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f ' 






(with Anna Caroline Maxwell) 




(SjMtniah Edition of Practical Nimixig) 


Physics and Chemistry 

for Nurses 


Amy Elizabeth Pope 

Gr«diiAto ol the School of Nartiiii of the Pratbytorian Hospital, 

in the City of New York ; Spodal Diploms ia Bdaoadoa 

from Teaohon College, Golumbie Uoivertity, New 

York ; Formerly Inttniotor in the School of Nnrt- 

ing, Pretbyterien Hotpitel ; Inttniotor in the 

School of Nnrsinl, St. Lnke't Hotpitel, 

Sen Preneitoo, Gel. 

Author of " Quiz Book of Nurttng," " Anetomy end Phytioloty 

for NurMt," " A Medioel Diotionery for NnrMe,'' end, 

with Anne MexweU, of " Preotioel Nurting^* 

Smeond Edition 

HmviMmd and Enlarged 


G. P. Putnam's Sons 

New York and London 
Vhc 'RntcftetbocHev press 

Copyright, x9iS 


Second Revised Edition 

Vbc Unfdteitecicf ^ctfib Itaw (tcft 



The material of the first edition of Physics and 
Chemistry for Nurses has been thoroughly revised 
with help from Mr. Roy Theodore Nichols of the 
Science Department of the San Diego High School 
and author of Syllabus and Laboratory Manual of 
Household Chemistry to whom my thanks are due. 

Amy Elizabeth Pope. 



f I ■■ 


Instruction in hospital-housekeeping is gradually 
attaining a well-deserved place in the curriculum of 
schools of nursing. Since for nurses to have a proper 
understanding of methods of cleaning, laundry work» 
cooking and diet is of infinite value both to the hospi- 
tal and to the nurses, especially those nurses who wish 
to prepare for executive positions in hospitals and for 
social-service work. 

To provide a f otmdation for such knowledge, by 
explaining the principles of the chemical and physical 
properties upon which the various actions that occtir 
in cleaning, cooking, digestion* metabolism, etc., 
depend, was one reason for compiling this book. A 
second purpose was to explain important chemical and 
physical processes constantly referred to in physiology, 
materia medica, and the other studies included in the 
school of nursing curriculum. 

Also, the book contains many important applica- 
tions of the chemical and ph3rsical processes described 
to disinfection, cleaning, cooking, and other procedures 
of interest to nurses. 

In compiling this work, I have consulted all avail- 
able books of chemistry and physics published within 
recent years, but those which were most frequently 
referred to are mentioned in the bibliography at the 
end of this volume, one or more of which books on 

vi Preface 

each subject should be in every school-of-nursing 
reference library. The majority of experiments here 
described^ I have seen performed in the Household 
Chemistry Class at Teachers College, Coltmibia 
University, New York, or in the Domestic Science 
Classes at the State Normal College, Santa Barbara, 

There are probably more experiments given than 
there will be time for pupils in the majority of schools 
to perform, but the book has been compiled with the 
intent that any or all of the experiments can be omitted 
without interfering with the value of the lessons. In 
fact, many of the experiments described were inserted 
to give the students a knowledge of how the facts they 
demonstrate were ascertained and to illustrate facts 
referred to, rather than that the experiments should 
be performed, except by those who are especially 

The tests for food adulteration and the illustrations 
of calorimeters were taken from the different U. S. 
Department of Agriculture publications mentioned in 
the text, with the kind permission of the Secretary 
of Agriculture. 

Amy E. Pope. 




Names and Nattire of Utensils and Chemicals Used for the 
Experimeats Given in this Book — Necessary Care of 
Utensils — Laboratory Maxims — Laboratory Methods 
— ^Weights and Measures i 


Chemistry and Physics Defiiled — Nature of Matter, Mole- 
cules, Atoms — States> of Matter — Molecular Motion— 
The Elements — Physical and Chemical Changes — 
Chemical and Physical Mixtures — Chemical Affinity 
^]^hesion — ^Adhesion 26 


Definition of Hypothesis, Theory, Law — What is Meant by 
Eneigy — Effects of Heat — Different Ways in which 
Heat is Transmitted — Difference between Amount and 
D^ree of Heat — Heat Units — Specific Heat — Latent 
Heat — Heat of Fusion— ^Relation of Pressure and Heat 
— ^Atmospheric Pressure — The Effect of Pressure upon 
the Boiling Point of Liquids — ^The Effect of the 
Specific Gravity of Liquids upon their Boiling Point 37 




Bvi^xuatioQ— Condensation — Humidity — Dew — Fog — 
Frost — Rain — Hail — Snow— Artificial Ice — Distilla- 
tion — Sublimation — Diffusion — Osmosis — ^Dialysis . 55 

. vii 

viii Contents 


RESULTS — {Continued) 

Contraction — Expansion — Vacuum — Suction — Siphooage 
— Capillarity — Conduction — Convection — Some Com- 
mon Practical Applications of Knowledge of the 
Nature and Action of these Processes. ... 71 


The Ether — Absorption, Radiation, Reflection, Refraction, 
and Polarization of Heat and Light — Color of Light 
and of Objects — Finsen Light — Phosphorescence and 
Fluorescence 84 


Theories Regarding the Nature of Electricity and Electrifi- 
cation — Conductors and Non-Conductors — Different 
Methods of Generating Electric Currents — Nature 
and Action of Chemical Cells and Batteries for Generat- 
ing Currents — ^Electrolysis — Electroplating. . 102 


The Dynamo — Different Kinds of Magnets->— Magnetism — 
Induction Coils — Transformers and Other Electrical 
Appliances — ^Electric Currents as a Source of Heat 
and Light — Measurement of Electricity — Static 
Electricity — Physiological Action of Electricity — 
Cathode Rays — X-Rays — Radio Rays . . .117 


Origin of Sound — Some Important Differences Between 
Sound and Light Waves — Transmission of Sound — 
Why Sounds Are Heard — Causes of Differences in 
Sounds — Methods of Intensifying Sound — ^Echoes . 138 

Contents ix 




Nature and Causes of Chemical Reactions — Nature of 

Valence — Radicals — Chemical FormulaB and Equations 147 



Definitions of Organic and Inorganic Chemistry — Char- 
acteristics of Oi*ganic Compounds — Isomers — Carbon 
Oxids — Hydrocarbons and Some of their Important 
Derivatives — ^Alcohols — ^Aldehyds . . . .157 



The Occurrence and Nature of Oxygen — Nature of Oxida- 
tion, Spontaneous Combustion, Oxids, Fireproof 
Material, Fire Extinguishers, Products of Qddatioii . 169 


The Nature and Origin of the Substances Commonly Used 

for Fuel and Lighting ...... 181 


Different Kinds of Solutions — Different Kinds of Adds — 
Characteristics of Acids — Tests for Acids — Properties 
of Bases and Alkalies — Neutralization — Different 
Kinds of Salts — Alkaloids and their Salts — Nature 
of Pats-— Saponification — Nature of Soaps. . 191 





City and Country Water Supplies — Ground Water — 
Springs — ^Wells — Classification of Foreign Substances 
Found in Water — Methods of Purifying Water — ^Hard 
and Soft Water — Methods of Softening Different 
Kinds of Hard Water— Objections to the Use of Hard 
Water 206 


Souroe and Composition of Some Common Detergents — 
Nature of Origin of Material Used for Utensils and the 
Action of Cleansing Agents in Common Use on these 
and on Paint, Varnish, and Wax .... 234 


Classification and Origin of Textiles — ^Effect of Detergents 
on Different Kinds of Textiles — Methods of Removing 
Stains — ^Textile Tests — Printing and Dyeing — Nature 
ofDyes — ^Fading of Colors 260 




Classificationt Nature, and Uses of the Substances Compos- 
ing Animal Bodies and Plants — ^Tests for Proteins, 
Starches, Sugars, Salts — Origin of Food Material . 376 




Classification of Foods— Nature, Digestibility, and Nutri- 
tive Value of the more Common Foods and Beverages 
— Nature and Action of Condiments and Spices • 307 

Contents xi 



The Actkm of Heat, Acids, and Sodium Chlorid on Protein — 
Sdubilities of Proteins — ^The Changes Caused in 
Meats by Cooking — ^The Action of Heat and Adds on 
Starches and Sugars — Solubilities of the Carbohydrates 
of Food — Comparative Thickening Power of Different 
Starches — ^MeUiods of Making Doughs and Batters 
Light — ^The Nature and Action of Pectin . . 345 




Causes for the Spoiling of Food — Nature of the Oiganisms 
that Cause the Spcaling — Chemical and Physical 
Changes that Occur in the Decomposition of Food 
Substances — Conditions Necessary to Prevent Con- 
tamination and to Preserve Food — Some Common 
Forms of Food Adulteration 365 


The Nature of the Changes Occurring in the Digestion of 
the Various Food Stuffs— The Oxgans in Which These 
Changes Occur — ^The Factors and Conditions Influenc- 
ing Digestion — Nature of Enzymes, Zymogens, and 
Kinases 387 



Changes that Occur in Pood Substances during Absorption 
— Nature of Metabolism — Composition of the Blood 
— Changes that Occur in Pood Substances during 
Metabolism— Some Causes and Results of Defective 
Metabolism— The.Fuel Value of Poods— Food Require- 
ments • •••••••• 404 

xii Contents 



Origin of Waste Matter in the Body and the Channels 
through which it is Eliminated — Quantity of Urine 
Voided — Composition of Urine — ^Foreign Substances 
sometimes Pound in Urine, their Origin and Signifi- 
cance — Nature of Urine Analysis — ^Methods of Deter- 
mining the Quantity of Total Solids in Urine — ^Tests for 
Acetone, Diacetic Add, Albumin, Glucose, Indican, 
Bile, Blood, and Pus 416 

Glossary • • . . 437 

Index of Subjects . . . ~ • ' • . ' . 431 

Indbx of Experiments 443 

Physics and Chemistry for Nurses 

Physics and Chemistry for 




Names and Nature of Utensils and Chemicals Used for the 
Experiments Given in this Book — Necessary Care of Uten- 
sils — Laboratory Maxims — ^Laboratory Methods — ^Weights 
and Measures 

Laboratory work, properly performed, is of the 
greatest assistance in gaining an understanding of 
chemical and physical action, but when carelessly 
done, it is a waste of time and material and is often 
dangerous. To get the best results, the student 
must,' from the beginning of her class work, be famil- 
iar with the nature and the use of her apparatus and 
chemicals and know how to work with and care for 
all her utensils; therefore, this first chapter should be 
read with attention. 

Names and Nature of the Principal Utensils Required 
for fhe Experiments Given in this Book 


Pro. 1. Bbaesi. 

Beakers ore made d 
thin highly annealed 
glass and can be used 
lor boiling liquids in if 
wire netting is placed 
between them and the 

Fig. 4. Cbucibls. 
This is made of 
fused silica. It will 
stand a very high 
temperature; even 
dry solid substanocs 
can be heated in it. 

Fig. a. Bom-y. 
Used to hold cold sub- 
stances and to collect 
gas. As it is of thick 
glass, it cannot be used 
tor boiling liquids. 

Fig. 5. Evaporating Dish. 

Liquids can be heated in porce- 
lain evaporating dishes, if wire 
gauze is placed between the 
dishes and the flame. 

Pio. 7. Flask, 

Flasks being of thin 

paas, liquid can be boiled 

in then if wire netting 

u put between tbemtuid 



Pig. 8. Eklsnhbtsk 


This is made of the 

same intiH of jjLus a9 

the flask ahown u Pig. 7* 

Pig. 9. Funnel. 

Fig. 10. Graduated Measures. 

Fig. II. Iron Stand, 


Fia 12. Petri Dish. 


Fig. 14 PtATiNUM 

Wire in Glass 


Fig. 13. Pipette. 

A pipette made as de- 
scribed on page 15 will 
answer the purpose for 
class work. 


Pig, 15. Spatula (Horn). 
Metals being injured by many chemicals, bom 

spatulas are used tor mining dry substances, and 
glass rods for etirriag liquids instead of spoons. 

Fig. 16. 

(a) slide, lb) cover glass for use with micioscc^te. 

For description of microscope, page 98. 

Pic. 18. Tbisils 


Pic. 19. Trianglk. 

Pig. 17. 
(o) Test tube. 
ib) Testrtubo holder. , 
(e) Tect-tube nek. ^ 

Pic. 31. Wates Baib. 

Fra. 23. Wiu Gavh. 

Pig. 36. ScALKs. 

-tales, as(&), are not highly enough sensitized for this purpose ; they are, 
however, necessary for heavier material 

(Pifs. 33~36arementioaedlastasthey wiUnot be found in the iodividnal 
equipment, tbeie being, usually, only a limited nuQiber of theaa arfirkw tof 

6 Physics and Chemistry 

In addition to the articles illtistrated, there will be 
needed fpr each individual equipment: 

A small asbestos mat. 

Stoppers, preferably of rubber, to fit a test tube, a 
flask, and a heavy glass bottle. The test-tube stopper 
should have one hole through the center. There 
should be two stoppers for the flask and bottle, one 
with one hole and the other with two holes through it. 
These holes must be exactly the size of the glass 
tubing that is used. 

Glass and rubber tubing about }i inch in diameter. 

A piece of glass about }^ inch thick and 3 inches 

A tin or enamel dish about 2}^ inches deep and 
io>^ inches in diameter. 



File for cutting glass. 

Glass rod. A fairly good substitute for the solid 
rods usually bought can be made as described on p. 14. 

Filter paper. 

Litmus paper, blue and pink. 

Thermometer, chemical. 

A piece of copper wire about 9 inches long.' 

Bunsen Burner 

This burner was so called after the inventor, a 
German chemist, named Bunsen, The principles of 
its arrangement have been adapted to nearly all 
forms of gas-stove burners. 

Experiment i . Object : To study the Bunsen burner. 

Procedure : Take the burner to pieces and examine 

' This list does oot include the apparatus for xnOk testing, see 
page 385* nor tlie articles required for ttriaalysts. 

Directions for Laboratory Work 7 

its different parts. Pot the parts together again and 

omnect the burner with the gas pipe. Turn on and 

light the gas; to do so, turn on a full current of gas 

and hold the lighted match about two inches above 

and to the ade of the top of the burner, then regulate 

the flow of gas so that there 

will be no waste. Close 

and open the air holes and 

notice the difference in 

the flame. Extinguish the 

flame by pinching the tube. 

Light the gas at the air 

holes. Extinguish the flame 

and relight the gas in th^ 

usual manner. Arrange 

the air holes so that there 

is a yellow flame. Do this 

by turning the small outer 

tube. Hold a piece of glass 

tubing in the flame. 

How long does it take to 
get the tubing soft enough 
to bend? 

Is the flame luminous, i. e., does it give light? 

Is there a deposit formed on the glass tubing? 

Is there mudi or little air entering the air holes of 
the burner? 

Arrange the air holes so that the flame becomes 

In what way does this arrangement differ from that 
required for a yellow flame? 

Is there a deposit on the tubing? 

How long does it take to get the tubing soft enough 
to bend? 

Fig. 37. Parts OP A BuNSBN 

(a) Air holes. 

(w) Wing top. This is 
used when a wide flame is 

8 Physics and Chemistry 

Is the flame more or less luminous than the yellow 

Is there more or less air entering the air holes than 
there was for the yellow flame? 

Which flame will be the best for cooking over? 

Mention two objections to the other flame for 

State a reason why the wrong kind of a flame some- 
times occurs in a cooking stove. 

Why does the gas sometimes strike back and bum 
in the pipe? 

The pupils should endeavor to answer the preceding 
questions before reading the following paragraphs. 

When the gas is turned on it flows through the tube» 
and, as it passes the holes at the bottom of the tube, 
which are provided to supply air, it will, if the 
holes are open, draw the air through them. The 
result is a blue flame, which is hot, but non-luminous. 
This is often spoken of as the Bunsen flame. It is 
the flame used for laboratory work, unless otherwise 
specified, and it is also the correct flame for cooking 

If the air holes are closed, there will not be sufiident 
oxygen admitted to the tube to unite with all the 
carbon of the gas, consequently, some of the latter 
will be separated in the flame by the heat and, at the 
same time, its temperature will be raised to a white 
heat and thus it will become luminous. If anything 
is held over the flame, this unoxidized carbon will be 
deposited upon it. This is often spoken of as sooL 
The flame will not be as hot as the non-ltuninous blue 
flame, because there will not be as much oxidation 
(the combining of oxygen with a substance) going on, 
pn account of the comparative smalln^ss of the m 

Directions for Laboratory Work 9 

supply. If too much air gets into the tube, it and 
the gas will unite to form an explosive mixture and, 
if this is ignited, the force of the explosion will cause 
the flame to strike back to the opening where the gas 
enters the tube. 

Natoie of the Bimsea Flame 

Experiment 2. Object, to study tiie nature of the 
Bunsen flame. 

Procedure: Secure a non-luminous flame and notice 
that it has three distinct color zones. 
Hold a piece of bright copper wire in 
the tip of the outer zone. Notice the 
discoloration that occurs. Hold the dis- 
colored part of the wire near the base 
of the central zone. Observe that 
the discoloration acquired in the tip 
of the outer zone disappears. Why 
does it do so? 

Experiment 3. Take a piece of tub- 
ing, bent as in Pig. 29, and hold one 
end with its opening in the tip of the 
lower zone. After a few minutes ap- Pio. aS. Parts 
ply the flame of a lighted match to *JVq^*^ 
the opening of the free end of the -^ ,,■. "^[^ 
tube. Explain the resiUt. jucing flame. 

The dark zone at the bottom of the 
Same is dark because of the gases issuing from the 
burner. In the middle zone, due to the heat, these 
gases are rapidly uniting with the oxygen of the air, 
but there is still a large quantity of gas present un- 
combined with oxygen. In the outer zone are the 
exceedingly hot products of combustion and some 

10 Physics and Chemistry 

uncombined oxygen that is being separated £rom the 
air. Due to the presence of this tincombined oxy- 
gen, anything that will unite readily with oxygen, as 

copper does when it is heated, 
will become oxidized (i. e., it 
will unite with oxygen) when 
held in the outer zone of the 
flame. This zone, therefore^ is called 
the oxidizing flame. In the central por- 
tion of the flame the hot tmcombined gases 
will remove oxygen from a substance and this 
part of the flame is therefore called 
Fig. 29. the reducing flame, reduction being 
Shape of tube ^jj^ ^ord used by chemists to denote 
or Experiment ^j^^ removal of oxygen from a sub- 
stance. Though there is a larger 
quantity of uncombined gas in the lower than in the 
central zone, reduction will not take place there, the 
heat not being sufEcient to allow of the removal of 
oxygen by the gas. 

Precautions Necessary in flie Use of Utensils 

Do not leave empty vessels of any kind over a flame. 

When about to heat anything in glass or porcelain 
utensils, place the burner in position, light the gas, and 
regulate the flame before putting the utensil over it. 

Use a low flame at first. 

Never heat glass or porcelain utensils that are wet 
in parts not in contact with the contained liquid. 
The reason why they may break if this is done will 
be seen in the sections on expansion and contraction. 

Always rotate test tubes in the flame imtil all por- 
^ons that are to be heated are uniformly hot. 

Directions for Laboratory Work n 

When heating liquids in a test tube, hold the tube 
slantwise as in Fig. 30. 

Put a piece of wire gauze between the flame and 
glass beakers and flasks and porcelain dishes, except 
crucibles. The wire spreads the heat and thus pre- 
vents any one part 
of the utensil be- 
coming much more 
highly heated than 
another. The rea- 
son why this is nec- 
essary, like many 
of the other pre- 
cautions essential 
in the care of glass- 
ware, will be found 
in the sections on 
contraction and ex- 
pansion. Crucibles 
can be placed in a 
triangle directly 
over the flame, if the heat is applied gradually. 

After removing flasks, etc., from the fire, place 
them on a warm asbestos pad, never on a cold 

Clean all utensils thoroughly after use and always 
be sure that they are clean before use, otherwise, 
experiments may be spoiled. 

Numbering test tubes. — In order to avoid confusion, 
it is often necessary to niunber test tubes, etc. Thia 
can be done by cutting Dennison's labels into small 
pieces (about ^ inch square), numbering these, and 
sticking them on the utensil or with a wax pencil. 

Pig. 30. Manner of Holding Tbst 


12 Physics and Chemistry 

to Remember about Chemicals 

They are costly, do not waste them. 

Many chemicals are inflammable; do not bring 
those which are near fire. 

Be careful not to inhale vapors. 

Remember that many chemicals are very corrosive, 
so do not spill any and do not put the bottles away 
wet on the outside. Never lay a stopper on the table, 
but hold it between two fingers with the point pro- 
jecting behind the hand. If a strong add is spilt on 
the flesh or clothing, wash with water and apply 
ammonia or other dilute alkali at once. 

Unless otherwise directed, when mixing strong 
adds — as concentrated nitric, hydrochloric, and sul- 
phuric — ^with a diluent — e. g., water — ^add the add 
to the diluent. 

Remember that many chemicals combine to form 
explosive mixtures and, therefore, be careful not to 
form the habit of bending over your work, and obey 
all precautions given in the instructions. 

Laboratoiy Maxims 

Be accurate, be methodical, be careful, be dean, 
be observing, remember that though the results of 
some experiments are very pronounced, others are 
difficult to discern. 

When performing experiments, keep your notebook 
at hand and record, at once, wdghts and measures 
and everything of importance observed. 

Be on the alert to see, smdl, and hear, but do not 
taste unknown substances tmless directed to. 

Directions for Laboratory Work 13 

Laboratory Methods 

The Preparatioii of Glass Tubing 

To cut 8^8 tubing. — Make a scratch on the tubing 
where it is to be divided with a triangular file; take 
the tube in both hands with the thumbs almost to- 
gether, as in Fig. 31, opposite the scratch, and push 

Pig. 31. Manner of Holding Glass Tubs While 

Breaking it. 

slightly upward with the thumbs. If the tube does 
not break readily, make the scratch deeper, do not 
use force. When cutting hard glass or heavy tubing, 
put a handkerchief or piece of doth between the tubing 
and the hands, 
in case the glass 
should splinter. 
After glass is 
severed in this 
way, the sev- 
ered ends shotild 
be rotated in a 
flame for a few 
minutes in or- 
der to remove 
sharp edges. 

Bending g^ass tubing. — Necessary precautions: 
Heat and cool the tubing slowly, therefore, coat the 


Pig. 32. 
Good bends. (6) 

A poor bend. 

14 Physics and Chemistry 

bend with soot by holding it in the yellow flame and 
do not lay the tubing on a cold surface while it is hot. 
Rotate the tubing while heating it, especially at first, 
so as to prevent cracking by uneven heating. Apply 
the heat continuously and do not attempt to bend 
the tubing tmtil the heat has rendered it perfectly 
pliable. Then remove from the flame and bend, 
being careful while doing so to keep the bend round; 
if the curve is so sharp that the tubing is flattened at 
any point the passage of liquid or gas will be inter- 
fered with, also such bends are brittle and break easily. 
Procedure: Use a wing-top burner. Secure a 
yellow flame. Keep this flame for thin-walled tubing. 

Fig. 33. Holding Glass Tubing in the Flamb. 

but for that with a thick wall, change to a colorless 
flame as soon as the tubing is slightly coated with 
soot at the part which is to be bent. Hold the tubing 
between the thumb and fingers and rotate it in the 
flame until it is pliable; then remove it from the flame 
and bend it into the required shape. It is well to 
keep the tube on an asbestos mat while bending it. 

To draw out glass tubing. — Rotate the central 
portion of the tubing in the flame until it is soft. 
Remove from the flame. Then make traction on both 
ends until the points are of the desired diameter. 

Let the glass become perfectly cold and then cut it 

Directions for Laboratory Work 15 

as previously directed. Tubing prepared in this way 
can be used for pipets. 

To make g^ss stirring rods. — Heat and draw the 
tubing as directed in the preceding paragraph, but 

Fig. 34. Glass Tube Dsawn to a Point, Ready to Cut. ] 

instead of cooling and cutting the point, draw the 
glass apart and fuse the ends in the flame tmtil there 
is no opening. This will result in two tubes eadi 
closed at one end. If a bulb is wanted at the end of a 
rod» rotate the closed end in the flamb until it is soft, 
remove it from the flame, and, at once, blow into the 
open end. Continue blowing until a bulb the desired 
size forms. Such rods are fairly good substitutes for 
solid glass ones. 


Filtering is a process by means of which finely 
divided solids are removed from liquids. It consists 

h c 

Fig. 35. Folding Filter Paper to Fit Funnel. 
(a) Filter Paper, (b) first folding, (c) second folding. 

in making liquids pass through a substance that is 
sufficiently porous not to interfere with the passage of 

i6 Physics and Chemistiy 

liquid matter, but dense enough to prevent or Impede 

the passage of solids suspended in the hquid. The 

methods of filtering will be discussed in Chapter XV. 

In the laboratory, 

filtering is usually 

done with filterii^ 

paper. This is 

folded as shown in 

Fig> 35> s^d placed 

in a fumiel. When 

folding the paper, 

be careful not to 

press it at the point 

or it will tear. 

Place the paper in 

the funnel with 

three thicknesses 

on one dde and 

one on the other. 

Do not allow the 

paper to project 

above the tunnel 

and fit it into the 

Fig. 36. PiLTBMNG. funnel in such a 

manner that its 

entire surface is supported, otherwise the weight of 

the liquid may tear the paper. When the Hquid to 

be filtered is thick, it is usually better to moisten the 

paper with distilled water before pouring in any of 

the liquid. Also, it is well to pour the Uquid down 

the side of a rod held with its point upon the single 

layer of paper, as in Fig. 36. 

To Introduce a powdered substance into a narrow 
necked flask or a test tube. — Fold a strip of paper as 

Directions for Laboratory Work 17 

shown in Fig. 37, place the powder in one end of the 
trough thus made; introduce the paper into the tube, 
turn the paper so that the powder will be deposited 
where desired; withdraw the paper. Slide heavy 
pieces in carefully; a 
flask is easily broken. 


When weighing chem- 
icals, put them on a 
piece of paper or in 
some utensil, as a watch 
crystal, beaker, etc. ; do 
not put them on the un- 
protected pan of the 
scales for many chemi- 
cals will corrode or 
otherwise injure the pan. 
The weight of this pa- 
per or utensil must be 
either noted, recorded, 

Fig. 37. Putting a Powdek 
INTO A Narrow-Necked Flask. 

(a) Paper trough with pow- 
(6) Powder deposited in 

and afterward deducted 

from the total weight of ^^^ 

utensil and chemical, or flask. 

else an object of equal 

weight must be placed in the other pan. The weights 

are put in the center of the right-hand pan. 

Pupils should form the habit of handling weights 
with forceps,for when small amounts are being weighed, 
even moisture from the fingers will interfere with an 
absolutely correct result. 

i8 Physics and Chemistry 


Liquids are measured in graduated glass measures, 

pipets, and burets. 

When using measures, hold the measuring 
glass so that the lowest point of the meniacus ' 
is on a level with the eye. 

To use a pipet, hold it between the thtunh 
and the middle finger of the right hand; placa 
the pointed end in the liquid and the other 
end in the mouth and suck up the liquid 
nearly to the top of the tube, but be very 
careful not to draw it into the mouth; while 
removing the tube from the mouth, quickly 
place the index finger over the top. Then, 
by slightly releasing the pressure of the fin- 
ger over the opening, either allow the num- 
ber of drops required to escape, or, if the 
pipet is a graduated one, allow the liquid to 
drop from the tube, back into the botUe, un- 
til the top of its column is on a line with the 
mark of the quantity required. Then hold 
the pipet over the utensil into which the 
liquid is to be put and release the finger over 
the opening; the pressure of the air entering 
the tube will force the liquid from it. 
When using a buret, pour the liquid to be 

Pig. 38. measured into the buret tube, place a recep- 

BuBET tacle under it, and, carefully, release the 

pressure of the stop cock on the rubber tubing 

until the amount of liquid required has passed into 

the receptacle. 

■ The upper surface of a fluid column, as that of mercury in a 
thermometer. The lowest point, «. e,, in the center, is considered 
the correct height of the column of liquid. 

Directions for Laboratory Work 19 

List of Chemicals, Solutionsi and Reagents Needed 

for Experiments 

Acetic add. CH3COOH. Commercial acetic acid 
is about 36%. Glacial acetic add is 99%. 

Acetic anhydrid. C4H6O3. 

Alcohol, amyl. CjHixOH. 

Alcohol, ethyl. CaHjOH. 

Alum. KAICSO^),. 

Ammonltmihydroxid. NH4OH. This as purchased 
is about 28%. Known also as ammonia water. 

Ammonium molybdate solution. (NH4)aMo04. 
This is prepared as follows: Add 25 gm. of molybdenum 
oxid (M0O3) to 100 cc. of NH4OH and stir the solu- 
tion tmtil the powder is dissolved. Cool and add 
250 cc. of nitric add. 

Ammonium oxalate. (NH4)aCa04. 

Barium chlorid. BaCl,. 

Benzoic add. CyH^Oa. 

Borax. NaaB407. loHaO. 

Boric add. HjBO^. 

Caldum carbonate. CaCO^. 

Caldum chlorid or chlorid of lime. CaCla. 

Caldum sulphate. CaS04. 

Carbon disulphid. CSa. This is very inflammable. 
It is only required for Experiment 75. 

Chloroform. CHCI3. 

Copper sulphate. CUSO4. 

Fehling's solution. This is prepared as follows: 

Solution A: Dissolve 34.64 grams of copper sul- 
phate in 400 cc. of distilled water. When this is dis- 
solved, add enough water to make 500 cc. of solution. 
Solution B: Dissolve 180 grams of Rochelle salt in 
500 cc. of sodium hydroxid solution, 10 %. 

20 Physics and Chemistry 

Ferric alum. KPe(S04)a. i2HaO. 

Fibrin. Dried blood fibrin can be obtained from 
dealers in chemical apparatus. 

Hydrochloric add. Known also as mtuiatic acid. 
HCL The concentrated solution is 40%. For the 
dilute solution add i volume of the concentrated add 
to 4 volumes of water. 

lodin. I. Tincture of. 

Lead acetate. (CH3 COO) a Pb. 

Litmus powder. 

Logwood, tincture of. 

Mercuric chlorid, corrosive sublimate, or bichlorid 
of mercury. HgCU. 

Millon's solution. Make as follows: Dissolve 5cc. 
of merctuy in 95 cc. of concentrated nitric add and, 
when action ceases, add twice the voliune of cold 

Nitric add. Known also as aqua fortis. HNO3. 
Concentrated nitric acid is 70%. For the dilute solu- 
tion add I volume of the concentrated add to 4 
volumes of water. 

Oxalic add. (COOH)a. 

Pancreatin solution. This can be made by dis- 
solving 2 grams of the.commerdal pancreatin in 300 
cc. of warm — not hot— water. Or it can be prepared 
as follows from the fresh pancreas of a pig: Free the 
pancreas from fat as far as possible; mince it, weigh it, 
put ia into a flask, and add three times its wdght of 
distilled water and its own wdght of alcohol. Shake 
the flask vigorously and then let it stand for three 
days at room temperature, shaking it occasionally. 
Then strain the solution first through muslin and 
afterward through filter paper. Measure the filtrate 
and, for every liter, add i cc. of strong HCL Let 

Directions for Laboratory Work 21 

this stand for a week and then filter. Pour the filtrate 
into a flask that can be tightly corked. It will keep 
indefinitely, the alcohol acting as a preservative. 
The solution contains trypsin and amylopsin, but no 
lipase. See Chapter XXII. 

Pepsin solution. This can be made from the com- 
mercial pepsin. The percentages required are given 
in the experiments, Chapter XXII., and the solution 
should be prepared on the day that it is wanted, as 
it does not keep. 

Potassitmi fenocyanid or yellow prussiate of potash, 

Potassium permanganate. KMn04. 

Potassium thiocyanate or potassium sulphocyanid. 

SaUcyHcacid. CfiH.OH.COOH. 

Silver nitrate. AgNOj. Solution 2%. 

Soap solution. Make as follows: Shave and dis- 
solve 50 grams of white castile soap in i liter of hot 
water. Filter the resulting solution. 

Sodium carbonate. NajCOj. 

Soditun chlorid. NaCl. 

Sodium hydroxid. NaOH. 

Starch solution. Blend one teaspoonftd of starch 
with one tablespoonful of cold water and then add 
slowly, while stirring, 250 cc. of boiling water. Boil 
the solution for three minutes. This should not be 
prepared long before it is required for use. 

Sulphuric acid. HaS04. Concentrated 94%. For 
the dilute solution add i volxmie of the commercial 
add to 4 volumes of water. 

Tumeric paper. 

22 Physics and Chemistry 

Points to Remember when Making Solutions 

When diluting the adds, add the acid to the water 
and use cold water. 

When dissolving solid substances, use boiling water 
unless otherwise specified. Two important excep- 
tions are pepsin and pancreatin; for these use warm, 
but not hot, water. 

When calculating the amount of a chemical to use 
remember that i per cent, means one part in one hun- 
dred. Therefore to make a i per cent, solution use I 
gram or i cc. of the substance to be dissolved to loo 
cc. of water or whatever solvent is to be used. For a 5 
per cent, solution, use 5 grams or 5 cc. in 100 cc. 
For a 10 per cent., use 10 grams or 10 cc. in 100 cc. 
For a :^ of a I per cent, use i gram or i cc. in 1000 cc. 
For a ^ of a I per cent, use 2 grams or 2 cc. in 
1000 cc. of solvent. 

Unless otherwise specified the strengths of the solu- 
tions for the experiments are to be as follows: Dilute 
adds, diluted according to the directions already 
given; concentrated axtmionia; 10% solutions of the 
other hydroxids and the salts. 

Mbtric Wbigbts 



.001 of a gram 
.01 " " " 




Principal unit 



10 grams 
' 1000 " • 

10,000 - 

Directions for Laboratory Work 23 

Comparative Values of Apothecaries* and Metric 

Fluid Measures 

Minims CuMc 

Minims CiOnc 

Flnid Cnhie 

Fluid Cubic 



Ounces Centimeters 

Ounces Centimeters 





9 — 59.30 

3Z— 63Z.00 

2 -0.13 

30— Z.90 

3 — 89.00 

33 — 650.00 . 

3 -o.x8 


4- ZZ8.40 

33 — 680.00 . 


40 —3.50 

5- Z48.00 

6- Z78.00 

34— 7Z0.00 

5 -0.30 


35— 740.00 
30- 769.00 


7- 307.00 

1 7-0.43 

8 -0.50 


8- 336.00 

37- 798.50 

9— 360.00 

38— 838.00 

zo —0.60 


zo— 395.70 

39— 858.00 
30- 887.35 

I, - 3.75 

zt- 335.35 

zz —0.68 

zj- 4.6s 

Z3— 355.00 

31- 917.00 


z}- S.60 

Z3- 335.00 


Z3 -0.80 

zf- 6.5Z 

Z4- 4x4.00 

or —946.00 ! 


3- 7.50 

is'^ 444.00 

z quart 

Z5 -0.9a 

3— ZZ.35 


48 -Z4 19.00 
56 — X055.00 
04 — Z893.00 
73— 3za8.oo 


or -473.XI 


5 - Z8.50 

z pint J 

17— 503.00 


7 —36.00 

x8— 533.00 

96 — 3839.00 


19— 563.00 


30— 59X.50 

XZ3— 33x3.00 

I — 30.001 



Grains Grams 





Drams Grams 

ilf— 0.00065 




- Z.70 


^ — 0.00ZOZ 




- X.75 

— X.83 






A -0.00x30 




— X.87 

«| —0.00x35 
A — O.OOZ63 




- X.95 

_ 7-37.30 




- 3.00 





— 3.X0 

X- 3T.Z0 
3 - 03.3O 

A — 0.00303 




— 3.X6 

tfl— 0.003X6 




— 3.30 

3 - 93.30 

A -0.00359 




— 3.35 

4- X34.40 

A -0.00370 




- 3.30 

iz ;ii:is 

iS -0.00334 




- 3.40 

A —0.00360 




- 3.47 

7- 3Z7.70 
S— 348.80 

9— 380.00 

A -0.00405 




- 3.55 

A — 0U>0433 




— 3.60 

A -0.00540 


- X.040 


- 3.73 

XO- 3ZX.0O 


1 -0.00648 


— I.X03 


- 3.80 

XX- 343.Z4 

-0.008 zo 



- 3.00 

X3- 373.33 

— O.OZO8O 


— Z.340 


- 3.35 

X4- 435.50 
x6- 497 >6o 

— O.OZ396 




- 3.40 

— 0.0Z63O 




- 3.65 

34- 746.40 
48 — 1493.80 

\ -0.03Z60 




- 3.75 

} -0.03340 
1 —0.04860 
t -0.065 








X- 3.90 
3- 7.80 


Physics and Chemistry 





- 14.17$ 

z ■" 38^50 
2- 56.700 
3"i 85.050 
4 -1X3^00 


8 ■■336.80 

9 -ass.iS 
zo«> 383.50 

Z3 —340.30 

X3 -368.54 
Z4 -396.90 

X5 -425.35 

I - 4S3.60 
a — 907.X8 
3.3 » 1000.00 
3 —1360.78 







Comparison of Centigrade and Fahrenheit 

Thermometric Scales 

Cbkt. Pabr. 

Cbkt. Pabr. 

Cknt. Pahr. 

Cbkt. Pahr. 

zoo — 3Z3 

63.3— 144 



X3.3- 8 


61. z — 143 



Z4.4- 6 
Z5.6- 4 

97.8- 308 

60 — Z40 




58.9- Z38 



Z6.7- a 


57.8 -Z36 

30 — 



94.4- 303 

56.7 - Z34 



Z8.9- a 


55.6- 133 

Z7.8 — 


30 - A 
3Z.Z— 6 

93.3— Z98 

54.4- 130 

Z6.7 — 


9I.Z— 196 

53.3— Z38 

Z5.6 — 


33.3— 8 

90 -194 




23.3— xo 

88.9— 193 

51. Z— 134 



34.4- Z3 

36!7- xo 

87.8— Z90 

50 -133 

Z2.3 — 


86.7- x88 

48.9 -Z 30 

ZI.Z — 


85.6- z86 

47.8 -zz8 

zo - 


37.8- Z8 

84.4 -Z84 

46.7 -z 16 



38.9— 20 

83.3 -z83 

45.6- z 14 



30 - 33 

83.3- z8o 




3Z.Z- 34 

33.3- 36 

8z.z— X78 




80 -Z76 

43.3 — 108 



33.3- 28 


41.1- 106 



34.4- 30 
35.0- 32 


40 -104 

3.3 — 


76.7 -z 70 

38.9 -103 

z.z — 


36.7- 34 

37.8- 30 

75-6 -z68 

37.8 — zoo 



74-4 -l^ 

36.7- 98 

1.1 — 


38.9- 38 

73-3 -X64 

35.6- 96 

3.3 — 


40 - 40 


34.4- 94 



4Z.Z- 42 


33.3- 92 



42.3- 44 
43.3- 46 

22 "'5? 

32.2— 90 



3Z.Z— 88 



44.4- 48 
45.6- 50 


30 - 86 




38.9- 84 



46.7- 52 


37.8- 83 

10 - 


47.8- 54 

48.9- SO 

64.4 -Z48 

36.7— 80 



63.3 -Z46 

35-6- 78 



Directions for Laboratory Work 25 

Method of Converting One Scale into Another 

1. To change a Fahrenheit reading into centigrade: 
Subtract 32 from the given degree (the freezing point 
in the Fahrenheit scale being this much higher than in 
the centigrade scale), mtiltiply the remainder by 5, and 
divide the result by 9. Thus: 

2i2*^F.— 32«i8oX5«900-§-9«ioo*^ C. 

2. To change a centigrade reading into Fahrenheit: 
Mtiltiply the given degree by 9, divide the result by 5^ 
and add 32 to the remainder. Thus: 

ioo^C.X9 =900-5-5 = 180+32 =2i2**F. 



Chemistry and Physics Defined — Nature of Matter, Molecules, 
Atoms — States of Matter — Molecular Motion — ^The Ele- 
ments — Physical and Chemical Changes — Chemical and 
Physical Mixtures — Chemical Affinity — Cohesion — Adhe- 

Chemistry and physics defined. — Chemistry and 
physics are very intimately related since they are 
both concerned with the study of the Aattire of matter, 
especially inanimate matter, and with the changes 
which matter may be made to undergo. Chemistry, 
however, is more particularly devoted to the study of 
the composition of matter and is therefore often de- 
fined as the study of the composition of matter, and 
physics being more especially concerned with the 
properties and activities of matter has been defined as 
the study of the properties of matter and as the study of 
matter in motion. 

Nature of matter. — ^By matter is meant anything 
which possesses weight and which occupies space* 
All matter is composed of inconceivably small par- 
ticles called molecules and molecules are composed of 
still smaller particles called atoms. 

Molecules. — ^A molecule is said to be the smaUesi 
part of a compound that can exist by itself and main'- 


Nature of Matter and its Elements 27 

tain its identity. Thus a molecule consists of two 
or more atoms. The atoms composing a molecule 
may be all of the same element, e. g,^ all hydrogen or 
all oxygen, etc., or they may be of different elements, 
e. g., a molecule of water consists of two atoms of 
hydrogen and one of oxygen. 

Atoms. — An atom was formerly defined as the 
smallest particle of an element that can exist and 
atoms were thought to be absolutely indivisible, but 
it has been shown that atoms of elements are made of 
still smaller particles to which the name electrons 
has been given and a definition used for an electron 
is a unit or atom of negative electricity. Atoms do 
not, however, separate in ordinary chemical reac- 
tions and they are still generally regarded as being 

Compounds and elements. — ^A compound is a sub- 
stance made up of two or more elements; an element 
is a substance which cannot be di\aded into simpler 
substances by any known means. For example, 
water is a compound of hydrogen and oxygen, but 
hydrogen and oxygen have never been subdivided and 
are therefore considered elements. 

States of matter. — Matter is generally described as 
existing in three physical states, viz., solid, liquid and 
gaseous. All matter, however, cannot be classified as 
belonging strictly to any one of these three states and 
thus we speak of semi-solids and semi-liquids. Neither 
is the ordinary physical state of any kind of matter 
a fixed unchangeable thing, for by increase of tem- 
perature, solids can be liquefied and liquids vaporized 
(i. e., made gaseous), and by putting gases under 
pressure in a low temperature, they can be changed 
to liquids and a low temperature will solidify liquids. 

28 Physics and Chemistry 

A very great change of temperature is not necessary 
to transform the physical state of some substances, 
but only very excessive changes will alter that of 

One of the great differences in the nature of matter 
in its different physical states is the dissimilarity of 
the motion of its molecules. 

Molecular motion. — It is the belief of scientists 
that the molecules composing all matter are constantly 
in rapid motion, but that differences exist in the kind 
of motion possessed by the different forms of matter. 
Thus, in solids, it is thought, the molecules oscillate 
with great rapidity about certain fixed points, but 
are held in their relative position by their attraction 
for each other or, as this is called in physics, cohesive 
force. However, even in solids, as will be discussed 
in the section on diffusion, the molecules sometimes 
break away. In liquids, though the molecules tend 
to ding together, they have no fixed position, but 
move about freely; thus liquids can adjust themselves 
readily to the shape of any vessel into which they are 
put, and when different liquids are poured into a 
vessel, they soon become mixed, as they would not 
do if their molecules were fixed and motionless. The 
movement of gas molecules is very marked and they 
exert no cohesive force whatever upon each other, 
but, on the contrary, they tend to separate and fly 
apart indefinitely, spreading in all directions. One 
evidence of this is the rapidity with which the odor 
of a gas (e. g, amimonia) will be perceived at a distance 
from an open vessel containing even a solution of the 
gas. The odor of the gas cotdd not become thus 
diffused if the molecules were stationary in the vessel 
for there would be no odor were there not some 

Nature of Matter and its Elements 29 

molecules of the gas present in the air that is in* 

Until the idea of molecular motion was conceived, 
scientists found it impossible to explain many com- 
mon phenomena, such as pressure of gases, evapora- 
tion, contraction, and expansion. 

Number and condition of elements. — ^There are 
about eighty-three elements known at the present time. 
Of these, eleven are ordinarily gaseous — the principal 
gaseous ones being oxygen, hydrogen, nitrogen, and 
chlorin — ^two are liquid — ^mercury and bromin, and 
the others are solid. 

Symbols. — ^In order to facilitate the explanation 
of the composition of chemicals and of chemical re- 
actions, chemists have adopted symbols to represent 
the elements. These symbols consist of the initial 
letter of either the Latin or the English name of the 
element, or when there are two or more elements 
having the same initial letter, of the initial and one 
other letter. For example, C stands for carbon, CI 
for chlorin, N for nitrogen and Na for sodium, the 
Latin name of which is natrium. A number placed 
slier a symbol shows that there are as many atOBis of 
the element as the number designates; thus HaO 
(water) signifies that in each molecule of water there 
are two atoms of hydrogen and one atom of oxygen. 

Atomic weight. — ^Atoms of the elements are believed 
to have fixed weights, but, as it would take about 
200,000,000 hydrogen atoms placed side by side to 
form a line one centimeter in length, their weight can 
be calculated only as relative to some fixed standard 
that is given a supposititious weight. For example, 
hydrogen, which, was formerly used as the standard 
was given a supposititious weight of one, called by some 


Physics and Chemistry 

writers one microcrith, ' and the weight of each of the 
other elements was determined by fibnding the weight 
of the amount that combined with a definite weight 
of hydrogen. Lately, oxygen has been chosen as a 
standard because as more elements unite to form de- 
finite compounds with it than with hydrogen it is 
easier to compare their weight with it than with the 
latter. The atomic weight of oxygen, however, is 

Molecular weight. — In studying chemistry, one 
hears constantly not only of atomic weights, but also 
of molecular weight. By the weight of a molecule 
is meant the stun total of the weights of all the atoms 
composing it. Thus, the molecular weight of calcium 
carbonate (CaCO,) will be lOo because, as shown by 
the symbols, it is a compound consisting of i atom of 
calcium, which weighs 40, one atom of carbon, which 
weighs 12, and three atoms of oxygen each one of 
which weighs 16; thus 40+12+48 = 100. 

The following table gives the names of the elements, 
their derivation and atomic weights. It is of course 
not necessary to memorize any of the weights, and 
only, the elements marked with an asterisk need be 

A Table of the Elements 





WiiBRR Found 
IN Naturb 





A white metal that 
is very light, stiff, and 
strong. It is a good 
conductor of neat 
and of electricity. 

In many soils and 
rocks, where it exists 
in the form of ozids 
and salts. 

> The microcrith is defined as the weight of one atom of hydrogen. 
It is not any definite weight and is so infinitely small that it 
cannot be compared with sach weights as grams and grains. 

Nature of Matter and its Elements 31 

































A bluish-wbite, 
hard, brittle, solid. 



A steel-gray brittle 
metallic^ooldng sub- 

A pale-yellow 


A grayish-white 
crystallme solid. 

Resembles silicon. 

A dark red liquid 
about three times as 
heavy as water. Its 
vapor has an offen 
sive odor and is very 
irritating to the eyes, 
throat, etc 

Resembles zinc. 

A white metal. 


Silvery-white met< 

A solid that is 
amorphous in char 
coal; crystalline in 
diamond and graph- 
ite. Its comi>ounds 
are numerous and oc 
cur as gases, liquids 
and solids. 

Resembles iron. 

A greenish-yellow 

f[a8. It has a pecu' 
lar suffocating odor, 
and, if inhaled, i>ro- 
duces a severe irrita- 
tion of the respira 
tory tract. It has a 
strong affinity for 
hjrdrogen and it com 
bmes readily with 
many metals. 
A hard metal. 

Whsrs Pound 
IN Naturb 

Occurs in nature 
chiefly as a sulphid 
called stibnite, but is 
found also as an ozid 
and as a constituent 
of various complex 

In the air. 

In various ores. It 
occurs most frequently 
in the form of salts 
and other compounds 
the majority of which, 
unlike pure arsenic, 
are highly poisonous. 

In minerals. 

In beryl and in 
various mmerals. 

Occurs in certain 
localities in uncom- 
bined state, and also 
as an oxid and sulphid. 

Chiefly in borax and 
boric acid. 

In sea salt and the 
salt ot various springs 
and salt deposits. 

In sine oree. 

Chiefly in mineral 

In various com- 
pounds as marble, 
limestone, fluorspar, 
phosphorite, gypsum, 

In all organic matter 
and a few inorganic 
substances as dia- 
monds, calcium car- 
bonate, sodium car- 
bonate, etc. 

In a few rare min- 

In sea-water and in 
salt-deposits in the 
forms of chlorids.espe- 
cially those of sodium, 
potassium,and magne* 
sium. It is never 
found free in nature. 

In chromite 
^chrome iron ortt. 



Physics and Chemistry 





Whbrb Pound 
IN Natubs 




A reddiah or white 
metal (some of its 
■aits are blue). 

Ooeors chiefly in 
combination with 
arsenic and sulphur. 





In columbite and a 
few other rare mia* 


(L«t. Cuprum) 



A reddish colored 

Pree and in varioot 






In the sun. 




A very inert gas. 

In the air. 



A metal-like solid. 

In some rare metals. 




Gas, resembles 

In a few minerals, 
chiefly fluorspar. 





In a few minerals. 





In some sine blends. 





In the metal argy- 





In beryl and a few 

♦Gold {Aurum) 




Pree and in ores. 




A light gas. 

In the atmosphere. 




A very light gas. 

In water and in 
many other com- 
pounds both organic 
and inorganic. 





In zinc ores. 




crystals which vapor- 
ize at ordinary tem- 
peratures, giving ofl 
a violet-vapor ofun- 
pleasant odor. 

lodin occurs free in 
sea-water, from which 
it is absorbed by cer- 
tain sea-planta, so that 

it is found in their 

ashes. Also it is found 

in salt springs and 

beds and in Chili salt- 






In a rare mineral 
called iridosmin. 

♦Iron {Penum) 




A common constit- 
uent of rocks and 
soils. It is assimi- 
lated by plants and 
animals and is essen- 
tial to their life. 





In the atmosphere. 





In a few rare metals. 

♦Lead {Plumbum) 




Occurs chiefly as a 
sulphid called galena. 
In a few metals, as 




Silvery-white alka- 

li metal. 

lepidolite. and, in the 
form of carbonates 
and chlorids. in some 
mineral waters. 



White metaL 

It is a constituent 
of many rocks, also 
salts of the metal are 
found in sea-water 
and salt-deposits. 




A hard gray metal 
somewhat like iron. 

In some iron ores 

and minerals and as 

a dioxid called pyro^ 


Nature of Matter and its Elements 33 





Whxrx Found 
IN Naturb 




A heaTjr vlvery 

It occurs chiefly as 



a sulphid called cin* 
nabar, and in globules 
of metal inclosed ia 
the cinnabar. 




A metal-like ele- 

In molybdenite. 



In a few rare mia« 




An inert bm. 

In the air. 





In metallic ores. It 
is usually found com- 
bined with arsenic or 

In the air and ia 





many organic and in- 

organic substances. It 

is an essential con- 

stituent of all living 





In platinum and 



Coloileis, odorleu, 
tasteless gas, slightly 

It occurs free in the 
air; in the combined 
state, it forms | of 
water and enters mto 
the composition of all 
organic^ and nearly all 
inominic, compounds. 
Free and in com- 



A iilver-w h i t e 


bination with other 
metals, especially gold 
and platinum. 




A yellowish, waxy, 
soft solid. 

In the form of vari- 
ous phosphates. P. 
occurs in many or- 
ganic and inorganic 



194* S 

A grayish-white 
metal of high luster, 

Chiefly alloved with 
ffold and what are 
known as the plati- 

very malleable and 


num metals. «. «., rho- 
dium, pallidium, and 




A soft alkali metal. 

In many rocks, min- 


It decomxxMes water 
very vigorously and 
the heat evolved in 
the chemical reaction 
is sufficient to ignite 
the hydrogen set free. 

erals, and organic 
compounds. It is 
never found free ia 




In a few minerals. 




• • • 

In pitchblend. 




White metal. 

Usually in conaeo> 
tion with platinum. 





In certain mineral 





Associated with 




In a few rare aita« 





« • • 

In a few mtaarale. 


Physics and Chemistry 



(Lat. Argtnium) 

(Lat. NaiHum) 





•Tin {Stannum) 








A non-metallic 



A non-metallic 
solid substance that 
occurs in both crys- 
talline and amor- 



A lustrous white 



A soft alkali metal 
that resembles potas- 



An alkaline earth. 



A paie*yellow crys- 
talline solid. 



A black Mwder- 
like solid. 



A silver-colored 



• • • 



A soft white metal 
bel6nKing to the 
same class as alumin- 



A gray metallic 
powder of the nature 

of cerium. (Oxids 

of these two elements 

are used in the pre- 


paration of Welsbach 
mantles, becaiue of 
the intense light giv- 
en out by a mixture 
of these oxids when 
they are hieated.) 



• . . 



A soft metal that 
melts at about 235* 
P. and is very mal- 


48. z 

Resembles silicon. 


A very hard, brit- 

tle, nearly infusible 



Whskb Found 
IN Natu&b 

In some minerali 
and sulphur. 

Next to oxygen, sili- 
con is the most abun- 
dant element in na- 
ture; it is never found 
free, but its com- 
pounds constitute a 
large portion of the 
earth's crust. It is 
senerally prepared 
from quarts. 

Free and in many 

It is never found 
free, but its com- 
pounds are numerous 
and widely distri- 
buted. They occur in 
rocks, sea-water, salt 
deposits, and organic 

^ In the metals stron- 
tianite and celestite. 

Free, especially in 
the neighborhood of 
volcanoes, and in the 
form of sulphates and 
sulphids in a variety 
of minerals and many 
organic substances. 
In a few mineriUs. 

In a few minerals. 

In a few minerals. 

In many ores, in the 
minerals known at 
p^ites, and in com- 
bination with sulphur. 

In a few rare min- 

In a few rare min* 

It occurs chiefly at 
the oxid called cassi» 
teriU or Hnstont, 

In soil and rocks. 

Chiefly as ferrous 
tungstate in the mia* 
eral wolf raa. 

Nature of Matter and its Elements 35 





Whssb Found 
IN Natuue 




A rare metal be- 
longing to the same 
dasB as tungsten. 

A crystalline me- 

In pttchblend and a 
few minerals. 




In a few minerals. 

tallic substance. 




In earth. 





In the air. 




A solid substance. 

In a few minerals. 




An earth metal. 

In a few minerals. 




A heavy bluish 

In a few ores. 




A solid that occurs 
in both crystalline 
and amorphous 

In a few rare min- 

Physical and chemical changes. — Eveiywhere in 
nature change is constantly taking place. Matter 
is being continuously broken down, complex sub- 
stances reduced to simple ones, and these simple sub- 
stances are as constantly being built up, sometimes 
into very different combinations from their original 
form. All life and growth are dependent upon such 
changes. According to their nature these changes 
are classed as physical and chemical; physical changes 
being those which do not affect the identity of the 
substance and chemical changes those which do alter 
its composition. Chemical changes are usually ac- 
companied by ph3^ical, either as a cause or effect. 
When cane sugar is dissolved in water, a physical 
change has taken place, because if the water is evap- 
orated, the sugar will be obtained in the same form 
as it was originally, but, if cane sugar is boiled with 
acid, it will be changed to quite a different substance, 
viz., glucose; this, therefore, is a chemical change. 
The freezing and vaporization of water are physical 
changes, because if the ice is melted or the steam con- 
dense, water, similar to that frozen or vaporized, 
will be obtained. If a substance (e. g.^ a piece of 

36 Physics and Chemistry 

wood) is btimed, a chemical change is perpetrated, 
for by no known means can the ashes which remain 
and the gases which have passed into space be put 
together again to form a piece of wood like unto that 
which was burned. 

Physical or mechanical mixtures and chemical 
compounds. — ^When two or more substances of a 
different nature are mixed together, but do not enter 
into direct combination with, or change the nature of » 
each other, the mass is called a mechanical mixture^ 
but when the substances combine, forming matter 
of a different nature, the result is known as a chemical 

Chemical aflinity. Cohesion, Adhesion. — One 
cause for both the stability and change of matter 
is chemical affinity. By this is meant the attraction 
that certain elements have for one another which causes 
them to combine, and which holds them together when 
combined. The reason for this attraction has not been 
proved, but it is thought that it may be at least 
partly due to electrical charges. This will be further 
discussed in Chapter X. In physics, the attraction 
which holds molecules of a like nature together is 
spoken of as cohesion and that which holds substances 
of tmlike character together is called adhesion. 

Surface tension. — ^The predominating reason for 
such phenomena as the spherical shape of drops of 
liquid and the separation of immiscible liquids, as oil 
and water, is the cohesive force of the molecules of the 
liquids which draws them together. When manifest 
in such ways it is known as surface tension. 



DefimtttQ of Hypothesis, Hwoiy, Latv^WKat is Meant by 
EDexcr-Bffects ol Heat— Different Ways in which Heat it 
Transmitted — Difference between Amount and Degree oC 
Heat— Heat Units— Specific Heat— Latent Heat— Heat o! 
Posion— Rdation o£ Pressure and Heat — ^Atmospheric 
Pressure— The Effect o£ Pressure upon the Boiling Point 
of Liquids— The Effect of the Specific Gravity of Liquids 
i;qx3n their BoiLing Point. 

The changes that occur in nature, either chemical 
or physical, are not carried on in a haphasard manner, 
but are controlled by absolute, often unalterable, 
forces. In referring to or describing these forces of 
nature, the scientist often speaks of them as laws. 
There are, in fact, three words often used by scientists 
in this connection, viz., hypothesis ^ theory ^ law. 

Definitions of above terms. — An hypothesis is 
sometimes defined as a suggestion^ the truth of which 
has not been proved, that is advanced as a reason 
for, or as a cause of, some fact or law. An hypothesis 
is also often spoken of as a working theory, because 
an unproved suggestion or idea of what may bo the 
cause for certain effects — in other words an hypothe* 
sis — is often the first step in the work of discover- 
ing hidden forces of nature or of the application of 
these forces to practical inventions. By theory is 


38 Physics and Chemistry 

meant a long-standing hypothesis for phenomena that 
accounts jot them so satisfactorily thai it seems to be 
true, though its validity ha^ never been proved. When 
a theory has been tested in every known way and is 
proven to be invariably accurate it is called a law. 

The following laws and hypotheses, which are a 
few of those frequently referred to in physics and 
chemistry, will be often alluded to in this or following 

Atomic hypotheses. — (i) All elements are made up 
of minute, independent particles called atoms, (2) 
All atoms of the same kind of element are alike, 
atoms of different kinds of elements are different. 
(3) All atoms combine by wholes to form compotmds; 
atoms are never divided in chemical reactions. 

Law of definite composition. — The composition 
of chemical compounds is not altered by changes in 
their phsrsical state; e. g,, water, whether it exists in 
liquid, solid» or gaseous form, consists of H^O. 

Law of the conservation of energy. — Energy can 
be changed from one form to another, but it cannot 
be either created or destroyed. For example, radiant 
energy from the sun produces chemical energy in 
plants which causes them to grow. This energy, 
which binds the atoms of the plant constituents 
together, remains locked in the molecules and is 
known as latent or potential energy, but, when the 
plants are used for food, the energy is liberated from 
as much of their substance as is oxidized in the body 
tissues and appears in the form of heat energy and 
mechanical energy. Or, for another example, the 
plants that have decayed and in the cotirse of time 
turned to coal, contain, stored in their substance, the 
energy, derived from the sun, which furthered their 

Energy, Heat, and Pressure 39 

growth, and when the coal is set on fire this stored 
energy is transformed into heat, light, or electrical 
energy; and though energy thus used may seem to 
have come to an end, it has simply assumed some 
other form and exists somewhere. Thus the amotmt 
of energy in the universe remains unchanged. 

Law of the conservation of matter. — Matter can 
be changed from one form to another, but it cannot 
be either created or destroyed. For example, a 
house may be burned, but the elements composing it 
are still in existence, some in the fonn of ashes, some 
as gases that have passed into space. The oxygen 
of the air, which maintained the combustion, united 
with some of the carbon and hydrogen in the burning 
matter, forming thereby carbon dioxid (CO a) and 
water (HaO) ; this will be absorbed by plants and by 
them changed to the substances they need for their 
growth, and while doing this they will give off oxygen 
and thus the oxygen will be returned to the air once 
more. If the plants die, the elements of which they 
are composed may be scattered, but they will still 

Laws of boiling. — (i) Under a given pressure, every 
liquid has a definite boiling point; for example water 
boils at 100^ C, alcohol boils at 80® C, mercury 
boils at 350^ C. (2) When the boiling point is reached 
the temperature remains constant unless the pressure 
is increased. 

Law of Boyle. — ^The volume of a gas varies inversely 
with the pressure that is put upon it; i. ^., when a gas 
is under heavy pressure, it will occupy but a small 
space, but when pressure is released, the gas will 
expand and thus increase its volume. 

Law of Charles* — ^Every true gas expands -^ of its 

40 Physics and Chemistry 

volume^or each degree centigrade that its temperatare 
is increased and it contracts rkr of its volume for 
each degree centigrade that its temperature falls. 

Laws of liquid pressure. — (i) Pressure in liquids 
is proportional to the depth alone and is not influenced 
by the size or shape of the vessels which contain 
them. (2) At any given depth the pressure is equal 
in all directions. 

Laws of pressure in gases. — (i) Pressure in gases 
increases with depth, but is not proportional to it. 
(2) At any given depth the pressure is equal in all 

Difference between the use of the terms gas and 
vapor. — ^The word gas is usually applied to matter 
like nitrogen, oxygen, and hydrogen which can be 
liquefied only under high pressure, and the term vapor 
is used to express the gaseous state of matter that is 
liquid under ordinary conditions, e. g., water, alcohol, 
ether. The term aqueous vapor is often applied to 
vapor derived from water. Vapors and gases are 
governed by the same laws. 


By energy is meant the power to produce motion^ or, 
in other words, the power to perform work. Energy 
manifests itself in several forms, — ^for example, we have 
heat, light, mechanical energy, electrical energy, and 
chemical energy, — and one form can be made to produce 
another form, or, in the words of the law of the conser- 
vation of energy, energy can be changed from one 
form to another. Heat, for example, or chemical 
action can be made to produce an electric current and 
an electric current will produce heat and promote 
chemical activity in matter. 

Energy, Heat, and Pressure 41 

When a body is at work its energy is spoken of as 
kinetic energy (from the Greek kinema — motion). 
When a substance containing the power of work within 
itself or of causing motion in other matter is appar- 
ently at rest, its power is spoken of as kUerU or potential 

A body possesses energy only because it has re- 
ceived energy in some form and it possesses only 
as much as it has received. Nearly all the available 
energy upon earth is derived primarily from the sun. 
The most obvious example of the sun as a source of 
energy is that given under the law of the conservation 
of energy. As there stated, the sun provides the 
energy which causes plants to grow, and plants pass this 
energy on to man and other animals who use plants 
as food, or when substances derived from plants, as 
wood, coal, etc., are burned the energy they liberate 
is used to run machinery, produce electric currents 
or perform other work. Other examples of the sun as 
a source of energy will be seen in the sections on 
radiation and reflection. 


As can be seen in the laws and hypotheses on page 
39, heat and pressure are two important factors in 
causing changes in matter. 

Definition. — Physics and physiology give somewhat 
different definitions for the term heat. A definition 
given in physics is the molecular motion of a body, 
for heat is due to the vibration of the molectiles of 
matter, and the greater the degree of vibration, the 
more intense the heat, and, conversely, the more 
intense the heat, the more rapid the motion. It is 
because heat increases molecular motion that it 

42 Physics and Chemistry 

changes the state of matter, for when moleculax 
motion increases it may overcome the cohesive 
force of the molecules which holds them together. A 
definition in physiology is the sensation perceived upon 
contact with hot matter due to the stimulation of certain 
nerve endings by the rapidly moving molecules of nuUter. 
The difference is in description, not in heat. 

Sources of heat. — ^These are (i) the sun; (2) chemi- 
cal energy, e. g., the heat produced (a) by combus- 
tion, (b) by the oxidation that goes on within the 
body and other forms of slow oxidation, (c) the heat 
evolved during certain chemical reactions, as the 
slaking of lime ; (3) electrical energy; (4) mechanical 
energy, e. g., (a) friction (machinery, for instance, 
becomes hot while working when its parts rub upon 
one another, thus causing friction), (b) percussion 
{e. g., when a nail is hammered, both nail and 
hammer become hot) ; (5) pressure, see page 48. 

Experiment 4. Object, to show the rapidity with 
which heat can be produced by chemical reactions. 

(a) Add some sulphuric acid to about four drams 
of cold water and keep a thermometer in the beaker 
while doing so and for a short time afterward. Note 
the temperature. 

(b) Add water to some quicklime and note the 
temperattu^ while the lime is slaking. 

Effects of heat — ^The more important effects of heat 
are: (i) Change of size — ^heat expands matter; (2) 
change of state — e. g., ice is melted, water is vaporized ; 
(3) change of temperature; (4) chemical change — 
e. g.f sugar is changed to caramel, glucose, etc.; (5) 
electric change — e, g., the production of an electric 
current by the heating of two different metals at 
their jimction. 

Energy, Heat, and Pressure 43 

How heat is transmitted. — The way in which heat 
is transmitted from one place or body to another 
depends upon the form of matter transferring the 
heat. Thus heat passes through solids by the pro- 
cess known as conduction; it is transmitted through 
liquids, mainly, by the process of convection, and 
through the ether by radiation. 

Difference between fiie amount and degree of 
heat. — ^The amount of heat in a body and the degree 
of heat of a body, or in other words the temperature 
of a body, are not dependent upon each other; e. g,, 
the temperature of 8 ounces of boiling water will be 
the same as that of 2000 ounces of boiling water, but 
there will be a much larger amount of heat in the 
vessel containing the 2000 ounces than in that holding 
the 8 ounces. The degree of heat of a body is ascer- 
tained by the thermometer and is recorded in degrees; 
the amount of heat in matter is ascertained by the 
use of a calorimeter and recorded in calories — a calory 
being the amount of heat necessary to raise i gram 
of water i degree centigrade, or what is known as the 
large calory, i kilogram of water i degree centigrade. 
The calory is spoken of as the heat unit. In Great 
Britain the amount of heat is often recorded in what 
is called the British Thermal Unit or B. T. U. By a 
B. T. U. is understood the amount of heat required 
to raise the temperature of i pound of water i degree 
Fahrenheit. A large calory is about the equivalent 
of 4 B. T. U. 

Spedflc heat. — By this is meant the amount of heat 
which is required to raise the temperature of a given 
amount of any substance I degree centigrade (or any 
other degree taken as a standard) 05 compared with 
that required to raise an equal quantity of water to the 

44 Physics and Chemistry 

same temperature. It requires i calory of heat to 
raise the temperature of i gram of water i degree 
centigrade; therefore the specific heat of water is 
said to be I. The specific heat of the majority of 
substances is less than that of water. As a rule the 
denser a substance is, the lower its specific heat; i. e.f 
it takes less heat to raise its temperature. Thus: 

The specific heat of gold is 0.032 




copper is 0.093 




gla^ is 0.19 




earth is 0.2 




air is 0.237 




steam is 0480 




ice is 0.504 




alcohol is 0.604 




water is i. 




hydrogen is 3409 

In some connections, the specific heat of substances 
is often spoken of as their heat capacity as it practi- 
cally signifies the capacity that they have for 
absorbing heat. 

Value of high heat capacity of water. — ^The large 
amount of heat that water can absorb and the slow- 
ness with which it parts with its absorbed heat is of 
great value to man. For instance, the land by the 
seashore becomes hot quicker and to a greater degree 
than the water while the sun is shining upon them, but 
the land parts with its heat more rapidly and becomes 
cooler than the water during the night. This, as 
will be seen in the section on convection, gives rise 
to the breezes that constitute one reason for the more 
even temperature and the greater coolness in summer 
of countries near large bodies of water than those of 
the same latitude in the interior. Another reason 

Energy, Heat, and Pressure 45 

for this is that, during the summer, the water of the 
oceans and large rivers and lakes, etc., is constantly 
absorbing heat which in winter unless frozen it slowly 
parts with. 

Conmion uses to which the capacity of water to 
absorb and part with a large amount of heat is put is 
the use of steam and hot water for heating houses, 
the use of hot-water bags, and the like. 

Relative heat of bodies. — The relative heat of 
different kinds of matter cannot be alwa3rs judged by 
touching substances, because the degree of the sensa- 
tion of heat experienced depends not only upon the 
degree of heat in the substance, but also upon the 
speed with which it absorbs and parts with heat when 
in contact with the hand; e. £., if a piece of iron and a 
piece of wood are heated to the same temperature, 
the iron will seem hotter to the touch than the wood 
because it gives up its heat more readily, but if the 
iron and wood are both equally cold, the iron will feel 
colder than the wood, because iron absorbs heat more 
rapidly than wood and will take heat from the hand. 

Latent heat« The heat of fusion* — The examples 
usually used to explain latent heat are the liquefaction 
of solids and the vaporization of liquids. When pieces 
of ice are heated their temperature rises until o^ C. 
(32^ F.) is reached, then the ice begins to melt and 
its temperature does not increase until the melting 
is accomplished because the heat is used to overcome 
the cohesion of the molecules of the matter and to 
move them apart, this being necessary for melting. 
Heat absorbed in this fashion without causing rise 
of temperature is said to be UUent and that used for 
the liquefaction of solids is often spoken of as the 
heat effusion. 

46 Physics and Chemistry 

Heat is always necessary for the liquefaction of 
solids, but the amount of heat required varies with 
different kinds of solids. It requires 80 calories of 
heat to melt i gram of ice at o^ C. without raising the 

The latent heat of steam. — ^As stated under the 
laws of boiling, when water reaches a temperature of 
100® C. (212® F.) the temperature ceases to rise unless 
the steam is put under pressure. One reason for this 
will be found on page 51; another reason is that at 
100® C. water is converted into steam — i. c, vapor- 
ized — ^and heat is required to further the process. It 
requires 536 calories of heat to change i gram of water 
into steam. In other words a gram of water must absorb 
the amotmt of heat reckoned as 536 calories, or a liter 
of water 537,000 calories, before it will be vaporiased. 

Why the heat used for the fusion of solids and the 
vaporization of liquids is said to be latent — ^When the 
term latent was first applied to the heat used to cause 
fusion or vaporization, heat was thought to be a 
weightless fluid that disappeared in matter dtiring 
liquefaction or vaporization and passed out once 
more when the liquid solidified or the vapor condensed. 
It is now known, however, that not only was this 
conception of heat wrong, but that, though the heat 
is not raising the temperature of the water, it is not 
quiescent, for it is at work increasing the molecular 
motion of the matter, thus breaking the cohesion that 
holds the molecules together, causing them to separate 
and keeping them apart. It will be remembered 
that cohesive force is stronger in solids than in liquids 
and that it does not exist in gases. As heat used in 
liquefying and vaporizing is doing work, the terms 
heat of fusion and heal of vaporization arc now con- 

Energy, Heat, and Pressure 47 

sidered more accurate than the expression UUerU heat, 
though this latter term is still much used. 

Recovery of the heat of fusion} etc. — ^Just as much 
heat as is used in matter in promoting the molecular 
motion that causes the changes described in the pre- 
ceding paragraph passes from the matter as it resumes 
its original form; thus, for every gram of water that 
freezes, 80 calories are liberated, and for every gram 
of steam that is condensed, 536 calories are set free. 

How water, cream, etc., are cooled by melting ice. — 
When ice is put into a pitcher of water, it cools the 
latter not only because the ice and the water from it 
are colder than the water in the pitcher, but because 
the ice takes the heat it needs for melting from the 
water. In making ice cream, etc., the cream is frozen 
because the ice takes the heat it needs for melting 
from the freezer and its contents. Salt is added to 
the ice because it hastens the freezing in several ways: 
(i) It hastens the melting of the ice, because the 
salt molecules attract the ice molecules and this helps 
in the separation of molecides th^t is essential for 
liquefaction, and the quicker liquefaction occurs, the 
more rapidly will heat be taken. (2) The salt, being 
soluble in water, absorbs the latter and takes the heat 
it requires for the process from the cream, etc. (3) 
The lowest temperature of unfrozen water is 32® P., 
that of an unfrozen, saturated salt solution is about 
6** P. ; thus the brine produced as the ice and salt melt 
is much colder than the water of melted ice would be. 

The greater the amount of salt used, the quicker 
the cream will be frozen, but if it is frozen very 
quickly, it will be of a coarse, granular texture. The 
usual proportion of salt to ice used is one part salt to 
three of ice. 

48 Physics and Chemistry 

Some other practical applications to which the 
reqtiirement of heat for fusion and vaporization are 
put will be given in the sections on evaporation and 

Pressure in Gases 

How pressure is increased. — ^To understand how 
gases and vapors can be made to produce increase of 
pressure, it is necessary to realize that the molecules of 
which matter is composed are not» even in solids, 
packed excessively tightly together and that the tight* 
ness with which they are packed is less in liquids than 
in solids, while gas molecules tend to separate and fly 
apart. Another point to remember is that molecular 
motion is increased by heat and lessened by cold. 

Bearing these things in nund, it can be realized 
that when a gas is restricted within a given space, 
the moving molecules strike and cause pressure against 
each other and against the walls of the vessel confining 
them: If the space is large in comparison to the amount 
of gas present the pressure will be slight, but if, by 
any means, the size of the space is lessened, the moving 
molecules will come more in contact with each other 
and the sides of the vessel and thus produce increased 
friction. If the gas is heated, the movement and 
consequently the friction and pressure will be still 
further increased, and the friction will increase the 
heat. Thus pressure produces heat and heat produces 

Comparative relation of pressure and heat. — ^When 
steam, for example, is put under pressure, as in an 
autoclave, there is a definite relationship between the 
amount of pressure exerted and the degree of heat 
obtained. The amount of pressure exerted is usually 

Enei^, Heat, and Pressure 49 

expressed as being so many pounds to the square inch 
of soifaoe exposed to the pressuie. The approximate 
comparative relation c£ the amount of pressure and 
degree of heat can be seen in the following table': 

Pounds pxcssoxe to - 
the sqaaie inch Teoipeimtiife 

I loa* C 

5 108* •* 

! 10 115.6* •* 

15 iai4* " 

20 126^* " 

30 I34-6* " 

In some strongly constructed boilers a pressure of 
even 200 pounds to the square inch can be obtained; 
in fact, so great is the pressure exerted by steam » even 
exceedingly strong boilers can be shattered by al- 
lowing the temperature to increase* and thus raising 
the pressure, above the degree that the boiler was 
constructed to stand. 

Atmospheric pressure. — Since the pressure of gases 
increases with depth, the pressure of the atmosphere 
is greater at sea level than in high mountains. At a 
height of three miles, the pressure is only about one 
half that exerted at sea level. Below sea-level, the 
air increases rapidly in density and, therefore, it 
naturally exerts much greater pressure. It is esti- 
mated that thirty-five miles below the sea the pressure 
must be a thousand times greater than that at the 
earth's surface. 

The barometer. — Torricelli, an Italian physicist, was 
the first individual to measure atmospheric pressure. 

> It will be remembered that steam not tmder pressure has the 
same temperatore as boiling water, i, «., loo* C, or 212* P. 


50 Physics and Chemistry 

He took a glass tube, about one meter in length and 
five millimeters in diameter, closed it at one end, and 
completely filled it with mercury. Then, putting 
his finger over the opening, he inverted that end of 
the tube into a pan containing mercury. Then he 
withdrew his finger and found that the mercury re- 
mained at a considerable height in the tube. This, 
by other experiments, he proved to be due to the 
pressure of the air upon the surface of the mercury 
in the dish. 

A common form of barometer is now constructed 
on the same principle as the Torricellian experiment. 
It consists of a mounted tube at the lower end of which 
is a bulb or crook of exceedingly thin glass for the 
mercury reservoir. The pressure of air upon this 
causes the mercury to rise 760 mm. in the tube when 
the barometer is at sea level and the temperature at 
zero centigrade (i. ^., 32® F.). Calculations that need 
not be given here show that if the mercury is raised 
to 760 mm. (or as it is sometimes expressed 76 cm.) 
in the tube, the atmospheric pressure is fifteen pounds 
to the square inch at sea level, when the temperature 
is zero centigrade. 

Common causes other than altitude that produce 
changes in atmospheric pressure. — Disturbances in 
the atmosphere, such as those produced by variations 
in temperature, winds, and humidity alter the degree 
of pressure in a locality. Heat reduces pressure be- 
cause it causes increased movement and expansion of 
the air, thus making it less dense. When pressure is 
thus reduced, currents of air from cooler regions pass 
in; if they do so quickly, there is a wind; if there is 
much humidity in the air, the cool currents will cause 
the vapor to condense and there will be rain or snow, 

Energy, Heat, and Pressure 51 

etc. Aqueous vapor is lighter than dty ain When 
the atoaospheric pressure is low, the mercury in the | 
barometer tails. These facts show why a falling f 
mercury is looked upon as presaging a storm« 

Effect of pressure upon boiling point Nature of 
boiling. — A liquid is said to be boiling when bnbblos 
of \-apor f<MTn within it. Bubbles cannot forhi in a 
liquid while the atmospheric pressure at the surf4ux> 
is greater than that of the vapor as there is no nx)m 
for their expansion, but the pressure of the vai)or that 
is formed from the water increases as its tem{)eratun' 
rises because its molecular motion increases and whon 
a temperature of loo® C. (212** P.) is reached* if the 
liquid is water, the pressure of the vapor is as grt^at 
as that of the air on the surface and the bubbles rise 
to the top. After a liquid begins to bubble its toni- 
perature cannot rise higher imlcss the steam is put 
under pressure for the reason given on page 46» and 
because the bubbles increase the surface at which 
evaporation takes place and this causes loss of heat* 
Consequently, to make water boil violently is simply 
a waste of fuel, for the larger the bubbles, the greater 
the loss of heat by evaporation and thus there is no 
rise of temperature. The temperature of flowing 
steam (i. e,^ that not under pressure) is the same as 
that of boiling water. 

Experiment 5. Object, to show the effect of at- 
mospheric pressure upon boiling point. 

Articles required: A flask about half full of water, 
a cork with one hole in it — ^the cork must fit the bottle 
perfectly, — a thermometer that will fit into the hole 
in the cork, a Bunsen burner, an iron stand, wire net- 
ting, a towel, and, unless the cold water faucet is in 
a good light, a pitcher of cold water and a basin. 


Physics and Chemistry 

Procedure: Boil the water in the flask for about 
ten minutes, then put the cork, with the thermometer 
in the hole (the thermometer must extend into the 

water), into the 
fiBsky and at once 
turn out the 
light, grasp the 
upper part o f 
the neck of the 
flask with the 
folded towel and 
run cold water 
over the upper 
part of the flask, 
above, not over, 
the part con- 
taining the wat- 
er. See Fig. 39. 
Watch the ther- 

Fig. 39. Manner of Pouring Cold 

Water Run over Flask in Order 

TO Reduce the Pressure above 

THE Water within it. 

What happens? 


Endeavor to answer these questions before reading 
the following paragraph. 

Explanation of experiment The air in the flask 
was heated, as well as the water, while the latter was 
boiling, therefore it expanded and, consequently, 
passed from the flask and its place was taken by the 
steam produced as the water boiled. When the flask 
was held under the cold water, the steam was con- 
densed and thus there was a partial vacutun above 
the water; this being the case, the pressure was, of 
course, reduced and the vapor, having less pressure 
to overcome, bubbled at a lower temperature. 

Energy, Heat, and Pressure 53 

It is because the pressure on high mountains is less 
than at sea level that water boils there at a lower 
temperature than it does in lower altitudes. At the 
top of Mount Blanc, water boils at 84® C. 

Why pressure makes it possible for some bodies to 
float — Due to the fact that the ibqtdds is 
equal in all directions, upwards as well as downwards, 
any body that does not weigh more than the amount 
of liquid which it displaces will float since its weight 
is not more than that of the amount of liquid that 
would otherwise have been in that part. 

The nature of specific gravity or density and its 
influence on floating bodies. — First what is specific 
gravity or density? These two words are used inter- ) 
changeably to signify the weight of a substance asi' 
compared with that of another substance which isj 
taken as a standard. Distilled water is the standard 
usually employed, especially for liquids. A liquid in 
which solids heavier than water are in solution or 
suspension will, of course, have a higher specific 
gravity than water. Naturally, the greater the den- 
sity of the liquid, the heavier the body that will be 
able to float in it. It is impossible for people to sink 
in the Great Salt Lake of Utah. 

How the specific gravity of liquids is ascertained. — 
The specific gravity of such liquids as water, milk, 
sugar solutions, acids, urine, blood, and the like is 
usually gaged with a hydrometer. This consists of a 
glass cylinder on one end of which is a bulb containing 
mercury or shot and on the other a slender stem within 
which is a scale (see Fig. 23). The scale varies slightly 
in different forms of hydrometer. The scale of an 
instrument intended for measuring the density of 
liquids lighter than water is usually marked in such 

54 Physics and Chemistry 

a manner that when the instrument is put into dis- 
tilled water, it sinks until the mark i is on a line with 
the water, and when put into pure alcohol, it sinks 
until the mark loo is reached. The scale of another 
variety of hydrometer is marked so that the instru- 
ment will sink to I in distilled water and the markings 
above the i indicate weights less than i and those 
below that point show densities greater than that of 
water. Thus the instrument will not sink to as great 
an extent in milk, blood, and other dense liquids as 
in water. The principle involved is that a floating 
body sinks until it displaces its own weight. Deter- 
mination of the sp. g. of a liquid is of value in testing 
for its purity. 

Experiment 6. Object, to show the effect of spe- 
cific gravity on the boiling point of liquids. 

Procedure: (a) Ascertain the specific gravity of 
tap water, boil, and notice the temperature at which 
boiling occurs, (b) Add three tablespoonfuls of salt 
to the water, cool, ascertain the sp.g., boil, and note 
the temperature at which boiling occurs, (c) Take 
equal parts of water and alcohol, find the sp.g., boil, 
and note the temperature. 

Prom this experiment it can be realized that liquids 
with a lower sp.g. than water boil before the tempera- 
ture reaches loo® C, while those of greater density 
than water have a higher boiling point than the latter. 
For example: 

The boiling point of ether is 37*C. 

" "alcohol 95% 79" 

" " water loo " 

" " " " spts. of turpentine. . 130 " 

" " phosphorus 290 " 

M " •• " mercury 357 " 




Evi^mratioii — Condensatkm — ^Humidity — Dew — Fog — Frost- 
Rain — ^Hail — Snow — ^Artificial Ice — ^Distillation — Sublima- 
tion — ^Diffttaon — Osmosis — Dialysis 

Evapormtioii compared with vaporizatioii. — Evapo- 
ration, like vaporization, is a process in which liquids 
pass to a gaseous state, but the term vaporization is 
used when the formation of vapor takes place through- 
out the entire mass of the liquid and evaporation when 
it occurs only at the surface of the liquid. In order 
for vaporization to occur, a liquid must be heated to 
its boiling temperature, evaporation takes place to 
some extent at all temperatures, but is, of course, in- 
creased by a high temperature. 

Why evaporation takes place. — ^As the molecules 
composing a liquid are in constant motion and their 
attraction for each other, which holds them together, 
is only fairly strong, some of the molecules at the sur- 
face escape from the liquid into the air. Many of 
these are drawn back again by the attraction of the 
molecules at the surface, but more molecules escape 
than fall back and thus after a time all the molecules 
of the liquid escape and move more quickly and fly 
apart and thtis become gaseous. 
• k 55 

56 Physics and Chemistry 

' Factors which influence the rate of evaporation. — 

Important factors in influendng the rate of evapora- 
tion are: (i) The nature of the liquid. To see this» 
expose in separate dishes a little water, alcohol, and 
ether. It will be seen that the liquids which have the 
lowest boiling point evaporate the quickest. (2) The 
temperature of the liquid. Heating a liquid, by increas- 
ing the rate of molecular motion, hastens evaporation. 
(3) The amount of surface exposed. Evaporation 
takes place from the surface of a liquid, consequently, 
the greater the extent of free surface, the more rapid 
the rate of evaporation. (4) Pressure. In order to 
pass into the air, the molecules from a liquid must 
overcome the pressure of the air upon the surface of the 
liquid, if therefore there is no air, as in a vacuum, 
evaporation will occur much more rapidly at a low tem- 
perature than under ordinary circumstances. For this 
reason, vaccutun pans are used in the preparation of 
condensed milk, much of the nutrient of which is lost 
if it is subjected to a high temperature. (5) The 
amount of vapor already in the air, i. e., the degree of 
humidity under ordinary conditions of temperature 
and pressure, the atmosphere can hold only a certain 
amount of vapor; for this reason, evaporation will not 
take place as quickly on a damp, as on a dry, day; e. g., 
wet dothes dry more slowly on a damp day. (6) The 
rapidity with which moist air is driven away from 
around the evaporating liquid — e. g., on a windy day, 
clothes will dry more quickly than when there is no 
wind, and fanning a moist surface hastens its dr}dng. 
Result of ev^K)ration on temperature. — ^A surface 
from which evaporation takes place and the air arotind 
it are cooled by evaporation. Thtis the air is cooled 
after rain while the moisture is evaporating. The 

Physical Processes and their Results 57 

evaporation of sweat from the stirface of the body is 
one of nature's principal means of preventing body 
temperature becoming too high, and bathing the body 
with water or alcohol while exposed to the air, so 
that evaporation will take place rapidly, is a means 
often employed for reducing body temperature in 
fever. As stated, page 51 , it is due to evaporation that 
the temperature of boiling water remains at 212^ F. 
and it is because of the evaporation of water in the 
lower part of a double boiler that the temperature of 
food in the upper part keeps relatively low. 

Why evqK)ration causes cold. — One reason for this 
is that it is the hottest molecules that move the fastest 
and consequently it is the hottest ones that escape 
first into the air. Another cause is that mentioned 
under vaporization, viz., liquids must have heat in 
order to become vaporized and they take it from the 
most available source. 

Liquids, such as ether and alcohol, which evaporate 
more rapidly than water create a greater degree of 
coolness than the latter during evaporation since the 
wanner molecules escape more rapidly, and, also, a defi- 
nite amount of heat being required to produce evapor- 
ation, the more rapidly the work is accomplished, the 
more rapidly the heat will be taken. Certain sub- 
stances, as ethyl chlorid, which evaporate very quickly 
win, if sprayed on a part of the body, cause it to freeze 
in a few seconds. 

Evaporation of solids. — ^As a rule, solids become 
liquefied before being vaporized, but there are a few 
solids that will pass into a gaseous state and disappear 
without forming any visible vapor. For example, 
wet clothes that are htmg out in winter and become 
frozen will lose the ice that formed upon them and 

58 Physics and Chemistry 

become qtiite dry, though the temperature is too low 
for actual melting to have occurred. Also certain 
solids, such as camphor, will volatilize and, disappear 
without apparently liquef3dng. A few other solids, 
such as arsenic and iodin, will, if heated, be converted 
at once into vapor. Iodin so treated is called re- 
sublimed iodin. (See page 65.) 


Nature and cause of condensation. — Condensation 
is the process by which gaseous matter is changed to 
liquid and the changes that occur are exactly the 
opposite of those which take place in vaporization; 
viz., due to the application of cold, molecular motion 
becomes less and less, the particles become packed 
closer together, and the heat of vaporization which was 
employed in keeping them apart passes from the 

A common use of the heat given off in condensation. 
— Heating houses by steam is a common use to which 
the heat given off in condensation is put. The steam 
generated in a boiler passes through the pipes with 
which the rooms are supplied and there condenses ; thus 
the pipes, which radiate the heat they receive to the 
room, are heated, not only by contact with the hot 
steam, but also with the heat liberated during con- 
densation. The water thus formed passes through 
pipes provided for the purpose, back to the boiler 
where it is once more converted into steam. 

Liquefied gases. — ^Aqueous or water vapor is as 
easily changed to water as water is to vapor, but gases 
such as oxygen and hydrogen can be liquefied only at 
extremely low temperatures and under great pressure, 
and, as soon as the pressure is released, the liquid 

Physical Processes and their Results 59 

expands and the natural form of the gas is sesumed. 
Such volatilizing matter takes the heat that it re- 
quires for the process from anything with which it 
comes in contact; for this reason, men, who have not 
taken proper precautions, have had their hands frozen 
while repairing tanks containing liquefied gases. 

Artificial ice. — The use of ammonia in the making of 
ice is a common practical application of the alter- 
nate condensation of gas and vaporization of the 
liqmd obtained by condensation. Ammonia gas is 
generally used for the purpose in preference lo other 
gases because it is easily condensed' by pressure at 
ordinary temperatures to a liqmd which boils, and 
consequently, vaporizes at a low temperature. The 
principles of an ice-making machine and the process of 
making ice are as follows : There are two large tanks 
containing coils of pipes. The coils in the two tanks 
are connected by pipes to which a pumping machine 
is attached. In one tank ate large cans which are 
filled with pure water and surroimded with brine, 
this is generally made of calcium chloride or sodium 
chlorid and water. The coil in the other tank is 
surrounded with water. The ammonia gas is com- 
pressed by a compression pump and, as a result of 
this process, becomes very hot. This hot compressed 
gas is then passed through pipes that, usually, are out 
of doors and over which cool water is allowed to run. 
This process reduces the temperature of the gas below 
its critical temperature (that at which it remains in 
gaseous state) and it becomes liquid. The liquid 
anmionia, which must not be confused with aqua 
ammonia, is carried in small pipes to the tanks of 
brine. Here it is passed through a needle valve into a 
large pipe. This releases the pressure and allows the 

60 Physics and Chemistry 

liquid to assume its gaseous state. As has been 
previously said, the heat necessary to produce this 
change is taken from the surrounding medium, hence 
the temperature of the brine is reduced below 32** P 
and the water in the cans is frozen. The gas from the 
pipes is then passed over the compressors again and 
the process is repeated. 

t Refrigerators and cold-storage rooms are sometimes 
cooled in much the same way as ice is made, the essen- 
tial differences being that the cans of water are omitted 
from the brine tank and the brine, after being reduced 
to a temperature of about 16** P. is pumped into pipes 
that extend from the tank to coils of pipes in the 
ceilings of the places to be chilled. The brine is kept 
in circulation between these pipes and the tank where 
it is cooled; thus the pipes are kept constantly cold 
and they keep the place in which they are situated 
cold in just the same manner as ice would. 

The air of cold-storage rooms and theaters is some- 
times cooled by forcing evaporating ammonia or 
carbon dioxid through pipes within the room. The 
principle is the same as in making ice, the essential 
difference being that the heat for the volatilization 
of the gas is taken from the room instead of from 
brine. The pipes in which the volatilization takes 
place may become as cold as 6** P. 


The term humidity is used in referring to the mois- 
ture of the atmosphere. The moisture of the atmos- 
phere is the result of evaporation from bodies of 
water, moist earth, snow, or ice. 

When there is as much moisture in the air as the 
latter can hold it is said to be saturated. How much 
moisture the air can hold without becoming saturated 

Physical Processes and their Results 6i 

depends upon the temperature. Naturally, as warm 
air is expanded and its molecules are thus farther 
apart than in cold air, warm air will hold more mois- 
ture than cold air without becoming saturated. 
Cooling of the air, especially when it is saturated, is 
likely to result in condensation of the vapor and con- 
sequent forming of dew, fog, rain, etc., which, depend- 
ing upon the temperature and where and how the 
condensation occurs. 

Absolute and relative humidity. — ^By absolute 
humidity is meant the amount of aqueous vapor which 
the air contains expressed in the number of grams of 
moisture per cubic foot, or other specified amount, of 
air.^ By relative humidity is tmderstood the amount 
of vapor that is present in the air expressed as a per- 
centage of the amount that the air will hold without 
the moisture being precipitated in the form of dew, rain, 
etc. — i, e, without becoming saturated. When air is 
saturated, the relative humidity is said to be loo per 
cent. How much moisture there can be in the air 
without its becoming saturated will, as stated in the 
preceding paragraph, depend upon the temperature. 

The degree of humidity is ascertained by the use of 
an instrument called a hygrometer. 

Effect of moisture on comfort and health. — The 
estimates given for the most desirable relative degree 
of humidity vary between 50 and 70 per cent. A 
higher per centage than seventy-five makes both cold 
and heat harder to bear, and it, when the temperature 
is high, increases the danger of heat prostration and 
sunstroke, because, for the reasons given under evapo- 
ration, it interferes with the evaporation of sweat from 
the body. Very dry air is also exceedingly injurious 
for it acts as a mental irritant and it parches the 

62 Physics and Chemistry 

membranes of the eyes, nose, throat, and lungs, and 
thus lays a foundation for catarrh and bacterial infec- 
tion. It has been found that steam-heated dwelling 
houses often have a relative humidity as low as thirty 
per cent, when the hiunidity out of doors is seventy- 
five per cent. 

A common device to keep the atmosphere of arti- 
ficially heated rooms moist is to have bulbs, or other 
water plants growing in wide shallow basins of water. 
The constant evaporation that occurs helps very 
considerably in keeping the air moist. 

Nature of dew, frost, fog, clouds, rain, hail, snow. — 
When moisture in the air comes in contact with a 
surface cooler than the air, the moisture will condense 
upon it. The earth, grass, flowers, etc., are likely to 
become cooler than the air at night, for though they 
absorb heat diuing the day, they radiate it very 
quickly after the sun goes down, consequently the 
vapor in the atmosphere condenses upon them as 
drops of water. This is known as dew.^ When the 
cooling that occiurs is so great that not only the ground 
and plants, but also the air above them, become colder 
than the higher strata of air, the moisture in the colder 
portion condenses on all the particles of dust and the 
like suspended in the air and the result is known as 
fog. Naturally, fogs occur most frequently near large 
bodies of water and following days in which heat has 
caused a large amount of evaporation or where, as in 
parts of California, the hot air of neighboring deserts 
becomes so expanded that its pressure is reduced to 
such an extent that the moist air from the Pacific, 

> The oollectiog of drops of water on the outside of a pitcher 
containing ice water, when it is in a warm place, is the result of 
the same cause as dew. 

Physical Processes and their Results 63 

where the presstire is greater is forced in to take the 
place of the hot dry air. When this air becomes at all 
chilled, the moisture condenses and envelops the land 
in mist or fog. Another factor influencing the amount 
of fog likely to occur in a place is the amount of dust 
for vapor condenses readily upon the chilled dust. 

Clouds, like fog, consist of masses of vapor con- 
densed into minute droplets, but clouds are higher in 
the air. 

When the condensation of water in the douds 
reaches the point of saturation the water falls upon 
the earth in the form of rain imless (i) the tempera- 
ture of the air in which the clouds are, is below freez- 
ing point, when the water falls as snow or (2) if the 
raindrops are whirled by the wind through regions of 
different temperatures some of which are below freez- 
ing point the drops of water fall as the small balls of 
ice known as hail. 


Nature of distillatioiit — If the vapor of a boiling 
liquid passes into a tube or pipe and is collected in a 
reservoir surrounded with ice as demonstrated in 
Fig. 40, the vapor will condense. This process is 
known as distillation. 

Fractional distillation. — Since, as shown in experi- 
ment 6, liquids of different specific gravities have 
different boiling points, one with a lower boiling 
p>oint than other substances in a compound can be 
extracted by keeping the latter at the boiling temper- 
ature of the liquid desired. For example, alcohol 
can be extracted from water by distillation, if the 
solution is kept at 80® C, the boiling point of alcohol. 


Physics and Chemistry 

The extraction of a Uqtiid from a compound in this 
way is spoken of as fractional distillation. 
Destructive distOlation. — When certain solid or 

Fig. 40. Distillation. 
(a) Flask containing 50% Alcohol, 

(b) Ther. 

liquid substances, as coal, wood, and petroletun are 
heated in closed vessels out of contact with the air, 
they break down into simpler substances some of 
which can be easily vaporized, and, therefore, distilled. 
This is termed destructive distillation. The term 
dry distillation is sometimes used, for destructive dis- 
tillation of solid substances. 

Physical Processes and their Results 65 


Nature of sublimatioiL — In the section on the evap- 
oration of solids it was stated that there were certain 
solids which passed into a gaseous state without 
any visible formation of liquid. If the vapor arising 
from these substances is collected and condensed it 
win solidify. This form of distillation is known as 
sublimalian and the condensed products are called 
sublimates. Sometimes chemicals that will, when 
heated, interact to form new compounds are sublimed 
together. This is the manner in which the well- 
known disinfectant, bichlorid of mercury is prepared. 
The chemicals used in its preparation are mercuric 
stdphate (HgS04) and sodium chlorid (NaCl). 
When proper proportions of these substances are 
heated together, the mercury and chlorin tmite in the 
proportion of one part mercury to two parts chlorin 
and sublime while the sulphate and the soditim unite 
to form a non- volatile, substance — sodium sulphate 
— ^which remains behind. Thus HgS04+aNaCl = 


Nature of diffusion. — ^When two or more gases that 
have no chemical affinity for each other are introduced 
into a room, vessel, or other space, the gases quickly 
spread and intermingle so that in a short time each 
gas is uniformly distributed throughout the whole 
space; just as it would be were it the only gas present. 
This Spreading of gases is known as the diffusion of 

Common proof of the diffusion of gases. — ^The 


Physics and Chemistry 

rapidity with which odors from strongly scented 
matter become distributed is a very common proof 
of the diffusion of gases. 

Experiment 7. Object, to observe the diffusion of 

Articles required: Two drinking glasses, the same 
shape and size, two swabs, a piece of stiff, smooth 
paper slightly larger than the open ends of the glasses, 
ammonia water (NH4OH) and hydrochloric add 
Procedure: Wet the interior of one glass with 

ammonia, using a swab for the pur- 
pose, and cover the glass with the 
paper, swab the inside of the other 
glass with hydrochloric add, invert 
this glass over the first one and then 
remove the paper, being careful not 
to separate the glasses while doing so. 
It will be noticed that, shortly after 
the paper is removed, the glasses 
become filled with a white cloud. 
This is ammonia chlorid, derived by 
the combining of the ammonia gas 
from the ammonia water and the 
hydrochloric add. ThusNH,+HCl« 

Diffusioii of liquids. — If two liquids, 
for example lemon jtiice and water, are put into a glass 
they will, after a short time, become thoroughly mixed, 
even though they are not stirred. The diffusion of 
liquids, however, will not take place as quickly as did 
that of the gases, since the molecules of U quids are 
not in such rapid movement as those of gases, and 
diffudon is dependent upon molecular motion. 

Pig. 41. 
Glasses in Po* 
siTioN FOR Dif- 
fusion EXPERI- 

Physical Processes and their Results Gj 

Diffusion of solids. — It has been found that if a 
mass of lead is placed upon a mass of gold, molecules 
of the latter will after a time be found scattered 
through the lead. The diffusion of solids, however, 
at ordinary temperatures is rare, but it is common 
at high temperatures. 

The phenomenon of diffusion is considered one of 
the strongest proofs of molecular motion. 


Nature of osmosis. — ^When matter diffuses through ) •, 
a membrane the process is spoken of as osmosisS ' 
Substances having a crystalline form, as sugar, will 
readily go into solution and osmose through mem- 
branes, but matter that is colloidal (as glue) or amor- 
phous (i. €.y not crystalline, without definite shape) 
is not capable of osmosing. It is for this reason that 
animal foods, vegetables, and starches 
must be digested and thereby made 
soluble, before they can be absorbed. 

Experiment 8. Object: To study 

Articles required: 2 gold-beater's 
bags or fish bladders, 2 one-hole rubber 
stoppers, 2 pieces of glass tubing of 
small caliber (^ inch in diameter) 
about 9 inches long, concentrated 
sodium chlorid, water, two jars or 
wide-necked bottles. 

Procedure : Pill a bag with salt solu- 
tion, fit a cork, with a glass tube in- 
serted in the hole through its center, j^^^ Jith^em- 
into the open end of the bag, and tie it brane Bag Se- 
in place. Suspend the bag in a jar of cured in Place. 

68 Physics and Chemistry 

water, as in Fig. 42. Arrange a duplicate apparatus, 
but put the sodium chlorid into the jar and the water 
into the bag. 

After some hours it will be noted that the so- 
lution has risen in the tube of apparatus i, show- 
ing that water must have enteral the bag, but 
that the solution has risen in the jar of apparatus 2, 
showing that water has passed from the bag into the 

Experiment 9. Object: Same as experiment 8. 

Procedure: Have a carrot, instead of the membrane 
bag, and syrup, instead of salt solution. Scoop out 
the interior of the carrot, fill the cavity with a thin 
syrup; insert the cork with the tube inserted in the 
hole through its center at the top of the cavity letting 
the tube extend about an inch into the syrup. Sus- 
pend the carrot in a jar of water. Some of the syrup 
will pass into the water, but a much greater amount 
of water will osmose into the syrup; enough, in fact, to 
cause the syrup to rise in the tube. 

Facts shown by experiments. — ^These experiments 
prove that when two solutions of unequal concentra- 
tion are separated by a membrane a force is exerted 
which causes them to pass through the membrane, 
the less concentrated one doing so more readily than 
the other. This fact is of interest to nurses who 
prepare salt solution for intravenous infusion; for if 
too much salt is used (1. e., more than enough to make 
the solution stronger than 0.9 per cent.) fluid will be 
extracted from blood corpuscles and they will become 
shnmken and shriveled. If, on the other hand, the 
solution contains too little salt (less than 0.6 per cent.) 
it will enter blood corpuscles and cause them to swell 
and perhaps rupture. If a little defibrinated blood 

Physical Processes and their Results 69 

can be obtained from the slaughter house, ' this effect 
can be easily demonstrated as follows: Put about 5 cc. 
of blood into each of four test tubes, to one of these 
tubes add an equal amount of water to another an 
equal amount of a 0.2 per cent, salt solution, to the 
third physiological salt solution (t. «., 0.9 per cent.) 
and to the fourth, add the same quantity of 5 per cent, 
salt solution. Notice the difference in the color that 
occurs in all the tubes, except that with the phy- 
siological salt solution, due to the action of the salt 
solution on the blood corpuscles. The disintegration of 
the red corpuscles is spoken of as hemolysis and blood 
in which hemolysis has occurred is said to be laked. 

For further study of the action of liquids of differ- 
ent concentration upon the blood, prepare a drop of 
the contents of each of the tubes for examination 
under the microscope. To do this smear the drop 
over the center of a clean glass slide. Place this so 
that it can be viewed with the microscope and note 
the difference in the shape of the blood-cells in the 
different smears. 

The blood can be also prepared for examination as 
follows: Wash the finger with alcohol, prick it with a 
sterile needle, put a drop of blood thus obtained on 
each of four sterile slides. To one drop, add a few 
drops of water and to each of the others a few drops 
of one of the different percentages of salt solution. 
Mix the blood and diluent with a platinum tip. 

A cause of edema. — ^Another fact of interest to 
nurses that the osmosis of fluid towards the location 

' WheQ blood is stirred rapidly as soon as it is shed, the fibrin 
collects on the stirring implement. Blood thus treated is said 
to be delibrinated and it will not clot, for the fibrin^ which has 
faeaa removed, is essential for the clotting of blood. 

70 Ph3^ics and Chemistry 

of the more concentrated solution explains is that, 
when the kidneys fail to eliminate salt, as is often the 
case when they are diseased, and the salt passes into 
the tissues, edema or dropsy results, one reason being 
that, on account of the excess amount of salt in the 
liquid in the tissues, the passage of fluid from the 
blood exceeds its absorption. 


Nature and use of dialysis. — Since all substances 
cannot pass through animal membranes, chemists 
often make ttse of what is known as a dialyter (a jar 
with a parchment bottom) to separate non-crystalline 
from crystallizable substances when the former are 
present in a solution in a finely divided form. The 
process is known as dialysis. 



— (ConUnued) 

Contraction — ^Expansion — Vacuum — Suction — Siphonage— Cap- 
illarity — Conduction — Convection — Some Common Prac- 
tical Applications of Knowledge of the Nature and Action 
of these Processes. 

Contraction and Expansion 

It is a well-known fact that even solid substances 
are expanded by heat and contracted by cold. For 
instance, railroad rails are laid with spaces between 
their ends to allow for the expansion that occurs during 
the heat of summer; it is difficult when the hands are 
hot to put on kid gloves that can be drawn on easily 
when the hands are cold. Liquids cannot be expanded 
to as great an extent as gases since high degrees of 
heat and cold change their state, i. e., change them to 
vapor or solid — but that some change is made can be 
easily seen if a graduated flask containing water is 
held over a flame, for the water will be seen to rise in 
the flask. The degree to which gases are expanded 
by heat and contracted by cold is stated in the law of 
Charles — j4t of their volume for every degree centi- 
grade that their temperature changes. The expan- 
sion of gases can produce great force as is demonstrated 

V 71 

72 Physics and Chemistry 

by explosions. For example, the dynamite used to 
blast out rock, etc., does so because a small amotmt of 
solid d3maniite is converted by heat into large quan- 
tities of gas which, by the heat produced as the result 
of the chemical interaction of the constituents of the 
dynamite, becomes very greatly expanded and forces 
apart even huge rocks that interfere with its expansion. 

Reason for expansion and contraction. — The change 
in the size or volume of matter as the result of heating 
is due to increase in the velocity of molecular motion 
by the heat in consequence of which the molecules 
jostle each other farther apart, thus increasing the 
voltune of the matter. Cold, on the contrary, lessens 
molecular motion and, consequently, contracts the 
majority of substances. 

Peculiarity of expansion and contraction in water. 
— Fortunately for mankind, water, when cooled, does 
not act in quite the same way as most substances; it 
contracts tmtil a temperature of 4®C. is reached; but 
after it attains this temperature, it begins to expand, 
and consequently its weight grows less in proportion 
to its bulk. For this reason, when ice forms in lakes, 
rivers, etc., it floats to the top. If the ice did not do 
this, bodies of water would freeze to the bottom and, 
if deep, could not be thawed, even in summer. 

Why glass and porcelain-ware break when heated 
or cooled quickly. — If glass and porcelain utensils 
are heated and cooled slowly they will stand wide 
variations in temperature without breaking, but, on 
the contrary, if they, especially glass ones, are heated 
or cooled quickly, particularly if the heat is directed 
against one point or if, when hot, they are placed upon 
a cold stand, they are Ukely to break. This is because, 
in such cases, the expansion or contraction is xmeven 

Physical Processes and their Results 73 

and a crack occurs where resistance is offered to the 
change in condition. 

If when pouring a hot liquid into a glass utensil, the 
liquid is poured over, as well as into it, there is less 
danger of its breaking and thin glass is broken less 
readily by heat than thick glass. The reason in both 
instances being that all parts of the utensil are brought 
more nearly to the same temx)erature at once. 

The thermometer. — The thermometer is a practical 
application of the expansion and contraction of 
liqtiid by heat and cold. A thermometer usually 
consists of a glass tube of capillary bore with a bulb 
that is filled with mercury at one end. When making 
a thermometer, the bulb and part of the tube are 
filled with merctiry and the instrument heated until 
the mercury boils and expels the air from the tube. 
After this the top of the tube is sealed. When the 
tube is cold, the bulb is placed in boiling water and 
the point to which the mercury rises is marked 212, 
if the thermometer is marked with the Fahrenheit 
scale, or 100 for the centigrade scale. The bulb is 
next placed in a vessel of melting ice and the point at 
which the mercury stops is marked 32 for the Fahren- 
heit scale and o for the centigmde. The space be- 
tween the freezing and boiling points is divided into a 
number of equal spaces, the size depending upon the 
kind of scale. 

Vacuum, Siphonage 

Vacuum. — ^By a vacuum is meant a space from 
which all air has been exhausted and which contains no 
material substance, 

A vacuum is usually created by means of some form 

74 Physics and Chemistry 

of pump, fan, or piston which will by pressure or other 
means remove air or other matter from a cavity. 

To maintain a vacuum it is necessary that all 
apertures to the cavity be absolutely sealed, the 
slightest crevice will allow air, etc., to enter because of 
(i) the tendency of gases and liquids to diffuse equally 
in all directions; (2) the fact that, when a vacuum has 
been created within a space or cavity, there is no 
pressure within it to oppose the entrance of any form 
of matter; (3) the pressure of the atmosphere upon the 
matter that is afforded entrance. 

The creation of a vacuum, is an essential principle 
in the raising of water from a lower to a higher level 
and in drawing fluids from and into cavities, it is the 
power that is being more and more used for the re- 
moval of dirt and dust from buildings and streets. Its 
chief values for the latter purpose is that the dust, 
etc., are removed without being scattered or inhaled 
and, in buildings, carpets and the like are not sub- 
jected to the same amount of wear that they are by 
other modes of cleaning. The creation of a partial 
vacuum is one of the resources utilized in the ventila- 
tion and heating of buildings as will be seen in the 
section on ventilation. 

Siphonage. — If a curved tube with one end longer 
than the other is filled with water and this not allowed 
to escape until the short end of the tube is inserted in a 
pail of water the water will flow from the pail, through 
the tube, though at first it must flow upward. Such 
forcing of water over an elevation is known as siphon- 
age. It is maintained by the pressure of the atmosphere 
on the water in the pail and the unbalanced pressure 
of the water in the tube. This difference in pressure 
is the result of the difference in the length of the two 

Physical Processes and their Results 75 

arms of the tube and the greater the difference, the 
greater will be the pressure and the greater the force 
of the flow of water. It is important to remembei 
this when using siphonage for therapeutic purposes; 
force being sometimes desirable, but often very tm- 

When a rubber tube is used 
if a syringe can be obtained, 
the tube can be filled after one 
end has been put into the 
water, otherwise, a funnel can 
be inserted in one end of the 
tube and, holding the latter so 
that its free end is on a level 
with, or a little above, the fun- 
nel, as in Fig. 43, the water, 
or whatever liquid is required, 
poured into the funnel until it 
appears at the opening of the ^ 
free end of the tube. Then, 
simultantously, the funnel ts 
lowered into the pail of liquid 
and the free end of the tube 
over the vessel or part into or Pig 43 

over which the liquid is to run. 

This must be lower than the pail in order to obtain the 
necessary unbalanced pressure of water in the tube. 
Two necessary precautions are: Not to allow the 
water to escape from the tube while inverting it ; to pre- 
vent the tube being compressed on the rim of the pail. 

Nature of capillari^ and reason for name. — If a 

tube of small diameter is placed in a Uquid that will 

76 Physics and Chemistry 

wet its interior, the liqtiid will rise somewhat higher 
in the tube than the level of the liquid on the outside, 
and the smaller the diameter of the tube, the 
higher the liquid will become. If the tube is placed in 
mercury or other liquid that will not wet it, the liquid 
will become depressed, rather than elevated. The 
force causing a liquid to rise in a tube is known as 
capillarity or capillary aUraction (from the Latin 
ca/>t7/am= hair-like) because it is only perceptible 
in tubes of small diameter. 

Cause of capillarity. — The molecules of a liquid 
have an attraction for each other which holds them 
together (cohesion) and also an attraction for the 
molecvdes in the sides of a tube which they wet (ad- 
hesion — see page 36). If the force of cohesion is 
stronger than that of adhesion the molecules of the 
liquid will be pulled down, but when adhesion is the 
stronger force the liquid clings to the sides of the glass 
and rises in the tube. 

It is due to capillarity that oil rises in the lampwick ; 
that a piece of muslin or other tubular fibered fabric 
will become wet throughout if a small end is left in a 
liquid; that gauze in a wound will act as a drain. 
Capillarity plays an important part in the flow of sap 
through plants and in the distribution of moisture 
through the soil. 


It was stated in a preceding chapter that heat was 
transferred from one body or part to another by 
either one of the three processes conduction, convec- 
tion, or radiation. 

The term conduction is used also in connection 

Physical Processes and their Results 77 

with the transmission of dectricity, nerve impulses, 
and sotmd. 

Nataxe of conduction. — Conduction as applied to 
heat, has been defined as the transfer of molecular 
motion from a mass of molecules vibrating with a given 
intensity to another nuiss vibrating with less intensity. 

Experiment 10. Object, to study the method of 
heat conduction. 

Procedure: (a) Hold one end of a piece of metal 
wire, preferably copper, in a flame. How long can 
you hold it thus before the end between your fingers 
becomes too hot to hold? 

(b) Hold a teaspoon by the handle and keep its 
bowl in boiling water. How long does it take for the 
handle to become too hot to hold? 

(c) Fill, to % its capacity, a large-sized test-tube 
with water, hold the tube, at the lower end, in the 
fingers and heat the water in the upper part by holding 
it in a flame. Notice how much longer it takes for 
the water in the bottom of the test-tube and even for 
the glass of the tube to become hot than it did for the 
wire or the spoon. 

(d) Refill the tube with cold water and, holding it 
by the upper end keep the lower part in the flame. 
Notice what a very much shorter time it takes for the 
water to be heated in this way, which is convection, 
and not conduction. This will be discussed in the 
following section. 

Explanation of experiment — The heat of the flame 
caused the molecules of matter within it to vibrate 
violently and these molecules, by striking against 
those in the part of the spoon, wire, etc., held in the 
flame, furthered the increase of molecular vibration 
that had already been increased by the heat. The 

78 Physics and Chemistry 

vibration of the molecules in this part of the metal 
started those above them vibrating and these set 
the masses above them vibrating and so on. 

As seen by the experiment, metal is a better con- 
ductor of heat than glass or water. This is because 
the molecules are packed more closely together in 
metal than they are in the other two substances used 
and thus they can influence each other more readily. 
Metals are the best heat conductors, but all solids 
are better than liquids and liquids than gases. The 
following table gives the rdative heat-conducting 
value of a few common substances. The one having 
the highest value is, for convenience, marked loo. 

Silver loo Mercuiy 1.7 

Copper 74 Granite 0.53 

Aluminium 35 Limestone 0.52 

Brass 27 Ice 0.21 

Zinc 26 Glass 0.2 

Tin 15 Water 0.124 

Iron 12 Felt 0.038 

German silver 84 Air 0.005 

A few of the common applications of a knowledge of 
the relative heat-conducting power of matter to house- 
hold purposes. — A common application of this knowl- 
edge is seen in refrigerators, ice-houses, and fireless 
cookers. The walls and doors or covers of these 
appliances are made with double walls that have a 
space between them. The space is filled with air or 
other non-conducting matter. An improvised fireless 
cooker is sometimes made by taking two boxes, one 
considerably smaller than the other, and filling the 
space between the two with some such porous, poor 
heat-conducting material , as sawdust , wool , or shredded 
paper. It must be possible to dose the covers of the 

Physical Processes and their Results 79 

two boxes securely and a cushion, stuffed with the 
same kind of material as that between the boxes, is 
placed between the covers. If ice — in a bowl or basin 
— is placed in the inner box, the latter can be used as a 
refrigerator or if, instead of ice, a covered pot of 
boiling food is placed in it, the food will continue to 

The walls of all such appliances must be air-tight 
for they will be valueless if air is allowed to enter or 
leave the space, since this would start convection 
currents, and though air is one of the poorest heat 
conductors known, it distributes heat very readily by 
convection. If, however, air currents are prevented, 
the temperature of the refrigerator or cooker will 
change very slowly. 

The thermos bottle, which consists of two bottles 
blown one inside the other, is made on the same 
principle as the refrigerator, but the space between the 
bottles is a vacuimi, the air being pumped out before 
the bottles are sealed together at the top. Naturally, 
heat cannot be conducted through a vacuum and thus 
it is only around the cover that heat can pass or enter 
a thermos bottle and thus hot liquids put into them 
will remain hot, and cold ones cold, for several hours. 

Flannel and other loosely woven woolen material 
owe their value for warm clothing largely to the air 
which is held within the meshes of the material, this 
interfering with the escape of heat from the body. 


Definition. — Convection has been defined as the 
transmission of heal by the transfer of the heated body 

8o Physics and Chemistry 

Nature. — In experiment lo, it was seen that if the 
upper part of a test-tube filled with water was held 
in the flame, the water at the bottom of the tube did 
not become warm for a long time, but that if the 
bottom of the tube was held in the flame, all the water 
soon became heated. The reason for the first fact 
was explained under conduction. The reason for the 
second is that as heat expands matter and consequently 
makes it lighter in proportion to its bulk than that 
which is cold, the heated water in the bottom of the 
tube became lighter than that at the top and, just as a 
cork, being lighter than water, will, if thrust to the 
bottom of a basin of water, rise and float, the lighter 
water rises above that which is colder and conse- 
quently denser and heavier. This results in the 
pressing down of some of the colder water toward the 
source of heat. Some of that pressed down at once 
becomes warmer than that directly above it and rises 
with the same results as before. Thus, there is a 
constant movement in the water and in time it all 
becomes heated by, as stated in the definition, the 
transfer of the heated matter itself, or, in other words, 
by convection. This transmission of heated matter 
occurs not only in water, but in all fluids, both liquids 
and gases. 

Convection currents in nature. — ^Winds are con- 
vection currents produced by differences in the density 
and pressure of the air. Such differences are usually 
the result of differences in temperature due to unequal 
heating of the earth and air by the sun. When air in 
any locality is heated it rises and, the atmospheric 
pressure near the earth being reduced, air from colder 
regions passes in. This movement of the air con- 
stitutes a breeze or, if there is enough difference in the 

Physical Processes and their Results 8i 

temperature to promote rapid motion, a wind. The 
land bordering on large bodies of water will, usually, 
during the day become hotter than the water, conse- 
quently the air over the land becomes warmer than 
that over the water and rises and the colder, denser 
air from the water moves forward over the land. 
This constitutes what is known as sl sea breeze. If, 
as usually occurs at night, the air over the land cools 
before that over the water, the air passes from the 
land toward the water thus giving rise to the so-called 
laTtd breeze. The trade winds, that make life in the 
tropics endurable during the hot seasons, are the 
result of the movements of the hot air, which, rising, 
passes to the north and south leaving space for the 
entrance of cooler air from the latter places. 

The various ocean currents that are of such impor- 
tance to the climate of many regions of the globe are 
convection currents due largely to different densities 
of the water, resulting from its unequal cooling and 
heating in different parts, and to the rotation of the 

Ventilation. — ^The two chief forces depended upon 
in the ventilation of buildings are convection and 
the creation of a partial vacuum. 

A good illustration of a combination of these two 
processes is seen in the open fireplace. The fire heats 
the air in and around the fireplace thereby making it 
h'ghter and causing it to rise through and from the 
chimney. This creates a partial vacuum in the 
chinmey and fireplace which the colder and, conse- 
quently heavier air from outside and from the room 
is forced in to fill. The same forces are at work also 
when radiator pipes are the source of heat and open 
windows the means of ventilation. The heat radiated 


82 Physics and Chemistry 

from the pipes causes convection currents in which the 
heated air rises and is forced, so great is the pressure 
of heated gases, even through cracks around windows 
and doors, thus the air pressure in the room is reduced 
and the colder air is pressed in. 

The locations where the greater amount of hot air 
will naturally escape and cold air enter can be seen 
by, on a cold day, opening a window at the top and 
at the bottom and holding a candle in front of first one 
and then the other opening. It will be seen that, at 
the lower opening, the flame is forced inward by the 
incoming air and, at the upper opening, it is forced 
outward by the outgoing air. 

Knowing these facts, it will be easily appreciated, 
that, if it is too cold outside to open a window wide, 
it is better to open it slightly at both top and bottom. 
A very important reason for an opening at the top of 
the window is that the air exhaled in respiration, 
being warmer than the air in the room, and gases that 
may escape combustion when gas is burned tend to 

The openings for the entrance and exit of air should 
never be placed directly opposite each other, for then 
two things will occur, (i) a wind or draught may be 
created and (2) the air passes directly from one open- 
ing to the other and thus that in parts of the room not 
in the direct current is little affected. 

Artificial ventilation. — In cold climates, in order 
to sectire good ventilation in large buildings without 
risk of draughts from ox>en windows, different forms 
of artificial ventilation are now in common use. The 
various methods by which ventilation is thus affected 
are classed under three headings, (i) extraction or 
vacuum system, (2) propulsion or plenum system* 

Physical Processes and their Results 83 

(3) vacuum-plenum system. Ventilation by any of 
these methods is usually effected with the aid of fans 
or pumps placed in chimneys or ventilating shafts. 
In the vacuum system, air is withdrawn from the 
building as the result of the vacuum created in the 
shafts and the pipes leading to the rooms, by means of 
the pumps, etc., and air from outside is, consequently, 
forced, by atmospheric pressure, into the pipes and 
ventilators provided for the purpose and from thence 
into the rooms. In the plenum system it is in the 
shafts in communication with the outer air that a 
vacuum is created and the air, which is forced into 
these by the weight of the atmosphere, is propelled, 
by fans or other apparatus, into the rooms. The 
entrance of this additional air forces some of that 
already in the rooms to leave through the apertures 
provided for the purpose. The vacuum-plenum 
system, as the name implies, is a combination of the 
other two methods. 

One means of discovering if artificial ventilation is 
proceeding as it should is to hold a handkerchief 
in front of the ventilators; if everything is in order, 
the handkerchief will be sucked toward a ventilator 
through which air should leave the room and it will 
be blown into the room by the incoming air at a 
ventilator intended for such purpose. 



The Ether — ^Absorption, Radiation, Reflection, Refraction, and 
Polarization of Heat and Light — Color of Light and of 
Objects — Finsen Light — Phosphorescence and Fluorescence. 


Nature of radiation. — The process of radiation 
was so named because heat and light transmitted in 
this way pass from their source in straight lines or 
radii. One proof that this is true of heat is demon- 
strated by holding a screen between the individual 
and the source of heat, since the direct heat then 
ceases to be felt. That any heat is then perceived 
is due to convection currents in the air. Likewise, 
if an object through which light rays cannot pass is 
held between the eyes and the light, the latter can 
no longer be seen and that there is any lighting of a 
locality screened from the direct rays of a light, is due, 
as will be seen later, to reflection. 

The Ether 

In order to understand radiation it is necessary to 
know of the existence of the ether. For various 
reasons, among others, the transmission of heat and 


The Ether, Heat, and Light 85 

light through the millions of miles between the sun 
and the upper strata of air and the nature of radiation, 
scientists concluded that there must be something 
besides air permeating all space, not only that above 
the air but also that existing in all matter, and to this 
invisible, intangible something they gave the name of 

Nature of ether waves. — ^All matter, but more 
especially that in which molecular motion is pro- 
nounced enough to cause sensible heat, will, by means 
of its molecular motion, start waves in the ether that, 
though not precisely similar, are likened to the 
series of circular waves that arise when a stone is cast 
upon the quiet surface of a pond. These waves 
spread out in all directions and, the hotter the body 
starting the vibrations, the more rapidly will the 
waves be formed and the greater will be the number of 
short waves (t. e., those in which there is only a short 
distance between successive waves). 

Length of ether waves. — Ether waves started by 
very hot bodies, such as the sun, vary greatly in length. 
Some, for example those made use of in wireless tele- 
graphy, are miles long and others are only about 
asolouo part of an inch. As the longer waves 
produce electric effects, they are termed electric 
waves. Waves which measure only a few thousandth 
part of an inch are capable of increasing molecular 
motion in matter and consequently of raising their 
temperature; they, therefore, are called heat waves. 
Waves that are as short as js^ part of an inch 
aflEect the endings of the optic nerve in the eye and 
are therefore called light waves. Waves that are less 
than ^5^ part of an inch do not affect the sight, 
but they do affect the chemicals upon a photographic 

86 Physics and Chemistry 

plate and they cause many chemical changes in nature, 
therefore, they are called chemical or actinic waves or 

Origin of color. — Light waves have different lengths 
and difference in length results in different colors. 



Color Wavelength* Color Wavelength 

Red .0007 mm. Green .00053 mm. 

Orange .0006 mm. Blue .00047 mm. 

Yellow .00058 mm. Violet .0004 mm. 

Only the molecules of very hot bodies vibrate 
with sufficient rapidity to produce waves of a length to 
affect the optic nerve, i.«., light rays. The tempera- 
ture of a body must be raised to 525** C. before waves 
short enough to be visible as light appear. When this 
temperature is reached, a red glow is seen and as the 
temperature is increased, though long waves are 
being generated, shorter and shorter ones (those 
that give rise to the different colors) are produced 
until, between a temperature of 860^ C. and 1200^ C, 
waves of all colors are being generated and con- 
sequently a so-called white heat or light is reached for, 
when all colors of the spectrum' are present in a com- 
bined state, a white light is produced. This is the 
case with sunlight. The sun, being t he hottest of all 
bodies, produces waves in the ether of aU^possible 
lengths ; thus, in the sunlight, as already stated, there 
are waves that will give rise to electric effects, heat, 

* A millimeter (mm.) equals 0.3937 of an inch. 
' The colors seen when light waves are refracted by passing 
through a prism, etc. 

The Ether, Heat, and Light 87 

light of all colors, and chemical reactions. That 
the sunlight contains all the colors of the spectrum is 
seen when it undergoes refraction, as in the rainbow 
and in passing through prisms, see page 100. 

In one sense, aU ether waves are heat waves, since 
waves of all lengths will increase molecular motion in 
bodies and thus raise their temperature. 

Retention of heat. — ^Light waves can penetrate 
many substances easily that the longer heat waves 
pass through only with difficulty and this is of great 
value to man. For instance, light waves pass 
through the glass of hot-beds and conservatories 
and through snow, paper, etc., covering plants, they 
are partly absorbed by the earth and plants the 
molecular motion of which is thereby increased and 
heat produced which, as it does not readily pass 
through the plant covers, remains and furthers the 
growth of the plants. Also, the light waves pass 
readily through damp air, smoke, and the like, but the 
heat waves only do so slowly and with difficulty; for 
this reason, clouds and smoke at night serve to 
maintain the warmth that the earth acquired during 
the daytime. Thus a clear night is likely to be cooler 
than a cloudy one. The fruit growers of California 
bum smudge fires in their orchards when there is 
danger of a frost, because heat and also a heavy low- 
lying smoke that prevents the escape of heat from the 
ground results from these fires. 

How the air is heated. — Heat being the result of 
molecular motion, it cannot, it is believed, exist apart 
from matter and consequently ether waves are not 
themselves hot, though, by increasing molecular 
motion in all matter which they strike, they are the 
cause of heat. 

88 Physics and Chemistry 

Ether waves would pass through absolutely dry 
air without producing any decided heating effect, 
but moisture and solid matter, as dust, in the air will 
give rise to heat. Moistiire also serves to hold the 
heat and to transmit it in all directions. Also, as 
stated in the preceding paragraph, it helps the earth 
to retain the heat it acquires during the da3rtime and 
yet, it acts as a screen between the earth and the 
sun's rays. On high mountains, above the clouds, 
where there is little moisture, people will suffer in- 
tensely from the heat formed in their own bodies by 
the impinging upon them of the ether waves, while 
the air surrotmding them is cold. These effects of 
moisture are among the several reasons why the tem- 
perature of places near large bodies of water are more 
tmiform the year round than those not so situated. 

Effect of different kinds of matter upon ether waves. 
— ^When ether waves strike any medium other than 
ether, any one of three things may happen ; they may be 
wholly or in part (i) reflected; (2) transmitted {i.e,, 
allowed to pass through the substance) ; (3) absorbed. 

Opaque, translucenti and transparent objects. — 
Such substances as metals, wood, etc., which do not 
permit the passage of light rays are said to be opaque. 
Those which allow some light to pass through their 
substance, e.g., ground glass and paper, but do not 
permit objects on their farther side to be seen, are said 
to be translucent. Objects, such as dear glass, through 
which light ray^ pass freely and allow objects on their 
farther side to be seen are said to be transparent. 


Nature of reflection. — ^Ether waves may be reflected 
or thrown back from matter which they strike in 

The Ether, Heat, and Light 89 

two ways; one of these is termed regular reflection 
and the other diffuse reflection. The straight 
beam of light that is seen striking back from a mirror 
upon which a ray of light falls on entering through a 
small aperture into a darkened room is an example of 
regular reflection. Diffuse reflection is the scattered, 
diffuse or irregular throwing back of light that occurs 
when light waves fall upon a rough or unpolished 
surface.. It is due to the diffuse reflection of light 
waves from dust and moisture in the air and from 
objects upon the earth that there can be light all 
about us and not only in the direct path of the light 
rays. The phenomenon, popularly known as "the 
sun drawing water" is produced by the reflection of 
light, from sunbeams coming from behind a cloud, 
by dust and moisture in the air. The light of dawn 
and twilight are due to reflection of the sunlight by 
moisture and dust in the air which catch the light even 
before the sun appears or after it disappears below the 
horizon. The colors of sunset also are due to the 
reflection of light waves by the clouds and particles 
in the air. The colors are seen in the evening because 
the atmosphere is then denser than earlier in the day 
and thus more light waves are absorbed and, as the 
light waves then strike the clouds from below, their 
reflection is facilitated. 

Why we see objects. — ^We see objects because they 
reflect light waves which fall upon them back into our 
eyes so that they strike upon the retina and form a 
picture there, as upon the sensitive plate of a camera, 
and thus stimulate the optic nerves which then 
transmit their impressions to the center of sight in 
the brain. 

Differences in the power of absorptioni reflection, 

90 Physics and Chemistry 

etc. — Matter varies greatly in the degree of absorp- 
tion, radiation, and reflection of which it is capable 
and it is useful to have some knowledge of these 
differences. For instance, one without such knowl- 
edge might think that asbestos would be a good 
protector to put behind a stove, but asbestos, though 
itself non-combustible, absorbs and thus has its 
molecular motion increased and is thereby heated by 
ether waves and therefore it would be likely to 
scorch paper or wood behind it. A highly polished 
tin or zinc mat, on the other hand, reflects so many 
ether waves, instead of absorbing and being heated 
through by their action, that it will protect a wall 
behind it. White paint reflects more heat and light 
waves than dark paints, which is one reason why white 
or light colored paints, papers, etc., make a room 
lighter than dark colors and why black and dark 
colored clothing is warmer than white and light colors. 
Rough, dull surfaces absorb and radiate heat better 
than smooth polished surfaces and thus radiator 
pipes are alwajrs rough, to have smooth ones would 
entail a great loss of heat. Bright smooth surfaces, 
as mirrors and polished metal, are the best reflectors, 
but practically all bodies reflect some light waves, 
were this not the case, we would not see them, for, as 
stated in a previous paragraph, we see objects because 
of the light which they reflect into our eyes. 

It is trying to the eyes to read what is printed or 
written on glazed paper and highly polished black- 
boards, because so much light is reflected from the 
shining surface that the words are obscured. An 
intense reflection or glaring light from any source is 
harmful to the eyes and the new method of artificial 
lighting, in which the light is thrown upon the ceiling. 

The Ether, Heat, and Light 91 

in order that it may be diffused and a more even, less 
concentrated, lighting be accomplished, is an attempt 
to obviate such defects. 

The differences in the power of absorption, reflec- 
tion, etc., are thought to be due, at least in part» to 
differences in the molecular motion of matter. 

Origin of the color of bodies. — ^The color of objects 
depends upon the ether waves which they absorb 
and reflect; e.g., grass is not green, but it appears to 
be green because it reflects green waves and absorbs 
those of other colors; a paint or dye appears to be a 
certain color because it reflects the wave of the 
particular color it appears to be and absorbs all other 
waves. Matter that does not absorb one set of 
wave lengths more than another, but reflects them all 
equally, appears white, and matter that absorbs 
practically all the ether waves incident upon it appears 

Number of colors. — ^Though sunlight, when re- 
fracted by passage through a prism, appears to be 
separated into but seven distinct colors, many hun- 
dreds of colors are possible. One reason for this 
is that waves of more than one length are reflected 
by the majority of the chemicals used for dyes and 
paints and other objects and if w£^vcs of different 
lengths are reflected, but not in suflSdent number or 
quantity to cause white light, a different shade or hue 
of the predominating color — i.e., the wave length 
reflected to the greatest extent — can be obtained. 
As will be seen later, mixing paints alters the degree 
of absorption and reflection of waves and thus gives 
rise to different colors and shades. 

Reason for changes of color under artificial lights. — 
Artificial lights, not being as hot as sunlight, do not 

92 Physics and Chemistry 

produce all the wave lengths that the latter does and 
different kinds of artificial lights vary in the lengths 
of waves that they produce. Consequently, as 
objects have not the color, but essentials for color, 
they may not be the same color by artificial light as 
they are by sunlight, or by electric light as by gas 
light, for the particular wave or waves may not be 
present to be reflected. 

Reason for the fading of colors. — The chemical 
rays of the sun and certain chemicals used for bleach- 
ing cause changes in the nature of the pigments used 
for dyes and paints which lessen their power of 
absorption of light waves, and thus more waves are 
reflected and this gives rise to the presence of a 
greater amount of white light, in consequence of which 
the color is lighter. The object is then said to be 
faded or bleached. 

Why color is perceived. — In order that color be 
perceived by the brain it is necessary for the retina 
to be stimulated in some way by the color rays enter- 
ing the eye. How it is stimulated is not known, 
but one theory advanced is that the retina contains 
a compound chemical substance which is acted upon 
by the incoming color waves in some way, as yet 
unknown, so that chemical changes are brought about 
which produce the sensations that give rise to the 
color sensations which we perceive. 

Color blindness. — ^About 4 to 5 per cent, of men 
and I per cent, of women have defective color vision. 
As a rule, this defect consists in not being able to 
distinguish some one or, more frequently, two colors, 
but occasionally there is an inability to distinguish 
any color and individuals with this disability can 
distinguish form, light, and shadows, only. Any 

The Ether, Heat, and Light 93 

defect of color vision is spoken of as color blindness. 
The cause of the condition is unknown. Some 
authorities consider it due to a lack of some chemical 
substance in the retina and others to defective forma- 
tion of the nerve-endings that should be affected by- 

Complementaxy colors. — ^When certain color waves, 
as red and green, yellow and blue, green and violet 
stimulate the retina at the same time, they produce a 
sensation of white. The pairs of colors which do 
this are called complementary colors. It is because 
yellow and blue waves produce a sensation of white 
that we use bluing to improve the color of white 
clothing that has become yellowed. 

Reason for colors produced by mixing different 
colored pigments. — The results obtained when colored 
lights fall upon the retina are not the s&me, it will be 
observed, as when paints are mixed; for instance, 
when yellow and blue paint are combined we get a 
green color, because yellow pigment absorbs all 
colors except yellow and some green while blue absorbs 
all colors except blue and some green, and mixing 
the two pigments causes the absorption of all color 
waves except green. A white paint added to another 
lessens its power of absorption, hence more waves 
are reflected and a lighter color results. On the other 
hand, the addition of a so-called black pigment to a 
colored paint increases its power of absorption and the 
color appears darker. 

Color of transparent objects. — The color of trans- 
parent objects depends upon the light waves they 
transmit — L e., allow to pass through them. All 
light waves pass through white glass, but if a color- 
ing matter that will allow the passage of red waves 

94 Physics and Chemistry 

only is added to glass in the process of its manu- 
facture, then onlj' red waves will pass through. 
Blue glass absorbs all color but blue waves and a 
little green and it transmits the blue and green. 
Yellow glass transmits yellow waves freely, green 
and red to a slight extent, but blue and violet not 
at all. 

The power of colored glass to absorb some waves 
and transmit others is made use of in heliotherapy. 
By looking at the table on page 86, it will be seen that 
the waves which give rise to a red color are nearest 
in length to those that have the greatest power to 
produce heat in matter and, therefore, if red glass is 
placed between a patient and the sun's rays the 
waves passing through will have a heating effect, 
but those which produce chemical reactions and, 
consequently, so-called sunburn are shut out. Violet 
rays, being nearest chemical waves in length, the 
waves that pass through violet glass produce chemical 
reactions but have not such a heating effect as those 
which pass through red glass. The waves that pass 
through yellow and green glass give rise to slight 
heating and slight chemical effects. Thus yellow 
or green glass placed between a patient and the sun's 
rays will prevent sunburn and intense heating. 

Ultra-VioIet Rays. Finsen Light 

When light is passed through a lens made of quartz 

r or certain other substances, all ether waves are ab- 

) sorbed except those which give rise to violet and ultra- 

l violet rays. The latter, partly, it is thought, by the 

chemical reactions that they promote in the tissues, 

are often very effectual in the treatment of such 

The Ether, Heat, and Light 95 

diseases as lupus. Ultra-violet light is obtained also 
by electrical means in somewhat the same manner as 
the X-rays, which will be discussed later. 

The ultra-violet light was named Finsen light in 
honor of Niels Ryberg Finsen, the Danish physician, 
who first advocated its use in the treatment of 


Nature of Refraction. — Ether waves of all lengths 
can be refracted, that is, bent from their course, in 
ner, but as it 
is the light 
waves that 
give the most 
obvious re- 
sults of their 
they are the 
ones that we 
will consider. 
The ref rac- Fig- 44- Linb Bent toward and away 
tion of lieht from the Perpendicular. 

waves occurs ^**^ Perpendicular line, (b) Line bending 

toward the perpendicular, (c) Line bending 
when they away from the perpendicular, 
pass oblique- 
ly from a medium of one density into that of another 
density. If the medium into which the waves pass is 
of greater density than that in which they are — tf.g., 
when they pass from air into glass or water — they are 
bent toward the perpendicular, but when the meditun 
into which they pass is of lesser density than that which 


Physics and Chemistry 

they leave — e.g., when they pass from glass or water 
into air — they are bent from the perpendicular. It 
is because the light rays coming from an object placed 
under the lens of the objective of a microscope are 
diverged, as in (b) Pig. 46, 
and thus enter the eye at a 
wider angle than the direct 
rays would, that the image 
of the object is magnified. 
CauM ai refraction. — 
The cause of refraction is 
that ether waves travel at 
different rates in media of 
different densities: for in- 
stance, light waves pass 
through water atonlythree- 
fourths the speed with 
which they travel through 
air, and when a ray of light 
strikes a body of water ob- 
liquely all portions of its 
front will not enter the 
water at the same time 
and the part which enters first becomes retarded before 
that entering later. In Fig. 45 the short parallel 
lines represent the wave front of a beam of light enter- 
ing obliquely from air into water; one part (a) reaches 
the water before (b) and, as it then travels more 
slowly than that part of the wave which is still in the 
air, it only reaches (c) while (b) is going to (d) ; thus 
the beam is bent. It is because of refraction that a 
stick held partly in the air and partly in water looks 
as though it were bent. Rays of light entering from 
one medium into another perpendicularly are not 

Pig. 45. The Bending of a 
Beau of Light Entbrino 


The Ether, Heat, and Light 97 

bent. It is due to refraction that the rays o£ light 
which are reflected by objects into our eyes both 
perpendicularly and obliquely come to a focus on 
the retina. The cornea, lens, and humors of the 
eye serving to cause refraction. 

When the suxface of a refracting medium is convex 
— >.«., thicker in the center than at the edges — light 

Pio. 46. (a) Showing how refraction by a convex auifaco 
will bring light rays to a focus, (b) Showing how light rays 
will be diverged on pngeing from a medium of greater into 
one of lesser densi^. 

rays come to a focus quicker than when it is flat, 
and the normal eye is provided with a means of 
becoming more convex when looking at objects near 
at hand.' When, for any reason, the eyes lose their 

* It is thought, that when the eye is at rest or fixed upon distant 
objects thesuspensoiy ligament (i.e., theligament that is fused to 
the anterior surface of the capsule inclosing the crystalline lens of 
the eye and attached at either end ta the ciliary processes be- 
tween the choroid and the iris) eierts a tension upon the leng 
which keeps it flattened, particularly along the anterior auiface, 
but when the eye becomes fixed on near objects the dliary musde 
contracts and in doing so draws forward the choroid coat and 
thus relaxes the tension of the ligament, in consequence of whiiA 
the anterior surface of the lens becomes more convex. 


Physics and Chemistry 

power of adapting themselves in this way to view 
near objects or when the 
eyeball is naturally shal- 
low, light rays would 
have to extend behind 
the retina to come to a 
focus and the vision of 
objects near at hand, es- 
pecially fine ones as the 
letters of printed matter, 
is blurred and indistinct. 
This condition is known 
as hypermetropia oi far- 
sightedness. The term 
far-sighted is applied to 
eyes with this defect 
because when it is not 
very great the individual 
can often see things at 
a distance better than 
people whose eyes are 
normal. Defective vis- 
ion due to this con- 
dition is corrected by 
wearing glasses, by 
means of which the rays 
are sufficiently refracted 
to make up for the de- 
fective structure of the eyeball or action of its refrac- 
tory apparatus, as the case may be. Failure of 
accommodation, due to old age, is known as presbyopia 
or old-age sight. 

Another defect of the eyes that interferes with 
proper refraction is that known as myopia or near- 

e, Eyepiece, d, Draw tube. 
Body tube, m, Revolving noae- 
piece. o. Objective, ph, Pin- 
ionhead. mh, Micrometer head, 
ha. Handle arm. s. Stage. 
Substage. m. Mirror, b, Base, 
r, Rack, p, Pillar, i, Inclina- 
tion elevation of handle ai 

The Ether, Heat, and Light 99 

sigkudness. This is usually due to a too great curva- 
ture or too great depth of the eyeball, in consequence 
of which light rays come to a focus before they reach 
the retina. To obviate the blurring of vision due to 
this condition concave lenses — i. e., those thinner in the 
center than at the edges — are worn, because they cause 
rays of light to diverge before entering the eye and 
thus it takes them longer to come to a focus afterward. 


8 C 


Fig. 48. DiFTBBENT TvFEs OF Lenses. 
A, Double convex, b. Plane convex, c. Concave 
convex, d, Double concave, e, Convex concave. 
P, Plane concave, c, Prism convex. B, Cylin- 
drical convex, t. Cylindrical ct 

Light is divei^ed by a concave lens because the mid- 
die of the wave is retarded less than the edges, as the 
lens is thinner in the center than at the edses. 

Astigmatism. — Still another cause for defective 
refraction in the eyes is the condition known as 
astizTnatism m which the curvature of the refractory 
apparatus is not equal in all parts. This makes it 
necessary for the ciliary muscles to be constantly in 
action while the individiial is reading, focusing for 
the lines of letters that run in different directions. 
This soon results in eyestrain. Cylindrical lenses, 
which have a plane surface in one axis and a curved : 

100 Physics and Chemistry 

surface in the axis at right angles to it, are worn to 
correct the condition. 

Prism glass. — Glass with a rough surface will be 
often seen in windows that open on to a court or 
narrow street or passage. This is called prism glass. 
It improves the light in a room because the prism- 
like projections on its surface refract the light waves 
passing through it, causing them to penetrate farther 
into the room than they naturally would. 

The rainbow* — ^When light waves enter drops of 
water or glass that is cut in the manner of the beveled 
edge of a mirror or of a prism, these of di£Eerent lengths 
suffer unequal refraction and thus they become 
separated and the di£Eerent colors are discernible. 
The rainbow, which is due to the refraction and re- 
flection of light in drops of water in the a:r, is an 
example of this kind of refraction of light waves. 

Nature of polarization. — By polarization is meant 
making light vibrations take place in one direction. 
The streak of regularly reflected light striking back 
from a mirror is an example. 

How light can be polarized. — Light is polarized 
by reflection from a flat, highly polished surface, as a 
mirror, by refraction and by passage through such 
substances as the mineral tourmaline and iceland 
spar. As these substances cause polarization, it is 
thought that their electrons must vibrate in one 
particular direction and that only waves that will 
vibrate in the same way can pass through them. 

Light is often polarized from a mirror in order to 
thoroughly illuminate body cavities. It is polarized 
by a special apparatus known as a polariscope^ in 

The Ether, Heat, and Light loi 

pathological work, for the detection of glucose in 
fluids, such as the tuine, for when polarized light 
falls upon glucose it is rotated to the right and the 
degree of rotation will depend upon the amount of 
glucose present and thus it is an easy and accurate 
way of determining the quantity of glucose in a 
solution. Levulose, on the contrary, turns polarized 
light to the left. Also, there are a number of other 
substances that turn it to either the right or left in 
varying degrees and thus it is used in many varieties 
of scientific work, especially as a means of identifying 
substances which rotate it. 

Phosphorescence and Fluorescence 

Phosphorescence. — Certain substances, after being 
exposed to a strong light, will emit light in the dark. 
This property is termed phosphorescence and matter 
which possesses this power is said to be phosphorescent. 
Paints which are luminous in the dark contain some 
phosphorescent material, usually baritun chlorid. 
A certain class of bacteria, called photogenic^ produce 
this quality in matter, especially fish, in which they 
produce decay. 

Fluorescence. — Certain substances, such as the 
mineral fluorite, fluoresdn, platino-cyanid of barium, 
uranium glass, and solutions of quinin sulphate, 
have the power to change the length of ether waves, 
and thus of changing heat waves to light waves and 
vice versa to a marked degree, and of reflecting color 
waves different from those thrown upon them. Sub- 
stances which do this are said to he fluorescent. This 
name was given, because the mineral fluorite was the 
first substance in which the property of fluorescence 
was noted. 



Theories Regarding the Nature of Electricity and Electrification 
— Conductors and Non-Conductors — Different Methods of 
Generating Electric Currents — Nature and Action of 
Chemical Cells and Batteries for Generating Currents — 
Electrolysis — Electroplating. 

Derivation of name. — The term electricity was 
derived from the Greek work electron ^axnher, 
because the first record of electrization was in connec- 
tion with this substance. This record, which was 
made by the Greeks, some 500 years before 
Christ, was to the effect that if amber was rubbed 
with a dry doth it would attract light objects to 

Experiment 11. Object: To study electrification. 

Procedure: (a) Rub a glass rod for a few minutes 
with a dry woolen doth or a piece of silk and then 
drag it through some small pieces of paper scattered 00 
the table. 

If the rod is rubbed long enough, under statable 
conditions, see page 107, it will attract the pieces 
of paper towards itself. 

(b) Hang this rod by a piece of silk thread to a 
wire bar or stirrup, dectrify another glass rod in thf 
same manner as the first rod and hold it against the 

Electricity 103 

free end of the suspended rod, the latter will swing 
away from it; i.e., it will be repelled. 

(c) Rub a piece of sealing wax with silk and hold it 
near the suspended glass rod, the latter will swing 
toward it; i. e., it will be attracted. 

(N. B. Be careful while doing this experiment 
not to let the part of the rod that is to be used come 
in contact with the hand or other object. The reason 
for this will be seen later in the section on conductors.) 
In the same section it will be also explained why this 
experiment is seldom successful in wet weather. 

There are two things to be learned from this ex- 
periment: (i) Friction will produce electrification. 
(2) Substances of similar material electrified in the 
same way repel each other, but electrified objects of 
different material or of the same material differently 
electrified may attract each other. This is because 
there arc two kinds of electrification — *. e., of electric 
charges — and one of the laws of electrical action is: 
Like charges repel each other and unlike charges 
attract. The two kinds of charges have been arbi- 
trarily named positive and negatioe, and a positively 
electrified body is often defined as: An electrified 
body which acts toward other dectrifi^ bodies cls 
does a glass rod that has been rubbed with silk. 
Likewise a negatively electrified body is said to be: 
One which acts toward other electrifi^ed bodies as does a 
stick of sealing wax which has been rubbed with flannel. 

But one kind of electricity. — ^Though the expres- 
sions negative deUricity, positive electricity, static 
electricity, current electricity, etc., are constantly 
used, there is but one kind of electricity. For this 
reason, it has been suggested that the terms negative 
Md positive electrification or negative and positive 

104 Ph3rsics and Chemistry 

electric charges be used instead of negative and 
positive electridty. By static electricity is meant, 
that which is not flowing, as, for example, when it is 
passing over a wire. In the latter case it is known as 
current electricity, or, more correctly, an electric current. 
The difference, however, lies, not in the electricity, but 
in the manner by which it is made manifest. 

Some theories regarding the nature of electricity. — 
Though a sufficient degree of knowledge, of the ways 
in which electric charges and currents can be produced 
and of the results of their action, has been obtained to 
allow of electridty being applied in a great many 
ways to the service of man, its nature is still a matter 
of conjecture. Some theories that have been ad- 
vanced are as follows : 

The two-fluid theory. — ^When the ease with which 
electridty moved over certain substances was first 
realized, the idea was conceived that it was a fluid. 
Or, rather, it was thought at first that there were two 
fluids, one giving rise to positive and the other to 
negative charges. 

The one-fluid theory. — About the year 1750, 
Benjamin Franklin advanced what is called the one* 
fluid theory, which holds that there is but one kind of 
fluid and that positive charges are the result of an 
excess of electridty and negative charges of a lesser 
amount. Because of this supposition, Franklin used 
the plus sign (+) as a s3rmbol for positive charges, and 
the minus sign (— ) as a s3rmbol for negative charges. 
These signs are still used, though, according to the 
electron theory, which many sdentists think is 
probably nearer the truth, a positively charged body 
has lost, instead of gained, electrons. 

The electron theory. — ^The electron theory is based 

Electricity 105 

on the assumption that the atoms of all elements are 
composed of electrons. It holds that each atom of an 
element consists of inconceivably small positive cor^ 
puscles that are surrounded by thousands of still 
smaller bodies called negative eUctrans. These nega^ 
tive electrons are, it is thought, constantly revolving 
with exceedingly great rapidity around the positive 
corpuscles and were it not for the attraction of the posi- 
tive corpuscles, they would, it is thought, fall away. 

Ordinarily, the majority of substances are in a 
state of electrical equilibritun — i.e., neither positive 
nor negative — ^but, it is assumed, some of the more 
easily detached revolving electrons may be transferred 
from one atom to another without dissociating the 
atom; the only change being that the atoms of the 
substance by losing some of their negative electrons 
have their positive charge strengthened and the sub- 
stance is then said to have an electro-positive charge. 
On the other hand, the substance that gained the neg- 
ative electrons has its negative charge strengthened 
and is said to be electro-negative. This is what it is 
thought happens in Experiment 1 1 . The friction of the 
silk on the glass caused the atoms of the latter to part 
with some of their negative electrons to the silk and 
thus the glass became positively and the silk nega- 
tively charged. On the contrary, the silk gave some 
of its electrons to the sealing wax and thus it became 
positively and the wax negatively charged. 

The reason why the silk and other material gain 
electrons in one case and lose them in another is 
thought to be due to some difference in the number 
and arrangement of the electrons by which certain 
substances are able to take electrons more readily 
from some materials than from others. 

io6 Physics and Chemistry 

It is believed that positive corpuscles are never 
dissociated from the atoms. 

Nature of an electric current. — ^As stated on page 
104; an electric current is simply a flow of electricity 
through some object and this flow, it is now believed 
by many scientists, consists simply of a passing of 
negative electrons from atom to atom, usually in one 
direction, along the object. 

Conductors. — ^There is a great difference in the 
ease and rapidity with which an electric current pas- 
ses through different kinds of matter. For example, 
copper wire will conduct electricity a million times 
better than water. Substances through which a 
current passes readily are said to be good conductors. 
Those through which it does not pass readilyare called 
poor conductors, and very poor conductors are termed 
nonconductors or insulators. No substance however 
is a perfect conductor nor a perfect insulator. 

ThefoUowing list shows the relative conducting value 
of some common substances. They are mentioned in 
the order of their conducting value beginning with the 
most efficient. The last nine are considered insulators. 


Dry air 




Sealing wax 




Hard rubber 

Carbon" . 


Dilute sulphuric add 




Human body 





Electricity 107 

Moist air is a much better conductor of electricity 
than dry air, which is why Experiment ii is not 
likely to be jmccessful when the humidity is very 
high. Dry air, being more rarefied than moist air, is 
a very poor conductor, thus in dry air a substance 
retains its charge for some time. A common example 
of the favorable influence of dry air on electrification 
is seen also when brushing the hair in cold, dry 
weather. For the crackling sound that occurs and 
the flying of the hairs apart are due to electrification ; 
and that the hairs fly apart, but cling to the brush, 
shows that like charges repel each other and unlike 
charges attract each other. Glass, sealing wax, 
silk, etc., were used for the experiments because, 
being poor conductors, they retain their charge for 
some time. Metals wotdd not serve such a purpose, 
since, being good conductors, they lose their electrifica- 
tion unless it is being continuously produced as for an 
electric current. If the hand is rubbed over the 
electrified rod, the latter will lose its charge, which 
will be imparted to the hand, and the same thing will 
happen if the rod comes in contact with metal or any 
substance that will act as conductor. 

How an electric current is produced. — ^In order to 
start and maintain an electric current along a conduc- 
tor some external force is necessary. This is generally 
obtained by the use of an electric cell or battery or of a 
dynamo. The force obtained by use of a cell or battery 
is the result of chemical action, and that obtained with 
a dynamo is, as will be seen later, due to some form 
of mechanical action or of heat. 

Chemical batteries. — Chemical electric batteries 
consist of two or more cells and the essential parts 
of a cell are: 

io8 Physics and Chemistry 

A jar An electrolyte 

Two electrodes A conductor 

The electrodes. — ^These are two flat plates or bars 
of metals or other substance by which the current 
enters and leaves the electrolyte. The electrode at 
which the current is started is known as the anode 
(from the Greek an » in and hodos^SL road) and the 
electrode by which the current has been supposed to 
leave the cell is known as the cathode (from the Greek 
cath^ away and hodos^a, road). 

Zinc is very generally used for the anode of battery 
cells for two reasons: (i) It is easily acted upon by 
liquids that are convenient to use for electrol3rtes» 
and this chemical action provides the energy necessary 
to procure the electric current; (2) As zinc is dissolved 
by the acid its atoms part with their negative electrons, 
leaving them with the undissolved metal. The neces- 
sity for this will be seen later. Since the anode 
thus becomes negatively charged, it is spoken of as 
the negative electrode and is represented by the 
minus sign (—) . 

A cathode for a chemical cell is generally made of 
either copper or carbon; these substances not being 
acted upon by electrolytes that dissolve zinc. As will 
be seen later, when a cell is in action, the cathode 
acquires a positive charge and it is therefore often 
referred to as the positive electrode and it is repre- 
sented by the plus sign {+). 

Electrolytes and electrolysis. — ^An electrolyte is a 
solution that conducts and is decomposed by elec- 
tricity. The process that occurs in an electrolyte 
is spoken of as electrolysis. 

The electrolytes generally used for chemical batteries 

Electricity 109 

are sal ammoniac and sulphuric add, but solutions 
of any inorganic adds, bases, and salts will undergo 

Nature of electrolysis. — It is thought that when 
inorganic adds, bases, and salts are dissolved in water 
a portion of their molecules become separated into 
two or more parts, called ions, which move about 
in the solution independently of each other and of 
other atoms and molecules (hence their name, which 
is derived from a Greek word meaning wanderer). 
Ions, are tmlike other atoms and molecules in that 
they have an electrical charge; in fact, a common 
definition for an ion is an atom or radical having an 
electric charge. 

When a substance undergoes electrolysis, one of 
the ions resulting from the dissodation will have a 
positive and one a negative charge. According to the 
electron theory, this is because the atoms of the ele- 
ment or elements forming one ion gave up some of 
their negative electrons to the other ion in the process 
of decomposition. The ion losing the electrons is, of 
course, the positive ion and the one gaining electrons, 
the negative ion. When sulphuric add (HaS04) is 
thus decomposed, the hydrogen ions are the positive 
ions and are said to have or carry a positive charge 
and the sulphate ion (SO 4) has a negative charge. 
When soditun chlorid(NaCl) is dissodated, the sodium 
(Na) has a positive charge and the chlorin (CI) a 
negative charge; when soditun hydroxid (NaOH) is 
dissodated, the sodium (Na) has a positive and the 
hydroxyl ion (OH) a negative charge, and so on. 

Positive ions are called cations, because they go to 
the cathode and, like a positive charge, they are 
represented by the (+) plus sign. Negative ions are 

no Physics and Chemistry 

called anions, because they collect at the anode and 
they are represented by the (— ) minus sign. 
Arrangement of a simple cell.— The simple cell, 
often used in laboratories 
for the purpose of observ- 
ing the action that occurs 
in chemical batteries, is 
known as a Galvanic or 
Voltaic cell; because Gal- 
vani. an Italian anatomist, 
in 1786, was the first to dis- 
cover that a continuous 
current of electricity could 
be procured by chemical 
means, and Volta, an Italian 
physicist, in 1800 invented 
an arrangement similar to 
this form of cell. It is ar- 
ranged as follows: A strip 
of zinc and a strip of cop- 
per, each having a piece of 
copper wire soldered, or 
otherwise attached to their 
upper end, are fixed, one 
on either side, in a jar con- 
Pig. 49. Voli«cCbll. ^"^""^ ^'^"^^ sulphuric 
(a) Anode or positive pole - . ^^ ^•"'•°''- '^'' «1«^- 
(e) Cathodeor negative pole +. trode, electrolyte, and con- 
ductors are known as the 
electric circuit, since it is through these things that 
the electric current passes. When the wires attached 
to the electrodes arc joined, the circuit is said to be 
made or closed and when the wires are disconnected 
the circuit is said to be open or broken. 

Electricity 1 1 1 

Chemical action that occurs in a cell. — ^When the 
zinc (Zn) and the sulphuric acid (HaS04) come in 
contact, the zinc begins to dissolve gradually and 
the HaS04 to split into H and SO 4 ions. The 
atoms of the dissolved zinc thereupon tmite with the 
sulphate ions, forming the salts known as zinc std^ 
phate, and the hydrogen appears in the form of 
bubbles first on the zinc strip and, after the circuit 
is closed by connecting the wires, on the copper plate 
or cathode. 

Theories of electric action. — ^The manner in which 
the electric ctirrent passes through the circuit has not 
been as satisfactorily ascertained as the nature of the 
chemical action and, at present, there are two theories 
regarding this. They are about as follows: 

Theory i. As the zinc goes into solution in the 
acid, the atoms separated from it leave some of their 
negative electrons behind in the undissolved portion 
of the metal ; thus, this soon acquires a negative charge, 
and the solution surrounding it, which contains the 
dissolved zinc, becomes positively charged. This 
part of the solution repels the hydrogen atoms, which 
are also positively charged, and, consequently, they 
I fly to the copper pole. Of course, as already stated, 

j the zinc unites with the SO 4 and becomes electrically 

neutral — i. e., neither positive nor negative, but, 
while the circuit is closed, there is always enough 
imunited positive zinc in the solution to repel the 
hydrogen atoms. When the hydrogen ions reach the 
' copper they part with their charge and collect as bub- 

bles of hydrogen gas upon it. As the copper electrode 
receives the charge from the hydrogen ions it becomes 
positively charged. The electric current thus started 
passes up the copper plate over the wire conductors 

112 Physics and Chemistry 

to the zinc electrode, down this to the electrolyte, and 
back to the copper electrode, and so on. 

Theory 2, which has been formulated since the 
electron theory of the nature of electricity was ad* 
vanoed, considers that the current leaves the cell from 
the zinc pole or anode and not, as has always been 
supposed, from the cathode.' It holds that, due to 
the force generated by the chemical action, the 
negative electrons left behind on the zinc electrode 
by the atoms of the metal which goes into solution 
in the acid, as described in Theory i, fly up the 
electrode and over the wires to the cathode, and sq on. 

If the two wire conductors are disconnected, thus 
breaking the circuit, chemical action in the cell soon 
ceases. The reason for this, it has been assumed, is 
that, when the current ceases, the zinc acquires such a 
strong negative charge that it holds on to the positively 
charged zinc atoms and keeps them from going into so- 
lution, and, at the same time, the copper pole acquires 
such a strong positive charge that it ceases to take the 
positive charge from the hydrogen. As soon, however, 
as the circuit is closed, the flow of the current is re^tab- 
lished and the chemical action proceeds as before. 

The wire conductors connecting the two electrodes 
need not be short, as in the cells used for demonstra- 
tions in the laboratory but for example the cells 
of a battery are often put in the basement of a house 
and the wires extend from this to a plate behind the 
bell push button at the front door. One of the wires, 
on its way to the front door, extends through the 
kitchen or other room where it is connected to the 
bell apparatus. The essential parts of the latter 

^Scientific Ideas oj Tfhday^ Chailes R. Gibson, Seeley, Service 
ft Co.. Chapter v. 

Electricity 1 13 

are: a bar of soft iron which is attached to the hammer 
that strikes the bell, and another iron bar, called an 
eUcUromagnet, that is in connection with the wire 
conductor and becomes magnetized when the electric 
caitTQftt passes thr ough it. 

Each of the two wires at its terminal behind the 
ptish button is attached to a small strip of metal. 
This is where the circuit is open and closed. Ordi- 
narily, the metal strips do not come in contact and 
the circuit is open, but when the button is pressed 
the metals come in contact and the circuit is closed 
and the current at once passes through the wire. As 
it passes through the electromagnet it, as previously 
stated, magnetizes it, whereupon it, since magnets 
attract iron, draws forward the bar to which the bell- 
hammer is attached and causes it to strike the bell. 
So long as the button is pressed and the circuit thus 
kept closed, the cvurent passes through the circuit 
and this type of a bell continues to ring. As soon, 
however, as pressure on the button is released, the 
circuit is opened and the bell ceases to ring. 

Electric batteries. — ^The current generated in one| | 
cell would not be sufficient to force its way over a | 4 
long conductor, such as described in the preceding' 
paragraph, and therefore, for such purposes, a battery, 
consisting of two or more cells is used. The different 
cells are connected by a wire extending, usually, 
from the cathode of one cell to the anode of the other. 

The principle of the cells of batteries in common 
use is the same as the simple cell just described, but 
carbon is often used for the cathode and sal ammoniac 
for the electrolyte. Sal anmioniac is usually pre- 
ferred to sulphuric acid because the latter, unless some 
means is taken to prevent it, causes polarization; ix.^ 

114 Physics and Chemistry 

the hydrogen gas which collects on the cathode, being 
a poor conductor of electricity, prevents the passage 
of the ctirrent, according to Theory i, to the cathode 
and, according to Theory 2, from the cathode. If the 
current is stopped in this way, the restdts will be the 
same as though the circuit were broken, and the battery 
is useless until the condition is rectified. 

Dry cells. — The so-called dry cdls (they are moist 
rather than dry) are used for so many purposes that 
require only a small current of electricity that a few 
words of description may not be out of place. A dry 
cell consists of a zinc cylinder (this acts both as a 
case for the cell and as the anode) lined with a moist 
paste made of strong sal ammoniac and plaster of 
Paris or other porous substance and containing in the 
center a rod of carbon and manganese dioxid. The 
top of the cell is sealed with wax or pitch to prevent 
evaporation of the moisture from the paste. There 
is a wire connected to the zinc cylinder and also one 
to the carbon rod. Two great advantages of dry cells 
for many purposes are that they are comparatively 
small and contain no liquid to be spilled. The action 
of a pocket flash lamp is obtained by means of one or 
more small dry cells, which are contained in its cylinder. 

Storage batteries. — Storage batteries or, as they 
arc also called, secondary batteries or acctuntdators 
arc much used for operating telephones, fire-alarm 
circuits, furnishing power for electric automobiles 
and the like. Also they are used in power houses to 
store excess electricity generated by the dynamo, 
thus providing a reservoir to draw upon when an extra 
amount of current is required. 

A common form of storage cell consists of perfo- 
rated plates of lead, the perforations of whicb are 

Electricity 115 

filled with a paste of red lead and litharg e mixed with 
sulphtiric add. These plates are kept in a suitable 
receptacle, covered with sulphuric add. They are 
charged with electridty by sending a current through 
them from an outside generator — e. g., a dynamo. 
This current dissodates the HaS04 and the hydrogen 
ions move to one set of plates and change the paste in 
them to a spongy metallic lead. These plates then act 
as a cathode. The SO 4 ions, at the same time pass 
to the opposite plates and change the paste in them 
to lead peroxid. This set of plates acts as an anode. 

When the circuit is closed, some of the lead peroxid 
is decomposed and gives rise to an electric current, 
just as occurred in the galvanic cell. 

These batteries are known as secondary batteries, 
because a primary current is used in their manu- 
facture. This name is really more appropriate than 
that of storage batteries; for these batteries do not 
store electridty, but rather the electric energy has 
been changed to latent energy, which, when the 
circuit is closed, is, by chemical action, transformed 
once more to dectrical energy. This action is analo- 
gous to that which occurs in plants and coal, as 
described in Chapter II. When the peroxid of lead 
has been all used, the battery can be recharged by 
allowing a current of electridty to pass through it 
as when it was made. Thus these batteries can be 
used for a long time. 

Electroplating. — Some of the cheaper metals are 
often coated with more expensive metals by means 
of a process known as electroplating. This process, 
though different in some respects, is similar to that 
which occurs in a voltaic cell. The electroplating 
of spoons with silver is a good illustration of the 

ii6 Phjrsics and Chemistry 

method. The apparatus used for this purpose con« 
sists of a tank across which copper rods are placed. 
These rods, which act as conductors, are connected 
with wires attached to the battery. The spoons are 
hung from the rod connected with the wire from the 
cathode of the battery, and bars of silver are suspended 
from the bar connected to the anode wire. Enough 
electrolyte is used to cover the spoons and silver 
bars. The electroljrte in silver plating consists of 
cdlver salts, such as silver nitrate. When the electric 
current is turned on, the silver salts are decomposed, 
the freed silver passes to the spoons, which thus be- 
come coated with the metal. At the same time, the 
silver bars, which act as anodes, are being slowly 
dissolved in the solution and, imiting temporarily 
with the nitrate ions, they provide fresh salts. 

If a gold plating is wanted, gold bars will be used 
for the anode and gold salts for the electrolyte. For 
a copper coating, copper bars will be used for the 
anode and copper salts for the electrol3rte. 

The chief difference between the action in electro- 
plating and that in a galvanic battery is that, in the 
former, the electric current is essential for the dissolv- 
ing of the anode, since there is no chemical action 
between it and the electrolyte, and in the galvanic 
cell, the chemical action between the electrolyte and 
the anode starts the electric current. 



The Dynamo — Different IQnds of Magnets — Magnetism — In- 
duction Coils — ^Transformers and Other Electrical Appli* 
ances — ^Electric Currents as a Source of Heat and Lights- 
Measurement of Electricity — Static Electricity — Physiologi- 
cal Action of Electricity— Cathode Ra3rs — ^X-Rays — Radio 

The Dynamo 

The electric current produced in a chemical cell or 
battery is not suitable for operating lighting and 
heating appliances, motors and the like. For one 
reason, the current would not be sufiSdently strong, 
and, for another, the anode and electrol3rte of a 
battery would have to be constantly renewed, if the 
circuit were kept closed for hours at a time. It has, 
therefore, been only since the invention of the dynamo 
that it has been possible to use electricity to any 
extent for such purposes. 

The dynamo is an apparatus in which the mechani- 
cal energy from a steam- or water-driven engine, or the 
heat energy developed in engines fed with gas, gasoline, 
or sintiilar fuel, is transformed into electrical energy. 
In other words, as the result of the force of steam or 
water power or of heat, the dynamo is started and kept 
in action and this action gives rise to an electric ctu:« 


ii8 Physics and Chemistry 

rent which, according to the electron theory, is a 
streaming of negative electrons along the wire con- 
ductor leading from and to it. 


Magnets. — One of the essential features of djmamoSy 
electrical motors, and many other electrical appliances 
being an electromagnet, it seen:is well to say a word 
here about magnets, magnetism, and electromagnets. 

Natural magnets* — In various parts of the earth, 
there is found an iron ore that will attract small par- 
ticles of iron and steel.' Such ore has been named 
magnetite (because it was found first near Magnesia 
in Asia Minor), natural magnet, and lodestone, 
meaning leading stone. 

Artificial magnets. — ^When iron and steel are rubbed 
on a natural magnet, or on steel that has been rubbed 
by a natural magnet, they will likewise attract steel 
and iron. Metals that have been thus treated are 
called artificial magnets. Cobalt and nickel also 
can be magnetized to a slight extent, but iron and 
steel are the only substances that assume strong 
magnetic properties. 

Magnetic properties. — ^The chief properties or char- 
acteristics of magnets are: (i) Induction, i, €., the 
power to induce magnetic properties in unmagnetized 
steel and iron, even at a distance. (2) Magnetic 
attraction, u €., the power to attract iron and steel. 
(3) Polarity. 

Polarity. — If a long narrow magnet, either natural 
or artificial, is suspended by a fixture at its center in a 
manner that will allow it to turn freely, it will be found 

> As will be seen in Chapter XVI., steel is a form of iron. 

Electricity and Magnetism 119 

that the magnet will always come to rest pointing 
approximately north and south. Also, it will be 
found that when a magnetized bar is put in the midst 
of iron filings, the latter will collect around the two 
ends of the bar and few if any filings will attach them- 
selves to the sides. If, however, the bar is broken in 
the center, the broken ends will attract the filings. 
The ends of a magnet have been named its poles and 
the two poles are known respectively as the norths 
seeking or north pole and the south-seeking or south 
pole. This property of forming poles is spoken of as 

Just as electrically charged bodies repel those with 
a similar charge and attract those with an unlike 
charge, so the north pole of one magnet repels the 
north pole of another magnet and attracts its south 
pole, and vice versa. 

Why magnetite was called lodestone. — ^The earth 
is a magnet and, like all magnets, it has its north and 
south poles. The north-seeking pole of the magnet 
was so named because it is attracted by the north 
magnetic pole of the earth, and the south-seeking pole, 
because it is attracted by the south magnetic pole. 
Thus, the north pole of the long narrow magnet, con- 
stituting the needle of a mariner's compass, points 
toward the north magnetic pole, and the degree of 
inclination of the needle shows the direction in which 
the ship is going. It was for this reason that mag- 
netite was named lodestone^ which means leading stone. 

Cause of magnetism. — It is thought that each 
molecule of iron and steel is a magnet at all times, 
but that, ordinarily, the molecules are not lying in 
any definite position and that, therefore, one molecule 

OQutralia^ the effect of th^ others, When the iron 

120 Ph3rsics and Chemistry 

is stroked by a magnet, however, all these small 
molecular magnets are foroed to turn with their north 
poles all in one definite direction, and when the mole- 
cules are thus placed their combined effect is strong 
enough to act. 

This theory accounts for at least three truths about 
magnetism: (i) Only the poles of a magnet show mag- 
netic attraction (naturally this would be the case 
when the molecules are in position, for then the south 
poles of one line of molecular magnets are in appo- 
sition with the north poles of another line, and thus 
they neutralize each other) ; (2) if the bar is severed, 
the severed ends act as magnets; (3) if a magnet is 
heated to red heat, it will lose its magnetic properties; 
presumably, because the heat increases molecular 
movement to such an extent that the molecules lose 
the position they were made to asstime by the magnet, 
and they then once more neutralize each other. 

Experiment 12. Object: To study magnetic fields 
and lines of force. 

Procedtire: Sprinkle some iron filings upon a piece 
of paper and place this over a magnetized bar. Then 
gently tap the paper. The filings will arrange 
themselves in curved lines extending from one pole 
to the other, these lines will run side by side as seen 
in Fig. 50, and will not cross each other. This is 
because the magnetic influence is not confined to the 
immediate vicinity of the magnet, and the filings 
coming within the field in which the magnetic force 
extends become magnetized. The area in which the 
magnetic force is felt is spoken of as the magnetic field 
or the fi^ld of force, and the attraction which tends to 
arrange the iron filings in the curved lines is spoken of 
as the lines of force. 

Electrici^ and Magnetism 121 

This property of magnets is of great value, for the 
action of the electromagnets in dynamos, motors, in- 
duction coils, and other kinds of electrical apparatus 
is largely dependent upon it. 

It was Michael Faraday, an English physicist, who, 
about the middle of the nineteenth century, discovered 
that a current of electricity 
could be induced in a wire by 
moving it in a magnetic field, 
and who devised the appliance 
that was the forerunner of the 
dynamo and many other elec- 
trical devices in use at the 
present time. 

Electromagnets. — Soft iron 
is more easily magnetized than 
steel, but the latter maintains 
its magnetic properties for a 
long time, while the former P'«-S'- ItONPoiNGa 

, ., c- I. • . OM Paper over Bar 

soon loses them. Soft iron is ,, o „, 


very readily magnetized by magnetic Fieu> and 
electricity, but it ceases to be Lines of Force. 
a magnet as soon as the cur- 
rent stops. Iron magnetized in this way is called 
an electromagaet. A common type of electromagnet 
consists of a core of soft iron or iron wire wound with 
insulated wire. The iron becomes magnetized by the 
cturent passing through the wire. 

A ample form of electromagnet and the method of 
its action were referred to in the description of the 
electric bell, page 113. Another similar form of electro- 
magnet is that inserted in the framework of the front 
door in some apartment houses, in sudi a way that, 
when it is magnetised by the closing of the circuit, it 

122 Physics and Chemistry 

draws the door catch back, allowing the door to be 
opened. The circuit is closed by the pressing of a 
button in an apartment. A large numb^ of electrical 
appliances and motors are operated in much the same 

Galvanic and faradic currents. — By a galvanic 
current or galvanism is meant a current obtained from 
a chemical cell or battery; by a faradic or induced 
current is understood a current that is induced in a 
conductor by the action of a magnet or an electrified 
body that is not connected to it. 

The current produced by dynamos and induction 
coils are examples of induced currents. Induced 
currents are known also as secondary currents. 
Induced currents that flow first in one direction and 
then in the other along the secondary coil are called 
alternating currents. Those that flow in one direc- 
tion only are called direct currents. 

Induction coils. — ^The essential parts of an indue- 
tion coil, see Fig. 52, arc a core of soft iron (c) around 
which are wound a few turns of coarse copper wire. 
This wire, which is known as the primary coil, is con- 
nected into the circuit of a battery (b). At its 
connection with the battery, it is in contact 
fine steel spring (d), at the end of which is a piece 
soft iron. This acts as a current interrupter. Over 
the primary coil is wound what is known as the sec* 
ondary coil. This consists of a great many turns of 
fine copper wire. The ends of the secondary coil ter- 
xninate in what are known as the spark points (sp). 
When the circuit is closed, the current flows through 
the primary coil, magnetizing the iron core. This 
attracts the spring, ptdling it back, which breaks the 

circuit, The core thereupon looes it$ magnetism, th^ 

Electricity and Magnetism 123 

spring falls back, and the current is remade. This 
cycle is repeated so long as the coil is in action, thus 
the current is being continuously interrupted, though 
only momentarily. This is of importance in the 

o o- 

J. d—.-O 

Fig. 52. Diagram Showing Paxt of an Induction 


(b), Battery, 
(c), Primary ooiL 
(D), Spring. 
(s, p), Spark points. 

action of the apparatus. The magnetic field created 
by the current in the primary coil induces a current 
in the secondary coil which, as the wire composing 
it is much longer and finer than that of the pri- . 
mary coil, is much stro nger than that in the latter. ^^ . 
The reason for this will be seen later. When the 
current is suflSciently strongs spark points pass be* 

124 Physics and Chemistry 

tween the secx)ndary terminals (s, p). Induction coils 
form essential parts of many kinds of electrical ap- 
paratus. The various varieties of faradic induction 
machines used in electrotherapy are modifications 
of it. 

Electric Currents as a Source of Heat and Light 

Heat effects of electric currents. — ^Whenever an 
electric current passes along a wire conductor, the 
latter becomes heated. The degree to which it will 
do so depends upon two things — viz., the strength of 
the current and the amount of resistance offered by 
the conductor to the passage of the current. The 
amotmt of resistance will depend largely upon : (i) The 
kind of wire used, some metals being poorer conductors 
and thus offering more resistance than others. (2) The 
length of the wire; the longer the wire, the greater 
the resistance. (3) The circumference of the wire; the 
greater the circumference of the wire, the easier it 
will be for the current to pass and thus the less 
will be the resistance. (4) The temperature of the 
wire; less resistance is offered by a cold, than by a 
hot, wire. 

Since resistance to a current causes heat, wires 
that will offer the least resistance are used for service 
wires and those intended to carry a current wanted 
to produce mechanical or chemical results; since, if 
heat is not required, to have any unnecessary energy 
expended as heat means a loss, as there will be then 
just that much less energy left to accomplish the 
work for which the current is intended. On the other 

Electricity and Magnetism 125 

hand, where heat is required, means ate taken to 
secure a varying amount of resistanoe» the amount 
depending upon the intensity of heat required. For 
instance, in the electric furnaces used to reduce ores, 
material is used that will offer tremendous resistance 
to the current, and an excessively high temperature, 
3000^ C and over, is attained. Of course, the greater 
the resbtance provided, the stronger must be the 
current used. Iron and platinum wire will offer more 
resistance than copper and will therefore become 

The heating element of an electric flatiron usually 
consists of a coil of fine wire. This is placed within 
a hollow iron casing which it heats. Electric warming 
pads consist of coiled wire enclosed in asbestos cloth 
and coverefl with flannel. Electric stoves are heated 
by a coil of wire embedded in enamel that is baked to 
the iimer side of the metal serving for the top. In 
electric broilers and toasters the heat is radiated from 
coiled wire fastened to the framework. The various 
other heating appliances in common use are made in 
these or similar manners, the heating principle of the 
majority being some kind of fine wire that is so coiled 
that a long piece can be used in a small space. 

Electric lights. — The two common forms of electric 
lights are the incandescent electric lights and the arc 

Incandescent lights. — Since a high degree of heat is 
necessary to produce light, two requirements of the 
wire filaments used as the lighting element of incan- 
descent lights are that they offer a high degree of 
resistance to the current and that they are melted 
only at temperatures considerably above that at which 
they become incandescent. Tungsten, tantalum, and 

126 Physics and Chemistry 

a carbon filament — made by carboni2dng a special 
kind of cotton thread — ^answer these requirements. 
Until lately carbon filaments were almost tmiversally 
used, but the metals tungsten and tantaltim, though 
more fragile and expensive, stand a higher temperature 
than the latter and can be arranged so that they will 
give a stronger light without the use of any extra 
current. They are, in fact, more than twice as efiBicient 
as the carbon lamp. Filaments of both these metals 
offer less resistance than carbon and therefore it is 
necessary for them to be longer than those made of 
carbon, and they are therefore differently arranged 
as can be seen by comparing a tungsten or mazda 
lamp with one that has a carbon filament. The 
longer the filament, the brighter the light will be. 
The lighting filament is encased in a glass ^lobe from 
which air has been exhausted and which is filled with 
gas. If air were present, the filament would be 
oxidized and rendered useless. The two ends of a 
filament are connected to platinum wires which are 
sealed into the small glass tubes that project from 
the screw into the bulb. Platinum is used for this 
purpose because it is one of the few substances that 
is contracted and expanded at the same rate as glass 
by changes in temperature, and the glass would be 
broken were it in contact with a substance that did 
otherwise. The platinum wires are separated from 
each other by insulating material and are connected 
in the screw to separate pieces of metal. The screw 
fits into a socket provided with similar pieces of metal 
to which the two service wires (that from the anode 
and the cathode of the electric machine) are connected. 
As the metals of the screw and lamp come in con- 
tact when the switch is turned, the circuit is then 

Electricity and Magnetism 127 

closed and the current flows through the lighting fila- 
ment, which is almost instantaneously heated to 

Arc lights. — ^The lighting principle of the arc light, 
formerly much used for lighting streets, large buildings, 
and other purposes requiring a powerful light, con- 
sists of two carbon rods. These are in contact when 
the current is turned off, but as soon as it is turned on 
it passes through an electromagnet which magnetizes 
an iron bar from which the upper carbon is suspended 
and this pulls the carbons about three-eighths of an 
inch apart leaving a space that is known as the arc. 
At the same time, the upper carbon is heated to a 
white heat and, when this happens, it gives off in- 
candescent particles which jump across the arc. 
The lower carbon also becomes heated, but the upper 
carbon always serves as the anode, the current passing 
from it to the lower one and out. The incandescent 
particles, likewise, pass from the anode tothe cathode "^ 
and, consequently, the upper carbon becomes dented ' 
in the center and the lower one becomes cone-shaped. 
Both carbons wear away, but the upper one more 
quickly than the lower. As this happens the gap 
between the two increases in size and they must be 
brought nearer together. On street lamps this is 
usually done automatically by electro-magnets but 
in some kinds of apparatus it must be done by hand. 
Long tungsten filaments in gas-fiUed globes are now 
being largely substituted for arc lights. 

Meaning of Terms Used in Connection witib tiie 
Measurement of Electricity 

Electromotive force. — ^This term is used to signify 
the pressure of electricity. A powerful current will 

128 Physics and Chemistry 

k\ 'have a high electromotive force and a weak one a low 
^ electromotive force. 

Unit. — In connection with measurement, this word 
is used to denote a quantity assumed as a standard of 

Volt. — The volt (so called after Alessandro Volta, 
an Italian physiologist and physicist, 1745-1827) is 
the unit of electromotive force, it is the force neces- 
sary to cause one ampere of ctirrent to flow against 
I ohm of resistance. 

Ordinary galvanic and storage cells furnish between 
I and 2 volts; batteries may furnish 20 or more volts, 
according to the number of cells. A very much higher 
voltage can be obtained by use of the dynamo. That 
employed on the trolley-car circuit is about 550 volts; 
that furnished houses is between no and 220 volts. 
' Ohm. — ^The ohm (named after George Ohm, a 
German electrician, 1 781-1854) is the unit of electric 
resistance. As stated on page 106, even the best con- 
ductors offer some resistance to an electric current. 

Ampere. — The ampere (called after Andr6 Maria 
Ampdre, a French physicist and mathematician, 1775- 
1836) is the unit of electro-current strength. It is 
the amotmt of current afforded by one volt of electro- 
motive force against one ohm of resistance. In other 
words amperes denote the quantity of current that has 
been driven through the conductor by the pressure of 
the volts. A miUiampere is the thousandth (o.ooi) 
part of an ampere. 

Watt — The watt (named in honor of James Watt, 
a Scotch physicist, 1730-1819) is the tmit of electric 
power. The number of amperes multiplied by the 
niunber of volts will give the ntunber of watts. A 
current of 10 amperes at' 100 volts' pressure gives 

Electricity and Magnetism 1^9 

1 .000 watts or I kilowatt. A current of 10 amperes at 
1 10 volts' pressure will give the same ntmiber of watts 
as a current of 5 amperes at 220 volts' pressure because 
the product in both cases is the same; thus 5X220 
»iioo watts and ioXiio«iioo watts. 

Formerly the lighting capacity of electric or other 
kinds of lights was compared with the lighting ca- 
pacity of candles, and an electric lamp was labeled as 
being of a designated candle-power, but electric lamps 
are now graded according to their watt consump- 
tion — i. e.^ according to the amount of electrical power 
or energy that they use, and, as previously stated, 
this is found by multiplying the ntmiber of amperes, 
or, in other words, the amount of current, by the 
ntmiber of volts, i. e,, the amount of force necessary 
to overcome the resistance offered to the passage of 
the current by the conductor and lighting filament. 

The current used on a i6-candle power carbon 
incandescent light on a iio-volt circuit (i. «., a circuit 
that offers an amount of resistance that requires no 
volts of electromotive force to overcome) is about J^ 
ampere and on a 220-volt circuit about X ampere. 
Such a light, therefore, would now be said to have a 
55- watt power since 1 10 -J- J^ = 55 and 220 4- >^ = 55. 
A 25-watt tungsten light or a i6-watt gas filled globe 
will replace a 55-watt carbon incandescent light; *. «., 
it will give as bright a light without requiring any 
extra energy. 

Electrical power, commonly spoken of as electricity, 

is sold on the basis of what is termed a kHatuaU hour; 

which is the amount of electrical energy that would 

exert a power of 1000 watts for one hour, or one of 100 

watts for 10 hours, or of 50 watts for 20 hours, etc. 

It is the quantity of current and the amount of force 

130 Physics and Chemistry 

necessary to overcome the degree of resistance offered 
to the passage of the current that are the principal 
factors in determining the amount of fuel necessary to 
use in producing the current. 

Electrical Measuring Instruments 

Instruments for measuring the magnitude of the 
current are called ammeters; those for meastmng the 
electromotive are called voltmeters. 

The appliances installed in houses for measuring the 
amoimt of electrical power used are called galvano- 
meters or wattmeters; they are, practically, combined 
ammeters and voltmeters. There are different types 
of these, but the e ssgntial pa rts in all kinds are a 
coil of wire, a magnet, a magnetic needle, and a 
dial. The main service wires and those from which 
the house wires are distributed are connected to the 
coil and all the current entering the house passes 
through it. As soon as the circuit is closed by turn- 
ing the switch for a light or other purpose, the current 
begins to flow, and this induces a magnetic field within 
the coil. This causes the deflection of the needle, 
which is suspended in the center of the coil, and thus 
the pointer on the dial is moved. The greater the 
mmiber of lamps, etc., in action, the greater will be 
the magnitude of the current entering; consequently, 
the stronger will be the magnetic field created, and the 
greater the deflection of the needle. 


When an electric current is very strong, and under 
certain other conditions, the conducting wires of cir- 
cuits and electrical appliances can become so highly 

Electricity and Magnetism 131 

heated that not only may they set fire to any combusti- 
ble substance in their neighborhood, but, also, the 
wires themselves may be melted. To obviate these 
dangers, fuses are used. These are made of metals or 
metal alloys that melt at a comparatively low tem- 
perature and, by melting, break the circuit. This 
accident, which is often spoken of as blowing out the\ 
fuse, may be caused by too strong a current, or as the , 
restdt of placing unusual resistance in the path of a ; 
current, as, for example, by attaching an appliance j 
that is wired for a current considerably different, 
either stronger or weaker, from that of the house / 
attachments, or by getting water between the pieces > ^ 
of contact metal in the socket and screw — ^water J ' 
being a very poor conductor of electricity offers much 
more resistance to a current than metal. 

Fuses, especially those used in houses, are encased 
in fireproof material. 


A transformer is a special variety of induction coil 
by means of which the strength of a current can be 
changed. For example, when buildings a long dis- 
tance from the power house are supplied with elec- 
tricity, a current must be sent along the main service 
wires that would be of too high voltage to introduce 
into the majority of buildings with safety; therefore a 
transformer is placed where the service wires for the 
building or buildings and the main wires connect. 
Sntiall trapsformers that can be attached to the electric 
light sockets in the same way as lamps or other 
appliances are often used in houses when a weaker 
current is needed for any purpose as, for instance, 

13^ Physics and Chemistry 

running electrical toys. It is important, before tising 
new electrical appliances, to ascertain if they have the 
same watt power as the lamps. The reason for this 
was given in the section on fuses. 

Rheostat ' 

The rheostat is an appliance placed on some kinds 
of electrical apparatus to control the amount of current 
passing to them. This, in the case of heating appli- 
ances, means also a control of the amount of heat, i j 

There are di£Eerent kinds of rheostats, but the 
variety generally used on household electrical appli- 
ances consists of series of coils of wire in a small case. 
Projecting from the interior of the case is what is 
called a contact arm. This can be moved from right 
to left, and vice versa. When its knob is opposite the 
word law, it is shutting off part of the current and the 
temperature of the appliance will be at its lowest; 
when the knob is opposite the word full, all the current 
is entering the apparatus and its temperatiire is 

Static Electricity 

The term static (from stasis a Greek word signif3dng 
standing) is, as previously stated, applied to electricity 
that is not flowing along a conductor — for example, 
that made manifest in Experiment ii by friction. 
Static electricity has been defined as electricity in a 
state of tension. It is, however, as stated in the pre- 
ceding chapter, exactly the same kind of electricity as 
that of the electric current, which we have been con- 
sidering; the difference being, not in the electricity, 
but in the conditions under which the electrification 
is produced. 

Electricity and Magnetism 133 

The chemical battery and the dynamo, as shown in 
the preceding pages, are, so long as their circuit is 
closed, and they are prepared for action, driving a 
constant stream of electrons along their conductors. 
Machines such as the Winchester static machine, 
which is much used in electrotherapy, cause their 

Pic. 53. Faradic Induction Machinb. 

poles, by friction or other means, to become differently 
charged — i. e., they cause one pole to assume an elec- 
tro-negative and the other an electro-positive charge. 
If the poles are then brought into apposition, or if 
any substance that will act as a conductor is placed 
between them, an electrical discharge takes place, 
and the poles then attain a state of electrical equi- 
librium, and there is no further discharge until one 
pole is once more made to acquire a positive and the 
other a negative charge. 
Thus static electricity is said to manifest itself by 

134 Physics and Chemistry 

attractions and reptilsions (this was demonstrated in 
Experiment ii) and in more or less violent discharges, 
a discharge bringing about a state of equilibrium. 

Nature of lightning. — Lightning is a discharge of 
electricity between two clouds or between a cloud 
and the earth, due to one cloud acquiring a positive 
and the other a negative charge, or, if the discharge is 
between a doud and the earth, the difference in charge 
is between them. 

Physiological Action of Electricity 

When electricity is applied to the animal body, 
nerve stimulation results; this induces muscular 
contraction, which increases metabolism, improves 
muscle tone, and stimulates the circulation of the 
blood and lymph. By these means body nutrition 
and tone may be much improved. 

When an individual takes hold of, or is between 
and in contact with, the electrodes, as the padded 
poles on the end of the rheophores' are called in 
electrotherapy, he becomes a part of the circuit. 

Cathode Rays 

When the terminals of an induction coil are sealed 
into a glass tube from which all air has been expelled, 
invisible radiations, called cathode rays, are found to 
be emitted by the cathode terminal. These fill the 
tube with a brilliant yellowish fluorescent light. 
Cathode ray^ are not, like light rays, reflected, re- 

' The circuit wires of a battery used in electrotherapy are so 

Electricity and Magnetism 135 

fracted, or polarized, but they are repelled by nega- 
tive electric charges, and several experiments have 
shown them to act in every way as negative electric 
chai|[es; they are therefore thought to be streams of 
electrons shot ofi from the cathode terminal. 

X-Rays or Rdntgen Rays 

In 1895, Conrad Wilhelm Rontgen, of Wurtzbtirg, 
Germany, discovered that if the cathode rays struck 
upon the walls of the vacutun tube in which they 
were generated or upon a platintun screen or other 
obstacle placed within the tube, a new kind of rays 
resulted. These he named X-rays^ but they are now 
often spoken of as Sdntgen rays. X-rays, like 
cathode rays, are neither reflected, refracted, nor po- 
larized, but, unlike cathode rays, they are not de- 
flected by a magnet nor repelled nor attracted by 
electric charges; thus, they do not possess the char- "> 
acteristi gjof e ither light or of electric charges. It is ' 
thought that they are simply irregular pulses or vi- 
brations in the ether caused by the sudden stoppage of 
the flying cathode rays, but this has not been proved. 

X-rays effect the same chemical changes in a photo- 
grapher's plate as light and hence can be used for 
taking photographs. A peculiarity of X-ray photo- 
graphs is that there is only a faint outline of the softer 
tissues, while hard substances, as bone, stand out 
clearly. This is because the rays have the power of 
passing through, not only the glass walls of the tube 
in which they are generated, but also, though in 
varying degrees, such substances as the tissues of the 
body. As hard matter, such as bone and metal, is 
more or less impervious to these rays, the outline of 

136 Physics and Chemistry 

fractures or of abnormal growth upon the bone will be 
clearly defined in a photograph, and, if present, any 
dense, foreign substance, as a needle or bullet, will 
show. Pus and other exudations in a part will ob- 
scure the outline and produce a faint shadow, and thus 
it is possible to detect abscess formations and the 
like by means of X-ray photographs. Bismuth is 
very impervious to these rays, and, if it is swallowed 
with food, the course of the latter through the stomach 
and intestines can be followed. This has greatly 
facilitated the study of the mechanism of digestion 
and is often of great assistance in diagnosing the 
nature of gastric and intestinal disturbances. 

X-rays are used also for therapeutic purposes in 
the treatment of such diseases as lupus, cancer, 
chronic ulcers, and exophthalmic goitre. The exact 
nature of the action of the rays on the tissues and 
abnormal deposits, which often results in the allevia- 
tion or cure of such conditions, is as yet not well tm- 
derstood, and neither is it known if the X-rays have 
any direct effect upon micro-organisms in the tissues. 

The flttoroscope. — ^This is a device used for making 
examinations with the X-rays. It consists of a taper- 
ing light-tight box, one end of which is provided with 
a cuff which will fit closely around the face of the 
examiner, and the other with a screen of cardboard or 
similar substance covered with fluorescent matter such 
as calcium tungstate and barium-platino-cyanide. 
If a portion of the body is placed between the X-ray 
tube and the fluoroscope screen, a view of the bones 
and of any foreign substance, such as would be photo- 
graphed, will be seen, if present in that part. The 
need for the fluorescent material is that the X-rays 
do not themselves affect the optic nerve in a way to 

Electricity and Magnetism 137 

give rise to vision, but the light which the rays cause 
the fluorescent material to emit does. 


In 1896, Henry Becquerel of Paris fotmd that ura- 
nitun and certain of its salts and other compounds 
emitted ra3rs that acted in much the same manner as 
X-rays, and, in 1898, Madame Curie of Paris found 
that thorium did likewise, and she fotmd later that 
a substance contained in pitchblende, in very small 
quantities, which she named radium^ possessed the 
same properties to a very much greater degree. Sub- 
stances which have this property are said to be radio- 

The rays emitted by radioactive substances are of 
three kinds, and have been named alpha, beta, and 
gamma rays. 

The alpha rajrs, which have very little penetrating 
power, are atoms of the gaseous element helium. 
The beta rays are thought to be negative electrons 
and thus they correspond to the cathode rays. The 
gamma rays, it is thought, are the same as the X-rays; 
they are produced by the beta rays striking against 
solid particles. 

Radium and its salts, chiefly the bromid and sul- 
phate, are tised in the treatment of abnormal condi- 
tions such as cancer, for the rays emitted by radium 
are capable of producing energy and destroying tissue, 
but they aSect abnormal tissue as cancer, to a greater 
degree than normal; thus, with care, the normal tissue 
will not be injured while the unhealthy growth is 
decomposed. If raditun is put into water and allowed 
to remain for some time, the water will become 
charged with the emanations of the radium. 



Origin of Sound — Some Important Differences between Sotmd 
and Light Waves — ^Transmission of Sound — ^Why Sounds 
Are Heard — Causes of Differences in Sounds — Methods of 
intensifying Sotmd — Echoes. 

Origin of sound.— Sound can be produced by any 
object that will start wave-like motion in matter that 
is capable of stimulating the auditory nerves. Objects 
produdng sound are usually in a state of vibration. 

Three points of difference between light waves and 
sound waves. — If an electric bell is suspended in a 
glass bell jar to which an air ptimp is attached and the 
circuit of which the bell forms a part is closed, the 
strike of the bell hammer will be both seen and heard. 
If, however, all the air is removed, by means of the air 
pump, the bell hammer will be seen, but not heard, to 
strike. This demonstrates one of the great differ- 
ences between light waves and sound waves — viz., 
light waves, being vibrations of the ether, will occtu* 
in a vacuimi, but sound waves, being caused by vibra- 
tions in matter, cannot occur in a vacuum. 

A second point of difference between light waves and 

sound waves is the rate at which they travel. Light 

travels, it will be remembered, at the rate of 186,000 


Sound — Hearing — Speech 139 

miles a second. The rate at which sound travels 
varies considerably in different kinds of media, but it 
takes about five seconds to travel one mile in air. 
It is for this reason that thunder is heard after the 
flash of lightning is seen, though, as the lightning is 

Pig, 54. The Beginning of a Series of Sound 
Wavbs Started by a Ringing Belu 

merely the spark occasioned by the discharge of 
electrons and thunder the waves arising in the air as 
the result of the vibration occasioned by the discharge, 
both phenomena originate at the same time. Thus 
the distance of the electrical disturbance can be 
estimated by counting the number of seconds that 
elapse between the flash of light and the sowid of the 
thunder; for, as light travels so quickly, the flash is 
seen the instant it occurs and, if it is posable to count 

140 Physics and Chemistry 

five before the thunder is heard, the electrical dis- 
charge must have taken place a mile away. 

The third important difference between light and 
sound waves is the nature of the waves. That of 
light waves has been already discussed. Sound 
waves, like light waves, are produced by vibrations, 
but the vibrating body giving rise to sound causes the 
molecules of air, or other matter, surrounding it to 
become compressed; these molectdes then rebound 
and there is more space between them than there was 
before they were compressed. At the same time, 
they cause compression of the molecules by which 
they are surrotmded, and these, in turn, act in like 
manner, and so on; thus, sound waves consist of series 
of alternate spherical compressions and rarefications. 
The conduction of sound is analogous to the con- 
duction of heat in as much as the molecules do not 
move onward, but simply by their own motion 
produce movement in the molecules by which they 
are surrounded. 

Sound transmitted by matter in its three phjrsical 
states. — ^Air is the usual meditun for the transference 
of sound, but it has been found to travel through 
denser media more rapidly and to a greater distance 
than through air. For examples: The vibrations of 
the paddle wheel of a steamer in motion, when the 
ear is under water, can be heard a mile away; if a long 
stick of wood with one end held against the ear is 
scratched with a nail, the sound will be heard by the 
person whose ear is in contact with the wood, though 
not by others standing equally near the source of the 
sotmd; the sound waves caused by footsteps, etc., 
will pass a much greater distance in the ground, than 
in the air, which is why Indians put their ears to 

Sound — Hearing — Speech 141 

the ground when listening for distant sounds; other 
conditions being similar, distant sounds will be heard 
more distinctly at the seashore than at high altitudes 
where the air is less dense. 

For sound waves to be transmitted by liquids and 
solids, however, the sounding body must, as a rule, 
act directly upon them — for example, sound waves 
would not induce waves in a stone wall, but would be 
thrown back from it, as will be seen later. 

The mechanism of hearing. — Though sound waves 
in the air will not themselves induce waves in another 
medium, they wiU start bodies that are specially 
arranged vibrating and thus transmit sound. It is 
upon this power that hearing depends. For example, 
when a person speaks, his vocal cords, by their vibra^ 
tory motion, cause compression of the molecules of 
the surrounding air and thus give rise to sound 
waves that pass by conduction, as already described, 
to the hearer's ears. On entering the ear, the waves 
impinge upon the drum membrane that is stretched 
across the opening between the external and the 
middle ears and start it vibratinjr. This membrane 
transmits its motion along the three small bones 
which stretch across the middle ear and connect with 
the membrane that separates the middle and the 
inner portions of the ear. The vibrations of this 
membrane produce waves in the Uquid within that 
part of the inner ear known as the cochlea. These 
waves cause movement of some of the fine fibrils 
stretched within the cochlea and thus stimulate the 
auditory nerves over which impulses are conducted 
to the center in the brain where sounds are interpreted. 

The telephone. — The telephone is an example of 
a more complicated means of transmitting sound. A 

142 Physics and Chemistry 

telephone, omitting details, may be said to consist of: 
(i) a box-like portion known as the transmitter — this 
has a mouthpiece in front and a diaphragm at the 
back and a portion of it is filled with granular pieces 
of carbon into which the electric circuit wires enter; 

(2) wires, which are in connection with others from 
the electric current generator and from the receiver; 

(3) the receiver, $. f., the part from which the sound 
is heard. The structure of the receiver is similar to 
that of the transmitter. When a person speaks into 
the mouthpiece of the transmitter, the sound waves 
produced start the diaphragm at the back of the 
transmitter vibrating; this causes fluctuations in the 
electric current that correspond with the sound waves 
produced by the voice, and, though transmitted from 
one wire to another at the central station, these cause 
the diaphragm in the receiver to vibrate and give rise 
to sound waves in the air in the receiver similar to 
those started in the transmitter by the voice of the 

The phonograph. — The phonograph is still another 
example of the manner in which sound waves can act 
upon and be reproduced by different media. Records 
are made by talking, singing, etc., in front of a cone at 
the back of which is a membranous diaphragm. The 
latter is set in motion by the sound waves produced 
by talking, etc., and transmits its motion to a sharp- 
pointed instrument, known as the stylus^ which is 
attached to its under surface. While the record is 
being made a wax-coated disc or cylinder is kept 
rotating under the stylus and the latter cuts into the 
wax the impressions of the wave forms received from 
the diaphragm. 

The essential parts of phonographs used to repro- 

Sound — H earing — Speech 143 

duce sounds are the same as those on which the records 
are ntiade, and when a record is placed and made to 
revolve under the stylus, the latter passes in the 
traces made by the other stylus and, by so doing, 
moves the diaphragm, causing it to produce the same 
form of waves as those which made the tracings on the 
record and it thus gives rise to similar sounds. 

The cones of the phonograph being different in 
every respect from the human pharynx, there is, 
however, a var3dng amount of difference in the tone 
of sounds reproduced by phonographs. 

Difference in sounds. — The differences in sotmd 
are classed under three headings — ^viz., pitch, quality, 
and loudness. 

Pitch. — By pitch is meant the position of a sound 
in the musical scale. The pitch is said to be high 
when the note is up toward the treble and low when 
it is down toward the base. The greater the nimiber 
of vibrations per second, the higher will be the pitch 
of a sound. The difference between the pitch of male 
and female voices is due primarily to the different 
size of the larynx and vocal cords in the two sexes, 
the larynx being larger and the cords longer in men 
than in women. A boy's larynx resembles the female 
larynx and therefore his voice is similar. The so- 
called breaking of the boy^s voice, which occurs at 
puberty, is due to faulty neiu-o-muscular control 
brought about in part by the very rapid growth of the 
larynx and vocal cords which takes place at that time. 

Quality, tone or timbre.— The quality, known also 
as the tone or timbre, of sound constitutes the various 
characteristics other than pitch by which one person's 
voice can be distinguished from another's and one 
type of musical instrument from another. Na- 

144 Physics and Chemistry 

turally, this depends largely upon the nature of the 
part or instrument in which the sound is produced. 

Differences in the nature of the material of which 
musical instruments are made and in the size, shape, 
and position of their different parts and the tension of 
their strings will completely alter the nature of the 
sounds that they can be made to produce. 

Differences in voices are due chiefly to differences in 
the size and shape of the vocal cords, larynx, pharynx, 
and mouth, and in the degree and kind of control that 
the individual has of the muscles that enter into the 
formation of, and surround, these parts. The muscles 
being pliable and elastic, the shape of the pharynx 
and other parts concerned can be altered in speaking 
and singing, and the methods of doing this most 
effectively constitute one of the most important 
fundamental principles of voice culture. 

Also, differences in the sounds of different letters 
and words are due to differences in the degree of ten- 
sion and in the position and- movements of the vocal 
cords and of the muscles of the pharynx, mouth, and 
tongue during articulation. 

Loudness. — Loudness or intensity of sound depends 
chiefly upon the degree of force exerted by the vibrat- 
ing body and the nearness of the hearer to the source 
of the sound. It is also greatly influenced by the 
density of the medium transmitting the sound (see 
page 140), the presence of reflectors, and the concen- 
tration of sound waves (see page 145). 

Noise. — By a noise is meant a loud sound that is 
disagreeable to the hearer. A noise is usually the 
result of lack of regularity and rhythm of the vibra- 
tions giving rise to the soimd. 

Reflection of sound. — Sound waves, like light and 

Sound — Hearing — Speech 145 

heat waves, can be reflected or thrown back by objects 
upon which they strike. Thus, the presence of a 
sounding board behind a speaker makes it easier to 
hear him, since the reflected wa\'es ser\*e to reinforce 
or strengthen the original waves. The walls of a 
room, if they are not too far from the speaker, act in 
the same way, and thus it is usually easier to hear 
in a room than in the open air. If, howe\^r, the walls 
of a room or hall are more than fifty-six feet from the 
speaker there may be an echo. The reason for this 
is as follows: The sensation of sound persists for 
about ii^ of a second, and as sound waves, under 
ordinary atmospheric conditions of temperature and 
pressure, travel at the rate of about iioo feet per 
second, or 100 feet in the tenth of a second, if the 
walls are not more than fifty-six feet from the speaker, 
the waves can reach the walls and be thrown back 
to the audience before the sensation caused by the 
original waves has ceased. If, however, the hall is 
so large that the reflected waves do not reach the 
audience before the original sensation has ceased and 
yet is not large enough to prevent reflection, the 
reflected waves will produce a secondary sensation 
like unto the first and this is what constitutes an 
echo. The nature of the reflecting surfaces greatly 
influences the reflection of sound. Sound waves are 
reflected much more strongly from smooth, hard walls 
than from those which are carved or hung with dra- 
peries. For this reason, draperies are sometimes 
used to prevent echoes. 

Megaphone. Stethoscope. Ear-Trumpet. — These 
are three examples of appliances used to intensify 
sounds by concentration of the sound waves and» to 
some extent, by reflection. 


146 Physics and Chemistry 

The megaphone, a hollow, cone-shaped appliance, 
starts the waves produced by anyone speaking into 
it in one direction and thus keeps them from spreading 
as widely as usual; this greatly intensifies the sound 
and increases the distance that it travels in the direc- 
tion in which it was started. 

The stethoscope is an instrument used for distin- 
guishing sounds produced within the body. Stetho* 
scopes vary in their structure, but usually consist of a 
tube on one end of which is an enlarged portion con-^ 
taining a very delicate diaphragm and on the othet 
end one or two projections that fit into the ears of the 
listener. The portion containing the diaphragm is 
placed over the part of the patient's body that is 
being examined, and the impulses of the sounds pro- 
duced by the heart, lungs, air in the cavities, or 
whatever is causing sounds in the part of the body 
being examined, start similar vibrations in the dia- 
phragm of the stethoscope, and the waves produced 
in the air in the tube by these vibrations, being con- 
fined "within a limited area, are so intensified that 
even slight abnormal differences of sound can be 

The concentration of sound waves by the ear- 
trtunpet so increases their force that they are able to 
produce vibration in the membranes and small bones 
of the ear when, as the restdt of disease or injury, these 
parts have become so stiffened that they are not acted 
upon by less forcible waves. 



Nature and Causes of Chemical Reactions — Nature of Valence— 
Radicals — Chemical Formulae and Equations. 

Chemical reactions. — By a chemical reaction is 
meant the chemical changes that take place be- 
tween certain substances when they are brought 

Agents which promote chemical reactions. Cata- 
lyzers. — Certain elements have such a strong aflSnity 
for each other that, if brought into contact, they will 
unite, sometimes even leaving other elements with 
which they are already in combination to do so. 
Many other elements, however, especially when 
already combined, do not unite thus readily, and 
the help of agents, such as light, heat, electricity, 
is necessary to promote chemical action. As a rule, 
solution facilitates — in fact, is otten necessary for — 
ch^lical reactions, and there are many chemical sub- 
stances and ferments that, in some unknown way, 
hasten them, but do not themselves enter into the 
reaction; such substances are called catalyzers ^ and 
the action is termed catalysis. The action of cata- 
lyzers will be demonstrated in Experiment 13. 


148 Physics and Chemistry 

Reason for chemical reactions. — In the preceding 
paragraph it was stated that some elements have a 
very strong affinity for each other, and in Chapter II 
it was said the chemical affinity meant the electrical 
attraction between different atoms. Thus, the prop- 
erty and action that were named, before their nattire 
was understood, chemical affinity and chemical union 
are, in reality, electrical attraction and electrical union, 
and the quality which causes certain elements to com- 
bine more readily than others is thought to depend 
upon the niunber and arrangement of the electrons 
of their atoms which give their ions, see page 109, a 
stronger or weaker negative or positive electrical 

Valence or Combining Power 

Nature. — It has been found that each of the ele- 
ments has the jDOwer to hold a definite number of 
atoms of another element or elements in combination. 
This capacity is known as valence, and valence has 
been defined as that property of an element which 
determines the number of atoms of another element 
that it can combine with. The valence of an element 
is measured by the niunber of hydrogen atoms with 
which one atom of the element combines to form a 
molecule. Hydrogen and all elements that combine 
with hydrogen atom for atom are called monovalent 
or univalent elements; those which combine witlj^wo 
atoms of imivalent elements are called divalent or 
bivalent; those which combine with three, trivalent; 
those which combine with four, tetravalent; those 
which combine with five, quinquivalent. Some ele- 
ments, under differing conditions, are able to exert 

Valence 149 

different valences; thus there are such compounds 
as PeCla (ferrous chlorid) and PeCl, (ferric chlo- 
rid). Such elements are said to exert a variable 
valence. In chemical reactions, elements that have 
the same valence replace each other atom for 

In order to explain the nature of valence, it is likened 
to arms or bonds and the atoms are picttu^d as hav- 
ing a varjring number of arms with which they can 
hold on to each other. Thus, atoms of the tmivalent 
elements, such as hydrogen, sodium, potassium, are 
considered as having but one arm, each atom of any 
one of these elements being able to hold on to — com- 
bine with — only one atom of another one-armed ele- 
ment; but the oxygen atom, for example, has two 
arms — is divalent — ^and can therefore hold on to two 
univalent or one-armed atoms, but only one divalent; 
likewise, the atoms of a trivalent element, having three 
arms, can hold on to three univalent atoms, or one 
univalent and one divalent, but only one trivalent, 
and so on. 

Valence due to electrical charges. — ^These arms are 
of course merely figurative, the real agent controlling 
the combining of the atoms of, at least, many of the 
elements* is the electrical charge of the ions of the 
elements. For instance, when a hydrogen-containing 
compotmd is decomposed in water or other dissoci- 
ating liquid — see page 109 — the hydrogen will have 
what is said to be one positive charge and, for this 
reason, it will imite with one atom of an element the 

' It has not been proved that this is true of the atoms com- 
posing the molecules of oxiganic substances which are not 
decomposed by the electric current. 

ISO Physics and Chemistry 

ion of which has, what is reckoned as one negative 
charge, or, if the negative charge of the ion is stronger, 
i. e., if it has two negative charges, two atoms of 
hydrogen will unite with it. For example, a chlorin 
ion has one negative charge and it and hydrogen, 
which has one positive charge, combine thus — HCl, 
but an oxygen ion has two negative charges and it 
and hydrogen combine thus — HaO. 

Stable and unstable compounds. — ^When the atoms 
of an element are combined with as many other atoms 
as they can hold on to, the element is said to be satis- 
fied, and unless all the elements of a compound are 
satisfied, the compound is unstable; for example, the 
caAon atom is tetravalent and, therefore, to be 
satisfied, it must be combined with four monovalent 
or two divalent, or one monovalent and one trivalent 
atoms, or one tetravalent atom. For this reason^ 
carbon dioxid (CO a) is a stable compound, but carbon 
monoxid (CO) is unstable and, as soon as it comes in 
contact with any element that it can unite with, it 
will do so. For another example, water (HaO) is a 
stable compound, but hydrogen peroxid (HaO a) is 
unstable and will very readily become decomposed 
into water and oxygen. 

Radicals. — In many common compounds, two or 
more of their atoms are very strongly united and do 
not under ordinary circumstances become dissociated 
in chemical reactions, but act, in every respect, as 
though they were one atom. Such a combination of 
atoms is termed a radical. 

The valence of some of the common elements, ions 
and radicals, can be seen in the following table': 

^ElemetUary Chemistry^ p. 142, HoUis Godfrey. Longmazis, 
Green, & Co. 

Chemical Formulas 


Ekmeni . 


























Ions and Radicals 


































Nitrate ion 





Sulphate ion SO4 





Chemical Fonntilas 

Definition. — By a chemical formtila is meant a 
combination of symbols used to show the chemical 
composition of a substance. In order to read or write 
a formula correctly, it is necessary to know the sym- 
bols of the elements — ^these were given in Chapter II. 
— ^and to understand the meaning of certain signs 
such as the following: A number placed after a sym- 
bol, as stated in Chapter II., shows that in the mole- 
cule there are as many atoms of the element as are 
specified by the figure, but a number placed before 
two or more symbols shows that there are the number 
of atoms of all the elements represented by the sym- 
bols following the number. For example, NajCO, 
shows that there are two atoms of sodium and three of 
oxygen in soditun carbonate, but sNaaCO^ implies 
three molecules of sodium carbonate. Sometimes 
instead of writing a number before the symbols, as in 

152 Physics and Chemistry 

2NAaC03, the symbols of groups of elements, of which 
there are a specified number, are enclosed in parenthe- 
ses. This method is more especially used when the 
group of elements constitute a radical or a simple 
molecule forming part of the molecule of a complete 
substance. For example, the formula for glycerin may 
be written C3H5 (OH) 3, there being three OH radi- 
cals in a molecule of glycerin; and the formula for the 
fat known as stearin, maj** be written (CiyHjsCOO),- 
C3H5 showing that in a molecule of stearin there 
are three molecules, each one of which consists of 
CifHjsCOO, attached to one molecule consisting of 
C3H5. Occasionally a period is placed before the 
symtx)l of an element or group of elements, instead of 
using a parenthesis, and a period is often used to 
mark off an element or elements that play a special 
part in a reaction; thus CUSO4.5H2O. The letter n 
placed after the symbol of an element or elements 
signifies an unspecified number of atoms, radicals, or 
molecules, as the case may be; for instance (CeHxo- 
05)n implies that a molecule of starch consists of a 
number of molecules each one of which consists of 
C6H10O5. When, as in the case of starch, the exact 
number of simple molecules forming the more com- 
plex molecule is not known the letter x is often used, 
instead of the letter n. 

In writing the formulae of inorganic compounds, 
the symbol of the electro-positive clement, as hydrogen 
and the metals, is written before that of the electro- 
negative element or radical, thus, potassium hydroxid 
is written KOH, and not OHK. 

Different kinds of formtite. — Different groupings 
of the elements are often made in writing formulae 
in order to bring out some special point regarding the 

Chemical Formulas 153 

structure or action of the molecule. For instance, 
acetic add may be written in all of the following 
ways: C3H40a« this shows simply the elements and 
the number of atoms constituting one molecule of the 
acid; or CHjCOOH, this is to show the presence of 
what is called the carhoxyl radical which is the char- 
acteristic radical of organic adds; or CaHjO.OH, this 
serves to show that in acetic add one hydrogen and 
oxygen are always linked together; CaHjOa-H. or 
H.CaHjOai are used to show that in chemical reactions 
there is one hydrogen atom that is always replaced 
by another element or radical; 

H O 

H O— H 

shows the manner in which, it is thought, the atoms 
are linked to each other in the molecule. 

A few other examples of the use of different formulae 
to represent the same compound are as follows: 
Water is written HaO and H-O-H ; nitrate of silver is 

written AgNO, and Ag-a-N<° ; carbonic acid is 

written CO,H. and C0<^«. 

Formulae which show merely the elements and the 
number of atoms in a molecule are called simple or 
empirical formukB; those showing elements grouped 
into radicals are called rational formtda; those which 
show some conclusions that chemists have formed 
regarding the position of atoms in molecules are called 
structural or constitutional formukB. Chemists have 

154 Phjrsics and Chemistry 

formed such conclusions from the way in which mole- 
cules act in chemical reactions. 


Purpose and nature. — An equation is used to show 
the nature of a chemical reaction in a concise form. 
In the writing of equations, chemical symbols are 
used. For example: NaOH+HCl = NaCl+HaO is 
the equation for the reaction that takes place when 
sodium hydroxid and hydrochloric acid are put to- 
gether, and it is a concise and clear way of writing 
that soditun hydroxid plus hydrochloric add forms 
sodium chlorid and water. 

Reversible equations, — In many chemical reac- 
tions there will be sometimes some action going on 
in a reverse direction; an equation to show that 
such action is taking place is written as follows: 
Ag-hCl ^ Aga. 


In nearly all chemical reaction there are at least 
two substances formed. The most important one 
of these is called the principal product, and the other 
or others the by-product or by-products. In writing 
an equation, the principal product is usually written 

Foimultt for Some Common Compounds 

Acetic acid. CaH40a, or CH3COOH. ' 
Alcohol (ethyl). CH^O. or CaHjOH. 
Alcohol (wood). CH4O, or CH3OH. ^ 
Aluminium chlorid. AICI3. 

Chemical Formulas 155 

Ammonium carbonate. (NH4)a CO3. 

Ammonium chlorid. NH4CI. 

Ammonium hydroxid or ammonis water. NH4OH. 

Baritmi chlorid. BaCla. 

Calcium chlorid. CaCU. 

Calcium oxid (or lime). CaO. 

Calcium hydroxid (or, when in solution, lime water). 

Calcium hypochlorite (or hypochlorite of lime or 
bleaching powder). CaOCla- 

Caldtmi STilphate. CaS04. 

Chloroform. CHCI3. 

Dextrin. CeHioOj. 

Dextrose. CeHiaOe. 

Ether. (CaHs)aO. 

Ferric chlorid. PeClj. 

Ferrous sulphate. PeS04. 

Pormaldehyd. CHaO. HcHO. 

Glycerol or Glycerin. C3H5(OH)3. 

Glycogen. (CeHxoOs),. 

Hydrochloric acid. HCl. 

Hydrogen peroxid. HaOa. 

Lactose. CxaHaaOn. 

Levulose. C6Hxa06. 
Magnesitmi sulphate. MgS04. 
Mercuric chlorid (or corrosive sublimate or bi- 
chlorid of mercury). HgCU. 

Mcrcurous chlorid or calomel. HgCl. 

Nitric acid. HNO3. 

Potassiimi bromid. KBr. 

Potassium carbonate (potash, lye). KaC03. 

Potassium chlorate. KCIO3. 

Potassium hydroid. KOH. 

Polassitun iodid. KI. 

156 Physics and Chemistry 

Potassium nitrate (saltpeter). ENO3. 

Potassium sulphate. KaS04. 

Silver nitrate. AgNOj. 

Sodium bicarbonate (or baking soda). NaHCX)^. 

Sodium carbonate (or washing soda). NajCOy 

Sodium carbonate crystals. NaaCX)|. loHaO. 

Soditun chlorid. NaCl. 

Starch. CaHxoOj. 

Sugar (cane, maple, etc.). CsaHaaO, 

Sulphuric add. HaS04. 




Definitions of Oiganic and Inor:ganIc Chemistry^ — Cbaracteristics 
of Organic Compounds — Isomers — Carbon Oxids — Hydro- 
carbons and Some of Their Important Derivatives — Alco- 
hols— Aldehyds, 

The study o£ chemistry has been divided into two 
main branches, viz. : inorganic chemistry, that dealing 
with non-living matter such as minerals ; and organic 

Formerly, organic chemistry was said to be the 
chemistry concerned with living matter or matter 
produced as the result of living processes. In the 
days when this definition was given, the chemist's 
work was largely analytical — i. e., the separation of 
the compounds being studied into their component 
parts or elements; but now, methods of synthesis — 
i. e.f the building of complex substances from elements 
or simple compounds by chemical reactions — are very 
common and every year adds to the number of com- 
pounds synthesized in chemical laboratories that it was 
once thought could be made only as the restilt of the 
life processes of living cells. Thus, the long accepted 
definition for organic chemistry has become incorrect. 

A definition that was proposed when the inade- 
quacy of that hitherto used became apparent was The 

158 Physics and Chemistry 

chemistry of the carbon compounds^ because all 
organic compounds contain carbon, but so also do a 
few inorganic substances, therefore this definition, 
though often used, is not very descriptive. 

Some important difference between organic and 
inorganic substances. — Though the supposed differ- 
ence in matter which gave rise to the division of 
chemistry into the two branches referred to in the 
preceding paragraphs, has proved, to some extent 
at least, to be non-existent, there are marked differ- 
ences between the substances classed under the two 
headings. Some of these are as follows: (i) Nearly 
all inorganic substances are, when in solution, good 
conductors of electricity, and they are dissociated by 
the electric current into positive and negative ions, as 
described in Chapter VII. On the contrary, very few 
organic compounds are thus affected by electricity. 
(2) The molecules of inorganic compounds do not 
contain a large ntunber of atoms, but many of the 
molecules of organic matter contain a very large 
number, even thousands, of atoms and the atoms may 
be combined in many different ways within the mole- 
cules. For this reason, there are many organic sub- 
stances, having different characteristics, that consist 
of molecules made up of the same number of atoms of 
the same elements. Such substances, it will be re- 
membered, are called isomers. (3) Though there is 
as much, if not more, variety in organic, as in inor- 
ganic comjDOunds, there is exceedingly little variety 
in the elements composing them, all organic substances 
being composed of two or more of the following ele- 
ments: carbon, hydrogen, oxygen, nitrogen, sulphur, 
phosphorus, and iron. (4) All molecules of organic 
substances contain carbon directly associated with 

Main Divisions of Chemistry 159 

either hydrogen, oxygen, or another carbon atom, 
while very few inorganic substances contain carbon, 
and the carbon in those which do is not combined with 
the same elements that it is in the organic compounds. 
Why it is possible for so many di£Ferent substances 
to be formed with the same elements. — One of the 
chief fundamental reasons for the production of so 
many different compounds from the same elements is 
that carbon atoms can combine with each other and 
in doing so use only one of their valences, thus leaving 
three links or arms free to combine with other elements ; 
this permits of very large molecules being formed. 
Also, the relative position of the carbon atoms in the 
molecule may differ. This difference, the chemist 
endeavors to show by certain structural formulae, 
which, judging by the way in which reactions occur, 
it has been conceived, may be somewhat the way in 
which the atoms are linked together in the molecules. 
The following are examples of such formulae: 

H H H— C— H 

H— C— H H— C— H H--C— H 

I I I 

H H— C— H H— C— H 

Methane (CH4) I I 

H H 

Ethane (CaHe) Pxx)pane (CjHs) 

H H 


H— O— C— C— C— C— C— C - O H— O— C— C^C--(>-C--<;--0--H 

Glucose or Gmpe Sugar Practose or Fruit Sugar 

(C6Hxa06) (C6HxaO<) 

i6o Physics and Chemistry 



H-C C— H 

"-1 A-H 

^H - 

Benaene (C«H6) 

In the first formulae the C atoms are in chains^ in 
the last one they are in a ring-like form. The benzene 
ring formation is often referred to in chemistry. 


Carbon is one of the most conunon elements in 
nature. It is, as already stated, a constituent of 
several inorganic and of all organic compounds. It 
exists in the free state, as well as in combination 
with other elements; also carbon atoms possess the 
power of combining with themselves and, though the 
element carbon is always the same, compounds of 
carbon atoms can have utterly different appearances; 
e, g., the dia^mond consists of nothing but carbon; yet 
coke, charcoal, and graphite — ^the black substance, in 
pencils known as lead — are almost, and sometimes 
quite, pure carbon. Difference in pressure i^ thought 
to be an important cause of different combinations of 
carbon atoms; thus, excessive pressure, it is thought, 
is one of the chief factors in producing the wonderful 
combination of carbon atoms that results in the 

Allotropism. Allotropic forms of carbon. — The 
existence of an element in more than one form with 

Main Divisions of Chemistry i6i 

different characteristics is known as allotropism and 
the different forms are said to be aUotropic. The 
allotropic forms of carbon are crystalline and amor- 
phous (t. e.t without definite shape), the diamond and 
graphite are crystalline, and coke, charcoal, etc., 
amorphous substances. 

Carbon oxids. — Carbon unites readily with oxygen 
to form CO 2 (carbon dioxid), a heavy odorless gas. 
If a carbon compound is burned where there is an 
instiflSdent supply of oxygen, CO (carbon monoxid) 
is formed. The gas burning with a bluish flame, seen 
between and directly above burning coal, is largely 

,The Hydrocarbons 

All organic substances will undergo disintegration, 
either in the presence, or more or less complete ab- 
sence, of air, but both the intermediary and final 
products of disintegration produced where there is no 
air differ from those arising in the presence of air. 
One reason for this is that when disintegration takes 
place in the air, a large portion of the carbon tmites 
with oxygen, forming CO a and, of course, where there 
is no air, there is no free oxygen to tmite with the 
carbon. Important substances produced in nature 
by the disintegration of organic substances out 
of contact with oxygen are the hydrocarbons and 

Nature of the hydrocarbons. — ^The hydrocarbons, 
of which there are a very large number, consist 
chiefly as their name implies, of carbon and hydrogen. 

Classification. — ^According to the relative proportion 
of carbon and hydrogen in their molecules, the hydro- 


Physics and Chemistry 

carbons are classified as belonging to the methane, 
ethylene, and acetylene series. This is shown in the 
following table: 

Methane Series 

Ethylene Series 











CaU4 Ethylene 
C3H6 Propylene 
C4H8 Butylene 

Benzene Series 



CeHd Benzene 



C7H8 Toluene 
C8Hio Xylene 

Acetylene Series 




These are only a few of the hydrocarbons known; 
compounds belonging to the methane series have been 
found up to Ca9H6o* In connection with chemical 
formulae, such combinations of carbon and hydrogen 
are spoken of as hydrocarbon radicals. 

It will be noticed that the different series differ 
only in the relative proportion of C and H that the 
molecules contain, and that the successive substances 
in each series differ from each other only in the 
addition of a CHa. 

Ph]rsical condition. — In general, at ordinary tem- 
peratures, the hydrocarbons with less than 5 atoms of 
carbon in the molecule are gaseous, those with from 
5 to 16 carbon atoms are liquid, and those with a 
larger number are solid. 

How obtained. — Pew of the simple hydrocarbons 
are found free in nature, but they occur in certain 

Main Divisions of Chemistry 163 

plants and as physical mixtures in petroletim and 
coal tar and other complex hydrocarbon mixtures, 
such as gasolene, naphtha, kerosene, natural gas, etc., 
that themselves are obtained from either petroleum 
or coal tar by destructive, fractional distillation. That 
the various constituents of the complex hydrocarbon 
mixtures can be separated by fractional distillation is 
due to the fact that they all have different boiling 
points — ^the simpler the molecules of the hydrocarbon, 
the lower its boiling point and thus of the temperature 
at which it can be distilled, as explained in Chapter IV. 
Another way in which some hydrocarbons can be pfe- 
pared is by bringing together carbon and hydrogen com- 
poimds that will, under existing conditions, react so that 
the carbon and hydrogen wiU combine in the desired 
proportions; e, g,, acetylene gas (CaHa) can be made 
by mixing water and calcium carbide together. The 
chemical reaction that occurs being as follows: 

Calcium Water Calcium Acetylene 
carbide hydroxid 

CaCa + HaO = Ca(OHJa + CaHa 

Source of petroleum and coal tar. — Crude petroleum 
is obtained in various parts of the world from springs 
and from wells dug in the earth. Coal tar is obtained 
from coal bv the destructive distillation of coal. 

Use of petroleum and coal-tar derivatives. — Many 
of the hydrocarbons derived from petroleum and coal 
tar are not only of great value in their uncombined 
state, but they react with other chemicals, thereby 
producing a very large ntunber of valuable compounds, 
some of which are used as medicines, some as disin- 
fectants, others as dyes, and others as a basis for the 
preparation of various equally useful substances. 

i64 Physics and Chemistry 

Methane and Ethane 

Two simple hydrocarbons that form bases for many 
well-known compounds are methane and ethane. 

Methane(CH4), commonly known as marsh gas 
and fire damp, occurs free, as well as mixed with other 
hydrocarbons. It is a colorless, inodorous gas that 
forms explosive mixtures with air and bums. It is 
the common cause of explosions in coal mines. It is 
formed when vegetable matter decomposes where there 
is little oxygen, and it is found rising from stagnant 
pools in marshy places where it causes the appearance 
of bubbles on the surface of the water. It sometimes 
rises from the earth, together with similar gases, in the 
neighborhood of petroleimi wells, and it is a constituent 
of natural gas, coal gas, and similar mixttu^s. 

Ethane (CaHe) is a gas that rises from the earth with 
CH^andothergasesnearregionsinwhich there are petro- 

Methyl chlorid, chlorofonn, etc. — ^The forming of 
these compounds from methane is an example of how 
this gas, ethane, and other hydrocarbons can be used 
for the synthesis of more complex substances. 

When methane and chlorin are put together in 
diffused daylight, action takes place gradually in 
which HCl (hydrochloric acid) is given off and one or 
more products are obtained according to the length 
of time the action is allowed to continue. These 
products are the result of the displacement of one or 
more hydrogen atoms by chlorin atoms as follows: 

(I) CH4 + Cla - CH3CI + HQ 

(2) CH,a + a, - CHaCia + HCl 

(3) CHjCla + CI, - CHCI3 + HCl 

(4) CHCl, + Qa - CCI4 + HQ 

Main Divisions of Chemistry 165 

Methyl chlorid (CH3CI) and ethyl chlorid (Ca- 
H5CI), which can be made from ethane in the same 
way as methyl chlorid is made from methane, are 
highly inflammable, volatile gases that on striking 
the skin, volatilize so quickly that they freeze the 
tissue. CHCI3 chloroform (tri-chlor-methan) is the 
non-inflammable volatile liquid much used as a 
general anaesthetic. Other compounds can be made 
from methane and ethane by using bromin or iodin, 
instead of chlorin. The yellow antiseptic powder 
known as iodoform (tri-iodo-methan), for example, is 

Though methyl and ethyl chlorid, iodoform, and a 
very large number of similar substances can be thus 
synthesized in the laboratory, for commercial pur- 
poses, they are usually made by using more complex 
substances that, by chemical reactions, will produce 
the same combination of elements as those obtained 
by synthesis. For example, chloroform is made with 
alcohol and bleaching powder (CaOCla) and iodo- 
form is made by bringing iodin in contact with an 


Alcohols are sometimes classed with the hydro- 
carbon derivatives, for they can be synthesized from 
hydrocarbons, though this is not the manner in which 
they are made for commercial purposes. 

The chemicals necessary for the reaction that pro- 
duces alcohols from hydrocarbons wiU not unite 
with the latter in their natural state and it is necessary 
to have a preliminary reaction that will form substances 
which will react with the essential elements. The 

i66 Physics and Chemistry 

halogens' — either chlorin, bromin, or iodin — are 
often used for this purpose. For instance: 

Methane^ Chlorin Methyl Chlorid Hydrochloric acid 
CH4 + CI2 - CH3CL 4- HCl 

Methyl Chlorid Sodium Hydrozid Wood Alcohol Sodium Chlorid 
ChjCl 4- NaOH - CH3OH + NaCl 

In the same way ethyl or grain alcohol (CaHjOH) 
can be made from ethane; propane alcohol from pro- 
pane, and so on. 

Methyl or wood alcohol and ethyl or grain alcohol 
are the alcohols in common use. Ordinarily, the 
former is made by the destructive distillation of 
wood (as described in Chapter IV.), and grain alcohol 
by the fermentation of glucose, see Chapter XIX. 

Alcohols are said to be hydroxids of the hydrocarbons 
for, as can be seen by the following formulae, they have 
a hydrocarbon and a hydroxid radical. 

CH3.OH (methyl-wood-alcohol). 
C2H5.OH (ethyl-grain-alcohol). 
C3H7.OH (propylalcohol). 
C4H9.OH (butyl alcohol). 
C5H1Z.OH (amyl alcohol). 

The above examples have only one hydroxid radical, 
but alcohols containing two or more can be made 
from the higher hydrocarbons. The only one of such 
alcohols that need be referred to here is glycerin or, 
as it is often termed in chemistry, glycerol. This 
can be made from propane and it has three OH 
radicals. As glycerin, C3H5(OH)3, has three radicals 
which can be replaced by other radicals or elements 
in a chemical reaction it is said to be trivalent. 

* The term halogen is derived from a Greek word meaning the 
sea . Chlorin , iodm , bromin , and flourin were so classed because 
obtained from sea salt or seaweed. 

Main Divisions of Chemistry 167 

Though glycerin can be made from propane, it is 
ordinarily prepared from fat, of which, as \rill be seen 
in Chapter XVI., it is the base. 


When a primary alcohol is oxidized (see page 174) it 
is converted first into an aldehyde, then into an acid, 
and finally into carbon dioxid and water. The 
difference in the composition of an alcohol and an 
aldehyde consists of a lack of two H atoms in the 
latter, since the 0, in the process of oxidation, com- 
bines with two H atoms of the alcohol to form water 
(HaO). Thus: 

Alcohols Aldehydes 

CH3OH + O « CH2O + H2O 
CaHsOH 4- O - CaH40 4- HaO 

The aldehyde formed by the oxidation of methyl 
alcohol is the disinfectant gas known as formaldehyde, 
and the aldehyde of ethyl alcohol is called acetic 
aldehyde. The add produced from formaldehyde is 
called formic acid, and that from acetic aldehyde, 
acetic acid. The chemical reactions that occur in the 
oxidation of these aldehydes and adds can be seen by 
the following equations : 

Aldehydes Adds 

CHaO + O - CHaOa + O - HaO + CO, 
CaH40 + O - CaH^Oa + 20 - 2HaO + COa 

The aldehydes can be made from alcohol by burning 
the latter in spedally constructed lamps, or by bring- 
ing the alcohol in contact with an oxidizing mixttue 

1 68 Physics and Chemistry 

(one that will readily part with some of its oxygen) , as 
potassium bichromate and dilute sulphuric add. 

Formaldehyde gas is soluble in water up to 40%. 
The solution of the gas is known as formalin. The 
gas can be quickly liberated from solution by the use 
of certain chemicals, such as potassium permanganate, 
which, when added to the formalin, oxidizes some of 
the formaldehyde and in so doing produces heat 
enough to volatilize the rest of it. It is often procured 
in this way for the disinfection of rooms. 




The Occiirreiice and Nature of O xy g en — N ature of Oxidation, 
Spontaneous Combustion, Oxids, Fireproof Material, Fire 
Extinguishers, Products of Oxidation. 

OccuiTence. — Oxygen is the most common element 
in nature. It exists free {i.e., not in chemical combi- 
nation with other elements) in the air; it, in combi- 
nation with hydrogen, forms water, and, united with 
different elements, it constitutes nearly one half of 
the rocks and other substances forming the earth's 
crust; also, it is one of the essential constituents 
of animal and vegetable matter. 

How obtained. — When the majority of compounds 

and elements are heated they will take oxygen from 

the air very readily, but, though oxygen exists free 

in the atmosphere; it is not easily extracted from 

it for laboratory purposes or when a large supply 

of the pure gas is required. Therefore, for such 

ptirposes, oxygen is usually obtained by extracting 

it from some substance that contains a comparatively 

large amount of it and parts with it readily. The 

substances most frequently used are potassium 

chlorate, manganese dioxid, and mercuric oxid. 

When potassium chlorate and manganese dioxid are 


170 Physics and Chemistry 

mixed, the oxygen is liberated at a much lower tempera- 
ture than it is when either of these two chemicals is 
used alone, and when it is used with the potassium 
no change occurs in the manganese. By what means 
the manganese hastens the liberation of oxygen 
from the potassiiun chlorate is not known. When 
used in this way the manganese is called a catalyzer. 
(See page 147.) 

Experiment 13. Objects: To study (i) a method 
of reducing a compound to its constituent parts; 
(2) a method of liberating a gaseous clement from a 
compound and collecting the gas; (3) the properties 
of oxygen; (4) the use of a catalyzer. 

Articles required: An iron stand with a clasp, 
a large-sized, hard-glass test tube, a Btmsen burner, a 
wide-mouthed bottle filled with water, a similar bottle 
empty, two glass squares large enough to cover and 
extend slightly beyond the mouth of each bottle, 
glass tubing bent as in Fig. 55, a pan about 5^ full 
of water, potassium chlorate (KaClOj), manganese 
dioxid (MnOa). 

Directions: Some members of the class put about 
10 grams of potassium chlorate into their test tubes, 
and the others 10 grams of potassium chlorate and 3 
grams of manganese dioxid (mix the two chemicals 
on paper before putting them into the test tube). 
Connect the apparatus as shown in Pig 55, cover the 
bottle filled with water with a glass square and invert 
it in the pan of water, being careful not to spill the 
water while doing so (because of the atmospheric 
pressure on the water in the pan, that in the bottle 
will not run out after the bottle is inverted). Apply 
gentle heat to the part of the test tube containing the 
chemical. Notice, and record, the time reqtiired to 



liberate the oxygen. When the gas begins to be 
evolved, insert the free end of the tubing under the 
bottle ; to do so, tip one end of the bottle slightly, being 
careful not to raise the opening above the surface of 
the water in the pan. After the gas has displaced all 

Fig. 55. (a) Apparatus for the preparation of oxygen, (b) 
Shape of tube. 

the water in the bottle, turn the bottle and stand it 
on the table, keeping it tightly covered with the 
glass square. 

Partly remove the glass plate and quickly thrust a 
glowing (not burning) splinter into the bottle. Re- 
move at once and blow out the flame. Repeat the 
process tmtil the splinter no longer ignites when thrust 
into the gas. 

17^ Ph3rsics and Chemistry 

Use the same method with the empty bottle. 
Compare results. 

Into each bottle pour a little Ume water and then 
shake the bottle. A milky precipitate indicates the 
presence of carbon dioxid. 
Experiment 14. Object: To study the result of 

the union of oxygen with an 

Articles required: A crucible, 
a triangle support, an iron stand 
with ring, a Bunsen burner, a 
balance, powdered zinc or iron, a 
pointed glass rod. 

Method : (All weights must be 
absolutely accurate and shotild be 
recorded at once.) Weigh the 
crucible, weigh about 3 grams of 
the powdered metal, weigh the 
crucible and metal together and 
see if the weight tallies with those 
^ y ^^ I of the crucible and metal weighed 
^ ^ separately. Arrange the crucible 

Fia «6 Appaiulths ^^ ^^® ^^^^ ^^ ^^ ^^' 5^' support- 

FOE ExpBWMBMT 14. ^^S ^^ ^ *^® tnanglc; hght the 

burner and secure alow flame; put 
this under, but at a distance from, the crucible. If the 
zinc begins to glow or give off a white smoke, lower the 
flame instantly, or there will be a loss of substance. If 
a crust forms on the zinc, pierce it with the pointed 
glass rod in several places so as to expose a fresh sur- 
face to the air; be very careful not to lose any of the 
powder in doing this, and if particles stick to the rod, tap 
the latter gently against the crucible so that they will 
fall back. Continue the heating for about ten minutes 



Oxygen 173 

and then let the crucible and its contents cool. When 
the crucible is cool enough to touch, weigh it with 
its contents. If the experiment has been properly 
performed there will be found to be a slight gain in 
weight due to the oxygen which has united with the 
metal. See under Oxids, page 179. 

Prom the results of these experiments answer the 
following questions : 

Does oxygen bum? 

Does oxygen support combustion? 

What became of the oxygen in the bottle during the 
burning? Where did the carbon dioxid come from? 

What was the difference in time required for the 
liberation of oxygen when the potassiiun chlorate 
was used alone and when it was used with the manga- 
nese dioxid? 

What is the manganese called when used in this way? 

Compare what happened to the wood — a compound 
— with the effect of the union of oxygen with the 
metal — ^an element. 

Has oxygen color? 

Has it odor? 

Is oxygen heavier or lighter than air? Pure air con- 
sists principally of about 21 per cent, oxygen, 79 per cent, 
nitrogen, an4 0.04 per cent, carbon dioxid. The atomic 
weights of these elements will be fotmd on page 31. 

Is oxygen lighter or heavier than pure water? 
(Water consists of hydrogen and oxygen.) 

Physical and chemical properties of oxygen. — 
Oxygen is a colorless, odorless, tasteless gas. It is 
a little heavier than air and than pure water and it is 
slightly soluble in the latter.' It can be liquefied 

* Fish will not live in boiled water since during boiling the 
fne oxy^etit which the fish need, is expeUed. 

174 Physics and Chemistry 

by putting it under great pressure at a low temperature. 
At low temperatures, oxygen is rather inert chemically, 
for it does not combine wth many substances, but 
at high temperatures, it is exceedingly active. Certain 
catalyzers, however, as, for example, the enzymes 
present in both animal and vegetable tissues, permit 
of oxidation at comparatively low temperatures. 

Oxidation and combustion. — The process of the 
union of oxygen with matter, either compounds or 
elements, is spoken of as oxidation. Oxidation is 
always accompanied by the generation of heat. If 
oxidation takes place very quickly, heat will be 
evolved so rapidly that the matter may be brought 
to a white heat (see page 86) or burst into flame. 
When this occurs, the process is often termed coni' 
bustion. When the union of oxygen with matter 
goes on slowly, the heat may be developed so slowly 
that it will be diflSctdt to detect it. The rusting of 
iron and other metal is an example of this slow oxida- 
tion, and iron rust is a form of iron oxid. Other 
oxidation processes are (i) the oxidation in the body 
tissues of the substances derived from food; (2) the 
changing of wine, cider, etc., to vinegar and of \'inegar 
and other organic acids to carbon dioxid and water; 
(3) some putrefactive processes; (4) the hardening 
of paint, as will be seen later, is partly due to 

Kindling temperature. — ^As stated in a preceding 
paragraph, oxygen does not ordinarily unite with 
many substances at a low temperature, and the temper- 
ature at which it will combine varies very greatly 
with diflFerent substances, but is always the same for 
each kind of substance. The temperature at which 
a substance will begin to combine sufficiently rapidly 

Oxygen 17s 

to take fire is called the kindling temperature of that 
substance or, especially in the case of liquids as the 
hydrocarbons, the flash point. 

Matches. — ^The various constituents of matches 
furnish a good example of dijQFerences in the kindling 
temperature of different substances. Formerly match 
heads consisted principally of yellow phosphorus and 
sulphur, and the kindling temperature of phosphorus 
is so low that even a slight amount of friction caused 
it to ignite; this provided sufficient heat to ignite 
the sulphur, the kindling temperature of which is also 
low, though not as low as the phosphorus, and the 
burning sulphur heated the wood to its kindling tem- 
perature. It would be too dangerous to have the 
match head composed entirely of a substance that 
could be ignited by friction. Even with sulphur, the 
use of yellow phosphorus for match heads is danger- 
ous, not only because it ignites so easily, but also 
because it is excessively poisonous, therefore, its use 
for matches is now forbidden by law and red phos- 
phorus is used instead. This is made by heating yellow 
phosphorus to about 250® C. ; it is not poisonous and it 
will be ignited by friction only when it is in contact 
with substances rich in oxygen, such as chlorate and 
chromate of potassium and peroxid of lead. The 
head of one kind of safety match contains the oxygen 
compounds and the red phosphorus is on the outer 
surface of the match box; thus the ignition of a 
match is impossible, unless it is struck on the box. 

Spontaneous combustion* — By this is meant the 
sudden ignition of matter at comparatively low 
temperatures when heat has not been intentionally 
applied. For example, hydrocarbons, such as kero- 
sene, have a low flash point, especially when they 

176 Physics and Chemistry 

contain certain impurities that are often present in 
cheaper grades, and fires have been caused in tene- 
ments in the summer time because the heat of the 
rooms became raised to the degree at which the 
kerosene conibined rapidly with oxygen. Painters' 
rags wet with oil and turpentine, heaped together, are 
the cause of many fires, because oil and turpentine 
having a strong affinity for oxygen keep uniting 
with it slowly and the rags, being in heaps, prevent 
the escape of the heat generated by the oxidation, 
so that the kindling temperature of the oil, which is 
low, is soon reached and the mass suddenly bursts 
into flame. 

Di£Ference and similarity of the results of the 
oxidation of compounds and of elements, — ^As de- 
monstrated by Experiments 13 and 14, when oxygen 
unites with a compound, the latter becomes dis- 
sociated into simpler compounds and its elemental 
constituents, but when oxygen combines with an 
element, a compound substance is formed. Judging 
from appearances, it might be thought that another 
point of difference was an increase of bulk and weight 
of the oxidized element and a loss of substance in the 
compound, but it has been found that when all the 
gases which escape from a compotmd as it bums are 
caught and weighed, as well as the ashes which 
remain, there is not only no loss of weight in the 
matter btutied, but, just as in the case of the oxidized 
element, a gain in weight that is equal to the amount 
of oxygen that has united with the matter in the 
course of combustion. 

Products of combustion. — The products of combus- 
tion, of course, vary according to the nature of the 
matter burned, but, as already stated, all oxidation 

Oxygen 177 

g^ves rise to heat and all orgatdc matter, whether of 
animal or vegetable origin, yields water and carbon 
dioxid, for all organic substances contain carbon, 
hydrogen, and oxygen. Also, there will be various 
other gases combustible and incombustible, which 
will pass off from the burning matter, and, usually, 
there will be some uncombined carbon, mineral matter, 
and other incombustible solids that wiU, for the most 
part, remain as ashes, but small particles will be carried 
off with the gases. 

Smoke. — The hot gases, water, and other matter 
arising from burning substances gradually cool as 
they pass into the air and in doing so condense to 
some extent, forming the doud-like matter known as 
smoke. When a large amount of incombustible 
matter and products of incomplete combustion are 
present, the smoke will be of a dark color and, 
especially when the burning material is of an oily 
nature, there will be a considerable amount of matter 
that will condense easily and in doing so absorb some 
of the carbon and other solid substances present 
in the smoke; this constitutes soot. The substances 
contained in soot are not all fully oxidized and, for 
this reason, if a large quantity is allowed to collect 
in a chimney, it may t£^e fire, when a fire is lighted 
in the stove, furnace, or fireplace. 

Experiments to study the nature of combustion. — 

Experiment 15. 

Procedure: Arrange apparatus as in Fig. 56A, 
using a hard-glass test tube for a and an ordinary one 
for b. Tube c must be drawn to a point. Have small 
pieces of wood in a and place lighted burner under 
them. When smoke begins to issue from c, apply a 
lighted match to it. There being combustible gases in 


178 Physics and Chemistry 

the smoke it will ignite. When the gases cease to 
bum and it is impossible to relight them, remove the 
charred wood from the test tube, examine it, and hold 
a piece of it with the forceps in the flame. 

Pig. 56A. Appakatus Used for 

Does it bum with or without a flame ? See page 1 79. 

Of what does this residue of the wood consist? 

Test the liquid in b with litmus paper. This is 
pyroUgneous add (wood vinegar) see page 193. 

Experiment 16. 

Articles required: Substitute a few pieces of coal 
for the wood, otherwise have the same articles as for 
Experiment 15, and perform experiment in same way. 

Experiment 17. 

Articles required: A hard-glass test tube, a test* 
tube holder, about ten grams of cane sugar, a Bunsen 
burner, matches. 

Procedure: Put the sugar into the test tube and 
hold the latter in the flame. Notice the changes that 
occur in the sugar. After the sugar has turned 
brown and smoke issues from the tube, apply a lighted 
match to the smolce. 

Oxygen 179 

How do the products of the burning and burnt coal* 
wood, and sugar compare? 

Experiment 18. 

Articles required: A wide-mouthed bottle, a glass 
square, a taper or strip of wood, lime water, a beaker, a 
piece of glass tubing about four or five inches in length. 

Procedure: Let the taper or wood bum in the 
bottle for some time, keeping the bottle covered with 
the glass square as much as possible without putting 
out the light. After a few minutes, put out the light 
and pour a little lime water into the bottle. 

Put some lime water into the beaker and blow 
into it through the glass tubing. 

The white substance that appears in the lime 
water is calcium carbonate (CaCOj), formed by the 
union of carbon dioxid (CO 2) and the calcium hydroxid 
Ca (OH) a, in the water. Thus, Ca (OH) ,+COa = Ca- 


Why do you get the same results from the burning 
of a taper or wood and from the breath ? 

Flame and incandescence. — Matter may bum 
with or without a flame. If the matter is a volatile 
substance, such as ether, kerosene, or alcohol, or if, 
though not itself volatile, it gives off combustible 
gases when heated, as do coal and wood, there will be 
a flame during combustion, but matter such as solid 
carbon will combine with oxygen and thereby become 
so hot that it will glow, and metals and oxids may be 
so highly heated that they will glow — i. e., they will 
become incandescent — ^but in neither case will there 
be a flame. As a rule, flame occurs only in the burning 
of volatile substances. 

Ozids. — ^An oxid is a compound of oxygen and an 
element or radical. Thus water (HaO) is an oxid 

i8o Physics and Chemistry 

of hydrogen, and carbon monoxid* (CO) and carbon 
dioxid (CO a) are oxids of carbon, sulphur dioxid 
(SO 2) is an oxid of sulphur, and so on. There are 
only two elements — ^bromin and fluorin — that will 
not, tmder any drcumstance, unite with oxygen. 

Nature of fireproof buildingSi clothingy etc. — 
Buildings are said to be fireproof when they are 
constructed of substances that are non-combustible, 
or that will not bum except at excessively high 
temperatures, or in the presence of free oxygen (such 
are iron, concrete, stone), and of matter saturated 
with oxids which have taken up all the oxygen that 
they can combine with and therefore cannot bum, 
btiming being nothing but the union of matter with 
oxygen. Wood, clothing, and other absorbent ma- 
terial can be made fireproof by being treated with 
such oxids. 

Fire extinguishers. — Since burning consists of the 
combining of matter and oxygen, if air is excluded 
from a substance, it cannot bum. Therefore, the 
quickest way to check a fire is to prevent the access 
of air to it. An effectual way of doing this is by the 
use of a fire extinguisher containing chemicals which, 
when combined, form carbon dioxid. As this gas 
holds all the oxygen that it can unite with and is ' 
heavier than air, it will, if poured over burning matter, 
act as a non-inflammable, air-proof covering. Many 
extinguishers contain a flask of sulphuric acid sur- 
rounded with sodiimi carbonate solution and when the 
extingtiisher is tilted the acid comes in contact with the 
soda and carbon dioxid is evolved. Thus: HaS04+ 

■ Oxids which have but one atom of oxygen in the molecule 
are called monoxids^ and those which have two atoms are called 



The Nature and Origin of the Substances Commonly Used tor 

Fuel and Lighting. 

ClasEdfication of fuels. — Fuels are usually classified 
as solid fuels, liquid fuels, and gaseous fuels. 

The solid fuels are coal, coke, peat, wood, and 

The liquid fuels in common use are alcohol, gaso- 
line, kerosene or coal oil, and crude fuel oil. 

The common gaseous fuels are coal gas, natural 
gas, gasoline or air gas, and acetylene gas. 

Solid Fuels 

Classification of coal. — The several varieties of 
coal are usually classified under three headings, 
viz., anthracite or hard coal, bittiminous or soft coal, 
and lignite. 

Reason for differences in coal. — ^The differences 
in coal are thought to be due to the stage of formation 
in which the coal is when it is taken from the earth. 

Origin of coal. — Coal is derived from vegetable 

matter that through many thousands of years has 

been undergoing decomposition out of contact with 


1 82 Physics and Chemistry 

the air and, during the process, losing its hydrogen 
and oxygen. 

Lignite. — Lignite, a brown coal, represents a 
comparatively early stage in the process of coal 
formation. The word lignite is from the Latin 
lignum meaning wood, and it is so called because it 
still shows traces of wood structure. It contains 
proportionately less ca^'bon and more oxygen and 
hydrogen than the other coals, and it therefore gives 
less heat than they do, because the heat value of fuels 
depends principally upon the union of the carbon in 
the fuel and the oxygen of the air. 

Bituminous or soft coal. — This coal has passed 
farther in the stage of decomposition than lignite and 
has therefore lost more of its ingredients other than 
carbon. The disadvantages of soft coal for heating 
purposes are : (i ) that being soft and easily powdered, 
it is very dirty; (2) many varieties cake as they bum, 
and the caked masses require to be broken constantly 
in order to allow a free draft through the fire ; and (3) 
there is usually a great deal of smoke and soot from a 
soft-coal fire. Bittuninous coal 3rields more heat than 
lignite, but less than anthracite. Medium grades of 
soft coal are considered the best coal for the manu- 
facture of coke and of coal gas. 

Anthracite or hard coal. — In its purest state, this 
coal has lost nearly all its ingredients other than 
carbon. Tlierefore it gives more heat than either 
of the other two varieties. It bums with little or 
no smoke, and the best varieties do not produce 
any clinkers. Sulphur, a common impurity in all 
kinds of coal is one of the principal causes of clinkers. 

Coke. — Coke is produced by the destructive dis- 
tillation of bituminous coal (see distillation, page 64), 

Fuels and Illuminants 183^ 

It consists of free carbon mixed with varying amounts 
of ash. It produces intense heat, but no flame or» if 
the fire is deep, a carbon monoxid flame. See page 161 . 

Peat. — Peat results from the decomposition of 
mosses a;id similar plants under water. In its 
natural state, it has not a high fuel value, for it con- 
tains a large per cent, of water, but, of recent years, 
ways of drying it have been devised that have in- 
creased its fuel value very considerably. 

Classification of woods. — ^Woods are classed as 
soft woods and hard woods. Wood, as used for fuel, 
consists principally of cellulose (C6HxoOs)2, mineral 
matter, and water, and the conifer woods contain a 
varying amount of resin. If there is much water, 
the heat value of the wood is lessened because much 
of the heat will be used in vaporizing the water; see 
page 45. The wood from trees cut in winter has 
less water than that from those cut at other times 
because, in cold weather, there is less sap fiowing 
through the trees. 

Soft woods. — The soft woods most used for fuel 
are pine, cedar, spruce, hemlock, poplar, willow, and 
redwood. Soft woods ignite easily and are therefore 
valuable for kindling, but they bum quickly and 
thus, if used alone, will yield a very hot fire for a short 
time, but it will reqtdre a large amount of wood to 
keep up the fire. The conifers yield more heat than 
other soft woods because of their resin. 

Hard woods. — The hard woods most commonly 
used for fuel are ash, beech, birch, sugar and black 
maple, oak. A cord of hard wood and a ton of coal 
are said to have about the same heat value. Weight 
for weight, if properly dried, hard and soft woods 
yield about the same amount of heat, but hard woods 

i84 Physics and Chemistry 

bum more slowly and thus last longer than soft 

The mineral matter left after wood is burned con- 
sists largely of potassium^ phosphorus, and calcium 
compounds; thus, if the ashes are kept dry and put 
into the ground they act as fertillizers, since phmts 
need these salts for their growth. If the ashes are 
wet, however, their value for this piupose is lessened, 
for the potassium salts, which are the most important 
ones, are changed to potassium hydroxid. 

Charcoal. — Charcoal is obtained from wood in the 
same manner as coke is from coal and its characteris- 
tics are very similar to those of coke. 

Liquid Fuels 

The liquid fuels in most conunon use are alcohols, 
gasoline, kerosene, and other so csXLedfuel oils.^ 

Alcohols. — ^Wood alcohol and denatured ethyl 
alcohol are the alcohols used for fuel. Wood alcohol, 
as stated in the preceding chapter, is made by the 
destructive distillation of wood. Denatured alcohol 
is ethyl alcohol plus some substance that has been 
added to it in order to render it unfit for drinking. 
This is used because it is cheaper than the pure alcohol, 
since it is tax free, while there is a heavy tax on the 
latter. Wood alcohol does not give as much heat as 
ethyl alcohol and it is very poisonous. A new pro- 
prietary preparation called stemo, in which the alcohol 
is incorporated in a waxy substance, is now much 
used instead of the liquid alcohol. Alcohol, in any 
form, would be an expensive and unsatisfactory fuel 

< Kerosene and similar hydrocarbon derivatives, though of aa 
oil-like nature, are not true oils. 

Fuels and Illuminants 185 

to use for large fires, but when only a small flame is 
required, as for chafing-dish cooking, it is very con- 
venient to use. It is always important that the 
wick of an alcohol lamp or stove should fit properly, 
for if it is too small the flame may reach the alcohol 
and, unless the utensil is constructed for the burning 
of the alcohol directly, the results may be disastrous. 

Gasoline. — This is obtained from petroleum by 
fractional distillation. Gasoline has a lower specific 
gravity and is more volatile than kerosene. The 
latter quality makes it a more dangerous fuel, because 
it volatilizes at a low temperature and the vapor, 
when mixea with a certain amount of air, becomes 
explosive. Quite a large amount of air is required, 
however, and if the following precautions are observed 
there is very little more danger attending the use of 
gasoline than of any other liquid fuel: (i) The stove 
must be properly cleaned and it must be always filled 
before it is used; (2) the stove must be in good condi- 
tion so that there will be no leakage and the wicks 
must fit the burners; (3) the cover of the tube through 
which the stove is filled must not be left off, nor even 
loose; (4) a good quality of gasoline must be used; 
(5) the light must be put out by ttiming down the 
wick, never by blowing. 

It is when stoves that have been partially empty 
for hours are first lighted that trouble usually occurs; 
because, while the stove has not been in use, the 
gasoline has been volatilizing and, as the vapor has 
not been burned, it has been filling the stove and mix- 
ing with the air in it. As a high temperature acceler- 
ates volatilization, explosions from this cause are 
most likely to occur in hot weather or in a hot room. 

Qualities of good gasoline. — Good gasoline has a 

1 86 Physics and Chemistry 

neutral reaction, a specific gravity of about .68 to 
•72, and, when filtered through chamois, it leaves no 

Kerosene. — Though kerosene is not as explosive as 
gasoline, the same precautions are necessary in its 
use and for the same reasons. It is to be remembered 
that explosions occur only when the reservoir of a 
stove or lamp contains definite proportions of air a;nd 
vapor, or when the hydrocarbon beconies ignited, 
which it can hardly do if the precautions mentioned 
under ga^line are taken. Kerosene that has a 
flash point below 100^ F. is not s^e for general use, 
and in many cities where the temperature is Ukely 
to be high at times, the law prohibits the use of a 
kerosene that has a flash point below 125^ F. or 150^ F. 

Kerosene stoves. — The blue-flame kerosene stoves 
are usually considered the best. In the majority of 
these, the oil is fed into a hollow ring at the bottom 
of the burner, where it is heated to a sufficiently high 
temperature to vaporize it. The vapor becomes 
mixed with air in the btimer, and thus just as was the 
case with the gas in the Bunsen burner, it gives a blue 

Especially in oil-producing regions, crude fuel oils 
that are sold under various trade names are often 
used for fuel in specially constructed ranges, but only 
the more refined hydrocarbons should be used in the 
ordinary kerosene and gasoline stoves. 

Gaseous Fuels and Illuminants 

The gases generally used for fuel and lighting 
ptirposes are coal gas, oil gas, water gas, nattu'al gas 
(the two last named are used for lighting only in 

Fuels and Illuminants 187 

connection with some of the higher hydrocarbons), 
acetylene gas, and gasoline or air gas. 

Coal and Oil gas. — Coal gas is a product of the 
destructive distillation of coal, and oil gas, of oil. 
Their principal constituents are hydrogen, methane, 
small quantities of other simple hydrocarbons, carbon 
monoxid, carbon dioxid, nitrogen, ammonia, and a 
small quantity of bisulphid of carbon. 

Incandescent gas lights. — ^The nature of the coal- 
gas flame was discussed in connection with the 
Bunsen burner, page 9. Also, it was there shown 
that the presence of free carbon in the flame increased 
the light-giving properties of the gas, because the 
carbon could be raised to a white heat and thereby 
be rendered luminous without being disintegrated or 
volatilized. As stated in the preceding chapter, 
matter rendered luminous in this way is said to be 
incandescent. To find a means of increasing the 
amount of matter that could be made incandescent 
in a flame was the object of many experiments, of 
which two well-known results are the Argand burner 
and the Welsbach mantle. 

The Argand burner — called after the inventor — 
gives a round flame in which a large amount of carbon 
is liberated. 

The Welsbach mantle — invented by Auer von 
Welsbach — ^is made by cutting and sewing some 
mercerized cotton into the reqtiired shape, using 
asbestos thread for the sewing, and then saturating 
the cotton with a solution of certain oxids, more 
especiajly those of two rare elements known a^ 
thorium and cerium. In the process of manufacture, 
the cotton is burned out and the liqtiid in which the 
oxids were dissolved is evaporated and the oxids 

i88 Physics and Chemistry 

thus hardened so that the mantle, when completed, 
consists of a thin, filmy cap-like structure of oxids. 
This is connected with a burner that gives a non- 
luminous, and, consequently, the hottest flame, and 
this heats the oxids to such a degree that they give a 
white luminous light six to eight times more powerful 
than that produced when an ordinary illuminating 
gas burner is used. 

Surface combustion. — Somewhat the same principle 
as that upon which the structure of the Welsbach 
mantles was based is used in the surface-combustion 
staves, though in the stoves heat, and not light, is 
the thing desired. The stove burners are placed in 
the midst of incombustible ntiaterial, such as alumina 
(AlaOj) and silica (SiOa), and are so constructed that 
just enough air to allow of the combustion of the gas 
can enter. The gas bums without a flame and heats 
the altunina, etc., to incandescence, and the heat 
reflected greatly exceeds that from an ordinary gas 

Natural gas. — Thjis is obtained in certain localities 
by boring wells in the ground. Methane (CHJ is 
its chief constituent, but it contains small quantities 
of ethane (CaHe) and other simple hydrocarbons. 

Water gas. — ^This gas is obtained by passing steam 
through coke or anthracite coal when they are in- 
tensely heated. It consists chiefly of carbon monoxid, 
hydrogen, and small amounts of methane, carbon 
dioxid, nitrogen, and oxygen. One great disadvantage 
of water gas is that it is odorless and, consequently, 
its escape from a gas pipe may escape detection. 
This gas, owing to its large content of carbon mon- 
oxid, is excessively poisonous; carbon monoxid 
causing death by asphyxiation because it unites so 

Fuels and Illuminants 189 

strongly with the hemoglobin of the blood that it 
is not easily displaced and, consequently, the hemo- 
globin cannot unite with oxygen. 

Natural gas and water gas btim with a blue flame 
and are suitable for illuminating purposes only when 
mixed with other gases. 

Acetylene (C3H:,). This gas, as stated in Chapter 
II., is, for practical purposes, produced by the inter- 
action of water and caldtun carbide. It is usually 
prepared in private plants for country houses that 
are away from the main gas and electric lines. It is 
used especially as an illuminant, but also for cooking 
and heating. Unfortunately, it is exceedingly explo- 
sive and not only forms explosive mixtures with air, 
but, when compressed, is itself explosive. When 
burned in the presence of oxygen, acetylene yields 
a flame hot enough to melt iron ; thus, it is sometimes 
used in a specially constructed apparatus, instead of 
solder, for fastening metal joints together. 

Gasoline gas. — This is another gas prepared in 
private plants for country places. It is made by 
allowing gasoline to volatilize in the presence of air, 
the combination being regulated so that an explosive 
mixture will not be formed in the pipes. 

Compressed gas. — Certain of the hydrocarbon 
gases are compressed and stored in cylinders that can 
be shipped to country houses and institutions and 
attached to their gas-supply pipes. Gas so treated 
is called compressed gas. 


Electricity is rapidly replacing gas as an illuminant 
and, as soon as the current can be produced more 

190 Physics and Chemistry 

cheaply, it will probably do so also for heating and 
cooking, for it has many advantages. Two of these 
are: The wires for its conveyance are cheaper to 
install than the gas pipes, especially when houses 
are far apart ; and it does not add to the impurities of 
the air in buildings, as do other forms of illuminants. 
The way in which heat and light are obtained from 
an electric current was described in Chapter VIII. 



Different Kinds of Solutions — Different Kinds of Acids.— 
Characteristics of Adds — ^Tests for Acids — Properties of 
Bases and Alkalies — ^Neutralization — Different Kinds of 
Salts— Alkaloids and Their Salts— Native of Pats— 
Saponification — Nature of Soaps, 


Definitions. — ^When the word solution is used as a 
verb it stands for the dissolving of a substance in a 
liquid; used as a noun, it implies a liquid with some 
substance dissolved in it. The liquid which is used 
to dissolve a substance is called the solvent, and the 
substance that is dissolved is termed the solute. 
An unlimited amount of solute cannot be dissolved in a 
solvent, and when the latter contains as much of a 
solute as it can hold in solution at certain tempera- 
tures it is said to be saturated at that temperature. 
Most solutes are more soluble in hot than in cold 
solvents, but there are some exceptions, e, g., calcium 
hydroxid, in water, and gaseous solutes. If a solution 
is saturated at a high temperature and then allowed 
to cool gradually without disturbance, it will often 
cool to room temperature without depositing any of 
the substance from the solution. Such a solution is 
said to be supersaturated. Such a solution is very un- 
stable; after it has cooled, even shaking the flask in 

which it is will precipitate the amount of solid that is 


192 Physics and Chemistry 

in excess of the quantity required for saturation. 
Heat lessens, instead of increasing, the amount of gas 
that can be held in solution, because heat increases 
the molecular motion and expansion of gases more 
quickly and to a greater extent than that of liquids. 

Nature of matter used for solutions. — Matter in 
any one of its physical states (i. e,, solid, liquid, and 
gas) can be used as a solute. There are, of course, 
many substances that can be dissolved only at ex- 
tremely high temperattu'es, and all substances are not 
soluble in the same kind of solvents. Fat, for example, 
is not soluble in water or in cold alcohol, but it is 
soluble in hot alcohol, alkaline solutions, ether, ben- 
zene, and similar substances. 

Water and alcohol are the solvents most frequently 
used in making solutions. A solution for which 
water is used as the solvent is called an aqueous solu- 
tion, and one for which alcohol is used as the solvent 
is termed an alcoholic solution, 

IsotoniCi hypertonic, and hypotonic solutions. — 
These terms are often used in physiology and medi- 
cine when comparing the relative percentage of 
salts of any kind contained in the blood and in other 
solutions. By an isotonic solution is meant one that 
contains the same percentage of salts as the blood; 
by hypertonic, one with a higher content of salts 
than the blood; by hypotonic, one with a smaller 
amount of salts than the blood. 


Acids are classified as organic and inorganic. 
Organic acids. — ^All organic adds contain carbon 
and the carboxyl or organic add radical, viz., COOH. 

Solutions. Acids. Bases and Salts 193 

Thus, for example, the rational formula for acetic add 
is CH3COOH, for formic acid, H.COOH; for oxalic 
acid (COOH)a. The following are some of the more 
common important organic acids: 

Acetic add CH3.CO2H Malic acid C4H6OS 

Butyric '• 




Carbonic " 


Oxalic *' 




Palmitic " 


Formic " 


Stearic " 




Tartaric " 


Acetic acid is derived principally from alcohol as 
the result of fermentation brought about by the 
agency of a minute organism commonly called mother 
of vinegar, or from the distillation of wood in the 
absence of air. It is formed also in decaying fruit 
from the fermentation of the fruit sugar. The sour 
taste of vinegar is due to the presence of acetic add — 
good vinegar containing about 6 per cent, of the apid. 
The glacial form of the acid is produced by lowering 
the temperature tmtil the add crystallizes. It has a 
strong affinity for water and is therefore used as a 
dehydrating agent (i. e, to remove water). 

Carbonic acid is a weak unstable add that breaks 
up into carbon dioxid and water whenever it is set 
free from its salts. 

Citric acid occurs in large quantities in the dtrus 
fruits {i.e., lemons, grape fruit, oranges, and limes) 
and slightly in quince, gooseberries, strawberries, 
raspberries, currants, and cranberries. 

Formic acid is fotmd in plants such as stinging 
nettles, in red ants, and in a secretion in the sting of 
the bee. It can be made by the oxidation of wood 

194 Physics and Chemistry 

Lactic add is formed from lactose (the sugar in 
milk) when, as the result of bacterial action, it fer- 
ments. The souring of milk is due to formation of this 

Malic acid and malates occur in apples, pears, 
currants, blackberries, raspberries, quince, pineapples, 
cherries, and rhubarb. 

Oleic acid will be referred to in Chapter XVIII. 

Oxalic acid is present in the form of salts in many 
plants, such as the sorrels. It can be made by the 
action of nitric add on carbohydrates and by heating 
wood shavings or sawdust with caustic potash or soda. 

Palmitic acidy see Chapter XVIII. 

Stearic acidy see Chapter XVIII. 

Tartaric acid and its salts occur chiefly in grapes. 

Other important organic adds are the amino adds 
and the add amides. These, of which there are a 
large number, are formed both in plants and in ani- 
mals. In the latter they result from the digestion 
and the metabolism of protein substances. 

The inorganic acids. — The more common important 
inorganic adds are: 

Hydrochloric or muriatic add (HCl). 

Hydrobromic add (HBr). 

Nitric add or aqua fortis (HNOj). 

Phosphoric add (H3PO5). 

Sulphuric add or oil of vitriol (HaSOJ. 

Acids and hydrogen. — The molecules of all adds 
have at least one atom of hydrogen that is detached 
in chemical reactions, and it is upon this atom that 
their add characteristics depend; losing this, they lose 
their add properties. Some adds contain more 
hydrogen than the detachable atom or atoms, and 
when writing the formulas for such adds the replaceable 

Solutions. Acids. Bases and Salts 195 

hydrogen is sometimes separated by a period — thus, 
H.CaHiOa. Hydrogen unites with certain elements 
to produce adds; for instance, hydrogen and chlorin 
unite to form hydrochloric add, hydrogen and 
bromin unite to produce hydrobromic add, hydrogen 
and fluorin combine to form hydrofluoric add. 

Anhydrids. — Adds are formed also by the union 
of certain gaseous oxids and water. For example, 
nitric add, sulphuric and sulphurous add, carbonic 
add, phosphoric add, are formed by the union of 
water and oxids of the elements nitrogen, sulphur, 
carbon, and phosphorus respectively. Such oxids are 
often spoken of as anhydrids. Anhydrids are also 
obtained by the abstraction of water from adds. 

Strong and weak acids. — Some adds are much 
•more active chemically than others; i.e., they react 
more quiddy and with a greater number of substances 
to form new compounds. Those which do are 
classed as strong acids and those which do not as 
weak acids. The important strong adds are hydro- 
chloric, nitric, sulphuric, and oxalic. Tartaric and 
dtric are moderately strong; and acetic, carbonict 
boric, and the fatty adds — as oldc, stearic, eta 
— are weak. 

Properties of acids. — All adds, whether organic or 
inorganic, have certain marked characteristics, viz.: 
they have a sour taste; they are very soluble in 
water; they contain hydrogen in loose combination 
and part with it when they come in contact with 
substances for which they have an afBnity. On 
account of this last characteristic, adds decompose 
and often dissolve many substa^nces, and they form 
different compounds in the process. They act in 
this way upon many metals, as will be seen in the 

196 Physics and Chemistry 

paragraphs devoted to salts and in Chapter XVI. 
In fact, adds have such a strong affinity for basic 
substances in nature and the a;nimal body that they 
occur more frequently in the form of salts than in the 
free state. The strong acids are very corrosive. 
Their action upon metals and fabrics will be discussed 
in Chapter XVI. When acids are perfectly free from 
water or when they are dissolved in liquids which 
do not dissociate them into ions, they do not show 
add characteristics. 

Tests for acids. — Certain substances that have been 
named indicators are used for the detection of add 
matter. The more conmion ones are: Litmus, 
which is derived from a small lichen and can be 
obtained in liquid or powder form or as paper dyed 
with litmus; and methyl orange and phenolphthaldn 
which are coal-tar products. Adds turn blue litmus 
and yellow methyl orange to red, and they make 
pink phenolphthaldn colorless. 

Nomenclature of acids. — Acids which consist of 
only one other element in addition to hydrogen are 
called binary acids; those which contain three ele- 
ments are dassed as ternary acids. Binary adds 
are given names consisting of the prefix hydro, the 
name of the second element, and the suffix ic — e.g., 
hydro-chlor-ic add. Oxygen is the third element in 
the majority of adds, and many adds differ from 
each other in composition only in the amount of 
oxygen which they contain. When there are several 
adds similar to each other save in this respect, the best 
known one is given the suffix ic, e.g., chloric, sulphuric, 
nitric, etc. If there is an add of the same name 
containing less oxygen than that with the suffix ic, it 
has the suffix ous, instead of ic; if there is a similar 

Solutions. Acids. Eases and Salts 197 

add with still less oxygen, it retains the suffix ous^ 
but it also has the prefix hypo. If a^a element forms 
an add with a greater amotmt of oxygen than the ic 
add, the suffix ic is retained and it has also the prefix 
per. The following table of the dilorin adds illus- 
trates this nomendature: 

Hydrodiloric add — ^HCl 
Hypochlorous " HCIO 
Chlorous " HClOa 

Chloric " HCIO, 

Perdiloric " HCIO4 

Bases and Alkalies 

Definitions. — The terms bases, hydroxids, and 
alkalies are often used interchangeably, but many 
chemists do not consider this correct because, though 
bases are alkalies, there are some substances that have 
an alkaline reaction that are not true bases and 
alcohols, which are hydroxids, though they resemble 
bases in some respects, are not alkalies. Bases and 
hydroxids are often defined as substances which produce 
hydroxyl ions when dissolved in water or other dissociate 
ing liquid; and alkalies as any one of a doss of compounds 
which forms salts with acids and soaps with fats. 

Reaction of the basesi etc. — ^The bases and majority 
of hydroxids and alkalies have an alkaline reaction ; i.«., 
they change red litmus to blue, red methyl orange to 
yellow, and colorless phenolphthalein to pink. 

Names of some of the important bases. — ^These are: 

Ammonium hydroxid or ammonia water (NH4OH). 

Caldum hydroxid [Ca(OHa]. When in solution, 
this is known as lime water. 

Potassium hydroxid or caustic potash or lye (KOH). 

Sodium hydroxid or caustic soda (NaOH). 

198 Physics and Chemistry 

Derivation of the term hydrozid. — The hydroxids 
received their name because the elements which 
form them do so by their interaction with water. 
For example, if the element sodivma is dropped on 
water, some of the latter will be decomposed and 
the metal will at once unite with the oxygen and half 
of the hydrogen, and the other part of the hydrogen 
will escape in gaseous form. The reaction takes 
place so quickly that sufficient heat is caused to melt 
the metal, but, if the remaining water is evaporated, 
the soditun hydroxid formed by the interaction will 
remain as a white solid. The reaction that occurs 
isasfoUows: Na+HaO = NaOH+H. 

Characteristics of hydroxids. — All true hydroxids 
contain the hydroxyl radical (OH) and the majority 
of them consist of a metal in combination with this 
radical. When bases are dissolved in water, they 
dissociate into two kinds of ions one of which is 
always the hydroxyl ion and the other the metal ele- 
ment, as described in Chapter VII. Bases have a 
soapy feeling, a brackish taste, and an alkaline re- 
action. They destroy tissues by abstracting their 
water, dissolving their albumin, and saponifpng the 
fat. They destroy bacteria by the same means. 

The action of alkalies upon albumin and fat makes 
them valuable for cleansing agents, but, as will be 
seen in Chapter XVI., they, like adds, cannot be used 
for cleaning all kinds of substances, and when strong 
basic solutions are used on absorbent material, their 
action must be neutralized by the use of an add. 


Experiment 19. Object: To study neutralization. 
Artides required: An iron stand or tripod, a 

Solutions. Acids. Bases and Salts 199 

Bunsen burner, wire netting, an evaporating dish half 
ftill of water, NaOH, HCl, litmus paper. 

Dissolve a small piece of NaOH in an evaporating 
dish half full of water. Add dilute HCl drop by drop 
tmtil the solution will slightly redden blue litmus 
paper. Place the dish on a wire netting, over the 
flame and allow its contents to evaporate to dryness. 
Continue the heating until the yellow color disappears 
— this being due to the excess HCl that was added. 
Add a little warm water and evaporate this in order 
to remove all traces of the add. Test the residue 
with litmus. Is it acid, alkaline, or neutral (i. «., 
neither add nor alkaline)? Taste the residue; what 
is it? 

Write the equation showing the reaction. 

The two chemicals used for this experiment were 
corrosive poisons, but, when they united, the add lost 
its hydrogen atom and the base its hydroxyl radical, 
these uniting to form water, while the Na and the 
CI united to form a salt that was ndther add nor al- 
kaline and, therefore, neutral. Thus : NaOH + HCl = 
NaCl+HaO. This operation is called neutraUzaUon. 

As alkalies and adds neutralize each other, adds 
are used in the treatment of poisoning by alkalies and 
to remove stains made by alkalies, and alkalies are 
used to counteract the action of adds. 


Salts and salt-like substances compose a very 
large proportion of the compounds forming the earth's 
crust; they enter into, and are essential for, animal 
and plant tissues; in fact, they are fovmd in great 
varieties everywhere in nature. 


Physics and Chemistry 

How salts are formed. — Salts may be formed by 
the addition of an acid to (i) a metal, (2) the oxid of a 
metal, (3) an hydroxid, (4) an alkaloid. For example : 








Sodium chlorid Hydrogen 
NaCl + H 




Zinc Sulphate 

ZnS04 + H 




Magnesium sulphate 

MgS04 + H 



SaU By-Produa 

Ferrous oxid 



Ferrous chlorid Water 
FeClt + H«0 



Salt By-Produet 

Sodium hydroxid 



Sodium sulphate 

2NaS04 + aH.O 

Alkaloids and their salts will be discussed later. 

How salts can be dissociated. — Salts are not only 
being constantly formed in nature, even in the am'mal 
body, but they are also being dissociated, and they 
often form new compounds after dissociation. How 
easily decomposition occurs when a salt comes in 
contact with a substance that has a stronger affinity 
for one of its elements than those with which it is 
combined, can be seen by the following experiment: 

Experiment 20. Articles required: A flask; two 
corks, one with one hole and the other with two holes 
through the center; a thistle tube; a piece of glass 
tubing bent as in F\^. 58; a bottle one third ftdl of 
water; sodium chlorid (NaCl) ; sulphuric add (HaS04) ; 
litmus paper. 

Procedure: Put about 16 grams of NaCl into the 

Solutions. Acids. Bases and Salts 201 

flask, connect the apparatus as in Fig. 57. Through 
the thistle tube, pour some H3SO4 upon the salt. 
After action ceases, test the water with litmus paper. 

The water, it will be found, is add, because the 
chlorin was liberated from the sodium and the hydro- 
gen from the sulphuric add, and these two gases, 
which passed through 
the tube to the water, 
united, forming HCl. 
The liquid in the flask 
contains a new salt, 
and it can be obt^ned 
by evaporating the 
liquid. Hie salt is 
sodium sulphate 

Write the equation 
showing what hap- 
pened in the reaction. 

Salts are also disso- 
dated to some extent 
when dissolved in „ 

™af— «^ =t«™« ;« P"=- 57- Apparatus Used fob 
water, as shown m e«=«ment «. 

Chapter VII. and the 

decomposition is hastened when an electric current 
is passed through the solution. The dissociation of 
many salts is also hastened when their solutions are 
heated. It is necessary for nurses to remember this. 
An example of a very common error arising from 
ignorance of the fact is the sterilizing of sodium 
bicarbonate solutions. When this is done, the 
patient gets very little sodium bicarbonate, the salt 
having been decomposed into its ions during the 
sterili^tion. If, however, as is done in many hospitals, 

202 Physics and Chemistry 

the qtiantity of sodium bicarbonate required for each 
flask of solution is wrapped in a separate package, 
sterilized by dry hecU at about 60® C. on three succes- 
sive days, and added to the sterile, distilled water 
shortly before use, the solution will be sterile and 
the soda will not be dissociated to any extent. 

Normaly acid» and basic salts. — Salts which have 
neither add nor alkaline characteristics are called 
neutral or normal salts. There are, however, some 
salts that have add and some that have alkaline 
properties. For example, any add that has more 
than one replaceable hydrogen atom may be made to 
form a salt with an add reaction; thus, HaS04+ 
2NaOH = NaaS04+2HaO. Sodium sulphate (NaaS04) 
is a normal salt; but the salt formed thus, HaS04-f 
NaOH = NaHS04+HaO, is an add salt, for, as can be 
seen by looking at the formula, NaHS04 (add sodium 
sulphate) still retains an atom of hydrogen, since there 
were not suflident hydroxyl ions provided to unite with 
all the hydrogen. In the same way, if a base, such as 
magnesium hydroxid [Mg(OH) a], and an add, as HCl, 
are brought together in such quantity that there will 
be an equal ntunber of molecules of each, there will 
be only half enough hydrogen for the hydroxyl ions 
present, there bdng, as can be seen by the formula, 
two hydroxyl ions in each molecule of the base, and the 
result will be as follows: Mg(OH)a+ HCl = MgOHCl 
+HaO. MgOHCl is called basic magnesium chlorid. 
When theHCl is in the proportionof Mg(OH) 2+ 2HCI, 
the reaction is MgCl+2HaO, and MgCl — magnesium 
chlorid — ^is a normal or neutral salt. 

Naming of salts. — (Read the names of the adds, 
page 197.) The names of the salts are derived from 
those of the bases or metals, etc., and of the adds 

Solutions. Acids. Bases and Salts 203 

which produced the salts. As in the case of the adds, 
the suflSx usually shows the lack of oxygen or the 
amount of oxygen present. A salt derived from a 
binary acid generally has the suflBx id or ide, thus 
chlorids are formed from hydrochloric add, bromids 
from bromic add, etc. The salts of a ternary add 
ending in ous have the ous changed to tie, the salts 
from a ternary add with a name ending in ic have the 
ic changed to ate; thus: nitrous add produces nitrites, 
nitric add, nitrates; sulphurous add, sulphites, 
sulphuric add, sulphates; acetic add, acetates. 

Class exercise. — ^Write the equations showing 
how the following salts are formed: 

Sodium chlorid. 

Potassium bromid. 

Add sodium carbonate (bicarbonate of soda). 

Carbonate of soda. 

Magnesitun sulphate. 

Caldtun nitrate. 

Silver nitrate. 

Copper sulphate. 

Silver chlorid. 

Alkaloids and Their Salts 

The term alkaloid is derived from two Greek words 
signifying aJkali-Uke, and the name was first given to 
certain tmsaturated ammonia compounds of vegetable 
origin which, like the alkalies, combine with adds to 
form salts. 

It was once thought that alkaloids were formed only 
in plants, and when they werefoimd in a post-mortem 
examination it was decided that the individual had 
been poisoned by one of the poisonous alkaloids 

204 Physics and Chemistry 

derived from certain plants. It is now known, 
however, that' many bacteria produce alkaloids — 
ptomaines — ^in animal matter and that, after decompo- 
sition of the body has set in, alkaloids from this source 
may be fotmd in animal organs. Some of the impor- 
tant vegetable alkaloids are morphin, strychnin, 
quinin, caffein, nicotin. The majority of alkaloids 
are insoluble in water, which is one reason why their 
salts, and not the free alkaloids, are used as medicine. 
Morphin sulphate is made from the alkaloid morphin 
and sulphuric acid; strychnin sulphate, from the 
alkaloid strychnin and sulphuric acid; iron and 
strychnin citrate, from iron, strychnin, and citric add. 

Esters or Ethereal Salts 

How esters are formed. — ^Whenever an acid acts 
upon an alcohol, the acid is neutralized, wholly or in 
part, and a substance analogous to a salt is formed. 
Thus nitric acid and ethyl alcohol combine to form 
ethyl nitrate : 

Alcohol Nitric add Ethyl Nitrate Water 

CaHsOH + HNO3 - CaHsNOa + HaO 

and acetic acid and ethyl alcohol when combined 
form ethyl acetate, thus: 



Nature of simple fats. — Fats, which in chemistry 
are often spoken of as glycerids, are esters of glycerin 
or, as it is often called, glycerol, and certain organic 

Solutions. Acids. Bases and Salts 205 

acids, known as fatty adds. The most common 
of these acids are stearic, palmitic, oleic, and butyric. 
Stearic add is solid, palmitic semi-solid, and oleic 
and butyric are liquid at ordinary temperatures. 
The fats which they form are known as stearin, 
palmitin, olein, and butyrin. Glycerol, as shown on 
page 166, being a triatomic alcohol, has three OH radi- 
cals that can be replaced, and as fatty adds are mon- 
atomic, having only one replaceable hydrogen atom, 
a molecule of any one of the glycerids will consist 
of one molecule of glycerin and three of fatty acids. 
For example : 

Glycerol Stearic Acid Stearin Water 

C,H5(OH)3 + aCxSHjdOa - C3Hs(Ci8HjsOa)3 -f 3HaO 

Fats will be further discussed in the chapters de- 
voted to food. 


When fat is boiled with an alkali, the glycerin 
separates from the fatty adds and these unite with the 
alkali, thereby forming soap. The process is called 

Saponification occurs also in the animal body, in 
the small intestine under the influence of an enzyme 
produced in the pancreas and the alkaline salts of the 
bile and the intestinal and pancreatic juices. 

Soaps, bdng formed by the interaction of acids 
and a base, are analogous to salts. They will be 
further considered in Chapter XVI. 



City and Country Water Supplies — Ground Water — Springs- 
Wells — Classification of Foreign Substances Found in 
Water — Methods of Purifying Water — ^Hard and Soft 
Water — ^Methods of Softening Different Kinds of Hard 
Water — Objections to the Use of Hard Water. 

Water Supply 

The city water supply. — A city's water supply is 
brought by aqueducts or pipes from the nearest 
suitable river or lake. 

The water is forced into the pipes in different ways. 
If the city is near a hill on which there is a lake of 
sufficient size, at a high enough level to be above the 
houses in the city, the pipes are arranged so that the 
water will flow from the lake to the city by gravity, 
and the pressure upon it by that in the lake is sufficient 
to force it from the main pipes into the house pipes 
and, if desired, up to a height almost to the level of 
the water in the lake. 

When there is no available lake, a common method 

is to build a reservoir on some high land near the city 

and force the water, by means of pumps, from its 

lower plane to the reservoir, from which it flows to the 

city in the same way as from the lake. It is often 


Water 207 

necessary to btdld an aqueduct or to lay pipes between 
the site of the reservoir and the sotirce of the water 

In flat countries, the water is often pumped directly 
into the main pipes at the source of the supply. 

Houses built on heights are often provided with 
supply tanks or, as they are often called, standpipes. 
This is because it requires a great deal of presstire to 
raise a large supply of water to a high level, and if, 
when there is not much water being used, any excess 
supply passes into a reservoir from which it will flow 
when the amount being provided is insufiident, it 
minimizes the amount of pressure that will be neces- 
sary to provide an adequate supply at all times. 

The cotmtry water supply. — If people living in the 
cotmtry, away from the line of the main pipes, want 
running water in their houses, it must be pumped 
directly into the pipes supplying each house. One 
form of pump used for this purpose is the windmill 
pump, in which the mechanism that produces the 
pressure and suction necessary to raise the water is 
operated by the wheel at the top of the mill, and 
the wheel is driven by the wind. As a rule, the 
water is raised to a tank that is placed considerably 
higher than the faucets through which it is to flow 
and with which it is connected by pipes, and thus 
gravity and the pressure of the water in the tank are 
the two chief forces driving the water through the 
pipes. Pumps that are operated by motors driven 
by electrical power or power derived from the com- 
bustion of gasoline or other fuel are now much used 
instead of windmill pumps, when the expense of the 
fuel need not be considered. The water thus pumped 
into country houses may be obtained from a neigh- 

2o8 Physics and Chemistry 

boring lake or river, but where such does not exist a 
well is the usual source of supply. 

Ground water and wells. — In order to understand 
how wells and springs can exist, even in countries 
where rain does not fall for months at a time, it is 
necessary to know that the crust of the earth is com- 
posed of several different kinds of material, some of 
which are very porous and others perfectly impervious 
to water. In many places, these different substances 
have become deposited in uneven layers or strata 
with a varying depth of porous material at the top. 
The water of rain and melting snow sinks through the 
porous strata until it comes to a stratum of rock or 
thick hard clay that prevents its passage and then it 
flows or filters along the surface of this bed tmtil it 
either finds an outlet into a stream, lake, or other body 
of water or else it forces its way to the surface, thus 
giving rise to a spring; the common cause of this is 
obstruction to the flow of the water by a mass of 
impervious material. The water flowing in this way 
underground is called ground water and its surface 
is known as the ground-water level. The depth of 
the ground water will depend upon the amount of 
rain or snow that falls. 

In many parts of the world a non-porous stratum 
dips and then rises, forming underground valleys or 
basins, and the ground water flows into and fills 
them. These are known as artesian basins and a well 
cut into an artesian basin is known as an artesian 
well. If the non-porous material forming the basin 
is higher at one side than the other and extends near 
enough to the surface of the ground, the water will 
force an exit, thus giving rise to an artesian spring. 
The size of artesian basins varies greatly; some are 

Water 209 

qtiite small, but some are known to be at least a 
hundred miles in circumference and very deep. 

Wells can be made where there is no artesian basin, 
if there is a plentiful supply of ground water at a 
moderate depth. It is usual in making such wells to 
dig somewhat below the surface of the non-porous 

Driven wells are now more used than the old- 
fashioned open well. A driven well is made by insert- 
ing a pipe, that has perforations in its lower end, into 
the ground to such a depth that its point is embedded 
in the non-porotis stratum and its perforations are 
smrounded by ground water. The upper end of the 
pipe is connected to a pump. This may be a simple 
hand ptunp, or a mill-wheel pump, or a motor-driven 

Composition of water. — Pure water, as its chemical 
symbol — HaO — shows, is an oxid of hydrogen. Water 
is, however, seldom found ptire in nature for, being 
an excellent solvent, it dissolves and absorbs sub- 
stances from the soil and rocks through and over which 
it flows, and even rain water holds in solution sub- 
stances absorbed during its passage through the 

Foreign substances likely to be found in water. — 
These may be both organic and inorganic and they 
are usually considered under three headings: (i) 
Those likely to be injurious to the health; (2) those 
which render water unfit for cleansing and culinary 
purposes; (3) those used for medidnal purposes* 

It is the organic matter that has usually to be 
considered with relation to the prevention of disease; 
for when there is a large amount of organic matter 
present, there is usually a large number of bacteria, 

210 Physics and Chemistry 

and some of these may be pathogenic. As a nile, 
the inorganic matter in water has no harmful effect 
upon the health ; in fact, its presence in drinking water 
is usually considered an advantage, but, as will be 
seen later, its presence in more than small amounts in 
water used for cooking and cleaning, especially th^ 
latter, is a very great disadvantage. 

Bacteria in water. — The water of streams, rivers, 
lakes, ponds, and even that of oceans contains varying 
numbers of bacteria. Rain water may contain a very 
large number that it has gathered with the dust in its 
passage through the air. The water of wells varies 
very greatly in the number of bacteria it contains; 
that from a deep driven well may be practically bacteria 
free, since the ground through which the water has 
passed has acted as a filter, but shallow wells, espe- 
cially those situated near stables, privies, or where the 
drainage from sinks has access, are likely to be terribly 
contaminated. For the bacteria will be carried down 
and for some distance through the soil with the rain 
water and other fluid matter. 

Kinds of bacteria in water. — The number of different 
species of bacteria occurring in water is very large. 
Some varieties seem to live on the surface of water as 
their natural habitat, but, as far as is known, these 
are not pathogenic and neither are the several varieties 
of soil bacteria found in streams and near the borders 
of lakes and rivers, especially after rain. The patho- 
genic bacteria most frequently found in water are those 
which are habitants of the intestine, and they occur 
most frequently in water that receives sewage. Many 
epidemics of typhoid and cholera have been traced 
to such a source. 

Methods of purifying water.— Large supplies of 

Water 211 

water are usually purified either by storing the water 
in reservoirs or by filtration. 

Sedimentation. — When water is stored in reservoirs, 
the solid matter, including bacteria, tends to fall to the 
bottom, and even pathogenic bacteria soon die for 
there is nothing in the water to provide them with 
food. Also, the sun's rays, to which the water is 
exposed, acts as a disinfectant. This process of self- 
purification by sedimentation is constantly going on 
also in rivers and lakes, and it has been found that 
rivers into which the sewage of a city is emptied may 
be free from pathogenic bacteria several miles from 
the city though highly contaminated within a con- 
siderable radius of it. 

Filtration. — By filtration is meant the act or process 
of passing liquids through porous solids. This process 
is very frequently used for the purification of both 
large and small supplies of water. It is often used 
in the form of filter beds in connection with reservoirs. 

A variety of filter bed frequently used consists of 
successive layers of stones and of coarse and fine 
gravel and sand; the whole bed being i to 2 meters 
thick. Such a bed is often connected by pipes with a 

Another method of filtering frequently used is the 
passing of water through filters of unglazed porcelain, 
such as the Pasteur-Chamberland and the Berkfeld 
filters. These two varieties of filters are very effective, 
if they are frequently baked and kept clean, otherwise 
they are useless. Before purchasing unknown kinds 
of filters for household use it is well to have water 
which has been passed through them tested, for many 
filters offered for sale are quite worthless. 

Sterilization. — Though a good filter will remove 

212 Physics and Chemistry 

nearly all germs present in water, filtration is not to be 
depended upon to sterilize water that is to be used for 
surgical work or, when the presence of pathogenic 
bacteria is suspected, for drinking. To be sterilized, 
water boiled. 

Distillation. — Filtration and sterilization will rid 
water of bacteria, but neither process will remove the 
salts that are in solution in the water. If the water is 
distilled, however, nothing with a higher boiling 
point than water will distill over, and thus the salts 
will be left behind. For certain purposes, e, g., dis- 
solving drugs and chemicals, it is often necessary to 
use distilled water, since some of the salts present in 
undistilled water, may tmite with a drug or chemical 
and entirely change its nature. To prove this, add 
about ten drops of 2% silver-nitrate solution to some 
distilled water; do likewise to some tap water. The 
distilled water will remain dear, but the tap water 
usually becomes more or less cloudy, because water 
that has not been distilled generally contains some 
chlorides, and the following reaction occurs between 
the chlorid and nitrate salts : 

Silver nitrate Sodium chlorid Silver chlorid Sodium nitrate 
AgNOj + NaQ - AgCl + NaNO, 

The silver chlorid thus formed is insoluble in water, 
hence the clouding of the latter. It is for this reason 
that distilled water must be used for diluting the silver 
preparations often used for irrigations in the treat- 
ment of gonococci infections, silver chlorid being 
absolutely useless for the purpose. 

Experiment 21. Object : To demonstrate the effect 
of distillation as compared with filtration. 

Water 213 

Articles required: 2 stands; 2 flasks, one half full of 
water; a cork with a hole in the center; glass tubing 
bent as in Fig. 58; a dish with ice in it; wire gauze; a 

Fig. 58. Apparatus Aksangbd for DisntXATtON 


Btmsen burner; a funnel; filter paper; 2 beakers, 
one three quarters full of water; copper sulphate. 

Procedure: Color the water in the flask and that 
in the beaker an equally bright blue by the addition 
of some copper sulphate. Line the funnel with filter 
paper and suspend it above the empty beaker. Pour 
the copper sulphate solution into the funnel, slowly, 
80 as not to tear the paper, and allow it to filter. 

214 Physics and Chemistry 

Arrange the distilling apparatus as shown in Pig. 58. 
Allow the water to boil. After it has done so for some 
time, it will be noticed that the vapor is passing 
through the tube and condensing in the empty flask. 
(The ice surrounding this flask is used to hasten the 
condensation by lowering the temperature.) The 
distilled water, it will be noticed, is quite colorless, 
since nothing but the steam (HaO) passed into the 
flask, but the filtered water is about as bright a blue 
after, as before, filtration. 

Mineral water. — Water that flows through localities 
rich in mineral matter, such as lithia, sulphur, iron, 
will often contain enough of the minerals to flavor 
the water; such waters are called mineral waters. 
They are sometimes used for medicinal purposes. 
Their nature will be further discussed in Chapter 

Nature of the salts usually present in water. — 
The mineral substances that occur most frequently 
in water are sodium chlorid and different compounds 
of calcitmi and magnesitun. 

Hard and soft waters. — When soap is put into 
water part of the soap is decomposed, and if there are 
lime or magnesium salts in the water they will unite 
with the fatty acids set free by the decomposition 
and form a lime soap which, being insoluble in water, is 
precipitated in the form of a hard curd-like substance. 
The soap will form no lather and, consequently, will 
be of no use until enough has been used to combine 
with all the calcium or magnesium present. Waters 
which contain salts of lime or magnesium are, therefore, 
said to destroy soap and they are called hard waters; 
waters which do not contain these salts or only very 
small amounts of them are said to be soft. 

* ■ 

Water 215 

How hard water can be softened. — Sometimes 
the lime and magnesitmi in water are in the form 
of bicarbonates (page 202) and sometimes in 
the form 6f sulphates, and as both the bicar- 
bonates and sulphates of lime and magnesium 
are soluble in water they remain in solution. Con- 
sequently, in order to remove them and thereby 
soften the water, it is necessary to do something 
that will render the salts insoluble so that they will 
be precipitated. 

Water that contains bicarbonates can be softened 
by boiling because during the boiling the salts lose 
CO a and are changed from soluble bicarbonate salts 
to insoluble carbonates ; thus : 

Cddum Calcium 

bicarbonate carbonate 

Ca(HC03)a + boiling - CaCOj+COa+HaO 

The calcium carbonate thus formed, being insoluble 
in water, is precipitated and theprecipitate is deposited 
upon the floor and sides of the utensil in which the 
water is boiled. Water that can be softened by 
boiling (*. «., water the hardness of which is due to 
bicarbonates of lime or magnesitun) is called temporary 
hard water. 

Hardness due to sulphates of lime, etc., cannot 
be overcome by boiling, and the hardness therefore 
is spoken of as permanent, thottgh, in reality, it is not 
permanent, for the salts can be easily changed to 
insoluble ones, and thus precipitated, by the use of 
sodium carbonate, borax, ammonia, and similar 
substances. When sodium carbonate is tised the 
following reaction takes place: 

2i6 Ph3rsics and Chemistry 

Calcittm Sodium Calcium Sodium 

sulphate carbonate carbonate sulphate 

CaS04 + NaaCOj - CaCOs + NaaS04 

The caldtun carbonate thtis formed, being insoluble, 
is precipitated; the sodium sulphate, being soluble, 
remains in the water, but it has not the objectionable 
qualities of the caldtun sulphate. 

Temporary hardness can be rectified in the same 
way as permanent, as well as by boiling; thus: 

Ca(HC03)a + NaaCOj - CaCO^ + aNaHCO^ 

The softening of water for use in laundries. — 

Carbonate of soda is the agent usually used to soften 
water in laundries for the general washing, and if 
the soda is dissolved before being allowed to come in 
contact with the clothes and no more used than re* 
quired to combine with the salts present in the water, it 
will do some fabrics no harm, but, if the soda is added 
to the clothes in solid form or in such amount that 
some of it remains uncombined in the water, it will 
adhere to the clothing and, as will be seen in Chapter 
XVII., this weakens and soon destroys the fabric. 

Ammonia, though too expensive for general use, is 
often employed to soften water for the washing of 
fine fabrics, for, as it is volatile at ordinary tempera- 
ttures, even if it is used in excess, it does not remain 
in the meshes of the fabric and, therefore, it is much 
less likely to injure material than soda. Borax, also, 
injures fabric less than soda. 
Objections to the use of soap for softening water. — 
i Water can of course be softened without the addition 

of an alkali, if a large amount of soap is used, but 
there are two great objections to this : (i) the insoluble 

Water 217 

calcium soap that is formed adheres to the material 
being washed and discolors it; (2) a much larger 
quantity of soap must be used than of soda and the 
soap is more expensive than soda. It has been 
estimated that it requires from 2 to 2H ounces of soap 
for every gallon of water that has one degree of hard- 
ness' and that about .75 grams of soda will be the 
equivalent of this amount of soap. As water fre- 
quently has from 5 to 10 degrees of hardness and soda 
is usually only about one-third the price of laundry 
soap, it will be seen that if large quantities of water 
are used the difference in cost will be considerable. 

Softening of municipal water supplies. — Municipal 
water supplies in districts where the water is unusually 
hard, are often softened by adding lime to the water. 
How it does so can be seen in the following equation : 

Caldum Calcium 


bicarbonate hydroxid 



Ca(HC03)a + Ca(OH)a 

- CaCOa + 


Objections to the use of hard water. — Some 
important objections to the use of hard water other 
than the waste of soap and harm to clothing already 
referred to are: (i) The calcium soap, formed by 
the union of the fatty acids of the soap and the lime 
of the water, adheres to the sides of the sinks, utensils, 
etc., and reqtdres time and frequently the use of some 
substance in which calcium soap is soluble, as kerosene, 
to remove it; also, it helps to block the sewer pipes 
into which the water is emptied. (2) In cooking 

< A water is said to have one degree of hardness when it con- 
tains, per gallon, as much calcium as there is in one grain of 
calcium carbonate. It is said to have two de gr ees of hardness 
when it has twice this amount, and so on. 

2i8 Physics and Chemistry 

with hard water, a deposit of lime salts forms upon the 
food and often hardens it and, in the case of tea 
and broths, this prevents the withdrawal of the 
extractives. It has been found in some instances that, 
using the same amount of tea leaves, ten ounces 
of tea made with ffurly soft water is as strong 
as eighteen 
ounces brew- 
ed with hard 
water. Also, 
the h*me u- 
nites with the 
legumin :n 
peas and 
beans and 
makes it so 
hard and 
insoluble that 
the vegeta- 
bles cannot 
be softened. 
Pig. 59. Apparatus Arranged for ^3J The fur- 
ExPERiMEM aa. like coating 

which forms 
on boilers and kettles in which hard water is 
used is a very poor heat conductor; consequently, it 
takes longer to heat water in utensils so coated and this 
necessitates waste of fuel ; besides, there is the expense 
of having the boilers deaned to be considered and 
the damage to the boilers, etc.. by the overheating of 
the metal which occurs when the heat is not carried 
away from it by the water; then there is the danger of 
an explosion should the coating crack suddenly, for, 
in such case, there will be a sudden, forcible burst of a 

Water 219 

large quantity of s^eam which will be generate^ when 
the water comes in contact with the highly heated 

Experiment 22. Object: To show differences in 
hard waters. 

Articles required: Apparatus for generating CO 3 
— viz., a flask, a thistle tube, a cork with two holes in 
it, a piece of glass tubing bent as in Fig. 60; — nitric 
acid; calcium carbonate; calcium sulphate; lime 
water; distilled water; 2 beakers. 

Procedure : (a) Arrange the apparatus for generating 
CO 2 as in Fig. 59, put about 30 grams of caldum 
carbonate into the flask, place the free end of the tube 
in a beaker half full of lime water; pour some nitric 
acid, slowly, through the thistle tube. The following 
reaction then occurs: 

Calcium Nitric 


carbonate acid 


L CaCOs + 2HNO3 

COa+HaO + Ca(NO,)a 

The CO a passes into the lime water [Ca (OH) a]. 
What is the white precipitate? Write the equation. 
Let the CO a continue to flow into the lime water 
until the latter becomes perfectly dear. Why does 
it become dear? 

Write the equation. 

(6) Prepare permanent hard water by dissolving 
0.1 gram of caldum sulphate (plaster) in 500 c. c. of 
distilled water; generate CO a as in (a). Why are the 
results not the same? 

Experiment 23. Object: To show some methods 
of softening water and of estimating the amount of 
soda necessary to use for the purpose. 
• Artides required: Soap solution made by shaving 

220 Physics and Chemistry ' 

50 grams of white Castile soap, dissolving it in i liter 
of hot water and filtering it ; 2 graduated c. c. measures ; 
2 small flasks or bottles; calcium sulphate; distilled 
water; tap water that has been boiled for 15 minutes 
or more, and some that has not been boiled. 

(a) Pour about 100 c. c. of the unboiled tap water 
into a small flask, add some soap solution, i c. c. at a 
time, and, between each addition of soap, shake the 
bottle and let it stand for one minute. Do this 
until a lather that will persist for one minute is formed. 
Note the quantity of soap that is used before this 

Repeat the experiment with some of the boiled 
water and notice the difference in the quantity of 
soap used. 

Experiment 24. Object : To estimate the amount 
of soda that it will be necessary to use to soften water. 

Procedure: Add: (i) a few drops of saturated 
solution of sodium carbonate (20%) to 100 c. c. of the 
unboiled water, or, if the water is not hard, water in 
which calcium sulphate has been dissolved, as in 
Experiment 23; and (2) i c. c. of soap solution; 
shake the flask and let it stand for one minute as in 
Experiment 23. If a lather is not formed, take more 
water, and add a slightly larger amount of the soda 
solution, and repeat the procedures. Fresh water 
must be taken for each trial as the soap that is used 
would assist in the softening. 

If the quantity of soda necessary to use to soften 
100 c. c. of water is known it will be an easy matter 
to reckon the amount needed for any ntunber of 

Anyone having the supervision of a laundry should 
know just how much soda per gallon of the water 

Water 221 

used in their laundry is required to produce a soap- 
suds, without waste of soap, and how many gallons 
of water is used in their washers. Knowing this, it 
is an easy matter to estimate the quantity of soda 
required and to regulate the amount used and thus 
prevent unnecessary destruction of clothing. 

Examples of fhe Different Ways in which Water is 

Held in Combination 

Water of crystallization. — Certain solids, when 
dissolved in water, will, if the resulting solution is 
allowed to evaporate, separate out in the form of 
crystals. Such crystals, when heated, will give up a 
definite amount of water and in so doing lose their 
crystalline character; thus showing that their crystal- 
line appearance was due to water. The water which 
enters into combination with solids in this way is 
spoken of as the water of crystallization. 

Crystals which do not give up water when heated 
— quartz, for instance — do not owe their crystalline 
character to water. 

Mechanically enclosed water. — Some crystals hold 
water mechanically enclosed and not in direct combi- 
nation. To see the difference of the manner in which 
the two kinds of crystals part with their water, per- 
form the following experiment: 

Experiment 25. Procedure: Place some crystals 
of copper sulphate in an evaporating dish and some 
sodium chlorld in another dish and heat both of 
these over Bunsen burners. The crackling sound 
that occurs when the sodium chlorid becomes hot is 
due to the bursting of the crystals as the water held 
within them is changed to steam and expands. Such 

222 Physics and Chemistry 

cr3rstals are said to decrepitate. The water in the 
soditim crystals is combined mechanically, that in 
the copper sulphate is water of crystallization. 

Examples of formttlae representing water of crys- 
tallization. — ^The amount of water that certain 
crystals hold mechanically is not alwa3rs the same» 
but the amount of water of crystallization is always 
definite for each substance that forms crystals in this 
way; e.g,^ copper sulphate and water combine in the 
ratio of i molecule of the copper sulphate to 5 mole- 
cules of water; therefore the formula for its crystals 
is CuSO^-sHaO. Calcium sulphate combines with 
water to form gypsum in the ratio of i part of the salt 
to 2 of water, therefore the formula for gypstun is 

Efflorescence. Deliquescence 

Some crystals give up their water of crj^tallization 
very readily, even exposure to the air resulting in 
such a loss. Such compounds are said to be efflores- 
cent. Other substances have exactly the opposite 
quality; they will, if exposed to the air, absorb moist- 
ure from it. Such compotmds are said to be delu- 

Experiment 26. Place some oystals of sodium 
sulphate in an evaporating dish; in another dish place 
caldtmi chlorid. Leave these exposed to the aJr for 
several hours and report the result. 

Because of its deliquescent property, calcium chlo- 
rid, in moist climates, is sometimes put, in open 
dishes, into cupboards where there are instnunents 
or other articles that are injured by moisture. 

Hydrated. Dehydrated* Anhydrous.— Hydrate 

Water 223 

and hydrated are other terms applied to hydroxids 
and to substances that contain water of crystalliza- 
tion, and the terms dehydrated and anhydrous are 
often applied to any substance from which water has 
been abstracted; e. g., anhydrous alcohol. 



Source and Composition of Some Common Determents — Nature 
and Origin of Material Used for Utensils and the Action of 
Cleansing Agents in Common Use on these and on Paint, 
Varnish, and Wax. 

Classification of substances used for cleaning. — 

According to the nature of their action, the majority 
of substances used for cleaning may be classified as 
solvents, saponifiers, and bleaching agents. Clean- 
ing is effected also by mechanical means; e. g., friction 
or rubbing, absorption and suction. 


By a solvent is meant a liquid that can dissolve 
and absorb matter of any kind. AU substances are 
not soluble in all kinds of liquids and there are some 
compounds that cannot be dissolved at ^U under 
ordinary conditions. To remove soiling matter that 
is not readily soluble, it is often necessary to add some- 
thing to it that will change it to a soluble substance; 
e. g,f the addition of an alkali to fat in order to sa- 
ponify it and thus make it soluble in water. 

Effect of the temperature of solvents upon sdling 


Chemistry of Cleaning 225 

matter. — Matter is usually more soluble in hot than 
in cold liquids. Protein matter (see page 277),howt 
ever, is an exception to this rule because heat coagu- 
lates protein; for example, it will be diflBcult to clean 
bottles and other utensils in which milk has stood if 
they are put into hot water before all residue of the 
milk has been removed by rinsing the utensils with 
cold water. Likewise, if woven fabrics, such as 
cotton, linen, etc., that are stained with matter con- 
taining protein — ^as blood — are put into hot water, 
the protein will become so hardened into the fiber of 
the material that it will be difficult to remove it. 
As there is always likely to be protein matter in the 
substance soiling clothing, bedding, and the like, 
such things are soaked in cold water before being 
subjected to hot water, and as there is usually fatty 
matter in such substance the soaking in cold water 
must be followed by washing in hot water — fat being 
insoluble in cold water — and the use of soap or an 
alkali will be necessary. 

Source, nature, and use of some common solvents. 
— ^Water is the solvent in most common use. Alcohol 
is often used as a solvent for the removal of stains 
made by drugs, many of these being soluble in alcohol 
but insoluble in water. Turpentine, a volatile oil 
obtained from certain species of pine, will dissolve 
paint, varnish, and, to a slight extent, fat ; it is therefore 
often used to remove stains made by such substances. 
Fat solvents frequently used are : ether, a very volatile, 
inflammable liquid obtained by the action of strong 
sulphuric add upon ethyl alcohol; benzene, a color- 
less, volatile, inflammable liquid obtained by distil- 
lation from coal tar; benzin, a volatile, inflammable 
distillate of petroleum; gasoline, which is similar to, 

226 Physics and Chemistry 

and derived from the same source as, benzin; carbon 
tetrachlorid, a non-inflammable coal tar product; 
organic acids, as citric acid, which is obtained from 
lemons, and oxalic add, which is made chiefly from 
wood by heating sawdust and shavings with caustic 
potash or soda. Ammonia will dissolve the oxids of 
copper and nickel and is therefore often added to 
polishes used for cleaning these metals. Kerosene 
or coal oil, a distillate of petroleum, will dissolve 
several of the metal oxids, especially that of iron, 
therefore it is much used to remove rust from iron; 
it will also dissolve the lime soap formed, as shown 
in Chapter XV., when soap is put into hard water. 
Oxalic acid is another oxid solvent and both it and 
kerosene act ajso, to some extent, by reduction — i, e,, 
uniting with oxygen and thus taking it away from 
another substance. 

Alkalies and Soaps 

Reason for use. — Pat is the most common constit- 
uent of soiling matter and thus one of the most neces- 
sary procedures in general cleaning is to render the 
fat soluble in water so that it can be washed away. 
Alkalies do this by saponification and soap has the 
same, but less pronounced, effect as the alkalies, 
because, when it is dissolved in water, some of its 
alkaline constituent is set free. Soap and soap pow- 
ders are more frequently used than the free alkalies 
for their action is sufficiently strong for ordinary 
purposes and they have not the harmful effect upon 
many substances that the stronger detergents have. 
Alkalies, however, are necessary for some purposes, 
as shown in the preceding chapter. 

Chemistry of Cleaning 227 

Nature and source oi fhe alkalies most frequently 
used for cleaning. — The alkalies in most common 
use as detergents are: Ammonia, borax, sodium and 
potassium compounds. 

Anunonia. — ^Ammonia water (NH^OH) can be 
made by, under spedal conditions, running ammonia 
gas (NH3) into water, but its common source is the 
ammoniacal liquor which is produced during the de- 
structive distillation of coal in the making of gas. 

Borax. — Borax is a compound of soditmi, oxygen, and 
boron — a non-metallic element that resembles silicon. 
Borax deposits occur in various parts of the world, 
principally in the deserts. Borax is much used, not 
only for cleaning, but also in many industries. It is 
too expensive to use for general laundry work and 
scouring, but it is used for cleaning material that 
would be injured by the stronger alkalies. 

Potassium and sodium carbonates. — The soft, 
light-weight, silver-white, metal elements, potassium 
and sodium, are never found free in nature, but their 
compounds are numerous and common. The com- 
pounds that are of special interest in connection 
with the study of detergents are the carbonates and 

Potash or potassium carbonate has been in use 
since early in the middle ages, when it was discovered 
that after wood was burned, certain soluble salts 
were found in the ashes which, if boiled in pots with 
water until the latter evaporated, left a solid resi- 
due that had cleaning properties. This residue was 
called pot-ashes. Later, it became known as potash^ 
lye, and potassium carbonate. Some of the potash 
used to-day is made in the old way, but its more com- 
mon sources are the refuse left in making beet sugar, 

228 Physics and Chemistry 

the grease that is taken from sheep's wool in the 
washing that precedes its being made into cloth, and 
natural deposits such as exist near Magdeburg, m 
Saxony. These deposits are thought to have been 
left after the evaporation of primeval seas. 

Sodium carbonate was, in early times, prepared 
from seaweeds, but during the French Revolution 
the supply of seaweed was hard to get in places where 
the soda was usually prepared and as, at that time, 
wood was the only source of potash, it was difficult to 
procure a sufficient quantity of these detergents to 
supply the demand. The Academy of Paris, there- 
fore, offered a prize of 25,000 livres for the discovery 
of a method of making sodium carbonate from sodium 
chlorid. In 1791, Le Blanc, a Frenchman, succeeded 
in doing this. He added sulphuric acid to sodium 
chlorid, thereby obtaining sodium sulphate, thus: 
2NaCl+H2S04 = NaaS04+HCl. He then reduced 
the sulphate to a sulphid by heating it with carbon, 
thus:Na,S04+2C = 2NaaS+2C0a, and, finally, by 
heating the sulphid with calcium carbonate, he got the 
desired compound: NaaS+CaC03 = NaaC03+CaS. 

Soditun carbonate can now be obtained by easier and 
cheaper methods than the Le Blanc process, but never- 
theless this is still extensively used in order to obtain 
the HCl, which is a by-product of the first reaction. 

Potassium and sodium hydrozid can be made as de- 
scribed on page 198, but, for commercial purposes, they 
are prepared from potassium and soditun carbonate. 
Some of the several methods used in their preparation 
depend upon electrolysis. The oldest method, which is 
still extensively used, consists in treating the carbonate 
with calcium hydroxid, thus : Na ,00 3 + Ca(OH) a « Ca- 

Chemistry of Cleaning 229 

Soaps. — Soaps are made by causing the interaction 
of a fat with an alkali. When this is done, the fat 
separates into its component parts — i.e., fatty adds 
and glycerin — and the adds unite with the alkali, 
thereby forming the soap. This interaction may be 
produced (i) by what is known as the cold process y in 
which the fat is combined with dther sodium or 
potassitun hydroxid and dther churned or subjected 
to heavy pressure ; (2) by boiling the fat with a strong 
solution of either sodium or potassitun hydroxid. 
Soap made by this process is in solution in the water 
and glycerin, but it may be salted out by the ad- 
dition of soditun chlorid to the solution, soap bdng 
insoluble in salt solutions. After the soap is re- 
moved, the glycerin can be freed from fordgn sub- 
stances. This is, in fact, the usual source of glycerin. 
Soap made by the cold process retains the glycerin in 
combination. Toilet soaps are often made in this 

Reasons for differences in soaps. — The various 
differences in soaps depend chiefly upon (i) which 
alkali is used; (2) the nature of the fat used; (3) the 
addition of extra substances to the soap; (4) faulty 
manufacture of the soap. 

Hard and soft soap. — Soaps made with sodium 
hydroxid are much harder than those made with 
potassium and are classed as hard soaps, while those 
made with potassium are called soft soaps. 

Fats of soap. — All kinds of fat are used for soap 
and various oils, e.g., fish oil, olive oil, cocoanut oil, 
and castor oil. Although, as stated in the preceding 
paragraph, soaps made with soda are harder than 
those containing potassium, the kind of fat used 
and the amount of water left in the soap cause con- 

230 Physics and Chemistry 

siderable variation in the degree of hardness of even 
the soda soaps; e, g.^ soaps made with olive and 
similar oils are softer and lather more easily than those 
for which tallow is used. 

Substances frequently added to soap. — Various 
substances, some of which are harmless and others 
very objectionable, are often added to soap. 

Some of the additions that, under ordinary cir- 
cumstances, are harmless are perfumes; medicinal 
substances — as tar and salicylic acid; emollients — 
as glycerin, almond oil, and oatmeal; disinfectants 
— as carbolic; such detergents as borax, kerosene, and 
naphtha. These detergents increase the cleansing 
value of soap for laundry purposes and, if not present 
in excess, do not injure fabrics. Other detergents 
sometimes added to soap are soditun and potassitun 
carbonate and rosin (the resinous substance that 
remains after the distillation of oil of turpentine from 
the fresh pitch of pine wood ; it is known also as colo- 
phony). The presence of these substances in soap 
that is used for rough cleaning is not a disadvantage, 
but, as will be seen in the experiments in Chapter 
XVII., even dilute alkaline solutions will injure silk 
and wool and they will also destroy paint and varnish, 
and solutions that are at all concentrated will injure 
some of the metals. Rosin, if present in more than 
very small amounts, will leave yellow spots on fabrics. 
For these reasons and, also, because sodium carbonate 
and potash are cheaper than even cheap soaps, it is 
generally considered better to buy pure soaps and, 
when required, add a stronger detergent to the water, 
or, for scrubbing, to use a scouring powder. 

Fillers. — By fillers are meant cheap substances 
with little or no detergent properties that are added 

Chemistry of Cleaning 231 

to soap in order to increase its weight and hardness. 
The substances most commonly used for the purpose 
are the sulphates of caldum and potassitun, silicates, 
and chalk. Naturally, fillers are objectionable, if 
for no other reason than that the buyer is pajdng for 
a substance that is valueless for the purpose for which 
it is bought; there is, however, another objection, 
viz., when such soaps are used for laundry purposes 
the fillers often leave an objectionable sand-like 
deposit in the clothes. 

Substances that may be present in soaps as the 
result of faulty manufacture. — Definite proportions 
of fat and alkali must be used in soap-making or there 
will be tmcombined in the soap some of whichever 
substance was present in excess. Also, the soap must 
be boiled the regulation time, if saponification is to 
be complete. Unless it is, there will be both free 
alkali and free fat in the soap. As already stated, a 
small amount of free alkali is not always objectionable, 
but free fat decidedly interferes with a soap's cleans- 
ing properties. 

Water in soap. — ^Well made soaps do not contain 
more than about 25 per cent, water, but the cheaper 
grades, especially those containing fillers, often have 
a much larger amount. Such soaps are comparatively 
soft and dissolve very rapidly in water; therefore, to 
prevent waste, they should be dried before use. This 
is done by exposing the soap to the air until it loses 
its moist appearance. 

Castile and olive oil soaps are made of either 
castor or olive oil and sodium hydroxid. 

Floating soaps are made by beating the hot soap 
before it solidifies and thus making it lighter by 
incorporating air. 

232 Physics and Chemistry 

Transparent soaps of good quality are made by 
dissolving soap in alcohol, filtering the resulting solu- 
tion, and allowing the alcohol to evaporate. The 
cheaper transparent soaps are generally made by a 
cold process and usually contain free alkali. 

Glycerin soaps are nearly always made by a cold 
process but do not necessarily contain free alkali, 
like the cheaper transparent soaps. 

Mottled soaps may owe their coloring to impurities, 
but that of the good grades is the result of the addi- 
tion of coloring matter that does not affect the quality 
of the soap. 

The so-called green soap, which is extensively used 
for cleaning the skin preparatory to disinfection, is 
made of potassitun hydroxid and linseed oil. 

The tincture of green soap is made by dissolving 
green soap in alcohol and adding oil of lavender 

Experiment 27. Object : To test for the presence of 
adulterants in soap. Articles required: Several sam- 
ples of soap; sulphuric acid; alcohol; acetic anhydrid. 

For each test, use both a pure soap and at least 
one soap known to contain the adulterant for which 
the lest is made. Compare all results with that ob- 
tained from the pure soap. 

Test for sodium and potassium carbonate. — In 
separate evaporating dishes, place some small, thin 
slices of each of the soaps to be tested. To each, add 
a little sulphuric acid. Effervescence shows the 
presence of excess of carbonates. 

Test for rosin.' — Dissolve the soaps in water; acid- 
ify the solution with sulphuric acid. Filter. Remove 

* Rosin is not considered an adulterant, if the soap is sold as a 
rosin soap. 

Chemistry of Cleaning 233 

the predpitate from the filter paper and dissolve it 
in acetic anhydrid. Add a few drops of this solution 
to about 2 c. c. of 50 per cent, sulphuric add. A 
violet color indicates the presence of rosin. 

Test for fillers. — Pure soaps are soluble in hot alco- 
hol; the substances used as fillers are not; therefore 
the test for fillers is to dissolve the soap in warm 
alcohol and filter the solutions. If fillers are pres- 
ent, an insoluble residue will remain on the filter 

Test for free alkali. — ^But a few small pieces of soap 
into a test tube with alcohol and shake the tube until 
the soap is dissolved, then add a few drops of phenol- 
phthalein. A pink color shows the presence of free 

Test for unsaponified fat. — Put a few thin, small 
pieces of soap into a test tube with either gasoline, 
ether, or benzene and shake the tube for some minutes ; 
any fat present will be dissolved by these solvents. 
Then filter the solution, put some of the filtrate in a 
watch crystal or Petri dish, and let this stand exposed 
to the air until the liquid has evaporated. If fat is 
present, it will remain in the dish. 

Scouring Powders 

The various scotiring powders consist chiefly of 
soap, soda, and, the majority of them, silica and other 
rough substances such as are used for soap fillers. 

Sapolio consists chiefiy of soap and sand. Its 
value as a detergent is dependent chiefly upon the 
friction it produces. 

These detergents are very effident cleansers, espe- 
cially such powders as Dutch cleq^nser and gold 

234 Physics and Chemistry 

dust, but they should not be used on stuf aces that 
are injured by alkalies or those that are easily 

Scooring Agents Other than Soaps and Alkalies 

Scouring agents that owe their cleansing properties 
to the friction they produce when rubbed upon a 
stuf ace are: (i) whiting and bonami, both of which 
are finely pulverized chalk, the latter being pressed 
into cakes; silica, an oxid of the non-metallic element 
silicon (the silver polish known as silicon contains 
silica compounds and whiting) ; (3) bath brick, a form 
of calcareous earth pressed into the form of a brick; 
it is used chiefly for cleaning steel knives; (4) rotten- 
stone, known also as Tripoli, after the country in 
which it was first found, a soft stone used for scouring 
and polishing metals; (5) powdered emery, a variety 
of corundum, a metal of extreme hardness; it is used 
for scouring the harder metals, as steel; (6) carborun- 
dum, a carbide of silicon that is even harder than 
corundtun. It is used for the same purposes as emery. 
It is made by heating coke and sand (which is an 
oxid of silicon) in an electric furnace. 

Bleaching Agents 

Nature of bleaching. — ^Bleaching signifies making 
white by removing color or dirt by the action of the sun's 
rays or by a chemical process. The chemical process 
may consist in: (i) The union of the bleaching agent 
with the coloring or staining matter and the con- 
sequent forming of a colorless compound or of a 
soluble one that can be easily removed. Sulphur 

Chemistry of Cleaning 235 

dioxid (SO a) and sulphurous acid' (HaSO,) (which is 
made by the chemical union of sulphur dioxid and 
water) act in this manner. (2) Reduction; i. e., the 
removal of oxygen from the staining agent thus chang- 
ing it to a colorless or a soluble substance; sulphurous 
add and oxalic add often remove stains in this way 
and cleansing pastes and liquids used for metals 
generally containing redudng agents. (3) The libera- 
tion of oxygen and the union of this element with 
the coloring matter thus oxidizing and, consequently, 
decomposing it. The oxidizing compounds used as 
bleaches may themselves contain the oxygen — e.g. 
potassium permanganate (KMnO^) and hydrogen 
peroxid (HaOa) — or they may act indirectly, — e. g,, 
chlorin, which is the prindpal oxidizing agent acting 
in this way, has a very strong affinity for hydrogen 
and unites with the hydrogen of steam, setting free 
the oxygen which, thereupon, unites with the coloring 
matter and oxidizes it. 

Chlorin also, as it is a very active element, some- 
times acts by uniting with substances in the coloring 
matter and forming colorless or soluble compounds. 

Chlorin compounds used for bleaching. — The em- 
ployment of dilorin in gaseous form for bleaching 
would be both inconvenient and dangerous; therefore, 
compounds which will part with their chlorin readily 
are used instead. One compound that is very gen- 
erally used both in factories, for the removal of the 
yellow hue characteristic of freshly woven cotton and 
linen fabrics, and in laundries, for the removal o^ dirt 
and stains, is chlorid of lime, known also as bleaching 

'The nsual method of obtaining and using sulphurous acid 
for this purpose is to hang the material, after wetting it, in a 
doset that can be sealed and bum sulphur in the closet. 

236 Physics and Chemistry 

powder. This is made by passing chlorin gas over 
moist slaked lime. As the gas passes over the lime 
it is absorbed by the latter. 

Though the use of a bleach in laundry work is not 
to be recommended, if used with care, a small amount 
of bleaching powder in solution in the water in which 
cotton and linen materials are washed; will not injure 
the fabric, but if solid particles of the powder come 
in contact with the material or if a concentrated solu- 
tion is used, or if the material is not well rinsed, so as 
to be absolutely freed from all trace of the bleach, the 
fibers of the fabric will be soon rotted. Therefore, 
to prevent damage to fabrics by the use of chlorid of 
lime two precautions should be taken: (i) the powder 
is to be thoroughly dissolved in water before use 
(about one pound of lime to 12 gallons of water); 
(2) a substance that will neutralize the action of the 
bleach should be added to the first rinsing water. 
Sodium thiosulphate, commonly known as hypostdphaU 
of soda is often used for the purpose, for it inter- 
acts with the chlorid of lime forming sodium hypo- 
chlorite and calcium stdphate both of which compounds 
will be removed from the material by second rinsing. 
Chlorin cannot, of course, be used for removing stains 
from colored material and it cannot be used for bleach- 
ing or cleaning silk and wool. See experiments in 
Chapter XVII. 

Sodium hypochlorite, known also as Labarrague's 
solution and JcmeUe water ^ is another common chlorin 
bleaching agent. This is somewhat more expensive 
than the bleaching powder, but it is often preferred 
to the latter for laundry purposes as it does not react 
with soap to produce an insoluble calcium soap as 
calcium chlorid does. The action of sodium hypo- 

Chemistry of Cleaning 237 

chlorite should be neutralized by the addition of some 
such substance as a dilute solution of hydrochloric 
add or oxalic acid to the first rinsing water. 

For the removal of certain stains (see page 267) 
sodium chlorid, water, and lemon juice are used. 
These act as follows : The citric add of the lemon juice 
unites with the sodium of the salt, setting free the 
chlorin, which, thereupon, unites with the hydrogen 
of the water, setting free the oxygen which unites 
with the staining agent and oxidizes it. This process, 
like many others, is hastened by exposing the stain, 
during the treatment, to the sun's rays. 


Material that will absorb readily, such as starch, 
shredded blotting-paper, and fuller's earth are often 
used, dther alone or in connection with other agents, 
for the removal of liquid staining matter. 

Fuller's earth, which is a form of day, is so called 
because used by fullers (certain cloth workers) to 
absorb the oil or grease with which woolen cloth is 
sometimes treated in the manufacturing process. 

After reading the foregoing pages, it will be realized 
that various adds and alkalies and, for cotton and 
linen materials, chlorin are, either alone or as con- 
stituents of compounds, the detergents in most com- 
mon use. It will be interesting, therefore, to test 
the action of these things on some of the materials 
used for ordinary household utensils and furnishings 
and for dothing; viz., metals, marble, porcelain, 
glass, paint, and cotton, linen, silk, and woolen fabrics, 
and to consider briefly the source and nature of these 

238 Physics and Chemistry 


Before testing the action of cleansing agents on 
metal, it will be well to consider the nature of the 
discoloration known as tarnish^ for this and» especially 
in the case of kitchen utensils, fat are usually the 
two most common soiling agents of metals and the 
ones that are most difficult to remove. 

Tarnish. — Tarnish of metals, except that of silver 
and one form of copper tarnish, is generally due to 
the union of oxygen with the metal. The majority 
of tarnishes are thus oxids of the metals. Nearly all 
metals form oxids when heated, but certain ones, 
notably iron and lead, do so rapidly at ordinary tem- 
peratures if there is moisture present. Under the 
same conditions, aluminium, zinc, and nickel tarnish 
slowly. Copper tarnishes very rapidly if heated, even 
slightly, and the CO a of the air, as wcdl as oxygen and 
moisture, is responsible for the reaction; thus, the 
common tarnish of copper is more often a carbonate 
than an oxid of copper. The tarnish of bronze and 
brass is similar to that of copper. Gold and platinum 
do not form oxids in the air. Tin and silver do so 
only at high temperatures, but the latter tarnishes 
very readily in the presence of sulphur. The usual 
tarnish of silver is therefore silver sulphid (AgaS). 

There is an important difference, easily perceived, 
between the oxid that forms on iron and on other 
metals; viz., iron oxid (FcaOj), known as rust, forms 
scales or granules which rub off, and thus a fresh sur- 
face is constantly exposed to the air and the metal 
may soon become much eroded. The tarnish that 
forms on the other metals, on the contrary, occurs as 
a thin film that adheres to the surface, dulling its 

Chemistry of Cleaning 2^g 

luster and causing discoloration, but, being adherent, 
it prevents air getting to the metal and its oxidation 
is thus soon stopped; consequently, the metals are 
not permanently injured. Rust on iron is partly 
ferric hydroxid [Fe(0H)3], because some moisture, 
the presence of which is necessary for the oxidation 
of iron at low temperatures, enters into the reaction. 

As will be seen in the descriptions of the metals, 
those which tarnish very readily, as iron and copper, 
are often protected from the air by coating them 
with a metal, lacquer, or other substance that does 
not tmite readily with oxygen. 

Requirements of cleansdng material for metals. — 
Since tarnish and fat are the two most common forms 
of soil on metal, something that will remove them is 
essential for an efficacious metal detergent. Acids 
and alkalies will, as previously stated, remove fat, and 
certain acids, partly by dissolving and partly by re- 
duction, will take off tarnish, but as will be seen in 
the experiment with metals neither acids nor alkalies 
can be used with all metals. The hydrocarbons, as 
kerosene and gasoline remove fat and some oxids. 
Whiting, silicon, and similar soft, but granular sub- 
stances, are valuable, for they help to provide the 
friction necessary to remove soil, and they, when metal 
is rubbed with soft material, stich as chamois, help 
to produce a thin film over the surface of the metal 
which reflects light and thus gives luster or polish. 

The majority of patented preparations consists of 
different combinations of substances here mentioned 
or similar ones, and good preparations contain the 
ingredients in proportions and combinations that 
frequent trials have shown to be most efficacious; 
therefore, though it costs somewhat more to buy the 

240 Physics and Chemistry 

combined ingredients, it is often advisable to do so. 
Preparations which contain acids should not be used 
on metals that are injured by adds and those con- 
taining alkalies on metals affected by alkalies. The 
presence of alkalies or acids in cleaning compounds 
can be determined by the litmus test. Of course, 
the acids, etc., likely to be present in cleaning pre- 
parations would not be as strong as those xised in 
experiment 28, and in such case the effect would not 
be as pronounced and might be visible only after 
repeated applications. Rough granular cleansing 
agents, as emery, should not be used on the softer 

Suitable detergents to use for the different metals 
will be mentioned in the paragraphs describing the 

Silicon and whiting are nearly always prepared for 
use by mixing the powder with water or dilute alcohol, 
and to get the best results from these and nearly all 
other kinds of cleansing pastes, the metal should be 
first washed with hot soapsuds, rinsed, dried, and 
the paste applied with a soft, clean cloth, allowed to 
dry, and then removed by rubbing with a soft, clean 
doth, or chamois skin. 

Experiment 28. Object: To study the effect of 
adds and alkalies on different metals. 

Material required: Small (about J^ inch) pieces 
of bright and tarnished metal; preferably, aluminium, 
copper, iron, zinc, and tin; an inorganic add, prefer- 
ably hydrochloric; an organic add such as acetic; 
sodium carbonate solution 10 per cent.; ammonia 
water; mercuric chlorid; evaporating dishes or test 
tubes; an iron stand; forceps. 

Procedure: Take three bright and three tarnished 

Chemistry of Cleaning 241 

pieces of each of the metals and put each i>iece into a 
separate evaporating dish or test tube. To a bright 
and to a tarnished piece of each metal add hydro- 
chloric add; to another piece of each metal, both 
bright and tarnished, add acetic add; to the third set 
add sodium carbonate solution. 

The interaction that takes place when some metals 
are treated with adds and alkalies is so great that 
visible results occur immediately; some metals are 
not acted upon at all by these substances and others 
are acted upon so slightly that a further test is neces- 
sary to see if any of the metal was dissolved. If 
it was, it will be in solution in the liquid, and the test 
will consist in adding something to the liquid that 
will, if the metal is present, combine with it and form 
a colored compound. It will be seen that there are 
some metals that, themsdves, are not affected by 
adds and alkalies and that have oxids that are soluble 
in dther or both such liquids. 

The test is as follows: After the metals have stood 
for a short time in the adds and alkalies, remove them 
with forceps and test the liquids, for iron, aluminium, 
and copper, by adding ammonia, and for tin by adding 
mercuric chlorid. 

If iron is present, a red color will develop. 

If altmiinium is present, a white predpitate will 

If copper is present, a blue color appears. 

If tin is present a white predpitate forms that 
turns black when the liquid is heated. 

What is formed by the action of hydrochloric add 
on aluminium? 

(N. B. Poods containing adds should not be put 
into utensils that are acted upon by adds.) 

242 Physics and Chemistry 

Occurrence of the metals. — ^The metals are usually 
found in nature in the form of oxids or of salts though 
a feWp notably gold, platinum, and copper, sometimes 
occur uncombined. The metal salts, as well as some 
other inorganic substances^ are called minerals, and 
minerals from which tiseful substances can be ex- 
tracted, espedally metals, are called ores. 

The metals most generally used for household 
utensils and hospital laboratory appliances are 
iron, zinc, nickel, tin, copper, aluminium, silver, and 

Varieties of iron. — ^The iron of commerce is never 
pure, but contains varying amounts of other elements, 
especially carbon, phosphorus, silicon, sulphur, and 
manganese. The percentage of these elements, es- 
pecially copper, present in iron changes its nature 
considerably, and the amount of carbon and the form 
in which it is present gives rise to three distinct 
varieties of iron which are known respectively as 
cast iron, wrought iron, and steel. 

Cast iron and pig iron are names given to the metal 
as it comes from the blast ftimace. This contains 
more carbon than the other varieties. It is hard and 
brittle and, therefore, cannot be forged or welded 
into shape, but must be melted and cast in molds. 
It has, compared to wrought iron, a low melting point ; 
i. e., 1 100^. Cast iron retains its heat better than 
other forms of the metal. It becomes, if frequently 
heated to redness and cooled suddenly, very brittle, as 
is demonstrated by the cracking of stove covers. If 
red-hot iron is covered, so that cooling takes place 
slowly, it will not become so brittle. 

Stoves, furnaces, and radiator pipes are made of 
cast iron. 

Chemistry of Cleaning 243 

Wrottght iron is made by btiming out some of the 
carbon, phosphorus, etc., from cast iron; thus it is a 
purer form of iron than the latter. It has a higher 
melting point than cast iron (1600^), but is not as 
hard and, consequently, it can be drawn out into wire, 
rolled into sheets, and wrought into various forms. 

Steely like wrought iron, is made by extracting most 
of the other elements from cast iron, but the process 
is carried out in a different way. Since the means of 
making steel at a reasonable price have been pro- 
vided, steel has taken the place of wrought iron for 
many purposes, for though, like the latter, it is, when 
heated, quite malleable and can thus be forged into 
shape, rolled into sheets, etc., it can be also cast in 
molds and it is much harder and stronger than 
wrought iron. Another exceedingly valuable prop- 
erty of steel is that it can be easily tempered; i, e,, 
made harder or softer as required. For example, if 
steel is heated to about 170^ C. and cooled suddenly, 
as by plunging it into very cold water, it becomes 
exceedingly hard, but, if it is heated to about 235^ C. 
and cooled slowly, it will be so pliable that watch- 
springs and fine wires can be made from it. The 
difference in temper is largely caused by differences 
produced in the nature of internal combination of the 
carbon by the different temperatures and method of 
cooling. In the softer steel, the greater part of the 
carbon is present in the form of graphite; in the harder 
steel, the carbon is in the form of a carbide. 

Galvanized iron is the name given to iron covered 
with zinc. It was so named after Galvani, the dis- 
coverer of the electric current, because, formerly, the 
zinc coating was obtained by means of electrolysis. 
At the present time, however, the more common 

244 Physics and Chemistry 

method is to dip the iron into molten zinc and then 
pass it between rollers. As seen in Experiment 28, 
when acids and zinc come in contact, the zinc is dis- 
solved and poisonous zinc salts are formed; therefore, 
galvanized iron cannot be used for culinary utensils, 
but as zinc seems to prevent iron rusting better than 
the majority of substances used for the purpose, 
galvanized iron is in great demand for out-of-door 

The enamel ware utensils in such common use for 
culinary utensils are made of iron covered with some 
form of glaze. The glaze is usually obtained by dip- 
ping the iron utensil into a molten solution of fusi- 
ble silicate (see page 253) and drying and hardening 
it in a furnace. 

Enamel is not affected by acids nor weak alkaline 
solutions; it is light in weight and easily cleaned. 
These qualities all enhance its value for culinary 
uses, but sudden cooling after heating, over-heating, 
as by leaving the utensil over the flame when it does 
not contain anything that will conduct the heat away, 
blows, scraping to remove matter that has dried upon 
the utensil, cleaning with strong alkalies, all tend to 
crack the enamel glaze and when this happens, the 
exposed iron rusts more easily than that which has 
not been so protected. 

The characteristics of iron that allow of its being 
used for the various household purposes to which it 
is put are: (i) its infusibility (i. e., it can be melted 
only at extremely high temperatures); (2) its light 
weight as compared with the majority of metals; 
(3) the readiness with which it radiates heat. Two 
characteristics of iron that are defects as far as such 
purposes are concerned are the manner in which it 

Chemistry of Cleaning 245 

reacts with adds and the ease with which it unites 
with oxygen and thus becomes rusty. Because of the 
chemical action that occurs when adds and iron come 
in contact, foods that contain adds should not be 
cooked in iron utensils unless they are protected with 
enamel or other substance that is not affected by 
adds, and only in such case should adds be used for 
cleaning ironware. To prevent iron rusting, it is 
necessary to keep it dry and clean. Highly polished 
steel or a well-blackened stove will not rust nearly as 
quickly as soiled or dull metal. 

Kerosene is one of the best substances to use to 
remove rust from iron. Stove blacking, the prindpal 
constituent of which is graphite, a form of carbon, is 
used for polishing stoves, stove-pipes, and the like. 
As steel is ver> hard, such substances as emery, car- 
borundum, and bath brick can be used for deaning 
and polishing it. AlkaHne solutions can be used for 
scouring galvanized iron, but only dilute ones should 
be used for enamel ware. Lemon juice, vinegar, and 
dilute oxalic add can be used for removing stains 
from enamd ware, but not from galvanized iron. A 
thin paste of whiting and kerosene is excellent for 
cleaning zinc and, consequently, galvanized iron. 

To prevent utensils, instruments, etc., made of any 
variety of iron rusting where they are stored, they am 
covered with some substance — as oil or vaseline— 
that will protect them from the air and, if they are 
not to be used for some time, they are wrapped in 
soft paper or other covering that will prevent the oil 
bdng removed or dust collecting upon it. 

Nickel is a somewhat rare metal element that is 
used prindpally as an alloy with, or as a covering for, 
other metals. It can be deposited upon the surface 

246 Physics and Chemistry 

of metals by electrolysis. It is often used in this way 
with iron, for it will take a high polish and it will pro- 
tect the iron from rust, for the tarnish that forms upon 
nickel, even at high temperatures, is very superficial. 
A paste made of whiting and either dilute ammonia, 
alcohol, or kerosene is suitable for cleaning. Very 
badly stained nickel can be cleaned by washing with: 
(i) a solution of one part sulphuric acid and 50 parts 
alcohol; (2) with alcohol. 

Pure tini known as block tin, is a soft white metal 
element with a silver-like appearance. It melts at a 
temperature of 228** G. It does not form oxids readily 
and is therefore often used to cover iron and other 
metals which do. The tin generally used for utensils, 
roofing, and similar purposes is known as tin plate and 
consists of iron covered with tin, the tin coating being 
applied by the same methods as is zinc in the manu- 
factiu-e of galvanized iron. The low melting point 
of tin is its objectionable quality for cooking purposes. 
If an empty tin utensil or one lined with tin is left 
over the flame even for a few minutes, the tin will be 

As seen by Experiment 28, pure tin is not acted upon 
by weak adds or alkalies, but it is by strong solutions; 
thus it can be used for cooking fruit and the like and 
it can be washed with weak sodium carbonate solu- 
tion; but only weak solutions of either acids or alka- 
lies should be used for cleaning it. Tin containing 
impurities is sometimes acted upon by acids and 
poisonous salts formed by the reaction. A soft paste 
of whiting and kerosene, plus rubbing, will both 
clean and polish tin. 

Copper is a strong, heavy metal, but, when highly 
heated, it becomes soft and malleable. It melts at 

Chemistry of Cleaning 247 

1084^. Next to silver, it is the best known conductor 
of electricity; therefore, as it is cheaper than silver, 
it is much used for electrical purposes. Copper is one 
of the best heat conductors and it does not radiate 
heat readily, but retains it much better than the 
majority of metals. These qualities make it a very 
good material for cooking utensils such as pots and 
saucepans, especially for the cooking of large qtianti- 
ties of food andwhen the utensils are subjected to hard 
usage, for copper is practically indestrucible. Unfor- 
tunately, it is heavy and hard to keep dean, and 
though, as shown in Experiment 28, bright copper is 
not acted upon by adds or alkalies, copper oxid and 
copper carbonate, popularly known as verdigris^ are 
soluble in adds and they interact with adds to produce 
poisonous salts. For this reason, copper cooking 
utensils, unless kept very dean, are dangerous to use. 
To obviate this danger, copper utensils are often 
lined with tin, but, as already stated, tin is likely to 
be mdted or removed by other means and the exposed 
copper tarnishes very readily and is exceedingly diffi- 
cult to keep clean. Copper utensils can, however, 
be retinned. 

Copper is extensively used for making alloys, i.V., 
combinations of metals. Some of the more important 
of these are: Brass, which consists of copper and zinc; 
bronze, which is copper, tin, and zinc; German silver, 
which is copper, zinc, and nickd; gun metal, which is 
copper and tin. 

The outer surfaces of copper appliances are some- 
times covered with lacquer, consisting, usually, of 
shellac, and sometimes a coloring substance dissolved 
in alcohol. Lacquer is spotted by water, and there- 
fore a lacquered surface should not be washed, but 

248 Physics and Chemistry 

sfaould be ktgt dean by nbbiiig witii a soft, dean^ 
dry doth. 

Both adds and alkalies can be used for deamng 
copper and solutions of both oxalic add and ammonia 
dther alone or in combination with sudi substances 
as whiting, silicon* and kerosene are much used; as 
are also putty powder, rottenstone, and various 
patented preparations. A hot solution of sodium 
chlorid in vinegar (i part of salt to 16 of vinegar) is 
very effectual in removing stains from both copper 
and brass. 

Alnmininm is a tin-white metal of very light wdght. 
On account of this latter quality and its nice appear- 
ance, aluminium is much used for cooking utensils. 
It has, however some disadvantages for cooking pur- 
poses, viz., it radiates heat so rapidly that food cooked 
in it takes longer to become hot than when cooked in 
utensils made of other metals, and it will not remain 
hot in aluminium utensils for any length of time after 
the latter are removed from the fire. Also aluminium 
is injured by both organic and inorganic adds, by 
alkalies and by salt solutions; therefore ndther fruit 
nor other add food nor salty food should be cooked 
in aluminium utensils, nor should milk be kept in 
them, in case it should sour. 

Altuninium is best cleaned with neutral soap and 
water. A paste made of whiting and very dilute 
ammonia can be used when necessary. Two patented 
preparations, the Universal Metal Polisher and Putz 
Pomade, have been found very effective in removing 
from operating-room utensils stains made with bi- 
chlorid and iodin and have not injured the metal. 
As aluminium is so easily injured by the common 
constituents of metal-deaning preparations, caution 

Chemistry of Cleaning 249 

must be observed in using those the effect of which 
is unknown. 

Silver is a heavy» rather soft» white metal, that can 
be highly polished. It is not affected by organic 
acids and does not oxidize at ordinary temperatures, 
but the presence of even very minute traces of sulphur, 
such as are usually present in the air, especially in the 
vicinity of places where gas is burned, will cause the 
silver to tarnish, for the sulphur will unite with it and 
form a thin film of silver sulphid (AgaS) over the 
surface. It is because of the sulphtir they contain 
that eggs discolor silver spoons and, for the same 
reason, woolen fabrics and material for the bleaching 
or dying of which sulphur has been used may cause 
a similar discoloration. It is therefore well, when 
storing silver articles, to coat them with vaseline and 
wrap them in soft tmbleached muslin or in tissue paper. 

Whiting, rouge, and silicon are all much used for 
removing tarnish from, and for polishing, silver. 
An effective substitute consists in boiling the articles 
to be cleaned in a solution of sodium chlorid and bi- 
carbonate of soda (one tablespoon of each of these 
salts to a quart of water) in a patented apparatus 
known as a sUver-^lean pan. The salts are decom- 
posed and the soda tmites with the sulphur forming a 
salt that is soluble in the water. After the silver has 
been boiled for three minutes, it is removed from the 
solution, rinsed in water, and dried with a clean, soft 
doth. In hotels and other places where a large num- 
ber of articles must be cleaned daily, the polishing is 
done by a polishing machine run by electricity, and 
sometimes especially large articles are cleaned by 
dipping them in hydrocyanic acid. The add unites 
with the sulphur of the tarnish forming a salt that is 

250 Physics and Chemistry 

soluble in the add. This is a very quick and effective 
method, but it must be carried out with caution and 
the fingers must not come in contact with the add for 
it is exceedingly poisonous. 

Lead is a heavy, lustrous metal that owes much of 
its usefulness to its softness and to the ease with 
which it is melted. It tarnishes readily and is acted 
upon by the majority of acids, except hydrochloric 
and sulphuric, forming salts that are injurious to 
health for, though pure lead is not poisonous, many 
of its salts and other compounds are. A common 
form of slow lead poisoning is that which painters 
often contract. The usual cause of this is taking 
their food in their hands while they are soiled with 
paint containing lead compounds. 

The majority of lead compounds are insoluble in 
pure water, but soluble in water containing carbon- 
ates and sulphates. Therefore, water containing 
such salts, after standing in lead pipes, may contain 
injurious lead compounds, but the danger, it is thought, 
has been overestimated, since, if such salts are present 
in water, they soon form a coating over the interior 
of the pipes. However, as lead pipes are much used 
in houses, it is a wise precaution, when the plumbing 
is new and when water has not been drawn for some 
time, as, for instance, when, a house has not been 
lived in for several weeks, to let water that is to be 
used for drinking or cooking flow for some minutes 
before use, so as to empty the pipes of that which has 
stood in them. 

An aUoy of lead and tin, known as solder^ that is 
easily melted, is much used for cementing severed 
metal surfaces together. 

Pewter is an alloy of tin and lead and therefore 

Chemistry of Cleaning 251 

acid food should not be put into pewter utensils nor 
should they be cleaned with add-containing substances. 
Platinum is a grayish-white metal of high luster. 
It is a good conductor of electricity. It is very mal- 
leable and ductile, but fusible only at extremely high 
temperatures. It is very inert (*. e., it does not 
combine readily with other elements) and there- 
fore it does not tarnish and is not attacked by many 
adds nor alkaline substances. These qualities make 
platinum of great value for utensils tised in elec- 
tricaly chemical, and bacteriological work. Platinum 
is acted upon by nitric add and by chlorin. 


Experiment 29. Object, to study the eflEect of 
adds and alkalies on marble. 

Material required: Powdered marble or caldum 
carbonate (CaC03), hydrochloric add, lemon juice, 
ammonia water, sodium carbonate solution 10 per 
cent., 6 test tubes. 

Procedure: Put a little caldum carbonate into 
each of the six test tubes and add to (i), hydrochloric 
add ; to (2), lemon juice, to (3) ammonia, to (4) sodiimi 
carbonate solution; to (5), water. Let the five test 
tubes stand. Watch results. To tube (6) add some 
hydrochloric add and, when action is well established, 
some ammonia water. 

It will be seen as the result of this experiment that 
marble is insoluble in water and alkaline solutions, 
but that it interacts with, and is dissolved by, adds, 
espedally n:iineral adds. Also that an alkali, by 
neutralizing the add, stops the reaction. Since add 
has this effect upon marble, if lemon juice, or other 

2S2 Iliysics and Chemistiy 

add, is spilled npon it, the suiface of the latter will 
be Toug^iened unless the action of acid is at once 
neutralized by the addition of ammoraa or other 
alkaline substance. Marble is best cleaned with hot 
soapsuds or alkaline solutions. Many stains can be 
removed by rubbing tiiem with NaQ or kerosene. 

Marble was formerly much used in kitchens and 
lavatories, but the ease with which it was affected by 
acids led to the exclusion of its use for many purposes 
as soon as the means of maldng suitable porcelains 
and cements were discovered. There are now a num- 
ber of cements and cement-like substances used as 
tiling, and in other form, for floors, table covers, sinks, 
etc., that are not affected by either adds, alkalies, or 
heat and that do not absorb grease — most important 
qualities to be considered in judging the value of such 
material for kitchen use. Tiling tinted gray, buff, or 
other dull hue is much better than white for floors 
and table tops, because (i) white shows every mark 
and (2), if the kitchen is as light as it should be, white 
causes a glare that is very trying for the eyes. 


Compomtion. — Glass consists of mixtures of differ- 
ent bases and various silicates (i. e,, salts of silidc 
add, an add that is obtained from silicon, a form of 

Crown glass, which is used for windows, consists 
of silicates of soda and lime; plate glass, also used for 
windows and for mirrors, consists of silicates of soda, 
lime» and potassium; fUnt glass, which, as it has a high 
refractive power, is much used for optical purposes, 
consists of potash and lead silicates; Bohemian glass 

Chemistry of Cleaning 253 

which, being very infusible, is much used for chemical 
purposes, is a silicate of potash and lime; the cheaper 
glasses, such as are used for bottles, consist of the 
same ingredients as Bohemian glass, but they contain 

Glass is made by fusing silica — ^in the form of sand 
or quartz — ^with the desired bases, at an exceedingly 
high temperatiure, for a nimiber of hours. The molten 
mass, when clear, is made into the desired shape, 
usually by blowing or pouring it into molds. It is 
then cooled rapidly, in order that it may retain its 
transparency, and afterward it is annealed, as this 
renders it less brittle. Annealing consists in heating 
the glass to a temperature just below its melting 
point and then allowing it to cool slowly. 

Opaque glass is made by adding some finely divided 
infusible matter to the molten glass before it is shaped. 
Colored glass is made by the addition of coloring 
matter — usually a mineral oxid — to the molten glass; 
«. g., a blue color is obtained by the use of an oxid of 
cobalt; a red color by the use of copper or gold oxid. 

Porcelain and Chinaware 

Porcelain and chinaware consist of different silicates 
of aluminiiun. These occur in certain clays. For 
the finer porcelains, all impurities are removed. In 
the making of dishes, etc., the clay is moistened with 
water, molded into shape on a wheel, and heated in 
a furnace to a strong red heat. Large portions of the 
silicates in the clay used are infusible, but some are 
fusible, and these, while the articles are in the ftimace, 
melt, and this molten naatter, spreading through the: 
mass, cements the infusible substances together. 

254 Physics and Chemistry 

When the articles are removed from the furnace, 
they are porous, and in order to render them imper- 
vious to liquids, they must be glazed. This is done 
by dipping them in a mixture of molten, fusible sili- 
cates and returning them to the furnace that the glaze 
may harden. The glaze is practically the same as 

Cleaning of glass and porcelain. — If hot alkaline 
solutions are used on glass and porcelain, some of the 
alkali combines with the silicates, and repeated treat- 
ment of this kind will diminish the luster of the glass 
or glaze; therefore, only neutral soaps or soap powders 
should be used for washing good glass and porcelain 
ware. This is true also of glazed or enamded sinks 
and utensils. Kerosene, benzene, and whiting can 
be used, and are usually very effectual for removing 
stains that soap will not eradicate. Glass and glaze 
are rather easily scratched, so that nothing rougher 
than whiting should be used. For cleaning windows, 
mirrors, and the like, a thin paste of whiting and 
water with, sometimes, a little soap is rubbed over 
the stuf ace of the glass ; the water is allowed to evapo- 
rate, and, afterwards, the dried whiting is rubbed off 
with a soft, clean, lintless doth. 

and Varnishes 

These substances serve two purposes: (i) they, 
except water paints, protect the surfaces they cover 
from the influence of air, moisture, etc. ; (2) they are 
used for decoration. 

Nature of paints. — Paints are classed as water and 
oil paints and the water paints used in masonry are 
x^fassed as whitewashes and kalsomines« 

Chemistry of Cleaning 255 

Whitewashes are usually either mixtures of water 
and lime, boiled soap and lime, or skimmed milk and 
lime, and, if colored, coloring matter. When a white- 
wash is spread upon a surface it loses water by evapo- 
ration and absorbs CO a* thereby becoming changed 
to chalk (CaCOj). 

Kalsomine consists of a finely ground chalk and 
coloring matter suspended in a warm solution of glue. 
It is applied while hot, and as it cools, it loses water 
by evaporation and becomes dry and hard. 

Since both whitewashes and kalsomines become dry 
by the loss of water, they will be dissolved by the 
addition of water. They cannot therefore be used on 
the exterior of buildings nor can surfaces covered with 
them be washed. Water paints, however, are cheaper 
than oil paints and are therefore often used for color- 
ing walls of new houses tor, as the plaster is apt to 
crack dining the first months following structure, 
due to shrinking of the wooden rafters, etc., the walls 
generally need to be repainted or papered in a year 
or two. 

Oil paints consist of coloring matter (which usually 
is composed of ground minerals), carbonate of lead 
(known also as white lead) , or zinc white, or both held 
in suspension in what is called a drying oU — ^linseed or 
poppy oils being the ones most commonly used. * 

The carbonate of lead and zinc white are bases 
and, when mixed with oil, they form a soap which, 
as sufficient oil is used for the purpose, is held in 
solution in the latter. 

The oils used are called drying oils because, espe- 
dally when spread out in a thin film, they unite with 
oxygen and, when oxidized, become dry and hard. 

Substances that will hasten the absorption of 

256 Physics and Chemistry 

oxygen — as compounds of manganese — are often 
added to paints to hasten the oxidation and, conse- 
quently, the drying. When used for this purpose, 
such substances are called driers. Sometimes, instead 
of using driers which act in this manner, matter that 
will readily part with its oxygen — as lead oxid — ^is 
used. Spirits of turpentine, called turps by painters, 
is sometimes added to paint to thin it or, especially 
in the first coat of paint applied to wood or plaster, 
to hasten the absorption by the surface upon which 
it is spread. 

Methods of cleaning painted suifaces. — ^As water 
paints are soluble in all liquids, including water, sur- 
faces covered with them cannot be washed, therefore 
dusting with a soft, dry cloth is the best means of 
cleaning them. Oil paints are insoluble in water, and 
surfaces covered with them can therefore be washed 
with warm water and neutral soap, or, with white 
paint, bonami can be used. (N. B. — ^Bonami and whit- 
ing should not be used on colored paints.) Alkalies 
unite with some coloring substances and thus cheap 
scouring soaps and other alkaline detergents should 
not be used. Neither should coarse, hard, cleansing 
agents be employed, for paint is easily scratched. 

Nature of varnishes. — ^Varnishes are usually classed 
as spirit varnishes and oil varnishes. 

spirit varnishes consist of gum resin, such as shellac, 
dissolved in alcohol; oil varnishes of fossil resin, such 
as amber, dissolved in hot linseed oil. When either 
form of varnish is spread over a surface, the solvent 
— ^the alcohol or oil — evaporates and the resin solidifies. 

Shellac is rather soft and is spotted by water, there- 
fore spirit varnishes are not suitable for surfaces 
exposed to weather or to rough usage. 

Chemistry of Cleaning 257 

Cleaning varnished snifaces. — Good oil varnish 
can be wiped with a soft, damp cloth, but the surface 
must be wiped dry, and water should not be allowed 
to get into seams of the woodwork. If the varnish is 
inferior, however, the use of a damp cloth will soon 
cause yellow or white spots to appear. A weak solu- 
tion of good Castile or other neutral soap can be used 
to remove grease stains if the soap is washed off with 
a cloth dampened in clean warm — never hot — ^water. 
After such treatment, a varnished surface should be 
rubbed with a soft doth moistened with a reliable 
varnish polish. Too much polish must not be used 
and the surface to which it is applied must be well 
rubbed, for such polishes nearly all contain some oily 
constituents and, if the surface is left wet, dust may 
collect and be difficult to remove. 

Both paint and varnish are to some extent soluble 
in alcohol, therefore if the latter is spilled on furni- 
ture it will cause spotting, unless its action is neu- 
tralized by pouring oil over it. This should be done 
before wiping off the alcohol. White spots on furni- 
ture, due to exposure to heat, may be removed by 
rubbing them with spirits of camphor, or equal parts 
of linseed oil and alcohol. 


Waxing is a very common way of treating floors. 
Before wax is applied to a new floor, the latter should 
be given two coats of a mixture of equal parts of pure 
linseed oil and ttupentine with sufficient japan to 
make the mixture harden overnight. This brings 
out the grain of the wood and prevents subsequent 
grease spots showing. The floor waxes commonly 


258 Physics and Chemistry 

sold are mixtures of beeswax, paraffin, and turpentine. 
Before applying the wax, it is, if necessary, thinned 
to the consistency of a paste with turpentine. It is 
most important not to put the wax on in a thick layer, 
for when this is done the wax takes a long time to 
dry thoroughly and it collects dust. After the wax 
is applied, it is left for about twelve hours to harden, 
and then a little more paste is rubbed over the floor 
with a soft doth. The turpentine in the paste dis- 
solves any surplus wax that may be on the floor and 
makes the coating more uniform. When the wax is 
perfectly dry, the floor is polished with a weighted 
brush and the rubbing should be done with the grain 
of the wood. 

For floors likely to be spotted with water, it has 
been recommended that they be saturated with paraffin 
by covering the floor with powdered paraffin, such as 
is scattered over the floor when preparing for danc- 
ing, and melting the paraffin with hot irons or to have 
the floor waxed in the usual manner and sprinkle 
powdered paraffin over it, and then, as in the ball- 
room, allow the feet of those passing over it to force 
the paraffin into the wood. This treatment gives the 
floor a hard, impervious surface, which will not be 
easily spotted with water. 

Cleaning waxed floors. — ^After a floor is properly 
waxed, the only treatment that it usually requires for 
some time is an occasional polish with a weighted 
brush. When the surface grows dull another thin 
application of wax can be made in the same manner 
as the previous one. If water is spilled, after it is 
dried, the subsequent spots can be removed by rub- 
bing them with wax and then with a warmed woolen 
doth and a weighted brush. Oil should never be put 

Chemistry of Cleaning 259 

on a waxed floor as it causes the wax to become dark 
and spotted. Ink stains can be usually removed by 
putting a little solution of oxalic add over the spots 
and allowing it to remain tmtil it dries ; the oxalic acid 
unites with the iron in the ink to form an oxalate of 
iron, which can be easily washed off. The subse- 
quent white spots can be obliterated by rubbing a 
little wax into them. There are some inks which are 
made from the aniline colors and do not contain iron, 
and to remove these and, also, grease spots, sodium 
carbonate can be used (except on oak floors, which 
are stained brown by alkalies). White spots caused 
by the soda must be treated as those due to other 



Classification and Origin of Textiles — ^Bffect of Detei^gents 6a 
Different Kinds of Textiles — Methods of Removing Stains— 
Textile Tests — Printing and Dyeing — Nature of Dyes — 
Fading of Colors. 

The variotis kinds of materials used for clothing, 
upholstery, and the like are classed as textiles. 

Source of textiles. — Textiles are made by spinning, 
weaving, and otherwise treating fibers which are ob- 
tained from animals, plants, and, in a few cases, 
inorganic matter. 

From fibers of animal origin are made wool, hair, 
and silk; the principal vegetable fibers are cotton, 
flax, jute, and hemp; the chief mineral fibers are 
asbestos, and the spun glass, silver, and other minerals 
classed as Unsds, 

Vegetable fibers consist mainly of cellulose. The 
cotton fibers from which cotton materials are made 
are procured from the cotton plant. Flax fibers, 
obtained from the plant of the same name, are, when 
woven, known as linen. 

The quality and nature of woolen materials depend 
both upon their source and the processes to which 
they are subjected in the course of manufacture. The 
wool of different animals varies greatly in strength, 


Textiles 261 

length, fineness, and softness and so does that of similar 
species of animals that are reared under di£Eerent 
conditions and in different climates. Also, the quality 
of wool taken from different parts of an animal varies 
very considerably. 

The chief difference between wool and hair is the 
greater fineness of the fiber of the former and its 
highly serrated surface. 

The fibers from which silk material is spun are pro- 
duced by silk worms, from liquid which they secrete, 
in much the same way as spiders spin their webs. 

Both silk and wool contain protein substances; this 
can be proved by Experiment 30. 

Experiment 30. Procedure: Dip some pieces of 
white (i) all wool material, (2) mixed wool apd cotton 
material, (3) silk, (4) linen, (5) cotton,into some Millon 
reagent (see page 284), and then allow them to dry. 
The wool and silk will assume the red color which 
always indicates the presence of protein (see page 284). 
In the mixed wool and cotton material the cotton 
threads can be easily discerned, for they remain un- 
colored. This is one of the tests used to discover if a 
material is all wool or a mixture of wool and plant 

Experiment 31. Object: To see if there is sulphur 
present in the different textiles. 

Procedure: Btuti a little of each kind of textile in 
a flame, notice the difference in the odor from the 
wool. Hold pieces of paper moistened with lead acet- 
ate solution in the smoke. Hydrogen stdphid (HaS) 
reacts with lead acetate to form lead sulphid (PbS) 
which is black. 

Wool and hair are the only textiles that contain 
sulphur as a part of their actual composition, but 


Physics and Chemistry 

stilphur may be present in new materials of other kinds 
for the bleaching or dyeing of which sulphur has been 

Ravel out threads of each kind of textile and 
examine them under the microscope. 

The cotton fibers, though orignally tubular, become 
flattened dtuing the manufacture of the textile and, 
under the microscope, show a characteristic twist 
with the ends gradually tapering to a point. 

Linen fibers, 
it will be seen, 
resemble cotton, 
but they are 
straighter and 
more tubular 
and they have 
slight serrated 
notches or joints 
along their walls 
which serve to 
hold the fibers together. These teeth in the notches 
are not so long as those in the wool fiber and thus, 
though linen shrinks, it does not do so to such an 
extent as wool. 

The wool fibers, it will be noticed, are marked by 
transverse serrated divisions. When woolen material 
is rubbed, or subjected to hot water or strong alkalies, 
these teeth-like processes become curled, knotted, or 
tangled together, and this causes shrinking of the 
material. If cotton fibers are mixed with the wool 
in a textile, there will be less shrinking. 

Silk fibers are perfectly smooth and when rubbed 
they slide over each other. This sometimes causes 
a slight shrinking in the width of silk textiles. 

Fig. 6o. (a) Cotton fiber, (b) Wool 
fiber, (c) Linen fiber. As they appear 
when viewed through the microscope. 

Textiles 263 

Mercerized textiles. — Mercerized materials were 
so called after a man named Mercer, who introduced 
the process. This consists in treating the fabrics with 
caustic soda or sulphuric add; the former being used 
for cottons and the latter for wools. This makes the 
fibers heavier and flatter and gives them a silky ap- 
pearance and feel. 

Artificial silks. — Various kinds of artificial silks are 
made from cellulose by different processes. They 
lack the tensile strength and elasticity of silk and thus 
do not wear as well. 

Asbestos is a silicate of magnesium and lime. It 
can be sptm into a fine thread and then woven into 
doth. It is incombustible. 

Experiment 32 . Object : To test the action of adds, 
alkalies, and chlorid of lime on different textiles. 

Procedure: Put small pieces of the different textiles 
into separate beakers containing: (i) concentrated 
oxalic add; (2) oxalic add 1%; (3) concentrated 
hydrochloric add; (4) hydrochloric add 5%; (5) hot 
sodium hydroxid solution 10%; (6) cold soditmi hy- 
droxid solution 10% ; (7) hot sodium carbonate solution 
10%; (8) cold sodiiun carbonate solution 10%; (9) 
a hot saturated solution of borax; (10) a dilute solu- 
tion of borax; (11) a hot dilute solution of ammonia; 
(12) a hot satturated solution of chlorid of lime; (13) 
a dilute solution (10%) of chlorid of lime; (14) dry 
chlorid of lime. Use colored pieces of material for 
the lime tests. 

Let the pieces of material remain in the solutions or, 
in 14, covered with the lime for half an hour, then 
remove them and cut each piece in half (be careful 
not to get those from the different solutions mixed) ; 
rinse one set of pieces thoroughly in hot water and 

264* Physics and Chemistry 

place them, and also those which were not rinsed, 
where they will dry. Note and record any changes 
that have occurred in the fabrics; ptdl the pieces of 
material and see if their fibers have been weakened. 

State which of the detergents can be used for each 
kind of material and in what strength. 

Why was the color not a£Eected by the dry lime? 

Cotton is not much affected by alkaline solutions, 
if the material is well rinsed, otherwise the alkali 
becomes concentrated as the water evaporates during 
drying and, as it acts for some time, it weakens the 
fibers of the material. 

Cold dilute add solutions do not injure cotton, if 
the material is well rinsed; strong solutions either cold 
or hot do, hot ones being more injurious than cold. 

The action of detergents and Reaches on linen is 
about the same as on cotton, but linen is more easily 
affected by alkalies. 

With the exception of nitric acid, dilute add solu- 
tions do not injure wool. Why does nitric add affect 
it? (See protein test, page 284.) A warm solution 
of sodium or potassitun hydroxid will dissolve wool ; 
the carbonates of these alkalies have not such an 
injurious effect, but they make it hard and harsh. 
Even weak solutions of chlorid bleaches injure wool. 

Experiment 33. Object: To test the effect of dry 
heat on wool. Pass a hot iron over a small piece of 
woolen material several times and note the result. 
Cover a similar piece of material with a piece of damp 
muslin, and pass the iron over it. Compare this 
piece with the other and with a piece that has not 
been pressed. 

The protein matter of wool contains considerable 
water which heat causes to evaporate, thereby caus- 

Textiles 265 

ing loss of luster and strength of the wool fibers. 
Why was the piece of material covered with the damp 
cloth not affected in the same way as that pressed 
without it? 

Silk is affected by the same substances as wool and 
in the same way except that it is not injured by moder- 
ately high degrees of heat and it is injured by adds. 

Some Ptactical Appiicati<m8 of Knowledge of Effect 
of AddSi Alkaliesi etc., on Textiles 

As the result of the foregoing experiments, it can 
be seen that weak soda solutions (the strength depend- 
ing upon the hardness of the water, see page 220) can 
be ttsed in washing cotton and linen materials, if the 
fabric is well rinsed, this care being especially impor- 
tant in the care of linen. Only weak borax solutions 
and neutral soaps should be used for woolen and silk 
materials. The reasons why the addition of an alkali 
to water used for laundry purposes is advisable were 
discussed in connection with hard water. 

Though it is better not to use bleaching agents in 
the laundry, weak solutions of such bleaches as chlorid 
of lime and Javelle water can be used for bleaching 
cotton and linen, if the precautions mentioned on page 
216 are taken, but neither of these substances should be 
used for wool or silk, or any kind of colored material. 

Woolen and silk materials should not be rubbed 
hard. Woolen material must not be exposed to a 
high temperature, therefore, it should be washed in 
warm, not hot, water and dried at a low temperature; 
it should not be dried in the driers. When pressing 
woolen goods, a damp doth should be put between 
the material and the iron. 

266 Physics and Chemistry 


Bluing is used instead of, or in addition to, bleach- 
ing, to renew the white color of fabrics that have ac- 
quired a yellowish hue. That it will do this is due 
to the fact that blue and yellow are complementary 
colors and when combined in proper proportions are 
seen as white. 

The blues in most common use are: (i) Ultranmrine, 
a prepared compound of the elements aluminium, 
soditun, silicon, sulphur, and oxygen; (2) various coal- 
tar products as indigo, indigo-carmine, and the alkali 
blues; (3) Prussian blue, acompotmdof iron, carbon, 
and nitrogen. Prussian blue is considerably cheaper 
than the others, but it is decomposed by soaps and 
alkalies and if any of these substances are left in the 
clothing, or when the goods are next washed, the blue 
will be decomposed and ferric hydroxid [Fe(0H)3] 
produced. This will cause yellow stains in the 

Experiment 34. Object: To discover if iron is 
present in blue. 

Procedture: Make a strong solution, — about a 
teaspoonf ul of liquid Prussian blue to a cup of water, 
— ^have two strips of white muslin cut from the same 
piece of material, dip one strip in the bltxing water, 
then dry it by pressing it with a hot iron. Compare 
the muslin thus treated with the other strip. If there 
was iron in the blue the blued strip will have yellow 
stains. To prove that this staining is due to ferric 
hydroxid, use a test for iron. A conmion test is: to 
pour a drop of (i) pure hydrochloric acid, (2) yellow 
prussiate of potash over the stain. If this has been 
caused by iron, a blue color will develop. 

Textiles 267 

The Removal of Stains from Textiles 

Some important things to remember in connec- 
tion with the removal of stains from woven fabrics 

(i) If the staining agent is allowed to become dry, 
it soaks into, and hardens in, the fibers, and it is then 
more diffictilt to remove. 

(2) Unless the staining agent is soluble in hot water, 
it will, probably, if put into hot water, be hardened 
by the heat. 

(3) When strong adds or alkalies are used to 
remove stains, they must be neutralized and the 
material thoroughly rinsed, or it will be destroyed. 

(4) When the detergent used acts by dissolving 
the staining matter (as when ether is used to dissolve 
fat stains), some absorbent material, as a loose pad of 
soft muslin, should be placed under the stained ma* 
terial so that the matter will be absorbed as quickly 
as it is dissolved, otherwise, it will spread and leave 
a mark. 

(5) When removing stains from colored materialt 
always try the reagent on a seam or other part that 
will not show ; for, as can be easily appreciated from 
what is said in the section on dyes, colors are affected 
in different ways by the various reagents. 

(6) Exposure to the sun's rays hastens such chemi- 
cal reactions as that which occurs when salt and lemon 
juice are used to remove a stain. 

(7) The sun is a powerful bleaching agent, conse- 
quently the whiteness of white fabrics will be increased 
by exposure to its rays, and the tint of colored ma- 
terial may be injtired ; the reason for this was given 
in Chapter VI. 

268 Physics and Chemistry 

Methods of Removing Stains 

Balsam of Peru stains. — Soak and wash the stained 
part in alcohol. 

Bichlorid stains. — Soak the stained part in a 34 per 
cent, solution of Javelle water for twelve hours. Then 
soak and wash it thoroughly in hot water. 

Blood stains. — If blood cannot be washed out with 
soap and tepid water, soak the stain in peroxid of 
hydrogen, or wash it in ammonia water. 

Coffee and chocolate stains. — These can be usually 
removed by washing them with hot water; if not, 
place the stain over a bowl containing boiling water, 
sprinkle the stain with borax, and wash it with hot 

Fruit stains. — These can be often removed in the 
same way as coffee; if this fails, use either of the 
following methods: (i) Rub the stain with a concen- 
trated solution of oxalic acid; then neutralize the 
acid with ammonia and wash as much of the material 
as was wet with the reagents in hot water. (2) Im- 
merse the stained part of the fabric in equal parts of 
boiling and Javelle water and, after a few minutes, 
wash it thoroughly in boiling water. Javelle water 
must not be used for silk or wool or colored material. 

Glue stains. — Apply vinegar to the spot with a 
piece of soft muslin until the stain is removed. 

Grass stains. — ^Wash the stained part of the mate- 
rial in either f els naphtha soap or anmaonia and water, 
ether, or alcohol. If no one of these is effectual, 
spread a paste made of f els naphtha soap and bicar- 
bonate of soda over the stain and allow it to remain 
for several hotu^, and then wash it off with hot water. 

Grease stains. — ^Wash the stained part with either 

Textiles 269 

vinegar, hot water a;cid soap, hot soda water, hot al- 
cohol, ether, benzene, carbona, or gasolene. Remem- 
ber the precautions given in section 6, page 267. 

Ink stains. — Stylographic and red inks can be gene- 
rally removed by washing with soap and tepid water, 
especially if the washing is done while the ink is still 
wet. Stains made with other inks can be usually 
removed with lemon juice, salt and water, or with 
oxalic add. To use lemon juice, soak the stained 
part in warm water until it is thoroughly moistened, 
then rub and cover the stain with salt and lemon juice 
and place the fabric where the stm will shine upon the 
stained portion. Make fresh applications of water, 
lemon juice, and salt when required. It may be 
necessary to continue the treatment for two or three 
hours, then wash the part with (i) ammonia, (2) hot 
water. Use oxalic acid as directed under fruit stains. 

lodin stains. — Soak the stain in either ammonia, 
ether, or chloroform. 

Iron rust. — Use either lemon juice, salt and water, 
or oxalic acid as directed for ink stains. 

Kerosene. — Soak the stain in hot water. and then 
cover it with a thick layer of moistened fuller's earth. 
Let this remain for several hours and then wash it oflE 
with hot water. 

Meat-juice stains. — Wash the stain with either 
peroxid or hydrogen or else with (i) cold water, (2) 
warm water and soapsuds. 

Medicines. — Either alcohol, ether, or ammonia 
will usually remove stains made with drugs. For 
drugs containing iron use the same reagents as for 
iron rust. 

Mildew. — Exposure to sunlight followed by hard 
brushing will sometimes remove mildew. If this 

270 Physics and Chemistry 

fails, soak, the stained part in lemon jtiice until it is 
thoroughly saturated and then place it in the sun- 
light. If this is not effectual, cover the stain with a 
paste made of one tablespoonful of powdered starch, 
one teaspoonful of salt, and the juice of one lemon. 
Allow this to remain for twenty-four hours. Repeat 
the application if necessary. Mildew is a species of 

I Paint. — Rub the stain with benzene, turpentine, 
chloroform, or naphtha. The two last named are best 
for delicate colors. Remember the precaution men- 
tioned in sections 4 and 5, page 267. 

Perspiration. — ^Wash the discolored part of the 
material with soapsuds and, while still covered with 
the suds, place the garment in the sunlight. 

Scorch. — Moisten the scorched material and hang 
it in the sunlight. 

Tea. — See coffee. 

Varnish. — Make repeated applications of alcohol, 
turpentine, chloroform, or vinegar. Chloroform can 
be used with the majority of colors except blue; use 
vinegar for blue. 

. TeztUe Tests 


Experiment 35. Object : To distinguish cotton from 
linen. Stain a small piece of the material to be 
tested with fuchine and then dip it into ammonia. 
Linen fibers will remain red, but cotton ones will part 
with the dye when wet with the ammonia. 

Experiment 36. Object : To distinguish cotton and 
linen fibers from wool. 

Procedure: Boil a small piece of the material to 
be tested in a 5% solution of sodium hj^droxid. Dip 

Textiles 271 

another piece Into a 5% sulphuric add solution and 
put the pieces where they will dry quickly. The cot- 
ton fibers are not affected by the alkali and the wool 
fibers are. The wool fibers are not affected by the 
add and the cotton fibers are carbonized. 

The Millon test (see Experiment 30) is another 
method of distinguishing between animal and plant 

Experiment 37. Object : To distinguish silk fibers 
from wool. 

Procedure: Place the fabric in cold concentrated 
hydrochloric add. Silk fibers will dissolve; wool will 
merdy swell. 

Dressing of Cotton and Linen Fabrics 

An important thing to consider in dedding the 
worth of cotton and linen materials is the amount of 
dressing substances that they contain. 

By dressing is meant such substances as starch, 
gum, dextrin, glycerin, and various mineral derivatives 
that are used in order to, in some way, improve the 
appearance of the material. When the dressing is 
applied to the warp, it is usually called sizing; when 
it is applied to the woven material, it is termed 
finishing. Some dressing is benefidal to many 
textiles, even certain woolen ones, but, when large 
amounts are used, it is generally to cover defects in the 

Experiment 38. Object : To detennine the amount 
of dressing in a fabric. 

If material contains a large amount of dressing, it 
will lose its stiffness when rubbed between the fingers. 
For this test, use some pieces of cotton and linen mate- 

272 Physics and Chemistry 

rial that will do so and some that are not much changed 
by rubbing, in order to compare the results. 

Procedure: Weigh the pieces of material and then 
boil them in a 3% solution of hydrochloric acid. 
Rinse them in water, each one separately, and test 
the water for starch with iodin. (See page 289.) If 
starch is present, in any of the pieces of material, 
boil those in which it is again. When they are all 
starch free, dry and weigh them. The difference in 
weight will show the amount of dressing that was 

Printing, Dyes, and Dyeing 

The difference between the dyeing and printing of 
fabrics. — By dyeing is meant the saturation of the fiber s 
of a textile with a coloring substance; by printing, the 
impression of a colored design upon a fabric. 

Printed materials can be tisually distinguished 
from dyed by examining the wrong side of the 
fabric, if the pattern does not show through, it is 

Material naay be dyed either before o^ after it is 

Dyes. — ^A few dyes are prepared from inorganic 
matter, notably, khaki, which is made by adding 
chrome alum to a solution of iron, but they are nearly 
all procured from organic matter. In the olden days, 
dyes were made principally from vegetable matter, 
and a few, as cochineal, from animal matter, but, at 
the present time, coal tar is their usual source. In 
fact, it has been estimated, that over fourteen thou- 
sand colors are secured directly or indirectly from 
coal tar. 

Textiles 273 

Coal-tar dyes are often spoken of as the aniline 
dyes, because the first ones obtained from this source 
were made from aniline — a coal-tar derivative — now, 
however, a large number are obtained from carbolic 
acid, naphthalene, anthracene, and various other 
products of coal tar. 

Coal-tar dyes vary greatly in their nature, some 
having acid and others basic properties as well as 
other different characteristics. 

Mordants and lakes. — On account of the differences 
in the nature of dyes and those of textiles, all fabrics 
will not be equally well dyed with the same kind of dye; 
e, g., the protein matter in silk and wool will unite 
with substances in some dyes that will find nothing 
to combine with in the cellulose fibers of textiles of 
vegetable origin. In such case what is known as a 
mordant is used. By a mordant is meant any sulh 
stance that wiU combine with some constituent of the 
textile or which can penetrate its fibers and which also 
has an affinity for the dyestuff so that it will unite with it 
and thus procure live saturation of the fibers with an 
insoluble colored substance. This insoluble compound 
formed by the use of mordants is called a lake. 

Permanence of dyes. — Even with the use of 
mordants, aU dyes will not be equally permanent, and 
their permanence or fastness will vary in different 

The more common auxiliary causes of change of 
color in material are washing, the action of the acids 
of perspiration, and exposure to the sun's rays. 

The following tests are ones that are frequently 
used to test the resistance of dyes to such things. 

Experiment 39. Object: To test the color fastness 
of materials. 


274 Physics and Chemistry 

Test for washing fastness. — Soak and rub a small 
piece of the material in boiling soap solution. Do this 
several times. If the color does not run and if com- 
parison with an unwashed piece of material shows 
that it has not faded, the color is fast to washing. 

Resistance to perspiration. — Soak a piece of the 
material to be tested in 30% acetic add that has been 
heated to about 99° F. and then dry it, without rins- 
ing, between parchment paper. When dry compare 
it with a piece of the material that has not been so 

Resistance to light. — Place the pieces of material 
to be tested where they will be in the direct sunlight 
a considerable portion of the time for a month. Coni- 
pare them daily with similar pieces that are not so 
exposed. Colors that will stand such exposure for a 
month are considered fast; those which have under- 
gone appreciable though not very great change, are 
said to be fairly fast; those which show considerable 
change in two weeks are classed as moderatdy fast^ 
and those which are much changed, os fleeting. 

The comparative permanence of the ftmdamental 
colors in different materials {9 about as follows: 

Brown lasts well in cotton materials, but is likely 
to fade in linen and woolens. 

Dark blue is generally a fast color in all the textiles, 
but light blue generally fades quickly. 

Black lasts well in wool and silk, but not in vege- 
table fibers. 

Red is fairly permanent in woolen and silk ma- 
terials, but only fairly so in others. 

Gray is fairly permanent in all materials. 

Pink fades soon, but usually does so unifonnly 
and becomes a pretty shade. 

Textiles 275 

Green cannot be depended upon except in high- 
priced woolens and silks. 

Lavender is likely to be a fleeting color in all 




Classification, Nature, and Uses of the Substances Composing^ 
Animal Bodies and Plants — Tests for Proteins, Starches, 
Sugars, Salts — Origin of Food Material. 

In order that the machinery of the human body 
(u c, the heart, lungs, muscles, etc.) may be kept at 
work, it must be provided with fuel and with matter 
containing the same elements as itself which its cells 
can utilize for their building and repair. The ele- 
ments that the body needs for these purposes are 
contained in many compounds that are very com- 
mon in nature, but almost the only combinations 
that the human body can utilize are those formed 
in certain plants and in some of the lower animals. 
Though the tissues of plants and of animals are 
so unlike in appearance, the compounds of which 
they are composed are so similar in their chemical 
composition that they, including those constituting 
the human body, are classified tmder the same 

Classification of the substances composiiig plants 
and animals. — The various substances that enter into 
the composition of both plants and animals are dassi- 


Chemical Constituents of Food 277 

fied as organic and inorganic. The organic compounds, 
are further classified as nitrogenous (those containing 
nitrogen) and non^niirogenous (those without nitro- 
gen). The majority of nitrogenous substances are 
known as proteins and the non-nitrogenous organic 
substances are classed as carbohydrates and fats. The 
inorganic constituents of plant and animal tissues are 
salts and water. 
Table showing classification : 


( Proteins and a few non- 
Nitrogenous < protein compounds that 

( contain nitrogen 

NoQ-nitrogenous \ 

( Carbohydrates 

^''^ {^2r 

Examples of proteins are: The substances in egg 
which solidify when heated; the substance in milk 
that forms as a scum when the latter is heated and 
that which clots or curds when rennin or acid is added 
to milk; the white substance which appears as a 
coating on meat when it is exposed to heat. 

Familiar examples of carbohydrates are starches 
and sugars. 


The proteins are indispensable constituents of 
animal and plant cells; without them all life would 

Composition of proteins. — Protein molecules have 
a very complex structtu-e, knowledge of which is still 

278 Physics and Chemistry 

very limited, though it has been greatly added to 
lately. Proteins consist of the elements carbon, 
hydrogen, nitrogen, oxygen, sulphur, and sometimes 
phosphorus and iron. The more complex proteins 
contain thousands of atoms of these elements. The 
non-mineral elements of protein molecules are* so 
combined that they form what are known as anhydrids 
of amino acids. These anhydrids are formed by 
reaction between the OH groups of two molecules of 
organic acid with a loss of water. 

acetic acid CH3.COO 

acetic acid CH3.CO 


->0 4" HaO 
OH CHj.dO 

acetic anhydrid 

Amino adds. — These differ from other organic 
acids chemically in that their hydrogen is replaced by 
what is known as amine or the amino group or radical, 
which is NHa. For example, acetic acid is repre- 
sented by the formula CH j CO a- H and amino acetic 
acid by the formula CH,COa. NHa. Amine is some* 
what similar to ammonia — NH3 — and ammonia is 
formed from it during the decay of protein-containing 

Classification of proteins. — ^A very large number of 
different amino adds have been obtained both by the 
decomposition of organic compounds and by S3mthesis, 
and as different kinds of proteins contain different 
ntmibers and kinds pf these adds it can be appredated 
that there is considerable variation in the nature of the 
protdn of different foods. 

Certain proteins, however, have similar characteris- 
tics and according to these they have been classified 
as follows: 

Chemical Constituents of Food 279 



Simple proteins * 




Alcohol solubles 













< Metaproteins 

(. Coagulated pxoteins 


Simple Proteins 

Simple proteins are those which, when digested or 
otherwise hydrolyzed,* yield only amino adds or their 

Albumins and globulins. — Proteins belonging to 
these two classes are found in many of the same 
substances. As a rule, however, there are more 
albtmiins than globulins in animal fluids, as blood, 
and more globulins in animal tissues and plants. 

The albumins and globulins have many characteris- 
tics in common. They are both colloidal and will not 
diffuse through animal membranes and, tmder the 
influence of heat, certain salts (as bichlorid of mercury, 
silver nitrate, etc.), and various other substances^ 

* By hydrolysis is meant, the spliUin^ of complex molecules due 
h Ikeir ahsorpiUm of water. 

28o Physics and Chemistry 

their molecules tend to aggregate together to form a 
coagulum. They are both soluble in dilute salt 
solutions, dilute adds and alkalies, but albumins are 
also soluble in distilled water and concentrated sodium 
chlorid solutions and globtdins are not. The classifica- 
tion of the simple proteins placed under these two 
headings was based largely upon these differences in 
their solubilities. 

The several different kinds of albumins and globu- 
lins are given different names. Thus, albumin in 
serous fluids and in blood is called serum-albumin; 
that in eggs, ova-albumin; that in milk, lact-albtunin; 
that in muscle tissue, myogen. The globulins of the 
blood are called fibrinogen and sertmi-globulin or 
paraglobulin; that in muscle tissue, myosin'; also 
there are a few albumins and various globulins in 
plants, but as their special names are not often used, 
they need not be given here. 

The glutemns and alcohol-soluble proteins. — 
The glutenins and the most common alcohol-soluble 
protein, gliadin, form the gluten of wheat flour, 
which is its principal nitrogenous constituent. Gluten 
is found also in other cereals, but, as will be seen later, 
that in the other cereals is not quite the same as that 
of wheat flour. 

Albuminoids. — These are protein substances ex- 
tracted from such matter as bone, cartilage, and 
similar substances. They form the basis of gelatin. 

' Myosin, it is thought, does not exist as such in the living 
muscle, but is formed there by coagulation after death. The 
change is thought to be similar to the transformation that occurs 
in fibrinogen when blood clots. Rigor mortis — the stiffening of 
the body after death — is due to the changes that occur in the 
proteins after death. 

Chemical Constituents of Food 281 

The composition of the albuminoids differs from that 
of the other simple proteins, and gelatin, though it 
contains nitrogen, cannot be used in the diet as a 
substitute for them, since it cannot be utilized in the 
body, as other proteins are, for the building of muscle 

Histones and protamines. — ^These two simple pro- 
teins are not common, they have been obtained from 
the blood corpuscles of some animals and from the 
spermatozoa of fish. 

Conjugated Proteins 

Conjugated proteins are those which have a mole- 
cule or molecules of matter other than mineral united 
to the protein molecule. 

Nucleoproteins. — ^These are compounds of simple 
proteins and nuclein or nucleic acid. They are con- 
tained in the nuclei of cells and are relatively abundant 
in such glandular tissues as the spleen, pancreas, 
and liver, the cells of such organs containing many 

Nucleic acid, on oxidation in the body, yields 
substances known as the purin bodies ^ e, g., uric acid. 
For this reason, foods containing a high per cent, of 
nucleoprotein are eliminated from the diet in diseases, 
such as gout, which are characterized by the presence 
in the system of a comparatively large amount of uric 

Glycoproteins. — ^These are proteins which contain a 
carbohydrate molecule attached to the protein. 
Mucin, which is a constituent of the secretions of 
certain glands and of the mucous membranes of the 
respiratory and alimentary tracts, is an example. 

282 Physics and Chemistry 

Phosphoproteins. — ^These are compounds of the 
protein molecule and some phosphorus-containing 
substance or substances. Caseinogen of milk (the 
protein that is clotted when rennin or add is added 
to milk) and vitellin, the principal protein of egg- 
yolk, are two of the most important proteins of this 

Hemoglobin. — ^This is a compound of a protein 
called globin and a pigment (coloring matter) called 
hematin that unites and parts with oxygen readily. 
Hemoglobin is the essential constituent of the red 
blood-corpusdes of the blood, for it is due to their 
hemoglobin that the corpuscles can fulfill their func- 
tion of carrying oxygen from the lungs to the tissues. 
Hemoglobin contains iron and this constituent is 
necessary both for its formation and functioning. 

Lecifhoproteins. — ^These are compounds of protein 
and lecithin, a peculiar phosphorized fat. They are 
contained in nerve tissue, in mucous membranes, and 
probably in small amounts in other tissues. Yolk of 
egg is the food material in which they are found in 
largest amounts. 

Derived Proteins 

Such proteins are derived from simple and conju- 
gated proteins as the result of digestion and they 
may be also obtained by boiling simple or conjugated 
proteins in add. 

The primary derivatives are those which have not 
undergone any great change from their original form. 
Secondary derivatives are those in which the change 
has been carried to a greater degree. They are not 
coagulated by heat. 

Chemical Constituents of Food 283 

Function of food proteins. — Protein food substances 
are oxidized in the body, consequently they yield 
heat and energy, but their special function is to pro- 
vide building and repair material for the proteins of 
the body. 

Non-protein nitrogenous compounds. — There are 
certain nitrogen-containing compounds in both plant 
and animal foods that are not proteins. They have 
little or no nutritive value, but they give flavor to 
the food and stimulate the secretion of the digestive 
juices. Examples of these compounds are the amids 
of plants and the extractives of meat. 

The amids are believed to be the form in which 
nitrogen compounds are transferred from one part 
of the plant to another. The extractives of meat are 
substances formed in the animal body in the course of 

Tests for Proteins 

Certain tests are often used to discover if protein 
substances are present in compounds. Some of these 
tests consist in adding something to the matter to be 
tested that will, if protein be present, tmite with it 
and form a colored compotmd. Others consist in the 
addition of a substance that will coagulate the protein 
if it be present, or in the application of heat, which 
will have a similar effect. As will be seen in the 
experiments connected with the study of digestion, 
derived proteins do not respond in the same manner 
as the undigested proteins to all of these tests. 

Three common tests which depend upon the forma- 
tion of colored substances are the Piotrowski, Rose, or 
biuret; the xanthoproteic; and the Millon. 

284 Physics and Chemistry' 

Methods of Pexforming Tests 

Biuret. To 3 c. c. of the solution to be tested (in a 
test tube) add an equal amount of sodium hydroxid 
and a drop of a 1% solution of copper sulphate. If 
protein is present, a violet or pink color is produced, 
which, depending upon the nature of the protein. 
See page 398. 

Xanthoproteic. To 5 c. c. of the solution to be tested 
add about one-third of its volume of strong nitric add. 
If protein is present, a white precipitate will form. 
Boil the solution for one minute; the precipitate will 
turn yellow and partly dissolve; cool and add enough 
anmionia to make the solution alkaline; an orange 
color indicates positively the presence of simple or 
conjugated proteins. I 

Millon. Treat 5 c. c. of the solution to be tested 
with half its volume of Millon*s reagent (see page 20), 
A white precipitate is formed. Boil the mixture. 
If protein is present, the precipitate turns brick red in 
color or disappears and leaves a red solution. 

Coagulation of Proteins 

The majority of proteins are coagulated by heat; 
important exceptions are albuminoids, the casein of 
milk, proteoses, and peptones. Heat is therefore 
sometimes used as a test for the presence of proteins in 
Hquids, especially tirine. When the heat test is used, 
a drop or two of dilute acetic add is usually added 
after the liquid has been heated, because it intensifies 
the coagulation and also dissolves earthy phosphates, 
which may also be present, and which are likewise 
predpitated by heat. 

Chemical Constituents of Food 285 

Dried protein matter is not coagulated as easily aa 
that containing water, and this fact has two important 
bearings on the destruction of bacteria, since heat 
kills bacteria by coagulating their protein constituents : 
(i) Dry heat causes evaporation of the moisture from 
bacteria and the soft matter surrounding them, which 
is one reason why it does not penetrate as thoroughly 
nor act as quickly nor at as low a temperature as 
moist heat. (2) Spores cont^n much less water than 
the rest of the bacterial protoplasm and are thus 
much more resistant to heat. 

Heat coagulation will be discussed farther in connec- 
tion with the chemistry of cooking. 

Proteins are coagulated also by: (i) the salts of 
heavy metals, as bichlorid of mercury, nitrate of 
silver, copper sulphate, lead acetate ; (2) strong solu- 
tions of alcohol (solutions of alcohol between 10 and 
50 per cent, will precipitate proteins, but they will 
noti as do stronger solutions, form an insoluble 
coagulum); (3) alkaloidal reagents, as potassium 
ferrocyanid; (4) tannic add and inorganic acids. 

It is due to their effect on proteins that bichlorid, 
silver nitrate, etc., act as poisons and as disinfectants, 
since coagulation of the protein of living organisms, 
be it of bacteria or human beings, will cause death. 
Bichlorid cannot be used for the disinfection of sub- 
stances containing much protein matter, because 
the coagulum that is formed with protein is not a 
disinfectant and it forms such a hard case around the 
bacteria that they are protected from the influence 
of the mercury. Alcohol 95 per cent, has no germi- 
cidal action but a 70 per cent, solution will destroy 
vegetative forms of bacteria in from fifteen to ten 
minutes or less. The failure of the 95 per cent, to 

286 Physics and Chemistry 

act as a disinfectant is due to the formation of 
a protecting envelope, by the coagulation of the 
outer protein substance of the genns through which 
the alcohol cannot pass to destroy their vital 

The difference of the nature of the coagulum pro- 
duced by different substances can be studied by 
combining the white of egg and about 300 c. c. water, 
putting about 5 c. c. of this solution into several test 
tubes, adding a few drops of a different coagulating 
reagent to each tube and carefully examining the 
comparative toughness and testing the solubility of 
the precipitates in water and dilute acid solutions. 

Iliough precipitation is often spoken of as coagula- 
tion, a precipitate that is readily dissolved is not a 
true coagulum. 

The clotting of milk and blood. — ^When milk is 
treated with rennin and kept at body tepiperature, a 
dot or curd is formed, due to the conversion of the 
soluble caseinogen of the milk into an insoluble pro- 
tein called casein. Likewise when blood is shed and, 
under some abnormal conditions, in the living blood- 
vessels, the soluble blood protein, fibrinogen, is changed 
to an insoluble protein called fibrin and forms a clot. 
This change in the fibrinogen is due to the action of 
a ferment called thrombin, which is formed from a 
substance called thrombokinase (that is liberated 
from the blood-platelets and leucocytes on their 
disintegration) by the influence of the calcium salts 
of the blood. 

The clotting of milk will be further referred to in 
connection with the chemistry of cooking. 

The clotting of milk and blood is often spoken of as 
coagukUian, but some authorities object to the latter 

Chemical Constituents of Food 287 

term being used for this reaction since it produces 
entirely new protein substances. 

The Carbohydntes 

Classification. — ^The carbohydrates are classified 
as follows: 

I Glucose or dextrose 
Fructose or levulose 

Disaccharids < Lactose 









Constituents. — The carbohydrates are composed of 
carbon, hydrogen, and oxygen. The proportions in 
which these elements exist in the molecules of the 
different carbohydrates are as follows: 

Monosaocharids — C6Hia06 
Disaccharids — CxaHaaOzx 
Polsrsaccharids — CeHzoOsx 

Polysacchaiids — Gr. poly ^ many; Lat. saccharum 
'^^ sugar. — The carbohydrates of this group are con- 
sidered chemically as being complexes of the simple 
sugars or monosaccharids, for though, up to this 
time, the chemist has not succeeded in building 
cellulose, starch, etc., from sugar, these polysaccharida 

288 Physics and Chemistry 

are made from sugar in plants, and starches are easily 
changed to sugar in the course of digestion and in other 
ways that will be discussed later. 


Cellulose is, next to water, the most abundant con- 
stituent of plants for it forms much of their frame- 
work. The nature of cellulose varies in different 
plants and in most plants at different stages of growth. 
Thus the cellulose walls that hold the starch grains 
of the potato are less fibrous than the stem of the 
celery plant, and that of the latter is less tough than 
the cellulose of the wood of trees. The cellulose of 
young plants is more tender than that of older ones, 
the cell walls of most plants becoming thicker and 
tougher as they grow, due to increase in the de- 
position of cellulose and decrease in the amount of 

Celluloses are insoluble in water, either hot or cold, 
and in weak adds and alkalies, but strong adds and 
alkalies hydrolyze them. When celluloses are partially 
hydrolyzed, they react to the iodin test in the same 
manner as the starches do. Nitric add converts cel- 
luloses into nitro-celluloses, which are the substances 
used as bases in the preparation of such matter as 
explosives, collodion, and nitro-glycerin. 

Digestibility of cellulose. — Some of the lower 
animals apparently digest cellulose quite readily, 
but, though the more tender forms are to a certain 
extent permeable to the digestive fluids of the human 
alimentary canal, all cellulose is very insoluble, and 
in man whatever digestion of this substance does 
take place occurs in the intestine, largely as the result 

Chemical Constituents of Food 289 

of bacterial action, and fatty adds seem to be the 
principal product yielded. Though a large portion 
of the cellulose of food may thus escape digestion, 
a certain amount of it is a valuble adjunct to the 
diet of normal individuals, except very young children, 
because it stimulates peristaltic action in the intes- 
tines and thus prevents constipation. 


Starch is the principal form in which plants store 
their food supply. It is stored more especially in the 
roots, tubers, fruit, and seeds. 

Properties of starch* — Starch is insoluble in water. 
When heated, starch grains swell and rupture and 
prolonged exposure to heat causes chemical changes 
which render them soluble. The substance thus 
produced is known as dextrin. If .heated with acid 
and as the result of digestion, starch is changed to 

When dry, starch will keep in good condition for 
a long time, but it is readily attacked by micro- 
organisms if it becomes moist, and in such case will 
mould or ferment and become sour. 

Starch is obtained chiefly from wheat, com, rice, 
and potatoes; and arrowroot, sago, and tapioca are 
nearly pure starch. 

Test for Starch 

A test very commonly used to detect the presence 

of starch in a substance is the iodin test. It is as 

follows: A drop of iodin solution, 3%, is added to 

the solution to be tested. If the material to be 


290 Physics and Chemistry 

tested is solid, it is boiled for a minute with water, 
so that it will be in solution, and cooled before the 
iodin is added. If starch is present, a blue color will 
develop, due to the formation of iodid of starch. 
(N. B. — The reaction will not take place properly If 
the material being tested is hot.) 


Occurrence. — Dextrin is only occasionally fotuid in 
imcooked foods. It is formed when starch is heated 
to about 200^ C. (the crust of bread is an example) 
and when starch is boiled. It is the first product 
formed in the digestion of starch. 

[Test for Dextrin 

The iodin test, as used for starch, is also fre- 
quently used to detect the presence of dextrin in 
a substance. If dextrin is present in the material 
tested, the iodin will turn either purple, red, or 
white. The reason for this difference in color is given 
on page 398. 


. Nature and occurrence. — Glycogen, known also as 
animal starch, is a white powder that is soluble in 
water. It is extracted from liver. It is formed 
in the animal body, in the liver, from glucose, and is 
stored in the liver and, to some extent, in the muscles, 
but that in the muscles is decomposed soon after death; 
therefore, liver is the only meat that contains any 
amount ot carbohydrate. Oysters and other shell<^ 

Chemical Constituents of Food 291 

fish, however, contain as much as 9 per cent, 


This is a soluble starch-like substance that is found 
dissolved in the sap of some plants, especially the 
Jerusalem artichoke. 


Pectin substances are related chemically to both 
starches and gums. It is thought that they are 
formed in plants by the combining of several simple 
carbohydrates. It is the pectin substances that, 
under conditions which will be discussed later (page 
362), allow of jellies being made from certain fruits 
without the aid of gelatin. The test for pectin will 
be found on page 362. 


These are various viscid substances contained 
in many plants and in the wood and bark of several 
trees. They have the same chemical composition as 
the other polysaccharids. 



The sugars belonging to this class are the sucroses, 
lactose, and maltose. 

The disaccharids were so called from the Gr. di^ 
double and Lat. saccharum^ sugar, because, when 

292 Physics and Chemistry 

hydrolyzed, one molectile of a disaccharid gives two 
molecules of simple sugars or monosacchari(te. 


The more common sucroses are cane sugar, beet 
sugar, and maple sugar. 

Sucrose is a common constituent of plants. It 
occurs in small qtiantities in several fruits, ustially in 
combination with dextrose and levulose, and in a few 
vegetables. It is found in largest amotmts in the 
sugar cane, beets, the maple tree, pineapple, and 
carrots. It is from the three plants mentioned first 
that it is usually extracted. 

Sucrose is easily hydrolyzed in digestion and by 
boiUng in water or other liquids, more especially acid 
solutions. When hydrolyzed every molecule of su- 
crose yields a moleaile of dextrose and a molecule of 
levulose. Sucrose can be changed to caramel by the 
application of dry heat. 

Test for Sucrose 

The presence of sucrose in food can be determined 
by boiling a few c. c. of a solution of the matter to be 
tested with an equal quantity of hydrochloric acid. 
If sucrose is present, a deep red color will develop. 


Lactose, known also as sugar of milk, occurs in the 
milk of all mammals. Experiments seem to show that 
it is made in the mammary glands from glucose which 
secretory cells of the glands take from the blood. 

Chemical Constituents of Food 293 

Lactose is easily changed to the monosaccharids 
glucose and galactose by heating it with adds, and 
in digestion. Lactose will reduce Fehling's solution, 
but it requires 0.68 gm. of lactose to reduce lo c. c. of 
Fehling's. As will be seen later (page 398) , one method 
of determining the nature of a sugar is to ascertain if 
it will reduce certain solutions and how much of the 
sugar is required to cause the reduction of a given 
amount of the solutions. 


Maltose or ntialt sugar is formed from starch by the 
action of diastatic enzymes (see page 389) that exist 
in certain plants. It is therefore an ingredient of 
germinating cereals, of malt and malt products, and in 
animals it is formed during digestion. It is easily 
changed to glucose by heating it with adds, by the 
action of yeast, and in digestion. 

Maltose is the prindpal constituent that the 
brewer extracts from malted grains for the making 
of beer, ale, etc. In the process to which it is subjected 
it is changed to glucose, and this is easily oxidized, 
thereby forming alcohol and, if the process is con- 
tinued, CO a and HaO. 


The monosaccharids were so named from the Gr. 
monos^one and Lat. saccharum^ sugar. 


Dextrose was so named from the Lat. dexter '^ 
right, because it turns polarized light to the right. IV 

294 Physics and Chemistry 

is known also as glucose, diabetic, and grape sugar. 
It is found in combination with other sugars, especially 
levulose, in many fruits and a few other plants. 

The disaccharids and starches are easily changed to 
glucose by boiling them with adds and much of the 
glucose sold is made from starch in this way. Glucose 
isonly about half as sweet as cane sugar. 

Normally, glucose is present in the blood in the 
proportion of o.i per cent. This will be further dis- 
cussed in the sections on digestion and metabolism, 


Levulose (Lat. IcBvus^left) so called because it 
turns polarized light to the left, is known also as 
fructose and fruit sugar. It is an isomer of glucose — 
{. e., it contains the same elements in the same propor- 
tions as glucose, but in a different combination. The 
way in which the chemist demonstrates this difference 
of arrangement is shown on page 157. Levulose is 
not found in the blood, other than that of the portal 
vein, being changed into glycogen in the liver. It is 
found associated with glucose in fruit and in honey. 


This monosaccharid is not found in nature, it is 
formed from lactose by hydrolysis. 

Tests for Monosaccharids 

It is often important to discover if glucose is present 
in a food or other matter — e.g., the urine. The Peh- 
ling's test is one very commonly used for this purpose. 

Chemical Constituents of Food 295 

FehBng's test. — ^Take eqtial parts of Pehling's solu- 
tions I and 2 (see page 19), about 2 c. c. of each. Boil' 
this, if it remains dear, add an equal amotint of the 
solution to be tested, and boil. If glucose is present, a 
red precipitate will form ; because the glucose by taking 
away oxygen from the cupric hydroxid changes it to 
the red insoluble cuprous oxid. 

Other conmion tests are as follows: 

Baxfoed's test — Boil a few c. c. of freshly prepared 
Barfoed's reagent and add, while the solution boils, 
drop by drop, some of the solution to be tested. If 
glucose is present, a red precipitate of cuprous oxid is 
formed, either at once or on standing. 

Benedict's test — To 5 c. c. of Benedict's reagent, in 
a test tube, add about 8 drops of the solution to be 
tested. Boil the solution for about 2 minutes and then 
allow it to cool. If glucose is present, the solution 
will become filled with a precipitate either red, yellow, 
or green in color, depending upon the concentration 
of the sugar. 

These tests aU depend upon the fact that the 
monosaccharids have the same chemical construction 
as the aldehydes and like them will reduce such 
substances as the reagents used in these tests, thereby 
changing certain soluble substances into insoluble 
ones with the colors mentioned. 

Moore's test — ^Boil the solution to be tested with a 
little sodium hydroxid. If glucose is present, the 
solution will turn yellow, due to the formation of 
caramel as the result of the hot alkaline on the glucose. 

Fermentation test* — Fill the long arm of a f ermenta- 

'This precautioa is necessary because the solution often 
deteriorates soon after It is prepared. If, when boiled, it becomes 
dottdy, it Is not fit to use* 

296 Physics and Chemistry 

tion tube (page 19) with the solution to be tested 
and add a small piece of yeast cake. The liberation 
of gas (carbon dioxid), as described on page 359, 
indicates the presence of sugar. 

Fats and Oils 

As stated in Chapter XIV., fats are esters of glycerin 
and fatty adds. 

They are classified as: 


Fixed oils 

Essential or volatile oils. 

The essential or volatile oils. — These oils are so 
called because they are volatilized at ordinary tem- 
peratures. If a little volatile oil and a little fixed 
oil are dropped on paper, the latter will leave a 
mark, but the former, being volatile, will quickly 

The essential oils vary considerably in their com- 
position, but the majority of them consist chiefly of 
such substances as the terpenes, or camphors, or 
similar substances. Thjsy are all entirely different 
in their chemical composition from the fixed oils. 

The essential oils are the important constituents of 
spices and similar substances; it being to their oils 
that these things owe their flavor. As the oils are 
volatile, they can be extracted from the plants con- 
taining thfim by distillation. Oil of cloves, oil of 
peppermint, and other oils used for flavoring are 
obtained in this way. 

Nature of the fixed oils aiid fats. — The fixed oils 
and fats are chemically alike and their classification is 
based on their physical condition; fats being solid at 

Chemical Constituents of Food 297 

ordinary temperatures and oils liqtdd, but a fat when 
melted is called an oil, and an oil when solidified a fat. 

Fixed oils and fats are derived from both plants and 
animals. They are composed of three or more simple 
fats. The molecules of the simple fats, it will be 
remembered, consist of three molecules of fatty add 
and one molecule of glycerin. 

The most common simple fats are stearin, palmitin, 
and olein. The first two mentioned are solid at 
ordinary temperatures, and olein is liquid, therefore 
the greater the amount of olein in a fat, the lower 
its melting point. The fats of beef and mutton, for 
example, contain a larger per cent, of stearin than lard 
and butter and are therefore harder. 

Nearly all animal fats are mixtures of these three 
fats, but the fat of milk (cream) and consequently 
butter contains several other simple fats of which the 
principal one is butyrin. Plant oils contain little or no 
stearin, but many of them have several other simple 

Solubility. — Fixed oils and fats are insoluble in 
water, but they are readily dissolved in hydrocarbons, 
ether, carbon bisulphid, chloroform, and hot alcohol. 
They are saponified by hot alkalies and in digestion. 

Function. — The function of fats in the body is to 
provide heat and energy and material for building 
fatty tissue. 


These are substances related chemically to the 
fats. They are compounds of glycerophosphoric 
add radicals and a nitrogenous base called chclin. 

Lecithins appear to be an active component of both 

298 Physics and Chemistry 

animal and vegetable cells, but they are especially 
abundant in the white matter of nervous tissue and 
in the yolk of eggs. 

Lecithins are digested in the same manner as the 
true fats. Their function is not understood, but it is 
thought that they may assist in the synthesis of the 

Mineral Matter 

The mineral matter of food and the human body is 
spoken of also as ash and salts. It is called ash 
because, being non-combustible, it is fotmd in the 
residue remaining when animal and vegetable sub- 
stances are burned. The compounds found in the 
ash are not necessarily exactly the same as those 
contained in plant and animal tissues, for during 
ignition many chemical changes and consequent 
transformations occur. The term salts is used be- 
cause the mineral matter occurs in plant and animial 
tissues chiefly in the form of salts. 

The salts present in largest amounts in food and 
the human body are the chlorids, sulphates, phos- 
phates, and carbonates of potassium, sodium, calcium, 
and magnesium. 

Function of salts in the body. — ^As salts are not 
oxidized in the body they do not yield heat and 
energy, nevertheless they are necessary for life; 
for, they are essential constituents of protoplasm; 
they maintain the neutrality or slight alkalescence 
of the body secretions, blood, and other fluids; they 
are necessary for the maintenance of the elasticity 
and irritability of muscle tissue; calcium salts are the 
source of the firmness and rigidity of the bones; 

Chemical Constituents of Food 299 

sodium chlorid is the substance from which the hydro- 
chloric add of the gastric jtiice is made ; iron is essential 
for the making of the hemoglobin of the red blood- 
corpusdes and for the oxygen-carrying power of the 
latter and it is an equally important constituent of the 
chlorophyl of plants. 

Solubility of salts. — All the chlorids and the potas- 
sium and sodium sulphates and phosphates are soluble 
in water ; the normal phosphates of caldum and magne- 
sium are insoluble in water, but soluble in dilute adds. 

Common Tests for Determining the Presence of 
Salts in Food and Other Matter 

To about 5 c. c. of the solution to be tested add a 
few drops of strong nitric add and then a few drops of 
a 1% silver nitrate solution (AgNOj). If chlorids are 
present, a white flocculent predpitate will appear; 
because, in the presence of nitric add, the chlorin of 
the chlorids unites with the silver, forming silver 
chlorid which is insoluble in water and dilute acid 
solutions. Write the equation for the chemical re- 
action that occurs. (The nitric add does not enter 
into the reaction.) 

Test for iron. — To about 5 c. c. of the solution to 
be tested, add a drop of nitric add and then 2 c. c. of 
potassitun thiocyanate (KSCN). If iron is present, 
a deep red color will develop. 

Test for phosphates. — ^To about 5 c. c. of the solution 
to be tested, add a few drops of (i) concentrated nitric 
add and (2) ammonitmi molybdate solution, (NHJa 
M0O4. If phosphates are present, a yellow predpi- 
tate of ammonium phospho-molybdate is formed. 

Test for sulphates. — ^To about 5 c. c. of the solution 

300 Physics and Chemistry 

to be tested, add a few drops of HCl and then, slowly, 
about 2 c. c. of a 5 per cent, solution of barium chlorid 
(BaCla). If sulphates are present, a white insoluble 
precipitate of baritim sulphate is formed. 

Before testing a solid substance for mineral matter, 
it must be incinerated (i. e., burnt until it is reduced 
to ashes') and the ash dissolved in water, or, for the 
extraction of salts that are insoluble in watep (see 
page 299), water plus a little concentrated nitric acid 
solution. This is filtered and it is the filtrate that is 
tested, since the salts, being soluble in the liqtdd for 
their extraction, will be present in it in solution. 


Functions. — ^Water, like the mineral matter of food, 
has no fuel value, but it is an essential constituent of 
all protoplasm, and it enters into the composition, 
not only of the fluids of animals and plants, but even 
of such hard substances as bone and wood. The 
water of the blood of animals and the sap of plants 
is the vehicle for distributing food material through 
the organism and for carr^dng away waste matter to 
parts from which it can be eliminated. Water dis- 
solves food so that it can be used by the body, and it 
is quite as essential to life as any of the other food 
materials. The plant bereft of water quickly perishes, 
and, though animal life will not succumb quite so 
quickly, water is as essential for the well-being of ani- 
mal cells as of those of the plants; therefore water lost 
from the body, as by excessive perspiration, diarrhea, 
or hemorrhage, shotdd be replaced as soon as possible. 

' The usual method of doing this in a laboratory is to place 
the material in a crucible and put this over a flame. 

Chemical Constituents of Food 301 

Origin of Food Material 

Photosynthesis (Gr. photos « light and synthesis 
^composiHon). — Photos3mthesis is the name given 
to the processes whereby, under the influence of 
energy derived from the sun and chlorophyl (the 
green coloring matter of plants), cells in the leaves of 
green plants put together COa, which they obtain 
from the air, and H3O, which they absorb from the 
soil, to form sugar and starches. 

The exact nature of the reactions that occur in 
these processes is not known, but the following equa- 
tions show how starch could be made from these 

i2CX)a + laHaO - aCeHioOs + 246 + aHaO 

The manufacture of starch, however, is probably 
seldom, if ever, such a simple matter as this. It is 
thought that sugars of the monosaccharid type are 
formed first and the more complex sugars and 
starches made from these. This could happen as 

6C0a + 6HaO - C6Hia06 + Oia 
C6Hia06 — HaO - CbHioOs 

but, even in the manufacture of simple sugars, it is 
considered that certain preliminary steps, in which 
formaldehyde and peroxid of hydrogen are formed, 
may be usual. Thus 

Fbmial- Rydrogtn 
dehydo peroxid 

COa + jHaO - CHaO + aHaOa 
6CHaO - C«HzaO« 

302 Physics and Chemistry 

Metafitasis (Gr. meta « beyond and histanai » to 
place). — In addition to sugars and starches, plants 
must make cellulose (which constitutes the basis of 
their own structures), fats, and proteins. Cellulase 
is chemically very similar to starch. Fats and proteins 
have the same elements as starch, but in very different 
proportions, and proteins contain in addition N, S, 
and sometimes P and Fe. These elements plants 
obtain from the earth in salts, such as nitrates, sul- 
phates, etc. Still less is known of the processes that 
occur in the making of fats and proteins than of those 
by which sugar and starch are formed, but it is thought 
that these substances are made from starch and that 
the latter is broken down into simpler substances 
before S3mthesis occurs. The forming of proteins 
and other complex compounds, including the destruc- 
tive processes necessary for their formation, are 
spoken of as metdstasis. 

Photosynthesis takes place only in the green leaves 
of plants and in the daylight or under strong electric 
lights, but metastasis takes place in all parts of growing 
plants and in the darkness as well as in the light. 

It is through their leaves that plants absorb the 
CO a which they require for their food and a small 
amount of water enters in this way, but by far the 
greatest amount of their water supply is obtained 
from the soil, being absorbed by the surface cells of 
their roots and root-hairs. This water has in solution 
salts, including the nitrates, etc., required for the 
manufacture of proteins. 

The nature and purpose of sap. — ^The sap of plants 
consists of water holding in solution the salts absorbed 
from the earth and the food material that was made 
in. the principal food factory — the leaves — some of 

Chemical Constituents of Food 303 

which must be carried to the storehouses — ^the roots, 
seeds, fruits, or flowers — ^f or storage and some to all 
the cells of the plants for their nutrition. Thus, 
sap is to the plant what blood is to the animal, 
and, like blood, it must circulate throughout the 

The forces which cause the circulation of sap. — 
The factors which cause the movement of sap in 
plants are still but imperfectly understood, but 
five important forces are: (l) the avidity that 
protoplasm has for water; (2) the life processes 
of the plant; (3) osmods; (4) evaporation; (5) 

Due to the avidity that protoplasm has for water, 
it will absorb water until it is saturated; therefore, as 
the water in the cells of the leaves evaporates or is 
used up in the life processes of the plant — e. g,, the 
manufacture of sugar — ^the uppermost cells absorb 
water from those beneath them, and these, in turn, 
take it from those which they overlie, and so on. This 
constant evaporation and absorption of water acts 
very much as a suction pump and it assists the factors 
upon which osmosis depends, see page 67, in causing 
the fluid in the soil to osmose through the root-hairs 
and roots and pass up the stem to the leaves, flowers, 

In warm, bright weather, evaporation and the 
chemical processes going on in the leaves occur much 
more rapidly than in cold weather, consequently the 
sap rises more rapidly and to a greater extent tmder 
the former conditions. 

The sap must descend, as well as ascend, for the 
stems and roots need to be nourished and, as already 
stated, most of the nourishment is formed in the 

304 Physics and Chemistry 

leaves. Less is known, however, of the forces 
which cause the sap to descend than of those which 
produce its ascent, but it is known that it descends 
through the large outer cells that, in the tree, con- 
stitute the bark. This is why removing its bark will 
kill a tree. 

Source of salts in the soil. — It was stated in a 
preceding paragraph that plants got their nitrogen 
and mineral supply from the soil. This being the case, 
the soil must be constantly losing its supply of such 
matter and it must be as constantly renewed if plants 
are to grow in it. This is done by the use of fertilizers. 
Many compotmds of the salts necessary for fertilizing 
the soil are now prepared by the chemist, but, until 
recently, animal excreta and decaying vegetable 
matter were the only fertilizers to be had and they are 
still very much used. 

To understand how animal excreta can supply 
the soil with mineral matter it is necessary to realize 
that animal excreta contain not only salts eaten 
in food, but also, especially the urine, salts formed 
in the body by chemical reactions occurring in 

The protein in plants and in animal excreta does not 
exist in the form of nitrates, but when decaying 
vegetable matter and manure are spread over the 
ground they, by the influence of bacteria, undergo 
decomposition, and their protein matter is slowly 
formed into ammonia compounds, some of which, 
uniting with oxygen, and in other wa3rs, are broken 
down to nitrates and other nitrogen salts which are 
capable of going into solution in the soil water and 
being absorbed by plants. 

Another way in which bacteria supply plants and 

Chemical Constituents of Food 305 

the soil with nitrogen is that various species are able 
to absorb nitrogen from the air and some of these 
species enter the roots of such plants as peas, beans, 
clover, alfalfa, and they live and multiply in little 
tubercles that develop on the roots in consequence of 
the invasion of the plants by these organisms. The 
bacteria, as they deVfelop in these nodules, in some 
unknown way, combine the nitrogen they absorb so 
that it is available for plants. It is thought that 
perhaps the bacteria after absorbing the nitrogen 
secrete a nitrogenous substance, some of which is 
absorbed by the plant cells while a portion osmoses 
into the soil. The nitrogen supply of the soil in 
which such plants grow is thus increased, instead of 
diminished, as it is when used for the growth of other 
plants. The soil nitrogen supply is still fiuther 
increased when the roots of such plants are allowed 
to rot in the ground. 

The food cycle. — ^As shown in the preceding pages, 
plants and animals, including man, are absolutely 
dependent upon each other for their sustenance, and 
there is a continual cycle in progress by which one 
form of life supplies the other with matter for their 
life and growth. Animals eat plants and, when these 
are oxidized in their bodies, they eliminate CO a and 
other waste matter that plants can use for their food 
and development. Man supplies CO, also by burning 
plants, as wood, and plant products, as coal, oil, and 

Effect of plant life upon the atmosphere.— Plants 
not only supply man and other animals with food, but 
they also keep the air pure by extracting CO a and 
supplying oxygen. One source of the oxygen supply 
can be seen in the equations on page 301. Oxygen is 


3o6 Physics and Chemistry 

freed also in the making of fats for, as can be seen in 
the following formulas of some of the simple fats, 
there is less oxygen in fat than in sugar and starch: 

Stearin— CjHjCCisHjsOa), 
Olein— CaHsCCisHjjOa), 
Palmitin— CjHs(Cx6H3xOa)j 

In some metastasis processes COa is liberated; 
therefore plants eliminate a small amount of CO,, 
especially at night when photosjmthesis is not taking 




Oasstficatioa of Poods — ^Nature, Digestibility^ and Nutritive 

Value of the more Commoa Foods and Beverages — 

Nature and Action ol Condiments and Spices. 

Animal Foods 

The more common animal foods include the ilesh 
of mammalia — generally spoken of as meat — birds, 
fish and other sea-food, eggs, milk, and honey. 

Nutritive value of animal foods. — ^With the excep- 
tion of honey, milk, liver, and shellfish, there is little 
or no carbohydrate found in animal foods. The 
reason for the absence of carbohydrate in meat is 
that that which is present in the living animal is 
drained off with the blood when the animal is slaugh- 
tered, or else changed to lactic acid and other products 
of the decomposition of glycogen and glucose shortly 
after the death of the animal. Consequently the 
only solids provided by the majority of animal foods 
are proteins, fats, and mineral matter. 

Animal foods arc usually a more expensive form of 
nutriment than vegetable foods, but, as can be seen 
by looking at the table on pages 340-344 they contain 



Physics and Chemistry 

more protein than other foods, and animal protein is 
more thoroughly digested and absorbed than vege- 

FiG. 6i. Cuts of Beef, i, neck; 
2, chuck; 3, ribs; 4, shoulder clod; 5, 
fore shank; 6, brisket; 7, cross ribs; 
8, plate; 9, navel; 10, loin; 11, flank; 
12. rump; 13, round; 14, second-cut 
round; 15, hind shank. 

table protein. Also, the flavor 
of meat, the stimulating effect 
of the meat extractives on the 
glands which secrete the gastric 
juice, the many uses of eggs and 
milk, all make animal foods very 
desirable articles of diet for the 
majority of people. 
Comparatiye digestibility of 
animal foods. — ^The following list of the comparative 
digestibility of common animal foods is one to be 
found in several books on dietetics. The foods are 
mentioned in the order of their digestibility, be- 
ginning with the most digestible. 

Nutritive Value of Foods 309 

Milky oysters, soft-cooked eggs, sweetbreads, white 
fish, chicken, lean beef, scrambled eggs, mutton, squab, 
crisp bacon, fowl, tripe, lamb, corned beef, veal, ham, 
ducks and game^ salmon, mackerel, herring, roast 
goose, lobster and crabs, pork; smoked, dried, or 
pickled fish and meats. 

Pig. 62. Cuts of Veal, i, neck; 
2, chuck; 3, shoulder; 4, fore shank; 
5, breast; 6, ribs; 7, loin; 8, flank; 9, 
1^; ic, hind shank. 


Factors which influence the digestibility of meats. — 

In general the amount of fat and connective tissue 
and the length and strength of the muscle fibers which 
make up the muscular tissue (i. «., the lean part of 
meat) are the determining factors of the digestibility 
of meat. If there is a large amount of connective 
tissue or if the fibers are long and coarse, the meat will 
be tough and, unless the condition is ameliorated in 
the cooking, difiicult to masticate and otherwise 
digest. The fibers in certain cuts of meat are coarser 
than those in others, but the consequent toughness 
can be often rectified by proper cooking, and as a rule 


Physics and Chemistry 

these cuts contain more nutximent and extractives 
than the more tender ones. 

The fibers of the flesh of young animals are shorter 
and, consequently, the meat is more tender than that 
of older animals, but an excess of fat in lamb and a 
lack of extractives in veal make these meats, especially 

Fig. 63, Cuts op Lamb and Mutton. 
I, Neck; 2, chuck; 3, shoulder; 4, flank; 5, 
loin; 6, 1^. 

veal, less easy to digest than beef 
and mutton. The large amount of 
fat in pork interferes with its diges- 
tion. Bacon, however, is usually 
comparatively easily digested, partly 
as the result of the action of the salt 
used for its preservation upon the fat. With the ex- 
ception of bacon, salted, pickled, and dried meats 
are not as easily digested as fresh meat for the 
fibers are hardened by the preservatives and by 

Structure of meat. — Meat is ntiade up of muscle 
fibers held together with connective tissue. Within 
the fibers are the so-called meat juices which consist 
of solutions of proteins, nitrogenous extractives, and 
^ts in water. The extractives, which consist chiefly 

Nutritive Value of Foods 3" 

of substances such as creatin, xanthm, proteoses, and 
peptones, ' give meat its flavor and they stimulate the 
secretion of the digestive juices, but the greater part 

Fig. 64. Cuts of Pokk. i. Head; a, 

shoulder; 3, ribs and back; 4, middle cut; 5, 
belly; 6, h*"*' ^ l-^i"* 

of these substances are absorbed from 
the intestine and excreted by the 
kidneys without undergoing oxidation 
and thus they have no real nutritive 
value. Nevertheless, the flavor of 
meat depending upon these extrac- 
tives, their preservation is one of 
the important considerations in the cooking of meat. 


The flesh of birds is similar to that of meat, but the 
musde fibers are shorter and therefore, especially in 
young birds, the flesh is more tender. Chicken, 
turkey, and squab are all easily digested, but ducks 
and geese have too much fat, and the majority of 

' Proteooes and peptones are not present in living muscle, but 
ensymes in the tissues, ia the presence of the lactic acid, which 
accumulates in the body after death, cause the hydrolysis t^ 
■ome of the simple proteins, thereby giving rise to these derived 

312 Physics and Chemistry 

birds classed with game are too rich in extractives to 
be a suitable food for all invalids who are able to have 
chicken and squab. The presence of extractives, 
within limits, increases the digestibility of a food 
because they stimulate the secretion of digestive juices, 
but large amounts are to be avoided when there is 
any gastric disturbance. 


Fish are usually classed as scaly or vertebrate fish 
and shellfish. The latter class includes the moUusks 
and crustaceans. 

Nature and nutritive value of the scaly fish. — These 
fish contain more water and rather more mineral 
matter, especially the phosphates of calciiun and 
potassitmi, than meat, also they contain more gelatin, 
but less fat and extractives. Consequently, pound 
for pound, fish have not quite as much nutritive ma- 
terial as meat, but they are more quickly digested, with 
the exception of a few kinds in which the per cent, 
of fat is above six, — e. g., eels, salmon, turbot, herring, 
and codfish, the fibers of which are coarser than 
those of the other white fish. Salting and drying fish 
hardens the fibers and thus preserved fish are not as 
quickly or as perfectly digested as fresh fish. 

MoUusks. — ^The moUusks most frequently used 
for food are oysters, clams, mussels, and scallops* 
They have not a very high nutritive content; oysters, 
for example, contain about 88.3 per cent, water, but 
they are valuable for their flavor, and oysters, raw or 
properly cooked, are quickly and fully digested. The 
flesh of the other mollusks, especially scallops and 
mussels, is tougher and therefore not as digestible as 

Nutritive Value of Food 3^3 

oysters. As can be seen in the table, page 340, the 
moUusks contain glycogen. 

Crustaceans. — ^The crustaceans usually used for 
food are lobsters, crabs, and shrimps. The fibers of 
the flesh of the crustaceans, especially lobsters, are 
coarse and consequently these foods are neither easily 
nor perfectly digested. 


The milk secreted by any of the mammalian class 
of animals is suited to the requirements of their young 
and, as these differ, the quantitative composition of 
the milk of different animals differs also. 

The two milks most frequently compared are human 
milk and cow's milk, the latter being often substituted 
for the former in infant feeding. 

The percentage composition of average samples of 
each milk is as follows: 

Casein' Lact 
Water ogen albumin Fat Lactose Ash, 

Human milk 8741 1.03 1.26 3.78 6.21 0.31 

Cow's milk 87.17 3.93 0.53 3.64 4.88 0.71 

' Digestibility and nutritive value of milk. — ^As can 

be seen by comparing the composition of milk with 
that of other foods (page 340), milk, though a liquid, 
contains less water and more solid matter than some 
vegetables, and, usually, it is one of the most per- 
fectly digested foods so that there is little or no waste. 
The high calcium content of milk makes it a particu- 
larly valuable food for children who need calcium 
for the hardening of their bones. 
As shown in the accompanying table, there is more 

314 Physics and Chemistry 

caseinogen and less albumin in cow's milk than in 
human milk, and this is an important difference when 
cow's milk is used for infant feeding, since the soluble 
caseinogen is changed by add and by the gastric 
rennin into an insoluble substance, casein, which 
forms a solid curd, and lact albumin undergoes no 
such change. When milk is heated above 150^ P. 
the caseinogen will not be clotted by rennin. The 
reason for this is not known, but it is thought that it 
is due to change in the nature of the calcium salts by 
the heat, the calcitun salts being, it is supposed, neces- 
sary for the change. The reason for this supposition 
is that caseinogen will not change to casein upon the 
addition of rennin to milk if the calcium salts have 
been changed by combining with oxalates. This can 
be seen by the following experiment. 

Experiment 40. Procedure: Into each of three 
test tubes potir about 5 c. c. of milk; heat that in tube 
2 to a temperature of 150^ P., and maintain this tem- 
perature for a few minutes ; add i o drops of ammonium 
oxalate solution to the milk in tube 3 and then, to the 
milk in all three tubes, add about 10 drops of rennin 
solution. Stand the tubes in a water bath and keep 
the temperature about 40° C. for 30 minutes. 

Only the milk in tube i should be affected by the 

Certified milk. — By certified milk is meant milk: 
(i) that is drawn from cows that have been declared 
disease-free by an authorized inspector; (2) that is 
drawn and kept under conditions laid down by the 
Board of Health; (3) that does not contain a larger 
number of bacteria than the law of the State permits; 
and (4) that contains the percentage of fat required 
by the State law. The detsdls of the law requirements 

Nutritive Value of Foods 315 

vary in diflferent States. New York State requires 
that there be less than 30,000 germs per cubic centi- 
meter of milk and that these be non-pathogenic, that 
the milk contain an average of 4 per cent, fat, that it 
be kept and sold in sealed, sterilized bottles and sold 
on the same day that it reaches the city. 

To prevent the multiplication of germs in milk it is 
most important that everjrthing coming in contact 
with it be absolutely clean and that it be kept at a 
temperature of or below 40° P. 

Pasteurized milk. — By pasteurized milk is meant, 
milk that is heated sufficiently to destroy non-spore- 
bearing bacteria. Milk pasteurized by what is known 
as the holder method is brought to a temperature of 
i45®P.,andlield there for thirty minutes; that pasteur- 
ized by what is known as the flash method is gradually 
brought to a temperature of 160® P. and the tempera- 
ture maintained for one minute. In both methods 
the milk must be cooled as quickly as possible, and it 
is just as important to keep pasteurized milk cold as 
fresh milk, since spores are not killed at a temperature 
of 145® P. or even 160® P. and they will develop into 
bacteria unless the milk is kept at a low temperature. 

Experiment 41. Object: To test the comparative 
effectiveness of the holder and the flash methods of 

Procedure: Into each of twelve sterile test tubes 
put about 5 c. c. of fresh milk, plug the tubes with 
sterile absorbent cotton, and put six of the tubes into 
one water bath and six into another. Have the water 
in both baths cold. Raise that in one to 145^ P., 
and maintain it at this temperattire for thirty minutes. 
Raise the temperature of the water in the other bath 
to 160^ P. And let it remain thus for one minute. 

3i6 Physics and Chemistry 

Chill the milk in both tubes as qtiickly as possible 
by standing them in cold water and, as soon as they 
are cool, put them in the ice-box. After twenty-four 
hours, and every succeeding day, taste the milk in a 
tube from each test. In which set of tubes did the 
milk remain sweet longest? 

There is a considerable difference of opinion as to 
whether the digestibility and wholesomeness of milk 
is increased or decreased by pasteurization. Some 
authorities contend that pasteurization is beneficial 
because it kills disease-producing germs and prevents 
the caseinogen forming a clot in the stomach. Others 
consider that it is better to use certified milk than 
pasteurized milk because: (i) they think the change 
in the salts which prevents the forming«>of casein is 
not beneficial; and (2} the bacteria which cause the 
fermentation of lactose and consequent production 
of lactic acid are more easily killed than other varie- 
ties which they, when present, prevent multiplying. 
Some of these varieties, often present, cause changes 
in the proteins of milk that give rise to substances 
that are injurious, especially to children, but which, 
unless present in excess, do not advertise their pres- 
ence, as does lactic add, by souring or otherwise 
flavoring the milk. 

Sterilized milk. — By this is meant boiled milk. 
This is not suitable for infant feeding because of the 
changes caused in the salts by the high temperature 
and the loss of nutriment in the scum that forms on 
the top of the milk when it reaches a temperature of 
about 170^ F. The chief constituent of this scum is 
lact albtunin, but it also contains some salts, casein- 
ogen, and fat. 

Evaporated and condensed milk and cream. — These 

Nutritive Value of Foods 3^7 

are prepared by heating the milk or cream in a vacuum 
pan until a large portion of the water is evaporated 
and germs are killed, and then putting the liquid into 
sterile cans and sealing these at once. 

Desiccated milk. — This is milk that has been eva- 
porated to a dry powder. It is prepared for use by 
adding water to it. 

KoumisSi matzooni artificial buttermilk. — ^These 
and similar preparations are fermented milks. In 
some preparations the fermentation is produced by 
the use of yeast, in others by that of pure cultures of 
lactic acid, producing bacteria. In any case, the 
substance fermented is the glucose, and the curding 
of the protein is caused by the lactic acid resulting 
from this fermentation. These milks are quickly 
digested and are often used by those suffering 
from impaired digestive power. They are used also 
in the treatment of intestinal putrefaction, for it 
is believed that the lactic add inhibits the action 
of the putrefactive bacteria always present in the 

Whey. — This is the watery, straw-colored liquid 
that separates from the curd formed in milk by rennin 
or acid. Whey consists of water, lact albumin, 
lactose, and mineral matter. 

Cream. — Cream is the name given to the fat which, 
in the form of an emulsion, rises to the top of milk 
when it is allowed to stand. The top layers of cream 
will contain more fat and less protein than those 
nearer the surface of the milk. Cream is also separa- 
ted from milk by the use of the centrifugal separator, 
and that obtained in this way is much richer than 
that obtained by gravity and it can be better freed 
from entangled caseinogen. The fat of cream being 

3i8 Physics and Chemistry 

in the form of an emulsion, is digested more easily 
than other fats. 

Butter and its substitutes. — ^Butter is made by 
agitating cream, usually in utensils known as chums, 
and thereby causing the particles of fat to ding to- 
gether in masses. The melting point of butter is low 
and it is thus one of the most easily digested of animal 
fats. When foods are fried in butter, however, their 
digestion is interfered with, because fat is not digested 
until it reaches the intestine, and if carbohydrates 
and proteins are encased in a hardened fat envelope, 
the digestive juices of the mouth and stomach cannot 
attack them properly. 

Renovated or process butter is made by melting 
rancid butter, removing any disagreeable odor and 
taste by various means, and churning the butter with 
some new milk to which, usually, cultures of bacteria 
that will develop an agreeable flavor have been added. 
The great objection to the use of renovated butter 
is that the germs which produce rancidity sometimes 
develop injurious substances in the butter. 

Margarini oleomargarini and the majority of other 
artificial butters are made from meat fats with, 
usually, a little butter or milk to improve the flavor. 
These substances can be sold at a lower price than 
good, fresh butter, and though not as good from any 
dietetic standpoint as fresh butter, they will, when 
properly prepared, keep better than butter and they 
are more wholesome than renovated or old butter. 

Cheese. — Cheese is made by coagulating the casein- 
ogen of milk. Usually this is done with rennin. As 
a rule, there is a considerable, though very varying, 
amount of fat entangled in the casein. As can be 
seen by studying the table on pages 340-344, cheese 

Nutritive Value of Foods 319 

contains less water and more protein than the major- 
ity of foods. As it is such a concentrated food, it 
cannot be eaten in large amounts, especially by per- 
sons of sedentary habits, and it is very likely to cause 
gastric disturbances in those whose digestion is im- 
paired, but it has been found that 95 per cent, of 
the fat and 92 per cent, of the protein are ultimately 
absorbed by the average healthy adult and that cheese 
stimulates the secretion of the digestive juices. As 
many cheeses are cheaper than eggs and meat, cheese 
is a valuable source of protein food for healthy adults 
of restricted means. Cooking cheese renders it less 
digestible since it hardens the casein. 


Eggs, though lacking carbohydrates, are a particu- 
larly valuable food, for they contain easily digested 
proteins, more lecithin than other foods, and an abun- 
dance of mineral matter, especially phosphates and 
iron, and the iron is in a particularly assimilable 

The protein of the white is chiefly albiunin, that 
of the yolk is partly albumin, but largely vitellin — a 
phosphoprotein; part of the fat is in the form of 
lecithin. The sulphur present in egg, both in the 
white and yolk, will sometimes give rise to flatulence, 
because, especially when a person is constipated, the 
sulphur is likely to unite with hydrogen and form 
hydrogen sulphid, a light ill-smelling gas. When 
silver comes in contact with eggs, its stirf ace blackens, 
due to the union of the sulphur with it and the con- 
sequent formation of silver sulphid which remains 
as a covering on the metal. 

320 Physics and Chemistiy 


This is a mixttire of sugars prepared by bees from 
substances they extract from the exudations of various 
plants. Genuine honey consists chiefly of Icvtdose 
and glucose, with a small amoimt of sucrose and about 
17 per cent, water. The quality and flavor of honey 
depend largely upon the nature of the flowers from 
which the bees secured their food material. As honey 
consists so largely of invert sugars, the greater portion 
of its substance is ready for absorption and does not 
undergo digestion. 

Plant Foods 

Classification. — ^The plant foods in common use 
are classified as cereals, vegetables, fruit, nuts, ftmgi, 
and sugars. 


This class of foods includes plants of the grass 
family such as wheat, rye, oats, barley, rice, and com. 
The composition of the cereals varies, but they are all 
rich in carbohydrates and mineral matter, and cooking 
does not entail any loss of nutriment. 

Wheat — ^Wheat, especially in the form of fiour, is 
one of the most universally used of the cereals. There 
are several varieties of wheat, and the fiours and 
breakfast foods made from them differ because of 
this and, more especially, as the result of different 
methods of preparation. The protein of wheat is 
chiefly gluten, a sticky, tenacious substance which is 
a compotmd of gliadin and glutenin. The elasticity 

Nutritive Value of Foods 321 

of gluten and its power to hold the gas produced in 
dough by yeast, baking powders, etc., is influenced 
by the proportions of gliadin and glutenin that it 
contains — ^about 65 per cent, of gliadin to 35 per cent, 
of glutenin is usually preferred for bread flour. Spring 
wheat (i. €., that sown in spring and maturing in the 
late summer) contains more gluten and less starch 
than winter wheat (that sown in the fall and maturing 
in the early summer) and is preferred for making 
bread, but winter wheat is the best for pastry. 

Oatmeal. — ^The meal of oats is also much used for 
food. Oatmeal contains more protein, fat, and min- 
eral matter than other cereals. The protein consists 
of a substance called avenin, which is somewhat simi- 
lar to the legumin of peas, and a small amotmt of 
gliadin. As oatmeal does not contain gluten, it 
cannot be used for bread-making. 

Barley. — ^Barley contains a relatively large amount 
of salts, fat, and cellulose, but less protein and digesti- 
ble carbohydrates than the other cereals. Its salts 
are soluble in water and hence are easily extracted. 
This is one reason why barley water is so much used 
for diluting top milk for infant feeding. 

Sprouted and dried barley, generally known as 
malt, contains a ferment called diastase which converts 
starch to sugar. 

Com* — Com is a widely used cereal both in its 
natural state and ground into meal and starch. Its 
protein has not all the characteristics of a true gluten 
and thus its meal has to be mixed with rye or wheat 
flotu" for bread-making. Starch is one of the most 
valuable products of com. The nutritive value of 
com compares favorably with that of wheat. When 
eaten in its natural state, com occasionally causes 


322 Physics and Chemistry 

irritation in the intestines on account of its cellulose 
exterior, which may resist digestion, but it is stated 
that analysis of feces has shown that young com, 
when properly cooked, is more thoroughly digested 
than is generally supposed. 

Rice. — Rice is very extensively used for food. It is 
poor in proteins and fat, but rich in starch; it contains 
a fair amount of mineral matter. 

Rye. — ^The composition of rye is very similar to 
that of wheat. Its gluten, however, contains more 
gliadin than does that of wheat and it is therefore 
more sticky and tenacious and, consequently, bread 
made with rye flotir is darker and less porous than 
wheat bread. 

Substances similar in composition to the cereals, 
though not belonging to the same botanical classifi- 
cation are: The grain buckwheat; tapioca, which is 
prepared from the root of the cassava plant; sago, 
which is prepared from the pith of the sago palm; 
arrowroot, a starch obtained from the roots of several 
plants grown in different tropical countries. 


Vegetables are often classified as the roots and 
tubers, green vegetables, and legumes. 

The roots and tubers. — ^The vegetables thus classi- 
fied are those of which the root or bulb is used for 
food, e, g., potatoes, parsnips, carrots, beets, turnips, 
salsify, onions. 

These vegetables contain from 75 to 95 per cent, 
water and they are all relatively poor in protein and 
in fat, nevertheless they are of value in the diet on 
account of their flavor and their mineral salts. 

Nutritive Value of Foods 323 

Potatoes have a higher nutritive value than the 
other roots and tubers and are easily digested; they 
are particularly rich in alkaline potash salts and are 
thus a valuable adjunct to meat in the diet, the latter 
being a source of acids in the system. Potatoes, 
however, contain little iron or calcium salts and there- 
fore, unless mixed with milk or egg, must not form 
too large a portion of children's vegetable supply. 

The carbohydrates of beets, carrots, parsnips, 
salsify, and turnips are largely cellulose and sugar, and 
as the latter is soluble in water there is a great loss 
of nutrient in the cooking of these vegetables. 

Green vegetables. — ^The vegetables often classed 
as greens are those of which the stalks and leaves 
are used; e. g,, cabbage, cauliflower, asparagus, French 
artichokes, spinach, lettuce. The majority of these 
vegetables have an even lower nutritive value than 
the roots and tubers, but they are valuable for their 
flavor and salts; also they give bulk to the diet, and 
their cellulose causes a mild irritation of the intestinal 
tract which stimulates peristalsis and thus helps to 
prevent constipation. 

Legumes* — ^The principal legiimes used as food are 
peas and beans — of which there are many varieties — 
and peanuts. 

The legiunes contain more protein than other vege- 
table foods, but the protein is in the form of legumin, 
and this is acted upon mainly by the ferments in the 
intestine; thus, legumes are not readily digested in 
the stomach and sometimes, especially when the 
vegetables are old and the cellulose thus hardened, a 
considerable portion may escape digestion. Passing 
peas and dried or Lima beans through a colander 
after they are cooked, and thus removing the harder 

324 Physics and Chemistry 

cellulose, greatly increases their digestibility. Flatu* 
lence is sometimes caused by eating a large amount 
of beans, because (i) the gas hydrogen sulphid may 
be formed from the sulphur they contain, and (2) 
methan gas is sometimes produced, probably by the 
decomposition of the bean germ by the bacteria that 
are always present in the intestine. 

Eggplant, cucumber,' vegetable marrow, ptunp- 
kins, tomatoes, from the manner of their growtib, are 
sometimes classed as fruit, though they are used as 
vegetables. Their nutritive value is not high, but 
they give bulk and variety to the diet and furnish 
mineral matter. The cellulose of cucumbers is too 
difScult of digestion to allow of the use of this plant 
by invalids and small children. 


Fruits consist principally of water holding in solu- 
tion sugars, small amounts of proteins, pectin, and, 
in some fruits, starch; also they contain acids, essen- 
tial oils and aromatic oils to which their flavor is due, 
and cellulose. The cellulose in the immature fruit 
is insoluble and very indigestible, but it becomes softer 
and more soluble as the fruit matures. Though the 
majority of fruits have not a ver>'^ high food value 
they are of use for their flavor, for the bulk which 
they add to the diet, for their mineral matter and 
their acids. The principal acids of fruit are: malic 
add, found more especially in apples, pears, currants, 
berries, grapes, cherries, pineapples ; citric acid, which 
occurs more especially in lemons, limes, grape fruit, 
oranges, currants, and gooseberries; tartaric acid, 
found chiefly in grapes; racemic acid, an add that 

Nutritive Value of Foods 325 

resembles tartaric add, and is found chiefly in grapes. 
Acetic acid is found in fruits undergoing decay, as 
it arises from the fermentation of grape sugar, but it is 
not a constituent of good fruit. 


By looking at the table on page 344, it will be seen 
that nuts contain comparatively little water and a 
high content of protein and fat, and experiments have 
shown that when nuts are not eaten in large quanti- 
ties at a time or at the end of a heavy meal, they are 
much more quickly and thoroughly digested than 
was previously supposed. Nuts and fresh fruit form 
a good combination, nuts being deficient in carbo- 
hydrate and a very concentrated food, and ripe fruit 
containing easily digested carbohydrate and being 
bulky in proportion to the food value of its contents. 


The ftmgus in most common use is the mushroom. 
Judging from the chemical analysis of the mushroom, 
as shown on page 343, this fungus would seem to have 
the same food value as the grieen vegetables, but it 
has been found that mushrooms are neither thoroughly 
digested nor absorbed, and this, of course, lessens 
their nutritive value. 

CondimentSi Spices, and Flavoring Extracts 

By condiments are meant substances, such as the 
various peppers and salts, used to flavor food. 
Condiments, with the exception of sodivun chlorid. 

326 ' Physics and Chemistry 

spices, and other flavoring maXter, are obtained from 
variotis parts of plants, some being prepared from the 
stems and leaves {e. g., bay leaf, sage, sweet marjo- 
nmi), others from the bark (e. g., cinnamon), others 
from the buds and flowers (e. g., cloves and saffron), 
some from fruit (e. ^., allspice, capsicum, juniper, 
pepper, vanilla), and still others from the seeds {e, g., 
anise, caraway, celery seed and salt, coriander, mus- 
tard, nutmeg). 

Many of these substances owe their properties to 
the presence of a volatile oil which can be extracted 
and used separately. One method of extraction is 
by distilling the oil with steam; oil of cloves, oil of 
cinnamon, and several others are prepared in this way. 
Pressure is another method of obtaining oil from 
plants. The oil of lemon, from which lemon extracts 
are prepared by dissolving the oil in alcohol, is ex- 
tracted from lemon rinds by pressure. In some in- 
stances the active principle or flavoring matter is 
extracted from a substance by the use of a solvent, 
e. g., vanilla extract is made by extracting the active 
principle of the vanilla bean — vanillin — by soaking 
the bean in dilute alcohol. Artificial, so-called, vanilla 
extracts are now made, which are cheaper than, but 
not as good as, the true extracts. One variety is made 
by oxidizing eugenol, a substance in the oil of cloves, 
with potassium permanganate. 

Food value.— Condiments have no food value in 
themselves, but if not used in excess they help in the 
digestion of food by stimulating the flow of digestive 
juices. They do this in two ways: (i) by improving 
the aroma and flavor of the food, and (2) by a slight 
irritation of nerve endings in the gastric mucous 
membrane. If the irritating condiments are used in 

Nutritive Value of Foods 3^7 

excess, the irritation they produce may cause con- 
gestion of the gastric mucous membrane and conse- 
quent digestive disturbances. 


Caffein and theobromin beverages. — ^The caSein 
and theobromin beverages in most common use are 
coffee, tea, chocolate, and cocoa. 


Coffee is prepared from the berry of the coffee tree 
by hulling and drying the berry and, later, roasting 
and drying the seeds. Sometimes the seeds are glazed 
in order to prevent a loss of the volatile substance to 
which the flavor and aroma of coffee are due. The 
glaze ordinarily used is prepared from sugar, and the 
pure food laws of the United States prohibit the use 
of other glazes unless their presence and nature are 
stated on the label, but some countries permit the 
use of resin, shellac, and similar substances. 

Sources of coffee supply. — True Mocha coffee, which 
has been always very generally considered one of the 
best coffees, comes from Arabia, but much of the so- 
called Mocha now sold comes from the West Indies, 
Brazil, and other South American countries. Java 
coffee, from the island of Java, is another favorite 
coffee, but much of the so-called Java comes from 
various places and may or ma}' not be good. That 
coming from Bogota, S. A., is said to be most like the 
true Java. More than half the coffee supply for the 
world now comes from Brazil and various localities 
in the northern part of South America. Other im- 

3^28 Physics and Chemistry 

portant sources of supply are Central America and 
the West and East Indies. 

Composition of coffee. — Roasted coffee contains 
0.6 to 2 per cent, of caffein, a varjring amount of 
caffeol — the volatile oil to which the aroma and flavor 
are due — and a large amount of caffeo-tannic acid. 
A cup of coffee solution, as usually prepared, may 
contain from iH to 3 grains of caffein; the amount of 
caffeo-tannic acid will vary according to the method 
of preparing the beverage. If the coffee is prepared 
without boiling, or if it is boiled but a short time and 
used, or removed from the grounds, at once, it will 
contain but a small amount of the acid. The caffeol 
is developed during the roasting of the seeds and, 
being volatile, it gradually decreases in amount after 
the seeds are ground. Therefore the flavor of coffee 
will be stronger if it is not ground until shortly before 
use, and there will be a great loss of flavor unless the 
ground coffee is kept in air-tight cans and the coffee- 
pot kept covered while the beverage is being prepared. 

Action of coffee constituents on the system. — ^The 
caffein of the coffee acts as a cerebral stimulant. If 
coffee is not taken in excess, it renders the mind clearer 
and more alert and it increases the power of concen- 
tration; in fact, all the higher intellectual faculties, 
as reasoning, self-control, judgment, may be stimu- 
lated. Through the influence of caffein on motor 
cells of the nervous system, coffee improves muscle 
tone, and stimulates the circulation and the respira- 
tion; also, it lessens fatigue and may promote a sense 
of well-being. If coffee is taken in excess, the caffein 
over-stimulates the nervous system and will lessen 
the powers of concentration, clear judgment, etc. 
Caffeol acts as a local irritant in the intestine, thus 

Nutritive Value of Foods 329 

promoting peristalsis and having a laxative effect. 
It will, if coffee is taken in excess, cause digestive 
disturbances, as will also the caffeo- tannic add. The 
latter, if much is present in the coffee, retards diges- 
tion and absorption. It does not, as does the tannic 
add of tea, predpitate alkaloids, albumin, and gelatin; 
therefore, coffee is useless as an antidote for poisoning 
by drugs the active prindples of which are alkaloids. 
As caffein stimulates the respiratory center, coffee is 
often used as an antidote for poisoning by drugs, 
such as opium, which depress it. Also, as caffein 
stimulates the vaso-constrictor and motor centers, 
coffee is sometimes used to counteract the conditions 
present in collapse, espedally that produced by over- 
doses of drugs which depress the nervous system, as 
the narcotics, anesthetics, and alcohol. 

Caffein— -Free Coffees 

' There are some coffees from which, by heating the 

I berries tmder spedal conditions, much of the caffein 

i has been removed. Some of these contain as little 

as 0.3 per cent, caffein, but it is doubtful if any of 
i them are actually free from it, as the name implies. 

It is claimed that the other ingredientsof these coffees 

are not altered by the treatment. 

Coffee Substitutes 

There are various preparations on the market that 
consist prindpally of such substances as parched 
com, baked wheat, dried peas, bread crust, and the 
like, which are called coffee substitutes. Many of them, 
however, contain a considerable amotmt of coffee. 

330 Physics and Chemistry 


Tea is made from thea, an evergreen shrub grown 
chiefly in India, Ceylon, China, and Japan. The 
finest qualities are made from the young, tender 
leaves. The chief difference between black and green 
teas is the smaller amount of tannin in the former. 
This difference is due to the manner in which the 
leaves are cured, those for black tea being allowed to 
undergo a certain amount of fermentation before 
they are dried. 

The chief teas from India and Ceylon are Flowery 
Pekoe, Orange Pekoe, Pekoe — ^these are made from 
the smaller leaves; Souchong, Congou, and Bohea — 
made from the larger leaves. The principal China 
teas are Young Hyson and Gunpowder, which are 
made from the smaller leaves, and Imperial and Twan- 
kay, made from the larger leaves. These are green 
teas. Various teas are often blended and different 
blends are known by different names. English break' 
fast tea, for example, consists of a mixture of teas. 

The principal constituents of tea. — ^These are: i 
to 4 per cent, caffein, 0.6 per cent, volatile oil — to 
which the aroma and flavor are due, — and a large 
amount of tannic add. Tannic acid precipitates 
gelatin, albumins, and alkaloids and is strongly astrin- 
gent. Due to the action of tannic acid upon alka- 
loids, a strong infusion of tea is useful as an antidote 
in poisoning by alkaloids; due to the astringency of 
tannic add, strong infusions of tea will retard digestion 
by inhibiting the flow of digestive juices. If tea is 
not boiled nor the water allowed to remain more than 
two or three minutes on the leaves, there will not be 
much tannic add in the infusion, but, infusions strong 

Nutritive Value of Foods 331 

enough to tan hide into leather can be made from 

Tea contains more caffein than coffee, but, as less 
of the tea is used per cup, a cup of tea will not contain 
as much caffein as a cup of coffee. Tea, however, 
has a more immediate stimulating effect, either be- 
cause of the nature of its volatile oil or because its 
absorption is more rapid. If tea is taken in excess 
or if it is made in a manner to extract a large amount 
of tannic add, it will have more injurious effects upon 
digestion than coffee, owing to the astringent nattu'e 
of the tannic add, but, on the other hand, if it is 
properly made, tea, probably because it contains 
less extractive matter, is less disttu'bing to the 

Ndther tea nor coffee is nutritive in itself, but 
the addition of cream and sugar gives them a slight 
food value. The tannic add of the tea predpi- 
tates the coagulable protdn of the milk, but this 
does not interfere with its digestion by the gastric 
juice; in fact, it is thought that milk or cream may 
be desirable additions in that they lessen the irritating 
action of the add in the stomach and retard the 
.absorption of caffein. 

Chocolate ' 

Chocolate is made from the ripe seeds of the bean 
of the theohfoma cacao, a plant which is now grown 
in many tropical countries. The seeds are fermented, 
dried, roasted, and deprived of their shells, which are 
known as cocoa nibs. 

Chocolate contains from 0.3 to 2 per cent, of theo- 
bromin, lo per cent, of starch, 15 per cent, of vege- 

332 Physics and Chemistry 

table protein, and 30 to 50 per cent, of a fat which is 
known as cocclo or cocoa butter. There is some 
tannic acid in the seeds, but this is removed in the 
fermentation process. The chocolate flavor is de- 
veloped in the roasting. This flavor is not pleasant, 
but is made so by the addition of sugar to the choco- 
late and, as a rule, vanilla or some other flavoring 

As shown by the list of its constituents, chocolate, 
unlike tea and coffee, is nutritious in itself, but, in 
the stomach, the fat retards both the secretion of the 
gastric juice and the motor action of the stomach, so 
that chocolate should not be eaten or drunk in large 
quantities and it does not make a suitable beverage 
for invalids. 

Theobromin stimulates both the cardiac and volun- 
tary muscles, but has no action, like caffein, on the 
vaso-constrictor centers and but little stimulating 
effect upon the brain. 


Cocoa is a powder prepared from chocolate by the 
removal of a portion of its fat by hydraulic pressure. 
Thus, cocoa contains a smaller per cent, of fat than 
chocolate (it has 15 to 30 per cent.) and a larger per 
cent, of theobromin. Considerable extra starch is 
often mixed with the cocoas sold cheaply and in such 
cases the percentages of both fat and theobromin are 

When preparing cocoa to drink, it should be cooked 
for at least five minutes to hydrolize the starch. When 
made with milk and sweetened with sugar, a cup of 
cocoa will yield about 250 calories. Thus it has a 

Nutritive Value of Foods 333 


comparatively high food value for a beverage and 
it is slightly stimtilating, but, even though it has 
less fat than chocolate, it sometimes interferes with 
digestion; especially in the case of invalids and of 


Coco-cola is a proprietary preparation that has 
recently come into use. When it was first put upon 
the market, it was reported to contain cocaine, but 
investigation proved the report untrue. The chief 
constituents are flavoring compounds and caffein. Its 
action is therefore similar to that of tea and coSee. 

Mineral and Carbonated Waters 

As stated on page 209, in certain localities the soil 
and rocks contain so much soluble mineral matter 
that water flowing through the district absorbs enough 
of the mineral to give it a decided flavor. 

There is so much demand for such waters that they 
are now bottled at the places where the springs occur 
and put upon the market. 

Both mineral and ordinary drinking waters are 
oft^n charged with carbon dioxid gas. The carbon 
dioxid used for the purpose is obtained from various 
sotu'ces. Some of these are: (i) Many of the mineral 
waters in their natural state contain carbon dioxid, 
and this is taken from the water at the springs where 
it arises from the ground, compressed in cylinders, 
and then used to charge the water when the latter is 
bottled. (2) Burning some form of carbon, as coke 
or charcoal. (3) Collecting the by-product (CO a) 

334 Physics and Chemistry 

that occurs in the manufacture of lime from calcium 
carbonate and that arising during the brewing of beer 
and other fermentative processes. 

Unfermented Beverages Made from Fruit Juices 

Agreeable and wholesome beverages are prepared 
by extracting the juice from fruit, sterilizing it, and 
bottling it in sterile, air-tight bottles. 

Fruit syrups are made in the same way plus the 
addition of sugar before the sterilization. S 

Imitation fruit syrups are made by combining sugars 
or saccharin, artificial coloring matter, fruit acids 
(e, g., tartaric, citric, phosphoric), and flavoring sub- 
stances prepared from such compounds as chloroform, 
nitrous ether, benzoic ether, butyric ether, etc., these, 
when in special combinations, having somewhat the 
same flavor as the delicate ethers and aldehydes to 
which the flavor of fruit is due. The syrups used at 
soda fountains are often the imitation products. 

Fruit vinegars are other common flavoring sub- 
stances used for beverages. They are made in about 
the same way as the fruit juices, except that the fruit 
is soaked in vinegar before the juice is extracted and 
this vinegar is used as well as the juice. 

Alcoholic Beverages 

The alcoholic beverages in common use are made 
byfermenting sugarsolutionswith yeast in the presence 
of nitrogenous substances. The sugar may be that of 
a fruit juice, or that produced by the action of the 
yeast, or ferments secured from other sources, on 
starch or cellulose. 

Nutritive Value of Foods 335 

Alcoholic beverages are usually classed as: wines, 
distilled liquors or spirits, elixirs, malt liquors. 


Wines are spoken of as red, white, dry, sweet, 
strong, light, sparkling, fortified. 

Red wines are prepared by fermenting the juice of 
grapes in the presence of their skins. They contain 
tannic add and are therefore more astringent than 
white wines. 

White wines are made from the juice of grapes the 
skins and seeds of which have been removed. 

A sweet wine is one that contains free sugar. 

A dry wine, one that contains no free sugar, e. g., 

A sparkling wine is one that contains CO 2, e. g., 

A light wine is one that has a low per cent, of alcohol, 
and a strong or heavy wine is one that contains a com- 
paratively large amount of alcohol, but not above 
17 per cent., while a fortified wine is one that contains 
a higher per cent, of alcohol than 17 per cent. Since 
the action of yeast is inhibited when 15 to 17 per cent 
of alcohol is produced in the fermenting material, 
to obtain a beverage containing more than 17 per 
cent, alcohol, the alcohol must be distilled from the 
fermenting material by fractional distillation — ^as 
described on page 63 — or else, as is done in the making 
of fortified wines, alcohol obtained by distillation must 
be added. Light wines, such as claret and sauteme, 
contain about 7 to 12 per cent, alcohol. Fortified 
wines, such as madeira, sherry, and port, contain about 
17 to 25 per cent, alcohol. 

336 Physics and Chemistry 

Apple and pear cider and similar beverages are 
often classed with wines since they are prepared by 
the fermentation of fruit sugar. They usually con- 
tain from 0.50 to I per cent, alcohol. 

Distilled Liquors or Spirits 

These are made by distilling different kinds of fer- 
mented liquors. Examples are : whiskey, gin, brandy, 
and rum. 

Whiskey {spiritus frumenti) is prepared by distil- 
ling the mash of fermented grain, such as com, rye, 
wheat, barley. To be good, whiskey must be not less 
than four years old. It contains 44 to 55 per cent, 
by volume of ethyl alcohol. 

Gin, sometimes called compound spirits of juniper ^ 
is made by redistilling the distillate obtained in making 
whiskey with juniper berries. It contains from 60 
to 70 per cent, alcohol and some volatile oil of juniper 
berries. The latter gives it diuretic properties. 

Brandy (spiritus vini gallici) is obtained by the 
distillation of the fermented juice of grapes. It con- 
tains 46 to 55 per cent, by volume of ethyl alcohol. 

Rum is the distillate from fermented molasses. It 
varies in strength, but usually contains from 45 to 
55 per cent, alcohol. 

The Elixirs 

These are aromatic alcoholic mixtures containing 
varying, but large, percentages of alcohol, flavoring 
substances, and sugar. Elixirs are often colored red, 
blue, yellow, or green with vegetable colors. 

The elixirs include the various liqueurs, cordials, 

Nutritive Value of Foods 337 

crimes, etc. Some of the best known beverages of this 
class are: Absinth, which is prepared from spirit 
flavored with wormwood and various aromatic sub- 
stances and colored green with extracts from the 
green leaves of wormwood, hyssop, and mint. Char- 
treusei made from alcohol distilled with angelica^ 
hyssop, nutmeg, and similar substances. Cr&ne de 
menthei made by distilling a fermented decoction of 
mint, cinnamon, sage, and other spices; it is sweetened 
with sugar and colored with chlorophyl. Curasao, 
made by macerating and distilling the dried peel of 
a variety of orange that grows in Curasao (Dutch 
West India Islands) with alcohol. Maraschino — 
genuine maraschino is made from Marasca cherries 
which are crushed with their pits, mixed with honey, 
fermented and distilled, but much of that sold is made 
by distilling the products obtained by crushing and 
macerating peach pits, wild cherries, cherry leaves, 
orris root, and other flavoring substances with alcohol. 
Vermouth, made in France and Italy from white 
wines and various flavoring extracts. 

Malt Liquors 

The malt liquors are made from starchy substances, 
usually grain. The grain is ground and boiled with 
water; barley malt is added after the mash has been 
reduced to the desired temperature, and as the barley 
contains the ferment diastase, it changes the starch 
to dextrin and some of the dextrin to maltose and 
glucose. Hops also are added and they yield a 
bitter principle and hypnotic substance to the liquid. 
When this part of the process is completed, the liquid 
is removed by filtration and yeast is added to the 

33^ Physics and Chemistry 

filtrate. After the fermentation caused by the yeast 
has been carried to the desired degree, the yeast is 
killed by heat. As the fermentation is always stopped 
before all the sugars are destroyed, the malt liquors 
contain varying amounts of free sugar. Also, they 
contain the various products of the fermentation of 
sugars, viz., alcohol (3 to 7 per cent.), adds and carboq 
dioxid, and the bitter principle derived from the hops. 

The principal malt liquors are ale, beer, porter, and 
stout. The ordinary varieties of ale and beer are 
very similar; the slight difference that exists being 
due chiefly to the different yeasts that are used: beer 
being fermented by bottom yeast (yeast that sinks), 
and ale by top yeast (yeast which floats). True 
lager beer — so called from the German lager ^ a store- 
house — is beer that is stored in a cool place for several 
months before use. Porter and stout are ales of 
which the malt, before it was fermented, was roasted 
until it changed to caramel. Stout is the richer and 
stronger of the two. 

Beers and ales made from xoots, herbs, etc. — Such 
beverages usually consist of sugar solutions flavored 
with essences consisting of extracts from special roots, 
etc. (as ginger, sarsaparilla), and fermented with 
yeast. They contain about i per cent, alcohol. 

Action of alcohol on the system. — ^Alcohol depresses 
the higher brain centers, /. «., those controlling reason- 
ing, judgment, etc., but, unless the alcohol is taken in 
large amotmts, the centers concerned with imagina- 
tion, emotion, etc., are not particularly depressed, 
especially when the drinker is where there are bright 
lights and congenial company; in fact, the depression 
of the higher centers often allows the others freer 
play. This effect is more pronoimced when gas-con- 

Nutritive Value of Foods 339 

taining beverages, as champagne, are used, on account 
of the stimulating effect of the CO,. But if alcoholic 
beverages are taken in excess, and sometimes even 
when taken in small amoimts in the absence of com- 
pany or other stimulant, they are narcotic. From 
the depression of the cerebrum by alcohol, after heavy 
drinking, sexual desires are less under restraint than 
usual, hence alcohol has been always an important 
factor in the whiteslave trade. Alcohol depresses 
the vaso-constrictor centers and, consequently, it 
causes the blood-vessels in the skin to become dilated; 
thus small doses may temporarily improve the super- 
ficial circulation and lessen internal congestion. 
Large doses of alcohol, however, depress this and 
centers regulating other vital activities to such an 
extent that, if the depression is constantly repeated, 
harmful changes will be caused in the body tissues 
which vnil interfere with the proper fimctioning of 
the body organs and result in mental deterioration. 
Alcoholic beverages, by stimulating the taste-buds 
and olfactory nerves act as appetizers and induce a 
psychic secretion of digestive juices. Beverages 
containing less than 20 per cent, alcohol do not seem 
to affect the digestive ferments, and they hasten the 
absorption of other substances, such as digestive 
products, water, and drugs, but vStrong solutions will 
precipitate the proteins of food and, to some extent, 
the pepsin of the gastric juice, and they retard diges- 
tion; also, they tend to produce a coat of thick mucus 
on the mucous membrane of the stomach which 
interferes with absorption. 

As to whether alcohol is to be considered a food or 
not is still an unsettled question. An accepted defini- 
tion of a food is a substance whose dominant property 

340 Physics and Chemistry 

in the body is to build up the tissues or to yield energy, 
and though every gram of alcohol oxidized in the 
body will yield 7 calories, this can be hardly called 
its dominant property. Also, experiments have 
shown that, though alcohol is easily oxidized in the 
body and thus spares food products and body tissue 
from oxidation, it is not used in the body for tissue 
building. The malt beverages and others containing 
sugar have, of course, a real food value on account of 
their sugar. This sugar, however, is particularly 
likely to undergo fermentation in the stomach and 
cause flatulence. 

Food maUruila (u punhued] 

'Chuck iib>... 


. Bib* 

Rib roll*... 

Hind qnuMr... 
' Reprinted fr 


Per Fer Per 






JO. 3 








1.1 OS 


cnmi, divida tbt Searm 

n Panntri- BtiOttin. Ho. 

|To Iraiulate tha psTceiiUgBi given in tb 
nprcHntiog the pcrcent>aei by loo ((. i 
toward the left), uid to find the amonnt of heat (caloriee) that each food inll 
yield, multiply the number of ■rami of protein by 4. of fat by p. and of carLo- 
hydtatei by 4. To find the amount oC protein, fat. etc. in one ounce, multiply 
the number of tnioi of protein, etc., by (which ii tha number of gnun* la 
one ounce), and to find the amount in one ponitd, nuUtiply by 413.60.) 

Nutritive Value of Foods 341 


PRODUCTS— C<m/»»««rf 

Food materials (as purchased) 

ANIMAL FOOD — Continued 

Beef, corned, canned, pickled, and 

Corned beef 

Tongue, pickled 

Dried, salted, and smoked . . 

Canned boiled beef 

Canned corned beef 




Leg cutlets 

Fore quarter 

Hind quarter 



Le^, hind 

I^om chops. 

Fore quarter 

Hind quarter, without tallow 


Leg, hind.. 

Pork, fresh: 


Loin chops 



Pork, salted, cured, and pickled: 

Ham. smoked 

Shoulder, smoked 

Salt pork 

Bacon, smoked 






Celery, cream of 


Meat stew 



Chicken* broilers 





Cod. dressed 

Halibut, steaks or sections. . 

Mackerel, whole 

Perch, yellow, dreMed. 

Shad, whole 

Shad, roe •.... 

Pish, preserved : 
Cod, salt 







24. S 


















































































































x.4 10 
























Physics and Chemistry 


FRODXJCTS— Continued 

Pood matertalt (m purchased) 

A^fiMAL FOOD — CofUinuH 

Fiah, canned: 

Salmon. ••.. , 



Oysten. *'aolid8*' 

Claxnt , 


Lobetert , 

Egga: Hens' eggs 

Dairy products, etc: 


Whole milk , 

Skim milk 

Buttermilk , 

Condensed milk 


Cheese, Cheddar. ....... 

Cheese, full cream 










Flour, meal, etc.: 

fintire-wheat flour. . • 

Graham flour 

Wheat flour, patent 
process — 
High-grade and medium 

Macaroni, vermicdli, etc . . . 

Wheat breakfast food 

Buckwheat flour 

Rye flour 

Com meal 

Oat breakfast food 




Bread, pastry, etc. 

White bread 

Brown bread , 

Graham bread , 

Whole-wheat bread, 

Rye bread , 


Cream crackers. . . . , 
Oyster crackers. . . • . 
Sodacrackara , 

Sugars, etc: 

Moliisos •....••< 

Candy < , 


Sugar granulated. 
Maple airup 










1 3.0 










































































































































« Refuse, oiL h Bafnew iML c Flaia ooaftetltMiy aot *^t* 'Ttfirf »«% 

Nutritive Value of Foods 343 



Food material! (as pmchaaed) 

VEGETABLE FOOD — Cotltintud 

Vegetables a: 

Beans, dried 

Beans, Lima, shelled 

Beans, string 




Com, green (sweet), edible 






Peas (PisuM sativum), dried . 

Peas {Pimm satifum), shelled 

Cowpeas, dried 



Sweet potatoes 





Vegetables, canned: 

Baked beans 

Peas {Pisum sativum), green 

Corn, green 



Fruits, berries, etc., fresh b : 


Bananas. • 






Persimmons, edible portion. 
















































• I 



































Per Per 
cent, eenL 









































































a Such vegetables as jwtatoes, squash, beets, etc, have a certain amount of 
inedible material, skin, seeds, etc The amount varies with the method of pre- 
paring the vegetables, and cannot be accurately estimated. The figures given 
for refuse of vegetables, fruits, etc, are assumed to represent approximately 
the amount of refuse in these foods as ordinarily prepared. 

h Fruits contain a certain proportion of inedible materials, as skin, seedst 
etc., which are properly classed as refuse. In some fruits, as oranges and prunes* 
the amount rejected in eating is practically the same as refuse. In others, as 
Apples and pears, more or less of the edtble material is ordinarily rejected with 
the skin and seeds and other inedible portions. The edible material which 
is thus thrown away, and should propwly be dassed with the waste* is hers 
classed with the refuse. The figures for refuse here given rsprssSBtt M assdlT 
iw CM bs MOfftainsd* tbs nnsiititlw ofdimiily ndsctod* 

344 Physics and Chemistry 




t Milk ind *hdl. 
c The iTBraEB of fln ■lulria of cereal coffee grain il: Water 6.1, pr 
bt 3.4. carbohTdntM 71.6, and ath 4.5 per cent. Onl)' a portios of 
anti, honnT, cnten iato tb* iotoiloii. The aTvms* ta 
available nntticou in tht bereracB. Inlndona of canulne Coffee 
Ilka (be abore eoiuaia 








ncRAKa noo-CmNitaad 
Fmiw. bemra.. etc, fmh •: 




















































The Action of Heat, Adds, and Sodium Chlorid on Protein- 
Solubilities of Proteins — The Changes Caused in Meats by 
Cooking — ^The Action of Heat and Acids on Starches and 
Sugars — Solubilities of the Carbohydrates of Food — Com- 
parative Thickening Power of Different Starches — Methods 
of Making Doughs and Batters Light — ^The Nature and 
Action of Pectin. 

A KNOWLEDGE of some of the more important 
chemical and physical changes that occur in food as 
the result of cooking is a valuable aid in preventing 
mistakes which greatly lessen the digestibility of food 
and, consequently, its nutritive value; for food is of 
no use to the body until it has been absorbed and it 
cannot be absorbed until it has been digested. Also, 
as will be seen in the following pages, mistakes in 
cooking entail a loss of food in other ways. 

The Effect of Heat, Acids, and Sodium Chlorid on 


Experiment 42. Object: (a) To discover the tem- 
peratures at which the albumin of milk and egg^ the 
vitellin of egg, and the proteins of meat coagulate; 
(b) to see the difference in the nature of egg-white 
when it is coagulated slowly and rapidly. 


346 Physics and Chemistry 

Procedure: (a) Into separate large test-tubes put (i) 
milk, (2) egg-white, (3) egg-yolk, (4) a few small pieces 
of meat, and about 10 c. c. of water to keep the meat 
from sticking and hardening to the glass. Place the 
four tubes in a beaker of water and set this over a low 
flame. Watch carefully and test the temperature of the 
contents of each tube as soon as it begins to coagu- 
late and every few minutes as coagulation increases. 
Notice particularly the difference in the temperature 
and the time required for the coagulation of the white 
and yolk of the egg. 

(b) Pour some egg-white into a beaker yi full of 
boiling water and let this boil for three minutes. Put 
some egg-white into a test tube, stand this in a beaker 
containing cold water, and bring this slowly, taking 
ten minutes to do so, to boiling temperature. Com- 
pare the nature of the two coagula. 

How would you cook a so-called sqfl-baUed egg? 

How would you poach an egg? 

Experiment 43. Object: To test the effect of salt 
and organic acids on coagulation. 

Procedtu^: Into each of seven test tubes put about 
3 c. c. of egg-white. To tube 4 add J^ c. c. of 10% 
NaCl solution; to tube 5 add i. c. c. of 10% NaCl 
solution; to tube 6 add i drop of acetic add 1%; 
to tube 7 add 5 drops of acetic add 1%. Put the 
seven tubes into a water bath and keep the water just 
below boiling point for five minutes. (Notice the 
difference in the toughness of the egg heated alone 
and that of the egg to which the add and the salt 
were added.) At the end of five minutes add: To 
tube I, 2 drops of 1% acetic add; to tube 2, J4 c. c. 
of 10% NaCl solution; to tube 3, i c. c. of 10% NaCl; 
to tube 4, 2 drops of 1% acetic add; to tube 5, 2 

The Chemistry of Cooking 347 

drops of 1% acetic acid; to tube 6, i c. c. of 10% 
NaCl and the same to tube 7. Replace the tubes 
in the water bath and leave them for five minutes. 
Watch their contents carefully to detect the changes 
that occur. 

As the result of these experiments, state your opin- 
ion as to the desirability of adding salt to the water 
in which eggs are cooked. 

Would you recommend the addition of vinegar to 
the water? 

Would acid, as vinegar or lemon juice, poured over 
tough meat have any desirable effect? 

Will salt rubbed over the surface of meat before 
roasting help to retain the extractives in the meat? 
Why? (If in doubt of the correct answer, put a few 
small pieces of raw meat into a beaker containing 
water and let this stand for half an hour or more and, 
in a second beaker, do likewise with some meat you 
have heated until the outside has been well browned. 
Judging from the color of the water in the two beakers, 
decide whether coagulating the protein on the out- 
side of the meat tends to retain the extractives.) 

What will be the result of cooking eggs and meat at 
a high temperature? 

From these experiments, it can be seen that if 
protein is heated in a slightly acid solution or a neutral 
salt solution, coagulation is accelerated, but that 
larger amounts of acids (and the same is true of 
alkalies} prevent coagulation. 

Result of cooking on the protein of meat — ^Both 
dry and moist heat coagulate the proteins of meat and 
thus harden its tissue, but moist heat disintegrates 
the fibers and softens the connective tissue and thtis 
tenders the meat easier to masticate. Thus, cuts of 

348 Physics and Chemistry 

meat that would be very tough if broiled or roasted 
can be made tender by cooking them in water at a 
temperature slightly below boiling point. Searing 
the outside of meat by exposure to a high temperature 
will prevent the escape of extractive; but, if the high 
temperature is maintained, the meat will be toughened, 
and, if the surface of the meat is hardened, the heat 
will not penetrate. It has been found that roasts are 
as quickly — ^and much more uniformly — cooked at 
175^ C. as at 200® C. 

Solubilities of some of the common food proteins. 
— These are as follows: 

Albumins are soluble in water, dilute acids, dilute 
alkalies, and sodium chlorid solutions. 

Globulins also are soluble in dilute add, alkali, and 
neutral salt solutions, but insoluble in concentrated 
sodium chlorid solutions and in water. 

CaseinogeUi the important phosphoprotein of milk, 
is insoluble in water, dilute acids, and salts, but dis- 
solves in alkalies to form a salt-like body. It is pre- 
cipitated by dilute acids, but dissolves in strong adds. 
It does not coagulate on boiling. It is clotted by 
rennin. This is due to the conversion of the case- 
inogen into an insoluble protdn called casein. The 
calcitmi salts of the milk are necessary for this change 
as was seen by Experiment 40. 

The curd that forms when the rennin acts upon the 
caseinogen entangles the greater part of the fat of the 
milk so that the fluid portion which separates from 
the curd — ^the whey — contains only the salts, lactose, 
and lactalbumin. The presence of fat in the milk 
rather interferes with the forming of a hard curd and, 
therefore, when milk is curded in order to obtain 
whey, it is imperative that skimmed milk be used. 

The Chemistry of Cooking 349 

Legumixii the chief protein of the legumes, combines 
with the lime in hard water and is thus rendered very 
insoluble. Consequently the legumes must be cooked 
in soft water or else sodium bicarbonate must be 
added to the water. 

Gluten is insoluble in water, but one of its con- 
stituents — ^glutenin — is soluble in very dilute acid 
and alkaline solutions and the other constituent — 
gliadin — is soluble in 70 per cent, alcohol. 

Nucleoproteins are soluble in dilute alkaline so- 
lutions, but insoluble in water and dilute salt and acid 

Gelatin is soluble in warm water and in warm acid, 
alkaline, and salt solutions, but insoluble in all of these 
liquids when cold. 

Derived proteins and extractives are soluble in 
water, dilute acid, alkaline, and salt solutions. 

Mention all the practical applications you can 
think of to which knowledge of the coagulation and 
solubilities of proteins can be put in cooking and in 
the cleaning of cooking utensils. 

Are there more albumins or globulins in the meat? 
(See page 270) 

Why is the salt solution used for corning beef 

How will you roast meat? 

How will you make a stew? 

How make broth? 

Give reasons for all procedures. 


Experiments 44 to 46. Object : To see which of the 
common carbohydrates arc soluble in water and the 

350 Physics and Chemistry 

effect of letting vegetables such as potatoes stand in 

Experiment 44. Cut a portion of a firm potato 
into thin strips and let these stand in a beaker of 
water for at least half an hour. Do likewise with a 
wilted potato (use a separate beaker). • 

Experiment 45. Put a little bread into a beaker of 
water and in a separate beaker a few strips of dry 
toast and water. 

Experiment 46. Put a few strips of cabbage in 
(i) a beaker containing water, (2) a beaker containing 

(Record the result of these experiments before 
reading further.) 

The white substance that collected in the bottom 
of the beakers in which the pieces of potato stood is 
starch; therefore Experiment 44 shows that starch is 
insoluble in water, but that it will be extracted from 
potatoes if they are allowed to stand for any length 
of time in water. It will be noticed that the wilted 
potato did not part with its starch to anything like 
the extent that the firm one did and also that the 
condition of the wilted potato was improved by 
standing in water. Nearly all vegetables, soon after 
they are gathered, lose water by evaporation; this 
water must be replaced before the vegetable is cooked 
or served, or it will be neither tender nor crisp. 

Since such vegetables as potatoes lose starch while 
in water, they must lose it diuing cooking and, as 
shown in Experiment 45, the loss is greater as the starch 
becomes dextrinized* by heat and when the carbo- 
hydrate present is a sugar, as in parsnips, etc. There 
will be less loss of nutrient from potatoes if they are 

> The brown of the toast is dextrin. 

The Chemistry of Cooking 351 

cooked before they are peeled and, when baked, a 
XX)tato loses practically none of its constituents except 

In Experiment 45, the water in which the bread 
was soaked remained unclouded, but that in which the 
toast stood very soon became colored, showing that 
dextrin is soluble in water. That sugar is soluble 
in water is seen too often to need demonstrating., , 

Experiment 46 shows the difference of the action 
of water and acid on cellulose, the acid dissolving the 
cellulose to a slight extent. This is why the addition 
of vinegar to cabbage is thought to aid in its digestion. 

To sunmiarize, celluloses and starches are insoluble 
in water, dextrin and sugars are soluble. 

Experiment 47. Object: To show the effect of 
heat and water on starch. 

Procedure: (a) Put i tablespoonful of starch or flotir 
into a beaker and poiir over it i cup of boiling water. 
Stir slightly. Put the beaker over the flame and boil 
the contents for two or three minutes. Remove it 
from the flame. Take out some of the larger lumps 
and break them open. 

Why was the interior of the Itmap so little affected 
by the heat? 

(fi) Repeat (a), but before adding the water, mix 
thoroughly two tablespoonfuls of sugar with the 

(c) Repeat (a), but blend the flour to a smooth 
paste with cold water before adding the boiling water. 

(d) Repeat (a), but mix the flour with melted butter 
before adding the boiling water. 

Why did not the starch lump in (6), (c), (d)? 
Starch grains are enclosed in a comparatively soft 
cellulose sac. This, when heated to boiling tempera* 

352 Physics and Chemistry 

ture, is softened, and the grains swell to many times 
their original size, and, tmless they are well separated 
from each other in some way as by cold water, sugar, 
or fat, they will stick together, forming Itmips. 
The grains of cereals that have a comparatively thick 
cellulose sac can be prevented from lumping, even 
though they are not mixed with sugar, etc., if the 
water is boiling violently when the cereal is put into 
it and kept boiling during the process, the bubbling 
of the water preventing adhesion. 

When a starch paste is made with water below 
boiling temperature, the covering of the grain is un- 
broken, though the grain swells considerably, and 
when such a paste stands, the starch grains sink to 
the bottom. 

The comparative thickening power, transparencyi 
and flavor of starches. — Some starch grains swell 
much more than others and some will make a more 
transparent paste and have a more delicate flavor than 
others. This can be seen by the following experiment. 

Experiment 48. Into separate beakers, put 2 
grains of each of the following starches: Arrowroot, 
corn, potato, rice and wheat starches, tapioca, dextrin. 
To each add slowly, 40 c. c. of cold water, bring to 
boiling point and boil for five minutes; stir con- 
stantly. Compare the diflferent mixtures as to con- 
sistency, clearness, and flavor. Boil the pastes for 
five minutes longer and compare them again. 

Which forms the clearest paste? 

Of which paste is the flavor improved by the longer 

If, when following the directions of a recipe, you 
substitute the starch specified for another, will you 
use the same quantity? 

The Chemistry of Cooking 353 

Which of the starches used has the greatest thick- 
ening power and which the least? 

Experiment 49. Object: To study the effect of 
heat and heat plus acid on starch. 

Procedure: Heat some starch in an evaporating 
dish over a low flame until it browns, dissolve ^ of a 
teaspoonful of this in water. Make a starch paste, us- 
ing J^ teaspoonful of starch to J^ cup of water. Divide 
this into two equal portions, (6) and (c). To (c) add 
I c. c. of HCl and boil for ten minutes. Divide each 
of these three mixtures into two portions and test 
one with iodin and one with Fehling's solution. It 
will be noticed that the amount of starch used in each 
case is such that there will be an equal amount in 
each of the mixtures tested with Fehling's. The 
reason why this is necessary can be seen on page 398. 
For the same reason, it is necessary that exactly the 
same amount of Fehling's solution be used in each 

Into what was the starch changed by heat? 

Into what was it changed by heat and add? 

If unable to answer these questions, see page 398. 

Experiment 50. Object : To show the effect of heat 
and add on sugar. 

Procedure: Make a sugar solution by dissolving one 
teaspoonful of sugar in 30 c. c. of water. Divide this 
into three equal portions. To the portion in tube i 
add 5 c. c. of lemon juice; boU this and the solution 
m tube 2 for fifteen minutes. Divide the three 
solutions into two parts and test for cane sugar and 
for glucose as described on page 294. 

It will be seen that boiling reduces cane sugar to 
glucose, but that the reduction is more quickly and 
thoroughly accomplished when add is present. Glu* 


354 Physics and Chemistry 

cose, it will be remembered, it only about half as 
sweet as cane sugar. 

Why is sugar, when possible to avoid it^ not added 
in cooking until the cooking is nearly completed, 
especially when there is add in the food? 

Will you need more sugar for a baked or for a 
steamed custard? 

Sugar heated without liquid will, at a temperature 
of i6o® C. (320** P.). melt and form a brown mass, 
known as caramel, which has a slightly bitter, but 
agreeable flavor. Caramel dissolved in water, milk, 
or other liquid is much used as a flavoring for confec- 
tions and as a coloring matter for gravies and sauces. 

Methods of Making Doughs and Batters Light 

Doughs and batters are made light by one or other 
of four methods; viz; : 

(i) The introduction of air. 

(2) The addition of volatile substances to the dough. 

(3) The addition of substances to the dough which 
will dissociate and thereby yield a volatile gas. 

(4) The production of a volatile gas as the result 
of fermentation. 

In all four methods the essential facts depended 
upon are (i) Air and gas are expanded by heat; 
(2) that gluten is sticky and expansive and thus 
serves to hold the air or gas until the heat sets the 
dough in this porous state. The gas obtained from 
baking powder and other combinations of acids and 
alkalies and by the action of yeast is carbon dioxid. 

Method I. Air is generally introduced into 
doughs, etc., by one of the following ways: (a) By 
beating and rolling the dough as when making paste; 

The Chemistry of Cooking 355 

in this process the dough is alternately rolled or 
pounded and folded over so as to enclose air. The 
butter, or other fat, by keeping the particles of flour 
apart, helps to obtain this result, (b) The addition 
of well-beaten eggs to batters. This is a very com- 
mon method of introducing air, for especially the 
white of egg, when beaten alone, will take in and 
hold for a time a large amount of air. (c) Snow is 
sometimes used as a means of getting air into batters, 
because the snow cr3rstals contain considerable air. 

When air is introduced into batters and doughs 
in the ways just mentioned, the ingredients must be 
mixed quickly and the substance cooked at once, for 
the air will not be held very long as is shown by the 
rapidity with which the beaten white of egg loses its 
frothy condition on standing. 

Method 2. (a) The most common eicample of the 
use of this method is the addition of carbon dioxid 
gas to dough. This is the way in which the aerated 
breads, much used in England, are made light, (b) 
The addition of an alcoholic liquor, as wine, to a 
batter helps to make it light, because the heat of the 
oven volatilizes and expands the alcohol. 

Method 3. The substances generally used to 
obtain carbon dioxid in dough in Method 3 are 
sodium bicarbonate (baking soda) and an acid. The 
acid is somettn^es obtained by the use of molasses, 
which contains, some free add and acid salts, or sour 
milk, which contains lactic add formed by the fer* 
mentation of its lactose. When the lactic add unites 
with the soda, the following reaction occurs: 

BkSbZue ^^^^^ Sodium LaciaU 

UkaObs + CaH«OCXX)H - CjH,OOOONa + HaO 4- COj 

35^ : Physics and Chemistry 

Baking powders axe the form in which soda and 
acid are most commonly used. These consist of 
sodium carbonate and add and starch, the starch 
being used to prevent interaction of the other two 
constituents before the powder is wanted for use» 
should it become moist. 

The acids commonly used in baking powders are 
tartaric acid in the form of cream of tartar (potassium 
bitartrate), phosphoric add, and alum. 

Experiment 51. Object: To show the action of 
baking powders. 

Procedtu-e: (i) Mix J^ teaspoonful of soditun bicar- 
bonate and I teaspoonful of cream of tartar in a small 
beaker. In a second beaker, mix i teaspoonful of 
sodium bicarbonate with 30 c. c. of cold water and 
stir. In a third beaker, mix 2 teaspoonfuls of cream 
of tartar and stir. Combine mixtures 2 and 3. What 
happens? Heat the mixture. 

Explain the experiment before reading the following 

The effervescence that occurs in Experiment 51 is 
due to the liberation of carbon dioxid gas; bearing 
this in mind and that water also is formed, state what 
salt will be left in a batter when baking powder con- 
taining sodium bicarbonate and cream of tartar is 
used. What salt will be left when phosphoric acid 
is used? 

As shown by the first part of this experiment, no 
reaction takes place between the alkali and the acid 
80 long as these substances are dry, but as soon as 
water is added the two combine as described in 
Chapter XIV. For this reason, baking powders will 
deteriorate if they are not kept in a dry place. 

Another lesson to be learned from this experiment 

The Chemistry of Cooking 357 

is that chemical action soon ceases and, though the 
presence of the various solid ingredients of the batter 
prevent the action occurring and ceasing as quickly 
as in the experiment, unless the batter is cooked as 
soon as mixed, the gas will escape before the heat has 
done its work and the cake, etc., will not be light and 

Fate of substances formed in the reaction. — As 
may be inferred from the preceding paragraphs, there 
are three things formed in the chemical action between 
the alkali and the acids used for the purpose under 
discussion; viz., CO a, HaO, and a salt. The COa 
and the HjO pass off during the heating, but the salt 
remains in the food. 

Action of salts in the body* — The Rochelle salts, 
formed when a baking powder contains cream of 
tartar and the sodium phosphate occurring when the 
powder contains phosphoric acid, are laxative, but, 
as they are present in only very small amounts, they 
have little or no effect on the system. The alum salts 
that remain when any alum preparation is used are 
astringent, and it is thought that even in small amounts 
alum may aggravate any tendency to constipation 
if people eating food containing it are so troubled. 

Experiment 52. A test to detect the presence of 
alum in baking powder: Dissolve about a teaspoonful 
of the powder in water, add to this an equal amount of 
dilute (one-third the usual strength) tincture of log- 
wood, and then add an equal volume of ammonium 
carbonate solution. If altun is present, the liquid will 
become a dark blue or lavender color. 

Method 4. Yeast is the substance most commonly 
used for the fourth method of making doughs, etc., 

35^ Physics and Chemistry 

J, Nature of yeast. — Yeasts are microscopic, one- 
celled plants that multiply by budding (t. e., a small 
bud or swelling appears on a cell which gradually 
increases in size and finally splits ofiE). There is more 
than one variety. 

How obtained. — Yeasts are very prevalent in the 
air and, in the olden days, dough was exposed to the 
air until enough yeast entered it to cause fermenta- 
tion. Also some of the fermented dough of one day*s 
baking was often kept to act as a "starter" or 
"leaven" for the next baking. One great objection 
to these modes of getting yeast was that other micro- 
organisms and yeasts with undesirable character* 
istics entered the dough and frequently inte|:fered 
with the action of the true yeast and, in this and other 
ways, spoilt the dough. For this reason, cultivaled 
yeasts are now much used; e. £., compressed and dried 

Compressed yeast. — ^This is made by sowing puro 
yeasts of a desired variety in vats containing material 
upon which they will thrive. The yeasts grow quickly 
and in a few hotirs collect in a sctun on the top of the 
material. This is removed and pressed into cakes. 
This is one of the best varieties of yeast when used 
soon after it is prepared, but the cells die from lack 
of nourishment. 

Dried yeast cakes consist of cultivated yeast mixed 
with other ingredients, chiefly starch, pressed into 
shape and dried at a low temperature. The drying 
may kill some of the cells, but, if the cakes are kept in 
a dry, cool place, the majority of them will survive 
for a long time. Warmth and dampness will cause 
temporary activity of the yeast and consequent 
souring of the cakes. 

The Chemistry of Cooking 359 

The brewers' yeast, often used by bakers, consists 
of the scum which grows on the top of the matter 
undergoing fermentation in the making of beer, etc. 

Food required by yeast — In order that they may 
grow well, yeasts must be given the kind of food that 
they require. The principal thing that all the com- 
mon species require is sugar. This must be in solu- 
tion and not too concentrated, as is shown by the 
fact that^fruit cooked in a large amount of sugar, as 
in the making of jam, keeps better than that stewed 
in a small quantity of sugar. 

Action of yeast and cause of this action. — The yeast 
plants secrete at least three enzymes, one of which 
facilitates the change of starch to glucose thus: 
CoHioOj+HaO— C6Hxa06; another causes the fer- 
mentation of the glucose and thus changes it to 
alcohol and carbon dioxid, thus: CeHuOd^sCjHj- 
0H+2C0a, while the third facilitates the oxidation 
of the alcohol which is thereby changed to carbon 
dioxid and water. (Give the equation for this re- 

It will be seen that in Method 4, as in Method 3, 
carbon dioxid is the agent which causes the dough to 

The addition to dough of sugar and of milk (on 
account of its lactose) hastens the fermentation, for 
the sugar provides nourishment for the yeast and 
makes, it more active. For this reason, dried yeast 
will act more quickly if soaked in sugar solution before 
being used. The presence of potatoes and rye flour 
in dough also seems to hasten (crmentation ; the reason 
for this is thought to be that their soluble proteins 
stimulate enzymic action. 

The temperature at whidi dough is kept is of im- 


Physics and Chemistry 

portance. Yeast is most active between 70® F. and 
90° F. and it is destroyed at a temperature of 131® F. 
If dough is allowed to rise too long, adds will develop 
from the alcohol (acetic acid), from the butter (butjoic 
add)) and from the milk (lactic add), and thus the 
dough will be sour. The same thing will happen if 
the dough is kept at a temperature exceeding 90® F., 
because the yeast cannot then thrive well and add- 
forming spedes of bacteria which can do so will 
increase in number. 

Experiment 53. Object: To determine the com- 
parative fermentating pbwer of yeastsi 
Procedure: Make a dilute mixture of flotir and 

water. Fill the long 
stems of three fer- 
mentation tubes 
with the mixture.. 
To one add about 
A of a compressed 
yeast cake dissolved 
in lukewarm water; 
to another add a 
piece of equal size of 
a dried yeast cake 
likewise dissolved, 
and to the third tube 
add a little brewers* 
yeast. Mix the con- 
tents of each tube by 
shaking the tubes, 
see that all the mix- 
ture is in the long 
stem, plug the tubes, stand them in a warm place, 
and leave them for twenty-four hours. Inspect them 

Fig. 65. 

(a) Liquid is in the long arm of 
the tube. (6) Liquid has been forced 
into the short arm by the gas. 

The Chemistry of Cooking 361 

from time to time. As gas is formed, it rises to the 
top of the liquid and forces the latter down into the 
short arm of a tube. Which yeast acted the quickest? 

Experiment 54. Object: To see why sugar is added 
to dough in bread-making. 

Procedure: Make a flour-and-water mixture as for 
the preceding experiment, di\4de it into two portions; 
to one portion add about a teaspoonful of cane sugar» 
to both add } of a cake of compressed yeast dissolved 
in lukewarm water. Put these mixtures into fer- 
mentation tubes as in the preceding experiment. In 
which does fermentation first occur? 

Fig. 66. Apparatus Areakgbd pot Bxpbszkbmt 55. 

Experiment 55. Object: To prove that it is the 
same gas (CO a) that is obtained by the use of baking 
powder and yeast. 

Articles required: 2 beakers* a test tube with a 

362 Physics and Chemistry 

one-hole cork to fit; glass tubing bent as in Pig. 66; 
lime water, starch paste, yeast, baking powder, 

Procedure: Put some of the starch paste, plus y% of 
an yeast cake dissolved in lukewarm water, into a test 
tube and lime water into the beaker. Arrange the 
apparatus as in Fig. 66 and put it in a warm place. 
Notice the condition of the lime water after twenty- 
four hours. Put some baking powder in another test 
tube, some lime water in a beaker, and connect the 
apparatus as in Fig. 66. Then add some water to the 
baking powder. 

Does the lime water assume the same appearance 
in the two beakers? 

What gas causes the change in the lime water? 

What does it form in the lime water? 

Write the equation. 


As previously stated (page 291) pectin is present, 
though in very varying amounts, in nearly all fruit 
and in some vegetables. There is usually a larger 
amount present before fruit is fully ripe than later, 
and better jelly will therefore be made if part of the 
fruit used for the purpose is not quite ripe, but, as 
ripening improves the flavor of fruit, a portion of it 
should be ripe. 

Pectin can be usually esctracted from fruit by soak- 
ing the latter in warm water, but sometimes it is 
necessary to boil it (as shown in Experiment 56), and 
this will always result in the extraction of a larger 
quantity of pectin. If the cooking is continued too 
long, however, the pectin will be decomposed to r^ 

The Chemistry of Cooking 363 

dudng sugars and its gelatinizing property thus 

Pectin, in the presence of vegetable acids, is precipi- 
tated or thrown out of solution by such substances 
as alcohol, salts, and sugar. When a sufficiently large 
amount of pectin and vegetable acid is present in a 
liquid the whole solution will be formed into a thick 
mass known as jelly by heating it with sug^ir. If more 
sugar is used than there is pectin to unite with, the 
mass will be soft and gtunmy or else the excess sugar 
will crystallize. 

The amount of acid present is also of importance 
for the formation of a firm jelly, and when making 
jellies from fruit that is not very add the juice of a 
fruit that is or a small amount of dtric or tartaric 
add is sometimes added. 

Thus, it can be seen that to make a good jelly from 
fruit, it is necessary to have proper proportions of 
pectin, sugar, and add, and to cook the fruit the exact 
time required. Consequently, the directions of a 
reliable redpe must be followed accurately. 

Experiment 56. A test for the presence of 

The common test for pectin is to add a little (about 
5 c. c.) ethyl alcohol to an equal amount of fruit juice 
or a water extract of the fruit. The formation of a 
clear gelatinous predpitate indicates the presence of 
pectin. At the completion of the experiment the 
quantity of predpitate obtained from each fruit should 
be compared. 

Any fresh fruit can be used for this experiment, but 
several should be tried, among others lemons, oranges, 
and berries, and also carrots; raw fruits, both juices 
and extracts, and similar cooked fruits shotdd be 

364 Physics and Chemistry 

tested; the juice, peel, and white part of oranges and 
lemons should be tested separately. 

A water extract of the fruit can be usually made by 
soaking the fruit, after squeezing out the jtiice, in 
warm water for about half an hour, but the pectin in 
the peel and white part of oranges and lemons is hard 
to extract; therefore, separate the two parts and (keep- 
ing them separate) grind or cut them into fine strips, 
cover these with water, heat this to boiling tempera- 
ture slowly; strain, cool, and add alcohol to about 
5 c. c. of the liquid. Repeat this treatment of the 
white and peel (using the same portions) until a 
filtrate is obtained that ceases to show the presence 
of pectin. 

Answer the following questions: 

How many extracts were made of the white and of 
the peel of the orange and the lemon before the filtrate 
ceased to contain pectin? 

Did you find more pectin in the juices or in the 
extracts from the solid portions of the fruits? 

What part of oranges and lemons causes marmalade 
to jeU? 

Will soaking oranges before cooking improve a 

In which fruits did you find the largest amounts of 

Can jellies be made from all fruits containing pectin? 

Is there the same amount of pectin in raw as in 
cooked fruits? 




Causes for the Spdlins: of Food — Nature of the Orgsnisms that 
Cause the Spoiling — Chemical and Physical Changes that 
Occur in the Decomposition of Pood Substances— Omdi- 
tions Necessary to Prevent Contamination and to Preserve 
Food — Some Common Forms of Food Adultetatioo. 

The Spoilliig of Food 

Causes of the spoiling of food. — ^Food spoils becatise 
it is attacked by the fungi known as molds, by yeast, 
or by certain species of bacteria. 


Nature. — Molds, of which there are many varieties, 
are a species of fungi which, when fully developed, 
consist of a mass of threads, known as myceliufn, on 
which are minute sacs, known as the spore cases or 
sporangia, that contain spores. 

Multiplication. — Molds mtdtiply and spread be- 
cause, when their spores mature, the sporangia burst 
and the spores fall upon the food on which the parent 
mold is growing or are blown about by the wind and 


366 Physics and Chemistry 

settle on other food, and, also, the spores are carried 
by insects that have lighted upon molded food. 

Experiment 67. Object: To study conditions that 
favor the growth of molds. 

Procedure: (i) Cut some pieces of bread into small 
— ^about two inchds — squares, put several of these 
together in layers, wrap them in paper, put them into a 
tin box, and set the box in a warm place. 

(2) Prepare some other slices of bread in a similar 
manner, store them in a cool dry place. 

(3) Put some pieces of bread loosely in a tin box 
that has a few small holes in either side, for the drcu* 
lation of air, and place the box in a cool, dry place. 

(4) Repeat i and 3 with stale bread. 

(5) Repeat i and 3 with fresh cheese. 

(6) Repeat 5 with cheese taken from a piece that 
has started molding. 

(7) Place some pieces of fresh bread where it is 
exposed to the air and where the sun will shine 
upon it. 

(8) Wrap some cereal in paper and place it in a 
warm, moist place. 

(9) Cut some pieces of fruit, including lemons, and 
place them in saucers or evaporating dishes. Leave 
them exposed to the; air. 

(10) Make a little dilute and saturated sugar solu- 
tions, boil them both for one minute, and then let them 
stand exposed to the air in evaporating dishes. 

Let these all stand for a week or longer; examine 
them from time to time. Notice which ones start 
to mold first; notice the difference in the appearance 
of the molds. 

As the result of your observations answer the fol- 
lowing questions: 

Spoiling and Preservation of Food 367 

Is there any apparent change in the appearance of 
the food? Has it grown less in quantity? 

Is there any odor? 

Will bread keep better where there is a free circula- 
tion of air or where air is excluded? 

How do temperature and moisture affect the growth 
of molds? 

Under what conditions must food be kept to prevent 
it molding? 

WiU dried food mold as quickly as that containing 
considerable water? 

Does the presence of a molded piece of food influence 
the spoiling of the remainder of food kept in the same 

Does fruit acid inhibit the growth of mold? 

Why will preserved fruits keep 
better when a large amount of 
sugar is used in their cooking? 

Examine some of the different 
molds under the microscope. 
To do this, remove a small por- 
tion of mold, with a platinum 
wire or point of a penknife, 
from the food upon which it is 
growing and place it on a glass 

slide; try to keep it in the same ^r.^^^.'L?!..^^ w*' ^ 

position as that in which it grew 

on the food. ' Examine it with 

the low-power objective of the 



Fig. 67. 


Common Form of Mold 

(a) Spores. 

(b) Sporangium. 

(c) Mycelium. 

The nature and action of yeasts were discussed in 
Chapter XX. 

368 Physics and Chemistry 


The bacteria concerned in the spoiling of food are 
the various species classed as saprophytes; i. e., those 
which feed on non-living organic matter and in doing 
so catise it to putrefy, ferment, or decay. 

Result of infection of food by molds, yeasts, and 
bacterid* — ^These organisms use the food upon which 
they fall for their nourishment, but they cannot do so 
while it is in its natural condition any more than 
human beings can assimilate the food they eat until 
it has been digested. Therefore, just as happens in 
the human alimentary canal, these organisms, by 
virtue of enzymes which they secrete, cause the dis- 
integration of food into simpler substances and from 
these they remove what they require for their sub- 
sistence. Some of the substances formed during the 
process are gaseous and these soon pass from the 
material; this is one reason for the loss of bulk and 
accounts for the odors that develop. Some of the 
other disintegration products are liquid and others 
are soluble and go into solution in the water present; 
thus food undergoing putrefaction, fermentation, etc.» 
is usually softer than unspoiled food. When the 
molecules of the food material are broken, they no 
longer contain all the elements that they can hold in 
combination and they unite with oxygen or other 
elements; oxidation is thus associated with decom-^ 
position processes. Read the following chemical 
formulas and decide which of the processes thus 
portrayed are associated with oxidation: 

spoiling and Preservation of Food 369 

CHftOj « COa + CaHs- OH 

CaHs,. OH + O - CH,. COH + HaO 

CH,. COH + O = CH3. COOH 

CH,. COOH + 30= 2C0a + HaO 
Ammonia Carbamate Urea 

COaNaHe - HaO = CONaH^ 

Butyric acid 

C6H,a06 = 2Ha + COa + C^HgOa 

Effect of changes caused by molds, etc., oa the 
wholesomeness of food. — Certain molds and bacteria 
are purposely cultivated in food in order to produce 
the desired flavor, e. g., the molds of Stilton and 
Roquefort cheeses, but in such case special cultures 
of the organisms are used. 

The common consequences of mold infection is the 
production of a musty disagreeable flavor in the food. 
As a rule, the substances formed by molds in food are 
not poisonous, unless the condition proceeds to such 
an extent that putrefactive bacteria are also at work, 
as usually occurs in advanced stages of molding. 
Consequently, when the molding is not extensive, if 
the mold and the material lying directly below it are 
removed, the food can be used. If it is to be kept for 
any length of time, however, it must be boiled for at 
least twenty minutes in order to destroy any spores 
that may have fallen into it. 

The substances produced by yeast are not un- 
wholesome and fermentation can be arrested in the 
same way as molding, but if the fermentation process 
continues the food will become so acid that it will be 
.The substances produced by bacteria that cause 

370 Physics and Chemistry 

fermentation are similar to those produced by yeast, 
but food in which putrefactive changes have occurred 
has, when eaten, caused severe and even fatal poison- 
ing. Just which germs are responsible for this so* 
called ptomain poisoning is not known, but it is known 
that they thrive better in the absence of air than in 
its presence, and in warm places. Food which has 
been in cold storage and later kept in a warm place 
is particularly apt to be so infected. 

Conditions and Food Most Conducive to the Life of 

MoldSi etc. 

As shown by Experiment 67, molds grow best in 
dark, damp places where there is no free circulation 
of air. Wliy moving air interferes with the growth 
of molds is not wholly understood, but it is thought 
that disttu'bance of their threads by the wind may 
interfere with their growth and also that air currents 
increase the rapidity of the evaporation of moisture 
from the surface of the food and thus renders it an 
unfavorable groimd for the molds. Thus, molds grow 
much more rapidly in tightly closed vessels or cup- 
boards than in those through which there is a current 
of air; in food piled up than in that spread out; in 
food filled with cavities, like bread and cheese, than 
in that with a smooth surface. Though dampness 
favors mold development, very moist food, as milk 
and meat, are not as likely to be attacked by molds 
as by bacteria. Molds, however, will grow upon food 
far too dry to be used by bacteria (e. g., cereals and 
dried fruit) when the atmosphere surro:unding the 
food is moist. 

Yeasts require food containing sugar or starchy 

spoiling and Preservation of Food 371 

substances that they can change to sugar. They grow 
best at a temperature between 70** and 90** F. Their 
growth is arrested at a temperature below 40^ F. 
and they are soon killed at boiling temperattu^. 

The majority of saprophytic bacteria thrive best 
at a tcmperattire of 70^ to 90^ F.» and are killed by 
moderate heat — 140® to 160® P. — if it is continued for 
from thirty minutes to one hour, but there are some 
species that thrive best at a temperature of about 140^ 
F. and can be killed at boiling temperature only if it 
is maintained for at least one hour. The growth and 
action of all species are inhibited at a temperature 
below 40^ F. Bacteria grow better in darkness than 
in light — direct sunlight will kill many varieties. 
Bacteria, even more than yeasts and molds, require 
, moisture for their development ; many kinds will not 
grow in food containing less than 25 to 30 per cent, 

Practical Application of the Knowledgement of the 
Requirements of Molds, Teasts, etc., to the 

Keeping of Food 

Since molds and bacteria prefer darkness to light, 
kitchens and pantries should be very light rooms and 
food cupboards and storerooms should be provided with 
ventilators and they should be as light as possible 
without raising their temperature. All these places 
and all utensils into which food is put must be dry 
and clean. ' Places where food is stored must be cold. 

' Such tttensils as bread and cake boxes and cereal jars should 
be frequently scalded and exposed to the air. Milk utensils 
should be well aired and sterilised after use. 

37^ Physics and Chemistry 

Keeping Fruit and Vegetables 

Such vegetables as potatoes and beets have some* 
what different requirements from the majority of 
f oodstuffs» for if given light and air, they will germi- 
nate and sprout». therefore they are kept in the 
dark, packed in bins or barrels. Carrots, turnips, 
and parsnips keep better if buried in sand. For 
all these vegetables, the storeroom must be cool 
and dry. Winter squash, unlike the other vege- 
tables, keep best if spread out in a rather warm 

It is most important for the preservation of fruit 
and vegetables that they be kept dry while in storage. 
Though, as shown by Experiment 67, some foods mold 
more quickly when rolled in paper, because they are 
then not exposed to air currents, soft, porous paper 
wrapped around fruit that is packed in boxes seems 
to prevent it molding and decaying, probably be- 
cause the paper absorbs the moisture from the surface 
of the fruit and prevents that in which decay has 
started coming in contact with sound fruit. Grapes 
are packed in sawdust for the same reasons. Drying 
fruit with a soft doth also helps to keep it fresh. The 
peel of fruit helps to protect it from molds and bac- 
teria; thick-skinned fruits, like oranges and winter 
apples, can be, with proper care, kept in their natural 
state for months, but thin-skinned fruit, like cher- 
ries, will not keep in good condition for any length 
of time. Only fruit in perfect condition should be 
stored; if the skin is bruised or broken, molds, etc., 
can easily enter and, as seen in Experiment 67, 
one piece of molded food will soon infect that which 
is sound. 

Spoiling and Preservation of Food 373 

Means of Preserving Food 

The means usually taken to preserve food are (i) 
sterilizing it and keeping it under sterile conditions. 
(2) Keeping it in a temperature below 40** P, (3) 
Drying it. (4) Adding substances to it that will in- 
hibit the growth of organisms. When used for this 
purpose such substances are called preservatives. 

Sterilization. — Food to be preserved in this way 
must be subiuitted to a high enough temperattu^, for a 
sufficient length of time, to kill bacteria. It has been 
found that the time and temperature necessary vary 
with different foods; therefore, when preserving or 
canning food, the directions of a reliable recipe book 
regarding these matters should be followed. Some 
foods, e. g,, peas, beans, and corn, require a very long 
time — ^from one to two hours — at a temperature of 
212° F., to be rendered sterile. Food will be better 
sterilized if put into cold water and brought to boiling 
point, than if put at once into boiling water. Sterilized 
food, if it is to be kept, must be put into sterile jars, 
while it is still hot, and sealed at once. The sealing 
must be perfect, so that it will be impossible for germs 
to enter. If, for instance, hard rubbers are used for jars 
into which jam is put, the sealing will not be perfect 
since the tightness with which the cover can be screwed 
down depends upon the softness of the rubber. 

In canning factories, tin jars are usually , used. 
The fruit and vegetables, with or without previous 
boiling, are put into the cans and the covers are sol* 
dered on. There is a small hole in each cover, to 
allow the air to escape as it becomes expanded by the 
heat. The cans are placed in the heating apparatus 
and left the required length of time. At the conclusion 

374 Physics and Chemistry 

of the sterilization, they are removed and the holes 
are at once covered with solder. 

Cold, — In order to preserve food by cold for any 
length of time the temperature must be kept even and 
below 40® F. — in fact, it is necessary for the preserva- 
tion of many foods to keep the temperattu^ as low as 
33® P. Even at this temperature, bacterial action, 
though inhibited, is not entirely prevented and thus 
food cannot be kept in cold storage indefinitely with* 
out deterioration occurring. 

Drying. — This is one of the most widely used means 
of preserving food — ^meat, fish, fruit, and vegetables 
all being preserved in this way. Some of the fruits 
that are frequently thus preserved contain enough 
sugar to aid in their preservation. Salt is often used, 
in addition to drying, in the preservation of meat and 
fish and these foods are sometimes smoked, as well as 
dried, since the creosote of the wood acts as a preser- 
vative by destroying germs upon the surface of the 
food and by so impregnating it that bacteria cannot 
grow in it. 

Drying is usually accomplished by exposing the 
food to heat from various sources and in various ways, 
or else by submitting it to hydraulic pressure and 
thus removing much of its water. 

Drying toughens the fiber of foods, both those of 
animal and vegetable origin, and causes considerable 
loss and change of flavor. In order to minimize the 
result of toughening, nearly all dried foods are soaked 
in water for several hours before being cooked. This 
does not, however, apply to the cereals, which are dry 
by nattu'e and subjected to little if any artificial drying. 

Preservatives. — ^These are often classed as legitimaie 
preservatives and adulieranls. 

spoiling and Preservation of Food 375 

By legitimate preservatives are meant substances 
that will inhibit the growth of germs, but in the 
quantities used have no injurious effect upon man. 
Those 'n common use are salt, sugar — used in suf- 
ficient quantity to be concentrated — , spices, and 

By adulterants are meant substances such as borax, 
benzoic add, salicylic add, and formaldehyd. Some 
people contend that these substances should not be 
classed as adulterants for reasons that will be seen 

"According to the law of many of the States of 
America, a food is dedared to be adulterated under 
the following conditions: 

"First, if any substance or substances have been 
mixed with it, so as to lower or depreciate or injuri* 
ously affect its quality, strength, or ptuity; second, if 
any inferior or dieaper substance or substances have 
been substituted wholly or in part for it; third, if 
any valuable or necessary constituent has been wholly 
or in part abstracted from it; fourth, if it is an imita- 
tion of or is sold under the name of another article; 
fifth, if it consists wholly or in part of a diseased, de- 
composed, putrid, infected, tainted, or rotten animal 
orvegetablesubstanceorarticle, whethermanufactured 
or not, or, in the case of milk, if it is the product of a 
diseased animal; sixth, if it is colored, coated, polished, 
or powdered, whereby damage or impurity is con- 
cealed, or if, by any means, it is made to appear better 
or of greater value than it really is; seventh, if it con- 
tains any added substance which is poisonous or in- 
jurious to health. Provided: that the provisions of 
this act shall not apply to mixtures or compounds 
recognized as ordinary artides or ingredients of food^ 

376 Physics and Chemistry 

if each and every package sold or offered for sale bear 
the name and address of the mantifacturer and be 
distinctly labeled tinder its distinctive name and in a 
manner so as plainly and correctly to show that it is a 
mixture or compound and is not in violation with 
definitions fourth and seventh of this section." ' 

Those who contend that the antiseptic preserva- 
tives mentioned on page 375 should not be classed as 
adulterants base their assertion on the fact that the 
preservatives are often of greater commercial value 
than the foods in which they are used and that in the 
small quantities in which they are used they are not 
injurious to health. Those who take the opposite 
view contend that even if the preservatives do them- 
selves cost more than the food, they allow the manu- 
facturers to use cheaper — even partly spoiled — food, 
for preserving, canning, etc. Also they hold that it has 
never been proved that even small quantities of sali- 
cylic acid, borax, etc. , if constantly used, are not to some 
extent injurious, especially to children and invalids. 

A few simple experiments to detect the presence 
of chemical preservatives in food*: 

The chemical reagents required for these experi- 
ments are as follows: 

Turmeric paper Potassium permanganate 1% 

Alum solution, 10% Ethyl alcohol 

Iron alum (crystal or powder form) Chloroform 
Sulphuric add Boric acid or borax 

Hydrochloric add Ammonia water 

Tincture of iodin 

' Bulletin 100, U. S. Department of Agriculture. 

* The majority of these experiments have been taken from 
Bulletin 100, U. S. Dept. of Chemistry: "Some Forms of Food 
Adulteration and Simple Methods for their Detection." 

Spoiling and Preservation of Food 377 

As in the tests to discover the constituents com- 
posing food, the majority of tests to discover food 
adulterants consist in the use of reagents that will, if 
the matter sought is present, combine with it and 
form a substance that will be precipitated or that 
will give a special color reaction. As a rule, the tests 
are better performed with the material being tested 
in solution or, at least, in a semi-liquid condition. 
Solid and semi-solid foods are therefore usually dis- 
solved, and, if necessary, macerated in distilled water 
before the reagent is added. 

Salicylic Acid 

Salicylic add is used for preserving condiments, 
sauces, and fruit products of all kinds — jellies, marma- 
lades, etc., — ^and it is a common constituent of the 
various powders sold as preservatives. 

Experiment 68. Put about 60 c. c. of the liquid 
to be tested into a small flask, add a few drops of 
sulphuric add, and shake the flask for two or three 
minutes. Filter this solution into another small 
flask. Add about 30 c. c. of chloroform and mix the 
two liquids by a somewhat vigorous rotary motion 
(shaking is to be avoided as it produces an emulsion 
which is difficult to break up). Pour the solution into 
a beaker. Let it stand until the chloroform settles 
at the bottom and then, with a medicine dropper or 
pipet, transfer as much of the chloroform as possible 
to a test tube. As salicylic add is soluble in chloro- 
form, it will now, if there was any present in the food, 
be in the chloroform. To the chloroform, add an 
equal amount of water and a small piece (a little 
larger than a pinhead) of iron alum. Shake the mix- 

378 Physics and Chemistry 

ture and then allow it to stand until the chloroform 
again settles at the bottom. If salicylic add is 
present, a pmple color will develop at the top of the 

Benzoic Acid 

Benzoic acid is often used for preserving jams, 
jellies, tomato catsup, and similar articles. 

Experiment 69. Extract the sample with chloro- 
form according to the directions given for salicylic 
acid, but, after removing the chloroform, put it into 
a beaker and put this in a warm place or a water 
bath. Let it stand thus until the chloroform evapo- 
rates. If benzoic acid is present, it will be seen in the 
form of characteristic flat crystals on the bottom of 
the beaker and these, if heated, will emit the tmmistak- 
able odor of benzoic acid. 

Boric Acid and Borax 

Boric acid — ^known also as boracic (idd — ^and its 
sodium compound borax are often used to preserve 
animal foods, such as sausages, butter, and milk. 

Experiment 70. To prepare solid food for this 
test, macerate it with distilled water, strain it through 
fine white cotton cloth, and then filter the liquid thus 
obtained through filter paper. 

To prepare butter, place a heaping teaspoon in a 
beaker, add about 10 c. c. of boiling, distilled water, 
stand the beaker in a water bath until the butter is 
thoroughly melted. Stir this with a teaspoon and 
place the beaker, with the spoon in it, in a cold place 
until the butter becomes solid. Remove the spooQ 

Spoiling and Preservation of Food 379 

and the butter (which adheres to it) and filter the 
liquid through paper. 

To prepare milk, pour about 60 c. c. into a small 
flask with about twice that amount of a 10 pef cent, 
solution of alum, shake the mixture vigorously, and 
then filter it. 

Test: Take about 5 c. c. of the liquid obtained as 
described, add and mix thoroughly 5 drops of con- 
centrated hydrochloric add. Dip a strip of turmeric 
paper into the liquid and then hold the paper in a 
warm place until it dries. If there is boric acid or 
borax in the liquid, the paper, when dry, will be a 
bright cherry red and a drop of ammonia will change 
the red color to dark green or greenish black. If too 
much hydrochloric add is used, the turmeric paper 
may become a brownish red, even though there is n6 
boric add in the solution; in such case, however, 
ammonia changes the color to brown, just as it does 
turmeric paper which has not been dipped into the 
add solution. 


Formaldehyd, being volatile, is useless as a pre* 
servative for food that is to be kept for any length 
of time, but it is often used in warm weather to pre- 
vent milk souring. It is probably the most com- 
monly used milk preservative at the present time, 
though boric and salicylic adds are also used. 

Experiment 71. Pour about 30 c. c. of milk into a 
flask and an equal quantity of concentteted hydro- 
chloric add. Add a small piece of ferric alum (about 
the size of a pinhead) and mix the fluids by rotating 
the flask between the hands. Then place the flask 

380 Physics and Chemistry 

in a water bath containing boiling water and let it 
stand for five minutes (do not keep heat under the 
bath during this time). If formaldehyd is present, 
the mixture will become purple. 

Copper Sulphate 

Copper stilphate is sometimes added to canned green 
vegetables, especially peas, to improve their color. 

Experiment 72. To about a teaspoonful of the 
mashed vegetable add three teaspoonfuls of water and 
30 drops of strong hydrochloric add. Stir the mix- 
ture with a piece of wood and set the beaker in a 
water bath. Drop a bright iron wire nail (tin carpet 
tacks will not do) into the mixture and keep the water 
surrounding the beaker boiling for twenty minutes. 
Stir the mixture frequently. At the end of twenty 
minutes, remove the nail and examine it. If there 
was any appreciable amount of copper in the mixture, 
the nail wiU be coated with it. 

Other Forms of Adulteration 

The mixing of a cheap article with a more expensive 
one is an even more common form of adulteration 
than the use of chemicals for preservation. For ex- 
ample, cheap cereals and flours are mixed with more 
expensive ones; chicory, ground beans, and the Uke 
are mixed with coffee; starch and saccharin are added 
to jellies; cheap fruits, as apples, are mixed with rarer 
ones in jellies and jams. As apples are as wholesome 
as any other fruit, their addition to jams, etc., is not 
considered an adulteration if their presence is stated 
on the label. 

Spoiling and Preservation of Food 381 

Experiment 73. To detect starch in jellies, jams, 
etc. In order to detect starch in any substance, the 
iodin test is used, but, so that change of color may 
be perceived if it occurs, it is necessary to decolorize 
colored substances such as jellies. To do this, dis- 
solve the material, heat it to boiling point, and add 
potassium permanganate, drop by drop, until the 
liquid is colorless. Then cool the mixture and add 
iodin. The presence of starch is indicated by the 
iodin becoming blue. 

Adulteration of Cereals and Flours 

Unchanged starch grains have the characteristic 
structure of the seed in which they were formed, and 
as the seeds of different plants vary in shape, micro- 
scopic examination of starch, etc., is a means often 
employed to detect adtdteration of one grain with 
another, as, for instance, wheat flour with com flour, 
which is cheaper. 

^_ Adulterations of Coffee j 

The presence of adulterants in coffee can be often 
detected by examining a sample under a magnif3ring 
glass. When seen under the glass, the coffee particles 
appear quite different from the coffee substitutes em- 
ployed. Chicory, especially, having a dark gtunmy 
appearance, stands out in strong contrast to the 
coffee. All the usual coffee substitutes, except chicory, 
contain starch and, therefore, the iodin test is another 
means of detecting adulterations other than chicory. 
A weak infusion must be used so as not to obsctu'e the 
color change. Still another method of testing ground 

382 Physics and Chemistry 

coffee is to put a small amount of coffee into a bottle 
half-full of water, shake the bottle vigorously, and 
then let it stand quietly. Pure coffee contains a 
large amount of oil and, consequently, it will float 
while the substitutes sink to the bottom of the flask. 

Adulterations of Butter 

The so-called spoon test is often used to distinguish 
pure butter from renovated or process butter and 

Experiment 74. Take a small piece of the butter 
sample in a large spoon and hold it over the Btmsen 
flame. If the sample is fresh butter, it will boil quietly 
with the evolution of a large amoxmt of froth. Oleo- 
margarin and process butter, on the other hand, 
crackle and sputter as they melt and boil. 

The Adulteration of Salad Oil 

The adulteration of salad oil with cotton-seed oil* 
is not uncommon. 

The Halophen test is very often used to detect this 

Experiment 75. Procedure: Put about 5 c. c. of 
oil into a test tube and add an equal quantity of both 
amyl alcohol and carbon disulphid. Cork the tube 
and place it in a beaker of hot water. Leave it thus 
for half an hour; keep the water hot during this time, 
but do so by the addition of boiling water when neces- 
sary; do not bring the tube near a flame, for carbon 
disulphid is excessively inflammable. At the end of 
that time, if even a small percentage of cotton-seed oil 
be present, the mixture will be of a distinct reddish 

Spoiling and Preservation of Food 383 

color, and if the sample consists largely or entirely of 
cotton-seed oil, the color will be deep red. 

The Adulteration of MUk 

The more common methods of adulterating milk 
are: The use of preservatives, the addition of water, 
the removal of a part of the cream. 

The preservatives most conamonly used are formal* 
dehyd and boric add. Means of detecting these have 
been already discussed. The presence of preserva- 
tives in milk is particularly objectionable because (i) 
it is so much used for invalids and young children 
who may be injured by such preservatives; (2) the 
action of lactic add bacteria is easily inhibited and 
the souring of milk thus retarded, but germs which 
cause putrefaction are not so easily affected and the 
changes which they cause in milk, while infinitely 
worse, are not so easily detected. Consequently, 
milk containing preservatives may also contain inju- 
rious products of putrefaction. It is such substances 
in milk that are often responsible for the gastro* 
intestinal disturbances in children that are so common 
in summer. 

The presence of water in milk is determined by the 
use of a lactometer or hydrometer. The spedfic 
gravity of water, it will be remembered, is said to be 
I and that of ordinary whole milk, as compared with 
water, is 1.027 to 1.033. If the milk contains more 
than 4 per cent, cream it may be slightly lower than 
these figures, but much difference indicates the pres- 
ence of the liquid with the lower specific gravity, 
i. «., water. 

The Babcock test. — ^This test is very commonly 

384 Physics and Chemistry 

tised for estiinating the per cent, of fat in milk. The 
test depends upon the fact that the organic mattar 
of loilk, except fat, is decomposed by sulphuric acid, 
while, practically, the only change in the fat is that it 
is set free. 

The articles required for the test are: A milk test 
bottle (see Fig. 66 ; this bottle has a long neck, gradu- 
ated in such a way that the nimibers i, 2, 3, etc., re- 
present I, 2, 3, etc., per cent, fat and the small lines 
between the numerals represent -nr of i per cent.) ; 
a graduated pipet; an acid measure; a centrifugal 
machine; the milk to be tested; hot water; sulphtuic 
acid with a specific gravity of 1.82. 

Procedure: The milk to be tested is measured with 
the pipet. To do this, hold the pipet between the 
thtunb and middle finger, put the pointed end of the 
pipet into the milk and the other end in the mouth, 
and, by suction, draw the milk up above the marks 
on the stem. Then, quickly, put the index finger 
over the upper end of the pipet, to keep the milk from 
running out. Next, hold the pipet vertically, with 
the 17.6 mark on a level with the eye and, by slightly 
relaxing the pressure of the finger covering the upper 
end of the stem, allow the milk to flow out until it is 
at the 17.6 mark. Then place the pointed end of the 
pipet in the mouth of the milk bottle, holding both 
bottle and pipet obliquely, remove the finger from the 
upper opening and let the milk run down the neck of 
the bottle. If the milk is put in otherwise, the air 
in the bottle may form bubbles in the milk and cause 
it to overflow. If the milk does not all leave the 
pipet, blow into the upper end of the tube. Fill the 
acid measure to the 17.5 mark with stdphuric acid 
Md add this to the milk slowly, holding the bottle 

w ■ {/) 

Pig, 68. Apparatus for Babcock Milk Test. 
[at MHk Bottle. (6) Pipct. (c) Acid Measure. 

[d), (e), ( n Different varictiL-S of Ctntrifujpil Machines. 
Id) A two-botlle Hand Machine (not in acllon). 
' A four-bottle Hand Machine (in action). 
An Electric Machine. 

386 Physics and Chemistry 

obliquely while doing so. (N. B., remember that 
sulphuric add is very corrosive.) Whirl the bottle in 
the centrifugal machine for five minutes. Remove 
the bottle, add enough hot water to bring the fat 
into the narrow neck. The fat can be easily dis- 
cerned, for it is lighter in color than the rest of the 
liquid, which holds the decomposed organic matter 
in solution. After the addition of the water, replace 
the bottle in the centrifugal machine and whirl it for 
three minutes. This brings all the fat to the top. 
Then remove the bottle and, holding it with the fat 
on a level with the eye, note the marks opposite its 
upper and lower levels. To estimate the per cent, 
of fat it is necessary to subtract the number below 
the level of the fat from the top reading. For example, 
if the upper level of the fat is on a line with the mark 
5.2 and the lower level with the mark i. 2, the correct 
reading will be 4 per cent, since 5.2 — 1.2=4. This 
would show that the milk tested contained 4 per cent, 




The Nature of the Changes Occurring in the Digestion of the 
Various Pood Stuffs — The Organs in Which These Changes 
Occur — ^The Factors and Conditions Influencing Digestion 
— Nature of Enzymes, Zymogens, and Kinases. 

Reason for digestion. — ^With the exception of the 
monosacchaxids and the disaccharids, organic food sub- 
stances are unable to pass through animal membranes 
and, consequently, they are of no use to the body 
until they undergo certain changes which transform 
them into substances that will go into solution and 
pass through the walls of the blood-vessels and lacte- 
als. For it is only after food has passed into the 
blood and been carried by it to the tissues that it bene- 
fits the body. The various changes that food tmder- 
goes in this process of preparation are classed as 

Mineral matter, monosaccharids, and disaccharids 
are readily soluble in water and the two first men- 
tioned are quickly absorbed from the stomach and 
the intestines. Disaccharids will be absorbed un- 
changed if eaten in large quantities, but, when this 
happens, they are qtiickly eliminated from the system 
in the urine, the tissues being unable to utilize them. 

Nature of digestion. — ^The digestion of proteins and 
carbohydrates consists of a process of hydrolysis — i. e., 


388 Physics and Chemistry 

decomposition due to the absorption of, and chemical 
combination with, water. The digestion of fats con- 
sists of a preliminary splitting of the fats into fatty 
acids and glycerin, followed by the saponification of 
the fatty adds. 

Results of hydrolysis and saponification. — ^As the 
result of hydrolysis, complex molectdes are divided and 
simpler substances thus formed; for example, one 
molecule of a disaccharid (CiaHaaOn) by hydrolysis 
gives 2 molecules of a monosaccharid 2(C6Hxa06). 
There is only one splitting of the molecules in the 
hydrolysis of the disaccharids, but the polysaccharids 
(C6Hxo05)x' pass through several stages before they 
are completely hydrolyzed. The substances yielded 
at the different stages in the digestion of starch are 
dextrins (known, according to the colors which they 
give with iodin, as erythrodextrin i, 2, or 3 and achro- 
dextrin, see page 398) , maltose, and glucose. The pro- 
tein molecule also undergoes several splittings, thereby 
giving rise to such substances as metaproteins, pro- 
teoses, peptones, and amino acids. The nature and 
the results of saponification whereby fats are digested 
have been already discussed (Chapter XVI.). 

How hydrolysis and saponification can be brought 
about. — Starches, sucroses, and proteins can be hydro- 
lyzed and thereby made to undergo the changes 
described in the preceding paragraph by boiling them 
with acid and by the use of ferments. The ferments 
used to digest starch outside the body are usually 
obtained from plants; one of the best known is diastase 
of malt, a substa/ice that is produced during the ger- 

« The X, it wQl be remembered, signifies that the molecules of 
polysaccharids contain an unknown number of molecules with 
the construction demonstrated by the formula. 

Chemistry of Digestion 389 

mination of certain seeds and that is contained in 
malt. The ferments used to digest proteins are 
extracted from the stomach or pancreas of animals, 
especially pigs. Within the body, hydrolysis is caused 
by the ferments or enzymes contained in the digestive 
juices. Saponification, outside the body, is brought 
about by boiling fats with alkalies and, within the 
body, by an enzyme contained in the pancreatic juice 
and the alkaline salts of the pancreatic and intestinal 
jmces and the bile. 

Nature of the digestive juices. — The digestive 
juices secreted by the salivary glands, by the gastric 
and intestinal glands, and the pancreas consist of 
water, salts, mucin, and specific enzymes. The re- 
action of the saliva is, normally, neutral or faintly 
alkaline; that of the gastric jtiice, add (due to the 
presence of hydrochloric acid) ; and that of the pan- 
creatic and intestinal juices, alkaline. The bile, 
which is secreted from the blood by the liver, consists 
of water, bile salts, and inorganic salts, mucin, 
cholesterin, lecithin, fat, and bile pigments. 

The bile pigments are derived from hemoglobin; 
it is thought that when red blood-corpuscles become 
disintegrated the freed hemoglobin is brought to the 
liver, where, under the influence of the liver cells, 
its iron is split off and it is converted into bilirubin or 
biliverdin, the characteristic pigments or coloring 
matter of bile. Normally, bile has an alkaline re- 

Enzymes, Zymogens, Kinases, Hormones 

The nature and action of these substances which 
are so essential to digestion and metabolism are as 
yet very imperfectly understood. 

390 Physics and Chemistry 

Enzymes. — ^Enzymes are protdn-containing sub- 
stances, of unknown composition, produced by living 
cells, both animal and vegetable. Enzymes act as 
catalyzers — ». e., they hasten chemical reactions, but 
they do not themselves enter into the reaction. 
Nearly all the processes, both of building and of dis- 
integration that take place in animals and plants are 
controlled to some extent by enzymes. Enzymes are 
easily influenced by temperature; those of animal 
origin act best at body temperature; those obtained 
from plants usually work better at higher temperattu'es 
than this, but all enzymes are destroyed by extreme 
heat and are rendered more or less inactive by cold. 
The majority of enzymes are also very sensitive to 
the reaction of the meditun in which they are con- 
tained; some needing an add and others an alkaline 
or neutral medium. They are all destroyed by strong 
adds and alkalies. Nearly all enz3niies are spedfic 
in their action — i, «., they each have their spedal work 
to perform and they do only that work. 

According to their action, the majority of enzymes 
fotmd in the animal body have been classified as 

(i) Hydrolytic enzymes — ^those which cause hydro- 
lysis. To this dass belong the proteolytic or pro- 
tein-splitting enzymes, the lipolytic or fat-splitting 
enzymes, the amyloljrtic or starch-splitting enzymes, 
and the invertases or sugar-splitting enzymes. 

(2) The coagulating enzymes — such as the throm- 
bin of the blood and the rennin of the gastric juice. 

(3) The oxidases — enzymes in the body tissues 
that are essential for oxidation processes. 

(4) Reduction enzymes — ^those which remove oxy» 
gen from matter. 

Chemistry of Digestion 391 

Zymogens. — Certain enzymes, notably the rennin 
of the gastric juice and the trypsin of the pancreatic 
juice, are secreted in an inactive form. This is neces- 
sary because the pepsin and trypsin, being formed for 
the purpose of hastening the digestion of proteins, 
would, if present in the gland secreting them in the 
active state, cause the digestion of the gland. Such 
inactive enzymes or precursor of enzymes are called 
zymogens. The zymogen of pepsin is called pep-' 
sinogen and that of trypsin, trypsinogen. 

Elnases. — Enzymes, or other substances, that pro- 
duce the necessary change in zymogens to render 
them active, are called kinases — for example, the 
enzyme enterokinase of the intestinal jtiice which 
activates the trypsinogen of the pancreatic jtiice. 

Hormones, secretins. — Hormones are chemic sub- 
stances that are produced in certain organs and then 
absorbed and carried by the blood to other organs 
which they stimulate. Of this nature is the secretin, 
a chemic substance of unknown composition, which 
is produced from a substance secreted in the intestinal 
mucous membrane, called prosecretin, by the action 
upon it of the acid material entering the intestine 
from the stomach in the course of digestion. This 
secretin, when absorbed by the blood, is carried to 
the pancreas, liver, and possibly to the intestinal 
glands, and produces or increases the activity of these 
glands. A secretin is also produced in the mucous 
membrane of the pyloric portion of the stomach, 
which, being absorbed and carried by the blood to 
the secretin cells of the gastric glan(^» excites them 
to activity. 

The names of the digestive juices, the enzymes 
they contain, the action of the latter upon food, and 


Physics and Chemistry 

the organs in which the digestive processes occur can 
be seen in the following table: 

Organ in 
WHICH Juice 
IS Secrbtbd 











entericus or 






( Kennin 
J Pepsin 

L Lipase 


Lipase or 





Action of 

Chaoges starch to 
dextrin and maltose. 

Changes maltase 
to fflucose. 

Curds milk. 

Starts the diges- 
tion of proteins. 

Splits emulsified 
fats, as cream, to' fat 
ty acids and glycerin. 

Same as ptvalin. 

Continues the work 
of the pepsin. 

Splits fats to fatty 
acias and glycerin 
and aids in the sapo- 
nification of the fatty 

Activates the tryp- 
stnogen of the pan 
creatic juice, chang 
inff it to trypsin. 

Continues the work 
of the pepsin and 

Changes maltose 
to glucose. 

Changes sucrose to 
glucose and fructose. 

Changes lactose to 
glucose and galac- 

Helps in the sapo- 
nification of fati and 
promotes absorption. 

Where Action 

In the mouth 
and, for a short 
time, in the stom- 

In the stomach. 

In the intestine. 

In the intestine. 

In the intestine. 

The hydrochloric acid of the gastric juice. — The 

gastric juice is the only secretion of the body that 
contains a free acid. This add — ^hydrochloric — ^is 
made, it is thought, from sodium chlorid (NaCl) 
taJken from the blood by certain cells situated in the 
middle region of the stomach. One reason for the 
supposition that these special cells secrete the add 
is that in the ftmdus and the pyloric region of the 

Chemistry of Digestion 393 

stomach, the gastric juice is less add than it is in 
the central portion. In these cells, it is thought, the 
NaCl is by some means broken into Na and CI and 
the CI combines with H, thus forming HCl. The 
per cent, of HCl in the gastric juice during digestion 
is usually estimated at from 0.3 to 0.5 per cent. A 
much lower or higher degree of acidity interferes with 

The prindpaj purposes of the hydrochloric add are 
as follows: It activates the pepsinogen and assists in 
the digestion of protdns; it regulates the passage of 
food from the stomach; it acts as a kinase in that it 
acts upon the pepsinogen and changes the prosecretin 
contained in the mucous membrane of the intestinal 
wall to secretin; it acts as a disinfectant. HCl arrests 
the action of ptyalin when the food with which that 
enzyme became mixed in the mouth becomes satu- 
rated with the add. However, as there is little or 
no add in the fundus of the stomach, the ptyalin may 
continue its action on starch while the latter remains 
in that part of the organ and, as the mechanical action, 
which chums apd pushes the food onward, is not very 
great in that region, some of the starch may remain 
there for twenty minutes or more. 

How hydrochloric acid regulates the passage of food 
from the stomach. — ^The reaction of secretions in the 
stomach, when the latter is empty, is, normally, neutral 
or slightly alkaline, the HCl being secreted only after 
food enters the stomach. As protein and HCl have 
a strong affinity for each other, the protein of the 
food and the add formed at once combine and it is 
only after all the protdn has become saturated with 
the add that there is any free HCl in the gastric juice. 
As soon as this happens, under the influence of the 

394 Pities and Chemistry 

acid, the pyloric sphincter muscle, which encircles 
the orifice between the stomach and the duodenum 
and is usually in a state of contraction, relaxes and 
some of the acid chyme^ passes into the intestine. 
This makes the alkaline contents of the intestine acid 
and the effect of acid on this side of the pyloric 
sphincter is to cause it to contract. The pylorus 
remains closed until the intestinal contents are alka- 
line when it once more relaxes and the procedure is 

Factors influencing the secretion of digestive 
juices. — ^Various experiments have shown that the 
secretion of the digestive juices is very largely con- 
trolled by (i) the nervous system and (2) secretins. 
The stimulation of the parts of the nervous system 
that are concerned with the digestive process is brought 
about in several ways; e. g., the smeU and taste of 
food — provided that they are agreeable — and the 
movements of the jaw in mastication all stimulate 
various nerve-endings in and around the mouth. 
This results in the stimulation of certain nerve- 
centers in the medulla oblongata from which impulses 
pass to the secretory cells of the salivary and gastric 
glands and stimulate them to secrete. The entrance 
of food into the stomach also excites nerve-impulses 
which stimulate the secretion of gastric juice, but the 
principal sources of gastric stimulation are thought 
to be the secretins formed in the pyloric mucous 
membrane and, during digestion, from food. The 
secretin formed, as already explained, in the small 
intestine after the acid chyme enters it from the 
stomach, stimulates the pancreas and probably the 

' This 18 the name given to the substance resulting from gastric 

Chemistry of Digestion 395 

intestinal glands to secrete and it increases the activity 
of the liver. 

The entrance of food into the small intestine also 
causes the sphincter muscle closing the duodenal 
opening of the common bile duct to relax, thus allow- 
ing the passage of bile from the liver and gall bladder 
into the intestine. 

The kinds of food eaten influence the nature and 
quantity of the digestive juices; fats, for instance, 
retard gastric secretion, and sugars, condiments, meat 
extracts, and alcohol increase it. The amount of the 
various enzymes present in the digestive juices varies 
with the kinds of food eaten, and it is thought probable 
that there are specific stimuli contained in food or 
produced during digestion whose action is of a kind 
to arouse reflexly the secretion best adapted for the 
digestion of the kind of food that is eaten. 

Digestion is aided also by the contractions of the 
stomach and intestinal walls. Weakness of the muscle 
tissues of these organs, or any form of interference 
with their mechanical action, is likely to be followed 
by digestive disturbances and, frequently, by an ac- 
cumulation of fermentation or putrefactive products. 
These are due to bacterial action upon food that re- 
mains too long within the stomach and intestines. 

Action of bacteria in digestion. — After birth, there 
are always a large number of difiEerent kinds of bac- 
teria present in the alimentary canal. The varieties 
that exist in the stomach and intestines are, tmder 
normal conditions, unless present in abnormally 
la;rge numbers, not only not injurious to man, but of 
use, for they help to protect the body against the 
invasion of harmful varieties, and they help in decom- 
posing food into simpler substances, causing, in fact, 

396 Physics and Chemistry 

much the same kind of changes as are produced by 
enzymes. Under abnormal conditions, however, as 
when the mechanical action of the stomach and in- 
testines are defective and food remains too long in 
these organs, or when, for any reason, the digestive 
power is impaired, fermentation and putrefactive 
changes may be carried too far a^d gases produced, 
thus causing flatulence. Also various substances 
may be formed that, when absorbed into the blood, 
are more or less injurious to the system. Of these 
substances, the best known is indol, which is produced 
in the intestine by the excessive putrefaction of pro- 
teins. It is changed, it is thought, in the liver, to 
indican a^d a? such is excreted by the kidneys. The 
a^mount of indican in the urine is therefore ap index of 
the degree of putrefaction occurring in the intestines. 

Kinds of bacteria in the alimentary canal. — The 
principal varieties of bacteria present in the alimen- 
tary tract are those which promote fermentation and 
putrefaction. The various organisms that produce 
these two processes do not thrive well together and, 
normally, bacteria which produce fermentation are 
found in the stomach — these requiring considerable 
air — and those which produce putrefaction and thrive 
best without air, in the intestine. So great is the 
inhibitory action of these organisms on each other 
that lactobacilli — organisms that produce lactic add 
fermentation — are used medicinally to lessen intestinal 

Products of digestion. — ^As the result of digestion, 
there are found in the intestine monosaccharids, soaps, 
peptones, and amino acids. Also, there will be present 
varying amounts of undigested and imperfectly 
digested food, nuneral matter, ajad water. 

Chemistry of Digestion 397 

The products of digestion, mineral matter, and 
much of the water are principally absorbed from the 
small intestine. The changes that occur in the soaps 
and protein derivatives during absorption will be 
discussed in Chapter XXIII. The sugars and pro- 
teins pass directly into the blood, via the capillaries 
that are contained in the villi covering the inner wall 
of the intestine. These capillaries connect with the 
portal vein through which these absorbed substances 
pass to the liver. A small portion of the fat may enter 
the circulation in this way, but by far the greater part 
only reaches the blood after it has passed through the 
lymphatic vessels that extend from the lacteals (the 
small lymph vessels in the villi of the intestine) to 
the thoracic duct which opens into the left innominate 
vein between the left subclavian and the left internal 
jugular veins. 

Feces. — All the matter not absorbed passes slowly 
through the intestine and is eliminated from the 
rectum. Chemical and microscopical examinations 
of feces show its principal constituents to be food resi- 
due mixed with digestive juices, dead and living 
bacteria, and a small amount of waste matter formed 
in metabolism. The last passes from the blood as 
it flows through the intestinal blood-vessels. 

Experiments on Digestion 

Nature of the experiments. — Many of the experi- 
ments used in studjring the progress of digfestion are 
the same as those described in Chapter XVIII. The 
iodin and reduction tests (see pages 289 and 290) are 
used in studying the digestion of starch, since if, when 
iodin is added to the solution being tested, a blue 

39* Physics and Chemistry 

color develops, it shows that starch is still present and 
that digestion has not started; the development of a 
purple color shows that the starch has been changed 
to erythrodextrin No. i , which is the first stage in the 
digestion of starch; a red color indicates the presence 
of erythrodextrin No. 2, a red-brown that of erythro- 
dextrin No. 3, and a loss of color from the iodin shows 
that the starch has been changed to either achro- 
dextrin, maltose, or glucose; which of the three can be 
determined by finding the amount of solution that it 
takes to reduce 10 c. c. or other given quantity of 
Fehling's solution since it takes 0.5 gm. of glucose, 
0.8 gm. of maltose, and about i.o gm. of dextrin to 
reduce 10 c. c. of Fehling*s solution. Consequently, 
there will be a greater amount of precipitate when 
the solution tested contains glucose than when it is 
maltose or dextrin that is present, and a sufficiently' 
accttrate judgment for class purposes can be made by 
comparing the relative color and amount of predpi- 
tate formed in all the tests of an experiment. Of 
course, the same amount of the solution to be tested 
and of the reducing solution must be used in all tests 
that are to be compared. 

i The reduction tests are used also to see if disaccha- 
rids have been hydrolyzed, since they, like starch, are 
changed to monosaccharids in digestion. 

The biuret and xanthoproteic tests — described on 
pages 283 and 284 — ^are much used in studying the 
digestion of proteins for they give different color re- 
actions with undigested and digested proteins. The 
biuret reagent assumes a violet color in the presence of 
undigested! proteins and a rose color in a solution of 
peptones, while the solutions used for the anthro- 
proteic test become orange-colored in solutions oon- 

Chemistry of Digestion 399 

taining undigested or only slightly digested proteins, 
but this color does not develop after the proteins have 
been changed to proteose and peptones. 

The progress of the digestion of fats can be observed 
by the use of litmus, for, as soon as the fats in a solu- 
tion are split to fatty adds and glycerin, blue litmus 
will become red, as it always does in the presence of 

N. B. — ^The measurements for these tests must be 
espedally accurate, very slight inaccurades bdng 
suffident to spoil many of them. Before beginning 
experiments number the tubes as described on page 
II. Differences in color in many of the tests is very 
slight and can be usually detected only by compari- 
son, therefore all results must be kept until a test is 

Experiments 76 to 78. 

Object: To study the digestion of starch. 

Articles reqtiired : Test tubes, test-tube racks, Bun- 
sen btuner, iron stand, c. c. measures, funnels, filter 
paper, ice, starch paste made as directed on page 21, 
distilled water, iodin, Fehling's solution, saliva. Be- 
fore attempting to collect the saliva, rinse the mouth 
with water. Thinking of something good to eat, 
chewing a little paraffin or moving the jaws as though 
doing so, or inhaling a little ether vapor will increase 
the flow of saliva. Collect the saliva in a test tube, 
add an equal amount of distilled water to it and filter 

Experiment 76. Object : To test the action of saliva 

Procedure: Into a tube marked i, pour 10 c. c. of 
starch paste, into tube 2 pour 5 c. c of starch paste 

400 Physics and Chemistry 

and 5 c. c. of saliva. In tube 3 put about 5 c. c of 
crackers mashed in a small amount of distilled water 
and 5 c. c. of saliva. Shake the tubes containing the 
saliva so as to mix the latter thoroughly with the 
starch or cracker. Put all three tubes into a water 
bath and keep them at a temperature of 40^ C. Af t^ 
five minutes pour 2 c. c. from each of these tubes into 
separate tubes, divide each 2 c. c. and test one portion 
with iodin and one with Fehling's solution. Repeat 
this procedure every five minutes for thirty minutes. 
Keep all the tests in order until the completion of the 
experiment and then compare the colors. 

Why did the crackers show the presence of glucose 
before the starch? 

Experiment 77. Object : To test the effect of adds 
and alkalies on the ptyalin. 

Procedure: Into each of three tubes put about i 
c. c. of starch paste and i c. c. of saliva. To tube 2 
add 2 c. c. of 0.4% HCl and to tube 3, 2 c. c. of 2% 
NaaCOj. Put the three tubes into a water bath and 
keep them at a temperature of 40** C. for twenty 
minutes, then divide the contents of each tube into 
two equal portions and test one portion with iodin 
and the other with Fehling's solution. 

Experiment 78. Object : To test the effect of tem- 
perature on the enzymes of the saliva. 

Procedure: Put about i c. c. of starch paste into 
each of three tubes. To tube i add an equal amount 
of saliva, to tube 2 add an equal amount of saliva that 
has been boiled for at least three minutes, put both 
these tubes into a water bath and keep them at a 
temperature of 40® C. for twenty minutes. To tube 
3 add saliva that has been chilled by keeping the tube 
containing it between pieces of ice. After miidng 

Chemistry of Digestion 401 

the starch and saliva, surround the tube with ice» 
leave it thus for twenty minutes. At the end of 
twenty minutes divide the contents of the three tubes 
into equal portions and test one portion of each with 
iodin and the other with Fehling's solution. 

Experiments 79 to 80. 

Object: To test the digestion of proteins. 

Articles required: The same apparatus, but not 
the solutions, as for the experiments with starch. 
Also, concentrated nitric acid, ammonia, sodium 
hydroxid io%, copper sulphate solution 1%, hydro- 
chloric acid 0.5% and 2%, sodium carbonate solu- 
tion 10%, pepsin solution, (see page 21), fibrin. Dried 
fibrin, derived from blood, can be obtained at dealers 
in scientific apparatus. Meat or egg can be used 
instead of fibrin, but the results are not as quickly 
obtained. The biuret test cannot be used with egg^ 
since egg albumin sometimes gives, unlike other un- 
digested proteins, a rose color. 

Experiment 79. Object : To test the efifect of hydro- 
chloric acid and alkali on pepsin. 

Procedure: Mark tubes i, 2, 3, 4. Into each tube 
put a small piece of fibrin and about 4 c. c. of neutral 
pepsin solution. To tube 2, add an equal amount of 
0.5% hydrochloric acid, to No. 3 add an equal amount 
of 2% hydrochloric acid,' and to tube 4 an equal 
amount of 10% sodium hydroxid solution. Let the 
four tubes stand in a water bath kept at 40 ® C. for 
twenty minutes. Watch the changes that occur in 
the fibrin during this time. At the end of twenty 

* Be careful not to use too much acid, for though, as this test 
should show, strong acid interferes with the action of pepsin, it 
will, if stronger than necessary, itself aid in the hydrolysis of the 

402 Physics and Chemistry 

minutes pour off about 2 c. c. of the fluid from each 
tube into separate tubes and apply either the biuret 
or xanthoproteic tests (see pages 283 and 284). Let 
the fibrin remain in the remaining i c. c. of solution 
until that in tube 2 is dissolved — this may require 
several hours — and then filter the solutions into sepa- 
rate tubes, divide each one into equal parts, and test 
one portion with the biuret and the other with the 
xanthoproteic test. 

Account for the results. 

Experiment 80. Object: To study the effect of 
temperature on pepsin. 

Procedure: Mark tubes i, 2, 3. Put a small piece 
of fibrin into each tube. Add enough HCl to 10 c. c. 
of neutral pepsin solution to make it a 0.2% add 
solution. Divide this into three parts. Surrotmd 
the tube containing one portion with ice and leave 
it thus until it is thoroughly chilled, then pour it over 
the fibrin in tube 3 and put this tube between ice. 
Boil another portion for at least three minutes and 
then pour it over the fibrin in tube 2, add the third 
portion to the fibrin in tube i. Put tubes i and 2 
into a water bath and keep them in a temperature of 
40° C. for twenty minutes. Then filter the contents 
of all three tubes into separate tubes and apply the 
biuret test. 

Experiments 81 to 83. Object: To study the action 
of the pancreatic juice. 

Articles required: The same apparatus used in the 
experiments with the saliva and gastric juice, also 
starch solution, pancreatic solution — see page 21 — 
hydrochloric acid 2%, sodium carbonate solution 
2%, soditun hydroxid solution 10%, litmus powder, 

Chemistry of Digestion 403 

Experiment 81. Object: To test the effect of pan- 
creatic solution on starch. 

Procedure: Repeat Experiments 76 to 78, using 
pancreatic juice instead of saliva. 

Experiment 82. Object: To test the effect of pan- 
creatic solution of protein. 

Procedure: Repeat the Experiments with pepsin 
solution, using the pancreatic solution instead of the 
pepsin solution, and in Experiment 79 substitute 
sodiimi carbonate solution 2 per cent, for the 0.5% 
hydrochloric acid solution. 

Experiment 83. Object : To test the action of pan- 
creatic juice on fat. 

Procedure: Into each of 2 test tubes put 10 c. c. 
of whole milk and enough litmus powder to color the 
milk a decided, but not dark, blue. To tube 2 add 
2 c. c. of pancreatic juice. Put both tubes into a 
water bath and keep them at 40® C; After a short 
time, it will be noticed that the blue color of the milk 
in tube 2 changes to pink. Why does it do so? 



Changes that Occur in Food Substances during Absorption — 
Nature of Metabolism — Composition of the Blood — Changes 
that Occur in Food Substances during Metabolism — Some 
Causes and Results of Defective Metabolism — The Fuel 
Value of Foods — Food Requirements. 


The changes that occur in food substances during 
absorption.— Of the substances formed during diges- 
tion from disaccbarids, polysaccharids, proteins, and 
fats, only monosaccharids are usually fotmd in the 
general circulation. Therefore, it is thought that 
during absorption and, probably, in the liver chemical 
changes the opposite of those occurring in digestion 
take place. These changes result in the transforma- 
tion of the soap into fats and of peptones and amino 
acids into blood proteins — the serum albumin or 
globulin. The passage of these substances into the 
blood IS thought to be partly due to osmotic pressure, 
but both their passage into the blood and their re- 
building are accomplished by the activity of cells in 
the mucous membrane of the intestine. Whether 
these cells form enzymes, or whether the enzymes 
with which the food beca;ne mixed in the process of 

4^ . 


Absorption and Metabolism 405 

digestion by a reverse' action aid in this synthesis, 
are still debated questions. 


Every living organism may be likened to a chemical 
laboratory, whether it be plant or animal, whether it 
be large and composed of millions of cells or so small 
that it cannot be seen without the aid of a microscope; 
for in the cells of all such organisms chemical reac- 
tions are constantly taking place whereby the tissues 
are built and repaired and» in the case of animals, 
heat and energy are generated to keep their body 
machinery in motion. The classification of such 
processes in plants was mentioned in Chapter XVIII.; 
those occurring in animals are spoken of as meidboU 
ism. Some of the reactions occurring in metabolism 
can be easily performed in any chemical laboratory, 
but after a great many years of study, even the most 
skillful chemists and physiologists have but an indefi- 
nite knowledge of the nature of some of the processes. 

Catabolism and anabolism. — The chemical reac- 
tions of metabolism, such as hydrolysis and oxidation, 
which result in the disintegration of complex sub- 
stances into simpler compounds, are classed as catc^ 
holism and the changes are said to be catabolic (from 
the Gr. kata-^down and metabole^ change), and the 
synthetic changes in which simple substances are put 
together to form complex compounds are classed as 
anabolism and the changes are said to be anabolic 
(Gr. ana ^ up and metabole^ change). 

' A common characteristic of enzymes is that an accumulation 
of the products of their action will check their activity and even 
cause them to reverse the nature of their action. 

4o6 Physics and Chemistry 

Compositioii of fhe blood. — Since the blood is the 
reservoir for the chemical supplies that the body tises 
for the numerous chemical reactions constituting 
metabolism, it may be well to recall its compo- 
sition before going further with the study of the 

The constituents of the blood are usually classified 
as follows: 









Scrum globulin or paraglobulin 

Serum albumin 

Nitrogenous substances such as urea, 

uric acid, creatin 

1 Oxygen 
Carbon dioxid 

Also, there are in the blood ferments, enzymes, 
internal secretions, antitoxins, and similar substances. 

The composition of the blood in the portal vein 
differs at times from that in the other vessels because 

' Substances, other than proteins, that may be extracted from 
driod residue of blood by water, alcohol, or ether. 

Absorption and Metabolism 407 

it contains all the substances absorbed from the in- 
testine and some of the^ the liver removes or changes 
before they enter the general circulation. For instance, 
glucose, over the amount necessary to provide the 
blood with a content of about o.i or 0.15 per cent., is 
removed by the liver cells and changed to glycogen, 
which is stored chiefly in the liver, but to some extent 
in the muscles.' Also, putrefactive products, such 
as indol, that are absorbed from the intestine are 
changed to substances less likely to injure the system 
before they enter the general circulation. 

Derivation of the blood constituents. — ^The con- 
stituents of the blood, other than the corpuscles, anti- 
toxins, and similar substances, represent: (i) food 
matter absorbed from the intestines; (2) oxygen 
taken from the Itmgs;' and (3) matter, useful and 
otherwise, that has been absorbed from the tissues 
and glands. 

Fate of the food constituents of the blood. — ^There 
is a constant osmosis of substances from the blood, 
through the capillaries into the tissues, and this matter 
is either used by the cells for their nutrition or build- 
ing or else it unites with oxygen and is broken down, 
just as fuel is when it combines with oxygen in a 
furnace. The result of this oxidation is the same as 
that which occurs in the furnace, viz., the production 
of heat. In the body, some of this heat is used for 
energy to keep the body machinery — ^heart, lungs, 
etc. — in action as well as to provide the body with 
power to perform its external work. 

'After the death of an animal the glycogen and glucose in the 
muscles and blood aie soon oxidized. 

' This is contained principally in loose combination with the 
hemoglobin of the led blood-cotpufldes. 

4o8 Physics and Chemistry 

Intennediate Stages in the Metabolism of Food 


Glucose, as already stated, is changed to glycogen 
and as such stored in the liver, but in health the 
blood maintains a constant content of about o.i to 
0.15 per cent., and as it parts with its sugar to the 
tissues the glycogen is reconverted to glucose. In 
the tissues, the glucose (C6Hia06), it is thought, is 
split to lactic add (C3H6O3). and then undergoes a 
series of oxidations with the formation first of various 
acids and finally of carbon dioxid and water which are 
eliminated through the lungs. If more food is eaten 
than the body requires for its heat and energy supply, 
glucose can be changed to fat and stored as fatty tissue. 

When metabolism of glucose is defective, as in 
diabetes, much of the glucose does not undergo com- 
plete oxidation and there is an acctimulation of glucose 
and of adds in the body, and glucose is eliminated in 
the urine. 

Fat may be stored as part of the body fat; it may 
be synthesized with other substances to form more 
complex body constituents — such as ledthin — or, as 
is in any case the final fate of fat, it is oxydized to 
carbon dioxid and water and during the process yields 
heat and energy. The stages through which fat 
passes before it is completdy oxidized are but imper- 
fectly understood. When its metabolism is defective, 
diacetic add and acetone are formed. 

The proteins that are eaten as food vary consider- 
ably in their composition and many of them are very 
different from body tissue, but, since they are aU 
composed of different combinations of amino adds 
and the combinations are parted in the process of 

Absorption and Metabolism 409 

digestion and in metabolism, the body is provided 
with the same fundamental constituents as those which 
compose its own substance and which its cells are 
capable of putting together, not in the order in which 
they were originally, but as they are needed for the 
muscle tissue and other proteins of the body. Since 
the proteins are the only foods containing these amino 
adds, they are the only ones that can be used in the 
body for the repair and building of its protein constitu* 
ents. The molecules of protein not used for these 
purposes are split to amino acids and these in turn are 
split to form ammonia (NH3) and organic acid radi- 
cals. The ammonia, it is thought, unites with carbonic 
acid (COa+HjO), which is being constantly formed 
in the course of metabolism, fonning ammonia car- 
bonate. This, by a loss of one molecule of water, 
leaves ammonia carbonate, which in turn, by a loss 
of water, yields urea. This is excreted by the kidneys. 


0«C Oa 


Ammonia carbonate 


0-C o 



Ammonia carbamate 




4IO Physics and Chemistry 

The organic add radicals left after the removal of 
the ammonia group consist, like fats and carbohy* 
drates of, COH and, like those substances, they may 
be oxidized to carbon dioxid and water, yielding heat 
and energy, or they may be synthesized to fat or 

The nucleo-proteins — ^which are the characteristic 
proteins of cell nuclei, both those of food and of the 
human body — ^when metabolized, give rise to sub- 
stances that are known as purin bases. These, on 
further decomposition, yield uric acid. It is thought 
that uric acid is formed both in the Uver and through- 
out the tissues of the body. As the acid is formed, 
most of it unites with alkaline substances, forming 
salts — urates — which are excreted in the urine. 

The formation of salts in the body. — Though adds 
are being constantly formed in the body in the course 
of metabolism, the body fluids, except the gastric 
juice and the urine, are alkaline or neutral. This is 
because the adds are either oxidized and thus broken 
down to substances such as carbon dioxid and water, 
which can be eliminated, or else they are neutralized 
by tmiting with alkaline substances obtained from 
food and carried through the body by the blood. 
Many of the salts excreted in the urine, sweat, and 
feces are formed within the body in this way. 

Factors influencing metabolism. — That the many 
chemical reactions which occur in metabolism can do 
so at body temperature is due to the presence in the 
tissues of various enz}mties, which are manufactured 
by the body cells, and internal secretions carried 
thither by the blood from the glands in which they 
are secreted. 

Results of defective metabolism.— As shown in the 

Absorption and Metabolism 411 

preceding paragraphs, broken-down body tissue and 
also food substances that are not built into tissue go 
through several stages of disintegration before they 
are eliminated. The intermediate products, only a 
few of which were mentioned, are principally adds 
and nitrogen compounds. If, for any reason, meta- 
bolism is defective, the final stages of disintegration 
are likely to be delayed ajid abnormal compounds are 
often formed, thus there is likely to be an accumu- 
lation of more or less injurious substances within 
the body. 

Some causes of defective metabolism. — Diseases, 
such as anemia, and conditions which prevent the 
body getting its necessary amount of oxygen, will 
result in defective metabolism, since many of the dis- 
integration processes are due to oxidation. Condi- 
tions of the tissues which retard enzyme formation, 
or diseases of those ductless glands which are con- 
cerned with metabolism, will interfere with it, as will 
also disturbances of certain parts of the nervous 
system, since metabolism and heat regulation, like all 
other vital processes, are, both directly and indirectly, 
controlled by this S3rstem. 

Heat Value of Food and Food Requirements 

The study of these things belongs to dietetics, but 
a brief stuvey of them here may be of advantage. 

How the heat value of a food is determined. — ^The 
heat value of food is calculated and recorded in the 
same manner as that of other substances as described 
in Chapter III. It was determined by burning foods 
in a form of apparatus known as a bonib calorimeter. 
By this means it was fovmd that each gram of carbo- 

412 Physics and Chemistry 

hydrate eaten should yield to the body 4 calories; 
each gram of fat, 9 calories; each gram of proton, 4 

Fig. 69. 

A Vaubtit of Calokiueter Used for AscEXTAunira 

THE Heat Value of Poods. 

calories. If proteins were as fully oxidized in the 
body as they are in the calorimeter, they would have 
a higher food value, but it will be remembered that 



Absorption and Metabolism 413 

much of the protein leaves the body as comparatively 
complex substances, urea and the like, which in the 
calorimeter tmdergo oxidation. 

Food requirements. — By the use of various forms of 
calorimeters, by the examination of excreta by various 
experiments, and by investigations of the amotmt of 
food eaten by healthy individuals in different coun- 
tries and engaged in various occupations, it has been 
found that the amoimt of food that an individual 
requires is dependent chiefly upon the rate at which 
oxidation occurs in the body, and variations in this 
are largely due. to differences in the muscula;r con- 
traction that occurs. This, in turn, is dependent 
upon such things as the mode of life, age, sex, climate: 
for certain occupations and exercises entail more 
muscular contraction than others; cold increases 
musculajT contraction, as is shown by the phenomenon 
of shivering, and it tends to induce an individual to 
exercise and make active movements, while warmth 
has the opposite effect; a strong person will expend 
more energy in his movements than a weak person, 
and a large person has a greater area of muscu- 
lar surface to undergo contraction than a small 

As oxidation uses up the fuel and muscular con- 
traction increases the rate of oxidation, the greater 
the amotmt of muscular contraction an individual's 
conditions and manner of living entail, the more 
food will he require. It has been found, by the means 
mentioned in the preceding paragraph, that a man 
of average weight (about 59.5 kilograms — 155 pounds) 
requires under differing conditions the following 
amounts of food: 

When at rest, enough to jrield 2000 calories. 

414 Physics and Chemistry 

When engaged in a sedentary occupation, enough 
to yield 2700 calories. 

When doing a moderate amount of muscular work, 
enough to give 3400 calories. 

When engaged in hard muscular work, enough to 
give 5000 to 6000 calories. 

A woman of equal size, engaged in an equally ardu- 
ous occupation and expending an equal amount of 
energy as a man, would require the same amount of 
food, but as the average woman is rather smaller and 
usually exerts somewhat less energy in her movements, 
it has been estimated that women require about 0.8 
the amount of food that men do. 

Though children require less food than adults, they 
need more in proportion to their size, because material 
is required to build their bodies as well as to repair 
waste and yield heat and energy. The following 
estimate of the food requirements is one that is often 

A boy of 14 to 

16 requires 


1^500 to 3000 calories 

" girl " 14 " 


2200 " 2500 " 

"child " 10 " 


1800 " 2200 " 

i« n u g II 

10 " 

1400 " 2000 " 

II tt tt 2 •* 


1200 " 1400 . " 

II It II . II 

2 " 

900 " 1200 " 

The comparative proportion in which the food prin- 
ciples are used is about as follows: sufficient protein 
to give about yi of the calories required, suflScient 
fat to yield a like number, and sufficient carbohydrates 
to make up the remaining %i of the calories. Thus 
the food for a meaj intended to furnish 1000 calories 
would be portioned as follows: Enough protein and 
fat to give 200 calories each and sufficient carbohy- 

Absorption and Metabolism 415 

drates to yield 600 calories. As each gram of pro- 
tein and carbohydrate furnishes 4 calories and each 
gram of fat 9, this wotdd mean 50 grams of protein 
(200-f-4»50), 22.2 grams of fat, and 150 grams of 



Origin of Waste Matter in the Body and the Channels through 
which it is Eliminated — Quantity of Urine Voided — Com- 
position of Urine — ^Foreign Substances sometimes Pound 
in Urine, their Origin and Significance — Nature of Urine 
Analysis — Methods of Determining the Quantity of Total 
Solids in Urine — Tests for Acetone, Diacetic Add« Albumin, 
Glucose, Indican, Bile, Blood, and Pus. 

Origin of waste matter and the channels through 
which it is eliminated. — As the restilt of oxidation 
and other chemical reactions occurring in the body, 
substances of no further use to the system are formed 
and they must be eliminated. It is by the lymph 
and blood that these substances are removed from 
the tissues, and they'are extracted from the blood and 
removed from the body by the kidneys, the sweat 
glands, the lungs, and the intestines. Unnecessary 
water, either that absorbed from the intestines or 
formed in the body by chemical reactions, is elimi- 
nated by the skin, kidneys, and lungs; the CO 3 passes 
off chiefly through the lungs; the protein waste and 
salts are excreted principally through the kidneys, 
though to a slighte xtent by the skin, and small amounts 
are excreted from the intestinal blood-vessels and pass 
off with the feces, and when the kidneys are diseased, 


The Urine and Urine Analysis 417 

volatile protein matter may be exhaled from the lungs. 
The kidne3rs are also the main channels for the elimi- 
nation of foreign matter, such as drugs, toxins pro- 
duced by bacteria, products of intestinal putrefaction 
and defective metabolism. If there is any abnormal 
exudate present in any part of the urinary organs 
as the result of inflammatory conditions some of it will 
be washed out with the urine, and if, as sometimes 
occurs when the kidne3rs are diseased, the kidney cells 
are not acting properly, substances that are normally 
not extracted from the blood may be present in the 
urine and, under such circumstances, there is likely to 
be a smaller amount than normal of the usual waste 
matter in the urine. 

Thus, analysis of the urine is an aid in discovering 
defective conditions in the intestines, defective metab« 
olism, and diseased conditions of the urinary organs. 

Quantity, Compositioni and Characteristics of Normal 


Quantity. — ^The average amount of urine voided in 
24 hours by a healthy adult is about 40 to 50 ounces; 
by a child of 

2 to 5 years, 15 to 25 ounces. 

5 to 9 years, 25 to 35 ounces. 

9 to 14 years, 35 to 40 ounces. 

Even in health, however, the amount of urine 
voided may vary very considerably. The principal 
points to consider in deciding if difference in quantity 
is normal or abnormal are the amount of liquid that 
has been drunk and the quantity of water that haa 

41 8 Physics and Chemistry' 

left the body by other channels, for the system tends 
to maintain its natural percentage of fluids and to 
get rid of excess. Thus, if much liquid is drunk, more 
will be eliminated than if only a small amount is taken, 
and if an unusual amount of water leaves the body as 
the result of vomiting, of watery evacuations from the 
bowels, or of excessive perspiration, there will be less to 
pass through the kidneys. In fever it is to be expected 
that the amount of urine will be diminished, partly as 
the result of the increased rate of evaporation of sweat, 
due to the high temperature. When the nervous 
system is depressed, as in shock, there may be either 
suppression or retention of urine. In some diseases 
of the kidneys, the secretion of urine is diminished, 
and in diseases such as diabetes mellitus, diabetes 
insipidus, and hysteria, secretion is increased; ner- 
vousness also often causes an increase in the amount 
of urine voided. Conditions causing a loss of fluid 
from the body are usually characterized by excessive 
thirst, which is another example of the body's endeavor 
to maintain its normal fluid content. The sensation 
of thirst is the result of the effect which the loss of 
water from the body protoplasm produces on some 
part of the nervous system. 

Physical properties of urine. — Normal urine is a 
transparent, yellowish or light amber-colored liquid 
with a characteristic odor, a slightly alkaline reaction, 
and a specific gravity of 1.012 to 1.030, 1.020 being 
the average. 

The specific gravity shows the relative proportion of 
water and solid matter constituting the urine; the 
greater the amount of solid matter present, the higher 
will be the specific gravity. This and the means of 
ascertaining the specific gravity of liquids were dis- 

The Urine and Urine Analysis 419 

cussed in Chapter III. Even in health there can be 
considerable variation in the specific gravity of the 
urine, for, as a rule, when only a small amount of 
tuine is secreted as the result of loss of water through 
other channels, as, for exa^aiple, through the sweat 
glands, the urine will contain a relatively high per- 
centage of solid matter and will have a high specific 
gravity; if, on the other hand, a large quantity of 
urine is excreted as the result of copious drinking or of 
diminished perspiration the urine will be dilute and its 
specific gravity will be low. In chronic nephritis, 
however, even though the secretion of urine is dimin- 
ished its specific gravity may be as low as 1.004, since 
it is not only the water but also solid matter that is 
not secreted in the usual amounts, and in diabetes 
mellitus, though a large amount of urine is voided, 
its specific gravity is high, due to the presence of 

The color of urine varies somewhat with its degree 
of concentration, the color being deeper when the 
amount of solid matter is in excess, and paler when 
there is a large quantity of water. Any great differ- 
ence in the color or transparence of urine is usually due 
to the presence of foreign matter such as sugar, bile, 
blood, drugs, etc. 

The acid reaction characteristic of htunan urine is 
due to the amount of foods that are eaten the end 
products of which are acid. If urine stands for any 
length of time it becomes alkaline as the result of the 
conversion of the urea into ammonitmi carbonate due 
to bacterial action. The same change may take place 
in the urine while it is in the urinary organs when 
they are diseased, and the urine is then alkaline when 
it is voided. 

Salts such as 


420 Physics and Chemistry 

The composition of urine. — ^The general composi- 
tion of urine is about as follows: 

Water 967. parts 


Urea 14^30 ** 

(creatmin 1 
xanthin I ,, 

hypoxanthiQ | * 

Mucus, pigments, ferments J 


phosphates \ 8.770 

Gases, principally nitrogen and carbon dioxid. 

The urea, which is the principal solid constituent 
of the urine, is the form in which the greatest amount 
of waste nitrogen derived from protein metabolism is 
excreted from the body. The average amount excreted 
daily, under normal conditions, is about 40 grams. 
The quantity will be increased by a high protein diet 
and decreased by a carbohydrate diet. It is increased 
in diabetes and decreased in some diseases of the liver. 

Creatinin. — Is thought to be formed in the body as 
the result of the metabolism of its muscle tissue. 

The uric acid and extractives such as adenin, 
xanthin, and hypoxanthin vary in amount according 
to the quantity of nucleo-proteins taken in the food, 
therefore it is considered that they represent the 
products of the metabolism of nucleo-proteins of the 
body and of food. Practically all the uric acid pres- 
ent in urine is in the form of salts (urates). 

Traces of mucus are found in normal urine, but the 
presence of large amounts is indicative of inflam- 

The Urine and Urine Analysis 421 

xnatory conditions of the urinary organs, especially 
the bladder. 

Abnormal Constituents of the Urine 

The substances indicating abnormal conditions 
which are most frequently found in the urine are: 
Albumin, glucose, acetone, diacetic acid, indican, bile, 
blood, casts, calculi, pus, and bacteria. 

Albuminuria is the name applied to the condition in 
which any form of heat-coagluable protein is present 
in the urine, and th^ protein is designated as albumin, 
though, as a rule, it is pliartly globulin. The con- 
tinued presence of such protein in the urine is usually 
due to disease of the kidneys or to abnormal pressure 
changes in the renal blood-vessels, such as occurs in 
diseases of the heart. 

Glucose may be present in the urine temporarily 
after the intake of a la^ge amount of carbohydrates, 
especially sugars, and sometimes during pregnancy and 
lactation, in concussion of the brain, and during con- 
valescence from febrile diseases, but its continued 
presence is always due to diabetes mellitus. 

Acetone and diacetic acid are formed in the tissues 
chiefly as the result of the defective oxidation of the 
fatty acids arising during the metabolism of fats, but 
sometimes they develop from certain amino acids 
as the result of the defective metabolism of proteins. 
These substances are found in the urine in advanced 
stages of diabetes; when metaboUsm is retarded, as in 
severe anemias; and when body tissue is metaboUzed 
at an abnormally rapid rate as in starvation and in 
long-continued febrile diseases. Diabetic acidosis and 

4^2 Physics and Chemistry 

coma are due to an accumulation of these substances 
within the body. 

Bile is present in the urine as the result of some 
obstruction to its discharge from the liver or gall 
bladder in consequence of which it is absorbed by the 

The presence of pus is due to a suppurative inflam- 
mation of some of the urinary organs. 

Blood may be present in the urine as the result of 
lesions in any of the urinary organs (this condition 
is known as hematuria), or disintegrated blood corpus- 
cles may be present as the result of hemolysis resulting 
from a^y of the various causes of this condition, 
e, £., the toxins of ccrtain> of the infectious diseases, 
transfusion of blood, snake bite. This condition 
is known as hemoglobinuria. In hematuria, the urine 
has a characteristic smoky appearance. If the blood 
comes from the bladder or genital organs it is likely 
to be clotted. 

Calculi or stones are the result of the precipitation 
of some of the solid constituents of the urine. They 
may form in any part of the urinary system and are 
of various sizes and shapes. The precipitation is 
usually the result of abnormal changes in the reaction 
of the urine or the presence of foreign substances. 

Casts consist of deposits of different kinds of sub- 
stances, such a,s pus, blood, fatty matter, etc., that 
have become hardened in the kidney tubules and are 
washed out with the urine. They are called casts 
because they retain the cast or form of the tubules in 
which they were deposited. Their presence in the 
urine, which is ascertained with the aid of the micro- 
scope, shows some abnormal condition of the kidney 
from which they came. 

The Urine and Urine Analysis 423 

Urine Analysis 

A complete urine anal3rsis includes taking the spe- 
cific gravity of the urine, testing its reaction, deter- 
mining the total quantity of solids and the percentages 
of the various solids, such as urea, extractives, and salts. 
As a rule, nurses need to know only the tests for sub- 
stances, such as albumin, glucose, acetone, and diacetic 
add, which* in certain diseases, it is necessary to keep 
track of from day to day, but a few other tests are 
described here since it is interesting to know how 
the data contained in the urine-analjrsis reports sent 
from the laboratory are obtained. 

The method of testing the specific gravity of liquids 
was described in Chapter III. and the manner of as- 
certaining their reaction was mentioned in Chapter 

I Methods of determining the total quantity of 
solids. — Stir the specimen of urine, or else shake 
the flask containing it, so that if any sediment has 
precipitated it will become mixed with the liquid por- 
tion of the urine. Then pour 25 cc, or other definite 
measure, of the urine into an evaporating dish, place 
this in a water bath over a flame, and let it remain 
until the water of the urine has evaporated and the 
residue is perfectly dry. Weigh the dish with the 
residue and deduct the weight of the former from 
the total. The amount remaining will be the weight 
of the residue and will show the quantity of solid 
matter in the amount of urine taken. 

When only an approximate estimate of the total 
solids is required, it is often calculated by multipl3ring 
the two last figures of the specific gravity by 2.33. 
Thus, if the urine has a specific gravity of 1.025, there 

4^4 Physics and Chemistry 

• • 

wilt be 58.25 grains of solid matter contained in 1000 
grains of the urine; since 25 X 2.33 « 58.25. 

A test for acetone. — ^To 10 c.c. of urine, in a test 
tube, add about 20 drops of concentrated NaOH and 
5 drops of a 5% solution of sodium nitroprussid. If 
acetone is present, the mixture becomes red and the 
red changes to purple upon the addition of an excess 
{i.e.f a larger quantity than there is of the mixture) of 
glacial acetic add. 

A test for diacetic acid. — ^Add, drop by drop, some 
ferric chlorid solution to about 5 c.c. of the urine until 
a precipitate ceases to form; filter the mixture, to re- 
move the precipitate, and add some more ferric chlorid 
to the filtrate. If diacetic add is present a deep 
red color will develop. As other substances, such as 
those excreted after taking salicylic add and similar 
drugs, give the same reaction, the solution is boiled, 
and if the color is due to diacetic add, it will dis- 
appear, the add being thereby dianged to acetone, 
but color due to the other substances will be per- 

Albumin tests* — The heat test for albumin was de- 
scribed on page 284. The Heller test, another of the 
tests in common use, is as follows: Pour about 3 c.c. 
of concentrated nitric add into a test tube and, with 
a pipet, add, slowly, so as to avoid mixing the two 
liquids, about 3 c.c. of filtered urine. A white ring 
at the junction of the fluids shows] the presence of 
albumin in the urine. 

Tests for glucose. — Several of the common tests for 
glucose were given in Chapter XVIII. 

A test for indican. — Put about 4 to 6 drops of a 1% 
solution of potassium permanganate into a test tube, 
add between i and 2 c.c. of chloroform, then 10 c.c. 

The Urine and Urine Analysis 425 

of hydrochloric acid, and lastly 10 c.c. of the urine. 
Invert the test tube two or three times so as to thor- 
oughly mix its contents and allow it to stand for about 
5 minutes. If indican is present in the urine, it will be 
broken down by the hydrochloric acid and oxidized by 
the potassium permanganate to indigo, which is dis- 
solved in the dhloroform and gives a blue color, the 
shade of which varies with the amount of indican 
present, being very pale if there is only a slight 

A test for bile. — One of the tests for bile very 
commonly used is that known as Gfndin*s test^ 
which is as follows: To 5 c.c. of concentrated HNO3, 
in a test tube, add 2 to 3 c.c. of urine, pouring 
the latter down the side of the tube so that the two 
liquids will not become mixed. If bile is present, 
circles of various colors will form where the liquids 
come in contact. 

A test for blood (Heller's test). — ^Add enough 
NaOH to 10 C.C. of tirine to make the latter decidedly 
alkaline, boil this, and then let it stand. If blood is 
present the a}kali converts the pigment into hematin 
which is precipitated as a red deposit. As there 
are other substances sometimes present in urine that 
give the same reaction, filter the liquid and pour a 
little acetic add over the precipitate. If this con- 
sists of substances other than hematin, it will be 
entirely dissolved; hematin may be slightly, but it 
will not be wholly, dissolved. 

A test for pus. — ^Before testing urine for pus, let it 
stand tmdisturbed so that any sediment present will 
fall to the bottom, then pour off as much of the 
overlying liquid as possible without disturbing the 
sediment, and to the latter add some concentrated 

426 Physics and Chemistry 

NaOH or KOH solution or some strong NH40H, If 
there is pus in the sediment, it will be converted into a 
viscid mass. If mucus is present, it will be curded, 
but it will not assume the tough, gelatinous appearance 
that the pus does. 


Allojy a mixture of two or more metals of differing nature and 

Anhydridy an oxid which unites with water to form an add; 
a substance formed from a compound, especially an acid, by the 
loss of a molecule of water. 

Anion, a negative ion. 

Anneal, to render a substance less brittle by heating it to a 
high temperature and then cooling it slowly. 

Anode, the positive pole of an electric celL 

Apposition, in contact with. 

Arbitiarily, depending on the will of an umpire, judge, etc 

Binary, composed of two elements. 

Calcareous, pertaining to or of the nature of lime. 

Cathode, the n^:ative pole of an electric celL 

Cation, an electro-positive ion. 

Caustic, corrosive. 

Colloid, glutinous; resembling glue; a non-crystalline substance. 

Commercial, as ordinarily furnished by dealers. 

Conifers, trees that bear cones. 

Decomposition, the separation of a substance into simpler 

Deflsgration, sudden, rapid burning. 

Deflected, bent from a straight line; turned aside. 

Degeneration, changing from a higher to a lower form. 

Dehydration, removal of water from a substance. 

Deliquescence, see page a22. 

Detttgent, deansmg. 

Diaphragm, a partition, such as a membrane stretdied between 
two cavities. 

Dissociation, partial decomposition. 

Ductile, pliant; easily stretched. 

4^8 Glossary 

Blmllitioii, the bubbling of a liqtiid caused by escaping gas. 

Bifervetceiica, the bubbling of gas in a liquid. 

Bffioreiceiicai see page 222. 

ElectrolyBiSy chemic decomposition pixxluced by electricity. 

Filamenti a fine thread or thread-like process. 

Flltratey the liquid which passes through a filter. 

Fofge, to form into shape by heating and hammering. 

Fotey to melt. 

Germinationt sprouting. 

Habitati the natural locality of animals, plants, etc, in their 
wild state. 

Heliotherapy, the treatment of disease by exposing the body 
to light. 

Hepatitis, inflammation of the liver. 

Hydrate, any compound of hydroxyl with a radical: a com- 
pound containing water of crystallization. See page 233. 

Hydrated, combined with water. 

^ydrolysIs, chemic decomposition in which a oompotmd breaks 
up as its molecules combine with one or more molecules of water. 

](gnlte, to set on fire. 

Incandescent, glowing, white with heat. 

Interaction, diemical action in which there is double deoom- 
position and combination. 

Ion, an electrically chaxged atom; see Chapter VII. 

Isomerism, see page 158. 

Nascent, beginning to grow or exist; an active state. 

Neutralize, to render inactive; to make neither acid nor alkaline. 

Nitrogenous, pertaining to or containing nitrogen. 

Polymer, one of a series of compounds of which the molecular 
weights of the members of the series are in numbers which ara 
multiples of each other. 

Precipitate, to render a soluble substance insoluble and thus 
cause it to oome out of solution and fall to the bottom of the con- 
taining vessel; the solid thus precipitated. 

Radical, see page 150. 

Reaction, a diemical change. 

Residue, that which remains after other substances have beea 

Rhythm, harmonical; periodical. 

[ Sadhnentation, settling to the bottom of a liquid. 

Saoatadt notched like the edge of a saw. 

Glossary 429 

Temaiyi made up of three elements or radicals. 

Tarpenes, hydrocarbons of the formula CioHi^; they are 
derived chiefly from volatile oils and resins. 

Vdatilei tending to evaporate rapidly. 

Warp, the threads whidi extend lengthwise in the loom and 
are crossed by the woof. 

Welded, united by hammering or heating. 


Absorbents, nature and action 

of, 237 
Absorption, changes that occur 

in tood substances during, 

Acetone in urine, 421 
Adds, amino, 276 
Adds and hydrogen, 194 
Adds, classification of, 193 
Adds, derivation of prindpal 

organic, 193 
Adds, inoi^ganic, igd. 
Adds, names of, 196 
Adds, properties of, 195 
Adds, tests for. 196 
Adulteration of food, 375 
Adulteration of soap, 230 
Air, how heated, 87 
Albumin, characteristics of, 

Albuminoids, nature of, 280 
Alcohol, action in system, 338 
Alcoholic beverages, 334-340 
Alcohols, classification of, 164 
Alcohols, how synthesized from 

hydrocarbons, 166 
Alcohols, origin of the diffeieat 

kinds used as fuel, 184 
Aldehydes, nature and deriva- 
tion of, 167 
Alkalies, nature of, 197 
Alkalies, reaction of, 197 
Alkalies, reason for use in 

deaning, 226 
Alkalies, source of those fre- 
quently used in cleaning, 227 
Alkaloids and their salts, 203 

Allotropism, meaning of, 161 
Alluminium, qualities of and 

methods of cleaning, 249 
Anabolism, 425 
Anhydrids, 195 
Anhydrous, meaning of, 223 
Amids, 283 

Amino adds, nature of, 278 
Ammonia, source of, 227 
Artificial ice, 59 
Astigmatism, 99 
Atomic weigh^ 29 
Atoms, definition of, 27 


Bacteria, action in alimentary 

tract, 395 
Bacteria concerned in spoiling 

food, 308 
Bacteria in water, 210 
Bacteria, why killed by heat, 

bichlorid, etc., 285 
Baking powders, 356, 357 
Barley, 321 

Barometer, invention of, 49 
Bases and alkalies, differences 

between, 197 
Bases, names of, 197 
Bases, reaction of, 197 
Batteries, chemical, nature of, 

107, 108 
Batteries, electric, 113 
Batteries, storage, 114, 115 
Batters, methcxls of malcing 

Ught, 2^ 
Beers and ales, 338 
Benzoic add, test to detect to 

food, 378 




Birds, food value of, 31 1 
Bleadung ageats, action of, 

234-237, 263 
Bleaching, chemistry of, 234 
Blood, composition of, ^^06 
Blood constituents, denvation 

of, 407 
Blues, different kinds of, 266 
Blues, experiment to detect 

iron in, 266 
Bluing, nature of, 266 
Boiling, effect of pressure upon. 

Boiling, effect of specific 

gravity upon, 54 
Boiling, nature of, 51 
Borax, source of, 227 
Borax, test to detect in food, 

Bone acid, source of, 227 

Boric add, test to detect in 

food, 378 
Brass, 247 

Breezes, land and sea, 81 
Bronze, 247 
Bunsen burner, experiment to 

study, 6 
Bunsen burner, nature of, 6 
Burner, Argand, 187 
Butter, 318 

Butter, adulteration of, 382 
Butter, renovated, 318 
Buttermilk, 317 
By-produd^ 154 

Capillarity, cause of, 76 
Capillarity in plants, 303 
Capillaritv, nature of, 75 
Carbohydrates, classification 

of, 287 
Carbohydrates, constituents 

of, 287 
Carbohydrates, experiments to 

test the solubilities of, 349, 

Carbon, different forms of, 160 
Carbon, occurrence of, 160 
Carbon oxids, i6z 
Catabolism, 405 

Cathode rays, nature of, 134 
Cells, dry, iif 

Cells, Galvamc or Voltaic, 1 10 
Cellulose, digestibility of, 288 
Cellulose, nature of, 288 
Cereals, adulteration of, ^81 
Cereals, composition ot, 320 
Chang^ physical and chemi- 

cal difference between, 35 
Charcoal, origin and nature of. 

Cheese, 318 

Chemical action that occurs in 

Galvanic cell, 11 1, 112 
Chemical affinit^r, 36, 148 
Chemical batteries, nature of, 

Chemical changes, 35 
Chemical formuks, definition 

for, 151 
Chemical formuls, different 

kinds of, 152, 153, 159 
Chemical reactions, agents 

which promote, 147 
Chemical reactions, nature of, 

Chemical reactions, reason for, 

Chemicals, list of, 19-21 
Chemicals, points to remember 

about, 12 
Chemistry, definition, 26 
Chocolate, 231 
Circuit, making and breaking 

of electric circuit, 1 11, 112, 

Ii3> 122 
Circuit, nature of electric 

circuit, III 
Cleaning, classification of sub- 
stances used for. 224 
Clotting of milk axid blood, 286 
Clouds, nature and causes of, 

Coagulation of proteins, 284— 

Coal, nature of different kinds 

of, 182 
Coal, origin of, 181 
Coal tar, origin and uses of, 163 
Cocoa, 332 
Coffee, 327-329 



Coffee, adulteration of, 381 

Coffee substitutes, 329 

Coils, induction, 122 

Coke, origin of, 182 

Color blindness^ 92 

Color, causes of, 86 

Color of bodies, origin of, 91 

Color of transparent objects, 93 

Colors complementary, 93 

Colors, length of waves pro- 
ducing different, 86 

Colors, number of. 91 

Colors, reason lor changes 
tmder artificial lights, 91 

Colors, reason for fading of, 

Colors, why perceived, 92 
Combustion, experiments to 
discover the nature of, 177- 

Combustion, surface, 188 
Compounds, stable and un- 
stable, 1^0 
Condensation, nature and 

causes of, 58 
Condiments, nature and use of, 
^ 32<-327 
Conduction, experiments to 

show heat, 77 
Conduction, nature of heat, 77 
Conductors, comparative value 

of substances as heat, 78 
Conductors, comparative value 

of substances as electric, 106 
Contraction, causes of, 71, 72 
Convection currents, 80 
Convection, nature of, 80 
Copper alloys, 247 
Copper, methods of cleaning, 

Copper, qualities of, 247 
Copper sulphate, test to detect 

in food, 380 
Com, 321 
Cotton, action of acids and 

alkalies upon, 263 
Cotton fibers, nature of, 262 
Cream, ^18 
Cream, how frozen, 47 
Crustaceans, 313 
Currents, seeElectxic 

Deh3rdratiQn, 223 

Deliquescence, 222 

Dew, 61, 62 

Dextrin, occurrence andnature, 

Dextrose, see Glucose 
Dialysis, nature of, 70 
Diffusion of gases, experiment 

to demonstrate, 66 
Diffusion of gases, nature of, 65 
Diffusion of fiquids, example 01, 

Diffusion of solids, 67 
Digestion, experiments on, 


Digestion, nature of, 587 
Digestion, products of, 396 
Digestion, reason for, 387 
Digestive juices, toctors in- 
fluencing secretion of, J94 
Digestive ;uices, nature ot, 389 
Disacchands, classification of, 

Distillation, destructive, 64 
Distillation, experiment to 

show, 212 
Distillation, fractional, 63 
Distillation, nature of, 63 
Distilled liquors, 336 
Doughs, methods of making 
_ light, 354 ' 
Dressing in cotton and linen 

fabrics, 271 
Dyes, origin of, 272 
Dyes, permanency of, 273-275 
Dynamo, nature and uses o^ 



Ear-trumpet, 146 

Edema, a cause of, 69 

Efflorescence, 222 

Eggs, composition of, 319 

Eggs, experiment to study 
coa^lation of, 346 

Electric changes, kmds of, 103 

Electric conductors, compara- 
tive value of substances as. 
106 ^ 



Electric current, nature of, io6 

Electric currents, alternating, 

direct, induced, secondary, 


Electric currents as source of 

heat and light, 124 
Electric currents, Galvanic 

and Faradic, 122 
Electric currents, how pro- 
duced, 107, III, 122 
Electric lights, 125-227 
Electricity, derivation of name, 

Electricity, physiological 

action of, 13^ 
Electricity, static, 132 
Electricity, theories r^;arding 

nature of, 104 
Electrification, experiments to 

show nature of, 102 
Electrolysis, nature of, 108, 109 
Electromagnets, 113, 121 
Electromotive force, 127 
Electroplating, nature of, 116 
Elements, number and condi- 
tion of, 29 
Elements, table of, 30-35 
Elixirs, 336 
Enamel ware, 244 
Energy, definition of, 40 
Enei^gy, different kinds of, 41 
Energy, law of conservation 

of, 38 
Enzymes, nature and action of, 

Enzymes, table showing action 

of, 392 
Equations, nature and ptupose 

of, 154 
Esters or ethereal salts, 204 
Ethane, nature, source, and 

derivatives of, 164-165 
Ether waves, effect of different 

kinds of matter upon, 88 
Ether waves, nature of, 85 
Evaporation compared with 

vaporization, 55 
Evaporation, factors which 

influence the rate of, 56 
Evaporation, why it causes 

cold, 57 

Expansion and oontractioa of 
water, peculiarities of, 72 

Experiments, see Index of 

Extractives, 283, 311 

Fading of colors, 92, 267, 274 
Far-sightedness, 98 
Fat, metabolism of, 408 
Fats, chemical composition of, 

Fats, classification of, 296 
Fats, function in body, 297 
Fats, nature of, 296 
Fermentation, 359, j68, 369 
Filtering, method of, 15, 211 
Fire-extm^sher, 180 
Fish, classification of, 312 
Fish, nature and nutritive 

value of, 312 
Flame and incandescence, 179 
Flame, Bunsen, 8 
Flame, oxidizing, 10 
Flame; roducini, 10 
Flame, study of, 7 
Fluorescence, nature of, loi 
Fluoroscope, nature of the, 136 
Fog, 61, 62, 63 
Food, adulteration of, 375 
Food, causes of spoiling, 365 
Food, conditions conducive to 

spoiling, 370 
Food cycle, 305 
Food, now to prevent spoiling, 

Food material, classification of , 

Food material, origin of, 301 
Food preservation, 370, 374 
Food requirements, 413-415 
Foods, classification of plaiit» 

Foods, com(>arative digesti- 
bility of animal, 308 
Foods, table of average com- 
position of. 340 
Formaldehyd, test to detect, in 

food, 379 



Pormals for some common 
compounds, I54-I57. '59 

Fonnuke, structural, 159 

Frost, nattire and cause of, 62 

Fruit, 324 

Fruit juices, unfermented 
beverages niade from, 334 

Fuel, cla&fication of material 
used for, 181 

Fungi. 325 

Fuses, nature and use of, 130 

Gas, acetylene, 189 

Gas, coal, 187 

Gas, comparison of terms 

vapor and, 39 
Gas, compressed, 189 
Gas, gasoline, 189 
Gas natural, 188 
Gas, water, 188 
Gaseous fuels, different kinds 

of, 186 
Gasoline, origin and fuel value, 

Glass, cleaning, 254 

Glass, composition of different 

kinds of, 253 
Glass tubing, bending, 13 
Glass tubing, drawmg to a 

point, 14, 15 
Glass, why it oreaks if heated 

or cooled ouickly, 72 
Globulins, oiaracteristics of, 

Glucose, metabolism of, 408 
Glucose, nature and occurrence 

Glucose, tests for, 294, 296, 
398, 400, 403 ^ 

Glutenms, nature of, 280 

Glycerin, how made syntheti- 
cally, 166 

Glycerin, how usually ob- 
tained, 220 

Glycerin in fat, 297 

Glycerin in soap, 230 

Glycerin soaps, 232 

Glycogen, occurrence and 
nature of, 290 

Glycoproteins, 281 
Gums, 291 


Hail, 63 

Hearing, mechanism of, 141 

Heat capacity of different 

kinds ot matter, 44 
Heat-conducting power of 

different kincb of matter, 78 
Heat conduction, 78 
Heat, definitions of, 41 
Heat, difference between 

amount and degree of, 43 
Heat, effects of, 42 
Heat of fusion, 45 
Heat of fusion, recovery of, 47 
Heat, latent, 4^ 
Heat, latent, of steam, 46 
Heat, means of transmission. 

Heat, nature and cause, 62 

Heat, reflection of, 92 

Heat, relative heat of bodies. 

Heat, retention of, 87 

Heat, sources of, 42 

Heat, specific, 43 

Heat value of foods, 411 

Heat, value of high heat capa- 
city of water, 44 

Hemoglobin, 282 

Hemo^^ experiments to 
show, 69 

Hemolysis, nature and causes 
of, 69 

Histones, 281 

Honey, composition of, 320 

Hormones, nature and action 

of, 391 
Humidity, absolute, 61 
Humidity, effect on health, 61 
Humidity, meaning of term, 60 
Humidity, relative, 61 
Hydration, 222 
Hydrocarbons, how obtained, 

Hydrocarbons, nature and 

classification, 161 



Hydrocarbons, physical condi- 

Hydrochlonc add, 194, 195 
Hydrochloric acid, action in 

digestion, 39a, 394 
Hydrolysis, 388 
Hydroxids, 196 
Hypennetropia, 98 
Hypotheses, at«nic, 38 
Hypotheda, definition td, 38 


Incandescent gas ushts, 187 

Induced currents, tee Electric 

Induction coils, 133 

Inultn, 391 

Iron, gajvanized, 343 

Iron, methods of deaning, 345 

Iron rust, 339 

Iron, vaneties of, 343-343 


330, 339, 354 
Kinases, action of, 391 
Kindling temperature, 174 
Koumiss, 317 

Laboratory maxims, 13 

Laboratory methods, 13 

Lactose, 393 

Lakes, nature of, 373 

Law of Boyle, 39 

Law of Charles, 39 

Law of conservation of energy. 

Law of conservation of matter. 

Ledthins, nature and functi<m 

of, 397 
Leathoproteins, 383 
Legumes, 323 

Lenses, different kinds of, 99 
Levulose, 394 
7 ' ' ' -c, 137 

insen, 94 

xwidesceot, 135 

iflection of, 89 

fraction of, 95 

g, nature of, 134 

nature of, 183 

action of adds and 

s upon, 363 
Linen fibers, 363 
Liquefied gases, 58 
Liquid fuels, classification of, 

Liquors, distilled, 330 
Liquors, malt, 337 


Magnetism, cause of, i3o 

Magnetite, IiS, iiq 

Magnets, nature of, 118 

Mi^ets, properties of, i30 

Malt, 331 

Maltose, 393 

Marble, experiment to study 
the effect of acids and alka- 
lies upon, 351 

Mariner's compass, 119 

Matter, itature of, 36 

Matter, states of, 37 

Matzoon, 317 

Measurement of electricity, in- 
struments used for the, 130 

Measurement of electridty, 

with, 137-130 

Measuring, 18 

Meat, factors which influence 
the digestibility of, 309 

Meat, faults of cooking, 347 

Meat, structure of, 310 

Megaphone, 146 

Metabolism, causes of defec- 
tive, 411 



Metabolism, factors influenc- 
ing, 410 

Metabolism, nature of, 405 

Metabolism of food products, 

Metabolism, results of defec- 
tive, 410 

Metal, tarnish of, 238 

Metals, experiments to show 
the action of adds, alkalies, 
etc., on, 2i^o 

Metals, requirements of clean- 
ing material for, 339 

Metastasis, 302 

Methane, nature, sotm^ and 
derivation of, 164 

Microscope, principles of, 98 

Milk, adulteration of, 383 

Milk, certified, 314 

Milk, composition of, 313 

Milk, dessicated, 317 

Milk, digestibility and nutri- 
tive value of, 313 

Milk, pasteurized, 315 

Milk, sterilized, 316 

Mineral matter in food and 
the human body, 298 

Molds, exi>erimcnts to study 
the multiplication of molds, 

Molds, nature and require- 
ments of molds, 365 

Molecular motion, 28 

Molecular weight, 30 

Molecules, demiition of, 26 

Monosaccluuids, 293, 294 

MoUusks, food value of, 312 

Mordants, nature of, 273 

Myopia, 98 


Nearsightedness, 28 
Neucleoproteins, 281 
Neutralization, experiment to 

demonstrate, 198 
Nickel, nature and method of 

cleaning, 246 
Nitrogen, how obtained by 

plants, 304 
Nitrogenous foods, see Protein 

Non-nitrogenous compounds, 

Nuts, 325 

Oatmeal, 321 
Oil, adulteration of, 382 
Oils, essential or volatile, 296 
Oils, fixed, 296 
Old-age sight, 98 
Oleomaigarin, ^18 
Organic and inoiganic sub- 
stances, differences between, 

Oiganic chemistry defined, 158 
O^osis, experiments to oe- 

monstrate, 68 
Osmosis, nature of, 67 
Oxidation and combustion, 

nature of, 174 
Oxidation, difference between 

the oxidation of compounds 

and elements, 176 
Oxidizing compotmds used as 

bleaches, 235 
Oxids, nature of, 179 
Oxids, uses of, 180 
Oxygen, action in bleaching, 

Oxygen, experiments to study 

the nature of, 170-173 
Oxygen occurrence of, 169 
Oxygen physical and chemical 

properties of, 173 

Painted surfaces, methods of 

cleaning, ^56 
Paints, nature of, 255 
Peat, origin and nature of, 183 
Pectin, nature and use of, 291 , 

Pectin tests, 363 
Petroleum, source and uses of, 

Pewter, nature of, 250 

Phonograph, 142 

Phosphoproteins, 282 

Phosphorescence, nature of, 




PhotosTnthesis, 301 

Plant life, effect upon the 
atmosphere of, ^05 

Plants and animsds, classifica- 
tion of substances compos- 
ing, 276 

Plants, how they grow, 301- 

Platinum, 251 

Polarity, nature of, 118 

Polarization, nature of, 100 

Porcelain, 253 

Potassium, source and uses of, 

Precipitation, difference be- 
tween coagulation and, 286 

Presbyopia, 98 

Preservatives, classification of 

' food, 374 

Pressure, atmospheric, 49 

Pressure, causes other than 
altitude that produce change 
in atmosphenc, 50 

Pressure, comparative relation 
of changes in heat and, 48 

Pressure, effect on boiling 
point, 51 

Pressure, how increased, 48 

Printing, difference between 
dyeine and, 272 

Prism gmss, 100 

Protamines, 281 

Proteins, alcohol soluble, 280 

Proteins, classification of, 278 

Proteins, coagulation of, 284, 

Proteins, composition of, 277 
Proteins, conjugated, 281 
Proteins, derived," 282 
Proteins, digestion of, 388, 392 
Proteins, experiments to test 

the effect of heat and add 

upon, 345-347 , , , 
Proteins, function of food, 283 
Proteins, metabolism of, 408- 

Proteins, precipitation of, 286 
Proteins, simple, 279 
Proteins, solubilities of, 348 
Proteins, tests for, 270, 283, 

384, 398, 401, 402, 403 

Radiation, nature of, 84 

Radicals, 150 

Radio-rays, nature and actaoa 

« o^» 137 

Rain, cause of, 62 

Rainbow, 100 

Reagents, list of, 19-21 

Reduction, 10, 235 

Reflection, nature of, 88 

Reflection, result of the xe* 

flection of light, 89 

Refraction, cause of, 96 

Refraction, difference in, 97 

Refraction, nature of, 95 

Rheostat, nature of, 132 

Rice, 322 

Roots and tubers, 322 

Rye, 322 

Salicylic add, test to detect In 
food, 377 . 

Salts, dissociation of, 200, 202 

Salts, ethereal, 204 

Salts, experiment to show dis- 
sociation, 200 

Salts, formation, 200, 410 

Salts, function in body, 298 

Salts, naming of, 202 

Salts, nomuu, add and basic, 

Salts, occurrence^ 199 

Salts, source of, m scnl, 304 

Salts, tests for, 299 

Sap, forces causing dxx^ulatioa 
m plants, 303 

Sap, nature and purposes of» 

Saponification, how caused, 
205, 229 

Sapjonification of fats in diges- 
tion, 388 

Scouring agents other than 
soaps and alkalies, 234 

Scounng powders, composition 
of, 233 

Secretins, nature and action ol| 




Silk, acttoa of alVaKwi, adds, 

heat, etc., on, 265 
Silk, artificial, 263 
Silk fibers, nature of, 263 
Silver, qtialities of and methods 

of deaning, 249 
Siphonage, 74 
Smoke, 177 
Snow, cause of, 63 
Soap, test for fillers in, 233 
Soap, test for free alkalies in, 


Soap, test for rosin in, 232 

Soap, test for unsaponified fat 

in, 230 
Soaps, how made, 220 
Soaps, reasons for mfferences 

in, 230 
Soaps, substances added to* 

Sodium, sources and uses of, 

Solder, nature of, 250 
Solutions, definitions for terms 

used in connection with, 

191, 192 
Solutions, list of solutions 

used for experiments, 19-21 
Solutions, nature of matter 

used for, 192 
Spedfic gravity, effect upon 

boiling point, 54 
Specific gravity, how ascer« 

tained, 54 
Spedfic gravity, nature of, 53 
Spedfic gravity of urine, 418 
Spedfic gravity, value of 

knowle(^e of, 54 
Spices, origin and food value 

of, 326 
Solvents, nature, origin and 

uses of those commonly 

used in cleaning, 224 
Sound, difference oetween 

sound and light waves, 138- 

Sound, how transmitted, 140 
Sound, origin of, 136 
Sounds, reasons for differences 

in. U3 
Stains, removal of« 267-270 

Starch, comparative thicken- 
ing power, transparency and 
flavor of, 353 

Starch, digestion of, 392, 399 

Starch, experiments to test 
the action of heat and water 
on, 351 

Starch, properties of, 289 

Starch, test for, 289, 400, 403 

Steel, 243 

Stethoscope, 146 

Sublimation, 65 

Sucroses, 292 

Suction, nature and common 
uses of, 74 

Symbols, 29 

Tarnish, nature of, 238 
Tarnish, requirement of agents 

for removal of, 239 
Tea, 330 

Temperature, kindling, 174 
Test, acetone, 424 
Test, adds, 196 
Test, Babcock, 383 
Test, bile, 425 

Test, blood (Heller's test), 325 
Test, dextrin, 290 
Test, diacetic add, 424 
Test, Halophen, 382 
Test, indican, 424 
Test, lactose, 293 
Test, pectin, 363 
Test, pus, 425 
Test, spoon, 382 
Test, starch, 289, 398, 400, 403 
Test, sucrose, 292 
Test tubes, manner of holding, 

Test tubes, numbering, 1 1 
Tests for adulterants in food, 

Tests for adulterants m soap, 

Tests for albumin, 424 
Tests for dextrose or glucose, 

294-296, 398. 400, 403 
Tests for monosaccharids, 294, 

296, 400, 403 



Tests for proteins, 383-284, 
398, 401, 402, 403 

Tests to determine the pres- 
ence of various salts in tood, 
etc., 299 

Tests to distinguish between 
cotton, ]inen, silk, and wool 
fibers, 270 

Textile tests, 170 

Textiles, expeiiments to study 
the nature of, 261 

Textiles, experiments to test 
the action of adds, alkalies, 
etc, on different, 263 

Textiles, mercerized, 263 

Textiles, removal of stains 
from, 267 

Textiles, some practical appli- 
cations of knowledge of 
effect of adds, etc., on, 265 

Textiles, source of, 260 

Thermometer, how made, 73 

Tin. qualities of and methods 
ot cleaning, 246 

Transformers, value of, 131 


Urine, abnonnal constituents 

of, 421 
Urine analysis, 423-426 
Urine, composition of, 420 
Urine, physical properties of, 

418. 419 
Urme quantity voided, 417 
Utensils, precautions neces- 
sary in tne use of chemical, 
10, II 

Vacuum, 7, 


Valence due to electrical 

chaiges, 149 
Valence, nature of, 148 
Vaporization, amount of heat 

required for, 46 
Vaporization, nature of, 40 
Varnishes, nature of, 2^6 
Vegetables, classification of, 


V^etables, green, 323 

Ventilation, 81 

Visible, why objects are, 89 


Waste matter, origin and 

elimination 01, 416 
Water, bacteria in, 210 
Water, carbonated, 333 
Water, dty supply, 206 
Water, composition of, 209 
Water, country supply, 207 
Water, difference between 

hard and soft, 214 
Water, expansion and contrac- 
tion of, 72 
Water, experiments to show 

the softening of, 219-221 
Water, fordgn substances in, 

Water, freezing of, 72 
Water, functions in the body, 

Water, hard, 219 
Water, mechanically endosed, 

Water, mineral, 214, 333 
Water, objections to me use of 

hard, 217 
Water of crystallization, 221 
Water, purification of, 210-212 
Water, softening of, 215-217 
Waxed floors, how to wax and 

dean, 257, 258 
Wdghing, 17 
Weights and measures, tables 

of, 22-24 
Wdsbach mantle, 187 
Wheat, 320 
Whey, 317 
Wind, 80, 81 
Wines, 335 

Woods, classification of, 183 
Woods, nature of different 

kinds of, 183 
Wool, effect of bleaching 

agents upon, 236, 264, 265 
Wool fibers, effect of heat, 

adds, and alkalies on, 264 
Wool fibersi xiatuxe of ^ 263 



X-Rays, nature and action of, 

Yeasts, food requirements of, 

Yeasts, nature of, and action, 

Yeasts, result on food of in- 
fection by, 368 

Zinc, 244 

Zymogens, nature and action 
of, 391 


MUMBBt Objed of Experiment ^^^b 

I. Study of the Bunsen burner 6 

2 & 3. Study of the Bunsen flame 9 

4. Demonstration of the production of heat by 

chemical reactions 42 

5. Demonstration of the effect of atmospheric pres* 

sure upon boiling point 51 

6. Demonstration of the effect of specific gravity 

upon boiling point 5A 

7. Demonstration of the diffusion of gases 60 

8 & 9. Demonstration of osmosis 67, 6S 

10. Study of heat conduction and convection 77 

11. Study of electrification 102 

12. Demonstration dt magnetic fields and lines of 

force X2X 

13. Stud^ of (i) a method of reducing a compound 

to Its constituent parts; (2) a method ot liber- 
ating a gaseous element from a compound and 
collecting the gas; the properties of oxygen; 
(4) the use of a catalyzer 171 

14. Study of the results of the oxidation of an ele- 

ment 172 

I5-X8, Observation of the nature of combustion I77''i79 

19. Demonstration of neutralization 198 

20. Decomposition of salts 20X 

21. Demonstration of the effect of distillation as 

compared with filtration 212 

22. Study the differences in hard waters 219 

23. To show some methods of softening water 219 

24. To estimate the amount of soda necessary to 

soften water 220 

25. To observe the difference in the manner in which 

water of crystallization and mechanically en- 
closed water escape from a compound when 
the latter is heated 221 

26. Observation of efflorescence and deliquescence. . . 222 

27. Tests for soap adulterations. 231-233 


444 Index of Experiments 



28. To Study the effect of acids and alkalies upon 

metals 240-341 

29. Demonstration of the effect of acids and alkalies 

upon marble 251 

30 & 31. To study differences in the composition of tex- 
tiles 261 

32. To test the action of acids, alkalies, and bleaches 

on textiles 263 

33. To note the effect of dry heat on wool 264 

34. To see if iron is present in a blue 266 

35~37' To distinguish different textiles 270 

38. To determine the amount of dressing in a fabric. . 271 

39. To test color-fastness of material 273 

40. To note the effect of the loss of calcium salts dE 

milk on clotting 314 

41. To test the comparative effectiveness of the 

holder and flash methods of pasteurization 315 

42. To discover the temperature at which albumin 

of egg, milk, etc., will coagulate 345 

43. To test the effect of salt and acids upon protein . . 346 
44-46. To see if the common forms of carbohydrates 

are soluble in water 349 

47. To see the effect of heat and water upon starch. . . 35 1 

48. To note differences in taste, transparency, etc., 

of different starches 352 

49. To study the effect of heat and of heat plus acid 

on starch 353 

50. To observe the effect of heat and add on sugar. . . 353 

51. To study the action of baking powder 356 

52. A test to detect the presence of alum in baking 

powder 357 

53. To determine the comparative fermentating 

power of different yeasts 360 

54. To see why sugar is added to dough in bread 

making 361 

55. To prove that it is the same gas which is ob- 

tained by the use of baking powders and of 
yeast 361 

56. A test for the presence of pectin 363 

57. To study conditions that favor the growth of 

molds 366 

58-65. Tests for food adulterants. 377-386 

66-73. Experiments on digestion 399~*403 

Unnalysis. ^ . .423-426 

APR 2 6 1920 


Quiz Book of Nursing 
for Teachers and Students 


Amy Elizabeth Pope 

Joint Aitlmr of '*Pnictical Nnrtiiig*' and **ffooontlili 

of Diototics** 

Thirza X. Pope 

Together wMh Chapters on Vlsltiiiff Nnrrfng 

Bf lUrgarot A. Bewlej, R. N. 

OndBBM of PnrigrtariaB ScImoI eC Nurfng. and of tiM SIohm Urtwiilty 

Hoipital, N«« Totk CIcys iMrractorm VWdac ud Dinrid 

NoaNf ia PmbytMaa Hotpica], New Yoik City* 

Hospltel Phumlngt Construction, and Equipment 
By Bertnuid B. Taylor, A. A. L A. 

Hospital Boolc-lceepinff and Statistics 

By Frederic B. Morlok 

Cbkl Ckilt IB the Prasbytcriaa Hospital, Naw Yotk Ol^ 

Third Ediiion^ Revised and Enlarged lUustraUd 
Uniform with "Practical Nursing'* 

TUi book ftioui to be iisefol, in the moit practical way » to 
nurses who teach, and to those who are studying under thexn. It 
is, in large part, a quiz book, offering in the form of terse ques- 
tion and answer essential information on jl wide range of sabjects 
—the information that is essential from the nnrseVi standpoint. 
Those who teadi will find these questions oi assistance when the 
time they have to devote to preparation for their class work is 
limited ; and those who are taking oonnes will find the book a 
great hdp ; especially when studying for examinations. 

A History of Nursing 

By Lavinia L. Dock, R.N. 


H. Adelaide Nattingt R.N. 

4 voU* Sua, Bach fully iUustratmd 

VoU. I n^ n. Th« Evolvtlom of th« Hclhoda of Cm* fw 
thtt Sick from th* EwllMt TIbm to th« PovadattoB off tho 
First EmiUak aad AMwIoaB Traialiitf SchooU for Nvrsoa. 

Two voUi, with So IliuMtrutionM 

Vols. Ill aad IV. Th* Story off Mod«ffB N«rstatf. ProMotla^ 
•B AcGOont of the Dev«lopiii«nt In Various Goantries ol 
ths Sdoace of Traiaed Nurslad with Spadal Baf araoca to 
tba Work of tka Past Thirty Yaars. 

Two vols., with 75 illustrations 

Bsglnniaff with ths eartteit sytlUble lacords of laiiitaiy oodss 
which wsro hoilt up into liealth religions, and coming down through 
tho sfas wfaerevor the care and leecne of the lick can he traced* 
through the pagan dTllizations, tlie early Christian works of mercy* 
the long and glofions histoiy of the religions nursing orders, military 
nursing orders of the Crusades* the secular communities of the later 
Middle Ages, and the reviTal of the deaconess order wUch cul- 
minated in the modem reviyal under Miss nightingale* this history 
Is the most serious attempt yet made to collect the scattered ncorda 
of the cars of the sick and bring them all into one unified and sympa- 
thetic presentation. 

The story Is not told In a diy technical fashion* but pcussnts its 
pictures from tho standpoint of general human interest in s subject 
which has always appealed to the sympathies of men* 

Both Ifiss Nutting and Miss Dock are wril known in the nursing 
world; Miss Nutting* as one of the foremost educators in hospital 
woik* who* as the head of the Johns Hopkins Hospital trsining 
school* has so distinguished herself for practical work that she has 
been called to Columbia University to take the chair of Institntianal 
Management* and her collaborator as s well-known woiksr for 
organisation and progress* and who* as the secretary of the In- 
ternational Counctt of Nurses* has already written much on nursing 
and hospital conditions. 

The history is amply illustrated* and contains a copious Ubiiof* 
raphy of nursing and hospital history. 

Nnr York Q. P. Putnain*s Sons lohOm