LIBRARY 
 
 , OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 Class 
 
NOTES 
 
 ON 
 
 ELECTROCHEMISTKY 
 
 BY 
 
 F. G. WIECHMANN, PH.D. 
 
 \ 
 
 NEW YORK 
 
 McGRAW PUBLISHING COMPANY 
 
 190$ 
 
W5 
 
 f>- 
 
 COPTBIGHT 1906, 
 
 BY 
 
 F. G. WlECHMANN 
 All rights reserved. 
 
TO 
 
 CHARLES H. SENFF 
 
 A TOKEN OF 
 ESTEEM AND REGARD 
 
PREFACE. 
 
 THE principal aim kept in view in the preparation of these 
 notes has been the giving of a clear and concise presentation 
 of the general principles which underlie electrochemical 
 science. 
 
 Endeavor has been made to meet the needs of students 
 entering upon the study of electrochemistry and of chemists 
 interested in the application of electrical energy to chemical 
 problems. 
 
 The literature of electrochemistry counts as its own a 
 number of standard works which treat in detail the theories 
 of the science, the methods of electrochemical analysis, and 
 the applications of electrochemistry. Differing from these, 
 the present notes aim merely to offer a general survey of the 
 subject, to serve as an introduction to its study and to aid 
 in the securing of a proper understanding and appreciation 
 of the work along individual lines. 
 
 In the chapter on electro technology, special endeavor has 
 been made to secure the most recent and reliable data and 
 full advantage has been taken of the information given in 
 leading technical journals and in the excellent monographs 
 of Foerster: Elektrochemie Wasseriger Losungen, and of 
 Wright: Electric Furnaces and their Industrial Applications. 
 
 It must however not be forgotten that exact data of 
 technical operations are often very difficult to procure, and 
 therefore the figures given, while well indicating the general 
 conditions obtaining, cannot in all cases claim to be actual 
 working formulae. 
 
 Prefacing each chapter there will be found a bibliography 
 
vi PREFACE. 
 
 of important treatises bearing upon the subject-matter dis- 
 cussed in the chapter. The works so indicated have all been 
 consulted in the preparation of these pages, and the writer 
 would here take opportunity to express his obligations to 
 their authors. 
 
 F. G. W. 
 
TABLE OF CONTENTS. 
 
 PREFACE v 
 
 CHAPTER I. GENERAL PRINCIPLES 1 
 
 General Principles of Science Matter and Energy 
 Forms of Energy Measurement of Physical Phenomena. 
 
 CHAPTER II. ELECTRICAL ENERGY ..." 8 
 
 Theories of Electricity Radio-activity Factors of Elec- 
 trical Energy Properties of Electricity Ohm's Law. 
 
 CHAPTER III. ELECTROCHEMISTRY 22 
 
 Evolution of Electrochemistry Electrolysis Electro- 
 motive Force Dissociation Voltage. 
 
 CHAPTER IV. ELECTROLYTIC DISSOCIATION 41 
 
 The Ion Theory Conductivity Migration of Ions. 
 
 CHAPTER V. ELECTRO-ANALYSIS 66 
 
 Electro-analysis Reversible Reactions and Cells 
 Sources of Current Current Measurement Current 
 Regulation Electrodes Currrent Density Records 
 Resume". 
 
 CHAPTER VI. ELECTROTECHNOLOGY 93 
 
 Introduction Direct Action Processes : Electrodeposition 
 from Solution Electroplating Chlorine and Alkali 
 Hydrates Indirect Action Processes : Electrodeposition 
 from Fused Electrolytes Electrothermic Processes : 
 Electro-furnaces Electro- furnace Products Electro- 
 Organic Processes : Direct Action Processes Silent Dis- 
 charge Electro-Osmosis. 
 
 NAME INDEX 139 
 
 SUBJECT INDEX 141 
 
 vii 
 
THE 
 
 UNIVERSITY 
 
 J 
 
 X^MFOP*. 
 
 NOTES ON ELECTROCHEMISTRY. 
 
 CHAPTER I. 
 GENERAL PRINCIPLES. 
 
 Literature: BERING, C.: "Ready Reference Tables," Vol. I. New 
 York, 1904. HOLMAN, S. W.: " Matter, Energy, Force, and 
 Work." New York, 1898. NOTES, A. A.: "General Principles of 
 Physical Science." New York, 1902. WHBTHAM, W. C. D.: 
 "The Recent Development of Physical Science." Philadelphia, 
 1904. 
 
 General Principles of Science. Before taking up for con- 
 sideration the subject to which these notes are to be devoted, 
 it will not prove amiss to refer briefly to some of the general 
 principles which underlie electrochemistry, as they do all 
 branches of physical science. 
 
 Science is defined as systematized knowledge. Physical 
 science, in its broader aspect, may be said to deal with all 
 phenomena of nature, the Greek word, physis, signifying all 
 nature. Physical science, then, seeks to give a thorough 
 presentation of all natural phenomena, and to formulate 
 principles which will permit of the prediction of such phe- 
 nomena. 
 
 There are two methods which may be legitimately followed 
 in scientific investigation, experience, and speculation based 
 on experience. These two methods are mutually supple- 
 mentary and interdependent, for, reduced to final terms, all 
 human science is knowledge based on experience. 
 
 The first step to be taken in experimental investigation is 
 the collection and accumulation of facts. When a sufficient 
 number of data have been secured, the more the better, the 
 
 1 
 
2 NOTES ON ELECTROCHEMISTRY. 
 
 proper grouping and correlation of these data are required. 
 This is achieved by the process of inductive reasoning. 
 
 Induction consists in the drawing of conclusions from 
 observed facts, in the inference of general principles from 
 the consideration of individual cases. 
 
 But it is not always possible to apply the inductive method, 
 owing to the great number and the complexity of natural 
 phenomena, and, therefore, recourse is often had to another 
 method of reasoning, deduction. 
 
 Deduction consists in the advancing of some general sup- 
 position provisionally adopted to account for certain phe- 
 nomena, and then submitting such supposition to the test of 
 experiment. 
 
 All suppositions of this kind are termed hypotheses. An 
 hypothesis is, therefore, merely a tentative conjecture as to 
 the nature and cause of phenomena. All logical deductions 
 drawn from an hypothesis, unless supported by experimental 
 demonstration, are called theories. 
 
 The crucial test as to the value and validity of all hypoth- 
 eses and theories is, of course, their concordance with re- 
 sults obtained by experiment. Discovery of any fact or 
 facts not in agreement with the tenets of a given hypothesis 
 or theory, at once forces the modification or even abandon- 
 ment of the theory. 
 
 Deduction, then, consists in the derivation of specific con- 
 clusions from a more general proposition; it is obviously the 
 inverse of induction. 
 
 When a general theory, evolved by either the inductive or 
 the deductive method, has been submitted to and verified by 
 experimental proof, it is termed a law. 
 
 A law must not only embrace all known facts and phe- 
 nomena to which it refers, but must also be able to account 
 for all phenomena of like character which may ever be dis- 
 covered. In fact, a law must, to a certain extent, be capable 
 of predicting such phenomena. 
 
GENERAL PRINCIPLES. 3 
 
 A law is simply a concise expression of the results of ex- 
 perience. As Whetham has so ably expressed it: " We must 
 look upon natural laws merely as convenient shorthand 
 statements of the organized information that is at present at 
 our disposal." 
 
 Matter and Energy. Matter and energy are primary con- 
 cepts employed to simplify and to systematize our impres- 
 sions of natural phenomena. 
 
 The two fundamental laws of physical science are concerned 
 with these concepts. These laws are the law of the conser- 
 vation of matter, due to Lavoisier, 1789, and the law of the 
 conservation of energy, due to Robert Mayer, 1842. The 
 first of these laws holds that matter, the second, that energy, 
 can be neither created nor destroyed. 
 
 If we are willing to accept an inseparable blending of mat- 
 ter and energy, giving to this concept the designation, sub- 
 stance, then both of the laws given may be incorporated as 
 one, the law of substance: Substance can be neither created 
 nor destroyed. This law of substance is as far as human 
 reason can conceive a law of universal validity, a law of 
 the cosmos. 
 
 Viewed as a component of substance, matter must be 
 regarded as its inert constituent; it may be defined as that 
 which has extension, which occupies space, which constitutes 
 the tangible portion of the universe. 
 
 Energy, the other component of substance, may be con- 
 sidered as the cause of all changes, of all physical phenomena. 
 As Maxwell has expressed it: " Energy . . . that which in 
 all natural phenomena is continually passing from one por- 
 tion of matter to another. Energy cannot exist except in 
 connection with matter." 
 
 The term " energy " was first introduced by Young, in 1832, 
 as a designation of the product mv 2 (vis viva) ; in the sense 
 in which it is now commonly accepted, it has been used since 
 about 1860. 
 
4 NOTES ON ELECTROCHEMISTRY. 
 
 The principle of the conservation of energy, or, the first 
 law of energetics as it is sometimes called, was first formu- 
 lated by Robert Mayer as a broad generalization from ex- 
 perimental evidence. About 1842 Joule furnished much 
 direct and valuable experimental testimony of its truth, and 
 every test ever made of this most important law has affirmed 
 its correctness. 
 
 Forms of Energy. Energy appears in various forme, for 
 instance as mechanical, as thermal, as chemical, and as electri- 
 cal energy. These forms are mutually convertible, and when- 
 ever a given quantity of some one kind of energy disappears, 
 an exactly equivalent amount of some one other or of several 
 other kinds of energy appear. 
 
 There is, however, one limitation that must be noted in 
 this connection. Whereas all forms of energy can be trans- 
 formed into thermal energy, the complete changing of ther- 
 mal energy into mechanical, or into other forms of energy, 
 cannot be effected. This principle is known as the second 
 law of energetics. 
 
 All forms of energy may be regarded as the product of 
 two factors, intensity and capacity. The former determines 
 whether the energy in a given system must be active or at 
 rest; the capacity-factor determines the quantity of energy 
 present in a given system. In all energy transformations a 
 part of the original energy is changed into heat, and thus, 
 eventually, all energy is doomed to pass into this form; at 
 least at present no process working to reverse this outcome 
 is known. 
 
 Furthermore, in all transformations of heat-energy a part 
 of this energy passes to a lower temperature; radiation, con- 
 duction, and convection aiding to bring about this result. 
 Temperature, however, is the intensity-factor of thermal 
 energy, and, as no work can be obtained from heat unless 
 there are differences in temperature, ultimately, it seems, 
 all energy must pass into the form of diffused heat. When 
 
GENERAL PRINCIPLES. 5 
 
 this shall have occurred, the universe will have attained to 
 one and the same temperature, and then all life and motion 
 must come to an end. This doctrine, known as the theory 
 of the dissipation or the degradation of energy, was first 
 suggested by Sir William Thomson (Lord Kelvin). 
 
 Measurement of Physical Phenomena. Besides matter 
 and energy there are two fundamental concepts which enter 
 into the contemplation of every physical phenomenon where a 
 quantitative study of the same is attempted. These con- 
 cepts are time and space. Time may be considered as a 
 recognition of sequence in human consciousness. The sim- 
 plest form of the concept of space is length. 
 
 Time, space, and mass are of primary importance in nearly 
 all measurements of physical phenomena. To effect such 
 measurements it is necessary to establish a system of stand- 
 ards tp which these measurements can be referred. Various 
 systems of standards have been devised; they differ from 
 one another principally in the selection of their fundamental 
 units. As a matter of fact, however, there is practically 
 only one system used in the scientific work of to-day. This is 
 the centimeter-gram-second system, the C.G.S. system, as it 
 is generally termed from the initial letters of its three units 
 of space, mass, and time. 
 
 The unit of length adopted in this system is the. centi- 
 meter. This is the one-hundredth part of the standard 
 meter, a bar made of an alloy consisting of 90% platinum 
 and of 10% iridium. This standard bar is preserved by the 
 International Bureau of Weights and Measures in Sevres, 
 near Paris, France. 
 
 The unit of mass * of the C.G.S. system is the mass of one 
 
 * Conception of mass, as this term is now used, is due to Newton. 
 A clear distinction must be made between mass and weight. The 
 mass of a body is invariable; it is the same throughout the universe. 
 The weight of a body depends on gravitation: on the earth, for in- 
 stance, the weight of a body measures the earth's attraction for that 
 
6 NOTES ON ELECTROCHEMISTRY. 
 
 cubic centimeter of water at a temperature of 4 Centigrade. 
 It is represented by the one-thousandth part of the Inter- 
 national kilogram, a cylinder made of the same alloy of 
 which the standard meter is made; it also is preserved by 
 the International Bureau of Weights and Measures in France. 
 Copies of these International standards are in the possession 
 of the United fcjtates Government at Washington, D.C. 
 
 The unit of time of the C.G.S. system is the solar second. 
 This is the ^iutf part of a mean solar day. The duration of 
 the latter is of course determined by the motion of the earth 
 with respect to the sun, the interval between successive 
 transits of the sun over the meridian. 
 
 All of the fundamental quantities used in the C.G.S. system 
 are fixed and un variable; and as definite amounts of these 
 quantities, the centimeter, the gram, and the second, have 
 been accepted, this C.G.S. system is designated as an abso- 
 lute system of units. 
 
 The unit of velocity adopted in this system is one centi- 
 meter per second. The unit of force, that force which, acting 
 on one gram-mass at rest, produces in one second a velocity 
 of one centimeter per second this is called a dyne. The 
 unit of energy is the erg: an erg is one dyne acting through 
 one centimeter. 
 
 The units of all forms of energy can be referred to the centi- 
 meter, the gram, and the second. In the measurement of 
 electrical energy there are two C.G.S. systems: the electro- 
 static and the electromagnetic system. In the electro- 
 static system all units are based upon the force exerted 
 between two quantities of electricity that amount of elec- 
 tricity which attracts or repels an equal amount of electricity 
 one centimeter distant with the force of one dyne. 
 
 body. Weight, however, is- the most convenient measure of mass, 
 and consequently these two terms are frequently, though errone- 
 ously, considered synonymous. 
 
GENERAL PRINCIPLES. 7 
 
 The electromagnetic system is based upon the force ex- 
 erted between an electric current and a magnetic pole. In 
 this system the unit current of electricity is defined as that 
 current which, flowing through an arc of one centimeter, 
 curved to a radius of one centimeter, generates a unit mag- 
 netic pole at the center.. The electrical units in common 
 use are based on this system. 
 
 
CHAPTER II. 
 ELECTRICAL ENERGY. 
 
 Literature: DESCHANEL, A. P., and EVERETT, J. D.: "Natural Phi- 
 losophy." New York, 1889. HABER, F.: "Grundriss der Tech- 
 nischen Elektrochemie auf Theoretischer Grundlage." Miinchen, 
 1898. HERING, C.: "Ready Reference Tables," Vol. I. New 
 York, 1904. LE BLANC, M. (English translation by WHITNEY, 
 W. R.): "Elements of Electrochemistry." London, 1896. RO- 
 SENBERG, E. (English translation by SEE, W. W. H., and KINZ- 
 BRUNNER, C.): "Electrical Engineering." New York, 1903. 
 RUTHERFORD, E: " Radio-Activity." Cambridge, 1904. SODDY, 
 F. : "Radio-Activity, an Elementary Treatise, from the Stand- 
 point of the Disintegration Theory." New York, 1904. 
 
 Theories of Electricity. The word " electricity " is derived 
 from the Greek, electron, amber, because the manifestation 
 of certain electrical properties attraction, repulsion 
 was originally noted in amber. Credit for having been the 
 first to observe these phenomena is generally given to Thales, 
 who lived some two thousand years ago. 
 
 Introduction of the word " electricity " is due to William 
 Gilbert, or Gilberd (1540-1603), who has been named " the 
 creator of the science of electricity." His principal work, 
 " De Magnete, Magneticisque Corporibus, et de Magno Mag- 
 nete Tellure, Physiologia Nova/' published in 1600, is re- 
 plete with interesting facts and observations of magnetic 
 phenomena. 
 
 Since the days of Gilbert innumerable observations of 
 electrical phenomena have been made, and a great number 
 of data bearing on them have been recorded. Still, although 
 so much is known of the properties of electricity, and al- 
 though electricity has unquestionably become one of the 
 
ELECTRICAL ENERGY. D 
 
 most potent agencies in the advancement of human welfare, 
 the true nature of electricity remains as yet an unsolved 
 problem. 
 
 At various times, various theories have been advanced in 
 explanation of electrical phenomena. Thus, Benjamin Frank- 
 lin (1706-1790) suggested the one-fluid theory of electricity. 
 All unelectrified bodies were supposed to possess a normal 
 amount of electricity; a positively electrified body contained 
 an excess, a negatively electrified body, a deficiency of this 
 electric fluid. 
 
 Franklin was the one to introduce the terms positive and 
 negative electricity. They are retained to this day as con- 
 ventional terms, indicating for one thing forces in opposite 
 directions, for instance, the direction of flow of electric 
 currents. 
 
 Dufaye, in 1733, originally advanced the two-fluid theory 
 of electricity; it was more precisely formulated by Symmer. 
 This theory holds that there are two kinds of electricity 
 positive and negative; union of equal amounts of the two 
 forms the neutral fluid, which is present in all unelectrified 
 bodies. The total amount of electric fluid in a body is a 
 constant quantity; additional gain of the one kind necessi- 
 tates an equivalent loss of the other. Whenever an electric 
 current of one kind flows through a conductor in one direc- 
 tion, an equivalent amount of current of the other kind flows 
 in the opposite direction. 
 
 Both of these " fluid " theories hold in common that the 
 electricity passing along a conductor the electric current 
 is continuous in character. 
 
 Recent studies, however, made in the discharge of elec- 
 tricity through gases, have brought about a decided change 
 of view concerning the nature of electricity. 
 
 Such discharges of electricity through gases are unquestion- 
 ably convective. Particles charged with positive, and par- 
 ticles charged with negative electricity, are present in gases; 
 
10 NOTES ON ELECTROCHEMISTRY. 
 
 these particles, ions, which term signifies wanderers, can be 
 induced in gases by Rontgen rays, by ultra-violet light, and 
 by other means. They move under the influence of elec- 
 trical energy, and it is their motion which constitutes the 
 electric current. 
 
 From the researches of J. J. Thomson it appears that the 
 negatively charged particles thus present in a gas have a 
 mass of approximately one one-thousandth that of a hydrogen 
 atom; positively charged particles of similar dimensions are 
 not known. 
 
 The electron theory, the theory which promises to become 
 the leading theory of electricity in the immediate future, is 
 based on these studies. According to the electron theory 
 there exists but one kind of electricity, that which is gen- 
 erally designated as negative electricity. 
 
 This negative electricity is assumed to occur in definite 
 unit charges, and these smallest particles of electricity, the 
 atoms of electricity, are termed electrons. 
 
 The term " electron " was originally given by G. Johnstone 
 Stoney to the definite charges of electricity associated with 
 ions; the concept of electrons as separate, distinct individual 
 particles was only arrived at later. However, in this con- 
 nection it is interesting to recall that W. K. Clifford, as early 
 .as 1875, made the following statement: " There is great reason 
 to believe that every material atom carries upon it a small 
 electric current, if it does not wholly consist of this current." 
 
 In a substance which is electrically neutral, the electrons 
 are so disposed with respect to the balance of the matter 
 that there is no evidence of an outside electric field. 
 
 In a substance which bears a positive charge of electricity, 
 there is a lack, a deficiency of electrons. A substance which 
 is negatively charged has an excess of electrons. As Sir 
 William Crookes has expressed it: " A : so-called negatively 
 charged chemical atom is one having a surplus of electrons, 
 the number depending on ttie valency, whilst a positive ion 
 
 
ELECTRICAL ENERGY. 11 
 
 is one having a deficiency of electrons. Differences of elec- 
 trical charge may thus be likened to debits and credits in 
 one's banking account, the electrons acting as current coin of 
 the realm. On this view only the electron exists; it is the 
 atom of electricity, and the words positive and negative, 
 signifying defect and excess * of electrons, are only used for 
 convenience of old-fashioned nomenclature." 
 
 Radio- Activity. In this connection reference must be 
 had to the subject of radio-activity, a theme so intimately 
 concerned with the theory of electrons, and of vital interest 
 and importance on account of the far-reaching influence it 
 is exerting on the present trend of physical science in par- 
 ticular, and of scientific thought in general. 
 
 Discovery of the X-rays by Ron tgen (1895) led to numer- 
 ous researches to determine whether analogous radiations 
 might not be given out by other substances. Thus, Bec- 
 querel, in 1896, discovered the radio-activity of uranium; 
 G. C. Schmidt, in 1898, that of thorium; and M. and Mme. 
 Curie, together with M. Bemont, also in the year last 
 named, isolated the new element radium from the mineral 
 pitchblende. 
 
 Radium gives out three kinds of rays, named the a-, -, and 
 y-rays. 
 
 The a-rays are material particles bearing charges of posi- 
 tive electricity. They have a mass equal to about twice the 
 mass of a hydrogen atom; they move with a velocity about 
 one-tenth that of light, i.e., about 20,000 miles per second, 
 and are readily arrested by an air-gap of a few centimeters, 
 by paper, and by thin layers of aluminium foil. The lumi- 
 nous phenomena shown by the spinthariscope of Sir William 
 Crookes are caused by the impact of a- particles on a screen 
 of sulphide of zinc, these impacts of the swiftly moving par- 
 
 .* In -the original, Bericht V. Int. Kong. Ang. Chem. 1903, Vol. I, 
 p. 96, the words "defect" and "excess" are printed in reverse 
 order. F. G. W. 
 
12 NOTES OX ELECTROCHEMISTRY. 
 
 tides evoking the flashes which make the screen appear a 
 seething sea of light. 
 
 The -rays are in all probability identical with the cathode 
 rays which appear at the negative electrode of a vacuum 
 tube on the passing of an electric discharge. These /3-rays 
 consist of negatively charged particles having a mass of 
 approximately one one-thousandth the mass of a hydrogen 
 atom; they travel with a velocity approximating to that of 
 light. The minuteness of these little particles will be appre- 
 ciated from a comparison made by Sir William Crookes, who 
 stated, that if the sun's diameter were taken to be about one 
 and one-half million kilometers, and that of the smallest planet- 
 oid about twenty-four kilometers, that then, if an atom of 
 hydrogen were magnified to the size of the sun, an electron 
 would have a diameter about two-thirds that of the planetoid. 
 
 The )8-rays are the chief agents in the photo-activity of 
 the radium rays. Like the a-rays, the /?-rays are also de- 
 flected by a magnetic field, but in a direction opposite to 
 that in which the a-rays are turned. 
 
 The y-rays are more penetrating than either the a- or 
 /3-rays. They are not deflected by an electric field, and thus 
 far no proof has been furnished that they are material par- 
 ticles; possibly they may be ethereal vibrations analogous to r 
 or even identical with, the Rontgen rays. 
 
 Considered as a whole, radium rays exercise certain re- 
 markable influences. They evoke luminosity in some sub- 
 stances, in sulphide of zinc, for instance, and in diamonds; 
 they destroy the power of germination in seeds; they can 
 extend the larvae stage of some insects, and can cause burns 
 and even bring death to living organisms. 
 
 The property which radium rays possess of ionizing dry 
 air and other gases, that is, of making these substances con- 
 ductors of electricity, is taken advantage of for their detec- 
 tion and for the measurement of the strength of radium 
 preparations. This determination is accomplished by bring- 
 
ELECTRICAL ENERGY. 13 
 
 ing a sealed tube containing radium into the neighborhood 
 of an aluminium-foil electroscope placed in dry air. The 
 radium transforms the air, which is normally an insulator, 
 into a conductor, and this enables the electric charge of the 
 electroscope to pass away. The speed with which this dis- 
 charge takes place allows of a quantitative estimation of the 
 radio-activity of the preparation. 
 
 In addition to the three kinds of rays which radium emits, 
 it also gives off an emanation which is more radio-active than 
 radium itself. This emanation is poisonous to animal life, 
 is very unstable, slightly soluble in water, and is condensed 
 at a temperature of 150 C. to 155 C. 
 
 As determined by Sir William Ramsay and Mr. Soddy, 
 this emanation has been found to yield another element 
 helium as one of its products of decomposition. Appar- 
 ently, radium passes through six other stages before it finally 
 appears in the form of helium, which is not radio-active. 
 This transformation proceeds undisturbed by changes in ex- 
 ternal conditions, such as changes in temperature, light, or dark- 
 ness. It has been estimated that about one two-thousandth 
 part of a given quantity of pure radium disintegrates per 
 annum. The change of radium into helium is thus far the 
 only authenticated instance known of a transmutation of 
 one element into another. 
 
 Induced radio-activity is caused by a very fine film of a 
 solid substance deposited by the radium emanation on sur- 
 faces exposed to it. This film may be mechanically removed 
 by brushing or by wiping it with a cloth; if left undisturbed 
 this film soon loses its radio-activity. 
 
 Radium also continuously gives out energy in the form of 
 heat. One gram of pure radium gives out about 100 calo- 
 ries per hour, and Rutherford has estimated that the heat 
 given out by the transformation of one gram of radium into 
 helium is about one million times as great as the heat given 
 out in the formation of one gram of water. 
 
.14 NOTES ON ELECTROCHEMISTRY. 
 
 An interesting hypothesis to account for the usual positive 
 electrification of the atmosphere and for the negative electri- 
 fication of the earth, has been based by Professor Ebert on 
 the activity of radio-emanations. He holds that these ema- 
 nations in passing from the earth into the atmosphere impart 
 their negative charge to the capillaries of the soil through 
 which they pass, and thus enter the air with high positive 
 charges, which they transmit to the atmosphere. 
 
 Factors of Electrical Energy. If one chooses to look upon 
 electricity as a form of energy, then electricity, like all other 
 forms of energy, may be viewed as the product of two fac- 
 tors, an intensity-factor and a capacity-factor. 
 
 The intensity-factor of electrical energy is termed its po- 
 tential or tension; the capacity-factor represents quantity of 
 electricity. To compare electrical with thermal energy, for 
 instance, electric potential corresponds to the temperature 
 of thermal energy, electric capacity corresponds to heat- 
 capacity. 
 
 Heat always passes from objects of a higher to objects of 
 a lower temperature; the extent of heat-exchange between 
 two points of unequal temperatures is determined solely by 
 the difference between those temperatures, but is wholly 
 independent of the absolute temperatures. 
 
 In a similar manner the passing of an electric current 
 between two points is determined by the difference in 
 tension-potential between those points. When positive elec- 
 tricity passes from a point of higher to a lower potential, a 
 corresponding amount of negative electricity must be con- 
 ceived of as passing in the opposite direction. This may, in 
 a way, be regarded as analogous to the conception that a 
 given amount of cold is raised to a higher temperature when- 
 ever an equal amount of heat passes from a higher to a lower 
 temperature. 
 
 Properties of Electricity. Electricity may be conveyed 
 from one location to another either by means of conductors 
 
ELECTRICAL ENERGY. 15 
 
 in which there is no evident, simultaneous movement of the 
 matter of which the conductor consists, or by means of sub- 
 stances in which a transportation of material particles ac- 
 companies the transference of the electric charge. Con- 
 ductors of the former kind are known as conductors of the 
 first class; the metals, metallic sulphides, and carbon belong 
 to this group. Conductors of the other kind are called con- 
 ductors of the second class; to these belong the salts, the 
 acids and bases when in solution, and salts and bases also 
 when in a state of fusion. 
 
 While the domain of electrochemistry lies essentially with 
 conductors of the second class, for the moment attention 
 shall be given to the phenomena to be noted when a current 
 of electricity flows along a conductor of the first class, for 
 instance, along a metal wire. 
 
 If a plate of copper and a plate of zinc are placed in a 
 vessel containing dilute sulphuric acid, and the two metal 
 plates are connected by a metal wire, outside of the fluid, 
 observation will show that this wire soon becomes heated, 
 and if a break is made anywhere in this wire so that an air- 
 gap intervenes between the two ends of the wire, a spark of 
 light will appear the instant the break is made. 
 
 If the wire remain unbroken, a magnetic needle brought 
 near to it will be deflected from its normal position. If the 
 wire be wound around a bar of soft iron, the iron becomes 
 magnetic, and remains so at least as long as the wire encircles 
 it. If the wire be cut or broken and the ends inserted in 
 acidulated water, bubbles will arise from the water, and the 
 water will be found to suffer decomposition into its compo- 
 nent elements, oxygen and hydrogen gases. 
 
 These phenomena make evident that some process is taking 
 place an electric current is passing along the wire, and 
 the phenomena referred to establish the fact that an 
 electric current can induce heating, lighting, magnetic and 
 chemical effects. 
 
16 NOTES ON ELECTROCHEMISTRY. 
 
 There is evidently a force at work which drives the electric 
 current along the wire. If we use two galvanic elements in- 
 stead of one, connecting the zinc-plate of element No. 1 with 
 the copper-plate of element No. 2, and then lead a connecting 
 wire from the copper-plate of No. 1 to the zinc-plate of No. 2, 
 a much stronger current will be secured than if only one 
 element had been used. It appears that the pressure driving 
 the electric current along the wire has been increased. The 
 pressure thus forcing the current along the wire is termed 
 electromotive force, and the unit in terms of which this is 
 measured is the volt. 
 
 The International volt is that electromotive force which 
 will maintain one International ampere through a resistance 
 of one International ohm. For practical purposes it is 
 represented by 1 -*- 1.434 of that of a Clark cell at 15 C. 
 
 The cause of the flow of the electric current is, as has been 
 said, a difference in the electrical pressure, a difference in 
 electrical potential between different parts of the circuit. 
 Water standing in two connecting vessels will remain at rest 
 whenever it stands at the same level in both vessels. If, 
 however, there is a difference of level in the two vessels, then 
 the force determined by the difference in height of these 
 levels will cause a current of water to flow from the higher to 
 the lower level. By analogy we can conceive a similar dif- 
 ference in electric pressure to be the cause of flow of an 
 electric current. 
 
 The rate of flow of an electric current per second is termed 
 its current strength. Current strength, or current intensity, 
 as it is also called, is measured in amperes. The International 
 ampere is the current which, under specified conditions, will 
 deposit 0.001118 gram of silver per second. 
 
 Amperes are comparable to the flow of water measured 
 in some unit of volume, for instance, in liters or in cubic 
 feet per second. Thus, a flow of water of 20 liters per second 
 under a pressure of 50 kilograms, increases to a flow of 40 
 
ELECTRICAL ENERGY. 17 
 
 liters per second under a pressure of 100 kilograms. In an 
 analogous manner an electric current of 20 amperes under 
 an electric pressure of 50 volts is changed to a current of 40 
 amperes under a pressure of 100 volts. Amperes do not 
 .decrease by doing work, neither does a volume of water 
 grow less in consequence of doing work, driving a turbine, 
 for instance; the work done is in direct ratio to the drop in 
 potential or pressure. 
 
 In passing through a conductor, the electric current has to 
 overcome the resistance in its path. The longer the con- 
 ductor, a wire, for instance, and the smaller its cross-section, 
 the greater is the resistance to be overcome. In other 
 words, it may be said that the resistance varies directly as 
 the length and inversely as the cross-section of the conductor 
 along which a current flows. 
 
 Resistance is measured in units called ohms. The Inter- 
 national ohm is represented by the resistance of a column 
 of mercury at C. 106.3 centimeters long, weighing 14.4521 
 grams, and having a uniform cross-section. The resistance 
 met by an electric current in its flow is directly comparable 
 to the friction encountered by a current of water flowing 
 through a pipe; there, too, the friction varies directly with 
 the length of the pipe and inversely with its diameter. 
 
 The names of the electrical units thus far considered are 
 derived from the names of men eminent in the development 
 of electrical science. Thus, the volt is taken from the name 
 of Alexander Volta (1745-1827), the ampere from that of 
 Andre Marie Ampere (1775-1836), the ohm from that of 
 Georg Simon Ohm (1789-1854). 
 
 Ohm's Law. There is an intimate relation between the 
 electromotive force, the current strength, and the resistance 
 of an electric current. 
 
 If these terms be represented by their initial letters, 
 thus: 
 
18 NOTES ON ELECTROCHEMISTRY. 
 
 Current strength *=* 0, fc 
 
 Electromotive force = E, 
 
 Resistance = R, 
 p 
 
 the expression C = indicates that the current strength is 
 R 
 
 equal to the electromotive force divided by the resistance. 
 
 This is the famous law of Ohm, the discoverer of the 
 relation here expressed; it is a law of fundamental impor- 
 tance in electrical science. 
 
 By transposition we have : 
 
 ..,, . -. ..... ii 
 
 E = CR, 
 
 and as the unit of current strength is the ampere, that of 
 resistance the ohm, and that of electromotive force the volt, 
 these formulae express that: 
 
 Amperes = volts -H ohms, 
 Ohms = volts -s- amperes, 
 Volts = amperes x ohms. 
 
 In addition to the units discussed, there are several others 
 which are frequently used in considering electrical data. 
 
 The coulomb is the unit of electrical quantity; the word 
 is derived from the name of Charles Augustm Coulomb 
 (1736-1806). The International coulomb is defined as the 
 quantity of electricity transferred by a current of one Inter- 
 national ampere in one second. 
 
 Sometimes the quantity of electricity transferred by a 
 current of one ampere in one hour is employed as a unit; 
 this is called an ampere-hour, and is a unit much used jn 
 electrochemistrv. 
 
ELECTRICAL ENERGY. 19 
 
 The farad, derived from the name of Michael Faraday 
 (1791-1867), is the unit of electrical capacity, for instance, 
 of a condenser, to hold electric charges under electric pres- 
 sure or stress. The capacity in farads equals the charge in 
 coulombs divided by the electromotive force in volts. The 
 unit actually used, however, for measurements of electrical 
 capacity, is the microfarad, one one-millionth of a farad. 
 
 The watt is the unit of electrical power; the name com- 
 memorates James Watt (1736-1819), the pioneer of modern 
 steam-engineering. The power in watts is the product ob- 
 tained by multiplying volts and amperes. Representing 
 power by P, the various relations between power, electro- 
 motive force, current strength, and resistance are indicated 
 
 by the formula?: P = EC; P = ~ ; P = C 2 R. The de- 
 
 H 
 
 pendence of electric power on both current strength and 
 voltage is evident from a consideration of the analogy pre- 
 viously introduced. In that case, it will be recalled, the 
 work effected by the flowing water was determined by both 
 the difference in height between the two water-levels and by 
 the amount of water passed. One kilogram of water flowing 
 down a height of one hundred meters, will do five times 
 the work that is done by one kilogram of water flowing down 
 a height of twenty meters. .The power of falling water is 
 thus measured in kilogrammeters per unit of time (second or 
 minute) ; 75.0 kilogrammeters per second are one metric horse- 
 power. The flow of water per second corresponds to the 
 electric current strength; the water-pressure due to the dif- 
 ference of the water-levels, to its voltage. Thus, 735:448 
 watts are equal to one metric horse-power. One thousand 
 watts are called one kilowatt, and are equivalent to 1.35972 
 metric horse-powers.* 
 
 * 1 H.P. = 76.0404 kg.-meters per second. 
 1 H.P. = 745,650 watts. 
 1.34111 H.P. = 1000 watts. 
 
20 NOTES ON ELECTROCHEMISTRY. 
 
 The unit of electrical energy or work is the joule. The 
 term is derived from the name of James Prescott Joule 
 (1818-1889), who practically prepared the way for the scien- 
 tific study of thermodynamics. 
 
 A current of one International ampere flowing through a 
 resistance of one International ohm for one second does one 
 joule of work. Joules are the product of coulombs and 
 volts; in other words, joules represent watts per second. 
 
 If the ampere-hour is taken as the unit of electrical quan- 
 tity, the corresponding unit of electrical energy or work is 
 the volt-ampere-hour; this is generally designated as the 
 watt-hour; 1000 watt-hours are termed one kilowatt-hour. 
 
 The relation between electrical energy and heat energy 
 was clearly established by Joule, in 1841. This relation is 
 expressed in the following law which bears his name: "The 
 heat generated in the whole or in a part of an electric circuit 
 in the unit of time, is proportional to the resistance and to 
 the square of the current strength." 
 
 Experimental study has shown that 4.18617 (approxi- 
 mately, 4.2) watts per second correspond to 1 calorie the 
 calorie being defined as the amount of heat necessary to raise 
 the temperature of one gram of water from 15 to 16 hy- 
 drogen scale. This is regarded as equivalent to one one- 
 hundredth of the amount of heat that will raise the tempera- 
 ture of one gram of water from to 100 C. 1-5- 4.18617 
 = 0.238882; therefore 0.238882 calorie is the heat equivalent 
 of one joule, and this means that one joule will raise the 
 temperature of 0.238882 gram of water 1 C. 
 
 The unit of inductance is the henry, named for Joseph 
 Henry (1797-1878). This unit is used in measuring the 
 intensity of that property in virtue o-f which changes of 
 current in the circuit itself, or changes of current in an 
 adjacent circuit, produce electromotive force. The henry is 
 the quotient obtained by dividing induced volts by rate of 
 change of amperes per second. 
 
ELECTRICAL ENERGY. 21 
 
 The values of the various electrical units discussed were 
 fixed by an International Congress of Electricians, which met 
 in Chicago, United States of America, in 1893. 
 
 It will be recalled that the absolute system of electrical 
 units used is electromagnetic in character; that is to say, 
 that the units in that system are based upon the force ex- 
 erted between an electric current and a magnetic pole. As 
 these regular C.G.S. units are, however, as a rule either too 
 great or too small for convenient practical use, the system 
 of practical units, which has just been so fully discussed, 
 has been devised. 
 
 These practical units, as they are called, are either exact 
 multiples or submultiples of the absolute C.G.S. units of the 
 electromagnetic system. The following table shows their 
 relation : 
 
 CORRESPONDS TO 
 UNIT OF : NAME : C.G.S., UNITS : * 
 
 Electromotive-force . . . Volt .... . . . . 10 8 
 
 Current strength .... Ampere 10~' 
 
 Resistance Ohm 10 8 
 
 Quantity Coulomb 10~ l 
 
 Capacity Farad 10~ 8 
 
 Power Watt 10 7 erg per second 
 
 Energy or Work Joule 10 7 erg 
 
 Inductance Henry 10* 
 
 * In index-notation a positive exponent indicates an integral 
 number; thus, 10 2 =100, 10 3 = 1000, etc. A negative exponent de- 
 notes the reciprocal of the indicated power of 10; thus, 10~ 3 =0.01, 
 10- 3 =0.001, etc. . . . 
 
CHAPTER III. 
 
 :-;v i..; ; , ,:j . '' . ..." 'P'i^ ;:-v^v; 
 
 ELECTROCHEMISTRY. 
 
 Literature: FERCHLAND, P.: "Grundriss der reinen und angewandten 
 Elektrochemie." HALLE, A. S. 1903. HABER, F.: "Grundriss 
 der Technischen Elektrochemie auf Theoretischer Grundlage." 
 Leipzig, 1898. JONES, H. C.: "Elements of Physical Chemistry." 
 New York, 1902. JONES, H. C.: "Outlines of Electrochemistry." 
 New York, 1901. LE BLANC, M. (English translation by WHIT- 
 NEY, W. R.): "The Elements of Electrochemistry." London, 
 1896. LE BLANC, M.: "Lehrbuch der Elektrochemie." Leipzig, 
 1903. LEHFELDT, R. A.: "Electrochemistry," Part I, General 
 Theory. New York, 1904. OSTWALD, W.: "Elektrochemie, ihre 
 Geschichte und Lehre." Leipzig, 1896. WIECHMANN, F. G.: "Lec- 
 ture-notes on Theoretical Chemistry." New York, 1895. 
 
 Evolution of Electrochemistry. Electrochemistry is the 
 study of the mutual relation and transmutation of electrical 
 and chemical energy. It deals with electrical phenomena 
 which are caused by chemical reactions, and with chemical 
 changes which result from the application of electrical energy. 
 
 Perhaps the earliest instance on record of the bringing 
 about of chemical change by electricity is the reduction of 
 metallic zinc and mercury from their respective oxides by 
 Beccaria, about the seventh decade of the eighteenth century, 
 who achieved his results by sparking the oxides of the metals 
 named by discharges from Leyden jars. 
 
 In 1775 John Priestley discovered that electric sparks 
 passing through air acidify the air. Priestley believed that 
 the acid produced was carbonic acid, but Cavendish, repeat- 
 ing the experiments of Priestley, showed that nitrous and 
 nitric acids were formed. 
 
 Ten years later Van Marum in Rotterdam, subjected many 
 
ELECTROCHEMISTRY. 23 
 
 gases and metallic substances to the discharges of a power- 
 ful electrical friction machine, and among other chemical 
 changes which he thus effected was the decomposition of 
 "alkaline air" (ammonia) into its components, nitrogen and 
 hydrogen. 
 
 Electrolytic decomposition of water into "combustible 
 air " (hydrogen) arid " life air" (oxygen) was accomplished, 
 in 1789, by Paets van Troostwijk, Deimann, and Cuthbert- 
 son. Their experiments were most carefully made with 
 distilled water and with water from which the absorbed air 
 had been removed under vacuum; they thus proved the 
 belief that water consists of hydrogen and oxygen gases to 
 be well founded. 
 
 The speculations which were indulged in at that time 
 regarding the nature of electricity are interesting. By 
 some, electricity was held to, be a substance dual in its char- 
 acter, which entered into union with the elemental constit- 
 uents of the compounds decomposed by its influence; others 
 believed it to be a highly concentrated form of fire and ac- 
 counted for its great powers on that supposition. 
 
 The experiments so far referred to, all relate to the 
 production of chemical effects by the agency of electrical 
 energy. The first attempt recorded to produce electrical 
 phenomena by chemical agencies is the experiment made by 
 Alessandro Volta, Lavoisier, and De Laplace, which con- 
 sisted in electrifying an isolated metallic plate by placing 
 on it, respectively, basins with burning charcoal and dishes 
 in which sulphuric acid was poured over iron filings. 
 
 About the same time, in 1782, these investigators at- 
 tempted, although with but indifferent success, to generate 
 electricity by the evaporation of water and the subsequent 
 condensation of the vapor, Volta having been led to the 
 conception of this idea through his studies of atmospheric 
 electricity, in which he had noticed indications of the presence 
 of electric charges in rain and in fog. < -\&iu\... 
 
24 XOTES ON ELECTROCHEMISTRY. 
 
 An incidental observation made during some physiological 
 experiments led Aloysius Galvani, professor at the University 
 of Bologna, in 1791, to the discovery of a form of electricity 
 until then unknown; he styled lit animal electricity, conclud- 
 ing that the electricity thus made manifest in his experi- 
 ments was produced by the brain of the animals on which 
 he worked, and that the electricity thus segregated from 
 the blood passed through the nerve-channels into the muscles, 
 these being practically a kind of Ley den jar. 
 
 Volta, although he originally shared the views of Galvani, 
 was gradually led to abandon the supposed biological origin 
 of these electrical manifestations, and ultimately showed 
 their origin to lie in the contact of two dissimilar metals. 
 This discovery led him to establish the contact theory of 
 electricity, 1792-1793, which held sway for many years. 
 
 In 1800 Volta published an account of the voltaic pile, 
 which made it possible to produce galvanic electricity - 
 "metallic electricity," as Volta termed it in sufficient 
 quantity and of sufficiently high potential to permit of a 
 study of chemical actions induced by the electric current. 
 The beginning of electrochemistry proper may, therefore, be 
 said to date from the invention of the voltaic pile, although 
 it should not be forgotten that Professor Fabroni, of Florence, 
 in 1792, had suggested chemical action to be " the nature of 
 the new stimulus," in speaking of electricity evoked by the 
 immersion of metals in water. 
 
 In 1800, the same year in which Volta announced the 
 construction of the voltaic pile, Carlisle and Nicholson 
 effected the electrolytic decomposition of water by means of 
 such a pile, an experiment which, it will be recalled, had 
 already been made by the aid of frictional electricity in 1789. 
 Carlisle and Nicholson also noticed the chemical reactions 
 taking place within the voltaic pile itself. A little later Dr. 
 Henry, of Manchester, England, effected the electrolytic decom- 
 position of ammonia, of nitric acid, and of sulphuric acid. 
 
ELECTROCHEMISTRY. 25 
 
 Dr. Wollaston, in 1801, ascertained that silver can be 
 electrolytically plated with copper, if the silver, in connection 
 with some metal more positive than itself, is immersed in a 
 solution of a copper salt. In 1803 Berzelius and Kissinger 
 effected the electrolytic decomposition of water and of some 
 neutral salts, while about the same time Cruickshank sug- 
 gested the use of the electric current for the analysis of 
 minerals, he having observed the electro-deposition of silver, 
 copper, and lead from some of their respective salts. In 
 1805 the electro-deposition of gold on silver, and the electro- 
 deposition of zinc were discovered by Brugnatelli. 
 
 In this same year Von Grothuss offered an explanation to 
 account for the electrolytic decomposition of water. At the 
 instant of such decomposition of a molecule of water, the 
 hydrogen is charged electropositively and the oxygen electro- 
 negatively. The former is repelled from the positive pole 
 and is attracted to the negative pole; the oxygen is repelled 
 from the negative, and is attracted to the positive pole. 
 The initial work the electricity was supposed to perform 
 was decomposition of the water molecules. This had to be 
 done ere electrolysis could be effected. When the electric 
 current had entered the water, the hydrogen atom adjacent 
 to the negative pole gave up its charge to that pole, and, 
 having become electrically neutral, separated in the form of 
 hydrogen gas. The oxygen atom which had been in union 
 with this atom, combined with the hydrogen atom of the 
 next water molecule, and thus the impulse passed along 
 until the last oxygen atom, in contact with the positive 
 pole, had its charge neutralized by the charge of this pole, 
 and then escaped as oxygen gas. 
 
 The first decade of the nineteenth century also witnessed 
 the separation of several of the alkali metals from their 
 hydrates, by Sir Humphrey Davy; thus, potassium and 
 sodium were first obtained by him in this manner in October, 
 1807. 
 
26 NOTES ON ELECTROCHEMISTRY. 
 
 Led thereto by the results of his experiments, Davy ad- 
 vanced his electrochemical theory, probably the first theory 
 of its kind ever formulated ; it rests upon the atomic hypoth-^ 
 esis of Dalton. According to its teaching, the atoms of 
 substances as such bear no electric charges, but they acquire 
 positive or negative charges by contact with each other. 
 Chemical affinity is caused by and depends on the attraction 
 of such opposite electrical charges. Electrolytic decomposi- 
 tion is effected by the neutralization of these charges. 
 
 This theory of Davy's met with considerable opposition, 
 and was soon displaced by the views advanced by Berzelius, 
 outlined in 1812 and published in detail two years later. 
 
 Berzelius held that every atom was charged with both 
 positive and negative electricity, and that the electrical 
 behavior of the atom depended upon whichever of these 
 charges was present in excess. Chemical attraction was also 
 ascribed to electrical attraction between opposite charges; 
 the one or the other of these predominated, and in accord- 
 ance therewith the resultant compound Exhibited either an 
 electropositive or an electronegative character. 
 
 Objections to this theory of Berzelius were, however, not 
 lacking. It was held that if the electrical charges of the 
 atoms determined chemical union, that then the properties 
 of a compound must be a function of those charges. The 
 fact that three atoms of chlorine (electronegative) could be 
 put in the place of three atoms of hydrogen (electropositive) 
 of the methyl group in acetic acid without causing a funda- 
 mental disturbance of the nature of the compound, was an 
 obstinate fact which Berzelius could not account for. 
 
 It remained for J. J. Thomson, in 1895, to show that an 
 element may, according to circumstances, bear either an 
 electropositive or an electronegative charge, and that " it 
 would appear that the chlorine atoms, in the chlorine deriv- 
 atives of methane, are charged with electricity of the same 
 kind as the hydrogen atoms they displace.'* 
 
ELECTROCHEMISTRY, 27 
 
 The brilliant -work and discoveries of Michael Faraday, 
 beginning in 1832, mark the next important epoch in the 
 history of electrochemistry. 
 
 Faraday first determined the identity of electricity pro- 
 duced by friction and by the voltaic pile. When he had 
 established this, he turned his attention to the relation be- 
 tween the amount of electricity passing through a circuit 
 and its magnetic and chemical effects, and found that the 
 amount of chemical decomposition produced in an electrolyte 
 is proportionate to the amount of electricity which passes 
 through the electrolyte. 
 
 Faraday further studied the relation between the amounts 
 of different elements set free from their compounds on pass- 
 ing a given electric current through solutions of these com- 
 pounds. Among the substances which he investigated in 
 this manner were solutions of some salts of copper, of silver, 
 and of zinc. He thus determined that the amounts of differ- 
 ent elements separated by the same quantity of electricity, 
 stand in the same relation to each other as the chemical 
 equivalents * of those elements. This means that all mono- 
 valent atoms bear the same amount of electricity, and that all 
 multivalent atoms bear some simple multiple of this amount. 
 
 It must be especially noted that these laws of Faraday 
 emphasize the fact that equal quantities of electricity sepa- 
 rate chemically equivalent amounts of the elements; the 
 electromotive force, the potential necessary to effect this, 
 is not referred to at all; this factor has different values 
 with different electrolytes, as will be discussed later. 
 
 In 1857 Clausius pointed out the shortcomings of the 
 theory advanced by Grothuss, and suggested that solutions 
 of an electrolyte must contain some part-molecules in addi- 
 tion to non-decomposed, entire molecules. This hypothesis 
 offered an explanation of the fact that even very weak 
 
 * The chemical equivalent of an element is the atomic muss of that 
 element divided bv its valence. 
 
28 .\OTES ON ELECTROCHEMISTRY. 
 
 currents, in some instances, can effect electrolysis, the cur- 
 rent exercising a directing influence on the part-molecules 
 originally present. This work of Clausius practically pre- 
 pared the way for the theory of electrolytic dissociation, 
 which was brought out thirty years later. 
 
 It was in 1887 that J. H. Van't Hoff published his valuable 
 article on the role which osmotic pressure plays in solutions. 
 This paper, in the same year, inspired the hypothesis of 
 Planck, based on thermodynamical considerations, and the 
 theory of electrolytic dissociation advanced by Svante 
 Arrhenius, who was able to furnish experimental proof of 
 the truth of Planck's assumptions, and who thus established 
 the famous theory which to-day holds the leading place in 
 electrochemical science. This theory will later be con- 
 sidered in detail. 
 
 Electrolysis. Conductors of electricity in which substance- 
 movement of the conducting material accompanies the pass- 
 ing of the electric current, have been termed conductors of 
 the second class. In this category are included all solutions 
 which can conduct an electric current, and also all fused 
 salts which can act as conductors. They are all designated 
 by the term electrolytes, and the particles into which mole- 
 cules of electrolytes dissociate are termed ions. 
 
 These ions are particles of matter associated with definite 
 charges of electricity. As Von Helmholtz, in his Faraday 
 lecture delivered in London in 1881, expressed it: "If we 
 accept the hypothesis that the elementary substances are 
 composed of atoms, we cannot avoid concluding that elec- 
 tricity also, positive as well as negative, is divided into 
 definite elementary portions, which behave like atoms of 
 electricity. As long as it moves about in the electrolytic 
 fluid, each ion remains united with its electric equivalent, 
 or equivalents." 
 
 The terminals of the wires by which the electric current 
 enters and leaves the electrolyte are called electrodes; the 
 
ELEC TROCHEMISTRY. 29 
 
 ^electrode by which the current enters the electrolyte is the 
 anode; the one by which it leaves, the cathode. The ions, 
 charged with positive electricity, which are discharged at 
 the cathode, are termed cathions; the negatively charged 
 ions which are set free at the anode are called anions. The 
 direction of current flow is understood to be the direction 
 of the current from its point of entry into the electrolyte, at 
 the anode, across the electrolyte, to, and emerging at, the 
 cathode. 
 
 The distinguishing feature of electrolysis is that the prod- 
 ucts of the reaction appear only at the electrodes. It was 
 Faraday who studied these questions of electrolytic phenom- 
 ena with the utmost care, and who formulated the laws which 
 govern these reactions. These laws have been previously 
 referred to; they may be concisely expressed as follows: 
 
 1. The amount of a substance set free or deposited by an 
 electric current is proportional to the quantity of electricity 
 passing through the electrolyte. 
 
 2. The amounts of different substances separated by the 
 same quantity of electricity bear the same relation to each 
 other as the chemical equivalent weights of those substances. 
 
 The most rigid experimental tests to which Faraday's laws 
 have been subjected, on the one hand by the use of very 
 large currents of electricity (Buff, 1853), on the other hand 
 by the use of very small electric currents (Ostwald and Nernst, 
 1889), as well as the most careful determinations of electro- 
 chemical equivalents, which have been made by many 
 investigators, have, one and all, only served to demonstrate 
 the exactness of these laws of Faraday. 
 
 The quantity of electricity which is passing through an 
 electrolyte is conveniently ascertained by measuring either 
 the weight or the volume of the products resulting from its 
 electrolytic action. 
 
 Apparatus designed for this purpose are generally called 
 -voltameters, or coulometers, a name suggested by Professor 
 
30 NOTES ON E&BGTROCHEM1STRY. 
 
 Richards, in 1902, to avoid confusing voltameters with volt- 
 meters. Various forms of coulorneters are used; the most 
 accurate instrument of the kind is probably the silver cqulo- 
 meter in which metallic silver is precipitated on the cathode 
 from a neutral solution of nitrate of silver, the anode con- 
 sisting of a bar of pure silver. 
 
 Copper and mercury coulometers of analogous construction 
 are also frequently employed. In the former, both electrodes 
 are of metallic copper and the electrolyte is some salt of 
 copper, generally sulphate of copper. In the mercury eoulo- 
 meter some rnercurous salt is used as the electrolyte, mer- 
 curous nitrate, for instance. Both anode and cathode consist 
 of metallic mercury in glass receptacles. 
 
 Another favorite form of coulometer is that in which 
 the electrolytic decomposition of water is effected and 
 in which the volume of the resulting gases is measured. 
 These gases, hydrogen and oxygen, may be caught either 
 separately or together, and their volume measured. One 
 ampere in one minute sets free 10.45 C. C. of these mixed 
 gases, measured at C. and 760 mm. pressure. In these 
 gas coulometers a solution of sodium hydrate or dilute 
 sulphuric acid is generally used; if the former, the electrodes 
 are preferably made of nickel; if sulphuric acid be employed 
 as the electrolyte, the electrodes are both made of platinum. 
 
 As the quantity of electricity passing through any given 
 conductor is determined by the current strength, measured 
 in amperes, and the time during which the current flows, an 
 identical quantity of current will flow and an identical 
 amount of work, electrolytic or other, will result, whether, 
 for instance, 100 amperes flow for 5 seconds, or whether 250 
 amperes flow for 2 seconds. It will be recalled that [the 
 amount of electricity conveyed by one ampere in one second 
 is termed a coulomb, and that this is t he < quantity of elec- 
 tricity which will deposit 0.001118 gram of silver in a-S;i}yer 
 coulometer. ?:*;, wter.rj|.?." 
 
ELECTROCHEMISTRY. K 31 
 
 This amount, 0.001118 gram, is termed the ^electrochemical 
 equivalent of silver. This term must be well distinguished 
 from the expression chemical equivalent or equivalent .-weight, 
 as it is also called. The latter, it will be remembered, is the 
 quotient obtained on dividing the atomic weight of an ele- 
 ment by its valency. Elements whose valency is one r the 
 so-called monads, have their chemical equivalent identical 
 with their atomic weight. Elements whose valency is two, 
 dyads, have their chemical equivalent equal to one-half their 
 atomic weight; in triads/it is one-third the atomic weight, 
 etc. In the case of complex ions the equivalent weight is 
 equal to the molecular weight that is, the sum of the 
 atomic weights of the complex ion, divided by its valency. 
 
 Application of Faraday's second law, of course, makes it 
 a simple matter to calculate the electrochemical equivalent 
 of every element when the electrochemical equivalent of 
 any one element has been accurately determined experi- 
 mentally. 
 
 To illustrate, let a determination of the electrochemical 
 equivalent of zinc be required. 
 
 The atomic weight of zinc is 65.4, its valency is 2, and con- 
 sequently its equivalent weight is 65.4 -4- 2 = 32.7. Accept- 
 ing the atomic weight of silver as 107.93 and its valency as 
 one, that quantity of electricity which will deposit 0.001118- 
 gram of silver must deposit of zinc: 
 
 107.93 : 32.7 :: 0.001118 :x 
 x = 0.0003387 gram. 
 
 This value is therefore the electrochemical equivalent of 
 zinc.* 
 
 The chemical equivalent weight of a substance in grams 
 is termed a gram equivalent of that substance. To deposit 
 
 *An excellent table of " Electrochemical Equivalents and their Deriva- 
 tives," by Carl Hering, M.E., is published in Electrochemical Industry, 
 New York, January, 1903. -;:: 
 
32 NOTES ON ELECTROCHEMISTRY. 
 
 one gram equivalent of any element requires an amount of 
 electricity, in coulombs, equal to the chemical equivalent of 
 that element divided by its electrochemical equivalent. 
 
 Thus, to deposit one gram equivalent of silver requires 
 107.93 -H .001118 = 96,538 coulombs. This value varies 
 slightly with different experimenters. The electrochemical 
 equivalent of silver was found' to be: 
 
 0.0011179 by Lord Rayleigh and Mrs. Sedgewick, 
 0.0011183 by W. and F. Kohlrausch, 
 0.0011172 by Richards, Collins, and Heimwood, 
 0.0011192 by Patterson and Guthe, 
 0.0011193 by Kahle. 
 
 Accepting the atomic weight, and hence, of course, the 
 chemical equivalent of silver, as 107.93, and employing the 
 several electrochemical equivalents above given, the deter- 
 mination by: 
 
 Lord Rayleigh and Mrs. Sedgewick = 96,547 coulombs, 
 W. and F. Kohlrausch = 96,513 coulombs, 
 
 Richards, Collins, and Heimwood = 96,608 coulombs, 
 Patterson and Guthe = 96,435 coulombs, 
 
 Kahle = 96,426 coulombs. 
 
 We will accept the value 96,540 coulombs as the ionic charge 
 for a monovalent gram ion, this being the value usually 
 employed. 
 
 It can be readily shown that 96,540 coulombs are required 
 to deposit or to liberate one gram equivalent of any element, 
 and this quantity of electricity, viz: 96,540 coulombs is called 
 a faraday. This constant is of the greatest importance in 
 electrochemical work, for on passing one faraday through 
 an electrolyte there is always set free one gram equivalent 
 of an ion at the cathode, and one gram equivalent of an 
 ion at the anode, provided that the electrolysis effected is 
 simple and not complex. 
 
ELECTROCHEMISTRY. 33 
 
 If complex, that is, if more than one kind of ion is set 
 free at one of the electrodes, the sum total of the ions thus 
 set free at that electrode amounts to one gram equivalent. 
 Thus, in the electrolysis of water one faraday causes the 
 liberation of 1.008 grams of hydrogen at the cathode and of 
 8.000 grams of oxygen at the anode. If, however, in the 
 electro-analysis of an alloy two metals were to be simul- 
 taneously deposited on the cathode, then the sum of the gram 
 equivalents of these two metals so deposited would corre- 
 spond to the work done by one faraday. 
 
 Taking the chemical equivalent of hydrogen as unity, one 
 coulomb will liberate 
 
 107.93:1::. 001118:z 
 x = 0.00001036 gram of hydrogen. 
 
 This value, which was determined by Lord Rayleigh as 
 0.000010352 gram, and by Kohlrausch as 0.000010354 gram, 
 is the electrochemical equivalent of hydrogen. The chemical 
 equivalent of any element multiplied by the electrochemical 
 equivalent of hydrogen is, of course, the electrochemical 
 equivalent of that element. 
 
 Designating the chemical equivalent of any element by 
 Z, the actual weight in grams of such element deposited 
 by electrolysis is calculated by the formula: 
 
 w = 0.00001036 Zct, 
 in which, 
 
 w = weight in grams, 
 
 Z chemical equivalent of the element deposited, 
 c = current strength employed (in amperes), 
 t = time oT passing of current (in seconds). 
 
 Or, designating the electrochemical equivalent of the ele- 
 ment deposited by z, this formula becomes: 
 
 w = zct. 
 
 OF THF 
 
 UNIVERSITY 
 
 OF 
 'FOR! 
 
34 NOTES ON ELECTROCHEMISTRY. 
 
 If the time be measured not in seconds but in hours T, 
 then cT represents ampere-hours, that is to say, the quan- 
 tity of electricity conveyed by the current in one hour, and 
 the formula first given would read: 
 
 w = .00001036 X 3600 ZcT, 
 w = 0.037296 ZcT, 
 or, for all practical purposes, 
 10 - 0.0373 ZcT. 
 
 From this formula the amount of current, C. is readily de- 
 duced which is required to set free or to deposit a given 
 weight of an element, w, in a given time: 
 
 [1.0 -*- .0373] w 
 ~ZT~ 
 
 26.81 w 
 
 The electrical power, in watts, needed to do this work is 
 calculated by the formula: 
 
 26. 
 
 in which E represents the electromotive force, the voltago, 
 employed. 
 
 At times the actual amount of chemical action obtained 
 take, for instance, the weight of a metal which should be 
 deposited in an electrochemical process does not corre- 
 spond with the amount called for by Faraday's laws. 
 
 There is some diversity of opinion concerning the causes 
 of such discrepancies. Professor Crocker* attributes the dif- 
 ficulty, in some instances, to the liberation of hydrogen gas 
 in place of the metal which should be deposited; this setting 
 free of the hydrogen may be due to an excessive current 
 
 * "School of Mines Quarterly," Vol. 22, p. 119. 
 
ELECTROCHEMISTRY. 35 
 
 density, to too great a dilution of the electrolyte, or to the 
 great affinity which some metals have for oxygen, the con- 
 sequent decomposition of the water resulting in a liberation 
 of hydrogen. An insufficient yield of metal may also be 
 due to a resolution of some of the metal by free acid, such 
 acid being sometimes added in order to improve the con- 
 ductivity of an electrolyte. But whatever the cause, if a 
 discrepancy exist between the output actually obtained and 
 the theoretical yield correctly figured according to Faraday's 
 laws, the fault of such discrepancy will be found not to rest 
 with the latter. 
 
 Electromotive Force. Electrical energy has been denned 
 as the product of two factors, quantity and intensity of 
 electricity. Attention has been given to the former phase 
 of the subject, now electromotive force must be considered. 
 
 Electromotive force is the pressure which drives an electric 
 current through a conducting medium; other terms employed 
 to designate this concept are voltage and difference of po- 
 tential. 
 
 The source of the electromotive force in an electrical cell 
 is to be sought principally at the points of contact of the 
 electrodes with the electrolytes in which they are respec- 
 tively immersed; this electromotive force is practically due 
 to chemical action between the metallic electrodes and the 
 chemical solutions in which these are placed. 
 
 In order that a chemical reaction may give rise to electro- 
 motive force, the substances concerned in its generation must 
 be located apart from one another, but must be in electrical 
 connection with each other through the agency of a metallic 
 conductor and an electrolyte. Whenever the substances 
 which are on one and the same side of the equation sign in a 
 true chemical reaction are placed under the above conditions, 
 an electrochemical process occurs. 
 
 Consider the reaction : 
 
 Zn + Cu SO4 = Zn SO 4 + Cu. 
 
36 NOTES ON ELECTROCHEMISTRY. 
 
 It will be recalled that these substances form an electro- 
 lytic cell when they are arranged so that they meet the 
 prescribed conditions; that is to say, when the zinc is away 
 from the copper sulphate and the copper is removed from 
 the zinc sulphate, but when both. are in electrical connection 
 by the intervention of an electrolytic medium and a metallic 
 wire. The system here referred to is, in fact, the well-known 
 Daniell cell. 
 
 Conversely, if under the conditions stated, electrical energy 
 is introduced into an electrolyte, chemical changes are caused 
 and electrochemical reactions are brought about. 
 
 To effect measurement of electromotive force, it is neces- 
 sary to establish standards for comparison and to have 
 instruments by means of which these standards may be 
 compared with the electromotive force to be measured. An 
 accumulator battery supplies a reliable and uniform source 
 of current; a direct lighting current can also be used for 
 this purpose by causing it to pass through proper resist- 
 ance and by using a part of the current for the work in 
 hand. 
 
 It is customary to employ either Clark cells or Weston 
 Cadmium cells as standards; of these the latter are preferable, 
 because they are scarcely affected at all by changes of tem- 
 perature. 
 
 Instruments used to record voltage are either direct- 
 reading voltmeters, or potentiometers. As it is desirable to 
 have these instruments use as little current as possible, they 
 are' generally constructed with high resistances, this being 
 insured by employing numerous windings of exceedingly fine 
 wire. If a hot-wire instrument is to be used as a voltmeter, 
 it must, of course, be put in series with high resistance. 
 
 Voltmeters are not as desirable as potentiometers because 
 they consume some current and require occasional recalibra- 
 tion. To measure electromotive force with a potentiometer, 
 the unknown force is balanced against the electromotive 
 
ELECTROCHEMISTRY. 37 
 
 force of another electric current of known value, a standard 
 cell being used in substitution for the unknown electromotive 
 force to be measured.* 
 
 Dissociation Voltage. It will be recalled that one faraday, 
 96,540 coulombs of electricity, is the quantity of electricity 
 which will separate one gram equivalent of any electrolyte; 
 the amount of electrical potential required to do this, how- 
 ever, varies with the heat of formation of the electrolyte to 
 be decomposed. 
 
 The amount of heat set free, or absorbed, in the formation 
 of one gram-molecule of a substance is called the heat of 
 formation, or, the heat of reaction of that substance. This 
 value, in a compound, is equal to the difference between the 
 heat of combustion of one gram-molecule of the compound 
 and the heats of combustion of the elements which form it. 
 It represents the loss of chemical energy of the substances 
 which take part in the reaction. 
 
 The fact that the amount of heat necessary to decompose 
 a compound into its constituents is precisely the same as 
 that which was set free when this compound was formed, 
 was determined by Lavoisier and Laplace. G. H. Hess, in 
 1840, formulated the law of constant heat summation: the 
 heat given out in a chemical process is the same whether 
 this process takes place in one or in several stages. This is 
 practically an individual case of the law of conservation of 
 energy, for, as energy can be neither created nor destroyed, 
 it is evident that the amount of energy required for the 
 decomposition of a compound must be identical with the 
 amount of energy produced when that compound was formed. 
 
 The heats of formation of chemical compounds are given 
 in many books on Physical Chemistry, and of course in all 
 works dealing with Thermochemistry. t 
 
 * Confer : Lehfeldt, liber ctt., p. 229. 
 
 f For instance in Muir, M.M.P. and Wilson, D.M.: "The Elements of 
 Thermal Chemistry," London, 1885. 
 
38 NOTES ON ELECTROCHEMISTRY. 
 
 Possessed of such thermal data, the heats of formation, 
 there only remains to be learned the relation between the 
 unit of heat energy and the unit of electrical energy in order 
 to make possible a calculation of the electric potential re- 
 quired to effect electrolytic dissociation. 
 
 The unit of heat energy is the calorie, the amount of heat 
 required to raise the temperature of 1 gram of water from 
 15 to 16 C., hydrogen scale. The unit of electrical energy 
 is the joule the product obtained by multiplying the 
 coulombs and the volts of an electric current. One joule 
 will raise the temperature of 0.238882 gram of water 1 C., 
 hence, in round numbers, 1 joule = 0.24 caloric. 
 
 Knowing the heat of formation of an electrolyte, it is only 
 necessary to divide this number by 0.24 to ascertain the 
 joules required to effect the electrolytic decomposition of 
 the compound, and the joules thus found, divided by 96,540 
 or a multiple thereof equal the number of volts re- 
 quired to effect the desired electrolysis. 
 
 Lord Kelvin was the first to make calculations of this kind. 
 It is, however, important to remember that such calcula- 
 tions involve acceptance of the assumption that all of the 
 chemical energy lost, reappears in the form of electrical 
 energy. This, however, is by no means always the case. 
 In some reactions, for instance, in Clark's cell (Zn : Zn SO 4 
 : Hg 2 SO 4 : Hg), about 25 per cent of the chemical energy 
 lost appears as heat. In other instances, however, the 
 agreement between the calculated values and the values 
 experimentally determined, is very close. Thus, for the 
 Daniell cell (Zn : Zn SO 4 : Cu SO 4 : Cu), the dissociation 
 voltage is, calculated, 1.0872 volts; experimentally deter- 
 mined, by Jahn at C., 1.0962 volts. 
 
 To illustrate the calculation of dissociation voltage let 
 us consider the electrolytic dissociation of potassium chlo- 
 ride. 
 
 The heat of formation of K Cl is 104,300 calories. The 
 
ELECTROCHEMISTRY. 39 
 
 amount of electrical energy equivalent to this amount of 
 heat energy is, therefore, 
 
 104,300 -*- 0.24 = 434,584 joules, 
 
 and 434,584+96,540 = 4.50 
 
 hence, 4.50 volts is the minimum voltage required to de- 
 compose potassium chloride into its constituents, potassium 
 and chlorine. 
 
 One faraday, 96,540 coulombs, will decompose one gram- 
 molecular weight of an electrolyte of which both components 
 are monovalent. Potassium chloride is such a compound; 
 
 the atomic weight of potassium --= 39.15 
 
 the atomic weight of chlorine = 35.45 
 
 hence, the molecular weight of potassium chloride = 74 . 60 
 Therefore, it will require 434,584 joules, or 96,540 coulombs 
 at a potential of 4.50 volts to decompose 74.60 grams of 
 potassium chloride into its constituents, viz: 39.15 grams of 
 potassium and 35.45 grams of chlorine. 
 
 If the electrolyte to be decomposed has a divalent con- 
 stituent, 2 faradays = 96,540 x 2 = 193,080 coulombs will 
 be required to effect the desired electrolysis, and it is this 
 number which must be divided into the joules required, to 
 ascertain the minimum dissociation voltage. This minimum 
 dissociation voltage may also be readily calculated by divid- 
 ing the heat of formation of the compound, expressed in 
 calories, by 23,062 times the valence, i.e. the number of 
 bonds. This factor, 23,062, is obtained by dividing 96,540 
 * 4.18617, for one calorie is equal to 4.18617 joules. 
 
 Thus, in the case of potassium chloride, where the valence 
 is one, and the heat of formation is 104,300 calories: 
 
 104,300 + 23,062 = 4.52 volts. 
 In the case of magnesium chloride, Mg C1 2 , where there 
 
40 NOTES OX ELECTROCHEMISTRY. 
 
 are two bonds to be considered, we would have taking the 
 heat of formation of Mg C1 2 as 217,300 calories: 
 
 217,300 -* [23,062 X 2] = 4.71 volts. 
 
 The dissociation voltages thus found are valid for elec- 
 trolytes in aqueous solution. Fused electrolytes require 
 somewhat lower voltages, because the heat of fusion, to a 
 certain degree, assists the reaction. 
 
CHAPTER IV. 
 ELECTROLYTIC DISSOCIATION. 
 
 Literature: ABEGG, R., and HERZ, W. (English translation by CALVERT, 
 H. T.): "Practical Chemistry." London, 1901. ARNDT, K.: 
 " Grundbegriffe der allgemeinen physikalischen Chemie." Berlin, 
 1900. GLASER, F. : "Indikatoren der Acidirnetrie und Alkali- 
 metrie." Wiesbaden, 1901. HOPKINS, N. MONROE: "Experimental 
 Electrochemistry." New York, 1905. KOHLRAUSCH, F., and HOL- 
 BORN, L.: "Das Leitvermogen der Elektrolyte." Leipzig, 1898. 
 LE BLANC, M. : "Lehrbuch der Elektrochemie." Leipzig, 1903. 
 LEHFELDT, R. A.: "Electrochemistry," Part I, General Theory. 
 New York, 1904. LOEB, W. : "Grundziige der Elektrochemie." 
 Leipzig, 1897. OSTWALD, W. : "Die Wissenschaftlichen Grundlagen 
 der Analytischen Chemie." Leipzig, 1901. PERKIN, F. M. : 
 " Practical Methods of Electrochemistry." London, 1905. 
 
 The Ion Theory. The Theory of Electrolytic Dissociation, 
 or the Ion Theory, as it is frequently termed, was formulated 
 by the Swedish scientist, Svante Arrhenius, now professor in 
 the University of Stockholm, after he had become acquainted 
 with the brilliant researches of J. H. Van't Hoff; these were 
 published in 1887, in an article entitled, "The Role of Osmotic 
 Pressure in the Analogy between Solutions and Gases." 
 
 By the term osmotic pressure there is understood the 
 pressure exerted by the molecules of a substance in solution 
 when such solution is brought into contact with the pure 
 solvent, or when such a solution is brought into contact with 
 another solution of a different degree of concentration. All 
 substances when dissolved in water exhibit osmotic pres- 
 sure. 
 
 The true cause of osmotic pressure is as yet unknown, but 
 the phenomena of osmotic pressure have been carefully 
 
 41 
 
42 NOTES ON ELECTROCHEMISTRY. 
 
 studied and some very important relations have been deter- 
 mined. 
 
 Van't Hoff's theory of osmotic pressure holds that the 
 osmotic pressure of a substance in solution is the same as 
 the pressure which that substance would exert if it were in 
 the gaseous form and occupied the same volume at the same 
 temperature. In other words, the laws of gases apply also 
 to dilute solutions; the laws of gas-pressure are valid also 
 for the osmotic pressure of solutions. 
 
 The gas-equation pv = RT states that the product of 
 the volume and the pressure of a gas is directly proportional 
 to the absolute temperature and to the value R. 
 
 7) V 
 
 R is a constant = -^^ In the equation of state for 
 
 ~ 4 O 
 
 V volume in cc. of a gram-molecule of the gas, 
 p = pressure in grams per square centimeter, 
 T = absolute temperature. 
 
 The molecular weight in grams (1 mol) of a gas at 
 C. and 76 cm. of Hg pressure, has a volume of 22.4 
 liters; in the space of 1 liter it must, therefore, exercise a 
 pressure of 22.4 atmospheres. Now it follows, according to 
 Van't Hoff's theory, that the osmotic pressure, exercised 
 by a solution of 1 mol of a substance in 1 liter, must like- 
 wise be equal to 22.4 atmospheres. 
 
 A solution of this kind (1 gram-molecular weight of a 
 solute in 1 liter) is called a normal solution. 
 
 A normal solution hence exercises an osmotic pressure 
 of 22.4 atmospheres; a tenth-normal solution exercises an 
 osmotic pressure of 2.24 atmospheres, and so on. 
 
 It is evident, then, that if the osmotic pressure of a solu- 
 tion is known, that the molecular weight of the solute can 
 be readily determined. 
 
 A 1 per cent solution of sucrose gives an osmotic pres- 
 sure of 49.3 cm. of Hg. 
 
ELECTROLYTIC DISSOCIATION. 43 
 
 A normal solution of sucrose would give a pressure equal 
 to 
 
 22.4 x 76 - 1702.4 cm. Hg. 
 
 The 1 per cent solution contains 10 grams of sucrose per 
 liter, hence 
 
 10 : x : : 49.3 : 1702.4, x = 345. 
 
 This is in close agreement with the molecular weight of 
 sucrose as calculated: 
 
 C 12 x 12 = 144 
 H 22 x 1 = 22 
 Oil x 16 = 176 
 
 342 
 
 Many solutions which wsre examined in this way yielded 
 returns which were found to agree with this theory and 
 which bore out its assumptions. But it was soon ascer- 
 tained that all the salts, acids, and bases did not behave in 
 accordance with its teachings. 
 
 Solutions of these substances gave osmotic pressures 
 greater than they would have given had they acted in con- 
 formity with the laws of gases. 
 
 It was furthermore determined that those substances 
 which in aqueous solutions exert an osmotic pressure greater 
 than is called for by the law of gas-pressure, likewise cause 
 greater lowerings in the freezing-point of water, produce 
 greater elevations of the boiling-point, and effect a lower- 
 ing in the vapor-tension of volatile solvents: last, but not 
 least, it was found that aqueous solutions of these substances, 
 and these only, could conduct the electric current. 
 
 To meet the exigencies .of the case it was proposed to 
 introduce an additional factor i into the gas-equation, thus 
 making the latter read : 
 
 pv = iRT. 
 This factor i was termed the Van't Hoff i, from its originator. 
 
44 NOTES ON ELECTROCHEMISTRY. 
 
 In all of the substances named, the salts, the acids, and 
 the bases, the value of i is always greater than unity. 
 
 Arrhenius, reflecting on this problem, on the probable 
 cause of these numerous discrepancies between Van't Hoff's 
 theory of osmotic pressure and the results found, recalled 
 the analogous case of abnormal vapor-pressures exhibited by 
 iodine and by some other substances when their vapor- 
 pressures were determined at high temperatures. 
 
 In these instances the explanation had at last been reluc- 
 tantly accepted, that a dissociation of the molecules prob- 
 ably occurred at high temperatures. 
 
 " Therefore," wrote Arrhenius, "it is natural to assume 
 that substances which in aqueous solution give pressures 
 that are too great, are likewise dissociated." 
 
 Arrhenius outlined his theory in a letter which he addressed 
 in the early part of 1887 to Oliver Lodge, secretary of the 
 British Association Committee for Electrolysis. Somewhat 
 later in the same year a full discussion of his views appeared 
 in the Transactions of the Swedish Academy of Sciences, in 
 which journal there had been published, in 1883, another 
 article by Arrhenius, " Galvanic Conductivity of Very Dilute 
 Aqueous Solutions-," in which he may be said to have, in 
 a measure, foreshadowed the theory of electrolytic dissocia- 
 tion which he formulated in 1887. 
 
 The essence of this theory of Arrhenius is, of course, the 
 deduction that the osmotic pressure exercised by the par- 
 ticles into which molecules may become dissociated is the 
 same as the osmotic pressure exercised by the molecules 
 themselves. 
 
 In other words, the ion theory holds, that in dilute aqueous 
 solutions there are more smallest particles of the dissolved 
 'substance (the solute) than correspond to the molecular 
 weight of the substance; the theory accounts for this by 
 assuming that a number of molecules arc dissociated, elec- 
 trolytically dissociated, in such solution. 
 
ELECTROLYTIC DISSOCIATION. 45 
 
 On the assumption that the forces holding chemical atoms 
 together in molecules are of electrical origin, J. J. Thomson 
 explains electrolytic dissociation of molecules into ions by 
 ireans of electrical induction. 
 
 On introducing an electrolyte, sodium chloride, for in- 
 stance, into a dissociant solvent, say water, the positive 
 atom, the sodium, will induce a negative charge in the water, 
 and the negative atom, the chlorine, will induce a positive 
 charge in the water. These induced electric charges almost 
 neutralize the electric charges on the atoms which originally 
 induced them, and thus the attraction between the atoms 
 of the original molecules is weakened and dissociation ensues. 
 
 The amount of energy possessed by two electric charges 
 held apart by any medium is inversely proportional to the 
 specific inductive capacity the so-called dielectric con- 
 stant of that medium. 
 
 The dielectric constant of water is 80. Calvert ascribes 
 a dielectric constant of 92.8 to hydrogen peroxide; that of 
 hydrocyanic acid is 95. In consequence of the high specific 
 inductive capacity of water electrolytic dissociation ensues 
 readily in this medium. 
 
 The actual existence of free ions in electrolytes, the fact 
 that they bear charges of electricity, and that they migrate 
 under the influence of electric force, was experimentally 
 demonstrated by Ostwald and Nernst. It is the movement 
 of these electric charges which constitutes an electric current 
 within an electrolyte. 
 
 As previously stated, when an electric current passes 
 through a conducting solution, part of the ions formed in the 
 solution move towards the negative electrode, the cathode. 
 These particles are termed cathions; they bear charges of 
 positive electricity. The other ions move towards the posi- 
 tive electrode, the anode; these ions are termed anions and 
 they bear charges of negative electricity. 
 
 These terms are derived from the Greek: Ion means wan- 
 
46 NOTES ON ELECTROCHEMISTRY. 
 
 derer; cathion means descending, because the cathions in 
 the electrolyte move with the positive current towards the 
 cathode; anion means ascending, to indicate that the anions 
 move in a direction opposite to that taken by the cathions. 
 This terminology is due to Faraday. 
 
 Williamson, in 1851, and again Clausius, in 1857, assumed 
 that a small portion of ions preexisted in solutions and that 
 these were capable of conducting the electric current; these 
 particles were designated as part-molecules. 
 
 In 1887, however, it was generally believed that the elec- 
 tric current itself induced the breaking up of chemical com- 
 pounds into the particles which conveyed the electric charge 
 through solutions capable of conducting electricity. 
 
 It was Arrhenius who determined that the number of 
 preexistent ions might be considerable, and that, up to a 
 certain limit, dilution of the solution increased their number. 
 
 An equivalent amount of positive and of negative elec- 
 tricity must always be conveyed by the ions, for no free 
 electricity can be detected in solutions of electrolytes, hence 
 for every cathion which separates at the cathode, an anion 
 must give up a corresponding electric charge at the anode. 
 
 Ions possess definite electric valencies, and for every dyad 
 ion which separates at one electrode, another dyad ion or 
 two monovalent ions must separate at the other electrode. 
 Among the more important monovalent cathions are: 
 
 H (in the acids), K, Na, Ag. . . . 
 Among the divalent cathions: 
 
 Ca, Ba, Mg, Fe (in ferro-compounds), . 
 Among the trivalent cathions : 
 
 Al, Bi, Sb, Fe (in ferri-compounds), . . . 
 Among the monovalent anions: 
 
 OH (in the bases), Cl, Br, I, N0 8 , C1O 3 . . . 
 
ELECTROLYTIC* DISSOCIATION. 
 Among the divalent anions: 
 
 4T 
 
 S, SO 4 , MnO 4 ..... 
 
 The following table of the chemical elements in their 
 electrochemical sequence, is given by N. Monroe Hopkins. 
 Each element is electropositive to every element whose 
 name is placed before its own, and is electronegative to all 
 elements whose names follow its own : 
 
 Oxygen 
 Sulphur 
 Nitrogen 
 
 Selenium 
 
 Phosphorus 
 
 Arsenic 
 
 Chromium 
 
 Vanadium 
 
 Molybdenum 
 
 Tungsten 
 
 Boron 
 
 Carbon 
 
 Antimony 
 
 Tellurium 
 
 Tantalum 
 
 Columbium 
 
 Titanium 
 
 Silicon 
 
 Tin 
 
 Hydrogen 
 
 Gold 
 
 Osmium 
 
 Iridium 
 
 Negative Atoms. 
 
 Fluorine 
 Chlorine 
 
 Positive Atoms. 
 
 Platinum 
 
 Rhodium 
 
 Ruthenium 
 
 Palladium 
 
 Mercury 
 
 Silver 
 
 Copper 
 
 Uranium 
 
 Bismuth 
 
 Gallium 
 
 Indium 
 
 Germanium 
 
 Lead 
 
 Cadmium 
 
 Thallium 
 
 Cobalt 
 
 Nickel 
 
 Iron 
 
 Zinc 
 
 Manganese 
 
 Bromine 
 Iodine 
 
 Lanthanum 
 
 Didymium 
 
 Cerium 
 
 Thorium 
 
 Zirconium 
 
 Aluminium 
 
 Scandium 
 
 Erbium 
 
 Ytterbium 
 
 Beryllium 
 
 Magnesium 
 
 Calcium 
 
 Strontium 
 
 Barium 
 
 Lithium 
 
 Sodium 
 
 Potassium 
 
 Rubidium 
 
 Caesium 
 
 It must, however, not be forgotten that the terms posi- 
 tive and negative in electricity are merely relative it all 
 depends on the conditions in which the substances are placed. 
 
4& XOTES ON ELECTROCHEMISTRY. 
 
 If two metals are placed in a solution which attacks the 
 one metal and does not attack the other, the metal which 
 goes into solution is electropositive to the other metal; the 
 metal which goes into solution forms the negative pole in 
 the outside circuit. 
 
 Zinc is attacked by dilute nitric acid and by dilute sul- 
 phuric acid, and even in solutions of ammonium chloride 
 and potassium hydrate it will go into solution replacing 
 other metals; zinc, therefore, is electropositive to them all. 
 
 It has been previously explained that all ions of the same 
 valency bear identical electric charges, although the masses 
 of the atoms with which these charges are associated are not 
 equal. Ions, in short, may be regarded as combinations of ma- 
 terial atoms with electric atoms, with the so-called electrons. 
 
 Ions of different substances vary considerably in their 
 electro-affinity, that is, in the degree of power with which 
 they hold their electric charges. Those ions which hold 
 their electric charges firmly are termed strong, those which 
 readily part with their charges are called weak ions. As 
 a rule, strong ions are given to the forming of soluble com- 
 pounds, compounds which dissociate readily when brought 
 into solution. Weak ions, on the other hand, are generally 
 given to the forming of compounds which are less soluble, 
 that is, to the forming of compounds which ionize only to 
 a slight degree when placed into contact with a solvent. 
 
 If an ion of a low degree of electro-affinity encounters a 
 non-ionized substance which possessess a greater degree of 
 electro-affinity when in the ionic state than it itself possesses, 
 then the electric charge will be transferred from the former 
 to the latter. 
 
 For instance, if metallic zinc is brought into contact with 
 lead in the ionic condition the lead suffers precipitation as 
 metallic lead, while the zinc goes into solution, zinc ions being 
 formed. Lead precipitates copper; copper, in turn, precipi- 
 tates mercury, and so on. 
 
ELECTROLYTIC DISSOCIATION. 49 
 
 When an electric current is passed through an electrolyte 
 the ions move through the solution to the electrodes and 
 there give up their charges of electricity, provided that the 
 tension of the electrodes is sufficient to overcome the electro- 
 affinity of the ions for their electric charges. When this 
 happens the atoms separate in their elemental condition, un- 
 less they take part in some secondary reactions in which 
 they enter into new chemical relations. 
 
 The capacity of forming ions does not depend alone on 
 the substance which goes into solution, the solvent plays 
 an important role in this transaction. This property is 
 referred to as the dissociative power of the solvent. Water, 
 as previously mentioned, has a high dissociant power; formic 
 acid, methyl and ethyl alcohol are fairly strong dissociants. 
 Chloroform, benzol, and many other organic substances lack 
 this dissociant power entirely; these substances are, there- 
 fore, not electrolytes, that is, they do not conduct an electric 
 current between electrodes immersed in them. 
 
 Gram- molecular equivalent solutions of most neutral salts 
 are practically completely ionized in 1000 liters of water. 
 As a rule, salts containing monovalent ions are ionized to a 
 greater extent than salts of multivalent ions. 
 
 The strong acids, among which must be counted hydrochloric, 
 hydroiodic, hydrobromic, nitric, and sulphuric acids, are under 
 like conditions all ionized to about the same degree as the 
 salts. Phosphoric and sulphurous acids are usually ionized 
 to the extent of only 10 per cent; silicic acid and boracic 
 acid are hardly ionized at all. 
 
 Walker and Cormack have determined the degree of ioniza- 
 tion of the following substances in one-tenth normal solutions: 
 
 Hydrochloric acid . .... . . . 91.4% 
 
 Acetic acid 1.3% 
 
 Carbonic acid ......... 0.174% 
 
 Sulphuretted hydrogen 0.075% 
 
 Boracic acid 0.013% 
 
50 NOTES ON ELECTROCHEMISTRY. 
 
 Among the strong bases are the hydroxides of the alkalies 
 and the hydroxides of the alkaline earthy metals. Ammonia 
 and magnesia are bases of a lower degree of ionization, and 
 the hydroxides of the di- and tri-valent metals and most 
 of the alkaloids must be counted among the weak bases. 
 
 The ion theory has proven of special value in the secur- 
 ing of a clearer understanding of the problems of analytical 
 chemistry, and it is to Wilhelm Ostwald that science is 
 chiefly indebted for signal achievements in this direction. 
 
 The study of many, if not of most chemical reactions, may 
 be regarded .as a study of the behavior of ions, for ions have 
 and preserve certain individual characteristic properties, 
 which they exhibit without regard to the presence or absence 
 of other ions and molecules. The properties of aqueous 
 solutions of most salts are but the sum of the properties of 
 their constituent ions. 
 
 That this point of view materially simplifies analytical 
 chemistry is evident when one considers that instead of hav- 
 ing to study and to remember the reactions of, say, one 
 hundred different compound substances, all that it is neces- 
 sary to know are the reactions of ten cathions and ten anions 
 which enter into the composition of the above-named one 
 hundred compounds. 
 
 The terms salt, acid, and base, have here been repeatedly 
 used, and it will be necessary to give their definitions as 
 understood in the light of the ion theory. Salts are com- 
 pounds which, when they are dissolved, break up, wholly 
 or in part, into cathions and anions. Acids are salts in 
 which the cathions are always hydrogen ions; bases are salts 
 in which the anions are ^lw;ays hydroxyl ions. 
 
 Strong acids are those which^ -contain numerous hydrogen 
 cathions in unit volume for the characteristic properties 
 of acids depend on their hydrogen ions. 
 
 Strong bases are those which contain many hydroxyl 
 anions in unit volume, for it is upon the presence of the 
 
ELECTROLYTIC DISSOCIATION. 51 
 
 hydroxyl ions that the characteristic properties of bases 
 depend. 
 
 Acidity and basicity of solutions hence rest solely upon, 
 and vary with, respectively, the amount of hydrogen and 
 of hydroxyl ions present. 
 
 The hydrogen ions of acids behave differently from hydro- 
 gen occurring in other combinations; the hydroxyl ions of 
 bases likewise react differently from the hydroxyl groups 
 occurring in other compounds. Thus, the hydrogen ions 
 of acids will redden litmus; the hydroxyl ions of bases will 
 turn red litmus blue. Water and hydrogen peroxide both 
 contain hydrogen and hydroxyl, yet neither shows the above- 
 mentioned reactions with litmus. Water and hydrogen 
 peroxide are, therefore, at once recognized as not belonging 
 to either the acids or bases. 
 
 Pure water is ionized only to a very slight degree, less 
 than one mol, that is to say, less than 18 grams in 10,000,000 
 liters 14 grams is the figure that approximates more 
 closely to the real value. To express it differently, in one 
 million liters of water there are 0.078 grams of hydrogen 
 ions and 1.326 grams of hydroxyl ions. These values are 
 the values for the temperature of 18 C. The number of 
 ions in a given solution increases very rapidly with the 
 temperature, approximately at the rate of 8 per cent per 
 degree. As water is so slightly dissociated, it is but 
 natural that hydrogen ions and hydroxyl ions when they 
 meet in a solution should immediately combine to form 
 non-dissociated water. 
 
 From the viewpoint of the ion theory the neutralization 
 of an acid in an aqueous solution is looked upon, not as the 
 union of an acid with a base radical, but as the union of 
 the hydrogen ions of the acid with the hydroxyl ions of the 
 base; the process of neutralization in an aqueous solution 
 hence consists essentially in the formation of water. 
 
 The heat of neutralization, for instance, of the reaction: 
 HC1 + NaOH = Na + Cl + H 2 O, 
 
52 NOTES ON ELECTROCHEMISTRY. 
 
 is due to the heat of chemical combination of the hydrogen 
 ions with the hydro xyl ions, the sodium cathions aixd the 
 chlorine anions remaining unchanged in the solution. 
 
 Bearing in mind that an ion consists of the atom of an 
 element plus one, two, three, or more electric charges ac- 
 cording to its valence a fraction of the unit charge is never 
 carried ions can, in writing, be readily differentiated from 
 the atoms of elements by adding to the chemical symbols 
 for the latter some conventional sign to indicate the char- 
 acter of the electric charge the ions bear, and to specify the 
 number of these charges. 
 
 A small circle or period has been selected to represent a 
 charge of positive electricity, a dash or a comma, to typify 
 a negative charge; the number of these symbols indicate 
 the number of electric charges borne by an ion. Thus, an 
 ion of hydrogen is represented by the symbol H*, an ion of 
 calcium by the symbol Ca'V The anion chlorine, is Cl'; 
 oxygen O"; the complex anion hydroxyl, OH'. 
 
 The term ion, introduced by Faraday, was by him em- 
 ployed in connection with the stems of the chemical names 
 of substances to indicate the substances from which the ions 
 originated. A systematic nomenclature of the ions has, 
 however, as yet, not been adopted, although James Walker* 
 has proposed a system of naming, as he expressed it, " the 
 material of the ions as distinguished from the particles them- 
 selves." Cathions he would indicate by adding the termi- 
 nation ion to the stem of the word, and, when necessary, 
 would disclose the electrical valency of the ion by prefixing 
 a Greek numeral. Thus he suggested: 
 
 Hydrion ............. H' 
 
 Sodion Na* 
 
 Calcion Ca" 
 
 Diferrion . Fe" 
 
 Triferrion . . ... . . . '. . . . Fe" % 
 
 * Chemical News, 1901, Vol. 84, p. 162. 
 
ELECTROLYTIC DISSOCIATION. 53 
 
 The names of the an ions he proposed forming in such a 
 manner as to indicate the kind of salt from which the anions 
 are derived. For instance, anions formed from -ate salts 
 would have the termination -anion ; those formed from -He 
 salts, the ending -osion to recall the -ous acids which give 
 rise to -He salts. Anions from -ide salts would receive the 
 termination -idion. For Instance: 
 
 Hydroxidion ...,,;..,. OH' 
 
 Sulphidion , . . S" 
 
 Sulphosion . . SOs" 
 
 Sulphanion :-..- SO/' 
 
 The term ionogen has been suggested by Alexander Smith * 
 to indicate any and all substances which can suffer ionization. 
 
 When a solid goes into solution it exercises pressure, the 
 so-called solution-pressure, and this corresponds to the osmo- 
 tic pressure of a saturated solution. If the molecules of a 
 solid are not dissociated in the process, the action ceases 
 when a certain pressure has been attained; if the substance 
 is an ionogen, the action continues until the ions and the 
 non-dissociated molecules respectively have attained to a 
 definite concentration. 
 
 This relation can be expressed by a formula which holds 
 true in many, but not in all, instances: 
 
 Km = ca. 
 In this formula: 
 
 K the constant of ionization, 
 
 m = the concentration of the non-dissociated molecules, 
 
 c = the concentration of the cathion, 
 
 a = the concentration of the anion. 
 
 The unit of concentration is one mol per liter. In other 
 words, the formula Km = ca, where it is valid, states that 
 
 * Chemical News, 1901, Vol. 84, p. 279. 
 
54 NOTES ON ELECTROCHEMISTRY. 
 
 the product of the ions present in a solution bears a fixed 
 relation to the amount of non-dissociated molecules in that 
 solution. 
 
 This formula is an interesting one. Nernst determined 
 that the concentration of the non-dissociated molecules does 
 not change in a saturated solution; in a case where both m 
 and K are unchanging the product ca must also have a 
 constant value. This product is termed the solubility pro- 
 duct. It represents the number of grams per liter to which 
 the concentration-product of the ions can attain and yet 
 have the ions exist as ions in the solution. 
 
 Should one add to a saturated solution wherein such an 
 equilibrium obtains, any other solution which has an ion 
 in common with an ion of the solution first named, then the 
 equilibrium would be disturbed and the solubility-product 
 having been exceeded, the respective values would suffer 
 readjustment. This indicates the condition which must 
 be established in order to secure a practically complete 
 precipitation of any given substance, an excess of the pre- 
 cipitating reagent must be employed. The same principle 
 applies to the washing of precipitates; in order to avoid the 
 solvent action of the washing-fluid care must be taken to 
 have the washing-fluid contain ions identical with some of 
 those instrumental in forming the precipitate. 
 
 The ions of most of the lighter-weight metals, and those 
 of the halogens, are colorless; those of the heavier metals 
 are colored; for instance, cobalt ions are red, nickel ions 
 and di-ferric ions are green. The use of indicators in aci- 
 dimetry and alkalimetry is based on the fact that in the in- 
 dicators used the color of the non-dissociated molecule is 
 different from the color of the ion or ions formed therefrom. 
 The ion theory affords a plausible explanation of the phe- 
 nomena involved and it will be of interest to consider a case 
 in illustration; phenolphthalein, which is much used as an 
 'indicator, will answer the purpose. 
 
ELECTROLYTIC DISSOCIATION. 55 
 
 The formula of phenolphthalein is C 20 H I4 O 4 . Its configu- 
 ration is probably 
 
 /C 6 H 4 OH 
 C-C 6 H 4 OH 
 \C 6 H 4 
 
 O-CO 
 
 Phenolphthalein is a weak acid, that is to say, it ionizes in 
 water only to a slight degree. Its non-dissociated molecule 
 is colorless, its cathion H* is colorless, its complex anion is 
 red. This anion shall here be denoted by the symbol P.P'. 
 
 If KOH is added to a colorless (alcoholic) solution of 
 phenolphthalein there will be present in the solution: 
 
 Ions from phenolphthalein: H* cathions and P.P'. anions; 
 
 From the KOH solution: K* cathions and (OH)' anions. 
 
 The H' cathions of the phenolphthalein will combine with 
 the (OH)' anions of the potassium hydrate and form non- 
 dissociated water-molecules. Abstraction of the H' cathions 
 will, however, induce other molecules of phenolphthalein to 
 dissociate in order to restore the equilibrium indicated by 
 the formula Km = ca. 
 
 These reactions continuing, there will ultimately be present 
 in the solution an accumulation of K* cathions and of com- 
 plex phenolphthalein anions. The latter, as previously 
 stated, are red and hence so says the ion theory the 
 red color of the solution. 
 
 By means of the reactions indicated, the potassium-salt 
 of phenolphthalein has been formed. As a rule the potas- 
 sium salts of weak acids are ionized to a greater degree than 
 the acids from which they are formed. In consequence, 
 the solution contains toward the end of the reaction a 
 greater number of phenolphthalein anions, and these impart 
 the red color to the solution. 
 
 If a strong acid, hydrochloric acid, for instance, be added 
 to a solution of this description, then there would be present 
 in the solution: 
 
56 NOTES ON ELECTROCHEMISTRY. 
 
 Ions from the potassium-salt of phenol phthalein: K* 
 cathions and P. P/ anions. 
 
 Ions from the hydrochloric acid : H* cathions and Cl' anions. 
 
 The H* cathions would come into contact with the phe- 
 nolphthalein anions, and as the ionization constant of phe- 
 nolphthale.'n, a weak acid, is smaller than that of its potassium 
 salt, the H* cathions and the phenolphthaleiii anions would 
 recombine to form non-dissociated phenolphthaleiii. These 
 molecules are colorless and in consequence the solution 
 would lose its red color which, it will be remembered, was 
 caused by the phenolphthalein anions. The solution would 
 again turn colorless. 
 
 Litmus is an acid indicator; azolithmin is its active color- 
 ing principle. The non-dissociated molecules are red, the 
 anions are blue. Addition of a base to litmus results in 
 the formation of water and of a more highly ionized salt, 
 and the blue color of the anions imparts a blue color to the 
 solution. Addition of a strong acid to such a solution will 
 cause some of the original non-dissociated red molecules of 
 litmus to reform, and, in consequence, a red color will again 
 appear. 
 
 If titrations are attempted in very dilute aqueous solu- 
 tions, then the H' cathions and the (OH)' anions of the water 
 will take an active part in the reaction. This phenomenon 
 is referred to as hydrolytic dissociation, or hydrolysis. 
 
 Hydrolysis is apt to prove a serious cause of disturbance 
 when weak acids or weak bases are titrated. In the case 
 of strong acids and strong bases, that is to say, with those 
 that are ionized to a considerable extent, hydrolysis is a 
 matter of but little moment. 
 
 An example of hydrolytic' dissociation is afforded by the 
 sodium salt of phenol. On ionization this yields Na" cath- 
 ions and phenol C 6 H 6 O' anions. The latter enter into chem- 
 ical union with the H* cathions of the water used as sol vent - 
 and, as a result, phenol, C 6 H^OH, is formed. This can be 
 
ELECTROLYTIC DISSOCIATION. 57 
 
 distinctly recognized by its odor. The (OH)' anions formed 
 by the ionization of the water impart an alkaline reaction 
 to the solution. 
 
 ' An aqueous solution of cyanide of potassium affords an- 
 other illustration of hydrolytic action. In consequence of 
 such action the solution always contains an appreciable 
 quantity of HCy. The reaction of the solution is alkaline; 
 this is owing to the presence of hydro xyl anions. 
 
 Application of the principles of the ion theory to problems 
 of physiological chemistry has also led to some very inter- 
 esting results, but a consideration of these here would take 
 us too far afield. 
 
 The principal lines of evidence to be adduced in support 
 of the theory of electrolytic dissociation, are in brief resume, 
 the following : 
 
 a. The parallelism of behavior of electrolytes and gases 
 osmotic pressure phenomena. 
 
 .b. The abnormal lowering of the freezing-point of solu- 
 tions by electrolytes. Where all normal solutions of non- 
 electrolytes, i.e., solutions containing one gram-molecule 
 of solute in one liter of solvent, lower the freezing-point of 
 pure water 1.86 C., all electrolytes depress the freezing-point 
 of pure water to a much greater degree, possibly again as 
 much. 
 
 c. The abnormal elevation of the boiling-point of water 
 by. electrolytes. Normal solutions of non-electrolytes raise 
 the boiling-point of water by a given amount, identical for 
 all non-electrolytes; electrolytes in normal solutions effect 
 this to a much higher degree. 
 
 d. The thermal-neutralization phenomena of acids and 
 bases. The neutralization of a normal solution of an acid 
 by a base, or vice versa, liberates an amount of heat that is 
 constant, 13,700 calories. This value represents the heat 
 of formation of water, and only this. In all neutralization 
 experiments of the kind referred to, water is an invariable 
 
58 NOTES ON ELECTROCHEMISTRY. 
 
 product. If molecules were formed of the other constituents, 
 besides the molecules of water produced by the chemical 
 combination of the hydrogen and hydroxyl, their respective 
 heats of formation would be manifest in the reaction. This, 
 however, does not occur, and hence the inference is drawn 
 that these constituents exist in the solution as ions, and not 
 as molecules. 
 
 To cite an illustration: 
 
 NaOH + HC1 = Nad + H 2 O 
 
 The heat of this reaction is 13,700 calories, the molecular 
 heat of formation of water. 
 
 The heat of formation of Nad is 9760 calories, and yet 
 this heat value does not appear. Why not? The reason is, 
 because the compound Nad is not formed in the reaction, 
 the components of this compound remaining in the solu- 
 tion as ions, as ions of sodium and of chlorine. 
 
 e. The fact that chemical reactions will not take place 
 between perfectly dry electrolytes; a dissociant is required 
 to loosen the affinity between the atoms of the molecules 
 and thus set free the ions which are assumed to be the re- 
 acting units of all chemical changes. 
 
 A great many data may be offered in support of the theory 
 of electrolytic dissociation. However, it must not be over- 
 looked that a number of facts, experimentally obtained, 
 have as yet not been brought into harmony with its teach- 
 ings. 
 
 Louis Kahlenberg* cites among other objections to this 
 theory, that the color of solutions is independent of their 
 ability to conduct electric currents, whereas the ion theory 
 holds that the color of aqueous solutions, at least, is due 
 to their ions; he denies that free ions are the immediate 
 
 * Journal Phys. Chem., 1901, Vol. 5, p. 339; Trans. Faraday 8oc. t 
 1905, Vol. 1, p. 42. 
 
ELECTROLYTIC DISSOCIATION. 59 
 
 agents concerned in chemical reactions, for the reason that 
 such reactions occur also in solutions that are insulators, 
 for instance, in benzene. 
 
 Again, the theory does not, as yet, accord sufficient weight 
 to the part which solvents play in the formation of solutions. 
 The interesting relations which rest on the interdependence 
 of solute and solvent still call for much further research and 
 explanation. Furthermore, numerous thermochemical data 
 appear to be at variance with the values the theory would 
 seem to call for; its teachings are not always valid even for 
 fairly dilute solutions. Reychler actually asserts the theory 
 of electrolytic dissociation to be in opposition to many 
 thermochemical data secured by experiment. 
 
 Notwithstanding these shortcomings, there can at least 
 be no doubt or question as to the great value of the ion 
 theory in the harmonization and correlation of numerous 
 data, and of the stimulus which it has given to scientific 
 thought and inquiry. Considering its bearing on the elec- 
 tron theory, it is an interesting fact that the electric charges 
 transported by ions in electrolytes are identical with the 
 charges conveyed by the particles in gases when electric 
 discharges are passed through gases. 
 
 Conductivity. By conductivity in general, there is 
 meant the property of conducting a current of electricity. 
 In an electrolyte, it is the joint effect of convection of the 
 cathions and anions; it is an additive property; and the 
 conductivity of an electrolyte represents the amount of 
 electricity which is conveyed in unit time by unit electro- 
 motive force. 
 
 Conductivity is the reciprocal of resistance; the greater 
 the latter, the smaller the conductivity. Conductivity is 
 usually expressed in terms of a unit styled the mho cubic- 
 centimeter unit; the term mho is simply the word ohm re- 
 versed in order to indicate that the unit of conductivity is 
 the reciprocal of the unit of resistance. This unit ohm 
 
60 XOTES OX ELECTROCHEMISTRY. 
 
 expresses the conductivity of a substance one centimeter- 
 cube of which has a conductance of one mho between two 
 parallel sides. In other words, if a current density is stated 
 in amperes per square centimeter and the potential gradient 
 in volts per centimeter, the conductivity will be expressed in 
 mhos per centimeter cube. 
 
 It has been experimentally demonstrated that the trans- 
 mission of electric impulses through electrolytes is practi- 
 cally instantaneous. This can only be accounted for by the 
 assumption of the presence of free ions about the electrodes 
 which give up their charges the instant an electric current 
 is sent through the electrolyte. 
 
 From the interesting researches of N. Monroe Hopkins *' 
 it appears that " electrolytes of equal resistance conduct 
 the electric current with a definite velocity, regardless of 
 the composition of the electrolytes or the length of the con- 
 taining vessel." This investigator also determined, that an 
 electrolyte conducts the electric current just as fast as a 
 metallic conductor, provided, that an equal ohmic resist- 
 ance, of a non-inductive type, is furnished. 
 
 Molecular conductivity is the appellation given to the 
 conductivity of solutions which contain one gram-molecule 
 of the electrolyte; it increases with the temperature and 
 with the degree of dilution. As first pointed out by Kohl- 
 rausch the molecular conductivity of an electrolyte is equal 
 to the sum of the velocities of migration of the ions. 
 
 Let, m = molecular conductivity, 
 
 a = velocity of migration of the anion, 
 c velocity of migration of the cathion, 
 x = fraction of electrolyte dissociated into ions,, 
 then, m = x (a + c). 
 
 On attaining to infinite dilution the dissociation of an 
 electrolyte into its ions becomes complete, an. 1 , in that case, 
 
 x = 1, and woo = a + c. 
 * Scient. Am. Suppl 1905, p. 24305. 
 
ELECTROLYTIC DISSOCIATION. 61 
 
 Prom these equations it follows that, 
 
 m 
 
 x = 
 
 m oc 
 
 which expresses the fact that the degree of dissociation at 
 .any dilution is equal to the ratio of the molecular conduc- 
 tivity at that state to the molecular conductivity at infinite 
 dilution. 
 
 Equivalent conductivity is the conductivity of equivalent 
 quantities; it is the quotient obtained by dividing the con- 
 centration into the conductivity. 
 
 Let K = conductivity, 
 
 t] concentration in grain-equivalents per cubic 
 
 centimeter, 
 
 v = volume in cubic centimeters per gram-equiv- 
 alent, i.e., the dilution, 
 A = equivalent conductivity, 
 jp" 
 
 then, A = . 
 
 f 
 
 or, A = Kv. 
 
 The equivalent conductivity of an electrolyte, base or 
 acid, increases with dilution, but for infinitely great dilu- 
 tion approaches a finite limit. Direct measurement of the 
 equivalent conductivity of an electrolyte can be made by 
 placing a one gram-equivalent solution between two elec- 
 trodes set one centimeter apart, these electrodes serving as 
 two walls of the vessel containing the electrolyte. 
 
 The direct determination of conductivity of an electrolyte 
 by passing an electric current through an electrolyte of uni- 
 form cross-section and measuring the current strength and 
 the voltage direct between the electrodes, is not always 
 feasible, as in many instances the electrodes become polar- 
 ized. In such cases the measurement is effected by aid of 
 
62 NOTES ON ELECTROCHEMISTRY. 
 
 an alternating current which precludes the polarization of 
 the electrodes, each of the electrodes serving alternately 
 as anode and as cathode. 
 
 The method of Kohlrausch, a modified Wheatstone bridge 
 arrangement, is frequently used in determining the resist- 
 ance of an electrolyte. An alternating current from the 
 secondary of a small induction coil is employed for the 
 reason given, and a telephone receiver is used in place of a 
 galvanometer. When the Wheatstone bridge is not in 
 balance a humming noise is heard in the telephone; in 
 making the measurement the bridge resistance must be 
 adjusted in such a way as to secure silence, or, at least, a 
 minimum of sound. Electrodynamo meters may also be 
 used in place of the telephone arrangement. As the con- 
 ductivity of an electrolyte is greatly affected by changes 
 in temperature, the vessel in which the measurements are 
 made should be placed in a thermostat. 
 
 Pure solids at ordinary temperatures have but a low 
 conductivity. It is therefore of interest to know that some 
 substances, notably the salts, exhibit a high conductivity 
 when fused; this conductivity increases with a rising tem- 
 perature. 
 
 The specific conductivity of fused nitrate of silver at 
 310 C. is, for instance, expressed in reciprocal ohms, equal 
 to 1.09; at 375 C. it is 1.32. The specific conductivity of 
 nitrate of silver in solution, dissociated into ions to the 
 extent of about 75 per cent, is only 0.11 reciprocal ohms at a 
 temperature of 25 C.; the conductivity of the fused salt 
 therefore far exceeds that of the salt in solution. 
 
 Thus far it has been found impossible to determine the 
 degree of dissociation of a fused salt into ions, and their 
 conductivity values can therefore only be determined at 
 given temperatures. R. Lorenz* has, however, demonstrated 
 that the laws of Faraday are valid also tor fused salts. 
 
 * Ziltschr. fur Elektrochemie, 1900, p. 277 ; 1901, p. 753. 
 
ELECTROLYTIC DISSOCIATION. 63 
 
 The fact that certain metallic oxides when at very high 
 temperatures, though not hi a state of fusion, will conduct 
 electricity has been taken advantage of by Nernst in the 
 making of his incandescent lamps, the filaments of which 
 consist of oxide of magnesium; the same property has also 
 been made use of in the construction of the tantalum lamps 
 manufactured by Siemens & Halske. 
 
 Migration of Ions. An electric field is a space wherein 
 electrical influences are exerted. An ion moving in a field 
 which is uniform is acted on by a constant force, but the 
 speed with which it moves is not a uniformly accelerated 
 speed, as might be supposed, because the resistance of the 
 liquid through which the ion moves causes its velocity to 
 be materially retarded. The intensity of the electric field 
 in which an ion moves determines its velocity; this is called 
 the potential gradient, and is expressed in volts per centi- 
 meter. 
 
 The velocity of an ion under a gradient of one volt per 
 centimeter is termed its mobility, and this is, as shown by 
 Bredig and Ostwald, a periodic function of the atomic weight 
 of the elements. Hence the mobilities of the different ions 
 differ, and the determination of these values is a matter of 
 importance. 
 
 The relative mobility of anions and cathions was deter- 
 mined by Hittorf in the following manner: Two porous 
 plates were inserted in a trough dividing the trough into 
 three compartments. These compartments were all filled 
 with an electrolyte, for instance, with a solution of sulphate 
 of copper; a copper anode and a copper cathode, respectively, 
 were inserted in the end compartments, and an electric cur- 
 rent was passed through the solution. 
 
 After the current had been passed through the electrolyte 
 for a short time, samples were taken from each of the three 
 compartments and analyzed. The sample removed from 
 the cathode chamber was found to be less concentrated, the 
 
64 NOTES ON ELECTROCHEMISTRY. 
 
 sample from the anode chamber was found to be more con- 
 centrated than before the current wad passed, while the 
 sample from the middle chamber was found to have retained 
 its original concentration. 
 
 Taking the whole current conveyed as unity, and x as that 
 part of the current conveyed by the anion, then 1 x of 
 course represents the fraction of the current transported 
 by the cathion. One faraday requires one gram-equivalent 
 of ions for its transport, in consequence there must pass 
 across any section in the interior of the liquid x equiva- 
 lents of anions in the direction opposite to the direction 
 taken by the current, and 1 x equivalents of cathions in 
 the direction of the current. This x is known as Hittorfs 
 number, the migration ratio of the anion. 
 
 Electric currents produced by the movement of the ions 
 are proportional to their mobilities: 
 
 cathionic anionic , 
 
 : , : : 1 x : x 
 
 current current 
 
 The loss in concentration of the solution in the cathode 
 compartment is equal to the gain in concentration of the 
 solution in the anode compartment. If, for instance, in 
 the case just discussed, 0.2 faraday had passed and the 
 change, in each chamber, had been found to be 0.124 equiva- 
 lents, the migration ratio of the anion would be: 
 
 0.124 -5- 0.2 = 0.620 
 
 Values differing slightly from this have been found by dif- 
 ferent experimenters, but the true value undoubtedly closely 
 approximates to the figure given. 
 
 Hittorf, the pioneer in this line of work, carried out a 
 great number of determinations on migration ratios; the 
 form of apparatus for the study of individual cases being, 
 of course, suitably modified to meet the requirements of 
 the occasion. A convenient model for the demonstration 
 
ELECTROLYTIC DISSOCIATION. 65 
 
 of Hittorf's theory of the migration velocities of ions, has 
 been described by Getman.* 
 
 Several methods have been devised for measuring the 
 absolute velocities of ions, among others by Whetham and 
 Lodge. The latter measured the absolute velocity of hydro- 
 gen ions in the following manner. Into a hot aqueous solu- 
 tion of gelatine, which he prepared, he incorporated some 
 sodium chloride as an electrolyte and colored the whole 
 mass red by the addition of a little alkaline solution of phe- 
 nolphthalein. This gelatine preparation, while hot, he poured 
 into a straight glass tube, both ends of which were bent at 
 right angles. Each end of the glass tube dipped into a 
 beaker containing dilute sulphuric acid; in one of these 
 beakers a platinum anode was placed, in the other, a plati- 
 num cathode, and a voltmeter was joined across these elec- 
 trodes to indicate the potential gradient of the current. 
 
 As soon as an electric current was sent through the system, 
 hydrogen ions proceeded to pass from the anode through 
 the gelatine preparation in the glass tube to the cathode 
 in the other beaker. The hydrogen ions displaced the 
 sodium from the sodium chloride, and, combining with the 
 chlorine, formed hydrochloric acid. This acid, of course, at 
 once decolorized the phenolphthalein, and thus the progress of 
 the reaction could be closely traced and accurately measured. 
 
 Through careful experiments of this kind Lodge ascer- 
 tained the velocity of a hydrogen ion to be 1.1580 centi- 
 meters per minute, or less than three-quarters of a meter 
 per hour, a low speed at best, and yet the hydrogen ions 
 exceed all others in speed of migration. 
 
 The absolute velocity of some one ion having been accu- 
 rately determined, the absolute velocities of other ions can 
 be easily deduced from their relative velocities, values which, 
 it will be remembered, can be readily determined by Hittorf's 
 method. 
 
 * Science, 1905, Vol. 21, p. 153. 
 
CHAPTER V. 
 ELECTRO-ANALYSIS. 
 
 Literature: CLASSEN, A. (English translation by HERRICK, W. H.): 
 "Quantitative Chemical Analysis by Electrolysis." New York, 
 1887. ELBS, K.: "Die Akkumulatoren. Leipzig, 1896. HOPKINS, 
 N. M.: "Experimental Electrochemistry." New York, 1905. 
 FOERSTER, F.: " Elektrochemie wiisseriger Losungen." Leipzig, 
 1905. LOEB, W.: "Die Elektrochemie der organischen Verbin- 
 dungen." HALLE, A. S. 1905. LORENZ, R.: " Elektrochemisches 
 Praktikum." Gottingen, 1901. NISSENSON, H.: "Einrichtungen 
 von Elektrolytischen Laboratorien." HALLE, A. S. 1903. PETERS, 
 F.: "Angewandte Elektrochemie," Vol. I. Wien, 1897. SMITH, 
 E. F.: "Electrochemical Analysis." Philadelphia, 1902. 
 
 Electro-Analysis. Various conceptions have been and are 
 entertained of the nature of the electrolytic process, but in 
 view of the most recent developments it may, perhaps, be 
 best to look upon the phenomena occurring in the electro- 
 lysis of solutions as actions and reactions in which ions 
 play the leading role. 
 
 It will be recalled that ions are denned as compounds 
 of atoms and electrons. Under the influence of the electric 
 current the ions move towards the electrodes, of course the 
 anions seeking the anode and the cathions seeking the cath- 
 ode. When the ions have come within acting distance of 
 the electrode towards which they are traveling, a discharge, 
 that is to say, a neutralization of the electric charges which 
 they bear, takes place. This division of ions into electrons 
 and into atoms, which were held in combination with these 
 electrons, liberates the atoms in a condition in which their 
 chemical affinity can come most strongly into play. This 
 condition is frequently designated as the nascent state, the 
 
ELECTRO- A NA L YSIS. 6 7 
 
 " status nascendi"; if the ions which have thus suffered 
 discharge are compound ions, the materialistic nuclei which 
 remain are unsaturated compounds, and as such also display 
 strong chemical affinity. 
 
 If there is no other substance present in an electrolytic 
 solution with which the atoms or unsaturated nuclei can 
 enter into chemical combination, these atoms or nuclei 
 assume the molecular state. Thus, for instance, in the 
 electrolytic decomposition of water, if the hydrogen and 
 oxygen set free find no other substance present with which 
 they can enter into chemical combination, then these ele- 
 ments are liberated as hydrogen and as oxygen gas respec- 
 tively. 
 
 The electric discharge of ions takes place in accordance 
 with Faraday's laws. If the conditions are such that sev- 
 eral reactions may occur, the speed with which iors are 
 discharged is a very important factor, for, if the speed of re- 
 action of the discharged ions with the depolarizer is greater 
 than the speed of discharge of the ions then there will be no 
 liberation of the discharged ions in the molecular state; 
 this can frequently be observed in processes of oxidation 
 and reduction. 
 
 As electrochemical reactions are confined to the imme- 
 diate neighborhood of the electrodes, the rate at which such 
 reactions proceed is dependent upon the concentration of the 
 ions. But the concentration of the ions is determined by 
 the current strength, the size of the electrode surface, and 
 the concentration of the depolarizer, and these items must 
 therefore be very carefully considered and adjusted in every 
 electrolytic- operation to ensure the desired result. 
 
 The chief characteristic of an electrolytic process, as com- 
 pared with a purely chemical process, is the consumption of 
 energy in the former in lieu of the consumption of material 
 in the latter; mother words, an electric current effects changes, 
 for instance, oxidations and reductions, which in chemical 
 
68 NOTES OX ELECTROCHEMISTRY. 
 
 processes are induced only by the intervention of chemicals. 
 If a chemical change is brought about directly by the 
 action of electrical energy, if the electric current is allowed to 
 act upon an electrolyte, the action is spoken of as a direct 
 action ; if the electric energy must first suffer transformation 
 into some other form of energy, for instance, into heat or 
 light, the process is spoken of as an indirect action. The 
 manner in which the electric action known as the silent dis- 
 charge is effected is as yet but little understood, although 
 unquestionably many electrochemical effects in nature arc 
 brought about by this agency. 
 
 In effecting the electrolysis of organic substances two cases 
 must be distinguished: the body acted upon may be an 
 electrolyte, or it may be a non-electrolyte. 
 
 In the latter case the ions which are to transport the 
 electric charges must be furnished from some other source^ 
 through addition of some electrolyte. The ions thus intro- 
 duced will, under the influence of the electric current, travel 
 towards the electrodes, and the organic substance is acted 
 upon by these ions only at the moment of their discharge. 
 A substance thus entering into chemical combination with 
 the atomic constituent of an ion at the moment of its dis- 
 charge is termed a depolarizer. 
 
 Two classes of depolarizers may be distinguished, anodic 
 and cathodic depolarizers. 
 
 Cathodic Depolarizers. The process taking place at the 
 cathode is termed reduction; the principal cathions, that is, 
 the ions liberated at the cathode, are ions of the metals and 
 of hydrogen; a few organic cathions are also known. Sub- 
 stances which can either take up hydrogen or give gut oxygen, 
 or do both, are known as reducible substances; in other 
 words, they are oxidizing agents, and their special function 
 is the neutralization of positive charges. 
 
 Anodic Depolarizers. Anodic depolarizers are agents 
 which destroy negative charges. If oxygen be added, or 
 
ELEC TRO-A NAL Y SIS. 6 9 
 
 if -hydrogen be abstracted, or if both of these phenomena 
 .proceed simultaneously, the process is designated as a process 
 Of oxidation. 
 
 Thus, a substance submitted to : 
 
 REDUCTION, OXIDATION, 
 
 Gains hydrogen, Loses hydrogen, 
 
 Loses oxygen, or both. Gains oxygen, or both. 
 
 Reversible Reactions and Cells. A process at a given 
 electrode is reversible when the substances formed in this 
 process are the same, whether the electric current flows 
 from this electrode or towards it. 
 
 Thus, in the Daniell cell: 
 
 Zn : ZnSO 4 : CuSO 4 : Cu 
 solution solution 
 
 if the electric current flows from the zinc into the electrolyte 
 zinc ions will go into solution; if the current is sent in the 
 reverse direction, zinc ions will travel towards the zinc elec- 
 trode and zinc will be deposited on that electrode. 
 
 Electrodes reversible with respect to cathions are termed 
 electrodes of the first order; these generally consist of a 
 metal placed in a solution of some one of its own salts. Elec- 
 trodes reversible with respect to anions are termed electrodes 
 of the second order; these can be made by placing some 
 insoluble compound containing the anion required on some 
 metal and then placing the electrode thus prepared into a 
 solution of the same anion. 
 
 Reversible cells may consist of any combination of elec- 
 trodes. A reversible cell may be defined as a cell which 
 can be restored to its original condition by an expenditure 
 of electrical energy equal to the maximum electrical energy 
 obtainable from it at constant temperature. An irrever- 
 sible cell is one in which the original condition cannot be 
 restored by reversing the direction of the current flow; for 
 
70 NOTES OA' ELECTROCHEMISTRY. 
 
 instance, the original voltaic pile, made of zinc, sulphuric 
 acid, and silver, is of this type. The water voltameter is 
 another illustration of an irreversible cell. Cells of this kind, 
 as a rule, furnish a rather high electromotive force at the 
 start; this, however, depreciates as the action proceeds, for 
 the electrodes suffer polarization. Reversible cells, on the 
 other hand, yield a current almost constant in electromotive 
 force as long as they continue in action, for in these the 
 electrodes do not suffer polarization. 
 
 If the electromotive force of a cell is determined, the 
 voltage represents the difference of potential between the 
 electrodes. Whenever there is a contact of dissimilar sub- 
 stances electromotive force appears, but it is only the 
 electromotive force caused by the contact between the 
 metal electrodes and the electrolyte in which they re- 
 spectively are immersed, that here calls for comment. To 
 this value the term electrode-potential is given ; it represents 
 the work expended in conveying the unit quantity of elec- 
 tricity between electrode and electrolyte. 
 
 An explanation of this action was first suggested by Nernst,* 
 who showed that the process might be conceived of as an 
 osmotic process by ascribing to each metal the property of 
 forcing electrically charged particles, ions, into a liquid with 
 which the metal is in contact. This forcing of the ions into 
 the liquid takes place with a pressure peculiar to each metal 
 and is invariable at constant temperature. The metal may thus 
 be regarded as a sort of reservoir of ions wherein these ions 
 are stored under a greater or less pressure, and this pressure 
 is designated as the electrolytic solution pressure of the metal. 
 
 Whenever electrical energy is developed, both positive 
 and negative electricity come simultaneously into existence. 
 In the metallic electrodes as such, the particles are without 
 electric charges; at the instant, however, that a particle 
 
 *Zeit8chriff, Phys. C'hemie. 1889, Vol. 4, p. 129. 
 
ELECTRO-ANALYSIS. 71 
 
 passes from an electrode into an electrolytic solution the 
 particle assumes a positive charge and thus becomes an ion; 
 at the same instance the metallic electrode acquires a nega- 
 tive charge of equal intensity. Each additional ion which 
 enters into the solution increases the positive charge of the 
 solution while the electrode becomes correspondingly more 
 and more charged with negative electricity. 
 
 Electric charges of opposite sign attract one another and 
 one can thus conceive of a layer of positively charged ions 
 held in attraction by a negatively charged electrode, a differ- 
 ence in potential being thus established. The electrostatic 
 attraction of this layer opposes the tendency of the electro- 
 lytic solution pressure of the electrode to force more ions 
 into the solution , and when these counterforces are in equi- 
 librium the action comes to a halt. As the electric charges 
 carried by the ions are very great, such equilibrium is estab- 
 lished even when but a few ions have passed from the elec- 
 trode into the solution. 
 
 If a metallic electrode be immersed in a solution of one 
 of its own salts, the metallic ions therein will by osmotic 
 pressure oppose the admission of more ions of their own 
 kind. If this osmotic pressure of the ions in the solution 
 is exactly in equilibrium with the solution pressure of the 
 electrode, no ions will be projected from the latter into the 
 solution, and the electrode will therefore not be charged 
 with negative electricity. 
 
 On the other hand, if the osmotic pressure is greater than 
 the electrolytic solution pressure, the metallic ions are driven 
 from the solution on to the electrode and the electrode is 
 thereby charged with positive electricity. The solution- 
 losing some of its positively charged ions while its content 
 of negatively charged anions is not decreased, becomes nega- 
 tively charged; the electrostatic difference is thus continu- 
 ously increased until it counterbalances the osmotic pressure, 
 and then equilibrium is restored. 
 
72 NOTES ON ELECTROCHEMISTRY. 
 
 The electromotive force of a cell can be calculated from 
 the osmotic pressure of the solutions about the electrodes, 
 for, if a substance is allowed to pass isothermally from one 
 condition into another it is immaterial how such a trans- 
 formation occurs, whether osmotically or electrically. 
 
 Knowing the maximum amount of external work which a 
 process can accomplish in an isothermal transformation, the 
 problem is a simple one, for the work which can be done by 
 ions in passing from a given osmotic pressure to another 
 can be transformed without loss into electrical energy. 
 
 The fundamental formula by which the electromotive 
 force of an element is calculated from the osmotic pressure 
 of the solutions about the electrodes, is: 
 
 In this formula 
 
 P potential, 
 r = valence of the ions, 
 E = quantity of electricity, 
 
 RTln = amount of energy transformed into work in a gas 
 which expands isothermally from a pressure p 1 
 to a pressure p 2 . 
 
 This last formula also holds for a solution which passes 
 isothermally from one osmotic pressure to another. 
 
 In a Dauiell cell the difference in potential between the 
 two electrodes is practically 1.1 volts. Of this, 0.5 volt is 
 the potential difference between the zinc electrode and the 
 zinc sulphate solution the electrolyte in which it is im- 
 mersed, and the balance, 0.6 volt, is the potential difference 
 between the copper electrode and the solution of copper 
 sulphate in which this electrode is: immersed. 
 
ELECTRO-ANALYSIS. 73 
 
 The term electro-affinity is used to designate the electrode 
 potential in solutions which contain 1 gram-equivalent per 
 liter of the ion given off by the electrode; solutions of this 
 concentration are called normal solutions. An electrode is 
 either positive or negative to a normal solution of its ions, 
 and its electro-affinity is, by the majority of writers, denoted 
 accordingly as positive or negative. The electromotive 
 force of a cell whose electrodes are reversible with respect 
 to any ion, is the algebraic difference between the electro- 
 affinities of the two ions. 
 
 In normal solutions the electrode-potential increases for 
 cathions and decreases for anions with the concentration 
 of the electrolyte. In other words, the electrode potential 
 is determined by the concentration of that part of the elec- 
 trolyte in actual contact with the electrode. It is therefore 
 important that the electrolyte be kept in motion by a stirrer, 
 or, that the electrode be kept revolving in the solution, for 
 by these means the concentration of a solution is kept fairly 
 uniform and an even deposition of the metal precipitated 
 by the electric current is secured. If some precaution be 
 not taken to secure a uniform concentration of the solution, 
 the concentration of the electrolyte about the cathode will 
 decrease and, in consequence, the electrode-potential of 
 the cathode will be lowered, while the concentration of the 
 electrolyte at the anode will be increased, and the electrode- 
 potential of the anode will be raised in consequence. When 
 this occurs, a fall of potential results, indicative of the work 
 done in bringing about these differences in concentration. 
 This phenomenon is known as concentration polarization; 
 it occurs whenever any perceptible amount of chemical 
 action is taking place. 
 
 The dissociation voltages previously discussed are, of course, 
 to be considered only as minimum voltages based upon the 
 assumption that the electrolytic process takes place slowly 
 and with weak currents. Heavier currents invariably cause 
 
74 NOTES ON ELECTROCHEMISTRY. 
 
 concentration polarization, and to overcome this higher volt- 
 ages are required. 
 
 The electrode-potential of an ion depends upon its chemical 
 nature and upon the amount in which this ion is present in 
 an electrolyte. If, therefore, more than one kind of cathion 
 is present in an electrolyte, that cathion will be first dis- 
 charged which has the greater electrode-potential. Through 
 such discharge, however, its concentration will be decreased 
 and thereby its electrode-potential will be lowered; when 
 the electrode-potential of both cathions is identical, both 
 will be discharged simultaneously. 
 
 If there are two anions present in an electrolyte, that 
 anion having the lower potential will be the first to be dis- 
 charged; through this its concentration will be reduced and 
 its electrode-potential will be raised. When both anions 
 have attained to the same electrode-potential they will suffer 
 simultaneous discharge. 
 
 These facts explain why the current density the quo- 
 tient obtained by dividing the current strength by the elec- 
 trode surface, and generally expressed in terms of amperes 
 per 100 square centimeters of electrode surface plays so 
 important a part in electrolysis. 
 
 Entirely distinct from concentration polarization is the 
 phenomenon termed chemical polarization. This is due to 
 some new chemical substance or substances formed by the 
 electric current and the consequent substitution of new 
 electrode surfaces for those electrode surfaces with which 
 the electrolytic operation was begun. Thus, in the elec- 
 trolysis of water the gases liberated by the action of the 
 electric current, hydrogen and oxygen, have a great tendency 
 to polarize the electrode surfaces chemically. 
 
 Such a polarization produces a back-pressure, a reverse 
 electromotive force, which, at times, diminishes the effective 
 electromotive force very materially. 
 
 The amount of such back-pressure can be practically 
 
ELECTRO-ANALYSIS. 75 
 
 measured by first reading the voltage across the two elec- 
 trodes as usual, then turning off the current and noting the 
 position at which the indicator in the voltmeter halts for 
 a brief space of time ere it travels on to zero. That point 
 where it halts marks the polarization voltage. 
 
 If, for instance, the full working voltage in an experi- 
 ment be 5 volts, the halting-point be at 3 volts, and the 
 amperage 3.5, then the resistance of the cell, i.e., the reverse 
 electromotive force of the cell is : 
 
 A means of overcoming chemical polarization is the plac- 
 ing of the anode in a solution of a salt of the metal of which 
 the anode is made, or the use of an oxidizing agent, a so- 
 called depolarizer, which oxidizes the product of electrolysis 
 that would otherwise polarize the electrode. 
 
 Sources of Current. In choosing a source for current 
 supply for analytical purposes, the great consideration is 
 the securing of a current which shall have sufficient strength 
 (amperage) and which shall possess a potential (voltage) 
 as constant as possible. 
 
 Use can be made of primary batteries (cells), of thermo- 
 piles, dynamos, accumulators, and of a direct lighting cur- 
 rent. 
 
 Generally speaking, electrical elements, or cells, are devices 
 for carrying on electrochemical reactions. Cells which yield 
 an electrical current are called voltaic cells. These can be 
 made to serve as sources of supply, but are open to several 
 objections. Some yield too weak a current, having an 
 internal resistance which is too high; others polarize too 
 rapidly, and this, of course, causes a- rapid falling off in cur- 
 rent; others again emit noxious fumes and vapors. 
 
 If cells are to be used possibly the best is the Edison 
 
76 NOTES OX ELECTROCHEMISTRY. 
 
 Primary battery, or the Daniell cell. The latter consists of 
 
 Zn: ZnSO 4 :Cu:CuSO 4 
 The Bunsen cell is made of 
 
 - Zn:ZnSO 4 :C:HNO 3 . 
 
 In this cell, the carbon, gas-carbon, or graphite, dips into 
 nitric acid which is contained in a cup or cylinder of porous 
 earthenware or clay. The zinc is generally well amalgamated 
 to avoid local currents which are very destructive to the 
 electrode. The chromic a,cid cell is a modification of the 
 Bunsen cell; it contains potassium dichromate as a depola- 
 rizer the positive pole is carbon, the negative pole is 
 zinc, well amalgamated. 
 
 Cells can be grouped for a high electromotive force or 
 for an increased quantity of current. 
 
 To obtain a high electromotive force the cells should be 
 linked in series, that is, the positive pole of one cell should 
 be linked to the negative pole of another cell; zincs, for in- 
 stance, to carbons. The total electromotive force of a set 
 of cells thus linked in series is equal to the voltage of an 
 individual cell multiplied by the number of cells so linked. 
 By thus linking in series, the internal resistance of the system 
 is, of course, also increased. 
 
 To increase the quantity of electric current cells must be 
 linked in parallel, that is, all the positive poles are joined 
 together, and all the negative poles are joined together. 
 This arrangement decreases the internal resistance; the total 
 internal resistance of a system linked in parallel is equal to 
 the resistance of an individual cell divided by the total num- 
 ber of cells so linked. Linking in parallel practically amounts 
 to a summation of all of the electrode surfaces. 
 
 Of course, if sufficient cells are available, they can be divided 
 into groups and linked partly in series, and partly in parallel. 
 The best current-yield is obtained by linking the cells in 
 
ELEC7RO-AXALYSIS. 77 
 
 such a way as to equalize, as nearly as may be, the external 
 and the internal resistance. 
 
 Thermopiles are practically feasible only in connection 
 with accumulators, for thermopiles do not furnish sufficient 
 current for analytical use. Dynamos can be constructed 
 for every desired current strength and potential. 
 
 A direct lighting current will be found very practical, 
 especially so if used with a lamp-resistance arrangement, 
 which will be described later. Among the most convenient 
 devices affording a reliable current supply are accumulators, 
 which can be charged from a lighting system. Accumula- 
 tors yield a very steady current and almost any amperage 
 desired can be secured by an adjustment of their electrode 
 surfaces. 
 
 An accumulator may be defined as a device wherein elec- 
 trical energy can be stored in the form of chemical energy 
 and from which electrical energy can again be secured at 
 will. As a matter of fact, every reversible cell may be re- 
 garded as an accumulator, in practice, however, lead accumu- 
 lators are almost the only ones used. Plante, in 1860, built 
 the first battery of this kind. 
 
 Accumulators of this type consist of two plates of lead 
 coated with a layer of oxide or of sulphate of lead immersed 
 in a 20 per cent solution of sulphuric acid. On passing an 
 electric current through such a cell, that is to say, while charg- 
 ing such an accumulator, the lead anode becomes coated with 
 a layer of lead peroxide, or of lead hydrate, while the cathode 
 receives a coating of spongy metallic lead. On the discharge 
 of the accumulator, both of these layers on the two electrodes, 
 the lead peroxide, or hydrate, on the anode, and the spongy 
 lead on the cathode, are again transformed into lead sulphate. 
 
 Streintz states the chemical equation of this change to be : 
 
 PbO 2 + 2H 2 SO 4 aq. + Pb = 
 
 2 PbSO, + 2 H 2 O + aq. + 87,000 calories. 
 
78 NOTES ON ELECTROCHEMISTRY. 
 
 M. Le Blanc, in 1895, was the first to give an explanation, 
 by means of the theory of electrolytic dissociation, of the 
 reactions taking place in an accumulator. According to 
 his views, the chief source of the electromotive force of a 
 lead accumulator is the transformation of tetravalent lead 
 ions (from the PbO 2 in water) into divalent lead ions. The 
 solid lead superoxide replenishes the tetravalent lead ions 
 which are consumed, and the divalent lead ions which thus 
 appear enter into chemical combination with the sulphuric 
 acid present, forming sulphate of lead. At the cathode the 
 metallic lead is transformed into divalent lead ions, and these 
 also combine with sulphuric acid to form solid sulphate of 
 lead. 
 
 The new Edison storage-battery consists of a nickel per- 
 oxide (NiO 2 ) anode and an iron cathode; caustic potash 
 (KOH) is the electrolyte used. 
 
 The electromotive force of this accumulator is low, about 
 1.1 discharge voltage, but it has certain advantages, for 
 instance, a good storage capacity per unit of mass, a pro- 
 nounced stability, and moreover, it can be quickly charged 
 and discharged without injury to the plates.* 
 
 Pole-papers. Whatever the source of current, pole-papers 
 so-called, are a convenient means for ascertaining at once 
 which is the positive and which is the negative pole in a 
 given circuit. 
 
 These pole-papers are small strips of filter paper charged 
 with a solution of some salt and with a solution of some 
 indicator which instantly indicates an ionic change in the 
 salt used, solutions of sodium sulphate, and of phenol- 
 phthalein, for instance. 
 
 When a piece of filter-paper moistened with the above 
 solutions is touched by the terminal wires conducting an 
 
 * Confer: R<x>ber E. F., Elec. World and Engineer, 1901. Schoop, 
 M. M., Electro-chem. Tnd., 1904, and Sc. Am. Suppl., 1905, p. 25064. 
 
ELECTRO-ANALYSIS. 79 
 
 electric current, the wires being held but a small distance 
 apart, a pink mark soon appears at the point where the 
 negative pole of the circuit touches the paper, the color 
 being due to the reaction of the phenolphthalein with the 
 alkali which is set free at the cathode. 
 
 Current Measurement. Exact measurements of the 
 working current conditions, of amperage and voltage, are, of 
 course, most essential in electrochemical work. Besides a 
 voltameter, which can be used to measure current strength 
 but which is principally serviceable in checking othei meas- 
 uring instruments, an ammeter and a voltmeter are required. 
 
 There are various kinds of ammeters. In the electro- 
 magnetic type, an electric current is sent through a coil of 
 wire which surrounds an easily movable core of iron. This 
 iron core is in connection with a pointer which moves across 
 a dial, and the deflection of this pointer indicates the strength 
 of the current which passes through the coil. 
 
 The hot-wire ammeter depends for its action upon the 
 heating by the electric current of a very fine wire. This 
 wire is fastened at two points and at its middle is connected 
 to another fine wire which passes around a small drum bear- 
 ing a pointer. A spring, while at normal temperature, keeps 
 the latter wire in a state of constant tension; when, however, 
 a current is sent through the first wire this becomes heated 
 and slackens, the spring draws on the second wire and thus 
 drum and pointer are set in motion. On account of its hav- 
 ing a low internal resistance an ammeter can be placed any- 
 where directly in the circuit. 
 
 Voltmeters are analogous in construction to ammeters; they 
 may be of the electromagnetic or of the hot-wire type. 
 If of the former description, the high resistance needed is 
 secured by the use of a great number of windings of very 
 fine wire, v/hich reduces the consumption of current to a 
 minimum. In the hot-wire type the required resistance is 
 obtained by introducing in series with the instrument the 
 
80 NOTES ON ELECTROCHEMISTRY. 
 
 requisite number of resistance coils; the greater the voltage 
 to be measured, the more of these coils generally made of 
 very fine wire are required. Voltmeters, having a very 
 high resistance, are always placed in a shunt-circuit, the 
 latter receiving only a small fraction of the current which 
 flows along the main line. 
 
 The resistance of a wire is directly porportional to its 
 length and inversely proportional to its cross-section. 
 
 If two paths are offered an electric current and both of 
 these paths have the same resistance, 50 per cent of the current 
 travels by each wire. If, however, a given wire, let us say, 
 wire A, has a resistance of 10 ohms, and wire B has a resist- 
 tance of 100 ohms, then 10 per cent of the current will pass 
 through wire B, and 90 per cent through wire A. 
 
 A voltmeter can also be conveniently used as an ampere- 
 meter provided that a known resistance is introduced into 
 the electric circuit and that the terminals of the voltmeter 
 are attached to this resistance. 
 
 As, E = CR, 
 
 hence, if R is known and E is ascertained by a voltmeter, 
 C can be determined at a glance. 
 
 If a resistance of 1 ohm is used in the circuit, the values 
 indicated by the voltmeter read directly in amperes, for 
 
 1 volt 
 
 1 ampere = - r 
 1 ohm 
 
 If the resistance introduced is 0.1 ohm, then each unit 
 indication of the voltmeter represents 10 amperes, for 
 
 1 volt 
 10 amperes = 
 
EL EC TRO-A NA L YSIS, 81 
 
 If the resistance employed is 10 ohms, each unit indication 
 in the scale represents 0.1 ampere, for 
 
 1 volt 
 
 0.1 ampere = ^-r r 
 10 ohms 
 
 It is therefore possible, by the proper selection of resistance, 
 to obtain a very wide range of current strength. 
 
 Current Regulation. --- The regulation of an electrical cur- 
 rent used for electrolytical purposes can be achieved by the 
 introduction of the proper amount of resistance into the 
 circuit, and by a regulation of the distance between the elec- 
 trodes in the electrolyte. 
 
 The so-called resistance boxes usually consist of coils or 
 spirals made of German-silver wire, or of some other alloy. 
 Among alloys specifically made for this purpose are nick- 
 eline, constantan, platinoid, and manganin. Mariganin is 
 an alloy of manganese, nickel and copper; it has a very high 
 resistance and a very small, negative coefficient of tempera- 
 ture, and it is therefore especially valuable for the manufac- 
 ture of electrical apparatus, where constancy of resistance 
 at various temperatures is called for. 
 
 A current passing through a wire heats the wire, and in 
 consequence the resistance rises. For some purposes it is 
 very desirable to avoid such a variation in the resistance, 
 and in such instances use can be made to advantage of an 
 alloy that has a low temperature coefficient. 
 
 Platinoid is an alloy of this description; its increased resist- 
 ance through a range of 100 C. (from to 100 C.) 
 is only 2.09 per cent, whereas silver, annealed or hard-drawn, 
 shows a rise of 40 per cent, and annealed copper a rise of 
 almost 43 per cent. 
 
 Another simple and serviceable device for introducing 
 resistance into an electric circuit is the lamp-bank.* Alamp- 
 
 * Consult Hopkins, liber, cit., p. 13. 
 
82 NOTES ON ELECTROCHEMISTRY. 
 
 bank is made by arranging a number of lamp-sockets partly 
 in parallel, partly in series, upon a slab of slate or marble, 
 and then inserting the necessary number of lamps properly 
 grouped to give the desired resistance. The current may 
 be conveniently taken from a direct lighting circuit. 
 
 When lamps are arranged in parallel, their combined re- 
 sistance is equal to the resistance of one lamp divided by 
 the number of lamps in parallel; when arranged in series 
 their combined resistance is equal to the resistance of one 
 lamp multiplied by the number of lamps in series. 
 
 Assume, for instance, that eight 16 candle-power lamps 
 are available and that the lamp-board is arranged in such a 
 manner that these lamps can be used either in parallel or in 
 series. 
 
 Let E = 110 volts, 
 
 R - 220 ohms, 
 
 and have the 8 lamps arranged in parallel, 
 therefore, in this instance, 
 
 i.e., 4 amperes would pass through the lamps thus grouped 
 If the 8 lamps were arranged in series, 
 
 110 110 0.062. 
 
 220 X 8 1760 
 
 i.e., only 0.062 ampere would flow through the combination. 
 
 It is thus evident, that by grouping some of the lamps in 
 parallel and some in series, and by using lamps of different 
 resistances, almost any desired amperage may be secured. 
 
 Of course, the introduction of resistance into the circuit 
 in such a manner is the reverse of economical; a 110- volt 
 
ELECTRO-ANALYSIS. 83 
 
 current cut down to, say, 4 volts, renders no more effective 
 service than the current of a 4- volt generator directly applied. 
 The actual current strength in any electrolytic circuit is 
 determined by the formula: 
 
 C = - 
 
 in which: 
 
 E voltage of the current, 
 e = counter-voltage, 
 R = resistance of cell, 
 
 R l = resistance of the conductor (the leads), be- 
 tween generator and cell. 
 
 In electrochemical analysis, however, the voltage is gen- 
 erally measured directly between the terminals of the cell, 
 that is, the value of R only is sought and the value R l not 
 taken into account. 
 
 The resistance of an electrolytic cell may also be calcu- 
 lated by the formula: 
 
 R ~ T1 /T 
 
 E.S 
 in which, 
 
 D = distance, in centimeters, between the electrodes 
 
 these being assumed to be perfectly parallel, 
 p = the specific resistance of the electrolyte, 
 E.S. = electrode surf ace, i.e., the area in square centimeters of 
 each electrode. 
 
 If there are three plates and the current flows from the 
 central plate to each of the other two, then the value of R 
 is found as above for either side, and the combined resistance 
 equals one-half of the value thus found. 
 
 The resistance of electrolytes varies with their chemical 
 nature, with their concentration, and with the temperature. 
 An increase in temperature markedly decreases the resist- 
 
84 NOTES ON ELECTROCHEMISTRY. 
 
 ance of electrolytes; in this respect electrolytes resemble 
 the behavior of carbon. 
 
 The cross-section of a wire, in square millimeters, for in- 
 stance, of a copper wire used for conducting an electric cur- 
 rent, is calculated by the formula : 
 
 r _ L.C. 0.01687 
 D.P. 
 
 in which: 
 
 C.S. cross-section in square millimeters, 
 
 L = total length of conducting wire that is, the sum 
 of the lengths of wire leading from the source 
 of current supply and back, 
 C the maximum current strength to be conducted 
 
 expressed in amperes, 
 
 Z). P. = the maximum permissible drop in potential ex- 
 pressed in volts, 
 
 0.01687 = specific resistance of copper, i.e., the resistance of 
 a copper wire 1 meter long and 1 square milli- 
 meter in cross-section. 
 
 The cross-sections of round wires are very often given in 
 circular mils. A mil is the one-thousandth part of an inch 
 (= 0.0254 millimeter). A circular mil is the area of a circle 
 the diameter of which is one mil; a circle having a diameter 
 d has an area of d 2 circular units. One circular mil is equal 
 to 0.000506709 square millimeter, and one square millimeter 
 is equal to 1973.52 circular mils. 
 
 In calculating the cross-sections of the conducting wires 
 between the sources of supply and the working-station a 
 safety-margin of from 20 to 25 per cent over and above the 
 amount calculated, should be allowed. 
 
 Electrodes. The electrodes used in electro-analytical 
 work are usually made of platinum. The cathode may, 
 according to conditions, be either a crucible, a dish, a flag 
 or foil, a cone, or a cylinder. 
 
ELEC TRO-A NA L YSIS. 85 
 
 If a dish be used it is generally selected to hold from 150 
 to 200 cubic centimeters; whatever the shape chosen, the 
 utmost care must be taken to have the surface which is to 
 receive the electrolytic deposit perfectly smooth and abso- 
 lutely clean and bright, above all, not a trace of oil or of 
 any other fatty matter may be present. 
 
 The anode may be a plain foil or a flag, a wire to the end 
 of which a small disk has been soldered, a spiral coil, or a 
 cylinder. To whichever shape preference is to be given 
 will, to a certain extent, be determined by the current den- 
 sity required. 
 
 A convenient electrode support consists of an upright rod 
 or bar of glass to which a metallic ring and a metallic bar 
 are attached in such a way that these can readily be set in 
 any position desired. The metallic ring is intended for the 
 support of the cathode a platinum dish for instance 
 and is in connection with the negative pole of the current. 
 The anode is fastened to the metal bar and this is connected 
 with the positive pole of the electric current. 
 
 As warm electrolytes are superior conductors, the plati- 
 num dish, which serves as the cathode, may conveniently be 
 placed on a thin plate of asbestos and heated by a small 
 gas-flame, electrically, or in some other manner. Various 
 analyses, of course, demand various temperature conditions, 
 but it seems that, as a rule, 50 C. should not.be exceeded. 
 
 The use of a stationary anode generally entails the em- 
 ployment of a weak current and hence necessitates the use 
 of considerable time for the electrodeposition of some metals. 
 This is due to the fact that concentration changes are set 
 up in the solution, a decrease in the concentration of the 
 cathions becoming noticeable near the cathode as the depo- 
 sition progresses. This difficulty can be avoided by the 
 use of a rotating anode driven by an electric or water motor 
 and revolving perhaps from 30 to 130 times per minute. By 
 this means the concentration of the electrolyte is kept uni- 
 
86 NOTES ON ELECTROCHEMISTRY. 
 
 form, a stronger current can be employed, and, in conse- 
 quence, considerable time be saved. 
 
 It is also possible to make use of a rotating cathcde, a 
 platinum crucible, for instance, answers this purpose well.* 
 Giving such a cathode a speed of rotation of from 600 to 
 700 revolutions per minute, and working with a normal 
 current density of from 5.0 to 6.6 amperes, 15 to 30 minutes 
 will suffice for an electrodeposition which ordinarily would 
 require hours for its completion. 
 
 In calculating electrode areas it is customary to measure 
 the surfaces of the electrodes only to the extent that the 
 same are in contact with the electrolyte. 
 
 Formula; for Calculation of Electrode Areas. 
 
 d = diameter, IT = 3.1416. 
 
 r = radius. 
 
 Circumference of a circle: d x *, 
 
 r X 2,1-, 
 Area of a circle : cP x .7854, 
 
 Surface areas. 
 
 1. Foil or flag: Height x length. 
 
 2. Cone or pyramid: Product of perimeter of base by half 
 
 the slant height, plus the area of the base. 
 
 3. Open-end cylinder or prism: Perimeter of one end x 
 
 height. 
 
 4. Closed-end cylinder or prism: Perimeter of one end x 
 
 height, plus twice the area of one end. 
 
 5. Interior surface of a dish (curve-surface of a segment or 
 
 a zone of a sphere) : Diameter of sphere x height of 
 segment or zone X rr. 
 
 * Am. Journal of Science, Vol. 15, p. 320. 
 
ELECTRO-ANALYSIS. 87 
 
 6. Cylindrical gauze: 
 
 d diameter of wire, 
 
 n = number of meshes per square centimeter, 
 
 "11 ( f gauze used. 
 b = width ) 
 
 Current Density. This term, as previously stated, desig- 
 nates the ratio of the electrode area to the flow of current. 
 It is customary to term the current strength per 100 cm 2 , 
 (one square decimeter, 1 dm 2 ) of electrode surface, the 
 normal density of current, and this value is symbolized by 
 
 For instance, N.D. m -= 0.5 signifies that the current flow 
 for every 100 square centimeters of electrode surface is 
 0.5 ampere. 
 
 Let, D = current density, 
 
 C = current strength, 
 
 E.S.= electrode surface on which electro-deposi- 
 tion takes place. 
 
 C 
 then, D - ^~-, 
 
 Q 
 
 and N.D. 100 = 
 
 If the N.D.iw and the electrode surface are known, the cur 
 rent strength is readily calculated by the formula, 
 
 For instance, let: 
 
 C = 5 amperes, 
 E.S.= 180 cm?. 
 
 * Winkler : Berichte, Vol. 32, p. 2192. 
 
88 NOTES ON ELECTROCHEMISTRY. 
 
 Then: D-- 0.028, 
 
 1 80 
 and, N.D. m = 5 - = 2.8. 
 
 1 SO 
 ard, C= 2.8 X = 5.0. 
 
 The current density may either be the same or unlike at 
 the two electrodes. If both electrode areas are alike, a 
 given current strength will, of course, ensure identical cur- 
 rent density at both electrodes. A given current strength 
 passing from a small electrode area naturally means a high 
 current density at that electrode. Thus let: 
 
 C = 5.0 
 E.S. = 1.0 
 
 then, D = - --= 5.0 
 
 The same current strength passing form a large electrode 
 surface determines a low current density at that electrode. 
 
 Thus: C = 5, 
 
 E.S.= 100, 
 
 Z> - = 0.05. 
 
 All electrochemical operations are greatly influenced by 
 the current density. 
 
 Records. The records of all electrochemical work should 
 be kept in such a manner as to permit of the exact repeti- 
 tion of such work at any time. What the specific data of 
 such record should be, is, of course, in a large measure deter- 
 mined by the nature of the work under consideration. 
 
ELEC TRO-A NA L YSIS. 89 
 
 In all cases, however, such record should include data of 
 the source of the current used, the time during which the 
 current passes, the material of which the electrodes consist, 
 the distance between the electrodes in the working -cell, 
 the active area of the electrodes, the voltage and amperage 
 employed, the current density, the character of the elec- 
 trolyte, its temperature throughout the reaction, and, in 
 addition, any specific phenomena which may be noticed at 
 anode and cathode. 
 
 Resum^. The principal facts to be borne in mind in 
 electro-analytical work and in the study of electrolytic 
 processes are the following: 
 
 Each ion bears a definite charge of electricity. The ionic 
 charge for a monovalent gram ion is = 96,540 coulombs. 
 The ionic charge is directly proportional to the valence of 
 the ion and is the same for all ions of the same valence, 
 whether such an ion be an individual ion or a complex ion. 
 Thus, the cathions silver and sodium bear equal charges of 
 positive electricity, while the anions, chlorine, iodine, and 
 NO 3 bear equal charges of negative electricity. 
 
 The amount of an element deposited or liberated electro- 
 lytically is proportionate to the current used. A given 
 current will deposit or set free of various elements, amounts 
 directly proportionate to the atomic weights of those ele- 
 ments and inversely proportionate to their valence. 
 
 Thus, taking the atomic weight of silver, 107.93, as the 
 basis, the number of grams of any element set free or de- 
 posited by one ampere hour is equal to : 
 
 0.037291 x atomicwei S ht 
 
 change of valency 
 
 For instance, of copper there will be deposited from a 
 solution of cupric chloride, CuCl 2 : 
 
90 NOTES ON ELECTROCHEMISTRY. 
 
 63.6 
 
 0.037291 X 
 
 2 
 0.037291 x 31.8 = 1.1858 grams. 
 
 One ampere hour will thus deposit of: 
 Silver, . . . 4.0248 grams, 
 Copper (from a cupric salt) 1.1858 grams, 
 and these values are in the same ratio as the respective 
 
 (107.93) (63.6) 
 chemical equivalents of silver and of copper 
 
 i.e. as 107.93 and 31.8. 
 
 Great stress must also be laid on having the current used 
 sufficient in amount, in other words, the current density 
 must be sufficiently large so that the rate at which a metal 
 is precipitated is greater than the rate at which it tends to 
 redissolve in the solution from which it is being deposited. 
 This is proportionate to the area of the surface of the elec- 
 trode at which the deposition occurs, hence the amount of 
 current per unit of surface area, the current density, is a 
 factor of prime importance. 
 
 While the various chemical elements are set free in equiv- 
 alent amounts at the electrodes, it is necessary to remember 
 that the amount of electrical energy requisite to effect an 
 electrolytic decomposition varies with the nature of the 
 chemical combination to be decomposed. 
 
 The minimum' dissociation voltage, the critical voltage, 
 differs for each element and is characteristic of it. Advan- 
 tage is taken of this fact to separate different metals ana- 
 lytically. For instance, in passing a current through a solu- 
 tion of several metals, the metal having the lowest critical 
 voltage will be deposited first; if the voltage be then in- 
 creased, metal after metal will be precipitated, and the metal 
 having the highest critical voltage will be the last one to be 
 deposited. 
 
ELECTRO-A NALYSIS. 91 
 
 As a rule, thermal units are employed to measure the 
 energy evolved or absorbed in the formation of chemical 
 compounds. As previously stated, the thermal units em- 
 ployed are either calories, or, Calories, the iormer repre- 
 senting the amount of heat needed to raise the temperature 
 of one gram of water one degree C., from 15 C. to 16 C.; 
 the latter, the amount of heat needed to raise the tempera- 
 ture of one kilogram of water one degree Centigrade.* 
 
 To effect an electrolytic deposition of a chemical sub- 
 stance in aqueous solutions, an amount of electrical energy 
 must be used equivalent to the number of calories involved 
 in the formation of the compound to be electrolysed. 
 
 The unit of electrical energy is the joule; one joule is 
 equivalent to, practically, 0.24 calorie, or to 0.00024 Calorie. 
 When the heat of formation of an electrolyte is known, this 
 value divided by 0.24 equals the joules required to effect its 
 electrolysis. 
 
 1 joule = 1 coulomb x 1 volt, therefore, the number of 
 joules divided by 96,540 or a multiple thereof repre- 
 sents the critical voltage, i.e. the minimum voltage neces- 
 sary to effect the desired electrolysis. 
 
 The fundamental facts then to be remembered are, that it 
 always requires a definite quantity of energy to effect the 
 electrolysis of a given substance at a given temperature, and 
 that such electrolysis can only be effected by the use of a 
 definite minimum voltage. 
 
 In passing upon the efficiency of any electrolytic process, 
 it is necessary to pay due regard to both current efficiency 
 and to energy efficiency. In other words, it is necessary to 
 determine how closely the weight of the product obtained, 
 compares with the weight of the product theoretically pro- 
 ducible by the number of coulombs used; furthermore, the 
 weight of the product obtained should be compared with 
 
 * Confer: Joseph W. Richards' " Electrochemical Calculations," Jour- 
 nal Franklin Im-tftute, 1900, p. 131. 
 
92 NOTES ON ELECTROCHEMISTRY. 
 
 the amount theoretically obtainable by a perfect utilization 
 of the total number of joules employed. 
 
 Thus, if the current efficiency in a given process is 90% 
 and the voltage efficiency is 60%, then the energy efficiency is 
 
 90 x 60 
 
 100 X 100 
 
 54%. 
 
 In obtaining the electrodeposition of an element from a 
 compound, it is a great advantage to effect such electro- 
 deposition from an ows-salt rather than from an re-salt for 
 the reason that the ous compound compared with the ic com- 
 pound, contains twice the amount of the metallic constitu- 
 ent per unit weight of the non-metalic radicle with which 
 it is combined. In consequence an electric current of a 
 given amperage will deposit twice as much metal from an 
 ous salt as it will from an ic salt, and although a somewhat 
 higher voltage is required in the former case, this is more 
 than compensated for by the increased output obtained. 
 
CHAPTER VI. 
 ELECTROTECHNOLOGY. 
 
 Literature: BLOUNT, B.: "Practical Electrochemistry." New York, 
 1901. FERCHLAND, P.: "Grundriss der Reinen und Angewandten 
 Elektrochemie. " Halle, A. S., 1903. FOERSTER, F.: "Elektro- 
 chemie Wiisseriger Losungen." Leipzig, 1905. HABER, F. : 
 "Grundriss dor Technischen Elektrochemie." Miinchen, 1898. 
 LOEB, W.: "Elektrochemie der Organischen Verbindungen." 
 Halle, A. 8., 1905. MOISSAN, H. (translated by Lenher, W.) : "The 
 Electric Furnace." New York, 1905. NERNST, W. and BOR- 
 CHERS, W.: "Jahrbuch der Elektrochemie." Halle, A. S., Vol. X, 
 1905. PETERS, F.: "Angewandte Elektrochemie." Leipzig, 1897. 
 PETERS, F. : "Elektrochemische Technik." Vol. IV. Gross-Lich- 
 terfelde West, 1905. SLOANE, T. O'C. : "Electricians' Handy 
 Book." New York, 1905. VOGEL, F. and ROSSING, A.: "Hand- 
 buch der Elektrochemie und Elektrometallurgie." Stuttgart, 
 1891. WRIGHT, J.: "Electric Furnaces and their Industrial Ap- 
 plications." New York, 1905. 
 
 Introduction. The applications of electrochemistry are 
 so numerous that it will he desirable to devise some sort of 
 a classification in order to gain a general survey of the sub- 
 ject. 
 
 In so doing, two principal groups may be established: 
 
 I. Direct action processes. 
 II. Indirect action processes. 
 
 In the first of these groups there must be counted all pro- 
 cesses in which the electric current acts directly; in the second, 
 all processes in which the electric energy suffers partial or 
 entire transformation into some other form of energy before 
 being applied to the work required. The first group would 
 thus embrace all processes of electrodeposition from solu- 
 tions metals and non-metals; the second group would 
 
 93 
 
94 NOTES ON ELECTROCHEMISTRY. 
 
 include electrodeposition from fused electrolytes, and all 
 electrothermic processes. 
 
 For the sake of convenience, the following sub-divisions 
 can be made: 
 
 A. Electro-inorganic Processes. 
 I. Direct Action Processes. 
 
 Electrodeposition from solution. 
 Electroplating. 
 
 Chlorine and Alkali-hydrates. 
 II. Indirect Action Processes. 
 
 Electrodeposition from fused electrolytes. 
 Electrothermic processes. 
 
 B. Electro-organic processes. 
 I. Direct action processes. 
 
 II. Silent discharge processes. 
 III. Electro-osmosis. 
 
 A. I. DIRECT ACTION PROCESSES. 
 Electrodeposition from Solution. 
 
 Copper. Although several processes have been devised 
 for obtaining copper from its ores by the aid of the electric 
 current, not one of these processes has attained to any great 
 importance in commercial practice. 
 
 In one of the earliest of these processes, that devised by 
 Marchese in 1884, the ore was prepared and brought into the 
 form of an impure sulphide, consisting of copper, lead, and 
 iron. This compound was cast into anodes and subjected 
 to electrolysis in a sulphuric acid solution. 
 
 In later processes solvents are used to extract the copper 
 from its ore, and the solutions thus obtained are subjected to 
 electrolysis, insoluble anodes being employed. 
 
 Thus, in the Siemens-Halske process the solvent employed 
 for extracting the copper present as sulphide, is an aqueous 
 
ELECTROTECHNOLOGY. 95 
 
 solution of ferric sulphate. In effecting the extraction of 
 the copper this ferric sulphate becomes reduced to the fer- 
 rous condition, but is, in turn, restored to its original condi- 
 tion by undergoing oxidation in the anode section of the 
 trough after the metallic copper has been precipitated from 
 its sulphuric acid solution at the cathode. Carbon anodes 
 are generally used. 
 
 In the Hoepfner process, the ore is not subjected to any 
 preliminary roasting; the copper, in the form of cuprous 
 sulphide, is leached out by means of a sodium chloride solu- 
 tion containing cupric chloride, cuprous chloride is thus 
 formed and is kept in solution by means of the sodium chlor- 
 ide which is present. The electrolytic troughs are separated 
 into anode and cathode chambers by means of diaphragms and 
 the electrolyte is first passed through the cathode chambers 
 where most of the copper is precipitated. In the anode 
 chamber the remaining cuprous chloride is changed to the 
 cupric form, and the process is thus made a continuous one. 
 
 While the extraction of copper from its ores by electro- 
 lytic action is as yet not well developed, the electrolytic 
 refining of copper is one of the most important, if not the 
 most important, application of electrochemistry. 
 
 The first suggestion of electrolytic copper winning is 
 credited to Becquerel (1836); the first obtaining of electro- 
 lytic copper on the commercial scale to James B. Elkington 
 of England (1865). 
 
 Two systems are employed in copper refining, the series 
 system and the multiple system; the latter is the older. 
 
 In the multiple system each anode is connected with the 
 conductor from the positive pole of the electric current; each 
 cathode with the conductor from the negative pole. 
 
 In the series system, due to E. S. Hayden of Connecticut, 
 only one end-anode in each tank is connected with the posi- 
 tive pole and at the opposite end only one cathode is con- 
 nected with the negative pole. Between these electrodes, 
 
 
96 NOTES ON ELECTROCHEMISTRY. 
 
 copper plates are set in an upright position; the circulation 
 of the electrolyte may be maintained by compressed air or 
 by some other device. 
 
 The plates of crude copper which serve as anodes, usually 
 have a surface of from 55 to 75 square decimeters, and are 
 from 2 centimeters to 4 centimeters thick; the cathodes con- 
 sist of thin plates or foils of pure copper. The distance be- 
 tween the electrodes is generally maintained at from 2.5 to 
 5.0 centimeters, the electrolyte used is a solution of sulphate 
 of copper acidified with sulphuric acid. The voltage em- 
 ployed is low, probably not exceeding one-half volt. 
 
 In preparing the electrolyte, copper sulphate solution and 
 sulphuric acid, care must be taken to insure a solution rich 
 in copper, and to have it contain sufficient sulphuric acid to 
 prevent the formation of hydratcd cupric oxide; on the other 
 hand, care must be taken to guard against an excess of sul- 
 phuric acid, as this would cause the liberation of hydrogen at 
 the cathode in the place of copper. The temperature of the 
 electrolyte is advantageously held at about 33 C. to 37 C. 
 
 The question of current density is of course a very impor- 
 tant one, the value of ND 100 ranges from 1.3 to possibly as 
 high as 4.00. However, too high a current density must be 
 avoided, as this causes the copper to be deposited in uneven 
 masses, possessing but poor coherence.* 
 
 The tanks in which the electrolytic deposition takes place 
 are generally lined with lead ; there are often several hundred 
 of these in a plant. When in the course of operation the 
 anodes have been reduced to thin sheets, the process is inter- 
 rupted, the anodes are removed and re-smelted, the cathodes 
 are likewise removed and recast, and the anode-slime, or 
 mud, as it is termed, is subjected to separate treatment for 
 the obtainment of the precious metals which occur therein 
 whenever such are present in the copper ores worked. 
 
 * Consult: S. Cowper-Coles, Trans. Faraday Society, 1905, p. 215, 
 and L. Addicks, Journal Franklin Jnst., 1905, p. 421. 
 
OF THF 
 
 UNIVERSIT 
 
 ELECTROTECHNOLOGY. 
 
 Among the impurities frequently found associated with 
 copper are iron, cobalt, nickel, zinc, gold, platinum, silver, 
 bismuth, antimony, arsenic, and lead. Of these impurities 
 iron, cobalt, nickel, and zinc dissolve in the electrolyte, but 
 are not apt to be precipitated on the cathode under the cur- 
 rent conditions employed for the electrolytic deposition of 
 the copper. 
 
 Among the impurities found in the anode-slime are gold 
 and silver. In some copper ores the amount of these metals 
 recovered from the anode-slime is very considerable. For 
 instance, an analysis given by E. Keller* shows the amount 
 of the precious metals contained in an anode-slime derived 
 from a copper ore mined near Butte, Montana, to have been 
 as high as 0.2% to 0.3% of gold and 53% to 55% of silver. 
 
 The purity of copper electrolytically refined is very high, 
 frequently ranging up to 99.95% and 99.99%. 
 
 To illustrate the manner in which the output of an electro- 
 lytic copper refining plant can be calculated, assume that the 
 normal current-density employed is one ampere per square 
 decimeter, i.e., ND 100 = 1.00. Further, assume that the 
 active anode surface in one vat is 372 square decimeters, then 
 each vat requires 372 amperes. 
 
 The weight, in milligrams, of any element set free by one 
 coulomb of electricity is equal to its atomic weight divided 
 by its valence and multiplied by 0.01036, the electrochemi- 
 cal equivalent of hydrogen. 
 
 Thus, one coulomb will deposit from a cupric salt solu- 
 
 no c 
 
 tion - x 0.01036 = 0.329448 milligram, say 0.33 milli- 
 gram of metallic copper. 
 
 One ampere-hour equals 3600 ampere-seconds, hence, one 
 ampere in one hour will deposit 0.33 X 3600 = 1.188 grams 
 of copper and in 24 hours 1.188 X 24 = 28.5120 grams. 
 
 * Journal of American Chemical Society, 1897, p. 778. 
 
 -. 
 
98: NOTES ON ELECTROCHEMISTRY. 
 
 In the same period 372 amperes will deposit 28.5120 x 372 
 = 10,606 grams, or, 10.606 kilograms of copper. This amount 
 multiplied by the number of vats in use, will of course give 
 the total output in 24 hours. 
 
 As to the question of energy consumption, assume a maxi- 
 mum current efficiency, and assume that the drop in poten- 
 tial is 0.25 volt. Each vat will thus require 0.25 x 372 = 93 
 
 93 
 watts, and this corresponds to - = 0.125 H.P. 
 
 One H.P. will therefore deposit in twenty-four hours, 
 0.125:1.0:: 10.606: x - 84.85 kilograms of copper, and a 
 plant of 5000 H.P. would therefore yield 84.85 X 5000 = 
 424,250 kg. of copper in twenty-four hours. 
 
 Silver. The principles underlying the process of re- 
 fining silver electrolytically, and especially adapted to 
 its separation from gold and copper, were worked out by 
 Moebius. 
 
 The electrolyte used is a solution of nitrate of silver con- 
 taining about 1% of silver and from 0.1 to 1% of free nitric 
 acid. The cathodes consist of pure silver foil and these 
 receive a very light coating of oil in order to permit of a 
 more ready removal of the crystals of silver, the form in which 
 the silver separates from the electrolyte under proper current 
 conditions. The anodes are made of crude silver, contain- 
 ing about 95% of this metal, the balance generally consisting 
 of gold, platinum, and copper. 
 
 As stated, the silver separates in a crystalline condition 
 and the removal of these crystals is effected by wooden arms 
 which are kept in slow movement, constantly freeing the 
 cathodes from these crystals; if this were not done the crystals 
 would readily grow to the anodes and in this manner of course 
 establish a short circuit. The anodes are inclosed in a 
 sheathing of canvas and in this the anode-slime accumulates. 
 This anode residue is of course separately treated for the 
 recovery of the precious metals it contains. 
 
 (I/ 
 
ELECTROTECHNOLOGY. 99 
 
 The current conditions generally employed for the electro- 
 lytic refining of silver are, voltage = 1.5 and ND 100 = 2.5. 
 
 Gold. The extraction of crude gold from its ores is gen- 
 erally effected either by the use of mercury, by one of the so- 
 called chlorination processes wherein chlorine is the active 
 agent, or else by use of potassium-cyanide acting in the 
 presence of atmospheric oxygen. 
 
 Potassium-cyanide is the reagent employed in the Siemens- 
 Halske process and the gold is recovered electrolytically from 
 the cyanide solution. The cyanide liquor contains not more 
 than 0.05% of potassium cyanide. The anodes are generally 
 made of iron, although carbon, Achcson-graphite, and lead- 
 per-oxide anodes are also used; they are inclosed in bags of 
 canvas or linen. 
 
 The cathodes are made of lead, and when sufficient gold 
 has been deposited on them they are cupeled and the gold 
 obtained. The crude gold thus secured contains about 
 85% to 90% of pure gold; this is subjected to electrolytic 
 refining while the lead recovered is reduced, recast, and again 
 used for cathodes. The current-de isity employed is very low. 
 ND 100 ranges from about 0.003 to 0.005; the voltage from 
 about 1.75 to 2.00 volts. 
 
 In Wohwill's process for the electrolytic refining of gold 
 the anodes of crude gold are placed into a hot solution of 
 hydrogen auric chloride (H Au C1 4 ) containing hydrochloric 
 acid. The cathodes consist of very thin sheets of pure gold. 
 To insure a well adherent cathode-deposit, the temperature 
 is kept at about 70 C.; the electrolyte contains 3% of gold 
 and from 3% to 4% of hydrochloric acid. The voltage em- 
 ployed is about 1 volt, the ND 100 = 10 amperes. The pro- 
 duct secured contains from 99.80% to 100% of gold. <| 
 
 Lead. While there seems to be little opportunity for a 
 commercially profitable process of winning crude lead elec- 
 trolytically from its ores, the process of refining crude lead 
 electrolytically is well established, one of the chief advan- 
 
100 NOTES ON ELECTROCHEMISTRY. 
 
 tages of such a process being that it permits the obtainment 
 of a pure lead and of a pure bismuth, the latter a common 
 impurity in lead won by metallurgical processes. 
 
 In the process of A. G. Betts, lead is obtained electroly- 
 tically by dissolving the metal in hydrofluosilicic acid, which 
 gives an electrolyte of lead-silicofluoride from which metallic 
 lead is deposited at the cathode in the form of a dense and 
 smooth deposit. Addition of a trace of gelatine, an organic 
 colloid, to the electrolyte insures the coming down of the 
 electrolytic deposit in a finely crystalline condition. The 
 solution is kept continuously circulating through the vats. 
 
 The anodes are crude lead, and are apt to contain as impur- 
 ities some copper, antimony, bismuth, and silver; these tend 
 to remain in the anode-slime provided the ND 100 does not 
 exceed 1.0 ampere. If iron, nickel, and zinc are also present 
 these pass into the solution. The voltage employed is about 
 0.4; the electrolyte is not heated. Starting from a crude 
 lead containing about 95% of the metal, the refined product 
 is practically chemically pure. 
 
 Nickel. The application of electrical energy to the winning 
 of nickel is practically confined to the refining of this metal. 
 
 The conditions to be observed in order to deposit nickel 
 successfully from an aqueous solution of its sulphate or its 
 chloride are a temperature of between 60 and 70 C., an elec- 
 trolyte containing about 3% of nickel together with a trace 
 of free sulphuric acid or hydrochloric acid, a normal current 
 density of from 0.5 to 2.5 and a voltage of from 1 to 2 volts. 
 Generally speaking, the higher the current density the smoother 
 and the brighter the deposit secured. 
 
 Electrodeposition of nickel from nickel solutions by means 
 of insoluble anodes is thoroughly practicable. Anodes of 
 lead-peroxide have been used for the purpose; when a sul- 
 phate salt of nickel is used as the electrolyte, the sulphuric 
 acid set free in the operation must be neutralized with nickel- 
 hydrate or nickel-carbonate. 
 
ELECTROTECHNOLOGY. 101 
 
 The D. H. Browne process, formerly used by the Canadian 
 Copper Company, was worked on an alloy of nickel and 
 copper, containing about 43% of the former and 54% of the 
 latter metal. 
 
 This alloy was cast for anodes; some of it was also used as 
 the electrolyte, being treated with chlorine and sodium 
 chloride, which brought these metals into solution as cuprous 
 chloride and as nickel chloride. Most of the copper having 
 been precipitated from this solution by electrolysis, the 
 remainder was thrown down by the action of sodium sul- 
 phide, while any iron and cobalt present were precipitated by 
 sodium hydrate and by chlorine. 
 
 The solution thus obtained contained practically only nickel 
 chloride and sodium chloride ; the latter was removed by con- 
 centration and crystallization and the nickel was finally pre- 
 cipitated electrolytically from a hot solution. The voltage 
 employed for this purpose was about 3.5 volts; the anodes 
 used in this operation were made of graphite, suspended in 
 vessels of porous earthenware. The electrolyte after coursing 
 through the vats returned to the evaporators, where it suffered 
 further concentration. The chlorine evolved at the anodes 
 was made to dissolve the copper-nickel alloy used as elec- 
 trolyte. The nickel won by this process attained to a purity 
 of 99.85%. 
 
 Tin. There is no electrolytic method in use for winning 
 tin from its ores, or for refining it, however, the securing of 
 tin from tin-plate scrap is quite an industry. 
 
 Tin plate is sheet iron coated with tin, and although only 
 a thin coating of this metal is used for the purpose, a large 
 amount of tin is consumed in this way. The scrap from 
 which the tin is thus recovered is in part the waste of new 
 tin plate and in part the scrap of old tinned articles. 
 
 Several processes have been devised for the recovery of 
 tin from this material. Thus Siemens and Halske employ 
 the scrap as anode, suspending the same in wooden or wicker 
 
102 NOTES ON ELECTROCHEMISTRY. 
 
 baskets; as cathodes they employ copper which has been 
 tinned. In the process chiefly developed by the Gold- 
 schmidts in Essen, Germany, the tin-plate scrap, containing 
 about 30% of tin, is placed in iron wire baskets which are 
 suspended, as anodes, in iron vats. The latter are made to 
 serve as cathodes, the electrolyte is a 10% solution of caustic 
 soda. The operation is conducted at a temperature of about 
 70 C., the voltage employed is 1.5 volts. In the tin thus 
 electrolytically deposited, lead and iron are apt to occur as 
 impurities. The iron from which the tin coating is originally 
 removed is fairly pure and can be reworked. 
 
 Tin might also be recovered from lead scrap, that is to say, 
 from sheet lead or from pipes upon which a layer of tin has 
 been rolled; this lead scrap could be made the anode, and 
 sulphuric acid might be employed as the electrolyte. In such 
 a process of course the metallic lead would remain, barring 
 a small percentage of the metal which would be transformed 
 into sulphate, while the tin was recovered. 
 
 Zinc. Electrolytic processes are of great value in the 
 obtainment of zinc from its ores. 
 
 In Silesia, Germany, during the last decade of the past 
 century, a process was in use wherein zinc sulphate was used 
 as the electrolyte, the anodes employed being made of lead 
 peroxide; it was, however, ultimately abandoned because it 
 could not compete commercially with other metallurgical 
 processes. Among more recent methods of winning zinc 
 electrolytically from its ores, must be named the Siemens- 
 Halske process, the Ashcroft process, and the Hoepfner pro- 
 cesses. 
 
 In the Siemens-Halske process, as well as in that of Ash- 
 croft, the ores worked are essentially compounds of lead 
 sulphide and of zinc sulphide, containing approximately 
 20% of zinc and 30% of lead; the ores are also argentiferous. 
 In one of the processes by Hoepfner the crude material 
 worked was essentially an iron ore containing about 10% of 
 
ELECTRO TECHNOLOG Y. 103 
 
 zinc; the electrolyte used was a solution of zinc chloride, 
 the anodes were made of carbon, the cathodes consisted of 
 revolving zinc plates and the anode and cathode-chambers 
 were separated by diaphragms. The ND 100 was 4 amperes, 
 the voltage ranged between 3 and 7 volts. 
 
 In another Hoepfner process, used in England, the zinc was 
 roasted, secured as an oxide, and then treated with a hot 
 concentrated solution of magnesium chloride in which the 
 oxide of zinc dissolves as a basic salt. This solution received 
 subsequent treatment with carbonic acid gas and with cal- 
 cium chloride solution, the zinc appearing ultimately as zinc 
 chloride, which solution was submitted to electrolysis. Car- 
 bon anodes were used, the ND 100 = 1 ampere and the voltage 
 about 3 volts; the purity of the resulting product was 99.95%. 
 
 A process for refining zinc electrolytically has been devised 
 by Roessler and Edelmann. In this method the crude zinc, 
 used for anodes, contains about 20% of impurities, among 
 which should be noted copper, silver, lead, nickel, and cobalt. 
 The ND 100 = 0.8 to 0.9 ampere, the voltage ranges from 1.25 
 to 1.50, the electrolyte is not heated. From the anode-slime, 
 silver, copper, and lead are recovered by separate processes. 
 In this process also the purity of the refined product is ap- 
 proximately 99.95%. 
 
 Electroplating. 
 
 Electroplating. The first electrotechnical process de- 
 vised seems to have been the electrodeposition of metals, 
 the art of electrotyping. The making of exact metallic 
 reproductions, replicas, of objects was discovered indepen- 
 dently by Jacobi, by Spencer, and by Jordan; the first-named 
 of these exhibited electrotype copies of medals before the 
 Academy of St. Petersburg in 1838. Two years later, Murray 
 discovered that non-conducting bodies when coated with 
 graphite would serve equally well as a base for electrodeposi- 
 
104 NOTES ON ELECTROCHEMISTRY. 
 
 tion. From this process of electrotyping, a few years later, 
 the process of electroplating was evolved. 
 
 The fundamental difference between the two processes is 
 that in electrotyping the electrolytic deposit is meant to be 
 removed from the surface on which it has been formed, and 
 therefore too firm an adherence of the deposit on the object 
 on which it is made must be avoided; this is effected by giving 
 to the object a preliminary thin coating of oil or of a solution 
 of some salt. In electroplating the deposit is meant to ad- 
 here as firmly to the object as if it had been welded on the 
 same; for a successful electroplating absolutely clean sur- 
 faces are therefore an essential condition. 
 
 While for a long time it has been known that the chemical 
 composition, the concentration, and the temperature of the 
 electrolyte, as well as the current density employed, are all 
 factors of importance if a well-adherent electrodeposit is to 
 be secured, a recent study of the subject by Wilder D. Ban- 
 croft,* " On the Chemistry of Electroplating," has thrown light 
 on many aspects of the problem which were but little under- 
 stood before. 
 
 Among other interesting facts Bancroft found that a poor 
 metallic deposit is nearly always caused by the precipitation 
 of some salt of the metal in place of the pure metal, for in- 
 stance, by the formation of an oxide, a hydro-oxide, or a cyan- 
 ide. Therefore, the addition of any chemical which will 
 dissolve a salt or which will prevent its formation must im- 
 prove the quality of the desired electrodeposit. 
 
 Maintenance of proper temperature conditions is likewise 
 essential, as is also the rate at which the electrolyte is stirred, 
 for a sufficiently concentrated solution must always be main- 
 tained at the cathode; too dilute a solution at the cathode 
 results in the formation of sandy or pulverulent deposits. 
 
 Determining the best conditions in individual cases re- 
 quires considerable care and experimenting, yet the general 
 * Journal of the Franklin Institute, 1905, Vol. 140, p. 139. 
 
ELECTROTECHNOLOGY. 105 
 
 principles underlying electroplating are very simple. The 
 object to be plated is put into an electrolyte which is a solu- 
 tion of some salt of the metal with which the plating is to be 
 done. This solution is termed the bath. The object to be 
 plated is attached to a wire leading in from the zinc plate of 
 a primary battery, or from the negative pole of a dynamo; 
 in short, the object to be plated is made the cathode of the 
 bath. The metal with which the object is to be plated is sus- 
 pended in the bath from another wire which comes from the 
 carbon, or copper electrode of the primary battery, or from 
 the corresponding pole of the dynamo. The metal which is 
 thus to be deposited on the object is termed the anode of the 
 bath. 
 
 In general it may be said that the working conditions for 
 electroplating are a low voltage and a fairly strong current. 
 The voltages employed range between 1 and 5 volts, the cur- 
 rent densities of course differ considerably for the different 
 metals; some ND 100 values are: 
 
 For gilding, 0.2 ampere, 
 
 For silvering, 0.3 to 0.6 ampere. 
 
 For nickeling, 0.3 to 0.6 amperes, 
 
 For copper plating, 0.4 ampere, 
 
 For zinc plating, 1.0 to 3.0 amperes. 
 
 A careful study of the conditions necessary to secure a good 
 and well adherent electrodeposit of zinc has been made by 
 Mylius and Fromm.* From this it appears that the best 
 working conditions when zinc sulphate is employed as the 
 electrolyte are to have 4 to 6% of zinc in the electrolyte, 
 a ND 100 = 1 to 3 amperes, and a voltage of from 3 to 4 volts. 
 Above all, it is necessary to suppress as far as possible the 
 liberation of free hydrogen at the cathode, for this causes a 
 basic condition in the electrolyte near the cathode, a condi- 
 tion conductive to the deposition of spongy zinc and inter- 
 * Zeitschrift f. Anorg: Chemie, 1895, p. 144. 
 
106 NOTES ON ELECTROCHEMISTRY. 
 
 fering with the precipitation of a firm, coherent deposit of the 
 metal. The presence of mere traces of some other metals 
 more electronegative than zinc, also tends to the formation 
 of spongy zinc, and such metals should therefore be removed 
 before electrolysis. 
 
 Alloys also can be deposited by electroplating; thus it is 
 possible to make an electroplate of brass by using a solution 
 of cyanide of zinc and of cyanide of copper, both dissolved 
 in potassium cyanide. Bronzes, that is to say, alloys of 
 copper and tin, can also be electroplated, the deposition 
 taking place from mixed solutions of their salts. Thus far, 
 however, alloys have not been extensively used in electro- 
 plating. 
 
 Chlorine and Alkali- Hydrates. 
 
 Chlorine and Alkali-Hydrates. In the electrolytic win- 
 ning of chlorine and of alkali-hydrates from solutions of 
 alkaline chlorides, the fundamental principle to be observed 
 is the keeping separate of the products produced at the 
 cathode from those produced at the anode. At the cathode, 
 alkali and hydrogen are generated, at the anode, of course, 
 chlorine. 
 
 To achieve this holding apart of the products of the reaction, 
 three different kinds of processes have been devised; these 
 may be designated respectively as: 
 
 I. The diaphragm process. 
 II. The bell process. 
 III. The mercury process. 
 
 The chlorine gas which is obtained by these processes is 
 either liquefied and thus made available for shipment, or it 
 is transformed into bleaching powder; the alkali obtained 
 can, of course, be readily turned into the caustic condition. 
 Probably the chief reason why the entire output of caustic 
 alkali needed in the chemical industry is not produced exclu- 
 
ELECTROTECHNOLOGY. 107 
 
 sively by electrolytic methods, for these methods are eco- 
 nomical, is the fact that there is not a sufficiently large 
 demand for the chlorine which, of course, is simultaneously 
 produced in quantity equivalent to the alkali obtained. 
 
 The hydrogen gas which is incidentally produced with the 
 alkali is in many factories allowed to escape unused; in some 
 places it is employed in the manufacture of fuel-gas, and in 
 others it is condensed under pressure and is thus made avail- 
 able for transportation. 
 
 The crude chemicals employed in the electrolysis of alkali- 
 chlorides are essentially chloride of potassium, obtained from 
 <jarnallite and common salt. It is very important that 
 only pure solutions of the alkali-chlorides be used for elec- 
 trolysis, for appreciable amounts of impurities interfere 
 seriously with the working of the processes and with the 
 quality of the products obtained. 
 
 In cases where the products liberated at the two electrodes 
 are not kept separate, and where a free intermixing of the 
 cathode and anode-solutions is allowed, hypochlorites and 
 chlorates will be formed, according to the temperature and 
 the current density employed. 
 
 The former salts, that is to say, the hypochlorites, are pro- 
 duced at the anode when a low temperature and a low current 
 density are used; such hypochlorite solutions, practically not 
 exceeding 2 or 3% in strength, are best used on the spot for 
 electrolytic bleaching. The formation of chlorates is, on the 
 other hand, favored by the use of a high current density and 
 the presence of some alkali. Thus, potassium chlorate is now 
 made almost exclusively by electrolysis, about 5 kilowatt- 
 hours being used per kilogram of potassium chlorate pro- 
 duced. If this product is subjected to further electrolytic 
 treatment with a high current density, at a low temperature, 
 potassium per-chlorate results. 
 
 I. Diaphragm Process. The principal problem to be 
 solved in processes of this description, is to find a suitable 
 
108 NOTES ON ELECTROCHEMISTRY. 
 
 material which shall prove resistant alike to chlorine and to 
 alkali. In Germany, after a great deal of experimenting, 
 plates of Portland cement were selected for the purpose: 
 in the United States, asbestos is the material generally 
 used. 
 
 From the very fact that any material serviceable for 
 diaphragms must be sufficiently porous to permit of the 
 passing of the electric current, it is unavoidable that a part 
 of the hydroxyl ions set free will also pass through, and these, 
 naturally leacting with some of the chlorine which is liberated, 
 will cut down the output of that gas. 
 
 Carbon anodes are preferably employed, the working 
 temperature is held at about 85 C., the ND 100 ranges from 
 about 1 to 2 amperes at the diaphragm. In some processes 
 the alkali-chloride solution is conducted only to the cathode 
 compartment (Griesheim-Electron system), in others the 
 solution of the electrolyte flows from the anode compartment 
 to the cathode compartment (Systems of McDonald, and of 
 Hargreaves and Bird ) . 
 
 II. Bell Process. The fundamental principle of processes 
 of this description is the use of some non-porous, non-con- 
 ducting medium, which serves to keep separate the solutions 
 at the anode and at the cathode, while it permits those parts of 
 the solution not in contact with the gases set free at the 
 electrodes to intermingle freely. 
 
 The bell device consists essentially of a vessel, technically 
 the bell, which is generally an open box made of sheet iron 
 and coated with some non-conducting material. This bell 
 is suspended with the open side downward in a vat or chamber, 
 likewise constructed of some non-conducting material; into 
 this chamber the electrolyte is placed. A perforated carbon 
 anode is hung inside of the bell and the chlorine generated at 
 this anode is carried away by an exit- tube which passes 
 through the upper part of the bell. The cathode is placed in 
 the outer vessel and the alkaline lye which is generated at the 
 
ELECTLOTECHNOLOGY. 109 
 
 
 cathode passes off through an overflow placed at the top of 
 
 the vat. 
 
 Generally a number of such bells are linked together in 
 parallel; the total number of bells employed in a plant, in 
 some works, runs up to twenty or thirty thousand. Details 
 as to the current density and other working conditions are 
 not publicly known, but Foerster* infers that the ND 100 ranges 
 from 2 to 4 amperes, that the temperature does not exceed 
 30 or 35 C., and that the voltage used is about 4 or 5 volts. 
 
 III. The Mercury Process. The essential feature of the 
 processes using mercury as the cathode is the formation of an 
 amalgam of the alkali metal liberated by electrolysis. 
 
 In Castner's process the Castner Electrolytic Alkali Com- 
 pany was the first to manufacture chlorine and caustic soda 
 the production and the decomposition of this amalgam are 
 carried out in the same apparatus. A box is divided into 
 three compartments by the use of partitions which reach 
 almost, but not quite, to the base of the box; this base is 
 covered with a layer of mercury. The two outside compart- 
 ments are closed on top and suspended in them are the car- 
 bon anodes which reach down almost to the mercury. 
 
 The electrolyte employed is a solution of sodium chloride, 
 which suffers electrolysis in the outer chambers. The central 
 chamber, which contains an iron electrode in a weakly alka- 
 line solution, serves for the decomposition of the amalgam 
 into mercury and sodium-hydrate. The whole apparatus is 
 so arranged that it can be given a rocking motion and during 
 the operation it is kept constantly moving. 
 
 The electric current is obliged to pass from the anodes by 
 way of the mercury to the cathode which is situated, as will 
 be recalled, in the central compartment. The mercury, act- 
 ing as cathode in the two outer chambers, amalgamates with 
 the sodium and then gives up this alkali in the cathode 
 chamber, where the mercury acts as anode, the alkali dissolv- 
 * Liber, cit. p. 417. 
 
110 NOTES ON ELECTROCHEMISTRY. 
 
 
 
 ing in the water and the hydrogen gas escaping. The ND 10() 
 
 at the cathodic mercury is about 7 amperes, at the anodic 
 mercury, about 12 amperes; the voltage is about 4 volts. 
 The product obtained by the Castner process is very pure. 
 The chlorine is generally turned into chloride of lime. 
 
 A process differing from but planned on lines similar to 
 those just referred to, is Kellner's process, and in England 
 the Castner- Kellner Company makes use of a method embody- 
 ing the fundamental principles of both of these systems. 
 
 A. II. INDIRECT ACTION PROCESSES. 
 Electrodeposition from Fused Electrolytes. 
 
 Introduction. In electrolytic processes where the prod- 
 uct is obtained from a fused electrolyte, the electrical energy 
 is in part used for the actual electrolytic work and in part for 
 the fusing of the electrolyte. 
 
 The relation between electrical energy and heat energy is 
 expressed by Joule's law (1841): " the heat developed in a 
 conductor is proportional to the resistance encountered and 
 to the square of the strength of the current." 
 
 If: resistance = R 
 
 current strength = C 
 heat = H 
 
 then, H = C 2 R 0.24. 
 
 The heat thus generated electrically, not chemically, is 
 termed Joule's heat. 
 
 To illustrate, assume: 
 
 Resistance equal to 2 ohms. 
 
 Current strength equal to 50 amperes. 
 
 Then, 50 X 50 X 2 x 1 = 6000 joules per second. 
 
 As one joule equals 0.00024 large Calorie, or 0.24 small 
 calorie, 5000 joules = 5000 X 0.00024 = 1.200 Calories or, 
 5000 X 0.24 = 1200 calories. 
 
ELECT ROT EC HXOLOG Y. Ill 
 
 In passing through a circuit embracing an electrolyte, 
 Joule's heat is generated in all parts of the circuit in amounts 
 proportionate to the resistance of the respective parts of the 
 circuit and to the square of the current. 
 
 The actual temperature to which an electrolyte thus attains 
 in a given time under given conditions of current strength 
 and resistance depends upon its mass, its specific heat, and 
 upon the success with which loss of heat by radiation, and 
 by other causes, can be avoided. 
 
 An important point to be borne in mind in attempting to 
 secure a metal from a fused electrolyte is that the boiling 
 point of the metal must not lie too close to the point of fusion 
 of the electrolyte, otherwise volatilization of the metal would 
 almost keep pace with its electrolytic production. 
 
 The metals whose production from a state of fusion shall 
 now be briefly considered are aluminium, magnesium, and 
 sodium. 
 
 Aluminium. Various processes have been devised for 
 the electrolytic winning of aluminium. The methods, how- 
 ever, principally employed are the Heroult process and the 
 Hall process. Chemically, these two processes are very much 
 alike, in both, pure alumina (A1 2 O 3 ) is added to the fused 
 double fluoride of aluminium and sodium, A1 2 F 6 , 6 NaF, a 
 mineral called cryolite. 
 
 In putting the process into operation the cryolite is first 
 brought into a state of fusion in iron furnaces and then the 
 anodes are lowered into it and electrolysis commences. As 
 the aluminium separates at the cathode, alumina is fed into 
 the bath so as to keep the amount of aluminium present in 
 the electrolyte about constant. The metal being specifically 
 heavier than the fused electrolyte, sinks to the bottom of the 
 fusion chamber, whence it is tapped, generally once a day. 
 The anodes are made of carbon, the cathodes are generally 
 made of iron, but these also can be made of carbon. 
 
 In the Hall process, the amperage used per fusion chamber 1 : 
 
112 NOTES ON ELECTROCHEMISTRY. 
 
 is about 10,000 amperes, the voltage employed, about 5 volts. 
 The temperature of the bath is held in the neighborhood of 
 1000 C., being kept as low as possible. The fusion chambers 
 are discharged at stated intervals. 
 
 In the Heroult process, about 8000 amperes per furnace are 
 required, the voltage ranges from 3 to 5 volts, the ND 100 = 190 
 amperes and the temperature is held between 750 and 850 C. 
 
 The chemical reactions taking place during electrolysis 
 consist in the liberation of aluminium at the cathode and of 
 oxygen at the anode; this oxygen of course combines with the 
 carbon anodes to form carbon monoxide. The pure alumina 
 which is used in the process is generally obtained from the 
 mineral bauxite, which is passed through a preliminary puri- 
 fying operation by roasting and by subsequent treatment 
 with caustic soda, or, according to a recent process devised 
 by C. M. Hall, bauxite as well as other impure aluminium 
 oxides are purified by fusion with the electric current, the 
 impurities present being reduced in the fused bath. 
 
 Estimates vary as to the amount of electrical energy nec- 
 essary in the Hall process, for the production of one kilogram 
 of aluminium. Bucherer places it at 32.7, Becker at 30, and 
 J. W. Richards at 22 kilowatt-hours. 
 
 Of the total electrical energy consumed in the production 
 of aluminium, it is calculated that about four-fifths are used 
 for the heating and the balance for the actual electrolytic 
 work. The electrical energy, which is expended in effecting 
 the separation of metallic aluminium from its chemical com- 
 binations, can of course be recovered as heat energy when the 
 metal is caused to re-combine with oxygen; this is the case, 
 for instance, in the Thermite process. 
 
 According to the report of the United States Geological 
 Survey, the world's production of aluminium in 1903 was 
 over eighteen million pounds, of which seven and a half 
 millions were produced in the United States, the balance being 
 made in Switzerland, France, and Great Britain. 
 
 
ELECTRO TECHNOLOG Y. 113 
 
 In 1904 production of this metal in the United States, 
 which in 1883 had amounted to only 83 pounds, was 8,600,000 
 pounds. The sole 'producer in the United States is the 
 Pittsburg Reduction Company, which at present has five 
 plants in operation. 
 
 The purity of commercial aluminium is about 99%, the 
 impurities constituting the balance are principally iron, 
 copper, silicon, and carbon. 
 
 Magnesium. The raw material from which magnesium is 
 won electrolytically is carnallite, a double chloride of potas- 
 sium and magnesium, which is carefully dehydrated before 
 fusion; its fusion temperature is be ow 700 C. 
 
 As in this process the product liberated at the anode is 
 chlorine, the apparatus must of course be arranged so as to 
 prevent this gas from combining with the magnesium which 
 is set free at the cathode. In one form of apparatus this is 
 accomplished by conducting the electrolysis in a steel vat, 
 the walls of which serve as cathodes; in the center of this vat 
 there is introduced the carbon anode, inclosed in a porcelain 
 cylinder, which is provided with a tube from which the chlo- 
 rine gas escapes. 
 
 The ND 100 used is from 11 to 15 amperes, the voltage is 
 about 4 volts. Care is taken to have the electrodeposition 
 of the magnesium take place in an inert atmosphere; for this 
 purpose either nitrogen, or some gaseous mixture devoid of 
 free oxygen, is introduced into the cathode compartment. 
 
 Sodium. The most important process for making sodium 
 electrolytically from caustic soda is Castner's process. The 
 products of the electrolysis are sodium, hydrogen, and oxy- 
 gen. The anodes are made of nickel, of iron, or of steel, and 
 are annular or cylindrical in shape. 
 
 The cathode, generally made of nickel, projects upward 
 into a collecting chamber and into a cylinder of wire gauze in 
 which the metallic sodium accumulates, and which hinders it 
 from passing into the anode-chamber; the hydrogen gas in 
 
114 NOTES ON ELECTROCHEMISTRY. 
 
 the cathode chamber prevents the oxidation of the sodium. 
 The temperature is carefully held between 310 and 330 C. 
 The voltage used is about 5 volts, and each furnace uses about 
 1200 amperes. 
 
 A recent process, devised by E. A. Ashcroft, consists of a 
 cell wherein fused sodium chloride, the electrolyte, rests on 
 fused lead, which acts as cathode; the anode is made of 
 carbon and the chlorine is there liberated. The sodium 
 alloys with the fused lead, and this alloy is conveyed to an 
 outside compartment where it acts as the anode, the cathodes 
 being either iron or nickel, and the electrolyte consisting of 
 fused sodium hydrate. In this outer chamber metallic 
 sodium is set free at the cathode. 
 
 A process devised by Acker Bros., makes use of fused 
 sodium chloride as the electrolyte, the same being well dried 
 before fusion. The anodes consist of graphite, and fused lead 
 serves as cathode, as in the Ashcroft process. 
 
 The lead-sodium alloy is decomposed at red heat by steam 
 blown in under pressure, the resultant products are molten 
 lead, sodium hydrate, and hydrogen gas. The voltage 
 employed is about 7 volts, the ND 100 about 290 amperes, each 
 furnace taking 8000 amperes; a part of this energy is used 
 to keep the sodium chloride in a state of fusion without 
 application of heat from any outside source. The chlorine 
 evolved was formerly turned exclusively into chloride of lime, 
 but recently the Acker Process Company have devised new 
 uses for the chlorine, and among other products now manu- 
 facture tetrachloride of carbon and tetrachloride of tin. 
 
 Electr other mic Processes. 
 
 Electro-furnaces. In conductors of the first class, that is 
 to say, in all metals and in carbon, all electrical energy can 
 be converted into heat energy. 
 
 The formula by means of which the heat equivalent, in 
 calories, of a given amount of electrical energy can be figured 
 
ELECTROTECHNOLOGY. 115 
 
 is, it will be recalled, very simple. Designating the heat 
 equivalent by H, the resistance by R, the current strength 
 by C, the result desired, expressed in gram calories, is: 
 
 H = C 2 R 0.24 
 
 Probably the first one to suggest the application of electri- 
 cal energy for electrothermic work on a commercial scale, 
 was Sir William Siemens, in 1880. 
 
 The transformation of electrical energy into heat energy is, 
 in practice, accomplished in several ways, and at least four 
 types of electrical furnaces may be distinguished: 
 
 1. The arc furnace. 
 
 2. The resistance, or incandescent furnace. 
 
 3. The transformer, or induction furnace. 
 
 4. The tube furnace. 
 
 Arc furnaces may be divided into two groups, direct and 
 indirect arc furnaces. In the former, the material to be sub- 
 jected to the influence of the heat generated by the trans- 
 formation of electrical energy, is exposed directly to the 
 electric arc; in the indirect type the material to be treated is 
 not exposed to the direct action of the arc but receives its 
 heat indirectly, the heat being reflected from the interior of 
 the chamber in which the reaction takes place and into which 
 the electrodes project. 
 
 Of course the forms which may be given to arc furnaces are 
 varied, but the principal feature embodied in all furnaces of 
 this description is a hearth constructed of some fire-resisting 
 material, fire-brick or the like, and carbon electrodes, which 
 project into this fusion chamber. The current is supplied by 
 means of heavy cables clamped to these carbon electrodes. 
 
 As before stated, the material to be acted on may be either 
 exposed to the direct heat of the arc, or else it may be so 
 placed that it receives only radiated and reflected heat from 
 
116 NOTES ON ELECTROCHEMISTRY. 
 
 the walls and the roof of the furnace chamber. An illustra- 
 tion of the former type is offered by the aluminium furnace 
 during the time when the cryolite and the alumina are being 
 fused, that is to say, before electrolysis proper has begun. 
 As an illustration of the indirect action type of arc furnace, 
 there may be mentioned the furnace used by Moissan in 
 some of his famous researches, and the De Chalmont furnace 
 employed for the reduction of metallic silic.des, for in these 
 the charge is also exposed only to the radiated heat of the arc. 
 
 Resistance, or incandescent furnaces, were probably first 
 devised by E. H. Cowles and A. H. Cowles, of Cleveland, 
 Ohio, in 1885. The principle upon which these furnaces are 
 constructed is to have some material in the circu t of the 
 electric current which will offer a high resistance to the 
 passage of the current, in consequence of which high temper- 
 atures are generated. 
 
 Where highest temperatures are sought, the arc furnace is 
 indicated, but where closer regulation and control of the 
 working temperatures are demanded, resistance furnaces 
 offer decided advantages. 
 
 The degree of temperature attained in the resistance fur- 
 nace is determined by the magnitude of the current, the 
 time during which this flows, and the amount of resistance 
 offered by the circuit through which the current passes. 
 
 The ultimate temperature attained is the outcome of the 
 rate at which heat is generated in the resistant body the 
 core, and the rate at which this heat suffers dissipation. The 
 point at which these two conditions counterbalance each 
 other determines the highest temperature of the furnace. 
 
 In the resistance furnace, the material to be heated can 
 itself be made the resistant body, or the latter can be em- 
 bodied as a core in the material to be treated. In such 
 cases, the material generally employed is carbon, coarsely 
 grained. 
 
 The Acheson furnaces well illustrate that type of the 
 
ELECROTECHNOLOGY. 117 
 
 resistance furnace in which the core is, in part, formed by the 
 material to be acted upon. 
 
 Borcher's furnace is an instance of the other type of resis- 
 tance furnace, that is to say, of a furnace in which the resis- 
 tance core is independent of the charge. A thin pencil of 
 carbon is imbedded in the mass to be subjected to heating, 
 and a powerful electric current is transmitted to this car- 
 bon pencil by carbon bars or cylinders very much greater 
 in diameter than the pencil. Naturally an intense heat 
 is generated at the pencil owing to the resistance offered, and 
 as carbon does not volatilize appreciably below 3000 C., 
 very high temperatures can conveniently be obtained. 
 
 In transformer, or induction furnaces, of which Kjellin's 
 furnace for steel production may serve as a type, the heat is 
 produced by induction, the current in the furnace being 
 induced by an alternating current passing through an outside 
 conductor near by, generally a coil of many turns which 
 incloses the furnace. 
 
 Induction furnaces are advantageously used for smelting 
 platinum; in Sweden they are used for working iron ores and, 
 as indicated above, for the production of a special grade of 
 steel. 
 
 The characteristic feature of tube-furnaces is the tubular 
 form of the hearth, the current passing through and heating 
 the walls of the tube, which is constructed of some refrac- 
 tory material. 
 
 H. Noel Potter has devised a number of furnaces of this 
 type in which he has sought to secure a uniform heating of 
 the whole tube, satisfactory terminal connections, and a 
 ready replacement of the worn parts. One of the forms he 
 has devised consists of a carbon tube supported by carbon 
 rings between which magnesia, covered by asbestos, is packed, 
 the whole being inclosed in a porcelain tube. 
 
 Another of Potter's furnaces consists of a tube made from 
 the oxides of magnesia, yttria, and zirconia inclosed in a 
 
118 NOTES ON ELECTROCHEMISTRY. 
 
 second tube made of one of these oxides. On this outer 
 tube, over a layer of mica, a coil is wound in which electrical 
 action is started; the actual heating effect, however, is pro- 
 duced in the interior tube. This furnace is chiefly used for 
 the baking of Nernst lamp glowers. 
 
 Among other tube furnaces, mention should be made of 
 the one designed by A. H. Eddy, used for the application of 
 enamels, and that of Nernst and Glaser, which has a resistance- 
 tube made of electrolytic oxides, the outer tube consisting of 
 loosely packed oxides and all inclosed in a jacket designed 
 to prevent loss of heat by radiation. 
 
 A very convenient electro-furnace for certain laboratory 
 purposes is used by the Technische Reichsanstalt at Char- 
 lottenburg, for high temperature work. It is made of several 
 concentric porcelain tubes, and the heating is effected by 
 passing an electric current through wires which are wound 
 upon some of these tubes. 
 
 Recently an electric furnace which can be used in connec- 
 tion with a vacuum, and for general analytical purposes, has 
 been devised by the firm of Heraeus, Germany.* These 
 furnaces can be used with direct current at a potential of 
 from 65 to 220 volts, and require only from 1.5 to 2.5 amperes. 
 The uniformity of temperature, which can be maintained in 
 these furnaces, and the avoidance of reducing gases, which 
 the use of fuel gas often entails, are valuable features. 
 
 In some electrothermic furnaces the process is a continu- 
 ous one, that is to say, the process is not interrupted for the 
 introduction of charges, nor for the withdrawal of the prod- 
 uct. It is, however, not always possible to arrange a working 
 system in this way, and therefore many furnaces are inter- 
 mittent in their action. 
 
 The electric furnace undoubtedly permits the securing of 
 a higher temperature than can be secured through any other 
 device. Whereas the maximum temperature obtainable by 
 * Chemiker Zeitung, 1905, Vol. 29, p. 1209. 
 
ELECTROTECHNOLOGY. 119 
 
 the combustion of fuel under the most favorable conditions 
 is probably not above 2000 C., the temperature of the elec- 
 tric arc has been estimated by Violle in 1893 at about 
 3600 C., and it will probably be reasonable to regard this as 
 the highest temperature maintainable in arc furnaces under 
 ordinary conditions. In furnaces provided with additional 
 protection against loss of heat by radiation, for instance, in 
 furnaces having an additional lining of some good non-con- 
 ductor, like magnesia or chalk, temperatures up to 4000 C. 
 can be secured; speaking, however, of practical electrical 
 furnaces working on a commercial scale, the working tem- 
 peratures of these will range from about 2000 to 3500 C. 
 
 Where no electrochemical, but only electrothermic work 
 has to be done, preference is given to the alternating rather 
 than to the direct current. 
 
 In considering the cost of electric furnaces, the cost of the 
 electrical energy to be used is naturally a factor of the great- 
 est importance. Where such energy has to be generated by 
 the combustion of fuel, the cost will necessarily be high, 
 because only a small percentage, possibly from 5 to 8% of 
 the heating power of the coal which is burned under the 
 boiler, is actually gained in the form of electrical energy. 
 Where water-power is available, the conditions are far more 
 favorable, and it does not appear improbable that in the near 
 future wind-power may be made to serve for the cheap gen- 
 eration of electricity for electrothermic, as it now does for 
 other purposes.* 
 
 Electro-Furnace Products. A number of substances have 
 been prepared by the aid of the high temperatures made 
 available through electro-furnaces. Some of these are metals 
 won in the free state through the dissociation of their com- 
 pounds for carbon at the heat of the electro-furnace can 
 
 * Paul la Cour (Aus dem Danischen iibersezt von J. Kaufmann): 
 Die Windkraft und ihre Anwendung zum Antrieb von Elektrizitats- 
 Werken, Leipzig, 1905. 
 
120 NOTES ON ELECTROCHEMISTRY. 
 
 remove oxygen from any metallic oxide known; other sub- 
 stances produced are compounds, the chemical union of 
 their constituents being effected by the aid of electrical 
 energy. 
 
 The metallic products of electro-furnaces shall be first 
 considered. 
 
 Chromium. This metal has been obtained in the electric 
 furnace from various raw materials. If a mixture of chromic 
 oxide (Cr 2 O 3 ) and carbon are fused, carbides of chromium 
 result, and from these, by fusion with lime, the greater portion 
 of carbon can be removed. The metal thus produced con- 
 tains between 97% and 98% of chromium, and carbon, iron, 
 and silicon as impurities. If perfectly pure chromium is 
 required, this can be secured by fusing together chromic 
 oxide, chromic carbide, and lime. 
 
 In the Aschermann process, a mixture of chromic oxide 
 and antimony sulphide are fused together in a graphite 
 crucible, and from the resultant alloy of chromium and anti- 
 mony the latter element is removed by heating. 
 
 Iron and Steel. Under existing economic conditions it 
 is evident that electro-smelting of iron ores and the electro- 
 production of steel is practically feasible only where pure ores 
 may be worked and where electric power can be cheaply 
 produced. 
 
 There is no question but that an ore so treated and a steel 
 so produced may be of superior quality, at least when pro- 
 duced in certain types of electro-furnaces, for in some types 
 of furnace the influence of impurities can be avoided to a 
 great extent. 
 
 A number of electric furnaces have been designed for the 
 purpose of working iron ores and of producing steel. 
 
 Paul He>oult, of France, was, in 1900, the first to make steel 
 electrically on a commercial scale. He devised several kinds 
 of electro-furnaces for ore smelting and for steel refining. 
 One of these somewhat resembles a Bessemer converter in its 
 
ELEC TRO TECH NO LOG Y. 121 
 
 construction, but contains two vertical carbon electrodes 
 between which and the conducting charge two arcs are 
 struck in series. An exceedingly fine tool steel can be pro- 
 duced in this furnace from steel scrap and cast iron. An 
 alternating current of 60 volts and 4000 amperes is used in 
 the process. 
 
 At present works are in process of erection at Syracuse, 
 N.Y., by the Holcomb Steel Company, where the refining of 
 steel will be done by the Heroult method. Further experi- 
 mental work with the Heroult process for the electro-smelt- 
 ing of ores and the manufacture of steel will shortly be under 
 way at Sault Ste. Marie.* As Canada is rich in high-grade 
 iron ores and commands vast water-power, the prospects there 
 for a successful outcome of an electro-process of this kind 
 are certainly promising. 
 
 The Gin furnace consists of a zigzag-shaped trough, in 
 which the premolten cast iron which is to experience treat- 
 ment acts as resistance and transforms the electric energy 
 into heat. The terminals are hollow steel blocks cooled by 
 circulation of water. The iron is changed to steel either 
 by the addition of oxide of iron, or else by the introduction 
 of scrap iron. 
 
 In the Keller furnace the charge is fed in from the top, as 
 in a blast furnace. The electrodes, four or more in number, 
 are inserted vertically and are independent of one another; 
 fusion begins near the hearth and extends upwards, the gases 
 formed preheating the ores. From the smelting furnace the 
 reduced iron flows into the steel fining furnace in which two 
 vertical electrodes are used. The voltage of the reducing 
 furnace is about 30 volts, of the steel furnace about 70 volts; 
 in France about 2800 kilowatt-hours are required for making 
 one ton of steel from ordinary ores. 
 
 In the resistance furnace devised by Dr. Borchers, the car- 
 
 *. Electrical Review, 1905, Vol. 47, p. 672. 
 
122 NOTES ON ELECTROCHEMISTRY. 
 
 bon to be used is placed between the electrodes as resistance, 
 and the ore to be treated is packed around this core. 
 
 F. C. Weber has devised an arc smelting furnace in which 
 the descending charge passes through a series of arcs, each 
 one of which can be independently controlled; this permits 
 of an accurate regulation of temperature in the various 
 zones of the furnace. 
 
 Among other processes devised for iron and steel work 
 mention should be made of the process of M. Ruthenberg, 
 especially adapted to the working of metalliferous sands and of 
 finely divided ores at a relatively small expenditure of energy, 
 and of the process of Kjellin, in Sweden, which, as previously 
 mentioned, is s"aid to produce a steel of excellent quality. 
 Kjellin's furnace is of the induction type; a current of 3000 
 volts is supplied and the current passing through the charge 
 is about 30,000 amperes. By avoiding the use of electrodes 
 the steel is not open to the absorption of impurities and hence 
 the high grade product. The cost is reported to be compara- 
 tively iow. 
 
 Manganese. A crude metal containing about 90% of 
 manganese is obtained by fusing the oxide of manganese in an 
 arc furnace. As manganese is rather a volatile metal the 
 temperature conditions require to be carefully regulated, for 
 the heat must not be allowed to become too great. 
 
 An iron manganese alloy (ferro-manganese) is prepared 
 by the Simon process in France, by fusing together an oxide 
 of manganese and fluorspar. Part of the electric energy 
 used is expended in electrolytic action, possibly about 25% 
 of the total being used for this purpose, while the balance 
 produces the necessary heating effect. The ferro-manganese 
 alloy resulting from this process contains about 85% of 
 manganese and from 7 to 8% each of iron and of carbon. 
 
 Molybdenum. Heating molybdenum sulphide with car- 
 bon produces a crude molybdenum which contains approxi- 
 mately 10% of impurities, of which carbon and iron are the 
 
ELECTROTECHNOLOGY. 123 
 
 most important. This crude metal when mixed with molyb- 
 denum oxide and subjected to fusion in an arc furnace 
 parts with its carbon and is won in a pure condition. 
 
 Titanium. The fusing point of titanium is higher than 
 that of any metal thus far obtained by thermo-electric 
 work. Moissan did not succeed in completely fusing a 
 small amount, possibly 350 grams, of a mixture of titanic 
 acid and carbon even by the expenditure of 2200 amperes 
 and 60 volts. The metal titanium combines readily with 
 nitrogen, but this compound, the nitride, can be broken up 
 by raising the temperature of the arc sufficiently high; in 
 so doing, however, some of the carbon of the arc is apt to 
 enter into chemical combination with the titanium, this 
 resulting in the formation of a carbide of titanium from 
 which it is most difficult, if not impossible, to obtain a pure 
 metal. 
 
 Uranium. This metal can be obtained in a pure state 
 from its oxide by heating the latter with carbon. Uranium 
 is volatile in the electric arc, and at a temperature of 1000 
 C. readily enters into chemical combination with nitrogen. 
 
 Vanadium. Vanadium can be obtained by the Gin pro- 
 cess* from the fluoride of vanadium. The anodes used are 
 rods especially prepared from vanadium trioxide, retort 
 carbon, and rosin, shaped under hydraulic pressure and 
 baked at very high temperatures. The cathode is made of 
 iron. The anode ND 100 is approximately 200 amperes, the 
 cathode ND 100 about 600 amperes, the voltage about 12 
 volts. 
 
 Alloys with iron, the so-called ferro-vanadium alloys, are 
 also prepared by this process. 
 
 Tungsten. Moissan succeeded in preparing this metal by 
 fusing together tungstic acid and pure carbon. It is impor- 
 tant that an excess of carbon be avoided and that the temper- 
 
 * Bericht des V. Int. Kongresses fur Angew : Chemie, Berlin, 1903, Vol. 
 4, p. 744. 
 
124 NOTES ON ELECTROCHEMISTRY. 
 
 ature be kept sufficiently low so that the metal may not 
 completely, for if it does, some of the carbon will enter into 
 chemical combination with it, forming carbide of tungsten. 
 
 Electro-furnaces are also used for the manufacture of other 
 substances not metals which, before the coming of the 
 electro -furnace were either unknown, or were made by other 
 processes. Of these products the following should be men- 
 tioned. 
 
 Alundum, or artificial corundum, is an abrasive, crystalline 
 in form, and extremely hard and sharp in grain, prepared in 
 the electric arc furnace from calcined bauxite or from gibb- 
 site, by the Jacobs process. 
 
 Barium-Hydrate. In a process also devised by C. B. 
 Jacobs, barium sulphate (Barytes) is treated in an electric 
 furnace in the presence of carbon. The ore is first reduced 
 to barium sulphide and this, reacting with additional barium 
 sulphate, forms barium oxide and sulphur dioxide gas. The 
 barium oxide is dissolved in water, and the hydrate thus 
 formed is obtained as crystallized barium hydrate of high 
 grade purity. 
 
 Carbides. A class of bodies termed the carbides is formed 
 in the electric furnace by reducing the oxides of some metals 
 and non-metals in the presence of an excess of carbon. Either 
 arc or resistance furnaces may be used for the purpose; often 
 both systems come into play in one operat'on through the 
 unavoidable arcing which occurs in the working of some 
 resistance furnaces. 
 
 While the list of carbides embraces possibly some twenty 
 odd compounds only a very few of these have any appreciable 
 commercial importance, calcium-carbide is probably the 
 most important of them all. 
 
 Calcium-carbide. In 1892 Moissan announced that he 
 had made calcium-carbide, a compound of calcium and car- 
 
ELECTROTECHNOLOGY. 125 
 
 bon, by means of the electric furnace. Towards the end of 
 the same year, T. L. Willson stated that he had, by fusing 
 lime and carbon together electrically, obtained a body yield- 
 ing acetylene when brought into contact with water. This 
 investigator, it appears, had made calcium-carbide as early 
 as 1888, at Spray, North Carolina, but did publish the data 
 at the time. 
 
 The formation of calcium-carbide is shown by the for- 
 mula: 
 
 CaO + 3 C = CaC 2 + CO 
 
 When the current density through the resistance core 
 attains to 1.2 amperes per square mm., the formation of the 
 compound begins and at a current density of 2 amperes per 
 square mm., complete fusion is attained at the core; the 
 rest of the charge, further removed from the core, assumes 
 a pasty condition, the temperature of the core experiences a 
 gradual lowering, and, in consequence, calcium-carbide, the 
 resultant product, is intermingled with other substances. 
 
 Practically, the formation of calcium-carbide does not occur 
 below a temperature of 2000 C. and probably a tempera- 
 ture higher than this is the true temperature of the reaction, 
 which, as previously indicated, is partly an arc and partly a 
 resistance reaction. 
 
 A slight excess of carbon should always be provided, for 
 otherwise calcium and carbon monoxide are apt to be formed 
 through the interaction of the lime and the carbon and the 
 carbide would in consequence be exposed to contamination. 
 In fact, it is important to aim at the production of a pure 
 calcium-carbide from the outset, because this carbide when 
 once formed is practically neither fusible nor soluble, and 
 therefore offers great, if not insurmountable, difficulties to 
 Any subsequent purification. 
 
 To obtain as pure a calcium-carbide as possible the addi- 
 tion, before fusion, of manganese peroxide and of calcium 
 
126 NOTES ON ELECTROCHEMISTRY. 
 
 carbonate to the original charge of lime and carbon has been 
 advocated; this process is known as the Hewes process. In 
 another process, devised by Rathenau, iron, or oxide of iron, 
 is added to the charge before fusion so that the iron may 
 combine with and remove all of the silicon present as ferro- 
 silicon. 
 
 In the manufacture of calcium-carbide, either the direct or 
 the alternating current may be used; for some reasons the 
 latter is preferable. 
 
 The commercial value of a given calcium-carbide depends, 
 of course, upon the amount of acetylene gas (C 2 H 2 ) which it 
 will yield on reacting with water. The equation reads: 
 
 CaC 2 + 2 H 2 O = C 2 H 2 + Ca (OH) 2 
 
 The theoretical yield of one kilogram of pure calcium- 
 carbide is about 350 liters of acetylene gas, at normal tem- 
 perature and pressure ; from the commercial product, however, 
 generally not more than 85% of this yield are obtained. 
 
 Carbon bi-sulphide. E. R. Taylor, at Penn Yan, New 
 York, produces carbon bi-sulphide in electric furnaces. These 
 measure about 41 feet in height and 16 feet in diameter, the 
 diameter decreasing towards the top. These furnaces are con- 
 structed of a steel shell and are lined with refractory fire brick 
 or some similar substance. 
 
 The electrodes, four in number, are placed 90 apart and 
 are re-enforced in the interior of the furnace by a continuous 
 supply of coke or broken carbons, which are fed into the 
 furnace by conduits. 
 
 The sulphur is placed at the bottom of the working chamber 
 o^ the furnace and extends up to and around the electrodes. 
 Annular chambers situated in the lower part of the furnace 
 are kept supplied with sulphur, which is fed in at the top and 
 which runs down into the furnace in a molten condition. 
 
 The vapors of sulphur passing through the charcoal, 
 which fills the body of the furnace, combine with it and form 
 
ELECTROTECHNOLOGY. 127 
 
 vapor of carbon bi-sulphide; this passes off through a tube 
 near the top of the furnace into a condenser, wherein the vapor 
 becomes liquefied. A subsequent distillation insures a product 
 almost entirely pure. 
 
 The furnaces are arranged with a view to economize most of 
 the heat generated in the process and are continuous in their 
 action. The output is about 4500 kilograms of carbon bi- 
 sulphide in 24 hours. The working power is furnished by tur- 
 bine water-wheels, although a steam engine is held in reserve 
 in case, for any reason, the water power should fail. 
 
 Glass. Glass when in a fused condition is an electrolyte, 
 and a number of electro thermic processes have been devised 
 for its manufacture. In some of these processes as in the 
 Shade process, an arc furnace is employed, in which between 
 four and six kilowatt-hours are required to produce one 
 kilogram of molten glass. 
 
 In other processes, for instance, in that of Reich, a resis- 
 tance furnace is used. In a recently designed furnace of the 
 resistance type, kryptol which is essentially pure carbon 
 of uniform grain, is utilized as the heating material.* The 
 kryptol is packed around the vessel holding the charge of 
 glass and by this arrangement the loss of heat by radiation is 
 materially reduced. Carbon electrodes are employed, the 
 current used is about 100 volts, and the operation is carried 
 on at a temperature materially below that of an arc furnace. 
 
 In still other furnaces for the manufacture of glass, a com- 
 bination of the arc and the resistance principle is employed; 
 an illustration of this type is the August Voelker furnace, 
 which is used in Germany and which is reported to be very 
 effective in its working. 
 
 Graphite. Artificial graphite f is another product made 
 by the Acheson Company at Niagara Falls. It is prepared in 
 
 * Electrical Review, 1905, Vol. 47, p. 445. 
 
 t Consult C. P. Townsend, Electric World, 1901, for an historical 
 resum3 of studies on artificial graphite. 
 
128 NOTES ON ELECTROCHEMISTRY. 
 
 a resistance furnace from anthracite coal or from coke. The 
 charge is separate from the core, which consists of carbon 
 rods extending through the charge. At the beginning of the 
 operation these carbon rods transmit the whole of the current 
 and, in consequence, become highly heated. The high tem- 
 perature thus generated, converts that portion of the charge 
 immediately adjacent to the core into graphite; this graphite 
 then conducts a part of the current and thus gradually the 
 zone of reaction extends farther and farther through the 
 mass. 
 
 The Acheson Company also graphitize electrodes, these in 
 the process being exposed to a temperature above the temper- 
 ature of volatilization of silicon, iron, and aluminium. 
 
 Nitrogen Fixation. Chemical combination of atmospheric 
 nitrogen and oxygen, and the union of the resultant nitrogen- 
 oxides with water to form nitric acid, has been achieved by 
 F. C. Crocker, C. S. Bradley, and D. R. Lovejoy. 
 
 The works are situated at Niagara Falls. Dry air is passed 
 through a chamber provided with stationary negative elec- 
 trodes which are placed in vertical rows and before which 
 there revolves a central shaft carrying the positive electrodes 
 ending in fine platinum wires. The negative terminals are in 
 connection with choke-coils which are kept submerged in oil. 
 A current of 10,000 volts is employed, and about 69,000 arcs 
 per minute are flashed through the air which passes between 
 the electrodes. The treated air contains between two and 
 three per cent of nitrogen oxides. Seven HP. hours are said 
 to produce about one-half kilogram of nitric acid; this acid 
 and calcium nitrate valued as a fertilizer, are among the 
 products manufactured at the Niagara Falls plant.* 
 
 Oxone. Oxone, a fused peroxide of sodium, is manufactured 
 
 * For a recent comprehensive review of the work done on atmos- 
 pheric nitrogen see: 
 
 A. Neubur^er, Die Verwerthung des Luftstickstoffs, Zeitschrift fur 
 Angeioandt* Chemie., 1905, pp. 1761, 1810, 1843. 
 
ELECTROTECHNOLOG Y. 1 29 
 
 by the Niagara Electrochemical Company.* It is a stony 
 compound which yields oxygen gas when brought into contact 
 with water. It is employed for therapeutical purposes and 
 its use for the sterilization of foods has also been recom- 
 mended. Analogous peroxides exist of calcium, magnesium, 
 and zinc. 
 
 Phosphorus. Various furnaces have been devised for the 
 electro-winning of phosphorus and a large proportion of the 
 world's supply of this article is now obtained by electro- 
 thermic methods. 
 
 In the Readman and Parker process, mineral phosphate, 
 finely ground, is mixed with sand and carbon and intro- 
 duced into a furnace from which all air is carefully excluded. 
 This furnace is of the resistance type; the electrodes are 
 made of carbon and enter the lower part of the furnace, 
 the hearth. The phosphorus is caught under water as it 
 distils from the furnace. 
 
 In the Machalske process an arc furnace is used and an 
 alternating current is employed. Tri-calcium-phosphate, 
 silica, and carbon are the crude materials used, phosphorus, 
 carbon-monoxide, and a slag of calcium silicate are pro- 
 duced. 
 
 Silicides. The silicides are a class of compounds similar 
 in type to the carbides, but with silicon in the place of carbon. 
 
 The silicides of calcium, barium, and strontium, expressed 
 respectively by the formula: CaSi 2 , BaSi 2 , SrSi 2 , were dis- 
 covered by C. B. Jacobs and are all manufactured by The 
 Ampere Electrochemical Company. f 
 
 To prepare these compounds the silicates of the above- 
 mentioned alkaline earth metals are reduced in the electric 
 furnace in the presence of sufficient carbon, or, a mixture may 
 be made of carbon and silica, together with some of the salts 
 
 * F. A. J. FitzGerald, Electrochemical and Metallurgical Industry, 
 Vol. 3, 1905, p. 253. 
 
 t Jacobs, American Institute of Electrical Engineers, 1902. j 
 
130 \OTKS ON ELECTROCHEMISTRY. 
 
 of the metals mentioned and the mixture fused in the electric 
 furnace. 
 
 These silicides are crystalline in structure; when brought 
 into contact with water they decompose it, and yield a silico- 
 hydrate of the metal and free hydrogen gas. Of the silicides 
 mentioned a given weight of calcium silicide furnishes the 
 greatest volume of hydrogen gas, a corresponding amount of 
 barium silicide will yield only about one-half as much. 
 Commercially, these compounds are used in the preparation 
 of hydrogen gas, and they are also employed as powerful 
 reducing agents. 
 
 Copper silicide (CuSi) is another member of this group; 
 it is principally used as a reducing agent in the preparation 
 of a certain class of copper alloys, the so-called silicon bronzes. 
 Copper silicide contains about 30% of silicon. 
 
 Ferro-silicon can be made from the slags of steel furnaces. 
 Two ferro-silicon alloys, the one containing about 30% and 
 the other about 50% of silicon and approximately 5% of 
 carbon, are used in the manufacture of steel, especially of 
 armor plate. Ferro-silicon is far more effective than carbon 
 as it evolves 7800 calories, where a corresponding amount 
 of carbon yields approximately but 2500 calories. 
 
 Silicon Carbide. Technically known as carborundum, 
 silicon carbide (SiC) is produced by the fusing of sand and 
 carbon, as expressed by the equation: 
 
 SiO 2 + 3 C - SiC 4- 2 CO 
 
 Acheson first made carborundum in 1893. The operation 
 is conducted in a furnace built up of loose brick, and each 
 furnace serves for one run only. An alternating current is 
 conveyed by leads to bronze end-plates to which the carbon 
 electrodes, bundles of carbon rods, are attached; between 
 these electrodes the core of coarsely powdered coke is laid. 
 The charge, consisting of sand, coke, sawdust, and a little 
 salt, is placed about this core. Each furnace takes about 
 
ELECTROTECHNOLOGY. 131 
 
 1000 HP. The initial voltage is about 200 volts, but this 
 drops by fully 60% as the heating of the core progresses. 
 The total process takes from twenty-four to twenty-six hours, 
 that is to say, the electric current is passed for that length 
 of time, then the furnace is allowed to cool and is dis- 
 mantled. 
 
 Various products are formed, segregated in layers. The 
 central core is graphite, next to this a layer of crystallized 
 carborundum, and then a layer of greenish silicon carbide, 
 amorphous in structure, generally intermingled with some of 
 the original charge which has not been transformed. This 
 substance, essentially a compound of carbon and silicon, is 
 termed white stuff; all of the material beyond the white stuff 
 is reincorporated with the next charge. The manufacture 
 of white stuff has been made the subject of a separate patent 
 by Acheson. 
 
 Carborundum consists practically of 70% of silicon and 
 30% of carbon; it is apt to hold as impurities some iron, 
 aluminium, and calcium. 
 
 About 8.6 kilowatt-hours are required to produce one kilo- 
 gram of carborundum and the temperature must be carefully 
 regulated to guard against volatilization of the silicon; 
 3800 C. is approximately the temperature of formation of 
 carborundum.* This substance is used largely as an abrasive, 
 for furnace linings, and for purposes of deoxidation in the 
 manufacture of steel. 
 
 Siloxicon. This substance, originally obtained as a by- 
 product in the production of carborundum is now a separate 
 article of manufacture. It is a chemical compound of the 
 elements carbon, silicon, and oxygen, and its constitution is 
 expressed by the formula, Si 2 C 2 O. 
 
 It is made at a temperature of about 2700 C., in furnaces 
 similar in construction to those used in the manufacture of 
 
 * J. Wright, Liber cit. p. 42. Confer; F. A. J. FitzGerald, Electrochemi- 
 cal and Metallurgical Industry, 1906, p. 53. 
 
1,32 NOTES ON ELECTROCHEMISTRY. 
 
 carborundum. Siloxicon is very refractory at high tempera- 
 tures and is soluble only in hydrofluoric acid; as it is self- 
 binding it needs only to be moistened with water and can then 
 be molded into any shape desired, preliminary to firing. It 
 is used for the manufacture of fire-bricks, crucibles, etc. 
 
 ELECTRO-ORGANIC PROCESSES. 
 
 B.I. Direct Action Processes. Electro-reactions in the 
 domain of organic chemistry, may also be divided into direct 
 action and into indirect action processes. The former group 
 would include all actions in which electrical energy is directly 
 applied, for instance, all electrolytic processes whether 
 these be processes of substitution, oxidation, or reduction; 
 it would also embrace reactions effected by silent discharge. 
 The other group would include all indirect effects such as 
 thermo-electric and photo-electric processes. 
 
 Speaking of the first of these groups, attention has been 
 given chiefly to processes of reduction for the reason that 
 these can be most conveniently studied with reference to 
 certain groups in the molecule, whereas processes of oxida- 
 tion are, as a rule, apt to involve the molecule as a whole in 
 chemical change. 
 
 Reference cannot here be made in detail to the many 
 interesting and valuable results obtained in organic chemis- 
 try by processes of electro-analysis and electro-synthesis, 
 which afford the great advantage of permitting the bringing 
 about of chemical reactions without necessitating the intro- 
 duction of any chemical reagents. It must suffice to remark 
 that within the past decade great advances have been made 
 in the application of electrical energy to the solving of numer- 
 ous problems in organic chemistry and that the field is still 
 a. very promising one for the investigator.* 
 
 C. W. Loeb, Die Elektrochemie der Organischen Verbindungen, 
 1905. 
 
ELECTROTECHNOLOGY. 133 
 
 Among electro-technological operations, dealing with the 
 manufacture of organic substances, there should be cited the 
 preparation of fine chemicals and of dye-stuffs; among the 
 chemicals thus made there may be mentioned, vanillin (from 
 iso-eugenol), iodoform, chloroform, and bromoform; among 
 the dye-stuffs so prepared, aniline, alizarin-black and fast 
 yellow dyes. 
 
 Experiments looking to the application of electrical energy 
 to agricultural problems were tried many years ago, and a 
 number of attempts have been made to foster the growth and 
 the yield of crops by stimulating the soil by electricity. 
 
 Thus Spechnew, in 1889, exposed seeds, after they had 
 been immersed in water, to the action of induction currents 
 and secured their germination in from two to eight days, 
 while control-seeds which had not been treated with elec- 
 tricity, required from four to fifteen days before they germi- 
 nated. These results were confirmed by other investigators, 
 and several cases are on record where it was found that both 
 the yield and the growth of flowers and vegetables were 
 remarkably improved and stimulated by passing electric 
 currents between large copper electrodes buried in the soil. 
 Interesting results along such lines were, among others, 
 obtained by the Hatch Experimental Station in Amherst, 
 Mass., as early as 1892. 
 
 B. II. Silent Discharge Processes. In the silent electric 
 discharge, electrical energy is continuously passing from one 
 conductor to another through an intervening space which is 
 filled with a gas or with a mixture of gases. 
 
 The apparatus employed for silent discharge work can be, 
 and is, constructed in various forms, but the essential feature 
 of construction in all of them is an arrangement which obliges 
 the electric discharge to pass through a layer of the gas acted 
 upon. 
 
 Frequently the current is passed between two layers of 
 sulphuric acid contained in very thin glass vessels, the elec- 
 
 7 
 
134 NOTES ON ELECTROCHEMISTRY. 
 
 trical energy being obliged to pass through the containing 
 glass walls and through the gas confined between them. In 
 other forms of apparatus a metallic foil tin-foil, aluminium- 
 foil or silver, is used instead of the acid conductors. The 
 simplest form of apparatus used for the purpose consists of 
 two metal plates between which the gas to be acted upon is 
 placed; as these metal plates are, however, apt to become 
 worn and roughened by the discharges, there is always 
 some danger of spark discharges. Aluminium is possibly the 
 metal best suited for constructions of this description. 
 
 In every case the thinner the layer of gas through wh'ch 
 the electric discharge must pass, the more effective is the 
 reaction. In rarefied gases the discharge is often accom- 
 panied by luminous phenomena, the so-called Geissler tube 
 effects. 
 
 As there is no appreciable elevation of temperature in these 
 reactions, endo thermic compounds may be formed under the 
 influence of the silent discharge, arid for this reason these 
 phenomena and reactions are of the greatest value in bring- 
 ing about simple organic syntheses, similar to those which 
 plants effect under the influence of sunlight. 
 
 Berthelot, experimenting with the silent discharge, showed 
 that atmospheric nitrogen could be bound in the form of 
 complex organic compounds, which, when treated with 
 soda-lime at high temperatures yielded ammonia. The 
 results he obtained are of special interest, as they point to the 
 possibility of the assimilation of atmospheric nitrogen by 
 plants under the influence of atmospheric electricity. 
 
 Thus Berthelot* pointed out, that in clear weather there 
 is a difference of potential of from 20 to 30 volts between 
 two layers of air which are but one meter apart, and in rain 
 storms this difference of potential may rise to about 500 
 volts. As Berthelot achieved a fixation of nitrogen by carbo- 
 hydrates by means of a difference of potential of 8 volts only, 
 
 * Compt. rend. 1900, Vol. 131, p. 772. 
 
 V 
 
ELECTROTECHNOLOGY. 135 
 
 his suggestion, that in nature the silent discharge is an active 
 agent in plant-life and growth is certainly most plausible. 
 
 A number of synthetic reactions have been achieved in the 
 laboratory by means of the silent discharge. Thus, under its 
 influence, carbon monoxide and nitrogen have been made to 
 yield formaldehyde and marsh-gas (Brodie, 1872), and, it is 
 interesting to recall that formaldehyde was used by 
 Butlerow more than forty years ago in the synthesis of 
 sugars. 
 
 Collie* found that carbon dioxide is readily converted into 
 oxygen and carbon monoxide under low pressure electric 
 discharge, and he too calls attention to the analogy between 
 the action of the silent discharge and the action of light in 
 plant life; the polymerizing effects of the silent discharge are 
 especially notable. 
 
 The action of this agent is certainly in part electrothermic' 
 and, possibly, in part electrolytic, although it is well known 
 that the output of any product secured by means of the silent 
 discharge does not conform to the theoretical yield which 
 would be expected were the reaction governed by Faraday's 
 laws. In the light of Our present knowledge it seems most 
 probable that in the silent discharge vast amounts of kinetic 
 energy transformable into chemical energy are introduced 
 into the system by speeding electrons.! 
 
 The principal technological application of the silent dis- 
 charge is the generation of ozone, by the process of Siemens 
 and Halske. A metal tube, cooled by water, is inserted in 
 a tube made of mica which is wound with copper ribbon. The 
 annular space between the two tubes is but narrow, and serves 
 for the passage of the air, the oxygen of which is to be trans- 
 formed into ozone. The silent discharge passes between the 
 metal cylinder and the copper ribbon on the mica cylinder; 
 
 * J. N. Collie, "Syntheses by Means of the Silent Electric Dis- 
 charge." Trans. Journ. Chem. Soc., London, 1905, p. 1540. 
 t W. Loeb, Liber cit. p. 279. 
 
136 NOTES ON ELECTROCHEMISTRY. 
 
 a series of such double tubes are combined to form a sort of 
 lattice work. An alternating current is employed; about 65 
 volts are transformed into 6500 volts, and about 18 grams of 
 ozone are produced per electric HP. hour; this amounts to 
 practically nine times the amount which could be secured 
 if this reaction were electrolytic in character. 
 
 Jt is estimated that in the best of ozone-generating plants, 
 riot more than 15% of the total energy supplied is con- 
 sumed in bringing about the transformation of oxygen into 
 ozone. 
 
 B. III. Electro-Osmosis. If a porous diaphragm be intro- 
 duced into an electrolyte and a sufficiently high voltage be 
 employed, the contents of one electrode chamber will be forced 
 bodily through the diaphragm into the other electrode 
 chamber until a certain difference of pressure will have been 
 established between the solutions in the two compartments. 
 
 Electro-osmosis, or kataphoresis, as it is also termed, has 
 been known for a long time and was submitted to careful 
 study by G. Wiedemann as early as 1852.* This phenome- 
 non is entirely different from that of osmosis, for in kata- 
 phoresis the whole solution passes through the diaphragm 
 unchanged, whereas in osmosis only the solvent passes, not 
 the solute. The phenomena of kataphoresis, as recognized 
 by Hittorf, are also independent of electrolytic action and' 
 are not subject to the laws of Faraday, although electrolytic 
 phenomena probably accompany the process to a certain 
 extent. 
 
 In aqueous solutions, as a rule, the solution travels through 
 the diaphragm from the anode to the cathode compartment,- 
 although in certain instances the direction of this flow is 
 reversed; the nature of the solution and the nature of the 
 diaphragm seem to be the determining factors in this matter; 
 The cause of kataphoresis is probably the taking on of oppo- 
 
 * G. Breaig, Ber. ties V. Iiit.KongressesfiirAngewandteChemie, 1903, 
 Vol. 4, p. 643. 
 
ELECTROTECHNOLOGY. 137 
 
 site electric charges by the walls of the diaphragm and by the 
 particles of the solution passing through it. 
 
 If no diaphragm is used, but if very finely divided particles 
 of some solid or colloid are suspended in a poorly conducting 
 fluid and an electric current passed through, then the parti- 
 cles of the solid and the particles of the fluid medium in 
 which these are suspended will assume opposite electric 
 charges, and the solid particles will be set in motion. In a 
 general way it may be stated, that substances which, in a 
 finely divided state, take on a charge electronegative to water 
 will travel to the anode; if such substances are made into 
 a diaphragm, they will induce water to travel to the cathode. 
 
 An application of kataphoresis causing a tanning solu- 
 tion to penetrate into and effect the tanning of hides, has 
 resulted in a great saving of time compared with the time 
 required in the former methods of doing this work. 
 
 The first attempts in this direction seem to have been made 
 as early as 1850, by Cross; however, his results do not appear 
 to have been very satisfactory. Since that time a consider- 
 able number of electro-tanning processes have been devised; 
 in the process of L. A. Groth, in which the hides are kept in 
 motion in a direction at right angles to the electric current 
 passing, it has been found that a treatment of eight hours 
 will give results equivalent to those secured by a full month's 
 tanning according to the old method. 
 
 , S5= = =j: '--- ;: =5^ K ^ 
 
 X>^ OF THE \ 
 
 f UNIVERSITY ] 
 
 V F ^ 
 
 Xfc-CA! !FOB^ N i^ 
 
NAME INDEX. 
 
 Addicks, 96 
 Ampere, 17 
 Arrhenius, 28, 41, 44, 46 
 
 Bancroft, 104 
 Beccaria, 22 
 Becker, 112 
 Becquerel, 11, 95 
 Be'mont, 11 
 Berthelot, 134 
 Berzelius. 25, 26 
 Bradley, 128 
 Bredig, 63, 136 
 Brodie, 135 
 Brugnatelli, 25 
 Bucherer, 112 
 Buff, 29 
 
 Calvert, 45 
 Carlisle, 24 
 Cavendish, 22 
 Clausius, 27, 28, 46 
 Clifford, 10 
 Collie, 135 
 Collins, 32 
 Cormack, 49 
 Coulomb, 18 
 Cowles, 116 
 Cowper-Coles, 96 
 Crocker, 34, 128 
 Crookes, 10, 11 
 Cross, 137 
 Cruickshank, 25 
 Curie, 11 
 Cuthbertson, 23 
 
 Dalton, 26 
 Davy, 25, 20 
 De Chalmont, 116 
 )eimann, 23 
 De Laplace, 23, 37 
 Dufaye, 9 
 
 Ebert, 14 
 Elkington, 95 
 
 Fabroni, 24 
 
 Faraday, 19, 27, 52, 62 
 FitzGerald, 129, 131 
 Foerster, 109 
 Franklin, 9 
 Fromm, 105 
 
 Galvani, 24 
 Getman, 65 
 Gilbert, 8 
 Groth, 137 
 Grothuss, 25, 27 
 Guthe, 32 
 
 Hall, 112 
 Hay den, 96 
 Heirnwood, 32 
 Henry, 20, 24 
 Heroult, 120 
 Hess, 37 
 Kissinger, 25 
 Hittorf, C3, 04, 136 
 Hopkins, 47. 60 
 
 Jacobi, 103 
 Jacobs, 129 
 
 139 
 
140 
 
 NAME INDEX 
 
 Jahn, 38 
 Jordan, 103 
 Joule, 4, 20 
 
 Kahle, 32 
 
 Kahlenberg, 58 
 
 Keller, 97 
 
 Kelvin, 38 
 
 Kohlrausch, 32, 33, 60, 02 
 
 La Cour, 119 
 Lavoisier, 3, 23, 37 
 Le Blanc, 78 
 Lodge, 44, 65 
 Loeb, 132, 135 
 Lorenz, 62 
 Lovejoy, 128 
 
 Marchese, 94 
 Maxwell, 3 
 Mayer, 3, 4 
 Moissan, 116, 123, 124 
 Murray, 103 
 Mylius, 105 
 
 Nernst, 29, 45, 54, 63, 70 
 Neuburger, 128 
 Nicholson, 24 
 
 Ohin, 17 
 
 Ostwald, 29, 45, 50, 63 
 
 Patterson, 32 
 Planck, 28 
 Plante", 77 
 Potter, 117 
 Priestley, 22 
 
 Ramsay, 13 
 Rayleigh, 32, 33 
 Richards, 30, 32, 91, 112 
 Rontgen, 11 
 Rutherford, 13 
 
 Schmidt, 11 
 Sedgewick, 32 
 Siemens, 115 
 Smith, 53 
 Soddy, 13 
 Spechnew, 133 
 Spencer, 103 
 Stoney, 10 
 Streintz, 77 
 Symmer, 9 
 
 Taylor, 126 
 Thomson, 10, 26, 45 
 Townsend, 127 
 
 Van Maruni, 22 
 Van Troostwijk, 23 
 Van't Hoff, 28, 41, 42, 44 
 Volta, 17, 23, 24 
 Von Helmholtz, 28 
 
 Walker, 49, 52 
 Watt, 19 
 Whetham, 3, 65 
 Wiedemann, 136 
 Williamson, 46 
 Willson, 125 
 Winkler, 87 
 Wollaston, 25 
 Wright, 131 
 
 Young, 3 
 
SUBJECT INDEX. 
 
 Absolute units, 6, 21 
 Accumulators, 75, 77, 78 
 Acetylene gas yield, 126 
 Acheson furnace, 116 
 Acheson process, 130 
 Acid, definition, 50 
 Acidity, 51 
 Acker process, 1 14 
 Alkali metals, isolation, 26 
 Alpha-rays, 11 
 Aluminium, 111 
 Aluminium production, 112 
 Alundum, 124 
 Ammeter, 79 
 Ampere, definition, 16 
 Ampere-hour, definition, 18 
 Anion, definition, 46 
 Arc furnaces, 115 
 Aschermann process, 120 
 Ashcroft process, 102, 114 
 Atmosphere, electrification, 14 
 
 Barium hydrate, 124 
 Base, definition, 50 
 Basicity, 61 
 Bell process, 106, 108 
 Berzelius' theory, 26 
 Beta-rays, 12 
 Betts' process, 100 
 Borcher' s furnace, 117, 121 
 Browne's process, 101 
 Buiisen cell, 76' ; 
 
 Calcium carbide, 124 
 Calorie, 20, 38 
 Capacity factor, 14, 35 
 Carbides, 124 
 Carbon bi-sulphide, 126 
 Carborundum, 130 
 Carnallite, 113 
 Castner process, 109, 113 
 Cathion, definition, 46 
 Cells, electric, 75, 76 
 C. G. S. system, 6, 6 
 Chemical equivalent, 27, 31 
 Chemical polarization, 74 
 Chlorates, production, 107 
 Chlorine and alkali-hydrates, 106 
 Chromic acid cell, 76 
 Chromium, 120 
 Clark cell, 36, 38 
 Concentration polarization, 73 
 Conductivity, equivalent, 61 
 Conductivity, molecular, 60 
 Conductivity, specific, 62 
 Conductivity, unit, 59 
 Constantan, 81 
 Conductors of electricity, 15 
 Copper, 94 
 
 Copper output calculation, 97 
 Corundum, artificial, 124 
 Coulomb, definition, 18 
 Coulometers, 29, 30 
 Cross-section of wires, 84 
 Current amount, calculation, 34 
 
 141 
 
142 
 
 SUBJECT INDEX. 
 
 Current density, 74, 87 
 Current measurement, 79 
 Current regulation, 81 
 Current sources, 75 
 
 Daniell cell, 38, 76 
 
 Davy's electrochemical theory, 26 
 
 Deduction, 2 
 
 Depolarizers, 68 
 
 Diaphragm process, 106, 107 
 
 Dielectric constant, 45 
 
 Dissociants, 49 
 
 Dissociation voltage, 37, 73 
 
 Eddy furnace, 118 
 Edison accumulator, 78 
 Edison primary cell, 76 
 Electric arc, temperature, 119 
 Electric conductors, 15 
 Electric current, nature, 10 
 Electric energy, 8, 14 
 Electric light current, 75, 77 
 Electric power, calculation, 34 
 Electric pressure, 16 
 Electric theory, Berzelius', 26 
 Electric units, absolute, 21 
 Electric units, practical, 21 
 Electric valencies, 46 
 Electricity, animal, 24 
 Electricity, contact theory, 24 
 Electricity, galvanic, 24, 
 Electricity, nature, 23 
 Electricity, properties, 14 
 Electricity, theories, 8 
 Electro-affinity, 48, 73 
 Electro-analysis, 66 
 Electrochemical equivalent, 31,32, 33 
 Electrochemical sequence, 47 
 Electrochemical theory, Davy's, 26 
 Electrochemistry, evolution, 22 
 Electrode-areas, calculation, 86 
 
 Electrodes, 84 
 Electrode potential, 74 
 Electrodepositiou from fused electro- 
 lytes, 110 
 
 Electrodeposition from solution, 94 
 
 Electro -furnaces, 114 
 
 Electro-furnace products, 119 
 
 Electro- organic processes, 132 
 
 Electro-osmosis, 156 
 
 Electrolyte, 28 
 
 Electrolytes, fused, 110 
 
 Electrolytic cell, resistance, 83 
 
 Electrolytic dissociation, 28, 41 
 
 Electrolytic dissociation theory, ob- 
 jections, 58 
 
 Electrolysis, 28 
 
 Electrolytic solution pressure, 70 
 
 Electromotive force, 35, 72 
 
 Electron, 8, 10 
 
 Electron theory, 10 
 
 Electro-plating, 103 
 
 Electrotechnology, 93 
 
 Electrothermic processes, 114 
 
 Electrotyping, 103 
 
 Electrozincing, 105 
 
 Elements, electrochemical 
 sequence, 47 
 
 Energetics, laws, 4 
 
 Energy, conservation, 3 
 
 Energy, dissipation, 6 
 
 Energy efficiency, 92 
 
 Energy factors, 4 
 
 Energy, forms, 4 
 
 Equivalent conductivity, 61 
 
 Evolution of electrochemistry, 22 
 
 Farad, definition, 19 
 Faraday, definition, 32 
 Faraday's laws, 29, 67 
 Faraday's researches, 27 
 Forms of energy, 4 
 Fused electrolytes, 110 
 
SUBJECT INDEX. 
 
 Gamma-rays, 12 
 
 Gas-equation, 42 
 
 General principles of science, 1 
 
 Gin furnace, 121 
 
 Gin process, 123 
 
 Glass, 127 
 
 Gold, 99 
 
 Goldschinidts' process, 102 
 
 Grain equivalent, 31 
 
 Graphite, 127 
 
 Griesheira Electron process, 108 
 
 Hall aluminium process, 111 
 
 Hargreaves and Bird process, 108 
 
 Heat equivalent, 20 
 
 Heat of formation, 37 
 
 Heat summation, 37 
 
 Helium, 13 
 
 Henry, definition, 20 
 
 Heraeus furnace, 118 
 
 Heroult aluminium process, 111 
 
 He"roult steel process, 120 
 
 Hewes process, 126 
 
 Hittorf's number, 64 
 
 Hoepfner processes, 95, 102, 103 
 
 Horse-power, definition, 19 
 
 Hydrolysis, 56 
 
 Hypochlorites, production, 107 
 
 Hypothesis, definition, 2 
 
 Indicators, theory, 54 
 
 Induction, 2 
 
 Induction furnace, 117 
 
 Intensity factor, 14, 35 
 
 Ion, definition, 45 
 
 Ions, existence in electrolytes, 46 
 
 Ions, migration, 63 
 
 Ions, mobility, 63 
 
 Ions, nomenclature, 62 
 
 Ion reactions, 50 
 
 Ion symbols, 52 
 
 Ion theory, 41 
 
 Ion-velocity measurement, 65 
 
 lonization, degree, 49 
 lonization of water, 51 
 lonogen, 63 
 Iron and steel, 120 
 Irreversible cells, 69 
 
 Jacobs process, 124 
 Joule, definition, 20 
 Joule, heat equivalent, 20 
 Joule's heat, 110 
 Joule's law, 20, 110 
 
 Kataphoresis, 136 
 Keller furnace, 121 
 Kellner process, 110 
 Kilowatt, definition, 19 
 Kjellin's furnace, 117 
 Kjellin process, 122 
 
 Lamp-bank resistance, 81 
 
 Law, definition, 2 
 
 Law of heat summation, 37 
 
 Lead, 99 
 
 Lead accumulator, 77 
 
 Length, unit, 6 
 
 Litmus, ionization, 56 
 
 Machalske process, 129 
 Magnesium, 113 
 Manganese, 122 
 Manganin, 81 
 Mass, definition, 6 
 Mass, unit, 5 
 Matter, conservation, 3 
 McDonald process, 108 
 Measurement of physical phe- 
 nomena, 5 
 
 Mercury process, 106, 109 
 Microfarad, definition, 19 
 Migration of ions, 63 
 Mobility of ions, 63 
 Molecular conductivity, 80 
 Molybdenum, 122 
 
144 
 
 SUBJECT INDEX, 
 
 Nernst lamps, 63 
 Nernst and Glaser furnace, 118 
 Neutralization, definition, 51 
 Nickel, 100 
 Nickeline, 81 
 Nitrogen fixation, 128 
 Nomenclature of ions, 62 
 Normal current density, 87 
 
 Ohm, definition, 17 
 
 Ohm's law, 17 
 
 One fluid theory, 9 
 
 Osmotic pressure, 41, 42 
 
 Oxone, 128 
 
 Ozone, generation, 135 
 
 Part-molecules, 46 
 
 Phenol-phthalein, ionization, 65 
 
 Phosphorus, 129 
 
 Physical phenomena, measure- 
 ment, 5 
 
 Platinoid,' 81 
 
 Polarization, chemical, 74 
 
 Polarization, concentration, 73 
 
 Polarization voltage measure- 
 ment, 75 
 
 Pole-papers, 78 
 
 Potentiometers, 36 
 
 Practical electric units, 21 
 
 Radio-activity, 11 
 Radium, 11, 12, 13 
 Radium emanations, 13 
 Rathenau process, 126 
 Readman and Parker process, 129 
 Records, 88 
 Reich process, 127 
 Resistance boxes, 81 
 Resistance, 'definition, 17 
 Resistance furnaces, 116 
 Resistance of electrolytic cell, 83 
 Resume 1 , 99 .- 
 Reversible cells, 69 
 
 Reversible reactions, 69 
 
 Rontgen rays, 10, 12 
 
 Roessler and Edelmann process, 103 
 
 Ruthenberg process, 122 
 
 Salt, definition, 50 
 
 Science, general principles, 1 
 
 Shade process, 127 
 
 Siemens- Halske processes, 94, 99 t 
 
 101, 102, 135 
 
 Silent discharge processes, 133 
 Silicides, 129 
 Silicon carbide, 130 
 Siloxicon, 131 
 Silver, 98 
 Simon process, 122 
 Sodium, 113 
 Solution pressure, 63 
 Sources of current, 75 
 Space, 5 
 
 Specific conductivity, 62 
 Spinthariscope, 11 
 Substance, conservation, 3 
 Symbols of ions, 52 
 
 Tanning by kataphoreais, 137 
 Tantalum lamps, 63 
 Taylor process, 126 
 Theories of electricity, 8 
 Thermal energy, 14 
 Thermopiles, 75, 77 
 Thomson's theory, 45 
 Time, definition, 6 
 Time, unit, 6 
 Tin, 101 
 Titanium, 123 
 Tarnsformer furnace, 117 
 Tube furnace, 117 
 Tungsten, 123 
 Two-fluid theory, 9 
 
 Uraniutn, 123 
 
SUBJECT INDEX. 
 
 145 
 
 Vanadium, 123 
 Voelker furnace, 127 
 Voltaic pile, 24 
 Voltameters, 29, 79 
 Volt, definition, 1<> 
 Voltmeter, 36, 79, 80 
 
 Water, ionization. ol 
 Watt-hour, definition, 20 
 
 Weber's arc furnace, 122 
 Weight, definition, 5 
 Weston cadmium cell, 36 
 White stuff, 131 
 Woh will's process, 99 
 
 X rays, 11 
 Zinc, 102 
 

 MS1TY OF CALIFOENIA LIBRARY, 
 BERKELEY 
 
 OK IS DUE ON THE LAST DATE 
 STAMPED BELOW 
 
 not returned on time are subject to a fine of 
 lume after the third day overdue, increasing 
 3r volume after the sixth day. Books not in 
 iy be renewed if application is made before 
 of loan period. 
 
 umvEi 
 
 THIS BC 
 
 Books 
 50c per vc 
 to $1.00 p 
 demand m 
 expiration 
 
 20?n-l/22