STORAGE BATTERIES 
 
THE MACMILLAN COMPANY 
 
 NEW YORK BOSTON CHICAGO 
 DALLAS SAN FRANCISCO 
 
 MACMILLAN & CO., LIMITED 
 
 LONDON BOMBAY CALCUTTA 
 MELBOURNE 
 
 THE MACMILLAN CO. OF CANADA, LTD. 
 
 TORONTO 
 
STORAGE BATTERIES 
 
 THE CHEMISTRY AND PHYSICS OF THE 
 LEAD ACCUMULATOR 
 
 BY 
 
 HARRY W. MORSE, PH.D. 
 
 ASSISTANT PROFESSOR OF PHYSICS 
 IN HARVARD UNIVERSITY 
 
 gorfe 
 
 THE MACMILLAN COMPANY 
 1912 
 
 All rights reserved 
 
Ml, 
 
 Engineering 
 Library 
 
 COPTBIGHT, 1912, 
 
 BY THE MACMILLAN COMPANY. 
 
 Set up and electrotyped. Published February, 1912. 
 
 
 J. 8. Cashing Co. Berwick & Smith Co. 
 Norwood, Mass., U.S.A. 
 
CONTENTS 
 
 CHAPTER PAGE 
 
 I. INTRODUCTORY AND HISTORICAL ... 1 
 
 II. SOME ELECTROCHEMICAL FUNDAMENTALS . 10 
 
 III. ABOUT IONS 30 
 
 IV. THE FUNDAMENTAL CELL-REACTION . . 39 
 V. THE ACTIVE IONS 47 
 
 VI. SOME PERTINENT PHYSICAL QUERIES . . 56 
 
 VII. ENERGY RELATIONS 64 
 
 VIII. REACTIONS AT THE ELECTRODES ... 80 
 
 IX. CHARGE AND DISCHARGE 94 
 
 X. CAPACITY 116 
 
 XI. EFFICIENCY 141 
 
 XII. INTERNAL RESISTANCE ... . . 148 
 
 XIII. PHYSICAL CHARACTERISTICS .... 172 
 
 XIV. FORMATION OF PLANTE PLATES . . . 179 
 XV. PASTE PLATES . ... . . .194 
 
 XVI. DISEASES AND TROUBLES ... . . 205 
 
 XVII. SOME COMMERCIAL TYPES ,, . . 225 
 
 XVIII. ACCUMULATORS IN GENERAL .... 246 
 
 APPENDIX . . . . . . . . . . 255 
 
 238199 
 
STORAGE BATTERIES 
 
 CHAPTER I 
 INTRODUCTORY AND HISTORICAL 
 
 1. Into our present age of power, where we reckon 
 by thousands and tens of thousands of kilowatts, 
 there has come down from a previous era one single 
 form of the galvanic cell which retains sufficient 
 commercial importance to be worth consideration in 
 connection with modern power plants and modern 
 power operation. This is the lead-sulphuric acid 
 accumulator. It was invented and perfected in the 
 heyday of galvanic cells at a time before the dy- 
 namo and the electric motor had any technical im- 
 portance. In our own laboratory, hidden away in 
 the attic where cast-off things are stored, lie the 
 remains of the big Bunsen cells which were once the 
 source of our heaviest currents and with which the 
 remarkable phenomena of current electricity were 
 shown to classes and in public lectures in those 
 days. These same cells were used to charge small 
 storage cells of the original Plante type mere strips 
 
STORAGE. BATTERIES 
 
 of lead, separated by soft rubber insulators arid rolled 
 into spiral form ; then formed with the aid of the 
 primary cells, by a series of reversals, until the plates 
 attained a certain capacity. One of these cells is 
 shown in Figure 1. With these storage cells, which 
 have low resistance and high current-giving capacity 
 even in comparison with the large Bunsen cells, the 
 most wonderful experiments could be 
 performed experiments which are to 
 us now so commonplace and so much a 
 part of our everyday life that their de- 
 scription brings a smile from the high- 
 school boy who has studied physics and 
 chemistry. These cells would run an 
 arc light for several minutes; heat 
 small platinum wires to the melting 
 point ; provide current for electro- 
 magnets of power enormous for that 
 FIG. i. Original time. It was the duty of the labora- 
 type of Plants ^ orv ass i s tants to set up the battery 
 
 accumulator. . 
 
 (About i full * Bunsen cells. Huge zincs in dilute 
 size.) sulphuric acid and great blocks of car- 
 
 bon were arranged in glass jars with porous cups, 
 and from this fuming source the storage cells were 
 charged all day, to be used the day following in 
 demonstrations of the power of the electric current. 
 After the charge was finished the big Bunsens were 
 taken apart and cleaned up, then stored away until 
 
INTRODUCTORY AND HISTORICAL 3 
 
 the time for the next lecture on electric currents 
 approached. 
 
 These early Plante batteries were so arranged that 
 they could be easily thrown into parallel connection, 
 and in this way they could be charged from the 
 Bunsen battery of a few large cells. We still use 
 one of these batteries of 20 cells, dating from the 
 early eighties or earlier. After charge was com- 
 plete the simple mechanism permitted all the cells 
 of the set to be connected in series by simply turn- 
 ing the handle through 90, and clips were provided 
 to show the melting of wires of various metals by 
 the current. 
 
 The current which could be drawn from these 
 small sets of storage cells reached its maximum at 
 forty or fifty amperes an enormous value then, a 
 mere bagatelle now, for we have electrolytic cells 
 and electric furnaces which require tens of thou- 
 sands of amperes for their operation. Since then 
 lead cells have grown in size along with everything 
 else electrical, and I have seen large batteries which 
 can furnish thirty or forty thousand amperes for a 
 short time and ten thousand for several minutes of 
 discharge. 
 
 2. No one of the very numerous primary cells 
 which have been devised and patented has ever 
 reached commercial importance for the heavier work 
 of the present period, though a few have survived to 
 
4 STORAGE BATTERIES 
 
 do the lighter tasks. The Leclanche and numerous 
 similar types are used in large numbers for bell- 
 ringing installations and similar open-circuit appli- 
 cations. And the dry cell has a very large and 
 distinct place of its own in sparking batteries for 
 motor cars and boats and everywhere that internal 
 combustion engines are used. Certainly well over 
 ten million of these little primary cells are made and 
 used each year in the United States. 
 
 From the beginning of the nineteenth century 
 until the early eighties was the era of the primary 
 cell. Then came the dynamo and the motor, ac- 
 companied by improvements in our main prime 
 source of power, the steam engine, and the stor- 
 age cell has grown along with all of these in a 
 somewhat subordinate place. It is a mere assistant, 
 to be called on for temporary aid in time of need, 
 either to help over an ugly peak in the load on the 
 prime source, or as insurance to be called in when 
 the main source is disabled for a short time, and its 
 aid is often quite invaluable under these conditions. 
 As a real factor in the problem of prime power 
 sources it has of course no place at all. 
 
 There is not much value in prophecies about scien- 
 tific or technical things and no particular credit is 
 due the prophet who utters them. Nevertheless, I 
 feel impelled to say that I believe the day of the 
 primary cell will come again. From every funda- 
 
INTRODUCTORY AND HISTORICAL 5 
 
 mental and theoretic point of view we must admit 
 that it should be possible to make a primary galvanic 
 cell which should be more efficient than a steam 
 engine can possibly be ; more flexible as a primary 
 source of power ; a better appliance in every way. 
 3. At first glance a lead-sulphuric acid storage 
 cell seems a very simple and uninteresting sort of 
 machine. It is only a plate of lead and a plate cov- 
 ered with lead peroxide, dipping into rather concen- 
 trated sulphuric acid. But for those who make 
 them and those who care for them in service they 
 become much more complex and puzzling, and worth 
 careful consideration. As an integral and essential 
 part of many power arrangements they are of inter- 
 est to the engineer and as a complex of puzzles and 
 problems they demand attention from the electro- 
 chemist and the physicist. Many books have been 
 written about them, some purely scientific and others 
 nearly purely technical. As far as the fundamental 
 chemical reaction is concerned we seem to be on 
 pretty firm ground, and there is every reason to be- 
 lieve that we know how the cell works. But there 
 is still plenty of room for speculation and research 
 on the more minute physical changes and a good 
 many questions on such important matters as forma- 
 tion, cementing of pastes, sulphation, and life under 
 various conditions cannot even now be answered 
 very clearly. 
 
6 STORAGE BATTERIES 
 
 A very large number of combinations have been 
 suggested for storage battery purposes since Plante 
 began to study his cell in the late fifties, but until 
 within the last few years no one of them has seemed 
 able to meet the rather difficult and peculiar require- 
 ments. Now comes the Iron-Nickel Oxide-Alkali 
 combination as applied by Edison in this country 
 and Jungner on the continent of Europe, and this 
 type seems destined to find a place of its own in 
 light traction work. But by far the greater part of 
 all storage battery plates now made are descendants 
 of the original Plante type hardly recognizable 
 with their highly developed, ribbed, or corrugated 
 surfaces, and formed in the factory by rapid methods, 
 but still " Plante " plates. We have in active use 
 in our own laboratory a unique battery which harks 
 back to the earliest form. It has twenty thousand 
 cells, made of test tubes, and the plates are merely 
 corrugated strips of lead. It is used to give the 
 small currents necessary for vacuum tube and spark 
 work, and it was formed by the old method of re- 
 versals (see page 179) until it reached the needed 
 capacity. 
 
 4. Faure was the inventor of the " paste " plate, 
 and this seemed at first so great an improvement 
 that prophets were not wanting to predict that the 
 older type, with its greater weight, comparatively 
 small capacity, and higher cost, would be completely 
 
INTRODUCTORY AND HISTORICAL 1 
 
 ousted by the new invention. These prophecies 
 have not been fulfilled. The. paste plate has been 
 gradually relegated to traction work and to duty 
 where weight is the important factor, and the plates 
 which are direct descendants of the Plante originals 
 do the really hard work. It took much experience 
 and expense to reach the decision that the Faure 
 plates could not compete in the more strenuous posi- 
 tions, but now we seem to appreciate fairly well the 
 limitations of both types. 
 
 5. As the storage battery developed to a point 
 where it could handle real power loads, there came a 
 time when its powers were somewhat overestimated. 
 It was suggested for many positions where it would 
 have been quite unfit for the work for farm pur- 
 poses, for motor cycles, and even for airships. For 
 long-continued discharge, where it must take the 
 place of the prime source of power over considerable 
 periods of time, the storage battery is often a cum- 
 brous and expensive substitute for the source itself. 
 But for many kinds of work, and especially where a 
 very large amount of power is needed suddenly or 
 for short periods, the battery is the ideal machine. 
 In many modern plants the load fluctuations are very 
 great a thousand per cent or more, and this within 
 a fraction of a minute. No mechanical arrangement 
 can absorb this and regulate the load on the power 
 source in a satisfactory way. But a storage battery 
 
8 STORAGE BATTERIES 
 
 can, for there is hardly a limit to the rate at which 
 large-surface Plante plates can be discharged or 
 charged without injury. 
 
 In certain classes of work in submarines, as a 
 source of under- water power, for example the bat- 
 tery is an absolute necessity. In the regulation of 
 irregular loads it is of the utmost importance, and in 
 emergency or " stand-by " work as well. Car and 
 train lighting systems demand its use. It has proven 
 itself economical and efficient in traction work, espe- 
 cially for electric road vehicles. 
 
 Study of the storage battery calls for attention to 
 two rather distinct viewpoints one chemical, the 
 other physical ; and these will be found of "nearly 
 equal importance. The questions about the funda- 
 mental reactions, and many others as well, are purely 
 chemical. Questions about the life of the cell, and 
 its behavior in service, are nearly purely physical. 
 In manufacture or operation the chemical side must 
 be kept in mind, but the anatomy and physiology 
 (and sometimes the pathology, too) of the individual 
 plate are matters of prime importance. Underlying 
 all, we will need as a foundation for study the funda- 
 mental ideas and laws of general electrochemistry. 
 
 The following chapters are based on lectures which 
 have been given for the last few years at Harvard 
 University. In the course the work on storage cells 
 is preceded by study of the general theory of gal- 
 
INTRODUCTORY AND HISTORICAL 9 
 
 vanic cells, and the simplest of this theory has been 
 included in this book. No attempt has been made 
 to give any of the detail of storage battery engineer- 
 ing, but only to introduce the reader to the peculi- 
 arities of the cell itself. 
 
CHAPTER II 
 SOME ELECTROCHEMICAL FUNDAMENTALS 
 
 6. Theoretically any chemical reaction whatever 
 which takes place of its own accord can be so 
 coupled and arranged that it will work as the source 
 of energy for a galvanic cell. Practically there are 
 difficulties which exclude a large percentage of the 
 known reactions of chemistry from such service. It 
 is also true that a great many of the combinations 
 which have practical value as primary cells can be 
 considered theoretically reversible enough to be used 
 as storage cells. As a matter of fact, only a very 
 few of the cells which have been used or thought of 
 are chemically and mechanically reversible enough 
 to fit them for actual use as storage cells. In some 
 cases the fault is in the reaction itself, and the cell is 
 not chemically reversible. In others, the reaction 
 reverses smoothly enough, but the materials of the 
 cell do not go into and out of solution well. Here 
 the fault is a mechanical one. As far as the general 
 theory is concerned, we must choose fundamentals 
 which fit all the cases, even those which cannot be 
 realized practically. 
 
 10 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 11 
 
 7. Faraday's Law. We have one general funda- 
 mental electrochemical law, which apparently fits 
 every case, and which brings order of the simplest 
 kind out of what at first appeared to be a most cha- 
 otic mass of unrelated material. This is Faraday's 
 law, and it states the relation between the quantity 
 of material used up in a galvanic cell and the quan- 
 tity of electricity which can be obtained from it. 
 
 This law says : 
 
 The amount of each substance which takes part in an 
 electrochemical reaction is proportional to the quantity 
 of electricity which passes through the circuit. 
 
 And when various substances enter an electrochemical 
 reaction, their amounts are proportional to their chemical 
 equivalent weights. 
 
 Numerically, and in terms of a unit later to be de- 
 fined : 
 
 96,540 coulombs pass through the cell and the external 
 circuit with each gram-equivalent of each substance 
 involved in the reaction. 
 
 8. Faraday's Definitions. This law applies to elec- 
 trolytes. Faraday himself felt the necessity of a 
 careful set of definitions for the new ideas involved 
 in this law and its application, and no one has since 
 given better ones, so we shall use them wherever it 
 is possible to do so. 
 
 To quote Faraday (" Experimental Researches," 
 Series VII, 1834): 
 
12 STORAGE BATTERIES 
 
 "... In place of the term pole, I propose using 
 that of Electrode, and I mean thereby that substance, 
 or rather surface, whether of air, water, metal, or any 
 other body, which bounds the extent of the decom- 
 posing matter in the direction of the electric current. 
 . . . The anode is therefore that surface at which 
 the electric current, according to our present ex- 
 pression, enters. It ... is where oxygen, chlorine, 
 acids, etc., are evolved; and is against or opposite 
 the positive electrode. The cathode is that surface 
 at which the current leaves the decomposing body, 
 and is its positive extremity ; the combustible bodies, 
 metals, alkalies, and bases, are evolved there, and it 
 is in contact with the negative electrode. 
 
 "... Many bodies are decomposed directly by the 
 electric current, their elements being set free ; these 
 I propose to call electrolytes. . . . 
 
 " Finally, I require a term to express those bodies 
 which can pass to the electrodes. ... I propose to 
 distinguish such bodies by calling those anions which 
 go to the anode of the decomposing body, and those 
 passing to the cathode, cations, and when I have 
 occasion to speak of them together, I shall call them 
 ions. Thus, the chloride of lead is an electrolyte, and 
 when electrolyzed evolves the two ions, chlorine and 
 lead, the former an anion, and the latter a cation. ..." 
 
 Figure 2 shows the different parts of a cell as 
 Faraday denned them. 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 13 
 
 These definitions of Faraday's were made with the 
 greatest care, but since they were formulated, rather 
 careless use has sometimes been made of them. Note 
 the term anode. It is the surface where the current 
 enters the cell, and Faraday meant just exactly this 
 whenever he used the word. The plates of a cell are 
 not anode or cathode in this sense, but the surface 
 between plate and 
 
 DIRECTION 
 
 cell solution is. OFCURRENT ^ 
 
 There will often be 
 occasion to retain 
 this strict meaning 
 of the word. 
 
 Again, an electro- 
 lyte is the body 
 which carries the 
 current and which 
 
 
 EL 
 
 
 TRODE ELECTR 
 INODE) (CATHOD 
 
 f 
 
 E 
 
 
 
 
 n 
 
 I ANIOM 
 
 
 
 
 
 
 
 ELECTROLYTE 
 
 
 
 
 
 
 
 CATHION 
 
 
 
 
 
 FIG. 2. The parts of an electrolytic cell. 
 
 is at the same time decomposed by it. In this sense 
 a dry salt is not an electrolyte, but a solution of a 
 metallic salt, or a molten salt, belongs in this class. 
 
 9. Electrical Units. Before we can apply this law 
 of Faraday's we should review a few more electrical 
 definitions. In what is called the practical system, 
 we use as unit of quantity of electricity one coulomb. 
 This is derived from the unit of current, the ampere, 
 and one coulomb is the quantity of electricity which 
 passes through a circuit altogether, when a current 
 of one ampere has been flowing constantly for one 
 
14 STORAGE BATTERIES 
 
 second. These units have been fixed with reference 
 to the magnetic effect of a current and not specially, 
 with reference to Faraday's law. It is, however, an 
 easy calculation to state them in terms of units which 
 bear directly on electrochemical effects. Suppose we 
 have in the circuit an amperemeter which measures 
 the current in amperes. We keep the current con- 
 stant and note the entire time during which it flows 
 through an electrolytic cell in which silver is being 
 deposited from silver nitrate solution. We will find 
 that one ampere flowing for one second deposits 
 0.00111775 gm. of silver. The equivalent weight 
 of silver is in this case the same number of grams as 
 its atomic weight, and has the value 
 
 107.88 gm. 
 
 The number of coulombs required to deposit this 
 weight of silver is then 
 
 107.88 
 
 0.0011175 
 
 96,540 coulombs. 
 
 This same number of coulombs will deposit the 
 equivalent weight of any other metal which can be 
 electroplated in the same way, and it is the electro- 
 chemist's unit of quantity of electricity. 
 
 If the silver were to be used in a galvanic cell as a 
 source of power, exactly the same relation holds be- 
 tween the weight of silver and the quantity of 
 electricity 107.88 gm. of silver always travels 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 15 
 
 through an electrolyte and dissolves or precipitates 
 at the electrode in company with 96,540 coulombs. 
 
 Silver ion is univalent, and the equivalent weight 
 is the same as the atomic weight. In most of its 
 reactions, chemical and electrochemical, copper 
 forms a bivalent ion. This means, that in company 
 
 'A B 
 
 FIG. 3. Diagram of apparatus to show Faraday's law. 
 
 with the atomic weight of copper (63.6 gm.) 
 twice 96,540 coulombs pass through the circuit; 
 so the equivalent weight of copper is 31.8 gm., 
 and this is the electrochemist's unit weight of copper. 
 10. Experimental Arrangement for Faraday's Law. 
 Figure 3 gives diagrammatic representation of an 
 experiment to illustrate Faraday's law. Current 
 is supplied by the battery A and passes first through 
 the tangent galvanometer B, which measures it, and 
 then on through the various cells in which electro- 
 
16 STORAGE BATTERIES 
 
 chemical reactions take place. In (7, a molten salt, 
 silver chloride, for example, is decomposed. D 
 might represent a copper coulometer, in which copper 
 is dissolved at one electrode and precipitated at the 
 other. The same arrangement might be used for 
 many other metals. HI is one form of silver 
 coulometer, and here the current enters at a silver 
 anode, which goes into solution, and leaves the cell 
 at the surface of a platinum crucible (cathode) on 
 which silver is deposited. The electrolyte is a 
 strong solution of silver nitrate. Last in the row 
 is a gas coulometer jP, containing dilute acid or 
 alkali as electrolyte and having platinum electrodes. 
 Oxygen gas is formed at the anode, the electrode 
 where the current enters the apparatus, and hydro- 
 gen gas is evolved at the other electrode. 
 
 Suppose we have sent a constant current of one 
 ampere through the circuit for 96,540 sec. We have 
 weighed the electrodes before and after the passage 
 of this current, and we have measured the volumes of 
 the two gases produced. We should find : 
 
 1. At (7, 107.88 gm. of silver dissolved from the 
 wire at which the current enters the cell and the 
 same weight of silver deposited on the other wire. 
 The electrolyte remains unchanged. 
 
 2. At Z>, 31.8 gm. of copper dissolved at one plate 
 and precipitated at the other. No change in the 
 electrolyte. 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 17 
 
 3. At E, the same amounts of silver dissolved and 
 precipitated as in C. 
 
 4. At F, 8 gm. of oxygen formed, or 5.6 1. if 
 measured at C. and 760 mm. pressure, and at the 
 other electrode, 1 gm. of hydrogen, having a volume 
 of 11.2 1. 
 
 5. Inside the cells at A, there will have been 
 exactly equivalent effects, and they will be the same 
 in each cell. Whatever the materials of the anode 
 and cathode, equivalent weights of each will have 
 entered into reaction, for as far as the application 
 of Faraday's law is concerned, it makes no difference 
 whether work is performed as the result of a reac- 
 tion, or must be performed from without in order to 
 make the reaction take place. The law describes 
 every electrochemical reaction, and has been shown 
 to be as exact as any law we have. 
 
 11. Practical Application. Let us examine some 
 applications of this law. A great deal of copper is 
 purified in this country by an electrolytic process. 
 It is interesting to calculate the quantity of electric- 
 ity needed to deposit a pound of copper in this way. 
 
 1 Ib. = 453 gm. 
 
 96,540 coulombs deposit 31.8 gm. 
 We therefore need 
 453 
 
 31.8 
 
 X 96,540 = 1,376,000 coulombs per pound. 
 
18 STORAGE BATTERIES 
 
 Since an ampere is 1 coulomb per second, it will 
 require 
 
 1,376,000 ouo 
 
 = 382 ampere-hours 
 ooOO 
 
 to deposit a pound of copper in a single cell. 382 
 amperes deposit 1 Ib. of copper per hour in a single 
 cell, and if we wish to obtain a ton of copper per 
 hour in such a cell, it would take a current of nearly 
 760,000 amperes to give the desired result. As a 
 matter of fact cells of this size are never used. It 
 is better to arrange a number of cells in series, so 
 that the current flows through one after the other 
 and produces the same effect in each. The yield of 
 copper is then to be found by multiplying the yield 
 per cell by the number of cells. 
 
 The atomic weight of lead is about 207, and 
 it is formed from a bivalent ion, so the equiva- 
 lent weight of lead is 103.5. Rather more than 
 three times as much lead as copper is deposited by 
 the same quantity of electricity. The calculation is 
 
 x 96,540 = 422,000 coulombs per pound of lead. 
 
 12. Electrolysis in the Daniell Cell. In the Daniell 
 type of primary cell the chemical reaction is a very 
 simple one : Copper is deposited as metal from cop- 
 per sulphate solution ; zinc (metal) passes into solu- 
 tion as zinc sulphate. 
 
 Zn + CuSO 4 = ZnSO 4 + Cu. 
 
SOME ELECTEOCHEMICAL FUNDAMENTALS 19 
 
 The reaction is indicated in the diagram of Fig- 
 ure 4. 
 
 How many ampere-hours can we get from a Daniell 
 cell per pound of zinc? 
 
 The atomic weight of zinc is 65.4, and it acts as a 
 bivalent ion, so we will get 96,540 coulombs from 
 
 ZINC 
 
 1 
 
 PART 
 
 ITION c 
 
 ra 
 
 op 
 
 PER 
 
 
 ZINC 
 
 su 
 
 LPHATE 
 
 COPPER 
 
 s 
 
 ULPHATE 
 
 
 SO 
 
 LU 
 
 riON 
 
 SOI 
 
 in 
 
 P 
 
 ION 
 
 
 65.4 
 
 FIG. 4. Diagram of the reaction in a Daniell cell. 
 
 = 32.7 gm. of the metal. A pound is 453 gin. 
 
 Per pound of zinc we can therefore obtain 
 453 
 
 32.7 
 
 x 96,540 = 1,337,000 coulombs, 
 
 and since an ampere-hour is 3600 coulombs, one 
 pound of zinc will give 372 ampere-hours. 
 
 We can get this same number of ampere-hours per 
 pound of zinc in any galvanic arrangement whatever, 
 and it requires the same number to deposit a pound 
 of zinc electrolytically from its solution. 
 
20 STORAGE BATTERIES 
 
 How much copper sulphate must we supply dur- 
 ing this time to keep the copper side of the Daniell 
 cell active ? 
 
 Its formula is CuSO 4 + 5 H 2 O, and the total weight 
 equivalent to 65.4 gm. of zinc is therefore 249 gm. 
 Copper ion passes through a bivalent step in its 
 deposition as metallic copper, so it requires -|^ = 
 124.5 gm. of "blue vitriol" to give 96,540 coulombs. 
 To furnish 1,337,000 coulombs we must use 
 
 x 124.5 = 1725 gm., or 3.8 Ib. 
 
 Since all our electrochemical reactions are really 
 only chemical ones arranged in such a way that they 
 furnish or require a current of electricity, we could 
 calculate the amount of copper sulphate needed for 
 our run with the Daniell cell directly from the pre- 
 ceding figure for the deposition of metallic copper in 
 the purification process. 
 
 />o (* 
 
 A pound of blue vitriol contains = 0.255 Ib. 
 
 of copper, and we found that it required 382 ampere- 
 hours to deposit a pound of copper. The same 
 quantity of electricity will pass through the Daniell 
 cell with a pound of copper, and to get 1,337,000 
 coulombs from the cell we must deposit 
 
 1*887.000 = Q.972 Ib. of copper. 
 382 x 3600 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 21 
 
 This amount of copper is contained in 3.8 Ib. of blue 
 vitriol. 
 
 13. Electrochemical Units. It is evident that the 
 96,540 coulomb unit which the electrochemist is 
 obliged to use is a rather cumbrous one and leads to 
 large numbers. If we had the choosing of our own 
 unit we would of course make 96,540 coulombs = 1 
 electrochemical unit of quantity of electricity, and 
 then the calculation for copper would look like 
 this : 
 
 63. 6 g. Cu~2 units, 
 1 Ib. copper ~ 14. 24 units, 
 
 and for zinc it would be equally simple. But elec- 
 trochemistry is not a big anough branch of science 
 to be able to dictate units to the dynamos which fur- 
 nish the current, and we must be content to accept 
 the electrical engineer's unit. 
 
 In every case it is necessary to know the complete 
 and exact chemical reaction with which we are deal- 
 ing before we can apply our law, for it very often 
 happens that metals carry different multiples of the 
 unit quantity of electricity with them in different 
 chemical reactions, and they sometimes complicate 
 things still further by changing the number of units 
 carried as the concentration of the solution from 
 which they are deposited is changed. But if we 
 arrange to have the conditions in the cell constant 
 
22 STORAGE BATTERIES 
 
 and have once found the correct chemical reaction, 
 the law can always be applied without fear of error. 
 
 14, Electromotive Force. Faraday's law gives a 
 complete statement of the quantity of electricity 
 which accompanies the reaction of gram-equivalent 
 weights of various substances in any galvanic com- 
 bination or electrolytic cell. But it can tell us no 
 more than this. It says nothing about the amount 
 of work we can do with this amount of electricity, 
 nor about the amount of work we must do to cause 
 the separation of a gram-equivalent of a metal from 
 solution. The driving force of the chemical reaction 
 and the corresponding electromotive force of the cell 
 are specific for each reaction and cannot be calcu- 
 lated by any inclusive general law. The driving 
 force is called the chemical potential of the reaction, 
 and it can be very conveniently and accurately 
 measured by coupling the reaction into the form of a 
 galvanic cell and measuring the electromotive force. 
 
 Very early in the development of galvanic elec- 
 tricity Volta found that the various metals could be 
 arranged in a series, such that the most favorable 
 combinations for producing current were to be made 
 by choosing metals as far apart as possible in the 
 series. Better results were obtained from cells using 
 zinc and copper than from those using iron and copper, 
 or zinc and tin. We know now that not only the 
 metal, but the whole reaction must be taken into ac- 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 23 
 
 count, but the " Voltaic series of the metals," as it is 
 called, gives an approximate view of the matter. 
 
 It was found very early that more work could be 
 obtained from a pound of zinc in a cell where copper 
 is deposited at the cathode, than from a cell where 
 iron is used in the same way. The same quantity of 
 zinc is used up in each case, and since we get different 
 results in the various combinations, there must be 
 some other factor of importance and some other law 
 besides Faraday's to be considered. 
 
 Suppose we have a very large Daniell cell, where 
 the reaction 
 
 Zn + CuSO 4 = Cu + ZnSO 4 
 
 is taking place. We choose a big cell in order that 
 we may send 96,540 coulombs through it without any 
 danger of changing the concentrations in the differ- 
 ent parts of the cell. When this quantity of elec- 
 tricity has passed through the cell, 32.7 gm. of zinc 
 have gone into solution at the anode and have become 
 zinc ion. During this same time 31.8 gin. of cop- 
 per ion have changed into metallic copper. The 
 SO 4 part of the reaction has not been affected at all. 
 Electrochemically we could write the reaction 
 
 15. Ions. The small sign + indicates that the sub- 
 stance carrying them is an ion and that it moves 
 toward the cathode it is a cation. Two of them 
 
24 STORAGE BATTERIES 
 
 indicate that this particular ion carries with it per 
 gram-atom twice the unit quantity of electricity 
 (2 x 96,540 coulombs). The SO 4 ion (SO 4 ), which 
 remains unchanged in this particular case, carries 
 two times the unit quantity also, but toward the 
 anode. It is an anion. And in chemical parlance 
 both of these are divalent ions. 
 
 Now suppose we connect the cell with an external 
 source of current and send 96,540 coulombs through 
 it in the opposite direction. 32.7 gm. of zinc will 
 deposit on the zinc plate, now the cathode, and 
 31.8 gm. of copper will go into solution at the copper 
 plate, now the anode. By the time we have sent 
 our unit quantity through the cell it has been com- 
 pletely restored to its original condition. The case 
 of the Daniell cell is theoretical rather than practical, 
 for zinc does not behave very well when it is forced 
 out of solution. It grows in sponge and trees and 
 often reaches across to the other plate and short- 
 circuits the cell. But we have chosen our cell so 
 large that this does not bother us, and the Daniell 
 cell can be considered completely reversible in its re- 
 actions. It might therefore be used as an accumu- 
 lator. 
 
 16. Other Electrical Units. Besides the coulomb, 
 we have been supplied with two other units, and these 
 fortunately fit electrochemical needs pretty well with- 
 out requiring so many figures. One of these is the 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 25 
 
 volt, the unit of difference of potential, and the other 
 is the ohm, the unit of resistance. 
 
 The following terms and relations are important: 
 
 Coulomb (<?) Quantity of electricity. 
 
 Ampere (i) Current. 
 
 Volt (0) Difference of potential. 
 
 Joule (/) Energy. 
 
 1 volt-coulomb = 1 joule. 
 
 watt = rate of furnishing energy. 
 1 volt-ampere = 1 watt. 
 1 joule per second = 1 watt. 
 
 3600 coulombs = 1 ampere-hour. 
 1000 watts = 1 kilowatt, KW. 
 746 watts = 1 horse power, H.P. 
 746 x 3600 joules = 1 horse-power hour, H.P.H. 
 
 Beside our units we can also get instruments for 
 measuring them from the electromagnetic branch of 
 electrical science. If we borrow a voltmeter from 
 our neighbor, the electrical engineer, and apply its 
 terminals to our Daniell cell, we measure what is 
 called its electromotive force in volts. The volt- 
 meter reads about 1.1 volts. 
 
 17. Electrical Energy. We can now calculate the 
 electrical energy obtainable from this cell. By ex- 
 pending 32.7 gm. of zinc and 31.8 gm. of copper ion 
 we can expect to get 1.1 X 96,540 volt-coulombs 
 (joules) with which to do useful work outside the 
 
26 STOBAGE BATTERIES 
 
 cell. If we are sending current through the cell in 
 the opposite direction, we can reverse the reaction 
 and return the cell to its original condition by an 
 expenditure of the same amount of work. 
 
 We can now calculate both work and power. 
 How many horse-power hours can be obtained from 
 a Daniell cell per pound of zinc ? 
 
 32.7 gm. of zinc give 
 
 1.1 x 96,540 = 106,300 joules. 
 1 H.P.H. is 
 
 746 x 3600 = 2,683,000 joules. 
 1 Ib. of zinc will give 
 
 ^! x 106,300 = 1,472,000 joules. 
 oZ.t 
 
 1 Ib. of zinc will therefore give 
 
 1,472,000 = Q55HRH 
 
 2,683,000 
 
 Or, we must use a little less than 2 Ib. of zinc per 
 horse-power hour. 
 
 Other forms of zinc-consuming cells were formerly 
 much in use, and some of these had electromotive 
 forces as high as 2 volts. One of these would re- 
 quire only 
 
 Ib. of zinc to produce 0.55 H.P.H., 
 
 a 
 
 and we would need only 1.07 Ib. of zinc per horse- 
 power hour in the case of one of these cells. 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 27 
 
 Resistance. The unit of resistance has an inter- 
 esting and simple relation to the units of current 
 and voltage. What is called Ohm's law states 
 
 electromotive force in volts 
 current in amperes = - ; - = 
 
 resistance in ohms 
 
 Or, an electromotive force of 1 volt will send a cur- 
 rent of 1 ampere through a circuit having a resist- 
 ance of 1 ohm. 
 
 A column of mercury 106.3 cm. long and one 
 square millimeter in cross-section has a resistance 
 of 1 ohm. A good-sized copper wire has a resistance 
 of an ohm for a length of a thousand feet or so. 
 
 18. If it is desired to furnish 0.5 H.P. from a 
 single Daniell cell, at what rate must zinc dissolve ? 
 
 0.5 H.P. is 373 watts (volt-amperes) (volt-cou- 
 lombs per second). Our cell gives 1.1 volts and 
 must therefore give a current of 349 amperes (349 
 coulombs per second). 
 
 32.7 gm. of zinc furnish 96,540 coulombs. 
 
 349 
 
 We must therefore furnish - x 32.7 gm. of 
 
 96,540 
 
 zinc per second; 0.118 gm. of zinc per second or 
 425 gm. per hour will give 0.5 H.P. 
 
 If we set up a whole row of Daniell cells as a 
 battery, and draw our 0.5 H.P. from this, we will be 
 much nearer the practical truth, for it would take 
 an enormous cell to give 350 amperes, owing to the 
 
28 STORAGE BATTERIES 
 
 rather high internal resistance caused by the porous 
 cup. 
 
 19. Cells in Series and Parallel. Suppose we have 
 100 cells in our battery, each with an electromotive 
 
 FIG. 5. Cells connected in parallel. The effect is the same as though 
 all the plates were placed in one large cell. 
 
 force of 1.1 volts. If they are connected so that the 
 zinc of each cell is fastened to the copper of the next 
 
 FIG. 6. Cells connected in series. 
 
 one as shown in Figure 6, their electromotive forces 
 will add, and our whole battery will have an electro- 
 motive force of 110 volts. To get 373 watts or 0.5 
 H.P. we need to draw only -f^o = ^4 amperes from 
 
SOME ELECTROCHEMICAL FUNDAMENTALS 29 
 
 our battery, and this would not be an unreasonable 
 current for large Daniell cells. You will notice that 
 the total weight of zinc dissolved and copper de- 
 posited is exactly the same as though it had taken 
 place in one huge cell, though now it is distributed 
 over 100 cells. 
 
 In our very first problem, on page 17, where we 
 calculated the current required to deposit a ton of 
 copper per hour by electrolysis, we obtained a value 
 for a single huge cell. Practically copper would 
 never be purified in that way, for the voltage nec- 
 essary to deposit copper is not more than 0.3 volt, 
 and it is not feasible to build a generator to work at 
 that voltage. Besides, it is not necessary, as it is just 
 as well to work a number of electrolytic cells in 
 series like a battery. In many copper refineries 200 
 such cells are used and a current of perhaps 4000 
 amperes is sent through the whole series. This re- 
 quires a generator capable of giving this number of 
 amperes at about 60 volts, and the power required is 
 therefore 240 KW. The copper deposited has the 
 same weight as though 800,000 amperes were sent 
 through a single cell, and is therefore a little over a 
 ton per hour. 
 
CHAPTER III 
 
 ABOUT IONS 
 
 20. All electrochemical processes follow Faraday's 
 law absolutely as far as any one can find out, and 
 they therefore invariably depend on ions in the sim- 
 ple sense in which Faraday himself used this term 
 (page 12). There is, nowadays, a whole field of 
 science which has to do with the study of the ions 
 of gases, and some of the most interesting and sug- 
 gestive of all modern developments are being made 
 in this field. These hypotheses and theories, now 
 just being cleared of their mysteries and made a 
 part of general science, will no doubt some day be- 
 come a safe and useful basis for the study of electro- 
 chemistry. But for the present, at least, we will be 
 safer if we stick close to Faraday, and call our ions 
 "... those bodies which can pass to the electrodes." 
 We shall meet with rather strange ones when we 
 come to the lead storage cell itself, and some general 
 knowledge of the simpler sorts will be found a useful 
 introduction. 
 
 21. Conductance by Ions. In the first place, the 
 ions are already there in a solution of a metallic salt 
 
 30 
 
ABOUT IONS 31 
 
 or in a molten electrolyte. They are not produced 
 by the action of the current. And they are able to 
 begin carrying electricity toward the electrodes as 
 soon as the circuit is closed. It is also certain that 
 they do all the work of carrying the current through 
 the cell. These last two statements are merely an- 
 other way of stating the extreme accuracy of Fara- 
 day's law. No current seems to pass through an 
 electrolyte unaccompanied by the movement of an 
 exactly equivalent amount of each of two ions 
 an anion and a cation. 
 
 Water itself is a conductor of the electrolytic kind. 
 It has a high resistance, to be sure, but it does con- 
 tain small concentration of the ions H + and OH~. 
 It is chiefly remarkable for the aid it gives to other 
 substances in the process of ionization. Metallic 
 salts, and acids and bases as well, are famous carriers 
 of current when they are in solution in water, and 
 they always follow Faraday's law. Many of them 
 are also good conductors in the molten state, and 
 their ions pass to the electrodes under these circum- 
 stances just as well as they do in water. 
 
 22. Chemical Facts connected with Ions. Since 
 Faraday offered his suggestion about the names to 
 be used in describing the process of electrolysis, and 
 gave to the ions their simple definition, much of 
 chemistry has been restated. The general facts 
 about solutions, and especially those which have to 
 
32 STORAGE BATTERIES 
 
 do with ions, even apart from their power of carry- 
 ing a current, have been brought together into one 
 of the most united and easy branches of the science 
 of chemistry. Let us consider a few of the simpler 
 generalizations. All acids in water solution contain 
 hydrogen ion, H + , and their acid properties are de- 
 pendent on its presence and are measured by its 
 concentration. All bases in solution contain OH~ 
 (hydroxyl ion). Solutions of metallic salts usually 
 contain an ion produced from the metal, like Cu ++ , 
 Zn ++ , Ag + , K+, Al +++ , Pb ++ , and an ion formed from 
 the other part of the salt Cl", Br~, NO 3 ~, C1O 4 ~, 
 SO 4 , CrO 4 . We quickly get into the habit of 
 thinking about the particular ion we want for any 
 special set of properties it may have, and I have 
 often heard a student just beginning chemistry 
 one who had not the slightest idea of Faraday's law 
 or of any electrochemical theory say to his neigh- 
 bor, " Pass the copper bottle," when he meant copper 
 sulphate or nitrate or any other soluble copper salt. 
 He needed copper ion for his experiment, and in 
 the same way a more advanced student will ask, 
 "Have you some acid?" when he wants hydrogen 
 ion. In neither of these cases does the other ion, 
 which is sure to be present, interest the chemist, pro- 
 vided it has not some special peculiarity of its own. 
 But if the other ion can form a difficultly soluble salt 
 with one of those in his test tube, he will be more ex- 
 
ABOUT IONS 33 
 
 plicit in stating the kind of copper salt solution or the 
 kind of acid solution he needs. If you will think over 
 your own experiences with solutions of acids, bases, 
 and metallic salts, you will see that the chemistry of 
 aqueous solutions can all be brought into the easiest 
 form by a classification of the properties of ions. 
 Besides this, one only needs knowledge of the solu- 
 bilities of salts to have a pretty full command of the 
 facts about aqueous solutions. 
 
 This same statement is almost equally true of 
 electrochemistry. A current only passes through 
 a solution when two ions carry it. These ions pass 
 back and forth at the electrodes and send their quota 
 of electricity out through the wires of the circuit as 
 a current. Each ion travels through the electrolyte 
 with its own special velocity and carries a fraction 
 of all the current flowing which is proportional to 
 this velocity. If we had space for a really complete 
 theory of galvanic cells, we would need careful study 
 of the changes which take place at various parts of 
 such a cell as the result of differences in ionic migra- 
 tion velocity. We should at the same time find 
 some very simple and interesting generalizations 
 about the part played by the individual ions in elec- 
 trolytic conductivity. 
 
 23. The Ionic Theory. In some of our explanations 
 we shall feel the need of a much more minute and 
 detailed picture of what happens than can be ob- 
 
34 STORAGE BATTERIES 
 
 tained by adhering closely to Faraday's careful defi- 
 nition of an ion. We shall need to bring in occa- 
 sionally a more hypothetical, or rather theoretical, 
 ion than Faraday's. This does no harm, for more 
 and more proof of the general usefulness and truth 
 of the general theory of ions is being accumulated 
 every day. The step from Faraday to the theoretical 
 picture is not a great one. 
 
 Ions are, in this picture, parts of molecules, each 
 one connected with a definite and constant quantity 
 of electricity, either positive or negative. If we 
 collect enough of these little carriers to make a 
 gram-equivalent, arid send them along to discharge 
 against an electrode, 96,540 coulombs will pass this 
 surface and flow out through the wires of the exter- 
 nal circuit. At the same time enough of the ions of 
 opposite sign to carry the same quantity of electric- 
 ity will have been discharged at the other electrode. 
 Faraday's ion was singular, and we shall refer to an 
 ion as it when we need no further statement than 
 that involved in Faraday's law. When we want to 
 describe the more complicated changes about the 
 electrodes, we shall make use of the other picture and 
 refer to the ions of copper or silver, using the plural 
 and picturing an electrolyte filled with them, each 
 carrying its unit quantity of electricity, and all 
 swarming toward the electrodes when current passes. 
 
 The electrolyte which is used in a storage cell is 
 
ABOUT IONS 35 
 
 a rather concentrated solution of sulphuric acid in 
 water. It contains considerable concentrations of the 
 ions H + and SO 4 , and these do the carrying of the 
 current across the space between the electrodes. 
 During the passage of current in either direction, H + , 
 the cation, moves toward the cathode, whichever 
 plate this may happen to be, and at the same time 
 SO 4 , the anion, moves toward the anode. The 
 direction of flow of the current is reversed when the 
 cell passes from charge to discharge and the direction 
 of the motion of the ions changes also. 
 
 24. Migration Velocities. If both the ions moved 
 through the electrolyte with the same velocity, there 
 would never be any difference in ionic concentrations 
 in any part of the cell. It was found a long time ago 
 that considerable differences are set up during elec- 
 trolysis, and from measurements of these concentration 
 differences it was found possible to calculate the 
 relative migration velocities of all the ions. Later 
 the actual velocity with which an ion passed through 
 the solution was measured, and, of course, as soon 
 as the real velocity of motion of one single ion was 
 found, all the other velocities could be calculated from 
 the relative numbers found by means of the concen- 
 tration differences. 
 
 H + ion moves through the solution about five times 
 as fast as SO 4 ~~. Figures 7 and 8 show the condition 
 of things in the cell (7) before any current has 
 
36 STORAGE BATTERIES 
 
 passed, and (8) after 6 SO 4 ions have separated at 
 the anode. 
 
 We must remember that the number of + and 
 ions must always be the same at any point in the cell. 
 
 ooooooooiooooojoooooooo 
 
 I 1 
 
 OOOOOOOOOOOOOOOOlOOOOOOOOOODOOOOOOOOOOOOOOO 
 
 I I 
 
 FIG. 7. Diagram of ion concentrations in an electrolytic before cur- 
 rent begins to flow. 
 
 The attraction of the -f and charges on these very 
 small bodies is so great that we can never hope to get 
 more than the most minute concentration of any one 
 kind of ion off by itself, and we have very good evi- 
 dence that our solutions are everywhere electrically 
 
 oo 
 oo 
 oo 
 
 o o o ioooooiooooooo 
 
 000000 1000000000000000000000000 
 
 I I 
 
 FIG. 8. The cell of Figure 7 after six SOr ~ ions have left the electro- 
 lyte at the anode. 
 
 neutral, which means that the concentration of + and 
 ions is everywhere the same. 
 
 This statement suggests the question : How can a 
 slow-moving ion get to its electrode fast enough to 
 keep up the supply there ? 
 
 And the answer is that it cannot keep the concen- 
 tration at its original value. During electrolysis the 
 
ABOUT IONS 37 
 
 electrolyte about the place where the slow-moving 
 ion is going out of solution is depleted. Its concen- 
 tration becomes less and less, until diffusion finally 
 stops the dilution. In the meantime the fast-moving 
 ion has become heaped up about its electrode. The 
 diagrams in Figures 7 and 8 will make this clear. 
 
 When the current begins to flow, the H + ions move 
 toward the right, and are removed at the cathode 
 (either as gas or by some secondary reaction), and at 
 the same time the SO 4 ~~ ions move toward the left, 
 and are removed at the anode. The H + ion moves 
 five times as fast as the SO 4 ion. By the time six 
 SO 4 ions have passed through the electrode, 12 
 hydrogen ions have gone out of solution. 10 H + 
 ions have in this period of time entered the region 
 about the cathode, and one SO 4 ~~ ion has entered the 
 region about the anode. The region in the center of 
 the cell has not changed in concentration, but the 
 parts of the cell on both sides of it have changed, 
 and the relative change has been a large one. 
 
 It will be seen at once that the relative migration 
 velocities are inversely as the losses about the electrodes. 
 The cathode has lost one, the anode has lost five, and 
 the migration velocities are as five (cation) to one 
 (anion). This means, too, that five sixths of all the 
 electricity that has passed through the cell has been 
 carried through by the cation, and only one sixth by 
 the anion. 
 
STORAGE BATTERIES 
 
 25. Ionic Reaction. In cells of the Daniell type 
 the ionic changes are very simple. A single cation 
 carries the current toward the cathode, and leaves 
 the electrolyte at that electrode, while a single anion 
 attends to all the cell activities at the anode. The 
 concentration changes which result from taking away 
 material from the electrolyte at the cathode and 
 from adding it at the anode are indicated in Figure 9. 
 
 In our storage 
 
 FIG. 9. 
 
 Concentration changes in the Daniell 
 cell. 
 
 we nave a 
 much more com- 
 
 plicated system. 
 H + and SO 4 " 
 do not pass in 
 and out at the 
 electrodes, and 
 the really fun- 
 damental cell 
 activities are cared for by other ions. The ions 
 which are active at the electrodes do not travel a 
 measurable distance into the main body of the elec- 
 trolyte. We must therefore expect two sets of ionic 
 reactions in a storage cell those between the con- 
 ducting ions and the active electrode ions and those 
 between the active ions and the substances of the 
 electrodes. We shall examine some possible and 
 plausible theories in Chapter VIII. 
 
CHAPTER IV 
 THE FUNDAMENTAL CELL REACTION 
 
 26. An active storage cell contains two quite 
 different kinds of plates immersed in a rather strong 
 solution of sulphuric acid. In storage battery par- 
 lance one of the plates is called the " negative " and 
 the other the "positive." In spite of the fact that 
 the cell reaction is completely reversed each time the 
 cell is charged and discharged, so that each plate is 
 really positive half the time and negative the other 
 half, these terms are about as good as any that can 
 be found. Anode and cathode are no more definite. 
 Lead plate and peroxide plate could very well be 
 used, and by " the positive plate " is meant the one 
 which has lead peroxide as its chief constituent. 
 The " negative " is the one which has as its chief 
 constituent spongy, finely divided metallic lead. 
 
 In order to apply the laws which we have developed 
 for galvanic cells in general to the case of the lead 
 accumulator we must first of all know exactly what 
 chemical reaction takes place when current flows 
 through the cell. 
 
40 STORAGE BATTERIES 
 
 27. The Lead Cell Reaction. The complete re- 
 action of a lead accumulator, working under ordinary 
 conditions of service, is 
 
 Pb + Pb0 2 + 2 H 2 SO 4 2 PbSO 4 + 2 H 2 0, 
 
 and the sign ^ indicates that it is perfectly revers- 
 ible. During discharge the reaction goes from left 
 to right. It takes place of its own accord and the 
 cell furnishes electrical energy which can be utilized 
 for work outside the cell. Under these circumstances 
 the sponge lead plate is the anode, lead goes into 
 solution as lead ion, Pb ++ , here, and the peroxide 
 plate is the cathode lead peroxide is reduced to 
 lead ion there. Everywhere in the cell the lead ion 
 which is produced finds SO 4 handy, and since lead 
 sulphate is a difficultly soluble substance, the two 
 ions unite to form non-ionic lead sulphate, which soon 
 saturates the solution and precipitates in solid form. 
 
 28. Effect of High Current Density. It has been 
 said that the reaction is completely reversible as long 
 as the currents sent through the cell are anywhere 
 near the limits of practical operation. If a very 
 large current is sent through a cell with very small 
 electrodes, secondary effects appear in measurable 
 amount. Persulphates are formed and some other 
 complex ions make their appearance. 
 
 Ordinary Currents. In ordinary practice all these 
 effects can be wholly neglected. If we are working 
 
THE FUNDAMENTAL CELL REACTION 41 
 
 with a comparatively large cell, we can take out the 
 electrochemical unit of quantity of electricity with- 
 out greatly changing the distribution of materials in 
 the cell, and by the time 96,540 coulombs have been 
 sent through, %-^i- gm. of lead have been changed 
 to lead ion at the anode (the lead plate) and -2-jp 
 gm. of lead peroxide have become lead ion at the 
 cathode (the peroxide plate). At each plate these 
 amounts of lead ion have found sulphate ion waiting 
 for them and equivalent amounts of lead sulphate 
 have been precipitated -2-|& gm. at each plate. 
 Nothing has yet been said about the nature of the 
 ion which travels back and forth at the peroxide 
 plate. Whatever this ion may be, it is evident that 
 its decomposition into Pb" 1 " 1 " leaves 2 O behind, and 
 from the reaction it can be seen that the sulphuric 
 acid which reacts with the lead ions furnishes enough 
 hydrogen to produce 2 H 2 O at the positive plate. 
 
 29. Reaction during Charge. If now we charge 
 the cell, after a period of discharge, we merely re- 
 verse everything that happens during discharge. 
 The peroxide plate is now the anode. Here lead 
 ion goes out of solution leaves the ionic state and 
 with the aid of the water in the electrolyte becomes 
 lead peroxide. At the lead plate, which is now the 
 cathode, lead ion changes into metallic lead, just as 
 at any other simple metal-ion electrode. At both 
 plates it is the lead sulphate which furnishes the 
 
42 STORAGE BATTERIES 
 
 constantly renewed supply of lead ion for the reaction. 
 This seems a little difficult at first glance, for is not 
 lead sulphate an insoluble substance ? If it were 
 really insoluble, of course our cell could not work in 
 this way, but it is not. It has a perfectly definite 
 and well-known solubility, and while the concentra- 
 tion of lead ion in the solution is very small indeed, 
 it must be remembered that the reservoir of lead sul- 
 phate is very near at hand, so that the supply of lead 
 ion has only " molecular " distances to travel to the 
 point where it is to be used. 
 
 30. Proof of the Formula. This fundamental re- 
 action has been tested with the greatest care by many 
 investigators. There are evidently several things 
 to be proven and there are several ways of proving 
 some of them. 
 
 What we must know is this. When we pass 96,540 
 coulombs through the cell in the discharging direction, 
 is the result the formation of -%$- gm. of lead sul- 
 phate and -^- gm. of water? During this same 
 period has the lead plate lost ^p- gm. of metallic 
 lead and has the peroxide plate lost %-%& gm. of lead 
 peroxide? And during the same period has the 
 electrolyte decreased its acid content by 1J& gm. 
 of H 2 SO 4 ? 
 
 These points must be proven for the discharge re- 
 action. We must also prove that the reaction is per- 
 fectly reversible and that during charge exactly the 
 
THE FUNDAMENTAL CELL EE ACTION 
 
 43 
 
 same amounts of exactly the same materials react, 
 and no others, the reaction being now from right 
 to left. 
 
 The change in the content of lead, lead peroxide, 
 and lead sulphate in the plates must be found by 
 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 ) PEROXIDE 
 
 528* 
 
 
 
 ^ 
 
 ^ 
 
 
 
 
 
 
 
 
 ^ 
 
 ^ 
 
 
 
 
 
 
 
 ^ 
 
 ^ 
 
 "^^ 
 
 
 ^ 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 
 < 
 
 ^ 
 
 
 
 
 
 
 
 R ? g 5 
 
 3V3T dO 3DVJ.N3OU 
 
 
 
 
 ^ 
 
 - ^**" 
 
 
 
 
 
 "^ 
 
 ^ 
 
 ^^ 
 
 
 
 
 ^ 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 ^^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 "^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 8" 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 t 34 56 7 6 9 10 II 14 13 14 15 
 
 AMPERE-HOURS 
 
 FIG. 10. Change in the PbO 2 content of the peroxide plate during 
 charge and discharge. 
 
 careful chemical analysis of plates after various times 
 of charge and discharge. 
 
 Figure 10 shows the results obtained by analyzing 
 the active material of the positive plate after various 
 times of charge and discharge. It will be seen that 
 the content of the plate in peroxide is accurately pro- 
 portional to the amount of electricity which has 
 passed through the cell, just as required by our fun- 
 
44 
 
 STORAGE BATTERIES 
 
 1.15 
 
 damental reaction. Similar analyses of the active 
 material of the negative plate show similar curves 
 for the lead content, and the lead sulphate content has 
 been found to be an equally good indication of the 
 condition of the cell as to charge or discharge. 
 
 The easiest of 
 all the changes 
 to follow is that 
 in the electrolyte. 
 Here we can fol- 
 low the change of 
 concentration by 
 merely measur- 
 ing the density 
 of the acid from 
 time to time. 
 This is shown in 
 Figure 11. Evi- 
 dently there will 
 be a lag of density behind the value properly belong- 
 ing to any given time after charge or discharge has 
 begun. For the acid is being formed or used up in- 
 side the plate, and must diffuse in or out as the re- 
 action goes on. This is a comparatively slow process, 
 and we must therefore expect that just at the begin- 
 ning of either charge or discharge the acid density 
 will remain constant, even though some current has 
 passed. The curves of Figure 12 are for the very 
 
 10 20 30 40 50 
 
 AMPERE-HOURS OF CHARGE AND DISCHARGE 
 
 FIG. 11. Change in acid density during 
 charge and discharge. 
 
THE FUNDAMENTAL CELL REACTION 
 
 45 
 
 beginning of charge and discharge, and they show 
 this lag effect very clearly. These are really pieces 
 which belong at the beginning of the curves of Figure 
 11, but they would not show if plotted in the time 
 units of that figure. In their own 
 diagram the time axis is greatly 
 drawn out to show the effect more 
 clearly. 
 
 When we have once decided that 
 this fundamental reaction really 
 represents what happens in a lead 
 accumulator during its practical 
 operation, we have made a great 
 step, and with the aid of the gen- 
 eral theory developed in earlier 
 chapters we can go a long way 
 
 AMPERE-HOURS 
 
 toward explaining the effect of va- FIG. 12. First part 
 
 f .-, ,! ofcurvesofFig.il. 
 
 riOUS factors on the Cell. Enlarged scale. 
 
 It has taken a long time to gather 
 the evidence which proves the correctness of our fun- 
 damental cell reaction, and there are probably a good 
 many storage battery experts who still feel doubtful 
 as to its completeness. Many of them have wished 
 to introduce intermediate steps, such as the forma- 
 tion of lead persulphate or persulphuric acid at the 
 peroxide plate during charge. It is evident that as 
 long as the processes assumed are reversible and lead 
 to the same final formula as the one we are using, any 
 
46 STORAGE BATTERIES 
 
 number of intermediate reactions could be assumed 
 without affecting the validity of our reaction in the 
 least. But even this opportunity for introducing 
 hypotheses and analogies is removed when we ex- 
 amine the electromotive force equations for the cell, 
 which we shall take up in a future chapter. When 
 all the evidence is taken into consideration, our fun- 
 damental reaction seems to be proven. 
 
CHAPTER V 
 
 THE ACTIVE IONS 
 
 31. It does not take any training in theoretical 
 science to make it quite clear that the actual carry- 
 ing of current through the storage cell is done by 
 the sulphuric acid, and we can be very sure that it is 
 done by the ions H + and SO 4 ~~. Both lead and 
 lead peroxide are so very slightly soluble in sulphuric 
 acid that their presence in the electrolyte can hardly 
 be shown by analytical means. The concentration 
 of the ions which pass back and forth at the elec- 
 trodes must always be exceedingly minute, and this 
 small amount of ion cannot have the least relation 
 to the huge current that can be sent through a large 
 storage cell. 
 
 In this respect the storage cell differs from most 
 galvanic cells. And it is precisely in this very point 
 that the remarkable properties of the lead cell as 
 an accumulator are all bound up. If the ion of the 
 electrodes reached any large concentration, we would 
 have all the difficulties in the way of trees and short 
 circuits which appear in most cells when we try to 
 reverse them and use them as accumulators. The 
 
 47 
 
48 STORAGE BATTERIES 
 
 active material would soften and move all about the 
 cell, growing at the favored points and not at the 
 others. In the lead cell material produced during 
 either charge or discharge is deposited "right in its 
 tracks," to use a homely expression, and the plates 
 preserve their condition. 
 
 32. What Ions carry Current? But if the current 
 is all carried by ions which do not pass back and 
 forth at the electrodes, there must somewhere in the 
 cell be a loading and unloading of electricity from 
 ion to ion, and the complete expression for the cell 
 reaction should show this transfer. As a matter of 
 fact it cannot be shown by any purely chemical 
 means, nor is it at all necessary to try. The reaction 
 we have adopted is the necessary and complete ex- 
 pression for everything that takes place in the cell, 
 from a merely chemical point of view. We can get 
 some theories which fit the facts pretty well, and 
 it will be seen a little later that these theories are 
 subject to rather severe tests of a quantitative sort. 
 At any rate, it is always interesting to develop the 
 possible theories for such a chemically unattackable 
 problem, and so we will examine one of the most 
 plausible. 
 
 33. At the Negative Plate. Let us start with the 
 negative plate. During discharge this is the anode 
 of the cell. The acid is doing the carrying of current 
 through the cell, and SO 4 ion is therefore moving 
 
THE ACTIVE IONS 49 
 
 toward the anode. The electrode is probably re- 
 versible with respect to Pb ++ ion, and lead goes into 
 solution as Pb ++ in proportion to the amount of cur- 
 rent which passes through the electrode. It never 
 gets far, for the SO 4 ~~ is moving toward it, even if 
 there were not enough in the electrolyte, and lead 
 sulphate is precipitated in the very spot where the 
 lead ion was formed from the metal. The only 
 thing that is left over after this reaction has been 
 completed is hydrogen ion, H + , and this is doing the 
 carrying of current through the electrolyte toward 
 the cathode, in this case the peroxide plate. If 
 we can take this extra H + into our reaction at the 
 cathode, we will be able to reach a balance, and our 
 theory will at least be a possible one. 
 
 Leaving aside for the moment the matter of the 
 ions, we can say with certainty : 
 
 Sulphuric acid carries the current across the space 
 from plate to plate. The acid is separated during 
 this time into 2 H and SO 4 . 
 
 For discharge 
 
 Pb + SO 4 -> PbSO 4 . 
 Pb0 2 + H 2 + H 2 S0 4 -> PbS0 4 + 2 H 2 O. 
 In sum 
 
 Pb + Pb0 2 + 2 H 2 S0 4 -> 2 PbS0 4 + 2 H 2 O. 
 
 34. At the Peroxide Plate. It does not require a 
 very vivid scientific imagination to discover a simple 
 
50 STORAGE BATTERIES 
 
 and reversible reaction which takes in the ionic 
 change at the lead plate. 
 
 Pb _> Pb ++ . 
 
 Metal 
 
 Solid 
 
 For the peroxide plate we need a more complicated 
 set of changes, and Liebenow has suggested an ion 
 which fits the facts very well indeed. Suppose the 
 peroxide plate to be reversible with respect to the 
 PbO 2 ion. We then have at this plate during 
 discharge 
 
 PbO 2 - PbO 2 -~, 
 
 Solid 
 
 PbO + 4 H + -> Pb + ^ + 2 HO, 
 
 Solid 
 
 and if we add the reactions at the lead and lead 
 peroxide plates, we get 
 
 Pb + Pb0 2 + 2 S0 4 ~ + 4 H+ * 2 PbS0 4 + 2 H 2 O, 
 
 Metal Solid Solid ' 
 
 which is our fundamental reaction 
 
 Pb + Pb0 2 + 2 H 2 SO 4 2 PbS0 4 + 2 H 2 O. 
 
 This is completely reversible, and it will also be 
 found that our separate ionic reactions represent 
 completely reversible changes. 
 
 35. Diagrams of Charge and Discharge. The accom- 
 panying diagrams may make all this still clearer. 
 The cell is discharging it is furnishing current 
 
THE ACTIVE IONS 51 
 
 for use in the external circuit. The current is flow- 
 ing into the cell at the lead plate, which is therefore 
 the anode. Here metallic lead passes through the 
 electrode (Fig. 13) and changes into lead ion, Pb ++ , 
 carrying 96,540 coulombs with it for each 2-^1 gm. of 
 lead that go into solution. The lead ion has hardly 
 passed the electrode before it meets with SO 4 in 
 the electrolyte (Fig. 14). Lead sulphate being so 
 slightly soluble, it requires only a very small concen- 
 tration of lead ion and sulphate ion in solution to 
 reach the limit of solubility of lead sulphate. This 
 substance is therefore formed from the two ions as a 
 solid, and removed from the electrolyte as fast as it 
 is produced. 
 
 36. Discharge. On discharge (see Figure 14) the 
 lead peroxide plate is the cathode. It is certainly 
 reversible with respect to some ion, and PbO 2 seems 
 to fit the necessary conditions. This PbO 2 is con- 
 stantly formed from the solid PbO 2 of the plate, just 
 as Pb ++ is formed from the solid lead of the anode. 
 It starts toward the anode, being an anion, as its 
 two signs indicate. Before it has more than 
 passed the electrode it meets with H + , of which 
 there is always plenty about in a concentrated sul- 
 phuric solution, even if it were not moving toward 
 the cathode carrying the current. It reacts with 
 this H + , forming Pb ++ and water (Fig. 15), and the 
 Pb ++ , finding SO 4 in plenty, soon saturates the 
 

 
 FIG. 13. The begin- 
 ning of discharge. 
 
 
 8 < 
 
 5 
 
 UJ 
 
 O 
 
 Ld 
 
 FIG. 15. The third 
 stage in the dis- 
 charge reaction. 
 
 
 n 
 
 FIG. 14. The second 
 stage in the discharge 
 reaction. 
 
 n 
 
 FIG. 16. Discharge com- 
 plete. 
 
THE ACTIVE IONS 53 
 
 solution with lead sulphate, which is precipitated 
 very nearly in the spot from which the peroxide 
 started (Fig. 16). 
 
 It will do no harm to go over the changes in the 
 reverse direction, just to fix the whole reaction more 
 firmly in our minds. 
 
 Charge. The cell is charging (see Figure 17) . The 
 peroxide plate is now the anode, and contains a con- 
 siderable proportion of finely divided lead sulphate 
 from the previous discharge. Pb ++ and SO 4 are 
 formed as fast as they are needed from this reser- 
 voir in the plate, and the Pb ++ reacts with the water 
 of the electrolyte, forming H + and PbO 2 (Fig. 
 18). The PbO 2 ~ passes through the electrode (Fig. 
 19) and is deposited as solid PbO 2 very close to the 
 point where lead sulphate went into solution. H + and 
 SO 4 are left in the electrolyte in proportion to the 
 amount of current which has passed (Fig. 20). 
 
 The lead plate is cathode during charge. Here 
 also there is a reservoir of fine lead sulphate from 
 the previous discharge. This furnishes a constant 
 supply of Pb ++ and SO 4 ~~, and the electrode is re- 
 versible- with respect to Pb ++ . So Pb ++ passes out 
 and changes to metallic lead, sending a correspond- 
 ing quantity of electricity along through the ex- 
 ternal circuit, while the SO 4 ~~ finds itself moving 
 toward the anode. It will find its equivalent of 
 H+ in the solution, and our equations show that 
 
E 
 
 II ge 
 
 ~*H5 3i 
 
 5n o 
 
 ^S <t 
 
 H LJ 5, 
 
 m li^ 
 
 Fia. 17. The beginning of charge. FIG. 18. Second stage of the charge re- 
 
 action. 
 
 / 
 / _ T1 
 
 \ 
 
 -N 1 1 i ft 
 
 >nr}| ^hH 
 
 Fio. 19. Third stage in charge reaction. FIG. 20. Charge complete. 
 
THE ACTIVE IONS 55 
 
 acid is produced during charge in proportion to the 
 amount of material reacting, and that it is used up 
 in the same proportion during discharge. It also 
 expresses everything else that is contained in our 
 fundamental reaction, and gives us at least a pos- 
 sible picture of what takes place at the electrodes 
 as well. We have shown that it is quite possible 
 to have all the current carried through the cell from 
 plate to plate by the ions of the acid, provided these 
 two ions react near the electrodes to produce ions 
 like the ones we have assumed. Our electrode 
 reactions are perfectly reasonable ones, and are, as 
 matter of fact, supported by a great deal more evi- 
 dence than we can yet call to their support. We 
 shall return to them in a later chapter. 
 
CHAPTER VI 
 
 SOME PERTINENT PHYSICAL QUERIES 
 
 37. A host of questions arises even at this early 
 point in the discussion of the lead storage cell. 
 Even if we suppose that we have satisfactorily dis- 
 posed of the chemical changes, and found a pair of 
 ions that might do the work at the electrodes, how 
 can we explain a good many things about the pe- 
 culiar nature of the materials of the cell ? 
 
 Premises. These questions can best be discussed 
 if the reader will keep in mind : 
 
 (I) The ions which pass back and forth at the 
 electrodes have only molecular distances to travel. 
 
 (II) The particles of active material are very 
 small indeed. 
 
 (Ill) The active materials: lead, lead peroxide, 
 and lead sulphate are all very slightly soluble in con- 
 centrated sulphuric acid. 
 
 38. Queries and their Answers. QUERY 1. How 
 can storage plates keep their shape? How does it 
 happen that a battery can be sent through thousands 
 of charges and discharges without much growth of 
 trees or sponge ? 
 
 66 
 
SOME PERTINENT PHYSICAL QUERIES 57 
 
 Just because all the solid substances concerned 
 are so very slightly soluble in the electrolyte. The 
 ion which passes back and forth at the electrode has 
 no chance to wander far enough to deposit at even 
 k a measurable distance from its point of origin. 
 SO 4 is everywhere waiting for the Pb ++ , and in- 
 soluble PbSO 4 is precipitated almost instantly. This 
 is one of the prime secrets of the success of the lead 
 cell, and the main reason why its plates preserve 
 their mechanical structure as well as they do. In 
 another sense it is a disadvantage, for it means that 
 the particles of active material will be exceeding fine 
 and small, and that there will not be much inter- 
 growth and interlocking between neighboring par- 
 ticles. In the ideal cell both extreme insolubility 
 and intergrowth of particles might occur simul- 
 taneously, but not in practice. 
 
 QUERY 2. The lead peroxide of the positive plate 
 is in contact with a lead support. Why does not 
 the plate discharge of its own accord? Does it not 
 contain all the necessary substances for the reaction 
 
 Pb + Pb0 2 + 2 H 2 S0 4 -> 2 PbS0 4 + 2 H 2 ? 
 
 It does ; and self-discharge always takes place 
 when a peroxide plate is standing fully charged. 
 But before it has gone far all the finely divided 
 rough lead on the surface of the lead support has 
 reacted and then the plate is protected by its dense 
 
58 STORAGE BATTERIES 
 
 layer of lead sulphate, just as a lead plate protects 
 itself in sulphuric acid. 
 
 If the surface of the lead support is roughened or 
 increased, the action will be stronger, and Plante 
 plates were originally formed for service by means 
 of this very action. Our modern plates have a very 
 much greater proportion of active material to surface 
 of lead support, and therefore the loss of energy due 
 to this "local action" is a comparatively small one. 
 (See page 182.) 
 
 QUERY 3. How does it happen that a lead accu- 
 mulator with a difference of potential of two volts 
 between its plates can stand on open circuit without 
 immediately discharging itself? Under proper con- 
 ditions water (made acid with sulphuric acid) can 
 be completely decomposed into hydrogen and oxy- 
 gen at 1.5 or 1.6 volts. Why does not our cell 
 begin to decompose its electrolyte and keep on form- 
 ing gas until the plates are quite discharged? 
 
 Because the plates of our cell are made of lead and 
 lead peroxide. There is a great difference in the 
 amount of work required to form bubbles of hydro- 
 gen rapidly on surfaces of various metals. It takes 
 2.5 or 2.6 volts to cause gas to form rapidly in a 
 lead accumulator, and at 1.6 volts the electromo- 
 tive force at which gas forms on platinum electrodes 
 hydrogen forms bubbles so slowly on a lead sur- 
 face that losses due to this cause are quite negligible. 
 
SOME PERTINENT PHYSICAL QUERIES 59 
 
 Even at 2 volts the evolution of hydrogen is so slow 
 as to be immeasurable. (See page 217 for the effect 
 of impurities.) 
 
 QUERY 4. How can it be that lead sulphate is 
 formed during the discharge of our cell, and how 
 can this substance change back so readily to lead 
 and lead peroxide ? Is not " sulphation " the most 
 dangerous disease that can come upon a battery ? 
 
 The explanation is a matter of surface, like so many 
 others in this subject. The lead sulphate which 
 forms in the plate during a healthy discharge 
 differs greatly in size of grain from the same sub- 
 stance taken from the bottle on the laboratory shelf, 
 and just as much from the material which causes what 
 is called in battery parlance "sulphation." If ordi- 
 nary commercial lead sulphate be made into a paste 
 and filled into a lead support, it does not change to 
 lead at the cathode and lead peroxide at the anode 
 easily. It can be subjected to the action of the cur- 
 rent for a very long time without being completely 
 transformed, arid it never does make a good coherent 
 plate. When a cell is allowed to stand discharged 
 for many weeks the fine grains of sulphate which 
 are formed during normal discharge suffer an inter- 
 esting change. True crystallization begins on the 
 larger particles, and the substance goes into solution 
 at the small ones. It moves through the solution 
 and continues to deposit on the large grains until 
 
60 STORAGE BATTERIES 
 
 the small grains have completely dissolved and the 
 large ones, fewer in number, have grown to consider- 
 able size. The plate is now sulphated, and if it is 
 charged for the ordinary time, it by no means returns 
 to its original condition of healthy charge. The large 
 crystals of sulphate do not go into solution com- 
 pletely. In fact, they hardly dissolve at all, arid 
 long before the cell has been brought back to its 
 charged state reaction has ceased and the current is 
 merely producing gas. It is possible to restore a 
 sulphated cell, but the charge must be continued so 
 long that gassing breaks up the active material, and 
 even when the remaining sulphate has all been forced 
 to react, a large part of the original capacity of the 
 cell has been lost. (See page 216.) 
 
 QUERY 5. Metallic lead in the form of a bar or 
 plate is not dissolved by sulphuric acid under ordi- 
 nary circumstances, and this is especially true of acid 
 of the concentration used in storage batteries. The 
 grids of paste plates and the main body of Plante 
 plates resist the attack cf the acid during the whole 
 life of the plates. Lead is one of the metals which 
 "protects itself" from solution in reagents by the 
 formation of a dense layer of slightly soluble material 
 on the surface. It is a familiar fact that lead pipes 
 cannot be used for pure distilled water without 
 danger of contamination, for in this case the sub- 
 stance formed is not dense and does not protect the 
 
SOME PERTINENT PHYSICAL QUERIES 61 
 
 metal. The hydroxide which forms under these cir- 
 cumstances is fluffy and breaks away from the sur- 
 face, and the plate rapidly dissolves. But if the 
 water passing through the pipe is not pure, if it 
 contains carbonates, chlorides, and sulphates even in 
 small amounts, dense protecting coatings of carbon- 
 ate, chloride, or sulphate are formed and the metal 
 is no longer dissolved. It is safe enough to use lead 
 pipes for ordinary water even if it is to be used for 
 drinking purposes. 
 
 How is it, then, that the lead of the negative plate 
 can pass easily and rapidly into the form of lead 
 ion? Why do not the particles of lead so protect 
 themselves and refuse to react? And if because of 
 their very fineness the protecting layer which might 
 be formed makes up a considerable part of the whole 
 bulk of the grains, why does not the self-discharge 
 necessary to produce this protecting layer greatly 
 reduce the activity of the lead plate? 
 
 While it is quite true that the particles of lead on 
 the negative plate are very small, they are still quite 
 large in comparison with the protecting layer of sul- 
 phate which is sufficient to prevent farther action. 
 At the end of charge a part of the energy is lost by 
 formation of sulphate at the lead plate, but in prac- 
 tice it is a very small fraction of the whole. But 
 when current is passing through the cell in the dis- 
 charge direction a very different state of things pre- 
 
62 
 
 STORAGE BATTERIES 
 
 vails. Suppose our cell to be first on open circuit 
 and that we are looking at what happens at the lead 
 plate and able to see everything that occurs. Lead 
 
 changes to lead ion, 
 Pb ++ , and this goes 
 into solution, leaving 
 the plate negatively 
 charged. The Pb ++ 
 finds SO 4 waiting 
 and precipitates as in- 
 soluble PbSO 4 , but it 
 leaves 2 H + behind it, 
 and the condition of 
 strain set up by the 
 positively charged ion 
 in the electrolyte and 
 the negatively charged 
 plate is not relieved 
 (Figure 21). It only 
 takes the presence of 
 a very small concen- 
 
 Fia. 21. Electrostatic equilibrium tratlon of ion in solu- 
 about a lead plate. , 
 
 tion to set up an at- 
 traction so strong that no more ion leaves the plate. 
 The electrode is in equilibrium with respect to Pb ++ . 
 It has protected itself sufficiently by sacrificing a very 
 minute fraction of its whole mass. 
 
 But as soon as the external circuit is closed and 
 
 LU 
 
SOME PERTINENT PHYSICAL QUERIES 63 
 
 current begins to pass, the H + is no longer bound by 
 an electrostatic attraction. The lead plate can dis- 
 charge itself through the wires and the H + can pro- 
 ceed on its way toward the cathode, carrying its 
 equivalent of electricity with it. The electrode is 
 no longer in equilibrium, and more lead goes into 
 solution, becomes Pb ++ , reacts with SO 4 , and frees 
 more H + . This continues as long as current is 
 being taken from the cell. 
 
CHAPTER VII 
 
 ENERGY RELATIONS 
 
 39. Any arrangement whatever which runs of its 
 own accord and which can furnish energy for doing 
 outside work as well must draw upon some store for 
 the energy expended. A charged storage cell con- 
 tains potential chemical energy. It differs in no way 
 from any other galvanic cell in this, and if we knew 
 of practical ways of manufacturing lead sponge and 
 lead peroxide of exactly the same physical character- 
 istics as those possessed by the active materials of 
 our charged accumulator, we could build a cell just 
 like it in every way without any charging process 
 whatever. It merely happens that the very best 
 way of manufacturing lead sponge and lead peroxide 
 of exactly the right quality is to pass a current of 
 electricity through a discharged storage cell. The 
 materials themselves are no more electrical than the 
 same substances in bottles on the laboratory shelf. 
 
 40. Transformations of Energy. There is hardly a 
 branch of science where we can be so sure of our 
 footing as in calculations which involve the trans- 
 formation of quantities of energy from one form to 
 
 64 
 
ENERGY RELATIONS 65 
 
 another, especially in the calculation of reversible 
 changes, and it is difficult to imagine any arrange- 
 ment which could be more perfectly reversible than a 
 storage cell. Small losses occur even in a big storage 
 cell. Some gas escapes and cannot be taken into 
 our calculation, and there is some local action at the 
 plates with corresponding evolution of a little heat. 
 But the same is true in any arrangement known to 
 man, and in most cases the losses are very much 
 greater than in our cell. 
 
 Electrochemical Reaction. We can apply the law 
 of the Conservation of Energy. Applied to our 
 own particular case this law says : If we have at our 
 disposal a system, represented by 
 
 Pb + Pb0 2 + 2 H 2 S0 4 
 
 and consisting of 207 gm. of lead, 239 gm. of lead 
 peroxide, and 196 gm. of sulphuric acid, and this 
 system changes of its own accord into another 
 
 2 PbS0 4 + 2 H 2 
 
 consisting of 606 gm. of lead sulphate and 36 gm. of 
 water, a definite and determined amount of energy 
 will be set free, which can be utilized for doing 
 work. If the reaction is perfectly reversible and no 
 energy has managed to get away from us, we can 
 restore the original condition of the system by ex- 
 pending the same quantity of energy on it. 
 
66 STORAGE BATTERIES 
 
 Our own special interest lies in a chemical reaction, 
 but the same law applies for any change whatever. 
 The original condition might be represented by a 
 certain mass of water at the top of a dam and the 
 final condition by the same mass at the bottom. 
 Here we would have no difficulty in calculating the 
 quantity of work obtainable by the fall of the water, 
 and the same amount of work would carry it back 
 to the top, provided all our machines were friction- 
 less and worked with 100 % efficiency. 
 
 41. Thermochemical Reaction. Now for the next 
 step. If we should take the amounts of the various 
 materials on the left side of our fundamental equa- 
 tion, and should mix them all up into a pasty mass, 
 we would not get any electrical current from it, but 
 we would get a definite amount of heat set free. 
 We will get the same total amount of energy from 
 the reaction in either case, provided our cell does 
 not itself heat up or cool down during the reaction 
 of these amounts of its materials. In the one case 
 we should measure the amount of available energy 
 in heat units, or calories, and a calorie is the amount 
 of heat required to raise the temperature of 1 gm. of 
 water 1 C. In the other case we should measure 
 the amount of available energy in electrical units, 
 joules (volt-coulombs). 
 
 42. Heat Changes in the Cell. If our cell does heat 
 up while it is sending out its 96,540 coulombs, we 
 
ENERGY RELATIONS 67 
 
 must remember the amount of heat which appears in 
 this way, and we must expect to get less energy 
 from the cell for use in the external circuit if a part 
 of the total energy of the reaction has been used to 
 heat the air of the room. If the cell cools while it 
 is working, we might expect to get more than the 
 calculated amount of energy, and to this point we 
 will come back later. 
 
 But if the cell neither heats nor cools during the 
 passage of 96,540 coulombs, the law of the Conser- 
 vation of Energy gives us our 
 
 First Fundamental Equation 
 
 chemical energy expanded = electrical energy produced. 
 
 Before we can go any farther we must know the 
 numerical factor for transforming joules to calories 
 (or vice versa), and this has been often determined. 
 It takes 4.18 joules to raise the temperature of 1 gm. 
 of water 1 C. 
 
 The determination of the heat of the reaction 
 
 Pb + PbO 2 + 2 H 2 SO 4 ;2 PbSO 4 + 2 H 2 O 
 
 cannot be carried out directly with accuracy because 
 of the slowness of the reaction when the substances 
 are mixed up together. It can only be determined 
 by indirect measurement, and the best results have 
 been obtained by using very dilute sulphuric acid. 
 
 Applying a correction to be explained immediately, 
 the heat of this reaction for acid of density 1.044 
 
68 STORAGE BATTERIES 
 
 (0.70 gm.-mol. H 2 SO 4 per liter of electrolyte) is 
 87,000 calories. A cell containing acid of this den- 
 sity neither heats nor cools while it is working. 
 Now see how simple our calculation becomes : 
 
 87,000 calories x 4.18 = 364,000 joules, 
 
 and this is the amount of electrical energy which be- 
 comes available when 207 gm. of lead and 239 gm. 
 of lead peroxide have reacted with 196 gm. of sul- 
 phuric acid (in rather dilute solution) to produce 
 606 gm. of lead sulphate and 36 gm. of water. 
 
 If we arrange things so that the reaction can take 
 place in a galvanic cell, 2 x 96,540 coulombs will pass 
 through the cell by the time these amounts have 
 reacted. These 193,080 coulombs will have given us 
 364,000 joules of work, and the voltage of the cell 
 must therefore be 
 
 364,000 volt-coulombs _ i QQ u 
 2 x 96,540 coulombs 
 
 This agrees closely with the measured voltage of a 
 cell containing this rather dilute acid as electrolyte. 
 While there is no doubt whatever about the cor- 
 rectness of this principle, there is often a great deal 
 of difficulty in obtaining accurate data on the heats 
 of reaction. In this case a number of reactions had 
 to be used, and the final result calculated in a round- 
 about way by eliminating the heats of the various 
 
ENERGY RELATIONS 69 
 
 intermediate steps. Even in this case there is no 
 doubt as to the correctness of the method, but the 
 final result is always afflicted with a large experi- 
 mental error. 
 
 43. Heating and Cooling of the Cell. The ordinary 
 practical storage cell contains acid of density about 
 1.210. It cools during discharge and heats during 
 charge, and can therefore not be brought under the 
 simple law we have just used. We can make some 
 qualitative statements about it, however. 
 
 Since it cools during discharge, it must take into 
 its system a certain amount of heat from the room 
 during the passage of 96,540 coulombs. At least a 
 part of this^ heat will be transformed into electrical 
 energy. Since we always calculate on the basis of 
 96,540 coulombs, the voltage of this cell must be 
 higher than it would be if it did not cool down while 
 it was working. 
 
 During charge, the cell gets hotter than the room. 
 A part of the energy supplied to charge it is used in 
 heating the surrounding objects, and it therefore 
 takes more energy to completely reverse the reaction 
 than it would if the cell did not change its tempera- 
 ture during charge. Since we use the same 96,540 
 coulombs for the reversal, the charging voltage must 
 be higher than it would be if the cell did not heat up. 
 
 44. The General Equation. We can handle this 
 case quantitatively just as easily as the simple previ- 
 
70 STORAGE BATTERIES 
 
 ous one, for we have what is called the Second Law 
 of Thermodynamics, which states 
 
 For our case 
 
 W ' available electrical energy. 
 Q = heat of the chemical reaction. 
 T= the absolute temperature. 
 
 = the temperature coefficient of available elec- 
 
 trical energy. 
 
 Since all our calculations are based on gram-equiv- 
 alents, 96,540 coulombs are always supposed to pass 
 through the cell, and the electromotive force of the 
 cell is therefore a measure of the available electrical 
 energy. 
 
 If e = the electromotive force of the cell, we can 
 put this formula into a form adapted specially for 
 the case of galvanic cells. 
 
 $ . m St+ r &> 
 
 F^ dT" 
 F being our 96,540 coulombs. 
 
 For an acid concentration corresponding to a den- 
 sity of 1.210 we have for Q (per gram-equivalent) 
 about 43,000 calories. 
 
 ^ is positive and has a value of about 0.0003 at 
 20 C. 
 
ENERGY RELATIONS 71 
 
 Numerically 
 
 e = 43,000x4^ + [290x0.0008], 
 
 e = 1.86 + 0.087 = 1.95, 
 
 which is a little lower than the usual measurement 
 of 2.04 to 2.06 volts. 
 
 The complete derivation of the formula will be 
 found in the Appendix, page 255. 
 
 This is the general form of the expression for the 
 electromotive fprce of a galvanic cell in terms of the 
 chemical heat of reaction and the temperature coeffi- 
 cient of the electromotive force. It is perfectly 
 general and suggests many interesting things. There 
 are cells which warm up a good deal while they work. 
 These are the ones whose electromotive force de- 
 creases rapidly when their temperature is raised. 
 Others cool down, and the reverse effect is produced 
 on these by warming them from without. In the first 
 class, part of the energy of the chemical reaction is 
 used to heat the room. In the second class some 
 energy is taken from the room in the form of heat 
 and converted in the cell into electrical energy. 
 There are cells in which the heat of the chemical 
 reaction is zero and in which all the electrical energy 
 is produced at the expense of heat absorbed from 
 the surrounding air. These are the "concentration 
 cells," and they are very interesting and important 
 
72 
 
 STORAGE BATTERIES 
 
 theoretically, even though none of them are used as 
 practical sources of current. 
 
 45. Temperature Coefficient. The usual commercial 
 storage cell has a fairly large positive temperature 
 coefficient about 0.0003 per Centigrade degree. 
 But it gains no energy from this fact because we 
 
 <X50 
 
 i.l 1.2 1.3 1.4 
 
 DENSITY OF ELECTROLYTE! 
 
 FIG. 22. Change in the temperature coefficient of the e. m. f. of a 
 storage cell with change in acid concentration (density). 
 
 reverse it when we charge it and lose from the 
 negative coefficient during this part of the cycle. 
 As far as this one factor is concerned we should 
 charge it as cold as possible and discharge it as hot as 
 possible. But as we shall see later, temperature has 
 much larger and more important influence on other 
 factors, and in comparison with them the change in 
 
ENERGY RELATIONS 73 
 
 electromotive force with temperature is quite negli- 
 gible. Figure 22 shows the change in the electro- 
 motive force of the cell with change in acid concen- 
 tration, and the ^ of the formula can be taken 
 
 from this curve. At acid concentrations higher than 
 2 gm.-mol. per liter the curve does not fit the meas- 
 urements perfectly, and the values obtained by cal- 
 culating backward from the heats of dilution are 
 probably correct. The departure is not great, but 
 requires explanation. It may be that the more con- 
 centrated acid attacks and combines with the lead 
 sponge of the negative plate, even when no current 
 is passing, giving out heat, and this loss of energy 
 would of course mean that the electromotive force 
 found by measurement will be too small. 
 
 46. The Heat of Dilution of Sulphuric Acid. The 
 determination of the heat of reaction for the mate- 
 rials of the storage cell was made in very dilute sul- 
 phuric acid. Under these conditions there would be 
 set free in the calorimeter, besides the heat of the 
 substances indicated in the equation for the cell re- 
 action, the heat of dilution of 2 gm.-mols. of H 2 SO 4 . 
 This is a considerable amount of heat, as every one 
 knows who has had occasion to dilute sulphuric acid 
 by pouring the concentrated acid into water. If we 
 used very dilute acid in our cells, we could also use 
 the heat of reaction found in the calorimeter, but 
 
74 
 
 STORAGE BATTERIES 
 
 since we use in practice rather concentrated acid, 
 we evidently cannot expect to get any more energy 
 than could be obtained from the heat of the cell 
 materials plus the heat of dilution from pure H 2 SO 4 
 to the acid concentration used in our cell. 
 
 The curves of Figures 23 and 24 show the heat of 
 
 1 
 
 . 
 
 \ 
 
 60 70 
 
 FIG. 23. Curve showing the heat of dilution of a gram molecule of 
 H2SO 4 to various concentrations. Heat given in thousands of calories. 
 
 dilution of sulphuric acid. Along the bottom of the 
 diagram of Figure 24 are given the densities of the 
 solutions formed, and along the top the concentra- 
 tion of these solutions in gram-molecules of H 2 SO 4 
 per liter of solution. 
 
 The Q which we use in our energy formula con- 
 sists evidently of two parts, one being the heat of 
 
ENEEGT RELATIONS 
 
 75 
 
 reaction of the materials according to the funda- 
 mental cell reaction, the other the heat of dilution 
 to the concentration used in the cell being tested. 
 Since the temperature coefficient also plays a con- 
 siderable part in our calculations of electromotive 
 
 HEAT OF DILUTION IN CALORIES 
 
 i i I i 1 I I I 1 
 
 GM.-MOLS. PER LITER 
 
 
 i r 
 
 --v^ 
 
 T r 
 
 -T- T 
 
 1 ' 
 
 1 ' 
 
 1 ' 
 
 1 ' 
 
 1 
 
 
 
 
 N 
 
 N^ 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 X 
 
 s 
 
 
 
 
 
 
 
 
 
 \ 
 
 \ 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 DENSITY 
 
 FIG. 24. Curve showing the heat of dilution of H 2 SO 4 to electrolyte 
 of various densities (at bottom) and to various concentrations in 
 gm.-mols. per liter (at top). 
 
 force, the easiest way of approaching the subject 
 seems to be to choose as our starting point an acid 
 concentration such that the cell has no temperature 
 coefficient of electromotive force. This we did by 
 choosing acid of density 1.044 (0.70 gm.-mol. per 
 liter), and we thus made one factor constant. 
 
76 STORAGE BATTERIES 
 
 47. Very Dilute Electrolyte. 87,000 calories is the 
 total heat of reaction when acid of this density is 
 used in the cell, and this is already so dilute an acid 
 that not very much more heat could be obtained by 
 diluting it a great deal further. It will be seen 
 from the curve (Figure 24) that the difference in 
 the heats of dilution of 0.70 normal acid and 0.0 
 normal acid is small. It is only a couple of hun- 
 dred calories at the most. Q will therefore be about 
 87,200 calories for the most dilute solution in which 
 the cell electromotive force could be measured. 
 
 From Figure 22 we see that the temperature co- 
 efficient for very dilute acid is negative, and that it 
 is rapidly increasing in the negative direction as the 
 acid density approaches zero. Dolazalek has meas- 
 ured this coefficient for very dilute acid (0.0005 gm.- 
 mol. per liter), and he finds it about 0.0025 volts 
 per Centigrade degree. 
 
 From these data we can calculate the electromotive 
 force of a storage cell having this very dilute acid as 
 electrolyte. 
 
 dT' 
 
 1.87-0.72 = 1.15 volts, 
 which is close to the measured value. 
 
ENERGY RELATIONS 
 
 77 
 
 48. Concentrated Acid. Passing to concentrated 
 acid, the agreement between the simple theory and 
 the measurements is not by any means so close. 
 This will be at once evident from an examination 
 of the curves of Figures 22 and 24 in connection with 
 
 13 
 
 1.6 
 
 T-i 
 
 GM.-MOLS. PER LITER 
 
 PERCENT OF H 2 SO 4 
 
 FIG. 25. Variation of cell voltage with change in acid concentration 
 (in percent of H 2 SO4 at botton, in gm.-mols. per liter at top). 
 
 the results of measurement on cells with various acid 
 concentration, given in the curve of Figure 25. 
 Measurement shows that the electromotive force of 
 a cell is nearly a linear function of the acid concen- 
 tration, only departing from a straight line in the 
 region of dilute acid, and certainly approximately 
 straight for all acid concentrations used in practice. 
 
78 STORAGE BATTERIES 
 
 Figure 24 shows that Q decreases with increasing 
 acid concentration, since the heat of dilution to be 
 subtracted from the constant part of Q becomes 
 greater and greater as the acid concentration in- 
 creases. On the other hand, the change in electro- 
 motive force with change of temperature is in the 
 right direction to counterbalance this only as far as 
 acid of density 1.15. Beyond this both the Q and 
 
 the ^= of our energy formula are decreasing, while 
 cl J. 
 
 the measurements show that the electromotive force 
 is constantly increasing. 
 
 At acid density 1.15 the formula still holds accu- 
 rately enough. 
 
 e = 1.85 + 0.14 = 1.99. 
 
 For the higher densities we can no longer expect 
 close agreement, if we take the data of our curves. 
 But at the usual acid density of 1.210 the agreement 
 is still fairly close. 
 
 = 85,000 x 4.18 29Q aoo032 
 
 2 x 96,540 
 e = 1.84 + 0.093 = 1.933, 
 
 noticeably lower than the measured value, which is 
 2.06 volts. 
 
 49. This lack of agreement of course arouses sus- 
 
ENERGY RELATIONS 79 
 
 picion of our data. The fundamental theory has 
 been so well and thoroughly proven in hundreds of 
 cases that we need hardly fear any trouble there. 
 
 While the thermochemical data for the heat of 
 reaction and the heat of dilution are hard to obtain 
 and undoubtedly fraught with considerable experi- 
 mental error, there is nothing in the course of the 
 curves expressing them to excite any suspicion of 
 the correctness of their general trend. 
 
 The curve connecting the temperature coefficient 
 of the electromotive force with the acid density 
 (Figure 22) is the one which seems to contain the 
 
 de 
 doubtful data. The droop in the value of comes 
 
 Ci JL 
 
 in those concentrations of acid where lead is rather 
 rapidly attacked and dissolved. Manufacturers have 
 stopped increasing the density of their electrolyte 
 at about 1.200, because they found local action to 
 be a factor just beyond that point. If there is local 
 action at the negative plate, and the acid is being 
 used up there as a result, the average density in the 
 cell would not be the same as that at the point of 
 cell activity. And since there is no current passing 
 when these measurements are made, diffusion alone 
 must replace the exhausted acid. This would cer- 
 tainly account for at least a part of the discrepancy, 
 but this still remains a point which demands further 
 investigation. 
 
CHAPTER VIII 
 REACTIONS AT THE ELECTRODES 
 
 50. In our discussion of the action of the Daniell 
 cell (page 26) we decided that we could get 
 
 1.1 x 96,540 volt-coulombs 
 
 of work from the cell when 32.7 gm. of zinc went into 
 solution as Zn ++ and 31.8 gm. of copper changed from 
 Cu ++ to metal. There are a great number of pos- 
 sible cells of the same type, for we can replace either 
 zinc or copper or both by any other metals immersed 
 in solutions of their salts, and in this way make cells 
 quite similar to the prototype. 
 
 51. Cells of the Daniell Type. The following list 
 indicates a few of the combinations and their electro- 
 motive forces. These are measured with the metal 
 immersed in a solution which is normal with respect 
 to the metallic ion. The Daniell cell itself contains 
 65.4 gm. of Zn ++ per liter of solution about the anode 
 and 63.6 gm. of Cu ++ per liter about the cathode. 
 Whenever we use silver as electrode, we measure it 
 in a silver salt solution containing 107.9 gm. of Ag + 
 per liter. 
 
 80 
 
REACTIONS AT THE ELECTRODES 81 
 
 e. m. f. 
 
 Cu/Cu + yZn ++ /Zn I- 10 Cu cathode, Zn anode 
 
 Cu/Cu ++ /Cd + V Cd - 750 Cu cathode, Cd anode 
 
 Cu/Cu ++ /Fe + yFe 0.986 Cu cathode, Fe anode 
 
 Cu/Cu ++ /Ni+YNi 0.926 Cu cathode, Ni anode 
 
 Cu/Cu ++ /Ag+/Ag - 469 A g cathode, Cu anode 
 
 Zn/Zn ++ / Cd+ V cd - 350 Cd cathode, Zn anode 
 
 Zn/Zn ++ /Fe + V Fe - 113 Fe cathode, Zn anode 
 
 Zn/Zn ++ /Ni ++ /Ni 0.173 Ni cathode, Zn anode 
 
 Zn/Zn + YAg + / A g !- 568 A g cathode, Zn anode 
 
 etc. 
 
 If a very little cross-calculation is undertaken, 
 some interesting things will be found. We did not 
 need nearly all these statements to cover the facts, 
 for we can calculate from 
 
 Cu/Cu+VZn ++ /Zn = 1.10 
 Cu/Cu ++ /Cd + yCd = 0.750 
 Cd/Cd ++ / z n ++ /Zn = 0.350 
 
 and others in the same way. We can also calculate 
 a good many combinations which we have not put 
 down. For example, 
 
 Zn/Zn ++ /Ni ++ /Ni = 0.173 
 Zn/Zn ++ /Ag + /Ag = 1.568 
 Ni/Ni ++ /Ag + / A g = 1-395 
 and in the same way for any other combination. 
 
 All these connected facts suggest a possible sim- 
 plification. Why not calculate the work at the two 
 
82 STORAGE BATTERIES 
 
 electrodes separately ? For the Daniell cell : (1) the 
 work available when 31.8 gm. of copper changes 
 from ion to metal, and (2) the work available when 
 32.7 gm. of zinc changes from metal to ion. And 
 of course we would not stop here. We would go on 
 and determine the work available when 107.9 gm. 
 of silver passed a silver electrode, and so on for all 
 the single electrodes. Dividing the work in joules 
 in each case by 96,540, we would then have a series 
 of single electromotive forces, and from this series 
 we could pick out any two we wished to combine to 
 make a galvanic celL 
 
 52. Standard Electrode. Before we can begin to 
 make such a series we must in some way fix a value 
 for one single electromotive force metal/ion There 
 has been a good deal of trouble in scientific circles 
 about this, but fortunately it does not make the least 
 difference for our elementary work what this stand- 
 ard metal/ion electrode is, or what we take for its 
 single electromotive force. If we should put any 
 one of the single metal/ion combinations equal to 1, 
 and then measure all the others against this, we 
 would arrive at exactly the same figures as those 
 given in our series on page 81. As a matter of fact 
 we have a so-called "normal electrode," and its elec- 
 tromotive force has been determined separately 
 in various ways. Measured against this single 
 electrode, it has been found that the electromotive 
 
REACTIONS AT THE ELECTRODES 83 
 
 force Zn/Zn" 1 " 4 " has the value 1.053 volts, the zinc 
 passing from metal to ion through the electrode. It 
 is given the negative sign and is written Zn/Zn ++ 
 = -1.053. 
 
 Cu/Cu ++ is +0.046, measured against the same 
 standard. 
 
 Using these values, and our series of cells of the 
 Daniell type, it is a very easy matter to write out a 
 list of the single potentials of all the metal/ion 
 electrodes which appear in that list. 
 
 Fe/Fe ++ -0.940 
 
 Ni/Ni ++ -0.880 
 
 Cd/Cd ++ - 0.703 
 
 Ag/Ag+ + 0.505 
 
 and we might add from other measurements 
 
 Pb/Pb ++ - 0.431 
 H/H+ -0.283 
 
 Hg/Hg++ - 0.46T, etc. 
 
 53. Work done at an Electrode. So here we have 
 the way opened for the calculation of the work done 
 at each electrode. We need only to multiply the 
 single electromotive force by 96,540 and the result 
 is the number of joules furnished by that half of the 
 cell during the change of a gram-equivalent of the 
 metal to ion, or vice versa. There would not be much 
 
84 STORAGE BATTERIES 
 
 need for any more minute theory of the process if 
 the single electrodes did not change their electro- 
 motive force considerably when the ion concentration 
 about them is changed. For instance, if we are 
 using Ag/Ag + as one of our electrodes and silver is 
 going out of solution, this half of the cell furnishes 
 0.515 x 96,540 joules of work. But if we change 
 the concentration of the ion from 107.9 gm. per liter 
 
 to 10.79 gm. per liter (from N to \ the half cell 
 
 only furnishes 0.457 x 96,540 joules for the same 
 amount of silver. 
 
 At the anode a change of concentration has 
 the opposite effect. Zn/Zn ++ N has 1.053 volts. 
 
 + measures 1.082 volts. 
 
 Nernst has suggested a generalization which makes 
 the whole subject matter easy to remember and 
 which at the same time opens the way to many inter- 
 esting and important numerical relations. 
 
 54. Nernst's Theory of Solution Pressure. Let us 
 think of the question in this way: Each metal has 
 a tendency to send ions into solution, and does it. 
 The ions carry with them a definite quantity of 
 electricity of + sign, for the metallic ions are all 
 cations. If the electric circuit is not a closed one, 
 this leaves the metal with charge, and before the 
 concentration of ions has reached a very high value, 
 
BE ACTIONS AT THE ELECTRODES 85 
 
 a true static attraction is produced between the 
 charged plate and the + charged ions in solution. 
 Unless this condition of things is relieved by dis- 
 charging the plate, the concentration of the ion in so- 
 lution no longer increases, and we have equilibrium. 
 (See Fig. 21.) 
 
 Theoretically, at least, we can reverse this process 
 by using a metal with a comparatively slight tend- 
 ency to go into solution, and placing it in a con- 
 centrated solution of its ion. Since a very small 
 concentration of ion is necessary to balance the 
 solution pressure of the metal and we have purposely 
 made the ionic concentration high, ion will change 
 to metal under these circumstances and the plate 
 will take on a + charge until static repulsion causes 
 equilibrium. So far this is rather hypothetical. But 
 measurements show that it fits the facts very closely 
 indeed. If a metal is going into solution as part of 
 a galvanic arrangement, we can better the electromo- 
 tive force of the cell by surrounding this anode with 
 an ionic concentration as small as possible. The 
 single electromotive force of the electrode goes up 
 as the solution about it is diluted. If a metal is to 
 go out of solution as part of a cell, we can assist it 
 by increasing the concentration of its ion to as high 
 a value as possible. 
 
 55. Electrode Equilibrium. A few simplifying 
 assumptions lead us to still more exact numerical 
 
86 STORAGE BATTERIES 
 
 relations. Let us assume that the solution pressure 
 of each metal is constant and that when it dips in a 
 solution it is constantly held in equilibrium by a 
 layer of charged ions about it. Then the passage 
 of 96,540 coulombs through the cell results in the 
 change (suppose this is the anode) of a gram-equiva- 
 lent of metal into ions of this definite equilibrium 
 concentration and subsequent diffusion of these ions 
 from the more concentrated solution about the plate 
 into the main body of the electrolyte. The whole 
 work of the electrode has been expended in main- 
 taining this ion concentration about the plate. We 
 can calculate the total work of the electrode as merely 
 the osmotic work corresponding to the change of a 
 gram-equivalent of the ion from its equilibrium con- 
 centration to the average concentration of the elec- 
 trolyte (see Appendix, page 256). 
 
 56. Osmotic Work. The osmotic work available 
 as the result of such a change in concentration is 
 
 where O 1 is the concentration in the equilibrium 
 layer about the electrode, <7 2 the concentration in the 
 main body of the cell, R is a constant for all dilute 
 solutions numerically the same as the gas constant 
 R, T is the absolute temperature, and In is the sign 
 indicating a logarithm to the natural base e. 
 
REACTIONS AT THE ELECTRODES 87 
 
 1 was the concentration which exactly balanced 
 the solution pressure of the metal. As far as we 
 are concerned we could put P, the solution pressure 
 of the metal, in place of C^ since the electrode is 
 in equilibrium. 
 
 Now let a gram-equivalent of the metal change to 
 ion and diffuse into a very large cell, in which the 
 ionic concentration is <7 2 . 
 
 The osmotic work is 
 
 and since a gram-equivalent has been used, 96,540 
 coulombs have passed through our electric circuit. 
 Electromotive force x 96,540 = osmotic work 
 
 The electrode electromotive force 
 
 RT 
 
 96,540 <7 2 
 
 If we put in the numerical values, using the gas 
 constant for R and changing it to joules, measuring 
 everything at 17 C., and changing to the ordinary 
 system of logarithms, we get 
 
 n being the valence of the ion. 
 
88 STORAGE BATTERIES 
 
 This for one electrode. At the other we will have 
 a precisely similar set of relations except that at the 
 cathode the change is from ion to metal, and the 
 electromotive force will therefore have the opposite 
 sign. The electromotive force of the cell as a whole 
 will be the difference of the two expressions. 
 
 57. Effect of Concentration on Electromotive Force. 
 Evidently if we want our cell to have a high electro- 
 motive force, we must choose 
 
 as anode, a metal with a high solution pressure ; 
 as cathode, a metal with a low solution pressure. 
 And we must also make 
 
 the ion concentration about the anode low ; 
 the ion concentration about the cathode high. 
 
 58. Application to Lead Accumulator. In the case 
 of the lead accumulator we have evidently chosen 
 a favorable set of conditions, for it has about as high 
 an electromotive force as any practicable cell. It is 
 a matter of interest to 1 examine this particular gal- 
 vanic combination from the new point of view. 
 
 No difficulty is found in applying it to the lead 
 plate. This is the anode during discharge, and we 
 can be quite sure that this electrode is reversible 
 with respect to the ion Pb + +. We have insured a 
 low concentration of this ion in the main body of the 
 
REACTIONS AT THE ELECTRODES 89 
 
 electrolyte, for lead sulphate is a very slightly solu- 
 ble substance. The only electrolyte which I can 
 think of that would possibly increase this single 
 electromotive force would be a soluble sulphide, for 
 lead sulphide is even less soluble than the sulphate. 
 For the lead plate, we have 
 
 e = 0.0288 log 
 
 59. Theory of Le Blanc. When we examine the 
 peroxide plate we find it a much more difficult 
 matter to decide upon our active ion. Whatever it 
 is, it must be present in the electrolyte in exceedingly 
 small concentration and quite beyond the limits of 
 chemical analysis. Two theories have been pro- 
 posed, one by Le Blanc and one by Liebenow, and 
 while each assumes the existence and importance of 
 a quite different ion, the final result is much the 
 same in each. Le Blanc's reasoning is in this form. 
 Lead peroxide has a small but perfectly definite 
 solubility in water, and reacts with it in the reaction 
 
 Pb0 2 + 2 H 2 = Pb++ + 4 OH-, 
 
 ++ 
 forming a quadrivalent lead ion Pb ++ , and OH~ ion. 
 
 During discharge the quadrivalent lead ion changes 
 to ordinary lead ion Pb ++ , and this meets with SO 4 
 and is precipitated as solid lead sulphate. 
 
90 STORAGE BATTERIES 
 
 The entire course of discharge is therefore given 
 by the set of equations 
 
 Pb0 2 + 2 H 2 = Ph 4 OH-. 
 
 Pb K + Pb met + 2 S0 4 - = 2 PbS0 4 , 
 4 OH- -f- 4 H+ = 4 H 2 O, 
 
 and during charge these reactions are completely 
 reversed : 
 
 2 Pb++ = Pb++ + Pb met , 
 
 Pb++ + 4 OH- = PbO 2 + 2 H 2 0, 
 4 H+ + 2 SO 4 ~ = 2 H 2 SO 4 . 
 
 The total result of these reactions gives a reaction 
 just like our fundamental one 
 
 Pb + Pb0 2 + 2 H 2 S0 4 = 2 PbS0 4 + 2 H 2 0, 
 
 for during discharge we lose lead and lead peroxide 
 and gain 2 of lead sulphate and 2 of water, and dur- 
 ing charge the reverse change takes place. As far 
 as the chemical facts of the reaction are concerned, 
 
 Le Blanc's theory fits very well. 
 
 ++ 
 The quadrivalent lead ion Pb ++ can be shown to 
 
 exist, but we have not much data as to its concentra- 
 tion in the electrolyte of a lead accumulator. 
 
 60. Liebenow's Theory. Liebenow's theory is in 
 several ways a more acceptable one than Le Blanc's. 
 
REACTIONS AT THE ELECTRODES 91 
 
 He assumes that the lead peroxide electrode is re- 
 versible and that the electrolyte contains PbO 2 ion. 
 Then during discharge this ion goes into solution at 
 the cathode (it is a negative ion) and reacts with the 
 H + ion of the acid to form Pb and water 
 
 PbO 2 -- + 4 H+ = Pb ++ + 2 H 2 O; 
 the lead ion finds SO 4 ion waiting for it, 
 Pb ++ + S0 4 = PbS0 4 , 
 
 and precipitates as solid lead sulphate (see Figures 
 14 and 15). 
 
 The reaction at the anode is the same as before, 
 and the sum of the whole is again our fundamental 
 reaction. 
 
 PbO 2 undoubtedly does exist in perfectly meas- 
 urable concentration in strongly alkaline solution, 
 and theoretically must also be present in the acid of 
 the cell. In the Appendix (page 261) will be found 
 the complete calculation, which leads to the remark- 
 able result that the concentration of PbO 2 in an 
 ordinary cell acid is about 4 x 10~ 50 gm.-mols. per 
 liter. In the same electrolyte the concentration of 
 the Pb ++ ion is about 2 x lO' 8 . 
 
 While it is true that 10" 50 means only a few mole- 
 cules in a volume equal to the oceans of the world, 
 this is the number we need to express the concentra- 
 tion ratio in our cell. It must be remembered that 
 
92 STORAGE BATTERIES 
 
 these ions only have to pass over molecular distances 
 and that the reservoir of sulphate from which they 
 are drawn can supply them as fast as they are needed. 
 In such statistical matters as this the unit may make 
 a great difference. There is nothing surprising 
 about the statement that ten children are born per 
 year in a certain village. The same fact is repre- 
 sented by the statement that 0.00000031 children are 
 born there per second. 
 
 In terms of Nernst's theory and Liebenow's 
 hypothesis, we have for the lead peroxide electrode 
 
 rbo,= -0.0288 log 
 and for the entire cell 
 
 e = 0.0288 log Pp 
 
 61. Conclusions to be Drawn. This equation gives 
 interesting qualitative relations. Evidently we can 
 hardly do better than to retain sulphuric acid as our 
 electrolyte. We are also to use it as strong as the 
 life of the plates will permit ; for while lead sulphate 
 is more soluble in concentrated acid than in dilute, 
 and we will therefore lose a little at the lead elec- 
 trode, the PbO 2 concentration decreases as the 
 fourth power of the hydrogen ion concentration, and 
 we should much more than make up for the loss. 
 As a matter of fact, manufacturers have gradually 
 
REACTIONS AT THE ELECTRODES 93 
 
 increased the commercial concentration of their elec- 
 trolyte, with a corresponding increase in the electro- 
 motive force of their cells. Ten years ago electrolyte 
 of density 1.15 was the rule. Now nearly every one 
 uses a density of 1.210, and for special work as high 
 as 1.225. In portable cells where the limit of weight 
 is fixed and a small total mass of electrolyte must be 
 carried, the density is permitted to go as high as 1.27. 
 We can also see from this formula that an alkaline 
 electrolyte, with its high concentration of PbQ 2 , 
 would greatly decrease the electromotive force of 
 the cell. In caustic soda solution it does in fact go 
 as low as 0.75 volt. An electrolyte containing a 
 large concentration of Pb ++ will also lower the elec- 
 tromotive force, and if we could manage an electro- 
 lyte which was both strongly alkaline and high in 
 Pb ++ , we could reach a very low value indeed. 
 
CHAPTER IX 
 
 CHARGE AND DISCHARGE 
 
 62. Up to now we have been considering the cell 
 as independent of the current flowing through it. 
 This point of view is necessary for a theoretical dis- 
 cussion, because the whole cell is changed as soon as 
 current passes. From a rather simple system, quite 
 open to formal investigation as long as it stands on 
 open circuit, the cell changes to a very complex 
 system as soon as it begins to work. The only way 
 to study this complicated thing is to keep all the 
 factors but one as constant as possible, and follow the 
 change in that one. Each factor in turn can some- 
 times be taken up in this way and the whole problem 
 cleared up. But in the case of our cell we shall find 
 that this general method of solving scientific puzzles 
 is hard to apply. So many of the factors which are 
 active in a storage cell are not within our direct con- 
 trol. For these reasons it is easiest to follow the 
 changes in an accumulator by study of curves and 
 families of curves. A single such curve shows the 
 mutual effect of two things. A family of curves 
 shows a great deal about three factors and their re- 
 
 94 
 
CHARGE AND DISCHARGE 95 
 
 lations. Let us take first of all the curves which 
 show how the voltage of an accumulator changes 
 with time, while it is being charged and discharged 
 at a constant rate. 
 
 In all that follows, the general theory of Chap- 
 ter VIII should be kept clearly in mind. Large 
 changes in voltage appear during complete charge 
 and discharge, but every change can be explained 
 satisfactorily and completely by reference to changes 
 in the concentration of the active ions. 
 
 The electromotive force of the Pb/Pb ++ electrode 
 is given by the formula 
 
 e= 0.0288 lo-^a,. 
 
 and that of the PbO 2 /PbO 2 ~ electrode by 
 e fbo , = 0.0288 log 
 
 at every point of a charge, discharge, or recovery 
 curve. 
 
 The only variables are the concentrations of Pb ++ 
 and PbO 2 . 
 
 It should also be kept clearly in mind that the 
 Pb ++ ion concentration varies inversely as the acid 
 concentration at the point of activity, and inversely 
 as the square of the H + ion concentration, while the 
 PbO 2 ion concentration varies inversely as the 
 
96 STORAGE BATTERIES 
 
 square of the acid concentration and therefore in- 
 versely as the fourth power of the H + concentration 
 (see Appendix, page 260, for the complete state- 
 ment of the theory). 
 
 63. Charge Curve. Our cell has been fully dis- 
 charged at a rather low rate. Lead sulphate has 
 been formed through each plate wherever sulphuric 
 acid of sufficient concentration was available for re- 
 action. Lead peroxide and lead sponge have been 
 more or less completely exhausted and partially 
 covered with a layer of sulphate. Sulphuric acid 
 has been taken from the electrolyte, which has a 
 lower acid concentration than before the discharge. 
 
 We connect -the terminals of the cell with a source 
 of current, and proceed to charge it. 
 
 The reaction is 
 
 2 PbSO 4 + 2 H 2 O = PbO 2 + Pb + 2 H 2 SO 4 . 
 
 The reservoir of lead sulphate supplies material, 
 and water is taken from the electrolyte as well. 
 The reactions described on page 55 begin, and sul- 
 phuric acid is set free in the two plates. 
 
 If the cell has been recently discharged, this reaction 
 begins immediately, and the voltage rises slowly 
 until diffusion balances the concentration of the acid 
 at the point where the reaction is taking place. But 
 if the cell has been rather completely discharged, 
 and has been standing for some time, the layer of 
 
CHARGE AND DISCHARGE 
 
 97 
 
 sulphate, which has had time to change into the 
 firmer and more stable modifications, must first be 
 broken through. In this case the charging voltage 
 overshoots a little just at first (Figure 26). It rises 
 rapidly for a short time, and then drops again slowly 
 to the value corresponding to the concentration of 
 
 tx\ 
 
 2.081 
 
 \ 
 
 678 
 
 MINUTES 
 
 FIG. 26. The very beginning of charge on a completely discharged 
 plate. (Vertical scale large.) 
 
 the acid at the active point in the plate (see A, 
 Figure 27). There is no positive evidence that this 
 kind of lead suphate is an insulator or even a very 
 poor conductor. Measurements of the internal re- 
 sistance of a discharged cell show that there is no 
 increase at this point sufficient to account for this 
 little rise in voltage. It seems much more probable 
 
98 
 
 STORAGE BATTERIES 
 
 that the acid concentration is, as usual, responsible, 
 and that the layer of sulphate merely prevents easy 
 diffusion until it has been broken through. It may 
 act for the moment as a semi- or nearly impermeable 
 membrane, retaining the concentrated acid, and so 
 causing the rise in electromotive force. 
 
 ae 
 
 24 
 
 A B 
 
 2345 
 
 HOURS 
 
 Fia. 27. Changes in cell e. m. f. during charge and discharge at the 
 5-hour rate. 
 
 In any case the electromotive force of our cell 
 very soon reaches a definite value, characterized by 
 the factors : 
 
 (a) Acid density. 
 
 (5) Temperature. 
 
 (c) Rate of charge. 
 
 (d) Type of plate. 
 (e~) Previous history. 
 
CHARGE AND DISCHARGE 99 
 
 64. Peculiarities of the Charge Curve. At the point 
 marked B on the charge curve (Figure 27) this 
 definite condition has been reached. The condition 
 is only momentary, and, as charge proceeds at con- 
 stant rate, the electromotive force increases slowly 
 throughout the part of the curve marked 0. Sulphate 
 is being transformed into lead and peroxide, and acid is 
 being produced throughout the plates. Diffusion is 
 becoming more and more difficult, for it must take 
 place through ever-increasing distances, and along tor- 
 tuous and minute passages. The slope at any point in 
 this part of the curve is also a function of the five fac- 
 tors, and the condition of the cell as to charge can 
 always be seen by one acquainted with the type of 
 plate, by merely reading the voltmeter, and taking 
 into account the time the cell has been on charge. 
 
 At D there comes an evident change. The curve 
 begins to rise much more rapidly, and gas is evolved 
 more freely. The curve rises through E, then drops 
 slightly at F, and runs along parallel to the time 
 axis. From this time on the cell is merely a machine 
 for the electrolytic manufacture of hydrogen and 
 oxygen. 
 
 The rapid change of curvature at D is significant. 
 It cannot be due to any further increase in the acid 
 concentration inside the plates, for they are nearly 
 completely changed into lead and peroxide by now, 
 and very little acid is being formed. What little is 
 
100 STORAGE BATTERIES 
 
 formed is greatly assisted in circulation and dilution 
 by the gas bubbles now rising from the plates. This 
 acts as a vigorous stirrer and equalizes the acid con- 
 centration through the whole cell. The rapid rise at 
 D must have another cause. Refer to the equation 
 on page 89. 
 
 Up to the point D we had plenty of lead sulphate 
 to work on, and the solution has always been 
 thoroughly saturated with PbSO 4 , except perhaps 
 immediately about the grains on which Pb and PbO 2 
 are depositing. But at D we begin to clear out the 
 last of the solid sulphate and from that point on the 
 solution becomes less and less concentrated in Pb ++ . 
 Part way up the curve at E there is so little Pb ++ pres- 
 ent that it is just as easy to cause hydrogen gas to 
 leave the solution as it is to force out solid lead. 
 This means a high electromotive force (page 92). At 
 E the last of the more concentrated acid and of lead 
 ion as well hold up the electromotive force for an in- 
 stant by their presence inside the plates ; they are 
 then cleared away by streams of gas bubbles, and the 
 charge is complete. 
 
 65. Now for the factors a, 5, 0, d, and e, and their 
 effect on the charge curve. 
 
 (a) Acid density. The effect of various concentra- 
 tions of acid on the open circuit electromotive force 
 of the cell is shown in Figure 25. The effect at any 
 point in the charge curve might also be found, but 
 
CHARGE AND '! 
 
 it would be so very lively and changeable a factor 
 as not to be very valuable as a criterion. From 
 what we have already learned of the effect of acid 
 concentration on electromotive force (page 92) we 
 can be sure that something like the following picture 
 expresses the factor in question. Diffusion is a func- 
 tion of gradient. Acid will diffuse out of the plate 
 into the ambient electrolyte at a rate proportional to 
 the difference of concentration at these two places. 
 But acid is produced in the interior of the plate in 
 direct proportion to the current which is passing, and 
 regardless of acid density in the electrolyte. The 
 same current will therefore give a greater gradient 
 with a weaker acid in the cell than with a strong one, 
 and the effect of the average acid on the electromotive 
 force will be less for high than for low concentrations. 
 (b) Temperature. This has an important effect 
 on diffusion. At the higher temperature diffusion 
 is rapid, and the concentrated acid formed in the 
 plate is rapidly removed. The voltage required to 
 charge our cell will be lower and the whole charge 
 curve will be changed in position and shape. This 
 effect is, of course, quite aside from any effect of 
 temperature on the electromotive force of the cell (see 
 page 72), and the latter factor is for any practical cell 
 so small as to be almost negligible, while the former 
 factor is by no means a small one. The temperature 
 coefficient of diffusion is about 2 % per Centigrade de- 
 
102 ; 8: 
 
 BATTERIES 
 
 gree and is for certain types of cell of great importance. 
 In electric vehicle work, for instance, winter tempera- 
 tures are most trying, and the effect is to reduce the 
 apparent capacity of the battery by a considerable 
 fraction. This almost wholly because of voltage 
 limits imposed by the slowness of diffusion at the 
 
 2.8 
 
 2.6 
 
 2.2 
 
 2.0 
 
 1.8 
 
 7 
 
 34567 
 HOURS 
 
 FIG. 28. Charge curves on the same plate at various rates. 
 
 low temperature. (See page 253 for data on practical 
 cells.) 
 
 (<?) Hate of charge. This determines the rate at 
 which acid is formed at the place where the action is 
 going on. Diffusion determines how fast this acid 
 shall be removed. At high rates the whole charge 
 curve is steeper. (See Figure 28.) 
 
 (d) Type of plate. The position and slope of the 
 charge curve vary with the plate tested. Surface, 
 thickness of active material, hardness, are all factors. 
 
CHARGE AND DISCHARGE 
 
 103 
 
 A large-surface Plante plate, with a comparatively 
 small content of active material, shows a curve like 
 A in Figure 29. An intermediate type has the 
 characteristics shown by B, in the same figure. The 
 extreme of high capacity, a light grid with a large 
 
 1- 
 
 -123 
 
 2.0 
 
 12345 
 HOURS 
 
 FIG. 29. Charge curves for plates of various types. 
 A. Plants plates. B. Mixed type. C. Paste plates. 
 
 percentage of active material, gives curve (7; all other 
 factors of course being constant for the three cases. 
 Here, as in every other case, the concentration of 
 acid at the point of action is the deciding factor. 
 The large surface plate is pretty freely open to the 
 acid. Diffusion is easy, since it takes place largely 
 through the main body of the electrolyte and not 
 through the pores of a packed mass of active material. 
 In the mass plate we have the other extreme. 
 
104 
 
 STORAGE BATTERIES 
 
 Diffusion, except at the very outside surfaces, must 
 proceed through long capillaries in a comparatively 
 thick mass of active material and is correspondingly 
 slow and inefficient. 
 
 66. Recovery after Charge. Our cell is fully 
 charged. The last remnants of available lead sul- 
 
 TIME Of CHARGE-MINUTES 
 
 FIG. 30. Curve showing end of charge and recovery after opening 
 
 circuit. 
 
 phate have been attacked and removed and the plate 
 is nearly pure lead or lead peroxide. Whatever 
 sulphate is left in the plate lies too deep to be easily 
 reached or is incapsulated with active material. 
 When the charge circuit is broken the electromotive 
 force drops along a recovery curve. Lead sulphate 
 will now go into solution until saturation is reached, 
 and the process of solution of the sulphate in the 
 quiet electrolyte is largely one of diffusion. The 
 
CHARGE AND DISCHARGE 
 
 105 
 
 curve is very much like a diffusion curve, dropping 
 rapidly at first and then more and more slowly 
 toward a limit. (See Figure 30.) 
 
 67. Discharge. If current be now drawn from the 
 cell by closing the circuit through an external resist- 
 
 06 
 
 u 
 
 O &6 
 
 $ 
 
 d 2-04 
 
 S 
 
 10 12 14 16 16 20 22. 
 
 MINUTES 
 
 FIG. 31. The beginning of discharge after complete charge. This 
 curve is an enlargement of the first part of the lower curve in 
 
 Figure 27. 
 
 ance, the electromotive force passes through the 
 stages shown in the curve of Figure 27. The little 
 hump in the curve at Gr (see Fig. 31) appears only 
 under certain conditions, and it may be due to the 
 formation of a supersaturated Pb ++ solution and a cor- 
 respondingly low electromotive force. This could 
 
106 STORAGE BATTERIES 
 
 occur in very fully charged plates where there is not 
 enough lead sulphate near the surface to release such 
 a supersaturatioii. And, as a matter of fact, it only 
 does appear in fresh and active plates which have 
 been very fully charged immediately previous to tak- 
 ing the discharge curve. This peculiar twist can last 
 but an instant, for then the limit of supersaturation 
 is passed and PbSO 4 begins to deposit everywhere. 
 The electromotive force then rises to its proper value, 
 corresponding to the concentration of the acid (now 
 being depleted) at the point of activity, and the curve 
 proceeds smoothly. As discharge goes on along the 
 curve at H, diffusion (now of acid into the plate) be- 
 comes more and more difficult. The active concen- 
 tration of acid droops, and at the point I the cell is 
 for practical purposes discharged. Its electromotive 
 force is still 1.7 volts, and it could be run for some 
 time longer at low rates before dropping to zero. As 
 storage batteries are used in practice, 1.7 may be 
 taken as the limit of useful discharge at a low rate. 
 (See page 118.) 
 
 The five factors of page 27 are just as important 
 during discharge as during charge and for the reasons 
 given at that place. Acid density determines starting 
 point and position of the curve, and simultaneous ex- 
 amination of discharge voltage and density, as given 
 in the curves of Figure 32, enables one to decide upon 
 the condition of the cell as to charge or discharge 
 
CHAEGE AND DISCHARGE 
 
 107 
 
 12 
 
 5.M 
 
 s | 
 
 1.9 12 
 
 FIG. 32. Discharge curves showing change in acid density and in 
 voltage. 
 
 from acid density as well as from voltage. Temper- 
 ature affects diffusion and therefore acid concentra- 
 tion at point of action and electromotive force. It 
 
 CIRCU 
 
 f OP! NED 
 
 8 d 10 It IZ 13 14 15 I a 3 4 
 
 MINUTES 
 
 FIG. 33. End of discharge and recovery. 
 
108 
 
 STORAGE BATTERIES 
 
 also affects the electromotive force directly. Rate of 
 discharge determines acid concentration and there- 
 fore the concentration of the active ions. Type of 
 
 L30 
 
 125 
 
 120 
 
 1.15 
 
 1.10 
 
 1.00 I 
 
 IS 
 
 0.95 l 
 
 X4- 
 
 vro 
 
 REACHES L9 
 
 IN 5HRS.2SMIN. 
 
 10 ZO 30 40 50 
 
 MINUTES 
 
 FIG. 34. Recovery after very long and complete discharge. 
 
 plate enters and previous history of the cell. (See 
 page 113.) 
 
 68. Recovery after Discharge. The curve along 
 which recovery takes place after discharge is shown 
 in Figures 33 and 34. It is very much like a diffu- 
 sion curve, and represents the rate of return to the 
 
CHARGE AND DISCHARGE 
 
 109 
 
 normal concentration of acid in the cell on the part of 
 the acid in the deep interstices of the plates. It is 
 not quite the right shape for a pure diffusion curve, 
 and the equalization of concentrations throughout 
 the cell is undoubtedly assisted by local action. 
 
 1 2 3 
 
 HOURS 
 
 FIG. 35. Charge and discharge curves of [A] Plante and [B] mass 
 
 plates. 
 
 69. Special Peculiarities of Charge and Discharge 
 Curves. The two extreme types of plate large sur- 
 face Plante on the one hand, and thick mass plates on 
 the other show evident differences in their curves 
 of operation. Figure 35 indicates the general char- 
 acter of these differences, and a resume of the theory 
 of the inflections of these curves will be found to 
 
110 
 
 STORAGE BATTERIES 
 
 agree with the physical characteristics of the plates. 
 It is quite possible to get composite curves from 
 composite plates. An interesting example is the 
 type of ribbed Plante plate now very common all 
 over the world and used for the hardest kind of 
 
 I 
 
 514 
 
 1.0 
 
 0.8 
 
 0.6 
 
 15 30 45 60 75 90 105 120 135 
 MINUTES 
 
 FIQ. 36. Full discharge curve of ribbed Plant6 plate. 
 
 work. Figure 36 shows the full discharge curve of 
 a Gould plate. For the greater part of its discharge 
 it behaves like a large surface plate, which it is. 
 Then the action reaches that part of the plate where 
 there is a considerable mass of active material, much 
 of it at about the same distance from the main bulk of 
 acid in the cells. Here the droop is stopped for a 
 short time, and only when the action has penetrated 
 
CHARGE AND DISCHARGE 
 
 111 
 
 far into this last reservoir of material does the final 
 drop begin. And the final drop, instead of being 
 like that of a large surface plate, is much more like 
 a mass plate. The only reason why these peculiari- 
 ties are not noticed every day is because they lie at 
 
 17 
 
 1.6 
 L5 
 
 14 
 
 13 
 H 
 
 I" 
 
 c 
 
 d 
 
 o 
 
 09 
 0.8 
 07 
 0.6 
 Q5 
 
 \ 
 
 N, 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 x^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^"^ 
 
 ^ 
 
 ^ 
 
 1 Z 34567 8 9 10. II 12 
 
 FIG. 37. End of curve of complete discharge at constant rate ( 
 Plant6 type). 
 
 voltages lower than those of practical service condi- 
 tions. (See also Fig. 37.) 
 
 70. Charge and Discharge at Various Rates. Figures 
 38 and 39 show series of curves of charge and dis- 
 charge for two types of plates at various rates. They 
 hardly require detailed discussion, for they fit very 
 closely the general principles so often invoked in 
 
112 
 
 STORAGE BATTERIES 
 
 explanation of changes in cell electromotive force. 
 The charge curves have much the same general char- 
 
 FIG. 38. Curves of operation of Plante plates at various rates. 
 
 The rates for the curves of Figure 38 are 
 
 For 8-hours of charge or discharge 1 ampere 
 5 1.4 , 
 
 3 
 
 1 
 
 20 minutes 
 5 minutes 
 
 2.0 
 
 4.0 
 
 8.0 
 
 16.0 
 
 These are the rates usually specified in practice. 
 The capacities corresponding to these rates are 
 
 For 8-hour charge or discharge 8 ampere-hours 
 
 3 ,, 
 
 1 
 
 20 minutes 
 
 5 minutes 
 
 7 
 
 6 
 
 4 
 
 2.67 
 
 1.33 
 
 acteristics at different rates, but show more rapid 
 changes as the rates are raised. The most interest- 
 
CHARGE AND DISCHARGE 
 
 113 
 
 ing thing about the set of curves is the information 
 it gives about the last factor in our list the " pre- 
 vious history " of the cell. It makes a great differ- 
 ence in the discharge curve of a cell whether the cell 
 has been charged at a high or a low rate, and just as 
 great a difference in the charging curve, whether the 
 
 HOURS 
 
 FIG. 39. Curves of operation of mass plates at various rates. 
 
 previous discharge has been fast or slow. Take a 
 single case. Suppose a fully charged cell has been 
 discharged at the 5-minute rate. It is evident from 
 the figure that only 1.3 ampere-hours have been drawn 
 from it. We only need to return a little more than 
 this to the cell to charge it completely. In the same 
 way, if our cell has been completely discharged at a 
 low rate, and then charged at the 5-minute rate, we 
 can only get about 1.3 ampere-hours into it. It may 
 be fully charged for a 5-minute discharge, but it is 
 
114 
 
 STORAGE BATTERIES 
 
 by no means fully charged for a 3-hour discharge. 
 When we come to the chapter on operation we shall 
 have another side of this same problem to look at 
 the one which deals with the effect of charge and dis- 
 charge rates on the life of the cell. 
 
 CHARGE 
 
 HARGE 
 
 PL Alt. N.PI W IRKING , 
 
 DISCHAiiGE 
 
 HOURS 
 
 FIQ. 40. Charge and discharge curves. Peroxide and lead plates 
 measured against an auxiliary electrode (lead plate). 
 
 71. Use of Auxiliary Electrode. It is very fre- 
 quently desirable to segregate the two plates in a 
 cell, so that the course of charge and discharge may 
 be followed for each separately. Several forms of 
 auxiliary electrode have been suggested, and the one 
 in most common use is metallic cadmium. A stick 
 of this metal is used as one electrode, and the electro- 
 
CHAEGE AND DISCHARGE 115 
 
 motive force Cd/dilute Cd ++ against one of the plates 
 is measured. 
 
 It is evident that this is not the most stable of 
 electrodes, for its readings are dependent on the 
 amount of current flowing through the cadmium cir- 
 cuit and also on temperature and other factors. It 
 answers very well for most practical purposes, how- 
 ever, and some of the curves for single plate poten- 
 tials which are given in this book were made with 
 its aid. 
 
 Another way of following the single electromotive 
 forces at the two plates is to use an idle lead or per- 
 oxide plate as a third electrode, measuring each of 
 the working plates against it. Figure 40 gives 
 charge and discharge curves for working positive 
 and negative plates, measured against an idle lead 
 plate. 
 
CHAPTER X 
 CAPACITY 
 
 In our observations on the curves of charge and 
 discharge we found that at least five factors were 
 active in fixing the shape and position of these 
 curves. These same factors, together with the limit 
 of voltage set by practical experience, determine the 
 capacity of a storage cell in the sense in which this 
 term is usually applied. 
 
 The lower limit of voltage the point to which 
 the cell is discharged in actual service is not by 
 any means invariable. At low rates, as in telephone 
 and train lighting service, it is about 1.8 volts. In 
 regulating power plant loads, and in much of the 
 other regular work which a battery does, it is about 
 1.7. At very high rates, as when an emergency 
 battery is called upon to take the entire load of 
 a large station, it may be carried as low as 1 
 volt. Just for the present we will assume 1.7 volts 
 as the limit below which we cannot usefully discharge 
 our cell, and we will base its capacity on this point. 
 
 72. Faraday's Law and Capacity. Of course ca- 
 pacity, in the basic sense of the word, is given by 
 
 116 
 
CAPACITY 117 
 
 Faraday's law, and can be calculated directly from 
 the equation 
 
 Pb + Pb0 2 + 2 H 2 S0 4 = 2 PbS0 4 + 2 H 2 O. 
 
 207 gm. of lead sponge 1 
 
 239 gm. of lead peroxide [ give 2 x 96,540 coulombs, 
 
 196 gm. of sulphuric acid J 
 
 and if we keep the current small enough, it might 
 
 be possible to get this theoretical current yield at 
 
 2 volts. 
 
 Since one ampere-hour is 3600 coulombs, we will 
 need for one ampere-hour, 3.86 gm. lead, 4.45 gm. 
 lead peroxide, and 3.6 gm. H 2 SO 4 , and these are the 
 amounts of active materials which are really used 
 up in any storage cell during the passage of current 
 to the amount of one ampere-hour. In actual prac- 
 tice the voltage of the cell would have fallen to zero 
 long before all the material in the plates and the 
 electrolyte had been acted upon, and in any actual 
 cell there is always a very large excess of all three 
 of the constituents, even at the time when the cell 
 is "discharged." Besides, there must always be 
 supports for the active lead and lead peroxide, and 
 these supports must in practice have strength and 
 weight enough to enable them to withstand many 
 complete cycles of charge and discharge. As we 
 shall see later, there are useful types of cells in 
 which the materials which really enter into reaction 
 
118 
 
 8 TOE AGE BATTERIES 
 
 only make up 10 or 15 / of the total weight of the 
 plates, and only 6 or 7 % of the total weight of the 
 installation. 
 
 73. End Voltage determines Capacity. There is no 
 doubt whatever about our oft-repeated fundamental 
 principle that it is the acid concentration within the 
 
 \ 
 
 I Z 3 4 56789 
 
 DISCHARGE TIME- (HOURS') 
 
 FIG. 41. Discharge curves at various rates. 
 
 pores of the plates, at the point where the action is 
 taking place, which determines the voltage of the 
 cell. At a high rate of discharge, the acid density 
 at the active point in the plate is low, and the vol- 
 tage curve drops after a comparatively short time. 
 It becomes too hard for the electrolyte to get to any 
 more active material, even though there is plenty 
 in the plates, and useful discharge must be stopped. 
 Figure 41 gives a set of discharge curves made 
 
CAPACITY 
 
 119 
 
 in actual test on a large cell. This cell was charged 
 each time at a constant and low rate, in order that 
 the charging part of the cycle might not be a vari- 
 able factor. It was then discharged at constant 
 temperature at the rates given. If we take as the 
 
 I 34 56789 10 
 
 TIME- HOURS 
 
 FIG. 42. Capacity curves, theoretical (dotted), and experimental 
 (full-line). 
 
 voltage for stopping discharge 1.70 for most of the 
 curves, and 1.65 for the 1 hr., and 1.6 for the 20 min. 
 discharges, we get the following table : 
 
 CURRENT 
 
 20 amp. 
 40 
 80 
 1GO 
 
 TIME OF DISCHARGE 
 
 8 hours 
 3 
 1 
 20 minutes 
 
 CAPACITY IN A-H 
 
 160 A-H 
 120 
 
 80 
 
120 
 
 STORAGE BATTERIES 
 
 These values can be equally well expressed by means 
 of a single curve, for there are really only two things 
 to be related, current and time. The expression of 
 the capacity in a separate column is merely for the 
 sake of having a direct statement of capacity. 
 Figure 42 contains this curve. It is the one which 
 is drawn as a full line. 
 
 2.0 
 
 1.9 
 
 1.8 
 
 40 
 
 50 
 
 io ao 30 
 
 AMPERE-HOURS DISCHARGED 
 
 FIG. 43. Discharge curves of Plante plates at the 1, 3, and 8-hour 
 
 rates. 
 
 Figure 43 gives discharge curves for Plante plates 
 at various rates, Figure 44 similar curves for semi- 
 Plante plates, and Figure 45 curves for thick mass 
 plates. In the three cases plates were chosen with 
 the same capacity at a medium rate of discharge (3 
 hours). It is evident that the large surface Plante 
 plates are best at the high (1-hour) rate, and that 
 they are by no means up to either of the other types 
 
20 
 
 1.8 
 
 X 
 
 40 
 
 50 
 
 10 20 30 
 
 AMPERE-HOURS DISCHARGED 
 FIG. 44. Discharge curves of semi-Plant6 plates at various rates. 
 
 at the low (8-hour) rate. At the 15-hour rate the 
 curve for this particular plate is not shown in the 
 
 2.0 
 
 1.8 
 
 X 
 
 X 3 
 
 40 
 
 50 
 
 10 30 
 
 AMPERE-HOURS DISCHARGED 
 FIG. 45. Discharge curves of thick mass plates at various rates. 
 
 figure. It would reach 1.8 volts at about 32 on 
 the horizontal axis. 
 
122 
 
 STORAGE BATTERIES 
 
 The mass plates of Figure 45 are very short of 
 capacity at the 1-hour rate, but they are far better 
 than the Plante type at the low (15-hour) discharge. 
 
 The semi- Plante plate lies between the other two. 
 
 345676 
 
 THICKNESS IN MILLIMETERS 
 
 JO II 
 
 FIG. 46. Capacity as a function of the thickness of a paste plate, 
 at various rates. Peroxide plates against auxiliary electrode. 
 
 The useful end voltage has been placed at 1.8 volts 
 in this case. 
 
 It is evident from these curves that the thickness 
 (and structure generally) of a plate is a factor of im- 
 portance in its working capacity. Experiments with 
 paste plates of the same surface and varying thick- 
 ness give the results shown in Figures 46 and 47, the 
 former for positive plates and the latter for negative. 
 
CAPACITY 
 
 123 
 
 The five curves in each figure are for different 
 rates, from 1 to 16 amperes. 
 
 7 
 
 7 
 
 234567 
 
 THICKNESS IN MILLIMETERS 
 
 8 9 
 
 FIG. 47. Capacity as a function of thickness of plate. Negatives 
 against auxiliary electrode. 
 
 The dotted line in Figure 46 is for an infinitely slow 
 rate capacity directly proportional to thickness. 
 
124 STORAGE BATTERIES 
 
 74. Formula for calculating Capacity at Various Rates. 
 It is usually possible to find a not very compli- 
 cated mathematical formula to fit a curve which 
 looks like Figure 42 and the dotted line in this figure 
 is plotted as an expression of the formula 
 
 I n t= constant. 
 
 n for this particular type of plate is 1.45, and the 
 constant is determined by putting in the actual 
 values for our plate at one rate and solving the 
 equation. See 75, below. 
 
 This exponent n is rather a good measure of the 
 physical qualities of a plate. It is large for thick, 
 dense, massive ones and becomes smaller and smaller 
 as the plate is given a larger surface in proportion 
 to its content of active material. It goes as high 
 as 2.0 for some plates of the most thick and tender 
 kind, and as low as 1.20 for the most active types of 
 large surface plates. See also Figure 48. A little 
 calculation will show what kind of a family of dis- 
 charge curves at different rates will be characteristic 
 of each of these extremes. The one with exponent 
 2.0 is the easiest to calculate. 
 
 75. Let us go through the course of the calculation 
 of such a curve for the simple case where n = 2.0. 
 Assuming that the cell gives 10 amperes for 8 hr. 
 
 ^ 2 = constant 
 10 2 x 8 = constant 
 
CAPACITY 
 
 125 
 
 1.5 
 1.4 
 1.3 
 
 1.2 
 1.1 
 
 1.0 
 .9 
 
 I" 
 ' 
 
 .6 
 .5 
 4 
 .3 
 .2 
 .1 
 
 !/ 
 
 24 6 8 10 12 14 16 18 20 
 
 HOURS FOR COMPLETE DISCHARGE 
 
 FIG. 48. 
 
126 STORAGE BATTERIES 
 
 Vt = 800 
 
 t = 3 z 2 x 3 = 800 ^ 2 = 267 i = 16.3 
 = 1 z2 = 800 ^=28.2 
 
 t = J ^ 2 = 2400 t = 49 
 
 t = 98 
 
 and from this, when, 
 
 current is = 10, capacity is 80. 
 
 current is = 16.3, capacity is 49. 
 
 current is = 28.2, capacity is 28.2. 
 
 current is = 49, capacity is 16.3. 
 
 current is = 98, capacity is 8.2. 
 
 If capacity is plotted vertically in place of current, 
 the family of curves for various exponents becomes 
 still more expressive. Figure 48 gives the calculated 
 curves for values of n from 1.10 to 2.0. 
 
 It is also possible to derive a curve like the one in 
 Figure 42 with the aid of the theory of diffusion, but 
 the assumptions necessary are far-reaching, and the 
 final formula is in fact only an empirical one like our 
 own. Diffusion has the chief role to play, however, 
 here as at every other point in the theory of the lead 
 (and any other) accumulator. 
 
 76. Liebenow's Diffusion Experiment. Liebenow, 
 one of the most brilliant of the students of the lead 
 cell, made an interesting experiment on the effect of 
 merely allowing acid to flow through a plate which 
 was discharging. His arrangement is shown in 
 
CAPACITY 
 
 127 
 
 Figure 49. A negative plate was used in his test, and 
 it was found that without flow it gave 14.4 ampere- 
 hours. With flow it gave 41.6 ampere-hours. Such 
 experiments have frequently been performed of late, 
 and it is a most interest- 
 ing thing to see a plate 
 which has been ex- 
 hausted without flow, so 
 that its voltage is zero, 
 pick up and come to life 
 again as soon as acid be- 
 gins to flow through it. 
 Its voltage rises to 
 nearly 1.7, and it is ca- 
 pable of doing a great 
 deal more work. 
 
 The object of the flow 
 through the plate is to 
 keep the acid concentra- 
 tion up during discharge 
 
 FIG. 49. Liebenow's experiment 
 to show the effect of forcing elec- 
 trolyte through the plate during 
 operation. 
 
 and down during charge 
 
 at the place in the plate 
 
 where the reaction is actually taking place. Practi- 
 cal applications are numerous. Large surface plates 
 are necessary where charge and discharge rates are 
 high. They contain much less total active material 
 than paste plates of the same weight, but the material 
 in them is in a thin layer, and diffusion is easy to all 
 
128 STORAGE BATTERIES 
 
 parts of it. Then, too, thin paste plates give a far 
 larger capacity per weight than thick ones operating 
 on the same rates and to the same end voltages. 
 Aids to diffusion are perhaps the most important 
 improvements which can be made in storage battery 
 work with the exception of the all-important one of 
 a reasonably long life under hard service conditions. 
 
 The positive plate needs help more than the nega- 
 tive, for besides using up or producing sulphuric 
 acid, water appears or disappears at that point. 
 It will be seen that it needs help 1.6 times as 
 badly as the negative. In spite of this need it is 
 harder to send it the necessary relief; for while 
 negative plates can be made both tough and porous, 
 the positive active material, lead peroxide, persists 
 in being merely a dense but rather loosely inter- 
 locked mass of fine grains. Some rather rough 
 measurements on the rate at which acid diffuses into 
 positive and negative paste plates are given in Figure 
 50. These are resting plates, however, and do not 
 take into account the greater need for acid of the 
 peroxide plate during action. 
 
 Lead grows on the negative plate as real trees and 
 sponges, and this can often be clearly seen in vener- 
 able negatives on which the lead has been deposited 
 and redissolved thousands of times. The positives in 
 the same cells look lean, for they have lost much of 
 their original material, and if they are healthy, and 
 
CAPACITY 
 
 129 
 
 of the kind that have proven themselves capable of 
 hard work, they have manufactured more active 
 material to take the place of that lost. It is easy to 
 apply Liebenow's principle to the negative plate. It 
 
 
 CHAW 
 
 io ao 
 
 MINUTES 
 
 FIG. 50. Diffusion into resting positive and negative plates. 
 
 is much harder to persuade acid to flow through one 
 of lead peroxide. 
 
 77. Diffusion. To digress for a moment to the 
 general subject of diffusion. A substance in solu- 
 tion can move about from point to point in either 
 of two ways by convection or by diffusion. The 
 difference in velocity with which a given amount 
 of a substance can be transported from "one place 
 
130 STORAGE BATTERIES 
 
 to another by the two methods is enormous. Sup- 
 pose a tall cylinder with a couple of inches of a 
 strong solution of a colored salt (copper nitrate, for 
 example) in the bottom, and with pure water filling 
 the rest of the cylinder. By convection we could 
 mix the whole to a homogeneous average solution 
 in ten seconds, by violent stirring or shaking. By 
 diffusion alone the same degree of mixing would 
 take months. 
 
 The process of convection could be delayed in the 
 cylinder by filling it with glass or cotton wool. In 
 this case the transfer of material from the concen- 
 trated solution out through the dilute one has to 
 take place through spaces in the inert substances. 
 It is much as though the cylinder were a mile long 
 instead of a foot. Diffusion will also be delayed 
 by the inert filling, but in much less degree. The 
 difference becomes still more evident if we fill the 
 cylinder, not with pure water solutions, but with 
 solutions which set to a jelly, such as gelatine or 
 agar a concentrated gel below; a pure water gel 
 above. Now convection is entirely stopped and 
 diffusion has all the work of transportation to do. 
 The process becomes a very tedious one indeed. 
 
 78. Diffusion and Convection in the Cell. In the 
 storage battery the real transport of all material is 
 a matter of diffusion. Solid material is there in 
 plenty, but the acid of the electrolyte is just as 
 
CAPACITY 131 
 
 necessary for the reaction as the solids, and it has 
 to come to the solid by diffusion through the fine 
 pores of the active material. At certain portions 
 of the cell cycle convection comes along to help, 
 especially when gas is being evolved in the plates. 
 The gas bubbles stir everything up and assist greatly 
 in bringing materials to the point where they are 
 needed. The difference in density between the con- 
 centrated acid formed during charge and the aver- 
 age acid of the cell also gives rise to convection 
 currents, which can be clearly seen by looking across 
 the face of a plate toward a bright source of light. 
 If the cell is charging, a thin stream of denser elec- 
 trolyte can be seen running down the face of the plate 
 and curling up on the bottom of the cell. The more 
 dilute acid can also be seen rising up along the face 
 of the plate during discharge. 
 
 79. Recovery Curves and Diffusion Curves. The 
 curves in Figures 30, 33, and 34 are very nearly like 
 diffusion curves. When the circuit is closed for dis- 
 charge, material is rapidly exhausted near the solid 
 particles which are active. The concentration gradi- 
 ent becomes steep and acid begins to diffuse toward 
 that point. Lead sulphate is formed in the solution 
 and presently a state of very dynamic equilibrium is 
 reached. Acid is being transported by diffusion just 
 fast enough to supply the demand at the point of 
 reaction ; and lead sulphate is being removed by pre- 
 
132 STORAGE BATTERIES 
 
 cipitation as fast as it is formed. The curves re- 
 ferred to are, of course, voltage curves, but the 
 relations of page 92 show clearly that the curves 
 can equally well express the average concentration 
 of reacting materials at the point of action. The 
 recovery curve of page 133 is of the same nature. At 
 the lower part, at the beginning of the recovery curve 
 in Figure 33, we have the final condition described 
 above. Materials are being supplied at a rate just 
 able to maintain the concentration at a rather low 
 and constantly decreasing value. When the circuit 
 is opened, consumption of material ceases. But the 
 concentration at the point where the reaction was 
 going on was different from that outside in the body 
 of the cell. Diffusion, therefore, continues and the 
 concentration differences become smaller until diffu- 
 sion becomes indefinitely slow. 
 
 Theoretically these curves take an infinite time to 
 become perfectly flat, but practically they approach 
 very near to a final value within a few minutes. One 
 exception to this last statement will occur to every 
 one who watches storage cells closely. A very fully 
 charged cell, which has been gasing freely, takes a 
 long time to return to its open circuit electromotive 
 force (see Fig. 51). This cannot be due to any high 
 concentration of acid in the pores of the plates, for 
 practically all the materials have long since been dis- 
 posed of and only an infinitesimal amount of acid is 
 
CAPACITY 
 
 133 
 
 being produced. There is another reason for this 
 slow approach to the normal open-circuit voltage. 
 At the end of full charge, practically all the dissolved 
 sulphate has been driven out of solution. Opening 
 the circuit at the end of such a charge permits lead 
 
 2JC 
 
 16 18 ZO iZ 24- 
 
 FIG. 51. Recovery curve after complete charge. 
 
 sulphate to form. Local action takes place at the 
 places where support and active material are in con- 
 tact. So lead sulphate is soon present inside the 
 plate. But before it reaches its normal maximum 
 concentration at all points in the plate it has to 
 saturate the entire electrolyte. The drop in voltage 
 is therefore not so rapid as it would be if only acid 
 diffusion were to be considered. Besides the diffu- 
 sion of an already dissolved substance, we have to 
 wait in this case for its formation. 
 
134 
 
 STORAGE BATTERIES 
 
 80. The Effect of Temperature on Capacity. Since 
 capacity is determined by a fixed voltage limit as 
 well as by other factors, we must expect to find that 
 the effect of temperature will be a considerable one. 
 Figure 52 gives a set of discharge curves at the same 
 rate but at the different temperatures indicated on 
 
 \ 
 
 135* 
 
 90 
 TIME- MINUTES 
 
 150 
 
 FIG. 52. Discharge curves. All made at same rate but at various 
 temperatures. 
 
 the curves. This was taken with constant charge 
 conditions. The cell was in every case charged at 
 25 C. Its temperature was then changed by heat- 
 ing or cooling the thermostat in which it was kept, 
 and after remaining constant for five or six hours, 
 charging at a low rate all the time, the discharge was 
 taken. The rate was such as should give complete 
 
CAPACITY 135 
 
 discharge in one hour under normal conditions of 
 service, and the 25 curve shows this. The voltage 
 dropped to 1.7 in just about one hour. At 48 the 
 same cell ran for an hour and three quarters; at 8 
 for half an hour. A difference of over 100 % for 
 quite possible limits of temperature, and of over 
 300 % within temperatures not really dangerous to 
 the life of these cells ! 
 
 This is a very high temperature coefficient, to be 
 sure, but it is hardly possible to make a cell which 
 has not a coefficient of at least one per cent per 
 degree in the ordinary working range of tempera- 
 tures. 
 
 Everything combines to make the storage cell work 
 better and more efficiently at the higher temperature. 
 For the usual acid concentration the temperature co- 
 efficient of electromotive force is positive, and has a 
 value not far from 0.0003 volt per Centigrade degree. 
 This, of course, has nothing to do with the ampere- 
 hour capacity of the cell, except to raise the voltage 
 a little, and thus lengthen the time of discharge a 
 little. Examination of the discharge curves at 
 various temperatures will show how very little this 
 affects the total number of ampere-hours which can 
 be taken from the cell. A difference of 30 C. means 
 0.0003 x 30, or a rise of only 0.009 volt in the 
 fundamental cell electromotive force due to the 
 higher temperature, and this is not even measurable 
 
136 STORAGE BATTERIES 
 
 on a curve which is drooping as rapidly as the low- 
 temperature curves of Figure 52. 
 
 81. Reaction Velocity. But the other two factors 
 are highly important. One of these is the diffusion, 
 which we have discussed at length. The other is not 
 less important, probably, though it is much more 
 difficult to isolate and examine. This is the increased 
 reaction velocity. Whatever the reactions which are 
 basic for the action of the cell, we have found very 
 good evidence that the transport through the elec- 
 trodes is cared for by ions which are present in very 
 small concentration. 
 
 The velocity with which these ions are formed from 
 the solid material of the plates, in reaction with the 
 electrolyte, is a determining factor of importance. 
 As a matter of fact the temperature effect on the cell 
 is too great to be ascribed to diffusion alone. And 
 while in most cases reactions between ions take 
 place so rapidly that they are quite unmeasurable, it 
 is not impossible that the effect should be evident in 
 such a case as this, where the ionic concentrations 
 are so very small. 
 
 82. Effect of Acid Density on Capacity. Measure- 
 ments of the capacity of a cell with varying acid 
 density, and with all the other factors which might 
 affect its behavior kept as constant as possible, give a 
 very simple and interesting result. The cell shows 
 its maximum of capacity for an acid of maximum 
 
CAPACITY 
 
 137 
 
 conductivity. This is in both cases, for sulphuric acid, 
 of density about 1.22. (See Figure 53.) We shall 
 be better able to explain the reason for this coinci- 
 dence when we have discussed the facts about the 
 
 10' 15* aO 25 30" 35* 
 
 ACID DENSITY 
 
 FIG. 53. Change in cell capacity at various rates (1, 2, 4, 8, and 16 
 amperes) with various acid concentrations. (See also Figures 72 
 and 73). 
 
 internal resistance of our cell, and we will therefore 
 leave it until we reach that chapter (page 167). 
 
 83. Watt-hour Capacity. It is, of course, the 
 energy capacity, or watt-hour capacity, of the cell 
 which really interests us. This is found by multi- 
 plying the ampere-hour capacity by the average vol- 
 tage of discharge. The curves of Figure 54 are the 
 same as those of Figure 41, and on each a straight 
 
138 
 
 STORAGE BATTERIES 
 
 line was laid out along the average cell electro- 
 motive force during the time of discharge. The 
 areas under these lines, including everything from 
 time zero to time-end of discharge, and from the 
 line of average electromotive force down to zero 
 electromotive force, give watt-hours if we multiply in 
 
 3456 
 HOURS OF DISCHARGE 
 
 FIG. 54. Watt-hour capacity areas at various rates, and discharge 
 curves from which they were taken. Discharge at 1, 1.4, 2, and 4 
 amperes. 
 
 each case by the discharge current. The rectangles 
 give the set of areas so produced, merely as visual in- 
 dication of the variation in energy capacity of a 
 storage cell with change in discharge current. The 
 same differences are given in Figure 55 for tempera- 
 ture variation, for one type of cell only. Other 
 curves for these same relations will be found on page 
 
CAPACITY 
 
 139 
 
 253, in the discussion of various types of cells under 
 actual working conditions. 
 
 84. Weight Capacity. For most purposes where 
 the battery has to be carried about the energy 
 capacity per pound of battery is a very important 
 ratio. This is especially true of batter- 
 ies which are used for electric vehicles, 
 and for submarine boats. The calcula- 
 tion of this factor is very simple. Divide 
 the total watt-hour output of 
 the battery at the desired rate 
 by the total weight of the 
 battery and con- 
 nections. Data on 
 actual tests will be 
 found in chapter 
 XVIII, page 254. 
 
 This factor is not 
 one of much interest 
 to the buyer of a large stationary battery, but it is a 
 matter of interest to the manufacturer who has to 
 pay for the lead used in making the battery, and 
 therefore has a good deal to do with the price which 
 he is obliged to ask for a battery to do a certain kind 
 of work. The modern tendency to install paste 
 plates in large emergency batteries is a good example 
 of this fact. The paste plates give a much larger 
 watt-hour efficiency per pound of total battery, and 
 
 8C 
 
 25C 
 
 48C 
 
 FIG. 55. Watt-hour capacity areas at 
 various temperatures. 
 
140 STORAGE BATTERIES 
 
 as they are also much cheaper to make per killo watt- 
 hour, they can be sold cheaper than the large-surface 
 plates of the same total capacity. It becomes merely 
 a question of life and cost of maintenance whether 
 this type, or the perhaps longer-lived Plant plates, 
 shall be used for this work. 
 
CHAPTER XI 
 
 EFFICIENCY 
 
 85. There are two ways of stating what is called 
 the efficiency of a storage cell. One of these is in 
 terms of ampere-hours; it is the ratio of the num- 
 ber of ampere-hours which can be taken out of the 
 cell to the number which must be put into it to bring 
 it back to its original condition. The other efficiency 
 is expressed in terms of watt-hours the ratio of the 
 watt-hours taken out to those put in. The first kind of 
 efficiency is more or less misleading as a criterion of 
 the quality of a cell, but the second is of decided 
 interest and importance. 
 
 86. Ampere-hour Efficiency. From what we have 
 already said about the behavior of a cell in charge 
 and discharge it is evident that the ampere-hour 
 efficiency of most cells under the usual conditions 
 will be high it will be nearly 100%. For the only 
 way in which current is lost is by local action and by 
 the evolution of gas during charge. If charge is 
 carried on at a very low rate, gas does not begin to 
 form on the plates until very near the end of charge. 
 The DE part of the charge curve (see Figure 27) 
 
 141 
 
142 STORAGE BATTERIES 
 
 is steep and occupies only a .small fraction of the 
 whole time. Gas begins to form rather suddenly, 
 and at this time the cell is practically fully charged. 
 Under these conditions the ratio 
 
 ampere-hours taken out 
 ampere-hours put in 
 
 is very nearly unity. 
 
 Even at fairly high rates the production of gas 
 only involves the expenditure of a comparatively 
 small fraction of the current sent into the cell, and 
 for working charge rates it leads to ampere-hour 
 efficiencies of 90% to 95%. 
 
 The losses due to local action are very small if the 
 cell is charging and discharging with only a small 
 interval of rest. And this is usually the case where 
 efficiency is a factor of importance. If a battery is 
 standing on open circuit for a long time, with only 
 an occasional charge to keep it in good condition, and 
 with a rare discharge at a very high rate (as in the 
 case of a stand-by or emergency battery), efficiency as 
 such is not a factor which need be considered at all. 
 The interest on the battery investment on this latter 
 case is so much greater than all the coal expended 
 on it that the latter item disappears completely. 
 The factor which is of importance in such an emer- 
 gency battery is watt-hour capacity, and if this could 
 be attained conveniently with a cheap battery of 
 
EFFICIENCY 143 
 
 efficiency 20%, we would see this type of battery 
 installed in stations which require this kind of " in- 
 surance." 
 
 Formally, ampere-hour efficiency is 
 
 ^charge ^charge 
 
 and for most purposes in service it will be found to 
 be from 90 % to 95 % . As far as this is concerned 
 the battery is about as efficient as any of the ordinary 
 electrical machinery. 
 
 87. Energy Efficiency. The other and more im- 
 portant kind of efficiency is energy efficiency, and 
 this is the ratio of the energy which can be taken 
 from the cell to that put into it. Or, 
 
 watt-hours taken out 
 
 watt-hours put in 
 This is also evidently expressible as 
 
 where i and t have the same meaning as above and 
 e c and e d are the average cell voltages of charge and 
 discharge respectively. 
 
 88. Data for Efficiency Calculation. The most direct 
 way to get data on the value of EE is for us to ex- 
 amine sets of curves like those in Figure 41 and 
 Figure 53 and calculate ampere- and watt-hour 
 
144 
 
 STORAGE BATTERIES 
 
 4.0 
 
 2.0 
 
 1.4 
 
 1.0 
 
 FIG. 56. Ampere-hour efficiencies at various rates. Plant6 plates 
 discharged at 1, 1.4, 2, and 4 amperes. Charge at 1 ampere. 
 
 efficiencies from them. Figures 56 and 57 give areas 
 so calculated from a similar set of charge and dis- 
 
 4.0 
 
 2.0 
 
 1.4 
 
 1.0 
 
 FIG. 57. Watt-hour efficiencies at various rates. Plant6 plates dis- 
 charged at 1, 1.4, 2 and 4 amperes. Charge at same rate as dis- 
 charge. 
 
EFFICIENCY 
 
 145 
 
 charge curves. It will be noticed that while the 
 ampere-hour efficiencies are good enough even at the 
 higher rates, the watt-hour efficiencies fall off pretty 
 rapidly, going as low as 60 % at the highest rates of 
 charge and discharge. These are rather extreme 
 cases, however, for storage cells in hard service are 
 
 4.0 
 
 2.0 
 
 1.4 
 
 .0 
 
 FIG. 58. 
 
 rarely charged as fast as they are discharged, and the 
 actual figures are a little higher than those obtained 
 by holding rigorously to a charge rate as high as that 
 of discharge. This will be very evident if we take a 
 medium rate for charge and determine efficiency for 
 this rate and various discharge rates. Figure 58 gives 
 these data. Here we have assumed the one-hour rate 
 of charge, and taken the corresponding curve through- 
 
146 
 
 STORAGE BATTERIES 
 
 out. At very low 
 rates the charge 
 and discharge vol- 
 tages may be nearly 
 the same through- 
 out the whole cycle 
 of operation. Fig- 
 ure 59 shows the 
 change in cell vol- 
 tage at the various 
 low charge and dis- 
 
 FIG. 59. Charge and discharge voltages charge rates ffiveil. 
 at very low rates. 
 
 At the lowest rates 
 the cell shows an efficiency of nearly 100 %. 
 
 Figure 60 shows charge and discharge voltage at 
 practical rates. 
 
 In batteries 
 which are worked 
 severely every day 
 and all day, at 
 rates which aver- 
 age perhaps as 
 high as the one- 
 hour rate of dis- 
 charge, the matter 
 of efficiency is 
 worth careful con- 
 sideration. Under 
 
 J 
 
 z i o 
 
 CURRENT DENSITY 
 
 - DISCHARGE CHARGE - 
 
 FIG. 60. Average voltages of charge and 
 discharge at various practical rates. 
 Plante cells. 
 
EFFICIENCY 147 
 
 these circumstances the difference in the coal bill for 
 an efficient and an inefficient battery may be of the 
 same order as the depreciation and maintenance of 
 the battery for the same length of time. In vehicle 
 batteries which are worked on regular runs leading 
 to a full discharge every day or oftener, the same 
 relations will be found to hold. A difference of 
 10 % in watt-hour efficiency will be of the same im- 
 portance in dollars and cents as the depreciation on 
 the battery for the year. It is on such points as 
 this that choice must be made between two types of 
 battery. The battery with the slightly higher de- 
 preciation or shorter life is sometimes to be chosen 
 for the sake of the saving which can be made with it 
 on account of its higher watt-hour efficiency. We 
 can of course discuss matters of price and cost only 
 in the most general way, but we shall often have 
 occasion to call attention to points like this. 
 
CHAPTER XII 
 INTERNAL RESISTANCE 
 
 89. Practical Cells. The internal resistance of a 
 storage cell of commercial dimensions is very small 
 indeed and may frequently be entirely neglected in 
 calculations on the circuit containing a battery of 
 cells. Even in small portable cells the resistance 
 seldom rises above 0.05 ohm and in large stationary 
 cells it may be as small as a few hundred-thousandths 
 of an ohm. 
 
 90. Specific Resistance. In calculating and stating 
 the resistance of a substance we always take as refer- 
 ence a cube of the substance 1 cm. on an edge, with 
 electrodes covering the two opposite faces. This 
 specific resistance once known, we can calculate the 
 resistance of a wire of any size or length made from 
 the same material. 
 
 where K is the specific resistance, I is the length, and 
 q the area of the cross-section of the conductor, and 
 R is the required resistance. 
 
 The table on page 263 gives the specific resistance 
 148 
 
INTERNAL RESISTANCE 
 
 149 
 
 of some important substances. All pure metals have 
 positive temperature coefficients they increase their 
 resistance when they are heated. All electrolytes, 
 on the contrary, decrease in resistance with rise of 
 temperature. An alloy may behave in either way or 
 
 R 
 
 10 
 
 LJ 
 
 6 
 
 l 
 
 1 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 I 
 
 f 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 / 
 
 / 
 
 
 \ 
 
 
 
 
 
 ^ 
 
 / 
 
 
 
 
 ^^ 
 
 
 
 ^~~~^ 
 
 
 
 
 
 
 
 10 ZO 30 40 50 60 70 60 9C 
 
 PERCENTAGE OF H 2 S0 4 IN SOLUTION 
 
 FIG. 61. Specific resistance of sulphuric acid solutions containing 
 varying percentages of 1.842 acid. 
 
 may have a positive coefficient at one temperature 
 and a negative one at another. 
 
 In the storage cell the solid substances all have 
 positive coefficients like metals. The electrolyte is 
 of course a member of the other class. The specific 
 resistance of sulphuric acid of various concentrations 
 is given in Figure 61. 
 
 For many calculations it is more convenient to 
 
150 STORAGE BATTERIES 
 
 use the reciprocal of the resistance, the conductance, 
 and the corresponding specific conductance. The 
 conductance of electrolytes forms one of the most 
 interesting chapters of general electrochemistry, but 
 we shall not have occasion to use many of its prin- 
 ciples, and it must therefore be looked up in some 
 other book. 
 
 Unit conductance and unit resistance refer to the 
 same thing. A wire with resistance 100 ohms has 
 conductance 0.01, and so forth. 
 
 91. Acid Resistance in the Cell. Let us calculate 
 the approximate resistance of the electrolyte alone 
 in some cells of very different size. First, a spark- 
 ing cell with three plates each 3 in. square 
 (7.6 x 7.6 cm.) and 0.4 in. apart (1 cm.). The 
 total acid area is 
 
 7.6 x 7.6 x 2 = 115 sq. cm. 
 
 The specific resistance of sulphuric acid of cell 
 strength is about 1.5, and since the plates are about 
 1 cm. apart, the resistance of the cell will be 
 
 1.5 X= 0.013 ohm. 
 
 The second calculation will be for a fairly large cell 
 such as would be used in a regulating battery. It 
 contains thirty-one plates, each 15 in. square and 
 with 0.4 in. separation. The acid area is in this case 
 
 42 x 42 x 30 cm. = 17,000 sq. cm., 
 
INTERNAL RESISTANCE 151 
 
 and the acid resistance of the cell is 
 
 L5x 
 
 or a little less than 0.0001 ohm. 
 
 About the largest cells which are in common use 
 have perhaps 131 plates about 15 x 30 in. In such 
 a cell the acid area is therefore about 290,000 sq. cm. 
 and the acid resistance is about 0.000005 ohm. 
 
 92. Acid Resistance and Temperature. The change 
 of resistance of the cell acid with temperature is 
 shown in the dotted curve of Figure 62, and it is 
 also given quite accurately by an equation of the 
 form 
 
 where a and are calculated from measurements 
 made at two temperatures. 
 
 93. Acid Resistance and Cell Losses. It may be 
 taken as an approximate general statement that the 
 total internal resistance of a cell is about double the 
 acid resistance. This approximation is usually suf- 
 ficiently close to be useful in the calculation of losses 
 inside the cell due to resistance. 
 
 Suppose we are drawing an average current of 
 2000 amperes from our biggest cell just considered. 
 The losses in the cell are 
 
 i*r= 2000 x 2000 x 0.00001, 
 
152 
 
 STORAGE BATTERIES 
 
 .07, 
 
 04 
 
 .03 
 
 80 30 40 50 60 C 
 
 TEMPERATURE 
 
 FIG. 62. Change in resistance of cell acid with temperature (dotted 
 
 line). 
 
INTERNAL RESISTANCE 
 
 153 
 
 40 watts in all. The cell is furnishing 2000 x 1.8 = 
 3600 watts, and our resistance loss is therefore just 
 about \%. This is so small in comparison with the 
 normal working losses of the cell at this rate (about 
 25%) as to be negligible. 
 
 y.06 
 
 35> 
 
 eo 90 iao 
 
 TIME OF DISCHARGE (IN MINUTES) 
 
 (80 
 
 FIG. 63. Resistance curves of Plant6 cell during discharge at va- 
 rious temperatures. 
 
 94. Resistance Curves. It is quite true that the 
 internal resistance of a storage cell is usually negli- 
 gible as far as loss of energy is concerned. There 
 are, however, many things of great theoretical 
 (and therefore practical) interest about this factor. 
 Hardly anything about a lead cell gives so clear 
 an insight into its internal workings as its internal 
 resistance. Even its voltage curve cannot tell more 
 
154 
 
 STORAGE BATTERIES 
 
 about the minute phenomena of charge and dis- 
 charge than can be seen from its resistance curve. 
 Figure 63 gives a set of curves of resistance taken 
 during the discharge of a Plante cell at various tem- 
 peratures, and Figure 64 gives both voltage and 
 
 RESISl 
 
 ANCE 
 
 TIME-MINUTES 
 
 FIG. 64. Curves of resistance and voltage during complete discharge 
 and partial reversal of a Plant6 cell. 
 
 resistance for the same cell at one temperature. It 
 will be noticed that the change in resistance is con- 
 siderable, if the cell is discharged down below its 
 usual end voltage say down nearly to zero. Fig- 
 ure 65 gives voltage and recovery curves during par- 
 tial discharge and recovery curves after open circuit 
 immediately following the discharge. 
 
INTERNAL RESISTANCE 
 
 155 
 
 95. Factors of Resistance. The total cell resistance 
 is evidently made up of at least three distinct 
 parts as indicated in the diagram of Figure 66 : 
 
 A. Support plate. 
 
 L7 
 
 g- 06 
 
 I 
 
 05 
 
 20 
 
 100 
 
 120 
 
 VO 60 SO 
 
 TIME-HINUTES. 
 
 FIG. 65. Curves of resistance and voltage during discharge and re- 
 covery. Plante cell. 
 
 B. Active material, including electrolyte in the 
 pores. 
 
 (7. Main body of electrolyte. 
 
 A and we can consider practically constant, and 
 if O changes, we can calculate the amount of the 
 change from the data of Figure 61, which gives the 
 relation between resistance and acid concentration. 
 B is the variable part of the system. 
 
156 
 
 STORAGE BATTERIES 
 
 During charge the active material first to react is 
 near the surface of the plate, and the electrolyte does 
 not have to diffuse far through the narrow channels 
 of the mass. As the diffusion path increases and 
 the cell becomes more fully charged, concentrated 
 acid is produced in the pores. But all through the 
 
 FIG. 66. Diagram of the parts of a Plante cell. 
 
 charge it is the solid plate itself which does most of 
 the conducting, and the change of resistance to be 
 expected during charge is therefore not great. 
 
 During discharge a very different state of affairs 
 exists. In this case also the action begins at the 
 surface, where there is plenty of both electrolyte 
 and active material. But as discharge proceeds the 
 area of activity moves back deeper into the mass, 
 acid is used up within the plate and must be replaced 
 by diffusion. The acid concentration becomes much 
 
INTERNAL RESISTANCE 157 
 
 lower at the point of activity, and there is added to 
 this the loss of conductivity by the solid plate itself. 
 The particles of lead and lead peroxide in the outer 
 layers have now become* covered with a layer of lead 
 sulphate and have been more or less insulated from 
 each other. The result is as if the distance between 
 the plates had been increased, for the plate surface 
 which is actually carrying the current has moved 
 from the surface back into the interior of the plate. 
 The surface of the plate in contact with electrolyte 
 has also been greatly decreased by this displacement 
 of the active plate surface. 
 
 Such changes as these are quite sufficient to 
 account for the change found in the resistance of 
 cells under the usual conditions of charge and dis- 
 charge. We should not expect, and we do not find, 
 any very large or very rapid changes in cell resistance. 
 
 96. Sulphation. On long standing, a storage cell 
 may acquire a very high resistance indeed as the re- 
 sult of complete "sulphation." This means that the 
 active lead sulphate formed during normal discharge 
 has gradually changed into the inactive crystalline 
 form, and that crystals of this inactive modification 
 have completely covered the particles of lead and 
 lead peroxide with an insulating coating. Authentic 
 cases are known of large cells with internal resist- 
 ance as high as 10 ohms. 
 
 As usual, it is hard to make things act properly 
 
158 STORAGE BATTERIES 
 
 when you want them to. I have left a completely 
 discharged cell for six weeks or more, carefully fol- 
 lowing its internal resistance every day, and found no 
 change of more than a few per cent in its resistance. 
 It seems very likely that the ordinary cases of sul- 
 phation, which are rather common and most annoy- 
 ing in their results, do not lead so much to a very 
 high internal resistance as to poor contact between 
 particles of active material. The electrolyte can get 
 into the plate or the grid well enough, and the in- 
 ternal resistance of the cell can therefore not be 
 very high. But the capacity of the plate has suf- 
 fered because a good deal of what ought to be avail- 
 able active material has been incapsulated by sulphate 
 and removed from the reach of plate activities. 
 
 In ordinary practice, the cell is discharged only 
 until its electromotive force sinks to about 1.7 volts. 
 This means that only perhaps a quarter of the active 
 material of the plates has entered into reaction, and 
 that the increased resistance in the active mass is due 
 rather to separation of particles by sulphate coatings 
 than to complete transformation of the active mate- 
 rial at any place into insulating material. During 
 the charge, sulphate coatings and bridges are rapidly 
 broken down, and the decrease in resistance during 
 charge is therefore more rapid than could be explained 
 by a change in concentration of electrolyte within 
 the pores of the plate. 
 
INTERNAL RESISTANCE 159 
 
 After a period of discharge, with corresponding 
 increase in resistance, the cell recovers its original 
 electromotive force along a carve nearly like a 
 diffusion curve when the circuit is opened. It also 
 recovers its original resistance along a very similar 
 curve. (See Figure 65.) This fact indicates the 
 dynamic nature of the equilibrium which causes the 
 cell to have any particular electromotive force or re- 
 sistance at a particular place in its discharge, charge, 
 or recovery curve. The particles of active material 
 cannot have been completely covered by insulating 
 sulphate, for on standing, the plate returns to its 
 original condition as far as we can measure it by an 
 examination of either electromotive force or resistance. 
 
 We must evidently think of the lead sulphate as 
 swelling up and almost plugging canals which lead 
 to unchanged lead and lead peroxide. The density 
 of the sulphate is much less than that of the materials 
 from which it is formed, and while the particles of 
 lead or peroxide may have had plenty of space be- 
 tween- them at the end of charge, the sulphate must 
 shut off much of this from activity at anything like 
 a practical rate of discharge. As long as no current 
 is flowing, acid does make contact with the remanent 
 active material and the active plane in the plate 
 draws out toward the exterior. 
 
 In Figure 62 the full-line curve gives the open 
 circuit resistance of a small Plante cell at various 
 
160 STORAGE BATTERIES 
 
 temperatures. The dotted curve shows only the 
 shape of the curve for the electrolyte, and not its true 
 value, which would be only about half that of the 
 cell at any point. The acid curve was plotted in this 
 way to show how the cell resistance departs from the 
 acid resistance at higher temperatures. Probably 
 the solid resistances of grid and active material be- 
 gin to make themselves felt, and as these have posi- 
 tive temperature coefficients, the increased resistance 
 makes the cell take a sharper turn than the elec- 
 trolyte. That the resistance of the plate material 
 becomes a factor is shown by the fact that pasted 
 plates of slightly greater area, placed as nearly as 
 possible the same distance apart, show a decidedly 
 greater resistance on open circuit than the Plante 
 plates. The cells with paste plates have about 25% 
 higher resistance. 
 
 97. Effect of Distribution of Material on Resistance 
 Curves. The curves of Figure 49 speak for them- 
 selves. The only queer thing about them is the flat 
 place which appears after 60 to 80 minutes of discharge. 
 This is characteristic of Plante plates with ribs, and 
 does not appear in the curves for paste plates. The 
 ribs of these plates are formed into active material, 
 which lies close to the ribs at their tops, but which 
 forms a solid mass down at the bottoms of the ribs. 
 (See Figure 67.) During the first part of the dis- 
 charge the electrolyte finds active material on the 
 
INTERNAL RESISTANCE 
 
 161 
 
 ribs, and diffusion takes place largely through the 
 open space between them, and only for a small dis- 
 tance through active material. As this easily avail- 
 able material is used up, the action moves farther 
 down into the plate and presently 
 reaches the mass of material at the 
 bottom of the grooves. Here for 
 a time there is material enough at 
 a nearly constant distance from the 
 surface of the plate, and after this 
 has been passed the resistance rises 
 very rapidly and the plate poten- 
 tial shows that the cell is com- 
 pletely discharged. 
 
 If there is anything in our fun- 
 damental theory of the dependence 
 of electromotive force on acid con- 
 centration, the curves of electro- 
 motive force of these Cells OUght FIG. 67. Diagram of 
 . distribution of active 
 
 to sllOW a Corresponding flat place material on ribbed 
 
 somewhere near the same point in Plant6 P late - 
 the discharge curve. The curves of Figure 52 show 
 it clearly except in the one for 8 C. We missed it 
 here by not taking points near enough together, for 
 it shows clearly in the curve of Figure 64, which was 
 made on the same cell at another time. This curve 
 gives the course of electromotive force and resistance 
 during a complete discharge followed by partial re- 
 
162 
 
 STORAGE BATTERIES 
 
 versal. If our explanation is correct, the resistance 
 ought to decrease very rapidly after passing through 
 a maximum at about the end of complete discharge. 
 The curve is in agreement with this idea. 
 
 7 
 
 X)9 
 
 .08 
 
 J07 
 
 15' 
 
 25 
 
 J05 
 
 60 
 
 80 
 
 160 
 
 TIME- MINUTES 
 
 FIG. 68. Change of internal resistance during discharge at various 
 temperatures. Paste plates. 
 
 98. Paste plates show smooth curves of resistance, 
 as shown in Figure 68. 
 
 Our resistance curves should also be characteristic 
 when taken for different rates, and Figure 69 shows 
 this for the same Plante plate cell at constant tem- 
 perature. 
 
 99. A most interesting idea of the lively dynamic 
 
INTERNAL RESISTANCE 
 
 163 
 
 nature of the momentary equilibrium existing in the 
 cell at any time during the cycle is obtained by 
 plotting curves of constant composition at various 
 times and temperatures. The curves of Figure 63 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 ^ 
 
 4c 
 
 y 
 
 J 
 
 &~ 
 
 
 
 Z- 
 
 r- ~ 
 
 ^ 
 
 
 
 7Q* 
 
 08 
 
 "AMPEF 
 
 r*" 
 
 
 
 
 
 
 
 20 40 60 80 100 120 (40 
 TlldE-MINUTES 
 
 FIG. 69. Change of internal resistance at various discharge rates. 
 Plante cell. 
 
 are isothermal curves. Each one shows the course 
 of the change of resistance during discharge at con- 
 stant rate and constant temperature. Since Fara- 
 day's law is true, the cell contains exactly the same 
 amount of lead, lead peroxide, lead sulphate, sul- 
 phuric acid, and water at the end of the same time 
 of discharge. Curves of constant composition will 
 
164 
 
 STORAGE BATTERIES 
 
 therefore result if we cut these isothermal curves at 
 times 30 min., 1 hr., 2 hr., etc., and plot the values 
 so found resistance against temperature. Figure 
 70 shows a set of curves so found. The curve T = 
 is for open circuit, and it gives the temperature 
 
 g 
 
 z. 
 
 <?x, 
 
 6 
 
 J04 
 
 
 
 TEMPERATURE 
 
 FIG. 70. Resistance curves corresponding each to constant composi- 
 tion of plates and electrolyte made by cutting the curves of Figure 
 63 at various times. 
 
 [For example, after 60 minutes of discharge at 25 C, the cell had 
 a resistance of 0.06 ohm.] 
 
 resistance curve for the cell, like the full curve of 
 Figure 62, but on a different scale. 
 
 The slope of the curve T=0 gives the tempera- 
 ture coefficient of resistance on open circuit at the 
 temperature corresponding to the point where the 
 slope is determined. The slope at any point on one 
 
INTERNAL RESISTANCE 165 
 
 of the other curves is the temperature coefficient 
 corresponding to the temperature where the slope is 
 taken. For all the curves except ^=0 the condi- 
 tion of the cell is one of momentary dynamic equilib- 
 rium. The materials are in the cell, without any 
 doubt, but their distribution depends to a great ex- 
 tent on the temperature at which discharge has 
 taken place. 
 
 100. Temperature Coefficient during Activity. The 
 open circuit temperature coefficient is about 1.5 % 
 per degree. The coefficient after 150 min. of dis- 
 charge is 23 % per degree. This latter value is of 
 course not like an ordinary temperature coefficient, 
 but it is most expressive of the lively nature of the 
 factors which determine the condition of a lead stor- 
 age cell at any moment in its life. 
 
 Corresponding curves for cell voltage are given in 
 Figure 71. 
 
 101. Capacity and Acid Density. At this point we 
 are prepared to examine the question left unanswered 
 on page 137. Why does the capacity of our cell 
 reach a maximum for acid of density about 1.22, as 
 appears from the measurements ? 
 
 The statement requires elaboration. It is not true 
 at all if the cell is examined at various working 
 rates, and if we measure merely the acid density in 
 the main body of the cell. It may very well be the 
 truth, if we take into account the dilution of the 
 
166 
 
 STOEAGE BATTERIES 
 
 acid in the pores of the active material, and if we 
 base our calculation on the density of acid inside 
 the plate. 
 
 The curves of Figure 53 show how the capacity of 
 the cell changes with the acid concentration in the 
 
 5 ' 
 
 TEMPERATURE 
 
 FIG. 71. Voltage curves corresponding to constant composition of 
 plates and electrolyte. 
 
 [For example, after 60 minutes of discharge at 25 C, the cell showed 
 a voltage of 1.69.] 
 
 electrolyte. This particular set of curves was made 
 with paste plates, and corresponding curves for large 
 surface Plante plates would show some difference 
 in shape and would have their maxima at other 
 points. But it is very evident in every case that 
 the maximum of capacity shifts toward the region of 
 higher acid density as the rate is raised. Rate must 
 evidently be taken into account in making any state- 
 
INTERNAL RESISTANCE 
 
 167 
 
 ment about the relation between capacity and acid 
 density. This becomes still more evident if we 
 examine into the change of capacity of positive and 
 negative plates separately. Figure 72 gives data 
 for the positive plate and Figure 73 for the negative. 
 
 10" 
 
 80 25" 
 
 ACID DENSITY 
 
 FIG. 72. Change in capacity with variation of acid density. At dis- 
 charge rates of 1, 2, 4, and 8 amperes. Paste positive plates, 
 measured against auxiliary electrode. 
 
 It is evident, that as far as the positive plate is 
 concerned we must go up to a very high value of 
 acid density to reach the maximum of capacity, 
 while for negatives at ordinary rates we need only 
 acid of ordinary density to bring us out to the maxi- 
 mum. For the positive we should have acid of 
 
168 
 
 STORAGE BATTERIES 
 
 density 1.32 and higher. For the negative we need 
 only to go as far as 1.2, which is well within the 
 range of practical operation. The facts have some- 
 what the appearance of contradicting the explana- 
 
 10 
 
 15 
 
 5' 
 
 ACID DENSITY 
 
 30 
 
 35 1 
 
 FIG. 73. Change in capacity with variation in acid density at va- 
 rious rates. Negatives. 
 
 tion which Dolazalek gives for the appearance of 
 this maximum. He says : 
 
 " At the beginning of discharge the current lines 
 enter only the outer layers of the active material, 
 where they find the least resistance. As the change 
 in concentration develops polarization in the outer 
 layers, the current lines penetrate deeper and deeper 
 into the plate, and these lines have density such that 
 
INTERNAL RESISTANCE 169 
 
 everywhere in the pores the drop in potential (ir) is 
 equal to the polarization prevailing in the outer 
 layers. This condition must of necessity be ful- 
 filled, for the active material, lead as well as lead 
 peroxide, is a good conductor, and the potential must 
 therefore be the same in the pores and out near the 
 surface of the plate. If the polarization in the outer 
 layers has reached 0.2 volt, the potential of the 
 whole accumulator has also fallen by the same 
 amount, and this would be the point at which dis- 
 charge would be stopped. At this time the current 
 lines have penetrated so far into the active material 
 that the drop of potential in the pores the product 
 of current and pore resistance (ir) has also reached 
 the value 0.2 volt. 
 
 " But the resistance of the pores is determined by 
 the conductivity of the acid which fills them. The 
 better the acid conducts, the later the moment will 
 appear when the product (ir) reaches the value 0.2 
 volt, and therefore the greater the capacity of the 
 cell. The conductivity of sulphuric solution increases 
 at first with increase of concentration, reaches a 
 maximum at 30% of H 2 SO 4 , and then decreases 
 again. The above discussion shows that the capacity 
 must also reach its maximum for 30% acid, and this 
 is splendidly confirmed by the measurements." 
 
 As a matter of fact, it is quite evident from the 
 curves that the measurements do not confirm this 
 
170 STORAGE BATTERIES 
 
 conclusion at all, if we confine our measurement of 
 acid density to reading a hydrometer placed in the 
 cell electrolyte between the plates. But if we con- 
 sider at the same time the difference between the 
 density of the acid in the pores and that in the main 
 body of the electrolyte, this same difference which 
 we have already had occasion to mention so often, 
 Dolazalek's hypothesis fits much better. 
 
 102. The Concentration of the Active Ion. The 
 ion which really determines the electromotive force 
 at the cathode (the peroxide plate during discharge) 
 is H + , and the current is driving this ion toward the 
 peroxide, 2 H + for each SO 4 sent in the opposite 
 direction, and five times more rapidly as well, because 
 of its greater migration velocity. The reaction at 
 this electrode requires 4 H + for each PbO 2 , and 2 H 2 O 
 is formed as the result of the reaction. Besides the 
 lowering of acid density due to the formation and 
 precipitation of PbSO 4 , we are diluting our elec- 
 trolyte by the addition of 2 H 2 O. Acid of maximum 
 conductivity is about 1 of H 2 SO 4 to 19 of H 2 O, 
 and it may very well be possible that the acid con- 
 centration out in the cell is much higher than it is in 
 the pores at the place where the reaction is taking 
 place. 
 
 At the negative plate (the lead plate) things are 
 not so bad. Here SO 4 is the determining ion, and 
 it is used up in the pores to form PbSO 4 , more being 
 
INTERNAL RESISTANCE 171 
 
 sent along as an ion by the current. Here we do not 
 have the formation of water to dilute the acid at the 
 point of reaction, and in spite of the fact that the 
 SO 4 moves much more slowly than H + , there is less 
 change of density inside the plate. A smaller excess 
 density in the main body of the electrolyte is sufficient 
 to maintain the concentration at the point of action. 
 
CHAPTER XIII 
 
 PHYSICAL CHARACTERISTICS 
 
 103. So far we have been considering the chemical 
 processes in the cell and the behavior of the elements 
 of the cell under varying conditions. We have not 
 paid much attention to the physical nature of the 
 plates and we have been judging them by their 
 works rather than by their looks. It is interesting 
 to examine the plates of our cell somewhat more 
 closely they sometimes give a good deal of valu- 
 able information. 
 
 Most of the hard battery service is done by plates 
 of the Plante type. This name does not now mean 
 the lead sheets used by the inventor, but indicates 
 that the active material of the positive plate has been 
 formed from metallic lead and not from a paste of 
 lead salts. For the hard service into which these 
 plates are called certain fundamental properties are 
 necessary. Most important of all is the power to 
 deliver current at a high rate with a reasonable 
 efficiency. A reasonable life must also be given 
 under these service conditions. 
 
 The type is a comparatively simple one. It may 
 172 
 
PHYSICAL CHARACTERISTICS 173 
 
 be represented diagrammatically by Figure 66. Its 
 special characteristics are : 
 
 Large surface. 
 
 Active material near conducting plate and elec- 
 trolyte. 
 
 Reserve of metallic lead for further formation in 
 service. 
 
 A certain minimum of mechanical strength. 
 
 A new positive plate of this type should have just 
 enough peroxide on it to give its rated capacity, 
 without much to spare. This peroxide has been 
 formed in the factory under the most favorable con- 
 ditions, and it may even contain a little cement sul- 
 phate from its rapid formation. If it goes into good 
 hard service, it probably loses a full quarter of this 
 original peroxide in a few months. Whatever there 
 was on the plate that was at all loose or liable to be- 
 come so, has been knocked off by the rapid evolution 
 of gas during charge. By this time the original 
 material, whatever its nature may have been, has 
 been replaced by a firmly adherent and dense layer 
 of peroxide which hugs close to the lead of the plate. 
 Ribs, rosettes, and pores have opened to better diffu- 
 sion of the electrolyte, and the plate with its rather 
 " skimpy " but readily accessible peroxide layer, is in 
 the pink of condition for hard work. Its capacity at 
 the high rate at which it is working is perhaps even 
 increased, in spite of the fact that it has lost a good 
 
174 STORAGE BATTERIES 
 
 quarter of the active material with which it started 
 to work and has probably regained but a very small 
 fraction of the loss. 
 
 If this same positive plate has gone into slow and 
 easy service, it will also change, though not so much 
 in external appearance, after a few months of service. 
 Its ribs or rosettes will become filled with peroxide, 
 and it will increase in total capacity. Too low a 
 charge rate is liable to crowd the spaces in the plate 
 and produce buckling or twisting. 
 
 In either case the plate seems to adapt itself as 
 well as it can to existing conditions to its "envi- 
 ronment." It increases its capacity at the rate at 
 which it is called upon to work. If now the high 
 and low rate plates were to be interchanged, the one 
 going into easy service instead of hard, and vice versa, 
 there might be trouble for a while. The " skimpy " 
 skin formation, which was just what was needed at 
 the high rate, will not give the low rate capacity 
 which the other plate has been easily delivering. 
 And the low rate plate will nearly explode when it is 
 first put on at the high rate. It throws off excess 
 active material for a time and as remanent sulphate, 
 always present in a plate worked at very low rates, 
 is cleared away, action on the support plate itself may 
 be severe for a time. Buckling or stretching may 
 appear. If the plate passes this danger point safely, 
 it settles down to the high rate pace and becomes 
 
PHYSICAL CHAEACTEE1STICS 175 
 
 before "very long much like its predecessor. In the 
 meantime the former high rater, which made so poor 
 a showing during its first few cycles at the low rate, 
 has picked up gradually. More material forms from 
 the reserve lead under the low charge rate, and most 
 of this remains in the plate. Gradually the capacity 
 rises until it is quite sufficient for the work, and by 
 this time the two plates have completely interchanged 
 their natures and looks. It seems to be generally 
 true that a plate that has been working at high rates 
 is in no special danger when put on easier work. The 
 reverse is not true by any means. It is a ticklish 
 operation to break in a plate for high rate work 
 which has been in operation for a long time in very 
 easy service. 
 
 104. Densities. If we examine the densities and 
 the relative volumes occupied by lead, lead sulphate, 
 and lead peroxide, it is immediately evident that 
 shrinking and expansion are sure to occur during 
 charge and discharge. The following table gives 
 the data : 
 
 DENSITIES 
 
 Metallic Lead 11.4 
 
 Peroxide, hydrated 7.4 
 
 Peroxide, dry 9.4 
 
 Lead Sulphate 6.2 
 
 Litharge , i . . ...'?. 9.3 
 
 Red Lead 8.9 
 
176 STORAGE BATTERIES 
 
 A good many pretty mysterious occurrences in 
 battery practice should be referred directly to these 
 differences of density. For instance, most Plante 
 plates, during the process of making them from pure 
 lead, grow in length. Some of those with long ver- 
 tical ribs without many breaks in them may grow an 
 inch in length per foot of plate. There is every rea- 
 son to believe that this stretching is caused wholly 
 by the crowding of sulphate as it is formed from 
 lead. A properly forming plate has its sulphate in 
 the form of a very dense and firmly coherent layer, 
 and as this is formed from the soft lead of the ribs 
 it hangs to them and crowds. The cumulative effect 
 is proportional to the length of unbroken rib along 
 which the crowding takes place, and the stretching 
 is proportional to this factor also. It is also very 
 different for various forming agents, probably be- 
 cause the coherence of the sulphate to the lead of 
 the plate is different for each. 
 
 It will be noticed from the table of densities that 
 the peroxide layer which is finally formed on the 
 positive as the result of formation is denser than the 
 sulphate from which it came. So the properly formed 
 Plante plate has a peroxide layer with just about the 
 right degree of porosity. If its active material were 
 more porous, it would be at the expense of coherence ; 
 and if it were denser, diffusion would be poor, and 
 the plate would give low capacity at high rates. 
 
PHYSICAL CHARACTERISTICS 177 
 
 Metallic lead is the densest of the materials in the 
 table, and negative plates, which are to be porous, 
 too, if they are to have reasonably good capacity, 
 must be made to have very large and highly devel- 
 oped surfaces. This can be more or less successfully 
 attained in the case of Plante plates by the natural 
 method of forming them. True Plante negative 
 plates are always made by formation first as perox- 
 ide, by attack of a forming agent and action of the 
 current on the pure lead of the grid. They are sub- 
 sequently completely reversed to sponge lead and 
 are then finished negatives. The surface is, of 
 course, enormously increased by the formation of 
 grains of peroxide from the solid lead, and when the 
 reversal is given to the negative condition, sponge 
 lead is formed right where the grains of peroxide 
 were. Since its density is greater, it only partially 
 fills the space occupied by the particle of peroxide or 
 sulphate, and as a matter of fact it is more like a 
 mere slender network when the plate is finished than 
 like the dense solid from which it came. 
 
 Paste plates make natural negatives. Litharge 
 and red lead are dense compared with sulphate, and 
 if the paste plate is allowed to sulphate as completely 
 as possible before formation and is then reduced to 
 lead, the resulting sponge has passed through the 
 state of lead sulphate, with its greater volume, and 
 has then gone on to become metallic lead, shrinking 
 
178 STORAGE BATTERIES 
 
 all the time during this latter change, and opening 
 pores everywhere during the final change. 
 
 The extremely small solubility of lead peroxide 
 probably accounts for the fact that it is always pres- 
 ent in fine grains, which never grow to any size, even 
 after many cycles of service. It cannot stay in solu- 
 tion long enough to move about and look for a place 
 to settle where there is already a crystal of peroxide. 
 Lead sulphate is comparatively soluble, and when 
 metallic lead is formed from it, the lead ion has a 
 chance to look for a nucleus of lead on which to 
 precipitate. The result is that negative plates in- 
 crease in average size of grain with service, and finally 
 show a much decreased capacity as compared with 
 their original one. Not because there is less lead in 
 the plate, but because the available surface has be- 
 come smaller. 
 
CHAPTER XIV 
 
 FORMATION OF PLANTE PLATES 
 
 105. In the early days of lead storage cells, forma- 
 tion was a very slow and expensive process, requiring 
 a month or more for its completion and the expendi- 
 ture of a great deal of primary battery material. For 
 at that time the primary cells were the only source 
 of current for the purpose, and primary cells have 
 never been very cheap as a source of power. The 
 plates of those early batteries were really plates of 
 lead, either quite flat or with slight corrugations 
 which enabled them to hold a little more active 
 material on the roughened surfaces. These plates 
 were set up in their final cell positions in dilute sul- 
 phuric acid, usually in acid much more dilute than 
 we now use for the purpose. The cells were then 
 subjected to a series of reversals they were charged 
 first in one direction and then in the other. 
 
 When the acid is poured into the cells, thin layers 
 of lead sulphate form on both plates, and this process 
 ceases as soon as the layer has become thick enough 
 to protect the plate from further action. Charge is 
 begun in either direction, as the plates are just alike 
 
 179 
 
180 STORAGE BATTERIES 
 
 and there is no reason to decide, at this point, which 
 plate is eventually to become peroxide and which is 
 to become sponge lead. Under the action of the 
 current the lead sulphate layer at the anode is 
 changed into peroxide and that at the cathode is 
 changed to sponge lead. The thin peroxide layer is 
 then a complete protection against further action and 
 the other plate is cathode, and needs no protection. 
 As soon as charge has been carried this far, the cell 
 becomes a gas generator and nothing more. All the 
 current is used to produce hydrogen at the cathode 
 and oxygen at the anode. 
 
 The capacity of such a cell is very small indeed. 
 It will give a spark if it is short-circuited, but not 
 much more. For the amount of lead sulphate which 
 is formed before a lead plate protects itself against 
 further action by the acid is minute, and no more 
 sponge lead can be formed at the negative than cor- 
 responds to the original quantity of sulphate on it. 
 At the peroxide plate there will be action on the lead 
 of the plate and formation of somewhat more sulphate 
 than was originally present, but this action takes 
 place only during a part of the charge, and before 
 long the dense peroxide layer shuts off the lead plate 
 completely from further attack. 
 
 If now the cell be immediately put on charge in 
 the opposite direction, the results are not good. The 
 active material formed during the first charge turns 
 
FORMATION OF PL ANTE PLATES 181 
 
 over very quickly and the plates reverse their po- 
 larity, but only a little more active material is pro- 
 duced. It took Plante only a short time to find out 
 that much better results were obtained by letting the 
 cell stand discharged before each reversal. After 
 standing at rest, discharged, for a day or so, the cell 
 is reversed. Not much is gained in the way of 
 capacity this time, but when the cell is again reversed 
 it is found that considerable gain has been made. 
 Local action, especially at the peroxide plate, has re- 
 sulted in deeper attack on the lead, and subsequent 
 reversals and periods of rest give finally an active 
 material layer of useful thickness. ' The two plates 
 look different after they have been formed. There 
 is a layer of brown peroxide on one and a layer of 
 gray sponge lead on the other. 
 
 If the capacity was forced too far by more forma- 
 tion, the peroxide layer was liable to slough off and 
 fall to the bottom of the cell. To be sure, more was 
 formed to take its place, but the battery has reached 
 its maximum capacity and further formation was 
 merely a waste of current an expensive article in 
 those days. 
 
 This was during the first stage in development. 
 Before long it was found that ribs and in general 
 mechanical development of the surface of the lead 
 plates permitted of much more formation and so 
 gave higher capacity. Then before long came the 
 
182 STORAGE BATTERIES 
 
 idea of rapid formation the use of chemical agents 
 to aid and hasten the electrolysis, and along these 
 lines the modern " rapid forming processes " gradu- 
 ally came into use. There are many points about 
 the older process which are interesting and which 
 lead directly to an explanation of the theory of the 
 later methods of formation. 
 
 The first point to be remembered is that lead sul- 
 phate does not form a dense enough layer on lead to 
 protect it from the action of an electric current in 
 sulphuric acid. A plate is quite protected by such 
 a layer, provided no current is passing, but it has no 
 power to resist the more active attack of the anion, 
 backed by the driving force of the current. 
 
 The second point is that a connected layer of 
 peroxide does protect against attack, even when the 
 plate is anode and current is passing through the 
 cell. The other point to be kept in mind is that 
 the positive plate can discharge itself by " local 
 action " while it is at rest. In the case of the Plante 
 plate, with its thin coating of active material, this 
 self -discharge may be pretty nearly a complete one 
 in the time of rest recommended for Plarite formation. 
 
 The curve of Figure 74 shows how rapidly this 
 action takes place in the case of a plate which has 
 been subjected to only a few Plante cycles, and which 
 has therefore a very thin layer of peroxide on its sur- 
 face. 
 
FORMATION OF PL ANTE PLATES 
 
 183 
 
 100 
 
 \ 
 
 80 
 
 60 
 
 It is the most natural thing in the world that such 
 a plate should discharge itself on standing, for it is 
 really a whole storage cell. Lead plate, peroxide 
 plate, sulphuric acid, all are present in every per- 
 oxide plate, and the surface of contact is very large 
 in proportion to the mass of peroxide. It discharges 
 during its period 
 of rest wherever 
 lead and peroxide 
 are in contact, and 
 lead sulphate is 
 formed at these 
 points. During 
 the subsequent 
 reversal all the ma- 
 terial on the per- 
 oxide plate is con- 
 verted into Sponge FlG . 74. _ Self-discharge of original Plants 
 lead, and this in- plate - 
 
 eludes new sulphate formed from the plate itself as a 
 result of the local action following the previous per- 
 oxidation. During the rest now taking place after 
 reversal local action is increasing the sulphate con- 
 tent of the other (peroxide) plate, and so on. 
 
 The pertinent query arises : Why does not every 
 peroxide plate discharge itself by local action ? It 
 does, but only to the same extent that the older 
 Plante plate would. Where lead and lead peroxide 
 
 \ 
 
 6 8 
 
 10 12 
 HOURS 
 
 14 16 18 20 
 
184 STORAGE BATTERIES 
 
 are in contact every positive plate discharges itself, 
 but the amount of material in contact in a modern 
 plate is so small in proportion to the total amount 
 of active material in the plate that the amount of 
 action on the plate is comparatively small, and only 
 a low percentage of the total capacity of the cell is 
 lost through the effect. The action is, however, 
 strictly proportional to the surface of contact be- 
 tween lead and peroxide, and the modern high-rate 
 plates are subject to much greater losses from this 
 cause than are the paste plates. Fortunately the 
 efficient large surface plate does its important work 
 under conditions of rapid reversal discharge and 
 charge follow each other very rapidly, and the cell 
 is never standing at rest for more than a few min- 
 utes at a time. 
 
 106. Modern Rapid Plante " Formation. After 
 the first excitement over Plante's discovery had 
 passed, it was not very long before the small ca- 
 pacity of the flat plates was felt to be a drawback. 
 The surface was increased by corrugating or other- 
 wise roughening it. At this same time the original 
 method of forming by a series of reversals began to 
 seem slow and wasteful of current. So methods 
 were sought which should permit of attaining the 
 same or better results more easily and rapidly, and 
 these methods were : 
 
 1. To begin the attack on the lead by treating the 
 
FORMATION OF PLANTS PLATES 185 
 
 plate with an etching agent, nitric acid, for example, 
 which dissolves some of the lead and roughens the 
 surface of the plate. This treatment was followed 
 by regular Plante formation, but the process* went 
 on much more rapidly than in the original method. 
 
 2. To produce on the surface of the lead plate 
 some compound which could afterward be changed 
 into peroxide by a single charge. One of these ideas 
 was to subject the plate to the action of sulphur. 
 Lead sulphide was formed, and this was changed first 
 into sulphate and then to peroxide during the period 
 of charge. 
 
 3. To add to the sulphuric acid used in formation 
 an agent which should attack and dissolve the lead 
 of the plate. This resulted in formation, first of a 
 soluble lead salt, then of sulphate by reaction with 
 the sulphuric acid of the electrolyte, and finally of 
 peroxide by the usual effect of the current. 
 
 This last method is the usual one nowadays, and 
 the great majority of all Plante plates are now 
 formed from lead plates by electrolysis in a sulphuric 
 acid solution containing a "forming agent." The 
 most efficient method of applying this principle seems 
 to be to use as agent a substance which can furnish 
 an anion capable of forming a soluble lead salt. 
 
 The common soluble lead salts are : the nitrate, 
 acetate (chloride), chlorate, perchlorate, and sulphite, 
 and these are (or have been) all used for the purpose. 
 
186 
 
 STOEAGE BATTERIES 
 
 It is not our business to examine technical recipes 
 or to study the minutiae of manufacturing processes. 
 But we can state a general theory of formation which 
 will be found applicable to all the different processes. 
 
 107. Theory of Rapid 
 Formation. Figure 75 
 gives a diagrammatic 
 picture of the different 
 zones and stages in the 
 formation of a lead plate. 
 All plates are formed into 
 peroxide first, if they fall 
 into this class at all, even 
 if they are eventually to 
 become negatives; so this 
 one picture covers all the 
 cases. 
 
 The solution contains 
 sulphuric acid and the 
 forming agent, which has 
 as an ion an ion which can 
 yield a soluble salt of 
 lead. The charging cur- 
 rent started, this forming ion and SO 4 migrate 
 toward the plate. The velocity of the forming ion 
 may apparently be either greater or less than that of 
 the SO 4 ion without making any difference in the 
 process. At any rate, we will suppose that the two 
 
 FIG. 75. Diagram to show mod- 
 ern "rapid Plant6" formation. 
 
FORMATION OF PLANTS PLATES 187 
 
 ions reach the plate at the same time. A layer of 
 soluble lead salt in solution is formed at once, but 
 this lasts only an instant. SO 4 is there and lead 
 sulphate is immediately precipitated. The regular 
 charging reaction then comes into play and the sul- 
 phate is transformed into peroxide. In the mean- 
 time the forming ion has been freed, and it bores into 
 the plate again to form more soluble material, which 
 is precipitated by SO 4 , and so on. 
 
 This insures formation, but the relative concen- 
 trations of the two active ions must be carefully 
 balanced if it is to proceed far enough to make it a 
 practical success. If there is too little forming ion 
 in proportion to the sulphate ion, sulphate will pre- 
 cipitate as a dense layer clinging closely to the plate, 
 and peroxidation follows so closely that the plate 
 soon protects itself. If there is too much forming 
 ion relative to the SO 4 ion, an actual layer of solu- 
 tion, containing a considerable concentration of the 
 soluble lead salt, forms between the plate and the 
 layer of precipitated sulphate. The sulphate layer 
 is thus kept from close contact with the plate at all 
 points, and when peroxide forms, the whole sheet of 
 active material, partly sulphate and partly peroxide, 
 is so loosely attached that it flakes off at the least 
 provocation, leaving the plate bare. 
 
 The formation of a tough and coherent peroxide 
 demands careful attention to the relative concentra- 
 
188 STORAGE BATTERIES 
 
 tions of the active ions. It may be taken as a general 
 rule that there is no one acid concentration and no 
 one forming ion concentration that produce correct 
 formation. For each acid concentration there will 
 be, however, an optimum concentration of the form- 
 ing ion, and other considerations usually make it 
 advisable to use a rather low acid concentration for 
 the forming solution. 
 
 Formation to a practical depth usually requires 
 eight or ten times the number of ampere-hours after- 
 ward to be required of the plate in service. This is 
 quite natural, for as we have seen in Chapter X, we 
 use in service only about 10 to 30 % of the total 
 active material of the plate. If the plate is an old- 
 fashioned thin-layered flat Plante plate, the maximum 
 proportion of the total will be brought into use. If 
 it is a modern plate with ribs or rosettes, a smaller 
 part of the total peroxide will be turned over in 
 practice. 
 
 108. Low Voltage Formation. A special mode of 
 formation has been invented and patented by Pollak, 
 and while it has apparently not been adopted as a 
 manufacturing method, it is of interest as an example 
 of a principle we have frequently applied. Lead 
 sulphate cannot protect a lead plate from attack 
 when current is passing and the plate is anode. If 
 we can prevent the formation of lead peroxide and 
 continue to form sulphate, there is no reason why 
 
FORMATION OF PLANTS' PLATES 189 
 
 formation without any special agent should not be 
 carried as far as we choose. 
 
 Peroxide is not formed from sulphate except at 
 cell voltages higher than 2 volts. If therefore we 
 send current through the cell at a voltage slightly 
 lower than this value, only sulphate will result, and 
 the plate will continue to be attacked. This con- 
 dition of things is best attained by connecting the 
 lead blank which is to be formed to a fully charged 
 peroxide plate of capacity sufficient to complete for- 
 mation. This means a charged peroxide plate of 
 eight or ten times the capacity desired for the 
 finished plate we are making. When enough sul- 
 phate has been produced to give final capacity, the 
 sulphate-formed plate is taken out of this cell and 
 formed to peroxide in another cell, either against 
 negative plates or flat lead dummies. In the mean- 
 time the auxiliary forming positives are receiving a 
 new charge to get them ready for the next forma- 
 tion. There seem to be practical reasons why this 
 idea has not been generally adopted. Theoretically 
 and as a laboratory experiment it works quite per- 
 fectly. 
 
 109. Changes in the Forming Agent during Forma- 
 tion. It is much to be desired that the activity of 
 the forming agent should cease as soon as the plate 
 is brought up to its proper capacity. If some of 
 this dangerous substance remains in the plate, it will 
 
190 STORAGE BATTERIES 
 
 continue its original behavior and attack the lead 
 of the peroxide plate during each period of charge. 
 Of course this attack is much weakened by the fact 
 that the plate is completely peroxidized and also be- 
 cause it is never discharged to such an extent that 
 much of the peroxide in contact with the lead sup- 
 port is changed to sulphate. But a lead cell must 
 have a life of several years and must go through a 
 great many cycles of charge and discharge, and even 
 a small amount of action can be cumulatively harm- 
 ful. 
 
 Some of the forming agents mentioned in the list 
 are only too ready to eliminate themselves. When 
 chlorine ion is used either as hydrochloric acid or as 
 a chloride, chlorine gas is evolved nearly quantita- 
 tively at the anode, and the forming agent must be 
 replaced accordingly. Chlorates are also broken up 
 with evolution of chlorine, but not so completely as 
 Cl~ ion. Nitric acid is reduced at the cathode, first 
 to nitrous acid and finally to ammonium sulphate. 
 This necessitates renewal during formation and final 
 saturation of the electrolyte with ammonium sul- 
 phate. This means that small quantities of nitric 
 acid, left in a plate as the result of formation, are 
 perfectly eliminated from the cell during its first 
 few cycles of active operation. 
 
 An interesting suggestion is that of Beckmann. 
 Sulphur dioxide in water solution forms some sul- 
 
FORMATION OF PLANTS PLATES 191 
 
 phurous acid, H 2 SO 3 , and this gives a forming ion 
 SO 3 , because lead sulphite is a fairly soluble sub- 
 stance. 
 
 During formation this ion leads the attack on the 
 lead plate as described, but it is itself oxidized rather 
 readily to SO 4 , and so a few cycles are sufficient 
 to remove completely every trace of extraneous ion 
 from the cell. This also seems rather difficult to 
 apply as a practical forming process, as SO 2 is not a 
 pleasant substance to have about in large quantities. 
 
 Acetate ion, C 2 H 3 O 2 ~, is most persistent and can 
 cause great damage if any of it is left in the plate 
 after formation. Even this is gradually destroyed 
 as the result of cell activity. 
 
 Perchlorate ion, C1O 4 ~, is apparently the only sub- 
 stance in the list which is perfectly resistant to the 
 effects of the current. It is therefore the most effec- 
 tive of all forming agents, as it does not need to be 
 renewed at all in the forming tanks. For this same 
 reason it might become a dangerous factor in the 
 cell after it goes into service. Fortunately the 
 limits of proportion between which perchlorate ion 
 can act as a forming ion in sulphuric acid solution 
 are narrow. In electrolyte the sulphuric acid con- 
 centration is comparatively high, and the little rem- 
 nant of perchlorate is therefore a very small fraction 
 indeed. Under these conditions it hardly has any 
 power of attacking lead, and while in proper propor- 
 
192 STORAGE BATTERIES 
 
 tions it is perhaps the most active of all forming re- 
 agents, it is much less dangerous than many of the 
 others in the conditions of ordinary service. 
 
 110. Plante Negatives. The negative Plante plate 
 is made in exactly the same way as the positive. It 
 is formed as a positive, with the aid of a rapid form- 
 ing agent, and is then reversed completely, so that all 
 the peroxide is changed to sponge lead under the 
 action of the current. 
 
 Such a plate has all the good qualities of the large 
 surface positive, especially during the first part of its 
 life. It is easily reached by the electrolyte and can 
 give large discharges without danger. Later in its 
 life it loses a considerable part of its original capacity 
 because of increase in size of grain and loss of 
 porosity. It must therefore be made to have a much 
 larger original excess capacity than the positive, 
 which increases its capacity by local action and slow 
 formation in service. Most Plante negatives are 
 made to give nearly 100 % excess capacity when they 
 go into service. This excess is rather rapidly lost 
 during the first six months or so of service, and at 
 the end of the first year the plate will usually show 
 an excess of only about 25%. 
 
 The curves of Figure 76 show how light Plante 
 positives and negatives change in capacity in service. 
 The curves are of course only averages, and differ- 
 ent types would show somewhat different curves, but 
 
FORMATION OF PLANTS PLATES 
 
 193 
 
 these can safely be taken as representing the gen- 
 eral course of events. 
 
 Many makers use pasted negatives entirely, even 
 in batteries which are to be called on for the hardest 
 
 o 
 
 r 
 
 - 
 
 8" 
 
 60 
 
 500 
 
 NUMBER OF CYCLES 
 
 FIG. 76. Change in capacity in hard service. Light Plante plates. 
 
 service. Their life is sufficient, and their excess 
 capacity is so great that no fear need be entertained 
 that the negatives will ever limit the discharge of the 
 cell. 
 
CHAPTER XV 
 
 PASTE PLATES 
 
 111. It was Faure who first conceived the idea of 
 producing active materials for accumulator plates by 
 the electrolysis of lead compounds instead of from 
 the lead of the plate itself, and he began the evolu- 
 tion of what are called paste plates. Faure probably 
 reasoned somewhat like this : Plante produces lead 
 sponge and lead peroxide by a wearisome and ex- 
 pensive attack on the solid lead. It would certainly 
 be much better to cover a lead plate with a mass 
 which can then be easily and completely converted 
 into lead at the cathode and lead peroxide at the 
 anode, and such a plate can be made to have capacity 
 enormously greater than the thin-skinned plates of 
 Plante. Some triumphs and not a few troubles for 
 many people began just at this point in the history 
 of galvanic cells. As we now know very well, Faure's 
 invention was not able to push Plante's out of the 
 field. Each of the two types of plate has a perfectly 
 definite place and service of its own, and while the 
 two types appear to cross into each other's territory 
 now and then, there is always some very definite 
 reason for the apparent intrusion. 
 
 194 
 
PASTE PLATES 195 
 
 The process of making a paste plate is a very 
 simple one. Perhaps the people who find most 
 difficulty in the process are the ones who have to 
 actually manufacture the plates for the market. The 
 difficulties are all practical ones and so minute and 
 difficult to sort out and describe and remedy that we 
 can only hope to touch the more evident and funda- 
 mental ones. 
 
 Suppose it is desired to make a set of fairly light 
 plates to be used in an electric automobile. They 
 must have good capacity per unit 
 of weight, mechanical strength 
 sufficient to withstand the jar of 
 road service, and a fairly long life FlG ' ? 7 ' ~ * ib . B f 
 
 * positive paste plate. 
 
 (say 250 to 300 cycles), if they 
 are to compete with other plates already on the mar- 
 ket. We will make the positive plates first. 
 
 For positives, a grid which can hold the peroxide 
 in place somewhat is usually considered best. Lead 
 peroxide has very little coherence and drops off the 
 plate surface very easily unless it is kept in some way 
 from doing so. We should therefore choose a grid 
 of the general form shown in Figure 77, having ribs 
 with inward dovetails to keep the material in the 
 plate. It is usual to cast the grids of 6 to 10 % anti- 
 mony alloy. This gives a much stiffer grid than 
 pure lead and prevents attack by the acid of the 
 electrolyte. Molds we will assume they are not 
 
196 STORAGE BATTERIES 
 
 within the province of our discussion and we will 
 also assume that we have a supply of grids ready 
 cast. The next thing is to paste them. 
 
 Recipes for positive pastes are legion. A very 
 simple one which can be made to give good results is 
 made by mixing litharge (PbO), or red lead (Pb 3 O 4 ), 
 or a mixture of the two, with rather dilute sulphuric 
 acid. A paste is made of the constituents, just 
 thick enough to permit of its being worked into 
 the holes and hollows of the grid. If then a plate 
 so pasted is set in the air, it dries and at the same 
 time sulphates, setting to a hard mass. Better re- 
 sults are obtained by soaking the freshly pasted plate 
 in dilute sulphuric acid for several days. During 
 this time what is perhaps the most important thing 
 in the whole life of the plate takes place. It cements. 
 
 Lead peroxide is a powdery, non-coherent mass at 
 best, and a plate pasted with pure peroxide has very 
 little mechanical strength compared with the plate 
 which has been treated in the way just described. 
 But lead sulphate, crystallizing into a firm, connected 
 mass all through the interstices between the grains of 
 oxide and peroxide, can become a most useful bind- 
 ing material. Just a word about what we mean by 
 the general term cement. 
 
 A cement sticks things together. It does this by 
 first of all penetrating, as a liquid, all the irregu- 
 lar holes and crannies and spaces between the solid 
 
PASTE PLATES 197 
 
 particles to be held together. It then afterward 
 hardens to a solid and fills all these irregular spaces, 
 thus dovetailing the various pieces of the whole mass 
 into a single piece. The resulting solid is as strong 
 as its two final constituents one of them the original 
 solid which was to be bound together, the other the 
 new solid formed by the hardening of the cement. 
 
 If red lead is used in the paste, the following reac- 
 tion takes place partially as soon as the acid used in 
 mixing has a chance to react : 
 
 Pb 3 4 + 2 H 2 S0 4 = 2 PbS0 4 + Pb0 2 + 2 H 2 O. 
 
 The plate therefore contains lead peroxide, red lead, 
 and lead sulphate, as soon as it has set and before 
 formation is begun. If litharge alone has been used 
 in the paste, the unformed plate contains only lead 
 oxide and lead sulphate. The lead sulphate reacts 
 quickly, and within a few minutes or at most a few 
 hours after the plate has been placed in the cement- 
 ing acid bath, the sulphation of the plate is quan- 
 titatively complete. But the second and equally 
 important step the locking together of the plate 
 by the sulphate takes place much more slowly. It 
 depends on the recrystallization of lead sulphate and 
 is an action very like the dreaded "sulphation" which 
 is so often the cause of trouble in the vehicle batteries 
 all over the country. The fine particles of sulphate are 
 more soluble than the larger ones, and the latter grow 
 
198 STORAGE BATTERIES 
 
 at the expense of the smaller ones. As the crystals 
 grow they interlace and lock themselves together, as 
 growing masses of crystals always do. One sul- 
 phate crystal, growing out from between grains of 
 oxide or peroxide, touches the one growing out from 
 the neighboring opening and the two coalesce. The 
 result of this crystalline growth and interlocking is 
 the cementing of the plate. It becomes hard, sounds 
 hard when it is struck, can be used as a hammer and 
 pounded on the floor without losing any paste ex- 
 cept at the place where the lead grid is actually bent 
 or broken. It is now ready to be formed. 
 
 i"J3 Formation of Paste Positives. The plate, des- 
 tined to become a positive, is now hung in a bath of 
 rather dilute sulphuric acid and made the anode for 
 the passage of the forming current for perhaps 60 
 hours. Figure 78 shows the changes which take place 
 in its composition during this time. At the start 
 the plate contained : 
 
 PbO 55 % 
 Pb0 2 25% 
 PbS0 4 20 % 
 
 The lead oxide begins to turn to peroxide right 
 away as soon as charge is begun, but the sulphate 
 content of the plate rises for several hours. This 
 may be because the plate is becoming more porous 
 as formation proceeds, so that the acid finds unused 
 
PASTE PLATES 
 
 199 
 
 oxide ready to hand as it enters new channels. But 
 before long the sulphate also passes over into peroxide 
 
 100 
 
 a 
 
 eo 
 
 Id 
 
 1 
 
 40 
 
 20 
 
 40 
 
 40 
 
 60 IZO 160 200 
 
 AMPERE-HOURS FORMATION 
 
 FIG. 78. Changes in composition of a paste positive during formation. 
 
 and at the end of the period of formation the active 
 material consists of : 
 
 PbO 
 PbO, 
 
 9% 
 88% 
 
 PbSO 4 3% 
 
 Our cement is nearly gone. But even this 3% 
 is a potent factor in the life of this positive plate, 
 and if formation has been carried on at the right 
 current density, there is also some cementing, or 
 rather loose interlocking, of the particles of peroxide. 
 
 It seems probable that this remanent lead sulphate 
 
200 STORAGE BATTERIES 
 
 is never removed from the plate under proper condi- 
 tions of charge and discharge and that it forms a net- 
 work which really helps to hold the peroxide together. 
 During each discharge sulphate is deposited on this 
 nucleus, and the plate may perhaps be partially held 
 together by the binding action so produced during 
 the succeeding period of charge, which is so trying 
 to the paste plate. 
 
 Surety this cannot be the whole story of the making 
 of a paste positive ? There are hundreds of secrets 
 carefully guarded, and hundreds of patents and reci- 
 pes for pastes. A glance at the patent literature 
 shows the nature of the various things that might be 
 added to the positive paste alcohols and organic 
 acids, salts and sugars, and almost anything else that 
 one could think of. The intention of these additions 
 is to aid in producing either one of two desirable 
 things : 
 
 (a) An increase in the hardness of the plate, and 
 therefore increased life. 
 
 (5) An increase in porosity, and therefore its 
 efficiency. 
 
 The organic acids carbolic acid, for example 
 hasten the cementing action. Probably a lead 
 phenolate or some such substance is formed and lead 
 sulphate is then rapidly produced from this. The 
 soluble lead salt would naturally hasten sulphation 
 just as a forming agent hastened it in the case of 
 
PASTE PLATES 201 
 
 Plante plates. The addition to the paste of a soluble 
 salt like magnesium sulphate has not much effect 
 unless the plate is allowed to dry after pasting and 
 before formation. The salt crystallizes all through 
 the plate while it is dr}dng and setting, and is then 
 dissolved again during formation, leaving spaces in 
 the formed active material and thus increasing po- 
 rosity. A good many manufacturers probably still 
 feel the need of a " hardening agent " or a " porosity 
 agent," or both. But it seems perfectly possible to 
 get along without either of them. And perhaps the 
 final result is just about as satisfactory if only lead 
 oxide and sulphuric acid are used instead of the more 
 mysterious and cabalistic formulae of some of the in- 
 ventors in this field. It is, as a matter of fact, very 
 hard to see how any good effect of the addition of 
 any of these agents to the paste can remain after the 
 resulting plate has been through fifty cycles of hard 
 work. Long before that time the hardening agent 
 has been completely decomposed and removed from 
 the cell so completely that chemical analysis will 
 often fail to show a trace of it. The porosity agent 
 is of course dissolved out and diluted through the 
 cell as a part of its activity. The active material of 
 the plate has been turned over and over and has dis- 
 posed itself in new ways filling up the old pores 
 and channels and making new ones for itself. All 
 that is left is a very small trace of lead oxide and the 
 
202 STORAGE BATTERIES 
 
 normal proportion of lead peroxide and lead sulphate. 
 Whatever coherence the paste now has is due to these 
 two substances, and as we have already seen, lead 
 peroxide is not inclined to bind together to give 
 much mechanical strength. The remanent network 
 of sulphate is all that holds the plate together. 
 Whenever particles of peroxide lose contact at the 
 surface of the plate their fate is to fall off sooner or 
 later and collect in the bottom of the containing jar. 
 The cementing sulphate has no chance to persist at 
 the surface. It is transformed almost completely 
 into peroxide at each charge. So the peroxide plate 
 naturally loses active material by " shedding," and 
 the rapid evolution of gas which accompanies the end 
 of each charge helps to throw off all the loose par- 
 ticles. It is the fate of all paste positives, even the 
 most healthy, to finally become a mere skeleton a 
 grid with nothing left on it but a few bunches of 
 peroxide clinging to its ribs. 
 
 113. Paste Recipes. Every manufacturer has his 
 own particular recipe for positive paste. This and 
 other facts lead to the conclusion that the propor- 
 tions are not of great importance. Many manufac- 
 turers make good plates, and they use 
 
 1. Pure litharge. 
 
 2. Pure red lead. 
 
 3. Mixtures of litharge and red lead in all propor- 
 tions. 
 
PASTE PLATES 203 
 
 Some makers mix their paste with strong sul- 
 phuric acid ; some use it weak. Evidently there is 
 much in knowing how to paste, dry, cement, and 
 form much more than in any secret of proportions 
 or materials. 
 
 This statement might almost be taken as an axiom 
 in battery manufacture. 
 
 114. Paste Negatives. The finished negative paste 
 plate has a very different set of characteristics and a 
 very different life history from its weaker positive 
 brother, but it begins in very much the same way. 
 Since it is to become spongy metallic lead, it may as 
 well be made of litharge unless there is some special 
 reason against this, for the step from PbO to Pb is 
 the easiest possible one and takes less energy than 
 the one from Pb 3 O 4 or PbO 2 to Pb. No hardening 
 agent is needed, for the negative has plenty of co- 
 herence. But it does need porosity, and a good 
 many makers use either a soluble salt like magne- 
 sium sulphate, or an inert substance like graphite, 
 in making their negative paste. It seems doubtful 
 whether the effect of the soluble salt is lasting, and 
 there seems to be a belief that graphite and the other 
 space-filling inert substances which are suggested 
 may be harmful in the ordinary open-grid negative 
 plate. So we will make our negatives as simply as 
 possible, using only litharge and rather dilute sul- 
 phuric acid, and allowing the plate to set and cement 
 
204 
 
 STORAGE BATTERIES 
 
 very much as though it were to become a positive. 
 It sulphates to the amount of about 30 % of the 
 whole mass, and during formation the changes shown 
 in Figure 79 take place. In this case the plate was 
 about 20 % sulphate before formation, and 80 % 
 
 40 
 
 80 120 160 200 
 
 AMPERE-HOURS FORMATION 
 
 40 
 
 Z80 
 
 Fio. 79. Changes in composition in a paste negative plate during 
 formation. 
 
 litharge. Lead begins to form immediately when 
 the current is started, but notice how the sulphate 
 content also rises during this period almost as fast 
 as lead is formed. The pores are opening. Metallic 
 lead occupies much less space than either the oxide 
 or the sulphate, and the acid has a chance to reach 
 and attack new oxide in the deeper pores of the 
 plate. Before long the sulphate reaches its maxi- 
 
PASTE PLATES 205 
 
 mum, and then it seems to reduce faster than it is 
 formed from the oxide. Finally the plate stops 
 when it contains about 98 % of metallic lead, the 
 rest being mainly oxide, with a very small remnant 
 of sulphate. 
 
 Lead sponge made in this way is tough, coherent, 
 and well interlocked all over the plate, and a 
 properly made negative has a chance of much longer' 
 life than the positive made in about 
 the same way. It is usually said 
 that one set of negatives will just 
 
 about OUtlast two Sets Of positives. ' IG p a ste negative. 
 
 The rites of negative grids are 
 often made with dovetails as shown in Figure 80, the 
 intention being to hold the contracting material in 
 better contact with the support. 
 
 115. "Chloride" and "Box" Negatives. Two vari- 
 ants on the usual processes have been of importance. 
 The " chloride " negative was made by casting a lead 
 grid around pellets made from molten lead chloride. 
 The whole plate was then reduced to sponge lead, 
 and the active material so formed had many good 
 qualities. This process is no longer in use. The 
 other plate in this class is the " box " negative, origi- 
 nated by the most important of the German battery 
 companies and now used in this country by the 
 Electric Storage Battery Company. The appear- 
 ance of the finished plate is shown in Figure 91. 
 
206 STORAGE BATTERIES 
 
 Pellets containing litharge mixed with some lamp- 
 black or other " expander " are made outside of the 
 plate and dropped into place in the openings. They 
 are then covered by the other sheet of perforated 
 lead, and the plate is complete. This particular 
 active material has 'no coherence at all, and would 
 fall out of the openings in an ordinary grid in a few 
 days of service, but by protecting it with this per- 
 forated cover it can be made to give good capacity 
 and life. 
 
CHAPTER XVI 
 
 DISEASES AND TROUBLES 
 
 116. Frequent mention has been made of action 
 between the peroxide and the lead support in the 
 positive plate, resulting in self-discharge proportional 
 to the quantity of material affected. Lead sulphate 
 is formed at the surface of contact. This action is a 
 perfectly normal part of the activity of every positive 
 plate. It is a large factor for the original flat plates 
 of Plante, fairly large quite measurable at any 
 rate for modern large surface plates, very small in 
 paste plates. 
 
 While this action is a normal one, and essential 
 in its nature, it may be so exaggerated by wrong 
 operating conditions that it becomes a source of 
 danger. 
 
 Between sponge lead and solid lead the difference 
 of potential is so small that self-discharge is very 
 slight. But in many of the modern negative plates 
 there are other things than lead. Many have graphite 
 in them to give contact, insure porosity, and make 
 the active material a better conductor. With this 
 substance in the negative material there is a good 
 
 207 
 
208 STORAGE BATTERIES 
 
 deal of local action, and the negatives may discharge 
 themselves quite as fast as the positives in the same 
 cell. 
 
 These normal effects of self-discharge we must 
 take with our storage cell, for they are a part of its 
 nature. There are many other substances which 
 might be in the cell impurities and which can 
 greatly increase the local action. Some of these are 
 so strong in their effects that they are dangerous to 
 the life of the cell. 
 
 Suppose, for example, that a very stable and per- 
 sistent forming agent has been used in the manufac- 
 ture of the plate and that this has not been carefully 
 removed after formation and before the plate is put 
 into service. During each charging period this 
 forming agent will bore into the peroxide plate 
 (anode) and continue formation at a rate determined 
 by the concentration of the forming ion. From our 
 discussion of rapid formation it will be remembered 
 that maximum rapidity of formation, and density 
 and coherence of material formed, result from using 
 a definite value for the ratio 
 
 concentration of forming agent 
 concentration of acid 
 
 and that the velocity of formation dropped very 
 rapidly when the concentration of forming ion was 
 carried much below the value indicated by this ratio. 
 
DISEASES AND TROUBLES 209 
 
 In the working cell there is not much likelihood of 
 enough of our stable and persistent forming agent 
 remaining in the plate to approach this value. If 
 such an agent were present at anything like the 
 optimum concentration, the positive plate would 
 have a total life of only a few cycles. By that time 
 the lead support would be completely peroxidized, 
 and the plate would fall to pieces. 
 
 Large surface plates attain a life of 1000 or more 
 discharges. If a plate is to compete on these terms, 
 even a minute amount of forming action makes a 
 difference in results, and so manufacturers have 
 learned to carefully remove the forming agent before 
 sending their plates into service. 
 
 Another thing helps very much. Most active 
 forming agents are soon completely decomposed by 
 the electrochemical action of the cell. Nitric acid 
 has been frequently used as an active forming agent. 
 It is reduced to ammonia at the cathode and remains 
 in the cell only as a slight impurity of ammonium 
 sulphate in the electrolyte. While this latter sub- 
 stance is not to be prescribed as good for the cell it is 
 not actively dangerous. 
 
 This danger is confined to the peroxide plate, 
 and the most unhealthy impurities are the forming 
 agents of the list given on page 185. Of course the 
 dangerous ions turn and go to the negative (lead 
 sponge) plate during discharge, but the voltage is 
 
210 STORAGE BATTERIES 
 
 much lower and the plate appears well able to pro- 
 tect itself by a layer of sulphate. 
 
 117. The lead sponge plate has its own class of 
 uncomfortable impurities the metals and they 
 have no power to affect the life of the plate. They 
 merely cause self-discharge. This they do by set- 
 tling on the plate and causing little local cells. 
 During charge the lead plate is catho/le. All the 
 metallic ions in the cell wander over to this plate, 
 and if they can go out of solution at the voltage 
 of charge and under the existing conditions in the 
 cell, they deposit as metal on the lead plate. Little 
 cells 
 
 metal/sulphuric acid/lead 
 
 discharge as soon as the voltage is removed, and 
 the current used in their discharge is lost as far as 
 external work is concerned. The cell appears on 
 test to have lost capacity. 
 
 Evidently the noble metals will be the chief of- 
 fenders, for they go out of solution very readily and 
 give a local cell with a good big electromotive force 
 for self -discharge. A very little platinum will keep 
 a negative plate from taking in more than a minute 
 fraction of its proper charge. This unpleasant effect 
 does not persist for many cycles ; for while the noble 
 metals are ready enough to go out of solution, they 
 are not ready to go back in again. At any rate, 
 
DISEASES AND TROUBLES 211 
 
 when the lead plate is cathode (charge) the noble 
 metal goes out before the lead does, and the latter 
 plates it over and eventually covers it away out of 
 reach. As the negative naturally increases the size 
 of its grain in service, the noble metals are gradually 
 incapsulated in the heart of the lead grains, which 
 no longer react completely to the very center at each 
 reversal. 
 
 Copper, silver, and gold can act in the same way as 
 platinum. Copper is not very active, and the ac- 
 tivity increases to the other end of the list. 
 
 118. There is still a third class of impurities which 
 can cause self-discharge, though its representatives 
 have no direct effect on the plates. This class in- 
 cludes those ions which can exist in two stages of 
 oxidation and which are easily converted from one 
 state to the other. Iron is the commonest example. 
 Suppose a workman drops a pair of pliers into a 
 storage cell during its installation. When the elec- 
 trolyte is poured into the cell, these pliers dissolve 
 gradually to form ferrous sulphate, and now the cell 
 contains Fe ++ ferrous ion. This travels about in the 
 cell, and during discharge it migrates along with the 
 H + to the cathode, now the peroxide plate. When 
 it meets with lead peroxide, it is oxidized to Fe +++ 
 ferric ion. Even if the cell is on open circuit, the 
 action will take place as fast as Fe ++ reaches the 
 peroxide plate, and as soon as a little Fe ++ has been 
 
212 STORAGE BATTERIES 
 
 oxidized to Fe +++ a slight concentration gradient is 
 set up which hastens the motion of Fe ++ toward the 
 peroxide plate and the removal of Fe +++ from the 
 neighborhood. In the meantime Fe +++ has wan- 
 dered over to the lead plate, and there it is reduced 
 to Fe ++ , setting up a diffusion gradient there in the 
 same direction as the one at the other plate. Every- 
 thing conspires to aid in the discharge so produced. 
 No metallic iron is deposited, but every bit of Fe ++ 
 and Fe +++ in the cell keeps busily at work running 
 from one plate to the other and discharging the cell. 
 Even a small amount of pliers in a large cell will 
 cause a considerable self-discharge in 24 hr. This 
 is, of course, an effect which is especially noticeable 
 on open circuit. If the cell is working hard, charg- 
 ing and discharging every few hours or every few 
 minutes, the loss of energy will be negligible. 
 
 Probable Impurities. The list includes : 
 
 Forming agent. From rapid forming process. 
 
 Iron. 
 
 Copper. 
 
 Tin. 
 
 Arsenic. 
 
 Antimony. 
 
 Platinum (noble metals in general). 
 
 119. A certain amount of depreciation must be 
 expected in a battery, even if it is kept in the best 
 possible condition. The effects of local action cannot 
 
DISEASES AND TROUBLES 213 
 
 be avoided, nor can the negative active material re- 
 tain its original porous structure throughout the 
 whole life of the cell. Plates shed their active ma- 
 terial. Positive peroxide loses its coherence and falls 
 off the plate even in the case of the toughest of Plante 
 type, and to a much greater extent in paste types. 
 
 These normal disturbances may be greatly magni- 
 fied by poor operating conditions. We will make a 
 list of the common diseases which are especially ap- 
 parent in Plante types. 
 
 1. Loss of capacity. This is due to wholly differ- 
 ent causes in positive and negative plates. A Plante 
 positive should retain ijbs capacity almost unchanged 
 up to nearly the end of its life. It has great power 
 of recuperation and can re-form lost active material 
 and should remain healthy for the rate at which it is 
 operating if it is carefully handled. Toward the end 
 of its life all the reserve lead will become exhausted. 
 If it is made with rosettes, like the Manchester type, 
 all the pure lead in the strips becomes changed into 
 peroxide, and the plate then becomes like a rather 
 low-surface paste plate. The grid remains unat- 
 tacked, but the capacity has reached a maximum, 
 and from this time on peroxide will be shed and no 
 more can be formed to replace it. Events follow 
 much the same course in a ribbed Plante plate. The 
 ribs will become entirely peroxidized and the main 
 supporting webs have not sufficient surface to keep 
 
214 STORAGE BATTERIES 
 
 up the supply. The ribs finally disappear, as do the 
 rosettes of the Manchester type. The plate is ap- 
 proaching the end of its useful life. 
 
 120. The Plante negative has a more peaceful ex- 
 istence and an almost indefinite life, but it diminishes 
 rather rapidly in capacity during the first hundred 
 cycles or so of service and continues to lose more and 
 more unless it is regenerated by some means. This 
 loss of capacity has been spoken of before (page 192).- 
 It is due to the increase in size of grain and the 
 general decrease in surface which results from many 
 cycles of charge and discharge. The large grains 
 persist and are not completely transformed into sul- 
 phate during discharge. The lead deposits on them 
 rather than to form new grains. Then, too, the 
 smaller grains are more soluble than the large ones, 
 and these two effects taken together combine to pro- 
 duce a continual and considerable droop in capacity 
 with service. One way to bring back the original 
 condition of the plate is to completely reverse it to 
 peroxide and then back to lead again, but this is not 
 very frequently feasible in practice, where the plate ' 
 is set up with many other positives and negatives in 
 a large cell. 
 
 121. Another way of restoring the original capacity 
 of a Plante negative is by means of a process called 
 " Permanizing. " The plate is soaked in a rather 
 strong solution of sugar and then heated to about 
 
DISEASES AND TROUBLES 215 
 
 300 C. for a time. The sugar is quite completely 
 carbonized at a point below the melting point of lead, 
 and the pores of the active material are filled with 
 very finely divided carbon. This carbon prevents 
 the pores from filling up with lead, and the grains 
 may also act as centers on which lead can precipitate. 
 At any rate, plates treated in this way seem to retain 
 their capacity longer than usual, and a plate which 
 has lost a part of its capacity by service has most of 
 it restored by the treatment. 
 
 2. Deformation. All Plante plates are more or 
 less subject to buckling or fracture. If they are 
 made of pure lead, they twist and stretch when any 
 strain is put on them, and if they are made of anti- 
 mony alloy, they are liable to crack instead. In the 
 case of pure lead plates, buckling may be caused 
 by improper formation. If one side of the plate is 
 formed more deeply or completely than the other, the 
 changes of volume which occur will twist or bend the 
 soft lead and the plate buckles. Almost all Plante 
 plates with ribs grow in length considerably during 
 formation, and if the resulting peroxide is dense and 
 firmly attached to the lead of the support, the 
 stretching may be as much as an inch or more. It 
 is almost wholly along the rib much less marked 
 across the plate ; a perfectly normal effect, and known 
 and allowed for by all manufacturers who make this 
 type of plate. Lead is so soft a metal that the 
 
216 STORAGE BATTERIES 
 
 material produced, which is greater in volume than 
 the lead from which it is made, and which adheres 
 strongly to the surface, exerts force sufficient to 
 stretch the whole plate. 
 
 Certain operating conditions may tend to cause 
 buckling. For example, if a battery has been on 
 very high rate work, its ribs and pores are very open. 
 If now it is changed over and put on low rates, espe- 
 cially of charge, its plates are very liable to buckle. 
 Much new peroxide will be formed away down near 
 the central support of the plate, and this can easily 
 fill the available space between ribs too full. 
 
 And sulphation, in the evil sense of the word, can 
 cause plates to tie themselves almost into knots. 
 Here the change of volume is as great as possible, 
 and all the pores and spaces in the plate are over- 
 crowded with material. It may be taken as a gen- 
 eral rule that any treatment which can cause more 
 than the normal change of volume in the deeper 
 active material of the plate will give rise to buckling 
 or fracture. 
 
 3. Sulphation. This is a " waste-basket word " 
 among all the people who have to deal with storage 
 batteries. Whenever anything whatever seems 
 wrong with a cell, the first diagnosis is u sulphated." 
 Lead sulphate usually has something to do with the 
 difficulty, but its connection may be of the most re- 
 mote. The most common cause of trouble is lack of 
 
DISEASES AND TROUBLES 217 
 
 proper charge. In days not so long past, batteries 
 were often sent out a long way into the country, to 
 a point miles distant from the power house, and 
 allowed to " float " on a trolley line to help the vol- 
 tage and save copper feeders. These lonely batteries 
 often had a hard time as far as proper charge was 
 concerned, and some of them furnished examples of 
 sulphation and buckling of the most aggravated 
 nature. Engineering practice has improved since 
 then, and boosters and feeders have been found eco- 
 nomical compared with the rapid depreciation of 
 batteries used in this way. In the case of station 
 batteries properly operated, there is not nowadays 
 much cause to use the word "sulphation." 
 
 4. Impurities and local discharge. Before the 
 danger of very low charging rates and the worse 
 danger arising from a net discharge were clearly 
 appreciated, many of the troubles with plates were 
 sought for in the presence of " impurities " in the 
 cells. Every rapid forming agent was suspected, 
 and water, acid, and even air were examined with 
 great care for possible explanations of trouble. It 
 will be evident from what has been said about the 
 elimination of the forming agent and its comparative 
 action in very dilute solution that these analyses and 
 examinations were without positive result. A stor- 
 age cell should contain nothing but sulphuric acid; 
 but it takes a long time to accumulate troublesome 
 
218 STORAGE BATTERIES 
 
 impurities if reasonably pure water is used to fill the 
 cells, and many of the troubles mentioned appeared 
 within a few months of service. It seems now fairly 
 certain that the whole effect could be explained by 
 undercharge, by the fact that the plates got a net 
 discharge, and by the fact that the charging rates 
 were much too low. Certainly these factors can 
 cause sulphation and buckling, and even destruction 
 of a whole battery, in the way these troubles used to 
 occur. 
 
 5. Shedding of active material. Plante positives 
 shed. So do paste plates, but the shedding is a more 
 healthy thing for the Plante plate, and is a part of 
 its physiology. On page 174 there was pictured the 
 way in which well-made Plante plates adapt them- 
 selves to the rate at which they are working. No 
 plate can do this so well as the simple ribbed type of 
 positive. Even the Manchester plate, nearly uni- 
 versal in its application though it may be, cannot 
 compete with the simple ribbed pure lead type in 
 adaptability, and especially in lively response to the 
 demands of very rapid rates. At low and inter- 
 mediate rates the sensitive pure lead plate is at a 
 disadvantage, for it is endangered by low charge 
 rates, and is by no means so excellent at low dis- 
 charge rates as at high ones. 
 
 Plante negatives have none of these weaknesses. 
 Their only failing is the one already described 
 
DISEASES AND TROUBLES 219 
 
 rapid loss of capacity. As far as health and tough- 
 ness are concerned, they are beyond criticism. 
 
 6. Short circuits in the cell. The almost universal 
 use of wood separators has nearly removed this once 
 common source of trouble. Any large surface plate 
 develops strips and flakes of surface sulphate or other 
 surface material. This drops off and sometimes 
 reaches across from positive plate to neighboring 
 negative. Often these delicate bridges are quite 
 innocuous, but they occasionally become formed part 
 way or all the way across, and the result is a complete 
 short circuit in the cell. Local action may be very 
 great indeed at the two points of contact of this 
 bridge, and many a plate has had a hole eaten right 
 through it by the very high local current within a 
 few days after the accident occurred. Rigorous in- 
 spection is the only way to avoid such an accident, 
 and the acid density is the very best indicator of 
 trouble. In small glass jars it is easy to see whether 
 anything has occurred, but in the big lead-lined tanks 
 used for large batteries it would be a great deal of 
 work to look down between each of the ten thousand 
 or more pairs of plates every day. If the cell is not 
 working properly, its acid density will not rise during 
 charge to the proper value, and this may always be 
 considered a sign of trouble. 
 
 As a battery grows old much sediment forms in 
 the bottom of the cells, and if this is not removed, 
 
220 STORAGE BATTERIES 
 
 the plates will eventually short-circuit across their 
 bottom edges. Pure carelessness or laziness only can 
 account for such a condition. 
 
 7. General debility. The " storage battery man " 
 learns to judge pretty well about the condition of a 
 battery by looking it over. " She don't look right," 
 is reason for a careful investigation. If a battery 
 has been doing well and then begins to show signs of 
 ill health, an examination of the charge and discharge 
 charts will usually show the reason for the change. 
 Perhaps the station has been called on for heavier 
 loads during a period of two weeks or so. A prime 
 power unit may have been out of commission in the 
 station. The old booster may not be large enough 
 for the work to be done. It usually turns out that 
 the battery has given a net discharge, or else the 
 necessary net overcharge cannot be given in the 
 time that remains after the hard work of the day. 
 Some such cause will usually be found. 
 
 122. A few years ago I had hundreds of plates 
 sent to me for chemical analysis from batteries where 
 troubles of this kind appeared. The plates and the 
 electrolyte were in all cases as pure as possible, but 
 in most cases investigation showed that the battery 
 was being charged at too low a rate and not fully 
 charged at that ; the plates had buckled and turned 
 in color. In every case where investigation was pos- 
 sible operating conditions were responsible, but it 
 
DISEASES AND TBOUBLES 221 
 
 sometimes took careful examination and even diplo- 
 macy to bring out this truth. A good starting point 
 in cases like this is the maxim "Look at the rates 
 under which the battery is working." If a compara- 
 tively new battery, once healthy and lively, turns 
 weak and sickly, and plates begin to buckle and shed, 
 do not suspect " impurities." Suspect operating con- 
 ditions. See that the battery is charged. See that 
 it is overcharged, and the chances are large that all 
 the troubles will disappear. 
 
 These directions are sometimes overdone, but not 
 very often in my experience. It is, of course, quite 
 possible to overcharge Plante plates until almost all 
 the active material is blown off the positive plates 
 by continued gassing. But few superintendents will 
 allow their battery men to waste current in this way. 
 Oftener they are obliged to beg for enough charging 
 current to keep the battery in good condition. 
 
 A well-made large surface plate seems to love 
 work. No battery looks so healthy (to me at least) 
 as one which has stripped itself for service, at, say, 
 the 20-min. rate or better. The plates look lean, 
 but their color is good. They do not gas very much 
 except at the very end of charge. The current which 
 can be drawn from such a battery, especially when 
 it is installed in a warm place, is astonishing. In 
 earlier days the 8-hr, rate was "normal." In pres- 
 ent-day service the 5-min. rate is more nearly the 
 
222 STORAGE BATTERIES 
 
 rate at which the battery is most useful. There is a 
 good reason for this. Suppose our battery can give 
 100 amperes for 8 hr. So can a 10 KW. 110-volt 
 generator. This battery can give 3000 amperes for 
 a minute or so. It would take fifteen or twenty 
 generators to safely handle such a peak. 
 
 123. After the catalogue of ills just recited it 
 might seem that the lead battery must be given up 
 as a bad job. But we have been acting in the role 
 of the pathologist in this case, and as a matter of 
 fact the lead cell is a pretty healthy and lively 
 machine, if it is well treated. Even under rather 
 adverse conditions it often shows surprising powers 
 of resistance. In our own laboratory we have cells in 
 use which are over twelve years old. This battery has 
 had occasional periods of a few months each of hard 
 service, with long rests between. The rests have 
 probably been harder on the plates than the work, 
 for it has sometimes been left pretty well discharged, 
 and the results have shown themselves in disintegra- 
 tion of the negative plates. 
 
 In easy service the life of positive plates should cer- 
 tainly Teach six years, and that of negatives is much 
 longer. In stand-by service positives may last ten 
 years and negatives twelve or fifteen. In hard regu- 
 lation work the positive life is three to five years and 
 negative life five to eight. 
 
 Paste plates in service are much shorter lived. 
 
DISEASES AND TROUBLES 223 
 
 Probably about 300 to 350 cycles for the positives 
 and about 400 to 500 for the negatives may be 
 taken as the average life. In stand-by service there 
 seems to be no reason why the life should not be 
 nearly as long as for Plante plates. Local action is 
 much less effective, and the battery is kept well 
 charged. 
 
 124. It is possible to give some general rules for 
 the operation of batteries. For Plante plates : 
 
 1. Keep the battery charged. 
 
 2. Charge at a fairly high rate. Usually this 
 means at the 8-hr, rate or a little higher. 
 
 3. Inspect frequently and remove all possible 
 short circuits immediately. 
 
 4. Keep acid density at the proper point. 
 
 5. Keep the acid above the top of the plates. 
 
 6. If plates buckle, straighten them as soon as 
 possible. 
 
 7. Do not let the temperature reach too high a 
 point. (100 F. is a safe limit.) 
 
 Discharge at almost any rate does not harm good 
 Plante plates provided they are charged immediately 
 after the discharge is finished. 
 
 For paste plates : 
 
 1. Charge at a low rate, 12 hr. or lower. 
 
 2. Overcharge occasionally by 10 % or so. Once 
 a week is often enough for the overcharge if the 
 battery is in daily service. 
 
224 STORAGE BATTERIES 
 
 3. Use an ampere-hour meter and regulate charge 
 and discharge by that. 
 
 4. Try to give a nearly complete discharge be- 
 fore recharging. If the discharge is extended over 
 two or three days, no harm is done. 
 
 5. Watch temperature carefully. High tempera- 
 ture is much more destructive to paste plates than 
 to Plante types. 
 
 6. Test each cell frequently and inspect at the 
 least sign of trouble. 
 
 The most usual trouble arises from continued net 
 undercharge, especially in private installations. 
 
CHAPTER XVII 
 SOME COMMERCIAL TYPES 
 
 125. The most important services performed by 
 storage batteries are in regulation of large station 
 loads and as " stand-by " batteries. The work per- 
 formed in these two applications is wholly different, 
 and there is a very evident movement toward the use 
 of quite different types of plates in the two kinds of 
 service. 
 
 Regulation (Trolley Service, Large Factory Service, 
 etc.). The battery is used in conjunction with a 
 large power plant and often with a " booster." The 
 charge and discharge rate vary from five minutes to 
 twenty seconds or so. This is the hardest and most 
 wearing service that a battery can 'be called on to 
 perform, and it is the most important from the point 
 of view of economy. High service Plante plates are 
 eminently fitted for the work, and paste plates are 
 quite out of their element. 
 
 A very large number of patents have been taken 
 
 out on plates of the Plante type, and most of them 
 
 have dealt with the methods of increasing the surface 
 
 of the plate or with the method of forming it. Not 
 
 Q 225 
 
226 
 
 STOBAGE BATTERIES 
 
 many of the really marked variations have met with 
 commercial success, and gradually practice has left 
 
 FIG. 81. Cross section and sectional view of a " Tudor " plate. 
 
 only a very few really fundamental Plante plate 
 types. 
 
 The fundamental intention is to increase the active 
 surface of the plate by forming ribs. This develop- 
 ment of the surface is carried out before formation 
 
 with a rapid forming agent. 
 The Tudor plate may be 
 taken as type (Figures 80 
 and 81). It is made by cast- 
 ing pure lead in a mold of 
 proper shape, and is prob- 
 ably the best known and 
 most generally used of all 
 European plates. 
 
 Other means than casting 
 
 FIG. 82. " Tudor 
 plate. 
 
 positive 
 
 are also used to produce 
 
SOME COMMERCIAL TYPES 
 
 227 
 
 the same increase of surface. The Gould plate 
 (Figures 83 and 84) is made from pure sheet lead 
 
 FIG. 83. Section and cross section of " Gould " plate. 
 
 by a process of " spinning." The sheet of lead is fed 
 back and forth between rapidly rotating mandrels 
 
 Jiniiiuunn 
 
 . 
 
 Ill/ 
 
 FIG. 84. Steps in the spinning of a " Gould " plate. 
 
 filled with steel disks spaced far enough apart to give 
 the right strength of rib for any particular service. 
 
228 
 
 STORAGE BATTERIES 
 
 FIG. 85. Cross section 
 of "Gould" plate 
 [drawn to scale]. 
 
 The National plate (Figure 86) looks much like the 
 Tudor, but is made by swaging ribs and webs from a 
 sheet of pure lead instead of by 
 casting. Other plates very simi- 
 lar in final appear- 
 ance are made by 
 plowing, by pressing 
 sheet lead through a 
 die under great pres- 
 sure, and in various 
 other ways. 
 
 One of the varia- 
 tions, and one of the 
 oldest and most gen- 
 erally used, is the "Manchester" posi- 
 tive, shown in Figure 87 and already 
 frequently mentioned in the more the- 
 oretical part of this book. This is not 
 a very high surface plate, but it has 
 shown itself well fitted for almost every 
 kind of work. As 
 will be seen from 
 the cut, the active 
 material is formed 
 from " rosettes " of 
 lead ribbon, and 
 
 FIG. 86. Longitudinal and cross sec- 
 tions of a " National " plate. 
 
 these are pressed into a cast frame of antimony lead 
 before formation. The frame is so stiff that buck- 
 
SOME COMMERCIAL TYPES 229 
 
 ling should not take place except under extreme ill 
 treatment, and the surface is sufficient 
 for any except the very highest rates. It 
 is perhaps not quite so efficient at high 
 rates as the plates with larger developed 
 surface (Tudor, 
 Gould, National), 
 but the latter de- 
 mand rather more 
 care in operation. 
 
 B 
 
 "t The Gould plate 
 \ (Figure 88) has 
 
 03* 
 
 sg the longest ribs 
 " of any of the 
 
 .2 types and its SUr- FIG. 87. "Manchester" 
 fl /. -, positive. 
 
 face is very large 
 
 " in proportion to its area. This is with- 
 | out question the plate most responsive 
 -% in high -rate work, and most efficient in 
 J the hardest service, but the greater sur- 
 OD face and longer rib mean greater inher- 
 J. ent danger from local action and greater 
 * probability of buckling unless operating 
 conditions are closely watched. 
 
 It is perfectly feasible to operate any 
 of these high-surface batteries at aston- 
 ishing rates, and in modern installations 
 it is usually the booster which limits the 
 
230 STORAGE BATTERIES 
 
 battery discharge. Most manufacturers are quite 
 willing to send their batteries out to work at the 
 5-min. or even the 1-min. rate of discharge. A 
 glance at the table will show what sort of an " over- 
 load" this is, if the term has any application to a 
 storage battery. 
 
 " Normal rate " 1 for 8 hr. 
 
 x 2 for 3 hr. 
 
 x 4 for 1 hr. 
 
 X 8 for 20 min. 
 
 X 16 for 5 min. 
 
 X 32 for 1 min. 
 
 Of course the term " normal " as applied to the 
 8-hr, rate has lost significance, since the most im- 
 portant work of the battery is nowadays performed 
 at a very much higher rate, and batteries of large 
 size are not often put in for service at this rate ex- 
 cept for stand-by or insurance purposes. The 20- 
 min. rate is more nearly " normal " in modern battery 
 practice. 
 
 In regulation work, batteries are usually operated 
 in conjunction with a large power plant. The cells 
 have each seventy-five to a hundred plates about 
 15 x 31 in., or 18 x 18 in. (See Figure 89.) Each 
 15 x 31 in. positive plate gives 40 amperes for 8 hr., 
 and from this the capacity of the battery at various 
 rates can easily be calculated. Suppose each cell has 
 101 plates. 
 
SOME COMMERCIAL TYPES 231 
 
 50 positives x 40 = 2000 amperes for 8 hr. 
 
 or 4000 amperes for 3 hr. 
 
 or 8000 amperes for 1 hr. 
 
 or 16,000 amperes for 20 min. 
 
 or 32,000 amperes for 5 min. 
 
 If the battery is working in conjunction with a 
 500-volt power circuit, it will consist of about 260 
 
 E.SB.Co.449. 
 
 FIG. 89. One cell of a large regulating battery. 
 
 cells. The power obtainable from the battery is 
 therefore 
 
 2000 amperes at 500 volts = 
 
 1000 KW. for 8 hr. 
 and from this on up to 
 32,000 amperes at about 400 volts = 
 
 12,000 KW. for 5 min. 
 
232 STORAGE BATTERIES 
 
 Such a battery would only be used in connection 
 with a very large power plant say of 5000 KW. 
 or more. 
 
 It will be quite evident how such a battery should 
 be used. Its little 1000 KW. would hardly be felt 
 at the 8-hr, rate, but its 12,000 KW. can give reg- 
 ulation of enormous short peaks. For momentary 
 peaks, lasting only a fraction of a minute at their 
 maximum, this battery could furnish up to 25,000 
 KW. 
 
 As a matter of fact the total quantity of energy 
 furnished by a single discharge of this battery is not 
 very large, as measured by modern requirements. 
 It can give 
 
 1000 x 8 = 8000 KW.H. 
 if discharged at the 8-hr, rate, and 
 
 12,000x^2 =1000 KW.H. 
 
 if discharged at the 5-min. rate. 
 
 Its main importance lies in its power to absorb 
 and give up very large quantities of energy in very 
 short times without danger to itself or trouble to any 
 one about the station. 
 
 "Stand-by" or Insurance Batteries. The most im- 
 portant of all the applications of the storage battery 
 is, strange to say, the one in which it is called upon to 
 do the least actual work. This is as a mere reserve of 
 power, to be used only in case of emergency. 
 
234 STORAGE BATTERIES 
 
 It is of the utmost importance that the supply of 
 light and power, in a city or in any large service, 
 should be continuous. The central power stations 
 of a city supply thousands of consumers in every 
 possible application of electric power. Lights, heat, 
 machinery of every description, elevators, all de- 
 pend on the continuous service given by the power 
 company. Any accident which resulted in stopping 
 the supply of energy, even for a few minutes, would 
 do a lot of damage and inconvenience many people. 
 The stopping of all the generators in one of the New 
 York stations would leave thousands of people in the 
 dark, without elevator service, with no work to do 
 because all the machinery in the factory was dead. 
 
 The great supply companies, like the various 
 Edison Companies of the country, take every pre- 
 caution to prevent such a stoppage in service. En- 
 gines, turbines, generators, all are installed in 
 separate units, each of which has only a fraction of 
 the work of the station. Enough extra sets are pro- 
 vided to allow for all necessary repairs and replace- 
 ments * without interruption of service. At the 
 bottom of all these precautions, the power house has 
 connected with it a huge storage battery, which is 
 kept constantly charged and which is called on for 
 active service only in case of the utmost need. 
 
 The engineer in charge of the station has taken 
 every precaution and has provided for every possible 
 
SOME COMMERCIAL TYPES 235 
 
 emergency. But if anything should happen which 
 puts the power house out of action for a time, the 
 battery is big enough to carry the whole station 
 load for a few minutes long enough to get aid 
 from neighboring stations or to make rapid repairs 
 and changes. The battery is the only source of 
 power which is wholly reliable. There are no mov- 
 ing parts, and there are no high pressures to cause 
 trouble. 
 
 One of these stand-by batteries may cost 1200,000 
 and be called on for only two or three real discharges 
 a year. Interest and depreciation is perhaps $25,000 
 a year, and so these discharges cost $12,000 apiece, 
 a couple of dollars per kilowatt-hour; but quite 
 worth the price, for the station was able to continue 
 uninterrupted service. The battery pays for itself 
 in " good will " alone. 
 
 For this particular class of service the manufac- 
 turers are beginning to use a new class of plate. As 
 far as life and capacity under high rate is concerned, 
 the large surface Plante plate is of course the best, 
 and many stand-by batteries of this type are in use. 
 But they are expensive to make. Local action is 
 considerable, and this may be especially true at the 
 very low charging rate at which it is often necessary 
 to charge such "a battery. Paste plates can do this 
 work quite as well as the more expensive Plante bat- 
 tery. They hold a charge longer, and work best on low 
 
236 STORAGE BATTERIES 
 
 charge rates. The life of a paste plate battery is 
 quite sufficient and its efficiency is good. 
 
 Figure 90 shows a large stand-by battery of paste 
 plates. The experience of European manufacturers 
 has shown that such batteries are economical, and we 
 have finally come round to using paste plates for 
 this work, but about ten years behind the practice in 
 Europe. 
 
 126. Negative Plates. Only a few manufacturers 
 use the true Plante* type of negative plate for any 
 service whatever. The Gould plates are the only 
 pure Plante negatives in general use in this country. 
 The negative differs from the positive in having thin- 
 ner ribs, and a thinner center web, and in having a 
 much larger percentage of the whole weight in the 
 form of active material. It is made by formation as 
 positive first, and the rapid forming process is carried 
 on until the lead of the original blank is nearly all 
 changed to peroxide, just enough being left to hold 
 the plate together. There is no danger of the plate 
 ever getting any weaker after it goes into service, for 
 once it has been reversed to the negative condition 
 there will never be any further action on the lead of 
 the support plate. 
 
 Paste Negatives. The commonest type of negative 
 plate for general service is a paste plate. It differs 
 from the negatives used in electric automobiles only 
 in being more heavily constructed. The grids for 
 
SOME COMMERCIAL TYPES 
 
 237 
 
 these plates are usually made with the dovetails of 
 the strips expanding outward to give the active ma- 
 terial, which contracts in service, an opportunity to 
 keep in good contact with the grid. I am not at all 
 sure that this is anything more than an inherited 
 idea, but it seems to be followed universally by 
 manufacturers of paste negatives. 
 
 Box Negative. The Plante negative is peculiar in 
 its ways, and not always easy to control. The paste 
 negative has not the ex- 
 tremely tough constitution 
 necessary for some of the 
 modern high-rate regulation 
 work. As a mean between 
 the two, and with the inten- 
 tion of avoiding, if possible, 
 the troubles of both the other 
 types, what is called the 
 "box" negative has been de- 
 veloped, and put into active 
 service both in Europe and in this country. It is 
 shown in Figure 91, and it consists of a frame of 
 antimony lead into which are pat the blocks of active 
 material. A front and back cover, both full of fine 
 perforations, complete the plate. The active ma- 
 terial is prepared in the form of blocks which fit the 
 openings in the frame. Some manufacturers have 
 sent them out into service without any preliminary 
 
 FIG. 91. "Box" negative 
 plate. 
 
238 STORAGE BATTEEIES 
 
 formation, the charge necessary for the development 
 of the positives being just about sufficient to form 
 the very porous active material of the negative. It 
 is usually considered better to form them before 
 sending them out. 
 
 At first sight it seems like a decided step backward 
 to place active material inside a box, forcing diffusion 
 to take place through small openings. But the much 
 more difficult diffusion through the fine pores of the 
 material inside the perforated cover completely over- 
 shadows any effect of the outside cover. Further- 
 more, the presence of the cover permits the maker to 
 use a very porous active material indeed. It need 
 have no coherence in the mechanical sense as long as 
 it has conductivity, and the latter property is aided by 
 adding finely divided carbon to the prepared block. 
 The increased porosity which can be attained in this 
 way more than makes up for the longer diffusion 
 path through the perforations in the plate. 
 
 127. Submarine Cells. Next in order of size after 
 the central station and regulating batteries come 
 the ones used in submarine boats. Here the design 
 is most exacting, for both space and weight are 
 sharply limited, especially the former, and a very 
 large amount of power must be furnished over a con- 
 siderable time. Paste plates are the rule, and the 
 average size is about 15 x 24 in., and from 21 to 35 
 plates to the cell. The containing tanks are of hard 
 
SOME COMMERCIAL TYPES 239 
 
 rubber, much like giant vehicle cells, and they 
 are fitted with arrangement for disposal of all gases 
 formed during operation. The mixture of hydrogen 
 and oxygen which is produced in the cell is about as 
 sharply explosive as anything possibly could be, and 
 serious accidents have resulted from faulty gas dis- 
 posal and ventilation. The best way seems to be to 
 fit each cell with its own tight cover and with escape 
 pipe, rather than to shut up the cells in a gas-tight 
 compartment, which is freed from gas by a fan. 
 
 The plates for this service are made to have a 
 capacity as high as is compatible with a reasonable 
 life. Tests include not only capacity at various rates 
 of discharge, but also tests for mechanical strength, 
 and a discharge while the cell is being rocked rather 
 violently through an angle of about 30. 
 
 Of course the boat is dependent wholly on its 
 batteries for power while submerged. Sixty cells 
 must give about 5000 ampere-hours at the 3- or 
 4-hr. rate. Even this only means 
 
 110 x 5000 
 3x746 
 
 which is not a very large amount of power to drive 
 a boat as large as a modern submarine. 
 
 128. Train-lighting and Car-lighting Service. In 
 Denmark cars have been carrying batteries for light- 
 ing service for more than twenty years, and they have 
 
240 STORAGE BATTERIES 
 
 found this application a valuable one. This branch 
 of storage battery engineering has been of increas- 
 ing importance in this country in the past few years. 
 Some day before long it will be statutory that every 
 railroad train shall do all its lighting by electricity. 
 
 The simplest system is "straight battery." The 
 charged battery is taken on at one terminal, dis- 
 charged at a rather low rate during the trip, at the 
 24-48 hr. rate and removed at another point, a 
 freshly charged battery taking its place. There is 
 much of this practice in the United States. The 
 regular cell for this work can give about 250 to 350 
 ampere-hours. Sixty cells in a battery give an aver- 
 age of 110 volts, and will run 60 16-candle-power 
 lamps for 24 hr. 
 
 Car-lighting Systems. Often an axle-driven dynamo 
 is added, which can furnish somewhat more than 
 power enough to run all the lamps when the train is 
 moving at a speed greater than thirty miles per hour. 
 The excess energy is absorbed by the battery when 
 the train is running at higher speeds than this, and 
 the battery must run the lights while the train is 
 standing still. Usually a complete system of regula- 
 tion is provided, so that the battery acts just as a 
 large regulating battery would in a power plant 
 absorbing energy whenever an excess is being turned 
 out by the dynamo and giving it out again at the 
 times when the speed is low or the car is standing still. 
 
SOME COMMERCIAL TYPES 241 
 
 Train-lighting Systems. In through trains which 
 make a run of many hours without change in make-up, 
 the generator for the whole train is sometimes in- 
 stalled on the locomotive and driven by a steam tur- 
 bine. A regular "booster" outfit is installed either 
 on the tender or in the baggage car, and this attends 
 to regulation of all load variations. The battery in- 
 stalled in each car is sufficient in capacity to run its 
 own lights for a time, and the train can therefore be 
 made up and broken up without interruption in ser- 
 vice. As soon as the train has been made up, the 
 generator takes the load and the batteries are kept 
 nearly fully charged. They then have to care only 
 for the regulation and to serve as reserve. 
 
 In all of these different kinds of lighting service, 
 the pure Plante plates have done well, and most of 
 the companies who do this work make special Plante 
 type plates for it. 
 
 129. Vehicle Service. A rapidly growing field of 
 usefulness for the storage battery is in vehicle 
 service. At first glance it seems a poor substitute 
 for the light and efficient internal combustion 
 engines of modern times. To drive a pleasure 
 vehicle at a reasonable speed over average streets 
 and good roads requires about 1.5 KW. If the 
 battery has 32 cells, its average voltage during dis- 
 charge will be 60, and each cell must be able to 
 give 25 amperes for four or five hours. Such a bat- 
 
242 
 
 STORAGE BATTERIES 
 
 tery will cost about $250, and will weigh not far 
 from 750 Ib. complete. 
 
 But this electric vehicle has many important ad- 
 vantages. It is clean and neat, it is simple to oper- 
 ate, and it is almost absolutely certain to go if there 
 
 is a charge in the battery. 
 Where a central charging 
 station can arrange to 
 charge many batteries each 
 night, the whole arrange- 
 ment is efficient and eco- 
 nomical. It is rather strange 
 to see how the heavy truck, 
 driven by electricity and 
 doing its hard work day 
 after day, has been the best 
 of arguments with which to 
 convince the doubter of the 
 economy of the electric ve- 
 hicle in light work and for 
 pleasure. 
 
 The plates used in vehicle work are legion in name 
 and varied as to fame. Paste plates are now almost 
 universally used over the world. European practice 
 runs toward thinner and lighter plates, cheaply made 
 and with a limited but well understood life. In this 
 country we make heavier and stronger plates of 
 lower weight capacity, but having longer life. 
 
 FIG. 92. Paste vehicle grid. 
 
SOME COMMERCIAL TYPES 243 
 
 WEIGHT EFFICIENCY OF PASTE BATTERIES 
 
 American Standard Plates 7^-8| watt-hours per pound 
 
 American Light, high capacity, 10 watt-hours per pound 
 
 Edison 12| watt-hours per pound 
 
 Medium European 11 watt-hours per pound 
 
 Light European 14 watt-hours per pound 
 
 Figures 93 and 94 show one of the commonest 
 types of grids used in making vehicle plates. Most 
 positive grids are so made as to give support from 
 outside to the rather loose and noncoherent per- 
 oxide. This support is supposed to be 
 given by making the ribs of the cross- 
 section shown in Figure 76. The neg- 
 ative grid is made with its dovetail in 
 the opposite sense, as already explained. 
 Many complicated forms of grid have 
 been patented and used, but gradually 
 the majority of manufacturers have 
 settled down to the similar types. 
 
 The old original ideas are sure to recur FIG. 93. Cross- 
 section of mold 
 at fairly regular intervals, sometimes and grid cast- 
 
 because the cause of trouble has been 
 removed, and sometimes because it has been forgotten. 
 About the only decided variation from the simple 
 grid type now in evidence is the so-called " iron- 
 clad " vehicle plate (Figure 95). The type is pe- 
 culiar in depending on an insulating support grid or 
 envelope of rubber, celluloid, porous biscuit ware, 
 
244 
 
 STORAGE BATTERIES 
 
 wood, etc. This surrounds the active material and 
 prevents shedding, and contact is made with a cen- 
 tral lead strip or wire. There seems every reason 
 
 to believe that the apparent 
 security is not a very real 
 one. It is quite possible 
 for positive active material 
 to lose coherence and ca- 
 pacity even though the ma- 
 terial cannot get away and 
 fall to the bottom of the 
 cell, as it does in the or- 
 dinary case. 
 
 This particular plate 
 has, however, been care- 
 fully tested by the makers, 
 and may prove an excep- 
 tion to the rule. 
 
 The present status of 
 the vehicle battery might 
 be summarized as follows : There is not very much 
 difference in standard plates by different makers. 
 Grids differ but slightly. Formation and other treat- 
 ment is becoming a well-known art. With proper 
 operation the good American battery should give 
 250 to 400 cycles without much trouble. It must 
 be cleaned once during this life, probably after 200 
 to 300 cycles. 
 
 FIG. 94. Type of grid for 
 paste positive. 
 
SOME COMMERCIAL TYPES 
 
 245 
 
 If operating con- 
 ditions are not right, 
 the same battery 
 may begin to give 
 trouble after 100 
 discharges or less. 
 I know of one com- 
 pany which man- 
 ages to get nearly 
 450 cycles in hard 
 service from any one 
 of several of the 
 standard American 
 types. 
 
 A set of vehicle 
 negative plates is 
 usually assumed to 
 outlast two sets of 
 positives. This is 
 usually conserva- 
 tive. 
 
 FIG. 95. " Iron-clad" vehicle plate. 
 
CHAPTER XVIII 
 ACCUMULATORS IN GENERAL 
 
 130. It is both strange and interesting that so 
 few galvanic combinations have been found which 
 are really fit for use as accumulators. Plante began 
 his experiments in 1859, at a time when the whole 
 scientific world was much interested in the subject 
 of galvanic cells, and he worked for more than thirty 
 years on the problem. During that time an immense 
 number of combinations were suggested for use as 
 primary cells, but hardly a new idea was brought 
 forward for the improvement of secondary cell, with 
 the exception of the Faure variation, which is me- 
 chanical rather than fundamental. The present 
 Edison- Jungner iron-nickel-alkali accumulator is 
 the first combination which seems to be a real rival 
 of the lead cell. This rivalry seems to be confined 
 to vehicle and traction work, and the alkaline battery 
 can hardly be said to compete at all in the heavy 
 work of the modern power plant. 
 
 It is hard to say just why progress has been so 
 slow. Evidently the problem is a difficult one. 
 Plante was exceedingly lucky in finding what seems 
 
 246 
 
ACCUMULATORS IN GENERAL 247 
 
 to be the best of all combinations, and the men who 
 have developed the alkaline accumulator to its present 
 mechanical perfection deserve all credit for that 
 achievement.. 
 
 Any categorical statement as to what can or can- 
 not be done in any line of scientific or technical 
 development is not likely to hold true very long. In 
 the accumulator problem we seem to have made ad- 
 vances only in one direction, and it may be that there 
 is some fundamental advantage in this direction. All 
 our successful accumulators have plates which are 
 very slightly soluble in the electrolyte used with 
 them. There is a host of other possibilities. The 
 electrolyte might be called upon to furnish a large 
 part or all of the cell energy. Soluble plates might 
 be used. The charge might be made by chemical 
 means, in which case the cell would cease to be an 
 accumulator in the usual sense of the word. 
 
 131. As far as our experience goes we can describe 
 the ideal accumulator as follows : 
 
 The active material is very slightly soluble in the elec- 
 trolyte. 
 
 Current is carried through the main body of the cell by 
 ions different from those which pass back and forth at the 
 electrodes. 
 
 These two conditions seem to us at present to be 
 necessary ones because we have found no other evi- 
 dent way of insuring mechanical reversibility. Even 
 
248 STORAGE BATTERIES 
 
 lead sulphate has almost too great solubility in sul- 
 phuric acid, for negative plates lose in capacity be- 
 cause of the increase in the size of lead grain. Lead 
 peroxide is ideal in this respect. 
 
 A reaction must be selected which yields a large amount 
 of energy per gram equivalent of material used. While 
 the substances used in the lead cell are unfortunate 
 by reason of their high equivalent weights, they are 
 fortunate in another way. Energy is obtained not 
 only from the anode reaction, where lead goes into 
 solution, but also from the PbO 2 reaction. Lead 
 peroxide is one of the electrodes which can furnish 
 energy during reduction. 
 
 The cell must have a low internal resistance, otherwise 
 its efficiency will be impaired. Again the lead cell is 
 a fortunate choice, for hardly any electrolyte has a 
 lower specific resistance than 30 % sulphuric acid, and 
 both lead and lead peroxide are good conductors. 
 
 The chemical reaction must be perfectly reversible. The 
 losses in the lead cell are almost wholly due to the 
 production of gas. 
 
 132. The first efforts toward the discovery of a 
 cell other than Planters start from his work and from 
 his point of view, as would be expected. Peroxide 
 of lead has been tried with most of the metals replac- 
 ing lead as the other plate. Zinc, cadmium, copper, 
 bismuth, etc., were all given a trial, and no one of 
 them has proven better than lead. Then, too, the 
 
ACCUMULATORS IN GENERAL 249 
 
 alkaline combinations, starting with the Lalande- 
 Chapeyron type, were given a trial. The following 
 may be mentioned : 
 
 Copper /potassium hydroxide/ silver peroxide. 
 Cadmium /potassium hydroxide/copper oxide. 
 Zinc/potassium hydroxide/ copper oxide. 
 Iron oxide/potassium hydroxide/manganese dioxide. 
 Iron (?) /potassium hydroxide/nickel peroxide. 
 Cobalt/potassium hydroxide/ nickel peroxide. 
 
 133. Until recent years the lead-sulphuric acid 
 cell has had the commercial field to itself. A great 
 many suggested combinations were tried, but no one 
 of them has stood the test. Usually it has been the 
 mechanical reversibility which has been at fault, 
 even when the chemical reaction has been a favorable 
 one and quite reversible. 
 
 Lately one combination has been developed which 
 bids fair to make a place for itself in practical serv- 
 ice. It is already a success as far as all tests of 
 reversibility, mechanical and chemical, are concerned. 
 This is the iron/potassium hydroxide/nickel per- 
 oxide cell, as developed by Edison to mechanical 
 perfection in this country. Figure 96 shows an 
 assembled cell. The cell and support plates are made 
 of nickel steel. The perforated hollow tubes of the 
 positive plate (see Figure 97) contain a mixture of 
 metallic nickel and nickel oxide before development. 
 After development the active material is perhaps 
 
250 
 
 STORAGE BATTERIES 
 
 NiO 2 , the peroxide of nickel. In the finely perfo- 
 rated flat boxes of the other plate (see Figure 98) is 
 a mixture of iron, iron oxide, and lampblack. This 
 
 is the negative plate, 
 and on charge metallic 
 iron seems to be formed 
 in part. The electro- 
 lyte is concentrated 
 caustic potash solution. 
 There is still much 
 to be learned about the 
 fundamental cell re- 
 action. The simplest 
 formula is 
 
 Ni0 2 +Fe = NiO + FeO, 
 
 and this is a fairly close 
 statement though not an 
 accurate one. This for- 
 mula indicates one inter- 
 esting point. The elec- 
 trolyte does not appear 
 at all. And it is quite 
 true that the change in 
 
 the density of the electrolyte, from complete charge 
 to complete discharge, is small. There is a slight 
 change of concentration, but not sufficient to be of 
 service as an indication of the condition of the cell. 
 
 FIG. 96. Edison cell. 
 
ACCUMULATORS IN GENERAL 
 
 251 
 
 J 
 
 It is of course perfectly certain that there are 
 
 changes of concentration of the electrolyte in the 
 active part of the plates, and that these 
 changes are proportional to the rate at 
 which the cell is working. It is quite 
 certain that the effect of diffusion, 
 which has been called on so often in 
 explanation of the course of charge 
 and discharge curves 
 of lead cells, plays just 
 as important part in 
 the Edison cell. Until 
 we know just what the 
 fundamental cell reac- 
 tion is, we cannot fore- 
 see just how great the 
 effect of change in the 
 
 OH~ concentration will be. 
 
 There are many interesting things 
 
 about the curves taken on this type of 
 
 cell. Figure 99 shows discharge curve 
 
 to a low voltage, much lower than 
 
 would be reached in practice. The 
 
 evident two stages in the curve, without any change 
 
 in the distribution of active material to account for it, 
 
 may mean a change in the cell reaction at that point. 
 This particular type of cell has the following 
 
 characteristics at 25 C. : 
 
 FIG. 97. Group 
 of Edison posi- 
 tive plates. 
 
 
 FIG. 98. Group 
 of Edison nega- 
 tive plates. 
 
252 
 
 STORAGE BATTERIES 
 
 205 
 
 135 
 
 M.90 
 
 170 
 
 0.2 
 
 HOURS 
 
 FIG. 99. Discharge curve of Edison cell. 
 
 5C 
 
 \ 
 
 2 
 
 HOURS 
 
 FIG. 100. Discharge curves of standard American paste type at 
 various temperatures. 
 
ACCUMULATORS IN GENERAL 
 
 253 
 
 13 
 
 V 
 
 
 
 
 
 
 
 
 
 
 
 
 
 125 
 
 \ 
 
 \ 
 
 5 
 
 
 
 
 
 
 
 
 
 
 
 
 ! 
 
 Ul 
 
 105 
 
 in 
 
 \ 
 
 \ x 
 
 ^^^ 
 
 ^s, 
 
 ^>s 
 
 
 
 
 
 
 
 
 
 \ 
 
 \ 
 
 x 
 
 \ 
 
 \ 
 
 ^ 
 
 ^J0. 
 
 -^. 
 
 
 
 
 
 
 
 ^^ 
 
 x 
 
 ^ 
 
 s^ 
 
 ^ 
 
 -^c 
 
 ^ 
 
 
 ~^ 
 
 x 
 
 
 
 
 
 
 ^ 
 
 \ 
 
 
 ^ 
 
 
 x 
 
 
 
 \ 
 
 
 
 
 
 
 
 X 
 
 \ 5 ' 
 
 x 
 
 \ 
 
 \ 
 
 
 
 \ 
 
 FIG. 101. Discharge curves of Edison cell at various temperatures. 
 
 Weight of complete cell, 19.25 Ibs. 
 
 [ampere-hours, 225. 
 
 Capacity 
 
 y [watt-hours, 248. 
 
 Ampere-hours per 
 pound of cell, 11.3. 
 
 Watt-hours per 
 pound of cell, 12.4. 
 
 Ampere-hour ef- 
 ficiency, 82%. 
 
 Watt-hour effici- 
 ency, 60%. 
 
 An examination 
 of the temperature 
 effect shows the im- 
 portant part which 
 
 FIG. 102. Summary showing change in diffusion plays in 
 ampere-hour capacity with temperature. . . 
 
 [Exide and Edison.] the Cell activity. 
 
 F256 
 
 a. 
 
 <I50 
 
 i 20 30' 
 
 TEMPERATURE(CENTIGRADE) 
 
 40* 
 
 50* 
 
254 
 
 STORAGE BATTERIES 
 
 350 
 
 300 
 
 I 
 
 The curves of Figures 100 and 101 show the relative 
 temperature effects on a standard type of lead cell 
 
 and on an Edison 
 cell, and these are 
 summarized in the 
 curves of Figures 
 102 and 103. 
 
 The factors which 
 determine the prac- 
 tical success of such 
 a cell are numerous. 
 Without any inten- 
 tion of either criti- 
 cizing or advertis- 
 
 FIG. 103. --Change in watt-hour capacity ing we can examine 
 with temperature. [Exide and Edison.] 
 
 the general charac- 
 teristics of some present-day types. The following 
 table gives data on three types a rather heavy 
 American plate, a rather light European type, and 
 the regular Edison type of approximately the same 
 watt-hour capacity. 
 
 IOC 
 
 30 
 
 50 
 
 
 STANDARD 
 AMKRICAN 
 
 LIGHT 
 EUROPEAN 
 
 EDISON 
 
 Watt-hours per pound . . 
 Life 
 
 8 
 1 
 
 12 
 
 3 
 
 12.5 
 
 3 
 
 Cost 
 
 1 
 
 1 
 
 2? 
 
 Watt-hour efficiency . . . 
 
 75% 
 
 80% 
 
 60% 
 
APPENDIX 
 
 The General Equation for the Electromotive Force of a Cell 
 in Terms of the Heat of the Chemical Reaction and the Tem- 
 perature Coefficient of the Electromotive Force 
 
 Assume 
 
 1. The law of the conservation of energy. 
 
 2. The second law, in the form 
 
 work done dT 
 
 heat used in doing it T 
 
 We send our cell through the following cycle : 
 
 1. At temperature T, send 96,540 coulombs through 
 at e volts. The work done is Fe joules. 
 
 Suppose the cell cool while it works. It will 
 absorb TFcalories from its surroundings. WeF Q, 
 Q being the chemical heat of reaction. 
 
 2. Raise the temperature of the cell to T+ dT. 
 This will take P calories. The electromotive force 
 is changed to e + de. 
 
 3. Now send 96,540 coulombs through in the oppo- 
 site direction, against e -}- de volts. The work done 
 is F(e + de) joules. The cell heats when it works 
 
 255 
 
256 STORAGE BATTERIES 
 
 in this direction. It gives out W + dW calories. 
 TF+ dW = F(e + de)-[Q + dQ}. 
 
 4. Cool the cell back to T. We get back our 
 P calories. 
 
 dW and dQ are vanishingly small. They can be 
 neglected, since d T is an infinitesimal temperature 
 difference. 
 
 The net result of this cycle is an amount of avail- 
 able work Fde. To produce this amount of available 
 work, a quantity of heat Fe Q changed its temper- 
 ature from T-}- dTto T. 
 
 Apply the second law, 
 
 Fde 
 
 df 
 
 Fe-Q T 
 
 Transforming, 
 
 II 
 
 Calculation of the Electromotive Force of a Cell in Terms of 
 the Solution Pressure at the Electrodes and the Osmotic 
 Pressure in the Solution 
 
 Assume the gas law to hold for osmotic pressures. 
 pv = RT. 
 
 p = osmotic pressure. 
 v = volume of a gram-molecule. 
 R = gas constant. 
 T '= absolute temperature. 
 
APPENDIX 257 
 
 The work obtainable by a change in concentration 
 from p 1 to p 2 at constant temperature is 
 
 p P 2 
 
 Solution pressure is continually balanced at the 
 electrode by osmotic pressure and work done is 
 osmotic work. 
 
 p 
 
 A= ET ln e -- where P is solution pressure, p is 
 
 osmotic pressure, and A is work done at the single 
 electrode. 
 
 We are calculating in gram-molecules. For a 
 univalent ion, 96,540 coulombs will pass the cell with 
 a gram-molecule ; and e, the electromotive force, will 
 be a measure of A, the work done at the electrode. 
 
 For a univalent ion 
 
 RT, P 
 
 e = -lu e -. 
 
 F p 
 
 If the ion which maintains equilibrium is bivalent, 
 only half as much of it need pass the electrode to 
 carry the 96,540 coulombs, and if it is ra-valent, 
 
 - as much will be enough. 
 rath 
 
 For an w-valent ion we have 
 
 .. 
 
 p 
 
258 STORAGE BATTERIES 
 
 At the other electrode we have a precisely similar 
 equation to express the action, but here the ion 
 passes the electrode in the opposite direction and e 
 has the opposite sign. The electromotive force of 
 the whole cell will be the difference of the two single 
 electromotive forces. 
 
 ,-,=... 
 
 nF p l nF p z 
 
 RT 
 
 - is constant at constant temperature. Its nu- 
 
 merical value at 17 C. is 
 
 8.31 x 290 x 2.303 
 
 96,540 
 
 0.0575. 
 
 We have introduced the factor 2.303 which changes 
 natural logarithms to common. The equation as 
 usually applied is 
 
 0.0575 
 e = 
 
 III 
 
 Calculation of the Concentration of the Active Ions in the Lead 
 Accumulator 
 
 (1) The concentration of Pb ++ ion. 
 The solubility of lead sulphate in pure water is 
 1.4 x!0~* gm.-mol. per liter. Assuming complete 
 
APPENDIX 259 
 
 dissociation and that the mass law holds for ionic 
 equilibrium, we have 
 
 Pb ++ S0 4 ~ =(1.4 x 10~ 4 ) 2 = 1.96 x lO- 8 . 
 
 Accumulator acid is about 2 N but is only about 
 50 % dissociated. In this acid SO 4 is therefore 
 1.0 N, and in the cell 
 
 Pb ++ = 2 x 10~ 8 gm.-mol. per liter. 
 
 (2) The concentration of H + ion. 
 
 As stated above, 2 N H 2 SO 4 is about 50 % dis- 
 sociated, the concentration of H + is therefore about 
 2 gm.-mol. per liter. 
 
 (3) The concentration of PbO 2 ion. 
 From the mass law : 
 
 Pb0 2 = Pb+ + . (O-) 2 
 and (H + ) 2 O = constant. 
 
 Therefore, 
 
 PK++ 
 PbO 2 = constant + ^ 
 
 The value of the constant can be calculated by 
 measurements of the solubility of lead hydroxide in 
 sodium hydroxide solution, and these measurements 
 are within the range of analytical attack. In Dola- 
 zalek's determination the sodium hydroxide was 
 0.066 normal, and it dissolved Na 2 PbO 2 to a Concen- 
 tration of 0.00305 gm.-mol. per liter. In this 
 
260 STORAGE BATTERIES 
 
 solution PbO 2 was therefore about .003 .ZVand the 
 remanent alkali contained 0.054 gm.-mol. OH~ per 
 liter. 
 
 The concentration of H + in this solution we can 
 calculate with the aid of the mass law. We have 
 H + OH = 1.1 x 10- 14 
 
 from measurements on water, gas cells, etc. 
 
 In our alkali solution, OH~ is about .05 normal. 
 
 H + is therefore about 2 x 10~ 13 N. 
 
 The lead ion concentration in the alkali we need 
 also. In pure water, lead hydroxide dissolves to 
 about 4 x 10~ 4 gm.-mol. per liter. 
 
 We have 
 
 Pb ++ (OH-) 2 = (4 x 10-4)3 = 6 x 10 -n 
 and for our . 05 N alkali 
 
 Now we can calculate our constant 
 
 Pb ++ 
 
 K _ (3 x IP" 3 ) (1.6 x IP" 51 ) 
 2 x 10- 8 
 
 K= 3 x 10- 46 . 
 From this, for 2 ^Vacid 
 
APPENDIX 
 
 From (1) Pb++ = 2 x KH. 
 From (2) H + = 2. 
 (H + ) 4 =16. 
 
 261 
 
 Finally PbQ,- 
 
 x 
 
 Pb0 2 = 4 x 10- 53 . 
 
 This is the concentration of the PbO 2 ion in the 
 ordinary lead cell, using as electrolyte 2 JVacid. 
 
 IV 
 
 Variation in Capacity with Volume of Electrolyte 
 
 An important factor in the design of a storage cell 
 is the permissible volume of the electrolyte. It is 
 
 123 
 
 FIG. 104. Variation in capacity with volume of electrolyte. 
 
 A, capacity with 2000 cu. cm. of electrolyte, at various rates, 
 a, density of electrolyte corresponding to A. 
 
 B, capacity with 1100 cu. cm. of electrolyte. 
 ft, density corresponding to B. 
 
262 
 
 STORAGE BATTERIES 
 
 quite evident from general considerations that in a 
 cell containing many plates and little electrolyte, 
 the latter may limit capacity by becoming so dilute 
 that the useful working voltage is soon passed. 
 
 Figure 104 shows the capacity of a cell and the 
 change in the density of the cell electrolyte at differ- 
 ent rates of discharge and with different volumes of 
 electrolyte in the cell. 
 
 The Gas given off from the Lead Cell 
 
 A mixture of oxygen and hy- 
 drogen is given off from a lead 
 accumulator during the latter 
 part of charge. This is a very 
 explosive gas mixture, and in 
 submarines and other places 
 where batteries are closely con- 
 fined, ventilation must be very 
 carefully looked out for. 
 
 Figure 105 gives a diagram- 
 matic picture of apparatus which 
 can be used to measure the rate 
 at which gas is evolved during 
 charge and discharge. The gas 
 escapes through the narrow cap- 
 rate of evolution of gas. illary, and the gas pressure . is 
 measured by the small mercury manometer. 
 
APPENDIX 
 
 263 
 
 Figure 106 gives curves of a test on the rate of 
 gassing of paste and Plante negative plates during 
 charge at the 8-hr. rate. 
 
 500 
 
 400 
 
 a 
 
 o 
 
 g 30 
 
 200 
 
 100 
 
 THEORET CAL LIMIfT 
 
 3456 
 HOURS OF CHARGE 
 
 FIG. 106. Curves showing evolution of hydrogen from paste and 
 Plante negative plates during charge. 
 
 VI 
 Specific Resistance 
 
 Aluminium 3 x 10" 6 
 
 Lead 2 x 10~ 5 
 
 Copper 1.7xlO-e 
 
 Graphite (about) 5 x 10~ 3 
 
 Quartz. 3x10* 
 
 30% H 2 S0 4 1.4 
 
 31% HN0 3 . 1.3 
 
 20% HCI. .; . : 1.3 
 
INDEX 
 
 Accumulators, general considera- 
 tions, 246. 
 
 Acid density during charge and 
 discharge, 44. 
 
 Auxiliary electrode, use of, 114. 
 
 "Box" negative, 237. 
 
 Capacity, 116. 
 
 and acid density, 134, 166. 
 
 and Faraday's law, 117. 
 
 arid plate thickness, 122, 123. 
 
 and temperature, 134. 
 
 and volume of electrolyte, 261. 
 
 calculations, 124. 
 
 change in, during service, 193. 
 
 curves, theoretical, 119, 125. 
 
 determined by end voltage, 118. 
 Car-lighting systems, 240. 
 Cementing of pastes, 196. 
 Charge curve, at various rates, 102. 
 
 complete, 98. 
 
 first part of, 97. 
 
 peculiarities, 99. 
 
 various types, 103. 
 Charge and discharge, 94 et seq. 
 Charge and discharge curves, 
 
 individual plates, 114. 
 
 various rates, 112, 113. 
 
 various types, 109. 
 Charge and discharge voltages 
 (average) at various rates, 
 146. 
 
 Charge reaction, 41. 
 Chemical potential, 22. 
 Commercial types, 225. 
 Current density, possible changes 
 at high, 40. 
 
 Daniell cell, 19. 
 Definitions of all parts, 11. 
 Deformation (buckling, etc.), 215. 
 Densities of lead compounds, 175. 
 Diffusion curves and recovery 
 
 curves, 131. 
 Diffusion, general discussion, 129. 
 
 in resting plates, 129. 
 
 Liebenow's experiment, 129. 
 Discharge curve, and acid density, 
 107. 
 
 at various rates, 120. 
 
 first part of, 105. 
 
 to low volleys, 110, 111. 
 
 various types, 121. 
 Discharge reaction, 49. 
 Diseases and troubles, 207, 213. 
 
 Edison cell, 250. 
 
 characteristics, 253. 
 
 discharge curves at various 
 
 temperatures, 253. 
 Efficiencies at various rates, 144. 
 Efficiency, ampere-hour, 141. 
 
 energy, 143. 
 Electrical energy, 25. 
 Electrical units, 13, 24, 25. 
 Electro-chemical unit, 21. 
 Electrode, standard, 82. 
 Electrode equilibrium, 86. 
 Electrode reactions, 81. 
 Electrolytic cell, 13. 
 Electromotive force, 22. 
 
 and acid density, 77. 
 
 theory, 256. 
 Electrostatic equilibrium about 
 
 an electrode, 62. 
 Energy relations, 64. 
 
 265 
 
266 
 
 INDEX 
 
 Faraday's law, 11, 15. 
 Formation at low voltage, 188. 
 
 Plants, 179 et seq. 
 
 rapid Plante, 184. 
 
 theory of, 186. 
 Forming agents, 185. 
 
 persistence of, 191. 
 Fundamental energy equations, 
 
 67, 70, 255. 
 Fundamental reaction formula, 40. 
 
 Gas evolved from lead cell, 263. 
 General equation for electro- 
 motive force, 255. 
 
 Heat of dilution of sulphuric 
 acid, 74. 
 
 Impurities and local discharge, 217. 
 
 effect of, 208, 212. 
 Ionic concentrations, calculation 
 
 of, 258. 
 
 Ionic theory, 33. 
 Ion reactions, 38. 
 Ions, 12, 23, 30 et seq. 
 
 active, during charge and dis- 
 charge, 50 et seq. 
 
 in electrolyte, 48. 
 "Iron-clad" plate, 245. 
 
 Lead cell reaction, 39 et seq. 
 Le Blanc's theory, 89. 
 Liebenow's theory, 90. 
 Load regulation, 229. 
 
 Migration of ions, 36. 
 Migration velocities, 35. 
 
 Non-lead types, 249. 
 
 Operation of batteries, 223. 
 Osmotic theory of galvanic cells, 
 
 256. 
 Osmotic work, 86. 
 
 Paste negatives, change during 
 formation, 204. 
 
 Paste plates, 194. 
 
 Paste positives, formation, 198. 
 
 types, 237. 
 Paste recipes, 202. 
 Physical characteristics, 172. 
 Plante negatives, 192, 236. 
 Primary cells, 3. 
 
 Reaction velocity, 136. 
 Recovery, after charge, 104. 
 
 and diffusion, 131. 
 
 after discharge, 107, 108. 
 
 after long discharge, 133. 
 Resistance, 27. 
 Resistance curves, 153 et seq. 
 
 factors of, 155. 
 
 of sulphuric acid solutions, 149. 
 
 specific, 148, 263. 
 
 temperature effect during activ- 
 ity, 165. 
 
 temperature effect on, 151. 
 Restoring capacity of negatives, 
 214. 
 
 Self-discharge of Plante plates, 183. 
 Shedding of active material, 218. 
 Short circuits, 219. 
 Solution pressure theory, 84. 
 Stand-by batteries, 232. 
 Submarine cells, 238. 
 Sulphation, 216. 
 
 and internal resistance, 157. 
 
 Temperature coefficient of electro- 
 motive force, 72. 
 Thermochemical data, 66. 
 Train-lighting systems, 241. 
 
 Vehicle grids, 242. 
 Vehicle service, 241. 
 
 Watt-hour capacity, 137. 
 
 at various temperatures, 139. 
 
 diagrams, 138. 
 Weight capacity, 243, 254. 
 Work done at an electrode, 64. 
 Work, osmotic, 83. 
 
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The Elements of Electrical Transmission 
 
 A Text-book for Colleges and Technical Schools 
 
 BY OLIN JEROME FERGUSON 
 
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The Elements of Electrical Engineering 
 
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