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\OUMK vii. PART i. 

In TEN VOLUMES. Medium 8vo. Cloth. All prices net. Postage extra, 





Carnegie Gold Medallist. 

PART I. An Introduction to Modern Inorganic 

VOLUME I. Chemistry. By J. NEWTON FRIEND, D.Sc. (B'ham), Ph.D. 

TUrd Edition] (Wiirz.); H. F. V. LITTLE, B.Sc. (Lond.), A.R.C.S., Chief 

Pp.i-x^+385. j Chemist to Thorium, Ltd. ; W. E. S. TURNER, D.Sc. (Lond.). 

12s. 6d. PART IL The j nert Gases ( Group o in the Periodic Table). 

By H. V. A. BRISCOE, D.Sc. (Lond.), A.K.C.S. 

YOLTJME II. The Alkali Metals and their Congeners (Group I. of the 
Intlie Press. Periodic Table). By A. JAMIESON WALKER, Ph.D. (Heid.). 

VOLUME III. The Alkaline Earth Metals and their Associates (Group 

II. of the Periodic Table). By Miss M. S. LESLIE, D.Sc. 
VOLUME IV. Aluminium and its Congeners, including the Rare 

Pp. i-xx + 485. Earth Metals (Group III. of the Periodic Table). By 
16s. H. F. V. LITTLE, B.Sc. (Lond.), A.R.C.S., Chief Chemist to 

Thorium, Ltd. 

Carbon and its Allies (Group IV. of the Periodic Table). 
By E. M. CAVEN, D.Sc. (Lond.), F.I.C. 

Pp. i-xxi + 468. 



Nitrogen and its Congeners (Group V. of the Periodic 

Table). By E. B. E. PRIDEAUX, M.A., D.Sc. 
/ PART I. Oxygen. By J, NEWTON FRIEND, D.Sc., and DOUGLAS 

F. Twiss, D.Sc., F.I.C. 
J PART II. Sulphur, Selenium, and Tellurium. By 

DOUGLAS F. Twiss, D.Sc., and Miss A. E. EUSSELL, B.Sc. 
PART III. Chromium and its Congeners. By ARTHUR V. 
ELDRIDGE, B.Sc., F.I.C., and E. H. VALLANCE, M.Sc., A.I.O. 
VOLUME VIII. The Halogens and their Allies (Group VII. of the Periodic 
Second Impression. Table). By GEOFFREY MARTIN, D.Sc., Ph.D., and ERNEST 
Pp. i-xviii + 337. A. DANCASTER, B.Sc. (Lond.). 
12s. 6d. 

PART I. Cobalt, Nickel, and the Elements of the 

Platinum Group. By J. NEWTON FRIEND, D.Sc. (B'ham). 

PAIIT!. Pp, 
i-xvii + 367. 


i-xxv + 265. 


In preparation. 

PART II. Iron 

and its Compounds. By J. NEWTON 

PART III. The Metallurgical Chemistry of Iron. By 


The Metal Ammines, with a General Introduction to the 
Theory of Complex Inorganic Substances. By Miss 


Modern Inorganic Chemistry. Vol. VIL, Part /.] 






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Mttb frontispiece anD Jllustiattons, 




[All rights reserved.] 

Printed in Great Britain by 


DURING the past few years the civilised world has begun to realise the 
advantages accruing to scientific research, with the result that an ever- 
increasing amount of time and thought is being devoted to various 
branches of science. 

No study has progressed more rapidly than chemistry. This 
science may be divided roughly into several branches : namely, Organic, 
Physical, Inorganic, and Analytical Chemistry. It is impossible to 
write any single text-book which shall contain within its two covers a 
thorough treatment of any one of these branches, owing to the vast 
amount of information that has been accumulated. The need is rather 
for a series of text-books dealing more or less comprehensively with 
each branch of chemistry. This has already been attempted by 
enterprising firms, so far as physical and analytical chemistry are 
concerned ; and the present series is designed to meet the needs of 
inorganic chemists. One great advantage of this procedure lies in 
the fact that our knowledge of the different sections of science does not 
progress at the same rate. Consequently, as soon as any particular 
part advances out of proportion to others, the volume dealing with 
that section may be easily revised or rewritten as occasion requires. 

Some method of classifying the elements for treatment in this way 
is clearly essential, and we have adopted the Periodic Classification 
with slight alterations, devoting a whole volume to the consideration 
of the elements in each vertical column, as will be evident from a glance 
at the scheme in the Frontispiece. 

In the first volume, in addition to a detailed account of the Elements 
of Group 0, the general principles of Inorganic Chemistry are discussed. 
Particular pains have been taken in the selection of material for this 
volume, and an attempt has been made to present to the reader a 
clear account of the principles upon which our knowledge of modern 
Inorganic Chemistry is based. 

At the outset it may be well to explain that it was not intended 
to write a complete text-book of Physical Chemistry. Numerous 
excellent works have already been devoted to this subject, and a 
volume on such lines would scarcely serve as a suitable introduction 
to this series. Whilst Physical Chemistry deals with the general 
principles applied to all branches of theoretical chemistry, our aim 
has been to emphasise their application to Inorganic Chemistry, with 
which branch of the subject this series of text -books is exclusively 
concerned. To this end practically all the illustrations to the laws 
and principles discussed in Volume I deal with inorganic substances. 

Again, there are many subjects, such as the methods employed in 
the accurate determination of atomic weights, which are not generally 
regarded as forming part of Physical Chemistry. Yet these are sub- 

viii OXYGEN. 

jects of supreme importance to the student of Inorganic Chemistry 
and are accordingly included in the Introduction. 

Hydrogen and the ammonium salts are dealt with in Volume II, 
along with the Elements of Group I. The position of the rare earth 
metals in the Periodic Classification has for many years been a source 
of difficulty. They have all been included in Volume IV, along with 
the Elements of Group III, as this was found to be the most suitable 
place for them. 

Many alloys and compounds have an equal claim to be considered 
in two or more volumes of this series, but this would entail unnecessary 
duplication. For example, alloys of copper and tin might be dealt 
with in Volumes II and V respectively. Similarly, certain double 
salts such, for example, as ferrous ammonium sulphate might very 
logically be included in Volume II under ammonium, and in Volume IX 
under iron. As a general rule this difficulty has been overcome by 
treating complex substances, containing two or more metals or bases, 
in that volume dealing with the metal or base which belongs to the 
highest group of the Periodic Table. For example, the alloys of copper 
and tin are detailed in Volume V along with tin, since copper occurs 
earlier, namely, in Volume II. Similarly, ferrous ammonium sulphate 
is discussed in Volume IX under iron, and not under ammonium in 
Volume II. The ferro-cyanides are likewise dealt with in Volume IX. 

But even with this arrangement it has not always been found easy 
to adopt a perfectly logical line of treatment. For example, in the 
chromates and permanganates the chromium and manganese function 
as part of the acid radicles and are analogous to sulphur and chlorine 
in sulphates and perchlorates ; so that they should be treated in the 
volume dealing with the metal acting as base, namely, in the case of 
potassium permanganate, under potassium in Volume II. But the 
alkali permanganates possess such close analogies with one another 
that separate treatment of these salts hardly seems desirable. They 
are therefore considered in Volume VIII. 

Numerous other little irregularities of a like nature occur, but it is 
hoped that, by means of carefully compiled indexes and frequent cross- 
referencing in the texts of the separate volumes, the student will 
experience no difficulty in finding the information he requires. 

Particular care has been taken with the sections dealing with the 
atomic weights of the elements in question. The figures given are not 
necessarily those to be found in the original memoirs, but have been 
recalculated, except where otherwise stated, using the following 
fundamental values : 

Hydrogen = 1-00762. Oxygen = 16-000. 

Sodium = 22-996. Sulphur 32-065. 

Potassium = 39-100. Fluorine == 19-015, 

Silver = 107-880. Chlorine = 35-457, 

Carbon = 12-003. Bromine = 79-916. 

Nitrogen = 14-008. Iodine = 126-920. 

By adopting this method it is easy to compare directly the results of 
earlier investigators with those of more recent date, and moreover it 
renders the data for the different elements strictly comparable through- 
out the whole series. 

Our aim has not been to make the volumes absolutely exhaustive, 


as this would render them unnecessarily bulky and expensive ; rather 
has it been to contribute concise and suggestive accounts of the various 
topics, and to append numerous references to the leading works and 
memoirs dealing with the same. Every effort has been made to render 
these references accurate and reliable; and it is hoped that they will 
prove a useful feature of the series. The more important abbreviations, 
which are substantially the same as those adopted by the Chemical 
Society, are detailed in the subjoined list. 

The addition of the Table of Dates of Issue of Journals (pp. xix-xxvi) 
will, it is hoped, enhance the value of this series. It is believed that 
the list is perfectly correct, as all the figures have been checked against 
the volumes on the shelves of the Library of the Chemical Society by 
Mr F. W.. Clifford and his Staff. To these gentlemen the Author desires 
to express his deep indebtedness. 

In order that the series shall attain the maximum utility, it is 
necessary to arrange for a certain amount of uniformity throughout, 
and this involves the suppression of the personality of the individual 
author to a corresponding extent for the sake of the common welfare. 
It is at once my duty and my pleasure to express my sincere appre- 
ciation of the kind and ready manner in which the authors have ac- 
commodated themselves to this task, which, without their hearty 
co-operation, could never have been successful. Finally, I wish to 
acknowledge the unfailing courtesy of the publishers, Messrs. Charles 
Griffin and Co., who have done everything in their power to render the 
work straightforward and easy. 


November 1023. 


OXYGEN is generally recognised as one of the most important elements 
known to science, and the literature referring to it is extraordinarily 
voluminous. Although the original intention was to issue Volume VII 
of this series in one part, it has been found necessary to divide it into 
three, the First Part dealing with oxygen alone, the Second with sulphur, 
selenium, and tellurium, whilst the remaining elements of Group VI 
are relegated to the Third Part. 

The Authors desire to express their sincere thanks to many friends 
who have assisted them in one way or another in the preparation of 
this work. In particular they would thank Mr. J. H. Coste, who has 
afforded considerable assistance in the sections dealing with the solu- 
bilities of gases in water, and last, but not least, Professor Wheeler 
and the Council of the Chemical Society for permission to reproduce 
the very beautiful photographs in Plate I. 

J. N. F. 

D. F. T. 
November 1923. 



THE PERIODIC TABLE (Frontispiece) . . . . iv 


PREFACE ....... . xi 

LIST or ABBREVIATIONS . . . . . xv 


CHAPTER I. General Characteristics of the Elements of 

Group VI . . . . .3 

Chemical Properties of Group VI Atomic Weights Physical Properties 
Allotropy Chemical Properties Isomorphism Valency Contrasts. 

CHAPTER II. Oxygen . . . . . .10 

Occurrence History Theory of Phlogiston Physical and Chemical Methods 
of Preparation Biological Processes Liquid Oxygen Production of 
Liquid Air and Oxygen. 

CHAPTER III. The Physical Properties of Oxygen . . 34 

Weight of a Litre of Oxygen Solubility Rate of Solution in Water Viscosity 
Specific Heat Coefficient of Expansion Refractive Index. 

Critical Constants Variation of Boiling-point with Pressure Density and 
Specific Heat of Liquid Oxygen Solid Oxygen. 

CHAPTER IV. The Chemical Properties of Oxygen . 49 

Definitions Active Oxygen Various Types of Oxides Slow Oxidation 
Selective Oxidation. 

Combustion Slow Combustion of Hydrogen, Gaseous Hydrocarbons, Phosphorus, 
and Coal Surface Combustion Combustion of Solid Carbon. 

.Flame Cool Flames Hydrogen Flame Candle Flame Cause of Luminosity 
Coal-gas Flame Smithells Separator Microphonic Flames Tempera- 
ture and Pressure upon Luminosity Cyanogen Flame Reciprocal Com- 
bustion Combustion of Carbon Monoxide -Equilibrium 2COzi3COo + C 
Equilibrium GO+H a O=CO a -|-H a . 

Limits of Inflammation The Gaseous Hydrocarbons Hydrogen Carbon 
Monoxide Organic Vapours -Influence of Temperature, Pressure, Oxygen 
Residual and Extinetive Atmospheres. 

Ignition Temperatures Flash-point. 

Slow Uniform Propagation of Flame Law of Speeds. 

Gaseous Explosions Explosion Pressures Explosion Limits. 

Valency of Oxygen Physiological Properties Applications Detection and 
Estimation Atomic Weight. 

CHAPTER V. - Ozone ...... 138 

Occurrence and History Preparation by Physical and Chemical Processes 
Commercial Production Physical Properties Chemical Properties 
Ozonides Physiological Action Applications Detection Estimation 
Molecular Weight and Constitution. 

*iv OXYGEN. 


CHAPTER VI. The Atmosphere .... 156 

Historical Composition Physiological Action Percentage of Oxygen Re- 
spired Air Carbon Dioxide Water- Vapour Desiccation of Air Atmo- 
spheric Ozone, Hydrogen Peroxide and Organic Peroxides Nitrogen and 
Inert Gases Carbon Monoxide Miscellaneous Substances Soil Atmo- 
sphere Mine Air Tunnel Air Dust Bacteriology Respired Air 
Ventilation Influence of Artificial Light Air a Mixture. 

General Properties of the Atmosphere Physical Properties Density Com- 
pressibility Specific Heat Solubility Radioactivity. 

Liquid Air General Properties. * 

CHAPTER VII. Water . . . . .205 

Occurrence Natural Waters Classification of Potable Waters Spring and 

Thermal Waters Well Water Upland Surface WatersRain Water 

Rainfall Lake and Inland Sea Waters Sea Water. 
Formation of Water Purification Storage Removal of Iron and Algae 

Filtration Hardness Softening of Hard Waters Permutit Sterilisation 

of Water Physical and Chemical Methods. 

CHAPTER VIII. Physical Properties of Water . . 250 

Solid Water Influence of Pressure on Melting-point Different Kinds of Ice 
Density Vapour Pressure Expansion Com pressibili ty Specifi c Heat 
Latent Heat of Fusion Colloidal Ice. 

Liquid Water Density Compressibility Viscosity Vapour Pressure 
Capillary Water Supercooled Water Thermal Conductivity Specific 
Heat Surface Tension Electrical Conductivity Spectrum Colour. 

Gaseous Water Critical Constants Latent Heat of Vaporisation Specific Heat. 

CHAPTER IX. Chemical Properties of Water . . 282 

Action of Water on Metals and Metallic Compounds Decomposition by Radio- 
active Substances and Ultra-violet Light Water as a Catalyst- -Influence 
of Desiccation upon the Properties of Substances Physiological Action. 

Dissociation of Steam Steam as an Oxidiser. 

Detection and Estimation of Water. 

CHAPTER X. Composition and Molecular Complexity of 

Water ....... 294 

Composition of Water Ratio of Hydrogen to Oxygen -Molecular Complexity 
of Ice Association of Water Association at the Critical Point Water- 

Constitution of Water Dihydrol and Trihydrol Water a Ternary Mixture. 

CHAPTER XI. Water as a Solvent. Water Analysis . 306 

Solubility of Gases The Inert Gases Henry's Law. 
Solubility of Liquids Critical Solution Temperature. 

Solubility of Solids Influence of Temperature, Pressure, and Physical Condi- 
tions of the Solid Phase. 
Supersaturated Solutions Combined Water. 
Water Analysis, Qualitative and Quantitative. 

CHAPTER XII. Hydrogen Peroxide .... 324 

History Occurrence Formation Preparation Concentration of Solutions 
Physical Properties Chemical Properties Catalytic Decomposition 
Decomposition with Self -reduction Oxidation ProcessesApplications. 

Composition and Constitution Detection and Estimation. 

NAME INDEX ....... 351 

SUBJECT INDEX ....... 363 


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Eng. and Min. J. 
Gazzetla .... 
Gehleris Allg. J. Ghem. 
Gilbert's Annalen 
Giorn. di Scienze Naturali ed 

Eton. '. 

Geol. Mag. 

Int. Zeitsch. Mctalloflraphie . 
Jahrb. JcL geol. Reichsanst. . 

Jahrb. Miner. 


Jenaisdie Zeitsch. 

J. Amer. Chem. Soc. . 

J. Chem. Soc. . 

J. Chim. phys. . 

J. Gasbeleiichtung 

J. Geology .... 

J. Ind. Eng. Chem. 

J. Inst, Metals . 

J. Miner. Soc. . 

J. Pharm. Chim. 

J . Physical Chem. 

J. Physique 

J. prakt. Chem. . 

J. RUAS. Phys. Chem. Soc. . 

J. Soc. Chem. 2nd. 
Landw. Jahrb. . 
Mem. Paris Acad. 

Mon. scient. 

Monatsh. .... 

Munch. Med. Wochenschr. . 
Nature .... 
Nuovo dm. 
d/vers. K. Vei.-Akad. Forh. . 

Oesterr. Chem. Zeit. 
P finger's Archiv 

Pharm. Zentr.-h.. 
Pharm. Post 
Phil. Mag. 

Phil. Trans. 
Phys. Review 
Physikal. Zeitsch. 
Pogg. Annalen . 

Proc. Chem. Soc. _ 

Proc. K. AJcad. Wetensch. 

Amsterdam . 
Proc. Roy. Irish Acad. 
Proc. Roy. Phil. Soc. Glasgow 
Proc. Roy. Soc. . 
Proc. Roy. Soc. Edin. . 
Rec. Tmv. chim. 

Roy. hist. Reports 
Schwcigger* s J. . 
Sitzungsber. K. Akad. Wiss. 



Engineering and Mining Journal. 
Gazzetta chimica italiana. 
Allgemeinea Journal der Chemie. 
Annalen der Physik (1799-1824). 

Giornale di Scienze Naturali ed Economiche. 

Geological Magazine. 

Internationale Zeitschrift fiir Metallographie. 

Jahrbuch der kaiserlich-koniglichengeologischen Eeichsau- 


Jahrbuch fiir Mineralogie. 
Jahresbericht iiber die Fortschritte der Chemie. 
Jenaische Zeitschrift fiir Naturwissenschaf t. 
Journal of the American Chemical Society. 
Journal of the Chemical Society. 
Journal de Chimie physique. 
Journal fiir Gasbeleuchtung. 
Journal of Geology. 

Journal of Industrial and Engineering Chemistry. 
Journal of the Institute of Metals. 
Mineralogical Magazine and Journal of the Mineralogical 


Journal de Pharmacie et de Chimie. 
Journal of Physical Chemistry. 
Journal de Physique. 
Journal fur praktische Chemie. 
Journal of the Physical and Chemical Society of Russia 


Journal of the Society of Chemical Industry. 
Landwirtschaftliche Jahrbticher. 
Memoires presentes par divers savants a 1' Academic dos 

Sciences de 1'Institut de France. 
Moniteur scientifique. 
Monatshefte fiir Chemie und verwandte Theile anderer 


Miinchener Medizinische Wochenschrift. 

II nuovo Cimento. 
Ofversigt af Kongliga Vetenskaps-Akademiens Forhand- 


esterreichische Ch emiker-Zeitung . 
Archiv fiir die geaammte Physiologie des Menschen und 

der Thiere. 

Pharmazeutische Zentralhalle. 
Pharmazeutische Post. 
Philosophical Magazine (The London, Edinburgh, and 


Philosophical Transactions of the Royal Society of London. 
Physical Review. 
Physikalische Zeitschrift. 
PoggendorfFs Annalen der Physik und Chemie (1824- 


Proceedings of the Chemical Society. 
Koninklijke Akademie van Wetenschappen te Amsterdam 

Proceedings (English Version). 
Proceedings of the Royal Irish Academy. 
Proceedings of the Royal Philosophical Society of Glasgow. 
Proceedings of the Royal Society of London.' 
Proceedings of the Royal Society of Edinburgh. 
Recueil des Travaux chimiques des Pay-Bas et de la 


Reports of the Royal Institution. 
Journal fiir Chemie und Physik. 

Sifczungsberichte der Koni^lich-Preussischen Akademic de 
Wissenschaften zu Berlin. 


Sitzungsber. K. Akad. Wiss. 
Wien .... 
Sci. Proc. Roy. Dubl. Soc. . 
Techn. Jahresber. 

Trans. Amer. Electrochem. 


Trans. Chem. Soc. 
Trans. Inst. Min. Eng. 
Trav. et Mem. du Bureau 

intern, des Poids et Mes . 
Verh. Oes. deut. Naturforsch. 

Wied. Annalen . 

Wis-senschaftl. Abhandl. 

phy&.'tech. Reichsanst.. 
Zeitsch. anal. Chem. 
Zeitsch. angew. Chem. . 
Zeitsch. anorg. Chem. . 
Zeitsch. Chem. . 
Zeitsch. Chem. 2nd. Kolloide. 

Zeitsch. Elektrochem. . 
Zeitsch. Kryst. Min. . 
Zeitsch. Nahr. Qenuss-m. 

Zeitsch. physical. Chem. 

Zeitsch. physiol. Chem. 
Zeitsch. wiss. Photochem. . 


Sitzungsberichte der Koniglich bayerischen Akademie 

der Wissenschaften zu Wien. 

Scientific Proceedings of the Royal Dublin Society. 
Jahresbericht liber die Leistungen der Chemischen 

Transactions of the American. Electrochemical Society. 

Transactions of the Chemical Society. 

Transactions of the Institution of Mining Engineers. 

Travaux et Memoires du Bureau International des Poids 

et Mesures. 
Verhandlung der Gesellschaft deutscher Naturforscher 

und Aerzte. 
Wiedermann's Annalen der Physik und Chemie (1877- 

Wissenschaftliche Abhandlungen der physikalisch-tech- 

nischen Reichsanstalt. 
Zeitschrift fiir analytische Chemie. 
Zeitschrift fiir angewandte Chemie. 
Zeitschrift fiir anorganische Chemie. 
Kritische Zeitschrift fiir Cbemie. 

Zeitschrift fiir Chemie und Industrie des Kolloide (con- 
tinued aa Kolloid-Zeitschrift). 
Zeitschrift fiir Elektrochemie. 
Zeitschrift fur Krystallographie und Mineralogie. 
Zeitschrift fiir Untersuchung der Nahrungs- und Genuss- 

Zeitschrift fur physikalische Chemie, Stochiometrie und 

Verwandt schaf t slehre . 

Hoppe-Seyler's Zeitschrift fiir phy s siologische Chemie. 
Zeitschrift fiir wissenschaftliche Photographic, Photo- 

physik, und Photochemie. 


FOR the sake of easy reference, a list is appended of the more 
important journals in chronological order, giving the dates of issue of 
their corresponding series and volumes. In certain cases the volumes 
have appeared with considerable irregularity ; in others it has occa- 
sionally happened that volumes begun in one calendar year have 
extended into the next year, even when this has not been the general 
habit of the series. To complicate matters still further, the title-pages 
in some of these latter volumes bear the later date a most illogical 
procedure. In such cases the volume number appears in the accom- 
panying columns opposite both years. In a short summary of this kind 
it is impossible to give full details in each case, but the foregoing 
remarks will serve to explain several apparent anomalies. 


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49, 50 







51, 52 








53, 54 









55, 56 









57, 58 



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vniv VTT T 





THE elements of the sixth vertical group of the Periodic Table resemble 
those of the seventh in that they can be divided into two sections 
possessing non-metallic and metallic properties respectively. But 
whereas in Group VII. the non-metals the so- 
called halogens are sharply divided from the 
metals, in Group VI. the non-metals, beginning 
with oxygen, gradually acquire decidedly metallic 
properties as the atomic weight increases on 
passing through sulphur to selenium and tellurium. 
Although all the elements in Group VI. possess 
certain characteristics in common, or manifest 
interesting gradations in properties, the general 
relationships arc not so marked as are those 
observed in each subsection. 1 

Chemical Properties of Group VI. With 
the exception of oxygen, all the elements in Group 
VI. are solid at the ordinary temperature. Oxygen 
is a typical non-metal, but as passage is made 
through sulphur to selenium and tellurium, metallic 
properties become increasingly pronounced, the 
two latter elements being usually regarded as 
metalloids. All the elements in the chromium 

subsection are characteristically metallic, but, in common with most 
metals of more or less high atomic weight, they yield, in addition 
to basic oxides, others that can form fairly powerful acids, which 
yield well-defined salts. Such, for example, are the chromates, the 
molybdates, the tungstates, and the uranates. 

1 The main characteristics of the elements of the chromium subdivision are dealt with 
in Chapter I. of Vol. VII., Part III. Those of sulphur, selenium, and tellurium are dis- 
cussed in Volume VII., Part II. Polonium (Radium F) is dealt with in VoJ. IIL 


Group VI. 
















4 * OXYGEN. 

In the accompanying table are listed a few of the more important 
types of compounds yielded by these elements. It will be observed that 
the maximum valency of the elements with regard to oxygen is numeri- 
cally equal to six. An interesting link between tellurium a heavy 
member of the oxygen subdivision and uranium the last of the 
chromium subdivision is afforded by their union with sulphuric acid 
to form sulphates of the type M(S0 4 ) 2 . The heaviest members of both 
subdivisions exhibit radioactivity. 





















MH 2 

OH 2 

SH 2 

SeH 2 

TeH 2 

MO 2 





M0 2 

00 2 

S0 2 

Se0 2 

Te0 2 

O0 2 

Mo0 2 

w6 2 

U0 2 

M 2 3 
M0 3 

sb 3 3 

? Se A 
Se0 3 

Te0 3 

Cr 2 3 
Cr0 3 

Mo0 3 

W0 8 

u6 3 



SC1 2 

TeCl 2 

CrCl 2 

MoCl 2 



MC1 4 
MF e 

SC1 4 
SF 6 

SeCl 4 

SeF 6 

TeCl 4 
TeF 6 

CrCl 3 

MoCl 4 
MoF 6 

(WC1 8 ) * 

WC1 4 

UC1 3 
U01 4 

ITF r 

MOF 4 

soci 2 


Teb'ci 2 

MoOF 4 

WOF 4 

>, j. g 

M0 2 Cf 2 
H 2 M0 3 

H 2 S0 3 2 

H 2 Se0 3 

H 2 Te0 3 

Cr0 2 Cl 2 

Mo0 2 01 2 

w6 2 ci 2 


M(S0 4 ? 2 

OAg 2 

H 2 S0 4 

H 2 Se0 4 
SeAg a 

H 2 Te0 4 

Te(S0 4 ) 2 
TeAg 2 

H 2 Cr0 4 

H 2 Mo0 4 

(H 2 W0 4 )t 

(H 9 U0 4 )t 

U(S0 4 ) 2 

M 2 Cf 

2 C 

s 2 c 2 



(SN) 4 




Atomic Weights.When the elements arc arran^c-d in the order 
of their atomic weights, several arithmetical regularities become 
apparent As long ago as the beginning of last century the attention 
of chemists had been drawn to the fact that certain triads of elements 
exist which exhibit not only a close similarity in their chemical and 
physical properties, but also an interesting regularity in their atomic 
weights i Jor several years, however, the subject was allowed to 
TK^, abeyance until Dumas, in 1851, again brought it to the fore,' 
and both he and otner chemists rapidly added to the list of regularities 

thJ? K el T ln \ and . ^ lh T m Were *yP ical - At first it. was hoped 
that .all the elements might ultimately be grouped into triads, and tLt 
m this way a complete system of classifying the elements mi <r it e 
evolved, inasmuch as the Periodic Classification had not as yet been 

* In combination only. f Q fl u a Q , n i 


introduced. These hopes were, however, doomed to failure, and a 
severe blow was struck at the utility of the triads when Cooke * showed 
that some of them actually broke into natural groups of elements. The 
halogens are a case in point, for chlorine, bromine, and iodine are but 
three out of four closely similar elements, and no system of classification 
that deals with these to the exclusion of fluorine can be regarded as 
satisfactory. A similar objection applies to the elements now under 
discussion, for whilst it is true that sulphur, selenium, and tellurium 
resemble each other very closely, a remarkable analogy exists between 
them and oxygen, these four elements thus constituting a natural 
tetradic group. 

Many triads exhibit an interesting relationship between the numerical 
values of their atomic weights, the mean of the first and third being 
almost identical with the middle value. The sulphur triads are no 
exception to this rule as is evidenced by the following table : 


Atomic weight. 


Mean of extreme 
atomic weights. 

Lithium . 




Calcium . 
Strontium . 




Selenium . 
Tellurium . 




Chlorine . 
Bromine . 




Dumas also noticed that, if oxygen and the sulphur triads are con- 
sidered together, the approximate atomic weights may be arranged as 
follow : 

OS Sc To 

16 16 + 16 16 + 16+3X16 16 + 16+2X3X16 

Such arithmetical coiiuectious might be regarded us u curious 
chance, were it not for the fact that nuuiy other analogous relationships 
occur amongst the elements. 

Physical Properties. Oxygen, in common with most of the 
elements in the first short horizontal series of the Periodic Table, exhibits 
several marked contrasts with the remaining elements in its own vertical 
group, and to these attention is directed in the sequel. Tellurium, 
again, is not typical of the group, partly in consequence of its increased 

1 J. P. Cooke, Ainer. J. Sci., 1854, 17, 387. 


tendency to resemble the metals. There is thus the most marked 
resemblance between sulphur and selenium. The following 
indicates a series of interesting gradations in physical properties 
increasing atomic weight. 





Atomic weight . 





Colour (solid) 


Pale yellow 

Red and grey 

Silvery grey 

Density (solid) . 



4-8 (grey) 

6-2 (approx.) 

Melting-point, C. 



217 (grey) 


Boiling-point, C. 




At bright red 


Allotropy. All of the elements exhibit allotropy. Oxygen yields 
two gaseous allotropes, namely, ordinary oxygen and ozone. These 
can co-exist at room temperatures for indefinite periods without mani- 
festing any tendency to reach a stage of chemical equilibrium. 

Sulphur does not exhibit allotropy in the gaseous condition in tlie 
ordinary acceptation of the term, although vapour density measurement s 
indicate considerable polymerisation at temperatures near the boiling- 
point, the vapour apparently consisting of S 8 , S 6 , S 4 , S 2? and even S x 
molecules in varying proportions according to circumstances. 1 Selenium 
vapour yields closely similar results ; below 550 C. it contains a sma.ll 
proportion of Sc 8 ; between 550 and 900 C. it consists essentially of 
Sc 2 and Se 6 molecules ; above 900 C. it is mostly Se 2 , with possibly it 
few Se x molecules. 2 

Liquid oxygen does not appear to manifest additional allotropy, 
but three allotropes of sulphur are recognised as existing in equilibrium 
in the liquid state. This phenomenon is termed di/iutni-ic allotropy., 
the allotropcs being designated as SA, S^ic, and STT respectively. SA is 
a yellow, mobile liquid containing, it is believed, eight atoms within its 
molecule, whilst S//, is a, thick, viscous liquid, formula S G . STT is probably 
tetratomiCj S 4 . The percentage of S^ rises with the temperature. 3 Thus : 

Temperature, C. . 120 140 180 220 Boiling-point 

S^ per cent. . . 0-1 1-3 20-4 32-2 30-9 

SA do. . . 96-4 93-7 73-1 62-7 59-1 

The freezing-point of the liquid accordingly varies botli with the 
nature of the solid phase that separates and with the percentage of S/x 
and in STT the liquid. 

Liquid selenium appears to exhibit allotropy, but tellurium docs not . 

In the solid form all four elements exhibit allotropy. Three forms 
of oxygen are recognised, mimely, a, j3, and y, the transition points 
being as follow : 4 

a ~ 

C. -230-5 


1 Premier and Scliupp, Zeilsch. ykysikal. Ghent.., 1909, 68, 129. 

2 Preuner and Brockniollcr, ibid.,\9l2, 81, 129. 

3 See this Vol., Part TT. Also this series, Vol. L, p. 07. 

4 See p. 48. 


Sulphur exists iu a variety oi' Ibnus, two of which are crystalline, 
namely, the rhombic and mouoclinie allot ropes. 

Solid selenium likewise exists in several allotropie forms. The red 
crystalline variety is labile, and may possibly occur in two modifications, 1 
both of which are monoelinie. 2 The grey crystalline form appears to 
consist of two varieties, Se A and Se B , in dynamic equilibrium \vith each 
other. 1 Solid tellurium manifests allotropy, but to a much less pro- 
nounced degree. 

Chemical Properties. Sulphur, selenium, and tellurium burn 
with blue flames yielding dioxides. If ozone is regarded as a dioxide, 
the series may be represented as follows : 

O = O = O O - S -:, (,) (..) ^ Se -- O O =- -. Te -= O 

ill which the central atoms are regarded as tefravalent. Cyclic schemes 
may, however, be preferred : 

A) ,.0 A) ,O 

0<| S( I Se I 'IV/ | 

X) X) O O 

The dioxides (save ozone) dissolve in water to form weak acids, 
I1 2 SO 3 , IIjjSeO a , and ILTeO.,, the salts of which may be regarded as 
analogous to the o/onates. Thus : 

K 2 ().() a K 2 SO 3 K 2 SeO :j K/Fe() a 

PotaHHium PottutHiiim PotaKHium INtliiKKiuin 

ozonato, K g () 4 . Hulphiio. Holo-nito. irllurito. 

The dioxides vary considerably in stability, o/,om\ O.O 2 , the 
analogue of SO,,, etc., being exceptionally unsiable. The hea,ls of 
formation of acjueous solutions of .sulphurous, selcnous, and tellurous 
acids are as follow : a 

(S, O.M A(j.) 7S,7S() calorics. 
(Se, <C A<j.) 5(1,100 
(IV, <C A(|.) 77,1 HO ,, 

The heats of formation of anurous solutions of tlic more highly 
oxygenated acids manifest a similar minimum with selenium : 

(S, (),,, Aq.) I tl\ I-H) eaJories. 
(S\ () a , A<j.) 7<, <H>() 
(Te, ();j, Aq.) J),S,:W() 

The dioxides of sulphur, selenium, and tellurium admit of oxidation 
to the trioxides S() a , Sc() a , and Te( ).,, which dissolve in w;il er to yield 
the corresponding acids, sulphuric acid hein^ tin- si ro!';esl ;i,n<l telluric 
the weakest. An analogy ma,y be found with ox\\";cn in lh<* fuse of the 
oxo/,onides. Oxygen is strict lv uon meta.llie, but selenium, a,nd to a 
greater extent tellurium, possess many pronounced mela-llic properties, 
and ure { hus amphoterie elements. Thus t he dioxide Te( )., c;i.n fuuelion 
as an acidic oxide, as metilioned nbo\c, or as a, basic oxi<l<\ yielding 
with sulphuric acid, tellurium sulphate Te(S(),),. The ;ra<lua,l tra-n- 
sition from non-metallic to im-tallie projirrties is r\-i<{cn<*ed in an 

1 Kruyi, XiilM'/i. nnnrtj. /"////#,, 11HUI, 64, :'<.. 

- Mutiiinann. ////.sr//. A*///,.7. Min., ISlMt, 70, :;.:;. 

:| Tlnunscn, T/urnnH'/n'nnxtri/. Translal'l 1\ liurUr ( LMMIMIIJIII: , 1*.M)S). 


interesting manner by the gradual fall in the heat of union of the 
elements with hydrogen. Thus : I 

Element O S Se Te 

"25-1 -34-9 

Heat of combination . 

(Calories) I 58 * 2 ' 7 

With positive elements, other than hydrogen, definite compounds 
are usually formed, analogous in composition to oxides. Thus, with 

Ag 2 Ag 2 S Ag 2 Se Ag 2 Te 

Oxide. Sulphide. Selenide. Telluride. 

The sulphur triads combine with fluorine to yield well-defined hexa- 
fluorides, but oxygen appears to be entirely unable to unite with fluorine 
to form any kind of compound. 

Element . . . Oxygen Sulphur Selenium Tellurium 
Compound . ... SF 6 . SeF 6 TcF 6 

Boiling-point C. . . . -62 -30 -35-5 

All of these compounds are stable gases, exhibiting the maximum 
valency of the elements. They neither attack glass nor decompose 
spontaneously. The selenium and tellurium fluorides attack mercury 
making it adhere to glass, and in this respect they resemble o/xnie. 
Sulphur hcxafluoride does not do this. 

Isomorphism. Although potassium tcllurate, K 2 TeO,,, is Dot 
isomorphous with the corresponding sulphate, 6 the hydrogen rubidium 
salts of selenic and telluric acids are isomorphous. 7 

Sulphuric, selenic and telluric acids yield double salts with alkali 
and certain divalent metals, which salts have the general formula 

M 2 'RO 4 . M"R0 4 . 6H 3 O 

where R stands for chromium or a sulphur triad ; M' for ammonium or 
an alkali metal, and M" for iron (ferrous), cobalt, nicked, manganese, 
copper, cadmium, magnesium, or zinc. These are isomorphous with 
one another. Both sulphur and selenium (but not tellurium) yield 
alums which are isomorphous, and of the general type 

M 2 'R0 4 . M a "(R0 4 ) 3 . 24JI 2 

where R stands for sulphur or selenium. 

Valency. All the elements have a valency of two in respect to 
hydrogen ; that is, they possess two free negative valences, as witness 
the compounds 

H 2 II 2 S H a Sc II 2 Tc. 

These exhibit a steady fall in stability with rise in molecular weight. 
The following per derivatives are also known : 

H 2 2 H 2 S 2 . 

1 Thomson, Thermochemistry. Translated by Burke (Longmans, 1908) 

2 To water at 18 C. ' 

3 To water- vapour at 18 C. 

4 From amorphous sulphur. 
: > From rhombic sulphur. 

6 Staudenmaier, Zeitsch. anorg. Chem., 1895, 10, 189. 

7 Pelliui, Atti R. Accad. Lined, 1906, [5], 15, i., 629, 711 ; ii., 40. 


The elements yield tetravalent derivatives in special circumstances, 
in which they function as the basic elements. In the case of oxygen 
they are termed oxonium salts ; sulphur yields sulphonium salts ; whilst 
selenium and tellurium offer an even wider range of derivatives. Thus. 
the following types of compounds are now well known : 

C 2 H \2T CH B / \i- C 2 H/ 6 \C1 

Di-ethyl Tri-methyl Tri-ethyl Tri-ethyl 

oxonium sulphonium selenium (or selenonium) tellurium 

chloride. iodide. chloride. iodide. 

Contrasts. Whilst these undoubted analogies exist between 
oxygen and the sulphur triads, there are many directions iii which 
oxygen differs from these elements. This is by no means an uncommon 
phenomenon in connection with the first element and its successors 
in a vertical column of the Periodic Table. 

Thus, for example, the boiling-points of the hydrides of sulphur, 
selenium, and tellurium steadily fall with the atomic weights of the 
electro-negative elements : " 

H 2 Tc -H 2 Sc H 2 S 

Boiling-point C. . V2 62 

The boiling-point of water, therefore, should be, if the analogy were 
followed, of the order of 70 C. instead of its actual value of 100 C. 
This is undoubtedly due to association (see Chap. X.). 



Symbol, 0. Atomic weight, 16-000. 

Occurrence, Oxygen is the most abundant clement in the earth. It 
is present in the uneombined state in the atmosphere to the extent of 
approximately 23 per cent, by weight (see Chap. VI.), but this amount 
is relatively minute when the immense quantities of oxygen in various 
forms of combination are considered. The sea contains roughly 86 per 
cent, and the earth's crust nearly 48 per cent, b}^ weight of this element ; 
indeed, it has been computed that almost exactly one-half of the mass 
of the whole earth (including the ocean and the atmosphere) is due to 
oxygen. 1 From the results of spectrum analysis it is probable that 
uneombined oxygen is also present in the sun. 2 

History. From ancient writings it appears that the Chinese, 
already in the eighth century, recognised that a. substance, on burning, 
combined with one of the constituents of the air ; it was also realised 
that this constituent of the atmosphere was present in water, and that 
it could be obtained in a pure condition by heating certain, minerals. 3 
In Europe it was not until the middle of the seventeenth century that 
the atmosphere was regarded as a mixture of which one of the in- 
gredients played an important part in combustion, respiration, and the 
change in colour of the blood. It was understood by Hooke (1665) 
and Mayow (1674) that saltpetre contains a substance of somewhat 
similar properties, but although the observation that saltpetre, when 
heated to decomposition, gives a vigorous evolution of gas was made 
only a little later, the actual discovery of oxygen was delayed until 
the next century, when the experimental methods first introduced by 
Mayow in 1674 * for the collection of gases began to bear fruit. The 
gas was first prepared and recognised as a new substance 5 by the Swedish 
chemist Scheele 6 about the year 1771 as the result, amongst other 
methods, of heating red mercuric oxide or " mercurius caleinatns per sc " 

1 Stoney, Phil. May., 1880, [5|, 47, 505 ; Clarke (this series, Vol. 1., p. 8) gives 49 ' 8 
percent. ; Fersmann (Bull. Acad. jSci. Petrograd., 1912, p. 367) estimates 53-8 L percent. 

2 Draper, Amer. J. Sci., 1877, 14, 89 ; Trowbridge, Phil. May., 1902, 4, 1.56 ; Meissner, 
Physikal. Zeitsch., 1914, 15, 668. 

:] Duckworth, Chem. News, 1886, 53, 250. 

4 See Alembic Club Reprints, No. xvii. 

5 Hales had, as early as 1727, prepared oxygen by heating potassium nitrate, but 
although he collected the gas over water and measured its volume, he did not recognise 
it as a new gas or determine its properties. 

Scheele, CreWs Annalen, 1785, 2, 229, 291; Chemische Abhandlung von der Luft 
und clem Feuer (Upsala, 1777). See Alembic Club Reprints, No. viii. (1894) ; Ortwed, 
Speter, and Jorgensen, Ahren's Sammlunrj, 1909, 14, 111. Scheele, Nachgelassene Brief e 
und Aufzeichnungen, Nordenskiold (Stockholm, 1892). 



by concentrating the sun's rays upon it with a lens. He termed the 
gas empyreal or fire air, and also showed that the same gas could be 
obtained from the yellow oxide produced by precipitation of a mer- 
curic salt from aqueous solution on addition of an alkali. Unfortunately 
for himself these results were not published for some four years after 
their discovery, and in the meantime, namely on 1st August 1774, the 
English chemist Priestley, 1 independently discovered oxygen, likewise 
by heating mercuric oxide. He communicated his results to Lavoisier 
in Paris in October of the same year, and shortly afterwards his discovery 
received general publication. 

The Theory of Phlogiston. In order to appreciate the enormous 
influence which the discovery of oxygen was destined to exert upon the 
further progress of chemistry, it is -necessary to gain some idea of the 
views then prevalent as to the nature of combustion. 

It is undoubtedly a fact that neither Scheele nor Priestley realised 
the important part played in combustion processes by the gas they had 

By gradual modification the ancient Aristotelean idea of fire, as one 
of the four " elements " of nature, had merged into the assumption 
that all substances capable of burning contained a common com- 
bustible constituent or " principle." For several centuries sulphur 
appears to have been regarded as this principle, and its presence was 
postulated in all metals capable of being burnt or calcined in air. Becher, 2 
however, in 1669 took exception to this latter view, maintaining that 
sulphur owed its combustibility to the fact of its containing a large 
amount of combustible principle, but that sulphur itself was not that 
principle. He therefore gave the name terra pinguis or " oily earth " 
to the last named, and explained the calcination of metals by heating 
in air as due to the expulsion of terra pinguis. What, precisely, this 
terra pinguis might be, whether of a material or non-material nature, 
Bccher did not say. Perhaps he regarded it as of a spiritual nature, 
like flame itself, and somewhat defying conventional definition. His 
views were accepted and amplified by Stahl, who, c. 1697, introduced 
the word phlogiston (Greek r/>A,oytfcti/, to set on lire) to denote the 
active principle producing fire. Like Bccher, Stahl hesitated to define 
exactly the nature of his phlogiston. It corresponded to the terra 
pinguis of Bechcr and the sulphur of the earlier chemists. Any substance 
that would burn was regarded as being rich in phlogiston, and carbon 
was considered to be nearly pure phlogiston. 

When metals are calcined in. air, oxides are usually produced. This 
was explained by Stahl on the supposition that the metal, on being 
heated, parted with its phlogiston., leaving a residue of calx? 

In the light of this idea a metallic calx or oxide was of simpler 
composition than the metal itself. Thus 

metal = en Ix + j > 1 il ogis toi i . 
Further, reducing agents such as charcoal were substances which, 

1 Priestley, Experiments and Observations on Different Kinds of Air., 1774, ii., 28. See 
Alembic Club Reprints, No. vii. (1894) ; Freund, The Study of Chemical Composition, 
chapter i. (Camb. Univ. Press, 1904). 

2 Bccher, Ph-ysicM Snbterranca, 1669. 

3 Latin, calx, lime. The process of " burning " chalk to form lime was known to 
the ancients, and as the result of analogy the term calx was used to designate the residue 
of oxide obtained after " burning " a metal. 

12 OXYGEN. ' 

being rich in phlogiston, could restore this to the metallic oxide and 
so regenerate the metal. In accordance with these views, Priestley 
named the gas which he obtained from mercuric oxide, dephlogisticated 
air as an expression of the readiness with which substances burned in 
or imparted phlogiston to it; nitrogen, on the other hand, which 
appeared incapable of supporting combustion, was regarded as being 
already saturated with phlogiston, and was termed by Priestley 
phlogisticated air. 

The theory of phlogiston was, during the eighteenth century, 
exceedingly popular amongst chemists, despite the fact that it was full 
of anomalies. For example, if phlogiston were a material substance 
it is evident, from the equation given above, that a metal must weigh 
more than its calx. If phlogiston were non-material, the metal and 
calx would possess equal weight. But Jean Key x had already, in 1630, 
shown that lead and tin increase in weight when calcined, and Baycn, 2 
in 1774, found that on heating mercury calx to a suHicieiitly high 
temperature, metallic mercury is obtained, accompanied by a diminution 
in weight. 3 Both of these facts are in direct opposition to the phlogistic 

Again, Stahl himself was not unaware of the fact that carbon would 
not burn in the absence of air, although, as mentioned above, he regarded 
it as almost pure phlogiston. The explanation offered was that 
phlogiston could not leave a substance unless it had somewhere to go. 
The air, however, could act as a sponge and absorb the phlogiston, and 
thus enable combustion to proceed. Such an explanation is, of course, 
inadequate in the case of the calcination of metals since no account is 
taken of the reduction in volume that invariably ensues. 

It was reserved for Lavoisier to discover the true cause of com- 
bustion. Having satisfied himself that metals do increase in weight 
upon calcination, he definitely proved that this is due to their combining 
with Priestley's dephlogisticated air, and was thus led to diseard the 
idea of a special principle of combustibility such us phlogiston. A new 
name was therefore necessary for Priestley's gas, and Lavoisier first 
called it "eminently pure air," but later o,tv/^ (French <wuRcnc.), in his 
belief that the element was an essential constituent of all acids. 4 The 
German name Sauerstoff embodies the same idea. Alt hough subsequent 
research has demonstrated the inaccuracy of this assumption, the 
names have retained their popularity. 


Physical Processes. The atmosphere, as a comparatively simple 
gaseous mixture, naturally suggests itself as a source oi" oxygen*. There- 
are various physical methods available for the separation" of two such 
gases as nitrogen and oxygen, chief among which are I lie following : 

1. Liquefaction. When liquid air is allowed to evaporate, the 
escaping vapour is exceedingly rich in nitrogen since t his gns hns a lower 
boiling-point (namely, 195-67 C.) than "oxygen (b.-pl., 1SU-9 C.). 

1 See Alembic Club Reprints, No. xi. 
a Bayen, J. Physique, 1774, 3, 135, 281. 

3 Bayen did not examine the gas evolved in this process, or lie would probably have 
recognised it as a new gas, and thus forestalled Priestley's discovery of oxygen. * 

4 From the Greek, 6vs, sour, and yiwdu, I produce. 


The residual liquid in consequence becomes increasingly richer in 
oxygen as evaporation proceeds. This has been made the basis of a 
very successful commercial method for the preparation of oxygen. 1 

2. Solubility. Oxygen is approximately twice as soluble in water 
as nitrogen, hence it follows that water, upon exposure to air, will 
absorb twice as much oxygen in proportion to nitrogen as corresponds 
to the partial pressures of these gases. If now the dissolved gases are 
expelled from the water by boiling or by the aid of a vacuum pump the 
resulting " air " will contain roughly one part of oxygen to two parts of 
nitrogen by volume. By repeating these processes several times, 
fairly pure oxygen can be isolated. Mallet, 2 in 1869, took out a patent 
for the commercial preparation of oxygen based on the foregoing 
principle. He found that after eight absorptions with water under 
pressure, a gas containing 97-3 per cent, of oxygen could be obtained. 
His results for successive absorptions were as follows : 

No. of absorptions .01234567 8 

Percentage of oxygen . . 21 33-3 47-5 62-5 75*0 85-0 91-0 95-0 97-3 
Percentage of nitrogen, etc. . 79 66-7 52-5 37-5 25-0 15-0 9-0 5-0 2-7 

At the present time this method does not appear to have any com- 
mercial importance. 3 The relative solubilities of oxygen and nitrogen 
in various other solvents have been determined, 4 but" the results do not 
encourage the idea that oxygen can be obtained any more readily than 
by the employment of water. 

3. Transfusion. Thin layers of caoutchouc allow ox3 7 gen to diffuse 
through them about 2-| times as rapidly as nitrogen, and a rough 
separation of the gases can be effected in this manner. 5 

4. Absorption in Charcoal. When coconut charcoal is cooled to 
1.85 C., and exposed to pure, dry air, it absorbs oxygen more readily 
than nitrogen, and the gas recovered at 15 C. contains some 56 per cent, 
of oxygen. If allowed to escape slowly, the absorbed gas can be frac- 
tionated, the later fractions containing as much as 84 per cent, of 
oxygen. 6 

It is also possible to separate oxygen and nitrogen by taking advan- 
tage of their differences in density as, for example, by direct diffusion 
through some inert, porous material, when the gases pass through at 
rates consonant with Graham's Law ; or by centrifugal force. 7 

Chemical Processes. The majority of the methods for obtaining 
oxygen fall into this category, and may be classified according to whether 
the parent substance is a normal oxide, a higher oxide, or a more complex 
oxygenated compound. Several of the processes can be extended to 
serve as methods for the extraction of atmospheric oxygen. 

A. Preparation of Oxygen from Normal Oxides. Water. Perhaps 

1 For details see p. 31. 

2 Mallet, Dingl. Poly. J., 1871, 199, 112 ; English Patent, 2137 (1869). 

3 See also Kubierschky, English Patent, 17780 (1899) ; Humphrey, ibid., 14809 (1905) ; 
Levy, ibid., 5931 (1909). 

4 Claude, Compt. rend., 1900, 131, 447. 

5 Graham, J. Chem. Soc., 1865, 18, 9. See also d'Arsonval, Compt. rend., 1899, 128, 
1545. Several processes based on this principle have been patented. See Helouis, 
English Patent, 2080 (1881) ; Neaver, ibid., 6463 (1890) ; de Villepique, Fournier, and 
Shenton, ibid., 19044 (1896) ; Bartelt, ibid., 24428 (1906). 

Dewar, Compt. rend, 1904, 139, 261 ; Ann. Chim. Phyx., 1904, [8], 3, 12. See also 
Montmagnon and de Laire, Bull. Soc. chim., 1869, n, 261. 
7 Bredig, Zeitsch. physikal. CJiem., 1895, 17, 459. 


the most important process by which water can be made to yield its 
oxygen in a free state consists in electrolysis in the presence of an 
alkaline substance such as potassium carbonate or an alkali hydroxide. 
The oxygen obtained in this manner, if due precautions are observed, 
presents a high degree of purity., and is hence particularly suitable for 
metal cutting and welding (sec p. 135). Care must be taken to avoid 
contamination with hydrogen during the process, owing to the danger- 
ously explosive nature of the mixture. 

For laboratory purposes a glass apparatus after the principle of a 
Kipp may be conveniently used. The electrolyte consists of a 30 per 
cent, solution of sodium hydroxide, whilst sheet-nickel plates serve as 
electrodes. The inner electrode functions as anode and the supply of 
oxygen regulates itself automatically, the liquid in the inner space 
surrounding the anode being gradually expelled, as in Kipp's apparatus, 
as the pressure of the gas above increases, until the anode is left high 
and dry, when, of course, electrolysis ceases. 1 Very pure oxygen may 
be obtained by the electrolysis of barium hydroxide solution. To a 
certain extent the electrolysis of water is used for the commercial 
preparation of oxygen. 2 To this end, containing vessels of iron are 
used, the electrodes consisting of this metal or of nickel. The electrolyte 
consists of 15 per cent, caustic soda solution, and the liberated hydrogen 
and oxygen are collected in separate dome-shaped vessels under a 
pressure of some 60 mm. of water. A higher pressure cannot safely be 
employed owing to the danger of mixing. By means of a metallic 
partition between the electrodes, this danger is still further minimised. 
The containing vessels are packed in wooden boxes with sand, whereby 
the heat of the reaction is conserved, the temperature rising to about 
70 C. Each vessel yields 110 litres of oxygen per hour of purity 97 
per cent. 3 Dilute solutions of acids, particularly sulphuric acid, may 
be employed instead of alkalies, but the latter are preferable. 

Electrolytic oxygen may contain as much as 4 per cent, of hydrogen. 
This may be removed as water by passage over platinised asbestos. 4 

Attempts have been made to cheapen the process by producing 
electrolytic oxygen without the simultaneous liberation of hydrogen 
by the adoption of depolarising electrolytes, or cathodes ; also of 
cathodes which absorb hydrogen and may subsequently be employed as 
elements in gas cells. 5 

At high temperatures steam dissociates into hydrogen and oxygen, 
and these gases admit of isolation by taking advantage of the greater 
velocity of diffusion of the hydrogen as explained on p. 287. This 
by no means constitutes a convenient method of preparing oxygen, but 
the process may be facilitated by the introduction of some substance 
capable of uniting with the hydrogen. Thus steam is readily decom- 
posed by chlorine when the two are passed through a red-hot porcelain 
tube. The reaction is accelerated by the presence of fragments of 
porcelain in the tube to increase the heating surface. 

2H 2 O+2C1 2 ==4HC1+O 2 . 

1 See Ruhstrat, Zeitsch. angew. Chem., 1912, 25, 1277. 

2 See Zeitsch. Elektrochem., 1901, 7, 857. 

3 The resistance of each cell is 2-8 volts. A current of 600 amperes is supplied, the 
theoretical yield of oxygen from which is 125 litres per hour. 

4 Moser, Zeitsch. anorg. Chem., 1920, no, 125. 

5 See Coehn, German Patent, 75930 (1893); Brianchon, French Patent, 439737 (1912). 



The hydrochloric acid may be absorbed by passage of the resulting 
gases through water or caustic soda solution. 

Silver oxide, Ag 2 O, is readily decomposed by heat, evolving oxygen, 
and the characteristic change in colour from brown to silver-white 
renders the reaction particularly suitable for lecture demonstration. 
The equilibrium pressures of oxygen havejbeen measured up to 800 C. 5 
and are found to conform with the following law : 

log jp=6-2853 2859/T 

where p is the pressure in atmospheres, and T the absolute temperature. 1 
The decomposition of mercuric oxide by heat has already been 
mentioned as the method by which Priestley was led to the discovery 
of oxygen. The oxide, which is yellow or brick red in colour, first 
becomes black a reversible, physical effect. Oxygen is then evolved 
and a sublimate of mercury collects on the cooler parts of the con- 
taining vessel. The reaction is reversible, thus : 

In the following table are given the dissociation pressures of mercuric 
oxide between 360 and 480 C. 2 

Temperature, C. 

Pressure, mm. 

Temperature, C. 

Pressure, mm. 















The rate of decomposition is accelerated by suitable catalysts such 
as finely-divided platinum, ferric oxide, and manganese dioxide. 
Aluminium and stannic oxides arc apparently without effect. 

The normal oxides of several other metals behave in an analogous 
manner to mercuric oxide. Thus palladous oxide, PdO, decomposes 
when heated, yielding metallic palladium and. oxygen, 3 the reaction 
being reversible : 

At 877 C. the dissociation pressure of the oxide is 760 mm. 

In the case of auric oxide, Au 2 3 , the reaction is not reversible. 
When heated at 150 to 165 C., oxygen is evolved and aurous oxide, 
AuO, remains. At 250 C. this latter oxide is completely converted 
into metallic gold. 4 Similarly, platinum dioxide, PtO 2 , upon ignition 
evolves oxygen, a residue of metallic platinum being obtained together 
with a solid solution of cither the monoxide or sesqui-oxidc in the 
dioxide. 5 

1 Keyes and Kara, J. Chem. Soc., 1922, 44, 479 ; Lewis, Zeitsch. physikal. Chem., 
1906, 55, 449. 

2 Taylor and Hulett, J. Physical Qhem., 1913, 17, 565. 

3 W6hler, Zeitsch. Elektrochem., 1906, 12, 781 ; 1905, n, 836. 

4 See Kruss, Annalen, 1887, 237, 296 ; Ber., 1886, 19, 2541. 

5 Wohler a,nd Frey, Zeitsch. Elektrochem., 1909, 15, 129. 


When chlorine is passed over zinc oxide at a high temperature 
oxygen is evolved, zinc chloride remaining behind. 

2ZnO+2Cl 2 =2ZnCl 2 +O 2 . 

Oxides of the alkaline earth metals, namely CaO, SrO, and BaO, 
may be similarly employed, as also litharge, PbO, and cadmium oxide, 
CdO. 1 

B. Preparation of Oxygen from Higher Oxides. In addition to their 
normal ones, many metals yield oxides in which the percentages of 
oxygen are greater than correspond to the valencies of the metals as 
manifested in their more common salts. Such compounds are con- 
veniently termed higher oxides, and may usually be made to part with 
their excess of oxygen either by heating alone or with sulphuric acid. 

Manganese dioxide, MnO 2> when heated to moderate redness, evolves 
oxygen and leaves a residue of the sesqui-oxide Mn 2 O 3 . 

4MnO 2 =2Mn 2 O 3 +O 2 . 

The reaction begins at 530 C. in air, 2 and if the temperature is raised 
to 940 C. the sesqui-oxide in turn decomposes, yielding a further 
supply of oxygen and a residue of trimanganic tetroxide, Mn 3 O 4 . 

6Mn 2 O 3 = 4Mn 3 O 4 +O 2 . 

The foregoing reactions at one time offered one of the cheapest 
methods of preparing oxygen for commercial purposes. The source 
of the dioxide was the mineral pyrolusite, but the high temperature 
required to extract the oxygen led to the superseding of this method by 
other more convenient processes. 

When heated with concentrated sulphuric acid, manganese dioxide 
evolves oxygen, leaving a residue of manganese sulphate. The reaction 
takes place in two stages, 3 namely : 

(1) At 110 C. 

4MnO 2 +6H 2 SO 4 =2Mn 2 (SO 4 ) 3 +6H 2 O+O 2 . 

(2) At the boiling-point of sulphuric acid 

2Mn 2 (SO 4 ) 3 =4MnSO 4 +2SO 3 +O 2 . 

Lead dioxide, PbO 2? when heated above 310 C., decomposes, 
yielding oxygen and lead monoxide. 

2PbO 2 =2PbO+O 2 . 

Similarly red lead, Pb 3 O 4 , when strongly heated evolves oxygen, a residue 
of lead monoxide remaining. This reaction is reversible. 4 

At 530 C. the red lead may be completely converted into monoxide 

1 See Gay Lussac, and Thenard, Recherch. physicochim., 180*0, 2, 143 ; Weber, Poga. 
AnnaUn, 1861, 112, 619. 

2 Meyer and Rotgers, Zeitsch. anorg. Chew., 1908, 57, 104. See also this series, 
Vol. VIII. , Chap. 6. 

:} Carius, Annalen, 1856, 98, 53. 

4 Keinders and Hamburger, Zeitsch. anorg. Chem., 1914, 89, 71, 


in a vacuum, but in the presence of air a higher temperature is essential, 
as is evident from the following data. 1 

Temperature C 445 500 555 636 

Dissociation pressure of Pb 3 O 4 in mm. . 5 60 183 763 

Alkali peroxides are rapidly decomposed by water, oxygen being 
evolved. In the case of sodium peroxide the reaction proceeds according 
to the following equation : 

2Na 2 2 +2H 2 = 4NaOH+O 2 . 

The reaction is conveniently carried out in a flask fitted with a drop 
funnel through which the water is slowly admitted. Some hydrogen 
peroxide is simultaneously produced. The evolution of oxygen is 
facilitated by the addition of a catalyst, such as a salt of nickel, cobalt, 
or copper. When pressed into small blocks or cubes, the mixture of 
sodium peroxide and catalyst may be placed in a Kipp or other gas- 
generating apparatus based on a similar principle, and a steady supply 
of oxygen obtained. The commercial commodity known as " oxylithe " 
has the following composition : 

Sodium peroxide . . . 98*32 per cent. 
Oxide of iron .... 1-00 
Copper sulphate . . . 0-68 ,, 

and is very suitable for this type of reaction. 2 

The preparation of small quantities of oxygen for laboratory purposes 
may be conveniently effected by gently warming a mixture of fused 
sodium peroxide with some salt containing water of crystallisation. 
For this purpose crystals of sodium carbonate or sulphate are very 
suitable. The oxygen is evolved in a steady stream which is readily 
kept under control. 3 

By the action of acids upon alkali or alkaline earth peroxides, 
hydrogen peroxide is liberated, which immediately undergoes partial or 
complete decomposition according to circumstances. Thus oxygen is 
readily obtained 4 by the employment in a Kipp of lumps of the mixture 
obtained by adding 100 parts of sodium peroxide and 25 parts of 
magnesium oxide to 100 parts of molten potassium nitrate. The liquid 
reagent consists of dilute hydrochloric acid. The magnesia does not 
serve as a catalyst ; on the contrary, it is added as an inert diluent to 
moderate the violence of the reaction. 

Hydrogen peroxide readily yields up its oxygen either under the 
influence of heat or of a catalyst. As examples of the last named, 
colloidal solutions of the platinum metals may be mentioned. 

In neutral solution hydrogen peroxide is decomposed catalytically 
by lead dioxide, but in acid solution the action is different and quanti- 
tative. 5 Thus, in the presence of nitric acid, 

PbO 2 +H 2 O 2 +2HN0 3 ==Pb(NO 3 ) 2 +2H 2 0+O 2 . 

Manganese dioxide behaves similarly in acid solution, and, if charged in 

1 Le Ghatelier, Bull. Soc. chim., 1897, [3], 17, 791. See also this series, Vol. V. 

2 See Hanman, English Patent, 9783 (1903). 

3 H. J. Turner, Amer. Chem. J., 1907, 37, 106. 

4 Wolter, Chem. Zeit., 1908, 32, 1066. 

5 Schlossberg, Zeitsch. anal Chem., 1902, 41, 735. 

VOL. VII. : I. 2 


lump form into a Kipp and subjected in the usual manner to the action 
of commercial hydrogen peroxide acidified with sulphuric acid, a steady 
stream of oxygen is obtained. 1 

Instead of using free hydrogen peroxide, barium peroxide may be 
used, lumps of a mixture of barium peroxide, gypsum, and manganese 
dioxide being introduced into the Kipp, the liquid reagent consisting 
of hydrochloric acid. 2 

Hydrogen peroxide reacts with potassium permanganate in acid 
solution evolving oxygen. In the presence of dilute sulphuric acid the 
reaction proceeds along the lines indicated by the equation 

2KMn0 4 +5H 2 2 +3H 2 S0 4 =K 2 S0 4 +2MnS0 4 +8H 2 0+50 2 . 

For laboratory purposes 3 a steady evolution of oxygen may be 
obtained by allowing a solution of 25 grams of potassium permanganate 
in 500 c.c. of water and 50 c.c. of concentrated sulphuric acid to flow 
from a dropping funnel into a litre flask containing 500 c.c. of hydrogen 
peroxide solution (10 vol.). 4 No heat is required. 

Hydrogen peroxide reacts in an analogous manner with potassium 
bichromate, evolving oxygen. A convenient way of preparing the gas 
in small quantities consists in adding 150 grams of concentrated sulphuric 
acid to hydrogen peroxide solution (10 vol.) 4 and allowing the mixture 
to come into contact with crystals of potassium bichromate 5 in a Kipp's 
apparatus. The crystals should be large and the process carried out 
with care in the cold, as otherwise the reaction is liable to be very violent. 
In order to prevent small pieces of the bichromate from falling into the 
lower chamber of the Kipp, a layer of small pieces of pumice may be 
introduced into the middle chamber prior to the admission of the salt. 
The reaction proceeds according to the equation 

K 2 Cr 2 7 +4H 2 SO 4 +3H 2 O 2 =K 2 SO 4 +Cr 2 (SO 4 ) 3 +7H 2 0+3O 2 . 

In alkaline solution potassium ferricyanide and hydrogen peroxide 
also yield a steady stream of oxygen which can be immediately checked 
by the addition of an acid. 6 

The reactions involved appear to be represented by the following 
equations : 

2K 3 Fe(CN) 6 +2KHO=2K 4 Fe(CN) 6 +H 9 O+O (nascent) 
0+H 2 2 =H 2 0+0 2 . 

Experiment shows that it is the amount of alkali present that controls 
the reaction an observation in harmony with the above equation. 

With bleaching powder, hydrogen peroxide in acidified solution 
readily yields oxygen gas, 7 

Ca(OCl)Cl+H 2 O 2 =:CaCl 2 +H 2 O+O 2 . 

1 See Baumann, Ber., 1890, 23, 324 ; Zeitsch. angew. Chem., 1890, p. 72. 

2 Neumann, Ber., 1887, 20, 1584. 

3 Gahring, Chem. Zeit., 1889, 13, 264 ; Seyewetz and Poizat, Compt. rend., 1907, 144, 
86 ; Mossier, Chem. Zentr., 1909, ii., 785 ; from Zeitsch. Allg. Oesterr. Apoth. Ver., 1909, 
43, 301. 

4 That is a solution of hydrogen peroxide, yielding upon decomposition into water 
and oxygen ten times its own volume of the latter. 

5 Blau, Monatsh., 1892, 13, 281 ; Erdmann and Bedford, Ber., 1904, 37, 1184. 

6 Kassner, Chem. Zeit., 1889, 13, 1302, 1338, 1407 ; Arch. Pharm., 1890, 228, 432. 

7 Yolh?rd, Annalen, 1889, 253, 246 ; Lunge, Zeitsch. angew. Chem., 1890, p. 7 ; Vanino, 
ibid., 1890, p. 80. 


Barium peroxide is readily decomposed by heat, the reaction being 
reversible : 

By continuous removal of the oxygen, therefore, decomposition will 
continue at constant temperature until the whole of the solid phase has 
been converted into the monoxide. 

If, on the other hand, the pressure of oxygen in contact with the 
solid phase is increased beyond the dissociation pressure at a given 
temperature, the barium peroxide is regenerated, the foregoing reaction 
now proceeding from right to left. 1 

In the following table are given the dissociation pressures of barium 
peroxide in contact with moisture 2 at various temperatures ranging 
from 618 to 868 C. 

Temperature C. . . 618 655 697 737 794 835 853 868 
Oxygen pressure (cm. mercury) 11-3 26-8 65-4 141 378 718 937 1166 
Water-vapour (cm. mercury) 7-3 13-7 26-3 47 98 159 195 231 

Boussingault attempted to use the foregoing reactions for the pre- 
paration of oxygen on a commercial scale, but found that after several 
rcheatings the barium oxide lost its power of absorbing oxygen. This 
difficulty was eventually overcome by the brothers Brin, 3 who formed a 
company for the preparation of oxygen for industrial purposes. 4 

The barium oxide was obtained in a hard and porous condition by 
ignition of the nitrate. Pieces about the size of a walnut were heated 
to 600 C. in vertical steel retorts into which air, purified from carbon 
dioxide and from most of its moisture, was conducted under a pressure 
of about 10 Ib. per sq. inch. After seven minutes the pressure was 
reduced to 4 inches (10 cm.) of mercury, the temperature remaining 
constant, whereon the absorbed oxygen was evolved. This process was 
repeated four times per hour, and a gas of 95 per cent, purity obtained. 5 

As late as 1907 three works were producing 30,000 cubic feet of oxygen 
per day by this process, which is now, however, obsolete in Great Britain, 
having been superseded by the liquid-air process, 6 which not only 
yields a cheaper but a purer gas, namely, 97 per cent, oxygen. 

In 1913 a process was patented 7 by which the oxygen of the air could 
be obtained by alternate oxidation and reduction of oxides of nitrogen. 
Vapour of nitric acid is passed over heated sulphuric acid whereby 
oxygen is liberated and water and nitrosulphuric acid arc produced. 
The latter is treated with water yielding sulphuric acid and a mixture 
of nitric oxide and nitrogen peroxide, the last named being reconverted 
into nitric acid by solution in water in presence of air. The reactions 
may be represented as follows : 

1 See Boussingault, Ann. CUm. Phys., 1852, [3], 35, 5 ; 1880, [5,] 19, 464 ; Conclolo, rend., 1868, 66, 488. The velocity of formation of barium peroxide has recently 
been studied by Sasaki, Mem. Coll. Sci. Kyoto, 1921, 5, 9. 

2 Which is necessary for the reaction. 'See Hillebrand, J. Amer. Ghent. Soc., 1912, 34, 
246. Compare Le Chatelier, Co nipt, rend., 1892, 115, 654. 

3 Brin, Mem. Soc. Ing. civ., 1881, p. 450 ; English Patent, 1416 (1880). 

4 The velocity of formation of barium peroxide has been studied by Sasaki, Mem. Coll. 
Sci. Kyoto, 1921, 5, 9. 

5 See English Patents, 1416 (1880) ; 4955(1889); 4292(1891); 17298(1891); 14918 
(1893). Also Murray, Proc. Inst. Meek. Eng. 9 1890, p. 131 ; Thome, J. Soc. Chem. I ml., 
1890, 9, 246. 

fi Seep. 31. 

7 Bergfeld, English Patent, 21211 (1913) ; J. Soc. Chem. Ind., 1914, 33, 831. 


(i) 4HNO 3 =4N0 2 +2H 2 0+O 2 . 
(ii) 4H 2 S0 4 +4N0 2 =4H(NO)S0 4 +2H 2 0+0 2 . 

(iii) 2H(NO)S0 4 +H a O = 2H 2 S0 4 +N a O a - 
(iv) N 2 3 +O 2 +H 2 O-2HNO 3 . 

C. Preparation of Oxygen from more Complex Compounds. Many 
oxygenated salts and other compounds yield oxygen when subjected to 
the influence of heat, either alone or in contact with other substances. 
They may even yield oxygen at ordinary temperatures in contact with 
suitable catalysers. 

When metallic chlorates are gently heated, oxygen is evolved, a 
chloride being generally left behind. The salt which, for various 
reasons, has been studied most carefully in this connection is potassium 
chlorate. The decomposition of this salt is liable to be explosive if 
the heating is carried out suddenly. 1 This is readily demonstrated by 
allowing very small drops of molten chlorate on the end of a glass rod 
to fall on to the bottom of a test-tube heated to redness. Sharp 
detonations result. When heated to 357 C. this salt undergoes no 
perceptible decomposition, but the powder cakes together and when 
examined under the microscope shows signs of incipient fusion. 2 The 
salt becomes liquid at a slightly higher temperature, 3 and at 370 to 
380 C. there is a rapid evolution of oxygen. 4 Several reactions now 
begin to take place : 

(1) The formation of perchlorate. This is a case of aut oxidation, 
one molecule of chlorate oxidising three other molecules of chlorate to 
perchlorate and being itself reduced to chloride. Thus : 

KC10 8 +3KC10 8 =KC1 +8KC10 4 . 

This reaction is exothermic, evolving 61,300 calories. 5 

The velocity of formation of potassium perchlorate has been measured 
at 395 C. and the reaction shown to be tetramolecular and to proceed 
in accordance with the above equation. 6 

(2) In addition to the foregoing reaction, potassium chlorate 
undergoes decomposition into oxygen and potassium chloride. This is 
a monomolecular reaction 7 and proceeds according to the equation 

2KC10 3 =2KC1+3O 2 . 

(3) If the temperature is raised sufficiently the potassium per- 

1 Berthelot, Compt. rend., 1899, 129, 926. 

2 M'Leod, Trans. Chem. Soc., 1889, 55, 184. 

3 Using an electrical method, C. D. Carpenter (Chem. Met. Eng., 1921, 24, 569) has 
determined the melting-point as 357-10 C. 

4 Oxygen is very slowly evolved at temperatures below the melting-point of the 
chlorate (Billiet and Crafts, B.A. Reports, 1882, p. 493). 

5 In many textbooks this reaction is described as taking place according to the 

2KC10 3 =KC10 4 +KC1+0 2 . 

It has long been known, however, that this is incorrect (Marignac, Jahresber., 1845, 24, 192 ; 
Teed, Proc. Chem. Soc., 1885, I, 105 ; 1886, 2, 141 ; Trans. Chem, Soc., 1887, 51, 283 ; 
Frankland and Dingwall, ibid., 1887, 51, 274). The formation of perchlorate is not per se 
accompanied by the evolution of oxygen. See Sodeau, Trans. Ohem. Soc., 1902, 81, 1006 ; 
Fowler and Grant, ibid., 1890, 57, 279. 

6 Scobai, Zeitsch. physikal. Chem., 1903, 44, 319. 

7 Scobai., loc. cit. 


chlorate formed in the first reaction begins to decompose, in the main 
according to the equation 

KC1O 4 =KC1+2O 2 . 

This reaction is inappreciable even at 411 C., 1 but readily proceeds to 
completion at -M5 C. 2 A small quantity of potassium chlorate is 
simultaneously regenerated. 3 

A trace of chlorine is usually found in the oxygen obtained by 
heating potassium chlorate in glass apparatus, a larger amount being 
obtained with Jena glass than with either soda or Bohemian com- 
bustion glass. When the chlorate is decomposed in platinum vessels, 
however, chlorine is either not evolved, or only in infinitesimal quantities 
whether at atmospheric or under reduced pressure. 4 

Sodium chlorate decomposes in a precisely similar manner to the 
potassium salt. 5 

The foregoing method of preparing oxygen possesses two disadvan- 
tages. Not only is the evolution of the gas inclined to be violent and 
difficult to control, but the temperature at which the reaction takes place 
is too high to be satisfactorily carried out in a glass vessel. These 
difficulties are overcome by mixing the chlorate with manganese dioxide 
prior to heating, a procedure first described by Doebereiner 6 in 1832. 
Under these conditions the evolution of oxygen is steady and com- 
mences at about 240 C. instead of 370 C 

It is important to remember that commercial manganese dioxide 
is occasionally contaminated with carbonaceous material such as coal 
dust. Such a mixture is very liable to explode when heated with 
potassium chlorate owing to the rapid combustion of the carbon in the 
oxygen. Manganese dioxide should, therefore, always be tested before- 
hand and rejected for the preparation of oxygen if it is found to contain 
any carbonaceous matter. 

The manner in which the manganese dioxide assists the decomposition 
of the chlorate has beeil made the subject of considerable controversy. 
The oxide may be used over and over again without any measurable 
diminution of its activity. 7 It has been suggested from time to time 
that its action is purely mechanical 8 analogous to that of sand, etc., in 
promoting the boiling of water. The analogy, however, is misleading, 
for reduction of pressure does not materially facilitate the evolution of 
oxygen from potassium chlorate, although it greatly reduces the boiling- 
point of water. 9 Again, were the action purely mechanical, all other 
finely-divided substances, irrespective of their chemical composition, 
might be expected to act in a similar manner just as they are known to 
do in the case of boiling water. This, however, is not the case, for 

1 Scobai, loc. cit. 

2 That is, at the boiling-point of sulphur. See JBYankland and Ding wail, Trans. C/iem. 
tioc., 1887, 51, 279. 

:j Teed, loc. cit ; Frankland and Diugwall, Loc. cit. 

4 Sodeau, Tram. Cham. Hoc., 1900, 77, 137. Compare Williams, Proc. Cheni. Soc., 1889, 

5 Scobai, Zeitsch. physikal. Client., 1903, 44, 319. 
Doebereiner, Annalen, 1832, I, 236. 

7 M'Leod, Trans. Chem. #oc., 1889, 55, 184. 

a Veley, Phil Trans. 1888, [A], 179, 270. 

9 Sodeau, Trans. Chem. Soc., 1900, 77, 144; 1901, 79, 939. 


although oxides of iron, cobalt, nickel, cerium, 1 and copper facilitate 
the reaction, the oxides of zinc, magnesium, etc., appear incapable of 
doing so. 

The most probable explanation is that alternately higher and lower 
oxides of manganese are formed 2 the higher oxide by the oxidising 
action of the heated chlorate, and the lower oxide by the decomposition 
of the higher, either alone or in contact with a further supply of chlorate. 
Mention has already been made of the fact that, when potassium 
chlorate is heated alone, some perchlorate is formed through self-oxidation 
simultaneously with the evolution of oxygen. This reaction does not 
occur in the presence of manganese dioxide, 3 since this oxide effects the 
decomposition of the chlorate into chloride and oxygen at a temperature 
considerably below that at which autoxidation of the chlorate proceeds 
at an appreciable rate. 4 

That several other minor or side reactions should take place, in 
addition to the main cycle indicated above, is only to be anticipated. 
Thus the fact that the oxygen invariably contains traces of chlorine 5 
suggested that a peculiar form of ozone was produced rather than 
chlorine ; but this is negatived by the results of M'Leod. 6 Small quan- 
tities of potassium permanganate are also undoubtedly formed in the 
solid mass, for when potassium chlorate is fused with a very small 
quantity of manganese dioxide a pink colour is observable on cooling. 
When this pink mass is fused over a flarne, oxygen is evolved, but 
the colour persists until nearly all the chlorate is decomposed ; it then 
becomes greenish and ultimately brownish. If the dioxide is present 
in considerable quantity any pink colour is masked by the blackness 
of the mixture. 

M'Leod explains these changes as follows : 7 

(1) The dioxide acts on the chlorate forming permanganate, chlorine, 
and oxygen. 

2KClO 3 +2MnO 2 =:2KMnO 4 +a 2 +0 2 . 

(2) The permanganate then undergoes decomposition by the heat 
yielding potassium mangaiiate, manganese dioxide, and oxygen. 

2KMnO 4 =K 2 MnO 4 +Mn0 2 +O 2 . 

This reaction begins at about 200 C., and is rapid at 260 C. 8 

(3) The manganate is decomposed by chlorine yielding potassium 
chloride, manganese dioxide, and oxygen. 

K 2 MnO 4 +Cl 2 =2KCl+MnO 2 +O a . 

1 Namely cerium dioxide ; German Patent, 1915, No. 299505. 

- Sodeau, Trans. Chem. tioc., 1902, 81, 1066. 

3 Eccles, J. Chem, Soc., 1876, 29, 857 ; Teed, Trans. Chan. Hoc., 1887, 51, 283. 

1 Sodeau, loc. cit. 

5 Brunck, Ber., 1893, 26, 1760; Zeitsch. attory. Chem., 1895, 10, 222. 

(i M'Leod, Tram. Ghent.. Soc., 1894, 65, 202 ; 1896, 69, 1015. 

7 M'Leod, ibid., 1889, 55, 184. For further details of the discussions on the 
decomposition of potassium chlorate the reader is referred to the following references 
in addition to those already cited : Berthelot, Co nipt, rend., 1899, 129, 92(5 ; Warren, 
Client. News, 1888, 58, 247 ; Hodgkinson and Lowndes, Chem. News, 1888, 58, 309 ; 1889, 
59, 63; Bottomley, ibid., 1887, 56, 227; Maumene, ibid., 1886, 53, 145; Jungfleisch, 
Bull. Soc. chim., 1871, [2], 15, 6; ,/. Pharm. Chun., 1871, 14, 130; Baudrimont, ibid., 
1871, 14, 81, 161; Debray, Ber., 1870, 3, 247; Wiederhold, Ann. Phys. Chem., 1862, 
116, 171. 8 Seep. 24. 


Oxygen may also be obtained by heating the chlorates of other 
metals, notably barium, 1 calcium, 2 strontium, 3 lead, 4 and silver, 5 or 
by decomposition of metallic bromates and iodates. 6 

Aqueous solutions of alkali hypochlorites readily yield oxygen at 
the boiling-point under the influence of catalysers. This is easily 
accomplished by passing a current of chlorine through a concentrated 
solution of caustic soda at the boiling-point, to which a small quantity 
of a cobalt salt has been added. 7 The cycle of reactions involving the 
liberation of oxygen may be represented as follows : 

2NaOH H-Cl 2 =NaC10 +NaCl +H 2 O 
NaC10+CoO=NaCl 4-CoO 
2Co0 2 =CoO+O 2 . 

An aqueous solution of bleaching powder, to which a trace of a 
cobalt salt has been added to serve as catalyst, readily evolves oxygen 
when warmed to about 80 C. The procedure may be varied by using 
a thin cream of bl eaching powder in water and warming this on a water- 
bath to 70 or 80 C. in the presence of a small quantity of a cobalt salt. 
The mixture froths excessively, but this tendency may be overcome 
by addition of a little paraffin oil. 

The mechanism of the process consists in the immediate conversion 
of the cobalt salt into an oxide which undergoes alternate reduction 
and oxidation. "What the composition of the higher oxide may be is 
uncertain ; probably it is either the sesqui-oxide, Co 2 O 3 , or the dioxide, 
Co0 2 . 8 Assuming it to be the latter, the reactions taking place may be 
represented as follows : 

2Ca(OCl)Cl+2CoO=2CaCl 2 +2CoOo 
2CoO 2 =2CoO+O 2 . 

The velocity of reaction indicates it to be monomolecular. 9 Salts of 
nickel, copper, or iron may be used instead of those of cobalt, but are 
less active. The theory that the catalyst effects the decomposition by 
its own alternate oxidation and reduction is supported by the result 
of passing chlorine into a 50 per cent, solution of sodium hydroxide 
containing dissolved copper hydroxide ; the blue solution at first 
deposits a yellow copper peroxide, which rapidly decomposes, evolving 
oxygen and regenerating the original solution. 10 The effect of adding 
two catalysts to bleaching powder is remarkable. If the bleaching 
powder is made into a cream with water, oxygen may be liberated at 

1 Potilitzin, J. Russ. Chem. Soc., 1887, p. 339 ; Ber., 1887, 20, Kef. 769 ; Schulze, 
J. prakt. Chem., 1880, [2], 21, 407. See also Sodeau, Trans. Chem. Soc., 1900, 77, 137. 

2 Sodeau, Trans. Chem. Soc. t 1901, 79, 247 ; Potilitzin, J. JKuss. Phys. Chem. Soc., 
1890, 22, 333. 

3 Potilitzin, loc. ciL, 1889, 21, 451. 

4 Sodeau, Trans. Chem. Soc., 1900, 77, 717 ; Wachter, J. prakl. Chem., 1843, 30, 329 ; 
Schulze, loc. cit. ; Spring and Prost, Bull. Soc. chim., 1889, [3j, I, 340. 

5 Sodeau, ibid., 1901, 79, 249. 

15 E. H. Cook, ibid., 1894, 65, 802. 

7 See Bleaching Powder below. 

8 See Camot, Compt. rend., 1889, 108, 610; Schroder, Chem. Zentr., 1890, L, 931 ; 
Hiittner, Zeitsch. anorg. Chem., 1901, 27, 81 ; M'Leod, Brit. Assoc. Reports, 1892, p. 669. 

9 Bell, Zeitsch. anorg. Chem., 1913, 82, 145. 

10 See Fleitmann, Annalen, 1865, 134, 64 ; Bottger, J. pmkt. Chem., 1865, 95, 309, 375 ; 
Stolba, ibid., 1866, 97, 309; Winkler, ibid., 1866, 98, 340; Deniges, J. Pliarm. Chini., 
1889, 19, 303 ; Bell, Zeitsch. unorg. Chem., 1913, 82, 145. 


the ordinary temperature by addition of a ferrous or manganous sa 
and in the presence of a copper or nickel compound. The best resu 
is obtained with a mixture of ferrous and copper sulphates. 1 

Practically the same reaction takes place when a stream of chlorii 
gas is passed through boiling milk of lime containing a trace of coba 
oxide as catalyst. The oxygen is steadily evolved. 

2Ca(OH) 2 +2Cl 2 =2CaCl 2 +2H 2 O+O a . 

Oxygen is readily evolved at the ordinary temperature on addi] 
water to a mixture of bleaching powder and an alkali or alkaline ear 
peroxide in the presence of a catalyst such as ferrous or copper sulphat 
If the solid mixture is pressed into small lumps or cubes, it may be us 
in a Kipp's apparatus and thus afford a convenient method of prepari] 
the gas for lecture or laboratory purposes. 2 

Ca(OCI)Cl+Na 2 O 2 +H 2 O = Ca(OH) 2 +2NaCl+O 2 . 

Concentrated sulphuric acid, when strongly heated, decomposes in 
water and a mixture of sulphur dioxide and oxygen. 

2H 2 S0 4 =2H 2 0+2S0 2 +0 2 . 

To this end the acid is allowed to drop on to a red-hot surface and t 
resultant gases treated with suitable absorbents to remove the sulph 
dioxide and steam. 3 

Concentrated nitric acid readily decomposes, when heated, ir 
water, nitrogen dioxide, and oxygen. The two former are read 
converted again into nitric acid by the action of the atmospheric air. 

Alkali nitrates, when heated above their melting-points, yield t 
corresponding nitrite and oxygen ; but the gas is contaminated w: 
nitrogen resulting from partial decomposition of the nitrite. In the a 
of potassium nitrate the reaction may be represented by the equation 

2KNO 3 =2KNO 2 +0 2 . 

Priestley had noticed as early as 1772 that, when a lighted candle 
lowered into the gas obtained by heating potassium nitrate, the fla: 
i4 increased," indicating more intense combustion. 6 

The decomposition of alkali nitrates appears to be a reversi 
reaction. When heated in oxygen at a pressure of 175 atmospheres 
a temperature gradually rising from 395 to 530 C. during nine hoi 
sodium nitrite is almost completely oxidised to nitrate. Thus : 

2[NaNO 2 ]+(O 2 )=2[NaNO 3 ] +45,000 calories. 

Calcium nitrite undergoes oxidation to nitrate in similar circumstance 

Potassium permanganate decomposes when gently heated. r ] 

pure, dry salt shows signs of decomposition at 200 C. 8 The react 

1 Jaubert, German Patent, 157171 (1905). 

2 Jaubert, Gompt. rend., 1902, 134, 778 ; English Patent, 11460 (1901) ; 14848 (1<J 

3 This process is used commercially, not for the preparation, of oxygen, but for 
paring a mixture of sulphur dioxide and oxygen in the requisite proportions to 3- 
sulphur trioxide. 

4 See .Bergf eld, J. Soc. Chem. Ind., 1914, 33, 831. 

5 Lang, Ann. Phys. Chem., 1863, [2], 118, 282. 

6 Priestley, Phil. Trans., 1772, 62, 245. 

7 Matignon and Monnet, Gompt. rend., 1920, 170, 180. 

8 Moles and Crespi, Zeitsch. physikal. Chem., 1922, ioo,-337. 


is appreciable at 215 C. and is complete at 240 C. The oxygen pressure 
of the residue corresponds with that of pure manganese dioxide up to 
-185 C. The heat of dissociation of potassium permanganate is 60,000 
calories. 1 

The reaction proceeds approximately according to the equation 

2KMiiO 4 =K a MnO 1 +MuO 2 +O a , 

a residue of potassium mangaiiate and manganese dioxide being 
obtained. 2 

When a mixture of manganese dioxide and sodium hydroxide is 
heated to dull redness in a current of air. sodium mangaiiate is formed : 3 

4NaOH+2MnO 2 +O 2 =2Na 2 MnO 4 +2H 2 0. 

The absorption of oxygen begins at 240 C., the rate of absorption 
increasing with the temperature, the optimum temperature being 600 C. 
The product, on treatment with steam at 450 C. 5 evolves oxygen, 
sodium hydroxide and manganese dioxide being regenerated : 

2Na 2 Mn0 4 +2H 2 O = 4NaOH+2MnO 2 +O 2 . 

The foregoing reactions were made the basis of a commercial method 
for the preparation of oxygen from the air, but, owing to the short life 
of the solid phase, the process has not proved particularly successful. 4 

Teissier and Chaillaux 5 suggest the employment of barytes and 
manganous oxide which are heated together to redness with the pro- 
duction of manganese dioxide and barium sulphide : 

BaSO 4 +4MnO = BaS +4MnO 2 . 

The temperature is now raised to white heat, whereby the dioxide 
dissociates. Thus : 

4MnO 2 =-4MnO+2O 2 . 

Finally steam is injected under pressure, reconverting the barium 
sulphide into sulphate and liberating hydrogen : 

BaS +4H 2 O=BaSO 4 +4H 2 . 

These reactions are interesting as constituting one of the few com- 
mercial processes in which hydrogen is simultaneously obtained in 
equivalent quantity to the oxygen. 

The alkali bichromates, when gently heated with concentrated 
sulphuric acid, are converted into chromium salts with liberation of 
oxygen. 6 Thus : 

2K 2 Cr 2 O 7 +8H 2 SO 4 = 2K 2 SO 4 +2Cr 2 (SO 4 ) 3 +8H 2 O+3O 2 . 

The change in colour undergone by the mixture during the reaction 

1 Moles and Crespi, loc. cit. 

- See Askenasy and Solberg, Festschrift W. Nernst., 1912, p. 53 ; Tessie du Motay and 
Marechal, Dingl. Poly. J. 9 1870, 196, 230; Rousseau, Conipt. rend., 1886, 103, 261; 
M'Leod, Trans. Chem. $oc., 1889, 55, 184. 

3 See this series, Vol. VIII., Chap. 6. 

4 Tessie du Motay and Marechal, English Patent, 85 (1866) ; Parkinson, ibid., 14925 
(1890); Bowman, ibid., 7851 (1890) ; Fanta, ibid., 3034 (1891) ; Chapman, ibid., 11504 

5 Teissier and Chaillaux, French Patent, 447688 (1912). 
'' Balmain, J. Pharm., 1842, 2, 499. 


is very marked, the deep red of the bichromate giving place to the deep 
green of chromic sulphate. 

Upon exposure to moist air cuprous chloride absorbs oxygen, being 
converted into the basic oxide Cu 2 OCl 2 . This, on heating to 400 C., 
yields free oxygen and a residue of cuprous chloride, from which the 
basic salt can be obtained again as indicated above. The initial supply 
of basic cuprous chloride may be conveniently obtained by heating a 
moist mixture of cupric chloride, sand, and clay in a current of steam 
at 100 to 200 C. 1 

Other processes that have been suggested involve the use of nitro- 
sulphonic acid 2 and haemoglobin. 3 

Plumboxan, a mixture of the manganate and meta-plumbatc ol 
sodium, namely, Na 2 MnO 4 . Na 2 Pb0 3 , readily evolves oxygen when 
heated in a current of steam at 430 to 450 C. The plumboxan is 
regenerated at the same temperature by replacing the steam with air, 
the issuing gas, during the initial stages of regeneration, consisting of a 
fairly pure nitrogen. 4 

The oxygen obtained by this process is very pure if the precaution 

is taken to remove the last traces of nitrogen from the pores of the 

plumboxan after regeneration by connecting to a vacuous vessel before 

"introducing the steam. The chemical reactions taking place are very 

complex, and but imperfectly understood. 

Orthoplumb cites of the alkaline earth metals yield oxygen when 
strongly heated. The calcium salt, Ca 2 PbO 4 , is readily obtained by 
heating calcium carbonate and lead oxide in the presence of air 5 at 
about 600 C. When heated more strongly, the salt dissociates, 
yielding free oxygen, the dissociation pressures being as follow : 6 

Temperature, C. . 880 940 1020 1060 1100 1110 
Pressure in mm. . 47 112 350 557 940 1040 

Although a higher temperature is required for the preparation of 
oxygen by this method than is the case with barium peroxide (sec p. 10), 
the calcium plumbate is more rapidly regenerated in the presence of air- 
when the temperature is lowered ; furthermore, it is not necessary to 
remove the carbon dioxide from the air as in Erin's process. 

The reactions entailed may be represented by the equation 

4CaCO 3 +2PbO +O 2 (from air )^^2Ca 2 Pb0 1 4 f C<X 
2Ca 2 PbO 4 ^4CaO +2PbO +O a . 

The oxygen may be derived from calcium plumbate, however, in 
other ways than by heat alone. One method consists in heating to 
about 700 C. in carbon dioxide : 

4C0 2 +2Ca 2 PbO 4 =5=4CaCO 3 +2PbO+O 2 . 

The residue is then heated successively in steam and air whereby the 
plumbate is reformed. 7 

1 Mallet, Compt. rend., 1867, 64, 226 ; 1868, 66, 349 ; English Patent, 2934 (18(>4) ; 
3171 (1866). - Bergfeld, English Patent, 21211 (1913) ; see also p. 19. 

3 Sinding-Larsen and Storm, ibid., 8211 (1910) ; 12728 (1910). 

4 Kassner, Arch. Pharm., 1913, 251, 596. 

5 Kassner, ibid. 9 1890, 228, 109 ; 1894, 232, 375. 
(1 Lc Chatelier, Compt. rend, 1893, 117, 109. 

7 Kassner, Chem. Zeit., 1898, 22, 225 ; 1900, 24, 615. See also iSalanum, En<ili#k 
Patent, 6553 (1890). 


Another method consists in exposing the calcium plumbate to moist 
furnace gases at a temperature of about 80 to 100 C. The carbon 
dioxide is readily absorbed, the solid phase being converted into a 
mixture of calcium carbonate and lead dioxide. On raising the tempera- 
ture, oxygen is evolved, the process being facilitated by the introduction 
of steam. The calcium plumbate is then regenerated by heating in air. 

Biological Processes. Under the influence of light the green parts 
of plants steadily assimilate carbon dioxide I and water, converting 
them into starch and evolving oxygen as a by-product. The voluitie 
of oxygen set free is approximately equal to that of the carbon dioxide 
absorbed, so that the initial and final stages of the very complex series 
of reactions involved may be represented by the equation 

6CO 2 +5H 2 O C 6 H 10 O 5 +6O 2 . 


The energy necessary for this reaction, which is endothermic, is obtained 
from the light, the most active rays being, curiously enough, those 
of the red, orange, and yellow portions of the spectrum, 2 and not the 
chemically reactive rays of the blue and violet end. 

The evolution of oxygen from plants is readily demonstrated by 
placing fresh green leaves, such as those of mint or parsley, in a jar of 
water more or less saturated with carbon dioxide and exposed to sun- 
light. If the mouth of the jar is closed with an inverted funnel fitted 
with a tap, sufficient oxygen will collect in an hour or two to admit 
of being tested with a glowing splinter. The experiment may be carried 
out in a glass cell in a projecting lantern, an image of the whole being 
thrown on to the screen by means of electric light. 3 Bubbles of gas will 
be seen to collect rapidly on the leaves under the influence of the light. 

This reaction is of particular interest inasmuch as it constitutes 
nature's method of replenishing the free oxygen content of the atmo- 
sphere. The efficiency of the process is evident when, to quote an 
example of medium assimilatory activity, it is remembered that one 
square metre of sunflower leaf can effect the decomposition of some 
40 grams of carbon dioxide, and the simultaneous evolution of 30 grams 
of oxygen in one summer day of 15 hours' duration. 


Oxygen was not obtained in the liquid state by Faraday in his 
elassieal investigations on the liquefaction of gases, because the refriger- 
ating agents used by him did not suffice for the attainment of the 
critical temperature of the gas, above which it is impossible to effect 
liquefaction, no matter how great the pressure. 

The gas was first reduced to the liquid state by Cailletet 4 in 1877, 
and almost simultaneously by Pictet. 5 The former investigator, who 
effected the cooling merely by the sudden expansion of the gas from a 
pressure of 300 atmospheres, obtained only a mist of small globules of 

1 See Baly, Heilbron and Barker, Trans. Chem. Soc., 1921, 119, 1025. 

3 See Pfeft'er, Pflaumen Physiol., 2nd ed., vol. i., sec. 60 ; Kohl, Bar. dent. But. G'es., 
1897, Heft. 2. 

3 The rays should be first passed through a water cell to intercept the heat before 
entering the cell containing the leaves. 

1 Cailletet, Compt. rend., 1877, 85, 1213, 1214 5 Pictet, ibid., p. 1276. 


liquid oxygen. Pictet, however, cooled the gas, already compressed 
to 320 atmospheres, to 140 C. in a bath of rapidly evaporating liquid 
carbon dioxide and was able to collect a small quantity of the liquid. 
Liquid oxygen was first produced in sufficient bulk for satisfactory 
examination by Wroblewski and Olszewski 1 who made use of liquid 
ethylene, boiling rapidly under reduced pressure, as a refrigerant. 
The rapid evaporation of liquid ethylene in vacuo leads to a temperature 
of 152 C, and Dewar 2 utilised this in preparing liquid air and oxygen 
in large quantities. 

Production of Liquid Air. 3 The methods for the production of 
liquid air are divisible into two classes according to whether the cooling 
of the gases is due to the external or internal work performed by them. 

The former method is based on the principle that the sudden, 
adiabatic expansion of gases against an external pressure causes external 
work to be done by them, accompanied by a proportional diminution 
in their own internal energy manifested by a reduction in temperature. 4 
Although this method was introduced by Cailletet in 1877 5 and was 
successfully applied by him to the liquefaction of oxygen, nitrogen, and 
air, it was not until 1905 that it was successfully applied on a commercial 
scale, namely, in the Claude Process. 6 

The difficulty of lubrication appears to have been mainly responsible 
for the failure of previous attempts, and this was first overcome by the 
employment of petroleum ether which does not solidify, but merely 
becomes viscous at such low temperatures as 140 to 160 C. Later, 
however, it was found that leather retains its ordinary properties at 
these low temperatures, and in 1912 leather stampings were fitted to 
the working parts of the machinery to the entire exclusion of lubricants. 
Claude's apparatus is shown diagrammatically in fig. 1. 

Air, compressed to 40 atmospheres, passes along the inner tube T x 
of the usual concentric system to the branched tube B, where it is placed 
in connection with a " liquefier " whilst much of the gas passes on 
through the expansion machine. Cooled by its loss of energy during 
expansion, it proceeds to the tubes inside the liquefier, and finally 
passes along the outer of the concentric tubes, thus cooling the oncoming 
air which reaches the expansion machine at 100 C. So cold does 
the expanded gas become that the compressed air in the liquefier 
finally condenses and is tapped off periodically, whilst the gas, after 
exerting this cooling effect, flows from the tubes of the liquefier into the 
outer tube T 2 and reduces to approximately 100 C. the temperature 
of the air reaching T x . 

The liquid air is usually collected and stored in Dewar vacuum 
flasks. These are double-walled glass vessels, the space between the 
walls being completely evacuated, so that the liquid in the flask is 
vacuum-jacketed. The heat conveyed by radiation across the vacuous 

1 Wroblewski and Olszewski, Compt. rend., 1883, 96, 1140, 1225 ; Wied. Annalen, 1883, 
20, 243 ; Wroblewski, Compt. rend., 1884, 98, 304, 982 ; 1885, 100, 979 ; 1886, 102, 1010 ; 
Olszewski, ibid., 1885, 100, 350 ; Monatsh., 1887, 8, 73. 

2 Dewar, Phil. Mag., 1884, 18, 210 ; Proc. Roy. Inst., 1886, p. 550. 

3 See discussion on the Generation and Utilisation of Cold, Trans. Faraday 8oc., 
1922, 18, part ii. 4 gee tllis ser i es> Vol. I., 3rd ed., p. 40. 

See Cailletet, Compt. rend., 1877, 85, 851, 101(5, 1213, 1270 ; Ann. Chim. Phvs., 1878, 
15, 132. 

6 Claude, Compt. rend., 1902, 134, 1568 ; 1903, 136, 1359 ; 1905, 141, 762, 823 ; 1906, 
143* 583. 



space is only about one-sixth of that which would reach the liquid by 
conduction and convection if the space were filled with air ; and this 
can be reduced to one-thirtieth by silvering the interior of the jacket. 
This latter procedure, however, is impracticable if for any purpose it is 
necessary to observe the contents of the flask. 

The second method of producing liquid air is based on the internal 
work performed by a gas upon expansion during passage from a high to a 
low pressure, the work being mainly that necessary to overcome the 
attraction between the gaseous molecules. This work is carried out at 
the expense of the sensible heat of the gas, and the effect is the greater 
the lower the temperature. It would not exist in the case of a perfect 


__ __ 7 Air 

FIG. 1. Claude's apparatus for the production of liquid air. 

gas upon free expansion, namely, into a vacuum, and must be carefully 
distinguished from the cooling already considered as the result of 
adiabatic expansion against the external atmospheric pressure, and as 
utilised in the Claude Process. This thermal effect was first studied by 
Joule and Thomson, 1 and is exhibited by oxygen and nitrogen and there- 
fore by air, in the case of the last named, up to a temperature of 259 C. 
under normal pressure. 2 The cooling, which is a small effect, amounting 
in the case of air at the ordinary temperature to only about 0-255 C. 
for a fall in pressure of one atmosphere, 3 may be calculated from the 

1 Joule and Thomson, Phil Trans., 1853, 143, 357 ; 1854, 144, 321 ; 1862, 152, 579. 

2 Olszewski, Bull Acad. Sci. Cracow, 1906, p. 792. 

3 For discussions of this value, see Keyes, J. Amer. Cliem. Soc., 1921, 43, 1452 ; Hoxton, 
Phys. Review, 1919, 13, 438 ; Bradley and Hale, ibid., 1904, 19, 391 ; 1909, 29, 258. 



where p^ is the initial high pressure, p 2 the final low pressure, and T the 
initial absolute temperature, the cooling being expressed in degrees 
centigrade. By employing high pressures the cooling effect is pro- 
portionately enhanced. Thus, if a pressure difference of 100 atmospheres 
is employed, working at C., the fall in temperature is 27-6 centigrade 

By allowing air to expand suddenly at ordinary temperatures a 
certain cooling is thus produced, and by applying this cooled gas to the 

reduction of the tempera- 
ture of yet unexpanded gas, 
the latter after expansion 
will attain a still lower tem- 
perature. In this way it is 
possible to make the cool- 
ing effect cumulative so that 
at last the temperature of 
the air is reduced to the li- 
quefying point. The Linde, 
Dewar, and Hampson lique- 
fiers are based on this prin- 
ciple. 1 

A diagrammatic repre- 
sentation of the Linde 
machine is given in fig. 2. 
Air compressed to 200 atmo- 
spheres passes through the 
steel bottle B where it de- 
posits its moisture, and 
thence proceeds to the 
worm surrounded by a re- 
frigerating medium. Here 
the temperature is reduced 
to 50 C. and the last 
traces of water-vapour are 
removed. The gas passes 
thence down the innermost 
of the concentric copper 
tubes T, by way of which it 
reaches the needle-valve V, 
where it expands to a pres- 
sure of 40 atmospheres. This limited expansion yields the major 
portion of the Joule-Thomson effect and at the same time reduces the 
subsequent necessary work of compression. The cooled expanded gas 
returns through the second concentric tube to the compressor, cooling 
the oncoming air as it passes. As this process is continued, the air 
reaching V steadily falls in temperature until at last it begins to condense 
to the liquid state, when the liquid is allowed periodically to pass through 
the valve Y where, on account of the further decrease of pressure to 
one atmosphere, the liquid evaporates vigorously until its temperature 

1 See Linde, Ber., 1899, 32, 925 ; Wied. Annalen, 1895, 57, 328 ; Olszewski, Bull. 
Acad. JSci. Cracow, 1902, p. 619; Hampson, J. Soc. CJiem. Ind. t 1898, 17, 411 ; English 
Patent, 1895, No. 10165 ; also this series, Vol. I., p. 41. 


FIG. 2. The Linde liquid-air machine. 


falls to its normal boiling-point for this pressure ; the eold gas from the 
evaporation passes away through the outermost concentric tube and so 
assists in cooling the compressed air, whilst the liquid air collects in 
the receiver R and can be drawn off as required by the tap C. The 
apparatus is enclosed in a packing of non-conducting material such as 
wool and is supported externally by a wooden or metallic case. In the 
earlier forms of this type of liqucfier the process was somewhat simpler 
because the pressure was allowed to fall directly to the ordinary external 
atmospheric pressure by one expansion only. Machines of the more 
modern type have been constructed to yield over 50 litres of liquid air 
per hour.* 

Production of Liquid Oxygen. On account of the great import- 
ance of oxygen and the increasing importance of nitrogen for industrial 
and other purposes, the liquid mixture of these elements provides a 
promising field for a successful process for the production of the gases 
on a large scale. 

As is indicated by the curves in fig. 35 the vapour of boiling liquid 
air is richer in nitrogen than the liquid, hence careful fractional distilla- 
tion or evaporation should finally yield the oxygen in a pure condition 
because the boiling-point rises steadily as the percentage of oxygen 
increases. Bearing in mind the proximity to the absolute zero, it will 
be easily recognised that the relative difference between the boiling- 
points of the two constituents, namely oxygen 182-9 C. and nitrogen 
195-67 C., is very considerable and that the main difficulties are 
likely to be of a mechanical type. 

Several forms of apparatus have been proposed. One of the earlier 
forms 2 suggested by Linde consisted of a modification of the apparatus 
represented in fig. 2 ; this was supplied with only one valve which 
allowed immediate expansion to atmospheric pressure, the liquid air 
produced by the cooling being collected in a suitable receiver. The 
compressed gas, before reaching the valve, was made to circulate 
through a copper coil actually inside the receiver so as to be covered by 
the liquid air already formed. The relative warmth of this gas caused 
an evaporation of the more volatile nitrogen, the liquid lost by evapora- 
tion being replaced by fresh liquid air produced by the expansion of 
the cooled gas. Proceeding in this way, the receiver soon contains 
fairly pure liquid oxygen which can be drawn off as necessary and 
transported, in the form of compressed gas, in steel cylinders. As the 
gaseous nitrogen which passes away from the apparatus is formed by 
the evaporation of a liquid containing at least 21 per cent, of oxygen, 
the nitrogen is not pure but must contain at least 7 per cent, of oxygen. 
A recent form of the Linde oxygen plant is shown in figs. 3 and 4. 3 

Prior to admission to the plant, the air is compressed to 135 atmo- 
spheres (2000 Ib. per square inch), and cooled to 20 C. in an ordinary 
refrigerating apparatus. This serves to freeze out atmospheric moisture. 
Carbon dioxide is removed by passage through a slaked lime purifier. 

1 The Hampson machine is described in this series, Vol. I., p. 41. 

2 See British Patents, 14111 (1902) ; 11221 (1903) ; 12528 (1895). The production of 
pure oxygen and impure nitrogen requires a slightly different plant from that for yielding 
pure nitrogen and impure oxygen. Hence slightly different forms of apparatus are used 
according to the object in view. Griffiths (Trans. Faraday Soc., 1922, 18, 224) discusses 
the production of liquid oxygen for use on air-craft. 

:j See Engineering, 1915, 99, 155. 



Thus treated, the air is admitted to the Linde plant at the mouth of the 
regenerator spiral AA' through three small pipes a, ^one of which is 
surrounded by a wider concentric pipe b, as indicated in fig. 4. 
These small pipes continue, inside AA', to encircle the rectifying column 
D and merge into the smaller spiral surrounded by liquid oxygen in B. 
The air on its passage becomes increasingly cooler, and escapes by 
way of the throttle-valve C to the top of the rectifying column D, a 
fall in temperature occurring at C owing to the Joule-Thomson effect. 
Ultimately a liquid rich in oxygen collects in B, whilst gas, rich in nitrogen 
and containing only about 7 per cent, of oxygen, escapes at E and 
leaves the apparatus through the regenerator spiral AA', cooling in its 

FIGS. 3 and 4. The Linde oxygen plant. 

passage, by conduction, the incoming air in a. The oxygen at F leaves 
through the tube b passing up inside. A' A 

When the apparatus has been at work a sufficient time to become 
steady, the liquid in B is continuously evaporated by the warmer air 
passing through the spiral, and the vapours escaping from B are rich in 
nitrogen, whilst the liquid remaining is rich in oxygen. The rectifying 
tower, with its baffle plates, reduces the amount of oxygen in the vapours 
escaping at E to about 7 per cent., for the ascending gases are con- 
stantly meeting liquids whose temperatures further up the rectifying 
column are increasingly lower. The oxygen thus condenses and joins 
the descending liquid stream. On the other hand, the nitrogen in that 
stream meets increasingly warmer gases as it falls, and having a lower 
boiling-point than the oxygen, it evaporates away and escapes at E. 
Liquid oxygen of 98 to 99 per cent, purity thus collects in B and is finally 
drawn off at H through b. 

The efficiency of the apparatus depends upon the temperature 
gradient between D and F, and this is controlled by the throttle-valve C. 



In practice it is found that a pressure of 50 to 60 atmospheres is sufficient, 
when the plant is in steady running, the 
temperature of the entering liquid air at 
D being -192 C., and at F -181-5 C. 

In Claude's x process compressed air, 
cooled by passage through a coil sur- 
rounded by the cold gases issuing from 
other parts of the apparatus, enters the 
lower portion of the apparatus (fig. 5) at 
A where it reaches the inner part of the 
tubular vessel B of annular cross-section ; 
this vessel is surrounded by liquid oxygen. 
During its ascent through B, the air be- 
comes partially condensed to a liquid 
which, as is shown by fig. 35, will contain 
up to 47 per cent, of oxygen. If the pres- 
sure of the incoming gas is correctly ad- 
justed, the residual gas will consist of 
almost pure nitrogen, which will pass over 
into the external tubular space C, where 
' it becomes entirely liquefied. The liquids 
condensed in D and E are therefore 
greatly enriched in oxygen and nitrogen 
respectively before admission to the 
" still " proper. The liquid collecting in 
D is caused by its pressure to rise through 
a regulating-valve into the fractionating 
column at F, and, overflowing down- 
wards, meets the ascending gases from 
the liquid oxygen in H. On account of 
the contact between these two currents, 
the descending liquid grows steadily richer 
in oxygen until it reaches the vessel H, 
which is in connection with the tubes in 
B, as liquid oxygen. The gases rising up 
the column beyond F become submitted 
to further " scrubbing " by the liquid 
nitrogen reaching G from E, the effect of 


FIG. 5. The Claude separator. 

this being to condense any oxygen still remaining in the gas so that it 
returns to scrub the ascending gases in the lower portion of the column, 
whilst the gas issuing at the top is reduced to pure nitrogen. Gaseous 
oxygen can be drawn from I above the condensed liquid. Tims almost 
pure oxygen and nitrogen are simultaneously produced. 2 

Commercial liquid oxygen may contain argon. Morey 3 found the 
composition of liquid oxygen to be as follows : 

Oxygen .... 96-9 per cent. 
Argon .... 2-8 ,, 
Nitrogen .... 0*3 

1 Claude, Compt. rend., 1905, 141, 823 ; also G. Claude, Liquid Air, Oxygen, Nitrogen, 
translated by H. E. P. Cottrell (Messrs J. & A. Churchill). 

2 For descriptions of Pictetfs process reference may be made to English Patent, 27463 
(1910) ; 9357 (1913) ; see also Maxted, J. Soc. CJiem. Ind., 1917, 36, 778. 

3 Morey, J.Amer.Chem.Soc., 1912, 34, 491. Compare Claude, Compt. rend., 19 10, 151, 752. 

VOL. vii. : i. 3 



GASEOUS oxygen is without colour, odour, or taste. The weight of 
1 litre of the" gas under standard conditions has been repeatedly deter- 
mined, the more important results being given in the following table. 
The same result is reached irrespective of whether the gas is obtained 
chemically or from the atmosphere. As the result of a critical con- 
sideration of modem data Moles 1 concludes that the most probable 
value is 1-42891 0-00003 grams. 

AT C. AND 760 mm. PRESSURE. 





Latitude 45 

Moles and Crcspi, Anal. Fis. Quim, 

1922, 20, 190. Compare, Moles 

and Gonzalez, iWd.,1922, 20, 72. 


Mean of 45 determina- 

Moles and Gonzalez, rend., 


1921, 173, 355. 


Mean of 15 determina- 

Germann, Compt. rend., 1913, 

tions at sea level and 

157, 926. J. Chim. phys. 9 1914, 

45 latitude 



Jaquerod and Pcrrot, Compt. 

rend., 1905, 140, 1542. 


Jaquerod and Pintza, ibid., 1904, 

139, 129. 


Paris 2 

Ledue, ibid., 1896, 123, 805. 


Sea level, latitude,"! 

45 . . > 

Thomson, Zeitsch. anorg. Chem. 9 


Paris 2 . ! J 

1896, 12, 1. 


Mean of several series 

Morley, Zeitsch. physical. Chem., 

1896, 20, 68. 


Paris 2 

Ravleio-h, Proc. Roy. Soc. 9 1893, 

53, 134. 


Sea level, latitude,""! 

45 . . 

Jolly, Wied. Annalen, 1879, 6, 


Paris 2 . . .J 



Paris 2 . 

Jolly, corrected by Rayleigh, I.e. 


Paris 2 

Regnault, 1847. 

Moles, J. Chim. physique, 1921, 19, 100. 

For Paris, the value of gravity {7=980-939. Latitude, 48 50' N. 



It may be mentioned that 1000 cubic feet of oxygen at 15 C. weigh 
S4-56 Ib. (avoir.), whilst 1 Ib. of the gas occupies 11-83 cubic feet. 

Assuming the mean weight of a litre of air at Paris to be 1*2930 
^rams (see p. 191) and of oxygen 1-42891 grams, the relative density 
of the latter is 1-1051. Since the air is a mixture, and its composition 
subject to slight variation, its density is not perfectly constant, so that 
"the above figure for the relative density of oxygen is merely a close 
approximation . 

With reference to hydrogen as unity, the density of oxygen is 
15-87. 1 

With reference to water at 4 C., the density of oxygen at N.T.P. is 
0-00142952. 2 

Despite its greater density, oxygen transfuses through a caoutchouc 
membrane some 2j times as rapidly as nitrogen 3 and a rough separation 
of the gases from ordinary air can be effected in this manner (see p. 13). 
Oxygen, when subjected to increase of pressure, does not strictly 
obey Boyle's Law. At first the gas is slightly more compressible than 
"the law demands, owing to the attraction between the gaseous molecules. 
Above 300 atmospheres, however, the product PV increases steadily 
ts the influence of the dimensions of the molecules themselves begins 
"to make itself felt. The gas thus becomes increasingly less compressible 
"than the law requires. This is well shown by the numerical data given 
in the table on p. 194. 

Considerable care must be exercised in compressing oxygen, for 
xinless proper precautions are taken there is considerable danger of 
explosion. Thus the gauges must be particularly clean and free from 
oil and other organic matter, the only permissible lubricant being 
water. 4 Cylinders containing compressed oxygen are painted black ; 
those with hydrogen, red ; whilst nitrogen and air are stored in grey 
cylinders. This device tends to avoid confusion 
find explosions due to mixing the gases. 

The diameter of a molecule of oxygen is given 
as 0-265 ju/x. 5 222-_-252 C.C. 

Solubility. Oxygen is slightly soluble in 

^water and in aqueous solutions. Several methods ' ' C ' C 

liave been devised for estimating the dissolved 
oxygen, and of these that due to Winkler is 
regarded as one of the most convenient and 
trustworthy. 6 As used by M'Arthur 7 the method 
consists in pouring the solution containing dis- FIG. 6. Apparatus as 
solved oxygen into a flask graduated to 250 c.c. used by M'Arthur (1916). 
and 252 c.c. respectively, as shown in fig. 6, 

tintil the former level is reached. One c.c. each of alkaline potassium 
iodide 8 and manganous chloride 9 solution are added, and the stopper 

1 See this series, Vol. II., also this Vol., p. 35. 

2 Rayleigh, loc. cit. 

3 Graham, J. Chem. Soc., 1865, 18, 9. 

4 Rasch, Zeitsch. komp. fluss. Gase, 1904, p. 141 ; Wohler, Zeitsch. angew. Chem., 1917, 
30, 174. 

5 Keesom, Proc. K. AJcad. Wetensch. Amsterdam, 1921, 23, 939. 

6 See Coste, J. Soc. Chem. Ind., 1917, 36, 846. 

7 M'Arthur, J. Physical Chem., 1916, 20, 495. 

8 Thirty-three grams NaOH, 10 grams KL Dilute to 100 c.c. 

9 Forty grams MnCl 2 . 4H 2 in 100 c.c. solution. 



inserted to the 252 c.c. level. On shaking, the manganous hydroxide 

liberated by the sodium hydroxide is oxidised by the dissolved oxygen. 

The stopper is removed and the whole acidified with 3 c.c. of concentrated 

hydrochloric acid and well shaken. Titration of the liberated iodine, 

preferably in another flask or dish, with thiosulphate * gives the amount 

of oxygen. 

Letts and Blake 2 use a large separating funnel (fig. 7), graduated to 

hold exactly 350 c.c. of liquid. It is filled with water, 7 c.c. removed 
and replaced by 5 c.c. of ferrous sulphate 3 solution 
and 2 c.c. of concentrated ammonia. The stopper 
is inserted, the whole well shaken and allowed to 
stand fifteen minutes. Upon inverting and filling the 
open tube with diluted sulphuric acid, 4 the tap may 
be opened. The acid enters owing to contraction 
caused by chemical action within the bulb, and, when 
all the ferrous hydroxide has dissolved, the solution 
is titrated with permanganate. 5 

Volumetric methods are frequently adopted, the 
volume of gas absorbed by a given volume of gas-free 
liquid, 6 or, conversely, the volume expelled from the 
saturated solution being directly measured. 

There arc several ways in which the solubility 
of a gas may be exprc k ssccl. By ft' is meant the 
volume of gas reduced to C. and 760 mm. which 
is absorbed by one volume of the liquid under a 
total pressure of 760 mm., which includes the vapour 
pressure of the solvent. 

j8 is the volume of gas at N.T.P. absorbed by unit- 
volume of the liquid under a partial pressure of the 

gas itself of 760 mm. irrespective of the vapour pressure of the liquid. 

It is known as Bunsen's absorption coefficient. Honor if f is the vapour 

pressure of the solvent at any temperature 


^ ~~^ 760 " 

Ostwalds solubility product, I, represents the ratio of the volume of 
absorbed gas to that of the liquid at the temperature and partial 
pressure of measurement. It is not reduced to C. and 760 mm. 
Hence, if the measurements are made at atmospheric pressure. 

Z=j8(l +0-00367*). 

In the following table are given the results obtained by different 
modern investigators for the absorption coefficient, /?, of oxygen in 
distilled water. 

FIG. 7. Apparatus 
as used by Letts 
and Blake (1899). 

1 Preferably N/100. 

- Letts and Blake, Proc. Eoy. Dublin Soc., 1899-1902, 9, 454. 

3 Twelve grams FeS0 4 per 250 c.c. of solution. 

4 Equal parts acid and water. 

5 A convenient strength, is N/10. 

6 Winkler, Ber., 1891, 24, 89; Estreicher, Zeitech. physikal. Chem., 1899, 31, 176- 
Fox, Trans. Faraday /Soc., 1909, 5, 68. 




Winkler, 2 1891. 

Bohr and Bock, 3 

Fox/ 1909. 

Adeney and 
Becker, 5 1919. 




























Several complicated empirical formulae have been given by means of 
which the solubility of oxygen may be calculated for any desired 
temperature. Winkler 6 gives, for temperatures between and 30 C., 
the formula 

=0-04890 0-0013413* +0-0000283J 2 -- 0-00000029534Z 3 . 

Fox 7 gives an analogous expression for- a temperature interval of 
to 50 C. : 

0=0-049289 0-0013440^+0-000028752^ -0-0000003024^. 

The solution of oxygen in water is accompanied by an expansion of 
the latter, 1 c.c. becoming 1-00115 c.c. on the absorption of 1 c.c. of 
oxygen. 8 

The Rate of Solution of Oxygen and Air in Water. 

Comparatively little work has been carried out on the velocity with 
which partially or completely de-aerated water reabsorbs oxygen and 
nitrogen from the atmosphere. Two cases merit consideration, namely : 

.(1) When the water is subjected to agitation so that fresh surface 
layers are continually formed, the rate of gaseous absorption is then 
at its maximum. 

(2) When the water is quiescent. In this latter case the process is 
not purely one of absorption followed by diffusion 9 into the body of 
the liquid from the surface layers, as has generally been supposed. It 
is considerably more rapid than this. Experiment shows that the gases 
do not remain concentrated in the surface layers, but tend to " stream " 10 
downwards under the influence of gravity, and thus to promote com- 

1 For a general review, see Coste, /. Soc. Chem. Ind., 1918, 37, 170 T. ; 1917, 36, 846 ; 
also Carlson, Zeitsch. angew. Chem., 1913, 26, 713. 

2 Winkler, Ber., 1891, 24, 3602 ; 1889, 22, 1764. 

3 Bolir and Bock, Wied. Annalen, 1891, 44, 318. 

4 Fox, Trans. Faraday Soc., 1909, 5, 68. 

a Adeney and Becker (Sci. Proc. Roy. Dublin Soc., 1918, 15, 385; 1919, 15, 609) also 
discuss the rate of solution of oxygen in water, giving mathematical formulae for deter- 
mining the same at different temperatures (see below). 

6 Winkler, Ber., 1889, 22, 1764. 7 Fox, Trans. Faraday Soc., 1909, 5, 68. 

8 Angstrom, Wied. Annalen, 1882, 15, 297. Adeney, Phil. Mag., 1905, 9, 360. 

10 Huffiaer, Wied. Annalen, 1897, 60, 134. Compare Carlson , Medd. K. Vetensk. 
Nobel-inst., 1911, 2, No. 6, 1. 


paratively rapid mixing. This is a point of very great biological and 
economic importance. 

Much of the modern research on the subject is due to Adeney and 
Becker, 1 whose initial researches were concerned with the rate of 
absorption of air by water under gentle agitation. They begin with the 
assumption that, 2 during the process of solution, the rate of passage, R, 
of gas into the liquid is proportional to the partial pressure of the gas, p, 
and the area, A, of the liquid exposed. Hence 

where u is the velocity of solution per unit area. Simultaneously with 
absorption, however, evaporation of the gas into the air takes place, 
with a rapidity proportional to the area A, and to the concentration, w, 
of the gas in the upper layers. If the coefficient of escape of the gas 
per unit area and volume of the liquid is denoted by/, the rate of escape, 
R 1 , of the gas from the liquid is given by the expression 

w being expressed as grams of gas per c.c. of the upper layer. 
The net rate of solution of the gas, therefore, is 

RH l =uAp fwA, 

and the two latter terms become equal upon saturation, when 


Denoting the volume of the liquid by V, it follows that the rate of 

dw uAp r A 

, - _ -* . -f-Mn* _ 


=a bw 
where a=uAp/V and b=fA/V, time being expressed as 0. 

The above equation may, for the sake of convenience, be expressed 
somewhat differently. Writing 


it follows that 

d 7 JQ 

- 77= bdO ; 
w a/6 


log, (w-a/b)=-bd+log e C; 
or, delogarising, 

C being a constant. When w=0, 8=0. Hence 

c r 

1 Adeney and Becker, Sci. Proc. Roy. Dublin Soc., 1918, 15, No. 31 ; 1919 15 No 44 
Preprinted in Phil Mag., 1919, 38, 317 ; 1920, 39, 385; 1923, 45, 581. Adeney, Leonard' 
and Richardson, Phil. Mag., 1923, 45, 835. 

2 See Bohr, Wied. Annalen, 1899, 68, 500; 1897, 62, 644. 


For practical purposes it is most convenient to express the results in 
terms of the percentage of saturation. So that if w is the amount of 
gas in solution initially, expressed as a percentage of total saturation, 
the amount w dissolved after a given time 6 is 

w>=(100 -w l )(l-e-) = (IWw l )(l-- 

Now / varies both with the temperature and the humidity. For an 
atmosphere saturated with moisture the following values for/have been 
determined, the water being gently agitated to ensure thorough mixing : 

For oxygen . . . /= 0-0096 (T 237) 
nitrogen . . . /=0-0103 (T 240) 
air . . . . /=0-0099 (T 239), 

T being the absolute temperature, and 6 expressed in minutes. 

An example will make the value of the above equation quite clear. 1 
Consider a cubic decimetre of water at 2*5 C. and containing 40 per cent. 
of its total saturation capacity for oxygen. If it exposes one side 
(100 sq. cm.) to oxygen, how much gas will be dissolved in one hour 
under gentle agitation ? 

It is unnecessary to consider the pressure of the gas since Henry's 
Law is obeyed and the desired result is to be calculated in percentage 
of total saturation. Since 6=60, W 1 =4 i ) /== 0-0096 (275-5237), it 
is easy to calculate that 


In other words, after an hour the oxygen content will have risen from. 
40 to 51-8 per cent, of saturation. 

The foregoing values for /were determined experimentally for water 
under gentle agitation in an atmosphere saturated with moisture. 
Such conditions are largely artificial. 

For quiescent bodies of water the following data have been obtained : 2 

Value of /at 15 C. 

Air dried over calcium chloride . . . 0-61 
Air of average humidity 3 . . . . 0-34 
Air nearly saturated with moisture . . 0-23 

These results are very striking, showing that dry air is much more 
rapidly absorbed than moist. This is interpreted as meaning that the 
process by which the dissolved gas is carried down into the body of the 
liquid is influenced by the rate of evaporation of the liquid surface, 
this being at a maximum when the air is dry. In the case of pure water 
this is merely a temperature effect, the evaporation causing a cooling 
of the surface layers and, at temperatures above 4 C., a gravitational 
circulation. In the case of solutions, such as sea-water, density changes, 
consequent upon variation in superficial concentration, are super- 
imposed on the temperature effect, so that more rapid mixing is 
likely to occur. This is confirmed by experiments which yielded the 

1 Taken from Adeney and Becker, loc. cit. 

2 Adeney and Becker, 3d. Proc. Roy. Dublin Soc., 1920, 16, No. 20. 

3 The actual humidity is not stated. 



following values for / at 15 C. under similar conditions of average 

humidity : T 

Tap-water . . . /=0-3S8 

Sea-water. . . . /= 0-509 

The rate of solution of oxygen in water docs not appear to be 
appreciably retarded by a thin layer of petroleum. 2 

As a general rule the presence of dissolved salts, chemically neutral 
towards oxygen, reduces the solubility of the gas. Thus, in the case of 
sea- water, the value for /? falls with rising chlorine content, as indicated 
in the following table : 3 



(Fox, 1009.) 

Parts of 

/^CLI __,'... 

Temperature, C. 

per 1000. 
































G-2 t 













<> 1 1 



These results may he expressed inathcinatically by the equation 
1000 j8"= 10-29! 0-2809/ -| -O-OOOOOJ)/ 3 -| 0-OOOOG32/ 3 

the chlorine being expressed as grains per litre. 

The; foregoing data, ha vet been recalculated to parts per million by 
Whipple. 4 Knrlic-r da.t.a. arc those of Clowes and Biggs,* 1 * who show 
that the solubility of atmospheric oxygen in diluted sea-water falls regu- 
larly with the amount of sea,- water present ; the sodium chloride, as the 
predominant salt, has a, determining effect upon the quantity of gas 

The following data, based on the results of M'Arthur,*' give the actual 
and relative solubilities of oxygen in solutions of various salts at 25 C. 

1 The actual humidity is not. .stated. 

- Friend, Garncyw Hdiolar^hip Memoir*, Iron and StrH Inslitutc, No. 3, 1911, p. 9; 
Stephenson, Analyst, 1919, 44, 288. 

3 Fox, loc. ciL The data, ft", tfivo (ho number of c,.r. of oxygen as measured at 
N.T.P. that would be absorbed under a total pressure of 7(>() mm. of dry air, but a partial 
oxygen pressure of 700 X 0*21 mm. 

4 Whipple, J. Amer. Chem. 8oc. t 1911, 33, 36:3. 

6 Clowes and Biggs, J. Soc. G/iem, Ind. 9 I904r, 23, ,'loS. 

6 M'Arthur, loc. cit. These data refer to oxygen as absorbed direct from the air at a 
partial pressure of 760x0*21 mm. 



(M ; Arthur, 1916.) 



Grams per 

Density at 
25 G. 

c.c. Oxygen 
per Litre. 


Water only 

. . 













































































m/8 ' 






























NH 4 C1 
















KNO 3 





















Na 2 SO 4 





















K 2 SO 4 




















Grams per 

Density at 
25 0. 

c.c. Oxygen 
per Litre. 


MgCl 2 



























Bad 2 








CaCl 2 











The solubility of oxygen in aqueous solutions of acids and alkalies 
is given by Geffcken as follows : * 

AND ALKALIES. (Geffcken, 1904.) 



Grams per Litre. 

c.e. Oxygen per e.c. at 
1 (15 0.). I (25 0.). 

Water only 

. . 



H 2 SO 4 











0-0285 a 



























HN0 3 



































1 Geffcken, Zeitsch. physikal. Chem., 1904, 49, 257. Other data for sulphuric acid are 
given by Bohr (ibid., 1910, 71, 47) and Christoff (ibid. 9 1906, 55, 622). 

2 Calculated by the present authors. There is clearly a misprint in Geffckcn's original 
paper at this point. 


Oxygen is much more readily soluble in blood than in water ; 
100 c.c. of average human blood is able, when fully saturated in contact 
with air, to hold between 18 and 19 c.c. of oxygen measured at N.T.P. 
(see p. 135). In ethyl alcohol, oxygen is several times more soluble than 
in water. 1 Its solubility at any temperature may be calculated from 
the following equation : 2 

/3=O2337 0-000746S8Z+0-000003288* 2 . 

The solubility of oxygen in aqueous solutions of ethyl alcohol at 
20 C. is as follows : 3 

Alcohol per cent, by weight 9-09 16-67 23-08 28-57 33-33 50-00 66-67 80-00 

I 2-78 2-63 2-52 2-4=9 2-67 3-50 4-95 5-66 

It will be observed that there is a decided minimum solubility at 
about 30 per cent, of alcohol. 

These data refer to an atmosphere of oxygen of partial pressure, 
760 mm. 

Oxygen is also soluble in certain molten metals, 4 e.g. platinum 
and silver, more than twenty times its own volume of the gas being 
absorbed in the case of the latter metal ; the dissolved gas is largely, 
but not completely, restored at the moment of solidification of the 
metal, and the phenomenon of " spitting " is thus produced. The power 
of oxygen to diffuse through heated silver, whereas glass is impervious, 
is probably due to this solubility of oxygen in the metal. 5 

Certain finely divided metals, especially platinum black and 
palladium black, can absorb many times their own volume of oxygen. 
In the case of the latter metal 6 absorption is probably attended by the 
formation of an oxide or mixture of oxides, but in the case of the former, 
although the product may include an unstable oxide, 7 the oxygen can 
be entirely recovered by reducing the pressure. 8 

Wood charcoal can absorb eighteen times its own volume of oxygen 
at C. and more than two hundred times its bulk at 185 C. ; the 
absorbed gas is liberated if the charcoal is heated. 9 

By thermal conductivity is understood the quantity of heat 10 that 
would pass between the opposite faces of a unit cube with unit tempera- 
ture difference between the faces. The value found n for oxygen at a 

1 Carius, Annalen, 1855, 94,134. 

2 TimofeiefT, Zeitsch. physikaL Chem., 1890, 6, 141. 

3 Lubarsch, Wied. Annalen, 1889, 37, 525. 

4 Deville, Compt. rend., 1870, 70, 756 ; Levol, Compt. rend., 1852, 35, 63 ; Dumas, 
Ann. Chim. Phys., 1878, [5], 14, 289 ; Sieverts and Hagenacker, Zeitsch. physical. Chem., 
1909, 68, 115 ; Donnan and Shaw, J. Soc. Chem. Ind., 1910, 29, 987. 

5 Bartoli, Gazzetta, 1884, 14, 544; Troost, Compt. rend., 1884, 98, 1427; Graham, 
Phil Mag., 1866, [4], 32, 503. 

G Neumann, Monatsh., 1892, 13, 40; Willm, Butt. Soc. chim., 1882, [2], 38, 611; 
Mond, Ramsay, and Shields, Proc. Roy. Soc., 1897, 62, 290 ; Zeitsch. physikal. Chem., 1898, 
25, 657. See also this series, Vol. IX., Part I. 

7 Engler and Wohler, Zeitsch. anorg. Chem., 1902, 29, 1 ; Mond, Ramsay, and Shields, 
loc. cit. 

8 Ramsay and Shields, Phil. Trans., 1896, 186, 657. See also Lucas, Zeitsch. Elektro- 
chem., 1905, n, 182. 9 Joulin, Compt. rend., 1880, go, 741. 

10 Expressed in calories. Adopting metric units, the conductivity is given by the 

k = calorie X cm.- 1 x sec.- 1 X temp. ( C.)- 1 . 

II Todd, Proc. Roy. Soc., 1909, [A], 83, 19. 



mean temperature of 55 C. is 0-0000593. According to the kinetic 
theory of gases the thermal conductivity, k, is given by the expression 

where T? is the viscosity of the gas and C v the specific heat at constant 
volume. / is a constant, apparently depending on the ratio of the 
specific heats, 1 and in the case of diatomic gases has the value 1-603. 

The viscosity of oxygen at 23-00 C. and 760 mm. pressure is 
2042-35 x 10~ 7 . 2 The viscosity rises with the temperature. Its mean 
specific heat at constant pressure rises with temperature as indicated in 
the following table : 3 


Temperature Interval, 

Mean Specific Heat at 
Constant Pressure. 

20 to 440 
20 to 630 


The ratio of the specific heat at constant pressure to that at constant 
volume is 

a value to be expected for a diatomic gas. 4 

The molecular specific heat at constant volume is given by the 



and at constant pressure by 6 

00 = 6-50 +0-0010T 

where t and T are on the centigrade and absolute scales respectively. 
The molecular specific heat at constant pressure at 20 C. is calculated 
as 6-924 from the velocity of sound in oxygen by Kundt's method. 7 

The coefficient of expansion per degree centigrade rise in temperature 
between and 100 C., measured at constant pressure of one atmosphere, 
was determined by Jolly 8 as 0-0036743, and found to be constant for a 
temperature ranging up to 1600 C. 

1 Meyer, Kinetisclie Theorie dcr Gase (Breslau, 1877) ; Schleiermacher, Wied. Annalen, 
1889, 36, 346. 

2 Yen, Phil. Mag., 1919, [6], 38, 582. See also Sclimitt, Ann. Physik, 1909, 30, 398 ; 
von Obermeyer, Sitzungsber. K. Akad. Wiss. Wien., 1875, 71, 281. 

3 Holborn and Austin, Sitzungsber. K. Akad. Wiss. Berlin, 1905, p. 175 ; earlier data 
are given by Regnault, Mem. de VAcad., 1862, 26, 1. 

4 Mercer, Proc. PJiys. Soc. London, 1914, 26, 155 ; see for earlier data Cazin, Ann. 
Chim. PJiys., 1862, 26, 1; Muller, Ber., 1883, 16, 214; Wied. Annalen, 1883, 18, 94; 
Lummer and Pringsheim, ibid., 1898, 64, 555 ; Kiister, Dissertation, Marburg, 1911. 

5 Pier, Zeitsch. Elektrochem., 1909, 15, 536; 1910, 16, 879. 

6 Lewis and Randall, J. Amer. Chem. Soc., 1912, 34, 1128. 

7 Schweikert, Ann. Physik, 1915, 48, 593. 

8 Jolly, Pogg. Annalen, Jubelband, 1874, p. 82. 


For a gas that obeys Boyle's Law the coefficient of expansion at 
constant pressure is numerically the same as the coefficient of increase 
of pressure with rise of temperature at constant volume. This has been 
determined for a temperature interval of to 1067 C. and has the 
value 0-0036652 in the case of oxygen. 1 

The refractive index 2 of oxygen is 1-000272 at C. and 760 mm. for 
the sodium D line (A 5S93xlO~ 8 cm.); the indices for other wave- 
lengths not widely removed may be calculated from Cauchy's equation 

/*-l=A(l+B/ A ,) 

where p, and A represent the refractive index and wave-length respect- 
ively, whilst A and B are constants ; the latter constant, B, is the 
coefficient of dispersion. For oxygen gas, A=26-63xlO~ 5 , and 
B = 5-07X10~ 11 . According to Cuthbertson, 3 the refractive index, ?^, 
of oxygen for any incident light of frequency,/, is given by the expression 

, 3-397 X10 27 

12804X10 / 2 

Examination, of long layers of the gas shows oxygen to exert a 
selective absorption for light in certain parts of the spectrum. 4 

The emission spectra obtained by an electric discharge through the 
gas under a reduced pressure and by the spark discharge are of a complex 

Both the magnetic susceptibility 6 and the magnetic rotatory 
power 7 of gaseous oxygen have been subjected to investigation. 

Liquid oxygen is a transparent liquid, possessed of a bluish tinge. 
Its critical constants have been variously determined as follows : 

1 Jaquerod and Perrot, Compt. rend., 1905, 140, 1542. 

2 Rentschler, Astrophys. J., 1908, 28, 345 ; see also Koch, Ann. Physik, 1905, 17, 658 ; 
Ramsay and Travers, Proc. Roy. Soc., 1897, 62, 225 ; Lorenz, Wied. Annalen, 1880, 1 1, 70 ; 
Craillebois, Ann. Ghim. Phys., 1870, [4,] 20, 136. In the infra-red region, see Statescu, 
Bull. Acad. Sci. Roumanie, 191^-15, 3, 211. 

3 C. and M. Cuthbertson, Proc. Roy. Soc., 1910, [A], 83, 151. 

4 Egoroff, rend., 1885, 101, 1143; 1888, 106, 1118; Janssen studied the 
absorption under pressures ranging up to 27 atmospheres, ibid., 1885, 101, 111, 649 ; 
1886, 102, 1352; 1888, 106, 1118; 1888, 107, 672. His results were supported by 
Liveing and Dewar, Phil. Mag., 1888, 26, 286. See also von Wartenberg, Physikal. 
Zeitsch., 1910, u, 1168; Bloch, Gompt. rend., 1914, 158, 1161; Warburg, Sitzungsber. 
Preuss. Akad. Wiss. Berlin, 1915, p. 230 ; Duclaux and Jeantet, Compt. rend., 1921, 173, 
581 ; Shaver, Trans. Roy. Soc. Canada, 1921, 15, [3], 7. 

5 See Schuster, Proc. Roy. Soc., 1878, 27, 383 ; Phil Trans., 1879, 170, 137 ; Vogel, 
JBer., 1879, 12, 332 ; Smith, Phil. Mag., 1882, 13, 330 ; Grunwald, Chem. News, 1887, 56, 
201, 223, 232 ; Eunge andPaschen, Wied. Annalen, 1897, 61, 641 ; Steubing, Ann. Pliysik, 
1910, 33, 553 ; 1912, 39, 1408 ; Stark, Physikal Zeitsch., 1913, 14, 770, 779 ; Scharbach, 
Zeitsch. wiss. Photochem., 1913, 12, 145; Croze, Gompt. rend., 1913, 157, 1061; 1912, 
155, 1607 ; Paschen and Back, Ann. Physik, 1912, 39, 897 ; Yoshida, Mem. Coll. Sci. 
Kyoto, 1919, 3 287 ; Bottcher and Tuczek, Ann. Physik, 1920, 61, 107 ; Bunge, Physica, 
1921, I, 254. For a study of the spectrum in the extreme ultraviolet, see Hopfield, 
Physical Review, 1922, 20, 573. 

6 Onnes and Oosterhuis, Proc. K. Akad. Wetensch. Amsterdam, 1913, 15, 1404 ; Bauer 
Weiss, and Piccard, Compt. rend., 1918, 167, 484; Weiss and Piccard, ibid., 1912, 155, 
1234 ; Piccard, Arch. Sci. phys. nat., 1913, 35, 458. 

7 Kundt and Rontgen, Ann. Phys. Chem., 1899, 8, 278 ; 1880, 10, 257 ; Becquerel, 
Compt. rend., 1880, 90, 1451. 





ture, C. 




to that of 
the Gas 



at N.T.P. 



Wroblewski, rend., 1883, 

97, 309. 



. , 

Olszewski, ibid., 1885, 100, 351. 



Be war, Chem. News, 1885, 51, 





Dewar, Proc. Roy. Soc., 1904, 

73, 251. 




MatMas and Onnes, Proc. K. 

Abaci. Wetensch. Amsterdam, 

1911, 13. 939. 



Onnes, Dorsman, and Hoist, 

ibid., 1915, 17, 950; 18, 409. 



Cardoso, Arch. Sci. Phys. Nat., 

1915, 39, 400 ; J. Chim. phys., 

1915, 13, 312. 

The boiling-point of liquid oxygen varies with the pressure, as 
indicated in the following table : l 


Absolute Boiling-point. 


Hydrogen Scale. 

Helium Scale. 

























The vapour pressure rises from 9-096 atm. at 
atm. at 118-70 C. 3 

-154-91 C. to 49-640 

1 Travers, Senter, and Jaquerod, Proc. Roy. Soc., 1902, 70, 484. 

2 Earlier data are those of Wroblewski and Olszewski, rend., 1883, 96, 1140 ; 
Wroblewski, ibid., 1883, 97, 1553 ; 1884, 98, 984 ; 1885, 100, 351, 979 ; Estreicher, Phil. 
Mag., 1895, 40, 458 ; Ladenburg and Kriigel, Ber., 1899, 32, 1818. 

3 Onnes, Dorsman, and Hoist, Proc. K. Akad. Wetensch. Amsterdam, 1915, 17, 950. 


The vapour pressure of oxygen at any temperature between 57 
and 90 abs. may be calculated from the expression 

log p= -419-31/T+5-2365 0-0648T 

where the pressure p is expressed in atmospheres, T being the absolute 
temperature. 1 

For p = l atm., the value for T becomes 90-13 , which agrees very 
satisfactorily with the boiling-point under normal pressure as given in 
the preceding table. 


Temperature, C. 





Drugman and Ramsay, Trans. Chem. 
Soc., 1900, 77, 1228. 



Dewar, Proc. Roy. Soc., 1904, 73, 251. 

5? JJ 59 99 
99 9> 99 ?9 



Inglis and Coates, Trans. Chem. Soc., 
1906, 89, 886. 

When the values obtained by Dewar for the densities are plotted 
against the absolute temperatures, they are seen to lie very closely to a 
straight line, so that the densities at intermediate temperatures can 
readily be calculated. The expression is 

Density =1 -5154 0-004420T 

where T is the absolute temperature. 

Using the data given by Ramsay and Drugman, the specific volume 
of oxygen at 183 C. is 0-8838, and the molecular volume 28-28. 

Baly and Donnan 3 give the data (included in the Table on p. 48). 

When exposed to the air, liquid oxygen absorbs appreciable quantities 
of nitrogen. 4 

Liquid oxygen is more compressible than water, its coefficient of com- 
pressibility (see p. 262) being 0-00195 between 10 and 20 atmospheres. 5 

The observed surface tension of the liquid is 13-074 dynes per cm. 
a value in fair agreement with that expected for a liquid of the same 
molecular weight as gaseous oxygen, although the possibility of slight 
association is not excluded. 6 From other data Inglis and Coates 7 

1 Oath, Proc. K. Akad. Wetensch. Amsterdam, 1919, 21, 656. 

2 Earlier data are those of Cailletet and Hautefeuille, Compt. rend., 1881, 92, 1086 ; 
Olszewski, Sitzungsber. K. Akad. Wiss. Wien, 1884, p. 72 ; Wroblewski, Compt. rend., 1886, 
102, 1010 ; Dewar, Chem. News, 1896, 73, 40 ; Ladenburg and Kriigel, Ber., 1899, 32, 
46, 1415. 3 Baly and Donnan, Trans. Chem. Soc., 1902, 81, 907. 

4 Erdmann and Bedford, Ber., 1904, 37, 1184 and 1432 ; see also Stock, ibid., p. 1432. 

5 Eucken, Ber. deut. physikal. Ges., 1916, 1 8, 4. 

6 Baly and Donnan, Trans. Chem. Soc., 1902, 81, 907 ; Grunmach, Sitzungsber. K. 
Akad. Wiss. Berlin, 1906, p. 679. 

7 Inglis and Coates, Trans. Chem. Soc., 1906, 89, 886. 



conclude that the degree of association of liquid oxygen at about 
195 C. is 1-09. 

(Baly and Donnan, 1902.) 





























These densities may be represented by the formula 

d-:l-248S74-0-004Sl (T 68). 

The specific heat of liquid oxygen between 200 and 183 C. is 
0-347, 1 and the heat of evaporation is 51-3 calories per gram at 763 mm. 
pressure, 2 its molecular heat of vaporisation being 1599 calories 3 accord- 
ing to another computation. Its coefficient of expansion with rise of 
temperature is 0-00157 at 252-6 C. The refractive index for sodium 
light, n D , is 1-2236, and the spectrum absorption similar to that of 
gaseous oxygen. 4 

Liquid oxygen is a non-conductor of electricity ; but it is strongly 
attracted by a magnet. 5 It readily absorbs nitrogen from the atmo- 
sphere, and can be mixed with liquid fluorine without suffering chemical 
change. The magnetic rotatory power and dispersion have been 
determined. 6 

Solid Oxygen. By rapid evaporation and consequent cooling, or 
by cooling in liquid hydrogen, liquid oxygen can be converted into a 
bluish-white solid of density 7 1-4256 at 252-5 C. and melting at 
219 C. under a vapour pressure of 0-9 mm. 8 The solid exhibits 
allotropy, a, /3, and y forms being recognised. The transition between 
the a and j8 forms occurs at 249-5 C. and between the j8 and y forms 
at -230-5 C. 9 

1 Scheel andHeuse, Sitzungsber. K. Akad. Wiss. Berlin, 1913, p. 44; Alt, Ann. Physik, 
1904, [4], 13, 1010; Barschall, Zeitsch. Mektrochem., 1911, 17, 345. 

2 Alt, Ann. Physik, 1906, [4], 19, 739. 

3 Eucken, Ear. deut. physical. Ges., 1916, 18, 4. 

4 Liveing and Dcwar, loc. cit. See also Shaver, Trans. Roy. Soc. Canada, 1921, 
IS, [3], 7. 

5 Tanzler, Ann. Physik, 1907, [4], 24, 931 ; Onnes and Perrier, Proc. K. Akad. 
Wetensch. Amsterdam, 1910, 12, 799. 

6 Chaudier, Compt. rend., 1913, 156, 1008. 

7 Dewar, Proc. Roy. Soc., 1911, 85, [A], 589 ; 1904, 73, [A], 251. 

8 Estreicher, Zeitsch. physikal. Chem., 1913, 25, 432. See also Onnes and Crommelin, 
Proc. K. Akad. WetenscJi. Amsterdam, 1911, 14, 163. 

9 Wahl, Proc. Roy. Soc., 1913, [A], 88, 61; Eucken, Ber. deut. pliysilcal. Ges., 1916, 
18, 4, 


OXYGEN is capable of uniting to form simple compounds with all the 
elements save fluorine and the noble or inert gases. Such combination 
is termed oxidation and can in general be produced by the direct 
union of the two elements, as for example in the oxidation of mercury 
when heated in air, although certain of the non-metals, particularly 
the halogen elements, show little tendency to direct combination in. 
this manner. Compounds also are capable of uniting with oxygen, 
sometimes yielding a stable oxidation product of higher molecular 
weight in consequence of addition of one or more atoms of oxygen ; or 
the molecule of the compound may be disrupted upon oxidation into 
two or more products. As an example of the former type of reaction, 
the oxidation of sodium sulphite in aqueous solution may be quoted, 
sodium sulphate resulting. Thus 

2Na 2 S0 3 +O 2 =2Na 2 SO 4 . 

The latter type of reaction is illustrated by acetylene which, when 
ignited, burns in air to form water and carbon dioxide. 

2C 2 H 2 +5O 2 ==4CO 2 +2II 2 O. 

Oxidation both of elements and compounds may be effected in the 
absence of free oxygen through the action of substances containing 
oxygen. Thus, for example, iron is oxidised by steam and potassium 
by carbon dioxide at high temperatures. The present section, however, 
is concerned more particularly with oxidation through the direct 
action of free elementary oxygen. 

Most cases of oxidation arc exothermic, that is to say they are 
accompanied by the evolution of heat, although a few cases are known 
which are ciidothcrmic in character. Such, for example, are the 
oxidation of water to hydrogen peroxide : 

2H 2 0+(0 2 ) 2H 2 2 Aq. 23059 calories, 
and the production of ozone from oxygen, 

30 a =2O 3 2 X 34000 calorics, 

both of which reactions are accompanied by an absorption of heat. 

It docs not necessarily follow, however, that reactions involving the 
exothermic oxidation of substances arc accompanied by a sensible 
rise in temperature. The rate of oxidation may be so slow that the 
heat is dissipated almost as rapidly as it is liberated, so that the 

VOL. vu. : i. 49 4 



i'-.i" rulmv is iniinitosimal. This is well illustrated by the 
.,xi.l:ii.,u ,-l mm iipun .-xposuvo to air, a reaction commonly known 

its His! Hi '4. J 

Oli tls( . V'?! 1 ' 1 ' h ;. IIIlL ''"'"iHnation with oxygen is often accompanied 
by thr rapid lib. ration <>i so mueh energy that heat and light are emitted. 
Ih ft mi combustion \\ then applied. 

Tfsr majority of substances ' require to be raised in temperature 
heioiv thry ran combine with oxygen to any appreciable extent. Thus 
electrolytic jas a imxftiiv of two volumes of hydrogen with one of 
oxygen is \ery stable at the ordinary temperature; combination, 
however, beirms to br appreciable at temperatures slightly above 
MM) t'.. and at lusher 1t -m | H matures proceeds with explosive violence. 
Chi Ihr of lii r hand, somr substances rapidly combine with oxygen when 
hrou'jhf into contact \\ith the gas at the ordinary temperature. Such 
bothrs ;nv said to br spontaneously oxidisable, and include the 
pyrophorir itMlaSs. phosphorus, coal dust, nitric oxide, ferrous and 
iitnu.L'jmoiis hyiiroxiiies. liquid phosphinc, silicon hydride, and many 
organic substances. l'm!er suitable conditions most of these steadily 
rise iii frniprnifmv as oxidation proceeds until rapid combustion, 
accompanied by liifhU ensues. 'This is termed spontaneous 
combustion, a familiar example on a large scale being afforded by the 
tiring of Iay n-ks. Autoxuliition is a term frequently used to designate 

spoilt aitrollS o\n!af MMt. 

Tin- rafr of \il;sf mn of any particular substance is dependent upon 
various fartors. In uif. its mvu physical condition as well as that of the 
o\\ jfru ; t In pr srnrr if iturisl ui\ i or of a catalyscr ; and the application 
of Iprlit. bat, aihi jrrssun. Thus, liquid oxygen does not affect 
phosphorus >r Ut alkali inrtals ; neither does it combine with solid 
nstnr o\i*li-. 1 aiihout,'h a small jet of burning hydrogen will continue 
to bunt IH \n\\ Ilif siirfarr of li<[uid oxygen, the water produced being 
riuuivid .r, ire ami a *-i msidorable amount of ozone being formed. 
Similarly vraphit*- .iml diamond, wlien once ignited, will burn on the 
tirfaf tf liijui'! \\"ii. the carbon dioxide produced being frozen 
ami '.om.- >/nt pa ii-* into solution. Oxidation is usually facilitated 
to a ruhMi'TahI'- %l. til hy increasing the superficial area of the sub- 
Jaiir, to br oM.h-.. d. \\"" 'II -kno wii illustrations arc supplied by the 
pM'uplionr ionir- t! mm. b-ad, etc. When a solution of phosphorus in 
raiSnH dr,ulj)hici- i (nnirrd on to a, sheet of filter paper, the solvent 
rajndly . \ apur.if . ,. having the phosphorus within the pores of the 
pa|nr'm an r\r. SSIM K line state of subdivision., so that vigorous 

C'< till) >H'J toll t 'HMI'N, 

Moisturr plavs an imfortanl role in many cases of oxidation. Its 
pnsrnrr is nrr'i-ssary, for 'example, to effect the spontaneous com- 
bustion of |.\ro|.!iorir in* fals. At ordinary temperatures, also, the 
majonlv of in.-tals an- slalm- in dry oxygen, although readily attacked 
b\ 'thr'miMsl r:is. Small quantifies of many foreign substances are 
raiiablr of ral a'lv t irally assist inu' the rate of oxidation of certain sub- 
st:mcs. Thus /, ! rarr of platinum black introduced into electrolytic 
r-is causes thr !o instantly unite with explosive violence; and 
the passair,. of a mixture of sulphur dioxide and oxygen over platinised 
asbestos effects their union to form sulphur trioxide. 

* U, -war, rh,n. AW,. IS'.Mi, 73, 40 ; Proc. CJiem. Soc., 1895, u, 221. 



Light frequently exerts a considerable influence on the rate of 
oxidation ; l thus phosphorus trichloride when illuminated undergoes 
more rapid conversion into the oxychloride 2 than in the dark ; and iron 
likewise corrodes more rapidly in similar circumstances. Oxidation 
may be catalytically accelerated by radio-active substances. Thus 
thorium-X has been found 3 to assist the oxidation of adrenaline and 

Many metals on being heated in dry air or oxygen yield an adhering 
coat of oxide which tends to protect the underlying metal from attack. 
The rate at which oxidation proceeds at any temperature is given by 
the expression 4 

where a is a constant independent of the temperature ; 6 is a 
constant depending on the temperature and on the delay of film 
thickening during time 6. y is the thickness of the oxide layer. 

The time required for a, visible film of oxide to form on the surface 
of some of the more common metals at 15 C. has been calculated to be 
as follows : 


Time in Years. 

Initial Velocity of 
Thickness of layer ////, 
per second. 





31 X 10 2 


Cop}) or 

GxlO 8 
36 x 10 8 



25 X 1C) 17 



475 xlO 17 


Oxidation processes arc, as a general rule, greatly accelerated by a 
rise in temperature ; the first effect of the application, of heat may be 
merely to initiate a slow oxidation which soon ceases on the removal 
of the source of heat ; but a, .higher temperature may cause so marked an 
increase in the rate of the chemical action that the heat produced 
suffices to maintain the temperature, and the oxidation or combustion 
will proceed unaided. This temperature at which the process of rapid 
combustion becomes independent of external supplies of heat is termed 
the ignition temperature of the substance (see p. 106). Phosphorus 
does not commence rapid combustion until a temperature of 60 C. is 
attained ; hydrogen will combine, albeit excessively slowly, with 
oxygen already at 180 C., but the reaction is not very appreciable 
below 400 C. s and continuous inflammation does not occur until near 

1 See Schevezoff, J. Russ. Pliys. Cham. Soc., 1910, 42, 219. 

2 Besson, Compt. rend., 1895, 121, 125. 

3 Lemay and Jaloustre, Compt. rend., 1922, 174, 171 ; 1921, 173, 916. 

4 Tammann and Koster, Zeitsch. anon/. Chem., 1922, 123, 196. These results apply 
only to dry air, and are not comparable with those for the slow oxidation of metals in 
the presence of water. See p. 55. 


530 C. ; a red-hot glass rod will cause the ignition of carbon disulphide 
vapour, but not of ether vapour. 

By flame is generally understood a, mass ot' gas raised to incan- 
descence. Flame is produced only in those eases of combustion in 
which gases or vapours are present, which become more or less luminous 
or incandescent on account of their high temperature. But a visible 
flame does not always accompany rapid gaseous combustion, a striking 
exception being afforded by the rapid oxidation of hydrogen or coal-gas 
mixed with air on a surface of platinised asbestos or porous firebrick. 
Such combustion is termed surface combustion, and is utilised com- 
mercially in a variety of ways. 

Pressure exerts an important influence upon the rate* of oxidation. 
Thus silicon, ethane, phosphorus, arsenic, and several other substances, 
arc found to oxidise more readily at low oxygen pressures ; on the other 
hand, the rates of the rusting of iron and the oxidation of ferrous sulphate 
solution are accelerated by increase of pressure. 

Active Oxygen. It is possible to prepare an active' form of oxygen 
analogous to active nitrogen by subjecting the dry, ozone-free gas to the 
influence of an electric discharge. It yields a weak, bluish-green after- 
glow, which is less persistent than that of hydrogen. When mixed with 
active nitrogen, this active oxygen yields oxides of nitrogen. Both 
oxygen and ozone are unaffected by active nitrogen. Hence active 
oxygen is different from these, but is capable of existing for only a short 
time. 1 


A few elements yield oxides only with difficulty, and such oxides arc 
frequently unstable at high temperatures. For example, when platinum 
foil or sponge is heated in dry oxygen, the monoxide, FtO, is produced as 
a superficial blackening. At higher temperatures, however, this oxide 
dissociates to metallic platinum and free oxygen. 2 Gold cannot be 
oxidised directly by gaseous oxygen, although several oxides can be 
prepared by decomposition of compounds containing gold atoms in 
their molecules. 3 

Fluorine appears quite incapable of yielding an oxide under any 
conditions. 4 

Types of Oxides. When oxygen combines with an element'., the 
resulting product is termed an oxide. 

The oxides of the various elements show marked differences in their 
chemical behaviour towards water and also towards acids. These 
differences form a convenient basis for the classification of the 

1. Basic Oxides. It is characteristic of the metallic elements that 
each forms at least one oxide which will react with acids producing salts, 
the valency of the metal remaining unaltered. Such oxides are termed 
basic oxides or sometimes merely bases. Some metals yield more 
than one oxide, and it is then generally observed that the oxide richer 
in oxygen possesses a more feebly basic character. In the case of the 
most electro-positive metals, for example the alkali metals, the oxides 
will combine with water, producing soluble hydroxides which are strongly 

1 Koenig and Elod, Ber., 1914, 47, 51C. 2 Sec this scries, Vol. IX., Part I. 

3 See this series, Vol. II. 4 Ruff and Zedner, Ber., 1009, 42, 1037. 


alkaline, and in fact constitute the typical alkalies; the less electro- 
positive the metal, the smaller the tendency of the oxide to combine 
with water, and the greater the tendency of the hydroxide, which can 
then generally be obtained by precipitation methods, to eliminate 
water with formation of the oxide. 

The suggestion has been made l that the hydrates of the metals of 
Groups I. and II. do not contain hydroxyl groups, but are true hydrates 
of the corresponding oxides. In other words, molecules of water are 
assumed to be associated with the metallic oxide in a similar manner to 
the so-called water of crystallisation of salts. Thus sodium hydroxide 
would be written Na 2 O . H 2 O, and not as NaOH. The constitutions 
of the hydroxides of Groups III. and IV. will depend, according to this 
theory, upon the electrochemical conditions under which they are 
produced. Thus A1(OH) 3 and A1 2 O 3 . H 2 0+2H 2 O are both regarded 
as capable of existing. The hydroxides of the metalloids and 11011- 
metals the acidic oxides (see 2 below) are true hydroxides containing 
hydroxyl groups. 

2. Acidic oxides, often termed acid anhydrides, are generally derived 
from the non-metals, but may also be higher oxides of certain of the 
metals. It is characteristic of such oxides that they combine with 
water, producing hydroxides, which are acids. Unlike the basic oxides, an 
acidic oxide rarely adds sufficient water to convert all its oxygen atoms 
into hydroxyl groups, e.g. 

SO 3 ->SO 2 (OH) 2 , N 2 O 5 ->2NO 2 (OH), Mn 2 O 7 ^2MnO 3 (OH). 

It is, however, sometimes possible to prepare organic derivatives of the 
completely hydroxylatcd (often termed " ortho- ") acids ; thus although 
the aqueous solution of carbon dioxide appears to contain no other acid 
than an unstable one of the formula CO(OH) 2 , ethyl ortho-carbonate, 
C(OEt) 4 , is known, corresponding with the hypothetical ortho-carbonic 
acid, C(OH) 4 . 

3. Mixed Oxides. In some cases so-called mixed acidic oxides are 
known which combine with water, producing a mixture of two acids ; 
nitrogen tetroxide is an example of this class, as also is chlorine dioxide - 

N 2 4 +H 2 O=HNO 2 +HNO 3 . 

Some basic oxides behave as mixed oxides, yielding with acids two 
salts derived from the constituent oxides, e.g. magnetic oxide of iron 
yields a ferrous and a ferric salt. A few oxides may be regarded as a 
special class of " mixed " basic oxides or as salts derived from a basic 
and acidic oxide of the metal according to the point of view ; thus red 
lead and lead sesquioxide behave as feeble compounds of lead monoxide 
and lead dioxide (2PbO.PbO 2 ; PbO.PbO 2 ), and chromium dioxide 
(Cr0 2 ) as a compound of chromic oxide with chromic anhydride 
(Cr 2 3 .Cr0 3 ). 

4. There is yet a small class of oxides, the neutral oxides, which do 
not belong to any of the classes before named ; they do not combine 
with water to form acids, nor do they neutralise acids. This class has 
tended steadily to decrease as chemical knowledge has extended. 
Carbon monoxide, nitrous oxide, and nitric oxide were once included 
in this class, but each of these can be obtained by the loss of the elements 

1 Tiemann, Chem. Zeit., 1921, 45, 1125. 


of water from a corresponding acid, so that in a wide sense they might 
be classed with the acidic oxides. Hydrogen peroxide, on account of 
its relationship with the peroxides, can hardly in the strictest sense 
represent a neutral oxide, and the only common oxide which may be 
regarded as representing this class is water ; this must be, in its total 
behaviour, a neutral oxide, because, as the formula H . OH indicates, 
any tendency to acidic properties must be accompanied by an equal 
tendency towards basic properties. 

It is worthy of note that, although the behaviour is by no means 
general, many oxides give indications that they are polymerised, i.e. that 
their simple molecules have combined together in certain numbers to 
form more complex aggregates. Water is a well-recognised example. 
The high melting-points of certain other oxides, e.g. silica and stannic 
oxide, is also attributed by some to this cause. 

5. Amphoteric ovides are capable of functioning either as acidic or as 
basic oxides. Thus tin dioxide, SnO 2 , functions as a basic oxide in 
stannic sulphate, Sn(SO 4 ) 2 , but as an acidic oxide in sodium a stannate, 
Na 2 SnO 3 . Lead dioxide yields the tetrachloride, PbCl 4 , and sodium 
metaplumbate, Na 2 PbO 3 , respectively. Similarly aluminium oxide, 
A1 2 O 3 , yields the trichloride, A1C1 3 , and the aluminate Na 2 Al 2 4 . 

6. Su1)oxide are of frequent occurrence amongst the metals, but are 
less \vell known amongst non-metals. The clement combined with the 
oxygen is admittedly unsaturatcd. Thus when lead is gently heated a 
little below its melting-point, the suboxidc Pb 2 O is 1'ormccl. 1 In the 
case of nickel, 2 three suboxides, Ni 4 O, Ni 3 0, Ni 2 O, have been postulated. 
One of the best known non-metallic suboxides is that of carbon, C 3 O 2 . 

7. Dioxides contain two atoms of oxygen combined with usually one 
atom of the metal. They usually yield up a portion of their combined 
oxygen with relative ease, but arc distinguished from isomeric peroxides 
in that they do not yield hydrogen peroxide on treatment with dilute 
acids. Familiar examples are manganese dioxide, MnO 2 ; lead dioxide, 
PbO 2 ; and nickel dioxide, NiO 2 usually incorrectly referred to as 
Ni 2 O 3 in the literature. 

Marino 3 has directed attention to the fact that sulphur dioxide and 
manganese dioxide react, yielding the dithionate : 

2S0 2 +MnO 2 =MiiS 2 O fl , 

whilst lead dioxide yields a mixture of sulphite and sulphate : 
SO 2 +PbOo=PbSO 3 +0; 

PbSO 3 +H 2 S0 4 =PbS0 4 +II 2 0+SO 2 . 

He therefore suggests that the structural formulae of these oxides are 

Mil/ and Pblf | 
^O X) 


8. Peroxides 4 are frequently isomeric with dioxides, but in acid 

* l See this series, Vol. V. 2 Sec this scries, Vol. IX., Part I. 

3 Marino, Zeitscfi. anorg. Chem,, 1907, 56, 233. 

* See Ta,natar, Ber., 1903, 36, 1893 ; 1914, 47, 87 ; Riesenfeld and Mau, er. } 1911, 44, 
3589; Tubandt and Riedel, ibid., p. 2565 ; Pellini and Meneghini, Zeitsch. anorg. Chem., 
1908, 60, 178 ; Antropoff, J. prakt. Chem., 1908, 77, 273. 


solution react like hydrogen peroxide. Sodium peroxide, Na 2 O 2 , is a 
typical example. The peroxides of divalent metals are usually regarded 
as having a cyclic structure. Thus nickel peroxide, obtained by the 
action of hydrogen peroxide upon the well-cooled hydroxide, Ni(OH) 2 , 
is written as 


Ni< | x . H 2 O. 

Other peroxides are those of manganese and mercury, obtained in an 
analogous manner to the above. Sometimes these oxides are known 
as peroxydates. 


In 1858 Schonbein noticed that when many substances were exposed 
to atmospheric oxidation, the oxidisable material appeared to combine 
with half a molecule of oxygen, leaving the other half in the form of 
hydrogen peroxide or ozone. This is well exemplified by the corrosion 
of many non-ferrous metals, such as lead and zinc. When, lead, mixed 
with mercury, is shaken with dilute sulphuric acid in the presence of 
air or oxygen, lead sulphate is formed, together with some hydrogen 
peroxide. The amount of the latter is readily ascertained by titration 
of a portion of the liquid with permanganate, and the quantity of 
sulphuric acid involved is estimated by titration with alkali. It is then 
found that the amount of peroxide formed is equivalent to that of the 
lead dissolved. Thus 

Pb+H 2 S0 4 +0 2 =PbO . SO 3 +H 2 O 2 , 

half of the oxygen molecule combining with the lead, and half with the 
liberated water. 

Schonbein pointed out that this was capable of explanation on 
Brodie's assumption 1 that the oxygen molecule consists of a positive 
atom united to a negative atom a revival of the Berzelian dualistic 
conception. The positive atom was termed antozone, and the negative 
ozone, so that upon oxidation the resulting oxides were termed anto- 
zonides and ozonides respectively terms that at the present time 
would, if employed, be most confusing. 

In contact with oxygen, therefore, metallic lead would tend to unite 
with the negative or ozone atom, and water with antozone. Thus 

Pb+O : O+H 2 0-PbO+H 2 O 2 

_ _[_ ~ Lead Water 

ozonide. antozonide. 

Such a theory, however, could not long prevail, for there is no direct 
experimental evidence whatever in favour of the assumption that one 
atom of oxygen in the molecule is different from another. This was 
urged by Hoppe-Seyler, 2 who in 1878 suggested that during oxidation of 
a substance one atom from the oxygen molecule is liberated in the 
nascent condition, and is thus free to oxidise any second substance 

1 Brodie, Phil. Trans., 1850, 141, 759 ; 1862, 151, 837 ; 1863, 152, 407 ; Proc. Roy. 
Soc., 1858, 9, 361 ; 1861, u, 44=2 ; J. Chem. Soc., 1852, 9, 194 ; 1855, 7, 304 ; 1863, 16, 
316; 1864, 17, 266, 281. 

2 Hoppe-Seyler, ZeitscJi. physiol. Chem., 1878, 2, 22 ; Ber., 1883, 16, 117. 


that may be present. This theory may be represented schematically 
as follows : 



H 2 0+ : 0=H 2 2 . 

Traube's theory was a considerable advance on both of the fore- 
going views. As the result of a large number of experiments Traube ] 
was led to the conclusion that dry oxygen does not combine with any 
substance at the ordinary temperature. Although this is a sweeping 
assertion to make, as is shown in the sequel (see p. 285), there is a con- 
siderable amount of evidence in favour of its being generally true. 
Such being the case, it seemed reasonable to suppose that the water 
and oxygen must act simultaneously in cases of oxidation, and not in 
series as Hoppe-Seyler's views would require. 

Traube therefore concluded that it is the water molecule that yields 
its oxygen to the metal (or substance) undergoing oxidation, the 
hydrogen thus liberated being simultaneously oxidised by a whole 
molecule of atmospheric oxygen yielding the peroxide. Thus, in 
the case of the lead already referred to, oxidation proceeds as follows : 

Pb+0 = H 2 +O 2 =PbO*+H 2 O 2 . 

The hydrogen peroxide does not accumulate unless the experimental 
conditions are specially arranged for its preservation, since 

Pb+H 2 O 2 -PbO+H 2 0. 

It follows from this theory that hydrogen peroxide is to be regarded 
as a reduction product of the oxygen molecule, and not as an oxidation 
product of the water molecule. Such a conception, though funda- 
mentally different, was not entirely new. Weltzien 2 had already in 
1860 suggested the same idea, and it receives support, Traube points 
out, from the heat liberated when hydrogen peroxide is decomposed. 
For if hydrogen peroxide were produced by the oxidation of water, 
already formed, an absorption of heat would be expected upon 

A modification of Traube's theory was introduced simultaneously 
in 1897 by Bach 3 and by Eiigler and Wild, 4 who laid emphasis on 
Traube's idea that the oxygen molecule combines as a whole, but 
extended its powers of combination to other substances than nascent 
hydrogen. In support of this, it was pointed out that sodium will burn 
on an aluminium plate to the peroxide, Na 2 O 2 , whilst rubidium is 
almost quantitatively converted into the peroxide, RbO 2 , in a similar 
manner. 5 

Probably all of these theories possess an element of truth ; against 
each of them some objection may be raised ; there is yet room for some 
comprehensive explanation which shall remove all difficulties. 

1 Traube, Ser. t 1882, 15, 659, 2325, 2421, 2824 ; 1883, 16, 1201 ; 1885, 18, 1877, 1887. 
* Actually 2PbO . H 2 is formed, but the water of hydration is omitted for simplification. 

2 Weltzien, Annalen, 1860, 115, 121 ; 1866, 138, 129. 

3 Bach, Compt. rend., 1897, 124, 951. 

4 Engler and Wild, Ber., 1897, 30, 1669. 

5 Erdmann and Kothner, Annalen, 1897, 294, 66. 


The solution of gold in potassium cyanide solution in the presence of 
air is believed by Bodlander to proceed as follows : 1 

2Au+4KCN+Oo+2H 2 0=2KAu(CN) 2 +2KOH+HoO 9 ; 
4KCN+H 2 O 2 +2Au=2KAu(CN) 2 +2KOH. " ~ 

The Activation of Oxygen in Slow Oxidation. The spontaneous 
oxidation of a substance at ordinary temperatures is often termed 
autoxidation (see p. 50). It frequently happens that during autoxida- 
tion processes other substances, which may be present and which are 
themselves stable in air, become oxidised. This suggests that a part of 
the oxygen in the system has become specially reactive or activated, 
and the stable substance is said to have been oxidised by induction. 121 
An interesting example is afforded in sodium sulphite which, in solution, 
is slowly oxidised to sulphate. An aqueous solution of sodium arsenite, 
Na 3 AsO 3 , on. the other hand, is stable in air. If, however, the two 
solutions are mixed and shaken in air, both salts undergo oxidation. 
The oxygen is termed the actor ; the sodium sulphite, which induces 
the oxidation of its companion, the inductor ; and the arsenite, which 
accepts oxidation, is the acceptor. The ratio 

Amount of acceptor oxidised T , _ ^ 

_ _i Induction factor. 

Amount of inductor oxidised 

The experiment may be varied by passing a current of air or oxygen 
through a suspension of nickel hydroxide to which small quantities of 
sodium sulphite solution are periodically added. This not only effects 
the oxidation of the sulphite, but also converts the nickel hydroxide 
into black iiickelic oxide, a change which is not producible by oxygen 
only. 3 

Many other examples might be instanced. 

Thus, if a piece of hydrogenised palladium is immersed in a solution 
coloured with indigo, and air or oxygen allowed to bubble through, the 
colouring matter is oxidised, the solution being bleached. In a similar 
manner iodine is liberated from potassium iodide and may undergo 
further oxidation to iodic acid ; even nitrogen gradually undergoes 
conversion into ammonium nitrite 4 ; whilst carbon monoxide is 
partially converted into the dioxide. 5 The last-named reaction is also 
induced by the slow oxidation of moist, yellow phosphorus. 6 

According to Traube's theory, the first-named reaction proceeds as 
follows : 

Na 2 S0 3 +OII 2 +O a =Na 2 SO 4 +H 2 O 2 . 

1 Bodlander, Zeitsch. angew. Chem., 1896, p. 583. See also Watts, Chem. Met. Eng. 9 
1918, 19, 652 ; Crowe, ibid., p. 283. 

2 Ostwald (Keitsch. physikal Ch-em.. 1900, 34, 248) suggested the term coupled reaction ; 
Mellor (Chemical Statics and Dynamics (Longmans, 1904, p. 333)) speaks of sympathetic 
reactions ; the usual term of induced reaction is adopted in this work. 

3 Habor, Zeitsch. physikal. Ghent., 1900, 35, 84. 

1 Hoppe-Seyler, Bar., 1879, 12, 1551; 1883, 16, 1917; 1889, 20, 2215; Zeitsch. 
physiol Chem., 1886, 10, 35. 

5 Baumann, Zeitsch. physiol. Cheni., 1881, 5, 244. 

6 Leeds, Chem. News, 1883, 48, 25 ; Baumann, Ber., 1883, 16, 2146 ; 1884, 17, 283 ; 
Zeitsch. physiol. Chem., 1881, 5, 250 ; W. A. Jones. Amer. Chem. /., 1903, 30, 40 ; Russell, 
Trans. Chem. Soc., 1903, 83, 1263. It was disputed by Remsen and Keiser, Ber., 1884, 17, 
83 ; Amer. Chem. J., 1883, 4, 454. 


This is the primary action, followed immediately by the secondary, 
induced, or sympathetic reaction : 

Na 8 As0 8 +H 2 2 -=Na 3 AsO 4 +H 2 O. 

The explanation offered by Bach and Engler's theory is clearly 

Na 2 SO 8 +0*=Na.,SO 6 ; 
Na 2 SO 6 +Na 3 AsO 8 = fcl Na 2 S6 4 +Na 3 As0 4 . 

From many points of view this latter explanation is the more 
acceptable. It is applicable in many cases of oxidation amongst 
organic compounds. 

The commonest example in all probability is that of turpentine ; 
this by slow oxidation, caused by a stream of air or of oxygen in the 
presence of moisture, is converted into a " peroxidised " product, which 
on account of its oxidising power possesses marked disinfectant pro- 
perties and forms the basis of the Sanitas disinfectants. In some cases 
the primary peroxide product can be isolated in a pure condition ; thus 
benzaldehyde, C 6 H 5 - CHO, readily undergoes atmospheric oxidation to 
benzoic acid, C 6 H 5 .CO 2 H, the primary product probably being per- 
benzole acid, C 6 H 5 CO 3 H, a relatively unstable substance which, on 
account of its tendency to decompose into benzoic acid, is capable of 
oxidising other substances which may be present. In the absence of any 
foreign substance, the perbenzoic acid oxidises a remaining molecule of 
benzaldehyde so that the autoxidation of benzaldehyde may be written 

2C 6 H 5 . CHO-*C 6 H 6 . C0 3 H+C 6 H 5 . CHO-*2C 6 H 5 . CO 2 H. 

Perbenzoic acid has been isolated and its characteristics are in accord 
with the requirements of the above explanation. 1 

There has been discovered in the tissues of animals and plants a 
class of complex organic compounds, termed ferments or enzymes, which 
arc capable of exerting marked catalytic influence on certain chemical 
reactions. Some of these substances are catalytically active towards 
oxidation processes by the atmosphere, and these bodies are frequently 
distinguished by the term oxydases. Oxydases are widely distributed, 
and the discoloration of the freshly-broken surface of some fruit is to be 
referred to atmospheric oxidation induced or aided by an oxydase. 
Alcoholic tincture of guaiacum resin in the presence of an oxydase 
undergoes oxidation by free oxygen with formation of a blue coloration, 
and so provides a convenient reagent for the identification of this type 
of substance. 2 Manganese, and also iron compounds, are frequently 
present in these oxydases, and it appears probable that in some cases 
one of these metals, if not both, actually plays an important part in the 
catalytic process. 3 In some cases, however, compounds of these metals 
are absent, so that in such oxydases the activating effect appears to 
be characteristic of the organic enzyme itself. 4 

These oxydases are not obtainable as pure substances, and it is quite 

1 Baeyer and Villiger, Ber., 1900, 33, 1509. 

2 Bertrand, Bull Soc. chim., 1894, [3], n, 717 ; 1895, 13, 361, 1095 ; 1896, 15, 793. 

3 Bertraiid, ibid., 1897, [3], 17, 619; Villiers, ibid., [3], 17, 675; Dony-Henault 
and others, Bull Acad. roy. Belg., 1907, p. 537 ; 1908, p. 105 ; 1909, p. 342. 

4 Bach, Ber., 1910, 43, 364, 366 ; Arch. Sci. phys. not., 1910, [4], 30, 162. 


tliat, at least in some cases, they consist of a mixture of two 
ids, one capable of producing hydrogen peroxide or some other 
5 and the other capable of imparting activity to the peroxide ; 
r substance may therefore be more strictly termed a peroxydase.^ 
'en also undergoes activation when exposed to ultraviolet radia- 
offect in this case being probably due to the formation of ozone, 
form the element attacks substances which are unattacked by 
oxygen (see p. 51). The radiations from radium 2 and radium 
:>n 3 also appear to effect an activation of oxygen towards such 
es as hydrogen, although the observed activity may not be due 
to the oxygen, inasmuch as hydrogen is itself activated by 
'aviations yielding the unstable tri atomic molecule, H 3 . 4 


.1 a mixture of oxidisable substances is so treated that certain 
nastituents only are oxidised to the more or less complete exclu- 
de remainder, the process is known as selective oxidation. 

of gaseous combustible mixtures, the passage over a catalyst 
ly effects the selective combustion of one constituent. Thus, 
aple, when a mixture of oxygen, hydrogen, carbon monoxide, 
;, and nitrogen is passed over spongy platinum at 177 C. the 
a and carbon monoxide are oxidised, but not the methane. 5 
eormed selective oxidation, and is the basis of Hempel's method 6 
r sing certain gaseous mixtures. The selective oxidation of 
monoxide in excess of hydrogen by passage over catalysts at 

temperatures has been studied by llideal, 7 who shows that the 
: copper (operative at 110 C.) and the oxides of iron and 
11.1 (operative at 250 to 350 C. ) are active in inducing the 
ix of the monoxide, although in no case is the selective oxidation 
3. Thus, for example, when mixtures of carbon monoxide, 
11 ? and oxygen, in the proportions 9, 14, and 77 per cent, respec- 
verc passed through iron oxide catalyst at 220 C., the mean 
r the ratio of monoxide to hydrogen burnt was 

CO/H 2 =4-32, 

the preponderating proportion of hydrogen in the original 

rates of oxidation of the two gases between 100 and 400 C. 
lected with their partial pressures by the following expression : 

dCtfdCs (CO) 

dt I dt ~~ (H 2 )(0 2 )i 

and C 2 are the concentrations of carbon monoxide and hydrogen 

in the original mixture, K being a constant. 

"ation of temperature effects a decrease in the apparent selective 
^Y- of the reaction, more hydrogen in proportion being oxidised. 

la/fc and Bach, Ber., 1903, 36, GOG. 

gert, ibid., 1913, 46, 815 ; Lind, Amer. Gheni. J., 1912, 47, 397 ; Davis and 
JT. Soc. Cham, hid., 1905, 24, 2GG ; Jodssen and Ringer, Ber., 190G, 39, 2093. 
teron and Ramsay, Trans. Cheat. Soc., 1908, 93, 971. 
Lett and Landauer, J. Amer. Chetti. Soc., 1920, 42, 930. 
ry, Annals of Philosophy, 1825, 25, 422. 
apel, Ber., 1879, 2, 1006. 
aal, Analyst, 1919, 44, 89 ; Trans. Ghe-m. Soc., 1919, 115, 993. 


Up to the present, reactions of this type have not been very thoroughly 
studied, 1 but would appear to offer a useful field for fruitful research. 

An interesting case of selective oxidation in solution is given by 
Jones, 2 who has studied the absorption spectrum of a solution of 
uranous bromide in a mixture of water and methyl alcohol. Addition of 
potassium perchlorate effects an alteration, in the absorption, bands in 
such a manner as to show that the portion of the uranous salt combined 
with the methyl alcohol has undergone no change, whilst that united 
with the water has become oxidised. 


Combustion has already been defined in a restricted sense as oxidation 
proceeding with such vigour and the liberation of so much energy, that 
heat and light are emitted. The term combustion is now applied 
broadly to any reactions in which heat and light are evolved, irrespective 
of whether or not oxygen is present. Thus it is correct to speak of the 
combustion of hydrogen in. chlorine, of phosphorus in bromine, or of 
copper in sulphur vapour. But owing to the fact that our atmosphere 
contains large supplies of oxygen, it is evident that by far the greatest 
number of examples of combustion in ordinary occurrence are due to 
oxidation. Combustion implies chemical change ; it does not include 
such purely physical phenomena as occur, for example, when electric 
discharges are passed through Geissler tubes. 

If oxidation is accompanied by the evolution of a small amount of 
heat only, and no light, it is frequently termed slow combustion. 
The term is not altogether an appropriate one, for although in most 
cases the oxidations referred to may be really slow, this is not 
always the case. A familiar example is afforded by nitric oxide, 
which readily combines with oxygen to yield the peroxide. The 
reaction is rapid and exothermic, a marked rise in temperature being 

2 ) = (N 2 4 )+40,500 calories. 

A pretty lecture experiment consists in admitting oxygen to a large 
glass bell jar filled with nitric oxide, and containing the bulb of an air 
thermoscope. As the brown fumes are formed, the thermoscope 
registers a sharp rise in temperature. 

Accepting, however, the extended use of the word " slow " in this 
connection, the reaction may be described as a good example of slow 
combustion. The term slow combustion is usually limited to cases of 
oxidation. Thus, for example, the slaking of lime is accompanied by 
considerable heat evolution : 

[CaO]+Aq.=CaO . Aq. +18,330 'calories. 

Such a reaction, however, is not generally regarded as an example 
of slow combustion. Slow combustion is usually facilitated by the 
presence of a solid phase which may be the combustible substance 
itself as in the case of phosphorus or even an inert substance, such as 

1 See also Bichardt, Zeitsch. anorg. Chem., 1904, 38, 65 ; Lamb, Scabone, and Edgar, 
7. Amer. Chem. Soc., 1922, 44, 738. 

2 Jones and Strong, Amer. Ckem. J., 1911, 45, 36. 



elain, when the combustibles are gaseous only. This is well illus- 
id in the slow combustion of hydrogen, which is dealt with in the 
el. When slow combustion is accompanied by decided luminosity 

termed phosphorescence. The term luminescence includes all 
s of light emission whether purely physical, as in Geissler tubes, or 
lical. But the term phosphorescence is conveniently restricted to 
lical luminosity. It is not an exceptional phenomenon, 1 but an 
mediate stage between typical slow and rapid combustion. The 

known example, of course, is that of phosphorus ; but under 
tble conditions sulphur, arsenic, and many other substances may be 
rved to phosphoresce. The reason why it is so obvious in the case 
liosphorus lies in the fact that its phosphorescent temperature 
% val ranges from 7 to 60 C., and thus includes ordinary atmospheric 
peratures south of the Arctic Circle. At 60 C. phosphorus catches 
or ignites in other words, phosphorescence has culminated in 
i. combustion. 

-lad Europe possessed an Arctic climate with a maximum tempera- 
below 7 C., it is possible that the discovery of the phosphorescence 
>hosphorus might have been long delayed. Upon ignition with 
hted taper the phosphorescent temperature interval would have 
L so rapidly passed that the phenomenon would not ordinarily be 

> hosphorescence, therefore, is a frequent accompaniment of slow 
ation. It does not necessarily imply incomplete combustion. In 
case of sulphur, for example, sulphur dioxide is produced just as 
tpid combustion, but ozone is produced if the temperature is of the 
;r of 200 C. 2 

rhe Slow Combustion of Hydrogen. Owing partly to its 
iliarity, and partly to the ease with which it can be obtained in 
Lghly pure condition, electrolytic gas has been studied by many 
stigators from the point of view of slow combustion. 
"11 1803 Hooke 3 observed that if the gas is allowed to stand for 
e months in the presence of water, the dissolved hydrogen and 
^en enter into combination. This has been confirmed by Marcacci 4 
nore recent years. 

Che presence of colloidal platinum in water in contact with electro- 
5 gas accelerates the reaction, 5 the rate of formation of water being 
>ortional to the concentration. t of the platinum and the pressure 

the rate of solution) of the gases. 6 Many other surfaces also 
ilcrate the reaction. 7 

[t has further been shown 8 that in the course of several months a 
turc of hydrogen and oxygen when moist and exposed to daylight 
vs signs of chemical combination, although the action is inappreciable 
rig the course of an ordinary experiment, 
[f the temperature is raised slightly in contact with certain metals, 

See Smithells, B.A. Reports, 1907, 77, 469 ; Perkin, Trans. Chem. Sac., 1882, 41, 363. 
Block, Compt. rend., 1909, 148, 782. 
Hooke, Nicholson's J., 1803, 5, 228. 
Marcacci, Atti R. Accad. Lincei, 1902, [5], n, i., 324. 
See Paal and Schwarz, J. praU. Ghem., 1916, 93, 106. 
Ernst, Zeitsch. physikal. Chem., 1901, 37, 448. 

Hofrnann and Ebert, Ber., 1916, 49, 2369 ; Paal and Hartmann, J. prakt. Chem., 
, 80, 337. 
Baker, Trans. Chem. Soc., 1902, 81, 400. 





such as platinum, the rate of union of the gases is greatly accelerated. 
Thus, compact platinum acts at 50 C., the gases combining with 
measurable velocity. 1 Finely divided silver acts at 150 C., thin gold 
leaf at 260 C., and even fragments of non-metallic bodies such as 
charcoal, pumice, porcelain, quartz, and glass are active at temperatures 
below 350 C. 2 Angular pieces of glass are found to be more efficient 
than glass balls of equal superficial area. 

Such being the case, it is clear that the walls of a containing vessel 
may exert an enormous influence upon the slow combustion of its gaseous 
contents. This is evidenced by the very varying results obtained for 
the lowest temperatures at which hydrogen and oxygen have been 
observed to unite with measurable velocity when heated in glass vessels. 
Thus, Bone and Wheeler 3 kept electrolytic gas in seven different 
glass bulbs at 350 C. for several days, and found no combination had 
taken place in six of them after one week, although in the case of the 
seventh bulb, in which the glass had become devitrified at one end, 
the presence of water could be detected. At 400 C. no change was 
observable in three bulbs, but after a week one of the bulbs contained 
water, although the other two were apparently unchanged. 

These results clearly indicate the influence of the glass, and it is 
interesting to compare them with those reached by Meyer and Raum, 4 
who obtained evidence of combination at considerably lower tempera- 
tures than the above. Their results were as follow : 


(Meyer and Raum, 1895.) 

Temperature, C. 

Period (days). 




No combination. 



Water detected. 



35 JJ 


Slow combination. 

Clearly the temperature of 400 C. may be regarded as the border-line 
temperature of the slow combustion of electrolytic gas. 

These data, however, are merely qualitative in character. In 1906 
Bone and Wheeler 5 published the results of a very thorough quantitative 
investigation of the reaction at about 450 C. in the presence of several 
different types of catalysers. These were as follow : 

(a) Refractory acidic oxide porcelain. 

(b) A basic refractory maghesite. 

(c) Easily reducible oxides oxides of copper, iron, and nickel. 

(d) Compact metals gold, nickel, platinum, and silver. 

1 Erman, Abhandl Akad. Wiss. Berlin, 1818-1819, p. 368. 

2 Dulong and Thenard, Ann. Chim. Phys., 1823, 23, 440 ; 1823, 24, 380. 

3 Bone and Wheeler, Trans. Chem. Soc., 1902, 81, 535. 

4 Meyer and Raum, Ber., 1895, 28, 2804. See also Briner, J. Chim. pliys., 1912, 
10, 129. 

5 Bone and Wheeler, Phil Trans., 1906, [A], 206, 1. 


The catalyst chosen was packed into a hard glass combustion tube, 
heated to the desired temperature, and the gases, measuring some 
1500 c.c. in tot,o, were continuously circulated throughout the system. 
Any combination to form water was measured by observing the fall in 
pressure. The majority of the experiments were carried out with 
porcelain 1 as catalyst., and it was found that the rate of combination of 
hydrogen and oxygen in electrolytic gas is directly proportional to the 
pressure of the dry gas. 

In other words, the reaction is monomolecular, although, from the 

2H 2 +0 2 =2H 2 

a reaction of the third order is to be expected. 2 By increasing the 
proportion of either the oxygen or the hydrogen above that required 
for the foregoing equation it was found that the rate of the reaction 
was directly proportional to the pressure of the hydrogen. A result 
so opposed to that which might be expected indicates that the reaction 
is indirect and complicated ; this conclusion receives support from the 
further observation that previous exposure to hydrogen appreciably 
enhances the catalytic activity of the porcelain, although chemical 
reduction of the porcelain by this preliminary treatment is out of the 
question. Indeed, if reduction did take place, a prolonged preliminary 
exposure to hydrogen might be expected to enhance the catalytic action. 
But experiment showed that such was not the case. Further, the 
hydrogen could easily be removed again by heating the porcelain to 
redness in a vacuum. A preliminary ignition in oxygen did not appear 
to influence the results. It may therefore be concluded that porous 
porcelain adsorbs both hydrogen and oxygen at rates which depend to 
some extent upon the physical condition and past history of the surface. 
In general, the adsorption of hydrogen is less rapid than that of oxygen, 
but the limit of saturation is higher. Combination between the adsorbed 
gases occurs at a rate either comparable with or somewhat more rapid 
than that with which the film of occluded oxygen is renewed, but at a 
rate considerably higher than that of the adsorption of hydrogen. 

When magnesite a typical basic refractory was used as 
catalyst, the temperature being 430 C., closely similar results were 
obtained. Ferric oxide and nickel oxide showed no reduction during the 
process, but behaved in an analogous manner to the magnesite. Copper 
oxide,* however, exhibited unique behaviour. The rate of formation 
of water was not only slow, but was proportional to the partial pressure, 
not of the hydrogen, but of the oxygen when the proportions of the 
two gases did not correspond to that in electrolytic gas. The authors 
explain this by supposing that the surface of the oxide becomes coated 
with a film of " active " oxygen, which protects it from the reducing 
action of the hydrogen. At low pressures water-vapour is formed 
because the hydrogen succeeds in penetrating the attenuated film. 

Gold was studied at 250 C., and from the fact that its surface 

1 Kaolin is also catalytically reactive. Its influence can be observed at 230 C, 
Joamiis, Compt. rend., 1914, 158, 501. 

2 Bodenstein (Zeitech. physikal. Chem., 1899, 29, 665) believed his experiments proved 
this to be the case. 

3 The influence of copper oxide has been studied also by Joannis, Compt. rend., 1914, 
159, 64. 


remained apparently unchanged throughout, the conclusion was drawn 
that the metal acted through adsorption or occlusion, and not in a 
chemical manner. The surface of silver gauze, however, when employed 
as catalyst, was observed to become frosted over, and its catalytic 
activity greatly increased. It would appear, therefore, that some 
chemical action takes place, such as the formation and subsequent 
decomposition of a hydride. An oxide is ruled out since silver oxides 
are unstable above 350 C. 1 

As is well known, the noble metals arc very powerful catalysts, 
and their activities have been carefully studied. 2 Pre-treatmerit of 
platinum, palladium, or iridium with oxygen greatly enhances their 
effectiveness as regards the catalysis of mixtures of hydrogen and 
oxygen. Pre-treatment with hydrogen produces a similar effect but 
to a less marked extent. 

The Slow Combustion of Gaseous Hydrocarbons. The fact 
that some substances unite with oxygen more readily than others paved 
the way for what may be termed the preferential theory of combustion, 
which was widely accepted during the greater part of last century. 
According to this theory, when a mixture of combustible substances 
is ignited, there is competition between the different elements for the 
oxygen. The same applies even in the case of a pure compound, such as 
a hydrocarbon, for the two constituent elements will compete for the 
oxygen. If the supply of air is limited the " most favoured " element 
will burn first, the remainder oxidising as opportunity serves. 

This theory afforded a very plausible explanation for the luminosity 
of hydrocarbon flames. 3 The hydrogen is to be regarded as the favoured 
element, and thus becomes preferentially oxidised, whilst the less 
favoured carbon is precipitated out into the flame in the white-hot 
condition, and either burns in excess of air at the outward fringe or 
escapes as smoke or soot in the uncombined condition. 

Although, as has already been mentioned (see p. 59), preferential 
combustion may take place in the presence of certain catalysts, the theory 
as applied promiscuously to all cases of combustion leads to many 
difficulties. For example, when methane is exploded with its own 
volume of oxygen that is, a volume insufficient for complete com- 
bustion hydrogen and carbon monoxide are produced as well as water- 
vapour, in accordance with the equation 

CH 4 +0 2 =CO+H 2 0+H 2 . 

Similarly, ethylene yields carbon monoxide and hydrogen : 

C 2 H 4 +0 2 =2CO+2H 2 . 

These facts were known to Dalton, 4 and received support from the 
work of Kersten 5 in 1861, who assumed that when once the hydro- 
carbon has been decomposed by the heat of the flame into hydrogen 
and carbon, the latter is preferentially oxidised to carbon monoxide, 

1 Carnelley and Walker, Trans. Cham. Soc., 1888, 53, 79. 

2 Hofmann and Zipfel, Ber., 1920, 53, [B], 298. 

3 See Dixon, Cantor Lectures, 1884. 

4 Dalton, A New System of Chemical Philosophy, 1808, vol. i. 

5 Kersten, J. prakt. Chem., 1861, 84, 310. 


after which any excess of oxygen distributes itself between this gas and 
the hydrogen. A similar view was apparently held by Misteli. 1 

The question therefore arises as to what factors decide whether or 
not an element shall be more favoured than another. If in the ordinary 
rapid combustion of ethylene, for example, hydrogen is the more 
favoured element, why should carbon be preferentially oxidised in an 
explosion ? To this, a satisfactory reply has not as yet been forthcoming. 

Although the preferential theory has not been disproved, modern 
opinion inclines towards the association theory of Bone and his 
collaborators. According to this, the oxygen of the air first combines 
with the hydrocarbons, forming more or less unstable hydroxylated 
products which ultimately, in a sufficiency of air or oxygen, decompose 
to carbon dioxide and water. 

This theory was arrived at as the result of a series of classical 
researches into the mode of combustion of hydrocarbon gases in oxygen 
in contact with suitable catalysts. 

In the preliminary series of experiments 2 the gases were sealed in 
glass bulbs and maintained at definite temperatures ranging from 325 to 
400 C. for several weeks. As only small volumes of gases (about 
70 c.c.) could be dealt with in this manner, and as, moreover, the 
detection of transient intermediate products was very difficult, the 
final experiments were conducted by continuously circulating the gases 
(some 1200 c.c.) through a combustion tube packed with porcelain, 
and maintained at the desired temperature in a furnace. 3 

A. It was first of all established that the following three reactions 
are incapable of taking place below 400 C. : 

(i) C+H 2 0=CO+H a ; 
(ii) C<X+C = 2CO; 
(in) 2C+O 2 =2CO. 

The reversible reaction 

(iv) CO+H 2 O^CO 2 +H 2 

gave no evidence of proceeding at 325 C. in the direction left to right 
even after a fortnight. At 350 C. some 1-7 per cent, of carbon dioxide 
was produced after ten days, and at 400 C. about the same quantity 
resulted after a week. On the other hand, mixtures of hydrogen and 
carbon dioxide gave no indication of change at 350 C. for a fortnight, 
or at 400 C. for a week. 

Mixtures of fairly dry carbon monoxide and oxygen underwent 
no change between 300 and 400 C. although the moist gases very 
slowly interacted at 325 C. and upwards in the course of a week, 
yielding carbon dioxide. The reaction 

(v) 2CO+O 2 = 2CO 2 

could, therefore, like the preceding ones, have but little effect upon the 
course of the experiments. 

(vi) 2H 2 +O a = 2H 2 O. 

1 Misteli, Ghem. Zentr., 1905, ii., 1075 ; from J. Gasbdeuc/itimg, 1905, 48, 802. Com- 
pare also Tanatar, Zeitsch. physikal Ghem., 1900, 35, 340 ; 1901, 36, 225 ; Bone and 
Cain, Trans. Chem. Soc., 1897, 71, 26 ; Lean and Bone, ibid., 1892, 61, 873. 

2 Bone and Wheeler, Trans. Chem. Soc., 1902, 81, 535. 

3 Bone and Wheeler, ibid. 9 1903, 83, 1074. 

VOL. VII. I I. 5 


This reaction has already been discussed (see p. 61 ). A temperature 
of 400 C. is 'on the border-line where the formation of water may be 
detected in the course of a week. The fact was also established that the 
following pairs of gases have no appreciable mutual action at or below 
400 C., namely : 

CH 4 +C0 2 , CH 4 +H 2 0, and CO+H 2 . 

The elimination of these secondary reactions from the slow com- 
bustion of methane greatly simplifies the problem. 

B. Bone and Wheeler next ascertained that methane combines 
with oxygen between 300 and 400 C. with an enormously greater 
velocity than does hydrogen itself, and in no case were they ever able 
to detect the liberation of free hydrogen or free carbon as an inter- 
mediate or final product. 

Since, if once formed, it would be impossible for them to be oxidised 
away in accordance with equations (ii), (iii), or (vi), their detection 
and isolation would be an easy matter, and hence it may be postulated 
that under normal conditions of slow combustion the methane is not 
first dissociated into its constituent elements. It is equally clear that 
the carbon monoxide and water which were always found when the 
supply of oxygen was insufficient to completely oxidise the methane, 
are two of the primary disintegration products of the partial oxidation 
of the methane molecule at these temperatures, for these are too low for 
reaction (vi) to take place. 

C. An unexpectedly large proportion of carbon dioxide was in- 
variably found in the gases at each stage, but especially towards the end 
of the oxidation. This cannot be explained on the supposition that the 
carbon monoxide first formed is oxidised to the dioxide, for reaction (v) 
takes place with extreme slowness at temperatures below 400 C. It 
would therefore result from the decomposition of some more complex 
oxygenated molecule. 

D. The presence of formaldehyde could be detected as an unstable 
intermediate product during the slow combustion of methane at 450 to 
500 C., and must be regarded as an oxidation product of methane, 
since it was not produced when mixtures of hydrogen and carbon 
monoxide were circulated through the apparatus under analogous 
conditions. 1 Formaldehyde readily decomposes when heated in the 
absence of air or oxygen yielding carbon monoxide and hydrogen ; 
whilst in the presence of air, carbon dioxide and water result. Formal- 
dehyde thus came to be regarded as the initial product of oxidation of 
methane, but upon the suggestion of Armstrong 2 the view was finally 
adopted that methyl alcohol is the first product ; this, however, cannot 
be detected on account of the rapidity with which it oxidised, pre- 
sumably by hydroxylatioii to the hypothetical dihydroxymethane, 
which immediately decomposes to formaldehyde and water. This is 
followed by the formation of formic acid, which is readily detected 
amongst the intermediate products. Further oxidation yields carbonic 
acid, which dissociates into water and carbon dioxide. Thus : 3 

1 Bone and Wheeler, Trans. Chew,. Soc., 1903, 83, 1074 ; Bone and Smith, ibid., 1905, 
87, 910. 

2 Armstrong, ibid., 1903, 83, 1088. 

3 Bone and Druginan, ibid., 1906, 89, 679. 



C . OH >H . C . OH-- >-H . C : 0-- >H . C : 0-- >HO . C : >C0 2 +H 2 

-j-H 2 Formic Carbonic 

H OH Formaldehyde acid - acid - 

ethyl Hypothetical + Steam. 

2ohol. dihydroxy 


.e most interesting features of this scheme is the assumption 
t act of the oxygen atom is to associate itself with the 
ideed, the oxygen atom appears to penetrate within the 
lecule, in much the same way as it is believed to enter the 
Drk in the combustion of solid charcoal (see p. 74). 
)w combustion of ethane, on the other hand, ethyl alcohol 
been detected amongst the oxidation products, 1 and an 
home is suggested 2 to that for methane. Thus : 

CH, OH, . CHO H . CHO 

CH(OH) 2 


H 2 

+ Steam. 

C0+H 2 Formic 
Formaldehyde, acld - 
carbon monoxide, 
and steam. 

->CO(OH) 2 


C0 2 +H 2 

i, methane, and ethylene are also at times to be found 
products of oxidation, without, however, any carbon being 
'heir appearance is believed to be due to the purely thermal 
>n of ethane, formaldehyde, and acetaldehyde. 3 Thus : 

C .jH 6 = C 2 H 4 +H 2 
CH 3 .CHO=CII 4 +CO 

se of ethylene, C 2 H 4 , it was not to be expected that vinyl 
1 be detected as a transient intermediate product ; 4 but 
logy leads to the assumption that the mechanism of the 
tioii is probably as follows : 

[, CHOH 

> II > 2H . CHO > H . COOH > CO(OH), 

[(OH) CHOH Formaldehyde. Formic Carbonic 

nyl Dihydroxy acid - acid - 

oliol. ethylene j. 

(hypothetical). CO,H-H 2 

)hol could not, of course, be experimentally detected among 

lene, the following scheme is suggested : 5 


>(,( > + _>H . COOH >CO(OH) a >C0 2 -fH 2 

C(OH) CO Formic Carbonic 

hetical hydroxy Formaldehyde acid - acid, 

erivatives. -1- Carbon 


no means improbable that the rapid combustion of the 

Jraginan, P-roc. Chem. Soc., 1904, 20, 127 ; Drugman, Trans. Chem. tSoc., 
Reports, 1910, p. 491 ; Bone and Stockings, Tratis. Chem. Soc., 1904, 

Smith, Trans. Chem. Soc., 1905, 87, 910. 
Vheeler, ibid., 1904, 85, 1637. 
Andrew, ibid., 1905, 87, 1232. 


hydrocarbon gases follows similar lines. Evidence on this point, 
however, is difficult to obtain. 

The slow combustion of phosphorus in moist air is an apparent 
exception to the law of mass action, for the rate of oxidation diminishes 
with rise of pressure, becoming practically nil at 500 mm. of oxygen. 
This is really a case of false equilibrium akin to passivity in metals. 
The surface of yellow phosphorus is exceedingly sensitive to the action 
of traces of impurity. The moisture appears to be the primary cause 
of the irregularity referred to, although the -modus operandi is not 
understood. 1 If, on the other hand, freshly distilled phosphorus is 
exposed to the action of air or oxygen dried by passage through sulphuric 
acid, and therefore having a moisture content of the order of 1 mg. 
per 400 litres, 2 the oxidation proceeds at all pressures and is inono- 
molccular above 500 mm. It is accompanied by a very feeble glow 
and the formation of some unknown oxide. 1 Below 500 mm. the 
reaction is accelerated, the glowing is more intense and phosphorus 
pcntoxide is formed. 

On the other hand, if the oxygen is very dry :i the oxidation proceeds 
exceeding!^ slowly, and probably if the system were entirely free from 
water no action would take place at all. Ozone and hydrogen peroxide, 
which are produced during the oxidation of moist phosphorus, 4 do not 
occur in the dry reactions. The slow oxidation of phosphorus in various 
oils has also been studied. 5 

The slow combustion of coal is, on account of its commercial 
importance, a subject of particular interest. Anthracite and anthraeitic 
coals are but little affected by exposure to air, but the majority of 
bituminous coals undergo appreciable oxidation and deterioration. A 
photographic plate is affected by them in the dark in the presence of 
air or oxygen possibly owing to the production of traces of hydrogen 
peroxide.' 6 The rate of oxidation increases with the surface area, and with 
the temperature; if the resulting heat is unable to escape sullieiently 
rapidly the temperature may rise to such a height as to cause spontaneous 
combustion. In coal mines the conditions arc peculiarly favourable to 
this, and the resulting lires are known as gobjirex. The: same dillicnlties 
present themselves in connection with the storage and transport of con Is. 
It was at one time believed that the spontaneous heating of coal was due 
solely to the oxidation of included pyrites or marcasite. Thus : 

FeS 2 +II 2 O - 1 Oo-FcSO,! +ILSO.P 
The researches of several investigators 7 have shown fairly conclusively 

1 Russell, Trans. Chc-tn. 8oc., 1903, 83, 1271. Sec also this scries, Vol. VI. 

3 Morley, Amer. J. tici., 1887, 34, '200. 

3 Dried with phosphorus pentoxidc. Jt then contains a maximum of only 1 m<;. 
H.,0 per 40,000 litres. 

" 4 Schonbein, Pogy. Annakn, 1845, 65, (59 ; Schmidt, -/. pntld. Chun., KSiHi, 98, 414; 
Russell, loc. cit. 

5 Centnerszwer, Ghent. Zeutr., 1010, ii., 1022. 

6 W. J. Russell, Proc. Roy. tfoc., 1908, [B|, 80, 370 ; Sinkinson, Trunx. /S'ofl., 
1920, 117, 1(55. 

7 See particularly Richtcrs, Dinyl. Poly. J., 18158, 190, 398; ISO!), 193, 54, 204; 
1870, 195, 315, 449 ; 1870, 196, 317 ; Fayol, Ball. *S'or. I ml. Minrralc, IS79, 8, iii., 3487 ; 
Lawton, Trans. Lnxl. Min. Ewj. 9 1904, 27, 112; ThrHfall, ,/. Hoc. Ulwm. ///'/., 190!), 
28, 759 ; Second Report of the Royal Commission, on Coal tiapj)licis 9 1904 (Cd. 1991), 2, 
227 ; Lewes, ibid., 232. Bulletin No. 110, Eiiyiiieeriiiy Experimental Station, Uniuvrsity 
of Illinois. - 


that this cannot be the wain cause. Indeed, it is not difficult to 
show, from thermochemical considerations, that if the coal contained 
as much as 2 per cent, of pyrites, 1 and the heat of the foregoing reaction 
were wholly accumulated in the mass of the coal, it would be totally 
inadequate to raise the temperature of the mass to ignition-point. 2 
On the other hand, a straightforward chemical reaction of this type 
is not the only manner in which a substance, such as pyrites, may 
possibly assist in the oxidation of coal. It is well known that iron 
compounds, by virtue of their power of alternate reduction and oxidation, 
frequently exert a marked catalytic action upon reactions of the above- 
mentioned type ; and evidence is not altogether wanting 3 that pyrites 
can and does exert a minor accelerating influence on the oxygen 
absorption of coal. 

Apart from its thermochemical and catalytic activities, it seems 
very probable that pyrites can assist in the oxidation of coal in a purely 
mechanical manner as well, inasmuch as it tends to swell on oxidation 
and thus to increase the mechanical disintegration of the coal, thereby 
exposing larger surfaces to aerial attack. 4 

When air is passed over coal free from occluded gases oxygen, is 
absorbed, water and oxides of carbon being produced. This reaction 
proceeds even at temperatures as low as 25 C. ; 5 indeed, with freshly 
mined coal, oxidation proceeds at the ordinary temperature, although 
in this case it may not be attended with evolution of carbon dioxide. 6 
Up to about 80 C., however, the reaction is relatively slow, and even 
when coal is exposed to oxygen under high pressure the oxidation is 
attended by only relatively small amounts of the oxides of carbon. 7 
At about 80 C. the rate of oxidation undergoes a marked increase, and 
at 120 C. in oxygen and 135 C. in air oxidation proceeds freely. 

Between 140 and 160 C. in oxygen and 200 to 270 C. in air 
oxidation becomes autogenous or self-propcllant, and as soon as this 
point is reached the temperature rises rapidly to the ignitiou-point. 8 

Moisture accelerates the oxidation of coal, but an excess of water 
retards it, partly because it enters the pores and thereby renders it less 
accessible to the atmosphere and partly also because its evaporation 
tends to keep down the temperature. Oxidation proceeds in the 
absence of bacteria. 9 

It has been suggested that, just as in the combustion of carbon and 
the slow combustion of hydrocarbon gases, the first step in the slow 
combustion of coal consists in the formation of an additive compound 
or complex, consisting of oxygen and one or more of the substances 
present in coal. 10 

1 Using the word pyrites in its broadest sense to cover any sulphide of iron. 

2 Bone, Coal and its Scientific Uses (Longmans, 1918), p. 1.50. 

3 Drakeley, Trans. Chem. floe., 1916, 109, "723; 1917, 111, 853. See also Haldanc and 
Mcachem, Trans. lust. Min. Eny., 1898, 16, 491 ; Jeffries, ibid., 1905, 29, 532. Compare 
Harger, ibid., 1913, 44, 318; Dresoher, Chew. Zeituny, 1922, 46, 802. 

4 Lewes, J. Gaslightinff, 1890, 55, 145 ; 1906, 94, 33. 

5 Mahler, CompL rend., 1910, 150, 1521 ; 1910, 151, 645. 

6 Parr and his Co-workers, University of Illinois, Bulletins Nos. 17 (1908) and 46 (1911). 

7 Bone, op. cit., p. 158. 

8 Parr, loc. cit.; also Tideswell and Wheeler, Trans. Chem. Soc., 1920, 117, 794. 

9 Godchot, Oompt. rend., 1920, 171, 32. 

10 Wheeler, Trans. Chem. Soc,, 1918, 113, 945; Tideswell and Wheeler, ibid., 1919, 
115, 895 . criticism by Partington, Chem. News, 1919, 118, 50. 


Surface Combustion. As has been seen, slow combustion of gases 
may be enormously accelerated by contact with catalysing surfaces. 
The rate may be so increased as to cause the evolution of light and 
intense heat,' but without any visible flame. All such phenomena are 
grouped together under the term surface combustion (see p. 52). 

Davy, 'in 181.8, 1 called attention to the fact that a spiral of 
platinum wire, when plunged in a warm condition into a mixture of 
coal gas and air, becomes incandescent and may cause the gases to 
burst into flame. By holding a piece of platinised asbestos, after 
warming in the Bunsen flame, in a stream of coal gas and air, the 
surface of the asbestos glows brightly, but as a rule no flame appears. 
If, however, the asbestos is held over a jet of hydrogen, sufficient heat 
is generated to ignite the gas. 

A pretty lecture experiment consists in suspending a spiral of 
platinum wire in a beaker over some methyl alcohol. The latter is ignited, 
and when the spiral has become warm a card, punctured with small 
holes, is laid over the top of the beaker. This extinguishes the flames, 
but sufficient air enters to allow some of the alcohol to burn on the 
surface of the platinum, which glows at red heat. 

The reaction, when once started, is self-supporting, and may be 
represented as follows : 

(i) CHoOH+0 = HCHO+H 2 O ; 

Methyl "alcohol. Formaldehyde. 

(ii) HCHO-f 0=HCOOH ; 
(iii) HCOOH+O=H 2 O-fC0 2 . 

By suitably adjusting the apparatus formaldehyde may be made the 
most important product, and advantage has been taken of this to 
construct the well-known formaldehyde lamp, 2 in which a, mixture of 
methyl alcohol vapour and air is passed over a warmed platinum wire. 

Finely divided platinum, on account of its enormous surface area, is 
very reactive, 3 and a small quantity introduced into electrolytic gas 
may cause instant explosion. 4 

Surface combustion phenomena are not confined to platinum or 
the noble metals. A warmed iron wire may be raised to incandescence 
by surrounding it with an atmosphere of air and coal gas. 5 

It is now established that : 

1. The property of accelerating gaseous combustion at temperatures 
below ignition point is shared by all substances irrespective of their 
chemical composition. 

2. Whilst at lower temperatures there exist very marked differences 
in the catalysing powers of various solids, at high temperatures these 

At bright incandescence all solids behave alike. 

1 Davy, Phil. Trans., 1817, 107, 77 ; Quart. J. Sci., 1818, 5, 128. 

2 Tollens, Ber., 1895, 28, 261. 

3 Doebereiner, Schweigger* s J., 1823, 34, 91 ; 1823, 38, 321 : 1823, 30, 159 ; 1824, 42, 
60 ; 1831, 63, 465. 

4 Hofmann, Annden, 1868, 145, 357; Ber., 1869, 2, 152 ; 1878, n, 1686; Thomas, 
J. Amer. CJiem. Soc., 1920, 42, 867. 

5 Fletcher, J. Gaslighting, 1887, i, 168. See also Meunier, Compt. rend., 1908, 146, 
539, 757. 


Bone l has applied the phenomena to industrial problems, mixtures 
of coal gas and air being caused to burn on the surface of porous fire- 
brick, generating enormous heat, but with no visible flame. 

Combustion of Solid Carbon. Owing to their importance as 
fuel, carbonaceous materials have for centuries been the subject of 
scientific consideration. For some time prior to the discovery of 
oxygen, carbon or charcoal was regarded as composed mainly of the 
essence of combustibility, and Stahl (c. 1697) considered it to be 
almost pure phlogiston (see p. 11). On this theory, the fact that only 
a certain quantity of charcoal could burn in a limited supply of air 
was readily explained on the assumption that phlogiston could not 
leave a substance unless it had somewhere to go. The air could only 
absorb a definite amount, and when once fully phlogisticated behaved 
like a saturated body and refused to take up any more. 

The discovery of oxygen by Priestley and independently by Scheele 
in the second half of the eighteenth century enabled Lavoisier to offer 
an ..entirely new explanation for the phenomena. The carbon was 
assumed to combine direct with oxygen to form the dioxide 

(i) C+0 2 =C0 2 , 

and the fact that carbon monoxide 2 was found to result in the presence 
of excess charcoal, was accounted for by reduction of the carbon dioxide 

(ii)C0 2 +e=2CO. 

For more than half a century this theory was accepted almost 
without question, 3 but in 1872 Sir Lowthian Bell concluded that the 
theory was inadequate in so far as the combustion of coke in a blast 
furnace was concerned. He suggested that " carbon monoxide and not 
carbon dioxide is the chief, if not the exclusive and immediate, action of 
the hot blast on the fuel." If this view is accepted, carbon dioxide is 
to be regarded as an oxidation product of the monoxide rather than of 
carbon itself, and carbon monoxide as the primary oxidation product 
of carbon instead of a reduction product of the dioxide. Thus : 

(i)2C+O 2 -2CO; 
(ii) 2CO+0 2 =:2CO 2 . 

Bell's theory received unexpected support from the work of C. J. 
Baker 4 some fifteen years later. This investigator studied the effect of 
admission of oxygen to charcoal that had previously been thoroughly 
exhausted of air and moisture by heating to redness in an evacuated 
tube containing phosphorus pentoxide. On admitting dry oxygen to the 
system, adsorption took place, and a temperature of 450 C. was required 
to expel it. It then escaped mainly as carbon monoxide. In the 
presence of moisture carbon dioxide was formed, but the more thoroughly 
free from moisture the substances were, the less the amount of carbon 

1 Bone, J. Roy. Soc. Arts, 1914, 62, 787, 801, 818 ; Coal and its Scientific Uses (Long- 
mans, 1918). 

2 A gas prepared by Lassone in 1776 and mistaken for hydrogen, but later recognised 
as a true oxide of carbon. 

3 As late as 1888 Lang (Zeitsch. physikal Chem., 1888, 2, 161) claimed-to have proved 
that in the combustion of carbon the formation of dioxide precedes that of the monoxide. 
His conclusions, however, were disputed by Dixon (Trans. Chem. Soc., 1899, 75, 630). 

4 C. J. Baker, Trans. Chem. Soc., 1.887, 51, 249. j 


dioxide produced- 1 This, coupled with the* iact proved by Hnker that 
driS caJbon dioxide is reduced by dry enrbon only wit h < ilheulty o the 
monoxide, strongly supports the conclusion that undrr these conditions 
carbon burns directly to the monoxide. . 

Still further support was forthcoming the following year from the 
researches of H. B. Baker, 2 who found that no visible combustion 
occurred when thoroughly dry oxygen 3 was led over highly purified 
su*ar charcoal at bright-red heat. That eombinat ion had taken place, 
however, was clear from the resulting gaseous mixture, namely : 

Oxygen .... 3S-1 prr cent. 
Carbon monoxide . - ^9-5 
Carbon dioxide . . . -*- 

Johnson and M'Intosh 4 found From (5-2 to S-!> per cent, of carbon 
monoxide in the gases evolved during the combustion of a mixture 
of carbon with excess of potassium chlorate, hot h in :iir and in a vacuum. 
As the temperature was only of the order of 1000 "., I he ant hors argue 
that the monoxide could not have resulted from the thermal decom- 
position of the dioxide., so that the monoxide would appear to be the first 
product in the combustion of solid carbon. 

In 1896 Dixon 5 showed that the rate of explosion of cyanogen in 
oxygen reaches a maximum when the gases are in m< >lecuiar proportions. 
Thus : 

C 2 KV| 2 =N tt +2('<>. 

Further, the pressure developed during the explosion is greater, and 
the reaction proceeds more rapidly, than when sufficient oxygen is 
present to convert the carbon into the dioxide. 

It would appear, therefore, that in so far as gasrous earbou is con- 
cerned, carbon monoxide is the initial product. 

For many years chemists appear to have been satisfied with one or 
other of these theories. In 1012 attention was agiiu directed to the 
subject by Rhead and Wheeler, 6 who point out that, if* it could be shown 
that cither the reaction 


proceeds at a temperature at which either 


takes place with inappreciable velocity, a decision between the 
foregoing theories could be arrived at. "Although unable to arrive 

1 In one experiment 98-91 per cent, of CO and only 1-08 por cent, of CO.* \\vri* obtained, 
the substances having been dried for two months over phosphorus pent oxide 

* H. B. Baker, Proc. Roy. Soc., 1888, 45, 1 ; Phil Tram., 1888, 170, | Aj, r71. 
Dried by prolonged exposure to phosphorus pentoxide. 

* Johnson and M'Intosh, Trans. Roy. Soc. Min., 191. % 7, iii., 1 (H. 

O U A Stran e > and Graham, Trans. CJiem. Soc., 1890, 59, 759 ; JHxuu, Mil Vrmis., 
o, Io4 97. 

6 Rhead and Wheeler, Trans. Chem. Ror., 1912, 101, RHi. 

TKK CHKMK'M* l*i:o!M')I!TM'S OF oKYURN ;:i 

complete solution of the problem in this simple inanm r, llh* j! jmi 
Wheeler succeeded in shotting th;if 

1. Some carbon monoxide is pt'odtte* d dun ni > t he ositiat ma it' e.rhua 
at low temperatures, under conditions f hat do not admit tf!h nduetina 
of carbon dioxide by carbon. 

ti. Carbon dioxide is produced a! luu h'lapi r.thm s sn |ii,nilif M -, 
that cannot he rnttreh aeentuitid tor uit flit- as^umphiMi tint tin 
monoxide is first formed and suisrjurnt!\ oxidi^d, 

The conclusion appears inrvitahlr that luH tit* 1 uiuui>\}h am! fit* 
dioxide are produeec! ,v////i///ai//v*/i,v/i/ In nthrr \\unls, ajthr '.j.r- i 
the 'primary product of oxitlation in that it takrs jn ri <I* ur nvr tin 
other. The two |>re\ioUs th '' ' 

correct, each as far as it jjors, Th* <|ii ',hot mat ,iir<* -, ;, t f h* unfair 
of the reaction between earboa auJ o\\ii, and thr. w .r* dnitv,/il ),v 
Rhead and Wheeler the I'ollmuu*' \f>ir. tl ua- iottini l| M | ^iMirn.i! 
that had been heated to !C*II (\ ut an i \anu!i| i.--, > I ,u*| aliu,^,| f' M 
cool, readily adsorbs oxy^ea at all Itiw.-r ti inp* r*itur,, %, t!i- ,", ! 
adsorption being very rapid duna^ tb* lir%t !- MI-OIM!-,', ( sii f i \%hM'h 
the velocity gradually slim*, dowa, but mulum* * Inr VIMM! hnur. 
(see lig. 8), The total amoua! of ueelad* d \\ *, n j^rr* tt ,, . Wl ||, j 4 || M j* 
tempera l;ur<% and is appro\bit;d l\ cuas^Mit lor mn ,'Uf a h inn. r'tti 
for the particular speemn-a of rh;uv* M i uu,!iV ubMfu/l?HtV 'VhJ, 
oxygen cannot beremo\ed h\ , \hiHHt n ,,i ,tfuae r hn! *mh h\ HUT. t H,.* 
the temperature <f the earitoa ihmnj* i vhuustitin 'Wlirji mu4 h* 
released in this manner it appnax m.t a- \v f /rji ( ! m i a % r^rlnm tli^vidi 
JUKI carbon monoxide, Thr pr.|urfiun, m wbieh n tl| ,, lf . ;>r . 4 , f | 4 ,., 4r 

1 JUwNul anil W!rrl i. /'/.i*;, M, .. v, 

74 OXY(,'KX. 

two oxides when completely* removed depend on the I einp< -rat in 1 *' at 
which the carbon has been heated during ox\;.:vn tixahon. 

If, for example, the temperature is raistd. \a\ from ,'loo to .'i.~o I .. 
oxygen is evolved in vaeiio, correspoiuim'> to fli amount \B m ii^. s 
as a mixture of monoxide and dioxide until ! he sat uration limit ol t h. 
charcoal al I his higher temperature has hern reached, and I h n eras*--.. 

The authors surest Ilia! this is more tiian a pun l\ physical 
" fixation *" of oxv<.vu, bein^ 1 in all prohabilil \ I he iu{ . et.nn n!' a ph\ Mm 
chemical attraction bet \\Tcn oxygen an<! cat')>on. Vh\ Meal, inasiuiii-lj 
as it seems hardly possible io assign any delinifr ninl* enlar htrumla in 
the complex Conned, which, indeed, sho\\s pri, r r-ssi\ \arialion nt 
composition; chemical, in lhal no isolation of the eompit \ ean 1. 
ciT< i cit k d by |)hysica! means. 

H would appear, 1 hereiore, thai the lirst prudnet of etsi 
carbon is a loosely formed physico-chemical etnip!t\, \s 
regarded as an uuslable compotniii of carln and OXV-M 
present unknown compost! ion, C,U,,. If is prolalIi 
formula can be assigned to (his ctnnp|e\. 

Stated mainly in 1 he words of t he anf hop, I IM ns% h ,, ! It.- c^ne, pi UMI 
of what takes place during the etunbnsl ion of e.irhun -, lij' l!\ . .1-, 
follows : each oxygen m<le< ule that coni'-s into e,.!JiMtn ujth f h e.ul'oss 
becomes " lixcd/" in so far as it is render* d inr.jpahl, nflmfhr r prtfr* .-. 
by the attraction of several carbon mnleetil.-s, Thrn . a, \t\ tn 
absolute knowledge of the number of atoms contain* d in the earboit 
molecule. The formation of beii/enrhr\aearbo\\ he aejd t iiirihtn- m-id 
by the oxidation of either amorphous carbon or "rapluh , u.m.snt-. I h 
assnm]>lion that the carbon molecule contains nut |rur titan f^-h* 
atoms, 1 and may be even more complex,- ft p, rosii-, -i\ all- , tb i-. ii-. , 
1. lie authors point onL that in the oxidation o! i\trhon tin n\\^,i- 
molecule actually t'Hlcrx the carbon molecule, a rearran-', iy. | } f M | ..tmu-, 
taking ))lace. However, ftr the j>resent if is Million nf ti.a-.suht.- thai 
si'vcral carbon molecules hold one u\\ !; rn ml.-eul.-, m bnd a. it f n 
and (to not allow it to escape in conjunction \\i\\\ one o! tin n .ttmn ., \ 
considerable evolution of heat takes place dunnv this at ! aehnn nl ol 
oxygen molecules, so much so that sitne of them \rntu;dl\ ar.{ujr 
suflicient. energy to seize hold of a carbon atom ami d par! \\ilh \! .r. 
carbon dioxide. Some of them become torn apart m th- pnu-i -.-, 
became atomised and lea\c I he <Mrlnn ntolec-ulr a% carbon m,,n4M,|* . 

This format iou of a complex, and partial dfrnipo%itini .r. 
oxygen molecules lun'onu' attached, nr -s on unld fin rarhon l r 
"" saturated/' the pnxlucls of combustion dunmr tlie. j nt.l 1.1 oiu 
})arat;ivcly short one) IH-JU^ (^..o^ ('(), mid CO, ' \ff, r n,, r ar u, M | lt . ( 
become salurati-d there is an aitenmtr" format inn and .1. eom|,,,.,itn,i i t | 
the complex. Kach oxy^t-u inolec-ulr that inipms^rs n the r.irhuu r 1.1 
once seized hold of to form the complex, but f hr .-nnvx v t ir,-,- '|i.'u 
this occurs decomposes an rcpuvalcn! jnpurltin of tJir'rinnni, y iuin ,,{ 
Irom previous oxy^-n moleculc-s, So that, linaliy, when air is ,, ,-.,-! 
over saturated carbon nniintained at a crjnstanf" mv U fj lr . 

* .D'\var\ (! linn. Xtn\^ HiuK, 97, HI 

~ Aschaii, Chan, 7.n\.^ liHHl, *^ ;r,I >,-,. ,!..,, tv.i-.j . . // * p. 

' '"'"' 1 " 1 

apphcat ion of an external source of lira!, carbon dioxide and carbon 
monoxide appear in tin" products ol' combust ton in volume sufficient 
t o at TOII n I i t r I h' b it al v ohint' of o\ \ ".< n in I in air ri M .mally passed. 

In thi- normal linnna". ot carbon. ! In n fore, tin- carbon tiiovitli* and 
carbon monoxide iom.u! a r -. !:! appaivnllv prunarv product-, ot com 
bust n n, an->e fn m the < lecom posit ion, at tin- It mperal nr of c< imhiisl ton, 
ol' a c< Hupl* -X fii- formal ion ol' w hid* is i In lirsl iv-ajlt of I In- n count efs 
between oxven and carbon molecule-,. 

The idea of " ox\''' ttalion of fin combustible as a preliminary to 
definite chemic.d r action i . not \Mtiioiit prc'cli-nt . 

Indeed, it r*<"i\)*" 9 *.t roa^ suppuft from the \\rl\ of Hone on the 
combustion of hsdrocarbon <;ast > (sec pp. <."> <1J j, Although lutl 
(Idinitcly pro\ed, this atlrae!r\r th-oi'\ is c<-rtainl\ a most Mt ( j'!,*'est \\ e 
one; it not >nl\ Jit . in s\c!l with kisn\\n lads, but is in harmony with 
t he \ arious point ni" i( d in fa \ our ol' each < >!' f he two e.irht r t h cones. 

Cnni imxitinit / ?i*f ( '"it 1 /*lt' r t \n attempt \\as niadi' to determine 
tin e|Uantil\ oi* c,\"i n adsorbed b\ a sampli 1 of charcoal at ."iUU t*. 
The result Htdicatfd an .nl-.orpt ion of (Ht ."ram <!' <\\t'i-n 1\ I* ''rams 
of carbon, corn spondni" to a I'nrmnl.i n\ ( j,,,,t ). This, !' c<nirvc, >ul\' 
refers to Hte bntperatmv chseu, naiueh , :;iu ('. The' rdalnc pro- 
}oi*t ion . of carbon dto\id and mon* *\n ie -\ >j \ d n raj sin"; t he t ?. 'jupera 
t ui'e o! sat urat ed chares a I \\ ej-e fntmii to \ arv with 1 he nut jal t emperaHir\ 
so t hat it appear-* impossible I o d< I * rmine t he \ aim - for * and // froni I he 
a\ atlable daf a. 

As nieiit t<nted aho\e, hi\\e\i-r, HaUcr has shown thai carlnHi <lio\idc, 
u lien t horoudil\ dn t i b\ prolonged cot jf act with pin splunis p n! o\id<\ 
is not {-educed by c.irhon e\u at bnht red InaL On t he <>! her hand, 
Hln ;nl am! \\lndM' halt shown that tin comjle\ ('..<). is read : il\ 
formed Jrm it''- dr\ enu-J it in nl s. 'I'hes*- l\\t> observations sn*'M'st 
a mdhoil bv m aits ol which the ratio - ?/ mi"ht be tii%co\ rre|, if not 
evactls at an\ raf* approxima t e| \ , J-'or b\ exposing; thonii"hi\ d.ry 
charcoal whh'h has In en ivhaustid at, sa\ , 1 ItHI (' . to t horotp'hly ilry 
o\\ "en a! a low er i i mpr rat lire, t he coin pit \ t ,. O., should be obi ained m 
an eiinaiU di'\ eintht itn, <h rajsni! ( lh - leiaprra! ure am! pumping 
off t he I uo o\ hi* s !' ear hon, t he si- should In- obtain '! in t hi- proporf ions 
in w hi eh t he at tins ol ox \ "en anil carbon a iv t ijsl nbut ei| m t be ctiuplr-\, 
inasmui'h as none ot fin carbon dm\nh om'c proihii'eo! in I hi*-* ua\ 
can be rednceii to uu*nxidt (itinit" the >xpirim<nt, as unlonbtedl\ 
tH'ctirs in fin fas*- ot tin moist MS s. 

( )ni\ t \\o series of i \p nnieu! , ha v e be n <MITH 1 1 nt w it h t his tbjed 
in \ i u , f hi- ri suit s beiss" inrn'hisi\ * , l 

Ft V M J . 

Flame has ahvad\ breii defun d as a mass ot" J.NIS raiseil to mean- 
de\rence. It will be obsn*d tJta! this ddiiiilion does not limit llanie 
to such pheft<*m< n.i its ajv allendaiil tipon combusl son ; it simply 
p-ostulatis tin- exr.trno ol" \:iptiir ir ^as, \\hd%t llames may and 
oiieii iln t \ist iiudi r eondifioiis rVflutlin;.^ all tvpes of rolutittst ion, as 
lor example iitnn;' the elect ti* 1 di%cl,tai'f*e\ thi*ou?<h rarriied f;isrs t in the 
ntajorif\ ol' casts ilanscs are \\n- j-j stilt of rapid o\idattnn, 

J l:h.-fcl uii.I \\hri !, fS'ir, ,, t / ; i.?;, ,V.r., PtM, |ri| a U'ltt; I! IF F'\UV Jtl*l Htilfff, 


ii. j MS l,>u- UM-U known that eirtajn il.inii -. are 
Cool flames. } |- xt ,| v | uu trmprratur*---. Tim-*, a erntur> 

capable of e ^*^ a'imt platiniun win- ua, mtrodue.-d into 

ago, Davy > ^ U)ulir a nd air, not onU lul fit- win- U rom<' r* d hot 
a mixtllie ( /J v . /k oirf'ier eoiuhustiou. but a pal- piuMilmn srml 

m consequent, o m is ,,, r l,,,,!,,K !,, th, l.,.l,r 

light could bo (ldt ' <U | d ( ;^;; S nm ,, ll u ,, v ' 1 ,, tl , iur ,,,| n, ., ; !.u-k ,,. 
ili<- s-iine phenoim-non, and uh-ntioiird that w h n 

cool to set fire to v,,, ,.,-,.,,, iwn i *i 

this phenomenon may be exhiint.d a I, rtiuv, Hi th.-s, . ,,, rh.i,,. , 
best is to heat an iron or copper liallto dull r, dn, ss ;dlo it in ,,,M| !,, 
such a temperature that it is just nivsdi.- m the dark, and, l.> ni- ans <, 
a wire, suspend it over a dish eoniaimn- sexerai hi . r pa.p, ly^turahd 
with ether. u As the ball approaeh, -s th- eth, r, a l,-:mtihd Han, 
will form, passing over its heated snrtae,- upuard% r v-\-ral m.-lt, ,. 
The ball may h( k let right down into fhe * th. r without IMUMUV onhiurv 


The blue (lame is rharaeterist-d ly it-, \\\ t.-mp. ratur. . H-- 
fingcrs may be placed in it without .iisemut'ort ; pap. r i. not t-liarn d 
bylt, and even carbon disulphide '^ not i<mh tl b\ it. 

In studying the limits of llame propa:^ation both in eth-r air an.! in 
acetaldehyde-aii: mixluirs. White- uliserxed that, upon i"nittou utfb a 
hot platinum spiral at the bottom of a \ertie.-d -la-, . tub*, "a ra i.t 
glowing gas often seemed to extend np\sanls Trtnn flu -.piral toi am 
distance up to SO em. The ra\ oi'tcn rrinainrd in I his po-,ih..u h*r inam 
seconds beJ'ore the top opened into a 'eonl' llaun trai.llni- up f h< 
tube." The cool (lame \vas found to rradti\ \ieldth* irdtnair\ ISM! il.iim-, 
particularly in th( k ease of aeetahleh) d , Thr author point-. tuf thai 
the existence of this type of eoo! Ham*' ma\ srr\e- to explain -.omr l 
the hitherto inexplicable explosions with eoiulustdl- \apoui .. < h, ! 
occavS'ion he was att-cniptin;' to <ieiuonst rat- m t h U'-aiai VK<\ m *i.n- 
light the (low of hea\"y ether \apour doun an oprn \\nini ';uMr 
4 metres long, the vapour heinjr o.|*tata-d from a, \pon,"- ^d 
with li(]iiid ether and held jus! abo\- th- top ni' flu "iitf>r Tin 
inclination of the gutter was 1 in I. After a tnnr tb alh mpf f s:*ml 
the ether-air mixture at the bottom of th- "iitt*-r b\ mr;ni% <[ ,\ t.tpi-r 
was apparently nnsueeessfui, although the ehuraeteristie -odour o! ih- 
so-called lampic acid was readih drfretabl-, \ IV w -eond-. hitii. 
however, the sponge burst into ilante. It would upprar, th?'iTtirr, that 
a cool flame, practically invisible in t h* d:i\ h;.'ht and unol. rud In fh* 
experimenters, had travelled up the r.ruttrr ;snd MNMI rr.r- toirdin:ir\ 
combustion a.t the top. 

The Hydrogen Flame, 

The hydrogen flame is a simple onr to study, for no solids an- juw nt 
either in the pure gas, in pun* air, or in any oHiie prodt$et%o|" enuibustioii. 

1 Perkin, Tram. On-ni. *S<*., !KSi\ 41 :u;;i s, r H!-.. l-i--h* <n f /*/ *!'.- J T * i r - 
1914, 18, 619. - . . .., 

2 White, Tram, Chan. SV. l'J:!;J ( i.i t | fl .>f 



AVheu first ignited, a jet of hydrogen issuing from a t^lass tube yields a 
colourless and almost invisible Ilame; hut as the *lnss becomes warm 
the tlanie acquires a yellow tint in consequence of sodium present in the 
i;lass. By employing a platinum noy./le the ilame is rendered colourless 
and practically invisible. It consists of two portions, namely, an inner 
/one initially of pure ijas % which rises in temperature and gradually 
becomes admixed with air as it passes towards the outer /one where 
combust ion is complete. 

It would appear 1 that the combustion of hydrogen between <>()()' 
and 1000 ('. proceeds in such a manner that ludrou'cn peroxide is 
formed in considerable quantity, but rapidly decomposes into water 
and nascent oxv*'cu. Sonic of the oxv^en atoms unite to form 
o/,ouc, which decomposes less rapidly than the peroxide. Kor this 
reason, under suitable conditions, both hydrogen peroxide and o/onc 
may be detected in the products. The temperat ure of ! he oxvhydro^en 
ilame has been det ermined as 1\ in,' bet v\ ecu l!200 and 2."iOO ('. accordinL f 
to the proportion of oxygen.- 

The dandle Flame. ;l 

The so-called wax ** of a candle is a solid fuel, v\ilh carbon and 
hvdro^cn as combustible roust it uent s. \\hen once the candle has been 
lighted, and equilibrium has established ilsrlf, the 
wax at the foot of the uiek melts by the heat 
radiated from tin tlanie, and ascends the v\iek 
by capillarv attraction. Arrived in the {lame, it 
vaporises with partial decomposition, \ leldmj* a 
combust i ble gaseous mass, apparent to t he- out side 
observer as a ntttt'liiinintttts in net' ,-jun\' i By in 
srrtinj* a short, narrow tflass tube into that pot 
tion of the {lame, the supply may be lapped, and 
the vapours ignited at the free end of the tube, 
As the vapours ascend She cone, slow combustion 
bei'uis and adinixt mv wit h a lit i le air takes place/' 
At the apex of tins cone enmbustion begins to be 
vigorous, for air has now diffused towards it, and 
the- t cUipcrat uiv rises towaids 1000 (', Above 
t his apex, and Ionium..? also a t htn mant le all round 
the lower |Hrt ions of t hi- cone, is a brightly ttttnin 
tniff iihintli'. In this region partial comiHislion is 
takinif place and the temperature ranges J'roju 

100O tc I.iOO ('. As the jjasrs How towards t he out rr \nrfaeeof this 
m;ustle they meet 1'rrsh supplies of air to enable complete combust ion 
to ensue. This takes place tti \\hal is termed the nun Intninnnx tinier 
itninttt't mitl it is in this n^iou that the tlaiur is hottest. Here, too, the 
bent \\i<'k, already charred,, projects its end, which heroines completely 

thiU'i H\ th' iint'l^l " .S'ylrji Syh tiffin, fr tt \tttttftlfi Ilt. 
ih vl. p. Ul. Qii,lr! by SHthrII;n /f. fit. 

" Hiltfunl, ,tmi/*, 1^*1, 9**, Utl ; i*iiiilt, J'nj' 

Hl,.*, 01. 'JI7. 

isi'jr \ {<i>|"iif ly I vv'arl.i llti- 
.-i^fi/ } 7*' n t'*ntuni'<i J*M'tfU, 

. Annul* n, ls*!i. yy. IlSll. 


oxidised so that the services of simfHm.Hnn.fs an- n,. Urvr in demand. 
Just beneath the wiek lies a small M/r- :,'*/< u!n<h .-., ...<il> .-- .iis 
thicniished but is t>f relative unimportance. Vir r .1:1 ; np . u- .u,M.i.- 
of the candle keeps f he walls of wax cool and ihu-, pr. s M! , ..ulf.-nii - 

Cause of Luminosity. In ixi:, l)a\y ! ,n-.,.sf,,l n...i th. Imnm- 
osity of a candle iianie is due to I lie pn-senc, m mmn!.,, ,n 
carbon at white heat. These particles "<T.- I., h. x l I" ', ,t is 
incomplete combustion of the Imiro.-arhon \.' - ti..- r--.fnete,l 
supplies of air available within I he llame, !> ln-ir." 'i <>l the ...q.Mur, 
beino' kt preferentially "oxidised (set- p. (il , II.-MM tin ' buj t N --liiit 
for itsc-ir. This theory \\as ,uvuerall\ ,iee,p! lt i i.n in ,M\ \ ; .r ,, .<nd i^ 
\vas not until ISO?' thai a mal theur\ \v,t , p-,,, il d n 1 iMnU.m.l, ! 
aiTonlin^ to which the luminosity of I he ilnn. " r. !H. tit r.idi;it n.n . 
[Voni tlense but transparent h\time,irbun \apmir-.. 

The relative merits and ilnwrits <f tlu-sr tli-n. > iu,i\ iiii.-.i .il\.jn 
ta^eonsly be. consulcn-tl by re\ie\uit"; ;i t'-' ' 
phvsieo-eheinieal phcnonu'iin <t' Iianie, 

*I. Tlie deposition of soot upon a fold 

candle llaine is a familiar obstacle to !h' ;d.pti"n !' tin. fh. r^.-i-.r 
convenient method of heating small iMdi--.. 'i'ii- d. p .if IM-J .erii! , 
only when the objeet is heated in the iwianu. .n-i., Ui- u! - r n>n 
lumiiious mautle in general \ieliltjt'.*- nusunl, Tin. ^.i . .td; .in--- d .1 , ...:* 
ar^'nmeut in favour of the existence of earnnn. p.srfiel. , in fit- i!,i!u.- . 
AVhilst this is exactly what nii.ifbt !" i \peel.-.l in -.ueb eirrsnaJ *.!ie, ,, 
it M'ould also result upon (he decomposition (| 1 d- n ^ h\ drm MI -bnii , 
under like treat ment . Ilmce this - p.-rnneut .don- i * in h.n isi : - 1 . e,,;;, 
both t heories, and does not enable a di-,f met ion I 1 m *d . 

li. The pr( v ferent ial theory of einlm-.t ion j. it! nn. f . r-'.iid d 
correct, having jjivcn place to the more >~.;il r,l,ie!ur\ .e, su *lr i-\, 
of Hone (see p. (>5), Hut \\hilsl I);i\\'-, tbtrv l I!UU A JJ" .1! > I'MI. 
loses a certain amount of support, it jve*nt i . -.iippm-i iniu "*U'r 
direct-ions. Thus it is well kmmu that thf hi'di- r h\dre,ij-iiMn . .11- .ui- 
to undergo decomposition at hii^'h temper.rhire",. In t: | ( |,i.f Me. 
this is termed k% cracking.' and it is quite eunevt\ ,iil. jh.. j .uidn^iej, 
reactions mi^ht occur in a candle llauie, 

iJ. \Yhen an intense beam t>f lt?,hf i*. pro]ei't-ol in ^ .? iLtju- 
the beam is both bent from its original dire!iun ,ini pti.irr. d. I 1 /.. 
other words, the llame behaves ,-is tinnu it < n- .1 tnriud ui diuiu, lii tt 
is, one containing minute particles, tenuI Ui->, pii,.t ,, , iln.iine; 
about in a continuous phase. 

If the diameters of thi- dispose p;u-l tries, \uppn 1 , > d .phfri > .i \i, 
bctwecu the limits of I and loo/i/<. f/i/i lo ll mm,? fh-!j-i , .u. * ! 
colloid dimensions, and the llame is eofloid.d. If r, leriu* d ,v .-./.ifr. /$.,,' .-/, 
but not a .v/f/Wrdispersoiil system by \ on NS'ejiu.inu* In .t J.ih!*- -,\ ,! m 
the particles would not, eltan^e, uberea.s in a ilune th> con'-.Kin(U 
disappear and arc as frequently renewed, 

1 See Davy, 7V///, VV//A-., I si 7, i 77. 

2 Sirci .Krnnkiand, /'/v*. ////. ,N'M-,, Lstis, id, !!* ; s^f.-/,. - ?> ..... ?". /,-.'' ' -.-. '. v - ; ; 
Frunkltuut (Spottiswoutlr, IlMrj}, pp. ^;j| ;,;,,i ; /,.,,,,! . /* -' /; ...;//', | ; ...,.,..-,?. i 
(L(tndon, IS77), p. IHMi. 

:t St'ilfllrbrn luul lJ('!H k flirt, l\nll'n<t Znt ..7,., t'.IJfi, ;(>, M; ,f ,j , ', . |vtj 

64, H>7. 

l von Wciuiam, .!.//. <>;/ mim* Huntl, l!Jl'.i j,, ji.irf ,\ .. 


Whilst, however, t iiis result cleaily indicates the diphasic character 
of the luminous /one; it does not indicate the nature of the disperse 
phase. Hence it does not enable a decision to be made between Davy's 
theory and that of Frankland. 

I. Similar!) , indecisive results an 4 obtained hx the spcct roscopic 
study of t he luminous /one. A continuous band of colour is observed, 
and this \\ould result whether the luminous particles were solids or 
dense hydrocarbon vapours. As is mentioned later i.see p. HI), even 
the tlame of hydrogen burning in oxvu'eu under hi'h pressures yields 
a continuous spectrum, and in this ease thr possibihtx of .solid particles 

beilljLf present is entirely rtllrd nut. 

.">. Thr luminosilv of a Maine can be jjiv.dlx increased bx the mtro 
duetion of solid particles x\hicli becmnr mea ndescent , l and the rapid 
combust ion of such substances as luxe non volatile solid oxidation 
products is usualh accompauii d b\ brilliant hmunnsits. A familiar 
example is the combustion of metallic ma?.j,nr-,ium. Iul h\dnLjen 
burns in oxygen under pressure \\ith hudi Iumun->it\, so thai solids are 
not essential to the phenomenon. 

From the' fol*e**om", it Will be eXld'lit thai a decision bet\\eell till 1 

theories of l)av\ and FranKland cannot br -a-,iU arnxrd at. Indeed, 
it is by no means impossible that both theories are correct m so far as 
tliey t*o. The ont\ l'\ altv certain {Vat lire Is that flu*' luminous /.one Is 

(loal-as Flame. 

The eual 'fas tlaiih is praelicalK a n plica n| the r.titdh tlanie, for 
if ma\ be dix tded into thne analogous /one 1 ., and ! he phenomena 
attendant upon its linnmo-afv are clo-,-l\ similar to those already 

F.xauunation f the p-efrum of lUumui.ii in", "MS Irads to I he con- 
elusion thai two superimposed UVet -, must be ciiusiiered.' 1 Firstly* 
I here' is t ft* eoitt juuotls tetnpTaf lire sp ct ruin, c,uis'ti b\ t he Uicaiuit^ccnt 
particles lloatUi'*; m the flam*-, and sei'euiit\, . baue! spectrum caused 
possibK b\ thr luminous [tartieli-s in thr act oi hlil'iuii! 1 , ill the olttil 
mant lr e>f t lit- tlame, nr perhaps b\ t hi ir pr iduet s uf ctimbu\1 ion. 

It air is .iduuttcd into the heart of the flauu m utlicient tjuautity, 
the luiiiiiiosit v ' siidilrulv i lisa pp-;M's almost entinK, and a llauic 
resembiui!' that of pure hsdro',n results. Owm?> to I he rapid com 
htistnMi of f he h\ droeariiotis, IH> luummiis jiarticles ar .separaird, and 

the tlanir, belli'* JUti lis 1\ imi , is a eojt\em Ul tUe to einplnV for heatillfj 
purposes, since if \ |i Ids uti %ouf \\lnii made^ to ttupm'e upon a cold 
obfecf. This i. Ih* pruicipl*' of th' Hunseii biuni'i', tiie llann of which 
consists of tuo parts i*u!\ , both ol vxhtch are umi luminous, The inner 

1 A }i,r< li ,ii .i|.ili-.ifj- -ji ! Hu'. '!!<-,? i. ..-n in \] t , ..irijnus im ml i-iil ns.tiiHr 
.-.uij.Mn.-tl ! .. 9j !r ,4' ili-iHSMi in.i iiiuiit !'.. .in .1.-.. ..iif ! i\.,- hr.l"i> *I l!t- KM ,m- 

lli-^l'Ut lU.Ulllf. - il:''!i-i, />: I ' M .-f^'i I.':/'. -e>- f ,U'<M| |/l.Ji., l'U 

Nrr Mi-tiHMiiU, Inr.^-,, Is,'!,, tHl, !l H , |H,t,, !/. 1 , f'/'.J \t-t-; , 1 S ,' , , {. i , Ml, 




zone is essentially a mixture of nnhurm-d .n-is uilh air/ If i - uantml 
by radiation from the outer /one, and ran-vs m h mp> ratnr. ironi about 
300 ( '. a little above the no/,/Ie, to 100O ('. a! fh. a p. \, utr iv rapid 
combustion commences. The outer /.one IN a hot mantl^o! i.m-mie? 
jjas, the temperature of which may rise io aboiil l.Viii ^ ., or .-,, M as 
high as 17(>0 ] 50 (V Combustion SN h.-re lairU e.mpi- f.-. 

^Carbon monoxide nny appear amon.'%! the produ i?i - M! , unou /;..!;. 
principally as the result ' of sudden eoolm- ol" fin- llan;. .* It app- ai - 
that an incandescent mantle lends to art in t hi -, u ? \, an.( .-an-.. 
appreciable amounts of carbon niono\idr to . -.cap< . I hr am^nm 
depends upon the type of burner, and U huh p'-nd. nt ! h. .un..i m ' 
of carbon monoxide in the original ei.inbu-.hbir -M , b. t'^---!, Ut. i: SU i! 
of and (50 per cent . 

Smithells Separator. \Vh-n a mi\fun <i a fombu.fibir -M . \\i\l\ 
air or oxygen is burning at the mouth !' a lnbr ( ti-r- i-. a eou-,tant 
tendency tor the tlam.- t k '--.tnk. bark, ' tins 
explosive tendency hrin 11 , count r.ietrd !\ flir 
velocity \\itb whieh t h- "a-. on-. nn\tmv j<,i',%^, 
aloni',' the tube. B\ ad|!i-.!ni" f h* rlafnn ! 
{\\ccn the j>roporfion ol o\\;^ n m fh* :.*a- a.nd 

the rate of tloU. it IN pov.lblr h .'ft', rf f| tJ - f( .. t 

ration of a ilanu- into its rompmiru! part'.. h> 
cause when the raff of \\n\\ ol !i.t -M-. r, nrJ 
insulliciciit to maintain tli- etiudiir.f in at f h> M{ 
of the tube, the ntnrr portion ol !h i],iui- r , i> , 
towards th<- ri:;m ol' !h -aipph ! t h> :.'.i. , u-- 
mixturc \\hdst the iutr mant! | th ll.nti- , 
although eiifrrblrd, rriuaiir. in t h oni'iu.d p-.i 
tion. By pn\idm^ a eoast nel ion nr.ii tin- tub-. , 
a local increase is canst d m t h iat* oi ilt^ <! 
tile j^as, and the receilm^ portion ol the ilamr IMII 
he arri'stcd at this pouif. This is fh? prm'ipl' 

KKJ. 10. Thr Sinitholls ui ' { , llr Siuithrlls Si parat or/ uhfdt mav }.- i-..n 

separator. Veliiclltly mad*' b\ tisilc', with t li- aid ol .t pins 

of rubber t nbini*, a short *!,tss tui %*i$t r j!j'}j , 

in length, on to {.he uo/;/,le tf a Ban.sen burn r. \ Mnmd, id r ttib, 
is slipped over and fixed in position hv mi\cn\ ol a eorK. Th- ti. oi 
the two <^lass tubes are protect i-d witlimrhd foil to j*tst.u?. -r.n-Km-: 
at A and B. The .^as is turned OH full and tqinh d at ! h* lop, \ h-ldin:' 
'the ordinary Bunsen tlamc. By turnne'doun ! hr JM-, and is:'ul,^in 
the air supply, the llame becomes un\tab!r and t h> mn- i porfiMn 
recedes down the tube taking up a iivrd ptsitiin al A. \! the. jmmt 
partial combustion only ensues, the prodneh, b iu: ? < U t to.,, U ., aatt 
II oO. In the upper llame eomhnstion is ivuder* d compl.-h . 

1 On the rlu'inical 'haiiin\s t 
th(^ ctun position of the !/ahMu: 

24 \ s -;l" 

a I5au'i\ Ctnnjtt. /T;///,, i'JO'J, 148, !MS ; IMs. j.jy, {;st/ 
4 Klin^aiKl Mon-ntin, Cumiit. //., i'Jl'J, i6f>, ltM 
' Siniihrlls and liiL'hs Truu*. ('/////. ,vw., Is'j,', c*i MM 
181)4, 65, ()();$. ' ' 






Thr ctTret is \ rry beautiful it" carried out in a darkened room. 

A curious experiment lias been described hy Frier l in which a (lame 
is obtained % rry similar to the inner llanic of thr Smit hells separator. 
Thr experiment consists iii fixing a jjlass 
chimney our tin- hast* of a Hunseii burner, 
and a hori/.ontal wire an, inch or two above 
its upper end iti'4', 11), I!" th- height of A * 
above thr hunter au<l thr rale (if ilou of tjas 
arr rurrrr{|y adjusted, upon applying a liijht 
at (' thr jas burns uith a pair blur flamr, 
and hrar.s a resemblance to I hr *;as rap 
tl' a miner's lamp. 

Whrii sodium rh!rnlr i\ sprtnk!r<l on a 
^lovviuu roal firr a rharart c-rist ic h!ur tlamr 
ri'siilts, \\hifh is at t rImtaiir to f hr prrsmrr 
of salts of r op prr tn*i ^inal up.t m t hr p\ nt rs in 
thr roal. *riu\ \\as dcmoitstratrd 1>\ Salrl * ! 
uho, in 1MM), ml onl\ idrntilnd thr Ilamr 
sprrlrtHH as thai of ropprr rhloridr, hut 

sUt'i'rrdrd in sr j a IIS"' inrfalhr s'ofjfHT t'l'om i 
1 " ! *' 

I lir hirl ash, I hr colour is not due torarnun 

IHono\tdr, I hr t \Vo tlaillrs In IIP* }U| I r dtst ilM't , J 

Micropllonic Fl;uiu*s. It lia^r-ccuti\ hi n 

that flantr\r,tn In- rsnplo\rd forihrc j ct production ol tl* phuic ciirrcuts 

I\ sound uavrs, 

Luminosity of ftu* Buns-en Flame/' Mention has already been 
made of t h fact that the introduction of air into thr heart of the flamr 
enables rapid combustion to take placr ujthotil the separation of 
luminous parhrlrs, sn that the Hunsrn tlamr tentls to losr the luminosity 
charaet mst i.r of rnal i.jas, This, iio\\r\rr, is not Hie entire cause* 1 ; 
there are several contributory factors. For e\amp!e t the an* introduced 
into the Jlatue is c-old aiui thus tends to coo! the uholc. A^ain, the 
formation of intermediate luminous bodies is retarded by the nitrogen 
which serves as a purr- diluent and elevates thr temperature necessary 
to effect the partial decomposition of t he hvdrocarbons. 

Inlluence of *I\ k inpi*ratin < c upon Luminosity* 

The liitjher the t mp- rat ure- of a ti.une, the greater \tili bcctiiuc its 
luminosity, the chantje beini! due to a f.feni-ral shrteiun^ of the \vavc 
length of I he raihattin. This can be readily demonstrated by a <*om- 
panson of the llam* s j*rodu'cd b\ I hr combustion of i'old an*! heated 
coal lias respi-ctiv e!\ ; by burning phosphorus or carlio-n distdphidr in 
air and m o\\j.jen respectively aa almosphere of the latter |,(as catislug 
a hotter and brighter tlame. 

it ml , MI I :\ xi.j 

8 Siilrl, /''>* 
iHt", 1 ,!, .!|, -$!7 , 


. , in;::', n i, v;j-j. 

The calculation of the flame temperature I 
like hydrogen, carUm monoxide, ur nu Hum at tir- 
a simple problem since the appmvntU n-r, ,,..rv 
heat of combustion and lh.- sp.viiii- h'-:H, -t 
calculations always yield \ cr\ luuh ivsiilt^mu.'u .: 
by direct experimental meaMUvtU'-uN. Tin- ,ii ,,- 
due to a combination of sr \erai cau>-s. <h t ;;.-.-. .ui; 
of the (lame the products an- par! i.dh di*.-.H-i.i!Mi, ! 
is not coinfilctc in Ihr Ilniu*-. Tin SJM nil.- h< ,sf M^ 
rise in trinperalnn-, snlh.-it tin \;ilu. bt, tl n| d ,it i 
lure for the specific leai is tun it.u. In ,dii*!"i 
another contributur> i'aefnr is tin- !.-. >i h- .n i\ i- 
i)c very considerable rsen ni umi bnuumu-, ll.nti. 
presence oi' an excess ii' I in- " -. ' 
instant,ai\eo\is chara< i ter ti' th- e.j'ihu-, 
accunu'y of the calculation." 

A convenient iiK-lhod {' d< t -nitu'ii fb 
flame consists 3 in inserting a I Inn \n, ni 
<j[old or platinnni, into the liana aiiii i ' iu 
pyronjeter. '1'lie loss of heat o-ea !>!' i 
coinpensaied Cor I>\ raising tin- vur f* I 
an electric current . \Yhen th- vur< h i 
as the llante there is no drpusjtii <i n 
exceed 1 mm. in diansrfer. 

Inlluence of Pressure on the Luminosity tt 1'hunes. 

Kranklaiul ' l bnrned sj\ stranu i',tnll* in 1 b.uit )iia\ . =.!,! t^- 
six afterwards in a tent t>u the tup it' Mt. Hi. me, Th- .i-^j-.'- !"'' 
>veiyhl. were : 

At Chumonnix . . . 

Summit of Mt . Ulauc . , 

Attnluitinfjf the small tlifiVrentv tu \,m,tf MIU ut i> in)'- i.iPn- , I !..i.: 
land concluded that 

///<* rate of cuinlnixlinn uj u ctintUc i* t'lttnt-hf tm!i ft < > * * 

of tin' air. 

lie explained the result as fulluus ; In, tin eMisiin-,t i*-, 8 .| f i, , ' 
radiant heat from t he Hani*' Itrst iiirjfs l In- \\,i\, ,ni| t h< . ii , ,, 
uetion of the xvick, rises into the il;uur. If js!hr. i-i- '^ ?b : * 
of consumption of the wax is eutin-ls tl-|*i-iitl-n! ii|..'i tu ,\>. s-5 t 
of the \vick, provitlc-d tlie lu-at radiated 1'nuu t h s ! v,u i'. 

to maintain the supply of liquid I'm -I and t \4,itih . r ', .* , MI, 
near the, apex of the cut I on. Sjun- e t pt!hn ,ietj.j, i i f . *' f )! 
variations in atjuospheric pn ssmv, ant! ;?% tltr ttmp t 1^3 , li, 
independent of the same inilurnv, sf is e!.-,r n^i^i i*^ 
will vary, and the above eun\tane\ yt r;t- !' rum!' ,*m' i t 

1 (Joiuparo HJI|M.T anl {hfi>., XtHit-l,. /*Ay,i/.-i/. / A^,. , P.HIM, fif / h,i _ ?,;-, . j . 

a BriL /l.v.wr. tiipftrtx, 1HUS, pji, :UH, :t;i,'; HIM'.*, |,, ;rj'.i f i'Un, '-,.;, i'' V'.'. 

a vSenftlelH-ii and Beniuiirt, WtyHiktii y.nt.wh,, l*i|s, ig> |HH 

4 Frankland, Kjciu-rimvni<il, ItrM-tm'ht-> (t^imUnt, 1*77 i.'i.. *7. 


During Ins e\prriwrnts on Ml. IJIaur, f'Yankfand was impressed with 
tiu- small amount of h<.hl emitted 1\ the eandles. Thr inner blue /onr 
was extended, aiui tin- si/.e oft he b umnous /one proportionately n-dun-d. 
I'poii returning to Ku^lam! h, earned out a -Jries of phot nmrf fit* 
measurements \\ith roal-;.cas Ham.-, and deduced the law that 

the ilhnunitinit tit Uln^iitnitin^ /j^^r/- is */mr//// /m*/^r//nm// // tin' 
ill mittiitimi if! iitt,;i>xjiiit'f'ir /w.w ////, 

down In a minimum ii ' almui II im-hrs ol' mrivurs . l-'orr\rr\ mrh [all 
in prrsstiiv of the at luosf iu-rr, fh- Itmiinosity IVl'l, nudt-r i hr partirular 
<-on<ii{ions 11!' thr lAjtrriiut-nts, in ;,-! p,-r tvnt. Thus, a ijuautity ol* 
coal .jras which in London wmild \ n -Id a h;hf .-cpial tu too -anillrs wtmld, 
if hnrnrd m Mnmrh t *ur an ilhinunatuui .-iTrrt r.jual to ttttir more than' 
JM canilli-s ; whilst Hi .\lr\ieo its ltiiniuoMt\ would he n-hu-nl to !>!:> 
<\'Utdles Ihrse lUUnhiTs hrllt- imlrp, mlnii i,|' thr efian^i' tf vollUU- 
offlieroal .as 1 y thr ivdtnvd |h ssiin-. 

J%\prnnirn{\ wn-r nr\f rarriMl on! on ! hr milumrr <f roinpivsMun. 

This uas a dlllirulf task to i v-rtitr %a f ist'arl onlx , |rr it Was M <H liHHld 
thai an\ roiiMdrrahlr in-rrasr of pn s%mv eau%r-d iofh eandlr ami oil 
ilamrs tu siuukr. Kraiiklarnl fhrivlon- dteidr,! ! , tnplov tlamrs fhaf 
\\t-ri' hut lVr!K huuinnns at i.rdmar\ pn sstin . In tin' iAprrinirnts 
l-lss-rn atiunsph, n ' ami tuo a! mo %phr iv > ' pn v-,ur , ., lamp f.'d with 
am\i alcohol was UM-<{. \., t hi-, M U tkr.i at soiii-uha.f iajdirr pn-v.un-s, a 
nnxlurr <!' ; parts rth\l alrolml wjlh 1 uf am\i u,i% rmplovrd. 'l'hi-> 
had no appr rtabir illnnnnaf un- power a! onluiarv pn-ssurc.' 

It was^lomtd that thr satin- law hJd as tor diminnt ion ii' pn-sstirr, 
an upper hunt *.. uui r. aeh, d at ainut ihn i ,it m* isptii-n-,. alfrr wlueh t hr 
of>\rr\rd InnnnoNify rapidU mrrrasei. 

The results ohiajlird tua\ he urt>uji.-l as !<!IrWN ; 


I I'mnktafitt, Ix'?7, i 

I par! am\ I alrihl , 


*^ IM ^ ''"- "I ' M'apiU'.? lieua f rtr, i-amil, -, huruuijj ttl)ii< r dlflerrfii 
pivs-,uies yi. id.d MiiuJar tv-.tilts, ,in,| '.|,m\,,i fhriv was no rsrap,- <>j 
Ulh'onsuiu. d roinhuslihl, v ajioill , 1 iiis.-ju utl\ 

011 flt ' lfli|1 ' 1 ' ll "* Sit| - 1 M4IJH-. I-Iids to i, -11,1,1- thr r.uulnutiim Irv 


i'>in|ilrt4-. \i tflur is the ivdurrd liijuuiusif) <tu* lia fall m trmprraf nrr, 




for although a slight fall docs fake place, if !, not %n.i!>*^ -; ! ' 
for tJie whole change. 1 It appears to depend " chi iU , 'i '. ; >> 
upon the ready access of atmospheric o\\ i>vu i o. nr if . c. 
exclusion from, the interior of t he Haute." 

Frankland also investigated the iniluencc of pr. ,...'. up.*;, 
bustion of hydrogen in oxygen. At 10 at iihspln r. tie Is *-, 
bright, and the spectrum continuous from red }. -, ;.! f 
monoxide, which normally hnrus with a fedl\ iuuim* '! ;l.i;j;- 
even more luminous at lu^'li pressures than a !lam< i h\dr 
same dimensions.- 

The Cyano&en Flame. 

The phenomena attendant upon t h* embushnu n e-. .,;, 
Smithells separator are distinctly beaut tfu!. : The ilam- MI 
burning at the no'/'/lc <'onsisls of two parts, h,uu< k , .?j i: 
of bright peach-blossom tint, and an outer eotu shadne' )'! h 
blue to greenish #rcy. On introducing air int th -.v J fa 
cone diminishes in si/,c and descemls the outer tuU n in 
this process of detachment. houe\er, is in pn."r .. f ?i n,-! 
seen to be surrounded by a rosy halo, uinch -Jd! aiiiti !- , N i 
descent, but disappears upon cut ry of more air, lem a3jn .f imjii i- ** 
replaced by a blue halo. The- whole of this tim- f h* mj? r CMSI- i ni.f. 
unaltered. Further addition of air causes UP- out. r n- r. d? ..-.pi- 
\vhilst. the inner one now becomes more llu-, and if , h.d . 'j"in , 
greener tint.' 1 

Dixon r> has shown that the rate nfiAplt>-,ion ,i evanM^ j. .-,:' h ,e..> 
reaches a inaximnm when th<' t wo a", % are prv,, nt m UMJ. .-ul.u j (! 
portions. Further addition of o\\jcn reduces Hi* \ei...-if\, tie - \ 

oxygen actinias a dilueid, pr.t hi- .<, n- u? r d -; 

such as nitioi.jei, nii'.'ht h.- r\p>eti f, ,{,,. 

appears, therefore, that t b hr.f pruduef *.! e,. 

bustion is carbon monoxide, \nlh bb-i.i^t'j. 


fC'X ), - O ; *J( \ ,. 

This is the main iv.irhon ta ti> 1.1,^,1 > 
of peach-blossom lift!. If is lollti^.-.i, uifh i.u? 
cone, by t he combust jon of e.trbtiiujiM!ii\id- , a! 
the ^rci-nislt fringe alliuled f 
I<J the presence of small i 

nit rourcn. 

FKJ. li. 

n bust inn. 

Reciprocal <;<. 

From the lort-i^.m;; if ^ d, .,r !h, t ' .,. jl.m 
resulting from chrniii\il affion mu-.! {> r,--Mi.i* 
as a meeting ground Iielv\ 4 ,-i, I'unii.ji j jl,|,-' ^, r , 
. a rc^i on uhi-rc chemical rouilm,..hMn i, 1.1 

c'eedm.u wil huTeat activity. F<r t he sake of rum, ,,ir,,,v - ; ,,r i-, ,.-MI,|. 
as a supj)orter oi combination, and coal .as a% fh- i-muhi, ,tj},!, !,,< 

1 See also Uhbclolideand Andwaudt^r, ,/. f,',t-J, t j, > fa i{ ' n ' i' ' 

2 Kranklaiid, /or. r/V. r p. ( .H)7. '' H " * ' '' ' ' f ''" 

s Sec SmiihcILs and Dont, 7'm/rx r/ /. ,v, J( - i,v,. t 6r n , a 

ntudy ,f the . 
L Chun., 1D14, 88, M. 



But this is simply a convention, and if a glass globe be (11 led with coal 
gas, as in fig. 12, and ignited at B to prevent its free escape into the 
room a lighted taper may be made to ascend A and ignite the air 
drawn by suction up the tube. This is air burning in an atmosphere of 
coal gas. 1 

Combustion of Carbon Monoxide. 

From the time of Lavoisier until 1880, the combustion of carbon 
monoxide was regarded as a simple oxidation process completely repre- 
sented by the equation 

In the latter year, .however, Dixon, 2 in his address to the Chemical 
Section of the British Association, made the startling announcement 
that when an electric spark is passed through a, thoroughly dried 
mixture of two volumes of carbon monoxide and one volume of oxygen, 
no explosion i$ caused. The introduction of a small quantity of water- 
vapour suffices to determine the explosion, which gains in intensity up 
to a certain point with increasing amounts of water. Gases like 
H 2 S, C 2 II 4 , NI-Lj, 1IC1, and ether-vapour act like water, but SO a , CO 2 , 
CS 9 , C 2 N 2 , CC1,, do not, if perfectly dry. It seems clear, therefore, that. 
such substances as will form steam under the conditions of the experiment 
are capable of determining the explosion. 

In. order to explain these 1 results, Dixon :i suggested that " the carbon 
monoxide is oxidised by the steam in the path of the spark, and that the 
hydrogen set free unites with oxygen to form steam at a high tempera- 
ture." The steam thus acts as an oxygen carrier itself, undergoing 
successive oxidation and reduction as follows : 

(i) 2CO 
(ii)2ll a +0 a =2ll a 0. " 

Moritz Traubc 4 rejected this explanation on the ground that carbon 
monoxide does not decompose.* steam at the temperature of the electric 
spark, for reaction (i) is reversible and under these conditions proceeds 
in the direction right to left. 

This objection, however, is not valid, for, whatever the temperature, 
the law of mass action requires that definite, even if small, amounts of 
carbon dioxide and hydrogen shall exist in equilibrium with the other 
gases in the system. Hence, if for any reason the partial pressure of 
the carbon dioxide or hydrogen falls below that required lor equilibrium, 
it is always possible for reaction (i) to proceed, even at high tempera- 
tures, in the direction of left to right. Traubc explained the reaction, 
however, on the assumption that the function of the steam is to unite 
with one atom of the. oxygen molecule, the second atom being occupied 
in the oxidation of the carbon monoxide. Thus 

CO I O : O | OH 2 -e() 2 + II 2 O 2 . 

1 A variation of this experiment is given hy Thomsen, C/iem. A r cww, '1871, 2^ 283. 

2 Dixon, B.A. Retorts, '1880, p. .503; Chew. Nnw, 1882, 46, 151 ; Phil. Trnnx., 1884, 
175, 030 ; Trans. Chem. Hoc.., 1880, 49, 05. 

:i Dixon, Trans. Olie.m. MM., 1881), 49, 05. 
4 Traube, Ber., 1882, 15, 066. 


The hydrogen peroxide is tln-n nune-. 

CO !! ,<>, i o 

This is reminiscent of ! he IJrnii- >! >...! 
lion (sec p. 5r> ), ;in<l in support of il m..;. 
hydrogen peroxide can hr dti'id \\i-.>i-. 
allowed to burn in air, tin- \\-.\u >> :> M: !t 
surface of \vater. 

The surest ion has also been mail* !l;a! 
rnay he formed inh-mu-iii.'ilciy, .sinn l\ iil! 
monoxide lo iinpin^v ou a eold, <ijluf M .i 
poljissiuin hydroxide, a ptvriptf.jh ?-, uhf ;{ 
yielded on adding potassium p iv.M'ioi?!.!? 
chloride, 1 The couihusiiou \\ould thu--. f r* *. 

CO |1,C ,t) u ll U ;;t ( i 

The evidence is not couclusix -, hue- >. . r, , " 
obtained with hydrogen prruxuit- in !!; ,i ,-.!,- ..; 
suit, solution. So t he aho\ r f rsi Mii-hl v. H ; , t -\\- t \ ' 

in favour of Trauhr's !hrnr\, 

The mere fact that hydroj{*-u p- !-t\ii <\,rj h .? ? 
manner is no proof I haf if pla\ s stu-h .it uuni -f.,j * j,,;* 
as Trauhc surest s. Anustmu"; '' .-M..HV* . ^ilh I)IMI * 
intcr-ntfcut, hut- \vhilst Di\un < ! (nsi!rrs if-, *\ v .. . 
to the carbon monoxide rnolrruir, hhrratin" ir. ii\.iii 
su^ocsts that the ovidaliou ot' tin- cerium inu{m\t.i- ! > 
t he water is dependent upon t hr sinntttniif^n \ ^xi.l.-.h, ,;. 
of the water by the free oxygen. Thus tin -> ! i 1( 
explosion may be represented b\ tin- seht-nu-. ; 

<> n,o i o 

i ami 

o n.,0 co , 

thcinivi .;* 

Von \Vnrtenberj: and Sir-y; :i s!ninly siipp 
surest the following seheine ; 

(I) The forination of formic acid 

('<> n,o u .c oon, 

The production of this acid as an inf.-nu.-.h 

|,- \\ ?f j , 

' *,- , r ,i.i M , 
condHistion of carbon monoxidi- uas lii-iu*!!^!!-., 

ISM 3. The llame of the burning gas u ;ls .dl*.\\r,i to , 
and formic acid was found in solution ju the uaf r, 

(2) The thermal decomposition of fonuir am! Pit 
and hydrogen, both of which gases e-ni ), drirrb-i 

II.COOH Co.. u 

1 OtmHtum and v<m Iljuiscn, %tit*rh. l\i* !,! ft <,-j<, i( . ism, , |-.- 

2 Armstrong, Trttnx. Chun. St\, issll in *M i1 ' " 

:t von Wart(*nlHT^ and Sic^, Jiu\ t l!> k *iV e* i M'I ''I'r* 
* Wieland, ?/;/>/., I!) 12, 45, G7il, " '"*-'' * " 

THK rHKMH'Ah PlinPKUTlKS OF <>\Y<:K\. S7 

Tliis is followed hv 

("J) Thr production of hydrnjjrn pmxidr : 

IL (), If,o,* 

and (I-) Drrompusit ion info \vatrr and o\v ! vn : 

11 <), II ,0 O. 

Honr ! has still further ilr\rlopnl lh\on\ thmry. I!r points out 
that ihr ilantr of hydn^.n huniinif in air u Mnallrr and " sharp, r " 
than a llanir of rarhon motioxidr, humim? 'at thr -,ainr on tin and nnd< r 
thr sanir pivssurr. Thr latulu n! riiarart'n of thr lath r Hani.- Mi-^.-.ts 
a slourr hunitn.j jfas than h\iroj/, n, A-jani. h\ iln.f.rrH air nnvtmvs 
have Io\\ri iirintion tnuprratun-s than CO air nnvtnns |s.-r p. M o . 
wliilst thr ns-sMinttin llanir spn d of thr form, r is m..rr than ih\ tnu. s 
tliat of thr lattrr (s.-r p. 11M,. Finally, ISonr and Ua\\arl ha\r -.h.\Mi 
that \\hrn rorrrspomhujif Ilv-air ami CO air mivtw.-. an- r\plod.-d in 
rlosrd \rssrls. thr prv,iirr rapidly ns.-s to a inaMiniun in thr ras.- of 
hydn.-rrn. hut mm-h inon- slouU uith rarh.m iiionoxi,!.-. Thr alditton 
nl <>JJl } ' pi rrnf, ot h\irorn to thr (t)air HH \fnr, is"\ *rafl\ 
art-i-l.-ratrs thr at taniin.-nt of maximum pr. s%urr. Ml of tli* t p.imt'-, 
indn-atr that rarhon mnnoxit},- ,M I( ,| r ; ,pahi, *i lmr oxiii-..-.| MirratliU 
as Indrotfm nndi r thrsr rondihons. 

Honr thrnforr stlj^rrsts that .\V!.-n m llalili . i-, rapahlr nf 

fnnrtjoniii-: in two distiiH-t. wa\%, uam.-K i n a-, th.- umhsM.rjatrd 
niojrrnlr' < ) and in i as ihssoriat*-il atonnr < ). 

An umitssorjatnl mojivulr, on Jrm.t t. a Mti!ii-, ntl\ hi;'h 
trniprraturr, !s prrsumni rapahlr of, \rrtm.jits latrnt \almri. ./and if 
rnmhimmt ith two hydr< molrrtili-. uifhotif it\rll lirrnmn* 
disrupt rii. Thus thr mistahlr ruinplr\ 1 1 t c K or 


Jsmuuirntanh iormrd. This, IIUIUA. r t unt.mth l.n-ak-. .J.,\vh, vr 

in part its r.nshtn.-nt rluu, nt s , m th.- lonn uf h\drn l n- u mulrrnh s and" 

atoUUrnSS-.rrn ; aid III pail ;is na^vnt uf ,ir| n at r,l Xt , alii lllul 

I hiis 

Thr mai!utnd*-of thr ratio n Moo in 4 II .!,u..uslv l.-p. nd upu 

^ jnv\aihn{,r at Ihr m,,mmt. Thr- |, n -h.-r f 
and thr sniitilp-r th.- hy*in^ri, ^.fu-.-ntration, f I,.- Um, T i-. Ihr udijr fur , 
C)vy^-n and rarlmit umo\i,!,- p IIOU.A.T, an- iv^inl.-.l a. nirapahlr 

<i associatintf m thr a |,o\r luaiinc-r, tltur iuflrrul,-s hcin" lunliialiv 
mrrt tn Ilainrs, lirfmv thr rarl.u inunuvitlr t-au unil.-ivo'M.viilatinn, 

thr 0\U f rn nillsl nfhrr ha\r djssonatrd, or hr m thr turiii of somr 


activated or nascent compound syeh as 
above. Thus, whilst the ivaefiou 

is impossible, carbon diovide ran n adiK i 
following ways : 

CO ;<) (O, 

The foregoing theory nrehts mdir. ef vnin^r? \> 
researches. For example. Russell 2 eau.d na-e,,, 
and nascent oxygen to eonie nttu run!, MI TV, 
exploding either \\iih a spark or b> heafn-< n,< , i. '.] 
of chlorine peroxide and earbusn \ siilplud. I: \ , 
explosion exerted very considerable milu, j/,-, r l' ? 
combination of carbon monoxide and ir.^.'u *H< 
decide whether the elTtet ua^dinef i)r ".lu, !,, 'i,' - 
action of (he Mhird substaner." " |j n | u* {{,,', ,'n 
VCTV plausible explanation is elrarh i,, j, ,. t |' lM ,' f ; 
More recently Lan.irmuir - has dirief.d ,',n'. , t ,, M . 
oxygen when bronchi into eonfaet uifh ,',,-!,., P..O 
piatmnm rapidly oxidises it to earhnn din\i,l t '//' 
nionoxidt* immediately reaets uilh atl^urt. ,1 ,,-'', 
resnts are sn W . s (i NV nf aeeeleraf mn ,,| usi.j'it, 
activated condition, 

The KquiHhriuiu 2i !O < ;< ) , $ ; 

The reversibility of this ivaetion uas diseuu r , ,| },, ' 

and its study receives renewed intensl m \ i, H M | ,, f '. 

in the theory of the combustion of earbua tn .* * ... ! ', 

has alrea<ly been made (see ,, ?!,. lh .-m-iihiV' 

/lr ^ n |, ttJ1t i >,,,, i i * % . n'u<a'ii* 

*K;!!L , ^ Unlh ; d W< <1 chareual jML*| m 

i ""' " ' '<% and subs* uiif 

, ;;:'. " 

J. Hhead and 'U h . |, t * 

' f I ' I . 

j ' . ' f : 

I *'..{,! 

' , t 





i:J7,-j j 


IV \<I; 



These results refer to atmospheric pressure, and K is calculated from 
a modification of Le Chatelier's formula, namely : 

38-055 +2-Q2T-Q-0031T 2 

where T is the absolute temperature, and C x and C 2 are as defined in 
the table. P in this case is unity so that log e P disappears. 

No matter how high the temperature, theory demands the existence 
of a small but definite quantity of carbon dioxide in equilibrium with 
the monoxide. 

A study of the velocity of reduction of carbon dioxide by carbon at 
850 C. shows that the reaction is monomoleeular, and the same is true 
for the reverse reaction, namely the decomposition of carbon monoxide, 
which, however, proceeds 166 times more slowty. Undoubtedly, 
therefore, the reactions arc essentially surface phenomena, the rates 
varying directly with the partial pressure of the gas in cither case. 
Since the decomposition of carbon monoxide is accompanied by a reduc- 
tion in volume, increase of pressure should facilitate the reaction at 
constant temperature, and shift the equilibrium 

in the direction left to right. That such is the case is shown by the 
following data : l 


Pressure in 

C0 2 

per cent. 


per cent. 




















The Equilibrium 

When hydrocarbon gases are fired with oxygen in certain proportions 
the cooled products consist of hydrogen, water, and the oxides of 

1 Rhead and Wheeler, loc. cit. For a study of the equilibrium between oxygon and 
the oxides of carbon, see Haber and Lc Rossignol, Zeitech. phymkal. Ghem., 1909, 66, 181 ; 
Haber and Hodsman, ibid., 1909, 67, 343. 


carbon in various proportions. 

the different constituents is >,ri\ -n iv tit j. 1 : >'."; 

K. ( ' 

where l\ t is thr iqmlibrium r,.n^-n! ai i-nr- r.";ir. : i . I; 
Dixon 1 obtained the \aiue lx, MM his . x p. !V,: S > '.'-":.' u .-: ; T-.-.r;:: 
of mixtures containing earbmi mtu.M xjd.-, h;, >i r .' '^ !;, .-; . -x-. .: ... 
was supported by the ivsul's oi' Snrl It. !i-, ..-s-i h,--.- . ? /.- MI:. 
of the intereottal ^as. -s of h\ drue.M-U.h l!.;.-n ... ::.! /, . . T.. .-,?: 
confirmed by Anehvu.** \\fni >lnii'i ni. <?!!, 1.3 ;.. *., . .);.. 
teases in oxygen and obtained \,du.-<. lo" K. r.r; ;"" ; i!"-.; : ? - J! ' 

Owinu; to experim'nt;d ditln-uif h". .i hi 'it d- ;;' i '-,-.>...: 
not to be expeetrd, and thr ab<\- r-'-.u!! . m.i.\ b- r. '.'; ! 
reasonable- agreement . Fnm Andfi-v, , r= -aii.' , j* ^.t-i; i .'.{-.' .=.r * i 
value of K/ is largely intii-prnd nl >! thr nuf!.'! -,';! . . V- 
carbon-oxygen mixture and uf ! b> pr. -,-an' ) 'is- ' > ' i *' 
It is apparently, thrivfmv, ah-> tir;.'- 1> ind> p-- i^.i -.. , ; */ ;.:,.:. 
Jlatne tc'iuperalnre, siuer this \\Mdl \.IJA '^.i!h !?: ;! . .-rr 
position of the mixturf to ir i"hit-d. Th >r ? :'.;.u', , i. .-, . - 
change wit h temprrat urr is to i-<- <-\p. ,-t * J, nid I! un, 4 .:!.,! * 
t-herniodynamieal prineiplrs, t hat thr,'; r. :M f , '! ' .. ?| ; -r. 

loo- K/ *J -.'*.* T U-UMti.'S It* 1 ' 'I* w oen ;:;.'$ KiT "! .'>'-, i 
f"> ' 

\vhcrt* T is the absolute trmperatur-. Th, i'l!o^ n:' .< : -, :.. K 
been derived from this equation ; 

Tent}). ' 1'. . . loo;* l'J; ! IH.' h .nit 

and these a^ree with reasonable appnixmiat* >:$ jilt ! 
Habcr and others. f> Possibly in Audiw\\rxp tun at, ^ . i tfr i 
temperature were not sntUeiritf ti prndm* \ ui f i:i K 

enough to exceed the experiint-rita! rrri\ Audi ii i* .. $ > 
calculate his llanie trmperattirr, but bh*-Ar% fba' in / 
be higher than HUH) ('. On the other hand, ,t mm ! ! 
and one fa\ l oure<l by Andreu is that K ? , as t| f u p, ,s , 
"does not correspond with the maximum turn f tu ' * *i 
characteristic of some hypothetteai tempi t.ttui , f ', -1*1 
condition at which corresponds xuth th- jut jqalma ! Ti 

chunm's which oc<ur in a ranidlv enuliitj* uuxfnt? IJ.MH li < 

rt i , *' T f 

atmospheric temperatures. This pur-h Inputh tj* ! iui* i 
which may be referred to as thr trminrtitnrr t*f fiatti n^> f < it,. 
b<* supposed that the teases are in equilibrium, ihdia ! **n'i 

1 Dixon, I'hiL 7'mw.v.. issl, 175, rJ7 

2 SniitlicllH and Inv'lf, Truii*. f'h*w, >>.,, IH*J M ', 61, !*l. 
:t Andrew, 7V<///.v. *'///. .s'>\, lull, in^, -l-f-l. 

1 Ilahn, '/iittfich, iJiit*il;nl, t'itttn,, I'tHll, ,|,|, .!**; i'^oi, 4^, ''i' 

llanu 4 , and for font {,HH, <iiSulrl \\ith cari<><ii h"\nlc, ,ys! IH-J!--*- > , : ,<,,-j , 
than nonnal, u valurlrsH tluifiH-f, S*-* II*i!-r ,-isi * w^riirr 1 ', ***?' , I"*" 1 *, f*?i, ,".'. 
ajiorf/. r'Af-m., HUM, 38, 5 ; Liu-y, i'/,jV/., I'.Hrs, ^4, tillll ; 
1DH ; Allncr, ( ftt'ntr,^ IDOfJ, i, ItO'J. 


at this temperature), is identified both on thermodynamic and experi- 
mental grounds between the limits 1500 and 1600 C." 1 
If this is accepted the results indicate that the equilibrium 

sets in with very great rapidity. 


It is a matter of common knowledge that a room may smell quite 
strongly of coal gas without its being dangerous to strike a match 
within it. When this observation is pushed to its logical conclusion 
it is evident that a certain minimum quantity of the coal gas must be 
present for its inflammation, to be self-supporting. This minimum 
quantity is termed the lower limit of inflammation of the combustible 
gas, and is influenced by two factors : 2 

1. The initial source of heat should be of sufficient volume, intensity, 
and duration to raise the layer of gases in its immediate vicinity to a 
temperature at least as high as the ignition temperature of the mixture. 

2. The heat contained in the products of combustion of this first 
layer must be sufficient to raise the adjacent layer to its ignition 
temperature and so on. 

If too low a proportion of combustible gas is present, only a small 
quantity of heat per unit volume of mixture is liberated when the layer 
surrounding the initial source of heat is inflamed, and the products of 
combustion have to impart heat to a considerable volume of " inert " 
gases. The number of collisions between molecules of combustible gas 
and of oxygen that arc chemically fruitful is therefore small. Such 
collisions, resulting in combination, will occur only in the neighbourhood 
of the initial source of heat, around which an aureole or " cap " will 
form of a size dependent on the nature and quantity of the combustible 
gas present. 

Upon increasing the proportion of combustible gas, not only is 
a greater quantity of heat evolved per unit of mixture, but there 
is a smaller volume of inert gases present to absorb it ; ultimately, 
therefore, a point may be reached when the amount of heat contained 
in the products of combustion of any given layer is just sufficient to 
raise the adjacent layer to its ignition-temperature. Flame is then 
propagated from layer to layer throughout the mixture without any 
necessity for the continued presence of the source of heat which 
started the inflammation, and the mixture either inflames or explodes 
according to the rapidity of the propagation. 

Consideration will show that there must also be a higher limit of 
inflammation of the combustible gas, for if its proportion over that of 
the oxygen be largely increased, the excess will function as a diluent, 
absorb heat, and tend to retard flame propagation. 

Since gaseous combustion is a reciprocal phenomenon, it follows that 
the amount of oxygen present in this latter case is the minimum quantity 
supporting combustion, and may be termed the lower oxygen limit 
of inflammation. 

It may happen that the lower oxygen limit is above that which can 

1 Andrew, loc. cit., p. 453. 

2 Burgess and Wheeler, Trans. Ghem. Soc., 1911, 99, 2013. 


be realised when the combustible gas is mixed with air. In that ease 
the gas will not normally burn in air, but may do so in an atmosphere 
enriched with oxygen. ^Ammonia, :l vapour is a typical example. If a 
lighted taper is applied to a jet from which this gas is escaping, the 
characteristic livid flame appears side by side with the ilame of the 
taper ; but it at once dies away upon removal of the latter. If, however, 
the jet is surrounded by air enriched with oxygen the (lame of ammonia 
gas becomes self-supporting, and continues to burn even when the taper 
has been withdrawn. 

The Gaseous Hydrocarbons. 2 

Amongst the earliest experiments carried out with a view to the 
quantitative determination of the limits of inflammability of combustible 
gases were those of Davy with (ire damp, which is mainly methane, 
CH 4 . Owing to the importance of this gas in connection with gob 
fires and explosions in coal mines, several other workers have also 
investigated it. The value of the results, however, is restricted by 
the fact that firedamp, like? most natural products, is subject to very 
considerable variation in composition. 3 Even Davy recognised thai; 
it was not pure methane ; indeed, perfectly pure methane is not easy to 
prepare in quantity. The gas, as obtained from sodium acetate, may 
contain as much as 8 per cent, of hydrogen, as well as ethylene. 4 No 
doubt this variation in composition is one contributory cause of the 1 very 
varied results listed in the table; on p. 9tf. 

Of these results the most reliable' are those of Burgess and Wheeler, 
and of Coward and his co-workers, which may now be briefly considered. 

Experiments of Ihirgcxfi and Wheeler* 

Several methods of attacking the problem were 1 devised, namely, 
central ignition in a large glass globe 4 by means of an electric spark ; 

Fin. 1.3. Apparatus used by Burgess and Wheeler (1911). 

employment of vertical tube, closed at both ends, and ignited either at 
the bottom or at the top; and a horizontal tube, closed at both ends, 
ignited at one end. 

1 For a thorough study of the ammonia-oxygen flame, see Rcis, ZeitecJi. yhuttikal. 
ient 1914, 88, 513. 

2 The limits of inflammation of organic substances, such as ether, alcohol, and acetone, 
in air have been determined by White and Price, Trana. Ohc-tn. #oc., 1919, 115, 1462. 

:t See analyses by Gray, Tratw. hist. Mining Eny., 1010, 39, 28(J. 

4 Kolbe, A'usfiilirl. LeJirbncJt Orgnniscfi. Ohem., .1854, i., 275. 

5 Burgess and Wheeler, Trans. Cham. Soc., 1911, 99, 2013; 1914, 105, 2592. This 
method was also used by Parker, ibid., 1914, 105, 1002. 




;>-S to U-I 

'JO f o li't U,i\\, ( W/fV/r</ jr/'/'/r.v, 1SH, Vol. \i.. ! 

I !:$ to KJ-7 |.'l!I ; t'liii. 7V///-v., ishi, p. 1, | 

n-7 M;i(l;inl :uiii L- Mi;itrljrr, ./////. .l///n'.v, 

Si % hlni\\\i'ttt i' l*'*nnitn\sinn< ISStJ, B, 3, 
!;;;> Iriirkm;ini. ,/, (I'tr'trt'lt'Ui'htnnt!* I SSI), 

^2 lsi. 
.. L-- l'h;iti-li-r, .///. Mint'*. istu,|s|. 1<>, 


tti l-j-.s I iU.-./ki.uski. Xrv/.M-//. jihuxiktil. C/tfni.. 
to i;j-'j /" ih!U, 7, is:>. 

l.i \ (, l\\rs, Drtt'rtimt "/' I n/linnnitthlt' OV/.v 
I 1 f *///</ l/r, I SIM;. 
17 Uuutf, /^/-., !Ms t U ii. 

lo H!-;!5 Cuuriot ,tu<l Mr-uuiiT. C*nni>t. rend,, I SOS, 

Lr t'h.if.iir! 



IN-nu.Hi, ,V*/////v. ItH i 87, II J. 
Huri.jfss aiul \\'|IT!I r, Titin?.. ('hrm. V^r, 
ltl I, *)<>, UMt.'i ; IHtl, 105, '-2.V.K 

I*;irk r, /A/W., ilHK 105, JOOL*. 

1 nuanl and Urmsl.-y, /'/*//., UU, 105, 

t ov,,ir<!, t .irjn'iit ri % , atnt P:i\ni;iu t /'/>///,, 
III! 1 .*, 115, *J7. 

94 <>XY<!KN. 

1. Central ignition in a Large Ulobr. Tin* apparatus consist i -d of a 
glass globe, of capacity about 2 litres, lit ted uilli pi, it mum ritvtrudes 
having looped ends. 'The electrodes pussrd aiuair a diata-irr of f hr 
globe ^through ground stoppers. 'IV juas.-s eutjld I*.- admitted and 
withdrawn through the tap. In all but a iVw spivial rxp -nuiriits a 
little distilled water was placed in flu :lobr to saturatr the ijasruus 
mixture' with water-vapour at the mow tt wpTahnv. The nu'thanr 
was obtained in a state of high punt) by tin- action u!" an aluminium- 
mercury couple on a well-cooled mixture of uu-thvl atenhol and tudtdr. 
The product was freed from traces of Imiru^-n b\ passa-v through 
kt oxidised " palladium sponge heated to is ('. ami by sfthsriptmt 
li(j[neiaetion with liquid air. 

The manner of determining tin- lourr iumt wi\hirrs u,s% that of 
"trial and error"; lor fxampi*-, a mixture t!' mrthaiu- and an eon 
taining (M per eent. of met ha nr lia\ tin: IMM-U tn-d and louml In prupa^alr 
inllaiumation on the passage of an rlretrie spark, a si.H'ouil mixture 
was prepan v tl containing 5*0 per rent, of mrthaue. Tlits al% projta^ati-tt 
llaine. The perecntage of methane vva\ tlivfetur*- t'urthrr r'>ht*'*-*l by 
()!() in a new mixture, and so on, until t\\u imxttin-s \u r titaiui*l, 
differing in their eontent of un-thanr i\ (Mfu prr ernf,, out iif uinrh 
enahleci ilame to be propagated, ulnist thr ul h* r did nut. Th' !o\\-r 
limit mixture was taken to be that eontamtnL* fh' ni-ait pi-nvntai'r of 
methane contained in tlu'se t.\vt> mtxturt^s, 

Thi' lower-limit mixture eould be tiisttntjiustirti with 'irtatnt\ I'roin 
tluit just eontaining sullu*ient ei)mi>ustii>li- i^as ; lur tlit- momentary 
passage of the eh'etrie spark sutlieetl to promutt* th inllanftualt*n ut' all 
the gas contained in the globe in the tornu-r rase, and on i'nrthrr sparkiut; 
no signs of eomliustion eould be observrd, YYlnM in thi- latt-r ea%*\ 
although the Ilame of the burning jijas mi^ht appear !u tm\*-l iti-arly 
through the whole mixture oti the first passjiyff uf tlu* spark, and stini- 
doubt might exist a.s to whether it had nut, m faet, lra\rlir*l lltnitt^iiuut , 
on causing the spark to pass a .second time, a " eap " ap|ifirrti *ibu\e it, 
showing that the ituxture still eouiainrt! tMituinstibir i^as., *riiis CMJ> 
remained whilst passage of the spark was rontitiUrd, ^ri^nn* ^ra 
smaller in size, until all the gas hud been burnt. 

All the experiments were made in a darkeiirti itiuut, M* a% It* 
the appc v arance of the Humes to be readily ubsrrvrd. 

The appearance is beautifully shown m Plat*- 1, 

The following results were obtained : 

(Burgess and Wlin-lrr, | 

" (!a,,rV^,,,r. 

iMuT biiiui Mi\iir 

HI All 

|V|-,-,.|,t, in \-..l,ui. 

Methane , 

:>:* it> ;, ;i 

Ethane , , , ' ;Hftttu- ;i i*tt 

Propane . 

' l.i to *' ."HI 
H50 to 1 -70 
l-;*5 to ! ill 

t*f iHortfHuic Chi'nntttn/* 1W. YH^Ptirt /. j 


j To fttct* p. 94. 


JHT rent. 

f Burj/rHK and \VIucUr, HM 1,} 


The vahu* for methane agrees quite well with that obtained both by 
("oquilion and Le Chatelier ; l for firedamp there are at least five factors 
concerned in the magnitude of the lower-limit mixture. These are : 

(I) The heat of combust ion of the gas; 

(!i) The relative volumes and specific heals of the diluent gases ; 

{;$) The ignition temperature of the mixture ; 

(4) The initial pressure ; and 

(5) The initial temperature. 

As Burgess and Wheeler point tint, the first fact or must undoubtedly 
exercise the preponderating influence. The last two factors can easily 
be kept constant , 

As a first approximation, therefore, it would appear probable that 
the lower limit of inflammation should van inversely as the calorific 
vahu* of t he gas ; t hat is to say, if I* is t he proport ion of t he combust iblc 
gas necessary to form a lower limit mixture, and I 1 its calorific value* 

L ,/d C) or L A- T 
where A" is a constant . 

The value obtained for the lower limit of inflammation of methane 
when mixed with air is ,V<i. The calorific value of methane is ISiH. 
Substituting in the ahoxe equation a value of I03l> is obtained for A*, 
and the relative \alues for L tor other gases can then be calculated, 

(Burgess and Wheeler.) 

L nitrtikUni, 


Kthime . 






i 'J7 


I -8*J 



The agn*enieitt betwtu-n the observed and Cideuluted vahics of L 
is very striking* and seems to point to a definite and dominating relation- 
ship between the* eidorttie values of the eombu.stibh's named in the table 
the pn ratlin hydrocarbons and their lower limits of inflammation 
when mixed with air. 

But when this method of calculation is applied to other combustible 
gases, the agreement is not so close. This, however, is scarcely nur- 
prising, tor there in nt reason why I* should be actually in direct 
proportion to (*, and this is the basic assumption of the calculations. 

if, Vertical Tube closed at I loth Knds, In these' experiments glass 
cylinders il cm. in diameter and some *2 met res in length arc employed, 
and the combustible mixture is fired by sparking between platinum 
terminals at either the upper or the lower end. Bottom ignition tends 
to j^ix'e a luw value for the low limit and a high value for the higher 

1 It it* tiiOtt'tiU t imi*rtftatt<l th lw viiiutt* ibtjiiipi by Ttwlu iwicl b % y Fertttitii 

|$, Mil). 8 Theu rs Ibe dftitt umni by Htitl VVIwi?k?f, 

96 OXYUFA*. 

limit of inflammation, in consequence of convection currents. Top 
ignition behaves in an exactly opposite manner. This is evident from 
the results in the table below. 

The quantitative values for the higher and lower limits are greatly 
affected by the diameters of the tubes 1 unless these exeeed ."> em. 
Narrow tubes raise the lower limit and depress the higher limit, thereby 
reducing the total range of inilammability. This is illustrated in the 
ease of mixtures of acetone and air in the accompanying table.* If the 
diameters are very small indeed, no <ombustion will take place. 



(Wheeler and Whitakcr, HU7.) 

Lower Acoluuo Limit. 








-to ! 






2- 15 


2-20 ; 



3. Hori'/ontai Tube, closed at Both Kiuls/ 1 Tlte ixnttiou is effretetlitt 
one end as already indicaf ed, and the Ihune creeps adou# I he upper port ton 
of the tube in a similar manner to a small air bubble in a spirit Irvrl, 

The diameter of the tubes, if Jess than a! tout 5 nu, everts ait 
analogous influence upon the results, as wits found to be the en%r with 
vertical tubes. This is shown b the data in the above titbit*. 

uf Cwvanl tnnl ///.v (*ttic*wf{fi"x* 
In carrying out some of these a bottle of capacity II litres was 
chosen, and fitted with a rubber stopper conveying giis and witter tubes 
and insulated leads for the sparking wires. The gases wrn- itdmtttrd 
by displacement of water, the air being first added tit nearly MiHicicnt 
amount, followed by a measured volume of inilammnitlc giw. KnutUy, 
the total volume was brought to 10 litres by the addition erf Htiillririif 
air. The water remaining in the vessel, amounting to alwut t litre, 
enabled the gases to be thoroughly admixed by shaking. This procedure 
necessitated the experiments being confined to gases saturated with 
moisture. In the ease of gases of hut slight solubility tnixt tires eon til he 
made accurately to one part per thousand. For upward ignition, tin- 
bottle was supported upside down on n tripod stand ittid the sparking 
gap extended about 2 cm, above the surface of the watrr. When 
downward ignition was required, the bottle stotxl on its Irnse. As the 
beautiful vortex rings of (lame rising through the mixture wen* MHHI 
extinguished owing to the limited capacity of the bottle it was int|*ofsihic 

1 Burgesa and Whoelrr, Trttn*, Ghem. ^ 
rend., 1914, 158, 1793, IfflH). 

s Whoelor and Win taker, Tmw. 67iw, /foe., I til 7, in, 2 

3 Burgass and Whooler, for. dL 

1914, 105, ; !^i>rttt<rJttiiutu*t s f V 

f ' 



to deeide whet her suoh rin^s were oapable of travelling indefinitely, 
or if they \vould tend to break up and produee a general inflammation, 
or eventually heeome extinguished. A lon# H reetangular tube was there- 
fore eonstrueted, two sides of which were of wood and two of plate glass. 
Square in eross-seetion, and of total length 1*N metres, its eapaeity was 
170 litres. Its top was of wood, and its bottom open, but water-sealed 
during experimentation by immersion in a tank. The gases wen* 
admitted by dtsplaeing water, and ignited electrically. An analysis of 
the gaseous mixture was made, as a cheek on the accuracy of mixing, 
just prior to the test of its intlammabiHty. The methane was prepared 
from aluminium carbide and water, with subsequent removal of acetylene 
and liquefaction to separate hydrogen, 


Mi'thuitt' JHT <*mit. by Volume*. 

ctnf. by Volume*. 

I**nvw Liiiiit, 

l*p|Hr Limit. 




5tt l 

1VH l 

not < 5-1 l 

not - 11-H 1 

JMJ 4 

25-0 4 

<) * 

121- 4- * 

JMI 4 

ia-7 4 

5' J> l flume travels 

only along top 

of tube , 

14*B * 

a- 1- 4 

14-1 4 

' 3*U l all('!I| burned 

, t 

iii,; . <, ' 

'""/' . m 

. * % t 


t. . . . 


(*ctrat ignition in large 

Vertical tube Hosed at! 

both ends : 
., Hot torn ignition , 
fe, Ignition at top 
Ilori'/otttal tube clos(*d 
both ends . 

Ignition one end 
Under nligbt shook 

I*erfeetly triui<juil 

' l)u " uw 

With a 5 ( 1 per rent, methane mixtftfe"inl.hiH large box, a ring of 
wa fortnc*d which travelled iibout 110 'tn., broke* quickly, and 
formed 11 tongue of Haute which travelled another BO cm. before extinction. 
With 5'1I per cent, methane u stout ring of flame travelled it few cms. 
and resolved itself into a steady (lame nearly IIH wide an the box, 
travelling right to the top with a swaying motion. This experiment 
could not be sat isfaotorily repeated, and even a 5*5 per cent, mixture 
failed to yield a Hume %uf!leiently strong to traverse the whole box ; 
but. with 5*0 per cent, of methane," a steady (lame with n convex front 

L Chfm, .Vac., 1014, 105, 250. 
;, Wrf.. 1010, IIS27, 

1 .mil! Whwfor, 

s < k <iwiuvi iI Hriiwlfy, > 

riwit4*r and 

Wrf., 1921, H9t 1077. 


pawii f hroujjhout the whole mixture. The authors therefore conclude 
thai the ilamrs of mixtures containing 5-3 to 5-6 per cent, of methane 
an- \iry snisitivi' to extinction by shock, and that a 5-6 per cent. 
ifiixiutv will in variably propagate Hume when the shocks are no 
;rmttT th t iii thosr occasioned by the somewhat violent bubbling of 
JJiis through witter. When, however, circumstances are such that 
a tranquil passatff i s assured, 5-3 per cent, is the lower limit of 

The ioreirointj data, in so far as methane and ethylene are concerned, 
may be summarised as shown on p. 97. 


Widely differing results have been obtained for the limits of in- 
flammability of hydrogen-air mixtures, as is evident from the following 



Lower Limit 

Per cent, by 

Hijrher Limit ; 

nf Hydrogen. ; 

Per cent, by | 

Volume. I 


7-7 to 8-3 

H-2 to 9-5 




9-78 to 9-96 

50 to 60 I Wagner, Bayerisches Industrie und Gewer- 

\ beblatt, 1876, 8, 186. 
8Cl I Mallard and Le Chatelier, Ann. Mines, 

j 1883, [8], 4, 347. 
75 ! Brooekmann, J. Gasbeleuchtung, 1889, 

32, 189. 

64-7 to 65-0 Roszkowski, ibid., 1890, 33, 491, 524-, 
535, 553 ; Zeitsch. physikal. Chem. 9 
1891, 7, 485. 
| Clowes, Detection of Inflammable Gas 

and Air, 1896. 
Le Chatelier and Boudouard, Compt. 

rend., 1898, 126, 1510. 
HO " Bunte, Ber., 1898, 31, 19. 

Eitner, HabHitations-schrift, Munchen, 


62-75 to 


In sphere of one litre. 
Downward ignition in cylinder. 
Upward ignition in cylinder. 
Teclu, J. prakL Chem., 1907, [2], 75, 212. 

Coward and Brinsley, Trans. Chem. Soc. 9 

1914, 105, 1859. 
Coward, Carpenter, and Payman, ibid., 

1910, 115,27. 

These divergences are due partly to the different methods adopted, 
as witness KitiK*r's results which may be useful compared with those 


found by Burgess and Wheeler, under analogous conditions for methane- 
air mixtures l and partly owing to lack of appreciation of the influence 
of minor factors upon the results. Of these results undoubtedlv the 
most reliable are those of Coward and his co-workers, obtained by 
methods already described. 

A similar want, of accord is manifest in the results given for the limit- 
mixtures of hydrogen and oxygen. 



Lower Limit 

of Hydrogen. 

Per cent, by 


Upper Limit 

of Hydrogen. 

Per cent, by 



9-5 to 10-0 

6-7 to 8-3 

4-4 to 5-1 

10-0 to 11-1 

5-7 to 6-7 
13 to 14 

5-8 to 6-4 
9-4 to 9-7 

9-1 to 9-8 

95-2 to 96-3 
95-8 to 96*7 
91-2 to 92-5 

92-4 to 93-2 
91 to 92 

90-8 to 91-0 


Humboldt and Gay Lussac, J. Phi/s., 

1805, 60, 129. 

Davy, Phil. Trans., 1817, p. 45. 
Turner, Phil. J. Edin., 1824, 11, 311. 
Regnault and Reisct, Annalen, 1850, 

73, 129. 

Bunsen, Gasometrische Methoden, 1857. 
Wagner, Bayerisches Industrie und 

Gewerbeblatt, 1876, 8, 186. 
Bunsen, 1877. 
Roszkowski, Zeitsch. physikaL Chew., 

1891, 7, 485. 
Eitner, Habilitations-schrift, Mil nchen , 

Fischer and Wolf, Ber., 1911, 44, 2956. 

Carbon Monoxide. 

The following results have been obtained by different investigators 
(sec p. 100) for the lower and upper limits of inflammability of mixtures 
of carbon monoxide and air. The wide divergence which characterises 
the published data for hydrogen is not so evident, for the results agree 
much more closely. Undoubtedly the most reliable are those of Coward 
and his co-workers. 

Organic Vapours. 

The limits for the propagation of flame by twelve organic 
vapours when mixed with air in glass tubes 5*0 cm. in diameter, 
determined, unless otherwise stated, at approximately 18 C., are given 
on p. 100. 2 

1 See Table, p. 93. 

2 White, Trans. Chem. Soc., 1922, 121, 1257. 




Lower Limit 

Upper limit 


of Carbon 

of Carbon 



Per cent, by 

Per cent, by 



14-3 to 16-7 

75 to 80 

Wagner (1876), loc. tit. 

14-1 to 14-3 

74-6 to 74-8 

Roszkowski (1891), loc. cit. 



Clowes (1896), loc. cit. 

15-8 to 16-0 

72-5 to 76-5 

Le Chatelier and Boudouard, Compt. 

rend., 1898, 126, 1344. 

16*4 to 16-6 

74-8 to 75-1 

Eitner (1902), loc. cit. 


. . 

Coward and Brinsley, Trans. Chem. 


1914, 105, 1859. 

. , 


Coward, Carpenter, and Payman, 


1919, 115,27. 


(White, 1922.) 






Ethyl ether 

1-84 to 48*0 

1-90 to 6-25 

1-88 to 33 

Acetone .... 

2-90 to 12-6 

2-99 to 8-40 

2-96 to 9-9 

Methyl ethyl ketone , 

2-05 to 9-9 

2-10 to 7-4 

2-05 to 8-5 

Benzene .... 

1-45 to 7-45 1 

148 to 5-55 1 

1-46 to 6-65 1 

Toluene .... 

1-31 to 6-75 1 

1-32 to 4-60 1 

1-30 to 5-80 1 

Methyl alcohol . 

7-10 to 36-5 1 

7-65 to26-5 1 

7-35 to 30-5 1 

Ethyl alcohol . 

3-69 to 18-0 1 

3-78 to 11-5 1 

3-75 to 13-8 1 

Ethyl acetate . 

2-32 to 11-4 1 

2-37 to 7-1 1 

2-35 to 9-8 1 

( 4-32 to 16-0 

Acetaldehyde . 

4-21 to 57 

4-36 to 12-8 

\ and 

( 25 to 45 3 

Ethyl nitrite . 

3-51 to > 50 

3-91 to 14-4 

3-63 to >45 

Pyridine .... 

1-81 1 to 12-4 2 

l-SSUo 7-2 1 

l-S^to 9-8 2 

Carbon disulphide 

1-41 toSO-0 1 

2-03 to 34-0 

1-83 to49-0 1 

The two ranges for acetaldehyde with horizontal propagation are 
noteworthy, due to the possible existence of two kinds of flame, namely 
the normal hot flame, and a " cool " flame (see p. 76) respectively. 

Influence of Temperature. Rise of temperature effects an 
appreciable reduction in the lower limit of inflammation as is to be 

Determined at 60 C, 2 Determined at 70 C. 3 " Cool " flame limits. 



anticipated from theoretical considerations. This is evident from the 
following data, which pertain to methane in air : x 


Initial temperature C. 
Lower methane limit 









Similarly, the upper limit rises with the temperature : 




400 600 
14-70 16*40 


Initial temperature C. . .20 

Upper methane limit . . . 13-40 

Thus the total influence of the temperature is to widen the limits of 
in Ilammability . 

Influence of Pressure. Both the lower and the upper limits of 
inflammation are raised by increase of pressure. Hence the total effect 
upon the limits of inflammability is the algebraic sum of these two. 
In the case of methane the data 3 are as follow : 


(Mason and Wheeler, 1918.) 

Initial Pressure. 

Lower Limit. 

Upper Limit. 

mm. Mercury. 

Methane, per cent. 

Methane, per cent. 








. . 







9 f 


f 4 





The lowest ignition-pressure of electrolytic gas observed 4 is 5 mm. 

Influence of Oxygen. In a series of experiments carried out with 
a Bunte burette (19 mm. in diameter and 115 to 120 c.c. capacity), top 
ignition being adopted, Terres 5 has found that whilst the lower limit 
of a combustible gas in air is but slightly different from that in oxygen, 
the upper limit is considerably higher in pure oxygen. His results are 
shown on p. 102. 

Parker, 6 using a glass globe with central ignition similar to that 
figured on p. 92, determined the lower limits of inflammation of 

1 Taffanel, Compt. rend., 1913, 157, 593. See also Burrell and Robertson, U.S 
Bureau of Mines, Technical Paper No. 121, 1916. TaffanePs results are in close accord 
with the later work of Mason and Wheeler (Trans. Chem. Soc. t 1918, 113, 45), and of 
BurreU and Robertson, J. Ind. Eng. Chem., 1915, 7, 417. 

2 Mason and Wheeler, loc. cit. The data refer to downward propagation of the flame 
in a vertical tube. 

3 Mason and Wheeler (loc. cit.) 9 who confirm, and extend the earlier work of Terres 
and Plenz, J. Gasbeleuchtung, 1914, 57, 990, 1001, 1016, 1025. See also Burrell and 
Robertson, loc. cit. ; Leprince-Ringuet, Compt. rend., 1914, 158, 1793, 1999. 

4 Coward, Cooper, and Warburton, Trans. Chem. Soc., 1912, 101, 2278. 

5 Terres, J. Gasbeleucht., 1920, 63, 785, 805, 820, 836. 

6 Parker, Trans. Chem. Soc., 1914, 105, 1002. 



methane with mixtures of oxygen and nitrogm, the oxygen ranging 
from 100 to 13-25 per cent, by volume. His results are .shown din- 
grammatically hi Jig. 14. 


(Trnvs, lii'JO.) 

Ua or Vapour. 

Carbon monoxide 



Ethane . 




Water gas 

Coal gas 

Light petroleum vapour 

Limit* *{ 

hi Air (fw-r n-j&t.j. 

LV<i li> 70-11 
IK"* to IM'U 
<i-a to ! I-!l 
!"J to !K"t 

HI to t Ml 
3'5 In 52 -:j 
2-K hi U-h 

12-1 tu *'(!! 
!>%S h* IH'.S 
1 K I tt 5-U 


!-ii i\*--r ri'iil, !. 
<'." to vtl "II 

11 ht r.i-s 

:!:> to vj t 

1*'H to 'JiHf 

H-o to ?a ti 

'.M hi 2S-| 



5 6-3 




FK:I, 14, y*wpr limit* IP! miittmiir (I'urkvri lifi-i*, 

' lower limit ofiiidlmnc i-i-wln-H iutiiiiiii mt ,| ^^i, m <s 

t ig 25 per cent, of oxygen ami 75 j*rr mil, of nit ru-n Ini-rras.- 

ui the oxygen eontent I-IJUM-H gnichiiil rinr in Ilir |ou,-i- l,i,,ii. i.lnKt 

! ""r S 7 f " y" 1 ^ FIHr ' This !lltlrr ri *' V IH- rx,i|i.,,t| in tl,,- 
Jereasecl rate ol combujtioii mid thr r.,M..mrut ^rmt'r Im. ..HM-..I 

ril. u tin MI 



The fact that the lower limit of methane is greater in the case of pure 
oxygen than with air is piobably connected with the fact that the 
specific heat of oxygen is higher than that of air. 

Residual and Extinctive Atmospheres. Closely connected with 
the foregoing study is that of the composition of the residual atmosphere 
in which a substance has been burning, and of one which just extinguishes 
a flame the so-called extinctive atmosphere. Their composition is not 
determined solely by the percentage of oxygen ; the nature of the inert 
or diluent gases also exerts an important influence. Thus, for example, 
nitrogen has a less powerful extinctive effect than carbon dioxide. 1 
Theoretically extinctive and residual atmospheres are the same, but, 
owing to the difficulty caused by the products of combustion raising 
the temperature of the contents of the containing vessel, the flame is 
apt to continue burning for a longer time than if the surrounding air 
remained at the original temperature. The percentage of oxygen in the 
residual air is thus slightly lower than that in an extinctive atmosphere. 
Under theoretically ideal conditions the results would be the same for 
both residual and extinctive atmospheres under identical conditions. 
The following results are interesting : 


Candle flame 2 


Alcohol, burning on cotton wool 3 

Wood charcoal glowing to ex- 
tinction 3 . 

Sulphur burning 3 . 
Glowing wood 4 

Residual Atmospheres 
(Volume per cent.). 

15-16 oxygen. 
80-81 nitrogen. 
3 C0 2 . 

13-15 oxygen. 


4-6 CO 2 

11 oxygen. 
82-5 nitrogen. 
6-5 C0 2 . 

9 oxygen. 
83 nitrogen. 
8 CO 2 . 

13-5 oxygen. 
16 oxygen. 

It will be observed that the residual atmosphere for a candle closely 
resembles that exhaled by human beings (see p. 185). It may be 
inhaled by most people for a considerable time without producing any 
noticeable ill effects. 

1 Dollwig, Kolls, and Loevenhart, J. JBiol. Chem., 1915, 20, xxxii. Compare Jorissen, 
Rec. trav. chim., 1920, 39, 715. 

a Clowes, Proc. Roy. 8oc:, 1894, 56, 2 ; 1895, 57, 353. 

3 Miiller, Chem. Zentr., 1917, i., 991. * Jorissen, Chem. WeeJcblad, 1913, 10, 1057. 

1()4 OXYflKN'. 

It is iutfivstiittf to mitr (hut <lmv;iM' <i' (uvsMtiv r.uvs tin- i\ym 
limit oi' tlu- msidual atmosphere as j,ho\vn in tlw t'ullwm Inlilc : ' 


j . U\Ytfrji |*'r I't'lll. IV ; 

| TUl lt*<^ttt% mm. V.-ittiiw MI Ur*itul 

Cmulle . , . 1 TM-7 I MM 

I !U UMi 

KUiyl alcohol burning from 1 7*tti-7 l*Vi 

asbestos wick '. . j t^' 1 i!|s|1 

The oxygen in rrsiclual atnit)s|tlt<Tt*s J'ruiu jrls til" turttitin iuutilm>ttlilf 
has htvn cldcnniiUHl hy Hlu'juJ a s fc 

Mcthaiu- ..... t^- 

Propiuu* . i^"* 1 

Ilufunc . MH 

IVutanf , MJ-i 

Cyanogen , 1 5'*$ 

Hydrogen . *i'7 

The slight inorciisr in oxyjjrti uutU*nthtr on ascrittliti^ ttn* iin- 
scries of hydrocarbons is [tfohahly due to tlir highly rxtiiirtivr rfffil 
of tlu k increasing proportion of curoou tito\iilt\ tt which rcfrtvtuv |$ii% 
already been nuuU % . Tlu 1 Itnv oxygen cmtlriii in the ra*e of Itytiro^t-ii 
is noteworthy. 

In the case of burning gasc-s, fhr coui|HMtiuu tif the r\l metier 
atmosphere is alfec'ted by sevcrul fit<*tirH uotttliiy the Hjicctl itt wlitrli 
cither the cornhustihle gas or the- ntmtwphere hitrrotmtlititf it i% nlio%vrtl 
to move. Hhead found that for it const nut %prrd of rciiiitnifiiililr 
issuing from a jet 1 , and fed at constant speed by itir into nn 

eneircling container* flu* extinct ive utin<tHpht*rcH of the four tn%%rr hytlro 4 
carbon gases wen* identical, wid etjntiiiiird upprtixiumtrty Itl'il JMT cent. 
of oxygen. Tins suggests a similar primary react ion in nirli nw. 
With increased speed the oxygen content fulls to a iiiiiiiiniiiti. Tin% * 
jirobably due to the fact that with it slow Hj*wt of ntmmphrrc thr 
oxygi'n is constnned ttio quickly, but upon inrrrii%iiig the the 

eoinbustil)le mixture is formed stiUicientiy rapidfy to iiiiiiiitisiii fliimt-. 
The limiting speed will be reached when the rate of inflammation of 
the mixture is balanced by the upward movement. Thin in a jttttnt of 
considerable practical import, inasmuch as 1111 atmosphere, tun 

1 Doll wig, KoH, and Ixiovtmhftrt, J. Amcr. Ch&m* fk*., I III 7, 39, ; J, ('ken,, 
1815, 20, xxxii.-xxxUi. 

2 Ilhoad, J. Soc*. Ckem. tnd., 191 B, 37, 274 T. 



in oxygen to maintain a flame under ordinary conditions or when fed 
to it at a slow speed, may be able to maintain that flame at a higher 

Coal gas, on the other hand, was found to behave quite differently. 
The oxygen content of the extinctive atmosphere was almost in- 
dependent of the speed of the atmosphere itself, but fell with increasing 
speed of the gas stream. This is undoubtedly due to the fact that coal 
gas is a mixture consisting mainly of hydrogen and methane, the 
extinctive atmospheres of which possess widely different oxygen 
contents. Hence, upon occasion, the atmosphere might contain 
sufficient oxygen to support a hydrogen flame, but not one of methane. 
With slow gas streams the hydrogen would be burned too quickly. By 
increasing the speed of the gas and hence of the hydrogen, the com- 
bustible mixture of oxygen and hydrogen is produced with sufficient 
rapidity to maintain a flame. The data in the following will serve to 
illustrate the foregoing conclusions : 


(Rhead, 1918.) 


of Jet, mm. 

Speed of Gas. 

Speed of 

Oxygen in 
Per cent. 

Methane . 
Propane . 





Propane . 






Coal gas . 






Coal gas . 

5J ' 





Closely allied to this is the very important problem of the inflamma- 
bility of hydrogen gas as used for the inflation of balloons and airships. 
The only non-inflammable gas that could be used economically for the 
purpose is helium, but, as this gas is twice as dense as hydrogen, its 
lifting power is somewhat reduced. It follows, therefore, that if a 
mixture of the two gases could be found which is non-inflammable, the 
result would be more efficient quite apart from financial aspects of the 
subject. It appears that, under favourable conditions, a jet of helium 
containing more than 14 per cent, of hydrogen can be ignited in air ; 
but in the case of a gas issuing from an orifice under conditions pre- 
vailing in balloon practice, a mixture containing even 18 to 20 per cent, 
of hydrogen will not burn with a persistent flame, and might, therefore 



be employed for military purposes with .safely. Mixtures containing 
upwards of 20 per cent, of hydrogen would he dangerous. 1 

I ( JNITION TKM IT, i; ATI* H t-;s. 

The temperature at which rapid combustion becomes mdepmdent 
of external supplies of heat is 'termed the ignition temperature. 
Wheeler 2 defines it; as k * the lowest temperature to \\hieh a mixture of 
a combustible gas \vith air or oxygen must be raised in order that the 
chemical action between the #as and the oxygen can become so rapid 
as to produce Hame." A clear conception of this phenomenon - 1 may be 
obtained by supposing a combustible mixture of jjases, sueh as that of 
air and the" vapour of carl>on disulphide, to issue through an onlice into 
an indifferent atmosphere. If the orifice is surrounded by a 1111*4 *!' 
platinum win*, which is gradually heated up by a currrtit of rlectneitv, 
a ilame will gradually make its appearance. If, as smai as this is 
observed, the heating of the wire by the current fe discontinued, tbr 
ilame will disappear; it. is, in fact, not self supporting, bnf dcpmds 1*11 
the accessory supply of heat- through the electrically heated wttv. If 
now the ring is raised to a higher temperature a brighter tlame results, 
owing to an increased rate of chemical action, and at last we shall tvaett 
a point where it, is possible to cut off the electric current without causing 
at the same time the extinction of the flame. This is the true 
temperature' of ignition, the temperature at which the reaction j*ncreds 
at a rate just suHicicnt to overbalance the loss of heat by radial tun* 
conduction, and convection from the burning layer of gases, su that the 
next layer is put in the .same state, and steady combust nm prtH'erts, 

The minimum temperature at which the react ion in a ri*iuhustiil- 
mixturc of gases becomes self-supporting is termed 1 tin- xnb-ignitiun 
temperature. This may not correspond to ordinary ignition. In iitany 
canes an ordinary flame, causing more or less complete and mpiil 
combustion, caunot be obtained by heating a gas tn its sitltj^uitiidt 
temperattire, and in those* <*ases in which Mich a llaiue ap|HMts it i> 
only produced through the inlermediury of n eool flame |p, 7UJ. 

In the case of a few substances the ignition temperature lies at 
or below that of the atmosphere. Liquid phosphorettetl hydrogen, 
P 2 H 4 , and certain metallic idkyl derivatives an- eases in point , Thcst- 
are spontaneously inHamnmble (see p. SO). Pure gaseous hydroum 
phosphide, FIl a , may be ignited by n tube of boiling water, and earlinii 
bisulphide vapour by a gently heated glass rod, the ignition temperature 
in this latter case being about 120"' (*. An interesting of ignit urn is 
afforded by ordinary ethyl ether. 6 Its vapour ignites when mixed with 
air and allowed to rush into a partly exhausted tube. The ctm\crsmu 
of the translationul energy of the* mixture into heat an the gases enter the 

1 Ledig, J, Itul, tiny. ClwM., HJ20, ia t lolm, t>ifri<rt?ttl t^ult* wr*< *4it 4 $iit-l t.y 
SatterJy and Burton (Tmm. Roy. Nor. (.fautdti, H)Hi, 13, fltf, 21 tK *!* !iiiil ihai, tit 
their particular experiment*, the ixwentage ! hytir'it imtil I it' riii^i i ;*ii U<f*r*' 
the mixture became inflammnhlv. With tiw* ihun 2H |r nnii, *4 hy*tr<^i>n t|$r 

3 Wheeler, Tram. ImL Mining JSng., 1 112*2, 63* 14. 

8 Borrowing Smithelb* illuatratitm. ll./t. Itrptrto, I1M.I7, 77, 4il!i, 

4 White and IMce, Trann. Chem. A'oc., 10H, 115, UtW. 

8 McClelland and Gill, tici. Pr&c. M&y. Itubtin ^oc., 1920, i6 t Ml 


tube effecting a rise in temperature sufficient to attain to the ignition 

In 1816 Davy 1 gave the results of the first systematic attempts to 
determine the ignition temperatures of the more common combustible 
gases. He found as follows : 

Ignition Temperature. 

Hydrogen . . . . . " Lowest visible heat of iron " 

(i.e. approx. 500 C.). 

Red heat (i.e. approx. 700 C.). 
Firedamp (methane) . . . Iron in brilliant combustion. 

The importance of the subject, particularly in connection with 
hydrocarbons, will be evident when its bearing upon explosions in coal 
mines is remembered. 2 Of modern methods of determining ignition 
temperatures, the following deserve consideration : 

I. A stream of the combustible gases mixed with air is passed 
through a tube, the temperature of which is raised until the gases 
inflame. 3 

In the experiments of Meyer and Munch the mixture of combustible 
gases and air (or oxygen) was passed through a capillary tube to the 
base of a small glass vessel, in which the ignition was destined to take 
place, and which was inserted in the bulb of an air thermometer. When 
the mixture inflamed, the temperature of the gases was calculated from 
the volume of the gas in the air thermometer. 

This method is simple and possesses the advantage of yielding results 
at atmospheric pressures. But the results are liable to be influenced by 
the catalytic activity of the walls of the tube. Some of the results 
obtained in this manner are given in the table on p. 108. 

It is important to remember that these results refer to the ignition 
temperatures of the gases when in motion. These are not quite the 
same as when the gases are at rest. Thus, it has been observed 4 that 
the ignition temperature of detonating gas at 150 mm. pressure falls as 
the velocity rises to a maximum, after which further increase in the 
velocity has but little influence. This is well shown by the following 
data : 

Velocity 5 .... 37 93 130 187 280 
Ignition temperature, C. . 601 594 593 592 592 

The ignition temperature rises with the pressure (vide infra). The 
diameter of the tube is without influence between the range 3-6 to 11 mm. 
With tubes of diameter less than 0-5 mm. no definite ignition temperature 
has been observed. 4 

1 Davy, Phil. Trans., 1816, 106, 7. 

2 A useful summary on the ignition of firedamp is given by Wheeler, Trans. Inst. 
Mining Eng., 1922, 43, 14. For researches on the inflammation temperatures of mixtures 
of organic vapours alcohol, acetone, ether in air or oxygen, see White and Price, Trans. 
Chem. Soc. t 1919, 115, 1462 ; Alilaire, rend., 1919, 168, 729 ; Moore, J. Soc. Chem. 
2nd., 1917, 36, 109 ; Holm, Zeitsch. angew. Chem., 1913, 26, [1], 273. 

3 Mallard and Le Chatelier, Compt. rend., 1880, 91, 825 ; Meyer and Freyer, Ber., 1892, 
25, 622 ; Zeitsch. physikal. Chem., 1893, n, 28 : Meyer and Munch, Ber., 1893, 26, 2421 ; 
Gautier and Heller, Compt. rend., 1896, 122, 566 ; Helier, Ann. Chim. Phys., 1897 [7], 10, 
521 ; Bodenstein, Zeitsch. physikal. Chem., 1899, 29, 665. 

4 A. Mitscherlich, Zeitsch. anorg. Chem., 1921, 121, 53 ; 1916, 98, 145. 

5 The velocity is expressed as the number of c.c. passing a cross-section of 1 sq. cm. 
per minute. 

It VI 1 MI s \N IlY 


,f i ; ^ 

*,, ] 

'A *'* * ,- f 

H - .'j , * M f ' 

^ " 112, Vf 

if i ', t ', r 

10, */.' 

M < , f I r ; X*-^^ , 

> I > M f i ' I M i j 

1 1' *) ^ i% ? s , , 4* ', i,i* *>**> 

t 4'fM'tl '> I ,*,.\!. J 

If "> 43 


*t I ,i^' * )<H! il * ti i ,iH** t utl* <Hi ! i >l 1 t ^s f<Ut I 

*h* n t M*< '"*'"* i i t t/ ^ ( j|** </^i*( A i* 4*1*1 'I ^t v ^ * 

f c i,it?fi%ti!fli 4 M v(,fl t) ,i t,*M I 1 Hit ^4 J *| ii' !i **> 

* l^lur, 4* 1 t '*<M 1rv* f kn r *, r , I #** ff ^4 

4 i H* I* ^i* I-AI^,'* ftii *' J 1# f *? II w ^A/J"" f S I '*!' 


only ensured u constant supply <iffrcsli hot jjas, Init jiNn Hi 
products of slow combustion. It was found flint 
constant results could be obtained provided t be- 
rate of flow of the combustible #as through t br n 
fice Gaud the diameter of the out ertnbe I) exceeded 
certain mininnim values. Thus, for example, in th 
case of hydrogen and oxygen, with an outer tube 15 
mm. in diameter and an orifice of I nun, diaim trr, 
a constant ignition temperature was obtained pro 
videcl the volume of hydrogen escaping through 
C exceeded c.c. per minute. With a widrr tube 
u more rapid How of hydrogen was cssrnhai. 
Catalytic action of the walls of the tubts is 
clearly reduced to a minimum. It will be <*b 
served that the temperature* of ignition yiilditl 
in this apparatus is not quite the saint* as tbat 
obtained by Method I. It is that to witirti tin 
gases must, be heated separately in ordrr to in 
flame immediately upon contact. 

Experiments carried out with hydrogen itntl 
oxygen at pressures ranging from 42H tutu, to 
1400 mm. yielded interesting results, MHUI **f 
which were as follow : 



(Dixott utul Cownnl, 1U.) 

Prwwurts nim. 










5 HI I 



1 0<JO 


11 IIS 


I -W 


Mr tin iif liir'i- 

Mrftll tif I Wit, 

^iriiii t if fiiiir, 

Mrnii iif 

The ignition tcmpcrattm* in srrn to rinr but n% t| lr 

falls to almost half an iitnicmplirrr but iniwii^r uf i, flr 

atmosphere effects 11 eonsidrntblr drji rr .^itiii t*f tttr 
ture. I he rate of <U-prr*sum, whiUt uvll miirkni tin tt> mir mni iniif 
atmospheres is much slower aftcrwardM, atul t iiitii 'i| tr 

Fairly al 

follow ; 

main results obUineti at 




(Dixou and Coward, 1909.) 



Combustible Mixtnro. 


Combustible Mixt nro. 



l> 0. 

Hydrogen -oxygon 


Carbon mouoxide*- 

Hydrogen-air . 


oxygen (dried ovt v r 


550- 700 

sulphuric aeid) 

089 (>95 


050 750 

Carbon monoxide-air 

Ethane -oxygen 

500 -030 


044 058 


500 630 

Cyanogen-oxygt v n 




Cyanogen-air . 

850 802 


500 519 

I lydrogen sulphidc- 

Ethyl one-air . 

542 5 -47 




41 0-140 

Hydrogen sulphide- 

Acetylene-air . 

400 140 


ft 10 379 

C ar b o n inonoxide- 


700 800 

oxygen (moist) 

<>;*7 (>(>(> 

It is interesting to note' that the ignition temperature* of hydro^n In 
oxygen was founel the same* as for hydrogen in air. The* same* is true* 
generally for carbon monoxide* and ethane ; but not for methane or 
ethylene, Cyane>gen and hydrogen sulphide* ignite 1 at te*mperature*s in 
oxygen considerably loweT than, in air. In the* latter case*, indeed, then* 
is a eliffe*rence of 1 M) u C. 

III. Adiabatic Comprcssiem. It is a matter of common knowledge 
that when a gas is rapidly eoinpn*sscd, a rise in temperature takes place*, 
the* relationship betwee^n (he initial and final temperatures being given 
by the* (*xpre i ssion 

when T is the* absolute temperature and y the ratio of the gaseous 
specific heats at constant pressure and volume*. 

It is ele*ar that if a mixture* of a combustible gas and air were employee! 
and the v eompre'ssion we're* suUicie*ntly great, the* temperature might- rise 4 
to the* ignition-point anel rapid <*ombustion i*nsue. This was suggested 
many years ago by Ne*rnst, anel carrie*d into effect by Falk l in 1JMHJ 
anel by J)ixon 2 eight years later. Kalk's method, which may be regardcd 
as of a pione*e*ring character, is open to criticism s anel has led to untrust- 
worthy results. 

The 4 apparatus employee! by Dixon and Crofts 2 is shown in fig. HI, 
and consisted of a stce'I cylinder, 5(1 cm. in length, bored with a central 

1 Falk, J. Arner. Chtm. Moc.,, 1006, 28, 1517 ; 1907, 29, 

Dixon and Crofts, Tran*. Chtm. Noc., 1914, 105, 2030. Soa also Ttxarti and Pye 

Mag., 1022, 44, 79, 
3 Dixon, Bradfthaw, and Campbell, Trantt. Chem. fi&c., 1914, 105, 2027. 






cavity, which at the base was enlarged abruptly so that it could be 

elosed with a steel plate, kept in place by means of a powerful 

screw. An annular washer of lead served to keep the joint gastight, 

the lead being squeezed well into place 

with the aid oi k the screw. A hole was 

pierced through the side wall A near 

the bottom of the narrow bore, and 

fitted with a steel plunger, so that the 

cavity could be elosed during compres- 

sion or opened in connection with a 

gas-holder or the outside ait when Till- 

ing or emptying. A cylindrical piston 

fitted loosely into the explosion cham- 

ber, its lower extremity being fitted 

with a leather washer and a, bron'/e 

cap, which made a, close sliding lit with 

the cylindrical walls. 

The 1 descent of the cylinder was 
centred by the steel collar, and hard 
chrome steel plates, cut with a, slot, 
could be placed on this collar to stop 
the piston-head at any point in its de- 
scent. The cylinder was held by an iron 
frame, which rested upon a large con- 
crete bed. It was surrounded by a 
brass water-jacket, not shown in the 
figure, for regulating the temperature. 
The compression was effected by allow- 
ing a mass of iron, weighing 70 kilo- 
grams (2-5 cwt.), to fall from a given 

was employed 

FKJ. 10. "Dixon and Crofts' 


height, usually 1*T> metres (5 feet) on 

to II. Lanolin c 


The value for y was taken as !!(), 
and the assumption made that there was no loss of heat during the 
compression of the gases in the cylinder. Actually that was not quite 
the case, but experiment showed that the compression lasted only about 
0*00 second in the ease of electrolytic gas, so that the loss of heat would 
be small. The effect would be to raise the calculated temperature of 
ignition. The experiments were carried out by the method of trial and 
error, by regulating the number of steel collars until an explosion just 
took place. Tin* initial and final volumes were thus known, and these 
data, coupled with the initial temperature*, enabled the ignition tem- 
perature to be calculated from the equation given above. The main 
results obtained are given in the table on p, 112. 

A study was made of the influence of the initial temperature upon the 
ignition, 1 but variation between the normal temperature of the room 
and 100 C. made no appreciable difference. Increase of pressure 
likewise appeared without effect, although reduction to half an atmo- 
sphere raised the ignition temperature from 520 to 549 C. Addition 
of excess of oxygen beyond that required for complete combustion 

THxon and Croftfl, lor,. cU. 



PRESSION. (Dixon and Crofts, 1914.) 

Relative Volumes of 
the Gases. 

Initial Tempera- 
ture, 0. 

Initial Pressure 

Ignition Tempera- 
ture, U 

2H 2 +0 2 









2H 2 +0 2 . 










2II 2 +0 2 . 




2H 2 +0 2 +0 2 


2H 2 +O 2 +70 


2H 2 +O 2 +150 2 . 


2H 2 +0 2 +310 2 . 

2H 2 +O 2 




2H 2 +0 2 +H 2 


2EU+0 2 +2H 2 . 


2Hj+O a +4H 2 . 


2H 2 +0 2 +8H 2 . 


2H 2 +O a +13H 2 t . 


2H 2 +0 2 . 




2H 2 +0 2 +N 2 


2H 2 +O 2 +2N 2 . 


2H a +0 2 +4N, . 


2H 2 +O 2 +8N 2 . 


2H 2 +O 2 +14N 2 . 



(Crofts, 1915.) 

Gaseous Mixture. 

Temperature, 0. 

2H 2 +O 2 














* Crofts, Trans. Chem. Soc., 1914, 105, 2036. 

f It is interesting to note that this mixture will not explode with a spark under normal 
conditions (Roszkowski, Zeitsch. physikal. Chem., 1891, 7, 485). 
1 Crofts, Trans. Chem. Soc., 1915, 107, 299. 



result i i d in a gradual depression of the ignition temperature * until, 
wlien the gases were in the proportions 2H 2 | ,T2O^ no explosion would 
take plaee. 

Addition of excess of hydrogen, on the other hand, served to raise 
the ignition temperature 2 steadily, with praetieally linear precision, so 
thai the temperature of ignition in the presence of ,r molecules of 
hydrogen, within the limits .r () and i:*, could he calculated from the 

OJIL | O, -| ,rll 2 ) explodes at (>!>(> \ lS,r)T. 

Nitrogen behaved similarly, 2 the corresponding expression between the 
limits ,r () and 14 being 

(2H 2 ! () 2 } ,rN 2 ) explodes at (52< | I !,*)" (\ 

IV. A fourth method, employed by Kiesel, 3 consists in raising the 
combustible gases separately to a given temperature, allowing them to 

. ( 

1 , 

w 1 



U~ r 

D l 



t y m , n<t WHIM * 

9 riJBl 


\\ (( 

0( V..__. 




HI t AH 


Ftu, 17, Fi','ii-lV iipjmmt IM ( H*J! ). 

mix, and noting ly means of j$ <tetieate membran< % or a manometer 
whether or not a difference in pressure* occurs. Variation in pressure 
indicates chemical change. 

The apparatus consisted of an iron globe (' (fig. 17), In which com- 
bustion took place. Into tins was Uxcl a thin-walled glass bulb CJ, 
attached to a manoinetrr M, and to tlu* oxygen supply * A small piece 
of metal is hung in the rubber-pressure tubing at H and can be re- 
leased at will, t' rests on an iron pillar A, and is kept in position by 
the iron tube I), which is pressed on to it by screwing up nuts K b K a . 

Tlu* apparatus was placed in an electric furnace and G filled with 

* FIrt otr-rwi by Mallard imI l# ClmfHttT, ( *;/<!. rt-ntt. t IKKO, 91, H'25, S<*r* alo 
ll/'lii*r Ann, <"A*w. !%/.*, IH!*7 10, * f t ; |l<lrii.Htiniu Zrit.irh. fthyxikuL (7*'/. IHIHI, 29 
Illlf* ; Kniirh, Mtwttt#h.\ iiH, 21, laiH ; Kulk, ./. .1wir. f 7/*'i. .Vw,\ llHMK 28, I f il7 ; ' ~ " 




oxygen. The temperature was now raised, and hydrogen introduced 
into C. A steady temperature being attained, as registered by two 
thermo-couples in C (not shown in the figure), the pressure of the oxygen 
in G was slightly increased, and the metal piece in B allowed to fall and 
break G, thus causing the oxygen to pour into the hydrogen. If com- 
bustion took place, a variation in pressure occurred which was registered 
either by the manometer or by a delicate membrane attached thereto. 
The following results were obtained : 


(Fiesel, 1921.) 

Gaseous Mixture. 

Dry Gases. 

Moist Gases. 

H 2 +0 2 . 


407 to 417 

3H 2 +20 2 


398 to 420 

2H 2 +0 2 


401 to 425 

3H 2 +0 2 



4H 2 +0 2 



The minimum ignition temperature was found to occur with 3 
volumes of hydrogen to 2 of oxygen, both in the dry and when moist. 
Further addition of hydrogen raised the ignition temperature, as was 
observed by Dixon and Crofts, but the results obtained by the latter 
investigators were very much higher (see p. 112). 

With the moist gases the rate of combination suggested a birnolecular 
reaction, which might proceed through the formation of hydrogen 
peroxide. For the dry gases the reaction was found to be trimolccular, 
as is to be expected from the equation : 

2H 2 +O 2 :=2H 2 O. 

The results for acetylene were not altogether satisfactory, the 
ignition temperature of a mixture of acetylene and air appeared to be 
about 390 C. 

V. Hot-wire Ignition. Attention has already been directed to the 
influence exerted by hot, solid surfaces upon gaseous combustion (see 
p. 70). Mallard and Le Chatelier examined the effect of heated wire 
gauze upon the combustion of firedamp, and several later investigators 
have studied the problem of gaseous ignition in contact with hot wires. 1 
These researches have been mainly concerned with methane and fire- 
damp. More extensive experiments were carried out by Thornton 2 in 
1919, who admitted various combustible mixtures to a small glass 
vessel A (fig. 18) of capacity 50 c.c. Thin wire B, soldered to thick 
copper leads C D, was then rapidly heated by an electric current. It 
was observed that there was for each diameter and metal a particular 

1 See Denoel, Ann. Min. Belg., 1907, 12, 1088 ; Cour|ot and Meunier, Compt. rend , 
1907, 145, 1161 ; 1898, 127, 559 ; Hauser, Lecons sur le Orison (Madrid, 1908). 

2 Thornton, Phil. Mag., 1919/38, 613. 




J ^S 

4 _. 





'MIX'] URF, 


Km. IK. Thurntun'H apparaf UH 

current which just caused ignition, provided the temperature rose 
suddenly and not gradually. The lowest, current required for ignit- 
ing the gases under these conditions was 
noted, and from this it was easy to cal- 
culate the temperature of inflammation. 
It was found that the phenomena of sur- 
face comhust ion played an important part, 
and temperatures of ignition were very 
much lower than those obtained by the 
methods previously described. Thus, for 
example, the ignition of hydrogen in air 
began when the temperature of the wire 
did not exceed 21*1*' (\, nearly 400 degrees 
lower than the value found by Dixon and 
Coward, namely, 582'' to 59-t" C. The in- 
fluence of variation of pressure* between 20 
and 000 em. of mercury was negligible, 
and the proportion of combustible gas 
exerted in general but. little effect Upon 
the igniting current. Clearly, therefore, 
these results an* more comparable with 
those* connected with surface combustion 
than with the ignition data determined by 
the methods previously described. 

In HUT McDnvid * suggested that igni- 
tion temperatures might, he determined by 

allowing the mixture of combustible gases and air to inflate* soap 
bubbles autl causing those to impinge upon a heated platinum wire. 
The* short time of contact with the* win* should reduce* to a minimum 
any surface net ion such as that detailed above. The results obtained, 
however* are of uncertain value,- 

Flash-point. The temperature at which the vapour of a liquid 
becomes inflammable in air when ignited is usually termed its flash- 
point* For legal purposes it. is often necessary to determine this 
temperature with accuracy, and carefully standardised apparatus is 
employed for the purpose. The flash-point of an oil is frequently a 
useful index of its purity. Thus, for example*, the presence of rosin 
oil, flash-point 155' to MJO C,, is readily detected in tins manner, hi 
linseed oil, flash-point 250' C, The following Hash-points refer to 

conuitou oils and spirits : :l 

Flnnh point " ( \ 

Linseed -oil ,.,... 250 

limit* oil 155 100 

Paraffin illuminating oils . , , IH 50 

Turpentine ,,.... H5-40 

itosin spirit ...... *$5 -40 

Naphtha . . . . . HI 21 

Methylated spirit , U- 10 

KUtyi alcohol. !MHf per cent. . , . 11 

KthiT * -41 

1 Mt'ltavul, Tfun*. r/ifw, ,S'r.,. UU7, III, HMKJ. 

3 \Vhit4 am! i*rir% i/wrf., lflH 11$* 1248. 

8 Further data urn givtm Iry Hnim, faltosh. anytiw, (Jhern., Itf 13, 26, 273. 

116 OXV<!K\'. 

The minimum le#d Ihish-point for illumiiutt iitif oils hi this etiuntry 
is 73 F., *>. J-S ('. 

For binary mixtures tf ethyl aleohul ami uatt/r tin- following vahu-s 
have been obtained : l 
Bthyl alcohol, permit. !>y weight , WMl 4 J7-2 t-Ht l-H *HH s.Vo SIM 7.V-I 

FlaBh-pomt u ( 1 . . . * . .II i:t l" it* lK* IT-.* i,v; '.MK> 
The Hash-point enuuot he calculated by simple proportion from the 

Hash-points of the eonslituents. 2 Increase of pressure tends to raise 

the flash-point. 3 Thus, in the* case of a kerosene, the fullmvititi data 

have been obtained : 

Pressure in nun, . 700 Kit X.'MJ nil:* 

Flash-point, ''('. . 'U :tti 'U VrJ> 

Flash-points determined in an oxygen atmosphere arc* appivetttblv 
lower than in air. 

The foregoing results refer to what may be termed the Inwr //*/*//- 
point, that is, the temperature of inflammation \\tini the combustible 
vapour is present in sutlteirnt quantity to reach the lower limit. Then- 
is a corresponding /*/i/rr s //f/.v//-yW///, uhiclt is st-Mont referred to 
and \vhi(*h may l determined by sparking in a fiure or less coidiued 
space. It represents the temperature of titHammatiou of the \apoMi' 
nt its higher limit. 4 

Several attempts have been made to connect the Hash -point with 
certain other physical constants of the substances concerned, such as 
the vapour pressure* and boiling-point/' but the most successful is that 
of Ormandy and Craven, who point out that, nt their t!a\lt-.ptttit% 
different hydrocarbons exert approximately the same vapour pressure, 
The following relationship is found to hold to a rough nppro\ttujition : 
Flash-point- If > hoiling-point, 

(atwtdut*' Tl (nifcMi!ut<< Tt 

where k is a constant which varies necording to the type of combustible 
and the nature of the Hash-point, namely, whether higher or loui-r. 
In the ease of the hydrocarbons n mean vidii' of U-jnil has been obtained 
for the lo\v<*r flash-point constant, and ll-Hilo tor the lusher. A few- 
values arc given in tin? tul>lt* on j>. 1 17. 

The temperatures nt which solids, in the eotttpitH fonu \vdl ignite in 
air without, the application of any spark or other local itnili temperature, 
have occasionally been determined. The fYillmvttiti ittv a lew of the 
better-knowu results (p, 117). 


In 1882 Mallard and Le Chatelier * gave the results of an investigation 
into the rate* of propagation of flame in mixture* of nir and a ritmiinstihlc 

l Ormandy and Cravon, J. /*. Petrt*. 7Vi-A., |j-Jl\ B. U/i, Sw h., ./. AW <<Ar,,,, 
Jnd., 1923,42, 1734, * Blicnimn, Clrny, and HRmmenting, */. /nt/. Kmt,t'h*m . l*m I I'l 

s Ormandy and Crawm, fat, nX 

4 A couveniont apparatiw for cifttermininic Iwith if llmw rt^h.|Hiiu^ ntii-r MHW or 
above atmosphere temperature IN dwdrib*d by Ornmnil.v l CravMt, J, l4, /Vir/, 

J. Grk) 19/2, o 140. 

, 2, 8. H ; 
, 2(l f ilf'K 

, f 
Mallard and JU Clwteifer, j&fMll, $cc. cAi M 1882, liij, 39, g(Hl. 



(Ormandy and Craven, 1922.) 



i> ] 

Low IT i 




SMibstumv. ; 

Point, ; "V. 

Mush- ; 
point, " ('. : 


point, (> 


Hcxanc . . . | 






Heptane . . ; 






Heir/cue . . 














Turps . 






Methyl alcohol 






Kthyl alcolu>l 












Kther . 






t'arhou-- Diamond . 
Graphite . 
Charcoal . 

Sulphur in air 

in oxygen 

Phosphorus red 


Ignitiou T< 

800 850 

255 '200. 
r. 00. 

<j[as sueh as hydrt^i'it and methane. It. was observed that, if the com- 
bustible mixture was ignited at the closed end of u horizontal tube, open 
to the air at the tit her end, the flame tended to travel with increasing 
velocity towards the open end, lu a detonating mixture of hydrogen 
and air a, speed of IOO metres per second WHS registered. If, ou the. 
other hand, the combustible mixture was ignited at the open cud, 
the flame was observed to travel for a short distance at a uniform speed* 
This was followed by a vibratory movement, in the course of which the 
flame travelled backwards and forwards in an irregular manner, the 
mean speed from point to point along the tube being usually greater 
than that of the uniform movement. These* vibrations usually continued 

1 Hit), /7wrw, ./., HH>7, 24, :i"iH ; 
3 MVn'u ami Wiirtttn, t'/irwi. .Vni 


frw. AYw, IHtHi, 6l, 12*1 
I!H7, 96, ^5. Si n : mmi' by Hill, 

a, 137, W7, 

118 OXYOKN, 

to the end of the tube, but sometimes, during a particularly violent 
vibration, the Hume mitfht he rxtin^ntHhrd, mvtiit* f contamination 
oi' the as yet uuburnl mixture with flu- products of combustion. 

The initial slow propagation of llaiin- ran he at a uniform 
speed over a considerable distance of tra\cl from tlu- point of i^nitiuu 
with all combustible mixtures of" #ascs under ordinars conditions oi' 
temperature and pressure, provided smtablr precautions an* taken. 1 
The conditions most favourable to obtain ami maintain tbis uniform 
movement are that tbe inflammable mixture should In- contained in a 
long, straight, and horixoatal tube open at our end and closed at the 
other; and that ignition should be effected at the open end of the tube 
by a source of heat not great h exceeding in temperature the 1*4111! imi- 
temperature of the* mixture, and not productive of mechanical dis- 
turbance of the mixture. Thr spt-iul of thr uuitorui luuvnttt'iit flirn 
depends on the composition of the mixture and on thr dtitntrtrt of tin* 
containing tube. Above a certain (small) diaim-trr the material of 
which the tube is made docs not appreciably affivt thr sjired of tin* 
flame. With it tube of given diameter thr \prrd of thr uniform move- 
ment of flame in a mixture may aerordittg to Mason and \\hrrltT 
be regarded us u deiinite phjMcal const uut tor that mi \ttuv. 1 

s, s, s , s., 

Fw, HK--A|tii*raiu uwnl by 

Several methods liavt* been adopted for the mrasmvmrut of tlamr 
speeds. If the ikmes are sullteiently uctuuc to affect it piioto|4rn|*ItH* 
plate, penuanout records may be obtained on revolving drums hearing 
the films. Mallard and Le Cliatelier a fiitployrd this mrthotl in tltcir 
researches on mixtures of cartmn (iisulphuU* with nitrit'oxittr or oxygen, 
the flames of which are well known to In* highly net 11111%. whilst Mason 
and Wheeler 3 were able to upply the method with conspicuous sticrrss 
to mixtures of acetylene mid itir, lite actual flittti*.* sjireil is olttiiinrd 
by eomparison with the waves made simultaneously oit the photographic 
drum by means of a timing-fork of known tVe*|tteuey. 

For the examination of Hntiu*s, siieh ais thtisr of mixtures of mrthaite 
and air, which are noa-uctimc, various clrvi< f es huvr hreii rtiijt!i*yt'd, A 
useful one used by Wheeler consisted 4 in lilling u htM*i/otitul tube with 
the gaseous mixture, the etuis of the tube being rloM**!, 11*% shown in liy, 1!, 
by flanged eud-pieec % H, bearing taps. S t , S a , S ;l , , . were MTeett wires 
of copper, 0*025 auu. in diameter,** threaded vertically a<*nes the tube 
through line holes pierced through tin- walls. 

ou aiul WktHsbr, Tmtw, f'/irwi. SV!., IM7, in, 

a Mallard aad U C'httUlr Ann. Miwx, t0 f |H| 8 4, :H2, Al^* Kiln, />.* rA*i 
^c., 1023, 123, i43r>, 

51 Maaoa and Whwlur, Trttn*. WU-M, iVoc , H>lll, 115* A7K. 

4 VVhcHiler, *6/rf., HH4, 105, 2(MW. 

fc Farkw and A. V, Rhwid (t'6ir/., UU4, xo$, *2I^>| uwnl tiitu Mhp^ "I \V*.4'. nl!i , 
melting- pom t 1T :> (I r fhtmi wt^ uiudt* by |xmrtity; thw itinltrii wllny tiimit llin rf 1111111**] 
produced by folding a piouo t>f |KI|K.U* at u>u iiiigk? uf till ' I ". 


in order to avoid including in the measurements of the speed of the 
Hume any impetus that might, be given KY ^ Uk igniting spark, the first 
screen-wire was fixed K) em. from the point of ignition. Other screen- 
wires were fixed r*0, 100, !*00, :iOO, and 100 em. respectively from the first. 

The method of recording the time of passage of flame along the 
tnhe was electrical. Kach screen-wire carried a small electric current, 
the interruption of this current when the (lame melted the wires being 
recorded by the movement of an electro-magnet. 

The electric current passing through the screen-wires was sutlicient 
to raise them nearly to red heat. This arrangement ensured the rapid 
melting of the wires as soon as the I la me touched them, and therefore 
gave very uniform results ; wires made from metals or alloys of low 
melting-point, which could not be drawn so fine or of so uniform a 
diameter as copper, were found to be unsatisfactory. 1 

All elect ricid connections through the screen-wires and chronograph 
having been established, the left-hand end-piece* of the explosion-tube 
was removed (by sliding it, downwards) and the mixture ignited at the 
now open end by passing an induct ion-coil spark at A. a 

As is evident from the results shown graphically in figs. 20 and 21, 
the si/.e of the tube exerts an important influence upon the flame speed. 
In tubes of ; small diameter, say less than about 5 cm., the cooling effect 
of the walls results in appreciable retardation of the (lame speed. It 
will be observed that there is not. much difference in speed in tubes 
from 5 to 10 cm. in diameter, whereas when the diameter of the tube is 
only 2-> cm., the speed is reduced by about #0 per cent. Cooling by 
the walls thus interferes with the measurement, of the true speed of the 
uniform movement of flame in mixtures of methane and air unless the 
diameter of the tube exceeds about 5 em. 

When, however, the diameter is increased above 10 cm., the speed 
of the thuues is affected by the coming into play of another factor, 
namely, convection. This is noticeable with the fastest moving flames 
in tubes 10 rin. in diameter, the visible effect- being a turbulence of the 
(hunt* front. This is essentially a swirling motion in a direction nearly 
normal to the direction of translation of the flume front, which, as in 
tubes of smaller diameter, progresses at a uniform speed for about 
150 cm. bcjorr backward and forward vibrations are set up. This 
swirling motion appears ttb Initio^ and is due to rapid movement of the 
hot gases from below upwards by convection. In tubes of comparatively 
siituil dhititctiT (5 tot cm.) this rapid movement- is suppressed. 

With tubes of diameter ranging from cm. to 17 cm. there is an 
apparent retardation itt the influence of the size of the tube. This was 
lirst observed by Parker a in I ill 5, but, as is evident from tig, 21, this 
effect is only temporary, for the maximum effect is not even reached 
with n diameter of iMI'/i cm. Hut it may reasonably be objected that 
a pipr of so great a diameter is no longer to he regarded as a tube. On 

1 Manna mitt WlirrltT, WHIM. Cht-nt. *SVr, HH7, ill, 1044, 

* Thr ifitlitrtit-r uf flu- imtun* f tin* .sfiurk UJMII ignition IHIH l*ru wtutlicd by Morgan 
itiiii Wfirrlrr* i/w/,, U2t. I IQ, 2H9 ; ThurntNii, t'hil. ,Um/,, 1920, 40, -Wi ; /Vm', /&///. A'w:. 
UIU. |A| 92, IlHf ; IW4, {Af, 91, 17 ; 1914, |A|, 90/272 ; /Vii7. ,1%., 1914, 28, 734 ; 
\Vh't'l*-r, Trim*, t* fa- HI. &t*: t l!2o 1x7, JHlIi ; Morgan, ifntt, t IUU, 1 15, !M ; Pat^raon and 
rumpU-U. /V'', /%/frfi| ,s'r, LwithiH, IlllU, 31, ION; Huntry, Trtnm. ('htm. SW. ItllO, 
10-9, 521$ ; Ti'i-i-*"* nl Ilt'ir/,. ('hrtn, %t-ntr. t UH5, il, 1*J78 ; j'fitifiht'lt'urht., 11H4, 57, 990, 
UKI. I*i!fl ; < W-iinl <*<i<t|iir Hiwl \Vnrlurtiu, Trttnx. Clit-nt. *%' 1912, IOX *J27H. 

* i'iirkw, i/>iW,, IWir>, 107, :I2K. 


the other hand, thrtv is a louvr limit to flit* iliaiiuli-r of tlsr lulu* that 
will allow a ilamr to pass through. 

^ o n i:i 

ifriM iipnriiii'itt +f lUiu*< iti tiitrn t 


, T tt|Hm t | 
, UI7.) 

, ftllli 


it i 



of ignition. This was discovered by Davy, 1 and constituted the starting- 
point of his researches on the construction of his well-known safety 
lamp for use in coal mines. He found that in tubes J-inch in diameter 
(i.e. 3-63 mm.) explosive mixtures of firedamp and air could not be fired 
as no (lame would pass along. 1 

Analogous results were obtained by Mallard and Le Chatelicr, 2 who 
found the speeds of llamc in a mixture of methane and air containing 
10*4 per cent, of methane, using tubes of glass of different diameters, 
to be as follow : 

Diameter of tube, mm. . 
Speed of ilamc, cm. per sec. 






The methane was impure, it is true, but the result closely agrees with 
that found by Davy with firedamp. A more thorough investigation of 






(/) ' 





. 40 






or . 

i / 


2 / 

3 / 
u / 



5 10 15 20 25 


Kio. 22. -iuiluenee of tube diamotor upon the propagation of ilame. 
(Paymau and Wheeler, 19180" 

the subject by Pay man and Wheeler, 3 whilst yielding analogous results, 
has revealed "several interesting features. One of the most important 
of these is that the apparent limits of iuilammability of methane in 
air become narrowed as the diameter of the tube decreases, until with a 
diameter of 4-5 mm. only one of the seventeen mixtures tested, namely, 
that containing 9-95 per cent, of methane, would propagate Hume. 
With 10-15 per cent, methane no Ilame would pass, whilst with 9-5 
per cent, methane the Ilame only travelled 20 cm. and then became 
extinguished. With a tube of diameter 3*0 mm. no Ilame propagation 

i Davy, Collected Works, 1810, <5, li. 

a Mallard and Le Chatelior, Ann. Mitiw, 1883, [8], 4, 319. 

a Pttynwn and Wheeler, Tmna. Chem. tioc., 1918, 113, 65(5. 



occurred with any of the inflammable mixtures. The results obtained 
with iK)5 and iH) per cent, methane an- shown in it!4 : . s ^- The nature 
of the tube itself is important, as l)a\y himself \\as aware. Mrta! tubes, 
on account of their greater cooling effect, arr more efficient extinguishers 
of flame than glass. Since \\ire-gau/.e utay he regarded as a series of 
thin, transverse sections of narrow metallic tithes joined to4ethei\ 
the bearing of these results upon Davy's salrt\ lamp is apparent. 

Consideration of the curves shown in tig. 'JO shows that I hi- tlaine- 
speeds of mixtures of methane and ah steadily rise to maximum \alues 
as the percentage* of the combustible gas IN raised from its lower limit 
of 5*(> to about IO per eent. Further additttMi of inrtltane jvdutvs tin' 
speed until the ilame is extinguishi'ii just hevottd the tipper Itintt \ahie. 


Q 80 




O | 






7 !* 1 ! 1 ; 


tllktloll flttd Win 

I tit- 



This was to be anticipated loi\ beyond n certain valnr, r\ivs.% u|" 
combustible gas will usually fmietton as a ditttmt. Tbr simpr >!' 
curve, therefore, is typical. * ' 

Interesting results are shown in iig, Ti, which yiu-s the tlittitr sp 
of mixtures of methane and oxygen with \aryiii*; prcipurhons i*|" 
neutral diluent nitrogen. 1 Not only tUn-s the bwrr iiirllntitr ii ut ,t 
slightly with increase of oxygen, hit! it will be tl>M<r\rcl Iftiif thrn- 
great increase^ in the upper-limit viihtrs and in the llaiiu- .sprrils. 

By decreasing the percentage of nitrogen from that pn-srnt in Ilir 
atmosphere to nil, the ilame speeds show enormously mitancrcl \alii-s. 
This i dcur from the data, shown graphically in tig. */M 

< The author points out that the mast striking rrsnlu are thtiM- tor 
mixtures of methane with pure oxygen. The .^tretl j s thm 5J5Mi cm. 

1 The diameter of th tulw WIIH B m. 

2 Payman^ymwwt. tVwm. #**., I!2f 117* 54. Thi-* r'!t nr^ itt*i ^fir% rMjiii^i^ 

whilBt Mawm and Whotslcromphtyni tuUw wf tIiaitteUrTnw/ ll Tl!^i^ 

huwovor y aro tho saiju?. * * ' ' ' '' 



per second more than fifty times that attained in air. It will be 
further observed that the maximum speed of the flame is obtained 
with the mixture in which the methane and oxygen are present in 




< 2000 


lOO/o 2 

5 10 20 30 40 50 



FIG. 24. Flame speeds in methane-air mixtures enriched with oxygen. 
(Payman, 1920.) 

combining proportions, namely, CH 4 +20 2 . This result is in noteworthy 
distinction 'to that obtaining when the detonation- wave is developed in 
mixtures of methane and oxygen, for the mixture in which the speed of 




a 200 


< TOO 











25 1 




1 T5 

MM ' 



20 40 



FIG. 25. Flame speeds of hydrogen in air. 
(Haward and Otagawa, 1916.) 

the detonation-wave is greatest contains equal proportions of methane 
and oxygen. The difference is the more striking when it is remembered 
that the uniform movement may give place to the detonation-wave 
after quite a short distance of travel of the flame. 

The flame-speeds of combustible mixtures of hydrogen and air are 
less easy to determine since the flame travels more rapidly and in some 

124 OXYt'.KX. 

mixtures the explosion-wave may he set up after thr tlaiur has travelled 
hut a short distance (about *2 metres) froru flu; rud of ihr tub*-. 

Nevertheless a series of drtfnninaliuns lt;is hrru published, 1 and 
these are shown in %. 25. Class tubrs of thtvr diuiurttTs \\nv employed 
namely, 9, 11-5, and 25 turn, respectively. Tin- curves show that an 
increase in diameter enhances the tlaine sprrd tiuly in those mixtures in 
which the hydrogen is not present in considerable escrss. It is inter- 
esting to note that the maximum ilame sprt-d is nu! attaitird with the 
mixture containing the hydrogen and o\yi,'ru tit finiibiisini' propoHiuiis, 
namely, 29-5 per ccut. of hydrogt*n, but wit ha mixtiin* ciiitaiuiuj( about 
40 per cent, of hydrogen, This is in preuliar contrast to thr tvsults 
obtained with mixtures of mrthauc au*l uxygeu, L*- i'batrlirr suggrstrd 
that as the thermal conductivity til" hydrogui is \i\ fiinrs tlytf of air, it 
may veil be that with mixtures ronlainiii" wotv tltau tun. third of tbrir 
volume of hy<lrogcn, the enlmwrd conductivity f thr uu'\turc more 
than compcnstttcs for its lower heating valur. 

357 9 



Fw. SiO*- "Fltuiici s|H*tHi in 



Measurements have idso been nmdc f Ihr spivtl iif lift' uniform 
movement in mixtures of air with each ottr of thr hydrocarbons **l" tin* 
paraffin, scries up to and including peittnttr. Thr tliirriitijintions \vrrc 
carried out with hori'/ontai glass tubrs, li-JS cm. in cliamrtrr, iA and tin* 
results are shown diagrnmmnticidfy in tig. *ltl With f-hr r. \rrpt inn of* 
methane,,, the nmxinuuu sperdn are approxittmtciy tlir sanu*. namely, 
about 82 cm. per second. The value for met hum* is rat her lowt-r than 
this, being 67 cm. per second. Owing to thr few liiitu auitlahh' fur the 
thermal constants of the* pnrailhi hydrocarbon*, it in nut rasv to rxphtin 
this difference. In each instance, the mixture having the mttxumutt 
speed of flame contains more combustible #as than in rri|titrrd for 
complete combustion. 

The higher and lower limit speeds tew! to approach the samr value 
of 20 em. per second for all the gases. It is ifitcrrHttng to iintr that 
iu every case, except that of methane, the maximum lluiw spivcl oeriirs 
with a* mixture containing more of the cumilmstthlc gun tlimi is 
for complete 

Haward and Otagawa Tratut. Cfmm. A'oc., till!!, 
, 115, 1454. 4 

Hit, Siw uU*i fn^mati, ilml., 
i, tillii, 115, 1447. 



Hesults obtained with carbon monoxide and air. and with mixtures of 
these two with other combust ihlr Cast's are shown ufraphicallv in ii<^. 27. 


't-t f 

40 M) uu o 
C.AJ. HK uio veuuw c of AW 

vilnu't'ii, aiui tiiH 

In thr following table (p. liJ<) are jjiven t he maximum uniiorm llame 

npeetls of various tHitnhust ihlt* ntixtnres, to^<'ther with the ilame speeds 
at ap|n>\imate!y the tipper and lower limits in hori/,outal tuhcs of 
dianieirr **."> eiu, 

The Law of SpeetlH. Careful study of the rah* of propagation of 
flame in lh 4 Combust i<u tf comph^ gaseous mixtures has led to the 
enuneiation of the' following law : l 

C/iVi"!! fw> nr innn* Hu.rttu't'N ttf air or <*.nfji?n with different individual 
rttinhutitihlr ^Jf/AV.v, in eneh t*f which nii.rhtrt'tt the xpeed of prn^ti- 
gutittn ttf fttnne Ix the sttint\ till t'tunhinatitinx of the nii.iiureu of the 
same //// a iirt*inigate Jltttne nl the name v/jm/.v under the same 

From this it follows that a mixture of a number of different; oom- 
Itustihtr Cast's \vjth air. tor exiimple* may be* n*|^arde'd as the algebraic 
sum of mixtures of t-ach iiidiv-ittttal eombustible ^as with air, the pro- 
portions of tht* two 3 bring*; siteh that the flame speed in it, if the* mixture* 
were burning nlone, uould be the same as in the complex mixture, 

Vertical Propttftatkm f Fhinu*. 4 In this ease the effect of 
convection currents bt'contes increasingly proncnUH*ed, The tube in 
which the Haute travels beconifs a ** chimney," and, witlt bottom 
i#nitinn % the sprrtl tf tlie flittrie is enhaneed by that id* the draught. 
With top ignition tin* llanu* tenth tti bu.rn at the mouth of the tube 
until all the combust iblr mixture bun risen to the top. 

i it*I 


- Thul 

tr all ( 

L*It, 123, l^fi 

., IU20, 117, 

120 OXY<KX. 


M*i \imum MUfttt* 

(JaHt'ims Mixfmv, : ,, 

lit citt* S H '' M| ' i vr ,*,';; *!"'*' j.,' ,'.' .V-irt'; s i jrri1 - 

by \Y4tttitiv r!il ' *"'' hv VMrna..,'' 1 "- "'' K- V-btltf. '" "' 

Unfair . . j mi KM ; 5fiO <H!> a ; lo 

CH 4 'fuir :i 
CjjH^Hiir :s 
(-3 Ha -{-air 3 

air 4 


CO fair 8 "* 

I "a 

\\t j I1 2 I UI 

SCO i H 4 lair- 
Coal gas j air a 
Aortont* i air 7 


i H! 

<J 5-su 2*l 







: 85 

il i 

* f !'* f l 


i ' 







'I : 

2 -a 


20 ' 


7 ' 





., S'J 















2-f* 1 













1 ! 





: 2HO 









: 4'tl.l 

: UI5 

'11 ' 







** I* 


i 1 %*I5 

i Si 











i UO 










1 5*115 

; !H 


.! 1 








i i5<> 




! 2 

2? ' 

1 57 




i .115 






; i 





: 211 



. t!l- 


7 t 





; I5i 

, j 

7 *2 



2 1 





i INI 






H ' 




C i AHK< >t?H Kx 1*1 ,C )SI < N.S. 

When two or niorv ^HHt*,H iutt*t*af*t with tvt*i* inr 
until a high maximum sprnl is ititiiijutl* uu ^xplotiioni N is suit I to tvsult", 
The velocity is many thottsatul ttntrs j^n*att*r tltitit of flit-' sh*vv f tuutortu 
propagation of flame dealt with in flu* previous s-rrttnii, iiittt its m*c*ttrntr 
cleternunation in a problem of considerable ivxperimetttai cliilii'tilly, 

In 1880 an explosion of eoal gas occurred in Tottctiimiit C'tiiiri Hmd 
in London, and during the* legal imcstigattim* subHcqueftt thrrctt>, the 
attention, of scientists was directed to the fact that practically nothing 
was known of the rate* at which an cxplmiou\vuvc eonld travel. The 
following year Mallard and Le Chatelier* guvr flu* renult-.s of an investign- 
tion on the subject carried out by themselves, and this was followed m 

1 Ha ward and Otogawti, 7Vm. f'iwnt, iSV., l!ltll 1119, H!i, 
a Payman, ibid., 1910, 1x5, 1454. 

3 Payman, itmL, p. 14Sli 

4 Chapman, ibid., p. 1077. 

Mason and Wheeler, ibid., 1910, 115, 578, 8w* nk* ifiiwiirfl mni Htuttry, i7*iW.. tit!7, 
in, 841. Numerical datA aro nt KVf*n. 

Saturated with mcisturc at 12 l * (*. ; {irwuttm* 7ro mm. 

7 Wheeler and Whttakcr, Tram. O/irw, Afoe., 1017, xxi, 2118, 

8 See alflo definition advanced by Ionghaiui, Zeitwh. qr* t Nrhir**, tfi>rrnq*tt*ffip., 19 IN. 
13, 310 ; J. Chem. Soc. Alrtr., 191I li., 327. ' * 

* Mallard wad Le Chatelier, 6 f o?|#i renrf., 1881, 93, 148, 


1882 by the memoirs of Berthelot and Vieille. 1 In 1893 Dixon 2 reopened 
the question, and as his researches were carried out with such consummate 
skill and yielded results so concordant in their values, brief reference 
may here be made to his method of experiment. The explosion tubes 
consisted of leaden pipes ranging in length from 55 to 100 metres, and in 
diameter from 8 to 13 mm. As no appreciable difference could be 
detected in the velocity of the explosion-wave through the tubes when 
lying straight on the floor and when, coiled on a drum about 2 feet in 
diameter, coiled tubes were used most frequently as their temperature 
admitted of easy control by immersion in a thermostat. It was found 
impossible to coil a small leaden pipe without stretching it somewhat 
about 2 or 3 cm. The outside of the tube was therefore measured after 
each coil was wound on the drum, and the length of the axis of the pipe 

Each end of the leaden tube was connected with a short, wider tube 
carrying a bridge of silver foil W x , W 2 (fig. 28), and one of the tubes was 
fitted with a platinum spark gap S. The explosive mixture was 
admitted in a thoroughly dry condition unless otherwise stated the 

T i 


FIG. 28. Dixon' a apparatus for determining the velocity of an 
explosion-wave (1893). 

pressure determined, and the spark passed. The explosion-wave 
ruptured the silver-foil bridge W 1? passed through the leaden coil and, 
upon emerging at the other end, ruptured W a . As these bridges were 
connected electrically with a chronometer, the time-interval between 
the ruptures was recorded, and from this the velocity of the explosion- 
wave was readily calculated. 

The foregoing researches have sufficed to establish the following 
facts : 

1. Both the composition and the diameter of the explosion tube arc 
immaterial, provided the latter is above a certain minimum about 5 mm. 

2. The velocity of the explosion- wave after the passage of the spark 
increases rapidly until a high maximum is reached, after which it remains 

The results obtained by Berthelot and by Dixon for several typical 
gaseous mixtures are given in the following table. They exhibit a 
remarkably close agreement : 

1 Berthelot and Vieille, Compt. rend., 1882, 94, 101 ; 95, 151, 199 ; Berthelot, ibid., 
94, 149. 

2 Dixon. Phil. Trans., 1893, 184, 97. See also the more recent paper by Dixon, and 
Walls (Trans. Chem. Soc., 1923, 123, 1025) on the propagation of the explosion-wave 
through hydrogen and carbon monoxide mixtures. ' 




I Mrttvs prr second. I 


L>H a I <>., 


ni 4 i*20 a 

IMI, -I () 

2*2 10 




8. Although Bert helot concluded that tbe velocity of tin* explosion- 

wave is independent of tlir Initiiil pressure ttf titr |ses, I)i\on IViiiii*! that 
this in approximately Inn* only after a errtatn nttntniuni pressure 
about 1| atmospheres has heen e\i*e'lril. Ift other eases I tit* explosion 
velocity rises with the pressure. Thin is ahtituhtntly evitlent from tin* 
following data. ; 


(1 Irani,) 

Gascons mixture . , Ull^ Oj. 
Velocity , , , metres per setuitut. 

mm% mm. 

\VWit y nI l i\ 











*2H*2 1 



4 2K30 

1 f 100 



t i;,o 



Reduction of pressure reduces the intensity of rxpkiMim, 1 itnti fur 
each gaseous mixture llurt* iippearn to Iw* ti\*rtti<'al presMtrt\ |H*!OW 
which cxploHioiiH will not tako plnct% This pn-sMtrr IH a ftitiHitm of tin- 
chemical com posit ion and pro|H>rtionsof the guncs, thr luotHttire < f itfeiil 
and the initial spark impulse. 'IV ettiiiplt-f riie**h tif c*utitltistioit likrwtm* 
falls with the prcHsurc, Tlnw, for fxumpt<\ in one srri*^ of rxprriiiirntH 
with mixtures of met ham* and air, it WH observed * t luit under it prc^tirt* 
of 40 mm. of mercury, II per cent, of the pin coiubim'd, whm*(tK under 
61 mm, 150 per cent, combined. 

m fwm 
103, 034. 

a Stavrmhagwi ami Hchuchtm), %eit*rh. 




4. The foregoing table also illustrates the retarding influence of rise 
of temperature upon the velocity of explosion, and similar effects were 
observed with other gases. 

5. The influence of water-vapour upon the rate of explosion of 
oxygen and carbon monoxide was studied with interesting results. The 
maximum velocity was attained when the. mixture was siiturated at 
#5" ('., /.<^it eontaiued some 5-(> per cent, of water-vapour. Further 
addition of steam is seen to retard the reaction, 





Dried with l a O a 

Moderately dry . 

Saturated with water-vapour at 10 

Wato I*- Vapour, 
I*or cent. 


Mfstrtia jx^r 

io" e. . 

i -a 

1 070 

20' ' (-. 



*2H (\ 



35" ('. . 



45" ('. . 



f>5 u ('. , 



05" ('. , 


1 5*20 

75" (\ . 



0. Addition of nu inert jtjas U> an explosive mixture usually results 
iti ii retardation of the* ex plosion- wave* If one of the c.omhustihlc ganes 
is in exwss. It in liable* to behave like an inc i rt pis of similar volume and 
clensiiy. This is evident From it consideration of the data in the following 

tfibtt* :* 




^Hj, * Oj 7K US! 

lit it., i* 1 1 i 

Mixtim* ] 4 e 

'' > * * 

M'^ i Oj * **\ f IHL^ 


ai ^* 



a H4 120,1 IN, 



130 OXY<;KN. 

Excess of hydrogen, on the other hand, artually werlerates tin* 
explosion velocity unless present In tun great a quantity. This is rvidcnt 
from the following data : 


UnxwMH nrixtun* . . 2H, . O, ','H , n. . lII , ? H, \\, HI, ,:!!, 

A similar acceleration has hern ubsened <m ;*<itiittm of e \eess of 
hydrogen to mixtures of nitrous oxide and h\dtug iu 

7. Finally, it has hern established that m tin t-xplnsion- \\avc, Hit 1 
combustion of electrolytic g;ts is not eowplrtr In th Nphtsioii uf 
carbon monoxide and oxygen a r'>iduuut ot' unf*Mrnrd is likcvxisr 

Explosion Pressures. --The propagatitm of tin* rxploMin-wa\r in 
gancs is accompanied by n very high pressure lasting fur 11 vrry short 
time. The early measurements of Hutisrn * wrrr rffr-Hnl by *\phHiing 
gaseous mixtures in a small cylinder tilted with n tuovable lui aitaeheti 
to a lever. The* latter was weighted until the force of the explosion 
was unable to force the* lid off. The results fur hydrogen mtd rarbun 
monoxide were* us follow ; 

I*n9* tin*. 

2!I t 4"O a . ir;5 

SiCO-i-O, . Hi-! 

Closely similar results were obtained by IIn*t helot uut Vifill\ 

Modern methods* consist in rxplodmg gaseutK mixtures in !tt*-hillti 
cylinders and automatically recording flir pre*stires evrt**} agattist 
pistons working with HpritiKH. NVtllti*r the teiiipcraturt s - 1 utir Hit* 

pressures obtiiinetl in pntetitv tin* eijiint ft* tlntst* to lie i*\pti'tt'il rnun 
theoretieid eotisideriitions, mtd xr^rnii t*vplattntiiiis lw\* In i it offered , 

namely : 

(1) Dinsoeiittion of thr gaKcous pnii!iirt\, 

(2) lucompldc ccuubustioii. 

(H) Variation in Hpeeifle ttiwts of gasin utidt r Ilir ^jirri.ti ruittitiiiis. 
which render^thellieoretind i*alc*utatioris fiiirrrtiitts* 

4. Loss of heat by radiation. 4 
Probably each of these factors* in ciMitrtlHittry to flit* main rft'n't. 

Explosion Limits, Attrition hm itlriwty IMTU dirrrlnl to thr 
inflm^nce of inert ganens upon the nti* of tnm-i of iltr fvptfisioti wan* 
through a eoiubtmtible mixture. In pvurrat tin* \rlnrit > fulls uitiii n 

(Jlfrk, r/flw, PHrt*, ami Ml Xttyiw (Uttimmitrt, ItMiU), mt. i, H*,|4in^ii s /'HIP, 


i4 123, 

r%w. AW. f I9IK, 113, 840; 
70, (), 

IAIA ^JJjJJ m ,(^f*- ti**- MM***. %frflifm t liltfi, u. tfitt. J, r s |i, ,\V, 

16 723 g4VW * * wMii*iii umi ftrmiila ; Miio^wr, r V IW *|4 ft w! tills*. 

4 See, for einpl\ Bwicl, Prw. /%, *s f if, IU2II, | A|, 63, IB% 



certain dilution is reached at and beyond which no explosion takes place. 
This is explained by the fact that the heat generated by union of the 
combustible gases is largely absorbed in raising the temperature of the 
indifferent gas instead of being employed in propagating the explosion. 
As is to be anticipated, therefore, by raising the initial temperature of 
the gases prior to liring, the dilution with inert gas may be carried 
further than in the cold. In other words, the lower limit of explosion 
of the combustible gas is depressed. 1 

Teclu 2 gives the following explosion limits for mixtures of com- 
bustible gases and air, the method of exploding consisting in firing by 
an electric spark : 

(Teelu, 1907.) 


Lower Limit. 
Per cent, by Volume. 

Upper Limit. 
Per cent, by Volume. 







1-58 1-77 


Closely connected with this is the problem of the completeness of 
combustion of gaseous mixtures when diluted with inert gases. This 
has been investigated by Parker 3 , who iincls that the effect of increase 
of initial temperature is much less in the case of hydrogen mixtures 
than with methane or carbon monoxide mixtures. The lower limit of 
hydrogen is much the same whether mixed with air or oxygen, but for 
carbon monoxide, methane, and coal-gas, the lower limits in oxygen are 
greater than in air, probably on account of the greater specific heat 
of oxygen. 

Valency. Oxygen is usually regarded as a divalent element, but 
many compounds have been prepared for which it is dillicult to write 
suitable structural formulae without assuming oxygen to have a valency 
of four. Thus, in 1888, Ileyes 4 suggested that in such oxides as Ba0 2 
and Mn() 2 one of the oxygen atoms is tetravalent, the general formula 
for the oxides being M^ -()=(). This enables a distinction to be made 
between these substances and compounds of the nature of carbon 

Fried el 5 had already shown in 1875 that methyl ether combines 
with hydrogen chloride to give an oxoniurn salt (CH 3 ) 2 O . HCl, and it 

1 Ko'/,kmvHki, Znkwh. yhyAikul. ('them., 1801, 7, 485. 
* Tcolu, J. fmkL Ohm., 1907, 75, 212. 

3 Parker, Tram. Ghem. tfws., 1913, 103, 934, 

4 Hoyoa, Phil. Mag., 1888, 25, 221. 

6 Model, BuU. $oc. Mm., 1875, [2], 24, 160, 241. 

132 . OXYGEN. 

is difficult to avoid the assumption that oxygen is here tetravalent. Its 
formula may be written as 


(i) 3 V>/ or(ii) 3N >0-C1H. 
CR/ \Cl CH/ 

The second formula harmonises with the fact that whilst hydrogen 
chloride is a very stable substance, the oxonium salt readily dissociates, 
and it is not improbable that the complex (ii) is formed first, which then 
undergoes more or less complete rearrangement to (i), the two forms 
remaining in equilibrium. 1 

As shown in Chapter X., water is believed to be associated to a con- 
siderable extent to dihydrol (H 2 O) 2 and, at low temperatures even to 
trihydrol molecules, (H 2 O) 3 . Assuming the strictly monovalent nature 
of hydrogen, a higher valency than two is required for oxygen. Thus 
dihydrol may be written H 2 =O=0=H 2 , and to trihydrol a cyclic 
formula may be given. 

Triphenyl methyl, (C 6 H 5 ) 3 C, unites with ethyl ether to form * 

(C 6 H 5 ) 3 C, ,C 2 H 5 
(C 6 H 5 ) 3 C C 2 H 5 

in which the oxygen is clearly tetravalent. The same may be said of 
compounds containing water or alcohol of crystallisation. 

Beckmann, 3 in 1890, directed attention to the interesting fact that 
substances exhibiting association in benzene solution frequently possess 
hydroxyl groups ; and this has been confirmed by later investigators. 4 
Careful study of the surface tensions of liquid phenols and various 
organic hydroxy derivatives has led to highly interesting results. 6 Not 
only are phenolic derivatives associated like fatty alcohols, but the 
association may undergo steric hindrance by the introduction of groups, 
such as NO 2 , in the ortho position. This is explained on the assumption 
that association is conditioned by the hydroxyl oxygen which functions 
as a tetravalent atom. Thus 



If, now, a polyvalent element or group is introduced into the ortho 
position, the tendency is for the extra valencies of the oxygen to be 
saturated intramolecularly, so that association with external molecules 

**/#?? ff*8nM. 1909), p. 96. Analogous derivatives of 

- -one 

' 1902 > 35. 239 P 7 , P 19ot 36, 376, 3928 , 

Beokmann, Zefeck pkjnkdL Chem., 1890, 6, 437 

S^^S 3 ^^*^ 

5 Heiadtt and Winmm, Tram. Chem. Soc. t 1907, 91, 441. 


becomes less easy. Thus, in the ease of ortho-chlorophcnol the valencies 
are assumed to he distributed as follows : 

J n 

Ammonium hydroxide, frequently behaves as if its atoms were 

arranged as follows : 

II ;I X IK I L.i 

Probably when ammonia dissolves in water, equilibrium is set up 

between the several molecules as indicated below : 

H a N ) OIl a ,..-iI a N. OIL. M^N/ 

In some cases of free oxidation it would appear that the* whole 
molecule* of oxygen lakes part. Thus, when the alkali metals oxidise 
in air, peroxides are formed, from which the extra atom of oxygen may 
be liberated with comparative ease. This, it has been su$L?ested, a is 
most conveniently explained on the assumption that the combination 
proceeds as follows : 

and in support of this may be cited the observations of many other 
investigators 3 who find that whole molecules of oxygen are absorbed 
in various reactions. It is dilHcnlt to account for this save on the 
assumption that oxygen can function as it tetruvaicnt atom. 4 The 
third and fourth valencies of oxy#en have been variously named as 
crypto valencies,** utu'itian/ valencies,** neutral affinities? electrical dtuihlc 
valencies* and residual or latent valencies.* 1 

Oxygen is not known with certainty to function MK n monovalcnt 
clement. 10 

Physiological Properties. A supply of five oxygen is necessary, 
not only for the continuance of human life, but for that of all organising 

1 Own, ,V/.7/i. Mauelwkr /'/ill AW,, 11104, 48, *iv., I -I I. 

1 KiigU'r wit! Wild, llff% IMI7, 30, Iflllll 

8 Knimiinu itnti Kothwr, A iniulm, lHi>7, 394, ml; Biwh, tWipf, mir/., lSII7 f 134, 

M&uchot, iliiil., liMHl, 39, 11711 ; AuMtknt 11*02^32$, i ? ; Miiiiflicit itwl Hr/.ug, /Icr,, liKKI, 

* Othor ciiita tlt'ftiiitg with tlit* t*triivuU*ut tmiurti if oxygen IIIHI givtii by Kuox lUitl 
Eiaharik, Tmjut. Chmti S'w., llllll, 115, liWM ; liptwlitlt, J* Amrr* ('hrm, S*w., 11)17, 39, 
2303; IDUJ, j8 131)11; 1!!I4 36, tl'2% ; ^VlnUmh ititil. c!ii.w?rkrw, *6ir/., iill*J 34, 1^73; 
^11*33.70? 1UIO, 33, f42 t:i:il; IIIIIS, 30, IOU7; liHHJ, a8, r )HH i HHI5, a*/, 2(1, 1013; 
7Vtf/M. C'Atwi. Vic, 11KI5, 87, 7K-1; IJMM. B$, Itlli* UHW ; Siuinltny, *Vw/., HMH>, 9S 231 j 
Critititmn by iiiulgrov<* v f'/irw, *VrtiM t IIKH), 99, IflP ; 'rhomlittMttti, i'6iW., 180. 

* Billow liiitl Bklt*ri*r llrr. !!Hll f 34, 3U20. 

Wrin*r, *Vf#iy AnMGh&ttiinytf.n uu/ dtttn f/r^w.'li? rft f r tiHvryttnitichv (Jfwrn^ (llniuii- 

7 Hptt^tit, awry. C.*lu, f tiH2, 39* lilift. 

* Arriutmu*, Thtvriw <lrr Cfomui {Unp%tf$, l&HH)}. 

Frstind, "/Viliw. t*/ii!//i. #c., 11KM4, 93, 2I.MI ; 7'Au 7Vor^ / Valency (U)ftgiiittRii, IWHI), 

l Tho ovidnnoo uf I*wrli?r and Tlmrlmr (J. Jintr. C'Acm. &*.> 19 s 2i> 43,.' Ili4) is uut 

134 OXYGEN. 

with the exception of certain lower forms which, on account of their 
common characteristic, are termed ancerobic. 1 With the higher animals 
the oxygen is absorbed by diffusion 2 through the lungs, and forms with 
the haemoglobin of the blood an additive compound 3 which readily 
yields its oxygen for oxidising purposes in the various parts ol the 
body, the resulting carbon dioxide being carried back to the. lungs 
whence it passes into the atmosphere. The nature of the respiratory 
process as one of slow combustion was recognised by Lavoisier., 4 and it is 
the heat evolution caused by this oxidation of organic carbonaceous 
matter that maintains the temperature of the living body. An increase 
in the proportion of the oxygen causes a more rapid absorption of oxygen 
into the blood and will therefore increase the amount of oxidation 
occurring in the body.. Although this may serve a useful purpose in 
assisting the maintenance or stimulation of the vitality of persons suH'er- 
ing from exhaustion or great physical strain, 5 an increased pressure 
of the atmosphere or of oxygen, for prolonged periods, may cause harm 
from the excessive oxidation and stimulation induced, as well as from the 
liability of the blood to yield bubbles of previously dissolved oxygen 
when the pressure is reduced. 6 Various types of animals are affected 
to different extents by an increased proportion of oxygen in. the 
atmosphere. 7 

It is an interesting fact that the solubility of oxygen in blood does 
not follow Henry's Law, according to which the solubility of a gas is 
proportional to the pressure. Experiment shows that large amounts 
of oxygen are absorbed at low pressures by blood as compared with high 
pressures. The explanation usually offered is that the oxygen combines 
with the haemoglobin of the blood to form the characteristically bright 
red oxyhsemoglobin of arterial blood which readily dissociates when 
the partial pressure of oxygen is reduced. 8 This, however, cannot be the 
whole explanation for several reasons. Thus, for example, complete 
absorption of oxygen is not effected even under a pressure of 10 atmo- 
spheres. Wolfgang Ostwald, 9 in 1907, directed attention to the fart 
that the amounts of oxygen and carbon dioxide absorbed by the blood 
at various pressures are expressed by the adsorption formula,, namely--- 


where k and n are constants, and x is the amount of gas adsorbed by 
m grams of blood under a pressure p. It appears probable, 1 hcrefore, 
that adsorption of the gases takes place, probably on the surface of the 
disperse phase in the blood. 

1 Pasteur, Compt. rend., 1863, 56, 416 ; 1861, 52, 344. 

"Douglas and Haldane, Proc. Roy. Soc., 1911, [B], 84, 1 ; 1910, [B], 82, 331 ; 
J. Physiol, 1912, 44, 305. 

3 Barcroft and Hill, ibid., 1910, 39, 411. 

4 Lavoisier, Mem. Acad. Sci., 1780, p. 355 ; 1789, p. 185. 

I SP Pf Flack - Proc - P^ysiol Soc., 1909, p. 33 ; Hill and Mackenzie, ibid., p. 38. 

Ine influence of variation of the relative proportions of oxygen and other imacs in 
the atmosphere is discussed in Chap. VI. 

! S ee > for exa ^pte, Hill and Macleod, Proc. Roy. Soc., 1902, 70, 454 455 
8 See Henri, Compt. rend., 1904, 138, 572. 

' See also Brown and Hffl, Proc. Say. 


It is interesting to note that the amount of oxygen thus taken up 
by the blood is very much greater than that absorbed by pure water. 
This is evident from the following data : 

c.c. Oxygen measured 

Solvent at N.T.P. absorbed 

by 100 c.c. of Solvent 
from the Atmosphere. 
Water ...... 0-7 

Dog's blood ..... 24 

Human blood .... 18-19 

The mean heat of reaction of oxygen with haemoglobin at 22 C. is 
given 1 as 6950 calories, whilst that of carbon monoxide and haemoglobin 
is 14,700 calories. The difference is noteworthy in view of the well- 
known poisoning action of the latter gas. In view of the wide dis- 
crepancies between the individual results, however, further investigation 
of the subject would appear desirable. 

Applications. It is clear that a supply of free oxygen will be of 
value to men working under such conditions as preclude a sufficient 
natural supply of this gas ; examples of such conditions are met during 
rescue work in mines when the air has been vitiated by fire or by an 
explosion. Oxygen is also administered to persons suffering from great 
exhaustion due to illness, suffocation, or excessive exertion. 

The autogenous welding and cutting of iron and steel also calls for 
a supply of tree oxygen, a fairly high degree of purity being desirable. 
Blowpipes are constructed for the production of an acetylene or hydrogen, 
flame fed with oxygen gas, the relative supplies of oxygen and com- 
bustible gas being so regulated that the flame is mainly of a reducing 
character ; two iron surfaces, which need not be previously cleaned, 
when placed edge to edge and heated at the joint, can be made to yield 
a weld due to the blending of the clean molten metal. In another type 
of blowpipe the oxy-hydrogeii or oxy-acetylene flame is used for heating 
the metal whilst a second jet, inside or outside this flame, directs a 
stream of oxygen on to the heated spot at which oxidation therefore 
occurs rapidly ; by gradually moving the blowpipe it is thus possible to 
cut thick sheets expeditiously and cleanly to any desired shape. 

The oxy-hydrogen or oxy-coal-gas flame is also commonly employed 
for the production of a high temperature and brilliant light ; thus the 
dazzling luminosity of a piece of lime, magnesia, or zirconia heated 
by the oxy-coal-gas flame renders possible the convenient limelight 
and similar methods for illuminating purposes. Blowpipe and other 
flames can also be fed with oxygen or with air enriched with oxygen for 
the fusion of such metals as those of the platinum group, and for various 
purposes in the glass and ceramic industries. 2 

Oxygen has been used for enriching the blast supplied to blast 
furnaces in pig-iron production, with consequent economy in the 
consumption of coke. This process yields particularly favourable 
results in the manufacture of ferro-silicon. 3 

In the fixation of nitrogen by the electric-arc process 4 it is found that 

1 Adolph and Henderson, J. Biol Chem., 1922, 50, 463. 

2 See .Fletcher, J. Soc. Chem. Ind., 1888, 7, 182. 

3 See this series, Vol. IX., Part III. ; also Johnson, Met. Chem. Eng. t 1915, 13, 483; 
Richards, ibid., 1910, 8, 123 ; and account in Engineering, 1913, 96, 374. 

4 See this series, Vol. VI. 

Iht' dHrirm-y i.s , r ivafh rnJMii.-,-, j m M>. TI /,,- 
t hi 1 air prim* tu .sparLii!;/. 

An mirivshi!'. iiv,- ; v. fun, i; ; .ja.i ..--. \ , :i h., , |,, , :. , , n - Jlt il} n v 

appllftj, ;ti,d t -i ti ' \\iii.ii hi:*, !;,=. KI./'MI j- ;;i ! ,'. \ ,!,,:, ', ' ' ';'''!;'' 
r nil ' lljun " ! '-' -p!i'M^- V.JM'I; uri',. ,i 3::' ,-.- r: r,'. .': , v, i T' ' , ' - ',''=', <L' -M 
ruf!lhlls!ll)1 '' MlJ-taii,-,N s.irj; . ; , ...di-iiur, ,-;..,,-,,,-! ,,- .,,--,,/, ,.' , i 
Such ah r:v|)Ii,.sivr puss, v-., > fit.- rnn^.l' r.-d.', -a.i\a::l. ' """ 

used \viihin a [\-\\ minuii --, if,, ,| ;i!J ., r , .jj , , , PI 

risk ut> iK'^i'-nt is .-r. , t ti\ iv.i*;,-, d. \ p.KJi.'.i. ,,i li,, s : .,., ; , 

highly r\p!\t'. J 

Detection and Kstiauition. n\-,. 
power of !vi..itiii n! r ; , ,,-i,,v,ih- -.plii.irV/ 

j'^.i^^^^i^niin^, ,,..,,1,, uhn-h, } 
h - vlls l;irk nl< '-'^iMi I..*.,,,,:, ^!n,. , 


"-;-".i.n.|.~,i. ...... , ..... H,,";:, ''.';;;;;; ;;;';;'-'"i ..... -' 

.A^f^,;^^;^'-.!- -".rr, ..... ,,, 

, J , '''M : .'I^ A 1 . JnW. /./^y. n ,, ;i , . . 



hm,i,.r,M \v,.ii,i mi ,i. /,, ,,,., J ;;,,' '"' -i 8 - ! "^- 

. , , ,, "^- 

N:.-, for-xu,,,,*.. B) ,HW,1I, ./. ,,;, / 7l , w ; .,..__ .,..,, ,,. . (i-t 


evident thai if their atomic weights were expressed relatively to this 
elesnrnl, aiis' revision of the. ratio 

hydrogen : oxvu'cn 

\\ould no! necessitate recalculation of a lariv part of the atomic weight 
fable. Accordingly, \\' OIL chose oxygen as his standard with an 
atomic \\ei_i'iit. of 10. Ber/.clius surest ed () 100, as this higher 
li^ure avoinleo! the necessity of a! i ribut ini( to hyilro^cii a value less than 
unity. 1 )uriur sueeei'iiiu( years various standards were j>ro{K>sed until, 
in 1S.")S lu IStJO, ('aniii/./.aro surest cd the adoption of the round figure 
O I(rOO. f rhf lull-mat tonal Atomic Weight Committee, appointed in 
liSSi>, mainly on ! In- lull iative of Hrauiu^r, took as standard II I, hut in 
11105 adopt <-d 

C> 16-000, 
and expressed all other atomic weights n-lativcly (hereto. 1 

1 lAu 1 ;i full iUTunul f tin* lft'nnin;t{inn,i f thr ratio hyirui f in ; osvi^'H, wr liiin 
srrit-s, Vol. 11. 

< : H. \ITKU V. 

Formula, 0... 
Occurrence and History. 1 

. " 4 1 * . : I u n S 1 1 i H , ; f f n s i f ' S 2n 

^rlvl^ ''!'' ''* ni ^'^'' ^!^'" .MJ^, .^u- / !.' V .VTiiu" 

nrofrnjsrd flu- pivsrncv (^'^ViVtniV 1 // -.M' I ' ; n 'jj^ J; h '''- V ' '" S ""'^ 
storms and rl.rlrir,,! d^tiirhaH,,, " ^ii H, , \ /''V'" '''t -' l * Mni(; ' 
oondiulcil that th<Mi(,t lr imlu-tt* .l'lh-- M "'' ' fi " !i! " lis s 

Ii<*avr thcnaiurur^M/iv. in.iij tiiv.-k .-./-.' "i ?'''., i'/ '' ^ ^ "'* '' *" ulll>t| * 

- is k 

, , ,, , ( 

" ' ' '' ' 

ru,,,,,,...,,, A , , , 

molecular Wfi.rhl a ' ' v >" 1 - ul l ' 1 " 1 '' ' !"' 

,, ll.i. , 

; i' 1 ; !i 

. . ,, 



Ozone occurs in small quantities in the atmosphere as is evidenced 
by certain absorption bands in solar and stellar spectra. 1 It is also 
present in certain natural waters in sufficient quantity to be recognisable 
by the smell. 2 

Preparation by Physical Processes. The preparation of ozone 
from oxygen is a, markedly endothcrmic process, being accompanied by 
the absorption of 3-i calories per gram molecule of the gas. Thus 

:3(a 2 ) = 2(O 3 )--2 X 34,500 calories. 

Hence its formal ion from oxygen by exposing this gas to high tempera- 
tures is to be expected. According to a calculation by Nernst 3 the 
percentages of ozone in equilibrium with oxygen at certain high tempera- 
tures are us follow : 

Temperature, C. 


Ozone, per cent. 



This equilibrium is represented by the equation 

Increase of pressure will favour the formation of ozone inasmuch as 
the transformation is accompanied by a decrease in volume. 

At high temperatures, however, the decomposition of ozone into 
oxygen is practically instantaneous. Indeed, oxygen containing only 
I per cent, of ozone would at 1000 C. have its ozone content reduced to 
0-001 per cent, in 0-0007 seconds; 4 and even at 250 to 300 C. 
decomposition is very rapid. 

lleiiec, no ozone can. be expected in the cooled gas unless the cooling 
is effected so cxpeditiously that the gas almost immediately attains a 
low temperature at which decomposition occurs relatively slowly. 
Thus Troosf and Iluutcfcuille 5 were able to detect ozone in the oxygen 
issuing from a strongly heated tube through which there passed a 
concentric silver lube cooled internally by a, current of water; with 
t his device of a, "" hot and cold tube " some of the ozone produced from 
the oxygen near the heated surface passes to the cold surface and so, 
becoming rapidly cooled, escapes the reverse decomposition into oxygen 
at intermediate temperatures. For a similar reason ozone can be 
detected in air or oxygen which has been rapidly removed from contact 
with a Nernst filament, and in liquid air under the surface of which a 
platinum wire has been raised to a white heat by means of an electric 

By the electrical beating of a, Nernst filament to 2000 C., whilst 

1 l<Wier jin<I Struti, 1'roc. Roy. #oc., 191.7, [A], 93, 577 ; Hartley, Tram. Chcm. Soc., 
IHNl, 39, <>(), 111; iMeyer, Annakn Physik, 191)3, 12, 849. See this Vol., Chap. VI. 
* NuHini and Podki'/.a, Atti M. Accdd. Lined, 1912, [5], 21, ii., 740, 803. 
a See Kernst, Zritxch. Jttcklrochtim., 1903, 9, 891. 
4 Clement, Aunale.n, 11)04, 14, 334. 
& Troost and Ilautefeuillo, Compt. rend.., 1877, 84, 940 

140 OXYUKX. 

immersed in liquid oxygen, an o/.oar eonleitt of .T* per eeut . hy weight 
has been obtained. (loselv eoitueeted uitit this tvsult IN tin- orrunvntv 
of ozone iu liquid air at the surfaer d" or wider \vhieh eiiubus!iblr 
substances such as hydrogen, earbonie nxide, aeelslne, rhareo.-d, ami 
wood have* been burned. 1 

The tendeney for o/,om to be form d at fi-\at-d tempera! wvs is 
further illustrated by the ptvsenee of the jjas in the u\> h\dri:eu Uame. a 
It should br mentioned* however, that the observations of many of the 
earlier investigators a t>n the oeeunvnee of o/.uur in the n-ii;hhourhood 
of iiaines are unfortunately rendered muvrtaw by the- probable simul- 
taneous presenee of oxides of nitrogen vvhieh respond to ih' sam trst % 
namely, t-he UberatuHi i>f iodine from potassium iuiid\ as was i-ntployed 
for deteetin^ oxoiu* (see pp. 177--I71*}* 

It is worthy of notr that, wh<Tea.s sltw e*olin^ *tf the hMti-*l ^i\ will 
cause the ciisappraratu*^ of any */,om % whieh may ha\*- lu-m prodttreti, 
any oxides of nitrogen will persist in the roolrd ^as. 

Oxygen is also <*on verted into tv/oiie by flit- aetiun *f ultra '-violet. 
light, 4 of cathode rays, & and of radium radiation, 1 * 

The change, however, is only partial ; indeed, it has breu d<-}uon^ 
strated experimentally that tbr action *>!' ultra i inlet fi^It! Irads ti an 
equilibrium, oy-unr bein^ partially derompnM-tl if pn sent in re!ati\rly 
large (quantify. 7 Solar radiation at uu nltitudi* of Ki*u jurtrrs iinrs 
not appear able to eonvert oxy^eu into o/.omv'* 

Appreeiable t|Uautif.ieH of o/tn f are protltiiu-d \\ln-u tiifiiitt air or 
oxygen is exposed to the rays emitted by a spark diM'hanje between 
yiuo eli i etriHles. u The nust eon\'eiueitt ttiethntt of prdii'in^ n/one 
consists in allowing a siU*nt w orglo\% eleet ric tliseliar^*- IJ topas% through 
air or preferably oxygen, u pr<eedurr first atlopteii by Sieturns m Js**7 
Simply subjecting oxygen tti c-leetrie sparks will nut jmtduer any 
quantity of o^one, as the^us is tleeoiiiposed In thr sparks praeiirallv as 
soon as it is formed. Kven at 1UI' ('. thr spark disrhar?.^" only 
yields about I percent, of o/oiie, aju! this is prubaltly attributable tu the 
silent dLsc'harKe siniuitaneuusly t>eeurrinj^.*'' Tit*" apparatus rmpln\ed 

1 K. KMuT nitd ( Wf*rkiT, ltte. t HHH*. j^ !H*<, 'N.,!,, :u;; i . r*^ 411, u.t. Ill, 

8 Mauehot, ibid., UM1I, 42, m$Ih; UHM, 4,4, i*i. 

3 Ki(% for ( xnmplo riiitu* ./, /wAf /'A*w',, H/it, J; (4 t t 4L, * in ^bll M,^ . \* /, 
1H1K), 6l 1I C J; Mma*i\ Hll, .S*r. r/nw , IiH ft, *M*. 

4 FiHchtTimd rw!tiar //r, H.'*, jH :'*U."I j UM**I. 4^, i*;'"s ; ,1. L ,- ,1* I M'Jnf *, 
/. Jwir, (Vnw, *SW,, IIMHI, ;|I Il4ti; \.w \>l 1 < -^..i . # , I* *. **$;. **sU . h*><, 
ISO, UU; Wttrbn% A'il ii/'6u'. /V*w r,i-/ Hi , /<-., I, ill |i /. t iiii %, i 
Bordier und Ntjr t iT, (''/////. /vjwf,, HIIH, 147, I.|, t *n i 4^, ** .; i.u f H I *n, 

liHHK 149, l*o, i> * 4 ^ ^ i , II**'' I. ti, CM'i;J. 

id Ix'Vt, .-Illi /**. Jnwl, /,?*' i, I!IH r/ 11 , li , I . j M 'M ^ r ,- . f 
, 129 KHa; lUflmr/, td . v Vh tik .S,f . ^ li r - if , |' ,/j 4 p.tMl, 
13, -HK); Lmd Mwitthh. I ! JIJ, j t. i'lC* ; I?/ n, f A. , , J , ill I / i ;i; 4 | f , I^H.J-, 
HH2, 9, 101. 

hi/mLut. <%nt., Iltl2 Bo 7K ; U.ulmt,', *>* 1 / / , A 1>. II >. II . '; , t''ti;', 
210; li:f, IW4. 

a Bitytnix, Couijtt. r*-w/.. 1 !Utt, 169, !l-,"7, 

f Warburg, #<r. f/rl, /i/i|/,ilnl, C/r^, liiir, 17, Ili-l, 

10 Ktw ShuiiMtotm iiiui KVJUIH, 7'rnw^, (.V^m, *%***, I HUH, y |, ;MII, 

11 The dtHtributkm uf <i%omi i tint dtrrut i s tirrt*iii VMtMiia Ii*!* U?m ^iuiir>.| l*y lti*lriil 
and Kunz, J. 1'kynicnl. Chrm^ I!*2I 24, :!i!i Antl^n^^* */ -l>w tV}-m. Nv , UI7 
39, 2581. 

18 .Hriiu^r and Durand, CunntL rt-Htl, t IIH>7, 145, l*J7. S-i* !/, I**ii4nir<i$i. llrr,. limlL 







H 2 S0 4 

for the preparation of ozone on a small scale usually consists of two 
concentric tubes, coaled with metal foil or some other conducting 
material, and connected with 
the terminals of an induction 
coil or electric machine. A 
slow current of oxygen is 
caused to traverse the space* 
between the two tubes and 
t hus becomes submitted to the 
action of the discharge. It is 
advisable to dry I he gas before 
use, 1 because if, is probable 
that the presence of water- 
vapour favours the formation 
of hydrogen peroxide at f he 
expense of the o'/oac, and also, 
if nitrogen is present, causes 
the production of oxides of 
nitrogen.- Many modifica- 
tions of this apparatus have 
been introduced ; the dia- 
gram represents a small experimental apparatus in which water or 
dilute sulphuric acid provides the conducting surfaces. 

By lowering the temperature it is possible* greatly to increase the 
yield of 07,01 ic which, under ordinary conditions, is less than 10 per 
cent, of the oxygen. By immersing an ozonising apparatus in a cooling 
mixture of ether and solid carbon dioxide and so working at. --78" (,!., u 
yield of It per cent, lias been obtained,' 1 whereas in liquid air it was 
found possible' to convert SH> per cent, of the oxygen into o'/onc, the, best 
results being obtained at, this temperature with a pressure of 100 mm., 
the o'/one liquefying out as it is formed, 

For demonstration purposes a. useful o'/oniscr of extreme simplicity 
can be made by drawing out a piece* of combustion tubing, some 18 
inches in length, to the shape shown in fig. #0, and litting a rubber cork 

Flo, 2ft.- -Preparation of oznno (Brodio, 1872). 

u. IKK- A Htmplci n'/omHW. 

carrying a glass tube* A into the wider end, simultaneously entrapping 
a piece of platinum or aluminium wire B of suttleient length to reach 
almost down to the 4 restricted end of the tube. A second piece of wire 

1 Witrimrtf ad lxit!iuti:-r, Ann. /7///.i7% IJH>, [4|, 20, 751. 

a Tht* n*MuitM *f iShrnstniti* ('/>*/*, ('//</. iS'w%, JH07* 71, 471), which Joel to tlw idoa 
tlsitt Htoistitro ltitidi*rM lh foriimtittu of t>7,ii<\ nptxur in iuiv IKM^II duo to tho pnw.nttc 
i if liitro^i'ii., \vhirh givi-M riw i iiitro^'it jHToxuhy; this in kiuwu to fuuwluralo tho 
wjxmtnn*'*UM i**'impi>4ition of O/OIM*. 

^ BrtiiiT ami Duntnd, dnmpt. n'wl n 1907, 145, 1^72. Smi alno CJoldntein, lkr. t HKKi, 
36, 3042. 

142 OXYUKX. 

C is coiled round the outside of the tube, and both It ami 1' are connected 
to the terminals of a Huhmkorff coil. Oxygen is admitted through A, 
and a stream of ozonised oxygen escapes at the open cud. The 
apparatus may advantageously be fixed on to a wooden stand, and, 
although its ellicicncy is not great, it possesses the advantage of being 

Various other forms of oy.oniscrs have been described, but for accounts 
of these the reader is referred tu the subjoined references. 1 

Obtained in this way, o/one may In* purified b\ fractional distillation 
at low temperatures, the boiling 'point of o/onc brim*' some i*;J above 
tlnit of oxygen. The o/omsed oxygen is liquefied b\ cooling m liquid 
air. The < lee p blue* liquid thus obtained cvohcs maiidy oxjgcn under 
reduced pressure* and at a certain composition separates into two 
layers. The UPJXT dark blue layer consists of a solution of <>/onc 
in liquid oxygen; the lower deep violet -black lu\er is a solution of 
oxygen in o/.one and contains, iit --IKM 4\, some no per cent, of 
oxvgon. a All but mere traces of oxygen arc removed in a single 
fractionation of this liquid/ 1 and by careful manipulation pure t/i*ne, 
B.IV-ntM" ('., may he obtained, 

Preparation by Chemical Processes, O-/om is formed to some 
extent during the slow combustion of certain substance* such as phos- 
phorus. In the case of phosphorus tin* uerunvnec of the o/.onc appears 
to l)e connected with the phosphorescence because substances \vhicfu by 
tlieir ])resen<H\ inhibit the phosphtnvsecuce, also prevent tbc format ton 
of o/xuu;. 4 

The formation of flu* OKOIIC is pruluibly tbic to th* nxidatioii p-n- 
eeeding by the addition of \vhulc molecules of fHygen t<* the ti\idjsablt< 
substance with the primary pruduetictti of pen\idic substartc-s uluch 
subsequently eliminate an atom of uxygru lor c*ach imJecuIc ongimdly 
absorbed; the atoms of oxygen then combine with *wc another and 
also possibly with molecules of oxygen, yielding o/tm*. O/unc is alst 
frecpiently present, in Humes/ 1 

The oxygen obtained by utility chemical processes j% frcquchtly 
contaminated with ozone, 

Fluorine decomposes water in the ectld with stieh vigotjr that it pt*rtii>ii 
of the liberated oxygen is ozonised, lly passing it current uf Uutintu* 
into wat<r niaintaiued at ()'' C 1 ., Moissau was able ftt ttblain 11 supply *>f 
oxygen containing 14-4 per cent, of tr/ow,* Sjiiall yidils art* tbtaMicd 
by the action of <oneeat rated std{>hurie uei<l upf)ii*|u>wcrfti! ovitti.scrs 
such as barium peroxide, potassium btchromutr, ttr 

102, , 

un<i S'hwikit, XfiV^r/i, l'hi$,nii\ Ifii!:*, u, ti!; llrr. 111:!:*, 5*;, 
Kur*r and Wulf, ./. Amrr. (*hrtn t & lli^:! 44^ U.'HM, 
4 S< IIUHW*!!^ Trnntt. C/trm. SVr,, UHKI, 83, !*Jli:i, 

f 'bciw f Zribtch. f7irw, 1H70, 6, ttft, L*nt> ;\Mnm*Io!, //rn, llllfli, 4^, rt*i-|H 
Braohmar, t'6w/., 1906, 39, 040, 

e MoisBan, ^4?*7t. 6 f A>m. Pky*.* 1891, [jlj, 24, ^24. 

OZONE. 143 

In the last-named case the reaction is dangerously explosive and should 
only be earned out with small quantities of the reagents. Ozone Is also 
formed during the decomposition by heat of potassium chlorate, and by 
the action of nitric acid, preferably of density 1-8,% on ammonium 
persulphate 1 carefully warmed up to u"f* u to?'5 C. The liberated gases 
are washed with caustic-potash solution and contain from $ to 5 per 
cent . of o/.one. 

O'/onc is produced during the electrolysis of neutral or alkaline 
solutions of potassium tluoride in consequence of the action of the* Cluorinc 
momentarily produced at the anode upon the water in its vicinity. 2 
Hlcct rolysis of aqueous hydrogen fluoride is stated to have yielded 3 
ozonised oxygen containing from 0-475 to JMS per cent, of oy,one. by 
volume. 4 With a saturated solution of potassium fluoride at O C, a 
yield of 0-05 per cent, o/,one has been obtained for a short time, l>ut the 
percentage of o/oiie tends to fall with the duration of the experiment. 
Variation of current density from 5 to 10 amperes per sq. decimetre does 
not appear to have any appreciable effect- upon the yield. 4 

Uut perhaps the most satisfactory chemical process for the prepara- 
tion of o/on' is Hit* electrolysis of dilute* sulphuric acid. A 15 per cent. 
solution of acid is recommended, coupled with a high current density, 
namely, SO amperes per sq, cm., at the (platinum) anode. With a 
platinum-foil anode sealed into glass so that, only a, thin edge is obtained 
projecting to an extent of about one-tenth of a. millimetre, it is possible 
to produce oxygen containing over 20 per cent, of ozone by volume. 5 

The amount of o/onc has been increased to *I7 per cent, when 
calculated in terms of the gas liberated at (he anode* by tlu; direct 
current by superimposing an alternating current on the last named. 6 
This rise in eHicirney is attributable to the depolarising action of the 
alternating current. The actual concentration of the ozone is, however, 
only <J pn* cent, of the anodic gases owing to dilution with the gas 
liberated by the alternating current. 

Commercial Production of Ozone. The electrical method is 
the only one suitable fur the technical production of ozone, and the con- 
ditions necessary for ensuring a maximum eHieiency have been c'urefully 
studied by many investigators. Thus it is found that. a. larger yield of 
o/,oiie is obtained when oxygen is passed through the oyjoniscr instead of 
air. Moisture exerts n noteworthy retarding influence, 7 and the gas 
should therefore be dried prior to passing into the oxoniscr. Hise of 
temperature likewise reduces the o'/ottc production, 1 * as is evident 
from the following data : 

1 Mnluquitt, ./. Mmrm. ('lnm, t Hilt, 3, ;i2t*. 
3 hiuli, #r-j/,W*. #/>r/w/;i-w., IHSI7, 3, 474. 
A <!wf'ilMM>?. X*-i/.ifA. /;/. f '/'>., HHKi, 36, a.Vi. 

* Pri*l*<iui\ (Tntu*. Ftirutt.'titH;, HMKi, 2, IU), twing a cuwnt <lmwty of IOO amptwH 

l*r M|, ifi'i'tif?Hr?% tl*f jiiftf**! ti yi^M *f *ity O'*t voltuu^ |w*r t.'t*ut. of "/>it. 

'' I**, Mnrtirr iUiil H'MiilJHHohtt,, ^ritsr/i, ttnttfif, ('/it'tn,, IIMM, 6l Ui f I* r ii : l'\ I^tHtOi^r Mid 
MU.HHIMI'/., tAy.Y,. Ii7, ^2, :02, Lv!0. 

;\r*'fisl,tia jiii! xn'it \VHrt*-niHT. %nt*dt. Klrklrm-hnn,, HUI, 17, Hit!, 

Wnrturtf !! {^ith<ttHcr. Ann. I'/iyxifc, ifHHI, ('4 |, 20, 7M. 

n - lli'iii, ,Vot<r -./I., |Sl*:t, 14, 71 ; * ntvt CVrtisitk, ('/n-m, font?., IIHH}, ii,, 585; Her. 
/>/. /r/ii/.<ii /.-**?. trt\-i,, ItMMl, 4, L'llH ; HrtipT iind Durunri. Cow/it, rt-ntt., 1907, 145* 1*272 ; 
Iil, ril, hit*wit, < '**n/. Aj*idirtt tfht-tn., 14HH>, w*. it., p. 143; Liudnr t Trttn*. Anwr. 
I nut. f7**. A'w/. I4HO/3, IHH, Piifwhiit uiu! Knuohtmrhtw {/, /6/w, /%/. Ofaem, /Voc., 
UI1. 46, ."7*'o ***t din* ri^' *f t**itt|M*ritfuri. from W to '2H y (I favoura tho*<>2otio production, 
whtlnt fiif1h**f rinti ttiutitttHhrH if. 




Temperature, j jvr^Xby 





The character of i,ht* disehzir**e is important, .H|;irkni ( 
ettieienc.y. Alternating currents art" usually rmplnyrl 
ccnta^i* of o'/*om* is found to ns* with tin- friMjumi'v 
nmxirunni value is rtachi*d l which varirs uith th** 
1*240 periods pt-r second at <f00 volts, *>;>n at TIHICI 
8000 volts in one scries ofcxperiinrnts* tin* ratr <f pa^ 
the" oxoniscr remaining constant. Incn*asc in ti>* 
displaces the point; of maximum o/twe |M'o*ltiti*tn in i 
increasing frequency. 

The influence of pressure up ft* 5 ittmosphrivs ii;i'* lr 
the results show that the optimum point for tltr prM<i 
lies between 0-5 and I atmosphere. 


\ - 



Fin. 31. Tho W 

lt* I'ri'ii' i>,'.tui"-r, 

-De /' t mr<>'/oiust*ris one of the hr,t kntiun, ami K shoun 
in diagrammatic section in %. :!l. Siv ur I'fht :!a ^ i'\hnlrs, 
measuring sonic 3 feet in height and 10 inchis in iliain li, ,t'iv li\id f 

1 Warburg un d IxuthitUKtT, Ann. l*hy*ilf, Him, Jlj, /H, I, I *, hi ,!* *-l*itnn>! 
data. HOO Warburg, tittzunytibrr. K, Afotil.'ll t v. lltthn, t!*lt,\ jt, lull , \, \t f,> n >'.;<r 
1JK)3 F ]>. 1010; /iw, l*hyfiik\ MHM, Hl *3 477; Km U, /V v ' f| ^ ^ I*** 11 * V "It' 1 ; 
FiHchcT and Bnw4nner ,/lrr., IttOf*. 38, 2tKt3 ; I *rt hn r, K* tl <h, l,*<!tt * , I 1 1 , 1 7, 411, 
Archibald and Vi>n Wftrt*nilxrtf. 7/iW., IK KTJ, I* .ohtd ,m| K**u i)- I 1, //*, f* 

3 von Wttrtfsnl)org and Mair, KeitocK. Ml^ilrwlttm^ HHl\ 19 H7U. 

OZOXK. 145 

two abreast, in a cast -iron box which is divided into three hor'r/ontul 
compartments. \Yatcr is passed through the middle ehamberio keep 
the apparatus cool. Kaeh glass cylinder holds one of aluminium, which 
rests on a glass plate on the bottom of the lowest, compartment, and is 
thus insulated from the metal box. If is further separated from the 
glass cylinder by an annular space about j 1 ,-- inch with 1 , up which a. current 
of air continually passes. 'Flu* cast-iron box is earthed, whilst, the 
aluminium cylinders are raised to a potential of nearly 10,000 volts. 
The air entering at A (tig. CM } escape^ at. 1> charged with ozone. 

The t'oxnittt'r o/oniscr consists of :i series of parallel iron tubes 
through which the air to be o/.onised is made to pass. A strip of metal 
with a saw-like edge passes down the length of each lube inside, but. is 
insulated on porcelain supports, The tubes are connected (o one pole 
of a high tension transformer, and the m'lal ships in lite oilier, an 
alternating current being used. The advantage of this apparatus lies 
in the fact that no dielectric oilier than the porcelain supports and 1. he 
air to be o/onised is required. A series of these lubes constitutes a 
" battery/" 

Physical Properties. The characteristic odour of o/.onc can always 
be observed in the atmosphere, near electrical apparatus working with 
a high voltage; indeed, so penetrating is 1 he odour that if will betray 
the presence of one part in *JA millions of air. 1 As already mentioned, 
it was t his odour I hat led Schonhein to suggest t he name triom* for the gas. 
The blue colour of o/onc is easily perceptible in the <jas obtained 
by evaporation of the liquid and can also lie detected in oxygen con- 
taining only 10 per cent, of o/onc - if layers <f at Jens! I mehv in depth 
an* examined. O/one exerts so marked an absorption for ultra- violet 
light, 11 especially in the neighbourhood of ,*iS m^ as to allow the amount- 
of ozone in ozonised oxygen to be determined photo electrically. 

Ozonised oxvgen is appreciably denser than pure oxygen. A litre of 
o'/oue at X.T.P, would weigh tM 145 grams, whereas oxygen weighs only 
1-12K9, Its density, thm-lore, is I-5O, when' that of oxygen is taken as 
unity. The contraction accompanying tin* format ion of o/one from 
oxygen was first observed by Andrews and Tail, in ISGO. The higher 
density of o/one is indicated by tin- relative velocities of diffusion of 
pure oxygen and o/otiised oxyi;cn, tin* results of Soivl and of Lalcnburg 
obtained with a mixture of known o/,oue eunten! indicating for oy,one 
a vapour density 1-5 tim-s that of'oxygMi (see p. 155). 

O/onc is distinctly more soluble in water than ix*yg<*n, but it has not 
been found possible to obtain concordant ligmvs for I he solubility, 
because in aqueous solution the K' s decomptiM-s so rapidly that equili- 
brium * is ditlicnlt to attain. Mouf:mg : ' stales fhat I litre of water 

1 Itiirfiry Kfitfi-H thut ntti iu-t f /m*' JMT 1*5 <illiu part.-i f air ly vuhnm* i-i th'tH't- 
alU* ly thf :i*iiH' nf mn-ll (Tmn*. Chun. *SV\, Issl, jg, 1 1 1 1. 

s Hfiufi'fetstllr iind < 'Ituppm-*. Cnittfil. r*'f/. IHHJI, 91, ":::! ; ('happtliM, Cttnti*t. n-//,, 
IKHO, 91, 085. 

^ IliU'Ury, TrttH.-i. Cht-tn. iVf'.. IHHI. 30. "? ; Fuiry anl Iui-,jit, Cnmj*t, nwt,, IUI.H, 
XS6.7K'2i R'ni^T tuul MMfll*T, rjwihtl' %'itvh., I'Jhf, r{/;iIH ; HniUv;c||M, Ann. /*%/% 
HioU, "fo, *Hlt ; !*iitlt'ijtur^ utul U 4 iinmnu, //*'. /'*/, /'/'//-^ ^'* >f -. 1^"*'. 4 !-**. 

< SVIiMiie, /l*r, t lK7:t. 6, l:!l*4 ; Milf'i1. ^V^w/^, f*/.. IMM, 119, ( ,.t ; lu^lK Trim*, 
('lit HI. N**r,, !!i;i, '|, iOtvJ; l,mi-nlun' t /^i\, IWS. ;{K **-MK 

Mtiufjinj.?, irtu : h, Jtnm-ni t !!!!, a8, -P.M. Maillrrl Vw/./, /-./,, iKiM, 119* '.T*U 
funl thut IiMHt irrainn tf wutrr iit * < ', <'*tili ;i!*:nrli H!* 1 1 tus'nn, nf n/.ur. S-i alnn 
Lwlrnhtir^, //*;.. I HUH. Jl, ;,*! H. 

tjr 1 1 . V 1 1 I tO 

146 OXYGEN. 

dissolves about 10 mg. of ozone at 2 C., but only 1-5 mg. at 28 C. If 
this is correct, the solubility curve is remarkably steep. 

The solution possesses the characteristic odour and oxidising 
properties of the gas. In dilute acid solution ozone is much more 
stable and the absorption coefficient in decinormal sulphuric acid hns 
been experimentally determined as 0-487 at O. 1 

The "ozone water" of commerce usually contains no ozone. Its 
activity is due to such substances as hypochloritcs, etc. 

Carbon tetrachloride dissolves approximately seven times as much 
ozone as does water, and when oxygen containing 6 per cent, of oxouo 
is passed through the former solvent a distinctly blue solution is easily 

obtained. 2 

The specific heat ratio has been determined by extrapolation Irom 
observed values for mixtures of oxygen and ozone and leads to the: value 


The magnetic properties of ozone are more marked than those of 
oxygen. 3 

The gas can be liquefied by cooling, 4 or by combined cooling and 
pressure, but great care is necessary in working with liquid o/oue 
because in the liquid or compressed state the substance is exceedingly 
unstable, and tends to explode if the pressure is suddenly reduced or 
the temperature suddenly raised ; 5 contact with grease or organic 
matter generally also may cause liquid ozone to explode. 

Liquid ozone has a deep blue, almost black, colour, and is opaque in 
layers exceeding 2 mm. in thickness. It boils under ordinary pressure 
at 112-4 C. 6 ; the considerable difference between the boiling-points 
or liquefying-points of ozone and oxygen supplies a convenient method 
for separating the former from a mixture of the two gases, oxygen 
remaining uncondensed at temperatures far below the temperature of 
liquefaction of ozone. 

On cooling liquid ozone in liquid hydrogen, it solidifies in violet -black 
crystals, melting at 249-7 C. Its critical temperature is 5 C. ; 
critical density 0-537 ; critical pressure 64-8 atmospheres. Its density 
at the boiling-point is 1-46. 7 

Chemical Properties. Ozone is an endothermic substance, its 
formation from gaseous oxygen being attended by a large absorption of 
heat, namely 34,500 calories per gram molecule" at constant volume. 8 

3(O 2 )=2(O 3 )-2X 34,500 calorics. 

1 Luther, Zeitsch. Elektrochem., 1905, II, 832 ; Rothmund, Festschrift W. NenwL, 1012, 
391 ; Rothmund and Burgstaller, Monatsh., 1913, 34, 665. Mailfert, Compt. rend., 1894, 
119, 951 ; Leeds, Ber., 1879, 12, 1831 ; Carius, Bar., 1872, 5, 520 ; 1873, 6, 80(5. 

2 Fischer and Tropsch, B&r., 1917, 50, 785. 3 Becquerel, Compt. rend., 1881, 92, 348. 
4 It liquefies with ease at atmospheric pressure at 181 C. (Olszowski, Monatxh., 

. zows, onax., 

1887,8,230). Hautefeuille and Chappuis (Comp. rend., 1880, 91, 522- 1882, 94, 1249) 
liquefied the gas under pressure at 23 C. T 

5 Erdmann (Ber., 1904, 37, 4737) describes a convenient apparatus for experiment.!* 
with liquid ozone. 

6 Riesenfeld and Schwab, Zeitsch. Physik, 1922, u, 12; Ber., 1922, 55 [Bl 2088 
Olszewski (Monatsh., 1887, 8, 69) gives -106 C. (hydrogen thermometer); Trooat 
(Compt. rend 1898, 126, 1751) -116 C. ; Ladenburg (Ber., 1898, 31, 2508) ~ 12C 0. 

7 Riesenfeld and Schwab, loc. cit. 

8 Kattan and Jahn, Zeitsch. anorg. Chem., 1910, 68, 243 ; Jahn, ibid., 1908, 60, 337 : 
see also Berthelot, Ann, Chim. Phys., 1877, 10, 162, 

OZONE. 147 

This figure has been obtained by decomposing ozone and noting the heat; 
evolut ion. 

As ini^ht ht 4 anticipated from its cndothcnnic nature, oxone is 
unstable, and dcconiposes slowly even at the ordinary temperature. 1 
At, 300" to -I-OO C. its decomposition is practically instantaneous. 

A phosphorescent. Ii#ht is observed on heating ozonised oxygen to 
350" ('. A more powerful phosphorescence results on decomposing the 
vapour of liquid with a hot #lass rod. 2 

Exposure to ordinary li % uht accelerates the decomposition/* even red 
and yellow Ii#ht exerting some influence. 4 Ultra-violet li<jht is par- 
ticularly reactive/ 1 but leads to an equilibrium, inasmuch as oxygen is 
converted into o/onc under the like influence.** Oy.onc is more eliemi- 
(ally reactive in sunlight than in the dark. u 

It is interesting to note that, whereas admixture with carbon dioxide, 
nitrogen, and oxygen does not considerably affect, the rate of decom- 
position, the presence of water-vapour, chlorine, or nitrogen dioxide* 
causes a marked acceleration. 7 

Certain substances, such as platinum black, copper oxide, and the* 
dioxides of lead and manganese, exert a catalytic' effect on the 
decomposition of oy.nnc, and solutions of the alkalis have a similar effect. 
The final result in all these decompositions is represented by the equation 

and although the mechanism of the decomposition is not. exactly 
understood, yet in the gaseous state and in solution its reaction is 
generally himoIeeular. H 

Oy,t>m* is remarkable* for its chemical activity which is manifested. 
in several ways, namely ; 

1. Oxidation, during the process of which there is no change in 
volume in so far its the o/one itself is concerned, each molecule of o'/one 
yielding a molecule of oxygen, tlie third oxygen atom entering the 
oxidised product. This is the most usual type of oxidation. 

2, Oxidation in which all three atoms of oxygen arc* absorbed in 

n. The formation of addition products such as oy.onates, oxouidcs, 
and oxo/ouides, in which the oy.onc molecule as a whole is attached to 
t he final product. 

1 Clark iwtl <1mpman, TrnnM. f'/irw. *Vr, t IflOB, 3, MiUH ; Cl<<m<*tif, Ann. l*hijmk* 
HW4, I4;i:i4; Nili'iiii^/irr A'. Akutl, Ww. Hrrtin* UMll 48, HIM ; IVrmnn inul (JnMivtm, 
yVcw. 1tny. N<\, HHiH, 8o [A|, JI5JI ; (1tiijimt itiit! Jonw, lAir/,, HilO, 97, ^MKJ ; Itll 1, 99, 
IMil ; J'Wh**r n<J Trujwrh, Mr., I1U7, 50, 7<m. 

s lfc'tfi*r, Zritorh. KtrktrtH-hein., HU>, 1 6, 7l ; Sturhtoy, Zrittteh. Witt*. /VwfwA'-w., HJUO, 
19, ll.' 

HiU'/t*iifi. f^mjil, n-m/,. IH72, 74, IUH7 ; vutt Hulir, Ann, /'A//*Jt, ID 10, 33, 

, %ritxflt, jtltymknt, C/ifw.t UU, 8o 78, 
IJHJii, I2 -HJ. 

4 <Jritltth nut! Shutt, 7Viw. ^7irw, AVw\, 1^1. 11 

ft Sri p. Mo, w!it<ri< furt hr n*f<ri'Ht''H art* ^ivon. 

fi IW'iun, f Viwi|f|, f'wr/., IH!K* OI, 125. 

7 Warlair^, N */. ;*/*/* r. A f . /U;w/. Il"iw. /lr-r|iw, |?ilU, p, 1144 ; HUti, p. 210; VVtng 
Ann. rhytikn 1SM7, 24* 243 ; rhajmum nfl .Itmi*, 7>w*. r'/ww. *SV., 1JHO* 97, *J4 
l*II, <>) I.HI1. *S|ti'ii.Httti* i'Vrtinn, (%-m. AV. IH1I7, 71, 477) !Klwv*U rnatHl n'/ami* t 
jiutn^ Htiihlo than dry. That w*u inMrriH't, 

iidiliti*u fi* this fort^gtihig rvftirontwH, w* Rtiihiuuntl iwid Burgnt.fillr f 

148 UXYUHX, 

These processes may uuw he eonsidered in turn, 

1, The reitciions normally F;dlinr undrr this hr.itiin^ \n;i\ !.- suit. 
divided into two jjroups, IK'TH* ly 

(d) Reactions resullin" i. pn'%- u\ii 'linn >t" Hi sui*..mer n/ouisrd, 

(6) Reactions result hi", in the ivduehon Ulh <i tin 1 n/tn- ami the 
substance f real* d. 

(f/) IhwtiHtix ///,"/./'.'; <' -"< '". 'He m,.jnt> of the iv;j*-t inu% 
with <v/one lal! under this sitUlm io<i. U\dr";>n .?nd nitnn^n are 
not affected b\ o/otie HIM!* r nrdn,in em.iht to'- ,. lnf tmluu', 1 sttlphitr, 
arsenic, nnliniony, :tnd the vari*>us ;llu!rn|*r.s uf |liM.,pht*rn\ an* run 
verted into oxides and, in f lu* |nvsrwv ti" nmist uns us!?* I ff rn-Njutndiu^ 

Under the inilunier of nit ravioh-f lujhi l*r*iii ;; ipiart/ uu-n-ury 
vapour lamp, howe\'ei\ o/>nt is i v i|>al*!r *l **\idi'-.t!p; lr;, h\*Ift*!,,frii t thr 
following reactions taking plaer : 

(il -JO, :U>. f ; 

(ii) II, <>. f!,fi n,. 

lleac(itn (i) is nonnally slow, Int is .!.'rraf!y an^|T;tf *-d lv i-\nt sjuul! 
quantities of hydrogen. Hyiln?r-n j-ri'\idr d**i--, nnl ,-ipjn-ar It* l*r 
formed under these eonditiuns.' 4 

Under the infhu'iMT of o/,onr all thr runimMii nutat^ fAtM-ptinf.f ;,.'>ld 
and ]>hitinuin are ccn\t rtt'il, siipt rlinally ii' thr turhd i' masM^r, into 
oxides ; thus silver Iwconies eoaf-ti with a hlack lihn !' a p* r\id*'. 

("cHuhiiu'd hydro.ujrn is !Vrt|nrn!l\ u\idJM'*l t* \^J!*T ;s m hydros-it 
sulphide 15 and palladiuut hydridr \\hi*'h v it-Id th- I'P-'' * Iriunit nut! 
wa.ter ; also phosphine and anuit<*ui;i, in x\h*'h nu! t*nl\ IA thr hydnt^ru 
oxidised, hut also t Strut h<'r elruti-n! prrsrnt i<i\ in?,' arid i'tnu *, Hytlrt.{-n 
chloride, hromide, ainl i<lidt % arr \idisr*I jlli hhi r,.ditti$ nl* thr hidtttfru 
element, 4 a conditi<u of equilibrium lriiiij r? at'hnl in tin- easr nt' th H 
lirst named . \vith steam to 1*.!0" ('., lty*lri*?.,'rn Milphidr r partially, hut 
not eompk't.cly oxiilised to sulptmric acid l\ /,ttus'd air,' 1 

Carhon monoxide is slowly fi 4r\iilisr<| 1y u/nic at t*rdm;iry trmpriM' 
lures, I he rea<*tion heiuj^ fa \ouret I |jy li'ihl and tn*>istur iv , ? At 1MH i\ 
the oxidation prtH*t*rtls rapidly, H and b\ Iiiil!>iii)^ tin- ^JIM-S run riiiii',* 
from the o'/oniser through linu^-'Watrr or li,u\f;i uat-r, fits- prrst-ntM- nl 1 
earhon dioxide is readily demonstrated, 

Sulphur dioxide and nitrous Fumes .uv rapidly n\iiiis<-ii by iutist 
o'/ouc, with formation of sulphurie nut! nitrie a^ids rrsp 

1 Muir Tmn, (-hem, *Vf. t UKUI, 95. tk'til ; Fn-fifrr iitut il^ttur 

2 Wtip>rt nnri Bthnu Stritxrh. ///>/ r/;n/, (iitrn., HJ/, go, I Ml 
80, 78; <T., IOIH, 46, KU>, 

:{ Ht* Kcltwur/. nnci MTmrhnu+yfr, f 'Afw. frvl?** !!H4 i., 5il, 

4 Voltn, (laszrtttt, tH71t 9, f*i!t. ; ()jn-r r'iwi/.f, i-nl <t , Jh77, US, !i,i7 ; IH7..H, 86, 7** ; 

n, Zntttch, nnttry. ( ! Arw, t I9(M, 42, Unit. 

, ('nmpt, rnttL, 1K7U, 87. 'HJ Wiitt% Jw-irn f 7i-w, J, l!:i, |o, .'<, iVnii- 
pan* Sc-hwnr/, and Muttc'htnf.vcr, /r\ r*7. 

7 (JlaiiHmnnn, Cmnpf, r*w'r/., I!Ho, 150, IMIH! JlriiiKrii mttl s Suiiiliii-illi. (//r-r , Jh7;i, 8, 
1414) failed to dHwt any .\ic|ntion uiiJi i r flu* inilitriiri- .f Minli^hr 

H fftnu'H, Awrr. Cfn'ttt, ./., HMIM, 30, -III, 

f 'RfrtliHnt, /!//. r//////. /%/;.?.*, (h7H, 14, :!iT i St-huur/ inl .Mimrhim-v*r, !*-. n'f, 
Helbig, y|//i it Aecntl., llMil*. II fit!, :$II; IfMiM, I*ii), ;!H ittr-M HIP! l'uU< juv, 
Mowittth., 1IH3, 34, 1027. 

OZONE. 149 

In the ease of sulphur dioxide at temperatures below 40 C. all 
three atoms of oxygen in the molecule are utilised. Thus 

But with nitrogen peroxide, 1 one molecule of ozone is required per 
molecule of peroxide at 25 (. Thus 

Potassium iodide in aqueous solution is oxidised to free iodine, the 
reaction having heen extensively applied in the early history of ozone, 
hut it has now somewhat lost in favour because a similar effect can be 
produced by nitrogen peroxide or chlorine.'' 1 If the action of the ozone 
is prolonged, the oxidation may proceed further to the formation of. 
hypokxlite, iodate, and penodate. a 

In a similar manner potassium bromide yields bromine' and potassium 
hydroxide, but the further formal ion of hypobromite and bromate is 
less rapid than the analogous reaction with potassium iodide. 4 

Ozone oxidises alkali nitrites in aqueous solution to nitrates, the 
reaction taking place quantitatively according to the equation 5 

NuN ? () 2 -|-0.,-..--NaNO a -l-O 2 . 

This reaction has been made use of in the determination of atmospheric 

Many other inorganic salts are oxidised by ozone; solutions of 
manganese and lead salts yield the corresponding brown dioxides 
unless the solution contains a relatively large quantity of nitric or 
sulphuric acid when t he former class of salts gives rise to permanganic 
arid,* 1 Chromic salt solutions are transformed into chromic acid, 
potassium IVrroeynnidc gives the ferrieyanide, ferrous, stannous, and 
bismulhous salts'yield precipitates of the ferric, stannic, and bismuthie 
hydroxides, whilst silver solutions form a precipitate of black silver 
peroxide. .Metallic sulphides, e.g. lead sulphide, arc changed into the 
corresponding sulphates. 7 Alkali thiosulphates yield ehielly sulphate 
and ditliiouat.t'. 8 

Some of the thiosulphate appears to be eatalytieally decomposed, 
depositing sulphur in accordance with the equation 9 

Na 2 S 2 O a .:Na a S(VfS. 

The sulphilc is then oxidised to sulphate by ozone. 

The oxides and hydroxides of the metals generally are raised to the 
highest degree of oxidation of the metal., thus ferric hydroxide in the 

1 VVulf, DanMHimcl Kaiwr, /. Am*-r. Cham, tioc., 1922, 44, 2398. 

Hi'o pp. lf>4 and 178. 

8 Kntfiur and Wild lir.r., IWW, 29, 1929. 

* (Jar/arolli-Tluirnlack, ^/oM., 1901, 22, 955. 

6 UHhoraml Hat>, Trtuiti. ('hem, AW,. 1917, in, 799. 
Maqm-nms Cwnpt. rewt., IHH2, 94, 795. 

7 Mnilfort, CMnpt. rend., 188*2, 94, 8(), 1 18 ; Yiunanchi, Amer. Chew. J., 1913, 49, o5 ; 
Janniwch ancl CiottHchulk, ,/. prakt. (J/um. t 190(J, 73, 497. 

Kioaenfuld and Kgidiua, Zeitoch. anory. Chem., 1914, 85, 217. 
Yttiuauclii, Amer. Chan. J., 11)13, 49' & r >- 

150 OXYGEN. 

presence of alkali yields a ferrate. With the alkali hydroxide's, however, 
ozone forms additive compounds or highly oxidised compounds oi' a 
special type; crushed potassium hydroxide absorbs omm* lorming a 
brown substance, potassium ozonate, of uncertain com posit ion but 
probably KH0 4 or KgO^. 1 This reaction may be regarded in two ways, 
namely : (i) as oxidation by addition of the whole o/oiu moltx'ulc. 

KOH+0 8 =KH0 4 . 

In that case the reactions would fall into the third category (pp. 1 17, 151 ). 
But (ii) it has been suggested that during the process of alkali o'/onat ion 
the ozone molecule decomposes into molecular and atomic oxygen, 
the latter, only, acting upon the alkali to form the o/onato. 2 Whoa 
freshly prepared, potassium ozonate is orange in colour like potassium 
bichromate, but on keeping, and on treatment with water, it decomposes 
into the hydroxide, oxygen, and potassium tetroxide. Rubidium, 
caesium, and possibly sodium yield orange-red ozonates. Liquid 
ammonia, to which a small quantity of water has been added, appears 
to behave in an analogous manner towards ozone, the liquid becoming 
orange-red, but the coloration persists only at temperatures below 
50 C. 3 By prolonging the reaction, the ammonia is converted into 
ammonium nitrate, with traces of nitrite. 4 llydroxylaiuine readily 
reacts with ozone, the nitrate alone being formed. 4 Ilydrazine hydrate 
is converted mainly into nitrogen and water. 

From the fact that the presence of at least a trace of water is necessary 
to effect oxidation processes by ozone, it is of interest to note that water 
is not oxidised by ozone to hydrogen peroxide; indeed, in the presence 
of hydrogen peroxide, ozone in alkaline solution 6 decomposes according 
to the equation 

H a 2 +0 8 =H 8 0+20 a , 

whilst in acid solution, except in the presence of a largo excess of 
hydrogen peroxide, there is a tendency for an undue proportion of 
ozone to undergo decomposition. 

Ozone affects a photographic plate. 6 It is also stated to cause 
the explosion of nitrogen chloride, nitrogen iodide, and also of nitro- 
glycerine. 7 

Towards organic substances ozone is strikingly active. Organic 
colouring matters are bleached ; for example, indigo is oxidised to isutm. 8 
Turpentine rapidly absorbs the gas, and if the liquid is exposed on 
filter paper in an atmosphere of ozone, inflammation may occur. 9 
India-rubber is rapidly attacked and so is of little value for connect ions 

i Baeyer and Villiger, Ber., 1902, 35, 3038 ; Bach, Bar., 1902, 35, 3424 ; Manchut and 
Kampschulte, Ber., 1907, 40, 4984 ; Traube, Ber., 1912 45 2201 
Traube, Ber., 1916, 49, 1670 ; 1912, 45, 2201. 

3 Manchot and Kampschulte, Ber., 1907, 40, 4984; Manchot, Ihr., 1913, 46, 1089. 

4 Strecker and Thienemann, Ber., 1920, 53, [B], 2096 

5 p&*> A r nna ^ 1879, 196, 239 ; Inglia, Trana. Ohm. Soc., 1903, 83, 1010 ; Roth- 
mund, E^gUh Inter. Congr. App. Chem., 1912, 26 611 

6 Schaum, Physical, 1905, 6, 73. 

7 Jouglet, Compt. rend., 1870, 70, 539. 

8 ^f <* s > Chem News, 1879, 40, 86 ; Thenard, Compt. rend., 1872, 75, 458 ; 
J. prdkl. Chem., 1857, 71, 209 ; Houzeau, Compt. rend 1872 W 349 

Harries, Ber., 1908, 41, 42. /:) ' 

OZONE. 151 

in ozone apparatus. Alcohol is oxidised into acetaldehyde and even 
cellulose is oxidised, giving an indefinite peroxide compound. 1 The 
oxidation of an alcoholic solution of tetramethyl-p-di-aminodiphenyl- 
methane by ozone produces a violet colour ; this solution, applied 
conveniently on absorbent paper (as " tetramethyl base paper"), 
sxipplics a delicate test for ozone, possessing the additional advantage 
of distinguishing this gas from nitrogen dioxide, with which a yellow 
colour is formed, 2 and from hydrogen peroxide, with which no colour is 

(b) Reactions involving Reduction. One of the best known of these 
is the reaction between hydrogen peroxide and ozone, both of which 
undergo mutual reduction. In alkaline solution, or in the presence of 
excess of peroxide in acid solution, the reaction proceeds in accordance 
with the. equation 

H 8 8 +0,=H 8 0+20,. 

2. All three atom a of ozone may on occasion be used up in oxidising 
a substance, but this is less usual. A common illustration is afforded 
by stunnous chloride 1 , the oxidation of which proceeds as follows : 3 

3SnCl 2 +6HCl+O 3 =3SiiCl 4 +3H 2 0. 

3. Additive Compounds. Under this category the ozonates of 
the alkali metals are frequently considered, but Traube concludes that 
this is not correct, the oxidation proceeding, in the case of potassium 
hydroxide for example, as follows : 

KOI-I +3O 3 = KHO 4 +3O 2 . 

The reaction thus falls into our first category and has been considered 
in that connection (see p. 150). 

Addition compounds are frequently formed when ozone acts upon 
unsaturated organic substances, possessing at least one double bond 
between two adjacent carbon atoms, and are termed ozonides . Benzene, 
C C II C , which possesses three such bonds, yields a tri-ozonide, C 6 H 6 (O 3 ) 3 . 
Oleic acid, :7 H.j a .OOOII, which possesses one double bond, yields a 
monozonitle, C 17 iI 33 (O a )COOIT, a viscous, transparent, and colourless 
liquid which decomposes above 90 C. With alkalies it breaks at the 
double bond, evolving oxygen and yielding nonylic and azclaic acids. 

OILj . (CHjJ, . 011=011 . (CH 2 ) 7 . OOOH (oleic acid) 

4, + ozone 
CII 3 . (CII 2 ) 7 . OH OH . (OH 2 ) 7 . COOH (oleic acid monozonide) 

boiling with j alkalies 

CII 3 . (OH 2 ) 7 . COOH+COOH . (CH 2 ) ? . COOH 
(nonylic acid ) (azelaic acid ) 

The formation of ozonides in this manner is of considerable value to 

1 Dor6e, Tram. Chem. Soc., 1913, 103, 1347. 

2 Arnold and Mentzel, Ber., 1902, 35, 1324 ; Fischer and Marx, Ber., 1906, 39, 2555 ; 
Wurstor, Ber., 1888, 21, 921. 3 Yamauchi, Amer. Chem. /., 1913, 49, 55. 

152 OXYGEN. 

the organic chemist in that he is enabled to determine the number and 
position of double, bonds in unsaturuted compounds, as indicated above. 

Oxozonides. When ordinary o'/oue is allowed to react with un- 
saturated organic compounds, the element is sometimes taken up by 
the latter in groups of four atoms instead of the usual tria tomie groups, 
whereas if the ozone is previously washed by passage through sodium 
hydroxide solution and sulphuric acid, the addition occurs only by 
groups of three oxygen atoms. The formation of oxoxouules, as Harries 
terms the products containing 4 groups, is attributed by Harries to 
the presence of oxozone 4 in the crude ozone. The evidence as to the 
possible existence of a tetr-atomic form of oxygen, however^ cannot 
yet be considered as satisfactory. 2 Vapour density determinations 
reveal no tendency on the part of even pure ozone to associate to higher 
complexes than that corresponding to O :J . 3 

Physiological Action. Owing to its powerful oxidising properties, 
ozone is both a deodoriser and a bactericide of considerable eilhieney. 
Schonbein 3 found that air, laden with organic matter liberated in the 
course of one minute from 4 oz. of putrid llesh, may be completely 
deodorised by its own volume of air containing 1 volume of o/.one per 
3 volumes of air. In 1875 Boillot 4 drew attention to the fact that fresh 
meat may be preserved for upwards of ten days without going bad, if 
exposed to ozonised air, whilst, if exposed to ordinary air, the meat will 
putrefy in half that time. These early observations have received 
ample confirmation in more recent years, 5 and the bactericidal action 
of ozone is well established. 

It is, however, impossible to make a general statement as to the 
minimum amount of ozone required to sterilise air, because so many 
factors are involved. Some organisms are more resistant than others, 
whilst time, temperature, and the presence of moisture have an im- 
portant influence upon the results. It is interesting to note, however, 
that Duphil 6 has drawn attention to the paucity of bacteria in the air 
of Bordeaux an air that is characterised by its high percentage of 

Unless the proportion of ozone is exceedingly small, the inhalation 
of ozonised air by human beings is liable to be accompanied by serious 
disturbances in the animal organism. The lung tissue is injured, the 
oxygen intake increased, and the output of carbon dioxide decreased. 7 
Exposure for a couple of hours to a concentration of 15 to 20 parts of 
ozone per million of air is not without risk to life, and even I part of 
ozone per million of air irritates the respiratory tract. 8 This latter 

IOAA See H ^ r ies S^^ co-workers, Ber., 1906, 39, 2844, 3732 ; 1909, 42, 440 ; Annalen, 
1806, 343, 318; Bar., 1912, 45, 936; Zeitsch. Mektrochem., 1912, 18, 129; 1911, 17 029 
See also Kailan, Zeitsch. Elektrochem.. 1911, 17, 966. Molinari and his co-workers' Her' 
1906, 39, 2735; 1908, 41, 2794. Numerous references to other workers are irivon in 
these papers. 

2 Biesenfeld and Schwab, Zeitsch. Physik, 1922, 11, 12; Ber., 1922, 55, [BL 2088- 
Karrer and Wulf, J..Amer. GJiem. Soc., 1922 44, 2391. ' ' 

3 Schonbein, see Ozone and Antozone, by C. Pox (Churchill) 

4 Boillot, Oompt. rend., 1875, 81, 1258. 

f &V ' 9- C ^-A'Ppl., 1905, 8, 387 ; Sigmund, Centr. Bttkt. Par., 1905, 

' 19 3 ' 55 > 23 


6 Duphil, Soc. sci.Stat. Zool d'Arcachon Univ. Bordeaux, Trav. Lab., 1900-1001 p 51 

vu* an /5T' C em ' % entr 'l 1905 > *" 945 ' from s **- ** ^oL, 1905 1641 
8 Hill and Flack, Proc. Roy. Soc., 1911, [B], 84, 404 

OZONE. 153 

dilution, however, may not be harmful ; in fact it may be directly 
beneficial in eases of bad ventilation by stimulating the olfactory nerve 
and thus relieving the monotony of close air. Air containing not more 
than 5 parts of ozone per million of air has been breathed by children 
without any ill effect. 

At still greater dilutions than the foregoing, the effect of ozone has 
been repeatedly proved to be beneficial. In cases of anaemia it appears 
to stimulate the multiplication of blood corpuscles, to increase the 
appetite, and to raise the general standard of health of the sufferer. 
Asthma, bronchitis, pleurisy, and pneumonia have likewise been re- 
lieved by inhalation of ozonised air, and it is not impossible that similar 
treatment may prove beneficial to consumptives. 

The odour of ozone is so penetrating that 1 part per 2 J million of air 
is perceptible to the sense of smell. 1 This is well under the danger limit 
mentioned above, so that the normal nose may be taken as a pretty safe 
guide in determining whether or not ozone is present in beneficial or 
dangerous quantity. 

Applications. 2 -- -As mentioned in the previous section, ozone, on 
account of its powerful oxidising properties, exerts a marked bactericidal 
effect. It is frequently employed, therefore, for improving the atmo- 
sphere of buildings that are liable to be crowded, for underground 
passages, and for the stations and tunnels of electric tube railways. 3 In 
these; cases great care has to be taken that the concentration of the ozone 
shall always be well under the danger limit. 

As is usual in the case of odoriferous disinfectants, there is always a 
danger of confusing disinfectant or bactericidal action with the mere 
masking of an unpleasant smell, 4 and the actual value of the ozone 
treatment for " stuffy " atmospheres is easily over-estimated. 

The bactericidal action of ozone has also been applied to the sterilisa- 
tion of water 5 and the preservation of foodstuffs. 

The oxidising properties of ozone have led to the application of this 
gas to the bleaching of such substances as starch, flour, oils, and wax, 
delicate fabrics, etc. It has been used in the production of artificial 
silk and synthetic camphor. It has also been used to aid the " ageing " 
or maturing of wines, spirits, and tobacco. The action of ozone on 
unstttu rated organic compounds provides a very convenient general 
method for the preparation of aldehydes and ketones, which has already 
been applied to the manufacture of vanillin for flavouring purposes 
and heliotropin for perfumery. 

Detection. -Many of the reactions described under the properties 

of ozone can be used for the detection of this gas in the air. Exposure 
to an ozone-laden atmosphere causes the formation of a film of oxide on 
the surface of a globule of clean mercury and so causes this to drag or 
" tail 5> when it moves. 6 The formation of a stain of silver peroxide on 
a clean silver surface 7 supplies a very trustworthy test for ozone, but 

1 Hartley, Trans. Chem. Soc., 1881, 39, 111. 

2 See Ckem. News, 1916, 113, 193, 205. 

3 The Central London Tube Railway is ventilated with ozonised air. 

4 Hill and Mack, loc. cit. 

5 See Chap. VII. 

6 Volta, Gazzetta, 1879, 9, 521. 

7 Fr6my, Compt. rend., 1865, 61, 939; TMele, Zeit. offentl Chem., 1906, 12, 11; 
Manohot and Kampschulte, Ber., 1907, 40, 2891 ; Manchot, ibid., 1909, 42, 3942. 


it Licks somewhat in delieaey and also iiiiijltt ijivr misiradht'.' jvsnlts in 
the presenee of hytfro^nt snlphidr. 

Tetrainetliyldi'/J-anunodiplu-nyhnrthiinr provides a %,tf ivfarfun sv 
agent for the* #as (see pp. 151, ITS), and thr u\id;itii*n nf u*did< % \\tth 
formation of iodine ran also hr applin!. Apart trow its histories! 
Interest, the* last method deservrs attrntion la-eaiisr it" its simplicity and 
the refinements of which it is capable. Thr lihrraf um ul' HH)UI* is usually 
detected by the formation of a blue euloratitm \ufh staivh ; it', In*\\rv-!\ 
the formation of alkali is eonennvntly dt-munstrn-trti i> IIMH;; st.-uvh- 
free paper soaked with potassiniu iodide and phnmlpht halt-in sutution, 
which becomes reddened In* t>/onr l tm acrntmi ut" tlt- i'urmation til* 
potassium hydroxide (see p. 17H), flu* possibility of ronlusion with 
chlorine or bromine is removed. To rentier the starch iodide trst 
ubsolulely couclnsive, Jnuwever, udditujiial tests are nrerssary , r..\ f . the 
success of the test should not be affected if flu" tjas is previously pas^rd 
through dilute pernian^anate st>lutiu!t, ii/onr beinj* unaffected by this 
reagent whilst hydrogen peroxide vapour is *leeoiup*si ii ; pa-^^avje 
through a heated tube or through a ta\rr uf manganese' dio\tde 'au-,es 
the decomposition of o/onc, and the I rue u/tiite react ton \\ith star*'h-- 
iodide should, therefore fail after fin- gas bus been v* treated," 

Li.(|uitl air provides a convenient agent tor the t let ret ion of o/one 
and nitrogen dioxidi* either together or separately, e\en alt}tou*|b onlv 
small (juanlities of the gaseous mixture are n^mlablr, \Vbrn the gas 
is passed into the liquid air the nitrogen dtostdc %rj,iratr- as a snhd 
and can be HItered off, whilst the t*/,uiir remains dtssoUrti and <*an br 
recovered by (Careful evaporation tf the solvent. 4 

Estimation. O/one in small quantities ^ u.stiallv rstuuated ly 
the oxidation of potassium iodide, the gas being pa.sseti thrtttt^b a neutral 
or alkaline solution of the salt. With ntt alkahu*- solution then- is Irss 
danger of the loss of iiuline, and in nny ease thr solution must m*t be 
acidified until after the o/,om* trmtmeut or tin- r'sults \\ill be liih, 
The extent of the oxidation is tteferitttttrtl by iietIi!y 111*4 ami then 
titrating the liberated iodine with thiosulpimtc lit thr ustial way, 1 

In acid solution, potassium hromitir is oxith-srd |tiau!itat!\rly by 
o/one yielding an cquimolmilar pruporttoit of br**iit!ii% ri amT this 
reagent can therefore be used lor tttr t-stimatiua nf* tiissttUeil n/nitf in 
the presence of hydrogen peroxide/ 1 

Ozone can also be estimated by slowly passing thr gaseous un \ttire 
through sodium hydrogen sulphit/stituitoit and ti'tratiug thr mirhaugrd 
sulphite with icHUui!, 7 or l>y the gritvtnirtrie |>nH'rss t*i* absnrbitig tin- gas 
in olcic acid or linseed oil and measuring thr iucivasr tit w-$ght.* 

^ Molecular Weight and Constitution* Altlmiigli Sfhiiibnii was 
quite deiinite in his views of oxonr as u distinct suhstaiuv,, thr gnu-ral 

, Ohem. N&m, 1878, 38, *!24, 227, 2* r i, tfltt ; Anl HIP! M' 

^ KeiwT and M*Mjitor, Amrr, Ufam. J IWiH. 39, li. K,, r ufiiMary .f f. 

trnguiahtng uxono from hydntgMt {wruxitto mill iiilmtii* fuiium ,, V<ii)M-t. */," j^r^il, 
1913, a., 88, (JI. a y m <l wr lim | i! rrt i4iiiirtr, llrr^ i*m, 

* hoo Imdoiiburg, Mtr n lW)l t 34, iiH-1 ; Trttiwiwrlt <! Aftnni*r. /r,i,,li. rt *,r,/ 
1905, 48, 80; J^ohiwr, ^i^cA. lMlrt'/ifj llitt, 17, 41^ ; H^^rviU,* u<i 
J. ^r/wr. 6 f AM. tiac., 11112, 34, 1332. * f^ti,, f rs|IM , /.^ Wi , s v,r, t 1 1*1:1. 1s 

RothmumI and Burgiitallw, Mvnatoh., i!li:i 34, iwa. Comiwim, liuttrvrr Ti 
and Annolor, toe. t 

7 Ladenburg, Jfor., 1003, 36, 115, Kniiruli f Hicul, ;w, ii,, -j^. 

OEONM. 155 

confusion with hydrogen peroxide vapour retarded the development 
of the subject. Andrews and Tait, in their formation of o'/one by the 
action of the electric discharge on pure oxygen, demonstrated that ozone 
was an allot Topic form of oxygen of higher molecular weight (see p. 138). 
Sorct then discovered t hat OHOUC is completely absorbed by turpentine, 
and was able to demonstrate that the decrease in volume during the 
o'/onisalion of oxygen is approximately one-half the observed 
when the ozone is subsequently absorbed by turpentine; assuming that 
the ratio is actually I : 2, it is easily seen that the total loss in oxygen 
is 1J times the volume of ozone, indicating for ozone a molecular 
weight li times that of oxygen. 1 The correctness of the assumption 
as to the ratio of the two volume changes was demonstrated later by 
Brodie whose experiments yielded the figures 1 : 2-02, 2 and so indicated 
in a convincing manner that the chemical change in the formation of 
o/one was to be represented 

Sorct also confirmed his earlier result by an independent investiga- 
tion 3 based on the relative velocity of diffusion of mixtures of oxygen 
with ozone, carbon dioxide, and chlorine respectively, in which he was 
able to show that the vapour density of ozone was a little higher than 
that of carbon dioxide*, but distinctly lower than that; of chlorine. Tins 
experiment has been repeated with greater accuracy by Ladcnburg who 
used a gas containing 8 1* l< per cent, of ozone obtained by evaporation of 
liquefied ozone, and, from the velocity of diffusion, was able, to calculate 
a density KJ<>98 referred to oxygen which leads to the value 1-4G9 
instead of the theoretical 1*5 for pure ozone of molecular formula, () ;l . 4 

Hcccnt determinations 6 of the vapour density of pure o/one confirm 
the* value 48 for the molecular weight. No tendency to associate to 
higher molecules has been observed cither in the pure liquid or the gas. 

Tin* greater molecular complexity of ozone relative 1 to oxygen is also 
distinctly discernible in the ratio of the specific heat at constant pressure 
and colistant. volume. For ozone this ratio has the value 1*21) which 
approximates closely to that expected of a tria tonne gas, whilst for oxygen 
the value is 1*404. % 

Various suggestions have been made as to the structure of the ozone 
molecule, the* most favoured being 

,<K ..(), ,O. S 

,""' \ / \ >S' ' % 
O () () () () 

According to Bruhl, the last representation is in closest agreement 
with the specific refraction of the gas, and it also gives at least as easy 
an explanation, as the others of the readiness with which the ozone 

molecule eliminates one atom leaving a stable molecule of oxygen. 

1 HorH, dtwiitt. mid, I SOU, 57, 004; Ann. Ohim. Phytt., 1800, 7, 113. Phil. 
I Him, 31, 82; 18(17, 34, 20. 

2 BnxUu, 1'rttc. Ruy. 8tx, t 1872, 21, 472. 

* Kntt't, Ann. tt/n'w. /%*., 1808, 13, 257. 

* Ul<*nljnur, Mr., I8U8, 31. SW508, 2830; 1899, 32, 321; 1001, 34, 1834; Stoedol, 
ibid., 1898, 31, 3143; Ornger, tfoW., 181)8, 31, 3174. 

6 UU'HWiffld and Seliwab, lttr. t 1922, 55, B, 2088. ttdtsch. Physik,, 1922, II, 12. 
Kurrc-r ami \Vulf, J. Amer. (Own. Noc. t 1022, 44, 2391. 

Hicharz, tiitewigitber. Out. Bef&rd. gea. JNoturew., 1004, p. 57. 


Historical. The fact that tin urtd H .nrruit nit*! i . ,Jm pm r l 
must have been realised by man at a \ r> i arh .la 'r 01 iu l v lopm* nl. 
A knowledge of the chemical composition * I a*r and t , \ In* ae IMMH 
living organisms, however, has onh bun i r ,jii , . j ,M 1, \l i I 
air was regarded as a simple 1 ub tanr* , and in h \r iftf > p'i I" MJ h\ 
ranked as an element, alow* with inv, at Hi ,uii ,\ ! *. 

Galileo (I50i<--KJ!*2) dn vv athntion luth map*' ' i, ^-. i 
demonstrating the apparent UP n *IM iu fit tt'i'tt i! . 1 i d 
when air is coinprtssetl into if. 

The development, of the eh niivtrs !' flu alia** 1 phi i v,i , .MIH- e*h.t 
delayed hy the early lack of ri-,dts'du*n I In r vut \ in**ts kind*. 
of gases. At first the term ** air " v\a apph. d to ,H k ' t - s *ti Mth J JH,^ , 
and not until the commenrt^nt ul of tin vuiihM*th e i*ttir\ w i* th* 
difference in the, nature of various f .is* ^ r * i*ju'.t d ; .it tin. iiiti' \.m 
Hehuont, who introduct'd the term ** *M/' ul* rvd li" uv ? t- 3 ^ - n 
the properties of gases fromdifft ivut \unr*'i s, and a-* an alm* J imm* ha!^ 
result carbon dioxide was accept rd a a m)ii*ir CMJ* M! u nt H|' tjjr 

In the sixteenth cenfitn it was nlr^l\ lunun IM 1* h m^.ts that 
the ealciiuitlon of metals is acompjnti d In an ni'-i* i ^ tu u* e*h< and 
in the seventeenth it had been notd that fhi au t l it**m : ! . b h,i JHV, 
must contain n u principle " anattiguits h* that in mlr* , 

The correct concepti<t of the main eoti'.htu* nl-> l Ih* afm.phrn 
imrnediiitely precedctl the* fall of tin* pltlo*tisttn ihioi^v uh n L,i\ti'i* r 
(1775-177G), who first ruognised tht frit* n.durr ui <ht- !I\M m;tin 
constituents also effected at rotij^h analj ^IN, At tit*' ^ani* p nud I*iit U v 
dctennined the itmount of o\>j$ea in tin* air l\ can-a-rf it In 
with nitric oxide, u gas which he had ltim<,/*if di^'Hi? r 4 f ; 
Seheele, with u similar purpose, absorbed thr o\\*ia ftoiu a iii<a-<urid 
volume of air by a solution of potassium sutplu*U {" h\ $' il Miiphnr M ). 
Cavendish, the first chemist to briiig piu'umat ic ehfiiii J i\ to u *.tatr of 
accurate measurement, estimated the amount <i* th- n*hVi ruiistitumt 
in air by removing it with nitric oxide* ami jiKo b\ f\|*ltMliujf if with 
hydrogen, and followed up this work by u tli inoii f M**u tb;it tin- 
inactive constitticnt was nhnosi *ntircty li*inogrm*ous, obvt\ui; r I bat 
the portion of atmospheric nitrogen which could itit br utaib In 

1 Greek topes, valour, and ^Aa^a, {>koro. 

* Priestley, Jtixperim&ti* m Air, 1774, l t 110; ntl 177*4 


with additional oxygen under the influence of electric sparks did not 
exceed ivo'th l^i't of the original air. 1 

As was indicated hy the. earliest experiments, the atmosphere shows 
but little, variation in chemical composition. Priestley could detect no 
difference between the composition of country air and air in a 
Birmingham workshop, and Cavendish, in 1783, obtained the ratio 
20-S.& : 7'iHC) as a surprisingly constant value for the relative volumes 
of oxygen and nitrogen. These results led. several chemists to the 
conclusion that air is a, definite compound of oxygen and nitrogen. 
Dalton, 2 however, maintained that air is simply a mechanical mixture 
of its constituent gases ; and this view was confirmed some years later 
when, as the result of more accurate analyses, small though decided 
difference's were detected in compositions of air obtained from different 
sources. 5 * Thus, in IS1G, Bunsen detected slight variations in the air 
at Marburg, and since, that date many similar observations have been 

For more than a century no explanation was forthcoming for 
Cavendish's observation that a, small portion of the nitrogen obtained 
From air exhibits a peculiar inertness, in that it refuses to unite with 
oxygen under Hit* influence of electric sparks. Indeed, the fact appears 
to have been entirely overlooked until .Lord Rayleigh drew attention 
to it in 1S9 k The air was regarded as consisting of a mixture of oxygen 
and nitrogen with more or less moisture, and containing traces of carbon 
dioxide, o'/oue, and several other minor constituents. In 1803 Rayleigh 4 
published the results of a scries of very accurate determinations of the 
densities of nitrogen obtained from various sources, and drew attention 
to the fact that atmospheric nitrogen invariably yielded a higher 
density than nitrogen obtained from chemical source's, such, for example, 
as by the decomposition of oxides of nitrogen, of ammonia, or of urea. 
I Sis results were as follow : 

Mfim weight of aim ns phc Ho nitrogen cantaiuod in largo globe . 2-3101G grams. 
MC.ILU weight of " ehrmic'RJ. " nitrogen contained in large globo . 2-29927 ,, 

Haylcigh satisfied himself thai; the density of none of his samples of 
nitrogen was affected by the action of the silent electric; discharge ; he 
also proved that the lightness of the nitrogen from chemical sources 
was not. due to admixture with any known gas such a,s hydrogen, 
ammonia, or water-vapour, possessing less density than itself. From 
this it was evident that cither the 44 chemical " nitrogen contained an 
unknown and less dense gas, or, what 'was more probable, that the 
atmospheric nitrogen was contaminated with a, heavier, but likewise 
unknown gas. 

Cavendish's experiments were therefore repeated in a more modem 
and refined manner, and it was found that, after sparking atmospheric 
nitrogen with an excess of oxygen, and absorbing the resulting oxides 
of nitrogen and any unattaeked oxygen by suitable reagents, a residue 
of an inert, gas was always obtained, the volume of which was pro- 

1 (,VvwKlinh, Wtil. '/Vv/w*., 1785, 75, ,172. Soe also Alembic Club Reprints //./., and 

thlrt fttTWH, X f ol. I,, p. I WO. 

a Dttitnn, Maw/water Mt'tnuiff*, 2nd HorioH, X, 244. 

:t Bunwn, (ttttimm'triwhc. Mcthndcn (Brautwehweig), 1857 ; also Kcgnault, rend., 
1848, 26, 4, lf5 ; 1852. 34, 8M ; Ann. (!frim. /%*.", 1852, 36, 385. 
* !ta.yi'i^h, /Vw;. liny. #<>., IHJKJ, 53, 140, 1804, 55, 340. 



portional to the original volume of air used. In conjunction with 
Ramsay, Rayleigh l isolated this new gas in sufficient quantity to 
determine many of its properties. Spectroscopic examination proved 
that it was not nitrogen, and as all attempts to make it combine chemi- 
cally with any other known elements proved futile, the new gas was 
christened argon. 2 

Soon after the discovery of argon, namely, towards the close of 1894, 
Ramsay was able to obtain helium in sufficient quantities to render an 
examination of the gas possible, by heating powdered cleveite. Up to 
that time helium had never been isolated ; indeed, its existence was only 
known through its spectrum. When this gas was found to resemble 
argon in its remarkable chemical inertness it was thought that possibly 
other similar gases might exist, and liquid air was therefore subjected 
to careful fractional distillation whereby three new gases were found, 
namely, 3 Neon, 4 Krypton, 5 and Xenon. 6 The presence of helium in 
the atmosphere was also established. All of these latter gases, however, 
are only present in the air in very minute quantities. 


The chemical composition of dry air varies slightly at different places 
and, indeed, at one and the same place at 'different times. The following 
may be regarded as a fair average : 


Per cent, by Volume. Per cent, by Weight. 

Nitrogen 7 

Oxygen 7 

Argon 7 

Carbon dioxide 8 . 

Krypton 9 

Xenon 9 

Neon 9 . 

Helium 9 . 

Ammonia .... 

Hydrogen 10 . 

Ozone and hydrogen peroxide . 








0-0004 to 0-0009 

0-0025 n 






In addition to the foregoing, the following gases are usually 
present in variable but minute proportions carbon monoxide, hydro- 
carbons, nitric acid, sulphur dioxide, sulphuric acid, hydrogen sulphide 
mineral salts, organic matter. The amount of water-vapour in the 
air is extremely variable. 

1 Rayleigb and Ramsay, Phil Trans., 1895, 186, 187. 

2 Greek dpyov, inactive. 

Eams *y an Trav ers, Proc. Roy. Soc., 1898, 62, 31 

f the 

405 437 - PUl 
1002) V Moore, 

hidden - 


9 Ramsay, Proc. Roy. Soc., 1908, 80, [A], 599. 

10 Claude, Compt. rend., 1909, 148, 1454 

'. 8tranger - 

g ee p 



The mean composition of Paris air, freed from carbon dioxide and 
water- vapour, is given by Leduc 1 as follows : 


Per cent, by Volume. 

Per cent, by Weight. 

Nitrogen .... 






Argon ..... 



Neon ..... 

15X10" 6 

8-4 XlO" 6 

Helium .... 

5 X 10- 6 

0-7 X ICT 6 

Hydrogen .... 

1 X 10- 6 

0-07 XlO~ 6 

Krypton .... 

5 X 10- 8 

14 X 10- 10 

Xenon ..... 

6 X 10- 9 

3 X 1C- 10 

Physiological Action of the Air. As a general rule any harmful 
effect produced on man by air must be due to some foreign impurity in 
the air ; the mixture of nitrogen and oxygen is an absolute necessity for 
prolonged existence. The fat of mammals, however, dissolves more 
than live times as much nitrogen as does an equal volume of water, and 
this fact may give rise to serious results with men working under con- 
ditions, For example, in caissons, in which the external atmospheric 
pressure undergoes sudden and considerable variations. If the reduction 
in pressure is too sudden the fat-containing tissues of the workers are 
liable to injury on account of the formation of gas bubbles. 2 

The Percentage of Oxygen in the Air. Oxygen and nitrogen 
(with argon and the other inert gases) are the most constant constituents 
of the atmosphere, and an estimation of their relative quantities in air 
which, if necessary, has been previously freed from carbon dioxide and 
moisture, may be made either by gravimetric or volumetric methods. 
In 1841 Dmnus and Boussingault 3 published the results of their classical 
experiments in which air, freed from moisture and carbon dioxide by 
passage over sulphuric acid and caustic potash respectively, was drawn 
through a tube of heated metallic copper into an evacuated metal globe 
of several litres capacity. From the increases in weight of the globe 
and tube containing the eopper, the relative weights of nitrogen and 
oxygen were ascertained, the mean results of six experiments being as 
follows : 

Weight of nitrogen 4 . . . . 76-995 
Weight of oxygen .... 23-005 


1 Lcduc, Engineering, 1919, 108, 569. See also Krogh, Math, fysiske Meddelelser, 
1919, i., No. 12. For a discussion of the chemical and geological history of the atmo- 
sphere, KC.O Stevenson, Phil, Mag., 1900, [5], 50, 312, 399; 1902, [6], 4, 435; 1905, [6], 
9, 88; 1900, [0|, 1 1, 220. On the origin of the oxygen of the air, see Phipson, Compt. 
rend., 1895, 121, 719. 

2 Vcrnon, Proc. .Rot/, tioc., 1907, 79, [B], 366. Twort and Hill, Proc. physiol Soc. 9 
1910, v-vi. 

3 DurmiH and BousBingault, Compt. rend., 1841, 12, 1005; Ann. Chim. Phy$. t 1841, 
3, 257. 

4 Including, of course argon and the other inert gases, which were unknown at the 


Other in\ estimators ohhdnid **lo< iv M"id 
portant researehes biti'f tlios,< u!" 

I-ewy (1810. , CMJM )du ; tt 

Mari<(tiae ( is it!) , ; t; { H. \^ 

Thr Bravimitri< ni;ilysis of ir <u inl> l UTJ.-.! u< uulMh 
of oonsultTahh* laiuirnturv a||*ar:hr,, ,111*! M- * ji,J* . ;f l.<j ( '. '''Mp 

air, A more t'ouu'tiii'ut tiirthiiti ut 4 ait.l\ snf iur rr, J , ?u it li n 

Iht^ rdutivt! ro/nwr,v of oxifvn aud ntrn", u, 11?s% i* r, r,*li!v -ff, 

by mixiuft a known voluuto of nir wild rvf.-v, of Itv.lro", it witm* * 
<otuhnu'<l volume, ami %|trkiu. Ilir VO!UIM*- i", a-^m . i|, MMI* linril 
oj tl^'outrac'ticm W tttl|! 

thirds ol its volmm* of liydro^n In urld Wll f rl% |j, ilir ,, ;, 
hydrogen , or nl any rate brfniv N|rkiu?f th- mixtur*, th 

b<* cwTfuIly trwl from cnrltoit ilinidi% ;tiuiniMim ( ;tisii ^nnb 

K their jmwwr would introtiiit*^ ait ii|i|ir*'piaW^ rrr-ir ii4i ?|r ivMilt 

obtained. This tnethui was lir{i-ly iinni ly Iliiifvi*. 

J Including, of oourm y argon ami the other Inert .mkiiniim -t, it* i 


July's method consists in heatini*' a spiral of copper wire to redness, 
by means of an electric eunvnt, in :i known volume of air. Copper 
oxide is formed, and from the diminution in volume i he relative pro- 
portions uf' oxyvfen and nitrogen (includiniy the inert, ^ascs) are readiiv 
obtained. A convenirnt form of i he apparatus is shown ttta^rannnati- 
ealh in liij. ."L*. The <;|;jss rlohe A, of approximately 100 e.e. capacity, 
is iiiled with pure. dr\ air, free front carbon dioxide, and connected by 
means of a capillary tube to t he graduated tube I! containing a mercury 
seal, After the volume af atmospheric pressure has been noted, C fs 
raised tint il I he air in II has been forced into A as indicated by t he rise of 
the mercury in H to the stop cock I). The spiral of copper wire in A 
is no\\ heated elect ricalK iu order to ** tt\ " the oxygen, after which 
the apparatus i\ alloued to cool and the residual volume of nitrogen 

Other inrthitds consist iu absorbing the oxygen by means of an 
alkaline solution of pyro^'allol l ; by means uf phosphorus; or some 
other suitable ivajLfeut. In is Mi Uunsm, usiujj his volumetric or 
Mitlioinctt'it' ~ method, coniirmed the obst-rvntion of Cavendish, that the 
air has not ;ihv;iys Iht' %aiur couiposilion, This was further illustrated 
by Ke#nauU, u \\ho analysctt air froiu a number of localities, with the 

fol!n\\ tltj result s : ' l 

(icucvn and Cham*mu\ 
Touln H*;*ls atid Mc<!it 
Atlantic Ocean , 
Krumlor , 

Suininil i" P 
Antarctic Seas 

^rii by \ i>ltutu\ 

UO-iHKS '20'1H> 

20-UI.H 20*11(15 


^O-iH-lf 20-9HH 
*JO-HO *Jt(J-Ol 

m/* \\liu always maintained that air was not a compound but 

a mixture, sn^cstrti that, since nitro^m is the lighter *{n?% the propor- 
tion of this gits to o\yj4*!t oftfiltt to increase with the altitude. This 
expectation \vns hornc mil sonn* ri*|hfy years Inter by the rrsrar(*hc*s 
of Morlcy, tt !"^tnitlii4|* from January IHWt to April IHH1, at Htidsotu 
Ohio, l\S.A. It was ohscnrd that scvi-rt* depressions of lcmpernt.tir<! 
were romu'ctctl uith the ilrscent uf i-old air from vt*ry high altitudes, 
and that thr proportion of oxygen wits usually slightly less than normal* 

U, 48. 2UCH1 ; 


3 {*I'r'k r f Wi'H, lilpl liMifliH, tff^UAUtt*. 

1 Uwmutt, A , ('ft int. /'A I/.*., lKfL*, |6 3H4 

1 Tfikpit fr**i H'<** nt$*l Si'lii*rlrfttiiii*r* Trniti 
Ifiiliiisi, HHlo), 

C/irwwIri/, v*l. i |i. fKfl (Mite* 

* Murlfv. Amt-r. J. .S'n' iHHl, 22. 417 : f 'Arm. AVii'^ tHHi!. A*. llHII. 



Owing to the intermixing of volumes of air by the winds it is ex- 
tremely unlikely that any appreciable difference can exist in the pro- 
portions of oxygen and nitrogen due to elevation alone, 1 although 
indications are not wanting that at the highest altitudes the percentage 
of oxygen is slightly reduced. This is evident from the accompanying 
table in which are given the results obtained by Leduc.' 2 At an altitude 
of 2060 metres on the Alps descending currents of air contained nearly 
0-2 per cent, less of oxygen than did ascending currents the following 
day. The same table shows a slight increase of oxygen in summer 
over that of winter and spring. 



Sorbonne . 


Nice, Nimes, Algiers 


Belgian Frontier 
Alps (2060 metres) 

Oxygen per cent, by Weight. 

23-14 to 23-20 



"23-16 (July) 
y 23-07 (April) 
y 23-17 (summer) 
^23-09 (winter) 

23-05 (descending air currents) 

23-23 (ascending air currents) 

The proportion of oxygen appears to vary somewhat with the 
latitude, there being if Hempel's analyses may be regarded as typical 
rather less oxygen in the tropics and more in. northern latitudes than in 
temperate regions. 3 




Mean Percentage of 
Oxygen by Volume. 

Tromsoe (Norway) 
Dresden (Saxony) . 
Para (Brazil) 

69 40' N. 
51 30' N. 

1 27' S. 


Not merely does the proportion of oxygen vary from place* to place 
it also varies at one and the same place from time to time. Thus Levy 4 

, Frankland (Trans. Chem. Soc., 1861, 13, 22), and 

^^ n aPPredable diff 

2 Leduc, Compt. rend., 1893, 117, 1072. 

3 Hempel, Ber., 1885, 18, 267, 1800 ; 1887, 20, 1864 

4 Levy, J. prate. Chem., 1851. 54, 253 ; Phil Maa.. 1S51 P4.1 


found that after great forest conflagrations the air of New Granada 
underwent remarkable changes, the oxygen-content falling from about 
21-01 to 20-33 per cent. Such a variation is decidedly abnormal, but 
in volcanic districts is perhaps more frequent than is generally known. 
The following data, compiled from the researches of a variety of 
investigators in different localities, will serve to indicate the results 
usually obtained. 




No. of 

Volume Percentage 
of Oxygen. 

Heidelberg . 

Bunsen .... 


20-84 -20-97 

Manchester . 

Angus Smith On Air and 

Rain, (Longmans, 1872) 


20-78 -21-02 

Bonn . 

Kreusler (Bar., 1887, 20, 

991) .... 



Cape Horn . 

Mui it/ and Aubin (Compt. 

rend., 1880, 102, 422) . 


2072 -20-97 



Morlcy (loc. ciL] 


20-90 -20-95 


Watson (Trans 1 . Chan. 


Hoc., 1911, 99, 1400) . 


20-93 -20-98 

The mean percentage of oxygen in the air may be taken as 21-00 
by volume and 23' 20 by weight. 1 

Physiological Importance of Oxygen in Air. It has already 
been mentioned (see p. 134) that the chief physiological function of 
oxygen is to aerate the system and thereby ensure the removal of waste 
material in the form of carbon dioxide, which escapes into the air 
through the lungs. The oxidation processes involved cause considerable 
heat evolution, arid it is through this means that the body temperature 
is maintained. Berthelot concluded 2 that six-sevenths of the heat 
developed by respiration is liberated in various parts of the body other 
than the lungs, one-seventh only being liberated in the lungs. This 
pulmonary heat was found to be almost completely compensated by 
the absorption of heat due to liberation of carbon dioxide and water. 
It would appear, therefore, that upon the temperature of the inspired 
air would depend whether or not the lung temperature rises. In 
any case the variation would be small. 

Respired air is saturated with moisture, after removal of which 
it contains normally some 4 per cent, of carbon dioxide and 16 to 17 per 
cent, of oxygen. These amounts vary both with the individual and with 
circumstances. Thus Thomson 3 found that the expired air of the 
average Manchester citizen contained 4 per cent, of carbon dioxide, 
whereas an average of 5 per cent, was observed in country districts, 

1 Leduo, Compt. rtwd., 1800, 123, 805. 

2 Jicrthelot, ibid, 1890, 109, 776, 

:1 W. Thomson, Vlt. Inter. Congr. Appl Chem., 1909, sec, viii., [A], 154. 

164 OXYGEN. 

reaching to 5-4 per cent, on high ground near Buxton. Under normal 
conditions the rate of breathing is subconsciously regulated so that the 
proportion of carbon dioxide in the arterial blood leaving the lungs 
contains a definite equilibrium pressure of carbon dioxide. A very 
slight increase in the amount of carbon dioxide excites the nervous 
centre controlling the breathing and stimulates respiration. Hence, 
during physical exercise or in cold weather, 1 when more carbon dioxide 
is being produced, the proportion of this gas in expired air remains 
substantially the same, but the volume of air passing through the lungs 
increases proportionately, the breathing being deeper and more rapid. 

During sleep, when both mental and physical activity are at a 
minimum" the amount of carbon dioxide produced is less than normal,- 
and the rate of breathing is proportionately reduced. 2 

When at rest, the average man consumes some 18 litres of oxygen 
per hour, an amount which may increase to 60 litres when walking at 
about three miles per hour, whilst in cases of more violent exercise such 
as running or jumping even 100 litres may not be quite sufficient. 

The Physiological Influence of Excess of Oxygen. This has been made 
the subject of a considerable number of researches, and the conclusions 
arrived at by different investigators are reasonably concordant. It 
would appear 3 from experiments on the cat and on man that the 
inhalation of pure oxygen does not materially augment the quantity 
of that gas in the blood, nor affect its average carbon dioxide content. 
Again, 4 in a series of experiments on men at rest, performed some 
twelve hours after the last meal, no noticeable difference could be 
detected, either in the gaseous metabolism or in the character, depth, 
or frequency of respiration when the men breathed air containing 40, 
60, and 90 per cent, of oxygen. The only difference that could be 
detected lay in the pulse rate which fell as the percentage of oxygen 
rose. It is very important to remember, however, that these experi- 
ments were only conducted for relatively short periods of time, and it 
has yet to be discovered whether or not a permanent increase in the 
percentage of oxygen in inspired air would have an influence upon the 
system in the long run. Thus J. L. Smith, 5 in 1899, drew attention 
to the fact that oxygen, at the tension of the normal atmosphere, 
stimulates the lung cells to active absorption ; but his experiments on 
mice indicated that at higher tensions inflammation might be produced. 

The Physiological Influence of Reduced Oxygen Tension. The effect 
upon respiration of a reduced oxygen tension is one of much greater 
importance from a practical point of view than the problem just con- 
sidered, inasmuch as the main difficulty in practice lies not in 'reducing 
the amount of oxygen in buildings, but in raising it to the normal. It 

* FaJlojse -.(Trav. M de L. Fredericq, Liege, 1901, 6, 183) found that a fall of tempera- 
ture from 21 C. to C. results in the production of an increased amount of carbon di- 
oxide. Above 21 C. there is also an increase, but it is not so marked 

i! A . OT ?8 to . L - 5* e St * Marian (Compt. rend., 1887, 105, 1124) sleep reduces the 
carbon dioxide output by one-fifth and the oxygen intake by one-tenth 

! ' uckmaster J^d J. A. Gardner, Proc. Roy. Soc., 1912, [B], 85, 56. 

, 4 J- G. Benedict and H. L Higgins, Amer. J. Ptysiol, 1911, 28 1. See also J. Loeb 

\ ^ y . 8 ' r*t m r Z ^\\ igi hl>r? 17 5 L ' E ' Hill and J. R. Macleod, Proc. 
Roy. Soc., 1902, 70, 455 ; L. E. Hill and M. Flack, Proc. Phvsiol Soc 1909 xxviii to 
xxxvi. ; W. Thomson, loc. cit. ; A. FaUoise, Trav. lab del Frederica LiLe , iqof fi 1^ 
P. von Terray, Pflugers Archiv., 1896, 65, 293. redencq, g ' 9 ] ' ' 135 ; 

5 J. L. Smith, J. PtysioL, 1899, 24, 19. 


is thus of the greatest importance to determine whether or not 21 per 
cent, of oxygen is essential to vigorous human life, and if not, what is 
the minimum amount of oxygen that may be safely permitted. A 
moment's consideration will show that no 'perfectly exact answer, at 
any rate to the second of these problems, can be arrived at, for not only 
do the needs of different persons vary, but those of the same individual 
are likewise influenced by the state of health and extent of physical 
and mental activity at the time of experiment. Further, after prolonged 
exposure to certain abnormal conditions, unless these latter are too 
severe, the body adapts itself to meet the new requirements. Thus 
persons who habitually live in ill-ventilated buildings are much less 
affected on any particular occasion than those who enter such buildings 
after a life in the open. This adaptive tendency is extremely well 
illustrated by the researches of Douglas, Haldane, Henderson, and 
Schneider, 1 who stayed at Pike's Peak, Colorado, for five weeks at an 
altitude of 1-1,000 feet, the barometer standing at 45-7 cm. A careful 
study of their persons showed that they gradually became accustomed 
to the altered conditions, except that hypcrpnoea upon exertion lasted 
longer than usual. 

The reduced tension of the oxygen was counteracted 

1 . By increased lung ventilation. 

2. A considerable increase in the red corpuscles and haemoglobin of 
the blood, the extent of which, however, varied with the individual. 
The volume of the blood likewise increased slightly, except during the 
first week. 

3. Finally, an increased secretory activity of the pulmonary 
epithelium was observed. 

Inasmuch as all these adaptations take considerable time to develop, 
they would not occur in rapid balloon or aeroplane ascents. On coming 
down from Pike's Peak, the normal state of the body began to assert 
itself, and in the course of four weeks all traces of the change had 

There is abundant evidence to show that the percentage of oxygen 
in the air may be reduced very considerably without producing any 
unpleasant symptoms. Dr. Whalley, in his report on the ventilation of 
Scottish coal mines, alludes to one in which considerable quantities of 
black-damp were evolved. "A light," he writes, "would not burn 
1| feet from the floor . . . but the men had no fault to find with the 
atmosphere, and the foreman told me it was better than usual." Upon 
analysis, the air on the pavement was found to contain only 13-13 per 
cent, of oxygen, and that at the coal face 18-97 per cent. Valenzuela 2 
caused his consumptive patients to breathe an artificial atmosphere, 
containing only IT per cent, of oxygen, and noted that this exerted a 
marked stimulating action upon respiration, increasing the chest 
expansion, and liberation of carbon dioxide, whilst the nutrition was not 
adversely affected. This apparently indicates that in a normal atmo- 
sphere we consume more oxygen than we need, just as we ordinarily 
partake of more food than is really necessary. In the case of a person 

1 C d Dowlas, J. y. Haldane, Y. Henderson, and E. Schneider, Proc. Roy. Soc. t 
1912, [BJ, 85, 05 ; E. 0. Schneider, Amer. J. Phyaiol, 1913, 32, 295, has recently published 
further data on similar lines. 

2 Quoted by J. Harger, Coal and the Prevention of Explosions, etc.. (Longmans & Co., 

1013), p. 41. 

166 OXYGEN. 

at rest, the percentage of oxygen may be reduced to 11 without 

very unusual being experienced, 1 and the respiratory exchange remain s 

the same. 2 Below 10-5 per cent, the body loses its compensatory 

and the amount of carbon dioxide increases. 3 The breathing 

becomes deeper and slightly laboured. By reducing the supply to 

per cent., the face becomes leaden in hue, and the senses deadened, 

a further slight reduction results in sudden loss of consciousness. 4 

Closely connected but not absolutely identical with this problem. 
the minimum partial pressure of oxygen in the atmosphere is that of 
effect of reducing the total pressure of the air. 5 This, for example, 
experienced in balloon ascents and in mountaineering. The avert 
individual does not feel himself inconvenienced at an altitude of 9OOO 
feet, in which circumstances the barometer stands at approximately 
50 cm., and the pressure of oxygen is correspondingly reduced to abo"Wt 
14 per cent, of an ordinary atmosphere. Above this altitude the avox*-^ 
age European begins to observe something peculiar during periods ol 
physical exertion, and at 14,000 feet the effect is very marked, 
amount of oxygen being equivalent to that of about 12 per cent, 
an ordinary atmosphere at sea-level. 

In view of the foregoing, it would appear that 11 per cent, of 
is the lowest limit to which it is safe to go. Below this the air is dangeroi<t"S 
and at 7 per cent, may prove fatal. 

When taking physical exercise, however, these limits are probably 
too low for the average person, and 14 per cent, of oxygen may then t>o 
taken as the lowest that can be breathed with safety. 

The greatest height ever reached by an investigator in a balloon. i*= 
probably that attained by Berson and Suring in July 1901, namely > 
35,400 feet (10,789 metres), although in 1862 Glaisher and Coxw r eli 
ascended over Wolverhampton to about 29,000 feet, when they becamo 
unconscious and are believed to have risen to nearly 36,000 feet foir *x 
short time. The two greatest heights recorded for aeroplanes are tlioso 
of Rohlfs, who, in September 1919, ascended to about 32,418 foot 
(9880-5 metres), and of Schroeder, in February 1920, who readied 
approximately 31,184 feet (9505 metres). 6 

Carbon Dioxide in the Air. It is to Dr. Black that we owe the fi:r fc 
proof of the existence of carbon dioxide in the air, during the yesxx-H 
1752-1754. 7 He termed it fixed air. Lavoisier, however, showed tlxtvfc 
it was a compound of oxygen and carbon. 

1 Haldane and his co-workers, J. PhysioL, 1905, 32, 225, 486. 

2 J. Tissot, Compt. rend., 1904, 138, 1454. 

3 P. von Terray, Pflugers Archiv., 1896, 65, 393. 

4 The rapidity with, which loss of consciousness sets in constitutes one of the poirilB 
that the diver has to face when working under water in an artificial atmosphere. W"lioii. 
Lieutenant Damant was testing the Jheuss apparatus for the Admiralty Commit, -fco<3, 
and was deep under water, he suddenly swooned, owing to the fact that he had unwittingly 
allowed the oxygen percentage to fall too low. Only the prompt application of artificial 
respiration saved his life. See Martin, Triumphs -and Wonders of Modern Chenw &tv~?/ 
(Sampson Low), p. 177. 

5 Many writers regard these two phenomena as identical, and from the point of ^rie w 
of respiration this is probably sufficiently near the truth. The personal equation, of 
persons experimented upon varies so much that such exact results cannot be obtaiiaocl, 
as is possible with analogous combustion experiments like the burning of a candle, etc. 

6 M'Adie, Nature, 1920, 105, 437. 

7 And not to M'Bride as Thorpe (J. Chem. Soc., 1867, 20, 189) and Symons 
Stephens (Trans. Chem. Soc., 1896, 69, 869), stated. See preface to Lectures on, 
Elements of Chemistry, by Jos. Black (Edinbro. 1803), p. xxiii. 

Til!-: ATMOSPHKUK. 167 

The actual proportion of carbon dioxide in the air varies very 
considerably according to circumstances, Whallcy reported that in u 
Scottish mine the carbon dioxide in the air near the coal face reached 
1-21 per cent,, whilst on tht- pavement it was no less than 4*50 per 
cent. Lewy, 1 in discussing the abnormal air of New Granada, points 
out that o\ving to forest tires the percentage of carbon dioxide in the 
air \vould often rise to O- to JHT cent. These eases* however, arc 

The average amount of carbon dioxide in pure, fresh air may be 
taken as f l parts per 10,000 by volume. This is subject, however, to 
alteration by a variety of factors. Thus over land it increases slightly 
during tile night,' 4 and it is somewhat greater over laud than over sea. 3 
In Antarctic regions it is less than in more' temperate climes. 4 Fog and 
mist likewise play an import nut part. Angus Smith/"* in his summary 
of the then available data, showed that I be average carbon dioxide 
content of Manchester air in tunes of fog amounted to <-7i) parts per 
KUMK), the normal amount lor Manchester being t-Ott. Similarly, 
Husscll * l observed as much as 1 !! parts of carbon dioxide in 10,000 of 
air in thick, \vhtte London tog. Indeed, his average for twenty-nine 
fogs was 7'U, whilst tor ordinary clear London air he found only J>*0 parts. 
Hain is accompanied by a diminution of carbon dioxide, but with 
snow the gas is in excess. Its \ariation with altitude is apparently 
inappreciable, 7 but thr evidence of the effect of latitude is conflict ing. 

Considerable variation may be due to local circumstances. Tims 
Hcisct found that the presence of a flock of *M)0 sheep on a fine, calm day 
in Dieppe induced n notable rise in flit- proportion of carbon dioxide 
in the immediate neighbourhood, which registered HK parts per 
10,000 instead of f HMl the normal value for Dieppe. The influence of 
vegetation upon the carbon dioxide content of the air has not received 
tht* consideration it deserves, although a few isolated experiments have 
been carried out. KlirMwycr," for example, found an excess of the gas 
in the forest, n result that, confirmed the earlier observation of Trwhot. 
In confined spaces, sueh us dwellings, the carbon dioxide shows a marked 
increase owing to its being u product of human metabolism, and may 
reach 0-5 per rent, 

A connection hits been traced bet \vecn tht* relative' amounts of carbon 
dioxide and o/,cue in the atmosphere, the amount of the former varying 
inversely with that of the latter for values below the normal, 10 

In the folknvifiii table arc listed it few of tht* more* important, and 
recent determinations of tht* amount of carbon dioxide in the 

1 U'tt-y, /, /'**/. rh*'tH. t IH:*J, 54. LV*;I ; /Vul, ,Vn/,. lHfl, |4|, a, foo. 

3 Thin ituifitit! turuitiMft iti'uh#iMy Mimil *r ttif-^Msf*ftt ov**r the* w*t, Their jits, 
/. <f~*4rw. sV, 4 IHH7, *0, tnit, itwwt, Jl Jj/mmjm., iH7iJ, 5, MH*. ('ttmjtt. rand,, 
I87t 88, UH7; 1HWI, fi s 1 144, 1467, 

m 3 Hi*t* lit*' r^rt'llt'itf- .niifitiintry witli fill! rtft'n*H***K by I<*tt Am) Iltttki% /'rtte. Itt/y, 
Dublin .SV*f., tW IWtf, $, lf*7 1*70. 

1 MUtit/. itnii I*iiifir t rw|il, frl,, t!HI, 153. tllii Munt/. uiul AuUin, <*'om;rf. rend., 
1HK1, oa, 247, lJi, iHHl. i)j, 7117 ; JMH2, ^/"iVifit ; IKMU, 96, J7$UI; IHH4, 98, 4H7, 

4 AII^UH Sitttth* Air tt mi Item, (i*fit{mittt.'(, IH7), 

* Hrr Utt*M<UVwMrk in thr Monthly Wwth'-r /iVpirl/i i/ tht: J/rl, Council, 1884 

? M. 4 Thierry* Cnmpt, fr*l, lHil!* 1^9, 1115, 

K KU<riuuyt<r, '/*> lk*ebuflrnhfit far WttMlufl, Sttiil^t 

1 Tni<*ht, *iiilf< Ayrttnttia.) Is77 3, IIU. 

H 146, !f77, 




Near Dieppe . 

Country air . 
In town of Gemb- 

loux, Belgium . 

H miles west from 
"centre of Sheffield 
Mt. Blanc : 

Altitude, 1080 m. 

Altitude, 3050 m. 

Kew . 

Monte Video 

Antarctic air over 
sea, lat. 64-67 

Bucharest . 


Parts of Carbon Dioxide 

by Volume in 10,000 Parts 

of Air. 

2-942 (mean of 92 determina- 
tions) .... 
3-352G (mean of 26(5 analyses) 

2-944 (mean) 
3-70 (mean) 

3-9 (mean of numerous de- 
terminations in centre of 

3-27 (mean) 

2-62 . . . \ 

2-69 .... .1 

2-91 (mean of 40 determina- 
tions) .... 

2-43 to 3*60 (minimum and 
maximum of numerous de- 
terminations during 1898 
to 1901). 

2-70 to 3-30 (mean value, 
2-98) .... 

I 3-02 (in the city) . \ 

\2-81 (surrounding plain) I 


J. Keiset, Conipt. m/., 1879, 88, 

1007 ; 1880, 90, 1144, 1157. 
Spring and Roland, Chew. Zeiitr., 

1886, p. 81. 
A. Peterman and J. Graftiau, 

Ckem. Zentr., 1892, ii., 201. 
A. Peterman and J. Graftian, 

Chem. Zentr., 1892, ii., 201. 
W. C. Williams, Bcr., 1897, 30, 


W. 0. Williams, Ber., 1897, 30, 

M. de Thierry, Comi>L rend., 

1899, 129, 315. 
Letts and Blake, M. Pror. Roy. 

Dub. Soc., 1900, 9, part 2, 

pp. 107-270. 
H. T. Brown and F. Jflsoombo, 

Proc. Roy. floe., 1905, [B|, 7<> 


Schroder, Chem. Z/citun.y, 1911, 
35, 1211- 

Miintz and Laine, ConipL re nil., 

1911, 153, 1110. 
St. Minovici and Grozca, /S'c-t. 

Roumanie, 1914, 2, 275. 

The Source of Atmospheric Carbon Dioxide.-- It is not generally 
realised that 3 parts of carbon dioxide in 10,000 of air amount to a total 
weight of 3 billion tons of gas in the whole atmosphere surrounding the 
globe, and correspond to the presence of 0-8 billion tons of carbon. 1 
Enormous quantities are evolved from volcanoes 2 and mineral springs. 3 
Boussingault 4 calculated in 1844 that Cotopaxi alone emitted more 
carbon dioxide than the whole of Paris, which at that time gave up daily 
some 3 million cubic metres of the *gas. The persistent respiration of 
human beings, 5 of animals, and of plants, the combustion of ever- 
increasing quantities of fuel, 6 and the decay of vegetation and 

1 Seep. 192. A. Krogh (Meddelelescr om Groetdand, 1904, 26, 419) gives 2-4 Xl0 l - 
tons of carbon dioxide ; van Hise (Mon. U.S. Geol. Survey, 1904, 47, 967) and Dittmar 
(Challenger Report, vol. i., part 2, p. 954) give figures of the same order ; Chamberlin 
(J. GcoL, 1899, 7, 682) gives a somewhat higher estimate. 

2 See Meunier, OompL rend., 1878, 87, 541, etc. 

* See Varigriy, Air and Life, Smithsonian Miscellaneous Collections. 

* Boussingault, Ann. Oldm. Phys., series iii., 1844, 10, 456. 

5 It has been calculated that the human race breathes about one million tons of carbon 
dioxide into the air daily. 

6 The estimated world's consumption of coal in 1912 was 1200 million tons. This 
mostly finds its way into the air as carbon dioxide. 


carbonaceous material are constantly adding to the carbon dioxide 
content of the air. 

The soil is continually evolvmg carbon dioxide ; part of this is no 
doubt of volcanic origin, and part is due to chemical processes of a more 
superficial character. As an instance of the former, it is interesting to 
note that after eruptions of Vesuvius the soil has breathed out such vast 
quantities of carbon dioxide that game have been poisoned wholesale. 
The famous Valley of Death in Java, the Death Gulch of Western 
America, the Grotto del Cane near Naples, and others, owe their poisonous 
atmospheres to carbon dioxide exhaled by the soil. 

It has been calculated that each square mile of fertile garden soil 
evolves some 4000 tons of carbon dioxide during the summer months. 
This is due to the decay of vegetation and organic matter, as well as 
to the continued respiration of small creatures. Thus, for example, 1 
earth-worms breathe out as much carbon dioxide as a human being, 
weight for weight. 

Nevertheless, the carbon dioxide content of fresh air remains fairly 
constant at 0-03 per cent., a fact which suggests that some reactions 
must be proceeding on a grand scale, tending to absorb or destroy the 
gas. Three such have been discovered. First there is the action of 
plants, 2 the green parts of which under the influence of sunlight inhale 
carbon dioxide and exhale pure oxygen. As illustrating this it may be 
mentioned that one square metre of leaf surface of Catalpa bignonoides in 
full sunlight is capable of assimilating 344-8 c.c. of carbon dioxide in a 
single hour. 3 When the vast amount of foliage in tropical and temperate 
climes is considered, it can readily be imagined that this plays no 
small part in the reoxygenation of the atmosphere ; indeed it has been 
calculated 4 , that leaf action alone would suffice for the purpose. There 
can be no doubt that the amount and luxuriance of vegetation does 
respond within certain limits to the amount of carbon dioxide in the 
atmosphere, 5 and existing coalfields probably represent Nature's attempt 
to reduce the percentage of this gas by locking it up as carbon beneath 
the crust of the earth. 6 

A second important regulator of the atmospheric carbon dioxide is 
to be found in the rocks of the earth's crust. T. C. Chamberlin 7 
calculates that the carbon locked up in the sedimentary rocks of the 
earth's crust is 30,000 times as much as is now existing in the air, and he 
further estimates that 1620 million tons of carbon dioxide are being 

1 Friend, Science Progress, 1912, 6, 393. See also von Fodor, Hygienische Unter- 
sac/u(.ngen uber Luft, Bode.n und Wasser (Viewig, 1882). 

2 We owe the discovery of this fact to Priestley in 1771, but Ingen-Housz was the 
first to show that light was essential to the process. See Ingen-Housz, Annales de Physique, 
1784, 24, 44. 3 H. T. Brown, Nature, 1899, 60, 479. 

4 E. H. Cook, Phil Mag., 5th series, 1882, 14, 387. 

"' See the researches of Deherin and Maquerine ; E. C. Teodoresco, Rev. Gen. BoL, 
1899, 2 ; J. B. Farmer and S. E. Chandles, Proc. Roy. Soc., 1902, 70, 413 ; H. T. Brown 
and F. Eseombe,n&iU, 1902, 70, 397 ; 1905, 76, 118; E. Denioussy, Compt. rend., 1903, 
136, 346 ; from which it appears the rate by assimilation of plants is within small limits 
proportional to the partial pressure of carbon dioxide ; but if the latter gas is present 
in very great excess the leaves curl as if to avoid assimilating too much. According to 
Godlewski, the Polish botanist, assimilation reaches a maximum in the case of Glyceria 
tt'pectabilia with 9 per cent, of carbon dioxide. A further increase of the gas decreased 
the assimilation again. The maximum varies for different plants. 

6 Letts and Blake, Proc. Roy. Dublin Soc., 1899-1902, 9, 162. 

7 T. C. Charnbeiiin, J. Gaol, 1899, 7, 682. 

170 OXYGEN. 

annually withdrawn from the air in the course of building up new 
sedimentary rocks. 

Finally, the ocean serves as a vast regulator, as was first pointed out 
by Peligot l in 1855. Rain-water dissolves carbon dioxide from the air, 2 
and on reaching the soil absorbs yet more, both in the free state and in 
combination as carbonates. The streams and rivers carry this away 
and discharge it into the sea. 3 There can be no doubt that each of these 
factors plays an important part in regulating the composition of the air, 
but the actual share borne by each will vary according to circumstances. 

Estimation of Atmospheric Carbon Dioxide. A convenient method 
is that of Pettenkofer, 4 which consists in introducing a standard solution 
of barium hydroxide into a large bottle containing several litres of the 
air to be examined. The bottle is shaken from time to time to keep the 
sides moistened with the solution, and after 5 or 6 hours the absorption 
of carbon dioxide may be regarded as complete. The baryta solution 
is decanted into a small stoppered bottle and allowed to stand until any 
suspended barium carbonate has settled. A portion of the clear liquid 
is then removed and titrated with dilute sulphuric acid, using phenol- 
phthalein as indicator. The diminution in alkalinity due to combination 
with carbonic acid is thus measured, and from the data obtained the 
percentage of carbon dioxide in the atmosphere may easily be calculated. 

The results obtained are frequently irregular and invariably indicate 
too high a percentage of carbon dioxide in consequence of the absorption 
of expired air from the operator during the titration. To obtain 
accurate results many precautions must be observed. 5 

Carbon dioxide may also be estimated volumetrically by absorp- 
tion in concentrated potassium hydroxide solution from a volume of 
air. The diminution in volume is noted by direct measuring, and results 
of considerable accuracy can be obtained in this manner within a very 
few minutes. 6 

Gravimetric methods are, in general, more accurate, but require a 
considerable amount of apparatus, and take a longer time to execute. 
The simplest method 7 consists in slowly aspirating some 40 litres of all- 
over caustic potash contained in U-tubes and noting the increase in 
weight. The air must first be dried by passage over concentrated 
sulphuric acid, which simultaneously removes any ammonia. 

The Physiological Significance of Carbon Dioxide. Carbon dioxide is a 
colourless, almost tasteless, and odourless gas, and it is consequently 
impossible by the unaided senses alone to detect its presence in the air. 
The odour of respired air is not due to carbon dioxide, but to other gases ac- 
companying it, and the close, stuffy effect of ill-ventilated buildings is due 
to the same cause. From a physiological point of view, carbon dioxide 
is of as much direct importance to us as to our complementary organisms, 
the plants. " A certain percentage of carbon dioxide in the atmosphere 

1 Peligot, Ann. Chim. Phys., 1855, [3], 44, 257. 

2 Both Levy and Fodor in their extensive researches found that after rain the carbon 
dioxide content of the air was reduced temporarily, showing it had dissolved in the rain. 

3 Schloesing, Compt rend., 1880, 90, 1410. See also ibid., 1872, 74, 1552 : 1872, 75, 
70 ; Miintz and Lain<, ibid., 1911, 153, 1116. 

4 Pettenkofer, J. Chem. Soc., 1858, n, 292. 

5 See Blochmann, Annalen, 1887, 237, 39 ; Letts and Blake, loc. cit. ; Walker, Trans. 
Chem. Soc., 1900, 77, 1110. 

6 See Haldane,/. Hygiene, 1901, I, 109. 

7 Saussure, Pogg. Annalen, 1830, 19, 391. 


is essential to our vrry existence from minute to minute ; not only is it 
the normal stimulus to the respiratory centre, hut it; assists in the 
splitting up of oxyha'moglohin in the tissues. If an animal is in axle to 
breathe a carbon dioxide free atmosphere, the normal circulating carbon 
dioxide in its blood is reduced, and there arises after a time a condition 
known as ttcttjiniu* in which the respiratory centre l missing its 
customary fillip goes on strike, stops breathing, and the result may be 
fatal; restore, however, the due proportion of carbon dioxide and* the 
breathing is resumed/* - In other words, the animal organism is so 
accustomed to breathe air containing traces of carbon dioxide that it 
cannot do without it, 

It is equally true that an excess of carbon dioxide is fatal to human 
life, although it is dillietdt to determine the exact amount that is so, 
inasmuch as it varies with a number of factors, such as the health and 
individuals! s of t he person, and t he time during which the gas is inspired. 3 
In breweries and mineral' water factories large quantities of the gas are 
regularly inhaled by t lie mem Beadnell mentions that *20 per cent, of "pure 
carbon dioxide has been inhaled for three hours without fatal results. 4 
On the other hand, earbon dioxide from a candle or gas llamc is harmful 
at much smaller concentrations/' Possibly this is due to the relatively 
large amount of moisture simultaneously produced, for Grsmdis, 6 in a 
series of experiments made upon the venous blood taken from the jugular 
vein of a dog, shows that dry air is capable of taking up more carbon 
dioxide from blond than damp air. Consequently, the lungs arc less 
easily relieved in moist air, and the presence of earbon dioxide in the 
inspired air must have a proportionately more baneful influence. la 1893) 
Kroncekcr and Jordi 7 published an account of an interest ing scries of ex- 
periments performed on themselves with the direct object of determining 
how much, carbon dioxide can be breathed with impunity in inspired air. 
The gaseous mixture was contained in a gas-holder of 40 litres capacity. 
It- was observed that a mixture of equal parts of air and carbon dioxide 
rendered breathing impossible by causing spasms of the glottis. Thirty 
percent, of carbon dioxide on being breathed for a minute changed the 
appearance of the person experimented upon, dyspnara resulting. 
A 22 percent, mixture caused less inconvenience. With an 8 per cent. 
mixture the breathing was ample, being .slightly more than normal. 
This tatter observation is in complete harmony with the recent work of 
Hough," who shows Unit by breathing in a confined space of some 
*iO litres, healthy individuals attempt to secure' an increased ventilation 
of their lungs by increasing the rate* or depth or both of the respiratory 
efforts. In IS95 two years after the publication of Kroneekcr and 
Jordi \ paper, I. S. llaldnnc" gave the results of some valuable experi- 

* Tltitf <-<irt**u dtuxitit* in an r\rif tutt t< tin* moratory mitro wan eouttmuul by Xuutz 
tiwl UH<*>- (Jiv/j, /'Ai/.W,, IHU7, |*. :i7t))mnl Uulntaml<Hivolmr(7V-t.?6.rf/x. tfr&dcricq, 

LitV, IWJl, 6, 1). 

a lfe'iilfii'U, ./, /% /w.W. /'/!/*> Hrnttht HH3, 21, 3, 

J This tttw ri!tflwiM'tI \ty L, <!< Sitmt Mnrtin, ('tntipl, rrntL t 18D3, Il6, 200. 

4 ilripIlP'-II, Iwf, rtl. St***tiUn ft, IWI. 
s Atintti **'^ |*r rt'lit, f**rit Itutius 

8 V. (tnmili's AHi II, ^!r4/. /*>/**'*, hMK>, |5], 9, i. 224. Hco also VV. Thomson 
{ r//. !nit-.t\ (.'tiuyr. Aj-tjtt, iVririirr, ItKHf, we. viii., p. IfH), who confintm (.hi. 

'* lipiiifi'krr iiipl Jttrtit. f'rttr. IVii/aiW, *SVi. t IH1KI, 21. 

* T, Hfiii||li ,'iiiirt, ,/. liiiimL t llitl, 28, :iti!t 
4, S, Iittiiltii% J, IVii/^ik* iHim, x8, 4:ill 

172 OXYGEN. 

meats carried out upon his own person. From these 

carbon dioxide is a cumulative poison, and that the 

upon the extent of saturation of hemoglobin with it Du ungics t 

is not until the corpuscles are about one-third satuiatc ^ ilwtthc 

symptoms become sensible ; headache and *f K r ^ 

pronounced on reaching half saturation. Haldanc ^ 

that when air containing carbon dioxide is breathed some 50 

of that actually inhaled Is absorbed. The maximum f* 

dioxide that the blood can absorb from an atmosphere con 

small but fixed percentage of it, depends upon two factors, viz t c 

relative affinities of haemoglobin for oxygen and carbon dioxide, and tlic 

relative tension of these two gases in arterial blood Upon bmithmg 

fresh air the disappearance of carbon dioxide from the blood is slower 

than its absorption was, and is due to the dissociation pi carbonated 

hemoglobin by the mass influence of the oxygen m the pulmonary 

capillaries and the consequent outward diffusion of the gas through the 

aveolar epithelium. 

From the foregoing it' is clear that the effect of breathing air con- 
taining relatively large quantities of carbon dioxide is very similar to 
that produced by diminution of oxygen and by high altitudes, and it is 
no doubt due partly to the deficiency of the oxygen, but partly also to 
the direct influence of the carbon dioxide itself ; in fact Haldaixe and 
Smith 1 regard this latter as the more potent cause of the hypcrpiicea 
and headache which result. 

The actual proportion of carbon dioxide that can be supported 
without inconvenience is seen to be much higher than is generally 
believed. It is impossible to fix with definiteness the limiting amount 
for safety, as this again depends upon the personal equation of the 
subject and upon the moisture and temperature obtaining at the time. 
It would appear, however, that from 8 to 10 per cent, of pure earbou 
dioxide may be inspired with impunity for many hours, and a slightly 
higher percentage for short periods. Above 10 per cent, the gas begins 
to have a narcotic effect, and at about 25 per cent, death may occur 
after several hours, although 50 per cent, may be breathed for a short 
time without fatal effects. 2 

Water- Vapour . 3 The amount of moisture in the air is an exceedingly 
variable factor, and is usually expressed in terms of relative humidity, 
that is the ratio, expressed as a per cent., of the amount actually present 
to that which the air could hold if saturated at the same temperature. 
The absolute humidity, on the other Iwid, is the weight, in grams, of 
moisture contained in 1 of air. 

In the following table (p. 173) are given the numbers of grams of 
water-vapour contained in 1 cubic metre, saturated at various tem- 
peratures, under a normal pressure of 76 cms. 4 

It is seldom that the atmosphere is actually saturated with moisture, 
and the temperature to which it must be cooled, on any given occasion, 

1 J. Haldane and J. L. Smith, J. Path. Bad, 1892, I, 168. See also H. Bulot and L. 
Guvelier, Trav. lab. de L. Fredericq, Liege, 1901, 6, 1. 

2 Foster and Haldane, Investigation of Mine Air, p. 144. 

3 An interesting account of the subject is given by Simpson, Nature, 1923, in, 
Supplement to April 14, pp. v.-xii. 

4 As corrected by Dibbits (Zeitsch. anal. Chem., 1876, 15, 121) from the results of 
Magnus (Ann. Phys. Chem., 1843, 61, 247) and Regnault (ibid., 1845, 65, 322). 



in order that its contained moisture may effect its saturation, is termed 
the dew-point. This is an important point in meteorological studies, 
for our sensations as to the dryness or moistness of the air are influenced 
more by the relative than by the absolute humidity. Thus, for example, 
on a hot summer's day the air may feel very dry and yet contain more 
water-vapour than would be required for saturation on a cold winter's 
morning, under which latter conditions we should experience an acute 
sense of dampness. 

Temperature, 0. 





























The water-vapour of the atmosphere is an important factor in 
preserving equability of temperature, inasmuch as it absorbs a large 
portion of the heat radiated from the earth. Water-vapour has a density 
of 9 (11=1), whilst that of dry air is 14-4. In consequence of this the 
humidity of the air affects its pressure and is thus an important factor 
in connection with fluctuations in the height of the barometer. The 
presence of water-vapour in air exerts a pronounced retarding action 
on the rate of aeration of natural waters. For this reason metals 
corrode much more rapidly when submerged in water exposed to a dry 
atmosphere than when the air above is humid. 

Determination of Atmospheric Moisture. The amount of moisture 
in the atmosphere may be estimated gravimetrically by aspirating air 
through U-tubes containing some desiccating agent such as sulphuric 
acid or, better, phosphorus pentoxide, and noting the increase in weight. 
Calcium chloride may be used for approximate estimations, but for 
accurate work it is not efficient. 1 

A more rapid and convenient method consists in a determination 
of the dew-point by means of a hygrometer. One commonly used 
is that devised by Regnault, 2 and consists of a glass tube, the lower end 
of which is encased in a silver thimble. The tube contains ether, into 
which dips the bulb of a sensitive thermometer. Air is aspirated through 
the ether causing evaporation and cooling. The temperature* is noted 
at which a film of moisture collects on the thimble, and again when it 
disappears after stopping the aspiration. The mean of these two data 
is taken as the dew-point. 3 

1 For the efficiency of the above drying agents, see Pettenkofer, Annalen SuppL, 1863, 
2, 29 ; Dibbits, Zeitsch. anal Chem., 1876, 15, 145 ; Morley, ibid., 1885, 24, 533. 

2 Regnault, Ann. Chim. Phys., 1845, 15, 129. 

3 For details of other types of hygrometers, including the wet and dry bulb thermometer, 
the reader is referred to text-books of Physics and Meteorology. 

174 OXYGEN. 

Desiccation of Air. It is frequently necessary to dry the air for 
chemical and metallurgical processes. For example, air required to be 
ozonised for ventilating or sterilising purposes must first be dried ; and 
the efficiency of a blast furnace in the production of pig-iron is greatly- 
enhanced by the desiccation of the blast. 1 One convenient method a 
consists in cooling the air by passage through chambers fitted with pipes 
through which cooled brine from a refrigerator is passed. The moisture 
is deposited as ice on the tubes, the escaping air having been cooled to 
about 5 C. (23 F.), and its moisture content reduced to approximately 
2-6 grains per kilogram of dry air. 

In the Daubine-Roy process 3 air is made to ascend a tower and 
during the process to pass through trays of calcium chloride, the 
temperature of which is kept low (namely, 4 to 5 C.) by means of water 
coolers. The limits of hydration range from the monohydrate to the 
octahydrate; thus 

CaCl a . H 2 +7H 2 O^CaCl 2 . 8H 2 0, 

the monohydrate being periodically regenerated by passing hot gases 
through the tower at a temperature not exceeding 200 C. 4 Experience 
shows that 240 kilograms of the monohydrate spread out in a layer 
24 cm. deep and cooled by tubes containing water to 4 or 5 C. will 
per hour desiccate 800 cubic metres of air percolating it from above 
downwards ; it will continue to do this for 4 hours, reducing the humidity 
of the air from an average of about 15 grams of moisture per cubic 
metre to one of about 1-5 grams. To desiccate a gas to this extent by 
refrigeration would require a temperature of about 15 C. 

For laboratory purposes small quantities of air are frequently dried 
by passage over anhydrous calcium chloride which is a slightly more 
powerful desiccator than the monohydrate. A better reagent is sul- 
phuric acid. Gases may be led directly through the concentrated acid 
or, better, through tubes or towers containing pumice, glass beads, or 
other suitable substances moistened with the acid. The concentrated 
acid reduces the moisture content to about 1 milligram in 4000 litres. 5 

The most powerful desiccator available to the chemist is phosphorus 
pentoxide. Prolonged exposure of a gas to this reagent, conveniently 
scattered over glass-wool, reduces the moisture content to about 
1 milligram in 40,000 litres. 5 

Atmospheric Ozone, Hydrogen Peroxide, and Organic 
Peroxides. For many years traces of oxidising substances have been 
known to exist in the atmosphere, 6 and have been variously characterised 
as ozone, hydrogen peroxide, and organic peroxides. % Unfortunately 
early investigators failed to appreciate the fact that it is extreme! v 
difficult to distinguish between and severally estimate such minute 

1 See this series, Vol. IX., Part III 

DanMn* and Roy, Bull. Soc. I n d. Min. W10, 11, 397, 479 ; ./. Iron Steel In*., 1911, 
3 = Morley, Amer. J. SoL, 1887, 34* soo"*" ***** *** ^ ^ Vo1 ' IX " Part "'- 

incomplete. ' '' ' regarded Schone's evidence 



traces of these substances as occur in the air, although but little diffi- 
culty occurs when they are present in larger amounts. It is also now 
known that oxides of nitrogen would vitiate the earlier tests, and as 
traces of these gases are likewise frequently present in the atmosphere, 
no little uncertainty has arisen as to the correct interpretation to be 
placed upon the majority of the results obtained by early workers. 

This confusion is further enhanced by the fact, which has only 
recently been ascertained with certainty, that hydrogen peroxide 
sometimes decomposes, yielding ozone and water (vide infra). 

In the following table are given a few of the more important results 
of the so-called determinations of ozone in the atmosphere. The data 
prior to 1917 should be interpreted as representing the amounts of 
oxidising substances expressed as milligrams of ozone per cubic metre 
of air. 


Oxidising Material expressed as 

Milligrams of Oxono in one Cubic Metro 

of Air. 

About "2*8 milligrams 

10-100 milligrams 

At an altitude of 1050 metres, 
0-085 to 0-039 milligram, rising 
to 0-094 milligram at 3020 

0-OL 0-03 milligram , 

By one method 31-G to 158 milli- 
grams ; by a, second method, 
8-0 to 31' milligrams. 

4*5 milligrams in 100 kilograms of 
air (equivalent to 0-06 milli- 
gram in one cubic metre), the 
proportion being independent of 
of the altitude. 

Up to an altitude of 8000 feet, the 
oxonc was less than 0-003 milli- 
gram. Above this and up to 
10 miles the o/xme lay between 
0-1 and 0*4 milligram. 

2-5 volumes per million volumes 
of air over Britain. In the Alps 
a mean value of 2*5 volumes was 
found at an altitude of 2100 
metres and 4-7 at 3580 metres. 

No ozone found in 14 tests between 
July 1910 and January 1917. 


Iloir/eau (Ann. Chim. Phi/s., 
1872, (4), 27, 5 ; Compt. rend, 
1872, 74, 712). 

Sehdne (Brochure, Moscow, 1897) 
Thierry ( . rend., 1897, 
124*, 4(50). 

U. de Varigny (Smithsonian and 

MiwM. Coll., 39, 27). 
Hatcher and Amy (Amcr. J. 
n.., 1000, 72, 9). 

R. Lespicau (Bull. Soe. Chiin., 
190G, 1 3], 35, GIG). 

W. Ilayhurst and J. N. Pring 
(Trails. Chem. Soc. 9 1910, 97, 


Pring, Proc. Roy. Soc., 1914, A, 
90, 204. 

Usher and Rao (Trans. Chem. 
Soc., 1917, 111, 799). 

176 OXYGEN. 

Hayhtirst and Pring were careful to introduce a correction for oxides 
of nitrogen, but did not distinguish between ozone and hydrogen 
peroxide. Usher and Rao appear to have eliminated all oxidisers 
except ozone, and it is remarkable that they should have discovered 
no ozone whatever in their series of experiments. In the neighbour- 
hood of London, Reynolds 1 finds one volume of ozone in about 20 
million of air. This amount is greatly increased after a, thunderstorm. 
From a study of the absorption of ultra-violet light by ozone, combined 
with measurements of the amount of the sun's light transmitted by tin* 
atmosphere, the conclusion has been reached 2 that, if the ozone were 
equally distributed throughout the air, its amount would equal 0-0 c.c. 
per cubic metre, or 6 parts of ozone per 10 million of air. 

Hydrogen peroxide is produced in nature in a variety of ways. 
According to Dixon 3 it occurs as a product of evaporation of water, 
and it has recently been shown that moist oxygen, when exposed to 
ultra-violet light, yields distinct traces of hydrogen peroxide in the course 
of seven or eight days, according to the temperature. 4 

In 1909 Kernbaum 5 produced hydrogen peroxide by exposing water 
to the action of penetrating rays from radium salts, and two years later 
Kailan 6 confirmed this result. How much of the atmospheric peroxide 
is due to the above causes it is difficult to say. Undoubtedly most of 
the peroxide, and certainly the bulk of the organic peroxides of the air, 
originate from the direct action of air, moisture, and sunlight upon the 
essential oils and other organic emanations of plants. 7 

Ozone may be produced in nature in a variety of ways. When water 
evaporates into the air, particularly when thrown up in the form of 
spray, traces of ozone are produced, and this accounts for its presence 
m the fresh sea breeze and in the neighbourhood of waterfalls. 8 The 
refreshing odour after a shower of rain or the passing 6f a water-cart 
over the road is probably due to ozone. The gas is also produced 
by silent electric discharges from thunder-clouds and accompanies the 
flash discharge of lightning. In 1886 Wurster called attention to the 
lact that ozone may result from the action of sunlight upon the clouds, 
and since then the results of numerous researches have pointed to the 
fact that the bulk of the atmospheric ozone is yielded by the action of 

1 Reynolds, Nature, 1923, 112, 396 
* Bieber, Ann.Physilc, 1912, 39, 1313. 

19 9 > '<> iie - 2 ^. 


H. J. M. &eighto7(?r Nova S^ti n ?* \ ^ T^ " is **ttog to note that 
peroxide wa* LompledVralum r^Tr^ le'^l 8 ' ^- 34) f Und that WS 

f ^ " 
5th ei, 1907 (Baffliere & Co &ngzett, summarised in his work Nature's Hygiene, 

8 See Bellucci (Gazzetfa l7 /c oo\ i 

time ; also H. Duphil, Soc! sTstat llol l^l^TT* ^ ^ ^ M ^ to his 
1901, p. 51, on the sea air of Arcachon A acJlon Umv ' Bordeaux, Trav. Lab., 1900- 

9 Wurster, Ber., 1886, 19, 3208. * 


ultra-violet rays from the sun's light upon the oxygen in the upper reaches 
of the air. 1 This would aeeount for the observation of Thierry 2 and of 
W. Hayhiirst and Pring 3 that the amount of oxidising material increases 
with the altitude. In clear weather ozone is probably produced also by 
the direet action of the sun's rays upon the lower layers of the atmo- 
sphere. 4 These observations probably explain why R. Lespieau 5 
found that in his experiments the proportion of atmospheric ozone was 
independent of the altitude. 

Ozone has recently been shown to result from the action of rays 
from radio-active substances upon oxygen, but to what extent 
atmospheric ozone is attributable to this cause is uncertain. Probably 
a small quantity of ozone is produced by the slow oxidation of the 
essential oils and other organic exhalations of plants, 7 and Duphil 8 has 
recently observed an excess of ozone in the air of the maritime pine 
forests in the neighbourhood of Bordeaux. 

From the point of view of ventilation, ozone 1 and peroxides arc of 
interest inasmuch as they impart a crispncss or freshness to the air, 
and the fact that they arc 1 readily decomposed by heat is probably 
one of the causes of the " ilatness " of heated air. The well-known 
Sanitas preparations arc 1 essentially solutions of hydrogen peroxide 
and of different organic peroxides. There can be no doubt that in nature 
the presence of hydrogen peroxide 1 is an important factor in removing 
foetid and putrid matter from the atmosphere. Bosisto 9 has calculated 
that 9<>,877,44(),0()(> gallons of eucalyptus oil " are held continually 
at one and the same 1 moment in the leaves of trees massed together 
and occupying a belt of country over which the hot winds blow " in 
New South Wales and South Australia alone. Kingzett concludes 
that this amount of eucalyptus oil " can and must produce in the 
atmosphere* surrounding the forests no less than 92,785,023 tons of 
peroxide of hydrogen, and about 507,587,945 tons of the soluble 
camphor, not to mention the other products of oxidation." 

Detection of Atmospheric Ozone. Sehfmbciu's method hinges on. 
the fact that since ozone liberates iodine* from potassium iodide, starch- 
iodide papers 10 are readily turned blue in its presence. But inasmuch 

1 R Fischer and P. Braehmer, far., 1905, 38, 2033; V. RUHH, ZtitttcJt. ttlcktrochem., 
1906, 12, 409 ; Honriot and Bonynsy, Oompt. rend., 1808, 147, 977 ; F. Fischer, ibid., 1909, 
42, 2228 ; PhyMal. %citec.h., 1909/10, 453 ; K. van Aubol, Vomyt. rend., 1909, 149, 983 ; 
1909, 150, 90; M. U. Johnnon and 1). MTntoHh, J. Amtv. Cticm, floe., 1909, 31, 140; 
W. J. Humphrey?^ Afttrop/it/ft. /., 1910, 32, 97 ; W. <. Chlopin, ,/. RUM. Phi/ft. Chcm. jSor.., 
1911, 43, 554. It iB iuteroHt-ing to note that, the winio rays accelerate the decomposition 
of ozone when once it. han been formed. Eva von Bahr, AMI. P/n/tiik, 1910, [4], 33, 598. 

* Thierry, (lompt. rcmf., 1897, 124, 400. 

:t Hayhui'Ht and Pring, Truntt. (-hem. A'w., 1910, 97, 8(58. Sec alno HolrneH, A-tncr. 
f'/icm. ./., 1912, 47, 497. 

4 W. Henriet and BOIIVHHV, (lompl, rend., 1908, 146, 977 ; IT. N. IIoImoH, Atner. (-hem. 
,/., 1912, 47, 4-97. (.JnntraHt Bayt'iix, ('otnpt. rend., 1919, 169, 957. 

s Lospioau, Hull 8oc. O/ih>tl, li)00, [3|, 35, 010. 

Cluric (VoMpt. rend., 1899, 129, 823) confirmed by R. Niifiitii and M. 0. Ltsvi, Atti. R. 
Aecad. Lincei, 1908, ("5], 17, ii., 4(5, See al^o Ricluir/ and Suhonck, SUzungftber, K. Akad. 
Wiss. Berlin, 1903, 12, 1,102 ; 1904, 13, 490. 

7 Clocz (Compt. rend., 1850, 43, 38; 1801, 52, 527) found that starch iodide papers 
are coloured by the exhalations of certain trees indicating the presence of some oxicliser, 
though not necessarily of ozone. 

8 Duphil, loc. cit. 

9 Bomsto, quoted by King/ett, Natural* Hygiene. (Bailliere, 1907), p. 488. 
10 k Ung]azad (filter) paper soaked in a solution containing 8tarch and potassium iodide. 

VOL. VTI. : i. 12 

178 OXYGEN. 

as peroxides of hydrogen and nitrogen have a like effect the test is 
valueless unless the absence of these other substances can be proved. 
Houzeau 2 therefore recommended a litmus-iodide paper. 3 Nitrogen 
peroxide liberates iodine but, unlike ozone, will not simultaneously 
liberate free alkali, so that the litmus either remains unchanged or is 
slightly reddened. Ozone, on the other hand, not only liberates iodine 
but alkali which turns the litmus blue. The main disadvantage oi tins 
method lies in the tendency of the iodine to mask the colour of the 
litmus, and thus render any change in the latter difficult to detect. 
It is true that hydrogen peroxide likewise liberates iodine, but by first 
passing the air over chromic acid, 4 hydrogen peroxide may be effectively 
removed 5 whilst the ozone is not affected. 6 Filter paper soaked in an 
alcoholic solution of tetramethyl base 7 has been recommended, since 
the paper becomes violet with ozone, yellow with nitrous fumes, but 
remains unaltered in contact with hydrogen peroxide. The reaction, 
however, does not appear to be sufficiently sensitive 8 for the tc k sts 
under discussion. 

Estimation of Atmospheric Ozone. The majority of investigators 
in the past have relied upon the liberation of iodine from potassium 
iodide solution as a convenient method of estimating ozone. Thus 
Hatcher and Arny 9 aspirated air through potassium iodide solution, 
whereby first iodine and subsequently potassium iodate are formed, as 
indicated in the following equations : 

2KI+H a O+0 8 =2KOH+0 2 +I 2 

2KOH+I 2 =KI 


On acidifying, free iodine is again liberated according to the equation 

KIO 3 +5KI+3H 2 SO 4 =3K 2 SO 4 H-3I 2 +3H 2 O, 

and is estimated by titration with thiosulphate. This method does 
not distinguish between ozone and hydrogen peroxide, neither does it 
guard against the disturbing influence of nitrogen peroxide. This 
difficulty was surmounted by Hayhurst and Pring, 10 who estimated the 
free alkali in addition to the iodine and were thus able to introduce a 
correction for the peroxide of nitrogen, although they were unable to 
distinguish between hydrogen peroxide and ozone. 

If, however, the air is first freed from peroxides of nitrogen and 
hydrogen, the liberated iodine owes its presence entirely to ozone. 
Keiser and M'Master, 11 therefore, recommend the passage of air through 
a solution of potassium permanganate prior to testing for ozone, as this 
gas is not affected by the permanganate whereas the two peroxides are 

Moifatt ' s results ( Brit ' Assoc > Shorts, 1870, p. 61) are in- 
27 > 5 ; Com ^' rend - 1872 > 74> 712. 

Hn x " ' > ; om ^' ren - 18 

Unglazed filter) paper containing litmus and potassium iodide 

4 Or over solid chromic anhydride crystals. 

5 Engler and Wild, B&r., 1896, 29, 1940. 

6 Usher and Rao, Trans. Chem. Soc., 1917 in 799 

7 Wurster Ber 1888, 21, 921 ; Arnold and Mentzel", Ber., 1902 
10U *otT ^ Pring ' TmnS ' 0h t m v S ^> 191 > 97, 868 ; also 

HayhuL and Pring, foe. cit. **** ^ Amy ' ^ J ' Pha 190 <>, ** * 

11 Keiser and M'Master, Amer. Chem. J., 1908, 39, 98. 


Potassium nrsenite is oxidised by ozone to arscnatc, and may be 
substituted For potassium iodide in the previous method [ ; although 
here a^ain it is necessary to first remove the peroxides of hydrogen and 
nitrogen from the air prior to testing. 

A method that appears capable of greater accuracy and less open to 
criticism than any of the foregoing is that, devised by Usher and Hao. 2 
It hinges on the fact that oy,one oxidises aqueous solutions of alkali 
nitrites to nitrates, the reaction proceeding quantitatively according to 
the equation 

XaN<Vl ().,- ' 

Two samples of air are taken and collected in large stoppered bottles 
of some 7-litres capacity. One sample, is admitted through two tubes 
containing respectively chromic anhydride and powdered manganese 
dioxide, the second sample through a tube containing chromic anhydride* 
only. They are then shaken with a dilute standard solution of sodium 
nitrite rendered slightly alkaline, and the nitrite content subsequently 
determined colorimetrteallvv 1 

The first sample of air contains only nitrogen peroxide, the hydrogen 
peroxide and oxonc having been destroyed by the chromic acid and 
manganese dioxide respectively. The increase in the amount of nitrite 
in the bottle thus gives the measure of the nitrogen peroxide absorbed. 

The second sample contains o/xmc and nitrogen peroxide and the 
difference between the nitrite contents of the two bottles is equivalent 
to the o'/one present. The presence in (he air of ammonia, sulphur 
dioxide, and hydrogen sulphide does not interfere with the estimation 
of o/xmc and nitrogen peroxide by this method as all three gases are 
completely absorbed during passage through the chromic anhydride tube. 

Nitrogen and the Inert Gases function mainly as diluents in the 
atmosphere, exerting a restraining influence upon the chemical activity 
of the oxygen. They exist in approximately the following proportions 
by volume : 

Nitrogen 4 78-00 per cent. 

Argon r ... 0'9-H 

Helium r . . . 1 part in 185,000 

Neon r> . . . 1 55,000 

Krypton r > . 1 20,000,000 

Xenon f> 1 170,000,000 

The nitrogen is not entirely inert, however. During thunderstorms 
it; can unite with the oxygen yielding, in the presence of the moisture, 
both nitrous and nitric* acids. Again, certain plants, such as the 
leguMinoMr, owing to the presence of bacteria in their root-tubereles, 
are liable to assimilate nitrogen direct from the atmosphere, and certain 
bacteria in the soil act similarly. These reactions, however, an* 
relatively of minor importance*. The inert gases, on the other hand, 

1 Hatcher and Arny, he. ciL 

2 UahcT and Rao, twin*, ('hem. >SV>&, 1917, in, 700. 

:| Tim CiricHH-IloHvay method in recommended. Hoe Sutton, Volumetric 
9th wl., p. 440. 

4 Lodw, CowpL rend., 189(1, 123, 805, 

f ' See also this widen, Vol. I., Part 11. This Vol., p. 158. 

w Sec pp. 62 and 217. 

180 OXYGEN. 

appear to be absolutely inert and to enter into no atniosphenV chcnm-ut 
reactions whatever. , 

To the presence of krypton in the ntniosphnv is due the phriminrnoit 
known as the /mmrr/ borealw or northern lights. The inrrt #IM-S linl 
their way into the atmosphere through escape from mineral spnit^ 
and, in the ease of helium, through the disintegration of radium, 

Hydrogen. The proportion of hydrogen in the nir varies con- 
siderably, although it is always minute. 1 The hydrogen rontmt, 
however, is believed 2 to increase with the altitude. In flu 4 spectrum 
of the aurora the intensity of the nitrogen lines diminishes ant! that of 
the hydrogen lines increases with increasing height. The hydrogen 
originates from volcanic emanations as well as from hue! erial aef ivif y, 

Carbon Monoxide is scarcely a normal constituent of fresh air, 
although it occurs in the minutest truce's in the air of towns and of 
volcanic districts. It also occurs in railway tunnels 3 and even in \vt-U- 
ventilated coal mines to the extent of (H)()2 to O-OOI- per cent, 4 It in a 
most dangerous gas, 0-43 per eent. being fatal to man r * in a short time. 
Even 0-2 per cent, may prove fatal if breathed for a long Him*. Head- 
aches and other unpleasant symptoms are produced by concentrations 
ranging from 0-03 upwards. 

Carbon monoxide is produced by the incomplete combust ion of fuel, 
and since it readily diffuses through heated iron, it: frequently happens 
that iron stoves, used for heating purposes in large buildings, constitute 
a source of this gas in the air, the carbon monoxide diffusing into the 
building, instead of being carried up the chimney or burned, 

Ordinary coal-gas may contain anything tip to 20 per cent, of carbon 
monoxide, and an escape of coal-gas into the air produces a proportionate 
vitiation of the same. 

Miscellaneous Substances in the Air. That oxidisablr organic 
compounds are present in the air has been known for many years, the 
Swedish chemist Berzelius 6 being one of the first to refer 'to the fat-l. 
This explains the observation of Levy and Heuriet 7 that air freed from 
carbon dioxide by treatment with caustic potash generates it again on 
standing, owing to the oxidation of the organic matter. The exact nutun- 
ol the organic compounds present in the air is uncertain. <Jantier* 
tods 1-21 parts of marsh gas or methane in 10,000 of Parisian air, and 
0-17 of benzene and its analogues. Formaldehyde and other organic 
derivatives have been detected in minute quantities.' The unhrallhv 

nr^LTE ,i! S T^ attributed to * volatile organic substances 
produced by the decomposition of the vegetation. Analyses of tin* 
gases evolved from marsh land show that methane cotistituto, in gen i ml 

to ^ftW^?; faf /U 35 ' S&TiiW ? T rt by voltt ""'- 

llTm "' ^ em " 1912 ' 75 ' 107 ; 

Mahler and Denet, Compt. rend., 1910, 151, 645 
Mosso, J. GasKgMng, 1902, 80, 1334. 
Berzelius, Jahrbuch, 1835, 22, 47 
^y and -Henriet, Compt. rend., 1889, 126, 1651 - 
Gautier Gomt ' 

' 107 ; P ' 101 i, ^ 170. w. 

-, . ren., , 

* Gautier, Gompt. rend., 1900, 131 535 

Soc. S^S^K HI' 2 3j "^ J ' 19% ^ 67 ^ "0* *3*> 1465. Fnilat, 


more than half the total volume of gases, 1 the remainder consisting of 
carbon dioxide, nitrogen, and in some cases of oxygen and hydrogen. 

Oxides of nitrogen and free nitric, acid occur in traces in the air, the 
former owing their existence 2 to the combination of oxygen and nitrogen 
under the influence of lightning flashes, and possibly also to a much 
smaller degree to the oxidation of ammonia. These oxides unite with 
water, yielding nitric acid. 

During thundery weather accompanied by very little rain 1 part of 
oxides of nitrogen, in 4 or 5 million of air has been found. 3 

Ammonia, mainly as carbonate but also as nitrate, is present in the 
air, and originates in the decomposition of organic nitrogenous sub- 
stances. II. T. Brown 4 found the air at Burton-oivTreut, during the 
years 1869 to 1870, to contain from 0-04 to 0-09 parts of ammonium 
carbonate in 10,000 of air. The analysis of rain-water 5 shows the 
presence of ammonium nitrate in appreciable quantities. 

Sulphur compounds arc detectable in the neighbourhood of active 
volcanoes and in towns and cities where much coal is binned. Thus at 
Lille, Latlureau found 1-8 c.e. of sulphur dioxide in 1 cubic metre of 
air, which corresponds to 0-018 parts per 10,000 of air. Sulphuretted 
hydrogen is present iu traces in coal-gas, and in the neighbourhood of 
decaying organic matter containing sulphur. It would appear that us 
much as 2-0 parts of this gas per 10,000 of air have no deleterious action 
upon the system, even if breathed for protracted periods. 7 All of these 
sulphur compounds are rapidly oxidised to sulphuric acid, which may 
or may not be neutralised by the ammonia of the air yielding ammonium 
sulphate. Warington 8 found the equivalent of 17-20 Ib. of sulphur 
trioxide fell annually on eae.h acre of land at Rotharnstecl, and this may 
be taken as a fair average, for Miller gives 20-89 Ib. for Sicily, and 
Gray 10 15-2 Ib. as the mean for four and a half years of observation in 
New Zealand. 

Soil Atmosphere. 11 By soil atmosphere is understood the air 
lilling the pores between the particles of the soil mass. Although part 
of the ordinary atmosphere, its composition is influenced by two opposing 
forces. On the one hand the various organisms of the soil abstract the 
oxygen and evolve carbon dioxide ; on the other hand gaseous inter- 
change with the outside air, brought about* by diffusion and other 
processes, tends to restore the normal oxygen content of the atmosphere. 
The net result, therefore, is determined by the difference in velocity 
between these two processes. 12 

1 Hoppe-Seyler, Zeitsch. physiol Chem., 1880, 10, 201. 

2 Hayhurst and Pring, Trans. Chem. 8oc. t 1910, 97, 1)68. 

3 Usher and Rao, Trans. Chem. Soc., 1917, in, 799. 

4 H. T. Brown, Proc. Roy. Soc., 1870, 18, 286. 

fi Warington, Trans. Chem. Soc.,, 1889, 55, 537. Hoc also p. 21.7. 
Laduroau, Ann. Chiw. Phys. 9 5 aeries, 1883, 29, 427. 800 also Witx, CompL rend., 
1885, 100, 1358. 

7 J. Habormaim, W. Kulka, and 13. Horn ma, Zcit. Anal. Chem., 1911, 50, 1. 

8 11. Warington, Trans. Chem.. tioc., 1887, 51, 500. ISeo also data given by Kidoal, 
Proc. Paint and Va-mishSoc., 1914, No. 3. N. H. J. Miller, ,/. Ayric. tici., 1905, i, 292. 

10 (}. Gray, Rept. Australasian Assoc. Adv. Science, 1881, i, 138. 

11 For early researchon on this Hiibjoct, Bee BoiiHsingault and Lewy, A tin. Chlni. Phyx., 
1853, [3J, 37, 1 ; Bchloesing, rend., 1889, 109, 618, (520, 673; Kisaling and FldHclW, 
Landw. Jahrbucfier, 1891, 20, 876. 

12 The subject has been studied by a considerable number of investigators since the 
middle of last century. A useful summary is given by KusseJl and Appleyard, J- Agric. 
Sci.y 1915, 7, part i., p. 1. 

182 OXYttRX, 

Analyses of the soil atmosphere show that it .suffers greater fltiHua- 
tions in composition than ordinary air. As a rulr it contains Irss oxygen, 
hut nearly ton times us much earhon dioxide UN the air* as sho\\n hy the 
following chit a : l 

SMI! ttr<im.iry 

i$>^|tttriv, ;ur. 

Carhon dioxide , . . <>'-* o-o;i hy \ohnne 


Oxygen ... 'JNMIU UHKI 

Usually tlu* stun of litest* two gases in the .soil atmosphere is only 
slightly less than that in the air although at periods \\ht-n nitrates 
rapidly increase, and in water-logged soils, there is a percept ihle reduction 
in oxygen. 

In addition to this free atmosphere titrre is a srfoiul soil atntosphrrf, 
consisting mainly of eurhon dioxtdr and ntnnt'n \vj!h praetieally iu 
oxy^i*n, whieh is dissolved in I lit- water ami eolhils til' Ilir sod. The 
existence of this second atmosphere is itttportant. m that it renders 
possible the existence of anierohjr organisms in th- soth* 

Mine Air. The nit* in mines has hern made the suhjrrt ot ecn 
siderahle investigation. Freshly hewn coal r\it|vrs methane and other 
gases, uiul ahsorhs or oc*ehtdrs j^ases frotu the 1111% ti\\ jeti ln-iiiii taken up 
rather more* rapidly than nitrogen, This is well evniiphlieii hy the 
following tahh* wliich ^jives the relati\e proportions of i\yj*en, nitrogen, 


Oxygen . } K-M t*a-,s 

Nitrogen . . . * H"7 7 1- 1 

Carhon dioxide . . ; I'll t IH 

Methane , . . ; 41*11 M-a 

(iirhon dioxide, and methane contained m snm|fies ol' ireshiy hewn 

coal, and in other samples of the smite coal aftt*r |in4n!i||rd expoMtrc 
to air. 3 

It is not surprising, therefore, that the air of mines should cxhthit 
a deficiency in oxygen and an incivasc in thr percent gc tf* eurhon 
compounds. Analyst's of air 4 taken at dtffeivtit; levels in a Scottish 
mine, are given hy Whulley us follows : 

l and AppUtyurft, /<% cit. S**< tiUo VVnllfiy, Pur*rhHn/rn mi/ tltm 6VI*$Vir rlrr 
iymic, 1880 3, 1; IHHI, 4, I ; IHHtt, 9, Ifl/i ; |HH!I, u, Illlfl ; IMfii, 13, i:H. 

Klwnnaycr, itw!., 1878, i t 1">H; IWMl, 13, hi. HIIIIIM*!!. /n*/,, lw*^, j Milrr, i^i>/.. 

1879,2,329, ' * 

a Thu ratiio-aotivity tf Hulwoii air i dimnmnml hy <'HHtp|ln fiipl Fpfwiinlr/^ 4l. Fi** 

Quitn., Will, XI, 107, 21H; Sattorly, /Vwr. Cttmh.'WtiL AV, HMl. 1 6, H'W ; .l*ly wwtl 

Smyth, *S'c'. /Voc. /%/. Dublin NM., i!>Il 13, 14K; 8ntii!0rmn. Jmt-r. ,/. SVi,, lifl'l. 32, 

69 ; Oookcl, PhynikaL ZeibiGh., IIM)8 9, 3114. 

>A BotUon, Tratui. /mL ItutL Jftw, Mn^ Aug. iiWl 

4 See ako Moureu and JLopapo, Vompt. mmL, 1HII P 153, H4tt, Ill-Ill 


Near I hr tloor 
Near th* roof 
Near t he eiwl faee 




Carbon Dioxide. 

Tuniu*! Air. The air in tunnels* through which coal -fired loeo- 
motix es pass, contains many impurities in except ional quantities, 
chief amongst winch are sulphur dioxide, carbon monoxide and dioxide. 1 

Itt flit' following tiibti' are given the average niuoiuiis of sulphur 
dioxidf uul c'arltou tuniu\uii* in 10,000 parts of air as found in tunnels 
in Biiltiwoiv, I'.S.A.. fhrtnigh whirh stt*ain and fleet rie locomotives, 





. Aiitithrr itnportaiit ronstituent is llu* so-called dust, the 
!' \vhtrh futist hint' brt-a uoti<H*d for ages. It is u highly 
iui\tttrr tit' itior^atur, lifVlfss organic, and living orgunie. 
nuitti-r, Th- first itniut'd cH'ijjtinatrs partly from natural causes, such 
as wind and volcanic acti\ity. Tims the writers have in their possession. 
sand found at Las t*ulmi!s,'\vhit*h had hccn hlown over 100 miles of sea 
from tht* (Jrcat Sahara Desert. During the great eruption of Krukutoa 
in IHHII vast (|uanttttfs of dust were hurled into the* air, and for several 
years nftcnvartls the sunsets wen* remarkable for their glow, indicating 
that the part teles of h*st continued to flout in the atmosphere* for a pro- 
portionately long time. In a speet roseopie, analysis of dust Hartley a 
has found a large ntunhcr of inorganic substances that must have 
tniNelletl from utility purls of the earth very wide distances apart. 
Among the moruaniV particles arc minute crystals, for example*, of 
.sodium chloride 4 which owe their origin to sea .spray, and may be 
carried inland for hundreds of miles ; sodium sulphate particles, pro- 
bably formed by the interwtion of the sodium chloride with sulphurous 
acid Vapour anil subsequent oxidation, are also present, and cause the 
rcitdy rrystitltiHultou of Huprrsitt united solutions of sodium sulphate 
when exposed to flit* nir, A good cletd of atmospheric dust is of artiiicial 
production, dm* to the combustion of coal, to factories, etc., thus a 

1 Hi*^ itfuUvnrft by I.^nigiitwtr* */. /r SV*'<f/ /*/., HH I, L, 147. 

* Ktiiit4I ii'ttil Mi^tvtn f.- f .A', /*ii//iV flmltk .SVr^iVr, tlygiruit Lab. ////., No, 92, 11)14, 
jl. 1 4?, 

;| Kiiig?4*lt II/IIM fit. t |1 4!M ; W. N. Httrtlt\y <! Kttiaj<, /V<wi. Roy. Moc. 9 iCK)l F 68, 

!7 j W, N, llnrfit^v, IVwc. /%, Ihtlh .V*M*. IH0$)-HK^, 9, 457 ; /Voc. Roy. *SV>c. 1011, [A], 

* (*nutit*r. ri|ii, rrW,, iHlfrli, 138, 

y. Nc., 1911, | 


massive bank of smoke in London has bei n seen to HM- to ;t height of 
several thousand feet and be earned ;ma\ m a sunhght -obscuring trail 
fifty miles in length.* Kneeht has ex*mun< d Man-h-shT soot and finds 
in it some 50 per cent, of substances that art not earhun, \uch as salts of 
ammonium, calcium sulphate* and th Isk* , K%en the purest atiuo- 
sphcrcs contain particles of tlust, and Aitkin d*ubts i! a ptrhcth dust - 
free atmosphere can exist. It is ran to fmd air with t w r loo 
particles of <lust per e.e. In London tt nuv us* to or even 
150,000 particles per e.c. Fndtatt-drr ' found ^tttii p.trtH'Us p* r e.c, of 
air on crossing the Atlantic Ocean, u th M dit riMti' m s t s75 the 
lowest results being obtained on I hf Pantit* and Iud,m i>ev;ins, the 
particles numbering 2-k"i and **HI respect t\ el\ . Nuinl-rrl) , M!.mder a 
lias studtcil the <lust of Swiss air, but tit 1 1 r lound b i th.ut lfli 
particles per e.c. 

In the* following table are given some ul the data tii,tn l b\ O\\i us * 
on the N f crfolk Coast in a series of tests during Aii'-ji^f I^'JI ; 


Awgtwt- I 1 

i a 


of Ail". 

I Mt*rti?i, 

i f*r> 




l s 't!lr d-iik eitloUied dust . : 

No t*r\ si als, 

\ 'r|*N ItliitHiiil ill sl/t*. i 


Nittlit- rr\ J.iU. ! 

All t*ittntf if, 

pi r 


It is interesting in this conmrtion to rrritll the r\|)ennu'itt.s tt' 
Lehniuun and his colleagues a \vhtMlcutunstraieti <jtat*- ret'eutly tlmf when 
a dust-luden air is breathed through the nose, approximately "itl jer rent. 
of the clust remains in the system, either in thr Iiiiig% or'stoiimi'h, tip- 
remaining 00 per cent, being either respired or rrfitiftrd by the nose mid 
mouth. If, however, the subject breathe* through thr mouth MHW 
80 per cent, i.s retained by the body* This tlhist rates thr iiiipurlitiirr 
of breathing through tht* nose, but* it idso illustrates !hr wrcHsity of 
reducing the dust in the at!iu>spiurcs of public room* niiii i\vfllitigK iu 
the smallest possible amount, us no mutter how careful ttir Mihjt*et is, 
some of the dust finds its way into the* system. 



* Sw Coltai Kiin:h, !f'frr (Alitttm Ki 
I'rtrnifih Xw.%, 11114, N. 3 ; UtiMtun, ./. ., 

a K. U. Fririianclor, Quart. J. /%. ,1/rl. Vw\, .luly. IHlMi, 

;J CJ. Mdauiit^r, L ( 'tm<i? twatitm ttr. In Vttprur fiKttit ttttn* 
1897). Hiic* alm> OWOIIH, /. tftw. (Jhrm. 7m/., i!*J2 41, 41IH II, 

4 OwaiiH, /Vent. Roy. *S'w. t Hjii> t [A|, xox, 18. 
IHiri, 3, 1 1. Bill J. IwL Hygietw, il, i, 7. 

' K. B. Lthnuum, V, Sttiti, uuti W. (ifruirr 

'.% 13, 


wn: ,/, l*liliV Ifttifflt, 
l'J, 75, 1W -IM^. 


Bacteriology of Air. -Fresh air contains a number of micro- 
organisms, I'ffelmauu l finding some 250 per cubic metre of air in the 
open fields near Rostock, and 4-50 in the University yard. Most of 
these, however, art 1 probably spores of moulds and yeasts, and of the 
bacteria proper in the air the majority are saprophytic and not 
disease producing.- Kijanit/,nan a found that by supplying sterilised 
air to rabbits the metabolic functions we're reduced and the. animals 
wasted away. It, seems reasonable to conclude, therefore, that the 
atmospheric micro-organisms play a useful part in metabolism. Possibly 
their .special function is to provide the blood with ferments for oxidation 
purposes, since in their absence the oxidation changes in the organism 
appear to be diminished, and an accumulation of waste products or 
leueomaines occurs. Sterilisation of perfectly fresh air supplied to 
buildings is not, therefore to be recommended, and herein no doubt lies 
a potent cause of the depressing effect produced by air that has been 
art iiieially heated t he consequent sterilisation, coupled with the 
dest met ion of o/ouc and peroxides, producing a lack of crispness. Whilst 
the spores of moulds are light and can remain floating in the air, the 
bacteria are heavy and are usually found adhering to particles of dust. 
Consequently the air over the sea and high mountains is poorer in 
bacteria than that in towns, 

Tlic dust of public buildings contains vast numbers of micro- 
organisms, and many of these are not merely detrimental but positively 
dangerous. Thus Cornet 4 found the tubercle bacillus in the dust of 
dwellings, and showed that this may easily prove a source of infection. 
Chour r * examined dust from infected barracks and found no fewer than 
I ! million typhoid bacilli per gram of dust. Clearly, therefore, either 
all dust should be removed, or else all operations tending to raise the 
dust should be avoided during occupancy of inhabited buildings. 

Buehan mentions that' 1 "in an experiment in the High School at 
Dundee with one of the classes in a room, under ordinary conditions 
the organisms amounted to 11 per litre. Upon the boys being told to 
stamp with their feet upon the iloor, a cloud of dust was raised, when 
upon being tested the atmosphere of the room showed 100 organisms 
per litre." 

Respired Air. It has long been known that respired air is un- 
suitable to support human or animal life, and the question is why V 

Assuming respired air to have the composition 

Carbon dioxide , . .4. 5 per cent. 

Oxygen. , . . .15 ,, 

Nitrogen . . . .70 ,, 

Water-vapour ... 5 ,, 

it is not at iirst sight easy to understand why it, should be unwholesome. 
The oxygen content is suHieiently high, for we have already seen that 
e\en li per cent, of this gas is ample for normal respirative purposes. 7 
\Ve cannot therefore complain of oxygen shortage. Neither can we 

1 Ufli'lmium, Arc/tin. llygivnv, IH8H, 8, ^U2. 

2 AwlruwH, Tram. 1'alh, #oc., 1902, 54, 43, 

1 J, il. Kijanitsinan, Virchow j n Arc/iiv., 1900, 162, 515. 

I t'ormit, %rit#c./t. Hygiene., 1889, 5, 1*8. 

quoted by Buohuiu Ventilation (CroHby, Loukwuod & Sou, l 

II Buehan, opus cit,, p. 119. 7 &eo p. 1(50. 


argue that Hit* carbon dioxide is excessive, fur H to 10 per cent, of the 
may be breathed lor protracted periods without any injurx. 1 

Brown-Sequard and d'Arsonva! * in IH-H! concluded, from a series of 
experiments* that- respired air contains small quantities tit* a powerful 
organic poison, HIM! that the unsuitableness of it tor further respiration 
lies, not so much in its carbon dioxide content, n\ in the presence* of this 
organic toxin. This view was supported b> Merkel ;| m lst'J, hut since 
then a large number of physiologists * have brutish! forward a formidable 
array of arguments, indicating that the unwholesome properties of 
respired air may be wore readily explained in otlur ways. Let us 
briefly consider these. 

Then* are at least, three important factors to consider. 

1. The Injlucnee uf Mnitttuw nu Krsjtirtttinn. lite presence of 
moisture in air has a two-fold action upon respiration. 

First. tluTe is the very obvious fact that if warm air saturated wtth 
moisture enters the lungs, the latter will have great dtfltculty iti disrharg- 
ing their superfluous moisture, and a sense of oppression must result. 
This explains the heavy feeling produced upon entering hot -houses, in 
which the air, apart from its moisture content, is perfectly gothl, and \ cry 
free from carbon dioxide. Cold air, even if saturated with moisture* will 
not. have anything like the same effect, for upon entering the lungs the 
temperature rises proportionately higher, iintl the air is thus able to take 
up much more moisture* before becoming saturated, I hereby allowing 
the lungs full opportunity to relieve themselves. Secondly air con--- 
taming moisture* cannot take up carbon dioxide from the blond as easily 
as dry air/'* consequently tin* ventilation of the lungs is retarded by 
inhaling moist air. 

These two factors working together are sufficient to show that 
respired air, being saturated with moisture at a warm temperature, 
cannot be wholesome, and L. K, Hill lf and his eu- workers regard the 
moisture content as the main cause uf thr discomfort of ill* ventilated 

2. The Injluenee nj" Cnrbnn /WwiVr MI Itmirintliun, Mfuttoit has 
been made 1 of the fact that relatively dry air containing H to 10 per cent, 
of pun: carbon dioxide can be breathed for a long time with impunity. 
For the reason given in the preceding paragraph* however, it follows that 
breathing warm air both saturated with moisture and containing some 
carbon dioxide must be attended by a greater difficulty in \nttilating 
the lungs, and that a proportionately smaller quantity of carbon dioxide 
will be capable of being breathed with impunity* * Since respired air 
may contain anything from \ to fr I per cent, of* this gas, it is easy to 
understand how this may be the potent cause of the 

1 Nw p. J7i>. 

a lirown-Httqiwrtl* /Vi/w/jf, n-utl. t iKKU, 108, 'Ml, Tin* .*iii|i|.finl ff*,%n t t ..i twiuni 
i' loxin/ 
cl, Awhit\ //^f/iVnr, 18U2, 15. 

t md Nowiwli, /VTii^rM Arrhii:. thill, M.%. ; Hi-ntmii'*. ,-ln-Air, ll^imr, 
1883,1. ; I)aj4tn nntt 1xy<% *S'm\ llir%i n tHHH v m ifi.fmniiii WHNiiti.f, '>.' A7n. 
l\t*lu>n*rhrift, iHHH; .?. ( Vy, r t Jnhrrdvr. Thirrrhnn., WHII, %,%, ; UhmAliit ititti .!*w*!t, 
Anhn\ t U\igu'n?, I HIM), .x. ; ttini t /. ////i/iVr htjrktiwlcmnlihni* , imia, \iv. ; llanrr, 
/. Hygirnr, \m\, xv. ; LubixTt mill IVti*tH. /%ini, ttu f M*tit t ! HIM ; ili!Iiiin, *7m/,, 
1897; lia^if'km IttMjtrtirt/c&tkr akwkwir. I*M, IHWI; Fi*ritilik ,|iT/nr, llw/irwr, MM. 
38, 1 ; Hnldano, >te. 

s 8ee refunttuv p. 17J. JU K. Hill, t., /'me. I'lij^wl. fc Vwr. t llflfi, iii. tu \iii. 


headache, resulting from inhabiting ill-ventilated rooms, Ilaldane and 
Smith l an* evidently of this opinion. 

:j. The Influence nj' Organic Material an /{expiration. -Then* ca.n be 
no reasonable doubt (hat expired air contains, in addition to moisture 
and carbon dioxide, some organic bodies of more complex composition. 
Thus \Yeiehardt * finds that by breathing into distilled water, or better 
still, into glycerine, 11 a ponderable residue is obtained upon evaporation, 
which contains organic products of high molecular weight ; and numerous 
other investigators have found evidence of organic matter in respired 
air. It is no doubt this, together with exhalations from the mouth 
(consequent upon bad teeth), and secretions from the skin, such as 
perspiration, etc., which give an unpleasant odour to the air of ill- 
ventilated rooms, tending to produce sickness and faint ness. 

The above three factors are quite suflieient in account for the un- 
wholesometiess of respired air without assuming the presence of any 
particularly toxic organic* poisons ; and when it is remembered that, in 
addition to these, micro-organisms of a harmful nature are hurled into 
the air by people snee'/ing, coughing, spitting, and even talking, the 
need for very thorough and systematic ventilation becomes evident. 

How much Fresh Air must each Individual have? -In very 
warm weather the windows may be thrown wide open and the air of 
rooms made almost as pun* as that- outside. But on cooler days when 
artificial heating is essential and draughts must, he avoided, a certain 
amount of vitiation of the air is unavoidable. The question which now 
arises is To what extent may that vitiation IK* permitted without 
harmful effects ? It is reasonable to assume that ii* the* air of a room is 
so pure as not to affect the* sense of smell, when a person enters it direct 
from breathtug the fresh air outside, then' cannot be much wrong with 
it -provided, of course, the only impurity likely to be present is respired 
air, and not inodorous gases such as pure carbon dioxide obtained from 
chemical sources, or carbon monoxide from heated stoves, etc., which 
gases have nu action upon the olfactory nerve. l)e Chaumont. investi- 
gated this limit very carefully in 1875, and concluded that, on the 
average, air containing <H)!2 per cent, or more of respired carbon dioxide 
possesses a detectable odour. This, of course, depends upon a variety 
of factors, such as I lie humidity, temperature, sensitiveness of the nasal 
organ, and last, but by no menus least, the personal cleanliness of the 
persons who have been breathing the air. This must, be evident, when 
we remember that it is not the pure* carbon dioxide* that we smell, but 
the organic* impurities respired with it, Let. us, however, fake* 0*02 per 
cent, of carbon dioxide us the maximum amount of respired carbon 
dioxide that ought to be* permitted in the atmosphere of inhabited 

In order to determine the amount of fresh air to be supplied to each 
individual on this basis we require to know the amount of carbon 
dioxide exhaled per hour. Thin may In* stated roughly as in table 
on }K 188. 

As an average for u mixed community we may take ()() cubic feet. 
If now we divide this by the permissible respired impurity, namely, 

1 UitMiinii uiul Smith, ./, /ViM,, /tort., lK:J f I, l8. 
3 Wtitchimlt, Arehiv. Hygkn** 1U, 74. l& 
51 NVetaimrdt uml flutter, ibid., Ittli!, 75, 5*05. 

188 OXYGEN. 

0-02 per cent., we have the amount of air required per hour per person, 


=3000 cubic feet per hour ; 

and this is the standard generally adopted. 

For general purposes the equation may be expressed as 

C ., 

it ' 

where C= Amount of carbon dioxide exhaled by each person per 

hour ; 

R= Respired impurity that may be allowed ; 
F= Amount of fresh air required, in cubic led per hour. 

For children we have 


=2000 cubic feel JHT hour. 


The U.S. Book on School Architecture allows only hall' tins amount, 
namely, 1000 cubic feet per hour for children. 


Adult males in heavy work 
Adult males in light work . 
Adult males at rest . 
Adult females at rest 
Children ." 

('ulm- I'Vrt i if < '.i rl 
Diu.vhlc '\halril JU 


1 -H I- 

The Influence of Artificial Light. The chemical changes induced 
by the combustion of coal-^as, as a source of artificial illumination, 
may be enumerated as follows : 

1. Oxygen is consumed, each cubic loot of eoal-^us usiu# up almost 
exactly its own volume of oxygen during combustion. 1 

2. Carbon dioxide is produced, I cubic. Foot of coal-gas yielding <)! 
to 0-5 cubic feet. 1 

3. Water-vapour is evolved, 1 cubic foot of gas yielding at normal 
pressure and room temperature approximately *2(> grams of water. 1 

4. Small quantities of sulphur dioxide result by the oxidation of 
traces of sulphuretted hydrogen, etc., normally present in coal-gas. 

5. Organic impurities are incinerated by the llame. 

From (4) and (5) above, we gather that if suilicient air is foHlu'um- 
ing to supply the necessary oxygen and to dilute down the carbon 
dioxide, a coal-gas llame should* be more healthy than electric inetm- 

1 The mean of many experiments carried out by tho writw on WonwhT (lily coal -m >. 
Rideal (next reference) gives 0-0 c. ft. carbon dioxide and 21)5 grain*, i.r, UH gram*, .f 
water fur London coal-gas. 


descent lamps. This has, in practice, proved to he the case. The 
sulphur dioxide is present in too minute a quantity to injure human 
heim,rx Imt, according to Uidcal, 1 ii can and does "tend to purity the 
air, and in conjunction with the incinerating action of the llame. it 
miners vrry sensibly the micro-organism content. SSaldane tj draws 
attention to the small vitiation of air produced when incandescent gas 
man! Irs aiv compared with any other form of gas burner. 'Hiis 
is^atfribnted to the very complete eomhnstion of the gas on the surface 
of the mantle and Jo 1 he incinerating activity. 

In addition Jo these chemical effects, we have two important physical 
factors to consider, namely 

(I ) The rise in temperature of the air ; and 

(2) The consequently increased rapidity in the circulation of the air. 

By having artificial gas lights above the heads of the inhabitants of 
a room the warm air is impelled upwards, and if suitable ceiling 
ventilation is provided there is considerably less danger of the bad 
air cooling and sinking, and thus vitiating the purer air below. In the 
absence of good ceiling ventilation, the air cools near the walls and slowly 
creeps down I hem, 

It is customary to regard, from the ventilation point of view, the 
presence of a gas Jlame as equivalent to that, of a, definite number of 
persons. As- we have already learned, however, it is the organic im- 
purities as w'Il as the moisture and carbon dioxide content which 
renders respired air injurious. Consequently we ought not tilrictly 
tijwttking to express gas (lames in terms of people. For the sake of 
convenience, however, and for want of a better method, we must 
continue to do so, ft is usually agreed that (H. per cent, of carbon 
dioxide produced by combustion of coal-gas, and hence accompanied by 
\vatcr-vapour, is as much as ought to be permitted in the 1 air of a room. 
Such bring the case, an average burner, consuming 5 or cubic feet, of 
gas per hour yields from *2-5 to tt cubic feet of carbon dioxide, and thus 
requires from 25(M) to 3000 cubic feet of fresh air per hour. In other 
words, in calculating the air required, a, gas (lame may be taken as 
numerically equivalent to a human being. 

Air it Mixture* As has already been mentioned, the apparent 
constancy of composition of the atmosphere led many early chemists to 
believe that it was a definite 4 compound of oxygen and nitrogen and not 
a mechanical mixture of these two gases, When later and more accurate 
analyses of air were made, however, small but decided variations in 
the* relative proportions of its oxygen and nitrogen were found a dis- 
covery that disposed entirely of the suggestion that air is a compound. 

Se\ end ot her lines of argument point to the same conclusion however. 
For example, when air is shaken with water each constituent dissolves 
to an extent dependent upon its own solubility and partial pressure. 
Since oxygen is approximately twice as soluble in water as nitrogen, 
the dissolved air is slightly richer in oxygen. 8 If air were a compound, 
on the other hand, the gases would dissolve in the water in the same 
proportions as they exist in the free air. 

s AH <x<'<H<nt mriuitr on tho '* IMutivc* flygkmie Valncw of Ons and Electric Light- 
ing" ititii'iiK ./. tiny *' /"*' IWMMftOO, 29,' 51-132. 

3 Hikldiuu*. ./, //i/f/iVw, HK)SS. 2, 414. 

;l Ailvimtagtt hn beim taken of these proportios to separate oxygen from nitrogen 
eommotci*Uy * p. IS. 



When oxygen and nitrogen gases are intermixed in the relative 
proportions necessary to form air, no heat is set free, yet the result n^ 
mixture possesses the properties of pure air, and its constituents admit 
of separation again by means of diffusion. It seems highly improbable, 
therefore, that a compound can have been formed. 

When air is liquefied and subsequently boiled, a vapour rich in 
nitrogen gas is the first to escape, leaving a liquid proportionately 
richer in oxygen. 1 If the air were a compound, however, the eseapmg 
gas would have the same composition as the liquid. 

Finally, the properties of air, whether in tin* gaseous or liquid 
phase, are intermediate between those of oxygen and nitrogen re- 
spectively, thereby suggesting a mixture, for, as a general rnle, com- 
pounds do not resemble their components either physically or chemically, 


Physical Properties of Air.- Pure air is a tasteless a nd inodorous gas 

which appears colourless, except in very deep layers when a imnUlue 
colour is visible, which has been attributed to its oxonc content. I'nder 
normal conditions of 760 mm. pressure and I'., the weight of a litre 
of air varies, as a rule, between 1-2927 and ]*2()tt# grams/- the variation 
being attributable to the fact that the air has not a perfectly constant 
chemical composition. For this reason it is useless to determine with 
great accuracy the density of u gas relatively to air unless the com- 
position of the latter is simultaneously ascertained, 1 * For most purposes 
a mean value of 1-2930 at C. and 700 mm. will be a suilicicntly accurate 
figure to adopt. One gram of air under the above condit ions will occupy 
773 c.c., and its density with reference to hydrogen is li'-(4. At 15" (*. 
1000 cubic feet of air weigh 70-5 lb., whilst, 1 Ib. of air occupies 111*07 
cubic feet. 

The more important determinations of the weight of I litre of air 
are given in table p. 1.91. 

With a knowledge of the density of each constituent of the air it is 
possible to calculate the relative proportions of nitrogen and oxygen in 
the atmosphere ; but such calculations at first indicated more oxygen 
than could be found by direct analysis, and not until the discovery of 
argon was the cause of the discrepancy realised. Knowing the density 
of oxygen, nitrogen, and argon, the proportion of these gases in the atmo- 
sphere can now be calculated to be as follows : 4 






Weight j>or cent. 







1 Advantage has been taken of these properties to aepnrato oxygon from 

commercially, see p. 31. 2 See Quvc, J. Chim, ptiy* n 1917, 15, fl. 

3 See Leduc, Compt. rend., 1893, 117, 1072. * Loduo, (Jompt. rend. f 1800, 123, 8CK>. 

Wright <{ 

I Ht ir of Air 

at N'.T.l'. 

I -292S 

1 "29JJ2 




Remark*. ! Authority. 


Paris, g. 9SOUO;> Ledue, Kt*RincmH& 1919, 108, 509, 

Mean of HO de 
terminations . 

Paris . . . 

Ucrmamu Ow*/;/. /rw/., 1913, 157, 
920; ./. (7mm />////*., 19U, 12, 

(Juye, Kovacs, and \Yourt'/el, ('OM/J/. 
/r//*/., 1912, 154, 112 K 158k 

LinltH', CW//>f, rend,, I8a, 117, 

H>72 ; 1801, 113, ISO. 

yh*i^Iu /Vw. /%. SV;r M 18im, 53, 

Jolly, IH80 (rivt'H by 

1*29301 j At Berlin . . j Kohlrauselu /'"$?. Annulcn* 1850, 

vtT sen. Int. 51" 

l'29SOi j Berlin 

1 -29:120 1 Paris 


1-21W17 ! . 

1-292H9 i , 

' i 98, 178. 


. j Laseh, Chcm. Xcntr., 1852, p. 148. 

^nnuli (I8-I-7). 

'^naull, c(>rrt'<'t(*<l by CrnfLs, 
Wj/tf. //;///., 1888, 106, UHI2. 

That Ihr nir ptissfssi*s wright was apparently first rc^'o^nisod by 
Jean Key, 1 r. 1(J<W), an obsrmitiou that wa.s rontiriued by Torricclli in 

ICMII and by Pascal in HU8. Hey niadt* his discovery by observing that 
tin, on calcination in air, increase in Wiinht^antJ thus anticipated the 
results of Lavoisier bv nearK; a century and a half. Torrit(*lli Cackled 
the problc'in in an et(firtl/difft*reiii tnutttter. lit* Iiik4 uitl^mercnuy 
u glass tube, <lose<t itf one end and measuring souu* ft feet in length. 
\Vlun the tubr was in\erted with its open cttil dipping undtT mercury 
in a trough, the tube no longer remained fitted *vvfth the liquid, It held 
a column of mercury some 30 inches in height, but above this the* tube 
was empty. This space came to he known as the Torricellian vacuum, 
and its discoverer correctly attributed its formation to the fact that the 
open air acting on the surface of the mercury in the trough is able to 
support by its pressure a column of mercury of definite lt*ngth, and no 

Mnurtrt* Potit, 

i/c Jean Itcy, Paris, ii>07. 

192 OXYGEN. 

more Pascal extended Torricclli's experiments by rmpluym- tuhes 
filled with other liquids such as oil, alcohol nut water. In every ease 
he found that the height of the column o liquid supported h> he i 
was inversely proportional, to the liquid density ; in oilier *ouls tlu 
pressure supported was constant, irrcsped i ye oi I he chci.m-al c|oni,K>si i, 
of the liquid. Pascal also surmised that li air is a ponderable thud, it 
will exert a greater pressure at sea level than on the top oi a mountain. 
and that this difference should be capable of measurement by observing 
the relative heights of mercurial columns in such sit uat ions. Kxpcrimcnt 
proved this to be the ease. Boyle christened lomcelli s tube, con- 
taining mercury, a barometer* and it is customary to express i he pressure 
of the air in terms of the height of a column of mercury which it is 
capable of supporting at any moment. t . 

The pressure of the air, as already mentioned, varies with altitude* ; 
indeed, at one and the same place it does not remain constant in con- 
sequence of variation in composition, the influence oi wind, ete. \ 
standard pressure, known as an afinoxpliere, has been ehoseii. I he 
British unit is a column of mercury 29-005 inches in bright, measmvd 
at 32 F. in London, and is equivalent to a pressure of ll-7tt lb. pi-r 
square inch. 

The metric unit is a column of mercury 700 mm. (*2<.Hi^ inclu-s) m 
height measured at C. at sea, level at latitude 45". The density oi 
mercury at C. is 13-59C}, and the acceleration <lue to gravity at st-a 
level and at latitude 45 is 981HW cm. per sec-. Hence the value of 
the metric standard qf pressure is 

7G-OX 13-59(5 X98<H)0- = l()i:J250 dynes per sq. em. 

which is equivalent to a, weight of lOtttt-3 grains per sq. cm. The- Hrit isb 
atmosphere is 0-999C8 that of the metric unit. 

The total weight of the atmosphere is approximately as follows ; 


Nitrogen (including argon, etc.) . .M>-M/-iOO,00(MMMMK)0 
Oxygen . . . . . l,iMH,04.(MHMM>0<UMW 

Carbon dioxide . ... 3,150,000,000,000 

Except at pressures hut little, removed from atmospheric, air does 
not obey Boyle's Law. Regnuult, 2 who was the first invest i^utor to 
obtain trustworthy results, found that air deviated appreciably from the 
Law between pressures of 1 and 27 atmospheres the nin^e used the 
gas being more compressible than the Law demands. Several other 
investigators then took up the work, the most important experiments 
being those of Amagat, 3 whose results are given in the following table, 
(p. 194) together with the data obtained by him for oxygen and nitrogen, 

The results for oxygen and nitrogen are shown dtagrnmnmticHlly in 
fig. 38 together with curves for hydrogen and carbon dioxide for the 
. sake of comparison. 

It will be observed that air gives results intermediate between those 
of nitrogen and oxygen, as is to be expected from a mixture of the two, 

1 See New Experiments on Cold, 1664-1665 ; Boyle's Work*, 1772, vol. 2, p. 487, 

2 Regnault, Relations des Experiences, 1847 ; Mtm. di VAwut., 1847, 21, 329. 

3 Amagat, Ann. Chim. Phyt., 1880, 19, 345 ; 1881, 22, 353 ; I8KU, 28, 4511, 4<M, 4HO. 
His results are summarised, ibid., 1893, 29, 68. 



At first the* values for 1'V fall, the attraction between the molecules 
causing the gases to he more compressible than Boyle's Law demands. 
As, however, the pressure increases, the volume ceases to contract in 
strict proportionality, since the dimensions of {.he molecules themselves 


1000 2000 

c'tmprftMnih2Uti<<xof nxy#<w ant I mtrogmt (Amagal, 1893). 


Ffo, 33," 

begin to make themselves felt. The gas thus becomes less compressible, 
than the lnw demands, 

AH the temperature fulls, air shown an ever increasing tendency to 
deviate from Boyle's Law. This is well demonstrated by the results 
of Witkowski l given in the. table on p. 1 05 and shown diagrammati- 
citlly in Fig. 114. 

1 WitkowMkt, /*Ai7. ,1/rtf/.. IHIHI, 41, 288. Further 
, Ann. l%il% HMf>, 47, 1O8; 1910. 31, !Mf>, 

given by Holborn and 






Pressure in At in. 












PV at 0" ('. 












PV at o < ' 

(Nil r*H<'iii, 

I -0000 


1 -(I.'IIIO 





t- 1970 



:-ti uo 


The mean specific heat of air at mtstmit pn-ssiuv ns. s ttttlt thi* 
temperature. The most reliabir data aiv tlwisr .-ixrii in tin- tjiM.- un 
p. 195. 


: 0'500 


10 20 SO 4V All fti^ i*ii 

f>ft$$ufte m 

FIG. 34. The comprtwubility uf uti 

The variation of the specific heat at <*instant jmssttre over a 
of 1 to BOO atmospheres is readily calculated ! lor a mean trinprn 
of 60 C. from the formula 

10 4 C0 = 2-H-H-2*8()/j-| 0-0005// 1 0*OOOO!Oi);>\ 
where p represents the pressure* in atmospheres. 

1 Holborn and Jakob, Zcitach. Vtrein. deut. /we/., MM7, 6l. 1 4il; MN, 58. 
Sitzungaber. K. Akad. Witut. Berlin, 1914, p. 2i:i, "lln* Iii^tt vltii' futtint ty " 
(Nuovo Gim., 1894, 36, 6, 70, 130) appear to bo Is 




(Witkowski, !<S9<>.) 


Vulurs for PV ut 



140 (i j iiio r. 7H-r c. o r. 


1 100" (!. 

1 i 


48(>2 0-5229 0-7119 1-0000 




I .. . . 0-9951 



1 -3(>78 


-380H 0-4410 (H77S 0-9897 




30(13 0-393(1 0-0599 0-98 t-2 

-0 MJ8 



1128 0-3329 (HU.23 0-9793 




0-2544 CHJ252 j 0-975 1- 




0-2013 (HHKH9 i 0-9723 




0-1089 0'5937 | 0-9701 


1 -382 1 


| 0-20 1>3 0-5790 ( 0-9088 


1 '38(50 


j . . 0-5080 i 0*9081 


1 -3908 


1 . . 1 . . \ 0*9(181 






1-400 1- 


! . . . . 0-9710 

1 -0 t32 


130 ; 

| . . ! . | 0-9738 



| ! 



* | Mt*utt H|M*{'ifi^ Hcnt 
at. ('(ttiHtitnt !*rtHHurt % . 




Sc*lu*c*l and 

II < -use, Her. dent. 



ptiyxilwl. d 

V.v., 1011, 13, 870, 

- 102 to i 

17 0-2372 

\Vitkow,ski, / 

V///. Mag., 1890, 41, 

(5), 288. 

I 20 

0-2417 (fxtrfiiK* 

Swann, Proc. 

Roy. Nttc., 1909, 82, 

| valuta 0-2418 

A, 147. 

and 0-2427). 

1 20 


S(*IUT! and 11 

t-us<\ Inc. cit. 


s 0'2t03 ScluH'l and Hcust*, //;/;/. Pln/sik, 

1912, 37, 79: 1913, 40, 473; 


Chew. %entr.< 1919, iii., 1 1.8. 



Swann, Itw. elf. 

20 to 440 i 0-23(! 

Iloli>i)rn and 

Austin, ffitzu nfiaber. 

20 to 030 0-2429 

K. Aktid. 

triffft. Ilerlin, 1905, 

20 to 800 l 0'2430 

p. 175. 



llolbora and 

Jacob, ffifzu ngsher. 

A'. Aknd. 

irixft. Berlin, 19 U, 


p. 213. 



Part ing ton, / 

*rtw. Roy.Noc., 1021, 

A, 100, 27. 


196 OXYGEN. 

The variation of the molecular heat at constant volume with rise of 
temperature between O C. and 700 C. is given by the expression 

C V =4-S+0'0004T, 

where T is the absolute temperature. 1 

Partington 2 gives the following results at 17 C. : 

Specific heat at constant volume 

pressure . 

Molecular heat at constant volume . 



The ratio of the specific heat at constant pressure to that at constant 
volume is given by the expression 

Other recent values for y, as determined by different investigators, 
are as follow : 





Moody, Physikal. Zeitsch., 1912, 13, 383. 
Scheel and Heuse, Sitzungsber. K. Akad. 

Wiss. Berlin, 1913, p. 44. 
Mercer, Proc. Phys. Soc. London, 1914, 26, 

Griineisen and Merkel, Ann. Physik, 

1921, 66, 244. 

These values agree well with that required theoretically for a diatomic 

The value for y is stated to remain constant to within 1 per cent, 
between and 500 C., 3 although most observers 4 agree that y tends 
to fall with rise of temperature. 

Increase of pressure, however, raises the value from 1-404 at 0-5 
atm. to 1-411 at 3-5 atm., 5 1-460 at 20 atm., 8 and 1-533 at 50 atm. 6 

1 Dixon, Campbell, and Parker, Proc. Roy. Soc., 1921, [A] 100 1 

2 Partington, Proc. Roy. Soc., 1921, [A], 100, 27. See also Womersley, ibid., 1922, 

L"_l IOO, 4oa. 

3 I-urstenau, Ann. Physik, 1908, [4], 27, 735; Ber. physikal. Qu., 1909. II, 137. 
'See Lussana, Nuamtom., 1894, 36, 5, 70, 130; Witkowski, J. Pl njs ,, 1890, 5, 123: 

Plvftt 1M? i ?8 IM -V '/sno *?***. 4- 131 ; HolboVand Kenning,' 
PM %% . io?n' rfi ; !An ' n l' 8 , 9 ; ^ n 8 en >Mitt.Forschungsarb e iten,8; Swonn, 
PM Trans., 1910, [A], 210, 199, 238 ; Moody, Physikal. Zeitsch., 1912, 13, 383. 

**> fqt ison"";/^ 14 ' v V 5 ' 913 ' See ttlso Jol y- P - *y- Soc., 1894, 55, 
TMW ' H T dVf ; f^^> &***" Z. Akad. Milnchin, 1903, p. 691 
Holborn and Jacob, Sitzungsber. K. Akad. Wiss. Berlin, 1914 p 213 Koch (Abh Baver 
Akad.W tSS ., 1907, 23 377) at high pressures found y to fall ' ( ^ 

Worthing, Physical Review, 1911, 33, 217. 



The* coefficient of e^pan^ion of dry air, with rise of temperature per 
('. and at. normal pressure, has been variously determined as follows : 



(Veilieirnt of fCx 





Arnault, CtnnpL rend., 1872, 74, ItiJK). 
Jolly, />/>/&'. Annttien, Jubdb., 1871, p. 82, 
Mendeleef and Kagander, Cotnpt. rend.., 1870, 
82 , 4,10. 


For a gas that obeys Boyle's Law, the eoeilieient of expansion at 
constant pressure is the same numerically as the coefficient of prepare 
ineredxe with rise of temperature at constant volume. The more im- 
portant results obtained for this latter coefficient are us follow : 


Pnwwn*. i IViujxTittur* 1 *, i C'tM-'flhufut uf 
om* H#. j Kiwigt% " 0. { I*nHMim% 



! 0-OOB70M 


5 0-0007172 


! o-ocmocnio 


^ 0'00CJ5II 


CM 0(17 j iHKKHHl'til 



100 I 0-003U7J4 



i 0-002)887 


Melander (1802). 

Ja({tu*rod and Perrot; 

Hrtfiwull (181-7). 

Kc^nault (1847). 

The coeilieicnt of w#mv% of air is given 2 as- 0-0001.80 at U-75 ('. 
The tlwrmal conductivity 3 of air at tlic mean temperature of 55 C. 
is 0-0000571, a vulut; intcnncdiute between that of o.xy^cn (0*00005Dd) 

and nitrogen (0-0000500) * 

The velocity of sound in free air at various temperatures has been 
determined us follows ; 8 

Temp., u (1 , . I (Ml 200 

Velocity, m. IHT mw. 3:*i-H :>87-5 4'M-H 

:HM> 400 r0o 
51H-B ftW-a 

tlOO 700 
5HD%$ (121-S 

ltcl I^rrot, thru id. rrntl.* HWW, 140, 154*2. 
2 Roberta, F/iil, 3/aj/., 191^, 23. *2uO. 
:i Stt p, 411, 

1 Tmltl, Pme. /%, ,S f wr., HHW, [A|, 83* Hi iStnuUno Htofan, tiitzunyxfirr. K. AM. 
Wiem, 1872, [2], 65/45, 

& Dixon, Oai^wtwil, au<l ^lurkor, Pmc, Hoy. tfoc., IU2I, [Aj, ioo 1. 


The 1 velocity of sound in free air as determined 'by thr Bureau ties 
Longitudes is ifcn-'J metres per second, whilst ItrbM tumid tin- \alue 
&tt'-14, and (Jriineisen and Merkel J JiJIKV? at o i ! . and 7UO mm. 

The refractive intles of dry air is HHitmtHh at ft I'.- 1 and 7<W mm. 
for the sodium i> line (A 581W.* 10 H nn.) ; the imhers fur uthrr \\a\e- 
leugths not widely removed may lu- ealeulatrd fniu Cauehy's equation 

n I Aft - B A-K 

where // and A represent the rrt'nietivr ui<!e\ and wave-length 
respectively, whilst A and H are constants uf \*i!urs 'JJH-7! * 10 "' and 
5*07 X I ()~ 1 * 1 respectively. The latter const unt ti in thr eorUtcirnt t>f 
dispersion. According to Cuthbt*rtson * tlu* rrfrartur tnde\ n of air 
for any incident li^ht, of frecjueiiey /is #ivcn t*y the f\p$vvsittn 

" HH*J5 - Ill 31 / a ' 

For the sake of comparison, thr ivfraefivr tttdiers ot thr morr impttrtunt 
individual gases present- in the atmosphere are ^tven in th^ t'o 
table* : 

Ciua or Vapour. 

ti fr l> linr, .^ 



Argon . 


I'OOOUJMN ' Heltret, ltc, ri/ 

1 so, m><>. 


1*000*257 , MuM*nrt IH7H, 
1*0(H>'25() 1 Lorrn/. 1H7L 

When entirely free* from dust, dry air |os**e,sse>. a InnJt tir^rrr of 
pareney to light, which the pmseiice of mtii-Htiirr and this!- ti-wlh to 
decrease. This is evident from the foliowing tjtlilr : 

Dry, dust free air . , | 

Moist, dust fne air , , j 

Air in a dusty dwelling-hottse nmiii i 




, HHtt f ij, (31 |0|. 

-u. lltill, 4itl, .Sri', 
.. IHW7. 6J. 

^. lievicw, !IK>r, 20 Htt s '/Vuiia, /%, *Vr, 
and Mrkt<l t Ann. l'/ii/il% l!2I f 6, 1144, 
School, Bcr. rf^Ml. ykymktil. f/iV.. I!i7, 5. 24, Hrr ! 

Jtoumanic, 1014-1915, 3, ai I - Kitriway find Truiwi, /W. 1% 

investigation c.f ' th ultrn-vit^it jmrk i4{H^trt.iiii nf ir, m<t* Wn 

Hill, 10, OIK Uu nlmtirptinii KiHTtrmii til nir hii* Iwn tiifJtw| |> v 

18HI 93, 788; 1882, 9Sf 447; Ik^quwl, i^.. IWI, 96. 12IA*; JmiM.ft. itel, 1HHA, 

lox, j)4. Iho band Hiwctrtutt by Wtillfior, /V/* vlmm/m, 1 |H7tf. 147, II^I. 
4 (.,. and M. (Jutlilwrtmrti, /Vw. /<y. ,SVif, Hllll, |A) Sj IftK 
! YJ ld 'wM?! ,! rom t I)a l ltl11 ^ ^^rpi/ii^If CAemur, lt. tti,, p. 44^, Tki 

quoted fur Wild (jf%/. AnnaUu, 1BOH, 40, /$8) !ir tu4 sii%r tbi* iliitii, 

1 I mnl. 



Dry air is highly dial hernuuums, that is to say, it absorbs but little 
of the sun's heat. 1 

Owin<4' to its o\y#rn content, air is magnetic, its magnetic, suscepti- 
bility bring about ()':>"> < 10 7 at 10 ' ('. 

Its xptn'Jic indnHirt'Htiutfiti/ or <//Y/*r/nV ctnixhtnt referred to a vacuum 
is 1-00058(5 at (' ami HW05?( at 'JO' 1 (V- 

Thr solubility of air in water has been made the subject of consider- 
able research, and possesses several points of interest. The independence 
of the two main constituents (arjjon being included with the nitrogen) 
is clearly observable front the table given below ; Further, owing to the 
Fact that the cocHicients of solubility of the individual gases arc affected 
differently with rise of" temperature the composition of the dissolved 
mixture is not constant. 

Since oxygen is practically twice as soluble in water as nitrogen, it 
Follows that the dissolved gas is proportionately richer in oxygen. By 
expelling the gas into a vacuum and reabsorbing it in water, the con- 
centration of the oxygen is still further increased. By repenting these? 
processes several times, a Fairly pure 1 oxygen can be obtained, and this 
has been made the 9 basis of a patent For the commercial separation of 
oxygen From the air (see p. l.'l). 

The number of cubic centimetres of oxygen and nitrogen (containing 
argon) dissolved in a litre of water saturated with air From a dry 
atmosphere at, 700 nun. pressure at various temperatures are given in 
the Following table : :i 











0-1 I- 



Kx & 





NU r ,, K ,, 
















2 **T2 



I- I*J 






Measurement has also been made of the solubility of air in sulphuric 

ahrr^ IK70, f. 71*; (*n^( 

1 TynditlK /W, liny. ,SW,, IHIKJ, 30, 10 ; Itulf, Juh 
^ /!, 188-1, B, :t04. * 

1 Tungl, Ann, Phyxik* ItHiK, 26. MM .SifilHrtiiit, /';. A*, /iA'd*/. 
I OKI, X5,'JW5. 

:i Kfir <!Hinitio!kM f // utui /f w j, .'III. 

4 Winklor, Wty*ikttliMh*(!hvmiMh<'. TttbdU-n, I^au<ltiit*UurariUnu, 
Fox, Twin.* Farad. *S"w%, lUOt), 5, OH. 
iiji uritiit. 

200 OXYGEN. 

acid of varying concentration. 1 At 18 C. the coefficient of solubility 
in 98 per cent, acid is 0-0173, and in 70 per cent, acid attains a minimum 
value of 0-0055. 

Radio-activity of the Atmosphere. In 1887 Linss 2 drew attention 
to the fact that a charged conductor, thoroughly well insulated in so far 
as its supports are concerned, loses its charge in the air. This was 
confirmed in 1899 byJElster and Geitel 3 who, two years later, 4 discovered 
the cause by finding that a negatively charged wire exposed to air 
becomes coated with a radioactive deposit which can be removed 
either mechanically by rubbing with felt, or chemically by solution in 
ammonia. 5 

Observations on the rate of decay of the radioactivity of this 
deposit indicate that it is due to the presence in the atmosphere of the 
emanations of thorium and radium. 6 

* Since air drawn from the soil exhibits radioactivity, it seems 
probable that ground air is the source of the atmospheric emanations ; 7 
and this theory receives support from the fact that atmospheric radio- 
activity rises with a falling barometer. 8 This would account for the fact 
that near and over the sea very low values have obtained. 9 The problem 
of the relative proportions of radium and thorium emanations in the air 
has been made the subject of considerable research. Balloon observa- 
tions made at a height of 3000 metres above the earth's surface indicate 
the existence of radium emanation even at that elevation. 10 In a series 
of tests in the Apennines, 1090 metres above sea level, the proportion 
of the total atmospheric activity due to thorium emanation %vas found 
to vary from 29 to 73 per cent. 11 On the other hand, a wire charged 
negatively in Manchester gathered an active deposit containing on an 
average 62 per cent, of thorium emanation, 12 whilst in Rome under 
analogous conditions results indicated 60 to 70 per cent, of thorium 
emanation, 13 the remainder consisting of the radium product. As a 
general rule, it appears that, in the lower regions of the atmosphere, 
thorium emanation preponderates, whilst at higher altitudes radium 
emanation is in excess. It would appear also that American air 
contains a lower relative percentage of thorium emanation than 
European air. 14 

Determination of the actual amount of radium emanation in the air 
indicates that on the average the quantity contained per cubic metre of 

1 Tower, Zeitsch. anorg. Chem., 1906, 50, 382. 

2 Linss, Meteorolog. Zeitsch., 1887, 4, 352. 

3 Elster and Geitel, Terrestrial Magnetism, 1899, 4, 213. 

4 Elster and Geitel, Physical Zeitsch., 1901, 76, 590. 

5 Allan, Phil Mag., 1904, [6], 7, 140. 

ion! Rl i th 1 erfo l, d ^ ^K* pm - M <*$.> 1902, [6], 4, 704; 'Bumstead, Amer. J. 8ci., 
1904, 18, 1. For data concerning the radioactivity of radium and thorium respectively, 
see this series, Vols. III. and V. 

7, l E ^^ d io^'m W ^^^ aflwd " W1 ' ]904 ' 9> 49; Mache and ^mmer, Chem. 
Zentr., 1906, 11., 1237 ; Physikal Zeitsch., 1906, 7, 617 

Simpson, Phil. Trans., 1905, [A], 205, 61 ; Gockel, Physikal. Zeitsch., 1908, o, 304. 

Compare Runge, Chem. Zentr., 1907, ii., 1353 ; 1911, ii 786 
10 Flemming, Physikal Zeitsch., 1908, 9, 801. 

t^/^i fll i Ze ?^' M 1910 ' "' 227 ' Com P are Gockel, Arch. sci. phys. nal, 
248 L Gockel and Wulf, Physical Zeitsch., 1908, o, 907. 
2 Wilson, Phil Mag., 1909, [6], 17, 321 

i > 1908 > [5] > ** * 10L 


air is equal to that which would be in radioactive equilibrium with 
1 X l()~ 10 grnm of radium. 1 There* can be no doubt that the presence of 
these emanations is the main cause of the atmospheric ionisation which 
manifests itself in permitting electricity to escape from a charged 
conductor. Whether or not they exert, any physiological influence 
has yet to be discovered.- 


When air, cooled below the critical temperatures of its constituents, 
is subjected to compression, liquefaction may occur, but the constituents 
will not separate out in strict proportionality :l because oxygen is more 
easily condensed than nitrogen. For a similar reason liquid air, when 
kept, loses nitrogen more rapidly than oxygen, so that the boiling-point 
gradually approaches that of the latter element and the gas evolved at 
iirst extinguishes a lighted match whereas the last portions increase its 
combustion. 4 

On account, of the uncertainty introduced by this behaviour of liquid 
air, it is important to bear in mind that statements of the physical 
properties are of relatively little value unless accompanied by figures 
giving the composition of the liquid air examined. Kreshly prepared 
liquid air usually has a boiling-point near 10.T ('. at 7(>0 mm./' a 
temperature as low as ii*20" (\ being attainable by rapid evaporation 
under a, pressure of a lew millimetres of mercury; under constant pressure 
the boiling-point gradually rises, approaching that of liquid oxygen. 
The compositions of the gaseous mixture in equilibrium with liquid air 
of varying oxygen content, are given numerically in the accompanying 
table (p. 203) and shown diagrummatically in Fig. J5. 6 

Smith, Wtt/xikal. Xntxcli., 1914, 15, :il ; 
Radioaktiv. tikklrunik., HMH, 15, if>s. 

ri Sno Knhnnnn. /fr., HHM/jy, UIKI. 

4 Stock and Nirlwu, ////>/., I 111 Mi, 39, IJItlKt. 

h OlHZowHki, ('ottipt. rctul., 1884, 99, 184 ; JHHa, 101, L!JH ; vein VVriillWHki i//tW., 1KH4, 
98,982; 1885 s ioi,B35; 1880,102,1010; Ann. I'hi/*, (Mi-m,, 1885, 25, 4(^ ; 26,1.14. 

6 Baly, ;Vii7. Mty., 1900, [5|, 49, r>l7. 

- 1 

Liquid oxygen and nitrogen mtx \uthut ;ippr. emhl*- eh;ne in 
volume ; hence the approximate entnposition i*l th*- Inpud niixture ran 
be calculated from its density at any partieular tempi ratun 
meats which have been ntatle lead to the < \presMn 

for the value at the hoihnu-point under unlmuiA pressure, when ,r 
represents the percentage of o\yen 3 anil ! thr dnnti) ivtfuirt-.t. 

Measurement., lias also hern nwde it' tlir h-at uf lAapnratton, 11 thr 
refractive index, 4 and thr alMrptiMt sp-rlrtttu *!' Itqutd air/ 
properties again bein^ jdiiitist I'titin-ly thr rrsiiltiiu! of tin- pniprrttrs 
of the constituents, 

The critical constants tf liquid air hair hrrii shuiatrd as Ji,i\iit^ 
the following valm-s : teniperattir*/ t to C',, pn-ssitn- :i'J attnusphrrrs t 
and volunu^ 0-(M) % 257. tt 

A distinction is sonu'tiuu^ tuatlr ? tt1\\*rn tlir point at Iiti-it thr 
two co-existing phase's, nainrly, \apuiir and hphl, JU-I'MUM- id-i!iMl 
the plait point and thr point rrprr.srutimj thr liiuiliiii* rMudittuu Jr 
the. separiitton into two phases tltr rriliVnl |n*inl **/ 'liiii, Tin- difft-r-- 
cncc bctwec k n the two is vrry stnalt* as is t-vidntt liitiii thr lii!Iftttin 
estimation : 7 

Plait point . . . , M-7a :7 -.; a.i 

Critical point of contact , , ; UO-IKJ .'$7-17 -;U 

The critical density of air, its nthniiatrd frutu I !i- rnti***il 
of oxygen and nitr(gen by the simple rttlr nf tut \lttn-*., 1*1 o-tt. Thi" 
lies within the range given above. 

The specific heat of lit|Utd air in about hnlf tlmt *if vvatrr, whdst the 
latent heat of evaporation is approximately M ejilurie?*. 

The viscosity of liquid air of hotiinj^potnt 71*'*^' ahnohile is giv-rn n 
as 0-001078. 

Liquid air is of relatively small value a.% a Mtrer i*l" i-nri^y ; its 
conversion into gas at the* ordinary teittjeriture is eapiible of yirldiiin 
only as much energy us the comlmstiott of intt-it'iitii its weight t*l' petrol, 
and the heat absorbed from the Mirronitdtit^H iltiniin the rhitje $H only 
sufficient to melt I J timen its \vt*i#ht of in% 

1 Inglis and GWUw, Tmna, fVi, iSV T . HMHl. H*> r HHIH 

2 ^Laclonburg and Kritgd, II* r., I Htm, p, 4*, UI * 1 * -, a VVi^Mnift 
rend., 1886, 102, 1010 ; tint I JMm Iit/i, /V*v*/., l l U. , I.* ''* 

a Estreichar, Zfitftfh. /^////.v'Jlri/. <Vi*//., Ifwil, jt) ,*/ 
4 Livcing and I)\vur, /'//</*/. Mm/,, iHii'i, 12 1, li;' 
f> Livoing and Itawtir* /Vu7. .U/., |h*:i, |.>j, |li ;U*H 
8 OlHxowHki, /or. rul. 

7 Kucnen and Clark, /Vw. A*. Jfof, Il'rlnj,*fli, J M f r f,|i 1*HI, to, IMHH 

8 Verschaiielt and Nicuwo, t6iW. t IttlO, 18, Itltli, 





(I July, 1000.) 

f lVinjKrutwv. ! iKygrn in Liquid, 

Uxy^on in Vapour. 

" ('. IVr rent. 





I Hi 

i)i p j>8 






7*^*^i / 

4 l-- fc J5 



a i!' J ! ; ? 





8- 10 





Applications. Although it cvaporuU^s rapidly in ordinary vessels, 
lic|uid air eaa be preserved for a considerable titu( v with relatively little 
loss in glass vessels, the hollow, silvered walls of which enclose an 





40 60 

00 40 




35.- Curvea showing compoHition of liquid and goBCouH air in equilibrium 
at various tomporaturuH under attuuBphcrio prctwurcs (Ilaly t 11K)0). 

204 OXYUKX, 

evacuated spare; 1 these atv manufactured tit various shapes and 

Liquid air is now a common commercial produrt ami ran he applied 
to various useful purposes. An obvious appliration is to tltr product ion 
of low temperatures for experimentation work,* and a valuable extension 
is to the production of high vacua by filltni* with rarhon dioxide the 
apparatus which has already been attarhrd by hrnnrtieaUy scaling to a 
bulb of coconut charcoal; whrn this bulb is itntnersfd in iiquid air, the 
carbon dioxide is absorbed so rapidly and cuwplrtrly that thr pressure 
may he almost immediately rrdueed tt> a fVartiun of a millionth of an 

Mention has already bent made ^ of thr rtnployiurnt <f liquid air 
lisa blasting agent. It also finds apphration as a rou\rttienf sourer of 
pure nitrogen and oxygen. 4 

By the rapid evaporation of liquid air undrr frdiirrd pressure 
suilicicnt further < t ooltng can be effrctrd t cause tin- air to solidify, when 
it, yields u colourless, transparent mass/' '1'hr tart that uitrotfr'u l\n\ u 
higher melting-point {namely *JJO ('.} than o\ygm ( 1*1!* C'V.I leiuls 
to the prcdonunaiH'e of the former rlcmmt in thr\tlitl 

1 Dtnvar, r/irw, .Vn/'.v, lH*.M, 69, 1M, ail ; IHSK', 71, III: 1 , j*t. Sr- ,il- M f<rrv, Vrt# 
Roy, AV>r., UKm, | A I, 78, 4;*H ; am) Ki't-faii.iisft, Znt,rh, *i^-. r /!** , tt*U, ,!?, r*V:j. 

a I)mvnr/w% eit. ; L<lrlmr|,^ /lir 
36 805. 



Occurrence. Of all compound substances occurring on the earth in a 
fairly pun* condition, water is by far the most abundant. Not only 
does it- exist in immense quantities in seas, rivers, glaciers, and lakes, 
but it is also remarkably widespread as a necessary constituent of the 
tissue of all living organisms whether animal or vegetable. It. is also 
present, as vapour in the atmosphere, whence it separates as clouds and 
rain. Some minerals, for example clay, also contain very appreciable, 
quantities of this substance in combination. 1 

Although there is a possibility that the compound nature of water 
was realised by the Chines*' at a very early date, 3 in Kurope the substance 
was regarded as an elementary substance, Aristotle grouping it with 
lire, air, and earth, as one of the basic or fundamental elementary 
bodies composing the universe. And so it remained until the latter 
portion of the eighteenth century when Cavendish, <\ 1781, demonstrated 
its formation by the combination of hydrogen and oxygen either by 
burning or explosion when the gases disappeared in the approximate 
ratio of 2 : I by volume/ 1 A year or so later, Lavoisier effected the 
synthesis from oxygen and hydrogen, the latter of wliich he* learned to 
obtain from steam by the action of heated iron.* Almost simultaneously 
an investigation was made' by Mongc, who demonstrated the combina- 
tion of two volumes of hydrogen with one volume of oxygen when a 
mixture was exploded, ami front this result, together with u knowledge* 
of the density of the gases, calculated tlit* relative proportions by 
weight./* On account of the presence of moisture in tin* gases the latter 
result; was innc'curatc, but the* method is of interest as anticipating the 
procedure adopted later by Scott and Morley in their well-known 
experiments.* In 1 800 Nicholson and Carlisle effected the* quantitative 
analysis of water by the passage of un electric* current, 7 an experiment 
which, us a proof of the composition, is not as sutisfuetory us might 
be wished because it is not possible with pure water, but requires the* 
presence of small quantities of an electrolyte. Henee the decomposition 
is actually a secondary result dependent on the interaction of the water 
with the discharged ions of the eleetrolytie impurity, 

1 For an attempt t <J*t*'rt tin* r'*h <f wtt**r in variotw imnrrtiln by tht* absorption 

tm Cnbltmt /./. Frttnklin ln*t., UH1* 172. 3UM. 
HH> p. 10. 

Alembifi ('lult Itr print*, ill. III 10, 
/A'wMvi df /rfiivwrfiYr, Ii, H:i5 Hill * 

Mon#t\ Mim. ArtuL M, /**iriX 178H, 78. Kwt titan Humboldt and Clay Luflftac, 
J. 1 hytiqur, 1805, 6o 120. 

See p. 295. ' Nifhtilttrn'M Jtturtutl t 1801 iv., 180. 

206 OXYGEN. 


For domestic and ordinary chemical purposes water is invariably 
obtained by the purification of natural waters from various source?*. 
Enormous quantities are required by civilised communities, as is evident 
from the accompanying data giving the average number of gallons 
consumed per head per day in the cities named : 


Glasgow . . .58 
Edinburgh . .38 
London . . .35 
Leeds . . .34 
Sheffield ... 25 
Bristol . . .22 


Buffalo . . .250 
Philadelphia . .211 
Chicago. . . 169 
New York . . 120 
Berlin ... 28 
Madras . . .25 

The above figures, of course, refer to the consumption of purified 
water for all purposes, and not merely for domestic use. 

A convenient method for classifying natural waters is that adopted 
for potable or domestic supplies. Such a classification must be based 
largely upon local conditions of climate, population, etc. For example, 
waters that would have been perfectly wholesome a century ago may now 
be suspicious and even dangerous, in consequence of the enormous 
increase in population. Bearing these reservations in mind, the following 
scheme is reasonably applicable to British waters : 


fDeep spring. 
Wholesome. . . < Deep well. 

^Upland surface. 

fStored rain. 
Suspicious . . . J Shallow spring. 

(^Surface, from cultivated areas. 

("Many lake. 

Dangerous . . . ^ Most river. 

L Shallow well. 

Unsuitable . . . Sea. 

1 . Spring water, particularly that derived from deep-seated springs, 
is usually beautifully clear and sparkling. The clearness is mainly due 
to thorough filtering during percolation through the soil, whilst the 
sparkle is caused by the presence of gases, mainly carbon dioxide, 
in solution. The temperatures of different springs may vary con- 
siderably. Water from deep springs is usually cold, whilst that from 
shallow springs varies with the seasons. Should the temperature of the 
water be appreciably above that of the atmosphere the spring is termed 
a thermal spring Typical thermal waters in England are those at 
Jatn (Somerset), the temperature of the different springs ranging 

^ (<*"**. 1916) ; Maason and 

WATKH. 207 

from ,'U" C. (KH t! F.) to 50 1 C. (lT R). The springs supplying the 
Corporation baths an- stated * to yield upwards of half a million gallons 
of water per day at 15 C. (ll,V R). At . Coulsworthy a (Shropshire) the 
temperature is li C. (52 F.), that is, the waters are warmer in winter 
but cooler in summer than the average temperature of the atmosphere. 
The Bath waters are aerated and sold in bottles as .v////,v ?iv/^T. 

\Vry frequently deep-spring waters contain dissolved salts which 
impart to them characteristic properties. Such springs as yield these 
art* termed mineral springs* and are classified according to the nature 
of the dissolved impurities, Many towns owe their popularity as health 
resorts entirely to the repute* I medicinal properties of their mineral 
waters. It is not improbable that many of the curative properties 
are either due to, or enhanced by, the presence of radioactive substances, 
and this would account for the well-known fact that artificially prepared 
mineral waters do not always possess the same medicinal values as the 
natural waters, Kndium or radioactive material, for example, has 
been discovered in the springs at Bath a and Buxton, in this country; 
numerous other springs in France, 4 Spain,'* the Jura, mountains, 
Tuscany, 7 Alps, 11 Switzerland,* Italy, 10 Austria, 11 Tyrol 12 Silesia, UJ 
Bohemia, 14 Indiana, 1 * at Carlsbad, 111 the Tuunus, 17 Wiesbaden, 18 
Kissingen, 1 * 1 Dnrkhciw,'-" and other parts of (icrmany * l , Hungary, 2 ' 2 
Norway ,** u Sweden, 24 Russia/* 1 Koumania,-" (treeee, 87 Canada, aH Yellow- 

* Biul<It<l*\Y*M (fuittr fa thttlt ami Itritiul (Nt<lH<m, HKiH), a iSV/i'rr\f ( 'um/jri/t to;*, otc. 
a Strut t, ./Yw, !it*tf t SW., IOO4, 7|. 101 ; Muxttun nuti Hamsav, ltn\ fiL ; KIUIIHHV, 

C/ifw, AYwx, HUH, 105, UKi. 

* ttatohi't, Cum jit. Wiitf,, UMK, 146, I7f ; Hopm, iVuV., HHiH, 147, 3H7 ; MIVMHO!, i7w/,, 
p. 844 ; HtwHim, /m/,, jt. H4K ; Muttrtnt nn! I^J>HJK% ihitl.. IIMW, 148. HIM ; HroohH-, iftiW., 
HUO, 150, 145, iJttl, 421$ ; Uiuiiii' umi ('rouiiru, i/JiW,, HM I, 153, H70 ; MHHHO!, tV*i*/. HKt), 
151, 1124 ; I*tHtl, lAii/., UH, 169, 7iH ; i^|m{K% i6iW M l!^n" 171, 731, HAH. 

clu (?tttiUt, ,'!/, AV>i. ^iiiiw.. J1MK 4 I IU, 147, IH, *JtW ; HM)H, 6, 2117, 2!)(^ l!tH, 3150, 
*t*. U...I,.' ;/,:*/* nn> vn ii'i * * * * / * j- 

IVrrot imtl JiM|tirrni, Arch* *SVi. phyx, iinf,, U)1H, |4|, 45. U77, WM\, 41H. 

7 ' 

5, 13. 2(1 

HMW, (4| t 27. ^f/i I MHO, 1 4 1, 30, 4fi, 

IB NftiMiai nnd l^vi, ,1//i /f. ,/lrr<n/, /,iWr t HKW, |5|. r/ s ii, full , .....,,... ...,.,..., 

14K)H. 29, H4t. u HiiinlH'fiiji'n Mtttuttufi., 1JIOH, 29, 11IU. 

"" " " '" " I/IM/,, )IUO, ;p, '!2i ; tilt I, 32,' 797. 

111 NVoy, %nt*rk. t tiffmtl. ('font.. IIHI/I7. IHI, 

14 HlHrtiit, Jtthrbtieh tfatlittttl'tir. KlfMrnnik,, ItKl, 8, LM. 

lft Itamw*y f F/'l, ,V*if/,. UUfi, ||, -|o, K15 i Stii-hi'n, V*iW., HHil, |0|, 31, 401. 

ltl Kmtt/rA*-wi. ^riilr,, HHMi, i./4K>j Kolhor*!i<r. ttrr. ttrut, phyxikttl. (}?*.> HH2, 
14, Ur>(J. l? Srluintlt, /*/!/***/, Xfihrh., !WH\ 6, 34 ; r'/irw, ^'W/r., UH)fi, i., 402. 

*" Hi'i* Hfiirich, Zrit*rh. i/r\ {'hrm., tiMH, 17, 17A7 ; Mnntttnh** HlOfl, 26, I41K 

11 f ht\t'/Hch, t*htf*iltttl. Zril*f/i, HM7, 8, HH? : HMW, 9, 1:10. 

att I^viii, iAi*/., ilMO, 1 1, :il>2 ; Kbltn- mill lVllwr, %nt*r/t. tinttry. Clu-M.. HH I, 72 aUIJ. 

81 Miil!*r. l*htt*ihtl. Zri^f/i., UH(>. n, 545. tci. 

sa Sztitlnt. fWi/j/. rrin/,, HH'JJ, 154, DH1 s;1 I'VittlnHnn. f'/irw. ^r/i/r., HH4. it. f 1400. 

81 Hj<niTti nnii SnhltMtm, Arkiv. Knit, Min. f/r/ tt HHIH, % L, No. 2; Nuhlbwii, ibid,* 
IIHO, 6, NIL 3. 

a? * M43u*niit7.kv, /. /6w*. /7i,v/*, <7ir/w. AV*, t iOII, 43* /*%. /*r/. 244. Swiiui<\ tVwi, 
Ittia, 45, /%i. >rt 4M. von VVVtmiint. i/wW M UM4, 46, 742; Htirkmr, iVW.. 1015, 
47, 21. ** iitirimt'/t'wtt initi Ptttriciu, A tin. SVi. r'/i>V, Jami/ t UK)8, 5, 1511. 

87 KomnrmiH, f'A*'i. Kmln, l!HO, I, t Hi:i4, 

** Kvi, Trail*, ffay* Nttf., f'ttwitttti 1010, (,*ij 4, iit, f,*i ; Hovlt* ii<l M*Int(uih, i7m/, t 1013, 
13], 7, Hill; Hiittrrly tisitl Klworthy. i&iW., IIH7 HUH, JJI), 1 1 , 17, 

20H o\YK\. 

stone Park, 1 (\>Ura<lo/ J New York, 11 t'nnary W.miK, 1 Tin- 
Iceland,* and Sardinia. 7 

The actual amount of radioaHn*- iu;ttrn;d in ih<- \\utrrs is of n*ursc 
infinitesimal, brim.? of tin* or*|*T, in s*m* t\ji*-.d f,i-*-s, ui in fl r,tms 
per litre,* whilst in others it i% \ r\ much }*-.v-,.* Th sprue,*-, at Havjnercs 
tie Luchou (i'Yanee) atv amongst tli- must rathoartn isi th- \\orld, 
and contain front 0-1 to IK1 im!himeneun<-- of nuimm limitation per 
litre, 10 equivalent to front I - III ilf to H"* JO n j^ram of radiutn per 

The term mineral spring has aUt* hrrti tAtt-utitd It* inelutti 1 eertain 
springs <'tmfaintn^ vrry Utttt\ it' an) 1 , more than tin- normal amount 
dissolved material, but which 111*1- n-'tardrd a** POSM-SN 
properties, Hueiu tor fxample, are tltt- tlttvton antl Mulvrrn \vnter\. 

i\ <*onvt*nient inrtliixi *f ehiHsiJ'ym^ mutt rat \\atrrs i% as totlous : 

1. Jliiriii/ffl. These etiiifiiiii eliirily MHhum ehlofulr with varying 
amounts of the chlorides *f putassium, eatetum, and inanjcstum, Hit* 
Droitwieh (\Vt>rcestershire) itntl twi* tit" fhr i'hfltrtdtatu f^ttlviilr and 
Lunsdown) springs art* eharaetrrist-tl by llwir htj-jh rou!-nt o| sodium 
chloridt*, the waters bein*; in eonsMlrrablr itv-mand ti' rhfUiuatte and 
sciatic affections. The Airthtvy \Vatt-rs | tlritl^e of Allan, Scotland) 
closely rescmhh* many continent nl spa waters, aiut eonhtm *'hloudrs of 
calcium and magnesium its writ as eommttn salt, 

2. ijtulphntic waters contain Nttlphutt-s mainly us suthum, eah'tum, and 
luugncsiutn salts % and !treeou\r|ii'titty *i|iiTiVwl, A'.^'. Hath, t'lu itf-nham 
(Chadnor Villa Well), and Seitrb*n*ttf.|lt, If frrrous Mtlpluitr is pivsmt, 
us ut Trcfriw ((^trnarvtin, N, Wales ) the uat t> ar- trriiit'tl 

*L Chnlybentc t>r Fcrntjlinunx, I \ually flirsi- \%atrfH eontam 11*011 
in solution, as the .soluble terruus liydro^eu tMrbonate ^^^(t'O.^^, 
Tunbridtfe \VclIs, Flit wick (Ueils) ilieltfttttam U'simlmty Wrjl), and 
Leiimington f are well-known examples. The c ( orrr^pontititt<i ut<u${4antUN 
suit may also be prtsctih 

4. Carbonated watern may hiili! witliiiiii h\ druj.;^i earb>hntr, XalU'O,,,, 
in solution, us their chief salt, as fur tAampir it* A|tii!inm*ts water, 
Alagnwittn waters contain magnesium hydfitgrii rnrbtuiate, Mj*H a (('O 4 ) tt , 
and calcareous waters flu* corrcspondm^ **uleuitu sa!t tVill J rrc> 4 J 3 , 1 
Such springs may be looked for in dolnmttir, liir\ttnif% ami rhalky 

5, Nitlphnrtih'tt waters arc rhararirriM'd by th*- preseurf <*f liyitnnrii 
sulphide which imparts to them its taste unit odour A enii^nit'iiibit* 

1 M now ami H^hhmcit, 7lli lntrr t fVm;. Apidird I'lirm,,, llt<i!l N*rtt>ii \ lt j, iS!, 

a Sohluncit, /. /%.simlr t /ii'i, IIII4, ii Iliii* ; !<<!'r ,ti/j-r. ,1, .svi.. PJ|H. } $j, 46, i'.'i, 

8 Namely tiw Sttrittoga Spring*. Mit*rtMmti Wliiifi'iii^rr, ./, li^f, #/. i^-w., HM4. 
6, 52. 

4 da ftfwia, Anal, f'i^ Qttim,* IIHIK, 6, 1*4*2, 

& Wright ami HHw% J. /*/ipinil C7irwi h!7, 2!,VJA; $!*'% /*Ai7ii*i>iir .1 .SVi,, l!H7 
[A], 13, 2, 309. 

tt Thtrki*tHM<m, Memoir dr f /Irml. {fat/tile tb# SVtM<*r.4 r| #!*>: /,r|irr /* ttonnnttrk t 
Caprnfiwjue, 1910. |7j, 8, IH2. " ' i^niint, A'mrim.. l!l|i |H|, t. i,. -IV, 

M Wright and H<MIKS /<, fil. *!, 

SH% fur example, Ixwwl (I'tmtjit. rr</,. t!H!* 16^, 7'h U!IM *i\* tl H |i |S gntui 
of (HriKulvt^ci rtuiium JHT litre iw tin* tiunn \.ilm* f*r tUyt4n ,j*mu 

10 I^|tnp<% he. cit. By fhii tteeimttn tf the lUitmiM^ rnt^*n"^ in Jtrr,J'i MI HU. 
ii u <.urit " IH deliiied IIM the quimttty of eituitmtitat in *f|tuitlntittt wtiti nr |j"riii i*l tiwlttiiii, 
A miUimicrocurie- IM cute thouHtmd-ttuUtotifh if u 'ti*. 1111*! ttttu erMit*iMl * ! M * >*rii 
f radium. 



number of these springs occur in the British Isles, perhaps the best 
known being (hose at I [arrogate (Yorks), The Leper's Well (l)insciale, 
Durham), Lisdoonvarna (Clare, Ireland), Llandrindod Wells (Wales), 
Llanwrtyd (Wales ), Moffat. (I himfries ), Peebles, and Stmthpeffcr 
(Ross). Such waters have frequently been used in bygone years for 
secret correspondence. Letters written with a, solution of lead acetate 
become legible when dipped, for example, in II arrogate water. 1 

C). Lithlated waters arc in high pharmaceutical repute, the lithium 
being usually present as chloride. Baden-Baden (Germany) and 
Kissingen (Bavaria) are two well-known resorts of this type. 

7. Arsenical, and H. Brommrdtcd (Woodhall, Lincolnshire) waters 
contain small quantities of arsenic and bromine: (as an alkali bromide) 

9. Goitrigenic. Certain waters are particularly liable to cause 
abnormal activity of the thyroid gland, resulting in the enlargement 
known as goitre or Derbyshire neck, This is usually attributed to 
the presence in the water of organic matter, possibly a protozoon, but 
the suggestion has also been made that a connection may exist between 
radioactivity and ^oitrigenie properties of certain springs. 2 

The following analyses of various well-known spring and spa waters 
are characteristic, : 


Density at 25-8" 

25-8" C. 

Calcium bi(*arbonatc 
Barinm sulphate 
Potassium ,, 

hidM PIT 100,000. 

UraiiiH |Kr (jullon. 4 

20-01 4 








































t wee 








Sodium nitratt* 
Calcium fluoride 
Sodium chloride 
Anunouiuni ,, 
Magnesium ,, 
Silicic acid 
Lit Ilium 
Phosphoric* acid 
Organic matter 
Free carbon dioxide 

1 Hoa (Jhcmical tiatrchifim, Ptirkm (Ixmdon, I Hit)), p, 255. 
1 H^pin, Compt. rend., H)8, 147, 387. 

3 Threah, Thr Kxttmiwttwn of Water* and Water tiupplie* (Churchill, 1913), p. 341. 

4 Thctie figures uw (l)tainiui by multiplying thtmo in the prt.wiU8 column by 0-70. 





Analyses of Cheltenham Spa Waters by Thorp,- K ,iv.- th,- following 
results : 

No. I. 1 
Cheltenham Magnesia Water. 

Sodium chloride 
Sodium bromide 
Sodium iodide 
Sodium sulphate 
Sodium silicate 
Potassium sulphate 
Lithium chloride 
Calcium carbonate . 
Calcium sulphate . 
Magnesium sulphate 
Manganous carbonate 
Ferrous carbonate . 
Aluminium phosphate 
Ammonium nitrate 
Organic matter 


per (Sal. 

. 27-980 

. 0-015 


. 60-893 


. 4-779 


. 36-372 

. 63-460 

. 117-659 

. 0-023 

. 0-038 

, 0-0 JI 

. 0-0 IB 


No. 2. 

No. J. 

Cheltenham Alkaline Water. . Ttu- ^^ 

Sodium chloride 
Sodium bromide 
Sodium iodide 
Sodium Hnlphate 
Sodium Hiiicate 
Sodium bicarbonate 
PotiiBHium milphate 
Litbiiun rhloride , 
Caioium carbonate . 
Calcium phoHphate , 
Magntwum carbonate 
ManganouH cnrbonate 
FtvrrouH Carbonate 
Ahnnininin pb<ts|ihate 
Amnunuuni bhuirbontite 
Orgiuiic mutter 

<Jr.iin . 

JK r <Ial. 

, trr *7 


f ni< i* 


f Tilt'l* 

In Xiit 

Siuiiffii i 



u J* 1 

* hi ' 

iJ, *i. 

f VM.*I ni i 



Droitwich brine contains : 

Sodium chloride .... *JJ*-WW {** *'*ut. 

Sodium sulphate* . * (KWO 

Calcium sulphate: . , . 0'HH7' 

Calcium carbonate . , * (>'(>52 

Magnesium carbonate . . O'llf* 

With traces of alkali bromides and iodidrs, p!usjihjitrs ul 
and iron, and silica." 

The II arrogate Minmil IfVi/rnv, 3 

Since the discovery of the Tewit \Yell by Caiptaiit Slin^by in ISTI, 
the mineral waters of Harrogute have attrueted ronsidt-rublr attnttiun; 
about eighty springs are known, differing in type and quality. Tttrw 
may be divided into two main groups namely* Knlphutif uiitl rltiilyltmtr 

The principal sulphur wells occur about n wile on rithrr siilt* *f 
Harlow Hill, the highest point of the distritt. 

Opinions differ as to whether the witters have u cotttiituit urigitt, ir 
each spring has its own independent stnirc*e, Tbf difJVrrttrr nf lr\rl 
of adjacent wells favours the Iatt<T view, whilst, tin* 
indicate that they are neither superficial nor ooiw fruiii 
depths. Most probably each spring has its own indt*|u*ftdr(tt 
with which it is connected by u separate and distinct Htatmrt 
by the alternating series of impervious and porous strain which 'wm-e.t 
Harrogate with the hilly regions to the west, for it in only from Mirh si 
source as this that a large body of water could How year aft IT yt-nt, witli 

1 To convert these into parte por 100,000 divitta ly 07(J. 

2 See Worth, The Tourist's QuitU to W'or(!wiirA*r/(Stiwifiirl 

3 Lowson, Analyst, 1921, 46, 125. 






iJ S 




jaj ^ 

o - O CD 

erf Cl " CO ' ''>0 * ' 

r-t Cl O O C'l l- 

ci r- 

O O <V 0? 

o co -H o o . o era . . . 'V o c 
o c- o 10 g . "-5 co . . .gg'* 

'9 2 

rH l,O r-4 O "*- -H CO 

>S Cl 1-^ CO g * *~> O 

rH Cl O O -M M CO 

*> *- CO rH 4^ CO i4 

S t- o> 2? s f2 o S 8 ^ 

rH O CO Cl |3 -5 4< iM ,jj rH 

Cl &> a) 

O O TO CD O f > 

o < *7 o SB ^i -< ci ca ffo 

ob 19 

JO 00 


^ H/t i 4< i -.5 10 jj w 

^^ -^ 

Cl CO 00 

! t< O ^ O t * -D 
70 $0 

* era -^ 3 -< MI r 

i O O . O i 


CO *i< 


tO CO O -< O Cl O 

A " " cb do 

f w ;U 

! - -^ a 1 s a a ? &* 









; i .. >i ^ ^ .^ , ^ A . / 

S 2 
3 5 






* t * ", 
-j ; * : i * * ' * 





such slight alteration both in quality and quantity. The chemical 
impregnation of the water appears to be effected during its passage 
through these strata, and it is from this source that the bases of all the 
salts are derived. 

The analyses are given by Lowson (pp. 211-212). 

As mentioned before, a century ago secret correspondence was often 
carried on by means of llarrogate water. 

Trcjriw Springs. 

These are situate* in the valley of the Con way (Carnarvon), and may 
be classed either as ferruginous or sulphutie springs. IlasselFs analyses l 
are as follow, expressed in grains per gallon : 

Spring No. I. 

Spring No, 11. 

Temperature* . 

48" K. (o 11 c.) 

50 F. (IOC,) 

Ferrous oxide 









Soda .... 



Lime .... 






Sulphuric acid 






Silica .... 



Total . 



The chalybeate spring of Tunbridge Wells contains the following 

constituents : a 

FartH per 100,000. 

Sulphate of lime 
Carbonate of lime . 

magnesia . 
Potassium chloride 

Sodium chloride 
Carbonate of iron 

manganese . 
Silica ..... 
Organic, matter 
Free carbon dioxide 


60-85 c.c. per litre. 

The relative richness of these waters in dissolved solids is easily 
recognised when it is realised that, a lake water of high purity such as 
that of Loch Katrine may total only 3 parts of solid matter per 1 00,000, 

J Sec Clitmitf and Mttth of Wwii liritain ami Ireland (Maomiiian, 1902), vol. ii., p. 327. 
2 J. TUommm, J. t'htm. j&foc., UiiS, xo, *2%3, 



2, Well Water. As a general rule, a writ drains it volume of earth 
much the shape of an inverted eone, the apex of whieh is the bottom of 
the well, whilst the base lies at the well's mouth and eover* a eireular 
area, of radius equal to tour times the depth tif the well. These state- 
lueuts are only approximately eorreet, tor the porosity of the soil, and 
the extent to whieh the well is used, exert an apprreiable intluenee. A 
well is considered shallow if 50 feet or less in depth. A deep well should 
be 100 feet or more. Shallow wells are open to suspieion owing to the 
relative ease with whieh surfaee water run tind entry. The top of the 
well is usually proteeted by u ring of masonry It* prevent surfare water 
from draining into the well without being filtered by soaking through the 

For temporary supplies, Abyssinian Tube wells are useful, eonsisting 
of iron tubes, perforated below, whirls are drhen into the ground* a 
pump being attached to the top. For domes! ie purposes, however, 
shallow well water is open to grave suspieion in this ruiiiitry, 

Deep wells still yield very valuable supplies of drinking witter, 
whieh has hud a proportionately better chanee of undergoing thorough 
filtration than that eolleeting in shalUm urlls. The ne\\ \v-!Is at 
Watford (Herts) are driven deep down into the chalk and yield an 
abundant supply of good water. 

Chalk dors not mressurily yield good \vatt.-r, btv\i-vei\ for, being 
soluble, fissures are frequently formed through \\hteh the uatrr ptiurs 
without being properly liiteretl, Thi* harilttess varies ; lite total 
dissolved solids average U) per 1 00,1100 of water, 

(Flirts per ! 00,000 ).' 


Canx, . 

C'aS<>' 4 . 



Na a rt) a '. 

NaCl " 4 ! ! 
NaN0 3 . 

SiO a> etc* 



Total . 






I -I 
Ml- 4 




I Pi 

wells have been known froiii vt*ry early tiiurs, having brrn 
used by the Arabs, Chinm*, and ot'lter tinctetif priiples, fhuUMtiuU of 
years ago. They are made by drilling thmtigh a Imrd, tniprr 
slratuni into a porous rock below, which ntny trqttire up to 23 |>rr 

WATKK, 215 

of its water to saturate it. Large stores of water may thus be held 
in the rock. The waters may rise* up through the bore-hole on account 
of hydrostatic pressure, or through the pressure exerted by imprisoned 
gases or the rock above. In any east 1 the waters have travelled some 
distance underground, and arc thus more likely to be pure and wholesome. 
Where the natural How is maintained without resort to pumping, the 
wells are known as "" boiling wells.' 1 

The state 1 of purity of well water must depend very largely upon the. 
nature of the rocks and soil through which it has flowed. Waters from 
granite and gneissie districts are usually very pure, soft, and palatable. 
Their organic content is low. Silurian rocks slate, shale, and sand- 
stone are also good, containing but little organic! matter, although 
their saline content may be slightly higher. The salts, however, arc 
generally innocuous, having been washed out of the rocks. Limestone 
rocks yield (dear, hard water, whilst Devonian and Permian sandstones, 
and millstone grit yield clear waters, but of variable hardness. 

#. Upland surface water may be very good, provided the sources 
are free from habitation. Vegetable organic matter is present, some- 
times in large quantity, so much so that the water may possess a, decided 
yellowish-brown tint. Animal matter will be absent, so that the. 
nitrogen content should be lo\v, any ammonia, nitrates, or nitrites 
present being in such amounts as art* contained in rain water. Chlorides 
are low and, unless the soil is calcareous, the* water is soft. 

I. Rain Water. Most countries are dependent, either directly 
or indirectly, upon rain for their water supplies. 

The average annual rainfall of t he earth is estimated at approximately 
tf.'J inches, and is equivalent to a volume of 200,000 cubic miles. 

The total annual rainfall on f/ie land of our planet is estimated l at 
21),3i'7- 1 cubic miles, and of (his quantity <i52-l cubic* miles, or approxi- 
mately one-fifth, drains off into the sea through rivers and streams, 
A cubic mile of river water weighs approximately 4200 million tons, 
and contains on the average some '1-20,000 tons of dissolved material. 
Each year, therefore*, some 27*15 million tons of dissolved matter find 
their way into the seas, irrespective of the enormous quantities carried 
down in suspension, or washed into the sea by purely mechanical force.* 2 
It is interesting to note that 

I inch of rain .--MJ7 gallons per square yard. 
. 22,01.7 gallons per acre*. 
::...; 101 tons per at* re, 

It has been calculated that, the rain falling on the land is apportioned 

as follows : 

25 per cent, of land surface receives <12 inches. 




Considering only the land which is drained by rivers into the sea, it 
is calculated that only MO per oeuL of the water returns to the sea in 
this way, the remaining 70 per cent, being removed by evaporation. 

1 Murray, *SV<if/wA (M. May.* IHH7, 3, <jr>. 

2 <.ttarkts timilfaoriMn Miwll. (ML, 1010, 56, No, 5. 


The distribution of rain, howexer, varies ennrutuusly even 
comparatively small areas. Thus, tor example, whilst at Shoehuryaess 
in 1005 the fall was only 1-1 iwhes, at the Sty** in Cumberland in HJOJ* it 
was 22JI inehes. 

hi some parts of Seotlaiul ami in th' iitirth of Kn^Iaiul some t or 7 
inches of ruin have heen known to fail in twenty four hours. During 
the so-called *' cloud-burst " at I.outh in l.mettlnsluiv, tit May l!>20, 
4-7 inches fell in two and a half hours ; but .sueh deludes in the British 
Isles an* exceptional. 

(All data are expressed in inehr 


s pi-r auimui.) 

Bar UK tuple 

Buxtcm . 
Carlisle , 
Claeton . 
Durham . 

117*1 1 ; (mnwirh 
ao-17 Harrogutr 

w>m Hull 
aa-sa j Kew 

27*4<> Lineoln . 
41HH* Liverpool 



Nonvirh , 




*!fii . ittthatns!ed . 21> 

"is . St, hednartis ., 28' 

72 Sahshnry . .12' 

IJ> S**nrborongij , 2t5' 

r.o Shr tii. id ' . :w- 

"flit Milt-Ids . , 2i- 

'ti7 Shut lnir\ in s , III 1 

'12 Smithprt , *I2' 


\\ * IN 21 

\ iirk 



41*74 j Llitnduditti 


Dundee . 
Fort William 




Glasgow . 

years) * 

''72 j t,iil!i . 
; SlnrntAVaV 

I " 

;-t j 

Armagh . . a 1*82 
Belfast . aa- 

Dublin (City) . 27*H4 


(LO.M.) 42-JW 

Guernsey . 30-71. 


Dublin (I*h<rnix 
Park) . , 2H'< 

Killurncy 51*: 


: Kiikeituy 
;i i Watrrfurd 

Seilly Is.. 

:J2 , Veliflitir 


(I.CMV.) 2 

1 Avcra^o for tho thirty-tivn yt* 
/wrfs, UlUi, vol. xxx, pp. 25O H #*' 

a Average for the kt lifty ytr, 

, IH7 to IlHft, 

Krni 7'Af ,llrlrff.i%iVuI 
, 1H2I, xo8 :u7. 

WATER. 217 

These amounts appear small when compared with some foreign falls. 

Cherra Punji, Assam, India . . (>1<) inches. 1 

Coimbra, Portugal .... 2iM< 

Belize, Honduras .... 153 

G luula loupe Matonba, \V. Indies . . 285 ,, 

S. Luis de Maranhao, Bra/jl . . 27( 

The world's record rainfall is -ll inches, which fell at Suva, Fiji, on 
8th August 1900, in about thirteen hours thai; is, at the rate of some 
3 inches per hour. 

The rain water that falls in country districts is highly aerated, soft, 
and wholesome. It usually contains 25 c.c. dissolved gases per litre, 

namely : 

c c. 

Oxygen . . . 8-5 
Nitrogen . . . UrO 
Carbon dioxide . . 0-5 

Both the quantity and relative proportions of these gases vary, not 
merely with the district, but also with the temperature, This is evident 
from the following table, hi which are given the figures obtained by 
Bunsen 2 about JH55, expressed as percentages of the total gas dissolved : 

Temperature I 1 . . 5 10 15 20 

Oxygen . . 03-20 <>;N*5 <;i-49 (>*'H2 (>;H>9 

Nitrogen . . 33-88 33-1)7 3-H)5 34-12 3I--17 

Carbon dioxide . 2-i>2 2-08 2-40 2-2(J 2-U 

Nitrogen compounds arc also usually present in rain water in the 
form of ammonia, nitrites, and nitrates, the two latter particularly 
during and after a thunderstorm owing to the combination of oxygen 
and nitrogen induced by the lightning and electric disturbances generally. 

Rain falling in inhabited areas is eon laminated with products of 
combustion, in consequence of domestic tires, either alone as, for example, 
at Malvern in Worcestershire, or in addition to industrial furnaces, as 
at Shetlield and Manchester. In normal times industrial smoke is 
fairly constant in quantity all the year round, whilst domestic? smoke 
varies largely with the weather, being greater in winter Hum in summer. 
The following results (p. 218) are interesting its showing the enormous 
effect of industrial smoke upon the composition of rain. 3 The data are 
expressed in metric- tons per square kilometre the unit chosen by the 
London Committee on Atmospheric Pollution but can be converted 
into tons per square mile by multiplying by 2*55. 

As is emphasised in the Report, however, the 4 foregoing data do not 
indicate the uctitai extent of atmospheric pollution. When curves arc 
drawn showing the monthly variations in rainfall and pollution, the 
periods of maximum pollution arc seen to coincide with those of 
maximum rainfall. For strictly comparative results, therefore,, rain 

1 \i\ iHtjI thu rainfall wiw H05 int'ht'H, nn ftwr than 1MW inchcM fulling iu July. Stso 
CulcM-Kinch, H'tf/rr, it* Ofiyin ttntl lUr (London, H)OH). 

* Hmmcn, An/wh-n, 1K5A, 93, 4H, Sw iilno Haum<*rt, iVnW., 185,'*, 88, 17; J'ottvrHHuu 
and Sunilin, .//rr., IHHU, 22, M3U. 

3 Tukou front th* IfcjHtrtttftht' Inwtitit/titwnuf Atnwitiitwrir- l*ulltttwn t 11)14- 'U)lfl t drawn 
up by Wynne und pn^rnivti t* thw Uualth Cunimittou uf Shutlivlil City (Juuueil 



should fall at a uniform rate, atul should euntinue rither all tiny or at 
the same period of eaeh date, Thrv eundttions, bt\\t-\ t-r, aiv not 
attainable in nature. Tin* tables do, howi-viT, tfi\f a elrar idea of the 
nature and quantity of thr siihstaiuvs aetually brought do\\n by the 
rain over a jjiven period. 

TO 30th APRIL 1*115. 


(I'll- 1 

Attereliffe . 
West on Park 
Aneoats Hos- 
Fallowiield . 


5-8< His o-si; ot;> 

LrlO 2tf'0l 7.VI t H ;| ri-7*i 
10-02 22- IS 41-50 !>-;u 2-77 

' II i 

Of"U Jtriia I '.it; o-:*o 
48'2I lu-rti 2 ;m o-iti 

An intcrt'stin^ coutrihutiou to this sfthjrrt r% affontrti by LuH^i 
who collc<*icd rain \vat.rr in ShrllirM in ilHt dnrni^ a sh\\i r of" Ihnv 
hours" duration. Thr tliflVrt'nt samiilrs \vrrr taki-u at tliffi-iTut points 
within an area, of half a square itttlt.% and an* sn-n to rxhthit a most 
muarkablr variatti>n in compomtton. 

(tuHtm. j t*itit. 








8* 08*10 

0- 1 1 5 1 









it IHI;! 

0-017 1 

II 02 M) 

No. 8 represents rain -dripping from the fttimgr of n trn% 
Another huiustrial area is that of Leech*. wht*n%" on the uverajyje 
working duy, 20 tons of soot, are sent into the iiir, til* whirl* half a ton 
fails on an area of I square miles, and nf thr luttrr fntn 20 Ib. fn 25 Ib. 
stick, that is, arc- not removable by rain. 

. Inn Nlrrl / W( ^, ( ||i| j t i, 4 147, 
8 Hw Utl*n itiid Kuutuft, A'uliirr, tlMI! t 8 1, -liW, 



The results of analyses of rain water from ten representative stations 
in the city, and, for the sake of comparison, one from Garlbrth, nearly 
cS miles due east of the city, and situated in the country, are given 
herewith : 

(Total lor Year, expressed in Founds per Acre.) 






^t fcj 


s &4 

T< , 


-4 "o 2 


Collecting Station. 

C & 


M W 







I"| I 

cd tj(> 

3 s 

i ^ 

c< ^ 

"*"< ^**< 





*2 ^ 

*3 S S 

fc ( ^ 


-J5 5 






1. U'cds Korp'. . 



1 lilt 


1 u:j 







2. Htmslct . 

1 5(>f> 










3. Bcc.stou Hill . 


i it) 









4. Philosophical 

Hull (Town) 












f. HrudinjjlVy 












IK Armley - 












7. Olwervntnry . 












8. Kirkxtall 












9. WcH wood Law* 












10. Houndlmy 











11. (Urforth* 




(h r > 







joules, rain from the se t is frequently highly charged with 
sodium chloride. It is rec'orded l from East Kent Unit, during tlie winter 
of 1010, a. very heavy pile from the south-east with a deluge of rain 
occurred in the night ; on the following day all the windows which 
faced south-east had quite a frosted appearance when dry. Some of the 
substance scraped off and dissolved in distilled water was proved to 
consist of common salt- 
Soot, which finds its way into the* atmosphere, is usually rich in 
sulphur compounds, as the following analyses indicate : 2 

Dining-room chimney 

Kitchen chimney 

-M * 


Sulphur an SO,, 
Par tuml. 

A shower, therefore, which brings to earth the soot floating in the air 
must be proportionately contaminated. 

The amounts of dissolved compounds of nitrogen, chlorine, arid 

1 \<itun\ 10H, 87, *2a7 ; from /<V;wrf.v and Trunfittctwn* of the float Kent Scientific and 
Natural History tiocit'ty, muling 3l)th fcktpt. It) 10. 

3 Ltmgmuir, /or. eii. 

220 OXYOKN. 

sulphur in rain water collected from various parts of the work! during 
the present century are given in the following: table, A pressed as parts 
per million : 


i nit*-. 

, tt 


A- NH,. XtirL-t 

Pretoria. l . 

1 IIHIi $ : wl'Hi 

Mill ; iMltil : ' 

Barbados a . 

I turn : Hl'iis 

ti'i,i:'fj o-as$ s-Mh 

Dehra Dim 5 

: I!HH 3 H7-ia 

o-i in <H7o 

Cawnpore 5 

: !WH 5 ' IIHiH 

tJ-lTUO it iltl** 

Lincoln (NY/.)* - 

,; IIRI7 8 : , IM'IH 

41' 1741 ! 1-^M,H ; tM 

> * 

i UM)K !! ; IW'lt 

fHfft-l iMIT . 5-3 

Hebrides 8 . 

i 1II0H IU ' ail '7 11 

ii-WII ii'tiML 1 

Iceland & 

! t!it t'J IIH'III 

ii'llfll , : O-UItO 

Grahamstown a . 

j till! i^. ^$^17 

0-171 O-KW -M*ii 

Blocmfontcin tl 

! HitCI !! \ J7sS*2 

0-J*N'J! il'lMH t'Oti 

i* * 

I Hilt tU l^'4! 

MI;H*| O'U-HS IMili 

Durban tt * 

j Hi!! :!! 

tl-fl.Hl ti'l^lt !MI!I 

i> * 

i 1*112 ni-0? 

tr^ii 0-17H 10-U! 

Cedara (Natal) fl , 

; uuo-i*Jts ^ti'tiH 

i ; 

. 0.7WI . iia ^tiH 

S() a , ! 



Seasonal ilnctnations ari* also t>li.srrve*l in the eoiwtttiirnt* of runt 
water. Thus sunnner rain is not suturutril with oxygen, atthcat^h that 
whieli fulls during ilie rest of the yrnr is praetieniiy HU. T As a jjrnrrai 
rule, rain water in nearly haturnted with \y#ru whrii iK trtiipfruture, 
us collected, Is below 15" C* n but when above (his point the dtssolvetl 
oxygen is ulwuys below* saturation, sometime* a* mtteh u* %3 prr eent. 
(see table below}. The rt^tson for this is not apparent. The tvlutive 
temperatures of the raineloiulH and uf the nir lit the ground tevrl in 
sunnner and winter, if they have any wlhteure iii all, siumld prtnlwe a 
result exactly opposite t-ti tlmt fotmd. lit other words, our wtnttd expect 
summer rain to be tupcrsutttrated. 

Results of numerous expt*rittients t the Huthuiustrd KxpenmentuI 
Station (HcrtfordKiure) indicate that ntin water is richer m chlorine 
but poorer in atnmontacul and nitrate nitrogen in winter tliiin in summer. 

This Is shown by the following table* * (p. li'JIt). 

As a rule the amount of nitrate nitrogen is nppruxtmntrly ftiitl" that 
of the uinmoniacul. The ummontu iipprnrii to iirise from several 
sources. The sen, the soil* niul the ntmoHplu*ric puUtstiuft ciKset|m*nt 
upon inhabited nrww nmy nil cumin butt*. Tlmt f lie soil is an important 

1 lngk% Tranttwil , 

51 UovoH, Iteiwt Agrie. Wnrk ItorbtMtot : lw, fat*. Avrir, IIV^I 

Ohem, JSnc. A fair., Wi^ . f 01M 

8 leather, /!. /fr|w^rl /;/*. M-/J|. .ij/nV,, I1NI4 t!M.i\ ji. ||i 
4 Uray, Cttnttrhury Agrir. t.'ttll. Mmj* A'rii^riilnnil, tlitti, 34, 
* MiU*r t /. *S'w/. Mrhm, ,S'MT,, IfHJtl 16 Ml, 
fi JuriU, *V. Afrmtn, J. SVi., I!H4 io f 170. 

mrtiM, /. /If/riV, Atei., I|ll? t 8, jmrt 3 j. 331, 
ell asui iticimrtlti, i6ir/. r llllll, 9, |irt 4, 3W, 



factor is suggested by the fact that the ammonia content of rain water is 
high during periods of great, hioehemienl activity in the soil, and low 
during periods of less vigorous biochemical activity. The close relation- 
ship between the amounts of anunoniacai and nitrate nitrogen indicates 
either the oxidation of ammonia, or a common origin for the two; 
conceivably both. 

(H pw Million. 

Nov.-]Vb. May -Aug. 

Ammoniaeal nil ro<jfen 
Nitrate nitrogen 
Dissolved oxygen 


I 1-2 



Lb. po 

r Acre. 

Nov. -Fob. 

May -Aug. 









It is on account of its softness and aeration that rain water is par- 
ticularly corrosive in its action on metals, and, if it is to be used for 
domestic purposes, great care must be exercised in its collection and 
storage. Iron tanks are reacnly corroded, and lead is dissolved. Stone 
or concrete 1 tanks may be used. 

5. River Water. The composition of river water is largely 
dependent upon the- nature of the soil through which both it and its 
tributaries How. Originating, perhaps, in a little spring of relatively 
pure water issuing from granitic or schistose* rock, it may pass through 
a mountainous district, gradually swelling in size as it absorbs the 
waters of other pure springs and streamlets, until it reaches the fertile 
plains below. Here it takes up large quantities of soluble matter both 
directly and through its tributaries, and finally discharges its burden 
into another river, into a lake, or direct into the sea itself. 

An excellent; illustration of this is the Cache la Poudre River in 
Colorado, which passes through country analogous to that described 
above and ultimately discharges into the River IMattc. Three analyses 
of the waters arc given l on p. 222 in which the dissolved substances are 
expressed as grains per imperial gallon, one taken near its mouth some 
three miles below (Jreeley, the second two miles above, (Jreelcy, and the 
third nearer its source* (above the north fork). The enormous increase 
in the* amount of dissolved solids as the river leaves the granite for the 
plains is noteworthy; rising from iNf to III grains per gallon above 

Whilst the absolute* amount of dissolved material carried to the sea 
will gradually increase from the source to the* mouth, the actual con- 
centration, as expressed in grains per gallon, may fall as the river 
increase's in bulk through dilution by purer tributaries. During times 
of Hood, too, the proportion of salts may differ very considerably from 
the normal, and the composition of the water near the mouth of a river 
may give a clear indication of the particular area in which the excessive 
rainfall or flooding has occurred. 
1 Clarke, 4 * Tim Data of UnochrmiHtry," U.M. Oeol Murvcy, BuMin 610, 3rd wi., 1910. 




(K\prvssrti a% L'raius JUT Cation.) 

Xmr l. S., lt ,v,v ''"" Mli 7 vl "' v " 'i'lv,- M,!,', U-Uv 

*ivrlry. <rtvh'V. 

CaO . . . j o-ri&iK is-i;iN ivos? 

MgC) , . . j 0-1^7 '- llHiMl ;,.*!> 

Nil/) . , . j ,U75O ^ tl-;*!iO !H17 

K a () . . . i oos">;> II- 1^1 -0-M72 j 

(AI, Kr) u O ;l , . j CHtm 0-07t> ' IMW'J i 

Mn.jO :i . . . i o-uoi.s tnin- II-CITH | 

SO,, , . . ; o-itMti 5$-*J7 :M>-ii7 1 ; 

J , *M t j 

( U . . . \ U'Hi:!7 2'77il 2-t fa j 

Total . , i :HJU!Mi JHMtlll fM"SI2 ! 

The following analyst's art- n'jwsftitathv t*|* thf data tihtaiitahir 
from the examination of tnrgt* rivfi-s : 


(Parts jirr KHMMM), 1 

t'hluriii^ , , , , MI ttr^nnir ttitrM^t-n 

Nitnigon IIH uitrat* nni nitrit** , 
Tntul coinlniiiui iutr>i{4ti 

(Parts pi'f II 

, IM1-HI X (as tiitnttr) . CM 1C! 

-i'HUO X (as liitritf) . ii-iitHiH 

<' S( >4 - - - I -750 ! CO., . . . iKfftfj 

NaC'l-f K(1 . , IMIHO i XII, (fi 
"^ . . . I.JH Nil,, 1 :| 

1 Hicluttl, Water and it* I*itrijlrtttittn (<*rtmby I^4i4'-i^I, |HU7| 
* R. M(rgan, (.'ktm* Neum t lll^l, iaj 111, K '' 



(Kxpressed as parts per 1 00,000.)* 


Calcium carbonate 
Magnesium ,, 
Calcium sulphate 
Sodium ,, 
Potassium ,, 
Calcium chloride 
Sodium ,, 
Sodium nitrate , 
Potassium ,, 
Iron oxide 
Alumina . 
Organic matter . 

Total solids 
(L Lake waters 

ThatWH <>J 






Danube 11 








1 -47 












I -00 






. . 

. . 



1 -20 



. , 






< 0-25 






\^l -88 










much of their solid material from the rivers 

feeding them. If the lake has an exit, in the form of a river or scries 

(Per cent, by weight.) 

.Kriodinann, 11 191^, 

Htutar and 

<J(uth,* 1857. 

Roioh, 6 1907. 

At HO em. 

At BOO cm. 






1 -5208 


NnCl . 





NuHr . 

* . 

. . 



CaiCl., . 










MgBrl . 

0-53 I- 


. . 

CaSO,* . 





CaC*() n 





Fc t Oj . 




tra<J( k 

Organic malt er 




Total solids . 







""*~ 1-1540 



at 17-5" C, 

at 17*5 l! C^. 

at 15 C. 

at 15 C. 

1 Kti k Knginwriny Che wintry, hy Phillijm (Crby LoekwcuxU 1894), numerous 
analywm ara givon. * a Iti!i*al, Water and it* /'nrijicaiion (f Vosby I.ookwood, 1897). 

:i * Hi-vcral othor itn.n!yH an* givon hy W*lfhau<T, Monttttth, 9 1883, 4, 417. 

4 QuoU'd by Slut '/.or* and Koich, ('hem. ZnL, 1907, 31, 845. 

6 Sc* Htut'/fr and Hoi<*h /or, cit. 

n Kritvitnann. i/;iW. HU2 f 36, 147. Stni alno KrenoniuH, Verh. (Jet. Dmt. Naturforftch. 
Aerztt*, 191IJ; p. 118. 

224 OXY<!KX. 

of rivers and streams, a natural balance, subject to minor Hurt tuitions, 
will be maintained between fit*' entering waters and those Inning fur 
thf sea, and the mean composition of tin- hiit* waters will nut he \ t -ty 
different from that of the enterin;: waters. Hut if the lake is completely 
surrounded hy high ground, entirely without channels through which 
the wat IT ran escape in a normal manner, the eserss ol" water must he 
expelled through percolation and evaporation, particularly thr latttT in 
hot climates. The result is that the lake becomes increasingly saline, 
ami saturation may, in course of a*!cs, Iir reached, and flu* excess 
salts deposited. Such, tor example, is the east" with the Dead Sen in 
Palestine* which receives the waters- of the Jordan and other minor 
streams and rivulets, hut nwmtaws a fairly constant level mainly 
through evaporation. 

It will he observed that in the results .t.ftvtii hy Fiirtlmattn the water 
is slightly more dense at the Itmet depths (JHtO rm.) than at 5O rnu 
The waters feeding the Head Sea are mainly hv\h antl, bun?.* much less 
dense, tend ft* remain in the surface layers, diffusion takuu? place 
relatively slowly. No doubt this accounts for iuan\ of the variations 
observed in the densitii's of the waters of inland lakes antl seas as 
deterntitU'd hy different invrst^ators \\ho hn\t- not usitally stated the 
pn*cisc <lt*pth at which their samples were taken. This phenomenon 
is very marked in the* cast* of ci-rtaiu tidal rt\ers aut lias lon^ been 
known. Mallet for example, in l*slfMltvw iilti'iilmii It* it m eottuet*tiou 
with the* River Hann in N, Ireluiid* 1 

7. Sea Water. The .sen may be regarded as nn enormous lake, fed 
by most of the rivers of the world, and itself without att\ means of 
discharging its excess water except through evaporation. Mention Juts 
alr<*ady been tnacle of the fact that the world's risers an* cuntmualty 
pouring enormous quantities of dissohrtl salts into ttt- sca cstunated at 
about, 27*15 millioit tons per uunum, with the result that the sea is 
becoming increasingly sulint*. This is prrilwilily not thf only factor 
affecting the composition of NCJI water. Another ties in the fact that 
the sea is continually encroaching on the laml in MJ$U- ihsirtets mid 
receding in others. Thus, oti lite Kast Vorkshin* euast, suiilh *f Ilrid- 
lington, near Kilnsen, it is eroding the btnikler rlny ait ntt nveni||e rate of 
7 feet per year. Hut for every square mile washed amity un the Virkshirc 
const, H scjnitr<* miles Iiave been ^aiiit-il in the Unmlirr untl thr Wash ; ;! 
but of course the composition of the new suit in diffiiTtil, mid the differ* 
cnee reprcKents the .solvent action of the srn. This type of change, 
taking pla<*e coutinxunisly all over the globe, i** 4 thereforr, n seetiml 

No doubt there are others, some* being of a compensatory nature. 
Such, for example, is the elimitnttinn of eideiiim carbonate as corah 
chalk, etc*., through biological agencies. 

The changes in composition of the water, hmvevu% on aeeouut of its 
vast bulk, are so minute that analysis is quite unable to detect tftcw. 
It has bee!! estimated 9 that 08<UM>o years would be required for the 
rivers of the world to discharge at their present rate suiUeinit calcium 
salts into the sea to double* the existing amount. 

The most abundant dissolved .substances in uca-watcr are s 

1 Maliot, ftr.jKtrt* ft,A. t I84CI, j. UiS7, 

a Avi'Iuiry, The Nn-nrry of Kngfantl fMiiriiiilliiii, l!HtL*), j. im, 
9 Murray and Irvim*. /'rrr, ttuy. V*r, AWiif., 1HMI, 17, lint. 


chloride and magnesium chloride, potassium salts and bromides also 
beintf present but in smaller quantity ; the presence of the last-named 
elass of salts is of interest been use practically the only sources of bromine 
at present are sea water and the saline deposits from dried-up seas. 

By the ,sv///////// of sea water is understood the number of grams 
of total salts in 1000 grams of the water. This may be determined 
gravimetrieally or volumet.rieally, the latter method* being the most 
usual, the chlorine being determined, and from it the total salts calcu- 
lated. This method of course implies suitable laboratory facilities, 
and if these are not available the water must be stored until such time 
as it can be tested. To obviate this dillieulty attempts have been made 
to determine salinity by electric conductivity measurements. By 
employing a standard sea water and comparing its conductivity with that 
of the unknown samples, it is claimed that, very accurate results are 
easily obtained at sea or under conditions entirely unsuitable for ordinary 
laboratory work. 1 

The analysis of Atlantic waters may be regarded as typical of large 
oceans. The Mediterranean waters are more concentrated, 2 partly 
because of the high rate of evaporation, and partly because few rivers 
How into it. Kveu more concentrated arc the waters of the Red Sea, 8 
for similar reasons. 

The water of the Baltic Sea, 2 on account of the continual influx of 
river water and its relatively limited contact, with the open ocean, is 
comparatively free from dissolved solid matter; it- contains up to 18 
parts per I (MM). An open ocean like the Atlantic contains from 32 to 
,18 parts 4 per 1000. 

An interesting comparison of the waters of the Atlantic Ocean and 
Mediterranean Sea is given by Schloesing as follows : * 


(Parts per 1000 at 20 C.) 

Calcium carbonate 

Lime (not included above) 

Sulphuric 1 acid 




Sodium oxidf 

Potassium oxide 

Total .salts per litre at 20" (V 





















1 Sec Thurns, ,/. HWmif/fow Awl. ,SV/., littl, II, UK). 

* nearly Hhown l>" the data in the tables, j. !<1. 

;< Altaian an* tfiven by Nutterer, Mt t nat*lt. t 1WM), 21, 1037 ; 1809, 20, I. 

* HchliXwinK, (fantpt. rnnt. t HH). 142, IWO. 

VOL. VII. ! L 15 

22K n\\t,K\, 

Prom thr ton ".one,, fit* i t-< *i ti. . \< Hat id ;dts in thr 
Atlantic* to that m lh M dit' n,m ,tu is u N:I*. 

Thr mran n stilt . ot .m,dv . > <*t :/! .jnj'l i w iti takrn from 
the Atlaiitir an "i\u lv M.iluu ] ,^ |M|| n\ ,r\j.n ,-. d an parts prr 
1000) : 
Sodium Hdia'idr , , NM t i , i . < ' * ^ 

Th<* watrrs uf thr Irish Sra rnjifiiiii lh- lo 
thi'in * rxprrssrtl as parts prr HHMJ ; 

a . 

Mgllr, . 

M , 

^ttfiti < f ,.ii'n,, 

!rar .\ll s l 

I* tH',* I V-l H. } 

I ;I:L* SIM, 

(1 , 
Itr . 
U) :l . 
S0 t . 

Na . 

(a ! 
K , 
Fe . 


(Parts iirr Hitlii, i 


IK-HI _ lH'!i;i 

tl'JKJ : O'^fl 


10" I*^ 




HI ,1 

io-;i7 .-:i7 is-ur* j 
o-oo:> ; o-:u ! 

"*'S*> ,*r;il 10-yii i 

Mil o-r* I'iw i 

ll-tll ; II- US II' IT i 


iH^7 ; , . i 

jK'UJt IT'llOit :i|70 ; 

Tlu* density of sea water may 1e ridi'ttiitlrd with a fair tli-grrf of 
ueeuraey by a determination of the ivfraetive itidrx,^ uliirh, for a ein* 
stunt temperature is dhvHly proportional to thr density ealetilated at 

0" V. In other words. 

1 Makin, Mtrm. A f *'i*w. 1HSW, 77, I.'Wi. 171, 

2 ThorjK* unit Morton, Trttn*. Chrm. iSW lt IM7K 24, r 
1 At CajK^ Horn. ittUru, Antuiten, IK5I. 77, !M, Hi*v 

<i(Tth t Arp*ntin(* tMust n* ffivm ly ("orti Hint Atvurry, 
6, 108, 

4 Hihrti, /r>r. nV. & At Miir^illi^t, l 

Huff* toAtmV/yrrW., 1817. 22, ^*7i. 

7 (Johr^U quotfd in Thorju^H l*irtitwttrtf(tf Aiyitirtl ('htutt/ttry f l 
J). (M>5. * Hilini* lc, nl, 

f Vnurnbourg, (W//f. rrr/,, 1921, 172* Hli:i 

i uiuilv^t *! Afiiiiilii' ttitt < r 
, .s'r, ijmm. 'lri/r/mi H*!H 

'ti^ ./, /'Airm, k JHH/*, 21, flit, 

tiM, t!Klf vJ. v., 
lrr fr*ii! intrfitrt*, 

WATRH. 227 

where //',, and u f arc* the refractive indices of sea, water and distilled 
water respectively at, / ' (', d' n and d t) their densities at 0, and K is a 
constant depending on the temperature. 


Water is produced in the oxidation of hydrogen by free or combined 
oxygen. The relative volumes of free oxygen and hydrogen at and 
TOO mm. which undergo combination arc 1 : 2-00288, or approximately 
1 : 2. Although a mixture of the two gases in those proportions, known 
as tw detonating gas/" is stable under ordinary conditions, no change 
being observable oven after prolonged periods of storage in the absence 
of light at room temperature, the interaction of the gases can be 
accelerated in various ways. 

1. Sunlight can produce a slow but appreciable combination between 
the gases, 1 the action being due to the ultra-violet rays. Ultra-violet 
radiation affects both detonating gas and water- vapour tending in each 
ease to product* an equilibrium between the vapour arid the constituent 
elements ; - wit h increase in intensity of the illumination the equilibrium 
shifts in favour of further dissociation, but the proportion of dissociated 
vapour at the position of equilibrium is very small. The process of 
combination probably proceeds by the stages : * 

II, | O, IU>,; 
lU)^ 1 III -SiH./). 

2. Radioactive* substances can induce the combination of hydrogen 
and oxygen ; the effect being possibly duo in part to a primary eon- 
version of the oxygen into o/onc, but this cannot represent, the solo 
mechanism as once more the change loads only to an equilibrium, and 
water-vapour under similar conditions becomes partially resolved into 
its elements. 4 The a-rays are most active in this respect, although it is 
possible that ft and y radiations also exert a subordinate influence. 5 A 
mixture of hydrogen and oxygen may even explode under the influence, 
of radium emanation,* 1 

The silent electric discharge appears to be* relatively inactive towards 
detonating gas. 7 

3. Rise in temperature is, in practice, the simplest process for in- 
ducing chemical action between hydrogen and oxygen. It is supposed 
by some chemists that the absence of chemical action in detonating gas 
at the* ordinary temperature in the absence of light or of radioactive 
substances is only apparent, the actual rate of combination merely 
being too small for detection by the usual methods ; with increase in 
temperature the combination is accelerated so that it becomes per- 
ceptible or even explosive. The necessary heat can be applied in 

1 linker, /W. Cln<M. Nw.. UMUJ % 1 8, 40, 

2 AwlrtVtt, /. KIM*. /'/.y.v. Chrm. *SVr,, MM 1, 43, KW2; Coohn, tier., MHO, 43, 880; 
Kornlmum, Hull, Awl. iS'n*.' Cr<tr<ni', 191 I. | A|, f>H3 ; Thirlo, Mr., 1907, 40, 4914 ; Tian, 
Cum pi. rend.. Hill, 152, lOl'J, I4KJJ. 

* DHVIH und I'M wards, ,/. S'w. ('font. ///., 1905, 24^IHJ; Lirid, ./. Amcr. T'/tr'/w. *SV!., 
1919, 41, f>:U. 

Jk Drtricrm*, Ana. /%**, MM 4, ix.. 2, 97. 

7 kirkhv.'/'Ai/. .!/'/., 1W*. II. V-^'; UK)5 9 J7L 

22H uXViIKN, 

various manners, fur example hv sudden compression, 1 \\\ ,iit electric 
spark, by a tlame, or by au incandescent solid, Tin i"mhon ft mperaturc 
in detonating ijas at which self -maintainim* eomhushon is initiated is 
variable on account of the iniluence f s-\end fjetors, hut is ^rnerally 
between 500 aiul <*OO IV Alt hoti-lt Midmanlv " div " tl-iiiii:itiinr yas 
will explode readily, a \er\ eaivfulh dud nu \tnr- , vitrft ;i-, that obtained 
by prolonged exposure to phosphorus prnti\j*ii , is much less prune to 
chemical change. A .silver wire may !* In, tint to fusion m this iras 
without causing more than local t*omhiuah*n n! hydro?*) u ami oxygen;' 1 
however* au t'lrctrit* spark will untun- tApiMMoit *jital!\ \u II m the drird 
and untlrird ijas % * prfl>ally tn artniut ! tit*- h)*.fht-r *l -j;r i '*' of hrat 
applied. (*<uihiualion ran orrur hflnw th- i';mtin t> inpri\itut*r t but 
will tlu*U in* continuous tin tin' altsrntv it t\ital\ -4 s i onl\ as !un.j as the 
tnuperat.ure is niitinhtiiied ly *-\tt-nial snurr-s !!' It. -at. 

" ' 

It is of hit ere*- 

t to not* that III pn ' lie- o! tor< r'i. " 

a a '. ha-, a eon- 

sidcrahlc inhibit it 

i* t fft et e*li thi expl*s| v j It* ' *t ^ HUXt I! 

tr ol hj lrotr rn 

and oxygen. Tl 

ir follti\\tn ir numb* r.' nim ih ult; 

nn of various 

gases required tt 

preXetit tll * Xplo't|o|i i*l M|J lit|uiil ii 

iff tni{ jas 

by an electric sj 

uirk f ire oid\ if r*ltti\ ii*d u! ot * 

tb .ultili \,dne 

because rather 

widi* di\er*; iei< m.s bf ob*,* t\*i 

wit h diffi rent 

conditions ; 

HytlrogiMi sulphide 

o-;. <wi.*. li..!u,i.- , , ii , >. 


Kthylono , 

I . ('jtrt** *!t i!t!tM%ptr .1 \ 



t : ltyili"S'i?"ii i'hln!' , 1 *,.. 


This is due probably in part to lite unripta) Jfr i t ul fit*- surtan- of tin* 
react iott vessel, 

The effect, of the walls of the containing \*-ss*-| on th- ronihination 
of hydrogen and oxygen is merely it spretal easr of ti ^mrral phenomenon 
which has already received mention (p, 7<M> Hvitr*Mt-n streaming on 
to a warm platinum spiral in air will miw thr tfmperaturr of fhr sptral 
to rednt'ss by the* bent of its combustion on fit*- ^lirtVu**- of the metal, 
and indeed may even inflame. 4 i'latintitn ure or foil will nut cause 
the ignition of detonating HUH unless previously tvarmetl to itf*M\-e Till ' C\ 
btit in a fitter state of division such as the *' spinrrr '" >r " black " 
. obtainable by decomposing ammonium e-iilnrplatutale r eiiltirplatiiite 
acid t platinum, even without previous wanning, will induce such 
vigorous combination of tin* two gases as to nttisi- an explosion. 7 Such 
finely divided platinum in a shod time lusrs its ae(i\ it v\ especially if 

1 Hw Dixon, TntHM, fitrm, SW., Illlfi, 97, 1174 ; 11*11, ||, t**;i-I, 2iail, 

9 HH' I>tX(n. /w\ </. I Fll!k ./. ,1wrf. r/**-i. iSW., Ifiltl,' ^i, iJilT ; |*flt7, a^, I^IItt; 

Mitlhirti uwl Ix* rhati'liiT. fVwi|*|, wtttl., IHW*. ! H**'i. S*-* i1'j K trr uttfi Mr\*-r, //r, 

IHlJL 1 , 25, 1>2; Mit " ' '' 

* l>ixon and HriKlHhuw, IVwr, Ht*y t ,sw., HMi7, |A| 7* i?U1, 

6 Honry, /tww. /'/n7. t IHHK. 25, 4<l'j, St-r itlmi Tttnmr. fWi. I'lul, /., I^l*4 
1825, I2 f IH I ; TurtitT uncl Pnrndfty, *-lii, /*Ai/.<, rh*-m, t JK:M, |;!|, |-|, 141.1 ; 
(}twunrtri< Mvthtxtcn. (Vii'Wt*n, IH77? ; !t*^fiitittt mul Ifri^rt, .,!, /''Aiwj. /'An*. 
|:i] t 26, 321); Brnltlt*, Zrittrh. nrumj. rAnu., HU2, jS lull; fMi*r<) an*! Hrttn|*\, 
6'Afw. iS'w., HIM. 105, IH51K 

f Dulttng mid Th^nnnl, /!. ('him., IK2H. 2|, -I-IM; 24, :!HII ; llrrisiirf, Jmt t'hii*tL 
IB8S, 1 21, 35,701. * ' ' " 

7 Urliirivr* nttti Mnrn't, Ann. ('him. /*Ai/. t |H2H, jf, :i;!M ; Jlrnri,, l*lnl, 1/**; . t *;!!!, 
6, 304 ; I H,*i 1 , 9, .T24 ; l>ft*lM*rt*im<r, A*r A ii'f%f *-?',* ./,, InVl?, t4, 1M lH'*'i -*H *| (| | ->o |Mi- 
1820, 42,0; 1831, 63. -Hiri. '* ' ".* "' 

WATER. 229 

brought into contact with certain substances such as ammonia, 
hvdrogcn sulphide, or carbon disulphide vapour. It can, however, be 
reviviiicd by moistening with nitric acid and drying at U00 C. 1 It 
ap)>cars probable that the presence of moisture, is necessary to the 
catalytic activity of finely divided platinum towards detonating gas 
at the ordinary temperature. 2 

Other metals than platinutn also can alTcet the rate of formation 
of water from gaseous hydrogen and oxygen. 3 Palladium resembles 
platinum in activity, but. many other metals are less effective, examples 
being osmium, indium, gold, and silver ; mercury appears to be without 
influence even at its boiling-point. Reduced copper, when heated 
in detonating gas, commences to oxidise near 250 (\, the oxide becoming 
vigorously reduced with incandescence at. a, somewhat higher tempera- 
ture; * copper oxide exerts a marked catalytic effect at 300" C. without 
undergoing visible reduction/* Such behaviour suggests that the 
catalytic action of the nobler metals cited above may depend on a 
primary combination with one of the constituents of the gaseous mixture 
followed by regeneration of the metal with formation of water. The 
activity of the noble metals may, however, be, at least in part, analogous 
to that possessed by all heated solid surfaces, especially porous ones, 
Tor example, pumice, glass, porcelain, carbon, although these have the, 
power only in a much less decree. In the colloidal condition platinum 7 
and palladium H accelerate the union of hydrogen and oxygen. 

The combination of hydrogen and oxygen is accompanied by the 
liberation of a large quantity of energy generally in the form of heat; 
this accounts for the vigour of the explosion of a mixture of the gases'* 

-(I'*) i l ( y -H a <) i *-ix<>MOO calories 

A calculation of the temperature produced by the combustion of 
hydrogen in oxygen or air, based on the above number and the speeiiie 
heat of the steam produced and of the nitrogen present in the case of 
air, gives a Itgurc greatly in excess of that actually observed. The 
discrepancy is due to a combination of several causes. Thus the; 
process is not instantaneous but gradual, so that there is time for loss 
of heat, radiation especially being an important, factor. The increased 
speeiiie heat of steam at such high temperatures and a somewhat 
incomplete change on account of a slight dissociation of steam at the 
temperature attained, are other factors (see p. 1*10). 

The water produced by the direct combination of hydrogen and 
oxygen frequently contains traces of hydrogen peroxide and of nitric 
aci'd. The occurrence of the former indicates the possibility that the 

" lVrw!i t'/nnt. \> 'S IlMMJ, Hi, S J! 

l l>uli awl Tht'-uui'd, /*w. n(, ; ht-innvr ami Mittvi't, !ot\ tit, ; g.ui'twowM'n, ('u)ii^L 
w</., liMM. 139, 7fi, Srr alM fln.-i :->'rii'N Vul. IN., l*arl I. 

4 riuailM'H, Amrr. t'hrm. ./,, ts*,i, 17, OKI, 

' flimuni^, CttHijit, />*/,, H)M. 159, tM. 

" SMI BrrliHiT, Ann. /Vi^ii", iHHh, j^j, 35, 7Ul. 

HIM- Knihf, Znl-'iii. /./i//^i7'/. Cltt-m., liMH t 37, -MS. 

!Hul untl iinrtnmiiu, J. }*r<tkl. ('hrw. t 11MH), So, aa?. 

Kinployiiig tho whtir <Ula f Thouwn, /^r., 1H72, 5, 7tJi) ; i873, 6, 1551); 1HK2, 
15, 2U08. Hcith (ZciUeh. Kkktruchem., li)2t), 26, a8) given 08,381) colorioB w at 18" <J. 
uiitiiT ( |t'i*wHyn'. 

230 OXYOKN, 

primary change may be a simple euupling of muleenles with formation 
of hydrogen peroxide, this compound .subsequently d-eomposiir j n i u 
the "more .stable substances, water and oxyru {eonipare p. 77); 
by continuous repetition of the proeess the UXN^'U is at last completely 
converted into water. This possibility recedes som<- continuation 
from the fuel that an equuuoleeular nuxtwv of oxygen and hydrogen 
has a lower ignition temperature than eleetrolytie detonating gas, 
although the evidence is nut final. 1 Traces of nitrogen as impurity in 
the gases used explain the frequent occurrence of small quantities of 
nitric acid in the water produced, 

4. Water may he produced by the union of hydn.jeii with combined 
oxygen, as, for example, dttring the reduction of oxides. Ad\anta^e 
has been taken oft his fact to determine gm\ ituetneally the composition 
of water, as witness Dumas' classical researches on the tonuation of 
water by the reduction of copper oxiile. 

5, Water may also be- tunned by the decomposition of a complex 
molecule containing hydrogen mid oxygfu atoms or b\ the mteraction 
of two ('otnplcx molecules. As iu\ example uf tb lormer may be 
mentioned the action of bent on a hydrox\ lated Mibstiiutv. Thus, 
sulphuric acid wlien dropped on ttt a ml -hut plate tfreomposcs to \\ati-r, 
sulphur dioxide, and oxygen. 

riSo* i*so., o, - tfll .o, 

* '-OH 
and copper hydroxide yields the anhydrous oxide 

I'tiO - 1LO. 

An illustration of the latter tvpe is afforded In tlt- mteractiun of 
sulphur dioxide aud hydrogen sulphiili* : 

so a t *2ii 3 s aii 3 o ^ as. 

OF WATIslt. 

t*n of iVtttcrJttr {' 

For aceurat.e sc*icntifu* work water must he freed from most of the 

impurities detailed above, and the usual procedure is I** distil from I In- 
ordinary tap supply. The liquid is heated prrlVnibly m n i'tppi-r vessel 
and the steam condense* i by passage through *uHi|ed tube uf some 
material, e.g. tin, .silver, or even platinum, which will resist the net ton 
of steam. Such " distilled water " is suHietciitly pure lor tuttst 
purposes, Imt for special purpisi*s a higher dcgivr. if purity is iir 
in such oases the water h redistilled after the itdtftftott i>f 
permanganate and potassium hydroxide a ; if traces uf auihiuma arc 
to be avoided yet another disUHnliou with the itddition uf a little 
potassium hydrogen sulphate is necessary. In all these distillations 
the first portion oft he distillate should be rejected itiid also a euiisidettiblr 
residue allowed to remain nudist tiled. 

The need for wafer of u high degree of purity in especially felt in 

1 Be Dixon, Tftwn, Uhrm. AV*r., Illlli, gj iiill. 
* Htan, JaltrwtKrwht, 181)7, 134, 

WATKH. 231 

experimental work on the electrical conductivity of aqueous solutions, 
and many modifications of the distillation apparatus and process have 
been proposed Tor preparing such water. 1 A relatively simple distilla- 
tion apparatus (Bourdillon) is outlined in Fig. *!(>. 

The boiler A, of approximately U5 litres capacity, is connected by a 
rubber bung with a copper tube B and cylinder C, which serve to remove 1 
particles of spray. In order to prevent excessive condensation B and C 

i tutw 

Tin ttttw 


titio/inff tubr 

Fiu, 3li'-~B<uriillun*n dint illation apparatus. 

arc jacketed with non-conducting niatc*rial. Th< vcrlical tin tube. 1) acts 
as condenser and is water-cooled at the two glass jacket cooling tubes; 
during the distillation a current of purified air slowly ascends from the 
inlet K. Tap water is placed in the boiler and a little potassium 
hydrogen sulphate is added. After a short time- the steam is free from 
carbon dioxide* Passing up the tin tube the steam is condensed at 
the upper glass jacket, so that the condensed water during its descent 

1 .lawn nn<l Murkuv, %titrh. /*////*/&*/. Cftftn.. lKi>7, 22, ill*? ; Bnuniic^i, Trans, (.'hem. 
Nr^., 1U05, 87. 740 ; tlH'J, 101, 144:1 ; Hartley, Cainplmll, and IooU, ibitl., UM>8, 93, 428 ; 
ThoUs ibirL, HM2, zoi, l!07 : .Hnunlilion. i7;w/.," 11)13, 103, 75) I ; Paul, 'Mitch. MleMrvcktm., 
1014,20, 170; Huitrtl, Znlxch. }*hy#ikal. Chctn., I8, 21, 207. Sets alno KohlrauBch, 

t'6W., HH>2, 42, I!:i 

is submitted hi a ** serubhiny * arhnn I*} tin .isivndm^ strain and purr 
air. The \vatrr eollreted is uf a luj,*h d*"j.jrrr f purity, hut of eourse 
contains dissohed mtro,;rii ami txyjjfrn, Its rlretnral conductivity 

is roughly I III" rreiproeal uhm at I* f tsrr j*. 1*7^1, 

This is a problem of rnormous ivnnomi* 1 import, intv. Ouiug In 
large number of factors tuiohrd, numt'rtus systrms i*l' uah-r 
lion jirt* in usr in \nrmus jtarls t4' Ihr ttuvM. 

Storage. K\|ii'niiirt situus that siioh natural walrr** as an- not 
vtTV pun* tu Ut'i'in ttitli, ar* 1 j'rratty uuprt*\rtt tr |tfa!*Ir purpusrs by 
,st(*ni^t\ Sttspi'iidfil iiiipiirilit'% tjri!tl!i*ill\ %uh%nI- i'arr\ in with tin-in n 
put'liou uf thi' hartrrial rtintfiil uf thr uattT, thus rrrnlfrnti,* tltr super- 
natani liquid miisiilrrahU jmrrr. 

In inldiliHii to tin 1 *, olln-r artitMr* tak p!*ir mi i*h lit'.* a tliuitiiutioti 
iu tlu' iiuuiher til* liiH'Iri'yt, 1 witlt**tii|li Miiurtuii* * thrr*' is an initial rise, 
iolU\Ye<i by tli-rlilir* Thr itirtriiritl,il ffi-rts .,!!'* iiiiltii'ril l\ a \arirty 
ol' niust's* the ututv itiipuilaii! <*f uhtrh ii* ; 

1. Sunlight, Alllitttinti tliffii^nl t|ii\ Infill IMS ititi Iitllt artuui, iliml 
sunlight is n p<\\rrl'ul twirtrht^tlr," 

*. Many <*oiu!iMMi turius ti" hlr, sitrh as prutu/iM, i-.tpiii> t'luiMinu* 
or exterminate ]mtho.urme yeruts/ 1 

*l Starvatiotu *I*he ha*ti't'ia tua\ rMtistuur tin- wh*lr t' thru* Jooii 

4. Toxins. The e\eretttry prtwluets ul' I IP haetrria ma\ aet'UUtltlatt* 
to siu*h an extent as to pitjsoti tliriii, Stirh tuxius tnay \fti prve 
clsuigrnnis to higher t'oinis of hJV, %t$ thai f*tMitptrti- ahsriier ul ttaeteria 
does not iifoessarily pro\ r that uatrr is uholcsuiitr, 

If, however, thr \vnter is \ery i*<i to h-^m ttitti, as, l*r (Aaiuple, 
deep well water, storage eantiol improxt it ; iiBln**! if uia\ I**- tletri' 
mental to store the witter, tiia.suiurlt sis Ihr tntr\ t" uiy pillutioti 
wuuhigivt* theiteeii!iipiin\'itt|4 }*u(*tertu n l"n-r lirld lur npnl uiuilipheatttiu, 
In addition to n reduetiou ul Ihr Imilrnal rnntnit, must natural 
waters undergo during st<.ra^e M-\rnil other i'haiiv;>-s tiiurli improvr 
them lor potable purposes. *J1is tin* or^atiu* matf rr ti tuts In disappear* 
either through settling or through oxitiation fi* ivjitrt, I'lirbmi dioxide, 
ete. The* hardness is reduced Cither by absh-at-tioit of soluble eittntiiii 
salts by plants mid animals, or through evolution ul" somr of thr dissolved 
enrbon dioxide into the atmosphere \v|it*tvliy thr ralriiim lurarboitntr 
beeomes trausiormed into the itomrni ntrbcmalr and sepunttes out as 
an insoluble deposit. The nitrogen eom|umuls, siieh a-s ammouia, 
nitrates, and nitrites, tend similarly tu dt*a|t|e;ir. 

Purilleatioii of water through sedttiimtittstin IHJIJ- ! greatly assisted 
by the inlrcKluHion of powdered sult*tttm*r<* mtt! |mrtiriilrly of fittluttls. 
although tliese latter tnke longer tu srtth\ FrasiklutMl, 1 t$i t series of 
experiments in which some 20 grams of powdrmt Hialk, rokt\ e*ltamnd t 

I Sw Ifuiwtuit, Jtwtiirh ttrjKtrt* <*J the Jlrlf|wlil Iliilrr fa*ttJ t ifiiiH l!i|i! ; J t *r*iwi 
KuMKctl. luicl 7rit, ,/, //i'flifin ( i />M<:*tw.4, J1MI4, i, till ilill 

* J Sfc C'tirriiv JJIJ. f*uMic tlrnHh, Hilt, 39, 1*14, 

II UiiutnaiUl*'*\ Archie. Hyjiw, IWl/t. 4 HIM Ufrlmmiwr. >ft**/.. i!H, 71* 1^.1, 

Sttkvw and hwt'lh'rigr^lirl, ./. //i/|/iVf, lull, n, 4x1, 

!t in ll'tilrr f Lfiiig.iiMiin 

WATER. 233 

or spon <ry iron \\*CTC added per litre 1 oi l water, \vas able to effect the 
removal of from 90 to 100 per cent, of the organisms present in polluted 
waters. Savage races have long used mucilaginous substances, such as 
quince seeds, the acid juices of plants, arid astringent and taiminoicl 
prccipitnnts, such as Peruvian bark, for purifying water for drinking 
purposes in the above manner ; the sweetening of the waters of Marali 
by Moses (Kxodus xv. V 2.'J) by easting a tree into them is probably an 
example of this primitive method of treating waters. 

It appears that the ancient Egyptians purilicd their water by allowing 
it to percolate through earthenware vessels containing alum. Colloidal 
aluminium hydroxide would thus collect in the pores of the earthen- 
ware and assist the process of nitration. 

In modern times alum or aluminium sulphate has been added to 
waters to assist in their purification. It reacts with any dissolved 
calcium (or magnesium) carbonate converting it into calcium (or 
magnesium) sulphate', aluminium hydroxide being simultaneously 
precipitated. Thus : 

( 'a('( ). { Al 2 (S( ) 4 ) a | ! I ,( ) 2 Al(( ) 1 1 ) a ;H'aS() (l | ;K!O 2 . 

The precipitate gradually settles, taking down with it organisms and 
other suspended impurities. Thus, for example, Leeds ' found that 
an addition of 0-5 grain of alum per gallon a of a certain sample of water 
reduced its bacterial content from SOOO to SO per c.e., that is, by 91) per 
cent. The precipitate' also acts as a decoloriscr :J and has been applied 
in this capacity for clearing the water at Antwerp. 

The foregoing, however, are not purely mechanical effects. Organic 
mailers, particularly coloured constituents of upland and peaty waters, 
are usually colloid in character 4 and exhibit cleetrophoresis, migrating 
to the anode or cathode according as they are negatively or positively 
charged. In most- cases their charge is negative, so that these are 
precipitable by positive* ions and positive colloids. Inasmuch as the. 
precipitating power of an ion is a function of its charge or valency, 
aluminium with a valency of three has a very much greater precipitating 
effect than sodium, of valency equal to unity. This serves to explain 
the particular effectiveness of salts of aluminium and ferric iron which 
has long been observed. It must, be remembered, however, that whilst 
a positive ion tends to precipitate u negative colloid, a negative ion 
tends to stabilise the same. Ilenee the total effect of, for example, an 
aluminium sulphate solution is the difference, between the opposing 
actions of the aluminium and sulphate ions. By reducing the number 
of the latter, therefore, the precipitating effect is enhanced. This 
explains the greater eHieiency of basic alums, which are now used iu 
the Brooklyn (U.S.A.) (liters, and in which the average deficiency of 
SO,j is some 8 per cent, of t hat required to form a neutral salt. 5 Electrical 
methods for the removal of colour, bused on cleetrophoresis, have been 
recommended *' and are of considerable scientific interest to the colloid 

1 Li-cdx, HIT RidcsiK Water Hnp/diM (Crosby Lnekwood, 1914), p. 80. 

'* Thai in <nn pud of uluni in 1 40,000 partn of wai<u% 

3 Sec Kfiunn, 7'/v/x. /w*/. Water Ktn/. t ISHti, pp. 218, 253, 2(H). 

1 S<H Hilt/, and Krohnko, Her., 1004/35, 17-15, 

& fcJoo luialyMou by Hair, J. I nil. Kng. (Jhem., 1914, 6, 032. 

6 Ratv, J. ,S'w. C7*cm. 2nd., 1921, 40, 159 T. 

- ,,um a,,, ,,, ,,, - <-"- 

lumliu-ss * r,,m,,-t,-,! ,, ,,,rm.m,,,i. Tins ,. ' ''> l '- | l--ry 
st^un-nuM,,,. punn-M-s. ThJ ,!!, ,,,-., ^ -T T '''' f " r 

T" 1 "' mm "' : "">">< i.-i. IMS j,,,,, ;,,;,, , u ,.; j : , y tllt- 

An-riran wntrrs. A,-,,,,-,!,,,,, |,, ,i, K ,,, ,,,,.'">' " tvr ' :i "' 

lu- watrr w|,, t vhv a ,, r t,,,,, , (il ,' |V '" V';"'""''' 1 """ 

iVrrous hylr,.|i rarl,,,uul, % K.-IJ .,, t r ,. Thul >"-''' M,|,,|,K. 


,,., ,,, ,;;',; ;',.;:;,' ,7" ....... ' r. 

ii,.- 1,,-,-,,- i,,.i,,.,, ,,; ,,; ;; ' """"" -\^ a 

nnal.i s ,,i,s ,,u,n,,,-r I,, ||,,,| ,|, I :, . , I'""""- Ik nl.-r in ,, 

, . 1 "' ''"""' ....... ' 

I;;:;;," ........ = ""<' ..... '^^^'l 


H' vitality of whi.-h HI.II. HA u 'A.iii.f,|.-. .,, th, 

',' ', ,: J, i -n""" 1 " 1 H " h Ih< "" 

,, , wrt s of i,,,, ( ,7^,, ,'; J 


1 r - 

, tt * !,,,,.,, , . ...- ,, r ,i, 

for i-xum,l., t Aii s t m | nm , , ! '' " !Mr ',," 1 '' v ' '""''""- Thus, 

" "" s ' ! " r " ai!|lli(lt " 

() . " "'- 111 " "-"' 

i, h, I," ,-r "'r S '''' 1 '' W '"' rr u !(% "" J! > itlt "''-' i 
down wards. The , '' A '" " i y*" ,,,, ( tin- 
'10 i" Salami I ' J* "" ""'''>; "'nin,,,i , . V( , ir 

!*, will, .lu-obS;,^ 11 . ;^.;; J ,, li ;j l : I ; H r a|k ' '"'" "' l>> ' tt ' ;f f 

unknown sH,,,,-,.. , 1 '.V' ; '''". .-!, r,,|nv i,, ,,. f | H 

.. , . 
cally appli,,, Imrt, S^'?,, "^' ^^V"' 1 , Krrtllklllili| ^> ;I| -' M - 

MMMlifllir Liiiii|i, \valrr supply 

'^eHSB-V-'"-' --^- := r- "' 

d, /' W . /%, AVif,, iHHa, jg, :|| M) Ml>/ * W C^'WWi*lis I!*ii;!|, ,,. y;, . J, f,, |, fi|H 



and found thai more than 1)J) per cent. of the micro-organisms present 
in Thames water at, lla.mj)ton were removed by passage through the 
sand {liters. This has since been confirmed times without number, and 
the Kcport of the London Metropolitan Water Board for 191.3 is oi' interest 
in this connection : 

Haw water 
Filtered water . 

No. of Micro-organiHinH per e.c. of Water taken from 



New River. 


A very striking instance of the value of sand (Htration was afforded 
by the outbreak of cholera, in Hamburg in 1892. The; city drew its 
water from the Kibe and used it in its raw condition for domestic pur- 
poses. No fewer than 1250 per 100,000 of the population perished 
through cholera. The contiguous town of Aitona lost but 221 per 
100,000, despite the fact that it drew its domestic 1 water from the Kibe 
below Hamburg, after it had received the sewage pollution from the hitter 
city. This relative immunity was due to the fact that the Aitonu 
authorities purified their water by passage through sand filters. 

Sand filtration is largely employed in this country, sand being laid 
to varying depths upon gravel which increases in coarseness with the 
depth, which ranges from <> to 8 feet in toto. The water is drained away 
through pipes at the base. 

Although it was formerly believed that a filter bed was most ellieient 
when freshly laid, it is now known that such is not the ease. The best 
results are obtained when the filter has been in operation sufficient time 
to allow a film or "*" dirt cover "' to form on the surface of the bed, which 
is the chief level at which purification proceeds. The water passing 
through the filter should not be used for domestic purposes until after 
the lapse of the necessary " filming time." The film obtained from 
natural waters is essentially organic and of a semi-colloidal nature. 
By adding an inorganic colloid, such as alumina, a film may be arti- 
ficially formed on the sand surface in a short space of time, thus saving 
delay in the use* of the filter. When once such a film, whether natural 
or artificial, lias been satisfactorily formed, micro-organisms will only 
pass through in small numbers. As time progresses the film becomes 
increasingly thicker, until ultimately the rate of filtration becomes too 
slow to be economically efficient, and the bed must be cleaned. 

In Cireat Britain the sand filters generally deal with from 2 to 3 
million gallons of water per acre per day, that is, with a downward travel 
of about 10 to 12 em. (! to 5 inches) per hour. The head of water 
ranges from 00 to 100 enu (2 to ttj feet}. 1 

1 Mitny town*, particHilarly in America, now unn " mechanical lilt-era" by mcatm of 
which water can lw HltiTwI much mn* rapidly than in ordinary open Hand iiltera. For an 
account <f thcttc, wn Dn and ("hinholm, o^/rv cit. 


Waters that lu nut ivadilv hnn a l.ith i \uiiiM i| n< it int. d html. 
Such hardness may h e,msd hy if* pi-. , u* . n$ *\n,-.,d. i, M |uantity 
of salts tif tin* alkali in* tuK, a*.. i*r \.,in|l , n in r. , ot - ,j w.ite'r 
and hrinc. More usually. howtur. fit. I nu ; . u 1 ii t wh hunt- 
ness as is due to the pr M ne u!\/r\ HIH*}I ns -li r <|u.u I iti s MI salts uf 
nta|4!H".sitnu or calrtuiu, 

Tlu' inajurity ot" vtjtt.ill anil ^uuti 4 MI. t t tats 1 consist 
fssrntmHv >{' art ur*,auir ,*!t, rutjMisnt ; -Ur-'iu , 4,II t iO!lij or 

ni.OlI.VHOU .i H.OII, as his, , .iNiilifii ,1 *'llh I'* . 

as stt'ari<- afid. t' ti ll ,.<OOii. ul* n- arjil, i , 1! . lU 

acul. ('if,! ! ;U ,U>OH. TltiiN, *!MH\| ^.,-i.t. 4,! i, M 

t if milt toil I'at , i% i |*! .* tils din tit !Minu!' 

tr^ll^.l CIO ( \l , 

i !,H S+ i oo.t II ; 

c $ JI f ,i finj It 
i ,,H M ,t oo.< ti . 

Olive oil is laivU "Isrt rvl <*K ati , ni jdn ^. h \ 
When wanuc'ii with solution* ut e.iU'.hr alKah. * k t*i* i tl , ,r, ( t runt- 
posed, yii'Itlinj* ,sr**//>.v, hi liei th IMIH - ,'/* / '// i,!;n. { hiiv, for 
example, with Mutinm h\tlr<\i<l , '!\*-MJI! ^l-.^jh u id, i , ^Ui rine 
and sodiuin stearatt*, \\hteh tat tf r t . .t*huiit ..,j*, Ifm 

',!!., aNiiOU I JI t .O|| , ;it , IJ ,.( 

The sodium snap i*. sotuttlr tu u.ttrr ,ii^l , % ?\ *!*.,! II *pt.utttty 
suilices to produce a Iath r litltt* utt> r is pn.> , It, !* *<* ij it ritutants 

dissolved salts of eatcinm nr iua;;in MIIIIJ th f ,iH^r >i* ,fi*i\idi*' thr'*f t 
yielding UK iamitutr insolntile ntnL MI *h,u,u nJn il !li< .'i-ium !' 
hard water on soap, Hits rrd i* r ,ilh Hi* *u hi)i ,ip i the 
alkaline earth metal tormtcl hy iluutl d k-fMnjuv iijn', ,. -Isown JM fli*- 
two following eqttatit>t)s % in which it r ,^>itm^l >h- h -jin . . r, *iu to 
the presence of calcium carltumttt' aint III.IVIP 411111 Mtiph^tt i* *prti\rly . 

^XallUI, .1 t If . 


Not nnlil the \vht>lc of ttie alk.dtnc i.utii m< ! I u^ * t> u ' u* i a^ 
insoluble eurd is the siittittm snap Iii . it* \i* M . I d! ? K f M*IH |>i nily 
the higher the percuitaje of t\ii*min m i t <> smni, lit* in ' r the 
amount, of soap retpiircd and thf ,.v,tlu- t nt, | f .iii' - **i th v,.i!rr, 
The amount of soap required to frodnr tJ itjlci i thu ui t*ur.- *tf 
the hardness of the \\atir and. a. indiMf d I-! o* 
tatively <h trrmimit" the saiiir, 

Two kinds of hardness are ordinarily ivengmM- 
and pentuttwnt. 

1 A /*/ in n ftuhii it 

WATKK. 2,17 

Temporary hardness is that caused by Mic presence of the bi~ 
enrbonates of calcium or magnesium. Whilst the normal carbonates 
of these metals, namely, ('a('(). t and MtfCO., respectively, are practically 
insoluble in pure water, (hey readily dissolve in the presence of carbon 
dioxide a normal constituent of natural waters, owin^" to the presence 
of this #ns in the atmosphere the soluble acid- or hi-earbonates, 
C 1 aH 2 (('O.j). i , and M.^l I. .,(('< ) a ).,, bein.ii: produced. The mere process of 
boiling temporarily hard water sullices to it,' for the expulsion 
of the dissolved leases effects the decomposition of the biearbonates 
with consequent precipitation of t he insoluble normal carbonates. 

Permanent hardness is caused by soluble salts of calcium and 
magnesium other than the biearbonates. The more common of these 
are the sulphates, chlorides, and nitrates, particularly the iirst named. 
Such waters cannot be softened by merely boiling. 

The total hardness of a jjiven sample of water may be due in part- 
to the presence of bicarbonate and in part to the presence of other 
soluble salts. When boiled, the normal carbonate is precipitated and, 
on account of the decrease in solubility of calcium sulphate with rise in 
temperature above IS ('., there is always a tendency for this substance 
to separate to some extent with the carbonate. This causes the deposit- 
to form a coherent, film on the containing vessel, whereas the pure 
carbonate ^ivcs a more or less powdery suspension. The boiled water 
is now softer than before, such hardness as if now possesses is termed 
permanent, whilst its temporary hardness is the difference between 
the total and permanent hardness, namely, that lost by boiling. 

Degree of Hardness. To render comparison easy it is usual to 
record the* hardness in terms of the calcium oxide, Ca(), or calcium 
carbonate, CaCO.,, that would product* the same amount of hardness if 
added to pun* water. 

In British water reports, according to a decision of the Local Govern- 
ment Board, the number of grains of ('a(*O ;l required per gallon (70,000 
grains) of pure water to render it. as hard as a jiven sample, constitutes the 
decree of hardness or the derive (lark of the sample. Thus a water of 
5 decrees of hardness would be obtained by dissolving 5 grains of CaCO.j 
per gallon of distilled water, According fo the metric* system, it is 
usual to express the hardness in terms of ('at'() :l per 100,000 of water. 
This figure' is readily obtained from the decree (lark by dividing the 
latter by 0-7. Thus 

I decree Clark Mtt parts of (WO., per 100,000, 

In Germany it is customary to express the hardness in terms of 10 m#. 
of CaO per litre, llcnct* 

I decree German I-7 parts ( '('<)., per 100,000, 

Determination of Hardness, Hardness, whether temporary or 
permanent, is conveniently estimated by means of ('lark's soap test, 
which consists in adding front a burette small quantities of standard 
soap solution (rWr inj'nt) to 50 e.c. of water which have been carefully 
measured out with a pipette into a iMO-e.r. bottle. After each addition 
of soap solution the IKK! fie is vigorously shaken, and the titration is 
complete when the lather remains unbroken for live* minutes after laying 
the bottle on its side at rest. 

1 Kuril riludy of min* *f flu* react imiH involved, HW Petit, MOIL *S'. 1914, 4, 537. 

Should the \\ater h- so hard f it J s v\ up\\anK l sap solution are 
required, a smaller \olum tlu?i "o e.e, sh*ud*l ) takiu ami thluted to 
this amount \\ith fivshlv bodl *itstitlr) \\ahr. Hetrreuei- t the table 
indicates the amount t*f hariln* ** r*n* siifintlin- to eaeh tit ration. The 
total hardness is i*i\ii b\ tli! v !M*thoii i! a send saiupl of \\atrr 
be boiled and after setthm r l'lt un**! in a Mnular manner, 
the permanent hardness is *M i'j. 1 sii*f iMetntti !4\i% t h. t. . mporary 
hart I ness. 










II -s 


I 'I 



Z-\ i 

ii -lilt 

,i ti 

." H 

*', O 

Ii V 

Ii I 

I* Ii 


7-1 I 

7 in 


s ou 

s HI; 

!! t 

ii 1:1 

So no 

tVlilliilili'il AVi|i Snltitiittt, 

This can be prepared in se\-ral tliffrrrnt uays. t'liiniipiiily *lry 
Castile soup is dissolved in HO per eriit, ulrujpil tit stieh prupuilmns as 
will yield at solnlion well biv the tiesirrd liiyil euiteriit rat 11*11 ; lUO^nMiis 
per litre is n convenient ratio. After lilltni'im* flit-^ Mthtliun t stand at 
r<*st for sevend days for the (Ujii>sttitH of untli<soi\rit inatft-r, a tptanttty 
of the clear liqttid in withdrawn (ustmity 7*1 tlifi e,t% p-r htre uf ttnal 
solution), and so diluted with NO percent, alcohol a*. ti jointure it solution 
which on tiirntion with a known weight of calcium chlnride solution 
under tlu* standard coiuiiiiotts will ive results in aceoniauee with 
Clark's table. The catcnuiu chloride* solutitin is fw-st prepared by 
dissolving 0-2 grains of Iceinnil spur m dilute hydrocblorte nenl ; e \eeCs 
of acid is removetl by evaporation tin a water bath ami the solution tlirii 
diluted to 1 litre with distilled water. A iui\ture of* ^.1 e,r, of thin 
solution, mixed with 2$ c.c, of water. shouUI r(*i|iitrc 7-H IM\ <if (lark's 
standard solution for the production of a permanent lather. 

The standard solution of sew p cuit also roitvcniriitly lie prrparni by 
neutralising un alcohol solution of oleie itcitl with it Hnlntioit of |!otjiv%ium 
hydroxide in the same solvent ; tht* tieiitriil solnlion of potassium oleatr 

\VATKR. 239 

is then suitably diluted. A solution of potassium soap for dilution can 
also be obtained by the interaction of lead plaster ("lead soap") and 
potassium carbonate. 

Although I be soap method is still widely applied to the determination 
of hardness, it is inferior in accuracy and general trustworthiness 1 to 
more recent methods, which also possess the additional advantage of 
allowing a direct determination of the temporary hardness. In this case, 
however, the conception of temporary hardness is narrowed so as to 
include merely the biearbonafes, the whole of the calcium sulphate, 
being included in the permanent hardness. In the simplest of these 
methods a measured volume of the water is carefully titrated with 
decinormal hydrochloric-acid solution. using methyl orange 2 as 
indicator ; alizarin is a still better indicator for the purpose, but titnvtiou 
must then be in boiling solution. The til rat ion depends on the decom- 
position of the bicarbonate of calcium and magnesium with formation 
of carbon dioxide and the corresponding chlorides. 

Permanent hardness can also be estimated by the alkalimetries 
method of Wartha and Pfeifer. A measured volume (200 c.c.) of the 
water is boiled wit h 50 e.e. of a mixture of deeinormal solutions of sodium 
carbonate and hydroxide 4 in equal amounts; after restoring to the 
original volume and allowing the solution to settle, the residual alkali 
is determined by tit rat ion with standard acid. As the biearbonates 
do not cause any consumption of alkali, there is a direct proportionality 
between the quantity of alkali which disappears and the total amount 
of sulphates and chlorides of calcium and magnesium. Sodium carbonate, 
alone does not eilieicntly precipitate magnesium salts from solution, 
but precipitation as the hydroxide is complete if excess of sodium 
hydroxide 4 is present ; it is for this reason that a mixture of sodium 
carbonate and hydroxide* is applied 3 (see also p. 21-1 ). 

The last method can also be extended to the measurement of total 
hardness by First neutralising the biearbonates as described above 
for the determination of temporary hardness, and subsequently treating 
with the mixed alkali solution. 

Another satisfactory process for the' determination of total hardness, 
based on a somewhat similar principle, is due to Blacher. 4 The water is 
first titrated with deeinormal hydrochloric acid until it is neutral to 
methyl orange, as in I he method described above for temporary hardness. 
After the* removal of the carbon dioxide by a current of air, the methyl 
orange is bleached by the addition of a drop of bromine water ; a little 
phenolphl halcin and a lew drops of alcoholic* potassium hydroxide arc 
added, the liquid is just decolorised with deeinormal hydrochloric acid 
and is then titrated with an alcoholic* dceinormal solution of potassium 
palmitatc until a decided red colour is produced. The quantity of the 
potassium palmitatc solution required is proportional to the total 

1 For further <it'f>ti!x, HW Maxtor* ant I Smith, Trans*. (Uu'Hi. >S f w.., 191,1, 103, 992; 
Winklor. (tmiL ('firm., MMU, 40, H*2 ; Hw.hniT, Chcm, %citnnt/ f 1892, 16, 1854; 
Twl,./. SV. C/H'tn. Intl.* IHHiK 8, 2f>!J ; .Ja<*kHon, C/n'tn, AVww, 1HH4, 49, 149; Magnanini, 
(Jttzzrtttt, HMHJ, 36, I. :W s JMwor, Analyst, 1883, 8, 77. 

Jt W'ifor, %t'it#clt, tnwu*. (*'//., 1902, IS HW ; Procter, J. *SV>r. Chem. Intl., 1904, 
2,"% H 

>4 *Blarhr nntl liu:hv. Chi'tn. %rit. t HMW, 32, 1)?7 ; lUac.hor, Korhor, and Jacoby, 
angnv. Chftn., MM)t, 22.' 1W7 ; Ulachor. C*runfHrg and KtHHa, Chrw, %cit. 9 191 ,'t, 37, 06 ; 
Winklor, ZnlM-h, ttnnl ('lt*-in. t MH1. 53, 4()9. 

A Watet\ the total IO.)"1< MU'U ,-rd e il'-njM *lf , M! whieh ettlild }< 

represented liy an t|in\jl i.t *>i ,i|*pi F m, f Is JMII>. *or less) of 
calcium carhonat* p * IOO.OOM, HUIU j, i -in !, eMn*idivii so |^ 
whilst it would In il M-iih. d s \vi. hu * i* *h< proht\ i \r ni rt | j?j 
parts per, 

THE SornKMNi; <)!' IlAlflt U Vi'KHs. 

As 11S already heell tnrlltionrd, U.;tTv aiv possessed of 

temporary hardnesn may h- sut'tmid by tnuiih^. This ftrivs\ \^ 
howr\'i't\ Vrry t'\prtiM\r alul Hnprat'tu'.dilt' U|I*MI ,i !,u*!,v srati*. \ iu*>rr 
couvniit'itt iiit'fhnil is that <4" C*hirk, patrntfd n |.s|t, afrordittt; to 
whirh tht* 4 ( x't's,s if carimtt lit*\id is {irrripitalrd ly . : nlilif im if ||| C . 
rt't|uisilr quantity of slnknl litnr. llir- \Mliiliii- alkahnr rarth hj, 
curtuHmti's arc tlu'ft'hy *t in vt*rti' I intci tlu-ir tnHhtlI- UMnual rarhnnatrs 
and st'pantft 4 <tit, Tin* rrarlion.s tnvulvt-d tna\ In- rrprrM-ntrd us 
follows : 

C'all^CIKi, ( \i\i\H ^ ;!t ui o .'!! <i 

MH)ttOY| t'jrUH ( M 4 O, f ,.( ?{1 O, 

In neither casr is |*r *t|ititjn jMtt'tl*. mtupi* I* , IMI .uiuhihu n a 

relative term, and 'dtliuu*h fli mutts ! iMiiinii.J. * FH ililnt"h tit 
soluble* \vhett tt>ui|mn d \\ttli tlnir !MM }*M it^ % ! h' \ .u n**f til*>nlntchi 
insoluble.* Abuut ! frain nf i%Jnttm (\irltM^Jt! |M i 'iil**n *l w.te\ 
rrtnains in solution ni theturmrr rru*tn, ulnt-t m I hi lift-r r,r* vntue 
*2H grains of ntu*!n<siunt rarbtmit* i$i,t\ inui ! htud dthtm*h this 
may he roisiderabl\ redtitvd h\ jtldthnii H| . \r. ', M| Inn* whtrh pre 
dpitittes msittu'snun h\ drttsjde, w ln'h >s h . '**tinl*i I .1 hi i \u bun.tte, 
Water treated in this tu.utnt r n-tau>*, th'i$Mr , ahutii tf d^i p M s of 
hurdnrss <ht' to dissohfii ralntttit,, and *tntiiii M-\<r;il 
decrees of hardness tine to di*Mi|\f d iiitti 4*1111 r^ibtuuiti m .tddttton 
to any pcrnuuM'ttt Imrdn* ss ilmt 4*11* n^dls JM- ',-jit \ilin*tih tin* 
treatment, even in the <MS* uf w*itj * J*,M -. .m*/ *u> j* nf hai'flness, 
doc*s not entiieiy nniu\i tlnir ltuniit< v,, if ifr*,tfh iifi|fttH** tlu-in, 
Furtht-rmort- (luriiuj siliittrti(uti<ui iln 1 riimuii f,ulttii.iti IMHI* *. 
with it any oxides of hr;n\ iiiit;d'*, MHi *i* tt*n and iii,iii/;in*-M , 
also iumsiderable quantities of uitf.ttnt'> rt.d ,uitl liun^ MpMit 
This partial stenltvitioit of tin \\at r 1% ;t \m **dtMbl- %jd ft 
of the process (see p, *J2W), 

Permanent hardnt*H is fr<|n<ii?h iinirli HKM diilifiilt tu rtMi 
Distillation will effeet its n-tmtuil riuupli !* |\, litit i.nh in i \n fit 
rases ran stirltdrastic* tnatiiH nt bntj*|ihd i-*, fn vnnpl* , m jt> f 
drinking water from sea wnter on steamui dtiun" luje? \o\a?;*s and 
in tlu- preparation of pure \utfir tViu tap ^,it*i t*n '|n&| %f*u!itiit(* 
purposes for which water of 4 hif t mt f r fl f j illri H t ., r.c|tutrd t lit 
softening witter for domestic |tiirpMM-s it i^* tt%tt;l IM iviuuu flu ft m- 
porary hanlness only, sinee sitiatl aiitiiuuU o| MtlplMtis *!' i%ilt'iiiu and 
magnesium Imve not iisualh an udversr tuldtmrr on tin tr m ral health 
of the public. But for nmn\ titannfaetiins pmfinilii'h tor *te*ini 
raising purpose^ it is <!esirahle to n mmr tin | rniant tit h.irdiM *s also. 

tl j^ttM tn<r lf.Hiiii *.f !rr^ nt 

,, |-:j it |ir r ; lliill^ , nil A 
nHic tnn^iu'Hitnn fjirlmnnti*, j>7 nl !:!"" r, ' 

WATKK. 241 

This tuny be done by the addition oi' caustic soda or sodium carbonate. 
The hitter reagent converts the dissolved calcium and magnesium salts 
into relatively insoluble carbonates and thus effects their removal by 
precipitation. Thus : 

CaSOj i Xa,>C<>. { ( aC(). t | NiuSOi 
MgSOj ! XaIC<>' :l MgCU, | NjuSOj. 

Caustic soda will convert the magnesium salts into the still less soluble 
hydroxide and thus soften the water more effectively." If suilieient 
free carbon dioxide is present, dissolved in the water, caustic soda, 
or a, mixture of sodium carbonate and milk of lime, may with advantage 
be added instead of sodium carbonate, as it is transformed into this 
hitter salt by the carbon dioxide, and then reacts according to the 
above equations. This '"Mixes" the dissolved carbon dioxide 1 and 
prevents if from converting into hiearhonales the normal carbonates 
precipitated when sodium carbonate is iirsf used, and thereby converting 
a permanently hard water into one possessing temporary hardness. 

In the Stanhope or Uaillct and Iluet process, Hint* water and sodium 
carbonate an* employed as softening agents. The former is prepared 
as a saturated solution by passage of a certain proportion of the incoming 
hard water through milk of lime in a saturator. The water enters ut 
the bottom and as the saturated solution rises, the suspended solid 
particles gradually sink and the clear liquid is discharged at the top. 
It now mixes with ban! water to which soda has been added, and the 
resultant mixture passes slowly up a clarifying tower, down which 
the precipitated solids gradually settle, and is freed from the last trams 
of suspended matter by filtration through wood-wool filters.- This 
mechanical removal of the gradually separated calcium and magnesium 
compounds is common to most precipitation methods of softening. 

The various commercial linn'-Mula prmv.v.vr.v for softening water arc 
based on the foregoing principles, and differ essentially only in their 
mechanical details. Their underlying principle is more commonly 
applied than any other for the purification of water for boiler-feed 

As already explained, it is desirable to precipitate the calcium 
compounds in* the form of ear&onate and the magnesium compounds as 
hydroxide. Commonly n mixture of dissolved sodium carbonate and 
suspended slaked lime is introduced in the correct proportion by an 
automatic measuring device. If the hardness is represented as the 
equivalent number of parts of calcium carbonate per 100,000 parts of 
water, a simple ealeulnt ion leads to t he following formula for the necessary 
amounts of sodium carbonate and lime in pounds per 100,000 gallons of 

Weight of sodium carbonate (Xa a < '<),,) KMJ P, 
Weight of lime (1'aO) (T-| M), 

when* P represents the permanent hardness, 
T represents the temporary hardness, 
and M represents hardness due to magnesium compounds. 

For this purpose the determination of the magnesium hardness 
is easily effected by treating a measured volume of the carefully 

1 The HwtttitiN tin* cuwiiUrutwl. S'n Bnrtou im<! Limlgmu J. Amvr. ahem. AV>r., 1907, 
29, nm, a N'< King, r//rw. AVww, 10H). 118, 14. 

242 uVMil-'. 


utralised water uith a d*Tuut*' quantity of sodium hydroxide or 
calcium hydrovidr solution *I knouii either})} ration, Atter allowing a 
sutttcirnt prriod for flu- pr* eipil ahon **!' th ma^m MUIII IB di f o\ide, the 
residual e\n-ss of flu- prn-ipitant r- <!>!, and h* m*- thr ;uttount 
of magnesium wlurh has U- n i. mo\id, A i * an all * mat i\ the iua^- 
nt'.siuu hardiu-ss ran }>* t!irrrfl\ %! isn.iti-t! h\ titratn.ii .it't* r thr rtiuoval 
oftlir calfituu rtut| 11111111!% hy ;iiltiitnii ui M wliuiii M\.l;tt- li t Itr in tit ntlisnl 
wattT, 1 

Durintj i'fiiitiiiiii*ti%. riiitiiifi*,! **t . lil r ^tt-r siitrnuu; plant it is 
not. iirrr\\ary It* niakt- tV-{U*-nti> r*-j;t<-il turasun ttimts 4 if thf 
nui|4nt'stuin pn-si-nt. thr *ul\ lutnriu.itiutt rrtjuir* tl I'nr tin- rt^nstaut 
luljttstlttf-nt of tlir amount nwl n-Liln- pMtptirtiuns ui' tlt- so)'ti*uin^ 
Uj^rnts bcin^f thr total hanbit-sH, thr trinpofarv hunittrss, anil thr 
alkalinity tt'thr \vatft* touanls pin-rjujphthatrm. 2 f n*- sol'tminy jin*rr,ss 
rraohrs its iitaxituuni i-Ht*ifU\v ulu-n flu- u!nl- *i' tin- ralritun hits 
lu-t'U c<in\frti'l into riitriiini rarl*onati- ami thr ma^ni-sitttti into 
hydroxidr without any tnni*'rrssar> -\rr %% *4 H>* ai**-jit*, 11t- solubility 
of calcium rarboiiatr, \vhirh is thr tuori- siiuMl- **t !hrs*' t\\o prmiut^ts, 
thrrtfori* n-prt'M'Uts thr approsuuatr hunt *! -f!ir-nt %i4"trtuui|. At 
tlus point thr l-uliil hardm-ss \\ *ntuviy " !rinpirar> " in rhararttT. 
Also, dissolved ridriiiin i^arbouatt-, hkr sodium rarliouatr, mi tit rat ion 
with luiurral iu*itl \vith phriuljihthnl-u a.s UMhr-ntor \n\t-\ a itrutral 
reartitiit as MUHI an iuntvri'Mu iijtn iiirarbouatr t* **omplrtr, whilst 
itu*thyl oruu^i* ituliratrs nrutrattsatton only uttvv 4i romjutsition *f th* 
bicarbonntt'. If, thrrrtoiv, tlu- iitn.1 usr| is if i-ipuxah-ut i^oitrt-ntratuku 
to tlu* soap solution, thr ioHowiu^ s %iiiijI*- vi-ii-ittunshtp udl ajtjro\iuuitrly 
hold at idfiil soft rut nil : 

M,, T. 


wlitTt* M|, rt'pmsrnts tlii' vuiuitir tJ* and rrf|turrd tt tirtttralisr th<* 
curboiiiitt* in tlu* prrsriirr of utrthyt uran^r, ami !h-ri-j'urr rrprrsriits 
nlso tlu* t.finjHrary hardnrxs, 

T rrprrHrlitH thr total hartliit^s, 

and P rt*prrsrtitH tbr amount i*l* arid |rijuin-d fur nrtilruhsatioii using 

All thcst* (ftmntiiirs rt-frr. of <*ottrM\ I** -|ml mluiurs of thr watrr 
under rxaniirmtion, 

If T Is grnttrr than M,,, tlti 8 watrr still mtitiiins Mum- |irrtitHUfut 
hardness nncl u grrlfr proportion of smitutti *arlomitr is nrrdrd fo-r 
the Hoftrniug o|u*ruti(iii. If V ih Irs* ttinit M ' f jf, th- Htrr .still contains 
bicarbonate and a greater proportion of eairmm liyt|pt\i*lr 1% rrqtiired. 
If M in greater than T, too tuurh **Miftrurr ^ has "hrm apphrd ; and if 
M C) is^less than *2P % an exeesMVi* tpiantity of liiur tin** la-rn tist-tl, 

If the haniuess is repreKeittrf) as parts of nileiiitu j-r KHI.OOO purts 
of water, flic* limit without rvrrss of Mftfliing ag-it is rrpre.nentetl 
approximately by the values 

MO- T 2. ami I 1 I. 
In all such precipitation ifirtlituls of softening water the actual 

* Fri.liirfW.J.^f. rhetn. JW,, Ittin, J4,Wi K4I, Xrtf.**A. **/< er /'A<m., IJ|H, '|If, !, 
3 KtVitwifturt. %rit#rh. riiifi* w, ('ftt-m,, Iflftt, a| } :ii;!, 

\VATKR. 243 

separation of the " insoluble " product's takes an appreciable time, and 
if the water is used or tested before precipitation is complete, misleading 
results may easily be obtained. 1 For satisfactory separation a, period 
of three hours is advisable during which the treated water circulates 
slowly through n large filtering chamber or chambers charged with pine 
wood shavings or similar material. This works more eliiciently after 
it has become coated with the precipitated compounds. 2 

The Permutit Process. An interesting process, fraught with 
great possibilities, lies in the utilisation of certain hydra. ted silicates 
of aluminium and the alkali metals. Such substances arc found in 
nature and are known to the mineralogist as zeolilex a, generic term 
which covers a series of well defined and inter-related salts. They are 
secondary minerals, occurring in cavities and veins of basic, igneous 
rocks, and when heated they swell up and appear to boil, whence the 
name zeolite * from (ireck <u*, to boil, and A/$os% stone. A curious 
property of the '/eolitcs is the readiness with which they exchange their 
bases without altering their aluminium and silicon contents. Thus, 
for example, a sodium xeolite reacts with u calcium salt yielding, 
according to tin* law of mass action, a certain amount of calcium '/eolite. 
For example, in the ease of calcium sulphate, 

Sodium /.eolite | ( < aS(), r ~:('uleium '/eolite | Na 2 S() t . 

If, therefore, a hard water containing a dissolved calcium or magnesium 
salt is passed through a layer of sodium zeolite, the calcium is abstracted 
and the corresponding sodium salt passes into solution. In this way the 
water is readily softened. 

In 1900 (Jans succeeded in producing '/colites synthetically and 
named his product /;m/m//V, from Latin pernmtare, to exchange. The 
sodium salt may be made by fusing together sodium carbonate, silica 
and alumina or kaolin. The product is treated with water and yields 
a crystalline substance* of empirical composition represented by the 
formula NaAI(Si() :l ),j . 21 !.,<), which thus closely approximates to the 
natural '/eolite nnnleitt\ NaAl(Si() a ) a . II a (). The commercial product, is 
usually prepared by fusing together soda, clay, felspar, and kaolin. 
The pennutit is placed in a suitable* container and hard water allowed 
to percolate through. The whole of the hardness is thereby removed. 
The sodium permutit is thus gradually converted into the calcium or 
magnesium salt. Thus: 

a -| C'aPm 

NiuPm fMgScfj N f a 2 S().j I'MgPm, 
and so on. 

The regeneration of the permutit is effected, by soaking with a 10 
per cent, solution of sodium chloride, whereby sodium pennutit is 
regenerated ami soluble calcium and magnesium chlorides pass into 
solution and aiv washed away. 

C'nPin i 2Na(1 C'ntl, |-Na a Pm 

MtfPw 1 tiNal'i ..... -MgCl, f Na, 2 Pnu 

J Wood, J. AVw, ('hem. Ind., 1917, 36, 12 
3 Set* M'MIttn, i'A/rf., 1017, 36, Oil. 

244 H\M;K\ 

When water is* very hard it is s*m-tun-s parthdlv suHrjird hy a pre- 
liminary treatnu-nt \\ith hun- and sda. In sunn- IMM-S tin prrmutit 
plant fed ttith such tival-l u.ilrs ha-. a^-d In work satisfactorily 
after a number of y-ars, fh p. rmutit b*euun>' I'nntamuiiitrd with 

chalk. 1 

Sodium permutit is jjradnalh ,it tarkni in hsslvid rarhon di- 
oxide ami more rapidly b\ tmn* -ral .irnl^. \\.if* r^ th, n tir' e<iutaiiuiir 
a<'ids in solution are lilt* ivd thn*u*.?h hm*-siMn. r iiusritlr lirinn- n-ai'Iunu 
the permutit. 

In this connection it may br m-ntu*nMi ,i man>.;.mi-sr permutit 
filter has hem invented for the rrim>\*d M! b rruu-. saHn, uhieh bet*ninc 
oxidised in some manner, jaissiblx m part thi'iou.;}i catalysis, but idso 
through rethtctitMi of tlir man^anrsr prrmutit, wtueh rnjutres prrtudit* 
revivifying hy tn-jttment with a solution if p-rmaiti'aiatr **f liiut\ 

The folknviii^ analyses f \\atrr brintv and alfT stttriim*f by per- 
nmtit are interesting. 3 The ilata iir- *-\prrssn| us parts prr miliitm 
(mc per litre) : 

Silica , 

Iron oxide and alumina . 

Lime . 


CO.J- bound . 

COjj free or half hound 

S(> :| . . 


Total hnrdiu*ss :l 
Permanent hitrdncss 






1 ntc 



II !i 


The water is beautifully Hoftciu-tl, hut 1 s * rewleml itMre rorrosive 

iowartlK iron and Ht-et4, 


By sterilisation is understood tlti- tlestrurtimi ot" all nr^'amsms 4 in 
the water, whether pathogenic nr iitif, In lltt- ithsruee of smtaMe 
mechanical filters or it* cases of dniibt as tn thr rHicti-ucy *f the litters 
in removing pathogcuit; germs, stcrilisatiith %Iin.i!l In resortnl to f for 
this is the only sure method tf preventing the ^jirnul of \vater--lornc 

Kinn.dhfm. AVti*. HM&. 118, 1ft. 

BlUHT lltu 

33. 1. 


* Kur the hiu?t'riitl t*xammntttm of witter, wn KrAitktfMl, Wrr*< rfyr 
(Lunniniifw, 1804); Kitvagt', JUtftrrivttipietil jmmtMlitm tf 
rnMM. JO Hi), 2nd !. 



Physical Methods of Sterilisation .One of the oldest and best 
known methods consists in boiling the water whereby very thorough 
sterilisation results. The boiled water is apt to be insipid and flat to the 
taste iu consequence of the expulsion of its dissolved gases, but this is a 
matter of minor importance in the preparation of beverages such as tea, 
coffee, and cocoa. As ordinarily carried out, boiling would be too 
expensive a process to carry out on a very extensive scale, but the 
cost may be greatly reduced by utilising the heat of the sterilised water 
to warm up fresh crude water, so that the purified water shall leave 
the steriliser at a temperature very little above that at which it entered. 
This is effected in the Forbes Patent Water Steriliser to mention one 
among many. It has been adopted by the American Army authorities 
and operates in the manner indicated in lig. 37. 

The feed water passes upwards through a series of narrow, vertical 
chambers H, (', I), K, separated by thin, metallic walls from the hot, 
sterilised water, and enters the boiler F at a high temperature. Here it 






r c. c. u rr^~ 















Kiu, 37." -The 


is raised to boiling and escapes into G, whence it passes clown the 
tower, giving up its excess of heat to the cold, raw water within the 
metallic partitions, and escapes at II at, a temperature only a lew degrees 
above that at which it entered the apparatus. As it passes down the 
tower it also draws with it from G the* dissolved gases which have been 
expelled during boiling, and reabsorbs them. The sterilised water, as 
it leaves II, is devoid of the insipidity so characteristic of water that 
has been boiled in the ordinary way. 1 

Ultra-violet light, such as that emitted by a mercury-vapour lamp, 
exerts a powerful germieidal action on water and ice. In a series of 
experiments carried out at, Marseilles it was observed that a lamp 
working with a amperes at 220 volts destroyed pathogenic organisms in 
water within a radius of 2| inches in two seconds. 2 In order to ensure 
complete* sterilisation in u stream of water, the latter is made to How, by 

1 Many other fwiiw of HtrriliwrH have boon devwed. Sec Kidcal, Water and itu 
J'urijir.ulwn. (OroHby Loukwooel, 18JK7), <tr. 

* S*ti Don imd Chinhulm, Muttem Met/nnh of Water Purification (Arnold, 1913), 
pp. 353 </ wq. ; H. and K. Uideal, Wakr Mupylie* (Croaby Lockwood, 1914) ; alao Engineer- 
ing A'fw-w, IUIO, 64, COT ; Trails. ltit. Water MityinetM, 1911, 16, 90. 



means of a series of battle plates, close to tin* lamp on three su 
occasions* as shown in fig. HH. 

The ettieieney of thr proerss upprars It* In independent, of th c . 
amount of dissohrd o\vrn, the Mrnui'id;d .jetiin lu-iti^ a pmvlv 
physical action not in\ol\ini* the pioduetiou nth* r uf h\dro^en peroxide 
or of o/otic* 


I A '/ 

* ! i Hit ISI I) 
WA ! !,,H 


Chemical M-^tliodH of StvriliHatioa. \'*-r\ rihn* ut strnhsatiun 

<f suspect eil \\atefs may lie rffrrlfil li\ rip IHIIM! iu* llpiis s ,iini Ilif rust 
may be* materially mhterd by liist pttrihuu* f li* \\,it r ,t-. tir a% may he 



H tl> J 
WATLR I.,,,. 


/ - '-\.:\E 












Fiin till. -Th* Hinu 

s t ! Hit 1*4, D 
WA I tH 

by mechanical filtration. The thud star ul* (mnfirittiii is tln-n * fleeted 
with a minimum quantity of the dtriuical reagent. 

One* of the most valuable Mibstniu*es for Ibis pttrpftsi is <>.;nnt\ t'*r it- 
acts rapidly, iiuparts uti taste tu the water, anil lr\rs n* .solid rrsitlnr. 
Numerous o/,onc instaHatious have been nvcted fur this purpose both ui 
Kuropc nud in America. In Hint Fruiter pushr.sMMl WMIH- thirty diflr-rmt 
plants, the largent being ut the Parthian waterworks wf St. Mmtr. Il^re 
the water is first sand lillernl and then o/unisrct, o\rr **! nuUion 



gallons being treated daily. 1 The ozone is prepared by commercial 
methods such as are described in Chapter V., and conducted into 
sterilisers, of whieh various forms have been designed. 

The Ilouwrd-Hridge Steriliser is shown in diagrammatic section iu 
lig. 39. 

Crude water enters at, A, and draws in from pipe B any unused 
ozonised air which has collected at C. As the water travels round the 
first bend, all the ozone is usually extracted from the air, which now 
escapes from the system at I). The thereby partially sterilised water 
now receives a charge of freshly ozonised air through the pipe E, and 
passes round the second bend and between the bailie plates until it 
reaches C. At this point it discharges its excess of air and escapes at 
F in a highly purified condition. The excess of air at C is continuously 
drawn away to H to partially sterilise the crude entrant water as 
explained above. 

This system possesses the deckled advantage that no external power 
has to be applied to force the o/.one into the water. The gas is drawn 
in by suction as the water descends the first limb of the apparatus. 

Several forms of ozone sterilisers have been described by Vosmacr, a 
a recent (10KJ) development, of 
which is shown diagntmmatically in 
Fig. -to. The feed water enters 
through the top left-hand tube, and 
as it passes down the cylinder meets 
the ascending stream of ozone which 
effects its sterilisation, and escapes 
at A. In the Siemeas-Halske steri- 
liser (lig. 11) the feed water passes 
down a tower containing lumps of 
some such material as Hint., coke, or 
gravel, to increase* its surface, and 
meets an ascending current of ozone 
which effects its sterilisation. The 
escaping air at the top of the vessel 
is still rich in ozone, and is dried 
and passed through the ozoniser in- 
stead of ordinary air, and thus raised 
to its previous ozone concentration, 
suffice to sterilise I cubic meter {1000 litres) of average water. 

An ingenious apparatus has been designed, 11 in which the ultra-violet 
light t produced simultaneously in the silent discharge employed for 
preparing ozone, is utilised to assist in the sterilisation of water. The 
lust named is first acted on by the light, the partial sterilisation thus 
induced being completed immediately after by contact with the 

Hydrogen peroxide theoretically constitutes an ideal steriliser, for, 
like ozone, it destroys bacteria without adding any foreign chemical to 
the water. One part in 10,000 sniliees to destroy ciliate infusoria, 4 
although it minimum of 1 part per 1000 is necessary for the destruction 

1 SHI Ktfli'ui, />/w nV. ; l><n iuil (Ihinhi 
; ' S?c! VoMmwr, (Jxtttw (Coiwiafoio & (Jo., 
J K. Kidwil. JKnyiinh Patent. IBilKO(UHO), 
1 Pnnrth. CliriH. Zrntr., I MM, i., 174. 


** AIR 


WAI LR " \\ 


['- -'.. 

1 A 





Km. 40. - A VoHmaur 

About Is'J grains of o/,onc will 


*\\i I \ 

of Iwrtt na s aittl \ , ^ ^<t/ihjs*" M* ,t < 
Owing tu its ns!,ilnhl\ u *l I i, ,',* ^ 
only In- usul ftir ^t, nil* jj % * jt 1 r, , t M ( . 4t 
certain nut.tlhi* jhj.*\j.l* , lo f ?^ , * . |, 

,'-!n*n is ralhrr slow 

H $ (i ^ 

W A 1 I II ** 

A in 

V* 4 ! I. ii 

I 1 VI i 

Htuhtltt ani 

, i , , i/ r ,' \ (l f) j<r 

\ puvsrssi-s a iuuttit 1*1 siiti* il tl ,Mtni) ,?nl , t | tit s.uurfmir 
serves us 11 hoffturr iW Imrii ,it IN, vmltttNi *Mihfu,it r I** HI" n m ratnl 
by uitMidiim ufiiisMthiii rarlttM* liiitvutt, fiinJn fd rttn:' tin" piv* ipi- 
tntiou of oitMuiu (*r nifn'in MUIU> i uhniMt^, in II*. t.iv *I t.tuporary 
hanliifss, hy msitniny tlir stihi nl t natin h iMlm- .nitf. ,111*! in Hi* r;isV 
of pennitiuiil huramsx, l\ ilmitili ittrump,, M tif*u with tin ndrwm 
(or nm^urMutn) sulpliatt*. Tliit% : 

Nu t O a i t'liiljti'OJa Xii. a 41l 4 : -I! 2 ll 3 : 
NS U'Oa i H.O Na^UI, ^ 11,0,; 

Xn,ro a i t*so 4 XH^SI^ c Hi'iij. 


bmi rcroinnu-iuUti, ilir fontT H*III ,ii imtrr i| tr ,, tl r - hi 
whilst un nitputT form <f thv in|.|i, r ^ tw . ( | ilt tllr ^ rri | tH tit f 
innioral waiters. 

Chlorine is a pcnvrrftil grritiiriilr, unii in IHH-IIIIMUU tiirmi 
popular lor tin* ptirptmc..^ I! , imy b r , |MH | itl ti|r forlll (l ni.,uil rotu. 
or as chlonnc water. It U Miititrttiiii-H iimrr rt.iitvrtiiri|, I,,,uVvt*r. in list 
10 ||>. U f wim-h iir*% in ut .,, ITII |. HuHiru-i,|. |u .strrtliM- 

1 St'<* Htit-ht4, ZrilMfi. Mt/yirnr, JUtm. 6l 411 

3 SIT Uiiiml. HV*r ^/^((nwhy I^^W.M^. Mm,, |la | H |. 

J SM,liuilHrt, A'wy/wA /'<t/rir/ ( t74iK) (HNNl) 

* C'n.r. ^-iV-rA. // M *Vr !!.g g 4 K 


1 J% " 

, /W, AW rArm. 
hr liil.iM-nr.ft, V..I, VI II, 

WATER. 249 

1 million gallons of water. 1 tiodium hypochlorite is also employed for 
the same purpose. 2 

tiodium hydrogen xulphntc* NallSC),, in tablet form has been recom- 
mended a for travellers, and was used in the Boer War, about 1.5 grains 
per pint or 1-75 grains per litre being required. 

Citric acid I part per 1000, is gcrmicidal, but imparts a strong aeid 
ilavonr to the water. Carbon dioxide under pressure is also elTeetive; 
and bottled mineral waters, such as soda water, are usually very sale, 
lo drink. 

Alkalit'n are also powerful germicides. The addition of lime to water 
in accordance with (lark's process for removing temporary hardness 
effects the removal of the hulk of the contained bacteria. 1 This is 
largely due to the mechanical effect of sedimentation which causes the 
bacteria to be carried down with the lime, only a portion of them being 
killed. After u time they rise again into the water. By addition of 
excess of lime, the germieidal action is increased, but even with 0-ii 
per cent, of lime* (calculated as I'aO) or 20 parts per 10,000, the sterilisa- 
tion is not usually complete, 1 * whilst at this concentration the water is 
too strongly alkaline for most purposes. 

S<T MiiHnn, t'hvm. ATr/w, 11)01), 100, &JL 

i !! \IMI H \ Ml 
IMnSK'U. rKorkttTII.S of \\VMU. 

I 1% not uid\ aM t* \i *t u ui **'. a J -. *^ laiit.r, n.uwly, 
as Iet\ liquid u it* i, .'*i<d \,ipiw **i ,!< n , >?**. '- P M * \\ t.dhn< modi- 
fications ofth Mud linu r.t'i ht pj lu I 

WJirit fill' hmpi latin, l pii* t* i' ? wiu.Ji' ? u < l fifftft i tljr 
inary ali>sji|i MI- jr ' ^tii< , ?"'!ti f ./ ^ \MJ ^ ' Ji.irph ,it a 

ttn itiv*it*t*illt ti Uijit i.if t*i? , ^JM b i H, * < ''<Jn< jiuft! hrtun is 
*. Un tt't'i*U!it ut lli * ,t . % if h ^Jat J 1 1- 1 ^ * ***' ^ it I I* mj f iltirr 
cull IH* uttnilii'it it has IIM li rhu .* u a 1 * th ,' u*i,'iil ; i> to! I h I '!siUs 

ffirtMi h\ |tn sau* > >i 1 J^M , *il t*i* .ifiMM f*lii^ lu^i 1111*4 
the transiiiou It IIIJH tattm *d ! luunf-i In ,ij*ji'* K nitiij;^ 

That such (Mi*;ht tul tli *MM 4^!'^ if *Ji J i \ J-nni 'Ii**ui uti ! 
\vho % in 1H|!^ siiu\\id that Uuia lh*pti i! inii*iii iJn*Si', .t rnninrliiiii 
must exist hit \\fi-u tin tiittfiin 1 ftojiii tit -Mini .ni Hi ji-* tn , The 
following year this w*s r\|n tttu* ut ith d-ut**i ti.? *1 In la* lti*thrr 
W. Tlumison |Ltl liihiii) ( x tth* i**Mi*d th f trdt ^ jtiiv.uir ut' H*I 
uttuoHphcrt^ th*' ttititiii}* puint nl m v l**u i it i^ n IKV < ,, MJIU- 
vnlcut t u full <tt O-OilTJl |* r fittintisph^ i . In th t.dil **ii p, *V! itrr 
given the tuotc accurate tit It 1141111, itntn * ul f (\iiM(u.uii> s th thuit * r ilutnn 
giving the n suits t*alt*utat(tl tti tuiir **i .utittmph' u , 3 

Thrne tlalu nr 1*1 prisi-ntul ^ in th pi''<.>m ( t't^p i.ttui* tiia >f iaai 
(fig. 4*2} by thi*fusit>u fiu^f All nitirii i-> %t * p, i*ul in ^ 1 huv.tiiK thf 
uhKcitisu^ iis the n suits tti th last mluMat *4 I 1 !* di\* f.iiil*' eh-arl) 1 
demand. This eur\e nphstitt* tin i|MthluittiM t*tu^n uidtitary 
ice or ice I and \\atrr, III* ftifili |nii*f \ ipi *uli ' th i'Miiditiuit tl 
t'tjuilihritiin of \vatei \aptttr, hijmd w*iti, .iiil j< f. t ud i a piin.ur* 
of iJtiOO kilograms, enrrt'spittidtif** tofh* |t*int II in Ih* ti^m? llirM 1 s **! 
hrenk in the fusion eune, a in \\ form t>t t**< a* ,itm?, KMM^U i % * it* 1 111 

J *f, TtinntMdtt. Tlttn . titty, .Sill', /,(/< JH|*, I(* *Vi 

a W, ThomHnttt /Vw. /Vv. H . |,*fjK t I^iii, A , ;M 

3 Tnmmnim, fl i**/. Jwiil* IM*, lii* ^/i t;'* , !?,-, ix- I *^ / 1,1/1 Ft* 1 

<*ttrliT <lutlt, H*M, /V# /t*/ |S* s |HH* fll, tt.'ii 

* A jr*HHUti of *!* ttiiiti*fftifft |Vf* i tii **l ! r*$*i m* *! l^nii^ , |t> |# i .*| MII 
or convoiwly ^ | } ** s * uri 4f i Ktln^t^tti |^i j * sii * |A! - **/ ^ ,, uJf*>g* 

f The? iliitgnuit t.i mt tlruun t* M *!*'. hut in i^,i^rt/iva i . i4i i i.*I^ ft**- M|!* 



the melting-point of which, in contradistinction to ice I, rises with the 
pressure 1 , as indicated by BC which slopes away from the ordinate. 


-point, u ( . 

kilograms per 

HtJ. ('.III. 

lYi'ssinv. in 

DeproHHion in 
Melting-point per 
















1 1 55 




11 10 





1 573 










22- i 





At llu* triple point B, tlicrt'lori 1 , liquid water, iee I and ice III are in 
equilibrium, the temperature bein^ 22" ('. Tauunann * Ibuud tliut 

'. diagram for water, ico, aiul waior-vapour. 

up to pressures ul" 2500 kilojujrnius, the solid produced by the spontaneous 
ery.slallisalion of \\ater is invariably iee I, even in the ie.e III region. 
Abo\'e this pressure, however, iee III forms, and it is interesting to note 
that wider these enttdiUotts the i<'e has a .smaller vohmu* than the liquid 
water, so that a vessel in whieh the pressure is greater than 2500 kilo- 

1 'rainumiin, 7*<itch. nhyxikal. ('/win., H)10, 72, tiOU. 

iMipl'*d ! i 1 m* 
. f l, v 4 i. 

th* expansive 

,!' ,tt ini'ivase of 
liquid \udtf dis- 

HI *ij. 

per sq. B iu, e.n>ut 
force i*t* in- format i*'<, 

Hrtllllil! ! ti* thi tup! 
pressure. aeei*nqaw< it i\ - i.'ii *^ ! '' 
appears and weiatN i*< th i;^ e!i", 1JM, 
bet \viru ice I ami if. HI, It I* i:la 
triple point r pi** * ntiie; lit* * q*a '' T ,M<> 
in* I, ic'r III, attil i*'r II. Il n*\ U '^ 
triujH'mtun ItttttJiti, fit Mh*i pK^ i 
uhitvj 11 lift* not *luwu HI tii i a t 
n|tiilitnutit lit I wi n u* t .*u*l j '< it- cti 
furtimtitiit tt trr ill, if r. jun.jh!, fMtia^ 

the potftt D illult! *i JlJU , 

i'tjuilibriuiu lrt w< ru ji'i I tul t*> III 

If, on the "tilt r liutl *n i - -hn M. 
pressure are both rar* *l, ns?.t*l J i>* ! ^ ^ 

Din whtrh mve* tht ruiptit i*i '. M| pni i 
ire V appears, 1 this lntJi- t h* Mipl pu 
it*i* \* own ro-rMst, II) i/4iii i,s^ i * ?ia 
in<*t'eusi' in pr'sstjr*"* tin tnpl |*M*if t * 
uliuinect fruiti It t\ .1 ennMl 1,1 14 U" 

At i* liquid \\atn *ipp> 41 *, .niJ i i* 
ice V. 

lucTriiM* i)f pi't sHttr* .ten iti| tui< l 1 
tis to pans alon^ tit* eurv < If !** iit f 

ife VI nppraiN, This pmnt i |n*'rftl. Hi 'MMij'p,. <i 'puhtmuitt of 
lee V, in* VI, and hquul wat*i, un! ii> i * .! H< o i , i? HI* U .if <Mfl C. 
By incrensinu flu* prtv%un *in*i i.*i m ' U<- i ?i} i,* f ui -441 !it?*IpT s 
ice V disappejirs, UK r*|ii s nltu * th* opuhliuuiu ; V I h}iutl w<itr. 
Ttu* rettmrKiible fiiittin itl er \ I h* * ii th >.! tint if i. '! MII/// |. 
tetnpcntfuwtt tthw to i'., 4!H*r*aM> *i ju *.iu '*'*tn J* n* if* tn*ltin;,- 
point* 1 lntli*ril if is |ntH%il*t* ti IIH *M|MJ * d i $n 1 1*. I iiii *J ie- VI 
even at HO" C*. The fr 
iu the following tuble : 


Fuint | ,. 

In \ MtttMw in 

'i m-., this itrw 

^ .h| phases 

iiur ! ami thr 

auI w pass 

<oniitit>its tf 

ut ! tr*ius 

*u J I* **! t* IUJH i.iture ami 

, fa r ,U . . pjs.atou^ 

ti^i * II ftil 10- 1 1 L At ( 

?f ^M It J>*' U, i i III, and 
f *j * ^tui^ ,iui !*v a slight 
,* ,h i, U*i p ii enulii also he 

1*1 i'.tn autt ,i - li <f lil rise m 

*"* III and 

H. .ii **h*h poutt 




\Yater-vapour liquid water 

ice I , 

Liquid Winter ice I ire III 
lee I -ice II ire III . 
Ice II ice III ice V . 
Liquid water tee III ice V 
Liquid water- ice V ice VI 

$ >*!* mitt . 



Th<* position of ice II is interesting lor it is stiri'iMi 
phases., and hence can never he in rquttilmtiiti willt liquid 

. Clci, Ilil^^ jj, 377. 

tn-a ; 

IT : 

; tHU 
-d bv Mlid 


It will ho observed that no mention has been made of ice IV, the 
existence of whieh is uncertain. Tammanu obtained certain indications 
of the possibility of its existence, but Bridgman was unable to confirm, 
so the term bus been left in order that the nomenclature shall not 
require alteration in the event of the possible existence of this particular 
form of iee beini>' substantiated. 

Ice I is tho lightest variety of ice known, having a density less than 
unity, all tho other forms being more dense than water/ It is the 
ordinary ieo \vhieh is always obtained during the normal crystallisation 
of water under atmospheric pressure. 

Numerous attempts have been made to determine accurately the 
specific gravity * of iee at C. with reference to that of water at C. 
The more important results are given, in the following table : 2 



0-9 ITS 


O-'.H <<><>() 
0-1)1 807 ! O-OOOO-t 
0'<)HU5 ! O-00009 

(MMMJ1 ! O-00007 


Artificial ice 

Natural ice such as 
icicles or blocks. 

Artificial ice produced 
by carbon dioxide 
and ether. 

Nodi ffercncc observed 
between old and 
new ice. 

Artificial iee weighed, 
mean of six deter- 

At 188-7 (-.. 

Artificial ice 


Dufour, Compt. rend., 
1862, 54, 1080. 

Bunscn, Pogg. Annalen, 
1870, 141, 1. 

Zakrzewski, Wied. Anna- 
len, 1892, 47, 155. 

Nichols, Phyff. Review, 
1S99, 8, 21. 

Barnes, P%9. Review, 1901, 
13, 55. ' 

Vincent, Proc. Roy. Soc., 
1902, 69, 422. 

Dewar, ibid., 1902, 70, 237, 
Leduc, Compt. rend., 1906, 
142, 149. 

The density of iee at 188-7 C. is given as 0-9300. 3 
The approximate densities of tho polymorphic forms of ice arc 
as follows : 

!<< II 
! Ill 

1 -03 
1 -01 

Ice V 
Ice VI 


' Tin- Mix'oitK- ifriivity lit 0" < !. diffcro from tho true density of ice at C. by an exceed- 
ingly Hmall amount, nine,- 1 K ram of water at, C. has a volume of 1-000132 0.0., and thus 
(Ittfortt from I co lv onlv 0-OKt pr cent. ,. 

K^rilw data arc now c,f hiitc.rical intwwrt only. The^first ^^^^ *| e 

if '*.'M!''' ^Ho' found.' that Ha'iwrtnTf wata yielded 91 j parts of ice by volume when frozen 

r,;;;;;!L iS*i .. y u, . W -U ,- * and ? t^~p^ 

i:ti s*' i * 

It \\iii h. n n , t ,M 

It \\i\\ h< m*tir i| *h ? t!>! 
diffrfs uuh 1 x li't^r o I . , i .1- 
nut hr su M >t . h >' i. ' ' i'i t 
had tiil i iiiH fc < *i v i * i f * 
all thi' r suit . K. i, i, I M' , ,. , 

Hot ll, 1 HI :i lit Jr.ii ,0! < * , f .'*'"' 

I .1 i ! th. Uttrr 

ThiN htm-* fiaiit^I t Hi iMhr* M I 
und lit*' ruutr.trtttw **n n,* Ituv* * f| M'*I* 
hits a \t4lllti? **l I'ftfNIItl i- t- *'!* 
magnitude tf this rhaiu/ tu \i4tiiii 
of thr fnllo^in^ d*it i %l,ii*h ? i*. f r l* 
of t In sr i **, \i ? ji . M- i H 

l I , j t *.MT ."MM M 

i a M) H,d* r jf fi (\ 

Vhun rli !*. |* ' MI* it 

It is liitt ri stu*" tf in f 

This \\-is tirst ohsi r\ d In 

on standiit*; ; iiltitiii s 'Ii tl, 
old ami n \\ it f * , In ,ii*\ 
of \\*itt r ntu it 



uiij t< i, Ji"htl\ 

, , } . -|f. / 'iU\tltrt.\ 

t, i t*\ \n*hi U jn 
-tn j !j- hi Hi.wjt 
>hff' i nr lutnnit 

<s 1, \n JI, Tin 
*tji,is.t j,ut m thr 
i.i'^uii M| itit'ks, 1 

t f *\,f*-tlli! iJ.tlh ll IllUll 

l tfi th T. Mi \ .rtf I $ Its fill 

lirf ,i v *l fi m *"% I IM!' i ^ it li air Ifi i 1 
l*,lfvr , lift fl,fllli\ i 'In Jli/ it \\lth H 

vtirll tit Jut' .'4 ^., iifi ,dl* ttiit'f il 

In li* I?* .1 !*n\tuj< | ir* iiitl %;lt 
th vt,*t. i h. , i , f iri I UV.t * tilt 

n tii4l f I lir ; ifiipU i lUfnltti 
'.thf **i Hi* \|t n< i 1 ,j| i* iifly 
fil\t >MM) J i|f In I!ii?Ijii\ Hi 

!'7 , * 11 ' %)< ifo it \ . * it 

|-i,ili| til I!* *l| ,** "\Uiit * ill |H7l, 
4 t IlijH Uilllli tI 'M I , I** Hi** ill 
tfltlifff Ultliitif I-MJ. Lttli4i ,4* Was 

proved by the fuel that tit UH|^M| ',!<! hall %IiI! iaftlnl ltui the 
eyliiuler was shaken. 

The* hardness of ier i*> !%"> (Mih* *eal ), 

At low teinperutiiies iee is i \*ttiiitul\ hanl *tiil \ii\ rrMst.utt to 
shock. Ah(Ae I*J < .it hfrmstsnttilt'.t|i|4i eMhl\. 7 He h* j* \\ -itsoit 

'l"iil, rAriu,, | mm, 6;|. -ill, 



M JHH7, 

, , ml tlw otiiy litfiiiii lliiif <*{**t)i(U in tl iiifmrr. t,iiuil titiiuflj 

antimony, and ir<m t4t,v0 niiiiilnrty, 

4 Hudirrff, for., IH70, 3, H>, " -^ |UijMjnrfttii. r^m^r. */., |7I, 71. 77, 

6 BuKHiH|fii|f, /or, ri>. ; HH iiliti Krt*)H, l^/f, Jnmi/m, |MT;* ( 1 46, Ji| , M-.ulm*** ttd 
(.lianwU^ww. r7iiw, /*/ii/,, JH72, 34 54 H ; Si*hr^t^r, Jfmi/ri. IHMI, iwi}, : . s-hf*.Hi-r. 
MtzuntjHtor. A*. /li'inl. B'IW. H'iV., IHTKI, lo f27 i Jlirf*lirt, t IH^I, i,. mt, 

7 Andrt'Wft, /*:. /?y. .SW. t IHHU, 40, M4> 




. the marriage of lrin<i (iaUit/.iu in 1730. , the Russians 
in honour of the event, the cannon W ,thstandm S the 
more than onee without, hurst hitf. 1 . 

I cxer s a detinite vapour pressure which, at (>" I'., is identical 
with tint of water, so that, at this point, the three phases solul, liquid, 
m c >-cxst. This is not tlu- real triple point, he-cause- pres- 
1 c low s he melting-point, of ice, ml by 0" - .H the 
n dti. -pcnnt. of i<r uncU-r a pn-ssun- of one atmosphere. I he truo 
tri, mJn tlu'n-fore lii-s at ! 0-0070" (\, and in t,lu> absence- ol air OH, 
wi!i( Uu- vapour pressure_of ! at. vanous tx-nvperatnrc-s, 
i<4 tornunl the sublimation curve* (li#, 44). 

n^im- cf icv at vanous h ; n M >cratutvs below t as 
, by several iuv.sii^tors^ the results l School and 

House beiuK given In tbe following table : 






Vapour IVoHHuro, 

, U J"t\ * 

nun. H'^. 





















The pressn.v, ,, <f ire at any lemperalnre /" ('. may 
calculated from eilh.-r of the following ,.(|ua1ioiis : 

(i) log /I/-1-S7U -<B(I 


Several a..l,TmlnuUw luivv hee,> nuule of 
tm( . tiou O f it ,. with rise ,,.! fall of tenq-eratu.,. 
results lor tlu- wjjleient /' <U ivi-n 
luhle : :i 

in th< 

1 irir nr, ih,, 

^-m,, IH45, 3S fl4 ' 

/* W . 

, 64, 110; Mohand ( 




Range, C. 

-27 to -2 

-5 to 
-8 to -12 

-189 to 
10 to 0-37 

Coefficient of 

0-0000514 (linear) 
0*000154 (cubic) 

0-0000528 (linear) 
0-000158 (cubic) 
0-000077 (cubic) 

0-000054 0-000002 


0-000162 (cubic) 
0-000081 (cubic) 

0-000152 (cubic) 


Struvc, Landolt-Bornstcin, Tabel- 

len, 1912, p. 336 ; .from Mem. 

Acad. Petrograd, 1850, [6], 4, 

Pliicker and Geisslcr, Pogg. An- 

nalen, 1852, 86, 265. 
Zakrzewski, Wied. Annalen. 1892, 

47, 155 ; Anzeiger AkacL Wiss. 

Krakau, 1892, p. 153. 
Nichols, Phys. Review, 1899, 8, 184 

Dcwar, Proc. Roy. Soc., 1902, 70, 

Vincent, ibid., 1902, 69, 422. 

Judging by the results of Dewar and Vincent the temperature 
coefficient is high, the expansion coefficient covering the lower tem- 
perature being only about half of that over the range 10 to C. 
The results of Struve (1850) closely agree with the more modern work 
of Vincent (1902). 

Ice, when free from air bubbles, is colourless and transparent, except 
in thick masses, when it appears slightly blue. When formed from 
water at temperatures of 1-5 to O 6 C. the ice is usually clear, and 
possesses a maximum density and cohesion. If produced at tempera- 
tures below 3 C., minute bubbles of air render the ice milky. 1 

Ice crystals usually belong to the hexagonal system, 2 the axial ratio 
being : 

A : C = l : 1-617. 

According to Hartmann, 3 the crystallites separating from various 
undercooled aqueous solutions are of three kinds, according to the 
concentration and extent of undercooling. Hexagonal crystal skeletons, 
consisting either of hexagonal plates with six rays or rectangular 
plates with four rays, are produced when the degree of undercooling 
is small. Spherulites are formed when the undercooling exceeds a 
certain limit, whilst feathery growths only occur with very dilute 

i Pictet Jahresber., 1877, p. 54 ; Arch. Sei. pJiys. not., 1877, 59, 154. See also Turettini, 
Jahresber., 1877, p. 54. 

7lys " 1878 > M' J 3> 283 ; Groth, Tabellarische Uebersicht Miner - 
Rinne > Jahrb ' Min '> 1919 %&> 2 5~27 ; J. Chem. Soc. Abstr., 
* \"- Wiss ' X**-PlW. Klasse, 1917, 69, 57; J. Chem. Soc. 

. , ii., 75; St. John, Proc. Nat. Acad. Sci., 1918, 4, 193 ; Dennison, Physical 

Remew, 1921, 17, 20 ; Bragg, Proc. Physical Soc., 1922, 34 98 
3 Hartmann, Zeitsch. anorg. Chern., 1914, 88, 128. 


solutions. That the different forms are identical is shown by the fact 
that muiereoolecl, pure water free'/es at the same temperature when 
inoculated with any one of them. 

Prcndel l has concluded thai ice is dimorphous, crystallising in both 
the hexagonal and cubic systems. lee crystals arc "brittle, and their 
viscosity varies with the direction of shear. 1 * 

The refractive index for sodium light is 1-310J' In conductivity of 
heat ice resembles ordinary water, 4 except that the value varies slightly 
with the direction in UK- ice crystal. Its eoeilieient; of compressibility 
between 100 and 500 nie^abars 5 at 7 ('. is 0-000,0120, as determined 
experimentally by Richards and Speycrs, a value only about one-fourth 
of that of liquid water at neighbouring temperatures,** about live times 
that of glass, and somewhat less than that of metallic, sodium. It 
appears to have an abnormally high temperature coellicicnt, as the 
following computations indicate : 7 


'IVwjiornt ur<\ *' ( '. 

ComproHHibiUty of fco botwoon %tirc 
'KHuro and tho Molting Prosnure. 
(Mega burn.) 


te ob\erve<i, however, that the computed compressibility 
is appreciably higher than that actually found, and the 

It will 

nt 7" ('. is ji _ 

authors quoted surest that in part, this "may possibly be due to a 

considerable softening of tin* ice* just before melting." 

When rubbed by liquid water, ice becomes positively electrified, 8 
a fact of considerable meteorological interest. 

The specific heat of ice is approximately half that of water, namely, 9 
0*5057 at ('., and expressed in 4 -i() calories (sec p. '271), Its heat 
capacity \\hrn pure varies but little with the temperature, 10 and the 
following equation is given as representing the specific heat, Q^ at 
various temperatures, / : 

<J, 0*5057 | 0-001, 8W. 

* I'rt'wM. Znterk. AVr/jf. J/iw,, I HIM, 22, 70. 

s Sn lWii<y. /Vw, fit,;/, ,SV,, HUM, |A|, 81, 2W) ; (Iwl. Mag., 1895, [4], 2, 408; 

M*('(ww<l, /Vor! /%, iSVir,. 'JHIU, 49, :W:i. 8 Pulfrich, W'w/. ylnw-aZflw, 1888, 34, 326. 

4 Tn.utitn, /W, /^ri/. Nf. Ihthlin* !H!W, 8, (JO I ; Htrancs, Alii II Accad Lincei, 1897, 

6 Tin* wrynfmr IK tin* <*.U.S. utmoMph^rt' of 1 million dynes per cm. 2 and equivalent to 
0-987 ttrtiitmry ntmtM|ht^v f Uii'hitnlH and Htull, /. /t-wfr. C/wn. *Voc., 1004, 26, 412). 

s Hidiitnb ttiid Hj^yrrn, /. Amvr. ('hftn. *S'r. % 1914, 36, 401. 

7 C'liintttitiMU l*y Hrtti^iiuut, givnt hy Ei<'h,rd and 8poyor loc. ciL, p. 494, 

ft OtwrviHi hv* Fiifitdiiv, rtnflrtiuid by Hohnoke, Witd, Annalc.n t 1886, 28, 550; 
* - * Dirkinwm AW! OHbonirs J. JVflirA. ^li^. *Sn. f 1915, 5, 338. 

3i8H. xo. 58, 

111 A. W, Smith, 

HKK>, 17, 


At low temperatures the specific heat falls considerably, us is evident 
from Dewar's l researches, the results of which are t(iven in the 
following table : 


IVwMTuf urr Ustni*i% ' <'. , SJHV.IU* Unit f l.-t\ 

18 to 7H (I'ltJM 

7K tu 1HH : 0-*28;> 

IKK tu ^5^-a : 0'1-HJ 

The latent heat, of fusion of" tee has hern thr subject of mueh research, 
The most noteworthy determinations arc given in the table on p, *259. 

Under atmospheric pressure. the value 711-7" would appear to be a 
fair mean, accurate to about CM per eent. employing the 15 calorie. 
Increase of pressure reduces both the inrttiug"point and latent heat of 
fusion, as the following data show ; 

Temperature, "C\ . 5 to IS 20 

Latent heat (calories) . 70*8 78-7 OK'O <W-r 57-7 a 

The latent heats of fusion of the polymorphic \arietirs approximate 
to thai of ice I, and but little exchange take* place dtirinfi transfozuna- 
turn from one variety to another. 

The* heat of formation of ice from gaseous hydrogen and oxygen itt 
C. is OiHH! Calories | V -. 3 

Pure ice, free from air twhbles, ttivitics iind suspended material, 
frequently exhibits u beaut ifttl blue colour when MTH in bulk. This is 
regarded as an absorption effect, due to thr tendency of large molecular 
aggregates to absorb the long rays of light. 4 The Murks of ice lose 
their colour upon prolonged exposure In light > ami tiiotv rapidly upon 
exposure* to direct sunlight, 

Colloidal Ice. Tee enn readily be obtained as an orgatnosul by 
rapidly cooling saturated solutions of water in organic media, \Vhen, 
for example, chloroform, saturated with water, is rapidly eoolrd to 
SO** (\, tlie ice separates out in partielrs of colloid dimensions, and 
the sol may IK* passed unchanged through filter pftprtv* 

B, /^i/A'iw/ /V/ifT/fV, (if Liquid fl'iifrr* 

Although water may be cooled below thr lVrr/jri||-potnt without 
, it is not possible to raise the temperature* of irr, under 

%, *SW. f 1W)5, |A|, 76* 11^5, Sw n\*t XMnltiiryrr itiitl l^ntilii /iff, 
Dtut. phyMkuL (Je* tt UMI7, 5, J7/>; .Inrkatii, /, Anur, /'A*-/, ,sW,, tPl-2* 34, 1 470; NVrtiftt 
and Kortf, Milzttng*for t K. AktuL Wi**. fcrtin, I!*lf* tip, U47, Srti ; littin mitl tiituwm, 
J, j4mer. CAm. Voc., 11*17, 39, 2384. 

3 Bridgmnn, l*ro. /JMIT, /ifinl., UM'J. 47. 441 ; ttwg. rA*-wi. III! 2, 77, 1177, 

8 Boe Roth, Zi'tof/i, tiletonvhnit,, U20. 26, *^HH. 

* H. T. Harnoft, A f lrr, 1910. 83. 188, Unman. iWrf., !5'.3, in, 13. 

8 Saa von Weimarn artd Wt. C)t%vIi1 KvUluid K*il*A 
J. j|?twj. /*Ay.*, CIi'w, /?r. t If! I II, 4 a, *tl, 



ordinary pressures, above C. If, therefore, heat is supplied to the 
system ice- vapour, the temperature remains perfectly constant at almost 
exactly C. until the whole of the ice has melted. As already ex- 
plained (see p. 255), the temperature is not exactly C., for this is 
by definition the temperature at which ice melts under atmospheric 
pressure, and since increase of pressure lowers the melting-point by 
(H)07G C 1 . per atmosphere, the melting-point of ice under its own 
vapour (pressure 0-4579 em.) is +0-0076 C. During melting a con- 
traction occurs, 10-00 volumes of ice yielding 10-00 volumes of water. 













I{egnault,\s result corrected by 

Mean of 17 experiments . 

Value depends on that assumed 
for contraction of ice on melt- 
ing. Hunscn used 0-91074 as 
density of ice. 

Bunseifs result recalculated by 
Lcduc, using the value 0-0176 
for the density of ice. 

Joules or mean calories, or 
calories 37 o a (Electrical 
method, assuming 1. (lurk at 
15" C. 1-434 volts, and 1 
calorie -I.- 1832 joules.) 

Siuitir.s result recalculated by 

Smith's result recalculated by 
Roth for calorie H a 

Mean of several not very Con- 
cordant results. 

Calorie K>" r. - 



Guttmann, J. Physical 

Chem., 1907, 11, 279. 
De la Provostaye and 

Desains, Ann. Chim. 

Phys., 1843, [33], 8, 5. 
Buns'en, Pogg. Annalen, 

1870, 141, 1. 

Lcduc, Compt. rend, 1906, 
142, 46. 

A. VV. Smith, Phys. Re- 
view, 1903, 17, 193. 

Guttmann, loc. cit. 

Roth, Zeitsch. physikal. 

Chem., 1908, 63, 441. 
Bogojawlcnski, Chew. 

Zentr., 1905, ii., 945. 
Dickinson, Harper, and 

Osbornc, J. Franklin. 

hist, 1913, 176, 453. 
Dickinson and Osbornef 

,/. Washington Acad. 

Sri., 1915, 5, 338. 
Lcduc, Ann. Physique, 

1916, [91, 5, 5. 
Calculated. Roth, Zeitsch 

Ekktrochew., 1920, 26, 


2M OXY<!KN. 

If the supply of heat is continued, further slight contraction ensues, 
hut accompanied by rise of tempi-rat mv until .'Hs ('. is reached, 1 This 
is the point of maximum density of water, further rise in temperature 
now resulting in expansion until the boiling-point is attained. 

In the accompanying table are jjiven (I | the i/m.v//// or mass in grains 
of 1 e.c. of water, and (2) the xjttrijic volume or the volume in e.e. of 
1 gram of water -at various temperatures. 11 



Dt'twity. 5 



U'lWlv, SjH-rilir 

' C. 

drum**. . 

Mumtv M-. 


ini*u. _ Vuhuiw. r.r. ! 

(K)008(J8 j 



0-908O19 I 1-OCH995 


0-999927 ! 

00007 'J 


0-907797 1-002208 


0'9999UK ; 



tl-!HJ75ii5 : 1-002 -14 1 


().()f)<i<l<^> : 



0'*.97*i2*'J ' 1-002085 1 


1-000000 : 




0-999992 ! 


2 It 

O-'.WOSIO i ) 00^20 1 


0*99990K ; 

OH! Wt*' 


i\, < HJ|! *1 *<! | ,11*1*1 t *"* *l 


0-999929 i 


' 0"91H25'J ' HMi:f?55 


0'999H7a ; 



0-J95071 ' l-OOi-OM 


0-090808 : 



0'995r7*l t-0(U;JMl 


0-999727 : 



0-*HU05S ' 1"005!I7.H 





0-9922 !> 1-00782 


0-999525 ;. 

000 170 


0-9IHI25 f *00985 


0-99940! ; 



0'!IS807 1-01207 


0-09027 1 I 


55 , 

0-9K57. 1 ! 1-01HS | 


0-000120 j 

00087 I 


<K)h:i2l 1-01705 


0-998970 ! 

00! (Kit 


0-0805!> '. I-CH979 ; 


0-01)8801 1 



O-077K1 1-02270 


0008022 ! 



0-07 18.H t '02800 


0"99H-!B2 ! 



(KMi&ll : Mh f $5!HI 


0*00822)0 ; 

00 177H 


0-!58:tH MHH-lll 

J On tht^ hydrtigi'ii rtt'iilt*, mvorttrnx t lhi< tmwt r*'i$iil>I* 1 ttntit, fiiiutly tliMt*i 
Trttwttx M*'M, Hurrutt iitfrrwil, /*mt/.< rl .\{e*urt'At HMI4, I J, -lit j itinl *f Thti^wi 
Dit-HwlhorHt. H'wx. Ahhtntttl. ^hi/Aiktititrb'Tfrh, l/rii"/w,f||f UKI>, j, UH, Ni 
({HcriiitiititMuut huvt* UH-H tnntlt* nf tht- tt*in|M*rutun* uf nut \ttMutn ilnt^ity, fit** r 
from 2-22" C', (l>Hltm) t* 4-<H (\ (Kijji) Thi* IHMIV ii|i*rliii f thnw- liiila 

(Jay l*u*wiw (Ann, ('kirn. /%., I Kill |^j. a, h'li| , , ,. , 
HallHtrim (/%</ *-iiiwi/r, lki5, 34, l"2> ,,,,,, 
Di*prtHy, (Ann. ('him. /%,, iHItlC |L*|, 7<> 4, r O , , , , , 
Fk*rr*(/trtw. f'^iw, /*/ii/*,, 1845, |3|, I J, U^.*, *i* t-nlrulutftt ly Krrtk'fihr 

frigg. Annnlw, 1852, 84 4al) . , , . 

)oub and t% % yfitir (/*/i7, .>/*/ 1K47, j:$|, 30, 41 1 ..,,, 
Knpp (/%{/ AnHtilrttt 1847, 72, If ,,,.,. 

'tw. f'Aiw. /%.,, IHI7, {41, *o. 4U > , , , , 

tin- i*-rriiry 

/V*^il\ /IriM, IHH4, 8, HtJ. r } 
DC C f itpjmt (Ann. ('him, /%, IWKi, |7|, 2 

i volume k thi rfaljir^rai *f th< 

The data art* lmci on thi* iwnttft of Thifmm, 8 
an obviww misprint, ln* t'rm'N*cl in Uiftfldlt' 

iiwl S>irrll$nr%f , /**, 
tlim $! 21 ' t\ 

- 1 * rrtti|*iii|* 
M (H*w ; 

itijt, t*. 

:i HI! 
4 -OH 
4 07 

41* 44 j, 




The explanation usually accepted for the anomalous behaviour of 
wait er between and -I- C. is that the observed change in volume is the 
algebraic sum of two iactors, namely, (a) normal expansion due to 
increased distance between the molecules in consequence of their 
increased energy, and (h) contraction due to depolymerisatiou of bulky 
kt ice " molecules into denser " water " molecules. 1 

Increase of pressure reduces the temperature of maximum density 2 : 
I he two factors being connected by the expression 

A,, ~- tf-08 0-0225 (p 1 ), 

where / is the temperature of maximum density under a pressure of 
/; atmospheres. 

If water is cooled below 0" ('. without solidifying, the expansion 
with fall of temperature continues, as shown below : a 

BETWEEN 0" AND --10" C. 

Tom}K'i'at tuv, " C. 


vS|KH'.ilic Volume. 


i-oooi ;* 









I -000 1-2 



1 -00055 



1 .00070 


1 00088 






1-001 31 







According to the foregoing data, unit volume of water at 0" C. 
hrcoiws 1-014295 volumes at 100 (I 4 

Tlu* coeilieienl of expansion, a, of water, with rise of temperature 
from 100 to 200 ('/' is tfiven by the 1 expression : 

a I j 0-000,1 08,<i7W i 0-000 % 003,007,:i(J5/-. 

* 0-000,000,002,873,0 1-2P 0'000,000,000,000,<U5,7J*. 

Bet wren mid 20 ('., the specific volume V at temperature f, may be 
eulculated from th< s equation 

V 1-00012(1 0-000,0()0/ 1 0-000,007,5/ 2 ), 

1 SM Chapter X, 

2 X-nn <h*r 'Wmths Arrhinx ncnitnuL SVi\, IH77, 12, 4.V7 ; MarHliall, Sinitli, uiul OHnunid, 
W in!. AnnaUn, 1883. 7, 2f>'2 ; Tait, ML, p. 7a2 ; Amagat, dumpt* rend., 1893, 116, 946 ; 
18K7. 105. 1121. 

a Sea Liinclolt-Bomst^in, opua cit. t p. 44 ; ba.wd on the roBultn of Pirrs Wcidner, 
and RojwHfi, 

* Kijp (AnHttlrn, lK.>fs 93, 123} found HM3 ; Ivrcinc-rM (hyy. Antudcn, 1861, 114, 
41), HH2D7'; Bid! (An nab a-, *f /;/)/., 1805, 4, 123), " 

; ' Him, Ann. ('him. /%* 1H07, l.4| 10, UL\ Ot). 

262 OXYGBN. 

between O u and '*3 ('. by l 

V = 1-000 UW(1 - 0--W-W7/ j <H)5H505;M- 0-0 7 0?SKS/ ; .j 
and between ,'fci" and 100 ('. from - 

V- (KMMMW3 1 <H)OlU)0517:tf'- 0-000,000,01 1 ,*2( 

the volume at 1" t 1 . bein# taken as unity/ 1 
Mendeieeff 4 ^uve the formula : 

(' *)* 
tt ' !(! VI * /)(70;*-3t I) 

wliieh is claimed to In* eorreet to t* parts in 100.000. 

Dissolved salts depress the temperature of I hi' maximum density 
of water, the depression hcin direct ly proportional to the concentration 
of the salt.. 5 The depression caused by a highly ionised binary electro- 
lyte, for example, sodium chloride, is the sum of two independent 
effects* namely, that due to the acid radicle, and thai dm- to I lie base. 
It is thus possible to calculate the depression caused In such a salt 
if the moduli corresponding to the two ions are known, 11 

The molecular volume of water ut the boiling point is given as 
I8'7tt. 7 

Water is slightly cumjWNsiMr. This was lirst established by Canton 
in 1702, and has been confirmed by several investigators smee that date, 
Owing to the* exceptional difficulty of determining experimentally the 
extent of its compressibility, the results obtained exhibit considerable 
variation. The coefficient of compressibility, |i is given numerically 
by the change in volume induced in unit volume In unit change in 
pressure. Hence 

K v v * 

* v.,, 

where V and V^ are the initial and iinal volumes under a change of 
pressure, p. 

The compressibility ut constant temperature varies somewhat with 
the degree* of pressure, becoming smaller us the pressure increases. 
The* best results to illustrate this are those of Htchants uud Stull H 
w r hieh are given on p* 2ll*l toget-her with dutu for mrreiiry for the sake 
of comparison* 

These* data mean that unit volume of the liquid lit W i\ uptn being 
subjected to a pressure of one mcgnlmr (or O't>87 atmosphere) above its 
original pressure, decreases in volume by the amount indicated in the 
same horizontal line as that giving the total pivssmv. Thus, for 
example, one litre of water at normal pressure would deerras* by 
0*0000452 litre or 0*0452 c.e. if* the pressure were raised by our utegabar. 

1 Ht'hwrl Witd. Annulm, IH2. 47, -l-H>. 

- MfttihiowMni, J. Chrw. 5**r,, 1HIHI, 19, U. 

4 Kure, Ann, Pkytik, /Irifcl/illrr, IHHtl io I -I. 

* M*n<taltoff, /*AiV. llf/ 9 IHItt, 33, W>, 

& Dctpr&tK, Ann. (-him. /'Ay*,, lH3i 70, 411; IM-IO, 7,1, :!!iil 

6 Wright, Trnn*. (//irw, ftt#. t JIHI^ 115, Hit, S-* ! <"i*|*|-t n^i -o u>.rk-r--s J 
tthim* l'hj/4., 1894, 3, 2411, 20B ; t''t>utj*t, f */ IH!7, l^j, , r :ta ; iwm, 1^8, t.VU MHH, I |i, 
178 ; itMJl, 132, 1*218 ; IIH)1 134, ft*fK ; Itiwltr, ;!, ChiM, /Viy.^.. |Hli7, 10. -I til ; Iniil*. 
X7, 370. > Krll$fl>;ilt?rllf| 8 iHHt, I S s rI7 

and Htull, /, Amer, (.'htm. &# Iii4, J6 IIIHI, 




AT 20 C. 

Pressure in 
Megalmrs. l 

Compressibility of 

Compressibility of 


1-52 XlO" 5 

:i-88XlO~ G 

100 200 

1-11 X 10 5 

3-82 X 10" 6 

200 300 

1-18X10 r> 

;j-79X10- 6 


l-ll X 10 5 

3-70 X 10- 

100 500 

;H)ixio f> 

;j-7i x 10 

The compressibilities of the majority of liquids at; constant pressure 
increase with rise of temperature. Water, however, is exceptional in 
this respect, its compressibility falling with rise of temperature, a 
minimum beino- reached, according to Pa^liani and Vicentini, in the 
neighbourhood of 00" 1-. According to Tyrer," the minimum occurs 
at 50 U C 1 . for the isothermal compressibility and at 70" (!. for adiubatic 
compressibility. This is usually attributed to the diminishing number 
of bulky and compressible " ice '' molecules as the temperature rises 
from 0" to 00" ('. At this latter temperature their number is negligibly 
small, and from this point onwards water behaves as a, normal liquid. 


Temperature, " (. 

( -omprcHHibiHly per 



5-o;* x 10 r> 

Pa^liuui and Vutcntini, 



4-00 < 10 

Cinicnto, 1884, 16, (3 

I ^7; 


4-50 < 10 

JNH. P///y,v/A', Bc,ihl(ittcr s 



1-03 x 10 

8, 791. 

01 1 

;}-8i)x 10 - 


a -89X10 > 


*H)8 X 10' 


1-09 X 10 " a 


3-12X 10 [> 

Hont^en and Schneider, 



4-8 i X 10 5 

Annalen, 1888, 33, 041. 


1*02 x 10 6 


4-5 X 10 :> 

i lulett, Xcitffdt. phifuikul. 



l-ldxio 5 

1900, 33, 237. 


1*19 X 10 '"' 

(0 100 atmospheres. 




9 Tyrei% 

atmoAphcnt. Oiui mi'^ahar in lO(K)/f/ where g 'Udtjolortttioa due to gravity 
O, or 10HJ8 per tmit. of a kilogram JHT H<I., or 98*70 \wr ecnit. of an 

at oaliival and 45" latitude. 
Trim*. Chrm. fioc., 1914, 105, 2534, 




(Tyrer, ItU 1.) l 



jH-rAt..,. 1 . 



; 5-07S 

10 : ' 





10 " 






!0 " 





1 KVJO - 

10 " 





i -l-liUi 

HI : ' 





i 4-462 

10 * 

I'JIO^ - 





III ' 





i-;m * 

let " 





: H;ti 

JO ' 





t'7 ja 

10 ' 




: 100 

i'hr>:i - 

HI '" 




Tnit * ^ivt-s thr lollauttit* <A|r*-sstu \\hfVt !\' fit*' *M!uj>rrs>iltihtirs 
of \vut<T Inl.wt'i'ti niul 15 (\ fun fir ralriilittril IVtr pvrssitrt's riin*in^ 
from 150 to 500 iitumsphrrrs : 

O 0'000000*jr/ 


whcrr V,, is thr \olumt' at / (', undi-r I ahunspitcrr, and \" tltr \-uluuu* 
tit /' C'. Utltlcr a [H't-ssUn* tfy ;ittuusplirr's. 

As a ^riirnd rult\ ni|Uf*ins suiuttons iiri- l*-ss tnuuprrssthir than purr 
\vat(r, a dut\ prol>ab!y, ttut rrdurtinn in thi- liiiiiiitrr nf ^i*'*-" nmlrrttlrs 
in tlu prc^st'iHT til* thr (iissotvvt! salt, llir viiliii- lor si-a-watrr at 
17-&- ('. is !:{ -. 10 V 

Although thr roiiiprr^sitiililirs of itaturat \vuh-rs art' thus r\.rr$'ttt!t^ly 
snmll, ihrir vllvct upon tin- distrihuittui of land ami \vatrr <iu fin- rrus! 
of th< rartli is important. It has brrn nilmilafnl that, in rnsr*jurncr 
of thiMnnnprrssilnlity of scn-wattr. the mean sea le\el is till IVet'liiwer 
than il would be if water were absolutrly inenniprrssibir. with the 
result that two million square miles of land an* mm tmrmrfvd whirh 
would otherwise be submerged/'* 

Water is not usually rrgiirdtif us possessing un\- appn^eiable ti-nsile 
strt'tiKth, If, however, prerauttotts are taken ti> jreveut \\\ iliameter 


Tttit, t'n 

Chi-ia. .svr. t MIU, 105, L f ;*:i 
,-Inim/r t 1HKJI, 19. -jo I ; U 
tnf. \tttttrr. IH^. j. HNI(lM 

fh vnlii* IHHMMMK fr th 

wii t<t r 

., . 

thin ttmi|riitun imwnrtl* to 4-4! .*. lit m 53 
wreiwjbility ln*twmt il :l nitd 4 ' (.'. wa* lot nmti 
(/or, fit), 

3 SM' tlw iuvi-HlipuiiuuH f !Unti*u ittul S 


, /'A/*,, lH'it, p, -U7. 

( J/rmmrr . /n^iftil f iim*-, 

|iri-Mtmttv ut r*m inn 

in,. r/uiw, /liy,*,, JH;|, f;ij 
jmi rm *!ii s ilii f,tilii^ ffHn* 

,n, ,f tlit iii%iiiifii' r,,m-= 
1>.V l^lwm <ni Virnitiiu 



from varying, a cylindrical coliuun of water may be shown to possess 
a high tensile strength. This was iirst demonstrated by Berthclot in 
1850, 1 who almost completely filled a, glass tube with water, leaving a 
small bubble of water-vapour after sealing hermetically. The whole 
was then warmed until the water, possessing a, higher coeilieient of 
expansion than the glass,, completely iilled the tube. On cooling, the 
liquid continued to fill the tube, thus showing that it resisted rupture 
under very appreciable tension. The result was only qualitative ; but 
repetition in a modified apparatus by Dixou and Joly 2 indicated a 
tension of 7 atmospheres. Results obtained by an entirely different 
method led Budget! a to conclude that under special conditions the 
tensile strength of water may amount to as much as GO atmospheres. 
At about 320" C. the tensile strength becomes negligible 4 ---a result to be 
anticipated from its proximity to the critical point (37-1 C.). 

The viscosity of water has been measured frequently since the 
classic research of Poiscuillc :> in 18 ttt. The most reliable data arc given 
in the accompanying table. 

(Dynes per cm.-) 

uf urt % , 










Thorpe and 
o<l#T (I HIM).' 1 


0-01 00 15 





Honking (H)09). 


0-01 31 05 

()(>] 00<> 







0-003 Hi 


Binglmm and Wliit 
(1912). 8 




0-0 1000 






0-0031 13 

(0-002993 at 95 


Poiscuille's results are included as illustrative of the high degree of 
accuracy attained by that investigator. Between 0" ami 25 C. the 
viseosily of water may be calculated from the equation 7 

O'0 17928 
' / 1 1 0-03 lib/ 1 0-000235/ 2 ' 

1 HtTlhoM, Ann, ("him. /'//*/., l"0, 3.0, 232. 
1 Dixoii HIM! tloly, Phil, Tninti,* 189*>, |B|, p. 508. 
:t liud^ctf. I'ruf, /to*/. *S'w. t 1012, |A| 86, 25. 
* SkiiimT und KntwiKtlc, //W, 1915, |A|, 91, 481. 

ft PotHcuilhs .-1/4W. ('him, /V///jv., 1843, (3), 7, f>0. Si-t idnu Girard, Mem. Acad. ScL, 
18KI; Sprung, /%{/. Antinlrn. 1*870, 159, 1 ; Slottts Winl. Annalen, 1883, 20,257. 
tt Thorjm mid Hodgr, Phil. 7V/M., IH04, [A], 185, 397. 

Hohkii% */. /%*, *SVw, Xtw Smith Wnlw, 1908, 42 34; 1908, 43, 34; P/7. Jfaf/,, 

IMngluun and VvhiU% Zntm'Ji. idiyxiknl. ('hem., 1912, So, 084. Sec also for critical 
<f viscosity mfiiHurt'mcntH, Binghum, Tram. Chcm. >SV;e\, 1913, 103, 959. 



The value for tj remains constant even wider e\eeedm*ly low rates 
of shear. 1 

The viscosity of supereooled water is as follows ; 2 

Temperature, ( 8 . . J.-7 ?!!.'* JKJO 

?/ . . 0-0170.** 0-02121 0-02.'ill 0-02511) 

Increase of pressure tends to reduce the x iseosity of water at tempera - 
iures below .W CV J In this respret water differs from most liquids that 
have been examined, as these become more viscous under increased 
pressure. Net doubt the explanation lies in the tendency of the higher 
pressures to reduce the percentage of bulky and \iseous ice molecules. 

The vapour jHWxtu'e of water rises with the temperature, as is 
evident from the following data, 1 which t|ive the tension in millimetres 
of mercury : 

15" AND ,170 i:. 

"t 1 . 


t 1 , nun. 

t ". lUIH. 

< '. intii. 




i 1 I O-St-5 

25 2.T7<;:i 

75 2SO-0 



12 . i()-5io 

20 25-217 

m ar>5-t 



18 1-288 

27 2<i-7 17 

85 " iaa-5 


11-' 1 -OHO 

2S 2H'85.S 

!HI 525-h 

] I 


15 2-700 

20 :M$52 

05 - oai-o 



it; : a- 087 

80 Ifl'HJII 

too 700-0 



17 t-588 

85 ' W-1SS 

120 : t ts8-t> 



IS ' : frl-KO 

10 55-iHl 

150 ir,l!K-7 



10 ' 10- IS! 

15 7 1 -00 

1*00 1 101-7 



20 ' 17-580 

5O 02-51 

250 ; 40-476 & 



21 : 1S-055 

55 1 17*85 

800 . 87-41 " 



22 i 10-S82 

MI ; 110' HI 

a:*o ; 16H-U - 1 


2:1 ! 21 '071 

05 187-80 

800 .: I89-6.i '* 



21 j 22-#HB 

7ii :2;m-5't 

.H70 2I.-7^ 

The vapour pressure of water he! ween ' nntl 50 ('. iuy be rnicuiatcd 

with great exactness by means of Thiessen*s furntitlii ; ** 

5-101K/ 100) 0-508 - 10 *|(:W5 I) 1 205*}. 

1 A* and (", UhHit , , f , , , 

- White nn<i Twining. Ji*n t'hrnt. ./.. I!KI, 50, ;IHI>' " 
;l Hauiter, Druth'*** Anmtlru* MMil. 5, ;|i7, 

* 'JVm]M^tttun*N l.V t* 0' ('. CHrip^l mil Htniw, ,4n l 
<J" to flO v * (*, CBfh4 and Ift*w !-. -i/. ( Ulo, flf, |i 7J5j, a 
Hnning v iWrf.. HKm, |4), 26, HIW), 2CKV to U70 <\ |Hit!irst'iiiiit 
31, 1)45). A <*i>itij>lit'Jit<H! fonnulii ii||4yin^ ttiflt nmtf arriifiir 
in given by Hchreibor, PkynihtL Zntorti,* liilll, 2d :x'l, >W I 

' 14, ii. f JW. 

nrn HM givon by Ihr itiitliMtn m kil.r*nn jn*r 

Many othtir formtiln) hiivr 

n. IKUSI. 67, l ; A 


iiiiAfin, iW*/., tiiHMH 

^'liii't^ii ii untl '*iJ (*. 
HrwUfllij, W V iinrti I'lwi,, 

rlii, ri|jiri-|rllt I* !ll!H 
-1 iilltl HrttHi*, !*', Cif, 


Mention has already been made (p. 250) of the fact that when the 
temperature of pure iee is gradually raised under the ordinary atmo- 
spheric' pressures melting always takes place exactly at C. The 
converse, however, is not equally true. 

If water is cooled, solidification may not occur immediately a 
temperature of 0" C 1 . is reached. Under suitable conditions it is possible 
to reduce the temperature many degrees below without freezing 
taking place, even at atmospheric pressures. 

This was lirsi observed by Fahrenheit., who, in 172-1% succeeded in 
cooling water in cleaned tubes down to 15 F. ( ..... 9-4 C'.) without 
solidification. 1 (Jay Lussne cooled water down to 12 C., the liquid 
condition being maintained until a fragment of solid ice Avas added. 
The surface of the water was covered with oil to prevent contamination 
with dust. 

Dnlton 2 staled that 

If the water be kept still, and the cold be not severe, it may be 
cooled in large quantities to 25" or below, without frcc'/ing ; if the water 
be confined in t he bulb of a thermometer, it is very difUeull to freeze it 
by any cold mixture above 15 U of the old scale ; but it is equally dillic.ult 
to cool the water much below that temperature without its freezing. 
I have obtained it as low as 7" or 8", and gradually heated it again 
without any part of it being frozen. " 

Halt on also knew that 

When water is cooled below free'/ing and congelation suddenly 
lakes place, the temperature rises instantly to JW'/ n 

C<tj) Water. Sorby 3 pointed out that "water kept in glass 
lubes of diameter ranging from 0*025 to 0-25 inch may easily be. cooled 
to 5 ' I'. without congelation, even when the tube is shaken. By 
keeping the tube quiet an even lower temperature may be obtained, as 
has been mentioned above. 

When contained in capillary lubes, water offers very great resistance 
to freezing, unless it is in contact with ice. Thus Sorby found that no 
congelation took place, even upon shaking, when water was cooled to 
15" ('. in glass lubes of diameter 0-003 to 0-005 inch. The temperature 
could even be reduced to 10" C. if the tubes wen* kept very quiet, 
alt hough at 17 " (' t lie water fnr/e immediately. In a tube of diameter 
approximately 0*01 inch the water ftmc at KJ C. but not at -11" C. 
In contact with iee, however, water freezes readily in capillary tubes, 
and ire thaws as usual at 0'* ('. when in lubes in which water will not 
congeal in the* absence of the solid phase above Ui u C. 

Muller-Thurgau 4 states that filter paper moistened with distilled 
water freezes at (H ('., whilst a clay sphere, under similar conditions, 
has been found to freeze at 0-7 (.'/'* These observations refer to the 
actual freezing-pom ts under the conditions named, and are quite apart 
from supercooling effects, which, as shown above, may be extended to 
much lower temperatures. 

fit, /Vu7. Tmm., 172-1, 39, 78. SIM*, atao ToUiiM-, rW//rf. rend., IH72, 75, 500. 
s Dalton, A AYw ,S'j/*f*7/f tlj ('thnttiettl />// //</% (l^mdou, 1HOH), Part, I., p. 11)8. The 
tonijH'rn,turt*H art* those* ou tho Fahrt*nh'it wntlc, 
3 Sorby. /*/n7. Mn-j. t !K"i. |4], x8, I Of,. 

I MullT.Thurau,' iMmlirirtwIiaft. Jtthrlt.* IHHO, 9, 17(>. 
" Biirhnf jtnv, Zt'itm'h. Win*. frx>l. t IHiW, 66, 584. 

II Sin' for furtlirr <kta F<tr antl Saxlon, ./. AMU: C/u>in. Nw., 11)17, 39, IW7 ; 11)10, 
18, 588. 


The presence of finely divided particles of stolid materials, such as 
ferric hydroxide, alumina, etc., causes an appreciable depression of the 
freezing-point., 1 

A convenient method of cooling water below o ('. consists in pre- 
paring a mixture of chloroform and olive -oil in such proportions that the 
product has the same density as water. Drops at" water suspended in 
this mixture may In* cooled down to very low temperatures (r. :JO (,*.) 
without free/ing. Such water is termed vi7/rmwW or xnjwr fused, and 
is stable only so long as the solid phase is absent. It is therefore said 
to he nn'ftt-xhihic. The wader will usually- solidif) immediately upon 
exposure* to air or dust, or on the introduction of some foreign material. 
Kven the act of scratching the inside wall of the containing % cssel will 
suffice to induce crystallisation. If the supcreoolmi; is earrietl beyond 
a certain amount, solidification takes place spontaneously without the 
introduction f tin* .solid phase or foreign luatcrtid, In either case the 
temperature rises to and remains there until solidification is 

The velocities of crystallisation of supercool* d water, as determined 
in a tube i metre in length and 0-7 cm. in diameter, and expressed as 
cms, per minute* are given in the accompanying table." 



NVlM'it % V, fill.'*. IliIIl, 

2-00 ' H> 

:HII ! IK- -i 

HIT ! 7M 

5'HI! ! 1117 -I 

M8 ; IH'7 



The maximum velocity of cryMaliisalioti rtnieiitly hes b 
- 0-07" (\, hut, owing to spoututtcous solidification of the wati-r, it 
not found possible to make tictcrmumtions at lo\v-r ti-mperntures, 

it is interesting to note that whereas icr jirnditri'tl \\iflt a cooling 
temperature within one or two degrees of the melt ing-' pom! is usually 
clear, the product obtained with stronger cooling is milky m itppnimner 
on account of t lie inclusion of minute hubbies of air which was ptvuously 
in solution. 

The vapour pressure of supercooled water is always greater than 
that of ice at the same temperature/ 1 Hits is evident from the data in 
the tiible. 1 

1 F, W. i'urto'r, /. Awtr. (%-w. sW, t liJI, 4 |. lull. 
8 Walton anil .Fwli't J, Witi*iwt 1 %-*., lOi-l, 18*7;!,* 
il YmuiK. /'i**\ faty. ,* IHHI, _|6, I 1 ,*!* 

nntl Hf*tiHt% Jww s I%I/AI|, l!KU |-ll 49, i3, 

L, imii, 17, L, ;H, 

Vapour Pressure in mm. Hg. 








3-11 S 



2 -337 


i -903 


I <>! 1 


i -;*73 


1 -253 




Temporal ure. 




Tliis is shown graphically in ii^. 11, the broken line indicating the 
vapour pressure of the supercooled water, and the continuous lines the 
pressures of liquid water above* 0" C. 
and of ice I below 0" ('. As already 
explained, in the absence of air and 
in presence of water- vapour only, T 
represents a triple point, and lies at 
| 0-0070 1 ' ('. A slight break occurs at 
T bet ween curves LT and TS, but TC 
is a continuation of LT, 

It will now be evident why TC! 
represents a meta-stable condition of 
water. If a piece of ice is introduced 
into the same closed vessel, the vapour 
is supersaturated with regard to the 
ice* and a portion condenses. But this 
leads to a vapour unsaturated with 
respect to the supercooled liquid, 
which, in consequence, vaporises to a 
corresponding amount. This condensation on the ice and vaporisation 
of the liquid continues until the whole of the latter has disappeared, 
leaving only ice and vapour. 

Water is generally regarded as a poor conductor of heat,, although, 
compared with other 'non-metallic liquids, its conductivity is high. The 
thermal conductivity* K, is defined as the number of units of heat (gram 
caloric's) which will pass by conduction across unit area, (sq. em.) in 
unit time (second) with unit temperature gradient (1 C. per cm.). 
The following values for K have been obtained (p. 270). 

The value for K at any temperature between 7-1 and 72-0 C. may be 
calculated from the equation * 

K 0-001325(1 HHW2081/). 
1 .lakub, loc, cit. 

+ 0*0076 

Fiu. 44. Vapour prcHsuro of ftuper- 
eooled water. 



IVmjKTUtun 1 , 


Auftti iH . 

.-, (1> 

Jakob, .inn, /V/i/.v/Vr, ti*UO 63 ,VJ? 


(oldschmidt. {'jnjxiknl. XuV.vr//., UM 1 ' 

12, H7. ' " ; 

o to a f' 


1L Weber. ,ltin. /*////>//*, ltHi;i, H, 1017, ; 



' Lees, /VT. /uti/. ,SV,, !!;>. 74* HU7 . : 


o-ooi in 

Milncr and t'hattot'k, />/**/. !/?. LSII i 

: 48. M*. " ' | 


0*00 1 :> 

Lees, /in*, o"/ 1 

This poor conductivity manifested by water plays an important 
part in nature's economies. 

Livingstone 2 mentions that the temperature of tttr surface water 
of ponds in the central regions of Southern Africa may reach as hujh us 
38 C., but, owing to the poor conductivity of heat, ** deheiottstv eool 
water may be obtained by anyone walking into tin- miiiille and 'lifting 
up the water from the bottom/* 

A study of the xpeeijie A/v// of water is particularly important, sine** 
the unit of heat, or $mw wluric is the amount of hi at rftpurcd to raisi 
1 gram of water through I deytve erntu*ratie. Somettinrs the iram 
calorie at 15" C 1 . (calori*' 15 (\) is chosen, sometimes that at C", 
(calorie 20 (!.), whilst at other times the tean \alne betwerti II an<t 
100 C. is adopted. These units are not identical, but tbe \anation \\ 
small. As wat<r, owing partly to its ubutttiuuce, and partly alst* hi tbe 
case with which it can be obtained in n purr t'tintltttnu, 1*1 the standard 
substance for the measurement of beat |tiautities, if. is uuportaut to 
determine with the utmost accuracy tbe variation of its specific heat 
with the temperature*. Numerous invrstt^nttous have bem earrie| otit. 
with this object in view, very reliiiblr data being tlmse of Callrtider 
and Barnes/' According to Calicndcr, the ?prn<}t f beat of ujtti-r, f^ fl 
in terms of the calorie at 20 ' (\, is niveii by fhr <*\prrssifui 

Q<- -0'9Hf)SO 1 0-50l-'(/ * *2CI) > H1lllIltlH4l . fHHIiltlliiiftl ' 0' and/ HMt t ? , 

According to Narbutt, the spcrilic ht-at of \va<vr fur a lmipi-mtur* 

range of O w to 100" ( f . may be ralruiiitnl tViiin flir luilim-ua' *-iii! 
formula : * l 

Specific heat : 1-007:*:} 0'OWI7H(/ LI) Mi"H!iiiililMir>fl 

1 Karliardata arc* tluini* of Luntl*|uiHf, triAft/f /* r/^ih, I HUM, p | ff {' \V* ltr>r 
Wied. Annakv, lBBC> f xo, 103; iHHii, u :if' ; (ir^irt/, iV / , tWi tH V*** On- I*!***- 
Roy. floe., 1888, 43, 30; WnchHrutit)}, Hm/, ,lnit!*n t lH*il, ^% s J *, 

a OallcniW, /'A7. 7Vnm t 1912, |A| ji? t \ .' l* tlltt " fa tltt %v |i| A A **! 
Barnag, /Vwl. Tram., 1JH)2, [A], 199, 149. * ' ' ' * * 

4 Narbutt, PhymkaL Zritwh^ HUH. 19, ft:$, 



which gives values in very dose agreement with tho. best experimental 

The specific heat of water is abnormally high, and this fact has an 
enormous influence upon elimate and geological phenomena. Liquid 
ammonia is the only liquid possessing a higher specific heat. 

In the following table arc the data, obtained by Callender and Barnes: 1 









1 -OOH5 















1 -0048 



1 '00 1*2 





1 -0032 


10 j 1-0027 



1 -002:$ 





1 1-0017 


14 ! I -00 II. 






1-00 11 



1 <)<)()<) 









1 -0002 















0-999 1< 


















It will be- observed that the gram calorie at 20 (.-. equals that at 
(JO (' whilst the mean value between 0" and 100 C. is 1-0010. A 
minimum value occurs at 40" (V 1 This fluctuation in specific heat at 
different temperatures is usually attributed to the influence of de- 
polywfrisation as the temperature rises (sec p. 200). For supercooled 
water at 5" ('. the value 1-OI5H for the specific heat has been obtained 
in terms (if the calorie at 16 (V* 

As the calorie is inconveniently small for some purposes, a larger 
unit, the Calorie, is sometimes used equal to 1000 smaller calories, the 
terms being frequently abbreviated into *"' eal." and " Cals." respectively ; 
occasionally a unit equal to 100 calories and described as a Kaloric 
(Kal. or K.) is used. 

1 Kor<thr data << Barloli nn<l Htmrrialn. KnblfiU-er, 1891, 15, 701 ; 189.1, 17, 542, 
OU8, 103K: (JrilHtliH, I'hil. 7V// w*., IH1KJ. 184, :U ; 1'rtw. /%. AW.., 187, 61, 479; Plnl 
Mug, inm, |;K 40. 4:!I ; HiwlunK /V^r Anirr, ArtttL, 1879, 15, 75 ; W. R. Bousficld and 
\V. K. HnWHlii'lil. /'Ai7. Y'W/M., 1$H1. | A j, 21 x. 1W) ; l>me. Hot/. A'w., 191 1, 85, tM)2. Earlier 
ilutamv thtM f Hurirhw. Wi*'*L Annttlrn, IK7. 8, HJi ; Waundlor, ibid., 1880, II, 237 ; 
MuwhhiiusiHi mid WiilliMT, i/W.. 1H77, x, 59*2. A rccaU^ulation of Ronault'H data is 
l^ivi'n by <!uillttun*. <V>//rf. rnnl., HH2. 154, 148,1, 

' * Takn from VI. I., p. H7. :s Artn^niing to .Iftgor and von. Stcinwohr (8itznn(jsbc.r. 
U-rt*/. Wtm, firrtin, HH5, p. 4*24), thtt minimum ocunirH at 33-5 G. 

* Barnm and C'iftk\ /'Ay*, /friwr, I1MW, 15, flfi. 



Thc k heat ol' formation of water from !..J;IM-UUN Iivdro^rn and nxy^rn 
at 18 I 1 , is OH-38 Calories I5 ' C. 1 

The surface tenttion of water* likr that of all liquids, dtminishrs with 
rise of temperature. A ready met Inn! of illustrating this ronsists in pour- 
ing water into a shallow, clean metal plate hrld hon/onf ally until a thin 
layer is formed. The surface is now dustrd ovrr \\ith HO\V<TS of sulphur, 
and heat applied locally to a point nrar the rrittiv tif thr imdrt* snrtwv 
of the plate by means of a fine ijas jet. As s*on as the lira! ivarhrs the 
water, 'the sulphur is rapidly pulled away towards th- nivnmtVrcinv 
of the plate in consequence of the reduction in tin* surface tensi<u of 
the warmed central liquid. '- 

The surface tension a t at / 1*. is pmettrully a linear fniirlinn of the 
temperature, and may he calculated a<*eordir^ ft* the ef|ttatinn 

<r tt (l u/j 


where v is the surface tension at 0" (\ aiut it ts a r*nstant. 

The value for a in the ease of water has been repent rilly defenninetl 
as follows : 


Hrunner, A/$f. Annulm* IM7, 70, Iht, 
Krankenheim, ihhl., IK-IT, 72, 177, 
Wolf, Ann, ('him, /V/i/,v., ls"*7, jllj, 4*1, *U*J, 
Volkinann, IVietL Annul* n* lss*J, I7 t la f l, 
TiinbtTjic, ///n/ M IHK7, *IC! Ttr>, 

Cantor, !!"/>(/, AHuakn* tN5* f j, 47, <!!*!* 
Humphreys and Mohlcr, /Vif/.v, lin-im, 1H!*>, 2 
Sent is, / /V 

A mean value of 0*0020 is prolmhly fairly at*i*ttrntr. Fi>rflt :| 
the equation 

^-o-o (1 O'OOUMHTftf O 

a^ for water has bien deiermiiu'd itt a viirirly uf ivny^ Ity thffft 
investigators, the results ran^in^ from 70-l tu* 7 dyitrs jw-r nn, 
A') i^ i 

The results obtained by Rumsuy niiii ShirliU * tn tlnir r-ht^t 
research m which wafer was in eontw>t with if % vaittittr Jiitil tltr walls 
the capillary tube only, an* iven on p, 27.'!. 

. Whilst the forcKofn results art* relatively t-urrrrl, it iipi*nn%. t 
certain that their absolute values nre all Huiitrwlmt tm Inw. Thr inr 
adopted by Ramsay and Y<iun raiiKi^ti-fi in utrnMtriittf tfir cliffr 
in level between water in a capillary lulu- itprn nt Itcith -itik unit 


1 Roth, jgrcttecA. Mlektrockem,, 1020, a6, IUHK. 

, ,, A', 1905, 17, 7fft. 

4 Ramsay and Shields, Zeittch. ykytti 

. id 

.. Ii:i ft ia. 433. 



pcmlcd in a wider glass tube. Richards and Coombs, 1 however, have 
shown that the diameter of the wider tube must be considerably greater 
than has hitherto been realised if the disturbing inlluenec of the walls 
is to be neglected. Thus, in a tube of diameter 2-54 cms. the water 
was found to lie 0-11 mm. above that in one of 3-8 mm. diameter. 
Experiments showed that this latter is about the limiting diameter, 
the effect of the surface tension under these conditions being reduced 
well below that of the other errors of experiment. 

m pern-tuns " ('. 

tf[i d viK'N/ein. 

fft (M")r;. 






















5?'- 15 





I U) 



a; X M. 

3-81. X 18 



Taking this and several other possible sources of error into con- 
sideration, the mean value for the surface tension of waiter was de- 
termined experiment ally as equal to 72-02 dynes per cm. at 20-00 C, 

As a general rule, the presence of dissolved inorganic salts enhances 
the value in accordance with the simple mathematical expression 

where <r a is the surface tension of the solution, cr w that of water at 
the* same temperature, // the: number of gram equivalents of the salt 
per litre, and H a constant, depending upon the chemical nature of the 
dissolved salt. For the undermentioned salts, H has the following 
values : 2 






'/nSO*, 1 


Organic salts, on the other hand, frequently reduce the surface tension 
of the solution. The oleates are oases in point. 

1 Hichanln and CuombH, ./. Amcr. Vhem. < 
'Ai7. A/(/.. 1807, 44* 9. 

., 101/5, 37, 1056. 

274 UXVUKX, 

Most other liquids, except mercury, have a lower surface tension 
than water. This is illustrated by the following data : 

\V rrhu Kihy! |,' f } ir , nbu* ., 

Surface tctimon . M7 72-r .'t!Hi 2lM lf-* U2 20-2 

Dissolved jascs tend to raise the surface tension. The following 
values obtained at IT* (*. illustrate this : ! 

In YiU'U. Hyilr*tftn, Xttr.^ni. ^j^V i\in\ii" Am 

SwrfiU't* ti'iMou , . TI%1 72'K,"J 7.'M 7IHH 72-Hi s i 7IH 

Water is an excellent v/jr/i/, dissolving not only many acids, bases, 
and salts, but also many organic compounds, especially such us contain 
hydroxyl and amino-tfroups. The solubility of solids and lit|uids 
generally increases with rise in temperature, \vluUt jases, all of which 
arc 4 soluble 5n wajer to stwie extent, are invariably less sttluhlr i\\ higher 
temperatures. The presence of dissolved solids causes a depression 
of the free/ing- and mcltwgpoint of water lit an amount proportional 
to the concentration. This is known as ///i^/*-/r.v /,*i;-, and is only true 
provided the solutions are dilute. The -stent of thr depression for 
un-ionised substances in dilute solution is such lluit proportionatt*ly 
one gram moleeiiinr wcij^lit of the M*lut- m HMI ,'riins if water wtmhl 
<*aust % it depression of IH-5 (*, the nmln'ttltn' ilfjtn'^irtn.^ 

The Mtilecultir rln'tiiinn of tin* boiling-point is calculated in a similar 
manner, and has tin* value 5*2' ('. 

The dic 4 le(*lri<* t'onstant of water is HI-7 at the oniinary tc-h*peraturc, a 
This vahu- is a high one whc-n ctititpared with the same const ant for 
other liquids and it is probably on account !" its considerable dielectric 
power that solutions of bases, acids, and salts nt wntcr can <*oiidu<*t the 
electric current, this conduction being dependent u the electrolytic 
dissociation of the solute. In aqueous solution, li\vevei\ some organic 
substances arc partly tixsnciittftl IM duublr or even more complex 
molecules. 4 

Purified water dH*s not appre<'iabty emidtiet the elect ne current, 
so that the conductivity of a sample of water enu be tisrd as an indication 
of freedom from saline impurities.* 

The purest water hitherto obtained possessed an rlcetrifal con- 
ductivity ofiHH X 10- lo lht>s at IK' (',* thr llH'I'rasr III thr Viillle with rise 
of temperature bdiifi rcprrsentetl by a cuetttcirnt of (MKWJ per drgrcc. 
This ctM-fllcicnt only holtK lor water of a high degree of purity, such 
tm hiw not. even been exposed t*> thr attno>phrrr, 7 brratisr nlight im- 
purities imvt* a relatively inordinate rffret on thr itMtdurt ivity and piissc>ss 
n imich lower coetlicietit of itifreit^r with teiiiperatiirr, nit'iitrlv, of the 
order of 0-021. Purt- wiitt*t% therrlbri% prciitbly pmscHsrH n very slight 

1 Bliatrmgiir, J. !%>.! f.'Arw,. I*i2i, 34, 71J, 
( Lftipdg, 1000), p, 85. * 

* tltli Vl, !,, |j, 122 Uotlt iftrifafh. i;lr||i<i*-lM-i, 1 

18*110 fts th mtJHt |iftiilili^ vnltit*. a Urtittiv %tii*fh, $t$$y.*tiwj. 

4 8e Padtlle and Turorr, TVn-fM. t'knn. s**r., I fill, 99, nnh, 

8 Kohlraunoh and Hi*yiiwpIIli'*r Zritwh* "/'A*- m,, \\" ' - * 

ibid., If02 ?i 4a E93. Ifoftiw^illur, /!, mm, 


but definite elect Heal eonduelivity which is to be attributed to the 
existence' of n minute proportion of the water in an ionised or electro 
lylienlly dissociated condition, that is as II- (positive) and OIF (negative) 
ions. As the conductivity due to the gram-equivalent weight of these 
ions in a definite volume can he calculated from the electrical conductivity 
of acids and a Ikaliesrespeetixely in dilute solution, it '.is possible to evaluate 
the proportion of pure water which is ionised at a, definite temperature,. 
the result is <>;* x 10 I0 grams per c.c. at 0", the corresponding dissocia- 
tion constant at 18 being 0-8 >; 10 7 . The. probability of the correctness 
of this reasoning is borne out; by the approximate agreement of the above 
value for the extent of dissociation with values obtained by quite. 
different physico-chemical methods, such as the hydrolytie action of 
water on ammonium acetate, etc. 1 In the presence of dissolved electro- 
lytes the dissociation of water is still further depressed." The electrical 
conductivity of solutions of water in other solvents bears no simple 
relation to that of the pure liquid, and, indeed, varies widely according 
to the solvent. 3 

The electrolytic dissociation of water increases with rise of tempera- 
ture. This is unusual, but is commonly explained on the assumption that 
most water molecules at ordinary temperatures are polymerised, thus 
(ILO).,., the value for ,r being mainly 'Jt, and that the existing ionisation 
is (hat of single molecules IU). As the temperature rises the pro- 
portion of these increases through depolymerisation of the complex 
molecules, so that whilst the actual percentage of single molecules eon- 
verted into ions may be reduced, the total number of ions is greater. 4 

In contact with ordinary fresh air, the conductivity of water is 
0-7 to CKSir 10 (l mho, the rise being due mainly to the dissolved carbon 

The absorption spectrum of water was studied by Soret a.nd Sarnsin 7 
in IH81, who passed a beam of light through 2-*2 metres of water. A 
faint and narrow hand was observed in the orange* at a wave length 
of approximately (iOOO. This band became slightly wore distinct and 
a general absorption of the extreme red was noticed as the thickness of 
the- water layer was increased from H-i to 4-5 metres. 

In .small quantities water appears colourless, but in deep layers 
it is possessed of a bluish tinge, which tends to become greenish as the 
temperature* is raised, 8 

The eutise of the coloured appearance of natural waters has been 
the subject of considerable discussion. The light blue hut* of water 

J X<>vfM, Kuto, ami tSosman, /, Anmr, C/M'in* *SW.., HHO, 32, 1"9 ; .Lnrtw/ and Buhi, 
Zrititrh. jthtfMaL t'hrw., HHW, 66, 7'.W ; Hut hum, ./. Amrr. ?7irw/. .SW., 11KW, 31, HUB ; 
Knirv and'Nicty,, /ft///., HHfi, 37, 22IW ; Ktmoli, itrid., 11)07, 29, 1402; Wallwr, Trim*. 
Pttrutfay *SV\, HHKJ, x, :UJ2 ; H\yUwtiH*r, Ann. /%&, UKW, |4|, 28, 503. 


:t Witltli^n, Trtttm. Pnrwtati iSW., H) 10, 6, 71. * Hc< p. lM)(l 

'* Si*i Ktn<Inil ./. Aturr. f'hrtn. Kor,. UHli, 38, 1480 ; nn the Hpt^uiic ui(lur*.t;iv^ oaparity 
of \vntT HI* lii^itilftrd, (!<nuj*L rrw//. t HKa, 141, ttfrtJ. 

fi Sr itlno Hartley aiul Huntin^totu /*///. !7Vx., IH71> 170, 2f>7 ; (Jdlloy, /. /^//.w 
/'%v, rht'M. *SVw., UHKi. 38, 4IU, ; 1SM)7. 39, 210; W<ii'hmann, Ann. PhyM, H)ti 4 J t [4], 66, 
filli ; l*hyitiknL Kritnch t * 1021, 22 Klfi, Thi* iivfrn-rcd ahnorptiott haw lx( Htudiwl ly 
('oHiiw, rht/*iw! fa-rim*. 1022, 20, 4Wi 

7 Sont'nd Surmun, ('(uujtt. remL* 18K4, 98, (124. 

ft Du^inux nncl Wollmftnn, ./. /%w/?m HH2, |fi|, 2, 2(K*l. 

s Hi'ii lh^ it*'tin HumniurioH by Bancroft, dhrm. N*wa t 1919, n8, H)7, 208, 222, 
*23ti, 24, 2M ; Tomkiiuum, i/wV/.. li)21, 122,205; imd Eammiathau, /Vu7. J%., 1923, 
46, 541 

27 OXYi.'KX. 

that has been softened by (lark's process has frequently been com- 
mented upon, 1 and points to the surest ion th.-it the colour is due tu 
the scattering of liyht by suspended particles. Thivlt'all - found fltut 
the following solution, \\hen viewed through a tub*- is mi. in length, 
matched with considerable precision th- colour of a sample of water 
from the* Mediterranean : 

500 e.e. distilled water. 
0-001 <*r. soluble Prussian blue. 

5 e.e. saturated ImteuattT just precipitated by the smallest excess 
of sodium hydrogen carbonate, 

Lord Hayleigh :I attributes the blue colour of the sea to that of the sky, 
seen by reflection. 

According to Ait kin * the Mediterranean sea t\\rs its colour to 
minute* suspended particles which reflect rays of all colours, whilst the 
water, by virtue of selective absorption, allows tidy the blur rays to 
escape. The solid particles thus determine the brilliancy of the colour, 
whilst the selective absorption by the water determines lite colour 
itself. Tltt* green colour, so frequently ntticet| in the sea, is attributed 
to the presence of yellowish particles in suspension. On the thcr hntu), 
th<' green colours of such lakes n\ (/tutstuttce and Neuehat*'! lire iiseribetl 
by Spring ft to the mixing of the natural blue uf the uaters with yellow 
produced by the presence of finely divided particles of suspended 
matter* which latter may thcmsehes be quite colourless. Sometimes 
lakes*, normally greenish in colour, become temporarily colourless. 
This is attributed to the presence of fine re!dish uitid, cMnt.uimujj <\ide 
of iron, whicli coiujtcriicts the jjrecu. 

Threlfall surest s that the ^rcctush cotittir tf th' se off the coast tf 
Western Australia niiiy be due to the presence of traces of *riaiuc colour- 
ing math 1 !* dissolved out of living or deml seuw-ei-tl, Httcltanuu ll 
attributes the green colour of Antarctic enters It? diatotits anil the 
excretions of minute aniumls, whilst the sea wjilrr at Mt*gadir {Morocc**) 
and off Valparaiso and San Francisco art* helii-vei! In be culour-d greet t 
by elilorophyll. 

Perfectly pun* witter is almost it Hit-mical iinj*ssit>thty, iitasiauch 
n coutuct with any containing vessel tuust Initt to contanituation. 
Even optically pure wider is dillteiilf of iiftiitiiinntt ; it cannot be 
prepared by were illlraliiitt or tiist illation. Hartley showed that water. 
obtained by distillation from acid pcrniaugunatc solution anl subsequent 
redistillation front a copper vessel in a hydrogen atmosphere, is not 
optically void. 7 Tyndall obtained optically pure water by inciting clear 
block ice in n vacuum. It showed a blue tinge when examined in it 
three-foot layer. 

Now, if pure wafer in coloured .slightly bine, as is generally conceded. 
the effect cannot be* due to either of the foregoing causes, namely, the 

Vilfirr, Hllti, || <M ; Hiirtlt*%% ifrit/., . 4H7. 
KW, S9 4iil, "' 
h, i'6iW,, tllli), 83* 4H; Ncirntifir- l*ii|irr,# f I!IL% 5, MH, 

* Aitkin, jP*r, /%. Mac, JSWiw., n % 411 

* Kpring, M Inttrnnt. Cmg> rlr, Liryr, ; ..Irrli, jsVi, /,Ay.* t ! 
], .217. 

4 Bttohftnan, A-iiliifi% 1910, 84* HI, 

? Hartley, t^/ M 1910, 83, 487 ; Spring* JFIall, nif, lfe%. t (III* 37* 174 


presence of suspended or dissolved materials, which are known to 
accentuate, if not to be the sole cause of, the colours of natural waters. 
It must be due to a, pure absorption effect of the water itself. The 
relation between colour and constitution is by no means clear, but the 
suggestion has been made 1 that the greenish tinge acquired on raising 
the temperature is a consequence of the depolymerisation of the water 
molecules, the polymerised molecules being bluish in colour, whilst the 
single monohydrols are green. This receives support from the fact that 
solutions of colourless salts, which may be expected to contain fewer 
polymerised molecules, are more green than pure water at the same 

The brown colours of natural waters are sometimes due to ferru- 
gincous suspensions, but in many cases are attributable to colloidal 
organic matter. 2 Typical waters of this class occur in the uplands of 
Lancashire and Yorkshire. The colloid is usually electronegative in 
character, exhibiting elect rophoresis in the direction of the anode, 3 and 
being preeipilable by positively charged ions and colloids, and by 
electrical treatment. 

The refractive index' 1 for sodium light at different temperatures is 
as follows : 

KofrucUvo Index. 

i Air at 


i -:j:w is 


to Vacuum. 


Variation of the refractive index, //, with temperature, /, is given by 
the expression 1 '' 

// i-;moi ur 7 (w/ i ^(i-2/ a -o-i8i7/ a -i 

For the iron K line* 1 at 15' C. the refractive index is KWoG.'W. 

The taste of water is largely dependent on its freedom or otherwise 
from dissolved foreign matter, especially carbon dioxide 7 ; with pure 
distilled water the taste is distinctly Hat and unpalatable. 

The magnetic! susceptibility of water has frequently been determined, 
the value for K ., 10* at 20 U I', being 0'702J) with a temperature eoeiUeient 

1 Durliiux ail \Vllmuim, '<'. <*' 
. a SH' Hiu-r, ./, .SV. T'/rrwi. /'/., H^K 40, l/l) T. 

a Sow Kill/, niwl Kruhiik*- (r., HMM, 35, 174"), wh Htmliod Howa<^ coUimk 

* Baxter, HurcM8.unfl Ortmlt,./. Anirr.(Un'in.tftit'. t 1JH1. 33, HiKL Sw aluo Briihl, Bcr. t 
lH!H t 24, IW4 ; (JitTitni, l*rw\ Uny. Nw., liMMJ, (A|, 7^, 4-0(>, 

K. K. Hull ami Pttytu*, /^///mi/ /? r/r//% l*22 t 20, 249. 

* Uiffor<l, ;m\ /fv.' Nw., 11M), | A|, 7^ *(. 

? Friwiumuu, ^nW*. ///!/ //cR Kranklt., 1UU, 77 ^5; .-i^A O'/a-m. ^wj., 11)14, 
106, ii. t U4a, 



of 0-00018. 1 According to Strums, it lien brtwtvn c-?hl anil 0-75(1 
at 22" C'. a The dieleetrie constant of water a! is ' (', K M 'f5, J 

Tlu 1 lH)iling-]H)int of a liquid is delim-d 4 as !b hi^iir\! t nipt ruhire 
iiltninable by a liquid under a tjUrn ptvvsmv t*f ilv *mn ^qtur \\hui 
heat is applied externally and r\ap*ratitn tnvnr<> tn-rU tVuiii thr 
surface, tinder a normal preNstirr ut' 7tU Him. ut inrt'rur\, w.ilrr Innls 
at 100*' ('., and the I>(>iliHtf-p<*iiits at \arii*us i*tht-r |iv%\utv\ are 1411 eu 
as follows & : 


1>WHguro ' 


Piv *tw l*-i> i- J 'tir 

IV -: lr,,,., rt |, 

mm. Hg. 


mi*i, !!/ * % 

1,,T II, "' 



710 i*'*-2;*.* 

;*u iiiiiiitui 



7-w . *.itaai 

ii* iiHiirTi 



7-11 tMI'KHJ 

;it iio-ii7 



7 -III i t H| 

"tii i mi ,*VJH 



7 IK '**j ;*;*;> 

+ li% I III! ^11*1 



7T0 < * i*lo 

**f itiii'iltitl 

7*12 : iW'tJsn 

7VJ UH70I 

; iVi tiiri'imi 



7al Ul*- 1 ; * %i * 

; 1 1 to-:*n 

7.10 1 OIHOl 

1M .!-s;U 

;;ii iitti'^Hi 



7fiH *i!* tci. 

T.s UMHtfU 

The hypsotnctcr h a small* jMrlitlilf {i e l ^n>jMiuUts \\iurh riiiUl-s 

the boiling-point of water to lir ili-trriiitind at ,nn pl.M'i , lit*- ttjitrr 
is phiCTtl in a .small tube or Intiler and r* Its ,4 t In i4ir*ins <*l ,s spirit 
lianie beneatlu whilst the vupciur in it% JM.'* f ** Hi* t*pru ir h-ats 
a delieate fchennonieler* The iftstritmi i*t i- oitMinM*-. HN-| im- tit 
tennining the altitiule of u plan*. MW* fh Itmlm^ |n*iut i*t wjitrr tail'. 
through one degree ('. for tniry iOHOtiet ti-> *ihu\ Mal-\*-L A MM*IV 
general expression is that of Sor*'t, 1111111*!% ; 

h Ultfif tittt l| 

where ^4 is the height above M*SI h-vrl f\|m\vM-ii in i*1rr%, ami I ib- 

ebullition temperature*, 11 


a KUwriw, /%#i. /^riVu% llKKI. 16. I, 

1^88,35,137; Townwiwl /Vm-. //y. .W , f ,, 

1808, 66, IWmj Ifrtutf** AttwUit. t!MI. 6. ."Mm ; .fti^r ami Mri^i. ir,V,|. 
67. 712 ; DrutU?* Antmlrn, I1KU, <S H70, 

r . " 0- I2I, jll|. 41. m * l'| l|8 ; r|rtt( y,.l I . j,, ;i; s 

lAndolt-BamHUnn. /%ii-<t/WA'rArmiVAr tWIi). 1*11 

R^gnault's meiuiurftmontii. 

1911 f^j'i ** 1 * ffoctill thl * ^^tt|t-l"'wt * *m 


A knowledge of the variation of the vapour pressure in the neigh- 
bourhood of 100 is frequently of value in cheeking the accuracy of 
thermometers by immersion in steam at atmospheric pressure. 

In this connection, therefore, the following data are of interest : 
Temperature, C. . . 95 96 97 98 99 100 101 

Vapour pressure, mm. Hg. 634-01 657-69 682-11 707-29 733-24 760-00 787-57 

Liquid water is incapable of existence above 374 C., this being the 
critical temperature, the corresponding pressure being 200 atmospheres 
and the volume 0-00386 approximately. 

The more important determinations of the critical constants for 
water are given in the following table : 









Mondoleelf, Pogg. Annalen, 

1870, 141, 618. 


105-5 (atm.) 

Strauss, Wied. Annalen, 

Bcibldtter, 1883, 7, 676. 




Nadejdinc, ibid., 1885, 9, 



200-5 (atm.) 

Cailietet and Colardeau, 

207 (kilograms 

Cornet, rend., 1888, 106, 

per sq. cm.) 



194-6 (atm.) 


Battelli, Mem. R. Accad. 

201 (kilograms 

Torino, 1890, [2J, 41. 

per sq. cm.) 


Dietoriei (1904). Quoted 

by Davis (vide infra). 


. . 

Traube and Toiohnor, Ann. 

Physik, 1904, 13, 620. 

(365 assumed) 



Davis, Phys. Review, 1909, 



29, 81. 

374-07 to 374-62 

217-8 (atm.) 

Hoi born and Baumann, 

225 (kilograms 

Ann. Physik, 1910, 31, 

per aq. cm.) 



Calculated below. 

The density, d, of saturated steam at various temperatures is given 
by the equation : 

rf=0-4552 0-0()(H757(< 100) 0-000000685(-1CO) 2 

in grams per e.e. where t is the temperature on the centigrade scale. 

Assuming the critical temperature to be 305 C., the eritical density 
beeomes 0-829 gram per e.e. 1 The more recent work of Holborn and 
Haumann, however, suggests that 374-3 is a closer approximation 
than 8(55 to the critical temperature, and if this value is inserted for 
t in the above equation, the figure for d c becomes 0-322. This is 
probably the most accurate value. 

The viscosity of water vapour at 20 C. is 0-0000975. 2 

J Davis, Phys. Review, 1909, 29, 81. 

51 Kundt and Warburg, Pogg. Annalen, 1875, 155, 337 ; Houdaille, Fortsch. Physik, 
1896, I, 442. 



The latent heat of vaporisation of watt-rat loo (', is 5#1> ralorirs tv, 
Sometimes the value is #iven for \vutrr at ('.. w \vlwli rasr tin* amount 
of heat required lo raise the watiT from to loo i", inttst ! juliinl to 
the above quantity. Thr follmvtm.' an- tin- most notr\\orth> attempts 
to determine the latent heat of strain, im<lnuhlrtil\ tin- must ammitr 
results beiiijL? those of Hiehanls ami of M;tthru-., It is n-markahlr 
that the values obtained by Blaek am! In \\att slmuM a|*jnMtuatr 
so closely to that aeecptrd at flu- pivM-n 



at G. 

From Water nt 











WW : ^iitltMH5J 

at loo (', 

*i, **;;,. 

Mn ( 


The muount of heat r<Mjwml tu nusi- I ^jniiu ut 

vapour at / u C. is ^ivt'it in eatt.tHr\ t , v ly tlir rvjti'rsstf 

0}J)'U |(>*il7K"H/ lilflf 

ii * /if M ; , mr?, ji, 

at o (', 

The moan spe<ifie hen! of strum nt cnustatit pr v*m- in-t urni 
1400 ('. is given by the rqtmtmtt : '* 


the ex})eriineut'al data Inin^ its follows : 




'$ 18*^*5 1*^1 SA *4*>*l 
Co nipt. rmtL, 1849, 29, 449; IH4II, 23. 411 ; ,|*n 
Berthek>t (tompt. rrnd. t 1877* 85, (HO j ,!, 

n WietL Annalen % IHHO, 9, 20H H5H ; ^rimfl 

- H. N. DaviH, /Vm% .4/<r. *'tif/.. Ill lit, 4c. 2117, 
11)20,2,107; SU'inwchr, 7m/, '" t " """ 

4 Holbor 
and Austin, 

\y, ,s, 

tJ. * 


11)20, Zj 107; St<inwt*hr, i7nW,, 11^0, i t t|*|*|. 

4 Holbom and Honninx, ^ww, l'hy*ik t \im ii 7:i|i - im7 jt Him .,^r -*! li*ll*ra 
and Auatin,^^ J^. ^^ 1JHI7 ; Bjtirntiii'. Mrilr^Arm i I?ii^" i. In! ; 








ll ('. 


(! j} . 










0" 1'720 







1 400 






The molecular specific heat al constant volume is ^ivcn by the 
expression : l 

(' 5-DI ! 0'00;*,70/ 0-000,000, 1 55/-; 

between ' and 2000 by : 

(V S-750 |-0-78rtx 10 a T 

| 0-020 .-; 10 "T- 

4-50 X l()- IO T a ..... 2-18X 10 ...... 

where T is the absolute temperature, 2 and 11 

(V (H)(J5-| 0-0005/ |'0-2X 10 !l / :l 

between I.'JOO" and 2500" ('. 

Tlu* ratio C 1 ,,/C',, has been esalnated at 1-20, a#reein# fairly well 
with the figure expected of a substance consisting of tnatoinie molecules.' 1 
The value falls with rise of temperature as is usual. Tims : c 

Temperature . 




Water- vapour exerts a distinct selective action on li#ht, tt the (Affect 
of atmospheric moisture bcin^t d(*teetablc speclroseopically in sunlight. 
It u umi tests absorption in the infra-red region, and the hfc a, " absorption 
band is interesting as beiujjf tlu 1 one by whic*h (he presence of water 
vapour on Mars was first determined by Slipher in I008. 7 

Milliard and Ui 
iSio^*l %1'itwh. f 

, |AN 100, 4B3i ; 
do Ijiioolii, .-!/<. 
ft *IV<it'/ / ^'/Jtr/' r/ 


11 tlanHMottt ^ 't*w jit, 
! L H74 ; vu liahr, 

iiT, rVw/il, mitl. % iHHt, 93, lot I. 

t. r'Ai7. l!H4, 87, (Ml. 

n'in^ HK)U, 15, r',Ml. S<^ alxn \VniiM'li\v. /Vr-, 

t* iitul van Kl'< 4 k *V/iW., l2.'t, 21, <>;>.'f, 

kt HriMiittt-r. 1HK'J 6, (Wl. 

ti$<tn*nntiMitwhtPiwtiiikril th'# tichdtlttf hi t'iniyt'H 

.t IHIUI, 63, 1*811, -III; bivrin^ and H<nviu\ /Vw, A'o//. s'<!., IBH2, 
th'ut. fthi/rikuL (frx. t IJMH, 15, 7IH ; llulHUw and liotttu^r, ibid., 
11) HJ. x8 1T4 ; Hot t rur, ,-lw/i. /V<i/.WA% HUS, 55, 170. * 
" SIT licit OH in Xtttun', HHW, 77, 4U7, WHI. 


WATER is readily decomposed at the ordinary temperature by alkali 
and alkaline earth metals in compact form. The temperatures at which 
water, in the form of ice, becomes measurably attacked by the alkali 
metals have been determined as follow : l 

Sodium . 98 C. Rubidium . 108 C. 

Potassium . -105 C. Caesium . -116 C. 

Many other metals liberate the hydrogen on warming, 2 particularly 
when in a finely divided condition. Thus pyrophoric iron rapidly 
decomposes water at 50 to 60 C., and its action is perceptible even 
below 10 C. Its reactivity appears to be independent of the presence 
of occluded gases or of carbon, 'and to be solely dependent upon its fine 
state of division. 3 Boiling water is slowly decomposed by granulated 
lead. 4 

Addition of magnesium powder to ten times its own weight of cold 
water, followed by a little palladous chloride, causes the evolution of 
hydrogen, which spontaneously ignites. 5 

Although aluminium is not readily attacked by water at the ordinary 
temperature, in contact with iodine the hydroxide is formed, hydrogen 
being liberated. This appears to be due to the formation of a little 
aluminium iodide, A1I 3 , which is immediately hydrolysed to the 
hydroxide and hydrogen iodide. This latter then attacks the aluminium, 
liberating hydrogen, 6 and yielding a further quantity of iodide, which 
immediately in its turn undergoes hydrolysis. Since the iodine does not 
enter into the final products, a very small quantity is sufficient to effect 
the oxidation of an indefinitely large quantity of aluminium ; in other 
words, it is a catalyst. 

Mention has already been made of the fact that the action of water 
is of considerable, value in discriminating between acidic and basic oxides. 
A somewhat similar series of reactions takes place with chlorides. Thus 
the acid chlorides PC1 5 , PC1 3 , SiCl^, AsCl 3 , are converted into free hydro- 
chloric acid, and the corresponding acid derived from the non-metal. 
In the case of chlorides derived from organic acids, analogous results 
obtain. Thus acetyl chloride, CH 3 . COC1, yields acetic acid, CH 3 . COOH, 
together with hydrochloric acid. 

1 HackspiJi and Bossuet, Compt. rend., 1911, 152, 874. 

2 See van Ryn, Chem. Weekblad, 1908, 5, 1. 

3 See this series, Vol. IX., Part II., p. 63. 

4 Regnault, Ann. Chim. Phys., 1836, 62, 337 ; Stolba, J. prakt. Chem., 1865, 04, 113. 

5 Knapp, Chem. News, 1912, 105, 253. 

6 Gladstone and Tribe, Chem. News, 1880, 42, 2. 



Metallic carbides are frequently decomposed by water, yielding 
hydrocarbons. One of the best known of these reactions is that with 
calcium carbide, 1 which yields acetylene. Thus 

CaC 2 +2H 2 0=Ca(OH) 2 -fC 2 H 2 . 

Even combined water or " water of crystallisation " may induce this 
reaction. Sodium carbonate, Na 2 C0 3 . 10H 2 0, is a useful salt to employ, 
and the reaction takes place at a more moderate temperature. 2 

By the action of water on aluminium carbide, methane is obtained 3 
admixed, however, with a little hydrogen. 4 

A1 4 C 3 +12H 2 0=4A1(OH) 3 +3CH 4 . 

Other carbides, such as those of thorium, uranium, and glucinum, 
likewise yield methane, but mixed with various hydrocarbons. 5 

This behaviour of metallic carbides led Mendeleeff 6 tentatively to 
suggest that the large natural reservoirs of petroleum in America have been 
formed by the action of water or steam on subterranean metallic carbides. 

Phosphides and silicides frequently behave in an analogous manner. 
Thus, calcium phosphide, Ca 2 P 2 , is decomposed by water yielding 
phosphorus trihydride, PH 3 , and liquid phosphoretted hydrogen, P 2 H 4 , 
which is spontaneously inflammable. 

3Ca 2 P 2 +12H 2 0=6Ca(OH) 2 +4PH 3 +2P ; 
Ca 2 P 2 +4H 2 O=2Ca(OH) 2 +P 2 H 4 . 

Even yellow phosphorus itself, when warmed with water, yields hydrogen 
phosphide. 7 

Metallic nitrides and hydrides are decomposed by water either in the 
cold or on warming, yielding respectively ammonia and hydrogen. 

Many organo-metallic derivatives are decomposed by water. Thus 
zinc methyl yields methane : 

Zn(CH 3 ) 2 +2H 2 O=Zn(OH) 2 +2CH 4 . 

Magnesium methyl iodide, Mg(CH 3 )I, behaves in an analogous manner : 8 
Mg(CH 3 )1 4-H 2 =CH 4 +Mg(OH )I. 

Some metallic peroxides, such as sodium peroxide, arc decomposed 
by water. An intimate mixture of powdered aluminium and sodium 
peroxide inflames when brought into contact with water. 9 

A few metallic sulphides are decomposed by water. The majority, 
however, arc stable in the presence of water, and this fact is made use 
of in routine methods of qualitative analysis. Water decomposes 
strontium sulphide, yielding a mixture of hydroxide and hydrosulphide, 
which can be readily separated on account of their widely differing 
solubilities, 10 the latter substance being the more soluble : 

2SrS+2H 2 0=Sr(SH) 2 +Sr(OH) 2 . 

1 tfirst observed by Wohler, Annalen, 1862, 124, 267. 

2 See Engineering, 1906, 81, 261 ; Masson, Trans. Chem. Soc., 1010, 97, 851 ; Turner, 
Amer. Chem. J., 1907, 37, 106 ; Dupre, Analyst, 1905, 30, 266. . 

3 Moissan, Oompt. rend., 1894, 116, 16. 

4 Campbell and Parker, Trans. Chem. Soc., 1913, 103, 1292. 

b See this series, Vol. V., p. 71. ' 6 Mendeleeff, Ber., 1877, 10, 229. 

7 Weyl, ibid., 1906, 39, 1307. 8 Grignard, Ann. Chim. Phys., 1901, 24, 438. 

d Ohmann, Ber., 1920, [B], 53, 1427. 
10 Torres and Bruckner, Zeitsch. Elektrocheni., 1920, 26, 25. 


Hence, hy extracting strontium sulphide with hot water and eivoling 
the dear filtrate, pun* crystallim- strontium hydro\idr is obtained. 

With barium sulphide tit* reactions aiv motv eimplr\, and pure 
barium hydroxide cannot be obtained in th- ab>\r mannrr. 1 

When" boiled with sulphur in th- pivsrne*- of M\\^-U in platinum 
vessels, water yields hydrojLjrii sulpiudr and sulphune acid." 

Many salts HIT deeomposid by \\atT, parheularK \\h-n their 
soiutit>ns an* ln>itrt! t Itasit* salts lirin.j pr*"Iu*' il/ 1 

Hismuth rhloritir attuost tntmrtifati ly unlrrv>* > siu'h " h\inlysis 
to thr basic bisuiuthyl ftilurult-, 

Hil^ - U,tK rtlifH ! -tlil, 

this rrat*tion affurtltu** a rou\ riu-nt mrthtHt il srp.-trahu,* bismuth suits 
quantitatively i'rom iHTtain nth* I*N. S*t|itMns t t* rri*' rblcrnl-, umt 
iuclrrct of tuaity suits ctiinptisril of a strong at'i*! umtf il uith a In-blr basi\ 
an* arid itt ivartion from a simiiar I'atisr : * 

Ftr attaIojL*oU rrasuus* salt** ri!tft!liPr'' 1^ lh T)lir raii'1rs ttltli 
Iy baisir tns **i nt rally 'in alK.tha< .Mhiti**!^, f.if. putassittm 
*, MKiituu earbituatt' rtf. ; 

Ki'N II O> kOH Hi \ 

Tlu* ui'tiuit is rrf< ntblr to th*- * ff * t ot th Mnr.ttn*ii i*l" th 
tlu* plTKrlitv ol tni- of its salt 1 , a w iL .rjl %*b *** hyl 
(lisso(*tntt*(i to an i*\trut %u slight as to br t'tMtiparablt- in thssurmtion 
with wiitrr itsrlf* i'nttrr surh roitiltttons mi apprrt'iublr romptlittoit 
\vill cHMU' bHwi't'H thr itriii ol" thr salt niitt Ilir wiili-r for possrssjou of 
ihf uu'lullic rndirli\ 

KthtTritl Hulls or rv/iTA tlrnvi-il lVi*iit thi- ni'iilr#!liH*iliiii tl' 1111 n-rttl 
by an alcohol nlst> tinrtrrgti hyilrolysis Ity ml-r itipt thr lats, %%!ttt*h HIT 
compound* of this type, nre fVrijtiriilly drcmupoM-d ut tins uay fur the 
niuuuftu'turc <f ^lycerim-, t*niid!t^s y in* s*t^p ; 11$*- h\dvt*IyMs ti" stieli esters 
is catalyticnlly nccrlerated by the iiiliiittitii of *i mtm-tal acid, 

When un nir-fn-e Milutiou of potasnium eobdto ruiinttr, ii|C"Clil"X} l4 
is hotted* hydrogen is exulted* Hit" \oltttiie of ttbu'li e|uds that <*i" the 
oxygen 4tbhorbed if the solution is rapidly oxidised m air, but ft* twice 
ilie vcilunu* ul>sot*bcd dttriitg stm%- o\tdjitioit isi atr. The evrvss il" ti.\y gvu 
in the former <me rctuutus at flir rltni^ of I In- rriiilntii as hy-ttrti^eii 
peroxide. Tltun* in tr ubseiHe t 

^Ii 4 i a o{l'X f ) fi ? 2H 3 O uKjio((\) 4 2 KOH Hjj 
with rapid oxidation 

^K^o^'X), i UH/)-j O a 2K 4 iM(C'\^ > 
but with hltiw <xidiitioit 

H a O 

Nuf. t MM'. 1 , 56. M, i-i, l. 
J, ,{wrr, TArwi. *SV*r,, IUI7, |9 IWI* ; 11iil|***il Hrt 

109, HII7 ; JII13,, 103, 7!K*, 

tiiw mrin, V*.i|, IV, 1*1.411 II, * Si* Itm* M-nj t \l, l\., i'*iri I.. 


The inihienee of water upon the direction of certain reactions., in 
consequence of the heat liberated by the solution of one product, is 
beautifully illustrated in the ease of sulphur, iodine, and their hydrides. 
The heats of reaction of li\dro<^en and solid iodine and sulphur in the 
dry are as follow : 

(U,) i |i,| t>(lll) -12,07:2 calories 
(H.>) [|S| -(ILS) |. 2,730 

hence sulphur will effect the decomposition of hydrogen iodide with 
marked heat evolution. On the other hand, if the reactions take 
place in the presence of liquid water, there is a, considerable evolution 
of heat in both eases in consequence of the heats of solution of the 
hydrides. Thus 

(IL) i |I.,| | Aq. UUI.Aq. | fc 2G,3lS calories. 

(Ill) I I W I I Aq. JUS.Aq. I- 7,200 

Owing to the greater heat of solution of hydrogen iodide, the relative 
heat evolutions are now actually reversed, and solid iodine, in its turn, 
can decompose aqueous hydrogen sulphide, the reaction being markedly 
exot hermte. 

Decomposition by Radioactive Substances and Ultra-violet 
Light. Water suffers decomposition when exposed to the action of 
radium emanation ' or radioactive substances yielding hydrogen, 
oxygen, and hydrogen peroxide in varying amounts according to 
circumstances. All three types of rays, a, j3, and y, appear to be active 
in this respect.'" With the ft rays hydrogen is the main gaseous product, 
owing to the reaction proceeding as follows : 


J-ltra-vioh't light behaves like [i rays in this respect. 3 Water-vapour, 
free from air, is decomposed by a silent electric discharge 1 in a similar 
manner, hydrogen and hydrogen peroxide being produced. 4 

Water* us a Catalyst. The' presence of water has considerable 
inlluenee on the course of some chemical reactions; thus an alcoholic, 
solution of potassium acetate reacts with carbon dioxide, yielding a 
precipitate of potassium carbonate, a result which is in striking contrast 
with the interaction of acetic acid and potassium carbonate, in aqueous 
solution. Also silver nitrate and hydrogen chloride fail to react in 
anhydrous benzene or ether. Many such precipitation and other 
reactions & fail in the absence* of water. 

Water-vapour is capable of functioning as a catalyst in many 
fractions. Attention has already been directed to the combustion of 
hydrogen (p. Ill ) and carbon monoxide (p. 85) in oxygen, the presence 
of small quantities of water being essential. Cnrbonyl sulphide, COS, 

Knmwiy, 7Y*. Chew. *S'or.. 11)07, 91, 931 ; Cameron and Ramsay, ibid-., 1907, 91, 
IflOH,* 93, JMW, DO'J. Compan* Rutherford and Koydn, Phil. May., 1908, 16, 812. 
lMwiw. Ann. /%**</*', H>14, 2, 1)7 ; (htnpt, rend., 11)09, 148, 703 ; Usher, Ja/w- 
buck KtulitHtkth', KMrmnk* HM1, 8, 323; Duuno and Hcheuor, ibitL, 1913, 156, 466; 
Koniliaum, Cwnyt. rrwl., WW, 148, 705; Antlr^ff, ./. Ru*. /*V- Ghem. Soe., 1911, 
43. 1342; BcTgwit'/, WiyMul Zril*c.h., 1UK), n 273. 
3 K(rnHiuii Cotnpt'rnnl., HK)9 t 149, 273. 
1 K*nitium, iAiW. f IttlO, 151, 3H). 
M, Phil Ma<j. % 1H1KJ, 35, 53L 

286 OXYGEN. 

will not combine either with oxygen or nitrous oxide when perfectly 
pure and free from water. 1 Thoroughly dry carbon dioxide is not 
reduced by dry carbon even at red heat, and no visible combustion of 
pure sugar charcoal is observed even at bright-red heat in oxygen, 
although carbon monoxide is being slowly produced. 2 Sulphur may be 
distilled in dry oxygen without visible combustion, and the same appears 
to be true for sodium and potassium. 3 Calcium is not oxidised by 
dry oxygen. 4 Boron and red and yellow phosphorus do not burn in 
the dried gas. 5 Indeed, amorphous phosphorus is not even converted 
to tlje red variety when heated to 278 C. in pure, dry nitrogen, 
although normally the conversion takes place with considerable violence 
just above 260 C. 6 

Water-vapour exerts a considerable influence upon the dissociation 
of nitrogen trioxide. The effect of prolonged drying of the liquid is 
apparently to reduce the number of NO 2 and NO molecules normally 
present by causing them to combine to N 4 O 6 molecules. On vaporisa- 
tion, these latter molecules dissociate to a mixture of N 2 3 , NO, and NO 2 
molecules, the N 2 3 not undergoing further dissociation. 7 Thus 

The activity of the halogens is greatly influenced by the presence of 
traces of water. Thus, dry chlorine does not attack copper, and dry 
hydrogen chloride does not unite with ammonia. 8 Although dry 
chlorine attacks mercury, mercurous chloride does not dissociate upon 
heating, when thoroughly dried. The same is true for ammonium 
chloride 8 at 350 C. and phosphorus pentachloride. 

Hydrogen and chlorine do not explode in sunlight when, dry 8 ; only 
slow combination takes place. Similarly ammonium chloride and lime 
do not interact. 8 

Nitric oxide does not unite with perfectly dry oxygen. Experiments 
indicate that perfectly dry sulphur dioxide and oxygen will not unite 
in contact with platinised pumice, 9 whilst sulphur trioxide has no action 
on calcium oxide. 10 

On the other hand, selenium, tellurium, arsenic, antimony, and 
carbon disulphide appear to burn readily in dry oxygen. 11 Dry ozone 
is decomposed on warming, but may be prepared in the usual way from 
dry oxygen. 12 Iron yields its characteristic "tempering " colours when 
heated in dry air or oxygen. 13 Both lead nitrate and potassium chlorate 
decompose when dry. 

Cyanogen bums and explodes with oxygen in the absence of water. 14 

1 Russell, Trans. Chem. Soc., 1900, 77, 361. 

2 H. B. Baker, Proc. Eoy. Soc., 1888, 45, 1 ; Phil Tram., 1888, [A], 179, f>71. ; 0. J. 
Baker, Trans. Chem. Soc., 1887, 51, 249. 

3 Holt and Sims, ibid., 1894, 65, 432. 

4 Erdmann and van der Sinissen, Annalen, 1908, 361, 32. 

5 The oxidation of the phosphorus is very slow. Russell, Trans. Chem. Soc,., 1903, 83, 
1263 ; 1900, 77, 340. * 

6 H. B. Baker, loc. cit. ? Jones, Trans. Chem. Soc., 1914, 105, 2310. 
8 Baker, Trans. Chem. Soc., 1894, 65, 611. Russell, loc. cit. 

10 Baker, Trans. Chem. Soc., 1894, 65, 432. 

11 H. B. Baker, Phil. Trans., 1888, [A], 179, 571. 

12 Shenstone and Cundall, Trans. Chem. Soc*, 1887, 51, 610 ; Baker, ibid 1894 6< 611 

13 Friend, J. Iron Steel Inst, 1909, II., 172. 

11 Dixon, Strange, and Graham, Trans. Chem. Soc., 1896, 59, 759. 



Influence of Desiccation upon the Physical Properties of 
Substances. Liquids that have been thoroughly desiccated by 
exposure to phosphorus pentoxide for several years manifest a decided 
elevation in boiling-point, ranging in extent from 30 to 60 C. This is 
well illustrated by the following data : l 




Carbon disulphide . 

Carbon tctra chloride 

Ethyl alcohol . 

Kthyl ether . 


Period of 


New Boiling- 
point, 0. 




106 . 























Similarly the melting-point of sulphur after nine years of desiccation 
has been found to rise from 112-5 to 117-5 C., and that of iodine under 
similar treatment from 114 to 116 C. The hypothesis that naturally 
suggests itself is that increased association takes place as desiccation 
becomes more perfect, and this appears to receive support from pre- 
liminary determinations of the surface tensions of the dried liquids. 2 

Physiological Effect. Pure or distilled water, on account of its 
freedom from dissolved solids, lias a, tendency to cause the saline con- 
stituents to diffuse from living cells, and so exerts a decidedly harmful 
influence on healthy protoplasm. 3 

It is quite possible, however, that many cases of the supposedly 
harmful action of distilled water on living organisms are in reality due 
to minute traces of foreign metals, such as copper derived from the still 
in which the water was prepared. 

Dissociation of Steam. From physico-chemical considerations it 
is probable* that even tinder ordinary conditions liquid water contains 
an exceedingly minute though definite proportion of uneombined 
hydrogen and oxygen in equilibrium with the compound molecules. 
Tins state of equilibrium is outside the scope of experimental detection 
unless disturbed in some way, as by the influence of ultra-violet light, 
when the decomposition may become appreciable. 

It is more easily observed at higher temperature, because with rise of 
temperature the* position of the equilibrium moves in favour of a higher 
proportion of dissociated molecules. In. 1847 4 Grove noticed the forma- 
tion of some* free hydrogen and oxygen when platinum, heated almost 
to fusion, was dropped into water, the experiment being repeated by 
Deville 6 a little later, with an even more decisive result. The main 
difficulties in detecting the thermal dissociation are the smallness of its 

1 Bukcr, Trail*. Cht'tn. SV>r., 1922, 121, 668. See also Smits, Zeitach. physilcal. Chem., 
1922, 100, 477." 

* Baker, he. nit. 3 JLoeb, Pfliiger* Archiv, 1903, 97, 394. 

4 Urovc% rhil. May, 1H47, [3], 31, 20, 91. ft Deville, Compt. rend., 1857, 45, 857. 

extent, ami rspri:i!l> t!i>- t tui< ntn t ilu- -M^-S f* n-* i witn- MU 
Thf latf rr 'ait hr ol\ iat t !> *'o*h!i" th*- :f,i^ - s r> i;ijnUy ; lr 
hv passing a rum-lit of strain \T .. ufiif* !mf phttintuo \\ir *r o\vr 
a'^Hp Ix'tWirll spJU'Kitii! r!ri*trul s l HI siirh a i.iiaitn*.T t hr **as is 
removed so rapitllv from tin- ha!fi arr.t that ,i {*rtt(u ut Ihr prutltu-fK 
fails tu ivotwtiwir. A similar t-ff* t-t was .tiliii-u-*! In tlrviHr -' hy ittratts uT 
his ** hot ami nUl ** tnli*", in ulnrit %f* aui as j*as%-l thmu^it ttt j NIIJU^V 
ht'twnii an i \trnially h-a!-! jMv*' tub-- .mi ,t *T '*nlrti n 
silver t uhr ; hvtlroyfu ami ti\\i:'*-n nriHiir ii in thsMH-tatutu a! tin,* 
surlatv hrt'tunt- roulrd l*rto\\ til*- I* isi|w ri,t nrr **! r.-i|it! r-*iiiiiiitiji 
hy thr iuu*-r t'ohl suH'atv, *i f ti'^ *tiflVi"*-iii'f m tlir \I|MII|V t*} iit((ti\u>n 
hy(tru|rn niui \vu'H fun als t**' apph*'*! i!)r\iUM ^*) |i*\%iujj st 
through n hrnti-d UHjjfla/t-il tuln- h*-n, *u arfoitnl t' tlsr niurr r 
pnssa^r oftlir liyirii*|iii, ui* tArrss it i\y^rii t** t* lr litiiml m the 
issuing frcnii th** ftilr 

Lrw< s nstrili*H :i iiit'f liil rt.iii'%i^f fil in |ni****l!i,i* a shnv rttiTritt nl 
vupoiir thruiijiii a lulr h-nt-il ft* \>4vins tcM*{u-ratur-s, aunt *'niit f 
<*losf<l platittuut vrssrl, !*, atta*'h*-t f a inatitniMrtu r> M itix?, l*i 

Htr Jissti f iatft!, aiiil hvilr5m psiv,r*l liirnii^li lip- 
\r in prrs%uri\ \\htrh lu-tMtut- I'tniHlaiif t'ir mtv nur trjjiprraturt*. 
platintttn fttttrtiutt's u* a s-iiu}irrni'*!l- iiiriuiii^iip m that it. 
is imptTltkciihlc to oxy^rit aiat w*ilri'^a|iii!" it \\>i^ rasy t< r<ttri|latr 

IVoilI till* pIVSsUlV rr^istt-rrtl hy til*' liiHimliii tr-r Ilir f\t lit **1" ilmtiriitt inn 

of the* stcatu* 

Unit * in his latrr rxpi-riiitriits tivtt n |,fli%* tjliiii*" t|' I litres rupurity 
routiiillili^ it short Ifiiifth of plat iiiiliii uirr ttliirlt \\n^ rirrturallv iifiit*<l. 
Tilt* ^flohc was rVitt'iliiird nftl flit-ii t*tiiifi*rtrti Uith a \i-s*i*-J rtfUttiiiiitt^' 
wntor, tlu* vnpotir frtnu wlttt^t ptsM-ti ititt* tdr ultilfi- jnnl ttitiirruvttt 
partial disstMnntititi in rfitttitrt with tfn- uirr, U Jim f{iiiltiiritiifi was 
attiunt'd for tlu* piiffirtilitr tcfttprrnturr riiti^m, thr vrsm-l was tMl*'d t 
tht* ^nsrs putitpt'd off nut! liii-ii^iiri-il itffrr tin- Wjtti-r- \tputir tint! Itrrti 
fro'/c*ii out. From thrsr ilitta Hit- iltHMiriation |i'rsittrr tt % * fiiti'iiliif "f L 

Holt also ftuiravourrd to <lctrrtumr tt- lo%^r*t trmprrutur** at. 
which wuttT- vapour apprrrjiinly ttr(*oiitposi'tt in t*oniirt u-itli hratt*'d 
piutiutiin wtr<\ Mitttttr i|imtitttirs of iin^ utj-*- t*otl<rtnl nt aht>ut 
750" C'. No <iouht liiitl if lit*! lirt-si for tht- Htiliiliiiif \ ui' tin- ^HM*H in 
tlu* t'ondt'ttHt'cI vitjiiiur at lltr rtmchtsiou of thr lAprrnuriits, trait***s 
would ha vt* IHTII drtrrtrti it! rw-u low-r trmr 

tL t 1H67, * 5T ; 

:| !xtwtmt<tm, ^iVirA. ^Vm., HHnl, 54, 71V 

4 Unit, l*/iil. l%n liKMI, fill. 17. 71ft. ***** ttt*i 1lSt itiwi, il*i-l , HMW, 16. O'Jf, 
Holt, iWrf,, MKI7, n,ll!UK 


Bjerrum l employed an explosion method and obtained the following 
results for 1 atmosphere pressure : 

Temperature abs. . . 1705 2257 2642 2761 2834 2929 

Percentage dissociation . 0-108 1-79 4-3 6-6 9-8 1M 

Nernst and Wartenberg have given several formulas, based on 
thermo-dynamic considerations, whereby the percentage degree of 
dissociation, x, of steam at any temperature may be calculated. The 
first one 2 was used in a somewhat simplified form both by Langmuir 3 
and by Holt, 4 namely : 


2=K -^_ +2-65 log 



By neglecting % compared to 1 and dividing by 3, 

log 0=fc 

log __o-00018(T--1000), 

where T is the absolute temperature. The value for k given by Nernst 
and Wartenberg is 3-83. Calculated from the experimental data of Lang- 
muir, 7c = 3-79 ; a slightly higher value is found by Holt, namely, 3-806, 
whilst Lowenstein's results yield the value, 3-80 (up to 1968 T). This 
latter may therefore be accepted as the most probable value for the 
equilibrium constant of water-vapour, oxygen, and hydrogen. 

In the following table are given the percentage degrees of dissociation 
of water-vapour at temperatures ranging from 1000 to 3500 abs., and 
under pressures varying from 0-1 to 100 atmospheres. 













()-0 4 556 

0-0 4 258 


0-0 5 556 


























Steam is slightly decomposed when subjected to an electric discharge, 
hydrogen and Oxygen being liberated, curiously enough, sometimes at 
one terminal and sometimes at the other. The nature of the spark 

1 Bierrum, Zeitsch. vhysikal. Chem., 1912, 79, 513. 
* Kemst and Wartenberg, Oottingen Nachrichten, 1905. 
published, Zeitsch. physical. Chem., 1906, 56, 534. 
3 Langmuir, J. Amer. Chem. Soc., 1906, 28, 1357. 

1921, p. 765. 

vil : i. 

Two later formula, were 


appears to IK* I hi dthmnnin" fi*'t 'S, 1 \\ith IMI.>" iifjus thr In fln^m 
appears at thr iuM-iti\ .indth* nv, ' n v t th> ft?r- { I* ; vMth short 
.sparks flu* positions ar* pV'T'd, .<ii th pit * ** i* *t|. 4 Mt- to that 
taking plaee in 111* 1 ordw.u) h 1 1 h s; , ni h*) 4 nt ^ <t \ 

Steam as an O\i<UsM& \i*t. SV ),- n '<! -fti-i .un s nmde 
to pass uvrr m,in\ silKt,ih'i s vinfis i JM/*,*!- i 'i tin I ,iK, ttNidatittu 
frequently takr. 'pl,tf , |,isli'n! n H at I ^-t If i,,p ratuhs. llitis, 
at tt*nip<Tatur's a!v HM I . sulphui i* l*!|i *\j^j.ii .1,1,1! n-ilurrel : ' ! 

j||,u as 'jll.s M>... 

With phtsphnis at -r*i i' ; : 

;iIIJI L!* HI, !U'0 X , 

Whfli stt'illll isail\\cii In i!ii|ilii^f UJHMI tiHMniit si-rut rUr, h\ tiru^t'lt 

Is Ithrnitrd and u\ilt-s nl' rartnu ar*- tunii* *l, \f rrl;tti\rl\ luu tt'tu. 
ptTutnrc's, su*h as ^no Iti tilin C\,tln- 1114111 pnnhM'ts an- \\\ tlr*.j-it anil 
cnrh(n tUoxitlr. Tints : 

(1) C^Jir.O-. - t'<K. *.*Hj IH,*MMI riilnrjrs. 

At 1000 ('. iilitl npwanls a jnt\fiir t" lii *li"M|,i-ii iiiiii *^tlfiiii tiuw- 

CiXick 4 t hi' st"t"illtftl U'fllf'l' git* !* ft*rtll*il, lllr tttf* t*,i\r% hrU 1 ^ pJ'rsrnt 

in rt|unl vohnnrs. Thus : 

ii r nji . c ci . IL ^ijtui r;iiMi-j-v 

At tfinprrnturrs intrnucihatr In-fwrt-u lit* i*ri \*innf ft 

und t\idfs uf t*arttoit i** *!! *uu i : , th> prMTutiii^i ul rarlutn 

tnonoxicit* iiH*rrH\iti|4 uttli th - t-upi riilnt'i , *f fh* utrliitii thusidr 

From thr 
(Hi) CO - ILO I O, 11 , tu 2IHI t.iiMtn * ! 

it is fvidfiit thiit UIIN utiMtmti in tli* j*tf -^nt* i t!i *\ < .t>tu a^ ji 
would IH* witlititit anv tntinritt'* ttptm thi tiiiuhhtnnn iit,istitnt*h r* no 
t*hartgiM vntunic* IN ititrtuturt-d l*\ ;n\ iii*u IHM*! 1 Hi* M|uthhrntin 
from ri/^ht ti> lc*ft ur in lhri*\r** dtrtrtiun, ||n*'r th* uiln*- li*i Ii tit 
the <xprfjsion 

is itulrpcndrnt f thf pn s>ttr* , 

SincH* an inrrrsisr in trinpf rattnv ii'mls !** shift th- sfntr tl" 
Imuiu rt'prrsi'nh'tt in ^{tmtittu tin) IVmn niflit ti* 1*1'!, ii ftJIw* thiit 
the valut' lor K will risi . This has hrm tAprnturiitjiliy rnitliriin'i.1 fur 
temperat un*K l>rt wirn 7KIV itud 1 -MKV T,,* tltr n-sults linn^ s fuilcav ; 

1 J, *L Thtimmm* ltrrent fa*nwfhv* AVrrfrt'ofi/ sfi| J|i^|iirf$ * fl 1tivii|*!!i I*f^* 
1803), p. 559* 

Hw I^win litul liaiitlull, J, ^wirr. I 'linn, ,W.. hl, 411, Itil;* ; ICiiinliili iiinl I!ir1i.nk)% 
t'6W., IK SIW; Hull untl iiriif, /fcr,, IW7. 40, 4IWi fV^ IP! Hnmiti, W*i^, f s A, 
/tec., 1879, 35, 2411 

3 Thin rritetitttt l*|iift ut al4if I'Wr I',, innt *! wn' t", m^m- \m JT '^tt. 4 thr <*tl 
in mt<iiwHi t CO, fKititittatiii iiiitl I*tiiii*r /fcr, IMH*', iH, ;*4"', ilulf *iiiI lf*4itpiiiit 
(./. rArm. *Vr,, IKM. i?, ^*H2j ili'*rvrti<ti tht* fart il^ii fiirnin 4\t*W^ n* *in<tt mditrftMit 
|mrlc am JM : WIM| tltrouuh fhi* rnhftt 



jonituro, ( 

K COH-H 2 









1 -95 





In the commercial preparation of hydrogen, since carbon dioxide is 
more easily removed than the monoxide, the aim will clearly be to 
work at a low temperature and thus reduce; the fraction ' p olpeo t 
to a minimum. For the production of water-gas, on the other hand* 
with a maximum combustible cllicicncy, the percentage of carbon 
dioxide must be reduced to a minimum, and high temperatures are 

The reaction between steam and carbon is facilitated by the presence, 
of certain inorganic salts, such as the carbonates of sodium and potassium, 
which function as catalysts, 1 

Steam reacts slowly with silicon at red heat, hydrogen being 
evolved, whilst the residue consists of silica. 

When electrolytic* iron foil is heated in steam to about 'W() C., 
tarnishing begins to take place. At 400" C. a small but measurable 
quantify of hydrogen is formed, and the velocity of the reaction in- 
creases rapidly with further rise of temperature. The reaction appears 
to take place in three stages, involving 2 

I. Dissociation of the* steam, 

H a (>^ >II., | 0. 

*2 Formation of ferrous oxide, 

Fe I O^rH'VO. 
3. Oxidation to ferroso-ferrie oxide, 

For ordinary iron shavings, the lowest temperature at which hydrogen 
is evolved is about #00' ('., and the optimum yield is obtained at 800 C. a 

If the reaction is allowed to take place in an enclosed space, it docs 
not proceed to completion. Kquilihrium is set up, and the reaction 
obeys the law of Mass Action. 4 The initial and final stages of the 
equilibrium may be represented as follows : 

:*Fe f 4!U)v ^Fe/VHHo. 

1 Taylor itnd NYvUlr, ./, Awtr. ('hem, *SV>r., 1921, 43, 2055. 

s Krind, ./. HY,<{ AVf/riw/ Iron Med Irmt., 1910, 17, 06 ; J. Iron tiled I ml., 1009, II., 
172 ; Ht'Mhin HW*M, Vtl. I X., Purt II., p. 4H. 8 lxtttrmanJi, Vht.m. Ze.nlr., 189(J, I., 952. 

1 Thin wiw tirrtt prnvtti hy l)<villo (Annulm, 1871, 157, 71 ; dompt. rend,, 1870, 70, 
1 tor ( 1201 ; 1K70, 71* HO) unit Chamlron ((-ftmpt. rend., UK 4, 159, 237), and Hubsequontly 
fonftnncd by Pnutwr (%nt#th. }ilnjmk(il, ahem., 1904, 47, $85), ami Hchroinor and Grimnea, 
///i<>r/. ('Itt-m,, I92O, 1 10, 'ill, SCM* ulno L. WfihUtr and Pragor, Zeihtch. Klekfrochem., 

Desiinwtiw: the pressure of \v;itT \apiur as /, uhrn npnlihrium ha* 
been reached, and the h>droti:<n ptvssutv ;*s /*,, l*n umr obtained tin* 
following mean \alucs fur Ihr ratio /* t / >t : 

The siiprrliciid oxidation of iron \vtth strain is used technically as 

of the Boxver-Barff process. 

When strain is passi d ox t r nwlxhdenuw at iin*it temperatures, 
hydrogen and molybdenum dioxide are formed. Hit- n-artton is 
reversible, antl has been studied trom th equilibrium point ot \ ii'\v over 
the temperature ranye 7<io to 1 1 -till C'\ 

JH,O Mo, vMnO, ^11 r 

It is found that the values for the it|tnhbnunt etmst-ant, 1 naine|\ , 

K /%,, /i,,,, 

obtaim-tl by the oxidation of the metal i^r-*-s elns |\ \vith that frttm 

rcducttttH of the dioxide tit !iytf**i|"ti, v! Steam has m* arttttn on copper 
or cuprous oxide, hut euprie oxtdc dtssuetatrs ttt strain x lehhnjj cuprous 
oxide. Magnesium readily ignites in steam yieldui^ magnesium oxide 
and free hydrogen, At red h*at mekel shu|y deet*mpses steam, and 

heat yielding the dioxide, SuO 3 . 

Metallic sulphides are decomposed by steam at liiuli temperatures, 
At incipient red heat ferrous sulphide yields imi&m-tic oxitle a.s follows ; :l 

At lusher temperatures sulphur tltoxitle ami sulphur art- jirmluerd. 
Leatl sulphide at bright red heat yirlih the frre im-tnl : :1 

al*hs s jll ? o al*b - '-sll r s - so., 
*2H r s i so ;i tilt^o ; as, 

and, probably, to a small extent. 

for a little* lead sulphate is generally iinwltiml stmulianeottsly. At 
white heat cuprous sulphide is converted into metallic euppi-r : :l 

t*u 3 s i-2H,o tft'u ' so, ^ ^ii, 

3 Thi* action f sti'itii* n tuii^Nlioti tia* l*i'ii sliitfil $n Aiinildir iiiiiiiurr hy v *< !,iiiii)t, 
rittich. anory. (.'hr.m., 11121, 120. L*<i7, * (*iuiti^r, *>*/!. *r*/., JWHl, i*|j, t-Mi r i, 


Detection and Estimation. The presence of water in a gas is 
easily recognised by the increase in weight suffered by desiccating 
agents, such as phosphoric oxide, sulphuric acid, anhydrous calcium 
chloride, and anhydrous copper sulphate when exposed in the gas. 
In neutral organic liquids, e.g. ether, chloroform, acetone, etc., calcium 
carbide supplies an easily applicable reagent, which can also be extended 
to the estimation of water of crystallisation, the volume of acetylene 
liberated being proportional to the water present. 1 On account of its 
change in colour on hydration, anhydrous copper sulphate can be used 
to detect the presence of moisture in organic liquids ; potassium lead 
iodide has also been recommended 2 as an especially sensitive indicator 
in such cases, the colour of strips of paper coated with this changing 
from white to yellow when immersed in a liquid containing even minute 
traces of water. 3 

The estimation of water in a substance is almost invariably effected 
by drying ; gases are passed through the desiccating agent, and the 
increase in the weight of the latter is recorded. Solids are placed in a 
conihu'd space also enclosing the desiccating agent, or may even be 
inm-ly heated in the open atmosphere, the amount of moisture being 
measured in either case by the loss in weight. 3 

1 Maaaoii, Trans. Chem. Soc., 1910, 97, 851. 2 Biltz, Ber. t 1907, 40, 2182. 

3 See Huntly and Coste, J. Soc. Chem. Ind., 1913, 32, 62. For the special methods of 
kk hygrometry " see Chap. VI. 





WATKH wats, aeeording to Aristutlau phdnsophv , ,m { mrutar\ sub- 
btanee, representative of the pr<*prrt\ *t MIMI .tu -,s .md liquidity. In 
1781 Cavendish showed that watt r euuld b* <ht,itn? <j In j,iv*tit elretrie 
sparks between terminads surround* d bv a intvhtn f ait .ud hydrogen, 
and satislird himself that fhr lujmd iMmnd und* r lit* * eHudttious 
was not always arid. His r\jrnw ,K iudit\ttil flu! fit* |>ni{Hrtit)us 
by vohuuo of hytlrop'U and H\\*ru it>iil uj* in |*ndufjh* vuttrr urrf 
approxinuitfly its *2 : I, 

In 17Bf$ LuvoisicT alU>wHj wlrr t dt*j iiili* it, ^uidnirt't-l hratrd 
to rcduc*ss t ittui by t*uII*Ttm tlir hytiru^nt ant! tuuli-i'nHijHvsrd strain, 
cunu* to tlu* ('oiu'lusuiu tftat wiilrr rtintatus h\tln^rn and **\\^i-n iu 
the volutui'trit* proportiiuis of H> tc* I, 

Monifc iti I7HH l adopt fd thr thru n-w pnurtplr *i|" fiu-aNMnn^ thr 
vohuui'S of tin* I't'iit'ting giisrs and ndculattn^ ty inrans u!' thr timsttirs 
of thr gases from tlu* vohuw niti to thr umss ratii*. Thr vattu- 
obtained for the former ratio was approximately 2 : t, but Jus data for 
the relative densities of the gases were far fwiu aeetiratr. 

From the idea, originally snggi'stt'd by l*rirst!ry, that f h- prrertitage 
of oxygen in the atnuisphere varied cuitsidt-rably, ami that thr uirasure- 
tnent of the proportion of oxygen was equivalent to a drtrrmiuattun <if 
the ^ gocxlness M of tlu* air, the appatratus ti^nl for thr iirtrrtuinatitn 
of oxygen wain termed a ** riiiliwwuiiT/* Tbr tirst ** r\pl*siot> rudu*- 
meter M wats thitt of Vciltiu 3 Sinee that time tt has brrumr ettstomary 
to apply the term ** eudiometer ** to all modiiteatttms of gas analysis 
apparatus, the prineipte of whieh is batseil it tfir explosion of gas m a 
grauluatted vt*ssel or tuln % . 

Another investigation of litstorieal impttrtaiier \\n\ that of Her/elttjs 
and Dnlong 3 in 18*20 ; their tnethtnl was improved b\ Mumns ' ! in tHI*i 
who estimated the mass wtio of hydrogen to oxygn* by passing puriited 
hydrogen over heated eopper oxidi* : the wetght i*I" ;ttrr pi'tniuerd 
was found by direet weighing, that *f the oxygen In thr loss in weight 
of the eopper oxide atul that of the hydrogen by <lffrreue-, Uumas* 
mean result wais oxygen : hydrogen 7-Uh; |, and until I?*HS this ua> 
tin* most reliable work done. 

1 Mungts Altm, Atad* *SVi. htri, 17HII, |i, 7H. 

* Volt Annnli fli C7iiwi$>n, 17iM), 1, 111 ; illlt, j jiil ; ;|, ;iii. 
4 litTwtiiiB mid Dulotttf, Ann, ('him. /*/*y.i, lH2i#, I* ami.' 

* Uum&n, ittM, t IH43, 8 9 !!>, 


These early experiments are of importance as marking distinct 
advances in our knowledge of the methods for demonstrating the 
composition <rt eonipounds. However, in common with Lavotsier's 
prooi (1783) of the composition of water by decomposing steam with 
heated iron, the methods have been improved both by modification 
and substitution. Thus the method of Dumas is not capable of such 
accuracy as 'was at one time believed, whilst the standard investigations 
of Scott, Morley, and Bnrt and Kdgar may be regarded as a later stao-e 
of development of the researches of Cavendish and of Mongc. 1 & 

The rat io of the amounts of hydrogen and oxygen in water is a number 
which in the past was perhaps of even greater importance than now, 
because* hydrogen is no longer generally accepted as the standard for 
atomic weights. With hydrogen as standard, each increase in the 
accuracy with which the above ratio was determined involved the 
alteration of the atomic weight of a, considerable number of elements, 
because hydrogen is not suited to direct comparison with many other 
elements. The majority of modern determinations of the composition 
of water have been made by synthetic experiments, but by so many 
different principles and with such a variety of forms of apparatus as 
to justify absolute confidence in the acceptance of a value between 
8 : 1-00(55 and 8 : 1-0085 for the ratio of the quantities of the two con- 
stituents ; the generally accepted value is 8:1-008. The exemplary 
investigations of Morley and of Scott have been of great value in 
providing trustworthy figures. Morley, by weighing hydrogen in the 
adsorbed condition in palladium and oxygen in two large glass globes, 
and subsequently allowing these to combine in a special glass combustion 
apparatus in which the water produced was subsequently weighed, 
obtained the ratio () : till 7-!W.)< and ILX) : 211 8-0392. Also by 
exploding mixtures of the two gases and measuring the residual volume 
of the excess of either, he arrived at the figures 1 : 2-00269 as the relative 
volumes entering into combination, and then making use of the relative 
density of the pure gases 15-9002 : I which he had determined with 
extreme accuracy, obtained by calculation a second independent value 
7-1NW5 : ! for the muss ratio O : 2H. a 

The method of Scott somewhat resembled the latter procedure of 
Morley. Hydrogen and oxygen of a high degree of purity were exploded 
together, and tin* relative volumes disappearing were found to be in 
the proportion 1:2-0024.5 at 11 C. or 1:2-00285 at C. Lord 
Haylei#h\s earlier determination of the relative densities of the gases had 
yielded the figure 15-882 : I (or 15-900 : I corrected to C.), and using 
this to convert his volume ratio into a mass ratio, Scott arrived at the 
value C) : 2ll 7 !>*' : L 3 

The accuracy attained by these two investigators has received strong 
t'oiiiinuatioii by a recent, very careful redctcrmination of the volume 
ratio, the value* found being I *: 2-00288 at: C. and 700 mm. 4 

* J*'or other important invHtijj;ationH on the componitiou of water, sec Gooke and 
Uirhiml*. Ann. C'lwnt. ./., IHHH, io, 191; Kc.wor, ibid., 1898, 20, 733; Erdmaim and 
Mnn-hnwl. Ann. r'Mw. I'lii/*., 1843, |'3'|, 8, 212 ; Noyen, Amcr. Chem. J., 1880, n, 441 ; 
IHOI, 13, 354 ; Uclu<% <"///*. rrntl,, 1892, 115, 41. 

- Mi.rliy f itltt/ftikut. f'ltnn., 1890, 20, 08, 242, 417; AM fir. Chem. J., 1888, io, 
1*1 ; IHlif> 17, 207. iSw'ulHo NoyoH and .Johnson, / Anicr. Chem. /S'oc., 1916, 38, 1017. 

4 Srutt, Mil. 7'ran*., IKW3, 184, 43 ; Rayleigh, Chem. Xcm, 1892, 65, 200. 
4 Hurt uud Edgar, Phil. Tran*., HUB, [A], 216, 393. 

To sum up, thri'et'orc, uatrr contains ! 
() It! parts of oxygen to I-UOTti'J - 1* parts nl h\dfo^-n ; 
or Ifr) 1 volume iif o.xvijru tn 4 J-<Mr.'s,s \nlimu-s t .f h\dro^-n. 


1. ICC. Frollt it stud) of X'l'a) photographs o| Id , Mrlilltstiit t! 

concludes that the niuli-euiar lormula tor ordinal) te ilUlK, The 
general opinion of chmusts, ln*w u-r, has, 4 mi -antac. h-nston ami othrr 
physical nteasmviurnts ol'h|uid wahT, Lnours Itn- xi^ u tit, it i*v 1% IUUIT 
romph-x lh:ui this, ami nMisists of ntolr*MiV, s IUMP- M| wltn*it an- l ss 
rctu|>ir\ than trihyitroK |1I : O' S , 

2. Liquid \V;itvr. Thr r it tuipoit u*- *i h.|'ui| uat'i as . 
Mil v rul ivwltTs a sttuls ut Us HIM! i ul u' ri*MM*lv<t\ M?I *4 ' nr'ular 


Thai wittrr in tlir lt|in*l %l it* i. .* .i'i t l ti . M ,jpi 4 
hits hrra rf't'<>^nis-*l Inr uianv >* .ts, ,/ttiM*u -i* <t i . * > * M 
to dt'trrmhu' tin- qitatititttn * \l nt tt , n /!IM v.;H, P f i^ .i.-fin.M'V . 

Thus llnthl :i tHiiirtutlt tl, 4*. tb it ,u!l *i m HP 4 s ,i *n ii thr 
nuiUrular rrtVafti\it\ **f \\at r, tit. t udi i HMH, tin d i -onpMttJ>l 
cuiitainiu^ trtravaU-ul n\\^n '! hr. u- u i in fiili^ i. i?ui*i*v ilh 
thr rrsults (U'smln-tl tiilinu autt .lpp!- a/t ^iti ifi^u t>$ th- 
n*adiurss <f \vat*r to luiui *nllfft\* 'im|fuuu (><i !^ r ilh alt . 
ill which CU\i f thr atitltd uat I I* rn}4tinul\ J*J'UM r, ^at-i tt 
rrystallisatiou.' 1 

As a JLjcncral rttlr, it liii\ In- saiit f thr H'f ! j inul'-rutar' assui-ja- 
tion tf a litjuitl is tti rulurr its \apitir pivssuiv, Van ! \\ aal. " has 
shown, frtuu iht'orrtinil iMinsiilrrattntis, thai 

1 i l' r * T 

1*!4 |V I* 1 !! I 1 /' f j. 

\vhcrr /' is flu* vaptiur prt'sstin- nt' a lt*|ii!ii at tip* ahshitn l-uip-r-ihM'' 
T, I*? Uiul T r the critii'lt! pivsstirr niut triiiprriitltV*- ri-sprrh\rh, autl h a 
ronst.nnt within (*t.*rtaiu limits. Now YMUMJ.? B ha.s J'*tinl tint lor all 
uoii-ussoc'iatrd litptids* tlu* \itlili' for k appn\nu:it" to f l, Ihr actual 
mean value tor si\tirii ht|ttids imt^lii^ilrii l*y lutu Iwm^ ;i ii, 7 
\Vatcr, however, givrs the v-alue i-*JO to *l-l, iiniit**itaf t apprrrtalilc 

Since association reduce* the vapour prrssurc ul" a li*|in<l si J**llo\\s 
that the hoilin^-point will he raised sititultjMteuit.Hiy . Now \nn'l 1 1 off* 
has shown that the hoilin^-potut i\ pn>portt(nal to the uiolrrular 
volume, and ndculutes that for tin- sintple moirrule Hi** Innlm^-inniil 

1 For full dot tutu of iiiinlinii dt<ti'rtttifijitiiit) ( tib r?*it$fs.*Jitttt .f u^trr >iwl ih*' .>t*i* 
weight of hydrogen, *.** llii <*ri<vi, Vi*l, IL, f 1m|*. !J, 

3 !><*niUHoit, C*/ifwi, AVv, lUlJI, 131, ** ; lifting ItwH*^ iwtll. /*Ay, /Vie-w f IP! 
9, Ho, ' * lUiilL //*"., I**M3, aH. *w 

1 Compare KtMi'iulii-iil, ( 'uwjtt, ii/, tWli, f% ***H 

*' clrr WiMnJN, Kwitinuitttt f/v <|i%/fni / ?# iii"* 1 *? * ^ . /..!* ,.< * 1 3U">ij* u^ > I ^ ' 
1HH1, Son nl->o Xi*iiiit, Thw/ttivht t'luts,** i.St^ftj'aiM, P*iL * I , I1*,*I, j -*$?, 

41 Vouilf< f /*/>/. .V*l;/,, lH!li! |ii|, *|*| *VJ7 

v Sft HainHii % v /V^\ /toj/. SW, t I Hill, 56 a 1*1. 

f ' vnn'l Hot!', farturtM nn Thntritiwl <i4 Jl*ltifin-i' I A 'is ?/. tt<404 it<"i i I**l4 4 ' 


of water under atmospheric pressure should be 65 abs. The fact 
that the boiling-point is actually 373 abs. clearly indicates appreciable 
association. L r 

When the boiling-points of the hydrides of sulphur, selenium and 
tellurium are compared, 1 it is evident that the boiling-point rises steadily 
with the molecular weight. 

Substance . . . H 2 S H 2 Se H 2 Te H,0 

Boiling-point, C. . 62 42 +100. 

Water, therefore, if it conforms to the general rule, must have a molecular 

weight greater than that of tellurium hydride, viz. 129-5. This su^ests 

very appreciable association. 

Waldcn 2 has directed attention to another fact of a similar nature. 
Methyl sulphide boils at a temperature 60 degrees higher than methyl 
ether, and ethyl sulphide 56 degrees higher than ethyl ether. Thus 


(CII 4 ) 2 S . . 37 C. 

(CH 4 ) 2 . . -23 
Difference . 60 


(C a H 5 ) 2 S . . 91 C. 

(C 2 H 5 )0 . . 35 

Difference . 56. 

Hence the replacement of oxygen by sulphur raises the boiling-point 
on the average by about 59 degrees. Now, applying this rule to water 
and hydrogen sulphide, since the boiling-point of the latter is 61 C. 
that of water should be 59 degrees lower, namely, 120 C. The fact 
that the boiling-point is actually +100 C. shows that considerable 
association exists at the boiling-point. Further evidence of the 
association of water at the boiling-point is afforded by an examination 
of its latent heat of evaporation. Trouton's Law, 3 usually expressed in 
mathematical form, is 

MZ/T= constant, 

where M is the molecular weight, T the absolute temperature of the 
boiling-point under atmospheric pressure, and I the latent heat per 

Now Walclen 4 concludes, as the result of a large number of measure- 
ments of normal substances, that the mean value to be assigned to the 
constant in the case of non-associated liquids is 20-7. If the observed 
value is appreciably higher than this, association in the liquid is to be 
presumed. For water the value 25-9 is found, which again confirms the 
view that water is associated at the boiling-point. 

Evidence of the molecular complexity of water is also afforded by the 
results of viscosity measurements. Experiment shows that, for non- 
associated liquids of analogous composition, 

JL x 10 6 = constant, 


where r) is the viscosity coefficient and Mv the molecular volume. 5 

1 Vernon, Chem. News, 1891, 64, 54 

* Walden, Zeitsch. physikal. Chem., 1906, 55, 683. 
3 See this series, Vol. I, 3rd ed., p. 157. 

* Walden, Zeitsch. physikal Chem., 1909, 65, 129, 257, 547. 

& Dunstan and Wilson, Trans. Chem. 8oc. t 1907, 91, 83 ; Dunstan, Zeitsch. physikal. 
Chem,., 1905, 51, 732 ; Dunstan and Thole, Proc. Chem. Soc., 1907, 23, 19. 

2(18 f\YUK\, 

Fur the majorit\ of suhxtatiri s thr v alur lor thr constant ram.*rs from 
U5 to about 70. In tin* easr of assoeiattd liquids, !o\\r\rr, tin- \alur of 
the expression is jLjrratly increased. For watrr if is morr than twelve 
times as rcat as for thr alky! chlondrs sUi*M'stiv r ot \rry apprreiahle 

In lH, r K r > Kopp l showed that thr luolrrnlar \ olmnr >J of a liquid may 

be regarded as an addithr proprrt), brim* thr sum of thr atomic 
volumes of thr <*onst it unit rlnurnts \\tthrrrtatn rrsrr\ations. : * The 
ohsrrvrd ntoirruiar \oluinr lor \\at*-r, hu\v*-\rr, is lan,;rr than that 
eal*ulatt'cl on an ;tNstunptitu of a muhvuhtr uri : ht t' IH tiuitt'ativr uf 

Kroni thrrnto-rlu'nura! riiiiMilrratiiiiis llitutiHtii l u^ts Int fu iiitVr tlu* 

JUX'SflUV of potyiurHsril inolrt*ulrs in ttatrr, hrfattst* thr Itrut f*\t*lill!!^r 

cluriti^ thr hytlrution of t'rrtuiit salts ruttlii ! r \ptaiurtl most sutis- 
faciorily on thr asstiutptiott (hat \\atrr nt*-t'*l mil* i'om!>iitatton in 

tlu* form of tliHlhlr molr-cttlrs, |II ,O t; . 

All tlu* forrUiHIIJ,; liirll|tis, htr^\>\i I' ,*r |Ut!llatH ill rhaiartrr, 

A nsrful method of drtrnmuut 1 ! fli *juantjtatj\ m*l nilar "om- 
ph'xity of a purr litptitt hrs tn me a'-uun" it-* '*mtar ?.jr;h ,tjul %ii'ti- 
latin^y thr nulrt*ular \vri}ht in ari'iuitiur* \vjth fh u^tfinti < \plamrft 
in Volume* I. (3rd riL* i?Ml>. jn irl tmnt tii. pnhu 

t/lM\ li A-u ill, 

\vlu*rr a IVprrsrnts thr MirfltiT trnsjuh, M"' thr flioirrtii.ii' \\rtijht, thr 

specific* volume, and A 1 a roust ant, thr m*'au \ahtr I"nv \\lnrh has in-rn 
detrniuurd as tM***, r is thr triujirratnr*- im asttrrd d*^iuards frtm 
thccritirid temperalnrr at \\hirh thr sUfl'arr li u\!iii has lirrn mrastu'rd, 
auuf */ has a valne apprt\imatin^ to ti, Tlir tlf'^in- **/ j/.t.ttirm/i'iiir, r, i% 
j^ivcn, in the case of \\atrr, by thr r\|rrs.sttn 

.r MVM M' is, 

assuming mo)u>hydt'il or H4I lu ! thr uonual tmassunairtl ittt>lrruir t M, 
The values ohfiiinrd for .r it! trm|MTutur ^ nuisiiuif tVum it It* JvfO (\ t 
as ^iven hy Itamsay and Shtt-!<K n- drtailrd lit thr Ititli rliifiiit tf thr 
table on p, *Jtl)$). It will br ohstTVi-d flint at low ti'!u|trra!mrs I fir \vater 
appears to apprt>\tmatr to the triraii%dnt fH^tj.1 motrrtiir. As the 
temperature rises, thr mean tnolrrular \veiht falls *win$ to inrrrasittj^ 

If has already been mentioned, hmtritr, that thr \alue.s tor thr 
surfatu' t-citsiou sis drtrrminrti by itatitsay and Slur Ids are ntorr than 
2 per cent, ten* low in consrtitteiice of a systematic i-rrnr throughout the 
series. Assuming the abo\-e retationstup brt \vn-u i aud M tti be strictly 
lnu% it. follows that the decree of nssuriatton tit" thr \%ati r is l*\\rr thaii 
that calculated. 

Another methtMl of cateulatui^ the iiiuireular eniii|ilr\tt\ from 
surface tension is that given by Dutoit and Mjuiti, a \vhu t'tu)tioy the 

1 Kt.pfi, Aurtttkn* iHft/n 96, I*i.1 t anil, - M^ln*ttl ft r tti-iht iliiplt'4 ly 

<>l Hrr Hortttmunn. #*r., IHH7 ao Itlfl ; 1Vil% Juwthn. I HIM, Ji), ll 

//rr,, IHjm. 28, 410, 2722, 27*2H, ^iL*4 s IKW2, Ii24 ; l*.tt. 99, !'J:$. 2732 ; I*. 

(ompt. rend., IH1M>. o8 f IUMK * 11tftt,vit ffrr 

s Dutnit itntl Mojoiu /. t'/iiwi, |i%.*, IlHtfi, 7, l7. 

whm-,,- is the wvijie. cohesion, deiined by a~=kr, h being the height 
to winch a hquul asrends m a capillary tube of radius r, and p the 
vaponr pressure, which, however, must not exceed 2 atmospheres. 
I lus latter places an upper limit upon the temperature and 
prevents the- lornmla Irom hdn s used to determine the molecular 
a.^n-atmn oi water at. the critical point. The decrees of association, 
''," ; s <'<.*< h .v this formula at various temperatures, are given in 
t he ollowmK table, together with those (,c 2 ) calculated by Ramsay and 
Shields, and also (.)-.,) by the Hamsay and Rose Innes formula, ' 

,r 3 l. 



K will be observed that both ^ and .r :$ are very much less than o? 2 . 





:* i 



(Dutoit and 
















(Ramsay and 

(Ramsay and 
Rose Innes). 















Thr vrry srrious divrr*jt k iuv bctwc't^n the values for x, ii' 2 , and z? a 
calls lor explanation. Attention has been very usefully directed by 
Dutoit, and Mojoiu to the fnet that nioleetilar weights, as determined by 
surfner tension phrnomena, are most, probably, in the ease of associated 
liquids* only the particular molecular weights of the surface layers of 
the liquids. If thr liquid is not associated, there will, of course, be no 
difference between the bulk and the surface, and the molecular weights 
calculated from the above formula? may be expected to be correct. 
Hut where association takes place, it is highly improbable that the surface 
layers will possess the same state of aggregation as the interior. The 
probability K that the association will be accentuated in the surface, 
so that the calculated molecular weights will be too high. 

The only conclusion that can he safely drawn from the above; data 
is that witter at all temperatures between and 120 C. manifests an 
appreciable degree of association. 

\\nldrn * has adapted Trottton's Hulc to a quantitative study of the 
molecular complexity of substances at the melting-point. Examination 
of a considerable number of normal, unassoeiated liquids shows that 

the expression 

M/ w /T m -13-5 

, Zdtich. tiltklrochem., 1U08, 14, 715. 

300 OXYOKX. 

may he regarded as "titmtlh tru\ M briut; the moireular wnijht, / TO 
the Intent -heat of fusion, ami T, ;> tin. mrltm^-pomt on I lit -absolute seale. 
In tlu* cast- of water, /, 7IM, T, ; , 27M, \\hmer M ir*-*j, tin- deyree of 
assentation, j\ briny l*i'~ I* 2C*7, Tins result a^rtH-% < \hviuely well 
with that oaleulated b\ the method of Hutoit and Mnjiu at I) ('. 

Front a stutK <f tht- <lt'j*r-ssi*u f th- t'rrf/ui:,' }>uiut of \ariuus 
M)l\'t*nts on addition of \\atrr, I Itt- iti an iir^i'fr uf asst>riatiou of thr 
latter has luH-ii ttrtrnutiiftt as toliows : l 

OF \VATKR, iUiIiIu. i 

Phrnol , L 

/i^ToluidiiH' , , , ;ia-l 

C'hlorncdir arid . . . '-!!! 


3. Molecular AsNwiation at tfu <!ritlc*ii ! > *>int. Tl*- 

aln*a<ly considcrt-d cattnot lr a|t|tlit-d to d*-tt riniu* thr molrrnlar 
u^rcjat ion of \vatrr al tin- <*nti**al |mt , T* ni'* t this iiilliriilf \ (uyr * 
has calculatt'tl that 


UK-87 P r (T f ; I07MJ 

whrrr f/,, is cntiral th^nMiy, that is, ihr tmtvt MI lu'tarus ul I r t t\ of a 
suhstitnt'r at thi 1 fritii'al jntint. rufortttnatr|\ thr itM-l'ulnrss il' this 
formula is utarrcd by thr diltirttlty of tirti-nutittuu 'lir \ahu- tor /,. with 

In tlti' cast* of watci* tltr ri-sults J4*vru *n j. *HU an- tihtiniifd arrtird- 
in^f to tht* vulut's assi^nt'ti to thr i*ritti*al roust ants, 

The fort 8 ||oin|| rrsnlts exhibit i'tnsitirnit*li' \artntion, thr ilf^rri" *f 
association ranging fn>in 0*77 to I '47 nrfttrdtti^ to tin* Uiltit -s c*iitsrn for 
Hit* critical constants. Thr final result in the table is, hourvrr, jirobnbly 
thr most etrrrel, the rritirn! density having b*--u ealeulat*-<l I'rttitt the 
r<{tiation on p. 271K usiitj^ tile un>st awtirate itutires n\jtthtbie Ijiniiirly* 
tluxsc of I lot horn and liauinanu j tor the eritieid tetupi -ratttre. The result 
clearly indicates that water at this temperature ts nut appreciably 

On tlu* <thcr hand, it shcntld be mentioned that other methods of 
calculation do not lead to quite the siuur result. Thus Uuye ;| tin*'. 
shown that 

1 (hldis tfautita, 1UHI, 46, i,, ,17;!, 
3 <uy*% Ann. t'Aiiii, /'Ay#,, tHiia. |j, 
3 (Jyi% ibid., IHttU, IttJ, ai, 1NM\ 21 1, 

when- M is the molecular weight, R the specific refraction, and F' a 
constant. As the mean of a large number of calculations, Guyc arrives 
at the value l-S tor 1/F. In the case of water, however, 1/F V is of the 
order of 1*1, indicating association. 



T f (aim.). 





Degree of 


27:* i MS ' 

0-421) 2 



27.*i i W I '* " l 

0-208 a 



27a i :i7 KI 

0-.T29 r> 



2?n ; .*,!:* l i 0-322 ( > 



4. Water-Vapour. The problem of the molecular state of water 
vapour is our of considerable dispute. The vapour density of water 
vapour corresponds f//)/jmn'//w/<'/// to a molecular weight of 18. 

As early as 1HHO attention had been directed by Winkelmann 7 to the 
fuel that the density of water-vapour in equilibrium with liquid water 
is higher than that calculated on the assumption of a molecular weight 
of 1H-OUJ. If the vapour conforms to the requirements of Avogadro's 
hypothesis, the obvious inference is that a, small portion is associated. 

In 1!H)H Komat*/ 8 published the results of a, further series of deter- 
minations of the- \apour density of water at various temperatures, which 
supported earlier work, 

Hose 11 showed that if water-vapour be regarded as an equilibrium 
lixture of many bydrol molecules with a few dihydrol, thus 


then the penvntagr of the latter could be calculated from the data given 
by Kornaf / by moans of the expression 


7 A y 



where /> is thf observed vapour pressure, d 1 the observed vapour density, 
and i/ tin* drnsity of pure dihydrol vapour, that of air being taken as 
unity, tl was tnkru as numerically equal to 1-2432, and the constant fc 1 

was etdettlated from the e<|nation 

Soi k l 4K57-1T-1 21455. 


association is as follows : 

. itncl Cllii.rt!i'!iii, C'twtpt r<w/. t 1888, 106, 1480. 
8 N f ttiii*jdtiti\ Wirtl, Annul* it. ttrihl&Urr, IHHfi, 9, 721. 
l lifttti'lli, Mrw. H, Areutt, Tnrintt. 1HJM), |2| t 41. 
4 HnlUitrn tiiiil Hntttiiitiui, Ann. Wit/*ik t 1010, 31, 045. 
f< On VIM, /%,-!, Urrint\ UHrtK 29, Hi". 

* Tin' vn!tif'fr fhr <*rttintl li'usity O-.'WO giv<*n by Davin (reforonco 8) is based on the 
iWMtinjrtii.n i.f ii rritit-ul t**titj'nttun'uf 365" (', (MW^P- 7 ^)- r ^ (} ^ logical, it should be 
nitruintftf fr flu* ulinvr juirpiw** nnnuminjr a ortticul tmnporaturo of 374 (1 Its valuo 
thru fwritiiifH ft'.'l:!! 1 , 7 Winkclttiaiui, Wicrf. Atrttalrn, 1880,9,208. 

8 Kriiiif/ /h.**rrtiitittn, Khij?lHiy t IOOS. 

* Iiit'* Zrit.*rh. Kir it twin- in.. HMiH. Id. 200. 


o j-'*"7i! 

"ill '.'.* 1 7 

10O 7tU-UO 

!5o ' MJHI 

The rise in vapour pressure aeeompam in; mrr ,i% l ti-mperature 
appears to counterbalance the dissoeiatm*,? mtlth-mv f fh- I*ittr, \\ilh 
tlu % result that fit*" extent of polymerisation remains fairly constant 

over a wide rnnjje. 

Oddo, 1 ill HM5 Was led to similar roiirhiMuits a\ tti thr rMsti-tit^- of 

an t 'equilibrium iiii \turr ofttiono atn! tli li\ Ir4 ttiolrrulcN in watrr \ aptiui\ 
but; courlutlt'il th:it at l C 5 '. thr amouut nl" a^^oriatmu N #H'/, tin* moli-' 
cular weight tf \vatrr--\apour tMin'rspMiiiliiif A*irtl\ to is-oiti. VSith risr 
of tc'ruprriittlfr assoriation takr* jla i r t ri^ii'luin* flu- In;.b vahtr uf it'll 
ptT CVUt, lit *7() (\ Kali of trlitptct'atlirr bi low 111* 4 . n ;irrotupaiut tf lt\ 
(lituinution of tin* tnolreular \\*-u?ht in fonsi'iiunir*- !' imr liissoriation, 

As Krnclall a has pttiutni fut, tiour\-r, tltr w*-.ik point in a!l tlifst- 
t'ltlrulalioiih lirs in tltr assumption that saturatni \apotirs tollotv flir 
^as laws with rxarturss, mor<- partir-ularty Aii*Mib-o's LIHI. Stirh i\ 
luosl probably not thrrasr. \VliiKf, thrri'Jon-, wati-r molrftjtrs may $ 
slightly assooiatrti in tin* \apottr phasr, flif prrsrnt i!<ita ilo not justify 
our arriving at HHV tithrr <**Mit*lusM*n tlum that thr * \t-nt t'I'sut'h asstM'iii- 
ticm is probably stnitll, 

Surh cont'iusiou, lit* it rriitiirkrti, is tu*vTth'l'SH i|tutf in 
with thr ronHusion prt'viottsly ilrawn that liffiiiil uati-r is itp 
aissiK'iaicii (set* p. *MH)), for, as Ctiiyr 4 has rmplijisiMctl, * l it ts 
for llu* polymt'risntioii in tltr ^HH^ntis *tat- tu ! ot" thr unlrr f 
1/10,000 lor il to br ii|pri*t'iiiblr in I lit- iti|tiiti plmsr." 


Tli* problc'Hl tlOW artsrs us* to till" (*utistitttttolt tt l*r asst^ftn) to uatrf. 

The results of tin* sttrfacf* tcitsioit mru.snrrmrnts f|t-at'l>' UMlteatr that 
water is associated, but thcrxtcn! of ftsMu-iatioit eiuiuot br 

from the mean value alone. Thus, for <-\iuti|itr, if thr turaii degree of 
nssot*intiou is $$ at 0" (**, tnking by wity of iltustratMiu the tii'iirt- urrixed 
at. by Dutoit and Mojoht, tlic*n, ni tlte^tHMtfitptiuit that only t\v<* ftiruts 
of water are present,* the t ( t|tiilibriuiii may be represented by 

r;^rw juir. 45, st inn. ^m- niw. it**t*vi 

1915, 47, 1 144, 

a Krmlnll. ./, Atntr. rhnn> Nw,, |UI0, 42, L*-$77 ; ii 

Mim*/4t J, ,-lwff, r/if<w. ,sv>r, t Hli 1 !, 43, f*l, ' IJiiy*'. 
11 Tho pnMMihility Iliat it iii.ilnili* (HjO),.* } rMi m 


Ii ? x and y are 2 and 3 respectively, clearly n=m, and 50 per cent, of 
dihydrol is m equilibrium with 50 per cent, of trihydrol. If, however, 
y > 3, the value for m must fall if as remains constant. Unless, therefore' 
the numerical values to be assigned to x and y are known, those for 
n and m cannot be deduced, and vice versa. Further, the system 
becomes even more complicated if more than two forms of water are 

The irregularities in the specific heats and densities of water at 
various temperatures, particularly the contraction observed when water 
is warmed from to 4 C., led Rontgcn 1 to suggest in 1892 that liquid 
water is a mixture of two sets of molecules in equilibrium, namely, 
ice molecules and water molecules. Thus : 

(H 2 ) ice ^i:(H 2 ) wa ter. 

The former were presumed to have a more complex structure but to 
be less dense than the latter. Hence, when water at C. is warmed, 
the equilibrium at is disturbed in the direction of left to right, some 
ice molecules melting to the more dense water molecules, and the 
contraction thereby resulting more than counteracts the normal thermal 
expansion of the liquid with rise of temperature. 

This idea has been further developed by Sutherland, 2 who concludes 
that ordinary water vapour is monohydrol, H 2 0; liquid water is an 
equilibrium mixture of trihydrol, (H 2 O) 3 , and dihydrol, (H 2 O) 2 ; 
whilst ice consists entirely of trihydrol. The high value found for the 
latent heat of fusion of ice thus receives explanation, for it is not due 
merely to the heat absorption consequent upon physical change of 
solid to liquid ; it is enhanced by the heat required to effect the simul- 
taneous dissociation or dcpolymerisation of a large proportion of tri- 
hydrol molecules to the dihydrol form, as indicated by the thermal 
equation which Sutherland writes as : 

3(H 2 O) 2 ^:2(H 2 0) 3 +6 x 18 X 177 calories. 

A similar explanation may be offered for the high values observed for 
the latent heat of steam. Thus, the thermal dissociation of dihydrol 
molecules is accompanied by an absorption of 189x18x2 calories, 
or, expressed as an equation : 

2H 2 O=^(H 2 0) 2 +2 X 18 X 189 calories. 

For dihydrol and trihydrol Sutherland calculates the following physical 
data (p. 304). 

According to Sutherland, the percentage amount of trihydrol in 
water at any temperature is given by the equation : 

37-5(1 +<?), 
where q is defined as equal to 



* RGntfien, Wied. Annakn, 1892, 45, 91. See also Piccard, Compt. rend., 1912, 155, 
1497 ; Oheneveau, ibid., 1913, 156, 1972 ; Duclaux, ibid., 1911, 152, 1387. 

a Sutherland, Phil Mag., 1900, [5], 50, 460. See also Hudson, Phya. Keview, 1905, 

21, 10. 

:M *\Ni,r\ 

FrutU thrse equations tin I^Hnum ;'* 

*' u 

f < , , . * k j >.* . f* I H I it J^J (MiS? 

IVri'i'tit*^'*' <f trili\4f'4 , . U7- : XM 


i Dcnsitv at t) ('. l wi-' -H^ 

(Critical temperature* , **** 4'. Vts ('. i 

Specific brat at i\ . . - **-H eal*<r>r tM* ealnrir j 

Latent liutt til* fusion . - - M calories | 

Latent heat 4f r\ap*ratOH ;t l**l I, . ^'"i? e,di'h-s *,Mil ealnrtrs ; 

Viscosity t o V, , . . uiinau oiiast 

It will br ohsrfVitl that thr jir*|*!'!iHj nl f i jln ilr*I ^fottfiK falls 
as t lu' Irinjif-riiturr is rats't{, At tin- rntiiMl f< uip*-raturt , *I7 I (',, 
it is still about t* |*'r rriit, a^stiuutti; thr i'tintiulj tu h f ri\( \\ort h\ 
tip to this p*nnt. 

But i'Vrtt if tltt 1 wutt-r nt its iTiliritt ttiitiii'mliiri- i"i*ii\i\tri| ni" urarly 
pur<* <iihy<ir<iK witlitmt any tniiyilr**! nt*!< t-nlrs, if u-tmttt still In* Fur 
highly ass<'iutrl thun riilt*tilifttii tr*m tiuv-\ Inriiiiihi utmM 
ir. As shown on p *!llll f wlirii tin- uust rrr*-'i$f mttint) data nrr 
yrtl in the raU'iUation, thr iito!f*rular Wright ut' wittf-r at tltt- rrtticnl 
tt*njj>rratun* works out at |H%\ nnti *orrrsjntls t*> niinost itiw!i!frly 
pure inonohycirol. 

For tlu*M\ awl othrr rrastins, it \vttithi njijwur that iiqiiiit wittrr 
is motv foinph'X than a hinary inixturt*, attfl tlir sit^|***sttuu lirst 
at by C'nllriidar, 1 itnil Iittrr <h-\c'!*j*Ml hv HiiUHtU-ld nntl i,i*wry/ 4 n 
that wittrr is a tenuity luixtun* has niiii'li to rrt'otiuttftui it, Art' 
to this theory liquid water coittins M*e- wiitt-t^, mid stratu^aioitrttles 
in oquilibritun. In othrr uords its rfiiupuMtiuit i\ rcprrtentrtl by UP* 

Whilst, this* theory renders flit.* problem eMUMdenibty more e 
than Kont^t*n\s binary theory, it enables explanation* *f a mre 
luctory elmrneler to be given for the iibniirmnttttrs in tlensity, speettie 
heat, etc*. It is, further* quite in Imrmotty \vitb aeerpti-d xii'Ws on 
molecular equilibria in general. If ice moleettlrs <*itn r\ist in water 
at the lower temperatures, there is uo apparent, reason why steam 

7V*iM.. IWI2, JAJ, If$ 147. 
triiry, 7Vii>. .SV^r,, |!i|it, 6, '***". 


molecules should be excluded from liquid water at the higher 

Assuming, then, that water consists of three types of molecule, 
namely, IM), (II 2 O) 2 , and (H 2 0) 3 , the question arises as to the manner 
in which the atoms are linked together. By assuming oxygen to be 
tetravalent, it^ is not difficult to construct formulae for the associated 
molecules. What difficulty exists lies in choosing which formula is to 
be regarded as correct, inasmuch as the associated molecules may 
theoretically assume several isomeric forms. 

Armstrong J has considered the structure of water molecules from 
the point of view of their chemical activities in promoting solution, and 
suggests that liquid water is to be regarded as a complex mixture of 
active and inactive molecules. The latter are regarded as having a 
closed structure, thus : 

Dihydrono. Trihydronc. 

II .,6 :OIL U.,O-OHo 


H 2 

whilst I he active molecules consist of hi/drone^ 1I 2 O, or of hydronol, 

/ ll 


Armstrong 2 has considered the possibility of even higher complexes 
such as tetrahydrone and pentahydrone. These bear comparison with 
I. he methylene* scries, pentahydrone being, by analogy, the most stable 
hydrone and possessing the highest, boiling-point as is the case with 
penlamef hylene. Thus : 

Oil, 01 1 ,v Olio Olio OII 2 ov 

" " x ,oir " " ~OH 2 


OIL, ( )1 1 / " OII 2 OIL OH 2 OH 

Dihydrono. Trihydnme. Totrahydrone. Pentahydrone. 

OIL CH, S Clio CH a CII 2 CH 2 v 

|| " | "Ndlo I I >CII a 

en, On/ " cri 2 --cH 2 cH 2 ~cn/ 

Kthvh'U^ Triinc'thyloiu' Totramofrhyleno Pcntamothylene. 

B. Pi. - KM" ( *. H. IM, :tr>" C1. B.Pt -f 3 l-- r > 0. B.Pt, + 50 C. 

A strrie lornuiln lor n tuolc'CuU 1 of water has been proposed. 3 

Armstrong, /Vor, Hoy. Hoc., 1908, [A], 81, 80. Nature, 1923, in, 689. 
8 ArniHtron^. (Jhc.m. Nnw, 1011, 113, 07. 
d, lirlv. CWm. Ada, 1922, 5, 72. 



WATKU is eharaeterised ly pmurful snhint a'tnn, parhetilarly its 
regards many inorganic' sultstanerv 

A. Solubility of Ganen. 1 This is usu*dl\ r\|iv*M-d in om- tt" tut* 
ways* namely, as Bimsen's .f/w/'^/fW {W//iYjVji/, ;f t nr as Ost\t aid's 
*SWfr////// rr^nxv/f*;/. I, Hirst- tmus Imvi alrradv Urn dt tinrd (p. #tf) 

(ases may lie divided $roa*il\ into iuu rlassr',, futiiicly, thisr that 
rnmhine with water, siu'h as ammonia, hvdnn<rn ehhtrid*-, sulphur 
ilioKi<ic% and thr likt* ; niui thsr that *in- rh'itut';dl\ im-rt, Attiun$4st 
the latter <lass may lif pluer*! *\yij-n, mtri*^-n, ftf, tin- luiiurr iiruup 
usually jMissi'ss hij^lj Jihsurptiuu <*trfli*-*triiK, minimi Ilii- hittrr are 
frequently so slightly s<*htih\ that tut* MI;U% chrmieitl purpusfs they 
may he re^anleil as instlu!ih" and 11*11} !* enih-rtr*! and rvni stured 
over water, X<*nun !<'s trtur<-n the tuti ^ntups, its sohtttttity hrinij 
greater than that of any other eheutiealK nn-utrat ;f.r., 




No 4 * 
N,< > ' 

lit . !;* 


li n) Hh I'i i 

illiI7l iii 

CiT'lH ii OH |t) ' ii ii ,;j i< ! 

1 7i;i i i;?i : i HI i . 

4 tin* i;u:t:*i ; mm,. : 

711-711 ' ii? m ; /+iitk> tl 

f*SV2 tSlil '17$ I 'tit 

I2WI 'loltt Hl we 

in $*;! 

7I' *.* 

The .solubility of most gases falls with risr of tettt|irmttir% httt in th<- 
*ase of the inert gaHes titiniumnt values r\ist, thr sohihthtv 1'iilliiiM in 

| A UHt'ful Muntnmry w nivt'it t*y C*^!s J, AW, i 

*- From Hindi*!!, AWii/nliliV* (Oiwlty L<irk'wMi, . 

8 liohr and litwk, WiVil, /iiiiKilfiiJlHUL 44, Itl* - %v 

4 Winklw, Brr,, I1IDI, 34, I4IIM, 

fi Htth, Zrit*fh, phyihtl CArm,, JHW7, 24, 111, 

M Kntimntwl frtnti tho Kiii^iitte! riin-r <ir?iwft fi'^itt tin* 

ni hv 



the oases of xenon mid argon as the temperature rises from to 40 C. 
Above this point the solubility rises again. For krypton the minimum 
lies between 80 and 4*0 C. ; for helium at 10 C., and for neon probably 
in the neighbourhood of C. 1 

In the preceding table are given the solubilities of a Pew typical gases 
in water at various temperatures. Unless otherwise stated the solubility 
eo-eflieient /3 is employed. /3 1 signifies measurement of the gaseous 
volume at N.T.P., but the pressure includes the vapour pressure of the 
liquid also, whereas j8 signifies the volume under the pressure of the gas 
itself of 700 mm. (see p. 36). 

Winkler 2 directed attention to the fact that, in the case of many 
chemically inert and " permanent " gases, the percentage decrease in 
the solubility eoclfitient between and 20 C. is approximately pro- 
portional to the cube 1 root of the molecular weight of the gas. Thus : 

decrease in [j. 


Cube Hoot of 
Molecular Weight. 



Nitrogen . 




Carbon monoxide 




Nitric oxide 




The decrease in jS is attributed by Winkler to a fall in the viscosity 
of the solvent consequent upon rise of temperature. The two factors 
may be equated as follows : 


where ?? arid f) t represent the viscosities of water at and t C. re- 
spectively, and k is a constant, M being the molecular weight. If j3$ is 
calculated from this expression, the value agrees well with that found 
experimentally between and GO" C. The following values for k have 
been deduced : 


Argon ...... 

Hydrogen, oxygen, and diatomic, gases 
CO 2 and triat.oinic gases .. 


those 1 gases that deviate 
A; tends to rise with 

Helium is exceptional, however. As a, rule, Tor 
markedly from Boyle's law, the value for 

The inert GUMS. The study of the solubility of the gases of group 
of the Periodic Table has proved very interesting. The data published 
by Antropoff :l are given in the following table : 

See p. 308 and fig. 46. 

Winkler, Zcitach. pki/mkal. Chem., 1892, 9, 171 ; 1900, 53 -* 

Anlropotr, Pwc. Roy. Mac,, 1910, [A], 83, 474. 



,. .. 

VMM, \l -.11.' 




(MUNI O 01 t I O 

o-oioo o-ous O- 


o-oiiii . o-O'joa i>- 

0-O7 '**-! 
0-07 M> 

II < 


0"! I0!l 

it-OS 1 2 

Thrst- rrsutts arr sln>\\u ;.:rajhtriiHy in l'*u;, III I rrtoarkahlr tVufttrr 
oft first* drfrrmumtt*ftK is Ilir tuiituotun !' sttlittuht v 'Jpnui h\ i\rr\ tfus. 

Fin, 40, Hf 

nf tl<* iiw*fl tit t^ 

KstmcluT Iwcl alrnuiy in IHIH'I su#urhtrd tlml %n*li a 111111111111111 
to exist, and inclt't'd fouiul such t In* tltr rani' with lu-timn. 

s Data obtaimxl by KNtrt*k*h*r (%rit*fh t f%w Illip, ji t7ti) iir| W 

by Antrt>|Kff. Ciulyt*K4Htyt ftwl lfc*rg*r {/. Amrr. Chrm, Nt# tt H*. 44, HUflt i 
ttolubility of ht*lium in wntir I^i,mtwi w 2 ! ' ! itittl IMi" <*,, ittil Iliwl IP* minimum vlin, ' 
fl f loc* eit t 



t* flu* 


minimum for xenon and argon lies at 40 C. ; for krypton between 30 
and 40 C. ; for helium, at 10 C., and for neon probably at C. As 
a general rule, the solubility rises with the atomic weight, helium 
and neon being exceptional, possibly on account of erroneous determina- 
tion. It is also worthy of note that the solubility of xenon is greater 
than that of any other gas which does not form a compound with the 

The solubility of a gas increases with the pressure ; for gases chemi- 
cally neutral towards water, 

<* P, 

since under moderate pressures Boyle's Law is obeyed with fair accuracy, 
it follows that a volume of water at a given temperature will absorb 
the same volume of gas whatever the pressure. This is Henry's Law, 1 
enunciated in 1803. The same year Dalton observed that the amount 
of a gas absorbed from a gaseous mixture is directly proportional to its 
partial pressure. In both of these cases it is assumed that the gas does 
not combine with the water. If combination takes place these laws are 
not obeyed. 

The methods employed for the determination of gases in water may 
be either chemical or physical. The former are useful in cases where 
chemically reactive gases such as oxygen, etc., are concerned. For 
neutral gases, like nitrogen, physical methods are essential. 2 

The presence of dissolved salts tends to reduce the solubility of neutral 
gases in water. 3 This is capable of explanation on the assumption that 
the electrolyte is hydra ted, and that the water thus " fixed " is no 
longer able to absorb the gas. If this theory is accepted, it becomes 
possible to calculate: the degree of hydration of the salt. 4 A solution of 
alcohol in water is peculiar in its behaviour towards oxygen. Although 
oxygen is several times more soluble in alcohol than in water, addition 
of alcohol to water reduces the absorption of oxygen, a minimum being 
reached with about 30 per cent, of alcohol. Further addition of this 
liquid raises the absorption coefficient. 5 

B. Solubility of Liquids. Liquids sometimes dissolve in water 
in all proportions without separating out into two phases. Such is 
the case with methyl and ethyl alcohols, and it is easy to pass from 
what may be termed, a solution of alcohol in water, by successive addi- 
tions of alcohol, to a- solution of water in alcohol, the latter liquid being 
so much in excess as to merit the term solvent, the water being the 

The majority of liquids, however, do not mix in all proportions with 
water at the ordinary temperature. When phenol is added to water, 
two layers are produced ; the upper one consisting of a solution of 
phenol in water ; the lower, of water in phenol. On gently warming 
and shaking the liquid becomes opalescent at about 68 C., and at 
08-3 C. the critical solution temperature the two liquids become 
entirely miscible. This is shown in Fig. 47. 

1 Henry, Phil. Tram., 1803, pp. 29, 274. 

2 8ec p. 3<>. 

:1 This is well illustrated by the data, given on p. 41 of the solubilities of oxygen in 
different concentrations of various salts in water. 

4 Philip, Trana. Faraday Soc., 1907, 3, 140 ; Trans. Chem. tioc., 1907, 91, 711. 

5 Sec p. 43. . 

3io OXYOKX. 

The mutual solubilities of eurhon ttisulphtth- awl watT a IT as follow : 

TrmjN'ruturi*. < '. , . . ** 
ca-,iii^'S ; i"rlm-wiii, 1 H : o '^s 

In mrhoit ! rt raehlorulr : 

Trm{M'ruturr, ''*'., . . 

<{raUH'(1 4 JUT l<H1i-ii-* 3 H,n *H 


ll.t* 1 *;? ' v*. 

;*$ ;"s ., 

M iM UU 

;i .1 ',v; H :ni 


M MS | ii Il-f't 







It will lit' r*liHt'rvrci tint!, ir% willi MM *. lit* %Mlnl'ilif i *- il tli ti 
fon'jijtmtj; litjuuls in wnlrr lull with ttv *t I- mj** Mt >u .tit imti ;h 
sultihilitti's of wiitrr in tlwsr !it|tittt\ ttw 4 itli t n f< t^fut* II s \ ]' 111* 1 intrrrsf tug niiHi f rvatt*ii m rownituw utli . rM* ti* i, 
nuiulHT of lic|ttttls that thr v.'ihi^ f**r A, in Uu!J*i luinisilj fr ' 
ifivcn nhovf, JUCMTJIM'S rt*|liii'i> \\ilh th w! -tiKin ^ Itt us tit? 
of siu*h stil>stau<'*'.s its rtitttititt a yivrji iiiuuli? *! j|iiu * ; tt ,tl * in**!* 
with flit* trnt|M'ratwv. Tiu-rr is tliti^ .1 *I%*. iiiilt^ I* tut'i* 
soluhilitirs tf nnitral liquids in vuilrr *s!ti th* *<h ,j jlj>i,i i<l r* uti.d 
hy wattT. 

Tlic* Koluhilit of water in bm/fiir >s 11% fullmi^ : s 



if witlrr tu HHI gram* C^lt r , 

Thr vt riuly nsr in sohtinlity in uotr 

C, Solubility of Solidh.^ Tlt- 

tiJI-l t IM M ;*.Wi 

*f iu*ntf<il utor^atur 


3 Hrx, /**. fil, ' 

Kir HU Htt'uitnl f tlw vu 
' thin m-t'iCMi VI, I, 

uuM tip 

^ , Mill, 17. :UH. 


arc readily soluble in water. This is the case for all nitrates, and most 
chlorides and sulphides, notable exceptions being the chlorides of silver, 
lead, and monovalent mercury, and the snlphates of lead, calcium, 
strontium , and barium. Kven these sul)stances are shortly soluble in 
water ; indeed, it is doubtful if any substances are absolutely insoluble, 
so that the terms soluble and insoluble must be regarded as relative 
Basic salts are -eneraHy insoluble; acid salts, on the other hand, are 
usually soluble. I be solubility of a salt in water is influenced by 
several factors such as temperature, pressure, and the dimensions of the 
particles constituting the solid phase. 

I. The Influence of Temperature. This is well illustrated by the 
various solubility eurves shown in Figs. 4.8 to 50, 

40 60 80 



Ki<. 'is. Sultthtitty if HidtH in water, 

A. (*nttthntni^ enreea. These may be roughly classified into the. 

following t yprs ; 

(tt) The solubility remains fairly constant, at all temperatures 

sodium chloride. 
(/*) The solubility rises steadily with the tcmpcra.turc ...... potassium 

(r) Thr Mlnbi!ity rises rapidly with the temperature ...... potassium 


(i/) Th S4iubiiity falls steadily calcium ehrotnute. 
(t 1 ) The solubility rises In a maximum and then falls caleiur 

{/) The solubility decreases to a minimum and then rises, as exe 

plilird by calcium acetate and propiormte l and by anhydrx 

sodium stitphiitc, the minimum in the latter case occurring 

about 120" C, 3 

n* i'hnn, ,S'<, |MIL\ 81, .'!.')'. 

3 TihU*n and ShtMihlono, Itw. ci(. 

312 OXYGEN. 1 

B. The curve exhibits sharp breaks. Two ]? / c 1 1 
a change of polymorphic form or a change of I" 1 - ^. ; , 
to a sudden break in the curve. The forrn e:t - f t 
ammonium nitrate, which is capable of existi***-* , t .^ 
crystalline forms. Of these the /3-rhombic pB^ 5 * ^ | 
variety at about 32 C. 2 At this temperature * 
solubility curve. 3 . { i 

The effect of change of degree of hydrati * . ^ ^ 
substances that can combine with water is show A* 
of sodium sulphate (fig. 49). 4 Below 32-8 C- * 4 . , 

Sell t 


i n * * .. tn 



ir pl> "- ! 

4 ' * M ' ' 

s, i *! I 

.< >ii - * '-lit 

the ***! tr p | ' 

rie c*l ^** * r ! * 

dra,t;t*<* '* ' 

the l*^ f ^ ! li! 



Tempera kure . 
FIG. 49. Solubility of sodium sulphate. 

The solubility of a substance in water is close- lv 
heat evolved or absorbed when solution occx.1 1**> * 
absorb heat on passing into solution, and in sixeli 
increases with temperature. Salts capable of erV>*< 
evolve heat when added in the anhydrous form, * s 
the solubility of the anhydrous form usually clt*e*'* -^ * 

Van't Hoff 5 - gives two rules, which, althoxi^** H J * I j 
only to the solution of a substance in one already | > ** - f * 
usually hold for ordinary solution. The rules aro **>* i t *il 
(i) If a substance on solution evolves heat, riKt* * f | 
will tend to reduce its solubility. 

(ii) If the substance absorbs heat under the tiJ..>c.>\ * 
temperature will cause an increasing amount top*i^>* ml 
Anhydrous ferric chloride is very deliquescent"., *i t I 
water is represented by four distinct curves corresj ><>* i * i 
ance of four hydrated salts, namely, 2FeCL . 411 .,< > ^ i 
2FeCl 3 .5H 2 (m.-pt. 56 C.), 2FeCl 3 .7H 2 O (m"!-| tf 

/.e. an alteration in the solid phase in equilibrium with 
See this series Vol. I., p. 66; also Vol. II., p. 120. 
Muller and Kauf mann, Zeitsch. physiJcaL Chem., 1903, 4^, *4$> 
For a careful study of the changes in the solubility of socli in** 
. Cftim. P7i^., 1907, [viii.], 10, 457 ; H. Hartley, B. M. <J'orji<^ f 

'AetTi. oc., 1908, 93, 825. * 

6 Van't Hoff, Lectures on Theoretical and Physical 
(Arnold), part i. pp. 37-9. 


ly-Cl, 12II 2 () (m.-,.t sr ('.) respectively. From the last point of 
discontinuity, namely, l< ,n li K . 50 (<>(>" ('.), onwards the salt is anhydrous 
and is deposited Irom solution in that condition. 1 

A study of t he curves in li K . 50 is partieularlv interesting from the 
pom ol. VH-W ol the Phase- Rule. AH represents the various states of 
rqmhbnum between ie,- and IVrrie chloride- solutions, a minimum 
temperature bemu readied al the cryohydric point B, which is - 55 C, 
At this point ice solution, mid the dodeeahvdrate of ferric chloride are 
m equilibrium. I he number of decrees of freedom is nil. in other words, 
the system is invariant, and if heat be subtracted the liquid phase, will 
soudy without chun-jr of temperature until the whole has become a 
solid mass ol ,<-,- and dodeeahydratc. Further abstraction of heat 
merely lowers the temperature of the system as a whole. 

! Anhydrous 

_ /%(?/,__ 

2 Fi>0/ ;i 4H,,0 " 


Kio, *4, Solubility tturvoH tf ferric chloride. 

If, starting at the jHint H, lu*at In* uddrcl to the system, ice will 
welt, ami tttorr of the tlodeeahytirate will dissolve in,ordauce with the 
equilibrium eurve IK'H, whieh is the solubility curve of this hydrate in 
water. At *I7"' C. tlu* tlinlreahydrate uu*lts, and if anhydrous ferric 
chloride be added to the system* the temperature at whieh the dodeca- 
hydrate remains in equilibrium \vith the solution is lowered until the 
cutectic fiuiiit C : * is reached at *7't' (\ At this point, the whole solidifies 
to a solid nti\tfitv of the dodecahydrate and h(*ptahydrate. 

The eur\ e has been followed in the* direction of the broken line Oil 
to ; H"' ('., the Mluti*n beinit sti|MTsalurate<l with respect to the dodeca- 
ItVilrate. Stiutlarty, the eur\e KI) has been continued haick wards until 
it interseeis ill lit II at IT> 1 s . This is a metastable triple' point or 
etitt"*tte t aud is eapable of realisation experimentally on account of the 
fact that the heptabydrate is not so readily formed. 

Cunes HI*" and Hi represent the solubilities of the tetruhydrate and 
the anhydrous salt tvspertixely. 

ti, Ttw Injlitt'in-f tij /V<'A,\///v. Sorby 2 eonchuU'd that a, rise of 
pressure liu-n-asrs the sotttbility of thtse suhstaiK'es whieh dissolve in a 

1 Uiii/.<<tiunfi, Xnr.v/t, iJtyitbtl. t'htm.t IWL*. It). 477. Srr tliw Hcrien, Vol. IX., 
i'iiri II. " * Ht.rby 1'roc. Ituy. 6'oc,, 1S03, 12, 538. 

;U4 OXY(!K\. 

liquid with contraction of volume. iwt that if deereases tin- solubilit y 
of such substances as dissolve in \\ater with an inenasi- in \oliuue. It 
was lirst indicated In Hraun ! that it' tin- rhaieje of \olunir on solution 
and the thermal effort an* known, the quantitative tilYet of alteration in 
pressure on tin* soluhilit y mav be ealettlated. "This is in hanttonv with 
thr Theorem of I*e Chatelirr. The following data * : .ire in harmony 
with this : 

(von Sf wkclher*. I 

ViilttlU*' * ; 

Hulutitiii in 

Wilier, i | Ai m ,,,. 4*111 ,\tifi*"t, 

Sodium rhlot'itU' , roittrnriiufi l*i- 1 
Ammonittm chiondt- rxpaiisiou *J7'* 
Alum . . , i'oiilrnrtiuii it'a 

l'*urtluT data for sodium rhlondr Iiuvr hi-ni pulfltshfd J whirh an- m 
t'iosc harmony with thosr i\rii alnt\i% hut rrfVr f ***.* t\ 

lVt'?^tirt< in I%}|t*^rii}ji?. ||- >- S f{, ffji, , I ;* 4 *i ,$ ^ r i 

d'miit.i >f XtiCt (Mr HM^vnmHM4i{utii*n :!il 14 ;*l ;*H :*fl 7'." ;*ti 4',! 

*L /V/i/A'/r*// Cnntlitiun if/ //if *SVliil /*lniAr, A% I*iu ii*4* as tH7U Stas 
ohscrvrd that the sottthtlity ot'siKt-r *'hli>rih- \urirs \\ith it 1 * tiu-thod of 
pivparatiou, 1 thr to! low in**: rrsults hnn^ tthtaiiM-d ; 


KhMvuh'ht. silvrr rhloridr , o-ui III ^ntw Iitrr at *'u t'. 

Powdort'd .. . fliiliilti ,, ,, 17 V, 

(Jranular , fHitit ,, l/ l\ 

(It'urly flit' stuaHrr thr parht'lrs til* tin- sat! thr irratrr tlir 
This is further support rd ly Iliilfll/ who tuv<-sttt.;atrd tltr sul 
calcium and barium sulphaifs it! *2"i ' (\ and fuiinii them lf> It*- ** tti tahl*- 
tu p. U5. 

Clt*arly\ tht'.rt'fon% brforr Ihr ahsolutr Mlufii)ity of a sail tit wtrr at 
any .stilted temperature* mid under, say. atiuospherie pri-sstire, nut he 
yivcn, the si/e of the partirles of thr M*ltd phase luust hr knowu. This 

has 11 U inttmat<* COIUiertiott With I In- piteiuiitteuoti of" sllprrsattU'attoa (sre 

p. H5), lor it is elc'itr that a saturated solution of harmm sulphate pre- 
pared in eontiu'i with particles of (liatueter o-l |i is suprrsattirated with 

- K, vim S(uckfllHr^, iViW 

; Sill, ./. Annr* f'/irwi, ,SVw,, |,l|, $8. '4t*;i2, 
lat'li, ithynthtl. T/irw,, I fill*, 75, i|f|, * 
1 iSf> % (Kitwt*, x, M7. SIT I)t'Ufk*'f. /Crsr-/i, r 

'' Hult'tt. Zrititeh, /i/il^ll'fll. /'Arw. t l!MM J7 :i 

,, IW)L\ :?4 (W7. 


spec! to particles of diameter 1-8/t, and, upon introduction of such 
irticles, the excess would hi* precipitated out. 



of PuruVU.H 

I'aleium sulphate- . J * ** -' 85 

Barium sulphate . , ^ ' ' ' 

Solubility at 25" ('.. 
(Mass pc.r Litre.) 

U-2!) mo-. 

SuiK*r**uturuUHi Solutions. When a solution of a solid in water, 
ready saturated at a iven temperature, is healed up with more of the 
ilid until the \\itolt* of the latter lias passed into solution, crystallisation 
1 precipitation uf the excess of solute does not always lake place upon 
ailing the system to the original tt*iuperat\ire. It is clear that the 
tlutitm must uo\v luilil a greater i|iiautity ofstihstaiicc than corresponds 
> the onluuiry soluhility uud is said to he xuitmulumfed. Such 
tutious eaii readdv hr prepare*! hy heating up sodium thiosulphatc, 
itliiiiii ae"ef}it\ or sodium stUphate \\ith \vat<*r, and allowing to eool 
ttltoii! agitation. 

Supersaturated sohitions, however, are always liahle to crystallise 
loiiiaueuusiy, parttc'ttlarly on exposure to air, L<">\vell l was apparently 
ie lir.s t I u sh\\ , hitut-i er, in t he ease of sodium sulphate, that crystallisa- 
on \vas lint indtierti l\ contact with air that had been previously 
issetl thruti*;h wntrr, \itlphtirieiietd, eaitstie alkalies, ^lass wool, or even 
tnttu'ti a series tit* empty Husks, Fifteen years later Violette a and 
erne/, ' uttlejientlently threw- ( k onsiderahh! li^ht nj>on t-hc subject by 
luwiny tb;it the sjttmt'iineotis rrystaUisation of supersaturated solutions 
" stidiuni sulphat*- in eniitact with air is due to the presence of minute 
\st.tls of the salt in suspension m the latter 4 which scrve as nuclei 
iiiiiibiHH! cvNstaHisatiun, lli'iitu- hy washing or iiltcrin^ the air 
i*\\i It hitil reiuiArii these suspended ntK'lei, and in <*onsec|uenci % reta.rdcd 
Astalltsattun, Lreiuj dr iititsttattciran '' showed, in the following year, 
tat not ouU etittltl uumite rrysttils tif the same substance serve as nuclei, 
if that erystaK t' isinmrjihiUs bodies yield precisely flu- same result ; 
itl it is now know!* thai this property is shared by many substance, 1 - 
Slit are fi*f stnetix isodtotjihotis \\ttli I he <liss<lveil salt-, provided thci 1 
oleetthtr volumes are elu.srty similar.* Ostwald showed that nuch 

t, Cltl, H;U, 

;i. NT *tl^ *in<t. t {j; ( 60, H:^7 ; iniMi, 63, H-i;t. 

;>ltt .H t |s|*'frt'Ii! til 'Hlf l^lnlt'l Itt tlit WJ)IiT% Ulld tl(*MI , 

iMMii ttilli llir \tiIi- nf .Miilphur jmHlumi during 

rA,-, /%.. I SlWi. ji\.|, 9, I7U. Srr iihu ,1. M. I h 
I, 4 W-i iMu*Ii, Lvfahuelt. vi|. ii., jmrt 2, j>. 78(1 

S.j>* I ti*liut't%iiiMi . l.liiii '.writ*.!*. ViiL I., till, 7^ **4 

316 OXYGEN. 

weighing only 10~ 10 to KT 8 grams were usually quite sufficient to induce 
crystallisation of supersaturated solutions. Furthermore, it appears 
from numerous researches x that mere mechanical friction is sufficient 
to induce crystallisation, such crystallisation taking place in the complete 
absence of crystalline nuclei. 

Supersaturated solutions of liquids in liquids have only been realised 
in a few cases, 2 but supersaturated solutions of gases in liquids are not 

Tap water saturated with air at 7 C. can be incubated at 18 C. for 
six days without appreciable loss of oxygen. At this higher temperature 
it is, of course, supersaturated, but so long as the containing vessel is not 
shaken, and chemical actions such as fermentation arc excluded, no 
appreciable loss of oxygen occurs. 3 

The addition of any powdered substance to such a solution, however, 
will break down the supersaturation since the gases in the pores of the 
powder act as nuclei. Supersaturation of this kind differs from that 
considered above, inasmuch as the nuclei immediately escape from the 
liquid, whereby their influence is severely limited. 

Combined Water or " Water of Crystallisation." When their 
concentrated aqueous solutions are cooled or allowed to evaporate 
many substances separate out with combined water or so-called water of 
crystallisation. This latter term is intended merely to imply that the 
actual crystalline form and not the crystalline nature of the deposit is 
dependent on the combined water present, because generally the 
anhydrous substances are also crystalline. 4 The simplest type of a 
substance with water of crystallisation is to be seen in the case of the 
crystalline compound chlorine hydrate, C1 2 . 8H 2 O, but the best known 
examples are amongst the salts, especially the " vitriols," CuS0 4 . 5H 2 ; 
ZnS0 4 . 7H 2 ; FeS0 4 . 7H 2 O, and the alums, of which potassium alum, 
K 2 S0 4 . A1 2 (S0 4 ) 3 . 24H 2 may be regarded as typical. Generally 
speaking, the presence of water of crystallisation is more common 
amongst the salts (simple and double) of the weaker acids. The number 
of molecules of water which thus combine with a molecule of a substance 
varies 5 with the substance and even with the conditions such as the 
temperature of crystallisation; e.g. above 32-4 C., sodium sulphate 
crystallises from aqueous solution in the anhydrous condition, whereas 
below this temperature the crystals have the composition Na 2 S0 4 . 10iI 2 0. 
Each salt containing water of crystallisation exerts a characteristic 
vapour pressure, 6 which increases with rise of temperature. Such 
hydrated compounds can therefore be deprived of their water, in part 
or entirely, by raising tjie temperature or by placing them in an atmo- 
sphere containing less water- vapour than corresponds with the vapour 

1 A. H. Miers and bis pupils, Trans. Chem. Soc., 1906, 89, 413, 1013 ; Proc. Roy. Soc., 
1907, [A], 79, 322 ; B. M. Jones, Trans. Chem. Soc., 1909, 95, 1672 ; Young, J. Amer. 
Chem. Soc., 1911, 33, 148 ; Young and Cross, ibid., 1911, 33, 1375. 

2 H. S. Davis, J. Amer. Chem. Soc., 1916, 38, 1166. 

3 Richards, J. Agric. Sci., 1917, 8, Part 3, p. 331. 

* Nordenskiold, Ber., 1874, 7, 475; Surawicz, ibid., 1894, 27, 1306. 

5 Prom an examination of a large number of salts, Rosenstiehl (Compt. rend., 1911, 
152, 598; Bull. Soc. chim., 1911, 9, 281) arrives at the conclusion that after the first 
molecule of water of crystallisation further molecules of water are added, generally in 
groups of three, and less frequently in groups of two, and regards this result as confirmative 
of the existence of the molecules (H 2 0) 8 , and (H 2 0)o in water ; see also p. 296. 

b Wiedemann, J. prakt. Chem., 1874, 9, 338 ; Debray, Compt. rend., 1874, 79, 890 ; 
Koozebooni, Zeitsch. pliysikal. Chem., 1889, 4, 31 ; 1892, 10, 477. 


pressure of the hydrate*. By enclosing a hydrotod salt, preferably mixed 
with a little of the dehydrated salt, in a desiccator over a drying agent, 
not only does dehydration take place, but, it may oeenr in stages revealing 
the existence of intermediate hydrates; l thus blue vitriol undergoes 
dehydration by the stages, CuS() 4 . 51U.) ; CnSO 4 . 31I 2 O; CuSO 4 .II 0; 
CuSO.!, eaeh stage being marked by a "reduction in th"e vapour pressure 
at any one tempera! ure. 

If the vapour pressure of the water of crystallisation in a substance 
exceeds the pressure of the atmospheric moisture, spontaneous de- 
hydration may occur so that the substance becomes coated with a 
powdery layer of a less hydra ted form. Glauber's salt, Na 2 SO. t . 1<)II 2 O, 
and % " washing soda," Na,('O a , 10ILO, are typical of this efass, to which 
the term " r///wmr/// " is applied. On the other hand, a hygroscopic. 
substance is one which absorbs moisture from the atmosphere; if the 
aqueous vapour tension of the atmosphere is much greater than that of 
the damp substance, the absorption may continue until finally a solution 
is obtained, the process continuing until the vapour pressure of the solu- 
tion attains that of the vapour in the atmosphere. Potassium carbonate, 
sodium nitrate, calcium chloride, and y,inc chloride are common examples 
of such </**//</ w.v(V///. substances. 

Both sunlight and ultra-violet light accelerate the escape* of water of 
crystallisation from salts in certain cases. 2 

The transition temperature at which a hyd rated salt liberates all 
or part of its water and passes into another less hydratcd form is almost 
as definite as an ordinary melting-point, and can therefore be used as a 
standard for the calibration of thermometers; thus the transition 
temperature for Glauber's salt, NiuSO 4 . lOlUC), occurs at JW'#88 n C., 
whilst that of sodium bromide, NaHr . till./), is at 50-074 (V* 

Krom the relative diUienlty with which the last molecule of water 
of crystallisation is expelled from certain salts, e.g. CuSO 4 .II.jO and 
MgS() 4 . H a O, the dehydration of these salts requiring a temperature 
above 200"'" C M whereas the other water molecules in the ordinary 
pentahydrute and beptnhydratc respectively are eliminated at a tempera- 
ture' a little above 100' (' it has been suggested that this last molecule 
is in some way more intimately associated than the others with the salt 
molecule and til** name fv//fr of constitution has been applied to it.* 
By some, it is considered that this molecule* may be especially associated 
with the ac-id radicle indicating, for example, in the above cases of 
rnonohydniteo! sulphates, that the salts are derived, not from sulphuric; 
acid ILSOj, but from an ortho-sulphuric acid, II 4 SO g . On the other 
hand, it is equally possible that the molecule of water of constitution 
may he associated with the basic radicle, in which ease the* monohydrated 
salt would in* regarded as a basic suit of the type Cu(()lI)S0 4 H, 6 which 
would thus be copper bcinisulphatc hcmihydrol. There hardly appear 
to be suiHcient grounds, however, for regarding water of constitution as 
distinct from ordinary water of crystallisation; in both eases it is 
probable that the molecules of water arc attached to the salt molecules 

1 Bilker jutti Atilnm, 7V#. t'hvm, S'0c., Mil, 99, (S07 ; dimming, ibid. t 1010, 97, 593. 
3 IUwtl. f'Arw. Zrnlr., IttilJ, ii., 638. 

3 KidinrtlH mti! VVVIIn^ %nt*eh> phyniM. Mfm.* 103, 43, 4(15 ; HH)0, 56, 348. 

4 (.jraimm^ /twlr iHUM, 20 141*. 

& Krlinuinn'^r, //r., I8<H> 2 *4iK (-ompare Mummery, /. 8or,. flhem. Irul., 1913, 
32, H89. 

318 OXYGEN. 

by additional valencies at the oxygen atoms, 1 and, as explained above, 
the removal of each successive molecule of water of crystallisation will 
be a matter of increasing difficulty. 

Interesting ideas as to the nature of water of crystallisation have 
been promulgated by A. Werner, 2 who regards six molecules of water of 
crystallisation as the normal quantity, and suggests that the water- 
is combined with the basic radicle forming a complex radicle, e.g. 
[Ca(OH 2 ) 6 ]Cl 2 and [Co(OH 2 ) 6 ]Cl 2 . Certainly a group of six molecules 
of water of crystallisation recurs frequently in hydrated salts. 

In hydrated salts containing seven molecules of water, the sulphates 
supplying numerous examples, the seventh molecule is supposed to be 
attached to the acid radicle. This view receives confirmation in the 
frequency with which such heptahydrated sulphates form derived double 
sulphates containing only 6H 2 O, the additional salt being a sulphate 
which, when alone, crystallises in the anhydrous condition. Thus 
ferrous sulphate, FeSO 4 .7H 2 0, and zinc sulphate, ZnSO 4 .7H 2 O, yield 
such derivatives as (NH 4 ) 2 S0 4 . FeS0 4 . 6H 2 O, and K 2 S0 4 . ZnS0 4 . 6H 2 
respectively. With salts containing more than seven molecules of 
water, the number is frequently twelve, and this is attributed to the water 
being combined in dihydrol molecules (see p. 298) ; and in accordance 
with this view potassium alum would be written [A1(H 4 O 2 ) 6 ](S0 4 ) 2 K. 

The application of Bragg's X-ray spectrum analysis to hydrated 
crystals is throwing further light upon the manner of attachment of 
combined water, 3 and, in many cases, it would appear that no distinction 
can be made between water of crystallisation and water of constitution. 

For a study of the optical behaviour of combined water, the reader 
is referred to the subjoined references. 4 

There is a possibility of small quantities of water being present in salts 
in another form than that of water of crystallisation. T. W. Richards, 5 
in his attempts to prepare salts in an extremely pure condition for 
the determination of atomic weights, has observed indications of the 
presence of water in a state of solid solution in crystals. 

Water Analysis. 6 On account of the considerable effect of certain 
impurities on the value of water for drinking and other purposes, 
the detection and estimation of these impurities is of the greatest 

The water is first examined visually for colour or turbidity, and by 
taste. Thus, for example, a green colour may be due to algae ; brown, to 
peat or possibly to ferruginous material. Iron salts impart a distinct and 
bitter flavour to water, 1 part of iron per million of water being per- 
ceptible to the average person. 7 In the case of common salt, 75 grains 
per gallon or approximately 110 parts per 100,000 are recognisable in 
this manner. Hard waters are supposed to have a more refreshing or 

1 See Rhodes (Chem. News, 1921, 122, 85, 97), who suggests a cyclic or shell con- 
figuration for the water molecules. 

2 Werner, New Ideas on Inorganic Chemistry, p. 132 ; translated by Hedley (Longmans, 

3 See Vegard and Schjelderup, Ann. Physik, 1917, 54, 146 ; Schaefer and Schubert, 
ibid., 1916, 50, 339 ; 1918, 55, 397 ; Niggli, Physical. Zeitech., 1918, 19, 225. 

4 Brieger, Ann. Physik, 1918, 57, 287. 

5 Richards, J. Amer. Chem. Soc., 1911, 33, 888. 

6 As many excellent text-books deal very fully with water analysis, it is only necessary 
to deal^vith the subject in brief detail in this work. 

7 See Rideal, Water Supplies (Crosby Lockwood, 1914). 


Intnl.!,. .,st, than soft > Less than 116 mg. of carbon dioxide per litre 
''''.'": <l Kv tin. lastc- whilst more than 246 mg. are distinctly 
, . . ,. C ' ''"iCTt-nt persons show varying suscepti- 

n ll u 1 : ,r ( lsmtc,-m,<l 1 ul. quantities. Carbon dioxide cL be detected 
hv th,- tnxt,. a Imvrr <-<mcvtrations in hard waters than in distilled 
vvatrr. In t hr last namrd, suspicion is aroused by 126 mg. per litre but 
H-loxv '-(.I. m -. ol rarlmu dioxide, the carbonic' acid is not distinctly 
fastcii as such. J 

Any .vi/. v /*'w/<v/ ,vo/M, the presence of which should be regarded with 
suspicion, is removed by filtration. The quantity of dissolved solid is 
determined by evaporating a measured volume to dryness. From a 
practical view-point, the portion of the dissolved solids which affects the 
behaviour ot a water towards lathering when treated with soap, is of 
especial interest, these constituents producing the so-called "hardness" 
ot a water, 

Qualitative Analysis. Useful information as to the suitability of 
\\ater for \sirious purposes may be rapidly obtained by means of a 
lew qualitative tests. The presence of chlorides is revealed by addition 
o|' a few drops of concentrated silver nitrate solution acidified with 
nitric acid, when a white ha/e or turbidity results. 

Linn- i\es a white turbidity on addition of saturated ammonium 
oxalate solution, and ,v /*/////<//<* with barium chloride acidified with 
hydrochloric wid. A useful reagent for nitrites is metaphenylene 
diiunine, 5 grains of which are dissolved in water, acidified with dilute 
sulphuric acid, and made up to one litre. It may be necessary to pre- 
vionsly decolorise the solution with charcoal. If nitrites are present 
in the water to IK* tested, on addition of the diamine, a yellow colour 
is produced, either immediately or upon standing. Starch-iodide 
solution jteiditied with dilute sulphuric acid may also be used, the 
characteristic blue colour of the starch-iodine complex indicating nitrites, 
hut this test, is not altogether satisfactory. 

SHnttt's are readily detected by adding a few drops 0-1 per cent. 
hrticinc solution to the sample of water, and then pouring concentrated 
sulphuric acid tot he bottom of the tube in as gentle a manner as possible; 
u pink and yellow /.one forms at the junction of the acid and water if 
nitrates are present. 

NYssler's solution (see p. .TJ2, note (>) gives a yellowish-brown colora- 
tion in the presence of ttniHionla. Traces of lead and copper give a dark 
colour with ammonium sulphide, acids being unable to destroy it. 
Discoloration due to copper may be removed by addition of potassium 
cyanide. The recognition of traces of lead by the above process, how- 
ever, is sometimes impossible in the ease of peaty waters, the brown 
colour of which entirely masks the reaction. In. such cases a convenient 
ittrthod consists in adding permanganate to the water until it is dis- 
tinctly jtink. The water is then rendered alkaline with ammonia and 
kept fur about forty eight hours, when a precipitate will have formed, 

eoiituming t he whole of the lead. The supernatant liquid will be colour- 
It SH unless too much permanganate has been added. The precipitate 
is rolU'i'trd on it filter, dissolved in hydrochloric acid, and, after dilution, 
tested with alkali sulphide in the usual manner. The composition of 
the pri etpitiitr has not been studied, but it appears probable that an 

* Kmulmann, Chem. Z?nlr. t 1914, i., 1615. 



oxide of lead is formed which is either carried down mechanically with 
the oxide of manganese or possibly as a compound. 1 Lead is also 
detected by addition of a few crystals of potassium bichromate, an 
immediate yellow turbidity occurring in the presence of 0-1 grain of 
lead per gallon (0-14 parts per 100,000). On standing for half an hour 
a turbidity is detectable with 0-02 grain of lead. 

The time-consuming operation of evaporating water in order to 
increase the concentration of lead which is necessary when the quantity 
is less than 0-1 mg. per litre, can be avoided by the procedure intro- 
duced by G. Frerichs. 2 

When water is filtered through pure cotton-wool, any lead is com- 
pletely retained by the latter. By filtering a litre or more of the water 
through a plug of cotton-wool, and subsequently extracting the lead 
from the plug by washing it with a little hot dilute acetic acid, it is 
possible without loss to obtain a solution in which the proportion of 
lead is many times as great as in the original water. The test for lead, 
. whether qualitative or quantitative, can then be applied in the usual 

The amount of lead in drinking water frequently diminishes on 
standing, probably in consequence of precipitation as lead carbonate. 3 

Iron gives a blue colour with a few drops of potassium ferro or ferri 
cyanide solution acidified preferably with dilute sulphuric acid. Colori- 
metric tests for iron are often uncertain in the presence of copper, etc., 
but if suitable precautions are taken this difficulty can be overcome. 4 

If the solution is rendered alkaline with ammonia, boiled and any 
precipitate removed by filtration, the presence of zinc may be demon- 
strated by addition of potassium ferrocyanide, when the liquid becomes 

These reactions are summarised in the following table : 





Delicacy of Teat. 
Parts detectable 
per 100,000. 

Silver nitrate . 

f White haze 
\ White turbidity 



Ammonium oxalate . 

/ White turbidity 
\ White ppte. 



Barium chloride 
Metaphenylene diamine 

White turbidity 
Yellow colour 


Brucine . . . 

Pink colour 



Nessler's solution 

Yellow - brown 



Ammonium sulphide 

Dark colour stable 

Lead or copper 

towards acid 

Crystal of potassium bi- 
Potassium ferro or ferri 

Yellow turbidity 


0-14 (immediately) 
0-03 (on standing) 

cyanide acidified . 

Blue colour 


1 Tickle, Analyst, 1921, 46, 240. 

3 Scheringa, PMrm. Weekblad, 1919, 56, 8. 

4 See, for details, Gregory, Trans. Chem. oc./1908, 93, 93. 

Frerichs, Apoth. Zeit., 1902, 884. 


If the water is first concentrated to one-fiftieth of its bulk, tests may 
be carried put for magnesia and phosphates. The former is precipitated 
as magnesium ammonium phosphate on standing for some twenty -four 
hours after addition of sodium phosphate solution to the water rendered 
alkaline with ammonium hydroxide in the presence of chloride. It is 
assumed that any lime has previously been removed with ammonium 
oxalate. Phosphates are precipitated as yellow phosphomolybdate on 
adding excess of ammonium molybdatc solution to the water acidified 
with nitric acid, and warming. 

Interpretation of the Results. The correct interpretation ' of 
water analyses is largely a matter of experience, and can only be arrived 
at after a thorough knowledge of local conditions has been attained. 
The presence of chlorides is usually to be regarded with suspicion as 
indicating possible contamination with sewage. But perfectly good 
potable waters may contain chlorides due to proximity to the sea or 
salt deposits. Thus the water in the lower reaches of the Severn in- 
variably contains sodium chloride resulting from the triassic salt springs 
of the neighbourhood round Droitwich. Again, chlorides may result 
from dee}) wells and mineral springs, or from waste effluents from 
factories. Ammonia and nitrites suggest recent contamination with 
animal refuse. They are gradually oxidised to nitrates. Whilst, 
therefore, nitrated water may be quite safe, owing to oxidation of all 
dangerous organisms, it should be regarded with suspicion until con- 
firmatory evidence is available. 

Lead in any appreciable quantity is a very dangerous constituent 
in potable waters, for the poisonous action of lead compounds is cumu- 
lative, so that repeated small doses may prove more serious even than 
one large dose. Chronic lead poisoning may result merely from drinking 
such water as has been conveyed in ordinary lead pipes. Waters con- 
taining (H)2 grain per gallon are dangerous. 

Iron is apt to be troublesome when present in quantities of 1 part 
per 100,000' and upwards. The metal oxidises, and hydrated oxide 
(rust) precipitates out on standing ; this may block the pipes conveying 
the water. This oxidation is assisted by certain lowly organisms 
known as iron bacteria. 1 Iron salts are not toxic, but have a certain 
medieinnl value and impart a bitter taste to the water. Copper salts 
are frequently employed to remove algse, 0-3 parts per 100,000 being 
about the minimum effective concentration of copper sulphate for this 
purpose. At such dilutions the salt is not prejudicial to the human 

organism. , . 1V 

The inhibiting action of copper salts upon the growth ot bacilli 
can be detected even at such dilutions as one part of copper in ten 
million of water. With 0-5 parts of copper per 100,000 a marked effect 
is observed ; zinc has a small effect, but lead and iron appear to be 
without effect at tlxese concentrations. 2 . 

Quantitative Analysis. Chlorides present in a water are estimated 
by titrution with a dilute standard solution of silver nitrate. 

Mumford (Proc. Chem. 8oc., 1913, 103, 645) describes an organism through the 

Med. Service, 1921. , 

tr/vr TJTT * T 

Nitrates and nitrites in water arr fmjumtty estnnatrd toirrthrr, <\g. 
by reduetion to ammonia,* whieh ean hr drtrrmmrd in the manner 

desei'ihed hrloW ; altrWathe pnuvss* s a!V hasrd Mil tin- ivdlletioll of 

these salts ti nitrie o\ide \\lwh may I"" m usiuvd \ tlnm-t neatly, a ami 
on reduetion of the nitrate to nitritr hn tin- t*t;d nitrite may be 
estimated eolorinutrirally iy thr addition <f stdphaiuhe ami and 
a-naphthylamine.* I-W the estimation !' nit nt* s ami* s srparately, 
orpmie eolorimetrie methods are usually ap|lini,* 

Thr nitritrs and nitrat*s m natural uatn- ^.nir;il!\ t^vr tlnir 
r\isfriii*i' to t hr u\|tlatu*u **t tiiaiHnitm nr aiuiunnuun salts \\hirlj havr 
thrinsrlu'S brin prtnlurnt li\ tlir ill riHJptNtMn *! liili'o^rtiOHs m'liauif 

inattrr. Tlir** IVrr " aiimttJtta is i \prll* tl l*\ liisJillm- with flu* atltlition 
of potassium hvtimviilr vnlulitiu \\lulst lh intrt^runus r^auit rum- 
pounds a iv titrtntpt>.-! illi rinitatnn t*I" innu*ma |iishnjutshrd as 
ullnnninuii! tintumnni) !>> lutiliu \\ith n alkalinr solution nt putussium 
jUTitmnpumtr ; & iit hnth tMsrs tin' amount i*t ammonia nhtauird in 
thr (iistiHatr is lurasurnl ri*!iini!irlni'riliy willi NrsslrrX Mtttiftott,* 1 
As thr *Hiiiiiiit*ii Mtiirrr ol' nitro^ruous t.r|.jant* niattur rv atumal rrt'usi* 
in a stutr of iirrowpo-sition, thr JMTM-JM*.- of thrsv lutro^-u t'onipounds 
is suggrstl\r ttf posstl*lr ront animation m a atr i\ th- pi nod wlurh has 
Hapst'd sincr t'ontaminahou hruii^ n llrrtnl ritit^Iiiv ui thr ivlation 
lu-twrrn tli* am*tmts of uiiratrs and lutnti-s, !> ammoma, ami 
adhutuinuid ammmuia. Thr total quatdity f **Mh'.iiM- or,jamr mattrr, 
nut nrtvssunly nitro,'rnius, may lr d t rinnu-d hv d>vrrt " rosutmstum ** 
of thr n'sidur*oi*tnnrd hy rvaporation ; if IN *d^*i mt-astirrd t*y ohs-r\in}i 
thtM*xtrnt <>f rrdwtion -sufiVrrd by a known \ohunr *1 stiindard potus^ 
siuui prrntimgittuttt' sulutioii uhnt K-pt ut >i *l Jinitr ti-iuprrattirr 
(often *J<>'7 ' i'.) tor srvt-nd hi*urs with a tu-isurrd \*huu- f ili< ! uatrr 
in thr pivst'Wv of.Mllphiii'ir arid llMrrhhamiur-\ pniressj ; 7 all rfiipirsrni 
fnc'tor is nm'ssury for tit*' f alruhitt4 if th- prrrrntaj^r ot ornitnir 
matter. 11 

titilphtth'fit silirtt t irun t MilrhtHt, inttgwsium, mill tlir- ullaili iiiiiiilx 
arc also soiwUfws rstintatrd, as art* jdso thr ths*ttlial ^n,vfv, rhirlly 
oxygen, carbon dioxidr, ami ttitro^-n, 

* Nonr i>f the elifiitiriil trsts. htwrvrr, with thr Arrjttioii of \ueli 
us reveal the pri-senee of putsotitHtH stihstann-s, r.||, Irtid, or rw|i|irr 
compounds, run he regarded as liititt r\-lrn*'i' *l the suitability or 
othtTwise of it water fur ilriiikiiit* j-urj*Ms's, and lor a ili-tmttr dreismit 
on this point a haeteriolo^ieal e\ninination is itrerssary,^ 

1 ThuriHs TMIM, f'Arwi. N*r., JH7II, 6, **4I, 

s Hw Hchtilxt* itiitl TiHtmtnt, ll'f a , |H7;i, 6, lll , 

7(K 9, --I, - s ilnrfMii. T>*. i' 


\ . 

, , , . . 

ft \Viitiklyii, (liiifiitMiti, Hint Smith,' Tfn., f 'Arm. .v^., Iwi^ yr, Mil. >r- *tl^ \VmU**r, 
Zfittfh. ttnyett\ rirwi,, HH, 37, 44i>* 

* N<>*Iir*i wltifttti ia i*nuvtM* 5 iilly jr"iwfr*l !<> li*.^h i*>^ *'* ** iitip* * k i JMI<IAUHI 

Miiliii*' in L*/0 t'.t*. WiittT iiml iuittifitf IM ii i**ilf, nAltirnfrnI r^--4n!i--'i* *f fi-i-*-n*-. til^ri^r* tinlil 

II faint |rtTlftuii*fit fttWfJiiifftr I.M ulitiiillrii, A*lil 1^1 |?f.iis *<f |io!.*5it|fn hylr^i*ti' l I r * 

Nikit in (J* /^w.w. r/*^ '***. A**'.. Mi;i, 45, M1U7 ) lr lit** iiiir.tlrr^nfr a f rlil^itilr* ; 
and Kityi* (rhtm. AV.s 11*14* no t III) !*r iitij! |*r^-*^ ii^ifin |**<*I^MMU frrri*\v*w*ti' 
with thin nu*tht*i. * T$*ly, 7V*i^. rA-rm., Sw., tH7i, 35, fW, 

f Hi*<* Kritiiklmi*!, ./. .SW, f'Arwt, 7m/., lull, 311, 3lP I'"** 1 liwl^y / il"lrffi's t 
KtrkfmtuVU (lirttih MHWWUM, ^itlr{., I!>I7, 


For the estimation of dissolved gases in water the former are gener- 
ally first removed by boiling the water or by generating carbon dioxide 
ii\ it ; in the latter ease the bubbles of this gas carry out any dissolved 
gas, from which the carbon dioxide is easily removed subsequently. 1 
Carbon dioxide itself may be conveniently estimated by titrating a 
measured volume of the water with sodium carbonate solution until 
phenolpht halein becomes coloured, the method depending on the 
neutrality of sodium hydrogen carbonate towards phenolphthalein. 2 

1 H(M Winklor, Zv.itach. an yew. Ohem., 1915, 28, 36G ; also this Vol., p. 36. 

*' Noll, Kntuch. aitfjew. C/, 1912, 25, 098; Auerbacli, ibid., 1912, 25, 1722. 

C'ltAP'l i,H XII, 


History. H\droru penMdr *r, r- i! is stint* tint* % i. mud, tt\dmtit 
dioxide, was first obtained by Thenard in IMS in an t-xniitiiiatittn ttf thr 
dilute aqueous solutions turmrd hy the aetton ut' variuttx mineral fteids 
ou barium pero\id\ l Id the early days ot' its ut\ -sh^at in considerable 

confusion was caused by tip* similarity betw-rn h\ dm^-n prroMtle mid 
o/.onc in aqueous solution. '** 

Occurrence* H\droen jn n\nl* oMtir.ji \M\ umnttr tjuantittrs 
in rain wntrf aitd itiMHtu/ 1 but it-* MH'W lh r i. un' it,nn, b int van 
ously at tributrd to th a**tjin tl ltt *.nii t'\ > *u ,'t unsphi rirnmisturt' 
and to tht* int<'ractin *i" i-.trbun Ii^ui utb u.itir \ ip*ur niidtn 1 thr 
iitllttt'iit't* <f sutili^lit fnniuii*' r*n4dd*Iud .md | UMI bttnt* 1 ;i*id, thr 
lattrr sulistnjirr thut dt c s tiht|m' iii" nilli {uttdut'tiun l rib*i diu\idr 
and hydrogtii prru\nl< ! 

.ill..( <>, Hi HO ^1! ,( (), 

:fU o t V.H'<> ;H1 u, 

Tht.* total rhanj;** in this CM si , tip i lurr, 111111*1111!** ft* *i d * Miujtosttion 
of rarbottit* at'id into i'onuaif]> hvl' .iiitf !t\dr**^"it |iit\id*-, hut this 
explanation in not M> proi^abh ,t . th ;trh r on" and th t'ofuhition of 
hydro^m prroxidr tVoni an ,nju nus ^oiiitinit ut w^ u in lntdi! suu!i*!it 
is a dt'liiiitr cxprrintcni'it l^rt,* 

Alihtntgh tin* point h.r* b i u Ilif ^iitiji-rt if tmii ailr rabj* t'*ilru\ i rs\ 
hydro||i'ii pc*ro\it|t- ivHv tpp.,is to b piiMtit in th pur* oj sotur 
plants, but unless t r;r i* taKiu *'' it tm ii'ine *\d itiou 
(at.alysts (,rWi/At*A') *i i\idi ue .i'n!* tni'h ui\ at -u In pr<fMUt> 
art* likely to lie tnistakiu lur b\ilru;*tn ptinvtri fl Tfi*- Murer ot the 
hydrogen peroxide ut plant is ptobabh a n melton btt^nti iMrltou 
dioxide and water of tin \iiiu eottrs* as lti*il **tUf*! std ;iin$u t'ur the 
ehetttieid change bit mint the*** %iib*,ttiin"i \ in *uid)t>M, 

Formation. I, /'V**/// /*</>** *</*.*, Ottlp \arnur. m> thuds b\ ttlueh 
hydrogen peroxide has been ailili^i.ilh ptuduetd th **Id st t ? * tint 

8 Ht*h^ni% llm t IH7I. 7* Iti!i;i Js', ,\ in, !*,', ,,ri H;I, JI;N , IHM i |, ttiCl 

26 .1011 ; 181N, 27. 12X1, I* I,, /; > , IHI|, jjy, r 

IHMtl, 49, IOH) l4i*vt'I Inifii^ni }j*tM\tdr HH ffiiip| tlntii*^ ,]' i { *ft f rt 

Hiiy f/Vw, r/irw, ,%'<-, tHHti, jf, ;*'**'!' r\4tnm* I ti it i I* i4 * tup u^Sr^I m 411 

89, 4M, 

> ^a, :|J, ;*HH i HA* It, (<mjjf > *! iv.i.'t. |6 III*. 
t ||*i, IfM*;*, |i|, til :i*tfl . jlw*;^ 46. :f, 1*1 i, I7"iti, 

M, 37, :w, L'l-iL 1 , :i7K*\ :IIIHS, 


involving the interaction of barium peroxide and a mineral acid. As 
already mentioned (p. 54), peroxides (superoxides ) in general exhibit 
this reaction. 

II. By Electrolysis. ~ln 1882 it was observed by M. Traube that 
during the electrolysis of dilute sulphuric acid, hydrogen peroxide may 
be found both at the anode and the cathode. 1 Its formation at the 
anode is to be ascribed to the decomposition of persulphuric acid, 
JL 2 S 2 O 8 , which is produced in some quantity. At the cathode the 
presence 1 of the hydrogen peroxide is due to the reduction of dissolved 
oxygen, and it has been shown more recently 2 that in solution in dilute 
sulphuric acid under a pressure of 100 atmospheres oxygen can be so 
successfully reduced to hydrogen peroxide as to give a yield of more 
than tSO per cent, of that calculated from the current used, and solutions 
of "2-3 per cent, concentration can be readily obtained. That the process 
is merely one of chemical reduction is confirmed by the fact that the 
dissolved oxygen can be reduced to hydrogen peroxide also by treatment 
with hydrogen in the presence of the metal palladium. 3 

Sn the electrolysis of solutions of alkali hydroxides under suitable 
conditions, hydrogen peroxide is produced at the anode by the com- 
bination of the discharged hydroxyl ions. 

In contradistinction to ozone, hydrogen peroxide is not produced 
during the electrolysis of solutions of fluorides. 4 

III. In- Processes of Autoxidation, and Slow Combustion. As has been 
mentioned earlier (p. 55), the slow atmospheric oxidation of substances 
at the ordinary temperature (autoxidation) frequently gives rise to 
peroxidie substances of powerful oxidising properties ; these substances 
arc unstable and in their decomposition give rise to ozone, and, if water 
is present, also to hydrogen peroxide. The slow oxidation of phosphorus 
in the presence^ of water is stated to be accompanied by the formation 
of a little hydrogen peroxide. 5 In such cases the mechanism of the 
change probably involves the formation of an additive compound of 
the unstable primary peroxide compound with water, which subsequently 
decomposes with formation of hydrogen peroxide. 

The corrosion of metals is another case of slow oxidation, and in the 
presence of water appreciable quantities of hydrogen peroxide may be 
produced ; the amalgams of the metals frequently give better results 
than t he metals themselves. If the hydrogen peroxide is removed from 
the solution as rapidly as it is produced (the addition of barium hydroxide, 
for example, will remove the hydrogen peroxide as a precipitate of barium 
peroxide), the yield of hydrogen peroxide may become almost quantita- 
tive, and in the case of aiiuc the final result of the reaction may be 

' ( " 

1 TnuUM\ /&/'., 18Hi5 t 15, 2434: ; 1889, 22, 15.18 ; -.*- , * - ~- 

183 1887, 31, 1M:! ;' Richurc and Lonnca, ZciterA. phytikal. Cheni., 1896, 20, ,147 ; nie- 
nm.m, ^A^. 6'Acw., 1903, 34, 1- 9 ^chor and i>ness, 5er. f 1913, 46, 698. 

Hm<-Ml & Cu., tiwiw 1'tttrnt, 1914, 03351), 03360. 

* l',iidi, /!*/*. k'Jfc/roc/rm., 1897, 3, 474; 8kinrow, ^itoc/*. /V. O'Ae/^, 1902, 33, 
L>5- lYidwuix. Tm/w. Farad AW.., 1900, 2, 34. 


6'Aew. ^oc., 1906, 89. 481, 

326 OXYGEN. 

Other metals, e.g. magnesium, cadmium, and lead, can be made to 
yield similar results, 1 as also does palladium hydride 2 when allowed to 
oxidise in the presence of water containing a little sulphuric acid. It 
is possible, however, that, at least in the case of lead, the hydrogen 
peroxide owes its formation to the reduction of dissolved oxygen by 
nascent hydrogen produced during the corrosion. 3 

Many organic substances, such as alcohols, ethers, acetone, and 
especially unsaturated compounds like turpentine, are capable of slow 
oxidation, the action being favoured by exposure to sunlight ; in the 
presence of moisture, hydrogen peroxide is frequently to be found 
amongst the products of the chemical change. 4 The disinfectant power 
of the " Sanitas " preparations, the basis of which is obtained by the 
atmospheric oxidation of wet turpentine oil, is largely due to hydrogen 

Hydrogen and oxygen, and even steam and oxygen, 5 can be made to 
combine at low temperatures under the influence of the silent electric 
discharge, and the process may be regarded as a slow oxidation of 
hydrogen comparable with the preceding. Also the silent electric 
discharge generally favours the production of unstable substances. 
For these two reasons, therefore, the formation of hydrogen peroxide 
might be expected, and the expectation is justified by experiment. By 
working with a well-cooled gaseous mixture, it is possible to obtain 
a considerable yield of hydrogen peroxide, 6 whilst at 80 C. the yield 
is almost quantitative and the product pure. 7 

IV. From Water by Radioactive Substances. Although radium salts 
will decompose hydrogen peroxide, they likewise form this substance 
when their rays act upon water. 8 Kernbaum 9 concluded that the 
/3 rays are the most effective agents, and suggested that the reaction 
takes places as follows : 

2H 2 O=H 2 O 2 +H 2 . 

V. From Hydrogen and Oxygen or from Water at High Temperatures. 
Hydrogen peroxide occurs frequently amongst the products of gaseous 
combustion in the presence of moisture, 10 and of the combination of 
hydrogen and oxygen by flame or explosion. 11 On account of the 
instability of hydrogen peroxide, it is advisable to cool the products as 
rapidly as possible, for example, by allowing the flame to impinge on 
the surface of cold water or ice, 12 when the condensed liquid will exhibit 
the reactions of hydrogen peroxide. 

1 Dunstan, Trans. Chem. Soc., 1911, 100, 1835. 

2 Leeds, Pharm. J., 1881, [3], n, 1068. 

3 Lambert and Cullis, ibid., 1915, 107, 217. 

4 Thenard, Compt. rend., 1872, 75, 458 ; Houzeau, ibid., 1872, 75, 349 ; Schaer, Ber. t 
1873, 6, 406 ; Kingzett, Trans. Chem. Soc., 1874, 12, 511 ; 1875, 13, 210 ; Dunstan and 
Dymond, ibid., 1890, 61, 237 ; Richardson and Fortey, ibid., 1896, 69, 1352. 

5 Fischer and Ringe, Ber., 1908, 41, 945. 

Fischer and Wolf, ibid., 1911, 44, 2956 ; Beason, Compt. rend., 1911, i^ 877 

7 Wolf, Zeitsch. Elektrochem., 1914, 20, 204. 

8 Kailan, Monatsh., 1911, 32, 1019. 

9 Kernbaum, Compt. rend., 1909, 149, 116, 273. See also this Vol., p. 227. 

10 Leeds, Chem. tfeww,.1884, 49, 237 ; Traube, Ber., 1885, 18, 1890 ; Finckh, Zeitsch. 
awry. Chem., 1905, 45, 118. 

11 Dixon, Trans. Chem. Soc., 1880, 49, 94; Charitachkoff, J. Rues. Phyts. Chem. tioc., 
1910, 42, 904. 

12 Engler, Ber., 1900, 33, 1109. JSee also Nernst, Zeitsch. EleUrochem., 1905, u, 710. 


Whether the production of hydrogen peroxide in the last case is a 
direct process or is due to the further interaction of water vapour and 
oxygen at high temperature is rather uncertain. Certainly at very 
high temperatures oxygen and water- vapour will combine, with formation 
ol some hydrogen peroxide which can be detected after rapid cooling. 1 
Indeed, the combination of water-vapour and oxygen may be effected 
even at 130 C. under the influence of a silent electric discharge, and at 
very high temperatures even water- vapour alone, without the addition 
of an excess of oxygen, will undergo slight conversion into hydrogen 
peroxide.- It is therefore possible that the slight formation of hydrogen 
peroxide in the combustion of hydrogen, of moist carbon monoxide, or 
cyanogen, may be due to a purely thermal influence on the water, or 
water and oxygen, present. The observation that traces of hydrogen 
peroxide are produced when an arc discharge is formed, using very 
dilute sulphuric acid as a cathode, 3 may have a similar explanation. 


I. From, Metallic Peroxides. For the preparation of hydrogen 
peroxide in quantity, use is generally made of the metallic peroxides. 
Sodium peroxide reacts with dilute mineral acids producing hydrogen 
peroxide, but the considerable solubility of sodium salts renders it 
dittieult to obtain a, pure solution of the substance except by distillation. 4 
Potassium hydrogen turtrate and potassium fluosilicate are sparingly 
soluble substances, so that dilute aqueous solutions of hydrogen peroxide 
may be prepared by treating potassium peroxide with dilute solutions 
of tartaric acid or hydrofluosiiicic acid. 4 Barium peroxide, however, 
is the substance commonly employed. 

Some of the earlier processes depending on the use of barium peroxide 
were inconveniently cumbrous. Thus Thenarcl, early in the nineteenth 
century, recommended a method of which the following description is 
merely an outline, many details being omitted. 5 Powdered barium 
peroxide was dissolved in dilute hydrochloric acid and the barium then 
precipitated by the careful addition of sulphuric acid. The resulting 
solution, containing hydrogen peroxide and hydrochloric acid, together 
with impurities from the barium peroxide and probably a little sulphuric 
ucid, was treated with a little barium hydroxide solution or barium 
peroxide emulsion when any heavy metals were precipitated at the same 
time as the sulphuric acid'; by the artifice of previously introducing a 
little* phosphoric acid, any manganese or iron could be simultaneously 
removed us their respective phosphates, whereas, if allowed to remain, 
they would have caused rapid decomposition of the hydrogen peroxide. 
After this treatment the; solution contained only hydrogen peroxide and 
barium chloride, the latter of which was removed by conversion with 
silver sulphate into silver chloride and barium sulphate. The clear 
solution of hydrogen peroxide thus obtained possessed a high degree of 
purity and was finally concentrated in a vacuum over sulphuric acid. 

* Finchcr and Hinge, Mr., 1908, 41, 945; Fischer and Marx, ibid., 1906, 39, 3031 ; 
1007, 40, 44:*, 1111 ; Kahibaum, for man Patent, 1908, 197023; Findlay, Zeitsch. Ekktro- 
chcm. 9 100(5, 12, 121). 2 Fischer and 'Ringe, loc. cit. 

3 Makowctxky, Zeituch. MeMrochcm., 1911, 17, 217. 

* Mm*ek, Ui-rnutn Patent, 152173; Hoffmann, Annakn, 1865, 136, 188. 
fi Tht'nurd, Ann. Chim. Phys., 1832, 50, 80. 

328 OXYGEN. 

The disadvantage attaching to the direct conversion of barium 
peroxide into an insoluble salt by treatment with such an acid as sulphuric 
or carbonic acid, lies in the sparing solubility of the first-named substance 
which causes the reaction to be incomplete. This difficulty can be 
remedied by previous prolonged agitation of the anhydrous barium 
peroxide with water, by which treatment it becomes converted into the 
hydrated and more reactive compound BaO 2 . 8H 2 0. This readily yields 
dilute solutions of hydrogen peroxide when treated with aqueous 
sulphuric, 1 hydrofluoric, 2 hydro fluosilicic, phosphoric, 3 or carbonic 
acid. 4 In the case of the last-named acid, it is important to use an 

Ba0 2 +H 2 S0 4 =BaS0 4 +H 2 O a . 

The resulting solution will contain saline impurities such as salts of 
iron and manganese derived from the barium peroxide. These can be 
removed by the addition of a little phosphoric acid followed by neutral- 
isation with barium hydroxide solution when the metals are precipitated 
as phosphates. If necessary, further addition of barium hydroxide may 
be made in order to precipitate the hydrogen peroxide as pure barium " 
peroxide, which on treatment with the correct quantity of dilute 
sulphuric acid will give a pure solution of hydrogen peroxide. 

Purification from mineral impurities can also be effected by extracting 
the impure solution with ether in. which hydrogen peroxide is very 
soluble, although less so than in water. 5 The value of the process is 
somewhat discounted by the possibility of formation of organic peroxidic 
compounds which may give rise to violent explosions during the dis- 
tillation of the ether. 6 Dilute aqueous solutions may be subsequently 
obtained by merely shaking the ethereal solution with pure water. 

II. From Per- Acids. Another process suited to the economical 
preparation of hydrogen peroxide is based on the decomposition of 
permonosulphuric acid under the influence of water. The acid, 
prepared by the electrolysis of sulphuric acid or by the interaction 
of potassium persulphate and sulphuric acid, undergoes gradual 
hydrolysis according to the equation 

H 2 S0 5 +H 2 O^H 2 S0 4 +H 2 2 . 

The hydrogen peroxide can be separated by distillation under 
reduced pressure. 7 

The use of other per-acid salts such as percarbonates and perborates 
has been suggested for a similar purpose, as also has the direct treatment 
of ammonium persulphate with steam. 8 

III. From Autoxidation Processes. The slow oxidation of metals, 
such as zinc or cadmium, especially in the form of their amalgams, in 

1 Thomsen, Ber., 1874, 7, 73. 

2 Hanriot, Compt. rend., 1885, 100, 57, 172. 

3 Lindner, Monit. Scientif., 1875, [iii], 5, 818; Davis, Chem. News, 1879, 39, 221 ; 
Bourgougnon, /. Amer. Chem. Soc., 1890, 12, 64. 

4 Duprey, Compt. rend., 1862, 55, 736 ; Balard, ibid., 1862, 55, 738 ; Lunge, Zeitsch. 
angew. Chem., 1890, 4, 3; Mond, Ber., 1883, 16, 980; Merck, German Patent, 1907, 
179771, 179826. 

5 Crismer, Butt. Soc. chim., 1893, 6, 24 ; Ossipoff and Popoff, J. Russ. Phys. Chem. Soc., 
1903, 35, 637. e Bruhl, Ber., 1895, 28, 2847. 

7 Consortium Elektrochem. Industrie, German Patent, 199958 (1908). 

8 Soc. 1' Air Liquids, French Patent, 476816 (1914); Cobellis, U.S. Patent, 1195560 (1916). 


the presence of water, has also been suggested as a basis for an industrial 
preparation of hydrogen peroxide. 1 

Concentration of Solutions. In dilute solutions such as are 
obtained as the first produet in most of the methods of preparation, 
h> driven peroxide is fairly stable. Very dilute solutions can be con- 
cent rat ed by careful evaporation on a, water bath, but it is not usually 
advantageous to concentrate in this way beyond 50 per cent, because of 
the increase in the rate of decomposition*. Another method of con- 
centrating a dilute solution is to submit it to 'partial freezing when the 
mother liquors are enriched in hydrogen peroxide; by repeating the 
treatment with the mother liquors several times it is possible to attain 
a ronrnit ratioM of ;U) percent, wit h little trouble.- The low temperature 
involved in this method introduces the advantage of reducing the ten- 
dency of the solution to undergo spontaneous decomposition. For the 
preparation of pun* hydrogen peroxide, fractional distillation is the most 
convenient process/ 1 the distillation being effected under reduced pressure 
in order that the temperature may be as low as possible ; water, being 
the wore \ olatile, distils first. The danger of explosive decomposition 
during distillation * appears to be much greater with solutions which 
ha\e already been concentrated by extraction with ether (see p. 332). 

Kxeeptiotwlly pure hydrogen peroxide was obtained by Maass and 
Hatcher' 1 from a *l per cent, solution prepared in the usual way from 
commercial barium hydroxide. This was first concentrated to 30 
per c-nt,, using a special type of sulphuric acid concentrator, tt but this 
product required \ ery eareful handling as all the non-volatile impurities 
had also hem concentrated in the process. The liquid was now distilled 
at t>r* ('. under a pressure of to nun. of mercury maintained with a 
sulphuric aeitl pump, Qualitative analysis of the distillate showed 
the absence tit" at! mm-'Volatilc impurities; sulphuric acid was also 
ahvnt, but in those eases where the original peroxide solution contained 
!iii*i.,f e amounts of chloride, .sonic hydrochloric acid was present in the 
distillate unless the original solution was first made alkaline. The 
distillate was now exceedingly pure and contained on the average 85 per 
cent, o!' jiero\itle, the remainder being water. This was concentrated 
to Uii jii-r cent, prroxiile over sulphuric acid in the special concentrator 
referred to uhove. It tio\v remained to remove, in so far as possible, 
the remaining 10 per cent, of water. This was effected by systematic 
fractional crystallisation, a product containing IMMKJ per cent. 7 of 
jir-roMil'- IH-IIIJ,,' ultimately obtained. 14 The most, concentrated com- 
mercial solution of hydrni/en peroxide, containing about 30 per cent. 
H 3 O. t i% known as yirr/f //*//'/ (see p, 2JIMJ). 

i'rt'ttin'vvtfitm. On account of its instability and even explosive 
f.i-ni|t*n**y it is atlvtsahtc to use hydrogen peroxide in the form of a 
solution', a roiii'i-iit rat tun oHlo per cent, heiiitf suilteienf for most purposes, 
whilst tittieli jiiurr itilutr solut ions will often .satisfy the needs of cxpcri- 

1 Limiti.*. |*nujl. /'/*/. J-> i*K7* j66, *I7, 

HiitiMi, ('*<*)>{ *;*/., ins;,, loo, r7, I7L*. Si-i' H!N Ahrl, J. i*ntkt, Vhcm., J901), 

\VMlKrtinKi-m. I!* r , IMi-K 27, :t.'W7, 

Nj.ruii.% /MM.-A, fi*ii'i, f i*- H i, !mi*j, H, 'l*-t, 

Mii.W*siii iliifrii^f, './. jriit-r, r^rwi, ,sv, 1W>, 42, 2?M> 

ii:, ->k *>H;.n W,>M tJi)-2 DOC cent. 

330 OXYtJKN. 

ments. Small traces of alkali, such as way he dissolved irtim jlass,* 
and of such impurities as iron oxtdr and r\i-n dust \\ill ^ivatlv accelerate 
the decomposition of the substance, th- stahditv **!' thr sluti4ins 
decreasing with concentration. In *rd*-r tu a\*nd iuntaet uitli *.dass, 
the bottles are fretjueiitly linrd and stupprtvd \\tth pari-iilin \\a\. A 
very small quantity of an acid is fnqurntU add* d as a PIVMTN atn r, 
stil|.hiiric acid bein^ eommonl\ ehi^fiu hut other aeids aiv effrettvr, and 
certain orianie substances * ha\*- hern found t* f\fi1 a marked pivsrr\a- 
five action, one of the most effective hi'iJiy aertanthdf isrt* Jt, *l*i!li, 

It is staled that pure udi\ dnttis h\dr*en prroNid.*- d**rs imt de> 
compose at ' (\ u 

rttis ynn^ u pero\i i\ an amt eonur* ^ > s\muv 
which in bulk is seen to liau a f.nut **i'i * i h hlu enintir i.sfln! niun 1 
marked than that ul' \\atir.* l*h *dui l fiir pm* i, fatt 
it) recall that of nit nt arid," hut t b dilut* *Mhiihn.-u* s^thout d<ui. 

Pure hytlrnnen pt roxtdt nadilv a- i U!ns M >i *d i*Mtld fMuhtMin 
and may refuse f.o r\stath-*f vn ;d t pip, r, I HI * , . tv .r, lti i ., 
although its melting point is !-7li i / ; II, hmv i * mall pi t*tit \ 
be 4 solidititHl by stron'l\ fttnhn", /,-f, \iifli t nuO)ii *! .nnd nbm 
dioxide and ether* tlu pmdurt ran hi tr. I a^ nu-l* *r* f* niiue 
orystallisatiou at Inapt rattu* put h JM fli- hi Ifjii^ jiMjut *|'1. 
solid then separati s ia prtstnaite er)st.*l i , and tiaetr>Hal r<\ .! dh .ti n 
may be applied us an *fftefn* uiithitd **} HIM! puuUr.itiMii, >|n\ 
evaporatitni oi" the h|md ran oerur .it tit iMdin.Hx t< mpi raftir/ SJ and, 
under reduced presstin , di fc *tiilation nui\ h* iftHtI uttii t*id\ *ir*hf 
iicccnnpositioiu the htnhu" jmt nnd* r "]i* iniii **i lanMtn h tu" 
<IU'2' !i I 1 . 10 Hydrogen pt ri\idt i% di u* r than \\at- r, Hi** l*ilt*i\\tii/ data 
being given for the anhydrous, tttjittd u i'ii *u p< t *n nt, j ; 

The variation in density with ttilutttit is shuujt wi the InJ 
table 11 (p. :!!). 

Water is miseible with hycirojjfeu pt-ro\nie in all |i'npf*rtiuii% it -sl 
evolution of bent itecoitipititytny theprorrss ; although tltltilr suhitiniis 
arc neutral in reaction, pure hydrogen prrovitle apjirars (* be ft-rbly 
ueidit'. 13 Tlu* aiqtteotts sttutions Iia\'f it elutntetf-nstir tinplrasaitt titste 

t:t, 85, 5HH; Mttrt'k* tfrruutn 
ri7? /l/w/r. ./. f.-hrtn. tfw,, 

3 MllftMH am 

* Wiilf1ftitrlli 

* Unnrint, Cunt ftt t 

i/ S f r,, lillll, n, I HI, 
111 Hriihl, Iw, ril, > 

\ ril. 

HYMU)(4KN PEROXIDE, H 2 O,. 331 

and, if i'airh concentrated, attack the skin, causing a prickling sensation 
and the formation of opaque white patches which slowly lade. Ether, 
aleohul, and aeetie acid are also <jfood solvents for hydrogen peroxide. 

(Maass and Hatcher.) 

) ; JHT fi-nt. 

IMwity at ()'' (', 

Density at 18 C. 






1 -0372 





I (KM 



-2iO i 

1 -2270 

Tit -20 


1 -2i<>5 

7M- 11 



HI- H( 



*.) 12 


I 395 5 

US -Nil 



In th** following table are tfiven the more iinporta.nt physical con- 
stunt'* it' !t>dru*4t-ii |H ( ru\ide as ctmipared with water, compiled from 
thr daLt sujifilirtl by Maass ami Hatcher. These may be. taken as 

ir* I> repliteiu^ the earlier data of Hrithl and others. 2 


M.-ltmu pnuit , . , j I"70 U C. 

t* * *' * ~ i i* i * 1 11 i f *it 

tensity >l li<|tii*i at fi \ . . ! i >>> 

\* II! til ; 211 C\l . . | 0-00107 

Ui-MSltV if fc **>lHl . . ; I'Uii 

l,utrnt Jjrat uf i'liMiHi -tt' solid , .' 7 i calories" 

S|-nltr hrat of suhtj , . : ^" ^0 '* 

Snri'ar- triMt*u at I) t'* . ' 7H-7< dynes 

Mtflrrtilar assitriatiou :i at ('.. 
Visrnsjt \ it! 

I In, 1 

0-OIH28 dynes 


0' J (\ 

0-9 108 

79*7 calories 

75-5 tt 

a-58 tt 

0-0 1793 dynes 

^ Hi *tV.r % *lur, I J.'H-i f.r ^'.i ;". i^r -*mt. i'fuxul' i-;* in fairly 'Iw HKronnuMit with this 

' - 5 riiii-uhihnl fi-im KnM!ty niul Vnun^'H furmulu, ^ 
ffl'-kMv A OP* tii^ *t iw*iwumw'iit Itriihl'M Kaninld <uly coutaiiuul 

i 1 *! 1 ". %il in 4 IHT wit, " Art izivi'ti by Mtiatw asui Hatcher. 

i, H-l f 

14 OXY(!KN. 

iniruls with other salts an* producible in a similar manner. 1 hi 
leh compounds the hydrogen peroxide is only feebly combined and 

removable by the addition of water or by ext raetion with etheiv 5 
uite frequently it- happens that the hydrogen peruvidc ** uf rrystallisa 
ou" is accompanied by water of crystallisation, the sodium salt/ 1 
\ r a,S()j -U.jO . HoO.t, corresponding with flu* abo\r animoninrn salt 
: j in^ a case in point, 

When a mixture of hydrogen peroxide and hydrochloric acid U 
/aporatcd in a platinum dish, a certain amount of ehlorplatinie acid 

formed. 4 Hydrogen peroxide is capable of displacing acids, notably 
ic halogen acids,*'* in <'crtain circumstances. Addition of saturated 
>pper nitrate solution to the peroxide results in the precipitation of 
rown hydrnted copper oxide with simultaneous evolution of c\y#en. 

similar precipitate is obtained when copper foil is introduced into a 
>lution of hydrogen peroxide containing alkali nitrates or sulphates. 
he reaction is presumed* to take place in several stages; thus, in the 
use of sodium sulphate solution 

Na,SO, J H a O., Na.*0, : !I,SO t ; 

N ? n.O. ( 1 IU> 2Xa()II - II a ().,; 

( f u-i lL,SO/'i II,O, CuSOj Jli-.o" 

; L'NuOIi NaSO nib. ILO. 

Hydrogen peroxide vapt>ur affects u photographic plntc in the same 
ay as exposure to li^ht, 7 the sensitised film detecting the pri'srnc** of 
; little as II x 10 !l grams of vapour per cubic centimetre ; H iu this 
:>\ver is prob-ably to be found the expluiuitton of the photographic 
"tton of some oxidisable metals,* The effret is u clteMiind onc, tn 
robahly analogous to the action of hydrogen peroxide on silver o,\tde 
;ee later), 

Towards protoplasm hydrotjru peroxitlc rxcHs a dfC'ttirdiy poistiiuus 
'tion t 11 and so onuses the death of organic IVrini'iits such as yeast, 
though it does not necessarily nffcct the iictivity of the c!t/*ymi's. 
uses have ht*cn observc<l of seeds, moulds, ami phagocytes the "rowfli 
' which was favoured by very dilute solutions of liydrontit peroxide,** 
;it it h possible that such results tuny he due to the presence in the 
^unisin of sonic organic nttalyst (i*atalase) which cunse.s the tlreom- 
;>sition of the peroxide and so prevents its u.stwl iietioi$, l;l lit dilute 

I Tnnatur, %nt*ch t ftiwrtj, Cht-m,, HMt, 28, !ia1 ; llrr,, lHSn, 'p, I"*I4; HtKintk**, 
RUM. My*, ('htm, *Vnf,/ti!2 t 44, tSP ; Mlikut! ift'*/. I!r;f 54, 37 ; Ka/AU^rkf k 

VI., HH4, 16, I ! 10. MiiitHrt itittl HiUt<h<*r. I**, fit, 
51 IVtrcmktt, */. Itiw. My** f'/irwi, .SV*, IWIL*. 14, ^M, '11*1, 

3 VVillHtiitttr. tirr., !),% 36, JH1H, * Mwn, //*//, /!. /nrw., IUI7. 56. 417, 

{ > Hpi'rltrr, rArw. %rntr., t14. i,, Tim, 2t:m ; HU:i, ii, 1 Hf ; Ht:i, i,, , l ii;! l-ItMi, 

II SiKrlKT, i/wl, HHtl, i., 453, 

7 t)cmy-!{i : nuu(t, i/m/.. HHHi, it,, JIUU ; tttt^^U. IV\ liVf, ,\V*r ( , |WH$, 64, 4<!i ; I>MV> 
nitult, //////. *Vw, f/iiwi, /irli/ t Hum, aa, ^-1. 
14 van AuiK*l, <Vi/rf. wm/. IJM>4, 138, IMU ; l*n*rht. ntitl * Ifsukt, /nrwA i4i|iinl. rii*-i . 

or. 62, m s ' 

* Sui*lun<l, Jww. Mtyttik, HHK, 26, H!ll, 

l " Atl not etui* to rmimttciii iw mtjiH;ifHti*ci l*y imt*t/ t l%f*il|, X^f^rA , HH4. 5, IUHHI , 
TckiTts, Kritwh. antjew* f-Virwi,, l$K'r, 18, -IS!*, 
11 lif-rt ntul Kt^itarct, row/il. /*/., IHHU. 94* JllH;i ; Jliiiiiii-n. 7V*i., rArw, ,%>-,, 

12 DiMnfiitHKy, rww/il. ri'Wi/., tlllfl, i6a 4.*la ; Cliitibt iiitd ilitt-ti, ltrr. t Hi'J. 35, 1215, 
, Intern. Siritwh. phy*..rhvm. lliwl. HH5, a t L*rA. 


aqueous solution hydrogen peroxide forms an excellent antiseptic 
wash for open sores ami \vonnds. 1 

Some of the most striking properties of the substance are connected 
with its ready decomposition and the closely related oxidising power 
which have proved very attractive fields for physico-chemical investiga- 

Catalytic Decomposition. Hydrogen peroxide can be regarded 
as stable only in cold dilute aqueous solutions free from even traces of 
alkali, compounds of the heavy metals, and suspended solid matter, 
and wht-n protected from exposure to bright illumination. Thus in 
solution in tap water decomposition occurs fifty times as rapidly as in 
conduct i\ ity \vateiv- Minute quantities of alkalis markedly accelerate 
flu rate of decomposition, 8 possibly by the intermediate formation of 
unstable % * salts ** of the peroxide (set* p. JfcM), the activity of the catalyst 
lu'injjt dependent upon concentration of the hydroxyl ion which it 
yields. 4 Kxposmv to ultra-violet radiation also induces the rapid 
decomposition of hydrogen peroxide, the reaction in this case being 
umuinlrettlntY* mid also differing from the spontaneous or purely thermal 
decomposition of the solutions in being accelerated both by alkalis and 
acids/ 1 

On account of the extreme sensitiveness of hydrogen peroxide to 
i*\trrn.'il influences^ it is almost impossible to consider the decomposition 
process apart frunt the rffcet of catalysts because the minute traces of 
for-jn matt IT inevitably present in a " pure " substance and the walls 
of Idr eontainiiuj vcssr'l arc capable in this case of producing a dis- 
prtpurtun;iti- effect ou the stability of the compound. Even water 
exerts a distinct catalytic effect. 7 Ordinary 'pure hydrogen peroxide 
jifid its suJutums, as is to be expected, decompose more rapidly when 
tin- trwpiTatwv is raised,* but, as has already been stated, the decom- 
position is sntftciently gradual to permit distillation under reduced 
prrssinv, The tlif-riual decomposition is a. bimoleeular process, and in 
the ease tf HP- purr compound the heat generated during the chemical 
t'hamje trnils tu make this become explosive. With pure hydrogen 
iMT\iie tip- oxygen liberated tnrasnred at 11" and TOO" mm, is 475 
times the \iiiisnir ui* til*.- tri*^nl hytlrt^en peroxide ; with solutions of 
ftif suUtituce the volume of <xyen (nt N'.T.P.) produeiblt^ by the de- 
<mi|i<sittcm iit" iiitit \oluwc tif (lie solnium supplies a. convenient; mothod 
uf exjiri-sMnj^ the eowmtralion ; solutions are therefore frequently 
Mild nut us uf a rrrtwu prrei'iitaue rnnentration but- as %t ton volume/' 

*' I WriitV VntuilM'," etc. I 

', !'**. 14**, .10 Km tho ut'tion of hylroj?tn poroxidcMm iho 
*m. .Ml< nh mtt. ltn. t 1HHJI, 16, I I0fi. 
t * A*/ HM. I*ttl IT, Hit 

H 'H, i*),, * ; , Brifltrltit / twijit, mttl., I KHO, 90, .TM ; Tainmann, 

yr .f t v * ' !/,.. JSHM, |, 111 , U'IU'*HHS rtUHJtt. fl'Wf/,, HUH. l6l.47. 

"* v. (t| i \ (l .,!.,, lt uj |IM, A.'./ '>./' r/i,-,,!,, HH4, 27,^iU. 

i i, t i ,? |HM 1^1, mitt, /'A* . hir>; ,-i^r. j. rv/f'/w. sw. t iir>, 

to 4 i.'s.^. Mi'J. * \fi.l ** it,, ./ I hi **l /'Ann,, IUI4. 18, I, 521 ; K<nifolcl, 

* " 

7. 40, 

^ '** s '^* ^l** 'N'* f ^ l ^*' M.y**Avi/, M*v., 1904, 46* 720; 
I w*', ti. "*! 

336 OXYGEN. 

A ten- volume strength corresponds approximately to a 3 per cent, 
solution, and a twenty-volume strength to a G per cent. Perhydrol 
(p. 329) is practically a 30 per cent, solution corresponding to a one 
hundred- volume strength. 

Many other substances than those mentioned above possess the 
power of markedly influencing the rate of decomposition of hydrogen 
peroxide, especially in feebly alkaline solution. Carbon, 1 silver, gold, 
the platinum metals, and many other substances 2 in a fine state of 
division are exceedingly active, but if the metal exposes only a smooth 
polished surface, the result may be relatively inappreciable. 3 In 
colloidal solution the activity of the noble metals is still greater, 4 and 
the effect of one part of colloidal platinum in more than 100,000,000 
times its weight of water exerts a distinct catalytic action. Whether 
the effect of such metals is due to a mere surface action or to the 
continuous formation and decomposition of an intermediate unstable 
oxide is uncertain, but the former view appears more probable, because 
all finely divided substances exhibit a similar although often feebler 
effect ; silica powder, for example, has a very considerable accelerating 
influence on the decomposition. 5 It is a very remarkable fact that 
these colloidal substances lose their power in the presence of almost 
equally small quantities of such substances as mercuric chloride, 
phosphorus and arsenic hydrides, hydrocyanic acid, and hydrogen 
sulphide, which are therefore described as " poisons " to the catalyst. 
Some organic substances such as alcohol act similarly. 7 The de- 
composition of hydrogen peroxide is usually regarded as a reaction of 
the first order 8 or monomolecular, whether in acid or in neutral solu- 
tion. The reaction is convenient to study, since its rate can be 
followed by titration with permanganate, or volumetrically, by measur- 
ing the volume of evolved oxygen. 

In alkaline solution the activity of the colloidal platinum increases 
to a maximum with increase of alkalinity, and then decreases. In this 
respect it behaves in an analogous manner to certain inorganic ferments. 9 
Exposure to Rontgen rays retards the reaction. 10 Colloidal rhodium, 11 
palladium, iridium, 12 silver, and gold behave in an analogous manner 

1 Lemoine, Compt. rend., 1916, 162, 725. 

2 Filippi, Chem. Zentr., 1907, ii., 1890. 

3 Spring, Bull Acad. roy. Belg., 1895, [3], 30, 32 ; Teletoff, J. Russ. Phys. Chem,. Soc., 
1907, 39, 1358 ; Lemoine, Compt. rend., 1916, 162, 657. 

4 Bredig and others, Zeitsch. physikal Chem., 1899, 31, 258 ; 1901, 37, 1, 323 ; Be.r. t 
1904, 37, 798 ; Kastle and Loevenhart, Amer. Chem. J., 1901, 26, 518 ; 1903, 29, 397, 563 ; 
Senter, Proc. Roy. Soc., 1904, 74, 566 ; Price and Friend, Trans. Chem. Soc., 1904, 85, 1526 ; 
Paal and Amberger, Ber., 1907, 40, 2201 ; Teletoff, J. Russ. Phys. Chem. Soc., 1907, 39, 
1358 ; LebedefF, Bull. Soc. Mm., 1908, 3, 56 ; Maclnnes, J. Amer. Chem. Soc., 1914, 36, 
878 ; Lemoine, loc. cit. 

5 Lemoine, Compt. rend., 1916, 162, 702. 

6 Bredig and Fortner, Ber., 1904, 37, 798. See also the above references to Bredig's 
papers ; Brossa, Zeitsch. physikal. Chem., 1909, 66, 162 ; Maxted, Trans. Chem. Soc., 
1922, 121, 1760. 

7 Meyerhof, Pfliigers Archiv, 1914, 157, 307. 

8 Disputed by Rocasolano, Anal Fis. Quim., 1920, 18, 361 ; Compt. rend., 1920, 
170, 1502. 

9 For further details the reader is referred to this series, Vol. IX., Part II. 

10 Schwarz and Friedrich, Ber., 1922, .[A], 55, 1040. 

11 Kernot and Arena, Rend. Accad. Sci. J?is. Mat. Napoli, 1909, [3], 15, 157 ; Zenghelis 
and Papaconstantinos, Compt. rend., 1920, 170, 1178, 1058. 

12 Brossa, Zeitsch. physikal. Chem. 9 1909, 66, 162 ; Kernot and Arena, loc. tit>, 
pp. 125, 145. 

1 1 Y DROCJ K\ PKROXI DE, K,0,, 337 

platinum. Uy increasing the pressure of oxygen in contact with 
thr decomposing solution from one to 200 atmospheres the rate of 
decomposition is not appreciably afiVeted. 1 

Other metak the commonest, bdnjr lead, 2 bismuth, and manganese, 
in pmvder form exert a more moderate effect on the decomposition. 
Mercury ucmld also (all into this elass of moderate accelerators, but the 
ra talNtu- art ion m this ease is remarkable in being periodic or rhythmic. 
\\ hen Hie nmcentratum of hydrogen ion is reduced to an almost negligible 
quantity by the addition of a little sodium acetate solution, a dean 
luerrury surface m eonlaet with hydrogen peroxide solution of approxi- 
iinilrl) 10 per cent, concentration, at. periodic intervals of about one 
sceumi becomes routed with a bron/e lihn which suddenly disappears 
with a burst of oxygen from the contact, layer of the two liquids'; the 
substance of flu- film, which is alternately formed and decomposed, is 
probably an unstable oxide, possibly mereurous peroxide. 3 

Copper. nickel, cobalt, and cadmium have only a feeble effect on 
Ilir niti uf iiccnmpnsit ton of t lie substance. 

Mmty mmpiMnuls, especially various metallic oxides, also induce 
*TV rapid decomposition of hydrogen peroxide without themselves 
tiring permanently changed.* In addition to the solutions of the alkali 
hydrovidrs already mentioned, manganese dioxide, cobalt oxide, and 
lead osidr (lunssicot ) arr remarkably active, and as might, be expected 
;t colloidal \ulutiuu of tiiimgaiiest* dioxide* r> is also able to < k xcrt powerful 
ratal) In* inHuriiee." Tlie rflVet in such cast\s may be partly a surface 
iffti't, but !-, also probably due in part to the intermediate formation 
anil drctHtipiisitJMtt <f unstable highly oxuliscd deriva-tives. 

'lite uvides uf ir*n, bisnutth, <*oppcr, ccriiun, a.nd magnesium arc 
capable it" e\ertuig an appreciable influence on the rate of decom- 
positiim, 7 but iiiui'h <it*peuds on the physical condition of the solid, 
freshly pfvnpif uf t-tl iron uxide, for 'xamplc, being mon v effective than 
fin' fi'mint substau<e; H aluminium hydroxide is rather exceptional 
in bf-Iiinmif as it "negative catalyst" 1 and retarding the dccom- 

AinMiu'st uthi-r itmrgattit* catalysts arc to be included the iodides 9 
fiilvtt bromides ami chlorides but less, active) and ehromatcs or di- 
citrunmtrs. The agent in the former <*asc u]>pears to be the iodide ion, 
tbe inrcbanistit if tbe reaction probably involving oxidation to hypo- 
itiiliff ivliii'h flirti reacts \vitb more hydrogen peroxide with formation 

* lit. I- Jf \\.IIM* >r, Xt.t'lt jlhyuhtt, r'/j*w. t HMd, 42, 001 ; iiuli and Wilke, 

J f-iti i *' , I'li*^, 77, :;;t' J(tfiittni\ Ctwijtt. mut., lOIrt, 162, HBO; (')kaya, Pron. 

; i/ n, ui , ' - .jt, i ^ I . l'M, 16-% 7<^, 

', !/ Jt-jii, -n .*n*i I^hiii.niii, fa thud. #f*V'A,, Il^U 29, Ii30. 

r - Utr i %i . t >it I Mai^-l . tf-ilx'Uuttl itttnytti, imti ttrmmflvn, IJUO, p. 342; Abutr. Chem. 
A" , J'Ml, KKI, it Ii** f 

H, * ' i, I".- 'Ai>- /'Ay.. l^lH, !;;,<>, Ml ; IH19, 10, !14 f 33H ; II, 85, 

0, f2], 5, 201; 

r Am. ,V<irv. lHHl t 43, 141K 249 ; Rings;tt 6 f Am. A r ^ww, 
//^ I, i /,, IHWI, 9o/ r Ki.'t ; I*<ohurd, ('ttmpt. rrnd. t 1000, 

I 40, i'. t i , HI! ,- / It'u < /'Av ( A i, ,s'iw 1012, 44, ir!m 102tt; Bohnwrn, -/. PhyAtfial 

I ^*f*i , I** *, ,4, i*7 / 

338 OXYGEN. 

of iodide, and water and free oxygen 1 (compare the reaction with 
hypochlorites, p. 341). 

H 2 O a +r=H a O+IO'; 

H 2 o 2 +io'==n a o+r+o a . 

The action of iodides is catalytic only in neutral solution ; in alkaline 
solution oxidation occurs with formation of free iodine. Whilst 
chromates and dichromates accelerate the decomposition of hydrogen 
peroxide, the action is not purely catalytic because some of the 
chromate or dichromate undergoes permanent reduction, so that the 
change falls more correctly into the next section. 2 

With iodine the following reactions are believed to occur : 3 

(i) 5H 4 O a +I a =2HI0 3 +4H a O, 

(ii) 5H a O a +2HI0 8 =50 a +I a +6H 2 0, 
(iii) 2H a O a =2H 2 0+O a , 

the last-named reaction being catalysed by the iodic acid -iodine couple. 
In ammonium hydroxide solution the reaction takes place 4 in accordance 
with the equation 

2NH 3 +I 2 +H 2 O 2 =2NH 4 I +O 2 . 

Manganous sulphate 5 and ferric salts in general accelerate the de- 
composition of hydrogen peroxide. 6 The sulphate is less active than 
the chloride or nitrate. With dilute solutions of the salts the effect is 
proportional to the concentration of the peroxide and that of the iron 
ions, whilst in the presence of acids it is inversely proportional to the 
hydrogen-ion concentration. The temperature coefficient of the reaction 
is 3-25 for ten degrees. 7 

If a few drops of potassium ferrocyanide solution are added to dilute 
hydrogen peroxide (1 per cent.), and kept in the dark, decomposition 
of the latter is exceedingly slow. On placing in direct sunlight for a 
few moments, however, brisk evolution of oxygen takes place and 
continues, even after removal from the light. The effect is not due to 
rise of temperature, but, presumably, to some catalyst generated under 
the influence of the light. 8 

Even carbon, in the form of charcoal, catalytically decomposes 
hydrogen peroxide, 9 its activity being apparently connected with its 
absorptive power for gases. 

Certain complex organic substances are known to catalyse the 

1 Bredig and Walton, Zeitsch. Elektrochem., 1903, 9, 114 ; Walton, Zeitsch. phytikal 
Chem., 1904, 47, 185 ; Bredig, Zeitsch. physical. Chem., 1904, 48, 3f>8. 800 also Abel, 
Zeitsch. Mektrochem., 1908, 14, 598. 

2 See Orlov, J. Russ. Phys. Chem. Soc., 1912, 44, 1576 ; Spitalsky, ibid., 1910, 42, 
1085 ; Riesenfeld, 3er. t 1911, 44, 147. 

3 Bray, J. Amer. Chem. Soc., 1921, 43, 1262. See also Abol, Zeitech. physical Chem., 
1920, 96, 1 ; Monatsh., 1920, 41, 405 ; Auger, Compt. rend., 1911, 152, 712. 

4 Broeksmit, Pharm. Weekblad, 1917, 54, 1373. 

5 Porlezza and Norzi, Atti R. Accad. Lincei, 1913, 22, i., 238. 

6 Bohnson, J. Physical Chem., 1921, 25, 19 ; Bertalan, Zeitsch. physikal Chem.., 1920, 
95, 328. 

7 Bertalan, loc. cit. 

8 Kistiakowsky, Zeitsch. physikal. Chem., 1900, 35, 431 ; Winther, Chem. Zentr., 1920 
i., 723. 

9 Lemoine, Compt. rend., 1916, 162, 725. 


dreumposition of hydrogen peroxide l : of these " eatalases " the best 
known is the " iurmase " present in blood, 2 in the presence of which 
the decomposition process is greatly accelerated and approximates to a, 
unimolreulur reaction. It is a. remarkable circumstance that many of 
the "poisons" which destroy the catalytic power of the colloidal 
noble metals huv<* a similar effect, on the power of luemase, bnt the list 
of poisons is not quite the same for the two types of catalyst/ 1 In view 
of the marked influence of these poisons or negative catalysts it is 
possible that the \arious preservatives mentioned earlier arc effective 
in a similar manner, namely, by checking the* activity of traces of 
positive catalysts such as alkali. 

It i\ interesting to note that metallic salts may catalytically decom- 
pose hydrogen peroxide in organic solvents such as ainyl acetate and 
quiiioiine. In tlif latter solvent, if not more than 2 per cent, of water 
is present, (he velocity of decomposition in the presence of manganese 
acetate corresponds to that required for a bimoleeular reaction. But if 
the quitiolittr is saturated with water, the reaction is monomolceular. 4 
On the- other band, not a few organic substances tend to stabilise 
h\drti;rit peroxide solutions. Amongst these are oxalic, 5 ' 7 uric and 
brii/oie acids, A aeetaniltde 11 (see p. JWO). 

t'oneentrated solutions of sodium chloride 8 preserve the peroxide, 
pro\idft( a catalyst such as sodium hydroxide 5 is excluded. Dilute 
sulphuric acid is very effect i\c % even (H)00<><> gram of the acid per litre 
everting a marked retarding effect upon the rate of decomposition 6 of 
,'U) jer crnt. peroxide solution, There would appear to be no simple 1 
I'flntionslup hrtwren the retardation effect and the concentration of the 
sulpbuhc acid. A yellow buttle is preferable to a white or blue one. 8 

Although not strictly a ease of catalysis, the effect, of radium radiation 
mi the rate *!' decomposition ofhydrogen peroxide is most conveniently 
lit* it! luiifd hrfv ; the penetrating rays are the most effective. 

IHTomptmithm with Self Reduction.' There is a. numerous class 
til" rtirituea! subsume*-* c<iutaining o.xygen which, when placed in contact 
uith li\iirtirii pt-rovidc, cause the latter to change into water and oxygen 
tvlttlst * ih<-\ thrmsrlves siwultnneously lost* oxygen. This result is 
tumtft tit ltr*tf tnittiti i\ hi many cases to the primary formation of unstable 
uin httflilv it\itii : H*"<I molecules. Many oxides of the noble metals, e.g. 
AtiJI , Ptc'l,,, antl Hj.;O, exhibit this behaviour with neutral or alkaline 
solutions iiutl I'tucrjfc in the metallic state. Silver oxide behaves 

' lirrli,niiji s r..w/.f, frn*/,, I.HHI*. 94, 17:10 ; Um-U ami (luutat, licr., 11)03, 36, (KM), 000, 
J7Mi li-wli '.( !<.. 1 IH7K; U'r!Jtt|/iifHtStl*rht\^nV^. fthlfxiol. dhrM.< UH!,72, 

ii *l!ii:i Hi.rU. 1 . 1 l!ii-ifH. H : \Vni-ti>,'. '*/., IttlL*. 79 177.-J-HI : l*hra,m<'n, AIM. 
V. I'rlfn^W'tUI \Mf*t. t HUH, 5. NM. I!'.', !. ,.,,/,! uw^ , 

^ Kriiirr %*\!vh i*h* t *tt, r'/inii,. iifff, 74, ll ; Xntxflt. i>hti#\lwL (JheM., 1WM, 44, 
if,,7i' Villr 'mil \l,t'wr. /:. .SW'. rhim.. IW>2, I|, 27, HM ; !(, W, 30, 1)78; 

F .*ut H^^i'^sr. J I<H7, .f t KIM 

''svnirr /-. /* NM- UHI; 74, lnt. Aflcl; Mnutig and Ikcdn, %rit*M. phywkal. 
t *>' !WI* 17 l' k*,\*< M n***^^^ MM)n.29,37. 


I, N'H-,, nun, 38, n>r>. 

/. /*'wn, MU:t. 22, i, 'JUS. 

v't*/. r '** IHI:J, 83. :ur. 

rt \\-ftjioi* 5 ini ,!ipfl Zrsf irii. /.Av't*/. r '** IHI:J, 83. :ur. 

!*i-Ji-r, /'^io. rv/r, A. t MH7. 48. ."", 7J. (Nrtitriwl Artlu f'/ww, ^t/ww/y, 1001, 

' ra. 

la. 424. 


imilarly and tlu 1 artiou iias brrn rwvfully mvrstufatrd ; apparently 
hr rhanur is not. strirth reprrsrntalile by flit- -ijuat!itn 

A : ,O llJO.j '.'Air tl ,0 ft, 

.S Illtjfht he rxperted. Mure 0\\ *! is i \ **h iithan Ufilil.Iln '<!itl%ittd 
)V thr hydrogen peroxide alone, hut til* iftLilittU is jji ! Vetl\ doubt* . 
Pile probable rourse til' the ivaetiuit t hv I* i Hi it nit i J .1 p<lu\idir 
lrriVati\r of silver \\llirh thrl* derMllpo<. s Hit** %lh J' and 0\\ ; n, 

he iiurly cliudi'tl silvi-r pnuturrtt, jsiiIs u-i uuijMUh it l\ iu*- 
JXVfffn <irri\ati\r nt' stl\rr, t'iifaivtir.illv ti-r* t l.tttn ' !!< iul p> i$l* nt 
Icconipositiou of thr liulruifi-ii prntviilr. 1 

In th** majority of suHi rrat'tioiis, hi>\\r\rr, th* - **\jilrsit| t'tiiii|*iiiit| 
iiul thr ltydroi*t'U prrnxiilf apprar tu iiiitli/rtfti rnliirlt**!! !i an 
'Xtt*Ut, O/,olir and hlrosru rii>\tdr fsiii't as litHous ; "* 

srt p. 1.11); this rrhtf toitship IpttiK only fr tl*r pri*'*-s% in alkaline 
iolution, in ut'itl stltition nit r\rrssu*- |uantif\ <t */onr 11111!* r^i HIJ* 
irconipositiou t'Xi'fpl \vhrn a \rry larjft- i-\v\s *!' h\ n pTo\t<l>- is 

n*rst'nt. 11 HUH is r\|ihi!JM-<! nil th*- assuniptMui that th- iiiti-r.ii'f inn 
H'twrc'ti ct/aiu* and hytlroynt pt'n*\til- is atH'tijupann-*! i*\ th- sp**n 

aJH'injS (i('<*tt)npositti>n ttf n/Ottr, this lattrr rractiMlt l*r-tn* rat;tt\ fH'itlly 

u**rh*ratril l*y thr prroxitlr. 

Atthon^'h utauijanrsi' o!i*Mttr li*-ha\*-s HM r 1% as a ratalv^t tovuink 
i iH'titral >r atkuliu^ solution of h\iroj;-n pi-roMtt* , \-t in arui ^ninliun 
*('<Iu<ti(>u owui's It* utan^atious oMilr, Mult, ir a rirr*-spitiiin*;* salt, ftp- 
iy<lro#i*u prroxitir tuuirt'uotn^ siutultaitfcnts ri"tftii'ti$*!i uith th !iln rutitin 
>f an equal amount of IVrr Jixyyrti, 4 I.ral Iii\!*l' : iif h\iiro^rti 
jtwxidr in itt'ili<* sotutttitt hkc'Wtsr tuufrr^t* intittiiil rriiip-ln*!!, In l*th 
.Hsos half thi' littcratni tixym'ii may lr iittnliiitr.*! fti tl$r I|IMMI|I- aitii 
lialf tt> flir prroxitir, hut it is also pnssihtr that tli- iiifi')taiti%in M" th- 
rc'ju'tioii tuny involve thr twn*ifVrrii*r ol' att ti\\rit iifniit JHMI tttr 
EurtalHt* por<\id< to thr hytlroyt-u p-ri*\i*t* ^liifh thm-hy iirt*utitt-s 
:ixidiscti to wiitrr niul xytft*u, If" tin- luttt-r vn-u- 1\ rnrrrft, tip- lih niti-tl 
')xyjLjfh rotiu's riitti'i'ly IVoin thr hyilrniirn pi-rnMtir, hut with nthrr 
['Xplimntion the* linul rrsutt is thr snmr, As tuau^Jiuous M\I*| , MuO, 
and Iriul cjxidt% FhO, arr oxuttst-cl hy hytirt^rit pi-mxitir t thr prrs 
inc*t* of alkali ^ivinu tin* c*4rrrsjMiMltnu tltt*\ttrs, it i\ qtuh- pussthlf* 
that thr catalytic c-ffrt-l of utaujLtattrsf diuxutr ami if thr Irss itrfHr 
IrticI dioxide 4 cin an alkittim* %tltitii i*f hyilro^ru prri\Ml' is ilur In 
the repi'atrd oxidation and rrduHion of thr inofioxidrs liy thr hydro^rn 

Already, in thr rotiMdcration of utrthtMis fur Ihr |ir-|*aratiuit **!' 
r>xy#<*n, mention has hrrn itntdr f U* iutrraHtuit of tiydruMirtt prrtixiilr 
with alkalinr solutins if ft*rru*yanttirh & and with aridir Huttitton^ of 

ttr. fit i tii*rth**t4. f '*//, rm./,, IHWI. g&, .Y7;* , I!*i| i;p HU7 ; Hull, 

Vor. f/"w, I8W>, J2|, 34* Kff* ; /ln, r'Auw. l%c |HH7, (73, II, 'JI7 ; IUvlv. Mtl 3fn*y * 

' . . . . 

iiii.% Annttkn, 
Rothniunct, Sl/i /n 
*r AlaruttHh., I0!7 

'ii*!,, IH72, 75, 17? t Hayhy, Jto*/,. 1H7H, 1/IJ. 12H, 

A. nwiil, df,,lIt*J n. I ! iiiiTnilrt. 70. iritl. 


hypoehlorltes x and permanganates 2 (hypochlorous and permanganic 
acids) with formation of the corresponding fcrrocyanides, chlorides, and 
manganese suits. In these eases the reactions occur quantitatively, 
ami ean he represented as follows ; 

II ..<>, 2K,Fe(\.N a | ^IL,() -| O., ; 
HOtl : 1I,,()., " " IK'l | IU) - 1 -(),;" 

L'HMnCVI'-'n.jSO, j 511,0, l>MnS() 4 +SH 2 (3+5O 2 . 

A",nm, the \iew is held by some chemists that in the interaction of 
permanganic arid and hydrogen peroxide the liberated oxygen originates 
entirely from tlu* latter substance, which is oxidised by the permanganic 
acid with production of water and free oxygen/* In addition to this, 
thr ohst-nation that at temperatures below 0" ('., interaction, as dcmon- 
st rated by the deeolori.sation of the permanganate, will occur without 
any marked. effervescence of oxygen, has led to the suggestion that 
a lusher o\idc, possibly hydrogen trioxidc, II 2 (). h 4 or hydrogen tetroxide, 
H a O|, a is an unstable intermediate product, and that the evolution of 
oxygen occurs in the decomposition of this. This view has been 
vigorously com! wtcd, rt and it appears highly probable that the lack of 
effervescence in the cold is due merely to the oxygen remaining in 
supersaturated solution and perhaps in part as persulphuric acid if 
sulphuric acid IN originally present. Kvcii below I'. most of the 
o\\ .; 11 may be liberated in the gaseous condition, and the reaction is so 
delimit in jfs results at the ordinary temperature as to constitute a 
trustworthy and convenient method Cor the estimation of the cou- 
e -uh'atitm oi hydrogen peroxide solutions. 

tn alkaline media, chromium oxide undergoes oxidation to a ehromate. 7 
Tin- importance of t he luedimn is again seen in this case, because in acid 
solution bjchroniatr or chromic acid yields an unstable blue solution 
containing a labile' pcrchromic acid which is stated to have the com- 
position IH"rO :| or H;j('rO tV according to the relative. 4 properties of the 
rtMi'ruts. The blue solution soon decomposes, giving, in tlu* presence of 
sulphuric in-lit, ordinary chromium sulphate and oxygen 8 ; the blue 
comju'iiiui cun IK- r.\tra'trd with ether in which u more stable.' solution is 
ftlitiiuii il, The blue coloration has for years been made use of as u con- 
\ctiti it! and delicate test for chromic acid and for hydrogen peroxide. 
I'tttuvtiitiH persulphate 1 * also reacts slowly with hydrogen peroxide 

lutions, .iftviini ptitassimu ftytlrogen sulphate and oxygen - 


I1 3 0, - K. r S,0 H 

>.-|..itr, .|HHII/*-H. IH7W. 196. :!;: Kairhiy. Trun* t r/-/w. *Vr., 1877, 31, I ; AHchoff, 
,1. m.*JU. # '/**., iHtpi, Hi, 4H7, ' 

- llini-.inl rw|rf /., IH7L', 75. 117; Mcrtb'Jut, Ami, Uliim. /'/*^., 1880, |5j, 21, 
I7H- ll.pnrr .titit 'Vilh^r. Mr.. UHH, JJ, 24HH ; KnjH f^ttt. A'oc. chm., 1801, 6, 17. 
Ttin ku*i'lir *.( Iliin ivrtJ'lmn liiw* U'vu f ttilnni Iy Xttwid/Ju, Roeznikt Chvwp, 1021, I, Uo, 

* Ttiitil^ ; it'fr rt'lif^.-% till J, .'i*i. 

> llriitirl'Mi JM. f/iiHi. /'Ai/x, lti!, J7j. 22. -i:t:; nl*/r. f^. 

- JWli, //*!., IIHHI. .u, !^il, :1U : I!MC>. 35, irH, IM24. 

- iWtrr ami Vjlh^rV; /* . -i/. i AnntrmK. /V*u r/r-/. .SV%, 1000, 16, I4 ; Kraiiway, 
7 Mir- r'Arj t N-- UHfl 7Q.1^24; rinviT, Awrr. (-In -m. ./.. UMKJ, 29, 4<W. 

' * Uii--ii .1 j^iii, r^-Mi,. !W*. i, l*7: Murtinn, /^//. ^,r, r// ////., 1880, 45, 8B2 ; 
I!, rrr ,>,u!, f^; rrm/.. iHW, 16, UiHT, s ,U. Vhim. l>hy. f IM7, 20 3U4 ; Brod,,, 
1',^ Wr,J ,w! I**U, !l IW; S|.HlHk\../. Ww-v^. /V/.VA r//r/w. Nor., 1^10,42, , I 85; 
111, |Ml7. 4., :UH7 ; XoU. ...1.4. /^-.i, Mi7, 53- I HI : 56, 72; KimMifolcl, ^^/, 

-' l!>ll> 44 ' " IKri^ud, T* Vl^. too.. 190U, 89, 10,2. 

342 OXYGEN. 

A suspension of silver chloride in potassium hydroxide solution is 
rapidly reduced by hydrogen peroxide in accordance with the equation 1 

2AgC]+H 2 O 2 +2KOH-2Ag+2KCl+2H 2 0+O 2 . 

Oxidation Processes. Hydrogen peroxide possesses exceptional 
activity as an oxidising agent. Nascent hydrogen is oxidised to water, 
so that, on electrolysis, hydrogen peroxide solutions undergo reduction 
at the cathode whilst at the anode also decomposition occurs, the nascent 
oxygen appearing to have a similar effect to permanganic or hypo- 
chlorous acid 2 

H 22 +O=H 2 0+O 2 . 

Hydrogen peroxide readily oxidises alkali nitrites to nitrates in acid 
solution. In alkaline or neutral solution oxidation does not take place. 3 

Silicic acid gel, when evaporated with a slight excess of 30 per cent. 
peroxide, yields a highly active amorphous residue which continuously 
evolves ozonised oxygen. It liberates chlorine from hydrochloric acid, 
iodine from potassium iodide, decolorises permanganate, and evolves 
ozone with concentrated sulphuric acid. 4 Possibly a persilicic acid is 
formed. Thiosulphates are at first oxidised to tetrathionates, the 
solution becoming alkaline : 5 

2Na a S 2 3 +H 2 O 2 =Na 2 S 4 O 6 +2NaOH. 

The reaction soon becomes more complex, a fact that will account 
for various published discrepancies. 6 

Concentrated sulphuric acid is oxidised by hydrogen peroxide giving 
permonosulphuric acid, also called Caro's acid, 7 

sulphurous acid yields sulphuric acid and hydrogen sulphide undergoes 
slow conversion into free sulphur and even into sulphuric acid, 8 the 
formation of the latter being easily demonstrated by heating together 
hydrogen sulphide, barium chloride, and hydrogen peroxide in aqueous 
solution. 9 Hydrogen selenide is oxidised more readily, with formation 
of selenium. The metallic sulphides become converted into sulphates, 10 

PbS+4H 2 2 =PbS0 4 +4H 2 0, 

and for this reason hydrogen peroxide is frequently applied in the 
restoration of old paintings in which the white-lead basis of the paint 
has become blackened by the action of atmospheric hydrogen sulphide. 

1 Kleinstiick, Ber., 1918, 51, 108. 

2 Tanatar, Ber., 1903, 36, 199. See also Lebedeff, Bull. Soc. chim., 1908, 3, 56. 

3 Usher and Rao, Trans. Ghem. Soc., 1917, in, 799. 

4 Komarovsky, Cheni. Zeitung, 1914, 38, 121 ; Jordis, ibid., p. 221. 

5 Nabl, Ber., 1900, 33, 3554 ; Tarugi and Vitali, Gazzetta, 1909, 39, i., 418. 

8 See Nabl, Ber., 1900, 33, 3093, 3554; Willstatter, Ber., 1903, 36, 1831; Abel, 
MonatsL, 1907, 28, 1239. 

7 Baeyer and Villiger, Ber., 1900, 33, 126 ; 1901, 34, 353 ; Caro, Zeitsch. angew. Chem., 
1898, p. 845. 

8 Particularly in alkaline solution. Passage of hydrogen sulphide through strongly 
alkaline perhydrol rapidly converts it into sulphuric acid. This reaction may be used to 
estimate the gas. Klemmer, Ghem. Zeitung, 1922, 46, 79. 9 Fairley, loc. cit. 

10 Thenard, loc. cit. ; Raschig, Ber. t 1885, 18, 2743; Hernandez, Anal. Us. Quim 
1908, 6, 476. 


In alkaline solution cobalt sulphide is oxidised to cobaltic hydroxide, 
manganese sulphide yields the hydroxide and a deposit of sulphur, 
whilst /4ue sulphide is converted into soluble zineates. 1 

Dilute solutions of hydrogen peroxide ((> per cent.) oxidise yellow 
phosphorus on wanning, phosphorous and phosphoric aeids resulting. 
Amorphous phosphorus is violently attacked by 8 per cent, peroxide, 
hydrogen phosphide being evolved, phosphorous and phosphoric aeids 
remaining in solution,- 

Metallic potassium and sodium are explosively converted into the 
hvdroMdrs when brought into contact with concentrated solutions of 
hydrogen peroxide ; many of the heavier metals such as zinc and iron, 
ami espreially aluminium/ 1 are readily changed into their respective 
h\ilro\ioVs, whilst chromium, arsenic, and molybdenum are oxidised 
n-s|M rti velv to ehromie, arsenic, and molybdie acids* Colloidal tellurium 
yields telluric arid with very dilute solutions of peroxide 4 ; the crystal- 
line tuntiitieaiioii reacts slowly with (JO per cent, peroxide at 100 C. 

Ordinary lead oxide becomes oxidised to the dioxide, and manganese 
u\tle also to its dioxide ; * inuny other oxides and liydroxides undergo 
suiitiar oxidation, I lie products frequently being unstable pcroxklic 

suhst .uit'cs. 

la in, my of titese oxidation processes a considerable proportion of 
the h\lro;-n peroxide undergoes concurrent; decompositiou with mti iii' *!aseotis oxidation. Thus an ucidiiicd solution of potassium 
tfiii|i- !\fs a slow- format ion of iodine, the change being representable 


Tins oxidation, and indeed many others with the same oxidising 
.ti'f-tit, HI-.' reatl> accelerated by the presence of certain inorganic sub- 
ststitres, }arttfuhtrly iron salts,* 1 and especially when these are in the 
irwitr. i'iiuhtiHu. v * The addition of a very small quantity of ferrous 
stUj*h;tte tn a dthite solution of potassium iodide containing hydrogen 
jti-roMtie, aerlte ienl, iind slureh, reduces in a remarkable manuer^the 
time mvessury fr tlit- prinluetitut of the well-known blue coloration. 
fttfiftrf salts 'are Irss artivi\ but a mixture of copper sulphate and 
I'en-ntis Mi!j*l*tte IN it iiiueb IwittT accelerator than would be expected, 
the enji|r Mtljtlmte ajperiur disproportionately to augment the 
the tVrnMts salt. 1 * C'oniplex organic catalysts have also 

I irrli l|t' v i.eii\ i i* vi, 

lit Ilir pri-M-un- uf hydrochloric* acid or hycirobromie acid the oxida- 
Iinii of li\tinn,ltr arid iiiay prueeed further, "the iodine being converted 

iifti* unite ,teni possibly by way of iodine trichloride or bromide. How- 
rvrr, |irriHltr and s ivduVed U> ludie acid by hydrogen peroxide and in 

fttlniV solution partial reduetitm even to iodine may occur. 10 

- H,n*,nl- ,'<.! _ a Wvyl, /^r., 1900, 39, 1307. 

* liiii I 11* ffA ttllll, 4?. !**. f/ , 

;iuii.w by thi nsaotton, not* bohloSHberg, Mil. 

1, IttU. IS 

ia, 33, KH. 

WU, 37. -R7 

344 OXYGEN. 

Iodides in general, and also to a less degree bromides and chlorides, 
even in small quantities, increase the rate of decomposition of hydrogen 
peroxide in neutral or alkaline solution. This catalytic effect has 
already been mentioned. Some metals will dissolve in cold, and some- 
times in diluted acid solutions in the presence of hydrogen peroxide, 
even if almost insoluble in them under ordinary conditions. Thus 
glacial acetic acid containing hydrogen peroxide will attack bismuth, 
copper, lead, mercury, and silver in the cold ; and dilute sulphuric acid 
charged with peroxide effects the solution of bismuth, copper, mercury, 
nickel, and silver. 1 

Manyper-acids or salts of such acids-have been prepared by the action 
of hydrogen peroxide on the corresponding derivative 1 of the normal 
acids ; thus pernitrates, perborates, pcrcarboiiates, permoiybdatcs, 
pervanadates, pertitanates, and others have been rendered accessible 
by the strong oxidising character of this substance. Details of such 
compounds will be found under the heading of the respective parent 
elements. In this connection it is interesting to note that hydrogen 
peroxide actually reduces many of these per-acids as well as leading to 
their formation. Thus an ethereal solution of perchromic acid is 
gradually decomposed by hydrogen peroxide, as arc also permono- 
phosphoric and pervanadic acids. 2 

With organic substances pure hydrogen peroxide is a powerful and 
valuable oxidising agent 3 ; it will oxidise acetyl chloride to peracetic 
acid, CH 3 .CO 3 H, and acetyl peroxide (CH 3 .CO) 2 O 2 , volatile unstable 
liquids ; another general method for the preparation of such organic 
per-acids is by the interaction of hydrogen peroxide with the acid itself 
in the presence of sulphuric or nitric acid as catalyst. 4 

CH 3 . CO 2 H+H 2 2 = CH 3 . CO 3 H+H 2 O. 

The organic per-acids of lower molecular weight are. generally 
pungent, unstable even explosive liquids ; those of higher molecular 
weight, such as perbenzoic acid, are crystalline compounds and rather 
more stable. 

For many organic oxidation processes, a solution of ordinary 30 
per cent, aqueous hydrogen peroxide in acetic acid is used, the latter 
solvent occasionally being essential. In such cases it is probable that 
the oxidation is really effected by peracetic acid. 5 

With such a solution of hydrogen peroxide, organic sulphides can be 
easily and conveniently oxidised to the corresponding sulphoxides 
and sulphones. 6 

RR'S -> RR'SO -> RJR/SO 2 

and azo-compounds to azoxy-compounds 7 

R 2 N 2 -* R 2 N 2 0, 
where R and R' represent organic radicles. 

1 Salkowski, Chem. Zeiiimg, 1916, 40, 448. 

2 Miro, Anal. Fis. Quim., 1920, 18, 35. 

3 See e.g. Perkin, Proc. Chem. Soc., 1907, 23, 1(56 ; Twiss, Trans. Chem. &oc. t 1914, 105, 
36 ; Clover and Houghton, Amer. Chem. J., 1904, 32, 43. 

4 d'Ans and Frey, Ber., 1912, 45, 1845. 

5 Hinsberg, Ber., 1910, 43, 289. 

6 Gazdar and Smiles, Trans. Chem. 8oc. y 1908, 93, 1833; Hinsberg, Ber., 1910, 43, 289. 

7 Angeli, Atti JR. Accad. Lincei, 1910, [5], 19, i., 793. 


Ketoues and aldehydes containing respectively the characteristic 

C \ . /^' 

atomic groups ">C : O and . C^ react readily with aqueous hydrogen 

C/ ^ 

peroxide especially in the presence of a little hydrochloric acid ; acetone, 
CII.j . CO . ClLj, for example, gives an explosive crystalline acetone 
peroxide of the molecular formula (C^IleO^, 1 and benzaldehyde, 
('(jHs-CIlO, yields a fairly stable substance (C 6 H 5 CHO 2 ) 2 . 2 Carbon 
monoxide appears to be unaffected by hydrogen peroxide. 3 

In the presence of a small quantity of ferrous sulphate an aqueous 
solution of hydrogen peroxide forms a valuable reagent for the oxidation 
of polyhydroxy compounds such as glycerol, glycol, and mannitol, a 
terminal hydroxyl group being invariably converted into an aldehydic 
one 4 the reaction, for glycerol being representablc as follows : 

C1I 2 (OII) . CII(OH) . CH 2 . OH -> CH a (OH) . CH(OH) . CHO. 

Tartaric acid with the same reagent undergoes oxidation to dihydroxy- 
maleie acid, CO 2 1LC(OH) : C(OH)"CO 2 H, which readily undergoes further 
oxidation to dihydroxy-tartarie acid, C0 2 H . C(OH) 2 . C(OH) 2 . C0 2 II, 
whicli possesses especial interest on account of the very sparing solubility 
of its sodium salt. 5 For this reason the acid is recommended by Fenton 6 
as a reagent for the quantitative estimation of sodium. The hexose 
sugars, glucose, fructose, etc., are oxidised by hydrogen peroxide 
containing the same catalyst (Fcnton's reagent) with production of 
the corresponding osones. 7 

OH a (OH) - OH(OH) . OH(OH) . CH(OH) . CH(OH) . CHO OH , OH) . CH(OH) . CH(OH) . 
Glucose. z. PTT/HTT/ rn run 

CH,(()H) . OH(OH) . CH(OH) . CH(OH) . CO . CH 2 OH^ Glucosone ' ' 


It is interesting to note that, whilst solutions of aniline green and 
magenta, arc not bleached by dilute hydrogen peroxide solution in the 
dark, yet upon exposure to the light of a quartz-mercury lamp the 
colours readily fade. It would appear, therefore, that under the 
influence of the light, the peroxide becomes increasingly active. 8 

The bleaching of litmus and of indigo solution (in the latter case with 
the aid of a little ferrous sulphate) is evidence of the oxidising power of 
hydrogen peroxide, but probably one of the most striking oxidations 
effected by hydrogen peroxide is that of benzene to phenol and further 
into quinol, pyrogallol, quinone, and other products. 9 

A remarkable property of hydrogen peroxide, which may be men- 
tioned here, although in the result the effect is not an oxidising one, is 
the power ol! causing organic cyanides to unite with the elements of 

i Wolffenstein, Ber., 1895, 28, 2265 ; Twiss, J. Soc. Chem. Ind., 1916, 35, 1027. 
* Baeyor and Vffliger, Ber., 1900, 33, 2479. 
:) Jones, Amer. Chem. J., 1903, 30, 40. 

S ; 1895, 67, 48; 1* 6 9 , W; 1905, 

87, 811. 

*, 1899, 75, 786= 1900, 77, 1219 ; 1BOS. 81, 6C6 ; 
H 83 1284; Morroll and Bellars, ibid., 1905, 87, 280. 
"VurtiH, -/. Amer. Chem. Soc., 1920, 42, 720. 
Martinon, Bull Soc. chim., 1887, 20, 2934. 

346 OXYGEN. 

water, undergoing hydrolysis to the corresponding amides. 1 In acid 
solution cyanogen gives rise to oxamide, and phenyl cyanide (benzo- 
nitrile) to benzamide * 

CN . CN+2H,O = CO(NHo) . CO(NH ) ; 
C 6 H 6 . CN+HaO = C 6 H 6 . CO . (NH 2 ). " 

Applications .Hydrogen peroxide is applied largely as a bleaching 
agent for materials such as feathers, hair, wood, bone, ivory, and skins 
where the action of chlorine or sulphur dioxide might harmfully afreet 
the article ; it has the especial advantage that, after its action, nothing 
more harmful than water remains ; in order to accelerate the action of 
the hydrogen peroxide, a small quantity of a mild alkali such as 
magnesium oxide or ammonia is often added. 2 Treatment with hydrogen 
peroxide has also been suggested as a method for the removal of the 
excess of chlorine or sulphur dioxide in compounds which have been 
bleached with these agents. 3 On account of its marked disinfectant 
and antiseptic action, hydrogen peroxide in dilute aqueous solution is 
of value as a wash for open wounds and is also frequently applied as a 
preservative in milk. 

The catalytic decomposition of hydrogen peroxide by linely divided 
metals has been suggested as the basis of a photographic process. 
An ethereal solution of the peroxide is wiped over the negative when, 
after the evaporation of the ether, the residual hydrogen peroxide film 
undergoes rapid decomposition at the dark portions of the negative. 
If a gelatinised but unsensitised paper is then applied to the glass, the 
undecornposecl hydrogen peroxide is partially absorbed by the gelatinised 
surface of the paper from the transparent portions of the negative' and, 
when subsequently dipped in a suitable solution, e.g. an ammoniaeal 
solution of manganese sulphate, a brown " positive " print appears on 
the paper. 4 

The value of hydrogen peroxide as an oxidising agent for analytical 
and preparative purposes can easily be realised from the foregoing descrip- 
tion of its properties and, indeed, was recognised early in its history. 5 


Hydrogen peroxide is, of all known compounds, the richest in 
oxygen. Its molecular weight has been shown by the freezing-points 
of its aqueous solutions to be represented by the formula II 2 O 2 . 6 

This formula leaves undetermined the actual structure of the molecule 
which needs further evidence. Two constitutions are possible, which 

1 Radziszewski, Ber., 1887, 20, 2934 ; 1885, 18, 355 ; Dubsky, J. prakt. Chem., 1916, 
[2], 93, 137. For the hydrolytic activity of hydrogen peroxide towards other types of 
organic compounds, such as albumin, gelatin, and starch, see Neuberg and Muira, Biochem. 
Zeitsch., 1911, 36,37. 

- Prud'homme, Compt. rend., 1891, 112, 1374; Bourgougnon, J. Amer. Chem. tioc., 
1890, 12, 64 ; Ebell, Chem. News, 1882, 45, 71 ; Schrotter, Ber., 1874, 7, 980. 

3 Lunge, Dinglers. Poly. J., 1886, 259, 196. 

4 For an account of this " Catatype " process, see Gros, J. Soc. Chem. Ind., 1903, 22, 
379, 380, 963 ; 1904, 23, 1044. 

c See, for example, Davis, Chem. News, 1879, 39, 221. 

* Carrara, Oazzetta, 1880, 10, 1 ; 1892, 22, 341 ; Orndorff and White, Amer. Chew. ,/., 
1893, 15, 347 ; Tammann, Zeitsch. physikal. Chem., 1893, 12, 431. 


may be described as the asymmetrical and the symmetrical, and which 

may be represented : 0<^ and (OH) 2 respectively. The latter formula 

is also referred to as the chain formula HO . OH. If the molecular actually involves the coupling of two hydroxyl groups as the 
symmetrical or chain arrangement suggests, a synthesis from hydroxyl 
groups might be expected. In spite of earlier failures, it has been recently 
shown that, under suitable conditions, especially at temperatures near 
40 C., hydrogen peroxide is produced in appreciable quantity during the 
electrolysis of potassium hydroxide ; the electrolysis was performed with 
pint i i in in electrodes and the formation of the hydrogen peroxide was clue 
to the anodic coupling of the hydroxyl groups after the loss of their 
ionic charge. 1 

20H'+2=H 2 O a 

Sodium hydroxide, probably on account of its more powerful 
decomposing action on hydrogen peroxide, fails to yield an appreciable 
amount of tins compound. 

Organic, derivatives of hydrogen peroxide are known, the organic 
jHT-ucids already mentioned (p. 344) belonging to this class. 
Kxainplcs of a simpler type the alkyl peroxides are produced when 
ethyl sulphate, (C 2 ll5) 2 SO 4 , is allowed to react with fairly concentrated 
hydrogen peroxide. 2 The products, ethyl peroxide, C 2 H 5 O.OH, and 
dicthyl peroxide, C 2 II 6 . O . . C 2 II 6 , are explosive liquids which on reduc- 
tion yield ethyl alcohol, C 2 II 5 .OII 5 without any ethyl ether, (C 2 H 5 ) 2 ; 
the asymmetrical formula,, (C 2 1I 5 ) 2 O:0, thus appears to be definitely 
disproved, and so presumably the alkyl peroxides and hydrogen peroxide 
itself are of the symmetrical constitution. 

On the other hand, the physico-chemical evidence appears to be 
almost entirely opposed to the view that the structure of hydrogen 
peroxide involves merely two hydroxyl groups, as indicated by the 
formula II . O. O . II. As has been mentioned already, the high dielectric 
constant and the absence of any exceptional power to absorb electric 
waves, likewise militate' against the likelihood of the presence of hydroxyl 
groups (see p. 332). Also from the fact that hydrogen peroxide never 
appears to be formed by the oxidation of water, but that molecular 
oxygen on reduction by hydrogen will yield hydrogen peroxide, it has 
been argued that this substance may be regarded as reduced oxygen, 
the hydrogen atoms being only feebly bound so that they readily undergo 
oxidation by permanganic acid and other oxidising agents with the libera- 
tion of the whole of the oxygen from the peroxide 3 ; this indicates the 
absence of hydroxyl groups which indeed would also be expected from 
the difference in stability between hydrogen peroxide and water. 

From the 1 refractive power of the substance also it has been demon- 
strated by Briihl that the presence of hydroxyl groups in hydrogen 
is extremely unlikely. 4 One method of reconciling the 

Rioflonfeld and Roinhold, .Ber., 1909, 42, '2977. 

a Baeyer and Villigor, jBcr., 1900, 33, 3387 ; 1901, 34, 738. 

3 Traube, tier., 1882, 15, 222, 059, 2421, 2434; 1886, 19, 1111, ,1115 ; 1889, 22, 1496, 

" * Wuhl'^rV 1895, 28, 2860 ; 1897, 30, 162 ; 1900, 33> 1709. See also Spring, Zetisch, 
anortf. Chem., 1895, 8, 424 ; Kiiigzett, Ohem. News, 1882, 46, 41, 183 ; Heyes, Phil. Mag., 
1888, iAJ, 25, 221. 


chemical and physk'o-chemu'al evidence apparently is to acknowledge 
the symmetrical nature of the moleeulr whilst simultaneously euncedinuf 
the point that no hydroxyl groups are pr-si nt ; th- >;,;rtif^ presi-nt are 
probably of the typeO. II, which will ha\- ijmtr tltt'lVr* nt eharartrustics 
from the, OH yroup, and the struetuial fnou).* Jnr tin milreu|r \\ilt lu- 
ll. O.O.IK the o\\!, f eu atoiij In in" pi* nl in its t(uadrt\ alrnt ein- 
dition (seep. 131 i This cnn^t it ut ion .ie^uulu \\t\\ uith lii>- taets. On 
the other hand, hydrogen p n*\td iti-n b r- ,adid a'* an * pnhbrium 
mixture, thus : 

II 0:> HO. OH, 

t he left -hand si rue! tire pit d*tmiiatui" o, t In j|ui . p-it\n.| . 
Miro ! surest s the suiiiiii tur.d luiii'iil : 

o ' (i 


but whilst this may haxe its adsaiitau*'s, if attubnf>' I** li\f|i,**-ri! a 
valency of t wo an assumption not yriu-ralU a*vptd b\ ehemr.t --., hut 
in harmony with Friend's \iewsol latent \ah-ney." 1 

Many of tin rrarhons ill sruh i in ti j*i >J<s p j > s ah 
tic applied t> tht (Ii t ftt<n ot h\hi"n p HM| 1 1* l*hr MIHI'H'I 
with t*hromir und, i \pi rtallv with Mihsi iju ut * \t i f nu* ol f I* * *inH d 
i'tuitpouud Ij rtlur. Th' ii\ii|atiM *J jt,f JHIH $ *hi* i^ * MJtittun 
coutiiiiiiiiy Hfrtu* at'ui antl stun'h, sp * ? iall\ IH fh* pn n ' *d i r.if il\ | 
.stirh its IVrrotts stilphatt * 01 iunl\ f|p* ;H-II , .itlii lit* LJl.t t\*.t ih *t 
Ihrn* is thr acithtioitat nth4iita* that HP \zt),th<*tt *I tit imiuii In 
atuiosplu'rit* ovvjijj* 11 is not a*i*i Ji iati l 5 ** thit it Mu-ph< in 1 \iLilsMi} 
has h*ss Hkchhoott *>f HitH'othtriiu* a ** null 1 , ilt Jtn Inii^ I o fm Hi 
lonuatioti of PrtlssMH hltH itii addtlinii in i i4iifi*ii M| I-siir $ii!<iuil 
and potassium frrricvttntdt k Ol th * thu. I* 1 ! . whuli *u M *I 
rousidct'ahh* s nsiti xriu-ss, tin last pi'.*s'* lfj .4ifhtiMnai ,iv,MitM> 
<f bring ittiiifiVt'h'tt Its tittro^i u iln*\nii , 

NttltitToUs (Mltur t'r*irtkoii\ d(|uiuitir* n th u^i)i ih,i *| i.tntii'* 
<t'|4iini*' cotitpotilids hair l*in %n;/'t s| d ; |4|^i tiuiti *,.af<d wjtii 
cohalt iiiiplttht'iiati* ohati^i s in mlttttr IIMIII i *>.i f* M. * M ; ' .1 ilhit 
soluttou of utttlint' or itiint th\ laiiiltit? *MSitaiKUi ' pot 1*^*111111* 
aud ft little* ovahr and \ilil\ a id I I H|*I!,I||I ; ** M ph* h% L n di uitiiM 
in hot atiltiioiuaral soluttou ^i\t * a hhi* rtilni.ttiuit and /< plMn-vi*!** 
iliainint* luts also IHTU iisul/ Th* M i-arttou ' air iff il-Ii*il' I**i 

CVrtaiii itiiir^anu* ivu**ritts IOSM ^ th ai 

I. 3, Ml. 

2 Frtt*i! '/Viii*. t^ifii, AW, t I 2 1 119, 

3 TrituU^ /Irr,, Ixrt4 t 17. IIHI2, 

s Hftliiiiuiiti itiitl !$nrnti4lipf% Mitmti. >&.,, tusii, J4, 

h. Mwitrur ^fiwf| : , iMMM4}/9 I .HI , I !..>% ^, lln , JH'XI, ^H, / 

iiig|tI t .1, /lir/, ^f/, t'hem,, I?U.%, *| l7li, 

'' J'W uthur f*iiiIi*r li|. f ** tHim^-^ J, c. /urn. ^^il,, itij;, j^ 114 


specific for hydrogen peroxide. Titanium sulphate in neutral or acid 
solution .;ives a deep yellow coloration due to the formation of a 
perittunie :eid, TiO ;l ,,r! 1,(U Aeid solutions of ammonium molybdatc 
ijivr an intense yellow coloration of permolybdie acid, H 2 MoO 5 . 2 ' Both 
these supply \ ery sensitive tests. 

For the purpose of distinguishing hydrogen peroxide vapour from 
nitrogen dioxide or o/.om\ potassium permanganate and manganese 
dioxide are useful reagents, the former leaving only ozone unaffected 
whilst tlif hitter tails only to decompose nitrogen dioxide. 3 

The liberation of iodine from an acidified solution of an iodide 
provides a convenient method for estimating hydrogen peroxide quanti- 
tatively, and by first allowing the solution or vapour to react with a 
slightly aeid solution of potassium bromide, any o'/one present may be 
previously determined quantitatively and removed in one process. 4 " 

The reaction of potassium permanganate or hypochlorite with 
hydrogen peroxide in acidified solution also can be conveniently made 
t be basts ut" a volumetric determination, the volume of liberated oxygen 
bent** twire that expected from the decomposition of the peroxide into 
an eijnnnoleeular proportion of water. If the solution of hydrogen 
peroxide is MtUieietitly dilute, direct tit ration with the permanganate is 
possible-' 1 in the presence of sulphuric acid, a molecule of hydrogen per- 
oxide deeolorismij t \\o-iifths of a molecule of potassium permanganate. 

lit those eases \\heiv then- exists a possibility of organic substances 
iiitrrtrtift?* with the estimation of hydrogen peroxide by treatment with 
;i solution of potassium permanganate or potassium iodide, the use of a 
vhitttl.inl solution of stannons chloride has been proposed; the reaction 

Slid, ; '-'iit'i i u,o 2 snt'i.4 i 2H 2 o 

ami may br applied by direct tit ration with methylene blue as indicator, 
itr by flu' mlthtion of'an excess followed by (itration of the superfluous 
stitnitotis s<dt \\itb iiline. rt 

* ,S>-l*Mi^. /*-r-A, ttntll. r/jfw., IH7U, 9, 41, 

5 K*-^-r .i/>l M'M^li-r, 1/Mr. rh* /.',/.'. t!H*H, 39, 1HL 

; |.\,r thr I'.-jijia-.u^'it "I U\<ti"i<u i-n\iilt in ihi' nrtwuco f a porHiilphato by a modifi- 
*-,il-i .< Ihii MM-ih.,,1, w< l'>'iniit.'7'Miiiv. Chun, ,XV., 1904, 85, 597, 1533 ; 1905, 87, 1307. 


ABEL, 338, 342. 

Adam, 134. 

Adeney, 37, 38, 39. 

Adlam, 317. 

Adolph, 135. 

Ahrle, 329, 330. 

Aitkin, 276. 

Alexander, 130. 

Alilaire, 107. 

Allain, 339. 

Allan, 200. 

Allen, 314. 

Allner, 80, 90. 

Alt, 48. 

Amagat, 192, 193, 194, 197, 261. 

Amberger, 336. 

Amerio, 79. 

Anderegg, 140. 

Andreeff, 227. 

Andrew, 67, 90. 

Andrews, 138, 145, 155, 185, 254, 278. 

Andwandter, 84. 

Angeli, 344. 

Angstrom, 37. 

Armeler, 154. 

Antropoff, 54, 307, 308, 337, 

Applebey, 278. 

Appleyard, 181, 182. 

Archibald, 132, 143, 144. 

Arena, 336. 

Aristotle, 156, 205, 293. 

Arloing, 152. 

Armstrong, 66, 86, 305, 341. 

Arnold, 151, 154, 178. 

Arny, 175, 178, 179. 

Arrnenius, 133. 

Arth, 339. 

Aschan, 74. 

Aschoff, 341. 

Ashman, 201. 

Askenasy, 25. 

Atkinson, 321. 

Aubel, van, 140, 177, 334. 

Aubin, 167. 

Auerbach, 233. 

Auger, 338, 343. 

Austin, 44, 195, 196, 278. 

Auwers, 132. 

Avebury, 224. 

Avogadro, 301, 302. 

BABO, VON, 142. 

Bach, 56, 58, 86, 133, 150, 324, 334, 339, 
341, 342, 348. 

Bachmetjew, 267. 

Back, 45. 

Bacon, 77. 

Baddeley, 207. 

Baeyer, 58, 150, 341, 342, 345, 347. 

Bahr, von, 140, 147, 177, 281. 

Bairstow, 130. 

Baker, 61, 71, 72, 75, 138, 227, 228, 286, 

287, 317. 
Balard, 328. 
Balmain, 25. 
Baly, 27, 48, 201, 203. 
Bamberger, 207, 333. 
Bancroft, 81, 275. 
Barcroft, 134. 

Barnes, 253, 254, 270, 271, 325, 332. 
Barralet, 340. 
Barreswil, 341. 
Barschall, 48. 
Bartelt, 13. 
Bartoli, 43, 270. 
Barton, 241. 
BaskerviUe, 154. 
Battelli, 279, 301. 
Baudrimont, 22. 
Bauer, 45, 77, 80, 244. 
Baumann, 57, 266, 279, 300, 301. 
Baumert, 217. 
Baxter, 277. 
Bayen, 12. 
Bayeux, 140, 177. 
Bayley, 340. 
Beadnell, 171. 
Beaulard, 275. 
Be'champ, 339. 
Becher, 11. 

Becker, 37, 38, 39, 80. 
Beckmann, 132, 204. 
Becquerel, 45, 138, 146, 198. 
Bedford, 18, 47. 
Bedson, 182. 
Beger, 147. 
Behn, 202. 
BeiU, 143, 144. 
Bell, 23, 71. 
Bellars, 345. 
Bellucci, 176. 
Bendixsohn, 143. 
Benedict, 78, 82, 164. 
Berger, 308. 
Bergfeld, 19, 24, 26. 
Bergwitz, 285. 
Berkeley, 278. 
Berlatan, von, 349. 




Itt'Hmrr. '.".!!. 
Bernini, -us, 

Brrry, ^04. 
Bi-r*in. Hill. 

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I* ',*v>"u'i n, :'\ :u<i 

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Bowman, 25. 

Boyle, 35, 192, 193, 207, 253, 300, 309. 

Bradley, 29. 

Bradnhaw, 110, 228. 

JKrwhmar, 140, 142, 144, 154, 177. 

Bratfg , 256, 31 8. 

Bnuuley, 284. 


BrauiHT, 137. 

Bray, 338. 

Bn<('%, 13, 332, 330, 337, 338, 339. 

Bn>Hciana, 148. 

Briauchon, 14. 

Bridge, 240. 

Bridgman, 252, 253, 257. 

Briefer, 318. 

Brin, 19. 

Briwr, 02, 140, 141, 143. 

Brinsluy, 93,' 97, 98, 228. 

Brix, 280. 

Broehel, 207. 

Broekmoller, 0. 

Brode, 342. 

Brodie, 55, 80, 138, 141, 142, 155, 341. 

BmrkHmit, 338. 

Bruoeknmnn. 93, 08. 

BruNHa, 330. 

Brown, 108, 109, 181. 

Brown-Sequanl, 180. 

Briiokner, 283, 284. 

Brtihl, 155, 277, 290, 328, 330, 331, 347. 

Brttnrk, 22. 

Brunclli, 20(5. 

BruiiiuT, Ui2, 255, 272. 

Bttlmuv, 79. 

Burhun, 185. 

Buchanan, 27<J. 

Bucidc, 228.* 
Butl^'i.t, 205. 
Buff. 199, 201,290. 
BuiHHtm, Mf>, 170. 
Biilow, 133. 

Bunnen, 3C 99, 130, 157, 100, 101, 103, 

219,228, 253, 254, 300. 
Bunt<% 93, 118. 
Burt'h, 79, 

BurtffMH, 91, 92, 93, 94, 95, 90, 97, 99, 277. 
BurKHtt.!lM\ MO, 147, 154, 340, 348, 349. 
Burke, H, 33 

Hurt, 198 f 29f>. 
Burtn, 100, 

<Uly 308. 

('nitlotvt, 27, 47, 279, 301. 

dun, Off, 133. 

diltomlar, 270, 27 1. 304. 

dilvcrt, 331, 332. 

dinifrtrti, rJ), 285. 

('aniplM'll, 110, 119, 190, 197, 229, 231, 

ri> i\Yi:i'.\, 

Cantor, ^7'J, ^ ii 

Cupranira, .1*1,"*, ^"J j 

CariUM, 1*1, 4a, I4fi, 

('arnica, ."Kin, ,"Ht, 
Carroll, H.'IV, 

Cn-**tillit !', l*"7. 

Cnlh 47, 

Cnurhy* 4.". Hs. Ci* .ju ;' 

CuviiHn. las, Ctt i,jr i, ;i;S 

Citvi*niiHii, i:ii. i;7, lui. .^Ci, ;f!n ;*M., $ ft ', H* Hi Ii , li'i. ni. *. 

Cn/iu, 44, *' ''^> ! n. ^ 

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ClitUH, I'll 1 , Ih'.lfr, |m* 

Cli*rk, IW*. I M it* i* I'i'*. 

cltfTon). :tlo. thu%, ;/*. '/;;, ,'M, ,**?*, ui, Mln, ;i;?*, :H 

Clnii/, 177, Ihii 7t, 7, i', T *, * , *:i, **. MiV. Iv 

Clv<r, HIJU, .141, !144, |is 

C|n\vtM 40 !!*! !*H, |ii*, i<*a. |*f|irf* , ", ,'* 

Cfiutt*N, 47, !, ;!:*, 1^-1 j M . *, t)i, 

CHtm, 14, *JU7, l*rl nL It*** 

Cuhrii, UIH, IU4. Ifrhn*. , I an, / x " 'i 

tVtii U-J, li 1 *, 1,1 S 

('nllirtM, ^7:i, t^fp^I, l"r* 

Cuiintt!, ^01 , twtif, HU 

CMtk, ill, tfifi, Ifc ull* , 14, **. ;*v/ ;*>*, ,* if, 

C<J>tci% />, *7I, t!!l', llrv if, I 'I, 2^ ,'lil, ||J, |t, 4H, All, 74, 



! Knll !J|J|L lII : )0 l 8 ' 47 > 5G 133, 146, 150, 201, 

i;,,-'. "" ';, f ^, 1 ;^^t7. 

H ! '''I'limn, l>2. 

ij\' J i i '!' Krn:4 ' (5I > ~~ < < ) - 

j S , l J \\ ! ttsrombo, 108, KJ9. 

"' t-ti;i'&WWl%i$'\p i ^KTA 4 * 48 - 8081 ' 08 - 

" ' ' I KvaiiH, 33t). 

1 n M ,, "ill, ,is, :i;i4. 
!- . I, I 

! Mxncr, 2(>0. 

i KvitiiY, 145, 17(>. 

In i , "J'i 
IN * . . I 

II * ! , % I 

I Karat lay, 228, 257, 
; Favn% 2SO, 

1 1 1 <l 4, t 't;f t 

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i KcrnaniN'/,, 1 82. 

! I'Vwmaun, 10. 

; I'rrv. HO, 

i Kii-iitrr, 14H. 
Kii-Mcl, 113. 

^ Knii'h, isf, ij|7. 

, Kiuillay, 1127. 

; KiMt-hri'. 7!, JHl, 140, 142, M3, 1,44, 146, 

; M7, 151, 154, 177, 325, 32(i, 327, 330, 

! Klai-L JIM. 152, 153, 104. 

i Klrrk, van, -Hi. 

iitui,.., 1*00. 
iT,' 70, iHfi. 
, Vujj, 1 UJ f 170. 

KII\, ,111, 37, 40, 138, 152, 109. 

FnmkrnfH'im, 2(10, 272. 

Kmnliliiiid, 20, 21 t 78, 79, 82, 83, 84, 162, 

232, 234, 244, 249, 322, 

j Kn'mv, l.'W, 153. 


FreumU 1 1. 

iMVundlirh, 274, 

I'Yt'y, 15, 344. 

FivyiT, 107, 108, 228. 

Fntlhmdor* 184. 

Frunlt4, 131. 

Frit'drrU'h, 333. 

Krit'clnmiui, 223, 277, 319. 

Fi'H'driclu 330. 

Friend, -10, 132, 133, 100, 280, 291, 33(5, 

341, 348, 349. 
FrifiuU ISO. 

Fl ( nlHtr.s\ 242. 
Ftirsfcijjui, 1JMJ. 


Gaillrf, 241. 

<a IS it /,in, 2fr>. 

<Jai4M, 243, 

(arh 4 P, 104. 

<nrtirj\ I HI, 

< <ar/.aroili-ThurnlaGk, 149. 

GautiiT, 107, 108, ISO, 292, 

<!ayl<-y, 174. 

Ua\-riiHHa<s l, 99, 162, 205, 200, 26;"). 

<Ja/,iai\ :I44, 

Cli'llVkrn, 42. 

('iMwli't\ 25t>. 

CU'Itrl, 2*H), 201. 

<(i'rinatin, IM 191. 

<ifru'*is 1H4. 
UiiVonl, 277. 
<JU1, Km. 
(tirani. 2i>r. 
(i(Yitwal<l, 333. 
<;imlHtuiits SI, 282. 
<UiuH!ipr, llltl 
(JtilM'I, 22H. 
tSfiokfl, 182, 200. 

ki, 100. 
<{tltlMtcnn 140, 141. 

CntibiTK, 132, 
Uuiuluio, 19. 
(ionxalox, 34. 
tJoltHt'.hulk, 142, 149. 
(inwt../., 270, 334. 
(.*nifc'nht*rK 143, 
(Sraftian. 168. 

Urj&ham, 13, 35, 43, 72, 284, 280, 317. 
fimndiH, 171. 
(,'rarit, 20. 
CraHsi, 2(J4. 

<,'ruy, 92, 1 Hi, 142, 144, 181, 220, 280. 
Cirrnv*H 147, 
Uivtfor, 199. 
(Jwtfdry, 320. 
<Jnf!'r, 249, 
(iricHs, 179. 
(irjilith, 147. 
UrilliOiH, 2<HI, 271. 
i f 283. 

Grimnes, 291. 

Grogcr, 155. 

Gros, 340. 

Groschuif, 310. 

Grote, 227. 

Groth, 256. 

Grove, 287. 

Grozca, 108. 

G run berg, 239. 

Griinciaen, 198. 

Gruninach, 47. 

Griinwald, 45. 

Guillaume, 271. 

Guyo, 190, 191, 207, 300, 301, 302, 304. 

HABRK, 57, 81, 82, 89, 00. 

Haborinann, 181. 

llackHpill, 282. 

Hagenacker, 43. 

Halm, 90, 290. 

Hulclaue, 09, 134, 105, 160, 170, 171, 172, 

180, 187, 189. 
Hale, 29, 233. 
Hales, 10, 
Halt, 277. 
HallHtrcim, 200. 
Halhvaoha, 145, 170. 
Halsko, 247, 248. 
.'Hatnburpfor, 16, 334. 

Hamlet, 334. 

, 110. 
n, 30, 31. 
Hauinan, 17. 

llannen, 182. 

Manriot, 328, 329, 330. 

HaiiHon, von, 80. 

Kara, 15. 

Barge r, 09, 105. 

Marker, 116, 280. 

MarrioH, 142, 150, 152. 

Harrow, 322. 

Hartley, 145, 153, 176, 183, 231, 275, 270, 

Hartmann, 01, 229, 256. 

Harvey, 201. 

Hansell, 213. 

Hatcher, 175, 178, 179, 329, 330, 331, 332, 
333, 334. 

Hauaor, 1 14, 200. 

Hautefeuille, 47, 139, 145, 146. 

Hautemuller, 232. 

Haward, 87, 124, 126. 

Hayhurst, 175, 176, 177, 178, 181. 

Hobb, 198. 

Hodloy, 318. 

Hohncr, 239. 

Heine, 208. 

Hclbig, 148. 

H61ier, 107, 108, 113. 

Helmont, van, 156. 

Helouia, 13. 

Hempel, 59, 162. 

Henokoll & Co., 325. 

Henderson, 135, 165. 

Henning, 196, 266, 280. 



Henri, 134. 

Henrich, 136, 161, 207. 

Henriehsen, 271. 

Henriehfion, 332. 

Hemiet, 167, 177, 180. 

Henry, 39, 59, 228, 309. 

Hermans, 186. 

Hernandez, 342, 343. 

Herzberg, 332. 

Herznn;, 133. 

Mettner, 281. 

Heumann, 79. 

He use, 48, 195, 255, 266, 268 

Hewitt, 132. 

Hevdweillor, 274, 275. 

IS eyes, 131, 347. 

Hitfyin, 290. 

Hijidns, ll, 134. 

Hil.U'ard, 77. 

Hill, 117, 134, 152, 153, 159, 164, 186. 

Iimebrand, 10. 

Hiller, 90. 

HhiHbertf, 344. 

Him, 2(U. 

Hise, van, 1 08. 

Ilod^kinson, 22. 

flodsiua.ii, H9. 

I! off, vaift, 312. 

Hoffmann, 327. 

Hofnmnn, ttl, 64, 70, 204, 290. 

Hofmann-Wellenhof, von, 186., 4-1, 193, 194, 105, 196, 266, 279, 

2 SO, 300, 301. 
Holm, 107, 1 15. 
Holmes, 17i>. 

Holt, ':><(, 288, 289. 
Houima, 181. 
Huoke, 10, (51. 
Hopfield, -15. 
Hopkiiwcm, 130, 288. 
Hoppe.Seyler, 55, 50, 57, 181. 
Hoi-hammer, 232. 
Horntmann, 298. 
Honking, 2(>5. 

Houston 2ti2. 

Hiir/eau f ,T42 t 147, 150, 175, 178, 326. 

Howard, 247. 

Hoxton, 29. 

HulHon, 275, 303. 

Huet, 241. 

HiUTner, 37. 

Huirhens, 254. 

Hui?he, HI, 285. 

Htiiett, 15, 231, 203, 314. 

Hull, 21W. 

Humboldi, 99, 205. 

Humphrey, 13. 

HmnphreyH, 177, 272, 

Hunt, UW. 

Huntingdon, 275, 

Huntlv, 1293- 

HI, 207. 

Hutcliinson, 312. 
Huttner, 23. 
Hyde, 332. 

IKEDA, 339. 

Ilosva, 348. 

Ilosvay, 174, 179. 

Ingen-Housz, 169. 

Ingle, 80, 90, 220. 

Inglis, 47, 145, 150, 154, 202, 340. 

Inouye, 314. 

Irvine, 224. 

JACKSON, 239. 

Jacoby, 239. 

Jager, 271, 272, 278. 

Jahn, 146, 148. 

Jakob, 194, 195, 196, 269. 

Jaloustre, 51. 

Jannasch, 142, 149. 

Janssen, 45, 198, 281. 

Jaquerod, 34, 45, 46, 197. 

Jaubert, 24, 248. 

Jeantet, 45. 

Jefiries, 69. 

Jentzsch, 207. 

Jessen, 186. 

Joannis, 63, 229. 

Job, 143. 

Johnson, 72, 135, 140, 177, 295. 

Jolly, 34, 44, 191, 197. 

Joly, 160, 196, 265, 280. 

Jones, 57, 60, 147, 148, 231, 284, 286, 312, 

316, 332, 339, 345. 
Jordan, 232. 
Jordi, 171. 
Jordis, 342. 
Jorgensen, 10. 
Jorissen, 59, 103. 
Jouglet, 150. 
Joule, 29, 260. 
Joulin, 43. 
Joyner, 332. 
Jucld, 268, 330, 339. 
Juhlin, 255, 268. 
Jungfleisch, 22. 
Juritz, 220. 


Kahlbaum, 327. 

Kahlenberg, 280. 

Kailan, 146, 152, 176, 326, 339. 

Kaiser, 249.