2(ZnCO3).3Zn(OH)2.

Precipitated zinc carbonate is a white, impalpable powder, odorless
and tasteless, insoluble in water, soluble in acids and in ammonia water.

Experiment 37. Dissolve 10 grammes of the zinc sulphate obtained in Experi-

ZINC. 315

ment 3, in about 200 c.c. of water, heat to boiling, and add slowly, while stir-
ring, concentrated solution of sodium carbonate until precipitation is complete.
After the precipitate has settled, pour off the liquid, and wash the former sev-
eral times with hot water by decantation. Then filter and wash the precipitate
again several times with hot water, drain, and dry.

Heat some of the dried zinc carbonate gradually to redness in a porcelain
crucible with the cover on. What is formed? What color has it while hot?
When the crucible is cold, place the residue in a tube and add dilute acid.
Does any effervescence take place. Write reaction. Compare with experi-
ments 25 and 26.

Zinc sulphate, Zinci sulphas, ZnSO4.7H2O = 285.4 ( White vit-
riol), is obtained by dissolving zinc in dilute sulphuric acid :
H2SO4 + a:H2O + Zn = ZnSO4 + xH2O -f 2H.

If zinc be added to strong cold sulphuric acid, no decomposition
takes place, because there are no ions present, and an acid does not
exhibit acid properties unless ions *are formed, as explained in
Chapter 15.

Dilute sulphuric acid scarcely acts on pure zinc, but addition of a few c.c. of
solution of cupric sulphate or platinic chloride causes brisk action. This is
due to the deposition of the copper or platinum on the zinc, thus forming an
electric couple, whereby solution of zinc is facilitated.

Zinc sulphate forms small, colorless crystals, which are isomor-
phous with magnesium sulphate ; it is easily soluble in water. It is
so much like magnesium sulphate in appearance that it is sometimes
taken in mistake for the latter salt. The tests given below will dis-
tinguish between the two salts.

Antidotes. Soluble zinc salts (sulphate, chloride) have a poisonous effect.
If the poison have not produced vomiting, this should be induced. Milk,
white of egg, or, still better, some substance containing tannic acid (with which
zinc forms an insoluble compound) should be given.

Tests for zinc.
(Use a 5 per cent, solution of zinc sulphate.)

1. Add to the solution some ammonium sulphide. A white precipi-
tate of zinc sulphide, ZnS, is produced, which is soluble in mineral
acids, but not in acetic acid. (Of the familiar metals, zinc is the only
one whose sulphide is white.)

If the zinc salt is not pure, the sulphide may appear more or less
gray instead of white :

ZnS04 + (NH4)2S = (NH4)2S04 + ZnS.

316

—

1

METALS AND THEIR COMBINATIONS.
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ZINC. 317

2. Hydrogen sulphide passed into the solution gives a partial pre-
cipitate of zinc sulphide because of the solvent action of the acid
liberated. In the presence of sodium acetate, however, the precipi-
tate is complete because of the liberation of acetic acid, in which the
sulphide is insoluble :

ZnS04 -I- 2Na(C2H302) + H2S = ZnS + Na2SO4 + 2H.C2H302.

3. Addition of caustic alkali or ammonia water gives a white pre-
cipitate of zinc hydroxide, Zn(OH)2. It is soluble in excess of the
alkali, forming zincates :

Zn(OH)2 + 2NaOH = Zn(ONa)2 + 2H20.

The hydroxide is also soluble in excess of ammonia water, forming
a complex compound, Zn(NH3)4.(OH)2. In this respect zinc differs
from magnesium. The ions of this compound are Zn(NH3)4" and
2(OH)'.

4. Addition of a solution of acarbftnate or phosphate, gives a white
precipitate of zinc carbonate or phosphate :

ZnSO4 -f Na2HPO4 = ZnHPO4 + Na2S04.

Zinc carbonate is soluble in excess of ammonium carbonate.

5. Solution of potassium ferrocyanide gives a white precipitate of zinc
ferrocyanide. (Distinction from magnesium and aluminum, which give
no precipitate.) The precipitate is Zn2Fe(CN)6, and is difficultly
soluble in hydrochloric acid.

Tests 1, 3, and 5 together are conclusive for zinc salts. Practically
all the compounds of zinc are colorless. The oxide, carbonate, phos-
phate, ferrocyanide, and sulphide are insoluble in water; the chloride,
bromide, iodide, nitrate, sulphate, and acetate are soluble in water.
These are the common salts. The soluble zinc salts are hydrolyzed
somewhat in water, and therefore show an acid reaction. This explains
the solvent action of a zinc chloride solution when used on metal sur-
faces in soldering. The coat of metallic oxide is thus removed.

Zinc forms the divalent ion Zn", which unites with acid radicals to form
the zinc salts. The ionic equations for the above tests are of the same form as
those given under the tests for calcium. Zn(OH)2 has weak basic properties,
and still weaker acid properties. Like aluminum and chromium hydroxides,
it is slightly soluble and ionizes in two ways, thus :

Zn(OH)2 ^± Zn" 4 2(OH)'.
With acids, zinc salts are formed by the union of (OH)7 and H* ions to form water.

Also, Zn(OH)2 ;± Zn02" 4- 2H',

and with considerable excess of alkali the hydroxide dissolves to form zincates

318 METALS AND THEIR COMBINATIONS.

by the union of H* ions with (OH)' ions of the alkali. The equation in sim-
ple form is written, 9
Zn(OH)2 + 2XaOH = Na.2ZnO2 -f 2H2O.

Cadmium, Cd = 111.6. Found in nature associated (though in very small
quantities) with the various ores of zinc, with which metal it has in common a
number of physical and chemical properties. Cadmium differs from zinc by
forming a yellow sulphide (with hydrogen sulphide), insoluble in diluted acids.
Cadmium and its compounds are of little interest here; the yellow sulphide is
used as a pigment, the sulphate and iodide sometimes for medicinal purposes.

Cadmium is a constituent of many alloys distinguished by very low fusing
points.

30. LEAD -COPPER -BISMUTH.

General remarks regarding the metals of the lead group. The
six metals belonging to this group (Pb, Cu, Bi, Ag, Hg, and Cd) are
distinguished by forming sulphides which are insoluble in water,
insoluble in dilute mineral acids, insoluble in ammonium sulphide ;
consequently they are precipitated from neutral, alkaline, or acid
solutions by hydrogen sulphide or ammonium sulphide.

The metals themselves do not decompose water at any temperature,
and are not acted upon by dilute sulphuric acid ; heated with strong
sulphuric acid, most of these metals are converted into sulphates with
liberation of sulphur dioxide ; nitric acid converts all of them into
nitrates with liberation of nitric oxide.

The oxides, iodides, sulphides, carbonates, phosphates, and a few of
the chlorides and sulphates of these metals are insoluble ; all the
nitrates, and most of the chlorides and sulphates are soluble.

In regard to valence, they show no uniformity whatever, silver
being univalent, copper, cadmium, and mercury bivalent, bismuth
trivalent, and lead either bivalent or quadrivalent.

Lead, Pb11 = 2O5.35 (Plumbum). This metal is obtained chiefly
from the native lead sulphide (galena), PbS, by first roasting it,
whereby part is converted into oxide and sulphate. By heating this

QUESTIONS. — How is zinc found in nature, and by what process is it ob-
tained? Mention the properties of metallic zinc, and what is it used for?
Mention two processes for making zinc oxide. How does heat act on zinc
oxide? Show by chemical symbols the action of hydrochloric and sulphuric
acids on zinc. State the properties of chloride and of sulphate of zinc. AVhat
is white vitriol? Explain the formation of precipitated zinc carbonate, and
state its composition. Mention tests for zinc compounds. How many pounds
of crystallized zinc sulphate may be obtained from 21.7 pounds of metallic
zinc? i

LEAD-COPPER-BISMUTH. 319

mixture with undecomposed sulphide to a higher temperature lead is
formed, thus :

PbS + 2PbO == 3Pb + S02 and PbS + PbSO4 == 2Pb + 2SO2.
Lead owes its usefulness in the metallic state chiefly to its softness,
fusibility, and resistance to acids, which properties are of advantage
in using it for tubes or pipes, or in constructing vessels to hold or
manufacture sulphuric acid.

Lead is exceedingly malleable and somewhat ductile, but not very tenacious.
It is a constituent of many alloys, as for instance of type metal, britannia metal,
shot, etc. Common solder is an alloy of equal weights of lead and tin. The
noble metals are rendered brittle and unworkable when alloyed with even a
small quantity of lead.

Experiment 38. Dissolve 1 gramme of lead acetate or lead nitrate in about
200 c.c. of water, suspend in the centre of the solution a piece of metallic zinc,
and set aside. Notice that metallic lead is deposited slowly upon the zinc in a
crystalline condition, while zinc passes into solution, which may be verified by
analytical methods. The chemical change taking place is this :

Pb(N03)2 + Zn Zn(N03)2 + Pb.

Electrolytic solution tension. The precipitation of lead from solution
by zinc in the experiment above is represented by the ionic equation :

Zn + Pb" + 2NO3' = Zn" + 2NO3' + Pb.

The lead ions lose their charges to zinc which becomes ionic, while metallic
lead is precipitated. This action is pretty much like the liberation of hydrogen
from acids by some metals :

Zn + 2H* + SO4" = Zn" + SO4" -f H2.

The explanation of this type of chemical change is found in the theory of elec-
trolytic solution tension proposed by Nernst. According to this, a metal when
immersed in water or a solution sends some positive ions into the solution, and
itself assumes negative charges of electricity. This proceeds to a point where
the metal is sufficiently charged negatively that it attracts its positive ions at
the same rate at which they tend to be given off from the metal. An equilib-
rium between the two tendencies is reached. The tension or pressure that
drives the ions into the solution differs for different metals, the order of decrease
being the same as the order in the electrochemical series of the metals (page
198). Any metal in the series has a higher tension than those following, and
will displace them from solutions of their salts, but not vice versa. Zinc has
a much greater solution tension than lead. When it is placed in the lead solu-
tion, it acquires a greater negative charge of electricity than does a piece of
lead when it is placed in a solution. The result is that the lead ions are
attracted to the zinc and discharged, and metallic lead is deposited. This
process continues until all the lead has been deposited from the solution, which
then contains an equivalent amount of zinc salt.

Lead oxide, Plumbi oxidum, PbO = 221.23 (Litharge). Obtained
by exposing melted lead to a current of air, when the metal is

320 METALS AND THEIR COMBINATIONS.

gradually oxidized with the formation of a yellow powder, known
as massicot; at a high temperature this fuses, forming reddish-yellow
crystalline scales, known as litharge ; by heating still further in con-
tact with air, a portion of the oxide is converted into dioxide (or
peroxide), PbO2, and a red powder is formed, known as red lead (or
minium), which probably is a mixture (or combination) of oxide and
dioxide of lead, PbO2(PbO)2.

Lead oxide is used in the manufacture of lead salts, lead plaster,
glass, paints, etc.

Nitric acid when heated with red lead combines with the oxide,
while lead dioxide, PbO2, is left as a dark-brown powder, which, on
heating with hydrochloric acid, evolves chlorine (similar to man-
ganese'dioxide). Lead dioxide is a conductor of electricity, differ-
ing thus from most oxides.

Accumulator or storage battery. This consists of two sets of lead
plates made in the form of gratings. One set, which are all connected, have
the spaces in the gratings filled up with spongy lead ; the other set, likewise
connected, are filled up with lead dioxide. When the plates are dipped into
dilute sulphuric acid they show a difference of potential, and when connected
a current flows. When in action or discharging, the SO/' ions of the sul-
phuric acid are attracted to the plates filled with spongy lead, give up their
negative charges to the plate, and form lead sulphate. The H* ions of the acid
pass to the plates filled with PbO2, give up their positive charges, and reduce
PbO2 to PbO, which combines with sulphuric acid and forms lead sulphate.
The current flows in the outside circuit from the plates filled with PbO2 to the
plates filled with spongy lead, and has a voltage of about 2. Both plates ulti-
mately become filled with PbSO4, and the battery then is exhausted. Sul-
phuric acid is removed from the solution, and the specific gravity of the latter
falls. By this means one can tell when the battery is approaching exhaustion.

Charging the battery consists in restoring the plates to their original state,
and is accomplished bypassing a current from a dynamo through it in a direc-
tion opposite to that of the current produced by the battery. By this action
electrical energy is stored up in the battery as chemical energy, which is given
back again as electrical energy when the battery is discharged. When the
dynamo current passes, H* ions of the acid solution pass to the plates originally
filled with lead, and form sulphuric acid with SO/X ions of the lead sulphate,
leaving the plate finally filled with reduced spongy lead. At the same time,
SO4X/ ions of the acid solution pass to the other plates, where they are dis-
charged and enter into reaction with the lead sulphate in the plates, thus :

PbS04 + SO, -f 2H20 = PbO2 + 2H2S04.

All the lead sulphate is ultimately converted into lead dioxide, and this set of
plates are restored to the original state. All the sulphuric acid is restored to
the liquid, and the battery is ready for use. The changes involved in the com-
plete cycle may be written in one equation, thus:

«— discharging.

2PbS04 -(- 2H20 ±^ Pb + 2H2S04 -f PbO2.
charging — *

LEAD— COPPER— BISMUTH. 321

Lead nitrate, Plumbi nitras, Pb(NO3)2 — 328.49. Obtained by
dissolving the oxide in nitric acid :

PbO + 2HN03 = H20 + Pb(N03)2.

Lead nitrate is the only salt of lead (with a mineral acid) which is
easily soluble in water ; it has a white color, and a sweetish, astrin-
gent, and afterward metallic taste. It is insoluble in strong nitric
acid ; hence lead is insoluble in this acid.

Experiment 39. Heat 30 c.c. of dilute nitric acid, but not to the boiling-
point, and dissolve in it, with stirring, small portions of lead oxide, until no
more is taken up. Filter the solution if necessary, and let it cool to crystallize.
If no crystals form, concentrate further. The crystals are octahedra. Examine
their appearance and form. Which one of the methods of forming salts does
this experiment illustrate ?

Heat some of the dried and powdered crystals in a porcelain crucible mod-
erately. Note the brown fumes of nitrogen tetroxide and residue of brown lead
oxide, which becomes yellow on cooling. This experiment illustrates the
instability of most nitrates when heated, and the method by which some oxides
are obtained :

Pb(N03)2 = PbO + N204 + O.

Lead carbonate, PbCO3, occurs in nature as the mineral cerussite,
and may be obtained by precipitation of a lead acetate solution with
sodium bicarbonate. While this normal salt is scarcely used, the basic
lead carbonate or white lead of the approximate composition 2PbCO3.
Pb(OH)2 is used very largely as a constituent of paints. It is man-
ufactured on a large scale directly from lead, by exposing it to the
simultaneous action of air, carbon dioxide, and vapors of acetic acid.
The latter combines with the lead, forming a basic acetate, which is
converted into the carbonate (almost as soon as produced) by the
carbon dioxide present.

The action of acetic acid on lead or lead oxide will be considered
in connection with acetic acid.

Lead carbonate is a heavy, white, insoluble, tasteless powder ; the
white-lead of commerce frequently is found adulterated with barium
sulphate, gypsum or lead sulphate.

Lead iodide, Plumbi iodidum, PbI2 = 457.15. Made by adding
solution of potassium iodide to lead nitrate (Plate III., 6) :
Pb(NO3)2 + 2KI = 2KNOS + PbI2.

It is a heavy, bright yellow, almost insoluble powder, which ma/
be distinguished from lead chromate by its solubility in ammonium
chloride solution on boiling, lead chromate being insoluble in this
solution.

21

322 .METALS AND THEIR COMBINATIONS.

Poisonous properties and antidotes. Compounds of lead are directly
poisonous, and it happens, not infrequently, that water passing through leaden
pipes or collected in leaden tanks becomes contaminated with lead. Water
free from air and salts scarcely acts on lead ; but if it contain air, oxide of lead
is formed, which is either dissolved by the water or is decomposed by the
nitrates or chlorides present in the water, the soluble nitrate or chloride of lead
being formed.

If the water contains carbonates and sulphates, however, these will form
insoluble compounds, producing a film or coating over the lead, preventing
further contact with the water. Rain water, in consequence of its containing
atmospheric constituents, and no sulphates, acts as a solvent on lead pipe ;
spring and river waters generally do not.

Water containing lead will show a dark color on passing hydrogen sulphide
through it ; if the quantity present be very small, the water should be evapo-
rated to ^ or even -^ of its original volume before applying the test.

The constant handling of lead compounds is one of the causes of lead
poisoning (painters' colic). As an antidote, mangesium sulphate should be
used, which forms with lead an insoluble sulphate ; the purgative action of
magnesia is also useful. (In lead works workmen often drink water containing
a little sulphuric acid.)

Tests for lead.
(Use a 5 per cent, solution of lead acetate or lead nitrate.)

1. Hydrogen sulphide or ammonium sulphide added to the solution
produces a black precipitate of lead sulphide (Plate III.,, 1), insol-
uble in dilute acids or alkalies. A very delicate reaction :

Pb(N03)2 + H2S PbS + 2HN03.

2. Dilute sulphuric acid or a solution of a sulphate gives a white
precipitate of lead sulphate, PbSO4. This is one of the four insoluble
sulphates. (See test 2 for sulphates.)

3. Other reagents which give precipitates with solutions of lead
salts are :

Hydrochloric acid or solution of a chloride, producing white lead
chloride, PbCl2. (See test 3 for hydrochloric acid.)

Potassium iodide, producing yellow lead iodide, PbI2 (Plate III.,
6). (See test 2 for iodides.)

Potassium chromate, producing yellow lead chromate (chrome-yel-
low), PbCr04 (Plate II., 6). (See test 2 for chromates.)

Alkali carbonates, producing white basic lead carbonate.

Alkali phosphates, producing white lead phosphate, PbHPO4.

Solution of sodium hydroxide, producing white lead hydroxide,
Pb(OH)2, which dissolves in excess of the alkali, forming sodium
plumbite, Pb(ONa)2. (See comments on tests for zinc, page 317.)

LEAD — COPPER — BISMUTH. 323

C When a charcoal reduction test (for which see directions in test
3 for sulphates) is made on any dry lead compound, a globule of
metallic lead is obtained, which is recognized by its softness and
malleability. Try its solubility in dilute hydrochloric, sulphuric, and
nitric acids.

Tests 1, 2, and 4 are sufficient for recognition of a lead compound.
Lead salts are mostly colorless. Lead nitrate has an acid reaction,
due to hydrolysis in water.

Copper, Cuu = 63.1 (Cuprum). Found in nature sometimes in the
metallic state — generally, however, combined with sulphur or oxygen.
The commonest copper-ore is Copper pyrites, a double sulphide of
copper and iron, CuFeS2 or Cu2S.Fe2S3, having the color and lustre
of brass or gold. Other ores are : Copper glance, cuprous sulphide,
having a dark-gray color and the composition Cu2S ; malachite, a
beautiful green mineral, being a carbonate and hydroxide of copper,
CuCO3.Cu(OH)2. Cuprous and cupric oxide also are found occasion-
ally. Copper is obtained from the oxide by reducing it with coke ;
sulphides previously are converted into oxide by roasting.

Copper is the only metal showing a distinct red color ; it is so
malleable that, of the metals in common use, only gold and silver
surpass it in that respect ; it is one of the best conductors of heat and
electricity, it does not change in dry air, but becomes covered with a
film of green subcarbonate when exposed to moist air.

Copper frequently is used in the manufacture of alloys, of which
the more important are :

Copper. Zinc. Tin. Nickel. Antimony.

Brass .... 64 36

German silver ... 51 31 ... 18

Bell-metal ... 78 ... 22

Bronze .... 80 16 4

Gun-metal ... 90 ... 10

Babbit-metal ... 43 ... 43 ... 14

Copper frequently is alloyed with gold and silver.

Copper forms two oxides, and corresponding to these are two series
of salts, known as cuprous and cupr/c compounds. Cuprous salts of
oxygen acids do not exist. The principal cuprous compounds are
Cu2O, CuCl, CuBr, Cul, Cu(CN), Cu2S. All these, except Cu2Oand
Cu2S, are white and insoluble in water. Cupric iodide, (CuI2), and
cyanide, (Cu(CN)2), cannot be obtained, as they decompose into the
cuprous salt and free iodine or cyanogen, CuI2 = Cul + I. These are
obtained when potassium iodide or cyanide solution is added to solu-
tion of cupric sulphate :

CuS04 -f 2KI = Cul + I + K2SO4,

324 METALS AND THEIR COMBINATIONS.

Cupric compounds are more numerous, as they embrace the salts of
oxygen acids as well as salts of some of the halogen acids. The
anhydrous salts are usually white or yellow, but the solutions as well as
the hydrated crystals are usually blue or greenish blue. The cupric
compounds are more important and familiar than the cuprous salts,
and those most frequently employed are the sulphate, acetate, and
oxide. The valence of copper in cupric compounds is 2. Some facts
indicate that in the cuprous compounds the valence of copper is 1,
while others indicate that it is 2. Some writers assign the valence of
2 to copper in all its compounds, and use double formulas for the
cuprous salts to account for the apparent univalence of copper, thus,
Cu2Cl2 or Cl-Cu — Cu-Cl, assuming that two atoms of copper are
united by one bond. The behavior of the cuprous salts can very
readily be represented by the simple formulas and univalence of copper,
and there is no need for using double formulas.

Cupric oxide, CuO (Black oxide or monoxide of copper). Heated
to redness, copper becomes covered with a black scale, which is cupric
oxide ; it is obtained also by heating cupric nitrate or carbonate, both
compounds being decomposed with formation of the oxide ; finally,
it may be made by adding sodium or potassium hydroxide to the
solution of a cupric salt, when a bulky, pale-blue precipitate of cupric
hydroxide, Cu(OH)2, is formed, which, upon boiling, is decomposed into
water and cupric oxide, a heavy dark-brown powder (Plate III., 2) :

CuS04 + 2KOH = K2SO4 + Cu(OH)2;
Cu(OH)2 = H2O + CuO.

Cuprous oxide, Cu2O ( Red oxide or suboxide of copper). When
cupric oxide is heated with metallic copper, charcoal, or organic
matter, the cupric oxide is decomposed, and cuprous oxide is formed.
(Excess of carbon or organic matter reduces the oxide to metallic
copper.)

CuO -f Cu = Cu2O;
2CuO + C = Cu2O + CO.

Some organic substances, especially grape-sugar, decomposes alkaline
solutions of cupric sulphate with precipitation of cuprous oxide, which
is a red, insoluble powder.

Experiment 40. To 5 c.c. of a 5 per cent, solution of copper sulphate add
about 20 c.c. of the reagent solution of sodium hydroxide. Note the blue pre-
cipitate of copper hydroxide, Cu(OH)2. Add to the mixture about 2 grammes
of Rochelle salt (sodium potassium tartrate) and shake. The precipitate dis-

LEA D— COPPER—BISMUTH. 325

solves to a deep blue solution, which is essentially Fehling's solution (see Index).
The copper enters the negative tartaric acid radical or ion, and while in the
cupric state is not precipitated by alkali. If the copper is reduced to the
cuprous state, it can no longer remain in solution and is precipitated as the
reddish cuprous oxide, Cu2O.

Heat the blue solution to boiling and add a little dilute glucose solution and
heat again a few minutes. A precipitate of cuprous oxide is produced, due to
the reducing action of the glucose. This is usually employed as a test for
glucose in urine.

Cupric sulphate, Cupri sulphas, CuSO4.5HO2 = 247.85 (Sul-
phate of copper, Slue vitriol, Blue-stone). This is the most important
compound of copper. It is manufactured on a large scale, either
from copper pyrites, or by dissolving cupric oxide in sulphuric acid,
evaporating and crystallizing the solution.

Cupric sulphate forms large, transparent, deep-blue crystals, which
are easily soluble in water, and have a nauseous, metallic taste. By
heating it to about 200° C. (392° F.) all water of crystallization is
expelled, and the anhydrous cupric sulphate formed, which is a white
powder. By further heating this is decomposed, sulphuric and
sulphurous oxides are evolved, and cupric oxide is left.

Experiment 41. Boil about 5 grammes of fine copper wire with 15 c.c. of
concentrated sulphuric acid until the action ceases and most of the copper
is dissolved. Dilute with about 15 c.c. of hot water, filter, and set aside for
crystallization State the exact quantities of copper and H2S04 required to
make 100 pounds of crystallized cupric sulphate.

Cupric carbonate is obtained by the addition of sodium carbonate
to solution of cupric sulphate, when a bluish-green precipitate is
formed, which is cupric carbonate with hydroxide (Plate III., 4); by
dissolving this in the various acids, the different cupric salts are
obtained.

Ammoniocopper compounds. A number of compounds are
known which are either double salts of ammonia and copper, or are
derived from ammonium salts and contain copper. Thus, cupric
chloride forms with ammonia the compounds : CuCl2(NH3)2, CuCl2
(NH3)4, and CuCl2(NH3)6. Cupric sulphate forms in like manner,
cupric- diammonium sulphate, CuSO4(NH3)2, and cupric tetrammo-
nium sulphate, CuSO4(NH3)4, which is a deep azure-blue compound
taking up one molecule of water during crystallization.

It is this formation of soluble ammonio-copper compounds which
causes the deep blue color in solutions of cupric salts on the addition
of ammonia water.

326 METALS AND THEIR COMBINATIONS.

All copper salts, except the sulphide, are soluble in ammonia water. Hence,
copper cannot be precipitated from ammoniacal solution by any reagent except
hydrogen sulphide or alkali sulphides. Copper hydroxide with excess of am-
monia water forms the deep-blue soluble compound, Cu(NH3)4.(OH)2, in which
the copper is held in the complex radical or ion, Cu(NH3)4". The ammonio-
copper salts are derived from the hydroxide above, and also contain the radical
Cu(NH3)4", which is the cause of the blue color. The sulphate has the for-
mula Cu(NH3)4.SO4.H2O.

With excess of alkali cyanides, copper also forms complex double cyanides,
from which copper cannot be precipitated by any reagent, not even hydrogen
sulphide.

Poisonous properties and antidotes. The use of copper for culinary vessels
Is frequently the cause of poisoning by this metal. A perfectly clean surface of
metallic copper is not affected by any of the substances used in the preparation
of food, but as the metal is very apt to become covered with a film of oxide
when exposed to the air, and as the oxide is easily dissolved by the combined
action of water, carbonic or other .acids, such as are found in .vinegar, the juice
of fruits, or rancid fats, the use of copper for culinary vessels is always
dangerous. Actual adulterations of food with compounds of copper have been
detected.

In cases of poisoning by copper the stomach-pump should be used, vomiting
induced, and albumen (white of egg) administered, which forms an insoluble
compound with copper. Reduced iron, or a very dilute solution of potassium
ferrocyanide, may be of use as antidotes.

Tests for copper.
(Use a 5 per cent, solution of copper sulphate.)

1. Add to the solution hydrogen sulphide or ammonium sulphide :
q, black precipitate of cupric sulphide is formed. (Plate III., 1) :

CuS04 + H2S == H2SO4 -f CuS.

2. Add solution of sodium or potassium hydroxide : a bluish pre-
cipitate of cupric hydroxide, Cu(OH)2, is formed, which is converted
into dark-brown cupric oxide, CuO, by boiling. (See equation
above.) (Plate III., 2.)

3. Add ammonia water : a bluish precipitate of cupric hydroxide
is formed which readily dissolves in an excess of the reagent, forming
a deep azure-blue solution containing an ammonio-copper compound.
(See explanation above.) (Plate III., 3.)

The delicacy of this test is shown by diluting the solution of the
copper salt until its color is no longer visible, and then adding
ammonia.

COPPER. LEAD. BISMUTH.

PLATE

Cupric sulphide or lead .sulphide,

precipiiateil from Milutioiih of nipper or
lead by liydi ouen sulphide.

Cupric hydroxide passing into cupric
oxide. Cupric solutions precipitated by
potassium hydroxide and boiling.

Cupric solutions treated with am-
monia water.

Cupric carbonate, precipitated from

cupric solutions by sodium carbonate.

Cupric ferrocyanide, precipitated
from cupric solutions by potassium, ferro-
cyanide.

Lead iodide, precipitated from lead
solutions by soluble iodides.

Lead solutions with soluble chlorides,
sulphates or carbonates. Bismuth solu-
tions with alkali hydroxides or carbonates.

Bismuth sulphide, precipitated from
bismuth solutions by hydrogen sulphide.

, Litti Balliinocr. . Ifd

LEA D — COPPER — BISM mi. 327

4. Add solution of potassium ferrocyanide : a reddish-brown pre-
cipitate of cupric ferrocyanide, Cu2Fe(CN)6, is obtained. (Plate III., 5.)

This is a very delicate test, and should also be made on a highly
diluted solution made as directed in test 3.

5. Add solution of sodium or potassium carbonate : green cupric
carbonate with hydroxide is precipitated. (Plate III., 4.)

6. Immerse a piece of iron or zinc, showing a bright surface, in an
acidified solution of copper : the latter is precipitated upon the iron, an
equivalent amount of iron passing into solution. (See page 319.)

CuS04 + Fe FeS04 + Cu.

7. Most compounds of copper color the flame green, cupric chloride,
blue. The cupric chloride flame can be made very striking by dis-
solving the copper salt in a little concentrated hydrochloric acid,
pouring this solution on the corner of a piece of iron wire gauze, and
holding it in the Bunsen flame.

8. Cupric compounds give a blue, cuprous compounds a red, borax
bead.

Tests 3, 4, 6, and 8 are sufficient to identify copper compounds. The
insoluble ones are made soluble by treating with mineral acids. The
sulphate, nitrate, chloride, acetate, and ammonio-salts of copper are
soluble in water, most of the other compounds are insoluble. The
soluble normal salts redden litmus, due to hydrolysis.

The ionic equations for the tests are of the same form as those given under
the tests for calcium.

Bismuth, Biiu = 206.9. Found in nature chiefly in the metallic
state, disseminated, in veins, through various rocks. The extraction
of the metal is a mere mechanical process, the earthy matter contain-
ing it being heated in iron cylinders, and the melted bismuth collected
in suitable receivers.

Bismuth is grayish-white, with a pinkish tinge, very brittle, gen-
erally showing a distinct crystalline structure. Occasionally it is
used in alloys and in the manufacture of a few medicinal prepara-
tions.

Bismuth has the property of expanding while passing from the liquid to the
solid state, and of greatly lowering the fusing point of other metals. These
properties make it a useful constituent of many alloys. The presence of bis-
muth in dental amalgams renders them sticky and adhesive and causes them
to require a larger proportion of mercury.

Bismuth is trivalent, as a rule, as shown in the chloride, BiCl3, or
oxide, Bi2O3, but it is also quinquivalent, as shown by the oxide,

328 METALS AND THEIR COMBINATIONS.

Bi2O5, corresponding to P2O5, Sb2O5, I2O5, or N2O5. In fact, bismuth
forms, besides the two oxides mentioned, two others of the composition
Bi2O2 and Bi2O4, corresponding to the respective nitrogen oxides.
A characteristic property of this metal is decomposition of the con-
centrated solution of any of its normal salts by the addition of much
water, with the formation and precipitation of so-called oxysalts or
subsalts of bismuth, while some bismuth with a large quantity of
acid remains in solution. This is due to the very weak basic charac-
ter of Bi(OH)3.

The true constitution of these subsalts is as yet doubtful, but a
comparison of them has led to the assumption of a radical Bismuthyl,
BiO, which behaves like an atom of a univalent metal.

The relation between the normal or bismuth salts, and the subsalts
or bismuthyl salts, will be shown by the composition of the following
compounds :

Bismuth chloride, BiCl3. Bismuth yl chloride, (BiO)CL

" bromide, BiBr3. " bromide, (BiO)Br.

iodide, BiI3. •' iodide, (BiO)I.

" nitrate, Bi(NO3)3. " nitrate, (BiO)NO3.

sulphate, Bi2(S04)3. " sulphate, (BiO)2SO4.

« carbonate, Bi2(CO3)3 j „ carbonate, (BiO)2CO3.

not known. )

The nature of normal bismuth salts and bismuthyl salts may be
explained by saying that the first are derived from the triacid base
Bi(OH)3, the latter from the monacid base BiO.OH. These two
hydroxides are related to one another thus :

Bi(OH)3 = Bi/°H + H20.

Bismuth subnitrate, Bismuthi subnitras, BiONO3.H2O ? (Oxy-
nitrate of bismuth}. By dissolving metallic bismuth in nitric acid, a
solution of bismuth nitrate is obtained, nitrogen dioxide escaping :
Bi + 4HNO3 = Bi(NO3)3 + NO + 2H2O.

Upon evaporation of the solution, colorless crystals of bismuth
nitrate, Bi(NO3)35H2O, are obtained.

If, however, the solution (or the dissolved crystals) be poured into
a large quantity of water, the salt is decomposed with the formation
of bismuthyl nitrate and nitric acid, which latter keeps in solution
some bismuth :

Bi(N(V3 + 2H20 = BiON03.H2O + 2HNO3

Subnitrate of bismuth is a heavy, white, tasteless powder, of a

LEAD- COPPER— BISMUTH. 329

somewhat varying chemical composition ; it is almost insoluble in
water, soluble in most acids.

Experiment 42. Dissolve by the aid of heat about 1 gramme of metallic bis-
muth in a mixture of 2 c.c. of nitric acid and 1 c.c. of water. Evaporate the
clear solution to about one-half its volume, in order to remove excess of acid,
and pour this solution of normal bismuth nitrate into 100 c.c. of water. Col-
lect the precipitate of bismuthyl nitrate on a filter, wash and dry it. Prove
the presence of bismuth in the filtrate by tests mentioned below.

Bismuth subcarbonate, Bismuth! subcarbonas (BiO)2CO3.
H2O (?) (Oxy carbonate of bismuth, Pearl-white). Made by adding
sodium carbonate to solution of bismuth nitrate, when the subcarbo-
nate is precipitated, some carbon dioxide escaping :

2Bi(N03)s + 3Na2CO3 + H2O = 6NaNO3 -f 2CO2 + (BiO)2CO3.H2O.
A white, or pale yellowish-white powder, resembling the subnitrate.
It readily loses water and carbon dioxide on heating, when the yellow
oxide, Bi2O3, is left.

A mixture of bismuth subnitrate, sodium bicarbonate, and water is often
prescribed, but, as such a mixture gives off carbon dioxide, it is better to sub-
stitute the subcarbonate for the subnitrate.

Tests for Bismuth.

Use a solution made by dissolving bismuth subnitrate or subcar-
bonate in the least possible quantity of dilute nitric acid, with gentle
heat. Dilute cautiously with water, adding a few drops more of the
acid if there is any tendency to precipitation.

1. Add to the solution hydrogen sulphide or ammonium sulphide :
a dark-brown (almost black) precipitate of bismuth sulphide, Bi2S3,
is produced (Plate III., 8) :

2BiCl3 + 3H2S = 6HC1 + Bi2S3.

2. Add solution of ammonium or sodium hydroxide, or carbonate :
a white precipitate of bismuth hydroxide, Bi(OH)3, or of bismuthyl
carbonate is produced. (See explanation above.)

3. Solution of potassium iodide precipitates brown bismuth iodide,
B5I3, soluble in excess of the reagent.

4. Solution of potassium dichromate precipitates yellow bismuthyl
dichromate, (BiO)2Cr2O7.

5. A small quantity of bismuth or of any bismuth compound,
mixed with equal quantities of sulphur and potassium iodide, and

330 METALS AND THEIR COMBINATIONS.

heated moderately upon charcoal before the blowpipe, forms a scar-
let-red incrustation of bismuthyl iodide, BiOI.

6. Apply the reduction test on charcoal (see directions in test 3
for sulphuric acid) to any dry bismuth compound. A hard, brittle bead
of metallic bismuth is produced, which, if dissolved in a little con-,
centrated hydrochloric acid, aided by a few drops of nitric acid, and
the solution then be strongly diluted with water, gives a dense white
precipitate of bismuth subchloride,

BiCL, + H20 = BiOCl + 2HC1.

Tests 1, 5, and 6 together are sufficient to identify a bismuth com-
pound. The insoluble or sub-salts are the most stable, and can be dis-
solved by acids, forming the normal salts. The latter cannot exist
in aqueous solution, except in the presence of an acid. The decomposi-
tion of normal salts of bismuth by water into insoluble sub-salts is the
most characteristic property of bismuth. One other metal resembles
it in this respect, namely, antimony, but its sulphide has an orange
color.

The most readily obtained sub-salt of bismuth is the subchloride,
BiOCl . If no precipitate occurs when diluting the nitrate solution
(because of too much acidity), addition of solution of ammonium or
sodium chloride produces a precipitate of the subchloride imme-
diately.

31. SILVER— MERCURY.

Silver, Ag = 107.12 (Argentum). This metal is found sometimes
in the metallic state, but generally as a sulphide, which is nearly
always in combination with large quantities of lead sulphide, such
ore being known as argentiferous galena. The lead manufactured
from this ore contains the silver, and is separated from it by roasting
the alloy in a current of air, whereby lead is oxidized and converted
into litharge, while pure silver is left.

QUESTIONS. — What are the properties of lead, and from what ore is it ob-
tained? What is litharge, and how does it differ from red lead? Give the
composition of nitrate, carbonate, and iodide of lead; how are they made?
State the analytical reactions for lead. How is copper found in nature ? How
many oxides of copper are known ; what is their composition, and under what
conditions are they formed? What is "blue vitriol"; how is it made, and
what are its properties? How does ammonium hydroxide act on cupric solu-
tions? Mention tests for copper. What is the composition of subnitrate and
subcarbonate of bismuth ; how are they made from metallic bismuth, and what
explanation is given in regard to their constitution ?

SILVER— MERCURY. 331

Silver is 'the whitest of all metals, and takes the highest polish ;
it is the best conductor of heat and electricity, and melts at about
1000° C. (1832° F.); it is univalent, and forms but one series of salts;
it is not affected by the oxygen of the air at any temperature, but is
readily acted upon by traces of hydrogen sulphide, which forms a
black film of sulphide upon the surface of metallic silver. Hydro-
chloric acid scarcely acts on silver, nitric and sulphuric acids dis-
solve it.

While many of the non-metallic elements have long been known to exist in
allotropic forms, none of the metals had been obtained in such a condition
until quite recently, when it was shown that silver is capable of assuming a
number of allotropic modifications. These are obtained chiefly by precipi-
tating silver from solutions by different reducing agents. While normal silver
is white, the allotropic forms have distinct colors —blue, bluish-green, red, pur-
ple, yellow — and differ also in many other respects. Thus they are converted
into silver chloride by highly diluted hydrochloric acid, which does not act
on common silver; they are soluble in ammonia water, and act as reducing
agents upon a number of substances, such as permanganates, ferricyanides,
etc. Allotropic silver can be converted into the common form by dift
ferent forms of energy — for instance, by heat, electricity, and the action of
strong acids.

This allotropic form of silver is known as colloidal silver, and its solution in
water is not a true, but a colloidal solution. Such a solution has the same freez-
ing- and boiling-point as water itself, and it has been shown that the colloid is
simply suspended in the liquid, although it is in too fine a state of division to
be retained by a filter-paper. Colloidal solutions of silver, gold, or platinum
result when electric discharges pass between wires of these metals held under
water.

Collargol (Argentum Crede) is a preparation of colloidal (soluble)
silver, said to contain 85.87 per cent, of silver and a small amount of albumin.
It is bluish-black, scale-like, soluble in 20 parts of water. Albumin is added
to prevent precipitation of silver from its solution by acids and salts, or by
heating. It is incompatible with the usual silver reagents.

Collargol Ointment (Unguentum Crede") is an ointment containing 15 per
cent, of collargol, of a dark, bluish-gray color.

Silver is too soft for use as coin or silverware, and, therefore, is
alloyed with from 5 to 25 per cent, of copper, which causes it to be-
come harder, and consequently gives it more resistance to the wear
and tear by friction.

Pure silver may be obtained by dissolving silver coin in nitric acid,
when a blue solution, containing the nitrates of copper and silver, is
formed. By the addition of sodium chloride to the solution a white
curdy precipitate of silver chloride, AgCl, forms, while cupric nitrate

332 METALS AND THETR COMBINATIONS.

remains in solution. The silver chloride is washed, dried, mixed
with sodium carbonate, and heated in a crucible, when sodium chlo-
ride is formed, carbon dioxide escapes, and a button of silver is found
at the bottom of the crucible :

2AgCl + Na2C03 = 2NaCl + CO2 + 2Ag + O.

Experiment 43. Dissolve a small silver coin in nitric acid, dilute with water,
and precipitate the clear liquid with an excess of solution of sodium chloride.
The washed precipitate of silver chloride may be treated with sodium carbon-
ate, as stated above, or may be converted into metallic silver by the following
method : Place the dry chloride in a small porcelain crucible and apply a
gentle heat until the chloride has fused ; when cold, place a piece of sheet
zinc upon the chloride, cover with water, to which a few drops of sulphuric
acid have been added, and set aside for a day, when the silver chloride will be
found to have been decomposed with liberation of metallic silver and forma-
tion of zinc chloride.

A simpler method is to heat the silver chloride with a solution of formal-
dehyde and a few drops of alkali, or with glucose and alkali. Metallic silver
in a finely divided state is obtained, which, after washing, may be fused into
a lump.

Silver nitrate, Arg-enti nitras, AgNO3 = 168.69. Pure silver is
dissolved in nitric acid :

3Ag + 4HN03 = NO + 2H2O + 3AgNO3.

The solution is evaporated to dryness with the view of expelling all
free acid, the dry mass dissolved in hot water and crystallized.

If the silver used should contain copper, the latter may be elimin-
ated from the mixture of silver and cupric nitrate by evaporating to
dryness and fusing, when the latter salt is decomposed, insoluble
cupric oxide being formed. The fused mass is dissolved in water,
filtered, and again evaporated for crystallization.

When silver nitrate, after the addition of 4 per cent, of hydro-
chloric acid, is fused and poured into suitable moulds it yields the
white cylindrical sticks which are known as moulded silver nitrate,
caustic, lunar caustic, or lapis infernalis.

When fused with twice its weight of potassium nitrate and formed
into similar rods, it forms the mitigated or diluted silver nitrate (mit-
igated caustic) of the U. S. P.

Silver nitrate forms colorless, transparent, tabular, rhombic crys-
tals, or, when fused, a white, hard substance; it is soluble in less
than its own weight of water, the solution having a neutral reaction.
Exposed to the light, especially in the presence of organic matter,
silver nitrate blackens in consequence of decomposition ; when

8IL VER—MERCUR Y. 333

brought in contact with animal matter, it is readily decomposed into
free nitric acid and metallic silver, which produces the characteristic
black stain ; it is this decomposition, and the action of the free nitric
acid, to which the strongly caustic properties of silver nitrate are
due.

Silver nitrate is used for various kinds of indelible inks and hair-
dyes, and very largely in the manufacture of those silver compounds
employed for photographic purposes.

Photography is the art of obtaining images of objects by means
of chemical changes produced in certain substances (chiefly com-
pounds of silver or platinum) by the action of light. Three separate
operations are required to obtain the image ; they are exposure, devel-
oping and fixation.

The exposure of a light-sensitive surface to a projected image of the object to
be photographed is made in the camera, which is so arranged that the image
can be thrown upon the surface by means of a lens. The surface used is gen-
erally that of a glass plate or a gelatine film, sensitized with the bromide or
iodide of silver.

On the exposed plate a chemical change has taken place in the silver salt
wherever light has acted on it. The exact nature of this change is not under-
stood, and nothing can be detected on the plate with the eye after exposure.
But when the exposed plate is treated with certain solutions, called developers,
that portion of the silver salt which has been acted upon by light is decomposed
with the formation of a deposit of metallic silver, forming the visible image.
The acting constituent of developers are deoxidizing agents, such as pyrogallol,
hydroquinone, ferrous sulphate, etc.

After the silver image has appeared there yet remains on the plate that por-
tion of the silver salt which has not been acted on by light, and consequently
not by the developer. This portion of the undecomposed silver salt must be
removed before the plate can be taken to the light, and this removal, called
fixation, is accomplished by immersion of the plate in a fixing solution of
sodium thiosulphate, Na2S203 (hyposulphite), which dissolves the salt in con-
sequence of the formation of a double salt of the composition Ag2S203. 2Na2S203 ;
this is eliminated by washing in water.

The image thus obtained is called a negative, because it shows dark what
ought to be light, and vice versa. By placing this negative upon sensitized
material (generally paper) and permitting light to pass through the negative
to the underlying paper the light-sensitive material is chemically affected most
where the silver deposit in the negative is the thinnest, and vice versa. By
developing and fixing the exposed paper the positive picture is obtained.

Silver oxide, Arg-enti oxidum, Ag2O = 23O.12. Made by the
addition of an alkali hydroxide to silver nitrate :

2AgN03 + 2KOH = 2KNO3 + H2O + Ag2O

334 METALS AND THEIR COMBINATIONS.

A dark-brown, almost, black powder, but very sparingly soluble
in water, imparting to the solution a weak alkaline reaction. It is a
strong base, and easily decomposed into silver and oxygen.

Antidotes. Sodium chloride, white of egg, or milk, followed by an emetic.

Complex silver compounds. A great many combinations of silver
with organic substances have been introduced and a few are extensively em-
ployed in medicine. These compounds usually differ in properties from the
inorganic salts of silver. They are antiseptic and less irritating than silver
nitrate.

Argonin, silver-casein, is a soluble casein compound containing 4.28 per cent.
of silver. It is a nearly white powder, soluble in water, from which the silver
is not precipitated by sodium chloride or hydrogen sulphide. It is also soluble
in alkalies, egg-albumin, blood-serum, etc.

Argyrol, silver vitellin, is a compound of a derived proteid and silver oxide,
containing from 20 to 25 per cent, of silver. It occurs as black, glistening
hygroscopic scales, freely soluble in water and glycerin, insoluble in oils and
alcohol. It is said to be incompatible with acids and most of the neutral and
acid salts in strong solution.

Protargol is a compound of albumin and silver, containing 8.3 per cent, of
silver. It is a yellow powder, soluble in 2 parts of cold water. The silver is
not precipitated by the usual reagents, such as alkalies, sulphides, chlorides,
bromides, iodides, nor by heat. It is compatible with picric acid and its salts
and with most metallic salts, but is precipitated by cocaine hydrochloride,
which, however, may be prevented by addition of boric acid. It is a non-irri-
tant bactericide and antiseptic, extensively used as a substitute for silver
nitrate.

Tests for Silver.
(Use a 1 per cent, solution of silver nitrate in distilled water.)

1. Add to the solution hydrogen sulphide or ammonium sulphide :
a dark-brown precipitate of silver sulphide is produced :

2AgNO, + HaS = 2HNO3 + Ag2S.

2. Add hydrochloric acid, or solution of any soluble chloride : a
white, curdy precipitate of silver chloride is produced, which is in-
soluble in dilute acids, but soluble in ammonium hydroxide and in
potassium cyanide :

AgN03 + NaCl = NaN03 + AgCl.

3. Add potassium chromate or dichromate solution : a red precipi-
tate of silver chromate, Ag2CrO4, is formed (Plate II., 7).

4. Add sodium phosphate solution : a pale-yellow precipitate of
silver phosphate, Ag3PO4, is formed, which is soluble in ammonia
and in nitric acid. Free phosphoric acid does not give a precipitate.

SILVER— MERCURY. 335

5. Solution of alkali hydroxides precipitates dark-brown silver
oxide, soluble in ammonia water, forming a complex hydroxide
Ag(NH3)2.OH.

6. Solution of potassium iodide or bromide gives a pale-yellow
precipitate.

7. Metallic copper or zinc precipitates metallic silver from solu-
tions of silver in any form of combination. (See page 319.) »

Test 2 is sufficient to identify silver in ordinary solutions, for,
although mercurous and lead chloride are insoluble in water and
dilute acids, silver chloride alone of these three insoluble chlorides
is soluble in ammonia water. Silver forms a number of complex
combinations with organic compounds from which it is not easily pre-
cipitated, but by reduction of the silver to the metallic state, and
solution of the metal in nitric acid, the tests may be applied. The
same procedure applies also to inorganic insoluble silver compounds,
as AgCl, AgBr, Agl, Ag2S.

All silver salts are soluble in ammonia water, except the iodide and sul-
phide ; hence the latter alone can be precipitated from an ammoniacal solution.
In these solutions complex combinations, as Ag(NH3)2.NO3, Ag(NH,)tCl, are
formed, which are salts of the hydroxide, Ag(NH3)2.OH. In this respect silver
acts very much like copper. These compounds dissociate thus:

Ag(NH3)2N03 5± Ag(NH3)2- + NO/.

The Ag(NH3)./ ions yield a slight amount of Ag* ions, but not enough to be
precipitated by any of the reagents except iodide and sulphide. The concen-
tration of Ag' ions given by the latter precipitates is less than that given by
the Ag(NH3)2* ions, hence precipitation takes place. (See page 193.)

Solutions of alkali cyanides and thiosulphates dissolve all silver compounds,
giving complex substances of the form KAg(CN)2 and Na3Ag(S2O3)2. The ions
of these are K* + Ag(CN)/, and 3Na* -f Ag(S2O3)///. Such a slight amount
of Ag* ions are formed from these compounds that no reagent will give a pre-
cipitate. That there are some Ag* ions, however, is shown by the fact that
active metals, like zinc, separates the silver from the solutions. Also that in
electroplating silver is deposited from cyanide solution.

Soluble silver salts are not hydrolyzed, and are, therefore, neutral.

Mercury, Hydrargyrum, Hg = 198.5 (Quicksilver). Mercury is
found sometimes in small globules in the metallic state, but generally
as mercuric sulphide or cinnabar, a dark-red mineral. The chief
supply was formerly obtained from Spain and Austria ; now, how-
ever, large quantities are obtained from California ; it is also
imported from Peru and Japan.

Mercury is obtained from cinnabar either by roasting it, whereby
the sulphur is converted into sulphur dioxide, or by heating it with
lime, which combines with the sulphur, while the metal volatilizes,
and is condensed by passing the vapors through suitable coolers.

336 METALS AND THEIR COMBINATIONS.

Mercury is the only metal showing the liquid state at the ordinary
temperature ; it solidifies at -40° C. (-40° F.), and boils at 357° C.
(675° F.) ; but is slightly volatile at all temperatures ; it is almost
silver-white, and has a bright metallic lustre ; its specific gravity is
13.56 at 15° C. (59° F.).

Pure mercury should present a bright surface even after agitation with air;
when dropped on paper it should form globules which roll about freely, retain
their globular form and leave no streaks. Commercial mercury is often con-
taminated with tin, lead, bismuth and zinc. Such impurities cause a trail of
dross when globules are made to roll over paper.

Mercury can be purified by repeated distillation, or by covering the metal
with nitric acid and agitating the mass frequently during two days. The total
of the base metals, with some mercury, pass in solution, which is washed out with
water, after which the mercury is dried by setting it in a warm place.

Mercury is peculiar in that its molecule contains but one atom, at
least when in the state of a gas ; in the liquid and solid states it may
contain two atoms, like most other elements, but we have as yet no
means of proving this fact.

Mercury forms, like copper, two series of compounds, distinguished
as mercuric and mercurous compounds. In the former, mercury is
bivalent, while in mercurous compounds the atom exerts a valence of
one. It was long supposed that this was due to the fact that two
mercury atoms were joined together, each atom thereby losing one
of its points of affinity, leaving but one point for combining Avith
another atom or radicle. This view necessitated the existence of two
mercury atoms in the molecule of every mercurous compound, the
composition, for instance, of mercurous chloride being CIHg-HgCl or
Hg2Cl2. There are, however, good reasons to believe that mercury is
univalent in mercurous compounds, the composition of mercurous
chloride being, consequently, HgCL Similarly, copper is assumed to
be univalent in cuprous compounds.

Mercury is not affected by the oxygen of the air, nor by hydro-
chloric acid, while chlorine, bromine, and iodine combine with it
directly, and warm sulphuric and nitric acids dissolve it.

Mercury is used in the metallic state for many scientific instruments
(thermometer, barometer, etc.); for making amalgams; for extracting
gold from the ore ; for manufacturing from it all of the various mer-
cury compounds, and those official preparations in which mercury
exists in the metallic state.

These latter preparations are : Mercury with chalky mass of mercury,
or blue pill, mercurial ointment, and mercurial plaster. Mercury exists
in a metallic, but highly subdivided, state in these preparations, which
are made by intimately mixing (triturating) metallic mercury with

SILVER— MERCURY. 337

the different substances used (viz., chalk, pill-mass, fat, lead -pi aster).
It is most probable that the action of these agents upon the animal
system is chiefly due to the conversion of small quantities of mercury
into mercurous oxide, which, in contact with the acids of the gastric
juice or with perspiration, are converted into soluble compounds
capable of being absorbed.

Amalgams. Alloys containing mercury are termed amalgams. Mercury
unites with most metals, and with some of them it forms definite compounds.
Dental alloys used for amalgamation are composed chiefly of silver and tin with
one or more of the following metals : gold, platinum, copper, zinc. Dental
amalgams are made by reducing the alloy ingot to fine shavings or filings,
which are triturated with the necessary quantity of mercury to form a plastic
mass, which becomes hard or sets.

The properties most essential for a good amalgam are strength, immutability
as to volume, freedom from discoloration, and resistance to the action of the
oral secretions. Many formulas have been suggested to obtain these results.

The addition of either gold, platinum, copper or zinc to a silver-tin alloy
facilitates setting, while this is retarded by an excess of mercury or by the em-
ployment of an alloy that has been long exposed to the air or has been annealed.
The change in form — i. e., expansion or contraction — which an amalgam under-
goes in hardening is very objectionable and difficult to completely overcome.

The discoloration of amalgams is in great measure due to the formation of
sul phides, particularly upon those amalgams in which there is not complete chem-
ical union of the metallic constituents. A proper proportion of zinc in an alloy
prevents discoloration considerably, making, however, the alloy difficult to amal-
gamate, while the presence of copper greatly increases the tendency to discolor.

Mercurous oxide, Hg^O (Black oxide or suboxide of mercury). An
almost black, insoluble powder, made by adding an alkaline hydroxide
to a solution of mercurous nitrate :

2HgN03 + 2KOH == 2KNO3 + H2O -f Hg.2O.

A similar decomposition takes place when alkaline hydroxides are
added to insoluble mercurous chloride. A mixture of lime-water and
mercurous chloride (calomel) is known as black-wash ; when the two
substances are mixed, calomel is converted into mercurous oxide, while
calcium chloride is formed :

2HgCl + Ca(OH)2 = CaCl2 -f H2O + Hg2O.

Mercuric oxide, HgO = 214.38. There are two mercuric oxides
which are official ; they do not differ in their chemical composition,
but in their molecular structure.

The yellow mercuric oxide, Hydrargyrioxidumflavum, is made by pour-
ing a solution of mercuric chloride into a solution of sodium hydroxide,
when an orange-yellow, heavy precipitate is produced, which is washed
and dried at a temperature not exceeding 30° C. (86° F.) (Plate IV., 3) :
HgCl2 + 2NaOH = HgO + SNaCl + H2O.

The red mercuric oxide, Hydrargyri oxidum rubrum, is made by

22

338 METALS AND THEIR COMBINATIONS.

heating mercuric nitrate, either by itself or after it has been intimately
mixed with an amount of metallic mercury equal to the mercury in
the nitrate used (Plate IV., 4). In the first case, nitrous fumes and
oxygen are given off, mercuric oxide remaining :

Hg(N03)2 = HgO + 2N02 -f O.
In the other case, no oxygen is evolved :

Hg(N08), + Hg = 2HgO + 2N02.

The red oxide of mercury differs from the yellow oxide in being
more compact, and of a crystalline structure; while the yellow oxide
is in a more finely divided state, and consequently acts more energeti-
cally when used in medicine. Yellow oxide, when digested on a
water-bath with a strong solution of oxalic acid, is converted into
white mercuric oxalate within fifteen minutes, while red oxide is not
acted upon by oxalic acid under the same conditions.

When mercuric chloride is added to lime-water, a mixture is
formed holding in suspension yellow mercuric oxide; this mixture
is known as yellow-wash.

Experiment 44. Shake a small knifepointful of mercurous chloride (calomel)
with 50 c.c. of lime-water. Note that the chloride instantly turns dark, due to
formation of mercurous oxide (see reaction in text). The lime-water must be
in excess.

Add about 1 c.c. of reagent solution of mercuric chloride to 50 c.c. of lime-
water and stir. Yellow mercuric oxide is formed at once (see reaction in text).
If the lime-water is not in excess, the precipitate will not be pure yellow, but
whitish, due to formation of an oxychloride, Hg2OCl2.

Caustic alkalies produce the same results as above, but any excess of these
stronger alkalies is objectionable for the purposes for which these " washes " are
used.

Experiment 45. Heat some mercuric nitrate in a porcelain dish, placed in a
ftime chamber, until red fumes no longer escape. The remaining red powder
is mercuric oxide, which, by further heating, may be decomposed into its ele-
ments.

Mercurous chloride, Hydrargyrum chloridum mite, HgCl =
233.68 (Calomel , Mild chloride of mercury, Subchloride or proto-
chloride of mercury). Mercurous chloride, like mercurous oxide,
may be made by different processes, but the article used medicinally
is the one obtained (except it be otherwise stated) by sublimation
and the rapid condensation of the vapor in the form of powder.

It is made either by subliming a mixture of mercuric chloride
and mercury:

HgCl, + Hg = 2HgCl.

SILVER— MERCURY. 339

or by thoroughly mixing with mercuric sulphate a quantity of mer-
cury equal to that contained in the sulphate ; by this operation mer-
curous sulphate is obtained, which is mixed with sodium chloride,
and sublimed from a suitable apparatus into a large chamber, so that
the sublimate may fall in powder to the floor :

HgS04 -f Hg + 2NaCl = Na2SO4 + 2HgCl.

Precipitated calomel, being in a finer state of subdivision, acts
more energetically when used medicinally. It is obtained by pre-
cipitation of a soluble mercurous salt by any soluble chloride:

HgNO3 + NaCl = NaNO8 + HgCl.

Mercurous chloride, made by either process, generally contains
traces of mercuric chloride, and should, therefore, be washed with
hot water until the washings are no longer acted upon by ammonium
sulphide or silver nitrate.

Mercurous chloride is a white, impalpable, tasteless powder, in-
soluble in water and alcohol ; it volatilizes without fusing previously ;
when given internally, it should not be mixed with either mineral
acids, alkali bromides, iodides, hydroxides, or carbonates, except the
action of the decomposition products be desired.

Mercuric chloride, Hydrargyri chloridum corrosivum, Hg-CL,
— 268.86 (Corrosive chloride of mercury, Corrosive sublimate, Perchlo-
ride or bichloride of mercury). Made by thoroughly mixing mercuric
sulphate with sodium chloride, and subliming the mixture, when
mercuric chloride is formed, and passes off in white fumes which are
condensed in the cooler part of the apparatus, while sodium sulphate

is left :

HgSO, + 2NaCl = Na2SO4 + HgCl2.

Mercuric chloride is a heavy, white powder, or occurs in heavy,
colorless, rhombic crystals or crystalline masses; it is soluble in 16
parts of cold and 2 parts of boiling water, and in about 3 parts of
alcohol, in 4 parts of ether, and in about 14 parts of glycerin; when
heated, it fuses and is volatilized ; it has an acrid, metallic taste, an
acid reaction, and strongly poisonous and antiseptic properties.

The halogen salts of mercury are very little ionized in solution. On this
account, mercuric chloride is much less hydrolyzed than mercuric nitrate, that
is, there is not so much tendency to precipitate a basic salt. Mercuric chloride
also has the tendency to form complex salts. Thus sodium chloride increases its
solubility in water and causes the solution to become neutral, because of the
formation of the salt, HgCl2.NaCl or NaHgCl3. Mercuric chloride tablets are

340 METALS AND THEIR COMBINATIONS.

made up witih sodium chloride, because the latter prevents the formation of in-
soluble chlorides and facilitates solution, although the activity of the mercury
compound is somewhat lessened. Mercuric chloride is sometimes used as a
preservative of specimens. It forms insoluble compounds with albumin and
prevents its decay. On this principle, albumin is given as an antidote in mer-
curic chloride poisoning.

Mercurous iodide, Hydrargyri iodidum flavum, Hgl = 324.4
( Yellow iodide, green iodide, or protiodide of mercury). Both iodides
of mercury may be obtained either by rubbing together mercury and
iodine in the proportions represented by the respective atomic weights,
or by precipitation of soluble mercurous or mercuric salts by potas-
sium iodide.

According to the U. S. P., mercurous iodide is made by the pre-
cipitation of a solution of mercurous nitrate, to which some nitric acid
has been added, by a solution of potassium iodide :

HgNO3 + KI = KNO3 H- Hgl.

The precipitate is collected on a filter, well washed with water and
alcohol, and dried between paper at a temperature not exceeding
40° C. (104° F.). During the whole operation light should be ex-
cluded as much as possible, as it decomposes the compound.

Mercurous iodide is a yellow, tasteless powder, almost insoluble in
water. It is easily decomposed into mercuric iodide and mercury,
becoming darker and assuming a greenish -yellow to green tint, due
to the admixture of metallic mercury, which, in a finely divided
state is blue, and consequently causes a greenish mixture with the
yellow iodide. (Plate IV., 5.)

Mercuric iodide, Hydrargyri iodidum rubrum, Hg-I2 — 45O.3
(Red iodide or biniodide of mercury). Made by mixing solutions of
potassium iodide and mercuric chloride, when a pale-yellow precipi-
tate is formed, turning red immediately (Plate IV., 6) :

HgCl2 + 2KI = 2KC1 + HgI2.

Mercuric iodide is soluble both in solution of potassium iodide and
mercuric chloride, for which reason an excess of either substance will
cause a loss of the salt when prepared. It is a scarlet-red, tasteless
powder, almost insoluble in water and but slightly soluble in alcohol ;
on heating or subliming it turns yellow in consequence of a molecular
change which takes place ; on cooling, and, more quickly, on pressing
or rubbing the yellow powder, it reassumes the original condition
and the red color.

SILVER— MERCUHY. 341

When mercuric iodide is dissolved in potassium iodide solution, a complex
salt is formed, HgI2.2KI, or K2HgI4, from which many of the usual reagents fail
to precipitate the mercury. For example, caustic potash has no effect on the
compound, and such an alkaline solution is known as Nessler's reagent. This
reagent gives a yellow color with traces of ammonia, and a brown precipitate
with larger amounts :

2HgI2 + 4NH3 Hg2NI + 3NHJ.

Nessler's reagent is used in water analysis for detecting traces of ammonia.
The compound, Hg2NI, is called dimercur-ammonium iodide.

Mercuric sulphate, Hg-SO4. When mercury is heated with strong
sulphuric acid (the presence of nitric acid facilitates the formation)
chemical action takes place between the two substances, sulphur
dioxide being liberated and mercuric sulphate formed, which upon
evaporation of the solution is obtained as a heavy, white, crystalline
powder :

Hg + 2H2S04 = HgS04 + 2H20 + SO2.

Yellow mercuric subsulphate, Hg-SO4.(Hg-O)2 (Basic mercuric
sulphate, Turpeth mineral, Mercuric oxy-sulphate). When mercuric
sulphate, prepared as directed above, is thrown into boiling water, it
is decomposed into an acid salt which remains in solution, and a basic
salt which is precipitated. As shown by its composition, it may be
looked upon as mercuric sulphate in combination with mercuric oxide.
It is a heavy, lemon-yellow, tasteless powder, almost insoluble in
water.

Mercurous sulphate, Hg2SO4. When mercuric sulphate is triturated
with a sufficient quantity of mercury, direct combination takes place,
and the mercurous salt is formed :

HgS04 + Hg = Hg2S04.

Nitrates of mercury. Mercurous nitrate, HgNO3, and Mer-
curic nitrate, Hg(NO3)2, may both be obtained as white salts by dis-
solving mercury in nitric acid. The relative quantities of the two
substances present determine whether mercurous or mercuric nitrate
be formed. If mercury is present in excess the mercurous salt, if nitric
acid is present in excess the mercuric salt, is formed, the latter espe^
cially on heating. Both salts are white and soluble in water contain-
ing free acid. Water alone causes decomposition of the nitrates,
similar to that of the sulphates, resulting in the formation of insoluble
basic salts, the composition of which depends on the relative propor-
tions of the mercury salt and water used.

Experiment 46.— Heat gently a small globule (about 1 gramme) of mercury
with 2 c.c. of nitric acid until red fumes cease to escape. If some of the mer-

342 METALS AND THEIR COMBINATIONS.

cury remains undissolved, the solution will deposit crystals of mercurous
nitrate on cooling. Use some of the solution, after being diluted with much
water, for mercurous tests. Use another portion as follows : Heat the solution,
or some of the crystals, with about an equal weight of nitric acid until no more
red fumes escape. Add to a few drops of the diluted liquid a little hydro-
chloric acid, which, if the conversion of the mercurous into mercuric salt has
been complete, will give no precipitate. If, however, one should be formed, the
solution is heated with more nitric acid until no precipitate is formed by hydro-
chloric acid, when the solution is evaporated and set aside for crystallization.
The respective changes may be represented by the following equations :

3Hg + 4HN03 == 3HgNO3 + 2H2O + NO ;
3HgNO3 + 4HN03 = 3Hg(NO3)2 -f 2H2O + NO.

Mercuric sulphide, HgS. This compound has been mentioned as
the chief ore of mercury, occurring crystallized as cinnabar, which
has a red color (Plate IV., 2). The same compound may, however,
be obtained by passing hydrogen sulphide through mercuric solutions,
when at first a white precipitate is formed (a double compound of the
sulphide of mercury in combination with the mercuric salt), which
soon turns black (Plate IV., 1) :

HgCl2 + H-jS = 2HC1 + HgS.

The black, amorphous, mercuric sulphide may be converted into the
red, crystallized variety by sublimation, and is then the preparation
known as red sulphide of mercury, cinnabar, or vermilion. It forms
brilliant dark-red crystalline masses, or a fine bright scarlet powder,
which is insoluble in water, hydrochloric or nitric acid, but soluble
in nitro-hydrochloric acid.

Mercuric and mercurous sulphides may be made also by triturating
the elements mercury and sulphur in the proper proportions, when
they combine directly.

Ammoniated mercury, Hydrargyrum ammoniatum, NH^HgCl
= 249.61 ( White, precipitate, Mercuric-ammonium chloride). This com-
pound is made by pouring solution of mercuric chloride into ammonia
water, when a white precipitate falls, which is washed with highly
diluted ammonia water and dried at a low temperature :

HgCl2 + 2NH4OH == NH2HgCl + NH4C1 + 2H2O.

As shown by the composition of this compound, it may be re-
garded as ammonium chloride, NH4C1, in which two atoms of hydro-
gen have been replaced by one atom of the bivalent mercury. The
mercuric-ammonium salts are of a different type from those combina-

SIL VER—MERCUR Y.

343

tions formed when copper, silver, zinc, etc., salts are dissolved in am-
monia water. The former are all insoluble in water.

Ammoniated mercury is a white, tasteless, insoluble powder.

Mercurous salts with ammonia water give black insoluble precipi-
tates consisting of a mixture of mercuric-ammonium salts and mercury,
which causes the black appearance. For mercurous chloride and
nitrate the reactions are :

2HgCl + 2NH3 = HgNH2.Cl -f Hg -f NH4C1.
2HgN03 -f 2NH3 = HgNH2.N03 + Hg + NH4NO3.

It should be noted that in the case of mercury salts, ammonia water
does not precipitate hydroxides, as it does in other cases.

Tests for mercury.

Mercurous salts.

(Mercurous nitrate, HgNO3 may
be used. )

1. Hydrogen sul-
phide, or ammo-
nium sulphide.

2. Potassium iodide.

3. Potassium or so-
dium hydroxide.

4. Ammonium hy-
droxide.

5. Potassium or so-
dium carbonate.

6. Hydrochloric
acid or soluble
chlorides.

Black precipitate of mercuric
sulphide, with mercury.
2HgN03 -f HaS =
2HN03 + HgS + Hg.

Green precipitate of mercurous
iodide (Plate IV., 7):

KN03 + Hgl.

Dark-brown precipitate of mer
curous oxide, Hg2O (Plate
IV., 5).

Black precipitate of a mixture
of mercury and mercuric-am-
monium chloride (see expla-
nation above).

Yellowish precipitate of mer-
curous carbonate, which is
unstable.

White precipitate of mercurous
chloride is produced :
HgN03 + HC1 =
HN03 -f- HgCl.

Mercuric salts.

(Mercuric chloride, HgCl2, may
be used.)

Black precipitate of mercuric
sulphide. (Precipitate may be
white or gray, with an insuffi-
cient quantity of the reagent.)
(See above) (Plate IV., 1.)

Red precipitate of mercuric
iodide (See above.) (Plate
IV, 6.)

Yellow precipitate of mercuric

oxide HgO. (See above.)

(Plate IV., 3.)
White precipitate of a mercuric

ammonium salt is formed.

( See explanation above.)

Brownish-red precipitate of
basic mercuric carb., mixed
with mercuric oxychloride.

No change.

7. Stannous- chloride produces, in solutions of mercury, a white
precipitate, which turns dark-gray on heating with an excess of the
reagent. The reaction is due to the strong reducing or deoxidizing
property of the stannous chloride, which itself is converted into stannic
chloride, while the mercury salt is first converted into a mercurous
salt and afterward into metallic mercury :

2HgCl2 + SnCl2 = 2HgCl -f SnCl4;
2HgCl + SnCl2 = 2Hg + SnCl,.

344

METALS AND THEIR COMBINATIONS.

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MERCURY. SILVER.

PLATE IV.

Mercuric sulphide, precipitated fro
mercuric solutions by hydrogen sulphid

Mercuric sulphide, Cinnabar.

Yellow mercuric oxide, precipitat*
from mercuric solutions by potassium h
droxide.

Red mercuric oxide, obtained 1
heating mercuric nitrate.

Mercurous oxide, precipitated fro
mercurous solutions by potassium hydro:
ide.

Silver sulphide, precipitated fro
silver solutions by hydrogen sulphide.

flercuric iodide, precipitated froi
mercuric solutions by alkali iodides.

Mercurous iodide, precipitated froi
mercurous solutions by alkali iodides.

8

Mercuric solutions with ammoniui
hydroxide, flercurous solutions wit
soluble chlorides. Silver solutions wit
soluble chlorides.

A.Hoen&CftLith

ARSENIC. 345

8. Dry mercury compounds, when mixed with sodium carbonate
and potassium cyanide, and heated in a narrow test-tube, are decom-
posed with liberation of metallic mercury, which condenses in small
globules in the cooler part of the tube.

9. A piece of bright metallic copper when placed in a slightly acid
mercury solution becomes coated with a dark film of metallic mer-
cury, which by rubbing becomes bright and shining, and may be
volatilized by heat. (See Solution tension, page 319.)

10. All compounds of mercury are completely volatilized by heat,
either with or without decomposition.

Tests 2, 4, 7, 8, and 9 will show the presence of mercury in any of
its compounds. Those that are insoluble in water may be dissolved
by a little concentrated hydrochloric with a few drops of nitric acid,
forming mercuric chloride. Excess of acid is removed by evaporation .

Antidotes. Albumen (white of egg), of which, however, not too much should
be given at one time, lest the precipitate formed by the mercuric salt and
albumin be redissolved. The antidote should be followed by an emetic to
remove the albuminous mercury compound.

Ionic conditions. The simple mercury compounds give mercurous ions, Hg",
and mercuric ions, Hg", which show different behaviors toward reagents, as
seen in the tests above. The mercury ions are colorless, and are not formed
extensively from any compound. The disinfecting and poisonous properties of
mercury compounds depend upon the presence of the ions. Mercuric chloride
in the dry state is inactive, and its solution in alcohol or ether is almost inert
as a disinfectant, because there are practically no mercury ions formed.

Salts in general have a high degree of ionization, but salts of mercury and
cadmium are remarkable exceptions. For this reason mercury salts show some
peculiar behaviors. For example, the halogen salts of mercury dissociate so
little (the bromide and iodide less than the chloride) that they are scarcely
affected by sulphuric or nitric acid. Sodium chloride with sulphuric acid gives
hydrochloric acid, and with nitric acid it gives chlorine. Mercuric cyanide,
Hg(CN)2, is so minutely dissociated, that the presence of either Hg" ions or
(CN)' ions cannot be shown by precipitation with many reagents. Thus, silver
nitrate does not precipitate the (ON)7 ions, as AgCN, nor do alkalies precipitate
Hg* * ions, as HgO. But hydrogen sulphide precipitates mercury from any of
its soluble compounds, because mercuric sulphide is practically completely in-
soluble and unionized. It is for this reason that the sulphide is not dissolved
by any acid, even when concentrated and heated, except nitrohydrochloric.

Mercury is deposited from all its compounds, whether soluble in water or
not, by the metals higher up in the electrochemical series. Hence, it is not
advisable to use vermilion in paint to be applied to metallic surfaces. Eed lead
is better for this purpose.

The complex salts which mercuric chloride forms with alkali chlorides dis-
sociate in part so that mercury is contained in the complex negative ion, and
to this extent loses its disinfectant property. The ionization equation for this

346 METALS AND THEIR COMBINATIONS.

type of compound is illustrated in the case of the sodium compounds, NaCl.-
HgCl2 or NaHgCl3, and 2NaCl.HgCl2 or Na2HgCl4:

NaHgCl3 Z± Na* -f HgCL,';
Na2HgCl4 ^± 2Na* + HgCl/'.

But there is considerable dissociation also into Hg* • ions and Cl' ions. Hence
with not too much sodium chloride present and in very dilute solution, the
mercuric chloride tablets containing sodium or ammonium chloride do not
lose materially in germicidal power, since a relatively large proportion of the
ions are the active Hg* • ions.

The complex potassium mercuric iodide, K2HgI4, gives K* ions and Hgl/7
ions, but very few Hg* * ions. Hence the failure of some reagents, as alkalies
and carbonates, to give a precipitate in a solution of the compound.

32. ARSENIC.
As = 74.4.

General remarks regarding1 the metals of the arsenic group.
The metals belonging to either of the five groups, considered hereto-
fore, show much resemblance -to each other in their chemical prop-
erties, and consequently in their combinations. This is much less
the case among the six metals (As, Sb, Sn, Au, Pt, Mo) which are
classed together in this group. In fact, the chief resemblance which
unites these metals is the insolubility of their sulphides in dilute
acids and the solubility of these sulphides in ammonium sulphide
(or alkali hydroxides), with which they form soluble double com-
pounds ; the oxides have also a tendency to form acids. In most
other respects no general resemblance exists between these metals.
On the other hand, arsenic and antimony have many properties in
common, and resemble in many respects the non-metallic elements
phosphorus and nitrogen, as may be shown by a comparison of their
hydrides, oxides, acids, and chlorides.

QUESTIONS. — How is silver obtained from the native ores, and how may it
be prepared from silver coin? State of silver nitrate: its composition, mode
of preparation, properties, and names by which it is known. Give analytical
reactions for silver. How is mercury found in nature ; how is it obtained from
the native ore ; what are its physical and chemical properties? Mention the
three oxides of mercury; how are they made, what is their composition, what
is their color and solubility ? State of the two chlorides of mercury : their
names, composition, mode of preparation, solubility, color, and other proper-
ties. Mention the same of the two iodides, as above, for the chlorides. State
the difference between mercuric sulphate, basic mercuric sulphate, and mer-
curous sulphate. What is formed when ammonium hydroxide, calcium hydrox-
ide, potassium or sodium hydroxide is added to either mercurous or mercuric
chloride ? Give tests answering for any mercury compound, and tests by which
mercuric compounds may be distinguished from mercurous compounds.

ARSENIC. 347

NH3 N203 NA NC13.

PH3 P20S PA H3P04 PC13.

AsH3 As2O3 As2O5 H3AsO4 AsCl3.

SbH. SbA Sb205 SbCl3.

Arsenic. Found in nature sometimes in the native state, but
generally as sulphide or arsenide. One of the most common arsenic
ores is the arsenio-sulphide of iron, or mispiekel, FeSAs. Realgar is
the native red sulphide, As2S2, and orpiment or aurijrigment, the native
yellow sulphide, As2S3. Arsenides of cobalt, nickel, and other metals
are not infrequently met with in nature. Certain mineral waters
contain traces of arsenic compounds.

Arsenic may be obtained easily by heating arsenous oxide with
charcoal, or by allowing vapors of arsenous oxide to pass over char-
coal heated to redness :

AsA + 3C = SCO + 2As.

In both cases the arsenic, when liberated by the reducing action of
the charcoal, exists in the form of vapor, which condenses in the
cooler part of the apparatus as a steel-gray metallic mass, which
when exposed to the amospheric air, loses the metallic lustre in conse-
quence of the formation of a film of oxide.

Experiment 47. Eub together in a mortar a small quantity of arsenous oxide
and about ten times as much charcoal. Heat the mixture in a covered porce-
lain crucible with a small flame. After a time examine the cover for a dark
deposit of arsenic.

When pure, arsenic is odorless and tasteless ; it is very brittle, and
volatilizes unchanged and without melting when heated to 180° C.
(356° F.), without access of air. Heated in air, it burns with a
bluish-white light, forming arsenous oxide. Although insoluble in
water, yet water digested with arsenic soon contains some arsenous
acid in solution, the oxide of arsenic being formed by oxidation of
the metal by the oxygen absorbed in the water.

Arsenic is used in the metallic state as fly-poison, and in some
alloys, chiefly in shot, an alloy of lead and arsenic.

The molecule of arsenic contains four atoms, and not two, like
most elements. It is trivalent in some compounds, quinquivalent in
others.

Although arsenic is grouped with the metals in the analytical system of
classification, in nearly all respects it behaves like a non-metal and should prop-
erly be classed as such. The oxides have only acidic character, and do not form
salts with acids, as nitrates, sulphates, etc. The chloride, AsCl3, can be obtained,

348 METALS AND THEIR COMBINATIONS.

but it decomposes at once in water, giving arsenous acid. It exists in solution
only in the presence of excess of hydrochloric acid. When the solution is
evaporated to dryness, arsenous oxide remains.

Arsenic trioxide, Arseni trioxidum, As2O3 = 196.44 (Arsenous
oxide. White arsenic, Arsenous anhydride, improperly Arsenous acid).
This compound is frequently obtained as a by-product in metallurgical
operations during the manufacture of metals from ores containing
arsenic Such ores are roasted (heated in a current of air), when
arsenic is converted into arsenous oxide, which, at that temperature.
is volatilized and afterward condensed in chambers or long flues.

Arsenous oxide is a heavy, white solid, occurring either as an
opaque, slightly crystalline powder, or in transparent or semi-trans-
parent masses which frequently show a stratified appearance;
recently sublimed arsenous oxide exists as the amorphous semi-
transparent glassy mass known as vitreous arsenous oxide, which
gradually becomes opaque and ultimately resembles porcelain. This
change is due to a rearrangement of the molecules into crystals which
can be seen under the microscope.

The two modifications of arsenous oxide differ in their solubility
in water, the amorphous or glassy variety dissolving more freely than
the crystallized. One part of arsenous oxide dissolves in from 30 to
80 parts of cold and in 15 parts of boiling water, the solution having
at first a faint acrid and metallic, and afterward a sweetish taste.
This solution contains the arsenous oxide not as such, but as arsenous
add, H3AsO3, which compound, however, cannot be obtained in an
isolated condition, but is known in solution only :

3H20 = 2H3As03.

A second arsenous acid, termed met-arsenous acid or meta-arsenous acid,
s02, is known in some salts, as, for instance, in sodium metarsenite, NaAsO*
which salt may be obtained by the action of arsenous oxide on the carbonate,
bicarbonate, or hydroxide of sodium :

As203 + 2NaOH = 2NaAsO2 + H2O.

When heated to about 218° C. (424° F.) arsenous oxide is volatil-
ized without melting; the vapors, when condensed, form small,
shining^ eight-sided crystals; when heated on charcoal, it is deoxi-
dized, giving off, at the same time, an odor resembling that of garlic.

Arsenous oxide is frequently used in the arts and for manufacturing
purposes, as, for instance, in the manufacture of green colors, of
opaque white glass, in calico-printing, as a powerful antiseptic for
the preservation of organic objects of natural history, and, finally, as
the substance from which all arsenic compounds are obtained.

ARSENIC. 349

The official Solution of arsenous acid, Liquor acidi arxcnosi, is a

1 per cent, solution of arsenous oxide in water to which 5 per cent,
of diluted hydrochloric acid has been added.

The official Solution of potassium arsenite, Liquor potassii arsenitis, or
Fowler's solution, is made by dissolving 1 part of arsenous oxide and

2 parts of potassium bicarbonate in 94 parts of water and adding

3 parts of compound tincture of lavender ; the solution contains the
arsenic as potassium met-arsenite.

Arsenic oxide, As2O5 (Arsenic pentoxide, Arsenic acid anhydride).
When arsenous oxide is heated with nitric acid, it becomes oxidized
and is converted into arsenic acid, H3AsO4, from which the water
may be expelled by further heating, when arsenic oxide is left :
2H3AsO4 = As2O5 + 3H2O.

Arsenic oxide is a heavy, white, solid substance which, in contact
with water, is converted into arsenic acid. This acid resembles phos-
phoric acid in composition, but diifers from it in not forming pyro-
and metarsenic acids. Arsenic acid when moderately heated loses all
its water and leaves the pentoxide, which at higher heat is decom-
posed into the trioxide and oxygen. Phosphoric acid, however, when
heated is converted into metaphosphoric which can be volatilized,
and phosphorus pentoxide does not decompose by heating. Sodium
pyroarsenate, perhaps, is formed when sodium arsenate is heated,
but when the mass is dissolved in water arsenate is formed at once,
whereas the pyrophosphate can be crystallized from water.

Arsenic oxide and arsenic acid are used largely as oxidizing agents
in the manufacture of aniline colors.

Disodium hydrogen arsenate, Sodii arsenas, Na2HAsO4.7H2O
= 3O9.84 (Sodium arsenate). This salt is made by fusing arsenous
oxide with carbonate and nitrate of sodium.

As2O3 -f 2NaNO3 + Na2CO3 = Na4As2O7 + N2O3 + CO,.

Sodium pyroarsenate is formed, nitrogen trioxide and carbon dioxide
escaping. By dissolving in water and crystallizing, the official salt is
obtained in colorless, transparent crystals :

Na4As207 -f 15H2O = 2(Na2HAsO4.7H2O).

Exsiccated sodium arsenate, Sodii arsenas exsiceatus, Na2HAsO4, is
the product obtained by driving off all the water of crystallization at
150° C. (302° F.). Liquor sodii arsenatis is a 1 per cent, solution of

350 METALS AND THEIR COMBINATIONS.

exsiccated sodium arsenate in water, corresponding to 1.68 per cent,
of the crystallized salt.

Lead arsenate, Pb3(AsO4)2, is used for spraying plants to exterminate
moths. It is a white, fusible powder, insoluble in water, ammonia, and ammo-
nium salts. It is obtained by precipitation of basic lead acetate (subacetate)
with sodium arsenate, or lead nitrate with excess of sodium arsenate :

3Pb(NO3)2 + 4Na2HAsO4 = Pb3(AsO4)2 -f 6NaNO3 + 2NaH2AsO4.

Hydrogen arsenide, AsH3 .(Arsine, Arsenetted or arseniuretted
hydrogen). This compound is formed always when either arsenous
or arsenic oxides or acids, or any of their salts, are brought in con-
tact with nascent hydrogen, for instance, with zinc and diluted
sulphuric acid, which evolve hydrogen :

As2O3 + 12H = 2AsH3 + 3H2O.
As-A + 16H = 2AsH3 + 5H2O.
AsCl3 + 6H = AsH3 + 3HC1.

Hydrogen arsenide is a colorless, highly poisonous gas, having a
strong garlic odor. Ignited, it burns with a bluish flame, giving off
white clouds of arsenous oxide :

2AsH3 + 6O = As2O3 + 3H2O.

When a cold plate (porcelain answers best) is held in the flame of
arsenetted hydrogen, a dark deposit of metallic arsenic (arsenic spots)
is produced upon the plate (in a similar manner as a deposit of
carbon is produced by a common luminous flame). The formation of
this metallic deposit may be explained by the fact that the heat of the
flame decomposes the gas, and that, furthermore, of the two liberated
elements, arsenic and hydrogen, the latter has the greater affinity for
oxygen. In the centre of the flame, to which but a limited amount
of oxygen penetrates, the latter is taken up by the hydrogen, arsenic
being present in the metallic state until it burns in the outer cone of
the flame. It is this liberated arsenic which is deposited upon a cold
substance held in the flame.

Arsenetted hydrogen, when heated to redness, is decomposed into
its elements ; by passing the gas through a glass tube heated to red-
ness, the liberated arsenic is deposited in the cooler part of the tube,
forming a bright metallic ring.

Sulphides of arsenic. Three sulphides of arsenic are known. Two
have been mentioned above as the native disulphide or realgar, As2S2,

ARSENIC. 351

and the bisulphide or orpiment, As2S3. Bisulphide of arsenic is an
orange-red, fusible, and volatile substance, used as a pigment; it
may be made by fusing together the elements in the proper propor-
tions. Trisulphide is a golden-yellow, fusible, and volatile substance,
which also may be obtained by fusing the elements, or by precipitating
an arsenic solution by hydrogen sulphide (Plate V., 1).

The pentasulphide, As2S5, has the same color as the trisulphide, and
is most readily obtained by acidifying a solution of a sulph-arsenate :

2(NH4)3AsS4 4- 6HC1 2H3AsS4 + 6NH4C1.

2H3AsS4 = 3H2S + As2S5.

The tri- and pentasulphide of arsenic have acid properties, similar to
the corresponding oxides. They unite with alkali sulphides to form
soluble meta-sulph-arsenites and sulph-arsenates :

As.2S3 + (NH4)2S = 2NH4AsS2.
As2S5 + 3(NH4)2S = • 2(NH4)3AsS4.

When the trisulphide is dissolved in a solution of a polysulphide
(yellow ammonium sulphide), a sulph-arsenate is formed,

As2S3 4- 3(NH4)2S 4- S, = 2(NH4)3AsS4,

from which acids precipitate the pentasulphide. Both sulphides are
also soluble in solutions of alkali hydroxides or carbonates, forming a
mixture of met-arsenite and meta-sulph-arsenite, and arsenate and
sulph-arsenate respectively.

Arsenous iodide, Arseni iodidum, AsI3 = 454.5 (Iodide of arsenic), may
be obtained by direct combination of the elements, and forms orange-red crys-
talline masses, soluble in water and alcohol, but decomposed by boiling with
either of these liquids. It is used in the official preparation, Solution of arsenous
and mercuric iodides, Donovan's solution, which is made by dissolving one part
each of arsenous iodide and mercuric iodide in 98 parts of water.

Tests for arsenic.

(For arsenous compound, use a solution of arsenous oxide made by dissolving 0.5
gramme in 100 c.c. of hot water and allowing to cool ; for arsenic compound, use a 5
per cent, solution of sodium arsenate.)

1. Hydrogen sulphide produces in the solution of arsenous acid a
yellowish coloration, but no precipitate. This is due to the fact that
the arsenic trisulphide remains in solution in the colloidal state and is
precipitated only after a long time. Addition of some hydrochloric
acid causes precipitation immediately of the yellow trisulphide (Plate

V, 1):

2H3AsO3 4- 3H8S ~ 6H.p 4- As2S3.

352 METALS AND THEIR COMBINATIONS.

When a rapid stream of hydrogen sulphide is passed into a hot acid-.
ified solution of an arsenate, a yellow precipitate of arsenic pentasul-
phide is gradually formed :

2H3AsO4 + 5H2S 8H2O + As2S5.

Solution of ammonium sulphide or caustic alkali readily dissolves
both sulphides of arsenic. Addition of acid reprecipitates the
sulphides.

2. Add 1 or 2 c.c. of silver nitrate solution to about 5 c.c. of the
arsenousacid solution ; no precipitate results. Now pour carefully upon
the surface of the mixture a little very dilute ammonia water ; a yellow
precipitate of silver arsenite (Plate V., 3) is formed at the line of con-
tact of the two liquids, which may be increased by cautiously mixing
the liquids. The precipitate is soluble in excess of ammonia or in
nitric acid. When solution of an arsenite instead of free arsenous
acid is used, silver nitrate gives a precipitate at once, without addition
of ammonia water :

H3As03 + 3AgN03 + 3NH4OH == Ag3AsO3 + 3NH4NO8 + 3H2O.

Na3AsO3 + 3AgNO3 == Ag3AsO3 + 3NaNO3.

Dissolve the precipitate in a slight excess of ammonia water, add a
few drops of caustic soda, and apply heat ; a mirror of metallic silver
is formed, due to the reducing action of the arsenite, which becomes
arsenate.

When silver nitrate is added to the sodium arsenate solution (about
3 c.c.), a reddish-brown precipitate of silver arsenate is formed, which
is soluble in ammonia water or nitric acid (Plate V., 4) :

Na2HAsO4 4- 3AgNO3 = Ag3AsO4 + 2NaNO3 + HNO3.

3. Add 2 or 3 drops (avoid excess) of copper sulphate solution to
about 5 c.c. of the arsenous acid, and overlay the mixture with very
dilute ammonia water as in test 2 (if an arsenite is used, ammonia
water is unnecessary) ; a green precipitate of copper arsenite, Scheele's
green, CuHAsO3, is produced (Plate V., 2). Add some caustic alkali
solution to the precipitate and boil ; red cuprous oxide is formed, due to
reduction by the arsenite, which becomes arsenate. (Schweinfurt green,
copper aceto-arsenite, 3Cu(AsO2)2.Cu(C2H3O2)2, is obtained by adding
solution of copper acetate to a boiling solution of an arsenite. This
and Scheele's green are often called Paris green.)

When copper sulphate solution is added to the sodium arsenate solu-
tion, a greenish-blue precipitate of copper arsenate, CuHAsO4, is

ARSENIC ANTIMONY, TIN.

PLATE V

Arscnous sulphide, precipitated fr<
arsenous solutions by hydrogen sulphii

Cupric arsenite, precipitated fr<
arsenous solutions by cupric-ammonh
sulphate.

Silver arsenite, precipitated frc
arsenous solutions by silver nitrate.

Silver arsenate, precipitated fro
arsenic solutions by silver nitrate.

Antimonous sulphide, precipital
from solutions of antimony by hydrog
sulphide.

Native or crystallized antimono
sulphide.

Stannous sulphide, precipitated frc
stannous solutions by hydrogen sulphic

Stannic sulphide, precipitated fn
stannic solutions by hydrogen sulphide.

Affoen & Co LiUi. Baltimore, .

ARSENIC. 353

formed. All these precipitates are soluble in ammonia water and in
acids.

4. Add to a little of the arsenate solution, a clear mixture of mag-
nesium sulphate, ammonium chloride and ammonia water, and shake ;
a white precipitate of ammonium magnesium arsenate is formed,
NH4MgAsO4 (see test 1 under phosphoric acid).

Magnesium arsenite is insoluble in water, but soluble in ammonia
water and in ammonium chloride solution.

5. Add to a few drops of the arsenate solution, excess of ammonium
molybdate solution (about 5 c.c.) and warm gently ; a* yellow precipi-
tate of ammonium arseno-molybdate is formed, similar in all respects
to the corresponding phosphorus compound. (Arsenic is the only
other element which behaves like phosphorus toward the molybdate
reagent.) Arsenites give no precipitate with the reagent.

6. Heat any dry arsenic compound, after being mixed with some
charcoal and dry potassium carbonate in a very narrow test-tube (or,
better, in a drawn-out glass tube having a small bulb on the end) : the
arsenic compound is decomposed and the element arsenic deposited
as a metallic ring in the upper part of the contraction. (Fig. 44.)

FIG. 44.

7. Heat arsenous or arsenic oxide upon a piece of charcoal by
means of a blow-pipe : a characteristic odor of garlic is percep-
tible.

8. Reimch's test. A thin piece of copper, having a bright metallic
surface, placed in a solution of arsenic, strongly acidified with con-
centrated hydrochloric acid, becomes, upon heating the solution, coated

23

354 METALS AND THEIR COMBINATIONS.

with a dark steel-gray deposit of arsenic, which can be vaporized by
application of heat. Antimony also responds to this test.

9. Bettendorf's test, U. S. P. Add to any arsenic compound, dis-
FIG 45 solved in concentrated hydrochloric acid, an equal vol-
ume of freshly prepared saturated solution of stannous
chloride in concentrated hydrochloric acid, and heat in
boiling water for 15 minutes ; a brown color or precipi-
tate is formed, due to separation of the arsenic. Anti-
mony does not respond to this test.

10. Gutzeit's test. Place a small piece (about 1
gramme) of pure zinc in a test-tube, add about 5 c.c.
of dilute (5 per cent.) sulphuric acid and a few drops
of any arsenic solution, which should not be alkaline.
Fasten over the mouth of the test-tube a cap made of
three thicknesses of pure filter-paper, and moisten the
upper paper with a drop of a saturated solution of
silver nitrate in water acidulated with about 1 per
cent, of nitric acid. (Fig. 45.) Place the tube in a
box so as to exclude all light, and examine the paper
cap after awhile. Upon it will appear a bright-yellow
stain, rapidly if the quantity of arsenic be considerable,
slowly if it be small. Upon moistening the yellow
stain with water the color changes to brown or black.
The action of hydrogen arsenide upon silver nitrate in
the absence of water takes place with the formation of a yellow com-
pound, thus :

AsH3 + 6AgNO3 = 3HNO, -f Ag3As.(AgNO3)3.

In the presence of water metallic silver is separated, showing a
black or brown color :

AsH3 + 6AgN03 + 3H20 =-- 6HNO, + H3AsO3 + 6Ag.

Compounds of antimony treated in the above manner produce a
dark spot upon the paper, but cause no previous yellow color.

Modified Gutzeit's test, U. S. P. This is employed in nearly all
instances in the U. S. P. where traces of arsenic are tested for in official
products. It cannot be used in the case of bismuth or antimony
compounds, for which Bettendorf's test is employed. The test is
carried out as follows :

All the tests for arsenic bearing proper names are intended to be
applied for the detection of minute quantities of arsenic. If arsenic

ARSENIC. 355

compounds themselves are used, only very dilute solutions should be
tested, in order to appreciate the delicacy of the tests. The arsenic
should be in the form of an arsenows compound for the above test, as
in this condition it is more readily reduced to arsine. This is insured
by adding to 5 c.c. of a 10 per cent, aqueous solution of the chemical
to be tested (in some instances special previous treatment is neces-
sary, which may be seen in the U. S. P.) 1 c.c. of a mixture of equal
volumes of concentrated sulphuric acid and water, and 10 c.c. of
fresh saturated solution of sulphur dioxide. The liquid is evaporated
over boiling water until it is free from sulphur dioxide and has been
reduced to 5 c.c. in volume. It is then introduced into a 75 c.c. flask
containing 2 or 3 grammes of granular zinc and 20 c.c. of 8 per cent,
hydrochloric acid, a small wad of clean dry gauze is inserted into the
lower end of the neck of the flask, followed by a wad moistened with
lead acetate solution. The mouth of the flask is then covered by
folding over it a filter-paper, the center of which has previously been
three times successively wet with a saturated alcoholic solution of
mercuric chloride and dried. After one-half to one hour, the paper cap
is examined for a yellow stain, which indicates arsenic. The presence
of arsenic much in excess of the permissible limit of the U. S. P.
(1 in 100,000) is shown by a distinct yellow to orange spot. All the
reagents used must be free from arsenic, which is determined by
making a blank test, omitting the chemical to be tested. The stu-
dent should carry out the test on 2 or 3 c.c. of a -§\-$ per cent, solu-
tion of arsenic trioxide, which need not be submitted to the reduc-
tion with sulphur dioxide. Antimony gives a dark coloration.

11. Fleitmann's test. This is similar to the Gutzeit's test, the
chief difference being that hydrogen is evolved in alkaline solution,
which has the advantage that the presence of antimony does not
interfere, because this metal does not form antimonetted hydrogen in
alkaline solutions.

Place about 1 gramme of pure zinc in a test-tube, add about 5 c.c.
of potassium hydroxide solution and a few drops of the arsenic solu-
tion, which should not be acid. Provide paper cap as described in
Gutzeit's test, and set the test-tube in a box containing sand heated
to about 90° C. (194° F.). A brown or black stain of metallic silver
will appear upon the paper.

12. Marsh's test. While this test is not used now for qualitative
determinations as much as formerly, it is of great value because it
may serve for collecting the total amount of arsenic present in a
specimen, thus permitting quantitative estimation. The apparatus

356 METALS AND THEIR COMBINATIONS.

(Fig. 46) used for performing this test consists of a glass vessel (flask
or WoulPs bottle) provided with a funnel-tube and delivery-tube
(bent at right angles), which is connected with a wider tube, filled
with pieces of calcium chloride or plugs of asbestos; this drying-tube
is again connected with a piece of hard glass tube, about one foot
long, having a diameter of J inch, drawn out at intervals of about
3 inches, so as to reduce its diameter to J inch. Hydrogen is gener-
ated in the flask by the action of sulphuric acid on zinc, and ex-
amined for its purity by heating the glass tube to redness at one of
its wide parts for at least 30 minutes ; if no trace of a metallic mirror
is formed at the constriction beyond the heated point, the gas and the
substances used for its generation may be pronounced free from
arsenic. (Both zinc and sulphuric acid often contain arsenic.)

FIG. 46.

lllillllillllllllMIMII1!linil1lll1tl)l1limnilinnitiiMiiiiitiiiiimni»

uliliililiilllillllillliilllllllllM

Marsh's apparatus for detection of arsenic.

After having thus demonstrated the purity of the hydrogen, the

uspected liquid, which must contain the arsenic either as oxide or

chlonde (not as sulphide), is poured into the flask through the funnel-

If arsenic is present in not too small quantities, the gas ignited

the end of the glass tube shows a flame decidedly different from

tiiut ot Durnino* hvdroo'pn TM fl K i

appt^whichfs'ml^ " f °Pf ^^^it a wSdteud

ovpr tli fl °r SS se > a c°ld test-tube held inverted

lame will be covered upon its walls with a white deposit of
ctahedral crystals of n,senous oxide. a piece rf coIdPporce.

coated with a brown stain (arsenic
above in connection with

ARSENIC.

357

>

The glass tube heated, as above mentioned, at one of its wide parts,
will show a bluish-black metallic mirror at the constriction beyond.

If quantitative determination is desired, the glass tube is heated in two
places so as to cause all hydrogen arsenide to be decomposed. To collect,
however, the arsenic from any gas that might escape, the end of the tube
is inverted and placed into solution of nitrate of silver, which is decomposed
by the hydrogen arsenide, silver and arsenous acid being formed. The arsenic
solution should be introduced into the hydrogen generator in small portions,
so as not to produce more hydrogen arsenide at a time than can be decom-
posed by the method given.

The only element which, under the same conditions, forms spots and mirrors
similar to arsenic, is antimony ; there are, however, sufficiently reliable tests
to distinguish arsenic spots from those of antimony.

Arsenic spots treated with solution of hypochlorites (solution of bleaching-
powder) dissolve readily ; antimony spots are not affected. When nitric acid
is added to an arsenic spot and evaporated to dryness and the spot moistened
with a drop of silver nitrate, it turns brick-red ; antimony spots treated in like
manner remain white. Arsenic spots dissolved in ammonium sulphide and
evaporated to dryness show a bright-yellow, antimony spots an orange-red,
residue. Fig. 47 represents a simpler form of Marsh's appara-
tus, which generally will answer for students' tests.

Preparatory treatment of organic matter for arsenic
analysis. If organic matter is to be examined for arsenic
(or for any other metallic poison), it ought to be treated as
follows : The substance, if not liquid, is cut into pieces, well
mashed and mixed with water; the liquid or semi-liquid sub-
stance is heated in a porcelain dish over a steam bath with
hydrochloric acid and potassium chlorate until the mass has a
uniform light yellow color and has no longer the odor of
chlorine. By this operation all poisonous metals (lead and
silver excepted, because insoluble silver chloride and possibly
insoluble lead sulphate are formed) are rendered soluble evgn
when present as sulphides, and may now be separated by filtra-
tion from the remaining solid matter The clear solution is
heated and treated with hydrogen sulphide gas for several
hours, when arsenic and all metals of the arsenic and lead
groups are precipitated as sulphides, a little organic matter
also being precipitated generally.

The precipitate is collected upon a small filter and treated with warm ammo-
nium sulphide, which dissolves the sulphides of arsenic and antimony, leaving
behind the sulphides of the lead group, which may be dissolved in nitric, or, if
mercury be present, in nitro-hydrochloric acid, and the solution tested by the
methods mentioned for the respective metals. The ammonium sulphide solu-
tion is evaporated to dryness, this residue mixed with nitrate and carbonate of
sodium, and the mixture fused in a small porcelain crucible. By the oxidizing
action of the nitrate, both sulphides are converted into the higher oxides,
arsenic forming sodium arsenate, antimony forming antimonic oxide. By
treating the mass with warm water, sodium arsenate is dissolved and may be

358 METALS AND THEIR COMBINATIONS,

filtered off, while antimonic oxide remains undissolved, and may be dissolved in
hydrochloric acid. Both solutions may now be used for making the respective
tests for arsenic or antimony.

Comments. Tests 1, 6, and 3 are sufficient to identify arsenic compounds.
Test 3 will detect an arsenite in presence of an arsenate, and tests 4 and 5 an
arsenate in presence of an arsenite. Test 10, especially in the modified form,
and Test 12 are most often used to detect traces of arsenic.

Alkali arsenites are soluble in water; all others are either insoluble or diffi-
cultly soluble in water. Alkali arsenates and acid arsenates of the alkaline
earths are soluble in water. All the salts are soluble in mineral acids.

Arsenous acid dissociates very slightly, and is therefore a weak acid. Its
soluble salts are hydrolyzed to a considerable extent, and show an alkaline
reaction. Boiling a solution of arsenous acid or its salts in hydrochloric acid
results in a loss of arsenic by volatilization as arsenous chloride. Solutions
of arsenic acid or its salts suffer no loss of arsenic in this manner.

Arsenic acid dissociates very much like phosphoric acid, but to a little less
extent than the latter in solutions of equal concentration. Even in high dilu-
tion the dissociation is mainly thus :

H3AsO4 ^ H- -f H2AsO4'.
Further dissociation into HAsO/' and AsO/" ions is very slight.

Antidotes. Moist, recently prepared ferric hydroxide or dialyzed iron are
the best antidotes. Vomiting should be induced by tickling the fauces or by
administering zinc sulphate, but not tarter emetic.

33. ANTIMONY— TIN-GOLD— PLATINUM— MOLYBDENUM.

Antimony, Sb : = 119.3 (Stibium). This metal is found in nature
chiefly as the trisulphide, Sb2S3, an ore which is known as black anti-
mony, crude antimony, or stibnite.

The metal is obtained from the sulphide by roasting, when it is
converted into oxide, which is reduced by charcoal. Antimony is a
brittle, bluish-white metal, having a crystalline structure ; it fuses at

QUESTIONS.— Which metals belong to the arsenic group ; what are their
characteristics? Which non-metallic elements does arsenic resemble? Men-
tion some of the compounds showing this analogy. How is arsenic obtained
in the free state; what are its physical and chemical properties; how does
leat act upon it? What is white arsenic? State its composition, mode of
manufacture, appearance, solubility, and other properties. Which three solu-
ns, containing arsenic, are official, and what is their composition ? How is
3 acid obtained from arsenous oxide, and which arsenate is official?
composition and properties of arsenetted hydrogen, and explain its for-
mation. What use is made of it in testing for arsenic ? State the composition
realgar, orpiment, Scheele's green, and Schweinfurth green. Give a detailed
tion of the process by which arsenic can be detected in organic matter.
Describe in detail the principal tests for arsenic.

ANTIMONY. 359

450° C. (842° F.), and may at a higher temperature be distilled without
change, provided air is excluded ; heated in air it burns brilliantly.

Antimony is used in a number of important alloys, for instance, in
type-metal, an alloy of lead, tin, and antimony.

The best solvent for antimony is hydrochloric acid, containing a
little nitric acid, whereby antimonous or antimonic chloride is
formed. Nitric acid converts it into antimonous or antimonic oxide,
which are almost insoluble in the liquid.

Three oxides of antimony are known, namely, trioxide, Sb2O3,
pentoxide, Sb2O5, and tetroxide, Sb2O4. Antimony differs from
arsenic in that the trioxide is more basic than acidic, forming salts
with mineral and organic acids. The salts with mineral acids, how-
ever, are decomposed by water, and require the presence of free acid
for solution. Antimony pentoxide is exclusively acidic in character,
forming met-antimonates and pyro-antimonates with caustic alkalies.
The tetroxide is neither basic nor acidic. It is formed when either
of the other oxides is heated in air to a dull redness for a long time.

The compounds of antimony commonly met with are the chloride,
sulphide, and double tartrate (tartar emetic).

Antimony trisulphide, Sb2S3 (Antimonous sulphide). The above-
mentioned native sulphide, the black antimony, is found generally
associated with other ores or minerals, from which it is freed by heat-
ing the masses, when the antimony sulphide fuses and is made to run
off into suitable vessels for cooling. Thus obtained it forms steel-
gray masses of a metallic lustre, and a striated, crystalline fracture,
forming a grayish-black, lustreless powder, which is insoluble in
water, but soluble in hydrochloric acid with liberation of hydrogen
sulphide.

Antimonous sulphide found in nature is crystallized and steel-gray
(Plate V., 6), but it may be obtained also in an amorphous condition
as an orange-red (Plate V., 5) powder by passing hydrogen sulphide
through an antimouous solution. By heating the orange-red sul-
phide, it is converted into the black variety.

The sulphides and oxides of antimony, like those of arsenic, combine with
many metallic sulphides or oxides to form sulpho-salts or oxy-salts. Thus the
sodium sulph-antimonite, Na3SbS3, and the sodium antimonite, NaSb02, are
formed when antimonous sulphide is boiled with sodium hydroxide.

Sb2S3 + 4NaOII = Na3SbS3 + NaSbO, + 2H2O.

By the addition of sulphuric acid, both salts are decomposed, sodium sulphate
is formed, and antimonous sulphide is precipitated :

Na3SbS3 + NaSbO2 + 2H2SO4 = Sb2S3 + 2Na2SO4 + 2H2O.

360 METALS AND THEIR COMBINATIONS.

While the above is the principal reaction, there is formed also some anti-
mony oxide.

Experiment 48. Intimately mix about 0.5 gramme of finely powdered black
antimony sulphide with some sodium carbonate and potassium cyanide.
Heat this mixture with a blowpipe flame on charcoal till it fuses thoroughly
and a bead of metallic antimony is obtained. Drop the molten antimony
from the height of about a foot upon a sheet of paper and notice that
characteristic grayish-white streaks are formed, radiating in all directions.
Test the crust (left on the charcoal) on a silver coin for sulphur. Examine
another bead of antimony for cplor, hardness, malleability, etc. ; then try its
solubility in acids in the order of hydrochloric, dilute sulphuric, nitric, and
nitre-hydrochloric acids.

Antimony pentasulphide, Sb2S5 (Golden sulphur et of antimony).
A red powder, which, like antimonotis sulphide, forms sulpho-salts.
It may be obtained by precipitation of acid solutions of antimonic
acid by hydrogen sulphide.

Antimonous chloride, SbCl3 (Antimony terchloride, Butter of anti-
mony). Obtained by boiling the native sulphide with hydrochloric
acid:

Sb2S3 4- 6HC1 = 3H2S 4- 2SbCl3.

The clear solution is evaporated and the remaining chloride dis-
tilled, when it is obtained as a white, crystalline, semi-transparent
mass.

By passing chlorine over antimonous chloride it is converted into
antimonic chloride, SbCl5, which is a fuming liquid.

Experiment 49. Boil about 2 grammes of black antimony with 10 c. c. of
hydrochloric acid until most of the sulphide is dissolved. Set aside for sub-
sidence, pour off the clear solution of antimonous chloride, evaporate to about
half its volume and use solution for next experiment.

Antimonous oxide (Antimony trioxide). When antimonous chlo-
ride is added to water decomposition takes place similar to the one
which normal bismuth salts undergo by the action of water, viz., a
white precipitate of oxy-chloride of antimony (antimonyl chloride),
BbOCl, is formed, which, however, is mixed with antimonous oxide,
as the following two reactions take place :

SbCl3 + H2O = SbOCl 4- 2HC1.
2SbCl3 4- 3H20 = Sb203 4- 6HC1.

The relative proportions of the two constituents depend on the
mode of manipulating and on the quantity of water used.

The white precipitate was formerly known as powder of Algaroth.

ANTIMONY. 361

It is completely converted into oxide by treating it with sodium car-
bonate :

2SbOCl + Na2CO3 = Sb,O3 -f 2NaCl + CO2.

The precipitate when washed and dried is a heavy, grayish-white,
tasteless powder, insoluble in water, soluble in hydrochloric acid, and
also in a warm solution of tartaric acid. Antimonous oxide, while
yet moist, dissolves readily in potassium acid tartrate, forming the
double tartrate of potassium and antimony, or tartar emetic, which salt
will be more fully considered hereafter.

Experiment 50. Pour the antimonous chloride solution (obtained by Ex-
periment 49), which should have been boiled sufficiently to expel all hydrogen
sulphide, into 100 c.c. of water, wash by decantation the white precipitate of
oxychloride thus obtained, and add to it an aqueous solution of about 1 gramme
of sodium carbonate. After effervescence ceases, collect the precipitate on a
filter, wash well and treat some of the precipitate, while yet moist, with a solu-
tion of potassium acid tartrate, which dissolves it readily, forming tartar emetic.
(For the latter compound see index.)

Antidotes. Poisonous doses of any preparation of antimony are generally
quickly followed by vomiting : if this, however, have not occurred, the stomach-
pump must be applied. Tannic acid in any form, or recently precipitated ferric
hydroxide, should be administered.

Tests for antimony.

(Use a solution of antimony chloride prepared as in Experiment 49, and diluted to
about 30 c.c. by adding, first, 2 or 3 c.c. of dilute hydrochloric acid, and then water
cautiously. Also a 5 percent, solution of tartar emetic, K(SbO)C4H4O6, in water.
Note that the latter dissolves easily and without decomposition.)

1. Add hydrogen sulphide to some of the solution of antimony
chloride : an orange-red precipitate of antimonons sulphide (Sb2S3) is
produced (Plate V., 5).

Hydrogen sulphide produces the same precipitate in the solution of
tartar emetic.

2. Add yellow ammonium sulphide to the precipitated sulphide of
antimony : this is dissolved and may be reprecipitated by neutralizing
with an acid. The same results are obtained with caustic alkalies.

3. Produce a concentrated solution of antimonous chloride by
evaporation or by dissolving the sulphide in hydrochloric acid, and
pour it into water : a white precipitate of oxychloride is formed. (See
explanation above.)

Add a few drops of dilute hydrochloric acid to some of the solution
of tartar emetic : a white precipitate of oxychloride is also formed. In
analysis, this might be mistaken for a chloride of silver, lead, or mer-
cury, but it differs from the latter by being soluble in excess of the acid.

362 METALS AND THEIR COMBINATIONS.

4. Add sodium hydroxide, ammonium hydroxide, or sodium car-
bonate to the antimony chloride solution : in either case white anti-
moDOus hydroxide, Sb(OH)3, is produced, which is soluble in excess
of sodium hydroxide.

The same reagents added to the solution of tartar emetic produce
scarcely any precipitate, due to the solvent effect of the organic (tartaric)
acid.

5. Boil a piece of bright metallic copper in the solution of anti-
monous chloride : a black deposit of antimony is formed upon the cop-
per. By heating the latter in a narrow test-tube, the antimony is volatil-
ized and deposited as a white incrustation of antimonous oxide upon
the glass.

6. Use Gutzeit's or Marsh's test as described under tests for arsenic.

Tin, Sn = 118.8 (8tannum). This metal is found in nature chiefly
as stannic oxide or tin-stone, SnO2, from which the metal is easily
obtained by heating with coal :

Sn02 + 20 = Sn + 2CO.

Tin is an almost silver-white, very malleable metal, fusing at the
comparatively low temperature of 228° C. (440° F.). It is used in
many alloys, and chiefly in the manufacture of tin-plate, which is
sheet-iron covered with a thin layer of tin.

Tin is bivalent in some compounds, quadrivalent in others. These
combinations are distinguished as stanuous and stannic compounds.

Stannous hydroxide, Sn(OH)2, is not known. When a solution of
sodium hydroxide or carbonate is added to a solution of stannous
chloride, a precipitate, H2Sn2O3, is formed, which is derived from
Sn(OH)2. When it is heated in an atmosphere of carbon dioxide,
black stannous oxide, SnO, is formed, which ignites when heated in
air, giving stannic oxide.

Stannic hydroxide (Stannic acid), H2SnO3, is formed when a solu-
tion of stannic chloride is boiled :

SnCl4 + 3H20 = H2Sn03 + 4HC1.

It is also formed when sodium hydroxide or carbonate is added to a
solution of stannic chloride, or when just enough of an acid is added
to a solution of a stannate to effect decomposition :

Na2Sn03 + 2HC1 = 2NaCl + H2Sn03.

It is a white substance insoluble in water, but easily soluble in
hydrochloric, nitric, or sulphuric acid, forming the corresponding salt,
and in caustic alkalies, forming stannates.

TIN. 363

Metastannic acid is formed when tin is treated with concentrated
nitric acid. It is a white powder insoluble in water and acids, hut
seems to have the same composition as stannic acid. It forms salts
with alkalies which are entirely different in properties and composition
from the stannates, and are known as meta stannates. Two sodium salts
are known, Na.^Sn^Oj! and Na2Sn9O19. When the acid is heated,
stannic oxide, SnO2, is formed.

Stannous chloride, SnCl2 (Protochloride of tin). Obtained by
dissolving tin in hydrochloric acid by the aid of heat :
Sn + 2HC1 = SnCl2 + 2H.

Sufficiently evaporated, the solution yields crystals of the composi-
tion SnCl2.2H2O. Stannous chloride is a strong deoxidizing agent,
frequently used as a reagent for arsenic, mercury, and gold, which
metals are precipitated from their solutions in the metallic state. It
is used also in calico printing.

Stannic chloride, SnCl4 (Perchloride of tin). Stannous chloride
may be converted into stannic chloride either by passing chlorine
through its solution or by heating with hydrochloric and nitric acids.

Tests for tin.
(Stannous chloride, SnCl.2, and stannic chloride, SnCl4, may be used.)

1 . Add hydrogen sulphide to solution of a stannous salt : brown
stannous sulphide is precipitated (Plate V., 7) :

SnCl2 + -H2S 2HC1 + SnS.

The precipitate is soluble in yellow ammonium sulphide.

2. Add hydrogen sulphide to a solution of a stannic salt : yellow
stannic sulphide is precipitated (Plate V., 8) :

SnCl4 + 4H2S = 4HC1 -f SnS2.

The precipitate is soluble in ammonium sulphide.

3. Sodium or potassium hydroxide added to a stannous salt pro-
duces a white precipitate of stannous hydroxide, Sn(OH)2. The same
reagents added to a stannic salt produce white stannic acid, H2SnO3.
Both precipitates are soluble in excess of the alkali, forming stannite,
Na2SnO2, and stannate, Na2SnO3.

Gold, Au = 195.7 (Aurum). Gold occurs in nature chiefly in the
free state, generally associated with silver, copper, and possibly with

364 METALS AND THP:1R COMBINATIONS.

other metals, sometimes also in combination with selenium and tellu-
rium. This impure gold is separated from most of the adhering
sand and rock by a mechanical process of washing, in which advan-
tage is taken of the high specific gravity of the metallic masses. The
remaining mixture of heavy material is treated with mercury, which
dissolves gold and silver, leaving behind most other impurities. The
gold amalgam is placed in a retort and heated, when the mercury
distils over, while the gold is left behind.

From ores containing but little gold the metal is now extracted
largely by treating the finely powdered material with a solution of
potassium cyanide, which forms a soluble double cyanide of gold and
potassium, AuK(CN)2. From the solution gold is precipitated elec-
trolytically or by adding metallic zinc.

Refining gold. Gold obtained by either of the above processes is not pure,
but has to be purified or refined by methods which differ according to the nature
or quantity of the impurities present, or according to the use to be made of the
gold. The methods employed may be divided into two classes, viz., dry and
wet processes. In the dry or crucible methods the operation is conducted at a
temperature sufficiently high to melt the gold, while in the wet processes the
dissolving action of acids is made use of.

Of dry methods may be mentioned the following : The gold is fused in a
clay or graphite crucible which has been glazed on the inside with borax, and
a stream of chlorine is passed through the molten mass. The chlorides of zinc,
bismuth, arsenic, and antimony, when present, are volatilized, while the chlo-
rides of silver and copper rise to the top, forming, with some of the borax, a
layer over the purified gold. Another method consists in melting the gold in
a crucible, prepared as before mentioned, and adding gradually a mixture of
potassium nitrate and carbonate with borax. All base metals are converted
into oxides which become dissolved in the borax; but silver is not eliminated
by this method. It may, however, be gotten rid of by heating to a temperature
just below fusion, the granulated gold with about one-sixth of its weight of
sulphur. The mixture should be protected with a layer of fine charcoal.
Silver sulphide is formed during the operation and the gold, after being fused,
may be cast into an ingot mold.

Another dry method, used, however, more for assaying gold ores or gold alloys
than for purifying gold on a large scale, is the cupellation process. It depends
on the solubility of gold in molten lead and the readiness with which lead takes
up oxygen when heated in an oxidizing flame. In carrying out the process the
material to be operated on is fused with a quantity of lead amply sufficient to
dissolve the metals present. The resulting alloy, called the lead button, is then
submitted to fusion on a very porous support, made of bone-ash, and called a
cupel. All metals except gold and silver are oxidized ; the lead oxide, which is
fusible, takes up all other oxides, and the whole of this mass is absorbed by the
porous bone-ash, on the surf ace of which is finally left a button of gold and silver.

Of wet processes for the separation of gold and silver is to be mentioned the
method known as parting. It depends on the extraction of the silver (and cop-

GOLD. 365

per, if present) by treating the granulated alloy with nitric acid of a specific
gravity of 1.32. This dissolves silver and copper, but does not act on the gold.
The process, however, is not applicable to an alloy containing more than 33
per cent, of gold, and it was believed that it should not exceed 25 per cent.
In order to subject to this process an alloy which is richer in gold, the alloy is
first fused with silver, and as it was customary to use 3 parts of silver for 1 part
of impure gold the process became known as quartation or inquartation. In
place of nitric acid, sulphuric acid of a specific gravity of 1.84 may be used. Gold
which has been freed from base metals and silver by any of the above-described
methods is known as refined gold, but it is rarely absolutely pure. It retains
traces of base metals or silver and all of the platinum if originally present.

Chemically pure gold, or as it is termed by the mints gold 1000 fine, may be
obtained by the following process. Nitro-hydrochloric acid, consisting of one
part of nitric acid and two parts of hydrochloric acid, is added in small por-
tions to the granulated gold, refined by one of the ordinary processes, until its
solution, with the aid of heat, has been effected. This solution of gold chloride
is evaporated nearly to dryness at a moderate heat. If platinum be suspected
the remaining mass is dissolved in very little water, and to the solution is added
an equal volume of alcohol and some ammonium chloride. If platinum be
present it is precipitated as ammonium platinic chloride and separated by fil-
tration. The filtrate is diluted with four parts of water and permitted to stand
for several days in order to cause complete precipitation of any silver chloride
present. To the filtrate a clear solution of ferrous sulphate is added which
causes the precipitation of gold. After decanting the supernatant liquid and
thoroughly washing the precipitate with distilled water it is treated with hot
concentrated acid, to eliminate traces of iron or copper. The purified gold is
again washed, dried, fused in a borax-lined crucible and poured into an ingot
mold. The chemical reaction which occurs in the precipitation of gold with
ferrous sulphate is this :

AuCl3 + 3FeS04 = FeCl3 + Fe2(SO4)3 + Au.

Many other reducing agents may be used in place of ferrous sulphate for
the precipitation of gold. Thus it is precipitated in a spongy or crystalline
condition by gently heating the gold solution with oxalic acid:
2AuCl3 + 3H2C2O4 = 6HC1 + 6CO2 + 2Au.

Sulphurous acid precipitates gold in scales:

2AuCl3 -f- 3H,SO3 + 3H20 = 6HC1 + 3H2SO4 + 2Au.
Zinc and many other base metals precipitate gold as a brown powder:
2AuCl3 -f 3Zn = 3ZnCl2 + 2Au.

Elementary phosphorus, and many other organic and inorganic reducing
agents, may be used similarly for the precipitation of gold from its solutions,
or this precipitation may be effected electrolytically.

Cohesive gold, used in dentistry, may be obtained by heating gold foil to
redness, by which is restored its cohesiveness, which is greatly diminished
during the conversion of pieces of gold into foil by beating.

Gold is orange-yellow by reflected light, and green by transmitted
light ; it fuses at 1200° C. (2192° F.), has a specific gravity of 19.36,

366 METALS AND THEIR COMBINATIONS.

and is a good conductor of heat and electricity. It is so malleable and
ductile that 1 grain can be hammered into a film covering 54 square
inches, and can be drawn into a wire, if protected by some more tena-
cious metal such as silver, so fine that 1 grain will measure 550 feet.
Tin, lead, antimony, arsenic, and bismuth destroy the ductility and malle-
ability of gold, making it very brittle. A small proportion of platinum con-
fers upon gold elasticity and increases its hardness.

Pure gold is too soft for general use, and therefore is alloyed with
various proportions of silver and copper. It is customary to express
the purity or fineness of gold in carats, an old term meaning a
twenty-fourth part. Pure gold is 24 carats, while an alloy contain-
ing 75 per cent, of gold is said to be of 18 carats fineness. Ameri-
can coin is an alloy of 90 parts of gold and 10 parts of copper ;
jeweller's gold contains generally 75 per cent, or more of gold, the
other metals being copper and silver ; the varying proportions are
well indicated by the color.

Gold is not affected by either hydrochloric, nitric, or sulphuric
acid, but is dissolved by nitro-hydrochloric acid, by free chlorine and
bromine, and by mercury, with which it forms an amalgam.

Gold is trivalent generally, as in auric chloride, AuCl3, but also
univalent in some compounds, as in aurous chloride, AuCl.

Gold chloride, Au013 (Auric chloride). Obtained by dissolving
pure gold in nitro-hydrochloric acid and evaporating the solution to
dryness. A mixture of equal parts by weight of gold chloride and
sodium chloride is official under the name of gold and sodium chloride.
It is an orange-yellow, very soluble powder, containing about 30 per
cent, of metallic gold.

Tests for gold.
(Solution of auric chloride, AuCl3, may be used.)

1. Add hydrogen sulphide to the solution : brown auric sulphide,
Au2S3, is precipitated, which is soluble in yellow ammonium sulphide.

2. Add ferrous sulphate to the solution and set aside for a few
hours— metallic gold is precipitated as a dark powder :

AuCl3 + 3FeS04 = Fe,(S04)s -f FeCl3 + AU.

3. Many other reagents cause the separation of metallic gold from
its solution, as, for instance, oxalic acid, sulphurous and arsenous
acids, potassium nitrite, etc.

PLATINUM. 367

Platinum, Pt =193.3. Platinum, like gold, is found in nature in
the free state, the chief supply being derived from the Ural mountains,
where it is associated with a number of metals (iridium, ruthenium,
osmium, palladium, rhodium) resembling platinum in their properties.

While the solubility of platinum in molten lead is sometimes used for its
separation by the cupellation process (see refining of gold) the abstraction of
platinum is usually accomplished by the wet process. The material contain-
ing it is treated with nitre-hydrochloric acid under slight pressure, when pla-
tinic chloride is formed. The solution is evaporated to dryness and the mass
heated to a temperature of 125° C. in order to decompose the higher chlorides
of iridium and palladium, which metals, if present, would otherwise accompany
the platinum. After dissolving the residue in water, ammonium chloride is
added, which precipitates platinum as ammonium platinic chloride, PtCl4.
2NH4C1. The washed precipitate when heated to redness is completely decom-
posed, metallic platinum being left as a gray, spongy mass, which may be fused
by means of the oxy-hydrogen flame or in an electric furnace.

Platinum is of great importance and value on account of its high
fusing-point and its resistance to the action of most chemical agents,
for which reason it is used in the manufacture of vessels serving in
chemical operations. While sulphuric, nitric, hydrochloric, and hydro-
fluoric acids have no action on platinum it is readily attacked by
chlorine, and at a red heat by caustic alkalies, sulphur, and phosphorus.

Platinum is of a silver-white color with a tinge of blue ; it is very malleable
and ductile ; its rate of expansion by heat is low, about that of glass. This
property is of value in the use of the metal for the pins of artificial teeth, and
as a base for continuous gum work. Addition of iridium renders platinum
harder, more rigid and more elastic, all of which properties platinum confers
upon silver and gold.

The property of platinum to condense oxygen upon its surface and to dis-
solve hydrogen is made very conspicuous in platinum sponge and platinum black.
The former is made by heating precipitated ammonium chloroplatinate, by
which a gray mass of finely divided platinum is left; the latter is obtained as
a black powder by adding zinc to chloroplatinic acid. Either of these forms
or platinum, when thrown into a mixture of oxygen and hydrogen, causes
instant explosion. This is an example of catalytic action, in which the speed
of a chemical change is enormously increased. The gases condensed in the
pores of the finely divided metal unite rapidly with production of sufficient
heat to cause the rest of the gases to unite with explosion.

Chloroplatinic acid, H2PtCl6.6H2O (often called Platinic chloride),
is obtained as reddish-brown deliquescent crystals when platinum is
dissolved in aqua regia and the solution evaporated. It serves as a
valuable reagent for potassium and ammonium, as explained in con-
nection with the analytical reactions of these bodies. In the acid and

368 METALS AND THEIR COMBINATIONS.

its salts platinum is in the anion, as PtCl,/'. The chloride, PtCl4, is
obtained by heating the chloroplatinic acid in a current of chlorine
at 360° C. Its solution in water gives red, non-deliquescent crystals
of the composition, H2PtCl4O.4H2O.

Chloroplatinous acid, H2PtCl4, results when platinous chloride,
PtCl2, is dissolved in hydrochloric acid. The potassium salt,
K2PtCl4, is used in making platinum prints in photography. The
corresponding barium platinocyanide, BaPt(CN)4.4H2O, forms light
yellow crystals. Screens coated with this salt become luminous when
Rontgen rays (#-rays) fall upon them. Such fluorescent screens are
used for observing x-ray pictures. Ultra-violet and radium rays also
affect the screens.

Iridium, Ir = 191.5. This element has been mentioned as one of the metals
which accompany platinum in nature. It is obtained from the material left
in the working of platinum ores.

Iridium has a grayish- white color and resembles polished steel ; it is harder,
more brittle, specifically heavier and less fusible than platinum. The increased
hardness, rigidity and elasticity which iridium imparts to platinum makes the
alloy a valuable dental material. Gold pens are often tipped with iridium
which renders them more durable.

Compact pieces of iridium are insoluble in all acids; when finely divided it
dissolves in nitro-hydrochloric acid. It is for these reasons that most of the
iridium is left in the residue of the material from which platinum has been
extracted. Several oxides, hydroxides and chlorides of iridium are known.

Molybdenum, Mo = 95.3. This metal is found in nature chiefly as sul-
phide, MoS.2, from which, by roasting, molybdic oxide. MoO3, is obtained. The
oxide, when dissolved in water, forms an acid which combines with metals,
forming a series of salts termed molybdates. Of interest is ammonium molyb-
date, a solution of which in nitric acid is an excellent reagent for phosphoric-
acid, with which it forms a yellow precipitate, insoluble in acids, soluble in
ammonium hydroxide.

QUESTIONS. — How is antimony found in nature, and what are the proper-
ties of this metal ? State the composition of antimonous sulphide, and its
color when crystallized and amorphous. How do hydrochloric acid and alkali
hydroxides act upon antimonous sulphide? Mention the two chlorides of
antimony and state their properties. How is antimonous oxide made, and for
what is it used? Give tests for antimony. State the use made of tin in the
metallic state; mention the two chlorides of tin, and the use of stannous chlo-
ride. Describe processes for refining gold by the dry and wet methods. How
are gold and platinum found in nature ; by what acid may they be dissolved,
and what is the composition of the compounds formed? Which is the most
important compound of molybdenum, and what is its use?

THE ARSENIC GROUP.

369

Summary of analytical characters of metals of the arsenic

group.

Arsenic.

Antimony.

Tin.

Gold.

Platinum.

Hydrogen sulphide .

Precipitate heated ^j
in strong hydro- y
chloric acid . . J

Potassium hydroxide

Yellow pre-
cipitate.

Insoluble.

Orange
precipitate

Soluble.
White

Yellow
or brown
precipitate.

Soluble.
White

Black
precipitate

Insoluble.
Brownish

Dark-
brown
precipitate.

Insoluble.
1 With ex-

Ammonia water

precipitate,
soluble
in excess.

White

precipitate,
soluble
in excess.

White

precipitate,
soluble
in excess.

Brownish

cess of
hydro-
chloric
f acid a
yellow

Gutzeit's test

Yellow stain

precipitate.
Dark stain

precipitate.

yellow
precipitate

precipi-
J tate.

Fleitmann's test

turning dark
with water.

Dark stain

24

V.

ANALYTICAL CHEMISTRY.

34. INTRODUCTORY REMARKS AND PRELIMINARY
EXAMINATION.

General remarks. Analytical chemistry is that part of chemistry
which treats of the different analytical methods by which substances
are recognized and their chemical composition determined. This
determination may be either qualitative or quantitative, and, accord-
ingly, a distinction is made between a qualitative analysis, by which
simply the nature of the elements (or groups of elements) present in
the substance under examination is determined, and a quantitative
analysis, by which also the exact amount of these elements is ascer-
tained.

In this book qualitative analysis will be considered chiefly, as the
methods for quantitative determinations of the different elements are
so numerous and so varied that a detailed description of them would
occupy more space than can be devoted to analytical chemistry in this
work. Some brief directions concerning quantitative determinations,
especially by volumetric methods, are given in Chapter 38. Every-
one studying analytical chemistry should do it practically, that is,
should perform for himself in a laboratory all those reactions which
have been mentioned heretofore as characteristic of the different ele-
ments and their compounds, and, furthermore, should make himself
acquainted with the methods by which substances are recognized
when mixed with others, by analyzing various complex substances.

Such a course of practical work in a suitable laboratory is of the
greatest advantage to all studying chemistry, and students cannot be
too strongly advised to avail themselves of any facilities offered in
performing chemical experiments, analytically or otherwise.

Apparatus needed for qualitative analysis.

1. Iron stand. (Fig. 48.)

2. Bunsen lamp with flexible tube (Fig. 48) or (where without gas-supply)

spirit-lamp and alcohol.

371

372

ANALYTICAL CHEMISTRY.

3. Test-tube stand and one dozen assorted test-tubes. (Fig. 49.)

4. Three beakers from 100 to 150 c.c. capacity. (Fig. 50, A.)

5. Two flasks of 100 to 150 c.c. capacity. (Fig. 50, B.)

FIG. 48.

FIG. 49.

FIG. 50.

6. Wash-bottle of about 400 c.c. capacity. (Fig. 51, A.)

7. Three small glass funnels, about one and a half to two inches in diameter.

(Fig. 51, B.)

INTRODUCTORY REMARKS.

373

8. A few pieces of glass tubing about ten inches long, and some India-rubber

tubing to fit the glass tubing.

9. Three glass rods.

FIG. 51.

10. Three small porcelain evaporating dishes, about two inches in diameter.

(Fig. 52, A.)

11. Blowpipe. (Fig. 52, B.)

12. Crucible tongs. (Fig. 52, C.)

FIG. 52.

13. Round and triangular file

14. Wire gauze, about six inches square, or sand tray.

15. One square inch of platinum foil (not too light), and six inches of

platinum wire.

16. Filter-paper.

17. Pair of scissors.

18. One or two dozen assorted corks.

19. Sponge and towel.

20. Two watch-glasses.

21. Small pestle and mortar. (Fig. 52, D.)

22. Small porcelain crucible.

23. Small platinum crucible. (Fig. 52, E.)

24. Wire triangle to support the crucible. (Fig. 52, F.)

374 ANALYTICAL CHEMISTRY.

Reagents needed in qualitative analysis.
a. Liquids.

1. Sulphuric acid, sp. gr. 1.84, H2SO4.

2. Sulphuric acid diluted, sp gr 1.068 (1 part sulphuric acid, 9 parts water).

3. Hydrochloric acid, sp. gr. 1.16, HC1.

4- Hydrochloric acid diluted, sp. gr. 1.049 (6 parts hydrochloric acid, 13 parts
water).

5. Nitric acid, sp. gr. 1.42, HNO3.

6. Acetic acid, sp. gr. 1.048, C2H4O2.

7. Hydrogen sulphide, either the gas or its solution in water, H2S.

8. Ammonium sulphide, (NH4)2S.

9. Ammonium hydroxide (ammonia water), NH4OH.

10. Ammonium carbonate, (NH4)2CO3. A solution of one part of the commercial

salt in a mixture of four parts of water and one part of ammonia water.

11. Ammonium chloride, NH4C1 ; ten per cent solution.

12 Ammonium oxalate, (NH4)2C2O4; five per cent, solution.

13. Ammonium molybdate, (NH4)2MoO4- A five per cent solution of the salt in a

mixture of equal parts of water and nitric acid.

14. Sodium hydroxide, NaOH. ~|

15. Sodium carbonate,

16. Sodium phosphate, Na«HPOA. m i .-

,_ c, ,. }- Ten per cent, solutions.

17. Sodium acetate, NaC2H3O2.

18 Potassium chromate, K2CrO4.

19 Potassium dichromate, K2Cr2Or
20. Potassium iodide, KI

21 Potassium ferrocyanide, K4Fe(CN)8. ,-,.

oo T> * f • -j T^ ™ /nxTx r Five per cent, solutions.

22. Potassium ferricyanide, K6Fe2(CN)12.

23 Potassium sulphocyanate, KCNS.

24. Magnesium sulphate, MgSO4. ^

25. Barium chloride, BaCl2. L Ten per cent, solutions.

26. Calcium chloride. CaCl2. )

27. Calcium hydroxide, CaiOH)2 (lime-water). 1

28 Calcium sulphate, CaSO, I Crated solutions.

29 Ferric chloride, FeCl3. n

30 Lead acetate, Pb.(C2H302)2.

31. Silver nitrate, AgNO3. [ Five per cent, solutions.

32. Mercuric chloride, HgCl2.

33. Platinic chloride, H2PtCle.

34. Stannous chldride, SnCl2.2H2O; ten per cent, solution.

35. Solution of indigo

36. Alcohol, C2H5OH.

37. Sodium cobaltic nitrite solution, Co2(NO2)6.6NaNO2 + H2O. Four grammes of

cobaltous nitrate, Co(NO3)2.6H2O, and 10 grammes of sodium nitrite, NaNO..,
are dissolved in about 50 c.c. of water, 2 c.c. of acetic acid are added, and then
water to make 100 c.c.

38. Alkaline mercuric-potassium iodide solution (Nessler's solution). Five grammes

of potassium iodide are dissolved in hot water, and to this is added a hot
olution, made by dissolving 2.5 grammes of mercuric chloride in 10 c.c. of
water. To the turbid red mixture is added a solution made by dissolving 16

INTRODUCTORY REMARKS. 375

grammes of potassium hydroxide in 40 c.c. of water, and the whole diluted to
100 c.c. Some mercuric iodide deposits on cooling, and may be left in the
bottle, the clear solution being decanted as needed.

b. Solids.

1. Litmus or blue and red litmus paper.
2 Turmeric paper.

3. Sodium carbonate, dried, Na2CO3.

4. Sodium biborate, borax, Na2B4O7.10H2O.

5. Sodium-ammonium-hydrogen phosphate (microcoamic salt),

Na(NH4)HPO4.4H2O.

6. Potassium carbonate, K2CO3.

7. Potassium nitrate, KNO3.

8. Potassium chlorate, KC1O3.

9. Potassium permanganate, KMnO4.
10- Potassium cyanide, KCN.

11. Calcium hydroxide, Ca(OH)2.

12. Ferrous sulphide, FeS.

13. Ferrous sulphate, FeSO4.7H2O.

14. Manganese dioxide, MnO2.

15. Zinc, granulated, Zn.

16. Copper, Cu.

17. Cupric oxide, CuO.

18. Cupric sulphate, CuSO4 5H,O.

19. Tartaric acid, H2C4H4O6.

20. Tannic acid, H CUH9O9

21. Pyrogallic acid, C6H3(OH)3.

22. Diphenylamine, (C6H5)2NH.

23. Starch, C6H10O5.

While the apparatus and reagents here enumerated are the more
important ones, the analyst will occasionally require others not men-
tioned in the above list.

General mode of proceeding- in qualitative analysis. Every
step taken in analysis should be properly written down in a note-
book, and these remarks should be made directly after a reaction has
been performed, and not after the nature of the substance has been
revealed by perhaps numerous reactions.

Not only the reactions by which positive results have been obtained
should be noted, but also those tests and reagents mentioned which
have been applied with negative results — that is, which have been
applied without revealing the presence of any substance, or any group
of substances. Such negative results are, however, positive in so far
as they prove the absence of a certain substance, or certain substances,
for which reason they are of direct value, and should be noted.

In comparing, finally, the result obtained by the analysis with the

376 ANALYTICAL CHEMISTRY.

notes taken during the examination, none of them should be contra-
dictory to the conclusions drawn. If, for instance, the preliminary
examination showed the substance to have been volatilized by heating
upon platinum foil with the exception of a very slight residue, and if,
afterward, other tests show the presence of ammonia and hydro-
chloric acid and the absence of everything else, and if, then, the con-
clusion be drawn that the substance is pure ammonium chloride, this
conclusion must be incorrect, because pure ammonium chloride is
wholly volatile, and does not leave a residue. It will then be the task
of the operator to find where the mistake occurred, and to correct it.

Use of reagents. A mistake made by most beginners in analyz-
ing is the use of too large quantities both of the substance applied
for testing and of the reagents added. This excessive use of material
is not only a waste of money, but, what is of greater importance, a
waste of time. Some experience in analyzing will soon convince the
student of the truth contained in this remark, and will also enable
him to select the correct quantities of materials to be used, which
rarely exceed 0.2-1.0 gramme. A smaller amount — in fact, as little
as a few milligrams — frequently may answer, and a much larger
quantity may occasionally be needed, as, for instance, in cases where
highly diluted reagents, such as calcium sulphate solution, lime-
water, hydrogen sulphide water, etc., are applied.

Preliminary examination. This examination includes the fol-
lowing points :

1. Physical properties. Solid or liquid; crystallized or amor-
phous; color, odor, hardness, gravity, etc. (On account of possible
poisonous properties, the greatest care should be exercised in tasting
a substance.)

2. Action on litmus. Examined by holding litmus-paper in the
liquid, or by placing the powdered solid upon red and blue litmus-
paper, moistened with water. (It should be remembered that many
normal salts, as, for instance, aluminum sulphate, ferrous sulphate,
etc., have an acid reaction to litmus-paper, and that such a reaction
consequently is not conclusive of the presence of a free acid, nor even
of an acid salt.)

3. Heating on platinum foil or in a dry glass tube, open at
both ends. (If the substance to be examined be a liquid, it should

INTRODUCTORY REMARKS. 377

be evaporated in a small porcelain dish to see whether a solid residue
be left or not. If a residue be left, it should be treated like a solid.)
The heating of a small quantity of a solid substance upon platinum
foil, or upon a piece of mica, held over the flame of a Bunsen burner,
is a test which should never be omitted, as it discloses in most cases
the fact whether the substance is of an organic or inorganic nature.

Most organic (non-volatile) substances when thus heated will burn with a
luminous flame, leaving in many cases a black residue of carbon, which upon
further heating disappears. In cases where the organic nature of a compound
is not clearly demonstrated by heating on platinum foil, the substance is heated
with an excess of cupric oxide in a test-tube or other glass tube, provided with
a delivery-tube which passes into lime-water. Upon heating the mixture the
carbon of the organic matter is converted into carbon dioxide, which renders
lime-water turbid.

The analytical processes by which the nature of an organic substance is
determined are not considered in this part of the book, but will be mentioned
when considering the carbon compounds. Some substances ruin platinum when
heated on it. Thus, salts of easily reducible metals, as lead, bismuth, antimony,
tin, especially their organic salts, are apt to do so, because these metals form
fusible alloys with the platinum. Thiosulphates corrode and hypophosphites
destroy platinum. Should the presence of any of the substances be suspected,
heating on platinum should be omitted. Indeed, tests 4 and 5 can be applied
first, as they may show the presence of these objectionable substances.

An inorganic substance heated on platinum foil may either be volatilized,
change color, become oxidized, suffer decomposition, or remain unchanged.
(See Table I., page 381.)

FIG. 53. FIG. 54.

Heating of solids in bent glass tube. Heating on charcoal by means of blowpipe.

Some substances, containing small quantities of water enclosed
between the crystals (common salt, for instance), decrepitate when
heated, the small fragments being thrown from the foil; such sub-

378 ANALYTICAL CHEMISTRY.

stances should be heated in a dry test-tube to expel the water and
then be examined on platinum foil.

In many cases it is preferable to heat the substance in a bent glass
tube, as shown in Fig. 53, instead of on platinum foil, because vola-
tile products evolved during the process of heating may become re-
condensed in the cooler part of the tube, and thus saved for further
examination.

The presence of water, sulphur, mercury, arsenic, etc., may often
be readily demonstrated by this mode of operating.

4. Heating1 on charcoal by means of the blowpipe. This test
reveals the presence of chlorates and nitrates by the vivid combus-
tion of the charcoal (known as deflagration), which takes place in
consequence of the oxidizing action of these substances.

Arsenic is indicated by a characteristic odor of garlic.

5. Heating- on charcoal with sodium carbonate and potas-
sium cyanide. A small quantity of the finely powdered substance
is mixed with twice its weight of potassium cyanide and dry sodium
carbonate. This mixture is placed in a small hole made in a piece
of charcoal, and heat applied by means of the blowpipe (see Fig. 54).
Many metallic compounds may be recognized by this test, the metals
being liberated and found as metallic globules or shining particles in
the fused mass after this has been removed from the charcoal and
washed with water in a small mortar. (See Fig. 55.)

FIG. 55.

A characteristic incrustation is formed by some metals, due to the
precipitation of a metallic oxide around the heated spot on the char-
coal.

If sulphur as such, or in any form of combination, be present in
the substance examined by this test, the fused mass contains a sulphide
of the alkali (hepar), which may be recognized by placing it en a
piece of bright silver (coin) moistened with a drop of water, when the

INTRODUCTORY REMARKS. 879

silver will be stained black in consequence of the formation of silver
sulphide. The presence of the alkali sulphide may also be demon-
strated by the addition of a few drops of hydrochloric acid to the
fused mass, when hydrogen sulphide is evolved and may be recog-
nized by its odor.

6. Flame tests. Many substances impart a characteristic color
to a non-luminous flame. The best mode of performing this test is
as follows : A platinum wire is cleaned by washing in hydrochloric
acid and water, and heating it in the flame until the latter is no
longer colored. One end of the wire is fused in a short piece of
glass tubing (see Fig. 56), the other end is bent so as to form a small

FIG. 56.

loop, which is heated, dipped into the substance to be examined, and
again held in the lower part of the flame, which then becomes colored.

Some substances show the color-test after being moistened with
hydrochloric or sulphuric acid.

A second method of showing flame reactions is to mix the substance
with alcohol in a small dish ; the alcohol, upon being ignited, shows
a colored flame, especially in the dark.

7. Colored borax beads. The compounds of some metals when
fused with glass, impart to it characteristic colors. For analytical
purposes not the silica-glass, but borax-glass is generally used. This
latter is made by dipping the loop, of a platinum wire in powdered
borax and heating it in the flame (directly, or by means of the blow-
pipe) until all water has been expelled and a colorless, transparent
bead has been formed. To this colorless bead a little of the finely
powdered substance is added and the bead strongly heated. The
metallic compound is chemically acted upon by the boric acid, a bo rate
being formed which colors the bead more or less intensely, according
to the quantity of the metallic compound used.

Some metals (copper, for instance) forming two series of compounds give
different colors to the bead when present in either the higher or the lower state
of oxidation.

By modifying the blowpipe flame so as either to oxidize (by supplying an
excess of atmospheric oxygen), or deoxidize (by allowing some unburnt carbon
in the flame), the metallic compound in the bead may be made to assume the

380 ANALYTICAL CHEMISTRY.

higher or lower state of oxidation. A copper bead may thus be changed from
blue to red, or red to blue, the blue bead containing the copper in the cupric,
the red bead in the cuprous form. In some cases microcosmic salt, NaNH4HPO4,
is used for making the bead.

8. Liquefaction of solid substances. Most solid substances
have to be dissolved for analysis. The solution obtained may be
either a simple or chemical solution. In a simple solution the dis-
solved body retains all of its original properties, with the exception
of its shape, and may be re-obtained by evaporation. Sodium
chloride and sugar dissolved in water form simple solutions. A
chemical solution is one in which the chemical composition of the sub-
stance has been changed during the process of dissolving, as, for
instance when calcium carbonate is dissolved in hydrochloric acid ;
this solution now contains and leaves on evaporation calcium
chloride. The solvents used are water, or the mineral acids for
substances insoluble in water, especially dilute, or, if necessary, strong
hydrochloric acid. The dissolving action of the acid should be facil-
itated by the aid of heat. Nitric or even nitro-hydrochloric acid
may have to be used in some cases.

Three mistakes ore frequently made by beginners in dissolving sub-
stances in acids , viz. : The substance is not powdered as finely as it
should be ; sufficient time is not given for the acid to act ; too large an
excess of the acid is used.

If a substance is partly dissolved by water and partly by one or
more other solvents, it may be well to examine the different solutions
separately.

Substances insoluble in water and in acids have to be rendered
soluble by fusion with a mixture of potassium and sodium carbonate,
or with potassium acid sulphate, or by the action of hydrofluoric
acid.

The insoluble sulphates of the alkaline earths, when fused with the
alkaline carbonates, are con verted into carbonates, while the sulphates
of the alkalies are formed. The latter compounds may be eliminated
by washing the fused mass with water and filtering : the solid residue
upon the filter contains the carbonates of the alkaline earths, which
may be dissolved in hydrochloric acid.

Insoluble silicates may be decomposed by the methods mentioned
on page 186.

I y TROD UCTOR Y REMA RKS.

381

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382 ANALYTICAL CHEMISTRY.

35. SEPARATION OF METALS INTO DIFFERENT GROUPS.

General remarks. The preliminary examination will, in most
cases, decide whether or not a metal or metals are present in the sub-
stance to be examined. If there be metals, the solution should be
treated according to Table II., page 344, in order to find the group
or groups to which these metals belong, and also to separate them
into these groups, the individual nature of the metals themselves
being afterward demonstrated by special methods.

The simplest method of separating from each other the 57 metals
known, if all were in one solution, would be to add successively 57
different reagents, each of which should form an insoluble compound
with but one of the metals. By separating this insoluble compound
from the metals remaining in solution (by filtration), and by thus pre-
cipitating one metal after the other, they all could be easily separated.
We have, however, no such 57 reagents, and are, consequently, com-
pelled to precipitate a number of metals together, and the reagents
used for this purpose are known as group-reagents.

They are :

1. Hydrogen sulphide, added to the solution previously acidified by
hydrochloric acid. Precipitated are : the metals of the arsenic and
lead groups as sulphides.

2. Ammonium sulphide, added after supersaturating with ammonium
hydroxide. Precipitated are : the metals of the iron group and of
the earths as sulphides or hydroxides.

3. Ammonium carbonate. Precipitated are : the metals of the
alkaline earths as carbonates.

4. In solution are left : the metals of the alkalies and magnesium.
The order in which these group-reagents are added cannot be

QUESTIONS. — What is analytical chemistry, and what is the object of quali-
tative and of quantitative analysis? What properties of a substance should
be noticed first in- making a qualitative analysis? By what tests may organic
compounds be distinguished from inorganic compounds? Explain the terms
decrepitation and deflagration. Mention some substances which are completely
volatilized by heat, some which are fusible, and some which are not changed
by heating them. What is meant by " hepar," and which element is indicated
by the formation of hepar? Mention some metals which may be liberated
from their compounds by heating on charcoal with potassium cyanide and car-
bonate. Which metallic compounds and which acids are capable of coloring a
non-luminous flame? Name the colors imparted. State the metals which im-
part characteristic colors to a borax bead. Which solvents are used for lique-
fying solids, and what precautions should be observed in this operation?

SEPARATION OF METALS INTO DIFFERENT GROUPS. 383

reversed or changed, because ammonium sulphide added first would
precipitate not only the metals of the iron group and the earths, but
also the metals of the lead group ; .ammonium carbonate would pre-
cipitate also most of the heavy metals.

For the same reasons, in separating metals of the different groups, the group-
reagents must be added in excess, that is, enough of them must be added to
precipitate the total quantity of the metals of one group, before it is possible
to test for metals of the next group. Suppose, for instance, a solution to con-
tain a salt of bismuth only. Upon the addition of hydrogen sulphide to the
acidified solution, a dark-brown precipitate (of bismuth sulphide) is produced,
indicating the presence of a metal of the lead group. Suppose, further, that
hydrogen sulphide has not been added in sufficient quantity to precipitate the
whole of the bismuth, then ammonium sulphide, as the next group-reagent,
would produce a further precipitation in the filtrate, which fact would lead to
the assumption that a metal of the iron group was present, which, however,
would not be the case.

If the solution contain but one metal, the group-reagents are added
successively in small quantities to the same solution, until tJ*e reagent
is found which causes a precipitation, which reagent is then added in
somewhat larger quantity in order to produce a sufficient amount of
the precipitate for further examination.

Acidifying- the solution. Hydrogen sulphide has to be added
to the acidified solution for two reasons, viz. : In a neutral or alkaline
solution some metals of the arsenic group (which are to be pre-
cipitated) would not be precipitated by hydrogen sulphide ; some of
the metals of the iron group (which are not to be precipitated) would
be thrown down.

The best acid to be used in acidifying is dilute hydrochloric acid ;
but this acid forms insoluble compounds with a few of the metals of
the lead group, causing them to be precipitated. Completely pre-
cipitated by hydrochloric acid are mercurous and silver compounds ;
partially precipitated are compounds of lead, chloride of lead being
somewhat soluble in water. The precipitate formed by hydrochloric
acid may be examined by Table III., page 387.

Hydrochloric acid added to a solution may, in a few cases (other
than those just mentioned), cause a precipitate, as, for instance, when
added to solutions containing certain compounds of antimony or bis-
muth (the precipitated oxychlorides of these metals are soluble in
excess of the acid), to metallic oxides or hydroxides which have been
dissolved by alkali hydroxides (for instance, hydroxide of zinc dis-
solved in potassium or ammonium hydroxide), to solutions of alkali
silicates, when silica separates, etc.

ANALYTICAL CHEMISTRY.

Addition of hydrogen sulphide. This reagent is employed
either in the gaseous state (by passing it through the heated solution)
or as hydrogen sulphide water. The latter reagent answers in those
cases where but one metal is present; if, however, metals of the
arsenic and lead groups are to be separated from metals of other
groups, the gas must be used.

FIG. 57 F'«-58-

Apparatus for generating hydro-
gen sulphide.

Apparatus for generating hydro-
gen sulphide.

For generating hydrogen sulphide the directions given on page 214 may,,
be followed. In place of the apparatus there mentioned for generating the
gas, others may be used which have the advantage to the analyst that the
supply of gas may be better regulated. Fig. 57 shows such an apparatus for
the continuous preparation of the gas. It consists of three glass bulbs ; the
upper bulb, prolonged by a tube reaching to the bottom of the lowest one, is
ground air-tight into the neck of the second. Ferrous sulphide is introduced
into the middle bulb through the tubulure, which is then closed by a perforated
cork through which connection is made with the wash-bottle. Acid poured in
through the safety tube, runs into the bottom globe and rises to the ferrous
sulphide in the second bulb. Upon closing the delivery tube, the pressure of
the generated gas forces the liquid from the second bulb through the lower to
the upper, thus preventing contact of acid and ferrous sulphide until the gas is
used again.

A convenient and cheaper apparatus is shown in Fig. 58. A glass tube,
drawn at its lower end to a small point and partly filled with pieces of ferrous
sulphide, is suspended through a cork (not air-tight) in a cylinder containing
the acid. The gas supply is regulated by closing or opening the stop-cock, and
also by raising or lowering the tube in the acid.

SEPARATION OF METALS INTO DIFFERENT GROUPS. 385

White.

Black.

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386 ANALYTICAL CHEMISTRY.

In some cases sulphur is precipitated on the addition of hydrogen
sulphide, while a change in color may take place. This change is
due to the deoxidizing action of hydrogen sulphide, the hydrogen of
this reagent becoming oxidized and converted into water, while sul-
phur is liberated. Thus, brown ferric compounds are converted into
pale-green ferrous compounds; red solutions of acid chromates
become green; and red permanganates or green manganates are
decolorized.

The same deoxidizing action of hydrogen sulphide is the reason
why this reagent cannot be employed in a solution containing free
nitric acid, which latter compound oxidizes the hydrogen sulphide.

Separation of the metals of the arsenic from those of the lead
group. The precipitate produced by hydrogen sulphide in acid solu-
tion contains the metals of the arsenic and lead groups. They are
separated by means of ammonium sulphide, which dissolves the sul-
phides of the arsenic group, but does not act on those of the lead
group.

Addition of ammonium sulphide. This reagent should never
be added to the acid solution, but the solution should be previously
supersaturated by ammonium hydroxide, as. otherwise, a precipitate
of sulphur may be formed. The yellow ammonium sulphide is
almost invariably a polysulphide of ammonium, that is, ammonium
sulphide which has combined with one or more atoms of sulphur. If
an acid be added to this compound, an ammonium salt is formed,
hydrogen sulphide is liberated, and sulphur precipitated :

(NH4)2S2 + 2HC1 =±= 2NH4C1 -f H2S + S.

Ammonium sulphide precipitates the metals of the iron group as
sulphides, with the exception of chromium, which is precipitated as
hydroxide ; aluminum is precipitated in the same form of combina-
tion.

Ammonium sulphide (or ammonium hydroxide) causes also the
precipitation of metallic salts which have been dissolved in acids, as,
for instance, of the phosphates, borates, silicates, or oxalates of the
alkaline earths, magnesium, and others. The processes by which the
nature of some of these precipitates is to be recognized are found in
Table VI., page 389.

Addition of ammonium carbonate. The reagent used is the
commercial salt, dissolved in water, to which some ammonia water

SEPARATION OF THE METALS OF EACH GROUP. 387

has been added. Heating facilitates complete precipitation of the
carbonates of the alkaline earths.

36. SEPARATION OF THE METALS OF EACH GROUP.
TABLE III.— Treatment of the precipitate formed by hydrochloric acid.

The precipitate may contain silver, mercurous, and lead chlorides. Boil
the washed precipitate with much water, and filter while hot.

Filtrate may contain lead
chloride. Add dilute
sulphuric acid ; a white
precipitate of lead sul-
phate is produced.

Residue may consist of mercurous and silver chlor-
ides. Digest residue with ammonia water.

Solution may contain sil-
ver. Neutralize with
nitric acid, when silver
chloride is re-precipi-
tated.

A dark gray residue indi-
cates mercury, the white
mercurous chloride having
been converted into mer-
curic-ammonium chloride
and mercury.

Treatment of the precipitate formed by hydrogen sulphide in
warm acid solution. The precipitate is collected upon a small
filter, well washed with water, and then examined for its solubility
in ammonium sulphide. This is done by placing a portion of the
washed precipitate in a test-tube, adding ammonium sulphide, and
warming gently. It is either wholly insoluble (metals of the lead
group), and treated according to Table IV., or fully soluble (metals
of the arsenic group), and treated according to Table V., or it is
partly soluble and partly insoluble (metals of both groups). In the
latter case, the total quantity of the washed precipitate is to be
treated with warm ammonium sulphide; upon filtering, an insoluble
residue is left, which is treated according to Table IV. ; to the fil-

QUESTIONS. — State the three groups of heavy, and the three groups of light
metals. By which two reagents may all heavy metals be precipitated? Why
is a solution acidified before the addition of hydrogen sulphide, when testing
for metals? Which metals are precipitated by hydrochloric acid? Which two
groups of metals are precipitated by hydrogen sulphide in acid solution ? How
are the sulphides of the arsenic group separated' from those of the lead group?
Why is an acid solution neutralized or supersaturated by ammonium hydroxide,
before adding ammonium sulphide? Which two groups of metals are precipi-
tated by ammonium sulphide, and in what forms of combination? Name the
group-reagent for the alkaline earths. Which metals may be left in solution
after hydrogen sulphide, ammonium sulphide, and ammonium carbonate have
been added ?

388

ANALYTICAL CHEMISTRY.

trate, diluted sulphuric acid is added as long as a precipitate is
formed, which precipitate contains the metals of the arsenic group as
sulphides, generally with some sulphur from the ammonium sulphide.

TABLE IV.— Treatment of that portion of the hydrogen sulphide
precipitate which is insoluble in ammonium sulphide.

The precipitate may contain the sulphides of lead, copper, mercury,
bismuth, and cadmium. Heat the well-washed precipitate with nitric acid in
a test-tube, and filter.

Residue may con-
consist of:
Mercuric sulph-
ide, which is
black and easily
dissolves in nitro-
hydrochloric acid,
which solution,
after sufficient
evaporation, is
tested by potas-
sium iodide, etc.
Lead sulphate is
white, pulveru-
lent, and soluble
in ammonium
tartrate.
Sulphur is yellow
and combustible.

Filtrate may contain the nitrates of lead, copper, bis-
muth, and cadmium. Add to the solution a few drops
of dilute sulphuric acid.

Precipitated is
lead, as white
lead sulphate
which is solu-
ble in ammo-
nium tartrate
with excess of
ammonium
hydroxide.

Solution may contain copper, bismuth,
and cadmium. Supersaturate with am-
monium hydroxide.

Precipitated is
white bis-
muth hy-
droxide.
Dissolve in
hydrochloric
acid and ap-
ply tests for
bismuth.

Solution may contain copper
and cadmium
Divide solution in two parts,
and test for copper by potas-
sium ferrocyanide in the
acidified solution; a red pre-
cipitate indicates copper.
To second part add potas-
sium cyanide and hydro-
gen sulphide. A yellow
precipitate indicates cad-
mium.

TABLE V.— Treatment of the hydrogen sulphide precipitate which is
soluble in ammonium sulphide.

The precipitate may contain the sulphides of arsenic, antimony, tin,
and a few of those metals which are but rarely met with in qualitative analysis,
such as gold, platinum, molybdenum, and others, which latter metals, if
suspected, may be detected by special tests.

Boil the washed precipitate with strong hydrochloric acid.

An insoluble yellow residue consists
of arsenous sulphide

The residue is dissolved by boiling
with hydrochloric acid and a little
potassium chlorate, and the solu-
tion examined by Fleitmann's
test.

A dark-colored residue may indi-
cate gold or platinum, for which
use special tests.

The solution may contain the chlorides of
antimony and tin.

The solution is introduced into Marsh's appara-
tus when all antimony is gradually evolved
as antimoniuretted hydrogen, while tin re
mains with the undissolved zinc as a black
metallic powder, which may be collected,
washed, dissolved in hydrochloric acid, and
the solution tested by the special tests for
tin.

SEPARATION OF THE METALS OF EACH GROUP.

389

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390 ANALYTICAL CHEMISTRY. .

The precipitation of sulphur, in the absence of metals of the arsenic group,
frequently leads beginners to the assumption that metals of this group are
present. The precipitate consisting only of sulphur is white and milky, but
flocculent, and more or less colored in the presence of the metals of the
arsenic group.

TABLE VII.— Treatment of the precipitate formed by ammonium

carbonate.

The precipitate may contain the carbonates of barium, caloium, and
Strontium.1 Dissolve the precipitate in acetic acid, and add potassium dichromate.

Precipitated is
barium, as
pale yellow
barium

chromate.

Solution may contain calcium and strontium Neutralize
solution with ammonia water and add potassium chromate.

Precipitated is stron-
tium, as pale yellow
strontium chromate.

Solution may contain calcium Add
ammonium oxalate: a white precipi-
tate indicates calcium.

TABLE VIII.— Detection of the alkalies and of magnesium.

The fluid which has been treated with hydrochloric acid, hydrogen sulphide, am-
monium hydroxide, sulphide, and carbonate, may contain magnesium and the
alkalies.

Divide solution into two portions.

To the first portion add sodium phosphate. A white crystalline precipitate indi-
cates magnesium.2

The second portion is evaporated to dryness, further heated (or ignited) until all
ammonium compounds are expelled, and white fumes are no longer given off. The
residue is dissolved in water, and sodium cobaltic nitrite added. A yellow precipitate
indicates potassium. The residue is also examined by flame test : a yellow color
indicating sodium, a red color lithium.

Ammonium compounds have to be tested for in the original fluid by treating
it with calcium hydroxide, when ammonia gas is liberated

1 If an insufficient quantity of ammonium chloride should have been present, some magnesia
may also be contained in this precipitate, and may be redissolved by treating it with ammonium
chloride solution.

2 If an insufficient quantity of ammonium chloride has been produced in the original solution
by the addition of hydrochloric acid and ammonium hydroxide, a portion of the magnesia may
have been precipitated by the ammonium hydroxide or carbonate.

QUESTIONS.— By what tests can mercurous chloride be distinguished from
the chloride of silver or lead ? How can it be proved that a precipitate pro-
duced by hydrogen sulphide in an acid solution contains a metal or metals of

DETECTION OF ACIDS. 391

37. DETECTION OF ACIDS.

General remarks. There are no general methods (similar to those
for the separation of metals) by which all acids can be separated, first
into different groups, and afterward into the individual acids. It is,
moreover, impossible to render all acids soluble (when in combination
with certain metals) without decomposition, as, for instance, in the
case of carbonic acid when in combination with calcium ; calcium
carbonate is insoluble in water, and when the solution is attempted
by means of acids, decomposition takes place with liberation of carbon
dioxide. Many other acids suffer decomposition in a similar manner,
when attempts are made to render soluble the substances in which
they occur.

It is due to these facts that a complete separation of all acids is
not so easily accomplished as the separation of metals. There is,
however, for each acid a sufficient number of characteristic tests by
which it may be recognized ; moreover, the preliminary examination,
as well as the solubility of the substance, and the nature of the metal
or metals present, will aid in pointing out the acid or acids which
are present.

If, for instance, a solid substance be completely soluble in water,
and if the only metal found were iron, it would be unnecessary to
test for carbonic and phosphoric acids and hydrogen sulphide, because
the combinations of these with iron are insoluble in water ; there might,
however, be present sulphuric, hydrochloric, nitric, and many other
acids, which form soluble salts with iron.

Detection of acids by means of the action of strong sulphuric
acid upon the dry substance. The action of sulphuric acid upon
a dry powdered substance often furnishes such characteristic indica-

either the arsenic or lead group? How can mercuric sulphide be separated
from the sulphides of copper and bismuth? How does ammonium hydroxide
act on a solution containing bismuth and copper ? State the action of strong,
hot hydrochloric acid on the sulphides of arsenic and antimony. Suppose a
solution to contain salts of iron, aluminum, zinc, and manganese, by what
process could these four metals be separated and recognized ? How can barium,
calcium, and strontium be recognized when dissolved together ? By what tests
is magnesium recognized? State a method of separating potassium when mixed
with other metallic compounds. How are ammonium compounds recognized
when in solution with other metals ?

392 ANALYTICAL CHEMISTRY.

tions of the presence or absence of certain acids, that this treatment
should never be omitted when a search for acids is made.

When the substance under examination is liquid, a portion should
be evaporated to dryness, and, if a solid residue remains, it should
be treated in the same manner as a solid.

Most non-volatile, organic substances (including most organic
acids) color sulphuric acid dark when heated with it.

Dry inorganic salts when heated with sulphuric acid either are
decomposed, with liberation of the acid (which may escape in the
gaseous state), or with liberation of volatile products (produced by
the decomposition of the acid itself), or no apparent action takes
place. See Table IX.

Detection of acids by means of reagents added to their
neutral or acid solution. Whenever a substance is soluble in
water, there is little difficulty of finding the acid by means of Table
X. ; but if the substance is insoluble in water, and has to be rendered
soluble by the action of acids, this table may, in some cases, be of no
use, because the acid originally present in the substance may have
been liberated, and escaped in a gaseous state (as, for instance, when
dissolving insoluble carbonates in acids), or the tests mentioned in
the table may refer to neutral solutions, while it is impossible to
render the solution neutral without re-precipitating the dissolved
acid. If calcium phosphate, for instance, be dissolved by hydro-
chloric acid, the magnesium test for phosphoric acid cannot be used,
because this test can be applied to a neutral or an alkaline solution
only ; in attempting, however, to neutralize the hydrochloric acid
solution, calcium phosphate itself is re-precipitated.

Table XI., showing the solubility or insolubility (in water) of over
300 of the most important inorganic salts, oxides, and hydroxides,
will greatly aid the student in studying this important feature. It
will also guide him in the analysis of inorganic substances, as it gives
directions for over 300 (positive or negative) tests for metals, and an
equal number for acids.

To understand this, it must be remembered that any salt (or oxide
or hydroxide) which is insoluble in water may be produced and pre-
cipitated by mixing two solutions, one containing the metal, the other
containing the acid of the insoluble salt to be formed. For instance :
Table XI. states that the carbonates of most metals are insoluble in
water. To produce, therefore, the carbonate of any of these metals
(zinc, for instance) it becomes necessary to add to any solution of

DETECTION OF ACIDS. 393

zinc (sulphate, chloride, or nitrate of zinc) any soluble carbonate
(sodium or potassium carbonate), when the insoluble zinc carbonate
is produced.

Soluble carbonates consequently are reagents for soluble zinc salts,
while at the same time soluble zinc salts are reagents for soluble
carbonates.

For similar reasons soluble zinc salts are, according to Table XI.,
reagents for soluble phosphates, arsenates, arsenites, hydroxides, and
sulphides, but not for iodides, chlorides, sulphates, nitrates, or
chlorates.

The insolubility of a compound in water is not an absolute guide
for preparing this compound according to the general rule given
above for the precipitation of insoluble compounds, there being some
exceptions.

For instance : Cupric hydroxide is insoluble in water ; therefore,
by adding solution of cupric sulphate to any soluble hydroxide, the
insoluble cupric hydroxide should be precipitated, and is precipitated
by the soluble hydroxides of potassium and sodium, but not perma-
nently by the soluble hydroxide of ammonium, on account of the
formation of the soluble ammonium cupric sulphate.

There are not many such exceptions, and to mention them in the
table would have greatly interfered with its simplicity, for which
reason they have been omitted.

For the same reason some compounds, which are not known at all,
have not been specially mentioned. For instance, according to Table
XI., aluminum carbonate and chromium carbonate are insoluble salts :
actually, however, these compounds can scarcely be formed, the
affinity between the weak carbonic acid and the feeble bases not
being sufficient to unite them. Also, bismuth nitrate and a lew
other salts are reported as soluble, while actually they suffer a
decomposition by water.

Finally, it may be stated that no well-defined line can be drawn
between soluble and insoluble substances. There is scarcely any
substance which is not slightly soluble in water, and many of the
so-called soluble substances are but very sparingly soluble, as, for
instance, the hydroxide and sulphate of calcium.

Table XII. shows the solubility of a large number of compounds
more accurately than Table XL ; it may be used for reference.

394

ANALYTICAL CHEMISTRY.

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DETECTION OF ACIDS.

395

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396

ANALYTICAL CHEMISTRY.

Table XI.

Systematically arranged table showing the solubility and
insolubility of inorganic salts and oxides in water.

The dark squares represent insoluble, the white soluble compounds.

Ca

Potassium

Sodium

Ammonium

M

Calcium

Barium

Strontium

Magnesium

Aluminum

Ferric

Ferrous

Zinc

Chromium

Nickel

Cobalt

Manganese

Stannic

Stannous

Arsenic

Arsenous

Antimony

Gold

Platinum

Copper

Bismuth

Cadmium

Mercuric

Mercurous

Silver.

Lead,

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DETECTION OF ACIDS.

397

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ALUMINUM.

AMMONIUM.

ANTIMONY.

BARIUM.

BISMUTH.

CADMIUM.

CALCIUM.

CHROMIUM.

COBALT.

COPPKR.

FERROUS.

FERRIC.

LEAD.

MAGNESIUM.

MANGANESE.

MERCUROUS.

MERCURIC.

NICKEL.

POTASSIUM.

STRONTIUM

ZINC.

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398 ANALYTICAL CHEMISTRY.

Special remarks. Often a solution is presented for analysis instead of a
solid substance, in which case some of it is evaporated to dryness. If a dry
residue is left, this is tested for acids, as already described. But no residue may
remain, and if the solution has a strongly acid reaction, the presence of the
volatile acids is indicated, and the student, guided by the odor and change of
color upon evaporation, should make tests for the following acids: hydro-
chloric, hydrobromic, hydriodic, nitric, sulphurous (hydrocyanic, acetic,
formic).

If a strongly acid, fuming, oily residue is left, sulphuric acid is indicated.

A strongly acid, pasty, non-fuming residue indicates phosphoric acid.

If the solution is strongly acid and leaves a solid residue, the substance may
be either an acid salt, or a salt held in solution by an acid, such as hydrochloric,
nitric, sulphuric, etc., in which case several acids would have to be looked for.
The presence of the volatile acids would be indicated by holding wet blue
litmus-paper in the vapor as the liquid approached high concentration. If the
residue upon evaporation is decidedly alkaline, this maybe due to a salt having
an alkaline reaction, or to a hydroxide, or both. The presence of a hydroxide
is shown by adding some solution of silver nitrate to the diluted solution, when
a dark precipitate of silver oxide is formed at once. In the absence of carbon-
ate, the presence of hydroxide is also shown by adding some dry ammonium
chloride to the solution and warming, when ammonia is liberated. A solution
containing a hydroxide must, of course, be neutralized before applying the tests
for acids. The acid usually employed for this is dilute nitric, but if tests are
also to be made for the latter acid, another portion of the solution is neutralized
with hydrochloric or acetic acid.

A solution may be colorless, odorless, practically neutral, leave no residue
upon evaporation, and still not be plain water. In such a case, the student may
suspect hydrogen dioxide. He would have reason to suspect this compound if
he proceeded to search for metals before evaporating and found none, but got a
precipitate of sulphur when using hydrogen sulphide, showing an oxidizing
action.

The presence of some metals interferes with certain tests for acids, and these
should be removed. After determining the kind of metal or metals in a sub-
stance or a mixture, and it is seen that there will be interference with the tests
for acids, boil some of the substance with a slight excess of sodium or potassium
carbonate for some time and filter. Non-alkali metals, except arsenic and
antimony, remain behind, while the acids pass into the filtrate as alkali salts
(with few exceptions). The filtrate is then exactly neutralized with nitric acid
and boiled to expel all carbonic acid, and used for the various tests for acids.
Arsenic and antimony may be removed by passing hydrogen sulphide into the
warm acidified solution and filtering.

Substances insoluble in water. When a single substance, or that part of a
mixture which is insoluble in water, is treated with hydrochloric acid in order
to prepare a solution for the analysis of metals, something can be learned as to
the nature of the acids in combination. Carbonates, sulphites, phosphates,
arsenates, and arsenites behave the same as when treated with concentrated
sulphuric acid in Table IX. Sulphides give the odor of hydrogen sulphide. If
chlorine gas is given oif, the presence of a higher oxide, like MnO2, PbO2, BaO2,
etc., or a chromate is indicated. If effervescence takes place and an inflamma-

DETECTION OF ACIDS. 399

ble gas is given off, the presence of a free metal is indicated. If the substance
simply dissolves and no acids are subsequently found, the presence of an oxide
or hydroxide is indicated, which can also be judged from a knowledge of the
known compounds of the metals present.

The tests distinguishing between an arsenite and an arsenate (see Chapter on
Arsenic) cannot be applied when the substance is insoluble in water (except the
inolybdate test, which can be used in an acid solution), but the treatment with
hydrogen sulphide can be used to differentiate, because an arsenite gives a pre-
cipitate instantly even in cold solution, while an arsenate precipitates only after
a long time.

If bismuth is present, remove it before testing for the acids by boiling with
sodium carbonate, filtering, etc., as described above.

Substances insoluble in water and hydrochloric acid are next treated with
nitric acid. Ordinarily very few such substances are presented. If brown
vapors are evolved and sulphur separates, a sulphide is indicated, which the
appearance of the substance will also suggest. If brown vapors alone are
evolved, a free metal is indicated.

If the preliminary tests for metals show the presence of mercury, and the
substance dissolves slowly on boiling with nitric acid, it is one of the halogen
salts. The mercury should be removed by boiling the substance with an excess
of caustic alkali, filtering, neutralizing the filtrate with nitric acid, and testing
it for chloride, bromide, or iodide.

Before examining for metals, nitric acid solutions must be evaporated to dry-
ness to expel excess of the acid. The residue is dissolved in water.

A few substances require nitro-hydrochloric acid for solution. The one most
likely to occur ordinarily is mercuric sulphide, which is indicated by the pres-
ence of mercury, its black or vermilion color, and volatility on heating.

Of substances insoluble in all acids, the sulphates of barium, strontium, and
lead are the most likely to be presented ordinarily. The treatment of these by
fusion with sodium carbonate has already been mentioned. The presence of
silver (as shown by the preliminary tests for metals) would indicate a chloride,
bromide, iodide, or cyanide of this metal. The metal should be removed by
boiling with caustic alkali and the filtrate tested. Silver iodide does not yield
to this treatment, but its color and insolubility in strong ammonia is sufficient
evidence of iodide. Silver cyanide with hydrochloric acid forms silver chloride
and hydrocyanic acid, which is in solution and recognized by its odor.

The insoluble halogen salts of silver, lead, and mercury, also mercuric chloride
and bromide, scarcely react when treated with concentrated sulphuric acid
(Table IX).

Most of the points in the discussion above are shown in more convenient
form in the following Tables, XIII and XIV, which are more detailed than Table
IX, and will perhaps be of greater help to the student. Table XIV deals with
difficultly soluble or insoluble substances, which may be subnitrate ; subchlor-
ide; chloride (Pb, Hg(ous),Ag) ; bromide (Pb, Hg(ous),Ag) ; iodide; sulphate
(Ca, Sr, Ba, Pb, Hg(ous) ; sulphite (except of alkalies) ; sulphide (except of
alkalies and alkaline earths) ; carbonate, borate, phosphate, arsenate, arsenite
(except of alkalies in each case); chromate (high color) ; fluoride; cyanide;
oxide or hydroxide (except of alkali and alkaline earth metals) ; and a few
others.

In the case of mixtures,, the tables may be used to determine as far as

400

ANALYTICAL CHEMISTRY.

possible the nature of the acids, after which such other acids must be
looked for as are not clearly indicated by the tables, but may be suggested
as probably present by the preliminary examinations and the nature of the
metals found.

TABLE XIII.— Substances soluble in water.

A. When the substance is
already in solution, test with
litmus paper and evaporate
20 c.c. to dryness :

B. When the substance is ir
to litmus paper and —

I. Warm a little with di-
lute sulphuric acid :

\, the dry state, test its reaction

II. If I gives no indication,
heat moderately a small quan-

tny with concentrated sul-
phuric acid.

strongly acid and

HC1, HBr, HI, HNO3,
HCN* or H2SO3. Note
odor of vapors and test for
the acid indicated by odor,
etc.

a. Copious effervescence,
no color or odor — test for
carbonate (strongly alka-
line) or bicarbonate (weakly
alkaline).

a. White fumes — test for
HC1, HF or HN03. Note
odor. The salt is neutral
or slightly acid.

L (-1 -i j f

6. A strongly acid, fum-
ing residue — test for free
H2S04.

b. Moderate efferves-
cence. TIO color, but with an
1. Odor of SO2 test for

1. Brownish — test for
bromide.
2. V i o 1 e t — test for
iodide.

c. A strongly acid, soft,
non-fuminq mass — test for
free H3PO4.

sulphite (alkaline).
Odor of SO2 -j- precipi-
tate of sulphur — test for
thiosulphate (neutral).

3. Greenish -yellow — test
for chlorate.
(Bromates and iodates,
like chlorates, also give

d. A strongly acid, com-
bustible mass — test for free

A. \JQOT ot ±i2o — test lor
a sulphide (alkaline).
3. Odor of HCN*— test

colored fumes and defla-
grate on charcoal.)

H3PO2: a neutral combus-
tible mass, indicates a salt
of H3PO2 (hypophosphor-
ous acid).

for cyanide (alkaline).
4. Odor of HCN and a
cryst. deposit, often bluish
— test for ferro- or ferri-
cyanide.

c. Chromates and dichro-
mates are recognized by
their color and give green
solutions in hot concen-

e. Strongly acid, leaving

5. Odor of HCN -f ppt.
of sulphur — test for a sul-

trated H2SO4.

a solid residue — it may be
an acid salt or a salt held
in solution by an acid, as

phocyanate.

d. No change takes place.
It may be sulphate (neu-

HC1, HN03, H2S04, etc.
Refer to B.

c. Colored fumes.

tral or slightly acid), phos-
phate (alkaline), arsenate
or arsenite (alkaline), bo-

f. A slightly acid white
residue which melts at high
heat — test for free boric
acid.

trite (alkaline).
2. Greenish, with odor
of Cl — test for hypochlorite
(alkaline).

rate (alkaline), boric acid,
or a free base. All these
acids would be indicated in
the preliminary examina-
tions and the analysis for
the metals. If the sub-

g. A weakly acid, neu-
tral, or alkaline residue —
it may be a salt or a free
base, or both. Refer to B.

* Caution. — Take care in
smelling vapors of HCN,
as they are poisonous.

stance is alkaline and gives
a precipitate (dark) with
solution of AgNO3, a free
base is present. Test also
on NH4C1.

DETECTION OF 'ACIDS. 401

TABLE XIV.— Substances insoluble or very difficultly soluble in water.

A. When the substance is
soluble in cold or hot, dilute
or strong hydrochloric acid:

Note.— It Pb, Hg(ous),
Ag, are indicated by the
preliminary examination,
omit treatment with HC1,
but use HNO3.

«. Note whether the
effects are the same as in
Table XIII, B, 7, a and b.
Make tests for the acids
indicated there.

b. If chlorine is given
off, a peroxide is present,
as MnO2, PbO?, BaO2, etc.,
or chromate (high color) .

c. If no change takes
place except solution —

1. Subnitrate (or sub-
chloride) is suspected if Bi
or Sb is found as metal.
Boil substance in slight ex-
cess Na2COs, filter, neutral-
ize filtrate and test for the
acid.

2. Test for phosphate by
molybdate solution.

3. Test for borate by al-
cohol flame.

4. Arsenate and arsenite
are detected in analysis for
metals: make further tests
to distinguish the two.

5. If no acid is found
and the substance is alka-
line, it is CaO or Ca(OH)2 ;
if neutral, it is an oxide, as
ZnO, MgO, PbO, etc., or
their hydroxides.

d. Effervescence and in-
flammable gas — indicate a
free metal, as Zn, Fe, Sn,
etc.

7>. When the substance is
insoluble or difficultly soluble
in hydrochloric, but soluble in
cold or hot, dilute or strong
nitric acid :

a. Brown vapors and a
precipitate of sulphur indi-
cate a sulphide.

6. Brown vapors alone
indicate free metal, as Ag,
Pb, Hg, Bi, Cu, etc.

c. If the substance is
white, volatile on foil by
heat, turns black with
XII4OH, and soluble in
HNO3 on long boiling, it
is likely HgCl or HgBr.
Test for the acid by boiling
some with dilute NaOH,
filter, acidify filtrate with
HNOS and add AgNO3.

(Likewise for Hgl and
HgI2, which are yellow and
red respectively.)

d. If no change except
solution, the substance is
likely an oxide or hydrox-
ide. This will also be indi-
cated by the metal present
and the appearance of the
compound.

C. When the substance is
insoluble in either hydro-
chloric or nitric, but is solu-
ble in a mixture of the acids :

It may be —

a. Mercuric sulphide,
HgS, black or red, and
volatile on foil by heat.

b. Gold.

c. Mercurous chloride,
HgCl. (Slowly soluble in
HNO3. See E, c.}

d. A few sulphides and
oxides.

D. When the substance is
insoluble in all acids :

It may be —

a. Sulphate of Ba, Sr,
Pb. These must be fused
with Na2CO3.

6. Lead chloride, PbCl2
(PbBr2, PbI2) (if not re-
moved by much hot water.)

c. Chloride, bromide,
iodide, or cyanide of silver,
AgCl, AgBr, Agl, AgCN.
Test solubility in XH4OH
and Na2S2O3.

(AgCN with HC1 forms
insoluble AgCl and leaves
HCN in solution recognized
by odor.)

d. Silicic acid and most
silicates, native A12OH,
Cr2O3, SnO2, CaF2.

402 ANALYTICAL CHEMISTRY.

38. METHODS FOR QUANTITATIVE DETERMINATIONS.

General remarks. Quantitative determination of the different
elements or groups of elements may be accomplished by various
methods, which differ generally with the nature of the substance to
be examined. But even one and the same substance may often be
analyzed quantitatively by entirely different methods, of which the
two principal ones are the gravimetric and volumetric methods.

In the gravimetric method, the quantities of the constituents of a
substance are determined by separating and weighing them either as
such, or in the form of some compound the exact composition of
which is known. For instance : From cupric sulphate, the copper
may be precipitated as such by electrolysis and weighed as metallic
copper, or it may be precipitated by sodium hydroxide as cupric oxide,
CuO, and weighed as such. Knowing that every 79.6 parts by weight
of cupric oxide contain of oxygen 16 parts and of copper 63.6 parts,
the weight of copper contained in the cupric oxide found may be
readily calculated.

In the volumetric method, the determination is accomplished by add-
ing to a weighed quantity of the substance to be examined, a solution
of a reagent of a known strength until the reaction is just completed,
no excess being allowed. For instance : We know that every 80.12
parts by weight of sodium hydroxide precipitate 79.6 parts by weight
of cupric oxide, containing 63.6 parts by weight of copper. There-
fore, if we add a solution of sodium hydroxide of known strength to a
weighed portion of cupric sulphate until all the copper is precipitated,

QUESTIONS. — Why is sulphuric acid added to a solid substance when it is to
be examined for acids ? Mention some acids which cause the liberation of
colorless, and some which cause the liberation of colored gases when the salts
of these acids are heated with sulphuric acid. Mention an acid which is pre-
cipitated by barium chloride in acid solution, and some acids which are pre-
cipitated by the same reagent in neutral solution. Which acids may be pre-
cipitated by silver nitrate from neutral solutions, and which from either neutral
or acid solutions? Mention some acids which form soluble salts only. Mention
three soluble, and three insoluble carbonates, phosphates, arsenates, sulphates,
and sulphides respectively. Which oxides or hydroxides are soluble, and
which are insoluble in water? Mention some metals the solutions of which
are precipitated by soluble chlorides, iodides, and sulphides. State a general
rule according to which most insoluble salts may be formed from two other
compounds. Why is it sometimes impossible to render a substance soluble in
order to test for the acid in the solution obtained ?

METHODS FOR QUANTITATIVE DETERMINATIONS. 403

we may calculate from the volume of soda solution used the weight of
sodium hydroxide, and from this the weight of copper which has been
precipitated. The operation of volumetric analysis is termed titration.

Gravimetric methods. While the quantitative determinations by
these methods differ widely in some cases, there are a number of oper-
ations so often and so generally employed that a few remarks may be
of advantage to the beginner. A small quantity (generally from 0.5
to 1 gramme) of the substance to be analyzed is very exactly weighed
on a delicate balance, transferred to a beaker, and dissolved in a suit-
able agent (\vater or acid). From this solution the constituent to be

FIG. 59.

Drying-oven.

determined is precipitated completely, which is ascertained by allow-
ing the precipitate to subside and adding to the clear liquid a few
drops more of the agent used for precipitation. The, precipitate is
next collected upon a small filter of good filter paper containing as
little of inorganic constituents (ash) as possible ; the particles of pre-
cipitate which may adhere to the beaker are carefully washed off by
means of a camelVhair brush. The precipitate is well washed (gen-
erally with pure water) until free from adhering solution, and dried
by placing funnel and contents in a drying- oven, Fig. 59, in which a
constant temperature of about 100° C. (212° F.) is maintained. The
dried filter is then taken from the funnel and its contents are trans-
ferred to a platinum (or porcelain) crucible, which has been previously

404

ANALYTICAL CHEMISTRY.

weighed and stands on a piece of glazed, colored paper in order to
collect any particle of the dried precipitate which may happen to fall
beside the crucible. The filter, from which the precipitate has been
removed as completely as possible, by slightly rubbing it, is now
folded, placed upon the lid of the crucible, which rests on a triangle
over a gas burner, and completely incinerated. The remaining filter-
ash, with particles of the precipitate mixed with it, is transferred to
the crucible, which is now placed over the burner and heated until
all water (or possibly other substances) is completely expelled. After
cooling, the crucible is weighed, the weight of the empty crucible and
that of the filter-ash (the latter having been previously determined
by burning a few filters of the same kind) deducted, and thus the
quantity of the precipitate determined.

As platinum crucibles and many precipitates, after ignition, absorb
moisture from the air, it is well to allow the heated crucible to cool
in a desiccator. This is a closed vessel in which the contained air is
kept dry by means of concentrated sulphuric acid. Fig. 60 shows a
convenient form of desiccator.

The empty crucibles should be weighed under the same conditions
— i. e., after having been heated and cooled in a desiccator.

FIG. 60.

FIG. 61.

Desiccator.

Watch-glasses for weighing filters.

Some precipitates (as, for instance, potassium platinic chloride),
cannot be ignited without suffering partial or complete decomposition.
It is for this reason that some precipitates are collected upon filters
which have been previously dried at 100° C. (212° F.) and weighed
carefully. The precipitate is then collected upon the weighed filter,
well washed, dried at 100° C. (212° F.) and weighed.

The weighing of dried filters is best accomplished by placing them

METHODS FOR QUANTITATIVE DETERMINATIONS. 405

between two watch-glasses held together by means of a brass or nickel
clamp, as shown in Fig. 61.

The above-described methods may be employed for the determina-
tion of those substances which can be precipitated from their solu-
tions in the form of some stable compound. Aluminum, zinc, iron,
bismuth, copper, etc., may, for instance, be precipitated as hydroxides
and weighed as oxides, into which the precipitated compound is con-
verted by ignition. Sulphuric acid may be precipitated and weighed
as barium sulphate, phosphoric acid may be precipitated by magnesia
mixture and weighed as magnesium pyrophosphate, etc. Some sub-
stances, like nitric acid, chloric acid, etc., cannot be precipitated from
their solutions, for which reason other methods have to be employed

for their determination.

FIG. 63.

FIG. 62.

10 CO

Liter flask.

Pipettes.

406 ANALYTICAL CHEMISTRY.

Volumetric methods. The great advantage of volumetric over
gravimetric analysis consists chiefly in the rapidity with which these
determinations are performed. Unfortunately, volumetric methods
cannot be employed to advantage for the estimation of all substances.

The special apparatus required for volumetric analysis consists of
a few flasks, some pipettes, burettes, and a burette-holder. The flasks
should have a mark on the neck, indicating a capacity of 100, 250,
500, and 1000 c.c. respectively. (See Fig. 62.)

FIG. 64. FIG. 65.

Mohr'8 burette and clamp. Mohr,g burette and hoMer

Of pipettes (Fig. 63) are mostly used those having a capacity of
5, 10, 25, and 50 cubic centimeters.

Of burettes many different forms are used; in most cases Mohr's
burette (Pigs. 64 and 65) answers all requirements, but its applica- •

METHODS FOR QUANTITATIVE DETERMINATIONS. 407

tion is excluded whenever the test solution is chemically affected by
rubber, as in the case of solutions of silver, permanganate, and a few
other substances. For such solutions pIQ 66

Mohr*s burette with glass stopcock, or
Gay Lussac's burette (Fig. 66) is generally
used.

Standard solutions are solutions con-
taining a known and definite quantity of
some reagent employed in volumetric
analysis. A standard solution may be
normal, or it may be an empirical solu-
tion. In the latter case it contains in
a liter some arbitrarily chosen weight of
reagent. As an instance may be men-
tioned Fehling's solution, used for the
determination of sugar. This solution
is so adjusted that 1 c.c. decomposes or
indicates 0.005 gm. of grape-sugar.

Normal solutions. The solutions gen-
erally used in volumetric analysis are
known as normal solutions, and are
chemically equivalent to each other be-
cause of the standard adopted in their
preparation. This standard is one gm.
of hydrogen, or the weight of one atom
of hydrogen expressed in grammes, or
the chemical equivalent of one gm, of
hydrogen, contained in one liter of solu-
tion. For the sake of convenience the terms
gram-atom and gram-molecule are often
used in connection with volumetric work, Gay Lussac's burette.
and refer, of course, to the atomic or molecular weight of the substance
considered, expressed in grammes.

A consideration of the application of these principles to practical work is
volumetric analysis may assist the student in understanding them fully.

Thus, a normal add solution may be defined as one containing in a liter
as much acid as contains one gram-atom of replaceable hydrogen. In such
acids as HC1, HBr, HN03, a liter solution containing the gram-molecule would
be normal, since each solution would contain one gram-atom of replaceable
hydrogen. In order to make a normal solution of such acids as H2SO4, H2C2O4,

408 ANALYTICAL CHEMISTRY.

one-half the gram-molecule must be taken, since this quantity contains one
atom of hydrogen, and so on.

A normal alkali solution may be defined as one containing that quantity of
alkali in a liter which is chemically equivalent to— i. e., neutralizes^ one gram-
atom of acid hydrogen. For such compounds as KOH, NaOH, NH4OH, the
whole gram-molecule must be taken to make a liter of normal solution. In
case of Ba(OH)2 or Ca(OH)2, one half the gram-molecule is taken.

It will easily be seen that all the acid solutions made as described are of
equivalent strength and are exactly equivalent to the solutions of alkali— i. e., one
liter normal HC1 will exactly neutralize one liter of normal KOH, or NaOH,
or Ba(OH)2. That this is so will appear at once on writing the equations
which express the reactions between these alkalies and acids, thus:

HC1 + KOH = KC1 + H2O.
36.18 55.74

2HC1 + Ba(OH)2 = BaCl2 + 2H2O.

36.18

L

KOH + H2SO* = K£O*- + H2O.
55,4 ^

The above equations show that 36.18 gramme of HC1 are equivalent to
55.74 gramme of KOH, but these are the quantities taken for a liter of normal
solution respectively, hence these normal solutions must be equivalent. Simi-
larly for HC1 and Ba(OH)2, for KOH and H2SO4, etc.

Conversely, if a solution of unknown strength be compared by titration with
a second solution known to be normal, and then be properly diluted so that the
two are equivalent, volume for volume, the first solution will also be normal,
and from the definition of normal solutions the quantity of reagent in a liter
of the solution becomes at once known. For example, if a solution of sul-
phuric acid be made equivalent to a normal solution of caustic alkali it will
then contain 48.675 grammes of absolute sulphuric acid per liter. It is thus
an easy matter to prepare normal solutions, although it may be impossible to
weigh exactly the amount of reagent necessary for a liter of such solutions.
All that is required is one normal solution as a starting-point.

Sodium carbonate, Na2C03, may be used as an alkali, just as KOH or NaOH,
because it neutralizes acids in precisely the same manner, for the carbonic acid
has no effect, being volatile and escaping into the air. The decomposition
taking place thus:

Na2CO3 + 2HC1 = 2NaCl + H2O + CO2, •

shows that one molecule of sodium carbonate neutralizes two molecules of
hydrochloric acid, consequently one-half gram-molecule of sodium carbonate
must be taken to make a liter of normal solution. A similar consideration
will show that of sodium bicarbonate the whole gram-molecule should be

METHODS FOR QUANTITATIVE DETERMINATIONS. 409

taken for a liter of normal solution, because this salt contains but one atom of
aodium in the molecule.

A normal salt solution may be defined as one containing in a liter the quan-
tity of salt resulting from the neutralization, or replacement of the hydrogen

in a normal acid solution by metal. Thus, ^^^ Na(j^ AgNO3, BaC12? ex-

L 2

pressed in grammes, would be contained in a liter of normal solution of the
respective salts.

Often normal solutions are too strong, and are diluted ten or a hundred
times. They are then called deci- or centi-normal solutions, respectively.

Normal solutions are generally designated by *, deci-normal solu-
tions by ~y centi-riorraal solutions by ^ ; solutions containing twice
the amount are designated as double normal, | ; half the amount
semi-normal, *.

Different methods of volumetric determination. Of these we
have at least three, which may be called the direct, the indirect, and
the method of rest or residue.

The direct methods are used in all cases in which the quantities of
volumetric solutions can be added until the reaction is complete : for
instance, until an alkaline substance has been neutralized by an acid,
or a ferrous salt has been converted into a ferric salt by potassium
permanganate, etc.

In the indirect methods one substance, which cannot well be deter-
mined volumetrically, is made to act upon a second substance, with
the result that, by this action, an equivalent quantity of a substance
Is generated or liberated, which may be titrated. For instance : Per-
oxides, chromic and chloric acids when boiled with strong hydro-
chloric acid, liberate chlorine, which is not determined directly, but
is caused to act upon potassium iodide, from which it liberates the
iodine, which may be titrated with sodium thiosulphate.

The methods of residue are based upon the fact that while it is im-
possible or extremely difficult to obtain complete decomposition
between certain substances and reagents, when equivalent quantities
are added to one another, such a complete decomposition is accom-
plished by adding an excess of the reagent, which excess is afterward
determined by a second volumetric solution. For instance: Car-
bonate of calcium, magnesium, zinc, etc., cannot well be determined
directly, for which reason an excess of normal acid is used for their
decomposition, this excess being titrated afterward by means of an
alkali.

Indicators. In all cases of volumetric determination it is of the
greatest importance to observe accurately the completion of the reac-

41() ANALYTICAL CHEMISTRY.

tion. In some cases the final point is indicated by a change in color,
as, for instance, in the case of potassium permanganate, which changes
from a red to a colorless solution, or chromic acid, which changes
from orange to green under the influence of deoxidizing agents. In
other cases the determination is indicated by the formation or cessa-
tion of a precipitate, and in yet others the final point could not be
noticed with precision unless rendered visible by a third substance
added for that purpose.

Such substances are termed indicators. Litmus, phenolphthalein,
methyl-orange, etc., are used as indicators in acidimetry and alka-
limetry. Starch paste is an indicator for iodine, potassium chromate
for silver, etc. Of indicators, a few drops are in most cases sufficient
for the purpose. (See colored Plate VII.)

Litmus solution. This is made by exhausting coarsely powdered litmus with
boiling alcohol, which removes a red coloring matter, erythrolitmin. The
residue is treated with about an equal weight of cold water, so as to dissolve
the excess of alkali present in litmus. The remaining mass is extracted with
about five times its weight of boiling water, and filtered. The solution should
be kept in wide-mouthed bottles, stoppered with loose plugs of cotton to ex-
clude dust but to admit air. Blue and red litmus paper is made by impregnat-
ing strips of unsized white paper with the blue solution obtained by the above
process, or with this solution after just enough hydrochloric acid has been
added to impart to it a distinct red tint.

Phenolphthalein solution. 1 gramme of phenolphthalein is dissolved in 50 c.c.
of alcohol and water added to make 100 c.c. The colorless solution is colored
deep purplish-red by alkali hydrates or carbonates, but not by bicarbonates ;
acids render the red solution colorless. The solution is not suitable as an indi-
cator for ammonia. Carbonates must be titrated in boiling solution to drive
off carbon dioxide.

Methyl-orange solution. 1 gramme of methyl-orange (also known as helian-
thin, tropseolin D, or Poirier's orange 3 P), the sodium or ammonium salt of
dimethylamido-azobenzol-sulphonic acid (CH3)2N.C6H4.N.NC6H4.SO3H, is dis-
solved in 1000 c.c. of water. To the solution is carefully added, with constant
stirring, jj sulphuric acid, in drops, until the liquid turns red and just ceases
to be transparent; it is then filtered. The solution is yellow when in contact
with alkaline hydrates, carbonates, or .bicarbonates. Carbonic acid does not
affect it, but mineral acids change its color to crimson. It should be used in
cold solutions.

Hcematoxylin solution. 0.2 gramme of hsematoxylin ((a vegetable coloring-
matter derived from hsematoxylon) is dissolved in 100 c.c. of alcohol. The alka-
line solution has a purple color which is changed to yellow or orange by acids.

Rosolic acid solution. 1 gramme of commercial rosolic acid (chiefly C20H]6O3)
is dissolved in 10 c.c. of alcohol, and water added to make 100 c.c. The solu-
tion turns violet red with alkalies, yellow with acids.

METHODS FOR QUANTITATIVE DETERMINATIONS. 411

Other indicators used at times in acidimetry are solutions of bra-
zil-wood, cochineal, methyl-violet, alizarin, iodeosin, Congo red, turmeric,
etc.

Ionic explanation of the action of indicators. The substances used to indicate
the neutralization point are themselves very weak acids or bases, capable of
forming salts with the bases or acids that are brought together in solution for
the purpose of neutralization. The undissociated molecules of the indicator
have a different color from its ions, and it must have feeble dissociating power
in the uncombined state. The latter is a characteristic of feeble acids in gen-
eral. The salts of the indicators are easily dissociated into ions. Substances
that are strong acids or bases cannot be used as indicators, because they disso-
ciate in the free state, and thus give no different color when they are neutral-
ized. The indicators that dissociate least in the free state are the most sensitive
in color changes when combined with traces of acids or bases. The neutral
point in neutralization experiments is really overstepped by the amount
of acid or alkali required to produce change of color with the indicator,
but in the case of sensitive indicators this amount is a mere trace and is
negligible.

Litmus is an acid with slight dissociating power, which in pure water gives
a violet color. Addition of acids represses the slight dissociation and the color
changes to red, which is the color of the undissociated molecules of litmus.
Alkalies form salts with litmus, which dissociate easily, the negative ions show-
ing a blue color.

Phenolphthalein is an acid of less dissociating power than litmus. In
pure water or acids it is colorless, in alkaline solutions it is red, which is
the color of the negative ions of the dissociated molecules of the salt of the
indicator.

Methyl-orange is an acid of greater dissociating power than litmus. It dis-
sociates slightly when greatly diluted in water, giving a yellow color, which is
the color of the negative ions. With less water the color is orange, which is
the resultant of the yellow color of the ions and the red color of the un-
dissociated molecules. In acid solutions the dissociation of the indi-
cator is repressed, and the color is pure red. In alkaline solutions, salts
of the indicator are formed which dissociate freely and give an intense
yellow color.

Because different indicators, as well as different acids and bases, show great
differences in their degrees of dissociation, marked variations in the sensitive-
ness of indicators to acids and bases are observed. Hence, indicators must be
chosen to suit the particular case of neutralization in hand for accurate work.
For example, if an active acid is titrated with ammonia and phenolphthalein
as indicator, color is not produced sharply at the neutral point, because am-
monium hydroxide is so little dissociated that it requires an appreciable excess
beyond the neutral point to produce the dissociated salt with the indicator. In
this case litmus or methyl-orange is suitable to use.

Titration. This term is used for the process of adding the
volumetric solution from the burette to the solution of the

412 ANALYTICAL CHEMISTRY.

weighed substance until the reaction is completed. We also
speak of the standard or titer of a volumetric test-solution, when
we refer to its strength per volume (per liter or per cubic centi-
meter).

Of the principal processes of titration, or of volumetric meth-
ods used, may be mentioned those based upon neutralization (acid-
imetrv and alkalimetry), oxidation and reduction (permanganates
and chromates as oxidizing, oxalic acid and ferrous salts as
reducing agents) precipitation (silver nitrate by sodium chloride),
and finally those which depend on the action of iodine and thio-
sulphate (iodimetry).

The substance to be titrated should be diluted with pure water to a
volume of about 75 c.c. The relationship between any two volumetric
solutions, for example, acid and alkali, should also be determined in
the same volume. Any convenient quantity, as 10 or 20 c.c., of one
solution is drawn from a burette into a beaker and diluted to about
75 c.c. before titrating with the other solution. If the comparison is
made in a much smaller or much greater volume, a somewhat different
relationship will be found. In general, the titer of a volumetric solu-
tion should be determined in a volume corresponding approximately to
that in which the titration of a substance is to be carried out. This
is usually the volume stated above, but sometimes, for certain reasons,
it may be much greater.

Acidimetry and alkalimetry. Preparing the volumetric test-
solutions is often more difficult than to make a volumetric deter-
mination. Whenever the reagents employed can be obtained in a
chemically pure condition it is an easy task to prepare the solution,
because a definite weight of the reagent is dissolved in a definite
volume of water. In many instances, however, the reagent cannot
be obtained absolutely pure, and in such cases a solution is made and
its standard adjusted afterward by methods which will be spoken of
later.

Neither the common mineral acids, such as sulphuric, hydro-
chloric, and nitric acids, nor the alkaline substances, such as sodium
hydroxide or ammonium hydroxide, are sufficiently pure to permit of
being used directly for volumetric solutions, because these substances
contain water, and an absolutely correct determination of the amount
of this water is an operation which involves a knowledge of gravi-
metric methods.

METHODS FOR QUANTITATIVE DETERMINATIONS. 413

It is for this reason that the basis in preparing a volumetric normal
acid solution is oxalic acid, a substance which can be readily obtained
in a pure crystallized condition.

Normal acid solution. Crystallized oxalic acid has the com-
position H2C2O4.2H2O and a molecular weight of 125.1. Being
dibasic, only half of its weight is taken for the normal solution,
which is made by placing 62.55 grammes of pure crystallized oxalic
acid in a liter flask, dissolving it in pure water, filling up to the
mark at the temperature of 25° C. (77° F.) and mixing thoroughly.

Normal solutions of sulphuric or hydrochloric acid are, for various
reasons, often preferred to oxalic acid. These solutions are best
made by diluting approximately the acids named, titrating the solu-
tion with normal sodium hydroxide, using phenolphthalein as an
indicator, and adding water until equal volumes saturate one another.
For instance, if it should be found that 10 c.c. normal alkali solution
neutralize 7.6 c.c. of the acid, then 24 c.c. of water have to be added
to every 76 c.c. of the acid in order to obtain a normal solution.
Normal sulphuric acid contains 48.675 grammes of H2SO4, and normal
hydrochloric acid 36.18 grammes of HC1 per liter.

These normal solutions can be made conveniently by diluting either 30 c.c.
of pure, concentrated sulphuric acid of sp. gr. 1.84, or 130 c.c. of hydrochloric
acid of sp. gr. 1.16 to 1000 c.c. The solutions thus obtained are yet too con-
centrated and are adjusted as described above.

Other methods of determining the exact standard of normal acids depend
upon the precipitation of 10 c.c. of the sulphuric acid solution by barium
chloride, or of 10 c.c. of the hydrochloric acid solution by silver nitrate, and
weighing the precipitated barium sulphate or silver chloride. Ten c.c. of
normal sulphuric acid give 1.1587 grammes of barium sulphate, and 10 c.c. of
normal hydrochloric acid 1.423 grammes of silver chloride.

A third method depends on the formation of, and the weighing as, an
ammonium salt. Ten c.c. of either acid are neutralized (or slightly super-
saturated) with ammonia water. The solution is evaporated in a previously
weighed platinum dish over a water-bath, the dry salt is repeatedly moistened
with alcohol, and finally dried in an air-bath at a temperature of 105° C.
(221° F.) for about half an hour. Ten c.c. of normal sulphuric acid give of
ammonium sulphate 0.65605 gramme, and 10 c.c. of normal hydrochloric acid
of ammonium chloride 0.5311 gramme.

Normal alkali solution. A normal solution of sodium carbonate
may be made by dissolving 52.655 grammes (one-half the molecular
weight) of pure sodium carbonate (obtainable by heating pure sodium
bicarbonate to a low red-heat) in water, and diluting to one liter.
This solution, however, is not often used, but may serve for standard-

414 ANALYTICAL CHEMISTRY.

izing acid solutions, as it has the advantage of being prepared from a
substance that can be easily obtained in a pure condition, which is
not the case in preparing the otherwise more useful normal solutions
of potassium or sodium hydroxide, both of which substances contain
and absorb water.

The solutions are made by dissolving about 70 grammes of potas-
sium hydroxide or 60 grammes of sodium hydroxide in about 1000
c.c. of water, titrating this solution with normal acid, and' diluting it
with water, until equal volumes of both solutions neutralize each
other exactly.

The indicators used in alkalimetry are chiefly solution of litmus
or phenolphthalein, only a few drops of either solution being needed
for a determination.

The method adopted by the U. S. P. for standardizing the caustic
alkali solution, prepared as above mentioned, depends on the use of
chemically pure potassium bitartrate which acts on the alkali thus :

KHC4H4O6 + KOH = K2C4H4O6 + H2O.

As the molecular weight of potassium bitartrate is 186.78 it follows
that this weight in grammes will neutralize one liter of normal alkali
solution. The Pharmacopoeia directs to dissolve 9.339 grammes of
potassium bitartrate in boiling water and titrating with a portion of the
caustic alkali solution, the remainder of which is then diluted until 50 c.c.
are required for neutralization. Phenolphthalein is used as indicator.
Whenever carbonates are titrated with acids, or vice versa, the
solution has to be boiled towaid the end of the reaction in order to
drive off the carbon dioxide, as neither of the two indicators men-
tioned gives reliable results in the presence of carbonic acid or an
acid carbonate. This boiling is unnecessary when methyl orange is
used, because it is not influenced by carbonic acid.

When salts of organic acids with alkali metals are to be titrated with normal
acids, these salts are first converted into carbonates. This is accomplished by
igniting the weighed quantity of the salt in a crucible of porcelain or platinum.
The chemical action which takes place during the ignition of potassium acetate
may be shown thus :

2KC2H302 -f 80 = K2CO3 + 3H2O + 3CO2.

In a similar manner the alkali salts of all organic acids are converted into
carbonates. Frequently some carbon is left unburned ; this, however, does not
interfere with the result of the titration. The titration is made with the liquid
obtained by dissolving in water the residue left after ignition.

Method for calculating results. Before one can calculate how
much, say, of an acid is in a solution which he is titrating with a

. METHODS FOR QUANTITATIVE DETERMINATIONS. 415

normal alkali, it is necessary to know how much of the acid in
question is equivalent to — i. e., is required to neutralize — one c.c. of
the alkali. Knowing this, it is easy to find how much acid is equiva-
lent to a certain number of c.c. of normal alkali used in titration.
These alkali equivalents of normal acid, or acid equivalents of a
normal alkali, are easily found by the student from the equation
of reaction.

Thus, to find how much HC1 is equivalent to one c.c. of normal alkali, we
use the equation :

HC1 + KOH == KC1 + H2O,
36.18 55.74
from which we see that

36.18 gm. HC1 = 55.74 gm. KOH == 1000 c.c. normal KOH,
or, 0.03618 gm. HC1 1 " «

2KOH + H2S04 = K2S04 + 2H2O.
2 X 55.74 97.35

97.35 gm. H2SO4 = 2 X 55.74 gm. KOH = 2000 c.c. normal KOH.
48.675 " " 55.74 " " = 1000 "

0.048675 " 1 "

Phosphoric acid presents a peculiar case. When tropaeolin is used as an
indicator the change in color takes place when this reaction is completed :

H3P04 + KOH = KH2P04 + H20.
97.29 55.74
Hence,

97.29 gm. H3PO4 =r 55.74 gm. KOH == 1000 c.c. normal KOH.

0.09729 " " = 1 "

With phenolphthalein, the indicator changes color when the subjoined reac-
tion is completed :

H3P04 + 2KOH = K2HPO4 + 2H2O.
Hence,

97.29 gm. H3P04 = 2 X 55.74 gr. KOH ~ 2000 c.c. normal KOH.
or 0.04864 " " 1 "

The calculation for the amount of acid or alkali is made in this way. Sup-
pose we weigh off 10 grammes of dilute sulphuric acid. On titrating with
normal KOH it is found that 20 c.c. are required to cause the change in the
indicator (litmus) — i. e., to completely neutralize the acid. We know from the
above that 1 c.c. normal KOH requires 0.04867 gramme H2SO4 for neutraliza-
tion, hence 20 c.c. normal KOH require 0.04867 X 20 = 0.9735 gramme H2SO4,
That is, in the 10 grammes dilute acid weighed off there are 0.9735 gramme
H2SO4, or in 100 grammes there are 9.735 grammes, or 9.73 per cent. This
instance will serve as a type for all calculations of percentages.

Use of empirical solutions. The primary advantage in using normal, deci-
normal, etc., solutions is the fact that the calculations of results is very much
simplified in a system which involves molecular and atomic weights, or simple
fractions thereof. But any solution of definite strength can be employed. All

416 ANALYTICAL CHEMISTRY.

normal, decinormal, etc., solutions deteriorate in time, some very slowly, others
rapidly, especially when not properly preserved. To restore the titer of such
solutions each time they are to be used involves an unnecessary outlay of time.
All that is necessary to know is the exact ratio between the solutions and a normal
or decinormal solution, to determine which an accurately standardized solution
should be always available. To illustrate, suppose 12.5 c.c. of a hydrochloric
acid solution exactly neutralize 10 c.c. of normal potassium hydroxide solution,
then 1 c.c. of the hydrochloric acid is equivalent to 0.8 c.c. of normal acid, and
the volume of acid used in any titration is readily converted into the equivalent
volume of normal acid by multiplying by the factor 0.8.

Neutralization equivalents. The normal solutions of acid and
alkali may be used for the determination of a large number of sub-
stances, either directly (as in the case of free acids, caustic and alka-
line carbonates and bicarbonates) or indirectly (as in the case of salts
of most of the organic acids, with alkalies, which are first converted
into carbonates by ignition).

One c.c. of normal acid is the equivalent of:

Gramme.

Ammonia, NH3 0.01693

Ammonium carbonate, (NHJ2CO3 0.04770

Ammonium carbonate (U. S. P.), NH4HCO3.NH4NH2CO2 . . 0.05200

Lead acetate, crystalHzed Pb(C2H3O2)2.3H261 .... 0.18807

Lead subacetate, Pb2O(C2H3O2)2 1 0.13593

Lithium benzoate, LiC7H5O2 2 0.12711

Lithium carbonate, Li2CO3 0.03675

Lithium citrate, Li3C6H5O7 2 0.06952

Lithium salicylate, LiC7H5O3 2 0.14299

Potassium acetate, KC2H3O2 2 0.09744

Potassium bicarbonate, KHCO3 ....... 0.09941

Potassium bitartrate, KHC4H4O6 * 0.18678

Potassium carbonate, K2CO3 0.06863

Potassium citrate, crystallized, K3C6H5O7 H2O 2 . . . .. 0.10736

Potassium hydroxide, KOH 0.05574

Potassium permanganate, KMnO4 3 0.03139

Potassium sodium tartrate, KNaC4H4O6.4H2O 2 . . . ' . 0.14009

Potassium tartrate, 2K2C4H4O6.H2O 2 0^11679

Sodium acetate, NaC2H3O2.3H2O 2 0.13510

Sodium benzoate, NaC7H5O2 2 ....... 0.14301

Sodium bicarbonate, NaHCO3 0.08343

Sodium borate, crystallized, Na^CVlOH.O ....'. Q.18966

Sodium carbonate, monohydrate, Na,CO3.H2O .... 0.06159

Sodium carbonate, Na2CO3 0.05265

Sodium hydroxide, NaOH .... 0 03976

Sodium salicylale, Na(C7H503)2 ..!!.'.' .' O.'l5889

One c.c. of normal sodium carbonate, potassium hydroxide, or
sodium hydroxide, is the equivalent of:

i With sulphuric acid and methyl-orange. 2 After ignition. 3 With OXalic acid only.

METHODS FOR QUANTITATIVE DETERMINATIONS. 417

Acetic acid, HC2H3O2 ........ 0.05958

Boric acid, H3IK), .......... 0.06154

Citric acid, crystallized, H.,C6H5O7.H2O ...... 0.06950

Hydrobromic acid, HBr ......... 0.08036

Hydrochloric acid, HC1 ......... 0.03618

Hydriodic acid, HI .......... 0.12690

Hypophosphorous acid, HPH2O2 . ...... 0.06553

Lactic acid. HC3H5O3 ......... 0.08937

Nitric acid,' HNO3 .......... 0.06257

Oxalic acid, crystallized, H2C2O4.2H2O ...... 0.06255

Phosphoric acid, H3PO4 (to form K2HPO4; with phenol-phthalein) 0.04864
Phosphoric acid, H3PO4 (to form KH2PO4 ; with methyl-orange) . 0.09729
Potassium dichromate, K2Cr2O7 (with phenol-phthalein) . . 0.14614
Sulphuric acid, H2SO4 ......... 0.04867

Tartaric acid, H2C4H4O6 . . ..... . . . 0.07446

Oxidimetry. A normal oxidizing solution is one which will
liberate from a liter as much oxygen as is chemically equivalent to
one gram-atom of hydrogen. This is one-half gram-atom, or 8
grammes of oxygen, for

H2 + O = H20, or H + =

The substances generally used in oxidimetry are potassium per-
manganate and potassium dichromate.

Potassium permanganate, KMnO4, 156.98, is chiefly used for
normal or decinormal oxidizing solution, and the titration is always
carried out in solution acidified with sulphuric acid. When the salt
breaks up to give off oxygen, it does so in this manner :

2KMn04 + 3H2SO4 = K2SO4 + 2MnSO4 + 5O + 3H2O.

The oxygen is used in oxidizing the substance which is titrated.
The object of adding the acid is to facilitate the decomposition of
the KMnO4 and to take up the potassium and manganese to form
salts, which being colorless form a colorless solution.

As 2 molecules of permanganate give up 5 atoms of oxygen, the

quantity to be taken to liberate \ atom or 8 gm. is - ^~* = -f^>

or l O — i. e., J the molecular weight in grammes, or 31.396 gm. It
is this quantity which is contained in one liter of normal solution.

When oxalic acid is oxidized with permanganate solution this reaction
takes place:

H2C204.2H20 + O = 2C02 + 3H2O,

or more fully,

5H8C204.2H20 + 2KMn04 + 3H,SO4 = 10CO2 + 1^H2O + K2SO4 -f 2MnSO4.

418 ANALYTICAL CHEMISTRY.

This shows that one molecule of oxalic acid requires one atom of oxygen
for oxidation, or one-half molecule of acid requires one-half atom of oxygen.
As one-half gram-molecule of oxalic acid is the quantity in one liter of normal
solution, it follows that the liter of normal oxalic acid is exactly oxidized by a
liter of normal permanganate solution — i. e., the two solutions are equivalent,
since a liter of normal permanganate solution gives off one-half gram-atom of
oxygen. Hence, it is convenient to use normal or deci-normal oxalic acid for
standardizing the permanganate solution.

Permanganate solution, when recently made, without observing certain pre-
cautions, will deteriorate for a certain length of time — i. e., until all traces of
organic and other deoxidizing matters have become oxidized by the per-
manganate.

To prepare a permanent ^ solution of potassium permanganate, dissolve
about 3.3 grammes of the pure crystals (Potassii Permanganas, U. S. P.) in 1000
c.c. of distilled water in a flask, and boil for 5 minutes. Close the flask with
absorbent cotton, and set aside for at least two days, so that suspended matters
may deposit. Then decant the clear liquid without stirring up the sediment,
or for greater precaution filter it through a layer of purified shredded asbestos
(paper or cotton should not be used). The water to be employed for di-
luting this solution should be distilled from about 1 gramme of potassium per-
manganate.

To determine the strength of the solution draw off 10 c.c. of deci-normal
oxalic acid solution into a beaker, add 1 c.c. of pure concentrated sulphuric
acid, heat the mixture to about 80° C. (176° F.), then add gradually from a
glass-cock burette the permanganate, while stirring constantly, until a faint
pink color is produced, which remains permanent for one-half minute. Note
the number of cubic centimetres consumed and dilute the solution so that it is
exactly equivalent to the deci-norrnal oxalic acid. Verify the accuracy of the
dilution by a new titration. When properly prepared and preserved in glass-
stoppered bottles, permanganate solution will keep for at least six months with-
out changing its strength.

A second method for preparing a deci-normal solution of permanganate through
the medium of a deci-normal thiosulphate solution is described in the U. S. P.
as follows :

To a solution of about 1 gramme of potassium iodide in 10 c.c. of dilute sul-
phuric acid, 20 c.c. of the permanganate solution to be standardized are added.
This reaction takes place :

2HI + O = H20 -j- 21.

The mixture is at once diluted with about 200 c.c. of pure water, and deci-normal
thiosulphate solution slowly added from a burette with constant stirring until
the color of the iodine is just discharged. The number of c.c. of the thiosul-
phate solution is noted, and the permanganate solution is diluted so that equal
volumes of the two solutions correspond to each other.

Instead of using oxalic acid for standardizing permanganate solution,
metallic iron may be used, and the operation should be conducted as follows :
0.2 gramme of pure, thin iron wire is dissolved in about 20 c.c. of dilute sul-
phuric acid (1 acid, 5 water) by the aid of heat, and in a flask arranged as
in Fig. 67. The flask is provided, by means of a perforated cork, with a

METHODS FOE QUANTITATIVE DETERMINATIONS. 419

piece of glass tubing, to which is attached a piece of rubber tubing in which
is cut a vertical slit about one inch long and which is closed at the upper
end by a piece of glass rod ; gas or steam generated in the flask may escape,
while atmospheric air cannot enter, the ferrous solution being thus protected
from oxidation.

The iron solution, obtained from the 0.2 gramme of iron, is cooled and
diluted with about 300 c.c. of water, and then deci-normal potassium perman-
ganate solution is added with constant stirring until the solution is tinged
pinkish.

As 1 c.c. of deci-normal permanganate solution corresponds to 0.00555

FIG. 67.

Flu.sk for dissolving iron for volumetric determination.

gramme of metallic iron, the 0.2 gramme of iron wire used will consume 36.03
c.c. of the solution.

Permanganate is often used in determinations of iron and iron compounds.
Many of the latter contain iron in the ferric state, which must be converted
into ferrous compounds before titration. This conversion is accomplished by
heating the solution of a weighed quantity of the ferric compound with nascent
hydrogen— i. e., with metallic zinc and dilute sulphuric acid — in a flask
arranged as the one spoken of above, and shown in Fig. 67.

A very much quicker reduction of the ferric into a ferrous compound may be
accomplished by adding very slowly with constant stirring a saturated solution
of sodium sulphite to the boiling, acidified iron solution contained in the flask
until the liquid becomes colorless. All excess of sulphur dioxide is expelled
before titrating, by boiling the solution (which should contain a sufficient
quantity of sulphuric acid to decompose all sodium sulphite) for about ten
minutes in a flask, arranged as the one mentioned above.

Equivalents. The equivalent of 1 c.c. normal KMnO4 for the
various substances which can be oxidized by it must be deduced
from the equations of reaction, just as in the case of acids and
alkalies.

420 ANALYTICAL CHEMISTRY.

All nitrites react thus :

MNO2 + O = MNO3, where M = metal.
MNO2 = 1 atom O = quantity liberated by 2 liters — KMnO4,

MNQ2 = i « = l liter *. KMn04,
2 1

MNO, = 1 liter ^ "

2 X 10 10

MNO,

= ! c c .

2 X 10 X 1000 10

In this manner all other equivalents are found. The reactions
between permanganate and ferrous salts, and hydrogen dioxide respect-
ively, are expressed in these equations :

2FeS04 -f H2S04 + O = Fe2(SO4)3 + H2O.
H202 + O = H20 + 20.

One c.c. of deci-normal potassium permanganate, containing of this
salt 0.0031396 gramme, is the equivalent of:

Gramme.

Ferrous ammonium sulphate, Fe(NH4)2(SO4)26H.,O . . . 0.038934

Ferrous carbonate, FeCO3 0.011505

Ferrous oxide, FeO 0.007138

Ferrous sulphate, FeSO4 ........ 0.015085

Ferrous sulphate, crystallized, FeSO4.7H2O 0.027601

Ferrous sulphate, dried, 2FeSO4 + 3H2O 0.017767

Hydrogen dioxide, H2O2 0.001688

Iron, in ferrous compounds, Fe - 0.005550

Oxalic acid, crystallized, H2C2O4.2H2O 0.006255

Oxygen, O 0.000794

Potassium nitrite, KNO2 . . . . . . . . 0.004227

Sodium nitrite, NaNO2 0.003428

Potassium dichromate, K2Cr2O7 = 292.28. Whenever this salt
oxidizes other substances in acid solution it breaks up according to
this equation :

KaCrA + 4H2S04 = K2SO4 + Cr2(SO4)3 -f 3O + 4H2O.

That is, one molecule of K2Cr2O7 gives up three atoms of oxygen.
Hence to make a normal solution one-sixth the molecular weight of
K2Cr2O7 (48.7133 grammes) is taken in the liter, and one-tenth this
quantity, equal to 4.8713 grammes of the pure salt, for deci-normal
solution.

The disadvantage of this solution is that the final point of titration cannot
be well seen, for which reason in the determination of iron, for which it is

METHODS FOR QUANTITATIVE DETERMINATIONS. 421

chiefly used, the end of the reaction is determined by the method of spotting,
— i. e., by taking out a drop of the solution and testing it on a white porcelain
plate with a drop of freshly prepared potassium ferricyanide solution ; when this
no longer gives a blue color the reaction is at an end.

In all determinations by this solution dilute sulphuric acid has to be added,
because both the potassium and the chromium require an acid to combine with,
as shown in the above equation.

The titration equivalents of this solution for ferrous salts are the same as
those of deci-normal potassium permanganate solution.

lodimetry. Solutions of iodine and of sodium thiosulphate (hypo-
sulphite) act upon each other with the formation of sodium iodide
and sodium tetrathionate :

21 + 2Na2S2O3 = 2NaI + Na2S4O6.

A normal solution of one can be standardized by a normal solution
of the other. As indicator, is used starch solution, which is colored
blue by minute portions of free iodine.

Starch solution is made by mixing 1 gramme of starch with 10 c.c. of cold
water, and then adding enough boiling water, with constant stirring, to make
about 200 c.c. of a transparent jelly. If the solution is to be preserved for any
length of time, 10 grammes of zinc chloride should be added.

Many other substances, such as sulphurous acid^ hydrogen sulphide,
arsenous oxide, act upon iodine with the formation of colorless com-
pounds, and may, therefore, be estimated by normal solution of iodine,
while the iodine may be standardized by the thiosulphate solution.
In many cases the latter solution is also used for the determination of
chlorine, which is caused to act upon potassium iodide, the liberated
iodine being titrated.

Deci-normal iodine solution. Iodine being a univalent element,
the weight of its atom, 125.90, in grammes, is used to make one
liter of normal solution. Deci-normal solution is generally employed,
and is made by dissolving 12.590 grammes of pure iodine in a solu-
tion of 18 grammes of potassium iodide in about 300 c.c of water,
and diluting the solution to 1000 c.c.

To the article to be estimated by this solution is added a little starch
solution, and then the iodine solution until, on stirring, the blue color
ceases to be discharged.

Iodine of sufficient purity to permit of weighing an exact amount for a stand-
ard solution does not occur in the market. It can be purified, but as this is
somewhat tedious, a simpler plan of making a solution, which is given in the
U. S. P., is generally followed. It consists in making a liter of solution, some-
what stronger than decinormal, by dissolving about 14 grammes of iodine

422

ANALYTICAL CHEMISTRY.

instead of 12.59 grammes as described above. 10 c.c. of this solution are titrated,
while stirring constantly, with deci-normalthiosulphate solution until the yellow
color of iodine just vanishes. The iodine solution is then properly diluted so
that it is exactly equivalent to the thiosulphate solution.

Many substances, such as sulphurous acid and its salts, hydrogen sulphide,
arsenous oxide, etc., are acted upon by iodine in such a manner that this
element enters into combination with constituents of the compounds named, or
iodine acts as an oxidizing agent through the medium of water. The quantity
of iodine thus taken up forms the basis for calculating the quantity of the sub-
stance acted upon.

In the case of arsenous oxide the titration is made in alkaline solution.
Arsenous oxide and sodium bicarbonate are dissolved in water, and this solu-
tion, containing sodium met-arsenite, is titrated with iodine solution, when
sodium met-arsenate and sodium iodide are formed :

NaAs02 + 21 + 2NaHC03 = NaAsO3 + 2NaI + H2O + 2CO2.

The essential change in the above reaction may be shown thus :
As203 + 41 + 2H2O = As2O5 + 4HL

That is, the arsenous oxide which may be considered present in the metarsenite
is oxidized to arsenic oxide in the metarsenates. Hence it is seen that 1 liter

As2O3
of one-tenth normal solution is equivalent to 4 y in in grammes.

When hydrogen sulphide, sulphurous acid, sulphites, or acid sulphites are titrated
with iodine the addition of an alkali is unnecessary ; but in titrating these sub-
stances they must be added to a measured excess of iodine solution, and the
excess after the reaction is complete determined by back -titration with thio-
sulphate solution ; the action is this :

H2S -f- 21 = 2HI + S.
H2SO3 + 21 + H2O = H2SO4 -f 2HI.
Na^SOg + 21 + H2O = Na.2SO4 + 2HI.

In the titration of antimony and potassium tartrate by iodine an alkaline solu-
tion is required, and for this reason sodium bicarbonate is added to the solution.
The reaction which takes place is somewhat doubtful, but the following equa-
tion, even if not absolutely correct, corresponds to the quantities of the substances
acting upon one another :

2KSbOC4H406 + H2O + 41 + 4NaHCO3 =
2HSbO3 + 2KHC4H406 + 4NaI + 4CO2 + H2O.

One c.c. of deci-normal iodine solution, containing of iodine
0.01259 gramme, is the equivalent of:

Gramme.

Antimony and potassium tartrate, 2KSbOC4H4O6.HaO . . 0.016495

Arsenous oxide, As2O3 . 0.004911

Hydrogen sulphide, H2S . 0.001691

Potassium sulphite, crystallized, K2SO3.2H2O . . 0.009648

Sodium bisulphite, NaHS03 ... . 0.005168

Sodium hyposulphite (thiosulphate), Na2S2O3.5H2O . . . 0.024646

Sodium sulphite, crystallized, Na.2SO3.7H2O 0.012520

Sulphur dioxide, SO2 . 0.003180

METHODS FOR QUANTITATIVE DETERMINATIONS.
Sodium thiosulphate (Hyposulphite). From the equation :

2Na.2S2O3.5H2O + 21 Na2S4O6 + 10II2O + 2NaI.

2X246.46 2X125.9

we see that 246.46 grammes of crystallized sodium thiosulphate are
equivalent to— £ e., will exactly decolorize — 125.90 grammes of iodine ;
hence, to make a f solution of this compound, 246.46 grammes must
be taken in a liter, and for a ^ solution 24.646 grammes are used.
If the salt should not be absolutely pure, a somewhat larger quan-
tity (30 grammes) should be dissolved in 1000 c.c. of water, and
this solution titrated with deci-normal solution of iodine and diluted
with a sufficient quantity of water to obtain the deci-normal solu-
tion.

If a decinormal iodine solution is not at hand, and perfectly pure sodium
thiosulphate cannot be obtained, the method adopted by the U. S. P. may be
followed. 30 grammes of the ordinary thiosulphate are dissolved and made up
to 1000 c.c. To a solution of about 1 gramme of potassium iodide in 10 c.c. of
dilute sulphuric acid in a flask, 20 c.c. of decinormal potassium dichromate
solution are slowly added from a burette, and the solution shaken after each
addition. The flask is then covered with a watch-glass and allowed to stand 5
minutes, after which about 250 c.c. of pure water are added, and the thiosul-
phate solution dropped in from a burette slowly, with constant shaking, until
most of the iodine is decolorized. Finally, a little starch solution is added and,
cautiously, more thiosulphate until the blue color changes to a light green.
After noting the volume used, the thiosulphate is diluted so that it is exactly
equivalent to the deci-normal dichromate solution.

Potassium dichromate can be obtained pure, and the decinormal solution
easily made by weighing the exact quantity needed. The solution, moreover,
is perfectly stable.

The article to be tested, containing free iodine, either in itself or
after the addition of potassium iodide, is treated with this solution
until the color of iodine is nearly discharged, when a little starch
liquor is added, and the addition of the solution continued until the
blue color has just disappeared.

The titration of iron in ferric salts by thiosulphate is based on
the liberation of iodine from potassium iodide by all ferric salts :

2FeCl3 + 2KI = 2FeCl2 + 2KC1 + 21.

The reaction shown in the above equation requires a temperature
of 40° to 50° C. (104° to 122° F.), and at least half an hour's time
to make sure of its completion. The digestion should be performed

424 ANALYTICAL CHEMISTRY.

in a closed flask. If iron be present in combination with organic
acids, the addition of some hydrochloric acid becomes necessary.
Before titration the solution is allowed to cool, and the titration
should be promptly finished, as otherwise errors by re-oxidation of
the ferrous salt may be made.

One c.c. of deci-normal solution of sodium thiosulphate, containing
of the crystallized salt 0.024646 gramme, is the equivalent of :

Gramme. ,

Bromine, Br 0.007936

Chlorine, Cl 0.003518

Chromium trioxide, CrO3 0.003311

Iodine, I 0.012590

Iron, Fe, in ferric salts 0.005550

Deci-normal bromine solution (Koppeschaar's solution). The
great volatility of bromine, even from aqueous solutions, interferes
very much with the stability of volumetric solutions. For this
reason a solution is prepared which does not contain free bromine,
but an alkali bromide and bromate, from which, by addition of an
acid, a definite quantity of bromine (7.936 grammes per liter) may
be liberated when required. The chemical change is this :
SNaBr -f NaBrO3 -f 6HC1 = 6NaCl -f 3H2O -f 6Br.

As the bromine salts are rarely chemically pure, a solution is made
which is stronger than necessary and is then adjusted to the titer of
thiosulphate solution.

The solution is prepared as follows : Dissolve 3.2 grammes of potassium
bromate and 50 grammes of potassium bromide in 900 c.c. of water. Of this
solution, which is too concentrated, transfer 20 c.c. into a bottle of about 250 c.c.,
provided with a glass stopper. Next add 75 c.c. of water and 5 c.c. of pure
hydrochloric acid, and immediately insert the stopper. Shake the bottle a few
times to cause liberation of the bromine, then quickly introduce 1 gramme of
potassium iodide, taking care that no bromine vapor escapes. Gradually an
equivalent quantity of iodine is liberated from the potassium iodide by the
bromine. When this has taken place add, from a burette, deci-normal thiosul-
phate solution until the iodine tint is discharged, using toward the end a few
drops of starch solution as indicator! Note the number of c.c. of sodium thio-
sulphate solution thus consumed, and then dilute the bromine solution so that
equal volumes of it and of g sodium thiosulphate solution will exactly corre-
spond to each other^

The use of bromine solution is directed by the U.S. P. in one case only, viz.,
for the volumetric determination of phenol (carbolic acid). This substance
forms with bromine tribromphenol and hydrobromic acid :
C6H5OH + 6Br = C6H2Br3OH 4- SHBr.

METHODS FOR QUANTITATIVE DETERMINATIONS. 425

The molecular weight of phenol is 93.36, and as ii reacts with 6 atoms of
bromine, one-sixth of 93.36, or 15.56 grammes of phenol correspond to 1 liter
of normal, and 1.556 grammes to deci-normal bromine solution — i. e., I c.c. of
deci-normal bromine solution corresponds to 0.001556 gramme of phenol. The
U. S. P. directs the assay to be made as follows : Dissolve 1.556 grammes of the
specimen in water to make 1 liter. Transfer 25 c.c. of this solution (0.0389
phenol) to a glass-stoppered bottle of about 200 c.c. capacity, and add 30 c.c. of
deci-normal bromine solution and 5 c.c. of hydrochloric acid. Shake the con-
tents of the bottle repeatedly, during half an hour, then quickly introduce 1
gramme of potassium iodide, allow the reaction to take place and titrate the
solution with deci-normal thiosulphate, as described above. Deduct the num-
ber of c.c. of thiosulphate used from the 30 c.c. of bromine solution. The
remainder multiplied by 4 indicates the percentage of phenol in the carbolic
acid examined.

Deci-normal solution of silver. The pure, dry crystallized
silver nitrate, AgNO3 = 168.69, is used for this solution, which is
made by dissolving 16.869 grammes of the salt in water to make
1000 c.c. The standard of this solution may be found by means of
a deci-uormal solution of sodium chloride containing of this salt
5.806 grammes in one liter.

Volumetric silver solution is used directly for the estimation of
most chlorides, iodides, bromides, and cyanides, including the free
acids of these salts. Insoluble chlorides must first be converted into
a soluble form by fusing them with sodium hydroxide, dissolving the
fused mass (containing sodium chloride) in water, filtering and neu-
tralizing with nitric acid.

The hydroxides and carbonates of alkali metals and of alkaline
earths may be converted into chlorides by evaporation to dryness
with pure hydrochloric acid, and heating to about 120° C. (248° F.).
The chlorides thus obtained may be titrated with silver solution.

In the case of chlorides, iodides, and bromides, normal potassium
chromate is used as an indicator. This salt forms wi*th silver nitrate
a red precipitate of silver chromate, but not before the silver chloride
(bromide or iodide) has been precipitated entirely. In case free acids
are determined by silver, these are neutralized with sodium hydroxide
before titration.

The operation is conducted as follows : The weighed quantity of
the chloride is dissolved in 50-100 c.c. of water, neutralized if neces-
sary, mixed with a little potassium chromate, and silver solution
added from the burette until a red coloration is just produced, which
does not disappear on shaking.

In estimating cyanides, the operation can be conducted as above
described, or it can be modified, use being made of the formation of

4-26 ANALYTICAL CHEMISTRY.

•

soluble double cyanides of silver and an alkali metal. The reaction
takes place thus :

2KCN + AgN03 = AgK(CN), + KNO3.

In the process adopted by the U. S. P., a suitable quantity of hydrocyanic
acid, or of a cyanide, is diluted with water, and 5 c.c. of ammonia water and
a few drops of potassium iodide solution are added. Silver solution is then
added until a slight permanent cloudiness is produced, at which point half of
the cyanide is converted into silver cyanide, which is held in solution by the
other half of the cyanide as a double salt. The least excess of silver solution
after this stage is indicated by the insoluble silver iodide formed. As but one-
half of the silver solution has been added which is needed for the complete
conversion of the cyanogen present into silver cyanide, the number of c.c. of
the standard silver solution employed will indicate exactly one-half of the
equivalent amount of cyanide present in the solution.

One c.c. of deci-normal silver nitrate solution, containing 0.016869
gramme of AgNO3, is the equivalent of:

Gramme.

Ammonium bromide, NH4Br . 0.009729

Ammonium chloride, NH4C1 . 0.005311

Ammonium iodide, NH4I . . 0.014383

Calcium bromide, CaBr2 ..,.,. . 0.009926

Ferrous bromide, FeBr2 0.010711

Ferrous iodide, FeI2 0.015365

Hydriodic acid, HI 0.012690

Hydrobromic acid, HBr . 0.008036

Hydrochloric acid, HC1 . . . . . . . . 0.003618

Hydrocyanic acid, HCN, to first formation of precipitate . . 0.005368

Hydrocyanic acid, HCN, with indicator 0.002684

Lithium bromide, LiBr 0.008634

Potassium bromide, KBr ........ 0.011822

Potassium chloride, KC1 0.007404

Potassium cyanide, KCN, to first formation of precipitate . . 0.012940

Potassium cyanide, ECN, with indicator 0.006470

Potassium iodide, KI 0.016476

Potassium sulphocyanate, KCNS 0.009653

Sodium bromide, NaBr 0.010224

Sodium chloride, NaCl 0.005806

Sodium iodide, Nal . 0.014878

Strontium bromide, SrBr2.6H2O . 0.017647

Strontium iodide, SrI2.6H2O 0.022301

Zinc bromide, ZnBr2 0.011181

Zinc chloride, ZnCl2 0.006763

Zinc iodide, ZnI2 0.015835

Deci-normal solution of sodium chloride is made by dissolving
5.806 grammes of pure sodium chloride in enough water to make
1000 c.c. The titration is made in neutral solution, normal potas^
sium chromate being used as an indicator. (See explanation in
previous paragraph on silver solution.)

METHODS FOR QUANTITATIVE DETERMINATIONS. 427

One c.c. of deci-normal sodium chloride solution, containing
0.005806 gramme of Nad, is the equivalent of:

Gramme

Silver, Ag 0.010712

Silver nitrate, AgNO3 0.016869

Silver oxide, Ag2O 0.011506

Deci-normal solution of potassium sulphocyanate ( Volhard's
solution). This solution, like the sodium chloride solution, is used
as a companion to silver nitrate ; it has the advantage that it can be
used in acid solutions, with ferric ammonium sulphate (ferric alum)
as indicator. Silver nitrate forms in the potassium sulphocyanate a
white precipitate of silver sulphocyanate :

KCNS + AgNO3 = AgCNS + KNO3.

As indicator is used ferric alum, which produces with sulpho-
cyanate a deep brownish-red color, which, however, does not appear
permanently until all silver has been precipitated.

As potassium sulphocyanate is rarely pure, 10 grammes, which is
about 3 per cent, more than the quantity required, are dissolved in
1000 c.c. of water. This solution has to be adjusted by standardizing
with deci-normal silver solution until equal volumes decompose one
another exactly.

The sulphocyanate solution is used in the determination of the
amount of ferrous iodide in the saccharated salt and in the syrup.

The operation is performed thus : To the solution of the ferrous
iodide are added nitric acid, ferric alum, and of deci-normal silver
nitrate solution a quantity more than sufficient to convert all iodine
into silver iodide. . The excess of silver nitrate present in the mix-
ture is determined by sulphocyanate solution. The ferric alum and
nitric acid must not be added until the silver nitrate has precipitated
all iodine, otherwise iodine will be liberated. This holds in all cases
where iodides are titrated.

Gas-analysis. The analysis of gases is generally accomplished by measur-
ing gas volumes in graduated glass tubes (eudiometers) over mercury (in some
cases over water), noting carefully the pressure and temperature at which the
volume is determined.

From gas mixtures, the various constituents present may often be eliminated
by causing them to be absorbed one after another by suitable agents. For
instance : From a measured volume of a mixture of nitrogen, oxygen, and
carbon dioxide, the latter compound may be removed by allowing the gas to

428 ANALYTICAL CHEMISTRY.

remain in contact for a few hours with potassium hydroxide, which will absorb
all carbon dioxide, the diminution in volume indicating the quantity of carbon
dioxide originally present. The volume of oxygen may next be determined by
introducing a piece of phosphorus, which will gradually absorb the oxygen,
the remaining volume being pure nitrogen.

In some cases gaseous constituents of liquids or solids are eliminated and
measured as gases. Thus, the carbon dioxide of carbonates, the nitrogen
dioxide evolved from nitrates, the nitrogen of urea and other nitrogenous
bodies, are instances of substances which are eliminated from solids in the
gaseous state and determined by direct measurement.

The gas volume thus found is, in most cases, converted into parts by weight.
The basis of this calculation is the weight of 1 c.c. of hydrogen, which, at the
temperature of 0° C. (32° F.) and a pressure of 760 mm. of mercury is 0.0000898
gramme. 1 c.c. of any other gas weighs as many times the weight of 1 c.c.
hydrogen as the molecule of this substance is heavier than that of hydrogen.
Thus the molecular weight of carbon dioxide is 21.835 times greater than that
of hydrogen, consequently 1 c.c. of carbon dioxide weighs 21. 835 times heavier
than 1 c.c. of hydrogen, or 0.0019608 gramme.

It has been shown on pages 26 and 45 that heat and pressure cause a regular
increase or decrease in volume. The data there given are used in calculating
the volume of the measured gas at the temperature of 0° C. (32° F.) and a
pressure of 760 m.m.

The reason for reducing volumes of gases to 0° C. and 760 m.m. pressure,
known as normal temperature and pressure, is that the densities of gases are
given for these conditions. Therefore, to find the weight of any volume of
gas it must be reduced to normal temperature and pressure.

A simple rule for reducing volumes of gases to 0° C. is this : The volume of
a gas is proportional to its absolute temperature. The absolute temperature is
obtained by adding 273° to the reading of the centigrade scale. Thus, if a gas
measures 66 c.c. at 54.6° C., its volume at 0° C. is found from the proportion :

66 c.c. : [54.6° + 273°] : : x : [0° + 273°],
or,

66 : 327.6 : : x : 273,
and •»

In this reduction the pressure is supposed to remain constant. That is, the
volume of 55 c.c. at 0° C. is still at the same pressure as the volume 66 c.c. was.

To reduce a gas volume under any pressure to the volume it would occupy
if the pressure were changed to the normal — i. e., to 760 m.m. — use is made of
Boyle's law, viz., the product of the pressure times the corresponding volume
of a gas is always constant when the temperature is the same. This law is
expressed in the equation, PV=pv, where PV and pv are corresponding
pressures and volumes.

If we assume that in the above case the volume of 55 c.c. is under a pressure
of 750 m.m., its volume at normal, or 760 m.m. pressure, is found by using the
equation :

55 X 750 = x X 760,

METHODS FOR QUANTITATIVE DETERMINATIONS. 429

This shows that the gas-volume of 66 c.c. at 54.6° C. and 750 m.m. pressure
becomes 54.28 c.c. at 0° C. and 760 m.m. pressure. Knowing the volume at
0° C. and 760 m.m. pressure, and the weight of 1 c.c. of the gas under these
conditions, the weight of the total volume is easily found.

The reduction for temperature and pressure can be made in one operation
by using the formula :

V = v X P X 273

760 X (273 -f t) '

V= volume at 0° C. and 760 m.m. pressure, which is to be found.

v = volume read at some pressure, p, other than the normal.

t = temperature in centigrade degrees at which volume v is read.

Thus, in above case :

V = 66 X 750 X 273 = ,, 2g

760 X (273° -f- 54.6)

Methods of gas-analysis have been adopted by the U. S. P. in the quantita-
tive determination of amyl nitrite and ethyl nitrite. The operation is per-
formed in an apparatus known as a nitrometer, consisting of two glass tubes held
in upright position and connected at the lower ends by a piece of rubber
tubing. One of the tubes is open, the other one is graduated and provided
with a glass stopcock near the upper end. In using the nitrometer for the
analysis of ethyl nitrite the graduated tube is filled with saturated solution of
sodium chloride, in which nitrogen dioxide is almost insoluble. Next are
introduced through the stopcock the measured (or weighed) quantity of ethyl
nitrite with a sufficient amount of solution of potassium iodide and sulphuric
acid. By the action of these agents nitrogen dioxide is liberated, and from the
volume obtained the quantity of nitrite present is calculated. The decom-
position is shown by the equation :

C2H5N02 -f KI + H2S04 = C2H5OH + I + KHSO4 + NO.

Water analysis. The objects of water analysis are various. Thus, the
analysis may serve to decide the fitness of a water for manufacturing, medici-
nal, or household purposes. Accordingly, more or less stress is laid on the
exact determination of certain constituents. While the student is referred to
special books treating on the different methods of water analysis, a brief outline
of the chemical examination of drinking-water is here given.

It should be remembered that the results obtained by chemical examination
only are sometimes insufficient to furnish positive proof of the fitness of a
water for drinking-purposes. The reason is that micro-organisms may be
present which cannot be detected by chemical means. It is the microscope,
aided by appropriate bacteriological methods, which has to be used in such
cases, and these methods cannot, of course, be considered in this book.

Standard of purity. A fixed standard has not as yet been generally
adopted for judging the purity of wholesome drinking-water, but most authori-
ties agree that the following maxima of admixtures should not be exceeded.
They are expressed in milligrams per liter — i. e., parts by weight in one million.
The following data refer to one liter of water used :

430 ANALYTICAL CHEMISTRY.

Total residue left on evaporation : 500 mg.

Potassium permanganate decomposed by organic matter: 10 mg.

(=31.71 c.c. ^KMn04).

Ammonia, present as such or as an ammonium salt : 0.05 mg.
Albuminoid ammonia— i. e., ammonia formed from nitrogenous organic

matter by distillation with KMnO4 : 0.1 mg.
Mtrates : 10 mg. of N2O5.

Nitrites : a mere trace, not to exceed Q.05 mg. of N2O3.
Sulphates : 60 to 100 mg. of H2S04.
Chlorine : 15 mg.
Phosphates : a mere trace.
The water should be clear, colorless, odorless and practically tasteless.

Total solids. If the water be turbid, a liter of it is passed through a small
filter, previously dried and weighed. After drying at 110° C., filter and con-
tents are weighed together and the difference is quantity of suspended solids.
The evaporation to dryness of one liter of the clear water in a platinum or
nickel dish at a moderate temperature, with subsequent heating to 110° C.,
gives the total inorganic and organic solids in solution.

The subsequent heating of the dried residue to redness causes the expul-
sion of all organic matter ; but as also inorganic matters, such as carbon dioxide
from acid carbonate, oxygen from nitrates, etc., may escape, the determination
is of relatively little value.

Organic matters. While we have no good method by which the quantity
of organic matter in water can be readily determined, the oxidizing power of
permanganate for organic matters is used for an approximate determination.
This is made by acidifying 100 c.c. of water with 5 c.c. of sulphuric acid, and
adding 10 c.c. of -~- potassium permanganate, or enough to impart a distinct

red color. The liquid is boiled for ten minutes. Should the red color disap-
pear, more permanganate must be added. When color remains permanent,
10 c.c. of ~ oxalic acid are added and the mixture is again heated. To this

solution permanganate is added until it shows a red tint. From the total
number of c.c. of permanganate used, 10 c.c. are deducted for the oxalic acid
added.

As the organic constituents in water at different times and places have no
uniform composition, the quantity of organic matter present cannot be calculated
from the quantity of permanganate used. It is therefore customary to speak
simply of the oxygen- consuming power of water. It should, however, be re-
membered that water may contain deoxidizing agents, other than organic
matters, such as hydrogen sulphide, nitrites, ferrous salts, etc.

Ammonia. Nitrogenous organic matters, when undergoing decomposition
by the agency of bacteria, generate ammonia, which is gradually converted
into nitrites and nitrates. It is for this reason that the presence of these three
compounds is looked upon as indicative of nitrogenous matters, though small
quantities of ammonia and nitrites may also be present in the water by ab?
sorption from the air.

METHODS FOR QUANTITATIVE DETERMINATIONS. 431

It is customary to speak in water analysis of free ammonia and albuminoid
ammonia. By free ammonia is meant the ammonia present as ammonium
hydroxide, or more generally as an ammonium salt, chiefly carbonate. Albu-
minoid ammonia refers to the ammonia obtainable from nitrogenous matter
by oxidation with alkaline permanganate solution.

The process for the determination of both kinds of ammonia is carried out
as follows: 500 c.c. of the water are placed in a flask of about one liter
capacity and 5 c.c. of a saturated solution of sodium carbonate are added. The
flask is connected with a suitable condenser whose outlet is so connected with a
receiver that no loss of ammonia can occur. Heat is then applied to the flask
until 300 c.c. have distilled over. To this distillate, containing all the " free
ammonia," is added enough pure water to restore the original volume of 500
c.c., and the distillate is s^t aside for Nesslerizing.

To the liquid remaining in the distilling flask are now added 50 c.c. of an
alkaline permanganate solution (made by dissolving 8 gm. of KMnO4 and 200
gm. KOH in water to make 1 liter), and distillation is resumed until 200 c.c.
have passed over, which distillate is also diluted to the original volume of
water used — i. e., to 500 c.c.

Both distillates, containing the free and the albuminoid ammonia respect-
ively, are now ready to be tested for ammonia by a method depending on
the intensity of color imparted to them by Nessler's reagent. This reagent
gives with highly diluted ammonia a color varying from pale straw-yellow to
brown. In order to have a standard for comparison of the colors, an empirical
solution of ammonium chloride is made, containing of this salt 3.137 gm. in 1
liter, corresponding to 1 mg. of NH3 in each c.c. Just before use, 5 c.c. of this
solution are diluted with pure water to 100 c.c., of which 1 c.c. now contains
0.05 mg. NH3.

To make the test there are required five small cylinders of colorless glass,
of about 30 m.m. diameter and about 100 m.m high, each having a mark at 50
c.c., and being numbered from 1 to 5. Into four of these cylinders are measured
0.5, 1, 1.5, and 2 c.c., respectively, of the standard ammonium chloride solu-
tion, and all are then filled with water up to the 50 c.c. mark. This makes the
contents of the four cylinders correspond to water containing 0.5, 1, 1.5, and 2
mg. of NH3 per liter.

Cylinder No. 5 is next filled with 50 c.c. of the water specimen prepared for
the ammonia determination, and to each of the five cylinders, standing on white
paper, is added 1 c.c. of ^essler's reagent (see index), which is well mixed with
the water. A comparison of the yellow color produced in the sample with that
of the cylinders 1 to 4, containing known quantities, will afford an estimate of
the quantity of ammonia in the water examined.

Should the color of the specimen be deeper than that of cylinder No. 4, or
lighter than that of No. 1, then the experiment has to be repeated, the water
or the standard solution being diluted in definite proportions until similarity
of color is reached. The calculation is based on the dilution made.

Of course, both distillates have to be treated in this manner. Great care
must be taken to make sure that the water, reagents, and apparatus used in
the operation are absolutely free from ammonia. When only free ammonia is
to be determined the distillation can be dispensed with. If the water should
contain any considerable quantity of calcium salts, these must be precipitated

432 ANALYTICAL CHEMISTRY.

by digesting the water with a little sodium carbonate and sodium hydroxide
before Nesslerizing.

Nitric acid. While there are methods by which nitric acid can be deter-
mined more accurately, it often suffices to make the tests with brucine,
diphenylamine, and pyrogallic acid, as described under the analytical reactions
of nitric acid on page 177.

Nitrous acid. A solution made by dissolving 1 gm. of metaphenylene-
diamine in 200 c.c. water, containing 5 gm. H2SO4, is used for the determina-
tion of nitrites in the same manner as Nessler's solution is used for ammonia.
The required standard nitrite solution is prepared by dissolving 0.406 gm. silver
nitrite and 0.225 gm. potassium chloride in hot water, mixing and, after cool-
ing, filling up to 1 liter. After filtering off the precipitated silver chloride,
lOo'c.c. of the nitrate are diluted to 1000 c.c. This solution contains nitrous
acid equivalent to 10 mg. of N2O3 per liter.

Metaphenylene-diamine solution, prepared as above, gives with nitrites a
yellow color, the intensity of which serves for the quantitative estimation of the
nitrites present. The test is made by using definite dilutions of the above
standard nitrite solution in the four test-cylinders, adding 1 c.c. of the meta-
phenylene-diamine to each 50 c.c., and comparing the colors produced with that
obtained in the water specimen, treated in like manner. Immersion of the
cylinders in warm water accelerates the reaction.

Sulphates. While there are volumetric methods for the determination of
sulphates, this can be conveniently made by the gravimetric method — i. e.t by
precipitating the sulphate with barium chloride and weighing the precipitated
BaS04. From 100 to 250 c.c. of water should be used.

Chlorine. If the water under examination has had an opportunity to
become charged with sodium chloride from its proximity to the sea coast, to
salt lakes, or by flowing through strata containing salt deposits, then a con-
siderable quantity of chlorides may be present and yet the water may be used
without detriment to health. But in other cases the chlorides are derived
from cesspools, sewage, etc., and their presence is then indicative of dangerous
pollution.

The determination of chlorine is made by titrating 100 c.c. of water with
^ AgN03, using potassium ~,hromate as an indicator. For water containing
much organic matter the gravimetric method should, be used.

Phosphates. The ammonium molybdate test (see analytical reactions of
phosphoric acid, page 228) should give no indication of phosphoric acid, as the
presence of soluble phosphates in water is almost positive proof that pollution
with urine has taken place.

QUESTIONS. — Explain the principles which are made use of in gravimetric
and volumetric determinations. Give an outline of the operations to be per-
formed in the gravimetric determination of copper in cupric sulphate. What
are normal and deci-normal solutions, and how are they made? What is the
use of indicators in volumetric analysis ? Mention some indicators and explain

DETECTION OF IMPURITIES. 433

39. DETECTION OF IMPURITIES IN OFFICIAL INOKGANIC
CHEMICAL PREPARATIONS.

General remarks. Very little has been said, heretofore, about
impurities which may be present in the various chemical prepara-
tions, and this omission has been intentional, because it would have
increased the bulk of this book beyond the limits considered neces-
sary for the beginner.

Impurities present in chemical preparations are either derived from
the materials used in their manufacture, or they have been intention-
ally added as adulterations. In regard to the last, no general rule
for detecting them can be given, the nature of the adulterating article
varying with the nature of the substance adulterated ; the general
properties of the substance to be examined for purity will, in most
cases, suggest the nature of those substances which possibly may have
been added, and for them a search has to be made, or, if necessary, a
complete analysis, by which is proved the absence of everything else
but the constituents of the pure substance.

Impurities derived from the materials used in the manufacture of
a substance (generally through an imperfect or incorrect process of
manufacture), or from the vessels used in the manufacture, are usually
but few in number (in any one substance), and their nature can, in
most cases, be anticipated by one familiar with the process of manu-
facture. For one not acquainted with the mode of preparation it
would be a rather difficult task to study the nature of the impurities
which might possibly be present.

their action. Why is oxalic acid preferred in preparing normal acid solution?
What quantity of oxalic acid is contained in a liter, and why is this quantity
used? Suppose 2 grammes of crystallized sodium carbonate require 14 c.c.
of normal acid for neutralization : What are the percentages of crystallized
sodium carbonate and of pure sodium carbonate contained in the specimens
examined. Ten grammes of dilute hydrochloric acid require 35.5 c.c. of nor-
mal sodium hydroxide solution for neutralization ; what is the strength of
this acid? Explain the action of potassium permanganate and of potassium
dichromate when used for volumetric purposes. Which substances may be
determined volumetrically by solutions of iodine and sodium thiosulphate?
Explain the mode in which the determinations by these agents are accom-
plished. Suppose 1 gramme of potassium iodide requires for titration 60 c.c.
of deci-normal solution of silver nitrate: What quantity of pure potassium
iodide is indicated by this determination? Describe in detail the volumetric
determination of carbolic acid. For what purposes is potassium sulphocya-
nate used volumetrically, and what is its action ? Explain the method used
for the analysis of ethyl nitrite.
28

434 ANALYTICAL CHEMISTRY.

The same remarks apply to the methods by which the impurities
can be detected. One familiar with analytical chemistry can easily
find, in most cases, a good method by which the presence or absence
of an impurity can be demonstrated ; but to one unacquainted with
chemistry it might be an impossibility to detect impurities, even if
a method were given.

For these reasons little stress has been laid upon the occurrence of
impurities in the various chemical preparations heretofore considered.
Moreover, the U. S. P. gives, in most cases, directions for the detec-
tion of impurities, so explicit that anyone acquainted with analytical
operations will find no difficulty in performing these tests satisfac-
torily.

However, while the Pharmacopeia gives exact instructions how to
manipulate, it furnishes no explanations why certain methods have
been adopted, or why certain operations are to be performed. It is
for this reason, and for the special benefit of the beginner, that a few
paragraphs are devoted to the consideration of official methods for
testing the chemical preparations of the U. S. P.

Official chemicals and their purity. Absolute purity of chemi-
cals is essential in some cases, as, for instance, when they are intended
as reagents ; such chemicals are commercially designated as C. P.
(chemically pure). For the majority of medicinal chemicals, how-
ever, such absolute purity is unnecessary, as the small proportion of
harmless impurities present in nowise interferes* with the therapeutic
action of the substance, and a demand for absolute purity, which
greatly enhances the cost of chemicals, is therefore unreasonable and
not required by the Pharmacopeia.

The presence of a small fraction of one per cent, of sodium chloride
in many official chemicals cannot be looked upon as objectionable,
while the same amount of arsenic would render the preparation unfit
for medicinal use.

The methods used by the Pharmacopoeia to determine the qualit/
of a chemical preparation may be divided into four classes, as follows :
1. Tests as to identity ; 2. Qualitative tests for impurities ; 3. Quan-
titative tests for the limit of impurities ; 4. Quantitative determina-
tion of the chief constituent.

Tests as to identity. These tests are partly of a physical, partly
of a chemical character. They include, in the physical part, the
examination of the appearance, color, crystalline structure, specific
gravity, fusing-point, boiling-point, etc.

DETECTION OF IMPURITIES. 435

The chemical tests given are sufficiently characteristic to leave no
doubt as to the true nature or identity of the substance. In order to
accomplish this object it is not necessary to apply all the analytical
reagents characteristic of the substance or its component parts, but
the U. S. P. selects from the often large number of known tests one,
or possibly a few, which answer best in the special case.

For instance, while we have a number of tests, both for potassium
and iodine, the U. S. P., in the article on potassium iodide, gives but
one reaction for each of these elements. Yet these tests have been
selected with sufficient judgment to admit of no doubt regarding the
nature of the substance.

Qualitative tests for impurities. These tests are in many cases
described minutely, i. e., the quantity to be taken of both the sub-
stance to be examined and the reagent to be added is stated. More-
over the amount of solvent (water, acid, etc.) to be used is mentioned,
and other details are given. The object of this exactness in describ-
ing the tests is not only to render the work easy for one not fully
familiar with analytical methods, but also, in some cases, to fix a
limit for the admissible quantity of an impurity. A certain reagent
may, in a concentrated solution, indicate the presence of a trace of
an impurity, while in a more dilute solution this reagent will fail to
detect it. The selection of the reagents used in certain tests is also
made with the view of establishing a sufficient purity for pharmaco-
poeial purposes of the article examined without demanding an absolute
purity.

A few instances may help to illustrate these remarks : Potassium
can be precipitated from a solution of its salts by a number of re-
agents, which, however, differ widely in sensitiveness. Thus, tartaric
acid will cause the formation of a precipitate of potassium bitartrate
in a solution containing at least 0.1 per cent, of potassium ; in solu-
tions containing a less amount no precipitate is formed. Platinic
chloride is somewhat more sensitive than tartaric acid, and sodium
cobaltic nitrite, which is still more delicate, causes a precipitate in
solutions containing even as little as 0.04 per cent, of potassium. It
is evident that by using either one or the other of the three reagents
mentioned for the detection of potassium, this metal may or may not
be found, according to the quantity present in a solution. The
Pharmacopoeia, in directing the use of one of these reagents, limits
the amount of a permissible quantity of potassium according to the
sensitiveness of the reagent.

ANALYTICAL CHEMISTRY.

Again, in testing for arsenic, the chemist has his choice between a
number of more or less delicate tests. Gutzeit's test is so sensitive
that by means of it arsenic can be detected in a solution containing
only 0.000001 gramme of arsenous oxide in a cubic centimeter. This
test would be, therefore, by far too severe when applied to a number
of pharmaceutical preparations, for which reason the Pharmacopoeia
directs in many cases the less sensitive hydrogen sulphide test.

Quantitative tests for the limit of impurities. While, as above
stated, even the qualitative tests are often so made as to be to some
extent of a quantitative character, the U. S. P. recommends in many
cases methods by which a stated limit of an impurity can be detected
without the necessity of determining by quantitative analysis the
actual amount of the impurity present.

Formerly it was, and to some extent it is now, customary to limit
the amount of a permissible quantity of an impurity by referring to
the intensity of the reaction. In case the impurity was to be detected
by precipitation (as, for instance, sulphates or chlorides in potassium
nitrate) it was stated that the respective reagents used for the detec-
tion (in the case named, barium chloride or silver nitrate) should not
produce more than a very slight precipitate, or turbidity, or cloudi-
ness, etc. These descriptions are, of course, very indefinite, and the
conclusion arrived at depends largely upon the individuality of the
observer.

In order to obviate this uncertainty the U. S. P. has introduced a
number of more exact methods. These depend upon the addition of
a definite quantity of a reagent capable of eliminating a certain quan-
tity of the impurity from a given quantity of the substance to be
examined. In thus examining a preparation the impurity may or
may not be present ; if present, the permissible quantity will be re-
moved by the operation, and if originally not present in larger quan-
tity, the substance will now be found free from the impurity, while
if present in larger proportions than can be removed by the quantity
of reagent added, the excess can be detected by appropriate tests.

If an excess of impurity is thus discovered, regardless of the fact
whether the excess be large or small, the substance examined does
not come up to the pharmacopoeial requirements.

Thus, in potassium bromide, the pharmacopoeial limit of potassium carbon-
ate is 0.068 per cent. In order to determine whether or not this limit is ex-
ceeded, the Pharmacopeia directs the addition of 0.1 c.c. of £ sulphuric acid

DETECTION OF IMPURITIES. 437

to a solution of 1 gramme of the salt in 10 c.c. of water. Since 0.1 c.c. of 5
sulphuric acid is capable of neutralizing 0.000686 gramme of potassium carbon-
ate, the whole quantity allowed would be neutralized by the addition of the
prescribed quantity of acid, and no red tint should be imparted to the heated
liquid by adding a few drops of phenolphthalein solution ; a red color would
indicate that more alkali carbonate was present in the weighed sample than
could be neutralized by the quantity of acid added.

Quantitative determination of the principal constituent.
These determinations are made in the majority of cases volumetric-
ally, and require no special explanation here, as the methods have
been fully considered in the previous chapter. Gravimetric methods
are used in the determination of several alkaloids and also in a few
other cases.

QUESTIONS. — What are the sources of the impurities found in chemical
preparations ? Why is it not obligatory to use chemically pure chemicals for
medicinal purposes ? Which are the leading features adopted by the U. S. P.
in the identification of chemical preparations? State the reasons why the
U. S. P. describes the tests for impurities so minutely. Why can we not use
indiscriminately either one of a number of reagents or tests by which the pres-
ence of the same impurity may be indicated ? What is the principle applied
in the methods of the Pharmacopeia for the determination of a permitted
quantity of an impurity ? How can we decide the question whether a sample
of potassium acetate contains more than 1 per cent, of potassium chloride with-
out making a quantitative estimation of chlorine?

VI.

CONSIDERATION OF CARBON COMPOUNDS,
OR ORGANIC CHEMISTRY.

40. INTRODUCTORY REMARKS. ELEMENTARY ANALYSIS.

Definition of organic chemistry. The term organic chemistry
was originally applied to the consideration of compounds formed in
plants and in the bodies of animals, and these compounds were
believed to be created by a mysterious power, called " vital force/'
supposed to reside in the living organism.

This assumption was partly justified by the failure of the earlier
attempts to produce these compounds by artificial means, and also by
the fact that the peculiar character of the compounds, and the
numerous changes which they constantly undergo in nature, could
not be sufficiently explained by the experimental methods then
known, and the laws then established.

It was in accordance with these views that a strict distinction was
made between inorganic and organic compounds, and accordingly
between inorganic and organic chemistry, the latter branch of the
science considering the substances formed in the living organism
and those compounds which were produced by their decomposition.

Since that time it has been shown that many substances which
formerly were believed to be produced exclusively in the living
organism, under the influence of the so-called vital force, can be
formed artificially from inorganic matter, or by direct combination
of the elements. It was in consequence of this fact that the theory
of the supposed " vital force," by which organic substances could be
formed exclusively, had to be abandoned.

The first instance of the preparation of an organic compound from inorganic
material occurred in 1828, when Wohler discovered that an aqueous solution
of ammonium cyanate, on evaporation, yields crystals of urea. The latter up

439

440 CONSIDERATION OF CARBON COMPOUNDS.

to that time had been believed to be formed in the animal system exclusively.
As potassium cyanate may be obtained by oxidation of the cyanide, and as the
latter can be made by passing nitrogen over a heated mixture of potassium
carbonate and carbon, it follows that urea can be made from the elements.

The conversion of ammonium cyanate into urea is due to a rearrangement
of the atoms within the molecule, thus:

Ammonium cyanate. Urea.

An organic compound, according to modern views, is simply a
compound of carbon generally containing hydrogen, frequently also
oxygen and nitrogen, and sometimes other elements. As this defini-
tion would include carbonic acid and its salts, such as marble, CaCO3,
spathic iron ore, FeCO3, and others — i.e.9 substances which we are
accustomed to look upon as belonging to the mineral kingdom — it is
better to omit carbon dioxide, carbonic acid, and carbonates, and
define organic compounds as compounds containing carbon in a com-
bustible form.

The definition usually given is : Organic chemistry is the chemistry
of the hydrocarbons and their derivatives. Hydrocarbons, as the name
implies, are compounds of carbon and hydrogen, which are to organic
chemistry what the elements are to inorganic chemistry.

In a strictly systematically arranged text-book of chemistry organic com-
pounds should be considered in connection with the element carbon itself,
but as these carbon compounds are so numerous, their composition often so
complicated, and the decompositions which they suffer under the influence of
heat or other agents so varied, it has been found best for purposes of instruc-
tion to defer the consideration of these compounds until the other elements and
their combinations have been studied.

Elements entering- into organic compounds. Organic com-
pounds contain generally but a small number of elements. These
are, besides carbon, chiefly hydrogen, oxygen, and nitrogen, and
sometimes sulphur and phosphorus. Other elements, however, enter
occasionally into organic compounds, and by artificial means all
metallic and non-metallic elements may be made to enter into organic
combinations.

Here the question presents itself: Why is it that the four elements
carbon, hydrogen, oxygen, and nitrogen are capable of producing
such an immense number (in fact, millions) of different combinations?
To this question but one answer can be given, which is that these
four elements differ more widely from each other, in their chemical
and physical properties, than perhaps any other four elements.

Carbon is a black, solid substance, which can scarcely be fused

INTRODUCTORY REMARKS. 441

or volatilized, while hydrogen, oxygen, and nitrogen are colorless
gases which can only be converted into liquids with difficulty. More-
over, hydrogen is very combustible, oxygen is a supporter of combus-
tion, while nitrogen is perfectly indifferent. Finally, hydrogen is
univalent, oxygen bivalent, nitrogen trivalent, and carbon quadri-
valent. These elements are, therefore, capable of forming a greater
number and a greater variety of compounds than would be the case
if they were elements of equal valence and of similar properties.

It will be shown later that carbon atoms have, to a higher degree
than the atoms of any other element, the power of combining with one
another by means of a portion of the affinities possessed by each atom,
thus increasing the possibilities of the formation of complex compounds.

The number of thoroughly investigated organic compounds is estimated at
150,000, and each year is increased by 8000 to 9000.

General properties of organic compounds. The substances
formed by the union of the four elements just mentioned have prop-
erties in some respects intermediate to those of their components.
Thus, no organic substance is as permanently solid l as carbon, nor
as permanently gaseous as hydrogen, oxygen, and nitrogen.

Some organic substances are solids, others liquids, others gases ;
generally they are solids when the carbon atoms predominate ; they
are liquids or gases when the gaseous elements, and especially hydro-
gen, predominate ; likewise, it may also be said that compounds con-
taining a small number of atoms in the molecule are gases or liquids
which are easily volatilized ; they are liquids of high boiling-
points, or solids, when the number of atoms forming the molecules
is large.

The combustible property of carbon and hydrogen is transferred
to all organic substances, every one of which will burn when suffi-
ciently heated in atmospheric air. (If carbon dioxide, carbonic acid
and its salts be considered organic compounds, we have an exception
to the rule, as they are not combustible.)

The properties possessed by organic compounds are many and
widely different. There are organic acids, organic bases, and organic
neutral substances; there are some organic compounds which are
perfectly colorless, tasteless, and odorless, while others show every
possible variety of color, taste, and odor ; many serve as food, while
others are most poisonous ; in short, organic substances show a greater
variety of properties than the combinations formed by any other
four elements.

1 Non-volatile organic substances are decomposed by heat with generation of volatile
products.

442 CONSIDERATION OF CARBON COMPOUNDS.

And yet, the cause of all the boundless variety of organic matter
is that peculiar attraction called chemical affinity, acting between the
atoms of a comparatively small number of elements and uniting them
in many thousand different proportions.

It would, of course, be entirely inconsistent with the object of
this book, if all the many organic substances already known (the
number of which is continually being increased by new discoveries)
were to be considered, or even mentioned. It must be sufficient to
state the general properties of the various groups of organic sub-
stances, to show by what processes they are produced artificially or
how they are found in nature, how they may be recognized and
separated, and, finally, to point out those members of each group
which claim a special attention for one reason or another.

Difference in the analysis of organic and inorganic sub-
stances. The analysis of organic substances differs from that of
inorganic substances, in so far as the qualitative examination of an
organic substance furnishes in many cases but little proof of the true
nature of the substance (except that it is organic), while the quali-
tative analysis of an inorganic substance discloses in most cases the
true nature of the substance at once.

For instance : If a white, solid substance, upon examination, be
found to contain potassium and iodine, and nothing else, the conclu-
sion may at once be drawn that the compound is potassium iodide,
containing 38.86 parts by weight of potassium, and 125.9 parts by
weight of iodine. Or, if another substance be examined, and found
to be composed of mercury and chlorine, the conclusion may be drawn
that the compound is either mercurous or mercuric chloride, as no
other compounds containing these two elements are known, and
whether the examined substance be the lower or higher chloride of
mercury, or a mixture of both, can easily be determined by a few
simple tests.

While thus the qualitative examination discloses the nature of the
substance, it is different with organic compounds. Many thousand
times the analysis might show carbon, hydrogen, and oxygen to be
present, and yet every one of the compounds examined might be
entirely different ; it is consequently not only the quality of the ele-
ments, but chiefly the quantity present which determines the nature
of an organic substance, and in order to identify an organic substance
with certainty, it frequently becomes necessary to make a quantitative
determination of the various elements present, and this quantitative
analysis is generally called ultimate or elementary analysis.

INTRODUCTORY REMARKS. 443

There are, however, for many organic substances such character-
istic tests that these substances may be recognized by them ; these
reactions will be mentioned in the proper places.

An analysis by which different organic substances, when mixed
together, are separated from each other is frequently termed proximate
analysis. Such an analysis includes the separation and determination
of essential oils, fats, alcohols, sugars, resins, organic acids, albuminous
substances, etc., and is one of the most difficult branches of analytical
chemistry.

Qualitative analysis of organic substances. The presence of
carbon in a combustible form is decisive in regard to the organic
nature of a compound. If, consequently, a substance burns with
generation of carbon dioxide (which may be identified by passing the
gas through lime-water), the organic nature of this substance is
established. (See Chapter on Carbon.)

The presence of hydrogen can be proven by allowing the gaseous
products of the combustion to pass through a cool glass tube, when
drops of water will be deposited.

It is difficult to show by qualitative analysis the presence or
absence of oxygen in an organic compound, and its determination is
therefore generally omitted.

The presence of nitrogen is determined by heating the substance
with dry soda-lime (a mixture of two parts of calcium hydroxide and
one part of sodium hydroxide), when the nitrogen is converted into
ammonia gas, which may be recognized by its odor or by its action
on paper moistened with solution of cupric sulphate, a dark-blue
color indicating ammonia.

Ultimate or elementary analysis. While the student must be
referred to books on analytical chemistry for a detailed description of
the apparatus required and the methods employed for elementary
analysis, it may here be stated that the quantitative determination of
carbon and hydrogen is generally accomplished by the following pro-
cess : A weighed quantity of the pure and dry substance is mixed
with a large excess of dry cupric oxide, and this mixture is introduced
into a glass tube, the open end of which is connected by means of a
perforated cork and tubing with two glass vessels, the first one of
which (generally a U-shaped tube) is filled with pieces of calcium
chloride, the other (usually a tube provided with several bulbs) with
solution of potassium hydroxide. The two glass vessels, containing
the absorbents named, are weighed separately after having been

444 CONSIDERATION OF CARBON COMPOUNDS.

filled. Upon heating the combustion-tube in a suitable furnace, the
organic matter is burned by the oxygen of the cupric oxide, the
hydrogen is converted into water (steam), which is absorbed by the
calcium chloride, and the carbon is converted into carbon dioxide,
which is absorbed by the potassium hydroxide. The apparatus repre-
sented in Fig. 68 shows the gas-furnace in which rests the coinbustion-

FIG. 68.

Gas-furnace for organic analysis.

tube with calcium chloride tube and potash bulb attached. Upon
re-weighing the two absorbing vessels at the end of the operation, the
increase in weight will indicate the quantity of water and carbon
dioxide formed during the combustion, and from these figures the
amount of carbon and hydrogen present in the organic matter may
easily be calculated.

For instance : 0.81 gramme of a substance having been analyzed,
furnishes, of carbon dioxide 1.32 gramme, and of water 0.45 gramme.
As every 44 parts by weight of carbon dioxide contain 12 parts by
weight of carbon, the above 1.32 gramme contains of carbon 0.36
gramme, or 44.444 per cent. As every 17.88 parts of water contain
2 parts of hydrogen, the above 0.45 gramme consequently contains
0.0503 gramme, or 6.213 per cent.

Oxygen is scarcely ever determined directly, but generally indi-
rectly, by determining the quantity of all other elements and deduct-
ing their weight, calculated to percentages from 100. The difference
is oxygen.

If, in the above instance, 44.444 per cent, of carbon and 6.213 per
cent, of hydrogen were found to be present, and all other elements,

INTRODUCTORY REMARKS. 445

except oxygen, to be absent, the quantity of oxygen is, then, equal
to 49.384 per cent, and the composition of the substance is as
follows :

Carbon „ . 44.444 per cent.

Hydrogen 6.213 "

Oxygen 49.343

100.000

Determination of nitrogen. Nitrogen is generally determined
by the Kjeldahl method, which consists in boiling in a suitable flask a
weighed quantity of the organic compound with 30 to 40 times its
weight of sulphuric acid and a little potassium permanganate or mer-
curic oxide. By this treatment all nitrogen present is converted into
ammonium sulphate, from which by the addition of an excess of
sodium hydroxide ammonia is liberated. This ammonia is distilled
over into a known volume of normal acid. By titration with normal
alkali the unsaturated portion of acid is determined and from the
result the percentage of nitrogen is calculated.

Nitrogen may also be determined by the Will- Varr entrap method, which is
based on the formation of ammonia whenever nitrogenous matter is heated
with soda-lime (a mixture of sodium hydroxide and calcium oxide). The
method is not applicable to all compounds, because the nitrogen of some is not
all converted into ammonia by the process.

A third method, known as the Dumas or absolute method, consists in oxidiz-
ing, at a red heat, the nitrogenous substance by means of cupric oxide and
then decomposing, by means of highly-heated metallic copper, any oxide of
nitrogen which may have been formed. By this operation all nitrogen is
obtained in the elementary state ; it is collected, measured, and from the volume
the weight is calculated.

For the details of manipulation in the above method, which are simply out-
lined, large works on quantitative analysis must be consulted.

Determination of sulphur and phosphorus. These elements are
determined by mixing the organic substance with sodium carbonate
and nitrate, and heating the mixture in a crucible. The oxidizing
action of the nitrate converts all carbon into carbon dioxide, hydrogen
into water, sulphur into sulphuric acid, phosphorus into phosphoric
acid. The latter two acids combine with the sodium of the sodium
carbonate, forming sulphate and phosphate of sodium. The fused
mass is dissolved in water, and sulphuric acid precipitated by barium
chloride in the acidified solution, phosphoric acid by magnesium
sulphate and ammonium hydroxide and chloride. From the weight
of barium sulphate and magnesium pyrophosphate (obtained by heat-
ing the magnesium ammonium phosphate) the weight of sulphur and
phosphorus is calculated.

446 CONSIDERATION OF CARBON COMPOUNDS.

Determination of atomic composition from results obtained
by elementary analysis. The elementary analysis gives the quan-
tity of the various elements present in percentages, and from these
figures the relative number of atoms may be found by dividing the
figures by the respective atomic weights. For instance : The analysis
above mentioned gave the composition of a compound, as carbon
44.444 per cent,, hydrogen 6.213 per cent., and oxygen 49.343 per
cent. By dividing each quantity by the atomic weight of the respec-
tive element, the following results are obtained :

11.91

= 3.731

La

15.88

49'34; =3.107

The figures 3.731, 6.213, and 3.107 represent the relative number
of atoms present in a molecule of the compound examined. In order
to obtain the most simple proportion expressing this relation, the
greatest divisor common to the whole has to be found, a task which
is sometimes rather difficult on account of slight errors made in the
quantitative determination itself. In the above case, 0.6213 is the
greatest divisor, which gives the following results :

3.731 6.213 _ . 3.107

0.6213 ' 0.6213 ' 0.6213

The simplest numbers of atoms are, accordingly, carbon 6, hydrogen
10, oxygen 5, or the composition is C6H10O5.

Empirical and molecular formulas. A chemical formula is
termed empirical when it merely gives the simplest possible expression
of the composition of a substance. In the above case, the formula
C6H10O5 would be the empirical formula. It might, however, be
possible that this formula did not represent the actual number of
atoms in the molecule, which might contain, for instance, twice or
three times the number of atoms given, in which case the true com-
position would be expressed by the formula C12H20O10 or C18H30O15.

If it could be proven that one of the latter formulas is the correct
one, it would be termed the molecular formula, because it expresses
not only the numerical relations existing between the atoms, but also
the absolute number of atoms of each element contained in the
molecule.

ELEMENTARY ANALYSIS. 447

The best method for determining the actual number of atoms con-
tained in the molecule is the determination of the specific weight of
the gaseous compound, taking hydrogen as the unit. For instance :
Assume the analysis of a liquid substance gave the following result :

Carbon 92.308 per cent.

Hydrogen 7-692 "

100.000

From this result the empirical formula, CH, is deduced by apply-
ing the method stated above. If this formula were the molecular
formula, the density of the vapors of the substance would, when com-
pared with hydrogen (according to the law of Avogadro), be equal to
6.455, because a molecule of hydrogen weighs 2 and a molecule of the
compound CH weighs 12.91.

Suppose, however, the density of the gaseous substance is found to
be 38.73, then the molecular formula would be expressed by C6H6,
because its molecular weight (6 X 11.91 -f 6 X 1) is equal to 77.46,
which weight, when compared with the molecular weight of hydrogen
= 2, gives the proportions 77.46 : 2, or 38.73 : 1.

Not all organic compounds can be converted into gases or vapors
without undergoing decomposition, and the determination of the
molecular formulas of such compounds has to be accomplished by
other methods. If the substance, for instance, is an acid or a base,
the molecular formula may be determined by the analysis of a salt
formed by these substances. For instance : The empirical formula of
acetic acid is CH2O ; the analysis of the potassium acetate, however,
shows the composition KC2H3O2, from which the molecular formula
HC2H3O2 is deduced for acetic acid.

In many cases, however, it is as yet absolutely impossible to give
with certainty the molecular formula of some compounds.

Rational, constitutional, structural, or graphic formulas.
These formulas are intended to represent the theories which have
been formed in regard to the arrangement of the atoms within the
molecule, or to represent the modes of the formation and decom-
position of a compound, or the relation which allied compounds bear
to one another.

The molecular formula of acetic acid, for instance, is C2H4O2, but
different constitutional formulas have been used to represent the
structure of the acetic acid molecule.

Thus, H.C2H3O2 is a formula analogous to H.NO3, indicating that
acetic acid (analogous to nitric acid), is a monobasic acid, containing
one atom of hydrogen, which can be replaced by metallic atoms.

448 CONSIDERATION OF CARBON COMPOUNDS.

• C H O.OH1 is a formula indicating that acetic acid is composed of
two univalent radicals which may be taken out of the molecule and
replaced by other atoms or groups of atoms. This formula indicates
also that acetic acid is analogous to hydroxides, the radical C2H3O
having replaced one atom of hydrogen in H2O.

CH .CO2Hl is a formula indicating that acetic acid is composed of
the two compound radicals, methyl and carboxyl.

It may be said finally, that quite a number of other rational
formulas have been applied, or, at least, have been proposed by
different chemists and at different times, to represent the structure of
acetic acid, but it should be remembered that these formulas are not
intended to represent the actual arrangement of the atoms in space,
but only, as it were, their relative mode of combination, showing
which atoms are combined directly and which only indirectly, that
is, through the medium of others.

41. CONSTITUTION, DECOMPOSITION, AND CLASSIFICATION
OF ORGANIC COMPOUNDS.

Radicals or residues. The nature of a radical or residue has
been stated already in Chapter 8, but the important part played by
radicals in organic compounds renders it necessary to consider them
more fully.

In most compounds there is one or several groups of atoms which re-
main unchanged in the various reactions to which the compounds may
be submitted. The group behaves like a unit or an element, although
it cannot exist in the free state. Such groups are called radicals.

QUESTIONS. — What is organic chemistry, according to modern views ? Men-
tion the four chief elements entering into organic compounds, and name the
elements which may be made to enter into organic compounds by artificial
processes. State the reason why the four elements, carbon, hydrogen, oxy-
gen, and nitrogen, are better adapted to form a larger number of compounds
than most other elements. State the general properties of organic compounds.
Why does a qualitative analysis of an organic*com pound, in most cases, 'not
disclose its true nature? By what test may the organic nature of a compound
be established? By what tests may the^ presence of carbon, hydrogen, and
nitrogen be demonstrated in organic compounds? State the methods by which
the elements carbon, hydrogen, oxygen, sulphur, and phosphorus are deter-
mined quantitatively. By what general method may a formula be deduced
from the results of a quantitative analysis ? What is meant by an empirical,
molecular, and constitutional formula ; how are they determined, and what is
the difference between them ?

CONSTITUTION OF ORGANIC COMPOUNDS. 449

Kadicals exist in organic and inorganic compounds ; an inorganic
radical spoken of heretofore is the water residue or hydroxyl, OH,
obtained by removal of one atom of hydrogen from one molecule of
water. Hydroxyl does not exist in the separate state, but it exists in
hydrogen dioxide, H2O2, or HO — OH, and is also a constituent of the
various hydroxides, as, for instance, of KOH, Ca(OH)2, Fe(OH)3, etc.

If one atom of hydrogen be removed from the saturated hydro-
carbon methane, CH4, the univalent residue methyl, CH3, is left,
which is capable of combining with univalent elements, as in methyl
chloride, CH3C1, or, with univalent residues, as in methyl hydroxide,
CH3OH.

If two atoms of hydrogen be removed from CH4, the bivalent resi-
due methylene, CH2, is left, capable of forming the compounds
CH2C12, CH2(OH)2, etc.

If three atoms of hydrogen be removed from CH4, the trivalent
residue CH is left, capable of combining with three atoms of univa-
lent elements, as in CHC13, or with another trivalent radical, etc.

Chains. The expression, chain, designates a series of multivalent
atoms (generally, but not necessarily, of the same element), held
together by one or more affinities. While such linkage of atoms into
chains occurs with a number of elements, it appears that silicon and
carbon have a greater tendency to form chains than other elements.

The linkage of carbon atoms may be represented thus :

II III I I I I

_C— C— , — C— C— C— , — C— C— C— C— , etc.

II III till

The above carbon chains have 6, 8, and 10 available affinities,
respectively, which may be saturated by the greatest variety of atoms
or radicals. The chain combination of carbon, above indicated by the
first three members of a series, may, as far as is known, be continued
indefinitely. This fact, in connection with the possibility of saturating
the other affinities with various atoms or radicals, indicates the almost
unlimited number of possible combinations to be formed in this way.
In fact, the existence of such an enormous number of carbon com-
pounds is greatly due to the property of carbon to form these chains.

It is not always the case that the atoms when forming a chain are
united by one affinity only, as above, but they may be united by two
or three affinities, as indicated by the compounds C2H4 and C2H2, the
graphic formulas of which may be represented by

H\ /H

450 CONSIDERATION OF CARBON COMPOUNDS.

Finally, it is assumed that the carbon atoms are united partially
by double and partially by single union, as, for instance, in the so-
called closed chain of C6, capable of forming the hydrocarbon benzene,
C6H6:

H

\CAC/ H\c/

ACA HACAH

' i

A chain has also been termed a skeleton, because it is that part of an organic
compound around which the other elements or radicals arrange themselves,
filling up, as it were, the unsaturated affinities.

Homologous series. This term is applied to any series of organic
compounds the terms or members of which, preceding or following
each other, differ by CH2, Moreover, the general character, the con-
stitution, and the general properties of the members of an homologous
series are similar.

The explanation regarding the formation of an homologous series
is to be found in the above-described property of carbon to form
chains. By saturating, for instance, the affinities in the open carbon
chains mentioned above, we obtain the compounds CH4, C2H6, C3H8,
C4H10, etc.

H HH HHH HHHH

H-C-H, H-C-C-H, H-C-C-C-H, H-C-C-C-C-H,

H HH HHH HHHH

Many homologous series of various organic compounds are known,
as, for instance :

C H3 Cl, C H4 O, C H2 02.

C2H5 Cl, C2H6 O, C2H4 02.

QA Cl, C3H8 O, C3H6 02.

C4H9C1, C4H100, C4H802.

c5Hnci, cjr.A cjw

etc. etc. etc-

Substitution is a term used for those reactions or chemical changes
which depend on the replacement of an atom or a group of atoms by
other atoms or groups of atoms. Substitution takes place in organic
or inorganic substances, and its nature may be illustrated by the fol-
lowing instances :

etc.

CONSTITUTION OF ORGANIC COMPOUNDS. 451

K + H2O = KOH + H.
Potassium. Water. Potassium Hydrogen.
hydroxide.

C2H402 + 2C1 : C2H3C102 + HC1.
Acetic acid. Chlorine. Monochloracetic Hydrochloric
acid. " acid.

C6H6 + HN03 = C6H5N02 + H2O.
Benzene. Nitric acid. Nitro-benzene. Water.

Derivatives. This term is applied to bodies derived from others
by some kind of decomposition, generally by substitution. Thus,
nitro-benzene is a derivative of benzene; chloroform, CHC13, is a
derivative of methane, CH4, obtained from the latter by replacement
of three atoms of hydrogen by the same number of atoms of chlorine.

Isomerism. Two or more substances may have the same elements
in the same proportion by weight (or the same centesimal composi-
tion), and yet be different bodies, showing different properties. Such
substances are called isomeric bodies. Three kinds of isomerism are
distinguished, viz., metamerism, polyinerism, and stereo-isomerism.

Metamerism. Substances are metameric when their molecules con-
tain equal numbers of atoms of the same elements. Thus, cane-
sugar and milk-sugar have both the composition C12H22On, and yet
they have different physical properties, and may be distinguished by
their solubility and by a number of characteristic tests.

The explanation given regarding this difference of properties is,
that the atoms are arranged differently within the molecule. In
some cases this arrangement is as yet unknown, in other cases struc-
tural or graphic formulas showing this atomic arrangement may be
given.

For instance : Acetic acid and methyl formate both have the com-
position C2H4O2, but the arrangement of the atoms (or the structure)
is very different, as shown by the formulas :

Acetic acid. Methyl formate.

C2HS0\0 CHO\0

a 0<

CH3X

As another instance may be mentioned the compound CN2H4O,
which represents either ammonium cyanate or urea :

Ammonium cyanate. Urea.

NH4\0 NHACO

CN/U NH2/OU'

Polymerism. Substances are said to be polymeric when they have
the same centesimal composition, but a different molecular weight, or.

452 CONSIDERATION OF CARBON COMPOUNDS.

in other words, when one substance contains some multiple of
the number of each of the atoms contained in the molecule of the

other.

For instance, some volatile oils have the composition C20H32, which
is double the number of atoms contained in oil of turpentine, C10H16 ;
acetylene, C2H2, is polymeric with benzene, C6H6, and styrene, C8H8 ;
formaldehyde, CH2O, acetic acid, C2H4O2> lactic acid, C3H6O3> and
glucose, C6H12O6, are polymeric compounds.

Stereo-isomerism. There has long been known a number of
bodies having the same molecular and constitutional formulas (i. e.,
behaving alike chemically), but which exhibit differences in prop-
erties, as, -for instance, in their behavior toward polarized light
and in the form of their crystals. The explanation at present
given of these differences is based on this assumption : that the dif-
ferent atoms or radicals in combination with a carbon atom may
occupy toward it different relative positions, and that actually
they do.

In order to understand what is meant by this statement we should
bear in mind that we represent the grouping of our atoms on the
flat surface of paper, while actually the formation of molecules takes
place in space — i. e.y in three directions. If we assume, for instance,
that four different radicals are in combination with a carbon atom,
we can well imagine that the relative positions in which these radicals
are grouped around the carbon atom have an influence on the nature
of the compound. There are bodies which contain the same elements
in the same quantities but in which the molecular structures seem to
be reversed, precisely as they would be if seen directly and then
observed after reflection from a mirror. In fact, there are known
isomeric bodies the crystals of which seem to exhibit exactly that
relation to each other.

The term stereo-isomerism is, therefore, used for that kind of
isomerism found in substances which contain apparently the same
radicals, show practically the same chemical behavior toward other
agents, but differ in certain physical properties. Of stereo-isomeric
substances may be mentioned 2 malic acids, 3 lactic acids, 4 tartaric
acids, etc. (For details of stereo-isomerism the student is referred
to works treating more fully on this subject.)

Various modes of decomposition. The principal changes which
a molecule may suffer are as follows :

DECOMPOSITION OF ORGANIC COMPOUNDS. 453

a. The atoms may arrange themselves differently within the mole-
cule. Ammonium cyanate, NH4CNO, is easily converted into urea,
CO(NH2)2. This is called molecular rearrangement.

b. A molecule may split up into two or more molecules. For
instance :

C6H1206 : : 2C2H6O + 2CO2.
Grape-sugar. Alcohol. Carbon dioxide.

This decomposition is spoken of as cleavage. When cleavage is
accompanied by the taking up of the constituents of water the change
is called hydrolytic cleavage or hydrolysis. The following reaction
belongs to this class :

C9H9NO3 + H2O = C7H602 + C2H3NH2O2.

Hippur'ic acid. Benzoic acid. Glycocoll.

c. Two molecules, either of the same kind, or of different sub-
stances, may unite directly :

C2H4 -f 2Br = C2H4Br2.
Ethylene. Bromine. Ethylene bromide.

d. Atoms may be removed from a compound without replacing
them by other atoms :

C2H60 + O = C2H4O + H2O.
Alcohol. Oxygen. Aldehyde. Water.

e. Atoms may be removed and replaced by others at the same
time (substitution) :

C2H4O2 + 2C1 = C2H3C1O2 + HC1.

Acetic acid. Chlorine. Monochloracetic Hydrochloric
acid. acid.

Action of heat upon organic substances. As a general rule,
organic bodies are distinguished by the facility with which they
decompose under the influence of heat or chemical agents ; the more
complex the body is, the more easily does it undergo decomposition
or transformation.

Heat acts differently upon organic substances, some of which may
be volatilized without decomposition, while others are decomposed
by heat with generation of volatile products. This process of heating
non-volatile organic substances in such a manner that the oxygen of
the atmospheric air has no access, and to such an extent that decom-
position takes place, is called dry or destructive distillation.

The nature of the products formed during this process varies not
only with the nature of the substance heated, but also with the tem-
perature applied during the operation. The products formed by
destructive distillation are invariably less complex in composition,

454 CONSIDERATION OF CAftSON COMPOUNDS.

that is, have a smaller number of atoms in the molecule, than the
substance which suffered decomposition ; in other words, a complex
molecule is split up into two or more molecules less complex in
composition.

Otherwise, the products formed show a great variety of properties ;
some are gases, others volatile liquids or solids, some are neutral,
others basic or acid substances. In most cases of destructive distilla-
tion a non-volatile residue is left, which is nearly pure carbon.

Action of oxygen upon organic substances. Combustion.
Decay. All organic substances are capable of oxidation, which
takes place either rapidly with the evolution of heat and light and is
called combustion, or it takes place slowly without the emission of
light, and is called slow combustion or decay. The heat generated
during the decay of a substance is the same as that generated by
burning the substance ; but as this heat is liberated in the first
instance during weeks, months, or perhaps years, its generation is so
slow that it can scarcely be noticed.

No organic substance found or formed in nature contains a suffi-
cient quantity of oxygen to cause the complete combustion of the
combustible elements (carbon and hydrogen) present; by artificial
processes such substances may, however, be produced, and are then
either highly combustible or even explosive.

During common combustion, provided an excess of atmospheric oxygen be
present, the total quantity of carbon is converted into carbon dioxide, hydrogen
into water, sulphur and phosphorus into sulphuric and phosphoric acids, while
nitrogen is generally liberated in the elementary state.

During the process of decay the compounds mentioned above are produced
finally, although many intermediate products are generated. For instance : If
a piece of wood be burnt, complete oxidation takes place ; intermediate pro-
ducts also are formed chiefly in consequence of the destructive distillation of
a portion of the wood, but they are consumed almost as fast as they are pro-
duced, as was mentioned in connection with the consideration of flame. Again,
when a piece of wood is exposed to the action of the atmosphere, it slowly
burns or decays. The intermediate products formed in this case are entirely
different from those produced during common combustion.

Common alcohol has the composition C2H6O ; in burning, it requires
six atoms of oxygen, when it is converted into carbon dioxide and water :
CaH«O + 60 = 2C03 + 3H2O.

But alcohol may also undergo slow oxidation, in which case oxygen
first removes hydrogen, with which it combines to form water, while
at the same time a compound known as acetic aldehyde, C2H4O, is
formed :

DECOMPOSITION OF ORGANIC COMPOUNDS. 455

C2H60 -f O C2H40 -f HaO.

This aldehyde, when further acted upon by oxygen, takes up an
atom of this element, thereby forming acetic acid :

C2H40 + O = : C2H402

The three instances given above illustrate the action of oxygen
upon organic substances, which action may consist in a mere removal
of hydrogen, in a replacement of hydrogen by oxygen, or in an
oxidation of both the carbon and hydrogen, and also of sulphur and
phosphorus, if they be present.

An organic substance, when perfectly dry and exposed to dry air
only, may not suffer decay for a long time (not even for centuries),
but in the presence of moisture and air this oxidizing action takes
place almost invariably.

Besides the slow oxidation or decay which all dead organic matter
undergoes in the presence of moisture, there is another kind of slow
oxidation, called respiration, which takes place in the living animal ;
this process will be more fully considered in the physiological part of
this book.

Fermentation and putrefaction. These terms are applied to
peculiar kinds of decomposition, by which the molecules of certain
organic substances are split up into two or more molecules of a less
complicated composition. These decompositions take place when
three factors are simultaneously acting upon the organic substance.
These factors are : presence of moisture, favorable temperature, and
presence of a substance generally termed ferment.

The most favorable temperature for these decompositions lies
between 25° and 40° C. (77° and 104° F.), but they may take place
at lower or higher temperatures. No substance, however, will either
ferment or putrefy at or below the freezing-point, or at or above the
boiling-point of water.

The nature of the various ferments differs widely, and their true
action cannot, in many cases, be explained; what we do know is,
that the presence of comparatively small (often minute) quantities of
one substance (the ferment) is sufficient to cause the decomposition of
large quantities of certain organic substances, the ferment itself suf-
fering often no apparent change during this decomposition.

Ferments have been divided into two classes : 1. Organized fer-
ments (sometimes called true ferments), being unicellular living micro-
organisms chiefly of vegetable origin. 2. Soluble ferments, unorganized

456 CONSIDERATION OF CARBON COMPOUNDS.

ferments, or enzymes (false ferments) which are in most cases nitro-
genous substances closely related to the proteins.

This classification was based on the belief that the living cell itself
was the acting agent. It has, however, been shown that this view is
incorrect and that the decomposing influence exerted by these fer-
ments is due to some substance produced by the living cell, from
which it may be separated or extracted in a more or less pure condi-
tion. It is consequently more in conformity with our present views
to apply the term enzyme to that agent which causes the decomposi-
tion. Enzymes are always products of the cell action of a living
organism, but this organism may be a micro-organism, such as the
yeast cell ; or it may be a highly developed plant, such as the almond
tree which produces emulsine, an enzyme which decomposes amyg-
dalin ; or it may be an animal or man, generating such enzymes
as ptyalin, pepsin, etc. (Enzymes will be more fully considered
later on.)

The nature of the ferment generally determines the nature of the
decomposition which a substance suffers, or, in other words, one and
the same substance will under the influence of one ferment decom-
pose with liberation of certain products, while a second ferment
causes other products to be evolved. Sugar, for instance, under the
influence of yeast, is converted into alcohol and carbon dioxide,
while under the influence of certain other ferments it is converted
into lactic acid.

The difference between fermentation and putrefaction is that the
first term is used in those cases where the decomposing substance
belongs to the group of carbohydrates, all of which contain the
elements carbon, hydrogen, and oxygen only, while substances be-
longing to the proteins, which contain, in addition to these three
elements, also nitrogen and sulphur, undergo putrefaction. The two
last-named elements are generally evolved as ammonia or derivatives
of ammonia and hydrogen sulphide, which gases give rise to an
offensive odor, the putrefying mass being generally designated as
fetid matter.

As a general rule the oxygen of the air takes no part in either fer-
mentation or putrefaction, but the presence or absence of atmospheric
air may cause or prevent decomposition, inasmuch as the atmosphere
is filled with millions of bacteria, which may act as ferments when in
contact with organic matter under favorable conditions.

DECOMPOSITION OP OttOANlC COMPOUNDS. 457

One of the fermentations in which oxygen takes part is acetic acid fermen-
tation, resulting in the conversion of alcohol into acetic acid by oxidation.
This conversion may be brought about by suitable oxidizing agents, or even by
atmospheric oxygen, and is then practically a slow combustion or decay. But
the transfer of oxygen may be brought about by micro-organisms and the pro-
cess is then defined as fermentation.

Whenever organic bodies (a dead animal, for instance) undergo de-
composition in nature, the processes of fermentation and putrefaction
are generally accompanied by oxidation or decay.

The conditions under which a substance will ferment or putrefy
have been stated above, and the non-fulfilment of these conditions
enables us to prevent decomposition artificially.

Thus, we make use of a low temperature in our refrigerators or by
cold storage. We expel water by drying or by dehydrating agents
such as absolute alcohol. We prevent the action of the ferments
either by antiseptic agents (salt, carbolic or salicylic acid, etc.) which
are incompatible with organic life, or by excluding the air, and with
it the ferments, by enclosing the substances in air-tight vessels (glass
jars, tin cans, etc.), which, when filled, are heated sufficiently to destroy
any bacteria which may have been present.

Antiseptics and disinfectants. While the term antiseptics is
applied to those substances which retard or prevent fermentation and
putrefaction, the term disinfectants refers to those agents actually
destroying the organisms which are the causes of these decomposi-
tions. If we assume that all infectious diseases are due to micro-
organisms, or germs of various kinds, disinfectants may be considered
as equivalent to germicides. Disinfectants are generally antiseptics
also, but the latter are not in all cases disinfectants. The solution
of a substance of certain strength may act as a disinfectant and
antiseptic, while the same solution diluted further may act as an
antiseptic only, but not as a disinfectant.

Deodorizers are those substances which convert the strongly smell-
ing products of decomposition into inodorous compounds. Strong
oxidizing agents are generally good deodorizers, as, for instance,
chlorine, potassium permanganate, hydrogen dioxide, etc. Among
the best antiseptics and disinfectants are mercuric chloride (a solution
of 1 : 500 or 1 : 1000) ; carbolic acid (5 per cent, solution) ; potassium
permanganate (5 per cent, solution) ; chlorine (generally used in the
form of a 4 per cent, solution of calcium hypochlorite) ; formaldehyde,

458 CONSIDERATION OF CARBON COMPOUNDS.

used in solution or as a gas ; hydrogen peroxide, salicylic acid, boric
acid, sulphur dioxide, ferrous or cupric sulphate, alcohol, chloroform,
thymol, etc.

The selection of a disinfectant depends on the respective conditions. While
the relatively harmless salicylic acid is often used as a preservative for articles
of food it is the powerful but strongly poisonous mercuric chloride which is
used externally in the operating room. The surgeon disinfects his hands by
first scrubbing with soap and water, immersing in a saturated solution of potas-
sium permanganate and washing finally in solution of oxalic acid. The latter
removes through its deoxidizing and dissolving power that portion of the per-
manganate which adheres to the hands. For the disinfection of rooms gases^
such as formaldehyde, sulphur dioxide or chlorine, are indicated. Instruments
may be disinfected by heat or by immersion in suitable solutions.

The term asepsis refers to the absence of living germs of fermentation, putre-
faction or disease, while the term sterilization is used for the process of destroy-
ing all living micro-organisms in the object or material operated on. Aseptic
conditions by means of sterilizing may be brought about either by the use of
antiseptic agents or by application of heat.

Action of chlorine and bromine. These two elements act upon
organic substances (similarly to oxygen) in three different ways, viz.,
they either (rarely, however) combine directly with the organic sub-
stance, or remove hydrogen, or replace hydrogen. The following
equations illustrate this action :

C2H4 + 2Br = C2H4Br2.
Ethylene. Bromine. Ethylene bromide.

C2H60 + 2C1 : : G2H40 + 2HC1.
Ethyl alcohol. Chlorine. Aldehyde. Hydrochloric acid.

C2H402 + 2C1 C2H3C102 + HC1.

Acetic acid. Chlorine. Monochloracetic Hydrochloric
acid. acid.

In the presence of water, chlorine and bromine often act as oxidiz-
ing agents by combining with the hydrogen of the water and liber-
ating oxygen ; iodine may act in a similar manner as an oxidizing
agent, but it rarely acts directly by substitution.

Action of nitric acid. This substance acts either by direct com-
bination with organic bases forming salts, or as an oxidizing agent,
or by substitution of nitryl, NO2, for hydrogen. As instances of the
latter action may be mentioned the formation of nitro-benzene and
cellulose nitrate:

DECOMPOSITION OF ORGANIC COMPOUNDS. 459

C6H6 + HN03 = C6H5N02 + H2O.
Benzene. Nitric acid. Nitro-benzene. Water.

C6H]005 + 3HN03 : C6H7«N(V,05 + 3H2O.
Cellulose. Nitric acid. Cellulose trinitrate. Water.

The additional quantity of oxygen thus introduced into the mole-
cules renders them highly combustible, or even explosive.

Action of dehydrating- agents. Substances having a great
affinity for water, such as strong sulphuric acid, phosphoric oxide,
and others, act upon many organic substances by removing from them
the elements of hydrogen and oxygen, and combining with the water
formed, while, at the same time, frequently dark or even black com-
pounds are formed, which consist largely of carbon. The black
color imparted to sulphuric acid by organic matter depends on this
action.

Action of alkalies. The hydroxides of potassium and sodium
act in various ways on organic substances.

In some cases substitution products are decomposed :

C2H5C1 -f KOH KC1 -f C2H5OH.

Ethyl chloride. Potassium Potassium Ethyl alcohol,

hydroxide. chloride.

Salts are formed :

C2H402 -f NaOH -= NaC2H3O2 + H2O.
Acetic Sodium Sodium Water,

acid. hydroxide. acetate.

Fats are decomposed with the formation of soap :

C3H5(C18H3A)3 + 3NaOH = C3H5(OH)3 -f 3NaC18H33O2.
Oleate of glyceryl. Sodium hydroxide. Glycerin. Sodium oleate.

Oxidation takes place, while hydrogen is liberated :

C,H6O -f KOH = KC2H3O2 -f 4H.

Ethyl Potassium Potassium Hydrogen,

alcohol. hydroxide. acetate.

From compounds containing nitrogen, ammonia is evolved :

NH2C2H30 -f KOH KC2H302 + NH3.

Acetamide. Potassium Potassium Ammonia,

hydroxide. acetate.

Action of reducing- agents. Deoxidizing or reducing agents,
especially hydrogen in the nascent state, act upon organic substances
either by direct combination :

C2H4O + 2H = C2H60.
Acetic aldehyde. Ethyl alcohol.

or by removing oxygen (and also chlorine or bromine) :

460 CONSIDERATION OF CARBON COMPOUNDS.

C7H602 + 2H = C7H60 + H20.
Benzoic acid. Benzole aldehyde.

C7H6O + 2H = C7H8O.
Benzoic aldehyde. Benzylic alcohol.

In some cases hydrogen replaces oxygen :

C6H5N02 + 6H = C6H5NH2 + 2H2O.
Nitro-benzene. Aniline.

Classification of organic compounds. There are great diffi-
culties in arranging the immense number of organic substances
properly, and in such a manner that natural groups are formed the
members of which are similar in composition and possess like
k properties.

Various modes of classification have been proposed, some of which,
however, are so complicated that the beginner will find it difficult to
make use of them. The grouping of organic substances here adopted,
while far from being perfect, has the advantages of being simple,
easily understood, and remembered.

1. Hydrocarbons. All compounds containing the two elements
carbon and hydrogen only. For instance, CH4, C6H6, C10H16, etc.

2. Alcohols. These are hydrocarbon radicals in combination
with hydroxyl, OH. For instance, ethyl alcohol, CjH^OH, glycerin,
C3Hiii5(OH)3, etc.

3. Aldehydes. Hydrocarbon radicals in combination with the
radical COH ; they are compounds intermediate between alcohols
and acids, or alcohols from which hydrogen has been removed.
For instance :

C2H60, CH3.COH, C2H402,

Ethyl alcohol. Aldehyde. Acetic acid.

4. Organic acids. Hydrocarbon radicals in combination with
carboxyl, a radical having the composition CO2H, or compounds
formed by replacement of hydrogen in hydrocarbons by carboxyl.
Instances : Acetic acid, CH3CO2H ; pyrotartaric acid, C3H6(CO2H)2.

5. Ethers. Compounds formed from alcohols by replacement of
the hydrogen of the hydroxyl by other hydrocarbon radicals, or,
what is the same, by other alcohol radicals. For instance :

Ethyl alcohol. Ethyl ether. Ethyl-methyl ether.

6. Compound ethers or esters. Formed from alcohols by replace-
ment of the hydrogen of the hydroxyl by acid radicals, or from acids

DECOMPOSITION OF ORGANIC COMPOUNDS. 461

by replacement of the hydrogen of carboxyl by alcoholic radicals.
For instance :

Q . CH3CO\0 C2H5\0 H\0

C C ~ ° h °

H/ ~ CH3CO/
Ethyl alcohol. Acetic acid. Acetic ether. Water.

The various fats belong to this group of compound ethers.

7. Carbohydrates. (Sugars, starch, cellulose, etc.) These are
compounds of carbon, hydrogen, and oxygen, in which the number
of carbon and oxygen atoms is the same, while the number of
hydrogen atoms is double that of the oxygen atoms. As the hydro-
gen and oxygen are present in the proportion to form water, they are
hence called carbohydrates. There are only a few exceptions to the
above statement. Most carbohydrates are capable of fermentation,
or of being easily converted into fermentable bodies. Instances :
C6H1206, C6HI005, etc.

Glucosides are substances the molecules of which may be split up
in such a manner that several new bodies are formed, one of which
is sugar.

8. Amines and amides. Substances formed by replacement of
hydrogen in ammonia by alcohol or acid radicals. For instance :
ethyl amine, NH2.C2H5, urea, N2H4.CO, etc. The alkaloids belong
to this group.

9. Cyanogen and its compounds. Substances containing the radical
cyanogen, CN. For instance : potassium cyanide, KCN.

10. Proteins or albuminous substances. These, besides carbon,
hydrogen, and oxygen, always contain nitrogen and sulphur, some-
times also other elements. Instances : albumin, casein, fibrin, etc.

In connection with each of these groups have to be considered the
derivatives obtained from them directly or indirectly.

As all those organic compounds the constitution of which has
been explained may be looked upon as derivatives of either methane,
CH4, or benzene, C6H6, a separation of organic compounds is made

QUESTIONS. — Explain the term residue or radical. What is understood by
the expression chain, when used in chemistry? What are the characteristics
of an homologous series ? Give an explanation of the terms isomerism, meta-
merism, and polymerism. How does heat act upon organic compounds?
What is destructive distillation? State the difference between combustion,
decay, fermentation, and putrefaction ; what is the nature of these processes,
and under what conditions do they take place? How do chlorine, nitric acid,
and alkalies act upon organic substances ? What is the action of hydrogen
and of dehydrating agents upon organic substances ? Mention the chief
groups of organic compounds.

462 CONSIDERATION OF CARBON COMPOUNDS.

into two large classes, each one embodying all the derivatives of one
of the two hydrocarbons named. The derivatives of methane are
often termed fatty compounds, those of benzene aromatic compounds.
Methane derivatives have representatives in each one of the above
ten groups : benzene derivatives are missing in a few. As far as
practicable, the two classes will be considered separately, because
the properties of fatty and aromatic compounds diifer so widely, in
some respects, that this method of studying the nature of carbon
compounds is to be preferred.

42. HYDROCARBONS AND THEIR HALOGEN DERIVATIVES.

Occurrence in nature. Hydrocarbons are seldom derived from
animal sources, being more frequently products of vegetable life;
thus, the various essential oils (oil of turpentine and others) of the
composition C10H16 or C20H32 are frequently found in plants.

Other hydrocarbons are found in nature as products of the decom-
position of organic matter. Thus methane, CH4, is generally formed
during the decay of organic matter in the presence of moisture ; the
higher members of the methane series are found in crude coal-oil.

Formation of hydrocarbons. It is difficult to combine the two
elements carbon and hydrogen directly; as an instance of such direct
combination may be mentioned acetylene, C2H2, which is formed
when electric sparks pass between electrodes of carbon in an atmos-
phere of hydrogen.

Many hydrocarbons are obtained by destructive distillation of
organic matter, and their nature depends on the composition of the
material used and upon the degree of heat applied for the decompo-
sition. Hydrocarbons may also be obtained by the decomposition
(other than destructive distillation) of numerous organic bodies, such
as alcohols, acids, amines, etc., and from derivatives of these sub-
stances.

The hydrocarbons found in nature are generally separated from
other matter, as well as from each other, by the process known as
fractional distillation. As the boiling-points of the various compounds
differ more or less, they may be separated by carefully distilling off
the compounds of lower boiling-points, while noting the temperature
of the vapors above the boiling liquid by means of an inserted ther-
mometer, and changing the receiver every time an increase of the
boiling-point is noticed. This separation of volatile liquids, known
as fractional distillation, is, however, not absolutely complete, because

HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 463

traces of substances having a higher boiling-point are simultaneously
volatilized with the distilling substance.

FIG.

Flasks arranged for fractional distillation.

For fractional distillation of small quantities of liquids as well as
for the determination of boiling-points, flasks arranged like those
shown in Fig. 69 may be used.

Properties of hydrocarbons. There are no other two elements
which combine together in so many proportions as carbon and hydro-
gen. Several hundred hydrocarbons are known, many of which
form either homologous series or are metameric or polymeric.

Hydrocarbons occur either as gases, liquids, or solids. If the mole-
cule contains not over 4 atoms of carbon, the compound is generally
a gas at the ordinary temperature ; if it contains from 4 to 10 or 12
atoms of carbon, it is a liquid ; and if it contains a yet higher number
of carbon atoms, it is generally a solid.

All hydrocarbons may be volatilized without decomposition, all
are colorless substances, and many have a peculiar and often charac-
teristic odor ; they are generally insoluble in water but soluble in
alcohol, ether, disulphide of carbon, etc.

464

CONSIDERATION OF CARBON COMPOUNDS.

First member.
CH4
C2H4
C2H2

In regard to chemical properties, it may be said that hydrocarbons
are neutral substances, behaving rather indifferently toward most
other chemical agents. Many of them are, however, oxidized by the
oxygen of the air, by which process liquid hydrocarbons are often
converted into solids. The action of halogens on hydrocarbons will
be considered later on.

A number of homologous series of hydrocarbons are known, of
which the following are the most important :

General formula.

Methane series or paraffins, CnH2U + 2

Ethene series or olefins, CnH2n

Eihine series or acetylenes, CnH2n _ 2

Terpenes, CnH2n _ 4 C10H16

Benzene series, CnH2n - e C6He

Of the acetylene series and of the terpenes only a few homologues
are known.

The univalent radicals of the members of the methane series are designated
by changing the termination ane to yl (methane, methyl, CH3!) ; the bivalent
radicals by changing ane to ene (rnethene, CH2]i) ; and the trivalent radicals
by changing the final e of ene to yl (methenyl, CHU1). The derivatives of the
bivalent radicals are indicated by the termination ylene, as methylene iodide,
CH2I2.

i

Hydrocarbons of the paraffin or methane series. The hydro-
carbons having the general composition CnH2n + 2 are known as
paraffins, the name being derived from the higher members of the
series which form the paraffin of commerce. The following table
gives the composition, boiling-points, etc., of the first sixteen mem-
bers of this series :

Methane or methyl hydride,
Ethane or ethyl hydride,
Propane or propyl hydride,
Butane or butyl hydride,
Pentane or amyl hydride,
Hexane or hexyl hydride,
Heptane or heptyl hydride,
Octane or octyl hydride,
Nonane or nonyl hydride,
Decane or decyl hydride,
Undecane or undecyl hydride,
Dodecane or dodecyl hydride,
Tridecane or tridecyl hydride,
Tetradecane or tetradecyl hydride,
Pentadecane or pentadecyl hydride,
Hexadecane or hexadecyl hydride,
etc.

B. P.

Sp. gr.

H

H

H

1°C.

38

0.628

70

0.669

99

0.690

125

0.726

148

0.741

166

0.757

184

0.766

202

0.778

218

0.796

236

0.809

258

0.825

280

HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 465

The above table shows that the paraffins form an homologous
series; the first four members are gases, most of the others liquids,
regularly increasing in specific gravity, boiling-point, viscidity, and
vapor density, as their molecular weight becomes greater.

The paraffins are saturated hydrocarbons, the constitution of which
has been already explained; they are incapable of uniting directly
with monatomic elements or residues, but they easily yield sub-
stitution-derivatives when subjected to the action of chlorine or bro-
mine, hydrogen in all cases being given up from the hydrocarbon.

Most of the paraffins are known in two (or even more) modifications ; there
are, therefore, other homologous series of hydrocarbons of the same composition
as the above normal paraffins, which show some difference from the normal
paraffins in boiling-points and other properties. In these isomeric paraffins the
atoms are arranged differently from those in the normal hydrocarbons, which
fact may be proven by the difference in decomposition which these substances
suffer when acted upon by chemical agents.

No isomeric hydrocarbons of the first three members of the paraffin series are
known, which fact is in accordance with our present theories. Assuming that
the quadrivalent carbon atoms exert their full valence, and that they are held
together by one bond only, we can arrange the atoms in the compounds,
CH4, C2H6, and C3H8, not otherwise than thus:

/H
^H

In the next compound, butane, C4H10, we have two possibilities explaining
the structure of the molecule, namely, these :

CEBH3

C=:H2 C=H3

(j=tiy O^=Ii3 — OH — G^^-tl3.

LH

L/ — r±3

Both these compounds are known, and termed normal butane and isobutane,
respectively.

The next member, pentane, C5H12, shows three possibilities of constitution,
thus:

C=H3

C=Ha CEEH3

| C=H3-C-H. |

C=H2 | C=H3— C— C^H,

C=H2 | _ O=H3.

C^5iHj|

C=H3

These compounds also are known. With the higher members of the paraffins
the number of possible isomers rises rapidly according to the law of permuta-
30

466 CONSIDERATION OF CARBON COMPOUNDS.

tion, so that we have of the seventh member 9, of the tenth 75, and of the
thirteenth member 80<>, possible isomeric hydrocarbons.

Methane, CH4 (Marsh-gas, Fire-damp). This hydrocarbon has
been spoken of in Chapter 14, where it was stated that it is a color-
less, combustible gas, which is formed by the decay of organic matter
in the presence of moisture, during the formation of coal in the
interior of the earth, and by the destructive distillation of various
organic matters. Methane is of special interest, because it is the
compound from which thousands of other substances are derived. It
may be made by the action of inorganic substances upon one another;
for instance, by the action of water on aluminum carbide, a compound
of the metal aluminum, and carbon, A14C3, the following change tak-
ing place :

A14C3 + 12H20 = = 3CH4 + 4A1(OH)3.

Bearing in mind that aluminum carbide, as well as water, may be
obtained by direct union of the elements, it is evident that methane
may be formed indirectly, by means of the above method, from the
elements carbon and hydrogen.

Experiment 51. Use apparatus shown in Fig. 35, page 87, omitting the bent
tube B. Mix in a mortar 20 grammes of sodium acetate with 20 grammes of
potassium (or sodium) hydroxide and 30 grammes of calcium hydroxide ; fill
with this mixture the tube A, which should be made of glass fusing with
difficulty, or of so-called "combustion tubing;" apply heat and collect the gas
over water. The decomposition takes place thus :

NaC2H3O2 + NaOH = NajCOg + CH4.

Ignite the gas, and notice that its flame is but slightly luminous. Mix some
of the gas in a wide-mouth cylinder, of not more than about 200 c.c. capacity,
with an equal volume of air and ignite. Eepeat this experiment with mixtures
of one volume of methane with 2, 4, 6, 8, and 10 volumes of atmospheric air.
Which mixture is most explosive, and why ? How many volumes of oxygen
and how many volumes of atmospheric air are needed for the complete com-
bustion of one volume of methane ?

Ethane, C-^Hg, is a constituent of natural gas and of crude petroleum. It
can be obtained from methane by first replacing in it a hydrogen atom by
iodine, when iodo-methane, or methyl-iodide, CH3I, is formed, which, when
acted on by sodium, is decomposed thus:

CH3I + CH3I + 2Na = 2NaI + C2Hfi.

This formation of ethane illustrates one of the methods for producing by
synthesis— i. e., for building up— more complex from simpler hydrocarbons.
Another method, accomplishing the same result, depends on the action of a

HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 467

zinc compound of the radicals on the iodides of the radicals. The radicals
may be the same or different ones; for instance:

Zn(CH3)2 + 2CH3T = ZnI2 + 2C2He,
Zinc methyl. Methyl iodide. Zinc iodide. Ethane.

Zn(CHs)2 + 2C2H5I = ZnI2 -f- 2C3H8.
Ethyl iodide. Propane.

Coal. As methane is one of the products generated during the
formation of coal, it may be well to consider this process here briefly.

The various substances classed togther under the name of coal con-
sist principally of carbon, associated with smaller quantities of hydro-
gen, oxygen, nitrogen, sulphur, and certain inorganic mineral matters
which compose the ash. Coal is formed from buried vegetable
matter by a process of decomposition which is partly a fermentation,
partly a decay, and chiefly a slow destructive distillation, the heat
for this latter process being derived from the interior of the earth, or
by the decomposition itself.

The principal constituent of the organic matter furnishing coal is
wood (or woody fibre, cellulose), and a comparison of the composition
of this substance with the various kinds of coal gradually formed
will help to illustrate the chemical change taking place :

Carbon. Hydrogen. Oxygen.

Wood 100 12.18 83.07

Peat 100 9.85 55.67

Lignite 200 8.37 42.42

Bituminous coal . . . .100 6.12 21.23

Anthracite coal 100 2.84 1.74

This table shows a progressive diminution in the proportions of
hydrogen and oxygen during the passage from wood to anthracite.
These two elements must, therefore, be eliminated in some form of
combination which allows them to move, viz., as gases or liquids.
The gases formed are chiefly carbon dioxide (which finds its way
through the rocks and soils to the surface either in the gaseous state
or after having been absorbed by water in the form of carbonic acid
springs) and methane, known to coal-miners as fire-damp, frequently
causing the formation of explosive gas mixtures in the coal mines, or
escaping, like carbon dioxide, through fissures to the surface of the
earth, where it may be ignited.

Natural gas. While methane and other combustible gases are
undoubtedly formed during the formation of coal, the gas mixture
now generally termed natural gas (a mixture of methane, ethane,
propane, hydrogen, and a few other gases), and used largely for

f Liquids
Coal-tar -!

470 CONSIDERATION OF CARBON COMPOUNDS.

B. P.

f Benzene .... C6H6 80°

Toluene . . • C7H8

Aniline C6H5NH2 182

Acetic acid . C2H4O2 117

Water H2O 100

Carbolic acid . . . C6H6O 188

Kresylic acid . . . C7H8O

Naphthalene .... C10H8 220

Anthracene .... CUH10 360

Paraffin C16H34 280

Solid residue : Coke, chiefly carbon and inorganic matter.

The gases are purified by condensing ammonia (and some other
gases) in water, carbon dioxide and hydrogen sulphide in calcium
hydroxide. The following is the composition of a purified illumi-
nating gas obtained from cannel-coal :

Hydrogen 46 volumes.

Methane 41 "

Ethene 6

Carbon monoxide .... 4 "

Carbon dioxide 2 "

Nitrogen 1 volume.

The poisonous properties of illuminating gas are due chiefly to car-
bon monoxide, all other constituents being more or less harmless.

Experiment 53. Use apparatus shown in Fig. 35, page 87. Fill the combus-
tion-tube A with sawdust (almost any other non-volatile organic matter may be
used), apply heat and continue it as long as gases are evolved. Notice that by
this process of destructive distillation are formed a gas (or gas mixture), which
may be ignited, a dark, almost black liquid (tar), which condenses in the tube
B, and that a residue is left which is chiefly carbon. The tarry liquid shows an
acid reaction, due to acetic and other acids present.

Coal-tar, obtained as a by-product in the manufacture of illumi-
nating gas, contains, as shown by the above table, many valuable sub-
stances, such as benzene, aniline, carbolic acid, paraffin, etc., which
are separated from each other by making use of the diiference in their
boiling-points and specific gravities, or of their solubility or insolu-
bility in various liquids, or, finally, of their basic, acid, or neutral
properties.

Unsaturated hydrocarbons. The terms saturated and un-
saturated compounds are used for inorganic and organic substances.
A compound is said to be unsaturated when it has the power to enter
directly into combination with elements or compounds. Thus, car-

HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 471

bon monoxide and phosphorus trichloride are un saturated, as they
combine directly with a number of substances ; for instance, with

chlorine, thus :

CO + 2C1 = COC12,

PC13 + 2C1 = PC15.

The hydrocarbons of the methane series are saturated ; they can-
not be made to enter directly into combination with other substances,
because there are no bonds left unprovided for.

On the other hand, we have several homologous series of hydro-
carbons which are unsaturated. The olefins belong to this kind,
and the reason is found in the structure of the molecules.

Looking at the graphic formulas of the normal hydrocarbons of the methane
series on page 465, we find all affinities completely saturated. The structure
of ethylene, C2H4, the first member of the olefines, may be represented by either
of the following formulas :

H H H H

H— C— C— H

Each of these representations shows that two bonds are left unsaturated, and
as certain considerations lead us to assume that two hydrogen atoms are in
combination with one carbon atom the second representation is the one agree-
ing with our views. Instead of leaving the affinities unsaturated in our for-
mulas as above, we use double linkage, and give to ethylene the formula

H H
H— C=C— H or H3C=CH2.

Whenever direct combination between ethylene and another substance
occurs the double linkage is broken and the bonds are utilized for holding

the respective atoms, or radicals, thus :

Br Br

H2C=CH2 + 2Br = H2C— CH2.

As the higher members of the ethylene series are obtained by replacement
of hydrogen atoms by hydrocarbon radicals in ethylene, which replacement
does not alter the double linkage of its carbon atoms, all members behave like
unsaturated compounds.

In a similar manner we represent the unsaturated hydrocarbon acetylene
C2H2, by the formula HC=CH, showing triple linkage between the carbon
atoms. That this view is in keeping with the facts is shown by the action of
bromine or of hydrobromic acid on acetylene, thus :

HC=CH + 4Br = Br2HC— CHBr^
HfeCH + 2HBr = BrH2C— CH3Br.

Coal-tar -

Solids

470 CONSIDERATION OF CARBON COMPOUNDS.

B. P.

f Benzene .... C6H6 80°

I Toluene . . . C7H8 110

Liquids -j Aniline C6H5NH2 182

' Acetic acid .... C2H4O2 117

Water H2O 100

Carbolic acid . . . C6H6O 188

Kresylicacid . . . C7H8O 201

Naphthalene .... CIOH8 220

Anthracene .... CUH10 360

I Paraffin C16H34 280

Solid residue : Coke, chiefly carbon and inorganic matter.

The gases are purified by condensing ammonia (and some other
gases) in water, carbon dioxide and hydrogen sulphide in calcium
hydroxide. The following is the composition of a purified illumi-
nating gas obtained from cannel-coal :

Hydrogen 46 volumes.

Methane 41 "

Ethene 6 "

Carbon monoxide .... 4 "

Carbon dioxide 2 "

Nitrogen 1 volume.

The poisonous properties of illuminating gas are due chiefly to car-
bon monoxide, all other constituents being more or less harmless.

Experiment 53. Use apparatus shown in Fig. 35, page 87. Fill the combus-
tion-tube A with sawdust (almost any other non-volatile organic matter may be
used), apply heat and continue it as long as gases are evolved. Notice that by
this process of destructive distillation are formed a gas (or gas mixture), which
may be ignited, a dark, almost black liquid (tar), which condenses in the tube
B, and that a residue is left which is chiefly carbon. The tarry liquid shows an
acid reaction, due to acetic and other acids present.

Coal-tar, obtained as a by-product in the manufacture of illumi-
nating gas, contains, as shown by the above table, many valuable sub-
stances, such as benzene, aniline, carbolic acid, paraffin, etc., which
are separated from each other by making use of the difference in their
boiling-points and specific gravities, or of their solubility or insolu-
bility in various liquids, or, finally, of their basic, acid, or neutral
properties.

Unsaturated hydrocarbons. The terms saturated and un-
saturated compounds are used for inorganic and organic substances.
A compound is said to be unsaturated when it has the power to enter
directly into combination with elements or compounds. Thus, car-

HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 471

bon monoxide and phosphorus trichloride are unsaturated, as they
combine directly with a number of substances ; for instance, with
chlorine, thus :

CO -f 2C1 = COC12,

PC13 + 2C1 = PC15.

The hydrocarbons of the methane series are saturated ; they can-
not be made to enter directly into combination with other substances,
because there are no bonds left unprovided for.

On the other hand, we have several homologous series of hydro-
carbons which are unsaturated. The olefins belong to this kind,
and the reason is found in the structure of the molecules.

Looking at the graphic formulas of the normal hydrocarbons of the methane
series on page 465, we find all affinities completely saturated. The structure
of ethylene, C2H4, the first member of the olefines, may be represented by either
of the following formulas :

H H H H

H— C— C— H— C— C— H

A1 ' '

Each of these representations shows that two bonds are left unsaturated, and
as certain considerations lead us to assume that two hydrogen atoms are in
combination with one carbon atom the second representation is the one agree-
ing with our views. Instead of leaving the affinities unsaturated in our for-
mulas as above, we use double linkage, and give to ethylene the formula

H H
H— C=C— H or HaC=CHr

Whenever direct combination between ethylene and another substance
occurs the double linkage is broken and the bonds are utilized for holding

the respective atoms, or radicals, thus :

Br Br

H2C=CH2 -f 2Br = H2C— CH3.

As the higher members of the ethylene series are obtained by replacement
of hydrogen atoms by hydrocarbon radicals in ethylene, which replacement
does not alter the double linkage of its carbon atoms, all members behave like
unsaturated compounds.

In a similar manner we represent the unsaturated hydrocarbon acetylene
C2H2, by the formula HfeCH, showing triple linkage between the carbon
atoms. That this view is in keeping with the facts is shown by the action of
bromine or of hydrobromic acid on acetylene, thus :

HfeCH + 4Br = Br2HC— CHBry
2HBr = BrH2C— CH8Br.

472 CONSIDERATION OF CARBON COMPOUNDS.

Olefins. The hydrocarbons of the general formula CnH2n are
termed olefins. To this series belong :

Ethylene or ethene C2H4.

Propylene or propene .... C3H6.

Butylene or butene C4H8.

Amylene or pentene .... C5H10.

Hexylene or hexene .... C6H12.

Methene, CH2, the lowest term of this series, is not known. The
hydrocarbons of this series are not only homologous, but also poly-
meric with one another.

Ethylene, C2H4 (Ethene, olefiant gas), the first member of the
olefins, is of special interest on account of its normal occurrence in
illuminating gas made from coal, as also in most common flames, the
luminosity of which depends largely on the quantity of this compound
present in the burning gas.

Besides destructive distillation there are several reactions by which ethylene
can be obtained. Of these two are of interest. The first one depends on the
action of an alcoholic solution of potassium hydroxide on ethyl chloride, bro-
mide, or iodide :

C2H5Br + KOH = C2H4 + KBr + H2O.

This reaction shows the possibility of preparing an unsaturated compound
of the ethylene series from a saturated hydrocarbon ; and as the method is
applicable to compounds of other classes it furnishes the means to pass from
any saturated compound to the corresponding unsaturated compound of the
ethylene series.

The second method for preparing ethylene depends on the dehydrating action
of sulphuric acid on ethyl alcohol :

C2H5OH H20 = C2H4.

Ethylene combines directly with an equal volume of chlorine forming ethy-
lene dichloride, C2H4C12, an oily liquid, whence the name olefiant gas.

Amylene, C5H10. Of the three isomeric hydrocarbons of the composition
C5H10, two have been used medicinally. It is especially the amylene of the

CH CH

composition Qjj3^>C = C<JT 3 — i. e., trimethyl-ethylene — which has been in-
troduced as an anaesthetic under the name of pental. It is formed from tertiary
amyl alcohol (amylene hydrate) by the action of dehydrating agents. It is a
colorless, very volatile liquid, insoluble in water, but miscible in all proportions
with chloroform, ether, and alcohol. It has a penetrating odor, reminding of
mustard oil.

HALOGEN DERIVATIVES OF HYDROCARBONS. 473

Acetylene, C2H2, is the first member of a hydrocarbon series of
the general composition CnH2n_2. It has been stated before that
acetylene is formed by direct union of the elements when an electric
current passes between two carbon poles in an atmosphere of hydro-
gen. It is also formed during the incomplete combustion of coal-
gas, such as takes place when the flame of a Btinsen burner " strikes
back " — i. e., burns at the base of the burner.

The method now extensively used in the manufacture of acetylene
for illuminating purposes depends on the decomposition of calcium
carbide by water :

C2Ca + H2O = CaO + C2H2.

Pure acetylene is a gas of agreeable ethereal odor, while the gas as ordi-
narily prepared possesses an unpleasant odor, due to impurities. With an
ordinary burner acetylene burns with a luminous but sooty flame, while by
the use of specially constructed burners flames may be obtained giving a very
pure, intensely luminous white light. Like ethene, it combines directly with
halogens, and when heated to a sufficiently high temperature it is converted
into the polymeric compounds, benzene, C6H6, and styrene, C8H8.

A characteristic property of acetylene is the readiness with which its
hydrogen may be replaced by metals ; thus, by treating acetylene with sodium,
either monosodium acetylid, C2HNa, or disodium acetylid, C2Na,, may be ob-
tained. Silver acetylid, C2Ag2, a white crystalline compound, and cuprous
acetylid, C2Cu2, a red powder, may be obtained by passing the gas through
ammoniacal solutions of silver and cuprous salts, respectively. When dry,
both compounds explode violently when heated, the silver compound even
when rubbed with a glass rod.

Halogen derivatives of hydrocarbons.

Substitution products. When a mixture of methane and chlorine
is exposed to diffused daylight chemical action takes place gradually,
resulting in the successive substitution of hydrogen by chlorine, thus :

CH4 + 2C1 = CH3C1 + HC1.
CH3C1 + 2C1 = CH2C12 + HC1.
CH2C12 + 2C1 == CHC13 + HC1.
CHC13 + 2C1 = CC14 + HC1.

These reactions between methane and chlorine are more or less
characteristic of the general interaction between the halogens and
hydrocarbons, most of the latter being very susceptible to the action
of halogens. The 4 substitution products formed are designated
respectively as monochlor-methane or chlor-methane, dichlor-methane,
trichlor-methane, and tetracUor-methane or carbon tetmcMoride. These
compounds may also be looked upon as chlorides of the radicals CH3',

474 CONSIDERATION OF CARBON COMPOUNDS.

methyl ; CH2H, methylene ; CHm, meihenyl ; and of carbon CUii. The
univalent radicals such as methyl, ethyl, propyl are called alkyl or
alcohol radicals, while the term alkylene designates bivalent radicals
such as methylene, ethylene, propylene, etc.

A characteristic feature of these halogen derivatives is the behavior of the
halogens towards such reagents as silver nitrate. Chlorine and iodine when in
combination with hydrogen or metals readily form with a soluble silver salt
insoluble chloride or iodide. The halogens which have replaced hydrogen in
organic compounds are, as a general rule, not affected by silver salts in solu-
tion. This behavior shows that the substitution products are not dissociable
— i. e., there are no halogen ions present. While above a general method has
been given by which the halogen compounds can be made, there are usually
employed other processes for their manufacture. Also the names given above
are not always those in general use. Thus, trichlor-methane or methenyl
chloride is generally called chloroform and the corresponding bromine and
iodine compounds bromoform and iodoform.

Methyl chloride, CH3C1 (Monochlor-methane), is readily obtainable by the
action of hydrochloric acid on methyl alcohol :

CH3OH + HC1 = CH3C1 + H2O.

It is a colorless, inflammable gas which can be liquefied by pressure. This
liquid which produces an intense cold by its evaporation has been used locally
for neuralgia.

Dichlor-methane, CH2C12 (Methylene chloride), is obtained by the action of
nascent hydrogen on chloroform :

CHC13 + 2H = CH8Cla + HC1.

It is a colorless, oily liquid, boiling at 40° C. (104° F.) ; sp. gr. 1.344. It has
an odor similar to that of chloroform, and has been employed as an anaesthetic.

Tetrachlor-methane, CC14 (Carbon tefrachloride), is obtained by the action
of chlorine on carbon disulphide, or by treating chloroform with iodine chloride :

CH.CL, -f IC1 = CC14 + HI.

It is a colorless liquid possessing anaesthetic properties, but, like the previous
compound, is dangerous.

By far the most important halogen derivatives of methane are the
trisubstitution products : chloroform, bromoform and iodoform. The
gaseous chlorine and the liquid bromine convert through their sub-
stitution the gaseous methane into colorless, heavy, volatile liquids,
while the solid iodine confers the solid state upon the compound.

Chloroform, Chloroformum, CHOI, = 118.45 (Trichlor-methane),
is obtained by the action of bleaching-powder and calcium hydroxide

HALOGEN DERIVATIVES OF HYDROCARBONS. 475

on alcohol. The three substances named, after being mixed with a
considerable quantity of water, are heated in a retort until distilla
tion commences ; the crude product of distillation is an impure chloro-
form, which is purified by mixing it with strong sulphuric acid and
allowing the mixture to stand ; the upper layer of chloroform is
removed and treated with sodium carbonate (to remove any acids)
and distilled over calcium chloride (to remove water).

A full explanation of the formation of chloroform by the above process will
be given later on in connection with the consideration of chloral, where it will
be shown that alcohol is converted by the action of chlorine first into aldehyde
and subsequently into chloral, which, upon being treated with alkalies, is
•decomposed into an alkali formate and chloroform.

The action of the chlorine of the calcium hypochlorite (which is the active
principle in bleaching-powder) upon the alcohol is similar to that of free
chlorine upon alcohol; in both cases aldehyde, and afterward chloral, are
formed, which latter, in the manufacture of chloroform, is decomposed by the
calcium hydroxide into chloroform and calcium formate. The last-named salt
is, however, not found in the residue of the distillation, because it is decomposed
by bleaching-powder and calcium hydroxide into calcium carbonate, chloride,
and water :

Ca(CHO2)2 + Ca(ClO)2 + Ca(OH)3 = 2CaCO3 + CaCl2 + 2H2O.

If the various intermediate steps of the decomposition are not considered, the
process may be represented by the following equation :

4C2H60 + 8Ca(C10)2 = 2CHC13 -f 3[Ca(CHO2)2] + 5CaCl2 + 8H2O.
Alcohol. Calcium Chloroform. Calcium Calcium Water,

hypochlorite. formate. chloride.

Chloroform is now made extensively by the action of bleaching-powder upon
acetone ; the reaction takes place thus :

2CO(CH3)2 -f 3Ca(C10)2 = 2CHC13 + 2Ca(OH)2 + Ca(C2H3<V2
Acetone. Calcium Chloroform. Calcium Calcium

hypochlorite. hydroxide. acetate.

Pure chloroform is a heavy, colorless liquid, of a characteristic
ethereal odor, a burning, sweet taste, and a neutral reaction ; it is but
very sparingly soluble in water, but miscible with alcohol and ether
in all proportions ; the specific gravity of pure chloroform is 1.50,
but a small quantity of alcohol (from one-half to one per cent.),
allowed to be present by the U. S. P., causes the specific gravity to
be about 1.48; boiling-point 61° C. (141.8° F.), but rapid evapora-
tion takes place at all temperatures.

Chloroform or its vapors do not ignite readily, but at a high tem-
perature chloroform burns with a green flame. When kept in a
partially filled bottle exposed to daylight it decomposes with the for-
mation of the highly irritating carbonyl chloride :

476 CONSIDERATION OF CARBON COMPOUNDS.

CHC13 + O = COC12 -f- HC1.

Chloroform containing some alcohol is less apt to undergo this oxida-
tion, but the latter also takes place when chloroform is used for inha-
lation near an exposed flame.

Analytical reactions for chloroform.

1. Dip a strip of paper into chloroform and ignite. The flame has
a green mantle and emits vapors of hydrochloric acid, rendered more
visible upon the approach of a glass rod moistened with ammonia water.

2. Add a drop of chloroform and a drop of aniline to some alco-
holic solution of potassium hydroxide and heat gently : a peculiar,
penetrating, offensive odor of benzo-isonitrile, C6H5NC, is noticed.
(Chloral shows the same reaction.)

CHClg -f 3KOH + C6H5.NH2 = C6H5NC + 3KC1 + 3H2O.

3. Add some chloroform to Fehling's solution and heat : red
cuprous oxide is precipitated.

4. Vapors of chloroform, when passed through a glass tube heated
to redness, are decomposed into carbon, chlorine, and hydrochloric
acid. The two latter should be passed into water, and may be recog-
nized by their action on silver nitrate (white precipitate of silver
chloride) and on mucilage of starch, to which potassium iodide has
been added (blue iodized starch is formed).

5. Heat some chloroform with solution of potassium hydroxide and
a little alcohol. Chloroform is decomposed into potassium chloride
and formate :

CHC13 -f 4KOH == 3KC1 + KCH02 + 2H2O.

Divide solution into two portions. Acidulate one portion with
nitric acid, boil, and add silver nitrate : white precipitate of silver
chloride. To second portion add a little ammonia water and a crystal
of silver nitrate : a mirror of metallic silver will be formed after
heating slightly.

6. Add to 1 c.c. of chloroform about 0.3 gramme of resorcin in
solution, and 3 drops of solution of sodium hydroxide ; boil strongly :
a yellowish-red color is produced, and the liquid shows a beautiful
yellow-green fluorescence. (Chloral shows the same reaction.)

In cases of poisoning chloroform is generally to be sought for in the lungs
and blood, which are placed in a flask connected with a tube of difficultly
fusible glass. By heating the flask the chloroform is expelled and decomposed
in the heated glass tube, as stated above in reaction 4. Another portion of
chloroform should be distilled without decomposing it, and the distillate tested
as above stated.

There is no chemical antidote which may be used in cases of poisoning by

HALOGEN DERIVATIVES OF HYDROCARBONS. 477

chloroform, and the treatment is, therefore, confined to the use of the stomach-
pump, to the maintenance of respiration with oxygen inhalation, and to the
use of strychnine hypodermically.

Bromoform, Bromoformum, CHBr3 (Tribrom-methane), is an
extremely heavy, colorless mobile liquid, with an ethereal odor, and
a penetrating, sweet taste, resembling chloroform, specific gravity
2.884 ; B. P. 148° C. It is sparingly soluble in water, soluble in
alcohol and ether. Its physiological action is similar to that of
chloroform.

Bromoform may be obtained by gradually adding bromine to a cold solution
of potassium hydroxide in ethyl alcohol until the color is no longer discharged,
and rectifying over calcium chloride. It is also made by the action of an alkali
hypobromite on acetone.

lodoform, lodoformum, CHI3 = 390.61 (Triiodo-methane). This
compound is analogous in its constitution to chloroform and bromo-
form. It is made by heating together an aqueous solution of an alkali
carbonate, iodine, and alcohol until the brown color of iodine has
disappeared ; on cooling, iodoform is deposited in yellow scales, which
are well washed with water and dried between filtering paper. (For
an explanation of the chemical changes taking place see chloral and
chloroform.)

lodoform occcurs in small, lemon-yellow, lustrous crystals, having
a peculiar, penetrating odor, and an unpleasant, sweetish taste ; it is
nearly insoluble in water and acids, soluble in alcohol, ether, fatty
and essential oils. It contains 96.7 per cent, of iodine.

lodoform digested with an alcoholic solution of potassium hy-
droxide imparts, after acidulation with nitric acid, a blue color to
starch solution. (See reaction in Test 5 under Chloroform.)

Experiment 54. Dissolve 4 grammes of crystallized sodium carbonate in 6
c.c. of water : add to this solution 1 c.c. of alcohol ; heat to about 70° C. (158°
F.), and add gradually 1 gramme of iodine. A yellow crystalline deposit of
iodoform separates.

Ethyl chloride, ^Jthylis chloridum, C2H5C1 = 64 (Chlor-cthane),
is prepared analogously to methyl chloride by the action of hydro-
chloric acid gas upon absolute ethyl alcohol :

C2H5OH + HC1 = C2H5C1 + H20.
In place of hydrochloric acid phosphorus pentachloride may be used :

C2H6OH + PC15 = C2H5C1 + POC1, + HCL

Ethyl chloride is a gas at ordinary temperature, but by pressure it
is converted into a colorless, mobile, very volatile liquid which boils at

478 CONSIDERATION OF CARBON COMPOUNDS.

12.5° C. The compressed liquid is sold in tubes, from which it is permit-
ted to escape through a small opening when used as a local anaesthetic.
It is highly inflammable. It is known also as kelene or chelene.

Ethyl bromide, C2H5Br (Brom-ethane, Hydrobromlc ether], is obtained by
the same reactions as ethyl chloride, substituting bromine for chlorine. It is
a colorless, heavy, volatile liquid. Specific gravity 1.473; B. P. 40° C. When
inhaled it rapidly produces anaesthesia, followed by quick recovery.

Somnoform is said to be a mixture of 60 parts of ethyl chloride, 35 parts of
methyl chloride, and 5 parts of ethyl bromide. It is used to some extent in
dentistry as an anaesthetic.

Ethyl iodide, C2H5I, may be obtained similarly to the chlorine or bromine
compound. It is a colorless liquid with the boiling-point of 72° C.

Compounds of hydrocarbon (alkyl) radicals with other elements. Some
metals, as zinc, magnesium, cadmium, aluminum, etc., can form compounds
with alkyl radicals; for example, Zn(CH3)2, Sn(C2H5)4. Likewise, alkyl rad-
icals can be substituted for one or more atoms of hydrogen in ammonia (NH3),
arsine (AsH3), and phosphine (PH3) ; for example, NH.2.CH3, AsH(CH3)2,
P(CH3)3. The alkyl derivatives of ammonia are treated in chapter 49. One
of the arsenic compounds possesses some interest because of its use in med-
icine, although its employment is limited. When arsenous oxide and potas-
sium acetate are distilled together, a heavy, horribly-smelling, poisonous,
fuming oil is formed, the principal constituent of which has the composition,
[(CH3)2As]2O. The reaction is, As2O3 + 4CH3COQK = K2C03 + 2CO2 +
[(CH3)2As]2O. Dimethyl arsine oxide is known best as cacodyl oxide, the
word cacodyl having been adopted in allusion to the disgusting odor of the
compound. It contains the univalent radical, (CH3)2As — , which acts like an
atom of a univalent metal. Cacodyl itself, (CH3)2As — As(CH3)2, also exists.
The oxide has a strong affinity for oxygen, and inflames in oxygen gas, but not
in air. By oxidizing cacodyl oxide with mercuric oxide, cacodylic acid is formed,
(CH3)2AsO.OH, which yields odorless prisms, easily soluble in water. Sodium
cacodylate, (CH3)2AsO.ONa -f 3H2O, also called sodium dimethyl arsenate, is
evidently closely related to mono-sodium arsenate. It is a white odorless
powder, very soluble in water, forming needle-shaped crystals, which are hygro-
scopic, but otherwise very stable. The aqueous solution is alkaline to litmus,
but nearly neutral to phenolphthalein. Its action is similar to that of other
arsenic compounds, but it is said to be much less toxic, and also less apt to
cause undesirable side-effects.

QUESTIONS. — How do hydrocarbons occur in nature, and by what processes
are they formed in nature or artificially? State the general physical and
chemical properties of hydrocarbons. State the composition and properties
of methane, and also the conditions under which it is formed in nature. What
is coal, what are its constituents, from what is it derived, and by what process
has it been formed ? What is crude coal-oil, what is petroleurn-benzin, and wh at
is petrolatum? How is illuminating gas manufactured, and what are its chief
constituents? Mention some of the important substances found in coal-tar.
State of chloroform : composition, properties, two processes for its manufacture,
and method of detection. Explain the action of chlorine on methane and
name the products. How is iodoform made and what are its properties ?

ALCOHOLS. 479

43. ALCOHOLS.

Constitution of alcohols. — The old term "alcohol" originally
indicated but one substance (ethyl alcohol), but it is now applied to a
large group of substances which may be looked upon as being derived
from hydrocarbons by replacement of one, two, or more hydrogen
atoms by hydroxyl, OH. In other words, alcohols are hydrocar-
bon radicals in combination with hydroxyl.

If hydroxyl replaces but one atom of hydrogen in a hydrocarbon,
the alcohol is termed monatomic ; diatomic and triatomic alcohols are
formed by replacement of two or three hydrogen atoms respectively.
(Diatomic alcohols are also termed glycols.) As an instance of a
diatomic alcohol may be mentioned ethylene alcohol, C2H4(OH)2,
while glycerin, C3H5(OH)3, is a triatomic alcohol. Tetratomic,
pentatomic, and hexatomic alcohols are also known.

It has been shown before that the higher members of the paraffin series are
capable of forming a number of isomeric compounds. Running parallel to the
various series of hydrocarbons (and their isomers) we have homologous series
of alcohols. The isomeric alcohols also show properties different from one
another, and yield different decomposition products.

Normal alcohols are those with a straight carbon chain derived from normal
hydrocarbons. Alcohols are also divided, according to the linkage between tho
hydroxyl groups and a carbon atom, into primary, secondary, and tertiary
alcohols.

A primary alcohol is one in which the hydroxyl group is linked to a carbon
atom which is united to but one other carbon atom, or, in other words, it is one
containing the univalent group, — CH2— OH. For instance, ethyl alcohol,
CH3— CH2— OH, represents a primary alcohol. Primary alcohols yield by
oxidation aldehydes and acids.

A secondary alcohol is one in which the hydroxyl group is linked to a car-
bon atom which is joined to two other carbon atoms-*. «., the hydroxyl forms
a side chain and the bivalent group characteristic of secondary alc(
is>CH-OH. For instance, iso-propyl alcohol, ggpCH-OH. Secondary

alcohols yield ketones by oxidation.

A tertiary alcohol is one in which the hydroxyl group is linked to a carbon
atom which is joined to three other carbon atoms, or one containing the tnva-

CH3\
lent group ^C-OH. For instance, tertiary butyl alcohol, CHpC

tiary alcohols by oxidation yield decomposition products.

By saturating with hydrogen the three bonds in the above tnatomic radical
methyl alcohof, H.O-OH, is obtained. Methyl alcohol » ato known as
carbinol, and the term carbinoh is used for the hydrocarbon derivative*,

480 CONSIDERATION OF CARBON COMPOUNDS.

methyl alcohol ; for instance, ethyl alcohol may be called methyl-carbinol.

Alcohols correspond in their composition to the hydroxides of
inorganic substances ; both classes of compounds containing hydroxyl,
OH, which, in the case of alcohols, is in combination with radicals
containing carbon and hydrogen, in the case of inorganic hydroxides
with metals, as, for instance, in potassium hydroxide, KOH.

If we represent any hydrocarbon radical by E, the general formula
of the alcohols will be :

Monatomic alcohol. Diatomic alcohol. Triatomic alcohol.

/OTT /OH

Ki— OH RJi<^ Riii— OH

^OH~ \OH

or

Kii(OH)2

corresponding to

KOH CaW(OH)2 Bim(OH)3.

Of the many reactions which justify our views regarding the
structure of alcohols, a few may be mentioned. We believe that
hydroxyl exists in metallic hydroxides, because they can be made by
the action of metals on water, and similarly, by acting with potassium
on an alcohol, we obtain a potassium compound and free hydrogen :

Also, when we act on a metallic hydroxide with an acid a salt is
formed and water produced ; the corresponding reaction takes place
between alcohols and acids :

K.OH + HC1 = KC1 + H20,
CH3.OH + HC1 = CH3C1 + H2O.

Many other reactions might be mentioned which furnish proof
that each oxygen atom contained in an alcohol molecule is in com-
bination with an atom of hydrogen— i. e., that alcohols are hydroxides
of hydrocarbon radicals.

Occurrence in nature. Alcohols are not found in nature in a free
or uucombined state, but generally in combination with acids as com-
pound ethers, Some plants,, for instance, contain compound ethers

ALCOHOLS. 481

mixed with volatile oils. The triatomic alcohol glycerin is a normal
constituent of all fats or fatty oils, and is therefore found in many
plants and in most animals.

Formation of alcohols. Alcohols are often produced by fermen-
tation (ethyl alcohol from sugar), sometimes by destructive distillation
(methyl alcohol from wood) : they are obtained from compound ethers
(which are compounds of acids and alcohols) by treating them with the
alkali hydroxides, when the acid enters into combination with the alkali,
while the alcohols are liberated according to the general formula :

RTO>° + KOH =

Alcohols may be obtained artificially by various processes, as, for
instance, by treating hydrocarbons with chlorine, when the chloride
of a hydrocarbon residue is formed, which may be decomposed by
alkali hydroxides in order to replace the chlorine by hydroxyl, when
an alcohol is formed. For instance :

C2H6 + 2C1 == C2H5C1 + HC1.

Ethane. Ethyl chloride.

C2H5C1 + KOH KC1 -f C2H5OH.

Ethyl Potassium Potassium Ethyl

chloride. hydroxide. chloride. alcohol.

Another method by which alcohols can be obtained depends on
the action of nitrous acid on amines containing radicals of the
methane series. For instance :

C2H5NH2 + NOOH = C2H5OH + 2N + H,O.

Ethyl amine. Nitrous Ethyl

acid. alcohol.

Properties of alcohols. Alcohols are generally colorless, neutral
liquids ; some of the higher members are solids, none is gaseous at
the ordinary temperature. Most alcohols are specifically lighter than
water; the lower members are soluble in or mix with water in
all proportions ; the higher members are less soluble, and, finally,
insoluble. Most alcohols are volatile without decomposition;
some of the highest members, however, decompose before being
volatilized.

Although alcohols are neutral substances, it is possible to replace
the hydrogen of the hydroxyl by metals, as has been shown above.
The oxygen of alcohols may be replaced by sulphur, when com-
pounds are formed known as hydrosulphides or mercaptans; these
bodies may be obtained by treating the chlorides of hydrocarbon
radicals with potassium sulphydrate.

C2H5C1 -f KSH = KC1 +
31

482 CONSIDERATION OF CARBON COMPOUNDS.

By replacement of the hydrogen of the hydroxyl in alcohols by
alcohol radicals ethers are formed ; by replacing the same hydrogen
with acid radicals compound ethers are produced. Suitable oxidizing
agents convert alcohols first into aldehydes then into acids.

Monatomic normal alcohols of the general composition

or CnH2n + 2O.

Methyl a
Ethyl

Icohol
u

. C H3OH
C H5 OH

B. P.

67° C.
78

Propyl

«

C H OH

07

Butyl

M

C4 H9 OH

115

Amyl
Hexyl

«
H

. C5HUOH

r H OH

132
150

Heptyl
Octyl
Nonyl
Cetyl
Ceryl

t(
U
it
«
It

. . C7H15OH
. C8H17OH
. C9H19OH
. . . CKH33OH
C97H~OH

168
186
204

50 i
yg 1 Fusing-

Melissyl

u

85 J P°int'

Methyl alcohol, CH3OH (Methyl hydroxide, Carbinol, Wood-spirit,
Wood-naphtha). Methyl alcohol is one of the many products obtained
by the destructive distillation of wood. When pure it is a thin color-
less liquid, similar in odor and taste to ethyl alcohol, and is often sub-
stituted for the latter for various purposes in the arts and manu-
factures.

Crude wood-spirit, which contains many impurities, has an offensive odor,
a burning taste, and is strongly poisonous. A more or less impure article is
sold under the name of Columbian spirit, while methylated spirit is ordinary
alcohol containing 10 per cent, of methyl alcohol.

The physiological intoxicating and poisonous properties of methyl alcohol
are similar to those of ordinary alcohol, but more pronounced. Cases of
poisoning, if recovery takes place, may be followed by more or less blindness,
due to atrophy of the optic nerve.

Ethyl alcohol, C2H5OH =45.7 (Common alcohol, Ethyl hydroxide,
Spirit), may be obtained from ethene, C2H4, by addition of the
elements of water, which may be accomplished by agitating ethene
with strong sulphuric acid, when direct combination takes place and
ethyl sulphuric acid is formed :

C2H4 + H,S04 = C2H3HS04.
Ethene. Sulphuric acid. Ethyl sulphuric acid.

Ethyl sulphuric acid mixed with water and distilled yields sul-
phuric acid and ethyl alcohol :

C2H6HS04 + H20 = H2SO4 + C2H5OH.

ALCOHOLS. 483

Ethyl alcohol may also be obtained, as already mentioned, by treat-
ing ethyl chloride with potassium hydroxide :

C2H5C1 + KOH KC1 + C2H6OH.

While the above methods for obtaining alcohol are of scientific
interest, there is but one mode of manufacturing it on a large scale,
namely, by the fermentation of certain kinds of sugar, especially
grape-sugar or glucose, C6H12O6. A diluted solution of grape-sugar
under the influence of certain ferments (yeast) suffers decomposition,
yielding carbon dioxide and alcohol :

C6H1206 = 2CO2 + 2C2H5OH.
Glucose. Carbon Ethyl

dioxide. alcohol.

From 94 to 96 per cent, of the sugar is decomposed, according to
the above reaction, the rest forming glycerin (3 per cent.), succinic
acid (0.6 per cent.), and higher alcohols designated " fusel oil."

Experiment 55. To a solution of 25 grammes of commercial glucose (grape-
sugar) in 1000 c.c. of water, add a little brewer's yeast and introduce this mix-
ture into a flask. Attach to the flask, by means of a perforated cork, a bent
glass tube leading into clear lime-water, contained in a small flask. After
standing (a warm place should be selected in winter for this operation) a few
hours fermentation will commence, which can be noticed by the evolution of
carbon dioxide, which, in passing through the lime-water, causes the precipi-
tation of calcium carbonate.

After fermentation ceases connect the flask with a condenser and distil over
50 to 100 c.c. of the liquid. Verify in the distilled portion the presence of
alcohol by applying the tests mentioned below. For condensation of the dis-
tilling vapors a Liebig's condenser, represented in Fig. 70, may be used.

The alcoholic strength of fermented sugar solutions is never over
14 per cent., since above this point the yeast ceases to act. On the
large scale this liquid is distilled in apparatus so arranged that the
vapors are repeatedly condensed and vaporized, thus yielding by a
single distillation an alcohol of about 90 per cent. This is further
purified by treatment with charcoal and rectifying in so-called column
stills, when alcohol containing as much as 94 to 95 per cent, is ob-
tained. To remove the last portions of water the liquid is distilled
over calcium oxide, which forms calcium hydroxide.

The alcohol thus obtained, and containing not more than 1 per
cent, of water, is known as pure, absolute, or real alcohol (alcohol
absolutum). The alcohol of the U. 8. P. contains 92.3 per cent, by
weight or 94.9 per cent, by volume of real alcohol, and has a specific
gravity of 0.816 at 15.6° C. (60° F.). The diluted alcohol, is made
by mixing equal volumes of water and alcohol, and has a specific

484

CONSIDERATION OF CARBON COMPOUNDS.

gravity of 0.936 ; it is identical with the proof-spirit of the U. 8.
Custom-house and Internal Revenue service.

Pure alcohol is a transparent, colorless, mobile, and volatile liquid,
of a characteristic rather agreeable odor, and a burning taste; it boils
at 78° C. (172° F.), has a specific gravity of 0.797, is of a neutral
reaction, becomes syrupy at— 110° C. (—166° F.), and solidifies at
— 130° C. ( — 202° F.); it burns with a non-luminous flame; when
mixed with water a contraction of volume occurs, and heat is liber-
ated ; the attraction of alcohol for water is so great that strong
alcohol absorbs moisture from the air or abstracts it from membranes,

FIG. 70.

Liebig's condenser with distilling-flask.

tissues, and other similar substances immersed in it; to this property
are due its coagulating action on albumin and its preservative action
on animal substances. The solvent powers of alcohol are very exten-
sive, both for inorganic and organic substances ; of the latter it readily
dissolves essential oils, resins, alkaloids, and many other bodies, for
which reason it is used in the manufacture of the numerous official
tinctures, extracts, and fluid extracts.

Alcohol taken internally in a dilute form has intoxicating proper-
ties ; pure alcohol acts poisonously ; it lowers the temperature of the
body from 0.5° to 2° C. (0.9° to 3.6° F.), although the sensation of
warmth is experienced. Alcohol is not a food in the ordinary sense
of the word. Small quantities of diluted alcohol are oxidized jn the

ALCOHOLS. 485

system to carbon dioxide and water ; larger amounts are eliminated,
for the most part unchanged, by the lungs and kidneys.

The treatment of acute alcohol poisoning is chiefly restricted to the evacua-
tion of the stomach, warm applications to the extremities, and possibly hypo-
dermic injections of strychnine to sustain the heart.

Denatured alcohol. Alcohol may be withdrawn from bond without the
payment of internal revenue tax for use in the arts and industries, and for
fuel, light, and power, provided said alcohol shall have been mixed, under
certain prescribed regulations, with specified denaturing material, whereby it is
rendered unfit for beverage or medicinal purposes.

Completely denatured alcohol must contain either methyl alcohol and ben-
zin, or methyl alcohol and pyridine bases. Tax-free alcohol may also be used
for manufacturing chemicals, where the alcohol is changed into some other
chemical substance and does not appear in the finished product as alcohol,
Inasmuch as the agents present in completely denatured alcohol render it
unfit for use in many chemical industries, special denaturants have been
authorized by the Commissioner of Internal Revenue where absolutely neces-
sary. About fifteen special denaturing formulas are in use at the present time.

Hospitals are allowed to denature alcohol with substances which render it
unfit as a beverage, but not for external use. For this purpose such substances
as camphor, thymol, boric acid, etc., may be used. .

For a full account of the subject of denatured alcohol, and the various for-
mulas for this purpose, see the article on Alcohol in the National Standard
Dispensatory.

Analytical reactions for ethyl alcohol.

1. Dissolve a small crystal of iodine in about 2 c c. of alcohol ;
add to the cold solution potassium hydroxide until the brown color
of the solution disappears ; a yellow precipitate of iodoform, CHI3,
forms. Many other alcohols, aldehyde, acetone, etc., show the same
reaction.

2. Add to about 1 c.c. of alcohol the same volume of sulphuric
acid ; heat to boiling and add gradually a little more alcohol : the
odor of ethyl ether will be noticed distinctly on further heating.

3. Add to a mixture of equal volumes of alcohol and sulphuric,
acid, a crystal (or strong solution) of sodium acetate: acetic ether is
formed and recognized by its odor.

4. To about 2 c.c. of potassium dichromate solution add 0.5 c.c. of
sulphuric acid and 1 cc. of alcohol: upon heating gently the liquid
becomes green from the formation of chromic sulphate, while alde-
hyde is formed and may be recognized by its odor.

Alcoholic liquors. Numerous substances containing sugar or starch (which
may be converted into sugar) are used in the manufacture of the various alco-

486 CONSIDERATION OF CARBON COMPOUNDS.

holic liquors, all of which contain more or less of ethyl alcohol, besides color-
ing matter, ethers, compound ethers, and many other substances.

White and red wines are obtained by the fermentation of the grape-juice ; the
so-called light wines contain from 10 to 12, the strong wines, such as port and
sherry, from 19 to 25 per cent, of alcohol ; if the grapes contain much sugar,
only a portion of it is converted into alcohol, while another portion is left
undecomposed ; such wines are known as sweet wines. Effervescent wines, as
champagne, are bottled before the fermentation is complete ; the carbonic acid
is disengaged under pressure and retained in solution in the liquid.

Beer is prepared by fermentation of germinated grain (generally barley) to
which much water and some hops have been added; the active principle of
hops is lupulin, which confers on the beer a pleasant, bitter flavor, and the
property of keeping without injury. Light beers have from 2 to 4, strong beers,
as porter or stout, from 4 to 6 per cent, of alcohol.

/Spirits differ from either wines or beers in so far as the latter are not dis-
tilled, and therefore contain also non-volatile organic and inorganic substances,
such as salts, etc., not found in the spirits, which are distilled liquids contain-
ing volatile compounds only. Moreover, the quantity of alcohol in spirits is
very much larger, and varies from 45 to 55 per cent. Of distilled spirits may
be mentioned : American whiskey, made from fermented rye or Indian corn ;
Irish whiskey, from potatoes ; Scotch whiskey, from barley ; brandy or cognac, by
distilling French wines ; rum, by fermenting and distilling molasses ; gin, from
various grains flavored with juniper berries.

Amyl alcohol, C5HnOH. Theoretically eight amyl alcohols are possible,
and all are known. The common amyl alcohol is iso-butyl-carbinol, (CH3)2.-
CH.CH2.CH2OH. It is frequently formed in small quantities during the fer-
mentation of corn, potatoes, and other substances. When the alcoholic liquors
are distilled, amyl alcohol passes over toward the end of the distillation, gener-
ally accompanied by propyl, butyl, and other alcohols, and by certain ethers
and compound ethers. A mixture of these substances is known as fusel oil,
and from this liquid amyl alcohol may be obtained in a pure state. It is an
oily, colorless liquid, having a peculiar odor and a burning, acrid taste ; it is
soluble in alcohol, but not in water. By oxidation of amyl alcohol valerianic
acid is obtained.

Amylene hydrate, Ethyl-dimethyl-carbinol, (CH3}2.COff.C2H5, is an alcohol
isomeric with the above amyl alcohol, but yielding only acetic acid on oxida-
tion. It is a colorless liquid, having a pungent, ethereal odor, and a, boiling-
point of 100° C. (212° F.). It has been used as an hypnotic.

Allyl alcohol, C3H5OH, is an unsaturated monatomic alcohol which can be
obtained from glycerin by several reactions. It is most readily obtained by
distilling a mixture of glycerin and oxalic acid between 220° and 230° C.,
when allyl alcohol, CH2 = CH — CH2OH, passes over. When glycerin is
treated with iodide of phosphorus, allyl iodide, CH2 = CH.CH2I, is obtained.
This reacts with silver hydroxide, forming silver iodide and allyl alcohol.
Allyl iodide is employed in the artificial preparation of oil of mustard, or allyl
iso-sulpho-cyanate, and oil of garlic, or allyl sulphide. These products are
found in nature and are salts of allyl alcohol.

By oxidation with potassium permanganate allyl alcohol is reconverted into
glycerin.

ALCOHOLS. 487

Allyl alcohol is a colorless liquid possessing a disagreeable penetrating odor.
It is soluble in water in all proportions ; B. P. 96.5° C.

Glycerin, Glycerinum, C3H5(OH)3 = 91.37 (Glycerol). This is
a triatomic alcohol, in which three OH groups have replaced three
hydrogen atoms in propane, CH3.CH2.CH3. Synthetic methods have
shown the glycerin to be CH2OH.CHOH.CH2OH.

Glycerin is a normal constituent of all fats, which are glycerin in which the
three atoms of hydrogen of the hydroxyl have been replaced by radicals of
fat acids. It is obtained as a by-product in the manufacture of soap, but it is
also largely manufactured by passing steam under 120 to 150 pounds pressure
into fats contained in large copper digesters. By this treatment the fats are
decomposed into glycerin, which remains dissolved in the water; non-volatile
fatty acids, floating on the surface of the solution ; and volatile fatty acids,
which escape with the steam. The aqueous solution of glycerin is first con-
centrated by evaporation, and then treated with superheated steam, with which
glycerin volatilizes and is condensed in suitably constructed vessels.

Pure glycerin is a clear, colorless, odorless liquid of a syrupy con-
sistence, smooth to the touch, hygroscopic, very sweet, and neutral in
reaction, soluble in water and alcohol in all proportions, but insoluble
in ether, chloroform, benzol, and fixed oils ; its specific gravity is
1.246 at 25° C. ; it cannot be distilled by itself without decomposition,
but is volatilized in the presence of water or when steam is passed
through it.

Glycerin is a good solvent for a large number of organic and inorganic sub-
stances ; the solutions thereby obtained are often termed glycerites ; official are
the glycerites of starch, carbolic acid, tannic acid, and a few others.

Boroglycerin is made by heating a mixture of boric acid and gly-
cerin, when an ether of the composition C3H5BO3 is obtained. It is
used as a mild antiseptic agent.

Analytical reactions.

1. A borax bead immersed for a few minutes in a solution of
glycerin (made slightly alkaline with potassium hydroxide) imparts
a green color to a non-luminous flame, owing to the liberation of
boric acid.

2. Glycerin slightly warmed with an equal volume of sulphuric
acid should not turn dark, but, on further heating, the characteristic,
irritating odor of acrolein is noticed.

Glycerin trinitrate, C3H5(NO3)3 (Nitro-glycerin, Glonoin). When
glycerin is treated with nitric acid, or, better, with a mixture of con-
centrated sulphuric and nitric acids, chemical action takes place

488 CONSIDERATION OF CARBON COMPOUNDS.

resulting in the formation of glyceryl mono-nitrate, or tri-nitrate,
substances belonging to the group of compound ethers, the constitu-
tion of which will be explained later.

C3H5(OH)3 + 3HN03 = C3H5(N03)3 + 3H2O.

The tri-nitro-glycerin is the common nitro-glyceriu, a pale-yellow
oily liquid, which is nearly insoluble in water, soluble in alcohol,
crystallizes at — 20° C. ( — 4° F.) in long needles, and explodes very
violently by concussion ; it may be burned in an open vessel, but
explodes when heated over 250° C. (482° F.).

Spirit of g-lyceryl trinitrate, Spiritus g-lycerylis nitratis (Spirit
of glonoiri) is an alcoholic solution of nitro-glycerin, containing of this
substance 1 per cent.

Dynamite. One kilogram of nitro-glycerin yields after explosion 713 liters
of gas, measured at normal temperature and pressure. As the gas temperature
is raised by explosion to about 7000° C. (13,000° F.), the volume is comparatively
larger, and the explosive power of nitro-glycerin compared with that of gun-
powder is about 13 to 1. Indeed, the explosions of pure nitro-glycerin are so
violent that it is generally mixed with inert substances, such as clay, sawdust,
infusorial (diatomaceous) earth, etc. When mixed with the latter it forms the
extensively used dynamite, which is more useful and less dangerous to handle
than pure nitro-glycerin. While it is not readily exploded by pressure or jar,
it is by percussion ; for instance,, by fulminating mercury explosion.

Mixtures of nitro-glycerin and gun-cotton form explosive gelatine, or gelatine-
dynamite.

Glycerin-phosphoric acid, C3H5(OH)2O.PO(OH)2. Compounds
of this acid are met with in blood, flesh, the brain, and the nerves.
It also occurs together with cholin, as a result of the splitting up of
lecithin (see Index).

The absolute acid is very unstable, decomposing easily into glycerin
and phosphoric acid. The commercial article is a 20 per cent, aqueous
solution. It is obtained by dissolving gradually glacial phosphoric
acid in an equal weight of 95 per cent, glycerin with moderate heat, and
subsequently heating the mixture for several hours at 110° C. Union
takes place thus :

C3H5(OH)3 -f HPO3 = C3H5(OH)2O.PO(OH)2.

The tenacious mass is dissolved in water, neutralized with milk of
lime, and filtered. The excess of lime is precipitated by a current
of carbon dioxide and filtered off. The filtrate is concentrated in a
vacuum and precipitated with alcohol or evaporated to dryness. The
calcium salt is washed with alcohol to remove glycerin, dissolved in
water, and decomposed with a calculated amount of diluted sulphuric
acid. (The filtrate is evaporated to the proper concentration.)

ALDEHYDES. KETOXES. 489

Glycerin-phosphoric acid is a clear colorless liquid which gradually
turns yellow, and decomposes slowly in the cold, more rapidly when
heated. It is a dibasic acid of decidedly acid taste and reaction.
The normal salts are soluble in water, but insoluble in alcohol, and
generally have an alkaline reaction. The usual reagents for phos-
phoric acid do not affect the solution of glycerin-phosphoric acid in
the cold. The calcium, potassium, sodium, lithium, iron, and quinine
salts of the acid have been introduced into medicine.

Calcium glycerin -phosphate, C3H5(OH).2CaPO4 + H,O, is a white
crystalline powder, soluble in 20 parts of water, but less soluble in hot water.
It is neutral to litmus, but the commercial product is sometimes acid. It loses
its water of crystallization at or above 130° C.

Sodium glycerin-phosphate, C3H5(OH)2.Na2PO4 + H2O, is obtained
by neutralizing glycerin-phosphoric acid. It occurs in the market as a 50 per
cent, solution of a clear, light yellow color.

44. ALDEHYDES. KETONES.

Aldehydes. The name aldehyde is derived from alcohol dehydro-
genatum, referring to its method of formation, viz., by the removal
of hydrogen from alcohols, as, for instance :

C2H6O — 2H = C2H4O.
Ethyl alcohol. Acetic aldehyde.

This removal of hydrogen may be accomplished by various methods,
as, for instance, by oxidation of alcohols, when one atom of oxygen
combines with two atoms of hydrogen, forming water, while an alde-
hyde is formed at the same time. Aldehydes, when further oxidized,
are converted into acids ; aldehydes are, consequently, the interme-
diate products between alcohols and acids, and are frequently looked
upon as the hydrides of the acid radicals. The constitution of acetic

QUESTIONS. — What is the general constitution of alcohols, and what is the
difference between monatomic, diatomic, and triatomic alcohols? How do
alcohols occur in nature ? By what processes may alcohols be formed arti-
ficially, and how may they be separated from their combinations ? State the
general properties of alcohols. Mention names and composition of the first
five members of alcohols of the general composition CnH2n+iOH. By what
process is methyl alcohol obtained, under what other names is it known, and
what are its properties? Describe the manufacture of pure alcohol from
sugar. Give the alcoholic strength of the alcohol and diluted alcohol of the
U. S. P., and also of spirit of wine, proof-spirit, light wines, heavy wines, beers,
and spirits. What are the general properties of common alcohol ? How is
alcohol denatured ? What is glycerin, how is it found in nature, how is it
obtained, and what are its properties ?

490 CONSIDERATION OF CARBON COMPOUNDS.

acid may be represented by the formula CH3.CO.OH ; the radical of
acetic acid or acetyl is the group CH3.CO, and the hydride of acetyl

/TT /FT

is acetic aldehyde, CH3.C^Q. It is the group — C\o which is char-
acteristic of, and found in, all aldehydes. Only a few aldehydes are
of practical interest, as, for instance, formaldehyde, acetic aldehyde,
paraldehyde, and benzoic aldehyde.

xTT

Formic aldehyde, CH2O or H.C/Q (Formaldehyde, methyl alde-
hyde). This is obtained by the dry distillation of calcium formate,
or by gentle oxidation of methyl alcohol. The latter process is
carried out by passing vapors of methyl alcohol with air over a
heated spiral of platinum or copper. The condensed vapors are
formaldehyde dissolved in undecomposed methyl alcohol. Another
process is by heating paraformaldehyde, which yields formaldehyde
in a pure condition.

Formaldehyde is a colorless gas, possessing a strong, penetrating
odor; it may be condensed to a liquid which boils at — 20° C.
(-4° F.).

Solution of formaldehyde, Liquor formaldehydi. Forma-lde-
hyde is readily soluble in water, and a solution containing 37 per cent,
by weight is official. It is a colorless liquid which has a pungent
odor and caustic taste ; its vapors act as an irritant upon the mucous
membrane. Sometimes on standing, always on slow evaporation, white,
solid paraformaldehyde separates. With ammonio-silver nitrate the
solution gives a precipitate of metallic silver. The solution is a
strong antiseptic, and when diluted to 4 or 5 per cent, it is one of the
best hardening and preserving agents for tissues.

Formic aldehyde may be recognized by Schijf's reaction: A solution of
fuchsin (rosanilin chloride) decolorized or nearly so with sulphurous acid turns
pink or violet when brought in contact with any aldehyde solution. For the
examination of air, suspended filter-paper, moistened with the decolorized
fuchsin solution, may be used.

Paraformaldehyde, C3H6O3 or (CH2O)3 (Formalin). On slow
evaporation of a solution of formaldehyde in methyl alcohol poly-
merization takes place, and paraformaldehyde separates in colorless
crystals which are insoluble in water. On heating the compound,
which is now found in the market in the form of tablets, it splits
up into three molecules of formaldehyde, which, escaping as a
gas, is used for disinfecting purposes. It acts powerfully on all
germs, and has the advantage over chlorine and sulphur dioxide that
it does not act injuriously on the fabric or color of household goods.

ALDEHYDES. KETONES. 491

Formaldehyde gas is now very generally used for disinfecting rooms, etc.,
and has practically displaced the method of burning sulphur to obtain sulphur
dioxide. The simplest method of filling a closed space with the gas is to pour
the commercial solution of formaldehyde upon small crystals of potassium per-
manganate, contained in a spacious metallic vessel. A vigorous reaction takes
place, with destruction of a portion of the formaldehyde, approximately
according to this reaction :

4KMn04 + 3HCOH + H20 = 4MnO(OH)2 + 2K2C03 + CO2.

The great heat produced causes nearly all the remaining solution to vaporize
and fill the space with formaldehyde gas and water vapor, which latter is an
essential factor in the disinfection. The temperature of the room should be
not less than 10° C. (50° F.), but a higher temperature is better. The propor-
tions adopted by some Boards of Health are 500 c.c. of formaldehyde solution
and 237 grammes of potassium permanganate per 1000 cubic feet of space. It
is well known that formaldehyde is mainly a surface disinfectant, having very
little power to penetrate objects, as clothing, etc.

The formaldehyde odor clinging for days to rooms which have been disin-
fected by it may be quickly removed by evaporation of some ammonia water,
hexamethylene tetramin, (CH2)6N4, being formed.

Acetic aldehyde, C2H4O or CH3.C (Ethyl aldehyde). Alcohol

may be converted into aldehyde by the action of various oxidizing
agents ; the one generally used is potassium dichromate in the pres-
ence of sulphuric acid, which oxidizes two hydrogen atoms of the
alcohol molecule, converting it into aldehyde :

C2H60 + O = C2H40 + H20.

Experiment 56. Place in a 500 c.c. flask, provided with a funnel-tube and
connected with a Liebig's condenser, 6 grammes of potassium dichromate.
Pour upon this salt through the funnel-tube, very slowly, a previously pre-
pared and cooled mixture of 5 c.c. of sulphuric acid, 24 c.c. of water and 6 c.c.
of alcohol. Chemical action begins generally without application of heat, and
often becomes so violent that the liquid boils up, for which reason a large flask
is used. The escaping vapors, which are a mixture of aldehyde, alcohol, and
water, are collected in a receiver kept cold by ice. From this mixture pure
aldehyde may be obtained by repeated distillation. Use the distillate for
silvering a test-tube by adding some ammoniated silver nitrate. How much
potassium dichromate is needed for the conversion of 5 grammes of pure
alcohol into aldehyde?

Aldehyde is a neutral, colorless liquid, having a strong and charac-
teristic odor ; it mixes with water and alcohol in all proportions and
boils at 21° C. (69.8° F.). The most characteristic chemical property
of aldehyde is its tendency to combine directly with a great number
of substances; thus it combines with hydrogen to form alcohol, with
oxygen to form acetic acid, with ammonia to form aldehyde-ammonia,

492 CONSIDERATION OF CARBON COMPOUNDS.

C2H4O.NHS, a beautifully crystallizing substance, with hydrocyanic
acid to form aldehyde hydrocyanide, C2H4O.HCN, with acid sulphites
and with many other substances. In the absence of such other sub-
stance it unites often with itself, forming polymeric modifications,
such as paraldehyde and metaldehyde.

Aldehyde is a strong reducing agent, which property is used in the
silvering of glass, which is done by adding aldehyde to an ammoniacal
solution of silver nitrate, when metallic silver is deposited on the walls
of the vessel or upon substances immersed in the solution.

Paraldehyde, C6H12O3. When a few drops of concentrated sul-
phuric acid are added to aldehyde, this becomes hot and solidifies on
cooling to 0° C. (32° F.). This solid crystalline mass of paralde-
hyde, which liquefies at 10.5° C. (51° F.), has been formed by the
direct union of three molecules of common aldehyde. Paraldehyde
is soluble in 8.5 parts of water, boils at 124° C. (253° F.), and is
reconverted into common aldehyde by boiling it with dilute sulphuric
or hydrochloric acid. It is official as Paraldehydum and a hypnotic.

Metaldehyde, (C2H40)3, is stereo-isomeric with paraldehyde ; it is obtained by a
process similar to the one mentioned for paraldehyde, but at a lower tempera-
ture. It is a solid crystalline substance, insoluble in water, but slightly soluble
in alcohol, ether, and chloroform.

Trichloraldehyde, Chloral, C^CLjO or CC13.C^Q (Trichlorace-
tyl hydride). This substance may be looked upon as acetic aldehyde,
C2H4O, in which three atoms of hydrogen have been replaced by
chlorine. It is made by passing a rapid stream of dry chlorine into
pure alcohol to saturation, keeping the alcohol cool during the first
few hours, and warming it gradually until the boiling-point is
reached. According to the quantity of alcohol operated on, the con-
version requires several hours or even days. The crude liquid pro-
duct separates into two layers ; the lower is removed and shaken with
three times its volume of strong sulphuric acid and distilled, the dis-
tillate is mixed with calcium oxide and again distilled ; the portion
passing over between 94° and 99° C. (201° and 210° F.) is collected.

The decomposition taking place between alcohol and chlorine may
be explained by the formation of aldehyde :

C2H6O + 2C1 = C2H4O + 2HC1,

and by the subsequent replacement of hydrogen by chlorine :
C2H4O + 6C1 = C2HC130 + 3HC1

ALDEHYDES. KETONES. 493

The actual decomposition is, however, somewhat more complicated,
numerous intermediate bodies and other decomposition products
being formed at the same time.

Chloral is a colorless, oily liquid, having a penetrating odor and an
acrid, caustic taste; its specific gravity is 1.5, and its B. P. 95° C.
(202° F.).

Hydrated chloral, Chloralum hydratum, CC13.CH(OH)2 =164.12.
When water is added to chloral the two substances combine, heat is dis-
engaged, and the hydrate of chloral is formed, which is a crystalline,
colorless substance, having an aromatic, penetrating odor, a bitter,
caustic taste, and a neutral reaction ; it is freely soluble in water.
alcohol, and ether, also soluble in chloroform, carbon disulphide,
benzene, fatty and essential oils, etc. ; it liquefies when mixed with
carbolic acid or with camphor; it melts at 58° C.(136° F.),and boils
at 95° C. (203° F.), and also volatilizes slowly at ordinary temperature.

Chloral, and its hydrate, are decomposed by weak alkalies into
chloroform and a formate of the alkali metal :

C2HC130 + KHO : KCHO2 + CHC13.
Chloral. Potassium Potassium Chloroform.

hydroxide. formate.

This decomposition was believed to take place in the animal body, and
especially in the blood, whenever chloral was given internally, but recent in-
vestigations seem to contradict this assumption. There is no chemical antidote
which may be used in cases of poisoning by chloral, and the treatment is,
therefore, confined to the use of the stomach-pump and to the maintenance of
respiration.

Analytical reactions for chloral.

1. Chloral or hydrated chloral heated with potassium hydroxide is
converted into potassium formate and chloroform, which latter may
be recognized by its odor. (See explanation above.)

2. Heated with silver nitrate and ammonium hydroxide a silver-
mirror is formed on the glass.

3. Heated with Fehling's solution a red precipitate is formed.
See also reactions 2 and 6 for chloroform.

Acrylic aldehyde, CH2 = CH.C (Acrolein), may be obtained by
the careful oxidation of allyl alcohol, or by the dehydrating action
of potassium acid sulphate on glycerin :

C3H803 - 2H,0 = C3H40.

It is also formed by the destructive distillation of glycerin, which is a
constituent of fats. Hence, acrolein is formed when fats are heated

494 CONSIDERATION OF CARBON COMPOUNDS.

to a point of decomposition, and its presence is noticed by the pecu-
liar penetrating odor.

Acrolein is a highly volatile liquid, boiling at 52.4° C. It has a
characteristic, penetrating odor and its vapors act on the eyes, causing
the secretion of tears. Acrolein shows in its chemical behavior its
aldehydic nature. It takes up oxygen forming acrylic acid; com-
bines with hydrogen forming allyl alcohol ; combines directly with
hydrochloric acid, ammonia, etc.

Ketones or acetones. These are compounds containing the
bivalent radical carbonyl, CO <, to which two hydrocarbon radicals
are attached. The relation existing between carbonic acid, organic
acids, aldehydes, and ketones is best shown by the following formulas,
in which R stands for any hydrocarbon radical :

Carbonic acid. Organic acid. Aldehyde. Ketone.

While aldehydes are obtained by the oxidation of primary alcohols, ketones
are the first product of the oxidation of secondary alcohols. For instance :

C2H5.CH2.OH + O = C2H5.COH + H2O.

Primary propyl Propionic

alcohol. aldehyde.

. O = ,CO + H20.

Secondary propyl Dimethyl

alcohol. ketone.

Ketones are neutral substances which resemble aldehyde in so far as they
have the power to unite directly with many substances with which aldehydes
combine ; as, for instance, with the acid sulphites. On the other hand, while
aldehydes readily take up oxygen directly and form acids, ketones are decom-
posed by oxidizing agents.

Acetone, Acetonum, CH3.CO.CH3 = 57.61 (Dimethyl-ketone).
This compound is obtained by the destructive distillation of acetates
(and of a number of other substances). The decomposition which
calcium acetate suffers may be shown by the equation :

CH3COO\p __ CHgXpp, | p_p/-i
CH3COO/Ca - CH3XC( CaC0*-
Calcium acetate. Acetone.

Acetone is a colorless liquid, boiling at 56.5° C. (133.7° 1?.), rnis-
eible with water, alcohol, and ether in all proportions ; it has a pecu-
liar ethereal, somewhat mint-like odor, and burns with a luminous
non-sooty flame.

ALDEHYDES. KETONES. 495

Sulphur derivatives. A comparison of such inorganic compounds
as H2S, CS2, NH4SH, with H2O, CO2, NH4OH, shows that sulphur
often replaces oxygen. Correspondingly, sulphur frequently replaces
oxygen in organic compounds. When this replacement takes place
in alcohols compounds are formed, called mercaptans, mlpho-alcohols,
or thio-alcohoh; when it takes place in aldehydes sulph-aldehydes are
formed. These bodies, as a general rule, are ill-smelling compounds,
some of which are the result of putrefaction in proteids.

When mercaptans are treated with oxidizing agents three atoms of oxygen
e taken up and compounds are formed which are called sulphonic acids,

na •

are
thus:

C2H5SH -f 30 = C2H5.S02OH.

Ethyl Ethyl sulphonic

mercaptan. acid.

Sulphonic acids correspond to sulphurous acid in which a hydrogen atom
has been replaced by a hydrocarbon radical.

Ketones form condensation products with both alcohols and mercaptans
thus:

CH3\m HO.C2H5 CH3\p/OC2H
CH3XCO + HO.C2H55 "

Acetone. Ethyl Ketol.

alcohol.

Acetone. Ethyl Mercaptol.

mercaptan.

By oxidizing mercaptol with potassium permanganate it takes up oxygen
(similar to mercaptans), with the result that a compound is formed containing
sulphonic acid :

CH3\r/SC2H5 CH3\r/S02C2H5

C + '• = CH3/C\S02C2H6'

Mercaptol. Diethylsulphon-

dimethyl-methane.

This compound is used medicinally under the name of sulphonal.

The relations between methane and some of its derivatives, which have been
considered in this chapter, may be shown graphically thus :

H\p/Cl H\n/I H\C/COH

H/\H C1XC\C1 I/C\I H/°\H •

Methane. Chloroform. lodoform. Aldehyde.

Cl\r/COH ^p/CH,, CH3\r/S02C2H6

Cl/Sd °/C\CH3 CH3X°\S02C2H6

Chloral. Acetone. Hul phonal.

Sulphonmethane, Sulphonmethanum, Sulphonal, (CH3)2C-
(C2H5SO2)2 = 226.55 (Diethylsulphon-dimethyl-methane). Sulphonal
is a white crystalline substance, having neither odor nor taste ; it is

496 CONSIDERATION OF CARBON COMPOUNDS.

soluble in 15 parts of boiling and 360 parts of cold water, soluble
with difficulty in alcohol; it fuses at 125.5° C. (258° F.), and vola-
tilizes at about 300° C. (572° F.), with partial decomposition. A
mixture of sul phonal with either wood charcoal or with potassium
cyanide evolves, on heating, the characteristic odor of mercaptan. It
is used as an hypnotic and soporific.

Sulphonethylmethane, Trional, (?H'>C<c22H?S022 (Diethylsulphon-

methyl-ethyl-methane), and Tetronal, c'EP^C^H-o^ (Diethylsulphon-
diethyl-methane), are both colorless solids, forming lustrous crystals, soluble in
hot water and in alcohol and ether. The therapeutic action of these bodies
is similar to that of sulphonal.

45. MONOBASIC FATTY ACIDS.

General constitution of organic acids. When hydroxyl, OH,
replaces hydrogen in hydrocarbons, alcohols are formed ; when the
univalent group, CO2H, known as carboxyl, replaces hydrogen in
hydrocarbons, acids are formed ; and all acids containing this radical
are termed carboxylic acids. Monatomic, diatomic, and triatomic
alcohols are formed by introducing hydroxyl once, twice, or three
times respectively into hydrocarbon molecules; monobasic, dibasic,
and tribasic acids are formed by substituting one, two, or three
hydrogen atoms by carboxyl. For instance :

Hydrocarbons. Monobasic acids. Dibasic acids.

CH4 CH3C02H CH2\C%H-

Methane. Acetic acid. Malonic acid.

C2H6 C2H5CO2H ^2^*\CO2H*

Ethane. Propionic acid. Succinic acid.

As stated before, organic acids may also be considered as carbonic

QUESTIONS. — What is an aldehyde, and what are its relations to alcohols
and acids ? Give composition, mode of manufacture, and properties of form-
aldehyde. Explain the action of chlorine upon alcohol. Give the compo-
sition and properties of chloral and hydrated chloral. What decomposition
takes place when alkalies act upon chloral ? Under what conditions is acro-
lein formed and what are its properties ? Give the general composition of
ketones and a general method of obtaining them. How is acetone prepared?
Which compounds are called mercaptans, and how are they converted into
sulphonic acids ? Give method for preparing sulphonal, and state its prop-
erties.

MONOBASIC FATTY ACIDS. 497

acid in which one of the hydroxyl groups has been replaced by a
hydrocarbon radical, thus:

Carbonic acid. Acetic acid. f^

D\OH
Malonic acid.

This shows that carboxyl, CO2H, is made up of hydroxyl, OH,
and the bivalent radical, CO, termed carbonyl. By replacement of
the hydrogen of the hydroxyl (or of the carboxyl, which is the same)
by metals the various salts are formed.

What is termed the acid radical is the group of the total number
of atoms present in the molecule, with the exception of the hydroxyl.
In acetic acid, C2H4O2, for instance, the radical is CH3CO, or C2H3O,
which group of atoms, known as acetyl, is characteristic of acetic
acid, and of all acetates, and may often be transferred from one com-
pound into another without decomposition.

The difference between alcohol radicals and acid radicals may also
be stated, by saying that the first contain carbon and hydrogen only,
while acid radicals contain carbon, hydrogen, and oxygen.

In a similar manner, as there are homologous series of alcohols
corresponding to the various series of hydrocarbons, there are also
homologous series of organic acids running parallel with the corre-
sponding series of hydrocarbons or alcohols.

Occurrence in nature. Organic acids are found and formed both
in vegetables and animals, and are present either in the free state, or
(and more generally) in combination with bases as salts, or with
alcohols as compound ethers. Uncombined or as salts are found, for
instance, citric, tartaric, and oxalic acids in plants, formic acid in
some insects, uric acid in urine, etc. ; as compound ethers are found
many of the fatty acids in the various fats.

Some organic acids are also found as products of the decomposition
of organic matters in nature.

Formation of acids. Many acids are produced by oxidation of
alcohols. As intermediate products are formed aldehydes, which
may be looked upon (as stated in the last chapter) as alcohols from
which two atoms of hydrogen have been removed.

The change of a primary alcohol into an aldehyde, and of this
into an acid, takes place according to the general formulas :

32

498 CONSIDERATION OF CARBON COMPOUNDS.

R.CH2OH + O == O=C^ + H20.
Alcohol. Aldehyde.

°=<H + O = °=<OH-
Aldehyde. Acid.

Acids are obtained from compound ethers by boiling them with
alkalies, Avhen salts are formed, which may be decomposed by sul-
phuric or other acids. For instance :

+ KOH =

Ethyl acetate.

2C2H3KO2

Potassium
acetate.

Potassium
hydroxide.

+ H2SO4 =

Sulphuric
acid.

Potassium
acetate.

= 2C2H4O2 -
Acetic acid.

Ethyl alcohol.

f K2S04.

Potassium
sulphate.

Acids are formed also by destructive distillation (acetic acid) ; by
fermentation (lactic acid) ; by putrefaction (butyric acid) ; by oxida-
tion of many organic substances (oxalic acid by oxidation of
starch), etc.

Properties. Organic acids show the characteristics mentioned of
inorganic acids, viz., when soluble, have an acid or sour taste, redden
litmus, and contain hydrogen replaceable by metals, with the forma-
tion of salts.

Most organic acids, and especially the higher members, show these
acid properties in a less marked degree than inorganic acids ; in fact,
they become so weak that the acid properties can often scarcely be
recognized. As stated above, mono-, di-, and tri-basic organic acids
are known, the latter two being capable of forming normal,, acid, or
double salts.

Most organic acids are colorless, some of the lower and volatile
acids have a characteristic odor, but most of them are odorless ; most
organic acids are solids, some liquids, scarcely any gaseous at the ordi-
nary temperature. Any salt formed by the union of an organic acid
and a non-volatile metal (especially alkali metal) leaves the carbonate
of this metal after the salt has suffered combustion. It is for this
reason that ashes contain metals largely in the form of carbonates.

While the hydrogen of the hydroxyl may be replaced by metals
or by other residues, the hydrogen of the acid radical may often be
replaced by chlorine, and the oxygen of the hydroxyl by sulphur.
The acids formed by this last reaction are known as thio acids, for
instance, thio-acetic acid, C2H4OS.

When the hydrogen of the hydroxyl is replaced by a second acid

MONOBASIC FATTY ACIDS,

499

radical (of the same kind as the one forming the acid) the so-called
anhydrides are produced, which correspond to the inorganic anhy-
drides. For instance :

Nitric acid.

N02\o
N02/°

Nitric anhydride.

C2H4O2 or C2H3O.OH.
Acetic acid.

C2H30\0
C2H30/a

Acetic andydride.

It is evident from the above that, while acids are hydroxides of
acid radicals, the anhydrides are oxides. They are often formed by
abstracting water from two molecules of an acid, thus :

C2H3O.Oin _ C2H30\0 , H0
C2H3O.OH/ - C2H30/° + H2°'

Amino-acids are compounds obtained from acids by replacement of
a hydrogen atom of the acid radical by NH2 ; these compounds will
be spoken of later in connection with amides.

Patty acids of the general composition,
CnH2n02 or CnH2n + 1C02H.

Occurs in :

Fusing- Boiling-
point, point.

Formic acid,

H CO2H

-f 4°C.

100'

Acetic acid,

C H3C02H

+17

118

Propionic acid,

C2 H5 C02H

—21

140

Butyric acid,

C3 H7 CO2H

—20

162

Valeric acid,

C4 H9 CO2H

—16

185

Caproic acid,

C5 HUC02H

— 2

205

(Enanthylic acid,

C6 H13C02H

—10

224

Caprylic acid,

C7 H15C02H

+14

236

Pelargonic acid,

C8 H17C02H

18

254

Capric acid,

C9 H19C02H

30

270

Laurie acid,

CUH23C02H

43

Myristic acid,

C13H27C02H

54

Palmitic acid,

C15H31CO2H

62

Margaric acid,

CieHssCOjjH

60

Otearic acid,

C17H35C02H

70

Arachidic acid,

/""I TT f~^r\ TT
L^igilggVAyg "•

75

Behenic acid,

C21H43CO2H

76

Hysenic acid,

C24H49C02H

77

Cerotic acid,

C26H53C02H

80

Melissic acid,

C^ TT C*f} TT

90

Vegetable and animal fluids.

Sweat, fluids of the stomach, etc.

Butter.

Valerian root.

Butter.

Castor oil.

Butter ; cocoanut oil.

Leaves of geranium.

Butter.

Cocoanut oil.

Palm oil, butter.
(Obtained artificially.)
Most solid animal fats.

Oils of certain plants.
Beeswax.

The name fatty acids has been given to these acids on account of
their frequent occurrence in fats, and also in allusion to the some-
what fatty appearance of the higher members of the series.

The gradual change of properties which the members of an homol-
ogous series show, is well marked in the series of fatty acids, thus :

500 CONSIDERATION OF CARBON COMPOUNDS.

First member. Last member.

Is liquid. Is solid.

Volatilized at 100° C. Not volatilized without decomposition.

Strongly acid . Scarcely acid.

Strongly odoriferous. Odorless.

Easily soluble in water. Insoluble in water.

Produces no grease spot. Produces a grease spot.
Forms salts easily soluble without Forms salts which are insoluble or de-
decomposition, composed by water.

The intermediate members of the series show intermediate proper-
ties, and this change in properties is in proportion to the gradual
change in molecular weight.

Formic acid, H.CO2H or CHO.OH. This acid is found in the
red ant and in other insects, which eject it when irritated. It is also
contained in some plants, as, for instance, in the leaves of the sting-
ing-nettle.

It is formed by the oxidation of methyl alcohol :

CH40 4- 02 = CH.202 4- H2O,
Methyl alcohol. Formic acid.

by the action of carbonic oxide on potassium hydroxide:

KOH 4- CO ; KCHO2,

Potassium formate.

by the action of potassium hydroxide on chloroform :
CHCla 4- 4KOH = 3KC1 4- 2H2O 4 KCHO2,

by the action of potassium on moist carbon dioxide :
2CO2 4- ttjO 4- 2K = KHCO3 + KCHO2,

by heating equal parts of glycerin and oxalic acid, when the latter is
split up into carbon dioxide and formic acid, which may be separated
from the glycerin by distillation :

C2H2O4 = CO2 4- CH2O2.
Oxalic acid. Formic acid.

It is also a product of the decomposition of sugar, starch, etc.
Formic acid is a colorless liquid having a penetrating odor, and a
strongly acid taste ; it produces blisters on the skin ; it is a powerful
deoxidizer, being, when thus acting, converted into carbon dioxide

and water :

CH2O2 + O = C02 4- H20.

Acetic acid, H.C2H3O2, or C2H3O.OH, or CH3.CO2H = 59.58.
The most important alcohol is ethyl alcohol, and the most largely
used organic acid is acetic acid, obtained from ethyl alcohol by oxi-

MONOBASIC FATTY ACIDS. 501

dation. Acetic acid is found in combination with alkali metals in
the juices of many plants, also in the secretions of some glands, etc.

There are many reactions by which acetic acid can be obtained
similar to formic acid. For all practical purposes, however, it is
made either by the oxidation of alcohol (and aldehyde) or by the
destructive distillation of wood. It is produced commercially on a
large scale as follows : A diluted alcohol (8 to 10 per cent.) is allowed
to trickle down slowly through wood shavings contained in high
casks having perforated sides in order to allow a free circulation of
the air ; the temperature is kept at about 24° to 30° C. (75° to 86°
F.), and the liquid having passed through the shavings is repeatedly
poured back in order to cause complete oxidation. When the latter
object has been accomplished the liquid is a diluted acetic acid.

It appears that the conversion of alcohol into acetic acid is greatly
facilitated by the presence of a microscopic organism (mycoderma
aceti) commonly termed " mother of vinegar." This serves in some
unexplained way to convey the atmospheric oxygen to the alcohol.
The term " acetic fermentation " is often applied to this conversion,
although it is not a true fermentation, since no splitting up of the
alcohol molecule into other less complex compounds, but a process of
slow oxidation, takes place.

The second process for manufacturing acetic acid is the heating of
wood to a red heat in iron retorts, when numerous products (gases,
aqueous and tarry substances) are formed. The aqueous products
contain, besides other substances, methyl alcohol and acetic acid.
The liquid is neutralized with calcium hydroxide and distilled, when
methyl alcohol, water, etc., evaporate and a solid residue is left, which
is an impure calcium acetate. From this latter, acetic acid is obtained
by distilling with sulphuric (or hydrochloric) acid, calcium sulphate
(or chloride) being formed and left in the retort, while acetic acid
distils over.

Experiment 57. Add to 54 grammes of sodium acetate contained in a small
flask which is connected with a Liebig's condenser, 40 grammes of sulphuric
acid. Apply heat and distil over about 35 c.c. ' Determine volumetrically the
amount of pure acetic acid in this liquid.

Pure acetic acid, or glacial acetic acid, is solid at or below 15° C.
(59° F.); at higher temperatures it is a colorless liquid having a
characteristic, penetrating odor, boiling at 118° C. (244.4° F.), and
causing blisters on the skin ; its specific gravity is 1.049 at 25° C. ;
it is miscible with water, alcohol, and ether, is strongly acid, forming
salts known as acetates, which are all soluble in water.

502 CONSIDERATION OF CARBON COMPOUNDS.

Vinegar is dilute acetic acid (about 6 per cent.), containing often
other substances, such as coloring matter, compound ethers, etc.
Vinegar was formerly obtained exclusively by the oxidation of fer-
mented fruit-juices (wine, cider, etc.), the various substances present
in them imparting a pleasant taste and odor to the vinegar ; to-day
vinegar is often made artificially by adding various coloring and
odoriferous substances to dilute acetic acid. Vinegar should be tested
for sulphuric and hydrochloric acids, which are sometimes fraudu-
lently added.

Acidum aceticum, Acidum aceticum dilutum, and Acidum aceticum
glaciale are the three official forms of acetic acid. The first-named
acid contains 36 per cent., the second 6 per cent., the third at least 99
per cent, of pure acetic acid.

Acetic acid shows an exceptional behavior in regard to the specific
gravity of its aqueous solutions. The highest specific gravity of
1.0748 belongs to an acid of 78 per cent., which is equal to an acid
containing one molecule of water and one of acetic acid, or C2H4O2.H2O.
When the acid and water are mixed in this proportion, a maximum
rise in temperature and contraction in volume take place, which fact
indicates the existence of ortho-acetic acid, CH3C(OH)3, some ethereal
salts of which are known. The addition of either acetic acid or of
water causes the liquid to become lighter. For instance, the specific
gravity of an acid containing 95 per cent, is equal to that containing
56 per cent, of pure acid, both solutions having a specific gravity of
1.066.

The specific gravity of dilute acetic acid cannot, therefore, be
used as a means of determining the amount of pure acid ; this is
done by exactly neutralizing a weighed portion of the acid with
an alkali ; from the quantity of the latter used, the quantity of
actual acid present may be easily calculated. (See also volumetric
methods in Chapter 39.)

The vapor density of absolute acetic acid at just a little above its boiling-
point is twice as great as that corresponding to the formula, C2H4O2. At
200° C. or above, the vapor density is normal. This kind of behavior has
been observed in the case of other substances.

While vinegar is used in our diet, it should be remembered that acetic acid
acts as an irritant and corrosive, having caused in some instances perforation
of the stomach, and death in 6 to 15 hours. Milk of magnesia should be given
as an antidote with a view of neutralizing the acid.

MONOBASIC FATTY ACIDS. 503

Analytical reactions.
(Sodium acetate, NaC2H3O2, may be used.)

1. Any acetate heated with sulphuric acid evolves acetic acid,
which may be recognized by its odor.

2. Acetic acid or acetates heated with sulphuric acid and alcohol
give a characteristic odor of acetic ether.

3. A solution containing acetic acid, or an acetate carefully neutral-
ized, turns deep red on the addition of solution of ferric chloride,
and forms, on boiling, a reddish-brown precipitate of an oxyacetate
of iroa

Potassium acetate, Potassii acetas, KC2H3O2 = 97.44. Sodium
acetate, Sodii acetas, NaC2H3O2.3H2O === 135.1. Zinc acetate,
Zinci acetas, Zn (C2H3O2)2.2H2O = 217.82. These three salts may
be obtained by neutralizing the respective carbonates with acetic acid
and evaporating the solution ; they are white salts, easily soluble in
water.

Ammonium acetate, NH4C2H3O2, is official in the form of a 7
per cent, solution, which is known as Spirit of Mindererus.

Iron acetates. Both the ferrous acetate, Fe(C2H3O2)2.4H20, and the ferric
acetate, Fe(C2H3O2)3, are known. The latter is formed by adding sodium ace-
tate to the solution of a ferric salt, as is indicated by the deep-red color which
the solution assumes. As stated above in reaction 3, on boiling, decomposition
of the salt takes place. The separation of manganese and some other metals
from iron depends on this reaction.

Lead acetate, Plumbi acetas, Pb(C2H3O2)23H2O = 376.15 (Sugar
of lead), is made by dissolving lead oxide in diluted acetic acid. It
forms colorless, shining, transparent crystals, easily soluble in water;
on heating, it melts and then loses water of crystallization ; at yet
higher temperatures it is decomposed ; it has a sweetish, astringent,
afterward metallic taste. Commercial sugar of lead contains often an
excess of lead oxide in the form of basic salts ; such an article when
dissolved in spring water gives generally a turbid solution, in conse-
quence of the formation of lead carbonate ; the addition of a few
drops of acetic acid renders the liquid clear by dissolving the pre-
cipitate.

When a mixture of lead acetate and lead oxide is digested or boiled
frith water, the acetate combines with the oxide, forming a basic lead

504 CONSIDERATION OF CARBON COMPOUNDS.

acetate, approximately Pb(C2H3O2)2.PbO, a 25 per cent, solution of
which is the Liquor plumbi subacetatis, or Goulard's extract, while a
solution containing about 1 per cent, is the Liquor plumbi subacetatis
dilutus, or lead-water. Other more basic compounds are known. So-
called tribasic lead acetate has the formula Pb(C2H3O2)2.2PbO.

Cupric acetate, Cu(C2H3O2)2H2O. The commercial verdigris is a
basic acetate of copper, Cu(C2H3O2)2CuO7 made by the action of
dilute acetic acid and atmospheric air on metallic copper. By adding
to this basic acetate more acetic acid, the neutral acetate is obtained,
but this may be made directly also by dissolving cupric hydroxide
or carbonate in acetic acid. It forms deep green, prismatic crystals,
which are soluble in water.

By boiling verdigris with arsenous oxide, cupric aceto-arsenite,
3CuAs2O4 -f- Cu(C2H3O2)2, is formed, which is the chief constituent
of emerald green or Schweinfurt green, a substance often used as a
coloring matter. Paris green is of a similar composition, but less
pure.

Chlorine substitution products of acetic acid. The action of chlor-
ine gas and of phosphorus trichloride on acetic acid furnishes an additional
proof of the correctness of our views regarding its constitution and, conse-
quently, of the constitution of organic acids in general. It has been shown
that chlorine in acting on a hydrocarbon (methane) will successively replace all
hydrogen present. Similarly we can, by treatment with chlorine, replace that
hydrogen in acetic acid which is derived from the hydrocarbon, with the result
that monochlor, dichlor, and trichlor acetic acids are formed :

CH3.COOH + 2C1 : : CH2C1.COOH + HC1,
CH2C1.COOH + 2C1 = CHC12.COOH + HC1,
CHC12.COOH + 2C1 CC13.COOH -f HC1.

The fourth atom of hydrogen cannot be directly replaced by chlorine. As it is
this carboxyl hydrogen atom to which the acid properties are due the above
three compounds have acid properties.

The action of phosphorus trichloride on water, on methyl alcohol, and on
acetic acid takes place thus :

3**>0 + PC13 « 3HC1 + P(OH)3,

+ PC13 = 3CH3C1 + P(OH)3,
3C2H30>0 + pcla = 3C2H3OC1 + P(OH)3.

In all three cases the hydro*xyl group is replaced by chlorine, with the result
that hydrogen chloride (hydrochloric acid), methyl chloride, and acetyl chloride
are formed.

MONOBASIC FATTY ACIDS. 505

'Trichlor-acetic acid, Acidum trichloraceticum, CC13.CO2H
162.12. As shown in the previous paragraph, this acid may be ob-
tained by the direct action of chlorine on acetic acid, but it is usually
made by the oxidation with nitric acid of chloral (tricolor-aldehyde),
which requires but one atom of oxygen for its conversion into tri-
chlor-acetic acid.

Trichlor-acetic acid is a white, deliquescent, crystalline substance.
It has a slight, characteristic odor, is readily soluble in water, alcohol,
and ether. The aqueous solution, on boiling, is decomposed into
chloroform and carbon dioxide. It is used as a local caustic and as
a reagent for albumin.

Acetyl chloride, CH3.COC1, is obtained by distilling a mixture of 9 parts
of glacial acetic acid and 6 parts of phosphorus trichloride on a water-bath at
a slightly elevated temperature. It is a colorless liquid, having a suffocating
odor, boiling-point of 55° C., and specific gravity 1.13 at 0° C. It fumes in
the air, and acts on water energetically, thus :

CH3COC1 + H2O = CH3COOH + HC1.

It is a valuable reagent for testing for alcoholic hydroxyl groups in organic
compounds, which may be illustrated by its action on ordinary alcohol, thus:

CH3COC1 + C2H5OH = CH3COOC2H5 + HC1.

Acetates are thus formed by the replacement of hydrogen of hydroxyl by the
acetyl radical.

Acetic anhydride or acetyl oxide, (CH3CO)20, is formed by distilling a
mixture of anhydrous sodium acetate and acetyl chloride :

CH3COONa + CH3COC1 = (CH3CO)2O + NaCl.

It is a colorless liquid with a disagreeable odor, boiling at 137° C., and having
a specific gravity of 1.073 at 20° C. It is soluble in about 10 parts of water,
the solution decomposing slowly with formation of acetic acid. Like acetyl
chloride, it unites with hydroxyl groups in organic compounds, forming ace-
tates. This process of making acetates from alcoholic compounds is called
acetylization, and is often used in analysis of substances.

Butyric acid, HC4H702. Among the glycerides of butter those of butyric
acid are found ; they exist also in cod-liver oil, croton oil, and a few other fatty
oils ; some volatile oils contain compound ethers of butyric acid ; free butyric
acid occurs in sweat and in cheese. It may be obtained by a peculiar fermen-
tation of lactic acid (which itself is a product of fermentation), and is also
generated during the putrefaction of albuminous substances. Butyric acid is
a colorless liquid, having a characteristic, unpleasant odor; it mixes with
water in all proportions.

Valeric acid, HC5H9O2 (Valerianic avid). This acid occurs in
valerian root and angelica root, from which it may be separated ; it

506 CONSIDERATION OF CARBON COMPOUNDS.

is, however, generally obtained by oxidation of amyl alcohol by
potassium dichromate and sulphuric acid. After oxidation has taken
place the mixture is distilled, when valeric acid with some valerate
of amyl distils over. The change of amyl alcohol into valeric acid is
analogous to the conversion of ethyl alcohol into acetic acid :

C5HnOH + 2O = HC5H902 + H2O.
Amyl alcohol. Valeric acid.

Pure valeric acid is an oily, colorless liquid, having a penetrating,
highly characteristic odor ; it is slightly soluble in water, but soluble
in alcohol ; it boils at 185° C. (365° F.).

Ammonium valerate and zinc valerate are official. Both are white solids hav-
ing the odor of valeric acid. The ammonium salt is readily, the zinc salt spar-
ingly soluble in water.

Stearic acid, Acidum stearicum, HC^H^C^ = 282.14. The
official stearic acid is the commercial, more or less impure article
made from solid fats, chiefly tallow. It is a hard, white, somewhat
glossy solid without odor or taste. It is insoluble in water, but solu-
ble in alcohol, ether and alkalies. Both stearic acid and palmitic
acid, HC16H31O2, occur largely in solid fats. The general properties
of palmitic acid are nearly identical with those of stearic acid. (See
analytical reactions of fats.)

Oleic acid, Acidum oleicum, HC18H33O2 = 280.14. As shown by
its formula, oleic acid does not belong to the above-described series of
fatty acids of the composition CnH2nO2, but to a series having the
general composition CnH2n-2O2.

These acids belong to the ethylene series — i. e., they contain two
carbon atoms held together by a double bond, in virtue of which
they are oxidized more readily than the corresponding saturated
acids. They also form addition products ; oleic acid, for instance,
combines directly with 2 atoms of hydrogen, forming stearic acid,
and with bromine to form dibrom-stearic acid.

Oleic acid is a constituent of most fats, especially of fat oils.
Thus, olive oil is mainly oleate of glyceryl. By boiling olive oil with
potassium hydroxide, potassium oleate is formed, which may be
decomposed by tartaric acid, when oleic acid is liberated.

Oleic acid is a nearly colorless, yellowish, or brownish-yellow,
neutral oily liquid, having a peculiar, lard-like odor and taste. It is
insoluble in water, soluble in alcohol, chloroform, oil of turpentine,
and fat oils, crystallizing near the freezing-point of water ; exposed

MONOBASIC FATTY ACIDS. 507

to the air it decomposes and shows then an acid reaction. Lead
oleate is soluble in ether, lead palmitate and lead stearate are
not.

The official oleates of mercury, quinine, veratrine, atropine, and
cocaine are obtained by dissolving the yellow mercuric oxide, quinine,
veratrine, atropine, or cocaine in oleic acid.

Dissociation of formic acid and its homologues. In Chapter 15 it is
stated that the " strength " or relative activity of acids and'bases is propor-
tional to their degree of dissociation in solution. Organic acids in solution are
dissociated only to a small degree and are much " weaker " than such mineral
acids as hydrochloric, nitric, and sulphuric, which are almost completely disso-
ciated in very dilute solutions. The following table shows the percentage of
molecules dissociated in aqueous solutions containing the molecular weight in
grams of the respective acids diluted to 8 liters :

Formic acid.

Acetic acid.

Propionic acid.

Normal butyric acid.

4.05

1.193

1.016

1.068

Further dilution does not increase the percentage of dissociation very much.
For example, the molecular weight of acetic acid in 16 liters of solution disso-
ciates only to the extent of 1.673 per cent., whereas in a similar solution of
hydrochloric acid the dissociation is 95.5 per cent. Formic acid dissociates
more than the others of the series, and is, therefore, the strongest acid of the
series. The salts of organic acids are dissociated much more than the acids
are. Thus, in a normal solution of acetic acid only 0.4 per cent, of the molecules
are dissociated, while in normal solutions of sodium and potassium acetate
53 per cent, and 64 per cent, respectively, of the molecules are dissociated.

QUESTIONS. — What is the constitution of organic acids, what group of
atoms is found in all of them, and how does an alcohol radical differ from an
acid radical? Give some processes by which organic acids are formed in nature
or artificially. Mention the general properties of organic acids. Which series
of acids is known as fatty acids, and why has this name been given to them ?
Mention names, composition, and occurrence in nature of the first five mem-
bers of the series of fatty acids. By what processes may formic acid be ob-
tained, and what are its properties? Describe the processes of manufacturing
acetic acid from alcohol and from wood. What is vinegar, and what is glacial
acetic acid ? Give tests for acetic acid and for acetates. Describe the pro-
cesses for making the acetates of potassium, zinc, iron, lead, and copper, and
also of Goulard's extract and lead-water ; state their composition and proper-
ties. Where and in what form of combination is oleic acid found in nature,
and what are its properties ?

510 CONSIDERATION OF CARBON COMPOUNDS.

tion. This fact indicates that the iron is held in a complex ion,

since the color of simple ferrous salts in solution is usually pale green.

The salt has strong reducing properties and is used as a developer in

photography.

Potassium ferric oxalate, K3Fe(C2O4)3, gives a green solution, and the iron is
^robably held in a complex ion, Fe(C2O4)3///. It is rapidly reduced by sun-
light, thus,

2K3Fe(CA)3 = 2K2Fe(C204)2 + K2C2O4 + 2CO2,
and, therefore, is useful in making platinotypes in photography.

Hydroxy-acids.

In the acids heretofore considered, the hydrogen is derived either
from the hydrocarbon radical or from carboxyl. There are, however,
compounds containing as a third radical hydroxyl — i. e., that radical
characteristic of alcohols. Consequently Ave may look upon these
compounds as acids into which alcoholic hydroxyl has been intro-
duced, or as alcohols into which carboxyl has been introduced. The
acid properties of these compounds are so predominating that the
compounds are spoken of as acids, and according to the number of
carboxyl groups present we have monobasic, dibasic, etc., acids. The
hydrogen of the carboxyl is, of course, replaceable by metals, while
the hydrogen of the alcoholic hydroxyl can be replaced by hydrocar-
bon radicals. In order to indicate this diiference in the function of
the hydrogen the number of the respective groups present is given in
the name. Thus, tartaric acid, which contains 2 hydroxyl and 2 car-
boxyl groups, is designated as a dibasic hydroxy-acid, or as dihy-
droxy-dicarboxylic acid, while citric acid, which contains 1 hydroxyl
and 3 carboxyl groups, is a monohydroxy-tribasic acid or hydroxy-
tricarboxylic acid.

Of the several methods known for obtaining hydroxy-acids only one shall be
mentioned. It corresponds to one of the methods used for the introduction of
hydroxyl into hydrocarbons ; in one case the halogen of a hydrocarbon, in the
other case the halogen of an acid is replaced by hydroxyl :

CH3Br + H20 : CH3OH + HBr,

Brom-acetic acid. Hydroxy-acetic acid.

It is evident from what has been said that we have running parallel to every
series of acids another series of hydroxy-acids. For instance thus :

POLYBASIC AND HYDROXY-ACIDS. 511

Fatty acids. Hydroxy-acids.

Formic acid, ILCO2H. Hydroxy-formic acid, OH.CO2H.

Acetic acid, CH3.CO2.H. Hydroxy-acetic acid, CH2.OH.CO2H.

Propionic acid, C2H6.CO2H. Hydroxy-propionic acid, C2H4.OH.CO;,H.

etc. etc.

The first member of these hydroxy-acids designated as hydroxy-formic acid

is simply carbonic acid and does not partake of the general character of
hydroxy-acids.

Monohydroxy-monobasic acids.

Gly colic acid, CH2.OH.CO2H (Hydroxy-acetic acid), is found in
unripe grapes and in the leaves of the wild grape. It can be obtained
synthetically, as shown in the previous paragraph. It may also be
made by the oxidation of ethylene alcohol or ylycol, C2H4(OH)2 thus :

C2H4(OH)2 -f 20 = CH2.OH.C02H + H2O.

Glycolic acid is a white deliquescent, crystalline substance, easily
soluble in water, alcohol, and ether.

Lactic acid, Acidum lacticum, C2H4.OH.CO2H — 89.37 (Hy-
droxy-propionic acid), occurs in many plant-juices; it is formed from
sugar by a peculiar fermentation known as "lactic fermentation,"
which causes the presence of this acid in sour milk and in many sour,
fermented substances, as in ensilage, sauer-kraut, etc. The formation
of lactic acid from sugar may be expressed by the equation :

C6H1206 = 2(HC3H503).

Sugar. Lactic acid.

For practical purposes lactic acid is made by mixing a solution of
sugar with milk, putrid cheese, and chalk, and digesting this mixture
for several weeks at a temperature of about 30° C. (86° F.). The
bacteria in the cheese act as a ferment, and the chalk neutralizes the
acid generated during the fermentation. The calcium lactate thus
obtained is purified by crystallization and decomposed by oxalic acid,
which forms insoluble calcium oxalate.

Lactic acid is a colorless, syrupy liquid, of strongly acid properties ;
it mixes in all proportions with water and alcohol. The official
lactic acid contains 75 per cent, of absolute acid.

Three isomeric lactic acids are known :

a. Fermentation lactic acid, obtained as described above from milk, is opti-
cally inactive.

b. Sarcolactic or paralactic acid is dextrorotatory and occurs in muscle and
other parts of the body. It forms a constituent of meat-juice, and, therefore,
of meat extract.

c. Lcevolactic acid is laevorotatory, and is obtained from cane sugar by fer-
mentation by a special micro-organism.

510 CONSIDERATION OF CARBON COMPOUNDS.

tion. This fact indicates that the iron is held in a complex ion, Fe(C2O4)2//,
since the color of simple ferrous salts in solution is usually pale green.
The salt has strong reducing properties and is used as a developer in
photography.

Potassium ferric oxalate, K3Fe(C2O4)3, gives a green solution, and the iron is
,»robably held in a complex ion, Fe(C2O4)3///. It is rapidly reduced by sun-
light, thus,

2K3Fe(CA)3 = 2K2Fe(C204)2 + K2C2O4 + 2CO2,
and, therefore, is useful in making platinotypes in photography.

Hydroxy-acids.

In the acids heretofore considered, the hydrogen is derived either
from the hydrocarbon radical or from carboxyl. There are, however,
compounds containing as a third radical hydroxyl — i. e., that radical
characteristic of alcohols. Consequently we may look upon these
compounds as acids into which alcoholic hydroxyl has been intro-
duced, or as alcohols into which carboxyl has been introduced. The
acid properties of these compounds are so predominating that the
compounds are spoken of as acids, and according to the number of
carboxyl groups present we have monobasic, dibasic, etc., acids. The
hydrogen of the carboxyl is, of course, replaceable by metals, while
the hydrogen of the alcoholic hydroxyl can be replaced by hydrocar-
bon radicals. In order to indicate this difference in the function of
the hydrogen the number of the respective groups present is given in
the name. Thus, tartaric acid, which contains 2 hydroxyl and 2 car-
boxyl groups, is designated as a dibasic hydroxy-acid, or as dihy-
droxy-dicarboxylic acid, while citric acid, which contains 1 hydroxyl
and 3 carboxyl groups, is a monohydroxy-tribasic acid or hydroxy-
tricarboxylic acid.

Of the several methods known for obtaining hydroxy-acids only one shall be
mentioned. It corresponds to one of the methods used for the introduction of
hydroxyl into hydrocarbons ; in one case the halogen of a hydrocarbon, in the
other case the halogen of an acid is replaced by hydroxyl :

CH3Br + H20 : CH3OH + HBr,

Brom-acetic acid. Hydroxy-acetic acid.

It is evident from what has been said that we have running parallel to every
series of acids another series of hydroxy-acids. For instance thus :

POLYBASIC AND HYDROXY-ACIDS. 511

Fatty acids. Hydroxy-acids.

Formic acid, H.CO2H. Hydroxy-formic acid, OH.CO2H.

Acetic acid, CH3.CO2.H. Hydroxy-acetic acid, CH2.OH.CO2H.

Propionic acid, C2PI6.CO2H. Hydroxy-propionic acid, C2H4.OH.CO.,H.

etc. etc.

The first member of these hydroxy-acids designated as hydroxy-formic acid
is simply carbonic acid and does not partake of the general character of
hydroxy-acids.

Monohydroxy-monobasic acids.

Gly colic acid, CH2.OH.CO2H (Hydroxy-acetic acid), is found in
unripe grapes and in the leaves of the wild grape. It can be obtained
synthetically, as shown in the previous paragraph. It may also be
made by the oxidation of ethylene alcohol or ylycol, C2H4(OH)2 thus :

C2H4(OH)2 -f 2O = CH2.OH.CO2H + H2O.

Glycolic acid is a white deliquescent, crystalline substance, easily
soluble in water, alcohol, and ether.

Lactic acid, Acidum lacticum, C2H4.OH.CO2H = 89.37 (Hy-
droxy-propionic acid), occurs in many plant-juices; it is formed from
sugar by a peculiar fermentation known as " lactic fermentation,"
which causes the presence of this acid in sour milk and in many sour,
fermented substances, as in ensilage, sauer-kraut, etc. The formation
of lactic acid from sugar may be expressed by the equation :

C6H1206 = 2(HC3H503).

Sugar. Lactic acid.

For practical purposes lactic acid is made by mixing a solution of
sugar with milk, putrid cheese, and chalk, and digesting this mixture
for several weeks at a temperature of about 30° C. (86° F.). The
bacteria in the cheese act as a ferment, and the chalk neutralizes the
acid generated during the fermentation. The calcium lactate thus
obtained is purified by crystallization and decomposed by oxalic acid,
which forms insoluble calcium oxalate.

Lactic acid is a colorless, syrupy liquid, of strongly acid properties ;
it mixes in all proportions with water and alcohol. The official
lactic acid contains 75 per cent, of absolute acid.

Three isomeric lactic acids are known :

a. Fermentation lactic acid, obtained as described above from milk, is opti-
cally inactive.

b. Sarcolactic or paralactic acid is dextrorotatory and occurs in muscle and
other parts of the body. It forms a constituent of meat-juice, and, therefore,
of meat extract.

c. Lcevolactic acid is laevorotatory, and is obtained from cane sugar by fer-
mentation by a special micro-organism.

512 CONSIDERATION OF CARBON COMPOUNDS.

Dibasic and tribasic hydroxy-acids.

Mono-hydroxy-succinic acid, or malic acid =

/OH CH.OH.COJH

C4H605 or C2H3^C02H or j

XCO2H CH2.CO2H

Di-hydroxy-succinic acid, or tartaric acid =

/OH

//OH CH.OH.CO2H

C4H6O6 or C2H2 or |

\>C02H CH.OH.C02H

\CO2H

Malic acid, H2C4H4O5, occurs in the juices of many fruits, as
apples, currants, cherries, etc. It may be extracted from these fruits
or prepared synthetically.

Tartaric acid, Acidum tartaricum, H2C4H4O6 — - 148.92. Fre-
quently found in vegetables, and especially in fruits, sometimes free,
generally as the potassium or calcium salt ; grapes contain it chiefly
as potassium acid tartrate, which is obtained in an impure state as a
by-product in the manufacture of wine. During the fermentation of
grape-juice, its sugar is converted into alcohol ; potassium acid tar-
trate is less soluble in alcoholic fluids than in water, and therefore is
deposited gradually, forming the crude tartar, or argol, of commerce,
a substance containing chiefly potassium acid tartrate, but also cal-
cium tartrate, some coloring matter, and traces of other substances.
Crude tartar is the source of tartaric acid and its salts.

Tartaric acid is obtained from potassium acid tartrate by neutral-
izing with calcium carbonate, and decomposing the remaining neutral
potassium tartrate by calcium chloride :

2(KHC4H4O6) + CaCO3 == CaC4H4O6 + K2C4H4O6 + H2O + CO2.
Potassium acid Calcium Calcium Potassium Water. Carbon

tartrate. carbonate. tartrate. tartrate. dioxide.

K2C4H406 + CaCl2 = CaC4H406 + 2KC1.
Potassium Calcium Calcium Potassium

tartrate. chloride. tartrate. chloride.

The whole of the tartaric acid is thus converted into calcium tar-
trate, which is precipitated as an insoluble powder ; this is collected,
well washed, and decomposed by boiling with sulphuric acid, when
calcium sulphate is formed as an almost insoluble residue, while tar-
taric acid is left in solution, from which it is obtained by evaporation
and crystallization :

CaC4H4O6 + H2SO4 = H,C4H4O6 -f CaSO4.

Calcium Sulphuric Tartaric Calcium

tartrate. acid. acid. sulphate.

POLYBASIC AND HYDROXY-ACIDS.

513

Tartaric acid crystallizes in colorless, translucent prisms ; it has a
strongly acid, but not disagreeable taste ; it is readily soluble in water
and alcohol, and fuses at 135° C. (275° F.).

FIG 71.

Isomerism of tartaric acid. Four tartaric acids are known. They are :
dextrotartaric or common tartaric acid; favot ar tar ic acid ; mesotartaric or inact-
ive tartaric acid; and racemic add. These four acids have the same composi-
tion and show the same chemical reactions, proving that they are built up from
the same radicals ; but in some respects they possess different physical proper-
ties. Thus, mesotartaric and racemic acids are optically inactive ; the others,
as indicated by their names, are active, one turning polarized light to the right,
the other to the left.

Pasteur first observed that the spontaneous evaporation of a solution of
ammonium sodium racemate yields two
kinds of stereo-isomeric crystals. These
crystals (Fig. 71) are rectangular prisms P,
M, T, having the lateral edges replaced by
the faces b' , and the intersection of these
faces with the face T replaced by a face h.
The crystals are hemihedral, having four of
these h faces placed alternately. In the two
kinds of crystals these hemihedral faces oc-
cupy opposite positions, so that if one kind
of crystal be placed before a mirror its re-
flection will represent the arrangement of
the hemihedral faces of the other kind of crystal. The crystals are called
right-handed and left-handed respectively.

From these two kinds of crystals two tartaric acids can be separated ; one is
dextrotartaric acid, the other laevotartaric acid. When the two acids are brought
together in solution they unite forming racemic acid. These observations, sup-
ported by chemical data, have led to assume in tartaric acids the existence of
two asymmetric carbon atoms, about which the hydrogen atoms and the radi-
cals are arranged differently. Three of these forms may be represented by the
formulas :

Isomeric salts of tartaric acid.

C02H

H— C— OH
OH— C— II

C02H

Dextrotartaric acid.

CO2H
OH— C— H

H

-OH

II-

-C-OH

C02H
Laevotartaric acid.

H— O-OH

!
CO,H

Mesotartaric acid

Racemic acid results from the combination of dextrotartaric and laevotartaric
acids.

In a tenth-normal solution of tartaric acid at 25° C., 8.2 per cent, of the acid
is dissociated into Hg and H.C^O/ ions.
33

514 CONSIDERATION OF CARBON COMPOUNDS.

Analytical reactions.
(Potassium sodium tartrate, KNaC4H4O6, may be used.)

1. A neutral solution of a tartrate gives with calcium chloride a
white precipitate of calcium tartrate, which, after being quickly col-
lected on a filter and washed, is soluble in potassium hydroxide ; from
this solution calcium tartrate is precipitated on boiling. (Calcium
citrate is insoluble in potassium hydroxide.)

Calcium tartrate is soluble in a solution of an alkali tartrate;
hence, unless a sufficient amount of calcium chloride is added, a pre-
cipitate will not be obtained.

2. A strong solution of a tartrate, acidulated with acetic acid, gives
a white precipitate of potassium acid tartrate on the addition of potas-
sium acetate. The precipitate, which forms slowly, is soluble in alka-
lies and in mineral acids.

In the case of potassium sodium tartrate, or potassium tartrate,
addition of acetic acid alone precipitates potassium acid tartrate.

3. A neutral solution of a tartrate gives with silver nitrate a white
precipitate of silver tartrate, Ag2C4H4O6, which blackens on boiling,
in consequence of the decomposition of the salt, with separation of
silver. If, before boiling, a drop of ammonia water be added, a
mirror of metallic silver will form upon the glass.

Silver tartrate is soluble in a solution of alkali tartrate ; hence the
silver nitrate solution must be added in sufficient quantity to obtain
a permanent precipitate.

4. Sulphuric acid heated with tartrates chars them readily.

5. Tartrates, when heated, are decomposed (blacken), and evolve a
somewhat characteristic odor, resembling that of burnt sugar.

The above reaction, 3, can be used to advantage for silvering glass by operat-
ing as follows : Dissolve 1 gramme of silver nitrate in 20 c.c. of water, add
ammonia water until the precipitate which forms is nearly redissolved, and
dilute with water to 100 c.c. Make a second solution by dissolving 0.2 gramme
of silver nitrate in 100 c.c. of boiling water, add 0.166 gramme of potassium
sodium tartrate, boil until the precipitate becomes gray, and filter. Mix the
two solutions cold and set aside for one hour, when a mirror of metallic silver
will be found.

Potassium acid tartrate, Potassii bitartras. KHC^O,, = 186.78
(Potassium bitartrate, Cream of Tartar). The formation of this salt in

POLYBASIC AND HYDROXY-ACIDS. 515

the crude state (argol) has been explained above. It is purified by
dissolving in hot water and crystallizing, when it is obtained in color-
less crystals, or as a white, somewhat gritty powder of a pleasant,
acidulous taste ; it is soluble in about 200 parts of cold, easily sol-
uble in hot water, but insoluble in alcohol.

The name cream of tartar was given to the salt for the reason that
small crystals, which float on the liquid, separate on rapidly cooling
a hot solution of potassium bitartrate.

Potassium tartrate, 2(K2C4H406).H,0. Obtained by saturating a solution
of potassium acid tartrate with potassium carbonate :

2KHC4H4Oe + K2C03 = 2K2C4H4O6 + H2O + CO,.
Potassium acid Potassium Potassium
tartrate. carbonate. tartrate.

Small transparent or white crystals, or a white neutral powder, soluble in
less than its own weight of water.

Potassium sodium tartrate, Potassii et sodii tartras,
KNaC4H4O6.4H2O = 280.18 (Rochelle salt). If in the above-described
process for making neutral potassium tartrate, sodium carbonate is
substituted for potassium carbonate, the double tartrate of potassium
and sodium is formed. It is a white powder, or occurs in colorless,
transparent crystals which are easily soluble in water.

Experiment 59. Add gradually 24 grammes of potassium acid tartrate to a
hot solution of 20 grammes of crystallized sodium carbonate in 100 c.c. of
water. Heat until complete solution has taken place, filter, evaporate to about
one-half the volume, and set aside for the potassium sodium tartrate to crys-
tallize. How much crystallized sodium carbonate is required for the conversion
of 25 grammes of potassium acid tartrate into Eochelle salt?

Seidlitz powders (Compound effervescing powders) consist of a mixture
of 7.75 grammes (120 grains) of Rochelle salt with 2.58 grammes
(40 grains) of sodium bicarbonate (wrapped in blue paper), and 2.25
grammes (35 grains) of tartaric acid (wrapped in white paper).
When dissolved in water the tartaric acid acts upon the sodium
bicarbonate, causing the formation of sodium tartrate, while the
escaping carbon dioxide causes effervescence.

Antimony and potassium tartrate, Antimonii et potassii
tartras, 2(KSbO.C4H4O6).H,O=659.8 (Potassium antimonyl tartrate,
Tartar emetic). This salt is made by dissolving freshly prepared
antimonous oxide (while yet moist) in a solution of potassium acid

516 CONSIDERATION OF CARBON COMPOUNDS.

tartrate. From the solution somewhat evaporated, tartar emetic
separates in colorless, transparent rhombic crystals :

2KHC4H4O6 + Sb2O3 = = 2KSbO.C4H4O6 + H,O.

Potassinm acid Antimonous Tartar emetic,

tartrate. oxide.

The fact that not antimony itself, but the group SbO, replaces the
hydrogen, has led to the assumption of the hypothetical radical SbO,
termed antimonyl.

Tartar emetic is soluble in water, insoluble in alcohol ; it has a
sweet, afterward disagreeable metallic taste.

Action of certain organic acids upon certain metallic oxides. The solu-
tion of a ferric salt (or certain other metallic salts) is precipitated by alkali
hydroxides, a salt of the alkali and ferric hydroxide being formed. When a
sufficient quantity of either tartaric, citric, oxalic, or various other organic
acids has been added previously to the iron solution (or to certain other metallic
solutions) no such precipitate is produced by the alkali hydroxides, because
organic salts or double salts are formed which are soluble, and from which the
metallic hydroxides are not precipitated by alkali hydroxides. Upon evapora-
tion no crystals (of the organic salt) form, and in order to obtain the com-
pounds in a dry state, the liquid, after being evaporated to the consistence of
a syrup, is spread on glass plates which are exposed to a temperature not
exceeding 60° C. (140° F.), when brown, green, yellowish-green, amorphous,
shining, transparent scales are formed, which are the scale compounds of the
U. S. P.

Instead of obtaining these compounds, 'as stated above, by adding the
organic acids (or their salts) to the inorganic salts, they are more generally
obtained by dissolving the freshly precipitated metallic hydroxide in the
organic acid.

The true chemical constitution of many of these scale compounds has not
as yet been determined with certainty.

Of official scale compounds containing tartaric acid may be mentioned the
iron and ammonium tartrate, and the iron and potassium tartrate. The first com-
pound is obtained by dissolving freshly precipitated ferric hydroxide in a solu-
tion of ammonium acid tartrate ; the second, by dissolving ferric hydroxide in
potassium acid tartrate. The clear solutions, after having been sufficiently
evaporated, are dried, as mentioned above, on glass plates.

Citric acid, Acidum citricum, H3C6H5O7.H2O = 2O8.5. Citric
acid is a tribasic acid containing three atoms of hydrogen replaceable
by metals ; its constitution may be expressed by the graphic formulas :

/OH CH2.C02H

/>C02H |

C3H4 or COH.CO2H

\\C02H |

\C02H CH2.C02H

Citric acid is found in the juices of many fruits (strawberry, rasp-
berry, currant, cherry, etc.), and in other parts of plants. It is
obtained from the juice of lemons by saturating it with calcium car-

POLYBASIC AND HYDEOXY- ACIDS. 517

bonate and decomposing by sulphuric acid the calcium citrate thus
formed. (100 parts of lemons yield about 5 parts of the acid.) It
forms colorless crystals, easily soluble in water.

Analytical reactions.
(Potassium citrate, K3C6H5O7, may be used.)

1. Neutral solutions of citrates yield with calcium chloride on
boiling (not in the cold) a white precipitate of calcium citrate, which
is insoluble in potassium hydroxide, but soluble in cupric chloride.

2. Neutral solutions of citrates are precipitated white by silver
nitrate. The precipitate does not blacken on boiling, as in the case
of tartrates. Silver citrate is soluble in a solution of an alkali ci-
trate ; hence, sufficient silver nitrate solution must be added to obtain
a permanent precipitate.

3. A solution of citrate made alkaline with a little sodium hydrox-
ide solution, to which a few drops of potassium permanganate solu-
tion are added, turns green slowly, whereas, atartrate under the same
conditions decolorizes permanganate quickly, with precipitation of
brown manganese dioxide.

4. When ignited, it is decomposed without emitting an odor resem-
bling burning sugar. (Difference from tartaric acid.)

5. Tartaric acid in citric acid may be detected by adding about 1
c.c. of an aqueous solution of ammonium molybdate to about 1
gramme of the citric acid, then 2 or 3 drops of sulphuric acid,
and warming on the water-bath. The presence of 0.1 per cent, or
more of tartaric acid gives a blue color to the solution.

Citrates. Potassium citrate, K3C6H5O7.H2O, and Lithium citrate,
Li3C6H5O7.4H2O, are official. Both are white deliquescent salts, easily
soluble in water, and obtained by dissolving the carbonates in citric
acid. Sodium citrate, 2Na3C6H5O7.llH2O, is also official.

The effervescent potassium citrate, lithium citrate, and magnesium sulphate are
granulated mixtures, all containing citric acid, tartaric acid, and sodium bicar-
bonate, mixed respectively with potassium citrate, lithium citrate, and mag-
nesium sulphate.

The official solution of magnesium citrate is made by dissolving magnesium
carbonate in an excess of citric acid solution to which some syrup is added,
and dropping into this mixture, which should be contained in a strong bottle,
potassium bicarbonate. The bottle is immediately closed with a cork in order
to retain the liberated carbon dioxide.

Bismuth citrate, BiC6H5O7, is obtained by boiling a solution of citric acid
with bismuth nitrate, when the latter is gradually converted into citrate, while

518 CONSIDERATION OF CARBON COMPOUNDS.

nitric acid is set free; the insoluble bismuth citrate is collected, washed, and
dried; it forms a white, amorphous powder, which is insoluble in water, but
soluble in ammonia water.

Bismuth ammonium citrate is a scale compound obtained by dissolving bismuth
citrate in ammonia water and evaporating the solution at a low temperature.

Ferric citrate, Ferri citras. Obtained in transparent, red scales, by dissolving
ferric hydroxide in citric acid and evaporating the solution as mentioned here-
tofore. By mixing solution of ferric citrate with either ammonia water or
quinine, strychnine, sodium phosphate, or sodium pyrophosphate, evaporating
to the consistence of syrup and drying on glass plates, the following scale com-
pounds are obtained respectively : Iron and ammonium citrate, iron and quinine
citrate, iron and strychnine citrate, soluble ferric phosphate, and soluble ferric pyro-
phosphate.

47. ETHERS AND ESTERS.

Constitution. It has been shown that alcohols are hydrocarbon
residues in combination with hydroxyl, OH, and that acids are hydro-
carbon residues in combination with carboxyl, CO.OH ; it has further
been shown that carboxyl may be considered as being composed of
CO, and hydroxyl, OH, and that the term acid radical is applied to
that group of atoms in acids which embraces the hydrocarbon residue
-f- CO. If we represent a hydrocarbon radical by R, and an acid
radical by R.CO, the general formula of an alcohol is R.OH, or

^>O, and of an acid, R.CO.OH, or R'C°>O.

Ethers are formed by replacement of the hydrogen of the hydroxyl
in alcohols by hydrocarbon residues, and esters, also called compound
ethers, or ethereal salts are formed by replacement of the hydrogen of
the hydroxyl (or carboxyl) in acids by hydrocarbon residues. While
alcohols correspond in their constitution to hydroxides, ethers corre-
spond to oxides, and esters to salts. For instance :

QUESTIONS. — Name the more common organic acids found in vegetables
and especially in sour fruits. What is the composition of oxalic acid, how is
it manufactured, and what are its properties? Explain the formation of crude
tartar during the fermentation of grape-juice, and how is tartaric acid obtained
from it? Give properties of and tests for tartaric acid. State the composition
and formation of cream of tartar, Rochelle salt, and tartar emetic. What are
Seidlitz powders, and what changes take place when they are dissolved ? Give
the general composition of hydroxy-acids, and state a method for preparing
them synthetically. From what and by what process is citric acid obtained ?
Mention tests by which citric acid may be distinguished from tartaric acid.
From what and by what process is lactic acid obtained ; what are its prop-
erties ?

ETHERS AND ESTERS. 519

Hydroxides. Oxides. Acids.

KOH = g\0 K20 = £\0 HN03 = N^)0 KNO3 - N(j£>O
Potassium hydroxide. Potassium oxide. Nitric acid. Potassium nitrate.

Ethyl alcohol. Ethyl ether. Acetic acid. Ethyl acetate, or

acetic ether.

ET R H R*

Alcohol. Ether. Acid. Ester.

It is not necessary that the two hydrocarbon residues in au ether
should be alike, as in the above ethyl ether, but they may be different,
in which case the ethers are termed mixed ethers. For instance :

CH3.C2H50 = g H»\o q,H,AHu.O =

Methyl-ethyl ether. Propyl-amyl ether.

In diatomic or triatomic alcohols, or in dibasic or tribasic acids,
containing more than one atom of hydrogen derived from hydroxyl
or carboxyl, these hydrogen atoms may be replaced by various other
univalent, bivalent, or trivalent residues. This fact shows that the
number of ethers or esters which are capable of being formed is very
large.

Formation of ethers. Ethers may be formed by the action of
the chloride or iodide of a hydrocarbon residue upon an alcohol, in
which the hydroxyl hydrogen has been replaced by a metal. For
instance :

C£<> + QftI = %!;> + Nal.
Sodium ethylate. Ethyl iodide. Ethyl ether. Sodium iodide.

Sodium Methyl Ethyl-methyl Sodium

ethylate. iodide. ether. iodide.

Ethers are also formed by the action of sulphuric acid upon alco-
hols ; the sulphuric acid removing water in this case, thus :

2(C2H5OH) : 2H5° +

Ethyl alcohol. Ethyl ether. Water.

Esters are formed by the combination of acids with alcohols and
elimination of water. (Presence of sulphuric acid facilitates this
action.)

+ C2HS0\0 =

Ethyl alcohol. Acetic acid. Ethyl acetate. Water.

520 CONSIDERATION OF CARBON COMPOUNDS.

They are also formed by the action of hydrocarbon chlorides (or
iodides) on salts. For instance :

C5HUC1 + CH°)0 : ^g)o + KC1

Amyl Potassium Amyl Potassium

chloride. formate. formate. chloride.

Occurrence in nature. Many ethers are products of vegetable
life and occur in some essential oils ; wax contains the compound
ether melissyl palmitate, C3(JH61.C16H31O.O, and spermaceti, a solid
substance found in the head of the whale, is cetyl palmitate, C^H^.
C16H31O.O. The most important group of esters are the fats and
fatty oils, which are distributed widely in the vegetable, but even
more so in the animal kingdom.

General properties. The ethers and esters of the lower members
of the monatomic alcohols and fatty acids have generally a character-
istic and pleasant odor. Fruit essences consist mainly of such esters,
and what is generally known as the " bouquet " or " flavor " of wine
and other alcoholic liquors is due chiefly to ethers or compound ethers,
which are formed during (and after) the fermentation by the action
of the acids present upon the alcohol or the alcohols formed. The
improvement which such alcoholic liquids undergo " by age " is caused
by a continued chemical action between the substances named.

All esters are neutral substances ; those formed by the lower alco-
hols and acids are generally volatile liquids, those of the higher
members are non-volatile solids. When esters are heated with alka-
lies, the acid combines with the latter, while the alcohol is liberated.
(The properties of the esters, termed fats, will be considered further
on.)

One of the chief points of distinction between ethers and esters is
that ethers are not acted on by alkalies, while esters are decomposed,
an alcohol and a salt of the alkali metal being formed.

Ethyl ether, Either, (C2H5)2O = 73.52 (Ether, sulphuric ether, Ethyl
oxide). The name of the whole group of ethers is derived from this
(ethyl-) ether, in the same way that common (ethyl-) alcohol has
given its name to the group of alcohols. The name sulphuric ether
was given at a time when its true composition was yet unknown, and
for the reason that sulphuric acid was used in its manufacture.

Ether is manufactured by heating to about 140° C. (284° F.) a
mixture of 1 part of alcohol and 1.8 parts of concentrated sulphuric
acid in a retort, which is so arranged that additional quantities of
alcohol may be allowed to flow into it, while the open end is connected

ETHERS AND ESTERS. 521

with a tube, leading through a suitable cooler, in order to condense
the highly volatile product of the distillation.

Experiment 60. Mix 100 grammes of alcohol with 180 grammes of ordinary
sulphuric acid, allow to stand and pour the cooled mixture into a flask which
is provided with a perforated cork through which pass a thermometer and a
bent glass tube leading to a Liebig's condenser. Apply heat and notice that
the liquid commences to boil at about 140° C. (284° F.). Distil about 50 c.c.,
pour this liquid into a stoppered bottle and add an equal volume of water.
Ethyl ether will separate into a distinct layer over the water, and may be
removed by means of a pipette. Eepeat the washing with water, add to the
ether thus freed from alcohol a little calcium chloride and distil it from a dry
flask, standing in a water-bath. The greatest care should be exercised and the
neighborhood of flames avoided in working with ether, on account of its
volatility and the inflammability of its vapors.

The apparatus described above for etherification can be constructed so as to
make the process continuous. This may be done by using with the boiling-
flask a cork with a third aperture through which a glass tube passes into the
liquid. The other end of the tube is connected by means of rubber tubing
with a vessel filled with alcohol and standing somewhat above the flask. As
soon as distillation commences alcohol is allowed to flow into the flask at a
rate equal to that of the distillation, keeping the temperature at about 140° C.
(284° F.). The flow of alcohol is regulated by a stop-cock.

The action of sulphuric acid upon alcohol is not quite so simple as
described above in connection with the general methods for obtaining
ethers, where the final result only was given An intermediate pro-
duct, known as ethyl sulphuric acid or sulpho-vinic acid, is formed,
which, by acting upon another molecule of alcohol, forms sulphuric
acid and ether, which latter is volatilized as soon as formed. The
decomposition is shown by the equations :

C2H5OH

Su
acid.

C2H5OH = (C2H5)20

Alcohol. Sulphuric Ethyl-sulphuric

acid.

Ethyl-sulphuric Alcohol. Ether. Sulphuric

acid. acid.

The liberated sulphuric acid at once attacks another molecule of alcohol,
again forming ethyl-sulphuric acid, which is again decomposed, etc. Theo-
retically, a given quantity of sulphuric acid should be capable, therefore, of
converting any quantity of alcohol into ether ; practically, however, this is not
the case, because secondary reactions take place simultaneously, and because the
water which is constantly formed does not all distil with the ether, and there-
fore dilutes the acid to such an extent that it no longer acts upon the alcohol.

Ether thus obtained is not pure, but contains water, alcohol, sulphurous and
sulphuric acids, etc. ; it is purified by mixing it with chloride and oxide of
calcium, pouring off the clear liquid and distilling it.

522 CONSIDERATION OF CARBON COMPOUNDS.

The official ether contains of ethyl-ether 96 per cent, and of
alcohol 4 per cent. It is a very mobile, colorless, highly volatile
liquid, of a refreshing, characteristic odor, a burning and sweetish
taste, and a neutral reaction ; it is soluble in alcohol, chloroform,
liquid hydrocarbons, fixed and volatile oils, and dissolves in ten
volumes of water. Specific gravity is 0.716 at 25° C. (77° F.);
boiling-point 35° C. (95° F.). It is easily combustible and burns
with a luminous flame. When inhaled, it causes intoxication and
then loss of consciousness and sensation. The great volatility and
combustibility of ether necessitate special care in the handling of this
substance near fire or light.

Spiritus cetheris and Spiritus cetheris compositus are mixtures of about one
part of ether and two parts of alcohol, 3 per cent, of certain ethereal oils being
added to the second preparation.

Methyl ether, (CH3)20, is made from methyl alcohol and sulphuric acid. It
is a gas at ordinary temperature, but readily convertible by pressure or cold
into a mobile liquid.

Methyl-ethyl ether, CH3.C2H5.0, is a mixed ether which can be prepared
by the action of ethyl iodide upon sodium methylate :

C2H6I -f NaOCH3 = Nal + C2H5.O.CH3.

Methyl-ethyl ether is a colorless, highly volatile, and inflammable liquid of
peculiar odor; it boils at 11° C. (52° F.). It has been used as an anesthetic,
and for that purpose is sold in cylinders.

Acetic ether, ^3ther aceticus, C2H5C2H.p2 = 87.4 (Ethyl acetate).
Made by mixing dried sodium acetate with alcohol and sulphuric
acid, distilling and purifying the crude product by shaking with
calcium chloride and rectifying :

C2H5OH + NaC2H302 + H2SO4 = C2H5C2H3O2 + NaHSO4 + H2O.
Ethyl Sodium Acetic ether. Sodium acid

alcohol. acetate. sulphate.

Experiment 61. Add to a mixture of 40 grammes of pure alcohol and 100
grammes of concentrated sulphuric acid 60 grammes of sodium acetate. In-
troduce this mixture into a boiling-flask, connect it with a Liebig's condenser
and distil about 50 c. c. Eedistil the liquid from a flask, as represented in Fig.
69, page 463. and collect the portion which passes over at a temperature of
IT C. (170° F.) ; it is nearly pure ethyl acetate.

Acetic ether is a colorless, neutral, and mobile liquid, of a strong
ethereal and somewhat acetous odor, soluble in alcohol, ether, chloro-
form, etc., in all proportions, and in 7 parts of water. Specific
gravity 0.894. Boiling-point about 72° C. (161° F.).

ETHERS AND ESTERS. 523

Ethyl nitrite, C2H,NO2 = 74.51 (Nitrous ether). Can be made by
distilling a mixture of alcohol, sulphuric acid, and sodium nitrite :
C2H5OH + NaNOj + H2SO4 = C2H6NO, + NaHSO< + H2O

The distillate, which contains, besides ethyl nitrite, some alcohol
and often some decomposition products, is washed with ice-cold water,
in which ethyl nitrite is nearly insoluble, and with sodium carbonate
to remove traces of acid ; finally, it is freed from water by treatment
with anhydrous potassium carbonate. It boils at 17° C. (62.6° F.).

The process adopted by the Pharmacopoeia differs from the former by
dispensing with the distillation and using the insolubility of the ether
in ice-cold salt solution for its separation. The process is carried out by
pouring a cold solution of sodium nitrite very slowly into an ice-cold
mixture of sulphuric acid, alcohol, and water. Decomposition takes
place as in the reaction given above. Some sodium-acid sulphate is
precipitated and has to be separated from the liquid, which is poured
into a separating funnel where two layers form. The lower aqueous
solution is drawn off and the remaining nitrous ether is purified like
the distillate obtained in the first process. (For assay-method of ethyl
nitrite, see paragraph on gas-analysis.)

Spirit of nitrous ether, Spiritus cetheris nitrosi, Sweet spirit of niter.
This is a mixture of about 4 parts of ethyl nitrite with 96 parts
of alcohol. It is a clear, mobile, volatile, and inflammable liquid, of
a pale straw color inclining slightly to green, a fragrant, ethereal
odor, and a sharp, burning taste. It is neutral, or but very slightly
acid to litmus paper but evolves no carbon dioxide with potassium
bicarbonate.

Amyl nitrite, Amylis nitris, C5HUNO2 = 116.24. Made by a
process analogous to the first one mentioned above for ethyl nitrite,
substituting amyl alcohol for ethyl alcohol.

The official amyl nitrite contains of this ether about 80 per cent.,
together with variable quantities of undetermined compounds ; it is
a clear, pale-yellowish liquid, of an ethereal, fruity odor, an aromatic
taste, and a neutral or slightly acid reaction. Specific gravity 0.865.
Boiling-point 96° C. (205° F.). The low boiling-point necessitates
special precautions in storing the article. It is best kept in sealed
vials and dispensed in sealed glass bulbs, each containing only a few
drops of the liquid.

Fats and fat oils. All true fats are esters of the triatomic alcohol
glycerin, in which the three replaceable hydrogen atoms of the hy-

524 CONSIDERATION OF CARBON COMPOUNDS.

droxyl are replaced by three univalent radicals of the higher members
of the fatty acids. For instance :

/OH

Glycerin = C3H5.(OH>3 or C3H /OH

\OH

Stearicacid = C18H35O.OH or C18H35O\O

H/

/(C18H350).0

Stearin or tristearin = C3H5.(C18H35O)3.O3 or C3H5^_(C]8H35O).O

\(C18H350).0

While all natural fats are glycerin in which the three hydrogen
atoms are replaced, we may by artificial means introduce but one or
two acid radicals, thus forming :

/(C18H35O)O /(C18H,50)O

Monostearin = C3H5^OH Distearin = C3H5/(C18H35O)O

\OH

Fats are often termed glycerides ; stearin being, for instance, the
glyceride of stearic acid.

The principal fats consist of mixtures of palmitin, C3H5.(C16H31O)3.
03, stearin, C3H5.(C18H35O)3.O3, and olein, C^C^O^O,,.
Stearin and palmitin are solids, olein is a liquid at ordinary tem-
perature ; the relative quantity of the three fats mentioned determines
its solid or liquid condition. The liquid fats, containing generally
olein as their chief constituent, are called fatty oils or fixed oils in
contradistinction to volatile or essential oils.

All fats, when in a pure state, are colorless, odorless, and tasteless
substances, which stain paper permanently ; they are insoluble in
water, difficultly soluble in cold alcohol, easily soluble in ether, disul-
phide of carbon, benzene, etc. The taste and color of fats are due to
foreign substances, often produced by a slight decomposition which
has taken place in some of the fat. All fats are lighter than water,
and all solid fats fuse below 100° C. (212° F.) ; fats can be distilled
without change at about 300° C. (572° F.), but are decomposed at a
higher temperature with the formation of numerous products, some
of which have an extremely disagreeable odor, as, for instance,
acrolem, which has been mentioned before.

Fats being lighter than, and insoluble in, water will float on it, but mechani-
cal mixtures of both substances exist in emulsions. These contain finely di-
vided fat globules, suspended in the water, or better in water containing some
gum-arabic or a similar substance. Milk and certain plant juices are examples
of natural emulsions.

Some fats keep without change when pure ; since, however, they gen-
erally contain impurities, such as albuminous matter, etc., they suffer

ETHERS AND ESTERS. 525

decomposition (a kind of fermentation aided by oxidation), which re-
sults in a liberation of the fatty acids, which impart their odor and taste
to the fats, causing them to become what is generally termed rancid.

Some fats, especially some oils, suffer oxidation, which renders
them hard. These drying oils differ from other oils in being mixtures
of olein with another class of glycerides, containing unsaturated acids
with less hydrogen in relation to carbon than oleic acid. Drying oils
are prevented from drying by albuminous impurities, which may be
removed by treating the oil with 4 per cent of concentrated sulphuric
acid ; the acid does not act on the fat, but quickly destroys the albu-
minous matters, which, with the sulphuric acid, sink to the bottom,
while the " refined " oil may be removed by decantation.

Fats are largely distributed in the animal and vegetable kingdoms.
They exist in plants chiefly in the seeds, while in animals they are found
generally under the skin, around the intestines, and on the muscles.

Human fat, beef tallow, mutton tallow, and lard are mixtures of
palmitin and stearin with some olein. Butter consists of the glycer-
ides of butyric acid, capro'ic acid, caprylic acid, and capric acid,
which are volatile with water vapors, and of myristic, palmitic, oleic,
and stearic acids, which are not volatile.

The principal non-drying vegetable oils (consisting chiefly of olein)
are olive oil, cottonseed oil, cocoanut oil, palm oil, almond oil.

Among the drying oils are of importance : linseed oil, castor oil,
croton oil, hemp oil, cod-liver oil.

Whenever fats are treated with alkaline hydroxides, or with a
number of other metallic oxides, decomposition takes place, the fatty
acids combining with the metals, while glycerin is set free. Some
of the substances thus formed are of great importance, as, for instance,
the various kinds of soap.

The term saponification, as used by physiologists, is applied to the
decomposition which occurs when neutral fat is split into its constitu-
ents, glycerin and fatty acid. This decomposition is a hydrolytic
cleavage, and can be produced by the action of boiling alkalies, super-
heated steam, various enzymes, etc. In other words, the formation
of a soap is not an essential part of the process.

Soap. Any fat boiled with sodium or potassium hydroxide will
form soap. Soft soap is potassium soap, hard soap is sodium soap.
The better kinds of hard soap are made by boiling olive oil with
sodium hydroxide :

C3H5(C]8H3302)3 + SNaOH = SNaC^O, + C3H5(OH)3.
Oleateof erlvceryl Sodium Sodium oleate Glycerin,

(olive oil). hydroxide. (hard soap).

526 CONSIDERATION OF CARBON COMPOUNDS.

Soaps are soluble in water and alcohol ; they contain rarely less
than 30 per cent., but sometimes as much as 70-80 per cent, of water.

Potassium or soft soap is usually yellowish, but it is sometimes tinted green
artificially, and is then called "green soap." It contains, besides the potas-
sium salts of the fatty acids, the glycerin liberated in the saponification and
relatively much water. Hard or sodium soap is separated from the solution
after saponification by adding common salt to the boiling mixture to satura-
tion. The soap, being insoluble in the salt solution, separates as a molten
layer, which can be removed after cooling and solidifying. This method of
separating the soap is known as the "salting out" process. The soap is free
from glycerin, but contains some water.

Ammonia liniment, Linimentum ammonice, and lime liniment, Lini-
mentum calcis, are obtained by mixing cottonseed oil with ammonia-
water and lime-water respectively. The oleate of ammonium or
calcium is formed, and remains mixed with the liberated glycerin.

Lead plaster. Chiefly lead oleate, Pb(C18H33O2)2. Obtained by boiling lead
oxide with olive oil and water for several hours, until a homogeneous, pliable,
and tenacious mass is formed. Lead oleate differs from the oleate of the alkalies
by its complete insolubility in water.

Experiment 62. Dissolve in a 500 c.c. flask 15 grammes of potassium hy-
droxide in 100 c.c. of alcohol. Melt 50 grammes of lard in an evaporating dish
and pour the liquefied fat into the flask. Heat over a water bath, and shake
cautiously when the alcohol begins to boil. Saponification takes place very
rapidly, and its completion is determined by pouring a few drops of the liquid
into a test-tube of water, when any unsaponified fat will float on the surface.
When saponification is complete the solution contains soap, glycerin, and any
excess of caustic potash.

Pour the contents of the flask into 250 c.c. of hot 5 per cent, sulphuric acid ;
the fatty acids separate as an oily layer which solidifies on cooling. The solu-
tion contains potassium acid sulphate, sulphuric acid, and glycerin. When the
solution is neutralized, evaporated to crystallization, and extracted with alco-
hol, glycerin can be obtained by evaporation of the alcoholic extract.

Reactions of fats and fatty acids.

1. Boil 5 grammes of suet with 25 c.c. of alcohol and filter while
hot. Wash the residue with a little ether, squeeze as dry as possible
and then dry in the air. The resulting fibrous mass is the connective
tissue network of the adipose tissue and a little fat. Show the pres-
ence of protein in connective tissue by the xanthoproteic and Millon's
reactions. On evaporation of the alcoholic filtrate, fat is left.

2. Rub a little fat on glazed white paper. Notice that this " grease-
spot" appears dark on a white background in reflected light, but
light (transparent) in transmitted light. The stain does not disappear
on heating.

ETHERS AND ESTERS. 527

3. Heat in a dry test-tube a small quantity of fat with an equal
portion of potassium bisulphate. Acrolein is formed and recognized
by its odor.

4. Heat about 2 grammes of fatty acids with 100 c.c. of water and
enough sodium carbonate to dissolve the fatty acids. A solution of
sodium soap is formed, of which use a few c.c. for each of the follow-
ing reactions :

a. Heat with an excess of hydrochloric acid ; fatty acids are lib-
erated.

6. Add calcium chloride solution ; insoluble calcium soap is formed,
and the solution does not foam on shaking.

c. Add lead acetate solution ; a white precipitate of an insoluble
lead salt (lead plaster) is formed, becoming sticky on heating.

d. Add some olive oil and shake well ; a homogeneous milk-like
mixture — i. e., emulsion — is formed.

Wool-fat, Lanolin, Adeps lanse. This is the fat, or a mixture of fats,
found in sheep's wool and obtained by treating the wool with soap-water, and
acidifying the wash liquor, when the fats separate unchanged. These fats
differ from the fats spoken of above in so far as the alcohol present is not
glycerin, but an alcohol, or rather two isomeric alcohols of the composition
C26H4:!OH and known as cholesterin and isocholesterin. These alcohols, which
are white, crystalline, fusible substances, when in combination with fatty acids
form the compound ethers known as lanolin.

Lanolin is a yellowish-white (or, when not sufficiently purified, a more or
less brownish), fat-like substance, having the peculiar odor of sheep's wool and
fusing at about 40° C. (104° F.), forming an oily liquid. Unlike true fats,
lanolin is capable of mixing with twice its weight of water or aqueous solutions
and yet retaining its fatty consistency ; it is, moreover, much less liable to de-
compose than fats, and it is this property and its power to mix with aqueous
solutions which have rendered lanolin a valuable agent in certain pharma-
ceutical preparations. Official is also hydrous wool-fat, the purified fat mixed
with not more than 30 per cent, of water.

QUESTIONS. — Explain the constitution of simple and mixed ethers ancfr
esters. To what inorganic compounds are they analogous? State the general
processes for the formation of ethers and esters. What is the composition of
ethyl ether ? Explain the process of its manufacture in words and symbols,
and state its properties. How is acetic ether made, and what are its proper-
ties? What is sweet spirit of niter, and how is it made? State the general
composition of fats and the chief constituents of tallow, butter, and olive oil.
What is the solubility of fats in water, alcohol, and ether; how do heat and
oxygen act upon them ; what is the cause of their becoming rancid? Explain
the composition and manufacture of soap, and state the difference between hard
and soft soap. How are ammonia liniment, lime liniment, and lead plaster
made, and what is their composition ? What is the source of lanolin ; what
are its constituents and properties ?

528 CONSIDERATION OF CARBON COMPOUNDS.

48. CARBOHYDRATES.

General remarks. The name carbohydrates was originally given
to a class of compounds found chiefly in plants, and containing in
the molecule 6 atoms of carbon (or a multiple of 6) in combination
with hydrogen and oxygen in the proportion to form water, as shown
in the formula for grape-sugar, C6H12O6, cane-sugar, C12H22OU, etc.
While even formerly the name was not well chosen, because it
implies that these subfetances are carbon in combination with water,
to-day it is still less suitable, because members of the group have been
found which do not contain oxygen and hydrogen in the proportion
mentioned ; as, for instance, a sugar, termed rhamnose, having the
composition C6H12O5. We also know now carbohydrates containing
carbon atoms in numbers which have no relation to 6. While, there-
fore, the term carbohydrate no longer implies what it formerly
did, and no longer refers to the restricted number of compounds
which it formerly included, yet it is retained for the whole group of
compounds now to be considered.

The group includes now, as heretofore, the different sugars, starches,
gums, etc., and also a number of compounds obtained by artificial or
synthetical processes. In order to show in its name that a substance
belongs to the carbohydrates, the ending ose is used to distinguish
these bodies from the members of other groups.

Constitution. While the true atomic structure of many carbo-
hydrates is as yet not fully understood, the structure of others is
well known. It appears that some carbohydrates are true aldehydes,
while others are closely related to ketones, and yet others are the
anhydrides, or condensation products of the former.

Thus, a sugar of the composition C3H6O3, termed glycerose, is obtained by the
action of mild oxidizing agents on glycerin, thus :

C3H803 + O = C3H603 + H20.

If we bear in mind the fact that glycerin, C3H5(OH)3, is a triatomic alcohol,
and that alcohols by oxidation yield aldehydes, we realize the analogy existing
between the above reaction and that leading to the formation of the aldehydes,
previously considered.

In a manner similar to the one producing glycerose from glycerin, a sugar
of the composition C4H8O4, and called erythrose, is obtained from the tetratomic
alcohol erythrite, C4H6(OH)4, while a sugar of the composition C6H12O6 is ob-
tainable from the hexatomic alcohol mannite, C6H8(OH)6. In both cases two
atoms of hydrogen are split off from the alcohol molecules.

The relationship existing between the sugars of the composition C6H]2O6

CA RBOH YDEA TES. 529

and other carbohydrates having the composition C6PTi0O5 or C12H22On can he
readily shown by the equations :

*(C6H1206 - H20) (C6H1005)z

2(C6H1206)- H20 : C12H22On,

which show that abstraction of water leads to the formation of compounds
having the composition of starch, C6H10O5, and cane-sugar, C12H22On, respec-
tively. While this abstraction of water is difficult, it is an easy matter to
cause starch or cane-sugar to take up water, with the result that sugars of the
composition C6H12O6 are formed.

Properties. Carbohydrates are either fermentable, or can, in most
cases, be converted into substances which are capable of fermentation.
They are not volatile, but suffer decomposition when sufficiently
heated ; they have neither acid nor basic properties, but are of a neu-
tral reaction. Oxidizing agents convert them into saccharic and
mucic acids and finally into oxalic acid. (Soluble carbohydrates
have generally the property of turning the plane of polarized light.)

Most carbohydrates are white, solid substances, and, with the ex-
ception of a few, soluble in water. Those carbohydrates belonging
to the sugars have a more or less sweet taste. Many of them,
especially glucose, are good reducing agents, as is shown by the
fact that they deoxidize in alkaline solution salts (or oxides) of
copper, bismuth, mercury, gold, etc., either to a lower state of
oxidation or to the metallic state.

Occurrence in nature. No other organic substances are found in
such immense quantities in the vegetable kingdom as the members
of this group, cellulose being a chief constituent of all, starch and
various kinds of sugar of most plants. Carbohydrates are also found
as products of animal life, as, for instance, the sugar in milk, in bees'
honey, etc.

Classification. The carbohydrates are conveniently divided into
the following three groups :

1. Monosaccharides, or simple sugars. To this group belong the
sugars which cannot be broken down into two or more simple sugars.
They contain from 3 to 9 atoms of carbon, in most cases the same
number of oxygen atoms, and double the number of hydrogen atoms.
(Dextrose, levulose, galactose, etc.)

2. Disaccharides, or complex sugars. These are sugars which, on
taking up 1 molecule of water, split up into two simple sugars.
(Cane-sugar, maltose, lactose, etc.)

3. Polysaccharides. These do not resemble sugars, have no sweet
taste, and form simple sugars only after repeated cleavages. (Starches,
gums, cellulose, etc.)

34

530 CONSIDERATION OF CARBON COMPOUNDS.

Monosaccharides.

The monosaocharides are white, odorless, sweet, crystallizable, neu-
tral substances, readily soluble in water, sparingly soluble in alcohol,
insoluble in ether. Like all aldehydes and ketones they are easily
oxidized, acting as strong reducing agents. Trommer's, Fehling's,
and Boettger's " reduction tests " depend on this property. Solutions
of monosaccharides, acidified with acetic acid, give with phenyl-hy-
drazine crystalline precipitates of substances called osazones. The tri-
oses, hexoses, and nonoses are capable of alcoholic fermentation, the
others are not. Most of the monosaccharides are optically active.

According to the number of carbon atoms present, the monosaccharides are
again subdivided into classes called trioses, tetroses, pentoses, hexoses, heptoses,
octoses, and nonoses, having the composition C3H6O3, C4H8O4, C5H10O5, C6H12CX.,
C7HUO7, C8H1608, and C9H18O9, respectively. The hexoses are the best-known
group, which is again subdivided into two groups, viz., the aldoses, containing
the alcohol group, CH.2OH, and the aldehyde group, COH ; and the ketoses,
containing the alcohol group and the ketone group, CO. The constitution of
these compounds is shown thus :

Aldoses

Ketoses

Glucose is an aldose-hexose, while fructose is a ketose-hexose.

Dextrose, Glucose, Grape-sugar, C6H12O6. This substance is
very abundantly diffused throughout the vegetable kingdom, and is
generally accompanied by fruit-sugar. It is contained in large quan-
tities in the juice of many fruits; the percentage of grape-sugar in
the dried fig is about 65, in grape 10-20, in cherry 11, in mulberry 9,
in strawberry 6, etc.

Dextrose is found also in honey and in minute quantities in the
normal blood (0.1 per cent, or less), and traces occur, perhaps, in
normal urine, the quantity in both liquids rising, however, during
certain diseases, as high as 5 per cent, or higher.

Grape-sugar is produced in the plant from starch by the action of
the vegetable acids present; it may be obtained artificially from
starch (and from many other carbohydrates) by heating with dilute
mineral (sulphuric) acids, which convert starch first into dextrin and

Trioses.

Tetroses.

Pentoses.

Hexoses.

f COH

COH

COH

COH

I
CHOH

(CHOH),

(CHOH)3

(CHOH)4

1

|

1

[ CH2OH

CH,OH

CH.2OH

CH.OH.

f CH2OH

CH,OH

CH2OH

CH2OH

1

1

1

I

CO

CO

CO

CO

1

1

1

1

CH2OH

CHOH

(CHOH)2

(CHOH)3

!
CH,OH

Cff,OH

CH2OH.

CARBOHYDRATES. 531

then into grape-sugar. Corn-starch is now largely used for that pur-
pose, the excess of sulphuric aoid being removed by treating the solu-
tion with chalk ; the filtered solution is either evaporated to a syrup
and sold as "glucose," or evaporated to dryness, when the com-
mercial " grape-sugar " is obtained.

Experiment 63. Heat to boiling 100 c.c. of a 1 per cent, sulphuric acid and
add to it very gradually and with constant stirring a mixture made by rub-
bing together 25 grammes of starch and 25 grammes of water. Continue to boil
until iodine no longer causes a blue color (which shows complete conversion of
starch into either dextrin or glucose), and until 1 c.c. of the solution is no longer
precipitated on the addition of 6 c.c. of alcohol (which shows the conversion of
dextrin into sugar, dextrin being precipitated by alcohol). Apply to a portion
of the glucose solution thus obtained, and neutralized by sodium carbonate, the
tests mentioned below. To the remaining solution add a quantity of precipitated
calcium carbonate sufficient to convert all sulphuric acid into calcium sulphate.
Filter, evaporate the solution to a syrup and notice its sweet taste.

Glucose is met with generally as a thick syrup which crystallizes
with difficulty, combining during crystallization with one molecule of
water; but anhydrous crystals, closely resembling those of cane-
sugar, are also known. Glucose is soluble in its own weight of
water and is less sweet than cane-sugar, the sweetness of glucose com-
pared to that of cane-sugar being about 3 to 5 ; when heated to 170°
C. (338° F.) it loses water, and is converted into glucosan, C6H10O5 ;
by stronger heating it loses more water and forms caramel, a mixture
of various substances ; it turns the plane of polarized light to the
right.

By gentle oxidation dextrose is first converted into monobasic glu-
conic acid, C6H12O7 = C5H6.(OH)5.CO2H, and then into dibasic sac-
charic acid, C6H10O8 = C4H4.(OH)4.(CO2H)2. Further oxidation
results in the formation of acids of lower molecular weight, due to
splitting up of the molecules. (Saccharic acid is soluble in less than
its own weight of water.)

Dextrose combines with various metallic oxides (alkalies, alkaline
earths, etc.), and also with a number of other substances, forming a
series of compounds known as glucosides.

Dextrose may be recognized analytically :

1. By causing a bright-red precipitate of cuprous oxide, when
boiled with a solution of cupric sulphate in sodium hydroxide, to
which tartaric acid has been added. (A solution containing these
three substances in definite proportions is known as Fehling's solu-
tion. See index.)

2. By precipitating metallic silver, bismuth, and mercury, when

532 CONSIDERATION OF CARBON COMPOUNDS.

compounds of these metals are heated with it in the presence of
caustic alkalies.

3. By easily fermenting when yeast is added to the solution, alco-
hol and carbon dioxide being formed :

C6H1206 = 2C2H5OH + 2C02.

4. By forming with an excess of phenyl-hydrazine, in a solution
acidified with acetic acid, a yellow crystalline precipitate of phenyl-
dextrosazone.

Levulose, Fructose, C6H12O6 (Fruit-sugar), occurs with glucose in
sweet fruits and honey ; it resembles glucose in most chemical and
physical properties, but does not crystallize from an aqueous solution ;
it may, however, be obtained in white silky needles from an alcoholic
solution ; it is met with generally as a thick syrup, is about as sweet
as cane-sugar, and turns the plane of polarized light to the left ; it is
formed by the action of dilute mineral acids or ferments on cane-
sugar, which latter takes up water and breaks up thus :

C]2H22On + H20 = C6HI206 + C6H1206.
Cane-sugar. Dextrose. Fructose.

Levulose has been made by the polymerization of formic aldehyde,
CH2O, and also by several other reactions.

Mannose, C6H12O6. Obtained by the oxidation of mannite ; it does
not crystallize and resembles grape-sugar.

Galactose, C6H12O6, is formed together with dextrose when either
milk-sugar or gum-arabic is boiled with dilute sulphuric acid. Galac-
tose crystallizes, reduces an alkaline copper solution, but does not fer-
ment with yeast.

When oxidized by heating with nitric acid, galactose forms galactonic add
and mucic acids, which are isomeric with the above-mentioned gluconic and
saccharic acids. Mucic acid is easily distinguished from saccharic acid by
being almost insoluble in water.

Inosite, C6H12O6 (Muscle-sugar). This compound was classed with
the carbohydrates on account of its sweet taste; its readiness to
undergo lactic and butyric fermentation; and the identity of its
molecular formula with that of the hexoses. It has, however, been
shown that inosite has an entirely different constitution, being a benzol
derivative, viz., hexahydroxy-benzol, C6H6(OH)6.

Inosite occurs somewhat abundantly in unripe beans and peas, and
sparingly in the liquid of muscular tissue ; traces are found in urine,
the quantity increasing in certain diseases. It does not ferment with
yeast, does not reduce alkaline copper solution, and is optically in--
active.

CARBOHYDRATES. 533

Disaccharides.

The general physical properties and the solubility of disaccharides
are identical with those of the monosaccharides. They differ from them
by not fermenting directly and by not forming osazones. The empiri-
cal formula is C12H22OU. By treatment with dilute mineral acids or
by the action of certain enzymes they undergo hydrolysis — i. e., take
up a molecule of water and are resolved into two hexose molecules.
Thus, cane-sugar splits up into dextrose and levulose ; lactose into
dextrose and galactose ; maltose into two molecules of dextrose.

Cane-sugar is dextrorotatory, but the mixture obtained by the hy-
drolysis of cane-sugar is laevorotatory, because levulose turns the
plane of polarization more to the left than dextrose does to the right.
For this reason the mixture is called inverted sugar and the hydrol-
ysis inversion. The term inversion is therefore used to designate the
splitting of disaccharides into simpler sugars. The building up of
complex sugars from simple sugars is called reversion.

Lactose and maltose reduce alkaline copper solution ; cane-sugar
does not.

Cane-sugar, Saccharum, C12H22OU = 339.6 (Saccharose, Com-
mon sugar, Beet-sugar}. Cane-sugar is found in the juices of
many plants, especially in that of the different grasses (sugar-cane),
and also in the sap of several forest trees (maple), in the roots, stems,
and other parts of various plants (sugar-beet), etc. Plants contain-
ing cane-sugar do not contain free organic acids, which latter would
convert it into grape-sugar.

Cane-sugar is manufactured from various plants containing it by
crushing them between rollers, expressing the juice, heating and
adding to it milk of lime, which precipitates vegetable albuminous
matter. The clear liquid is evaporated to the consistency of a syrup,
which is further purified (refined) by filtering it through bone-black
and evaporating the solution in " vacuum pans" to the crystallizing-
point; the mother-liquors are further evaporated, and yield lower
grades of sugar; finally a syrup is left which is known as molasses.

Cane-sugar forms white, hard, distinctly crystalline granules, but
may be obtained also in well-formed, large, monocliuic prisms. It
dissolves in 0.2 part of boiling, in 0.5 part of cold water, and in 175
parts of alcohol ; when heated to 160° C. (320° F.) it fuses, and the
liquid, on cooling, forms an amorphous, transparent mass, known as
barley sugar; at a higher temperature cane-sugar is decomposed,
water is evolved, and a brown, almost tasteless substance is formed,
which is known as caramel or burnt sugar. Oxidizing agents act

534 CONSIDERATION OF CARBON COMPOUNDS.

energetically upon cane-sugar, which is a strong reducing agent. A
mixture of cane-sugar and potassium chlorate will deflagrate when
moistened with sulphuric acid ; potassium permanganate is readily
deoxidized in acid solution ; cane-sugar, however, does not affect an
alkaline copper solution, and does not itself ferment ; but when heated
with dilute acids or left in contact with yeast in the presence of vari-
ous bacteria it is decomposed into dextrose and levulose, both of which
are fermentable. Like dextrose, cane-sugar forms compounds with met-
als, metallic oxides, and salts, which compounds are known as sucrates.

Experiment 64 Make a one per cent, cane-sugar solution ; test it with
Fehling's solution and notice that no cuprous oxide is precipitated. Add to
50 c c. of the cane-sugar solution 5 drops of hydrochloric acid and heat on a
water-bath for half an hour. Again examine the liquid with Fehling's solu-
tion ; a precipitate of cuprous oxide is now formed, proving the conversion of
cane-sugar into dextrose (grape-sugar) and levulose.

Maltose, C12H22On, is obtained by the action of diastase on starch.
Diastase is a substance formed during the germination of various
seeds (rye, wheat, barley, etc.), and it is for this reason that grain
used for alcoholic liquors is converted into malt — i. e., is allowed to
germinate, during which process diastase is formed, which, acting
upon the starch present, converts it into maltose and dextrin :

3(C6H1005) + H20 = C12H220U + C6H1006.
Starch. Maltose. Dextrin.

Maltose is also formed by the action of dilute sulphuric acid upon
starch, and is hence often present in commercial glucose ; by further
treatment with sulphuric acid it is converted into dextrose. Maltose
crystallizes, reduces alkaline copper solutions, and ferments with
yeast.

Melitose, C12H22On, is the chief constituent of Australian manna.

Sugar of milk, Saccharum lactis, C12H22On + H2O = 357.48
(Lactose). Found almost exclusively in the milk of the mammalia.
Obtained by freeing milk from casein and fat and evaporating the
remaining liquid (whey) to a small bulk, when the milk-sugar crys-
tallizes on cooling.

It forms white, hard, crystalline masses ; it is soluble in about 6
parts of water (at 15° C., 59° F.) and in 1 part of boiling water,
insoluble in alcohol and ether; it is much harder than cane-sugar,
and but faintly sweet; it is not easily brought into alcoholic fermen-
tation by the action of yeast, but easily undergoes " lactic fermenta-
tion" when cheese is added. During this process milk-sugar is

CARBOHYDRATES. 535

converted into lactic acid. By hydrolysis, lactose is split into dextrose
and galactose.

Milk-sugar resembles dextrose in its action on alkaline solution of
copper, from which it precipitates cuprous oxide ; it differs from it by
not fermenting with yeast, and in forming mucic acid when heated with
nitric acid.

Polysaccharid.es.

To the poly saccha rides belong the starches, gums, cellulose, glyco-
gen, etc. They differ from the two previous groups by being insoluble
in water or soluble with difficulty ; by not crystallizing and not being
diffusible. These latter properties are generally characteristic of sub-
stances of high molecular weight. By hydrolysis polysaccharides split,
forming dextrins, disaccharides, and monosaccharides ; their general
composition is indicated by (C6H10O5)X, which means that the mole-
cules are made up of an unknown multiple of C6H10O5. The consti-
tution is unknown.

Starch, Amylum, (C6H10O5)X. Starch is very widely distributed
in the vegetable kingdom, and is found chiefly in the seeds of cereals
and leguminosa?, but also in the roots, stems, and seeds of nearly all
plants.

It is prepared from wheat, potatoes, rice, beans, sago, arrow-root,
etc., by a mechanical operation. The vegetable matter containing
the starch is comminuted by rasping or grinding, in order to open
the cells in which it is deposited, and then steeped in water; the
softened mass is then rubbed on a sieve under a current of water
which washes out the starch, while cellular fibrous matter remains on
the sieve; the starch deposits slowly from the washings, and is
further purified by treating it with water.

Starch forms white, amorphous, tasteless masses, which are pecu-
liarly slippery to the touch, and easily converted into a powder; it
is insoluble in cold water, alcohol, and ether; when boiled with water,
it yields a white jelly (mucilage of starch, starch-paste) which cannot
be looked upon as a true solution, but is a suspension of the swollen
starch particles in water ; by continued boiling with much water some
starch passes into solution.

Starch, when examined under the microscope, is seen to consist of
granules differing in size, shape, and appearance, according to the
plant from which the starch was obtained. Concentric layers, which
are more or less characteristic of starch-granules, show that they are
formed in the plant by a gradual deposition of starch matter.

The most characteristic test for starch is the dark-blue color which

536 CONSIDERATION OF CARBON COMPOUNDS.

iodine imparts to it (or better to the mucilage). This color is due to
the formation of iodized starch, an unstable dark-blue compound of
the doubtful composition C6H9IO5L

Starch is an important article of food, especially when associated, as in
ordinary flour, with albuminous substances. In the body starch, as well as
other carbohydrates, must be converted into monosaccharides before being
absorbed. This hydrolysis of starch may be made outside the body acting on
starch paste with some diastatic enzyme, or by prolonged boiling with very
dilute (1 per cent.) mineral acid. The intermediate products of the hydrolysis
are the same in either case. Starch is first converted into soluble starch or
amylo-dextrin, which gives a blue color with iodine ; the soluble starch next
passes into malto-dextrin and ery thro- dextrin, giving a red color with iodine ;
erythro-dextrin passes into malto-dextrin and achroo-dexfrin, giving no color
with iodine, but forming a white precipitate with alcohol. Achroo-dextrin
passes into maltose, and maltose into dextrose. The hydrolysis is a progressive
reaction, all these compounds being present in the solution at one time.

Dextrin, C6H10O5 (British gum). This name is given to a mixture
of the dextrins just mentioned, and formed by hydrolysis of starch
by means of diluted acids, or by subjecting starch to a dry heat of
175° C. (347° F.), or by the action of diastase (infusion of malt) upon
starch. Malt is made by steeping barley in water until it germinates,
and then drying it.

Dextrin is a colorless or slightly yellowish, amorphous powder, re^
sembling gum-arabic in some respects ; it is soluble in water, does not
reduce alkaline copper solution, and is colored light wine-red by iodine.
It is extensively used in mucilage as a substitute for gum-arabic.

Gums. These are amorphous substances of vegetable origin,
soluble in water or swelling up in it, forming thick, sticky masses;
they are insoluble in alcohol, and are converted into glucose by boil-
ing with dilute sulphuric acid. Some gums belong to the saccharoses,
others to the amy loses.

Acacia, Gum-arabic is a gummy exudation from Acacia Senegal ;
it consists chiefly of the calcium salt of arable acid, C12H22OU. Other
gums occur in the cherry tree, in linseed or flaxseed, in Irish moss,
in marsh-mallow root, etc.

Gum-arabic dissolves slowly in 2 parts of water ; this solution
shows an acid reaction with litmus, and yields precipitates with lead
acetate or ferric chloride.

Cellulose (C6H10O5)X, perhaps C18H30O15 (Plant fibre, Lignin).
Cellulose constitutes the fundamental material of which the cellular
membrane of vegetables is built up, and forms, therefore, the largest
portion of the solid parts of every plant ; it is well adapted to this
purpose on account of its insolubility in water and most other sol-

CARBOIIYDRA TES. 537

vents, its resistance to either alkaline or acid liquids, and its tough
and flexible nature. Some parts of vegetables (cotton, hemp, and
flax, for instance) are nearly pure cellulose.

Pure cellulose is a white, translucent mass, insoluble in all the
common solvents. It is not colored blue by iodine.

The best solvent for cellulose is an ammoniacal solution of copper hydrox-
ide, known as Schweizer's reagent, a very efficient preparation of which is
obtained as follows : 2 grammes of pure crystallized copper sulphate are dis-
solved in 100 c.c. of water to which a few drops of a concentrated solution of
ammonium chloride have been added. 1 gramme of potassium hydroxide is
dissolved in 100 c.c. of water and a little of a solution of barium hydroxide
added to precipitate any carbonate in the alkali. The two solutions are mixed
and the precipitate thoroughly washed by decantation and on the filter-paper.
The moist copper hydroxide is finally covered in a beaker with just enough
concentrated ammonia water to dissolve it. The clear solution is decanted or
filtered through glass wool. It must be preserved in a dark place.

Cellulose is precipitated from its solution in Schweizer's reagent by acids as
a gelatinous mass which forms a grayish powder when dried.

Treated with concentrated sulphuric acid it swells up and gradu-
ally dissolves ; water precipitates from such solutions a substance
known as amyloid, which is an altered cellulose giving a blue color
with iodine. Upon diluting the sulphuric acid solution with water
and boiling it, the cellulose is gradually converted into dextrin and
dextrose.

Unsized paper (which is chiefly cellulose), dipped into a mixture
of two volumes of sulphuric acid and one volume of water, forms,
after being washed and dried, the so-called " parchment paper,"
which possesses all the valuable properties of parchment.

Official purified cotton, known commercially as absorbent cotton, is prepared
from raw cotton by boiling it in a weak solution of alkali to remove fatty
matter, then treating it with a weak solution of chlorinated lime to bleach it,
It is then washed and dried.

Medicated cotton is usually prepared by impregnating absorbent cotton with
a solution of the medicinal agent in alcohol and glycerin, and drying. The
glycerin is not volatilized and serves as an adhesive agent for retaining the
active ingredient on the fiber of the cotton. Benzoated, borated, carbolated,
iodized, salicylated, and other medicated cotton is prepared in this or a simi-
lar manner. The percentage of medicinal agent present must be calculated on
the basis of finished product ; thus, 25 grammes of 10 per cent, borated cotton
should contain 2.5 grammes of boric acid, or 10 grammes of 5 per cent, carbo-
lated cotton should contain 0.5 gramme of pure carbolic acid.

Pyroxylin, Pyroxylinum, chiefly cellulose tetm-nitrate, C12H16O6-
(NO3)4. (Soluble gun-cotton, Nitro-cellulose.) Cellulose has the

538 CONSIDERATION OF CARBON COMPOUNDS.

power to unite with acids to form ethereal salts (esters), thus exhibit-
ing alcoholic character. When immersed in varying mixtures of con-
centrated nitric and sulphuric acids, and for different lengths of time,
di-, tri-, tetra-, penta-, and hexa-nitrate are formed, thus :

C12H20010 + 2HNO, - 2H20 + CuH18O8(NO,)a.
C12H20010 + 4HN08 - 4H20 + CUH16O6(NOS)4.
C12H20010 + 6HN03 = 6H20 + CUHMO4(N08)6.

The sulphuric acid used takes no part in the reaction, but facilitates
the same by absorbing the water which is eliminated.

The di-, tri-, and tetrad-nitrate are soluble in a mixture of alcohol
and ether, which solution is known as collodion. These lower soluble
nitrates, better known as collodion cotton, are official in the U. S.
and British Pharmacopoeias as pyroxylin ; -colloxylin is also used as a
synonym in this country. In Europe, pyroxylin is applied to the
higher (penta- and hexa-) nitrates, which are insoluble in a mixture
of alcohol and ether, while colloxylin is applied to the soluble collo-
dion cotton. The penta- and hexa-nitrates form the highly explosive
gun-cotton. A solution of collodion cotton in molten camphor hard-
ens upon cooling and is then known as celluloid. When warmed it
becomes plastic and can be molded into various shapes.

Flexible collodion is a mixture of collodion, castor oil, and Canada
balsam, which is much less constringent than official collodion. Can-
tharidal (blistering) collodion contains extract of cantharides and has
blistering properties. Styptic collodion contains tannin. For medi-
cation, any substance, soluble in ether, may be added to collodion,
such as iodine, iodoform, salicylic acid, croton oil, extract of Indian
cannabis, mercuric chloride, resorcin, pyrogallol, atropine, etc.

Smokeless gunpowder is gun-cotton, first made gelatinous by
acetone, acetic ether, or like substances, then dried and granulated.
Smokeless powder occupies less space and burns more slowly than
gun-cotton.

Experiment 65. Immerse 2 grammes of dry cotton for ten hours in a pre-
viously cooled mixture of 28 c.c. of nitric acid and 44 c.c. of sulphuric acid.
Wash the pyroxylin thus obtained with cold water until the washings have no
longer an acid reaction. Dissolve 1 gramme of the dry pyroxylin in a mixture
of 25 c.c. of ether and 8 c.c. of alcohol. The solution obtained is collodion.

Pyroxylin in well-closed bottles exposed to light decomposes with
evolution of nitrous vapors and a carbonaceous mass is left. It
should be kept dry and in a carton. The compound ether nature of
all cellulose nitrates is shown by the fact that the nitric acid is elimi-

CARBOHYDRATES. 539

nated and cellulose reformed by the action of alkalies, of concentrated
sulphuric acid, and by reducing agents. Treated with a solution of
a ferrous salt in hydrochloric acid, they decompose just as any
nitrate, liberating nitric oxide gas.

Glycog-en (C6H10O5)X. Found exclusively in animals ; it occurs in
the liver, the white blood-corpuscles, in many embryonic tissues, and
in muscular tissue. Pure glycogen is a white, starch-like, amorphous
substance, insoluble in alcohol. It forms an opalescent solution with
water, gives a red color with iodine, and by hydrolysis is converted
into glucose.

Glucosides. This term is applied to a group of substances (chiefly
of vegetable origin) which, by the action of dilute acids or enzymes,
are decomposed with the production of a sugar, and one or two other
substances not carbohydrates. To this class of bodies belong amyg-
dalin, digitalin, indican, myronic acid, salicin, etc. Some of these
compounds will be considered later on.

49. COMPOUNDS CONTAINING NITROGEN.
Organic compounds may contain nitrogen in three forms, viz., as
nitric (or nitrous) acid, ammonia, cyanogen, or derivatives of these
compounds.

Derivatives of nitric acid.

Organic compounds containing nitrogen in the nitric acid form do
not occur in nature, but are obtained exclusively by artificial means,
often by treatment of the organic substance with concentrated nitric
acid. Many of these compounds are highly combustible or more or
less explosive, as, for instance, cellulose trinitrate, mercuric fulminate,
and others.

QUESTIONS. — To which group of substances is the term " carbohydrates "
applied ? State the general properties of carbohydrates. Mention the three
groups of carbohydrates, and the composition and characteristics of the mem-
bers of each group. Mention some fruits in which grape-sugar, and some
plants in which cane-sugar is found. What is the difference between grape-
sugar and cane-sugar, and by what tests can they be distinguished ? From
what source, and by what process, is milk-sugar obtained ? What is starch,
what are its properties, by what tests can it be recognized, and what substance
is formed when diastase or dilute acids act upon it ? Where is cellulose found
in nature, and what are its properties? What compounds may be obtained by
the action of nitric acid upon cellulose, and what are they used for? What
substances are termed glucosides ? Mention some of the more important glu-
cosides.

540 CONSIDERATION OF CARBON COMPOUNDS.

Nitric or nitrous acid may combine with organic bases, forming
salts, such as strychnine nitrate, urea nitrate, etc. ; or with alcohols
when esters result, such as glyceryl nitrate, ethyl nitrite, etc. Some
of these compounds have been considered before.

Nitro compounds. These consist of radicals in combination with the
nitric acid residue N02 ; thus, R.NO2. They are isomeric with the esters of
nitrous acid, but behave quite differently from these; for instance, they yield
no alkali nitrite when treated with alkalies, as is the case when esters are thus
treated. The difference in structure is represented thus :

K— O— NO, R— NO2,

Nitrite. Nitro compound.

The highly important nitro compounds of the benzene series can be
obtained by treating the hydrocarbons directly with nitric acid; thus:

C6H6 + HON02 = C6H5N02 + H2O.

Nitric acid does not react with fatty hydrocarbons, but their nitro deriva-
tives can be obtained by indirect processes, for instance, by treating the halo-
gen derivatives with silver nitrite:

CH3C1 + AgNO2 r= CH3N02- + AgCl
Methyl chloride. Nitro-me thane.

This reaction is anomalous, since we would expect to obtain a true ester of
nitrous acid, corresponding to silver nitrite, whereas the resulting product is
not an ester, but a uitro compound. A rearrangement takes place during the
reaction of the two substances on each other. Other cases of this kind are
known, for example, the formation of organic isocyanides (which see) from
silver cyanide.

Nitroso and isonitroso compounds. While compounds containing the
group — NO2 are called nitro compounds, those containing the group — NO are
termed nitroso derivatives, and those containing = N — OH are known as iso-
nitroso derivatives.

When a compound containing the group = CH — is treated with nitrous acid
a reaction takes place which results in the formation of a nitroso compound,
thus :

E3.CH + HNO2 R3.C.NO + H2O.

Nitroso compound.

Isonitroso compounds are formed by the action of hydroxylamine on alde-
hydes or ketones :

H2NOH + £>CO = ^>C = N — OH + H2O.

Hydroxylamine. Ketone. Isonitroso compound.

Isonitroso compounds are isomeric with nitroso compounds; the different
linkage of carbon and nitrogen in the two classes of compounds is indicated in
the two equations given above.

Both nitro and nitroso compounds, when treated with nascent hydrogen,
yield ammonia derivatives, as will be shown later. Isonitroso compounds are

COMPOUNDS CONTAINING NITROGEN. 541

also termed oximes ; those obtained from aldehydes are designated as aldoxiine* ;
those derived from ketones as acetoximes, or ketoximes.

C=N— OH
Fulminio acid, C2N2O2H2, || , seems to be an isonitroso com-

C=N— OH

pound. The free acid is extremely unstable, but some of its metallic salts are
well known, especially mercuric fulminate, which is used as an explosive in per-
cussion caps, etc. It is made by adding alcohol to a solution of mercury in
nitric acid. Silver fulminate can be obtained by a similar process.

Ammonia derivatives.

Several groups of organic compounds are known, which are formed
by replacement of hydrogen in ammonia by different radicals. Ac-
cording to the nature of the latter the compounds are known as
(tin hies, amides, or amino acids, respectively. There are, however,
other compounds, such as the proteins, containing nitrogen in the am-
monia form, which do not belong to either one of these three groups.

Formation of amines and amides. These substances are found
as products of animal life (urea), of vegetable life (alkaloids), of
destructive distillation (aniline, pyridine), of putrefaction (ptomaines),
and may also be produced synthetically — for instance, by the action
of ammonia upon the chloride or iodide of an alcohol or acid radical:
C2H3.I + NH3 = HI + NH2C2H5.

Ethyl iodide. Ammonia. Hydriodic Ethylamine.
acid.

C2H3O.C1 -f 2NH3 = NH4C1 -f NH2.C2HSO.

Acetyl Ammonia. Ammonium Acetamide.

chloride. chloride.

By using in the above reaction two or three molecules of ethyl
iodide for one molecule of ammonia, diethyl or triethyl amine is
formed.

Amines may also be formed by the action of nascent hydrogen
upon the cyanides of the alcohol radicals :

CH3CN + 4H = NH2.C2H5.
Methyl cyanide. Ethyl amine.

They are also formed by the action of nascent hydrogen upon
nitro-compounds ; the manufacture of aniline depends on this de-
composition :

C6H5N02 + 6H = 2H20 + NH2 C6H5.
Nitro-benzene. Hydrogen. Water. Phenylamine,

or aniline.

Occurrence of organic bases in nature. The various organic
basic substances found in nature are either amines or amides. But

542 CONSIDERATION OF CARBON COMPOUNDS.

a small number of organic bases is found in the animal system,
urea being the most important one. In plants organic bases are
frequently met with, and are grouped together under the name of
alkaloids. While the constitution of many alkaloids has not yet
been sufficiently explained, we know that many of them are deriv-
atives of aromatic compounds, for which reason the consideration of
the whole group will be deferred until benzene and its derivatives
are spoken of. The large number of basic substances found in putre-
fying matter and termed ptomaines will also be considered later on.

^xll /G%H§ /xC2H5 //C2H5 /C H3

\ TT \ rT \ TT \O TT \/^ TT

U2-tL5 ^4*19

Or

NH3, N(C2H5)FT2) N(C2H5)2H, N(C2H5V NCH3.C2H5 C4H9.

Ammonia. Ethylamine. Diethylamine. Triethylamine. Methyl-ethyl-butylamine.

The above formulas show that by replacement of either 1, 2, or 3
hydrogen atoms, mono-, di-, or tri-amines are obtained. These are
also sometimes designated as primary, secondary, and tertiary amines,
respectively. Primary ajnines may also be considered as hydrocar-
bons, with one hydrogen atom replaced by the radical NH2, which is
called the amine- or amino-group, and compounds containing it are
designated as amino compounds. Thus, CH3NH2 is amino-methane,
or methyl-amine. The radical NH is known as the imine- or imino-
group, and as this group occurs in secondary amines, these are also
termed imino compounds.

Amines resemble ammonia in their chemical properties ; they are,
like ammonia, basic substances; they combine with acids, directly
and without elimination of water, thus :

NH3 + HC1 = NH4C1;

N(C2H5)3 + HC1 = N(C2H5)3HC1.
Triethylamine. Triethylamine

chloride.

The methyl amines are gases at ordinary temperature; the ethyl amines are
liquids. Many of them are inflammable ; they have a strong ammoniacal,
fishy odor, are readily soluble in water, have strong basic properties (some of
them more so than ammonia), and precipitate metallic salts like ammonia.

The most important reaction of primary amines is that taking place with
nitrous acid, thus :

CH3NH2 + HONO = CH3NH3ONO = CH3OH + H2O + 2N.

Methyl Nitrous Methyl

amine. acid. alcohol.

The reaction shows the possibility of replacing the amino group, NH2, by
hydroxyl, which in this way may be introduced into various compounds. The

COMPOUNDS CONTAINING NITROGEN. 543

reaction is analogous to the decomposition of ammonium nitrite by heat, thus :
NH4ONO == HOH + H20 + 2N.

Aromatic amines behave differently toward nitrous acid, as will be shown
later.

Another characteristic reaction which, as in the previous case, distinguishes
primary from the other amines, is that with chloroform and alkalies, giving rise
to the formation of iso-nitriles, substances having a most disagreeable odor.
(See tests for chloroform.) The reaction is this :

C2H5NH2 + CHC1.3 = C2H5NC + 3HC1.
Ethyl amine. Chloroform. Ethyl isonitrile.

Poly-amines. Whenever two or more ammonia molecules are
linked together by hydrocarbon radicals, this is indicated by desig-
nating them as diamines, triamines, etc.

Diethylene diamine (O2H4)2(NH)2, (Piper azine), is a white, crystalline
substance, used medicinally on account of its solvent action on uric acid.

Hexamethylenamine, Hexamethylenamina, (CH2)6N4 = 139.18
(Hexamdhylene tetramine, Urotropin). This compound results from
the action of ammonia on formaldehyde :

6CH20 + 4NH3 = (CH2)6NA -f- 6H2O.

It is due to this reaction that ammonia is used to remove the
odor of formaldehyde after its use as a disinfectant. The compound
forms colorless, odorless crystals, which are soluble in 1.5 parts of
water; this solution has an alkaline reaction on red litmus. On
heating it sublimes with partial decomposition. When heated with
diluted sulphuric acid, it is decomposed into formaldehyde and
ammonia.

This substance is sold under various trade names, such as cystogen, amino-
form, formin, uritone, urotropin. These are all identical with the official
hexamethylenamine.

Some derivatives of hexamethylenamine have been introduced under
special names, such as salicylate (saliform), bromethylate (bromalin, bromo-
formin), tannate (tannopin or tannon), iodoform (iodoformin).

Amides are substances derived from ammonia by replacement of
hydrogen atoms by acid radicals. Thus :

Ammonia. Acetamide. Diacetamide. Carbamide or urea.

Amides also resemble ammonia in their chemical properties ; to a

544 CONSIDERATION OF C A EBON COMPOUNDS.

less extent, however, than amines, because the acid radicals have a
tendency to neutralize the basic properties of ammonia.

The introduction of an acid radicle into ammonia may be accomplished by
one of three generally applicable methods:

1. By heating the ammonium salt of organic acids,

CH3.COONH4 = CH3.CONH2 + H2O.

Acetamicle.

2. By the action of ammonia on ethereal salts,

CH3,COOC2H5 -f NH3 CII3.CONH2 + G2H5OH.

Ethyl acetate.

3. By the action of ammonia on acid chlorides. This reaction is most fre-
quently used :

CH3.COC1 + NH3 = CH3.CONH2 + HC1. .
Acetyl chloride.

Formamide, H.CONH2, is a colorless liquid, obtained by heating ethyl for-
mate with an alcoholic solution of ammonia. This compound is of interest
because it combines with chloral, forming Chloralformamide, Chloralformami-
dum (CMoralami.de}, H.CONH2.CC13CHO, a substance used as a hypnotic. It
is a colorless, odorless, crystalline substance, having a faintly bitter taste. It
is soluble in about 20 parts of cold water and in 1.5 parts of alcohol. By heat-
ing the aqueous solution to 60° C. (140° F.) it is decomposed into chloral and
formamide.

Amino-acids are acids in which hydrogen has been replaced by
the amino-group, NH2. Consequently, amino-acids bear the same
relation to acids that amines bear to hydrocarbons. Amino-acids
have both acid and basic properties — i. e., they unite with bases to
form salts by replacement of the carboxyl hydrogen ; and they com-
bine with acids to form weak salts ; they also combine with other salts
to form double salts.

Amino-acids may be obtained by the action of ammonia on a halo-
gen derivative of an acid :

CH2C1.CO2H -f 2NH3 = CH2.NH2.CO2H -f NH4C1.
Monochloracetic acid. Ammo-acetic acid.

Amino -acetic acid, obtained as above, is also known as glycocoll
or glycine. It is a product of the decomposition of either glycocholic
or hippuric acid by hydrochloric acid. By oxidation amino-acetic
acid splits up thus :

CH2NH2C02H -f 30 : 2CO2 -f NH3 + H2O.
Amino-acids occur in the animal system, and by oxidation suffer

COMPOUNDS CONTAINING NITROGEN. 545

the change indicated above. Ammonia and carbon dioxide unite to
form ammonium carbamate:

2NH3 + C02 = NH4.NH2.CO2.
By removal f water this salt is converted into urea :
NH4.NH2.COa = (NH2)2CO + HaO.

Amino-formic acid or carbamic acid, NH2.COOH, is the acid
which, in the form of the ammonium salt, is a constituent of the com-
mercial ammonium carbonate. It is formed by the direct action of
carbon dioxide upon ammonia, as shown above.

Urethanes are ethereal salts of carbamic acid, a class of comr
pounds having hypnotic properties. The class name is derived from
one member, which is official and generally known as " Urethane."
It is ethyl urethane, or

Ethyl carbamate, ^Jthylis carbamas, CO.OC2H5.NH2 = 88.42.
Obtained by the action of alcohol on urea or on one of its salts :

It is a white crystalline powder, readily soluble in water, alcohol, or ether.
Heated with solution of potassium hydroxide, ammonia is liberated, while the
addition of sodium carbonate and iodine causes, on warming, the precipitation
of iodoform.

Several similar compounds have been introduced under specific names,
thus: Euphorin, or phenyl-urethane, C6H5NH.COOC2H5, a crystalline powder,
sparingly soluble in cold water; neurodin, or acetyloxyphenyl-urethane,

pr > colorless, sparingly soluble crystals ; thermodm, or phe-

nacetin-urethane, C6H4C^ * <COOC2H ' colorless> verv sparingly sol-

O FT

uble needles ; hedonal, ormethylpropylcarbinol-urethane, NH2.COOCH<Q jj

a difficultly soluble white powder.

The amino-acids and acid-amides are of considerable interest because many
products of animal and plant life belong to these classes of compounds. Some
of these are considered in the subsequent chapters on Physiological Chemistry,
but may be briefly mentioned here.

Sarcosine, Methyl-glycocoll, CI^NH.CI^CC^H, a product of the
decomposition of creatine, which is found in flesh, and of caffeine, and may be
obtained by boiling these compounds with a solution of barium hydroxide. It
is much like glycocoll in properties.

Cystine, (SC(CH3)NH2CO2H.)2, a derivative of a-araino-propionic acid,
sometimes found in the sediment of urine (see Index).
35

546 CONSIDERATION OF CARBON COMPOUNDS.

Leucine, a-amino-caproic acid, CH3.(CH2)3.OH(NH2).CO2H, is widely
distributed in small quantity in glands of animals and in the sprouts of plants.
It is one of the products of the decomposition of albumins and gelatin (see
Index).

Taurine, Amino-ethyl-sulprionic acid, NH2.CH2.CH2.SO3H, is com-
bined with cholic acid to form taurocholic acid, which is one of the constitu-
ents of bile. It forms very stable monoclinic prisms (see Index).

Aspartic acid, Amino-succinic acid, C2H3(NH2).(CO2H)2, occurs in
pumpkin seeds, and is often formed when natural compounds are boiled with
dilute acids. In this manner it may be obtained from casein and albumin. It
forms prisms difficultly soluble in water. When treated with nitrous acid, it
yields malic acid.

CH2.CONH2

Asparagine, Amino-succinamic acid, | occurs in

CH(NH2).CO2H,

asparagus, liquorice, vetches, beans, beets, peas, and in wheat. It forms large
crystals, difficultly soluble in cold water. Boiling with acids or alkalies con-
verts it into aspartic acid and ammonia.

Guanidine, (NH)C(NH2)2, is obtained by the oxidation of guanine which
occurs in guano. Guanine, C5H3(NH2)N4O, is the amirio derivative of xan-
thine (see Index), which is closely related to uric acid, and which is found in
all the tissues of the body and in the urine. Guanidine is an imide of urea,
OC(NH2)2, is strongly alkaline, and when boiled with dilute sulphuric acid or
barium hydroxide solution yields urea and ammonia.

Creatine, Methyl-guanidine-acetic acid, (HN)C<NG|j Q-^ QO,H

is found in the muscles of all vertebrates, and is closely related to guanidine
and to sarcosine. It forms colorless, transparent prisms, soluble in 75 parts
of cold water. When evaporated in dilute acid solution, it loses water to
form the anhydride,

NH-CO

Creatinine, (HN)C\ which forms prisms, readily soluble in

\NCH3-CH2,

water. It is a strong base. It is a constant constituent of urine. Creatine and
creatinine are discussed at greater length further on (see Index).

Urea, Carbamide, CO(NH2)2, is the amide of carbonic acid. It occurs
in the urine and blood of all mammals, particularly of carnivorous animals.
It has been made by various synthetic methods, but is most easily obtained
from urine (see Index). It crystallizes in rhombic prisms, melting at 132° C.,
easily soluble in water and alcohol. When boiled with dilute acids or alka-
lies, it yields carbon dioxide and ammonia, thus :

CO(NH2)2 + H20 : C02 + 2NHS.

Urea unites with acids, thus : urea hydrochloride, CO(NH2)2.HC1 ; urea ni-
trate, CO(NH2)2.HNO3, which is difficultly soluble in nitric acid; urea phos-

COMPOUNDS CONTAINING NITROGEN. 547

phate, CO(NH,)2.H3PO4. It also unites with metallic oxides, thus : CO(NH3)a.-
HgO, and also with salts, of which HgCl2.CO(NH2)2 and HgO.CO(NH2)2.HNO,
are examples.

Ureids. Urea contains ammonia residues and, therefore, acts in many
respects like ammonia. Thus, one or more hydrogen atoms of the NH3 groups
can be replaced by acid radicals, forming compounds analogous to the acid
amides. These are known as ureids. The following ureids are of interest.

CO— NH,

Oxalyl urea, Parabanic acid, | \CO, is formed when uric

CO— NHX

acid is boiled with concentrated nitric acid, and also when a mixture of urea
and oxalic acid is treated with phosphorus oxychloride,POC!3, which abstracts
the elements of water. It acts as an acid, since the hydrogen of the NH group
can be replaced by metals.

Malonyl urea, Barbituric acid, CH2<£JQ~*J|*>CO, like the previous

compound, can also be obtained from uric acid, and synthetically by treating
a mixture of urea and malonic acid with phosphorus oxychloride. It breaks
up into urea and malonic acid when treated with an alkali. Closely related
to it is

Veronal, Diethyl-malonyl urea, c2H5>C<CO— NH>CO' which oc~
curs as a white, faintly bitter, crystalline powder, melting at 191° C., and sub-
lirnable without residue. It is soluble in about 145 parts of water at 20° C., in
about 12 parts of boiling water, and readily in warm alcohol. Veronal is one
of the most valuable hypnotics, being prompt and relatively innocuous in small
doses (8 grains), and dangerous only in large doses.

Uric acid, C5H4N4O3, xanthine, C5H4N4O2, theobromine (dimethyl-xanthine),
C5H3(CH3)2N4O2, and caffeine (theine, trimethyl-xanthine), C5H(CH3)3N4O2 +
H2O, are all interesting and important compounds, but rather complex, for a
discussion of which see Index.

Cyanogen compounds.

Cyanogen itself does not occur in nature, but compounds contain-
ing it are found in a few plants (amygdalin), and also in some animal
fluids (saliva contains sodium sulphocyanate). Gases issuing from
volcanoes (or from iron furnaces) sometimes contain cyanogen com-
pounds. Their formation from inorganic matter can be shown by the
action of ammonia on red-hot charcoal, when ammonium cyanide and
methane are generated :

4NJEL, -f 3C = 2(NH4CN) -j- CH4.

The univalent radical cyanogen, — C = N, or CN, was the first
compound radical distinctly proved to exist by Gay-Lussac in 1814.

548 CONSIDERATION OF CARSON COMPOUNDS.

The name cyanogen signifies " generating blue/' in allusion to the
various blue colors (Prussian and TurnbulPs blue) containing it.

Cyanogen and its compounds show much resemblance to the halo-
gens and their compounds, as indicated by the composition of the
following substances :

C1C1,
Chlorine,

na,

Hydrochloric
acid.

KI,

Potassium
iodide.

HC10,

Hypochlorous
acid.

CNCN,

Cyanogen.

HBr,

Hydrobromic
acid.

KCN,

Potassium
cyanide.

HCNO,

Cyanic acid.

CNC1,

Cyanogen
chloride.

HCN,

Hydrocyanic
acid.

AgCN,

Silver
cyanide.

HCNS,

Sulphocyanic
acid.

Dicyanogen, (CN)2. The unsaturated radical CN does not exist
as such in a free state, but combines whenever liberated with another
CN, forming dicyanogen. It may be obtained by heating mercuric

cyanide :

Hg(CN)2 = Hg + 2CN.

It is a colorless gas, having an odor of bitter almonds, and burn-
ing with a purple flame, forming carbon dioxide and nitrogen; it is
soluble in water, and may be converted into a colorless liquid by
pressure ; it acts as a poison, both to animal and vegetable life, even
when present in but small proportions in the air.

Hydrocyanic acid, HCN = 26.84 (Prussic acid). This compound
is found in the water distilled from the disintegrated seeds or leaves
of amygdalus, prunus, laurus, etc. It is also found among the prod-
ucts of the destructive distillation of coal, and is formed by a great
number of chemical decompositions. For instance :

By the action of ammonia on chloroform :

CHC13 + NH3 : HCN + 3HC1.
Chloroform. Hydrocyanic Hydrochloric

acid. acid.

By heating ammonium formate to 200° C. (392° F.) :

NH4CH02 : HCN + 2H20.
Ammonium Hydrocyanic Water,
formate. acid.

By the action of hydrogen sulphide upon mercuric cyanide :

Hg(CN), + H2S = : HgS + 2HCN.

COMPOUNDS CONTAINING NITROGEN. 549

By the decomposition of alkali cyanides by diluted acids :

KCN 4- HC1 = KC1 + HCN.
By the action of hydrochloric acid upon silver cyanide :

AgCN + HC1 = AgCl -f HCN.
By distilling potassium ferrocyanide with diluted sulphuric acid :

2K4Fe(CN)6 + 6(H2SO4) K2Fe2(CN)6 + 6KHSO4 + 6HCN.

Potassium Sulphuric Potassium ferrous Potassium acid Hydrocyanic

ferrocyanide. acid. ferrocyanide. sulphate. acid.

Experiment 66. Place 20 grammes of potassium ferrocyanide and 40 c.c. of
water into a boiling-flask of about 200 c.c. capacity ; provide the flask with a
funnel-tube and connect it with a suitable condenser, the exit of which should
dip into 60 c.c. of diluted alcohol, contained in a receiver, which latter should
be kept cold by ice during the operation. After having ascertained that all
the joints are tight, add through the funnel-tube a previously prepared mixture
of 15 grammes of sulphuric acid and 20 c.c. of water. Apply heat and slowly
distil until there is little liquid left with the salts remaining in the flask.

Determine the strength of the alcoholic solution of hydrocyanic acid thus
prepared volumetrically and dilute it with water until it contains exactly two
per cent, of HCN.

Pure hydrocyanic acid is, at a temperature below 26° C. (78.8° F.),
a colorless, mobile liquid, of a penetrating, characteristic odor resem-
bling that of bitter almonds ; it boils at 26.5° C. (80° F.) and crystal-
lizes at — 15° C. (5° F.). It is readily soluble in water, and a 2 per
cent, solution is the diluted hydrocyanic acid, Acidum hydrocyanicum
dilutam.

According to the U. S. P., this diluted acid is made by the decom-
position of 6 grammes of silver cyanide by 15.54 c.c. of diluted hy-
drochloric acid, mixed with 44.10 c.c. of water, allowing the silver
chloride to subside and pouring off the clear liquid.

The diluted acid has the characteristic odor of bitter almonds, a
slightly acid reaction, and is completely volatilized by heating. Pure
absolute hydrocyanic acid may be kept unchanged, but when water
or ammonia is present, the acid decomposes comparatively rapidly,
giving ammonia, formic acid, oxalic acid, and other products. The
official 2 per cent, acid deteriorates appreciably within several weeks,
and, therefore, should not be kept in stock for a long time, but should
be prepared as it is needed.

The salts of hydrocyanic acid are called cyanides, and are nearly
all insoluble in water. The cyanides of the alkali metals, the alka-
line-earth metals, and of mercury are soluble.

Dissociation of cyanogen compounds. Hydrocyanic acid is an extremely
weak acid, and its aqueous solution conducts electricity very badly, that is, it

550 CONSIDERATION OF CARBON COMPOUNDS.

has a very low conductivity, due to its extremely small degree of dissociation.
In a tenth-normal solution at 18° C., only 0.01 per cent, of the acid molecules
are dissociated, thus :

HCN ^± H- f CN'.

As in the case of the mercury salts, the poisonous character of hydrocyanic
acid and its salts depends upon the degree of dissociation into CNX ions. A
number of complex cyanides are known, in which the cyanogen groups are
combined with metals to form complex radicals, in which both the cyanogen
and the metals are masked, and do not respond to the usual analytical reagents.
The best examples of such compounds are the ferrocyanide and ferricyanide of
potassium, K4FeCN6 and K3Fe(CN)6, respectively. These compounds are not
poisonous because they do not form CNX ions, being dissociated in solution
according to the following equations :

K4Fe(CN)6 ^± 4K- + Fe(CN)6""

Ferrocyanogen ion.

K3Fe(CN)6 ^± 3K- + Fe(CN)6'"

Ferricyanogen ion.

The alkali cyanides are decomposed by such a weak acid as carbonic acid,
hence they have the odor of hydrocyanic acid, due to the action of the carbonic
acid of the atmosphere. In aqueous solution they have a strong alkaline re-
action, due to hydrolysis :

KCN ;± K- + CN'\ _ TTPV
HOH ^± (OH)/ + H- / '

The action is due to the extremely weak dissociating power of hydrocyanic
acid (see Chapter 15).

For peculiarities of mercury cyanide see chapter on Mercury.

Potassium cyanide, Potassii cyanidum, KCN — 64.7. The pure
salt may be obtained by passing hydrocyanic acid into an alcoholic
solution of potassium hydroxide. The commercial article, however,
Is a mixture of potassium cyanide with potassium cyanate. It is
obtained by fusing potassium ferrocyanide with potassium carbonate
in a crucible, when potassium cyanide and cyanate are formed, while
carbon dioxide escapes, and metallic iron is set free and collects on
the bottom of the crucible. The decomposition is as follows :

K4Fe(CN)6 -f K2CO3 ±= 5KCN + KCNO + Fe + CO2.
Potassium Potassium Potassium Potassium Iron. Carbon

ferrocyanide. carbonate. cyanide. cyanate. dioxide.

A mixture of pure potassium and sodium cyanides, free from cyanate,
is now manufactured on a large scale by heating together anhydrous
potassium ferrocyanide and metallic sodium :

K4Fe(CN)6 -f 2Na = 2NaCN + 4KCN + Fe.

Potassium cyanide, U. S. P., should contain at least 95 per cent, of
potassium cyanide ; it is a white^ deliquescent substance, odorless when

COMPOUNDS CONTAINING NITROGEN. 551

perfectly dry, but emitting the odor of hydrocyanic acid when moist ;
it is soluble in about 2 parts of water ; this solution has an alkaline
reaction but is unstable, decomposition soon taking place with the
formation of potassium formate and ammonia, along with other

products :

KCN + 2H2O = CHK02 + NH3.

A solution of potassium cyanate decomposes slowly in the cold,
but rapidly on heating, with the formation of potassium and ammo-
nium carbonates :

2KCNO + 4H2O = K2CO3 + (NH4)2CO8.

Potassium cyanides and other alkali cyanides show a tendency to
combine with the cyanides of heavy metals, forming a number of
double cyanides, such as the cyanide of sodium and silver, NaCN.
AgCN, etc., which are soluble in water. Hence, precipitates formed by
addition of alkali cyanides to solutions of metallic salts, are dissolved
in excess of the reagent. Double cyanides of silver and gold are used
in commercial electroplating. A large proportion of the alkali cyanides
manufactured is used in extracting gold from its ores, especially in
Transvaal. In 1889 not more than 50 tons of cyanide per annum
were consumed, while in 1905 the consumption was about 10,000 tons,
one-third of which was used in Transvaal.

Silver cyanide, Argenti cyanidum, AgCN = 132.96. A white
powder, obtained by precipitating a solution of potassium cyanide
with silver nitrate. It is insoluble in water, slowly soluble in ammonia
water, sodium thiosulphate, and potassium cyanide • when heated it
evolves cyanogen, metallic silver being left.

Mercuric cyanide, Hg(CN)2. A white crystalline salt, obtained by
dissolving mercurous oxide in hydrocyanic acid ; it is soluble in water
and alcohol and evolves cyanogen when heated.

Mercuric oxycyanide, Hg(ON)2.HgO. (Basic mercuric cyanide.) This is
obtained by triturating mercuric oxide, dilute sodium hydroxide solution, and
mercuric cyanide until the mixture becomes colorless. The salt is purified by
washing with cold water, or recrystallizing from hot water. It occurs as a
white, crystalline powder, soluble in 17 parts of water, and turns red litmus
blue. It is recommended as a substitute for mercuric chloride, as it is claimed
to have greater antiseptic power, to be less irritating, and to have no corroding
action on steel instruments.

Analytical reactions for hydrocyanic acid.

(Potassium cyanide, KCN, may be used.)

1. Hydrocyanic acid, or soluble cyanides, give with silver nitrate
a white precipitate of silver cyanide, which is sparingly soluble in

552 CONSIDERATION OF CARBON COMPOUNDS.

ammonia, soluble in alkali cyanides or thiosulphates, but insoluble
in diluted nitric acid.

HCN + AgNO3 = AgCN -f HNO3.

2. Hydrocyanic acid, mixed with yellow ammonium sulphide and
evaporated to dry ness, forms sulphocyanic acid, which, upon being
slightly acidulated with hydrochloric*acid, gives with ferric chloride
a blood-red color of ferric sulphocyanate. (Excess of ammonium
sulphide must be avoided.)

3. Hydrocyanic acid, or soluble cyanides, give, when mixed with
ferrous and ferric salts and potassium hydroxide, a greenish precipi-
tate, which, upon being dissolved in hydrochloric acid, forms a pre-
cipitate of Prussian blue, Fe4(FeC6]S"6)3. This reaction depends on
the formation of potassium ferrocyanide by the action of the cyanogen
upon both the potassium of the potassium hydroxide and the iron of
the ferrous salt. In alkaline solutions, the blue precipitate does not
form, for which reason hydrochloric acid is added.

4. Hydrocyanic acid heated with dilute solution of picric acid gives
a deep-red color on cooling.

In cases of poisoning, the matter under examination is distilled (if neces-
sary after the addition of water) from a retort connected with a cooler. To
the distilled liquid the above tests are applied. If the substance under ex-
amination should have an alkaline or neutral reaction, the addition of some
sulphuric acid may be necessary in order to liberate the hydrocyanic acid.
The objectionable feature to this acidifying is the fact that non-poisonous
potassium ferrocyanide might be present, which upon the addition of sulphuric
acid would liberate hydrocyanic acid. In cases where the addition of an acid
becomes necessary, a preliminary examination should, therefore, decide
whether or not ferro- or ferricyanides are present.

Antidotes. Hydrocyanic acid is a powerful poison both when inhaled or
swallowed in the form of the acid or of soluble cyanides. As an antidote is
recommended a mixture of ferrous sulphate and ferric chloride with either
sodium carbonate or magnesia. The action of this mixture is explained ia
the above reaction 3, the object being to convert the soluble cyanide into an
insoluble ferrocyanide of iron. In most cases of poisoning by hydrocyanic
acid there is, however, no time for the action of such an antidote, in conse-
quence of the rapidity of the action of the poison, and the treatment is chiefly
directed to the maintenance of respiration by artificial means.

About ten years ago, hydrogen dioxide was proposed as an antidote, by
which hydrocyanic acid is converted into the harmless oxamide, CONH2 —
CONH2. A solution of hydrogen dioxide is introduced into the stomach and
then siphoned out. It is also used subcutaneously. In case a cyanide is the
poison, vinegar may be mixed with the hydrogen dioxide solution given inter-
nally in order to liberate the hydrocyanic acid.

Cyanogen derivatives obtained directly from nitrogen of the atmos-

COMPOUNDS CONTAINING NITROGEN. 553

phere. When calcium carbide is heated 'to redness in contact with nitrogen,
calcium cyanamide is formed, thus :

CaC2 + 2N = CN.NCa + C.

This substance is an excellent fertilizer, and is manufactured in large quanti-
ties and sold under the name of nitrolim or lime-nitrogen (Kalkstickstoff). It
is slowly decomposed in the soil by moisture and carbon dioxide into calcium
carbonate and cyanamide :

CN.NCa 4- H20 -f CO2 = CaCO3 + CN.NH2.
The cyanide is further decomposed probably into urea :
CN.NH2 -f H20 = CO(NH2)2.

Steam under high pressure converts all of the nitrogen of calcium cyanamide
into ammonia, which thus furnishes a method of obtaining ammonia from at-
mospheric nitrogen.

When mixed with sodium carbonate and fused, calcium cyanamide forms
sodium cyanide. By the action of acids on the calcium compound, cyanamide,
CN.NH2, is formed, which easily polymerizes to the beautifully crystallized
dicyandiamide, C2N2.N2H4, which is now made by the ton and used for various
purposes. It can very easily be made to unite with water to form urea, which
is manufactured thus in great quantities.

Barium carbide, when heated in nitrogen, acts differently from calcium car-
bide, forming barium cyanide, thus:

BaC2 + 2N = Ba(CN)2.

Cyanic acid, HCNO, and Sulphocyanic acid, HCNS, are both
colorless acid liquids, the salts of which are known as cyanates and
mlpho-cyanates. These salts are obtained from alkali cyanides by
treating them with oxidizing agents or by boiling their solutions with
sulphur, when either oxygen or sulphur is taken up by the alkali
cyanide :

KCN + O = KCNO = Potassium cyanate.

KCN -f S = KCNS = Potassium sulphocyanate.
The acids themselves are obtained by indirect processes, as they
decompose when the salts are treated with mineral acids. Sulpho-
cyanates give with ferric salts a deep-red color, which is not affected
by hydrochloric acid, but disappears on the addition of mercuric
chloride.

Metallocyanides. Cyanogen not only combines with metals to
form true cyanides, which may be looked upon as derivatives of
hydrocyanic acid, but cyanogen also enters into combination with
certain metals (chiefly iron), forming a number of complex radicals,
Which upon combining with hydrogen form acids, or with basic
elements form salts. It is a characteristic feature of the compound
cyanogen radicals, thus formed, that the analytical characters of the

554 CONSIDERATION OF CARBON COMPOUNDS.

metals (iron, etc.) entering into the radical are completely hidden.
Thus, the iron in ferro- or ferricyanides is not precipitated by either
alkalies, soluble carbonates, ammonium sulphide, or any of the com-
mon reagents for iron, and its presence can only be demonstrated by
these reagents after the organic nature of the compound has been
destroyed by burning it (or otherwise), when ferric oxide is left,
which may be dissolved in hydrochloric acid and tested for in the
usual manner.

The principal iron-cynogen radicals are ferrocyanogen [Feu
(CN),,1]*, and ferricyanogen [Fe^CNy]111. These two radicals con-
tain iron in the ferrous and ferric state respectively, and form, upon
combining with hydrogen, acids which are known as hydroferroeyanic
acid, H4Fe(CN)6 (tetrabasic), and hydroferricyanic acid, H3Fe(CN)g
(tribasic) ; the salts of these acids are termed ferrocyanides and ferri-
cyanides. (For dissociation of these, see p. 549.)

Potassium ferrocyanide, Potassii ferrocyanidum, K4Fe(CN)6.
3H2O = 419.62 ( Yellow prussiate of potash). This salt is manu-
factured on a large scale by heating refuse animal matter (waste
leather, horns, hoofs, etc.) with potassium carbonate and iron (filings,
etc.). The fused mass is boiled with water, and from the solution
thus formed the crystals separate on cooling.

The nitrogen and carbon of the organic matter (heated as above
stated) combine, forming cyanogen, which enters into combination
first with potassium and afterward with iron.

Potassium ferrocyanide forms large, translucent, pale lemon-yellow,
soft, odorless, non-poisonous, neutral crystals, easily dissolving in
water, but insoluble in alcohol.

Analytical reactions :

1. Ferrocyanides heated on platinum foil burn and leave a residue
of (or containing) ferric oxide.

2. Ferrocyanides heated with concentrated sulphuric acid evolve
carbonic oxide ; with dilute sulphuric acid liberate hydrocyanic acid ;
with concentrated hydrochloric acid liberate hydroferroeyanic acid.

3. Soluble ferrocyanides give a blue precipitate with ferric salts
(Plate L, 5) :

3K4Fe(CN)6 + 4FeCl3 = 12KC1 + Fe4(FeC6N8)3.

Potassium Ferric Potassium Ferric ferro-

ferrocyanide. chloride. chloride. cyanide.

The blue precipitate of ferric ferrocyanide, or Prussian blue, is
insoluble in water and diluted acids, soluble in oxalic acid (blue

COMPOUNDS CONTAINING NITROGEN. 5§5

ink), and is decomposed by alkalies with separation of brown ferric
hydroxide and formation of potassium ferrocyanide. The addition
of an acid restores the blue precipitate.

4. Soluble ferrocyanides give with cupric solutions a brownish-red
precipitate of cupric ferrocyanide. (Plate III., 5.)

5. Soluble ferrocyanides produce, with solutions of silver, lead, and
zinc, white precipitates of the respective ferrocyanides.

6. Ferrocyanides give with ferrous salts a white precipitate of
ferrous ferrocyanide, soon turning blue by absorption of oxygen.
(Plate I., 4.)

Potassium ferricyanide, K3Pe(CN)G (Red prussiate of potash). Ob-
tained by passing chlorine through solution of potassium ferrocyanide:

K4Fe(CN)6 -f Cl = KC1 + K3Fe(CN)6.

Potassium Chlorine. Potassium Potassium

ferrocyanide. chloride. ferricyanide.

While apparently this decomposition consists merely in a removal
of one atom of potassium from one molecule of potassium ferro-
cyanide, the change is actually more complete, as the atoms arrange
themselves differently, the iron passing also from the ferrous to the
ferric state.

Potassium ferricyanide crystallizes in red prisms, soluble in water.
It forms, with ferrous solutions, a blue precipitate of ferrous ferricy-
anide, or TurnbuWs blue :

2K3Fe(CN)6 + 3FeSO4 = 3K2SO4 + Fe3Fe2(CN)12.

With ferric solutions no precipitate is produced by potassium ferri-
cyanide, but the color is changed to a deep brown.

Sodium nitroferricyanide, Na2Fe(CN)5N0.2H2O. (Sodium nitroprusside.)
This is a salt of nitroferricyanic acid, which is obtained by the action of nitric
acid on potassium ferrocyanide. Potassium nitrate is crystallized out by con-
centrating and cooling the solution, which is then neutralized by sodium car-
bonate, and the sodium salt crystallized. Addition of alcohol increases the
separation of potassium nitrate. The salt forms large ruby-red crystals, solu-
ble in 2.5 parts of water and in alcohol. The aqueous solution decomposes on
standing. It serves as a delicate test for soluble sulphides (but not free H2S),
giving a purple color which quickly passes into violet. It is also used as a test
for acetone (Legal's test).

Cyanides and isocyanides of organic radicals. Only one form of hydro-
cyanic acid and of metallic cyanides is known, but among organic cyanide*
two isomeric forms exist, known respectively as cyanides or nitrites, and isocyan-
ides or carbylamines. Experiments show that the constitution of these com-
pounds is represented by the formulas :

R-C=N,

Cyanide. Isocyanide.

556 CONSIDERATION OF CARBON COMPOUNDS.

In one case the organic radical is in combination with carbon ; in the other,
with nitrogen. These compounds are apparently esters of hydrocyanic acid,
but they behave quite differently from esters, as they do not yield alcohols or
metallic cyanides on treatment with alkalies.

Cyanides or nitriles. These may be formed by heating together iodides
of hydrocarbon radicals with potassium cyanide :

CH8I + KCN = CH3CN + KI.

The cyanides are volatile liquids or solids. When heated with water in
presence of mineral acids or alkalies, they yield organic acids, thus :

CH3.CN + 2H20 = CH3.C02H 4- NH3.
Methyl Acetic acid,

cyanide.

This is an important reaction, as it furnishes a simple means of introducing
carboxyl into compounds, thus forming organic acids. For this reason the
cyanides are called nitriles of the acids, just as the acid oxides are called an-
hydrides of the corresponding acids. Thus, methyl cyanide is called aceto-
nitrile, because it yields acetic acid. In fact, the ammonium salts of organic
acids, by abstraction of water, yield cyanides :

CHS.CO2NH4 = CH8.CN + 2H2O.

Isocyanides or carbylamines. These compounds are distinguished by a
disgusting odor. They are formed by heating silver cyanide, instead of potas-
sium cyanide, with iodides of hydrocarbon radicals, thus :

CH3I + AgCN = CH3NC + Agl.

It is strange, and as yet not explained, why hydrocarbon iodides produce
cyanides with potassium cyanide, and isocyanides with silver cyanide.

Isocyanides are also formed by heating together chloroform, primary amines,
and an alkali, as shown above in the paragraph on amines.

The isocyanides behave differently from the cyanides when heated with
water and acids, thus :

CH3NC + 2H2O = CH3NH2 + HCO2H.

Methyl Methyl Formic

isocyanide. amine. acid.

Isosulphocyanates or mustard oils. The difference in structure between
sulpho- and iso-sulphocyanates is expressed in the following formulas :

R — S — C^N, sulphocyanate. E — N=C— S, isosulphocyanate.

The organic sulphocyanides are of no importance here. The principal member
of the mustard oils is allyl-isosulphocyanate, C3H5NCS, one of the decomposi-
tion products of myronic acid.

Treated with water and alkali, mustard oils break down, thus :

C^NCS + 2H20 = C3H5NH2 + H2S + CO2.

This reaction is similar to that which takes place in case of isocyanides. (See
above.)

Myronic acid, C10H19NS.2010, is found as the potassium salt, which is known
as sinigrin, in black mustard seed. When treated with solution of myrosin, a

BENZENE SERIES. AROMATIC COMPOUNDS. 557

substance also contained in mustard seed and acting as a ferment upon myronic
acid or its salts, potassium myronate is converted into dextrose, allyl mustard
oil, and potassium bisulphate.

KC10H18NS2010 == C6H1206 + C3H5NCS -f KHSO4.

Potassium Dextrose. Allyl mustard Potassium

myronate. oil. bisulphate.

Allyl mustard oil, C3H5NCS. Mustard oils are esters of isosulphocyanic
acid, HNCS. Ordinary mustard oil, obtained from sinigrin, as stated above,
contains the radical allyl, derived from the unsaturated hydrocarbon propylene,
C3H6. The univalent radical allyl is isomeric, but not identical, with the tri-
valent radical glyceryl, C3H5, derived from propane, C3H8. The difference may
be seen from the structural formulas :

— CH2— CH=CH2, allyl. — CH2— CH-CH2— , glyceryl.

The triatomic alcohol glycerin, C3H5(OH)3, may be converted into the
monatomic allyl alcohol, C3H5OH, by various processes. From allyl alcohol
an artificial allyl mustard oil is manufactured.

Mustard oil is a colorless or pale yellow liquid, which has a very pungent
and acrid odor and taste. When brought together with ammonia, direct combi-
nation takes place and crystals of thiosinamine (allyl-thio-urea), CS.N2H3.C3H5,
are formed .•

C3H5NCS + NH3 = CS.N2H3.C3H5.

Allyl sulphide, (C3H5)2S, is the chief constituent of the oil of garlic.

50. BENZENE SERIES. AROMATIC COMPOUNDS.
General remarks. It has been stated before that most organic com-
pounds may be looked upon as derivatives of either methane, CH4,
or benzene, C6H6, these derivatives being often spoken of as fatty and
aromatic compounds respectively. The term aromatic compounds
was given to these substances on account of the peculiar and fragrant
odor possessed by many, though not by all of them. Benzene and

QUESTIONS. — What are the three chief forms in which nitrogen enters into
organic compounds? What are amines and amides; in what respects do they
resemble ammonia compounds ? What is cyanogen, what is dicyanogen, and
how is the latter obtained ? How does cyanogen occur in nature, and which
non-metallic elements does it resemble in the constitution of various com-
pounds ? Mention some reactions by which hydrocyanic acid is formed, and
state the two processes by which the official diluted acid is obtained. What
strength and what properties has this acid ? State the composition of pure
potassium cyanide and of the commercial article. How is the latter made ?
Give reactions for hydrocyanic acid and cyanides. Explain the constitution
and give the composition of ferro- and ferricyanides. Give composition, mode
of manufacture, and tests of potassium ferrocyanide. What is red prussiate
of potash, how is it obtained, and by what reactions can it be distinguished
from the yellow prussiate ?

558 CONSIDERATION OF CARBON COMPOUNDS.

*

methane derivatives differ considerably in many respects, and, as a
general rule, aromatic compounds cannot be converted into fatty
compounds, or the latter into aromatic compounds, without suffering
the most vital decomposition of the molecule, and in many cases this
transformation cannot be accomplished at all.

On the average, aromatic compounds are richer in carbon than fatty
compounds, containing of this element at least G atoms ; when decom-
posed by various methods, aromatic compounds, in many cases, yield
benzene as one of the products ; most aromatic substances have anti-
septic properties, and none of them serves as animal food, although
quite a number are taken into the system in small quantities, as, for
instance, some essential oils, caffeine, etc.

While some aromatic compounds are products of vegetable life,
many of them (like benzene itself) are obtained by destructive distil-
lation, and are, therefore, contained in coal-tar, from which quite a
number are separated by fractional distillation.

Constitution. — There is not known any benzene compound which
has less than six atoms of carbon. In all of the various decomposi-
tions and replacements which occur in the formation of benzene
derivatives, the six carbon atoms persist, like a unit. These condi-
tions have led chemists to look upon the six carbon atoms as being
joined together, forming a nucleus to which other atoms or groups
are attached, in all of the known aromatic compounds. Thus, in
benzene, C6H6, which is the fundamental or mother-substance of
these compounds, the six carbon atoms are joined to six atoms of
hydrogen.

If benzene were of the nature of a fatty compound, we should
expect to find its structure correspond to a formula of this kind :

H H

This representation would indicate that benzene ought to behave
like a highly unsaturated compound. Moreover, we should expect
to obtain two isomeric compounds by replacing either a centrally
located hydrogen atom or one occupying a terminal position.

As a matter of fact, benzene does not behave like an unsaturated
chain compound (although it can be caused to unite directly with
some elements), and by replacement of a hydrogen atom but one kind
of substitution product has ever been obtained. These facts lead us
to believe that benzene is not an unsaturated chain compound, and

BENZENE SERIES. AROMATIC COMPOUNDS. 559

»

that all the hydrogen atoms are equivalent ; in other words, the mole-
cule C6H6 is perfectly symmetrical.

In view of these and many other facts the conclusion is that the
six carbon atoms in benzene are united into a cycle or ring, and that
each carbon atom is in combination with one hydrogen atom. This
view was first put forth by August KekulS in 1865. Graphically
the closed carbon chain and also benzene (usually referred to as
Kekul6's benzene hexagon) are represented thus :

1 H

c/2 H\CAC/H

3 H/ \C^ \

i

This formula for benzene accounts for the facts mentioned above.
Moreover, if two hydrogen atoms are replaced by substituting atoms
or radicals, three isomeric products are obtained.

For instance, we know three different substances which have been
obtained by replacement of two hydrogen atoms in benzene by two
hydroxyl groups. This would indicate that it makes a difference, as
far as the properties of a compound are concerned, in which relative
position the introduced radicals stand to one another, and as a result
of a great deal of investigation it was found that the following
formulas represent the three relative positions which the two replac-
ing groups may occupy in a benzene molecule :

OH OH OH

H^ tf^ X)H Hv ,C.

A > -*

\TT TT/ \C\4>

H H OH

Ortho-position. Meta-position. Para-position.

1:2. 1:3. 1:4-

Designating the hydrogen atoms in benzene with numbers, thus :

122456

C6 H H H H H H, the above 3 compounds show that in one case
the hydrogen atoms 1 and 2, in the second 1 and 3, in the third 1
and 4 have been replaced by OH. The compounds formed in this
way are distinguished as ortho-, ineta-, and para-compounds.

560

CONSIDERATION OF CARBON COMPOUNDS.

The molecular formula of the above three compounds is C6H6O2,
apparently indicating benzene in combination with two atoms of
oxygen or dioxybenzene ; actually they are dihydroxy benzene.

Otfto-dihydroxy benzene, C6H4OHOH, or C6H4(OH)2 1 : 2, is known

1 3

as pyro-catechin, wefa-dihydroxy benzene, C6H4OHOH, or C6H4(OH)2

1 4

1:3, as resorcin, and £>ara-dihydroxy benzene, C6H4OHOH, or
C6H4(OH)2 1 : 4, as hydroquinone.

Benzene derivatives. The analogy existing between methane-
and benzene-derivatives may be shown by comparing the composition
of a few derivatives :

Methane,

CH4

Benzene,

C6H6

Methyl,

CH3

Benzyl,
Phenyl,

}C6H5

Ethane, 1
Methyl-methane, /

CH3.CH3

Toluene,
Methyl-benzene,

}C6H5.CH3

Methyl-hydroxide, \
Methyl-alcohol, /

CH3OH

Phenyl-hydroxide,
Phenol,

} C6H5.OH

/OH

/OU

Glycerin,

C3H5^OH

Pyrogallol,

XOH

SXOH

Acetic acid,

CH3.CO2H

Benzoic acid,

C6H5.CO2H

Acetic aldehyde,

CH3.COH

Benzoic aldehyde,

C6H5.COH

Ethyl-sulphonic acid,

S°2\OH5

Benzene-sulphonic
acid,

SO*\OH5

Malonic acid,

CH /C°2H

Phthalic acid,

C H /C°2H

Tartaric acid,

C2H2/2°2H

Salicylic acid,

c H /'OH

Ethyl ether,

g:pH

Phenyl-ether,

f C6H5\0
lC6H5/°

Methyl-ethyl ether, j

C2H5V°

Methyl-phenyl
ether, anisol,

ic6H53)°

The following graphic formulas may serve to illustrate the consti=
tution of some aromatic compounds :

OH

J

^

A

Benzene, C«H».

C02H

r I

H

i

H

Phenol or carbolic acid, Benzoic acid, C6H5.CO9H.
C6H5.OH.

BENZENE SERIES. AROMATIC COMPOUNDS.
NO, OH

561

H C

\cx

II

H

H

Nitro-benzene, C6H6NOa.

CH

Toluene, methyl-benzene.
C6H6.CH3.

CH3

H

H

Xylene, di-methyl-benzene,

CH,

H

C02H

XC02H

A

H

Resorcin, CeH4(OH)2. Phthulic acid, C0H4(CO2H)a.

H

OH

L

J

OH

\OH

H

OH

I

C02]

Pyrogallol, C6H3(OH)3. Galb'c acid, C6H2.CO2H.(OH),.

OH
H\A

OH

H

/

XCH3
\H

H

H

/

H

Cresol, C6H4.CH3.OH.

CH

Salicylic acid, C6H4.CO2H.OH.
COH

\

\^f

i3H7

H

Cymene, methyl-propyl benzene. Thymol, C6H3CH3.C8H7.OH. Benzaldehyde, oil of bitter
C6H4 CH3.C3H7. almond, C6H6.COH.

The preceding graphic formulas show in the first column (besides
nitro-benzene) a number of hydrocarbons, in the second column
phenols, obtained by introducing hydroxyl into the hydrocarbon
molecule, and in the third column chiefly aromatic acids, formed by
introducing carboxyl, CO2H, or carboxyl and hydroxyl.

Differences between aromatic and fatty compounds. Substitution pro-
ducts with nitric acid, sulphuric acid, bromine, hydrocarbon radicals, etc., are
much more easily formed and held much more strongly in aromatic compounds
than in fatty ones. The phenols, which in composition correspond to alcohols,
36

562 CONSIDERATION OF CARBON COMPOUNDS.

are more acid than the fatty alcohols ; aromatic amines are less alkaline than
in the fatty series. The phenols do not form esters like the alcohols.

Fatty amines with nitrous acid yield alcoholic compounds ; aromatic amines
behave quite differently, viz., a new series of bodies, known as diazo compounds,
is formed. Fatty compounds are easily oxidized, while benzene is very stable
in the presence of oxidizing agents.

Benzene series of hydrocarbons.

By replacing the hydrogen atoms in benzene by methyl, CH3, a
series of hydrocarbons is formed having the general composition
CnH2n_6. To this benzene series belong :

Benzene . . . C6H6 B. P. 80.5° C.

Toluene . . . C7H8 = C6H5CH3 110

Xylene . . . C8H10 - = C6H4(CH3)2 141

Cumene . . . C9H12 = C6H8(CH3)8 169

Tetra-methyl-benzene C10HU = C6H2(CH3)4 190

Penta-methyl-benzene C,,H16 = C6H(CH3)5 231

Hexa-methyl-benzene Ci2H18 = = C6(CH3)6 264

The first four members of this series are found in coal-tar ; the
last three have been obtained by synthetical processes. While but
one toluene is known, the higher members form quite a number of
isomeric compounds. Instead of adding two or more methyl groups
it is possible to add an ethyl group, C2H5, or even higher homologous
groups, thus producing a great many isomeric compounds. Thus,
cymene, C10H14, found in the oil of thyme, is not tetra-methyl-ben-
zene, but para-methyl-iso-propyl-benzene, C6H4CH3.C3H7. This com-
pound is of interest on account of its close relation to the terpenes
and camphors, which will be spoken of later.

Benzene, C6H6 (Benzol). When coal-tar is distilled, products are
obtained which are either lighter or heavier than water, and by col-
lecting the distillate in water a separation into so-called light oil
(floating on the water) and heavy oil (sinking beneath the water) is
accomplished. Benzene is found in the light oil and obtained from
it by distillation after phenol has been removed by treatment with
caustic soda and some basic substances by means of sulphuric acid.
Pure benzene may be obtained by heating benzoic acid with calcium
hydroxide :

C6H5.CO2H -f- Ca(OH)2 == CaCO3 + H2O + C6Hfl.

Experiment 67. Mix 25 grammes of benzoic acid with 40 grammes of slaked
lime and distil from a dry flask, connected with a condenser. Add to the dis-
tilled fluid a little calcium chloride and redistil from a small flask. The

BENZENE SERIES. AROMATIC COMPOUNDS. 563

product obtained is pure benzene. Notice that it solidifies when placed in a
freezing mixture of ice and common salt. Observe the analogy between Ex-
periments 67 and 51. In one case a fatty acid is decomposed by an alkali with
liberation of methane, in the other an aromatic acid with liberation of benzene,
tin- carbonate of the decomposing hydroxide being formed in both cases.

Pure benzene is a colorless, highly volatile liquid, having a peculiar,
aromatic odor and a specific gravity of 0.884 ; it boils at 80.5° C.
(177° F.) and solidifies at 0° C. (32° F.) ; it is an excellent solvent
for fats, oils, resins, and many other organic substances.

Nitro-benzene, C6H3.NO2. When benzene is treated with concen-
trated nitric acid, or with a mixture of nitric and sulphuric acids,
nitro-benzene is formed .

C6H6 + HN03 == C6H5N02 + H2O.

Experiment 68. Mix 50 c.c. of sulphuric acid with 25 c.c. nitric acid ; allow
to cool, place the vessel containing the mixture in water, and add gradually 5
c.c. of benzene, waiting after the addition of a few drops each time until the
reaction is over. Shake well until all benzene is dissolved and pour the liquid
into 300 c.c. of water. The yellow oil which sinks to the bottom is nitro-
benzene. It may be purified by washing with water and redistilling, after
removal of water and shaking with calcium chloride.

Nitro-benzene is an almost colorless or yellowish oily liquid, which
is insoluble in water, has a specific gravity of 1.2, a boiling-point of
205° C. (401° F.), a sweetish taste, highly poisonous properties, even
when inhaled, and an odor resembling that of oil of bitter almond,
for which it is substituted under the name of essence of mirbane. It
is manufactured on a large scale, and is used chiefly in the preparation
of aniline. Dinitro benzene is also known.

Toluene, C6H5CH3 (Methyl benzene}. This was first obtained by dry distilla-
tion of balsam of tolu, whence its name. It occurs in coal tar, from which it
can be separated, but may also be made from benzene by using a reaction gen-
erally employed for the introduction of the methyl groups, thus:

C6H5Br + CH3Br + 2Na = C6H5CH3 + 2NaBr.

Toluene, as well as the other hydrocarbon derivatives of benzene, possesses
properties of the fatty hydrocarbons as well as benzene properties. This is
quite natural, because of the fatty radicals present in the molecule. Thus,
when oxidized, toluene yields benzoic acid, C6H5CO2H, the methyl being
oxidized while the benzene ring is unchanged.

Xylenes, CeH^CHg^ (Dimethyl benzenes}. Three xylenes are found in coal-
tar, and are distinguished as ortho-, meta-, and para-xylene. They can be
made synthetically from toluene in the same manner as toluene is made from
benzene. When oxidized they yield ortho-, meta-, and para-phthalic acids, of
the composition C6H4(C02H)2.

564 CONSIDERATION OF CARBON COMPOUNDS.

Cymene, C10H14 or CgH^CH^.CgHy (para-methyl-isojjroj^-benzene).
This hydrocarbon occurs in the oil of thyme and in the volatile oils
of a few other plants ; it has also been made synthetically ; it is a
liquid of a pleasant odor, boiling at 175° C. (347° F.).

Cymene is of special interest, because it is closely related to the
terpenes and camphors, from all of which it may be obtained by
comparatively simple processes.

Amino compounds of benzene.

Aniline, Phenyl-amine, C6H5NH2. The constitution of amines,
to which class aniline belongs, has been considered in Chapter 49.
Aniline is found in coal tar and in bone-oil; it is manufactured on
a large scale by the action of nascent hydrogen upon nitro-benzene,
iron and hydrochloric acid being generally used for generating the
hydrogen.

Experiment 69. Dissolve 20 c.c. of nitro-benzene (this may be obtained
according to the directions given in Experiment 68, using larger quantities of
the material) in alcoholic ammonia and pass through this solution hydrogen
sulphide as long as a precipitate of sulphur is produced ; the reaction takes
place thus :

C6H5NO2 -f 3H2S = C6H5NH2 + 2H2O + 3S.

Evaporate on a water-bath to expel ammonium sulphide and alcohol ; add to
the residue dilute hydrochloric acid, which dissolves the aniline, but leaves any
unchanged nitro-benzene undissolved. Separate the nitro-benzene from the
aniline chloride solution, evaporate this to dryness, mix with some lime, in
order to liberate the aniline, which may be obtained by distillation from a dry
flask.

Pure aniline is a colorless, slightly alkaline liquid, having a pecu-
liar, aromatic odor, a bitter taste, and strongly poisonous properties.
It boils at 184.5° C. (364° F.). Like all true amines, it combines
with acids to form well-defined salts.

Aniline dyes. The crude benzene used in the manufacture of aniline
dyes is generally a mixture of benzene, C6H6, and toluene, C7H8.
This mixture is first converted into nitro-benzene, C6H6NO2, and
nitro-toluene, C7H7NO2, and then into aniline, C6H5NH2, and tolu-
idine, C7H7NH2. When these substances are treated with oxidizing
agents, such as arsenic oxide, hypochlorites, chromic or nitric acid,
etc., various substances are obtained which are either themselves dis-
tinguished by beautiful colors or may be converted into numerous
derivatives showing all the various shades of red, blue, violet, green,
etc.

BENZENE SERIES. AROMATIC COMPOUNDS. 565

As an instance of the formation of an aniline dye may be men-
tioned that of roaaniline, which takes place thus:

C6H7N -f 2C7H9N + 30 : C20H19N3 + 3H2O.
Aniline. Toluidine. Rosaniline.

Experiment 70. To some of the aniline obtained by performing Experiment
69 add a little solution of bleaching powder: a beautiful purple color is ob-
tained. Treat another portion with sulphuric acid to which an aqueous solu-
tion of potassium dichromate has been added : a blue color is produced. A
third quantity treat with solution of cupric sulphate and potassium chlorate:
a dark color is the result.

Acetanilide, Acetanilidum, C6H5.NH.(CH3CO) — 134.09, (Anti-
febrine, Phcnylacdamide). The term anilide is used for derivatives
of aniline obtained from this compound by replacement of the am-
monia hydrogen (or amino hydrogen) by acid radicals. If the radical
introduced is acetyl, C2H3O, the resulting compound is acetanilide,

C* TT

the constitution of which is represented in the formula NH^p6TT5r\

It is obtained by boiling together for one or two days equal weights
of pure aniline and glacial acetic acid, distilling and collecting the por-
tion which passes over at a temperature of about 295° C. (563° F.).
The distillate solidifies on cooling and may be purified by recrystalliza-
tion from solution in water. The chemical change taking place is this :

C6H6NH2 + C2H4O2 = C6H5.NH.C2H3O + H2O.

Pure acetanilide forms white odorless crystals of a silky lustre and a greasy
feeling to the touch. It fuses at 113° C. (235° F.) and boils at 295° C. (563° F.) ;
it is but slightly soluble in cold, much more soluble in hot water, readily solu-
ble in alcohol and ether ; the solutions have a neutral reaction and are not
colored by either concentrated sulphuric acid or by ferric chloride.

Analytical reactions:

1 . When 0.1 gramme of acetanilide is boiled for several minutes with
2 c.c. of hydrochloric acid, and to this solution are added 3 c.c. of an
aqueous solution of phenol (1 in 20) and 5 c.c. of a filtered, saturated
solution of bleaching powder, a brownish-red liquid is obtained which
turns deep blue upon supersaturation with ammonia water.

2. On heating 0.1 gramme of acetanilide with a few c.c. of concen-
trated solution (1 in 4) of potassium hydroxide, the odor of aniline
becomes noticeable ; on now adding chloroform, and again heating,
the disagreeable odor of the poisonous phenyl-isocyanide, C6H5NC, is
evolved (distinction from antipyrine).

3. A mixture of equal parts of acetanilide and sodium nitrite

566 CONSIDERATION OF CARBON COMPOUNDS.

sprinkled upon concentrated sulphuric acid produces a bright-red
color.

Compound acetanilide powder, Pulvis acetanilidi compositus, is
a mixture of 70 parts of acetanilide, 10 parts of caffeine, and 20 parts of sodium
bicarbonate. It is one form of the numerous headache powders in the market,
in which acetanilide, the cheapest of the common antipyretics, is a common con-
stituent. Sodium bicarbonate increases the solubility of the acetanilide.

Methyl acetanilide C6H5.N.CH3.C2H30, (Exalgin], may be made by the
acetylating of monomethyl-aniline. It occurs as a crystalline powder or in
large crystalline needles ; it is tasteless and almost insoluble in water.

Sulphanilic acid, Amline-para-sulphonic acid, C8H4.NH,.S03H. Obtained
by heating 1 part of pure aniline oil with 2 parts of fuming sulphuric acid,
and purifying the product by crystallization.

C6H5.NH2 + H2SO, = C6H4.NH2.SO3H + H2O.

It is a colorless crystalline substance, soluble in 182 parts of cold water.
When sulphanilic acid is acted upon by nitrous acid, it is converted into diazo-
benzol-sulphonic acid, C6H4N.N.SO3, which is of interest because it is used as a
reagent in Ehrlich's diazo-reaction in urinary analysis.

Diphenyl-amine, (C6H5)2NH, is obtained by the destructive distillation of
triphenyl-rosaniline (aniline-blue) as a grayish crystalline substance, slightly
soluble in water, more soluble in acids. A 0.2 per cent, solution in diluted
sulphuric acid (forming diphenylainine sulphuric acid) is colored intensely
blue by nitric acid; also, temporarily by nitrous acid and, somewhat less
intensely, by hypochlorous, bromic, and iodic acids, and a number of other
oxidizing agents.

Diamino-benzene, Meta-phenylene-diamine, CgH^NHa^, is obtained by
the reduction of meta-dinitro-benzene as a grayish crystalline powder. It has
strongly basic properties, is somewhat soluble in water, readily soluble in alco-
hol or ether. It is a valuable reagent for nitrites, as it forms, with even traces
of nitrous acid, an intense yellow color.

Methylthionine hydro chloride, Methylthioninae hydrochlori-
dum, C16H18N3SC1 = 317.36 (Methylene blue). This is a very complex
dye obtained by treating dimethyl-paraphenylene-diamine, C6H4.-
(NH2)N(CH3)2, in hydrochloric acid solution with hydrogen sulphide
and subsequently with ferric chloride. It occurs as a dark-green
powder or in prismatic crystals having a bronze-like lustre, readily
soluble in water and somewhat less so in alcohol, giving solutions of
a deep-blue color. Alkalies change the color of the aqueous solution
to a purplish shade, and in excess cause a precipitate of a dull-violet
color. It is incompatible with potassium iodide, and reducing agents
decolorize it.

BENZENE SERIES. AROMATIC COMPOUNDS. 567

Methylene-blue should not be confounded with the commercial article, which
is often the zinc chloride double salt of methylthionine, is employed as a dye or
stain, and is unfit for medicinal purposes. The presence of zinc can be told by
incinerating 2 grammes of the substance and testing the ash in the usual way
for zinc. Methylene-blue should also not be confounded with methyl blue,
which is the sodium salt of triphenyl-pararosaniline-trisulphonic acid. A solu-
tion of the latter with alkalies changes to reddish-brown,

Methylene azure, C18H18N3S03C1, is derived from methylene-blue by the ad-
dition of oxygen. It is present in "ripened" methylene-blue and almost
always in even the best specimens of the medicinal article. It may be detected
by adding ammonia to a solution of methylene-blue and then shaking with
ether ; the methylene-azure passes into the ether, which is colored red.

Diazo compounds of benzene.

When fatty amines are treated with nitrous acid the ammo group
is replaced by hydroxyl, thus :

C2H5.NH2 + HONO = C2H5OH -f 2N + H2O.

When, however, an aromatic amine is treated with nitrous acid,
in acid solution, a new class of compounds is formed, known as
diazo-compounds, thus :

C6H5.NH2HC1 + HONO = C6H5.Na.Cl -f- 2H20.

Aniline Diazo-benzene

hydrochloride. chloride.

The characteristic diazo grouping is expressed thus : R — N2 — , and
this group combines with acid residues to form diazo-salts, such as
diazo-benzene nitrate, C6H5.N2.NO3, sulphate, C6H6.N2.SO4H, etc.

The diazo-compounds are colorless, crystalline, unstable, and even explosive
substances ; soluble in water, insoluble in ether. They are of great scientific
and technical importance, as they form the starting-point for a large class
of dyes. Diazo-compounds are decomposed by water, either in the cold or upon
heating, the N2 group being usually replaced by the (OH) group, thus :

C6H5.N2.NO3 + H2O = C6H5OH -f N2 + HNO3.

It is thus possible to introduce hydroxyl into the benzene nucleus through the
medium of nitre-compounds, and obtain substances belonging to the class of
phenols.

Diazo-compounds have a marked tendency to react with other substances,
especially amino-compounds and phenols, to form a class known as azo-com-
pounds, which are characterized by having the group — N = N — in combina-
tion with two residues. Azobenzene, C6H5 — N = N — C6H5, is the mother-
substance of all azo-compounds, most of which are highly colored, and many
are used as dyes. The formation of colored azo-compounds is involved in the
test for nitrites in drinking-water by meta-phenylene-diamine (see page 432),
which gives triamino-azobenzene, NH2.C6H4— N = N— C6H3(NH2)2, a dye
which has been on the market since 1866 and known as Bismark brown ; also

568 CONSIDERATION OF CARBON COMPOUNDS.

the test in which sulphanilic acid and alpha-naphthylamine are used. In
Ehrlich's Diazo Reaction for typhoid fever, it is believed that some unknown
phenolic or amino compound in the urine unites with the diazo-sulphanilic
acid reagent, and forms an azo-dye. Some of the indicators used in volumetric
analysis are azo-dyes, for example, methyl-orange (see page 410). Dimethyl-
amino-azobenzol, C6H5 — N = N— C6H4.N(CH3)2, is used to detect hydrochloric
acid in stomach contents.

Phenyl hydrazine, C6H5.NH.NH2. When diazo-compounds are reduced,
they yield derivatives of the mother-substance, H2N — NH2, known as hydra-
zine, or diamine. Thus, diazo-benzene yields phenyl hydrazine. It is a
strongly basic substance and unites readily with acids to form salts ; it is a
colorless crystalline substance, sparingly soluble in water, but soluble in acids.
Phenylhydrazine is of interest because it is used in the manufacture of anti-
pyrine, and as a valuable reagent for the detection of aldehydes and sugars.
It combines with both classes of compounds, forming with aldehydes bodies
known as hydrazones, with sugars, osazones. Most of these compounds are solid
and crystalline; the crystalline structure often serves for identification.

Arsenic and phosphorus derivatives. A number of compounds of aro-
matic hydrocarbons containing arsenic and phosphorus, and having compo-
sitions similar to nitro-, azo-, and amino-compounds, are known. The simi-
larities are shown in the following table :

C6H5.NO2

Nitrobenzene.

C6H5.N,C6H5

Azobenzene.

C6H5.NH2

Phenylamine.

C6HVP02
Phosphinobenzene.

C6K5.P2.C6H5

Phosphobenzene.

C6H5.PH2

Phenylphosphine.

C6H5AsO2

Arsinobenzene.

C6H5.As2.C6H5

Arsenobenzene.

Arsenobenzene, C6H5.As : As.C6H5, is obtained by the reduction of phenyl-
arsine oxide, C6H5.AsO, by phosphorous acid, as yellow needles. By oxidation
it is converted into phenylarsonic acid, C6H5.AsO(OH)2.

Sodium para-aminophenyl arsonate, NH2.C6H4.AsO(OH).ONa.3H2O (sodium
arsanilate, sodium aniline arsonate, atoxyl), is a white, odorless, crystalline salt,
soluble in about 6 parts of water, and having a faint salty taste. The aqueous
solution on standing assumes a yellowish tint. It is used in sleeping sickness
(trypanosomiasis), syphilis, malaria, etc. It should be given hypodermically,
and not by the mouth. Atoxyl is made by heating aniline arsenate to about
200° C. for several hours, when a reaction takes place analogous to that by
which para-amino-benzene sulphonic acid (sulphanilic acid) is formed by heat-
ing aniline sulphate :

C6H5NH2.(HO)3AsO = NH2.C6H4.AsO(OH)2 + H2O
Aniline arsenate. Para-aminophenyl arsonic acid.

The sodium salt of this acid is atoxyl.

IKoxydiaminoarsenobenzene, ^)^C6H8.Afl : As.C6H3<^^^ ffi. The

dihydrochloride ("bichloride," as it is called in the market) of this diamine
compound was prepared by Ehrlich and Bertheim, and was the 606th com-
pound made in a search for a specific remedy for germ diseases. It is known
as " 606," or salvarsan. The arsenic occupies the para position in the benzene

BENZENE SERIES. AROMATIC COMPOUNDS. 569

nucleus. This substance has basic properties due to the NH2 groups, and
therefore unites with acids ; it also has acid properties due to the (OH) groups,
and forms salts with alkalies just as phenol does.

Salvarsan is a lemon-yellow powder, which comes in sealed tubes. It is
soluble in water with a decided acid reaction, due to hydrolysis and liberation
of hydrochloric acid. The sodium salt gives an alkaline reaction in solution,
due to hydrolysis and liberation of sodium hydroxide. The free base is insolu-
ble in water and is precipitated by the cautious addition of alkali to the solu-
tion of the hydrochloride, or of acid to the solution of the sodium compound.
For injections, either a suspension of the free base or a solution of the mono-
or di-sodium salt is prepared from salvarsan.

Hydroxyl derivatives of the benzene series.

Phenols are hydroxyl derivatives of benzene. The name is a gen-
eral one for all such compounds. Phenols are allied to the tertiary
fatty alcohols, as they contain the characteristic grouping = C — OH.
According to the number of hydrogen atoms replaced by hydroxyl,
we find mono-, di-, and tri-hydroxy phenols, corresponding to the
similarly constituted alcohols. Phenols differ from common alcohols
in not yielding aldehydes or acids by oxidation.

Phenols are either liquid or solid, and often have a peculiar odor. Most of
them can be distilled without decomposition, and are readily soluble in alcohol
and ether ; some are readily soluble in water. Many are antiseptic, for example,
phenol, cresol, resorcin, thymol, etc. Many individual phenols are found in the
vegetable and animal kingdoms. Destructive distillation of complex carbon
compounds usually results in the formation of phenols among the products;
thus, wood-tar and coal-tar are rich in phenols.

Phenols act like weak acids, forming salts with caustic alkalies, which are
soluble in water and far more stable than the alcoholates. But they do not
decompose carbonates.

Phenols can be obtained readily by first preparing sulphonic acids, and fusing
the alkali salts of these with caustic soda or potash. The actions are shown in
the following equations, which relate to synthetic phenol :

C6H6 + H2S04 C6H5S03H + H20.

Benzene
eulphonic acid.

C6H5SO3Na + NaOH C6H5OH. + Na2SO3.

Phenol.

The phenol is liberated from its alkali salt by an acid, and is purified by
further appropriate treatment.

Phenol, C6H5OH = 93.34 ( Carbolic acid, Phenyl hydroxide). Crude
carbolic acid is a liquid obtained during the distillation of coal-tar
between the temperatures of 170°-190° C. (338°-374° F.), and con-
taining chiefly phenol, besides cresol, C7H7OH, and other substances.

570 CONSIDERATION OF CARBON COMPOUNDS.

It is a reddish-brown liquid of a strongly empyreumatic and dis-
agreeable odor.

By fractional distillation of the crude carbolic acid, the pure acid
is obtained, which forms colorless, interlaced, needle-shaped crystals,
sometimes acquiring a pinkish tint ; it has a characteristic, slightly
aromatic odor, is deliquescent in moist air, soluble in from 15 to 20
parts of water, and very soluble in alcohol, ether, chloroform, glycerin,
fat and volatile oils, etc. ; it has, when diluted, a sweetish and after-
ward burning, caustic taste; it produces a benumbing and caustic
effect, and even blisters on the skin ; it is strongly poisonous, and a
powerful disinfectant, preventing fermentation and putrefaction to a
marked degree ; fusing point of the official article not less than 40° C.
(104° F.); boiling point 188° C. (370° F.).

Phenol, though generally called carbolic acid, has a neutral or but
faintly acid reaction, and the constitution of a tertiary alcohol, but it
readily combines with strong bases, for instance, with sodium hy-
droxide, forming sodium phenoxide or sodium phenolate :

C6H6OH -f NaOH = C6H6OXa + HaO.

Phenol obtained by synthetical processes is now sold in a state of
great purity ; it has comparatively little odor.

Phenol is readily liquefied by a small amount of water and is
usually dispensed in this form. The Liquefied phenol of the U. S. P.
contains about 13.6 per cent, of water.

Phenol often becomes colored when exposed to air and light. This is due
to oxidation. When pure it remains colorless even in sunlight if it is kept in
an atmosphere of inert gases, as hydrogen, nitrogen, or carbon dioxide. The
rate of oxidation varies with the temperature, being rapid at the boiling-point
of phenol. The products of oxidation are quinol, quinone, and catechol, and
the principal colored compounds are probably quinone condensation products.
The formation of the intensely red substance called phenoquinone is probable.
Glass which most completely absorbs ultra-violet light retards the action of
oxygen on phenol in the greatest degree.

Phenol or carbolic acid coefficient (Rideal- Walker coefficient}. Bacte-
riological standardization of disinfectants was proposed in 1896 by C. G. Moor.
In 1903 Samuel Rideal and Ainslie Walker developed the method now in use,
which, with later improvements, is the best available in spite of some defects.
In this method carbolic acid is taken as the standard of comparison for other
disinfectants. The phenol or carbolic acid coefficient is the ratio of the strength
in which a given disinfectant kills a given organism to that of carbolic acid
which effects the same sterilization in the same time. The colon or typhoid
bacillus is employed in the experiments of comparison.

The meaning of the coefficient will appear clear from the following exam-
ple, which refers to a culture of bacillus pestis. A 1 in 40 formaldehyde solu-
tion was equivalent to a 1 in 110 solution of carbolic acid, both sterilizing in

BENZENE SERIES. AROMATIC COMPOUNDS. 571

ten minutes, but not in seven and a half minutes. Hence, carbolic acid coeffi-
cient of the formaldehyde in this instance was ^, or 0.36.

The laws of some states require the labels of substances sold as disinfectants
to state the carbolic acid coefficient. The following table shows the coefficients
and the relative money values of various disinfectants in the market:

Carbol' ' C°St °f the Quantity of dls'
Disinfectant. acid " Infectant equivalent to 1

coefficient EngUsh gttll°n °f 98 per

cent, carbolic acid.

Carbolic acid, 98 per cent 1.00 $ 0.25

Chinosol . 0.30 127.87

Condy's fluid 0.90 2.00

Cyllin (a cresol) 11.00 0.08

Formaldehyde 0.30 4.40

Izal 8.00 0.12

Listerine 0.03 324.62

Lysoform 0.10 36.49

Lysol 2.50 0.76

Pearson's antiseptic 1.40 0.42

Sanitas 0.02 42.56

The coefficients of some other disinfectants are : sulphonaphthol, 2.2 ; zeno-
leum, 2.49 ; kreso, 2.5 ; chloronaphtholeum, 5.4 ; hyco, 19 ; Platt's chlorides, 3.

Antidotes. Alcohol is the best antidote ; it prevents the corrosive action of
phenol. But the stomach should be at once emptied and washed out, else the
phenol will be absorbed and then alcohol would prove worse than no antidote.
Soluble sulphates have been recommended on the supposition that harmless
phenolsulphonates are formed, but recent experimenters have asserted that
they are useless as an antidote. Hot applications to the extremities, hypo-
dermic injection of cardiac and respiratory stimulants, intravenous injection of
normal saline solution, and morphine to relieve pain, are valuable aids in phenol
poisoning.

Tests for phenol.
(Use an aqueous solution.)

1. It coagulates albumin and collodion.

2. It colors solutions of neutral ferric chloride intensely and per-
manently violet-blue.

3. Bromine water, added in excess, produces, even in dilute solu-
tions, a white precipitate of tri-brom-phenol, C6H2Br3OH, which has
been used medicinally under the name of Bromol.

4. Millon's reagent (see Index), heated to boiling with phenol solu-
tion, gives an intense red color on addition of a few drops of nitric
acid.

5. On heating with nitric acid it turns yellow, nitre-phenols being
formed.

572 CONSIDERATION OF CARBON COMPOUNDS.

Bismuth tribrom-phenolate, Bi2O2.OH.(OC6H2Br3) (Xeroform},is a fine
yellow, nearly odorless and tasteless powder, insoluble in water or alcohol, but
soluble in 2 per cent, hydrochloric acid in the proportion of 30 : 100. It is incom-
patible with alkaline media and should not be heated above 120° C. It is a non-
irritant and non-toxic antiseptic, recommended as a substitute for iodoform.

Nitro-plienols. Mono-, di-, and trinitro-phenols are known. Mononitro-
phenol is formed by the action of dilute nitric acid on phenol ; the di- and tri-
nitro- derivatives are formed by further nitration. Mononitro-phenol is of in-
terest also because it is used in the manufacture of acetphenetidiu.

Acetphenetidin, Acetphenetidinum, C6H4.O(C2H5).NH(C2H3O) =
177.79 (Phenacetin). When mononitro-phenol, C6H4.NO2.OH, is
treated with reducing agents, the oxygen of NO2 is replaced by hy-
drogen, and amino-phenol, C6H4.OH.NH2, is formed. The methyl
ether of this compound, C6H4.O(CH3).NH2, is known as anisidin,
and the ethyl ether, C6H4.O(C2H5).NH2, as phenetidin. By the
action of glacial acetic acid upon para-phenetidin, one hydrogen atom
in NH2 is replaced by acetyl, C2H3O, when para-acetphenetidin is
formed. The compound is used as an antipyretic under the name
of phenacetin.

It is a colorless, odorless, tasteless powder, sparingly soluble in
water, readily soluble in alcohol; it fuses at 135° C. (275° F.).
Fresh chlorine water colors a hot aqueous solution first violet, then
ruby-red. The same color is obtained by boiling 0.1 gramme of
phenacetin with 1 c.c. of hydrochloric acid for one minute, diluting
with 10 c.c. of water, filtering when cold, and adding 3 drops of
solution of chromic acid.

Acetphenetidin is the best-known one of a large number of derivatives of
para-aminophenol, known as the phenetidin series. These derivatives, as well
an acetphenetidin itself, are contained in many migraine and headache powders.
Lactophenin is lactyl-para-phenetidin, C2H5OC6H4NH.COCH(OH)CH3, a diffi-
cultly soluble white powder. Sal-ophen, saliphen, phenocoll, salocoll, etc., are
similar derivatives.

Trinitro-phenol, C6H2(NO,)3OH (Picric acid, Carbazotic acid).
This substance is formed by the action of nitric acid on various mat-
ters (silk, wool, indigo, Peruvian balsam, etc.), and is manufactured
on a large scale by slowly dropping phenol into fuming nitric acid.
Picric acid forms yellow crystals which are sparingly soluble in
water ; it has a very bitter taste, strongly poisonous properties, and
is used as a yellow dye for silk and wool and as a reagent for albumin.
While phenol has but slight acid properties, picric acid behaves like

BENZENE SERIES. AROMATIC COMPOUNDS. 573

a strong acid, forming salts known as picratcs, most of which an-
explosives.

Phenolsulphonic acid, C6H4(OH)SO3H (Sulphocarbolic acid).
There are three varieties of this acid, namely, ortho, meta, and para.
The ortho and para acid are most easily obtained. When pure phenol
is mixed with an equal weight of sulphuric acid in the cold, only the
ortho acid is formed :

C6H5OH + H2S04 : C6H4(OH)S03H + H2O.

At 100° C. (212° F.) only the para acid results. Both varieties form
clear solutions with water, but differ from each other in the character
of their salts, both as regards solubility and form of the crystals.
They are monobasic acids.

Ortho-phenohulphonic acid (Sozolic acid, Aseptol) occurs on the
market as a 33 per cent, solution. It is a syrupy liquid, having a
reddish color and a feeble odor. It is used as an antiseptic.

Sodium phenolsulphonate, Sodii phenolsulphonas (Sodium sulpho-
carbolate), C6H4(OH)SO3Na -f 2H2O, and Zinc phenolsulphonate, Zinci
phenolsulphonas (Zinc sulphocarbolate), (C6H4(OH)SO3)2Zn -f- 8H2O,
are official salts of para-phenolsulphonic acid. They are obtained by
precipitating a solution of barium para-phenolsulphonate by sodium
carbonate and zinc sulphate respectively, filtering off the precipitate
of barium carbonate or sulphate, and evaporating the filtrate to crys-
tallization. Both salts are readily soluble and have antiseptic and
astringent properties.

Sulphonic acid has been spoken of before, when it was shown that inercap-
tans are converted into compounds termed sulphonic acids. These acids may
be looked upon as derivatives of sulphurous acid, obtained from it by replace-
ment of hydrogen by radicals. The relation existing between carbonic and
sulphonic acids may be represented by the following formulas :

Carbonic acid, c°CoH Sulphuric acid, SO2\OH

Formic acid, CO\QH Sulphurous acid, SO*\OH

Acetic acid, CO\OH3 Methyl -sulphonic acid,

Any compound CO^w Anv sulphonic acid,

carbonic acid,

According to this view, phenolsulphonic acid is represented by the formula,

so / Q>H4OH
5Ua\OH

Ichthyol, Sodium ichthyo-sulphonate, C.^H^Na-Pe. Ichthyol is the sodium or
ammonium salt of a complex sulphonic acid, obtained by the dry distillation

574 CONSIDERATION OF CARBON COMPOUNDS.

of a bituminous mineral found in Tyrol. It is a brown, tar-like liquid, having
a disagreeable odor.

Cresol, C7H7OH==1O7.25. The official cresol is a mixture of the
three isomeric cresols, (CCH4.CH3.OH), or hydroxyl derivatives of
toluene, the ortho-, para-, and meta-cresol. The cresols bear the same
relation to toluene that phenol bears to benzene, and they resemble
phenol very closely in their properties. Cresol is a colorless or straw-
colored refractive liquid having a phenol-like odor. It is soluble in
60 parts of water, miscible with alcohol, ether, and glycerin in all
proportions. It boils at about 200° C. (392° F.).

Cresol is slightly soluble in water, hence it is often used in the form of emul-
sions, or dissolved with the aid of salts or of soap. Compound solution of cresol,
Liquor cresolis compositus, is a linseed-oil-soap solution of cresol, of 50 per cent,
strength. It is of much more definite composition than many commercial prep-
arations of similar nature. Lysol is about the same as the official solution.
The mixtures known as creolins usually contain impure cresol dissolved with
the aid of rosin soap. They usually form emulsions when diluted with water.
Solveol and solutol are solutions of cresol made with the aid of salts. Tri-cresol
(enterot) is said to contain 35 per cent, of ortho-cresol, 40 per cent, of meta-cresol,
and 25 per cent, of para-cresol, and is soluble to the extent of 2.2 to 2.55 per
cent, in water. A vast number of other similar solutions are on the market. It
is generally held that cresol is more toxic to bacteria than phenol is. Losophan
and europhen are iodine compounds of cresol.

Creosote, Creosotum. Two different preparations of this name
are sold in the market. One is coal-tar creosote and is chiefly an
impure carbolic acid. The official creosote is a liquid product of the
distillation of wood-tar, especially of beechwood-tar, which contains
sometimes as much as 25 per cent, of creosote ; it resembles carbolic
acid in many respects, especially in its antiseptic properties and its
action on the skin. It is a mixture of substances, but consists chiefly
of guaiacol, C6H4.OCH3.OH, and creosol, C6H3.CH3.OCH3.OH.

From carbolic acid beechwood creosote may be distinguished by
requiring as much as 150 parts of water for solution; by being
miscible with the official collodium in equal volumes without form-
ing a coagulum ; by not being solidified on cooling ; by not coloring
ferric chloride permanently ; and by its boiling-point, which rises
from 205° to 215° C. (401° to 419° F.).

Creosote carbonate (Creosotal] is a mixture of carbonic acid esters, anal-
ogous to guaiacol carbonate, prepared from creosote by passing a current of
carbonyl chloride into a solution of creosote in sodium hydroxide. It is a yel-
lowish, thick, clear, and transparent liquid, odorless, and has a bland oily taste.

BENZENE SERIES. AROMATIC COMPOUNDS. 575

It is insoluble in water, but soluble in alcohol and in fixed oils. It is non-toxic
and non-irritant and is used as a substitute for creosote.

Guaiacol, C6H4.OH.OCH;{ = 123.13, found in beechwood creosote to the
extent of from 60 to 90 per cent., is a derivative of the diatomic phenol catechol
(pyrocatechin), C6H4(OH)2, obtained from it by replacing a hydroxyl hydrogen
atom by methyl, CH3. Guaiacol is consequently monomethyl catechol. It is
a colorless, crystalline solid, melting at 28.5° C. (83.5° F.), or a colorless re-
fractive liquid, boiling at 205° C. (401° F.), and possessing a strong aromatic
odor. It is difficultly soluble in water, easily soluble in alcohol and ether. In
alcoholic solution ferric chloride produces an immediate blue color, changing
to emerald green, later to yellowish. It is obtained either synthetically or
from creosote.

Veratrol, C6H4(OCH3)2, the dimethyl ether of catechol, is a colorless,
aromatic, oily liquid, having the same boiling-point as guaiacol.

A number of derivatives of guaiacol are in the market, being chiefly com-
pounds with acid radicals, such as the camphorate (guaiacamphol), carbonate,
benzoate (benzosol], cinnamate (styracot), phosphate, phosphite, salicylate
(guaiacol-salol), valerate (geosote), etc., one of which is official, namely,

Guaiacol carbonate, Guaiacolis carbonas, (C7H7O),.CO3, is prepared by satu-
rating guaiacol with sodium hydroxide, and treating this compound with car-
bonyl chloride, COC12. It is a white crystalline powder, insoluble in water,
sparingly soluble in alcohol, soluble in ether and chloroform.

Creosol, C6H3.CH3.OH.OCH3, the second constituent of creosote, is the next
homologue to guaiacol — i. e., the methyl-ether of dioxytoluene.

Eugenol, C6H3(OH)(OCH3).C3H5. 4 : 3 : 1 = 162.86, is an unsaturated
aromatic phenol obtained from oil of cloves and other sources. It is a color-
less> or a pale yellow liquid, having a strongly aromatic odor of cloves.

Safrol, Safrolum, C6H3.C3H5.OOCH2, 1:3:4 = 180.86 (Shikimol, Allyl-
pyrocatcchol methylene ether), is found in oil of sassafras, oil of camphor, and
other volatile oils. It is a colorless liquid with a sassafras-like odor.

Thymol, C10HUO or CGH3.CH3.C3H7.OH — 149.66 (Mdhyl-isopro-
pylphenol). Thymol is found in small quantities as a constituent of
the volatile oils of wild thyme, horse-mint, and a few other plants.

Thymol crystallizes in large translucent plates, has a mild odor, a warm,
pungent taste, melts at 50° C. (122° F.) and boils at 230° C. (446° F., It is now
largely used as an excellent and very valuable antiseptic, preference being
given to it on account of its comparative harmlessness when compared with
the strongly poisonous carbolic acid.

Thymol dissolved in moderately concentrated warm solution of potassium
hydroxide, gives on the addition of a few drops of chloroform a violet color,
which on heating soon changes into a beautiful violet-red.

Thymol iodide, Thymolis iodidum, (C6H,.CH3.C3H7.OI)2 = 545.76 (Di-

thymol-diiodide, Aristol, Annidalin}. Obtained by the action of a solution of

576 CONSIDERATION OF CARBON COMPOUNDS.

iodine in potassium iodide upon an alkaline solution of thymol. Condensation
of two molecules of thymol takes place with the introduction of two atoms of
iodine into its phenolic group. It is a bright, chocolate-colored, or reddish-
yellow, bulky powder, with a very slight aromatic odor; it contains 46.14 per
cent, of iodine and is used as a substitute for iodoform.

Resorcinol, CGH4(OH)2. 1:3 = 1O9.22 (Resorcin 9 Meta-dihydroxy-
benzene). It is formed by fusing different resins, such as galbanum,
asafoetida, etc., with caustic alkalies, but it is now made almost alto-
gether from benzene by heating the latter with fuming sulphuric acid
to 257° C., whereby benzene-meta-disulphonic acid, C6H4(SO3H)2,
is produced. The sodium salt of this acid is fused with sodium
hydroxide for several hours, forming sodium resorcin, C6H4(ONa)2.
The mass is dissolved in water, acidified, and extracted with ether,
which dissolves out the resorcin. This is further purified by sub-
limation and recrystallization.

Resorcinol is a white, or faintly-reddish, crystalline powder, having a some-
what sweetish taste and a slightly aromatic odor; it fuses at 119° C. (246° F.),
boils at 276° C. (529° F.), and is soluble in less than its own weight of water.
A dilute solution gives with ferrric chloride a bluish-violet color. Resorcinol,
when heated for a few minutes with phthalic acid in a test-tube, forms a yel-
lowish-red mass, which, when added to a dilute solution of caustic soda, forms
a highly fluorescent solution. Other fluorescent compounds are obtained by
heating resorcinol with very little sulphuric and either citric, oxalic, or tar-
taric acid, dissolving in a mixture of water and alcohol and supersaturating
the solution with ammonia. Resorcinol is largely used in the manufacture of
certain dyes. It must not be confused with the proprietary preparation of the
same name, composed of equal parts of resorcin and iodoform fused together.

Quinol, C6H4(OH)2.1 : 4 (Hydroquinone, Para-dihydrozy-benzene), is formed
by dry distillation of quinic acid (from Peruvian bark), by reduction of
quinone, and by fusing para-iodophenol with sodium hydroxide. It occurs
combined with sugar as the glucoside arbutin, in uva ursi (Bear-berry) leaves.
It forms small plates or hexagonal prisms, melting at 169° C., easily soluble in
hot water, alcohol, and ether. Oxidizing agents, such as ferric chloride, chlo-
rine, etc., convert it into quinone, C6H4O2. It is used as a developer in pho-
tography.

Solution of lead acetate gives a white precipitate with pyrocatechol, none
with resorcinol, and a precipitate only in the presence of ammonia with
hydroquinol.

Pyrogallol, Pyrogallic acid, C6H3.(OH)3. When gallic acid is
heated to 200° C. (392° F.) it is decomposed into carbon dioxide and
pyrogallol, a substance which is not a true acid, but a tri-hydroxy-
benzene — i. e., a phenol. Pyrogallol crystallizes in colorless needles,
melts at 131° C. (268° F.), is easy soluble in water, ether, and alco-
hol. In alkaline solution it absorbs oxygen rapidly, assuming a red,

BENZENE SERIES. AROMATIC COMPOUNDS. 577

then reddish-brown and dark-brown color. Nitric acid also colors it
yellow, then brown, and this property is made use of in testing for
traces of nitric acid. Solutions of silver, gold, and mercury are
reduced by pyrogallol even in the cold.

Gallacetophenone or Gallactophenone, ^^<3 obtained by

heating a mixture of pyrogallol, zinc chloride, and glacial acetic acid to 148°
C. It is a crystalline powder of dirty flesh-color, soluble in water, introduced
to replace pyrogallol, which is poisonous.

Phloroglucinol, C6H3(OH)3. 1:3:5 (Phloroglucin, Symmetrical trihy-
droxy-benzene), results when resorcin and several resins, as gamboge, dragon's
blood, etc., are fused with potassium hydroxide. It forms colorless prisms,
melting at 218° C., very soluble in water and alcohol, and of a sweet taste. It
stains lignin red and, together with vanillin, is used to detect hydrochloric acid
in stomach contents.

Hydroxy-hydroquinone, C6H3(OH)3. 1 : 2 : 4, is the third trihydroxy-
benzene. It is an interesting fact that according to the theory as to the struc-
ture of the benzene molecule, three isomeric dihydroxy-benzenes and trihy-
droxy-benzenes should exist, and in each case three actually do exist.

Most of the phenols give colors with ferric chloride solution, and are acted
on by the oxygen of the air with formation of colored bodies. They are un-
stable toward oxidizing agents, forming in many cases carbon dioxide. The
di- and trihydroxyl derivatives are less stable than the simple phenols. The
same is true also of hydroxy acids of benzene, for example, salicylic and gallic
acids.

Aromatic alcohols and aldehydes.

Aromatic alcohols. These are aromatic derivatives of the fatty alcohols —
i e., alcohols in which hydrogen of the fatty hydrocarbon residue is replaced by
a benzene derivative. The aromatic alcohols have the properties of true fatty
alcohols.

Benzyl alcohol, CJJ^CHVOH, is the simplest member of the class; it is

isomeric with cresol, C6H4<Q^3, but has entirely different properties. Benzyl

alcohol is found in balsam of Peru and Tolu, mostly in combination with ben-
zoic or cinnamic acid.

Aromatic aldehydes. These are aromatic derivatives of the fatty alde-
hydes and behave in all respects like the latter ; thus they combine readily
with oxygen to form acids and behave generally like unsaturated compounds.

Benzaldehyde, Benzaldehydum, C6H5.COH = 1O5.25. This is
the simplest one of the aromatic aldehydes, and is produced artificially
or obtained from natural oil of bitter almonds or other oils. It is a
colorless, strongly refractive liquid, having a bitter-almond-like odor.
It is easily converted into benzoic acid by oxidation.

37

578 CONSIDERATION OF CARBON COMPOUNDS.

Oil of bitter almond, Oleum amyg-dalse amarse. Benzaldehyde
does not occur in a free state in nature, but is formed by a peculiar
fermentation of a glucoside, amygdalin, existing in bitter almonds, in
cherry-laurel, and in the kernels of peaches, cherries, etc., but not in
sweet almonds. The ferment causing the decomposition of amygdalin
is a substance termed emulsin, which is found in both bitter and
sweet almonds. As water is required for the decomposition, the
emulsin does not act upon the amygdalin contained in the same seed
until water is added, when the decomposition takes place as follows ;

C20H27NOn + 2H20 = 2C6H1206 -f HCN + C7H6O.
Amygdalin. Water. Glucose. Hydrocyanic Benzaldehyde.

acid.

The oil is obtained by maceration of bitter almonds with water,
and subsequent distillation when it distils over with hydrocyanic
acid and steam, and separates as a heavy oil in the distillate.

It is an almost colorless, thin liquid of a characteristic aromatic
odor, a bitter and burning taste, and a neutral reaction. Pure benz-
aldehyde is not poisonous, but the oil of bitter almond is poisonous
on account of its containing hydrocyanic acid.

Sitter-almond water, Aqua amygdalae amarce, is made by dissolving
1 part of the oil in 999 parts of water.

Cinnamic aldehyde, Cinnaldehydum, C6H5.CH : CH.COH = 131.07 (Arti-
ficial oil of cinnamon, Cinnamyl aldehyde, Phenyl acrolein}. This aldehyde is
prepared synthetically, or is obtained from oil of cinnamon by extracting with
acid sodium sulphite. Cinnamic aldehyde is a colorless oil, having a cinna-
mon-like odor and a burning, aromatic taste. When exposed to the air it is
oxidized to cinnarnic acid.

Vanillin, Vanillhmm, C6H3.OH.OCH3.COH. 4:3:1 = 150.92 (Methylpro-
tocatechuic aldehyde}. Vanillin is the active constituent in vanilla bean, and is
made artificially in a variety of ways. One of these is the action of chloroform
and caustic potash on guaiacol. It occurs in white, crystalline needles, having
the odor and taste of vanilla, and melting at 80° to 81° C. It is soluble in 100
parts of cold and 15 parts of warm water, easily soluble in alcohol, ether,
chloroform, and dilute alkalies. It is extracted completely from its solution in
ether by shaking with a saturated aqueous solution of sodium bisulphite, from
which it may be precipitated by sulphuric acid ; it is also extracted by ammo-
nia water.

,0 — CO

Ooumarin, C6H,( the anhydride of ortho-hydroxy-cinnamic

XCH=CH,

acid, is found in the Tonka bean and resembles vanillin in odor. It forms
white, shining prisms, melting at 67° C., and soluble in 400 parts of cold, 45
parts of hot water, and in 7.5 parts of alcohol ; easily soluble in ether.

An aqueous solution of vanillin is turned blue by a few drops of ferric chlo-
ride solution, coumarin is not. An aqueous solution of coumarin, unlike va-

BENZESE SERIES. AROMATIC COMPOUNDS. 579

nillin, forms a precipitate when iodine in potassium iodide is added in excess,
at first brown and flocculent, and afterward, on shaking, forming a dark-green
curdy clot.

" Extracts of vanilla," made not from the vanilla bean, but consisting of
alcoholic tinctures of synthetic vanillin or coumarin, can readily be detected by
evaporating off the alcohol, making up the original volume with water, and
acidifying with acetic acid. A reddish-brown precipitate of resin is formed in
the case of a true extract, but none in the artificial. The filtrate from this
resin gives a copious precipitate with basic lead acetate solution, the artificial
extract gives none.

Vanillin has been found adulterated with benzoic acid, acetanilide, boric
acid, terpin hydrate, and coumarin.

Acids of the benzene series.

These are derivatives in which one or more carboxyl groups
(COOH ) have replaced hydrogen in the benzene molecule. Benzoic
acid is the simplest, and bears the same relation to benzene as acetic
acid bears to methane. Many of these acids are found as natural
products, but the carboxyl group may be introduced by various reac-
tions, of which the following are the principal ones :

1. Oxidation of benzene compounds containing fatty hydrocarbon
radicals or substituted radicals :

C6H5CH2OH + 20 = C6H5COOH + H2O.

2. Hydrolysis of a cyanide by heating with dilute acid :

C6H5CN + 2H2O = C6H5COOH + NH3.

3. The treatment of alkali salts of phenols with carbon dioxide
(see Salicylic Acid).

Benzoic acid, Acidum benzoicum, HC7H5O2 or C6H5CO2H =
121.13. Found in benzoin and some other resins; also in combination
with other substances in the urine of herbivorous animals; it is
obtained from benzoin by heating it carefully, when the volatile
benzoic acid sublimes. It is now also manufactured from toluene,
which is first converted into benzo-trichloride (trichlormethyl-ben-
zene) by passing chlorine into hot toluene :

C6H6CHS + 6d == C6H5CC13 + 3HC1.

Benzo-trichloride, when treated with water under pressure, yields
benzoic and hydrochloric acids, thus:

C6H5CC13 + 2H20 : : C6H5C02H + 3HC1.

Benzoic acid forms white, lustrous scales or friable needles, which
are but slightly soluble in cold water, but easily soluble in alcohol.

580 CONSIDERATION OF CARBON COMPOUNDS.

ether, oils, etc. Shaken in solution with hydrogen dioxide, benzoic
acid is converted into salicylic acid.

Benzoic acid, prepared by sublimation from gum benzoin, has a
slight aromatic odor resembling that of benzoin ; the acid obtained
synthetically is odorless.

Benzoic acid, when neutralized with an alkali, gives a flesh-colored
or reddish precipitate of ferric benzoate on the addition of a neutral
solution of ferric chloride.

By neutralizing benzoic acid with either ammonium hydroxide,
sodium hydroxide, or lithium carbonate, the official salts ammonium
benzoate, NH4C7H5O2, sodium benzoate, NaC7H5O2.H2O, and lithium
benzoate, LiC7H5O2, are obtained. The three salts are white, soluble
in water, and have a slight odor of benzoin.

Benzoic acid and its derivatives, taken internally, are eliminated in the
urine as hippuric acid, C6H5CO.NH.CH2COOH (benzoyl-amino-acetic acid),
and its derivatives.

Many halogen, nitro- and amino-benzoic acids exist which are interesting
in pure and technical chemistry.

Ethyl para-amino-benzoate, C6H4(NH2)(COOC2H5) (Anesthesiri), is a
local anesthetic, introduced as a substitute for cocaine. It is a white, odorless,
tasteless powder, melting at 90° to 91° C., almost insoluble in cold and diffi-
cultly soluble in hot water. It is soluble in 6 parts of alcohol. When placed
on the tongue it produces a sensation of numbness.

Benzoyl chloride, C6H5.COC1, is obtained by distilling benzoic acid with
phosphorus pentachloride. It is a colorless, irritating oil, boiling at 200° C.,
slowly decomposed by cold water, but more stable than acetyl chloride. It
acts on hydroxyl compounds, forming benzoic acid esters, thus :

C6H5.COC1 + C6H5OH C6H5COOC6H5 + HC1.

Phenyl benzoate.

This process of introducing the benzoyl radical is known as " benzoylation." It
is greatly facilitated when carried out in the presence of alkali.

Benzosulphinide, Saccharin, Benzosulphinidum, C6H4.CO.SO2.-
NH = 181.77 (Anhydro-ortho-sulphamide-benzoic acid, Benzoyl sul-
pJionic-imide). This substance is a derivative of benzoic acid,
C6H5.CO2H, obtained by the discoverers from toluene by the trans-
formations indicated in the following formulas :

CH3

,CH3 /COOH /CO,

C.H / __> C.H/ _> C6H / >NH.

-\soajra, NSCVNH, Nao/

Other methods of preparing saccharin have been devised.

BENZENE SERIES. AROMATIC COMPOUNDS. 581

Saccharin is a white, crystalline, odorless powder. It is but sparingly
soluble in water, requiring about 250 parts for solution ; this solution is
slightly acid and has an extremely sweet taste, which is yet perceptible when
saccharin is dissolved in 125,000 parts of water, which shows that it is about
500 times sweeter than cane-sugar, a solution of which in 250 parts of water is
yet perceptibly sweet. Saccharin is soluble in alcohol and ether, and it is this
latter property which is made use of in testing sugar (or other substances in-
soluble in ether) for saccharin. The substances are treated with ether, which
is filtered off and evaporated, when the saccharin may be recognized by its
taste in the residue.

Saccharin forms very soluble and well-crystallizing salts with the alkalies,
which are also intensely sweet ; they are articles of commerce. The sodium
salt is known as soluble saccharin or krystallose. Saccharin is known in the
British Pharmacopoeia as Glusidum (Gluside), and in commerce as glucusimide,
saccharol, saccharinol, saccharinose, agucarine, etc. A number of preparations,
such as antidiabetin, contain saccharin. Dulcin or sucrol, another very sweet
substance, is para-phenetol-carbamide.

Phthalic acid, C6H4QQg Of the aromatic polybasic

acids, the dibasic acids are the most important. They are called
phthalic acids in allusion to the fact that one of them can be obtained
from naphthalene. Theoretically, three dibasic acids are possible and
all are known. When mixed with lime and distilled they yield
benzene.

Phthalic acid can be obtained by the oxidation of derivatives of
benzene containing two side-chain hydrocarbons in the ortho-position,
but it is manufactured by oxidizing naphthalene by hot fuming sul-
phuric acid with the help of a catalytic agent, as mercury. The sul-
phuric acid loses oxygen to the naphthalene and forms sulphur diox-
ide, which escapes in great quantities. Enormous quantities of phthalic
acid are employed in the manufacture of synthetic indigo. It is a
crystalline white substance, readily soluble in hot water, alcohol, and
ether. When heated it decomposes, yielding water and phthalic
anhydride, which latter sublimes in long needles :

Phthalic anhydride.

Iso-phthalic acid (Meta-phthalic acid), C6H4(COOH)21 : 3, may be obtained by
oxidizing benzene derivatives containing two side-chains in the meta-position,
and from rosin by oxidation with nitric acid. It is difficultly soluble in water
and does not give an anhydride when heated.

Terephthalic acid (Para-phthalic acid), C6H4(COOH).2l : 4, can be formed by

582 CONSIDERATION OF CARBON COMPOUNDS.

oxidation of turpentine and in other ways. It is nearly insoluble in water,
alcohol, and ether, and does not yield an anhydride.

Phenolphthalein. When phthalic anhydride is heated with phenols
and concentrated sulphuric acid, a class of substances is obtained
known as phthaleins. The simplest of these is phenolphthalein, the
composition of which is shown in the following reaction :

C6Hl\co>0 + 2C6H5-OH = C

Phthalic anhydride. Phenol. Phenolphthalein.

It occurs as a creamy-white powder or crystals, soluble in 600 parts
of water and in 10 parts of alcohol. It dissolves in alkaline solu-
tions with a beautiful red color, and is used as a sensitive indicator in
acidimetry and alkalimetry. Acids destroy the red color by reform-
ing the colorless phenolphthalein from its salts. Taken internally, it
acts as a purgative, but appears to possess no further physiological
action. For adults the average dose is 0.1 to 0.2 Gm., given as
powder, in cachets, capsules, or pills. In obstinate cases 0.5 Gm.
doses may be given.

Resordnolphthalein or fluorescein is obtained by heating phthalic anhydride
and resorcinol at 210° C. with zinc chloride as a dehydrating agent. It is a
reddish-brown substance which exhibits an intense yellowish-green fluores-
cence in an alkaline solution, hence its name. By treatment with bromine it
forms tetrabromfluorescein, the potassium salt of which is the dye known as
eosin, C20H6O5Br4K2. This is a valuable stain for animal and plant tissues. In
dilute solution it shows a beautiful rose tint.

Phenolsulphonephthalein, C6H4^gQX) . This substance is anal-

ogous to phenolphthalein, and may be obtained in a similar manner
by heating together phenol and the anhydride of orthosulphobenzoic acid,

C H /CO \
6 4\cjn /^> which is analogous to the anhydride of phthalic acid. The

source of the anhydride of sulphobenzoic acid is saccharin.

Phenolsulphonephthalein is a red or brownish-red powder, soluble in alcohol,
but not in ether. It is slightly soluble in cold water, giving a deep yellow
color to the solution, but readily soluble in alkalies, the mono-sodium salt
having a bordeaux red color, while with excess of alkali the solution has a
beautiful purple color similar to that of phenolphthalein in alkaline solution.
It is used as a diagnostic test of renal efficiency by injecting 6 Mgm. in the
form of the mono-sodium salt. The test depends upon the fact that normal
kidneys excrete 40 to 60 per cent, of the dose during the first hour after its
first appearance in the urine, whereas kidneys not functioning properly
excrete a much smaller per cent. The readings are made by means of a
colorimeter.

BENZENE SERIES. AROMATIC COMPOUNDS. 583

Hydroxy-acids of the benzene series.

These derivatives, which are known also as phenol-acids, contain
the (OH) and (COOH) groups in the benzene nucleus, and accord-
ingly possess the properties of phenols and acids. The hydrogen of
the (OH) group as well as that of the (COOH) group can be replaced
by a metal or hydrocarbon radical. The radical introduced into the
(COOH) group is easily removed by saponification, as in the case of
any ethereal salt, whereas that introduced into the (OH) group is not.

The simplest hydroxy-acids are those containing one (OH) group
and one (COOH) group. There are three such acids, namely, ortho-,
meta-, and para-hydroxy-benzoic acid. Of these, the ortho acid,
known better as salicylic acid, is the most important.

Salicylic acid, Acidum salicylicum, HC7H5O3 or C6H4OH.CO2H
= 137. Derived from benzene by introducing one hydroxyl and
one carboxyl radical. It is found in several species of violet, and in
the form of methyl salicylate in the wintergreen oil (oil of Gaul-
theria procumbens). May be obtained by fusing potassium hydroxide
with salicin.

Nearly all salicylic acid used medicinally or otherwise is obtained by syn-
thesis. The first step is the conversion of phenol into sodium pheiiolate by
treatment with sodium hydroxide, thus :

C6H5OH + NaOH = C6H5ONa + H2O.

Sodium phenolate is next dried and treated with carbon dioxide, when direct
combination takes place and sodium phenol carbonate is formed, thus :

C6H5ONa + C02 -a NaC6H5C03.

Sodium Sodium phenol

phenolate. carbonate.

Sodium phenol carbonate is isomeric with sodium salicylate and is actually
converted into the latter compound by being heated to 130° C. (266° F.), in
tightly closed vessels, or in vessels through which carbon dioxide passes.

Salicylic acid is a white, solid, odorless substance, having a sweet-
ish, slightly acrid taste, and an acid reaction ; it is soluble in 308 parts
of water and in 2 parts of alcohol ; it fuses at about 157° C. (315° F.),
and sublimes slowly at 100° C. (212° F.) and rapidly at 140° C.
(281° F.). It is a valuable antiseptic.

By the action of the alkali hydroxides on salicylic acid, the various
salts may be obtained, as, for instance, sodium salicylate, NaC7H5O3,
ammonium salicylate, NH4C7H5O3> and lithium salicylate, LiC7H5O3>

584 CONSIDERATION OF CARBON COMPOUNDS.

all of which are official. They are white salts, readily soluble in
water. In the presence of free alkali, the solutions absorb oxygen
from the air and become colored. Solutions of salicylates are incom-
patible with acids, salicylic acid being precipitated.

Bismuth subsalicylate is official and has approximately the com-
position, C6H4(OH)CO2BiO. It is a white, amorphous or crystalline,
odorless and tasteless powder, permanent in the air, and almost insol-
uble in water. Alcohol or ether extracts salicylic acid, with decom-
position of the salt.

Strontium salicylate, (C6H4(OH)CO2)2Sr + 2H2O, which is official,
is a white crystalline powder, odorless, and having a sweetish saline
taste. It is soluble in 18 parts of water and 66 parts of alcohol. It
is incompatible with ferric salts, mineral acids, quinine salts in solu-
tion, spirit of nitrous ether, sulphates and carbonates, and sodium
phosphate in powder.

Mercuric salicylate, C&H^QQ /Hg, is prepared by heating on a water-
bath 21.5 parts of yellow mercuric oxide, 15 parts of salicylic acid, and a little
water until the mixture is perfectly white. It occurs as a white, amorphous
powder, tasteless, and neutral to litmus paper, slightly soluble in water or alco-
hol, but soluble in solutions of sodium hydroxide and sodium carbonate, form-
ing a double salt. It is soluble also in warm solutions of chlorides, bromides,
and iodides. It is used as a disinfectant, and as a remedy in syphilis and in
certain skin diseases.

Analytical reactions.

1. Add to solution of salicylic acid or its salts ferric chloride: a
reddish-violet color is produced, yet noticeable in solutions containing
1 part of salicylic acid in 500,000 parts of water.

2. Add some cupric sulphate : a bright green color will result.

3. Dissolve some salicylic acid or sodium salicylate in methyl alco-
hol and add one-fourth the volume of sulphuric acid. Heat gently
and set aside for a few minutes. On reheating, the odor of methyl
salicylate is developed.

Aspirin, C6H4.0(CH3CO)COOH (Acetyl-salicylic acid ), is obtained by the
prolonged action of acetic anhydride on salicylic acid at about 150° C. It forms
colorless needles, melting at 135° C., odorless, and of an acidulous taste, solu-
ble in 100 parts of water and freely in alcohol or ether. Boiling water or
alkalies decompose it, liberating acetic acid.

Salicin, C13H1807. This glucoside is found in several species of Salix (wil-

BENZENE SERIES. AROMATIC COMPOUNDS. 585

low), and is mentioned here because it splits into glucose and salicylic alcohol,
C6H4.OH.CH2OH, when boiled with dilute acids:

C13H1807 + H20 = C6H1206 + C,H8Or

Salicylic alcohol is converted by chromic acid into salicylic aldehyde, C6H<
OH.COH, which by further oxidation is converted into salicylic acid.

Salicin forms white, silky, shining needles, which are soluble in less than an
equal weight of water, have a neutral reaction and a very bitter taste.

Salicin sprinkled upon concentrated sulphuric acid produces a red color.
Boiled with very dilute hydrochloric acid for a few minutes, and this solution
nearly neutralized with sodium carbonate, a violet color is produced on the
addition of a drop of ferric chloride solution.

Methyl salicylate, Methylis salicylas, CH3,C7H503 or C6H4(OH)COOCHS

1 ". 2 = 150.92. Oil of wintergreen is chiefly methyl salicylate, a nearly color-
less liquid with a characteristic, strongly aromatic odor. It is made by the
method so extensively used in the manufacture of esters, viz., by heating of
salicylic acid with methyl alcohol in the presence of sulphuric acid. (See
above reaction 3 of salicylic acid, ) It is also found in many other volatile oils,
especially in oil of betula

Phenyl salicylate, Salol, Phenylis salicylas, C6H5.C7H5O3 or
C6H4(OH)COOC6H5 1:2 = 212.47. This ester is a white, crystalline,
almost tasteless powder, which is nearly insoluble in water, readily
soluble in alcohol, ether, and benzol, and fuses at 42° C. (107.4° F.).
It is used as an antiseptic and antipyretic.

Salol heated with potassium hydroxide solution causes its decom-
position into phenol, which can be recognized by its odor, and potas-
sium salicylate, from which crystalline salicylic acid will separate
upon supersaturating the liquid with hydrochloric acid. An excess
of bromine-water produces a white precipitate in an alcoholic solution
of salol.

Salol is made by the action of suitable dehydrating agents upon a
mixture of phenol and salicylic acid :

C6H5OH -f HC7H503 = C6H5.C7H503 + H2O.

A more simple method for its manufacture consists in the heating
of salicylic acid between 220° and 230° C. (428° and 446° F.) in an
atmosphere of carbon dioxide, in a flask with a long, narrow neck.
The reaction is this :

Anisic acid, O6H4<°£j^| (Para-methoxy-benzoic acid), is isomeric with
methyl salicylate, but, unlike the latter, it is not saponified when heated with

586 CONSIDERATION OF CARBON COMPOUNDS.

alkalies. This is due to the fact that the methyl group is combined as in an
ether. The ether groups, as OCH3, OC2H5, OC6H5, etc., are often called methoxy,
ethoxy, phenoxy, etc. Anisic acid is formed by the oxidation of anethol,

OOH

3, an ether contained in oil of anise.

Gallic acid, Acidum gallicum, HC7H5O5 -f H2O or C6H2(OH)3.-
CO2H + H2O = 186.65. Obtained by exposing moistened nut-galls
to the air for about six weeks, when a peculiar fermentation takes
place, during which taimic acid is converted into gallic acid, which
is purified by crystallization. The crystals contain one molecule of
water, which may be expelled at 100° C. (212° F.). It is a white,
solid substance, forming long, silky needles ; it has an astringent and
slightly acidulous taste and an acid reaction ; it is soluble in about
100 parts of cold or in 3 parts of boiling water, also readily soluble
in alcohol, but sparingly in ether and chloroform ; it gives a bluish-
black precipitate with ferric salts, and does not coagulate albumin,
nor precipitate alkaloids, gelatin, or starch (difference from tannic
acid). A piece of potassium cyanide added to solution of gallic acid
produces a deep rose-color.

Bismuth subgallate, a salt which is somewhat variable in composition, is
official. It is a yellow, amorphous, insoluble powder, known as Dermatol.

Tannic acid, Acidum tannicum, C13H9O7.COOH = 319.66
(Gallotannic acid, Digallic acid). There are a number of tannic
acids, or tannins, found in various parts of different plants (oak-bark,
nut-galls, cinchona, coffee, tea, etc.), the properties of which are not
quite identical. All tannins, however, are amorphous, have a faint
acid reaction and strongly astringent properties; they all precipitate
albumin and most of the alkaloids ; they give with ferric salts a dark-
colored solution or precipitate, the color being dark green or dark
blue ; they form with animal substances compounds which do not
putrefy. Use is made of this property in the process of tanning —
i. e., converting hides into leather.

The official or tannic acid is obtained by extracting nut-galls with
ether and alcohol, and evaporating the solution ; it forms light-yel-
lowish, amorphous scales, having a faint and characteristic odor, a
strongly astringent taste, and an acid reaction ; it is easily soluble in
water and diluted alcohol.

Analytical reactions :

1. To solution of tannic acid add ferric chloride: a blue-black pre-
cipitate falls, soluble in large excess of tannic acid with violet color

BENZENE SERIES. AROMATIC COMPOUNDS. 587

If ferric chloride is added in excess, the black precipitate dissolves in
it with green color.

2. Add a few drops of potassium hydroxide : a brown coloration
results.

3. To a dilute solution (1 in 100) of tannic acid add a small quan-
tity of lime-water. A pale bluish-white, flocculent precipitate is
formed, which is not dissolved on shaking (difference from gallic acid),
but becomes more copious and of a deeper blue than pinkish by the
addition of an excess of lime-water.

4. Tannic acid precipitates solutions of gelatin, albumin, gelatinized
starch, tartar emetic, and most of the alkaloids.

The Naphthalene series.

Naphthalene, Naphthalenum, C10H8 = 127.10. The constitution
of all benzene derivatives considered so far may be explained by the
introduction of radicals in benzene. Naphthalene and its derivatives
must be assumed to be formed by the union of two benzene residues
in such a way that they have two carbon atoms in common, as repre-
sented in these formulas :

H H H OH

H\CACAC/H

<J <!! <"•

P/*\0/W\0/\H H/ Hc/ \c^ \H

j. i A 1

Naphthalene, Ci0H8. Naphthol, Ci0HT.OH.

Naphthalene has been mentioned as a product of the destructive distillation
of coal, and is obtained from that portion of coal-tar which boils between 180°
and 220° C. (356° and 428° F.). This distillate is treated with caustic soda and
then with sulphuric acid and distilled with water vapor.

When pure, naphthalene forms colorless, lustrous crystalline plates, having
a penetrating, but not unpleasant, odor and a burning, aromatic taste. It fuses
at 80° C. (176° F.), and boils at 218° C. (424° F.), but volatilizes slowly at ordi-
nary temperature, and readily with water vapor. It is only sparingly soluble
in water, but easily soluble in alcohol, ether, chloroform, etc. Impure naph-
thalene assumes, when exposed to light, a reddish or brownish color. Naph-
thalene is converted into phthalic acid by oxidizing agents.

Derivatives of naphthalene. While benzene yields only one kind
of mono-substitution product, naphthalene yields two varieties in
every case. Thus, there are two mono-hydroxy derivatives (naph-

588 CONSIDERATION OF CARBON COMPOUNDS.

thol), two mono-amino derivatives (naphthylamine), etc. This is
exactly what would be expected if the formula for naphthalene given
above be true. The 8 hydrogen atoms in the molecule fall into two
groups of 4 each, the atoms of each group bear the same relation to the
molecule, but different from the relation that the atoms of the other
group bear. This is shown in the following formulas, in which the
hydrogen atoms are designated in a manner that permits of reference
in the formulas for the derivatives of naphthalene :

Ha3 Ha 8H HI

/33H .a X Hj3 7H (X H2

\c/ \c/

o

x^Cs /G^ /C\ ^C\

\H3

II II

Ha'2 Ha1 H 5 H 4

In the first formula, hydrogen atoms «, a1, a2, a3 are alike, and £,
/51, /52, /5s are alike, but bear a different relation from that of the a
hydrogen atoms. In the second formula, the corresponding groups
are 1, 4, 5, 8 and 2, 3, 6, 7. The mono-substitution products in which
the a hydrogen is replaced, are known as alpha- or a-derivatives, the
others as beta- or ^-derivatives.

Theoretically, the number of di- and tri-substitution products of
naphthalene is very large. Thus, ten di-chlor and fourteen tri-chlor
derivatives are possible, and all are known. Such facts as these leave
very little doubt as to the truth of the structural formula of naphtha-
lene as given above.

Naphthol, C10H7OH = 142.98. This monatomic phenol bears to
naphthalene the same relation as phenol to benzene — /. <?., hydroxyl
replaces hydrogen in the respective hydrocarbons. Two isomeric
naphthols, the alpha- and beta-naphthol, are known, which differ in
their physical properties and in their physiological action. The
naphthol which is used medicinally is beta-naphthol, a solid compound
crystallizing in thin, shining plates, having an odor similar to phenol
and a sharp, pungent taste. It fuses at 122° C. (252° F.), boils at
286° C. (547° F.), is soluble in about 1000 parts of cold, or 75 parts
of boiling, water ; and readily soluble in alcohol, ether, chloroform,
and fatty oils. The aqueous solution is colored greenish by ferric
chloride. A few drops of iodine solution added to an aqueous solution
of beta-naphthol, followed by an excess of alkali solution, should pro-

BENZENE SERIES. AROMATIC COMPOUNDS. 589

duce no color, but if alplia-naphthol is present, an intensely violet
color is produced.

Naphthol occurs in coal-tar, but it is prepared synthetically from
naphthalene in the same manner in which phenol is prepared from
benzene. When concentrated sulphuric acid is heated with naphthalene
for several hours at 200° C., the beta-sulphonic acid is formed, C10H7-
SO3H ; during the early stage of the process, and particularly at 80°-
90° C., much alpha-sulphonic acid is formed, but at a higher temper-
ature this is converted into the beta variety. The sodium salt of the
beta acid is fused with sodium hydroxide, forming sodium naphthol
and sodium sulphite. By treating the former with an acid, beta-naph-
thol is liberated, which must be further purified.

Microeidine, C10H7.ONa, is the name given to sodium naphthol.
ItS aqueous solution is used as a disinfectant for cleansing dental
instruments.

Alpha-naphthol is obtained in the same manner as the beta product, from
the sodium salt of alpha-naphthalene sulphonic acid. It forms lustrous needles,
melting at 95° C. and boiling at 278°-280° C. It is more readily soluble in water
than beta-naphthol, and is said by one author to be three times more powerful
as an antiseptic and only one-third as poisonous as the beta compound. It is
official in the French Pharmacopoaia. Most authorities state, however, that it is
more poisonous than beta-naphthol. It has been used as a test for sugar in urine
and is employed in the preparation of certain azo dyes, as is also beta-naphthol.

The naphthols act in general like the phenols, but the (OH) group reacts
more readily than in the phenols. Thus, it can easily be replaced by the amido
(NH2) group. Naphthols readily form sulphonic acids, of which many are
known and are used in the manufacture of azo dyes. The 1, 4, naphthol-sul-
phonic acid is used most.

Beta-naphthol benzoate, C6H5COOC10H7 (Benzoyl-naphthol},\& obtained by the
action of benzoyl chloride on beta-naphthol at 170° C. It is a white crystalline
powder, melting at 107° C., tasteless, odorless, and insoluble in water, but solu-
ble in alcohol, chloroform, and hot ether. It splits into beta-naphthol and
benzoic acid in the intestines.

Beta-naphthol-bismuth (Orphol] has approximately the composition, C10H7O.-
Bi2O2(OH), and is said to be formed by the action of an alkaline solution of
naphthol on a solution of bismuth nitrate in dilute glycerin. It is a light-
brown, odorless, almost tasteless powder, insoluble in alcohol as well as water.
In the intestines it splits into naphthol and bismuth hydroxide.

Alpha-amino-naphthalene, C10H7.NH2 (Alpha-nap hthy famine], is obtained by
the reduction of the corresponding nitro-naphthalene, the chief product of the
action of nitric acid on naphthalene in the cold. It is also formed by heating
alpha-naphthol with the ammonia compound of zinc chloride. It melts at
50° C., has a pungent odor, and turns red in contact with air. It is easily
soluble in alcohol, and forms crystalline salts with acids, the solutions of which
with oxidizing agents give a blue precipitate, which soon turns red.

590 CONSIDERATION OF CARBON COMPOUNDS.

Beta-amino-naphthalene, C10H7.NH2 (Beta-naphthy famine), is easily obtained
by heating beta-naplitbol with the ammonia compound of zinc chloride to 210°C.
It forms pearly scales, soluble in hot water, ordorless, and melting at 112°C. It
does not give a colored compound with oxidizing agents.

Naphthionic acid, C10H6(NH2)SO3H (1, 4, Naphthylamine-sulphonic add). A
number of sulphonic acids are formed when the naphthylarnines are treated with
sulphuric acid, some of which are valuable in the preparation of dyes. The
sodium salt of naphthionic acid is used in making congo red, which has the

composition :

C6H4.N2.C10H5(NH2)S03Na.

C6H4.N2.C10H5(NH2)S03Na.

Four mono-sulphonic acids are formed when beta-naphthylamine is treated
with sulphuric acid.

Santonin, Santoninum, C15H18O3 = 244.29, is an anhydride of
santonic acid, C15H20O4. As several reactions point to a relationship
between this acid and naphthalene, santonin is mentioned in this place.

Santonin is the active principle of wormseed, the unexpanded
flowerheads of Artemisia, from which it is obtained by extraction
with alcohol and lime-water, and decomposition of the soluble com-
pound of lime and santonin by an acid. Santonin crystallizes in
colorless prisms, which turn yellow on exposure to light ; it is but
sparingly soluble in water, more soluble in alcohol and ether.

Santonin taken internally confers upon the urine a dark color re-
sembling the color of urine containing bile; upon heating such urine
it turns cherry-red or crimson, the color disappearing on the addition
of an acid, and reappearing on neutralization.

Analytical reactions :

1. Santonin added to alcoholic solution of potassium hydroxide
produces a bright-red liquid which gradually becomes colorless.

2. To 1 c.c. of sulphuric acid add a few drops of ferric chloride
solution and a crystal of santonin : on heating, a dark-red color is
produced, changing into violet-brown.

Aromatic compounds containing- nitrogen in the cycle.

Pyrrol, C4H4NH. During the destructive distillation of certain
nitrogenous matters (chiefly bones), a liquid known as bone-oil is ob-
tained, which contains a number of nitrogenous basic subtances,
among which pyridine and pyrrol are found. Pyrrol has but weak
basic properties, is insoluble in water, and has an odor like chloroform.

BENZENE SERIES. AROMATIC COMPOUNDS. 591

A solution of pyrrol in alcohol, treated with iodine in the presence
of oxidizing agents, such as ferric chloride, deposits after some time
crystals of tctra-iodo pyrrol. This compound is official under the
name of iodol, iodolum, C4I4NH = 566.17. It is a pale-yellow, crys-
talline powder, almost insoluble in water, soluble in 9 parts of alcohol,
1 to 2 parts of ether, and 15 parts of fatty oils; it is, when pure,
tasteless and odorless, and contains of iodine 88.97 per cent.

Antipyrine, Antipyrina, CUH12N2O = 186.75 (Phenyl-dimethyl-
isopyrazolon). When phenyl-hydrazine is heated with diacetic ether,
CH3CO.CH2.COOC2H5, a substance is formed known as phenyl-
methyl-isopyrazolon.

In this compound a second hydrogen atom may be replaced by
methyl, when phenyl-dimethyl-isopyrazolon is formed, which is the
substance to which the name antipyrine has been given.

Antipyrine is a white, crystalline, odorless powder, having a slightly bitter
taste; it fuses at 113° C. (235° F.), is soluble in less than its own weight of
water, in 1 part of alcohol, in 1 part of chloroform, but only in 50 parts of
ether.

The structure of antipyrine and its relation to pyrrol and isopyrazoltm inay
be shown by the constitutional formulas:

HC— CH HC— CH HC— CH2

HS JH I JH HH.

NH NH NH

Pyrrol. Pyrazol. Pyrazolin.

HC— CH2 HC=:CH CH3— C=

i!r co HN co

co

NC6H5

Pyrazolon. Isopyrazolon. Phenyl-dimethyl-

isopyrazolon.

Analytical reactions :

1. 0.2 gramme of antipyrine dissolves in 2 c.c. of nitric acid with-
out change of color. On heating slightly the liquid assumes a yellow,
then an intense red color.

2. 12 c.c. of a 1 per cent, solution of antipyrine treated with 0.1
gramme of potassium nitrite solution yield a colorless solution, which
turns intensely green on the addition of 1 c.c. of dilute sulphuric acid.
In a more concentrated solution green crystals of isonitroso-antipyrine
form on standing.

592 CONSIDERATION OF CARBON COMPOUNDS.

3. The addition of ferric chloride to solution of antipyrine causes
a deep-red color, changing to yellow on the addition of sulphuric
acid.

4. Mercuric chloride, as well as tannic acid, produces a white pre-
cipitate.

Incompatibilities. In addition to those indicated in the above tests, the
following may be mentioned : A mixture of antipyrine and calomel produces
a poisonous organic mercury compound ; with phenol, even in dilute aqueous
solution, an oily mass is formed; rubbed with sodium salicylate, a pasty mass
is produced, in solution, however, there seems to be no eftect ; with beta-naph-
thol, a moist mixture results ; rubbed with chloral hydrate, an oil is produced.
On the other hand, antipyrine increases the solubility in water of caffeine and
the quinine salts.

Salipyrin is antipyrine salicylate, obtained by direct combination of anti-
pyrine and salicylic acid. It is a white odorless powder, with a harsh, sweetish
taste, and is almost insoluble in water.

Resopyrin is a compound of antipyrine and resorcin. Hypnal is a com-
pound of antipyrine and chloral hydrate. Pyramidon is a dimethyl-amido
substitution product of antipyrine. Ferripyrine is a combination of anti-
pyrine and ferric chloride. Many other combinations are known.

Antipyrine is a constituent of many " migraine powders."

Pyridine, C5H5N. This substance has been mentioned above as
being a constituent of bone-oil. Other substances have been isolated
from this oil and have been found to form a homologous series :

Pyridine, C5H5N Lutidine, C7H9 N

Picoline, C6H7N Colliding C8HUN

Pyridine is of special interest, because it has been found that sev-
eral of the alkaloids, such as quinine, cinchonine, etc., when oxidized,
yield acids containing nitrogen, which bear to pyridine the same
relation that benzoic acid bears to benzene, or that acetic acid bears
to methane.

Thus, when nicotine is treated with oxidizing agents, nicotinic
acid, C6H5NO2, is obtained, which, when distilled with lime, breaks
up into pyridine and carbon dioxide, thus :

C6H5N02 = C5H5N + C02.

The relation of nicotinic acid to pyridine, of benzoic acid to ben-
zene, acetic acid to methane, may be shown thus :

BENZENE SERIES. AROMATIC COMPOUNDS. 593

CH3.H C6H6.H C6H4N.H

Methane. Benzene. Pyridine.

CH3.C02H C6H5.C02H C5H4N.CO2H.

Acetic acid. Benzoic acid. Nicotinic acid.

Pyridine is also obtained together with another basic substance,
termed quinoline, C9H7N, by distilling quinine or cinchonine with
potash. These observations, showing an intimate relationship between
alkaloids and the pyridine and quinoline bases, have led to numerous
experiments made with the view of either solving the problem of
making alkaloids synthetically, or of obtaining substances which
might have physiological actions similar to those of the alkaloids.
The result of these efforts has been the introduction into the materia
medica of quite a number of new remedies.

Pyridine is a colorless liquid, having a sharp, characteristic odor,
strongly basic properties, and a boiling-point of 116° C. (241° F.).

Quinoline, C9H7N ( Chinoline), has been mentioned above as a product of the
distillation of quinine with potash ; it may also be obtained by the action of
sulphuric acid upon a mixture of aniline, nitro-benzene, and glycerin. It is,
like pyridine, a colorless liquid, but its aromatic odor is less pleasant and its
basic properties are less marked than those of pyridine. Boiling-point 237° C.
(458° F.).

The constitution of pyridine and quinoline is supposed to correspond to
benzene and naphthalene respectively, one of the groups CH having been re-
placed by an atom of nitrogen, thus :

H H H H H

!

CX /Cx //CH HQ, /(\

^/ ^^ ^cx x

HC\ /CH H

\N/

H H H

Pyridine. Quinoline. Isoquinoline.

Isoquinoline is very similar to quinoline, but differs slightly in its proper-
ties. Like quinoline it is closely related to a number of alkaloids, especially
those of the opium group. It is found together with quinoline among the bases
of coal-tar and bone-oil.

Kairine, C10H13.NO.HC1. The name kairine has been given to the hydro-
chloride of methyl-oxychinoline hydride. It is a white, crystalline, odorless
powder, soluble in 6 parts of water or in 20 parts of alcohol.

Thalline, C10HnNO (Tetra-hydro-paramethyt-oxy quinoline). Quinoline serves

in the manufacture of thalline, a white, crystalline substance, which has an

aromatic odor, fuses at 40° C. (104° F.) and is soluble in water, alcohol, and

ether. The most characteristic feature of the substance is that it is colored

38

594 CONSIDERATION OF CARBON COMPOUNDS.

intensely green by various oxidizing agents, such as ferric chloride and others.
Some of the salts of thalline, chiefly the sulphate, tartrate, and tannate, have
been used medicinally.

51. TERPENES AND THEIR DERIVATIVES.

The group of hydrocarbons of the general formula (C5H8)X, found
largely in the volatile oils, has been called by the generic word ter-
penes, but this term has been more specifically applied to the sub-
group C10H16. According to the molecular complexity this group has
been classified into :

Hemiterpenes C5H8,

Terpenes proper Ci0Hl6,

Sesquiterpenes C15H24,

Diterpenes C20H32,

Polyterpenes (C10H16)X.

Isopene is the only representative of the hemiterpenes found in a
volatile oil, and does not occur naturally, but is formed by the de-
structive distillation of rubber or gutta percha. The terpenes proper
and sesquiterpenes are among the principal constituents of the vola-
tile oils. The diterpenes and higher polyterpenes are more rarely
found and but little studied.

Volatile or essential oils. The term essential oil is more a phar-
maceutical than chemical term, and is used for a large number of

QUESTIONS. — What is the difference between fatty and aromatic compounds,
and from which two hydrocarbons are they derived ? From what source is
benzene obtained, how can it be made from benzoic acid, and what are its
properties ? Give the graphic formulas of benzene, nitro-benzene, phenol,
thymol, benzoic acid, and salicylic acid. Mention methane derivatives which
have a constitution analogous to that of the substances mentioned. Give com-
position, properties, and mode of manufacture of, and tests for carbolic acid.
What relation exists between benzoic acid and oil of bitter almond? What is
the source of amygdalin, to which class of substances does it belong, and what
are the products of its decomposition under the influence of emulsin ? Explain
the process for the manufacture of salicylic acid, and state its properties.
Give composition and properties of naphthalene and naphthol. Give tests for
tannin, state the source from which it is derived and for what it is used. From
what, and by what process, is aniline obtained; what is its composition and
what its constitution? How are aniline dyes manufactured from aniline?
State the properties and some reactions characteristic of antipyrine. What
is saccharin, and what are its properties ? State the composition of iodol.

TERPENES AND THEIR DERIVATIVES. 595

liquids obtained from plants, and having in common the properties
of being volatile, soluble in ether and alcohol, almost insoluble in
water, and having a distinct and in most cases even highly charac-
teristic odor. They stain paper as do fats or fat oils, from which
they differ, however, by the disappearance after some time of the
stain produced, while fats leave a permanent stain.

The specific gravity of volatile oils ranges generally between 0.85
and 0.99. Being nearly insoluble in, and specifically lighter than,
water, they will float on it. The water, however, retains in most
cases enough of the oils to assume their odor (medicated waters).
Most volatile oils are optically active, turning the plane of polarized
light either to the right or left. While chemically pure oils are
colorless, many, even when freshly prepared, have a distinct color;
some are pale yellow, dark yellow, reddish or reddish brown, while
a few are green or blue. The oils generally darken with age, espe-
cially when exposed to light and air, the atmospheric oxygen acting
on them and converting the oils often into a sticky and resinous mass.

Volatile oils are found in different parts of plants, and are the
principles imparting to the respective plants their characteristic odor.
The extraction of volatile oils from plants is accomplished generally
by distilling with water the vegetable matter containing the oil, the
oil passing over with the steam and floating on the surface of the
condensed water. In some instances mechanical pressure is used for
the separation, as in case of the oils of orange, lemon, bergamot, etc.
In other cases the oils are extracted by suitable solvents, or special
methods are used.

In their chemical composition essential oils differ widely ; some are
compound ethers (oil of wintergreen is methyl salicylate), others are
aldehydes (oil of bitter almonds is benzaldehyde), but most of them
are hydrocarbons of the aromatic series, or mixtures of them, often
associated with oxygen derivatives, alcohols, phenols, ketones, alde-
hydes, esters, etc.

Oil of doves. The principal constituent of this oil is eugenol, C8HS.C3H,.
OCH3.OH, a monatomic phenol ; a sesquiterpene, C15H24, culled caryophylleue
is also present.

Oil of cinnamon consists chiefly of cinnamic aldehyde, C6H5CH.CHCOH,
a compound which has been prepared synthetically. Oil of cinnamon also
contains cinnamyl acetate, C9H9.C,H3O2, and a small amount of cinnamic acid
C8H802.

Oil of peppermint. The oils found in the market differ widely from one
another, and there is no other volatile oil containing so many different con-

596 CONSIDERATION OF CARBON COMPOUNDS.

stituents ; as many as seventeen having been found in one sample. Besides
three different terpenes and one sesquiterpene, were found acetaldehyde, acetic
acid, isovalerianic acid, amyl alcohol, menthol, menthon, C10H180, menthyl
acetate, C10H19O.C3H30, and others.

Terpenes, C10H16. The terpenes are widely distributed in the
vegetable kingdom, especially in the coniferse and varieties of citrus,
etc., and are found in the volatile oils obtained from the individual
plants. The terpenes are readily acted upon by many agents and
hence undergo numerous changes. One of these changes is polym-
erization— i. e., conversion into compounds of the composition C^H^
and CjjoHgg, which may be effected by heating a terpene in a sealed
tube, or by shaking it with concentrated sulphuric acid or with cer-
tain other substances. Many of them also show a great tendency to
pass into more stable isomers under certain conditions — i. e., when
acted on by acids. Gaseous chlorine acts violently upon them, and
bromine and iodine convert many of them into cymene. Many ter-
penes are therefore closely related to cymene, C10H14, and may be con-
sidered as dihydrocymene ; others, however, show a quite different
structure. They are oxidized quite readily with the formation of a
number of organic acids, and unite with gaseous hydrochloric acid to
form mono- or dihydrochlorides. With bromine they often form
characteristic tetrabromides, C10H16Br4. They readily yield com-
pounds with nitrosyl chloride, of the formula C10H16.NOC1, known
as nitrosochlorides, and with the oxides of nitrogen compounds of
the formulas C10H16.N2O3 and C10H16.N2O4, known as nitrosites and
nitrosates respectively. The terpenes are almost all optically active,
and most of them exist both in dextro- and in Isevorotatory modifi-
cations.

Pinene is the chief constituent in most of the volatile oils obtained
from the coniferse, and is also found largely in other volatile oils.

Oil of turpentine, C10H16, is chiefly composed of pinene. It is a
thin, colorless liquid of a characteristic aromatic odor, and an acrid,
caustic taste ; it is insoluble in water, soluble in alcohol, and an excel-
lent solvent for resins and many other substances. When treated
with hydrochloric acid gas direct combination takes place and a white
solid substance of the composition C10H16HC1 is formed, which is
known as pinene hydrochloride, or artificial camphor, on account of
its similarity to camphor both in appearance and odor.

Experiment 7L Through 10 or 20 c.c. of oil of turpentine pass a current of
hydrochloric-acid gas for some time, or until a quantity of a solid substance

TERPENES AND THEIR DERIVATIVES. 597

has separated. Collect this substance, which is artificial camphor, upon a filter ;
notice its characteristic odor. Heat some of it; hydrochloric acid is set free.

Camphene is the only solid hydrocarbon of the terpene group, and occurs in
the oil from Pinus Sibirica. It is obtained by heating the above pinene hydro-
chloride with alcoholic potash.

Limonene is the principal constituent of orange oil, and is found in a large
number of other oils, as the dextro modification. Laevolimonene occurs in
pine-needle oil.

Dipentene is the inactive modification of limonene, and can be prepared by
heating pineiie, camphene, sylvestrene, or limonene to 250°-270° C. for several
hours.

Terebene, Terebenum, consists chiefly of dipentene with other hydrocar-
bons, and is obtained from oil of turpentine by mixing it with sulphuric acid,
distilling, washing the distilled oil with soda solution, redistilling, and collect-
ing the portions which pass over at a temperature of 155°-165° C. (311°-
329° F.). Terebene resembles oil of turpentine in most respects, but has not
the unpleasant odor of this oil.

Sylvestrene is found in Swedish and Russian oil of turpentine.

Phellandrene is widely distributed in volatile oils; notably in the water-
fennel oil and eucalyptus oil.

Sesquiterpenes, C15H24. These are likewise widely distributed in
the vegetable kingdom, and are very similar in their general proper-
ties to the terpenes proper, but have a higher boiling-point. Of
those, well characterized, may be mentioned : cadinene, from oil of
cade and a large number of other volatile oils ; caryophyttene, from oil
of cloves ; humulene, from oil of hops ; santoleney from oil of sandal-
wood; cedrene, from oil of cedarwood ; and zingiberene, from oil of
ginger.

Rubber, Elastica (Caoutchouc) is the dried milky juice found in
quite a number of trees growing in the tropics. It consists chiefly
of hydrocarbons of the terpene series, having a very large molecular
weight and a complex molecular structure.

The commercial article is yellowish-brown, has a specific gravity
of 0.92 to 0.94, is soft, flexible, insoluble in water and alcohol,
but soluble in carbon disulphide, ether, chloroform, and benzene. It
is not acted upon by dilute mineral acids ; concentrated nitric and
sulphuric acid, as well as chlorine, attack it after a time. It is hard
and tough in the cold ; when heated it becomes viscous at 125° C.
(257° F.), and fuses at 170°-180° C. (347°-356° F.) to a thick liquid,
which, on cooling, remains sticky, and only regains its original char-
acter after a long time.

Vulcanized rubbw is India-rubber which has been caused to enter

598 CONSIDERATION OF CARBON COMPOUNDS.

into combination with from 7 to 10 per cent, of sulphur by heating
together the two substances to a temperature of 130°-150° C. (266°-
302° F.). Vulcanized rubber differs from the natural article by
possessing greater elasticity and flexibility, by resisting the action of
solvents, reagents and atmosphere to a higher degree, and by not
hardening when exposed to cold.

Hard rubber, vulcanite, or ebonite, is vulcanized rubber, containing
from 20 to 35 per cent, of sulphur, and often also tar, white-lead,
chalk, or other substances. It is hard, tough, and susceptible of a
good polish.

Preservation of rubber. Various substances have been recommended
for preserving articles of rubber. For undeteriorated rubber, it is said that a
3 per cent, solution of either phenol or aniline is the best, while for deterior-
ated rubber, or such as has been exposed many times to boiling water, a 1 per
cent, solution of potassium pentasulphide is best, the restorative properties of
the latter depending on the absorption of the sulphur from the pentasulphide.
The articles are immersed in the solutions in vessels of appropriate shape. It
has been observed that black rubber immersed in the aniline solution under-
goes an increase in volume. For example, rubber tubing shows a marked in-
crease in length.

Gutta-percha is the concrete juice of a tree — Isonaudra gutta. It
resembles india-rubber both in composition and properties. At ordi-
nary temperature it is a yellowish or brownish, hard, somewhat
flexible, but scarcely elastic substance ; when warmed it softens, and
is plastic above 60° C. (140° F.) ; at the temperature of boiling-water
it is very soft. It is insoluble in water, alcohol, dilute acids and
alkaline solutions ; soluble in oil of turpentine, carbon disulphide,
and chloroform.

Oxygen derivatives of terpenes.

Stearoptens or camphors are substances closely related to the
terpenes and to cymene both in physical and chemical properties;
while terpenes are liquid, camphors are crystalline solids. Borneo
camphor has the composition C10H18O, while the camphor found
in the camphor-trees of China and Japan has the composition
C10H160.

Camphor, Camphora, C]0H16O (LaurinoT), forms white, translucent
masses of a tough consistence and a crystalline structure ; it has a
characteristic, penetrating odor and poisonous properties ; in the pres-
ence of a little alcohol or ether it may be pulverized ; it is nearly
insoluble in water, but soluble in alcohol, ether, chloroform, etc. ;
boiled with bromine it forms the monobromated camphor, carnphora

TERPENES AND THEIR DERIVATIVES. 599

monobromata, C,0H15BrO, a white crystalline substance having a mild
camphoraceous odor and taste. Heating with nitric acids converts
camphor into camphoric add, acidum camphoricum, CgH^CO.,!!)^
a colorless, crystalline, fusible substance having an acid taste ; it is
slightly soluble in water, readily in alcohol and ether.

Cineol. Eucalyptol, C10Hi80, is found in the volatile oils of different species
of eucalyptus, as also in the oils of some other plants. It is liquid at the ordi-
nary temperature, but solidifies when cooled to a little below the freezing-point
of water. It has an aromatic, distinctly camphoraceous odor.

Menthol, C10H19OH (Mint-camphor). Found together with a ter-
pene in oil of peppermint, and separates in crystals on cooling the oil.
Menthol is nearly insoluble in water, fuses at 43° C. (109° F.), and
boils at 212° C. (414° F.). It has the characteristic odor of pepper-
mint.

Terpin hydrate, Terpini hydras, C10H20O2.H2O, is the hydrate of
the diatomic alcohol terpin, and is formed from pinene under the
influence of alcohol and nitric acid. It forms colorless crystals, melt-
ing at 117° C. (243° F.), is readily soluble in alcohol, but sparingly
soluble in water, ether, or chloroform.

Resins are obtained, together with the essential oils, from plants.
Mixtures of a resin and a volatile oil are known as oleo-resins, while
mixtures of a resin or oleo-resins and gum are known as gum-resins.
The name balsam is also used for a certain group of oleo-resins.

The resins are mostly amorphous, brittle bodies, insoluble in water,
but soluble in alcohol, ether, fatty and essential oils ; they are fusible,
but decompose before being volatilized ; they all contain oxygen and
exhibit somewhat acid properties.

Turpentine, the oleo-resin of the conifers, contains besides the oil of
turpentine a resin called colophony, rosin, or ordinary resin, consisting
chiefly of the anhydride of abietic acid, C44H64O5.

Copaiva balsam consists of a volatile oil and a resin, the latter
being principally copaivic acid, C20H30O2.

Of fossil resins may be mentioned amber and asphalt, the latter
having most likely been formed from petroleum.

QUESTIONS. — What substances are known as terpenes : where are they found
in nature? Give the composition of the principal groups of terpenes. Men-
tion the general properties of essential oils, and name some of the important
ones. What is the source of rubber ; how is it converted into vulcanized and
hard rubber ? State the composition and properties of camphor.

600 CONSIDERATION OF CARBON COMPOUNDS.

52. ALKALOIDS.

General Remarks. The basic substances found in plants are
grouped together under the name of alkaloids, this term signifying
alkali-like, in allusion to the alkaline or basic properties of these
substances. They show their derivation from ammonia to a more or
less marked degree, as, for instance, in their power to combine with
acids to form well-defined salts, to combine with platinic chloride to
form insoluble double compounds, etc.

The compounds formed by the direct combination of alkaloids with
acids are, in the case of oxygen acids, named like other salts of these
acids, for instance, sulphates, nitrates, acetates, etc. In the case of
halogen acids, however, a different method has been adopted, because
it would be incorrect to apply the terms chlorides and bromides to
substances formed not by the combination of chlorine or bromine with
other substances, nor by the replacement of hydrogen in the respective
hydrogen acids of these elements, but by direct combination of these
acids with the alkaloids. The terms hydrochloride and hydrobromide
have been adopted by the U. S. P. for the compounds obtained by
direct union of alkaloids with hydrochloric and hydrobromic acids.
Formerly the terms hydrochlorate and hydrobromate were used.

Alkaloids are found in the leaves, stems, roots, barks, and seeds of
various plants ; it often happens that a certain alkaloid is found in
the different species of one family, and it is often the case that

various alkaloids of a similar composition are found in the same plant.

General properties of alkaloids:

1 . They combine with acids to form well-defined salts, and are set
free from the solutions of these salts by alkalies and alkali carbonates.

2. In most cases those containing no oxygen are volatile liquids,
those containing oxygen are non-volatile solids.

3. The volatile alkaloids have a peculiar disagreeable odor, remind-
ing of ammonia ; the non-volatile alkaloids are odorless.

4. Most solid alkaloids fuse at a temperature above 100° C. (212°
F.) without decomposition, but are decomposed when the heat is
raised much beyond the fusing-point.

5o Most alkaloids are insoluble, or nearly so, in water, but soluble
in alcohol, chloroform, benzene, acetic ether, and many also in ether.

6. The hydrochlorides, sulphates, nitrates, acetates (and most other
salts) of alkaloids are either soluble in water, or in water which has
been slightly acidulated, and also in alcohol ; but they are insoluble,
or nearly so, in ether, acetic ether, chloroform (except veratrine and

ALKALOIDS. 601

narcotine), amyl alcohol (except veratrine and quinine), benzene, and
benzin.

7. The solid alkaloids, as well as their salts, may be obtained in a
crystalline state.

8. Most alkaloids are white, have a very strong, generally bitter,
taste, and act very energetically upon the animal system.

9. From the aqueous solutions of alkaloid salts, the solid alkaloids
are precipitated by alkali hydroxides, in an excess of which reagents
some alkaloids (morphine, for instance) are soluble. Alkali car-
bonates and bicarbonates liberate all, and precipitate most alkaloids ;
not precipitated by bicarbonates are strychnine, brucine, veratrine,
atropine, and a few rare alkaloids.

Most alkaloids give precipitates with tannic acid, picric acid,
phospho-molybdic acid, potassium mercuric iodide; and the higher
chlorides of platinum, gold, and mercury. These precipitates are
similar in properties and composition to those formed with ammonia.

Most alkaloids give beautiful color reactions when treated with
oxidizing agents, such as nitric acid, chloric acid, chromic acid, ferric
chloride, chlorine water, etc.

A decinormal solution of mercuric-potassium iodide, HgI2.(KI)2, made by
dissolving 13.546 grammes mercuric chloride and 49.8 grammes potassium
iodide in 1000 c.c of water, is known as Mayer's solution. This precipitates all
alkaloids, forming with them white or yellowish-white, generally crystalline
compounds. The solution has been used for volumetric determination of alka-
loids, but the method is now discarded, as the results are not accurate. (In
most cases the alkaloid replaces the potassium in the potassium-mercuric iodide.)

Phospho-molybdic acid, mentioned above as a reagent for alkaloids, is pre-
pared as follows : 15 grammes ammonium molybdate are dissolved in a little
ammonia water and diluted with water to 100 c.c. This solution is poured
gradually into 100 c.c. of nitric acid, specific gravity 1.185, and to this mixture
Is added a warm 6 per cent, solution of sodium phosphate as long as a precipi-
tate is produced. This precipitate is collected on a filter, washed and dissolved
in very little sodium hydroxide solution ; the solution is evaporated to dryness,
further heated until all ammonia has been expelled and the residue dissolved
in 10 parts of water. To this solution is added a quantity of nitric acid suffi-
cient to redissolve the precipitate which is formed at first. This reagent gives
precipitates not only with the alkaloids, but also with the salts of potassium
and ammonium.

General mode of obtaining1 alkaloids. The disintegrated veg-
etable substance (bark, seeds, etc.) is extracted with acidified water,
which dissolves the alkaloids. When the alkaloid is volatile, it is
obtained from this solution by distillation, after having been liberated
by an alkali.

602 CONSIDERATION OF CARBON COMPOUNDS.

volatile alkaloids are precipitated from the acid solution by
the addition of an alkali, and the impure alkaloid thus obtained is
purified by again dissolving in an acid and reprecipitating, or by dis-
solving in alcohol and evaporating the solution.

As the quantity of alkaloids in plants, and consequently in the aqueous
extract made from them, is often so small that the precipitation process gives
unsatisfactory results, a second method known as the shaking-out process is often
employed for the separation of alkaloids. In using this process the con-
centrated aqueous extract, to which a suitable alkaline precipitant has been
added, is agitated with a liquid (such as chloroform) not miscible with water
and acting as a solvent upon the alkaloids. The operation is performed in an
apparatus known as separator or separatory funnel, consisting of a globular or
cylindrical glass vessel, provided with a well-fitting stopper and an outlet-tube
containing a glass stopcock. Having introduced into this vessel the extract
and solvent, the latter is made to dissolve the alkaloids present by a rapid
rotation of the separator. As the aqueous solution and the solvent do not mix,
but form two distinct layers one above the other, they may be conveniently
separated by opening the stopcock until the heavier liquid has run out. By
evaporation of the liquid, used as a solvent, the alkaloids may be obtained in a
more or less pure condition.

Assay methods. As the medicinal value of many drugs, such as opium,
cinchona bark, etc., as also that of the galenical preparations, such as tinctures,
extracts, etc., obtained from such drugs, depends chiefly on the alkaloids pres-
ent, and as the quantity of the alkaloids in drugs varies considerably, the
U. S. P. gives specific assay methods for the estimation of the percentage of the
alkaloids contained in drugs or in certain preparations.

These assay methods must be closely followed by the analyst, as otherwise
results may be obtained which are either too high or too low. This is due to
the fact that these methods in many cases do not give absolutely correct results,
but give results sufficiently accurate for all practical purposes, provided the
directions of the Pharmacopeia are closely followed. To bring about a
standard and uniformity in alkaloidal strength is the object of these assay
methods.

Antidotes. In cases of poisoning by alkaloids the stomach-pump and emetics
(zinc sulphate) should be applied as soon as possible ; astringent liquids may be
given, because tannic acid forms insoluble compounds with most of the alkaloids.
In some cases special physiological antidotes are known, and should be used.

Detection of alkaloids in cases of poisoning1. The separation
and detection of poisonous alkaloids in organic matter (food, contents
of stomach, etc.), especially when present in very small quantities, as
is generally the case, is one of the most difficult tasks of the toxi-
cologist, and none but an expert who has made himself thoroughly
familiar with the methods of discovering minute quantities of organic
poisons in the animal system should undertake to make such an

ALKALOIDS.

PLATE VI

norphine treated with nitric acid.

Morphine treated with solution of
ferric chloride.

Codeine treated with bromine water
and ammonia water.

Quinine treated with chlorine water
and ammonia water.

Strychnine treated with sulphuric
acid and potassium dicbromate.

Brucine treated with nitric acid and
with sodium thiosulphate.

Physostigmine treated successively

with ammonia water, alcohol, acetic acid,
and again with ammonia water.

Veratrine treated with sulphuric acid.

A Jfofit&Co Litli Bulttntorr, . \(d

ALKALOIDS. 603

analysis in case legal proceedings depend on the result of the
chemist's report.

Of the various methods applied for the separation of alkaloids from organic
matter, the following may be mentioned :

The substance to be examined is properly comminuted (if this be necessary)
and repeatedly digested at 40° to 50° C. (104° to 122° F.) with water slightly
acidulated with sulphuric acid. The filtered liquids (containing the sulphates
of the alkaloids) are evaporated over a water-bath to a thin syrup, which is
mixed with three or four times its own volume of alcohol ; this mixture is
digested at about 35° C. (95° F.) for several hours, cooled, filtered, and again
evaporated nearly to dryness. (By this treatment with alcohol many substances
soluble in the acidified water, but insoluble in diluted alcohol, are eliminated
and left on the filter, while the alkaloids remain in solution as sulphates.)

A little water is now added to the residue, and this solution, which should yet
have a slight acid reaction, is shaken with about three times its own volume of
acetic ether, which dissolves some coloring and extractive matters, but does not
act upon the alkaloid salts. The two strata of liquids which form on standing
in a tube are separated by means of a pipette, and the operation is repeated, if
necessary, i. e., if the ether should have been strongly colored -

The remaining acid aqueous solution is next slightly supersaturated with
sodium carbonate, which liberates the alkaloids. Upon now shaking the solu-
tion with acetic ether, all alkaloids are dissolved in this liquid, which, after
being separated from the aqueous solution, leaves upon evaporation, at a low
temperature, the alkaloids generally in a sufficiently pure state for recognition
by special tests. It may, however, be necessary to purify the residue further
by neutralizing with an acid, allowing to crystallize in a watch-glass, and sep-
arating the small crystals from adhering mother-liquor.

The above method for detecting alkaloids in the presence of organic matter
generally answers the requirements of students.

The practical toxicologist has in most cases of poisoning some data (deduced
from the symptoms before death, or from the results of the post-mortem exam-
ination) pointing to a certain poison, which, of course, facilitate his work con-
siderably.

Classificati9n of alkaloids. While the constitution of many alka-
loids has as yet not been determined, others have been shown to be
derivatives, or to contain the nuclei of either pyridine, quinoline, or
isoquinoline. Closely related to pyridine are the liquid bases coniine,
nicotine, and sparteine, as also the solid alkaloids atropine, cocaine,
ecgonine, and others. Among alkaloids derived from quinoline are
those found in cinchona bark and in nux vomica. Related to iso-
quinoline are the opium alkaloids.

The pyridine group of alkaloids.

The close relationship between pyridine and some of the vegetable
alkaloids may be shown by considering their structure, which is this :

604 CONSIDERATION OF CARBON COMPOUNDS.

CH CH2 CH2

/% /\ /\

HC CH H8C CH2 H2C CHa

II I II I I

HC CH H,C CH2 H2C CHC3HT

N NH NH

Pyridine. Piperidine. Coniine.

Piperidine has been made by adding 6 atoms of hydrogen to pyri-
dine by means of sodium and alcohol ; coniine, which is propyl-piperi-
dine, was the first true alkaloid prepared artificially.

Piperin, Piperina, C17H19NO3 =-- 283.04. This compound is found
in black and white pepper. While it is isomeric with morphine, it
differs widely from it in all its properties. It can hardly be called
an alkaloid, as it has no alkaline reaction, is but feebly basic, and does
not show the general alkaloidal reactions. The U. S. P. emphasizes
this by giving to piperin the ending in and not ine, which is used for
all true alkaloids. It forms colorless or pale yellowish crystals
which are, when first put in the mouth, almost tasteless, but produce
on prolonged contact a sharp, biting sensation.

Piperin dissolves in concentrated sulphuric acid with a dark blood-
red color, which disappears on dilution with water. Treated with
nitric acid it turns rapidly orange, then red.

Coniine, C8H17N, occurs in conium maculatum (hemlock), accom-
panied by two other alkaloids. It is a colorless, oily liquid, having
a disagreeable, penetrating odor.

Pilocarpine, OUH16N2O2. Found in the leaflets of pilocarpus
species. The alkaloid crystallizes with difficulty ; its solutions in
ether, alcohol, or water have an alkaline reaction. It is a white,
crystalline powder, which dissolves in fuming nitric acid with a
faintly greenish tint. The aqueous solution is precipitated by most
of the common reagents for alkaloids. The hydrochloride and nitrate
are official.

Nicotine, C10H14N2. Tobacco leaves contain from 2 to 8 per cent,
of nicotine, which is a colorless, oily liquid, having a caustic taste
and a disagreeable, penetrating odor. It gives with hydrochloric
acid a violet, with nitric acid an orange, color.

Sparteine, C15H26N2. This alkaloid, found in scoparius (broom,
Irish broom), is a colorless, oily liquid, turning brown on exposure
to air and light. It has a slight aniline-like odor.

ALKALOIDS. 605

Sparteine sulphate, Ci5H26N.2H2S04 + 5H20, is obtained by saturating the
alkaloid with sulphuric acid ; it is a colorless, crystalline salt, readily soluble
in water. An ethereal solution of the salt, to which a few drops of ammonia
water have been added, deposits, on the addition of an ethereal solution of
iodine, minute dark greenish-brown crystals.

The tropine group of alkaloids.

Atropine, Atropina, C^H^NOs = 287.O4 (Daturine). Obtained
from Atropa belladonna. It is a white, crystalline powder, having a
bitter and acrid taste and an alkaline reaction ; it is sparingly soluble
in water, but very soluble in alcohol and chloroform. The commer-
cial article generally contains a small quantity of hyoscyamine.
Atropine sulphate, (CtfH^NO^.ELjSO^ is a white, crystalline powder,
easily soluble in water.

Analytical reactions :

1. Atropine dissolves in concentrated sulphuric acid without color.
This solution is not colored by nitric acid (difference from morphine),
and not at once by potassium dichromate (difference from strychnine).
•" 2. A mixture of atropine and nitric acid, when evaporated to dry-
ness over a water-bath, leaves a yellow residue, which turns violet on
the addition of a few drops of an alcoholic solution of potassium
hydroxide and a fragment of the same reagent.

3. On warming a mixture of atropine and concentrated sulphuric
acid a pleasant odor, reminding of roses and orange flowers is evolved.
The addition of a few fragments of potassium dichromate changes
this odor to that of bitter almond.

4. Solutions of atropine dilate the pupil of the eye to a marked
extent.

Homatropine, C16H21NO3. This alkaloid is obtained by the con-
densation of tropine and mandelic acid. The hydrobromide is offi-
cial. It is a white crystalline powder, and resembles atropine in its
mydriatic properties.

Hyoscyamine, C17H23NO3. Found in small quantities together
with hyoscine in the seeds of Hyoscyamus niger (henbane), and in
some other plants belonging to the solanaceae.

Hyoscyamine resembles atropine closely in most of its chemical,
physical, and physiological properties, but the corresponding salts of
the two alkaloids crystallize in different forms ; the hydrobromide and
sulphate are official.

606 CONSIDERATION OF CARBON COMPOUNDS.

Hyoscyamine differs from atropine by yielding with gold chloride
a precipitate which, when recrystallized from a hot aqueous solution,
acidified with hydrochloric acid, deposits lustrous, golden-yellow
scales.

Hyoscine, C17H21NO4. Found together with hyoscyamine in
Hyoscyamus. The alkaloid is known only in an amorphous, semi-
solid state, but the salts, of which the hydrobromide is official, crys-
tallize readily. Hyoscine evaporated to dryness on a water-bath with
a few drops of fuming nitric acid leaves a nearly colorless residue
which turns violet on the addition of some alcoholic solution of
potassium hydroxide.

Scopolamine hydrobromide, C17H21NO4HBr3H2O, is the hydro-
bromide of an alkaloid obtained from plants of the Solanacese, and is
chemically identical with hyoscine hydrobromide.

Cocaine, Cocaina, C17H21NO4 = 3OO.92. This alkaloid is found
in the leaves of the South American shrub Erythroxylon coca, in
quantities varying from 0.15 to 0.65 per cent. It is a white crystal-
line powder, soluble in about 600 parts of water, easily soluble in
alcohol, ether, and chloroform ; it fuses at 98° C. (208° F.). A frag-
ment of cocaine placed on the tongue causes the sensation of numb-
ness without acrid or bitter taste ; the solution in water is faintly bitter.

Cocaine heated with acids in sealed tubes is decomposed into methyl alcohol,
benzoic acid, and ecgonine, showing it to be methyl-benzoyl-ecgonine :

C12H21NO4 + 2H2O = CH3HO + G6H5CO2H + C9H15NO3.
Cocaine. Methyl alcohol. Benzoic acid. Ecgonine.

Ecgonine is found in the coca leaves as benzoyl-ecgonine, C9HI5(C7H50)N03
+ 4H2O ; this is a white, crystalline substance from which cocaine may be
obtained by heating it with methyl-iodide. The mother-liquors obtained in
the manufacture of cocaine from the leaves contain the alkaloid in an amor-
phous state and possibly one or two other alkaloids, one of which has been
named hygrlne. Whether these alkaloids are contained in the coca-plant, or
are products of the decomposition of cocaine, are questions not yet decided.

Of the various salts of cocaine, the hydrochloride, C17H21NO4HC1,
is official. This salt crystallizes from alcohol in short, anhydrous
prisms; from aqueous solution, however, with two molecules of water,
which are completely expelled at a temperature of 100° C. (212° F.).
The anhydrous salt fuses at 190° C. (374° F.) and is readily soluble
in water ; this salt solution has a somewhat more bitter taste than the
alkaloid itself.

ALKALOIDS. 607

Analytical reactions :

1. Cocaine salts are precipitated from an aqueous solution as fol-
lows : Platinum chloride produces a yellowish-white, mercuric chlo-
ride a white nocculent, picric acid a yellow pulverulent, the alkali
carbonates and hydroxides a white precipitate, which latter is soluble
in ammonia.

2. To a cocaine solution, strongly acidified with hydrochloric acid,
add some potassium dichromate, when an orange-colored crystalline
precipitate of cocaine chromate forms.

3. Add 1 c.c. of a 3 per cent, solution of potassium permanganate
to 1 centigramme of cocaine hydrochloride dissolved in 2 drops of
water; a violet precipitate forms which appears brownish-violet when
collected on a filter.

4. Boil a small quantity of cocaine solution for a few minutes with
dilute sulphuric acid ; neutralize carefully with potassium hydroxide
and then add a few drops of ferric chloride solution. A pale, brownish-
yellow precipitate of basic ferric benzoate will form.

Substitutes for cocaine. Several synthetics have been introduced to
take the place of cocaine. Some of these are the following :

Alypin, (CH3)2N.CH2.C(C2H5)(C6H5COO).CH2.N(CH3)2.HC1, is the hydro-
chloride of the benzoyl-ethyl-tetramethyldiamido derivative of secondary
propyl alcohol. It is a white hygroscopic powder, very soluble in water and
alcohol, of a neutral reaction and bitter taste. It is a local anesthetic, claimed
to be equal to cocaine, but not a mydriatic, and less toxic than cocaine. It is
used externally in a 10 per cent, solution and hypodermically in a 1 to 4 per
cent, solution.

Beta-eucaine hydrochloride, C5H7N.(CH3)3( CeHsCOO^HCl, is a salt of
trimethyl-benzoyl-hydroxypiperidine. It is a white powder, soluble in 20
parts of water and in 14 parts of alcohol. Its solutions can be boiled without
change, and are precipitated by alkalies or carbonates. It is a local anesthetic
like cocaine, but weaker, and does not dilate the pupil or contract the blood-
vessels. It is used in a 2 to 3 per cent, solution in the eye, and 5 to 10 per
cent, solution or ointment on other parts.

Holocaine hydrochloride, CH3,C( :N.CeH4.OC2H5)(.NH.C6H4.OC2H5)JICl,

is the salt of a basic condensation product of paraphenetidin and acetparaphe-
netidin (phenacetin). It forms colorless, neutral or faintly alkaline crystals,
odorless, slightly bitter, and producing transient numbness on the tongue. It
is soluble in 50 parts of water, easily in alcohol. The solution is precipitated
by alkalies and carbonates and the alkaloidal reagents. Porcelain should be
used in making solutions, as alkali from glass causes a turbidity.

The salt is a local anesthetic like cocaine, but having a quicker effect and
antiseptic action. A 1 per cent, solution is employed. It is more toxic than
cocaine.

608 CONSIDERATION OF CARBON COMPOUNDS.

Pelletierine tannate of the U. S. P. is a mixture of the tannates of four
alkaloids (ptmicine, iso-punicine, inethyl-punicine, and pseudo-punicine) ob-
tained from Punica Granatum.

The quinoline group of alkaloids.

Cinchona alkaloids. The bark of various species of cinchona
contains a number of alkaloids, of which the most important are
quinine, cinchonine, quinidine, and cinchonidine. These alkaloids
exist in the bark in combination with a peculiar acid, termed kinie
acid. The quantity and relative proportion of the alkaloids vary
widely in different barks, but the official bark should contain not less
than 5 per cent, of total alkaloids, and at least 4 per cent, of anhy-
drous ether-soluble alkaloids.

Quinine, Quinina, C20H24N2O2.3H2O = 375.46. This formula
represents the official alkaloid, but it is also known anhydrous, and
in combination with either one or two molecules of water. The
anhydrous quinine is a resinous substance, while the crystallized
quinine is a white, flaky, amorphous or crystalline powder, having
a very bitter taste and an alkaline reaction. It is nearly insoluble in
water, but soluble in alcohol, ether, ammonia water, chloroform, and
dilute acids. When heated to about 57° C. (134° F.) it melts ; at
100° C. (212° F.) it loses 2 molecules of water, the remainder being
expelled at 125° C. (257° F.).

Quinine sulphate, Quininse sulphas, (C20H24N2O2)2H2SO4.7H2O
= 866.15. This salt, containing two molecules of the alkaloid in
combination with one of sulphuric acid and seven of water, is the
common form of quinine sulphate. It forms snow-white, silky, light
and fine, needle-shaped crystals, fragile and somewhat flexible, making
a very light and easily compressible mass ; it has a very bitter taste
and a neutral reaction ; it is soluble in 720 parts of cold and in 30
parts of boiling water ; soluble in 65 parts of alcohol, but nearly
insoluble in ether and chloroform ; it readily dissolves in diluted
sulphuric or hydrochloric acid.

Quinine bisulphate, Quininse bisulphas, C20H24N2O2.H2SO4.7H2O
= 544.33. This salt is formed when the common sulphate is dis-
solved in an excess of diluted sulphuric acid. It crystallizes in color-
less, silky needles, has a strongly acid reaction, and is soluble in 8.5
parts of water.

ALKALOIDS. 609

Quinine hydrochloride, C20H24N2O2.HC1.2H2O =393.76.
Quinine hydrobromide, C20H24N,O2-HBr.2H2O = 420.06.
Quinine salicylate, 2(C20H24N2O2.C7H6O3)H2O = 935.54.

The above three salts are obtained by treating quinine with the respective
acids ; they are white, crystalline substances ; the first two are easily, the sali-
cylate is sparingly soluble in water.

Iron and quinine citrate is a scale compound obtained by dissolving ferric
hydroxide and quinine in citric acid, evaporating, etc.

Analytical reactions :

1. Quinine or its salts, dissolved in water or in dilute acids, give,
after having been shaken with fresh chlorine water, or bromine
water, an emerald-green color on the addition of ammonium hydrox-
ide. (Plate YL, 4.)

The reaction is readily shown by treating 10 c.c. of a solution
(about 1 in 1500) with 2 drops of bromine water, and then with an
excess of ammonia water. The green color is due to the formation
of thalleioquin.

2. Solutions of quinine, treated with chlorine water, then with
fragments of potassium ferrocyanide, turn pink, then red on the
addition of ammonium hydroxide not in excess.

3. Solutions of quinine give with ammonia water a white pre-
cipitate of quinine, which is readily dissolved in an excess of
ammonia. The precipitate is also soluble in about twenty times its
own weight of ether (the other cinchona alkaloids requiring larger
proportions of ether for solution).

4. Most solutions of quinine, especially when acidulated with sul-
phuric acid, show a vivid blue fluorescence.

5. Neutral solutions of quinine are precipitated by alkaline oxa-
lates.

6. Quinine and its salts form colorless solutions with concentrated
sulphuric acid. A dark or red color indicates the presence of other
organic substances.

Quinidine, C20H24N2O2. Isomeric with quinine; it gives, like the
latter, a green color with chlorine water and ammonia, and forms
fluorescent solutions. Unlike quinine, it is precipitated from neutral
solutions by potassium iodide.

Cinchonine, C19H22N2O. This alkaloid is found in cinchona bark
in quantities varying from 0.5 to 3 per cent. It crystallizes without
water, forming white needles ; it is almost insoluble in water, soluble

39

610 CONSIDERATION OF CARBON COMPOUNDS.

in 116 parts of alcohol or in 163 parts of chloroform, readily soluble
in dilute acids.

By dissolving the alkaloid in sulphuric acid is obtained:
Cinchonine sulphate, Cinchonince sulphas, (C19H22N2O)2H2SO4.2H2O.
It is a white, crystalline substance. Cinchonine differs from quinine
by its greater insolubility in ether, by its insolubility in ammonia
water, by not forming fluorescent solutions, and by not giving a
green color with chlorine water and ammonia.

Analytical reactions:

" 1. Chlorine water added to the solution of a cinchonine salt pro-
duces a yellowish-white precipitate insoluble in excess of ammonia.

2. Potassium ferrocyanide solution added to a neutral solution of
cinchonine produces a white precipitate soluble in excess of the re-
agent. Upon adding an acid to this solution a golden-yellow
precipitate is formed.

3. With alkali hydroxides, carbonates, and bicarbonates, cincho-
nine salts form white precipitates insoluble in ammonia.

Cinchonidine, C^H^N^p. An alkaloid isomeric with cinchonine;
soluble in 75 times its weight in ether. The sulphate, which crystal-
lizes with 3 molecules of water, is official.

Strychnine, Strychnina, C^H^N^ = 331.73. This alkaloid is
found, together with brucine, in the seeds and bark of different
varieties of Strychnos, and is generally obtained from nux vomica.
Strychnine is a white, crystalline powder, having an intensely bitter
taste, which is still perceptible in solutions containing 1 in 700,000.
It is nearly insoluble in water and in ether, soluble in chloroform
and in dilute acids.

Strychnine has strong basic properties and is one of the most
powerful poisons known, one-quarter of a grain having caused death
within a few hours.

By dissolving it in sulphuric acid or nitric acid the official strych-
nine sulphate, strychnines sulphas, (C21H22N2O2)2.H2SO4.5H2O, or
strychnine nitrate, strychnince nitras, (C21H22N2O2.HNO3), is obtained.

Analytical reactions :

1. Strychnine dissolves in sulphuric acid and nitric acid without
color.

j^2. A fragment of potassium dichromate, drawn through a solution
of strychnine in concentrated sulphuric acid, produces momentarily a
blue, then brilliant violet color, which slowly passes to cherry-red,

ALKALOIDS. 611

then to rose-pink, and finally to yellow. This reaction may still be
noticed with -g^-g^ grain of strychnine (Plate VI., 5).

3. Sonnemchein's ted. When to a very small quantity of strych-
nine, dissolved in a drop of sulphuric acid, some ceroso-ceric oxide is
added, and the mixture is stirred with a glass rod, a deep-blue color
is produced, changing soon to violet, and finally remaining cherry-
red. One part of strychnine in one million parts of water can thus
be recognized. The reagent may be made by heating cerium oxalate
to redness and dissolving it in 30 times its weight of sulphuric
acid.

4. Solutions of strychnine give with diluted solution of potassium
dichromate a yellow, crystalline precipitate, which, when collected,
washed, and heated with concentrated sulphuric acid, shows the play
of colors described in test 2. A play of colors similar to the above
is shown under identical conditions by mixtures of other alkaloids ;
for instance, by morphine containing 10 per cent of hydrastine.

5. Neutral solutions of strychnine give yellow precipitates with
the chlorides of gold and platinum and with picric acid; a white
precipitate with mercuric chloride, potassium hydroxide, and with
chlorine-water ; a greenish-yellow precipitate with potassium ferro-
cyanide.

Brucine, C23H26N2O4.4H2O. This alkaloid is found associated
with strychnine in various species of Strychnos. It is readily soluble
in alcohol, amyl alcohol, and chloroform, but sparingly soluble in
cold water and in ether.

Analytical reactions :

1. To 1 c.c. of water add 5 drops of nitric acid and 5 milligrammes
of brucine ; a deep blood-red color results. Heat the liquid until it
has assumed a yellow color, then add 9 c.c. of cold water and a few
milligrammes of sodium thiosulphate (or a small crystal of stannous
chloride) ; a beautiful amethyst or violet color results (Plate VI., 6).

2. Fresh chlorine water, added drop by drop to a concentrated
brucine solution, produces a red color, turning violet, and becoming
colorless on addition of an excess of chlorine.

Veratrine, Veratrina. This is a mixture of alkaloids obtained
from the seed of Asagraa officinalis. It is a white, amorphous, rarely
crystalline powder, highly irritating to the nostrils ; nearly insoluble
in water, readily soluble in alcohol.

Analytical reactions :

1. Concentrated sulphuric acid causes with veratrine first a yellow,

612 CONSIDERATION OF CARBON COMPOUNDS.

then reddish-yellow, intense scarlet, and, finally, violet-red color.
(Plate VI., 8.) The yellow or orange-red solution exhibits, by re-
flected light, a greenish fluorescence.

2. Veratrine, when heated with concentrated hydrochloric acid,
dissolves with a blood-red color.

3. Bromine water colors veratrine violet.

4. Veratrine forms with nitric acid a yellow solution.

The isoquinoline group of alkaloids.

Opium is the concrete, milky exudation obtained, in the Orient,
by incising the unripe capsules of papaver somniferum, poppy.
Chemically, opium is a mixture of a large number of substances,
containing besides glucose, fat, gum, albumin, wax, volatile and
coloring matter, meconic acid, etc., not less than sixteen or eighteen
different alkaloids, many of which are, however, present in minute
quantities.

Ordinary opium should contain not less than 9 per cent., and when
dried at 85° C. (185° F.) not less than 12 per cent, nor more than
12.5 per cent, of morphine, to be the official article. Dried and pow-
dered opium, after having been exhausted with purified petroleum
benzene (which dissolves chiefly the narcotine, but not the morphine
salts), is the deodorized opium of the U. S. P.

Morphine, Morphina, C17H19NO3.H2O = 303 (Morphia). A
white crystalline powder, or colorless, shining, prismatic crystals,
odorless, of a bitter taste, and an alkaline reaction to litmus ; almost
insoluble in ether and chloroform, very slightly soluble in cold
water, soluble in 300 parts of cold, and 36 parts of boiling, alcohol ;
heated for some time at 100° C. (212° F.) it becomes anhydrous ; at
254° C. (489° F.) it melts, forming a black liquid.

The following salts are official :

Morphine acetate, Morphines acetas, C17H19NO3.C,H4O2.3H2O.

Morphine hydrochloride, Morphinse hydrochloridum, C17H19NO3.HC1.3H2O.
Morphine sulphate, Morphinae sulphas, (CnH19NO3)2H2SO4.5H2O.

The above three salts are white, and soluble in water.

Analytical reactions :

1. Morphine or a morphine salt sprinkled upon nitric acid assumes
an orange-red color, and then produces a reddish solution, gradually
changing to yellow. (Plate VI., 1.)

^,2. Neutral solution of ferric chloride causes a blue color with
morphine or with neutral solutions of morphine salts ; the color is

ALKALOIDS. 613

changed to green by an excess of the reagent, and is destroyed by
free acids or alcohol, but not by alkalies. (Plate VI., 2.)

3. A fragment of iodic acid added to a strong solution of a mor-
phine salt is decomposed, with liberation of iodine, which imparts a
violet color to chloroform upon shaking the latter with the mixture.

4. A mixture of 2 parts of morphine and 1 part of cane-sugar
added to concentrated sulphuric acid gives a rose-red color.

5. Morphine dissolves in cold, concentrated sulphuric acid, forming
a colorless solution, which, after standing for several hours, turns
pink or red on the addition of a trace of nitric acid.

6. Aqueous or acid solutions of morphine salts are precipitated by
alkaline hydroxides ; the precipitated morphine is soluble in potas-
sium or sodium hydroxide, but not in ammonium hydroxide.

7. Neutral solutions of morphine afford yellow precipitates with
the chloride of gold or platinum, with potassium chromate or dichro-
mate, and with picric acid, but not with mercuric chloride.

Heroin, C17H17(C2H3O2)2NO, is diacetyl-raorphine, obtained by heating
morphine with acetyl chloride. It is a white powder, having a bitter taste,
alkaline reaction, and practically insoluble in water, easily soluble in hot alco-
hol. It readily forms salts with acids, the one usually employed being the
hydrochloride, which is a white powder, of bitter taste, soluble in 2 parts of
water and in alcohol. It is precipitated by alkalies, carbonates, and alkaloid
reagents.

Apomorphine, C17H17NO2. When morphine is heated for some
hours with an excess of hydrochloric acid, under pressure to 150° C.
(302° F.), it loses water and is converted into apomorphine, a crys-
talline alkaloid valuable as an emetic.

Apomorphine hydrochloride, C17H17NO2.HC1 (U. S. P.), is a grayish-
white salt which turns greenish when exposed to light and air.

Analytical reactions :

1 . Nitric acid produces a deep purple color fading to orange.

2. Sulphuric acid containing a trace of nitric acid produces a blood-
red color fading to orange.

3. Sulphuric acid containing a trace of selenious acid produces a
dark blue color, fading to violet, then turning black.

4. Sulphuric acid containing a trace of ferric chloride produces a
pale blue color.

Codeine, Codeina, C18H21NO3.H2O =-• 314.83. A white crystalline
powder, sparingly soluble in cold water, easily soluble in alcohol and
chloroform. It is neutral to litmus and has a faintly bitter taste.

614 CONSIDERATION OF CARBON COMPOUNDS.

Codeine has been found to be morphine methyl-ether, and is made
synthetically by heating morphine with methyl-iodide.

Codeine combines with acids to form salts soluble in water, of which
the following are official :

Codeine phosphate, Codeinae phosphas, C18H21NO3.H3PO4.2H2O.
Codeine sulphate, Codeinse sulphas, (C18H21NO3)2.H3SO4.5H2O.

Analytical reactions :

1. On adding to 5 c.c. of an aqueous solution of codeine (1 : 100)
10 drops of bromine water, shaking so as to redissolve the precipitate
formed, and adding after a few minutes some ammonia water, the
liquid assumes a claret-red tint. (Plate VI., 3.)

2. Codeine heated with sulphuric acid containing a drop of nitric
acid gives a blood-red color.

3. Codeine, dissolved in sulphuric acid, forms a colorless liquid,
which, upon being warmed with a trace of ferric chloride, becomes
deep blue.

4. Crystals of codeine sprinkled upon nitric acid assume a red
color, but the acid will acquire only a yellow, not a red color. (Dif-
ference from morphine.)

5. Sulphuric acid containing a trace of selenious acid gives a green
color, changing rapidly to blue, and then slowly back to grass-green.

Dionin, C19H2303N.HC1 4- H20, is the hydrochloride of the ethyl ester of
morphine, which is similar to codeine, the methyl ester of morphine, and is
prepared in the same manner as the latter. It is a white, odorless, slightly
bitter powder, soluble in 7 parts of water and 2 parts of alcohol ; insoluble in
ether and chloroform. It is distinguished from morphine salts by its insolu-
bility in excess of alkali. Some authorities claim that it possesses no advan-
tage over codeine.

Narcotine, C22H23N07, and Narceine, C23H27N08.3H.,0, are white crystalline
opium alkaloids, which are almost insoluble in water, soluble in alcohol.
Concentrated sulphuric acid forms with narcotine a solution which is at first
colorless, but turns yellow in a few minutes, and purple on heating. Narceine
dissolves in concentrated sulphuric acid with a gray-brown color, which changes
to red when heated.

Stypticin, C12H1303N.HC1 ( Cotarnine hydrochloride), is a salt of cotarnine,
an oxidation product of narcotine, similar to hydrastinine. Cotarnine is ob-
tained by boiling narcotine for a long time with water, or by heating it with
dilute nitric acid. Stypticin is a yellow powder, soluble in water and in alco-
hol. Its solution gives, with iodine solution, a brown precipitate of cotarnine
periodide. It is a hemostatic, analgesic, and uterine sedative.

ALKALOIDS. 615

Meconic acid, C7H4O7.3H2O. A tribasic acid, characteristic of
opium, in which it exists to the extent of 3 or 4 per cent., most
likely combined with the alkaloids. It is a white, crystalline sub-
stance, soluble in water and alcohol.

Meconic acid forms with ferric chloride a blood-red color, which is
not affected by dilute acids or by mercuric chloride (different from
ferric sulphocyanate), but disappears on the addition of stannous
chloride and of the alkali hypochlorites. This test may be used in
cases of poisoning to decide whether opium or morphine is present.

Hydrastine, Hydrastina, C21H21N06 = 380.32. Found together with ber-
berine in the rhizome of Hydrastis Canadensis (golden seal) in quantities vary-
ing from 0.1 to 0.2 per cent. Hydrastine crystallizes in four-sided, colorless
prisms ; it fuses at 131° C. (268° F.), is insoluble in water and benzin, soluble
in about 2 parts of chloroform, 124 parts of ether, and 135 parts of alcohol at
the ordinary temperature.

Hydrastine answers to all the. general tests for alkaloids; treated with con-
centrated sulphuric acid it shows a yellow color, turning red, then purple on
heating. Concentrated nitric acid produces a yellow color, changing to orange.
The fluorescence noticed in solutions of hydrastine or its salts is due to pro-
ducts formed from it by oxidation. While hydrastine itself crystallizes very
readily, especially from solutions in acetic ether, its salts can scarcely be
obtained in crystals.

Hydrastinine, C11H11NO2. When hydrastine is treated with
oxidizing agents it is converted into hydrastinine, the hydrochloride
of which is official. This salt has a pale-yellow color, a bitter, saline
taste, and is soluble in 0.3 part of water, and also readily soluble in
alcohol, but difficultly soluble in ether or chloroform. A dilute
aqueous solution of the salt (up to about 1 in 100,000) has a decided
blue fluorescence.

Berberine, C20H17N04. Found in a number of plants (Berberis Tulgaris,
Hydrastis Canadensis, etc.) belonging to entirely different families. It is a
yellow, crystalline substance, soluble in 7 parts of alcohol, 18 parts of water,
insoluble in ether, chloroform, and benzene.

Berberine not only forms well-defined, readily crystallizing salts with acids,
but it also enters into combination with a number of other substances, as, for
instance, with alcohol, ether, chloroform, etc. Some of these compounds crys-
tallize well, as for instance, berberine-chloroform, C20H17NO4.CHC13.

The xanthine alkaloids.

Caffeine and theobromine are xanthine derivatives and are closely
connected with uric acid. They show the properties of alkaloids to
a much less degree than the majority of the compounds considered in
this chapter ; they do not act on red litmus and are but feebly basic.

616 CONSIDERATION OF CARBON COMPOUNDS.

Theobromine has been obtained from xanthine, C5H4N4O2 (a base found in
animal liquids), by treating its lead compound with methyl-iodide, CH8I, when
lead iodide and dimethyl-xanthine are formed. By introducing a third methyl
group into the molecule of theobromine trimethyl-xanthine, i. e., caffeine or
theine is formed. These facts show the close relationship between the active
principles of the vegetable substances used so extensively in the preparation
of the beverages, coffee, tea, and chocolate. And again, these principles show
a relationship to a series of substances (such as xanthine, uric acid, and others)
which are found in animal fluids.

Caffeine, Caffeina, C8H10N4O2.H2O or C5H(CH3)3N4O2.H2O =
210.64 (Trimethyl-xanthine, Theine, Guaranine), occurs in coffee, tea,
Paraguay tea, and a few other plants. It forms fleecy masses of long,
flexible, silky needles, which are soluble in about 45 parts of water
and in 53 parts of alcohol ; it has a slightly bitter taste and a neutral
reaction.

Caffeine is dissolved by sulphuric acid without color ; when evapo-
rated to dryness with hydrochloric acid and a little potassium chlorate
the mass assumes a purple color on holding it over ammonia-water.

Two volumes of a saturated solution of caffeine in water mixed
with one volume of mercuric chloride solution form after a short time
large crystals of caffeine-mercuric chloride.

Oitrated caffeine (U. S. P.) is obtained by adding caffeine to a solu-
tion of citric acid and evaporating the mixture to dryness.

Theobromine, C7H8N4O2 (Dimethyl-xanthine^). Found in the seeds
of Theobroma cacao, a tree growing in the tropics. It is white, crys-
talline, sparingly soluble in cold water, alcohol, and ether, volatilizes
without decomposition at 290° C. (554° F.), has a neutral reaction,
but forms with acids well-defined salts.

Theobromine sodium salicylate, C7H7N4O2.Na -f C7H5O3.Na (Diure-
tin), is a double salt of theobromine-sodium and sodium salicylate. It is
obtained by dissolving in water molecular proportions of sodium hydroxide,
theobromine, and sodium salicylate, and evaporating the solution to dryness.
It is a white powder, containing 50 per cent, of theobromine, readily soluble in
water, and easily decomposed by exposure to carbon dioxide or by acids. It is
incompatible with acids, bicarbonates, borates, phosphates, ferric salts, chloral,
etc. Its effects are like those of theobromine, but it has the advantage of
greater solubility.

Unclassified alkaloids.

Physostigmine, C15H21N3O2 (Eserine). Found in the seeds of
Physostigma venenosum (Calabar bean). The pure alkaloid does not
crystallize well, is almost tasteless, and assumes gradually a reddish
tint. The sulphate and salicylate are official. Both are white or
yellowish-white crystalline powders, which have a bitter taste. The
sulphate is readily, the salicylate sparingly soluble in water.

ALKALOIDS. 617

Analytical reactions :

1. Five milligrammes of physostigmiue dissolved in 2c.c. of
ammonia water yield a yellowish -red liquid which, on evaporation
on a water-bath, leaves a blue or bluish -gray residue, soluble in
alcohol, forming a blue solution. Upon supersaturation with acetic
acid this becomes violet and exhibits a strong reddish fluorescence.
The violet solution leaves on evaporation a residue which is first
green and afterward blue. (Plate VI., 7.)

2. Physostigmine or its salts give with calcium oxide and water a
red liquid which turns green on heating.

Aconitine, Aconitina, C34H47NOn. Found in various species of
aconitum to the amount of about 0.2 per cent. It is a white crystal-
line powder, requiring for solution 3200 parts of water or 22 parts
of alcohol.

Aconitine is one of the most poisonous substances known and
should never be tasted except in highly diluted solutions, which cause
a characteristic tingling sensation when brought in contact with the
mucous surfaces of the tongue. A dilute aqueous solution is precipi-
tated by alkalies, tannic acid, mercuric potassium iodide, but only
concentrated solutions yield precipitates with platinic chloride, mer-
curic chloride, and picric acid.

Any soluble salt of aconitine in dilutions of 1 : 1000 produces
with a drop of potassium permanganate solution a blood-red precipi-
tate of aconitine permanganate.

Colchicine, Colchicina, C^H^NOg = 396.23. This alkaloid is
obtained from Colchicum. It is a pale yellow amorphous powder or
leaflets, having a very bitter taste. It is soluble in 22 parts of water
and very soluble in alcohol and chloroform. It melts at 142° C.
(288° F.). Sulphuric acid produces a citron-yellow color, changed
to greenish-blue, then to red, and finally to yellow by the further
addition of nitric acid. Excess of potassium hydrate changes this
to red.

Ptomaines (Putrefactive or cadaveric alkaloids). It has been
known for a long time that vegetable, and more especially animal
matter, when in a state of decomposition (putrefaction) acts generally
as a poison, both when taken as food or when injected under the skin.
Though many attempts had been made to isolate the poisonous pro-
ducts, this was not accomplished successfully until the years 1873 to

618 CONSIDERATION OF CARBON COMPOUNDS.

1876, by Francesco Selmi, of Italy. He demonstrated that a great
number of basic substances can be extracted from putrid matter by
treating it successively with ether, chloroform, amyl alcohol, and
other solvents. He also showed that these substances resemble vege-
table alkaloids in many respects, and assigned to them the name
ptomaines, derived from TITS/MO, that which is fallen — i. e., a cadaver.
Although Selmi did not succeed in isolating any of the ptomaines
completely (he experimented with extracts only) his investigations
stimulated other scientists, and by the united efforts of many workers
our knowledge of ptomaines has now advanced so far, that general
statements can be given in regard to their origin, composition, phys-
ical and chemical properties, action upon the animal system, etc.

Formation of ptomaines. It has been shown in Chapter 41 that
albuminous substances under favorable conditions undergo a decom-
position termed putrefaction. Presence of moisture, a suitable tem-
perature, and the action of a ferment are the essential factors in
putrefaction. The ferments are living organized beings, termed
germs, bacteria, bacilli, microbes, organized ferments, etc.

It is during the growth, development, and multiplication of these
micro-organisms that the decomposition of the albuminous sub-
stances into simpler forms of matter takes place. A full explanation
of the exact mode of the formation of decomposition-products from
organic matter by the action of bacteria has not been furnished yet,
but we do know that ptomaines are found among these products.
We also know that certain bacteria split up organic molecules in a
certain direction, i. e., with the formation of certain products. We
also know that while micro-organisms live chiefly in dead organic
matter, they also have the power of existing and multiplying in the
living organism, causing the decomposition of living tissues, often
with the formation of ptomaines.

General properties of ptomaines. Ptomaines resemble veg-
etable alkaloids in all essential properties. Some contain carbon,
hydrogen, and nitrogen only, corresponding to the volatile alkaloids,
such as coniine and nicotine, while others contain oxygen also, corre-
sponding to the fixed alkaloids.

Ptomaines and alkaloids both have the basic properties and the
power to combine with acids to form well-defined salts ; they have in
common a number of characteristic reactions, such as the formation of
precipitates with the chlorides of platinum, mercury, gold, as also
with tannic acid, phospho-molybdic acid, picric acid, etc. ; and both

ALKALOIDS. 619

show corresponding solubility and insolubility in the various solvents
generally used for the extraction of alkaloids.

Ptomaines not only possess the general characters of true alka-
loids, but even the often highly characteristic color-tests of the latter
are in some cases almost identical with those of ptomaines. Thus,
ptomaines have been found which resemble in their chemical
properties as well as in their physiological action upon the animal
system, the alkaloids morphine, atropine, strychnine, coniine, digi-
taline, etc.

Many attempts have been made to find some characteristic prop-
erties by which to differentiate between the putrefactive and the
vegetable alkaloids, but practically without results. It is true that
most vegetable alkaloids are optically active, while ptomaines are
inactive, but it does not often happen that ptomaines are obtained in
such quantities as to permit of an exact determination of optical
properties.

Under these conditions it is evident that the toxicologist has a most
difficult task, when called upon to examine a body (especially when
already in a state of decomposition) for alkaloidal poisons. How
many times, in former years, chemists may have unjustly claimed the
presence of poisonous vegetable alkaloids in material given them for
examination, we cannot say, but we do know of a number of cases
of recent date in which such claims were shown to be based upon
errors, made in consequence of the close analogy between ptomaines
and alkaloids.

While the poisonous properties of some ptomaines are well marked,
others are more or less inert. The poisonous ptomaines are now
often termed toxines, in order to distinguish them from the inert
basic products of putrefactive changes.

The toxines are of special interest to the physician, because it is
now known that infectious diseases are caused by the poisonous prod-
ucts formed by the growth, multiplication, and degeneration of micro-
organisms in the living body. This statement is of far-reaching im-
portance, as it opens a new field for investigation in connection with
the treatment of infectious diseases.

Non-poisonous ptomaines. A number of these basic substances
have been known for a long time. Some of them are also formed by
other processes than those of putrefaction, and the term ptomaines
may, therefore, not well be chosen for all of them. However, the

620 CONSIDERATION OF CARBON COMPOUNDS.

close relationship between these substances unites them into a natural
group, of which the following members may be mentioned:

Methylamine, NH2.CH3, the simplest organic base that can be formed, has
been found in decomposing herring, pike, haddock, poisonous sausage, cultures
of comma bacillus on beef-broth, etc. It is an inflammable gas of strong ain-
moniacal odor.

Dimethylamine, NH(CH3)2, has been found in putrefying gelatin, decom-
posing yeast, poisonous sausage, etc. It is, like the former, a gas at ordinary
temperature.

Trimethy famine, N(CH3)3, has been shown for a long time to occur in some
animal and vegetable tissues. Its presence has been demonstrated in leaves
of chenopodium, in the blood of calves, in human urine, etc., but it also occurs
as a product of putrefaction in yeast, meat, blood, ergot, etc. It is a liquid,
possessing a strong, fish-like odor. Boiling-point 9° C. (48° F.).

Ethylamine, NH2.C2H5; DiSthylamine, NH.(C2H5)2; Triethylamim, N.(C2H5)3;
Propylamine, NH2.C3H7; Neuridme, C5N2H14, are other non-poisonous volatile
ptomaines belonging to the amine group, while of the non-volatile amides
may be mentioned : My dine, C8HUNO ; Pyocyanine, CUHUNO2 ; Betaine, C5H13
N03, etc.

Poisonous ptomaines. While no strict line of demarcation can
be drawn between poisonous and non-poisonous substances, the fol-
lowing list of ptomaines embraces those which cause serious dis-
turbances when brought into the animal system :

Isoamylamine, C5H13N, a colorless, strongly alkaline liquid, has been found
in putrefying yeast and in cod-liver oil . It is strongly poisonous, producing
rigor, convulsions, and death.

Cadaverine, C5HUN2, occurs very frequently in decomposing animal tissues,
and seems to be a constant product of the growth of the comma bacillus,
irrespective of the soil on which it is cultivated. It is a syrupy liquid, pos-
sessing an exceedingly unpleasant odor, resembling that of coniine. The sub-
stances which have been described by various scientists as " animal coniine "
were most likely cadaverine. This base is not very poisonous, but is capable
of producing intense inflammation, necrosis, and suppuration in the absence of
bacteria.

Neurine, C5H13NO, is a base which has been obtained by boiling protagon
with baryta, and has been formed by synthetical processes. It also occurs,
however, frequently in decomposing meat. It is exceedingly poisonous, even
in small doses. Atropine possesses a strong antagonistic action toward neurine,
and the injection of even a small quantity is sufficient to dispel the symptoms
of poisoning by neurine.

Choline, C5H15NO2, has been found in animal tissues, in a number of plants
(hops, ergot, Indian hemp, white mustard, etc.), and in putrid matters. It is
much less poisonous than neurine.

Mytilotoxine, C6H15NO2, is the poison found in poisonous mussels. It has a
strong paralysis-producing action, resembling curara in that respect.

ALKALOIDS. 621

Typhotoxine, C7H17NO2, is looked upon as the specific toxic product of the
activity of Koch-Eberth's typhoid bacillus. The poison throws animals into a
paralytic or lethargic condition, so that they lose control over the muscles and
fall down helpless. Simultaneously frequent diarrhoeic evacuations take place,
and death follows in from one to two days.

Tetanine, C13H30N2O4, has been obtained from cultures of tetanus microbes,
from the amputated arm of a tetanus patient, and from the brain and nerve
tissues of persons who died from tetanus. It produces in animals the symp-
toms characteristic of tetanus, such as tonic and clonic convulsions. While
mice and rabbits are strongly affected by tetanine, dogs and horses seem to be
but slightly susceptible to its action.

Mydatoxine, C6H13NO2, has been obtained from human internal organs which
were kept for four months at a temperature varying from — 9° to -f 5°C. (16°
to 41° F.). It is an alkaline syrup, which does not possess strong toxic
properties.

Tyrotoxlcon. The composition of this highly poisonous ptomaine has not
been established yet. It has been found in decomposing milk, in poisonous
cheese, ice-cream, and cream-puffs.

Spasmotoxine. Composition yet unknown. Obtained from cultures of the
tetanus-germ on beef-broth. Produces violent convulsions.

Leucomaines. The basic substances formed in the living tissues
by retrograde metamorphosis, during normal life, are known as leuco-
maines, in contradistinction to the ptomaines, or basic products of
putrefaction. To the group of leucomaines belong many substances
known long ago, such as creatine, creatinine, xanthine, guanine, and
others. Most of these bodies are non-poisonous, but some have been
discovered of late, possessing strong poisonous properties. The
accumulation of these substances in the body, because of incomplete
excretion or oxidation, produces auto-intoxication. The more impor-
tant leucomaines will be mentioned in the physiological part.

QUESTIONS.— State the general physical and chemical properties of alka-
loids. Give a general method for the extraction and separation of alkaloids
from vegetables. Mention the chief constituents of opium. Mention the prop-
erties of morphine and its salts; give tests for them. Mention the principal
alkaloids found in cinchona bark. State the physical and chemical properties
of quinine and cinchonine. Which of their salts are official, and by what tests
may these alkaloids be recognized and distinguished from each other? Give
tests for strychnine, brucine, atropine, and veratrine. What is the chemical
relationship between xanthine, caffeine, and theobromine ? Mention proper-
ties of, and give tests for, cocaine. Mention the characteristic physical, chem-
ical, and physiological properties of ptomaines.

VII.
PHYSIOLOGICAL CHEMISTRY.

53. PROTEINS.

General remarks. Physiological chemistry is that part of chem-
istry which has more especially for its object the various chemical
changes which take place in the living organism of either plants or
animals. It considers the chemical nature of the different substances
used as "food/' follows up the changes which this food undergoes
during its absorption and assimilation in the organism, and treats,
finally, of the products eliminated by it. The chemical changes tak-
ing place in the organism are either normal (in health) or abnormal
(in disease). The abnormal products formed under abnormal condi-
tions are generally termed " pathological " products.

Of the three classes of organic compounds, viz., fats, carbohydrates,
and proteins, from which our food-supply is chiefly derived, the first
two have been considered in the part on Organic Chemistry, while the
study of proteins is taken up in this chapter.

Occurrence in nature. Proteins form the chief part of the solid
and liquid constituents of the animal body ; they occur in blood,
tissues, muscles, nerves, glands, and all other organs ; they are also
found in small quantities in nearly every part of plants, and in larger
quantities in many seeds. They have never yet been formed by arti-
ficial means, but are almost exclusively products of vegetable and
animal life.

General properties. The word protein (formerly proteid) re-
fers to a member of that group of substances which consist, so
far as is known at present, essentially of combinations of a-amino-

623

624 PHYSIOLOGICAL CHEMISTRY.

acids l and their derivatives, e. g.y a-amino-acetic acid or glycocoll ;
a-amino-propionic acid or alanine ; phenyl-a-amino-propionic acid or
phenylalanine ; guanidine-amino- valeric acid or arginine, etc., and are,
therefore, essentially polypeptides. The various proteins resemble one
another closely in their properties. Their composition is so complex
that, as yet, no chemical formula has been assigned to them with any cer-
tainty; they all contain carbon, hydrogen, oxygen, and nitrogen; most
contain sulphur, several phosphorus, and some iron. Various other
metallic and non-metallic elements have been found in certain proteins.

Nearly all proteins are amorphous, non-diffusible, colorless, odor-
less, nearly tasteless, and non-volatile. When heated under such
conditions that the volatile products formed are not burnt at all, or
only partially, a disagreeable odor is noticed, due chiefly to ammonia
derivatives. Proteins vary in solubility ; all are optically active,
most of them being laevorotatory, while haemoglobin and the nucleo-
proteins are dextrorotatory. Proteins are distinguished by the ease
with which they undergo chemical change under the influence of
reagents, ferments, or variations in temperature ; they all undergo
the process of putrefaction, which has been considered in Chapter 41.

By boiling with dilute acids or alkalies, and also by the action of
certain enzymes, the proteins undergo hydrolytic cleavage, forming
many simpler compounds. (The terms hydrolytic cleavage and
hydrolysis -will be explained more fully later on ; they refer to a
splitting up of complex molecules, while water or its constituents are
taken up at the same time.)

Classification. The classification here used is the one which has
been adopted by the American Society of Biological Chemists and
the American Physiological Society, and is as follows :

I. SIMPLE PROTEINS. — a, Albumins; b, Globulins; c, Glutelins ;
d, Prolamines, or Alcohol-soluble proteins; e, Albuminoids; f, His-
tones ; g, Protamines.

II. CONJUGATED PROTEINS. — a, Nucleoproteins ; b, Gtycoproteins ;
c, Phosphoproteins ; d, Haemoglobins ; e, Lecithoproteins.

III. DERIVED PROTEINS :

1. Primary protein derivatives: a, Proteans ; b, Metaproteins ; c,
Coagulated proteins. 2. Secondary protein derivatives : a, Proteases;
b, Peptones; c, Peptides.

1 Greek letters are, in some cases, used to indicate the position of substituting groups in a
molecule. In organic acids, the carbon atom next to the carboxyl group (COOH) is designated
by a, the next one by /3, the next one by y, etc. Thus, lactic acid is a-hydroxy-propionic
acid, CH3.CHOH.COOH; alanine is a-amino-propionic acid, CH3.CHNH2.COOH; glycocoll is
a-amino-acetic acid, CH2NH2.COOH ; hydracrylic acid is £-hydroxy-propionic acid, CH2OH.-
CH2COOH.

PROTEINS. 625

I. Simple proteins.

These are protein substances which yield only a-amino-acids or
their derivatives by hydrolysis.

The simple proteins occur in all animal and vegetable organisms.
In the animal body they are the most prominent solid constituents
of the muscles, glands, and blood-serum, and are found to a greater
or less extent in all tissues, secretions, and excretions. The percent-
age composition of simple proteins is as follows :

Carbon 50.0 to 55.0 per cent.

Hydrogen 6.5 " 7.3 "

Nitrogen 15.0 " 18.0 "

Oxygen 21.0 " 24.0

Sulphur 0.3 " 2.5 "

A few simple proteins contain phosphorus to the extent of 0.42—
0.85 per cent., and a few contain also a trace of iron.

The nitrogen of proteins is split off in four forms, viz., as ammo-
nia, as diamino-acids, as monami no-acids, and as a guanidine residue.
Part of the nitrogen is easily split off as ammonia by the action of
alkalies.

By boiling proteins with alkalies, part of the sulphur is split off
as sulphide, while the remainder can be obtained as sulphate, after
fusing the residue with potassium nitrate and sodium carbonate. As
about one-half of the total sulphur present is obtained by each opera-
tion, it is assumed that there are at least two atoms of sulphur in the
protein molecule.

When acted upon by enzymes or other hydrolytic agents, the
simple proteins form first proteins of lower molecular weight, which
are diffusible and not coagulated by heat. By the prolonged action
of certain ferments (trypsin, bacteria, etc.), or by long boiling with
acids, they give rise to the formation of amino-acids (tyrosine, leucine,
aspartic, and glutamic acids), of the hexone bases (lysine, arginine,
histidine), and a number of undefined bodies.

In solubility the simple proteins vary ; some are soluble in water,
others only in water containing either acids, alkalies, or certain
neutral salts, while yet others are insoluble. The soluble proteins
are converted into insoluble modifications by the action of heat or
certain reagents. This change is called coagulation, and is distin-
guished from precipitation by the fact that proteins when once coagu-
lated cannot return to their original condition. The temperature at
which coagulation takes place depends on the nature of the protein
present, the reaction of the solution, and the presence of neutral salts.
40

626 PHYSIOLOGICAL CHEMISTRY.

An alkaline solution of a protein will not coagulate on boiling ; a neutral
solution will do so partially ; a solution showing an acid reaction will be
coagulated completely on boiling, provided the quantity of neutral salt present
be not too small, and the protein solution not too dilute.

Tests for simple proteins.

a. Coagulation or precipitation tests.

(Use a solution made by dissolving white of an egg in about 10 parts of a
2 per cent, sodium chloride solution.)

1. Heat test. To 5 c.c. of protein solution add a few drops of
dilute acetic acid, and heat. The protein is completely coagulated.

2. Heller's test. Place 1 c.c. of nitric acid in a test-tube, and allow
a few c.c. of protein solution to flow down the side of the tube, taking
care that the liquids do not mix. A white, opaque ring of coagu-
lated protein forms at the line of junction. (Strong sulphuric,
hydrochloric, and metaphosphoric acids coagulate proteins in the
same way.)

3. To 5 c.c. of protein solution add solution of cupric sulphate ;
repeat with solutions of mercuric chloride, lead acetate, and silver
nitrate. In all cases coagulation takes place. (These reactions
explain the use of proteins, such as the white of egg, as antidotes in
cases of poisoning by metallic compounds.)

4. To 5 c.c. of protein solution add a few drops of acetic acid and
some potassium ferrocyanide solution ; coagulation takes place.

5. Saturate 10 c.c. of protein solution with ammonium sulphate ;
all proteins are precipitated except peptones.

6. Solutions of picric, trichloracetic, phosphotungstic, phospho-
molybdic, tannic, taurocholic, and nucleic acids, potassium mercuric
iodide, alcohol, all precipitate proteins under special conditions.

b. Color tests.
(Use any dry protein.)

1. Xanthoproteic reaction. Heat a small quantity of protein with
concentrated nitric acid ; the protein, or the solution, turns yellow.
Allow it to cool, and add an excess of ammonia : the color changes
to orange. (Plate VIII., 1.)

This reaction is due to the presence of the tyrosine and the trypto-
phane radicals in the protein molecule.

2. Milton's reaction. Pour a few c.c. of water on a small quantity
of protein ; add 1 c.c. of Millon's reagent, and boil : a purple-red
color develops. (Millon's reagent is made by dissolving 10 grammes

PROTEINS. 627

of mercury in the same weight of pure nitric acid, and adding to the
cool solution 2 volumes of water.) This reaction is given by tyrosine.

3. Biuret reaction. Boil a small quantity of protein with 5 c.c.
of solution of sodium hydroxide, and after cooling add one or two
drops of dilute solution of cupric sulphate : a violet to pink color is
obtained, according to the amount of copper solution and the nature
of the protein. (Plate VIII., 2.) (It may be necessary to heat the
solution before a distinct color appears.)

This reaction is given by biuret, hence its name.

Boil a small quantity of protein in a test-tube with absolute alcohol ; filter,
wash with absolute alcohol, then with ether, and use the dry material for the
following tests.

4. Adamkieivicz's reaction. Dissolve a small quantity of the pro-
tein by boiling with glacial acetic acid. Allow to cool, and, holding
the test-tube in an inclined position, let 2 c.c. of concentrated sul-
phuric acid flow down the side of the tube. A violet or purple
color develops where the liquids meet.

This reaction is due to tryptophane, and is produced by an impurity
in the acetic acid used, i. e., glyoxylic acid, CHO — COOH (Hopkins-
Cole). A few drops of a dilute solution of glyoxylic acid can be
added when the acetic acid used fails to give a positive test.

5. Lieberman's reaction. To some of the dry protein add concen-
trated hydrochloric acid : the protein turns deep blue to violet. On
standing, the color fades. Probably due to tryptophane.

Many of the above color-reactions will be given by the cleavage-products
of proteins, and by various other substances, but the proteins alone will
respond to all of the five tests.

(a) Albumins. These substances are soluble in water and are pre-
cipitated from their aqueous solution by large quantities of mineral
acids and by saturation of their solution with ammonium sulphate.
In a solution containing 1 per cent, of neutral salt they are coagulated
between 60° and 75° C. (140° and 167° F.).

They include ovalbumin (white of egg) ; serum-albumin of blood-
serum and serous fluids ; lactalbumin of milk ; and vegetable albumins.

(b) Globulins. These compounds are insoluble in water, but dis-
solve in water containing from 0.5 to 1 per cent, of some neutral salt.
The solution coagulates on heating, is precipitated by saturation with
magnesium sulphate or sodium chloride, and by the addition of an
equal volume of saturated solution of ammonium sulphate. Globulins
are precipitated if the salt be removed from their solution by dialysis.

628 PHYSIOLOGICAL CHEMISTRY.

Serum- or para-globulin of blood, lacto-globulin of milk, and
fibrinogen are globulins.

(c) Glutelins are simple proteins insoluble in all neutral solvents,
but readily soluble in very dilute acids and alkalies. They occur in
abundance in the seeds of cereals.

(d) Prolamines or alcohol-soluble proteins. These are soluble
in 70 to 80 per cent, alcohol, and in dilute acids and alkalies, but in-
soluble in water, absolute alcohol, and other neutral solvents. Similar
to glutelins, they are found chiefly in the vegetable kingdom. For
instance, zein is found in maize, gliadin in wheat, hordein in barley,
etc.

(e) Albuminoids. Simple proteins which possess essentially the
same chemical structure as the other proteins, but are characterized
by great insolubility in all neutral solvents. They occur chiefly as
constituents of the skeleton, of the skin and its appendages, and
exist, as a rule, in an insoluble condition. To the albuminoids
belong : Keratins, elastin, collagen, and a few other substances.

Keratins occur as the principal constituents of the horny por-
tion of the skin and its appendages. A special keratin, neurokeratin,
is found in the nervous system. The keratins contain proportion-
ately more sulphur than other proteins, part of it in very loose com-
bination. The darkening of the hair by the use of a lead comb,
forming black lead sulphide, is due to the action of this sulphur.
The products of deep cleavage of the keratins are the same as those
of the proteins, but with relatively greater quantities of the sul-
phurized products, mainly in the form of cystine.

Keratins dissolve slowly in cold caustic alkalies, more rapidly on
heating. They are insoluble in water, alcohol, ether, and in gastric
and pancreatic juices. They give the xanthoproteic, biuret, and
Millon's reactions.

Elastin occurs in the connective tissue, particularly in yellow
elastic fiber; it contains very little sulphur (less than 0.5 per cent.),
and yields on deep cleavage the same products as simple proteins,
giving, however, glycocoll, little glutamic acid, and no aspartic acid.

Elastin is insoluble in water and in cold solutions of caustic alka-
lies ; it dissolves slowly in alkalies on boiling and in cold sulphuric
acid ; it is easily dissolved by warm nitric acid, as also by the action
of proteolytic enzymes. It shows the same color-reactions as the
keratins.

Collagen occurs in the fibre of connective tissue. Ossein, the
chief organic constituent of bone, is a collagen; and chondrin, a

PROTEINS. 629

constituent of cartilage, is collagen mixed with a small quantity of
other material.

On boiling with water (more readily with acidified water) collagen
is converted into gelatin, while the latter, when heated to 130° C.
(266° F.), is converted into collagen. (Collagen may, therefore, be
considered an anhydride of gelatin.)

Gelatin yields no tryptophane, no tyrosine, and contains a rather
small percentage of sulphur.

Reticulin, occurring in reticular tissue, and skelatins, forming the skeletal
tissues of invertebrates, are classed with the albuminoids.

(/) Histones. Soluble in water and insoluble in very dilute
ammonia, and, in the absence of ammonium salts, insoluble even in
an excess of ammonia ; yield precipitates with solutions of other pro-
teins. On hydrolysis they yield a large number of amino-acids,
among which the basic ones predominate, such as arginine and histi-
dine, while others of them are absent (cystine, tyrosine).

(g) Protamines. Simpler polypeptides than the proteins included
in the preceding groups. They are soluble in water, uncoagulable by
heat, have the property of precipitating aqueous solutions of other
proteins, possess strong basic properties, and form stable salts with
strong mineral acids. They are the simplest natural proteins.

II. Conjugated proteins.

Substances which contain the protein molecule united to some
other molecule or molecules otherwise than as a salt.

(a) Nucleoproteins. These are compounds of one or more pro-
tein molecules with nucleic acid. They occur chiefly in the cell
nuclei, but are found also in the protoplasm. Nucleoproteins yield,
on digestion with pepsin, a simple protein, usually a histone or a pro-
tamine, and nuclein. Nuclein is generally but not always resistant
to peptic digestion. On treatment with caustic alkali it is split into
protein and nucleic acid, which is the important portion of the
nucleoproteins. This nucleic acid consists of a carbohydrate group
linking together nitrogenous bases and phosphoric acid. As there
are many different nucleic acids these constituent groups vary within
certain limits. The carbohydrates may be pentose or hexose. The
nitrogenous bases may be one or more purine bodies (guanine, adenine,
etc.) or pyrimidine derivatives (thymine, cytosine, uracil). The phos-
phoric acid is said to be metaphosphoric acid. The purine bodies in
nucleins are the origin of the uric acid of human urine.

630 PHYSIOLOGICAL CHEMISTRY.

The nucleoproteins give all the color reactions, are soluble in water con-
taining a small quantity of alkali, and are precipitated from this solution by
acetic acid. "They are dextro-rotatory.

(6) Glycoproteins. Compounds of the protein molecule, with a
substance or substances containing a carbohydrate group other than a
nucleic acid. This carbohydrate group is capable of reducing cupric
oxide. Several groups of glycoproteins are differentiated as follows :

Mucins are secreted by the larger mucous glands of the body,
by certain mucous membranes, and are found also in the connective
tissue and umbilical cord. The mucins are soluble in water con-
taining a little alkali. The solution is mucilaginous, and with acetic
acid gives a precipitate insoluble in an excess of the acid. This
precipitate is not formed in the presence of 5 to 10 per cent, of
sodium chloride. The solution is not coagulated by heat nor pre-
cipitated by potassium ferrocyanide. An acid solution containing
salts is precipitated by tannic acid, and a similar neutral solution by
alcohol, as also by salts of heavy metals. Mucins when pure are
acid in reaction, and give the protein color-reactions.

Mucoids are certain mucin-like substances, such as colloid and
ovomucoid, and differing from the mucins in solubility and certain
other physical properties. The mucoids are not precipitated by
acetic acid.

Chondroproteins (chondromucoid, amyloid) yield chondroitin-
snlphuric acid as one of the decomposition-products. This latter
has the power to reduce cupric oxide and to precipitate proteins ; it
is sometimes found in the urine.

Chondromucoid occurs in cartilage; it resembles the mucins in
solubility and other properties.

Amyloid occurs pathologically as an infiltration in the spleen, liver,
kidneys, and other organs. Amyloid is insoluble without decomposi-
tion. It gives the biuret, xanthoproteic, Millon's, and Adamkiewicz's
reactions.

The reactions with the following coloring-matters are characteristic for
amyloid : It is colored red by aniline-green ; also red by methyl-aniline iodide,
especially after the addition of acetic acid ; violet or blue by iodine and sul-
phuric acid ; and reddish-brown or violet by iodine.

(c) Phosphoprotein. Compounds of the protein molecule with
some, as yet undefined, phosphorus-containing substance other than
a nucleic acid or lecithin. Caseinogen, the principal protein con-
stituent of milk, belongs to this group.

PROTEINS. 631

(d) Haemoglobins. Compounds of the protein molecule, with
hseinatin or some similar substance. Haemoglobins form the coloring-
matters of the blood. On hydrolysis they yield a simple protein and
a substance called haemochromogen, which contains iron and is read-
ily oxidized to hsematin. (Further discussion under Blood.)

(e) Lecithoproteins. Compounds of the protein molecule with
lecithins, which will be considered later. (See Index for lecithins.)

III. Derived proteins.

These substances are derivatives of proteins, and are obtained from
them by hydrolytic changes of various kinds, e. g., through the action
of acids, alkalies, heat, or enzymes.

1. Primary protein derivatives.

Derivatives of the protein molecule apparently formed through
hydrolytic changes which involve only slight alterations of the pro-
tein molecule.

(a) Proteans. Insoluble products which apparently result from
the incipient action of water, very dilute acids, or enzymes on pro-
teins originally soluble.

(6) Metaproteins. Products of the further action of acids and
alkalies, whereby the molecule is so far altered as to form products
soluble in very weak acids and alkalies, but insoluble in neutral
fluids. The two principal metaproteins are the alkali metaprotein or
alkali albuminate and the acid metaprotein or acid albuminate.

Alkali metaprotein is formed when native proteins are acted upon
by alkalies to such an extent that part of the nitrogen, and occasion-
ally sulphur also, is eliminated from the molecule. The change
takes place slowly at the ordinary temperature, more rapidly on
heating.

Acid metaprotein is obtained by digesting a native protein with
dilute acid.

Alkali and acid metaproteins (album inates) have certain properties
in common. Both are insoluble in water or neutral salt solution, but
easily soluble in the presence of a small amount of either an acid or
an alkali. The solution does not coagulate on boiling, but is com-
pletely precipitated when neutralized. A solution in dilute acid is
also precipitated by saturation with magnesium sulphate, ammonium
sulphate, or sodium chloride, while a solution in alkali is not precipi-
tated by similar treatment. Although agreeing in many reactions,
alkali and acid metaproteins are essentially different. Thus the

632 PHYSIOLOGICAL CHEMISTRY.

alkali metaproteins have decided acid properties, as can be shown by
the fact that on the addition of calcium carbonate they dissolve in
water with the liberation of carbon dioxide, a property not possessed
by acid metaproteins.

As part of the nitrogen is eliminated during the formation of alkali
metaproteins, the latter cannot be converted into acid metaproteins by
treatment with acids ; the reverse change, however, may be brought
about.

(c) Coagulated proteins. Insoluble products, which result from
the action of heat on their solutions, or from the action of alcohols on
the protein. The nature of the process of coagulation is unknown ;
the result is the formation of protein substances insoluble without
decomposition. In the liver and other glands coagulated proteins
have been found. Hard-boiled white of egg and fibrin are coagu-
lated proteins.

The temperature of coagulation is constant for any certain protein ;
it is, however, considerably modified by the presence or absence of
acids, alkalies, and salts in the solution. Fractional coagulation by
gradual heating of a solution of several proteins aifords a rough means
of separation.

2. Secondary protein derivatives.

Products of the further hydrolytic cleavage of the protein mole-
cule by acids, alkalies, superheated steam, or enzymes.

(a) Proteoses. Soluble in water, uncoagulated by heat, and pre-
cipitated by saturating their solutions with ammonium sulphate or
zinc sulphate.

Primary proteoses (protalbumoses) are precipitated by one-half
saturation with ammonium sulphate.

Secondary proteoses (deutero-albumoses) are precipitated by com-
plete saturation with ammonium sulphate.

There are several subdivisions of primary and secondary proteoses,
viz., hetero-proteoses, dysproteoses, the different properties of which
are not definite.

(6) Peptones. Soluble in water, uncoagulated by heat, and not
precipitated by saturating their solutions with ammonium sulphate.
They are the result of the digestion of proteins ; their solutions in
water are readily diffusible. The peptones are divided into anti-pep-
tones, hemi-peptones, and ampho-peptones. Here, again, the proper-
ties of the different classes are not definite.

The proteoses and peptones give a biuret reaction showing more
red color than the natural proteins.

PROTEINS. 633

(c) Peptides. Definitely characterized combinations of two or more
ami no -acids, the carboxyl group of one being united with the amino
group of the other with the elimination of a molecule of water. The
peptones are peptides or mixtures of peptides, the latter term being
at present used to designate those of definite structure, such as poly-
peptides, dipeptides, etc.

Products of proteolysis.

Proteolysis is the change effected in proteins during their diges-
tion, and is brought about by the action of bodies termed proteolytic
agents, or enzymes. The products formed vary in quantity and com-
position with the nature of the proteins and enzymes, and depend
also on the condition under which the changes take place. While
the compounds grouped together as proteins differ widely in their
properties, yet the end-products of any proteolysis will be comprised
in a few amino-acids and nitrogenous bases. This would indicate that
there exists a close relation between the different proteins, the differ-
ence being due more to the atomic arrangement within the molecule
than to the quality and quantity of the elements present in protein
molecules.

These decomposition products of proteins are :

(1) Monamino-acids :

Glycocoll (amino-acetic acid), CH2.NH2.CO2H.

Alanine (aminopropionic acid), C2H4.NH2.CO2H.

Valine (amino-iso-valeric acid), C4H8.NH2.CO2H.

Aspartic acid (aminosuccinic acid), C2H3.NH2.(CO2H)2.

Glutamic acid (amino-pyrotartaric acid), C3H5.NH2.(CO2H)2.

Phenylalanine (phenyl-amino-propionic acid), C6H5.C2H3.NH2.CO2H.

Iso-leucine (amino-methyl-ethyl-propionic acid), C6H10.NH2.CO2H.

Leucine (amino-caproic acid), C5H,0.NH2.CO2H.

Serine (amino-oxypropionic acid), C2H3(OH).NH2.CO2H.

Proline (pyrrolidine-carboxylic acid), C4H7.NH.CO2H.

Oxyproline (oxypyrrolidine-carboxylic acid), C4H7O.NH.CO2H.

Tryptophane (indol-amino-propionic acid), CU.H]2N2O2.

Cystine (disulphide of aminothio-propionic acid (cysteine), (C2H3S.NH3.-

C02H)2.
Tyrosine (oxyphenyl-amino-propionic acid), C8H8O.NH2.CO2H.

(2) Diamino-acids (hexone bases) :

Arginine (guanidine-aminovaleric acid), C6H,4N4O2.
Histidine (amino-iimdazol-propionic acid), C6H9N3O2.
Lysine (diamino-caproic acid), C6H14N2O2.

An enormous amount of work is being done in the attempt to solve
the protein molecule by studying these substances (proteoses, peptones,

634 PHYSIOLOGICAL CHEMISTRY.

peptides, ammo-acids) obtained by proteolysis. They are successively
simpler, more soluble, and more diffusible as the proteolysis proceeds.
The constitution of many of these simpler decomposition products has
now been well substantiated (amino-acids). It has been found pos-
sible to make a beginning in the synthesis of protein by forming com-
binations of amino-acids, linking the carboxyl group of one to the
amino group of another, with the elimination of a molecule of water.
This procedure can be repeated, and substances have been formed
containing thirty-six or more amino-acid molecules. These substances
are apparently entirely analogous to the peptides derived from the
proteins, as some of them give a biuret test, are acted upon by prote-
olytic enzymes (erepsin), and have other common properties. It is
probable, therefore, that this grouping is one of the many forms of
combination that must be present in the protein molecule. While all
of these amino-acids have been found in protein, they are not neces-
sarily all present in any one protein, and in different proteins they
are present in markedly different proportions. Experimental work
is beginning only now to show the significance of these differences
in the proteins. The molecular weights of the proteins cannot be
determined by any known methods, and the actual structural consti-
tution is entirely unknown.

As leucine and tyrosine are readily isolated (see Pancreatic Diges-
tion), their more important properties are stated here.

Tyrosine, C6H4.OH.C2H3(NH2)CO2H (Para-oxyphenyl-amino-pro-
pionic acid). This is obtained from all proteins, except collagen and
reticulin, by trypsin digestion, by prolonged boiling with dilute acids
or alkalies, by fusion with alkaline hydroxides, and by putrefaction.
Tyrosine is generally found with leucine ; both these substances have
nearly the same physiological properties and pathological significance.
They occur in the intestine during the digestion of proteins, and, patho-
logically, they are found in atheromatous cysts, in pus, in abscess and
gangrene of the lung, in the urine during yellow atrophy of the liver,
and in phosphorus poisoning.

Tyrosine crystallizes in colorless, fine, silky needles, often tufted
(Fig. 81). It is very slightly soluble in water, more so in the pres-
ence of alkalies and mineral acids, insoluble in alcohol and ether.
(For a method of preparing tyrosine and leucine from proteins, see
Pancreatic Digestion.)

PROTEINS. 635

Analytical reactions of tyrosine.

1. Place a few crystals of tyrosine on a slide, and warm gently ;
they do not melt. (Crystals of fatty acids found in pus resemble
tyrosine in general appearance, but melt when heated, and are insolu-
ble in hydrochloric acid.)

2. To a very small quantity of tyrosine add water and a few drops
of Millon's reagent. On boiling, the mixture turns rose red ; and
on standing a deeper red color develops. (All phenols and their
derivatives show this reaction.)

3. Peria's reaction. Place a small quantity of tyrosine upon a
watch-glass, add a few drops of concentrated sulphuric acid, and
heat for half an hour over a boiling water-bath. Allow it to cool and
pour into 15 c.c. of water contained in a porcelain evaporating dish.
Warm, neutralize with powdered barium carbonate, filter while hot,
evaporate the filtrate to a few cubic centimeters, and add a very
dilute ferric chloride solution : a violet color appears.

Leucine, C5H10.NH2.CO2H (Amino-caproie acid). This is a con-
stant product of the cleavage of proteins. It is easily soluble in
hot water, less so in cold water, soluble in alcohol, insoluble in ether.
It is easily soluble in acids and alkalies, forming crystalline com-
pounds with mineral acids. When impure, leucine crystallizes in
rounded lumps which often show radiating striations (Fig. 80).
AVhen pure it forms white, glittering, flat crystals.

Analytical reactions of leucine.

1. Heat slowly in a dry test-tube a very small portion of leucine ;
it sublimes in the form of woolly flakes. If heated above its melting-
point, 170° C. (338° F.), it decomposes into carbon dioxide and
amylamine, the latter substance having a characteristic odor. The

reaction is this :

C6H13N02 = C02 + CBHuNHa.

2. Heat a little leucine in a dry test-tube, add a piece of caustic
soda and a few drops of water. Heat until the caustic soda melts,
when ammonia is given off. Allow to cool, dissolve in a little water,
and acidulate with dilute sulphuric acid : the odor of valeric acid is
noticeable. (Leucine, by this treatment, takes up oxygen and de-
composes into valeric acid, ammonia, and carbon dioxide.)

3. Dissolve a little leucine in water, decolorize if necessary with
animal charcoal, filter, render alkaline with caustic soda, and add
2 drops of cupric sulphate solution. The cupric hydroxide which is

636 PHYSIOLOGICAL CHEMISTRY.

precipitated at first dissolves on shaking, giving a blue solution which
is not reduced on heating.

4. Sherer's reaction (applicable only to very pure leucine). Evapo-
rate carefully to dryness on a platinum foil a small portion of leucine
with a few drops of nitric acid. The residue is almost transparent,
and turns yellow or brown on the addition of caustic alkali. If this
mixture be again carefully concentrated, an oil-like drop is obtained,
which runs over the foil in a spheroidal state.

Hydrolysis.

In the animal body a certain kind of decomposition, called hydro-
lysis or hydrolytic cleavage, is particularly prominent. By cleavage
is meant the breaking up of a complex molecule into simpler ones, for
example, the splitting up of dextrose into alcohol and carbon dioxide :

C6H12O6 == 2C2H5OH + 2CO2,

When the splitting is accompanied by the decomposition of water
and the taking up of its constituents by the decomposition-products,
it is known as hydrolytic cleavage or hydrolysis. The special kind
of hydrolysis is sometimes indicated by adding the suffix " lysis " to
a root designating the nature of the substance decomposed, as pro-
teolysis for hydrolytic cleavage of proteins. A familiar example of
this kind of cleavage is the inversion of cane-sugar by boiling with
acidified water :

C12H22On + H20 : : C6H1206 + C6H1206,

Hydrolytic cleavage, as has been shown, can be brought about out-
side the body — by heat, with or without the aid of acids or alkalies,
and by the action of certain substances called enzymes.

Enzymes (ferments).

Enzymes, as mentioned in Chapter 41, are substances that decom-
pose others without themselves undergoing permanent change, i. e.,
they are catalysts. The activity of all enzymes is impeded by accu-
mulation of the products of the fermentation. The activity of enzymes
is controlled by the temperature and character of the solution in
which they act. There is a certain temperature at which every
enzyme is most active — the "optimum" temperature. A higher
temperature first impairs, and then destroys its activity. All enzymes
are destroyed by heating to 100° C. (212° F.) with water. Cooling
impairs their activity ; but even after freezing they regain their
power when carefully brought to the proper temperature. Some act

PROTEINS. 637

best in neutral, others in either acid or alkaline, solution of certain
concentration. The action of enzymes is in many cases reversible.
Thus, ethyl butyrate is split by lipase into ethyl alcohol and butyric
acid ; and under certain conditions lipase will produce the opposite
effect and cause the combination of alcohol and butyric acid with the
formation of ethyl butyrate.

As it has been shown that living " organized ferments " owe their
activity to the enzymes which they secrete, there is less stress laid
now upon the distinction between organized and unorganized fer-
ments, and the term ferment is reserved mainly for yeast.

The chemical composition of the enzymes is not known. As yet,
no enzyme has been prepared in the pure state ; they may be extracted
from the cells by means of water and glycerin. The solution in
glycerin is very stable. When in solution they are easily obtained
by precipitation of some other substance from the same solution, the
enzyme being carried down with the precipitate. The activity of
their solution is generally destroyed by heating to 80° C. (176° F.).

The quantitative estimation of enzymes is based on the amount of
decomposition-products formed, or the amount of material decom-
posed in a given time and under certain conditions.

Enzymes occur widely distributed in animal and vegetable organ-
isms, and possess great diversity of function. At present, enzymes
are classified according to the nature of the changes they produce ;
the more prominent groups are :

Amylases or amylolytic enzymes, converting starches into simple
sugars : ptyalin, amylopsin, malt, diastase.

Proteases or proteolytic enzymes, converting proteins into peptone or
simpler compounds : pepsin, trypsin.

Steatases or steatolytic enzymes, splitting fats : steapsin.

Invertases or inverting enzymes, splitting sugar : invertin.

Coagulases or coagulating enzymes, converting soluble proteins into
insoluble forms : rennin.

Oxidases or oxidizing* enzymes. Oxidases produce oxidation in
the presence of oxygen, peroxidases (catalases), only in the presence
of a peroxide. Oxygenases are theoretical enzymes, capable of first
combining with oxygen and then transferring it to some other sub-
stance.

Of glucoside-splitting enzymes has been mentioned, in Chapter 50,
emulsin or synaptase, which decomposes amygdalin, while myrosin
acts on sinigrin found in mustard seed.

Not infrequently the enzymes of the body are secreted in an inac-

638 PHYSIOLOGICAL CHEMISTRY.

tive state, and are then spoken of as zymogens or pro-enzymes. These
zymogens become active in the presence of certain supplementary
substances. These substances are called kinases if of organic nature,
and activators if of inorganic nature. Thus, enterokinase is the kinase
of trypsinogen, converting it into trypsin, while hydrochloric acid is
the activator of pepsinogen, converting it into pepsin.

While enzymes will be fully considered later, the following two
are mentioned here because they furnish official preparations.

Pepsin is one of the active principles of gastric juice, capable of
converting albumin, in the presence of hydrochloric acid, into soluble
peptones. While pure pepsin is not known, a number of preparations
containing more or less of this ferment are sold as pepsin. They are
obtained by dhTerent processes of extraction from the glandular layer
of fresh stomachs from healthy pigs.

Pepsin, U. S. P., should be either a fine, white, or yellowish-white,
amorphous powder, or consist of thin, pale yellow or yellowish,
transparent or translucent grains or scales. It should be capable
of digesting not less than 3000 times its own weight of freshly
coagulated and disintegrated egg albumin.

Experiment 72. Use the U. S. P. process for the valuation of pepsin, as fol-
lows : " Mix 9 c.c. of diluted hydrochloric acid with 291 c.c. of distilled water,
and dissolve the pepsin in 150 c.c. of the acid liquid. Immerse a hen's egg,
which should be fresh, during fifteen minutes in boiling water ; remove the
pellicle and all of the yolk ; rub the white, coagulated albumin through a clean
No. 40 sieve. Reject the first portion that passes through the sieve, and place
10 Gin. of the succeeding portion in a wide-mouthed bottle of 100 c.c. capacity.
Add 20 c.c. of the acid liquid, and with the aid of a glass rod tipped with cork
or black rubber tubing, completely disintegrate the albumin ; then rinse the rod
with 15 c.c. more of the acid liquid and add 5 c.c. of the solution of pepsin.
Cork the bottle securely, invert it three times, and place it in a water-bath that
has previously been regulated to maintain a temperature of 52° C. (125.6° F.).
Keep it at this temperature for two and one-half hours, agitating every ten
minutes by inverting the bottle once. Then remove it from the water-bath,
add 50 c.c. of cold distilled water, transfer the mixture to a 100 c.c. graduated
cylinder, and allow it to stand for half an hour. The deposit of undissolved
albumin should not then measure more than 1 c.c.

"The relative proteolytic power of pepsin stronger or weaker than that just
described may be determined by ascertaining through repeated trials the
quantity of the above pepsin solution required to digest, under the prescribed
conditions, 10 grammes of boiled and disintegrated egg albumin. Divide 15,000
by this quantity expressed in c.c. to ascertain how many parts of egg albumin
one part of the pepsin will digest."

Pancreatin, U. S. P. This preparation is a mixture of the
enzymes existing in the pancreas of warm-blooded animals, and is

CHEMICAL CHANGES IN PLANTS AND ANIMALS. 639

usually obtained from the fresh pancreas of the hog. It consists
principally of amylopsin, myopsin, trypsin, and steapsin. It is a
yellowish or grayish, almost odorless powder, soluble in water to the
extent of 90 per cent., insoluble in alcohol. It has the power to
digest proteins, and should convert not less than twenty-five times its
own weight of starch into sugar.

Experiment 73. Introduce 7.5 grammes of starch into a flask, add 120 c.c.
of distilled water, and boil until a translucent mixture results. Cool the
resulting paste to 40.5° C. (105° F.), and add to it 0.3 gramme of pancreatin,
previously dissolved in about 10 c.c. of distilled water at 40.5° C. (105° F.).
Shake the flask well, maintaining the temperature of the mixture at 40.5° C.
(105° F.) during five minutes ; at the end of this time all of the starch should
be converted into substances soluble in water, and a thin liquid be produced.
Mix 2 drops of tenth-normal iodine V. S. with 60 c.c. of distilled water, and
add to it 2 drops of the warm converted starch solution ; no color should result,
or, at most, a wine-red color, showing the presence of dextrin and maltose.
The appearance of a blue or purple color indicates the presence of unconverted
starch and that the pancreatin is below the standard— i. e., that of converting
not less than 25 times its own weight of starch into substances soluble in water.

54. CHEMICAL CHANGES IN PLANTS AND ANIMALS.

Difference between vegetable and animal life. As a general
rule, it may be stated that the chemical changes in a plant are pro-
gressive or constructive, in an animal regressive or destructive. That is
to say, plants take up as food a small number of inorganic substances
of a comparatively simple composition, convert them into organic
substances of a more and more complicated composition with the
simultaneous liberation of oxygen, while animals take up as food
these organic vegetable substances of a complex composition, assim-
ilating them in their system, where they are gradually used (burned
up) and finally discharged as waste products, which are identical (or
nearly so) with those substances serving as plant food.

QUESTIONS. — To which class of substances is the term protein applied, and
which elements enter into their composition? How are proteins classified, and
how do these groups differ from each other? Describe the five color-reactions
of proteins. Mention the conditions necessary for the coagulation of a protein
solution by heat ; and state how coagulation differs from precipitation. De-
scribe the products of proteolysis. Describe the nucleoproteins. Give a full
description of the nature and action of enzymes. State the composition and
properties of tyrosine and leucine. Define hydrolytic cleavage. Mention two
enzymes that are official; state their sources and their function in the process
of digestion.

640 PHYSIOLOGICAL CHEMISTRY.

Plant food. Waste products of animal life.

Carbon dioxide. Carbon dioxide.

Water. Water.

Ammonia, NH3. Urea, CO(NH2)2.

Nitrates, MzNO3. Urates, MzCsH2N4O3.

f Calcium. f Calcium.

Phosphates , | M ium_ Phosphates | , M ium.

Sulphates - of Sodi(]m Su phates . of godium

Chlorides ) potassium^ Chlondes J Pw^ium.

It should be remembered that no sharply defined line of demarca-
tion can be drawn between plants and animals. Synthetic processes
occur in the body of animals, and cleavage processes take place in
some plants. However, in the animal organism the processes of oxi-
dation and cleavage are predominant, while in plants those of deoxi-
dation and synthesis are prevalent.

Formation of organic substances by the plant. As shown in
the preceding table, plants take up the necessary elements for organic
matter from a comparatively small number of compounds. All carbon
is derived from carbon dioxide ; hydrogen chiefly from water ; oxygen
from either of the two substances named, as well as from the various
salts ; nitrogen either from ammonia, or from nitrates or nitrites ;
while sulphur and phosphorus are derived from sulphates and phos-
phates respectively. These substances are taken into the plant chiefly
by the roots, the assimilation of the necessary mineral constituents
being facilitated by an acid secretion (discharged from the roots)
which has a tendency to render these salts, present in the soil and
surrounding the roots, soluble.

Water having absorbed more or less of carbon dioxide, of ammonia
or ammonium salts, and of nitrates, phosphates, and sulphates of
potassium, calcium, etc., enters the plant through the roots by a simple
process of diffusion, and is carried to the various green parts of the
plant (chiefly to the leaves), where, under the influence of sunlight, a
chemical decomposition and the formation of new compounds take
place, the liberated oxygen being discharged directly through the
leaves into the atmosphere.

It is difficult to explain fully the process of the formation of highly complex
organic compounds in the plant, because we know so little in regard to the
intermediate products which are formed. However, it is fair to assume that
the various compounds above mentioned as plant food are first decomposed
(with liberation of oxygen) in such, a manner that residues or unsaturated
radicals are formed, which combine together. From these compounds, pro-

CHEMICAL CHANGES IN PLANTS AND ANIMALS. 641

duced at first, more complicated ones will be formed gradually by replacement
of more hydrogen, oxygen, or other atoms by other residues.

The following equations, while not showing the various radicals and inter-
mediate compounds formed, may illustrate some of the results obtained by the
plant in forming organic compounds :

C02 + H20 == H2CO3

H2CO3 — O = H2C02 = Formic acid.
2C02 + H20 = H2C205

H2C2O5 — O = H2C.,O4 = Oxalic acid.
6C02 + 6H20 = C6H12018

C6H12O18 — 12O = C6H12O6 = Glucose.
10C02 + 8H20 = C10H16028

Ci0H16O,8 — 28O = C10H16 = Oil of turpentine.
10C02 + 4H20 + 2NH3 =* C,0H14O24N2

C10HU024N2 — 24O = C10HUN2 = Nicotine.

The above formulas show that the formation of organic compounds in the
plant is always accompanied by the liberation of oxygen, and it may be stated,
as a general rule, that no organic substance (produced in nature) contains a
quantity of oxygen sufficient to convert all carbon into carbon dioxide and all
hydrogen into water, which fact also explains the combustibility of all organic
substances.

Why it is that the living plant has the power of forming organic substances
in the manner above indicated, we know not, and we know very little even in
regard to the means by which the living cell accomplishes this formation, fcut
we do know that sunlight furnishes the kinetic energy necessary in the forma-
tion of complex substances from the simpler ones. This kinetic energy is
transformed into the potential energy, or chemical tension, of the new com-
pounds and of the liberated oxygen.

Animal food. Those substances which when taken into the body
yield energy, build tissue, or prevent the consumption of tissue,
without injury to the organism, are called animal foods. The food
taken by animals is (beside water and a few of its mineral con-
stituents) all derived from vegetables, but it is taken from them
either directly or indirectly ; in the latter case it has been taken pre-
viously into and assimilated by other animals, as in case of food
taken in the form of meat, milk, eggs, etc. While some animals
(herbivora) feed upon vegetable, and some (carnivora) upon animal
food exclusively, others are capable of taking and assimilating either.

The fact that animal food is derived from vegetable matter renders
it superfluous to state that the elements taking an active part in the
formation of either vegetable or animal matter are identical. Of the
total number of the elements, only 15 are found as necessary con-
stituents of the animal body. These elements are carbon, hydro-
gen, oxygen, nitrogen, sulphur, phosphorus, chlorine, iodine, fluorine,
silicon, calcium, magnesium, sodium, potassium, and iron. A few

41

642 PHYSIOLOGICAL CHEMISTRY.

other elements, such as aluminum, manganese, copper, etc., are some-
times found in the animal system, but they cannot be looked upon
as normal or necessary constituents.

, The various kinds of animal food are derived chiefly from three
groups of organic substances, viz., carbohydrates (sugars, starch, etc.),
fats, and proteins or nitrogenous substances. The inorganic sub-
stances, such as phosphates, chlorides, etc., required by the animal in
the construction of bones, for the liberation of hydrochloric acid in
the gastric juice, etc., are generally found as constituents of various
kinds of food or are derived from drinking water. Milk contains all
the necessary organic or inorganic constituents ; bread is rich in phos-
phates, which latter are also found in smaller or larger quantities in
nearly all kinds of vegetable and animal food.

Through the food are supplied those compounds which supply the
constituents that replace the exhausted material of the living cells,
and by chemical changes their inherent potential energy is converted
into the heat of the body and into the kinetic energy used in work-
ing the living mechanism. While the nitrogenous substances have
primarily the task of continuously replacing the wear and tear of the
nitrogenous tissues, they also serve, together with non-nitrogenous
food, to yield the animal heat, as also muscular and other power for
the work which the body performs. To a certain extent the different
nutrients can do the work of one another. Thus, the body can burn
protein in place of fats or carbohydrates, but neither of the latter can
replace the protein in building or repairing tissue. On the other
hand, the fats and carbohydrates, while being consumed, protect the
proteins.

To some extent, the animal body may be regarded as a complicated machine,
in which the potential energy, supplied by the food, is converted into actual
energy of heat and mechanical labor. The main difference is that in our
machines the fuel serves as the source of energy only, while in the body the
food is mainly changed first into tissue (thus building up and renewing the
body constantly), serving as fuel afterward. While in the best steam-engine
only one-tenth of the fuel is utilized as mechanical work, one-fifth of the energy
of the food is realized in the human body.

Heat and muscular power are forms of energy developed by the
consumption of food in the body. The amount of energy developed
is the measure of the food value of any nutrient, and the unit of
value is the calorie.

While each individual substance generates a definite number of
calories during combustion, for practical purposes it is sufficiently
accurate to estimate the average amount of heat and energy in 1

CHEMICAL CHANGES IN PLANTS AND ANIMALS.

643

pound of either proteins or carbohydrates as 1860 calories, while
that in a pound of fat is equal to 4220 calories.

It is important to notice that carbohydrates and fats are oxidized
to carbon dioxide and water, thus producing the theoretical yield of
energy in the body, while only part of the protein molecule is reduced
to carbon dioxide and water, the remainder appearing as urea and
other nitrogenous bodies possessing latent energy, which must be sub-
tracted from the theoretical heat value of the protein.

Composition and fuel values of several important food materials are
given in the following table:

•

Water.

Proteins.

Fats.

Carbohy-
drates.

Mineral
matter.

Value of 1
pound in
calories.

Bread . .
Wheat flour
Oatmeal
Kice . .
White beans
Dried peas .
Potatoes
Sweet potatoes
Turnips
Milk

32.0
12.5

7.6
12.4
12.6
12.3

78.9
71.1
89.4
87 0

9.0
11.0
15.1
7.4
23.1
26.7
2.1
1.5
1.2
36

2.0
1.1
7.1
0.4
2.0
1.7
0.1
0.4
0.2
40

56.0
74.9
68.2
79.4
59.2
56.4
17.9
26.0
8.2
47

1.0
0.5
2.0
0.4
3.1
2.9
1.0
1.0
1.0
07

1300
1645
1850
1630
1615
1565
375
530
185
325

Butter
Cheese, full cream
Cheese, skimmed milk
Egg

10.5
30.2
41.3
738

1.0

28.3
38.4
149

85.0
35.5
68
10.5

0.5

1.8
8.9

3.0
4.2

4.6
08

3615
2070
1165
721

Beef, sirloin
Mutton, shoulder
Veal, shoulder .
Pork, fresh ....

60.0
58.6
68.8
50.3

18.5
18.1
20.2
16.0

20.5
22.4
9-8
32.8

•

1.0
0.9
1.2

0.9

1210
1260
790
1680

The relative proportions in which the two kinds of food are taken
by animals depend upon the nature of the animal and upon its par-
ticular condition of existence.

Below are given in column A the daily quantity of food required
to maintain a grown person in good health, with neither loss nor
gain in weight, while the figures in column B refer to the quantities
of food for a working man of average height and weight.

Proteins 125 grammes.

Fats 79

Carbohydrates . . . .485 "
Inorganic salts . . . .25 "

Water 2600

Equivalent to 3050 calories.

The above nutrients will be furnished by a diet consisting of 1.5

B.

130 grammes.
85 "
400

30 "
2600 "
3800 calories.

644 PHYSIOLOGICAL CHEMISTRY.

to 2 pounds of bread, 10 to 14 ounces of lean beef, 2 to 3 ounces of
butter, with 2 quarts of water.

Digestibility. In providing a diet, it must be borne in mind that
the digestibility of a food is more a measure of its nutritive value than
its elementary composition. Different foods show great differences
in the rapidity and completeness with which they are absorbed.
Thus eggs, fresh meat, white bread, and butter are absorbed and
assimilated more readily than pork, rye bread, potatoes, green vege-
tables, and bacon.

By digestibility of food many different conditions are, or may be, implied.
Some of these, as the ease with which a certain food is digested, the time re-
quired for the process, the influence of different substances and conditions on
digestion, and the effects on health and comfort, are so dependent upon indi-
vidual peculiarities, that no definite rule for the measurement of food-digesti-
bility can be established. Fortunately, the most important factor, viz., the
amount digested, can be determined accurately by experiment. The method
consists in analyzing and weighing both the food consumed and the feces
excreted, the difference being taken as the amount digested.

In general it can be said that animal protein is easily and completely di-
gested, while protein of vegetable food is less so. Thus, of the protein contained
in potatoes, whole wheat, and rye flour, one-fourth, or more, may escape diges-
tion, and thus be rendered useless as nourishment. About 5 per cent, of fats
escape digestion, while carbohydrates are, in general, completely digested,
cellulose being the only exception.

In adjusting a diet, it is important to provide sufficient protein for the build-
ing and repair of tissue, and enough of other materials to furnish the body
with heat and energy for the work to be performed. A proper diet for a grown
person doing moderate work should provide about 3500 calories of energy with
a nutritive ratio of from 1 : 4 to 1 : 6.

The nutritive ratio is the ratio of the protein to the sum of all the other
nutritive ingredients. The fuel value of fats is two and a quarter times that
of proteins and carbohydrates, that of the two latter being considered to be
alike. In calculating the nutritive ratio, the quantity of fats is multiplied by
2.25, and the product added to the weight of carbohydrates. The sum divided
by the weight of protein gives the nutritive ratio.

If less protein be administered than is needed for repair, although a sufficient
number of calories be provided, more nitrogen will be excreted in the urine
than is contained in the food. When the protein is given in sufficient quantity
to replace the worn tissues, sufficient calories being also provided for, a nitroge-
nous equilibrium is established — i. e., the nitrogen excreted equals the nitrogen
administered. Should more protein than is necessary be administered, with
sufficient calories, then more nitrogen is excreted and thereby the equilibrium,
as far as nitrogen is concerned, is rapidly re-established.

During the periods of growth and convalescence from acute disease the pro-
teins can be increased in the body by increase of protein food. The nitrogenous
equilibrium is then less rapidly re-established, as nitrogenous matter is utilized

CHEMICAL CHANGES IN PLANTS AND ANIMALS. 645

in the construction of new tissue. When the quantity of food absorbed is
greater than is required for repair and energy, the carbohydrates are converted
into fat, and this, with the excess of fat from the food, is stored up in the
fatty tissue of the body, to be drawn upon whenever needed. In starvation no
tissue decreases as much as the fatty. The fatty tissue of the animal body is a
depot where, during proper alimentation, nutritive material of great value is
stored, to be given off as it may be needed.

Nutrition. In the process of nutrition five phases may be distin-
guished, viz. : Digestion, absorption, anabolism, catabolism, and excre-
tion of waste products. These processes are commonly spoken of
collectively as metabolism.

Digestion is the process of converting food material into dialyzable
compounds, or into other forms of matter capable of absorption. Ab-
sorption is the mechanical process of transferring the digested mate-
rials from the alimentary canal into the circulation. Anabolism
includes the synthetic changes taking place after they are absorbed
until they have become a part of living cells. Catabolism includes
those destructive changes which take place chiefly in consequence of
oxidation, the oxygen being supplied during the process of respira-
tion. Excretion of waste products is the discharge of that material
which is no longer needed in the system.

Digestion. It has been stated before that foods are divided into
two classes, inorganic and organic, and that the latter are subdivided
into proteins, carbohydrates, and fats. As a rule, the inorganic foods
are taken into the body without chemical change. Before the organic
foods can be absorbed they have to undergo digestion. This is the
process by which organic compounds capable of acting as foods are so
altered that they may be absorbed. The process of digestion will be
fully considered in a later chapter.

Absorption, anabolism, catabolism, excretion. While these subjects,
particularly absorption and excretion, are considered later under the
various organs concerned (see Index), a brief statement of the changes
in the various food-stuffs, subsequent to their absorption, is made
here.

Carbohydrates. The carbohydrates, mainly as dextrose, are carried
from the intestine by the portal system to the liver, where the bulk
of them is dehydrated and converted into glycogen. Some of the
dextrose is changed into glycogen by the muscle, and in this organ
and the liver a reserve-supply of glycogen is stored up. This gly-
cogen forms the most readily available source of energy for the body.
When used it is first split into dextrose, and then oxidized to carbon
dioxide and water, passing probably through a lactic acid stage. The

646 PHYSIOLOGICAL CHEMISTRY.

sugar metabolism is so carefully controlled and is influenced by so
many factors that the details are not clear. The question has been
largely studied by observation of cases of spontaneous and experi-
mental diabetes. This term implies much more than a mere glyco-
suria ; hyperglucsemia (excessive amount of sugar in the blood) must
be present, and there is a profound change in the handling of carbo-
hydrates by the body, as well as some derangement of the protein and
fat metabolism. The pancreas plays an important role and furnishes
an internal secretion from the islands of Langerhans, which probably
enables the muscle to split and oxidize the glycogen as it needs it.
The muscle is thus involved, as well as the liver, in sugar control.
The adrenal is thought perhaps to control the transportation of sugar
in the body, for example, its removal from the liver to the muscle ;
while the thyroid seems to have an inhibitory action upon both the
pancreas and the adrenal. Phloridzin produces an increased perme-
ability of the kidney to sugar, but not a true diabetes.

Fats. Shortly after the emulsified fats reach the blood through
the thoracic duct from the intestine, there occurs a peculiar change in
them whereby they become dialyzable, soluble in water, and insoluble
in ether. The nature of this change is entirely obscure. The fats
are deposited in the body as fats and form a reserve store of potential
energy. A small proportion is synthesized into the lecithins. While
the fat of any animal tends to remain true to the composition charac-
teristic of that animal, there is so little change in fat during digestion
that it is possible to recognize, in the tissue of the animal, foreign fats
which have been introduced with the food. The fat of the body is
derived primarily from the fat of the food, but is also formed in con-
siderable amount from carbohydrates. The location of this transfor-
mation of carbohydrate to fat is unknown. There is a possibility that
protein also may form fat, as it can undoubtedly form sugar, which
might be further changed to fat. Experiments in feeding foreign
fats have shown that the so-called fatty degenerations of the liver,
etc., are not transformations of protein into fat, but that the fat is
brought by the blood and deposited in the diseased organ. When fat
is burned it is first saponified. The final products are carbon dioxide
and water. The acetone bodies of the urine are believed to represent
steps in the incompleted oxidation of the fats.

Proteins. After the proteins enter the portal blood as native pro-
teins they pass through the liver, probably with little change, and
are distributed to the tissues. Here a part enters into the repair or
the growth of the protein tissues (" tissue protein "), while a part is

CHEMICAL CHANGES IN PLANTS AND ANIMALS. 647

immediately broken down without actually being incorporated by the
tissues ("circulating protein"). This is evidenced by the marked
increase in the nitrogenous excretion which appears shortly after
protein ingestion. It is important to notice that carbohydrate and
fat can replace one another in the diet, but that neither can replace
protein to more than a slight extent. Indeed, it has very recently
been shown that not all proteins have the same nutritive value (Os-
borne and Mendel). Thus, an animal can thrive upon a single pro-
tein, such as casein, egg-albumen, or glutenin (wheat). It will live,
but will not grow to maturity upon gliadin (wheat) or hordein (bar-
ley) alone. It will not even live upon zein (maize). This difference
in typical proteins is undoubtedly due to differences in the amino-
body content of the protein. Zein contains no lysine or tryptophane.
It has long been known that the albuminoid substance, gelatin, con-
taining no tryptophaue and no tyrosine, cannot replace protein.

It is believed that these deficiencies in amino-acids make it im-
possible for the organism to build up its native protein from such
material.

The specific waste products of protein (meat) metabolism, the
nitrogenous excreta, appear mainly in the urine, and will for the
most part be considered in that connection, while the formation of
urea and certain other substances will be discussed with the liver.

Respiration. The most important changes in respired air are the
changes in the quantities of oxygen and carbon dioxide. Pure air,
after being dried, contains, by volume, of oxygen 20.8 per cent., of
nitrogen 79.2 per cent., and a quantity of carbon dioxide (0.04 per
cent.) so small that it need not be considered. When 100 volumes of
air have been breathed once, it gains a little more than four parts of
carbon dioxide and loses a little more than five parts of oxygen ; so
that the composition of 100 volumes of inspired air, when expired, is,
after being dried, oxygen 15.4 parts, nitrogen 79.2 parts, and carbon
dioxide 4.3 parts by volume.

Much the greater portion of the oxygen lost from respired air
enters into combination with the haemoglobin ; a small portion is
absorbed by the blood-serum. The immediate source of the carbon
dioxide is the blood, in which it exists partly in simple solution and
partly in a loose combination with hemoglobin.

The blood is the common carrier of the body : from the alimentary
canal it receives ultimately all the food material ; from the lungs it
receives oxygen ; these it carries to the tissues for their sustenance ;

648 PHYSIOLOGICAL CHEMISTRY.

from the tissues it receives the products of catabolism, and carries
them to their proper organs of elimination.

The bright red color of the arterial blood is due to oxyhaBmoglobin.
A large portion of this oxygen absorbed by the haemoglobin is given
up to the tissues as the blood passes through the capillaries, and we
have then the reduced hemoglobin, to which is due the dark color of
the venous blood.

In almost the reverse manner, the hemoglobin takes up carbon from
the tissues and conveys it to the lung. It is important to note that
carbon dioxide, in distinction from carbon monoxide, is not attached to
hemoglobin in the same manner in which the oxygen is attached. It
has been shown that the dark color of the venous blood is not due to
the presence of carbon dioxide, but to a decrease of the oxygen.

The details of the manner in which oxidation in the animal body is induced
and how it proceeds are not known. In some way the atmospheric oxygen,
which under ordinary conditions has no action on the proteins, fats, and carbo-
hydrates, is so changed as to become active. It is commonly believed that the
process is carried on by enzymes, some of which (peroxidases) have been actually
demonstrated, while others (oxygenases) are merely hypothetical (see page 637).

Waste products of animal life. The changes which the food
suffers after having been absorbed by the animal system are ex-
tremely complicated, and far from being thoroughly understood.
Numerous products and organs are formed and nourished from and
by the blood ; among them muscular, nerve, and brain substance, ex-
cretions and secretions,1 such as milk, saliva, bile, gastric and pan-
creatic juice, etc., together with bones, teeth, hair, and many others.

Most of these substances (some secretions, such as milk and others,
excepted) suffer a constant oxidation in the system, and are finally
eliminated as waste products ; in regard to the intermediate com-
pounds formed in the tissues we know little, but it is highly probable
that the reduction of the complicated food material to the simple
forms of the waste products is very gradual. There are three chan-
nels through which the waste products are given off; they are the
lungs, the skin, and the kidneys. By the lungs are eliminated
chiefly carbon dioxide and some water, by the kidneys urine (which
is a weak aqueous solution of urea, uric acid, urates, phosphates,
chlorides, and sulphates of calcium, magnesium, sodium, potassium,
etc.), and by the skin are constantly eliminated carbon dioxide and
water, and during the process of sweating also more or less of the
constituents of urine.

1 An excretion consists of material detrimental to the organisms, and removed from it by
certain glands. A secretion contains peculiar compounds especially elaborated by the glands
for the purpose of serving certain requirements of the organism or its offspring. Thus, urea
and sweat are excretions, while pepsin and milk are secretions.

ANIMAL FLUIDS AND TISSUES. 649

There is also excretion through the intestinal tract.

Chemical changes after death. After the death of either a
plant or an animal, a chemical decomposition commences which finally
results in the formation of those inorganic compounds from which
the plant originally derived its food, viz., carbon dioxide, water,
ammonia, sulphates, phosphates, etc. This decomposition of a dead
body is generally a simultaneous fermentation or putrefaction, aided
by decay or slow combustion.

There are numerous intermediate products formed, which differ
according to the nature of the decomposing substance, or according
to the conditions (degree of temperature, amount of moisture and air
present, etc.) under which the decomposition takes place.

During the decomposition of dead vegetable matter (especially of
moist wood) the intermediate products are frequently called humus,
which substance (or better, mixture of substances) forms the chief
part of the organic matter in the soil.

During the decomposition of dead animals, the sulphur is first
eliminated as hydrogen sulphide, and a number of other intermediate
products have been shown to be formed ; among them certain organic
bases called ptomaines or cadaveric alkaloids, substances which have
been spoken of in Chapter 52. The decomposition of organic matter
may be prevented under conditions which have been mentioned here-
tofore in connection with putrefaction.

55. ANIMAL FLUIDS AND TISSUES.

Constituents of the animal body. The animal body consists
mainly of three kinds of matter, viz., water, organic, and inorganic
matter. It contains of water about 70 per cent., of organic matter
25 per cent., and of inorganic matter about 5 per cent. The water
may be determined by drying a weighed quantity in an air-bath at a
temperature of 100° to 105° C. (212°-221° F.); the organic matter
is estimated by burning the dried substance, and the inorganic matter

QUESTIONS. — What is the difference between vegetable and animal life from
a chemical point of view ? Mention the chief substances serving as plant food.
Explain the formation of organic substances in the plant. What elements
enter into the animal system as necessary constituents? The members of which
three groups of organic substances are chiefly used as food by animals? Give
a full explanation of respiration. Explain the term calorie, and state the use
made of it in valuation of food. Which points should be considered in the
selection of a diet? What are the waste products of animal life, and through
which channels are they eliminated? What is the final result of the decom-
position of dead plants or animals ?

650 PHYSIOLOGICAL CHEMISTRY.

(ash) by weighing the residue. Some of the elements which are left
in the inorganic residue have, however, been actually constituents of
organic compounds ; iron, for instance, wrhich is left in the ash, has
been chiefly a constituent of haemoglobin ; sulphur, left as a sulphate,
may have been a constituent of albumin, etc.

The complex nature of the various organic matters has been referred
to in the preceding chapter, and will be more fully considered below;
but it may be mentioned here, that some of these organic substances
(or groups of substances) may be separated by a successive treatment
of the animal matter with various solvents. Thus, by treating with
ether or carbon disulphide, all fats may be extracted ; by then treat-
ing with alcohol and water successively other substances (generally
termed extractive matter or extractives) are dissolved, which may be
obtained by evaporating the solution.

The relative quantities of the three constituents in some of the
animal fluids and tissues is shown in the following table :

Water.

Organic and
volatile matter.

Inorganic resi-
due (ash).

Saliva ....

. 99.50

0.32

0.18

Gas trie juice

. 9943

0.33

0.24

Pancreatic juice .

. 90.97

8.18

0.85

Bile ....

85.92

13.30

0.781

Chyle ....

. 91.80

7.40

0.80

Lymph

. 91 80

7.40

0.80

Pus ....

. 87.00

12.20

0.80

Cows' milk .

. 87.00

12.25

0.75

Human milk

. 86.80

12.85

0.35

Blood . . . .

. 79.50

19.70

0.80

Blood- corpuscles .

. 54.60

44.68

0.72

Blood- serum

. 90.50

8.68

0.82

Urine .

. 95.70

3.00

130

Bone (varies widely) .

. 22.00

26.00

52.00

Dentine

. 10.00

2500

6500

Enamel

0.40

3.60

96.00

Among the extractives are found creatine and creatinine, urea, uric
acid, organic salts, etc. After the fatty matter and the extractives
have been removed there remains an elastic and somewhat horny
mass, which consists chiefly of proteins (albumin, fibrin, globulin, etc.).

The complete separation of all substances is extremely difficult on
account of the great similarity in properties of many of these sub-
stances, and the rapid changes which they suffer when acted upon by
solvents or chemical agents.

As the nature or composition of many of the inorganic salts present
in the animal tissues is changed during the burning off of the organic

1 The metals in combination with the biliary acids are not included.

ANIMAL FLUIDS AND TISSUES. 651

matter, it is necessary to determine them either in the aqueous solution
(extract) or by subjecting the animal matter to dialysis, by which process
they may be more or less completely separated from the organic matter,
which is left in the dialyzer, while the salts pass through the membrane.

Blood. Two kinds of blood are distinguished, the arterial or oxi-
dized and the venous or deoxidized blood. Arterial blood as it is
present in the system, or immediately after it has been drawn from
the body, is a red liquid of an alkaline reaction and a specific gravity
of about 1.055. Upon examination under the microscope blood is
seen to consist of a colorless fluid, called plasma, in which float small
globules or corpuscles, which make up about 40 per cent, of the whole
volume of blood. These corpuscles are of three varieties, viz., red
and white corpuscles, and blood-plates. The red corpuscles of blood,
or erytkrocytes, which give to the blood its color, are biconcave, cir-
cular, non-nucleated disks, about ^W of an inch in diameter. When
viewed through the microscope they are of a faint greenish-yellow
color, while en masse they show the color of arterial blood. The
white corpuscles of blood, or leucocytes, are round or irregularly shaped
nucleated cells ; they are devoid of coloring-matter, and are far less
numerous than the red corpuscles. The blood-plates are colorless,
oval, round, or lenticular disks, measuring generally less than one-
half of the diameter of red corpuscles.

Specific gravity. This varies in healthy adults between 1.046 and
1.067, but under pathological conditions may vary between 1.025
and 1.068.

The specific gravity can be determined by permitting a drop of blood to fall
into a mixture of chloroform and benzol presenting a specific gravity of about
1.055. If the drop sinks to the bottom, more chloroform must be added ; if it
floats on the surface, benzol has to be added until it floats midway in the
liquid. The specific gravity of the mixture, which is now identical with that
of the blood, is determined by a delicate hydrometer.

Reaction. The alkaline reaction of blood is due to the presence
of sodium bicarbonate, NaHCO3, and disodium phosphate, Na2HPO4,
both of which have a weak alkaline reaction. "While blood reacts
alkaline to litmus, it is neutral to phenol phthalein, and according to
the newer concept of alkalinity (an excess of dissociated hydroxyl
ions over the dissociated hydrogen ions present) it is nearly neutral.
For clinical purposes it is still regarded as alkaline, and the extent
of this alkalinity to litmus or lacmoid has some importance. There
are no very satisfactory methods of titration. That one most used
(Dare) depends upon the disappearance of the spectrum of hsemo-

652 PHYSIOLOGICAL CHEMISTRY.

globin as a solution of blood is gradually neutralized. Tartaric acid,
2^^, is the acid used, and the addition of acid is made by means of a
specially devised pipette until the two absorption bands become no
longer visible through the spectroscope.

The alkalinity of the blood may be estimated by mixing 5 c.c. of freshly
drawn blood with about 45 c.c. of a 0.25 per cent, solution of ammonium
oxalate (which prevents coagulation) and titrating this mixture with a |^ solu-
tion of tartaric acid, using as an indicator lacmoid paper soaked in a concen-
trated solution of magnesium sulphate.

For clinical purposes, where often but small quantities of blood are avail-
able, the following method may be used. The blood is drawn into a capillary
pipette up to the mark etched on the stem; the pipette is next tilted to
admit a bubble of air into the bore, and then —^ sulphuric acid is drawn in to
the mark. The exactly equal volumes of blood and acid thus obtained are
transferred to a watch-glass, well mixed, and a drop of the mixture then
tested with lacmoid paper. If an acid or alkaline reaction be shown, the
operation is repeated with weaker or stronger acid until the resulting mixture
is neutral.

Odor. The peculiar odor of blood, differing widely in different
animals, is due chiefly to the presence of certain volatile fatty acids.
Addition of sulphuric acid renders the odor more distinct.

The composition of blood. The following table, taken from Howell,
lists the more important constituents of blood-plasma :

f Fibrin ogen.

I Paraglobulin. { Euglobulin.
Proteins. -< <- Pseudoglobulm.

Serum-albumin.
[ Nucleo-protein.
Fats.
Sugar.
Urea.

Jecorin.
Extractives. ^ Glucuronic acid<

Lecithin.
Cholesterin.
Lactic acid.

Chlorides "| f Sodium.
Carbonates I j Potassium.
lts' 1 Sulphates j of -j Calcium.

Phosphates \ I Magnesium.

L Iron,
f Internal secretions.

Enzymes. { ^Pas^
Enzymes and unknowns. ^ Glycolase, etc.

I Immune bodies (amboceptors).
Complements.
I Opsonins.

ANIMAL FLUIDS AND TISSUES. 653

The proteins of blood-plasma. There are three important proteins
in blood-plasma : serum-albumin, serum -globulin (paraglobulin), and
fibrinogen. Of the other proteins described, the nucleo-protein seems
to be the best founded. As fibrinogen is directly concerned in the
clotting of blood, it will be described in that connection. The albumin
and the globulin of the blood are typical members of their respective
classes, and possess all the qualifications of these classes and of pro-
teins in general. They are found together also in the lymph and in
various other fluids of the body. There is some evidence that the
albumin is in reality made up of two or three different albumins,
while the globulin can be divided into two portions by fractional pre-
cipitation. Thus, on adding saturated ammonium sulphate solution
to plasma, all the globulin will be precipitated before the sulphate
solution amounts to 50 per cent, of the resulting mixture. The
so-called euglobulin will precipitate between 28 and 36 per cent,
of saturation with ammonium sulphate, and the pseudoglobulin
between 36 and 44 per cent. Under these conditions no albu-
min will be cast down. If, however, solid ammonium sulphate be
now added to the point of saturation, all of the albumin will be
precipitated.

Coagulation. When blood leaves the body and is allowed to stand
a while, it will be seen that the entire mass has coagulated — /. e., has
been converted into a semi-solid, gelatinous material known as the
blood-clot, or the placenta sanguinis. Later it will be observed that
a small quantity of straw-colored liquid, known as the blood-serum,
appears on top of the clot. While the latter shrinks in volume the
quantity of serum increases, the clot finally floating in the liquid,
which itself ultimately gelatinizes in consequence of the coagulation
of the serum-albumin. Clot consists of fibrin holding in its meshes
blood-corpuscles, which may be removed by washing the clot in a
stream of water.

The coagulation of blood can be prevented in various ways. After
the injection of albumose into a vein of a dog the blood does not coag-
ulate on leaving the body. If the blood be drawn directly into a sat-
urated solution of magnesium sulphate, in the proportion of 3 to 1,
or into a solution of potassium oxalate, so that the mixture contains at
least 1 per cent, of oxalate, no coagulation takes place. The plasma
obtained from such blood is known as peptone, salt, and oxalate plasma,
respectively.

Coagulation of blood may be retarded by rapidly cooling it. If
the blood of a horse, whose blood always coagulates slowly, be re-

654 PHYSIOLOGICAL CHEMISTRY.

ceived into a cold, narrow glass cylinder, and allowed to stand at
0° C., the blood may be kept fluid for several days. The corpuscles
will deposit in a red layer from the plasma.

It may readily be shown that the clotting of blood is due to a
change of some kind which converts the soluble protein fibrinogen
into an insoluble form called fibrin. Fibrinogen is one of the globu-
lins, it coagulates at a temperature of from 50° to 60° C., and is pre-
cipitated by half- saturation with sodium chloride. It is present also
in lymph.

It is well known that the clotting of fibrinogen is produced by an
organic substance formerly called fibrin-ferment, but preferably called
thrombin, as it is probably not an enzyme. It is also known that this
thrombin is active only in the presence of calcium salts ; that is, that
inactive thrombin (prothrombin or thrombogen) is changed by cal-
cium into the active form. It is, however, possible to remove the
calcium from activated thrombin without impairing its activity ;
therefore the calcium does not enter directly into the conversion of
fibrinogen into fibrin.

As calcium is present in all blood, it is evident that in cir-
culating blood either prothrombin must not be present as such,
or, if present, its activation by the calcium must be prevented by
some antagonistic substance (antithrombin), for otherwise clotting
would occur within the blood-vessels, which does not happen under
normal conditions. Accordingly, there are two theories to explain
these facts.

Morawitz believes that in order to convert prothrombin into throm-
bin, not only calcium but also a secondary organic substance (throin-
bokinase) must be present, and that this thrombokinase is furnished
to blood which has escaped from the blood-vessels by the injured
leucocytes and platelets. The other view, to which Howell inclines,
is that prothrombin is transformed into thrombin by calcium salts
alone, and that this change is prevented by the antithrombin of
the circulating blood, and that when the blood is shed the injured
cells set free a zymoplastic substance which counteracts the anti-
thormbin and leaves the calcium free to convert the prothrombin
into thrombin.

The different methods of preventing the clotting of blood
are to be explained thus : The cooling of blood probably pre-
vents the formation of the thrombokinase, or the thromboplas-
tic substances, by preserving the cells intact. The addition of

ANIMAL FLUIDS AND TISSUES. 655

oxalate solution removes the calcium salts by precipitation. The
injection causes the production of antithrombin in the injected
animal.

Blood-serum differs from plasma only in containing no fibrinogen
and much active thrombin.

Experiment 74. (Separation of the proteins of blood-plasma and of blood-serum.)

a. Fibrinogen. To 5 c.c. of salt or oxalate plasma add an equal volume of
saturated solution of sodium chloride. Fibrinogen is precipitated, carrying
with it the prothrombin. Filter and preserve the nitrate for the separation of
albumin and globulin, as detailed below.

Dissolve the fibrinogen and protlirombiu in a little dilute salt solution, add
an excess of calcium chloride, and keep the mixture at 40° C. for a few minutes.
Shreds of fibrin are formed and precipitated.

b. To 25 c.c. of blood-settim, contained in a mortar, add 20 grammes of
ammonium sulphate and rub with a pestle until the fluid is saturated with
the salt. Filter through dry filter-paper, acidulate the filtrate with acetic
acid, and boil. No change occurs, as both proteins have been precipitated
completely.

c. To 25 c.c. of blood-serum add 25 c.c. of a saturated solution of am-
monium sulphate; filter; and wash with a saturated solution of the salt.
Under this treatment only serum-globulin is precipitated, while serum-
albumin is kept in solution. Heat the filtrate to boiling: serum-albumin
is coagulated. Place some of the residue left on the filter (globulin) in a
test-tube and pour water on it; the protein dissolves by virtue of the small
quantity of salt adhering to it. Heat the solution to boiling : coagulation
takes place.

d. Saturate 25 c.c. of serum with magnesium sulphate : serum-globulin is
precipitated, serum-albumin remains in solution.

Serum-albumin and serum- globulin give the ordinary protein reactions.

A quick method to obtain fibrin is to stir or whip blood with twigs im-
mediately after it has been shed. Under these conditions the fibrin
does not entangle the blood-corpuscles, but separates as a stringy mass,
which adheres to the twigs used for stirring. The remaining part, being
made up of the corpuscles suspended in the serum, is designated as defibrin-
ated blood.

Red blood-corpuscles when wet contain of water, 54.63 per cent. ;
haemoglobin, 41.1 per cent.; other proteins, 3.9 per cent.; fats
(chiefly cholesterin and lecithin), 0.37 per cent. The quantity of
water in corpuscles varies widely, and most likely ranges in healthy
blood from 76 to 80 per cent. Dried corpuscles contain about 90
per cent, of haemoglobin.

While red blood-corpuscles can be broken up (laked) by the
addition of various substances to the blood, the simplest way is by

656 PHYSIOLOGICAL CHEMISTRY.

the addition of water, which reduces the osmotic pressure of the
plasma, and consequently causes the salts of the corpuscles to attract
an excess of water, whereby the corpuscle is ruptured and its con-
stituents go into solution. In order to avoid this action on the blood-
cells and a similar action on the tissue cells, it is customary in sur-
gical procedures, and especially in intravenous injections, to use a
solution of equal osmotic pressure with the blood. Such a solution
is the "normal salt solution" made up usually of 0.9 per cent, sodium
chloride in distilled water, which is the simplest solution that has
been found to have no very deleterious effect.

Blood-pigments. The haemoglobins or blood-pigments are the
chief constituents of red blood-corpuscles ; they contain from 0.4 to
0.6 per cent, of iron, and show a slight difference in composition ;
when in powder form they all have a blood-red or brick-red color;
they all crystallize, but not with equal facility. Hemoglobin is the
substance which carries oxygen to the various tissues, as described in
the previous chapter. It belongs to the class of conjugated proteins.

Experiment 75. Pour some freshly drawn venous blood into four volumes of
a saturated solution of sodium sulphate contained in a vessel which stands in
ice ; mix and set aside for several hours ; no coagulation occurs and the cor-
puscles settle to the bottom of the vessel. Pour off the supernatant liquid,
collect the sediment on a filter, and wash it first with cold solution of sodium
sulphate and then with water.

Prepare haemoglobin from these corpuscles as follows : agitate the collected
mass violently with small quantities of ether until the corpuscles are nearly
dissolved ; allow the liquid to settle, filter, render the filtrate slightly acid with
acetic acid, and add alcohol as long as the precipitate first formed continues to
dissolve ; cool the red solution to 0° C. (32° F.) for several hours, when crystals
of haemoglobin will form ; collect these on a filter and wash with an ice-cold
mixture of alcohol and water.

Hcemoglobin, also called reduced hcemoglobin, occurs only in small
quantity in arterial blood, in larger quantity in venous blood, and is
almost the only coloring-matter in the blood after asphyxiation. A
solution of hemoglobin has a most remarkable attraction for oxygen,
with which it enters into a molecular combination, forming oxyhazmo-
globin. The power of hemoglobin to take up oxygen depends on
the iron it contains. The solution of oxy hemoglobin will give up
oxygen to reducing agents or when subjected to a sufficiently low
oxygen pressure. It is due to this property of the oxyhernoglobin
that arterial blood gives up oxygen to the tissue.

ANIMAL FLUIDS AND TISSUES. 657

Mdhcrmogtobin is a transformation-product of oxyhsemoglobin found
in sanguinous transudates and cystic fluids ; it also occurs in the urine
during haematuria and haemoglobin uria; and in the blood and urine
after poisoning with potassium chlorate, amyl nitrite, alkali nitrates,
and several other bodies.

Hcemochromogen. When haemoglobin is acted upon by acids, alka-
lies, etc., it is split into globin (a histone) and hsemochrornogen. The
latter forms only about ^V of the haemoglobin molecule, contains all
of the iron present, and consequently the group to which the oxygen
is attached when oxyhsemoglobin is formed. In the presence of
oxygen haemochromogen is rapidly converted into haematin.

Ilcematin. Just as haemochromogen is split from haemoglobin,
haematin is derived from oxyhaemoglobin. It is a comparatively
simple substance, having the formula C34H34N4FeO5. It is found in
the feces after hemorrhage in the intestine, and also after a diet con-
sisting largely of red meats. Haematin has been found in urine after
poisoning with arsenetted hydrogen. Haematoporphyrin (^H^N^Oj
is obtained when haematin is hydrolyzed.

Haematoporphyrin occurs in traces in normal urine ; it is found in
greater quantity in urine after the use of sulphonal. Haematopor-
phyrin is isomeric with the bile-pigment bilirubin, and a pigment
closely resembling urobilin has been obtained by the action of reduc-
ing agents on haematoporphyrin. It is noteworthy that this substance
does not contain iron.

Carbon monoxide haemoglobin is a molecular combination of one
molecule of haemoglobin and one molecule of carbon monoxide. The
combination is stronger than that between oxygen and haemoglobin and
this explains the poisonous action of carbon monoxide, which causes
death by replacing the oxygen of the blood. A similar and even
more stable chemical combination is formed with haemoglobin by
nitric oxide.

Carbon dioxide haemoglobin (carbo-hwmoglobin). Haemoglobin has
the property of forming an unstable compound with carbon dioxide,
the CO2 is, however, not attached to the same portion of the molecule
as that to which the oxygen (in oxy haemoglobin) is attached. Thus,
the presence of carbon dioxide does not prevent the absorption of
oxygen by haemoglobin, which is in great contrast to the action of
carbon monoxide, and is important in the process of respiration.

Spectroscopic examination. The different haemoglobins are distinguished
chiefly by their absorption -spectra. In the following description the violet end
of the spectrum is assumed to be on the observer's right.
42

658

PHYSIOLOGICAL CHEMISTRY.

a. Oxyh&moglobin. Dilute 10 c.c. of blood with 90 c.c. of water, and filter.
Place part of the solution in a glass vessel with parallel sides and examine
with a spectroscope. When the solution is so concentrated the spectrum
will probably be entirely shut off as far as the yellow or orange, but on gradu-
ally diluting with water a spectrum is finally seen which shows two absorption -
bands to the right of the D line. The right-hand band is broader, fainter, and
less sharply denned than the other, and the color of the light which emerges
from the left limb of the left hand is yellow. When the solution is further
diluted the bands disappear simultaneously. (Fig. 72, a.}

b. Reduced haemoglobin. When a solution of oxy haemoglobin is treated with
a reducing agent the coloring-matter loses oxygen and is changed to hsemo-

FIQ. 72.

Yellow

Qreen

Cyan-blue

Absorption-spectra of blood constituents, a, oxyhaemoglobin.
6, reduced haemoglobin, c, methsemoglobin. d, haematine. e,
reduced hsematine. /, hsematoporphyrin. g, carbon monoxide
haemoglobin.

globin. Stokes' fluid is the most suitable reagent for reducing, and is prepared
as follows: Dissolve 3 grammes of selected crystals of ferrous sulphate in cold
water and add a cold aqueous solution of 2 grammes of tartaric or citric acid.
Make up with water to a volume of 100 c.c., and immediately before using add
ammonia-water until the precipitate which forms at first is redissolved.

Prepare a solution of oxyhsemoglobin which will show the characteristic ab-
sorption-bands. Allow a few drops of Stokes' fluid to flow into the solution, when
its color changes to a purple or violet, and the spectrum shows a single broad

ANIMAL FLUIDS AND TISSUES. 659

diffused and poorly defined band, as though two oxyhsemoglobin bands had
gone together and had been displaced to the left (Fig. 72, 6). When the solu-
tion is agitated with air its color changes to bright red and the spectrum again
shows oxy haemoglobin.

c. Methcemoglobin. To a dilute solution of blood add a drop or two of a
freshly prepared 10 per cent, solution of potassium ferricyanide. The color of
the solution becomes brown. Add just enough sulphuric acid to give a slightly
acid reaction and examine spectroscopically, when the spectrum is seen repre-
sented in Fig. 72, c. On rendering the solution slightly alkaline and adding
a few drops of Stokes' fluid the methaenioglobin changes to haemoglobin, and
on agitating with air into oxyhsemoglobin. These changes can easily be fol-
lowed with the spectroscope.

d. Add hcematin. To a few drops of undiluted blood add a drop or two of
acetic acid. The haemoglobin is broken up into a histon called globin, and a
non-protein substance called hsemin. The solution which results is almost
black, but on diluting with water is seen to be red. The spectrum has a band
in the red, almost coincident with the band shown by methsemoglobin in
neutral or acid solution.

e. Alkaline hcematin. To a portion of acid hsematin solution add sodium
hydroxide until the precipitate which forms has redissolved. The solution
will be alkaline and, if properly diluted, will show a poorly defined band to
the left of the D line. It is usually observed, however, that the entire spec-
trum is absorbed except the red. (Fig. 72, d.)

f. Reduced hcematin (Hsemochromogen). Reduce a portion of alkaline
haematm solution with Stokes' fluid, and after properly diluting examine
Bpectroscopically. Two sharply defined dark bands are seen between D
and E, which seem to be coincident with the bands produced by oxyhaemoglo-
bin. It will be- noted, however, that the light which emerges on the left of the
left band is plainly green. By diluting the solution with water the band on
the right may be made to disappear, while the other band is still very dark.
(Fig. 72, e.)

g. Hcematoporphyrin. Add a drop of blood to a few c.c. of concentrated
sulphuric acid, mix well, dilute with water, and render alkaline with sodium
carbonate. The spectroscope shows four bands. (Fig. 72, /.)

h. Carbon monoxide hcemoglobi?i. Pass a slow current of carbon monoxide
(illuminating-gas, containing carbon monoxide, may be used) through 50 c.c.
of blood until its color is bright red. Examined spectroscopically, the bands
seen occupy nearly the same position as those of oxy haemoglobin, but they do
not disappear on treatment of the solution with Stokes' fluid. (Fig. 72. g.)

On adding to 10 c.c. of carbon monoxide haemoglobin solution 15 c.c. of a
20 per cent, solution of potassium ferrocyanide the mixture shows a bright-red
color. On treating oxyhsemoglobin solution in the same way, it assumes a
grayish-brown or green color.

Examination of blood-stains. Blood-stains may be recognized,
after having been washed off with as little water as possible, by the
following methods :

1. Examine the reddish fluid under the microscope for blood cor-
puscles.

660 PHYSIOLOGICAL CHEMISTRY.

2. Evaporate a drop of the fluid on a microscope slide with a
minute fragment of sodium chloride, cover with a cover-glass, allow
a drop of glacial acetic acid to enter from the side and warm gently ;
abundant crops of hsemin crystals are seen under the microscope
after cooling.

3. Add a drop of the fluid to some freshly prepared tincture of
guaiacum in a test-tube and float on the surface of an ethereal solu-
tion of hydrogen dioxide ; a blue ring forms at the junction of the
ethereal solution and the guaiacum. (Blood is, however, not the only
substance showing this reaction.

4. The spectroscope shows bands characteristic of haemoglobin.

5. The biologic blood-test. This test depends upon the fact that
animals (rabbits) injected with human blood-serum will develop a
specific antibody. This antibody is present in the blood-serum of
the injected animal and is termed a " precipitin," because it produces
a visible precipitate when the serum of the animal is mixed with a
solution of human blood-serum. As the technique is very intricate,
and the results are worthless unless carefully controlled, no details
can be given here. Positive results can be obtained with blood or
blood-stains many years old. Human protein of other origin (milk,
semen, etc.) and protein from the higher anthropoid apes will also
give positive results.

The immune bodies of the blood-serum. When foreign protein
is introduced into an animal by injection or, as in disease, by infection
with bacteria, it is found that there is a response on the part of the
animal which causes the presence of certain substances (immune
bodies, antibodies) in the circulating blood. These have a specific
action upon the foreign protein. To this class belong agglutinins,
lysins, etc. Agglutinins are capable of causing an agglutination or
clumping of the corresponding bacteria. They have proved of great
clinical value in the diagnosis of typhoid fever by means of the Widal
reaction. This test consists in observing microscopically or macro-
scopically a mixture of active typhoid bacilli and the blood-serum of
the patient. If agglutinins are present, and the bacteria are clumped
within a certain time by a certain dilution of serum, it is shown that
the patient has, or in some cases has had, typhoid fever. Bacterio-
lysins are antibodies capable of dissolving the corresponding bacteria.
Opsonins are capable of producing some change in bacteria, whereby
it becomes possible for the leucocytes of the blood to ingest them
(phagocytosis). They are normally present in varying amounts. It
is manifest that these bodies form a part of the defensive mechanism

ANIMAL FLUIDS AND TISSUES. 661

of the body. They have so far not been of great assistance thera-
peutically, but promise to be of great value in the prophylaxis of
certain diseases, as in the typhoid vaccination by injections of killed
cultures of B. typhosus.

In this connection it is important to note that bacteria form several
classes of toxins or poisons. Ptomaines are produced by the effect
of bacteria upon the medium in which they are growing. Bacterial
toxins are substances which, in distinction to ptomaines, are elab-
orated by the bacteria within the bacterial cells. These are substances
of doubtful chemical structure and are divided into two classes : (1)
Endotoxins, toxins existing mainly in connection with the bacterial
cell, going into solution with difficulty and possessing in such solution
only a moderately poisonous action. (2) Soluble toxins, readily re-
moved from the bacterial cell by solution and giving a solution of
strong toxic action.

It has been found that an animal which has been treated with bac-
teria-producing soluble toxins has present in its blood a specific anti-
body which is capable of neutralizing the toxin of the corresponding
bacteria. This substance is called an antitoxin and protects, from
the poisonous effects of the toxin, not only the original animal (active
immunity), but also other animals into which the antitoxin-containing
serum may be injected (passive immunity). This production of
passive immunity has been widely used in the treatment of diphtheria
and the prophylaxis of tetanus. In other bacterial diseases, such as
typhoid and streptococcus infections, where the toxins present are
mainly endotoxins, the production of an antitoxin conferring passive
immunity has not been successful.

In the case of some of these antibody reactions it is found that a
third substance is necessary. This substance is commonly called the
complement ; and in this connection the antibody is termed the am-
boceptor, and the foreign protein the antigen. The amboceptor and
the complement are both present in the blood-serum. Complement
is an unstable substance present in all fresh blood, and is not specific,
that is, it will enable any amboceptor to act upon the corresponding
antigen. Amboceptor is fairly stable, is usually present only in re-
sponse to the introduction of some antigen, and is specific, that is, it
will act only upon its corresponding antigen.

As amboceptor will act upon antigen only in the presence of com-
plement, the presence or absence of complement in a solution may
readily be shown by mixing the solution with a suitable amboceptor
and antigen, when the presence of complement is shown by the occur-

662 PHYSIOLOGICAL CHEMISTRY.

rence of the interaction of the amboceptor and antigen, while its ab-
sence is shown by the failure of the reaction. The reagents com-
monly used are red blood-corpuscles and the corresponding haemolysin
(amboceptor), since the interaction is shown by a visible change,
haemolysis, and if no reaction occurs the mixture remains unchanged.

This procedure is used in the Wassermann reaction for syphilis.
If a mixture be made of the blood-serum of a syphilitic patient, an
emulsion of animal lipoids, and complement, it is found that the com-
plement becomes absorbed or fixed, so that if the mixture be tested
for complement by the addition of red blood-corpuscles and the cor-
responding haemolysin, no haemolysis will occur. If, on the other
hand, the patient has not syphilis, no fixation of complement will
occur, the complement will be left free to act, and will produce hae-
molysis when the corpuscles and haemolysin are added.

Ehrlich, in explaining his theory of immunity, begins by describ-
ing the cell as consisting of a certain group of atoms forming an
essential nucleus which is combined with several different groups of
atoms, called side-chains, varying in composition and structure.

Each of these side-chains has atoms arranged in such a way that
they present affinities for combining with groups of atoms of nutrient
or other material circulating in the animal fluids. These groups he
calls receptors, and the arrangement of atoms, by virtue of which
combination occurs, a haptophore group.

Thus, specific lysis is due to the action of a complement on a spe-
cific cell through a specific amboceptor, the chemical reaction being
due to the presence, in the chemical structure of the cell, of a re-
ceptor having a group of atoms haptophorous with a group of atoms
of the amboceptor, which, in turn, has a group haptophorous with one
of the complement.

Lymph is a clear, colorless, or slightly yellow liquid of a faint
alkaline reaction ; in composition it closely resembles blood-serum.
It contains less protein, particularly less fibrinogen, the salts and ex-
tractives are present in about the same amount. Lymph coagulates
more slowly and less firmly than blood. The term " chyle " is applied
to the lymph of the lacteals and thoracic duct when it is clouded by
the fat absorbed from the food in the intestine.

Bone is chemically distinguished from other tissues by the large
quantity of inorganic salts which it contains. Dried bones contain
about 31 per cent, of organic matter combined with 69 per cent, of
mineral matter. Different bones (and even different parts of the same

ANIMAL FLUIDS AND TISSUES. 663

bone) of the same person differ somewhat in composition ; more-
over, the bones of a child contain somewhat more of organic matter
than those of a grown person, as may be shown by the following
analyses of the corresponding bone in children and a grown person :

Child one year. Child five years. Man twenty-five years.

Organic matter, 43.42 per cent. 32.29 per cent. 31.17 per cent.

Tricalcium phosphate, 48.55 " 59.74 " 58.95 "

Magnesium phosphate, 1.00 " 1.34 " 1.30 "

Calcium carbonate, 5.79 " 6.00 " 7.08 "

Soluble salts, 1.24 « 0.63 " 1.50 "

Ferric phosphate, Traces. Traces. Traces.

Frequently human bones contain calcium fluoride, which substance,
to the amount of 1 to 2 per cent., is a normal constituent of the
bones of many animals. The organic matter of bone is ossein, a
collagen, yielding gelatin on boiling with dilute hydrochloric acid.

Experiment 76. Pour upon 3 grammes of bone 10 c.c. of water, and then
10 c.c. of hydrochloric acid. (Notice that carbon dioxide is liberated.) The
dilute acid dissolves the mineral constituents of the bone, leaving the organic
matter (ossein) as a swollen mass, which retains the shape of the bone.

Decant the acid solution, and to part of it add an excess of ammonia, then
acidify with acetic acid. The greater part of the precipitate formed by am-
monia will dissolve. The insoluble part contains traces of silica, but is chiefly
ferric phosphate, most of which is derived from the blood in the bone. Filter
and test portions of filtrate for phosphoric acid with ammonium molybdate
and for calcium with ammonium oxalate. Dissolve the washed precipitate on
the filter with a little hydrochloric acid, and test for phosphoric acid as above,
and for iron with potassium ferrocyanide. (The detection of the mineral con-
stituents of bone may be carried out with the ash left from incinerating bone.)

Wash the ossein, obtained above, first with water, then with dilute solution
of sodium carbonate, and finally with water again. Put the washed ossein in
a beaker with a little water and boil until most of the ossein has been dissolved.
Neutralize, if necessary, with sodium carbonate, and filter while hot into a test-
tube. On standing, the solution gelatinizes more or less completely. Ossein
is converted into gelatin by this treatment.

Gelatin. The purest commercial form of gelatin is known as
isinglass, prepared from the sounds or air-bladders of certain fishes ;
it is much used as an article of food in creams and jellies. An
impure gelatin, prepared from animal refuse (hoofs, bones, hides, etc.),
forms common glue, and its solution in acetic acid is sold as liquid
glue. In a pure state gelatin is a colorless or slightly yellowish,
transparent, tasteless mass. The presence of gelatin often prevents
the formation of precipitates by holding them in suspension in a
finely divided state, so that they may pass through filter-paper.

664 PHYSIOLOGICAL CHEMISTRY.

The nutritive value of gelatin is discussed under Metabolism
(page 646).

As gelatin contains no tyrosiue and no tryptophane, it will be
found that the results obtained with the xanthoproteic and Mil Ion
tests below are only faintly positive, being due to impurities.

Tests for gelatin. Pour upon a gramme of gelatin 25 c.c. of water and allow
to stand twenty-four hours. The gelatin now is swollen, but not dissolved.
Decant the water, add 8 c.c. of distilled water, heat over a water-bath until the
gelatin dissolves, then cool. To the gelatinous mass, thus obtained, add about
50 c.c. of water and heat again until dissolved. Use this solution for the fol-
lowing tests :

1. Add tannin, or hydrochloric acid and phosphotungstic acid: voluminous
precipitates are formed.

2. Boil a portion with one-third its volume of nitric acid : a faint-yellow
color is produced, showing the presence of an aromatic radical.

3. Add caustic potash and a little cupric sulphate : a blue to violet color
appears without a trace of red. (Difference from albumoses and peptones.)

4. Boil with Millon's reagent: a faint pink or red color. (Difference from
proteins in general.)

5. Add bromine-water: a heavy yellow precipitate is formed, possessing
tough, adhesive properties.

6. Add a few drops of acetic acid and boil ; add acetic acid and potassium
ferricyanide ; add mercuric chloride. Precipitation takes place in neither case.
(Difference from simple proteins.)

Note that gelatin solidifies on cooling and becomes liquid again on
the application of heat (difference from proteins in general).

Teeth consist of three distinct tissues, viz., dentine, forming the
chief mass, in its interior being the pulp cavity ; enamel, investing
the crown and extending some distance down the neck ; and cement,
covering the fangs. The composition of cement is almost the same as
that of bone, its organic and inorganic constituents having the rela-
tive proportions of 30 : 70.

Dentine contains less water than bone and is also poorer in organic
matter. The following table gives the composition of the dentine of
an adult woman and man respectively :

Woman. Man.

Organic matter — ossein and vessels . . . 27.61 20.42

Calcium phosphate 66.72 67.54

Calcium carbonate 3.36 7.97

Magnesium phosphate 1.08 2.49

Soluble salts, chiefly sodium chloride . . 0.83 1.00

Fat 0.40 0.58

Enamel is distinguished by the very small proportion of water and

ANIMAL FLUIDS AND TISSUES. 665

organic matter contained in it. Its average composition may be thus
stated :

Water and organic matter 3,5

Calcium phosphate and traces of fluoride .... 86.9

Magnesium phosphate 1.5

Calcium carbonate ........ 8.0

Tartar is the name given to the substance which deposits from
alkaline saliva on the teeth. It is of a grayish, yellowish, or brown-
ish color, and consists chiefly of calcium phosphate, with a little
carbonate, but contains also bacteria and other organic matter, salts
of the alkalies, and silica.

Hair, nails, horns, hoofs, feathers, epithelium, are nearly iden-
tical in composition. They all contain cholesterin and nitrogenous
substances termed keratins, which are probably not distinct chemical
compounds, but mixtures of several substances similar in composition
and properties.

Cholesterin fats are very resistant to the action of putrefactive bacteria, and
the occurrence of these fats in combination with the keratins serves as a pro-
tection to the skin surface from the attacks of the ever-present bacteria.

Muscle. The chemical composition of the various morphological
elements of striated muscle is not definitely known. Fresh, inactive
muscle has an amphoteric reaction — i. e., it colors red litmus-paper
faintly blue, and blue litmus-paper slightly red. After activity or
death the reaction becomes acid. If the blood is removed from
muscle immediately after death, and the muscle is then quickly cut
and frozen, an alkaline fluid can be pressed out, the muscle-plasma,
which contains the proteins of muscle. Muscle-plasma coagulates
spontaneously, separating a protein body, myosin, and yielding a
serum, muscle-serum. A similar change takes place in the muscle
shortly after death, causing the hardening of the muscle observed in
rigor mortis.

The more important constituents of muscle are considered here
without attempting a morphological distinction.

Proteins of muscle. There is at present no generally accepted view
as to the nature of the essential proteins of muscle tissue. This is
due largely to the many different names given them, which are in
almost hopeless confusion. It seems certain that there are at least
two proteins in living muscle which have the power of coagulating
after death. V. Fiirth calls the less abundant of these myosin and
its coagulated form myosin fibrin ; the second he calls myogen, and

666 PHYSIOLOGICAL CHEMISTRY.

says that it is converted first into an intermediate stage, and finally
into myogen fibrin. Myosin belongs to the globulins and myogen
resembles the albumins. The coagulation of these proteins appears
to take place spontaneously, as no enzyme has been satisfactorily
demonstrated. The process is probably not analogous to the clotting
of fibrinogen.

Carbohydrates of muscle. There are present in muscle varying
amounts of dextrose and glycogen, which form probably the most
important source of energy for the work of the muscle. The dex-
trose is brought by the blood-stream, and any excess over the amount
needed for immediate use is converted into glycogen by the muscle,
and "is held in reserve in this form. When a muscle does work, i. e.,
when it contracts, the glycogen is split again into dextrose, which is
then oxidized with a resulting liberation of energy. It is possible to
show that the carbon dioxide of the muscle is increased in amount,
and that there is also a formation of lactic acid. It is believed that
this lactic acid represents an incomplete oxidation of the sugar. In
the burning of dextrose by the muscle tissue, an internal secretion or
hormone produced by the pancreas is believed to play an important
part.

Muscle extractives. The extractive bodies of the muscle are
important, and are both nitrogenous and non-nitrogenous. Among
the first, creatine, the xanthine bases, urea, and uric acid deserve men-
tion. Non-nitrogenous extractives always present are inosite, gly-
cogen, sugar, and lactic acid.

Creatine (Meihyl-guanidine-acetic acid), NH = ^\TC/ip2TT \ p TT o

=C4H9N3O2, occurs in muscles of vertebrates, in the brain, blood,
transudates, and the amniotic fluid. When pure, it forms colorless,
transparent, rhombic prisms. The crystals are soluble in 75 parts
of cold, much more soluble in hot water, slightly soluble in alcohol,
insoluble in ether. The solution is neutral to litmus, though creatine
is a weak base, combining with some of the acids to form crystal-
line salts. Creatine may be obtained by the action of cyanamide on
sarcosine (methyl-glycocoll).

dride of creatine, and may be obtained by boiling creatine with acids,
when a molecule of water is split off. Vice versd, creatinine may
be converted into creatine. Creatinine is readily soluble in water
and alcohol, but nearly insoluble in ether ; it crystallizes in colorless

ANIMAL FLUIDS AND TISSUES. 667

prisms ; the solution is slightly alkaline to litmus. Creatinine is a
strong base, forming well-defined salts ; it also forms an insoluble
double compound with zinc chloride, for which reason the latter is
often used to precipitate creatinine. The occurrence of creatinine
in urine will be considered later.

Experiment 77. a. Preparation of creatine. Digest 400 grammes of finely
divided lean beef with 500 c.c. of water at a temperature of 50° C. (122° F.) ;
filter the mass through cloth, press out well, and repeat the operation twice
with 1000 c.c. of water, bringing the mixture to the boiling-point each time ;
then evaporate the mixed filtrates to about one liter. (In place of the liquid
extract, thus obtained, a solution of commercial extract of beef may be used.)
Acidify the solution with acetic acid, heat to boiling, and filter off the coagu-
lated proteins ; to the cold filtrate add basic lead acetate as long as a precipitate
is formed, filter and precipitate excess of lead by passing hydrogen sulphide
through the solution. Finally filter, evaporate filtrate over a water-bath to a
syrup, and set aside. After a day or two crystals of creatine will be found,
which, if too highly colored, may be redissolved in water, decolorized with
bone-black, and recry stall ized.

b. Conversion of creatine into creatinine. Heat 0.5 gramme of creatine with
10 c.c. of dilute sulphuric acid for half an hour over a water-bath ; then dilute
with 25 c.c. of water and add a sufficient quantity of powdered barium car-
bonate to neutralize the acid. Next filter, evaporate the filtrate to about 5 c.c.,
and use this solution of creatinine for the following tests :

1. To a few drops of the solution add an equal volume of an alcoholic solu-
tion of zinc chloride. Creatinine zinc chloride, (C4H7N3O)2.ZnCla, crystallizes
in warty lumps, composed of fine needles or prisms.

2. Weyl's reaction. Add, drop by drop, a freshly prepared, dilute solution
of sodium nitroprusside, Na2Fe(CN)5lSTO, until the solution is colored yellow;
then add drop by drop a dilute solution of sodium hydroxide : a fine transient
ruby-red color is obtained which soon passes into yellow. Acidulate solution
with acetic acid and warm : solution turns green, then blue, the color being
due to the formation of Prussian blue.

3. To a very dilute solution of creatine add a trace of an aqueous solution
of picric acid and render faintly alkaline: the solution turns intensely red.

Xanthine bases are a group of nitrogenous substances produced in
the organism as the result of the cleavage of nucleins. They are
closely related to one another, as also to uric acid, from which they
may be obtained by synthetic processes. Indeed, an increased secre-
tion of uric acid follows their ingestion as food. While eleven
xanthine bases have been isolated from the cell, only four (xanthine,
hypoxanthine, guanine, and adenine) are found in the muscle. Con-
jointly the xanthine bases are also termed alloxur bases or purine
bases. The first named refers to the fact that the nucleus of xanthine
bases is assumed to be made up of the carbon-nitrogen nuclei of
alloxsm, C4H2N2O4 (an oxidation-product of uric acid), and wea,

668 PHYSIOLOGICAL CHEMISTRY.

CN2H4O. When the two nuclei occur joined together into one
nucleus the latter is known as the purine-nueleus. Purine itself is a
hypothetical compound containing this nucleus.

N— C

C

u

N/~1 XT /""I TT

— O JN =Url

II II

Nx C C— N. HC C— NH.

' U->: 1J-N>H-

Alloxan Urea Purine

nucleus, nucleus. nucleus.

By oxidation, or by replacement of hydrogen atoms in purine with
the radicals OH, NH2, NH, or by introducing the methyl group,
CH3, the different purine bases or allied compounds have been
formed. These bodies are also closely related to the vegetable bases
caffeine and theobromine, and also to uric acid, as shown in the fol-
lowing table :

Purine

Hypoxanthine (oxypurine) .... C5H4N4O

Xanthine (di-oxy purine) ..... C5H4N4O2

Uric acid (tri-oxy purine) ..... C5H4N4O3

Heteroxan thine (methyl-xan thine) . . . C5H3(CH3)N4Oj
Paraxanthine (dimethyl-xanthine) \ .

Isomeric with theobromine / ' ' M^CH^I^O,

Caffeine (trimethyl-xan thine) .... C5H(CH3)3N4O2

Adenine (amino-purine) ..... C5H3(NH2)N4

Guanine (amino-oxypurine) .... C5H3(NH2)N4O

Carnine (dimethyl-uric acid) .... C5H2(CH3)2N4O,

Uric acid and the xanthine bases take up water and yield qualitatively the
same decomposition-products when treated with fuming hydrochloric acid
under pressure, viz., ammonia, carbon dioxide, glycocoll, and formic acid.

Xanthine and hypoxanthine (sareine) occur generally together,
though in small quantities, in urine and in almost all tissues. In
larger quantity they are found in the meat-extracts. When pure
these bodies are colorless powders, almost insoluble in water, alcohol,
and ether. With acids they form crystallizable salts, and with silver
nitrate double compounds, which are employed in the separation of
the bases from fluids.

Phosphocarnic acid is a glyco-nucleoprotein, occurring in muscle ; it yields
on hydrolysis succinic acid, carbon dioxide, phosphoric acid, a carbohydrate,
and carnic acid, a protein almost identical with peptone. It forms soluble
compounds with the alkaline earths, and also an iron compound (carniferrin)
soluble in alkalies ; these properties serve as a means to carry these metallic
compounds through the body. (Lacto-phosphocarnic acid is an analogous
compound found in milk.)

ANIMAL FLUIDS AND TISSUES. 669

Muscle pigment. Muscle, even when completely freed from blood, has a red
color, due to a pigment which is some slight modification of blood haemoglobin.

Of non-nitrogenous bodies found in muscle, inosite and sarcolactic acid, which
have been previously considered, deserve mention.

Experiment 78 (Preparation of sarcolactic add). Dissolve 20 grammes of
commercial meat-extract in 200 c.c. of water, add basic lead acetate as long as
a precipitate is formed ; filter and evaporate filtrate to a syrupy consistence.
Then add 200 c.c. of 96 per cent, alcohol ; filter and evaporate the filtrate to
dry ness over a water-bath. Dissolve the residue in 40 c.c. of water and 20 c.c.
of sulphuric acid. Extract this solution twice with an equal volume of ether
in a separatory funnel. Filter the ethereal solutions and evaporate the ether
with proper precautions. The residue, consisting of a colorless liquid, is sar-
colactic acid, to which apply :

Uffelmann's test for lactic acid. To an aqueous solution add a few drops of
Uffelmann's reagent (10 c.c. of a 2 per cent, solution of carbolic acid in
water, to which a few drops of ferric chloride solution have been added). A
yellow color is produced.

Inorganic constituents of muscle are chiefly mono- and dipotassium
phosphate, with smaller portions of sodium bicarbonate, salts of
magnesium and calcium, some iron salts, and traces of sulphates
and chlorides.

Meat- extracts are of two kinds, those from which the proteins and peptones
have been removed, and those containing besides proteins large quantities of
the basic extractives. Articles of the first class are destitute of nutritive
value, and the second derive no nutritive value from the extractive con-
stituents. The physiological effect of the flesh bases seems to be in the direc-
tion of nerve stimulants, and for this reason they are to be classed with tea
and coffee as adjuncts to food, not as true foods.

The thyroid gland contains iodine in some form of protein com-
bination, known as thyro-iodine ; this compound contains 9.3 per
cent, of iodine.

Desiccated thyroid glands, Glandulae thyroideae siccae. Numerous
extracts of the thyroid are upon the market. The preparation of the Pharma-
copoeia is the cleaned, dried, and powdered glands of the sheep, freed from fat.
It is a yellowish amorphous powder, partially soluble in water.

Thyreoidectin and rodagen are unofficial preparations prepared respectively
from the blood and from the milk of animals from which the thyroids have
been removed. Their action is stated to be exactly the opposite of that of the
thyroid preparations.

The thyroid gland, and also the adrenals, have some influence on sugar
metabolism, which is not yet understood.

The suprarenal glands contain a substance which has the power of con-
stricting the blood-vessels of the body, and thus causing a great but transient
rise in blood-pressure. This substance has been found to be methylamino-
ethanol-dioxy-benzol, C6H3(OH)2.CH(OH).CH2.NH.CH3. It is used particu-

670 PHYSIOLOGICAL CHEMISTRY.

larly to produce local anaemia, and is called by various names : suprarenalm,
suprarenin, adrenalin, epinephrin.

Desiccated suprarenal glands, Glandulae suprarenales siccse. These
are the cleaned, dried, and powdered suprarenal glands of the sheep or ox,
freed from fat. A light-yellowish, amorphous powder, partially soluble in
water.

Brain consists of so many individual parts that the analysis of it
as a whole is of little value, and to separate these parts successfully
is a task not yet accomplished. Brain, as a whole, contains lecithin,
cholesterin, protagon, and many other substances, some of which are
distinguished by the large quantity of phosphorus they contain.

The gray matter contains albumin, globulin, nucleoprotein, and nuclein.
Neurokeratin forms the neuroglia. In the white matter is found protagon, a
very complex substance containing nitrogen and phosphorus. It yields on
hydrolysis a lecithin, fatty acid, and cerebroside. The cerebrosides are nitro-
genous substances free from phosphorus, yielding on hydrolysis galactose,
sometimes called brain-sugar. Fused with caustic potash, or boiled with nitric
acid, they form palmitic or stearic acids. Three cerebrosides are known:
cerebrin, kerasin, and encephalin.

The term " lipoids :> is applied to an indefinite group of organic substances,
which are, like the fats, soluble in ether and alcohol. These substances are
present in many kinds of tissue, and are particularly abundant in the brain
and in nerve fibres. The more important membranes are cholesterin and the
phosphorized fats (phosphatides, lecithins). The cerebrosides are also classed
here. The function of these substances is entirely unknown. Their abun-
dance in brain tissue is the basis of the well-known theory that the anaesthesia
produced by ether and chloroform is due to the solvent action of these sub-
stances upon the lipoids.

Lecithins, C^H^NPOg or C42H84NPO9. Lecithin, one of the con-
stituents of bile, is a member of the group of substances generally
termed phosphorized fats or lecithins. These bodies are highly com-
plex in composition, and may be looked upon as fats formed f Von/
glycerin-phosphoric acid by substitution of hydrogen atoms with two
fatty acid radicals and a base, choline.

Glycerin-phosphoric acid, C3H5<^ QpQ2QTj\ ^s obtained by the

action of glycerin on phosphoric acid, when combination takes place
with elimination of water, thus :

C3H5(OH)3 + H3P04 C3H5(OH)2.H2P04 + H2O.

Glycerin-phosphoric acid is a syrupy liquid yielding easily soluble
salts, some of which are used medicinally. The hydroxyl hydrogen
is replaceable by acid radicals and the hydrogen of phosphoric acid
by bases. Thus, by introducing the radicals of stearic acid and
of choline distearyl-lecithin is obtained of the composition, C3H5
(C18H3502)2.HP04.C2H4N(CH3)3OH.

ANIMAL FLUIDS AND TISSUES. 671

Choline (Trimethyl-oxyetJiyl-ammonium hydroxide), N(CH3)3.C2H5O.OH, has
been mentioned as one of the ptomaines. It is a colorless fluid of oily con-
sistency, has strongly basic properties, and is extremely unstable. By removal
of the elements of water choline is converted into the strongly poisonous
substance neurine, mentioned on page 620. On the other hand, choline by
oxidation is converted into muscarine, a ptomaine even more poisonous than
neurine.

Cholesterin, C27H45OH. This substance has been classed by
physiologists among the fats, because it is greasy and soluble in
ether, but its chemical constitution is that of an alcohol. It is found
chiefly in bile, but also in blood, nerve-tissue, brain, contents of the
intestines, feces, etc. ; its presence in certain vegetables, as pease,
beans, etc., has also been demonstrated. Cholesterin combines with
fatty acids to form fats.

Cholesterin crystallizes in colorless, rhombic plates, which are
insoluble in water, alkalies, and dilute acids, but soluble in ether. It
sometimes forms in the organism solid masses, known as biliary cal-
culi or gall-stones, some of which are almost pure cholesterin.

Cholesterin is an unsaturated, secondary alcohol, and a derivative
of the terpenes.

Reactions of cholesterin:

1. Place a small quantity of cholesterin on a slide, moisten with a
drop of 80 per cent, sulphuric acid, and cover with a cover-glass.
Allow a little iodine solution to run in under the cover-glass and
examine it with the microscope. The cholesterin crystals pass through
many shades of colors, gradually becoming brown or violet or clear
blue.

2. Evaporate, in a shallow porcelain dish, a small quantity of
cholesterin Avith hydrochloric acid containing a trace of ferric chloride.
A blue residue is formed.

QUESTIONS. — What three kinds of matter are found as constituents of the
animal body, and how can they be determined quantitatively? Mention the
chief constituents of blood, and state those which predominate in serum and
in the corpuscles respectively. What substances cause the clotting of blood,
and what explanation can be given ? How may blood-stains be recognized ?
What are the characteristics of the different haemoglobins? Describe methods
for determining the specific gravity and the alkalinity of blood. How can the
proteins of blood-serum be separated ? Mention the principal constituents of
muscles, bone, teeth, and hair. State the properties and reactions of creatine
and gelatin. What is the composition of glycerin-phosphoric acid, and in
what form of combination does it exist in the body?

672 PHYSIOLOGICAL CHEMISTRY.

56. DIGESTION.

General remarks. It has been stated that foods are divided into
two classes, inorganic and organic, and that the fetter are subdivided
into proteins, carbohydrates, and fats ; and also that the term diges-
tion refers to the process by which organic foods are altered in such
a manner that they may be absorbed.

The process of digestion is both mechanical and chemical. By
the mechanical part of the process the food-material is disintegrated,
propelled along the alimentary canal, and mixed with the different
digestive secretions. These latter cause a chemical change, usually
hydrolysis, of the food, converting it into soluble and easily absorb-
able substances. For convenience of study the process is divided
into salivary, gastric, and intestinal digestion ; and the secretions
and chief alterations of the nutrients in these portions of the tract are
considered separately. It should be remembered, however, that these
three processes are closely interdependent, and any disturbance of
function, mechanical or chemical, in one part of the digestion will
disturb and derange all.

Salivary digestion. The first part of the process of digestion is
accomplished in the mouth, and consists in the breaking up of the
food by the teeth and mixing it with saliva, the process being known
as mastication. In addition, the saliva, to a limited extent, converts
starch into maltose. This action of the saliva is due to its ferment
ptyalin. Other functions of the saliva are to keep the mucous mem-
brane of the mouth moist and to lubricate the food bolus.

Saliva is the mixed secretion of the parotid, submaxillary, sub-
lingual, and buccal glands. The quantity secreted in a day varies
from 600 to 1500 c.c. The flow is easily excited by reflex stimula-
tion, as by the smell or sight of food, or by chewing of some insolu-
ble substance. Saliva appears as a viscid, frothy, tasteless, inodor-
ous liquid, of a sp. gr. of 1.002 to 1.008. The reaction to litmus is
generally slightly alkaline, but may become acid under pathological
conditions. Saliva as it appears in the mouth contains food particles
and numerous micro-organisms. The average composition of saliva
is as follows :

Water 99.49

Mucin and epithelium 0.13

Fatty matter 0.11

Ptyalin, maltase, and other organic matter . . . .0.12
Salts 0.15

The salts are alkali and earthy phosphates, carbonates and chlo-
rides, and potassium sulphocyanate. The latter occurs in variable

DIGESTION. 673

quantity in the saliva of different individuals. Pathologically, saliva
may contain sugar in diabetes, melanin in Addison's disease, bile-
pigment in icterus. Leucine and urea have been found in saliva
during uremia. The iodides and some other drugs are habitually
secreted by the salivary glands. This function is used in measuring
the rapidity of absorption.

Ptyalin, the diastatic enzyme, occurs in the saliva of all animals
except the pure carnivora. It is characterized by its action in con-
verting starch into sugar. It acts best at 40° C. (104° F.) in a
neutral solution, although it is active in a weak alkaline solution,
and also in acid solution up to 0.2 per cent, of mineral acid.

The conversion of starch into sugar by ptyalin is a progressive hydrolysis.
The first change is the formation of soluble starch, which gives a blue color
with iodine. Soluble starch is split into maltodextrin and erythrodextrin ; the
latter gives a red color with iodine. These dextrins are next split and yield
maltose, maltodextrin, and achroodextrin, which are not colored by iodine.
From achroodextrin more maltodextrin and maltose are derived, and finally
the hydrolysis results in the formation of maltose with some maltodextrin.
The maltose is converted into glucose by the action of the enzyme maltase.

Experiment 79. Mix intimately 1 gramme of starch with 10 c.c. of water,
pour this mixture into 90 c.c. of boiling water and stir until a smooth paste is
formed. Place 10 c.c. of paste in a test-tube, heat to 40° C. (104° F.), add 1
c.c. of saliva and 1 c.c. of 1 per cent, solution of sodium carbonate, mix well,
and keep at the stated temperature. At the expiration of one minute take out
a drop of the mixture, place it on a white plate, and add a drop of dilute
iodine solution. The mixture will turn blue. Eepeat testing the mixture,
which is to be kept at the same temperature, every minute until iodine has no
longer any effect on the solution, indicating the conversion of all starch into
simple sugars. With normal saliva the color reaction will cease within six
minutes ; a longer time would indicate an insufficient quantity of ptyalin in
the saliva used for the experiment.

When the solution no longer is affected by iodine add to 1 c.c. of solution 6
c.c. of alcohol : a precipitate of dextrin is formed. Allow the digestion to
proceed for half an hour, then heat some of the digested mixture with Feh-
ling's solution: the formation of red cuprous oxide shows the conversion of
starch into glucose.

Action of adds and alkalies on salivary digestion. In each of three test-tubes,
A, B, and C, place 5 c.c. of starch paste, prepared as above, and 1 c.c. of saliva.
To A add 3 c.c. of 0.25 per cent, hydrochloric acid ; to B add 3 c.c. of 1 per
cent, sodium carbonate. Keep the tubes at 40° C., and note the time required
for the disappearance of the iodine color reaction with the contents of each
tube. The reaction will disappear first in B, then in C, and finally in A.

In order to obtain saliva for experimental purposes a small glass
rod or a piece of rubber should be placed in the mouth. This will
stimulate the flow of saliva, which is to be collected and filtered.

43

674 PHYSIOLOGICAL CHEMISTRY.

General tests for mixed saliva.

1. Allow a few c.c. of saliva to stand a day or two : a cloudiness
will be observed, due to the precipitation of calcium carbonate, which
has been held in solution by carbon dioxide.

2. Acidify saliva with acetic acid : a precipitate of mucin is formed
insoluble in an excess of the acid.

3. Apply the xanthoproteic, Millon's, and biuret reactions for
proteins (see page 626).

4. Acidify with acetic acid and add ferric chloride : a red color,
due to the formation of ferric sulphocyanide, is produced.

Gastric digestion. The food, after mastication, passes through
the oesophagus into the stomach. Here the mass is kneaded by the
contractions of the muscular wall of the stomach and is acted on by
the gastric juice. By this treatment with the aid of the fluids
ingested the food is converted into a turbid liquid, known as chyme.
A small portion of the digested mass is absorbed through the stomach
wall, but most of the food, after being completely acted upon, passes
through the pylorus into the duodenum.

Gastric juice is a liquid secreted by the follicles of the stomach.
It can be obtained, in a fairly normal condition, either from animals
(dogs) or from man, by the aid either of gastric fistulse or of the
stomach-pump. It is a thin, nearly colorless liquid, having a some-
what sour taste, an acid reaction, and a specific gravity varying from
1.002 to 1.003. The total solids are about 0.5 per cent., nearly one-
half being inorganic salts, chiefly the chlorides and phosphates
of alkali and alkaline earth metals. The organic matter present,
and amounting to about 0.3 per cent., is chiefly pepsin and a little
mucin.

The secretion of gastric juice is not continuous, and is brought
about by chemical irritation of the gastric mucuous membrane or by
psychic influence. A strong desire for food will cause a flow of the
juice ; chemical irritation, as by the alkaline mass of food and saliva,
causes a slower but more continuous flow. The quantity of juice
secreted during digestion varies with the quantity and quality of the
food.

The average composition of pure gastric juice may be approxi-
mately stated thus :

Water 99. 26 per cent.

Pepsin and other organic matter . . . .0.30
Rennin . y

Free hydrochloric acid .... 0.22

Alkali chlorides 0 20

Phosphates of calcium, magnesium, and iron . 0.02

DIGESTION. 675

The acidity of gastric juice is due chiefly to hydrochloric acid,
present in quantities varying from 0.1 to 0.3, or even 0.4 per cent.;
to a slight extent also to organic acids and acid salts. The presence
of free acid in gastric juice cannot be demonstrated until about
twenty minutes after the swallowing of food ; this is due to the
power of proteins to form compounds with hydrochloric acid. During
this time the ptyalin of saliva is active in the hydrolysis of starch.
The gastric juice is the only secretion of the body containing free
acid. The mode of production of the hydrochloric acid is not under-
stood. While it is known that it is derived from the chlorides of the
blood, the details of the process are not yet worked out. The function
of the acid is to activate the enzymes of the stomach which are se-
creted in the zymogen state, and to aid in peptic digestion. It also
has a marked antiseptic action upon the contents of the stomach and
upper intestine. Organic acids, chiefly lactic, are frequently found in
the stomach, but these are not secreted in the gastric juice itself, but
are produced by some fermentative action from the food after it has
entered the stomach. Lactic acid is never found in a normal stomach
unless it was present in the food before ingestion. It is often present
in cases of gastric stagnation with a decreased hydrochloric output.
These cases may be either benign or, more often, malignant in origin.
Thus, the persistent occurrence of lactic acid with a diminution or
absence of hydrochloric acid is an indication of serious disturbances,
possibly of cancer of the stomach.

The origin of the lactic acid is the carbohydrate food ; other food
material may of course produce other organic acids (e. g., butyric acid
from butter).

The enzymes of gastric juice. The two important enzymes of the
stomach are pepsin and rennin, which are secreted in an inactive or
zymogen form, and are activated by the hydrochloric acid of the gas-
tric juice. In addition to these there is probably a lipolytic enzyme
(gastric lipase) present. In the cardiac end of the stomach the reaction
does not become acid for some time after digestion commences, and the
ptyalin of the saliva continues its action on the starches during this time.

Digestive action of gastric juice. The conversion of proteins into
peptone is a progressive reaction due to the action of pepsin in hydro-
chloric acid solution. Simple proteins are first changed into syn-
tonin, an acid albuminate ; this is split into compounds known as
primary proteoses (proto-proteoses, protalbumoses). By further action
these primary proteoses form secondary proteoses (deutero-proteoses,
deutero-albumoses), which are finally split, forming peptones.

676 PHYSIOLOGICAL CHEMISTRY.

Peptone is the end-product of gastric digestion, is diffusible, and
is not further changed by pepsin. The intermediate products exist
at the same time in gastric digestion, their relative quantities depend-
ing on tiie length of time the action has progressed.

While it is believed that gastric digestion normally carries the de-
composition of proteins no further than this, it is possible to split
proteins into the amino-bodies by pepsin-hydrochloric acid digestion
outside of the body.

Compound proteins are split by gastric juice, the simple proteins
formed being digested as above stated. The nucleoproteins yield a
peptone free from phosphorus, the nuclein split off being unchanged.
Collagen is first converted into gelatin, which then forms successively
an acid albumin, proto-proteose, deutero-proteose, and gelatin-peptone.
Elastin is changed slowly, while keratins are not changed at all.

Rennin is a milk-curdling enzyme present in all normal human
gastric juice. It is absent in chronic catarrh of the stomach and
other diseases. Its presence in gastric juice is shown by its action
on milk, and will be considered in the article on clinical examination
of gastric juice.

Absorption in the stomach. It has been shown that the stomach is
able to absorb sugars, peptones, salts, and some drugs. However,
the absorption is not extensive unless concentrated solutions are
present, and probably plays no great part in normal metabolism.

Experiment 80. (Artificial gastric digestion.) Dissolve 2 grammes of scale
pepsin in 1000 c.c. of 0.4 per cent, hydrochloric acid. To this solution add
about 250 grammes of protein. The protein material may be fresh or dried
blood-fibrin, the meat- residue from the preparation of creatine (Experiment 77),
or the whites of 18 eggs, previously boiled and finely divided. The fresh fibrin
or the egg-albumin may be added directly to the digestive fluid. The meat-
residue or dried fibrin should first be boiled with a liter of water, containing
1 c.c. of hydrochloric acid, until the material gelatinizes ; it must be cooled
before mixing it with the digestive fluid. Keep mixture in a thermostat at a
temperature of 40° C. (104° F.) for ten days. Filter the solution, heat the
filtrate to 50° C. (122° F.), and neutralize with sodium carbonate, when syntonin
is precipitated.

Evaporate filtrate from syntonin to about 200 c.c., adding sodium carbonate
if necessary to keep solution neutral during evaporation, filter, and saturate
solution with ammonium sulphate, when protease is precipitated, while peptone
remains in solution.

To purify the proteose, dissolve the precipitate in water, heat to boiling, and
add barium carbonate until all ammonium sulphate is decomposed. Filter,
evaporate filtrate to a small volume, and pour solution into double the volume
of 95 per cent, alcohol, when proteose is precipitated as a sticky mass. To
obtain it as a powder, allow the mass to remain in contact with the alcohol for

DIGESTION. 677

two hours, transfer to absolute alcohol for one hour, and then to ether for an
hour; then collect on a filter and dry between filter-paper. The proteose thus
obtained is a mixture of primary and secondary proteoses.

Use an aqueous solution of this proteose for the following tests : Acidulate
a portion with acetic acid and add an equal volume of saturated solution of
sodium chloride. The solution becomes cloudy, clearing again when heat is
applied, and becoming cloudy again when cool. (Characteristic of proteoses.)
Other portions of the solution use for the xanthoproteic, Millon's, and biuret
reactions.

Proteoses will give positive precipitation tests with acetic acid and ferro-
cyanide, and with trichloracetic acid. Peptones will give negative results with
the same tests.

To obtain peptone, the filtrate from the proteose is heated and 20 grammes
of ammonium sulphate are added to remove traces of proteose. The filtrate,
after being concentrated by evaporation, is treated with barium carbonate,
alcohol and ether, exactly as directed above for proteose. Use some of the
peptones for the xanthoproteic, Millon's, and biuret reactions.

Clinical examination of gastric juice. The chemical examina-
tion of gastric juice, or of contents of stomach, is now considered of
great importance in the diagnosis of diseases of the stomach. The
juice for examination is obtained as follows : On an empty stomach,
the patient partakes of a test-meal, consisting usually of bread and
water, and an hour after or later (depending upon the form of meal
administered) the contents of the meal are withdrawn by means of a
stomach-tube. The liquid is filtered and used for further examina-
tions. These examinations consist of the following determinations :
a. reaction ; b. presence of free acids ; c. presence of free hydro-
chloric acid ; d. presence of lactic and other organic acids ; e. total
acidity ; /. estimation of free acids ; g. estimation of free hydrochloric
acid ; h. estimation of combined hydrochloric acid ; i. estimation of
total organic acids ; j. presence of pepsin and pepsinogen ; k. presence
of renuin and rennin zymogen ; I, detection of proteins ; m, detection
of carbohydrates.

In case a sufficient supply of gastric juice cannot be obtained for the reac-
tions below, the student should prepare the following solutions : A. A 0.25 per
cent, hydrochloric acid ; B. A mixture of 10 parts of A and 40 parts of water;
C. A solution of 0.8 gramme of lactic acid in 100 c.c. of water ; D. A 2 per
cent, solution of albumose in water. Make reactions b and c with solution A,
repeat with B, and with a mixture of 1 part of B and 2 parts of D.

a. Reaction. This should be, and in all normal juices is, distinctly
acid to litmus-paper.

6. Free acids. The presence of free acids is detected by congo-red
paper. This paper is prepared by soaking unsized paper in a 1 per
cent, aqueous solution of congo-red, and drying. If a drop of juice

678 PHYSIOLOGICAL CHEMISTRY.

is placed upon the paper, the presence of free acids is indicated by
the change of color from red to blue ; if the blue color is intense,
free hydrochloric acid is present. (Neither combined hydrochloric
acid nor acid salts, such as acid phosphates, act on congo-red.)

c. Free hydrochloric acid. There are a number of reagents for the
detection of free hydrochloric acid. The more important of these
are : tropaeolin 00, phloroglucin-vanillin, resorcin, and dimethyl-
amino-azobenzol.

Tropceolin 00. Dissolved in water, the 1 per cent, brownish -yel-
low solution of tropaeolin 00 (diphenylamine-orange) is changed to a
brown-red or deep-red color upon the addition of juice containing
free hydrochloric acid. Upon gentle evaporation and heating a lilac
color is produced. The same reaction may be made with filter-paper,
soaked for some time in an alcoholic solution of the reagent, allowed
to dry, and used as test-paper. Hydrochloric acid turns this paper
brown, and upon heating the brown color changes to blue. (The
paper does not keep unchanged over a month.)

Phloroglucin-vanillin. This reagent is made by dissolving 2 parts
of phloroglucin and 1 part of vanillin in 30 parts of alcohol. It is
a very sensitive and reliable agent for the detection of free hydro-
chloric acid. ^Five drops of the solution mixed with an equal quan-
tity of gastric filtrate are gently heated over a Bunsen flame. On
complete evaporation a distinct red color or tinge appears in the
presence of not less than 0.01 per cent, of hydrochloric acid. The
formation of cherry-red crystals indicates the presence of large quan-
tities of the acid. Organic acids have no action on this reagent.

Resorcin. This reagent is equally as sensitive as, and more stable
than, phloroglucin-vanillin. The solution is obtained by dissolving
5 parts of resublimed resorcin and 3 parts of cane-sugar in 100 parts
of dilute alcohol. The manner of testing with this reagent is the
same as described above for phloroglucin-vanillin ; a bright-red tinge
or color appears, even when very small quantities of free hydrochloric
acid are present.

Dimeihyl-amido-azobeMzol. A 0.5 per cent, solution of this substance
in alcohol is mixed with a few drops of the stomach contents, and in
the presence of as little as 0.002 percent, of free hydrochloric acid a
cherry-red color develops.

d. Lactic acid. (Use solution C.) Uffelmann's reagent answers
best for detecting this acid. It is made by adding 1 or 2 drops of
ferric chloride solution to 10 c.c. of a 1 per cent, carbolic acid solu-
tion, and diluting this solution with water until it assumes an

DIGESTION. 679

amethyst-blue color. To 2 c.c. of this solution an equal volume of
gastric juice is added. In the presence of at least 0.01 per cent, of
lactic acid the liquid assumes a pure yellow color. As the presence
of too much hydrochloric acid (or even of some other substances)
prevents the change, it is well to shake (in doubtful cases) 10 c.c.
of juice with 50 c.c. of ether, evaporating the ethereal solution
to dryness, dissolving the residue in a few drops of water, and
adding to this solution, which contains the lactic acid, the above
reagent.

Butyric acid changes Uffelmann's reagent to brownish yellow.
Butyric and acetic acids may be recognized by their odor.

It has been mentioned that the total acidity of gastric juice is due to acid
salts, organic acids, free and combined hydrochloric acid. Clinically it is
sometimes necessary to estimate the acidity due to each. This is done by the
following method.

e. Total acidity. This is best determined by titration with an
alkali ; the estimation is conducted as follows : To 10 c.c. of the
filtered liquid a few drops of phenolphthalein solution are added, and
to the mixture deci-normal potassium hydroxide solution is slowly
added from a burette until the liquid assumes a slight reddish tint,
which does not disappear on stirring.

It is customary to express the acidity in percentages, according to
the quantity of deci-normal potassium hydroxide used. Thus, 52
per cent, acidity would indicate that every 100 c.c. of gastric fil-
trate are exactly neutralized by 52 c.c. of deci-normal potassium
hydroxide.

Though the total acidity is due to a mixture of free and combined
hydrochloric acid, organic acids, and acid salts, it is frequently
expressed as hydrochloric acid. As 1 c.c. of deci-normal alkali
solution corresponds to 0.003618 gramme of HC1, the number of
c.c. of alkali used multiplied by the factor stated, gives the grammes
of HC1 in the 10 c.c. of juice used. Suppose 5.2 c.c. of alkali were
required; this would correspond to 5.2 X 0.003618, equal to 0.0188
gramme of HC1 in 10 c.c., or to 0.188 per cent.

/. Estimation of free acids. Both free hydrochloric and organic
acids change the bright-red color of congo-red to blue, while alkalies
restore it to red. Acid salts, such as acid phosphates, have no effect
on this indicator. If, therefore, a titration of 10 c.c. of filtered gas-
tric juice, to which enough of congo-red solution has been added to
impart a distinct blue color, is made (as above described for total
acidity), then the number of c.c. of deci-normal potassium hydroxide

680 PHYSIOLOGICAL CHEMISTRY.

solution used to restore the red color indicates the quantity of free
acid present. The calculation is made as above mentioned.

g. Estimation of free hydrochloric acid. The use of dimethyl-
ami no-azobenzol as an indicator for free hydrochloric acid has been
mentioned above. For quantitative work 10 c.c. of gastric filtrate
are mixed with 5 drops of the dimethyl-amino-azobenzol solution,
and this mixture is titrated with ^ sodium hydroxide solution. The
disappearance of the reddish color indicates when the reaction is
completed. The difference between the estimation of total free acids
(/) and that of free hydrochloric acid (g) indicates the quantity of
organic acids present.

h. Estimation of combined hydrochloric acid. To 10 c.c. of gas-
tric juice add 3 drops of a 1 per cent, alizarin solution and titrate
with YQ alkali until the solution assumes a clear violet color. The
acidity thus determined is due to free hydrochloric acid, acid salts,
and organic acids. The difference between the results of titration
with alizarin (A) and with phenol-phthalein (e) shows acidity due to
combined hydrochloric acid, while the difference between the titra-
tion with alizarin (h) and that with dimethyl-amino-azobenzol shows
acidity due to organic acids and acid salts.

i. The total organic acids, free and combined, may be determined
by neutralizing 10 c.c. of gastric juice, using phenolphthalein as an
indicator, evaporating the neutral solution to dryness and incinerating
the residue. By this operation the organic acids are converted into
carbonates, which are titrated with ^ acid, and from the result the
quantity of organic acid is calculated, usually as lactic acid.

j. Pepsin and pepsinogen. In case free acid is present, 10 c.c. of
gastric juice are placed in a beaker, and a small bit of dried fibrin
or a lamella of blood albumin (Merck), is added, and the beaker
placed in a thermostat at a constant temperature of 38° to 40° C.
(100° to 104° F.). Pepsin is indicated by the rapid solution of the
flake of albumin. If free hydrochloric acid is absent, the juice is
rendered acid with a drop of this acid and then tested in the manner
described.

k. Rennin enzyme and rennin zymogen. Rennin is tested for as
follows : 10 c.c. of gastric juice are exactly neutralized with deci-
normal alkali and mixed with an equal volume of neutral unboiled
milk. The mixture is placed in a thermostat at 38° C. (100° F.).
If a casein coagulum is formed in ten to fifteen minutes, the coagula-
tion is due to the rennin enzyme.

Rennin zymogen is detected thus: 10 c.c. of gastric juice are

PLATE VII

INDICATORS FOR ALKALIES AND ACIDS.

Litmus.

Congo red.

3

Phenolphthalein.

flethy 1- orange ; Dimethj I-amido-
azobenzol ; Tropseolin D.

5

Alizarin for acids.

I ffelmann's test for lactic acid.

Gunzburg's phloroglucin- vanillin
test or Boas' resorcin test for free hy-
drochloric acid.

Methyl-violet.

Haematoxylin.

A ffocn & Co Lie/i. Baltimore., .Wd.

The colors on the left indicate alkaline, those on the right acid reaction.
For explanation see page in Index.

DIGESTION. 681

rendered feebly alkaline and mixed with 2 c.o. of a 1 per cent,
solution of calcium chloride and 10 c.c. of milk. If the rennin
zymogen be present, a heavy cake of casein is precipitated in a few
minutes.

1. 'Detection of proteins. Of these, syntonin, albumoses, and pep-
tones are to be looked for. Syntonin : The gastric filtrate is exactly
neutralized, whereupon a cloudiness or precipitate is formed, which
is soluble both in alkalies and in acids. Albumoses: These are pre-
cipitated by a saturated solution of ammonium sulphate, while pep-
tones remain in solution. Peptones : These are recognized by the
biuret-test. The juice is rendered strongly alkaline with potassium
hydroxide and a few drops of a cupric sulphate solution (1 in 1000)
are added. A red color indicates the presence of peptones.

ra. Detection of carbohydrates. Starch is recognized by the blue
color produced by iodine solution (1 iodine, 2 potassium iodide, 100
water). The reaction is less marked in proportion to the amount of
starch converted into dextrin and sugar.

Erythrodextrin gives a mahogany-brown color, and achroodextrin
remains unchanged by the iodine solution. Inasmuch as sugar is
present in the test-meal itself, it is useless to test for this substance.

Intestinal digestion. The changes in food taking place in the
small intestine are much more complex and far-reaching than those
occurring in the stomach. Little or no absorption takes place from
the stomach, and the alterations in the food brought about by the
gastric juice can be considered as being largely preparatory for the
action of the digestive fluids of the intestine. The close dependence
of one part of the process of digestion on the other is shown by the
normal effect of the entrance of chyme into the duodenum. The
acid chyme causes a reflex secretion of the pancreatic juice, the bile,
and the intestinal juice, the digestive fluids of the intestine. These
fluids are all alkaline, and are secreted in sufficient quantity to neu-
tralize the chyme and to provide the degree of alkalinity most suit-
able for the action of the ferments which complete the process of
digestion. A slight increase of the acidity of the gastric contents is
followed by an increase in the secretion of the digestive fluids of the
intestine. Intestinal digestion depends upon three secretions : (1)
the pancreatic juice ; (2) the bile ; (3) the succus entericus, the secre-
tion of the intestine.

Pancreatic secretions. The secretions of the pancreas are of
two kinds, an external, the pancreatic juice, which flows into the

682 PHYSIOLOGICAL CHEMISTRY.

intestine, and an internal secretion, which passes directly into the
blood, and has a governing power over the metabolism of sugar and
the conversion of glycogeu into sugar by the liver.

Pancreatic juice. There is no thoroughly reliable analysis of this
highly complex liquid on record. It is an alkaline liquid containing
from 3 to 6 per cent, of solids, two-thirds of which are of organic,
one-third of inorganic nature. Among the organic constituents are
a number (certainly three, probably four) of enzymes : 1. Amylopsin
converts starch into sugar (this action is more energetic than that of
ptyalin) ; 2. Trypsin converts proteins into peptones (this action takes
place in alkaline, but not in acid solution, as in case of pepsin) ; 3.
Steapsin decomposes fats into glycerin and fatty acids ; 4. A milk-
curdling enzyme. The inorganic solids are chiefly alkali chlorides
and carbonates, with some calcium, magnesium, and iron phosphates.

The quality of the food has an unmistakable influence on the com-
position of the juice and on the quantity of the different enzymes.
Thus, the juice is always richest in diastatic enzyme after a bread
diet, and richest in steapsin after a meal consisting of much fat.

The secretion of pancreatic juice is thought to be caused by stimuli
reaching the pancreas by two routes : (1) nervous stimuli by the sym-
pathetic nerves; (2) chemical stimuli by the blood-stream. The
chemical substance concerned is termed secretin, and is formed in the
intestine as soon as hydrochloric acid is admitted from the stomach
during the course of digestion. The HC1 acts upon a substance
normally present (prosecretin), transforming it to secretin, which is
absorbed and carried by the blood to the pancreas. Secretin belongs
to the class of bodies called hormones.

The trypsin of the pancreatic juice is for the most part secreted in
an inactive or zymogen state (trypsinogen), and becomes active when
it meets the kinase of the intestine (enterokinase). The other enzymes
(amylopsin, steapsin) are secreted mainly in the active condition.

Amylopsin (diastase) is closely related to ptyalin, and converts raw
or boiled starch into erythrodextrin, achrobdextrin, and finally into
maltose and dextrose. The dextrose is probably formed by the in-
vertin of the intestinal juice.

Experiment 81. (Diastatic action of pancreatin.) Dissolve 1 gramme of pan-
creatin in 500 c.c. of water, and after standing at 40° C. (104° F.) for two hours
filter the solution. Mix in a test-tube equal volumes of the solution and starch
paste, prepared as directed in Experiment 79, and heat at 40° C. (104° F.).
Notice that the material gradually* becomes transparent, reduces Fehling's
solution, and is not colored blue by iodine solution. Repeat the experiment
with a boiled solution of pancreatin, and notice that it has no effect on starch,

DIGESFION. 683

the enzyme having been destroyed by heat. (The pancreatin solution itself
should be tested with Fehling's solution, as the commercial article is frequently
adulterated with sugar.)

Steapsin (lipase) splits the neutral fats into fatty acids and glycerin.
The liberated fatty acids combine with alkali of the pancreatic juice,
forming soap. The action of lipase is materially aided by the pres-
ence of bile, although it is not understood how this occurs.

Experiment 82. (Fat-splitting action of steapsin.} (Fresh pancreas must be
used for the experiment.) Shake about 2 grammes of butter with a few c.c. of
lukewarm water, to which a drop of caustic soda solution has been added.
After cooling shake with an equal volume of ether, pour the ethereal solution
on a watch-glass and allow the ether to evaporate. To the neutral butter fat
thus obtained add a piece of fresh pancreas the size of a pea, mix the materials
intimately by rubbing, and place in a thermostat at 40° C. (104° F.). After a
few minutes the odor of butyric acid will be recognized.

Shake a gramme of butter fat, obtained as above, with about 5 c.c. of luke-
warm water, render slightly alkaline with sodium carbonate, using rosolic acid
as an indicator, add some fresh pancreas converted into a thin paste by grind-
ing with water, and keep the mixture at 40° C. (104° F.) for twelve hours.
Notice that the mixture turns yellow, due to the acid liberated from the butter
fat. The experiment when made with boiled pancreas does not show liberation
of acid.

Trypxin breaks down proteins by a series of changes almost iden-
tical with those produced by pepsin. It is, however, most active in
an alkaline medium, and has a more rapid and complete action than
that of pepsin. The digestions by pepsin and trypsin are to a certain ex-
tent supplementary to each other, for it is found that proteins subjected
to both are more thoroughly decomposed than by either one alone.
Under normal conditions it is probable that tryptic digestion produces
a considerable amount of amino-bodies, and that the remainder of the
peptones and proteoses are split up by the intestinal enzyme, erepsin.

Experiment 83. (Artificial tryptic digestion.} To 250 grammes of protein add
a solution of 5 grammes of sodium carbonate, 3 grammes of pancreatin, and
5 c.c. of chloroform. Keep in a thermostat at 40° C. (104° F.) for ten days.
Then filter off a few c.c. of the liquid and add bromine-water. A violet color
is produced, due to tryptophane. Acidify the digested mixture with acetic
acid, boil, filter, evaporate filtrate to 150 c.c., and allow to stand in a cool
place. In a few hours crystals of tyrosine will be deposited. Decant the
mother-liquor and purify the tyrosine by recrystallizing from a solution con-
taining a little ammonia. Use the crystals to test for tyrosine (see Index).

Evaporate the mother-liquor from the tyrosine to a thin syrup, add 200 c.c.
of hot alcohol, allow the mixture to cool, and filter. Evaporate the filtrate to
dryness, dissolve the residue in water, and boil with freshly prepared lead
hydroxide. Allow to cool, filter, free the filtrate from lead by means of

684 PHYSIOLOGICAL CHEMISTRY.

hydrogen sulphide, and evaporate to a small volume. The leucine which is
precipitated on standing is best separated from the mother-liquor by placing
the mass on a plate of porous clay. Use the crystals to make reactions for
leucine (see Index).

Bile, secreted by the liver, is a thin, transparent liquid of a golden-
yellow color, and a specific gravity of 1.020 ; it has a very bitter taste
and an alkaline reaction ; it varies widely in composition, the total
solids ranging from 9 to 17 per cent., being always highest after a
meal ; its composition, moreover, is highly complex ; the following is
an average of five analyses of bile from subjects with healthy livers :

Water 91.68 per cent.

Mucus and pigment 1.29 "

Taurocholate of sodium 0.87

Glycocholate of sodium § 3.03 "

Fat . 0.73

Soaps • . . 1.39 "

Cholesterin 0.35 "

Lecithin 0.53 «

Bile obtained after death is of a brownish-yellow color ; freed from
mucus it will remain undecomposed for an almost indefinite period.
The mucus may be separated by the addition of diluted alcohol and
subsequent filtration.

The quantity of bile discharged daily by a grown person may be
put at from 1000 to 1700 c.c., or from 23 to 47 ounces, but a con-
siderable quantity of this discharged bile is reabsorbed in a changed
form by the intestines; only a small amount of bile matters (in a
decomposed state, however) is contained in the feces.

Bile is to be regarded both as a secretion and an excretion, as will
be seen below in the statements concerning its constituents. It has
long been believed that bile is an intestinal antiseptic. Its action is,
however, weak and probably unimportant, as it has been found that
certain bacteria (B. typhosus, B. coli) grow well in media containing
bile.

Biliary pigments. Several pigments have been found in bile, but
it is probable that only two, bilirubin and biliverdin, occur in normal
bile.

The bile-pigments are formed in the liver from haemoglobin by a
process in which the iron is split off and retained in the organism.
While the pigments of the bile are regarded as waste products of
metabolism, a certain portion of them is absorbed in the intestine, is
excreted again by the liver, and also by the kidneys (as urochrome
and urobilin). That portion which passes out with the feces is re-
duced to stercobilin (isomeric with urobilin).

DIGESTION. 685

Bilirubin, C16H18N2O3, is a reddish-yellow pigment derived from
hsematin, which it resembles. It is sparingly soluble in water,
alcohol, and ether, readily soluble in hot chloroform and carbon
disulphide.

Biliverdin, C32H36N4O8, is a green powder existing in green biles ;
it is formed from bilirubin by mild oxidation.

Tests for biliary coloring-matters. A reaction known as Gmelin's
test may be applied in different ways :

1. Place into a test-tube a few c.c. of a chloroform solution of
bilirubin, and pour down the side of the inclined tube an equal
volume of yellow nitric acid in such a manner that the liquids do
not mix. At the line of junction colored rings appear, being green
nearest the solution of the coloring-matter, and progressively blue,
violet, red, and yellow. (Plate VIII., 7.)

2. Place on a white porcelain slab a few drops of the solution and
alongside of it a drop of yellow fuming nitric acid. On causing
the two liquids to come in contact a play of colors as above is seen
at the junction.

3. Expose an alkaline solution of bilirubin to the air in an open
vessel ; it turns green, owing to the formation of biliverdin. The
latter answers also to Gmelin's test.

Biliary acids. Glycocholic acid, C^H^NOg, and taurocholic acid,
C26H45NO7S, exist as sodium salts in the bile^bf man and most
animals. Both salts may be obtained as colorless crystals, which
dissolve in water, forming solutions with an acid reaction and an
intensely bitter taste. Both acids are easily decomposed by heating
with alkalies or with dilute acids, also by the action of putrefying
material or by chemical changes taking place in the intestines. In
all these cases are formed cholic acid, C24H40O2, and a second product,
which in the case of glycocholic acid is glycocoll, amino-acetic acid,
CH2.NH2.CO2H, and in the case of taurocholic acid, taurine, amino-
ethyl-sulphonic acid, NH2.C2H4.SO3H.

These acids are formed in the liver, and very likely from some
protein material ; the mode of formation is, however, not known. As
in the case of the bile-pigments, the bile acids in part represent waste
material, while a part is reabsorbed by the intestine. The physio-
logical activity of bile acids is concerned mainly with the fats ; they
aid the saponification by lipase, and promote the absorption of fat
(probably by their solvent action). They are believed to hold the
cholesterin of the bile in solution.

686 PHYSIOLOGICAL CHEMISTRY.

Test for biliary acids. The biliary acids and their salts show a
characteristic reaction known as Pettenkofer's test. This reaction is
shown by adding very little cane-sugar to the liquid substance under
examination, and adding concentrated sulphuric acid in such a
manner that the temperature does not rise above 70° C. (158° F.).
In the presence of biliary acids a beautiful cherry-red color is devel-
oped, which gradually changes to dark reddish-purple. The red
liquid when examined spectroscopically shows two absorption-bands,
one at F, the other near E, between D and E. Bile acids are not
the only substances which show the colors of Pettenkofer's test, but
the spectroscopic examination will clear up doubtful cases.

Experiment 84. Evaporate ox-bile to a thick syrup, digest it with 5 parts of
pure, cold alcohol for two hours, and filter. Mix the filtrate, which contains
sodium glycocholate and taurocholate, with freshly prepared animal charcoal,
boil and filter ; evaporate to dryness in a water-bath, redissolve in the smallest
possible amount of pure alcohol, and add ether until the solution becomes
markedly turbid. A white, crystalline mass is deposited in a few hours or days ;
this is known as Planner's crystallized bile, and is a mixture of the two sodium
salts mentioned.

Dissolve the mass in a small volume of water, adding a little ether and then
dilute sulphuric acid; glycocholic acid crystallizes out in shining needles.
Taurocholic acid is easiest prepared by using -dog's bile, which contains no
glycocholic acid.

Apply the Pettenkofer test to the glycocholic acid obtained.

Cholesterin and lecithin in the bile are present in considerable
amount. They are regarded here as waste products.

Siiiary calculi consist chiefly of cholesterin, and in addition they
contain bile-pigment, the bile acids combined with calcium, calcium
soaps, and calcium carbonate.

Experiment 85. (Examination of biliary calculi.} Boil the freshly powdered
stones with water to remove bile, filter, and extract the dry residue with a
mixture of alcohol and ether. Filter, and evaporate the filtrate to a small
volume, when crystals of cholesterin will be deposited. Purify the crystals by
dissolving them in boiling alcohol to which a fragment of sodium hydroxide
has been added, and treating the mixture in a separatory funnel with ether.
By evaporation of the ethereal solution cholesterin is obtained in a pure con-
dition. Apply the tests for the same (see Index).

The residue of the calculi, insoluble in ether and alcohol, consists of the
inorganic salts and bile-pigments. Dissolve the salts by pouring dilute hydro-
chloric acid over the contents in the filter, and show in filtrate the presence of
calcium by neutralizing with ammonia, acidifying with acetic acid, and adding
ammonium oxalate, when calcium oxalate is precipitated. To a portion of the
hydrochloric acid solution add potassium ferrocyanide ; sometimes a red pre-
cipitate is formed, due to the presence of traces of copper in the calculus.

DIGESTION. 687

The residue left on the filter consists of bilirubin. Purify it by washing
with water, drying, and heating the mass with chloroform. On filtering and
evaporating the solution in a watch-glass rhombic plates or prisms of bilirubin
are left, which examine microscopically, and to which apply the tests men-
tioned above.

Succus entericus. The small intestine secretes several important
enzymes : erepsin, which acts mainly upon the proteoses and peptones,
splitting them into peptides and amino-bodies; inverting enzymes act-
ing upon the disaccharides (invertase, maltase, lactase) ; and entero-
kinase, which is necessary for tryptic digestion. In addition the
small intestine forms the prosecretin, from which the stimulating
hormone secretin is derived and carried to the pancreas. The succus
intestinalis is alkaline, and aids in neutralizing the acid from the
stomach.

Fermentative and putrefactive changes. In addition to the
alterations brought about by the digestive enzymes, the food also
undergoes fermentative and putrefactive changes, due to the action
of bacteria, always present in the intestine. Some of these bacteria
convert carbohydrates into acetic, butyric, lactic, and succinic acids,
while carbon dioxide, methane, and hydrogen are also liberated.
Certain fats probably form neurine and similar toxic substances.
By putrefaction of proteins are formed : phenol, several aromatic
derivatives, notably indole and skatole, volatile fatty acids, carbon
dioxide, methyl-mercaptan, and hydrogen sulphide.

As intermediate products, the bacteria convert to some extent the
food material into the same substances which are formed by the
action of pancreatic juice ; these products, however, are not useful
to the organism, but are only intermediate stages of far-reaching
decompositions. The end-products of bacterial action pass out of
the intestine in the feces and as flatus, or are absorbed and carried
to the liver, where most of the aromatic compounds are conjugated
with potassium acid sulphate, and in this form are secreted in the
urine. Thus the quantity of aromatic sulphates in the urine is a
measure of putrefaction in the intestine.

Absorption in the small intestine. It seems advisable under
this heading to follow in outline the foodstuffs from their ingestion
to their delivery into the circulation.

The carbohydrates are first acted upon by the saliva, ptyalin split-
ting the starches into maltose, and maltase splitting the maltose into
dextrose. While this action continues for some time in the cardiac
end of the stomach, it is, in all, not very extensive. There is no

688 PHYSIOLOGICAL CHEMISTRY.

gastric enzyme acting upon carbohydrates, but a small amount of the
simple sugars may be absorbed here. In the intestine the starches
are energetically attacked by the amylopsin (diastase) of the pancreas,
and the disaccharides are converted into the monosaccharides by the
inverting enzymes of the succus entericus. In this manner almost
all of the starch and sugar of the food is normally reduced to the
hexose form, the greater part being dextrose, with some laevulose,
galactose, and pentose (from cane-sugar, milk-sugar, and various vege-
tables respectively). These simple sugars are absorbed by the small
intestine, transferred as such to the blood-stream, carried directly to
the liver by the portal vein, and here stored up as glycogen. If an
excessive amount of sugar, particularly a simple sugar, be eaten, it is
absorbed more rapidly than the organism is able to care for it, and it
will appear unchanged in the urine (alimentary glycosuria, Icevulo-
suria, etc.). The exact mechanism of this fact is not known. It is
commonly believed that the liver is unable to convert more than a
certain amount of sugar into glycogen, hence there results an exces-
sive quantity of sugar in the blood, which excess is excreted by the
kidneys. The amount of sugar which can be eaten at one time with-
out a resulting excretion is termed the assimilation limit of that sugar.
The assimilation limit differs for the different sugars and in different
individuals.

Fats undergo less digestive change than either carbohydrates or
proteins. Their digestion occurs mainly in the intestine, and consists
primarily of a saponification into glycerin and fatty acid by the lipase
of the pancreas. The biliary fatty acids combine with the alkali of
the intestinal contents to form soaps, which produce an emulsification
of the neutral fat still present. This emulsification is believed to be
of importance in offering a greater surface of fat for the action of the
lipase. The bile has two important actions in fat digestion, the bile
salts aid the action of the lipase and also act as solvents for both the
fatty acids and the soaps. It is believed now that little or no fat is
absorbed in the form of an emulsion, and that the greater part is
taken up as glycerin and fatty acid (soap). The glycerin is, of
course, readily soluble, while the fatty acid is very likely in solution
with the bile salts. Apparently the glycerin and fatty acid are at
once resynthesized in the mucous membrane of the intestine to neutral
fat and passed into the lacteals as an emulsion, which, in turn, is
carried to the general circulation by the thoracic duct.

Proteins are digested by three enzymes, pepsin (stomach), trypsin
(pancreas), and erepsin. The three carry out what is fundamentally

DIGESTION. 689

the same process. The pepsin action is exerted mainly to effect the
earlier actions, i. e., the change from protein through primary and
secondary proteose to peptone ; the erepsin is concerned mainly with
the later transformation from peptone to polypeptide and amino-
bodies (arnino-acids), while the action of trypsin is important through-
out the entire decomposition. The general course and ultimate results
of protein digestion are now fairly clear, and it is universally accepted
that proteins are absorbed in the form of the amino-bodies or, perhaps,
in part as fairly simple polypeptides, the protein nuclei of Abder-
halden. The digestion of protein is believed to have a deeper signifi-
cance than (as in the case of the carbohydrates and fats) the mere pro-
duction of soluble and dialyzable substances. As the protein material
absorbed by the intestine is converted again to protein, and as the
ingested (foreign) protein must give rise to a different (native)
protein, it is easy to see that this change must be much more readily
carried out if the foreign protein is first split into its component parts,
the amino-bodies. Abderhalden believes that not all the protein is
necessarily split entirely to amino-acids, but part may remain in the
polypeptide form and serve as a nucleus to which the other amino-
bodies may be added which are needed for the production of the
native protein. The native protein thus formed is conveyed by the
portal system to the liver.

Absorption in large intestine. As the large intestine secretes no
enzymes, the only digestive action here is due to the enzymes which
have been brought down from above. This is probably not of any
great moment, as experimental work has shown that, with the excep-
tion of water, there is little absorption by the large intestine. It is,
however, true that clinical work with rectal feeding shows that per-
sons may be sustained to a certain extent by rectal injections of pre-
digested food mixtures.

Feces consist of the unabsorbed material from the food, the waste
material excreted from the blood, detached epithelium, and the secre-
tions of the intestine. The odor depends largely on the indole and
skatole, to a less degree on valeric and butyric acids, and on hydro-
gen sulphide present. The quantity and composition of feces passed
depend on the nature of the food and the energy of the digestive
powers. A grown person in normal condition discharges from 100
to 250 grammes (4 to 9 ounces) daily. A diet rich in animal proteins
causes the quantity of feces to be small, while a diet rich in vegetable
44

.

.

. 77. 3 per cent.
23 "

es

biliary,
residue

and coloring-matters .
of food

. 5.4
. 1.8 "
. 1.5 «
. 1.8
. 5.2
4.7

690 PHYSIOLOGICAL CHEMISTRY.

and starchy foods increases the quantity. An approximate analysis
of the feces of a healthy adult shows :

Water

Mucin

Proteins

Extractives

Fats

Salts

The proteins, other than mucin, are chiefly keratins and nucleins.
The principal salts are ammonium-magnesium phosphate, calcium
carbonate, calcium and magnesium phosphate. The bile-pigment
normally is stercobilin, derived from bilirubin by reduction.

A large proportion of the feces consists of bacteria. The micro-
scopic examination of feces for intestinal parasites and bacteriological
examinations are of great value in clinical work. The significance
of the chemical findings are not yet well understood except in a few
instances (e. g., presence of blood and bile).

Experiment 86. (Chemical examination of feces.}

a. Reaction. Normally the reaction of feces is slightly alkaline to litmus.

b. Fat. Extract the feces with ether and evaporate the ethereal solution.
Mix a portion of the residue with potassium acid sulphate and ignite ; in the
presence of neutral fat the characteristic odor of acrolein is noticed. Dissolve
another portion of the residue in a mixture of alcohol and ether which has
been colored blue-violet by alkanet (a dye derived from a plant of the same
name, and used as .an indicator for certain acids) ; a red color indicates the
presence of fatty acids. (The occurrence of large amounts of fats or fatty acids
in the feces may be the result of the ingestion of an excessive quantity of fat,
or of imperfect digestion and absorption due to pathological conditions.)

c. Mucin. Mix the feces with lime-water, allow to stand for several hours,
filter, and acidify filtrate with acetic acid. A precipitate indicates mucin. To
verify the nature of the precipitate, boil it with dilute hydrochloric acid for an
hour, then neutralize, and heat with Fehling's solution. A red precipitate
proves the substance to have been mucin. (Mucin occurs in the feces in con-
siderable quantity whenever there is catarrh of the large intestine, and in cases
of membranous enteritis.)

d. Albumin. Mix the feces with water, acidify with acetic acid, and filter,
est the clear filtrate by adding potassium ferrocyanide. Albumin, when

present, coagulates. (Albumin is found in the feces of typhoid fever patients.)

e. Proteose and peptone. Make a thin paste of feces with water, boil, and
;er while hot. To the filtrate add lead acetate, filter, and apply the biuret

aon. (Proteose and peptone are found in the feces whenever much pus is
produced in the intestine.)

/ Carbohydrates. Boil the residue, left from the extraction with ether (6),

DIGESTION. 691

with water, filter, and evaporate filtrate to a small volume. Test the liquid for
sugar with Fehling's solution, and for dextrin and starch with iodine.

g. Blood. When the blood in the feces is derived from the lower portion
of the intestine the red color is so characteristic that further examination is
unnecessary. When the blood comes from the upper intestine and the pig-
ment has been altered, it becomes necessary to make a spectroscopic examina-
tion or the ha3min test, for which see page 658. For the spectroscopic exami-
nation, the feces are extracted with water containing a little acetic acid, and
the liquid is extracted with ether. If blood is present, the ethereal solution
is brownish red. Evaporate the solution to dryness and dissolve the residue in
water containing a little sodium hydroxide. The solution is haematin in alka-
line solution, and will show the characteristic bands, Fig. 72, e. Hrematin may
occur in feces physiologically as a result of a meat diet ; pathologically, it is'
found after hemorrhage into the intestine from any source.

Occult blood is the name given to traces of blood occurring in the feces after
small hemorrhages from ulcer of the stomach or duodenum. Its presence is
shown as follows : Extract 10 grammes of feces with 25 c.c. of ether to remove
fat. To the residue add 5 c.c. of glacial acetic acid and then extract again
with 20 c.c. of ether. To this ethereal extract add a little powdered guaiac
and then 1 or 2 c.c. ozonized turpentine. A blue color develops on shaking
and standing, rendered more intense by the addition of chloroform.

Klunge's aloin test may be used in place of the guaiac reaction. Mix the
acetic acid and ether extract of feces, obtained as above, with 1 or 2 c.c. of tur-
pentine, and add immediately about 1 c.c. of a 2 per cent, solution of aloin in
70 per cent, alcohol. In the presence of blood the fluid rapidly becomes bright
red in color.

h. Bile-pigments. Shake the feces with a saturated solution of mercuric
chloride, filter, and add chloroform. A rose color develops at the junction of
the fluids in the presence of urobilin, which is the normal bile-pigment of
feces. (The absence of bile-pigment in the feces indicates disease of the liver
or obstruction to the flow of bile.)

Extract feces with chloroform, and to the chloroform solution apply Gmelin's
test for bile-pigments. (The presence of bilirubin or biliverdin in the stools
of adults indicates catarrh of the intestine.)

i. Bile acids. Extract feces with alcohol and evaporate the filtrate to dryness.
Dissolve the residue in water containing a little sodium hydroxide, and to the
solution apply Pettenkofer's test. (Normally, bile acids are completely absorbed,
therefore their presence in feces is pathological.)

j. Ferments. Extract the feces with glycerin, precipitate the solution with
alcohol, and dissolve the precipitate in water. To part of the solution add a
little starch paste, keep the mixture at 40° C. (104° F.) for several hours, and
test for glucose. A positive test indicates the presence of diastatic enzyme.
Digest another portion of the solution at the stated temperature with coagu-
lated protein and a little sodium carbonate. Filter and apply the biuret
reaction, which, if positive, indicates the presence of proteolytic ferment.
(The various digestive enzymes are found in the feces when there is diarrhoea
resulting from inflammation of the upper intestine.)

Jc. Inorganic constituents are determined in the usual manner after drying and
incinerating the feces. Present are chiefly earthy phosphates, silica, sodium
chloride and sulphate, iron compounds, etc.

692 PHYSIOLOGICAL CHEMISTRY.

Fecal calculi. Feces sometimes contain hard masses, known as
coproliths and enteroliths. Coproliths are inspissated feces. Entero-
liths usually consist of concentric layers of earthy phosphates and
insoluble soaps around a nucleus of a piece of bone, a fruit-stone,
etc. Pancreatic stones consist of calcium phosphate and carbonate
without cholesterin or bile-pigment. Intestinal sand is the name
given to certain small calculi occurring in the feces. They are com-
posed of magnesium and calcium soaps, cholesterin, bile-pigment,
salts of magnesium, and some of the hydroxy acids, such as succinic
acid. The clinical significance of these concretions is not definitely
known.

The liver. The anatomical relations of the liver indicate the im-
portance of this organ in assimilation, digestion, and excretion. The
digestive function of the liver, which is comparatively slight, and the
excretory function are carried out largely by means of the bile. The
digestive properties of bile have been considered.

While it is probable that the liver has some action on the protein
material brought to it by the portal system directly after its digestion
and absorption in the intestine, this has not been proved. It is, how-
ever, known that the main nitrogenous excretion of the body, the
urea of the urine, is formed here, and is merely excreted by the
kidneys. The mechanism of this urea production is not clear. It is
likely that the waste nitrogen is brought to the liver in the form of
ammonium salts (carbonate or carbamate), and by it is transformed
into urea. Liver tissue has the power of producing such a change
under experimental conditions, but it has not been proved that the
process occurs normally in this manner. In birds the main nitrog-
enous excretion, uric acid, has also been shown to be formed in the
liver.

Glycogen is one of the most important constituents of the liver, and
undoubtedly represents a storage supply of carbohydrate material. It
is derived for the most part directly from the carbohydrates of the
food which have been split in the intestine, absorbed as dextrose and
laevulose, and carried directly to the liver by the portal vein. Here
these simple sugars are converted into the more complex glycogen by
a process of dehydration. It is probable that some of the simple as
well as the conjugate proteins can also form sugar and, hence, gly-
cogen. Some of the sugar excreted in diabetes is certainly derived
from the proteins. It is not clear, however, that such a change takes
place under normal conditions. The question with regard to the fats
is in somewhat the same condition. It has been shown that glycogen

DIGESTION. 693

can be derived from glycerin ; hence it can be derived from the fats
which contain glycerin, but whether it is normally derived from the
fats is not known. When the tissues are in need of sugar to supply
them with a source of energy, the glycogen of the liver is split and
is distributed by the blood-stream in the form of dextrose. This is
seen especially clearly in the case of the muscles, which require a
large amount of sugar, and have also the power of storing up a local
supply very much as the liver stores up a general supply for £he
whole body. It is found that in starvation, and particularly in
starvation with extensive muscular work, that the store of glycogen
in both the liver and the muscles is rapidly exhausted.

Indole and skatole, formed by putrefaction in the intestine, are

brought to the liver by the portal vein. Indole, C6H /NH ">CH,

is oxidized, forming indoxyl, C8H7NO, which combines with potas-
sium acid sulphate, with elimination of water, forming indoxyl
potassium sulphate, C8H6NKSO4, which is excreted in the urine.
Skatole, methyl-indole, C6H4(CCH3CH)NH, is similarly converted
into the oxidation product skatoxyl, C9H9NO, and skatoxyl potassium
sulphate, C9H8NKSO4. These substances appear in the urine as the
conjugate or ethereal sulphates.

The formation of glycogen from sugar has been mentioned, and its physical
properties were considered in Chapter 48.

Experiment 87. (Preparation of glycogen.} Digest 50 grammes of fresh liver
with 500 c.c. of boiling water containing about 5 c.c. of acetic acid. Strain
the liquid through muslin. The solution contains besides glycogen some pro-
tein, which remove by concentrating the liquid to a small volume and adding
alternately a few drops of hydrochloric acid and of potassium mercuric iodide
as long as a precipitate is formed. Filter and mix filtrate with 2 volumes of
alcohol, when glycogen is precipitated ; purify it by pouring off the super-
natant liquid and washing it with 65 per cent, alcohol by decantation. Then
cover with absolute alcohol, let stand for an hour, collect the glycogen on a
filter, and dry between filter-paper.

Tests for glycogen.

1. Dissolve some glycogen in warm water : an opalescent solution
resembling soluble starch solution is formed.

2. To a portion of solution add iodine solution : a reddish-brown
color resembling the one produced by erythrodextrin is produced.

3. Heat some of the solution with Fehling's solution : no change
occurs.

4. Acidify solution with hydrochloric acid, boil a few minutes,

694 PHYSIOLOGICAL CHEMISTRY.

cool, and neutralize. Divide solution, and heat one portion with
Fehling's solution, when the formation of a red precipitate indicates
the conversion of glycogen into dextrose. To the second portion add
iodine : no change.

5. To some glycogen solution add about half its volume of saliva,
keep the mixture at 40° C. (104° F.) for about ten minutes, and test
part of solution with iodine, the other portion with Fehling's solu-
tion. The results show that glycogen has been changed as in
previous test.

The liver has also a neutralizing function, by virtue of which it
retains and renders innocuous various toxins and putrefactive pro-
ducts which are absorbed by the intestine.

57. MILK.

General properties. Milk is the secretion of the mammary
glands, the presence of which is characteristic of mammalia. The
milk of different animals differs somewhat in composition, but it
always contains all the constituents necessary for a normal develop-
ment of the various tissues, liquids, organs, etc., of the young
mammal, which generally feeds exclusively upon milk for a shorter
or longer period of its early life.

Milk is an opaque, aqueous solution of casein, albumin, lactose, and
inorganic salts, holding in suspension small globules of fat, invested,
most likely, with coatings of casein or with some other albuminous
envelope. The reaction of woman's milk and that of the herbivora
is normally alkaline, but that of carnivora is acid. Its specific
gravity ranges from 1.029 to 1.033, but may in extreme cases vary
between 1.018 and 1.045.

Experiment 88. a. Examine milk microscopically ; notice the variously sized
globules of fat, and compare the appearance of milk, cream, and skimmed milk.

b. Test with sensitive litmus-paper the reaction of fresh cows' milk and of
milk that has been exposed to the air for a day or two. The former will be
alkaline or amphoteric, due to the presence of mono- and di-calcium phos-

QUESTIONS.— What is the active principle of saliva, and how does it act on
starch? Explain the process of the absorption of protein. State the compo-
sition of gastric juice, explain its physiological action, and describe methods
for determining its chief constituents. What substances are formed during the
conversion of a simple protein into peptone? What are the functions of ^pan-
creatic juice? State the composition of the different kinds of calculi found in
feces. How are fats digested and absorbed ? State the general properties of
bile and mention its chief constituents ; describe Gmelin's and Pettenkofer's
tests. What are the principal constituents of feces ? State properties and re-
actions of glycogen.

MILK.

695

phate ; the latter will be acid, because lactic acid has been formed by the
fermentation of milk-sugar.

c. Boil some fresh milk; no coagulum, but a scum is formed. After re-,
moval of the scum it is reformed on boiling. Repeat the experiment with
milk that has stood some time ; a coagulum is formed.

Composition. The average composition of various kinds of milk
is given below, but it must be remembered that milk not only differs
in certain species, but also in the same animal at different times ;
for instance, the quality and quantity of food taken, as also various
physiological changes, have decided influence upon the milk secreted.

Human milk.

Cows' milk.

Variations. Average.

Variations. Average.

Water .

90.8 to

85.3

88.30

90.2 to 83.7

86.70

Casein and albumin

1.4 to

2.5

2.00

3.3 to

5.5

4.40

Fat (butter) .

3.0 to

3.8

3.40

2.8 to

4.5

3.65

Lactose

4.0 to

8.0

6.00

3.0 to

6.0

4.50

Inorganic salts

0.2 to

0.4

0.30

0.7 to

0.8

0.75

Goat.

Sheep.

Ass.

Mare.

Cream.

Water .

86.0

83.3

90.6

90.6

56

to 71

Casein and albumin

3.8

5.4

2.7

2.2

4

to 3

Fat (butter) .

5.2

5.3

1.0

1.1

35

to 22

Lactose

4.3

5.2

5.3

5.8

4

to 3

Inorganic salts

0.7

0.8

0.4

0.3

0.7

to 0.7

Skimmed
milk.

Condensed „ .
milk.

Buttermilk. Curd.

• Whey.

Water .

90.6

25

15.0

90.2

59.4

93.5

Casein and albumin

3.1

14

2.2

4.1

27.7

0.8

Fat (butter) .

0.8

10

82.0

1.0

6.4

0.3

Lactose

4.8

491

0.3

3.7

5.0

4.5

Inorganic salts . .

0.7

2

0.5

0.7

1.5

0.6

Lactic acid .

. .

. .

0.3

. .

0.3

The inorganic salts consist chiefly of calcium or sodium phosphate
and sodium and potassium chloride, but contain also some magnesium
and iron. The proteins consist mainly of casein with some albumin,
the proportion being in cows' milk about as 6 to 1, in woman's milk
as 3 tc 4.

Besides the constituents mentioned in the above analyses, milk also
contains a very small quantity of extractives, among which are found
urea, creatine, lecithin, citric acid, phospho-carnic acid, etc. The
principles which give to milk its peculiar odor have not yet been
conclusively pointed out. The gaseous constituents of milk are
mainly carbon dioxide, oxygen, and nitrogen : 100 volumes of milk

i Including cane-sugar added by the manufacturer.

696 PHYSIOLOGICAL CHEMISTRY.

contain of carbon dioxide 7.06, of oxygen 0.1, of nitrogen 0.7
volumes.

Milk contains several enzymes, whose natures vary with their
sources. One of these, an oxidizing ferment (oxidase, catalase), is a
constant constituent, and is of importance because its absence shows
that the milk has been heated for preservation.

The presence of an oxidizing ferment in milk can thus be shown : Shake 10
c.c. of milk with 1 c.c. of tincture of guaiac, 5 c.c. oil of turpentine, and 5 c.c.
of solution of hydrogen dioxide. A blue color is developed when the ferment
is present.

Milk-proteins. The proteins of milk are caseinogen, lactoglobulin ^
and ladalbumin. Lactoglobulin and lactalbumin closely resemble the
globulin and albumin of the blood-serum, and are believed to be de-
rived from them with little constitutional change. Caseinogen is, on
the other hand, a specialized protein containing phosphorus and be-
longing to the group of phospho-proteins. It is present in milk
either in solution or perhaps in combination with phosphates in a
partially insoluble form, and this combination may be responsible for
some of the opacity of the milk. When milk is acted upon by rennin
there is a coagulation of the caseinogen and the formation of a clot.
It may readily be shown that this process takes place in two steps.
First, the caseinogen is changed by the rennin to a form called para-
casein. This substance remains in solution, and the nature of the
change is not understood. In the second stage the paracasein forms
a combination with the calcium salts of the milk and is precipitated
as casein (calcium-casein). The calcium enters only in the second
step and has no part in the formation of paracasein. The significance
of this coagulation of milk in the stomach is not known. It is fre-
quently stated that a peptone is split off from the caseinogen in the
production of paracasein. The process may be hydrolytic in nature,
and a preliminary step in the digestion of caseinogen. As implied
above, no coagulation will take place if the calcium salts be removed
from the milk.

Caseinogen occurs only in milk ; it is a phospho-protein, yielding
on hydrolysis a pseudonuclein. When dry it is a fine, white powder,
insoluble in water, but soluble in dilute salt solution and in water
containing a little alkali.

Caseinogen resembles the alkali albuminates in dissolving in water in the
presence of calcium carbonate with evolution of carbon dioxide. The solution
is precipitated by hydrochloric and acetic acids, the precipitate being soluble
in slight excess, and reprecipitated by a large excess of the acid. The solution

MILK. 697

in lime-water is not precipitated by phosphoric acid, but an opaque fluid is
obtained containing casein and calcium phosphate in suspension. The solu-
tion is precipitated by alum, zinc sulphate, cupric sulphate, etc. Caseinogen
solutions are not coagulated by heat, but, like milk, are covered with a scum.

Experiment 89. (Preparation of casein.} To a mixture of 400 c.c. of milk
and 1 liter of water add gradually enough (but not more) of acetic acid to pre-
cipitate the casein, which also carries down the fat. Decant the liquid, then
filter, first through muslin, then through paper, reserving liquid for Experi-
ment 93. Wash the coagulum well with water, press it as dry as possible,
then grind it with 100 c.c. of alcohol, and allow to stand for an hour. Filter,
dry the coagulum between filter-paper, place it with 200 c.c. of ether into a
stoppered bottle and let stand for a day. Collect the precipitate on a filter and
add filtrate to the alcoholic filtrate from above; the mixture will be used for
Experiment 92. Rub the casein in a mortar until the ether is evaporated.
To purify it from fat, mix with water and add drop by drop a 1 per cent,
solution of sodium hydroxide until the greater part of the casein is dis-
solved. The mixture, which should not be alkaline after thoroughly stirring
it, is then filtered, when some fat and suspended matter is left behind, while a
fairly clear filtrate is obtained. Acidify faintly with acetic acid, wash the
precipitated casein with water, alcohol, and ether, and dry between paper.

Tests for casein.

1. Apply the xanthoproteic, Millon's, and biuret reactions.

2. Dissolve casein in a 1 per cent, solution of sodium carbonate;
neutralize with acetic acid, when casein is precipitated.

3. Mix some casein in a mortar with freshly precipitated cal-
cium carbonate and water. Casein dissolves, while carbon dioxide
is liberated.

4. Dissolve casein in lime-water and add dilute phosphoric acid
until the solution is neutral. No precipitate is formed, but the
liquid becomes turbid.

5. Heat a mixture of casein with sodium carbonate and potassium
nitrate in a crucible (or dry test-tube) until all organic matter has
been destroyed. Dissolve mass in water, acidify with nitric acid,
filter, and add ammonium molybdate. A yellow precipitate is formed,
showing the presence of phosphorus in the casein.

Experiment 90. (Separation of the proteins.} Saturate 20 c.c. of fresh milk with
powdered sodium chloride: a precipitate consisting of caseinogen and fat is
formed. Filter, wash the precipitate with saturated solution of sodium
chloride, rub the moist precipitate with 20 c.c. of water, allow to stand for
twenty-four hours, and filter. The solution contains caseinogen in the
same condition in which it is found in milk. To a portion of the solution
add acetic acid : casein is precipitated. To another portion add a solution of
rennin and some calcium chloride, heat to 40° C. (104° F.) for a short time,
when a precipitate of paracasein is formed.

Saturate the filtrate from caseinogen and fat with magnesium sulphate :

698 PHYSIOLOGICAL CHEMISTRY.

lactoglobulin is precipitated. The filtrate contains lactalbumin, which can be
precipitated by saturating the solution with ammonium sulphate.

Experiment 91. (Action of rennin on milk.} To 20 c.c. of milk add 4 c.c. of
a 0.1 per cent, solution of rennin, mix well, and digest at 40° C. (104° F.).
A coagulum consisting of casein and fat soon forms, while an aqueous fluid
(whey), containing proteins, milk-sugar, salts, and extractives, is pressed out.
After adding a drop or two of acetic acid heat a portion of the whey to boiling :
a voluminous coagulum of simple proteins is formed.

Eepeat the above experiment with milk from which, by the addition of 2
c.c. of a 1 per cent, solution of ammonium oxalate, the calcium salts have
been removed. No coagulum occurs until calcium chloride is added in a
quantity sufficient to precipitate any ammonium oxalate left in solution, and
to furnish the calcium salt required for precipitation.

Kepeat again, boiling the mixture in order to destroy the rennin before the
addition of the calcium solution ; clotting will occur, showing that calcium is
necessary only for the precipitation, not for the interaction between the casein-
ogen and the rennin.

Milk-fat. It has been mentioned above that the fat of milk is
held in suspension as small globules, which are surrounded by a
protein envelope. The latter prevents the solution of fat when
ether is added directly to milk. If, however, a few drops of caustic
alkali be added with the ether, then the envelope will be destroyed
and the fat dissolves. Whenever a precipitate occurs in milk the fat
is carried down with the insoluble substance and the envelope is
generally destroyed. The fat of milk is a mixture of the glycerides
of several fatty acids, chiefly of palmitic and oleic, with small quan-
tities of butyric, caproic, caprylic, and stearic acids. Butter fat may
be recognized by liberating the butyric acid, which has a character-
istic odor.

Experiment 92. (Liberation of butyric acid.) Use the mixed ethereal and
alcoholic filtrate from Experiment 89. Allow the ether to evaporate spon-
taneously, and add to the alcoholic solution of butter fat about 5 grammes
of potassium hydroxide. Heat the mixture on a water-bath until a drop of
it is found to be completely soluble in water, indicating complete saponifica-
tion. Evaporate until odor of alcohol has disappeared; add 30 c.c. of dilute
sulphuric acid, when the fatty acids are set free and butyric acid can be recog-
nized by its odor.

Butter. Even in the thickest varieties of cream there is no cohe-
sion between the fat globules, while in butter the fat has actually
cohered. This change is accomplished by violently agitating (churn-
ing) the cream, when the fat particles gradually combine with each
other, while the liquid (buttermilk) separates.

Chemically, butter is a milk-fat, containing a certain proportion^

MILK. 699

15 or 16 per cent., of water, besides traces of casein, salts, coloring-
matter, etc. For curing butter, common salt is often used ; the
quantity added should not exceed 5 per cent.

The composition of buttermilk has been given above ; when
freshly obtained from sweet cream it is a pleasant drink and a whole-
some food.

Milk-sugar. Lactose. The general properties of milk-sugar
have been mentioned on page 534. By hydrolysis it yields two
simple sugars, dextrose and galactose ; when boiled with nitric acid,
saccharic and mucic acids are formed, the latter being a characteristic
product of the oxidation of galactose. Solutions of milk-sugar are
dextrorotatory. Lactose occurs occasionally in the urine of preg-
nant women, and also in the urine after ingestion of large quantities
of milk-sugar.

Experiment 93. (Preparation of milk-sugar.) Use the aqueous filtrate obtained
in Experiment 89. Free the solution from the remaining proteins by boiling
and filtering; evaporate to about 75 c.c., when calcium phosphate will be
deposited. Filter, evaporate to a syrup, and set aside, when crystals of lactose
will be formed. The crystals may be purified by treating their solution with
bone-black aud recrystallizing.

Tests for milk-sugar.

1. To solution of milk-sugar apply Fehling's, Trornmer's, Moore's,
Boetger's, and Nylander's tests, for which see Index.

2. Add ammonio-silver nitrate and a drop of sodium hydroxide.
A mirror of metallic silver forms on heating the mixture.

3. Indigo-test. To a dilute solution add enough indigo-carmine to
produce a blue color, and render alkaline with sodium carbonate.
On heating, the blue solution becomes successively red, yellow, and
colorless, or nearly so, in consequence of the deoxidizing power of
the lactose. Pour the cooled solution repeatedly from one test-tube
into another; the colors are reproduced in reverse order in con-
sequence of the absorption of oxygen.

4. As grape-sugar responds to the above tests, the fermentation-
test may be used for distinguishing between the two sugars. Fill
two fermentation tubes with glucose and lactose solution, respectively ;
add yeast, let stand in a warm place, and notice that a gas rises from
the glucose, but not from the lactose solution.

700 PHYSIOLOGICAL CHEMISTRY.

Physical and chemical changes in milk on standing.

After leaving the body milk undergoes physical and chemical
changes. The principal physical change is the separation of milk
into two layers : the upper, cream, contains practically all the fat,
and its proportionate quantity of other constituents; the lower,
skimmed milk, is almost fat-free. By removing varying quantities
of skimmed milk by siphon or otherwise, the proportion of fat in the
remainder of the milk is increased.

Of chemical change, occurs, particularly on standing in a warm
place, conversion of lactose into lactic acid through lactic acid fer-
mentation. The reaction of milk then becomes acid, the casein coag-
ulates and separates as a solid white curd carrying with it fat. The
remaining thin, transparent liquid, whey, contains all the inorganic
salts, that portion of lactose which has not been decomposed, as also
the lactic acid formed.

There has recently been an extensive use of milk which has been
fermented by the Bacillus Bulgaricus, a powerful lactic acid pro-
ducer. This use has been based upon the belief of Metchnikoff that
acid-producing bacteria are antagonistic to the putrefactive bacteria
which are normally present in the intestine, hence the milk is advised
in cases of intestinal disorder.

Milk also undergoes another peculiar fermentation, by which it is
converted into a thick, ropy, gelatinous mixture.

The decomposition of the milk-sugar and with it the "curdling"
may be prevented — 1, by chemical treatment with alkaline salts or
antiseptics ; 2, by physical treatment, such as cooling or icing, boil-
ing and aeration ; 3, by condensation or evaporation, with or without
the addition of a preservative agent. All these systems of preserva-
tion, however, are subject to serious disadvantages because they either
interfere with the natural constitution and properties of the milk, or
because they serve their purpose for too limited a time.

The addition of alkalies such as lime-water, sodium carbonate or
bicarbonate, does not prevent the lactic fermentation, but prevents
the action of the liberated acid on the casein by forming a lactate of
calcium or sodium.

Milk preservatives. The chemical changes in milk are best pre-
vented by cleanliness and preservation at a low temperature. Various
antiseptics, such as salicylic acid, boric acid, formaldehyde, benzoic
acid, etc., are added to milk with the view of preventing decomposi-
tion. While the small quantities used appear to be harmless, yet

MILK. 701

there can be no doubt that the continued use of milk containing these
preservatives is detrimental to health, especially in the case of human
nurslings. For this reason many countries, States, and cities prohibit
legally the use of preservatives.

Tests for preservatives in milk.

Formaldehyde. Float a mixture of 10 c.c. of milk and 10 c.c. of water in a
test-tube, on concentrated sulphuric acid made pale yellow by addition of
ferric sulphate. A blue to violet color at the line of junction shows the pres-
ence of formaldehyde. Pure milk gives a greenish color.

Salicylic acid. Acidify 25 c.c. of milk with acetic acid, boil, and filter. Ex-
tract the nitrate with an equal volume of ether. Shake the ether extract with
a dilute (straw-colored) solution of ferric chloride, On separating, the aqueous
solution shows a reddish-violet color when salicylic acid is present.

Benzole acid. Proceed as in the foregoing test, but shake the filtrate with
an equal volume of solution of hydrogen dioxide before extracting with ether.
By this treatment benzoic acid is converted into salicylic acid, which is then
tested for by ferric chloride.

Boric acid and borax. A few drops of the filtrate obtained as in the prece-
ding test are mixed with a drop of strong hydrochloric acid and a drop of satu-
rated alcoholic solution of turmeric. The mixture is evaporated to dryness on
a water-bath, and a drop of ammonia added to the residue when cold. A dull-
green stain shows the presence of boric acid or borax.

In addition to the test for chemical preservatives, commercial milk
is now examined by bacteriological methods, the number and, if pos^
sible, the character of the organisms being determined. By extreme
care in the production of milk it is possible to keep the count lower
than 30,000 per cubic centimeter ("certified milk"). A cheaper
method of producing good milk is by heating the milk for a certain
time to a temperature below the boiling-point, which will kill all the
pathogenic and many of the non-pathogenic bacteria. This method
is commonly called " pasteurization." It has the disadvantage that
the digestibility of the milk is lessened, an important point in infant
feeding.

Experiment 94. (Analysis of milk?) As the proportion of fat varies at dif-
ferent periods of the milking, it is necessary to secure a sample from the well-
mixed yield of milk. a. Determine the specific gravity of milk, cream, and
skimmed milk by means of the lactometer (a urinometer answers the purpose).

b. Fat. Determine the total butter fat by using Babcock's method, which is as
follows : Place 10 c.c. of milk into a small, specially constructed bottle provided
with a long, slender, graduated neck ; add 2 c.c. of a mixture of ainyl alcohol
37, methyl alcohol 13, and hydrochloric acid 50 parts; then fill the bottle grad-
ually with sulphuric acid. Place the bottle in a centrifugal machine and
rapidly revolve for three minutes, when the fat is forced to the top of the
mixture. Add enough warm water to float the separated fat into the neck,
when the exact percentage can be read on the scale. A special form of bottle,

702 PHYSIOLOGICAL CHEMISTRY.

arranged for small quantities, is manufactured for the examination of human
milk.

c. Total protein. Separate the skimmed milk from the cream of the sample
under observation. Dilute the skimmed milk with 4 parts of water and with
this solution fill Esbach's albuminometer (see Index) to the mark U, add
Esbach's reagent to R, and allow to stand 24 hours. Multiply the reading by
5; the result gives the number of grammes per liter. Skimmed milk is used
in order to avoid the fat which would be carried down with the protein if
whole milk were used.

d. Albumin and globulin. Dilute 25 c.c. of milk with 15 c.c. of water in a 50
c.c. flask, heat on a water-bath to 38° to 40° C. (100° to 104° F.), and add very
gradually a saturated solution of potassium alum until a rapidly subsiding
coagulum of casein forms. Add water to make 50 c.c., filter, and estimate the
simple proteins (albumin and globulin) in the filtrate by means of the albu-
minometer, as above, multiplying the reading on the instrument by 2. Another
method for the estimation of total protein or of the simple protein depends on
the accurate determination of nitrogen in milk or in milk after the removal of
casein. The percentage of nitrogen multiplied by 6.25 gives the percentage of
protein.)

e. Determination of milk-sugar. Lactose can be estimated by titration with
Fehling's solution ; for details of the operation see chapter on Urine-analysis.
A second method depends on the rotatory power of lactose : milk is freed from
protein and then examined by the polarimeter.

/. Determine total solids, as well as all other constituents, by following the
directions given above.

Human milk. The quantitative differences between human milk
and cows' milk have been shown in the table on page 695 ; they con-
sist chiefly in this, that human milk contains only about one-half the
quantity of protein and of inorganic salts, but one-third more of
lactose, as compared with cows' milk. In addition, it may be said
that human milk is richer in lecithin ; moreover, the proteins of
human milk differ from those of cows' milk. When human milk
is treated with acids or rennin, casein or paracasein is formed less
readily than by treating cows' milk in the same way. The precipi-
tates show marked physical differences from one another. Casein
from human milk is easily and completely soluble in gastric juice,
and human paracasein is precipitated in a loose and flocculent form,
which is much more readily digested than the tough and more
compact masses from cows' milk. The casein of human milk shows
a lower percentage of carbon, nitrogen, and phosphorus, but a higher
percentage of hydrogen, sulphur, and oxygen, than casein of cows'
milk. Finally, opalisin, a protein rich in sulphur, is found in human
milk exclusively.

Modified milk, used for infant feeding, is cows' milk, the composition of
which has been changed so as to resemble that of human milk. The quantity

URINE AND ITS CONSTITUENTS. 703

of fat is increased by adding cream, or by removing part of the lower layer
from milk which has separated into two layers (top milk). This mixture is
diluted with water to lower the percentage of protein ; milk-sugar and lime-
water are then added in different proportions, according to the quantity desired.
Although the difference in the composition of human and cows' milk is con-
siderable, the fuel value of both is nearly the same, about 315 calories to the
pound of milk.

58. URINE AND ITS CONSTITUENTS.

Excretion of urine. It has been explained in a former chapter
how blood absorbs the digested food as chyle, how this is acted upon
by the atmospheric oxygen in the lungs, and how this arterial blood,
while passing through the system, deposits proteins and other sub-
stances, receiving in exchange the products formed by the oxidation
of the various tissues. These products are either gases (chiefly car-
bon dioxide), liquids (chiefly water), or solids held in solution by the
water. These waste materials must necessarily be eliminated from
the system, and this result is accomplished principally by the kidneys.

The urine is the most important animal excretion ; in it are elimi-
nated the nitrogenous waste materials as well as most of the water
and soluble mineral substances. A study of the composition of the
urine will give important information regarding metabolism, the
nature of the chemical processes taking place within the body, as
also of the condition of the urinary organs.

General properties. Normal human urine, when in a fresh state,
is a clear, transparent aqueous liquid, of a lighter or deeper amber
color, having a peculiar, faintly aromatic odor, a bitter, saline taste,
a distinct acid reaction on blue litmus-paper, and a specific gravity
heavier than water (averaging about 1.020).

In urine, shortly after cooling, especially if it be concentrated, a
light, cloudy film of mucus is formed, which slowly sinks to the
bottom ; the acid reaction gradually increases, small yellowish-red

QUESTIONS. — Mention the five principal constituents of milk. To what
group of compounds does casein belong, how is it obtained, and what are its
reactions? Give tests for milk-sugar, and state how it may be distinguished
from grape-sugar. What physical and chemical changes does milk suffer on
standing? Describe the processes used for preserving milk; what are their
advantages and disadvantages? Give approximately the quantities of the
chief components of cream, skimmed milk, butter, buttermilk, curd, whey, and
cheese ; also state how the materials are obtained from milk. Describe the
advantages of the combined use of the lactometer and creamometer in testing
milk. What are the differences between human and cows' milk ? What is
paracasein? Give a process for the complete quantitative analysis of milk.

704 PHYSIOLOGICAL CHEMISTRY.

crystals of acid urates, or uric acid, are deposited. In this condition
the urine may often continue unchanged for several weeks, provided
the temperature be low. If, however, the temperature be above the
mean, decomposition speedily takes place. The urine is then found
to be covered with a thin, shining, and frequently iridescent mem-
brane, fragments of which sink gradually to the bottom. The urine
then becomes turbid, acquires a pale color, its reaction becomes alka-
line, and it begins to develop a nauseous ammoniacal odor, due to the
products formed by the decomposing action of certain microorganisms
(chiefly bacterium ureaB and micrococcus urea?) upon urea, which is
converted into ammonium carbonate and ammonium carbamate. The
change from an acid to an alkaline urine causes the precipitation of
earthy phosphates, ammonium-magnesium phosphate, ammonium
urate, etc.

Points to be considered in the analysis of urine. They are :

1. Color, odor, general appearance — whether clear, smoky, cloudy,
turbid, etc.

2. Reaction — whether acid, neutral, or alkaline to test-paper.

3. Specific gravity, and amount for twenty-four hours.

4. Examination of sediments, microscopically and chemically.

5. Chemical examination for the various normal and abnormal
constituents.

Samples of urine should always be drawn from the well-mixed and
exactly measured quantity of the total urine discharged in twenty-
four hours.

If the specimen cannot be examined promptly it should be pre-
served in a stoppered bottle by the addition of a very small amount
of chloroform (3 to 5 c.c. to one liter of urine).

Color. Normal urine is generally pale yellow or reddish yellow,
but it may be as colorless as water, or as dark brownish-black as
porter ; a reddish and smoky tint generally indicates the presence of
blood, and a brownish-green suggests the presence of the coloring-
matter of bile.

The nature of the normal coloring-matters of urine is as yet
doubtful ; the existence of three separate pigments has been demon-
strated ; they have been named urobilin, urochrome, and uroerythrin,
and, most likely, are products of the decomposition of biliary mat-
ters. Numerous other substances, such as indican, occur occasionally
in the urine, and produce various colors, especially when the urine is
exposed to air and light, or when acted on by reagents.

URINE AND ITS CONSTITUENTS. 705

Urochrome is the yellowish pigment of urine ; the quantity excreted,
as far as known, has no clinical significance. It is probably a deriva-
tive of bilirubin.

Uroerythrin is a red pigment, and causes the pink color often seen
in urinary sediments. It occurs in very minute quantity in normal
urine, and is increased by muscular activity, profuse sweating, ex-
cessive eating, alcohol excess, digestive disturbance, circulatory dis-
turbance of the liver, malaria, pneumonia, and many other patho-
logical conditions. Whenever present in sufficient quantity to give
a rose color to the sediment or to the precipitate produced by adding
barium chloride to the urine, uroerythrin is excreted in increased
quantity.

Urobilin y a reddish-brown pigment, occurs normally in very small
quantity, but it increases considerably whenever there is great de-
struction of haemoglobin in the body (internal hemorrhage, pernicious
anemia, poisoning by antipyrine), in cirrhosis of the liver, and dur-
ing high fever. When present in excessive quantity urobilin colors
the urine a dark brownish-red, and the foam shows a yellow or yel-
lowish-brown color.

It is thought to be usually present in the condition of a chromogen,
called urobilinogen, producing the pigment urobilin after being acted
upon by light or by an acid.

The presence of urobilin can be demonstrated by the spectroscopic exam-
ination of urine to which a small amount of hydrochloric acid has been added.
It may be necessary to let this mixture stand a short time, or to dilute it, or to
examine the amyl alcohol extract. The characteristic spectrum shows a
single band between B. and F. Urine containing urobilin will give a green
fluorescence on the addition of 1 per cent, zinc chloride, if it has been previ-
ously made alkaline with ammonia and filtered.

Abnormal coloring-matters are chiefly those of blood, bile, and of
certain vegetables and drugs.

Blood-pigment is usually present alone as methaemoglobin in hgemo-
globinuria, and associated with the red blood-corpuscles in haematuria.
Bile-pigment will be discussed later.

The ingestion of rhubarb, senna, or santonin produces a bright
yellow color in the urine which becomes red on the addition of an
alkali. Methylene-blue is excreted by the kidneys and colors the
urine blue. Urines which become very dark on standing occur after
the ingestion of phenol, in cases of melanotic sarcoma (melanogen),
and in alkaptonuria, an unexplained pathological condition in which

45

706 PHYSIOLOGICAL CHEMISTRY.

homogentisic acid and uroleucic acid (alkapton) are excreted by the
kidneys.

Odor. The normal odor of fresh urine is characteristic, and is
sometimes spoken of as aromatic; it is not known by what substance
or substances this odor is caused. The arnmoniacal and putrescent
odor which urine acquires on standing is due to the products of de-'
composition formed, chiefly ammonia.

A number of substances taken internally and separated by the kidneys from
the blood, cause the urine to assume a characteristic odor ; aromatic substances
especially impart such odors; oil of turpentine gives an odor reminding of
violets, and the odor of cubebs, copaiba, asparagus, garlic, valerian, and other
substances is promptly transferred to the urine of persons using these drugs
internally. A sweetish smell sometimes attends the presence of large quantities
of sugar in urine.

Volume. The amount of urine in twenty-four hours varies greatly
under physiological conditions. It is usually between 900 and 1500 c.c.
It is influenced very largely by the amount of water ingested, by
sweating, by diarrhoea, etc. It is decreased in acute nephritis, in-
creased in chronic nephritis, diabetes mellitus, and diabetes insipidus.

Reaction. This is generally acid in healthy urine which has been
recently passed, but may become neutral or alkaline within a short
period, by decomposition of urea and formation of ammonium car-
bonate and carbamate. The acid reaction of urine is due to mono-
sodium ortho-phosphate, NaH2PO4, and to free organic acids. These
organic acids have not as yet been identified.

While urine shows an acid reaction generally, it may have a neutral
or even alkaline reaction. In many cases this alkaline reaction points
to decomposition of urea in the bladder, but it may be due also to the
elimination of alkali carbonates, derived from food taken or drugs
administered.

Thus, the alkali tartrates, citrates, acetates, etc., have (after diges-
tion) a tendency to neutralize the urine, and an excess of them is
eliminated as carbonate.

To distinguish between the harmless alkaline reaction caused by
fixed alkalies and the alkaline reaction produced by decomposition of
urea, a piece of red litmus-paper may be used. If this, after having
been moistened with the urine, remains blue on drying (by warming
gently) the reaction is due to the fixed alkalies ; if the red color
reappears, the alkaline is due to ammonia compounds.

This distinction possesses no importance in urine which has become
alkaline on standing.

URINE AND ITS CONSTITUENTS.

707

FIG. 73.

Urine sometimes is amphoteric in its reaction, i. e., it colors red litmus-paper
faintly blue, and blue litmus-paper slightly red. This condition is caused most
likely by the simultaneous presence of monosodium orthophosphate, NaH2PO4,
which has an acid, and of disodium orthophosphate, NaH2PO4, which has an
alkaline, reaction.

The acidity of the urine is best determined in the following manner
(Folin) : 25 c.c. of urine are shaken in a flask with 15 to 20 grammes
of powdered potassium oxalate, 1 to 2
drops of phenolphthalein (J per cent,
solution in alcohol) are added, and the
mixture titrated at once with •£$ sodium
hydroxide. The end-reaction is the for-
mation of a distinct pink color. The
acidity of the urine is usually expressed
in terms of -^ acid or alkali for twenty-
four hours.

The oxalate is added to precipitate
calcium, and thus avoid the deposition
of calcium phosphate as the mixture
becomes alkaline. It also reduces the
error due to ammonium.

Specific gravity. The normal spe-
cific gravity of an average amount of
1500 c.c. of urine passed in twenty-four
hours is about 1.020, but it varies, even
in health, from 1.012 to 1.030 or more.
A specific gravity above 1.030 may
indicate the presence of sugar, larger
quantities of which may cause the spe-
cific gravity to rise to 1.050. Albumi-
nous urine is frequently of low specific
gravity, 1.010 to 1.012, especially in
chronic nephritis.

It should be remembered that the
specific gravity of urine considered
separately from the quantity of urine passed in twenty-four hours is
of no value, and that in some diseases (for instance in acute nephritis
with albuminuria) the specific gravity of albuminous urine may be as
high as 1.030, while a diabetic urine may have a specific gravity of
1.025, or less, in consequence of a large volume passed.

The determination of the specific gravity of urine is generally accom-

Urinometer.

708 PHYSIOLOGICAL CHEMISTRY.

plished by the urinometer, which is a small hydrometer indicating spe-
cific gravity from zero (or 1000) to 60 (or 1060). (See Fig. 73.) As
the temperature influences the density of liquids, a urinometer can
only give correct results at a certain degree of temperature, which is
generally marked upon the instrument.

Composition. Urine is chiefly an aqueous solution of urea and
inorganic salts, containing, however, always some uric acid, coloring-,
and other organic matters.

Urine also contains gaseous constituents, amounting to about 16
per cent, by volume ; these gases are chiefly carbon dioxide (88 per
cent.) and nitrogen (11 per cent.), with very little oxygen (1 per cent.).

The quantity of urine passed in a day also varies widely, an adult
discharging from 500 to 2300 c.c. in twenty-four hours ; a normal
average quantity is about 1000 to 1500 c.c. (about 36 to 54 ounces).
The quantity of total solids contained in this urine varies from 55 to 60
grammes (840 to 920 grains), and about one-half of this quantity is urea.

As many of the .so-called pathological constituents of urine are
actually present in minute quantities in normal urine, it is difficult to
make an absolute distinction between physiological and pathological
constituents. Below is given a working classification of the more
important constituents, regarding as normal those whose presence may
readily be shown by clinical tests. Accordingly, indican, for ex-
ample, is placed with the normal bodies, while acetone is placed with
the pathological substances, though both are normally present in
small amounts.

Normal constituents.
Urea.
Ammonia.

Nitrogen as

Creatinine.

Uric acid. ( Xanthine bases.
Other bodies < Allantoin.

( Hippuric acid.
Chlorine as chlorides.

Phosphorus as phosphoric acid. ( ( 1 ) Inorganic (K, Na, etc.).

Sulphur as { Neutral sulPlmr- (2) Organic (ethereal).

(Oxidized sulphur = sulphates: \ Indole (indican).
Sodium, } Skatole.

Potassium, I . . [ Phenol.

Calcium, Combined with acids.

Magnesium, I
Oxalic acid.
Pigments.
Enzvmes.

URINE AND ITS CONSTITUENTS. 709

Pathological constituents.

f Serum albumin.
Serum globulin.

Albumose (proteose).
Proteins :

Peptone.

Bence-Jones albumin.
. Haemoglobin.

Carbohydrates :

Glycuronic acid.

Glucose (dextrose).

Levulose.

Maltose.

Lactose.

Pentose.

f /3-oxy-butyric acid.
Acetone bodies -j Diacetic acid.
I Acetone.

Biliary acids, biliary pigments.

Melanin.

Alkapton.

Unknown body or bodies giving the Ehrlich diazo-reaction.

Determination of total solids. An approximate determination
of total solids may be deduced from the specific gravity of the urine,
as it has been found that the last two figures of the specific gravity
of urine, multiplied by 2.2, correspond to the number of grammes in
1000 c.c. of urine. If, for instance, 1450 c.c. of urine, of a specific
gravity of 1 .018, have been discharged in twenty-four hours, then the
quantity of total solids in 1000 c.c. will be 18 X 2.2, or 39.6 grammes ;
and in 1450 c.c., 57.42 grammes.

A more exact method of determining the total solids in urine is the evapora-
tion of about 10 c.c. in a weighed platinum dish over a water-bath (or, better,
under the receiver of an air-pump over sulphuric acid), until it is found that no
more loss in weight ensues on continued exposure of the dish in the drying
apparatus. By now reweighing the dish, plus contents, and deducting from
the weight that of the empty dish, the weight of total solids is found. This
determination has practically no clinical value.

Determination of inorganic constituents. The platinum dish
containing the known quantity of total solids is exposed to the action
of a non-luminous flame, and the heat continued until all organic
matter has been destroyed and expelled. By reweighing now, and
deducting the weight of the platinum dish, plus ash, from the weight

710 PHYSIOLOGICAL CHEMISTRY.

of the dish, plus total solids, the quantity of total organic matter is
determined ; and by deducting weight of dish from weight of dish
plus ash, the total quantity of inorganic matter is found.

The analysis of the ash is effected by the methods given in con-
nection with the consideration of the various acid and basic constitu-
ents themselves. Chlorine is determined by precipitating the solution
of the ash in nitric acid with silver nitrate, sulphuric acid by barium
chloride, phosphoric acid by ammonium molybdate, calcium by ammo-
nium oxalate, potassium by chloroplatinic acid, iron by potassium
ferrocyanide, etc.

As the methods outlined above are too involved for clinical wrork,
no details are given. Modern methods for quantitative urinary analy-
sis are practically all volumetric, and will be described for the various
constituents of the urine.

Nitrogen in the urine. The nitrogen in the urine is derived di-
rectly from protein metabolized. As only a small part of the nitro-
gen is excreted in the feces and sweat, the estimation of the urinary
nitrogen is the most commonly used procedure for determining the
amount of protein broken down in the body. The total nitrogen
varies from 10 to 16 grammes a day, and, as indicated above, varies with
the protein metabolism. Thus it is increased with a heavy meat diet,
with fever, in diabetes, etc. The approximate distribution of the
urinary nitrogen is :

Urea 85 per cent.

Ammonia 5-6 per cent.

Creatinine 4 per cent.

Uric acid 0.5-1 per cent.

Other nitrogen 3-5 per cent, (hippuric acid, xanthine

bases, etc.).

The estimation of nitrogen alone has little clinical value, but it is
frequently done in order to find the percentage of ammonia, which is
very valuable. The method used is the customary Kjeldahl method
(p. 445), using the Gunning mixture of sulphuric acid, sodium sul-
phate, and copper sulphate.

Normal nitrogenous constituents of urine. The more important are
urea, uric acid, ammonia, creatiniiie (creatine). Less important are
the xanthine bases, hippuric acid, etc.

Urea, Carbamide, CO(NH2)2, or COli<^ *. Urea, the most im-
portant constituent of urine, is the chief nitrogenous end-product of
the metabolism of proteins in the body, and carries off by far the

URINE AND ITS CONSTITUENTS. 711

largest quantity of all nitrogen ingested with the food. From 85 to
86 per cent, of the total nitrogen of the urine is found in urea, the
formation of which in the liver has been considered heretofore. Urea
has never yet been found as a product of vegetable life, but is found
as a normal constituent of the urine of the mammalia, and in smaller
quantity in the excrement of birds, fishes, and some reptiles. It
occurs in small quantities also in blood, muscular tissue, lymph, per-
spiration, and many other animal fluids. Pathologically urea may
appear in all fluids and tissues.

When pure, urea crystallizes from an aqueous solution in colorless
prisms ; it is colorless, and has a cooling, bitter taste ; it easily dis-
solves in water, the solution having a neutral reaction ; it fuses when
heated at 130° C. (266° F.), but decomposes at a higher temperature,
giving off ammonia gas and water, while a number of other sub-
stances are formed at the same time. A pure solution of urea does
not decompose at ordinary temperature, but on boiling, and especially
under pressure, it takes up water, and is decomposed into ammonia
and carbon dioxide, or into ammonium carbonate :

CO(NH2)2 4- 2H20 = C02 + 2NH3 + H2O = (NH4)2CO3.

The same decomposition takes place in urine under the influence
of a bacterial enzyme, if the temperature be not too low.

A solution of urea is decomposed by the action of chlorine or
bromine with generation of hydrochloric (or hydrobromic) acid, car-
bon dioxide, and nitrogen :

CO(NH2)2 + 6C1 + H20 = 6HC1 + CO2 + 2N.

Alkali hypochlorites or hypobromites cause a similar decomposi-
tion, upon which is based the quantitative estimation of urea.

Urea forms with acids definite salts, and with certain oxides and
salts definite compounds.

Urea is formed artificially by numerous decompositions, as, for instance :

a. By a process similar to the one taking place in the animal system, viz.}
by limited oxidation of albuminous substances by potassium permanganate.

b. By oxidation of uric acid in the presence of water :

403 + H20 + O = CO(NH2)2 +
Uric acid. Urea. Alloxan.

c. By the action of caustic alkalies upon creatine :

C4H9N,O2 + H2O = CO(NH2)2 + C3H7NO2.
Creatine. Urea. Sarcosine.

d. By the molecular transformation of ammonium cyanate, which tahea
place when its solution is evaporated and allowed to crystallize :

NH4.CXO = CO(NH2)2.

712 PHYSIOLOGICAL CHEMISTRY.

e. By the action of carbonyl chloride, COC1.2, on ammonia :
COC12 + 2NH3 = : 2HC1 + CO(NH2)2.
/. By the action of ammonia on ethyl carbonate :

(C2H5)2C03 + 2NH3 2C2H5OH + CO(NH2)2.

Urea may be obtained from urine by evaporating it to the consist-
ence of a syrup and mixing the cooled residue with an equal volume
of nitric acid, when crystals of urea nitrate, CO(NH2)2.HNO3, form,
which may be decomposed by barium carbonate into urea and barium
nitrate :

2[CO(NH2)2.HNO3] + BaCO3 = 2CO(NH2)2 + Ba(NO3)2 + CO2 + H2O.

Experiment 95. Evaporate about 200 c.c. of urine to a syrupy consistence,
allow to cool, place the vessel containing the syrup in ice and add slowly with
stirring a volume of nitric acid equal to that of the evaporated urine. Set
aside for twenty-four hours, collect the crystalline mass of urea nitrate on a
filter, wash with very little cold water, allow to drain well, dissolve in hot
water, and, while the solution boils gently, add small quantities of potassium
permanganate until the solution is colorless. To the hot solution add freshly
precipitated barium carbonate as long as carbon dioxide escapes. Filter and
evaporate the solution to dryness over a water-bath ; boil the mass with alco-
hol, which dissolves the urea, but does not act on the barium nitrate. Allow
the urea to crystallize from the alcoholic solution.

Reactions of urea. There are no very characteristic reactions by
which urea can be well recognized. From organic mixtures it is
separated by digesting them with from 3 to 4 volumes of alcohol in
the cold ; the filtered liquid is evaporated to dryness and extracted
with alcohol, which again is evaporated. The dry residue may be
tested for urea as follows :

1. Dissolved in a few drops of water, the addition of an equal
quantity of colorless nitric acid causes the formation of white, shin-
ing, crystalline plates or prisms of urea nitrate.

2. If a strong solution of oxalic acid is added, instead of nitric
acid, rhombic plates of urea oxalate form.

3. The residue (or urea) heated in a test-tube to about 160° C.
(320° F.) until no more vapors of ammonia are evolved, leaves a
substance termed biuret, C2H6N3O2, which, upon the addition of a few
drops of potassium hydroxide solution and a drop of cupric sulphate
solution, causes the solution of the cupric hydroxide with a reddish-
violet color.

Determination of urea. The amount of urea in twenty-four hours
is normally from 25 to 35 grammes. The greater part of it is derived

URINE AND ITS CONSTITUENTS. 713

from the exogenous protein metabolism, and the total quantity is
thereby largely affected by the diet. It is increased by a meat diet,
as is the total nitrogen output ; it is decreased in fever. In disease
of the two organs most concerned with urea elimination, the liver
(formation) and the kidney (excretion), it is usually, though not always,
decreased.

The quantitative estimation of urea in urine may be effected by
various methods, of which but one will be mentioned, because it re-
quires less time and less skill in manipulation than most other
methods. This determination is based upon the fact that urea is
decomposed by alkali hypobromites into carbon dioxide, water, and
nitrogen :

CO(NH2)2 + 3(NaBiO) = SNaBr + CO, + 2H2O + 2N.

The liberated nitrogen is collected, and from its volume the weight
of the urea is calculated. The carbon dioxide is absorbed by the
excess of alkali present. The hypobromite solution must be prepared
freshly by making the following mixture of:

(a) 1 volume of a solution containing bromine, 125 grammes ;
sodium bromide, 125 grammes; water, 1 liter.

(6) 1 volume of 22.5 per cent, sodium hydroxide solution.

(c) 3 volumes of water.

2NaOH + 2Br = NaBr + NaOBr -t H2O.

Of the many instruments recommended for the determination of urea, the
latest modification of Doremus' apparatus (Fig. 74) is most convenient. The
operation is carried out thus : Some urine is poured into B, while the stopcock
C is closed and then opened for a moment so as to fill its lumen. After having
washed the tube A with water, it is filled with the hypobromite solution. From
the tube B, previously filled with urine. 1 c.c. (or less if much urea is present)
is allowed to mix with the hypobromite solution, and after the reaction is com-
pleted the reading is taken. The degrees marked upon the tube A indicate
directly the number of grammes of urea contained in -the quantity of urine
employed.

Albumin must be removed, if present, and for careful work the specimen
must contain not more than 1 per cent, of urea, which can be readily accom-
plished by diluting a second specimen.

For careful work this method is not sufficiently accurate, and the Folin
method should be used.

Experiment 96. Determine urea in urine by the above-described methods.

Ammonia in the urine. Ammonia is normally present in the
urine in small amount, representing about 5 or 6 per cent, of the total
nitrogen. The amount seems dependent upon two factors : the ability
of the organism to convert the waste nitrogen from the proteins into

714

PHYSIOLOGICAL CHEMISTRY.

urea, and the necessity of neutralizing the acid radicals of the urine
which are normally in excess of the basic radicals. Accordingly,
the urinary ammonia is increased when the urea-forming apparatus is
deficient — •/. e., in certain disease of the liver. It is likewise increased
in the presence of an abnormal excess of acid — e. g., the acidosis of
diabetes and of the pernicious type of vomiting in pregnancy. As
the absolute amount of ammonia in the urine is greatly modified by

FIG. 74.

Doremus' ureometer.

the amount of total nitrogen, it is necessary to estimate the amounts
of each in order to obtain the important point — the ammonia fraction
of the total nitrogen.

Estimation of ammonia in the urine. The ammonia in a measured
amount of urine is set free by the addition of sodium carbonate. By
means of a suitable closed system of apparatus and an ordinary suc-
tion pump a current of air is carried through this mixture and
allowed to bubble up through a measured amount of £ sulphuric acid.
At the end of an hour and a half all of the ammonia will have been

VRINE AND ITS CONSTITUENTS. 715

carried over, and the excess of acid is titrated with ~ sodium hydroxide
with alizarin as an indicator.

Creatinine is normally present in urine to the amount of 1 or 2
grammes in twenty-four hours. It is believed to be derived from the
creatine of muscle, and mainly from the body muscle, not the food.
Its significance is still much disputed, as an accurate method of esti-
mation has been only comparatively recently devised (Folin, 1905).
Creatine is not normally present in urine.

Creatinine is best recognized in the urine by removing the phos-
phates and coloring-matter by milk of lime, concentrating the filtrate
by evaporation, and applying the tests mentioned before. As crea-
tinine is a reducing agent, its presence in urine will influence the tests
for sugar based on its deoxidizing power.

Make tests 2 and 3 of Experiment 77, to show the presence of creatinine in
urine.

NH— CO

Uric acid, H2C5H2N4O3. 2.6.8. Oxypurine, CO C-NH^

,co.

NH— C— NHX

Uric acid is found in small quantities in human urine, chiefly in com-
bination with sodium, potassium, and ammonium, but also with cal-
cium and magnesium. In larger proportions, uric acid is found in
the excrement of birds, mollusks, insects, and chiefly of serpents, the
solid urine of the latter consisting almost entirely of uric acid and
urates. It is also found in Peruvian guano. The proportion of uric
acid to urea in human urine is normally between 1 : 50 and 1 : 70.
The normal amount for twenty-four hours is about 0.7 gramme.

Pure uric acid is a white, crystalline, tasteless, and odorless sub-
stance, almost insoluble in water, requiring 1900 parts of boiling and
15,000 parts of cold water for its solution; it is also insoluble, or
nearly so, in alcohol and ether. The great insolubility of uric acid
causes its separation in the solid state, both in the bladder and in the
tissues.

It is believed that uric acid is derived by oxidation from the purine
bodies of the nucleins, and is increased when there is an increase in
nuclein metabolism. That coming from the tissue nucleins is termed
" endogenous " uric acid; that from the food nucleins is termed
" exogenous." While uric acid is formed synthetically in the liver
of birds, such a synthesis has not been proved for man. It seems
probable that most of the waste nitrogen in birds, as in man, is con-
verted into urea ; but is further changed to uric acid for excretion.

716 PHYSIOLOGICAL CHEMISTRY.

The exogenous uric acid is increased on a diet rich in nucleopro-
teins (sweetbreads) ; the endogenous uric acid, being derived mainly
from the muscles and the leucocytes, is increased after exercise, in
leukaemia, etc.

Experiment 97. (Preparation of uric acid.) Add 100 c.c. of hydrochloric
acid to 1 liter of urine and set aside for a day. Collect the highly colored
crystals of uric acid, wash with water, transfer them to a beaker with a little
water, heat, and add enough sodium hydroxide to dissolve the crystals. Decol-
orize the solution of sodium urate with boneblack, filter while hot, acidify with
hydrochloric acid, and allow to crystallize. Examine the crystals microscop-
ically and chemically.

Tests for uric acid.

1. Murexide test. Place a few fragments of uric acid in a porcelain
dish, add a drop of nitric acid, and carefully evaporate over a flame.
To the dry residue add a drop of ammonia- water, which produces a
beautiful purplish-red color. (Plate VIII., 4.)

To distinguish from xanthine and guanine, add a drop of caustic
soda, when the red changes to a deep blue color. Moisten with water
and evaporate to dryness, when the color disappears. With xanthine
or guanine the color persists.

For the following tests use solution of sodium urate prepared by dissolving
uric acid in warm water with the aid of sodium carbonate.

2. Schif's reaction. Place a drop of the solution on a piece of
filter-paper previously moistened with silver nitrate. A dark stain
is formed, due to the reduction of the silver salt.

3. Boil with Fehling's solution. A gray precipitate is formed when
uric acid, a reddish precipitate when the copper solution, is in excess.
(The reaction shows the necessity of exercising judgment in drawing
conclusions when testing for sugar in urine with reducing agents.)

4. Add magnesia-mixture and then silver nitrate. Uric acid is
precipitated as a gelatinous magnesia-silver salt. (This reaction may
be used to precipitate uric acid from urine, especially in those cases
in which hydrochloric acid fails to precipitate the acid.)

Quantitative estimation of uric acid. Of the many methods de-
scribed for this purpose, the one which is based on the separation of
uric acid and its subsequent titration with potassium permanganate
is best adapted for the needs of the physician. It is carried out
thus :

Uric acid is precipitated by ammonium sulphate as ammonium
urate, which is filtered off and isolated. On the addition of sul-

URINE AND ITS CONSTITUENTS. 717

phuric acid, uric acid is set free and the amount is titrated with ^
potassium permanganate solution.
Reagents used :

1. Ammonium sulphate, 500; uranium acetate, 5; acetic acid
(10 per cent.), 60 ; water, 650.

2. Ammonium sulphate, 10 per cent, solution.

3. f-Q potassium permanganate. .

To 100 c.c. of urine add 25 c.c. of reagent 1 ; let stand until the
precipitate has settled (five to ten minutes) and filter through two
folded filter-papers. To 100 c.c. of filtrate add 5 c.c. of concentrated
ammonia water and let stand for twenty-four hours. Pour off the
supernatant fluid through a filter and collect on it the precipitate of
ammonium urate with the aid of some 10 per cent, ammonium sul-
phate ; wash with the same solution for a short time. Open the
filter and collect the precipitate in a beaker with about 100 c.c. of
water. Add 15 c.c. of concentrated sulphuric acid, which will dis-
solve it. Titrate at once (while hot) with potassium permanganate
-/-$. The end-reaction is the first trace of rose color present through-
out the beaker after the addition of two drops of the reagent in
excess.

Calculation : As there is used in the titration only £ of the original
amount of urine (taking 100 c.c. of the first filtrate, not the whole
125 c.c.), J of the result of the titration is the amount of permanga-
nate which would correspond to 100 c.c. of urine. Each cubic centi-
meter of the permanganate corresponds to 0.00375 gramme of uric
acid from which it is simple to calculate the amount of uric acid
present in the urine.

Correction : As ammonium urate dissolves to the extent of 0.003
gramme in 100 c.c., this amount must be added for every 100 c.c. of
urine.

Xanthine bodies. The xanthine bodies are normally present in
urine in small amount. Those present in largest amount are para-
xanthine, heteroxanthine, and methylxanthine, which arise from the
similar bodies, caffeine, theobromine, and theophylline, in the food.
Otherwise the origin and significance of the purine bodies are thought
to be the same as those of uric acid.

Allantoin (glyoxyldiureide), C4H6N4O3, is normally present in
minute amounts in adults, more abundantly in the newborn. While
it will reduce Fehling's solution, the amount present is never suf-
ficient to give a positive test.

Hippuric acid, CgHgNOj (Benzoyl-glycocoll, Benzoyl-amino-acetic

718 PHYSIOLOGICAL CHEMISTRY.

acid), is a normal constituent of human urine, but is found in much
larger quantities in the urine of herbivora. Its constitution is
CH2.NH— CO2H,

| and is the result of the combination of glycocoll

C6H5CO

and benzoic acid. This synthesis occurs in the kidney. Hay, and
especially aromatic herbs, contain benzoic acid, or compounds having
a similar composition, and a portion of these compounds is eliminated
in hippuric acid. Administration of benzoic acid increases the amount
of hippuric acid in urine.

When pure, hippuric acid crystallizes in transparent, colorless,
odorless prisms, which have a bitter taste, and are sparingly soluble
in water.

Experiment 98. (Preparation of hippuric acid.} To 400 c.c. of horse's urine
add some milk of lime, heat, filter, evaporate the filtrate to a small volume,
and acidify with hydrochloric acid. The calcium hippurate which had been
formed is decomposed and the liberated hippuric acid separates either at once
or on standing. If too highly colored, dissolve crystals in hot water contain-
ing some ammonia, decolorize solution with boneblack, filter, acidify with
hydrochloric acid, and recrystallize. Examine crystals microscopically and
chemically.

Tests for hippuric acid.

1. Heat in a dry test-tube : a sublimate of benzoic acid is formed
and the odor of hydrocyanic acid is noticed.

2. To solution add ferric chloride : a brown precipitate is formed.

3. Heat the dry acid with calcium hydroxide in a test-tube : ben-
zene and ammonia are evolved.

4. Evaporate to dryness with a few drops of nitric acid : an intense
odor of nitrobenzene is evolved.

Chlorides in urine. Chlorides are present in larger amount than
any other inorganic constituent. As sodium chloride is the most
abundant, the total quantity is usually expressed in terms of sodium
chloride, and normally amounts to 10 to 15 grammes in twenty-four
hours. While the origin of the chlorides is in the ingested food, they
bear some relation to the body metabolism, which as yet is not un-
derstood. In nephritis there is a retention of chlorides, particularly
with the development of oedema. In pneumonia there is a great
decrease in the chlorides, with a return to normal amounts at, or even
slightly before, the crisis. The significance of these facts is not
known. 4

Qualitative test for chlorides. To a few c.c. of urine, acidified with
nitric acid, add a few c.c. of 5 per cent, silver nitrate solution. A

URINE AND ITS CONSTITUENTS. 719

white precipitate of silver chloride forms. By comparing the result
with that obtained with a known normal urine, a rough estimate
can be gotten as to the amount of chlorides present.

Estimation of chlorides. The chlorides in a measured amount of
urine are precipitated by the addition of an excess of silver nitrate
solution of known strength. The silver chloride is removed and the
amount of silver nitrate remaining in solution is determined by the
method given on page 427. The following solutions are used : (1)
Silver nitrate of such strength that 1 c.c. corresponds to 0.01 gramme
of sodium chloride. (2) Potassium sulphocyante of such strength that
1 c.c. corresponds to 1 c.c. of the silver solution. (3) Ammonio-
ferric alum, saturated solution.

To 10 c.c. of urine in a 100 c.c. graduated flask add 4 c.c. of con-
centrated nitric acid and 50 c.c. of distilled water. Add 15 c.c. of
the silver solution and dilute the mixture to the 100 c.c. mark, shak-
ing well. Filter off 50 c.c. and titrate with the sulphocyanate solu-
tion, after adding 3 c.c. of ammonio-ferric alum. The result multi-
plied by 2 shows the number of cubic centimeters of silver nitrate
which was in excess. The difference between this number and 15
is the number of cubic centimeters of silver nitrate which corresponds
to the chloride content of the 10 c.c. of urine.

Phosphoric acid is found in urine, in part (about two-thirds) com-
bined with alkalies, and in part (about one-third) with lime and
magnesia. These phosphates have in acid or neutral urine the com-
position NaH2PO4, CaH4(PO4)2, MgH4(PO4)2 ; in amphoteric urine,
in addition to the above, there occur Na2HPO4, CaHPO4, MgHPO4 ;
in alkaline urine compounds of the composition Na2HPO4, CaHPO4,
MgHPO4, Na3PO4, Ca3(PO4)2, Mgs(PO4)2, MgNH4PO4 may be pres-
ent. A small quantity is present as glycerin-phosphoric acid.

The phosphates in urine amount normally to about 3 grammes of
P2O5 in twenty-four hours. They are derived mainly from the food,
and to a much smaller amount from the body protein. They are in-
creased in certain cases of diabetes, and are decreased in most of the
fevers. The determination of the phosphatic output has little clinical
importance.

On adding any alkali the phosphates of calcium and magnesium
(generally termed earthy phosphates) are precipitated ; the phosphates
of sodium or possibly potassium remain dissolved, and may be pre-
cipitated as magnesium ammonium phosphate by the addition of
magnesia mixture.

720 PHYSIOLOGICAL CHEMISTRY.

Experiment 99. ( Volumetric determination of phosphoric acid.) Soluble
uranium salts give with phosphates a dirty-white precipitate of uranium phos-
phate : Na2HPO4 + UO2(NO3)2 = UO2HPO4 + 2NaNO3. The precipitate is
soluble in mineral acids, insoluble in acetic acid. Tincture of cochineal is not
affected by uranium phosphate, but is colored greenish by soluble uranium
salts. These reactions are used for determining phosphoric acid, thus :

Make up a solution of sodium acetate, 100 grammes ; acetic acid (glacial),
30 grammes ; and water to make 1000 c.c.

Prepare a volumetric solution of nitrate or acetate of uranium so adjusted
that 1 liter is equivalent to 5 grammes of P2O5. To 100 c.c. of filtered urine
add 5 c.c. of the acetate solution and a few drops of solution of cochineal. Heat
to boiling and titrate with uranium solution until the liquid assumes a green
color. The number of c.c. required multiplied by 0.005 indicates the quantity
of P2O5 in the urine used.

Sulphur in the urine. Sulphur is present in the urine in three
forms :

Neutral (unoxidized) sulphur ; cystine, etc.
Oxidized (acid) sulphur :

a. Inorganic (preformed) sulphates, Na, K, etc.

b. Ethereal (conjugate) sulphates ; sulphuric acid in combination

with skatole, indole, phenol, etc.

The origin of the urinary sulphur is the protein metabolism, while
a small portion may arise from the ingested sulphates. The total
amount has little clinical importance. It is increased in fever and
with a meat diet. The inorganic sulphates are largely in excess,
their amount being about ten times that of the ethereal sulphates.

Experiment 100. 1. Demonstrate neutral sulphur by adding HC1 to urine
with a fragment of zinc ; hydrogen sulphide will be evolved and will blacken
lead acetate paper.

2. Demonstrate inorganic sulphates by adding barium chloride solution to
urine acidified with acetic acid ; a white precipitate of barium sulphate will
form. Filter this solution ; and,

3. Demonstrate ethereal sulphates by adding HC1 and barium chloride solu-
tion to the filtrate. On boiling the organic sulphates will be broken up and a
second precipitate of barium sulphate will form.

Neutral sulphur in the urine. While there is normally present
about 10 per cent, of the total sulphur in this form, the bodies which
contain it are so far almost unknown. Sulphocyanates are found
in small amounts.

Pathologically the best known body is cystine, which is believed
to indicate an inability on the part of the body to completely break
down the protein residues.

Cystine, diamino-dithw-dipropionic acid, ^'2 is

URINE AND ITS CONSTITUENTS. 721

secreted by the members of some families, and seems to be without
pathological significance, except that it may be deposited in the
bladder and form calculi.

Cystine is insoluble in water, alcohol, and ether, but is readily soluble in
ammonia- water ; boiled with solution of sodium hydroxide a sulphide of sodium
is formed which stains silver black. Cystine crystallizes in characteristic regu-
lar six-sided tablets, and is best recognized microscopically in the precipitate
formed by adding acetic acid to urine. Inorganic sulphates of sodium, potas-
sium, and magnesium are present, but possess no great interest.

Ethereal sulphates. As the conjugated substances (phenol, para-
cresol, skatole, indole, etc.) are formed in the intestine as putrefac-
tion products of the proteins, and are conjugated (in the liver) merely
for excretion, the resulting organic sulphates are increased whenever
the intestinal putrefaction is increased. The estimation of these
bodies as sulphates is, however, seldom carried out, as the increase is
important only when it is marked, and it is simpler to show an in-
crease of the non-sulphate portion. The indican tests are commonly
made use of in this connection.

Indican, indoxyl-sulphuric add, C8H7NSO4,

/NH\

C6H <^ ^CH This compound is not identical with the

XC^_O— SO2.OH.

indican found in woad and a few other plants. The vegetable indican
is a glucoside, C26H31NO7, yielding by fermentation, among other
products, dextrose and indigo-blue, C16H10N2O2. The latter is iden-
tical with the indigo obtained from indoxyl-sulphuric acid, which
decomposes into sulphuric acid (or a salt of it), and indoxyl, which
latter, by oxidation, yields indigo, thus :

C8H6KNSO, + H,0 = C8H7NO + KHSO4

Potassium Indoxyl.

indoxy 1-sul ph ate.

2(C8H7NO) + 2O = C16H10N202 -f 2HjO
Iiidoxyl. Indigo.

The source and formation of indican in the body have been men-
tioned. In urine it occurs normally to the extent of 0.002 per cent.,
while pathologically the quantity may be much greater. Indican is
pale yellow, but is easily converted into indigo-blue, and it is this
property which is used for its detection.

Tests for indican.

1. Mix equal volumes of urine and strong hydrochloric acid ; then
add drop by drop a solution of bleaching-powder until the maximum

Afi

722 PHYSIOLOGICAL CHEMISTRY.

of color is attained ; add chloroform, which is colored blue. (Care
should be taken to add the hypochlorite slowly, as an excess destroys
the color ; highly colored urine should be decolorized with basic lead
acetate ; in doubtful cases the mixture of urine, hydrochloric acid, one
or two drops of bleach ing-powder solution, and chloroform should
be set aside for several hours.)

2. ObermayeSs test depends on the conversion of indican into indigo
by ferric chloride ; and as this reagent has no further action on indigo,
the method has a great advantage over the previous ones. The test
is made by following the directions given in the above test, using an
equal volume of strong HC1 containing 0.2 per cent, of ferric
chloride and no bleaching-powder solution.

Indigo-red appears in the urine in the same conditions in which
indican is found. It is recognized by Rosenbach's reaction : Urine
is boiled, and, while it is still boiling, nitric acid is added drop by
drop, when a deep red color appears if indigo-red is present. The
foam on shaking the test-tube is bluish red.

Skatole (skatoxyl-sulphuric acid) is rarely present in the urine. Its
formation is analogous to that of indole.

Phenol, C6H5OH, and paracresol, C6H4.CH3.OH, occur in urine
in combination with potassium acid sulphate. The combined quan-
tity of the two substances is about 0.002 per cent. The quantity is
increased during intestinal putrefaction from all causes (except simple
obstruction), when there is absorption of pus from abscess or wounds,
and after ingestiou of carbolic acid.

Experiment 101. (Determination of phenol.}

a. Qualitative determination. Render alkaline 100 c.c. of urine with sodium
carbonate, evaporate to a syrup, add 20 c.c. of hydrochloric acid, and distill.
To the distillate apply the tests for phenol.

b. Quantitative determination. To 500 c.c. of urine add 25 c.c. of hydrochloric
acid and distill 200 c.c. Neutralize distillate with sodium hydroxide, in order
to convert benzoic and possibly other acids present into salts, and again distill
200 c.c. Determine the quantity of phenol in the distillate by means of deci-
normal bromine solution, as directed on page 424.

Pyrocatechin, ortho-dioxy benzene, C6H4(OH)2, occurs in urine as
pyrocatechin sulphuric acid. It is derived from the putrefaction of
vegetable food, and is found in large quantity in urine after taking
carbolic acid. Urine containing pyrocatechin turns dark on exposure
to air, especially if it is made alkaline.

To show the presence of pyrocatechin, add a little sulphuric acid
to the urine, boil, and when cool extract with ether. Evaporate the
ether, dissolve the residue in a little water, and apply tests.

URINE AND ITS CONSTITUENTS. 723

Tests for pyrocatechin.

1 . Add dilute ferric chloride solution : a green color is evolved.
Add a little tartaric acid and then ammonia : the green color changes
to violet, but on acidifying with acetic acid the green color reappears.

2. Add sodium hydroxide : the solution turns green, brown, and
black.

3. Add lead acetate : pyrocatechin is precipitated as a lead com-
pound.

4. Show that Fehling's solution and ammonio-silver nitrate solu-
tion are reduced by pyrocatechin, but that it does not act on alkaline
bismuth solution.

Sodium, potassium, calcium, and magnesium occur in the urine
mainly as inorganic salts. They are derived from the food. The
amount present is not important clinically.

Oxalic acid. The source of this acid in urine is unknown. Many
vegetables and fruits contain oxalates, which, after ingestion, are
secreted to a great extent unchanged. That oxalic acid occurs as a
metabolic product is shown by its excretion during starvation, and
also when the diet is exclusively protein and fat. It is believed that
the protein, and not the fat, is concerned here. An increased elimi-
nation of oxalic acid occurs in diabetes, icterus, and in the condition
called oxaluria.

Enzymes in urine. Pepsin has been shown to be present in small
amount in normal urine ; lipase and a diastase have been found in a
few cases.

Pathological constituents. While the normal constituents of
urine, and especially the quantity excreted in twenty-four hours,
give valuable information in regard to the whole process of metab-
olism taking place in the body, pathological constituents often show
with great precision abnormal conditions existing in the body, and
the qualitative or quantitative determination of pathological con-
stituents is therefore a valuable aid in diagnosing disease. Of patho-
logical constituents are of chief interest the proteins (albumin, globu-
lin, albumoses, peptones), sugars, and the constituents of blood or
bile. But many other substances occur at times, and should not
be overlooked in the examination. To these substances belong
acetone, diacetic acid, melanin, a compound giving the diazo-reac-
tion, etc.

724 PHYSIOLOGICAL CHEMISTRY.

Proteins in urine. Albumin in urine is always serum-albumin,
and is usually associated with serum-globulin. The pathological con-
dition is termed albuminuria. While transient albuminuria may
follow severe muscular or mental strain, cold baths, etc., and leave
no permanent effect, it must always be regarded as a pathological
condition. The most common cause of continued albuminuria is or-
ganic disease of the kidneys, acute and chronic nephritis, or even
chronic passive congestion. It occurs in all severe febrile conditions,
in- blood diseases (pernicious anemia, leukemia), after chloroform and
ether anaesthesia, and after many poisons (cantharides, phenol, etc.).
Albumin is present in all urines containing blood or pus arising from
any portion of the urinary tract.

Tests for albumin.

1. Heat and acid. Heat to boiling the upper portion of urine in a
test-tube. If a cloud appears it is due to albumin or phosphates.
The lower cold urine serves as a guide for comparison. If no cloud
forms, albumin may or may not be present ; in any case add a few
drops of 5 per cent, acetic acid until the reaction is acid — boiling
again after each drop. A cloud already present, due to phosphates,
will disappear; one due to albumin will become more distinct. In
case albumin is present, but has not already been coagulated, it will
form a cloud on the addition of the acid, showing that there was not
sufficient acid present originally, the urine being either neutral or
alkaline. The test is made more delicate by the addition of one-eighth
of the volume of the urine of saturated salt solution, which should
always be done with very dilute urines. It is important to avoid an
excess of the acid, as the coagulated albumin may go into solution
again. If the test is made with the addition of salt solution, it is
extremely delicate and rarely misleading. The acetic acid may be
replaced Ijy nitric acid, with which an excess of acid is less to be
feared, and fa to y1^ volume of concentrated acid can be added.
With nitric acid the urine should not be boiled after the acid has
been added.

2. Nitric acid test. About 20 c.c. of clear urine are placed in a
conical test-glass of about 50 c.c. capacity ; from 5 to 10 c.c. of nitric
acid are added by means of a pipette in such a manner that the acid
flows slowly from the pipette, which is carried to the bottom of the
vessel. Operating carefully, two distinct layers of liquid are obtained,
and in the presence of albumin a distinct white cloud will appear at

URINE AND ITS CONSTITUENTS. 725

the zone of contact, the extent and intensity of the cloud varying
with the quantity of albumin present. Very small quantities of
albumin cannot be detected at once, but will appear on standing, the
cloudiness extending gradually upward. A distinct ring from 1 to 2
cm. above the zone of contact, and appearing within five to ten
minutes after the addition of nitric acid, was formerly thought to be
due to uric acid, and was called the urate ring. It is believed now
to be in some cases composed of protein material. In urines contain-
ing a high percentage of urea, a ring may form at the plane of con-
tact, consisting of urea nitrate, which is distinctly crystalline in
appearance. Following the ingestion of turpentine and various bal-
sams, this test may show a precipitate of resinous acids at the junc-
tion of urine and acid, which is recognized by its solubility in alcohol
or ether. Albumoses produce a ring which dissolves on heating and
reappears on cooling.

At the zone of contact a change in color is generally noticed. In
normal urine this varies from pale red to intense brick red ; in biliary
urine a color- play similar to the colors of the rainbow may be noticed,
while the presence of indican is indicated by a violet or blue tint.
It is important to distinguish between color rings and precipitate
rings.

3. Trichlor acetic acid may be used for the detection of albumin by
dropping a fragment into a few cubic centimeters of urine contained
in a test-tube. As the acid dissolves, a cloudy ring forms in the pres-
ence of albumin, which is not dissolved on warming.

4. Potassium ferrocyanide test. 5 to lOc.c. of cold urine are acidu-
lated with 5 to 10 drops of acetic acid, and to the mixture are added
a few drops of solution of potassium ferrocyanide. In the presence
of even traces of albumin a turbidity is caused. A precipitate which
dissolves on heating is due to albumose. This test is extremely deli-
cate, especially when modified so as to allow a few cubic centimeters
of diluted acetic acid, to which a few drops of potassium ferrocynaide
solution had been added, to flow down the side of the test-tube con-
taining the urine. A decided turbidity at the point of contact of the
two liquids shows albumin.

In case the addition of acetic acid to the cold urine should cause a
turbidity (which may be due to mucin or nucleo-albumin) it must be
filtered before adding the potassium ferrocyanide.

In the above methods the manipulations and precautions are mi-
nutely described, in order to detect small quantities or even traces of
albumin. When albumin is abundantly present, there is no difficulty

726 PHYSIOLOGICAL CHEMISTRY.

whatever in its detection, as heat will precipitate it in most cases from
an acid, neutral, or sometimes even alkaline urine ; the precipitate
should, however, always be tested by the addition of a few drops of
nitric acid, and the previous addition of a few drops of acetic acid is
also advisable.

Quantitative estimation of albumin. The average amount of
albumin present in acute cases of albuminuria is 0.1 to 0.5 per cent.,
rarely over 1 per cent., though it may rise to 4 per cent. An
approximate method for the comparative estimation of albumin is to
precipitate it (with the precautions above given) in a graduated test-
tube by heat and setting aside for twelve (or, better, for twenty-four)
hours. At the end of that time the proportion of the coagulated
albumin which has collected at the bottom of the fluid is noticed. If
the albumin occupy one-fourth, one-sixth, one-tenth of the height of
the liquid, there is said to be one-fourth, one-sixth, or one-tenth of
albumin in the urine. If, however, at the end of twelve or twenty-
four hours scarcely any albumin has collected at the bottom, there is
said to be a trace.

The volumes of coagulated albumin indicate the following quantities of dry
albumin :

Slight turbidity indicates about 0.01 per cent.

& of tbe tube is filled 0.05 "

rV " " ....... 0.10 "

j « • * 0.25

I " " ....... 0.50 "

£ " " ....... 1.00 "

Complete coagulation . 2 to 3 "

Esbach's albuminometer (Fig. 75) is a conveniently arrnnged tube for deter-
mining approximately the quantity of albumin. The tube is rilled with urine to
U, and then with the reagent to R. The reagent is a solution containing 1
gramme of picric acid and 2 grammes of citric acid in 100 c.c. of water. After
having filled the tube it is closed with a stopper, inverted twelve times, and set
aside for twenty-four hours. At the end of that time the albumin will have
settled down, when the amount pro mille in grammes may be directly read off
from the scale.

Tsuchiya's reagent possesses many advantages over Esbach's, and is used in
the same manner. It is, Phosphotungstic acid, 1.5 grammes; hydrochloric
acid (concentrated), 5 c.c.; alcohol, 95 c.c.

A better method of exactly estimating the amount of albumin is its
complete separation and weighing, as described below.

Experiment 102. Acidify 100 c.c. of clear albuminous urine with acetic acid ;
heat to the boiling-point in a water-bath for half an hour, and filter through a

URINE AND ITS CONSTITUENTS.

727

small filter, previously dried at 110° C. (230° F.) and weighed ; wash with boil-
ing water to which a little ammonia water has been added (to remove uric
acid and urates), then with pure water until the filtrate is not rendered turbid
any longer by silver nitrate, next with pure alcohol, and finally with ether.
Dry filter and contents at 110° C. (230° F.) and weigh.

As it may happen that the precipitated albumin encloses earthy phosphates,
it is well to burn filter with contents in a platinum crucible, and to deduct the
weight of the remaining inorganic residue (less the weight of the filter ash)
from that of the albumin.

Serum-globulin is detected by rendering the urine alkaline with
ammonia water, filtering off the precipitate of phosphates, and add-
ing to the clear filtrate an equal volume of a saturated
solution of ammonium sulphate. The appearance of a FIG. 75.
precipitate indicates globulin.

Albumoses answer to the nitric acid test and the
potassium ferrocyanide test for albumin ; the precip-
itate formed by these reagents dissolves on heating,
but reappears on cooling. Albumoses are further rec-
ognized thus : To the urine strongly acidified with hydro-
chloric acid is added an equal volume of a saturated so-
lution of sodium chloride. On boiling, serum-albumin,
if present, is precipitated and filtered off while hot.
Albumoses separate from the filtrate on cooling.

The solution, filtered while hot, gives a red biuret
reaction. As albumose is frequently present in albu-
minuria, its demonstration is important only in the
absence of albumin. Albumosuria occurs with the
absorption of purulent exudates, in acute yellow atrophy
of the liver, and in other conditions.

Peptones are not uncommonly present in the urine aibuminometer.
in albumosuria, but are rarely present alone. Peptonuria
exists when it is possible to obtain a red biuret reaction after the
careful removal of protein and albumose. Both here and in the case
of albumosuria urobilin may mislead one when the biuret reaction is
tried. It may be removed by extraction with alcohol.

Bence- Jones body is present in the urine in certain cases of
bone disease (multiple myeloma). It is thought to be a unique
albumin and not an albumose, as held by the earlier view. It is
coagulated in urine acidified with acetic acid on heating to 50° or
60° C., and redissolves as the temperature reaches the boiling-point.
It is very rarely present.

Esbach's

728 PHYSIOLOGICAL CHEMISTRY.

Nucleo-albumin. If the ring occurring in Heller's test some dis-
tance above the place of contact becomes more distinct when the
urine is diluted, it is believed to be of protein origin, and has been
called nucleo-albumin, mucin, euglobulin, Morner's body, etc. Its
true nature is not yet known. The cloud produced by acetic acid
in the cold is believed to be due to the same body. As urates may
be precipitated in both of these methods, it is important to rule them
out by diluting the urine, when the precipitate due to urates will not
appear. True nucleo-albuminuria is rare.

Blood. The presence of blood in urine manifests itself generally,
unless the amount be too slight, by a blood-red or browrnish color
with a bluish, smoky, or greenish tint, and deposits a red or reddish-
brown sediment after standing. As a general rule, all constituents
of blood, including the corpuscles, are present (haematuria), but in
some cases only haemoglobin (methaemoglobin) is found (haemoglobin-
uria).

The tests for blood depend either on the microscope, spectroscope,
or on chemical changes. By the microscope is examined the deposit
which forms on standing ; almost unaltered blood-corpuscles may be
found, or they may be much swollen, decolorized, and deformed.

Haematuria is common and occurs in diseases of the kidney (acute
nephritis, stone, tuberculosis, trauma) ; similar conditions of the ure-
ters and bladder ; general conditions (malignant forms of smallpox,
malaria, etc. ; haemophilia).

Haemoglobinuria occurs occasionally in severe fevers (scarlet fever,
yellow fever) ; after severe burns or exposure to cold ; in certain
poisonings (potassium chlorate, carbon monoxide). It is always pre-
ceded by haemoglobinaemia, i. 6., the presence of free haemoglobin in
the circulating blood. The spectroscope shows the absorption-bands
of the blood-pigments, for which see Fig. 72.

Tests for blood in urine.

1. Render alkaline with sodium hydroxide and boil. In the pres-
ence of blood coloring-matter the precipitate of phosphates produced
is colored red. In a urine containing other coloring-matters (bile-
pigments, etc.) the test may be misleading ; in such cases, filter off
the precipitate, wash, and dissolve it in acetic acid. In the presence
of blood-pigment the solution becomes red, but the color gradually
disappears on exposure to air.

2. Allow a mixture of freshly prepared tincture of guaiacum and

URINE AND ITS CONSTITUENTS. 729

ozonized oil of turpentine to flow down the side of a test-tube in
such a manner as to form a distinct layer above the urine. A white
ring, gradually turning blue, will appear at the surface of contact.
(Ozonized oil of turpentine is oil which has been exposed to air for
some time ; in place of it may be used peroxide of hydrogen or a
mixture of this compound with ether.)

3. Add a little of a solution of egg-albumin to 100 c.c. of urine,
heat to boiling, and filter off the coagulum, which has taken up the
hsematin. Mix the precipitate in a mortar with 20 c.c. of absolute
alcohol and a few drops of sulphuric acid, transfer to a flask, heat
to boiling, and filter. After cooling, render alkaline with sodium
hydroxide, reduce with ammonium sulphide, and examine spectro-
scopically for reduced ha3matin. (Fig. 72.)

The direct spectroscopic examination of urine is generally unsatisfactory>
because it often contains a number of substances giving absorption spectra.

Carbohydrates in urine. Dextrose (glucose) in urine is normally
present in minute amount. When the amount is sufficient to give
the customary reduction tests, the condition is spoken of as glyco-
suria. If dextrose be eaten in large amount the body is unable to
burn all of it, and a temporary glycosuria results. This is called ali-
mentary glycosuria and is not a serious condition. The amount of
sugar, the " assimilation limit," which can be ingested without the
appearance of the sugar in the urine, differs for the different sugars
and differs in different individuals. A more serious condition, per-
sistent glycosuria, exists in diabetes when the body is unable to carry
on the normal sugar metabolism. In this disease the amount of dex-
trose in the urine may be very large, and frequently dextrose is
present, even when the patient is on a carbohydrate-free diet. In
both of these conditions the glycosuria is secondary to an increase
in the dextrose content of the blood, while in experimental " phlorid-
zin diabetes " the change is in the kidneys, and there is no increase
in the dextrose of the blood.

There are many tests by which dextrose can be detected. They
depend chiefly on the following properties of dextrose, viz. : 1, to act
as a deoxidizing or reducing agent upon certain metallic oxides (cop-
per, bismuth, silver, mercury) in the presence of alkalies ; 2, to pro-
duce a yellow or brown color when in contact with alkalies, slowly
in the cold, rapidly on heating ; 3, to ferment with yeast ; 4, to unite
with phenyl-hydrazine to a crystalline compound; 5, to have the
power of rotating the plane of polarization to the right.

730 PHYSIOLOGICAL CHEMISTRY.

Tests.

1. Trommer's test. A few drops (2-4) of a 5 per cent, solution of
cupric sulphate are added to about 5 to 8 c.c. of urine in a test-tube
and then an equal volume of potassium (or sodium) hydroxide solu-
tion is added. The alkaline hydroxide precipitates both earthy phos-
phates and cupric hydroxide, the latter, however, dissolving (espe-
cially if sugar be present) in the excess of the alkali, producing a
beautiful blue transparent liquid. (If no sugar is present, the color
is less blue, but more of a greenish hue.) The liquid is now heated,
when, if sugar be present, a yellow precipitate of cuprous hydroxide
is formed which subsequently loses its water and becomes the red
cuprous oxide, which falls to the bottom or adheres to the sides of
the test-tube. (Plate VIII., 5.)

In drawing conclusions from the above test, it should be remem-
bered that a change of color does not indicate sugar ; that a precipi-
tate of earthy phosphates must not be mistaken for cuprous oxide ;
and that substances other than sugar may deoxidize cupric oxide at
the temperature of 100° C. (212° F.).

A disadvantage of Trommer's test is the formation of black cupric
oxide whenever too much copper solution is used in proportion to the
sugar present. The formation of the black oxide, which may mask
a small quantity of cuprous oxide, is avoided in the next test.

2. Fehling's test differs from Trommer's test in merely using a pre-
viously mixed reagent instead of producing this reagent, as it were,
in the urine by adding to it cupric sulphate and an alkaline hydroxide
successively. This reagent, known as Fehling's solution, or as alkaline
cupric tartrate volumetric solution, is made by mixing exactly equal
volumes of the below-mentioned copper solution and the Rochelle
salt solution at the time required.

Copper solution :

Crystallized cupric sulphate 34.64 grammes.

Water, sufficient quantity to make .... 500 c.c.

Rochelle salt solution :

Potassium sodium tartrate 173 grammes.

Potassium hydroxide . . . . . . .125 "

Water, sufficient quantity to make .... 500 c.c.

Both solutions are preserved in small well-stoppered bottles, and
mixed only at the time needed, because the mixture is apt to decom-
pose when kept some time.

The addition of sodium-potassium tartrate in Fehling's solution prevents the
precipitation of cupric hydroxide by the alkaline hydroxide. This action is anal-

URINE AND ITS CONSTITUENTS. 731

ogous to the formation of the soluble scale compounds of iron, where the pre-
cipitation of ferric hydroxide is also prevented by tartaric or other organic acids.

The test is made by heating in a test-tube 10 c.c. of Folding's solu-
tion which has been diluted with 2 to 5 volumes of water and add-
ing drop by drop the suspected urine ; if the latter contains larger
quantities of sugar, a yellow or red precipitate of cuprous hydroxide
and oxide will be produced very readily ; if but small quantities are
present, the reaction will appear only on standing for some time.

Haines' test is a modification of Fehling's test. The reagent is as
follows : " Dissolve 30 grains of cupric sulphate in \ ounce of water,
add \ ounce of glycerin and then 5 fluidounces of liquor potassse."
The advantage of the reagent is that it is very stable. It should be
used by boiling about 1 drachm in a test-tube, adding 8 to 10 drops
of the suspected urine, and again bringing to a boil. In the presence
of sugar a precipitate of cuprous oxide is thrown down.

3. Botgcr's bismuth test consists in adding to a mixture of equal
volumes of urine and potassium (or sodium) hydroxide solution a few
grains of subnitrate of bismuth and boiling for half a minute. If
sugar be present, a gray or dark -brown, finally black, precipitate of
bismuthous oxide, Bi2O2, or of metallic bismuth is formed. If but
very little sugar is present, the undecomposed excess of bismuthic
nitrate (or bismuthic hydroxide) mixes with the metallic bismuth,
imparting to it a gray color ; the test should then be repeated with a
smaller amount of the bismuth salt. (Plate VIII., 6.)

The above test may be advantageously modified by using a bismuth
solution instead of the powder. The solution known as Nylander's
reagent is made by dissolving 2 grammes of bismuth subnitrate, 4
grammes of Rochelle salt, and 10 grammes of sodium hydroxide in
90 c.c. of water, and filtering. One-half c.c. of this solution is heated
with about 5 c.c. of urine, when, in the presence of sugar, a brown
or black precipitate will form after a few minutes7 boiling.

If the urine contains hydrogen disulphide (sometimes produced by decom-
position of certain urinary constituents), black bismuth sulphide will be formed,
which may be mistaken for metallic bismuth ; albumin itself may be the cause
of the formation of alkaline sulphides : the previous complete separation of
albumin is therefore indispensable.

4. Moore's or Heller's test is made by heating urine with about
one-fourth its volume of solution of potassium hydroxide. In the
presence of sugar the color of the mixture will deepen to a dark yel-
low or brown, and the depth of color is a fair indication of the quan-

732 PHYSIOLOGICAL CHEMISTRY.

tity of sugar present. In case but a slight change takes place in
color, it is well to compare it with that of an unchanged specimen
of the urine.

5. Fermentation test. This is based upon the decomposition of
dextrose by yeast with the generation of carbon dioxide. A piece
of yeast about the size of a pea is ground up in urine and the mixture
used to fill a fermentation tube. The tube is then kept for twenty-
four hours at a fairly constant temperature of 22° to 28° C. If dex-
trose be present, fermentation will commence within twelve hours
and will manifest itself by the formation of carbon dioxide gas, which
will collect at the upper end of the long arm of the tube.

The urine and the fermentation apparatus should be sterilized by heat to
destroy any gas-producing bacteria present. For a control of the test, two
more fermentation tubes should be prepared, one with a mixture of a glucose
solution and yeast (to determine that the yeast is efficient),, and another with
sterilized water and yeast (to show that the yeast itself does not generate

The disadvantages of this process are the length of time required for its per-
formance, the unreliability of the ferment, and the fact that small quantities
of sugar (less than 0.5 per cent.) evolve so little carbon dioxide that a doubt
may be felt as to the presence of sugar at all.

6. The pTienyl-Tiydrazine test. To 10 c.c. of urine in a test-tube,
add phenyl-hydrazine hydrochloride, 0.4 gramme and sodium ace-
tate, 1 gramme, warm until dissolved, adding water, if necessary, and
keep in a boiling water-bath for half an hour. Filter while hot, and
allow to cool slowly. The presence of dextrose will be shown by the
deposition of yellow crystals, which are seen with the microscope to
be needles arranged in sheaves. This precipitate is an osazone
(phenyl-dextrosazone) and melts at 205° C. Pentoses and maltose
give similar osazones, as do lactose and glycuronic acid. The latter
are rarely present in sufficient amount to give a positive test with the
urine directly. The melting-points are of value in recognizing the
different osazones.

7. Polariscopic test. Before urine can be examined by the polari-
scope it should be freed from proteins and from the greater part of
coloring-matters by precipitation with neutral lead acetate. The
sensitiveness of the test depends on the construction of the instru-
ment, but even the best polarimeters do not show traces of sugar,
for which reason it is generally useless to apply the test unless sugar
has been indicated bv other tests.

URINE AND ITS CONSTITUENTS.

733

The following table shows the tests for distinguishing dextrose
from other reducing agents occurring in the urine :

Fehling's test.

Bismuth test.

Fermenta-
tion test.

I'hfiivl-hv- Polarisropic
drazine test. test.

Dextrose .

Reduction

Reduction

Positive

Positive

f Dextro-

\ rotatory

Pentoses .

Reduction

Reduction

Negative

Positive

( Dextro-
\ rotatory

Lactose

Reduction

Reduction

Negative

Positive

f Dextro-
1 rotatory

Laevulose .

Reduction

Reduction

Positive

Positive

f Lsevo-

(partial)

\ rotatory

!Laevo-ro-

Glycuronic acid

Reduction

Reduction

Negative

Positive

tatoryin

urine

Alkaptonic acids
Uric acid .
Creatinine
Pyrocatechin

Reduction
Reduction
Reduction
Reduction

Negative
Negative
Negative
Negative

Negative
Negative
Negative
Negative

Negative
Negative
Negative
Negative

Inactive
Inactive
Inactive
Inactive

Allantoin .

Reduction

Negative

Negative

Negative

Inactive

Quantitative estimation of sugar. By far the best method is
the decomposition of a copper solution of a known strength, and
Fehling's solution prepared as stated above, answers this purpose
well.

1000 c.c. of Fehling's solution, containing 34.64 grammes of crys-
tallized cupric sulphate, CuSO4.5H2O, are decomposed by 5 grammes
of grape-sugar, or 1 c.c. of solution by 0.005 of grape-sugar.

To make the quantitative determination, operate as follows : 10 c.c.
of Fehling's solution are poured into a porcelain dish of about 200 c.c.
capacity, placed over a flame. The copper solution is diluted with
about 40 c.c. of water, and heated to boiling ; to the boiling liquid,
urine (which has been previously diluted with 9 parts of water) is
added from a burette very gradually, until the blue color of the solu-
tion has disappeared, and there remains, upon subsidence of the
cuprous oxide, an almost colorless, clear liquid. A filtered portion
of this liquid, acidified with hydrochloric acid, should not give a
reddish-brown precipitate with potassium ferrocyanide (a precipitate
would show that all copper had not been precipitated, and that more
urine was needed), while a second portion of the filtered fluid should
not produce a red precipitate on boiling with a few drops of Fehling's
solution (a precipitate would indicate that too much urine had been
added, in which case the operation has to be repeated).

The calculation of the amount of sugar present is easily made.
10 c.c. of Fehling's solution are decomposed by 0.05 gramme of
sugar ; this quantity must, therefore, be contained in the number of

734 PHYSIOLOGICAL CHEMISTRY.

c.c. of urine used. Suppose 30 c.c. of urine, diluted with 9 parts of
water, or 3 c.c. of pure urine, have been required to decompose the 10
c.c. of Fehling's solution, then 3 c c. of urine contain of grape-sugar
0.05 gramme, or 100 c.c. of urine 1.666 grammes, according to the
proportion :

3 : 0.05 : : 100 : x

1 = 1.666.

If the urine contains but very little sugar, it may be used directly
without diluting it, or instead of diluting it with 9 parts of water, it
may be diluted with 4 volumes or with an equal volume of water.

In using Fehling's solution for the volumetric estimation of lactose,
it should be remembered that 1 c.c. of solution is decomposed by
0.0067 gramme of lactose.

Modified Fehling method (Rudisch and Celler). The only change is
in diluting the 10 c.c. of Fehling solution with 40 c.c. of 50 per
cent, potassium stilphocyanate instead of with 40 c.c. of water. The
end-reaction here is the same, i. e., the disappearance of the blue. As
there is no precipitate to obscure the end-point, the estimation is
readily made and the method is an improvement over the original
procedure. As the same amount of Fehling's solution is used, the
calculation is carried out in the same way.

Harvey G. Beck has devised the following method :

The apparatus used consists of a suitable beaker ; four centrifugal tubes
graduated at 2 c.c. ; a pipette of 2 c.c. capacity, graduated into twentieths c.c.,
and a wire tube-holder to support the tubes when placed in the beaker. A
centrifuge will greatly facilitate the work.

The procedure is as follows : The beaker, one-third full of water, is placed
over a.Bunseu flame, and the four centrifugal tubes, after being filled to the
graduation mark (2 c.c.) with standard Fehling's solution, are placed in the
tube-holder and suspended in the beaker. The tubes are numbered respectively
1, 2, 3, and 4, according to their position in the tube-holder. The urine is added
from the pipette in quantities of twentieths c.c., as follows: fa to No. 1, -fa to
No. 2, fa to No. 3, and -fa to No. 4. The tubes, after being thoroughly shaken,
are suspended in boiling water for at least three minutes, when they are removed
and either set aside in the tube-stand until the cupric oxide is precipitated, or
centrifugalized in order to hasten precipitation. If all the tubes still show a
blue color, the urine is increased to ^, -fa, $%, and fa respectively, by adding
•fa e.c. to each tube, and the foregoing steps are repeated. This process is con-
tinued until one, or more, of the tubes is completely decolorized. The first tube
in the series in which the blue color has entirely disappeared is noted; the
number of twentieths c.c. required to reduce it, divided into twenty, gives the
percentage of sugar present.

Estimation by fermentation can be readily done, using specially
graduated tubes, which can be read directly in percentages of dextrose.

URINE AND ITS CONSTITUENTS. 735

Estimation by means of the polariscope furnishes the quickest method ;
the details cannot be given here.

Other carbohydrates in urine. Laevulose is rarely present in the
urine; in almost all of the cases dextrose is also presen t(diabetes).
Laevulosuria should be suspected when a urine reduces copper solu-
tions, rotates polarized light to the left or not at all, and shows no
Ia3vorotation after being fermented.

Lsevulose reduces copper and bismuth solutions, ferments with
yeast, is laevorotatory, and forms the same osazone with phenyl-
hydrazine as is formed by dextrose.

Maltose is very rarely present in urine. Such urines show a
higher percentage of sugar with the polariscope than with Fehling's
solution.

Lactose occurs in the urine of lactating women, and occasionally
in the urine of persons on an exclusive milk diet. It gives a delayed
and incomplete Fehling test, reduces Nylander's solution, does not
ferment with yeast, rotates polarized light to the right. While it
forms a yellow osazone with phenyl-hydrazine, the amount present in
the urine is rarely sufficient to give a positive test.

Pentoses, C5H10O5, occur in many fruits and vegetables as complex
carbohydrates, known as pentosanes. When taken into the body the
pentosanes are split and pentose is excreted in the urine. Consid-
erable pentose is found in the urine of persons addicted to the use
of morphine. Pentoses owe their chief importance to the similarity
of their reactions to those of glucose. Normally, the quantity of
pentose in the urine is not such as to interfere with the reactions for
sugar.

Pentoses reduce Fehling's and bismuth solutions ; they are dextrorotatory ;
with phenyl-hydrazine they form a crystalline compound, melting between
153° and 158° C. (307° and 317° F.). Pentoses do not ferment with yeast, and
are characterized by responding to Tollen's orcin reaction. This is made by
adding 3 c.c. of a saturated solution of orcin in hydrochloric acid to 5 c.c. of
urine previously decolorized with boneblack. In the presence of pentose a
green color develops on heating, beginning at the top and gradually extending
through the mixture.

Glycuronic acid, CHO.(CHOH)4.CO2H. Glycuronic acid occurs
in normal urine in minute amount. It is an oxidation product of
glucose, and is usually present in the form of the conjugated glycu-
ronates, i. e., glycuronic acid linked to aromatic bodies (phenol, cresol,
etc.). It is increased after the taking of camphor, chloral, menthol,
and other substances, which produce aromatic substances in the urine

736 PHYSIOLOGICAL CHEMISTRY.

to which the glycuronic acid is linked. The amount usually present
is not sufficient to reduce Fehling's solution, unless the boiling is con-
tinued for a long time. The conjugate glycuronates are Isevorotatory.

Glycuronic acid reduces Fehling's and bismuth solutions, forms an osazone
melting at 115° C. (239° F.), does not ferment with yeast, and is dextrorotatory.
5 c.c. of urine containing glycuronic acid when decolorized with boneblack,
mixed with an equal volume of hydrochloric acid and 0.025 phloroglucin, de-
velops a deep-red color on heating. (This reaction is also shown by pentoses ;
glycilronic acid does not give the orcin reaction.)

Acetone, diacetic and /3-oxy-butyric acids. These substances,
commonly called the " acetone bodies/' are believed to be due to an
abnormal metabolism of fat, though the protein metabolism may also
be concerned. As can be seen from the following reactions acetone
is derived from diacetic acid, and diacetic acid from /9-oxy -butyric
acid :

CH3CH(OH).CH2.COOH + O = CH3.CO.CH2COOH + H2O
/3-oxy-butyric acid. Diacetic acid.

CH3.CO.CH3.COOH = CH3.CO.CH3 -f CO2
Acetone.

As oxy-butyric acid and diacetic acid are unstable, acetone is the
first of these bodies to appear in the urine, and it is only as the
pathological conditions increase that diacetic and finally oxy-butyric
acid are found. Acetone is, indeed, normally present in minute
amounts, and is always increased in the presence of the other two.
As these bodies have the same origin, their presence has the same sig-
nificance, the higher members showing merely a graver aspect.

They are increased, in many conditions : with a carbohydrate-free
diet, in any cachectic condition, in many types of fever. They are
markedly increased in diabetes.

The more severe cases of acetonuria are also referred to as acido-
sis (acid intoxication). The term emphasizes, of course, not the acid
excreted in the urine, but the acid remaining in the system. In
order to neutralize this abnormal acidity without using the fixed
alkali of the body the organism converts less nitrogen into urea
than is normally done, and uses it as an alkali in the form of ammonia.
Thus the proportion of the urinary nitrogen in the form of ammonia
is increased in acidosis, becoming even 40 per cent., the normal being
5 or 6 per cent. This percentage is the best index of the severity of
the condition.

Acidosis is most common in diabetes and pernicious vomiting of
pregnancy, and indicates the danger of coma.

URINE AND ITS CONSTITUENTS. 737

Legal's test for acetone. To 25 c.c. of urine add an equal volume of a strong,
freshly-made solution of sodium nitroprusside, and then a few drops of sodium
hydroxide solution. In the presence of acetone a red color develops, which, on
addition of an excess of acetic acid, becomes darker red. (Compare WeyPs
reaction for creatinine.)

Acetone may also be recognized in the following manner : 500 c.c. of urine
are acidified with a few drops of hydrochloric acid and distilled. To the dis-
tillate a few drops of iodine solution (1 iodine, 2 potassium iodide, 100 water)
and of potassium hydroxide are added. If acetone is present, a characteristic
yellowish- white precipitate of iodoform is formed.

Diacetic acid is recognized by adding to the urine drop by drop a
fairly strong solution of ferric chloride, filtering off any precipitate
of phosphate, and adding more ferric chloride, when in the presence
of diacetic acid a deep-red color is produced, which disappears on
boiling. The test should also be made with an ethereal extract, ob-
tained by shaking urine previously acidified with sulphuric acid with
ether ; the ferric chloride solution, on being agitated with the ethereal
extract, becomes red. (As salicylic acid and a number of other sub-
stances give a red or violet color with ferric chloride, care must be
taken not to confound diacetic acid with these substances.)

The detection of /3-oxy-butyric acid is difficult, and is rarely done
in clinical work. Its presence is probable when urine, after being
fermented, still contains a tavorotatory body.

Bile may be present in the urine in any case of jaundice.

Detection of bile-pigment. The presence of bile in urine is gen-
erally indicated by a decided color, which varies from a deep brown-
ish-red to a dark brown ; the foam of such urine (produced by shak-
ing) has a distinct yellow color, and a piece of filtering-paper or a
piece of linen dipped into the urine assumes a yellow color, which
does not disappear on drying.

The further detection of bile depends upon the reactions of the
biliary coloring-matters or biliary acids.

Tests for bile.

1. Gmelin's test for biliary coloring-matters has been considered,
and may be applied to urine either by allowing a small quantity
of nitric acid, containing some nitrous acid, to flow down the sides
of a test-tube (containing the urine) in such a manner that the two
fluids do not mix, or by placing upon a porcelain plate a few drops
of the urine, near it a few drops of nitric acid, to which one drop of
sulphuric acid has been added, and allowing the two liquids to ap-
proach gradually. In both cases (if bile-pigment is present) a play of

47

738 PHYSIOLOGICAL CHEMISTRY.

color is seen at the point of union between the two fluids, the colors
changing from green to blue, violet-red, and yellow or yellowish-
green. While the appearance of the green at the beginning is indis-
pensable to prove the presence of bile, the presence of all the other
colors is not essential. (Plate VIII., 7.)

The above test may be made in a somewhat modified form by mix-
ing the urine with a concentrated solution of sodium nitrate, and
pouring down the sides of the test-tube concentrated sulphuric acid in
such a manner as to form two distinct layers ; the colors are seen at
the point of contact as above.

If the urine be very dark in color, it should be diluted with water
before applying the above tests.

2. Add a few drops of sodium carbonate solution to the urine until
it has a distinct alkaline reaction, then add calcium chloride and
shake well. The precipitated calcium carbonate carries down the
pigments and leaves the urine nearly colorless or of its normal color.
Collect the precipitate on a filter, wash, and transfer it with alcohol
to a test-tube. Dissolve by the addition of hydrochloric acid and
boil the clear solution, when it turns green. Allow to cool and add
nitric acid, when the green solution turns blue, violet, and red.
(This test may show the presence of biliary coloring-matters when
Gmelin's test fails to do so, and is recommended when the urine con-
tains a large amount of indican.)

While bile acids are always present with bile-pigment in urine,
their demonstration is usually difficult.

Pettenkofer's test for biliary acids is made by dissolving a few
grains of cane-sugar in urine contained in a test-tube, and allowing
concentrated sulphuric acid to trickle down the side of the inclined
test-tube ; a purple band is seen at the upper margin of the acid, and
on slightly shaking the liquid becomes at first turbid, then clear, and
almost simultaneously it turns yellow, then pale cherry-red, dark
carmine-red, and finally a beautiful purple violet. The temperature
must not be allowed to rise much above 38° C. (100° F.).

As many substances (other than biliary acids) show a similar
reaction, it is often necessary to separate the bile acids by the process
described in connection with the consideration of bile itself.

In case the quantity of biliary constituents is so small that they
cannot be noticed by the tests mentioned, the urine should be shaken
with about one-fourth of its volume of chloroform, which dissolves
the biliary matters. Some of this solution is dropped upon blotting
paper, and after evaporation a drop of red fuming nitric acid is

PHYSIOLOGICAL REACTIONS.

PLATE VIII.

Xanthoproteic Reaction.

Biuret Reaction. Most albumins sho^
the color on the left, peptones that on th<
right.

Indican Reaction.

Murexid Test for uric acid.

Fehling's Test for sugar.

6

Botger's bismuth Test for sugar.

Gmelin's Test for biliary colorin
matters.

8

Diazo Reaction.

Affoen&Ca Litti Bultiinorf, ,\td.

For explanation of reactions see page in Index.

URINE AND ITS CONSTITUENTS. 739

placed in the centre of the remaining stain, when concentric color
rings appear. The second portion of chloroform solution is evap-
orated and the residue used for making the reactions, as described
above.

Melanin (melanogen), the black pigment of the skin of the negro, has been
found in the urine of persons suffering from melanotic cancer and certain wast-
ing diseases. Urine containing melanin darkens on standing, turns black on
the addition of either nitric or chromic acid, and forms with bromine-water a
yellow precipitate rapidly turning dark.

Alkaptonic acids. Two of these acids occur in the urine of certain
otherwise healthy persons, and seem to be without clinical signifi-
cance. The acids are : Jiomogentisic acid, dioxphenyl-acetic acid,
C6H3(OH)2.CH2.CO2H, and uroleucic acid, dioxyphenyl-lactic acid,
CGH3(OH)2.C2H3.OH.C02H.

Both acids reduce Fehling's solution, as also ammoniacal silver nitrate solu-
tion, but not bismuth solution ; they are optically inactive, do not form an
osazone, and do not ferment with yeast.

To test for alkaptonic acids, the urine should be acidified with hydrochloric
acid and then extracted with ether. The ethereal solution is evaporated, the
residue dissolved in water, and heated with Millon's reagent. In the presence
of alkaptonic acids a purple-red color is observed.

Diazo-reaction. Some abnormal constituent (which has not yet
been isolated) is found in the urine of certain diseases. The presence
of this unknown substance is indicated by a very characteristic reac-
tion with diazo-benzene-sulphonic acid, which compound is produced
by the action of nitrous acid on sulphanilic acid. Two solutions are
required : a. 5 grammes of sulphanilic acid dissolved in a mixture
of 50 c.c. of hydrochloric acid and 1000 c.c. of water; 6. a 0.5
per cent, solution of sodium nitrite. To perform the reaction 50
parts of a and 1 part of b are mixed, and equal volumes of the reagent
and of urine are mixed in a test-tube and saturated with ammonia.
In those cases in which the reaction is positive the solution assumes
a carmine-red color, which, on shaking, must also be visible in the
foam. If the test-tube is allowed to stand twenty-four hours, a
greenish precipitate is formed. Normal urine, thus treated, shows a
deep-yellow or orange to orange-red color; the precipitated phos-
phates as well as the foam are colorless. On Plate VIII., 8, the
color of the diazo-reaction is represented. Normal urine may show
the orange-red on the left, but the carmine-red on the right is char-
acteristic of the diazo-reaction.

If, instead of mixing the urine and reagent with ammonia water,

740 PHYSIOLOGICAL CHEMISTRY.

the latter be allowed to float on the mixture, a carmine-red ring will
form at the zone of contact, when the reaction is positive.

It was formerly held that this test is pathognomonic of typhoid
fever. Later work has, however, shown that it usually is present in
typhoid fever and measles ; it is frequently present in erysipelas,
pneumonia, scarlet fever, diphtheria, and pulmonary tuberculosis ; it
is rarely present in acute rheumatic fever and cerebrospinal men-
ingitis.

It is, however, of much value in the diagnosis of typhoid fever, and
is thought to indicate a bad prognosis in pulmonary tuberculosis.

Functional tests of the kidney. Many attempts have been made
to find a substance which, when injected into the body, would be
excreted by the kidney in such a manner that examination of the
urine would show the ability of the kidneys to carry on their func-
tion of excretion. Among the substances tried are methylene-blue,
salicylic acid, and phloridzin. By far the most suitable substance
has recently been found in phenolsulphonephthalein (Geraghty-
Rowntree). This substance has no poisonous action, and is excreted
very rapidly by normal kidneys. It produces a red color in alkaline
solution, and its amount may thus be readily estimated by noting the
extent to which a standard solution must be diluted to produce the
same depth of color. It is somewhat more accurate to use a special
instrument, a colorimeter. After the injection of this drug (0.006
gramme) the unchanged drug will, under normal conditions, appear
in the urine in from five to eleven minutes, 50 per cent, is excreted
during the first hour, and from 60 to 80 per cent, during the first and
second hour together.

In diseases of the kidneys the initial appearance is delayed and the
hourly output is decreased.

Urinary deposits (sediments). Normal urine is always clear, but
occasionally, and particularly in abnormal conditions, it is turbid.

Urine may be turbid when passed, and this indicates an excess
of mucus, or the presence of renal epithelium, pus, blood, chyle,
semen, bile, fat-globules, or phosphates or urate of sodium in excess,
etc. A turbidity subsequent to the passage of the urine is generally
due to the precipitation of phosphates or urates, or it may result
from fermentation or decomposition. Either of the substances named
will form a deposit on standing.

When such a deposit is to be examined, a few ounces of the urine
should be set aside for several hours in a tall, narrow, cylindrical

URINE AND ITS CONSTITUENTS.

741

glass or whirled in the centrifuge for a few minutes ; when the
sediment has collected at the bottom the supernatant urine may !><>
decanted, or the sediment may be taken out by means of a pipette
for examination.

Sediments are either organized or unorganized. To the first
belong: mucus, blood, pus, fat, urinary casts, epithelium, sprrmato-
zoids, fungi, infusoria, etc. ; to the second belong : uric acid, urates,
calcium oxalate, phosphate, or carbonate, magnesium-ammonium
phosphate, cystine, hippuric acid, etc.

The chemical examination of any urinary sediment should always
be preceded by a microscopical examination, which latter is in many

FIG. 76.

Various forms of uric acid crystals. (Finlayson.)

cases the only way of determining the nature of the sediment, espe-
cially of the organized substances.

Organized sediments. Red blood-corpuscles appear under the
microscope as reddish, circular disks, sometimes laid together in
strings. If seen in profile, they appear biconcave.

Pus cells (leucocytes) appear as round granular cells, in which the
nucleus frequently is not made out until dilute acetic acid is added.

Epithelial cells, from the urinary tubules, ureter, bladder, vagina,
etc. Their place of origin is frequently difficult to determine.

Casts. Hyaline, waxy, finely granular, coarsely granular, pus
casts, blood casts, epithelial casts.

Unorganized sediments, (a) In acid urine. Uric acid is deposited
in colored crystals from acid urine ; it is not dissolved by heat, nor

742

PHYSIOLOGICAL CHEMISTRY.

by acetic or hydrochloric acid, but dissolves on the addition of caustic
potash and burns on platinum foil without leaving a residue ; it is
recognized by the murexide test. Uric acid crystallizes in many forms,
usually in rhombs with rounded corners, the so-called "whetstone
crystals." The crystals are usually brow7n. The sediment has a

FIG. 77.

Calcium oxalate crystals. (Finlayson.)

red crystalline appearance (" brick-dust "), and occurs in any concen-
trated, strongly acid urine.

Add urates (Na, K) form a voluminous sediment, amorphous under
the microscope, of a yellowish-brown or reddish color. This is the only
sediment which dissolves on heating.

FIG. 78.

Crystalline phosphates. (Finlayson.)

Calcium oxalate is rarely found in more than microscopic amounts.
The crystals are peculiarly clear, and have a double envelope, or
sometimes a dumb-bell appearance.

Magnesium-ammonium phosphate, or triple phosphate, MgNH4.-
PO4.6H2O, is found generally in triangular prisms with bevelled.

URINE AND ITU CONSTITUENTS.

743

ends, but sometimes also in star-shaped, feathery crystals, due to the
partial dissolving of the first type. These crystals are most abundant
in alkaline urine, but are also present in faintly acid urines. They
dissolve in acetic acid.

(b) In alkaline urine. Ammonium-magnesium phosphate (vide supra).

FIG. 79.

Ammonium urate crystals. (C. E. Simon.)

Calcium and magnesium phosphates. These are basic phosphates.
They form the commonest sediment in alkaline urine, are amorphous,
dissolve with acetic acid, but not with heat.

FIG. 80.

y-©

Crystals of leucine (different forms). (Crystals of creatinine-zinc chloride resemble the
leucine crystals depicted at a.) The crystals figured to the right consist of comparativelj
impure leucine. (Charles.)

(c) In ammoniacal urine. Ammonium-magnesium phosphate (vide

supra).

Ammonium urate is found, generally associated with amorphous or
crystalline phosphates, in urine which has become ammoniacal.
crystalline globules are generally covered with spinous excrescences,
which give them the characteristic "thorn-apple" appearance, and
have a yellow color. They are soluble in acetic acid.

744

PHYSIOLOGICAL CHEMISTRY.

The following crystals occur only in abnormal urines :
Leucine, or amino-caproic acid, C6Hn(XH2)O2, and Tyrosine,
C9HUNO3, are but rarely met with in urinary deposits. Leucine is
found either as rounded lumps, showing but little crystalline structure,

FIG. 81.

Tyrosine crystals. (Charles.)

or as spherical masses, exhibiting fine radial striation. Tyrosine
appears generally in fine, long, silky needles, forming bundles or
rosettes.

Cystine occurs occasionally as a grayish, crystalline deposit, form-

FIG. 82.

Crystals of cystine spontaneously voided with urine. (Roberts.)

ing transparent six-sided plates ; it also occurs in calculi. The latter
may be recognized by the chemical properties mentioned below, or by
dissolving a little in hydrochloric acid and neutralizing with ammonia,
when cystine is reprecipitated and shows the characteristic six-sided
plates under the microscope.

URINE AND ITS CONSTITUENTS. 745

Urinary calculi are solid deposits of various sizes formed from
the urine within the kidney, ureter, bladder, and urethra. They
may contain all the constituents of urine which occur as sediments,
and also certain pathological constituents deposited around an organic
framework.

Calculi are cal led primary when formed in unchanged urine, and secondary
when they are formed in urine which has undergone decomposition. Uric
acid, calcium oxalate, calcium carbonate, xanthine, and cystic calculi are
primary formations, while ammonium urate, phosphatic and urostealith calculi
3,re secondary.

During the development of a calculus the original deposit may be covered
by a layer of a different material, which in turn may be covered by another
substance. For this reason a simple stone may be converted into a compound
one. In this way a primary stone, by irritation of the bladder producing
cystitis, accompanied by alkaline fermentation, causes a deposition of phos-
phates, and is converted into a secondary calculus. The further action of the
alkaline urine may dissolve the primary calculus, replacing it with phosphates.

In examining calculi it is necessary to make a section through the
centre of the calculus and scrape off a little from each layer, the
portions being examined separately. They may be found to be alike
(simple calculi) or unlike (compound or mixed calculi) in composi-
tion. The following scheme serves for a qualitative examination of
calculi. Heat some of the powdered calculus on platinum foil, when
the material will either burn and char without a flame (A), or burn
with a flame (B), or will not burn at all (C). (It should be remem-
bered that a calculus generally contains a little organic matter, so that
slight carbonization is always to be expected on heating it.)

A. To the material burning without a distinct flame apply the
murexide test. If affirmative, uric acid or urates are indicated.
Heat some powder with potassium hydroxide; a strong odor of
ammonia proves the calculus to consist of ammonium urate; a nega-
tive result shows it to be uric acid. If the murexide test was nega-
tive, test for xanthine. The powder wall dissolve in nitric acid
without effervescence, leave on evaporation a yellow residue, turning
orange with alkali and red on heating.

B. Material burning with a distinct flame may either be soluble
in alcohol and ether (urostealith) or insoluble in these solvents, but
soluble in potassium hydroxide solution on heating (fibrin), or soluble
both in hydrochloric acid and in caustic alkalies (cystine). Urostea-
lith burns with a yellow flame and emits the odor of burning resin.
Fibrin burns also with a yellow flame, but emits odor of burnt
feathers. Cystine burns with a pale-blue flame, emitting a peculiar

746 PHYSTOLOGICAL CHEMISTRY.

sharp odor. On evaporation of its solution in ammonia it separates
in characteristic six-sided plates.

C. Material which does not burn may consist of calcium car-
bonate, calcium oxalate, or phosphates. Calcium carbonate shows
effervescence with all acids, and the solution, after being neutralized,
is precipitated by ammonium oxalate. Calcium oxalate does not
effervesce with hydrochloric acid directly, but does so after being
heated, when carbonate is formed and is tested for as such. The
presence of phosphates is indicated by the presence of a yellow pre-
cipitate, produced in the solution in nitric acid by ammonium molyb-
date. When the phosphates, on heating with caustic potash, evolve
ammonia gas, magnesium ammonium phosphate is present ; when the
test is negative the calculus consists of calcium phosphate, which can
be verified by dissolving the powder in hydrochloric acid, neutral-
izing with ammonia, redissolving the precipitate in acetic acid, and
adding ammonium oxalate, when a white precipitate is formed.

Most common are calculi of uric acid ; often met with are those of
urates, phosphates, and oxalates ; rarely, however, those of xanthine,
cystine, fibrin, and urostealith.

QUESTIONS. — What is urine, where and by what process is it formed in the
animal body, and what is its function? Mention the general physical and
chemical properties of urine. Give the composition of human urine, and state
by what conditions the composition is influenced. State the composition and
properties of urea. By what process is urea formed in the animal body, and
how can it be obtained artificially ? Describe a process by which urea may be
estimated quantitatively in urine. In what forms is uric acid found in urine,
and what are its properties? Describe the murexide test. How can uric acid
be determined quantitatively in urine? What is hippuric acid, and by what
tests may it be recognized ? What points are to be considered, and what sub-
stances determined, in the analysis of normal and abnormal urine? What is
the color of urine, and what are the chief causes influencing the color ? What
is the specific gravity of healthy urine, how is it determined, and how is the
total amount of solids approximately calculated from the specific gravity?
Describe the different tests by which albumin may be recognized, and state the
precautions necessary in making these tests. How may the quantity of al-
bumin in urine be determined approximately, and also accurately? Describe
the various tests for sugar. On what principles are they based, and how can
sugar be distinguished from other reducing substances occurring in urine?
How is sugar determined quantitatively ? By what tests are biliary pigments
and acids recognized in urine? What is the nature of urinary sediments, and
by what means are they recognized? What are urinary calculi generally com-
posed of, and by what simple tests can their nature be determined?

APPENDIX.

TABLE OF WEIGHTS AND MEASURES.

Measures of length.

1

millimeter

=

0.001

meter

= 0.0393/

1

centimeter

—

0.01

meter

= 0.3937

1 decimeter —

0.1

meter

= 3.937

1

meter

= 39.37

1

decameter

=

10

meters

= 32.8083

1

hectometer

=

100

meters

= 328.083

1

kilometer

r=r

1000

meters

= 0.6213'

1

1

yard or 36
inch

inches

= 0.9144
= 25.4

inch.

inches.

inches.

feet.

feet.

mile.

meter.

millimeters.

1 milliliter
1 centiliter
1 deciliter
1 liter
1 decaliter
1 hectoliter
1 kiloliter
1 U. S. gallon
1 imperial gallon
1 minim
1 fluidrachm
1 fluidounce
1 liter

Measures of capacity.

1 c.c. == 0.001 liter =

10 c.c. =• 0.01 liter =

100 c.c. = 0.1 liter =
1000c.c.

= 10 liters =

= 100 liters =

= 1000 liters =

0.0021
0.0211
0.2113
1.0567
2.6417
26.417
264.17
3785.43
4543.5
0.06
3.70
29.57
33.81

U. S. pint.

U. S. pint

U. S pint.

U. 8. quart.

U. S. gallons.

U. S. gallons.

U. S. gallons.

c.c.

c.c.

c.c.

c.c.

c.c.

fluidounces.

Weights.

1 milligram

=

0.001

gramme

1 centigram

=

0.01

gramme

1 decigram

=

01

gramme

1 gramme

1 decagram

=

10

grammes

1 hectogram

=

100

grammes

1 kilogram

=.

1000

grammes

1 kilogram

1 grain Troy

1 drachm Troy

1 ounce Troy

1 ounce avoirdupois

1 pound avoirdupois

0.015 grain

0.154 grain

1.543 grain

15.432 grains

154.324 grains

0.268 pound Troy.
2.679 pounds Troy.
2.2046 pounds avoirdupois.
0.0648 gramme.
3.888 grammes.
31.103 grammes.
28.350 grammes.
453.592 grammes.

(747)

748 APPENDIX.

Commercial weights and measures of the U. £ A.

1 pound avoirdupois = 16 ounces.

1 ounce = 437.5 grains.

1 gallon = 231 cubic inches.

1 gallon = 4 quarts = 8 pints.

1 pint of water weighs 7291.2 grains at a temperature of 15.6°.

Apothecarie^ weights.

The apothecaries' ounce is of the same value as the now obsolete English Troy
ounce.

1 ounce 8 drachms 480 grains.

1 drachm 3 scruples 60 grains.

1 scruple 20 grains.

1 ounce 31.103 grammes.

1 grain 64.799 milligrams.

Apothecaries' fluid measures.

These are derived from the U. S. gallon ; the liquid pint of this gallon is identical
in value with the apothecaries' pint.

1 pint 16 fluidounces 7680 minims.

1 fluidounce = 8 fluidrachms 480 minims.

1 fluidrachm 60 minims.

Jewelers' weight.
1 carat = 0.205 gramme 3.163 grains.

TABLE OF ELEMENTS AND ATOMIC WEIGHTS.

On the basis H^= 1 (U. S. P., VIII.) and O = 16 (International \\Vights, 1912).

Name.

Atomic weights.
Symbol. H==1 Q==16

Name. Symbol

Atomic weights.
H = 1 0 = 16

Aluminum

. . Al

26.9

27.1

Neodymium . .

.Nd

142.5

144.3

Antimony . .

. . Sb

119.3

120.2

Neon

. Ne

19.9

20.2

Argon . . .

A

39.6

39.88

Nickel

Ni

58.3

58.68

Arsenic . . .

. . As

74.4

74.96

Nitrogen . . .

.N

13.93

14.07

Barium .

Ba

136.4

137.37

Osmium

Os

189.6

ion q

Bismuth . .

. . Bi

206.9

208

Oxygen ....

.O

15.88

1 *7U. »7

16

Boron

B

10.9

]1

"P?i 1 1 Q f\ i n m

Pd

10^ 7

lOfi 7

Bromine . .

. . Br

79.36

79.92

i .1 1 i.u 1 1 1 in i

Phosphorus . .

• JTil

. P

J.UO. t

30.77

-lUv). /

31.04

Cadmium . .

. . Cd

111.6

112.4

Platinum . . .

.Pt

193.3

195.2

Caesium . . .

. . Cs

131.9

132.81

Potassium . . .

. K

38.86

39.1

Calcium . .

. . Ca

39.8

40.07

Praseodymium3

. Pr

139.4

143.6

Carbon . . .

. . C

11.91

12

Radium ....

. Ra

223

226.4

Cerium . . .

. . Ce

139.2

140.25

Rhodium . . .

.Rh

102.2

102.9

Chlorine . .

. . Cl

35.18

35.46

Rubidium . . .

.Kb

84.8

85.45

Chromium

. . Cr

51.7

52

Ruthenium . .

.Ru

100.9

101.7

Cobalt . . .

. . Co

58.56

58.97

Samarium . . .

.Sm

148.9

150.4

Columbium1 .

. . Cb

93.3

93.5

Scandium . . .

.80

43.8

44.1

Copper . . .

. . Cu

63.1

63.57

Selenium . . .

. 8e

78.6

79.2

Erbium

Er

164.8

167.7

Silicon ....

. Si

28.2

28.3

J; luorine

F

18.9

19

Silver

As

107.12

107.88

Gadolinium

• • 17

. . Gd

155.8

157.3

Sodium ....

' -"o

.Na

22.88

23

Gallium . .

. . Ga

69.5

69.9

Strontium . . .

.Sr

86.94

87.63

Germanium .

. - Ge

71.9

72.5

Sulphur ....

.S

31.83

32.07

Glucinum2 .

. . Gl

9.03

9.1

Tantalum . . .

. Ta

181.6

181.5

Gold ....

. . Au

195.7

197.2

Tellurium . . .

.Te

126.6

127.5

Helium - . .

. .He

3.99

3.99

Terbium . . .

.Tb

158.8

159.2

Hydrogen . .

. . H

1.00

1.008

Thallium . . .

. Tl

202.6

204

Indium . . .

. . In

113.1

114.8

Thorium . . .

. Th

230.8

232.4

Iodine

I

125.9

126.92

Thulium . .

.Tm

169.7

168.5

Iridium .

Tr

mK

1Q<J 1

Tin

. Sn

118.1

119

Iron ....

. ir
. . Fe

.O

55.5

-L«/O. i.

55.84

Titanium . . .

.Ti

47.7

48.1

Krypton . .

. . Kr

81.2

82.92

Tungsten . . .

. W

182.6

184

Lanthanum .

. . La

137.9

139

Uranium . . .

.U

236.7

238.5

Lead ....

. . Pb

205.35

207.1 Vanadium .

. V

50.8

51

Lithium . . .

. . Li

6.98

6.94 Xenon .

. Xe

127

130.2

Magnesium .

• • Mg

24.18

24.32

Ytterbium . .

. Yb

171.7

172

Manganese

. Mn

54.6

54.93

Yttrium ....

. Yt

88.3

89

Mercury . .

Hg

198.5

200.6

Zinc

. Zn

64.9

65.87

Molybdenum

. . Mo

95.3

96

Zirconium . . .

. Zr

89.9

90.6

1 Also called Niobium,

Nb. 2 Also called Beryllium, Be. 3 Also called Didymium, Di.

749

INDEX.

A.

ABSOLUTE temperature, 47

weight, 32

zero, 48
Absorption, 676, 687, 689

by charcoal, 39

by liquids, 39

by solids, 40

spectra, 61
Acacia, 536
Accumulator, 320
Acetanilide, 565
Acetates, 503
Acetic aldehyde, 491

anhydride, 505

ether, 522
Acetone, 494

in urine, 736
Aceto-nitrile, 555
Acetoximes, 541
Acetphenetidin, 572
Acetyl chloride, 505

oxide, 505
Acetylene, 473
Acid, abietic, 599

acetic, 500

glacial, 501

mono-, di-, and trichlor-, 504

acetyl-salicylic, 584

acrylic, 494

amino-acetic, 544

ammo-formic, 545

amino-succinamic, 543, 546

amino-succinic, 543

anisic, 585

arabic, 536

arsenic, 349

arsenous, 348

aspartic, 546

barbituric, 547

benzoic, 579, 701

beta-oxybutyric, 736

boric or boracic, 187, 701

bromic, 240

butyric, 505

cacodylic, 478

camphoric, 599

carbamic, 269, 545

carbazotic, 572

carbolic, 569

carbonic, 180

chloric, 237

Acid, chlorpplatinic, 235, 367
chromic, 308
citric, 516
cyanic, 553
diacetic, 736
dichromic, 308
digallic, 586
disulphuric, 212
ethyl-sulphuric, 521
formic, 500
fulminic, 541
galactonic, 532
gallic, 586
glacial acetic, 501

phosphoric, 226
gluconic, 531

glycerin-phosphoric, 448, 670
glycocholic, 685
glycolic, 511
glycuronic, 735
hippuric, 717
homogentisic, 739
hydrazoic, 170
hydriodic, 242
hydrobromic, 239
hydrochloric, 232
hydrocyanic, 548
hydroferricyanic, 554
hydroferrocyanic, 554
hydrofluoric, 244
hydrofluosilicic, 186
hydroxy-acetic, 511
hydroxy-propionic, 511
hypobromous, 240
hypochlorous, 236
hyponitrous, 173
hypophosphorous, 223
hyposulphurous, 213
indoxyl-sulphuric, 721
iodic, 243
lactic, 511
malic, 512
malonic, 508
manganic, 303
meconic, 615
metaboric, 187
metaphosphoric, 226
met-arsenic, 349
met-arsenous, 348
meta-stannic, 363
molybdic, 368
mucic, 532
muriatic, 232

751

752

INDEX.

Acid, myronic, 556
naphthionic, 590
naphthylamine sulphonic, 590
nicotinic, 593
nitric, 174

ionic explanation of liberation

of, 195

nitro-hydrochloric, 235
nitro-muriatic, 235
nitrosyl-sulphuric, 209
nitrous, 173

estimation by metaphenylene-

diamine, 432
oleic, 506
oxalic, 508
palmitic, 506
parabanic, 547
perchloric, 238
perchromic, 310
permanganic, 303, 305
persulphuric, 214
phenolsulphonic, 573
phosphocarnic, 668
phospho-molybdic, 601
phosphoric, 226
phosphorous, 225
phthalic, 581
picric, 572
prussic, 548
pyrogallic, 576
pyrophosphoric, 226
pyrosulphuric, 212
pyrotartaric, 508
racemic, 513
rosolic, 410
saccharic, 531
salicylic, 583, 701
salts, definition of, 122
santonic, 590
sarcolactic, 511, 669
silicic, 186
sozolic, 573
stannic, 362
stearic, 506
succinic, 508
sulphanilic, 566
sulphocarbolic, 573
sulphocyanic, 553
sulpho-vinic, 521
sulphuric, 208
sulphurous, 206
tannic, 586
tartaric, 512

isomerism of, 513
tauro-cholic, 685
tetraboric, 187
thiosulphuric, 213
triazoic, 170
trichlor-acetic, 504
uric, 715, 741

estimation of, 716
uroleucic, 739
valeric, 505
Acidic oxides, 117

Acidimetry, 412

Acids, activity or strength of, 200

alkaptonic, 739
amino-, 544
aromatic, 579
definition of, 117
detection of, 391

dissociation theory applied to, 199
fatty, 496

monobasic, 496

hydroxy-, organic, 510

ions formed by, 200

thio-, 212
Aconitine, 617
Acrolein, 493

phenyl, 578
Acrylic aldehyde, 493
Actinic waves, 56
Actinium, 84
Action, catalytic, 154

contact, 154

endothermic, 91

exothermic, 91

reversible, 114
Activators, 638
Activity, optical, 67
Adamkiewicz's reaction, 627
Adhesion, 37
Adrenalin, 670
Affinity, chemical, 92
After-damp, 184
Agglutinins, 660
Agucarine, 581
Air, analysis of, 166

expired, 182

liquefaction of, 166
Alabaster, 277

Albumin, tests for, in urine, 726
Albuminoids, 628
Albuminometer, Esbach's, 726
Albumins, 627
Alcohol, 482

absolute, 483

allyl, 486

amyl, 486

benzyl, 577

denatured, 485

diluted, 483

ethyl, 482

methyl, 482

salicylic, 584
Alcoholic liquors, 485
Alcoholometers, 34
Alcohols, 479

aromatic, 577

primary, secondary, and tertiary,
479

sulpho-, 495

thio-, 495
Aldehyde, acetic, 491

acrylic, 493

benzoic, 577

cinnamic, 578

formic, 490

INDEX.

753

Aldehyde, methylprotocatechuic, 578
Aldehydes, 489

aromatic, 577
Aldoses, 530
Aldoximes, 541
Alkali-metals, remarks on, 255

summary of tests, 272
Alkalimeter, 34
Alkalimetry, 412
Alkaline-earth metals, 277

summary of tests, 285
Alkaloids, 600

antidotes for, 602

cadaveric, 617

classification, 603

detection of, in poisoning, 602
Alkyl, definition of, 474
Alkylene, definition of, 474
Allantoin, 717
Allotropic modifications, 129

silver, 331
Allotropy, 129
Alloxur bases, 667
Alloys, 253, 323

aluminum, 286

antimony, 358

arsenic, 347

bismuth, 327

copper, 323

dental, 254, 337

gold, 366

iron, 294

lead, 319

manganese, 303

manufacture of, 254

platinum, 367

pot-metal, 254

properties of, 254

silver, 331

tin, 323

zinc, 313, 323
Allyl alcohol, . 486

iodide, 486

isosulphocyanate, 556

mustard oil, 557

sulphide, 557

thio-urea, 557
Alpha-derivatives, 588, 624

-naphthol, 589

-naphthylamine, 589
Alum, ammpnio-ferric, 299

ammonium, 287

burnt, 287

chrome, 310

definition of an, 286

iron, 299

potassium, 287
Alumina, 287
Aluminates, 288
Aluminum, 285

acetate, 287

alloys of, 286

and ammonium sulphate, 287

and potassium sulphate, 287

48

Aluminum-bronze, 286

carbide, 466

chloride, 289

hydroxide, 287

oxide, 286, 288

silicate, 289

sulphate, 288
Alypin, 607
Amalgams, 253, 337

dental, 337
Amber, 599
Amboceptors, 661
Amides, 543
Amine, di- and triethyl-, 620

di- and trimethyl-, 620

diphenyl-, 566

ethyl, 620

isoamyl, 620

methyl, 620

propyl, 620
Amines, 541

primary, secondary, and tertiary,

542

Amino-acids, 544
Aminoform, 543
Ammeter, 77
Ammonia, 167

albuminoid, 431

aromatic spirit of, 269

determination by Nessler's solu-
tion, 431

from atmospheric nitrogen, 553

in urine, 714

ionic explanation of liberation of,
194

liniment, 526

water, 169
Ammonium, 268

acetate, 503

acid urate, 743

-amalgam, 268

benzoate, 580

bromide, 270

carbamate, 269

carbonate, 269

chloride, 269

hydrogen sulphide, 270

hydroxide, 169

iodide, 270

molybdate, 368

nitrate, 270

persulphate, 214

phosphate, 270

salicylate, 583

sesquicarbona '?, 269

sulphate, 270

sulphide, 270

sulphydrate, 270

urate, 743

valerate, 506
Amorphism, 21
Ampere, 77
Amperemeter, 77
Amphoteric reaction, 707

754

INDEX.

Amygdalin, 578
Amyl alcohol, 486

nitrite, 523
Amylases, 637
Amylene, 472

hydrate, 486
Amyloid, 537, 630
Amylopsin, 682
Analysis, 151

of air, 166

definition of, 371

gas, 427

gravimetric, 402

milk, 701

proximate, 443

qualitative, 371

of organic compounds, 442

quantitative, 371, 402

spectroscopic, 62

ultimate or elementary, of organic
compounds, 442

volumetric, 402

water, 429
Analytical chemistry, 371

reactions. See Tests.

ionic explanation of, 200
Anesthesin, 580
Anethol, 584
Anhydride of acids, 117, 141

acetic, 505

arsenic, 349

arsenous, 348

chromic, 308

phthalic, 581

Anhydrous, definition of, 152
Aniline, 564

-blue, 566

dyes, 564
Animal charcoal, 280

fluids and tissues, 649

food, 641
Anions, 190
Annealing, 252
Annidalin, 575
Anode, 75, 190
Antibodies, 660
Antidiabetin, 581
Antidotes to acetic acid, 502

alkalies, 257

alkaloids, 602

antimony, 361

arsenic, 358

barium, 284

copper, 326

hydrochloric acid, 233

hydrocyanic acid and its salts, 552

hydrogen sulphide, 214

lead, 322

mercury, 345

nitric acid, 177

oxalic acid, 509

phenol, 571

phosphorus, 222

silver, 334

Antidotes sulphuric acid, 212

zinc, 317
Antifebrin, 565
Antigen, 661
Antimonites, 359
Antimony, 358

alloys, 358

and potassium tartrate, 361, 515

black, 358

butter of, 360

chlorides, 360

crude, 358

golden sulphuret of, 360

oxides, 359

oxychloride, 360

spots, difference from arsenic, 357

sulphides, 359

sulpho-salts, 359
Antimonyl chloride, 360
Antipyrine, 591

derivatives, 592

incompatibles, 592

isonitroso, 592
Antiseptics, 457
i Antitoxin, 661
| Apatite, 219
I Apomorphine, 613
Apparatus for qualitative analysis, 371

quantitative analysis, 403-407
Apparent weight, 32
Aqua fortis, 174

regia, 235
Argentum, 330

Crede, 331
Argol, 512
Argon, 166
Argonin, 334
Argyrol, 334
Aristol, 575
Armature, 74, 78
Aromatic acids, 579

alcohols, 577

aldehydes, 577

compounds, 557

containing arsenic and phos-
phorus, 568
difference from fatty, 558, 561

hydroxy-acids, 583
Arsenetted hydrogen, 350
Arsenic, 346

alloys of, 347

chloride, 347

detection in cases of poisoning, 357

group of metals, remarks on, 346
summary of tests, 368

and mercury iodide, 351

pentoxide, 349

spots distinguished from anti-
mony, 357

sulphides, 347, 350

trioxide, 348
Arsenobenzene, 568
Arsenous anhydride, 348

iodide, 351

INDEX.

755

Arsenous oxide, 348
Arsine, 350
Artiads, 104
Asbestos, 272
Asepsis, 458
Aseptol, 573
Asparagine, 546
Asphalt, 599
Aspirin, 584
Atmospheric air, 165

pressure, 36
Atomic theory, Dalton's, 96

weight, definition, 98

determination of, 105
Atomicity, 103
Atoms, definition, 98
Atoxyl, 568
Atropine, 605
Attraction, capillary, 37

molecular, 19
Auric chloride, 366
Auripigment, 347
Avogadro's law, 30
Azo compounds, 567

dyes, 567

B.

BABBIT-METAL, 323
Bacillus bulgaricus, 700
Baking-powders, 264

-soda, 264
Balsam, 599

copaiva, 599
Barite, 283
Barium, 283

carbonate, 283

chloride, 283

cyanide from barium carbide, 553

dioxide, 283

nitrate, 284

oxide, 283

platinocyanide, 368

sulphate, 283
Barley sugar, 533
Barometer, 34
Basalt, 286
Bases, activity of, 201

definition of, 118

dissociation theory applied to,
200

organic, 541

Basic salts, definition of, 122
Battery, storage, 320
B< inuerel rays, 84
Beer, 486
Beet-sugar, 533
Bell-metal, 323

Bence-Jones body in urine, 727
Benzaldehyde, 577
Benzene, 562

diamino-, 566

nitro-, 563

series of hydrocarbons, 562

Benzene theory, 558
Benzin, 468
Benzol, 562

hexahydroxy-, 532
Benzosulphinide, 580
Benzoyl chloride, 580

-ecgonine, 606

-naphthol, 589
Benzoylation, 580
Benzyl alcohol, 577
Berberine, 615
Beta-derivatives, 588, 624

-eucaine hydrochloride, 607

-naphthol, 588
bcnzoate, 589
-bismuth, 589

-naphthylamine, 590
Betaine, 620
Bettendorf's test, 354
Bile, 684

detection in urine, 737
Biliary acids, 685

calculi, 686

pigments, 684
Bilirubin, 685
Biliverdin, 685
Bismark brown, 567
Bismuth, 327

alloys, 327

and ammonium citrate, 518

beta-naphthol, 589

citrate, 517

nitrate, 328

oxides of, 327

oxy-, or subcarbonate, 329
or subchioride, 330
subnitrate, 328
subsalts, 328

subgallate, 586

subsalicylate, 584

tribrom-phenolate, 572
Bismuthyl salts, 328
Biuret, 712

reaction, 627
Black antimony, 358

-ash, 263

-lead, 178

-wash, 337

Bleaching-powder, 280
Blood, 651

coagulation of, 653

in urine, 728

occult, 691

-pigments, 656

plasma, 652

-serum, immune bodies of, 660

-stains, examination of, 659
Blue mass, 336

pill, 336

Prussian, 301, 554

stone, 325

Turnbull's, 301, 555

vitriol, 325
Boiling, 52

756

INDEX.

Boiling-point, 53

determination of, 54

of solutions, 161
Bonds, double and triple, 471
Bone, 662

-ash, 279

-black, 279

-oil, 590
Borax, 187, 266

glass, 266

in milk, 701
Boroglycerin, 487
Boron, 187

trioxide, 187

Botger's bismuth test, 731
Boyle's law, 26
Brain, 670
Brandy, 486
Brass, 323
Braunite, 303
Bricks, 289

Bright line spectra, 61
Brimstone, 205
Erin's process, 138
British gum, 536
Brittleness, 26
Bromalin, 543
Brom-ethane, 478
Bromine, 239

deci-normal solution, 424

iodide, 243
Bromoform, 477
Bromoformin, 543
Bromol, 571
Bronze, 323
Brucine, 611
Butter, 525, 698

-milk, 695

of antimony, 360

C.

CACODYL, 478

oxide, 478
Cadaverine, 620
Cadinene, 597
Cadmium, 318 /
Caesium, 267

salts, 268
Caffeine, 616

citrated, 616
Calamine, 312
Calcined magnesia, 273

plaster, 279
Calcium, 277

acid phosphate, 279

bromide, 280

carbide, 281

carbonate, 278

chloride, 280

cyanamide, 553

glycerin-phosphate, 489

hydroxide, 278

hypochlorite, 281

Calcium hypophosphite, 280

oxalate, 508, 742

oxide, 277

phosphate, 279

sulphate, 279

sulphide, 281

superphosphate, 279
Calc-spar, 277

Calculations, chemical, 100, 111, 139
Calculi, biliary, 671

fecal, 692

urinary, 745
Calomel, 338

Caloric value of foods, 642
Calorie, 48
Calorimeter, 49
Camphene, 597
Camphor, 598

artificial, 596

mint-, 599

monobromated, 598
Cane-sugar, 533
Caoutchouc, 597
Capillary attraction, 37
Caramel, 531
Carat, definition of, 366
Carbamide, 546, 710
Carbide, 178

aluminum, 466

calcium, 281
Carbinol, 479, 482
Carbohydrates, 528, 729

classification of, 529
Carbolic acid, 569

coefficient, 570
Carbon, 178

dioxide, 180

ionic explanation of liberation
of, 195

disulphide, 217

monoxide, 183

silicide, 186

tetrachloride, 474
Carbonic oxide, 183
Carbonyl chloride, 184
Carborundum, 186
Carboxyl, 496
Carboxylic acids, 496
Carbylamines, 555
Carniferrin, 668
Caryophyllene, 595
Casein, 696

silver-, 334
Caseinogen, 696
Catalysis, 154
Cathode, 75, 82, 190

rays, 83

Cations, 83, 190
Caustic, lunar, 332

mitigated, 332

potash, 256

soda, 262
Cedrene, 597
Celestite, 282

INDEX.

757

Celluloid, 538
Cellulose, 536

nitrates of, 537
Celsius thermometer, 46
Cement, 290

Centigrade thermometer, 46
Cerebrosides, 670
Cerite, 291
Cerium oxalate, . 291
Chains, definition of, 449
Chalk, 277
Charcoal, animal, 280

reduction test, 212
Charles' law, 45
Chelene, 478
Chemical affinity, 92

calculations, 100, 111, 139

changes after death, 649

in plants and animals, 639

effects of light, 68

energy, 91, 142

equations, definition, 110
types of, 113

equilibrium. 114

formulas, 99

reaction, definition, 92

work, 142
Chemistry, analytical, 371

definition of, 18

organic, 440

physiological, 623

thermo-, 143
Chile saltpeter, 266
Chinoline, 593
Chloral, 492

hydrated, 493
Chloralamide, 544
Chloralformamide, 544
Chlorate of potash, 258
Chloride of lime, 280

nitrogen, 243
Chlorinated lime, 280

soda, 237
Chlorine, 230

compound solution of, 232

iodides, 243

oxides of, 235

water, 232
Chloroform, 474
Choke-damp, 184
Cholesterin, 527, 671
Choline, 620, 671
Chondrin, 628
Chondromucoid, 630
Chondroproteins, 630
Chromates, discussion of, 308
Chrome alum, 310

-iron ore, 306

-yellow, 311
Chromic anhydride, 308

chloride, 309

hydroxide, 310

oxide or sesquioxide, 309

salts, 309

Chromite, 306
Chromium, 306

and ammonium sulphate, 310

and potassium sulphate, 310

trioxide, 308
Chyme, 674
Cinchona alkaloids, 608
Cinchonidine, 610
Cinchonine, 609 ,
Cineol, 599
Cinnabar, 335, 342
Cinnamic aldehyde, 578
Cinnamyl acetate, 595
Clay, 289

Cleavage, hydrolytic, 453
Coagulases, 637
Coal, 467

-oil, 468

-tar, 470
Cobalt, 312

blue glass, 312
Cocaine, 606

substitutes, 580, 607
Codeine, 613

Coefficient of expansion, 48
Cognac, 486
Cohesion, 19
Cohesive gold, 365
Colchicine, 617
Collagen, 628
Collargol, 331

ointment, 331
Collodion, 538

medicated, 538
Colloidal silver, 331

solution, 331
Colloids, 41
Colloxylin, 538
Colophony, 599
Color, 56

Columbian spirit, 482
Combining weights of elements, 95
Combustion, 141

spontaneous, 141
Commutator, 78
Complement, 661
Compound acetanilide powder, 565

definition, 88

effervescing powder, 515

solution of cresol, 574

spirit of ether, 522
Conduction of heat, 49
Conductivity, 197
Conductors of electricity, 69
Congo red, 411
Coniine, 604

Constitutional formulas, 123
Contact action, 154
Convection, 50
Copaiva balsam, 599
Copper, 323

acetate, 504
basic, 504

aceto-arsenite, 504

758

INDEX.

Copper alloys, 323

ammonio-compounds of, 325

arsenate, 352

arsenite, 352

oxides, 324

carbonate, 325

-glance, 323

ions of, 326, 327

pyrites, 323

sulphate, 325
Copperas, 298
Coproliths, 692
Corpuscles or electrons, 85
Corrosive chloride of mercury, 339

sublimate, 339
Corundum, 286
Cotarnine, 614
Cotton, collodion, 538

medicated, 537
Coumarin, 578
Cream, 700

of tartar, 514
Creatine, 546, 666
Creatinine, 546, 666, 715
Crede's ointment, 331

silver, 331
Creolins, 574
Creosol, 575
Creosotal, 574
Creosote, 574

carbonate, 574
Cresol, 574

Critical temperature, 141
Cryoscopic method, 160
Crystal systems, 22
Crystallization, 20
Crystalloids, 41
Crystals, 20

acicular, 25

clinometric, 22

laminar, 25

orthometric, 22

prismatic, 25

tabular, 25

Cupellation of gold, 364
Cuprous compounds, remarks on,
323

oxide, 324
Curd, 700
Currents, alternating, 78

dynamo-electrical, 78

faradic, 79

induced, 78, 79

interrupted, 79

magneto-electric, 78

secondary, 79
Cyanamide, 553
Cyanides, detection in poisoning, 552

double salts, 551

organic, 555
Cyanogen, 548

complex radicals of, 553

compounds, 547

dissociation of, 549

Cyanogen compounds obtained from

atmospheric nitrogen, 552
Cymene, 564
Cystine, 545, 720, 744
Cystogen, 543

D.

DALTON'S atomic theory, 97

Daniell's cell, 75

Daturine, 605

Decay, 454

Decomposition by electricity, 90

heat, 87

light, 90

mutual action of substances, 90

with formation of a precipitate,

116, 193

volatile product, 116, 194
Decrepitation, 377
Deflagration, 378
Deliquescence, 152
Denaturants, 485
Denatured alcohol, 485
Density, 33
Dental alloys, 337
Dentine, 664
Deodorizers, 457
Deoxidation, 147
Deoxidizing agents, 147
Derivatives, definition of, 451
Dermatol, 586
Desiccator, 404
Destructive distillation, 453
Detection of acids, 391

special remarks, 398
Dextrin, 536
Dextrorotation, 67
Dextrose, 530
Diads, 103
Dialysis, 40
Dialyzed iron, 298
Diamine, 169
Diamino-benzene, 566
Diamond, 178
Diastase, 534
Diazo-compounds, 567

-reaction, Ehrlich's, 568, 739
Dichlor-methane, 474
Dichromates, discussion of, 308
Dicyandiamide, 553
Dicyanogen, 548
Diethylene diamine, 543
Diffusion, 40

of gases, 42

rate of, for different substances, 40
Digestion, 645, 672

gastric, 674

intestinal, 681

salivary, 672
Dimethyl benzene, 563
Dimorphism, 22
Dionin, 614
Dipentene, 597

INDEX.

759

Diphenyl-amine, 566
Disaccharides, 529, 533
Disinfectants, 457
Disinfection by formaldehyde, 491
Dispersion of light, 59
Displacement, 113
Dissociation, 172

electrolytic, 189

of acids and bases, 199

of formic acid and its homologues,
507

table of degree of, 203
Distillation, 53

destructive, 453

fractional, 462
Dithymol-diiodide, 575
Diuretin, 616
Divisibility, 28
Dolomite, 272
Donovan's solution, 351
Double decomposition, 113

refraction, 63

salts, definition of, 122
Drinking-water, 149
Drying oils, 525
Ductility, 26
Dulcin, 581

Dulong and Petit's law, 107
Dumas method for determination of

nitrogen, 445
Dyes, aniline, 564

azo, 567
Dynamite, 488

E.

EARTH metals, 286

summary of tests, 292
Earthenware, 289
Ebonite, 598
Ecgonine, 606
Effervescence, 152
Efflorescence, 152
Ehrlich's theory of immunity, 662
Elasticity, 26
Elastin, 628
Electric circuit, 76

current, 76

discharge through gases, 83

energy, 72

conversion of, 80, 82

furnace, 80

induction, 71

insulators, 69

light, 82

motors, 78

poles, 75

spark, 71, 83

units, 76
Electrical machines, 71, 78

potential, 76

tension, 76
Electricity, 69

by chemical action, 74

Electricity by magnet ism, 77

conductors of, (>!)

current, 72

duality of, 70

frictional, 69

galvanic, 74

nature of, 72

negative, 70

positive, 70

resinous, 70

static, 71

vitreous, 70

voltaic, 74
Electro-chemical equivalents, 197

series of metals, 198
Electrodes, 75, 82

polarized, 198
Electrolysis, 82, 195

electromotive force required for,
198

secondary changes in, 196
Electrolytes, 82
Electrolytic dissociation theory, 189

solution tension, 319
Electromagnetism, 77
Electromagnets, 77
Electromotive force, 76
Elements, classification of, 125

combining weights of, 95

definition, 88

metallic, 247

classification of, 251
derivation of names, 247
melting-points, 248
occurrence in nature, 250
properties of, 252
specific gravity of, 249
tune of discovery, 249
valence of, 250

natural groups of, 125

non-metallic, 126, 135

derivation of names, 135
time of discovery, 136
valence of, 136

periodic system of, 128, 130

physical properties of, 129

relative importance of, 124
Emanation, 87
Emerald green, 504
Emery, 286
Empirical formulas, 446

solution, 407
Emulsin, 578

Emulsion, definition of, 152
Emulsions, 524
Enamel, 664
Endosmosis, 40
Endothermic actions, 91
Energy, 19

chemical, 142
Enterol, 574
Enteroliths, 692
Enzymes, 456, 636
Eosin, 582

760

INDEX.

Epithelial cells, 687
Epithelium, 665
Epsom salt, 274
Equations, chemical, 110, 113

thermal, 143
Equilibrium, chemical, 11'4

ionic, 192

effect hi chemical reactions,
192

nitrogenous, 644
Equivalence, 102

Equivalents of volumetric solutions,
416, 419, 422, 426

electro-chemical, 197
Erepsin, 687
Erythrite, 529
Erythrose, 528
Esbach's albuminometer, 726
Eserine, 616
Essence of mirbane, 563
Essential oils, 594
Esters, 518
Ethane, 466

halogen derivatives, 477
Ethene, 472
Ether, 50, 520

acetic, 522

diacetic, 591

ethyl, 520

hydrobromic, 478

luminiferous, 50

methyl, 522
-ethyl, 522

nitrous, 523

sulphuric, 520
Ethereal salts, 518
Ethers, 518

compound, 518

mixed, 519
Ethoxy, 586
Ethyl acetate, 522

alcohol, 482

amine, 620

bromide, 478

carbamate, 545

chloride, 477

iodide, 478

nitrite, 523

assay of, 429

oxide, 520

para-amino-benzoate, 580
Ethylene, 472

dichloride, 472

series of hydrocarbons, 472
Eucalyptol, 599
Eudiometer, 427
Eugenol, 575
Euphorin, 545
Europhen, 574
Evaporations, 52
Exalgin, 566

Excretion, definition, 649
Exothermic actions, 91
Expansion, coefficient of, 48

Explosive gelatin, 488
Extension, 18

Extraction, definition of, 157
Extractive matter, 650
of muscle, 666

F.

FAHRENHEIT thermometer, 46
Faraday's laws, 197
Fats, 523, 646
Fatty acids, 496

oils, 523
Feathers, 665
Fecal calculi, 692
Feces, 689

examination of, 690
Fehling's solution, 730

test, 730
Feldspar, 286
Fermentation, 455
Ferments, hydrolytic, 636

organized, 455

soluble or unorganized, 455

unorganized, 636
Ferrates, 296
Ferric acetate, 503

ammonium sulphate, 299

chloride, 297

tincture of, 297

citrate, 518

hydroxide, 296

with magnesium oxide, 296

hypophosphite, 300

oxide, 295

phosphate, 300

soluble, 300, 518

pyrophosphate, soluble, 300, 518

subsulphate, 300

sulphate, 299

tartrate, 516
Ferricyanogen, 554
Ferripyrine, 592
Ferrocyanogen, 554
Ferro-manganese, 303
Ferrous acetate, 503

ammonium sulphate, 299

bromide, 298

carbonate, 300

saccharated, 300

chloride, 296

hydroxide, 295

iodide, 298

oxide, 295

phosphate, 300

sulphate, 298

exsiccated, 299

sulphide, 298
Fertilizers, 279
Fibrinogen, 654

Fineness of gold, definition, 365
Fire-damp, 184, 466
Fixed oils, 524
Flame, 184

1XDEX.

761

Flame tests, 261, 379
Flashing-point, 469
Fleitmann's test, 355
Flowers of sulphur, 205

of zinc, 313
Fluorescein, 582
Fluorine, 244
Fluor-spar, 244
Food, animal, 640

composition and fuel values, 642

digestibility of, 643

plant, 638
Force, definition of, 19

vital, 439
Formaldehyde, 490

disinfection, 491

in milk, 701

para-, 490
Formalin, 490
Formamide, 544
Formin, 543
Formulas, constitutional, 123, 447

empirical, 446

graphic, 123, 447

molecular, 99, 446

rational, 447

structural, 447
Fowler's solution, 349
Fractional distillation, 462
Frauenhofer lines, 62
Freezing-mixtures, 44

-point method, Raoult's, 109

-points of solutions, 160
Fructose, 532

Functional test of kidney, 740
Fusel oil, 486
Fusion, change of volume by, 52

latent heat of, 52

-point, 51

G.

GALACTOSE, 532
Galena, 318

argentiferous, 330
Gallacetophenone, 577
Gall-stones, 671
Galvanic electricity, 76
Galvanized iron, 313
Gamma derivatives, 624
Gas, analysis of, 427

definition of, 26

elasticity of a, 26

illuminating, 469

laughing, 172

natural, 467

olefiant, 472

tension of a, 26

volume, reduction of a, 428

water-, 184

Gases, absorption by charcoal, 39
by liquids, 39
by platinum, 39

diffusion of, 42

Gases, ionic explanation of liberation of,
194

solution of, 159

weight of, 34
Gasoline, 468
Gastric digestion, 675

juice, 674

examination of, 677
Gay-Lussac's law, 100
Gelatin, 663

-dynamite, 488

explosive, 488
German silver, 323
Germicides, 457
Gin, 486
Glass, 289

borax, 266

cobalt, 312

soluble, 186
Glauber's salt, 264
Gliadin, 628
Globin, 657
Globulins, 627
Glonoin, 487
Glucosan, 531
Glucose, 530
Glucosides, 539
Glucusimide, 581
Glue, 663
Gluside, 581
Glutelins, 628
Glycerides, 524
Glycerin, 487

phosphates, 488

trinitrate, 487
Glycerites, 487
Glycerol, 487
Glycerose, 528
Glycine, 544
Glycocoll, 544
Glycogen, 539, 692
Glycols, 479
Glycoproteins, 630
Glycozone, 155
Gmelin's test, 685, 737
Gold, 363

alloys, 366

and potassium cyanide, 364

and sodium chloride, 366

chlorides, 366

cohesive, 365

fineness of, 365

refining by cupellation, 364
parting, 364
quartation, 365

Golden sulphuret of antimony, 360
Goulard's extract, 504
Graham's law of diffusion, 42
Gram-atom, 407
Gram-molecule, 407
Granite, 286
Grape-sugar, 530
Graphic formulas, 123
Graphite, 178

762

INDEX.

Gravimetric methods, 403

Gravitation, 31

Green iodide of mercury, 340

vitriol, 298
Group-reagents, 382
Guaiacamphol, 575
Guaiacol, 575

carbonate, 575

derivatives, 575

-salol, 575
Guanidine, 546
Guaranine, 616
Gum arabic, 536

British, 536

-resins, 599
Gun-cotton, 537

-metal, 323
Gunpowder, 258, 538

smokeless, 538
Gutta-percha, 598
Gutzeit's test, 354

modified, 354
Gypsum, 279

H.

ELEMATIN, 657

Hsematoporphyrin, 657
Haematoxylin, 410
Haemin crystals, 659
Haemoglobin carbon monoxide com-
pound, 657
Haemoglobins, 631
Haemolysis, 662
Haine's test, 731
Hair, 665
Halogens, 230
Haptophore group, 662
Hardness, 25
Hartshorn, spirit of, 169
Hausmannite, 303
Heat, 43

bright red, 48

conduction of, 49

convection of, 50

dark red, 48

decomposition by, 87

effects, 45

incipient red, 48
white, 48

latent, 44

mechanical equivalent of, 48

of neutralization, 203

of solution, 158

radiation of, 50

rays? 50

sources of, 44

specific, 49

waves, 51

white, 48

yellow, 48
Heavy spar, 283
Hedonal, 545

Helianthin, 411

Helium, 167

Heller's test, 626, 731

Hematite, 293

Hemiterpenes, 594

Henry's law, 159

Hepar, 212, 378

Heptads, 103

Heroin, 613

Hexads, 103

Hexamethylenamine, 543

Hexone bases, 633

Histidine, 630

Histones, 629

Holocaine hydrochloride, 607

Homatropine, 605

Homologous series, 450

Hoofs, 665

Hordein, 628

Hornblende, 286

Horns, 665

Humidity, 165

Humulene, 597

Humus, 649

Hydracids, 117

Hydrastine, 615

Hydrastinine, 615

Hydrazine, 169

Hydrazones, 568

Hydrocarbons, benzene series, 561

ethylene series, 472

general remarks, 462

halogen substitution products,
473

methane or paraffin series, 464

terpene series, 594

unsaturated, 470
Hydrogen, 144

arsenide, 350

dioxide, 153

nascent, 148

peroxide, 153

phosphide, 229

phosphoretted, 229

sulphide, 214
Hydrolysis, 201, 453, 636
Hydrolytic cleavage, 453, 636

ferments, 636
Hydrometers, 34
Hydroquinone, 576

hydroxy-, 577
Hydroxides, 119, 151
Hydroxyl, 119
Hydroxylamine, 169
Hygrine, 606
Hygrometers, 166
Hygroscopic, 152
Hyoscine, 606
Hyoscyamine, 605
Hypertonic solutions, 163
Hypnal, 592
Hypochlorites, 237
Hypotonic solutions, 163
Hypoxanthine, 668

INDEX.

7C3

ICELAND spar, 63
Ichthyol, 573
Illuminating gas, 469

oil, 468

Imino-compounds, 542
Immunity, Ehrlich's theory of, 662
Impurities, detection of, 433
Indestructibility, 42
India-rubber, 597
Indican, 721
Indicators, 410

ionic explanation of action, 411
Indigo, 721

-red, 722
Indole, 693
Indoxyl, 721
Induction, 71

coil, 79

voltaic, 78
Ink, blue, 554

indelible, 333
Inosite, 532
Internal energy, 91
Intestinal digestion, 681

sand, 692
Inversion, 533
Invertases, 637
Iodide of nitrogen, 243

sulphur, 243
lodimetry, 421
Iodine, 240

chlorides of, 243

compounds of nitrogen, 244

Lugol's solution, 242

pentoxide, 243

sulphide of, 243

tincture of, 241

decolorized, 270
lodoform, 477
lodoformin, 543
lodol, 591
Ionic equations, 192

equilibrium, 192

mechanism of solution, 217
lonization constant, 192

theory of, 190
Ions, 75, 190

composition of, 190

independence of, 199
Iridium, 368
Iron, 292

acetates, 503

alloys, 294

alum, 299

and ammonium sulphates, 299

and potassium oxalates, 510

and quinine citrate, 518

and strychnine citrate, 518

bar-, 294

bisulphide, 293

bromide, 263, 298

Iron carbonate, 300

saccharated, 300

cast-, 293

chlorides, 296

citrate, 518

dialyzed, 298

galvanized, 313

-group of metals, 292

summary of tests, 316

hydroxides, 293

hypophosphite, 300

iodide, 298

monoxide or suboxide, 293

ores, 293

oxides, 293, 295

oxychloride, 298

perchloride, 297

phosphate, 300

soluble, 300, 518

pig-, 293

protochloride, 296

pyrites, 293

pyrophosphate, soluble, 518

reduced, 295

rust, 294

scale compounds of, 516, 518

sesquichloride, 297

subsulphate, 300

sulphates, 298

sulphide, 298

tartrate, 516

tersulphate, 299

trioxide, 296

wrought-, 294
Isocholesterin, 527
Isocyanides, organic, 555
Isomerism, 451
Isomorphism, 22
Iso-nitriles, 555
Isonitroso compounds, 540
Isoquinoline, 593
Is-osmotic solutions, 163
Isosulphocyanates, 556
Isotonic solutions, 163

K.

KAIRINE, 593

Kaolin, 289

Kelene, 478

Kelp, 241

Keratins, 628

Kerosene, 468

Ketones, 494

Ketoses, 530

Ketoximes, 541

Kidney, functional test of, 740

Kieserite, 274

Kinases, 638

Kjeldahl determination of nitrogen,

445

Koppeschaar's solution, 424
Krystallose, 581

764

INDEX.

L.

LABARRAQUE'S solution, 237
Lactalbumin, 696
Lactoglobulin, 696
Lactometers, 34
Lactophenin, 572
Lactose, 534, 699
Lakes, 288
Lanolin, 527
Lapis infernalis, 332

lazuli, 290
Lard, 525
Latent heat, 44

of fusion, 52
of vaporization, 54
Laughing gas, 172
Laurinol, 598
Law, Avogadro's, 30

Boyle's, 26

Charles', 45

Dulong and Petit's, 107

Gay-Lussac's, 100

Graham's, 42

Henry's, 159

Mariotte's, 26

Mendelejeff's, 126

Newton's, 31

Ohm's, 77

Raoult's, 161

of atomic heats, 107

of combination by volume, 100

of constancy of composition, 93

of correlation of energies, 42

of equivalents, 102

of mass action, 116

of multiple proportions, 94

of specific heats, 107

of the conservation of energy,

42
Laws of electrolysis, Faraday's, 197

of osmotic pressure, 163
Lead, 318

acetate, 503
basic, 503
tribasic, 504

alloys, 319

arsenate, 350

carbonate, 321

chloride, 322

chromate, 322

dioxide or peroxide, 319

group metals, 318

summary of tests, 344

iodide, 321

nitrate, 321

oleate, 526

oxide, 319

phosphate, 322

plaster, 526

red oxide, 319

subacetate, 503

sugar of, 503

sulphate, 322

Lead sulphide, 318

-water, 504

white, 321

Leblanc's process, 263
Lecithins, 670
Lecithoproteins, 631
Legal's test, 737
Leucine, 546, 635, 744
Leucomaines, 621
Levorotation, 67
Levulose, 532
Lieberman's reaction, 627
Light, 56

chemical effects of, 68, 90

dispersion of, 59

infra-red, 56

plane-polarized, 64

rays, 57

reflection of, 57

refraction of, 58

ultra-violet, 56

waves, 56
Lignin, 536
Lignite, 467
Lime, 277

acid phosphate of, 279

air-slaked, 277

chloride of, 280

chlorinated, 280

-kilns, 277

liniment, 526

milk, of 278

nitrogen, 553

phosphate of, 279

sulphurated, 281

superphosphate of, 279

-water, 278
Limestone, 277
Limonene, 597
Liniments, 526

Linkage, double and triple, 471
Lipase, 683
Lipoids, 670
Liquids, absorption of gases by, 40

definition of, 26
Litharge, 319
Lithium, 267

benzoate, 580

bromide, 267

carbonate, 267

citrate, 517

hydroxide, 267

phosphate, 267

salicylate, 583
Litmus paper, 410

solution, 410
Liver, function of, 692
Lodestone, 296
Losophan, 574
Lugol's solution, 241
Lunar caustic, 332
Lupulin, 486
Lymph, 662
Lysine, 628

INDEX.

765

Lysins, 660
Lysol, 574

M.

MAGNESIA alba, 273

calcined, 273

milk of, 273
Magnesite, 272
Magnesium, 272

ammonium phosphate, 742

carbonate, 273

citrate, 517

nitride, 274

oxide, 273

sulphate, 274

effervescent, 274, 517
Magnetic field, 74

iron ore, 73, 293
Magnetism, 73
Malachite, 323
Malleability, 26
Malonyl urea, 547
Malt, 534
Maltose, 534
Manganese, 303

alloys, 303

carbonate, 303, 306

oxides of, 302

spar, 303
Manganous hydroxide, 306

hypophosphite, 304

sulphate, 304
Mannite, 529
Mannose, 532
Mariotte's law, 26
Marsh-gas, 466
Marsh's test, 355
Mass, definition of, 18

-action, law of, 116
Massicot, 320
Matches, safety, 222
Matter, action of heat on, 28

definition of, 18

fundamental properties of, 18

radiant, 85
Mayer's solution, 601
Measures, metric, 32
Meat-extracts, 669
Mechanical equivalent of heat, 48
Meerschaum, 272
Melanin, 739
Melitose, 534
Melting-point, 51

determination of, 52
Membranes, semipermeable, 162
Mendelejeff's periodic law, 126
Menthol, 599
Mercaptans, 495
Mercurial ointment, 336

plaster, 336
Mercuric ammonium chloride, 342

chloride, 339

compounds, remarks, 336

Mercuric cyanide, 551
fulminate, 541
iodide, 340
nitrate, 341
oxide, 337

oxy- or subsulphate, 341
and potassium iodide, 341
and sodium chloride, 339
salicylate, 584
sulphate, 341
sulphide, 335, 342
Mercurous chloride, 338

compounds, remarks, 336
iodide, 340
nitrate, 341
oxide, 337
sulphate, 341
Mercury, 335

ammoniated, 342
and arsenic iodide, 351
complex salts of, 345
cyanide, 551
fulminate, 541
iodides, 340
mass of, 336
mild chloride of, 338
oxides of, 337
oxy cyanide, 551
proto- or subchloride of, 338
purification of, 336
salts, action of ammonia on, 343
with chalk, 336
Meta-compounds, 559
Metaldehyde, 492
Metals, 247

alkali-, remarks on, 255

summary of tests, 272
of alkaline earths, 277

summary of tests, 285
of the arsenic group, remarks on,
346

summary of tests, 369
classification of, 251
derivation of names, 247
earth group, summary of tests, 292
electro-chemical series of, 198
iron group, remarks, 292

summary of tests, 316
lead group, remarks, 318

summary of tests, 344
manufacture of, 253
melting-points of, 248
noble and base, 253
occurrence in nature, 250
properties of, 252
remarks on tests for, 274
separation of, 385
specific gravities of, 249
time of discovery, 249
valence of, 250
Metamerism, 451
Meta-phenylene-diamine, 566
Metaproteins, 631
Met-arsenites, 348

766

INDEX.

Metathesis, 113
Methaemoglobin, 657
Methane, 466

halogen derivatives of, 474

series of hydrocarbons, 464
Methoxy, 586
Methyl acetanilide, 566

alcohol, 482

amine, 620

benzene, 563

blue, 567

chloride, 474

ether, 522

-ethyl ether, 522

-glycocoll, 545

hydroxide, 482

-orange, 410

salicylate, 585
Methylated spirit, 482
Methylene azure, 567

-blue, 566

chloride, 474

Methylthionine hydrochloride, 566
Mica, 286
Microcidine, 589
Microcosmic salt, 380
Milk, 694

analysis, 701

certified, 701

changes on standing, 700

clotting, 696

cows', 695

-fat, 698

human, 702

modified, 702

of lime, 278

of magnesia, 273

of sulphur, 205

preservatives, 700

-proteins, 696

skimmed, 700

-sugar, 534, 699
Millon's reaction, 626
Mineral waters, 149
Minium, 320
Mint-camphor, 599
Mirbane, essence of, 563
Mispickel, 347
Modified Gutzeit's test, 354
Mohr's salt, 299
Molecular formulas, 99, 446

motion, 43

theory, 28

weight, definition, 99

determination of, 108

weights, relation to densities of

gases, 108
Molecules, 99
Molybdates, 368
Molybdenum, 368
Monads, 103
Monazite sand, 291
Monosaccharides, 529
Monsel's solution, 300

Moore's test, 731

Mordants, 288

Morphine and its salts, 612

diacetyl-, 613
Mortar, 278

hydraulic, 290
Mucins, 630
Mucoids, 630
Murexid test, 716
Muscarine, 671
Muscle, 665

extractives, 666

sugar, 532
Musculin, 666
Mustard oils, 556
Mydatoxine, 621
Mydine, 620
Myosin, 666
Myosinogen, 666
Myrosin, 556
Mytilotoxine, 620

N.

NAILS, 665
Naphthalene, 587

amino-, 589

derivatives, 587
Naphthol, 588
Naphthylamines, 589
Narceine, 614
Narcotine, 614
Nascent hydrogen, 148

state, 148
Natural gas, 467
Nessler's solution, 341, 374

estimation of ammonia by, 431
Neuridine, 620
Neurine, 620
Neurodin, 545

Neutral substances, definition of, 120
Neutralization, 119, 202

equivalents, 416

heat of, 203

ionic explanation of, 202
Newton's law, 31
Nickel, 312
Nicol's prisms, 65
Nicotine, 604
Niter, 258

cubic, 266
Nitriles, 555
Nitro-benzene, 563

-cellulose, 537

compounds, 540

-glycerin, 487

-phenols, 572
Nitrogen, 164

chloride, 244

compounds in urine, 710

determination by Dumas or abso-
lute method, 445
Kjeldahl method, 445
soda-lime, 445

INDEX.

767

Nitrogen iodide, 244

oxides of, 170
Nitrolim, 553
Nitrometer, 429
Nitroso compounds, 540
Nitrous ether, 523

oxide, 172
Nomenclature, 131
Non-metallic elements, 135
Nordhausen oil of vitriol, 212
Normal salt solution, physiologic, 656

salts, definition of, 121

solutions, 407

equivalents of, 416, 419, 422,

426

Nucleoproteins, 629
Nutrition, 645
Nylander's reagent, 731

0.

OBERMAYER'S test, 722
Ohm, 76
Ohm's law, 77
Oil, bitter almond, 578
bone-, 590
cinnamon, 595

artificial, 578
cloves, 596
fusel, 486
illuminating, 468
of garlic, 557
of vitriol, 208
peppermint, 595
phosphorated, 222
turpentine, 596
wintergreen, 585
Oils, drying and non-drying, 525
essential or volatile, 594
fatty, 523
fixed, 523
mustard, 556
Oleates, 507
Olefiant gas, 472
Olefins, 472
Olein, 524
Oleo-resins, 599
Opalisin, 702
Opium, 612
Opsonins, 660
Optic axis, 63
Optical activity, 67
Organic chemistry, 440

compounds, action of heat upon

453

classification of, 460
elementary analysis of, 442
elements in, 440
general properties 441
various modes of decomposi

tion, 452
cyanides, 555
ispcyanides, 555
Organized ferments, 455

Orphol, 589
Orpiment, 347
Ortho-compounds, 559
Osazones, 530, 568
Osmose, 40
Osmotic cells, 162

pressure, 162
Ossein, 628
Oxalates, 509
Oxalyl urea, 547
Oxidases, 637

Oxidation, definition of, 141
Oxides, acid-forming or acidic, 117

basic, 141

definition of, 141

neutral, 141
Oxidimetry, 417
Oxidizing agents, 142
Oximes, 541
Oxyacids, 117
Oxygen, 137
Oxy haemoglobin, 656
Oxypurine, 715
Ozone, 142

thermochemistry of, 144

P.

PAINTER'S colic, 322
Palladium, 367
Palmitin, 524
Pancreatic juice, 682

secretions, 682

stones, 692
Pancreatin, 638
Paracasein, 696
Para-compounds, 559
Paraffin, 469

series of hydrocarbons, 464
Paraformaldehyde, 490
Paraldehyde, 492
Parchment paper, 537
Paris green, 352, 504
Parting of gold, 364
Pasteurization, 701
Pearl-white, 329
Peat, 467

Pelletierine tannate, 608
Pentads, 103
Pental, 472
Pentosanes, 735
Pentoses, orcin reaction, 735
Pepsin, 638
Peptides, 633
Peptones, 632
Peria's reaction, 635
Perissads, 104
Petrolatum, 469
Petroleum, 468

-benzin, 468

Pettenkofer's test, 686, 738
Phellandrene, 597
Phenacetin, 572
Phenetidin, 572

768

INDEX.

Phenetidin derivatives, 572
Phenol, 569

amino-, 572

coefficient, 570

determination in urine, 722

nitro-, 572

titration of, 424

tri-brom-, 571

trinitro-, 572

Phenolphthalein, 410, 582
Phenolsulphonphthalein, 582
Phenoxy, 586
Phenylacetamide, 565

acrolein, 578

-amine, 564

hydrazine, 568

salicylate, 585
Phloroglucinol, 577
Phosgene, 184
Phosphides, 221
Phosphine, 229
Phosphoprotein, 630
Phosphorated oil, 222
Phosphoretted hydrogen, 229
Phosphorite, 219
Phosphorus, 219

antidotes to, 222

detection of, 222

determination in organic com-
pounds, 445

oxides of, 223

oxychloride, 229

pentachloride, 229

pills of, 222

red or amorphous, 221

spirit of, 222

trichloride, 229
Photography, 333
Phthaleins, 582
Phthalic anhydride, 581
Physical properties of elements, 129
Physics, definition of, 17
Physiological chemistry, 623
Physostigmine, 616
Pilocarpine, 604
Pinene, 596

hydrochloride, 596
Piperazine, 543
Piperidine, 543
Piperin, 604
Pitch-blende, 84
Plant food, 640
Plaster, calcined, 279

lead, 526

of Paris, 279
Platinic ammonium chloride, 367

chloride, 367
Platinum, 367

alloys, 367

and barium cyanide, 368

black, and sponge, 367

absorption of gases by, 39
Plumbago, 178
Poirier's orange 3P, 411

Polariscope, 65
Polarization, 63
Polarized electrodes, 198
Polonium, 84
Poly-amines, 543
Polymerism, 451
Polymorphism, 22
Polysaccharides, 529, 535
Polyterpenes, 594
Porcelain, 289
Porosity, 36
Porter, 486
Pot-metal alloys, 254
Potash, bichromate or red chromate of,
307

caustic, 256

chlorate of, 258

crude, 256

red prussiate of, 555

yellow chromate of, 307

prussiate of, 554
Potassium, 255

acetate, 503

acid or bitartrate, 514
oxalate, 509

and antimony tartrate, 515

arsenite, 349

bicarbonate, 257

bisulphate, 259

bromide, 260

carbonate, 257

chlorate, 258

chromate, 308

citrate, 517

cyanate, 553

cyanide, 550

dichromate, 307

ferrate, 296

ferricyanide, 555

ferrocyanide, 554

gold cyanide, 364

hydroxide, 256

hypophosphite, 259

iodide, 259

iron oxalates, 510

manganate, 305

mercuric iodide, 341

nitrate, 258

oxide, 257

percarbonate, 257

perchlorate, 238

permanganate, 305

persulphate, 214

sodium tartrate, 515

sulphate, 259

sulphite, 259

sulphocyanate, 553

tartrate, 515

tetroxalate, 509
Powder of Algaroth, 360
Precipitate, definition of, 116
Precipitation, definition of, 121

ionic explanation of, 193c
Precipitins, 660

769

Preston salt, 269
Principle of Archimedes, 34
Prismatic spectrum, 59
Prisms, 58

Nicol's, 65
Pro-enzymes, 638
Prolamines, 628
Proof-spirit, 484
Propylamine, 620
Protagon, 670
Protalbumoses, 632
Protamines, 629
Protargol, 334
Proteans, 631
Proteases, 637
Proteids. See Proteins.
Proteins, 623

alcohol-soluble, 628

classification of, 624

coagulated, 632

conjugated, 629

decomposition products, 633

derived, 631

simple, 625
Proteolysis, 633
Proteoses, 632
Prussian blue, 554
Prussiate of potash, red, 555

yellow, 554
Ptomaines, 617
Ptyalin, 673
Purine bases, 667
Putrefaction, 555
Pycnometers, 34
Pyocyanine, 620
Pyramidon, 592
Pyridine, 592
Pyrites, 293
Pyrocatechin, 575

tests for, in urine, 723
Pyrogallol, 576
Pyrolusite, 303
Pyroxylin, 537
Pyrozone, 155
Pyrrol, 590

tetra-iodo, 590

Q

QUANTIVALENCE, 102

Quartation of gold, 365
Quartz, 186
Quick-lime, 277
Quicksilver, 335
Quinidine, 609
Quinine, 608

salts, 608
Quinol, 576
Quinoline, 593

iso-, 593

R.

RADIATION of heat, 50
Radical, compound, 122
definition of, 122, 448

49

Radio-activity, 84
Radium, 84, 284

bromide and chloride, 285
Raoult's freezing-point method, 161
Rays, Becquerel, 84

cathode, 83

of heat, 50

of light, 57

Rontgen, 83

Reaction, reversible, 114
Reagents, list of, 374

use of, in analysis, 376
Realgar, 347

Reaumur thermometer, 46
Receptors, 662
Recording thermometers, 47
Red lead, 320

prussiate of potash, 555
Reduced iron, 295
Reducing agents, 147
Reduction, 147
Reflection of light, 57
Refraction, double, 63

of light, 58
Reinsch's test, 353
Rennin, 673

Residue, definition of, 122
Resins, 599

gum-, 599

oleo-, 599
Resopyrine, 592
Resorcin, 576
Resorcinol, 576

-phthalein, 582
Respiration, 647
Reticulin, 629
Reversed spectra, 62
Reversible actions, 114
Reversion, 533
Rhigolene, 468

Rideal-Walker coefficient, 570
Rigor mortis, 665
Rochelle salt, 515
Rock, phosphatic, 280
Rodagen, 669
Rontgen rays, 83
Rosaniline, 565
Rosin, 599
Rosolic acid, 410
Rouge, 296
Rubber, 597

preservation, 598

vulcanized, 597
Rubidium, 267

salts, 268
Ruby, 286
Ruhmkorf coil, 79
Rum, 486

SACCHARIN, 580

soluble, 581

Saccharinol, 581

770

INDEX.

Saccharinose, 581
Saccharol, 581
Saccharose, 533
Safety matches, 222
Safrol, 575
Sal ammoniac, 269

sodse, 263

volatilis, 269
Salicin, 584
Saliform, 543
Salipyrin, 592
Saliva, 672
Salol, 585
Salt cake, 263

common, 262

of lemon, 509

of sorrel, 509

Preston, 269
Saltpeter, 258

Chile, 266
Salts, acid, definition of, 121

basic, definition of, 121

definition of, 120

double, definition of, 122

ethereal, 518

hydrolysis of, 201

ions of, 201

normal, definition of, 121

reaction to litmus, 121, 201

various methods of obtaining, 120
Salvarsan, 568
Santolene, 597
Santonin, 590
Saponification, 525
Sapphire, 286
Sarcine, 668
Sarcosine, 545
Scale compounds, 516
Scheele's green, 352
Schiff's reaction, 716

for formaldehyde, 490
Schweinfurt green, 352, 504
Schweizer's reagent, 537
Scopolamine hydrobromide, 606
Secretin, 682
Secretion, definition, 649
Sediment, definition of, 116
Seidlitz powders, 515
Selenium, 217

Semi-permeable membranes, 162
Serpentine, 272
Sesquiterpenes, 597
Sherer's reaction, 636
Shikimol, 575
Shot alloy, 347
Silica, 186
Silicates, 186, 286
Silicon* 186

carbide, 186
dioxide, 186
fluoride, 186
Silver, 330

allotropic forms of, 331
alloys of, 331

Silver, ammonio-chloride of, 335

compounds of, 335
bromide and iodide, 335
-casein, 334
chloride, 332
colloidal, 331.

complex compounds of, 334
Crede's, 331
cyanide, 551
fulminate, 541
German, 323
mirror, 514
nitrate, 332

moulded, 332
oxide, 333
tartrate, 514
vitellin, 334
Sinigrin, 556
Skatole, 693, 722
Skeletins, 629
Slag, 293
Slate, 286
Soap, 525
Soapstone, 272
Soda ash, 263
baking-, 264
bichromate of, 307
caustic, 262
-lime, 443
washing, 263
Sodium, 262

acetate, 503
-ammonium-hydrogen-phosphate,

380

arsanilate, 568
arsenate, 349
benzoate, 580
bicarbonate, 264
bisulphite, 264
borate, 266
bromide, 266
cacodylate, 478
carbonate, 263

monohydrated, 264
chlorate, 266
chloride, 262
citrate, 517
cobaltic nitrite, 374
cyanide, 551, 553
dichromate, 307
glycerin-phosphate, 489
and gold chloride, 366
hydroxide, 262
hypochlorite, 237
hypophosphite, 266
hyposulphite, 265
ichthyo-sulphonate, 573
iodide, 266

mercuric chloride, 339
met-arsenite, 348
metastannate, 363
-naphthol, 588
nitrate, 266
nitrite, 266

ISDEX.

771

Sodium nitroferricyanido, 555

nitroprusside, 555

perborate, 189

peroxide, 263

phenolate, 570

phenolsulphonate, 573

phosphate, 265

effervescent, 265
exsiccated, 265

potassium tartrate, 515

pyrophosphate, 265

salicylate, 583

stannate, 363

sulph-antimonite, 359

sulphate, 264

sulphite, 264

sulphocarbolate, 573

tetrathionate, 213

theobromine salicylate, 616

thiosulphate, 265
Solder, 319

Solids, definition of, 19
Solubility, definition of, 158

table of, 396, 397
Soluble ferments, 455
Solute, 158
Solution, colloidal, 331

complex or chemical, 151

definition of, 151, 157

heat of, 158

ionic mechanism of, 217

of gases, 159

saturated, 151

simple, 151

tension, 319

Solutions, boiling- and freezing-points
of, 160

hyper- and hypotonic, 163

is-osmotic or isotonic, 163
Solutol, 574
Solvay process, 263
Solveol, 574
Somnoform, 478
Sonnenschein's test, 611
Sources of heat, 44
Sparteine, 604
Spasmotpxine, 621
Spathic iron ore, 293
Specific gravity, 32

heat, 49

weight, 32
Spectroscope, 59
Spectrum, 59

continuous, 61
Spermaceti, 520
Spirit, 482, 486

Columbian, 482

methylated, 482

of ammonia, aromatic, 269

of ether, 522

compound, 522

of glonoin, 488

of glyceryl trinitrate, 488

of hartshorn, 169

Spirit of Mindererus, 503

of nitrous ether, 523
assay of, •}•_".)

of phosphorus, 222

proof-, 484

wood-, 482
Stannic chloride, 363

hydroxide, 362

oxide, 362

sulphide, 363
Stannous chloride, 363

hydroxide, 362

oxide, 362

sulphide, 363
Starch, 535

iodized, 536

solution, 421
Stassfurt salts, 256
Steapsin, 683
Stearin, 524
Stearoptens, 598
Steatases, 637
Steel, 294

Stereo-isomerism, 452
Sterilization, 458
Stibnite, 358
Stokes' fluid, 657
Stoneware, 289
Storage battery, 320
Stout, 486
Strontianite, 282
Strontium, 282

chloride, bromide, and iodide, 282

hydroxide, 282

nitrate, 282

oxide, 282

salicylate, 584
Strychnine, 610
Stypticin, 614
Sublimation, 21
Substitution, 450
Succus entericus, 687
Sucrates, 534
Sucrol, 581
Sugar, cane-, 533

estimation in urine, 733

fruit-, 532

grape-, 531

muscle-, 532

of lead, 503

of milk, 534
Sulph-antimonites, 359

-arsenates, 351
Sulpho-alcohols, 495
Sulphonal, 495
Sulphonethylmethane, 496
Sulphonmethane, 495
Sulphur, 204

determination in organic com-
pounds, 445

dioxide, 206

flowers of, 205

iodide of, 243

milk of, 205

772

INDEX.

Sulphur, oxides of, 206

precipitated, 206

sublimed, 206

trioxide, 208

washed, 206
Sulphurated lime, 281
Sulphuretted hydrogen, 214
Sulphuric anhydride, 208

ether, 520

Sulphurous anhydride, 206
Supersaturation, definition of, 158
Suprarenal glands, desiccated, 669
Surface-action, 36

tension, 38

Sweet spirit of niter, 523
Sylvestrene, 597
Symbols of compounds, 99

of elements, 99
Synthesis, 151

T.

TABLE of solubility, 396, 397

Talc, 272

Tallow, 525

Tannin, 585

Tannon, 543

Tannopin, 543

Tartar, 665

cream of, 514
crude, 512
emetic, 361, 515
Taurine, 546
Tellurium, 217
Temperature, 44, 46
absolute, 47
critical, 141
kindling, 142
Tempering, 252
Tenacity, 26
Tension, 26

of saturated water-vapor, 53
Terebene, 597
Terpenes, 594
Terpin hydrate, 599
Test, charcoal reduction, 212

definition of, 155
Tests for acetanilide, 565
acetic acid, 503
albumin in urine, 723
aluminum, 290
ammonium compounds, 271
antimony, 361
antipyrine, 591
apomorphine, 613
arsenic, 351
atropine, 605
barium, 284
bile, in urine, 737
biliary acids, 686
pigments, 685
bismuth, 329
blood in urine, 728
boric acid and borates, 188

Tests for brucine, 611

calcium, 281

carbohydrates in urine, 730

carbonates, 183

casein, 697

chloral, hydrated, 493

chlorates, 238

chloroform, 476

cholesterin, 671

chromium, 311

cinchonine, 610

citric acid, 517

cocaine, 607

codeine, 614

copper, 326

creatinin, 667

dextrose, 531

ethyl alcohol, 485

fats and fatty acids, 526

ferrocyanides, 554

fluorides, 244

formaldehyde, 490

gelatin, 664

glycerin, 487

glycogen, 693

gold, 366

hippuric acid, 718

hydrobromic acid and bro-
mides, 240

hydrochloric acid and chlo-
rides, 234

hydrocyanic acid, 551

hydrogen dioxide, 155

sulphide and sulphides,
216

hypochlorites, 238

hypophosphites, 224

indican, 721

iodine and iodides, 242

iron, 301

lead, 322

leucine, 635

manganese, 305

magnesium, 276

mercury, 343

metals, remarks on, 274

metaphosphoric acid, 226

milk-sugar, 699

morphine, 612

nitric acid and nitrates, 176

nitrous acid and nitrites, 173

oxalic acid, 509

phenol, 571

phosphates, 228

phosphites, 225

physostigmine, 617

potassium, 260

preservatives in milk, 701

pyrocatechin, 723

pyrophosphates, 226

quinine, 609

salicylic acid, 584

santonin, 590

silicic acid and silicates, 186

L\DI-:X.

773

Tests for silver, 334

simple proteins, 626
sodium, 267
strontium, 282
strychnine, 610
sugar, in urine, 729
sulphuric acid and sulphates,

211
sulphurous acid and sulphites,

208

tannic acid, 586
tartaric acid, 514
thiosulphates, 213
tin, 363
tyrosine, 635
urea, 712
uric acid, 716
veratrine, 611
zinc, 315
Tetanine, 621
Tetrachlor-methane, 474
Tetrads, 103
Tetra-iodo-pyrrol, 591
Tetronal, 496
Thalleioquin, 609
Thalline, 593
Theine, 616
Theobromine, 616

sodium salicylate, 616
Theory, atomic, 96

of equivalents, 102
molecular, 28
Thermal equations, 143
Thermo-chemistry, 143
Thermodin, 545
Thermometers, 46
Thio-alcohols, 495
Thiosinamine, 557
Thymol, 575

iodide, 575
Thyreoidectin, 669
Thyro-iodine, 242, 669
Thyroid glands, desiccated, 669
Tin, 362

alloys, 323
chlorides, 363
hydroxides, 362
oxides, 362
perchloride, 363
-plate, 362
protochloride, 363
-stone, 362
sulphides, 363

Tincture of ferric chloride, 297
of iodine, 241

decolorized, 270
Titer, 412
Titration, 403, 411
Tollen's orcin reaction, 735
Toluene, 563
Tourmaline, 63
Toxines, 619

bacterial, 661
endo-, 661

Toxines, soluble, 661
Triads, 103
Tribrom-methane, 477
Trichloraldehyde, 492
Trichlor-methane, 474
Tri-cresol, 574
Triiodo-methane, 477
Trinitro-phenol, 572
Trional, 496
Triple linkage, 471
Trommer's test, 730
Tropseolin D, 411
Trypsin, 683
Tryptophan, 684
Turnbull's blue, 301, 555
Turpentine, 599
Turpeth mineral, 341
Type metal, 318, 358
Typhotoxine, 621
Tyrosine, 634, 744
Tyrotoxicon, 621

U.

UFFELMANN'S test, 669

Ultramarine, 290

Unguentum Cred6, 331

Urates, 742

Urea, 546, 710

compounds, 546
determination of, 712
manufacture of, 553

Ureids, 547

Ureometer, Doremus', 714

Urethane, 545

Urinary calculi, 745
sediments, 740

Urine, 703

albumin in, estimation, 726
alkaptonic acids in, 739
ammonia in, estimation, 713
analysis of, 704
carbohydrates in, 729
chlorides in, estimation, 719
composition of, 708
estimation of sugar in, 733

Urinometer, 707

Uritone, 543

Urobilin, 705

Urochrome, 705

Uroerythrin, 705

Urotropin, 543

V.

VALENCE, 102
Vanillin, 578

distinction from coumarin, 578
Vaseline, 469
Veratrine, 611
Veratrol, 575
Verdigris, 504
Vermilion, 342
Veronal, 547

774

INDEX.

Vinegar, 502
Vital force, 439
Vitriol, blue, 325

green, 298

white, 315
Volatile oils, 594
Volhard's solution, 427
Volt, 77
Voltaic electricity, 74

induction, 78
Volumetric methods, 406

solutions equivalents of, 416, 419,

422, 426
Vulcanite, 598
Vulcanized rubber, 597
Vulcanizers, 80

W.

WASHING soda, 263
Wassermann reaction, 662
Waste products of animal life, 648
Water, 148

analysis, 429

bitter almond, 578

of crystallization, 152

distilled, 150

drinking-, 149

-gas, 184

hard, 149, 181

lead-, 504

mineral, 149

soft, 149

-vapor, tension of, 53
Waves, actinic, 56

of heat, 51

infra-red, 56

light, 56

ultra-violet, 56
Wax, 520
Weight, absolute, 32

apparent, 32

atomic, definition of, 98

definition of, 31

specific, 32

metric, 32

molecular, 99
Welsbach mantle, 291
Weyl's reaction, 667
Whey, 700
Whiskey, 486
White arsenic, 348

-lead, 321

I White precipitate, 342

vitriol, 315
Widal's reaction, 660
Will-Varrentrap determination of nitro-
gen, 445
Wine, 486'
Witherite, 283
Wood-naphtha, 482

-spirit, 482
Wool-fat, 527
Work, chemical, 142

X.

XANTHINE, 668

alkaloids, 615

bases, 667

bodies, 717

Xanthoproteic reaction, 626
Xeroform, 572
Xylenes, 563

Y.

YELLOW prussiate of potash, 554
-wash, 338

Z.

ZEIN, 628
Zinc, 312

acetate, 503

alloys, 313, 323

amalgam, 313

-blende, 312

bromide, 314

carbonate, 314

chloride, 314

flowers of, 313

hydroxide, 313

iodide, 314

oxide, 313

oxy chloride, 314

oxy phosphate, 314

phenolsulphonate, 573

silicate, 312

sulphate, 315

sulphocarbolate, 573

valerate, 506

-white, 313
Zincates, 317
Zingiberene, 597
Zymogens, 638

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Manual of chem
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