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Full text of "Applied electrochemistry"

APPLIED ELECTROCHEMISTRY 



THE MACMILLAN COMPANY 

NEW YORK BOSTON CHICAGO 
SAN FRANCISCO 

MACMILLAN & CO., LIMITED 

LONDON BOMBAY CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, LTD. 

TORONTO 



APPLIED 



ELECTROCHEMISTRY 



BY 



M. DEKAY THOMPSON, PH.D. 
h 

ASSISTANT PROFESSOR OF ELECTROCHEMISTRY IN THE 
MASSACHUSETTS INSTITUTE OF TECHNOLOGY 



gorfc 

THE MACMILLAN COMPANY 
1914 

All rights reserved 



COPYBIGHT, 1911, 

BT THE MACMILLAN COMPANY. 



Set up and electrotyped. Published May, 1911. Reprinted 
April, 1914. 



Nortooot) 

J. 8. Gushing Co. Berwick & Smith Co. 
Norwood, Mass., U.S.A. 



PREFACE 

THE following book was written to supply a need felt by 
the author in giving a course of lectures on Applied Electro- 
chemistry in the Massachusetts Institute of Technology. There 
has been no work in English covering this whole field, and 
students had either to rely on notes or refer to the sources 
from which this book is compiled. Neither of these methods 
of study is satisfactory, for notes cannot be well taken in a 
subject where illustrations are as important as they are here ; 
and in going to the original sources too much time is required 
to sift out the essential part. It is believed that, by collecting 
in a single volume the material that would be comprised in 
a course aiming to give an account of the most important elec- 
trochemical industries, as well as the principal applications of 
electrochemistry in the laboratory, it will be possible to teach 
the subject much more satisfactorily. 

The plan adopted in this book has been to discuss each 
subject from the theoretical and from the technical point of 
view separately. In the theoretical part a knowledge of theo- 
retical chemistry is assumed. 

Full references to the original sources have been made, so 
that every statement can be easily verified. It is thought that 
this will make this volume useful also as a reference book. 

An appendix has been added, containing the more important 
constants that are needed in electrochemical calculations. 

Thanks are due to the following individuals and companies 
for permission to reproduce cuts, or to use the material in the 
text, or for both: the American Academy of Arts and Sci- 
ences ; the American Electrochemical Society ; the Carborun- 
dum Company ; Wilhelm Engelmann ; Ferdinand Enke ; the 
Electric Storage Battery Company; the Engineering and 
Mining Journal; the Faraday Society; the Franklin Insti- 



387459 



VI PREFACE 

tute ; Charles Griffin and Company ; Gould Storage Battery 
Company ; Dr. Eugene Haanel ; the Hanson and Van Winkle 
Company; Mr. Carl Hering; Mr. Walter E. Holland of 
Thomas A. Edison's Laboratory ; International Acheson 
Graphite Company; Wilhelm Knapp; Longmans, Green and 
Company ; Progressive Age Publishing Company ; Dr. E. F. 
Koeber, Editor of the Metallurgical and Chemical Engineer- 
ing ; Julius Springer; Spon and Chamberlain; John Wiley 
and Sons. 



TABLE OF CONTENTS 

CHAPTER I 

PAGES 
COULOMETERS OR VOLTAMETERS 1-12 

1. General Discussion 2. The Silver Goniometer 3. The 
Copper Goniometer 4. The Water Goniometer 5. The Silver 
Titration Goniometer. 

CHAPTER IT 

ELECTROCHEMICAL ANALYSIS 13-29 

1. Nonelectrolytic Methods 2. Electrolytic Methods. 

CHAPTER III 

ELECTROPLATING, ELECTROTYPING, AND THE PRODUCTION OF ME- 
TALLIC OBJECTS 30-42 

1. Electroplating: Nickel Plating ; Copper Plating ; Zinc Plat- 
ing ; Brass Plating ; Silver Plating ; Gold Plating 2. Gal- 
vanoplasty : Electrotyping ; Copper Tubes, Foil, and Wire. 

CHAPTER IY 

ELECTROLYTIC WINNING AND REFINING OF METALS IN AQUEOUS 

SOLUTIONS 43-67 

1. The Winning of Metals: Copper and Zinc 2. The Elec- 
trolytic Refining of Metals: Copper Refining; Nickel Refining; 
Silver Refining ; Gold Refining ; Lead Refining ; Zinc Refining. 

CHAPTER V 

ELECTROLYTIC REDUCTION AND OXIDATION .... 68-79 
1. Reduction 2. Oxidation. 

CHAPTER VI 

ELECTROLYSIS OF ALKALI CHLORIDES 80-136 

1. Theoretical Discussion : The Chemical Action of Chlorine on 
Water and Alkali Hydrate; The Electrolysis of Alkali Chloride on 

vii 



TABLE OF CONTENTS 

PAGES 

Smooth Platinum Electrodes without a Diaphragm; The Electrolysis 
of Alkali Chlorides with Platinized Platinum Anodes; The Electrol- 
ysis of Alkali Chlorides on Carbon Anodes; The Maximum Concen- 
trations of Hypochlorite and the Maximum Current and Energy Yields 
of Hypochlorite and Chlorate; The Production of Perchlorates ; The 
Electrolysis of Alkali Chlorides with a Diaphragm; Decomposition 
Points and Potentials of Alkali Chloride Solutions; Fluorides, 
Bromides, and Iodides 2. Technical Cells for Hypochlorite, 
Chlorate, Hydrate, and Chlorine. 



CHAPTER VH 
THE ELECTROLYSIS OF WATER 137-141 

CHAPTER VHI 
PRIMARY CELLS . 142-151 

CHAPTER IX 

THE LEAD STORAGE BATTERY 152-172 

1. History and Construction 2. Theory of the Lead Storage 
Battery. 

CHAPTER X 

THE EDISON STORAGE BATTERY 173-184 

1. General Discussion 2. Theory of the Edison Storage 
Battery. 

CHAPTER XI 

THE ELECTRIC FURNACE 185-201 

1. General Discussion 2. Electric Furnace Design. 

CHAPTER XII 

PRODUCTS OF THE RESISTANCE AND ARC FURNACE . . . 202-238 

1. Calcium Carbide 2. Carborundum 3. Siloxicon 4. Sili- 
con 5. Graphite 6. Carbon Bisulphide 7. Phosphorus 
8. Alundum 9. Aluminum 10. Sodium and Potassium 
11. Calcium. 



TABLE OF CONTENTS IX 

CHAPTER XIII 

PAGES 

THE ELECTROMETALLURGY OF IRON AND STEEL . . . 239-264 

1. General Discussion 2. The Electrothermic Reduction of 
Iron Ores 3. The Electrothermic Refining of Steel. 

CHAPTER XIV 

THE FIXATION OF ATMOSPHERIC NITROGEN .... 265-287 

1. Introduction 2. Absorption by Calcium Carbide 3. The 
Oxidation of Nitrogen 4. The Synthesis of Ammonia 5. Con- 
clusion. 

CHAPTER XV 

THE PRODUCTION OF OZONE 288-314 

1. General Discussion : The Maximum Concentration; Yield per 
Coulomb for Negative Point Electrode ; Yield per Coulomb for Posi- 
tive Point Electrode ; Yield per Kilowatt Hour for Positive and for 
Negative Points; Theory of Ozone Formation by Silent Discharge; 
The Siemens Ozonizer 2. The Technical Production of Ozone. 

APPENDIX 315-321 

Atomic Weights Electrochemical Equivalents Numerical 
Relation between Various Units Legal Electrical Units. 

NAME INDEX 323-325 

SUBJECT INDEX 327-329 



LIST OF ABBREVIATIONS 

Ann. d. Phys Annalen der Physik. 

Ann. d. Chem. und Pharm. . . Annalen der Chemie und Pharmacie. 

Ann. d. Chim. et de Physique . Annales de Chimie et de Physique. 

B. B Berichte der Deutschen Chemischen Gesell- 

schaft. 
Berg- und Hiittenm. Ztg. . . Berg- und Hiittenmanische Zeitung. 

Chem. News Chemical News. 

Chem. Zeitung Chemiker Zeitung. 

C. R Comptes Rendus des Seances de 1'Academie 

des Sciences. 

Dingler's polyt. J Dingler's Polytechnisches Journal. 

Electrochem. and Met. Ind. . Electrochemical and Metallurgical In- 
dustry. 

Electroch. Ind. Electrochemical Industry. 

Elektrotech. Z Elektrotechnische Zeitschrift. 

El. World Electrical World. 

Eng. and Min. J Engineering and Mining Journal. 

Gilbert's Ann Gilbert's Annalen. 

J. f. prakt. Ch Journal fur praktische Chemie. 

Journ. of the Franklin Inst. . Journal of the Franklin Institute. 

J. Am. Chem. Soc Journal of the American Chemical Society. 

Met. and Chem. Eng Metallurgical and Chemical Engineering. 

Min. Ind Mineral Industry. 

Phil. Mag Philosophical Magazine. 

Phil. Trans Philosophical Transactions. 

Phys. Rev Physical Review. 

Pogg. Ann Poggendorff's Annalen. 

Proc. Am. Acad Proceedings of the American Academy of 

Arts and Sciences. 

Proc. Am. Phil. Soc. .... Proceedings American Philosophical So- 
ciety. 

Proc. Royal Soc. of Edinburgh Proceedings of the Royal Society of Edin. 

burgh. 

Proc. Soc. Arts Proceedings of the Society of Arts, Boston. 

Trans. Am. Electrochem. Soc. . Transactions of American Electrochemical 

Society. 

Z. f. anal. Ch Zeitschrift fur analytische Chemie. 

xi 



Xii LIST OF ABBREVIATIONS 

Z. f. angew. Ch Zeitschrift fiir angewandte Chemie. 

Z. f. anorg. Ch Zeitschrift fiir anorganische Cheraie. 

Z. f. Berg-, Hiittenm.- und Salinen-Wesen. Zeitschrift fiir das Berg-, Hut- 

tenmanische- und Salinen-Wesen in 

preussische Staaten. 

Z. f. Elektroch Zeitschrift fiir Elektrochemie. 

Z. f. phys. Ch Zeitschrift fiir physikalische Chemie. 



APPLIED ELECTROCHEMISTRY 



APPLIED ELECTROCHEMISTRY 

CHAPTER I 

X 

COULOMETERS 1 OR VOLTAMETERS 
1. GENERAL DISCUSSION 

AN important application of electrolysis is the determination 
of the amount of electricity passing through a circuit in a given 
time. According to Faraday's laws, (1) the magnitude of the 
chemical effects produced in a circuit is proportional to the 
quantity of electricity that passes through the circuit, and (2) 
the quantities of the different substances which separate at 
electrodes throughout the circuit are directly proportional to 
their equivalent weights. 2 The first statement is true under all 
conditions, but the second only for the case that a single sub- 
stance is liberated on any given electrode. If several sub- 
stances are deposited together on the same electrode, there is, 
of course, less of each than if only one is deposited. 

The electrochemical constant, or the quantity of electricity 
necessary to deposit one equivalent weight of any substance, 
has been accurately determined by measuring the amount of 
silver deposited for a known quantity of electricity. The 
value of this constant generally accepted is 96,540 coulombs, 
and is accurate to a few hundredths of a per cent. 3 

1 This name was proposed by T. W. Richards, Proc. Am. Acad. 37, 415, (1902). 

2 Le Blanc, Electrochemistry, English translation, p. 42, (1907). 

3 Nernst, Theoretische Chemie, 6th ed., p. 716, (1909) ; Guthe, Bulletin of the 
Bureau of Standards, 1, 362, (1905). 

B 1 



2-- 



' 

"* ALLIED.. ELECTROCHEMISTRY 



It is evident from the above that the amount of electricity 
passing through a circuit can be determined from the amount 
of chemical change produced at any electrode if this chemical 
change can be measured. There are three general methods of 
making this measurement : (1) by weighing the substance de- 
posited or liberated, (2) by measuring its volume, and (3) by 
titration. It seems hardly necessary to call attention to the 
fact that in any coulometer the current can be computed from 
the quantity of electricity that has passed through the circuit, 
if the current has been constant and if the time is measured. 
Current in amperes equals quantity in coulombs divided by 
time in seconds. 

The errors of coulometers are those inherent in the measure- 
ment of weight and volume or in titration, and also those due 
to imperfections in the coulometer itself. The latter may 
come from a variety of causes, such as the liberation of other 
substances than the one assumed, or the loss of the substance 
after deposition and before weighing. The errors of each 
coulometer described below will be pointed out. 

2. THE SILVER COULOMETER 

The silver coulometer is the most accurate of all electro- 
chemical coulometers. It is for this reason that it is used to 
determine the electrochemical constant. It consists of a plati- 
num dish cathode, a neutral silver nitrate solution made by 
dissolving 20 to 40 grams of nitrate in 100 grams of distilled 
water, and a pure silver anode. By weighing the platinum 
dish before and after the current has passed, the amount of 
electricity may be computed from the value of the electro- 
chemical equivalent of silver given above. To obtain the best 
results, the anode should be wrapped in filter paper, 1 in order to 
prevent any silver mechanically detached from the anode from 
falling into the platinum dish, or contained in a porous cup, 
which also separates the anode solution from the cathode. The 
solution from the anode would deposit too much silver on the 

1 Richards, Collins, and Heimrod, Proc. Am. Acad. 35, 143, (1899). 



COULOMETERS OR VOLTAMETERS 



cathode, due to the formation of a complex silver ion, prob- 
ably Ag + , which does not break up at once to the normal ion 
Ag + and 2 Ag, and which, if deposited, would give too great a 
quantity of silver. 2 This is the main source of error, and when 
it is excluded, the mean error of one determination is about 
0.03 per cent, for a deposit 
weighing not less than 
half a gram. 3 The cou- 
lometer used by Richards, 
Collins, and Heimrod is 
shown in Figure 1. 

The solution of silver 
nitrate may be used until 
a deposit corresponding to 
3 grams of silver from 100 
cubic centimeters of solu- 
tion has been reached. 
The current density must 
not exceed 0.2 ampere per 
square centimeter on the 
anode, or 0.02 ampere per 
square centimeter on the 
cathode. The silver ni- 
trate solution must be 
thoroughly washed out 
before weighing, until the 
wash water gives no test 
for silver with hydro- 
chloric acid. The dish is 
then dried and weighed. 

The silver deposit from 
the nitrate solution is crystalline, and does not form a smooth 
coating, and for this reason there is danger of losing some of 
the crystals in washing. Silver can be deposited with a smooth 
surface from the double cyanide of silver and potassium, and it 

2 Richards and Heimrod, Proc. Am. Acad. 37, 415, (1902). 

3 Ostwald-Luther, Hand- und Hiilfsbuch, 3d ed. p. 497, (1910). 




FIG. 1. Porous cup coulometer ( actual size) 

A, glass hook for supporting anode. , glass ring for 
supporting porous cup. O, silver anode. D, porous 
cup. E, platinum cathode. 



APPLIED ELECTROCHEMISTRY 



has been found that a coulometer using this liquid, on exclud- 
ing oxygen, gives accurate results without the danger of de- 
taching any silver in weighing. 4 



3. THE COPPER COULOMETER 

The copper coulometer consists usually of two sheets of 
copper for anodes, with a thin copper sheet hung between 
them as cathode, in an acid solution of copper sulphate. It 
is not so accurate as the silver coulometer for several reasons. 
In the first place, only 0.29 gram copper is deposited to every 
gram of silver. This reduces the percentage accuracy of the 
weight to about one third of the value it would have for an 
equivalent amount of silver. More important than this are 
the chemical reactions that tend to change the weight of 
copper deposited on the cathode from the correct weight. 
The copper cathode dissolves slightly in acid cupric sulphate, 
forming cuprous sulphate : 

Cu + Cu ++ = 2 Cu + , 

thereby reducing the weight of the cathode. This takes place 
to a less extent if oxygen is excluded. On the other hand, in 
a neutral solution the plate gains in weight, due to a covering 
of cuprous oxide coming from hydrolysis of the cuprous 
sulphate. With increasing temperature not only does the 
velocity of the above reaction increase, but also the amount 
of cuprous ions in equilibrium with cupric ions, and conse- 
quently more cuprous ions are deposited. Wherever cuprous 
ions are deposited, the weight of copper is too great, as the 
electrochemical equivalent of cuprous copper is double that of 
cupric. 

The solution generally used in the copper coulometer is that 
recommended by Oettel, 1 consisting of 1000 grams of water, 
150 grams of crystallized copper sulphate, 50 grams of concen- 

* Farup, Z. f. Elektroch. 8, 669, (1902). 
1 Chem. Zeitung, 17, 643, and 677. 



COULOMETERS OR VOLTAMETERS 




FIG. 2. Copper coulometer 



6 APPLIED ELECTROCHEMISTRY 

trated sulphuric acid, and 50 grams of alcohol. The alcohol 
drives back the dissociation of the cupric sulphate, reducing 
the concentration of the cupric ions and therefore of the cu- 
prous ions in equilibrium with them. 2 For ordinary purposes 
the exclusion of air is not necessary. The current density on 
the cathode should lie between 2 and 20 milliamperes per 
square centimeter. The advantages of the copper over the 
silver coulometer are its greater cheapness and the greater 
adhesiveness of the deposit on the cathode. The average error 
of a single determination is from 0.1 to 0.3 per cent. 3 A 
convenient form of the copper coulometer is shown in Fig- 
ure 2. The inside dimensions of the glass vessel are approxi- 
mately 4.3 centimeters in width, 16 centimeters in height, 
and 17 centimeters in length. 

4. THE WATER COULOMETER 

The water coulometer measures the quantity of electricity 
passing through a circuit by the amount of water decomposed 
between unattackable electrodes dipping in a solution through 
which the current flows. The amount of water decomposed 
may be determined by measuring the loss in weight of the 
coulometer, by measuring the total volume of gas produced, 
or by measuring the volume of either one of the gases 
separately. 

The decomposition of water by the electric current was first 
observed by Nicholson and Carlisle l in 1800. In 1854 Bunsen 2 
used a water coulometer in which the loss in weight was deter- 
mined ; and since then others have devised coulometers on the 
same principle. 3 Figure 3 shows a convenient form of the 
apparatus, having a drying tube sealed directly to it ; for be- 
fore leaving the cell the gases must, of course, be thoroughly 

2 Foerster and Seidel, Z. f. anorg. Ch. 14, 135, (1807). 

8 Ostwald-Luther, Hand- und Hiilfsbuch, 3d ed. 497, (1910). 

1 Gilbert's Ann. 6, 340, (1800). 

2 Pogg. Ann. 91, 620, (1854). 

8 L. N. Ledingham, Chein. News, 49, 85, (1884). 



COULOMETEKS OR VOLTAMETERS 



Glass wool 



Sealed joint 



dried so that no water vapor is carried off with them. It is 
evident that this instrument cannot give great accuracy on 
account of the relatively small change 
in weight produced by the passage 
of an amount of electricity equal to 
the electrochemical constant. In 
the case of water the change in 
weight is only 9 grams, as com- 
pared with 31.2 grams of copper 
and 107.9 grams of silver. The 
errors inherent in the instrument 
itself are due to the formation of 
other products than hydrogen and 
oxygen. If a solution of sulphuric 
acid is used between platinum elec- 
trodes, the oxygen liberated on the 
anode contains a certain amount of 
ozone. 4 Persulphuric acid, H 2 S 2 O 8 , 
and hydrogen peroxide, due to the 
oxidation of water by the persul- 
phuric acid, are also produced. The 
production of persulphuric acid is a 
maximum when the concentration of 
the solution is between 30 and 50 
grams of sulphuric acid to 100 
grams of water. 5 For this reason a 
10 to 20 per cent solution of sodium 
hydrate is often used, in which none 
of the above disturbing reactions 
occur. 

The presence of even a small 

amount of salt of a metal with two different valences, such as 
iron, may cause a very large error. Table 1 shows what the 
magnitude of this error is for iron impurities. 6 

4 Schonbein, Pogg. Ann. 50, 616, (1840). 

6 Franz Richarz, Ann. d. Phys. 24, 183, (18oo); 31, 912, (1887). 

e Elbs, Z. f. Elektroch. 7, 261 (1900). 





FIG. 3. Water coulometer 



8 



APPLIED ELECTROCHEMISTRY 
TABLE 1 



IRON CONTENT IN 
PER CENT 


CURRENT DENSITY PER 
SQUARE DM. 


Loss IN DETONATING GAS 
IN PER CENT 


1.0 


2.23 


48.3 


1.0 


0.228 


97.4 


0.1 


6.4 


3.0 


0.1 


0.35 


25.1 


0.01 


2.22 


1.7 




0.360 


6.3 




It is to be noticed that this error is diminished by increasing 

the current density. 

Sulphuric acid of 1.14 specific gravity has been shown by 

F. Kohlrausch 7 to give results 
as accurate as the measurements 
themselves in coulometers 
where the total volume of gas 
is measured. He simultane- 
ously devised a form of coulom- 
eter shown in Figure 4. The 
glass tube is 4 centimeters in 
diameter and is divided into 
units of 5 cubic centimeters. 
The base contains 500 cubic 
centimeters. The anode is 
platinum foil, 4 centimeters 
long and 1.7 centimeters wide, 
placed between two cathodes of 
the same size. To refill the 
tube it is simply turned upside 
down. A thermometer is sealed 
in for determining the tempera- 
ture of the gas. On account of 
the limited volume of this ap- 

FIO. 4. Kohlrausch water couiometer paratus, large quantities of elec- 

7 Elektrotech. Z. 6, 190, (1885). 




COULOMETERS OR VOLTAMETERS 



9 



tricity cannot be measured; it is intended for the measurement 
of currents between 3 and 30 amperes. The relation between 
the volume of gas generated in one second, saturated with 
water vapor at the vapor pressure corresponding to a sulphuric 
acid solution of specific gravity 1.14, and the current is as 
follows: For 20 and a pressure of 72.5 centimeters of mercury, 
one ampere in one second produces 0.2 cubic centimeter of gas, 
including the water vapor. Therefore, under these conditions 
of temperature and pressure, the number of cubic centimeters 
of gas generated per second, when multiplied by 5, gives the 
current in amperes. The corrections for the volume in thou- 
sandths of a cubic centimeter for different temperatures and 
pressure are given in Table 2. 

TABLE 2 

Corrections, in Thousandths of a Cubic Centimeter, for Reducing the Volume of Gas 
generated in One Second to the Value which, multiplied hy 5, gives the Current. 
Specific Gravity of Sulphuric Acid : 1.14 



TEMP. CENTIGRADE 
DEGREES 


700 

mm. 


710 

mm. 


720 

mm. 


730 

mm. 


740 

mm. 


750 

mm. 


760 

mm. 


10 


9 


24 


38 


53 


68 


82 


97 


11 


5 


19 


33 


48 


63 


78 


93 


12 


1 


15 


29 


44 


59 


73 


88 


13 


-4 


10 


24 


39 


54 


69 


83 


14 


-8 


6 


20 


35 


49 


64 


78 


15 


-13 


2 


16 


30 


44 


59 


73 


16 


-17 


-3 


11 


26 


40 


54 


68 


17 


-22 


7 


7 


21 


35 


49 


63 


18 


-26 


-12 


2 


16 


30 


45 


59 


19 


-31 


-17 


-3 


11 


26 


40 


54 


20 


-35 


-21 


-7 


7 


21 


35 


49 


21 


-40 


-26 


-12 


2 


16 


30 


44 


22 


-44 


-30 


-17 


-3 


11 


25 


39 


23 


-49 


-35 


-22 


-8 


6 


20 


34 


24 


-54 


-40 


-26 


-12 


1 


15 


29 


25 


-58 


-45 


-31 


-17 


-4 


10 


24 



10 



APPLIED ELECTROCHEMISTRY 



The following example will illustrate the use of this table. 

Barometer, 754 millimeters of mercury. 

Height of sulphuric acid in tube 112 millimeters of mercury. 
Pressure in gas = 754 - -^ = 745. 
Temperature of gas : 17. 8. 

Volume of gas 198.0 cubic centimeters. 

Correction : + 0.038 x 198.0 = 7.5 cubic centimeters. 

205.5 cubic centimeters. 
Duration of experiment : 39 seconds. 
Therefore in one second 5.27 c.c. of gas were generated. 
Current = 5.27 x 5 = 26.3 amperes. 

> k ._. On comparison with a tangent galvanom- 

X^A eter the current indicated 

YJU by this coulometer was 

found on an average to be 

\ per cent low. 

In order to avoid correc- 
tion for the height of the 

solution, the instrument 

may be made like a Hem- 
pel gas analysis burette, as 

shown in Figure 5. 

A very convenient form 

of water coulometer has 

been devised by F. C. G. 

Miiller, 8 shown in Figure 

6. The whole apparatus 

is placed in a water bath, 

so that the temperature of 

the gas can be determined. 

A is the electrolytic cell 

filled with barium hydrate, 

which does not foam like 

sodium or potassium hy- 
drate. 





Fio. 5. Water cou- 
lometer 



ceiver. 



F is the gas re- ~~ 

mi ,, FiG.6. Miiller's water 

The three-way coulometer 



8 Z. f. d. phys. und chem. Unterricht, 14, 140, (1901). 



COULOMETERS OR VOLTAMETERS 11 

stopcock at the top allows the gas to escape through H when 
no measurement is to be made. By turning the stopcock at a 
given second, the gas passes into H, which is previously filled 
with water to the upper mark. When H is filled with gas, 
the stopcock is turned to allow the gas to pass out H and the 
time noted. This apparatus can thus be left connected in the 
circuit and a measurement made at any time. 

The water coulometer may be transformed into a direct read- 
ing ammeter by a method first applied in 1868 by F. Guthrie. 9 
If the gas is allowed to escape through a small hole, a definite 
pressure in the instrument is developed, depending on the cur- 
rent and size of the hole. The pressure is measured by a 
mercury or water manometer. This same principle has been 
rediscovered by J. Joly, 10 Bredig and Hahn, 11 and Job. 12 In 
Bredig and Hahn's apparatus the gas escapes through capillary 
tubes, and by using a tube with different bores the range of 
the instrument is varied. Their apparatus is accurate to 
about 5 per cent. 



5. THE SILVER TITRATION COULOMETER 

The silver titration coulometer of Kistiakowsky l is some- 
times convenient where the current does not exceed 0.2 ampere 
and where the duration of the experiment does not exceed an 
hour. A silver anode is dissolved in a 10 per cent potassium 
nitrate solution by the passage of the current, and is then 
titrated. In the improved form the silver anode is at the 
bottom of a tube 18 to 22 centimeters long, 3.5 centimeters in 
diameter at the top, and 1 centimeter at the bottom. The 
cathode is of copper and dips in a 7 per cent copper nitrate 
solution to which ^ of its volume of a 10 per cent potassium 

9 Phil. Mag. 35, 334, (1868). 

10 Proc. Royal Dublin Soc. 7, 559, (1892). 

11 Z. f. Elektroch. 7, 259, (1901). 

12 Z. f. Elektroch. 7, 421, (1901). 

i Z. f. Elektroch. 12, 713, (1906). 



12 



APPLIED ELECTROCHEMISTRY 



nitrate solution has been added. This solution 
is contained in a porous cup at the top of the 
tube. After the experiment the potassium 
nitrate solution containing the dissolved sil- 
ver is drawn off and titrated with 0.02 normal 
potassium thiosulphate, and a saturated iron 
alum solution as indicator. The error of a 
single determination may amount to 0.5 per 
cent. 

In the original form, which is the one still 
generally used, the cathode is of platinum and 
dips into a J to ^ normal solution of nitric acid. 
The division between the acid and the nitrate 
is shown in Figure 7 by the dotted line. In 
order to have the silver dissolve with 100 per 
cent efficiency, it should be freshly deposited 
electrolytically ; 2 also, all of the anode should 
be the same distance from the cathode, as shown 
in the figure ; otherwise the current density will 
be too great on the part nearest the cathode, and 
bubbles of gas may be given off. It is conven- 
ient to have the anode made of a platinum spiral 
of the form shown, on which a little more silver 
is deposited electrolytically before a measure- 
be dissolved off in the measure- 

tion coulometer ment. 



F ^S: ment than 



2 Ostwald-Luther, Hand- und Hiilfsbuch, 3d ed. p. 600, (1910). 



CHAPTER II 

ELECTROCHEMICAL ANALYSIS 
1. NONELECTROLYTIC METHODS 

THERE are four different electrical methods of quantitative 
analysis. These are (1) potential measurements, which give a 
means of determining the concentrations of ions too dilute to 
determine gravimetrically ; (2) conductivity measurements, 
which is a method very convenient for determining concentra- 
tions of solutions; (3) titration with a galvanometer in place 
of an ordinary indicator, and finally (4) the ordinary electro- 
analysis, in which the metal is deposited on a platinum electrode 
and weighed. 

The principle of the first method, originally pointed out by 
Ostwald, 1 is as follows : Suppose the concentration of silver 
chloride in its saturated solution is desired. If the electro- 
motive force of the cell 

Ag | T V NAgN0 3 1 T V NKN0 3 1 saturated solution of AgCl | Ag 

were measured, and the concentration ^ of the silver ions in 
the nitrate were known, as it is from conductivity measure- 
ments, the concentration c z of the silver chloride ions could be 
computed by the Nernst formula 



In practice some conducting salt is added to the silver chloride 
solution in order to lower the resistance of the cell. If potas- 

i Lehrbuch, 2d ed. II, 879. 
13 



14 APPLIED ELECTROCHEMISTRY 

sium chloride is chosen, the solubility of silver chloride is 
reduced, but its value in pure water can be computed from this 
result. 2 If potassium nitrate were used, no reduction in the 
solubility would take place. Where the concentration of the 
salt is so small, the ion concentration is very nearly equal to 
the total concentration on account of the fact that the salt is 
nearly 100 per cent dissociated. Other instances where this 
method of measuring ion concentrations has been found use- 
ful are in the determination of the solubility of mercurous 
chloride from the electromotive force of the cell : 

Hg | Hg.CI, in T V NKC1 1 T V NHg 2 N 2 O 6 + HNO 3 1 Hg, 

and from this result the solubility of mercurous sulphate from 
the electromotive force of the cell, 3 

""^ 'Hg. 



and NKNO 



and NKNO 



These examples are sufficient to illustrate the method. Some 
of the errors that attend these measurements may now be men- 
tioned. One difficult}'' is to get different electrodes of the 
same metal to show exactly the same electromotive force when 
placed in the same solution of one of their salts. This seems to 
depend on the surface of the metal, and some method has to be 
used to make them as nearly identical as possible. This can 
often be accomplished by using an electrode covered electrolyti- 
cally with a layer of the metal, or if the metal is more electro- 
positive than mercury, amalgams of equal concentrations may 
be used. 4 The electrolytic solution pressure is thereby some- 
what changed, but by the same amount for each electrode, and 
since the electrolytic solution pressure drops out, the resulting 
electromotive force is unaffected. Another method of obtaining 
constant results is to use the metal in a finely divided form. 
This may be done by depositing electrolytically with a high- 
current density or by decomposing some compound of the metal 

a Goodwin, Z. f. phys. Ch. 13, 641, (1894). 
Wilsmore, Z. f. phys. Ch. 35, 20, (1900). 
4 Goodwin, I.e. p. 676. 



ELECTROCHEMICAL ANALYSIS 15 

in question. 5 Another source of error is the potential at the 
junction of the different solutions, but this can generally be 
either calculated or reduced to an insignificant amount by 
adding some indifferent salt 6 or by connecting the liquids with 
saturated solutions of potassium chloride 7 or ammonium nitrate. 8 

A method based on potential measurement has been worked 
out for determining the amount of carbonic acid in gases. 9 The 
gas bubbles through a solution of bicarbonate, and the result- 
ing hydrogen ion concentration of the solution is determined by 
potential measurements, from which the partial pressure of the 
carbonic acid can be computed. 

The principle involved in determining the amount of sub- 
stance in a solution by conductivity measurement 10 is the 
same as when any other physical property, such as specific 
gravity, is used for the purpose ; that is, the relation between 
the conductivity and quantity of substance in solution must be 
known. These data have already been obtained in a large 
number of cases and have been collected by Kohlrausch and Hol- 
born. If the solution contains a single electrolyte whose con- 
ductivity at given concentrations has already been determined, all 
that is necessary is to interpolate graphically or arithmetically 
in the table. If, however, there is a maximum conductivity, as 
in the case of sulphuric acid, there would be two possible con- 
centrations for a given value of the conductivity. It is easy 
to tell on which side of the maximum such a solution lies by 
diluting a little and redetermining the conductivity. If the 
solution were more dilute than corresponds to the maximum 
value, further dilution would decrease the conductivity ; if less 
dilute, the conductivity would be increased. In case the solu- 
tion has a concentration near that of maximum conductivity, 

5 Richards and Lewis, Z. f. phys. Ch. 28, 1, (1899) ; also Lewis, J. Am. Chem. 
Soc. 28, 158, (1905). 

6 Bugarszky, Z. f. anorg. Ch. 14, 150, (1897). 

7 Bjerrum, Z. f. phys. Ch. 53, 428, (1905). 

8 Gumming, Z. f. Elektroch. 13, 17, (1907). 

9 Bodlander, Jahrb. d. Elektroch. 11, 499, (1904). 

10 See Kohlrausch and Holborn, Das Leitvermogen der Elektrolyte, p. 124, 
(1898). 



16 APPLIED ELECTROCHEMISTRY 

where the determination would be inaccurate, it can be diluted 
enough to remove it from this point, and the contents of the 
new solution determined. From this the concentration in 
the original one can be calculated. 

This method has been shown to be useful in the determina- 
tion of impurities in sugar and of mineral waters. 11 On account 
of the fact that the equivalent weights of the impurities likely 
to be present in mineral waters vary only within certain limits, 
it has been found that the quantity of the impurities can be 
estimated with a fair degree of accuracy from conductivity 
without analyzing the water to see which of the usual impurities 
are present. 

This method is also useful in the case of mixtures of two 
salts when the conductivity of the mixture is the arithmetical 
mean of the single conductivities. This is often the case with 
nearly related compounds, which are generally difficult to sepa- 
rate chemically. For two substances for which this rule holds, 
having at equal concentrations the specific conductivities K 
and jfiQ, the conductivity of a mixture of the same total concen- 
tration would have the conductivitv K = K \P\ + K iP*. By 

Pi+Pt 
this means it has been found possible to analyze satisfactorily 

mixtures of potassium chloride and bromide, and sulphates of 
potassium and rubidium. 12 Conductivity has also been applied 
extensively for the determination of the solubility of very 
insoluble salts. 10 

The use of a galvanometer as an indicator depends for the 
end point either on a sharp change in the resistance of the cell 
containing the solution titrated or in the change in the electro- 
motive force on electrodes dipping in this solution. An example 
of the first case is the titration of silver nitrate with a standard 
solution of potassium chloride. 13 A measured quantity of a 
standard solution of potassium chloride is placed in a beaker 
with two silver electrodes. In series with the two electrodes 

u Reichert, Z. f. anal. Ch. 28, 1, (1889). 

12 Erdmann, B. B. 30, 1175, (1897). 

18 Salomon, Z. f. Elektroch. 4, 71, (1898). 



ELECTROCHEMICAL ANALYSIS 17 

are connected a galvanometer and a source of electromotive 
force, which must be less than the decomposition value of the 
potassium chloride. On closing the circuit, only a very small 
residual current will be detected. On adding a little of the 
silver nitrate to the solution, silver chloride is precipitated, and 
a certain amount of silver ions, corresponding to the solubility 
of the chloride, will be in solution. We now have the cell 

Ag | AgCl solution | Ag, 

which has no decomposition point, but the quantity of silver is 
so small that the large resistance prevents the current from 
increasing to any great extent. As nitrate is added, the 
quantity of silver in solution changes very little until the last 
of the potassium chloride is used up. The first drop of silver 
nitrate in excess now increases the silver ions enormously, and 
there is a corresponding large increase in current, due to the 
reduced resistance of the cell. The following table shows the 
sharpness of the change : 13 



CUBIC CENTIMETERS OF AoNO 8 


GALVANOMETER BEADING 


3.00 


15 


4.40 


20 


5.00 


16 


5.50 


21 


5.60 


20 


5.65 


42 



The use of a galvanometer as indicator when the electro- 
motive force changes suddenly at the end point is illustrated by 
the following examples : 14 Suppose two beakers, one containing 
a tenth normal solution of mercurous nitrate, the other a definite 
quantity of mercurous nitrate solution to be titrated, are con- 
nected by a siphon containing tenth normal potassium nitrate. 
The bottom of each beaker is covered with a layer of mercury 
which makes contact with a platinum wire sealed in the glass. 

w Behrend, Z. f. phys. Ch. 11, 482, (1893). 



18 APPLIED ELECTROCHEMISTRY 

Such a cell would have the electromotive force R T log -l, where 

'2 

e l is the concentration of the mercury ions in the tenth normal 
solution and c z is their concentration in the unknown solution. 
If tfj is equal to c 2 , the electromotive force would be zero, but 
in general e l and <? 2 would be somewhat different, so that there 
would be a reading in a galvanometer connected across the 
terminals of the cell. If a standard solution of potassium 
chloride is now added from a burette to the unknown solution, 
the concentrated <? 2 will be diminished, due to the precipitation 
of the mercury, and consequently the electromotive force will 
increase. As the end point is approached the change in electro- 
motive force for each drop of potassium chloride added will 
be greater and greater, because of the larger percentage change 
in the concentration. With the drop of chloride which throws 
out the last of the mercury, the percentage change will be the 
greatest of all, and there will be a corresponding change in 
the reading of the galvanometer. The quantity of mercury ions 
now in the solution is due to the solubility of the mercunr 
chloride. Since this solubility is diminished by adding a salt 
with a common ion, the electromotive force will continue to 
increase slowly on adding more chloride, but no further sudden 
change will occur. This change then indicates the end point. 
It is evident that this method would serve equally well to 
determine the strength of the chloride and that the titration can 
be carried out, starting with potassium chloride in one beaker in 
place of mercury nitrate. In this case there would be a decrease 
in voltage at the end point instead of an increase. Bromides 
can be titrated as well as chlorides, but a sharp end point is not 
obtained with iodides. 

Since the determination of the end point depends on the 
concentration of the ions, the final volume of the solution must 
be kept within such limits that a drop of the solution from the 
burette will cause a marked change in the galvanometer read- 
ing. Starting with tenth normal solutions, for this reason the 
final volume should not exceed 30 cubic centimeters, and 
therefore not over 10 cubic centimeters of the unknown 



ELECTROCHEMICAL ANALYSIS 



19 



solution should be taken for analysis. Since the end point 
can be obtained only to 0.05 cubic centimeter, this means an 
accuracy of 0.5 per cent. In titrating potassium chloride the 
change in voltage at the end point is from 0.1 to 0.15 volt; in 
the case of the bromide it is 0.2 volt. Silver electrodes and 
silver nitrate can be used in place of mercury and mercury 
nitrates, and by this arrangement it is possible to determine 
directly the iodine in the presence of chloride and bromide, if 
an ammoniacal solution is used. Silver iodide, unlike silver 
chloride and bromide, is nearly insoluble in ammonia. There- 
fore on adding silver nitrate to an ammoniacal solution of 
potassium chloride, bromide, and iodide, only the silver iodide 
will precipitate. When all the silver iodide is precipitated, 
there is a sudden change in the galvanometer reading. On 
acidifying, the combined amount of chloride and bromide may 
be determined. If also the total quantity of silver chloride, 
bromide, and iodide is weighed, the original amount of potas- 
sium chloride, bromide, and iodide can be calculated. This 
procedure, however, is not very accurate for the chloride and 
bromide, as is shown by the following analyses. 14 





GRAMS TAKEN 


AMOUNT FOUND 




GRAMS TAKEN 


AMOUNT FOUND 


KC1 


0.0223 


0.0246 


Kl 


0.0448 


0.0431 


KBr 


0.0359 


0.0314 


KBr 


0.0354 


0.3800 


KI 


0.0662 


0.0666 


KI 


0.0167 


0.0169 




0.1244 


0.1226 




0.0969 


0.0980 



An exactly similar method has been shown to be useful in 
the titration of acids and bases. 15 Neglecting the small poten- 
tials due to the liquid-liquid junctions, the electromotive force 
of the cell 



II. 



acid of 



cone, c 



is given by the equation 



neutral salt 



e= ETlog- 



acid of 
cone. <? 2 



W. Bottger, Z. f. phys. Ch. 24, 253, (1898). 



20 APPLIED ELECTROCHEMISTRY 

assuming complete dissociation. If alkali is now added to 
one of these acids, the hydrogen ion concentration diminishes, 
causing a gradual increase in the electromotive force. As in 
the cases described above, there will be a sudden change in the 
galvanometer reading when the end point is reached. The 
hydrogen electrode is shown in Figure 8, and consists of palla- 
dium-plated gold, which gives more constant val- 
OrV ues than platinized platinum. The concentration 
(f of the hydrogen soon becomes constant in the 
electrode, as it is not absorbed by the gold at all. 
In place of a hydrogen electrode as standard in 
the above cell, a normal electrode would do 
equally well. 

In carrying out a titration, the acid or alkali to 
be titrated is placed in a beaker and the hydrogen 
electrode put in position so that the palladium - 
plated gold is partly immersed. This electrode 
is then connected with the standard electrode and 
with some means for measuring the electromotive 
force; for example, a Lippmann electrometer and 
slide wire bridge. Hydrogen is then bubbled 
F gen 8 eilcu-ode" over tne hydrogen electrode till a constant poten- 
tial is reached, which should require only a few 
minutes, and then alkali or acid, as the case may be, is added 
from the burette. After each addition the liquid is stirred up 
and the potential measured. This will be found to increase 
gradually till the end point is reached, where there will be a 
sudden change in the potential. 



2. ELECTROLYTIC METHODS 

The methods of analysis described above have not come into 
general use. The electrolytic method, on the contrary, is ex- 
tensively employed, and in some cases has entirely displaced 
other methods. It consists in depositing by electrolysis the 
substance to be determined on one of the electrodes in a form 
that can be dried and accurately weighed. A number of 



ELECTROCHEMICAL ANALYSIS 



21 



different cases may be distinguished. A metal is usually 
deposited on the cathode in the pure state or in a mercury 
cathode as an amalgam. Lead and manganese are exceptional 
in that they are deposited on the anode as peroxide. By the 
use of a silver anode, chlorine, bromine, and iodine may be 
obtained and weighed as the chloride, bromide, and iodide of 
silver, though such determinations are not often carried out. 

The possibility of electroanalysis was first pointed out by 
Cruikshank in 1801. It was very little used, however, until 
subsequent to the work of Wolcott Gibbs on the electroanalysis 
of copper and nickel in 1864. 1 ' It has since formed the subject 
of a great number of investigations and has been employed 
extensively in analytical laboratories. A considerable number 
of improvements have been made in electroanalytical methods 
during this time. One of the greatest of these is the saving of 
time by stirring the solution during the electroanalysis, in 
place of trusting to electrolytic migration and diffusion to 
bring the ions to the electrode on which they are to be 
deposited. Table 3 gives an idea of the difference in time 
required for analyses with and without stirring. 2 



TABLE 3 

Average Duration of Electroanalysis with and without Stirring 



METAL 


TIME IN MINUTES WITHOUT 
STIRRING 


TIME IN MINUTES WITH 
STIRRING 


Nickel 


180 


40 


Zinc 


120 


15 


Copper 
Cadmium 


360 
180 


20 
10 


Lead 


60 


15 


Silver 


180 


15 


Mercury 
Antimony 
Tin 


105 
105 
360 


15 
30 

20 



1 A. Fischer, Elektrolytische Schnellmethoden, p. 11, (1908). 

2 A. Fischer, I.e. p. 13. 



22 



APPLIED ELECTROCHEMISTRY 



A second improvement consists in increasing the number of 
metals that can be determined electrolytically, by substituting 
a mercury for a platinum cathode. Mercury was first sug- 
gested for this purpose by Wolcott Gibbs, 3 but not much atten- 
tion has been paid to its use until recently. With a mercury 
cathode the metal deposited is dissolved by the mercury and is 
weighed as an amalgam. E. F. Smith showed that even the 
highly electropositive metals belonging to the alkali arid alka- 
line earth groups can be determined by this means. 3 

In order to explain the theory of electroanalysis, an acid 
sulphate solution of some metal standing below hydrogen in 
the electromotive series, given in Table 4, will first be con- 
sidered. 4 The concentration of the hydrogen ions and metallic 
ions is assumed to be one gram ion per liter. 

TABLE 4 

Electrolytic Single Potential Differences between Elements and a Solution contain- 
ing one Gram Ion of the Element per Liter. The Normal Electrode on the Scale 
Chosen = 0.56 volt 



Magnesium 2.26? 

Aluminum +0.999? 

Manganese +0.798 

Zinc +0.493 

Cadmium +0.143 

Iron +0.16 5 

Thallium +0.045 

Cobalt + 0.173 6 

Nickel ...... +0.323 6 

Tin ...".... <- 0.085 

Lead -0.129 

Hydrogen -0.277 

Copper .... -0.606 



Arsenic < 0.57 

Bismuth <- 0.668 

Antimony <- 0.743 

Mercury 1.027 

Silver -1.075 

Palladium ..... <- 1.066 

Platinum < -1.140 

Gold <- 1.356 

Chlorine 1.680 

Bromine 1.372 

Iodine -0.905 

Oxygen ...... -0.670 



Suppose two platinum electrodes are dipping in this solution, 
and that a gradually increasing electromotive force is applied. 

8 E. F. Smith, Electroanalysis, p. 65, (1907). 

4 Le Blanc, Electrochemistry, English translation, p. 248, (1907). 

6 Calculated from Richards and Behr, Carnegie Institution of Washington, 
publication No. 61, p. 31, on the assumption that normal FeSO 4 is 24 per cent 
dissociated. e Approximately. 



ELECTROCHEMICAL ANALYSIS 23 

At first only a small diffusion current will flow, but when the 
decomposition voltage of the salt is reached, electrolysis will 
begin. The decomposition point is the sum of the potential 
differences at the anode and the cathode. Since the sulphate 
radical does not escape from the solution, the potential at the 
anode will remain nearly constant during the electrolysis, and 
the potential at the cathode at the decomposition point is equal 
to the potential which the precipitating metal would itself 
have in the solution. 7 This will be clear from the following 
considerations. 8 Suppose a metallic electrode dips in a solu- 
tion of one of its salts in which the osmotic pressure of the 
ions of the metal is p. There will be a certain tendency for 
the metal to go into solution as ions, called the electrolytic 
solution pressure, which will be designated by P. Suppose 
that P is less than p, g as must be the case if the metal stands 
below hydrogen. A certain amount of the ions of the metal 
will then be deposited on the electrode, charging the solution 
negatively and the electrode positively. The metallic ions in* 
solution will then be repelled by the positively charged elec- 
trode with a force &, increasing with the quantity of metal 
deposited. This force finally becomes so great that equilib- 
rium is established according to the following equation : 



The potential difference between the electrode and solution 
is then given by the equation 

RT, P 



where R is the gas constant, T the absolute temperature, n the 
valence of the metal, and F the electrochemical constant. Sup- 
pose now the force k is diminished slightly by applying an 
external electromotive force in a direction tending to deposit 
the metallic ions on the electrode. The value of e will be 

7 Le Blanc, Z.c. p. 219. 

8 See H. M. Goodwin, Z. f. phys. Ch. 13, 579, (1894). 

9 There will be no change in the method of the demonstration if 



24 APPLIED ELECTROCHEMISTRY 

changed only slightly from that given by the equation above, 
but the metal will be deposited continuously, because the sum 
of the forces P and k, tending to send the metal in solution, 
is now slightly less than the force jt?, tending to cause the 
metal to deposit. 

As the ions of the metal become more dilute, p becomes less, 
and the potential difference e, as well as the decomposition 
voltage of the solution, will consequently increase in value. 
The potential difference between the solution and the cathode 
eventually becomes so great that the value necessary for the 
deposition of hydrogen is reached. This potential difference, 
e h , is given by the equation 



where 77 is the overvoltage of hydrogen on the metal deposit- 
ing. After this condition has been reached, the metal and 
hydrogen are deposited simultaneously. The following rela- 
tion then holds as long as the electrolysis continues : 



If electrolysis is continued, the overvoltage 77 gradually in- 
creases, due to the increasing proportion of the current used 
to liberate hydrogen, 10 and consequently p becomes less. It is 
evident that the reduction can never be absolutely complete, 
for if p = 0, e would be infinite. 

RT P 

From the equation e = - loef ., it is evident that to 

nF p 

reduce the quantity of metal in solution to a negligible 
amount, for example, to j$fa$ ^ ^ ie original quantity, 



7? T 

the increase in voltage at the cathode will be e log 10000 

F 

= 0.23 volt for a monivalent metal, or half this value for a 
bivalent metal. Monivalent and bivalent metals must there- 
fore stand respectively 0.23 volt and 0.12 volt below the 

10 F. Foerster, Elektrochemie w&jseriger Losungen, p. 183. 



ELECTROCHEMICAL ANALYSIS 25 

potential at which hydrogen would be deposited on the metal 
in question in order to be so completely separated from the 
solution considered. 

In consequence of overvoltage and of the possibility of re- 
ducing the concentration of hydrogen ions, the potential dif- 
ference at which hydrogen is deposited may, under certain 
conditions, be very much greater than that given in table of 
electrolytic potentials. Consequently, metals standing above 
hydrogen in the electrolytic series can be deposited in case the 
overvoltage of metal in question is high and the concentration 
of the hydrogen ions is low. 

It is evident from what has been said that hydrogen plays an 
important role in electrolysis. It acts as a safety valve in pre- 
venting the potential difference at the cathode from rising 
above a certain value. This value depends on the concentra- 
tion of the hydrogen ions and on the overvoltage, and it is 
therefore possible to vary this maximum voltage by changing 
the concentration of the hydrogen ions. For example, the po- 
tential difference of a hydrogen electrode in a normal acid solu- 
tion differs by 0.81 volt from a hydrogen electrode in a normal 
alkali solution. 11 The lower the concentration of the hydrogen 
ions, the higher will be the voltage necessary to deposit hydro- 
gen, and for this reason solutions of low hydrogen ion concen- 
tration must be employed for depositing electropositive metals. 
Such solutions are those containing ammonia, ammonium, or 
sodium sulphide, and potassium cyanide. In these solutions 
the metals form complex salts, and the concentration of their 
ions is greatly reduced, and a greater potential difference is 
also required to deposit metals from such solutions than from 
solutions of their simple salts. Solutions of complex salts are 
of great importance in electroanalysis ; some metals, such as 
iron, nickel, antimony, and tin, can be reduced quantitatively 
only from such solutions. 12 

Two metals can in general be separated in an acid solution 
when they stand in opposite sides of hydrogen in the electro- 
lytic series, for the hydrogen prevents the cathode potential 

11 Le Blanc, I.e. p. 209. 12 Fischer, I.e. p. 31. 



26 APPLIED ELECTROCHEMISTRY 

difference from becoming great enough to deposit the metal 
standing above hydrogen. When both metals are below hydro- 
gen, they can sometimes be separated by keeping the voltage 
below that necessary to deposit the more electropositive metal. 13 
As explained above, if the metal to be reduced is monivalent, 




FIG. 9. Platinum dish for electroanalysis 

the potential difference between it and the solution must be at 
least 0.23 volt less than that of the metal from which it is to be 
separated, while for a bivalent metal a difference of only 0.12 



13 Le Blanc, I.e. p. 



ELECTROCHEMICAL ANALYSIS 



27 



volt is necessary. This applies only when the two metals do 
not alloy with each other ; if they form an alloy, the decompo- 
sition point of each is affected by the presence of the other. 
For this reason it is difficult to separate mercury from other 
metals. 14 

The above theory makes no attempt to explain why some 
metals deposit in a compact form and why others do not. This 
is a very important question in electroanalysis ; for if the deposit 
does not adhere well to the cathode, it cannot be washed and 




FIG. 10. Platinum gauze cathode for electroanalysis 

weighed. The structure of the deposit depends, first of all, on 
the nature of the metal itself. Some metals, such as zinc, 
cadmium, and bismuth, have a tendency to deposit in a spongy 
form. Others, among which is silver, deposit in large crystals. 
The character of the dissolved salt from which a metal is de- 
posited is of great influence on the properties of the deposit. 
In general, metals are deposited in a compact, smooth layer from 

w Fischer, I.e. p. 37. 



28 



APPLIED ELECTROCHEMISTRY 



solutions of a complex salt, which is frequently the only reason 
for using them. 

The temperature of the solution in electroanalysis is of great 




Fio. 11. Mercury cathode for electroanalysis 

importance in the case of complex salts. The velocity with 
which the ions are produced from the complex is not so rapid 
as from the simple salt, but this velocity is increased by an in- 



ELECTROCHEMICAL ANALYSIS 29 

crease in the temperature. 15 In general, the more complex the 
salt, the greater is the effect of high temperature in accelerating 
the reduction. 

The apparatus 16 commonly used in electroanalysis consists in 
a platinum dish cathode 6 centimeters in diameter and 3 
centimeters deep. Figure 9 represents such a dish with a 
rotating anode. In place of a dish, the cathode may be 
platinum gauze. In this case the liquid to be analyzed is held 
in a beaker or separatory funnel, as shown in Figure 10. Figure 
11 represents an arrangement for using a mercury cathode. A 
beaker of 50 cubic centimeters' capacity has a platinum wire 
sealed into the bottom by which contact is made with the mer- 
cury and the copper plate on which the beaker is placed. 

15 Fischer, I.e. p. 34. 

16 The illustrations are taken from Edgar F. Smith's Electroanalysis, P. 
Blakiston's Son and Company (1907). 



CHAPTER III 

ELECTROPLATING, ELECTROTYPING, AND THE PRODUCTION 
OF METALLIC OBJECTS 

1. ELECTROPLATING 

THE object of electroplating is to cover a metal with a layer 
of another metal for the purpose of improving its appearance 
and durability. The principal metals used for the coating are 
nickel, copper, zinc, brass, silver, and gold. 

In plating, the first step is to clean the surface thoroughly, in 
order to make the deposited coating adhere well. In case the 
surface is rough, it must be ground smooth and polished on a 
suitable buffing wheel. The next operation is the removal of 
the grease and oxide from the surface. The grease is removed 
by dipping in a hot solution of sodium hydrate or carbonate. 
The alkali is then washed off, and the object is dipped into a 
bath called a pickle, the purpose of which is to remove the 
oxide and to make it bright. The pickle varies with the metal 
to be treated, since a solution which works well with one metal 
is not necessarily suited to others. Cast iron and wrought iron 
are pickled in a solution made by mixing 1 part by weight of 
concentrated sulphuric acid with 15 parts of water. 1 A 
suitable pickle for zinc is simply dilute sulphuric or hydrochloric 
acid. Copper, brass, bronze, and German silver are treated 
with a preliminary pickle consisting of 200 parts by weight of 

1 Langbein, Electrodeposition of Metals, 4th ed. p. 162. The English 
measures used by Langbein are converted to the metric system when quoted. 
Unless otherwise stated, the formulae given for solutions in this chapter are taken 
from the above work. 

30 



ELECTROPLATING AND ELECTROTYPING 



31 



nitric acid of specific gravity 1.33, 1 part of common salt, and 
1 of lampblack. The last ingredient has for its purpose the 
formation of nitrous acid. After all impurities are removed by 




FIG. 12. Plating tank 

this bath, the object is washed in boiling water so that on re- 
moval it will dry quickly, and it is then immersed in a so-called 
bright dipping bath, to give a bright surface. This is made up 
of 75 parts by weight of nitric 
acid, of specific gravity 1.38, 
100 parts of concentrated sul- 
phuric acid, and 1 part of 
common salt. The object is 
then washed off in water and 
put while wet in the plating 
bath, where all electrical con- 




FIG. 13. Tray for plating small 
objects 



nections should have been 

made so that the plating begins 

immediately. Instead of the acid pickles following the removal 

of grease by alkali, brass is sometimes pickled in a hot solution 

of potassium cyanide, which dissolves the oxides, somewhat 



32 APPLIED ELECTROCHEMISTRY 

more slowly, however, than the acid, but does not alter the 
original polish. After the plating is finished, the object is 
dipped in hot water and put in warm sawdust to dry. 

The tanks used for holding the plating solutions are usually 
of wood and are lined with lead or a mixture of pitch, resin, 
and linseed oil. The anodes are hung on brass bars running 
lengthwise with the tank, and the objects to be plated are hung 
on similar bars between two rows of anodes, in order to plate 
both sides uniformly. This is illustrated in Figure 12. 
Small objects which are to be carefully plated are strung to- 
gether in rows on wires and hung in the bath. Where not so 




FIG. 14. Drum for holding small objects while plating 

much care is required, as in the case of small nails, it is suffi- 
cient to place them in a tray, shown in Figure 13, and hang 
them in the solution, or in a drum whose sides are perforated, 
as in Figure 14. The drum turns on its axle slowly, and the 
current is conducted from the pile of small objects to the axle 
by metal strips. Of course the tray or the axle and metal 
strips are also plated. 

When plating is done on a large scale, the current required 



ELECTROPLATING AND ELECTROTYPING 



33 




34 APPLIED ELECTROCHEMISTRY 

is always supplied by a dynamo, but there are the two other 
following methods, sometimes used for small jobs, which do not 
require a battery or dynamo. If a metal is dipped into a solu- 
tion of a salt of a metal standing below it in the electrolytic 
series, the more electropositive metal will go in solution and 
the more electronegative will be precipitated on the former. A 
well-known example of this is the precipitation of copper on 
iron, when iron is dipped into solution of copper sulphate. 
This is known as plating by dipping. As soon as the metal is 
thinly coated, the action, of course, stops. In case the metal is 
not electropositive enough to precipitate the one in solution, 
the same result can be produced by connecting it with a piece 
of zinc placed in the solution. The zinc is dissolved as the 
negative pole of a battery and precipitates the metal in solu- 
tion on the cathode, which is the metal to be plated. This 
method is known as plating by contact. Neither of these 
methods is used on a large scale. 

Figure 15 shows the plating plant of the National Cash 
Register Company, 2 where nickel plating with nickel, copper, 
silver, and zinc are all carried out. 

Nickel Plating l 

Nickel cannot be deposited from a strongly acid bath, since 
it is above hydrogen in the electrolytic series. The solution 
ordinarily used consists of nickel-ammonium sulphate of the 
formula NiSO 4 (NH 4 ) 2 SO 4 6 H 2 O, with an additional amount 
of ammonium sulphate to increase the conductivity. The 
exact proportions of the salts are not important. Different 
receipts are given, varying from 25 to 50 parts of ammonium 
sulphate to 50 parts of the double sulphate, in 1000 parts of 
water. The solution is made acid enough to redden litmus 
paper faintly by adding sulphuric acid, or citric acid, as some 
receipts specify. This slight acidity is supposed to give a 

2 Met. and Chem. Eng. 8, 275, (1910). 

1 For an account of the origin of nickel plating, see Adams, Trans. Am. 
Electrochem. Soc. 9, 211, (1906). 



ELECTROPLATING AND ELECTROTYPING 35 

whiter nickel than alkaline or neutral solutions. Baths of 
nickel chloride may be used for plating any metal but iron, for 
iron always rusts if plated in a bath of this salt. The anodes 
are of cast or rolled nickel. 

The proper current density at the cathode is 0.6 ampere per 
square decimeter. The whole surface will then be perceptibly 
coated with nickel in two or three minutes, and a few bubbles 
of gas will come off continuously. If the current is too weak, 
the surface becomes discolored. If the current is too strong, 
gas is evolved more violently, and the color of the nickel soon 
turns dark. In large objects the current density is not uniform. 
The more deeply immersed in the solution, the stronger is the 
current, so that unless turned during plating, large objects 
would receive a thicker coating on the surface that is deepest 
in the tank. Iron is sometimes copper plated to prepare it for 
nickel plating. This is supposed to make the nickel adhere 
better, but nickel adheres perfectly well to iron if the surface 
is properly cleaned. 2 

Copper Plating 

The metals usually copper plated, such as zinc, iron, and tin, 
are more electropositive than copper. If these are dipped 
into a bath of copper sulphate, they are coated immediately 
with copper. The copper, however, frequently comes down in 
a spongy form that does not adhere well, so that plating from 
such a bath is impossible. It is therefore necessary to reduce 
the concentration of the copper ions to such an extent that the 
copper will be relatively more electropositive than the metal to 
be plated, without at the same time reducing the total amount 
of copper in the solution. This is accomplished by using 
the double cyanide of copper and potassium of the formula 
KCu(CN) 2 . The only copper ions present come from the dis- 
sociation of the anion Cu(CN) 2 , which is very slight. Copper 
will therefore not be precipitated from this solution by zinc or 
any other metal that is to be plated. The solution can be made 

2 Langbein, I.e. p. 203. 



36 APPLIED ELECTROCHEMISTRY 

up by dissolving cuprous cyanide in potassium cyanide to form 
a 3 to 8 per cent solution, or the double cyanide may be used. 
In either case 0.2 per cent potassium cyanide and from J to 1 
per cent sodium carbonate is added. 3 The object of the car- 
bonate is probabty to increase the conductivity, that of the free 
cyanide to dissolve the anodes more readily. In case the 
cuprous cyanide is prepared by starting with a cupric salt, the 
latter must be reduced to the cuprous state before adding 
the cyanide; otherwise poisonous cyanogen would be liberated. 
Sodium sulphite is generally used for this purpose. The 
copper cyanide bath is heated by a steam coil to 50 to 60 C. 
and electrolyzed with such a high current density that there is 
a violent evolution of gas. Copper plating is used not only as 
a preliminary coating for other metals, but largely also for a 
final ornamental covering for iron. Various colors are then 
produced on the copper by dipping into a bath of sodium sul- 
phide, producing the so-called oxidized copper. 

Zinc Plating 

A zinc covering is very useful as a protection for iron. It 
has the advantage over tin for this purpose that it is more 
electropositive than iron, so that in case a part of the iron 
becomes exposed and wet, zinc tends to dissolve in place of the 
iron. Iron is covered with zinc by the two methods of electro- 
plating and of dipping in a bath of melted zinc. A third method, 
called sherardizing, consists in heating objects in zinc dust to 
300 C. 1 The zinc deposited electrolytically is not so bright 
and pleasing in appearance as the dipped zinc, but it has 
been shown to protect the iron much more thoroughly. 2 A 
good solution for zinc plating is 200 grams of zinc sulphate, 
ZnSO 4 7 H 2 O, 40 grams of sodium sulphate, Na 2 SO 4 - 10 H 2 O, 
and 10 grams of zinc chloride per liter, slightly acidified with 
sulphuric acid. The current density is from ^ to 2 amperes per 

8 Haber, Grundriss der technischen Electrochem. p. 283. 

1 Electrochein. and Met. Ind. 5, 187, (1907). 

8 Burgess, Electrochem. and Met. Ind. 3, 17, (1905). 



ELECTROPLATING AND ELECTROTYPING 37 

square decimeter. 3 The anodes are of zinc. Since a little 
more zinc dissolves than is deposited, the solution would lose 
its acidity unless a small amount of sulphuric acid is added as 
it is used up. The resistance may be reduced by warming to 
40 or 45 C. 

Brass Plating 

In order to cause copper and zinc to deposit simultaneously, 
it is necessary that the metals should be dissolved in a solution 
in which a zinc and a copper plate would have potentials nearly 
equal. This is the case in a cyanide solution. By replacing 
half of the copper cyanide in the bath given above by zinc cya- 
nide, a suitable bath for brass plating is obtained. Brass anodes 
are used. If a current density of only 0.1 ampere per square 
decimeter is used, only a small amount of zinc is deposited with 
the copper ; with 0.3 ampere per square decimeter, however, the 
deposit contains only 80 per cent of copper. Increasing the 
current density changes the composition of the brass only 
slightly, though the color becomes greenish. 1 

There is quite a large resistance to be overcome in deposit- 
ing both copper and zinc from their cyanide solutions, as meas- 
ured by the potential difference that must be produced between 
the solution and the cathode. This potential difference is 
found to be greater than the potential of the metal dipping 
into its cyanide solution when no current is flowing, and this 
resistance increases with the current density, so that the poten- 
tial is soon reached at which hydrogen is deposited on the cop- 
per or zinc cathode, in place of the metal. 2 

Zinc and copper are deposited together from a solution of 
zinc and copper cyanides considerably below the potential of a 
pure zinc electrode, which shows electrolytic brass is an alloy 
and not a mixture of particles of pure copper and pure zinc. 2 

8 Foerster, Elektrochemie wasseriger Lbsungen, p. 255. 

1 Foerster, I.e. p. 253. 

2 Spitzer, Z. f. Elektroch. 11, 367, (1905). 



38 APPLIED ELECTROCHEMISTRY 

Silver Plating 

The double cyanide of potassium and silver is universally 
used for silver plating, because of the smooth deposit obtained 
from this solution. As stated in Chapter I, silver is deposited 
from a nitrate solution in a granular form entirely unsuited for 
plating. A solution containing from 1 to 5 per cent silver, 
as potassium silver cyanide, KAg(CN) 2 with | per cent of free 
potassium cyanide, has been found satisfactory. 1 Too little or 
too much free cyanide causes a bad color in the deposit. The 
anodes are silver, and the current density on the cathode is 
from 0.15 to 0.5 ampere per square decimeter. Silver is de- 
posited only on a copper surface. Other metals than copper 
or copper alloys which are to be silver plated are first copper 
plated. In order to make the silver adhere to this surface it 
must be amalgamated before plating. This is accomplished by 
dipping into a quicking bath, consisting of a solution of 30 
grams of the double cyanide of potassium and mercury, 
K 2 Hg(CN) 4 , and 30 grams of potassium cyanide, in one liter 
of water. Articles are washed after quicking and placed im- 
mediately in the silver-plating bath. 

Grold Plating 

The solution used for gold plating consists of the double 
cyanide of gold and potassium, KAu(CN) 2 . This can be pre- 
pared by precipitating gold with ammonia in the form of ful- 
minating gold, AuNH NH 2 + 3 H 2 O, from a solution of gold 
chloride. This is washed and dissolved in potassium cyanide, 
and the ammonia boiled off. The concentration of gold varies 
between 0.35 and 1 per cent of gold, with twice as much potas- 
sium cyanide. 1 The anodes are of gold, and the current density 
on the cathode is about 0.2 ampere per square decimeter. Gold 
plating is carried out in both hot and cold baths. The metal 
deposited from a hot solution is more dense, uniform, and of a 
richer color. 

i Haber, I.e. p. 284. 
i Haber, I.e. p. 287. 



ELECTROPLATING AND ELECTROTYPING 39 

2. GALVANOPLASTY 

Galvanoplasty, or the art of reproducing the forms of objects 
by electrodeposition, was discovered by Jacoby of Petersburg 
in 1838. It is now used extensively for electrotyping and the 
production of copper tubes and of parabolic mirrors. 

Electrotyping 

The first operation in making an exact duplicate of type set 
up ready for printing is to take an impression of the type in 
wax. The wax sometimes used is ozokerite. The thickness of 
the sheet of wax used for the purpose is about half an inch. 
After this has been carefully inspected to see that every letter 
is perfect, fine graphite powder is well worked into the surface 
by soft brushes. This is done in several operations, by machines 
and by hand. Copper sulphate is then poured over the surface 
and iron powder sprinkled over it to produce a thin layer of 
copper, which will make the whole surface more conducting than 
the graphite could do. This is an example of the use of plating 
by contact, explained above. The sheet is then hung in an acid 
copper sulphate bath and electrolyzed for an hour and a half. 
It is then removed from the tank, and the wax is warmed and 
separated from the thin copper sheet. The copper is next backed 
to give it mechanical strength by pouring on it an alloy of lead 
and antimony. The subsequent purely mechanical operations 
of making the sheet perfectly level, so that each letter will print, 
and of mounting them on wood need not be described in this 
place. The advantages of electrotyping are the saving of wear 
on the type, and the fact that a small stock of type will prepare 
unlimited number of pages ; for when once a page is electro- 
typed, the type used for preparing this page may be used over 
again for another. Nearly all books are now printed in this 
way. 



40 



APPLIED ELECTROCHEMISTRY 



Copper Tubes, 1 Foil, and Wire 

Tubes are produced by depositing copper evenly on a cylin- 
drical cathode, and the copper is removed when it has become 
sufficiently thick. In order to keep the outer surface of the 

tube smooth, it must be pol- 
ished during the electrolysis; 
this is done in the Elmore 2 
process by means of an agate 
wheel whose edge bears on 
the tube, as shown in Figure 
16. The wheel turns on its 
axis and polishes the surface 
over which it travels. In 
the process of the Societe 
des Cuivres de France, the 
polishing is obtained by 
allowing two tubes to rotate 







FIG. 16. 



Agate wheel for polishing tubes 
during electrolysis 



in contact with each other. 
Polishing not only keeps the surface smooth, but also makes 
the use of higher current densities possible. 

The tubes made by the Elmore process are usually 3 meters 
long and vary up to 1.6 meters in diameter. 3 In order to sepa- 
rate the finished tube from the axle, the surface of the axle 
must be specially prepared so as to conduct and yet not make 
the contact with the copper deposited too intimate. This may 
be done by slightly oxidizing the metal on which the copper is 
precipitated. The tube can then be worked loose by pressure. 

Numerous patents have been taken out for the production of 
copper wire, but only those would be of special interest which 
have proved their value in actual use. It is not apparent, how- 
ever, from an examination of the literature that any electrolytic 
process for making copper wire is in actual use, and the same 



1 See Pfannhauser, Die Herstellung von Metallgegenstanden auf Elektro- 
lytischem Wege, Engelhardt Monographs, Vol. 6, (1903). 

2 Electrochemist and Metallurgist, 3, 151, (1903). 
Pfannhauser, I.e. p. 109. 



ELECTROPLATING AND ELECTRO-TYPING 41 

is true in the case of metal foils. Nevertheless a few of the best 
known patents will be described. 

In 1891, J. W. Swan patented a method of producing copper 
wire, which consists in depositing copper on a wire so as to 
thicken it, and in then drawing down the wire to the original 
size. The apparatus is so planned that this is a continuous 
process. Saunders has patented a method in which the copper 
is deposited on a conducting spiral wound on a drum. The 
wire is stripped off when sufficiently thick, and is then drawn 
down. 

For the production of metal foil, Reinfeld's patent calls for 
an oxidized nickel cathode. When a thin deposit of metal has 
formed, it can be stripped off. The principle of Endruweit's 
method is the same. The cathode is a metal ribbon which passes 
through an oxidizing solution, then through a bath for clean- 
ing, after which the metal foil is deposited upon it. 

Besides the production of tubes the only other galvanoplastic 
industry which is of importance is the production of parabolic 
mirrors. 4 This process has been worked out by Sherard Cow- 
per- Coles. It saves the expensive grinding of a parabolic surface 
for each mirror, for by this method any number of parabolic mir- 
rors can be produced from one mold. The details of the pro- 
cess are the following : First a perfectly parabolic glass surface 
is prepared by pressing a glass plate about 3 centimeters thick, 
and hot enough to be soft, into a cast-iron mold of approxi- 
mately a parabolic form. The glass surface which was next 
the iron is now made perfectly parabolic by polishing on a 
lathe with more refined means as the surface approaches nearer 
to perfection. The next step is to clean the surface and cover 
it with a thin layer of metallic silver by the ordinary process 
used in silvering. The glass form, covered on the parabolic 
side with silver, is then placed in a copper sulphate bath, ro- 
tated at the rate of five times a minute, and copper plated. 
The object of the copper is to give the mirror mechanical 
strength. In order to separate the silver and copper from the 
glass, they are placed in a water bath and heated to 50 C. 

4 See Coles, Engelhardt Monographs, Vol. 14, (1904). 



42 APPLIED ELECTROCHEMISTRY 

The unequal expansion easily separates the glass from the 
metal. The concave side is now a perfect mirror, but the 
silver would soon tarnish and must therefore be protected. 
For this purpose a thin layer of platinum is deposited on the 
silver electrolytically. The solution used for platinizing is 
ammonium platinic chloride in sodium citrate. The only pro- 
cess that now remains to make the mirror complete is its 
mounting, the description of which in this place is unnecessary. 



CHAPTER IV 

ELECTROLYTIC WINNING AND REFINING OP METALS IN 
AQUEOUS SOLUTIONS 

1. THE WINNING OF METALS 

ATTEMPTS have been made to extract metals from their ores 
by electrolyzing the ore as an anode, in the hope that it would 
dissolve and be deposited at the cathode in the pure state. No 
such process has ever been successful, but as failures are in- 
structive, the three best known processes for the electrolytic 
winning of metals will be briefly described. 

An attempt to put the Marchese process in operation is 
described by Cohen. 1 The matte from which the copper was 
to be won had the following composition: 

Copper 17.20 per cent 

Lead 23.70 per cent 

Iron 29.18 per cent 

Sulphur 21.03 per cent 

SO 3 0.69 percent 

Silica 0.88 per cent 

Silver 0.062 per cent 

The solution was obtained by treating a matte similar to the 
above with dilute sulphuric acid, and consisted principally of 
copper and ferrous sulphate. On electrolyzing, copper de- 
posits on the cathode and copper and iron are dissolved at the 
anode as sulphates. In order to make the oxidizing power of 
ferric sulphate available, the matte from which the solution is 

i Z. f. Elektroch. 1, 50, (1894). 
43 



44 APPLIED ELECTROCHEMISTRY 

made is treated with the electrolyte in which ferric sulphate 
has accumulated. The ferric sulphate is reduced to ferrous 
sulphate, and cuprous sulphide and oxide is changed to copper 
sulphate. The solution is then returned to the electrolyzing 
baths. 

Favorable results were obtained in the laboratory in Genoa, 
and on a larger scale at Stolberg from February to April, 1885. 
The copper obtained was 99.92 per cent pure. A large plant 
was then built to produce 500 to 600 kilograms of copper in 24 
hours with 58 vats, 2.2 meters long, 1 meter deep, and 1 meter 
wide. At first all expectations were realized. The baths 
worked well and the copper produced was pure. Within a few 
days, however, the voltage across the baths began to rise, in 
some cases to 5 volts. This was due to the deposition of sul- 
phur on the anode and the disintegration of the anode due to 
the dissolving of the copper and iron. Large pieces became 
detached from the anode and fell to the bottom of the tank, 
filling up the space between anode and cathode and producing 
a short circuit. The copper also became impure, containing 
antimony, bismuth, lead, iron, zinc, and sulphur. Insoluble 
lead electrodes were then tried, but the polarization due to the 
formation of lead peroxide was excessive, and the yield in cop- 
per fell to 60 per cent of the theoretical amount. The Siemens 
and Halske process was then tried by the same company. The 
principal difference between this and the Marchese process is 
the use of insoluble anodes and the separation of anode and 
cathode by a diaphragm. Copper is deposited from a solution 
containing ferrous sulphate and copper sulphate. The solution 
then circulates to the anode, where ferrous sulphate is oxidized 
to the ferric state. The oxidized solution is then used to dis- 
solve more copper from the ore. For three months an attempt 
was made to carry out this process, but it was finally given up, 
partly at least on account of mechanical difficulties, such as the 
tearing of the diaphragm and disintegration of the carbon 
anodes. 

The Hoepf ner 2 process is similar in principle to the Siemens 

2 Z. f. angew. Ch. p. 160, (1891); Chem. Zeitung p. 1906, (1894). 



REFINING OF METALS IN AQUEOUS SOLUTIONS 45 

and Halske process. The unroasted ore is dissolved by cupric 
chloride, and the cupric chloride is reduced to cuprous chloride. 
This is kept in solution by sodium chloride. The action of the 
cupric chloride is the following : 3 

Cu 2 S + 2 CuCl 2 = 4 CuCl + S. 

The solution containing cuprous chloride is electrolyzed in 
the cathode compartment, where it loses part of its copper. The 
solution then circulates to the anode compartment, from which 
the cathode compartment is separated by a diaphragm, arid the 
remaining copper is oxidized to cupric chloride. The anode 
solution is then ready for treating the ore a second time. This 
process was also tried on a large scale, but seems to have failed 
largely on account of mechanical difficulties, especially with the 
diaphragm. 

The Winning of Zinc 

Zinc is one of the few metals in the winning of which elec- 
trolysis may take an important part. This is due to the fact 
that in the ordinary metallurgical process a loss amounting 
sometimes to 25 per cent of the metal occurs. 1 Only under 
peculiar circumstances is zinc refined by electrolysis, on account 
of the fact that commercial zinc never contains noble metals, 
and also because there is not much demand for zinc of a high 
degree of purity. 2 

In either a refining or a winning process it is of the first 
importance to find the conditions under which a smooth deposit 
of the metal can be obtained. 

Under certain conditions zinc is deposited in a spongy form 
that cannot be melted down on account of its tendency to 
oxidize. 3 The nature of sponge zinc is still unknown, 4 though 
the conditions under which it forms and the ways to avoid it 

8 See Blount, Practical Electrochemistry, p. 81, footnote. 

1 Foerster, Elektrochemie wasseriger Losungen, p. 289. 

2 Giinther, Die Darstellung des Zinks, p. 26. 

8 Mylius and Fromm, Z. f. anorg. Ch. 9, 144, (1895). 
4 Foerster, I.e. p. 291. 



46 APPLIED ELECTROCHEMISTRY 

have been the subject of numerous investigations. The factors 
which determine the character of the deposit are the tempera- 
ture, the current density, the concentration of the solution, and 
the impurities present. 

From a dilute solution of zinc sulphate, the zinc is always 
deposited in a spongy state 6 with a simultaneous evolution of 
hydrogen. With a low current density even in a strong solu- 
tion the same is true. High temperature, 6 oxidizing agents, 
and metals more electronegative than zinc 7 cause the forma- 
tion of sponge. A slight acidity tends to prevent the sponge 
from forming. 8 Therefore the conditions to obtain zinc in a 
compact form are high current density, low temperature, a con- 
centrated, slightly acid solution, and the absence from the solu- 
tion of oxidizing agents or more electronegative metals than 
zinc. As to the limits of current density allowable, different 
results have been obtained by different observers. According 
to Mylius and Fromm, 9 the current density must be at least 
one ampere per square decimeter to prevent the formation of 
spongy zinc, while Hasse 10 obtained solid deposits with one 
third this density. The strength of the solution is not given. 
Kiliani's 11 deposits were spongy at a current density of 2.7 am- 
peres per square decimeter, from a zinc sulphate solution of 
specific gravity 1.38. Nahnsen seems to have investigated the 
condition of deposit with regard to temperature and current 
density more systematically than any one else. He obtained 
the following results : 

6 Kiliani, Berg- und Huttenm. Ztg., 1883, p. 250. 

6 Nahnsen, Berg- und Huttenm. Ztg. 1891, p. 393. 

7 Mylius and Fromm, I.e. p. 165. 

8 Mylius and Fromm, I.e. p. 167. 

9 Mylius and Fromm, I.e. p. 169. 

10 Z. f. Berg-, Htittenm- und Salinenwesen, 45, 327, (1897). 

11 Kiliani, I.e. p. 251. 



REFINING OF METALS IN AQUEOUS SOLUTIONS 
TABLE 5 



47 



AMP. PER SQ. METER 





10 


20 


80 


10 
50 


Firm 
Firm 


Incipient 
sponginess 
Spongy 


Spongy 
Incipient 


Spongy 
Spongy 


100 


Firm 


Firm 


sponginess 
Spongy 


Incipient 


150 

200 


Firm 
Firm 


Firm 
Firm 


Firm 
Firm 


sponginess 
Spongy 
Firm 



In the winning of zinc by electrolysis, the steps are to roast 
the ore if it is insoluble, to dissolve the resulting product, and 
to deposit the zinc from the solution by electrolysis with in- 
soluble anodes. A process devised by Hoepfner to carry out 
the winning of zinc in this way was in operation for a while in 
Fiirfurth, Germany, and is now in operation in Hruschau, 
Austria, and at the works of Brunner, Mond, and Company, 
at Winnington, England. 12 The process consists in electrolyz- 
ing zinc chloride with carbon anodes, separated by a diaphragm 
from the cathode. 13 One great difficulty is to obtain a 
diaphragm that will last, and it seems doubtful if this problem 
has yet been satisfactorily solved. The chlorine obtained 
from the anode compartments is collected and used in making 
bleaching powder. 1 * 

2. THE ELECTROLYTIC REFINING OF METALS 
Copper Refining 

The object of copper refining is to get as pure a copper as 
possible for electric conductors, since a very small amount of 
impurity lowers the conductivity materially, 1 and also to ob- 
tain the gold, silver, and other impurities. 

12 Kershaw, Electrometallurgy, p. 272. 

18 For a detailed description see GUnther, I.e. 

14 Kershaw, I.e. p. 273. * Addicks, Electrochem. Ind. 1, 580, (1903). 



48 APPLIED ELECTROCHEMISTRY 

In copper refining, copper anodes containing only a small 
percentage of impurities are electrolyzed with the proper 
current density in an acid copper sulphate bath of suitable 
concentration. The copper and the soluble impurities, which 
are not more electronegative than copper, dissolve, while the 
insoluble impurities become detached from the anode and fall 
to the bottom of the tank, forming what is known as anode 
mud or slime. The soluble impurities gradually accumulate 
in the solution till purification is necessary. As long as the 
impurities are below a certain concentration in the solution, the 
copper deposited on the cathode is of much greater purity than 
that of the anode. The reason the impurities in solution are 
not deposited when dilute is that the voltage drop from solu- 
tion to cathode has not reached the decomposition point of 
these ions. The decomposition point of an ion changes with 

its concentration by the amount ' volt at 17 C., where n 

n 

the valence of the metal, for a change in concentration of the 
ion in the ratio of one to ten. As the concentration of any 
given ion increases, its decomposition point is gradually lowered 
until it equals the potential difference between the solution and 
the cathode. At this point it is deposited with the copper. 
But not all of the impurities found in the cathode are deposited 
from the solution. Some are taken up from the slime, of which 
a certain amount is always suspended in the solution, on account 
of the circulation of the electrolyte. This is true in the case 
of silver and gold. 2 

It will be interesting next to see what the impurities of 
anode copper commonly are, how they behave when the anode 
dissolves, and what impurities are deposited on the cathode. 
The following table gives a representative composition of 
anodes for American refineries : 

Copper 98-99.5 per cent 

Silver to 300 oz. per ton 

Gold to 40 oz. per ton 

Arsenic to 2 per cent 

2 Addicks, Electrochem. and Met. Ind. 4, 16, (1906). 



REFINING OF METALS IN AQUEOUS SOLUTIONS 



49 



with small amounts of antimony, bismuth, iron, nickel, sulphur, 
selenium, tellurium, and silicon. 

A more specific case is given in the following tables, showing 
the composition of the anodes and cathodes at the Great Falls 
and the Anaconda refineries. 3 

COMPOSITION OF ANODES IN PER CENT 





GREAT FALLS 


ANACONDA 


Copper . 


99 27 


99 25 


Arsenic and antimony . 


07 


10 




61.40 


90.00 


Oz. gold per ton 


0.22 


0.50 









For comparison the cathodes are given below. 

COMPOSITION OF CATHODES IN PER CENT 





GREAT FALLS 


ANACONDA 


Copper . 


99.95 


99.96 


Arsenic 


0012 


0009 




0.0033 


0.0023 


Oz. silver per ton 


1.0 


0.25 









The behavior of these impurities in the anode under the 
action of the current was first determined by Kiliani. 4 His 
experiments were carried out with a constant current density 
on the anode of 20 amperes per square meter and with a solu- 
tion of 150 grams of copper sulphate and 50 grams of concen- 
trated sulphuric acid per liter. His results will be briefly 
recapitulated. Excepting the above statement regarding cur- 
rent density and concentrations, his method of experimenting 
is not indicated. 

Cuprous oxide is not attacked by the current, but goes into 
the slime, where it is slowly dissolved, making the bath richer 
in copper and poor in sulphuric acid. 

8 H. O. Hofman, Electrochem. Ind. 1, 416, (1903). 

4 Berg- und Huttenm. Ztg. 1885, pp. 249, 261, and 273. 



50 APPLIED ELECTROCHEMISTRY 

Copper sulphide and selenium sulphide go into the slime. 

Silver, gold, and platinum go into the slime. 

Bismuth and bismuth oxide go partly into the slime and 
partly into solution, from which they are precipitated as a basic 
salt. 

Tin goes into solution and precipitates, on standing, as basic 
salt. 

Metallic arsenic goes into solution as arsenic acid. If pres- 
ent to less than one per cent in the anode, it goes more rapidly 
into the slime. 2 

Antimony behaves like tin. 

Lead goes into the slime as insoluble sulphate. 

Iron, zinc, nickel, and cobalt are dissolved by the current 
and remain in solution. 

A common composition of the slime is the following: 2 

40 per cent silver, 

2 per cent gold, 
25 per cent copper, 

5 per cent selenium and tellurium, 
10 per cent arsenic and antimony, 
18 per cent lead, silicon, sulphuric acid, etc. 

The slimes at Great Falls and Anaconda are the following : 3 



GBEAT FALLS 


ANACONDA 


18 per cent copper 
15,000 oz. of silver per ton 
38 oz. of gold per ton 


10 per cent copper 
18,000 oz. of silver per ton 
100 oz. of gold per ton 



The large amount of copper in the slime is due to part of the 
dissolving in the cuprous state and then breaking up into 
cupric ions and finally divided copper according to the 
equation : 

2 Cu+ = Cu+ + + Cu. 5 

The slimes are worked up for the gold, silver, copper, and 
arsenic. The gold and silver have to be purified, and for this 

* Foerster, Z. f. Elektroch. 3, 497, (1907) ; Wohlwill, ibid. 9, 311, (1903). 



REFINING OF METALS IN AQUEOUS SOLUTIONS 



51 



reason copper refineries sometimes have a plant for silver 
refining. 6 

The electrolyte used in copper refining consists of a solution 
of copper sulphate and sulphuric acid. The quantity of cop- 
per sulphate (CuSO 4 + 5 H 2 O) varies between 12 and 20 per 
cent, the acid between 4 and 7 per cent. 7 Table 6 gives the 
conductivities per centimeter cube of two acid copper sulphate 
solutions, one containing approximately the smallest amounts 
of salts and acid used, and the other, the largest amounts. 8 

TABLE 6 



TEMP. CENTIGRADE 


CONDUCTANCE OF A SOLUTION CONTAINING 


3.75% H 2 S0 4 
12.5% CuS0 4 5 H,0 
Spc. gr. at 22.2, 1.007 


9.2% H,S0 4 
18.3%CuS0 4 -5H 2 
Spc.gr. at 21.2, 1.199 


25 
40 
60 


0.1573 
0.1752 
0.1895 


0.3260 

0.3754 
0.4252 



This shows the limits between which the conductance of a 
copper sulphate solution used in copper refining would proba- 
bly lie. The actual composition of the baths at Great Falls 
and Anaconda are the following : 



GREAT FALLS 



ANACONDA 



150 grams sulphuric acid per liter 
40 grams copper per liter 



170 grains sulphuric acid per liter 
42 grams copper per liter 



A small amount of hydrochloric acid is also added to prevent 
the solution of silver and antimony, as well as to produce a 
smoother deposit on the cathode. Where a current density as 
low as ten amperes per square foot is employed, as at Anaconda, 

6 Easterbrooks, Silver Refining Plant of the Raritan Copper Works, Electro- 
chem. and Met. Ind. 6, 277, (1908). 

7 Ulke, Die Elektrolytische Raffination des Kupfers, p. 42, (1904). 

8 Thompson and Hamilton, Trans. Am. Electroch. Soc. 17, 292, (1910). 



52 



APPLIED ELECTROCHEMISTRY 



the electrolyte can be used for many years without purification, 9 
while with a 60 per cent higher value some part must be re- 
newed frequently. A foul solution at Great Falls has the fol- 
lowing composition : 3 

51.80 grams copper per liter, 
13.20 grains iron per liter, 
14.00 grams arsenic per liter, 

0.62 grams antimony per liter, 
48.00 grams sulphuric acid per liter. 

This shows that the impurities can become fairly concentrated 
before purification is necessary. 

In those refineries where the electrolyte has to be purified, 
the operation of purifying is carried out continuously on a cer- 
tain fraction of the total amount of electrolyte. The copper is 
separated either by electrolyzing with lead anodes or by crys- 
tallizing as copper sulphate. 

The circulation of the electrolyte, which is maintained by 
arranging the vats as in Figure 17, is an important factor. 
With no circulation the solution at the cathode would become 



1 --EL 

- : -'--' " -^"" ~ ~~ ""*"* ^-1-"-! ? J 




FIG. 17. Circulation of electrolyte 

too dilute for satisfactory deposition, while with too much cir- 
culation the slime would be stirred up and contaminate the 
cathode. The higher the current density the higher must be 
the rate of circulation. This is illustrated by the fact that 
at Great Falls, with tanks 9J feet in length, 2J feet in width, 
and 3| feet in depth, where the current density is about 40 am- 
peres per square foot, the circulation through a tank is 6 gal- 

9 Magnus, Trans. Am. Electrochem. Soc. 4, 77, (1903). 



KEFINING OF METALS IN AQUEOUS SOLUTIONS 



53 



B 



Ions per minute; while at Anaconda, with tanks 8J feet in 
length, 4 feet in width, and 4 feet in depth and a current 
density of 10 amperes per square foot, the circulation is 3 
gallons per minute. 3 At the Raritan Copper Works the rate 
of circulation would empty a tank in 1| hours. 10 

There are two different systems of arranging the electrodes 
used in refining copper, known as the series and the multiple 
systems. In the se- 
ries system a num- 
ber of copper anodes 
are suspended in 
the bath at equal 
distances apart, and 
only the two end 
ones are connected 
to the dynamo, as 
shown in Figure 18. 
The current then dissolves copper from the first plate, which is 
connected directly to the opposite pole of the dynamo, and 
deposits it on the near side of the next plate. The other side 

of the second plate 

c c c c c 



+ 








C 









E 




F 


C 


i 





























* ~ 


// 


































- 


J. 




4- "= 




* - 




f - 




+" - 


- 


~ % 




























~ '// 




























^ 
















- 








- 


- 


-I 






- 


-_ 


















n_r 


_ 


- \ 




u. 




Tvrmrrr, 




~ * 




J 







- 





J -1 


j 



FIG. 18. Series system 






FIG. 19. Multiple system 



is dissolved and 
deposited on the 
third, and so on 
throughout the 
whole series. In 
order to separate 
the deposited cop- 
per from that 
which has not been 
dissolved, the sides 



facing the positive pole are covered with some conducting 
material which allows the refined copper to be stripped off. 
Of course in this system the tanks cannot be lined with con- 
ducting material, for such a lining would cause a short circuit. 
Another difference between these tanks and those of the multi- 



10 Addicks, Min. Ind. 9, 270, (1900), and Ulke, I.e. p. 63. 



54 APPLIED ELECTROCHEMISTRY 

pie system is their greater size. Those at the Nichols Works 
in Brooklyn are 16 feet long, 5 feet wide, and 5J feet deep. 11 
The anodes are from to f of an inch thick, and are placed 
from | to -f$ of an inch apart. 

In the multiple system the anodes and cathodes are arranged 
alternately, as shown in Figure 19. All the anodes are con- 
nected to the positive pole of the dynamo and the cathodes to 
the negative pole. The cathodes are thin sheets of electrolytic 
copper, made by depositing copper on lead or copper covered 
with a conducting material from which the copper can be sepa- 
rated. At the Raritan Copper Works 6 the cathodes remain in 
the tanks 14 days. At the end of 28 days 13 per cent of the 
anodes are still undissolved, but at this stage they are removed 
and cast into fresh anodes. 

In order to reduce the power required, the temperature of 
the baths in practice is between 40 C. and 50 C., though from 
some experiments of Bancroft 12 70 C. and a current density 
between 3.5 and 3.75 amperes per square decimeter would 
seem to be more economical as far as power is concerned. 

The voltage between the anode and cathode varies between 
0.1 and 0.3 volt, depending on current density, temperature, 
distance between anode and cathode. 13 This voltage is used 
up partly in overcoming the ohmic resistance of the bath and 
partly in overcoming the electromotive force of polarization. 
Polarization, of course, varies with the current density and the 
rate of circulation, but a representative value is 0.02 volt. 14 

The actual cost of refining 98 per cent copper has in recent 
years been reduced from $20 to |4 or |5 a ton. This im- 
provement is due to the more economical use of power 15 and 
the more practical handling of the material. About 24 per 
cent of the power is still lost in the contact resistance. 16 

11 Ulke, I.e. p. 6 et seq. 

12 Trans. Am. Electrochem. Soc. 4, 73, (1903). 
i* Ulke, I.e. p. 43. 

14 Addicks, Trans. Am. Electrochem. Soc. 7, 62, (1905). 

i* Ulke, I.e. p. 3. 

i 6 Magnus, Electrochem. Ind. 1, 661, (1903). 



REFINING OF METALS IN AQUEOUS SOLUTIONS 55 

Nickel Refining 

If nickel is deposited from a cold solution of nickel chloride 
or sulphate in a layer more than 0.01 millimeter thick, it has a 
great tendency to separate from the underlying metal, but this 
difficulty can be overcome by heating the solution from which 
the nickel is deposited to 60 or 70. l At this temperature and 
with a current density of from 0.01 to 0.02 ampere per square 
centimeter, nickel is obtained of such ductility that it can be 
rolled. Nickel is more electropositive than hydrogen, and the 
overvoltage of hydrogen on nickel is not great. Nickel must 
therefore be deposited from a very weakly acid solution. 

The Balbach Company at Newark, New Jeresy, was one of 
the earliest refiners of nickel, as well as of copper. Nickel was 
refined by this company from 1894 to 1900 by a secret process. 
The product contained 0.25 per cent iron and a small amount 
of cobalt. 2 Another process that was in successful operation 
for some time is that of David H. Brown. 3 This was not a re- 
fining operation, as it had for its object the separation of nickel 
and copper in an ore. The ore contained 2 per cent nickel 
and as much copper. Anodes were made consisting of 54.3 
per cent copper, 43.08 per cent nickel, and the remainder of 
iron and sulphur. They were 75 centimeters in width, 60 in 
length, and 2J in thickness. The connections were those of 
the multiple system. The tanks were of concrete, 256 centi- 
meters long, 85 centimeters wide, and 67| centimeters deep. 
Each held 1.534 cubic meters of electrolyte. The circulation 
was effected as in copper refining, by overflow from bath to 
bath. The solution at one time consisted of 44. 3 grams of copper 
per liter as cuprous chloride, 55.6 grams of nickel as nickel chlo- 
ride, and 100 grams of sodium chloride, but these concentrations 
were subsequently modified. The voltage for 24 baths in series 
was 6 to 10 volts and the current 500 amperes. In this stage 
copper was deposited in a coherent but not dense form. The 

iFoerster, Z. f. Elektroch. 4, 160, (1897). 

2 Ulke, Electrochem. Ind. 1, 208, (1903). 

3 Haber, Z. f. Elektroch. 9, 392, (1903). 



56 



APPLIED ELECTROCHEMISTRY 



relative amount of copper and nickel in the solution flowing into 
the baths was the same as that in the anodes. On leaving the 
baths the ratio of copper to nickel was reduced to 1 : 80. Sodium 
sulphide was then added to the solution, to precipitate the 1.25 per 
cent of copper still remaining. After filtering, the solution was 
treated with chlorine to change the iron to chloride, which was 
precipitated with sodium hydrate and filtered. As much as pos- 
sible of the sodium chloride was then removed by concentrating 
the solution by evaporation. The nickel was then obtained by 
electrolyzing the hot solution with graphite anodes. The current 
yield was 92.5 per cent of the theoretical. The chlorine pro- 
duced at the anode was used in another part of the process. 
The nickel obtained was of the following average composition: 
99.85 per cent nickel, 0.085 per cent iron, 0.014 per cent 
copper, and was free from arsenic, sulphur, and silicon. 

Up to 1902, 454 kilograms of nickel were produced daily in 
Cleveland, when it was discontinued by the International Nickel 
Trust, in favor of the Orford * Process with which it formerly 
competed. The nickel produced by the latter process has vary- 
ing compositions, as the following table of percentage composi- 
tion shows: 



NICKEL AND 
COBALT 


COPPER 


FLUORINE 


CARBON 


SULPHUR 


SILICON 


98.91 


0.13 


0.40 


0.23 





0.05 


98.34 


0.41 


0.93 





0.078 






This is pure enough for anodes in nickel plating and the 
manufacture of steel. For other purposes, however, such as 
making German silver, a better quality is required, and since 
1906 the Orford Copper Company has taken up the electrolytic 
refining of nickel. 6 Very little is known about the details of 

4 This process depends for the separation on the fact that sodium sulphide 
forms double compounds with iron and copper sulphides, which float on the top 
of melted nickel sulphide. 

6 Electrochem. and Met. Ind. 4, 2tf, (1906). 



REFINING OF METALS IN AQUEOUS SOLUTIONS 57 

this process. The cathodes are said to be 3 by 4 feet in area 
and | inch in thickness, and their purity is 99.5 per cent. The 
nickel is deposited from a chloride solution. 

Silver Refining 

Two different cases arise in refining silver : one being the 
problem of separating silver and copper in an alloy consisting 
mainly of these two metals ; the other, the separation of silver 
from relatively small amounts of gold and platinum. From 
the relative positions of silver and copper in the electrolytic 
series, it is evident that if the attempt were made to separate 
these metals by electrolyzing an anode containing approximately 
equal amounts of each in a solution which dissolves them both, 
more silver would deposit on the cathode than dissolves at the 
anode. The copper in solution would therefore become so con- 
centrated that its decomposition point would be reduced to a 
value equal to that of silver. In carrying out this operation it 
is therefore necessary either to find a solvent in which only one 
of the metals dissolves, or to precipitate one of them by some 
other means. In 1877 to 1878 Wohlwill 1 succeeded in separat- 
ing silver and copper at the Norddeutsche Amnerie in alloys 
containing as much as 30 per cent of silver. The solution was 
copper sulphate, more dilute than is used in refining copper, and 
the current density was lower. A sponge rich in silver re- 
mained adhering to the anode, which had to be removed me- 
chanically, and the copper was deposited at the cathode. Another 
method for accomplishing the same result, due to Dietzel 2 and 
used at the Gold- und Silber-Scheide Anstalt at Pforzheim, de- 
pends on dissolving both copper and silver in a weakly acid solution 
of copper nitrate at the anode and carrying this solution im- 
mediately into another vessel where the silver is precipitated by 
contact with copper. After the silver has been thus completely 
removed, the copper nitrate solution is made slightly acid and 
enters the electrolyzing vat, where a certain amount of the copper 

1 Borchers, Electric Smelting and Refining, 2d English ed. p. 309 et seq. 

2 Z. f. Elektroch. 6, 81, (1899-1900). 



58 



APPLIED ELECTROCHEMISTRY 




FIG. 20. The Dietzel apparatus for silver 
refining 



is deposited as it passes the cathode. The arrangement is shown 
in Figure 20, which represents a cross section of the dissolving 
vessel. JOT are the rotary cylindrical copper cathodes, coated 
with a thin layer of grease or graphite, on which the deposition 
of copper takes place. When the copper grows out in the form 

of trees, it is knocked off. 
The copper cylinders are 
suspended on flanged con- 
tact rollers, which, when set 
in motion, cause the cylin- 
ders to rotate. Thus the 
shafts and driving mecha- 
nism are out of contact with 
the solution. P is a loose 
bottom for supporting the 
material to be treated, #, 
and is of hard rubber, cellu- 
loid, or glass. The plates 
P are provided with plati- 
num wires for conducting the current to S. DD are filter 
cloths, the object of which is to catch any copper falling from 
the cathodes and to prevent any of the anodic silver solution 
from rising to the cathode. The desilverized electrolyte is 
admitted from above, as shown. A small amount of silver 
0.03 per cent is deposited at the cathode with the copper. 
The solution contains from 2 to 5 per cent of copper and 0.05 
to 0.4 per cent of free nitric acid. The current density is 1.5 
amperes per square decimeter (14 amperes per square foot) and 
the voltage is from 2| to 3 volts. 

The electrolytic separation of silver and gold was first carried 
out by Wohlwill in 1871. These experiments were made simply 
to reduce silver from the solution obtained by boiling the metal 
in sulphuric acid. The electrodes were platinum, and the silver 
was deposited in loose, pure crystals. When the silver became 
dilute, the current decomposed the hot concentrated sulphuric 
acid, separating sulphur. No copper was deposited with the 
silver, as copper sulphate is very slightly soluble in hot con- 



BE FINING OF METALS IN AQUEOUS SOLUTIONS 



59 



centrated sulphuric acid. In 1873 experiments were made 
with the same solution, but with anodes of auriferous silver. 
Pure silver crystals were obtained on the cathode, to which they 
adhered sufficiently well to be removed from the bath. The 
anode slime also adhered firmly to the anode. The slime con- 
tained all the gold and most of the copper. This process was 
in operation for some time, during which 2000 kilograms of 
silver were refined. It was given up, however, on account of a 
number of practical difficulties, which increased when the pro- 
cess was carried out on a larger scale. One objection was the 
loss of silver caused by the crystals becoming detached from 
the cathode before it could be removed from the bath. These 
fell to the bottom of the tank and became mixed with the slime 
which also became detached from the anode to a certain extent. 

The process now most extensively used for refining silver 
electrolytically is due to Moebius. There are two processes 
known by this name, the old and the new. The former uses 
fixed cathodes, and is in operation at the Deutsche Gold- und 
Silber-Scheide Anstalt at 
Frankfurt-am-Main, at 
the Pennsylvania Lead 
Company's works near 
Pittsburg, and at Pinos 
Altos, Mexico. 3 The new 
process has a rotating 
cathode and is in opera- 
tion at the Guggenheim 
Works at Perth Amboy, 
New Jersey. 4 

The following descrip- 
tion of the plant of the 
Deutsche Gold- und Sil- 
ber-Scheide Anstalt is condensed from Borchers. The cells 
are made by dividing a wooden tank 12 feet long and 2 feet 
wide into 7 equal compartments. The anodes and cathodes 




FIG. 21. Vertical section of the old Moebius 
apparatus for silver refining, showing anode 



Min. Ind. 4, 351, (1895). 

4 Maynard, Eng. and Min. J. 51, 556, (1891). 



60 



APPLIED ELECTROCHEMISTRY 




are suspended parallel to the ends of the tank, as shown in 
Figures 21 and 22. The anodes a are of such width that five 

can be hung side by side 
across the width of the 
cell and are from 6 to 10 
millimeters thick. The 
cathodes k are thin, rolled 
sheets of silver that ex- 
tend across the whole cell. 
Each contains four cath- 
odes and three rows of 
anodes. The anodes are 
inclosed in filter cloth 
bags for collecting the 
anode mud. Each cath- 
ode has two wooden scrap- 
ers 8 on each side to scrape 
off the silver, which falls 

FIG. 22.- Vertical section of the old Moebius j to t covering the 

apparatus for silver refining, showing cathodes J 

whole area of each cell. 

The bottom of the tray is of filter cloth supported by a wooden 
grid. 

The electrolyte is an acid silver nitrate solution, which soon 
takes up copper from the anodes as copper nitrate. The con- 
centration of the acid varies from 0.1 per cent to 1 per cent, 
and the silver con- 
centration amounts K 
to about 0.5 per cent. 
The copper concen- 
tration may be as 
high as 4 per cent. 

The current density FIG. 23. Longitudinal section of the new Moebius 

is largely dependent apparatus for silver refining 

on the amount of copper in solution. At first, when not much 
copper is present, 3 amperes per square decimeter is allowable, 
but when the concentration increases to 4 per cent, the current 
density must be reduced to 2 amperes per square decimeter on 




REFINING OF METALS IN AQUEOUS SOLUTIONS 61 

account of the danger of depositing copper with the silver. 
The principle on which the silver is separated from the copper 
is explained above under electroanalysis. Every twenty-four 
hours the whole apparatus suspended in the bath is raised out 
and the silver removed, washed, pressed by hydraulic power, 
dried, and melted. The anode slime is removed from the bags 
once or twice a week. In the later form, shown in Figure 23, 
the tanks are 14 feet 3 inches long, 16 inches wide, and 7 inches 
deep. An endless sheet of silver (7, -fa inch thick, moves under 
the anodes Gr and carries the deposited silver to one end of the 
tank, where it is carried out of the tank by the belt D, and is 
scraped off by S. Electrical contact is made by F. The 
anodes are separated from the cathode by filter cloth, as in the 
old process. 

G-old Refining 

The electrolytic refining of gold was first accomplished by 
Wohlwill 1 at the Norddeutsche Affinerie in Hamburg. The 
process consists in electrolyzing gold anodes in a hot acid solu- 
tion of gold chloride. A cyanide solution would not do, be- 
cause silver and copper would be deposited with the gold. 
Wohlwill found that gold anodes do not dissolve when electro- 
lyzed in a solution of gold chloride, AuCl g , or of chloroauric 
acid, HAuCl 4 , but that in both cases chlorine is set free. In 
the solution of chloroauric acid the chlorine may be mixed 
with oxygen when the current density is low or the solution 
dilute. In order to have the gold dissolve, there must be some 
free chloride present, either hydrochloric acid, which is com- 
monly used, or some alkali chloride. At a definite temperature 
there is a definite amount of free acid for every current density 
that will prevent the evolution of chlorine. The amount of 
free acid required decreases with increasing temperature. 
With a solution containing 3 per cent of hydrochloric acid and 
30 grams of gold per liter, at 70 C., as much as 3000 amperes 
per square meter can be used without liberating chlorine, but 
in practice as much as 1000 amperes per square meter would 
hardly ever be used, for other reasons. In case chlorine ap- 
1 Z. f. Elektroch. 4, 379, 402, 421, (1898). 



62 APPLIED ELECTROCHEMISTRY 

pears at the anode, its evolution can be stopped by adding 
hydrochloric acid, or by raising the temperature. 

The gold is formed on the cathode in large crystalline de- 
posits which adhere in such a way that they can be easily 
removed mechanically. The more gold in solution, the more 
compact the deposit, while an increase in the current density 
has the opposite effect. The impurities coming from the anode 
also make the gold deposit more compact. With the largest 
current density allowable for the anode, 30 grams of gold per 
liter is sufficiently concentrated for precipitating the gold in a 
convenient form. 

The solution of the gold anode shows a certain similarity to 
that of copper anodes, in that a portion of the gold is dissolved 
in the monivalent state. This decomposes into trivalent gold 
chloride and metallic gold, which latter goes into the slimes. 
This reaction does not take place as rapidly as with copper, 
however, and the monivalent gold exists through the entire 
solution and is even deposited at the cathode, causing an in- 
crease in the current yield. The higher the current density, 
the greater will be the potential difference between the anode 
and the solution, and the larger the proportion of gold that 
will be oxidized to the trivalent state. This will make the loss 
in weight of the anode more nearly equal to the gain at the 
cathode. The following table illustrates this statement. The 
solution contained 50 cubic centimeters of concentrated hydro- 
chloric acid per liter and was at 65 or 70 C. 2 



CURRENT DENSITY 


ANODE Loss PER 


CATHODE GAIN PER 


AMP./SQ. DM. 


AMP. HR. GRM. GOLD 


AMP. HR. GRM. GOLD 


4.4 


3.35 


3.06 


7.4 


3.02 


2.79 


15.0 


2.50 


2.48 



With 15 amperes per square decimeter more hydrochloric acid 
had to be added to prevent the evolution of chlorine. 

2 Foerster, Elektrochemie wasseriger Losungen, p. 279. 



REFINING OF METALS IN AQUEOUS SOLUTIONS 63 

The impurities 3 in the anode may consist of silver, lead, 
bismuth, and the platinum metals. Silver is converted to silver 
chloride which drops into the slime or is removed mechanically. 
Lead is changed to the chloride which dissolves slightly. If 
present to any considerable extent, it is precipitated by adding 
sulphuric acid to the solution from time to time. The anode 
then becomes covered with sulphate, which either drops off 
itself or is removed mechanically. Bismuth is changed to 
the oxychloride and is also removed from the anode mechani- 
cally. Platinum and palladium both dissolve completely, while 
the other platinum metals go into the slimes. Platinum can 
accumulate in the solution till its concentration becomes twice 
that of the gold, without being precipitated at the cathode, but 
when the solution contains 5 grams or more of palladium per 
liter, traces of this metal are found in the gold cathode. The 
platinum and palladium are allowed to accumulate to this ex- 
tent and are then recovered. Since only gold is deposited, 
while other metals are dissolved, the solution, if left to itself, 
would become poor in gold. This therefore has to be made 
up by adding gold chloride from time to time. 

Besides the platinum metals, the slimes contain one tenth the 
weight of the gold in the anodes, due to the decomposition of 
aurous chloride, as explained above. The gold obtained is not 
infrequently 1000 fine and only in quite exceptional cases is 
less than 999.8 fine. 

At the mint in Philadelphia * the cells are of white porce- 
lain 15 inches long, 11 inches wide, and 8 inches deep. Each 
cell contains 12 anodes and 13 cathodes, 1J inches apart, con- 
nected in multiple. The anodes are 6 inches long, 3 inches wide, 
and | inch thick. The cathodes are fine gold yJ 7 inch thick. 

Electrolysis is also used for precipitating the gold from the 
very dilute solution obtained in the cyanide process. 5 The an- 
odes are iron plates 2 to 3 millimeters thick, covered with filter 

8 Z. f. Elektroch. 3, 316, (1897). Extract of the German patent, No. 90,276. 

4 Electrochem. Ind. 1, 157, (1903). For the mint at San Francisco, see ibid. 
6, 355 and 408, (1908). 

6 See Cyanid Progresse zur Godgewinnung, by Uslar and Erlwein, Vol. 7, p. 14, 
of the Engelhardt Monographs; also Borchers, Z. f. Elektroch. 7, 191, (1901). 



64 APPLIED ELECTROCHEMISTRY 

cloth, and the cathodes are of thin lead foil. The solution 
used for extraction contains from 0.01 to 0.1 per cent of po- 
tassium cyanide. The cells are of iron and are 7 meters long, 
1.5 meters wide, and 1 meter deep, divided into several com- 
partments. The electrolyte circulates from one compartment 
to another. The current density is about 0.5 ampere per square 
meter at 2 volts. 5 The gold sticks to the lead cathodes, which 
are taken out every month and melted with the gold. In some 
places the iron anodes have been replaced by peroxidized lead 
and the lead cathodes by tin plate, on which the gold is pre- 
cipitated as slime. 6 

Lead Refining 

Lead is an ideal metal to refine electrolytically, on account 
of its high electrochemical equivalent and of its relatively high 
position in the electrolytic series. Its greater tendency to go 
into solution than that of most of the metals occurring in it as 
impurities makes it possible to dissolve the lead, leaving the 
impurities behind in the metallic state. This avoids contami- 
nating the electrolyte, which consequently does not need fre- 
quent purification. The principal electrolytic difficulty to 
overcome was to obtain the lead in a coherent, compact form, 
from a solution that would not be too expensive to use on a 
commercial scale. The chloride or sulphate, which are usually 
the salts employed for metal refining, cannot be used in the 
case of lead on account of their insolubility. The problem has 
been solved by A. G. Betts, 1 who found that a solution of 
lead fluosilicate with a small quantity of gelatine fulfilled the 
requirements. The fluosilicate solution is not the only one 
from which a good deposit can be obtained ; but it was selected 
on account of its low price as compared with other solutions 
giving equally good deposits. 2 The object in refining lead is to 
recover the copper, antimony, and bismuth, as well as the gold 
and silver. 

Electrochem. Ind. 2, 131, (1904). 

1 See Lead Refining by Electrolysis, by A. G. Betts. John Wiley and Sons 
(1908). 2 Betts, ibid. p. 17. 



REFINING OF METALS IN AQUEOUS SOLUTIONS 65 

The solution of lead fluosilicate (PbSiF 6 ) is prepared by 
adding white lead or lead carbonate to fluosilicic acid. Fluosi- 
licic acid is prepared by allowing a solution of hydrofluoric 
acid, made from sulphuric acid and calcium fluoride, to trickle 
through a layer of pure sand or broken quartz. Heat is applied 
to start the reaction, which then furnishes sufficient heat itself 
to maintain the necessary temperature. No precipitate is 
formed on adding the lead to the acid unless an excess of lead 
is added, 3 and the solution obtained is colorless. The strength 
of the solution ordinarily employed in practice is from 6 to 7 
grams of lead, and from 12 to 13 grams of SiF 6 per 100 cubic 
centimeters. 4 This means about 8 grams of free fluosilicic acid 
per 100 cubic centimeters of solution. The gelatine is added 
to the solution as a hot strong solution of glue. Enough is 
added to make its concentration 0.1 per cent. The temperature 
of the electrolyte has been found to have no effect in the 
character of the lead deposit. 5 In practice about 30 C. is 
maintained by the current itself. 

The impurities in the anode may consist of iron, zinc, sulphur, 
copper, nickel, tin, antimony, arsenic, bismuth, cadmium, gold, 
selenium, and tellurium. Only the zinc, iron, nickel, and tin 
would go into solution. The other metals are all below lead in 
the electrolytic series and would therefore remain in the anode 
slime. Zinc, iron, and nickel are above lead and would therefore 
not be precipitated from the solution with lead. Tin, however, 
is so near lead in the series that it dissolves and precipitates 
with the same facility and can therefore not be separated from 
lead electrolytically. It must be removed by poling, before 
casting the anodes. When only 0.02 per cent of tin is in the 
anode, it is found in the cathode. 6 With this exception, the 
impurities are easily prevented from reaching the cathode, even 
when present in the anode in large quantities. Pure lead can 
be obtained when the anode contains only 65 per cent lead, the 
rest being impurities of bismuth, antimony, arsenic, silver, and 

8 Betts, I.e. p. 30. See also Senn, Z. f. Elektroch. 11, 230, (1905). 
4 Betts, I.e. p. 255. 5 Senn, I.e. Betts, I.e. p. 46. 

F 



66 APPLIED ELECTROCHEMISTRY 

copper. 7 A low current density, 4 amperes per square foot, 
was required with anodes of this composition. 

The slime nearly all adheres to the anode and is consequently 
easily removed from the bath. Its composition of course 
depends on that of the anodes. It has been stated that the 
handling of the anode slime has not been satisfactorily settled, 8 
and from the large amount of space given to this subject by 
Betts in his book, it would seem to be an unusually difficult 
problem. The method employed at Trail, British Columbia, by 
the Consolidated Mining and Smelting Company of Canada, 
consists in treating the slime with sodium sulphide, which 
extracts 80 per cent of the antimony and some arsenic. The 
antimony is then deposited electrolytically on steel cathodes 
using lead anodes. 

The cathodes used in lead refining are thin sheets of pure lead. 
The current density allowable depends on the purity of the 
anodes. As stated above, anodes containing only 65 per cent 
lead can be refined if the current density is as low as 4 amperes 
per square foot. In practice the anodes are about 98 per cnt 
pure, 9 and the current density is from 12 to 16 amperes per 
square foot. The analysis of refined lead from Trail shows a 
purity of about 99.995 per cent. The average voltage per tank 
is from 0.30 to 0.38 volt and the polarization amounts to 0.02 
volt. The tanks, made of southern yellow pine, are arranged 
in the multiple system. The electrolyte is caused to circulate 
by having the difference in the level of two successive tanks 
from 2J to 3 inches. Five gallons per minute is a fair amount 
of circulation for a 4000 ampere tank. 

Lead is refined electrolytically at Trail, British Columbia, 
New Castle on Tyne, England, and by the United States Metals 
Refining Company at Grasselli, Indiana. The capacity of the 
first plant in 1908 was about 80 tons a day, of the third 85 tons. 
A detailed description of the plants at Trail and Grasseli will 
be found in Betts's treatise, referred to above. 

7 Betts, I.e. p. 56. 8 Min. Ind. 15, 545, (1906). 

For the following statements, see Betts, I.e. p. 287, Table 110 ; p. 255, Table 
91 ; p. 287, Table 108, and p. 189, Table 73. 



REFINING OF METALS IN AQUEOUS SOLUTIONS 67 

Zinc Refining 

It is possible to refine zinc electrolytically, but commercial 
zinc contains no metals that it would pay to recover, and the 
demand for very pure zinc is limited. 

The only impurities occurring in commercial zinc are iron, 
lead, and cadmium. In the slightly acid chloride solution, con- 
taining about 56 grams of zinc per liter, with a current density 
of 1.8 to 1.9 amperes per square decimeter, zinc can be freed 
from its impurities to as great an extent as copper. The analysis 
of some refined zinc is as follows : 1 

99.955 per cent zinc, 
0.036 per cent lead, 
0.0012 per cent iron, 
0.0080 per cent cadmium. 

Though the refining of commercial zinc electrolytically is 
seldom carried out, certain alloys of zinc rich in silver, obtained 
in other metallurgical processes, have been successfully refined 
on a commercial scale at Tarnowitz in Silesia. 2 When lead con- 
taining silver is treated with zinc, most of the silver is taken up 
by the zinc, forming an alloy which floats on the lead. This 
zinc scum, containing the silver, is cast into anodes one centi- 
meter thick, weighing from 20 to 30 kilograms, which are 
electrolyzed in a solution of zinc sulphate. The composition of 
the anodes is the following : 

Silver 11.32 per cent 

Lead 3.13 per cent 

Copper 6.16 per cent 

Nickel 0.51 per cent 

Iron 0.24 per cent 

Zinc 78.64 per cent 

Antimony, arsenic, bismuth, traces. 

The current density is 80 to 90 amperes per square meter, 
requiring 1.25 to 1.45 volts. The purity of the resulting zinc 
is not given. 

1 Foerster and Gxinther, Z. f. Elektroch. 5, 16, (1898), and 6, 301, (1899). 

2 Hasse, Z. f. Berg- Hutten- und Salinenwesen, 45, 322, (1897). 



CHAPTER V 

ELECTROLYTIC REDUCTION AND OXIDATION 

1. REDUCTION 

REDUCTION is a term now applied to several really different 
processes. It may mean the loss of a positive electric charge 
by an ion, as when ferric ion changes to ferrous, or the acquir- 
ing a negative charge, as when chlorine changes to a chlorine 
ion, or it may mean the direct addition of hydrogen or the 
removal of oxygen from a molecule. All of these different 
kinds of reduction may be produced electrolytically by bring- 
ing the substances to be reduced in contact with a cathode. 
Of course the reduction resulting from the addition of hydro- 
gen is dependent on the deposition of hydrogen on the cathode, 
which reacts while in the nascent state with the reducible sub- 
stance with which it comes in contact. The loss of positive 
charge may also be represented as being produced by the 
hydrogen liberated on the cathode, while in the nascent state, 
as illustrated by the equation : 

Fe +++ + H = Fe ++ + H + . 

Reduction by acquiring a negative charge is illustrated by the 
chlorine electrode, made by saturating a platinum electrode 
with chlorine. When chlorine changes from the molecular to 
the ionic state on a chlorine electrode, the positive current 
flows from the solution to the electrode and molecular chlorine 
takes a negative charge : 

C1 2 + 2 H = 2 Cl- + 2 H+. 

68 



ELECTROLYTIC REDUCTION AND OXIDATION 69 

Molecular hydrogen has very little reducing power, and con- 
sequently the reducing power of a cathode must be ascribed 
to the hydrogen liberated on it while in the nascent state. 
According to the mass action law, the reducing power of 
nascent hydrogen is proportional to its concentration. The 
potential difference between the cathode and the solution is 
also dependent on the concentration of the nascent hydrogen, 
as can be shown as follows : The potential of the hydrogen 
electrode is given by the equation 1 

(1) 

where P Ha is the electrolytic solution pressure, and p n+ the 
osmotic pressure, of the hydrogen ions in solution. But P^ 
= ktp, in which &j is a constant and p is the pressure of the 
gaseous hydrogen in contact with the electrode and solution. 2 
By Henry's Law, p must be proportional to the concentration 
<?i, 2 of the molecular hydrogen in the solution immediately on 
the electrode. The concentration of the molecular hydrogen 
must in turn be proportional to the square of the concentration 
of the nascent hydrogen on the electrode, since the reaction is 
2 H = H 2 , and by the mass action law, for equilibrium, 



The electrolytic solution pressure is therefore proportional to 
the concentration of the nascent hydrogen on the cathode, 
since, as explained above, 




Obviously, any pf the quantities proportional to P 2 Ha may be 
substituted in equation (1). Substituting & 3 <? H , 

(2) 

which shows that the potential of the cathode is a measure of its 
reducing power, since it is determined by the concentration of 

1 Le Blanc, Electrochemistry, p. 183, (1907). 
2 Le Blanc, Electrochemistry, p. 195, (1907). 



70 



APPLIED ELECTROCHEMISTRY 



the nascent hydrogen, e H , assuming e H+ , the concentration of 
hydrogen ions, is constant. 

If the cathode potential is to be expressed in terms of the 
pressure of the hydrogen gas in contact with it and the solu- 
tion, it may be done by transforming equation (1) and substi- 
tuting as follows : 



ETlog 




(3) 



These equations give only the numerical value of the poten- 
tial difference between the electrode and the solution, and take 
no account of which is positively and which is negatively 
charged. The charge on any electrode whose potential can be 
represented by a formula similar to those above may be either 
positive or negative, depending on whether the value of the 
fraction following the logarithm sign is greater or less than one. 

The two principal advantages of electrolytic reduction, over 
that produced by adding some chemical reducing agent, which 
must of course be oxidized itself, is that no such oxidized sub- 
stance is left in the solution, and that the reducing power of a 
cathode can be varied within wide limits and in small steps. 
One method of varying the reducing power of the cathode is to 
vary the current density on it. The increase in the potential 
difference that can be obtained in this way, however, is not 
very great. This is shown in Table 7, in which are given the 
current densities and the corresponding potentials referred to 
the normal hydrogen electrode as zero, of cathodes of different 
metals dipping in twice normal sulphuric acid : 3 It will be 

TABLE 7 



AMPERES PEE 
SQUARE CM. 


MEKCUEY 


TIN 


GOLD 


COPPEB 


NICKEL 


PLATINIZED 
PLATINUM 


0.01 


1.19 


0.97 


0.74 


0.57 


0.56 


0.05 


0.05 


1.26 


1.11 


0.89 


0.70 


0.67 


0.06 


0.11 


1.30 


1.16 


0.95 


0.77 


0.73 


0.08 


0.15 


1.32 


1.18 


1.09 


0.82 


0.76 


0.09 



8 Tafel, Z. f. phys. Ch. 50, 710, (1906). 



ELECTROLYTIC REDUCTION AND OXIDATION 71 

seen that the potential difference between electrode and solu- 
tion does not increase much with increasing current density, 
but that for a given current density it is quite different for 
different metals. This is due to what has been called the over- 
voltage for the metal in question, which means the excess 
voltage necessary to liberate a gas on the metal over that 
necessary to liberate it on a reversible electrode. 4 The reduc- 
ing power of a cathode can therefore be greatly varied by mak- 
ing the cathode of different metals. 

This change in reducing power may be made to appear in 
much larger numerical values by calculating the number of at- 
mospheres to which these higher potentials, due to overvolt- 
age, correspond ; that is, by assuming that the higher potentials 
are produced by compressing the gaseous hydrogen surround- 
ing a reversible electrode, and computing the number of atmos- 
pheres pressure that would be necessary to make the potential 
difference between electrode and solution some definite amount, 
0.1 volt, for example. This can be done by writing the expres- 
sion for the electromotive force of the cell : 



at 1 atmosphere 



Electrolyte 



Pt + H 2 at 

x atmospheres, 



and placing it equal to 0.1 volt. The electromotive force of 
this cell by (3) is then : 

RT, x 0.058 , 



Q%. 

Solving this equation for x gives 2800 atmospheres. For 0.2 
volt the value of x is 8 million atmospheres. This is the mean- 
ing of the statement frequently met with, 6 that the pressure 
of the hydrogen evolved by electrolysis can be increased to 
millions of atmospheres. The values thus calculated, however, 
can hardly represent the physical state of the gas evolved on 
a cathode. 

Another important factor in electrolytic reduction is the 

* Le Blanc, Electrochemistry, p. 287, (1907). 

* Nernst, Theoretische Chemie, 6th ed. p. 756, (1909). 



72 APPLIED ELECTROCHEMISTRY 

catalytic effect of the metal composing the cathode. As a 
result of this effect a substance may be more easily reduced on 
one cathode than another, even though the overpressure is the 
same for both cathodes. 6 

The electrolytic reduction of galena, or lead sulphide, in a 
sulphuric acid solution was carried out for a while on a large 
scale at Niagara Falls, but had to be given up eventually 
on account of the poisonous effect of the hydrogen sulphide 
produced. 

The galena, which had been ground to pass a 40 to 50 mesh 
sieve, was spread in a layer J inch thick and covered with 
dilute sulphuric acid. 7 The current density was 30 amperes 
per square foot, and the current efficiency was about 66 per 
cent. 8 About 97 per cent of the lead sulphide was reduced to 
spongy lead, which was washed free of sulphuric acid, and con- 
verted into litharge by roasting. 

In case the substance to be reduced is in solution, it must be 
prevented from coming in contact with the anode, where it 
would be oxidized again. This is accomplished by separating 
the anode from the cathode compartment by some kind of 
diaphragm, such as porous clay, that allows the electrolytic 
passage of the current, but which prevents the mechanical 
mixture of the liquids in the two compartments. An example 
of this kind is the production of chromous sulphate from chromic 
sulphate. The solution contains 500 grams of chromic sulphate 
in 500 cubic centimeters of concentrated sulphuric acid, and is 
electrolyzed on a lead cathode with 0.1 to 0.15 ampere per 
square centimeter. The blue-green chromous sulphate deposits 
on the cathode, as the solution about the cathode becomes satu- 
rated with it. 9 

6 Foerster, Elektrochemie wasseriger Losungen; p. 315, (1906). 

7 Salom, Trans. Am. Electrochem. Soc. 1, 87, (1902). 

8 Salora, Trans. Am. Electrochem. Soc. 4, 101, (1903). 

9 Foerster, Elektrochemie wasseriger Losungen, p. 319, (1905). 



ELECTROLYTIC REDUCTION AND OXIDATION 73 

2. OXIDATION 

The oxidizing power of an anode is related to the potential 
difference between the electrode and the solution in the same 
way as the reducing power of a cathode and the potential dif- 
ference between it and the solution. There is also an over- 
pressure for oxygen on different metals, as in the case of 
hydrogen. 1 The results of the following table were obtained 
in a normal solution of potassium hydrate. The potential dif- 
ferences given between anode and solution were measured when 
oxygen first appeared on the anode against a hydrogen elec- 
trode in the same solution. 

TABLE 8 
Potential Difference between Anode and Solution when Oxygen first Appears 



METAL 


POTENTIAL 


Gold 


175 




1 67 




1 65 




1 65 


Silver 


1 63 


Lead 


1 53 




1.48 




1 47 




147 


Cobalt 


136 


Nickel, smooth 


135 


Nickel spongy 


128 







The number of metals that can be used as anode is much less 
than those that can be used as cathode, and is limited to those 
metals that would not be dissolved by an action of the current. 
Platinum, lead, and carbon are the principal materials for un- 
attackable anodes in acid solutions, while besides these both 
nickel and iron may be used in alkaline solutions. 

Coehn and Osaka also found a decomposition point of 1.1 
volts for all of the metals investigated, which they identified 

1 Coehn and Osaka, Z. f. anorg. Ch. 34, 86, (1903). 



74 APPLIED ELECTROCHEMISTRY 

with the value of the hydrogen-oxygen cell, then thought to be 
1.06 volts. The true value of this cell, however, has since been 
found to be 1.22 volts, 2 so that their first point cannot have this 
significance. The overvoltage of a spongy nickel electrode is 
evidently very small, for its value in the above table is only 
a little greater than 1.22 volts, the true potential of an oxygen 
electrode, assuming a hydrogen electrode in the same solution 
equal to zero. 

There is also a catalytic effect of the anode material on oxi- 
dation, which may be of more practical importance than the 
overpressure. For example, the yield in oxidizing iodic to 
periodic acid on smooth platinum was found to be 1 per cent, 
on platinized platinum 3 per cent, and on lead peroxide 100 per 
cent, though the potential differences between the anodes and 
the solution were 1.72, 1.48, and 1.52 volts respectively. 3 In 
the oxidation of chromium sulphate, described below, smooth 
platinum anodes give practically no yield of chromate, while 
with lead peroxide anodes current yields between 20 and 97 
per cent are obtained, depending on the concentration of the 
chromium sulphate, though the overpressure of oxygen on the 
peroxide is only a few hundredths of a volt higher than on 
platinum. 4 

The following are some of the most important technical ap- 
plications of electrolytic oxidation. 

In dye works, solutions of sodium or potassium bichromate 
and sulphuric acid are used for oxidizing anthracene to anthra- 
chinon : 

,CH, ' CO 



, 

H 4 / I 
CH 



CO 



The bichromate is thereby reduced to chromium sulphate and 
must be regenerated before it can be used again. Formerly 
this was accomplished by precipitating with calcium hydrate 

2 Nernst, Z. f. Elektroch. 11, 835, (1905) ; Haber, ibid. 834 ; Lewis, Journ. 
Am. Chem. Soc. 28, 185, (1906). 

Mtiller, Z. f . Elektroch. 10, 61, and 62, (1904). 
* Mtiller and Seller, Z. f. Elektroch. 11, 863, (1905). 



ELECTROLYTIC REDUCTION AND OXIDATION 75 

and heating the resulting pasty material, consisting of chromium 
oxide, calcium hydrate, and calcium sulphate, to red heat. 
This treatment produces calcium chromate, which, when treated 
with sodium sulphate, gives sodium chromate and calcium sul- 
phate. On removing the insoluble calcium sulphate the sodium 
chromate can be used for oxidation. This method is uneco- 
nomical on account of the loss of sulphuric acid and of chromium 
which it involves, and it has been superseded by the electro- 
lytic process patented in 1898 by the Farbewerke vorm. Meister, 
Lucius, und Brunig. 5 This process consists in oxidizing on a 
lead peroxide anode a solution of chromium sulphate contain- 
ing free sulphuric acid, in the anode compartment of a lead- 
lined electrolytic cell. The anode and cathode compartments 
are separated by a diaphragm. The chromium is oxidized from 
a cation to an anion in changing from a chromium salt to 
a chromate, and at the same time sulphuric acid concentrates 
in the anode compartment, due to the migration of the sulphate 
ions. After using the anode liquid for oxidation, it is first 
placed in the cathode compartment, where the sulphuric acid 
concentration decreases, after which it is again oxidized. 

It is very difficult to construct diaphragms of size great 
enough for technical use that can resist the action of the 
chromic acid produced. Le Blanc, 6 after a number of experi- 
ments, produced diaphragms consisting of 25 per cent alumina 
and 75 per cent silica, which he considered satisfactory at the 
time, but it seems eventually not to have been successful, for he 
has since patented a process for this oxidation in which the two 
compartments are separated by a partition reaching not quite 
to the bottom of the cell, in place of a conducting diaphragm. 7 
The liquid is circulated from the cathode to the anode com- 
partment. 

Another example of technical oxidation is the production of 
insoluble salts and oxides of metal by a process patented in 
1894 by C. Luckow. 8 The difficulty encountered in the electro- 

6 Z. f. Elektroch. 6, 266, (1899). 6 Z. f. Elektroch. 7, 290, (1905). 

7 Z. f. Elektroch. 13, 791, (1907) ; 14, 12, (1908). 

8 Borchers, Z. f. Elektroch. 3,482, (1897). 



76 APPLIED ELECTROCHEMISTRY 

lytic manufacture of insoluble salts or other compounds by the 
oxidation of the metallic anode is that the compound sticks to 
the anode and produces a high electrical resistance. In the 
Luckow process this difficulty is overcome by using a 1^ per 
cent solution of a mixture of two salts, the anion of one forming 
a soluble salt with the metal of the anode, and the anion of the 
other forming the insoluble salt desired. The mixture consists 
of 80 parts of the first, or auxiliary salt, to 20 parts of the 
second, or principal salt. The anions of the principal salt, 
being present in a much smaller number than those of the aux- 
iliary salt, are soon used up in the layer of solution next to the 
anode, and are replaced slowly because the auxiliary anions 
carry most of the current on account of their greater number. 
The ions of the anode, on dissolving, do not, therefore, come in 
contact with the anions of the principal salt directly on the 
anode, but the precipitate is formed a slight distance from the 
anode and therefore does not stick, but falls down to the bottom 
of the cell. 9 

If the auxiliary salt is not added, the salt desired cannot be 
produced with a satisfactory yield, for either the anode is 
covered with an insulating layer of the insoluble salt, or the 
desired salt is not produced at all. For example, in electro- 
lyzing a lead anode in a 0.12 per cent solution of potassium 
chromate, a mixture of lead peroxide and lead chromate formed 
on the anode, but practically no yield of lead chromate could be 
obtained. 10 Even when the two salts are in the right propor- 
tion, if the solution is too concentrated, the same difficulties are 
encountered. 

In manufacturing white lead, for which the Luckow process 
seems well suited, a 1J per cent solution of a mixture of 80 per 
cent sodium chlorate and 20 per cent sodium carbonate is elec- 
trolyzed with a soft lead anode and a hard lead cathode, with a 
current density of 0.5 ampere per square decimeter. Carbon 
dioxide is passed through the solution over the anode to replace 
that removed by the lead. If enough of the gas is passed 

Le Blanc and Bindschedler, Z. f. Elektroch. 8, 262, (1902). 
loisenburg, Z. f. Elektroch. 9, 275, (1903). 



ELECTROLYTIC REDUCTION AND OXIDATION 



77 



through the solution, the pure carbonate of lead is produced, and 
in order to get basic carbonate the quantity of carbonic acid 
must be limited. The same result can be accomplished by 
diluting the carbonic acid with an indifferent gas, such as air, 
and passing an excess through the solution. Table 9 shows the 
relation between the concentration of the gas and the product : 10 

TABLE 9 



EATIO OF AIR TO C0 2 BY 
VOLUME 


PER CENT PbO IN PRODUCT 


PER CENT PbO IN WHITE LEAD 
2PbC0 3 .Pb(OH) 2 


97:3 


86.50 


86.31 


80:20 


85.92 


86.31 


60:40 


83.41 


86.31 



It is evident that the carbon dioxide is too concentrated when 
mixed with air in the proportion of 40 to 60. 

In producing oxides by this metal, the mixture of salt elec- 
trolyzed contains only 0.5 per cent of the auxiliary salt. For 
lead peroxide, a 1J per cent solution of a salt mixture con- 
sisting of 99.5 per cent of sodium sulphate and 0.5 per cent of 
sodium chlorate, acidified with sulphuric acid, is used. The 
current density on the anode is about 0.2 ampere per square 
decimeter. 

The electrolytic method of producing iodoform has almost 
entirely displaced the older chemical method. The electrolytic 
method was patented as early as 1884 by the Chemische Fabrik 
auf Aktien, vorm. E. Schering. 11 According to this patent, 
iodoform is made by electrolyzing a hot solution of potassium 
iodide and alcohol, through which carbon dioxide is passed. 
The addition of alkali carbonate also was found advantageous, 
when the study of this subject was taken up. 11 The final 
result of the chemical reaction of iodine on alcohol in the pres- 
ence of alkali carbonate is represented by the equation : 

C 2 H 5 OH + 10 I + H 2 = CHI 3 + C0 2 + 7 HI. 

11 Elbs and Herz, Z. f. Elektroch. 4, 113, (1897). 



78 APPLIED ELECTROCHEMISTRY 

The iodine may be furnished by liberating it electrolytically 
from potassium iodide on a platinum anode. This is an oxida- 
tion, since the iodine ion is deprived of a negative charge. 
A suitable solution for this electrolysis is made up of 5 grams 
of sodium carbonate, 10 grams of potassium iodide, 20 cubic 
centimeters of alcohol, and 100 cubic centimeters of water. 

The iodine does not act on the alcohol directly, as given by 
the above equation, but first forms alkali hypoiodite with the 
hydroxyl ions from the hydrolysis of the carbonate according 
to the equation : 



The hypoiodite is hydrolytically dissociated as follows : 
NalO + H 2 = NaOH + HIO. 

Hypoiodous acid, being unstable, decomposes in the following 
two ways : 12 

3HIO = HIO 3 + 2HI 

and C 2 H 5 OH + 5 HIO = 2 HI + CHI 3 + CO 2 + 4 H 2 O. 

That iodine does not act directly on alcohol was proved by 
determining the decomposition point of the solution with and 
without the addition of alcohol. If the alcohol combined di- 
rectly with the iodine liberated, it would reduce the concen- 
tration of the free iodine on the electrode and lower the de- 
composition point. Since the potential of an iodine electrode 
is 13 



in which <7 Ia is the concentration of the free iodine and <7j_ is 
that of the iodine ions, any substance in solution which reduces 
the value of (7 Is will change the numerical value of the potential. 
It was found that alcohol has not such depolarizing effect, 
but that the carbonate has, which fact points to the explana- 
tion given above. 

12 Dony-H^nault, Z. f. Elektroch. 7, 67, (1900). 

Foerster, Elektrochemie wasseriger Losungen, p. 124, (1906). 



ELECTROLYTIC REDUCTION AND OXIDATION 79 

A high current density decreases the yield, since a greater 
concentration of alkali hypoiodite tends to produce a larger 
amount of iodate. With a solution made up of 10 grams of 
alcohol, 5 grams of sodium carbonate, 16 grams of potassium 
iodide, and 100 grams of water, Foerster and Meves obtained 
the following results : 14 



AMPERES PER SQUARE DECIMETER 


CURRENT YIELD IN PER CENT OP THE 
THEORETICAL 


1 


95-97 


2 


80-93 


3 


73-79 



Since iodine is continuously removed from the solution, and car- 
bon dioxide is added, the alkali carbonate will increase in con- 
centration. When it had increased to six times the amount 
given in the formula just above, the yield fell to 43 per cent, 
with a current density of 2 amperes per square decimeter, and 
the iodoform formed in a thick crust on the anode and con- 
tained free iodine. The carbonate should therefore not be 
allowed to accumulate to this extent. 

Bromoform and chloroform cannot be produced in this way, 
but other oxidation products are formed, especially chlor- or 
brom- aldehyde. This is due to the higher potential at which 
bromine and chlorine are liberated, which is sufficient to oxi- 
dize the alcohol. Bromoform can be produced with a good 
yield, however, if acetone is used in place of alcohol. 

i* Z. f. Elektroch. 4, 268, (1897). 



CHAPTEE VI 
THE ELECTROLYSIS OF ALKALI CHLORIDES 

1. THEORETICAL DISCUSSION 
The Chemical Action of Chlorine on Water and Alkali Hydrate 

THE electrolysis of sodium and potassium chlorides is one of 
the largest electrochemical industries that is carried out in 
aqueous solution. Chlorine and sodium hydrate, hypochlorite,. 
chlorate, or perchlorate may be produced from sodium chloride, 
depending on the conditions of the electrolysis. 

The first products obtained on electrolyzing the solution 
of an alkali chloride are chlorine at the anode and alkali 
hydrate at the cathode. If these two primary products are 
the ones desired, they must not be allowed to mix, while if 
hyperchlorite, chlorate, or perchlorate is desired, the chlorine 
and hydrate must be allowed to react with each other. Before 
describing the electrolysis of the alkali chlorides, it will be nec- 
essary to give a brief account of the purely chemical reactions. 
that take place between chlorine and the alkali hydrates, and 
between chlorine and pure water. 

Chlorine enters into a reaction with pure water to a slight 
extent, according to the equilibrium represented by the equa- 
tion : 1 

C1 2 + H 2 O ^ H+ + Cl- + HOC1. (1) 

The equilibrium constant of this reaction is 



=2 570, 



i Jakowkin, Z. f. phys. Ch. 29, 613, (1899). 
80 



ELECTEOLYSIS OF ALKALI CHLORIDES 81 

if the concentrations are taken in moles per liter. 2 It is evi- 
dent from the large value of this constant, and from the fact 
that the concentration of free chlorine in a saturated solution 
at 25 is only 0.064 mole per liter, 3 that the concentration of 
hydrochloric and hypochlorous acids that can exist together in 
solution are very small. If brought together in greater con- 
centrations, chlorine will be produced, according to equation 
(1), taken from right to left. 

If chlorine is passed into a solution of alkali hydrate, the 
following reaction between the chlorine and hydroxyl ions 
takes place : C1 2 + OH- ^ HOC1 + Cl~ (2) 

The value of the equilibrium constant of this equilibrium is 
given by the following equation : 4 



which is derived from the equations 

Cci. K w 1.4 x 10- 14 

- -- l2 -- =2570 and C H+ = ^ = ^- - 

^H+ * ^Cl- * ^HOCl ^OH- ^'OH- 

In all of these equations the concentrations are in moles per 
liter. Hypochlorous acid then reacts with the unchanged 
hydrate to produce a hypochlorite, and this reaction also 
leads to an equilibrium represented by the equation : 

HOC1 + OH- ^> OC1- + H 2 O, (4) 

for which the equilibrium constant is 

C OH _ 



This is the hydrolysis constant of the hypochlorite. The value 
of K 3 can be obtained from the dissociation constant of hypo- 

chlorous acid : 6 r r 

K = ^oci- ^H+ = 3. 7 x lQ-8, 



2 Luther, Z. f. Elektroch. 8, 602, (1902). 

3 Foerster, Elektrochemie wasseriger Losungen, p. 341, (1905). 

4 Foerster and Miiller, Z. f. Elektroch. 8, 921, (1902). The value of K w is 
taken from van Laar, Theoretische Elektrochemie, p. 174, (1907). 

6 Sand, Z. f. phys. Ch. 48, 610, (1904). 



82 APPLIED ELECTROCHEMISTRY 

and the dissociation constant of water: 

K W = C H+ COH- = 1.4 X 10-". 
Dividing K w by K 4 , 

KW _ CH+ COH- CHOCI _ _ 1.4 X 10~ 14 _. 3 g x 
K 4 C OC1 -.C H+ "8.7x10-8 

When therefore any quantity of chlorine acts on alkali hydrate, 
the resulting quantities of hydrate, chlorine, chloride, hypo- 
chlorous acid, and hypochlorite are determined by the equilibria 
represented by equations (2) and (4). Only when there are 
at least two equivalents of hydrate to one mole of chlorine does 
the following reaction hold : 

C1 2 + 2 NaOH = NaCl + NaOCl + H 2 O. (5) 

This is the sum of equations (2) and (4), and is the one usually 
given to represent the reaction between chlorine and hydrate. 
Since the equilibria represented by equation (3) and the equa- 
tion for the value of K 3 exist simultaneously, the values of C OII _ 
and CHOCI are the same in both. From the equation for K 3 , 

CHOCI _ vr C OC1 _ 
P 3 * 77 2 

^OH- *-* OH- 

and combining this with the equation for K 2 , 



^Cl- ^OH- ^ OH- 

This equation is convenient for predicting what effect a change 
in the concentration of one substance will have on that of the 
others. 

From equation (6) it would seem that for a given value of 
C cla and C C1 _, the value of C OC1 _ could be increased in propor- 
tion to the value of C OH _. This would be true, if the concen- 
tration of the hypochlorite, C OC1 _, were not limited by another 
reaction, the oxidation of hypochlorite to chlorate by hypo- 
chlorous acid, according to the equation : 6 

2 HOC1 + QC1- = ClOg + 2 Cl- + 2 H+. (7) 

Foerster and Jorre, J. f . prakt. Ch. 59, 53, (1899) ; Foerster, ibid. 63, 141, 
(1901). 



ELECTROLYSIS OF ALKALI CHLORIDES 83 

The free hydrochloric acid then sets free an equivalent amount 
of hypochlorous acid according to the equation : 

2 H + + 2 Cl- + 2 OC1- = 2 HOC1 + 2 Cl~, (8) 

and the hypochlorous acid thus set free oxidizes more hypo- 
chlorite. This process continues until all of the hypochlorite 
has been changed to chlorate. 

Substituting the numerical values of K 2 and K 3 in (6), we 
have 

1.4 xlO-tto^- (9) 



In order to illustrate the use of the above equation, the rela- 
tive concentrations of chlorine ions, hydroxyl ions, free chlorine, 
and hypochlorous acid in a neutral solution normal with respect 
to hypochlorite ions will be calculated. From the value of K 3 , 
the values of C HOC1 and C OH _ are each 6.2 10~ 4 mole per liter, 

and from (9) the value of the fraction ^- is 3.6 x lO' 11 . If 

^ci- 

the concentration of chlorine ions is also normal, that of the 
free chlorine is only 3.6 x 10~ n mole per liter. 4 

If chlorine is led into a solution of alkali hydrate, nothing 
but hypochlorite and chloride are produced as long as some of 
the hydrate remains unneutralized. This is because the excess 
of hydroxyl ions drives back the hydrolysis of the hypochlorite 
and therefore prevents the formation of a free hypochlorous 
acid. When an amount of chlorine equivalent to the hydrate 
has been added, there is still so small a quantity of free hypo- 
chlorous acid present that the solution is fairly stable. An 
excess of chlorine, however, increases the concentration of the 
free hypochlorous acid to such an extent that the hypochlorite 
is rapidly oxidized to chlorate, according to equation (7). The 
fact that an excess of chlorine was necessary to produce chlo- 
rate was first discovered by Gay-Lussac. 7 The addition of a 
small quantity of free acid would have the same effect as an 
excess of chlorine, for it would set free hypochlorous acid. 

7 Liebig Ann. 43, 153, (1842). 



84 APPLIED ELECTROCHEMISTRY 

If chlorate were formed only by means of free hypochlorous 
acid, hypochlorite would be more stable the greater the excess 
of hydroxyl ions in the solution. Chlorate is produced, how- 
ever, slowly in alkaline solutions, presumably by the reaction 

3 NaOCl = NaClO 3 + 2 NaCl. (10) 

Hypochlorous acid breaks up in exactly the same way, when it 
decomposes of itself. The solution has to be heated to 70 C. to 
make this reaction proceed with an appreciable velocity, 6 and 
it is also catalyzed by light. With increasing alkalinity the 
velocity of the reaction increases somewhat, and it is always 
accompanied by the reaction : 

2 NaOCl = O 2 + 2 NaCl. (11) 

The last reaction is catalyzed by some metallic oxides, espe- 
cially by the oxide of cobalt, to such an extent that all of the 
hypochlorite can be decomposed in this way without forming 
any chlorate. 6 

Perchlorate cannot be formed by the further action of 
chlorine on chlorate, but is produced by the decomposition of 
chlorate, as will be explained below. 

The Electrolysis of Alkali Chloride on Smooth Platinum Elec- 
trodes without a Diaphragm 

If a concentrated neutral solution of alkali chloride is electro- 
lyzed between smooth platinum electrodes, the alkali is de- 
posited on the cathode and reacts with the water according to 
the equation : 

2 Na + 2 H 2 O = 2 NaOH + H 2 . (12) 

The hydrogen produced escapes, unless it is used up in reduc- 
ing some substance in the solution. On the anode, chlorine is 
liberated from the ionic form to free chlorine, as follows : 

2C1- + 2F=C1 2 . (13) 

The liberated chlorine partly dissolves in the water and at 
first partially escapes from the solution. Soon, however, the 
alkali hydrate produced at the cathode and the dissolved 



ELECTROLYSIS OF ALKALI CHLORIDES 85 

chlorine are brought together by the stirring produced by the 
escaping hydrogen, and after this no more chlorine escapes 
from the solution. Chlorine and alkali hydrate are produced 
in equivalent quantities, so that the equation (5), 

C1 2 + 2 NaOH = NaCl + NaOCl 4- H 2 O, 

is practically quantitative. It is evident that only 50 per cent 
of the chlorine liberated is obtained in the active form as hypo- 
chlorite. As the electrolysis proceeds, the hypochlorite becomes 
more and more concentrated, until finally a limiting concentra- 
tion is reached, whose value is determined by a number of factors, 
such as the material of the anode, the current densities on the 
anode and cathode, the temperature, and the original concentra- 
tion of the chloride solution. This is due to the fact that the 
hypochlorite, almost from the start, is also decomposed by the 
current, and this decomposition increases as the concentration 
of the hypochlorite increases, until the amount decomposed is 
just equal to the amount produced. This decomposition takes 
place in two ways ; at the cathode the hypochlorite is reduced 
by the hydrogen as follows : 

NaOCl + H 2 = H 2 4- NaCl, (15) 

and at the anode the hypochlorite ion is liberated, since it is 
more easily discharged than the chlorine ion, 1 and reacts with 
the water, producing chlorate and oxygen according to the 
following reaction : 2 

6 CIO- + 3 H 2 = 2 C10 3 - + 4 Cl- + 6 H+ + lO a . (1Q) 

This has been called the anode chlorate formation, since it takes 
place only on the anode and not throughout the solution. 

It may help in understanding the chloride electrolysis if, 
before discussing it further, a method of analysis is explained 
which has been extensively used in the study of this subject 
for following the reactions taking place during the electrolysis. 

1 Foerster and Miiller, Z. f. Elektroch. 8, 634, (1902). 

2 Foerster and Miiller, Z. f. Elektroch. 8, 667, (1902). This equation is con- 
sidered fairly well established, as will be shown below, though other explanations 
of the results are possible. 



86 APPLIED ELECTROCHEMISTRY 

This consists in analyzing the gas evolved from the cell and 
comparing the amount of hydrogen and oxygen in it with that 
evolved by the same current from a water coulometer. 3 If there 
is less hydrogen from the chloride cell than from the coulometer, 
the difference must have been used in reducing the hypochlorite, 
according to equation (15), as this is the only reducible substance 
in solution. The oxygen in the gas evolved from the cell con- 
taining the chloride solution must be due to the discharge of the 
hypochlorite ion, which reacts with the water according to equa- 
tion (16), producing chlorate and oxygen. Oettel believed 
that the reaction was simply the evolution of oxygen according 
to the equation : 

2 CIO- + H 2 = 2 HOC1 + i 2 , (IT) 

and he therefore called this portion of the current loss " water 
decomposition," but this view has since been found to be incor- 
rect. Since the proportion of oxygen evolved to the hypo- 
chlorite ions discharged is the same in either case, Oettel's 
calculations will not be changed, but the explanation of the 
oxygen evolution will be given by equation (16) in place of 
(17). According to equation (17), the oxygen evolved is pro- 
portional simply to a current loss without destroying hypochlo- 
rite already formed, while according to (16) it is proportional to 
a fraction of the current that changes hypochlorite to chlorate. 

The following example, illustrating the use of gas analysis for 
determining the yield in hypochlorite as the electrolysis pro- 
gr,esses, is taken from Oettel. 3 

The cell containing the chloride solution was connected in 
series with a water coulometer. During a given time, at the 
beginning of the electrolysis, 60 cubic centimeters of gas were 
evolved from the coulometer and 32 cubic centimeters from the 
chloride solution. In the coulometer, 40 cubic centimeters of 
the gas must have been hydrogen. By analysis it was found 
that the gas from the chloride solution had the following com- 
position : 30 cubic centimeters of hydrogen, 1.6 of oxygen, and 
0.4 of chlorine. This shows a difference in the amount of hy- 

* I\ Oettel, Z. f. Elektroch. 1, 354, (1894). 



ELECTROLYSIS OF ALKALI CHLORIDES 87 

drogen in the two cells of 10 cubic centimeters. This amount 
must therefore have been used to reduce the hypochlorite 
already formed. Since 40 cubic centimeters of hydrogen repre- 
sents the total current, or 100 per cent, the loss of current due 
to reduction was 100 x |$ = 25 per cent. The loss due to the 

evolution of chlorine equals 100 x - 1 , or 1 per cent. The 1.6 

cubic centimeters of oxygen are equivalent to twice as much 
hydrogen, or 3.2 cubic centimeters. The loss of current by 

o n 

changing hvpochlorite to chlorate was therefore 100 x = 8 

40 

per cent. The current used to produce hypochlorite is propor- 
tional to the amount of hydrogen evolved from the chloride 
solution, diminished by the quantity of chlorine evolved, and 
twice the amount of oxygen: 30 (3.2 -j- 0.4)= 26.4 cubic 
centimeters. The current yield is therefore 100 x J| = 66 per 
cent. This, of course, means that 66 per cent of the current 
produces hypochlorite according to equation (5) : 

Cl a + 2 NaOH = NaCl + NaOCl + H 2 O. 

The rest of the current destroys hypochlorite already produced, 
or produces chlorine which escapes from the cell. Chlorine is 
evolved, however, only at the very beginning of the electrolysis, 
before the hydrate and chlorine have had time to mix. The 
following table sums up the results of this calculation : 

Current used to produce hypochlorite 66 per cent 

Current used to reduce hypochlorite 25 per cant 

Current loss by changing hypochlorite to chlorate .... 8 per cent 

Current loss due to evolution of chlorine 1 per cent 

100 per cent 

The curves in Figure 24 4 will illustrate the results of the elec- 
trolysis of a neutral 4.37 normal sodium chloride solution with 
a current density on the anode of 0.075 ampere per square centi- 
meter and on the cathode of 0.18 ampere per square centimeter. 
The electrolysis was continued for 18 hours, but the plots are 
given for only 8 hours, as no change in the direction of the 

* Miiller, Z. f. anorg. Ch. 22, 33, (1900), and Z. f. Elektroch. 6, 14, (1899). 



88 



APPLIED ELECTKOCHEMISTRY 




FIG. 24. Electrolysis of a neutral, 4.37 
normal sodium chloride solution 



curves took place during the following 10 hours. The quanti- 
ties of hypochlorite and chlorate were determined by direct 

analysis, and are plotted in 
terms of oxygen contained by 
each in grams per liter. The 
corresponding scale of ordi- 
nates is on the left. The 
other curves were obtained by 
gas analysis as described 
above. The scale of ordiiiates 
for these is given on the right, 
in per cent. 

It will be seen that the 
fraction of the current used in 
evolving oxygen and for re- 
duction, and the concentration 
of the hypochlorite become 
constant at the same time. 
At first the concentration of the chlorate remains low, but 
increases steadily as soon as the concentration of the hypo- 
chlorite becomes constant. This shows that hypochlorite is 
the first product of the electrolysis and that it is the starting 
point for the formation of chlorate ; also that it is responsible 
for the evolution of oxygen, as would be expected from equa- 
tion (16). 

The same general effect is produced by electrolysis at 50 C., 
except that the concentration of the hypochlorite becomes con- 
stant at a lower value. This is due to the increase in the 
hydrolysis of the chlorine as the temperature rises, thus pro- 
ducing a greater concentration of hypochlorite ions on the 
anode from the beginning. The quantity of hypochlorite ions 
that has to be supplied to the anode from the solution before 
they are discharged is therefore less than at a lower temper- 
ature; consequently the concentration in the solution will not 
reach as high a value as in the cold solution before the amount 
of hypochlorite decomposed equals the amount produced. 6 

6 Foerster, Elektrochemie wasseriger Losungen, p. 364, (1905). 



ELECTROLYSIS OF ALKALI CHLORIDES 89 

Both the reduction of the hypochlorite at the cathode and 
the discharge of the hypochlorite ion on the anode are made 
more difficult by increasing the current density, as will be seen 
from the following considerations. The greater the quantity 
of chlorine coming from the anode, the more it tends to prevent 
the hypochlorite from reaching the anode, where it would be 
discharged, 6 and the smaller the cathode is made, the less oppor- 
tunity will the hypochlorite have of coming in contact with 
nascent hydrogen. This is the explanation of the experimen- 
tal fact that increasing the current density on the cathode low- 
ers the reduction, and on the anode it makes the evolution of 
oxygen less in the first stages of the electrolysis, which is equiv- 
alent to making the concentration of hypochlorite attainable 
greater. 

In a dilute solution of chloride, the maximum hypochlorite 
concentration is less than in a concentrated solution, because at 
a given concentration of chloride the hypochlorite must carry 
relatively more of the current than when there is a greater 
amount of chloride present, and this results in its being changed 
to chlorate. Table 10 illustrates the effects of temperature, 
current density, and concentration changes on the electrolysis 
of alkali chloride solutions. 

The reduction of the hypochlorite can be nearly entirely pre- 
vented by the addition of a small amount of potassium chro- 
mate to the solution. 6 Under the action of the current a thin 
diaphragm is produced that gives the cathode a brownish yel- 
low appearance when compared with a fresh piece of platinum, 
and which gives a test for chromium when dissolved in nitric 
acid. 7 This diaphragm is probably an oxide of chromium, 
since a cathode of metallic chromium does not prevent reduc- 
tion. Potassium chromate is as effective with a low-current 
density as with a high density. The curves 8 in Figure 25 show 
the effect of adding 0.18 per cent of chromate to a solution con- 

6 E. Miiller, Z. f. Elektroch. 5, 469, (1899); Imhoff, German Patent, 110,420, 
(1898). 

7 E. Mtiller, Z. f. Elektroch. 7, 401, (1901). 

8 E. Miiller, Z. f. Elektroch. 5, 470, (1899). 



90 



APPLIED ELECTROCHEMISTRY 



taining 30 per cent of sodium chloride. The broken lines refer 
to the solution without the chromate. The current density 
on the anode in both cases was 0.075 ampere per square centi- 
meter ; on the cathode, 0.18 ampere. The temperature was 
from 42 to 50 C. 



11X) 
80 
CO 

i 

40 
20 



C 


\ 












V 


s*^ 


CURRENT 


YIELD 














r 




REDUCTION 




+ .+.- 














N N^ 




CURRENT 


YIELD 




-+ 


> 








| , 




OXYGEN EVOLUTION 




F 

H> s^ P - 




OXYGEN EVOLUTION 


---- 


1- 




REDUCTION 1 




1 






4 8 12 16 20 24 



FIG. 25. Electrolysis of sodium chloride 

Full lines refer to solutions containing 0.18 per cent chromate, broken lines to solutions containing 

no chromate 

When potassium chromate is added, the whole loss in current 
will therefore be due to oxygen evolved according to equation 
(16), which may be written : 

6 CIO- + 3 H 2 O + 6 F = 6 H + + 2 C1O 8 - + 4 Cl~ + 1J O 2 

But 12 equivalents of electricity are required to produce 6 equiv- 
alents of hypochlorite, according to equation (5), which may be 
written : 

12 Cl- + 12 F + 12 NaOH = 6 NaCl + 6 NaOCl + 6 H 2 O, 

while 6 equivalents are required to discharge the hypochlorite ions 
required by (16). If as much hypochlorite is to be decomposed 
by (16) as is produced by (5), it is evident that twice as much of 
the current must be used in producing hypochlorite as is used in 
changing it to chlorate. That is, f of the current produces active 



ELECTROLYSIS OF ALKALI CHLORIDES 



91 



oxygen in the solution and -J produces free oxygen, at the same 
time changing the active oxygen from hypochlorite to chlorate, 
according to (16). Therefore, excluding reduction and the for- 
mation of chlorate by equation (7), when the concentration of 
the hypochlorite has reached a maximum, in a neutral or slightly 
alkaline solution, 33.3 per cent of the current will be used to 
produce free oxygen, and 66.7 per cent to produce active oxygen 
in the solution. 9 The oxygen evolution can never be greater 
than 33.3 per cent unless the concentration of the solution is 
small, in which case oxygen would be evolved by the discharge 
of hydroxyl ions. Except for these points, this relation is inde- 
pendent of the other conditions of the experiment, such as tem- 
perature, current density, and, within certain limits, the 
concentration. This is illustrated by the results in Table 10, 10 
column 5. 

TABLE 10 
Solution : 4.8 Normal NaCl and 2 Grams K 2 CrO 4 per Liter 







LIMITING CONC. OF OXYGEN 
IN NaClO. GRM. PER 


PER CENT OF CURRENT PRO- 




AiMPERES PER 


100 c.c. 


DUCING OXYGEN 


TEMPERATURE 


SQ. CM. ON 








ANODE 














Smooth 


Platinized 


Smooth 


Platinized 






Pt. Anode 


Pt. Anode 


Pt. Anode 


Pt. Anode 


13 


0.017 


0.34 


0.61 


33.3 


31.0 


13 


0.17 


0.68 


0.89 


30 to 33 


34.5 


50 


0.017 


0.17 


0.31 


30 to 31 


22.0 


50 


0.17 


0.42 


0.64 


30 


28.0 



The Solution Changed to One 1.7 Normal NaCl and Containing 2 Grams K 2 CrO 4 per 

Liter 



13 


0.017 


0.28 


0.48 


34 


33.5 


13 


0.17 


0.47 


0.65 


32.5 


35 


50 


0.017 


0.15 


0.23 


33.5 


29 to 31 


50 


0.17 


0.35 


0.40 


33 


33 to 34 


75 


0.017 


0.09 


0.15 


34 


25 to 27 


75 


0.17 


0.25 


0.32 


35 to 36 


29 



9 Foerster and Miiller, Z. f. Elektroch. 9, 199, (1903). 
10 Foerster and Miiller, Z. f. Elektroch. 9, 196, (1903). 



92 APPLIED ELECTROCHEMISTRY 

In the above experiments, when the oxygen evolution is less 
than 33.3 per cent, hypochlorite is lost by the secondary forma- 
tion of chlorate. Columns 3 and 5 show that the maximum 
concentration of hypochlorate is different under different con- 
ditions, but that when this concentration is reached, the frac- 
tion of the current used in oxygen evolution is practically the 
same under widely differing conditions. 

If the solution of sodium chloride is made acid with hydro- 
chloric acid at the beginning of the electrolysis, the first effect 
of electrolysis is to decompose the acid until the solution be- 
comes nearly neutral. 10 There always remains a small quantity 
of the free acid throughout the solution, however, liberating free 
hypochlorous acid, which oxidizes the hypochlorate to chlorate 
through the entire solution, according to equation (7). This 
gives a method of increasing th&^ yield in chlorate over that 
attainable in neutral or alkaline solutions, in which it has been 
shown above that the maximum yield is 66.7 per cent. If, 
before the maximum concentration of hypochlorite has been 
reached, a quantity of acid is added to the solution which is 
equivalent to only a fraction of the hypochlorite in the solution, 
the latter is completely oxidized to chlorate. Further elec- 
trolysis produces more hypochlorite, to which acid may again be 
added, producing more chlorate. 11 By this means, chlorate can 
be produced on smooth platinum electrodes with nearly 90 per 
cent of the theoretical current yield. In place of adding the 
requisite amount of hydrochloric acid from time to time, the 
solution may be kept slightly acid by the addition of potassium 
acid fluoride, KHF1 2 , as patented by the Siemens and Halske 
Company, 12 or of alkali bicarbonate, which is patented by the 
Aktiengesellschaft vorm. Schuckert & Co. 13 

Oettel found in his early experiments that adding 0.3 gram 
of potassium hydrate to 100 cubic centimeters of a solution 
containing 20 grams of potassium chloride does not materially 
affect the result of the electrotysis, but that as the alkalinity is 

n Foerster and Miiller, Z. f. Elektroch. 8, 13, (1902). 

12 Foerster and Miiller, Z. f. Elektroch. 10, 731, (1904). 

1 3 Foerster and Miiller, Z. f. Elektroch. 8, 12, (1902). 



ELECTROLYSIS OF ALKALI CHLORIDES 



93 




GRAMS OF N a O H PER LITER 



FIG. 26. Effect of alkalinity on the elec- 
trolysis of a solution of sodium chloride 



increased, the maximum concentration of hypochlorite becomes 
less, and the principal product of the electrolysis "is chlorate 
and free oxygen. 14 The curves in Figure 26 15 show the quanti- 
ties of chlorate and hypochlorife produced per liter by electro- 
lyzing for one hour solutions 
containing 200 grams of so- 
dium chloride and varying 
quantities of sodium hydrate 
in one liter. The ordinates 
are grams of oxygen per liter 
contained in the chlorate or 
hypochlorite of the solution, 
and the abscissae, the number 
of grains of sodium hydrate 
added to one liter of the solu- 
tion. The current density on 
the anode was 0.04 ampere 
per square centimeter. 

This reduction in the hypo- 
chlorite concentration and increase in that of the chlorate with 
increasing alkalinity is explained as follows : The reaction by 
which the chlorate is formed in strongly alkaline solutions is 
the same as that in neutral or slightly alkaline solutions, and is 
given in equation (16), and the difference produced by the 
strong alkalinity is that the chloride finds hydroxyl ions with 
which to react immediately on the anode, forming hypochlorite. 
There is therefore a much higher concentration of hypochlorite 
immediately on the anode than throughout the rest of the solu- 
tion, and consequently its discharge and the production of 
chlorate take place when the concentration throughout the 
solution is very low. 16 When the alkalinity is further in- 
creased, the hydroxyl ions also begin to be discharged and the 
yield in chlorate falls below 66.7 per cent, which accounts for 
the maximum point in the chlorate curve. 

14 Z. f. Elektroch. 1, 474, (1895). 

15 Miiller, Z. f. Elektroch. 6, 20, (1899) ; Z. f. anorg. Ch. 22, 72, (1900). 

16 Foerster and Miiller, Z. f. Elektroch. 9, 182, and 200, (1903) ; also Foerster, 
Elektrochemie wasseriger Losungeu, p. 366, (1905). 



94 



APPLIED ELECTROCHEMISTRY 



Another difference in the electrolysis of strongly alkaline 
solutions is the effect of temperature. Higher temperature in 
neutral solutions decreases the maximum concentration of hypo- 

chlorite obtainable, but in 
strongly alkaline solutions 
the effect of temperature is 
just the reverse, as shown in 
the curves in Figure 27. 15 
The ordi nates are the number 
of grams of oxygen contained 
in the hypochlorite or chlo- 
rate in one liter of a solu- 
tion originally containing 200 
grams of sodium chloride and 
40 grams of sodium hydrate 
the same volume. The 



40 

TEMPERATURE 



FIG. 27. Effect of temperature on the 
electrolysis of an alkaline solution of 
sodium chloride 



111 



electrolyses lasted one hour each, with a current density on the 
anode of 0.045 ampere per square centimeter. Increasing the 
anode current density tends to counteract this temperature 
effect. From the explanation given of these curves 17 it does 
not seem that the effect of temperature in strongly alkaline 
solutions is thoroughly understood. 

The Electrolysis of Alkali Chlorides with Platinized Platinum 

Anodes 

Lorenz and Wehrlin 1 showed that the use of a platinized 
platinum anode increases the maximum concentration of hypo- 
chlorite, and that the oxygen evolution and the production of 
chlorate do not begin at a time when, on smooth platinum, 
under the same conditions of the experiment, the oxygen evolu- 
tion would be considerable. When the electrolysis is continued 
for a longer time, however, oxygen evolution and chlorate for- 
mation begin just as on smooth platinum anodes, and according 
to the same reaction. 2 The only difference is that a higher 

17 Foerster and Muller, Z. f. Elektroch. 9, 205, (1903) 

1 Z.f. Elektroch. 6, 437, (1900). 

2 Foerster and Muller, Z. f. Elektroch. 8, 515, (1902). 



ELECTROLYSIS OF ALKALI CHLORIDES 



95 




i 

4 



80 



=== 



GO 




40 



concentration of hypochlorite is produced before the quantity 
decomposed in a given time is equal to that produced. This is 
illustrated by the curves in Figure 28, obtained with a 5.1 
normal solution of 

10 1 J 4- I L^ c/,T~l 1 1 100 



sodium chloride, con- 
taining 2 grams of 
potassium chromate 
per liter. 2 The brok- 
en curves were ob- 
tained with a smooth 
platinum anode, the 
solid curves with a 
platinized anode. 
The ordinates on the 
right give the per 
cent of the current 
yield and the per 
cent of the current 
used for the evolu- 
tion of oxygen, while 
on the left the ordi- 
nates give the num- 
ber of grams per liter of oxygen in the form of chlorate and 
hypochlorite. The current density on the anode was 0.067 
ampere per square centimeter. An explanation of the higher 
concentration of hypochlorite obtained with platinized anodes 
will be given below in discussing potentials and decomposition 
points. 



FIG. 28. The electrolysis of a 5.1 n. sodium chloride 
solution, containing 2 grams of potassium chro- 
mate per liter 

Dotted lines refer to smooth platinum anode, full lines to 
platinized platinum anode 



The Electrolysis of Alkali Chlorides on Carbon Anodes 

All carbon electrodes are more or less porous ; that portion 
of their entire volume which consists of pores, or the porosity, 
varies from 11.2 to 27.8 per cent for different kinds of carbon. 
For Acheson graphite the porosity is 22.9 per cent. 1 The 
porosity is calculated from the true and the apparent densities. 



1 Foerster, Elektrochemie wasseriger Losungen, p. 372, (1905). 



96 APPLIED ELECTROCHEMISTRY 

The apparent density b is the weight of one cubic centimeter of 
the material, while the true density a is the weight divided by 
the volume actually occupied by the material. The value of a 
is determined by mixing bromoform and chloroform in such 
proportions that small pieces of the carbon will neither sink nor 
float when saturated with the mixture. 2 The density of the 
mixture is then determined by any of the well-known methods, 
and thus gives that of the carbon directly. The value of the 

porosity is then 100 - per cent. 

On dipping a carbon electrode into a solution, the pores become 
filled with the solution, and the solution contained in the electrode 
is electrolyzed as well as that on the surface ; but since the dis- 
solved salt cannot be replaced in the pores as rapidly as in the 
solution on the surface of the electrode, where stirring replaces 
the salt decomposed, the solution contained in the pores becomes 
more dilute than on the surface. Consequently the evolution 
of oxygen and the production of chlorate will begin sooner, 
and the maximum concentration of hypochlorite will be less 
than on a platinum electrode, when the other conditions of the 
experiment are the same. 3 

The effect of changing the chloride concentration or the 
anode current density on the yield of hypochlorite and on the 
maximum concentration attainable with carbon anodes is in 
the same direction as with platinum electrodes. 

A part of the oxygen liberated oxidizes the carbon to carbon 
dioxide, part of which, remaining in the solution, makes the 
solution slightly acid, and therefore changes the hypochlorite to 
chlorate by equation (16). The formation of carbonic acid 
takes place in solutions at 20 only to a small extent and after 
several hours, but at 60 it begins at once, and the total quantities 
contained in the gases evolved and dissolved in the solution 
amount to as much as 27 per cent of the amount that would be 
produced if this were the only product on the anode of the 
electrolysis. 4 

2 Zellner, Z. f. Elektroch. 5, 450, (1899). 

8 L. Sproesser, Z. f. Elektroch. 7," 1083, (1901). 

* Z. f. Elektroch. 7, 944 and 1014, (1901). 



ELECTROLYSIS OF ALKALI CHLORIDES 97 

Carbon anodes are also subject to mechanical destruction, due 
to crumbling, and in some kinds of carbon this may exceed the 
loss due to chemical action. 

The solution in the pores of the carbon may eventually be- 
come so dilute that hydroxyl ions are discharged, causing the 
production of hydrochloric acid around the anode ; for hydrogen 
ions are left behind by the discharge of hydroxyl ions and, com- 
ing in contact with chlorine ions migrating from the anode, 
form hydrochloric acid. This fact will be shown later to be 
of some practical importance. 

Acheson graphite has been found to last better in the elec- 
trolysis of chlorides than any other kind of carbon. 1 



The Maximum Concentrations of Hypo chlorite and the Maxi- 
mum Current and Energy Yields of Hypochlorite and 
Chlorate 

From what has preceded, it will be evident that the best 
conditions. for obtaining a high concentration in hypochlorite 
are to have a neutral, concentrated chloride solution, a low tem- 
perature, platinized anodes, and to prevent reduction by potas- 
sium chromate. Column 4 in Table 11 shows the maximum 
amount of hypochlorite obtainable under different conditions 
of the experiment. 1 The values given in grams of oxygen may 
be changed to grams of chlorine by multiplying the former by 

5^4^ = 2:22. 2 The solution was 4.79 normal with respect to 
16 

sodium chloride and contained 2 grams of potassium chromate 
per liter. In the last experiment the solution was only 1.73 
normal. Both electrodes were platinized. 

Since the decomposition value of a concentrated solution of 
sodium chloride on either smooth or platinized platinum is 2.2 
volts, the minimum amount of energy necessary to produce 

1 Foerster and Muller, Z. f. Elektroch. 8, 10, (1902). 

2 Foerster and Muller use the ratio 4.44, which is the ratio of the chemical 
equivalence of the chlorine and oxygen contained in hypochlorite. The ratio of 
the weights contained, however, is 2.22. 



98 



APPLIED ELECTROCHEMISTRY 



one gram of oxygen in the form of hypochlorite is 7.4 watt 
hours. From the table it is evident that with the lowest 
current density this value is very closely approached. 



TABLE 11 









GKAMS PER LITER 






CENTIGRADE 


PEK SQ. CM. 


VOLTS 


Of 0, in 


OfCljin 


YIELD IN 


PER GRAM 2 IN 


DEOBEES 


ON ANODE 




Hypochlo- 


Hypochlo- 


PER CENT 


HYPOCHLORITE 








rite 


rite 






13 


0.017 


2.40 


4.20 


9.3 


96 


8.4 


13 


0.017 


2.40 


5.24 


11.6 


90 


8.95 


10 


0.07 


3.10 


6.8 


15.0 


96 


10.84 


13 


0.17 


3.6 


5.28 


11.7 


99 


12.2 


13 


0.17 


3.6 


8.7 


19.8 


87 


13.5 


14 


0.17 


4.7 


5.20 


11.5 


95 


16.6 



If chlorate is produced entirely secondarily by acidifying the 
solution from time to time, no energy is required for its forma- 
tion beyond the 7.4 watt hours necessary for the production of 
the hypochlorite. By working in this way and by using plati- 
nized electrodes, an average current yield of 98 per cent was 
obtained in a run in which 3.66 volts were applied to the cell. 3 
This is 12.5 watt hours per gram of oxygen in the form of 
chlorate. The current density was 0.117 ampere per square 
centimeter. By reducing the current density the theoretical 
value of 7.4 watt hours could of course be more nearly 
approached. 

The Production of Per chlorates 

A perchlorate is a more stable compound than a chlorate, since, 
as is well known, a chlorate on heating first breaks up into 
perchlorate, chloride, and oxygen, according to the equations : * 

2 KC1O 8 = 2 KC1 + 3 O 2 , (18) 

4 KClOg = 3 KC1O 4 + KC1. (19) 

Foerster and Mtiller, Z. f. Elektroch. 8, 16, (1902). 

1 Roscoe and Schorlemmer, Treatise on Chemistry, 1, 235, (1905). 



ELECTROLYSIS OF ALKALI CHLORIDES 99 

A solution of chloric acid is also unstable when its concentra- 
tion exceeds a certain value, and breaks up as follows : 2 

2 HClOg = HC10 4 + HC10 2 . (20) 

The chloric and chlorous acids then react according to the fol- 
lowing reversible reaction : 

HC10 3 + HC10 2 ^ H 2 + 2 C10 2 . (21) 

These reactions are similar to those by which hypochlorous 
acid breaks up, 

3HC1O = HC1O 3 +2HC1, 
HC1O + HC1 ^ Cl 2 + H 2 O. 

Perchlorates are produced in a purely chemical way only by 
the breaking up of a chlorate, and not by direct oxidation. 

The electrolytic production of perchlorate and of perchloric 
acid was discovered by Count Stadion 3 in 1816, but the way 
in which this oxidation takes place was not understood until 
recently. This is not a direct oxidation of chlorate to per- 
chlorate, as would be expressed by the equation : 

ClOg- + 2 OH- + 2 F = ClO^ + H 2 O, 

but is due to the discharge of the chlorate ions and their sub- 
sequent reaction with water, as follows : 4 

2 C10 3 - + H 2 + 2 F = HC10 4 + HC1O 2 + O. (22) 

The oxygen does not escape, but oxidizes the chlorous acid 
back to chloric acid : 

HC1O 2 + O = HC10 3 . (23) 

The principal facts concerning the production of perchlorate 
are : (1) If the concentration of the chlorate is over 8 per cent, 
a change in its concentration has no appreciable effect on the 
current yield ; (2) the yield increases with increasing current 
density; (3) the yield falls with increasing temperature; 
(4) platinizing the anode decreases the yield and (5) in 

2 Oechsli, Z. f. Elektroch. 9, 807, (1903). 

3 Gilbert's Ann. 52, 218, (1816). 

4 Oechsli, I.e., p. 819. 



100 APPLIED ELECTROCHEMISTRY 

electrolyzing alkali chlorides, perchlorate is not produced until 
nearly all of the chloride has been changed to chlorate. 

In an acid or neutral chlorate solution, perchlorate can be 
produced with a high current yield, as Table 12 shows, giving 
the results of an experiment in which 66 per cent sodium 
chlorate solution was electrolyzed with a smooth platinum 
anode on which the current density was 0.083 ampere per 
square centimeter. The temperature was 9 C. 

TABLE 12 



TIME IN MINUTES FROM BEGINNING 
OF ELECTROLYSIS 


CURRENT YIELD PER CBNT 


5 


96.4 


20 


99.5 


35 


99.9 


180 


99.9 


210 


99.8 


300 


99.1 



Alkalinity prevents the formation of perchlorates ; the cur- 
rent yield falls to 16 per cent for a solution 0.242 normal with 
respect to sodium hydrate, with the same current density as in 
the experiment above. This is probably due to the smaller 
number of chlorate ions that are liberated as the alkalinity is 
increased, furnishing hydroxyl ions that are more easily dis- 
charged than the chlorate. An increase in the current den- 
sity would be expected to counteract this effect of the alkali, 
and experiment shows that it does. The lower yield with 
platinized anodes is due to the lower current density produced 
by the larger surface. 

The reduction in the yield by an increase in the temperature 
is supposed to be due to the greater concentration of hydroxyl 
ions of water from the increase in the dissociation with the 
temperature. 



ELECTROLYSIS OF ALKALI CHLORIDES 101 

The Electrolysis of Alkali Chlorides with a Diaphragm 

If the object in electrolyzing an alkali chloride is to produce 
an alkali hydrate and chlorine, the anode and cathode must be 
separated in order to prevent the hydrate and chlorine from 
mixing. There are four ways in which the separation of the 
hydrate and chlorine is effected. These are: (1) by the use of 
a diaphragm ; (2) by inclosing the anode in an inverted, non- 
conducting bell, with the cathode outside ; (3) by charging a 
mercury cathode with sodium in an electrolytic cell and decom- 
posing the sodium amalgam with water in another vessel ; and 
(4) by a mercury diaphragm, which acts as an intermediate 
electrode. 

(1) Since electrolytic conduction takes place through a dia- 
phragm, it is evident that the separation in this case will not 
be perfect, for the diaphragm prevents only mechanical mixing. 
The hydroxyl ions will migrate through the diaphragm and 
react with the chlorine in the same way as described above. 
The hydroxyl ions also pass through the diaphragm by ordi- 
nary diffusion. Electro-osmosis, on the other hand, drives the 
liquid through the diaphragm from the anode to the cathode, 
and therefore opposes the diffusion and migration of the 
hydroxyl ions. 1 

If diffusion and osmosis just balance each other, the yield in 
hydrate can be calculated as follows. 1 Before sodium hydroxide 
appears at the diaphragm, the sodium chloride transports all 
of the electricity, but when the hydrate is mixed with the 
chlorine, the hydrate will also take part in carrying the current 
through the diaphragm. If the fraction of the current carried 
by the hydrate is x, that carried by the chloride will be 1 - x, 
and x and 1 x must be proportional to the conductivities of 
the hydrate and of the chloride in the solution. If L is the 
conductivity of the chloride and L 2 that of the hydrate, this is 
expressed by the equation : 

1 X 




1 Foerster and Jorre, Z. f. anorg. Ch. 23, 158, (1899). 



102 APPLIED ELECTROCHEMISTRY 

in which c and c 2 are the concentrations in moles per liter, a x 
and 2 are the dissociations, and A/oc and X"oc are the conduc- 
tivities at infinite dilution, of the chloride and hydrate respec- 

X' 
tively. For potassium chloride and potassium hydrate, ^ = 

A <x 

0.545, and for sodium chloride and sodium hydrate, the value 
of this fraction is 0.502. For potassium chloride and potas- 
sium hydrate, equation (24) becomes 

1= = 0.545^, 



or 

(25) 



+ 0.545 



, 

1 



and for sodium hydrate and sodium chloride, 



x" = - - - . (26) 

1 + 0.502^ 



Now if all of the current were carried by the hydrate, and if 
n were its transference number, n equivalents of hydrate would 
pass out of the cathode compartment through the diaphragm in 
the same time that one equivalent is produced. In this case 
the yield in hydrate would be 

A = 100 (1 - n) per cent. 

The hydrate carries only a fraction of the current, however, 
equal to x. The yield is therefore 

A = 100 (1 nx) per cent. 

The transference number, w, for potassium hydrate is 0.74, and 
for sodium hydrate it is 0.83. 2 Substituting the values for x 
in equations (25) and (26), and the values for n just given, for 
potassium, 



ioo - ' 74 



1 + 0.545 ^3 
3 Foerster, Elektrochemie wasseriger Losungen, p. 400, (1905). 



(27) 



ELECTROLYSIS OF ALKALI CHLORIDES 103 

and for sodium, 

__mn - 83 _l 

(28) 



1+0.502 



It is evident from these equations that, as the hydrate becomes 
more concentrated, the fraction in the parenthesis becomes 
greater, which reduces the value of A. Table 13 shows how 
the yield decreases as the concentration increases. 3 The elec- 
trolysis was carried out with 700 cubic centimeters of a solution 
containing 200 grams of potassium chloride per liter in the 
cathode compartment, and 500 cubic centimeters of the same 
solution in the anode compartment. The electrodes were plati- 
num, and the diaphragm was of Pukal clay. The current 
density on the diaphragm was 0.016 ampere per square centi- 
meter. The yield which was being obtained at the end of each 
period was calculated by formula (27) from the values of the 
concentrations of chloride and hydrate existing at the end of 
the period, assuming that the dissociation of the hydrate and 
chloride are equal. 

TABLE 13 











EQUIVALENTS PER 




TIME 


GRAMS OF 
KOH PRO- 
DUCED 


GRAMS Cu 

DEPOSITED IN 
COULOMETER 


MEAN CURRENT 
YIELD FOR THE 
CORRESPONDING 


LITER IN THE 
CATHODE COM- 
PARTMENT OF 


COMPUTED 
CURRENT 
YIELD 










Chloride 


Hydrate 




1st 2 hrs. 


17.78 


11.47 


88.08 


2.382 


0.418 


81.3 


2d 2 hrs. 


14.29 


11.71 


69.30 


2.224 


0.754 


70.4 


3d 2 hrs. 


13.60 


11.61 


66.50 


2.096 


1.071 


62.6 


4th 2 hrs. 


11.11 


11.85 


58.02 


2.066 


1.331 


55.0 



It will be seen from the numerical values in equations (27) 
and (28) that the yield of hydrate with potassium chloride will 
be better than with sodium chloride, at 18 , to which temperature 
these numbers apply. Since, however, all transference numbers 
approach the limit 0.5 as the temperature is raised, these formulae 
indicate that the yield in hydrate would increase with the tem- 
Foerster and Jorre, Z. f. anorg. Ch. 23, 193, (1899). 



104 



APPLIED ELECTROCHEMISTRY 



perature and approach the same value for sodium and potassium 
chlorides. Since a rise in the temperature also increases the 
diffusion, the increase in the yield which would be predicted by 
the formula would be somewhat too large. 3 

Since the hydroxyl ions that migrate to the anode compart- 
ment find an excess of chlorine, hypochlorous acid will be pro- 
duced according to equation (2) : 

C1 2 + OH- = HOC1 + C1-. 

If this proceeded indefinitely, the loss in chlorine would be twice 
the loss in hydrate. On platinum anodes this has been found to 
be true in the first stages of the electrolysis. As the hypochlo- 
rous acid becomes more concentrated, compared to the chlorine, 
it will be neutralized by the hydroxyl ions coming through the 
diaphragm, forming hypochlorite. This is then immediately 
oxidized to chlorate by the excess of hypochlorous acid, accord- 
ing to equation (7). Consequently, no hypochlorite is found 
in the anode compartment. 

The process in the anode compartment is essentially the same 

when carbon anodes are 
substituted for platinum, 
with the exception, of 
course, that carbon dioxide, 
as well as oxygen, is pro- 
duced. 

(2) The principle of the 
bell process is illustrated in 
Figure 29. The anode is 
placed in a bell and the 
cathode outside. The cur- 
rent flows under the lower 
rim of the bell from anode 

to cathode. Chlorine is evolved and passes out through the 
tube in the top of the bell, while hydrate is formed on the 
cathode. The process that takes place in this cell is very simi- 
lar to that in a cell with a diaphragm. 4 At first the solution 




Fio. 29. Bell process 



4 Gustav Adolph, Z. f. Elektroch. 7, 581, (1901). 



ELECTROLYSIS OF ALKALI CHLORIDES 105 

in the anode compartment is divided into three sharply denned 
layers, the upper one saturated with chlorine, next to this a 
layer of unchanged chloride, and below this a layer containing a 
large number of hydroxyl ions. The hydroxyl ions migrate 
towards the anode, and on coming in contact with an excess of 
chlorine react in the same way as when a diaphragm is used. 

With carbon anodes in the bell process, a much higher 
hydrate concentration can be obtained without destroying the 
middle layer of the neutral solution separating the chlorine 
from the hydroxide; at the same time, however, the current 
yield is less than the theoretical. This is due to the fact that 
free oxygen is always evolved on carbon anodes, producing free 
hydrochloric acid. The hydrogen ions from this acid migrate 
towards the cathode and neutralize the hydroxyl ions migrating 
towards the anode, and thus prevent their coming in contact 
with free chlorine. In consequence of this, much more highly 
concentrated solutions of hydrate can be produced by the bell 
process with the same energy yield than by the diaphragm 
process. 5 

In actual practice the bell process is always carried out with 
a circulating electrolyte. Fresh chloride solution flows into 
the anode compartment, where it must be spread out uniformly 
over the entire area of the bell, so that the neutral layer will 
not be disturbed. 

In the bell process the losses of chlorine and hydrate are 
equal, so that the current yields in chlorine and hydrate 
must also be equal. The chlorine dissolved in the anode solu- 
tion is carried through the neutral layer by circulation and is 
changed to hypochlorite on coming in contact with the hydroxyl 
ions below. This is reduced on the cathode, producing an 
equal loss in hydrate. The loss in chlorine at the anode by 
the evolution of oxygen also produces an equal loss in hydrate, 
for the hydrochloric acid left behind by the oxygen neutralizes 
an equivalent amount of hydrate. 6 

With a circulating electrolyte a current yield of from 85 to 

5 Adolph, I.e. p. 589. 

6 Otto Steiner, Z. f. Elektroch. 10, 320, (1904). 



106 APPLIED ELECTROCHEMISTRY 

94 per cent can be obtained, with the concentration of potassium 
hydrate 120 to 130 grams per liter, and the chlorine 97 to 100 
per cent pure, using a current density referred to the area of 
the bell of 2 to 4 amperes per square decimeter, and from 3.7 
to 4.2 volts. 7 

(3) The third method of separating the hydrate from the 
chlorine consists in depositing the metal in a mercury cathode, 
which is then removed from the cell and treated with water. 
The sodium or potassium reacts with the water, forming the 
hydrate, and the mercury is returned to the cell to be used over 
again. The losses in this process are due to the recombination 
of chlorine dissolved in the solution with the alkali metal in the 
amalgam, and to the reaction of the alkali metal with the water 
before leaving the electrolyzing cell. The former loss may 
amount to 100 per cent under some circumstances, while the 
loss due to the decomposition of water is small. 8 In order to 
reduce the recombination of the chloride and the alkali metal, 
the current density on the cathode should be high and also the 
concentration of the amalgam. Strange as it may seem, the 
potassium amalgam is more resistant to chlorine, the more con- 
centrated it is. For example, increasing the concentration of 
the amalgam from 0.012 per cent to 0.06 per cent increased 
the yield in comparable experiments from zero to 90 per cent. 
A current density of 0.1 ampere per square centimeter gave an 
88 per cent current yield. Since the principal loss is due to a 
recombination of the chlorine and the alkali metal, the yield 
will be the same for both alkali and chlorine. If the amalgam 
is covered with a diaphragm to protect it from the chlorine, 
current yields of 98 per cent can be obtained. 8 

(4) The fourth method of separating the hydrate from the 
chlorine consists in using mercury as an intermediate electrode. 
The principle of this process is illustrated in Figure 30. The 
electrolytic cell is seen to consist of three compartments ; the 
two outer are the anode compartments containing the graphite 
anodes AA, and the middle compartment contains the cathode 

7 Z. f. Elektroch. 10, 330, (1904). 

8 F. Glaser, Z. f. Elektroch. 8, 552, (1902). 



ELECTROLYSIS OF ALKALI CHLORIDES 



107 




(7, consisting of an iron grid. The covers of the anode com- 
partments have pipes, not shown in the figure, for leading off 
the chlorine, but the cathode compartment is only loosely cov- 
ered, so that the hydrogen escapes in the air. 

The partitions separating the compartments do not quite 
reach to the bottom of the cell, 
but the opening is closed by a 
layer of mercury covering the 
bottom of the cell. The alkali 
metal is electrolyzed into the 
mercury in the anode compart- 
ment and is electrolyzed out in 
the cathode compartment. In 

the Cathode compartment the FIG. 30. Cell with mercury diaphragm 

amalgam is the anode, and the 

alkali metal unites with the hydroxyl ions liberated on it and 
forms hydrate. In order to stir up the amalgam so that the 
alkali metal will get into the cathode compartment as soon as 
possible, the whole cell is slowly tilted back and forth, causing 
the mercury to flow from one compartment to the other. 

In this system the current density on the cathode must also 
be at least 0.1 ampere per square centimeter. 9 The speed of 
rocking the cell also affects the yield, an increase in the rapidity 
decreasing the yield. One of the difficulties encountered in 
this process is that if the alkali metal becomes too dilute in the 
amalgam, the mercury is itself oxidized in the anode compart- 
ment. To avoid this, a part of the current is taken directly 
from the mercury by a shunt circuit in which there is a suitable 
resistance to make the shunted current about one tenth of the 
total current. A decrease in the concentration of the chloride 
solution reduces the current yield. With a 30 per cent potas- 
sium chloride at a temperature of 40, and with a current 
density of 0.1 ampere per square centimeter, Cantoni obtained 
a current yield in hydrate of 90 per cent. 

Le Blanc and Cantoni, Z. f. Elektroch. 11, 611, (1905). . 



108 APPLIED ELECTROCHEMISTRY 

Decomposition Points and Potentials of Alkali Chloride /Solutions 

In a chloride solution before electrolysis there are only the 
hydroxyl and chlorine anions, while after the electrolysis there 
are also hypochlorite and chlorate anions. The cations are 
the alkali metal and hydrogen both before and after electrol- 
ysis. A knowledge of the potential differences between anode 
and solution at which the different anions are discharged will 
help in understanding the chloride electrolysis. 

The potential difference at which an ionized substance is 
discharged, or, what is the same thing, if the process is reversi- 
ble, the potential difference produced by the substance when 
brought in contact with a platinum electrode, is dependent on 
its chemical nature and on its concentrations in the charged 
and discharged conditions. Thus the potential difference 
between a platinum electrode charged with chlorine and a 
chloride solution is 

T> rji Tf /T n rn\~ i~1 

-flJ- i "'VcL MJLl i 7. i i VCL. (^9^ 




where' <7 clj is the concentration of free chlorine in moles per 
liter surrounding the anode, tf cl _ is the concentration of chlo- 
rine ions in the solution, and k is a constant. If <7 C1 and <7 C1 _ 

RT 

are both equal, the value of e is - log k, and is called the 

electrolytic potential. For a solution saturated with chlorine 
at atmospheric pressure containing 0.064 mole per liter, and 
normal with respect to chlorine ions, e = 1.667 volts, 1 assum- 
ing the potential of the dropping electrode to be zero. The 
negative sign indicates that the solution is negatively charged. 
Chlorine, cannot therefore be liberated at atmospheric pressure 
at a potential difference less than this value. On a platinized 
platinum cathode in an acid solution, normal with respect to 
hydrogen ions, hydrogen would be liberated at 0.277 volt. 
But the solution around the cathode is neutral to start with, 
and soon after the electrolysis has begun is alkaline, due to the 

i Miiller, Z. f. phys. Ch. 40, 158, (1902). 



ELECTROLYSIS OF ALKALI CHLORIDES 



109 



formation of alkali hydrate. The hydrogen ion concentration 
is then very much reduced below its value in the original 
neutral solution. This alkalinity might have any value, but 
for the purpose of calculation the solution around the cathode 
will be assumed normal, though it would not reach such a high 
value in a cell not containing a diaphragm. The value of the 
potential of the cathode on tvhich hydrogen is being liberated 
would then be 0.54 volt, 0.82 volt more positive than the po- 
tential in a normal acid solution. 2 The cell would then have 
an electromotive force of its own of 

e = 0. 54 - ( - 1. 66) = 2.20 volts. 

The decomposition point of a concentrated solution of sodium 
chloride, determined, as usual, with a very small current, is 
1.95 volts, but this is because the solution around the cathode 
is more nearly neutral than assumed above. Continuous elec- 
trolysis requires from 2.3 to 2.1 volts. 3 




1.6 1.8 

ANODE POTENTIAL 



FIG. 31 . Curves showing the relation between current and anode potential, in 
solutions of sodium chloride and of sodium hypochlorite 

As was shown above, when the hypochlorite reaches a certain 
concentration, the hypochlorite ion is also deposited on the anode. 
It has never been possible to determine the decomposition point 
of this ion, however. It is evident from the curves in Figure 
31, 4 in which the decomposition points of two solutions are 

2 Le Blanc, Electrochemistry, p. 209, (1907). 

Lorenz, Z. f. Elektroch. 4, 247, (1897). 

* Foerster and Muller, Z. f. Elektroch. 8, 634, (1902). 



110 



APPLIED ELECTROCHEMISTRY 



given, one normal with sodium hypochlorite and 0.025 normal 
with sodium hydrate, the other normal with sodium chloride 
and 0.01 normal with sodium hydrate, that hypochlorite ions are 
not liberated before hydroxyl ions. This is shown by the fact 
that there was no increase in the current below the potential 
1.16 volts, approximately the point at which hydroxyl ions 
are liberated in a normal hydrate solution. It is also evident 
that the electrolysis of a normal chloride solution begins at a 
higher potential than the hypocholorite solution. The decom- 
position point of the hypochlorite ion therefore lies between 
those of the hydroxyl and the chlorine ions. 

Since there is a difference of about 0.5 volt between the de- 
composition points of chlorine and hydroxyl ions, it would 
seem impossible to liberate chlorine ions in a strongly 
alkaline solution. This would be the case if it were not 
that the potential of an anode on which oxygen is liberated 
increases continuously, and eventually reaches the potential 
at which chlorine is liberated. If it were not for this in- 
crease in the potential, caused by the liberation of oxygen, the 
decomposition of a chloride in an alkaline solution would be 
impossible. 5 Another effect which tends to make chlorine de- 
posit in an alkaline solution is the fact that the hydrate has a 
depolarizing effect on the chlorine, in consequence of which 
chlorine will be liberated at a lower potential than that neces- 
sary for its deposition at atmospheric pressure. Table 14 shows 

TABLE 14 







PER CENT YIELD IN ACTIVE OXYGEN 








POTENTIAL 


AMPEBES 


Total 


As Hypo- 
chlorite 


As Chlorate 


-1.09 


- 


1 


0.0 





-1.21 to -1.27 


0.016 





0.9 





- 1.30 to - 1.51 


0.28 to 0.14 


3.2 


2.6 


0.6 


- 1.51 to - 1.595 


0.5 to 0.4 


16.4 


8.2 


8.2 



6 Foerster and Mtiller, Z. f. Elektroch. 9, 184, (1903). 



ELECTROLYSIS OF ALKALI CHLORIDES 



111 



that hypochlorite and chlorate are formed in a solution normal 
with sodium hydrate, and 3.6 normal with sodium chloride, at 
an anode potential below 1.667 volts, the potential at which 
chlorine is liberated at atmospheric pressure. 6 The anode was 
platinized platinum, of 14 square centimeters area. 

It will be noticed that as the anode potential increases in nu- 
merical value, the proportion of chlorate to hypochlorite in- 
creases. This is due to the fact that the hypochlorite ions, 
which are more easily discharged than the chlorine ions, are 
more subject to deposition as the potential of the anode in- 




1.1 



1.3 ' 1.5 1.7 1.9 2.1 

ABSOLUTE POTENTIAL DIFFERENCE BETWEEN ANODE AND SOLUTION 



FIG. 32. Curves showing the relation between current and anode potential for 
smooth and for platinized platinum anodes 

creases, with the subsequent production of chlorate according 
to equation (16). 

On smooth platinum anodes the potential difference during 
electrolysis is about 0.58 volt greater than on platinized plati- 
num. 7 The decomposition points of sodium chloride on plati- 

e Foerster and Miiller, Z. f . Elektroch. 9, 183, and 201, (1903). 
7 Z. f. Elektroch. 6, 437, (1900). 



112 APPLIED ELECTROCHEMISTRY 

nized platinum and on smooth platinum anodes shows the same 
difference, as is seen from the curves in Figure 32. 8 It is evi- 
dent that the overpressure of an anion is a function not only of 
its own chemical nature, but also of the solution from which it 
is deposited, of the current density, and of the material com- 
posing the anode. 

The cause of this overpressure of 0.58 volt on platinum is not 
well understood; it may be due to the resistance of a film of gas 
liberated on the anode. There is a corresponding overvoltage 
in other solutions, such as sodium hydrate and sulphuric acid, 
where oxygen, in place of chlorine, is liberated. These over- 
pressures are not equal for the same current density in these 
different solutions. 9 

Though the overpressure on smooth platinum anodes may 
not itself be understood, its presence offers a possible explanation 
of the higher concentration of hypochlorite obtained with a 
platinized anode, for the relation between the decomposition 
potential and the concentration of ions is that the decomposition 
potential decreases as the concentration increases. Therefore, 
with a lower anode potential, the concentration of the hypo- 
chlorite ions would have to be greater before decomposition 
takes place. 10 

It is an experimental fact, as has been stated above, that very 
little perchlorate is produced until most of the chloride has been 
changed to chlorate. This is due to the fact that the decom- 
position potential of normal sodium chlorate is 2.36 volts, 11 while 
that of the chloride is 1.95 volts. 3 The high potential re- 
quired for the deposition of the chlorate cannot therefore be 
reached until most of the chloride has been used up. 

When chlorine- is dissolved in water, according to equations 
(2) and (4), a certain amount of hypochlorous acid and hypo- 
chlorite will be produced. Both hypochlorous acid arid hypo- 
chlorite are oxidizing agents, and therefore give an unattackable 

s Miiller, Z. f. Elektroch. 8, 426, (1902). 

Foerster and Miiller, Z. f. Elektroch. 8, 533, (1902). 
i Foerster and Miiller, Z. f. Elektroch. 9, 199, (1903). 
11 Wohlwill, Z. f. Elektrocb. 5, 52, (1898). 



ELECTROLYSIS OF ALKALI CHLORIDES 113 

electrode a definite potential. If the reactions by which they 
give off oxygen, or what is the same thing, hydroxyl ions, are 

HOC1 = OH- + Cl- + 2 F, (30) 

CIO- + H 2 O = Cl- + 2 OH + 2 F, (31) 

the potentials would be given by the equations 
RT , 






(33 > 



* V OH- 

and for equilibrium concentrations, 



tfj being taken from equation (29). When chlorine is liberated 
on an unattackable anode, the equilibrium represented by (9), 



= 3.6 x IP" 11 " ocl = 1.4 xlO' 17 



must be established, and, assuming the chlorine electrode is re- 
versible, the production of hypochlorite and hypochlorous acid 
must be, according to (31) and (32), taken from right to left. 
This means that a primary production of hypochlorite and 
hypochlorous acid takes place on the anode to a small extent. 

Fluorides, Bromides, and Iodides 

The electrolysis of the other alkali halogen compounds has 
not attained anything like the commercial importance of the 
electrolysis of chlorides ; still, for the sake of completeness, the 
behavior of the other alkali halides on electrolysis will be briefly 
described. 

Fluorine decomposes water with the evolution of oxygen and 
ozone : 

2 OH- + 2 Fl- = H 2 O + O. (35) 

No oxygen compounds of fluorine are known, consequently the 
electrolysis of fluorides offers nothing to compare with what 
is obtained in the case of chlorides. 



114 APPLIED ELECTROCHEMISTRY 

Bromine enters into exactly similar equilibria when added 
to alkali hydrate to those already described in the case of 
chlorine. They are represented by the equations : l 

Br 2 + OH- = HOBr + Bi-1 
HOBr + OH- = BrO- + H 2 OJ ' 

Hypobromite is therefore always the first product of the reac- 
tion when bromine acts on alkali hydrate. When one mole of 
bromine acts on one equivalent of hydrate, the reaction is not 
as complete as in the case of chlorine, but appreciable quantities 
of bromine and hydrate remain unchanged. 

The formation of bromate according to the equation 

2 HOBr + NaBrO = NaBrO 3 + 2 HBr (37) 

takes place with over 100 times the velocity of the correspond- 
ing reaction for chlorate. This reaction takes place even in 
slightly alkaline solutions with a high velocity, on account of 
the greater hydrolysis of hypobromite, but in solutions that are 
at least 0.1 normal with respect to hydrate, the hydrolysis has 
been so far reduced that hypobromite is as stable as hypo- 
chlorite. When a concentration of the hydrate is still further 
increased, the rate at which bromate is produced increases, 
probably according to the reaction : 

3 NaBrO = NaBrO 3 + 2 NaBr. (38) 

This differs from the corresponding reaction for chlorate, in 
that it proceeds with scarcely any evolution of oxygen. This 
reaction, however, is very much slower than that represented 
by equation (37), and need not be considered in the practical 
preparation of bromate. 

In electrolyzing a bromide solution, free bromine is liberated 
on the anode, accompanied by oxygen from the discharge of 
hydroxyl ions, and produces hypobromite with the hydrate 
formed at the cathode. The concentration of the hypobromite 
increases up to a certain point, after which it remains constant, 
and the only product of the electrolysis is then bromate. As 

i Horst Kretzschmar, Z. f. Elektroch. 10, 789, (1904). 



ELECTROLYSIS OF ALKALI CHLORIDES 115 

the hypobromite increases in concentration, the evolution of 
oxygen also increases, the hydroxyl ions for which are fur- 
nished by the hydrolysis of the hypobromite. 

Bromate is formed partly by the secondary oxidation of hypo- 
bromite by hypobromous acid, which is always present to a 
certain extent on the anode, and partly by direct oxidation 
according to the equation : 



(39) 

The hypobromite ion is not discharged, so there is no reaction 
between it and water, as there is in the case of the hypochlorite 
ion. 

The concentration of hypobromite attainable is greatest with 
a high current density, a high concentration of bromide, and a 
low temperature. It is also higher on platinized anodes than 
on smooth, as is the case with hypochlorite. The highest con- 
centration of hypobromite attainable is about the same as that 
of hypochlorite, but the current yield is less, on account of the 
greater tendency to form bromate. Unless potassium chro- 
mate is added to the solution, bromate, as well as hypobromite, 
is subject to reduction on a smooth platinum cathode, 2 which 
is another point of difference between chlorate and bromate. 

Perbromic acid and its salts cannot be produced by elec- 
trolysis, and it is doubtful whether they exist at all. 3 

When iodine is brought in contact with hydrate, the 
equilibria 

I 2 +OH-=HOI + I- 1 

HOI + OH- = 01- + H 2 I 

are established exactly as in the case of chlorine and bromine. 4 
Hypoiodite is very considerably hydrolyzed, and therefore, 
unless the solution is very alkaline, it changes rapidly to iodate 
by the reaction : 

2 HOI + KIO = KIO 3 + 2 HI. (41) 

2 H. Pauli, Z. f. Elektroch. 3, 474, (1897). 

8 Roscoe and Schorlemmer, Treatise on Chemistry, 1, 358, (1905). 

4 Foerster and K. Gyr, Z. f. Elektroch. 9, 1, (1903). 



116 APPLIED ELECTROCHEMISTRY 

If an excess of alkali is present, however, the hydrolysis is 
driven back, and hypoiodite can be obtained free from iodate. 
The formation of iodate is accelerated by an increase in the 
temperature and concentration of the iodide, and by decreasing 
the alkalinity. 

The rapidity with which hypoiodite changes to iodate is 
shown by the following facts : If 50 cubic centimeters of a 
0.1 normal iodine solution are mixed with 50 cubic centimeters 
of a normal sodium hydrate solution at zero degrees, a 0.05 
normal hypoiodite solution would be 100 per cent yield. Imme- 
diately after mixing, however, there is only 95 per cent of this 
amount of hypoiodite, and after 2 minutes, only 75 per cent 
remains. On dilution it is more stable ; a 0.01 normal hypoio- 
dite solution remains practically unchanged for a few minutes 
in a 0.1 normal alkaline solution at room temperature. 

On electrolyzing a neutral solution of alkali iodide, 5 the io- 
dine liberated on the anode comes in contact with the hydrate 
from the cathode, and the first product is hypoiodite. This 
changes over to iodate rapidly, as shown above, even in an alka- 
line solution, so that the electrolysis of an alkali iodide solution 
is similar to that of a slightly acid chloride solution. Conse- 
quently the hypoiodite solution reaches a limiting concentra- 
tion, after which the product of the electrolysis is exclusively 
iodate. This limiting concentration of hypoiodite is determined 
by the current density, temperature, and the concentration of 
iodide and alkali. An increase in the alkalinity increases the 
limiting concentration of the hypoiodite, while it decreases 
that of the hypochlorite. This is due to the different ways 
in which iodate and chlorate are formed in alkaline solutions. 

As the hypoiodite never can become concentrated, the possi- 
bility of the electrolytic discharge of the hypoiodite ion is 
very small. Therefore the oxygen evolution, which takes place 
only when the iodide is dilute and the solution is alkaline, 
must be due nearly entirely to the discharge of hydroxyl ions. 
It is therefore in no way connected with the formation of io- 
date. 

6 Foerster and Gyr, Z. f. Elektroch. 9, 215, (1903). 



ELECTROLYSIS OF ALKALI CHLORIDES 



117 



Periodates cannot be produced by the electrolysis of iodates 
except with a diaphragm. 6 This is shown by the fact that 
without a diaphragm no hydrogen is evolved on electrolysis, 
but is all used in reducing the iodate. After electrolysis has 
proceeded a while, the oxygen evolution also becomes zero. 
There is then a constant amount of iodide and iodate in the 
solution ; as fast as iodate is formed on the anode, it is reduced 
on the cathode. In neutral solutions iodate is not oxidized to 
periodate, and in alkaline solutions, potassium chromate does 
not prevent the reduction of iodate to iodide. 

By using a diaphragm, a current yield in periodate of about 
26 per cent can be obtained. The best conditions are low tem- 
perature, low-current density, and at least 4 per cent alkalinity. 



2. TECHNICAL CELLS FOR HYPOCHLORITE, CHLORATE, HY- 
DRATE, AND CHLORINE 

Hypochlorite. Hermite's cell, patented in 1887, was the 
first cell to be even moderately suc- 
cessful for the electrolytic manufac- 
ture of hypochlorite. 1 It consisted 
of a rectangular box of ceramic with 
a grooved channel around the top for 
carrying off the solution of sodium 
and magnesium chlorides, which 
entered at the bottom. The cathode 
consisted of numerous disks of zinc 
supported on two slowly rotating 
shafts running through the box and 
separated from each other by a parti- 
tion. The anodes, consisting of thin 
sheets of platinum held on a noncon- 
ducting frame, were placed between 
the zinc disks. In practice this cell 




FIG. 33. Elevation of Kellner 
cell 



6 E. Muller, Z. f. Elektroch, 7, 509, (1901). 

1 W. H. Walker, Electroch. Ind. 1, 440, (1903); Engelhardt, HypochJorite 
and Elektrische Bleiche, p. 77, (1903). 



118 



APPLIED ELECTROCHEMISTRY 



g.ives a current yield of about 40 per cent and an energy yield 

of one kilogram of chlorine for twelve kilowatt hours. 2 

The Kellner cell, made by the Siemens 
and Halske Company, is shown in Figures 
33, 34, and 35. A glazed stoneware vessel 
is divided into a number of compartments 
by glass plates fitted into grooves in the 
sides of the cell. The plates are wound 
with platinum -iridium wire, which acts 
as intermediate 

electrodes, form- [f] [i fj H H'H \] 1} fi H] 

ing the anodes 
on one side and 
the cathode on 
the other side of 
of the glass plates. 
The solution 

enters through holes in the bottom of 

the cell and the electrolyzed solution flows out spouts at the 



FIG. 34. Electrodes 
Kellner cell 











a 



FIG. 35. Plan of Kellner coll 




FIG. 36. Kellner cell 



top into a vessel containing a cooling coil. From here it is 
pumped up through the cell again. This circulation continues 



2 Engelhardt, I.e. p. 86. 



ELECTROLYSIS OF ALKALI CHLORIDES 



119 



until the desired strength of hypochlorite has been obtained. 
This is illustrated in Figure 36. 

The Schuckert cell is also made by the Siemens and Halske 
Company. It is made of stoneware and is divided into eight 




FIG. 37. Horizontal section of Haas aud Oettel cell 

or ten compartments, each having two graphite cathodes and a 
Pt-Ir foil anode. The solution enters at one end and travels 
in a zigzag direction through the different compartments. Each 
cell has a cooling coil, and no pumps are needed for circulation. 
The units are built in pairs and are designed for 110 volts. 



120 



APPLIED ELECTROCHEMISTRY 



The Haas and Oettel cell is shown in horizontal and vertical 
cross sections in Figures 37 and 38. 3 The electrolyzer b is im- 
mersed in the solution in the storage vessel a. The electrolyzer 
consists of a vessel divided into several compartments c by 
divisions r, made of carbon or any suitable material, and form- 
ing the intermediate electrodes. The liquid enters the elec- 
trolyzer through the passage d, one of which leads into each 
compartment. As soon as the current is turned on, gas is pro- 
duced in each compartment, which rises and, carrying the liquid 
with it, causes it to flow through the channels e, as shown by 
the arrows. This automatic circulation is very efficient. A 
cooling coil in the container prevents the temperature from 
rising too high. The electrolysis is continued till the concen- 
tration of the hypochlorite has reached the desired value. 






Ibsss^^^^^ 



1" 



FIG. 38. Vertical section of Haas and Oettel cell 

This cell was never put on the market in this country in the 
form shown, 4 but an improved cell is made by the National 
Laundry Machinery Company of Dayton, Ohio, the details of 
which are not now available. 

Among a number of other factors, the cost of the production 

8 U. S. Pat. 718,249, (1903). 

4 Communication from the National Laundry Machinery Company. 



ELECTROLYSIS OF ALKALI CHLORIDES 



121 



of hypochlorite depends on the cost of salt and of power, and 
on the concentration of the hypochlorite produced ; for, as was 
shown above, the current efficiency of the production of hypo- 
chlorite approaches zero as the concentration increases. For 
cotton bleaching the hypochlorite is diluted to three grams of 
active chlorine per liter, and is discarded after using. 5 Less 
salt will therefore be lost if as much as possible is changed to 
hypochlorite, but the cost of power increases as the concentra- 
tion increases. The concentration to which it will be most 
economical to continue the electrolysis will therefore depend 
on the relative cost of power and of salt, assuming all other 
conditions of the experiment constant. There will then be a 
concentration of hypochlorite for which the cost will be a mini^ 
mum, assuming a definite cost for the salt and the power. 
This minimum cost is found by plotting as ordinates the cost 



TABLE 15 

The Kellner Cell 



ORIGINAL NaCl 
CONC. KG. PER 
100 L. 


AMPERES PER 
CELL 


GRM. ACTIVE 

C1 2 PER L. 


PER CENT 
CURRENT 
YIELD 


KW. HR. PER 
KG. ACTIVE 
Cl, 


KG. SALT PER 
KG. ACTIVE 
01, 


6.3 


120 


1.84 


77.8 


5.9 


34.2 


6.3 


120 


3.34 


68.8 


6.7 


18.9 


6.3 


120 


7.06 


61.8 


7.4 


8.9 


6.3 


120 


10.01 


44.5 


10.3 


6.3 


10.0 


137 


3.09 


81.5 


5.2 


32.4 


10.0 


137 


6.85 


68.6 


6.2 


14.6 


10.0 


137 


10.44 


58.2 


7.3 


9.6 


10.0 


137 


12.96 


45.9 


9.2 


7.7 


15.0 


126 


3.00 


82.3 


5.1 


50.0 


15.0 


126 


6.28 


73.0 


5.7 


23.9 


15.0 


126 


10.50 


65.3 


6.4 


14.3 


15.0 


126 


13.50 


54.2 


7.7 


11.1 


20.0 


130 


2.48 


90.1 


4.5 


80.7 


20.0 


130 


6.58 


78.0 


5.2 


30.4 


20.0 


130 


10.09 


70.0 


5.8 


19.8 



6 W. H. Walker, Trans. Am. Electrochem. Soc. 9, 23, (1906). 



122 



APPLIED ELECTROCHEMISTRY 



of power for a definite amount of hypochlorite at different con- 
centrations, and also as ordinates the cost of the salt required for 
the different concentrations of hypochlorite. The curve repre- 
senting the sum of these costs will be found to have a minimum 
value. 

Table 15 gives some data on the yield of active chlorine in 
the Kellner cell, taken from cells in actual operation. 6 

The yields of active chlorine in the Haas and Oettel appara- 
tus are given in Table 16 7 



TABLE 16 
The Haas and Oettel Cell 



GEM. ACTIVE 

Clj PER L. 


PER CENT CURRENT YIELD 


KW. HR. PER KG. 
ACTIVE C1 2 


KG. SALT PER KG. 
ACTIVE C1 2 


2.55 


95.0 


3.31 


66.6 


4.59 


82.4 


3.82 


37.0 


8.82 


64.8 


4.85 


19.3 


12.30 


56.7 


5.54 


13.8 


14.31 


52.8 


5.96 


11.9 



The yields in active chlorine for the Schuckert cell are given 
in Table 17. 1 



TABLE 17 

The Schuckert Cell 



ORIGINAL NaCl 
CONC. PER CENT 


GRM. ACTIVE C1 2 PER L. 


KW. HR. PER KG. 
ACTIVE C1 2 


KG. SALT PER KG. 
ACTIVE C1 2 


10 


10-22 


7 


5- 5.3 


10 


16 


6 


6- 6.5 


10 


10-12 


5 


10-10.6 


15 


20-22 


5.5-6 


7.5- 8 


15 


10-12 


4.5-5 


15-16 



6 Englehardt, I.e. p. 158. 

7 Oettel, Z. f. Elektroch. 7, 315, (1900). 



ELECTROLYSIS OF ALKALI CHLORIDES 123 

Chlorate Cells. Since chlorate is made directly from hypo- 
chlorite, a chlorate cell would not be expected to differ from a 
hypochlorite cell in any mechanical details. The earlier chlo- 
rate cells, however, contained a diaphragm, and the cathode 
solution was allowed to circulate to the anode compartment. 
This was to prevent the reduction of the hypochlorite from 
which the chlorate is produced ; but since the discovery of the 
action of potassium chromate, reduction can be avoided with- 
out a diaphragm. 

The first process to be used in practice was that of Gall and 
Montlaur, patented in 1884. 8 This cell originally contained a 
diaphragm to prevent reduction, and the solution circulated 
from the cathode to the anode by means of external pipes. The 
solution must, of course, leave the anode compartment as rapidly 
as it flows in, but whether it leaves the cell entirely or returns 
to the cathode compartment is not stated. Since 1897 the 
diaphragms have been given up. A plant employing this pro- 
cess was put in operation at Vallorbe in 1891, and another in 
St. Michel, Savoy, in 1896. Very little information concerning 
these plants has been published. 

In 1892 the National Electrolytic Company at Niagara Falls 
employed the chlorate cell of W. T. Gibbs. 9 A number of 
these cells clamped together are shown in Figure 39, and a side 
elevation of one cell on the line 22 of the preceding figure, in 
Figure 40. 10 Each cell consists of a frame A made of wood with 
a metallic resistant lining B. The rods forming the cathode 
are attached on one side of this frame, and on the other, the 
anode, consisting of a metallic plate D faced with platinum E. 
Copper is preferred for the cathode and lead for the plate D. 
Successive frames are separated from each other by gaskets F. 
G- are supply tubes and .ff are vents for the escape of gas and 
liquid. The cells are clamped together by the plates JK and 
the bolts L. Each pair of electrodes is separated by the corre- 
sponding gasket. The horizontal insulating rods prevent 

8 J. B. C. Kershaw, Die Elektrolytische Chloratindustrie, p. 19, (1905). 

9 J. W. Richards, Electrochern. Ind. 1, 19, (1902). 
10 TJ. S. Pat. 665,426, (1901). 



124 



APPLIED ELECTROCHEMISTRY 



short circuit between the anodes and cathodes, which are only 
from 1 to 3 millimeters apart. The electrolyte circulates from 
the cell to a cooling vessel where the chlorate is precipitated. 




FIG. 39. Gibb's cells clamped together 

More chloride is then added, and the solution is returned to the 
electrolyzing cell. A convenient size for these cells is 65 by 
4-3 centimeters and 7.5 centimeters thick. 



ELECTROLYSIS OF ALKALI CHLORIDES 



125 



The cell of Lederlin and Corbin, used at Chedde, is of the 
open type. 11 It contains a platinum anode and two cathodes of 
copper, bronze, brass, or iron. The anode has an area of 10 
square centimeters and the cathode, 32. 




FIG. 40. Section of single Gibb's cell 



The chlorate is generally purified by recrystallization, and 
the recrystallizing apparatus is an important part of a chlorate 
plant. 

The yield at Vallorbe was at first 55.9 grams per kilowatt 
hour, though this has since been considerably increased. 12 



11 Kershaw, I.e. p. 38. 



Kershaw, I.e. p. 



126 



APPLIED ELECTROCHEMISTRY 



The yield obtained at Chedde with the Lederlin and Corbin 
cell in a slightly acid solution containing potassium bichromate 
was 0.69 gram per ampere hour, or 90 per cent of the theoretical. 

Perchlorates. The cells used for the production of chlorates 
can be used equally well for perchlorates. Whether there is a 
difference in practice cannot be stated, for no description of a 
perchlorate cell has been published. 

Alkali Hydrates and Chlorine. In cells in which hydrate 
and chlorine are to be the final product, the anode must be sep- 
arated from the cathode so that the chlorine and hydrate can- 
not mix. In the first type of cell to be considered, this is 
accomplished by means of a porous diaphragm. A very large 
number of such cells have been patented, but only a few need 
be described. 

One of the simplest of the diaphragm cells is McDonald's, 
used by the Clarion Paper Mill at Johnsonburg, Pennsylvania, 13 
and the United States Reduction and Refining Company in 
Colorado. At the latter plant, there are 75 cells, producing 
1500 pounds of chlorine in 24 hours. 14 Two vertical sections of 




LENGTHS SECTION. 



CROSS SECTION. 



BBBBSBBBB 






FIG. 41. McDonald cell 

the cell are shown in Figure 41. It consists of a cast-iron tank, 
1 foot wide, 1 foot high, and 5 feet and 2 inches long, with 
two longitudinal perforated partitions. The perforations are 
% inch in diameter, and there are 4 or 5 to the square inch. 
A diaphragm is placed next each partition in the middle com- 

13 Electrochem. Ind. 1, 387, (1903). 

14 J. B. procker, Electrochem. and Met. Ind. 5, 201, (1907). 



ELECTROLYSIS OF ALKALI CHLORIDES 127 

partment, containing the anode. The diaphragms consist of 
asbestos paper fastened to asbestos cloth by sodium silicate, and 
are held in position by cement placed over both end walls and 
the bottom of the anode compartment. This compartment is 
closed by a cast-iron cover 5 inches deep, 6 inches wide, and 
nearly 5 feet long, into which the anodes are cemented. It is 
lined with cement and painted inside with asbestos varnish. 

The anode cohsists of blocks of graphitized carbon, 4 inches 
square and 10 inches long, into each of which a copper rod is 
fastened by lead for the electrical connection. The partition 
walls form the cathode. 

The partition walls are flanged, forming a seat to hold the 
cover, which is surrounded by a layer of cement. The chlorine 
is conducted from the anode compartment by a lead pipe to a 
gas main which leads to absorbing towers containing lime- 
water. Brine circulates through the anode compartment. 

The diaphragms last about 8 months, 16 after which time the 
pores become clogged. 

The sodium hydrate solution leaving the cathode compart- 
ment contains from 7 to 18 per cent sodium hydrate. When 
the diaphragm is new, the level of the liquid in the anode arid 
cathode compartments is nearly the same, but when it becomes 
more or less stopped up, the depth of the liquid -in the cathode 
compartment is only an inch or two. 

The Hargreaves-Bird cell consists of a cast-iron box 10 feet 
in length, 14 inches in width, and 5 feet in height. 16 It is 
divided into three compartments by two diaphragms made on 
heavy copper gauze, which forms the cathode. The space 
between the diaphragms is the anode compartment, through 
which brine circulates. There is no liquid in the anode com- 
partment except what percolates through the diaphragm. 
Steam and carbonic gas are blown through the two outer com- 
partments and change the hyrate formed on the outside of the 
diaphragm to sodium carbonate. This cell takes 2000 amperes 
at from 4 to 4.5 volts. The anode is a row of gas carbons, 

is L. Rostosky, Z. f. Elektroch. 11, 21, (1905). 
is Electrochero. and Met. Ind. 3, 350, (1905). 



128 



APPLIED ELECTROCHEMISTRY 



which last 30 to 40 days. The diaphragms last about the same 
length of time. 

The Hargreaves-Bird cell is shown in Figure 42, which is a 
partial longitudinal section and side elevation, and in Figure 
43, which is a section perpendicular to the length. 17 The 
outside frame I is of iron lined with cement and bricks w, 
which are saturated with tar to prevent leakage.- The space 




FIG. 42. Hargreaves-Bird cell, side elevation 

/ is the anode compartment through which the chloride solution 
circulates, entering through the pipe g and leaving through h. 
The diaphragms are made of asbestos paper, the pores of which 
have been filled with hydrated silicate of lime or magnesia. 18 
In the cathode chamber a number of copper strips b are placed, 
imbedded in cement e, extending from the cover plate c to the 
cathode c?, and inclined downwards. These direct the 



17 U. S. Pat. 655,343, (1900). 



U. S. Pat. 596,157, (1897). 



ELECTROLYSIS OF ALKALI CHLORIDES 



129 



densed vapor against the cathode to wash away the alkali as it 

is formed. The lower edges of the strips have openings, in 

order to allow the steam and gas to 

pass freely over the cathode, a', a r are 

the injectors for supplying carbonic 

acid gas and steam to the cathode 

chambers. Z 2 , Z 2 are pipes for draining 

the cathode chambers. The chlorine 

passes from the anode chambers to the 

towers, where it is absorbed by milk 

of lime. 

The West Virginia Pulp and Paper 

Company, Me- 

chaiiicsville, 

New York, use 

this cell for 

making their 

bleaching solu- 
tions. 19 This 

plant consists 

of two rows of 

14 cells each, 

n 



LJ\ 




FIG. 43. Harsreaves-Bird cell, 
end section 



all connected in series. 

Perhaps the most efficient diaphragm 
cell in use is the Townsend cell, repre- 
sented in cross section in Figure 44, 
and in perspective in Figure 45. 20 The 
anode space is inclosed between a lid (7, 
two vertical diaphragms D, and a non- 
conducting body H. Graphite anodes 
pass through the lid on the cell. The 
perforated iron cathode plates S are in 
close contact with the diaphragms. These plates are fastened 
to two iron sides J, which form the cathode compartment. The 
anode compartment is filled with brine T, and the cathode corn- 

is Electrochem. and Met. Ind. 6, 227, (1908). 
20 Electrochem. and Met. Ind. 5, 209, (1907). 



FIG. 44. Townsend cell 



130 



APPLIED ELECTROCHEMISTRY 



partment with kerosene oil K. The brine percolates through 
the diaphragm, and, when the current is turned on, it contains 

hydrate. The 
aqueous solution, 
on passing the dia- 
phragm, comes in 
contact with the 
kerosene and 
forms drops which 
fall to the bottom 
of the compart- 
ment, are collected 
in the pocket A, 
and are drained off 
through P. The 
solution leaving P 
contains 150 grams 
of sodium hydrate 
and 213 grams of 
salt per liter. The 
salt is separated 
by evaporation and 
is used over again. 

The continual percolation prevents nearly all diffusion of hy- 
drate back to the anode. The rate of percolation for a 2500- 
ampere cell is from 15 to 30 liters an hour. 21 

The Town send cell is 8 feet in length, 3 feet in depth, and 
1 foot in width, and consists of a U-shaped concrete body 
against which the two iron side plates are clamped. A rubber 
gasket is placed between the concrete and the iron to make a 
tight joint. Brine circulates through the anode compartment, 
and during its passage the specific gravity falls from 1.2 to 
1.18. On leaving the cell it is resaturated and is then ready to 
be passed through again. There is a loss in kerosene which 
amounts in cost to about two dollars a day for a large plant. 
The diaphragms of the Townsend cell consist of a woven 

21 Baekeland, Electrochem. and Met. Ind. 7, 314, (1909). 




FIG. 45. Townsend cell 



ELECTROLYSIS OF ALKALI CHLORIDES 



131 



sheet of asbestos cloth, the pores of which are filled with a mix- 
ture of iron oxide, asbestos fiber, and colloid iron hydroxide. 
This mixture is applied with a brush like ordinary paint. Di- 
aphragms may be renovated by scrubbing and washing the 
surface with water, allowing to dry, and repainting with this 
mixture. This operation is not. necessary more than once in 
five weeks, and sometimes not for several months. 

The current efficiency of the Townsend cell is as high as 96 
or 97 per cent under ordinary conditions, with a current density 
on the anode of 1 ampere per square inch and about 4 volts on 
each cell. 22 This cell has been in use at Niagara Falls in the 
plant of the Development and Funding Company since 1906. 
This plant originally consumed 1000 kilowatts, and according 
to latest accounts it was being increased to four times this 
capacity. 21 

Not much information concerning the bell process as actually 
arranged in practice is available. The process is carried out by 
the Oesterreiche 
Verein fur 
Chemische und 
Metallurgische 
Production in 
Aussig, and at 
several places in 
Germany. Fig- 
ure 46 shows 




FIG. 46. Cell for Bell process 



two cross sections of the cell, 25 of which are placed side by 
side in each bath. 23 The solution leaving the bath is said to 
contain 100 to 150 grams of alkali hydrate per liter, at a cur- 
rent yield of 85 to 90 per cent and with 4 to 4.5 volts per cell. 24 
The Castner cell 25 is represented in Figure 30. It is a slate 
box 4 feet square, and 6 inches deep, the joints of which are 

22 For laboratory tests on the efficiency of this cell, see Richardson and Patter- 
son, Trans. Am. Electrochem. Soc. 7,311, (1910). 
28 Z. f. Elektroch. 7, 925, (1901). 
24 Haeussermann, Dinglers polyt. J. 315, 475, (1900). 
25 U.S. Pat. 528,322, (1894). 



132 



APPLIED ELECTROCHEMISTRY 



made tight with rubber cement. 26 Two partitions, reaching to 
within ^g inch of the bottom, divide the cell into three compart- 
ments. The two outside compartments contain the graphite 
anodes A, and the middle compartment, the iron cathode 0. 
Brine circulates through the anode compartments, and pure 
water is supplied to the cathode compartment. The cell is piv- 
oted on two points at one end and the other is raised and lowered 




FIG. 47. Whiting electrolytic cell, plan 

about J inch once a minute, causing the mercury to circulate be- 
tween the anode and cathode compartments. The hydrate 
leaving the cathode compartment has a specific gravity of 1.27. 
This is evaporated to solid hydrate in large iron pans. Each 
cell takes about 100 pounds of mercury, which is a very large 
item of expense. The current for each cell is 630 amperes at 
4.3 volts, and the current efficiency is about 90 per cent. 

ae J. W. Richards, Electrochem. Ind. 1, 12, (1902). 



ELECTROLYSIS OF ALKALI CHLORIDES 133 

The Whiting mercury cell is 27 of a different type from the 
Castner cell. The sodium is not electrolyzed out of the amal- 
gam, but the amalgam is withdrawn from the electrolyzing 
chamber and treated with water in a decomposing chamber 
where the hydrate is formed. A number of electrolytic com- 
partments are placed in parallel and are operated successively. 



B 




"b 



FIG. 48. Whiting electrolytic cell, cross section 

so that the cell is continuous in its action, though intermittent 
in principle. 

This cell, shown in Figures 47, 48, and 49, is a massive con- 
crete structure supported on four concrete pedestals, from 
which it is insulated. It consists of a shallow box divided into 
two compartments, A and B, by a concrete partition. The 
bottom of the decomposing chamber is divided by low glass 
partitions into a number of sections having V-shaped bottoms 

^ Jasper Whiting, Trans. Am. Electrochem. Soc. 17, 327, (1910). 



134 



APPLIED ELECTROCHEMISTRY 



sloping at a slight angle towards the central slot D. These 
slots lead through the concrete partition into the oxidizing 
chamber B, where they turn upward and are closed by valves 
E. The valves are operated by the cams F, which are attached 
to a slowly revolving shaft Gr. The other ends of the slots are 
connected by the channel H, called the distributing level. 
This connects with a secondary channel /, which leads through 
one of the side walls of the cell to a pump J", at the extreme 
end of the oxidizing compartment. Mercury covers the bottom 
of the decomposing compartment, filling the above-described 
sections to a common level. The anodes K are slabs of 
Acheson graphite, perforated to allow the chlorine to escape, 
and rest upon the ledges L, placed at the ends of the section in 




FIG. 40. Whiting electrolytic cell, longitudinal section 

such a way as to make a very short distance between the anode 
and the mercury cathode. The anodes are connected to the 
dynamo by the leads M. 

The oxidizing chamber is divided into three compartments 
P, lined with graphite and sloping downward in successively 
opposite directions, forming a zigzag path to the pump pit Q, 
where the stoneware rotary pump J is placed. Brine fills the 



ELECTROLYSIS OF ALKALI CHLORIDES 135 

decomposing chamber, and water or alkali hydrate fills the oxi- 
dizing chamber. 

The action is as follows : The floor of several sections of the 
decomposing chamber is covered with mercury, maintained at 
a common level by the distributing level. The current flows 
from the anode through the brine to the mercury and out by 
the iron rods R, partly imbedded in the concrete. When the 
electrolysis has proceeded about two minutes, the valve at the 
point of exit of one of the sections is opened by the action of 
the cam, and the entire mass of sodium amalgam in the section 
sinks into the slot and through the connecting pipe into the 
oxidizing chamber. When the mercury is out of the cell, the 
valve is closed by the cam. Mercury free from sodium then 
flows into the empty chamber by way of the distributing level, 
until the common level is reached. In the meantime the 
sodium amalgam in the oxidizing chamber flows by gravity 
over the graphite plates P to the pump pit. On reaching this 
point the mercury has been deprived of its sodium, and is 
raised by the pump into the wall pipe of the decomposing 
chamber, completing the cycle. 

The brine is fed in between the electrodes from the recep- 
tacles S, equal in number to the sections of the decomposing 
chamber. They are formed in the cover of the decomposing 
compartment, and are connected by a channel T. Glass tubes 
lead from the bottom of the receptacle S through the anode 
and terminate below the surface of the mercury near the middle 
of each section. As long as the sections are filled with mer- 
cury the lower ends of the tubes are sealed, but when the 
mercury is drawn off, a definite quantity of concentrated brine 
flows into the section. 

The graphite slabs in the oxidizing chamber contain a large 
number of channels through which the mercury flows. The 
sides of the channels extend into the caustic solution and form 
the cathode of a short-circuited couple. It is difficult to main- 
tain good contact between the graphite and mercury on account 
of the hydrogen evolved, but this difficulty was overcome by 
boring holes j- inch deep and J inch in diameter at frequent 



136 APPLIED ELECTROCHEMISTRY 

intervals in the channels, and filling them with pure mercury 
at the start. This mercury remains pure and makes good con- 
tact with the amalgam and the graphite. 

The cell used at the Oxford Paper Company's works in Rum- 
ford, Maine, is 1.8 meter square. It consists of five sections 
and takes a current of from 1200 to 1400 amperes at 4 volts. 
This corresponds to an anode current density of 11 amperes 
per square decimeter. The current efficiency is from 90 to 95 
per cent. The temperature is about 40 degrees. Each cell 
requires from 350 to 375 pounds of mercury. A 20 per cent 
hydrate solution is obtained, though one with 49 per cent can 
be made if desired. The chlorine gas is 98 per cent pure, the 
remaining 2 per cent being hydrogen. 



CHAPTER VII 



THE ELECTROLYSIS OF WATER 

HYDROGEN and oxygen have a number of technical applica- 
tions that require their manufacture on a large scale. Such 
uses are welding with the 
oxyhydrogen flame, as is done 
in joining the lead plates of 
storage batteries; hydrogen 
is used for filling balloons, 
and oxygen is used for chem- 
ical and medicinal purposes. 

Hydrogen and oxygen are 
produced on a commercial 
scale by the electrolysis of 
aqueous solutions, and of 
course the object of the large 
number of patents taken out 
in this field is to keep the 
hydrogen and oxygen separate 
from each other. For this 
purpose the anode and cathode 
compartments have to be sep- 
arated by a partition of some 
kind. The different methods 
of separating the gases will be 




Schnitt 



FIGS. 50-53. Schmidt's apparatus for the 
electrolysis of water 



illustrated in the description 
of the following cells. 

The cell designed by Dr. O. Schmidt 1 is shown in sections 
in Figures 50-53, and a general view in Figure 54. It consists 

1 Engelhardt, Die Elektrolyse des Wassers, p. 24, (1902); Z. f. Elektroch. 7, 
294, (1901). 

137 



138 



APPLIED ELECTROCHEMISTRY 



of a number of iron plates e having thick rims and separated 
by diaphragms d. These plates are the cathode in one cell and 
the anode of the following cell. Each plate has two holes in 
the thick rims h,o and w, w' , so that the apparatus is traversed 
above and below by two canals. The lower canals are for sup- 
plying the water as it is decomposed, and the upper are for al- 




FIG. 54. Schmidt's apparatus for the electrolysis of water 

lowing the gases to escape. The canals w and h connect with 
the cathode chambers, w' and o with the anode chambers. The 
two canals for adding water, w and w', are connected with a 
common filling tube W by the pipes w 2 , up, and at the other end 
of the apparatus the two gas canals connect with reservoirs .ZTand 
0, where the gas is separated from the liquid carried along with 
it. The liquid then returns to its respective chamber in the 
electrolyzer. The stopcock a is for emptying the apparatus. 

The diaphragms are of asbestos with rubber edges to prevent 
leakage. The electrolyte is a dilute solution of potassium car- 
bonate. Each cell has 2.5 volts impressed, and the current 
yield is nearly 100 per cent. The oxygen is on the average 



THE ELECTROLYSIS OF WATER 



139 



97 per cent pure, while the hydrogen is 99 per cent. Either 
gas may be purified by passing through red-hot porcelain tubes. 




TS* 




FIG. 55. Garuti and Pompili's electrolyzer 

which combines the small impurity of hydrogen in the oxygen, 
or of oxygen in the hydrogen, to water which is easily removed. 




FIG. 56. Garuti and Pompili's electrolyzer 

This apparatus is made at the Maschinenfabrik Oerlikon. 
near Zurich, Switzerland. 



140 



APPLIED ELECTROCHEMISTRY 



An apparatus in which the separation of the hydrogen and 
oxygen is effected by a different method is that of Garuti and 
Pompili. 2 In this cell a partition of iron separates the anode 
from the cathode, and this partition is prevented from becom- 
ing an intermediate electrode 
by keeping the voltage ap- 
plied to the cell too low for 
this to take place. The cur- 
rent flows from the anode to 
the cathode around the bot- 
tom of the iron partition. 

Figure 55 is a longitudinal 
vertical section through the 
center, Figure 56 is a horizon- 
tal section of one end, Figure 

57 is a vertical cross section 
of the apparatus, and Figure 

58 a plan view of conductor 
and electrodes. 

A tank A of wood lined with 
iron a contains the electro- 
lyzer, which consists of an 
inverted tank A 1 which is di- 
vided into cells E by longitu- 
dinal diaphragms. This cell 
is made of iron and is open 

4^ ^ only at the bottom. The 

l^\ I \ anodes b and cathodes c are 

placed one in each cell, taking 
care that each anode is be- 




FIG. 57. Garuti and Poinpili's electro- 
lyzer 



tween two cathodes. The gas passes through an opening at 
the top of each chamber into the reservoir containing the same 
gas. The electrodes are insulated from the diaphragms by 
combs I made of wood, the teeth of which enter the cells and 
fill the spaces between the electrodes and diaphragm. L is a 
handle for lifting out the electrolyzer. 

2 U. S. Patent 629,070, (1899). 



THE ELECTROLYSIS OF WATER 



141 



A 25 per cent solution of potassium hydrate is used. The 
voltage per cell is not allowed to exceed 3 volts, so there is no 
danger of the diaphragm acting as an 
electrode. The diaphragms may be per- 
forated near the bottom with a large num- 
ber of small holes, as there is very little 
danger of the gases becoming mixed at 
this point. 

The hydrogen obtained from this ap- 
paratus is 98.9 per cent pure, the oxygen 
97. This apparatus is used in Rome, 
Tivoli, Brussels, and Lucern. 

The cell of the Siemens Brothers and 
Company and Obach 3 employs a parti- 
tion which consists of metal gauze below 
the water line. The current is con- 
ducted through the meshes, which are 
small enough to prevent the mixture of the gases. 

Other cells, such as that of Schoop, 4 have nonconducting 
partitions. 

These examples complete the different principles on which 
technical cells for the decomposition of water are built. 




FIG. 58. Garuti and Pom- 
pili's electrolyzer 



3 Engelhardt, I.e. p. 67. 



4 Engelhardt, I.e. p. 44. 



CHAPTER VIII 

PRIMARY CELLS 

A PRIMARY battery is a cell so arranged that the energy of 
a chemical reaction is obtained as an electric current, and in 
which the chemicals are not regenerated by passing the current 
through the cell in the opposite direction. When the battery 
is run down, fresh chemicals must be supplied. A secondary 
battery, or accumulator, is a battery in which chemicals are 
regenerated by passing through the cell, after discharge, a 
reverse current from some other source. 

Before the invention of dynamos, primary batteries were the 
main source of electric energy; but since this method of gener- 
ating electricity is too expensive for use where a large quan- 
tity of energy is needed, they were employed only for very 
light work and for experimental purposes. They are still used 
extensively for electric bells, for exploding the gases in engines 
by electric sparks, railroad signals, and similar purposes. 
Primary batteries of special forms are also the standards of 
electromotive force, but this is rather a purely scientific branch 
of the subject than a technical application, and will therefore 
be omitted. 

The first primary battery was due to Volta, and consisted in 
a negative pole of zinc and a positive pole of copper dipping 
into a solution of salt or dilute acid. The electromotive force 
of this battery rapidly falls off if an appreciable current is 
taken from it, on account of the hydrogen liberated on the 
positive pole. This develops a back electromotive force and 
also increases the resistance of the cell itself. The battery is 
then said to be polarized. In order to have a battery that is at 

142 



PRIMARY CELLS 143 

all efficient, polarization must be avoided. In the Smee cell, 
this was done by substituting platinized silver for the positive 
pole in place of the copper in the Volta cell. The rough sur- 
face caused the bubbles of hydrogen to escape more rapidly. 
In the Grove battery, devised in 1831, 1 the cathode consisted 
of platinum dipping into nitric acid contained in a porous cup. 
Outside the cup was dilute sulphuric acid and a zinc negative 
pole. In this case the nitric acid acts as a depolarizer, oxidiz- 
ing the hydrogen to water and itself being reduced to nitrous 
gases. The electromotive force of this battery is between 1.6 
and 1.7 volts. 

The Bunsen cell is a Grove cell with carbon in place of plat- 
inum for the positive pole. 

In the chromic acid battery, due to Poggendorff, the electrolyte 
is a solution of sulphuric acid and potassium bichromate. The 
positive pole is carbon and the negative zinc, which is withdrawn 
from the battery when not in use. The chromic acid acts as 
depolarizer. The electromotive force is about 1.3 volts. 

These batteries have at present little more than historical inter- 
est. The use of primary cells is now nearly entirely confined 
to the Leclanche, the Lalande, and the Daniell cells. Leclanche 
brought out his cell in 1868. 2 It consists of a zinc rod forming 
the negative pole and dipping into a solution of ammonium chlo- 
ride. The positive pole is carbon in contact with manganese 
dioxide for a depolarizer. When the circuit is closed, zinc goes 
in solution as zinc chloride and the ammonium radical is deposited 
on the carbon, which breaks up into ammonia and hydrogen. 
The ammonia dissolves and the hydrogen is oxidized by the 
manganese dioxide to water. This depolarization is not rapid, 
however, consequently not much current can be taken from a 
Leclanche cell at a time without the voltage dropping consider- 
ably, but it recovers on standing. The electromotive force of 
this cell on open circuit differs from one cell to another, varying 
from 1.05 to 1.8 volts. 

This cell is put on the market under a large number of different 

1 Wiedemann, Die Lehre von der Elektricitat, 1, 867, (1893). 

2 Wiedemann, I.e. p. 850. 



144 



APPLIED ELECTROCHEMISTRY 




FIG. 59. Carbon 
of Sampson cell 



forms and under different names. One of the best Leclanche 
cells on the market is the Sampson cell. 3 The carbon of this cell 
is shown upside down in Figure 59. It consists 
of a fluted hollow cylinder of French carbon pro- 
vided with a removable seal at the lower end and 
filled with a mixture of carbon and manganese 
dioxide. The cell set up is shown in Figure 60. 
The Lalande cell, brought out in 1883, 4 con- 
sists of zinc for the negative pole, a 30 per cent 
solution of potassium hydrate for the electro- 
lyte, and a plate or box of iron or copper in 
contact with black copper oxide as depolarizer. 
The hydrate is protected from the carbonic acid 
of the air by a layer of oil. The zinc goes in 
solution as sodium zincate, and the hydrogen 
deposited on the positive plate is oxidized by 
the copper oxide. The positive plate may also be an agglom- 
erate porous plate of copper oxide. The electromotive force 
of this cell is about 0.9 volt and is very constant. The oxide 
when reduced to copper is easily 
oxidized again by heating in the 
air. The original method of La- 
lande of making the porous copper 
oxide plates was to press a moist 
mixture of oxide, 4 or 5 per cent 
clay, and 6 to 8 per cent tar, and 
then to heat to redness. The 
plates so produced were porous 
and lasted well. This plate must 
be reduced to copper over its en- 
tire surface before its normal rate 
is reached, on account of the poor 
conductivity of copper oxide. This is done before assembling 
the plates. 

A modern type of the Lalande battery is made by the Edison 

8 N. H. Sneider, Modern Primary Batteries, p. 10, (1905). 
4 Wiedemann, I.e. p. 854. 




FIG. 00. The Samson cell 




PRIMARY CELLS 145 

Manufacturing Company at Orange, New Jersey, and is called 
the Edison-Lalande Battery. This battery, shown in Figure 
61, consists of a copper oxide plate between two zinc plates 
dipping in a 20 or 25 per cent solution of sodium hydroxide. 
The containing jar is porcelain. The zinc plates have mercury 
added to them during casting, so that they are amalgamated 
throughout. The copper oxide ^-^ 

plates are made from copper scale 
which is finely ground and then 
roasted until thoroughly oxidized. 
The oxidized powder is then 
moistened with a solution of so- 
dium hydroxide and pressed into 
cakes a little larger than desired 
in the finished product. These 
cakes are then dried and baked at 
a bright red temperature, which 

partially Welds the particles to- FIG. 61. -Edison Lalande battery 

gether. After cooling, the plates are reduced to copper at 
the surface by zinc dust, to make them conduct. They are 
then washed and are ready for use. 5 The hydroxide solution 
is covered with a heavy mineral oil to prevent its creeping up 
the zinc plates and corroding them. This battery has an initial 
electromotive force of 0.95 volt, but on continuous discharge 
at normal rate it drops to about 0.6 volt. The capacity varies 
from 100 to 600 ampere hours, depending on the size of the 
battery. 

The Daniell cell, brought out in 1836, 6 belongs to a different 
class of cells, in which there are two liquids separated by a 
porous partition. The positive pole is copper dipping in a con- 
centrated solution of copper sulphate, and the negative is zinc 
dipping in sulphuric acid. Copper is deposited on the positive 
in place of hydrogen, thus avoiding polarization, and zinc goes 
in solution forming zinc sulphate. The electromotive force of 
this cell is about 1.1 volt. 

The gravity cell, Figure 62, is a form of the Daniell cell 
5 Private communication from the company. 6 Wiedemann, I.e. p. 859. 



146 



APPLIED ELECTROCHEMISTRY 





FIG. 62. The gravity cell 



patented by Varley in 1854, but which did not become generally 
known until 1884. It is now the principal commercial form of 
the Daniell cell. 7 The gravity cell derives its name from the 
way in which the two solutions are prevented from mixing. 
At the bottom of a glass jar is a horizontal copper electrode 

covered with cop- 
per sulphate crys- 
tals and a saturated 
solution of copper 
sulphate. On this 
solution is care- 
fully poured a di- 
lute sulphuric acid 
solution, in which 
a horizontal zinc electrode is immersed. When in use the 
migration of the copper ions towards the cathode prevents their 
reaching the zinc, while if the cell stands on open circuit the 
copper sulphate would finally reach the zinc by diffusion and 
cover it with a layer of copper. This cell should therefore al- 
ways be kept on a closed circuit through a few ohms resistance. 
Dry cells are a type of primary battery that have recently 
come into very general use. It is estimated that 50 million 
a year are manufactured in the United States, a large majority 
of which are of a standard size, cylindrical in shape, 15 centi- 
meters long and 6.25 centimeters in diameter. 8 They are 
essentially Leclanche cells with a very small quantity of elec- 
trolyte. Their greatest field of usefulness is probably tele- 
phony and next the ignition through spark coils. 9 

The container or outside insulation is usually pasteboard, 
sometimes waterproofed by paraflfine or pitch. Just inside of 
the container is the cylindrical zinc negative pole, usually 15 
centimeters high, 6.25 in diameter, and 0.3 to 0.55 millimeters 
thick. Lining the zinc on the inside is a layer of a special 
grade of pulp board, moistened with a solution of zinc and 

i Schneider, I.e. p. 54. 

8 D. L. Ordway, Trans. Am. Electrochem. Soc. 17, 341, (1910). 

Burgess and Hambuechen, Trans. Am. Electrochem. Soc. 16, 97, (1909). 



PRIMARY CELLS 147 

ammonium chlorides. The zinc chloride is added for reducing 
the local action. Inside the pulp board containing the electro- 
lyte are placed the depolarizer and the positive pole. The de- 
polarizer is manganese dioxide, mixed with carbon, graphite, or 
a mixture of both. Graphite is used to give the cell a lower 
resistance. A carbon rod at the center and surrounded by this 
mixture is the positive pole. An average composition of this 
filling mixture is the following : 9 

10 parts of manganese dioxide, 

10 parts of carbon or graphite, or both, 

2 parts of ammonium chloride, 

1 part of zinc chloride. 

Sufficient water is added to give a proper amount of electro- 
lyte to the cell, depending on the original dryness of the ma- 
terials, their fineness, the quality of the paper lining, and 
similar factors. The usual specifications for the manganese 
dioxide are that it shall contain 85 per cent of the dioxide and 
less than 1 per cent of iron. The cell is sealed up on top 
with a pitch composition to hold in the filling material and to 
prevent the cell from drying. The carbon rod extends above 
the seal and is provided with a binding screw. 

The electromotive force of this cell is between 1.5 and 1.6 
volts. On a short circuit through an ammeter, a cell will give 
from 18 to 25 amperes. The energy output of a cell of the 
dimensions given above, discharged to 0.2 volt continuously, 
varies from about 20 watt hours when discharged through 
2 ohms to 57 watt hours when discharged through 40 ohms. 8 

The primary cells described above are comparatively unim- 
portant compared with one which is not yet realized, but on 
which a great deal of time and work has been spent. This is 
the cell in which carbon and oxygen are the elements con- 
sumed. The present method of producing work by the com- 
bustion of coal to run steam engines is very inefficient, as only 
about 15 per cent of this energy is obtained as work, the rest 
being lost as heat. If it were possible to devise a cell in which 
carbon and oxygen would unite with the production of an 



148 APPLIED ELECTROCHEMISTRY 

electric current and no other form of energy, at ordinary tem- 
perature, a much greater amount of energy could be obtained. 
In order to calculate 10 the free energy, or energy that is 
obtainable as useful work, of the reaction in question, 

C + 2 =C0 2 , 

consider a reaction chamber, as shown in Figure 63, containing 
carbon, oxygen, carbon monoxide, and carbon dioxide in equi- 



Cfe CO Ok 

A"t^<Y\&VVX 



FIG. 63. Reaction chamber 

librium at a given temperature. The chamber has two pis- 
tons separated from it by semipermeable membranes. The 
semipermeable membrane at the end of the cylinder containing 
oxygen is permeable to oxygen only, and that at the end of the 
cylinder containing carbon dioxide is permeable only to carbon 
dioxide. The maximum work that this reaction can produce 
is then obtained by the following reversible process : one mole 
of oxygen is admitted to the oxygen cylinder at atmospheric 
pressure and is allowed to expand reversibly to the equilibrium 
pressure of oxygen p 0z in the reaction chamber. The work 
produced is 



The oxygen is then forced into the reaction chamber through 
the semipermeable membrane. In order to preserve equi- 
librium, one mole of carbon dioxide must be simultaneously 
withdrawn at the equilibrium pressure p COz into the carbon di- 
oxide cylinder. The work produced in these two steps is evi- 
dently zero. The carbon dioxide must then be compressed to 
atmospheric pressure, in which step the work produced is 



10 Nernst, Theoretische Chemie, 6th ed. p. 698, (1909). 



PRIMARY CELLS 149 

The sum of W l and TF 2 is the maximum work obtainable : 

Tf,+ Wt = RTlog?!. (1) 

^o 2 

It would be impossible to measure the pressure of oxygen in 
this mixture directly, but its value at 1000 C. can be obtained 
as follows: It has been found experimentally that at 1000 C. 
carbon dioxide dissociates to 0.06 per cent, according to the 
reaction : 

2 CO 2 ^ O 2 + 2 CO. 

At a total pressure of one atmosphere, the equilibrium pressures 
for this system are then : 

Carbon dioxide 0.9991 atmosphere 

Carbon monoxide .... 0.0006 atmosphere 
Oxygen ....... 0.0003 atmosphere 

Substituting in the equation for the mass action law, 

K(Pco.^ = Po s (pco)*, (2) 

K (I) 2 = (0.0003)(0.0006) 2 . (3) 

It has also been found that at 1000 C. and atmospheric pressure 
an equilibrium mixture of carbon monoxide and dioxide in the 
presence of carbon has the following pressures : 

Carbon monoxide .... 0.993 atmosphere 
Carbon dioxide 0.007 atmosphere 

Since jfiTis known from equation (3), the pressure of oxygen in 
this system can be computed by substituting in equation (2) : 
JT(0.007) 2 = z (0.993) 2 . 

From this, x = 5.4 x 10~ 15 atmosphere. 
Substituting in equation (1), 

Tr l+ TT 2 = 1273 7? log 54 x 00 ^_ 16 

= 70600 calories at 1000 C. 

This gives the free energy of the reaction at 1000 C., and it may 
be found at room temperature as follows : The heat of the 
reaction at room temperature is Q = 97650 calories, and it would 
be approximately the same at the absolute zero, on account of 



150 APPLIED ELECTROCHEMISTRY 

the small change in the heat capacity of carbon and oxygen 
before and after uniting. This would also be the free energy 
at the absolute zero, since free energy and the total energy of a 
.reaction are equal at this temperature. The free energy at the 
absolute temperatures 1273 and being known, it may be 
interpolated for 20 by the formula, 

Fi + TT 2 = 97650 - 9765 "J 0600 x 293 

1.273 

= 91470 calories at 20 C. 

The ratio of the free to the total energy is therefore approxi- 
mately |i*-, corresponding to 94 per cent. 

If the carbon of the carbon electrode enters the electrolyte as 
an ion with four positive charges, and the oxygen as an ion with 
two negative charges, the electromotive force of this cell would 
be found from the equation, 

4 .EF= 91000 calories ; 



from which E = = 0.99 volt. 

4 x 23100 

The difficulties in realizing this cell consist in finding an elec- 
trolyte in which carbon will dissolve, and in making an oxygen 
electrode. So far they have been insuperable, and at present 
there seems very little prospect of success. 

Attention has been called by Ostwald n to an important point 
in this cell, that the carbon and oxygen must form the opposite 
poles of the cell and must act on each other through an inter- 
vening electrolyte. If the carbon and oxygen acted directly on 
each other, local action would result, and no current would be 
produced. 

A number of attempts have been made to make a carbon 
oxygen cell, all of which employed some fused salt or hydrate as 
electrolyte. This is a disadvantage to start with, for energy 
will be lost by radiation in keeping the cells at a temperature of 
several hundred degrees centigrade. One of the first of these 
attempts was made by Jablochkoff 12 in 1877. In this cell the 

11 Z. f. Elektroch. 1, 122, (1894). 

12 E. de Fodor, Elektricitat direkt aus Kohle, p. 41, (1807). 



PRIMARY CELLS 151 

carbon was dipped into melted potassium nitrate, and the posi- 
tive electrode was iron. This cell could never be successful, 
for the carbon is brought directly in contact with the oxidizing 
substance. Also, the oxygen was not taken directly from the 
air, but was in the expensive form of a nitrate. 

In 1896, W. W. Jacques patented a cell which excited a 
good deal of interest at that time. This consisted of an iron 
pot containing a melted mixture of potassium and sodium 
hydrate, into which a carbon rod dipped ; air was blown against 
the iron pot, which formed the positive pole, the idea being that 
this oxygen would combine with the carbon through the inter- 
vening electrolyte and produce a current. It is evident that 
the hydrate would be changed to carbonate and that some 
method would have to be used to regenerate it. The carbon 
was in the expensive form of electrodes. There was a certain 
amount of direct oxidation of the carbon, for the air also came 
in direct contact with the hot carbon electrode. For these 
and other reasons this cell has not been a success. 

In conclusion, it may be said that the chance of finding any 
solvent in which carbon would dissolve as ions is very remote, 
and to find one in which both oxygen and carbon would thus 
dissolve is still more remote ; consequently it seems hardly 
possible that this problem will be solved by such a direct 
method. 



CHAPTER IX 
THE LEAD STORAGE BATTERY 

1. HISTORY AND CONSTRUCTION 

THE lead storage battery in the charged state consists of 
a positive plate of lead peroxide and a negative plate of finely 
divided lead, both dipping in sulphuric acid of about 1.2 specific 
gravity. When discharged, the surface of both plates has been 
changed to lead sulphate. The plates may be brought back 
to their original condition by sending a current through the 
battery in the reverse direction. 

This battery was invented in 1860 by Gaston Plante. 1 The 
original battery consisted of two lead plates separated by 
flannel and rolled together, and immersed in sulphuric acid. 
The flannel was soon replaced by thin strips of rubber, on 
account of its being eaten away by the acid. The battery 
was charged from two Bunsen elements in opposite directions 
six or eight times on the first day, allowing the cell to discharge 
itself between each change in direction of charging. It was 
noticed that the period of discharge continued to increase 
regularly. The period during which the battery was sub- 
mitted to the action of the current in the same direction was 
then increased, and the battery was allowed to rest for eight 
days, after which it was charged in the opposite direction. 
The period of rest was then extended to two weeks, one month, 
two months, and so on, and the duration of discharge continued 
to increase. When sufficient capacity was reached, the plates 

1 Gaston Plant^, The Storage of Electrical Energy, p. 30, (1887). 

152 



THE LEAD STORAGE BATTERY 153 

were considered formed, and the charging current was then 
always sent through the cell in the same direction. The reason 
a thick layer of peroxide cannot be produced in one charge is 
that it conducts the current and prevents the lead below it from 
being attacked. 

It is evident that this method of formation would be very 
expensive. To overcome this difficulty, Metzger and Faure, 
independently and approximately simultaneously, devised 
methods of applying the active material to the plate in the form 
of lead oxides. This method was patented by Faure 2 in 1880, 
and has since been known by his name.^ Faure's original method 
of applying the oxides was to coat the plate with a paste made 
of the material and to hold it in place by means of some porous 
material, such as felt or asbestos paper. 

Charles F. Brush of Cleveland applied for a patent covering 
this same field about a month before Faure, and the patent was 
finally awarded to him. Eventually all of the essential patents 
were acquired by the Electric Storage Battery Company of 
Philadelphia. 3 

The two general methods of making storage battery plates 
now in use are only modifications of the original Plante or 
Faure process. 

The Plante process includes all methods in which the active 
material is made from the plate itself, which must be of pure 
soft lead. 4 Formation is accelerated in a number of ways. 
Usually the first operation is to work up the surface mechanically 
by cutting grooves, unless it is cast in this form. The next 
operation is to produce the necessary amount of active material. 
This is frequently done by allowing the plates to stand for a 
certain time in some corroding solution of acids that produces 
a thick layer of lead sulphate. This may then be reduced 
electrolytically to lead or oxidized to lead peroxide. The acids 
other than sulphuric must be thoroughly washed out before the 
battery is ready for use. For example, a mixture of nitric and 

2 U. S. Patents 252,002, (1882) and 309,939, (1884). 
8 Watson, Storage Batteries, p. 10, (1908). 
4 Watson, I.e. p. 21. 



154 APPLIED ELECTROCHEMISTRY 

sulphuric acids would have this effect of producing a layer of 
sulphate. The other method of rapid Plante formation is 
entirely electrolytic, according to the following principle : 

The plate is electrolyzed as ail anode, but lead peroxide, 
which would protect the plate from further action, is prevented 
from forming by adding some salt or acid to the solution, the 
anion of which separates at a lower potential than the peroxide 
ion and causes the production of sulphate. Lead sulphate does 
not conduct, so the current' has to penetrate to the lead below, 
and as much sulphate may be produced in one step as is desired. 
Such additions are acetates, tartrates, chlorides, nitrates, chlo- 
rates, perchlorates, and the corresponding acids. 

Peroxide is not always formed on a lead anode in sulphuric 
acid, even when no substance is added to the solution to prevent 
it, as is shown by the fact that the lead plate, which is the 
anode, on discharging, becomes covered with sulphate. If 
therefore a lead plate is short circuited in a solution of sul- 
phuric acid with a peroxide plate, it will become covered with 
sulphate, proportional in amount to the current that flows 
through the plate. 5 

In the Faure batteries the plates for holding the active ma- 
terial consist of lead with about 5 per cent of antimony. 
The active material is made by making a paste of lead oxide 
and sulphuric acid and applying it to grooves cast in the sup- 
porting grid. This paste sets and becomes hard, after which it 
is changed to lead sponge and peroxide by electrolysis in a solu- 
tion which may, or may not, be sulphuric acid. 

The negative plates of the chloride battery, formerly made 
by the Electric Storage Battery Company of Philadelphia, but 
given up about eight years ago, 6 were made in an entirely dif- 
ferent way. Lead and zinc chlorides were melted together and 
poured into the supporting grid. The zinc chloride was then 
dissolved in water, leaving the lead chloride in a porous condi- 
tion. This was then reduced to sponge lead electrolytically. 
The positive plates of this battery were made by the Plante 

6 Dolezalek, The Theory of the Lead Accumulator, p. 194. 
6 Private communication from the company. 



THE LEAD STORAGE BATTERY 



155 



process. Though the method is no longer employed, the name 
is retained. Figure 64 shows the positive and negative plates 





FIG. 04. Positive and negative plates of the chloride accumulator 

of one type of the so- called chloride accumulator. The positive 
,plate contains buttons of lead strips wound up and held in a 
grid. In the negative plate the active material is held in posi- 




niiniui 

juuuwuuuum 



m 
w 




FIG. Go - The Gould battery plate 



156 



APPLIED ELECTROCHEMISTRY 



tion by perforated sheet lead, while the positive plate is of 
the Plante type. 

In the Gould battery, both plates are made by the Plante 
method. A pure lead sheet is stamped out, and the surface is 
worked up into the shape shown in cross section in Figure 65, 
by rolling the surface a number of times with steel disks. 
This process is called spinning. An unspun portion of the 
plate is left where the wheels stop, forming a number of cross- 
bars in each plate. A thin layer of lead peroxide is then pro- 
duced by an electrolytic process. Negative plates are made by 



FIG. (Hi. Positive Gould plate 

reducing peroxide plates. 7 Figure 66 shows a positive plate 
ready to be formed. 

7 Catalogues O f the Gould Company. 



THE LEAD STORAGE BATTERY 157 

There are a large number of different types of batteries made 
by different companies, information concerning which is best 
obtained from their catalogues. 

2. THEORY OF THE LEAD STORAGE BATTERY 1 

The theory of the lead storage battery now generally ac- 
cepted is known as the sulphate theory, and is due to Gladstone 
and Tribe. According to this theory sulphuric acid combines 
with the plates on discharge, and is set free on charge. On 
discharge hydrogen is deposited on the lead peroxide and re- 
duces it to lead oxide, which is changed to lead sulphate. This 
is represented by the equation : 

Pb0 2 + H 2 + H 2 S0 4 = PbS0 4 + 2 H 2 0. (1) 

At the same time the sulphate radical is deposited on the lead 
plate and changes it to lead sulphate : 

Pb+SO 4 = PbS0 4 . (2) 

The total change in the storage battery on discharge is the 
sum of equation (1) and (2): 

Pb0 2 + Pb + 2 H 2 S0 4 = 2 PbS0 4 + 2 H 2 0. (3) 

In the discharged state both plates are covered with sulphate. 
On charging, the reaction on the positive plate is : 

PbSO 4 + S0 4 + 2 H 2 = Pb0 2 + 2 H 2 S0 4 ; (4) 

and in the negative plate : 

PbSO 4 + H 2 = Pb + H 2 SO 4 . (5) 

The sum of equations (4) and (5) represents what takes 
place in the whole battery on charging : 

2 PbS0 4 + 2 H 2 = Pb0 2 + Pb + 2 H 2 SO 4 . (6) 
Equation (6) is identical with equation (3) read from right to 
left. The changes taking place both on discharge and charge 
may therefore be represented by the following reversible equa- 
tion : 

Pb0 2 + Pb + 2 H 2 S0 4 : 2 PbS0 4 + 2 H 2 0. (7) 

1 This discussion is taken mainly from Dolezalek's The Theory of the Lead 
Accumulator, translated by Carl L. von Ende. John Wiley and Sons, (1904). 



158 



APPLIED ELECTROCHEMISTRY 



From right to left this represents the discharge, and from 
right to left the charge. 

In order to show that this equation represents what takes 
place in the lead cell, it is necessary to show that the formation 
or disappearance of each of the substances involved is propor- 
tional to the amount of electricity that has passed. It must 
also be shown that the substances involved are those given in 
the equation. 

That the charged positive plate is the peroxide of lead and 
not some other oxide or hydrate was shown by measuring the 
electromotive force of different lead oxides and hydrates on 
lead against a zinc electrode and comparing with a charged 
positive plate. The results were the following : 



Pb 
Pb 
Pb 
Pb 
Pb | Pb0 2 



Pb 2 
PbO 
Pb 3 4 
H 2 PbO, 



- Zn = 0.42 volt 

- Zn = 0.46 volt 

- Zn = 0.75 volt 

- Zn = 0.96 volt 
Zn = 2.41 volts 



1.15 



A charged positive plate has a potential of 2.4 volts, showing 
that lead peroxide is the compound that exists on the positive 
plate. 

Gladstone and Tribe showed, by analyzing the active mass 
of the plates at different stages of charge and discharge, that 
the production of sulphate on each plate is proportional to the 

quantity of electricity 
that has been taken 
from the cell. 

The same thing was 
shown by W. Kohl- 
rausch and C. Heim 
by measuring the 
specific gravity of the 
acid on charge and 
o 10 20 30 40 so eo discharge. The den- 

AMPERE HOURS ., i ' - . -. 

sity changed exactly 

FIG. 67. Change in density of acid with charge and . J . J 

discharge in proportion to the 




1.11 



THE LEAD STORAGE BATTERY 159 

quantity of electricity that had passed through the cell, as 
shown in Figure 67. A calculation of the change in specific 
gravity by means of equation (7) agrees with that found. 
This calculation is as follows : 

The uncharged battery contained 3350 cubic centimeters of 
acid of 1.115 specific gravity, corresponding to 16.32 per cent 
acid. The total solution therefore weighed 

3350 x 1.115 = 3735 grams, 
and contained 

0.1632 x 3735 = 610 grams of acid, 
and therefore 3125 grams of water. 

After charging with 50 ampere hours, according to equation 
(7), the amount of water that disappeared was 
50 x 2 x 0.336 = 33.6 grams, 
and the amount of sulphuric acid formed was 
33.6 x f| = 183 grams. 
The solution therefore contained after charging 

3125 - 33.6 = 3091.4 grams of water, and 

610 -|- 183 = 793 grains of sulphuric acid. 

The total weight was therefore 3884 grams, and the amount 
of sulphuric acid contained was -ggfa X 100 = 20.42 per cent, 
corresponding to a density of 1.146. The observed density 
was 1.147. 

In order to see whether the heat of the reaction of equation 
(7) and the electromotive force of the cell are in agreement, 
the heat of the reaction may be substituted in the equation : 2 

E= Q +T B , (8) 

23070^ dT' 

when E is the electromotive force and 2 Q is the heat of the 
reaction of equation (7). Half of this value is used in equa- 
tion (8), for 2 Q corresponds to the amount of material 
changed by the passage of 2 coulombs of electricity. The 
value of Q has been measured by Tscheltzow and by Streintz, 
who found 43,800 calories and 42,800 calories respectively, for 

2 Le Blanc, Electrochemistry, p. 173, (1907). 



160 



APPLIED ELECTROCHEMISTRY 



acid of a density 1.044, corresponding to 0.70 mole of acid per 
liter. This concentration is taken, since at this value the tem- 
perature coefficient of the electromotive force is zero. The 
values of JE computed are 

E= 1.86 volts (Streintz), 
j=1.90 volts (Tscheltzow), 

and the measured value for this density of acid gives 1.89 to 
1.90 volts. 

For acid of specific gravity 1.15, the values of Q are 42,600 

r) 7^ 

calories and 43,600 calories respectively, and the value of is 

+ 0.4 x 10- 3 volt. At 17 C., T= 290. Substituting in equa- 
tion (8), .#=1.96 and 2.01 volts respectively. The measured 
value is 1.99 to 2.01 volts. This calculation furnishes a con- 
clusive proof that the reaction given in equation (7) is the one 
that takes place in the lead accumulator. 

It is evident that since the acid becomes more dilute on dis- 
charging a lead battery, the electromotive force must decrease 
with decreasing concentration. Table 18 shows the relation 
between the concentration of the acid and the electromotive 
force, from direct measurements. 

TABLE 18 



DENSITY OF H,SO 4 


PER CENT H 2 SO 4 


ELECTROMOTIVE FORCE AT 15 C 


1.050 


7.31 


1.906 


1.150 


20.91 


2.010 


1.200 


27.32 


2.051 


1.300 


39.19 


2.142 


1.400 


50.11 


2.330 



It will be noticed that the electromotive force of the lead 
storage battery, with the concentration of acid ordinarily used, 
has the unusually high value for a battery of over two volts. 
Sulphuric acid, if electrolyzed between platinum and electrodes, 
gives a weak evolution of gas at 1.7 volts and at 1.9 a strong 
evolution. If lead sulphate were spread in platinum, it would 
therefore not be possible to reduce it to lead and oxidize it to 



THE LEAD STORAGE BATTERY 



161 



peroxide, for the potential required could not be reached. On 
lead, however, the overvoltage is so great that the gas evolu- 
tion does not take place below 2.3 volts, which is greater than 




y-mol. U^SO t 



FIG. 68. Temperature coefficient of electromotive force of lead storage battery a& 
function of the acid concentration 

the voltage needed to change the sulphate in lead on one elec- 
trode and peroxide on the other. If it were not for this high 
overvoltage on lead, the lead storage battery would be an im- 
possibility. 

The temperature coefficient of the lead storage battery for 
the concentration of acid used is positive, but on decreasing the 
concentration of acid the temperature coefficient falls to zero 
and then becomes negative. This is shown by the curve in 
Figure 68, representing the results of experiments in which the 
temperature coefficient was determined between and 24 C. 
The temperature coefficient is constant in value between 10 
and 70 C. The heavy line in the plot gives the experimental 
results, and the dotted curve the values calculated from equa- 
tion (8). 

The mechanism of the reactions taking place in the lead storage 
battery has been explained with the help of the osmotic theory 
by Le Blanc and by Liebenow. The difficulty in applying this 
theory to the lead storage battery is to know what are the ions 
in the case of the lead peroxide plate. According 'to Le 



162 APPLIED ELECTROCHEMISTRY 

Blanc's theory, the lead peroxide, having, a definite, though 
slight solubility, dissolves in the dilute sulphuric acid and then 
reacts with water according to the equation: 

Pb0 2 + 2 H 2 = Pb + 4 OH-. (9) 

During discharge the tetravalent lead ions give up two charges 

of electricity and combine with the SO 4 ions to form lead 
sulphate. The tetravalent lead ions are replaced, as they are 
used up, by the solution of more lead peroxide. There is no 
loss in free energy in this solution and reaction with water, for 
both of these reactions take place at equilibrium concentrations. 
The spongy lead electrode is similar to the zinc in a Daniell 
cell. It goes in solution as a lead ion, but is precipitated on the 
lead plate because of the low solubility of lead sulphate. The 
hydrogen ions of the sulphuric acid combine with hydroxyl 
ions of equation (9) to form water. The equations repre- 
senting the reactions that take place subsequent to the reac- 
tion of equation (9) for the entire battery are accordingly : 

Pb + Pb + 2 S = 4 = 2 PbS0 4 , (10) 

On charge the reverse of the above reactions takes place. 
Both the positive and negative plates are covered with lead 
sulphate, and the sulphuric acid surrounding the plates must 
also be saturated with lead sulphate. On the negative plate 
the lead ions are deposited as spongy lead, and on the positive 
plate the bivalent lead ions are oxidized to tetravalent lead. 
The solution and electrolysis are represented by the equations: 

2 PbSO 4 solid = 2 Pb + 2 SO 4 , (12) 






2Pb=Pb + Pb. (13) 

The tetravalent ions then react with the hydroxyl ions accord- 
ing to equation (9) taken in the reverse direction : 

4 H 2 = 4 OH- 4- 4 H+, (14) 

Pb + 4 OH- = Pb0 2 + 2 H 2 0. (15) 



THE LEAD STORAGE BATTERY 163 

The hydrogen ions corresponding to the hydroxyl ions and the 

sulphate ions from equations (12) unite to form sulphuric acid : 

4 H + + 2 S0 4 = 2 H 2 S0 4 . (16) 

The sum of equations (9) to (11) and of equations (12) to 
(16) will be found to result in equation (7). In support of 
Le Blanc's theory it may be stated that tetravalent lead ions do 
exist, and they are therefore probably capable of forming by 
the electrolysis of lead sulphate solutions. 

Liebenow's theory differs from Le Blanc's only as to the 
action of the peroxide electrode. According to this theory the 
lead peroxide goes into solution as doubly charged lead per- 
oxide ions, so that the peroxide plate is to be considered a 
reversible electrode with respect to the peroxide ions. On 
discharge, the peroxide passes into the solution surrounding 
the peroxide plate, which is already saturated with respect to 
these ions. They then react with the hydrogen ions of the 
acid as follows : 

PbO 2 + 4 H+ = Pb + 2 H 2 O. (17) 

The lead ions then combine with the sulphate ions to form 
solid lead sulphate : 

Pb + Sl) 4 = PbSO 4 solid. (18) 

During charge, just the reverse reactions take place. The 
lead peroxide ions are deposited on the positive plate, and are 
replaced as they are used up by the solution of the sulphate 
from the electrode and its hydrolysis : 

Pb + 2 H 2 = Pb0 2 + 4 H+. (19) 

In order to give Liebenow's theory some foundation it is neces- 
sary to prove the existence of lead peroxide ions. This was done 
by showing that on electrolyzing a solution of lead in sodium 
hydroxide the concentration of the lead in anode compartment 
increased. This shows that the sodium plumbite must be dis- 
sociated according to the equation : 

Na 2 PbO 2 = 2 Na+ + P~bO 2 . (20) 

The electromotive force of the lead storage battery can be 



164 APPLIED ELECTROCHEMISTRY 

expressed by the Nernst formula by the aid of Liebenow's 
theory. If P Pb o 2 is the electrolytic solution pressure of lead 
peroxide and P Pb that of lead, and if the jt?'s refer to the osmotic 
pressure of the ions, the potential difference between the per- 
oxide plate and the solution is 

(21) 




and between the lead plate and the solution is 



e2 = ^lo g ^. (22) 

2 2 8 .. V J 



The electromotive force of the cell is therefore 

(23) 



In confirmation of this theory, it has been found, as would 
be predicted from equation (23), that in an alkaline solution, 
in which the concentrations of the lead and lead peroxide 
would be greater than in acid solutions, the value of E is less 
than in acid solutions. 

The work obtainable from a storage battery depends on its 
capacity and the electromotive force measured at its poles 
while the current is flowing. If V is the voltage on charging, 
E is the open circuit electromotive force, I is the charging 
current, and R is the resistance of the battery, then 

F= E + IR, (24) 

and on discharge 

V = E - IR. (25) 

If the current is kept constant and the value of Vis meas- 
ured at short intervals, the charge and discharge curves ob- 
tained are of the form shown in Figure 69. The value of V 
rises rapidly in the first few minutes of the charge from 2.0 to 
2.1 volts, and during the rest of the charge continues to rise 
slowly, until at the end it suddenly rises to 2.5 to 2.7 volts. 
During this period of rapid rise in the value of F", the cell 
begins to evolve gas, after which the value of V changes only 
slightly. On allowing the battery to stand on open circuit 



THE LEAD STORAGE BATTERY 



165 



for several hours, the electromotive force E falls to the value 
corresponding to the density of the acid. If the battery is 
then allowed to discharge with the same constant value of the 
current as used in charging, the value of V at first falls rapidly 



Volt 
2.8 
2.6 
2.4 
2.2 
2.0 
1.8 
1.6 
1.4 
1.2 
1.0 



"0 4 Hours 

FIG. 69. Charge and discharge curves of the lead storage battery 

to 1.9 volts and then gradually to 1.85 volts, after which it 
decreases more rapidly to zero. The curves given in Figure 69 
were obtained with about 20 per cent acid and a current density 
of about 0.005 ampere per square centimeter of electrode sur- 
face. With a greater current density the distance between the 
charge and discharge curves would increase. The general 
character of the curves for different makes of batteries is the 
same, though for those having a thin layer of active material 
the curves are more marked, and for those having a thick 
layer, they are more rounded. 

From the fact that the charging potential V is several tenths 
of a volt higher than the discharging potential V, as is shown 
in Figure 69, it is evident there is a loss of from 20 to 30 per 
cent in the energy stored. It might seem at first sight that it 
is due to the loss of energy due to the resistance of the cell 
itself, to the IR value in equations (21) and (22), but the 
value of the resistance of the cell is too small to account for 
such a large loss. On open circuit the resistance of the 



166 APPLIED ELECTROCHEMISTRY 

smallest cells used is only several hundredtlis of an ohm, and 
no large increase in its value takes place when a current is 
passing. The cause of this loss in energy is the polarization of 
the electrodes caused by the change in concentration of the acid 
in the pores of the plates. On charging, acid is formed in the 
pores of the plates where it becomes more concentrated than in 
the rest of the battery on account of the fact that diffusion 
does not take place with sufficient rapidity to equalize it. 
Since the electromotive force of the battery increases with the 
concentration of the acid surrounding the plates, a higher im- 
pressed electromotive force will therefore be necessary in charg- 
ing. On discharge, the acid is used up in the plates and 
becomes more dilute than in the rest of the battery, and the 
voltage falls correspondingly. The charge and discharge 
curves of the lead battery may now be taken up in detail. 

The Charging Curve. On closing the charging current, sul- 
phuric acid is immediately set free at both electrodes and the 
electromotive force therefore rises rapidly, as shown by the 
portion of the curve AB. The rate of diffusion increases with 
the difference in concentration of the acid on the plates and in 
the rest of the battery, and when concentration difference has 
become so great that the rate of diffusion and of formation are 
equal, this rapid increase ceases. The maximum point at B is 
probably due to the destruction of the thin continuous layer of 
sulphate which forms on the electrodes during rest, thus reduc- 
ing the resistance of the cell. The slow regular rise to O is due 
to the gradual increase in the density of the acid and also to 
the deeper penetration of the current lines into the active mass 
and the corresponding greater difficulty in equalizing the acid 
concentration by diffusion. The final rise CD takes place when 
all of the lead sulphate on the surface of the plates has been 
used up, and consequently the sulphate does not dissolve rapidly 
enough to replace that electrolyzed out. Very soon the lead 
and peroxide ions become so dilute that the work necessary to 
deposit these ions is equal to that required to produce hydrogen 
on the cathode and oxygen on the anode. If allowed to stand 
on open circuit, sulphate diffuses from within the plate and brings 



THE LEAD STORAGE BATTERY 167 

back the electromotive force to the normal amount. The maxi- 
mum point at D is due to the mixing of the concentrated acid 
in the electrodes with that outside by the gas bubbles. 

The Discharge Curve. In discharge the acid is used up in 
immediate proximity to the electrodes, and this continues until 
the concentration difference between the acid on immediate 
proximity to the electrodes and in the rest of the battery has 
become so great that diffusion just supplies the quantity used 
up. During this time the value of V falls rapidly along AE* 
The minimum point at ^is possibly caused by the formation of 
a supersaturated lead sulphate solution. The solubility of lead 
sulphate in a 20 per cent solution of sulphuric acid decreases 
with decreasing concentration, so that at the beginning of the 
discharge, when little solid sulphate is present, a supersaturation 
of short duration is probable, and the electromotive force of the 
battery decreases with increasing concentration of lead ions, as 
seen from equation (23). The subsequent gradual fall in the 
value of V represented by EF is due to the gradual decrease 
in the density of the acid in the entire accumulator, but more 
especially to the greater difficulty in the acid diffusing deeper 
into the plate as the current penetrates deeper. Finally the 
rate at which the acid diffuses cannot supply the acid used up 
by the action of the current, and the value of V 1 falls off 
rapidly. 

According to this explanation, the loss in energy on charge 
and discharge is due entirety to the concentration changes that 
take place in the electrolyte within the active mass. The 
smaller these concentration changes are, the more nearly will 
the accumulator approach complete reversibility. This is il- 
lustrated in Figure 70. These curves were obtained with 
accumulator of 200 ampere hours capacity. It is seen that for 
a current of 0.1 ampere, corresponding to a current density of 
0.0017 ampere per square decimeter, the charging and dis- 
charging potential differ by only 0.006 volt, or 0.3 per cent of 
the electromotive force of the cell, and that by reducing the 
current this loss may be still further reduced. 

This loss is not distributed equally between the two plates. 



168 



APPLIED ELECTROCHEMISTRY 



The porosity of the lead plate made from the same sulphate 
paste as the peroxide is about 1.4 times as great as the peroxide, 
the potential of the peroxide plate falls off about 1.6 times 
more than the lead plate for a given change in the concentni- 



Volt 



2.080 



2.078 



2.076 



2.074 




C.C5 



0.1 Amp. 



FIG. 70. Pole potential of the lead storage battery on charge and discharge as a 
function of the current 

tion of the acid, and finally the concentration change on the 
peroxide plate is greater than on the lead, because not only is 
sulphuric acid used up on discharge, but water is also formed. 
All of these facts tend to make the loss on the peroxide plate 
greater than that on the lead plate. When the positive and 
negative plates are made of similar frames and paste, and have 
approximately the same capacity, it has been found that 60 to 
70 per cent of the loss takes place on the peroxide plate. 

The capacity of an accumulator in actual practice means the 
number of ampere hours that can be taken from it if discharged 
to about nine tenths of its original electromotive force, the point 
where the rapid falling off in the electromotive force takes place. 
The capacity therefore is determined by the rate of discharge, 
for the smaller the current the more time the acid has to pene- 
trate by diffusion deeper into the plate, when all of the active 
material on the surface has been used up. It is also evident 



THE LEAD STORAGE BATTERY 169 

that the conductivity of the acid will affect the capacity, for the 
higher the conductivity the deeper will the current lines be able 
to penetrate into the plate. Since there is a density of sul- 
phuric acid at which there is a maximum conductivity, it would 
be expected that the capacity of a lead storage battery would 
have a maximum value for this density, and this has been shown 
experimentally to be the case. 

The current efficiency of a lead storage battery, or the ratio 
of the number of ampere hours obtainable on discharge to the 
number put into the battery on charge, is from 94 to 96 per 
cent. The small loss of 4 to 6 per cent is due to self-discharge 
and to the small amount of gasing that cannot be avoided. 
The energy efficiency, on the other hand, which is the ratio of 
the energy obtainable in the external circuit on discharge to the 
energy put into the battery on charge, is only from 75 to 85 per 
cent. The, cause of this comparatively low value, as explained 
above, is the difference between the charge and discharge po- 
tential. The loss in voltage due to the internal resistance is 
only about 3 per cent with the usual acid concentration and 
current density. The loss due to polarization is a minimum 
when the conductivity of the acid in the battery is a maximum, 
for in that case the lines of current spread over a larger surface 
by penetrating deeper into the plate. 

If a battery is allowed to stand on open circuit after charg- 
ing, the electromotive force falls in fifteen or twenty minutes to 
the value corresponding to the density of the acid. This is 
due to solution around the plates becoming saturated with lead 
sulphate. On discharge, when the voltage has fallen below the 
value corresponding to the density of the acid, standing on open 
circuit brings it back to the normal value. In this case the 
recovery, as it is called, is due to the diffusion of the sulphuric 
acid into the pores of the plate -where it has become exhausted. 

If a charged cell is allowed to stand idle, the density of the 
acid slowly decreases, and the amount of electricity obtainable 
from it becomes less from day to day. This is known as self- 
discharge, and for a cell in good condition amounts to from one 
to two per cent a day ; if the acid contains impurities, however, 



170 



APPLIED ELECTROCHEMISTRY 



it may amount to 50 per cent a day. The self -discharge of the 
lead sponge plate is more likely to take place than that of the 
peroxide plate, as it is affected by a greater number of causes. 
It is fatal for the lead plate if the acid contains any metal more 
electronegative than lead in contact with sulphuric acid, such 
as platinum or gold, for the impurity would be precipitated on 
the plate and produce a short-circuited local element. The 
lead would then tend to dissolve and deposit hydrogen on the 
impurity. If the over-voltage of the impurity is not too great, 
this would in fact take place, and the lead plate would be 
changed to sulphate. Now the potential of the cell: 

Pb sponge | Sulphuric acid | Platinized Pt -f- H 2 
is 0.33 volt, hydrogen being the positive pole. A current could 
be taken from this cell on closing the external circuit ; lead 
sulphate would be formed on the lead pole and hydrogen would 
be deposited on the positive pole. But if some metal were 
substituted for platinum for which the over- voltage is 0.33 volt 
or more, evidently hydrogen could not be liberated, and no 
action would take place. Consequently only the metals stand- 
ing on the left in the following table would be dangerous for 
the accumulator ; those on the right could exist as impurities 
in the acid without the least danger, even though some of them 
are more electro-negative than lead. 





OVER- 
VOLTAGE 




OVER- 
VOLTAGE 


Platinized Platinum . 


0.005 


Palladium 


0.46 


Gold 


0.02 


Cadmium 


48 


Iron . . ... 


0.08 


Tin 


53 


Platinum, polished 


0.09 


Lead 


0.64 




0.15 


Zinc 


0.70 


Nickel 


0.21 


Mercury .... 


0.78 




0.23 















As seen from this table, platinum is the most injurious impu- 
rity. It has been found that one part of platinum in a million 
of acid will produce a rapid self-discharge of the lead plate. 



THE LEAD STORAGE BATTERY 171 

It has been found, however, that metals when present together 
can produce a rapid self -discharge, which alone cause scarcely 
any action. An explanation of this cannot be given at present. 

Contamination by platinum can easily occur when sulphuric 
acid is used that has been concentrated in platinum retorts, 
and plates once contaminated cannot be made available again. 
All other metallic contaminations, if present only in traces, 
become inactive on continued use of the cell, probably by 
gradually alloying with the lead. 

The self-discharge of the positive plate takes place more 
slowly than that of the lead sponge plate. Metallic impurities 
are of no effect on the lead peroxide, for they would not be 
precipitated on it. The only kind of spontaneous discharge is 
due to local action between the peroxide and the lead of the 
support, which together form a short-circuited element, and 
this is of importance only for plates with a thin layer of per- 
oxide. 

Another cause of self-discharge of a battery is the presence 
of salts of metals that can exist in more than one stage of oxi- 
dation. For example, an iron salt would be oxidized to the 
ferric state on the lead peroxide, and would then diffuse to the 
lead plate and oxidize it to sulphate, thus gradually discharg- 
ing both plates. 

Sulphating. The plates of a strongly discharge battery on 
standing gradually become covered with a white coat of lead 
sulphate. If we attempt to recharge the battery, it is found 
that the internal resistance has considerably increased, and it 
does not begin to diminish until the charging current has 
passed through the cell for some time; it then gradually ap- 
proaches its normal value. A test of the capacity would show 
that this has lost considerably in value. The phenomenon just 
described is known as sulphating. This is not a very suitable 
term, since in every discharge sulphate is formed on the plates, 
which is changed back into peroxide and lead without any diffi- 
culty. Elbs explains sulphating as follows : During discharge 
there is formed on every particle of lead or peroxide a thin 
layer of finely divided sulphate in contact with an acid solution 



172 APPLIED ELECTROCHEMISTRY 

saturated with the sulphate. If the accumulator is allowed to 
stand in this condition, and is subject to any variation in tem- 
perature, the large crystals will grow at the expense of the 
smaller ones, for the sulphate increases in solubility as the tem- 
perature rises, and the smaller crystals would be used up first, 
both on account of their size and because the solubility of small 
crystals is greater than that of large ones. When the tempera- 
ture falls, the sulphate would be precipitated on the crystals 
still remaining, and in this way the plate gradually becomes 
covered with a continuous layer of lead sulphate crystals. Sul- 
phating may be so bad that it is cheaper to replace the plates 
than to regenerate them by charging. 



CHAPTER X 
THE EDISON STORAGE BATTERY 

1. GENERAL DISCUSSION 

THE Edison storage battery is the only accumulator besides 
the lead battery that has any commercial importance. In this 
battery the active material of the positive pole is an oxide or 
oxides of nickel, and that of the negative pole, very finely 
divided iron. The solution is 21 per cent potassium hydrate 
with a small amount of lithium hydrate. 1 

Edison began to investigate alkaline accumulators in 1898, 
and after trying a great number of different combinations had 
the nickel-iron combination fairly well developed in 1900. 2 
It fhen passed through several more stages of development, and 
arrived in 1904 at what was called the type E 18 battery. This 
had twelve nickel plates arid six iron plates. The active mate- 
rial of each plate was held in 24 perforated nickel-plated steel 
pockets 7.5 centimeters in length, 1.27 centimeters in width, 
and 8 millimeters in thickness. The iron plate was mixed 
with mercury, the effect of which will be explained below, and 
the nickel oxide with graphite, to increase its conductivity. 
This battery had two defects : (1) the nickel plate continually 
expanded on charging and did not contract on discharge, so 
that the contacts between the active material and the supports 
became bad, and (2) the graphite mixed with the nickel oxide 
gradually disintegrated and did not fulfill its function of con- 
ducting the current into the interior of the nickel plate, caus- 
ing the battery to lose its capacity. 1 

1 Walter E. Holland, El. World, 55, 1080, (1910). 
2 Kennelly and Whiting, Trans. Am. Klectroch. Soc. 6, 135, (1904). 

173 



174 



APPLIED ELECTROCHEMISTRY 




FIG. 71. Iron electrodes of tlie Edison storage battery 




FIG. 72. Nickel electrodes of the Edison storage battery 



THE EDISON STORAGE BATTERY 175 

Both of these difficulties seem to have been overcome in the 
latest form of this battery, the A type, which has been on the 
market since 1908. The construction of the iron electrode, 
shown in Figure 71, has not been altered, and its dimensions are 
the same as in the E type, but the nickel electrode has been con- 




FIG. 73. Section of pencil from the nickel plate of the Edison storage battery 

siderably changed. The nickel plate, shown in Figure 72, was 
formerly made just like the iron plate, but in the A type it 
consists of two rows of 16 round pencils, held in position by a 
steel frame. They have flat flanges at the ends by which they 
are supported and by which electrical connection is made. 
These pencils are perforated nickel-plated steel tubes filled with 
the active material, 0.65 centimeter in diameter and 10.5 centi- 



176 APPLIED ELECTROCHEMISTRY 

meters in length. They are put together with a spiral seam to 
resist expansion, and each cylinder also has eight steel rings 
slipped over it as a further precaution. The graphite is re- 
placed by nickel made into thin flakes, and distributed in 
regular layers through the active material, as shown in Figure 




FIG. 74. Containing can of the Edison storage battery 

73, a section of a pencil taken through its axis. The dark 
layers are nickel flake, and the light-colored layers are the ac- 
tive material. A pencil contains about 350 layers of each kind 
of material, each layer of active material being about 0.01 inch 
thick. 

As in the earlier battery, the containing can is of nickel- 



THE EDISON STORAGE BATTERY 



177 



plated steel, as shown in Figure 74. The top of the can is 
permanently put in place after the plates are in position. 
There are four openings in the top, two of which are for the 
terminals bolted to the groups of positive and negative plates, 
while the third is for filling, and the fourth contains a valve 
which allows the gas to escape, but which does not allow any to 
enter from the outside. The valve is covered with a fine wire 
gauze to hold back any particles of water coming off with the 
gas during charging. 

The batteries are now made in five sizes. Table 19 gives 
the principal facts regarding these cells : 3 

TABLE 19 



TYPE 


No. OF POSI- 
TIVE PLATES 


NORMAL DIS- 
CHARGE RATE. 


NORMAL OUT- 
PUT. AMP. II RS. 


WT. OF ONE 
CELL. KGS. 


PRICE PER 
CELL. DOLLARS 






AMP. 








A4 


4 


30 


150 


6.1 


13.50 


A6 


6 


45 


225 


8.7 


20.00 


A8 


8 


60 


300 


11.4 


26.00 


B2 


2 











6.00 


JB4 


4 











8.00 



The average discharge voltage for any type is 1.2 volts, when 
discharged to 1 volt. As will be explained below, the capacity 
can be considerably increased by overcharging. According to 
the catalogue of the Edison Storage Battery Company, the 
normal capacity of these cells can be increased 30 per cent when 
charged at the normal rate for ten hours. The continuous rate 
of discharge may be 25 per cent above the normal rate without 
injury, and for occasional short intervals it may be four times 
the normal rate. A cell may stand unused for any length of 
time without injury, but it is said to be better to leave it dis- 
charged in this case. As stated above, this must never be done 
in the case of a lead storage cell. 

8 Catalogue of the Edison Storage Battery Company, and a private communi- 
cation from Mr. Holland, of this company. 



178 APPLIED ELECTROCHEMISTRY 

2. THEORY OF THE EDISON STORAGE BATTERY l 

The active material of the nickel plate when first manufac- 
tured consists of green precipitated nickelous hydroxide com- 
pressed in a steel pocket under hydraulic pressure. Since it 
has been found that when nickelous hydroxide is oxidized 
chemically, it always first changes to nickel peroxide, NiO 2 , it 
is assumed that the same is true of electrolytic oxidation. This 
assumption is justified, for it offers an explanation of the behav- 
ior of the nickel plate that is in agreement with all of the facts. 
When the nickelous hydroxide is electrolyzed as anode in a 
potassium hydroxide solution, it therefore first changes to 
nickel peroxide. In fact, analysis shows that a freshly charged 
plate contains as much more oxygen than corresponds to the 
formula Ni 2 O 3 as would correspond to at least 8 per cent of 
nickel peroxide. The nickel peroxide then reacts on the nickel- 
ous oxide as follows : 

NiO 2 +NiO = Ni 2 O 3 , (1) 

or if no nickelous oxide is in immediate contact with it, it 
decomposes of itself : 

2NiO 2 = Ni 2 3 + 0. (2) 

Analysis showed that the charged nickel plate,. when dried 
over sulphuric acid, has the composition represented by the 
formula Ni 2 O 3 1.3 H 2 O to Ni 2 O 3 - 1.1 H 2 O. Any nickel 
peroxide originally in the plate therefore disappears on drying. 
It is of course impossible to tell from this whether the nickel 
oxide is combined with more water before drying or not. In 
the hydrates given above, the ratio of atoms of nickel to moles 
of water is 1 : 0.55 to 1 : 0.65, while after the discharge the ratio 
is 1 : 1. The nickel plate therefore takes up water on discharg- 
ing, assuming that the oxides have the same amount of water 
in combination while in the potassium hydrate as after drying. 
The nickelous compound formed when the nickel plate dis- 
charges would 'then be Ni(OH) 2 . 

The potential difference between a freshly charged nickel 

1 F. Foerster, Z. f. Elektroch. 13, 414, (1907). The discussion of the nickel 
plate is taken from this article, except where the contrary is stated. 



THE EDISON STORAGE BATTERY 



179 



plate and a 2.8 normal solution of potassium hydrate is 0.88 
volt, referred to the dropping electrode as zero. The negative 
sign refers to the charge on the solution surrounding the elec- 
trode. In 50 minutes this potential difference falls to 0.86 
volt and in 61 days to 0.75 volt. Analysis of this plate 
showed the nickel oxide to correspond to the formula Ni 2 O 3 . 
It was also found that the potential difference of an electrode 
covered electrolytically with nickelic oxide was 0.77 volt. 
This constant potential reached by the charged plate on stand- 
ing therefore corresponds to nickelic oxide, and the potential of a 
freshly charged plate must be due to the nickel peroxide. The 
peroxide is not stable, but gradually decomposes with the 
evolution of oxygen, changing to nickelic oxide, and this ex- 
plains the constant potential arrived at. There is no sudden 
change when all the nickel peroxide is used up, consequently 



40 



30 



AMPERE MINUTES, CHARGE 
25 20 15 



10 



-0.9 



g-0.7 

I 
u 

z-0.5 



-0.3 



+ 0.1 



-{-0.3 



CHARGE 




10 



80 



35 



15 20 25 

AMPERE MINUTES, DISCHARGE 

FIG. 75. Potential of nickel electrode on charge and on discharge 



40 



180 APPLIED ELECTROCHEMISTRY 

the nickel peroxide and nickelic oxide must form one phase, 
such as a solid solution. This evolution of oxygen is the cause 
of the loss in capacity on standing, amounting to 10 per cent 
in 24 hours, for in this battery the capacity is determined by 
that of the positive plates. 

The change in the potential of the nickel electrode on dis- 
charging is shown by the curve in Figure 75. It is of course 
similar to the discharge curve of the whole battery, since the 
capacity is determined by this plate. The first part of the 
curve, concave upwards, is due to the discharge of the solid 
solution of nickel peroxide in nickelic oxide, as is shown by 
the fact that this part of the curve entirely disappears if the 
battery stands idle for twelve hours after charging. The drop 
towards the end of the discharge of 0.55 volt was shown by 
analysis to be due to an oxide of nickel lying between Ni 2 O 3 
and NiO, possibly Ni 3 O 4 , as this oxide is known to exist. This 
second constant potential becomes shorter as the current density 
increases, and finally disappears altogether. 

The charging potential of the nickel plate is more above the 
potential corresponding to nickelic oxide than the discharge 
curve is below. This is because the first action in charging 
is to produce nickel peroxide, which requires a potential at 
least equal to that of a solid solution of nickel peroxide. The 
nickel peroxide at first finds a large amount of nickelous oxide 
which it oxidizes to nickelic oxide. The nickel peroxide there- 
fore disappears rapidly at first, and with a low current density 
the potential of the plate is not much above that of nickelic 
oxide. Gradually, however, the peroxide becomes more con- 
centrated and the potential rises. The nickel peroxide then 
begins to decompose with the evolution of oxygen, until its 
rate of decomposition equals its rate of formation. Nickel 
peroxide is formed also by the electrolytic oxidation of nickelic 
oxide, so that its formation continues even after all of the 
nickelous oxide ha?s been oxidized. 

The efficiency of charging the nickel plate is determined by 
the amount of oxygen evolved. The curves in Figure 76 show 
this efficiency for three different current densities, when the 



THE EDISON STORAGE BATTERY 



181 



discharge was stopped before the second stepwas reached. It 
is evident from these curves that the full capacity cannot be 
obtained without a loss in the current efficiency. This is quite 
different from the lead storage battery, in which the efficiency 
of charging is nearly 100 per cent throughout the whole charge, 
and then suddenly falls to zero at the end. In speaking of the 
current efficiency in an Edison storage battery, the capacity 
must therefore also be given. 

The Negative Plate. The negative or iron plate when 
charged consists of finely divided metallic iron in the active 
state. If iron is reduced at a high temperature by hydrogen 



100 




40 



0.2 



0.3 



0.4 0.5 0,6 

AMPERE HOURS 



o.r 



O.S 



to 



FIG. 76. Efficiency of charging the nickel plate 

and then placed in potassium hydrate, it remains inactive, but 
after electrolyzing for a short while as cathode in a potas- 
sium hydrate solution it becomes active and has considerable 
capacity. 2 

The iron electrode also has two stages in its discharge, 8 as 
seen in Figure 77. The first consists in the oxidation of iron 
to ferrous oxide. 2 The second step is due to the oxidation 
of ferrous to ferric iron, due to the iron becoming passive 
and the velocity of the oxidation of metallic iron becoming too 

2 F. Foerster and V. Herold, Z. f. Elektroch. 16, 461, (1910). The discussion 
of the iron electrode is taken from this article, where the contrary is not stated. 

3 M. W. Schoop, Electrochem. Ind. 2, 274, (1904). 



182 



APPLIED ELECTROCHEMISTRY 



slow. The oxidation of iron to ferrous hydrate is then replaced 
partly or entirely by the oxidation of ferrous to ferric iron. If 
the ferrous hydrate is not supplied rapidly enough by electro- 
chemical oxidation, the metallic iron is oxidized to the ferrous 
state by the ferric iron. The result of the second step is, there- 



40.6 




-0.2 



5 10 15 20 25 30 

AMPERE MINUTES 

FIG. 77. Potential of iron electrode on discharge 



fore, to change metallic iron to the ferric state. In a 2.85 
normal solution of potassium hydrate the potential of the first 
process is + 0.60 volt referred to the dropping electrode as 
zero, the positive sign referring to the charge on the solution 
surrounding the electrode. The potential difference between 
the ferro-hydroxide electrode arid a 2.85 normal potassium 
hydrate solution is + 0.47 volt. This difference in voltage 
between the two steps for the iron electrode is therefore only 0.13 
volt, while in the case of the nickel electrode it is 0.55 
volt. This second step is of no practical importance, for the 
iron plate would not reach it when its capacity is greater than 
the nickel. 

The effect of the addition of mercury to the iron plate is 
to increase its capacity by keeping the iron in the active state. 
The beneficial effect of mercury was discovered by Edison 
empirically, but just how it keeps the iron active is not yet 
understood. The mercury makes it possible, however, for the 
plate to have a constant capacity for the first step, independent 



THE EDISON STORAGE BATTERY 183 

of the current density, and is therefore of great practical impor- 
tance. It has no effect on charging. The reason for making 
the capacity of the iron plate greater than that of the nickel is 
that the iron electrode should never be discharged as far as the 
second step, for ferric iron cannot be completely reduced again, 
and the plates lose in capacity. It has an equally bad effect 
to allow the iron plate to stand unused in potassium hydrate 
exposed to the air or to allow it to stand in the air when moist. 
In charging, hydrogen is liberated on the iron plate from the 
start, so that the iron plate causes a greater loss in current than 
the nickel, on which no gas is liberated during the first part of 
the charge. It was shown above that the nickel plate changes 
from Ni 2 O 3 -1.2 H 2 O to Ni(OH) 2 on discharging, and the iron 
plate from iron to ferrous hydrate. These changes may be rep- 
resented by the equations : 4 

Ni 2 3 1.2 H 2 + 1.8 H 2 ; 2 Ni(OH) 2 + 2 OH- + 2 F (3) 
and Fe + 20H-^>Fe(OH) 2 -2F. (4) 

The sum of these equations is 

Fe + Ni 2 O 3 - 1.2 H 2 O + 1.8 H 2 O ^ 2 Ni(OH) 2 

+ Fe(OH) 2 +. (5) 

This equation represents the final result in the whole cell on 
discharge, when taken from left to right, and on charge, w r hen 
taken from right to left. These equations are not reversible in 
the ordinary sense, however, for they do not show that hydrogen 
and oxygen are evolved on charging or that the nickelous 
hydrate is first oxidized to nickel peroxide. The Edison cell is 
therefore not strictly reversible, and the equations, though 
written as reversible, are to be taken only as referring to the initial 
and final states of the cell. It is also to be noticed that in adding 
the two equations for the iron and the nickel plates the two 
quantities of electricity, 2 F, cancel out. This means the two 
quantities neutralize each other, thereby producing the current. 
The Electrolyte. From the equation (5) it is evident that 
water is taken up from the electrolyte on discharging by the 
plates and is given up again on charging. This can be seen by 
* Foerster, Z. f. Elektroch. 14, 285, (1908). 



184 APPLIED ELECTROCHEMISTRY 

the change in level in the solution on charging and discharging. 
According to equation (5), 0.9 mole of water would be com- 
bined or set free to one faraday of electricity passing through 
the cell. Other experiments made for the purpose of deter- 
mining this quantity gave an average of 1.45 moles of water. 
This agreement is not all that could be desired. There is no 
question, however, that water is removed from the solution on 
discharging, and it therefore follows that the electromotive 
force of the battery will decrease with the increasing concentra- 
tion of the electrolyte. This is verified by the measurements 
of the following table : 4 



NORMALITY OF HYDRATE SOLUTION 


E. M. F. OF CELL 


1.0 


1.3510 


1.15 


1.3368 


2.82 


1.3377 


5.3 


1.3349 



From what has preceded, it will be evident that the current 
efficiency and capacity depend on each other. If the battery 
is not fully charged, the current efficiency will be high, but the 
full capacity is not obtained. This can be obtained only by 
charging after gas evolution has begun, which reduces the 
current efficiency. When the cell was charged and discharged 
at the normal rate of 4 hours, the ampere hour efficiency was 
about 75 per cent, and the voltage efficiency about 70 per cent, 
making the energy efficiency about 50 per cent. 6 

5 Kennelly and Whiting, Trans. Am. Electrochem. Soc. 6, 146, (1904). 



CHAPTER XI 
THE ELECTRIC FURNACE 
1. GENERAL DISCUSSION 

THE electric furnace industries are at present in a state of 
rapid development. This is due partly to the manufacture of 
a large number of new products made possible by the high 
temperature attainable in the electric furnace, and partly to 
improved methods in the manufacture of products previously 
obtained by other methods. 

The electric furnace was probably first used on a commercial 
scale by the Cowles Brothers in 1884 in their manufacture of 
aluminum alloys, but the rapid increase in its use began about 
1893 with the production of calcium carbide, carborundum, and 
aluminum. 

In the manufacture of many electric furnace products, heat 
at a high temperature is the form of energy that brings about 
the change desired. The question naturally arises, how is it 
possible that it should be economical to obtain heat from such 
an expensive form of energy as electricity. There are several 
reasons why it is economical. In the first place, the temper- 
ature required for the formation of many electric furnace prod- 
ucts is above that attainable by any commercial fuel. In such 
cases it is evident that if the product is to be formed at all, it 
must be formed in an electric furnace. On the other hand, it 
has been found economical to use heat generated from electricity 
in cases where fuel was formerly used. This is due to a simplifi- 
cation in the apparatus and a saving of time and labor. While 
electric heat costs more per unit, it may be possible to reduce 
the time during which it has to be applied to such an extent 

185 



186 APPLIED ELECTROCHEMISTRY 

that the quantity of heat required is so much less than when 
fuel is used that it more than saves the extra cost per unit. 
This is often the case on account of the fact that electric heat 
is generated inside the furnace or container just where it is 
wanted, while in the use of fuel the heat is generated outside 
the furnace and has to penetrate the walls before reaching the 
material to be heated. It is evident that more heat will be lost 
in the latter than in the former process. 

In those furnaces in which the electricity flows through a 
core especially made for the purpose and not through the 
charge itself, the temperature to which the core is raised is one 
of the factors that determines the time required to bring the 
charge up to the desired temperature, since the flow of heat 
between two bodies is proportional to their difference in tem- 
perature. 

Furnaces may be divided into three classes : arc furnaces, 
resistance furnaces, and induction furnaces. In the first, as the 
name indicates, the source of heat is an arc. A solid body to 
be heated is placed near the arc and is heated by radiation. 
By adjusting this distance the temperature to which it is raised 
may be regulated. In case a gas is to be heated, the passage of 
the arc through the gas itself brings about the desired result. 
In the resistance furnaces the current generates heat by passing 
some suitable resistor. It is evident that arc furnaces are simply 
resistance furnaces where the resistor is a gas; but nevertheless 
this distinction is a convenient one. Resistance furnaces may 
be of two kinds, first, those in which the current passes through 
the charge to be treated and develops heat in consequence of the 
resistance of the charge, and second, those in which the current 
passes a resistor surrounded by the charge. The latter furnace 
is used in those cases where the charge itself does not conduct 
well. The first class of resistance furnace may be divided into 
two classes, in which (1) the thermal effect is alone active, and 
(2) in which electrolysis also takes place. 

The induction furnace is the latest type, and is used in the 
steel industry. The metal to be heated forms the secondary 
winding of a transformer, and forms a closed ring in an annular 



THE ELECTRIC FURNACE 187 

crucible. A current is induced from the primary winding 
sufficiently great to melt the metal. 

The following table summarizes this classification. 

ELECTRIC FURNACES 

1. 2. 3. 

Arc Resistance Induction 



1. The charge con- 2. Current conducted 

ducts the current. by a special resistor. 



1. Withelec- 2. Without elec- 

trolysis, trolysis. 

2. ELECTRIC FURNACE DESIGN 

In spite of the fact that the heat is generated inside the furnace, 
there is always some heat lost by conduction through the walls 
of the furnace, through the electrodes, and in some cases by 
hot gases. To increase the economy of furnaces these losses 
must be made as small as possible. The case when the loss is 
due to gases requires no special consideration, but it will be 
desirable to consider the losses through the walls and the 
electrodes. 

If H equals the number. of calories conducted in one second 
through a wall of cross section S, thickness I, and specific con- 
ductivity &, when the difference in temperature of the two 
faces is T and no heat is lost through the ends of the walls, 

rr SkT 

then H- 

l 

In the case of a furnace, the cross section of the wall is not 
constant, but increases from the inner to the outer surface. 
Generally in making this calculation the average cross section 
is taken. Where the walls are thin, this is fairly accurate, but 
with thick walls a very great error may be introduced. 1 

1 Carl Hering, Trans. Am. Electrochem. Soc. 14, 215, (1908). The discussion 
in the text is taken from this article. 



188 APPLIED ELECTROCHEMISTRY 

For a complete sphere, inner surface s, outer surface S, and 
thickness of wall I, the heat conducted per second for unit dif- 
ference of temperature is 2 



TT _ 



where D is the outside and d the inside diameter. For a cube 

6 TcDd 



I I 

where D is the length of the outer edge and d that of the inner 
edge. For a cylindrical shell of length (7, thickness of wall Z, 
outside diameter 2>, and inside diameter c?, 



2-3 log" 



2 The derivations of this and the following formulae, not given by Bering in 
the article referred to, are very simple. The resistance of a spherical shell of 
thickness dx, where the radius of the shell is x, is 

dE = , if r specific resistance. 

4 7TX 2 

Integrating between the limits x = ai and x 2 , where a\ and 2 are the inner 
and outer radii respectively, 

T-J T f Ct2 

~T^\~a^L 

But if 8 is the outer surface and s the inner, #=4 7ra 2 2 , s=4 IT i 2 , and 2 i = 
the thickness of the shell. Substituting these values, 



To get the formula for the cylinder of length O all that is necessary is to integrate 
the equation 

dE= between x = a 2 and x = ai, 

2 TTCX 

giving JR^-^- log, 2S. 

^ TTO (Zl 

For the cubical frustum 

dB = r** , whence 7?= - r f ^A = -iL = H, 
wx 2 n V ai2 / Vs^ ^-D 

where n is given by the equation S= 



THE ELECTRIC FURNACE 



189 



The curves in Figure 78 give an idea of the error that would 
result from using the mean value of the cross section in place 
of the above formulae. As abscissae are taken the thickness of 
wall in terms of the inner diameter or edge, and as ordinates 
the conductivity for one degree difference in temperature and 
for a substance whose specific conductivity is one. The dotted 








FIG. 78. Heat loss as function of thickness of walls 

lines show the conductivity as given by the approximate formula, 
and the full lines show the true value. It is evident that the 
greatest errors occur in the cases of the cube and sphere, 
where they are quite appreciable when the thickness of the 
wall equals one half the diameter or one half the inner edge. 
In Table 20 the values of the heat conducted through the walls 
of the three typical furnaces are collected, which are those given 



190 



APPLIED ELECTROCHEMISTRY 



in the plot. 3 The conductivity and difference in temperature 
are assumed unity. 

TABLE 20 
Heat Conductivity of Spherical, Cubical, and Cylindrical Furnaces 



THICKNESS 


SPHERES 


CUBES 


CYLINDERS 


CONDUCTANCE 


CONDUCT ANCE 


CONDUCTANCE 


By Correct 
Formula 


By Approxi- 
mate Formula 


By Correct 
Formula 


By Approxi- 
mate Formula 


By Correct 
Formula 


By Approxi- 
mate Formula 


0.10 


37.70 


38.3 


72.0 


73.2 


34.40 


34.60 


0.15 


27.20 


28.2 


52.0 


53.8 


23.90 


24.10 


0.20 


22.00 


23.2 


42.0 


44.4 


18.70 


18.80 


0.25 


18.90 


20.4 


36.0 


39.0 


15.50 


15.70 


0.30 


16.80 


18.6 


32.0 


35.6 


13.40 


13.60' 


0.35 


15.30 


17.5 


29.1 


33.3 


11.80 


12.10 


0.40 


14.10 


16.7 


27.0 


31.8 


10.70 


11.00 


0.45 


13.30 


16.1 


25.3 


30.7 


9.79 


10.10 


0.50 


12.60 


15.7 


24.0 


30.0 


9.06 


9.43 


0.60 


11.50 


15.3 


22.0 


29.2 


7.97 


8.38 


0.70 


10.80 


15.2 


20.6 


29.0 


7.18 


7.63 


0.80 


10.20 


15.2 


19.5 


29.1 


6.58 


7.07 


0.90 


9.77 


15.4 


18.7 


29.5 


6.10 


6.63 


1.00 


9.42 


15.7 


18.0 


30.0 


5.72 


6.28 


1.50 


8.38 


17.8 


16.0 


34.0 


4.53 


5.24 


2.00 


7.85 


20.4 


15.0 


39.0 


3.90 


4.71 


3.00 


7.33 


26.2 


14.0 


50.0 


3.23 


4.19 



The following example will show how this table may be used 
in the case of a furnace of one of these types. Let the inner 
diameter of a spherical furnace be 15 inches, the thickness of 
wall 9 inches ; to find the heat conductance if the wall consists 
of infusorial earth whose specific heat conductivity is "k = 0.001 
in gram calorie cubic inch units, and if the difference in tem- 
perature between the inside and outside face is 700 C. The 

8 Hering, I. c. In the original table four and five places of significant figures 
are given. Since the specific conductivity of refractory substances at high tem- 
peratures is not known to more than two places, only three places are here 
retained. 



THE ELECTRIC FURNACE 



191 



thickness in terms of the diameter is -= = 0.6. Opposite 

d 15 

0.6 in the table the conductance is 11.5. This number evi- 
dently must be multiplied by c?, &, and 700, giving a loss of 121 
grams calorie per second. On the other hand, if the loss is 
given and the temperature difference and conductivity are 
known, the corresponding thickness can be found. 

In the case of the cylinder, the conductivity calculated is for 
the cylindrical part alone. These values must therefore be 
multiplied by the length of the cylinder, but not by the inside 
diameter, and the loss at the two ends must be added. 

Unfortunately heat conductivities of refractory substances 
are not accurately known above 1000 C. Recently, however, 
the mean conductivities between room temperature and 1000 C. 
of a number of refractory substances have been determined un- 
der the direction of Le Chatelier by Wologdine. The results 4 
have been collected by Queneau in Table 21. Data are also 

TABLE 21 
Conductivity of Refractory Materials 



MATERIAL 


CONDUCTIVITY 


Gram Calorie per Cm. Cube 
per 1 C. Diflf. in Temp. 


Relative Conductivity in Per 
Cent of Value for Graphite 




0.0250 
0.0231 
0.0071 
0.0057 
0.0042 
0.0039 
0.0038 
0.0035 
0.0033 
0.0027 
0.0023 
0.0020 
0.0018 


100.0 
92.0 

28.0 
23.0 
17.0 
16.0 
15.0 
14.0 
13.0 
12.0 
9.3 
7.8 
7.1 


Carborundum brick .... 




Fire brick 


Checker brick 












Silica brick .... 


Infusorial earth brick . . . 



Electrochem. and Met. Ind. 7, 383, (1909). 



192 APPLIED ELECTROCHEMISTRY 

given in the same article on the porosity and gas permeability 
of these materials. 

The principal refractory substances for electric furnaces are" 
carbon, carborundum, and siloxicon. 5 The use of siloxicon is 
limited to temperatures below that at which it is converted 
into carborundum, and of carborundum to temperatures below 
which it breaks up into silicon and graphite. These sub- 
stances all have a higher thermal conductivity than the other 
less refractory materials, as seen in the above table, and for 
this reason it is usual to build furnace walls in sections, with 
highly refractory material inside, where the temperature is 
highest, and with material offering a high resistance to the 
passage of heat outside. Carborundum, for instance, is one 
of the most refractory materials, but as seen from the table 
its conductivity is high. It would, therefore, be well to use 
this as a lining of such a thickness that the temperature on the 
outside of the lining would not be too high for some material 
with a lower heat conductivity, such as fire brick or infusorial 
earth. Knowing the dimensions, the total loss in power, and 
the conductivity, the temperature of the cool side of the lining 
is easily calculated. 6 

The loss of heat due to conductance through the electrodes 
will next be considered. This loss is made up of two quanti- 
ties, the heat generated in the electrode by the passage of the 
current and the heat which would flow from the hot to the cold 
end if the temperature at the hot end were maintained without 
passing a current through the electrode. The following dem- 
onstration 7 will show how the total heat loss due to the elec- 
trodes is related to these two losses, and how electrodes should 
be proportioned to make this loss a minimum. 

In Figure 79, let ab be a conductor of heat and electricity 
imbedded, except at its ends, in a perfect insulator of heat and 
electricity. Let the temperature at a be T C. and at 6, C. 

5 FitzGerald, Electrochem. and Met. Ind. 2, 349, (1904). 

6 For examples see Hering, Electrochem. and Met. Ind. 7, 11, (1909). 

7 Hering, Trans. Am. Electrochem. Soc. 16, 287, (1909) ; also Electrochem. 
and Met. Ind. 7, 442, (1909). 



a 



THE ELECTRIC FURNACE 193 

Let a current also ^ JH 

pass through the ^ K?TT*T"T!T^f?.T^ ; * 

electrode. The ^ 

problem is to find 

the quantity of FlQ 79 

heat flowing out 

the cold end, when a steady state has been reached. 

Let X total energy in watts pressing out of the cold end. 

x = energy passing any cross section at distance I from the 

hot end. 
H= number of watts that would flow from the hot to the 

cold end were there no current. 
h number of watts entering the hot end. 
W= number of watts generated by the current in the 

electrode. 

W 

w = where L = total length of electrode. 
L 

T= total fall in temperature from hot to cold end, when 

cold end is at 0. 

t = temperature at any length I from hot end. 
L = total length in centimeters. 
I = any distance from hot end. 
S = cross section in square centimeters. 
k = mean heat conductivity for the given range of temper- 
ature in gram-calorie centimeter centigrade degree 
units. 
r = mean electrical resistivity for the given range in ohms 

for a cube of one centimeter edge. 
1= current in amperes. 
R = total resistance. 

j is the factor 4.19 by which a given number of calories 
per second is multiplied to change to watts. 

Let dl be an infinitely short section at distance I from the 
hot end, and let the heat flowing into this section be x. The 
heat generated in the section by the current will be 

wdl=dx. (1) 



194 APPLIED ELECTROCHEMISTRY 



Also .-/feS (2) 

dl 

where is the heat gradient at I. 
dl 

Differentiating this gives 

dl, (3) 



and eliminating dx between equations (3) and (1) 

d?t = w_ Pr 

dl* jkS JkS* 

Since r and k are functions of , to be strictly accurate these 
quantities should be expressed as such before integrating. For 
the sake of simplicity, however, mean values for r and k for the 
temperature interval considered are taken, and these quantities 
in equation (4) are treated as constants. Integrating once 
under this assumption gives 



dt Wl 

TJ = a ~~ "v"? ' 
dl jkS 



and a second time 



In this equation a and b are determined by the fact that when 
Z = 0, t=T, and when l=^t = Q. 

Substituting these values in (6) gives 




Substituting this value of a in (5) and the value of thus ob- 

dl 

tained in (2) gives 



This equation states that the energy passing any given cross 
section is equal to the energy that would pass were no current 
flowing, minus one half the PR energy, plus the PR energy 
generated in the hot end. When L = l, since wL = W, 



THE ELECTRIC FURNACE 195 



This states that the energy passing out the cold end as heat 
equals the energy that would pass out when no current is flow- 
ing, plus one half the I^R energy. 



W 

Suppose that in (7) I = 0, then x h and h = If -- - . In 

order that no heat shall enter the hot end, h = 0, whence 

W 

ff= . The last equation states that if no heat enters the hot 

2 

end from the furnace, the heat flowing from the hot to the cold 
end of the electrode if there were no current equals ^ I*R. 

Now the product of H x - =? - , which is independent of S 

2 2 

and L. When the product of two variables is a constant, their 
sum is a minimum when the two variables are equal; that is, in 

TTT -prr 

the equation JT= H-\ -- , X will be a minimum when H= -> 

2 2 

or the minimum loss = I^R. Substituting the values of H and 

TF 

W in H = , we have the equation 

2 



Solving this for 
L 

y = 0.346jfy-^-, (9) 

and substituting this value in the equation (8), 



If, in place of using mean values of the specific heat conductiv- 
ity and electrical specific resistance, the variable values 8 

k t = & (1 + at) 

and r t = r (l + a^) 

are substituted in the formulse above, the following results are 
obtained : 

8 H. C. Richards, Trans. Am. Electrochem. Soc. 16, 304, (1909). 



196 



APPLIED ELECTROCHEMISTRY 



= 0.346 



5 a \ ~ 3 a 

12 



T\ 

/ 



and 



The errors introduced by using mean values of k and r and 
treating them as constants will be small unless the temperature 
coefficients are enormous. 

As was shown above, the minimum loss of one electrode is 
J?R or le. Substituting this in (10), 

e = 2.89V&r2 r . 0-1) 

This voltage is seen to be dependent only on the thermal con- 
ductivity, electrical re- 
sistivity, and tempera- 
ture difference of the 
ends of the electrodes, 
which means that for 
every material there is 
a characteristic mini- 
mum drop of potential 
in the electrodes for 
one degree difference 
in temperature below 
* which it is not possible 
to go without increas- 
ing the loss. This 
minimum drop in 

potential has been called the electrode voltage. 

The temperature distribution in the electrode is given by the 

equation : 

t^T-^^^L-.-^ n^ 

T * Ct .'7_* Ct '1. O' 




FIG. 80 



obtained from equation (6) by substituting in the values of a 
and b. The variables being t and Z, the curve is evidently a 
parabola. If no current flows, w = and the equation becomes 
the straight line ceb in Figure 80. 



THE ELECTRIC FURNACE 197 

Making T=Q gives t = o"Vy ' ^e P ara bola p. To find 
the temperature distribution for minimum loss, solve for T in 

'. 



O -TTT 

the equation JKT = , and substitute in (12), obtaining 



the parabola P. When - is greater or less than H, the tem- 

perature distribution is given by P f or P" respectively. 

In any problem involving the design of electrodes, the tem- 
perature difference between the hot and cold ends of the elec- 
trode and the kilowatts to be absorbed in the furnace will be 
given. From the value of the power the voltage would then 
be made as high and the current as low as practicable. From 
formula (9) compute the proportion of the section to the 
length. The length, which should be as short as possible, 
will be determined by the thickness of the walls of the fur- 
nace. Having fixed the length, the section is then obtained 
from the ratio of the section to the length. The two remain- 
ing factors which must be known are the values of the heat 
and electrical conductivities of carbon and graphite, the only 
two substances used for electrodes in resistance furnaces. 
These values have not yet been determined accurately for high 
temperatures, but the mean values have been determined by 
Bering between 100 C. and 900 C. 9 The method of deter- 
mining heat conductivity depends on the demonstration above. 

If in equation (13) Z=0, then t= ^and k= 



In order to measure &, a conducting rod of length L and sec- 
tion S, embedded in a nonconducting material, is heated by a 
measured amount of electrical energy and the temperature T 
measured at the center. In order to have no heat pass out the 
sides of the rod, it is surrounded by a number of similar rods 
at the same temperature as the one measured. The electrical 
conductivity is obtained from the ammeter and voltmeter read- 
9 Trans. Am. Electrochem. Soc. 16, 317, and 315, (1909). 



198 



APPLIED ELECTROCHEMISTRY 



ings and the dimensions. The values in Table 22 have been 
obtained by this method. 9 The units are centimeters, gram 
calories, and ohms, and centigrade degrees. 



TABLE 22 





GKAPHITE 


CARBON 


BETWEEN 100 C. AND 






TEMPERATURE GIVEN 


Heat 


Electrical 


Heat 


Electrical 




Conductivity 


Kesistivity 


Conductivity 


Eesistivity 


900 


0.291 


0.000820 


0.129 


0.00276 


390 


0.339 


0.000838 








360 








0.0890 


0.00422 



The accuracy of these figures is estimated at a few per cent. 
The electrode voltage (equation (11)) from these data for one 
degree for graphite is 0.0447 and for carbon is 0.0639, which 
means that the minimum loss for carbon is about 50 per cent 
greater than for graphite. Later measurements by Hering 10 
gave results from which the following Table 23 has been com- 
puted. The values of heat conductivity and for electrical 
resistivity are for centimeter cubes. 

TABLE 23 



TEMPERATURE, C. 






Hot End 


Cold. End 










Carbon 


300 


40 


0.0891 


0.00422 


701 


50 


0.124 


0.00381 


902 


60 


0.130 


0.00377 






Graphite 


355 


66 


0.339 


0.000837 


516 


70 


0.325 


0.000827 


707 


87 


0.309 


0.000802 



10 Trans. Am. Electrochem. Soc. 17, 166, (1910). 



THE ELECTRIC FURNACE 



199 



The following data were obtained by Hansen. 11 The units 
are the same as in the table above. 



TABLE 24 





ACHESON GRAPHITE 


NATIONAL CARBON Co.'s ELECTRODES 


TEMPERATURE 


Heat Con- 


Electrical 


Heat Con- 


Electrical 




ductivity 


Kesistivity 


ductivity 


Resistivity 


25 





0.00066 to 





0.00287 to 






0.00260 




0.0254 


Between 










3200 and 200 





0.00081 








2830 and 30 


0.155 











3500 and 30 







0.0155 








The electrical and thermal conductivities of carbon elec- 
trodes cannot be determined above 1600, because on cooling 
the values do not come back to the original ones, due to a par- 
tial conversion of the carbon into graphite. 11 

Besides the loss in the electrode itself, a large loss occurs at 
the contact between the electrode and the cable, due to the 
contact resistance. This resistance varies with the current 
density, and where brass clamps are used on graphite it 
amounts to 0.0117, 0.0045, and 0.0039 ohms per square centi- 
meter for current densities of 3.7, 5.6, and 7.4 amperes per 
square centimeter. 11 

With the aid of the constants above, a numerical example 
may be given. Let the capacity of the furnace be 500 kilo- 
watts, the current 10,000 amperes, and the temperature 1700 C. 
inside and 100 at the cold end of the graphite electrode. 
Assuming r = 0.000820 and k = 0.291, by formula (10), 
X= 17.8 kilowatts for each electrode. Assuming for carbon, 
r = 0.00276 and Jc = 0.129, X= 21.8 kilowatts. Of course, the 
cross sections of the graphite and carbon electrodes are not 
equal for equal lengths. 

11 Trans. Am. Electrochem. Soc. 16, 329, (1909). 



200 APPLIED ELECTROCHEMISTRY 

The discussion so far has been for the case that the dimen- 
sions of the furnace and the power to be applied in order to 
bring about a desired result are known. If these are not 
known, an experiment would usually be made on a small scale 
in order to determine the relation between the size of fur- 
nace and the power. There are two cases to be considered, 
(1) when there is a central core for carrying the current, 
and (2) when the charge to be heated itself carries the 
current. 

In the first case the heat has to be conducted from the core 
to the surrounding charge. 12 The rate of this flow is propor- 
tional to the difference in temperature of the core and the sur- 
rounding charge, the thermal conductivity of the charge, and 
the surface area of the core. If heat is generated in the core 
at a given rate, the temperature to which it will rise in a given 
time will depend on the specific heat of the core and the rate 
at which the heat flows into the surrounding charge. This 
rate of flow depends on the area of the core and the conduc- 
tivity of the charge. Suppose that to bring about the desired 
reaction in a given charge with a core of a given material ex- 
periments are made with a small furnace until the conditions 
are found under which the desired reaction is brought about. 
This means that a definite amount of heat must pass per unit 
surface of the core, which is a constant for these materials and 
is independent of the dimensions. If the voltage is E and the 

TFT 

current J, the energy in watts per unit surface is a = - > 

2 irJrL 

when P is the radius and L the length of the core. Collecting 
the constants in one factor, this may be written PL = AEI. 
If r is the specific resistance of the core, we also have 

XT T T 

= = B . For any furnace of any other dimensions 

L v and P v the voltage and current E l and I are given by the 

XT T 

equations P^ = AE^ and -1=1? 1. From these equa- 

~l *! 

tions we could solve for the new values E and I v if L 1 and P 1 
M FitzGerald, Electroc-hem. and Met. Ind. 2, 342, (1904). 



THE ELECTRIC FURNACE 201 

are given. Usually, however, the power is given, and the 
proper dimensions L^ and P l are desired. Solving for these 



quantities, P 1 = 

and , A 

The following is an example of the use of these formulae. It 
was desired to design a 200-kilowatt furnace using a current 
of 4000 amperes and 50 volts. Experiments on a small scale 
showed that the right conditions were obtained with 200 am- 
peres at 100 volts and a core 365 centimeters long and 5.1 cen- 
timeters in radius. From these values the proper length and 
radius for the large furnace are found to be 495 centimeters 
and 37.6, respectively. 

For the second case, where the current passes through the 
charge itself, it is simply necessary to know the amount of heat 
required to raise a given mass to the desired temperature, that 
is, the number of watts per unit mass. If the specific heat of 
the charge is known, this can be computed ; if not, an experiment 
on a small scale with a given mass will determine the energy 
required. 



CHAPTER XII 

PRODUCTS OF THE RESISTANCE AND ARC FURNACE 

1. CALCIUM CAKBIDE 

THE discovery of calcium carbide is due to Wohler, 1 who 
prepared it by the action of carbon on an alloy of calcium and 
zinc. Even previous to Wohler, E. Davy had also produced it 
in an impure state without identifying it. 2 The commercial 
importance of calcium carbide, however, dates from its redis- 
covery by Thomas L. Willson, 3 which was nearly simultaneous 
with that of Moissan (1892). 

The reaction between lime and carbon by which calcium 
carbide is produced is the following : 



As indicated, this is a reversible reaction, and according to the 
Phase Rule has one degree of freedom ; that is to say, at a given 
temperature there is one definite pressure of carbon monoxide 
which corresponds to equilibrium. At 1475 C. this pressure 
has been found to be 0.82 millimeter of mercury. 4 Above 
1500 calcium carbide decomposes into its elements, but of course 
not as rapidly as it is produced, otherwise its manufacture 
would be impossible. 

When calcium carbide is formed from calcium and diamond, 
7250 calories are absorbed at room temperature. When formed 
from lime and carbon, 121,000 calories are absorbed at room 
temperature, and the temperature coefficient of the heat of the 

1 Ann. d. Chem, und Pharm. 125, 120, (1863). 

2 Lieb. Ann. 23, 144, (1836). See Abegg, Handbuchder anorganischen Chem. 
2, 119. 8 Lewes, Acetylene, p. 24, (1900). 

4 Thompson, Proc. Am. Acad. 45, 431, (1910) ; also Met. and Chem. Eng. 8, 
327, (1910). 

202 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 203 

reaction has been calculated to be 3.3 calories per degree. 6 The 
fact that heat is absorbed when the above reaction proceeds 
from left to right shows that the equilibrium pressure of carbon 
monoxide increases with the temperature, and it can be calcu- 
lated that at about 1840 the pressure equals one third of an 
atmosphere. If carbon were heated in the presence of air much 
above red heat, all the oxygen would be converted to carbon 
monoxide, and if none escaped, its resulting partial pressure 
would be one third of an atmosphere. It would therefore be 
necessary to heat carbon and lime to a temperature above 1840 C. 
before carbide could be formed. In actual practice, however, 
the partial pressure of carbon monoxide would be less than one 
third of an atmosphere, in which case carbide could be formed 
at a lower temperature. Taking these facts into consideration, 
it does not seem probable that 2000 C. is exceeded in actual 
practice, for high temperature would accelerate the decomposi- 
tion of the carbide already formed. This explains the fact that 
a resistance furnace, in which the temperature is lower than in 
the arc, gives better yields than an arc furnace. 6 

Commercial calcium carbide is dark colored and crystalline 
but if pure it is colorless and transparent. 7 It has a density at 
18 of 2.22, and is insoluble in all known solvents. It is a 
powerful reducing agent. If heated with metallic oxides it 
gives, according to circumstances, an alloy of the metal in 
question with calcium or the metal itself, probably according 
to the reaction. 7 

3 M 2 + CaC 2 = CaO + 3 M 2 + 2 CO 
or 5 M 2 O + CaC 2 = CaO + 5 M 2 + 2 CO 2 . 

It further has the property of absorbing nitrogen according to 
the equation 

CaC 2 + N 2 =CaCN 2 + C, 

forming calcium cyanamide. This is an important method of 
fixing atmospheric nitrogen, and will be referred to later under 
that heading. 

6 Thompson, Trans. Am. Electrochem. Soc. 16, 202, (1909). 
6 Tucker, Alexander, and Hudson, Trans. Am. Electrochem. Soc. 15, 411, 
(1909). 7 Abegg, Handbuch der anorganischen Chem. 2, p. 121. 



204 



APPLIED ELECTROCHEMISTRY 



The principal use of calcium carbide is to produce acetylene 
for illumination. This gas is evolved when the carbide is 
treated with water, according to the reaction: 



CaC 



H 2 



CaO 



C 2 H 2 . 



The first to produce calcium carbide on a commercial scale, 
as stated above, was Thomas L. Willson, at the Willson 
Aluminum Works at Spray, 8 North Carolina. Willson was 
attempting to reduce lime by heating with carbon, hoping to 
get calcium with which to try the reduction of alumina. It was 
by accident that the material produced was found to react with 
water and give off an inflammable gas. Soon after this discovery 
Willson's plant at Spray was investigated by Houston, Ken- 

nelly, and Kennicutt. 9 
Two runs were made with 
the purpose of determin- 
ing the cost of manufac- 
turing calcium carbide 
under conditions existing 
at that place. There 
were two furnaces built 
in one structure, as shown 
in Figure 81, the walls 
and partition of which 
were brick, while the 
front was only partly cov- 
ered by cast-iron doors. 
The floor space of each 
furnace was 3 by 2J feet. 
The furnaces united at a 
height of 8 feet into a 
single chimney for carry- 
ing off the gases. The 
base of the furnaces con- 




FIG. 81. Carbide furnace at Spray, North 
Carolina 



8J. W. Richards, Electrochein. Ind. 1, 22, (1902). The date given by 
Richards is 1891. This is evidently too early ; see note 3. 

9 Progressive Age, 14, 173, (April 15, 1896). (Published at 280 Broadway, 
New York City.) 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 205 




sisted of a heavy piece of iron between, 1 and 2 inches in thick- 
ness, 6 feet in length, and 2| feet in 
width. The iron plate was completely 
covered by two carbon plates between 
6 and 8 inches thick. These formed the 
lower electrode. The upper electrode 
of each furnace was a carbon block 12 
by 8 inches in section and 36 inches long, 
protected by an iron casting -fa inch 
thick. The space between the casting 
and carbon was filled with a mixture of 
hot pulverized coke and pitch. The 
first run lasted 3 hours with an aver- 
age activity supplied to the furnace of 
144 kilowatts at approximately 100 volts. FlG - 82. - Longitudinal ver- 

. tical section of the first car- 

ThlS made a total power consumption of tide furnaces at Niagara 

432 kilowatt hours, yielding 98.0 kilo- Falls 

grams of 79 per cent pure carbide. The second run lasted 2 
hours and 40 minutes with an average 
activity of 146.7 kilowatts, making the 
^ / total power consumption 388.5 killowatt 
hours and yielding 87.5 kilograms of 84 
per cent carbide. This is about 0.225 
kilograms of carbide per kilowatt hour. 
The cost of producing carbide at Spray, 
working the furnaces 365 days a year and 
24 hours a day, was estimated at about 
$33 per 2000 pounds of impure carbide. 
This estimate, however, is made up of 
a large number of items that would be 
considerably changed for other places. 
The largest producer of carbide in the 

FIG. 83. Transverse ver- United States is the Union Carbide Com- 

S35?i; p^y. whose W01 ' ks are at Nia s ara Falls -' 

ara Falls Their first furnaces were of the Willson 

type, in which the lower electrode was a small car which could 
be removed, when filled with an ingot of carbide, to make room 



\ 



LJ 




Air 



206 



APPLIED ELECTROCHEMISTRY 



for another, as shown in Figures 82 and 83. This type has been 
displaced at Niagara Falls by the Horry rotary continuous fur- 
nace, introduced in 
1898 and shown in Fig- 
ure 84. 10 It consists 
of an iron wheel 8 feet 
in diameter and 3 feet 
in width, with an an- 
nular-shaped space 
around the circumfer- 
ence in which the car- 
bide is formed. The 
electrodes project ver- 
tically down into this 
space. Lime and car- 
bon are fed in, and as 
carbide forms, it is removed from the electrodes by the rotation 
of the furnace. Iron plates hold the carbide in place while 
under the influence of the current. When the rotation has 
carried it to the other side of the furnace, it has had time to 
cool, as there is only one complete rotation a day. The outer 
plates are then removed, and the carbide is broken off in pieces 
6 to 9 inches thick. Each furnace takes 3500 amperes at 110 
volts and produces 2 short tons of carbide a day. 




FIG. 84. Horry carbide furnace 



COUNTRY 


PRODUCT IN 
METRIC TONS 




38,000 


Italy 


32000 




27000 


Norway 


25000 


Switzerland 


20000 


Austro- Hungary 


12,000 


Sweden .... . . . . 


12000 




9,000 







10 Lewes, ibid. p. 207 ; Richards, Electrochem. Ind. 1, 22, (1902) ; Haber, Z. f. 
Elektroch. 9, 834, (1903). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 207 

The production of the Union Carbide Company from year to 
year has not been made known. The preceding table shows 
the estimated output of the world for 1908. u 

In 1902 the Union Carbide Company sold carbide to home 
consumers at about $70 a ton, but exported it for $50 a ton. 12 
In 1907 the price was still $ 70 a ton in this country. 

In Europe 13 the form of furnace still used is of the Willson 
type. In some cases the ingot is formed on a truck that can be 
removed when full, and in others a stationary crucible is used. 
In the former case it has been found an improvement to have 
two electrodes suspended over the truck, so that the truck is no 
longer in the electric circuit. In the case of fixed crucibles the 
capacity has been increased in some cases up to 6000 kilowatts, 
and a more satisfactory method of tapping has been devised. 
Formerly the solid carbide formed around the tap hole had to 
be broken away, but the later method consists in inserting an 
iron rod connected to the upper electrode into the tap hole, 
where an arc is formed between the rod and the solid carbide. 
The iron and carbide are both melted by the arc, and an opening 
is formed through which the melted carbide can flow out. 

With regard to the power required for the production of car- 
'bide, the only figures of any practical importance are not those 
obtained by calculation, but those obtained in actual practice. 
The original plant of Willson produced 5.4 kilos per kilowatt 
day of 24 hours 9 of 80 to 85 per cent carbide. At Meran the 
yield is 5.8 kilos of 78 per cent carbide per kilowatt day. 14 
At Foyers in Scotland the yield per kilowatt day of 24 hours is 
4.2 kilos of 87 per cent carbide. 15 At Odda, Norway, it lies 
between 4.5 and 5.2 kilograms. 16 

The materials 17 used in making carbide are freshly burnt 
lime and carbon in the form of anthracite coal, metallurgical 
coke, or charcoal. Ordinary gas coke has too many impurities 
for this purpose. Charcoal is used only where one of the other 
forms of carbon cannot be obtained, as it generally contains 

u Min. Ind. 17, 100, (1908). 12 Min. Ind. 11, 76, (1902). 

13 See Conrad, Electrochem. and Met. Ind. 6, 397, (1908). 

14 Lewes, Acetylene, p. 242. 16 Lewes, I.e. p. 262. 
is Electrochem. and Met. Ind. 7, 213, (1909). 17 Lewes, pp. 264-284. 



208 APPLIED ELECTROCHEMISTRY 

considerable traces of phosphates, which appear in the acetylene 
generated from the carbide in the form of phosphureted hydro- 
gen. The reaction requires 36 parts of carbon to 56 of lime. 
In most ingot carbide furnaces 100 parts of lime to 70 of car- 
bon are used. In furnaces from which the carbide is drawn 
off in the liquid state a higher proportion of lime is used in 
order to lower the melting point of the carbide. This, of 
course, has the result of making the carbide less pure. 

It was at first supposed that fine grinding of the materials 
was necessary, but it has since been found that pieces as much 
as one inch in diameter may be used. 18 

2. CARBORUNDUM 

Carborundum is the trade name for the carbide of silicon, 
which has the formula CSi. It was probably first produced 
by Despretz in connection with experiments on refractory ma- 
terials, 1 in the course of which he heated a carbon rod em- 
bedded in sand by passing an electric current through the 
rod. He obtained a very hard tube of six times the diameter 
of the carbon rod, lined on the inside with quartz in the form 
of lampblack. It seems probable that in this experiment some 
carborundum was formed, though no mention is made of crystals. 
It seems more certain that carborundum crystals were obtained 
by R. Sidney Marsden, 2 by heating for several hours silver or an 
alloy of silver and platinum in a Berlin porcelain crucible with 
amorphous carbon considerably above the melting point of silver 
and then cooling slowly for 12 to 14 hours. On dissolving the 
silver in nitric acid it yielded from its interior a number of 
beautiful crystals of the hexagonal system and varying in 
color from light yellow to dark brown, or even black. Other 
crystals were found in the form of hexagonal prisms, but these 
were in most cases colorless and transparent. The colored 
crystals were doubtless crystallized carborundum, formed from 
the silica glaze on the crucibles and the amorphous carbon. 

18 Blount, Practical Electrochemistry, p. 230, (1901). 

1 C. R. 89, 720, (1849). 

2 Proc. Royal Soc. of Edinburgh, 11, 37, (1880-1881). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 209 

The white crystals were evidently silica, as they dissolved when 
boiled in hydrofluoric acid. 

In 1886 A. H. Cowles 3 obtained some hexagonal crystals 
from his furnace on attempting to melt quartz. This was an- 
alyzed and thought to be a suboxide of silicon. On seeing Ache- 
son's Carborundum at the Chicago Exposition in 1893, Cowles 
recognized its similarity with his so-called suboxide of silicon. 
This resulted in a lawsuit between the Cowles Electric Smelting 
and Refining Company and the Carborundum Company. 4 Schut- 
zenberger and Colson hacLsuspected the existence of a com- 
pound of the formula Si 2 C 2 as early as 1881, 5 and in 1892 
Schiitzenberger 6 obtained the amorphous carbide of silicon by 
heating together silicon, silica, and carbon, and determined its 
composition. Its color was a clear green. Finally, Moissan 7 has 
made crystallized carbide of silicon in the following different 
ways : 1. Carbon was dissolved in melted silicon between 1200 
C. and 1400 C. from which crystals of carbide several milli- 
meters long were obtained by dissolving the silicon in a boiling 
mixture of concentrated nitric acid and hydrofluoric acid. 2. By 
heating silicon and carbon in the proportion of 12 parts of carbon 
to 28 parts of silicon. The mass of crystals obtained was easily 
purified by first boiling in a mixture of concentrated nitric acid 
and hydrofluoric acid and by then treating with nitric acid and 
potassium chlorate. The crystals were frequently colored yellow, 
but could be obtained completely transparent. 3. By heating a 
mixture of iron, silicon, and carbon in the electric furnace, giv- 
ing a metallic fusion containing crystals of carbide of silicon. 
The excess of iron or silicon was then dissolved. 4. By heating 
silica and carbon in the electric furnace. 5. By the action of 
the vapor of silicon on the vapor of carbon. This experiment 
was made in a small carbon crucible containing fused silicon. 
The bottom of the crucible was heated to " the highest tempera- 

8 Proc. of the Soc. of Arts for 1885-1886, p. 74, Boston. 

4 FitzGerald, Carborundum, in the Engelhardt Mongraphien iiber Ange- 
wandte Elektrochemie. 

*C. R. 92, 1508, (1881). 6 C. R. 113, 1089, (1892). 

7 Moissan, The Electric Furnace, translated by Lehner, p. 274, (1904). 



210 APPLIED ELECTROCHEMISTRY 

ture of the electric furnace." After the experiment, slightly 
colored, very hard and brittle crystals in prismatic needles of 
carbon silicide were found. The description of this experi- 
ment is far from convincing. If the crystals were found in the 
silicon, there is no evidence of the action of one vapor on the 
other, but even the original article 8 does not state where 
the crystals were found, which would be necessary to decide 
the question. 

In 1891 at Monongahela, Pennsylvania, E. G. Acheson 9 dis- 
covered the crystallized carbide of silicon, in carrying out some 
experiments with the object of producing crystallized carbon. 
The object was to dissolve carbon in melted silicate of alu- 
minum, or clay, and by cooling to cause the carbon to crystallize. 
The first experiments were carried out in an iron bowl lined 
with carbon in which was placed a mixture of carbon and clay. 
The mixture was fused by means of an electric current passing 
between the bowl and a carbon rod directly over it. On fusion 
a violent reaction took place, and after cooling a few bright 
blue hard crystals were found. These were first supposed to 
be carbon, but later were taken for a compound of alumina or 
corundum and carbon, from which the name carborundum was 
made up. Subsequent to this it was found that better results 
were obtained when silica was used in place of clay, and when 
common sodium chloride was added. The reason for this was 
evident when the following analysis of the product was made: 

Silicon 62.70 per cent 

Carbon 36.26 per cent 

Aluminum oxide and ferric oxide . . . . . . 0.93 per cent 

Magnesium oxide 0.11 per cent 

This showed the substance in the pure state to be CSi. 

The furnace in which these experiments were carried out 
was made of refractory bricks, the interior dimensions being 
10 by 4 by 4 inches. The current was carried by a core of 
granulated carbon, as shown in Figure 85. 

8 C. R. 117, 425, (1893). 

8 Journ. of the Franklin Inst. 136, 194 and 279, (1893). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 211 



Figure 86 shows an end view of this furnace and the layers 
of different materials after a run. B is a solid mass of sand 




FIG. 85. Longitudinal section of Acheson's experimental carborundum furnace 

and carbon held together by fused salt. C is chief product of 
the reaction, crystallized carbide of silicon. W represents a 
white or gray-greenish-looking shell, 
and consists of small pieces the size 
of the original grains. They are 
soft, and may easily be reduced to 
fine powder, and are of no value as 
an abrasive, though analysis shows 
them to be principally carbide of sili- 
con. It is amorphous carborundum, 
or carborundum fire sand. G- is 

, ., , ... , , FIG. 86. Transverse section of 

graphite mixed with carborundum, Aches0 n's experimental carbo- 
and D is the core, only , portion of rundum furnace 
which becomes graphitized even though used repeatedly. The 
output of this small furnace was \ pound a day. 10 

The furnaces used at Monongahelainl893 were 18 inches wide, 
12 inches deep, and 6 feet long. The core was of granular 
carbon in the form of a sheet 10 inches wide, 1 inch deep, and 
5J feet long. In 7| to 8 hours a portion of the charge was 
transformed into 50 pounds of crystallized carborundum. 

On moving to Niagara Falls the furnaces were construe ted as 
shown in Figure 87. n The end walls are built of refractory 




10 FitzGerald, Journ. Franklin Inst. 143, 81, (1897). 

11 FitzGerald, Carborundum, p. 8. . 



212 



APPLIED ELECTROCHEMISTRY 



brick and clay, and carry electrodes, 5 2 , consisting of rectangu- 
lar carbon rods clamped together. Contact is made with the 
copper cables by the copper plates, > 5 , as shown. A are the 
brick side walls of the furnace put together without cement. 
D is the mixture, C the core of granulated carbon, and c is fine 
carbon powder for the purpose of making contact between the 
carbon electrodes and the core. Up to 1907 the total length of 
this furnace was 7 meters ; the inside dimensions were, length, 
5 meters, width, 1.8 meters, and height, 1.7 meters. The elec- 
trodes consisted of 25 carbon rods, 86 centimeters in length, 
and 10 by 10 centimeters in cross section. The core was 53 




FIG. 87. Longitudinal section of carborundum furnace 

centimeters in diameter. A perspective of the furnace in oper- 
ation is shown in Figure 88. 

The power absorbed by each furnace is 746 kilowatts. The 
voltage varies from 210 volts at the start to 75 volts when the 
resistance of the core had dropped to its final constant value. 
Soon after the current is turned on, carbon monoxide is pro- 
duced, due to the oxidation of the carbon in the core and in the 
charge. The gas is always lighted, and burns during the run. 
When the temperature has become sufficiently high, carbo- 
rundum is formed according to the following reaction : 

Si0 2 + 3 C = CSi + 2 CO. 

The heating lasts 36 hours, and produces 3150 kilograms of 
crystallized carborundum, surrounding the core to a depth of 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 213 




214 APPLIED ELECTROCHEMISTRY 

from 25 to 30 centimeters, This corresponds to 8.5 kilowatt 
hours per kilogram, which is a great improvement over the first 
furnaces of the Carborundum Company at Monongahela, which 
were built for 100 kilowatts, and yielded one kilogram of car- 
borundum for an expenditure of 17.6 kilowatt hours. The 
present electrical equipment of the Carborundum Company at 
Niagara Falls has a capacity of 5300 kilowatts. 12 

The raw materials used by the Carborundum Company con- 
sist of ground quartz 99.5 percent silica, coke, such as is used 
in blast furnaces, sawdust, and sodium chloride. The object 
of the sawdust is to make the charge porous to facilitate the 
escape of the carbon monoxide. The coke used for the core is 
sifted to get rid of the powder; that used for the charge is 
powdered. The charge is made up in lots of 500 kilograms, and 
has the following composition : 

Quartz 261 kilograms 

Coke 177 kilograms 

Sawdust 53 kilograms 

Salt 9 kilograms 

500 

In 1907 the furnace plant was remodeled, 13 and the furnaces 
were made 9.15 meters long and 3.67 meters wide. These are 
presumably outside dimensions. The power absorbed is now 
1600 kilowatts with the maximum current 20,000 amperes. 
The yield of each furnace in one run is 15,000 pounds, or 
6800 kilograms, of crystallized carborundum. On coining from 
the furnace the carborundum is ground, treated with concen- 
trated sulphuric acid to remove harmful impurities, and is washed 
with water. It is then sorted into different sizes. 

Table 25 gives the production of carborundum in this country 
and its value including the year 1909. 14 

12 Electrochem. and Met. Ind. 7, 190, (1909). 

13 Min. Ind. 16, 155, (1907); 17, 112, (1908). 
" Min. Ind. 18, 86, (1909). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 215 
TABLE 25 



YEAR 



METRIC TONS 



VALUE IN DOLLARS 



1891 . 0.023 

1892 ..'..... 1 

1893 .'-...-. 7 

1894 24 

1895 . 102 

189G 540 

1897 564 

1898 724 

1899 791 

1900 . . ' 1089 

1901 1742 

1902 1698 

1903 2160 

1904 3203 

1905 2539 

1906 '. . 2824 

1907 3418 

1908 2226 

1909 2983 



366,000 
154,000 
151,000 
157,000 
168,000 
268,000 
261,000 
333,000 
494,000 
391,000 
435,000 
452,000 
294,000 
389,000 



In 1902 the cost of manufacture was 4 cents to 5 cents a pound, 
and during this year the average selling price was 10 cents a 
pound. 15 The only producer in this country is the Carborundum 
Company of Niagara Falls. In Europe it is produced at La 
Bathie, France, Iserhohn, Germany, and Prague. 16 

Carborundum is used principally as an abrasive and as a sub- 
stitute for ferrosilicon in the manufacture of steel. In 1902 
one third the total output was consumed in this industry. 17 The 
abrasive qualities of carborundum are affected by its great 
brittleness, on account of which it will not cut diamond unless 
reduced to a fine powder. 9 It is made into polishing wheels by 
mixing with a certain amount of kaolin and feldspar as a binder, 
compressing in a hydraulic press, and burning in a furnace such 
as is used in the manufacture of porcelain. Carborundum is 



15 Min. Ind. 11, 78, (1902). 
"Min. Ind. 11, 227, (1902). 



"Mm. Ind. 10, 253, (1901). 



216 



APPLIED ELECTROCHEMISTRY 



also used in wireless telegraphy as a detector, and in a different 
form, known as Silundum, 1 * 1 us a resistance for heating purposes. 
Silundum is made by exposing rods of carbon to the vapor of 
silicon, which penetrates the carbon, changing it to silundum 
arid thereby increasing its electrical resistance to a sufficient 
extent to make it a good resistor. In the form of bricks car- 
borundum is used as a refractory material in building furnaces, 
when the temperature to be withstood is very high. 

Silicon carbide is colorless when pure, 10 but the commercial 
product is black, due either to carbon, iron, or to a" thin film of 
silica 19 on the surface. The following analysis is due to Moissan : 



PER CKNT 



Theoretical 



Silicon 69.70 69.85 70.00 

Carbon 30.00 29.80 30.00 

The following is an analysis of Acheson's product : u 

Silicon 64.93 per cent 

Carbon and oxygen 33.26 per cent 

Loss in beating 1.36 per cent 

Aluminum 0.25 per cent 

Calcium, magnesium, iron .... trace 

99.80 per cent 

When the same material was purified by hydrochloric acid and 
sodium hydrate, by heating in oxygen, and finally by heating 
with hydrofluoric acid, its analysis gave the following result : 

Silicon 69.10 per cent 

Carbon 30.20 per cent 

A1 2 O 3 and Fe 2 O 3 0.49 per cent 

CaO 0.15 per cent 

99.94 per cent 

The density is 3.2. The crystals have been found by Frazier 
to be rhombohedral. 20 It easily scratches ruby, and, as stated 
above, when finely powdered, will polish diamond. 

re Boiling, Electrochem. and Met. Ind. 7, 25, (1909). 

w Min. Ind. 16, 155, (1907). 20 Journ. Franklin Inst. 136, 289, (1893). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 217 

When carborundum is heated to a sufficiently high tempera- 
ture silicon is vaporized, leaving carbon in the form of graphite. 
The temperature at which decomposition takes place has been 
found by Tucker and Lampen 21 to be 2220 and the temperature 
of formation, 1950C. There is hardly a doubt that both the 
reactions, 

SiO 2 + 3 C = SiC + 2 CO 

and SiC = Si + C 

are reversible. The temperature of formation therefore depends 
on the partialpressure of carbon monoxide, and the temperature 
of decomposition on the partial pressure of silicon vapor, for 
according to the Phase Rule each of these systems has one 
degree of freedom. These values, however, probably represent 
fairly well the temperatures of formation and decomposition in 
the Acheson furnace. 

Carborundum is not attacked by sulphur or oxygen at 
1000 C., 7 but according to Acheson it is oxidized in an at- 
mosphere containing considerable oxygen at 1470 C. 22 It is 
attacked slightly by chlorine at 600. Fused potassium nitrate 
and chlorate, boiling sulphuric and hydrofluoric acids are all 
without action. The same is true of a boiling mixture of con- 
centrated nitric and hydrofluoric acids. On the other hand it 
is attacked by fused potassium hydrate, forming potassium 
carbonate and silicate. 

3. SlLOXICON 1 

There are a number of compounds, besides the carbide of 
silicon, that contain carbon and silicon in the same proportions 
as the carbide. In 1881 Schiitzenberger and Colson 2 prepared 
a compound of the formula SiCO by heating silicon in an at- 
mosphere of carbon dioxide. The reaction is stated to be 

3 Si + 2 CO 2 = SiO 2 + 2 SiCO. 

21 Journ. Am. Chem. Soc. 28, 853, (1906). 

22 Electrochem. Ind. i, 373, (1903). 

1 The name given by Acheson to compounds of carbon, silicon, and oxygen in 
varying amounts. 2 C. R. 92, 1508, (1881). 



218 APPLIED ELECTROCHEMISTRY 

The same compound was formed at a higher temperature by 
the direct union of silicon and carbon monoxide. A compound 
of the formula Si 4 4 N was formed in a similar way. On heat- 
ing silicon in a stream of hydrogen saturated with benzene at 
50 to 60 C. two compounds were obtained, one of the 
formula C 2 Si, and the other of a variable composition, but fre- 
quently containing more oxygen than corresponds to the 
formula CSiO 2 . 3 On heating silicon in a vapor of carbon sul- 
phide two compounds deposited in the cold part of the com- 
bustion tube corresponding to the formulae SiSO and SiS. In 
the boat containing the silicon a greenish powder was obtained 
which, when purified by boiling in potassium hydrate and treat- 
ing with hydrofluoric acid, had the composition Si 4 C 4 S. This 
when heated in a current of oxygen gave Si 4 C 4 O 2 . These 
bodies all look alike and can be distinguished only by analysis. 4 
They are pale green powders, infusible, unattackable by hydro- 
fluoric acid or strong solutions of caustic alkali. Fused caus- 
tic alkali decomposes them, giving alkali silicate and carbonate. 
They resist oxidation at red heat. It will be seen that these 
compounds also resemble the compound obtained by Schiitzen- 
berger 4 in 1892, and which analysis showed to be SiC, though 
the color of the latter compound is described as a clear green. 
It, therefore, seems that carborundum exists in two forms, one 
crystalline and the other amorphous, while the amorphous form 
has all the appearance of other compounds containing silicon 
and oxygen in the same proportions as carborundum, together 
with a variable amount of oxygen. From the contradictory 
statements 6 found in the literature it seems that the layer of 
material which is formed just outside the carborundum consists 
of silicon, carbon, and oxygen in varying amounts, and that it 
goes by the names of amorphous carborundum, carborundum 

8 Colson, C. R. 94, 1316, 1526, (1882). 

4 Schiitzenberger, C. R. 114, 1089, (1892). 

6 In Min. Ind. 15, 93, (1906), it is stated that another product of the carborun- 
dum furnace is amorphous carborundum or carborundum fire sand, and that 
siloxicon is a second product obtained when insufficient coke is present, consist- 
ing of carbon, silicon, and oxygen, while on p. 96 the statement is made that 
amorphous carborundum contains carbon, silicon, and oxygen. 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 219 

fire sand, or siloxicon. The latter name is due to Acheson, 
who took out a patent for its production in 1903. 6 

In the manufacture of siloxicon it is important not to have 
sufficient carbon in the charge to reduce the silica completely, 
and to keep the temperature constant within certain narrow 
limits. For this purpose the furnace is built with more than 
one core, thus making the distribution of temperature more 
even. The charge, consisting of one third carbon and two 
thirds silica, is made up of powdered carbon, powdered silica, 
and sawdust, the silica and carbon contents of the sawdust 
being taken into account. 

The density of siloxicon is 2.7. 7 When heated in an atmos- 
phere containing a large amount of oxygen to about 1470 C., 
it is oxidized, giving silica and carbon dioxide, 8 while in the 
absence of oxygen at a higher temperature it is converted into 
carborundum. 

Siloxicon is used to make crucibles and for furnace lining, as 
it is not attacked by melted metals or by slags. 

4. SILICON 

The manufacture of silicon is now carried out by the Carbo- 
rundum Company according to patents of F. J. Tone. 1 

Arc furnaces are used in which two vertical electrodes ex- 
tend for a considerable depth into the charge of coke and sand. 
The furnace is built of fire brick lined inside with carbon. Each 
furnace has a capacity of 910 kilowatts, and the metal is tapped 
out at intervals of a few hours in ingots weighing from 600 to 
800 pounds. It is made in different grades, varying from 90 to 
97 per cent pure. Silicon is used principally in the steel in- 
dustry in place of ferrosilicon. The production of silicon in 
1908 was 600 long tons, valued at $72,000. 2 Previous to its 

Electrochem. and Met. Ind. 1, 287, (1903). 

7 FitzGerald, Electrochem. and Met. Ind. 2, 439, (1904). 

e Acheson, Electrochem. and Met. Ind. 2, 373, (1904). 

1 Electrochem. and Met. Ind. 7, 192, (1909). 

2 Min. Ind. 17, 13, (1908). 



220 APPLIED ELECTROCHEMISTRY 

manufacture by the Carborundum Company the price of silicon 
was $4 a pound. 

Silicon can also be made in small laboratory furnaces. 3 

5. GRAPHITE 

Graphite was known to the ancients, but up to the time of 
Scheele no distinction was made between it and the closely similar 
substance molybdenum sulphide, MoSg. 1 Both leave a mark on 
paper and were called plumbago on account of the belief that 
they contained lead. 

In order to define graphite more definitely, Berthelot 2 proposed 
that only that variety of carbon be given this name which, on 
oxidation with powerful oxidizing agents at low temperatures, 
gives graphitic oxide. Graphitic oxide has different properties, 
depending on the differences in the graphite from which it is 
made, but all varieties are insoluble and deflagrate on heating. 
Amorphous carbon, when oxidized with a mixture of potassium 
chlorate and fuming nitric acid, the oxidizing agent used by 
Berthelot, is changed to a soluble substance, and diamond is not 
affected. This is a method of separating the three different 
kinds of carbon. 

The artificial production of graphite by dissolving carbon in 
cast iron and allowing to cool slowly was first observed by 
Scheele in 1778. 1 It has since been made by Moissan by dis- 
solving in iron, as well as in a number of other metals, and by 
heating pure sugar carbon in the electric arc. 3 Diamond also 
may be changed to graphite by heating in the electric arc. 
Despretz, 4 in his work on carbon, produced graphite by heating 
carbon in an electric furnace. These observations do not agree 
with those of Acheson, who early in his experience in the manu- 
facture of carborundum noticed that graphite occasionally formed 

8 Tucker, Met. and Chem. Eng. 8, 19, (1910). 

1 Roscoe and Schorlemmer, Treatise on Chemistry, 3d ed. Vol. 1, p. 730. 

2 Ann. de Chim. et de Phys. (4) 19, 393, (1870). 

3 Moissan, The Electric Furnace, p. 61. See also FitzGerald, Kunstlicher 
Graphite, Vol. 15 of the Engelhardt Monographien. 

* C. R. 28, 755 ; 281, 48 and 709, (1849). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 221 

next to the core, 5 and that when coke from bituminous coal was 
used for the core quite a large amount of it was converted into 
graphite, whereas when the purer petroleum coke was used very 
little was so changed. The greater the amount of impurity in 
the coke, the larger was the amount of graphite produced. These 
facts led Acheson to the theory that graphite is not produced 
by simply heating carbon, but that a carbide must first be pro- 
duced and then decomposed by a higher temperature, volatilizing 
the metallic element and leaving the carbon in the form of 
graphite. The effect of the impurities is catalytic, since the 
amount of graphite formed was always too great to be accounted 
for by the simple decomposition of the quantity of carbide cor- 
responding to the impurity present. If only a small amount of 
impurity is present, it is lost by volatilization before all the carbon 
can be graph itized. Acheson also found that the production of 
graphite was greatly increased by adding a considerable quantity 
of any substance that could form a carbide, such as silica, alumi- 
num oxide, lime, or iron oxide. 6 At first the charge was made up 
with enough impurity to change all the carbon to carbide at 
once. For example, a charge would consist of 50 per cent coke, 
with sand, salt, and sawdust. Carborundum was then formed 
and by heating to a higher temperature the carborundum is 
decomposed, leaving graphite. It was found, however, that so 
much carbide-forming element was not necessary and that such 
substances as anthracite coal that had impurities evenly dis- 
tributed through them could be converted into very pure graph- 
ite. 7 This is at present one of the principal kinds of carbon used 
in this industry. 

Intimate mixture of carbon and the impurity is not necessary, 
as the carbide-forming element can be vaporized and caused to 
penetrate the entire charge, thereby converting it to graphite. 8 
Petroleum coke is one form of carbon used in this process. 
Lumps of the coke are imbedded in powder formed from the 
same material and 5 per cent of iron oxide is sprinkled in. The 
iron oxide is reduced, iron is formed at the bottom of the furnace, 

5 Journ. Franklin lust. 147, 476, (1899). 7 U. S. Pat. 645,285, (1899). 

6 U. S. Pat. 568,323, (1893). U. S. Pat. 711,011, (1900). 



222 



APPLIED ELECTROCHEMISTRY 



and as the temperature is raised volatilizes and penetrates the 
whole charge. A very soft quality of graphite is obtained when 
the carbide-forming material is more than 20 per cent by weight 
of the charge, but less than the amount necessary to change all 
the carbon to carbide at once. 9 

The furnaces for graphitizing carbon in bulk have a central 
core similar to the carborundum furnace. 10 




FIG. 89. Section of graphite furnace for rectangular electrodes 




FIG. 90. Section of graphite furnace for circular electrodes 

In making graphite into electrodes, crucibles, or other finished 
products, a mixture of 97 per cent carbon and 3 per cent iron 

9 U. S. Pat. 836,355, (1906). 10 Richards, Electrochein. Ind. 1, 54, (1902). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 223 

oxide 11 is mixed with a binding material consisting of water and 
a little molasses, and is molded into the desired form. The 
molded objects are then dried and placed in the furnace, where 
they are changed to graphite without altering their shape. Fig- 
ures 89 and 90 show the methods of arranging rectangular and 




FIG. 91. Electric furnace in which graphite is made artificially by the 
International Acheson Graphite Company, Niagara Falls 

circular electrodes respectively. The base of the furnace consists 
of bricks, covered with a refractory material, h. The end walls, 
6, are of brick and hold the carbon electrodes, c. The bottom 
of the furnace is covered with a layer of granulated coke about 
5 centimeters thick, on which the electrodes are placed in piles 
at right angles to the axis of the furnace, separated from each 
other by about one fifth the width of the electrodes. This space 
is then filled .with granulated coke, g, arid the furnace is covered 
with a mixture of coke and sand, i. Figure 91 is from a photo- 
graph of the furnace now used for graphitizing carbon in all 
forms. 

u U. S. Pat. 617,029, (1898). 



224 



APPLIED ELECTROCHEMISTRY 



The following data are given by FitzGerald : 12 

Distance between terminals 360 inches 

Length of space filled by electrodes 302 inches 

Length of space filled by granular carbon .... 58 inches 

Length of electrodes under treatment 24 inches 

Width of electrodes under treatment 5 inches 

Height of pile of electrodes 17 inches 

Initial voltage 210 volts 

Initial amperage 1400 amperes 

Final voltage 80 volts 

Final amperage 9000 amperes 

In 1902 the plant of the International Acheson Graphite 
Company consisted of ten furnaces and 1000 available horse 
power. In 1909 the plant was increased to 22 furnaces and 4000 
horse power. 13 

The yearly production of manufactured graphite is given in 
Table 26. 14 " 



TABLE 26 
The Production of Graphite 



YEAR 


POUNDS 


VALUE IN DOLLARS 


1897 


162,000 


10,100 


1898 


186,000 


11,600 


1899 


406,000 


32,500 


1900 . . 


861,000 


68,900 


1901 


2,500,000 


119,000 


1902 . . . 


2,359,000 


111,000 


1903 


2,620,000 


179,000 


1904 


3,248,000 


218,000 


1905 


4,596,000 


314,000 


1906 


4,868,000 


313,000 


1907 


6,924,000 


484,000 


1908 


7,386,000 


503,000 


1909 . . 


6,871,000 


467,000 









12 Electrochem. and Met. Ind. 3, 417, (1905). 

1 3 Electrochem. and Met. Ind. 7, 187, (1909). 

i* Min. Ind. 18, 384, (1909). The figures in the table are rounded off. 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 225 



6. CARBON BISULPHIDE 

Great improvement has been made in the manufacture of 
carbon bisulphide by using an electric furnace in place of the 
small clay or iron retorts 
which have to be heated ex- 
ternally. In the old process, 
only a small fraction of the 
heat applied to the outside of 
the retort penetrated to the 
mixture of carbon and sulphur 
inside, and the process was 
so disagreeable on account of 
small leaks and the high tem- 
peratures of the retort room 
that some manufacturers gave 
it up altogether. E. R. Tay- 
lor, 1 however, has succeeded in 
overcoming these difficulties 
entirely by the use of the fur- 
nace shown in cross section in 
Figure 92, patented in 1899 2 
and in operation at Perm Yan, 
New York. This furnace is 
12.5 meters high and the diam- 
eter at the base 4.87 meters. 3 
At a height of 3.68 meters the 
diameter is reduced to 2.5 me- 
ters for a distance of 4.87 me- 
ters, where it narrows down to 
the top for the remaining 
length. The electrodes are at 
the base and are four in num- 
ber, arranged 90 degrees apart. FIG. 92. Taylor's electric furnace for 
Opposite electrodes are Con- making carbon bisulphide 

1 E. R. Taylor, Trans. Am. Electrochem. Soc. 1, 115, (1902) and 2, 185, (1902) 

2 U. S. Pat. 688,364, filed 1899, renewed 1901. 

3 Haber, f. Elektroch. 9, 399, (1903). 

Q 




226 APPLIED ELECTROCHEMISTRY 

nected to the same terminal of the alternating current machine. 
Wear on the electrodes is reduced to practically nothing by 
covering them with conducting carbon, which acts as the re- 
sistor. Charcoal is fed in at the top and sulphur through the 
annular spaces in the walls, thus preventing loss of heat. The 
sulphur is melted by the heat which would otherwise be lost 
through the walls, and flows down on to the electrodes, where 
it is heated to a temperature at which it combines with carbon. 
The carbon bisulphide vaporizes, passes off through the top of 
the furnace, and is condensed in cooling coils. The furnace is 
so tight that no odor is noticeable, and its operation is contin- 
uous. The production in 1903 was 3175 kilograms per day, with 
a consumption of 220 horse power 3 and the furnace had been in 
operation for two and a half years with only one interruption 
for the purpose of cleaning out. 

7. PHOSPHORUS 

Phosphorus is another product the manufacture of which 
has been improved by the use of heat derived from electricity. 
The older method consists in treating calcium phosphate with 
sulphuric acid, which changes the triphosphate to monophos- 
phate : 

Ca 3 (P0 4 ) 2 + 2 H 2 S0 4 = 2 CaSO 4 + CaH 4 (PO 4 ) 2 . 

The monophosphate is then mixed with carbon and dried, by 
which it is changed to metaphosphate : 

CaH 4 (P0 4 ) 2 = Ca(P0 8 ) 2 + 2 H 2 O. 

The metaphosphate is then heated in small retorts in which 
the following reaction takes place : 

3 Ca(PO 3 ) 2 + 10 C = Ca 3 (PO 4 ) 2 + 10 CO + 4 P. 

This process is imperfect in that a portion of the phosphorus 
is changed in the last operation to the product with which the 
operation is begun. Wohler proposed the use of silica and 
carbon, by which all the phosphorus would be recovered, as 
shown by the following reaction : 

Ca 3 (PO 4 ) 2 + 3 SiO 2 + 5 C = 3 CaSiO 3 + 5 CO + 2 P, 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 227 



but it was never successful till the introduction of the electric 
furnace, on account of the difficulty of obtaining the necessary 
temperature and of finding vessels to withstand it. 1 In 1889 
the use of electric furnaces for the manufacture of phosphorus 
was patented by J. B. Readman. 2 The process does not seem 
to have been immedi- 
ately employed on a 
large scale, however. 
In 189T the firm of 
Allbright and Wilson 




built works at Niagara 
Falls, using 300 horse 
power, for making 

phosphorus in the 

fnr The Roadman-Parker electric furnace for produc- 



ing phosphorus 
The furnaces FlG . 93. Vertical FIG. 94. Horizontal 

are illustrated in Fig- section section 

ures 93 and 94. Each produces 170 pounds a day. 

Over half the world's production of phosphorus is now 
made in electric furnaces. 4 



8. ALUNDUM 

Fused aluminum oxide, chemically identical with corundum, 
has received the trade name of Alundum. The process for 
making this abrasive in the electric furnace was patented in 
1900 by C. B. Jacobs. 6 His furnace was rectangular in shape, 
made of sheet iron and brick, and was lined inside with car- 
bon. An arc was formed between four pairs of electrodes near 
the movable bottom of the furnace. As the aluminum oxide 
fused and covered the bottom of the furnace, it was gradually 
lowered, thereby making a layer of fused aluminum oxide 
which cooled slowly. This process gives the abrasive a hard- 
ness greater than corundum. 

i Min. Ind. 14, 494, (1905). Min. Ind. 6, 637, (1897), 7, 557, (1898). 

2U. S. Pat. 147,943, (1889). *Min. Ind. 9, 768, (1900). 

6 U. S. Pat. 659,926, (1900). 



228 



APPLIED ELECTROCHEMISTRY 



The Norton Emery Wheel Company of Worcester are the 
sole manufacturers of alundum. Their factory is at Niagara 
Falls. Bauxite, the raw material, is dehydrated before feeding 
into the furnaces. The yearly production is given in Table 27. 6 



TABLE 27 
Production of Alundum 



YEAR 


POUNDS 


VALUE IN DOLLARS 


1904 


4 020 000 


281 400 


1905 


3 612 000 


259 840 


1906 


4,331,000 


303 190 


1907 


6,751,000 


405,090 


1908 ... 


3,160,000 


189,600 


1909 


13,758,000 


814,680 









9. ALUMINUM 

With the exception of silicon and oxygen, aluminum is the 
most widely distributed element in nature, 1 occurring princi- 
pally as silicates in clays. Only a limited number of its com- 
pounds can be used for extracting aluminum, however, chief 
among which is bauxite, A1O 3 H 3 . The name aluminum is 
derived from alumen, a term applied by the Romans to all 
bodies of astringent taste. 

The attempts to isolate aluminum date from 1807, when Davy 
was unsuccessful in applying to this problem the method em- 
ployed in isolating the alkali metals. Oersted seems to have 
made aluminum in 1824 by heating the chloride with potassium 
amalgam. Wohler in 1827 obtained aluminum by decompos- 
ing the anhydrous chloride with potassium, and in 1864 Bunsen 
and Deville obtained it independently by the electrolysis of 
fused aluminum chloride. Previous to the production by the 
method of electrolysis now used, the halide salts were the 
source of the metal and were reduced by metallic sodium. 

Alumina can be reduced by carbon to metallic aluminum by 



6Min. Ind. 18,25, (1909). 



1 Thorpe, Die. of Chem. 1, 63, (1890). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 229 

heating to a temperature above 2100 C., 2 but it is always mixed 
with aluminum carbide, from which it can be removed by 
remelting, and obtained in a compact form. This is evidently 
not a method of making aluminum that could be satisfactorily 
carried out commercially. If, however, a metal such as copper 
is added to the mixture, the aluminum can be obtained as an 
alloy with this other metal. This process was patented in 
1884 by the Cowles brothers. 3 The cheap production of pure 
aluminum, however, was made possible by the discovery of 
C. M. Hall 4 that alumina, dissolved in a molten mixture of 
aluminum fluoride and the fluoride of another metal, forms an 
electrolyte which may be decomposed by an electric current, 
liberating aluminum at the cathode and oxygen at the anode. 
Hall's original patent specifies a mixture of 169 parts by weight 
of aluminum fluoride and 116 parts of potassium fluoride, 
corresponding to the formula K 2 A1 2 F 8 , and states that this may 
be made more fusible by replacing part of the potassium 
fluoride by lithium fluoride, or by simply adding the latter to 
the above mixture. Another receipt is 84 parts of sodium 
fluoride to 169 of aluminum fluoride, which may be made by 
adding aluminum fluoride to cryolite, a mineral of the com- 
position A1F 8 3 NaF. He placed the carbon-lined crucible in a 
furnace, melted the mixture, added alumina, and electrolyzed 
with an anode of copper or carbon. Copper is said to be 
covered with an oxide which protects it from further action. 

Subsequent patents show that these mixtures worked well 
at first, but became less efficient after being electrolyzed some 
time. A dark substance formed which interfered with the 
electrolytic action, increased the resistance, and necessitated a 
change of the bath. This Hall attempted to overcome by 
using a bath of calcium and aluminum fluoride of the com- 
position 2 A1F 3 ' CaF 2 . 6 This increases the density to such an 
extent that the aluminum floats to the surface. It evidently 

2 Hutton and Petavel, Phil. Trans. 207, 421, (1907) ; Askenasy and Lebedeff, 
Z. f. Elektroch. 16, 565, (1910). 

8 U. S. Pat. 319,795, (1884). Also Proc. Soc. of Arts, 1885-1886, p. 74. 

* U. S. Pat. 400,664 and 400,766, filed 1886. 

U. S. Pat. 400,664, filed 1888. 



X 
230 APPLIED ELECTROCHEMISTRY 

was not satisfactory, for subsequently a bath made up of 234 
parts calcium fluoride, 421 parts cryolite, 845 parts aluminum 
fluoride, and 3 to 4 per cent calcium chloride was patented. 6 
It was claimed that the chloride prevented the clogging of the 
bath even when in continuous operation. It is evident the 
dark color must have come from carbon, as no clogging 
occurred with any of the baths when a metal was used as 
cathode. 7 In this case, of course, an alloy of aluminum would 
be obtained. 

As carried out on a large scale, the crucibles were never 
heated externally, but simply by the passage of the current it- 
self. This double use of the current to keep the bath melted 
and to electrolyze at the same time was patented by Charles S. 
Bradley. 8 In describing his process, cryolite is considered the 
electrolyte. The two patents of Hall and Bradley taken to- 
gether represent the process as actually carried out. 

In 1887 Paul Heroult patented a very similar process for 
producing aluminum alloys. 9 This process consisted in fusing 
pure alumina and keeping it in the fused state by the current, 
which at the same time decomposes the oxide electrolytically. 
The cathode is a melted metal, with which the aluminum is to 
be alloyed, and the anode is carbon. Serious objections were 
found to using any flux. Among those tried and discarded was 
cryolite. The patent states that satisfactory results were ob- 
tained with a carbon crucible 20 centimeters in depth and 14 
centimeters in diameter at the top, a carbon anode 5 centimeters 
in diameter, and a current of 400 amperes at from 20 to 25 volts. 
This voltage is four or five times that specified by Hall. Brad- 
ley's patent for the simultaneous use of the current for electrol- 
ysis and heating was therefore earlier than Heroult's, and as it 
is stated in Heroult's patent that he had failed to get good re- 
sults when any flux was mixed with the aluminum oxide, there 
is no question of priority over Hall's patents. It does not seem, 
therefore, that the statement often met with, that the processes 

s U. S. Pat. 400,666, filed 1888. 7 U. S. Pat. 400,667, filed 1888. 

8 U. S. Pat. 464,933, filed 1883, granted 1891. 
U. S. Pat. 387,876, filed December, 1887. 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 231 



of Hall and Heroult are identical, is borne out by the patents. 10 
The Hall patents for the composition of the bath expired in 
1905 and the Bradley patents in 1909. u 

The only producer of aluminum in this country is the Alumi- 
num Company of America, previous to 1907 known as the Pitts- 
burg Reduction Company. 12 This company controls three plants, 
situated at Niagara Falls, Massena, New York, and Shawinegan 
Falls, Canada. These plants were enlarged in capacity in 1907 
to 40,000 horse power, 20,000 horse power, and 15,000 horse 
power respectively. 13 The six European companies producing 
aluminum show a maximum consumption of 97,500 horse power. 13 
The furnaces used by the American company consist of cast 
iron troughs lined with carbon. 14 The anode is composed of 48 
carbon rods 3 inches in diameter and 15 inches long, manufac- 
tured by the aluminum company for its own use. 12 Each fur- 
nace takes about 10,000 amperes at about 5.5 volts. The yield 
is 1.75 pounds of aluminum per horse power day. 1 * The metal 
sinks to the bottom and is drawn off, while alumina is thrown 
in as it is used up. The temperature of the bath may be in- 
ferred from the following melting points of mixtures of cryolite 
and alumina. 16 

TABLE 28 
Melting Points of Mixtures of Cryolite and Alumina 



PEE CENT 
CRYOLITE 


M. P., DEGREES 
CENTIGRADE 


PER CENT 
CRYOLITE 


M. P., DEGREES 
CENTIGRADE 


100 


1000 


92 


992 


97 


974 


90 


980 


96 


960 


85 


994 


95 


915 


80 


1015 


94 


960 






93 


982 







10 See for example Pring, Some Electrochemical Centres, p. 26 (1908). 
" Min. Ind. 17, 23, (1908). 18 Min. Ind. 6, 11, 15, (1907). 

12 Min. Ind. 15, 11, (1906). u Min. Ind. 14, 15, (1905). 

is Pyne, Trans. Am. Electrochem. Soc. 10, 163, (1906). 



232 



APPLIED ELECTROCHEMISTRY 



The production of aluminum in the United States and Canada 
is given in Table 29. 16 

TABLE 29 
Production of Aluminum in the United States and Canada 



YEAR 


POUNDS 


VALUE IN 
DOLLARS 


VALUE PER POUND 
IN DOLLARS 


1897 


4,000,000 


1,400,000 


0.35 


1898 


5,200,000 


1,690,000 


0.33 


1899 


6,500,000 


2,113,000 


0.33 


1900 


7,150,000 


2,289,000 


0.32 


1901 ....... 


7,150,000 


2,238,000 


0.31 


1902 


7,300,000 


2,285,000 


0.31 


1903 . . . 


7,500,000 


2,325,000 


0.31 


1904 


7,700,000 


2,233,000 


0.29 


1905 


11,350,000 


3,632,000 


0.32 


1906 


14,350,000 


5,166,000 


0.36 


1907 ..... 


26,000,000 


10,920,000 


0.42 


1908 


13 000 000 


4,095,000 


0.32 


1909 


15,000,000 


3,345,000 


0.22 











The total production of the world for 1909 is estimated at 
24,200 metric tons, or 53,300,000 pounds. The cost of manu- 
facture excluding amortization is said to be about 15 cents a 
pound. 16 

On reading a description of the different expedients patented 
by Hall to prevent the baths from clogging, becoming discolored, 
and ceasing to operate properly, it is not surprising that diffi- 
culties are encountered on attempting to use the reduction of 
aluminum as a laboratory experiment. Haber and Geipert 17 
succeeded in a few runs, though in the last run they met with 
irregularities. The immediate difficulty that stops an experi- 
ment on a small scale is a polarization at the anode, due to a 
thin film of gas, 18 which reduces the current to such a point that 
the bath freezes up. If a higher voltage is applied it heats the 

is Min. Ind. 18, 17, (1909). 
IT Z. f. Elektroch., 8, 1, and 26, (1902). 

i 8 Thompson, Electrochem. and Met. Ind. 7, 19, (1909). Also Neumann and 
Olsen, Met. and Chem. Eng. 8, 185, (1910). 



PKODUCTS OF THE RESISTANCE AND ARC FURNACE 233 

bath too much locally and burns up the aluminum. By the 
use of an anode with a large area this can be prevented to a 
certain extent. 18 

One of the principal uses for aluminum is in the iron and 
steel industry as a reducing agent. 19 As is well known, it has 
replaced copper, tin, and brass to a great extent in the manu- 
facture of a large number of objects in which lightness is 
desired. 

10. SODIUM AND POTASSIUM 

Sodium and potassium were first isolated by Davy l by electro- 
lyzing the corresponding fused hydrates. In this process 
sodium is liberated at the cathode while the negatively charged 
hydroxyl ion is liberated at the anode. Two of these ions when 
discharged react together according to the reaction: 

2 OH = H 2 O + O. 

A certain amount of metallic sodium dissolves in the hy irate, 
diffuses to the anode, and coming in contact with the water 
reacts to form hydrate with the liberation of hydrogen. 2 It is 
therefore possible to have both hydrogen and oxygen evolved 
at the anode, resulting in explosions. At the same time sodium 
peroxide (Na 2 O 2 ) is formed. The water formed at the anode is 
not driven off by the temperature of the bath ; on the contrary 
it has been found that very moist air is dried to a certain extent 
in passing through the melted hydrate. 2 

The apparatus nearly universally used for the production of 
sodium and potassium is due to Hamilton Young Castner 3 and is 
shown in Figure 95. It consists in a cast-iron box with an iron 
cathode, H, insulated from the box and held in an iron pipe 
fastened into the bottom of the cell. The space between the 
pipe and electrode is filled with melted hydrate which is allowed 
to solidify before the electrolysis is begun. Surrounding the 

19 For a detailed account of the various purposes to which aluminum is applied, 
see A. E. Hunt, Journ. Franklin Inst., Vol. 144, (1897). 

1 Phil. Trans., 1808, pp. 5 and 21. 

2 Lorenz, Elektrolyse Geschmolzener Salze, I, 25, (1905). 
8 U. S. Pat. 452,030, filed 1890. 



234 



APPLIED ELECTROCHEMISTRY 



cathode is a fine iron gauze diaphragm, M, outside of which is 
the iron anode, F. The metal is liberated on the cathode and 
floats to the surface of the hydrate, where it collects in an iron 
cylinder forming a continuation of the diaphragm. It is re- 
moved by an iron spoon with fine perforations, which allow the 
hydrate to drain off, but which holds the metal. The hydrate 
is added as it is used up, and the process is continuous. An 
important point is to maintain the temperature as low as pos- 
sible, not over 20 above the melting point of the hydrate. The 




FIG. 95. Castner's cell for producing sodium and potassium 

higher the temperature the less the yield in metal, due of course 
to its greater solubility in the melted hydrate. As the temper- 
ature increases, the yield becomes less, until it finally reaches 
zero. At best the current efficiency is said to be only about 45 
per cent. 4 In the patent gas heating is provided, though it is 
stated that the current can be so regulated as to keep the proper 
temperature without external heating. 

There are other processes very similar to that of Castner, 
some of which are in use, 6 which will be omitted as presenting 

4 Ashcroft, Trans. Am. Electrochem. Soc. 9, 123, (1906). 

6 See H. Becker, Die Elektrometallurgie der Alkalimetalle, p. 52, (1903). 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 235 



no new principles; but the principle of the following process, 
due to Ashcroft, 4 will be described because of its novelty and 
in spite of the fact that it does not seem as yet to have been 
carried out on a commercial scale. Melted sodium chloride is 
electrolyzed with a lead cathode. The lead sodium alloy formed 
is let into another cell containing melted sodium hydrate. Here 
the lead alloy acts as the anode and forms sodium hydrate with 
the hydroxyl ions liberated on its surface, thus avoiding the 
formation of water and oxygen. At the cathode sodium is lib- 
erated and removed. To decompose the chloride 7 volts are 
required, and 2 volts for the hydrate when this anode is used. 
The voltage is therefore about twice that required in the 
Castner cell; but as the current efficiency is about 90 per cent, 
or twice that in the Castner process, the yield per unit of 
power is the same in the two cases. The advantages claimed 
by Ashcroft are shown in the following table: 





ASHCKOFT PROCESS 


CASTNER PROCESS 




0.5 cent 


5 cents 


Cost of power per pound of sodium . . 


per pound 
1 to 5 cents 
1 cent 


per pound 
1 to 5 cents 
2 cents 


Upkeep and standing charges .... 


2.5 cents 


2 cents 


Total 


5 to 9 cents 


10 to 14 cents 




per pound 


per pound 



The saving comes in the greater cheapness of the raw material, 
and there would be a further saving in the value of the chlorine 
produced. 

The world's production of sodium in 1907 is estimated at from 
3500 to 5000 tons. 6 In the United States there are two com- 
panies producing about 2000 tons a year. The Electrochem- 
ical Company at Niagara Falls uses the Castner process, while 
the Virginia Electrolytic Company at Holcomb Rock, Virginia, 
is said to employ a process in which fused sodium chloride is 
electrolyzed. 

e Min. Ind. 17, 772, (1908). 



236 APPLIED ELECTROCHEMISTRY 

A large part of the sodium made is consumed in the manu- 
facture of sodium cyanide and sodium peroxide. The process 
for cyanide 7 consists in passing ammonia over the metal heated 
in an iron retort to 300 to 400 C., forming sodamide : 

2 Na + 2 NH 3 = 2 NaNH 2 + H 2 . 

This is then treated with charcoal previously heated to redness, 
giving the cyanide 

NaNH 2 + C = NaCN + H 2 . 

A recent purpose to which the metal has been put is the dry- 
ing of transformer oils. Ashcrof t 4 believes a reduction in the 
price may increase its uses materially, such as making primary 
cells, obtaining hydrogen by the decomposition of water, and 
even for transmitting electric power. The specific conductiv- 
ity is only about one third that of copper, 8 but if equal weights 
of metal are considered between two given points, the conduc- 
tivity would be three times that of copper, as the density of 
copper is about nine times that of sodium. Some experiments 
have actually been carried out in power transmission with the 
sodium protected in iron pipes. 9 

11. CALCIUM 

Calcium was first isolated by Davy in 1808, by combining 
the methods previously used by him with those of Berzelius 
and Pontin. 1 Lime was mixed with red oxide of mercury, 
slightly moistened and placed on a piece of platinum. A glob- 
ule of mercury in a cavity at the top acted as negative elec- 
trode, giving on electrolysis an amalgam of calcium, from which 
the mercury was distilled. 

Bunsen 2 obtained calcium in very small quantities contain- 
ing a little mercury by electrolyzing with a high current 
density a boiling concentrated solution of calcium chloride 

7 Roscoe and Schorlemmer, 2, 276, (1907). 

8 Landolt-Bornstein Tables, 3d ed. 

Belts, Min. Ind. 15, 688, (1906) and El. World, 48, 914, (1906). 

1 Alembic Club Reprints, No. 6, p. 48, Ostwald Klassiker, No. 45. 

2 Fogg. Ann. 91, 623, (1854), in an article on the preparation of chromium. 



PRODUCTS OF THE RESISTANCE AND ARC FURNACE 237 



acidified with hydrochloric acid. The cathode was amalga- 
mated platinum wire. Rathenau 3 was first to obtain calcium 
in a compact form in fairly large quantities by a rather original 
method. The bath 
consists of calcium 
chloride very little 
above its melting 
point. An iron 
rod is used as cath- 
ode, which just 
touches the surface 
of the bath. As 
the melting point 
of calcium is a little 
higher than that of C 
the bath, it solidi- 
fies on depositing 
and adheres to the 
rod, which is grad- 
ually raised, thus 
drawing out a stick 
of calcium with a 
certain amount of 
chloride adhering 
to it. The melt- 
ing point of the 
electrolyte may be 

lowered by adding FIG. 96. Cell of Seward and von Kiigelgen for the pro- 

calcium fluoride. duction of calcium 

The anode may be a carbon crucible in which the salt is contained, 4 
though Rathenau does not specify his arrangement. The ex- 
perience of the author has been that this is a much better plan 
than that adopted by P. Wohler, 5 where the salt is held in an 
iron vessel and a carbon anode dips into the bath. Due to the 

8 Z. f. Elektroch. 10, 608, (1904). 

* J. H. Goodwin, Proc. Am. Phil. Soc. 43, 381, (1904). 

6 Z. f. Elektroch. 11, 612, (1905). 




238 APPLIED ELECTROCHEMISTRY 

high anode current density in this case, the gas is more likely 
to stop the current by polarization. The heat due to the cur- 
rent is sufficient to keep the salt melted. 

Calcium is made in this country only by the Virginia Elec- 
trolytic Company at Holcomb Rock, Virginia. 6 The process 
is supposed to consist 7 in electrolyziiig melted calcium chloride 
in a cell patented by Seward and von Kiigelgen, 8 shown in 
Figure 96. This cell consists of a circular iron box, J., through 
the bottom of which projects a conical iron cathode, B, insulated 
from the box by insulating material, aa. The anode, (7, is a car- 
bon lining also insulated from the iron box. Above the cathode 
and concentric with it is a water-cooled collecting ring, E, which 
separates the metal rising to the surface from the chlorine. 
The metal accumulates till the ring is full. The top layer is 
solid, due to the cooling of the air, and the bottom is soft or 
melted. The solid part is fastened to a hook, F, and gradually 
drawn out. 

The production of calcium by the Virginia Electrolytic Com- 
pany in 1907 was 350 pounds, valued at $613, and about the 
same amount was produced in 1908. 6 

6 Min. Ind. 17, 99, (1908). 
'Min. Ind. 16, 131, (1907). 
U. S. Pat. 880,760. 



CHAPTER XIII 

THE ELECTROMETALLURGY OF IRON AND STEEL 
1. GENERAL DISCUSSION 

BEFORE giving an account of the application of electric heat- 
ing to the iron and steel industry, a short sketch of the older 
methods of winning and refining iron will not be out of place. 

The extraction of iron from its ores, consisting principally of 
oxides of iron mixed with clay, silica, and other impurities, is 
accomplished by reducing the ore with some form of carbon, usu- 
ally coke. This operation is carried out in a blast furnace, a cir- 
cular brick structure lined with silicious brick, and varying in 
size from 48 feet to 106 feet in height, and from 8 feet to 15 
feet in diameter at the base. Figure 97 shows the elevation of a 
blast furnace. It consists of three principal parts : (1) the cru- 
cible or hearth at the base, cylindrical in shape, (2) the bosh 
directly above, which gradually widens, and (3) the stack, from 
which point the furnace contracts for the rest of its height. 
The furnace is filled with alternate layers of ore, coke, and flux, 
the latter usually consisting of calcium carbonate. The object 
of the flux is to form a fusible slag with the constituents of the 
ore which are not reduced by the carbon, such as silica and 
alumina. The heat necessary to raise the charge to a temper- 
ature high enough for reduction is produced by the combustion 
of the coke in the charge, by means of air forced in through the 
tuyeres, F, projecting through the wall of the furnace just below 
the bosh. The carbon therefore serves the double purpose of 
furnishing the heat and of reducing the ore. 

The highest temperature of the furnace is near the tuyeres 
and a few feet above them ; in this region the slag and iron 
melt and drop into the crucible, where they separate, the slag 

239 



240 



APPLIED ELECTROCHEMISTRY 



floating on the iron. These are drawn off from time to time 
through the tap holes Or and H, and fresh material is fed into 
the top of the furnace by mechanical means. The iron thus 




FIG. 97. Elevation of blast furnace 

produced is known as pig iron, and contains from three to four 
per cent of carbon, as much as four per cent of silicon, and one 
per cent of manganese, and a few hundredths of one per cent of 
sulphur and phosphorus. Only about 23 per cent of the pig 
iron made in this country is used without subsequent purifica- 
tion. 1 Purification or refining of iron is accomplished by oxi- 
dizing the impurities and causing them to form a slag, which 
floats on the iron. 

1 Stoughton, The Metallurgy of Iron and Steel, p. 52. 



THE ELECTROMETALLURGY OF IRON AND STEEL 241 

One method of refining consists in blowing air through the 
liquid metal in a Bessemer converter. The lining of the con- 
verter may be either basic, consisting of calcined dolomite (cal- 
cium and magnesium oxides), or acid, consisting of silica. The 
Bessemer method is very rapid, silicon and manganese oxidizing 
in about four minutes from the time when the air is first blown 
in. The carbon then begins to oxidize to carbon monoxide, 
which boils up through the metal and comes out of the con- 
verter in a long flame. In about six minutes from the time the 
carbon begins to oxidize, it is reduced to approximately 0.04 
per cent, and the operation is then stopped. The temperature 
is higher at the end of the process than at the start, due to 
the heat of oxidation of the impurities. A calculated amount 
of carbon is then added, also 1.5 per cent of manganese to 
remove the oxygen, and 0.2 per cent of silicon to remove the 
other gases. The steel is then cast into molds. 

The second method of refining is known as the open hearth or 
Siemens-Martin process. This consists in melting the pig iron 
in a large reverberatory furnace, whose lining may be either 
basic or acid. The oxidation of the impurities is brought about 
by the excess of oxygen in the furnace gases over that neces- 
sary to burn the gases. A much longer time is required for 
purification by the open hearth than by the Bessemer process. 
In the basic open hearth process enough lime is added to form 
a very basic slag, which, unlike an acid slag, will dissolve phos- 
phorus. The lining must also be basic to prevent its being 
eaten away by the basic slag. 

The third method of purification is known as the puddling 
process, in which the iron is melted on the hearth of a rever- 
beratory furnace lined with oxides of iron. The pig iron is 
charged by hand through the doors of the furnace and is melted 
as quickly as possible. During melting, silicon and manganese 
go into the slag, as well as some of the oxide of the lining. 
Iron oxide is then added in order to make a very basic slag ; 
the charge is thoroughly mixed, and the temperature is lowered 
to the point where the slag begins to oxidize the phosphorus 
and sulphur before the carbon. After the removal of these 



242 APPLIED ELECTROCHEMISTRY 

impurities, the carbon begins to oxidize and comes off as carbon 
monoxide, which burns on coming in contact with the air. 
During this time the puddler stirs the charge vigorously with a 
long iron rabble, an instrument shaped like a hoe. As the iron 
becomes pure, its melting point rises and it begins to solidify, 
since the temperature of the furnace is below the melting point 
of pure iron. The iron is finally removed in the form of a ball 
dripping with slag, and is put through a squeezer to remove the 
slag as much as possible. This product is known as wrought 
iron. It is converted into steel by two methods, (1) the ce- 
mentation, and (2) the crucible process. In the cementation 
process the wrought iron is carburized by heating, without 
melting, in contact with carbon. The carbon slowly penetrates 
the iron and changes it to steel. In the crucible process the 
wrought iron is cut up into small pieces and is melted in covered 
crucibles with the desired amount of carbon or other element 
that is to be alloyed with it. When the process is finished the 
steel is cast into molds. By thus remelting the iron, the slag 
is removed and the required amounts of carbon, silicon, and 
manganese are added. 

2. THE ELECTROTHERMIC REDUCTION OF IRON ORES 

The conditions under which electric heating can economically 
be substituted for the heat of combustion of coke in the reduc- 
tion of iron ores are purely local. In places where iron ore 
can be obtained cheaply, where metallurgical coke is expensive, 
where water power is cheap, and where iron would have to be 
hauled from a great distance to supply the local demand, it 
may be possible to produce iron by electric heating at a price 
low enough to compete with that brought from a distance. 
These conditions exist in Canada, Sweden, and California. 1 

The first attempt to apply electric heating to the metallurgy 
of iron was made in 1853 by Pinchon, 2 and in 1862 Monkton 
took a patent in England for the reduction of ores by the 

1 Eugene Haanel, Trans. Am. Electrochem. Soc. 15, 25, (1909) l and P. McN. 
Bennie, ibid. p. 35. 

2 B. Neumann, Electrometallurgie des Eisens, p. 3, (1907). 



THE ELECTROMETALLURGY OF IRON AND STEEL 243 




FIG. 98. Stassano's first furnace at Rome 



electric current. Sir Wil- 
liam Siemens again called 
attention to this subject 
in a lecture before the 
Society of Telegraph En- 
gineers in London in 1880. 3 
The first, however, to show 
by experiments on a large 
scale that iron can be re- 
duced commercially by 
electric heating was the 
Italian army officer, Major 
Stassano. 4 Patents were 
taken out by him in the year 1898 in different countries, con- 
sequently this date 
marks the beginning 
of the actual appli- 
cation of electricity 
to the metallurgy of 
iron. The contrac- 
tion of the carbide 
industry in 1899 to 
1900, due to over- 
production, leaving 
idle a number of 
water-power stations 
in southeastern 
France, for which 
some new application 
of electric power was 
needed, also hastened 
the introduction of 
electric heating in the 
iron industry. 6 

Stassano's prelim- 




FIG. 99. Horizontal section of Stassano's electric 
furnace at Darfo 



Elektrotech. Z. 1, 325, (1880). 

4 Askenasy, Technische Elektrochemie, 94, (1910). 

6 J. B. C. Kershaw, Electrometallurgy, p. 175, (1908). 



244 



APPLIED ELECTROCHEMISTRY 



inary experiments on the reduction of iron ore were carried 
out at Rome in 1898, 6 with the 150 horse power furnace repre- 
sented in Figure 98. It is seen to resemble an ordinary blast 
furnace. Since there was no combustion of carbon, no reduc- 
ing gases were produced ; consequently, in order to bring the 




FIG. 100. Vertical section of Stassano's electric furnace at Darfo 

carbon and ore in intimate contact, they were powdered, mixed, 

and made into briquettes with pitch as a binder. The furnace 

6 See an article by Stassano reprinted in Haanel's Keport, p. 178, (1904). 



THE ELECTROMETALLURGY OF IRON AND STEEL 245 



was first heated without a charge ; an iron grating was then 
placed in the furnace 20 centimeters above the arc, and the mix- 
ture was charged in from the hopper at the top and was held 
up by the grating. The grating eventually melted, and the 
ore in contact with it was reduced. In this state the mixture 
which lay on the grating became fused and formed an arch, 
which supported the charge even when the grating melted 
away. As the heat from the arc penetrated the mass above the 
arch, iron was reduced and dropped into the crucible below. 
In the course of twelve hours the arch increased so in thickness, 
due to the slag produced, that it prevented the efficient heat- 
ing of the charge above. Consequently this form of furnace 
was given up, and one was adopted in which the material was- 
introduced below the arc, as is done in refining furnaces. The 
final form adopted at Darfo, 
in northern Italy, is shown 
in Figures 99 and 100. 
Movement of the entire 
chamber in which the fu- 
sion takes place is effected 
by rotating about an axis 
inclined to the vertical. 
The electricity is conducted 
to the furnace by sliding 
contacts on two metal rings 
at the top of the furnace. 
This, furnace worked per- 
fectly satisfactorily, even 
when run for several days. 
The most difficult ques- 
tions to decide were the re- 
lation between the size of the cavity and the energy to be 
supplied, and the manner of making the refractory lining. The 
carbon electrodes were 1.5 meters long and lasted sixty consec- 
utive hours. The furnace was supplied with 1000 amperes at 
100 volts, and since the value of the cosine of the phase differ- 
ence between electromotive force and current was 0.8, the power 




FIG. 101. The Keller electric furnace for 
reducing iron ore 



246 APPLIED ELECTROCHEMISTRY 

consumed was 80 kilowatts. The best yield with this furnace 
was one kilogram of soft iron for 3.2 kilowatt hours, and the 
iron obtained was always over 99 per cent pure. The ore, 
which was from the island of Elba, had the following com- 
position : 

Fe 2 O 3 93.020 per cent 

MnO 0.619 per cent 

SiO 2 3.792 per cent 

CaO, MgO 0.500 per cent 

Sulphur , 0.058 per cent 

Phosphorus 0.056 per cent 

Moisture 1.720 per cent 

According to Stassano, the plant at Darfo was shut down 
for reasons not directly connected with the success of the 
process. 

The Keller furnace for making pig iron is shown in Figure 
101. This furnace was seen in operation by the Canadian 
Commission at Livet, France, in 1904. It T consists of two 
iron castings of square cross section, forming two shafts com- 
municating with each other at their lower ends by a lateral 
canal. The castings are lined with refractory material. The 
base of each shaft is provided with a carbon block, these two 
blocks being connected to each other outside the furnace by 
copper bars. On starting, before there is metal in the canal, 
the current flows from one block to the other through the copper 
bar, but when enough metal has been reduced to partially fill 
the canal, most of the current flows through the melted metal. 
The electrodes are 1.4 meters long and 85 by 85 centimeters in 
cross section. The cost of electrodes per metric ton of pig iron 
is estimated by Keller at 3.85 francs. The energy absorbed 
per metric ton of pig iron in a furnace supplied with 11,000 
amperes at 60 volts was 0.390 kilowatt year for the run, and 
with a smaller furnace supplied with 7000 amperes at 55 volts 
it was 0.186 kilowatt year for the run. 8 

Haanel's Report, p. 15, (1904). Haanel's Report, p. 20, (1904). 



THE ELECTROMETALLURGY OF IRON AND STEEL 247 



.EXPERIMENTAL. 
ElZCTRICfURNACt 



Following the tour of inspection by the Canadian Commission, 
an investigation was carried out for the Canadian government 
in 1906 by Heroult, to see (1) whether magnetite could be eco- 
nomically smelted by the electrothermic process ; (2) whether 
ores containing sulphur, but not manganese, could be made into 
pig iron of marketable composition ; and (3) whether charcoal 
could be substituted for coke. The 
furnaces were slightly modified as the 
investigation proceeded, and the final 
form is shown in Figure 102. It 
consists of a cylindrical iron casting 
| inch thick, bolted to a bottom plate 
of cast iron 48 inches in diameter. 
The casting was made in two sections 
bolted together by angle irons. In 
order to make inductance small, the 
magnetic circuit was broken by re- 
placing a vertical strip of 10 inches 
width in the casting by copper. Rods 
of iron were cast into the bottom plate 
to secure good contact with the car- 
bon paste rammed into the lower part 
of the furnace. The electrodes, 6 
feet long and 16 by 16 inches in cross 
section, were manufactured by a pro- 
cess of Heroult's and were imported 
from Sweden. The pipe k was for the purpose of cooling the 
electrode holder by a current of air. The current was between 
4000 and 5000 amperes at 36 to 39 volts, and the power factor 
was 0.919. The ores used in the experiments below were of 
the following composition: 




FIG. 102. Heroult experimen- 
tal furnace at Sault Ste. 
Marie, for reducing iron ore 



248 



APPLIED ELECTROCHEMISTRY 



TABLE 30 
Composition of Ores investigated by Heroult for the Canadian Government 





HEMATITE 


MAGNETITE 


ROASTED 
PYRRHOTITE 


TlTANIPEROUS 

IRON ORE 


1 


2 


3 


Fe 


62.23 


56.69 


55.85 


58.29 


45.80 


43.59 


SiO 2 


5.42 


6.20 


6.60 


4.00 


10.96 


7.12 


Fe 2 3 
FeO 
A1 2 3 


88.90 


55.42 
23.04 
2.56 


60.74 
17.18 
1.48 


55.31 
25.20 
2.24 


65.43 
3.31 


30.30 
28.78 
7.00 


2.51 


CaO 


0.61 


2.00 


2.48 


2.40 


3.92 


1.00 


MgO 
Mn 


0.30 
0.16 


6.84 


5.50 


4.00 


3.53 


4.14 


MnO 





0.258 


0.13 











P 


0.044 


0.01 


0.016 


0.415 


0.016 


0.028 


S 


0.0002 


0.05 


0.57 


0.45 


1.56 


0.04 


CO 2 and unde- 
termined 
Loss on ignition 
Cu 
Ni 




3.609 


4.923 


M6 


2.23 





2.48 





TiO 2 

















17.82 






100.426 


100.00 


100.00 


100.00 





99.648 



The consumption of the electrode in these experiments was 
8.9 kilograms per metric ton of pig iron produced. The yield 
per unit of energy vafried somewhat, but was approximately 
0.25 kilowatt year of 365 days per metric ton of pig iron. 
The results of these experiments were : 

1. Canadian ores, chiefly magnetites, can be as economically 

smelted as hematites by the electrothermic process. 

2. Ores of high sulphur content can be made into pig iron 

containing only a few thousandths of one per cent of 
sulphur. 

3. The silicon content can be varied as required for the class 

of pig iron to be produced. 



THE ELECTROMETALLURGY OF IRON AND STEEL 249 

4. Charcoal which can be cheaply produced from mill refuse 

or wood which could not otherwise be utilized, and peat 
coke, can be substituted for coke without being briquetted 
with the ore. 

5. A ferro-nickel pig can be produced practically free from 

sulphur, and of fine quality, from roasted nickeliferous 
pyrrhotite. 

6. Titaniferous iron ores containing up to five per cent can 

be successfully treated by the electrothermic process. 

These results demonstrated the feasibility of applying the 
electrothermic process to the reduction of iron ores. 9 All that 
was necessary to put it 
on a commercial basis 
was the construction of 
a furnace that could be 
economically and suc- 
cessfully used in prac- 
tice. This was under- 
taken by three Swedish 
engineers, Messrs. Gron- 
wall, Lindblad, and Stal- 
hane, at Domnarfvet, 
Sweden. They concen- 
trated their attention on 
the construction of a 
furnace following the 
suggestions contained in 
the report of Heroult's 
experiments for the 



Canadian government, 
which were, (1) charg- 
ing by labor-saving ma- 
chinery, (2) collection 
and use of carbon monoxide produced by the reduction of the 
ore, (3) automatic regulation of electrodes, and (4) a sufficiently 




fire BricA 3 Masncsitt 
FIG. 103. Electric furnace at Domnarfvet, Swe- 
den, for reducing iron ore 



9 Haanel, Trans. Ain. Electrochem. Soc. 15, 25, (1909). 



250 APPLIED ELECTROCHEMISTRY 

high shaft containing the charge to permit the heated carbon 
monoxide to produce the maximum reduction of the ore. 
Seven furnaces were constructed and tested before arriving at 
the one which they considered practical and commercial. This 
required over two years and an expenditure of $ 102,000. 1(> 
A vertical section of the furnace is shown in Figure 103, from 
which the general construction is perfectly obvious. It evi- 
dently resembles somewhat Stassano's original furnace, and, 
like his, is started as an ordinary blast furnace. 10 The crucible 
is 2.25 meters in diameter and 1.5 meters high. The most 
important point in the construction is the manner in which 
the electrodes are brought into the melting chamber. As seen 
from the section, they enter through that portion of the roof of 
the crucible that does not come in contact with the charge, 
and pass into the charge at the slope formed by the materials 
of which it is composed. The electrodes dip into the charge, 
but not into the melted iron beneath it. 11 Experiments had 
shown that the brickwork lining around the electrodes was al- 
ways destroyed if brought in contact with the charge, even 
when the electrodes were water cooled. The brickwork com- 
posing the lining of the roof of the melting chamber was 
cooled by forcing against it, through tuyeres, the compara- 
tively cool tunnel-head gases. The heat absorbed by these 
gases is given back to the charge above. 

A three-phase current is supplied to three electrodes 11 by 
22 inches in cross section and 63 inches in length. The water- 
cooled stuffing boxes through which the electrodes enter the 
melting chamber are provided with devices to prevent the hot 
gases under pressure from leaking out around the electrodes. 
The results of a short run that was made in the presence of 
Dr. Haanel showed (1) that the furnace operated uniformly 
and without trouble of any kind for five consecutive days, the 
electrodes requiring no adjustment whatever; (2) that the 
energy consumption was remarkably uniform ; (3) that a free 

10 For the evolution of the furnace, and dimensions, see Met. and Chem, 
Eng. 8, 11, (1910). 

11 Assar Gronwall, Electrochem. and Met. Ind. 7, 420, (1900). 



THE ELECTROMETALLURGY OF IRON AND STEEL 251 



space was maintained between the charge and the roof of the 
heating chamber ; (4) that the charge did not jam at the lower 
contracted neck of the shaft, but moved with regularity into 
the melting chamber; and (5) that the lining of the roof of 
the melting chamber was effectively cooled by the circulation 
of gas. 

Since the short run witnessed by Dr. Haanel, the furnace has 
been in continual operation 
for 85 days, and met all the 
requirements that indicate a 
durable furnace. 10 The de- 
signers of this furnace have 
contracted to erect three large 
furnaces for the reduction of 
iron ores at Sault Ste. Marie, 
Canada, to be in operation by 
the middle of 1910. 12 The 
first electric smelting plant in 
Canada was under construc- 
tion at Welland, Ontario, in 
1907. 13 It was to consist of 
a 3000 horse power furnace 
of the latest type brought out 
by Heroult. 

In 1909 an electrothermic 
plant for reducing iron ore 
was in existence on the Pitt 
River at Heroult, Shasta 
County, California." From the 
section of this 1500 kilowatt 
furnace shown in Figure 104, its resemblance to the furnace at 
Domnarf vet will be evident. A general view is shown in Fig- 
ure 105. Though this furnace is on a commercial scale, in 
July, 1910, it was still in the experimental stage, on account 

12 Electrochem. and Met. Ind. 7, 535, (1909). 

is Haanel's Report, 1907, p. 147. 

" D. A. Lyon, Trans. Am. Electrochem. Soc. 15, 39, (1909). 




252 APPLIED ELECTROCHEMISTRY 

of numerous difficulties that had been encountered. Several 
changes have been made and it is expected that the furnace 
will be perfected shortly. When this is accomplished, the 
Noble Electric Steel Company will build four or five others 
of a similar type. 15 Pig iron on the Pacific coast brings $23 
to $26 a ton, 16 and the cost from this furnace is expected to 
be $15 a ton, which leaves a good margin of profit. 

3. THE ELECTROTHERMIC REFINING OF STEEL 

While the application of electrothermics to the reduction of 
pig iron is scarcely an established commercial industry, the case 
is quite the reverse in steel refining, for a large number of fur- 
naces for this purpose are in operation in Europe and America. 
Even in this case, however, the electric furnace cannot compete 
with the Bessemer or with the open-hearth process for making 
structural steel. Electric furnace refining is used only to pro- 
duce very high-class steel for special purposes, 1 for which it is 
far superior to the crucible process, on account of the greater 
cheapness and higher quality of the steel produced. 2 The 
reason for the better quality of the product is that the atmos- 
phere is neutral, and a much higher temperature can be obtained 
than by other means, resulting in a more complete removal of 
impurities, especially gases. Phosphorus and sulphur disap- 
pear nearly completely, and deoxidation is more complete 
than that attained by any other means. Another advantage 
of electric heating is the reliability and certainty of the 
process. 3 

A number of different electric furnaces have been designed 
for refining steel, and some of the principal ones will now be 
described. 

15 private communication from Professor D. A. Lyon, the manager of the 
company. 

16 Bennie, Trans. Am. Electrochem. Soc. 15, 36, (1909). 

1 Haanel's Report, (1904), p. 31; Hibbard, Trans. Am. Electrochem. Soc. 15, 
231, (1909). 

2 Askenasy, Technische Elektrochemie, p. 56, (1910). 

3 Askenasy, Technische Elektrochemie, p. 156, (1910). 



THE ELECTROMETALLURGY OF IRON AND STEEL 253 




FIG. 105. Electric furnace at Heroult, California, for reducing iron ore 



254 APPLIED ELECTROCHEMISTRY 

The furnace used by Stassano at his works in Turin is 
similar to the one he finally adopted for reducing iron ore 4 
(Figures 99 and 100). The charge is heated by radiation 
from arcs formed between three electrodes placed above the 
charge and supplied with a three-phase current. This furnace 
also rotates on an axis slightly inclined to the vertical, in order 
to mix the charge thoroughly. The lining is magnesite brick. & 
Starting with scrap and oxidized turnings, about one kilowatt 
hour is required for one kilogram of finished steel in the 250 
horse power furnaces used at Turin. 

A furnace designed by Charles Albert Keller for steel refin- 
ing, which was put into industrial use in 1907, is shown in 
Figures 106 and 107. It consists of a crucible with a conduct- 
ing bottom for one electrode and a vertical carbon rod for the 
other. 6 Since carbon must not be brought in contact with 
the melted iron in refining, the bottom must be made conduct- 
ing without the use of carbon, and this was accomplished by 
Keller as follows : Iron bars from 1 to 1| inches in diameter 
are regularly spaced about one inch apart, and are made fast to 
a metallic plate at the bottom, covering the entire area on which 
the bath will rest. Agglomerated magnesia is then rammed, 
while hot, in between the bars. The whole base is surrounded 
by a metallic casing for water cooling. Electrical contact is 
made by the lower plate to which the bars are fastened. The 
furnace is closed by a cover through which the other electrode 
passes. After several months' use a hearth constructed in this 
manner was found to be in as good condition as on the first 
day. The advantage claimed for this arrangement over a 
furnace with two vertical electrodes is that the current is more 
evenly distributed through the charge, and consequently heats 
it more evenly. Of course, the iron bars are melted at their 
upper ends where they come in contact with the melted iron to 
be refined, but the water cooling prevents them from melting 
for more than a few inches of their length. 

4 Trans. Am. Electrochem. Soc. 15, 63, (1909). 
6 Trans. Am. Electrochem. Soc. 15, 86, (1909). 
6 Trans. Am. Electrochem. Soc. 15, 96, (1909). 



THE ELECTROMETALLURGY OF IRON AND STEEL 255 




I _ 1 



> 

/ <* V v ^;oc.a> 






FIGS. 106 and 107. Keller conducting hearth furnace 



256 



APPLIED ELECTROCHEMISTRY 



The Heroult steel refining furnace, 7 as shown in Figure 108, 
consists of a crucible a with a cover b holding a small chimney 
c. As the figure shows, it is arranged for tilting, d are car- 
bon electrodes, which may be moved in a vertical or in a hori- 
zontal direction. In order to use the furnace for Bessemer- 




FIG. 108. The Heroult electric steel furnace 

izing, the tuyeres x are provided. The two electrodes do not 
quite touch the slag on the surface, so that two arcs are pro- 
duced. In passing through the bath, the current, of course, 
divides between the slag and the melted iron in proportion to 
their conductivities, and as melted iron conducts better than 
the slag, a larger proportion would flow through the metal than 
through the slag. The poorest kinds of scrap, high in sulphur 
and phosphorus, are refined in this furnace. The following 
table shows the average refining ability of a 2 J-ton furnace at 
La Praz, Savoy : 

7 Electrochem. Ind. 1, 64, (1902) ; U. S. Pat. 707,776. 



THE ELECTROMETALLURGY OF IRON AND STEEL 257 
TABLE 31 





PEE CENT 


Sulphur 


Phosphorus 


Manganese 


Silicon 


Carbon 


Scrap charged 
Finished steel 


0.052 
0.006 


0.150 
0.009 


0.638 
0.254 


0.062 
0.172 


0.211 
1.013 



For a 5-ton furnace, starting with cold scrap, 600 kilowatt 
hours are necessary to partially refine one long ton of steel, 
and 100 more for the finishing slag. For a 15-ton furnace, 
less power would be required. 

Figure 109 shows a 15-ton three-phase Heroult furnace at 
the South Chicago Works of the Illinois Steel Company. 
The steel to be treated is brought directly from the Bessemer 
converters, and two refining slags are used in the electric 
furnace, the first an oxidizing slag to take out the phosphorus, 
and the second, a deoxidizing slag for removing the sulphur 
and the gases. 8 Power is supplied to the three electrodes by 
three transformers, each of 750 kilowatts capacity. Two 
hundred and forty tons of steel are turned out per day in 16 
heats. The electrodes, 2 feet in diameter and 10 feet in length, 
are the largest ever made in one piece. In cold melting and in 
continuous work, the consumption of electrode is from 60 to 65 
pounds per ton of steel, but when the metal is charged in the 
melted state, the consumption would be reduced to 10 or 15 
pounds per ton of steel. This includes the short ends that 
cannot be utilized. The linings last from three months to 
one year, depending on the care with which the furnace is run; 
the roof suffers most, and generally has to be renewed once a 
month. The best lining for this furnace is magnesite mixed 
with basic slag, with tar for a binder. 

The Paul Girod electric furnace 9 is somewhat similar to the 
Keller furnace, as seen from Figure 110. One or more elec- 



8 Robert Turnbull, Trans. Am. Electrochem. Soc. 15, 139, (1909). 

9 Paul Girod, Trans. Am. Electrochem. Soc. 15, 127, (1909). 



258 



APPLIED ELECTROCHEMISTRY 




THE ELECTROMETALLURGY OF IRON AND STEEL 259 



trodes of like polarity are suspended above the crucible, while 
the electrode of opposite polarity consists of a number of pieces 
of soft steel buried in the refractory material of the hearth at 
its periphery and water cooled at their lower ends. The 
upper ends come in contact with the bath and are melted to a 
depth of 2 to 4 inches. About 55 volts are applied to this 
furnace. For fusing, refining, 
and finishing a charge of cold 
scrap in a 2-ton, furnace, about 
900 kilowatt hours per metric 
ton of steel are required, and in 
an 8 to 10 ton furnace, 700 kil- 
owatt hours. The electrode con- 
sumption is 16 to 18 kilograms 
per metric ton of steel produced 
in a 2-ton furnace, and 13 to 15 
kilograms in an 8 to 10 ton fur- 
nace. The short ends are in- 
cluded as having been used. The 
lining is magnesite or dolomite 
brick or paste, and lasts 40 to 50 
heats without any repairs what- 
ever. 

An entirely different class of 
steel-refining furnaces are those 
having the melted metal in the 
form of a ring, forming the sec- 
ondary of a transformer which is 
heated by an induced current 
from a primary coil of copper 
wire. This type of furnace was 
patented in 1887 by Colby in the 
United States and by Ferranti 
in England. The same principle was applied on a small scale 
in 1900 by F. A. Kjellin at Gysinge, Sweden, without knowing 
at the time that it had been patented by others. 10 Kjellin, 
10 Kjellin, Trans. Am. Electrochem. Soc. 15, 173, (1909). 




Fia. 110. The Girod electric steel 
furnace 



260 



APPLIED ELECTROCHEMISTRY 



however, seems to have been the first to carry this idea out on 
a commercial scale. In 1902 a 225 horse power induction fur- 
nace was in operation at Gysinge, with an output of 4 metric 
tons in 24 hours. This furnace had a magnesite lining in 





FIGS. Ill and 112. Elevation and plan of the Kjellin induction furnace 

place of silica used in the smaller furnace. A silica lining 
lasted only about one week, while the magnesite lasted twelve. 



THE ELECTROMETALLURGY OF IRON AND STEEL 261 

Figures 111 and 112 show the principle of the Kjellin 
furnace. The magnetic circuit C is built up of laminated 
sheet iron. D is the primary circuit, consisting of a number 
of turns of insulated copper wire or tubing. The ring-shaped 
crucible A, for holding the melted metal, is made of refractory 
material. This furnace cannot be started by placing cold 
scrap in the crucible because of the low induced electromotive 
force, but an iron ring must be placed in the crucible and 
melted down, or the crucible must be filled with melted metal 
taken from another source. The power consumption of the 
furnace at Gysinge, starting with cold pig iron and scrap, is 
about 800 kilowatt hours per metric ton of product. This 
furnace has been found very satisfactory for making the 
highest-class steel from pure raw materials. 

There is a limit to the current that can be sent through 
the liquid metal, and consequently a limit to the temperature 
attainable. This is due to a phenomenon first observed by 
Paul Bary in 1903, 11 to which the name " pinch effect " was 
given by Hering. 12 This phenomenon is as follows : When a 
direct or an alternating current passes through a liquid con- 
ductor, the conductor tends to contract in cross section, forming- 
a depression, and if the current is large enough, the metal in 
the trough will separate entirely and break the circuit. This 
is due, of course, to the attraction the different elements of 
the current exert on each other. It is most likely to happen 
at some particular place where the cross section of the ring is 
smaller than elsewhere, and if any infusible material falls into 
this depression, it may prevent the reunion of the liquid and 
cause the charge to .freeze. The largest possible current that 
could be passed through liquid iron in a trough 2 inches deep 
and 1 inch wide is about 3300 amperes ; in a trough 4 by 2 
inches, 9400 amperes ; and in a trough 6 by 3 inches, 17,000 
amperes. 13 Larger currents would cause the metal to separate 

11 Northrup, Trans. Am. Electrochem. Soc. 15, 303, (1909). 

12 Hering, Trans. Am. Electrochem. Soc. 11, 329, (1907) j 15, 255 and 271, 
(1909). 

18 Trans. Am. Electrochem. Soc. 15, 269, (1909). 



262 APPLIED ELECTROCHEMISTRY 

entirely. When a depression is formed, hydrostatic pressure 
balances the pressure due to the current, so that this effect 
is not so likely to give trouble in a deep channel as in a shallow 
one, nor with a heavy metal as with a light one. It has been 
found impossible, for instance, to raise aluminum much above 
its melting point, in a 60 kilowatt induction furnace on account 
of this effect. 14 

The Kjellin furnace is not adapted to working with dephos- 
phorizing and desulphurizing slags, as the annular ring is not 
a convenient shape and offers too small a surface to the attack 
of the slag. 15 A combined induction and resistance furnace 
was therefore invented by Rodenhauser, known as the Rochling- 
Rodenhauser furnace for refining Bessemer steel. A plan and 
an elevation of this furnace are shown in Figures 113 and 114. 
HH &VQ the two legs of the iron transformer core, surrounded 
by the primary windings AA. Surrounding the legs of the 
transformer are the two closed circuits of melted metal, forming 
together a figure 8, in which currents are induced. BB are 
two extra primary coils, from which the current is conducted to 
the metallic plates EE. These are covered by an electrically 
conducting refractory material, through which the current passes 
into the main hearth, D. The result is that the main hearth 
can be made with a much larger cross section than the ring in 
the original Kjellin furnace, and a good power factor can be 
obtained in large furnaces without such a low periodicity as 
was necessary with the original induction furnaces. The mag- 
nitude of the current from the secondary coils is limited by the 
carrying capacity of the refractory material 6r, which would be 
destroyed if too heavily loaded. In refining, the furnace is 
worked as follows : Fluid steel from the converters is poured 
into the furnace, and burnt limestone and mill scale are added 
for forming a basic dephosphorizing slag. This is removed, 
after the reactions are ended, by tilting the furnace. For mak- 
ing rails the phosphorus is reduced sufficiently in one opera- 
tion, but for the highest-class steel it has to be repeated. 

14 FitzGerald, Trans. Am. Electrochem. Soc. 15, 278, (1909). 
16 Kjellin, Trans. Am. Electrochem. Soc. 15, 175, (1909). 



THE ELECTROMETALLURGY OF IRON AND STEEL 263 





FIGS. 113 and 114. Elevation and plan of the Rochling-Rodenhauser furnace 



264 APPLIED ELECTROCHEMISTRY 

After removing phosphorus, carbon is added in the pure state 
when carbon steel is to be made, and a new basic slag is formed 
to remove the sulphur. 

Rochling-Rodenhauser furnaces are also built for three-phase 
currents. 



CHAPTER XIV 

THE FIXATION OP ATMOSPHERIC NITROGEN 

I. INTRODUCTION 

NITROGEN, though chemically an inert element, is of great 
importance to plant and animal life. It forms 80 per cent by 
volume of the atmosphere, but it has been impossible until 
recently to get atmospheric nitrogen in a combined state for 
use in fertilization or in the chemical industries. This was a 
problem of the greatest importance, as the nitrogen removed 
from the soil by crops must be replaced either by adding it 
in the form of some nitrogen compound or by raising a crop, 
such as clover, that assimilates the nitrogen of the air by means 
of a certain kind of bacteroid existing on the root of the plant. 
Consequently, Chili saltpeter is used in large quantities for fer- 
tilization, but as this supply is not expected to last later than 
1940, 1 the discovery of some other means of supplying the 
demand became imperative. 

At present there are three different methods in operation 
of combining atmospheric nitrogen. The first method con- 
sists in heating calcium carbide in pure dry nitrogen to about 
1000 C., whereby nitrogen is absorbed, forming calcium cyana- 
mide, according to the reversible reaction : 

CaC 2 + NCaCN + C. 



The second method consists in oxidizing nitrogen to nitric 
oxide in the electric arc and absorbing the oxide in water or in 
an alkaline solution, and the third and most recent method is 
the direct synthesis of ammonia from its elements. 

1 Edstrom, Trans. Am. Electrochem. Soc. 6, 17, (1904). 
265 



266 APPLIED ELECTROCHEMISTRY 

2. ABSORPTION BY CALCIUM CARBIDE 

According to Moissan, pure carbide is unaffected by nitro- 
gen at 1200 C. 1 The discovery that nitrogen is absorbed by 
commercial calcium carbide and barium carbide was patented 
in 1895 by Adolph Frank and N. Caro. 2 In the case of barium 
carbide 30 per cent forms cyanide in place of cyanamide, 3 while 
in the case of calcium only a trace of cyanide is formed. 

Since 1895 this reaction has been the subject of a number of 
investigations. With regard to the temperature required, it 
has been shown that finely powdered carbide must be heated 
to from 1000 to 1100 C. to bring about complete transforma- 
tion to cyanide. At 800 to 900 some nitrogen is absorbed, 
but the reaction ceases before all the carbide is used up. 4 By 
the addition of other calcium salts, such as calcium chloride, or, 
to a less extent, calcium fluoride, complete nitrification can be 
produced at 700 to 800 C. 5 That the commercial carbide 
can be completely nitrified at 1100 is due to the presence 
of calcium oxide. 6 Commercial calcium carbide containing 75 
to 80 per cent carbide can be made to take up 85 to 90 per 
cent of the theoretical amount of nitrogen, forming a black 
mass of calcium cyanamide, lime, and carbon containing 20 to 
23.5 per cent of nitrogen. 3 Pure calcium cyanamide contains 
35 per cent nitrogen. The reaction by which it is made is 
accompanied by a large evolution of heat, which of course 
is advantageous in its manufacture. According to Caro, this 
heat is sufficient to cause the reaction to proceed of itself when 
once started. 7 

The system consisting of calcium carbide, calcium cyanamide, 
carbon, .and nitrogen, is monovariant, that is, for every tem- 
perature there is a corresponding pressure of the nitrogen at 
which equilibrium exists. This equilibrium has been meas- 

1 C. R. 118, 501, (1894). 2 F ra nk, Z. f. angew. Ch. 19, 835, (1906). 

8 Erlwein, Z. f. angew. Ch. p. 533, (1903). 

4 Foerster and Jacoby, Z. f. Elektroch. 15, 820, (1909). 

5 Bredig, Z. f. Elektroch. 13, 69, (1907). 

6 Foerster and Jacoby, Z. f. Elektroch. 13, 101, (1907). 
* N. Caro, Z. f. angew. Ch. 22, 1178, (1909). 



THE FIXATION OF ATMOSPHERIC NITROGEN 



267 



ured between 1050 C. and 1450 C., and the results are given 
in the plot in Figure 11 5. 8 If the initial pressure of nitrogen 
lies in the region above the line, absorption of nitrogen takes 
place, while if below, any calcium cyanamide present would 



50 



40 



30 



20 



10 



4B 



1000 



1100 



1400 



1500 



1200 1300 

v TEMPERATURE 

FIG. 115. Plot showing pressures and temperatures at which equilibrium of the 
reaction CaC 2 +N 2 ^:CaCN2 + C exists. Pressures are in centimeters of mer- 
cury ; temperatures in centigrade degrees. 

decompose until the nitrogen produced brings the pressure up 
to that corresponding to equilibrium, or until all of the cyan- 
amide is used up. 

The velocity of absorption of nitrogen is proportional to its 
pressure, 9 assuming other conditions constant. At a constant 

8 Thompson and Lombard, Proc. Am. Acad. 46, 247, (1910) ; Met. and Chem. 
Eng. 8, 617, (1910). During proof reading the experiments of Le Blanc and 
Eschmann, with results different from those above, appeared ; see Z. f. Elek- 
troch. 17, 20, (1911). They find that the pressure depends on the nitrogen con- 
tent of the solid phase as well as on the temperature. 

Bredig, Fraenkel, and Wilke, Z. f. Elektroch. 13, 605, (1907). 



268 APPLIED ELECTROCHEMISTRY 

temperature, with a constant surface of carbide exposed, and 
a given amount of nitrogen in a given volume, this law is 
expressed by the differential equation : 



where p is the pressure, t the temperature, and k is a constant. 
Integrated this becomes 



0.43 1 Pi 

where p 2 and p l are the pressures at the beginning and end 
respectively of the time interval t. 

Calcium cyanamide acts in some cases as the calcium salt of 
cyanamide : Ca = N C s N, and in others as the calcium salt 
of the diimide 



With superheated steam the nitrogen is changed to ammonia 
according to the reaction 2 

CaCN 2 + 3 H 2 = CaCO 3 + 2 NH 3 

with a yield 99 per cent. 10 Dicyandiamid, a compound con- 
taining 66 per cent nitrogen, can be made by treating calcium 
cyanamide with water. It has the appearance of ammonium 
chloride, and is probably formed by the following reaction : 

2 CaCN 2 + 4 H 2 = 2 Ca(OH) 2 + (CNNH 2 ) 2 . n 

Calcium cyanide can be made from technical calcium cyana- 
mide by melting with a suitable flux, such as sodium chloride, 
according to the following reversible reaction : 



This use of calcium cyanamide is second in importance only to 
its direct application as a fertilizer. 2 

According to Frank 2 one horse power year can produce 
enough carbide to absorb 772 kilograms of nitrogen, though 
the value actually realized amounts to only 300 to 330 kilo- 

10 Erlwein, Z. f. Elektroch. 12, 551, (1906). 

11 Z. f. angew. Ch. p. 520, (1903). 



THE FIXATION OF ATMOSPHERIC NITROGEN 269 

grams. According to a later statement by Caro, 7 3 horse power 
years is more than sufficient to absorb one metric ton of nitro- 
gen, including the manufacture of the carbide and all the other 
power required in the factory for the grinding and moving 
apparatus, the Linde machines for liquefying air, and so forth. 
Thus a factory with 12,000 horse power produces yearly 20,000 
metric tons of calcium cyanamide containing 20 per cent nitro- 
gen, corresponding to 4000 metric tons of nitrogen. It is in- 
teresting to compare these data with the power required to 
produce the corresponding amount of calcium carbide. An 
average yield of carbide has been shown above to be 5.5 kilos 
of 80 per cent carbide per kilowatt day, corresponding to 1500 
kilos per horse power year. 376 kilograms of nitrogen would 
have to be absorbed by this amount of carbide in order that the 
product should contain 20 per cent nitrogen. This is a little 
above the value 300 to 330 actually obtained as given by Frank. 
If the statement of Caro is correct, and carbide is produced with 
the efficiency assumed above, it means that 90 per cent of the 
power in a cyanamide factory is used for producing the carbide 
alone. 

Nitrogen is obtained by the Linde process or by removing 
the oxygen with hot copper. It must be free from oxygen, for 
this would produce carbon monoxide, which decomposes both 
carbide and cyanamide. 7 Caro states that moisture must be also 
absent, though Bredig, Fraenkel, and Wilke's 9 experiments 
showed that when the nitrogen was saturated with water vapor 
at 22, a little more nitrogen was absorbed than when dry. 

Besides lime and carbon, there are impurities in technical 
cyanamide, consisting of nitrogen compounds, such as urea, 
guanidine, and calcium carbamate. In fresh samples these 
impurities are small in quantity, but increase on standing or 
by the presence of water vapor. All of these substances are 
easily assimilated by plants. 7 

The manufacture of calcium cyanamide was begun on a large 
scale in 1905 at Piano d'Orta, Italy, 10 and in 1908 there were 
11 factories in Europe making this substance. 12 Norway and 
i2Min. Ind. 17, 105, (1908). 



270 APPLIED ELECTROCHEMISTRY 

Sweden are unusually favorable localities for the nitrogen 
industry on account of the large amount of cheap water power. 
Recent estimates on power in these countries are as follows : 13 





AVAILABLE 


DEVELOPED 


Sweden 


4,000,000 h. p. 


400,000 h. p 


Norway . 


5 000 000 h. p. 


500 000 h p 









The figures under " developed " refer to plants in operation or 
under construction. There is a 20,000 horse power plant for 
the production of cyanamide and calcium carbide at Odda, 
Norway, having a capacity of 32,000 short tons of carbide and 
12,500 tons of cyanamide per year. The nitrogen, which must 
not contain over 0.4 per cent oxygen, is obtained by the Linde 
process. The furnaces in which the carbide is heated with 
nitrogen are charged with about 700 pounds and produce 2000 
pounds of cyanamide containing 20 per cent nitrogen per week. 
In 1909 this industry was introduced on this side of the 
Atlantic by the American Cyanamide Company, which owns 
the exclusive rights for manufacturing nitrolime in this country. 
A factory is now in operation at Niagara Falls, Ontario. 14 The 
product is to contain 12 to 15 per cent nitrogen, 10 per cent 
carbon, and 25 per cent calcium sulphate. Free lime is to be 
eliminated as is demanded by American trade. 

3. THE OXIDATION OF NITROGEN 

Priestley l was the first to observe that electric sparks in air 
produced an acid, though he mistook it for carbonic acid. 
Later Cavendish 2 repeated the experiments and showed the 
true nature of the acid produced, which is now known to be a 
mixture of nitrous and nitric acids. From the time of Caven- 

13 Electrochem. and Met. Ind. 7, 212 and 360, (1909). 

14 Met. and Chem. Eng. 8, 227, (1910). 

1 Experiments and Observations on Different Kinds of Air, 4, 286. Preface 
dated 1779. Also Ostwald, Elektrocheinie, p. 11. 

a Phil. Trans. 75, 372-384, (1797). Also Alembic Club Reprints, No. 3, p. 39. 



THE FIXATION OF ATMOSPHERIC NITROGEN 



271 



dish until within the last twenty years nothing of importance 
was done toward explaining this phenomenon. Since 1890, 
however, it has received considerable attention, so that now, 
principally due to the work of Nernst and Haber, the conditions 
under which the reaction N 2 + O 2 ^ 2 NO takes place are well 
known. 

Nernst and his assistants have measured the thermal equilib- 
rium concentrations of nitrogen, oxygen, and nitric oxide at 
different temperatures with the results in Table 32. 3 

TABLE 32 
Per cent by Volume of Nitric Oxide in the Equilibrium Mixture formed from Air 



DEGREES ABSOLUTE 


PER CENT 


NO 


OBSERVER 


1811 


Observed 

0.37 


Computed 

0.35 


Nernst 


1877 


0.42 


0.43 


Jellinek 


2023 


0.52 to 0.80 


0.64 


Jellinek 


2033 


0.64 


0.67 


Nernst 


2195 


0.97 


0.98 


Nernst 


2580 


2.05 


2.02 


Nernst-Finckh 


2675 


2.23 


2.35 


Nernst-Finckh 











The values in the third column were computed by the Van't 
Hoff equation, with Berthelot's value of 21,600 calories for 
the heat of the reaction. These experiments show that at the 
temperatures given the velocity of decomposition is so low that 
the gas can be cooled without decomposition of the nitric oxide 
already formed. 

The free energy of the reaction is given by the equation 4 



= Q -ET log- 



+ 2.45 T, 



in which Q = 21,600 calories. By means of this equation 
the per cent of nitric oxide corresponding to the equilibrium 
at any temperature can be computed by placing the right-hand 

Z. f. anorg. Ch. 49, 213, (1906). 

* Haber, Thermodynamics of Technical Gas Reactions, p. 105, (1908). 



272 



APPLIED ELECTROCHEMISTRY 



side equal to zero, which is the equilibrium condition. The 
experiments of Finckh were carried out by exploding air mixed 
with detonating gas ; the others by drawing air through plati- 
num or iridium tubes heated electrically. The good agreement 
between the calculated and observed values shows that at least 
in these experiments the nitric oxide formed is due only to the 
high temperature, as the concentration is that required by 
thermodynamics. 

This reaction is bimolecular between 650 C. and 1750 C., 5 
that is to say, it should be written N 2 + O 2 = 2 NO. Le Blanc 
and Niiranen, however, have found that above 3000 C. the 
reaction is monomolecular. 6 Tables 33 and 34 give the veloci- 
ties of the reaction in both directions at different temperatures. 6 

TABLE 33 

Time in Minutes necessary to decompose Pure Nitric Oxide at Atmospheric Pres- 
sure, Half into Nitrogen and Oxygen 



DEGREES ABSOLUTE 


TIME IN MINUTES 


DEGREES ABSOLUTE 


TIME IN MINUTES 


900 


7.35 10 3 


2100 


1.21 10- 3 


1100 


5.80 10 2 


2300 


8.40 10- 5 


1300 


4.43 10 1 


2500 


5.76 10- 6 


1500 


3.30 


2700 


3.92 10- 7 


1700 


2.47 10- 1 


2900 


3.35 10~ 8 


1900 


1.47 lO- 2 


3100 


2.25 10- 9 



TABLE 34 
Time required to produce from Air One Half the Possible Amount of Nitric Oxide 



DEGREES ABSOLUTE 


TIME IN MINUTES 


DEGREES ABSOLUTE 


TIME IN MINUTES 


1500 


1.81 10 8 


2500 


1.77 10~ 4 


1700 


5.90 10 1 


2700 


8.75 10- 6 


1900 


2.08 


2900 


5.75 10- 7 


2100 


8.43 10- 2 


3100 


3.10 10- 8 


2300 


3.75 10-8 







5 Jellinek, Z. f. anorg. Ch. 49, 229, (1906). 

6 Z. f. Elektroch. 13, 303, (1907). 



THE FIXATION OF ATMOSPHERIC NITROGEN 



273 



From these results it would appear that the best yield of 
nitric oxide would be obtained by heating the gas to the 
highest temperature from which it could be chilled so suddenly 
that decomposition would not take place. It has been shown, 
however, that nitric oxide can be produced by the silent dis- 
charge of electricity where there is very little elevation of 
temperature. 7 This fact suggested to Haber and Koenig 8 the 
possibility of obtaining better yields by using a comparatively 
cool arc, which could be realized by inclosing it in a tube 
surrounded by water. Below 3000 C. any oxide produced by 
the impact of electrons would not be decomposed rapidly by 
the heat even if the concentration due to the electrical effect 
were greater than that due to the thermal. In fact they found 
that by using a cooled arc and by reducing the pressure to the 
most favorable value of 100 millimeters, concentrations of 
nitric oxide were obtained which could be explained thermally 
only on the assumption that the thermal equilibrium correspond- 
ing to over 4000 absolute had been obtained and that the gas 
had been chilled suddenly enough to preserve it. Such a high 



TABLE 35 

Concentrations of Nitric Oxide obtained at 100 mm. Pressure by an Arc inclosed in 

a Cooled Tube 



INITIAL GAS MIXTURE IN 






THERMODYNAMICALLY COM- 


PER CENT BY VOL. 


7>NO 


NO CONTENT 


PUTED TEMP. ABS. 




i i 


IN PER CENT 






_) O 2 ft N^2 


-y 




o, 


N, 






Haber 


Nernst 


20.9 


79.1 


0.284 


9.8 


4365 


4334 


48.9 


51.1 


0.337 


14.4 


4686 


4650 


44.4 


55.6 


0.337 


14.3 


4686 


4650 


75.0 


25.0 


0.357 


12.77 


4805 


4767 


81.7 


18.3 


0.397 


12.1 


5042 


5000 



7 Warburg and Leithauser, Ann. d. Phys. (4) 20, 743, (1906), and 23, 209, 
(1907). 

8 Z. f. Elektroch. 13, 725, (1907). 



274 APPLIED ELECTROCHEMISTRY 

temperature in their arc seemed impossible ; consequently the 
oxide must have been produced directly by the impact of ions. 
Table 35 gives the concentrations of nitric oxide obtained with 
the temperature corresponding, on the improbable assumption 
that this concentration corresponds to a thermal and not to an 
electrical equilibrium. The temperatures were computed both 
by Haber's formula given above and by the Van't Hoff formula 
as used by Nernst. 

In later experiments as high as 17.8 per cent nitric oxide was 
obtained. 9 It was further found that the same concentration 
is obtained under similar conditions from either nitric oxide 
or from air and oxygen, showing that we have in this case 
an electrical equilibrium. If the temperature is too high, the 
electrical equilibrium is obliterated by the thermal. On the 
other hand, the electrical energy necessary to produce ioniza- 
tion increases considerably when the temperature falls below 
white heat. There will therefore be a most favorable region 
of temperature within which the nitric oxide produced by the 
impact of ions will not be decomposed and when too much 
electrical energy is not required for ionization. 8 It would, 
therefore, seem that the best way to try to obtain better re- 
sults is to employ a cool arc rather than by attempting to heat to 
a higher temperature and chill more suddenly. 

The energy efficiency was not determined in these experi- 
ments. In later ones, 10 with a cooled arc, the efficiency, when 
the concentration of the nitric acid obtained was 3.4 per cent, 
was 57 grams of nitric acid per kilowatt hour, or 500 kilo- 
grams per kilowatt year of 365 x 24 hours. With a cooled 
arc and a direct current, Holweg and Koenig n obtained 
nitric acid at a concentration of 2.5 per cent and an efficiency 
corresponding to 80 grams of nitric acid per kilowatt hour, 
the most favorable energy efficiency ever reached. Increas- 
ing the pressure above atmospheric does not increase this 
efficiency. 12 

Z. f. Elektroch. 14, 689, (1908). 10 Z. f. Elektrock. 16, 795, (1910). 

" Z. f. Elektroch. 16, 809, (1910). 
12 Haber and Holweg, Z. f. Elektroch. 16, 810, (1910). * 



THE FIXATION OF ATMOSPHERIC NITROGEN 



275 



On cooling down, the colorless nitric oxide changes to the 
brown dioxide of nitrogen, since the reversible reaction 

NO + \ r 2 ^ N0 2 

is displaced from left to right on cooling. 

Table 36 shows how the dissociation of nitrogen dioxide is 
affected by the temperature : 13 



TABLE 36 



DEGREES CENTIGRADE 


PRESSURE IN CENTIMETERS 


PER CENT OF NO 2 DECOMPOSED 


130 


71.85 




184 


75.46 


5.0 


279 


73.72 


13.0 


494 


74.25 


56.5 


620 


76.00 


100.0 



It will be interesting to compute from a purely thermal 
standpoint the energy necessary to produce nitric acid and to 
compare this result with those actually found by different ex- 
perimenters. Assuming the temperature of the high tension 
arc to be 4200 C., the calculation is as follows. 14 From the 
equation given above at this temperature 



=0.29, 



and if the original mixture is air, the final composition is : 

NO O 2 N 2 

10 per cent 16 per cent 74 per cent 

Ten moles of nitric oxide with air and water yield 630 grams of 
nitric acid. Therefore, in order to get this amount of acid, 
100 moles must be heated to 4200 C., besides which 10 x 21,600 
calories must be supplied for the reaction. Assuming the spe- 

18 Nernst, Theoretische Chemie, p. 455, 6th ed. See also Bodenstein and Kata- 
yama, Z. f. Elektroch. 15, 244, (1909). 

14 Haber, Thermodynamics of Technical Gas Reactions, p. 268. 



276 APPLIED ELECTROCHEMISTRY 

cific heat of the permanent gases to be 6.8 -f 0.0006 calories 
per mole, the total energy will be : 

100 (6.8 + 0.0006 x 4200) 4200 + 216,000 = 4,130,000 calories. 

This corresponds to 4.71 kilowatt hours for 630 grams of nitric 
acid, or 134 grams per kilowatt hour. If the arc were 1000 
lower, the result would be 93.5 grams per kilowatt hour. 

The results obtained with a cooled arc are not due to ther- 
mal equilibrium, and of course have no relation to this calcula- 
tion. Unless special precautions were taken to use a cooled 
arc, the results may be assumed to be due to thermal and not 
to electrical causes. This is the case in the following examples. 

Lord Rayleigh 15 obtained an absorption of 21 liters an hour 
with 0.8 kilowatt, using a mixture of 9 parts of air and 11 of 
oxygen. This corresponds to 46 grams of pure nitric acid per 
kilowatt hour, assuming the gas was measured at 20 C. and at 
atmospheric pressure. McDougall and Howies 16 with an ar- 
rangement similar to that of Lord Rayleigh obtained 33.5 grams 
of nitric acid per kilowatt hour. McDougall and Howies were 
the first to make a small experimental plant for the production 
of nitric acid from the air. 17 It seems not to have got beyond 
the experimental stage, however. 

The first 18 attempt to carry out the oxidation of nitrogen on 
a commercial scale was that of the Atmospheric Products Com- 
pany at Niagara Falls, using the patents of Bradley and Love- 
joy. Their first apparatus 19 was similar to that of McDougall 
and Howies and consisted in a number of small compartments 
in which an arc was formed between electrodes in the form of a 
hook at the points nearest together, as shown in Figure 116. The 
arc then ran along the electrodes, thereby becoming longer, 
until it went out, whereupon the arc was formed again. This 

i 5 Journ. Chem. Soc. 71, 181, (1897). 

, 16 Memoirs and Proceedings of the Manchester Literary and Phil. Soc. (IV) 
44, 1900, No. 13. 

17 Huber, Zur Stickstoff Frage, p. 41, Bern, (1908). 

18 Donath and Frenzel, Die Technische Ausinetzung des Atmospharischen 
Stickstoffes, p. 126, (1907). 

U. S. Pat. 709,867, (1902). 



THE FIXATION OF ATMOSPHERIC NITROGEN 



277 



arrangement was supplanted by a single apparatus, shown in 
Figures 117 and 118, in which 6900 arcs were formed per 
second. 20 This consisted in an iron cylinder 5 feet high, 4 feet 
in diameter, in the center of which was a rotating shaft carry- 
ing a series of radial arms, the ends of which were tipped with 




FIG. 116. First apparatus of 
Bradley aud Lovejoy 



platinum. Six rows of 23 inlet wires projected through the 
cylinder and terminated in a platinum hook. As the radial 
arms rotated, their platinum tips passed the hooks on the inlet 
wires, coming within one millimeter of touching at the nearest 
point. An arc was formed which was drawn out from 4 to 6 
inches before going out. The arms were so arranged that the 

20 J. W. Richards, Electroch. Ind. 1, 20, (1902) ; U. S. Pat. 709,868, (1902). 



278 



APPLIED ELECTROCHEMISTRY 



arcs between them and the inlet wires were formed successively 
rather than simultaneously. The central shaft made 500 rota- 
tions per minute. Each inlet wire had in series with it an in- 
duction coil 12 inches long and 5 inches in diameter, wound 
with very fine wire and immersed in oil. The self-induction of 
the coil caused the spark to be drawn out to a greater length 
than would be possible without induction. A direct current 




FIG. 117. Vertical section of final 
apparatus of Bradley and Lovejoy 



generator was especially designed for this plant, giving 8000 
volts and 0.75 ampere. Air passed in at the rate of 11.3 cubic 
meters per second and came out of the cylinder containing 2.5 
per cent nitric oxide. 21 The yield is said to have been one 
pound of acid per 7 horse power hours, or 87 grams per kilo- 
watt hour. The process was not successful, however, and the 
company was forced to give up the experiments in 1904. 
21 Haber, Z. f. Elektroch. 9, 381, (1903). 



THE FIXATION OF ATMOSPHERIC NITROGEN 



279 



Though the yield compared favorably with the calculations 
given above, the . apparatus was very complicated and subject 
to considerable wear. The iron drum corroded rapidly in spite 
of the inside coating of asphalt paint. 18 

The first successful process for oxidizing nitrogen on a com- 
mercial scale is that of Birkeland and Eyde. A factory for 
carrying it out was started at Notodden, Norway, in May, 1905. ^ 
The high voltage flame is formed between two electrodes con- 
sisting of water-cooled copper tubes 1.5 centimeters in diameter 




FIG. 118. Horizontal section of final apparatus of Bradley and Lovejoy 

with 0.8 centimeter between the ends. An alternating current 
of 50 cycles per second is supplied to the electrodes at 5000 
volts. In order to spread the flame over a large area an 
electromagnet is placed at right angles to the electrodes so that 
the terminals lie between the poles of the magnet. The 
voltage is sufficiently high to cause the flame to form of itself 
between the electrodes at their nearest points, whereupon the 
magnetic field causes the ends of the flame to travel along the 
electrodes until the current is reversed. A new flame is then 
started on the other side of the electrodes. When the furnace 
22 Birkeland, Trans. Faraday Soc. 2, 98, (1906). 



280 



APPLIED ELECTROCHEMISTRY 



is running properly a flame is formed at each reversal of the 
current every ^ of a second, though if the distance between 




FIG. 119. Electric disc in the furnace of Birkeland and Eyde 

the electrodes is too short or the magnetic field too strong, 
several hundred flames may be started during one period. The 

magnetic field is 

J V 4000 to 5000 lines 

per square centi- 
meter at the center. 
The result of this 
combination is an 
electric disk flame, 
as shown in Figure 
119. This is in- 
closed in a narrow 
iron furnace lined 
with fire brick, form- 
ing a chamber from 
5 to 15 centimeters 
wide, shown in 
Figure 120. Air 

120. - Vertical section of furnace of Birkeland I* 8808 in tlir U S h 

and Eyde the walls and leaves 




THE FIXATION OF ATMOSPHERIC NITROGEN 281 

the furnace at a temperature between 600 and 700 C., con- 
taining one per cent of nitric oxide. From the furnace the 
gases pass through a steam boiler in which they are cooled 
to 200 C., and then through a cooling apparatus in which 
their temperature is reduced to 50 C. They then enter 
oxidation chambers with acid proof lining, where the reaction 
NO + $ O 2 = NO 2 is completed. 

The next step is to absorb the nitrogen dioxide. This is 
done in two sets of five stone towers whose inside dimensions 
are 2 x 2 x 10 meters. The first four towers are filled with 
broken quartz over which water trickles. The fifth tower is 
filled with brick, and the absorbing liquid is milk of lime, giving 
a mixture of calcium nitrate and nitrite. Nitric acid is 
formed in the first four towers with concentrations as follows : 

FIRST SECOND THIRD FOURTH 

50 % HXO 3 25 % HNO 3 15% HNO 3 5% HNO 3 

The liquid from the fourth tower is raised by compressed air 
to the top of the third, that from the third to the top of the 
second, and so on until fifty per cent nitric acid is formed. 
Some of this acid is used to decompose the nitrate-nitrite 
mixture from the fifth tower. The nitric oxide thereby 
evolved is sent into the absorbing system again. About 97 
per cent of the entire quantity of nitrous gases passed through 
the absorbing system is absorbed. 23 The resulting solution of 
calcium nitrate and the rest of the stored-up acid is treated in 
another set of tanks with lime, producing neutral calcium 
nitrate. This is evaporated in iron by the steam from the 
boilers above mentioned till a boiling point of 145 C. is reached, 
corresponding to 75 or 80 per cent nitrate and containing 13.5 
per cent of nitrogen. This is poured into iron drums of 200 
liters capacity, where it solidifies. Another method is to 
crystallize from a boiling point of 120 C. This yields calcium 
nitrate with four molecules of water. 

In 1906 at the Notodden Saltpeter Manufactory there were 
three 500-kilowatt furnaces in constant activity. The volume 
28 Eyde, Electrochem. and Met. Ind. 7, 304, (1909). 



282 APPLIED ELECTROCHEMISTRY 

of air treated was 75000 liters per minute. The yield was 
about 500 kilograms of pure nitric acid per kilowatt year, or 
57 grams per kilowatt hour. 

In place of the smaller furnaces those now used absorb 1600 
kilowatts, of which 35 are now in operation at Notodden, 8 in 
series. The disk flame has a diameter of 2 meters and a 
thickness of 10 centimeters. 24 

During the year 1908 the profits of the Notodden factory were 
25 per cent of the total receipts, amounting to 500,000 krone, 
or $ 135,000. M The company using the Birkeland-Eyde process 
has combined with the Badische Anilin und Sodafabrik, which 
has developed another furnace, described below, so that the re- 
sults of a factory under construction at Notodden in 1909 will 
decide which furnace will be the one for the final large plant. 25 
Up to February, 1909, 16,000,000 had been invested at Notodden 
and Svalgfos and on the rivers Rjukan and Vamma. By the 
end of 1910 these plants will be completed and the investment 
will amount to fl^OOO^OO. 25 

The furnace of the Badische Anilin und Sodafabrik of 
Ludwigshafen, Germany, was invented in 1905 by Schonherr 
and Hessberger. 26 An alternating current arc is very easily 
extinguished, especially if air is blown across it. The principle 
underlying this furnace is that an alternating current arc loses 
its unstable character and becomes as quiet as a candle if a cur- 
rent of air is passed around it in a helical path. With this 
method of air circulation the arc may be included in a metallic 
tube without risk of its coming in contact with the sides of the 
tube. A cross section of the apparatus is shown in Figure 121. 
It consists of a number of concentric vertical iron tubes. The 
electrode at the bottom is an iron rod adjustable within a water- 
cooled copper cylinder. The iron is slowly eaten away, and is 
fed in at about the rate of one electrode in three months. The 
electrode Z is for starting the arc by bringing it in contact with 

24 Birkeland, Electrochem. and Met. Ind. 7, 305, (1909). 

25 Eyde, Z. f. Elektroch, 15, 146, (1909). 

2^ Electrochem. and Met. Ind. 7, 245, (1909) ; Trans. Am. Electrochem. Soc. 
16, 131, (1909). 




FIXATION OF ATMOSPHERIC NITROGEN 283 

E. There is of course an induction coil 

in series with the arc to make it steady 

\ and prevent the current from being too 

large on starting. When Z is drawn 

back the arc is formed between E and 

* the walls of the tube. The air then 

| drives it up along the tube until it 

| reaches the other water-cooled end, JT, 

within which the arc terminates. 6r r 

2 6r 2 , and 6r 3 are peep holes for observing 
! , the ends of the arc. In the 600 horse 
1 .- power furnaces at Kristianssand, Nor- 
bj> way, the arc is 5 meters long, and 7 
8 | meters in the 1000 horse power fur- 
H ' naces. The circulation of the air is 
g evident from the figure. 

The plant at Kristianssand, the fur- 

3 nace room of which is shown in Figure 
122, has been in operation since the 
autumn of 1907. Three-phase currents 

4 are used, and the furnaces are connected 
in star. The power factor varies between 

H 0.93 and 0.96. It is estimated that 3 per 
cent of the power is used in the formation 
of nitric oxide, 40 per cent is recovered 
in the form of hot water, 17 per cent is 
lost by radiation, 30 per cent is used in 
the steam boiler, and 10 per cent is 
removed by water cooling after the 
erases have passed the steam boiler. 

O T 

The nitric oxide is absorbed by milk of 
lime. The final product is calcium 
nitrite containing 18 per cent nitrogen. 
The yield per kilowatt hour is not given. 
A third process for the fixation of at- 
mospheric nitrogen, invented by H. and 
G. Pauling, is carried out near Inns- 



284 



APPLIED ELECTROCHEMISTRY 



bruck, Tirol, by the " Salpetersaure-Industrie-Gesellschaft." 27 
The arcs are produced between curved electrodes, as shown in 
Figure 123. The arc is lighted where the electrodes are near- 
est together, is blown upwards by the hot air rising between 




FIG. 122. Furnace room at Kristianssaud 

the electrodes, and is broken every half period of the alternating 
current. Another arc is then formed, and so on. In Figure 123 
c represents two thin adjustable blades for starting the arc. 
Air is blown in through the tube e. The electrodes are iron 
pipes, water-cooled and separated by about 4 centimeters at 
, 27 Electrochem. and Met. Ind. 7, 430, (1909). 



THE FIXATION OF ATMOSPHERIC NITROGEN 



285 



their nearest point. Their life is about 200 hours. With a 
400 kilowatt furnace of 4000 volts the length of the flame is 
about one meter. Cooling is produced by passing cold air into 
the upper part of the flame from the side. The concentration 
of the nitric oxide is about 1.5 per cent. The furnaces used 
have two arcs in series. 
Six hundred cubic 
meters of air per hour 
pass through the fur- 
nace, excluding the 
cooling air. The 
yield is 60 grams of 
nitric acid per kilo- 
watt hour. At pres- 

* FIG. 123. Electrodes in lurnace of 

ent there are 24 fur- H. and G. Pauling 

naces in operation at 

Innsbruck, having a capacity of 15,000 horse power. The 

products are nitric acid and sodium nitrite. Two other plants 

for carrying out this process, each of 10,000 horse power, are 

in course of erection, one in southern France and the other in 

northern Italy. 

A number of other furnaces for the oxidation of nitrogen 
have been invented, but their descriptions are omitted here 
because they are not in operation on a commercial scale. 




4. THE SYNTHESIS OF AMMONIA 

The third method of fixing nitrogen, that has just recently 
been taken up by the Badische Anilin und Sodafabrik, 1 is to 
make it combine directly with hydrogen to form ammonia, ac- 
cording to the reversible reaction : 



This reaction takes place from left to right with the evolution 
of about 12,000 calories, 2 so that the quantity of ammonia gas in 
the equilibrium mixture decreases as the temperature rises. 

1 Haber, Z. f. Elektroch. 16, 242, (1910). 

2 Landolt and Bernstein's Tables, 3d ed. p. 427. 



286 



APPLIED ELECTROCHEMISTRY 



The velocity of the reaction, on the other hand, of course in- 
creases with the temperature, but does not reach a value that 
adjusts the equilibrium rapidly below a temperature of 750 C. 3 
The composition of the equilibrium mixtures for different tem- 
peratures and two different pressures, when the free hydrogen 
and nitrogen are present in the same proportion as in ammonia, 
is given in Table 37. 4 

TABLE 37 



DEGREES 


PRESSURE IN 


VOL. PER CENT 


PRESSURE IN 


VOL. PER CENT 


CENTIGRADE 


ATMOSPHERES 


NH, 


ATMOSPHERES 


NH 3 


700 


30 


0.654 


1 


0.0221 


801 


30 


0.344 


1 


0.0116 


901 


30 


0.207 


1 


0.00692 


974 


30 


0.144 to 0.152 


- 1 


0.0048 to 0.0051 



It is evident from this table that unless some catalytic agent 
can be found that would give the reaction high velocity at a 
temperature considerably below 750, very little ammonia could 
be obtained at atmospheric pressure. Since, however, there is 
a decrease in volume when ammonia is formed from an equiva- 
lent amount of nitrogen and hydrogen, there must be an in- 
crease in the relative amount of ammonia in an equilibrium 
mixture when the pressure is increased. It is evident from 
the table that the volume per cent of ammonia in such a mixture 
is directly proportional to the pressure, as long as the relative 
amounts of free hydrogen and nitrogen are kept constant. 

Jost 5 has obtained somewhat lower values for the amount 
of ammonia in the equilibrium mixture. Table 38 gives his 
results obtained at a total pressure of one atmosphere, and those 
of Haber taken from the table above for comparison. 

Haber's results at one atmosphere are in good agreement 
with the values calculated from his results at 30 atmospheres, 
and therefore are more reliable than Jost's. 

8 Haber, Thermodynamics of Technical Gas Reactions, p. 202, (1908). 
* Haber and Le Rossignol, Z. f. Elektroch. 14, 193, (1908). 
5 Z. f. Elektroch. 14, 373, (1908). 



THE FIXATION OF ATMOSPHERIC NITROGEN 
TABLE 38 



287 





VOLUME PER CENT NH 8 


T* r* 






Haber 


Jost 


700 


0.0221 


0.018 


800 


0.0116 


0.0090 


900 


0.0069 


0.0050 


974 


0.0048 to 0.0051 


0.0035 



Haber lias subsequently developed this process further and 
showed in a lecture 1 a small apparatus working at 185 atmos- 
pheres that produced hourly 90 grams of liquid ammonia. In 
the earlier experiments finely divided iron on asbestos was used 
as a catalyzer, but in these later experiments, uranium was 
substituted for iron. This method is said to require compara- 
tively little power, and will therefore not be confined to places 
where cheap water power is available. No numerical values of 
the efficiency of this method, however, are given. 

5. CONCLUSION 

Having described the three general methods of fixing atmos- 
pheric nitrogen now in operation, it will be interesting to com- 
pare the actual amounts of nitrogen fixed for a given amount 
of power by the three methods. This is possible only for the 
absorption by carbide and the direct oxidation. 

Since 12,000 horse power or 8850 kilowatts can fix 4,000,000 
kilograms of nitrogen l per year as calcium cyanamide, one kilo- 
watt hour corresponds to 51.6 grams of nitrogen. The yield 
by the Birkeland-Eyde process is about 57.1 grams of pure 
nitric acid per kilowatt hour, 2 corresponding to 12.7 grams of 
nitrogen. The cyanamide process therefore fixes about four 
times as much nitrogen as the direct oxidation for the same ex- 
penditure of power. 

i Frank, Z. f. angew. Ch. 19, 835, (1906). 

2 Birkeland, Trans. Faraday Soc. 2, 98, (1906); Haber, Z. f. Elektroch. 10, 
551, (1906). 



CHAPTER XV 

THE PRODUCTION OF OZONE 

1. GENERAL DISCUSSION 

IN 1785 Van Marum observed that oxygen through which 
an electric spark had passed had a peculiar odor, and that it at 
once tarnished a bright surface of mercury. 1 Nothing was 
done to throw light on this phenomenon until 1840, when it 
was investigated by Schonbein. He had observed for a num- 
ber of years previously that during the electrolysis of aqueous 
solutions an odor is produced in the gas evolved at the anode 
similar to that resulting from the discharge of electricity from 
points. 2 He described a number of the properties of this sub- 
stance, and suggested the name ozone, from 6'&>i>, meaning 
smelling. For many years the chemical nature of this oxidiz- 
ing principle was unknown, but it was found eventually, after 
a great number of investigations, to be simply condensed 
oxygen with the formula O 3 . 

The formation of ozone from oxygen is an endothermic 
reaction. The heat absorbed in the production of one mole 
of ozone, as determined by different investigators, is given 
in the following table : 3 

Berthelot, indirect, 1876 29,800 calories 

Mulder and v. d. Meulen, indirect, 1883 . . . 33,700 calories 

v. d. Meulen, indirect, 1882 32,800 calories 

v. d. Meulen, direct, 1883 36,500 calories 

Jahn, direct, 1908 . 34,100 calories 

1 Roscoe and Schorlemmer, Treatise on Chemistry, 1, 256, (1905). 

2 Pogg. Ann. 50, 616, (1840). 

8 Stephan Jahn, Z. f. anorg. Ch. 48, 260, (1905). 

288 



THE PRODUCTION OF OZONE 289 

Since heat is absorbed in the production of ozone, thermo- 
dynamics requires that the equilibrium existing in a mixture of 
oxygen and ozone be displaced in the direction of a greater 
ozone concentration by an increase in the temperature of the 
mixture. In order to prove this experimentally, it is necessary 
to heat the oxygen to a temperature high enough to produce a 
measurable quantity of ozone, and then, by cooling suddenly, to 
prevent the decomposition of the ozone formed. This has been 
done by blowing air or oxygen against a hot pencil, such as is 
used in a Nernst lamp, 4 and also by dipping a hot Nernst 
pencil, or hot platinum, in liquid air. 5 

The free energy decrease which accompanies the decomposi- 
tion of ozone into oxygen has been determined from potential 
measurements. 6 At C. the potential of the cell O 3 | electro- 
lyte H 2 equals 1.90 volts, and that of the cell O 2 | electrolyte H 2 
equals 1.25 volts. The reactions which take place in these two 
cells, with the corresponding free energy changes, are therefore 
given by the following equations : 

2 O 3 + 2 H 2 = 2 O 2 + 2 H 2 O + 4 F x 1.90 joules, 
O 2 + 2 H 2 = 2 H 2 O + 4 F x 1.25 joules, 

where F is the electrochemical equivalent. The difference 
between these two equations gives : 

2 O 3 = 3 O 2 + 4 F x 0.65, or O 3 = f O 2 + 30,000 calories. 

From this result the following equilibrium concentrations at 
high temperatures may be calculated : 

Temperature on absolute scale . . 1000 1400 1800 2200 

Pres. ozone in atmospheres, in equi- 
librium with oxygen at one 

atmosphere 0.000029 0.0032 0.038 0.18 

(0.007) (0.03) 

The above results are only approximate, for the very divergent 
values inclosed in parentheses are within the experimental 
error. 

4 Fischer and Marx, B. B. 40, 443, (1907). 

5 Fischer and Braemer, B. B. 39, 996, (1906). 

6 Stephan Jahn, Z. f. anorg. Ch. 60, 332, (1908). 



290 APPLIED ELECTROCHEMISTRY 

It will be seen from these results that ozone, in the concen- 
trations ordinarily prepared, amounting to several per cent by 
volume, is in a state of unstable equilibrium, and it conse- 
quently decomposes slowly on standing. This reaction is 
lii molecular ; 7 that is, 
'J' dn = -kn* dt, 

where n is the number of moles per cubic centimeter, k is a 
constant, and t is the time. The velocity of this reaction is 
given in Table 39. ft is the number of grams of ozone in one 
liter that would decompose per minute if its initial concentra- 
tion were one gram per liter. 

TABLE 39 



TEMPERATURE 





16 


0.0000492 


100 


0.157 


126.9 


1.77 



At 16 one per cent of pure ozone would decompose in 1.7 
hours, and 50 per cent in 167 hours. These values apply to 
ozone in contact with concentrated sulphuric acid, over which 
the pressure of water vapor is 0.0021 millimeter of mercury. 
If the pressure of water vapor is 0.154 millimeter, the velocity 
of decomposition at lOO^is found to be 22 per cent greater. 

The decomposition of ozone takes place in steps, the reaction 
whose velocity is measured being 

O + 3 = 2 2 . 8 

Ozone may be produced by the action of ultra-violet light, 
and of the silent discharge of electricity on oxygen ; by heat- 
ing and suddenly chilling oxygen, and by electrolysis. While 
the silent electric discharge is the only method used commer- 
cially for the manufacture of ozone, it will be interesting to 

7 Warburg, Ann. d. Phys. 9, 1286, (1902), and 13, 1080, (1904). 

8 Jahn, Z. f. anorg. Ch. 48, 260, (1005). 



THE PRODUCTION OF OZONE 291 

compare the yield per kilowatt hour attained by the silent dis- 
charge with some of the other methods. By blowing air 
against a hot Nernst pencil, the yield was found to be one 
gram 4 per kilowatt hour ; and by dipping hot bodies in liquid 
air, about 3.5 grams. 5 The concentration of the ozone in bot'^i 
cases was less than three per cent. By electrolyzing solutions 
of sulphuric acid of specific gravity between 1.075 and 1.1 
with a water-cooled platinum anode, as high as 17 per cent by 
weight of the oxygen given off at the anode has been obtained 
in the form of ozone. 9 Assuming three volts sufficient to 
electrolyze the solution, the yield in oxygen per kilowatt hour 
would be 10 grams, and if 17 per cent of this were ozone, the 
yield would be only 1.7 grams per kilowatt hour. When com- 
pared with 70 grams per kilowatt hour, the yield obtained with 
the silent discharge, these methods are seen to be inefficient 
from an economical standpoint, though if a high concentration 
is desired, this can be best obtained by electrolysis. 

There are two distinct forms of silent discharge of electricity, 
which differ in their appearance, in the amount of ozone which 
they produce, and in the current which is required to produce 
them. 10 If a point one centimeter distant from a plate con- 
nected to earth is charged negatively to 7000 volts in air, a 
bluish light surrounding the point can be seen with the naked 
eye. If the potential is raised, a reddish broad brush appears, 
separated from the bluish light by a dark space, while the oppo- 
site plate remains dark. These different parts of the discharge 
correspond to what is observed in a vacuum tube in which the 
air is at a pressure of a few millimeters of mercury. The 
bluish light corresponds to the negative glow, the dark space 
to the Faraday dark space, and the reddish light to the positive 
column of light. 

With a positively charged point and a low potential differ- 
ence, a reddish envelope of light is first observed, from which 
a brush is developed on increasing the potential. The ability 

9 Fischer and Massenez, Z. f. anorg. Ch. 52, 202, (1907). 
10 Askenasy, Technische Elektrochemie, p. 240, (1910); and Warburg, Ber. d, 
deutsch. phys. Ges., (1904), 209. 



292 



APPLIED ELECTROCHEMISTRY 



to form this brush is important for the ozone formation, and is 
lost by points after use. In place of it a spark discharge is 
produced ; but the brush discharge can be 
produced even on old points by placing a 
spark gap 0.1 millimeter long before the 
point. 

If the discharge takes place between paral- 
lel conducting plates, either one or both being 
covered with a dielectric, the case is more 
complicated. 11 This type of ozonizer was 
devised by W. von Siemens and is usually 
called by his name. 12 Siemens's original ozon- 
izer consisted of concentric tubes, as shown 
in Figures 124 and 125. Two such tubes, 
with the sides a and d covered with a conduc- 
tor, such as tin foil, may be looked upon as a 
series of condensers connected in series, with 
an ohmic resistance in parallel with one of 
them. In this case there would be three con- 
densers : ab, be, and cd ; while if the inner 
tube is bare metal there would be only two : 
be and ab. When the space be is filled with a 
perfect insulator or with a perfect conductor, 
the current has its small- 
est or its largest value, re- 
spectively. In both cases 
the apparatus is a perfect 
condenser and absorbs no 
energy, since cos <f> = 0, 

FIG. 124. Longi- &J ' . V. ' 

tudinai section of where $ is the angle of 

Siemens's original p nase difference between FIG. 125 Transverse sec- 

the voltage and the cur- *" M .'.o,ir 
rent. For an average conductivity in 6<?, such as a gas can 
have, cos < assumes its largest value. In actual practice all 

11 Askenasy, p. 242 ; Warburg and Leithauser, Ann. d. Phys. 28, 1 and 
17, (1908). 

12 Fogg. Ann. 102, 120, (1857). 




THE PRODUCTION OF OZONE 293 

possible values of cos <f> between and 1 may occur. With 
increasing current strength cos $ decreases, probably because 
the resistance of the gas decreases with increasing current. If 
the frequency of the alternating current increases, cos <f> in- 
creases and approaches 1. High frequencies, between 200 and 
500 per second, should therefore be used. Ozonizers with one 
tube bare metal are better than those with both tubes glass, 
for cos (j) is larger, and a larger current passes, for a given vol- 
tage, than in a glass apparatus of the same dimensions. 

If an alternating electromotive force is applied between a 
point electrode and a plate connected to earth, the positive 
brush appears. By means of a rotating mirror the positive 
and negative light can be seen alternately on the point, and its 
appearance is not much changed when the plate is covered with an 
insulator. 11 If a Siemens apparatus has a large current passing, 
a uniform luminosity appears in the space between the elec- 
trodes, but if the current density is sufficiently lowered, brushes 
are formed at single points on the electrodes. From the ap- 
pearance of these discharges, there is no doubt that the same 
process takes place in the Siemens apparatus as in one with 
point and plate electrodes, except that in the Siemens ozonizer 
the effects on positive and on negative points are superimposed, 
as in the case of a direct current between two metallic points. 

The production of ozone by the silent discharge of electricity 
may be considered from the following different points of view : 
(1) the maximum concentration that can be obtained, (2) the 
maximum number of grams that can be produced per coulomb 
of electricity, and (3) the maximum number of grams per unit 
of power. The latter consideration is, of course, of the most 
technical importance. As stated above, ozonizers with point 
electrodes give different results, depending on whether the 
points are positive or negative to the plate. The Siemens ozon- 
izer is a third case to be considered. The amount of ozone 
produced per coulomb is therefore a variable quantity, and fol- 
lows no known law, such as we have in Faraday's law in the 
case of electrolysis. In the absence of such a law, it will be 
necessary to show what the yield is under different conditions 



294 



APPLIED ELECTROCHEMISTRY 



and how this is affected by changing the conditions. In ordei 
to give a systematic survey of this subject, the maximum con- 
centration will first be discussed for the three cases enumerated 
above, and the yields per unit of electricity 
and per unit of power, including the factors 
that affect them, will then be taken up in the 
following order, (1) for points negative, 
(2) for points positive, and (3) for Siemens 
ozonizers. 







The Maximum Concentration 



The silent discharge of electricity has a 
deozonizing effect on ozone, as well as an 
ozonizing effect on oxygen. The ozonizing 
effect of the discharge is proportional to the 
concentration of the oxygen, and the deozo- 
nizing effect to that of the ozone. In other 
words, this reaction follows the mass action 
law. If the discharge passed for an infinite 
time, a limiting concentration of ozone would 
be reached, at which the amount decomposed 
per second would equal the amount pro- 
duced. These two different effects have 
been studied separately by E. Warburg. 1 

The experiments were carried out in the 
apparatus shown in Figure 126. The ozon- 
izer was connected with an auxiliary ves- 
sel H by a capillary tube filled with sulphuric 
acid to a proper distance above B. and 
H each had a volume of a little over one 
cubic centimeter. The point electrode e l 
was a platinum wire 0.05 millimeter in diam- 
eter; the earth electrode 2 was a platinum 
wire 0.5 millimeter in diameter bent in the 
form of a U to increase the surface. After filling the appara- 



FIG. 126. Apparatus 
for determining the 
maximum attaina- 
ble concentration of 
ozone 



i Ann. d. Phys. 9, 781, (1900). 



THE PRODUCTION OF OZONE 



295 



tus with oxygen and sealing off at ^, 0, and 5, the rate at which 
ozone was produced, and the concentration, could be observed 
by the change in the height of the sulphuric acid in the ma- 
nometer. Table 40 gives the results obtained with e l connected 
to the negative pole of an electrostatic machine and e z through 
a galvanometer and to earth. is a constant proportional to 
the rate of formation of ozone at a given temperature, and a is 
a constant proportional to its decomposition. 



TABLE 40 



TEMPERATURE 


PEE CENT OZONE BY 
VOLUME 


/3 = A CONSTANT PRO- 
PORTIONAL TO KATE 
OF FORMATION 


o = A CONSTANT PRO- 
PORTIONAL TO THE RATE 
OF DECOMPOSITION 


+ 93 


1.23 


0.0177 


1.42 


50 


2.22 


0.0214 


0.939 


17 


3.53 


0.0225 


0.616 





4.19 


0.0219 


0.503 


-71 


5.74 


0.0232 


0.380 



This table shows that the maximum concentration decreases 
as the temperature rises, and that this is due to the increasing 
decomposing effect of the discharge, and not 
to a smaller ozonizing effect. This is evident 
from the values of a and /3. The spontaneous 
decomposition of the ozone was negligible. 
The ozonizer was then replaced by the one 
shown in Figure 127 with a volume of 7.5 
cubic centimeters. The point electrode e 
consisted of a platinum wire 0.05 millimeter FIG. 127. Ozonizer 
thick, and the earth electrode e 2 was a half 
cylindrical platinum plate. In this ozonizer 
the positive, as well as the negative, point discharge could be 
obtained. In both cases faint, luminous points were visible in 
the dark on the thin wire, while the earth electrode remained 
dark. With a current of 33 microamperes the results in Table 
41 were obtained. 




296 



APPLIED ELECTROCHEMISTRY 



TABLE 41 
Point Electrode Negative 



TEMP. 


MAXIMUM CONCENTRA- 
TION PEE CENT OZONE 
BY VOL. 


/3= CONST. PROPORTIONAL TO 
BATE OP FORMATION 


a = CONST. PROPORTIONAL 
TO KATE OF DECOM- 
POSITION 


48 


2.41 


0.00824 


0.332 


19 


3.38 


0.00807 


0.231 





4.45 


0.00929 


0.198 



Point Electrode Positive 



48 


0.81 


0.00243 


0.297 


19 


1.06 


0.00258 


0.233 





1.42 


0.00278 


0.198 



From these results it is evident (1) that the maximum 
concentration with the point negative is about three times as 
great as with the point positive ; (2) that this is due to the 
greater ozonizing effect of the discharge when the point is 
negative, since the deozonizing effect is approximately the same 
in both cases ; and (3) the temperature effect is the same for 
the positive as for the negative point discharge. 

For the Siemens type of apparatus the limiting concentration 
of ozone produced from 96 per cent oxygen diminishes slightly 
with increasing current, as shown by the following table : 2 

TABLE 42 



TEMPBRATTTBE 


AMPEKKS x 10 8 


OZONE 


GRAMS PER CUBIC 
METER 


PER CENT BY 
VOLUME 


19 
19 


1.21 
3.00 


168 
165 


8.02 
7.90 



Apparatus changed 



24 
24 


1.33 
2.16 


114 
110 


5.46 
5.27 



2 Warburg and Leithauser, Ann. der Phys. 28, 31, (1909). 



THE PRODUCTION OF OZONE 



297 




FIG. 128. Experimental ozonizer 




Fig. 129. Experimental ozonizer 



298 



APPLIED ELECTROCHEMISTRY 



The limiting concentration is evidently a quantity that 
varies with the apparatus used. The highest value obtained 
is 211 grams per cubic meter, or 10.1 per cent by volume. 3 



Yield per Coulomb for Negative Point Electrode 

In order to produce the maximum amount of ozone per 
coulomb, the deozonizing effect of the electric discharge must 

be excluded. This may be ac- 
complished by passing the oxy- 
gen through the ozonizer so 
rapidly that the concentration 
of the ozone produced remains 
very low compared with the 
maximum concentration attain- 
able. In a number of the ex- 
periments referred to below, 
the concentration of ozone did 
not exceed one per cent of the 
maximum. A number of dif- 
ferent forms of apparatus with 
a point electrode were used by 
Warburg in determining these 
yields. In the apparatus shown 
in Figure 128, E, the earth 
electrode, is a platinum plate ; 
in Figure 129 E is a platinum 
cylinder ; and in Figure 130, 
consisting of a liter bottle, E is 
concentrated sulphuric acid. 
Figure 131 shows an ozonizer 
with a number of point elec- 
trodes. 

FIG. 130. Experimental ozoiiizer 

With the point negative, for 
a given current strength the yield per coulomb is independent 




Warburg and Leithauser, Ann. der Phys. 28, 25, (1909). 



THE PRODUCTION OF OZONE 



299 



of the voltage, as shown by the results of Table 43, 1 obtained 
with oxygen 93 per cent pure by volume. In the following 
tables the current given is for one point only, in case the appa- 
ratus contained more than one point. 



TABLE 43 



AMPERES x 10 


VOLTS 


GRAMS OZONE PER COULOMB 


57 


4200 


0.0375 


57.5 


9880 


0.0386 


57.2 


11,700 


0.0387 




FIG. 131. Experimental ozonizer 

The yield is also independent of the form of the anode, and 
decreases slowly with increasing current, as is shown by the 
following results obtained with different forms of anode : l 



Warburg, Ann. der Phys. 13, 472, (1904). 



300 



APPLIED ELECTROCHEMISTRY 
TABLE 44 



APPARATUS IN FIG. 128 


APPARATUS IN FIG. 129 


Amperes x 10 6 


Grams Ozone per 
Coulomb 


Amperes x 10 6 


Grams Ozone per 
Coulomb 


17.4 


0.0484 


29.1 


0.0431 


25.1 


0.0459 


57.5 


0.0386 


57.2 


0.0375 


94.2 


0.0370 



These results are for the case where negative light appears 
only on the point. If it appears at other parts of the electrode, 
the yield may increase with the current. The yield depends 
further on whether the points have been previously used, being 
greater for previously used points : 2 

TABLE 45 
Oxygen, 96 per cent pure, by volume 



TIME DURING WHICH 
OZONIZER WAS USED 
BETWEEN EXPERIMENTS 


VOLTS 


AMPERES x 10 6 


GRAMS OZONE PER 
COULOMB 


_^__ 


6080 


14.6 


0.0408 


125 min. 


6960 


21.9 


0.0452 


165 min. 


6420 


17,6 


0.0803 


75 min. 


6300 


17.5 


0.0873 


30 min. 


8800 


17.5 


0.0908 



This increase in the yield is accompanied by a change in the 
character of the light on the electrode. When the final state 
of the electrode has been reached the yield decreases for increas- 
ing current to a certain point, as shown by the results in Table 
46 of experiments with 98.5 per cent oxygen : 3 



2 Warburg, Ann. d. Phys. 17, 6, (1905), 
* Warburg, Ann. d. Phys. 17, 6, (1905). 



THE PRODUCTION OF OZONE 
TABLE 46 



301 







GRAMS OZONE PER 


GRAMS OZONE PER 


VOLTS 


AMPEBES x 106 


COULOMB 


KILO WATT-HOUR 


7230 


8.83 


0.0950 


47.3 


8800 


17.50 


0.0908 


37.1 


12,500 


52.30 


0.0485 


14.0 



If the current is increased to a still higher value, the yield 
reaches a minimum and then increases with the current. This 
is shown by the results in Table 47, obtained with new points 
and with oxygen 96 per cent pure by volume : 4 

TABLE 47 



VOLTS 


AMPERES x 10 6 


GRAMS OZONE PER 
COULOMB 


6080 


14.6 


0.0423 





21.9 


0.0340 


9610 


52.4 


0.0307 


12,510 


130.7 


0.0422 


7000 


21.9 


0.0375 



In this case also a marked change in the appearance of the 
light accompanies the increase in the yield after passing the 
minimum. After a certain amount of practice, it is even pos- 
sible to predict from the appearance of the light what the yield 
will be. 6 

In changing the temperature and pressure of the gas, not only 
the substance which is to be acted upon is altered, but also 
the agent which brings about the reaction ; for the light changes 
its character when the physical state of the gas through which 
the current is passed is altered. This fact complicates the 
study of this subject. The results in Table 48 with oxygen 
98.5 per cent pure by volume show how the yield increases 
with the pressure : 6 

4 Ann. d. Phys. 17, 10, (1905). 6 Ann. d. Phys. 17, 7, (1905). 

e Ann. d. Phys. 17, 12, (1905). 



302 



APPLIED ELECTROCHEMISTRY 
TABLE 48 



PRESSURE IN MM. 
OF MERCURY 


VOLTS 


GRAMS OZONE PER 
COULOMB 


REMARKS 


460 


3810 


0.0365 


Points previously sub- 


784 


5220 


0.0522 


jected to long use. Current 


1210 


6900 


0.0903 


= 37.4 x 10~ 6 ampere 


465 


5520 


0.0355 


Fresh points. Current 


780 


7410 


0.0477 


= 17.5 x 10~ 6 ampere 


1208 


9700 


0.0597 





Between 780 and 460 millimeters pressure, the yield A p for any 
pressure p is given by the equation 7 

A p = A 7QO [1 - (760 -p) 0.00089]. 

The temperature of the gas in all of these experiments lay 
between 17 and 23. Table 49 shows the effect on the yield 
of changing the temperature : 

TABLE 49 
Oxygen 98.5 per cent pure by Volume. Current 37.4 X 10~ 6 Ampere 



PRESSURE IN 
MM. OP MERCURY 


TEMPERATURE 


VOLTS 


GRAMS OZONE PER 
COULOMB 


785 


16.5 


7530 


0.0418 


782 


79.5 


6560 


0.0376 


789 


14.8 


7500 


0.0430 


789 


80.1 


6440 


0.0395 


788 


14.2 


7470 


0.0430 


780 


79.7 


6320 


0.0387 


786 


15.4 


7350 


0.0429 


786 


79.8 


6320 


0.0394 



This decrease in the yield is largely due to the decrease in the 
density of the oxygen when the temperature is raised. If the 
pressure is increased enough to keep the density constant, 
the yield is very little affected. This is shown in Table 50, 
obtained with points not previously used : 
7 Ann. d. Phys. 28, 21, (1909). 



THE PRODUCTION OF OZONE 
TABLE 50 



303 



PRESSURE IN MM. 
OP MERCURY 


TEMPERATURE 


VOLTS 


AMPERES x 10 6 


GRAMS OZONE PER 
COULOMB 


783 s 


12.4: 


6440 


17.5 


0.0403 


951 


80.0 


5970 


17.5 


0.0413 


775 


11.8 


6350 


17.5 


0.0458 


963 


80.0 


6180 


17.5 


0.0480 


782 


10.4 


10,190 


52.4 


0.0389 


979 


80.3 


8860 


52.4 


0.0370 


792 


15.0 


9470 


52.4 


0.0394 


980 


80.0 


8920 


52.4 


0.0388 



It is therefore evident that if the density is constant, the yield 
is changed only a few per cent between 10 and 80 degrees. 

The relation between the yield per coulomb and the concen- 
tration of the ozone produced from 98 per cent oxygen is linear. 8 
If the concentration is allowed to reach 12.9 grams per cubic 
meter, the yield falls to 75 per cent of its value for a concentra- 
tion of 1.3 to 1.6 grams per cubic meter. The formula 

^ = 0.166- 0.00215 c 

gives the yield per coulomb for different values of the concen- 
tration c between 1.6 and 12.9 grams per cubic meter, and for 
a current of 0.0175 x 10~ 3 ampere. The yield per kilowatt 
hour is given by the equation : 

B = 71.0 - 1.58 c + 0.00090 c 2 . 

These results were obtained with spheres, in place of points, 1.5 
to 2 millimeters in diameter, melted on a wire 1 millimeter in 
diameter. The yield for this kind of electrode is much higher 
than for points, and when used as the positive pole, spheres do 
not show the aging effect that is observed with points. 

The presence of water vapor in oxygen reduces the yield 
nearly proportionally to the pressure of the water vapor. 9 
The reduction in the yield for seven millimeters pressure is 

s Warburg and Leithauser, Ann. d. Phys. 20, 734, (1906). 
9 Ann. d. Phys. 20, 751, (1906). 



304 



APPLIED ELECTROCHEMISTRY 



about 94 per cent of its value for dry oxygen. There is also 
a great tendency for the formation of sparks when the gas is 
moist. 

When oxygen is mixed with only 7 per cent of nitrogen, the 
silent discharge produces no oxide of nitrogen, 10 but when air 
is used oxides of nitrogen are produced. The spark discharge 
produces only oxides, and these prevent the formation of 
ozone. 11 For air, the yield per coulomb is independent of the 
voltage for a constant current, as in the case of oxygen, but it 
is much smaller than for oxygen. This is shown in Table 51. M 

TABLE 51 
Air. Temperature 20. Six Points. Current for One Point = 21.9 X 10-6 ampere 



VOLTS 


DISTANCE BETWEEN 
POINT AND PLATE IN 
MILLIMETERS 


GRAMS OZONE PER 
COULOMB 


8240 


12.8 


0.0112 


8300 


12.8 


0.0110 


3930 


3.4 


0.0110 


7950 


13.5 


0.0110 



For air, the yield first decreases with increasing current and 
reaches a minimum, after which it increases more rapidly than 
for oxygen, as shown in Table 52. 

TABLE 52 



AMPERES x 10 6 


VOLTS 


DISTANCE BETWEEN 
POINT AND PLATE IN 
MILLIMETERS 


GRAMS OZONE PER 
COULOMB 


21.9 


8300 


12.8 


0.01100 


54.5 








0.00935 


55.2 


7830 


7.5 


0.00766 


163.0 


12,200 


7.5 


0.01880 


219.0 


12,940 


7.5 


0.02500 



10 Warburg, Ann. d. Phys. 13, 470, (1904). 

11 Warburg and Leithauser, Ann. d. Phys. 20, 743, (1906). 

12 Warburg, Ann. d. Phys. 17, 25, (1905). 






THE PRODUCTION OF OZONE 305 

The change that takes place in the luminosity when the yield 
begins to increase is similar to that in the case of oxygen. 

The effect of the concentration of the ozone produced on the 
yield in air is approximately the same as in oxygen. 13 A, the 
yield in grams per coulomb, and B, the yield in grams per kilo- 
watt hour, are given by the following equations, for values of 
the concentration c between 2.19 and 9.62 grams per cubic 
meter : 

A = 0.0780 - 0.00220 c, 

B = 42.6 - 1.60 c + 0.0036 c 2 . 

The effect of moisture is greater for air than for oxygen, 7 
millimeters pressure of water vapor reducing the yield to 69. 7 
per cent of its value for dry air. 14 

The effect of temperature on the yield for negative points 
in air has not been determined. 



Yield per Coulomb for Positive Point Electrode 

The effect of increasing the current on a positive point 
electrode is quite different from the effect on a negative point. 
With positive points the yield is smallest for small currents, 
but increases as soon as the positive brush appears, and, with 
points not previously used, it finally reaches values exceeding 
the highest ones obtainable with negative points. This is 
shown in Table 53. l The yield is very much affected by the 
character of the positive brush, which depends on a number of 
circumstances difficult to control. 

The effects of temperature and pressure on the yield with 
positive points in oxygen have not been investigated. 

The relation between the yield in grams per coulomb, A, and 
the concentration of ozone, <?, produced, is given by the equa- 
tion : 

-4 = 0.166- 0.00853 c, 

13 Warburg and Leithauser, Ann. d. Phys. 20, 734, (1906). 
" Ann. d. Phys. 20, 734, (1906). 
i Warburg, Ann. d. Phys. 17, 19, (1905). 
x 



306 



APPLIED ELECTROCHEMISTRY 



which holds for values of c between 1.18 and 8.49 grams per 
cubic meter. 2 The corresponding equation for grams per 
kilowatt hour is 

=67.0- 3.44 c. 

These results are for spheres in place of points, and for a 
current on one sphere of 0.033 x 10~ 3 ampere. 



TABLE 53 
93 per cent Oxygen by Volume 





DISTANCE 








GRAMS OZOXE 


WIRE OF + POLE 
IN MILLIMETERS 


BETWEEN 

POLES IN 
MILLIMETERS 


CENTI- 
GRADE 


YOLTS 


AMPERES 
xlO 


Per 

Coulomb 


Per 
Kilowatt 
Hour 


0.1 


13.5 


16 


12,900 


77.2 


0.0372 


10.4 


0.5 


3.6 


17 


5710 


22.9 


0.0499 


31.4 


0.5 


13.5 


16 


12,900 


87.4 


0.0795 


22.2 


1.0 


4.0 


18 


6900 


42.5 


0.0871 


45.4 


1.0 copper 


4.0 


18 


5590 


29.4 


0.0760 


48.9 


1.0 


4.0 


18 


5970 


43.9 


0.0856 


51.5 



98.5 per cent Oxygen 



1 

2 


4.4 

5 


20 
19 


7830 
7710 


47.9 
62.4 


0.0947 
0.0680 


43.8 
31.8 



The reduction in the yield by water vapor is much greater 
for positive points in oxygen than for negative. When the 
vapor pressure of the water is seven millimeters, the yield is 
only 64 per cent of its value for dry oxygen. 3 

Positive points in air act similarly to positive points in 
oxygen, except that the positive brush is more capricious in 
air. 4 The yield is much smaller than for negative points as 
long as no positive brush appears, and while the positive glow 
covers the point in a thin layer; but with the appearance of 

a Warburg and Leithauser, Ann. d. Phys. 20, 739, (1906). 

3 Ann. d. Phys. 20, 753, (1906). 

* Warburg, Ann. d. Phys. 17, 26, (1905). 



THE PRODUCTION OF OZONE 



307 



the positive brush the yield increases and reaches values much 
higher than any obtained with negative points in air. This 
will be seen from the results of Table 54. 

TABLE 54 
Atmospheric Air. Positive Points of wire 0.25 mm. in Diameter 









GRAMS OZONE 


DISTANCE BETWEEN 
POINT AND PLATE 


VOLTS 


AMPERES x 10 6 














Per Coulomb 


Per Kilowatt Hour 


13.5 


7950 


14.6 


0.00294 





13.5 


8060 


14.5 


0.00288 





7.5 


8060 


32.7 


0.00307 





3.5 


5340 


36.4 


0.0377 


25.4"! Voltage near 


3.5 


5340 


36.4 


0.0387 


26.1 [ sparking 


9.8 


10,800 


100.7 


0.0505 


16.8 J point 



The yield in grams per coulomb, A, and in grams per 
kilowatt hour, J9, in air are given by the equations: 

.4 = 0.114- 0.008670, 
B = 60 - 6 e 

for values of c between 0.58 and 3.94 grams per cubic 
meter. 

The effect of water vapor on the yield with positive points in 
air is the greatest of any so far considered. In this case, for a 
pressure of water vapor of 7 millimeters, the yield falls to 
49.1 per cent of its value for dry air. 

It is evident, from the fact that positive points near the 
sparking potential give a better yield than negative points, 
both for oxygen and for air, that if an alternating current is 
used the yield will not be as good as with a direct current with 
positive points, for with an alternating current the points will 
be negative half of the time. This has been tested by direct 
comparison for oxygen and air. The results are given in 
Table 55. 6 



6 Warburg, Ann. d. Phys. 17. 29, (1905), 



308 



APPLIED ELECTROCHEMISTRY 



TABLE 55 
98.5 per cent Oxygen. Temperature 19 











GRAMS OZONE 


DISTANCE OF 










POINT FROM 


CURRENT 


VOLTS 


AMPERES x 10 






PLATE IN MM. 








Per Coulomb 


Per Kilo- 












watt Hour 


6.8 


Alternating 


6780 


53.0 


0.0258 


13.7 


6.8 


Direct 


8860 


70.8 


0.0612 


24.9 


4.4 


Alternating 


5340 


37.0 


0.0128 


8.6 


4.4 


Direct 


7830 


47.9 


0.0947 


43.5 



Atmospheric Air 



5 


Alternating 


5220 


42.0 


0.0190 


13.0 


5 


Direct 


6720 


52.6 


0.0523 


28.2 


5 


Alternating 


5590 


62.1 


0.0142 


9.1 


5 


Direct 


7120 


54.2 


0.0443 


22.4 



The Yield per Kilowatt Hour for Positive and for 
Negative Points 

It is evident from what has preceded that the yield per unit 
of energy depends on a large number of factors. For negative 
points, it is best to use the smallest possible current and a short 
distance between the points and the plate, and the points should 
not be fresh. For positive points, heavy, new wires one milli- 
meter thick are best, and the potential should be as high as 
possible without producing sparks. The distance between 
point and plate should not be too great, for though the yield 
per coulomb increases, the yield per kilowatt hour decreases, as 
seen in Table 54. 

Much better yields both for positive and for negative points 
are obtained by substituting small spheres 1.5 to 2 millimeters 
in diameter for the points, as is seen in the results on the effect 
of concentration on the yield of ozone. It can be calculated 
from the equations given above, that for air, concentrations up 
to 4 grams per cubic meter are produced most economically 



THE PRODUCTION OF OZONE 309 

when the points are positive and the current high, while con- 
centrations between 4 and 9 grams per cubic meter are most 
economically produced with negative points and low currents. 1 
About 30 grains per kilowatt hour can be obtained in the latter 
case for a concentration of 8 to 9 grams per cubic meter. 

Theory of Ozone Formation by the Silent Discharge 

That the formation of ozone is not electrolytic in its nature 1 
can be shown from the yields given above, which vary between 
0.003 and 0.1 gram per coulomb. Since one equivalent of 
hydrogen reduces 24 grams of ozone, 24 may be taken as the 
latter's equivalent weight. The number of coulombs required 
to produce 24 grams of ozone therefore lies between 8000 and 
240, numbers not at all comparable with the electrochemical 
equivalent, 96,540 coulombs. On the other hand, the energy 
required is considerably greater than the heat of the reaction. 
On the basis of the highest yield of 70 grams per kilowatt hour 
(see the equation for yield with negative points in oxygen), the 
energy required for one mole of ozone is 589,000 calories, 20 
times as much as the heat of the reaction. Warburg's theory 
is that ozone is formed by those electrons that have a velocity as 
high as that required for the production of luminosity. Ozone 
may be formed directly by the impact of such electrons with 
oxygen molecules or by the intermediate production of short 
ether waves. 2 

The Siemens Ozonizer l 

The effect of pressure is the same in a Siemens ozonizer as 
for a point and plate, both being represented by the formula 
given above : 

A = Aeo[l -(760-^)0.00089]. 

1 Warburg and Leithauser, Ann. d. Phys. 20, 742, (1906). 

1 Warburg, Ann. d. Phys. 13, 474, (1904). 

2 Warburg, Ann. d. Phys. 17, 7, (1905). 

1 Warburg and Leithauser, Ann. d. Phys. 28, 17, (1909). The following dis- 
cussion is taken from this article, except where other references are given. 



310 



APPLIED ELECTROCHEMISTRY 



In air the pressure of oxygen is 160 millimeters, and in 96 per 
cent oxygen, 730 millimeters. Substituting these values in the 
above equation, 



This relation is verified by the following results, in which the 
gas was passed through the ozonizer at such a rate that the 
concentration remained low. The effective current was meas- 

ured. 

TABLE 56 





GRAMS OZONE PER COULOMB 






CURRENT PER 




-^160 




SQUARE METER 












In Oxygen 


In Air 






0.146 


0.0634 


0.0194 


0.31] 


50 alternations per 


0.193 


0.151 


0.0662 


0.44 I 


second. Apparatus : 2 


0.133 


0.238 


0.115 


0.49 j 


concentric glass tubes 


0.159 
0.182 


0.216 
0.204 


0.106 
0.106 


0.48] 
0.52 \ 


Central tube is bare 










metal 


0.182 


0.288 


0.146 


0.51 J 





The quantity of ozone produced per coulomb for a given 
apparatus increases with the potential as in the case of positive 
points, and the effect of water vapor is to lower the yield. 2 

A factor not considered in Warburg's work, but one which 
has a great effect on the yield, is the transparency of the glass 
of the ozonizer for ultra-violet light. 3 An ozonizer of quartz, 
for example, which is transparent to ultra-violet rays, gives 
only half as much ozone, other conditions being equal, as a 
glass ozonizer of the same dimensions. 

The relation between the yield and the concentration of the 
ozone leaving the ozonizer is similar to that for points, and is 
given in Table 57. 

The formation of ozone is proportional to the mean current, 



idt, and not to the effective current, 



1 C 

-J 



tne value 



2 A. W. Gray, Phys. Rev. 19, 362, (1904). 
F. Russ, Z. f. Elektroch. 12, 409, (1906). 



THE PRODUCTION OF OZONE 



311 



given by measuring instruments ; consequently, if the effective 
current is measured, the yield will also depend on the wave 

form of the current. 

TABLE 57 

Oxygen 96 per cent pure. Maximum Concentration of Ozone equals 168 Grams 
per cubic meter 



CONC. OZONE IN GKAMS 
PER CUBIC METER 


GRAMS OZONE PER 
COULOMB 


CONC. OZONE IN GRAMS 
PEE CUBIC METER 


GRAMS OZONE PER 
COULOMB 


16.1 


0.121 


53.1 


0.104 


23.2 


0.120 


62.4 


0.102 


29.9 


0.116 


68.4 


0.100 


31.2 


0.115 


80.6 


0.095 


41.1 


0.111 







The effect of temperature is similar to that in the apparatus 
with point and plate electrodes : the yield for zero concentra- 
tion changes very little, while the deozonizing effect of the 
current on the ozone already formed increases with the temper- 
ature. 

The yield per kilowatt hour is greater where one electrode is 
not covered with an insulator, because of the greater current 
for a given voltage and the greater value of cos <f>. The thick- 
ness of the dielectric has no effect. 4 The following table gives 
the yield obtained by Warburg and Leithauser in grams ozone 
per kilowatt hour. 5 

TABLE 58 

Air 







GRAMS PER KILOWATT- 




DISTANCE BETWEEN 
PLATES IN MM. 


FREQUENCY 


HOUR FOR 


AMPERES PER SQUARE 
METER 


Cone. =4 


Cone. = 10 






grms. per 


grins, per 








ma. 


m3. 




2.26 


50 


78.4 


72.2 


0.182 


2.26 


100 


81.4 


75.7 


0.308 


2.26 


500 


66.0 


57.1 


1.580 


4.66 


50 


62.4 


53.3 


0.169 


4.66 


100 


63.0 


54.0 


0.280 


4.66 


500 


58.0 


33.0 


1.190 



4 See also Ewell, Phys. Rev. 22, 243, (1906). 
6 Ann. d. Phys. 28, 36, (1909). 



312 



APPLIED ELECTROCHEMISTRY 



It will be noticed that the yield for a Siemens ozonizer is 
considerably higher than for those having a point and a plate 
electrode, for which the highest value was 36 grams per kilo- 
watt at a concentration of 4 grams per cubic meter. 

2. THE TECHNICAL PRODUCTION OF OZONE 

Ozone is produced commercially for the purification of water, 
for bleaching, and for use as an oxidizing agent in organic 

chemistry. 1 In water pu- 
rification, the action of 
ozone is to oxidize the 
organic matter and to 
destroy germs. 

Siemens and Halske 
make the ozone apparatus 
shown in Figure 132. 2 
The discharge chamber is 
between two concentric 
metal cylinders, between 



la 




'Ozone 



FIG. 132. The Siemens and Halske ozonizer 

which 8000 volts alternating are applied. The cylinders are 




Cooling Water 



T 



FIG. 133. The Tindal ozonizer 



immersed in water for cooling, and the outer one is connected 
to earth. One of the surfaces from which the discharge takes 



1 J. W. Swan, Z. f. Elektroch. 7, 950, (1901). 

2 Z. f. Elektroch. 10, 13, (1904); Electrochem. Ind. 2, 67, (1904). 



THE PRODUCTION OF OZONE 



313 



T Pef,fugrat03r 



place is covered with a glass dielectric. Air enters at the top, 
is partly changed to ozone in passing between the walls of the 
concentric cylinders, and leaves the apparatus from below. 
The concentration of the ozone is about 2 grams per cubic 
meter, which is high enough for all ordinary purposes. The 
yield varies between 18 and 37 grams per kilowatt hour. 3 

The Tindal ozonizer is 
shown in Figure 133. 
It is in the form of a 
box, the inner walls of 
which are water-cooled 
electrodes and are con- 
nected to earth. The 
other electrodes are metal 
plates inside the box and 
insulated from it. Be- 
tween 40,000 and 50,000 
volts are applied to the 
electrodes. 

The Abraham-Mar- 

rnier 2 apparatus is shown in Figure 134. It consists of a num- 
ber of cylindrical, parallel, hollow electrodes of about a square 
meter area, covered with glass and mounted in a box. Water cir- 
culates through 
the electrodes 
for cooling, be- 
tween which 
about 40,000 
volts are ap- 
plied. 

The Otto 
apparatus 4 is 




FIG. 134. The Abraham-Marmier ozonizer 




The Otto ozonizer 

FIG. 135. Longitudinal-vertical FIG. 136. Transverse 

section vertical section , . ,,,. 

shown in r ig- 

ures 135 and 136. It consists of a chamber, K, the metal wall, 
EV of which forms one electrode. The sheet steel rings, $, 

Askenasy, Elektrochemie, 1, 246, (1910). 
* Z. f. Elektroch. 7, 790, (1901). 



314 



APPLIED ELECTROCHEMISTRY 



sharpened at M, and mounted on an axle on which they rotate, 
are the other electrode, E%. There is no solid dielectric. Air 
passes in the box at B arid comes .out at A. While in the box 
it is ozonized and thoroughly mixed by the rotating electrode. 
If an arc were to form between the electrodes, it would be ex- 
tinguished as the grooves RR in the 
rotating electrode pass the insulat- 
ing base of the box, aa. About 25,000 
volts are applied to the electrodes, 
the distance between which may be 
from 10 to 100 millimeters. 

Small ozonizers are now made for 
sterilizing water where it is drawn 
for use, as shown in Figure 137. 5 
The transformer and ozonizer are in 
a metal case, 0. P and S are respec- 
tively the primary and the secondary 
of the transformer. The primary is 
supplied with 100 to 250 volts, which 
is transformed to 15,000 volts in the 
secondary. The ozonizer consists of 
six or more glass plates, 6r, supported 
on a grooved bracket at the bottom, 
and by grooved slips at the sides and 
top. Three pairs of plates, each plate 
covered on one side with tin foil, are 
shown in the sketch. The discharge 
takes place between two opposite 
FIG. 137. Small ozonizer con- sheets of tin foil one millimeter apart, 

without an intervening dielectric. 

The air enters the space between the plates at the top and 
sides, and is sucked down through the opening at the bottom 
of the ozonizer by the action of the water at B. The water 
carries the ozone to .A, where mixture and sterilization take 
place. The current in the transformer is of course turned on 
only when water is drawn. 

5 Electrochem. and Met. Ind. 6, 304, (1908> 




APPENDIX 



TABLE OF ATOMIC WEIGHTS 

O = 16.00 







(1910) 1 






(1910) 


Aluminum* 


. . Al 


27 1 


Helium ... 


. . He 


4 


Antimony 


Sb 


120 2 


Hydrogen 


. . H 


1 008 




. ". A 


39.9 




. . In 


114.8 




. . As 


74.96 




. . I 


126.92 




. . Ba 


137.37 




. . Ir 


193 1 


Bismuth. . . . 


. . Bi 


208 




. . Fe 


55 85 


Boron .... 


. . B 


11 


Krypton ... 


. . Kr 


83 


Bromine . . 


. . Br 


79 92 


Lanthanum . . 


. . La 


139 


Cadmium . 


Cd 


112 40 


Lead 


. . Pb 


207 10 




. . Cs 


132 81 




. . Li 


7.00 


Calcium 


. . Ca 


40 09 




. . Lu 


174 


Carbon .... 


. . C 


12 00 


Magnesium . . 


. Mg 


24 32 


C6rium .... 


. . Ce 


140 25 


Manganese . . 


jAtg 
. . Mn 


54 93 


ChlorinB ... 


Cl 


35 46 


M^ercury . . * 


. Hg 


200 




. . Cr 


52.0 


Molybdenum 


. . Mo 


96.0 


Cobalt .... 


. . Co 


58.97 


Neodymium . . 


. . Nd 


144.3 


Columbium 


. . Cb 


93.5 




. . Ne 


20. 


Copper .... 


. . Cu 


63.57 


Nickel. . . . 


. . Ni 


58 68 


Dysprosium . . 


Dy 


162 5 




. . N 


14 01 


Erbium 


*-v 

. . Er 


167 4 




. . Os 


190 9 


Europiu m 


. Eu 


152 




. . O 


16 00 




. . Fl 


19.0 


Palladium . 


. . Pd 


106.7 


Gadolinium . . 
Gallium 


. . Gd 
Ga 


157.3 
69 9 


Phosphorus . . 
Platinum * . 


. . P 

. . Pt 


31.0 

195 


Germanium . . 
Glucinum . 


. . Ge 
. . Gl 


72.5 
9 1 


Potassium . . 
Praseodymium . 


. . K 
. . Pr 


39.10 
140.6 


Gold 


. . Au 


197 2 




. . Rd 


226.4 















1 International Committee on Atomic Weights, J. Am. Chem. Soc. 32, 3, (1910). 

315 



316 



APPENDIX 
TABLE OF ATOMIC WEIGHTS Continued 







(1910) 






(1910) 


Rhodium. , 


. . . . Rh 


102.9 


Thallium . 


. . . . Tl 


204.0 


Rubidium 


. . . . Rb 


85.45 


Thorium . 


. . . . Th 


232 42 


Ruthenium 


Ru 


101.7 


Thulium . 


.... Tm 


168 5 




. . . . Sm 


150.4 


Tin . . . 


. . . . Sn 


119.0 


Scandium 


. . . . Sc 


44.1 


Titanium 


. . . . Ti 


48.1 




. . . . Se 


79.2 


Tungsten . 


. . . . W 


184 




.... Si 


28 3 


Uranium 


... U 


238 5 


Silver . . 


. Atr 


107 88 


Vanadium 


y 


51 2 




. . . . Na, 


23.00 




. . . . Xe 


130.7 




. . . . Sr 


87.62 


Ytterbium 


. . . . Yb 


172.0 


Sulphur 


. . . . S 


32 07 


Yttrium . 


. . . . Y 


89 


Tantalum 


. . . . Ta 


181 


Zinc . 


Zn 


65 37 


Tellurium . 


. . . . Te 


127.5 


Zirconium 


. . . . Zr 


90.6 


Terbium . 


. . . . Tb 


159.2 





















TABLE OF ELECTROCHEMICAL EQUIVALENTS OF THE MORE 
IMPORTANT ELEMENTS 1 







VALENCE 


MILLIGRAMS 
DEPOSITED BY 1 
AMPERE IN 1 SECOND 


GRAMS DEPOSITED 
BY 1 AMPERE IN 
1 HOUR 




. . . Al 


3 


0.0935 


0.3366 




. . . Sb 


3 


0.4152 


1.495 




... As 


3 


0.2589 


0.9319 




. . . Ba 


2 


0.7115 


0.1976 




. . . Bi 


4 


0.5387 


1.939 




. . . Br 


1 


0.8279 


2.981 




. . . Cd 


2 


0.5821 


2.095 




. . . Ca 


2 


0.2077 


0.7476 




. . . Ce 


3 


0.4843 


1.744 




. . . Cl 


1 


0.3673 


1322 




. . . Cr 


2 


0.2694 


0.9696 


f| 

Cobalt .... 



... Co 


3 

2 


0.1795 
0.3054 


0.6462 
1.099 



Copper .... 



. . . Cu 


3 
1 


0.2036 
0.6586 


0.7331 
2371 













1 Based on the atomic weights of 1910 and on the value 96,540 for the electro- 
chemical constant. 



APPENDIX 



317 



TABLE OF ELECTROCHEMICAL EQUIVALENTS Continued 



VALENCE 



MILLIGRAMS 

DEPOSITED BY 1 

AMPERE IN 1 SECOND 



GRAMS DEPOSITED 

BY 1 AMPERE IN 

1 HOUR 



Copper Cu 2 

Fluorine Fl 1 

Gold Au 1 

" " 3 

Hydrogen H 1 

Iodine I 1 

Iron Fe 2 

" 3 

Lead Pb 2 

Lithium Li 1 

Magnesium . . . . . Mg 2 

Manganese Mn 2 

" " 3 

Mercury Hg 1 

Nickel Ni 2 

" 3 

Oxygen O 2 

Potassium K 1 

Silver Ag 1 

Sodium Na 1 

Tin Sn 4 

Titanium Ti 4 

Zinc . . Zn 2 



0.3293 

0.1968 

2.043 

0.6810 

0.01043 

1.313 

0.2894 

0.1929 

1.073 

0.0725 

0.1260 

0.2845 

0.1897 

2.071 

0.3039 

0.2026 

0.08287 

0.4051 

1.118 

0.2382 

0.3082 

0.1251 

0.3386 



1.186 

0.7086 

7.353 

2.451 

0.03758 

4.733 

1.042 

0.6947 

3.863 

0.261 

0.4534 

1.024 

0.6827 

7.457 

1.095 

0.7290 

0.2984 

1.458 

4.025 

0.8576 

1.109 

0.4504 

1.219 



NUMERICAL RELATION BETWEEN VARIOUS UNITS 

ENGLISH AND METRIC MEASURES 

NOTE. Values taken from "Tables of Weights and Measures," U. S. Coast 
and Geodetic Survey, 1890. 

LENGTH 

1 meter = 39.37 inches (legalized ratio for the U. S.) 

1 meter = 1.093611 yard 

1 meter = 3.280833 feet 

1 kilometer = 0.621370 mile 

1 inch = 25.40005 millimeters 

1 foot = 0.304801 meter 



318 APPENDIX 

1 yard = 0.914402 meter 
1 mile = 1.609347 kilometer 

MASS 

1 kilogram = 2.204622 pounds av. 
1 grain = 15.43235639 grains 
1 pound =0.4535924277 kilograms 
1 ounce av. = 28.34853 grams 
1 ounce troy = 31.10348 grams 
1 metric ton = 1000 kilograms 

VOLUME 

1 liter = 1.05668 quarts 
1 liter = 0.26417 U. S. gallon 
1 liter = 33.814 U. S. fluid ounces 
1 quart, U. S. = 0.94636 liter 
1 gallon, U. S. = 3.78544 liters 
1 fluid ounce = 0.029573 liter 

MECHANICAL EQUIVALENT OF HEAT 

1 kilogram-calorie (1 kilogram water raised 1 C. at 15 C.) = 427.3 
kilogrammeters (at sea level, latitude 45, g = 980.6 c.g.s.) 

1 British thermal unit (1 pound of water raised 1 F. at 59 F.) = 778.8 
foot pounds at sea level, latitude 45 

1 gram-calorie (1 gm. of water raised 1 C. at 15 C.)= 4.190 x 10 7 ergs 

1 joule = 10 7 ergs 

= 0.2387 gram-calorie 

ENERGY 

[Winkelmann, Handbuch der Physik, 1, 79, (1908)] 
1 kilowatt = 1000 watts 

1 horse power (HP) = 550 foot pounds per second 
= 746 watts 
= 0.746 kilowatt 
1 kilowatt = 1.34 horse power 

The metric horse power, called in German Pferdekraft or Pferde- 
stdrke (PS) 

= 75 kilogrammeters per second 
= 736 watts 
Therefore 1 English horse power = 1.014 metric horse power. 



APPENDIX 319 



LEGAL ELECTRICAL UNITS 1 

The legal electrical units in the United States are defined as 
follows : 

(1) The unit of resistance is the international ohm, represented 
by the resistance offered to a steady current by a column of mercury 
at C. whose mass is 0.4521 gram, of a constant cross section, and 
whose length is 106.3 centimeters. 

(2) The unit of current is the international ampere and is the 
equivalent of the unvarying current, which, when passed through 
a solution of silver nitrate in water, in accordance with standard 
specifications, deposits silver at the rate of 0.001118 gram per 
second. 

The specifications for the practical application of this definition 
are the following: 

In employing the silver voltameter to measure currents of about 
1 ampere, the following arrangements shall be adopted : 

The cathode on which the silver is to be deposited shall take the 
form of a platinum bowl not less than 10 centimeters in diameter 
and from 4 to 5 centimeters in depth. 

The anode shall be a disk or plate of pure silver some 30 square 
centimeters in area and 2 or 3 millimeters in thickness. 

This shall be supported horizontally in the liquid near the top of 
the solution by a silver rod riveted through its center. To prevent 
the disintegrated silver which is formed on the anode from falling 
upon the cathode, the anode shall be wrapped around with pure filter 
paper, secured at the back by suitable folding. 

The liquid shall consist of a neutral solution of pure silver nitrate, 
containing about 15 parts by weight of the nitrate to 85 parts of 
water. 

The resistance of the voltameter changes somewhat as the current 
passes. To prevent these changes having too great an effect on the 
current, some resistance besides that of the voltameter should be 
inserted in the circuit. The total metallic resistance of the circuit 
should not be less than 10 ohms. 

Method of Making a Measurement. The platinum bowl is to be 
washed consecutively with nitric acid, distilled water, and absolute 

1 Bulletin of U. S. Coast and Geodetic Survey, Dec. 27, 1893. 



320 APPENDIX 

alcohol ; it is then to be dried at 160 C., and left to cool in a desic- 
cator. When thoroughly cool it is to be weighed carefully. 

It is to be nearly filled with the solution and connected to the rest 
of the circuit by being placed on a clean insulated copper support to 
which a binding screw is attached. 

The anode is then to be immersed in the solution so as to be well 
covered by it and supported in that position ; the connections to the 
rest of the circuit are then to be made. 

Contact is to be made at the key, noting the time. The current is 
to be allowed to pass for not less than half an hour, and the time of 
breaking contact observed. 

The solution is now to be removed from the bowl and the deposit 
washed with distilled water and left to soak for at least six hours. 
It is then to be rinsed successively with distilled water and absolute 
alcohol and dried in a hot-air bath at a temperature of about 160 C. 
After cooling in a desiccator it is to be weighed again. The gain in 
mass gives the silver deposited. 

To find the time average of the current in amperes, this mass, 
expressed in grams, must be divided by the number of seconds 
during which the current has passed and by 0.001118. 

In determining the constant of an instrument by this method the 
current should be kept as nearly uniform as possible and the readings of 
the instrument observed at frequent intervals of time. These obser- 
vations give a curve from which the reading corresponding to the mean 
current (time average of the current) can be found. The current, as 
calculated from the voltameter results, corresponds to this reading. 

The current used in this experiment must be obtained from a bat- 
tery and not from a dynamo, especially when the instrument to be 
calibrated is an electrodynamometer. 

(3) The unit of electromotive force is the international volt, 
which is the electromotive force that, steadily applied to a conductor 
whose resistance is one international ohm, will produce a current of 
an international ampere, and is practically equivalent to ^ of the 
electromotive force of a Clark cell, at 15 C., when prepared accord- 
ing to the standard specifications. 1 

(4) The unit of quantity is the international coulomb, which is 
the quantity of electricity transferred by a current of one interna- 
tional ampere in one second. 

1 See Bulletin of U. S. Coast and Geodetic Survey, Dec. 27, 1893. 



APPENDIX 321 

(5) The unit of work is the joule, equal to 10 6 (see under Mech. 
Equiv. of Heat) ergs, and is practically equivalent to the energy 
expended in one second by an international ampere in an inter- 
national ohm. 

(6) The unit of power is the watt, and is practically equivalent 
to the work done at the rate of one joule per second. 



NAME INDEX 



ABRAHAM and Marmier, 313. 

Acheson, 210, 217, 219, 220, 221. 

Adams, 34. 

Addicks, 47, 48, 53, 54. 

Adolph, 104, 105. 

Alexander, 203. 

Ashcroft, 234. 

Askenasy, 229. 

Baekeland, 130. 

Bancroft, 54. 

Becker, 234. 

Behr, 22. 

Behrend, 17. 

Bennie, 252. 

Berthelot, 220. 

Berzelius, 236. 

Betts, 64, 236. 

Bindschedler, 76. 

Birkeland, 279, 282, 287. 

Bjerrum, 15. 

Blount, 208. 

Bodenstein and Katayama, 275. 

Bodlander, 15. 

Boiling, 216. 

Borchers, 57, 75. 

Bottger, 19. 

Bradley, 230, 276. 

Braemer, 289. 

Bredig, 11, 266, 267. 

Brown, 55. 

Brush, 153. 

Bugarsky, 15. 

Bunsen, 6, 143, 228, 236. 

Burgess, 36, 146. 

Cantoni, 107. 
Caro, 266. 
Castner, 131, 233. 
Cavendish, 270. 
Coehn, 73. 
Cohen, 43. 
Colby, 259. 
Collins, 2. 

Colson, 209, 217, 218. 
Conrad, 207. 
Corbin, 125. 
Cowles, 185, 209, 229. 



Cowper-Coles, 41. 
Crocker, 126. 
Cruickshank, 21. 
Gumming, 15. 

Daniell, 143. 

Davy, E., 202. 

Davy, H., 228, 233, 236. 

Despretz, 208, 220. 

Deville, 228. 

Dietzel, 57. 

Dolezalek, 154. 

Donath and Frenzel, 276. 

Dony-Henault, 78. 

Easter brooks, 51. 

Edison, 173, 182. 

Edstrom, 265. 

Elbs, 7, 77, 171. 

Elmore, 40. 

Endruweit, 41. 

Engelhardt, 117, 118, 122, 141. 

Erdmann, 16. 

Erlwein, 64, 266, 268. 

Eschmann, 267. 

Ewell, 311. 

Eyde, 281, 282. 

Faraday, 1. 

Farup, 4. 

Faure, 153. 

Ferranti, 259. 

Finckh, 271, 272. 

Fischer, A., 21, 25, 27, 29. 

Fischer, F., 289, 291. 

FitzGerald, 192, 200, 209, 211, 219, 220, 

224, 262. 
Fodor, 150. 
Foerster, 6, 24, 37, 45, 50, 55, 62, 67, 72, 

78, 79, 81, 82, 85, 88, 91-95, 97, 98, 

101-103, 109, 110, 112, 115, 116, 178, 

181, 183, 266. 
Fraenkel, 267. 
Frank, 266, 268, 287. 
Frazier, 216. 
Fromm, 45, 46. 

Gall and Montlaur, 123. 
Garuti and Pompili, 140. 
323 



324 



INDEX 



Gay-Lussac, 83. 
Gibbs, Walcott, 21, 22. 
Gibbs, W. T., 123. 
Girod, 257. 
Gladstone, 157, 158. 
Glaser, 106. 

Goodwin, H. M., 14, 23. 
Goodwin, J. H., 237. 
Gray, 310. 
Gronwall, 250. 
Grove, 143. 
Giinther, 45, 67. 
Guthrie, 11. 
Guthe, 1. 
Gyr, 115, 116. 

Haanel, 242. 

Haas, 120, 122. 

Haber, 36, 38, 55, 74, 206, 225, 271, 273, 

278, 285, 287. 
Haeussermann, 131. 
Hahn, 11. 
Hall, 229. 
Hambuechen, 146. 
Hamilton, 51. 
Hansen, 199. 

Hargreaves and Bird, 126. 
Hasse, 46, 67. 
Heim, 158. 
Heimrod, 2, 3. 
Hering, 187, 192, 198, 261. 
Hermite, 117. 
Herold, 181. 

Heroult, 230, 247, 249, 256. 
Herz, 77. 
Hessberger, 282. 
Hibbard, 252. 
Hoepfner, 44, 47. 
Hofman, 49. 
Holborn, 15. 
Holland, 173, 177. 
Holweg, 274. 
Horry, 206. 
Houston, 204. 
Howies, 276. 
Huber, 276. 
Hudson, 203. 
Hunt, 233. 
Hutton, 229. 

Isenburg, 76. 

Jablochkoff, 150. 
Jacobs, 227. 
Jacoby, H., 266. 
Jacoby, M. H., 39. 
Jacques, 151. 
Jahn, S., 288, 290. 
Jakowkin, 80. 



Jellinek, 272. 
Job, 11. 
Joly, J., 11. 
Jorre, 82, 101; 103. 
Jost, 286. 

Keller, 254. 
Kellner, 118, 121. 
Kennelly, 173, 184, 204. 
Kennicutt, 204. 
Kershaw, 47, 123, 125, 243. 
Kiliani, 46, 49. 
Kistiakowsky, 11. 
Kjellin, 259, 262. 
Koenig, 273, 274. 
Kohlrausch, F., 8, 15. 
Kohlrausch, W., 158. 
Kretzschmar, 114. 

Lalande, 144. 

Lampen, 217. 

Langbein, 30, 35. 

Lebedeff, 229. 

Le Blanc, 1, 22, 23, 25, 26, 69, 75, 76, 107, 

109, 159, 161, 267, 272. 
Le Chatelier, 191. 
Leclanche, 143. 
Lederlin, 125. 
Ledingham, 6. 
Leithauser, 273, 292-311. 
Le Rossignol, 286. 
Lewes, 202, 206, 207. 
Lewis, 15, 74. 
Liebenow, 161, 163. 
Lindblad, 249. 
Lombard, 267. 

Lorenz, 94, 109, 233. 
Lovejoy, 276. 
Luckow, 75. 
Luther, 81. 
Lyon, 251, 252. 

McDonald, 126. 

McDougall, 276. 

Magnus, 52, 54. 

Marchese, 43, 44. 

Marsden, 208. 

Marx, 289. 

Massenez, 291. 

Maynard, 59. 

Metzger, 153. 

Meves, 79. 

Moebius, 59. 

Moissan, 202, 209, 216, 220, 266. 

Monkton, 242. 

Miiller, E., 74, 81, 85, 89, 91-94, 97, 108- 

110, 112, 117. 
Muller, F. C. G., 10. 
Mylius, 45, 46. 



INDEX 



325 



Nahnsen, 46. 

Nernst, 1, 71, 74, 148, 271. 
Neumann, 232. 
Nicholson and Carlisle, 6. 
Northrup, 261. 
Niiranen, 272. 

Obach, 141. 
Oeschli, 99. 
Oersted, 228. 
Oettel, 4, 86, 92, 122. 
Olsen, 232. 
Ordway, 146. 
Osaka, 73. 
Ostwald, 13, 150. 
Otto, 314. 

Patterson, 131. 
Pauli, 115. 
Pauling, 283. 
Petavel, 229. 
Pinchon, 242. 
Plannhauser, 40. 
Plante, 152. 
Priestley, 270. 
Pyne, 231. 



Queneau, 191. 

Rathenau, 237. 

Rayleigh, 276. 

Readman, 227. 

Reichert, 16. 

Reinfeld, 41. 

Richards, H. C., 195. 

Richards, J. W., 123, 132, 204, 222, 277. 

Richards, T. W., 1, 15, 22. 

Richardson, 131. 

Richarz, 7. 

Rochling and Rodenhauser, 262. 

Rostosky, 127. 

Russ, 310. 

Salom, 72. 
Salomon, 16. 
Sand, 81. 
Saunders, 41. 
Scheele, 220. 
Schmidt, 137. 
Schneider, 144. 
SchSnbein, 7. 
Schonherr, 282. 



Schoop, 141, 181. 

Schuckert, 119, 122. 

Schiitzenberger, 209, 217, 218. 

Seidel, 6. 

Senn, 65. 

Seward and von Kugelgen, 238. 

Siemens, 243. 

Siemens Brothers, 141. 

Siemens and Halske, 44, 312. 

Smith, 22. 

Soller, 74. 

Spitzer, 37. 

Sproesser, 96. 

Stadion, 99. 

Stalhane, 249. 

Stassano, 243, 254. 

Steiner, 105. 

Streintz, 160. 

Swan, 41. 

Tafel, 70. 

Taylor, 225. 

Thompson, 51, 202, 203, 232, 267. 

Tindal, 313. 

Tone, 219. 

Townsend, 129. 

Tribe, 157, 158. 

Tscheltzow, 160. 

Tucker, 203, 217, 220. 

Turnbull, 257. 

Ulke, 51, 54, 55. 
Uslar, 64. 

Varley, 146. 
Volta, 143. 

Walker, 117, 121. 

Warburg, 273, 290-311. 

Watson, 153. 

Wehrlin, 94. 

Whiting, J., 133. 

Whiting, S. E., 173, 184. 

Wilke, 267. 

Willson, 202. 

Wilsmore, 14. 

Wohler, F., 202, 226, 228. 

Wohler, P., 237. 

Wohlwill, 50, 57, 58, 61, 112. 

Wologdine, 191. 

Zellner, 96. 



SUBJECT INDEX 



Alkali hydrate and chlorine ; diaphragm 
process, 101-104; bell process, 104; 
mercury cathode process, 106 ; mer- 
cury diaphragm process, 107 ; bell cell, 
131 ; Castner cell, 135 ; Hargreaves-Bird 
cell, 127 ; McDonald cell, 126 ; Town- 
send cell, 129; Whiting cell, 133-136. 

Aluminum, first isolated, 228 ; reduction 
of oxide by carbon, 229 ; Hall's process, 
229-230; Bradley's process, 230; 
Heroult's process, 230 ; furnace for 
electrolytic production, 231 ; yield per 
horse power day, 231 ; temperature of 
bath, 231 ; table of production, 232 ; 
electrolytic production as laboratory 
experiment, 232. 

Alundum, 227 ; table of production, 228. 

Bell alkali chlorine cell, 131. 
Brass plating, 37. 
Bright dipping bath, 31. 
Bromate, electrolytic production of, 115. 
Bromoform, electrolytic production of, 
79. 

Calcium, first isolated, 236 ; electrolytic 
production by Rathenau, 237 ; by 
Seward and von Kiigelgen, 238 ; by P. 
Wohler, 237. 

Calcium carbide, discovery, 202 ; heat of 
formation, 202 ; equilibrium with 
carbon monoxide, 202 ; chemical 
properties, 203 ; Willson's original 
furnace for manufacture of, 204 ; 
first furnace at Niagara Falls, 205 ; 
Horry furnace, 206 ; yield per kilowatt 
day, 207 ; raw materials for, 207 ; 
table of production, 206. 

Calcium cyanamide, discovery of produc- 
tion from carbide, 266 ; pressure of 
nitrogen in, 267 ; chemical behavior, 
268; manufacture, 269. 

Carbon, different forms distinguished, 
220. 

Carbon bisulphide, electrothermic pro- 
duction; 225. 

Carbon electrodes, thermal and elec- 



trical conductivities of, 198-199 ; 
porosity, 95-96 ; as anodes in alkali 
chloride electrolysis, 95-97, 105. 

Carborundum, first produced, 208 ; dis- 
covery by Acheson, 210 ; named, 210 ; 
furnace at Niagara Falls for production 
of, 212 ; reaction of formation, 212 ; 
raw materials for, 214 ; yield per kilo- 
watt hour, 214 ; table of production, 
215 ; uses, 215 ; analysis of, 210, 216 ; 
temperature of formation and of de- 
composition, 217 ; chemical properties, 
217. 

Carborundum fire sand, 211. 

Chlorate, production by electrolytic dis- 
charge of hypochlorite, 85 ; current effi- 
ciency when so formed, 90 ; electro- 
lytic production in acid solution, 92 ; 
in alkaline solution, 84, 93 ; current 
and energy yields, 98 ; Gall and Mont- 
laur cell for production of, 123 ; Gibbs 
cell, 123; Lederlin and Corbin cell, 
125. 

Chlorine, chemical action on hydrate, 
80-84 ; electrolytic production, see 
Alkali Hydrate. 

Chloroform, electrolytic production of, 
79. 

Complex salts in electroanalysis, 25, 28. 

Conductivity measurement as method of 
chemical analysis, 15-16. 

Conductivity, thermal ; method of de- 
termining for carbon electrodes, 197 ; 
table of values for refractories, 191. 

Copper, refining, object of, 47 ; electro- 
lytic method, 48 ; composition of 
anodes, 48, 49 ; composition of cathodes, 
49 ; composition of slime, 50 ; com- 
position of fresh electrolyte, 51 ; of 
foul electrolyte, 52 ; behavior of im- 
purities in anodes, 49 ; circulation of 
electrolyte, 52 ; size of tanks, 52-54 ; 
multiple and series systems of connec- 
tions, 53 ; effect of temperature on 
power required, 54 ; voltage per tank, 
54 ; polarization, 54 ; cost, 54. 

Copper, winning of, 43-45. 



327 



328 



INDEX 



Copper plating, 35. 

Coulometers, silver, 2-4 ; copper, 4-6 
water, 6-11; silver titration, 11-12. 

Diaphragms, construction of, 75. 

Edison storage battery, history and con- 
struction, 173-177 ; table of different 
sizes, 177 ; theory of, 178-184 ; nickel 
electrode, composition of, 178 ; po- 
tential of, 179 ; efficiency of charging 
181 ; iron electrode, potential of, 182 
effect of mercury contained, 182 ; 
chemical changes in battery, 183 ; elec- 
tromotive force of, 184 ; capacity, 184 ; 
efficiency, 184. 

Electric furnace, classification, 186 ; 
design, 192, 199, 200; heat loss 
through walls, 187 ; through elec- 
trodes, 193-198. 

Electrochemical analysis, by potential 
measurement, 13-15 ; by conductiv- 
ity measurement, 15-16 ; by titration, 
with a galvanometer as indicator, 17- 
20; by electrolytic deposition, 20- 
29 ; change in potential at cathode 
during, 24. 

Electrochemical equivalent, 1. 

Electrode voltage, 196. 

Electrolytic bleaching solution, see Hy- 
pochlorite. 

Electromotive series, 22. 

Electroplating, 30-34 ; by contact, 34 ; 
by dipping, 34. 

Electrotyping, 39. 

Faraday's laws, 1. 
Fluoride, electrolysis of, 113. 
Foil, metallic, electrolytic production of, 
41. 

Galvanometer as indicator in titrations, 
17-20. 

Galvanoplasty, 39. 

Gas analysis as a means of determining 
yield of hypochlorite, 86-87. 

Gold plating, 38. 

Gold refining, 61-64; cyanide process 
for extracting from ore, 63. 

Graphite, first made artificially, 220; 
theory of formation, 221 ; furnace for, 
222 ; table of production, 224 ; thermal 
and electrical conductivities of, 198- 
199 ; electrodes, see Carbon. 

Hydrogen, electrolytic production of, 
137-141; Schmidt cell, 137; Garuti 



and Pompili cell, 140 ; Schoop cell, 141 ; 
Siemens Brothers and Obach cell, 141. 

Hydrogen electrode, in electroanalysis 
20. 

Hypobromite, 114. 

Hypochlorite, production by action of 
chlorine on hydrate, 80-84; by elec- 
trolysis of alkali chloride solution on 
smooth platinum electrodes, 84-94; 
effect of temperature, 88; effect of 
current density, 89 ; prevention of re- 
duction by chromate, 89; effect of 
alkalinity on electrolytic production, 
93 ; effect of temperature on production 
in alkaline solution, 94 ; decomposition 
point of, 109 ; production with platin- 
ized anode, 94 ; with carbon anode, 
95 ; effect of concentration of chloride 
solution on yield, 89, 96 ; maximum 
concentration attainable, 98 ; current 
and energy yields, 98 ; Hermite cell for 
electrolytic production of, 117; Kell- 
ner cell, 118, 121 ; Haas and Oettel 
cell, 120, 122; Schuckert cell, 119, 
122. 

Hypoiodite, 115; electrolytic discharge 
of, 116. 

lodate, 115, 116. 

lodoform, electrolytic production of, 77. 

Iron, metallurgy of, 239-242; electro- 
thermic reduction from ores, 242 ; 
Stassano's preliminary experiments on, 
244; Keller furnace for, 246; He- 
roult's experiments on, 247-249 ; fur- 
nace of Gronwall, Lindblad, and Stal- 
shane, 249 ; furnace at H6roult, Cali- 
fornia, 251. 

Lead refining, 64-67. 

Mercury cathode in electroanalysis, 22. 
Multiple system of connections in metal 
refining, 53. 

Nickel plating, 34. 

Nickel refining, 55-57; Orford process, 
56. 

Nitrogen, fixation of ; by carbide, 266 ; 
pressure of, in calcium cyanamide, 267; 
yield of calcium cyanamide per unit of 
power, 269, 287 ; by oxidation by elec- 
tric discharge, discovered, 270 ; ther- 
mal equilibrium in, 271 ; electrical 
equilibrium, 274; velocity of oxida- 
tion, 272 ; yield per unit of power, 276, 
287 ; apparatus of Bradley and Love- 
joy for, 276, 277; of Birkeland and 



INDEX 



329 



Eyde, 279-282 ; of Schonherr and Hess- 
berger, 282-283 ; of H. and G. Pauling, 
283-285 ; by direct union with hydro- 
gen, 285 ; equilibrium, 286, 287. 
Nitrolime, 270. 

Overvoltage, in electroanalysis, 24 ; in 
lead storage battery, 170 ; in reduction, 
71 ; in oxidation, 73. 

Oxidation, electrolytic, 73 ; catalytic 
effect of anode on, 74 ; of chromium 
sulphate, 74 ; of attackable anodes, 
75. 

Oxygen, electrolytic production of, see 
Hydrogen. 

Ozone, discovery, 288 ; heat of formation, 
288 ; free energy of, 289 ; velocity of 
formation by silent electric discharge, 
290 ; yields by different methods of 
production, 291 ; maximum concen- 
tration by silent discharge, 294-296 ; 
yield per coulomb, for negative points, 
298-305 ; effect of temperature, 302 ; 
of pressure, 303 ; of concentration of 
ozone produced, 303 ; of water vapor, 
303; of current strength; yield per 
coulomb for positive points, 305-308 ; 
effect of current strength, 305 ; of 
temperature, 305 ; of concentration of 
ozone produced, 305 ; of water vapor, 
306 ; yield with alternating current, 
307 ; yield per kilowatt hour for posi- 
tive and for negative points, 308 ; 
theory of formation, 309 ; effect of 
transparency of glass ofozonizer, 310; 
ozonizer, of Siemens, 292, 309; of Sie- 
mens and Halske, 312 ; of Tindal, 313 ; 
of Abraham and Marmier, 313 ; of 
Otto, 314. 

Parabolic mirrors, electrolytic produc- 
tion of, 41. 

Perbromate, 115. 

Perchlorate, chemical formation, 84, 
electrolytic formation, 99 ; technical 
cells for, 126. 

Periodate, 117. 

Phosphorus, 226. 

Pinch effect, 261. 

Potassium, electrolytic production of, see 
Sodium. 

Potential, at liquid-liquid junctions, elim- 
ination of, 15. 

Potential measurement as method oi 
analysis, 13. 

Primary battery, denned, 142 ; Volta's 
Smee's, Grove's, Bunsen's, chromic 
acid cell, Leclanche's, 143 ; La- 



lande's, 144 ; Daniell's, 145 ; dry cells, 
146 ; Jacques's cell, 151 ; Jablochkoff 's 
cell, 150 ; ideal carbon cell, 147 ; free 
energy of, 148. 

Quicking bath, 38. 

deduction, electrolytic; denned, 68; 
reducing power of cathode measured 
by its potential, 69 ; pressure of hy- 
drogen corresponding to different po- 
tentials, 71 ; catalytic effect of cathode 
on, 72 ; of chromic sulphate, 72 ; of 
galena, 72. 

Secondary battery, defined, 142. 

Series system of connection in metal 
refining, 53. 

Silicon, electrothermic production, 219. 

Siloxicon, 217-219. 

Silundum, 216. 

Silver plating, 38. 

Silver refining, 57 ; Dietzel process, 57 ; 
Moebius process, 59. 

Sodium, production by electrolysis of 
fused hydrate, 233; Castner cell for, 
233 ; Ashcroft process, 234 ; uses of, 
236; world's production, 235. 

Steel, electrothermic refining of, 252 ; 
Stassano's furnace, 254 ; Keller's, 
254; Heroult's, 256; Girod's, 257; 
Kjellin's, 259; Rochling and Roden- 
hauser's, 262. 

Storage battery lead, history and con- 
struction, 152-157 ; chloride cell, 154 ; 
Gould cell, 156 ; theory of, 157-172 ; 
chemical changes in, 157 ; change in 
density of acid on charge and discharge, 
158 ; electromotive force, 160 ; tem- 
perature coefficient, 161 ; Le Blanc's 
theory of, 161 ; Liebenow's theory, 
163 ; charge and discharge curves, 
165-167; capacity, 168; current effi- 
ciency, 169 ; self-discharge, 169 ; 
sulphating, 171. 

Tubes, electrolytic production of, 40. 
Voltameter, see Coulometer. 

White lead, electrolytic production of, 

77. 
Wire, electrolytic production of, 40. 

Zinc, electrolytic winning of, 45 ; spongy, 

45, 46; refining, 67. 
Zinc plating, 33. 



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JAMES WALKER'S 

Introduction to Physical Chemistry 

Fourth Edition, 8vo, $3.25 net 

" This volume by Dr. Walker might well be made the basis of a course 
of lectures, intended to give students who do not mean to specialize in 
physical chemistry a general idea of the subject, while the same course 
might be taken with profit as an introductory one by those who expect 
to go farther in the subject. The author has been very successful 
along the lines that he has laid down, and his book can be recom- 
mended heartily." Journal of Physical Chemistry. 

TABLE OF CONTENTS 

Units and Standards of Measurement The Atomic Theory and 
Atomic Weights Chemical Equations The Simple Gas Laws 
Specific Heats The Periodic Law Solubility Fusion and Solidi- 
fication Vaporisation and Condensation The Kinetic Theory and 
Van Der Waal's Equation The Phase Rule Thermochemical 
Change Variation of Physical Properties in Homologous Series 
Relation of Physical Properties to Composition and Constitution 
The Properties of Dissolved Substances Osmotic Pressure and the 
Gas Laws for Dilute Solutions Deductions from the Gas Laws for 
Dilute Solutions Methods of Molecular Weight Determination 
Molecular Complexity Dimensions of Atoms and Molecules Elec- 
trolytes and Electrolysis Electrolytic Dissociation Balanced Ac- 
tions Rate of Chemical Transformation Relative Strength of 
Acids arid of Bases Equilibrium between Electrolytes Neutrality 
and Salt Hydrolysis Applications of the Dissociation Theory 
Electromotive Force Thermodynamical Proof Index. 

WILLIAM OSTWALD'S 
The Scientific Foundations of Analytical Chemistry 

Cloth, I2mo, $2.00 net 
Translated with the author's sanction by George M'Gowan. 

TABLE OF CONTENTS 

PART I THEORY. The Recognition of Different Substances The Sepa- 
ration of Substances Physical Methods of Separation Chemical 
Separation The Quantitative Determination of Substances. 

PART II APPLICATIONS. Introduction The Hydrogen and Hydrox'yl Ions 
The Metals of the Alkalies The Metals of the Alkaline Earths 
The Metals of the Iron Group The Metals of the Copper Group 
The Metals of the Tin Group The Non Metals The Calculation of 
Analyses. 

APPENDIX Lecture Experiments. 



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HARRY C. JONES'S 

The Elements of Physical Chemistry 

Revised Edition, 8vo, $4.00 net 

*' This new and enlarged edition of Professor Jones's well- 
known text-book will be welcomed by teachers and students 
of physical chemistry. . . . This edition has been exten- 
sively revised, contains a large amount of new matter, and 
is a satisfactory realization of the author's aim, as stated in 
the preface, to bring the book up to date. The volume has 
been increased in size by 85 pages, but the space devoted 
to new material is somewhat greater than this, a result made 
possible by judicious omissions. Subjects newly or more 
fully treated include J. J. Thomson's electron theory ; radio- 
activity ; the work of Morse, and of Lord Berkeley and 
E. G. J. Hartley on the direct measurement of osmotic pres- 
sure ; colloidal suspensions ; hydrolytic dissociation ; conduc- 
tivity of fused salts ; dissociation in non-aqueous solvents ; 
catalysis ; the author's hydrate theory ; researches of the 
author and co-workers on conductivity and viscosity in mixed 
solvents." American Chemical Journal. 

" The brief, but carefully prepared, historical sketches, intro- 
ducing many of the chapters, as, for instance, the one on 
' Chemical Dynamics and Equilibrium,' and the great num- 
ber of references to original papers form excellent features 
of the book. The marked enthusiasm with which the author 
writes as a worker in the field is bound to interest the stu- 
dent in the subject as a living one, with many vital problems 
yet to be solved." Journal of the American Chemical Society. 



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LOUIS KAHLENBERG'S 
Outlines of Chemistry 



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A text-book for college students by the Professor of Chemistry 
and Director of the Course in Chemistry in the University of 
Wisconsin. 

" The first five chapters are mainly devoted to experimental 
work on hydrogen, oxygen, and chlorine as a foundation of 
fundamental facts and laws for the sixth chapter in which the 
atomic and molecular theories are presented. After two chap- 
ters devoted to ozone, hydrogen peroxide, allotropy, and the 
halogens, in Chapter IX, acids, bases, and salts, hydrolysis, 
mass action, and chemical equilibrium are concisely defined on 
the basis of facts. Chapter XVII includes the elements of 
thermochemistry ; Chapter XX, classification of the elements 
and the periodic system, and Chapter XXIV, solutions, elec- 
trolysis, and electrochemical theories. In this arrangement of 
the essential parts of chemical theory, and with this mode of 
treatment, it would seem that the author has kept well within 
the limits of what the average college student can readily com- 
prehend and assimilate. As stated in the preface, the student 
becomes a clear logical thinker and he does not look upon the 
atomic and molecular theories as something arbitrary, meta- 
physical, and well-nigh incomprehensible ; it is also mentioned 
that in principle this is the method of Bunsen and of many 
other successful teachers of chemistry. Historical connections 
are kept sufficiently in view by frequent allusions. The cuts 
are clear and well made and the subject matter well printed. 
... A critical examination of this work gives the impression, 
I think, that the author has accomplished his purpose and that 
he has given us one of the best books and in some respects the 
best book that has been prepared on this subject." Journal 
of the American Chemical Society. 



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