! , .1*77 ELEMENTARY TREATISE ELECTRIC BATTERIES. FROM THE FRENCH OP ALFRED J^IAUDET, TRANSLATED BY L. M. OF THE BELT- TELEPHONE CO. OF MISSOURI. THIRD EDITION. NEW YORK: JOHN WILEY & SONS, 15 ASTOB PLACE. LIBRAW OF THE W1YEKSITT of GALff OBIU, COPYRIGHT, 1880, JOHN WILEY & SONS. PBEFACE. THE English translation of Mr. Alfred Niauclet's " La Pile Electrique " scarcely requires my commendation to render it acceptable to the English-speaking community interested in the subject, since the author's name is so well known to electricians. This work will serve to guide the uninitiated in the choice and management of batteries, and even the profes- sional electrician may find not only new matter but even old material presented in a new form, and worked to new developments. Telegraphers generally will find many of their fre- quently recurring problems solved in its pages, and its perspicuity will save both inventor and investigator from making useless experiments or errors, while at the same time the work offers to all new fields for careful research. Although the subject treated is so useful and interest- ing, yet this is, I believe, the first time it has received such recognition in English as its importance demands. The translator was happily fitted for his task, having studied under the direction of the author himself, and with whose sanction he undertook his task. GEO. D'LSTFKEVILLE, Electrician, Western Union Telegraph Co. NEW YORK, July 23, 1880. 749495 PKEFACE TO THE ENGLISH EDITION. The work which we here present to the public is in con- formity with the second French edition of a book the first edition of which appeared in 1878, and which has been exhausted in less than two years. ~No other treatise upon the "Electric Battery" has hitherto been published either in English, French or Ger- man. It has appeared desirable to meet this need, and to offer a complete guide to those who wish to thoroughly study or even to improve upon batteries, which are to-day so extensively applied to different uses. The order that the author has adopted in his exposition is in some sense obligatory. Single-liquid batteries are the first, historically and logically, to present themselves. In connection with this first part are naturally placed the exposition of principles, definitions of terms, and the study of the phenomenon of polarization, wherein lies the whole difficulty of the subject. Next in order come two-liquid batteries, in which polari- zation is suppressed or reduced according to circumstances. CONTENTS. PAET FIKST. SINGLE-LIQUID BATTEKIES, CHAPTER I. INTRODUCTION. PAGE Definitions, ....... 1 Origin of the Name Pile, ..... 1 First Idea of the Battery, Properties of Amalgamated Zinc, .... 7 Inconstancy of Simple Batteries, .... 8 Battery Cells joined in Intensity, .... 10 CHAPTER II. DESCRIPTION OF VOLTA'S BATTERY AND ITS DERIVATIVES. Column Battery, ...... 13 Volta's " Couronne de Tasses," .... 13 Cruikshank's Battery, ..... 14 Wollaston's Battery, . . . . . .15 Spiral Battery, 17 Muncke's Battery, ...... 18 Sand Battery, ...... 19 Nature of the Chemical Action in Volta's Battery, . 20 Action of Air upon Batteries, .... 22 V CONTENTS. CHAPTER III. GENERAL REMARKS UPON BATTERIES. PACK Ideas upon Electric Resistance, .... 23 General Remarks upon Electro-motive Force and Resistance, 24 Electro-motive Force, ..... 26 Measurement of Electro-motive Forces, ... 31 Internal Resistance of the Battery, ... 32 Various ways of Joining Voltaic Cells, ... 34 The Voltameter, ...... 38 Secondary Currents, Polarized Electrodes, ... 41 Polarization of a Voltaic Cell, . . . . 42 Polarization in a Battery of several Cells, . . . 47 CHAPTER IV. SULPHURIC-ACID BATTERIES. Batteries with Carbon Electrodes, .... 49 Manufacture of Carbon Electrodes, .... 50 Use of Carbon Electrodes, ..... 51 Zinc-Iron Battery, ...... 53 Iron- Copper Battery, ..... 53 Other Combinations, ...... 53 Smee's Cell, ....... 54 Walker's Platinized Carbon Battery, .... 56 Tyer's Battery, ...... 57 Baron Ebner's Battery, . ... . .58 Batteries analogous to that of Smee, ... 59 Remarks upon Polarization in the preceding Batteries, . 59 CHAPTER V. ACID BATTERIES ANALOGOUS TO THAT OP VOLTA. Hydrochloric-Acid Batteries, ..... 61 Nitric-Acid Batteries, . . . . , 61 Various Acid Batteries, ..... 62 CONTENTS. Vll CHAPTER VI. BATTERIES WITHOUT ACIDS. PAGK Sea-salt Batteries, . . . . . 63 Duchemin's Electric Buoy, ..... 64 Sea-water, Zinc and Copper Battery, ... 68 Zinc, Iron, and Sea- water Battery, .... 67 Accidental Reversing of the Current, ... 68 Chemical Action in Sea-salt Batteries, 70 Marine Batteries, ...... 71 Sal-Ammoniac Batteries, . . . 72 Bagration Battery, ...... 72 Carbon-Electrode Battery, ..... 72 Action of Air upon the preceding Battery, . . 75 Chemical Action in Sal-Ammoniac Batteries, . . 76 OTHER BATTERIES. Zinc-Iron-Water Battery, . . 76 Iron- Tin Battery, ...... 77 Alum Battery, ... ... 78 Remarks upon Single-Liquid Batteries, ... 79 PART SECOND. Two-LiQuiD BATTERIES. CHAPTER I. THE DANIELL BATTERY. Introduction, ...... 81 Description of the Daniell, ..... 88 Improved Daniell Cell, ...... 99 Balloon Battery, . . . . . . 101 A Reversed form of Daniell's Battery, . . .102 Trough Battery, 104 Conventional Figure, . .... 106 Vlll CONTENTS. PAGE Muirhcad's Battery, ...... 107 Carre's Battery, 108 Siemens and Halske's Battery, .... 109 Varley's Battery, ...... 110 Minotto's Battery, ...... Ill Trouve's Blotting-Paper Battery, . . . .112 CHAPTER II. GRAVITY BATTERIES. Callaud's Battery, 118 Applications of Callaud's Battery, . . . . 122 Trouve-Callaud Battery, 123 Meidinger's Battery, ..... 124 Meidinger's Flask Battery, ..... 127 Kruger's Battery, ...... 128 Sir William Thomson's Battery, . . . .130 Electro-motive Force of the Daniell Gravity Battery, . 133 CHAPTER III. GENERAL REMARKS UPON DANIELL BATTERIES. Amalgamation of Zinc in the Daniell, .... 134 Copper-Plating, ...... 135 Irregularity of the Chemical Action in Daniell's Batteries, . 137 CHAPTER IV. BATTERIES DERIVED FROM THE DANIELL. Marie Davy's Sulphate-of -Mercury Battery, . . . 140 Weakening of the Sulphate-of -Mercury Battery, . 143 Sulphate-of Mercury Gravity Battery, . . . 146 Trouve's Reversible Battery, .... 147 Gaiffe's Battery, 147 Latimer Clark's Standard Battery, . . . 148 Sulphate-of -Lead Battery, ..... 150 Weakening of the Sulphate-of -Lead Battery, . . 152 Various Salt Batteries, . . . . . 153 CONTENTS. IX CHAPTER V. ACID BATTERIES. PAdE Grove's Battery, . . . . . . 154 Chemical Actions in Grove's Battery, . . . 156 Bunsen's Battery, French Model, .... 158 Bunsen's Battery, German Model, . . . 172 Bunsen's Battery, Faure's Model, . . . 174 Electro-motive Force and Resistance in Nitric- Acid Batteries, 174 Maynooth's Battery, . . . . . 175 Daniell's Experiments upon the Size and Place of the Elec- trodes, . . . . . . .176 Chloric- Acid Battery, . . , . . 177 Chromic- Acid Battery, . . . . .177 Various Acid Batteries, . . . . . 177 CHAPTER VI. OXIDES IN BATTERIES. Peroxide-of-Lead Battery, .... 179 Peroxide-of-Manganese Battery, .... 180 Lcclanche's Battery, ..... 180 Leclanche's Agglomerated Mixture Battery, . . 189 Clark and Muirhead's Modification of the Leclanche, . 193 Electro-motive Force, Polarization, .... 194 Chemical Action, . . . . . . 194 Weakening of the Leclanche Battery, . . .196 Practical Durability of the Leclanche Battery, . . 197 CHAPTER VII. CHLORIDE BATTERIES. Chloride-of -Platinum Battery, .... 200 Chloride-of-Silver Battery, . 201 Gaiffe's Battery, . . . . . .206 Chloride-of -Lead Battery, ..... 208 Perchloride-of-Iron Battery, ..... 208 X CONTENTS. CHAPTER VIII. DEPOLARIZING-MIXTURE BATTERIES. PAGE Potassium-Chlorate and Sulphuric- Acid Batteries, . . 210 Bichromate of-Potassium and Sulphuric- Acid Batteries . 211 Chemical Action in the Bichromate Battery, . .213 Application to the Telegraph, . . . . 216 Gaugain's Experiments, ..... 217 Use in England, 218 Fuller's Battery, 218 Military Batteries, ...... 220 Grenet's Bottle Battery, ..... 222 Trouve's Battery, ...... 224 Byrne's Pneumatic Battery, ..... 226 Agitation of the Liquid, ..... 228 Camacho's Battery, . . . . . 231 Delaurier's Battery, ..... 232 PAKT THIRD. VARIOUS BATTERIES. Dry Piles, 235 Identical Electrode Batteries, . . . . 237 Unattacked Electrodes in Batteries, . . . .238 Becquerel's Oxygen-Gas Battery, .... 239 Coke-Consuming Battery, ..... 240 Gas Batteries, ...... 242 Secondary Batteries, ...... 243 TABLES. Electric Conductibility of Solids, . . . .253 Specific Resistances, ..... 254 Conductibility of Liquids, ..... 255 CONTENTS. xi PAGE Resistances of Liquids, ..... 256 Dilute Sulphuric Acid, ...... 257 Resistance to Different Liquids, .... 258 Electro-motive Forces, ..... 259 Remarks upon the preceding tables, .... 264 Conclusion, . . . . . . 265 PART I, SINGLE LIQUID BATTERIES. OHAPTEE I. INTRODUCTION. A BATTERY, or pile as it is sometimes called, is an ap- paratus arranged to furnish a continued flow of electricity, to which the name of "electric current" is given. If one should wish to make a complete enumeration, it would be necessary to note : 1. Hydro-electric batteries, to the study of which the present work is devoted ; 2. Thermo-electric batteries, which have as yet received but few applications. It may be well to state, however, that batteries are not the only apparatus able to produce currents ; certain ma- chines produce effects exactly similar. OEIGIN OF THE NAME OF PILE. The word pile, though not as frequently used as the word battery, is, however, more correct. The invention of electric piles is due to Yolta, Profes- 2 SINGLE LIQUID BATTEEIES. sor of Natural Philosophy at PajVia, and dates from the yea-' 1800. One of the first that he constructed was composed of a certain number of discs made of zinc, copper, and cloth piled one upon another. In all courses of natural philosophy models of Velio's pile are shown, and FIG. 1. Fig< 1 shows the appearance of the instrument called the column-pile, which has to-day but an historical in- terest ; it is a pile of discs.* FIKST IDEA OF THE PILE, OB BATTERY, AS WE SHALL HEREAFTER CALL IT. If you immerse a thin plate of commercial zinc into * This figure is a fac-simile of the first cut published of the bat- tery. The original cut is to be found in the "Philosophical Trans- actions" for 1800. INTRODUCTION. 3 dilute sulphuric acid, a very lively action takes place ; the zinc dissolves, and a considerable quantity of hydro- gen is given off. It is indeed this process which is gen- erally employed in the preparation of hydrogen gas. But if, instead of ordinary zinc, which contains im- purities, zinc rendered perfectly pure by distillation be employed, the action takes place very slowly, the bub- bles of hydrogen remain attached to the plate of zinc and protect it from further action of the acid. If a thin plate of platinum, or a platinum wire, be now placed in the same, as soon as the two metals touch at one point the action becomes extremely energetic ; the zinc dissolves and hydrogen is given off, but from the platinum and no longer from the zinc. As soon as the contact of the two metals ceases, all action upon the zinc and all giving off of hydrogen are suspended. This important experiment, due to De La Rive, throws a great deal of light upon all that follows. It is equally successful when you substitute for the platinum silver, copper, or even iron ; it gives the same result when the metals have their point of contact either in the liquid or out of it. It permits us to explain the difference in the action of the sulphuric acid upon pure zinc and impure zinc ; the heterogeneous particles (of iron or of other metals) found at the surface of commercial zinc play the same part as the platinum. You will observe, in effect, that the hydrogen is only given off within very limited points, and at the end of a certain time the surface becomes rough, which shows that the attack has been more active at some points than at others. Let us resume the fundamental experiment of De La Rive. 4 SINGLE LIQUID BATTERIES. Suppose the two metals to have their point of contact not in the liquid but out of it, as Fig. 2 represents. The chemical action takes place in the liquid, as stated above. It also takes place if, instead of bringing the two plates of metal into direct contact, you put one upon the up- per part of the tongue and the other upon the under part. FIG. 2. You will experience a slight sensation like that of a feeble electric shock, and also a peculiar taste. If you place upon the dry part of the zinc a strip of paper dipped in iodide of potassium, and then touch this dampened paper with the platinum, a blue spot is imme- diately produced, which shows that the iodide has been decomposed and iodine set free. These experiments can also be made if you attach to the zinc and platinum two wires (indeed very long ones may be used), and operate with the two loose ends. If you place one of these in the neighborhood of a freely suspended magnetic needle, you will notice that the INTRODUCTION. 5 needle deviates slightly from its north-south direction as soon as the contact is established between the two loose ends of the wires. These different observations prove that a singular phenomenon takes place in the two wires, which is the cause of various actions, physiological (upon the tongue), chemical (upon the iodide of potassium), magnetic (upon the needle). The analogy of these phenomena with those which electric machines with circular glass plates produce, and which were known long before, is easy to comprehend. It is said that an electric current runs over the wire, and one can see from its effects that it is continual. The two metal plates immersed in the liquid (Fig. 3) FIG. 3. are called electrodes ; the wires, long or short, attached to electrodes, and which permit the transference to a dis- tance of the effects produced by the battery, are called 6 SINGLE LIQUID BATTERIES. The rheophores are generally short, and often end in a longer wire, cccc, to which the name of conductor is given. The name circuit of the current is applied to the whole, formed by the battery, the rheophores, and the solid or liquid conductor through which the current passes. In the experiments mentioned above, the tongue and the paper dipped in iodide of potassium formed part of the circuit. Every apparatus which produces a current is indeed a battery. However, the simple apparatus mentioned above (Fig. 3) is, to be more exact, a cell, or an element, of a battery, and a number of these cells grouped together is properly a battery. It is said that the circuit is open when at any point whatever the conductor be disconnected ; all the effects of the current then cease and the current does not circu- late. The current is closed when the two parts of the conductor, which were separated, are brought into con- tact with each other and the current commences to flow. It is said that a battery is in short circuit when the conductor connecting its poles has a null resistance ; that is, when it is very short. We will frequently have occa- sion to use this expression in the course of the present work. It has thus come to be said that, in the conductor, the current flows from the positive pole of the ~battery (+plate of copper) to the negative pole (-plate of zinc) ; a transfer- ence of a peculiar fluid from one to the other of these points is thus implicitly admitted. Let us say, in pass- ing, that this way of looking at things, after having been abandoned in science, shows a tendency towards reaccept- ance with a few changes, so that the conventional Ian- INTRODUCTION. 7 guage, which had not been changed, finds itself again in accordance with the theoretical ideas admitted. The cell formed of the electrodes of zinc and copper immersed in sulphuric acid is more particularly known under the name of Yolta ; by changing the nature of the liquid and the electrodes, you can obtain an indefinite number of cells which produce the same kind of energy. PKOPEKTIES OF AMALGAMATED ZINC. We have shown, in that which precedes, how differ- ently the pure zinc arid the ordinary commercial zinc act in the voltaic cells. The result is that when pure zinc is employed there is no local current at its surface, and that the electricity which is produced passes entirely into the circuit be- tween the poles, and also that the hydrogen is given off from the copper. If, on the other hand, impure or commercial zinc be employed, the giving off of hydrogen takes place, for the most part, upon its surface ; there is reason to conclude, from this, that a very large proportion of the chemical action is lost for the production of the electric current. Thus, in the construction of batteries, the use of pure zinc presents very important advantages ; but the price of this material is almost fabulous, and it can almost be called a curiosity of the laboratory. Happily, a very simple artifice has been discovered, by which the properties of pure zinc may be given to com- mercial zinc. It suffices to amalgamate itthat is, to spread mercury over its surface in such a manner as to form a layer of amalgam of zinc. This amalgam is an 8 SINGLE LIQUID BATTERIES. alloy, or, in other words, a combination of zinc and mer- cury. The experiment shows that the amalgamated zinc im- mersed in sulphuric acid diluted with water, is scarcely attacked, and if it be employed as the positive electrode of a voltaic cell, it occasions no local actions ; the giving off of hydrogen takes place entirely upon the negative electrode, of copper or platinum. In short, amalgamated zinc presents, for use in bat- teries, the same advantages as the chemically pure zinc, and with a few exceptions zinc should always be amalga- mated. INCONSTANCY OF SIMPLE BATTEEIES. All the cells of which we have spoken, formed of two electrodes immersed in a liquid, present an immense drawback ; namely, their action decreases very rapidly from the beginning of the action. The causes of this decrease are twofold, which we will analyze summarily here. The first is the loss of acid from the dilution. It can be easily understood that water acidulated in the propor- tion of 1 to 100 will act less energetically than water acidulated in the proportion of 1 to 10. This cause of the weakening of the battery is not felt until the expira- tion of a certain time, and it is easily avoided by adding, from time to time, acid to the dilution. The second is the deposit of hydrogen upon the cop- per. If the current be interrupted during a length of time sufficient for the freeing of the hydrogen, it will be seen, as soon as the current is again closed, that the in- tensity assumes its original worth ; it suffices indeed to INTRODUCTION. 9 \ agitate the plate of copper in order to cause the gas to free itself and to give to the current its initial intensity. Constant batteries are those in which this second cause of weakening, called polarization of the electrode, is re- moved. The presence of the hydrogen upon the elec- trode opposes a double resistance to the passage of the current, a passive resistance and an active resistance it is the latter that is properly called polarization of the electrode. To depolarize the electrode, is to provide against these resistances by suppressing the freeing of hydrogen. It is very important to comprehend perfectly every- thing pertaining to this question ; therein lies the whole difficulty concerning the improvement and perfecting of batteries. "We will return to it in the course of our ex- position. Various reasons have combined to designate the posi- tive electrode as that one which represents the negative pole of the cell (zinc, in Yolta's battery), and negative electrode as that one which represents the positive pole (copper or platinum, in the cells which have occupied us up to the present). One of these reasons has been indicated above, which is that the current enters the liquid of the battery by the negative pole, and goes out by the positive ; in other words, the positive electrode is that by which the elec- tricity enters the cell. However excellent may be this reason and those which we will give further on for the choice of these denomi- nations, it is not to be denied that they are difficult to employ. In reality, this difficulty may be avoided by speaking of the positive pole and negative pole, when you want to designate the corresponding electrodes ; that 10 SINGLE-LIQUID BATTElilES. is what the majority of practical men do. But if you wish to employ absolutely correct and scientific terms, take great care not to apply them wrongly, as you will only arrive at confusion by an awkward research for pre- cision in the language. "We find in the excellent book, " Darnell's Introduction to Chemical Philosophy," another denomination which ought to be employed more frequently than it is, because it presents the expression of a fact and does not depend upon theoretical ideas, which are always open to discus- sion. He calls the generating electrode that one which plays a part in the chemical action ; it i& the zinc in the cell that we have considered. He calls the conducting electrode that one which is not attacked, and which serves, however, to complete the cell. The first can also be called soluble electrode. BATTERY CELLS JOINED IN INTENSITY. We have described above the most simple cell that can be prepared, composed of two electrodes of copper and zinc immersed in acidulated water. The cell of Yolta's column-battery does not differ es- sentially from this one ; it is composed of two discs, one of copper and the other of zinc, separated by a circular piece of cloth saturated with acidulated water. Two " rheophores," or copper wires, are soldered to these two discs and conduct the current to apparatus upon which it is to act. But as we have summarily indicated from the com- mencement, Yolta placed upon this first group of three discs (zinc, wet cloth, copper) a second group entirely INTRODUCTION. 11 identical and disposed in the same order ; then a third, a fourth, and so on. These discs, in various quantities, the one at the top being of copper and the one at the bottom of zinc, con- stitute the battery of Yolta. Yolta discovered, by delicate means, that the force of the current increased as the number of cells was aug- mented, and made one of the most brilliant inventions of modern times. He thus showed that it was possible to add one source of electricity to another and to a third in such a manner as to obtain a multiple source of an indefinitely increas- ing power. Although three quarters of a century have passed since this discovery, it is not certain whether all of its resources have been exhausted, and it is probable that unlooked-for consequences may yet be brought to light. It is remarkable that he made at the same time an invention and a discovery ; he invented an apparatus, a machine, an implement, which has received and will re- ceive many applications : at the same time he discovered one of the most fruitful principles of physics, to which he opened a new road. If you should wish to show the increase of force of a battery with the number of cells or groups of three discs, the most simple means consists in causing the current to act upon a galvanometer or detector. The deflection of the galvanometric needle would be seen to increase in proportion to the number of cells ; that is indeed a funda- mental truth, verified by experiments at every moment. The copper electrode of the cell of Volta (Fig. 3) is the positive pole, the zinc electrode is the negative pole of the cell. 12 SINGLE-LIQUID BATTERIES. When the cells are piled up or joined in intensity as in Yolta's battery, the positive pole of the battery is that of the last cell, and the negative pole is that of the first cell. In order to give an exact definition of the positive pole of a battery, or of a cell of a battery, it is necessary to say that it is that one whence the current starts circu- lating in the exterior conductor, and that the negative pole is that one towards which this same current flows, as shown by the arrows, Fig. 3. To be complete, it must be added how the direction of the current may be recognized. The wire through which the current flows being placed directly over a freely suspended magnetized needle, causes the north pole of the needle to deflect towards the west, when the current flows from south to north. These preliminaries being established, we may enter upon the description of the principal arrangements of Yolta's Battery. CHAPTER II. THE VOLTAIC BATTERY AND ITS DERIVATIVES. COLUMN BATTEEY. WE have described this battery in the preceding pages. We add that it may be vastly improved upon by soldering the disc of copper of each cell to the disc of zinc of the following cell; all faulty contacts of the metal plates are thus avoided. The discs of cloth should be smaller than the metal discs. It is noticed, however, after a short time that the weight of this column squeezes out the liquid from the cloth ; this liquid runs out over the edges of the discs and soon disappears, so that the battery rapidly weakens, and after a certain time produces no effect whatever. YOLTA'S "COUKONKE BE TASSES." It is generally admitted that the column battery was the first one that Yolta arranged. This is, however, not correct ; the " couronne de tasses" was the first ; and according to us is much preferable. A series of glasses or cups were placed in a circle, forming a kind of a crown ; plates of copper and zinc were so arranged that, being connected at the top, the plate of zinc was placed in one cup and the plate of copper in the next. This battery is truly the model of all those existing 14 SINGLE-LIQUID BATTERIES. to-day, and will be our model for reference in the descrip- tion of others. It is interesting to note that Yolta did not think of the column-battery until afterwards, and then it was with a view to produce an instrument that might be easily trans- ported into hospitals for medical purposes. FIG. 4. CEUIKSHANK'S BATTEKY. This battery is composed of a wooden trough, inter- nally coated with marine glue and divided into cells separated by metallic partitions ; these partitions are composed of two thin plates, one of zinc and the other of copper, soldered together. They are arranged in such a manner as to have all the plates of zinc on the same side and all the plates of copper on the other. The cells thus disposed in the wooden trough are nearly filled with acidulated water, and if they are water-tight the battery thus constructed is very satisfactory. It is not necessary to enumerate the inconveniences of Cruikshank's battery, which is no longer in use ; we would only point out the impossibility of changing the plates of zinc when they have been partially destroyed by the action of the acid. THE VOLTAIC BATTERY AND ITS DERIVATIVES. 15 WOLLASTON'S BATTEKY. The difficulty mentioned above is not to be found in the battery combined by Wollaston. The pairs of metallic plates (zinc and copper) are at- tached to a cross-bar of wood, which allows them to be FIG. 5. lifted out or immersed all at the same time in the glass vessels. This arrangement is excellent, and is still employed very frequently. Wollaston made another change in the combinations adopted before his time : he placed the plate of zinc in the centre and surrounded it with a thin sheet of copper, thus giving to the negative element a surface double that of the zinc. The reasons of this disposition are several, upon which we will remark : 1. When two plates are immersed in a liquid, the 16 SINGLE-LIQUID BATTERIES. two sides facing each other alone combine in producing the current ; the other sides could be covered with an insulating coating without notably diminishing the cur- rent. In Wollaston's disposition, the two sides of the zinc become active. To this it might be opposed that an inverse disposition would present the same advantages, and that a plate of copper might be placed between the two plates of zinc FIG. 5 . FIG. 5 . so as to make use of the two sides of the copper and only the half of the surface of the zinc. But as the zinc is subject to local action or waste, its size should be reduced to just that amount which is requisite to maintain the current required. There is, on the other hand, no dis- advantage whatever in increasing the immerged surface of the copper, as this metal is not attacked by the dilute sulphuric acid. There is, we repeat, an advantage in reducing the sur- face of the zinc as much as possible ; for when the battery is not in use and the electrodes, however, remain immerged in the liquid, the attack upon the zinc continues, although THE VOLTAIC BATTERY AND ITS DERIVATIVES. 17 with less intensity, and this dissolving of the sine is pure loss. As this waste is evidently in proportion to the immerged surface, it is best to have the least possible surface of zinc ; or better, to have no part of that sur- face which may be useless for the producing of the cur- rent. 2. We have stated above that hydrogen is given off from the positive electrode, and that this polarization of the electrode was a cause of weakening of the current of the battery. If the hydrogen would free itself as it is generated, the production of the electricity would not be perceptibly diminished ; but it does not free itself that is, not wholly and what remains, tends to reduce considerably the inten- sity of the current. It is evident that the smaller the surface the more rapidly a certain quantity of hydrogen, being produced upon the positive electrode, will act ; in other words, the larger the surface to be polarized, the more slowly the effect of the polarization will be felt. This is the second reason given for the disposition o.f Wollaston, in which the surface of the zinc is entirely surrounded by the surface of the copper. We will re- turn to this subject farther on, in speaking of the action of the air upon batteries. SPIRAL BATTERY. The two electrodes of this battery are rolled parallel to each other in the form of a helix, and separated by a tissue of osier ; in the centre is a wooden handle to which the whole apparatus is attached, and by which it may be lifted. It is immersed in a bucket of acidulated liquid^ and thus you have electrodes with very large surfaces 18 SINGLE-LIQUID BATTERIES. separated by a very short distance ; the interior resistance of the battery is consequently much reduced, and the quantity of electricity produced very considerable. Tin's battery presents some of the advantages of that of Wollaston, inasmuch as both surfaces of the zinc are FIG. 6. used ; on the other hand, both surfaces of the copper are also used. Cells of this description may be joined in intensity as those of an ordinary battery ; but they were more fre- quently used separately. The spiral battery has indeed been entirely abandoned since the inventions of Grove, and Bunsen of Poggen- dorff (with bichromate of potash). MUNCKE'S BATTERY. Wollaston's battery being cumbersome and unwieldy, Muncke, Young, the illustrious Faraday, and others im- THE VOLTAIC BATTERY AND ITS DERIVATIVES. 19 agined various ingenious arrangements for joining a large number of cells in a small volume. In Muncke's arrangement, the parts where the elec- trodes of zinc and copper are soldered together are placed vertically ; they are divided into two series, the one fit- ting in the other as Fig. Y represents. This battery, and the one arranged by Faraday, which FIG. 7. differs from it very slightly, were employed for several years in laboratories, as the whole battery could be im- merged in one trough, which was very convenient. They are completely put aside to-day. SAND BATTEKY. This battery is composed of a trough made of teak, divided into cells by partitions of slate or of wood ; to make it water-tight it is coated internally with marine glue. A plate of amalgamated zinc placed in one cell is joined to a plate of copper in the adjoining cell, and resting, at their point of contact, upon the partition ; the cells are then filled with sand saturated with acidulated water. This battery is to-day abandoned, but it presented 20 SINGLE-LIQUID BATTERIES. many practical advantages. It was used for a long time in the telegraph service, needing no attention for several weeks at a time, and was much more easily moved from one place to * another, than batteries wherein the liquid might be spilled when carried about. NATUKE OF THE CHEMICAL ACTION IN YOLTA'S BATTEEY. All the batteries that we have just described differ only in their arrangement from that of Yolta's ; in every one we find the zinc, the copper, and the water acidulated with sulphuric acid. The chemical action is very simple. Under the influ- ence of the water and sulphuric acid, the zinc becomes oxydized ; the oxide of zinc uniting with the acid pro- duces sulphate of zinc, and the hydrogen of the water is given off upon the electrode of copper. Thus, on one hand we have the dissolving of a metal (zinc) in the liquid, and on the other the freeing of a metal (hydrogen) which is extracted from the liquid of the battery. Hydrogen, although gaseous, is considered by chemists as a metal. It will be seen, as we advance, that the action is the same in nearly all batteries: dissolving of one metal, freeing of another. On account of its importance in nature and in chemistry, hydrogen will, of all metals with which we will have to do, be the one the most fre- quently freed under the influence of the battery. Far from presenting an exception to the preceding rule, this is a confirmation and a capital example. All our readers know that when they prepare hydro- THE VOLTAIC BATTERY AND ITS DERIVATIVES. 21 gen gas for use in laboratories, they place small bits of zinc in an appropriate jar with acidulated water. Since there is an attack upon the zinc without the intervention of any other metal, it can be seen that in all the forms of Yolta's battery hydrogen gas will be given off and the zinc will be dissolved without closing the circuit ; that is, without the production of electricity by the battery. This is one of the greatest faults -of these batteries ; they are consumed without doing any useful work, like a horse who stands in the stable and eats without working. In will be seen, in that which follows, that nearly all batteries present this same difficulty ; there are, however, a few exceptions, upon which we will bestow particular attention. The hydrogen given off under the chemical action of the battery appears upon the negative electrode of cop- per ; it is seen in the form of bubbles which rise and leave the liquid more or less rapidly. But in addition to these visible bubbles, there is a large quantity of gas deposited upon the surface of the electrodes and which is not seen. This invisible layer of gas is of great im- portance in the study of batteries, and produces, as we have already stated, the polarization of the electrode. We are thus brought again to speak of this phenomenon, so important in the study of batteries, and of which it is the most delicate point. We have taken the opportunity of showing how this injurious action may be overcome, and how to obtain a partial depolarization. 22 SINGLE-LIQUID BATTERIES. ACTION OF THE AIE UPON BATTEKIES. The air acts very favorably upon batteries on account of the oxygen it contains. At the time of the discovery of the battery, it was noticed that ordinary cells exposed to the air absorbed the oxygen, and that the current had a tendency to stop when there remained nothing but nitrogen. But obser- vation shows that the effect is due, not to the action of the oxygen upon the zinc, but to a depolarization of the other electrode. In the cells of Volta and Wollastou, the action of the oxygen is experimentally demonstrated. It will be noticed that this depolarizing action is great- er in Wollaston's battery, which is a new reason explain- ing the advantages of giving to the negative or conduct- ing electrode a considerably larger surface than that of the generating electrode.* * These remarks are only correct when concerning single-liquid batteries. There is no action of air in batteries totally depolarized, like that of Daniell. OHAPTEE III. GENERAL REMARKS UPON BATTERIES. IDEAS UPON ELECTKIC EESISTANCE. WE have said that the most simple way of showing the passage of electric currents in a conducting body is to bring its force to bear upon a magnetic needle. Let us suppose that the conductor of a galvanometer, or of a simple detector, be inserted in the circuit of the current of a battery, and that the deflection of the needle be 25, for instance. Now if the circuit be lengthened by the addition of a wire, the deflection will be seen to diminish to 15, and if the circuit be made still longer, the deflection of the needle will not exceed 10. From this experiment several conclusions may be drawn : 1. The intensity of the current is less in the second in- stance than in the first, and less in the third than in the second. 2. The influence of the additional wire being only passive, the reduction of the intensity of the current is due not to the decrease of the generating force, but to the increase of the resistance. These experiments give an idea of the resistance that conducting bodies offer to the passage of currents ; and they also demonstrate that the resistance of a conductor increases with its length. Yery exact and oft-repeated measurements have proved 24 SINGLE-LIQUID BATTERIES. that the resistance of a conductor is in proportion to its length and in inverse proportion to its sectional area. We will not dwell upon the demonstration of these laws, which are found in all works upon physics. It suf- fices for practical men to know the formulae of these rules which are constantly being applied. GENERAL REMARKS UPON ELECTRO-MOTIVE FORCE AND RESISTANCE. In all machines in motion is seen a power or cause of movement; and there are also resistances which tend more or less to slacken this movement or to stop it alto- gether. Let us take, for instance, a windmill. The large arms, under the pressure of the wind, cause the mill- stones to turn which crush the grain. In the working of the mill we see first a power, the wind, which pro- duces the movement. Then there is a resistance offered by the grinding; this resistance moderates the pace of the arms, and if the wind falls it stops them entirely. At first sight there are two mechanical elements ap- parent : the power or cause of movement, or motive force ; and the resistance, or work. A careful examination will show, however, that the resistance is complex, and that that offered by useful work, as the grinding, should be distinguished from that which is the result of the friction of the different parts of the machine in motion, and of certain secondary phe- nomena. All practical men know that a badly oiled rub- ber is sufficient to slacken the movement of a machine, or even to stop it ; all know the importance of friction in the different parts of the machine, and of the stiffness GENERAL REMARKS UPON BATTERIES. 25 of tlie belts and ropes. These inevitable causes of the slackening, which absorb a part of the motive power at the cost of the useful work desired, are called passive re- sistances. Every one knows that these resistances should be diminished as much as possible, and that they cannot be totally suppressed. Attention should be called to the fact that in many cases no useful work is done, and that there then remain only passive resistances. If the miller takes away his millstones and still permits the mill to turn, it is evident that there remain only those passive resistances (friction and others) which are produced by the machinery remain- ing in motion. If all the machines of a large factory be disconnected from the motion-giving steam-engine and the engine continues to turn, there will only be present the motive force furnished by the engine itself and the passive resistances existing in the engine, in the shafts, and in the different agents of -the transference of the movement which are still in motion. If now the steam-engine runs entirely alone, not being connected with any shaft or any piece of machinery outside of it- self, we have not only the example of a system in which there are force and passive resistances, but also that par- ticular instance where these passive resistances' are inhe- rent to the force-giving machine and inseparable from the production of that force. In a circuit through which an electric current flows, the same terms are to be found : first, a force residing in the battery and which is called electro-motive force next, the work ; and finally the passive resistances. The work may be found in the movement of the clapper-spring of an electric bell ; it may be in the movement of a tele- graph instrument placed at a great distance from the 26 SINGLE-LIQUID BATTERIES. battery ; it may be in the movement of an electro-motor or an electro-magnetic machine which lifts a weight ; it may be in a chemical decomposition produced by the passage of a current in the production of heat and con- sequently of light in a voltaic arc, etc. etc. Passive resistances are the results of the circulation of the current in the different parts of the circuit. We have explained how their existence may be ascertained, and we have designated them by this one word resistance. If the current produces no real work that is, if the circuit is composed solely of conductors without the interposition of any apparatus which puts the current to any use the resistance is entirely passive. These con- siderations explain and justify the use of the word resist- ance applied to that property of reducing the intensity of the electric current which the conductors possess, and which we have demonstrated in the preceding chapter. ELECTEO-MOTIYE FORCE. The cause which produces the electric current we have called electro-motive force. Before going farther we will show several experiments, which will render the ideas upon this force more precise. Let us take a battery cell (Fig. 3 zinc, copper, and water acidulated with sulphuric acid) and cause the cur- rent which it produces to act upon a galvanometer, and we will see that the needle is deflected, for instance, towards the right. If we change the communications of the battery with the galvanometer, the direction of the needle's deflection will be altered, which shows that the direction of the current in the galvanometer has been changed. GENERAL REMARKS UPON BATTERIES. 27 But let us consider the first conditions : the needle is deflected towards the right. Let us now take a second battery cell, differing in no way from the first, and insert it in the circuit. If the negative pole of the second be attached to the posi- tive pole of the first, the two currents flow in the same direction and join each other ; the intensity of the result- ing current is increased, and consequently the deflection FIG. 8. of the needle is greater. In these conditions the two battery cells are joined in intensity (Fig. 8) ; they form a battery of two cells. A battery of any number of cells could thus be formed as we have stated above, but that is not the point upon which we wish to insist ; we only desire to recall the expression, battery cells joined in intensity, and to determine its exact meaning. Suppose now that the second cell be inserted in the circuit of the first ; by uniting the positive pole to the 28 SINGLE-LIQUID BATTERIES. positive pole, and the negative to the negative, in such a manner as to have two poles of the same name ending at the galvanometer (Fig. 9), the needle will remain stationary. This is not to be wondered at, if it be re- membered that the two cells tend to produce equal cur- rents in opposite directions. It is quite natural that these currents balance each other, and that there is no movement either in one direction or the other. It is FIG. 9. " said in this case that the two battery cells are opposed to each other, or are joined in opposition. We have assumed, in the preceding, that the opposed cells were of equal dimensions. Each one acting alone would produce the same deflection of the needle, one to- wards the right and the other towards the left ; both acting simultaneously in opposite directions cause no deflection whatever: which is quite natural and easily understood. Let us now vary the experiment, and place in the GENERAL REMARKS UPON BATTERIES. 29 same circuit (Fig. 10) a small voltaic cell in opposition to a larger one of the same nature ; the needle will remain stationary, thus showing that there is no current. This result will appear very strange to the uninitiated reader, and deserves to be dwelt upon. If they are made to act separately, they cause the needle to deflect, one towards the right, the other towards the left. The current fur- nished by the larger one is more intense than the current FIG. 10. produced by the smaller one, as the deflections of the needle show. But if these two cells be opposed to each other, the effect of one is counterbalanced by the effect of the other, and no current flows through the circuit. The conclusion of this capital experiment is that the electro-^rrwtive force of battery cells does not depend upon their dimensions. The above experiment may be slightly modified. "When cells of equal dimensions are opposed to each other, there 30 SINGLE-LIQUID BATTEEIES. is no deflection of the galvanometric needle. You may lift up the zinc or the copper of one of the cells, or even the zinc and copper together of one of the cells ; you may, in a word, increase or diminish the immersed part of the electrodes of one of the cells, and still there will be no deflection of the needle, and the electro-motive forces remain equal. To elucidate still further this subject, we will present a few more experiments. FIG. 11. Place two cells in opposition to each other, the one similar to those of which we have spoken (zinc, copper, and dilute sulphuric acid), and the other differing but slightly in appearance (iron, copper, and dilute sulphuric acid). The difference is the substitution in the second of iron for zinc. A first trial will show that the copper is the positive pole in the second cell as in the first ; that is, the current flows from the copj>er to the iron in the GENERAL REMARKS UPON BATTERIES. 31 second, as it does from the copper to the zinc in the first. Place them now in the same circuit, in opposition to each other that is, join the two zinc poles and connect the other two with the wires of a galvanometer (Fig. 11) ; the needle will be seen to deflect in the same direction as if the voltaic cell were acting alone, although the deflection is less. We have a right to conclude from -this that the first cell has a greater electro-motive force than the second, and that the substitution of iron for zinc in Volttfs battery would be detrimental. In this experiment we have supposed the two cells to be of equal dimensions, and that the electrode of iron was the same size as that of zinc. We can now modify these dimensions. Let us suppose, for instance, that a very small voltaic cell be placed in opposition to a very large cell (iron, copper, and acid). The direction of the deflection will be the same as in the preceding experiment ; that is, the electro-motive force of the smaller cell is greater than that of the larger one. This new experiment proves again, and more clear- ly than ever, that the electro-motive force of battery cells does not depend upon their dimensions, but upon the ma- terials used in their composition. MEASUKEMENT OF ELECTKO-MOTIYE FORCES. It has been seen how, by means of an ordinary galva- nometer, the electro-motive forces of different batteries may be compared. The method that we have used is called method of opposition, because it consists in oppos- ing equal or unequal forces to each other. 32 SINGLE-LIQUID BATTERIES. It can be easily understood how the electro-motive forces of different cells may thus be measured and tables of these forces made out. Let us take two batteries, A and B, of unequal electro- motive forces. A first experiment will show us, for in- stance, that A io stronger than B. By opposing A to 2B we find that 2B is stronger than A. Let us now oppose 2 A to 3B, and if there is no deflection of the galvano- metric needle w r e may conclude that twice the electro- motive force of A is equal to three times that of B, or that A = | B, or, finally, that A = 1B. It is seen that this method is general ; it may be varied advantageously in different ways. We will not insist upon it any longer, as we only wished to show the possi- bilities of these measurements and not the way to obtain them. HSTTEBNAL KESISTANCE OF THE BATTEEY. It has been seen from the foregoing that the conduc- tors outside of the battery offer a certain resistance to the electric movement, or, in other words, a resistance to the passage of the current. We w r ill now show by several simple experiments that the battery itself offers a resistance to the current it pro- duces. The elementary battery (Fig. 3) is made to act upon a galvanometer. Observe the deflection. Lift up gradually one of the electrodes, and as the immersed surface be- comes less the deflection diminishes. The result shows a decrease in the intensity of the cur- rent. As our former experiments have shown, however, that the electro-motive force does not vary under these GENERAL REMARKS UPON BATTERIES. 33 circumstances, and that the other parts of the circuit do not change, we are justified in saying that the resistance of the battery has increased. The result would be the same if the two electrodes were lifted at the same time. The experiment may be made by separating the two electrodes from each other, still having the same extent of surface immersed. It is perhaps in this manner that the experiment is made the most clear. In these experi- ments the intensity of the current is seen to change with the distance that separates the two electrodes in the trough of liquid and with the section of the trough. It maybe concluded that batteries have an internal resistance in themselves, and that the resistance increases with tlie dis- tance between the electrodes in the liquid, and diminishes when the immersed surfaces are increased. If the battery be considered as a force-producing ma- chine, it is not to be wondered at that it at the same time produces force and offers a resistance to that force. This condition is common to all machines ; a part of the force they produce is absorbed by those passive resist- ances resulting from the action of the different parts of the machine. In a steam-engine, for instance, the fric- tion of the steam in the pipes, the friction of the piston in the cylinder, etc. etc., cannot be avoided. This resistance of the battery has to be taken into ac- count in nearly all cases for the explanation of phenome- na and for the calculation of results. It can be seen that of two batteries in which the elec- trodes are of unequal dimensions, the distance between them being equal in each, the one having the larger elec- trodes offers less resistance than the other ; and it can be said in general that large cells, when compared with small 34 SINGLE-LIQUID BATTERIES. ones, offer less resistance, because the increase of surface of the electrodes is greater than the increase of the dis- tance between them. The resistance of the batteries varies with the nature of the liquids in which the electrodes are immersed. It can be easily understood that all liquids have not the same specific power of resistance. The conductivity of di- lute sulphuric acid varies with the proportions of water and acid mixed, and the greatest conductivity is found in a mixture of 29 parts of sulphuric acid (HSO 4 ) for 71 parts of water. It has been observed that it is this mix- ture which, in an apparatus for the production of hydro- gen, attacks the zinc the most energetically. These reasons would lead to the use of this mixture in preference to all others in Volta's battery, and indeed in all others in which dilute sulphuric acid is used ; but this mixture, being that of about one part of acid (HSO 4 ) for two parts of water, is not used in the practice, as it would be too dangerous to handle, and as it is also rather costly ; therefore the mixture of ten or twelve parts of acid for one hundred parts of water is adopted. It is understood that as soon as a battery is put into working order and the chemical action takes place, the composition of the liquid changes, and consequently the resistance. We will return more than once to this important point. VAKIOUS WAYS OF JOINING VOLTAIC CELLS. We have seen (Fig. 9) how two battery cells of the same kind may be placed in opposition to each other in such a manner as to counterbalance each other. Let us GENERAL REMARKS UPON BATTERIES. 35 now take away the galvanometer that we had placed in the circuit of these cells and we will still have two cells joined in opposition. Let us consider the two cells thus joined. If the gal- vanometer be put into communication, on one hand with the wire connecting the two positive poles, and on the other hand with the wires connecting the two negative poles, the passage of a very strong current will be ob- served. The currents of the two cells, which were at first FIG. 12. opposed to each other, now flow together in the galva- nometer. The two battery cells are then said to be joined in quantity. The metallic piece which connects the two zinc poles may be considered as the negative pole common to both cells, and the other as the positive pole common to both cells. It may be observed that the two cells ought to pro- 36 SINGLE-LIQUID BATTERIES. duce the same effects as a single one, in which the elec- trodes would have a double surface, while the distance between them would remain the same. The internal resistance offered bj the two cells is only half of that offered by each one alone, while the electro- motive force remains the same. This may be demonstrated by placing a third cell of the same size and kind in opposition to these two cells joined in quantity, Fig. 12. The galvanometric needle does not deflect, which shows once more that the electro-motive force does not depend upon the size of the elee trodes, but solely upon their nature. There is, finally, a third way of joining these two cells ; namely, joining them in in- tensity, of which we have already spoken. This manner consists in uniting the positive pole of one pf the cells to the negative pole of the other. In this arrangement the electro- motive force of the two taken together is double that of each separately; the resist- ance is also double. These different ways of joining battery cells may be applied to any number of cells. ^ e * us ^6, ^ or instance, six cells and join them in intensity, Fig. 13. If the electro- motive force, of one cell be symbolized by E, and its resistance by K, it is evident that a battery of six cells joined in intensity will have an electro-motive force equal to 6E, and a resistance equal to 6E. If all be joined in quantity, Fig. 14, the electro-motive force of the battery will be E, and the resistance - FIG 13 GENERAL REMARKS UPON BATTERIES. 37 If they be joined by twos in intensity and by threes in quantity, Fig. 15, the electro-motive force will be 2E, and the resistance f R. FIG. 14. They may, finally, be joined by threes in intensity and by twos in quantity, Fig. 16 ; the electro-motive force will be 3E, and the resistance f K. FIG. 15. FIG. 16. 38 SINGLE-LIQUID BATTERIES. As long as, in this last combination, there is no con- nection with any outside circuit, the three cells on the right are in opposition to the three on the left.' It is not necessary for us to insist longer upon this subject, or to make calculations which are indeed very simple, to make the reader understand that, with a suf- ficient number of cells, a battery may be obtained whose electro-motive force will be as great, and whose resistance will be as little, as can be desired. In most applications, and notably in the electric tele- graph, there is only the need of increasing the electro- motive force,. and very little attention is paid to the re- sistance. In certain instances, however, too great a resistance would be very detrimental ; it is then that the cells may be joined in quantity. In practice, large cells having a very slight internal resistance are employed. VOLTAMETER Before proceeding with the study of batteries, it would be well to stop and examine some of the effects they pro- duce. Of all the chemical actions that can be brought about by means of electric currents, the decomposition of water is the most striking. It is done i-n an apparatus called voltameter, and is represented in Fig. IT. Two wires or plates of platinum, are placed parallel to each other in a jar containing dilute sulphuric acid. These two electrodes pass through the bottom of the jar and are attached to binding screws, or terminals, to which the wires of a battery are fastened. If a sufficiently energetic current be made to pass in this apparatus, bubbles of gas will be seen to free them- GENERAL REMARKS UPON BATTERIES. 39 selves from the surface of the electrodes. If these gases be collected in proper gas-measuring jars, oxygen will be found in one and hydrogen in the other. If they be collected together in a single jar, they will be found to be sensibly in those proportions whose combination pro- duces water. We say sensibly, for the proportion is nearly always altered by complicated disturbing actions, upon which we cannot here enlarge. FIG. 17. The electrode by which the current enters the appa- ratus is called positive electrode of the voltameter ; it is that which is connected with the positive pole, or, in other words, with the negative electrode of the battery which furnishes the current. The negative electrode of the voltameter is connected with the negative pole, or positive electrode or generat- ing electrode of the battery. The oxygen which appears upon the positive electrode of the voltameter is termed electro-negative; the hydrogen which is seen at the surface of the negative electrode of the voltameter is termed electro-positive. These denominations may embarrass beginners. In order to employ them correctly the key is needed, and 40 SINGLE-LIQUID BATTERIES. this may be found in the old theoretical ideas upon the two electric fluids, the one positive and the other nega- tive. There is, at each point in a circuit through which a current flows, a reuniting of positive and negative elec- tricity ; the negative electricity of the oxygen is attracted by the positive electricity of the positive electrode, and so on. This circuit is considered as a chain, in which one end of each link is positive and the other nega- tive. The theoretical ideas have changed, but the expressions have remained, the alteration of which would only involve difficulties, because they are not in disagreement with the new scientific views. We will not enter into the details of this demonstration, but will return to the exact appli- cation of these terms, in order to spare the reader the annoyance of certain errors to which he may be exposed. In general, every liquid decomposed by the passage of an electric current is called an electrolyte, and it is said to be electrolysed as long as the electric action continues. Faraday has established, by numerous experiments, the laws of definite electrolysis. We cannot enlarge upon this delicate subject. We will only say that, if two or three cells joined in intensity produce a current used to electrolyze water, for instance, for each chemical equiv- alent of hydrogen set free in the voltameter there will be an equivalent of zinc dissolved in each cell of the battery. The law of Faraday may be said to be the equivalence of chemical work in all parts of the cir- cuit. If the experiment be made with six cells, instead of with three as indicated above, the quantity of hydrogen set free in one minute is much greater. An idea of the quantity of electricity is thus obtained, and it can be un- GENERAL EEMARKS UPON BATTERIES. 41 derstood how the instrument called voltameter permits one to measure this quantity. It owes its name to Fara- day, who was perfectly justified in so calling it, as it is in truth an instrument of measurement. The same can- not be said of the galvanometer, which it would be better to call galvanoscope ; for in general it does not measure the intensity of the current which passes through it, and it is only by means of complicated contrivances that any measurements can be obtained from its indications. Unhappily the voltameter is not convenient for use. In many cases it gives no indications, and in others produces false results, on account of the resistance which it intro- duces into the circuit. It presents other causes of error, as will be seen in the following pages. SECONDARY CURRENTS. POLARIZED ELECTRODES. If the voltameter be submitted for a short time to the action of a current, its electrodes acquire remarkable properties, which may be recognized in the following manner : Detach the wires connecting the voltameter to the bat- tery, and then connect the voltameter with a galvanome- ter ; the galvanometric needle will be seen to deflect, thus making manifest the passage of a current furnished by the voltameter. The direction of the current is such as to show that that which was the negative electrode of the voltameter in the experiment with the battery has be- come, in the experiment with the galvanometer, the posi- tive pole of this new source of electricity. In other words, the current flows in one direction in the first case, and in the opposite direction in the second case. It may 42 SINGLE-LIQUID BATTERIES. be said that the voltameter has been charged with a part of the current of the battery, and that the voltameter re- turns this current in the contrary direction. It has been said that the electrodes are polarized, which is indeed true ; for they have been rendered capable of acting as poles. This is the origin of the expression polarization of the electrodes which we have already used, and which we will frequently have occasion to employ. The current furnished by the polarized electrodes of the voltameter in the conditions indicated above is called a secondary current ; the voltameter acts as a secondary battery. The secondary current thus obtained lasts but a short time, and its intensity is seen to diminish rapidly from the moment it begins to circulate in the galvanome- ter and is soon reduced to nothing. "We will again have occasion to speak of secondary bat- teries, of which we have just given an example, and which have lately undergone vast improvements. POLARIZATION OF A VOLTAIC CELL. If the current furnished by a voltaic cell (one of Wol- laston's, for instance) with well-amalgamated zinc be examined by means of a galvanometer, the intensity is seen to diminish from the moment the circuit is closed. This diminution is very rapid if the circuit has but very little resistance ; it is, on the other hand, very slow if the circuit offers great resistance, as in a long line of telegraph. If, after having allowed the current to flow for five minutes, for instance, the circuit be left open for five minutes, it will be seen when again closed that the cur- GENERAL REMARKS UPON BATTERIES. 43 rent has nearly assumed its first intensity. It can be said then, the battery when not at work regains its initial power. It may be understood from these observations how it has been possible to use the sand-battery for a number of years in the telegraph service ; the telegraph lines offer- ing indeed great resistances, but only needing intermit- tent currents. By closely examining that which takes place while the circuit is closed, different circumstances of the phenome- non will be seen, which will throw a great deal of light upon the causes to which it must be attributed. At first bubbles of hydrogen are seen to form them- selves upon the copper electrode, as we have already stated ; this will lead to the belief that imperceptible bubbles form themselves upon the entire surface in such a way as to interpose, more or less completely, between the electrode and the liquid, a gaseous layer. Thus appar- ently the principal cause of the diminution in the intensity of the current should be sought at the surface of the cop- per electrode. Several simple experiments will confirm this. If, after a marked diminution in the deflection of the galvanometric needle, the electrodes be shaken without lifting them out of the liquid, the current is seen to partly recover the force it had lost. The same thing is observed if the liquid alone be shaken without moving the electrodes, and consequently without changing the extent of the immersed surface. The moving of the copper electrode alone will show, as a result, the recovery of the lost force. By rubbing the copper, without taking it out of the liquid, with a small brush, the same result is noticed. 44 SINGLE-LIQUID B-ATTEKIES. In these three experiments the disappearance of bubbles of hydrogen from the surface of the conducting electrode is accompanied by a renewal of the intensity of the current. If, on the other hand, the zinc electrode alone be agi- tated, no perceptible modification in the decrease of the current takes place. Henceforth there can be no doubts as to the impor- tance of the phenomenon which takes place at the surface of the copper electrode. The diminution of intensity that we have observed may be attributed to two causes : either to the increase in the internal resistance of the battery, or to the decrease in the electro-motive force. In fact, the two causes are present at the same time. That the resistance increases cannot be doubted, since the active surface of the copper electrode is diminished ; but a simple and direct demonstration of this does not seem easy to obtain. That the electro-motive force is diminished is ex- tremely easy to demonstrate. For this experiment we employ the method of opposition which we have already described, and which is as convenient for the comparison of electro-motive forces as are scales for the comparison of weights. The instant the electrodes are immersed in the liquid and the battery begins to work, it attains its maximum intensity. Let us now take two identical battery cells and close the circuit of one of them for five minutes, leaving the other inactive. At the expiration of five minutes, place the one that has been working in opposition to the fresh one, and a galvanometer interposed in the circuit will show the superiority of the electro-motive force of the fresh cell. GENERAL KEMARKS UPON BATTERIES. 45 If now these two cells be made to act separately, each upon itself that is, without the insertion of any resist- ance during five minutes it will be found at the end of that time, by placing them in opposition, that the second one still has a greater electro-motive force than the first one. The experiments could be varied, and it could be ascer- tained, for instance, how long the decrease continues in a cell of a certain size and form and under well-known circumstances. It can be easily shown that the electro-motive force of a voltaic cell can, by constant action, be reduced one half. For this it is only necessary to cause two cells to work a considerable length of time ; when they are sup- posed to be exhausted as much as they can be, join them in intensity and place this battery of two cells in opposi- tion to an entirely new cell ; the galvanometer will still mark the superiority of the latter, and the necessary con- clusion is that the electro-motive force of each one of the two exhausted cells has been reduced to less than half of that of the new cell. It is admitted that the diminution in the electro-motive force of batteries is due to the production of an electro- motive force (upon the surface of the negative electrode) contrary to that of the principal current. This view is founded upon that which we have said of the electro-motive force found in a voltameter, from whose electrodes gases are given off. It may be shown by a direct experiment that the con- ducting electrode C of a weakened battery has acquired peculiar properties. It is only necessary to immerse in the liquid a second plate of copper, C', and to connect the two with a galvanometer. The passage of a current is 46 SINGLE-LIQUID BATTERIES. thus made manifest, and its direction shows that the copper plate C acts as the soluble electrode, or electro- positive, when compared with the other, C', which assumes the part of a conducting electrode, or electro-negative. This current commences to decrease from the moment it is established, and soon becomes imperceptible. Thus the electrode C, which was electro-negative in the voltaic cell before and during its weakening, is electro-positive in the test cell of two copper electrodes. Finally, if after the above experiment the voltaic cell be re-established, it as- sumes its original intensity, at least for a moment, and then .begins to weaken again, as in the first instance. It is then that the conducting electrode is said to be in a state of polarization. Such is the phenomenon of the polarization of the negative electrode of batteries, a knowledge of which is so important. It will be seen, in the following pages of this work, that the less the polarization, the better the batteries. The most important improvements in batteries are those which have had in view the diminution or suppression of polarization. In other words, the principal aim and effort of inventors worthy of that name has been to depolarise the electrode. It has been established that polarization remains the same when the size of the cell and the intensity of the current are in proportion to each other. It is here neces- sary to define polarization : it is the difference between the electro-motive forces in a polarized battery and a depolarized battery. It can be understood indeed that the quantity of hydrogen given off upon the negative electrode is in proportion to the intensity of the current 5 and that if GENERAL REMARKS UPON BATTERIES. 47 this quantity distributes itself upon the surface of an electrode also proportional, the thickness of the deposit will be the same, and consequently its intrinsic action will not have changed. The practical conclusion of this law is that polarization will be less in a battery having large electrodes than in a smaller one, although the total resistance be the same. POLARIZATION IN A BATTERY OF SEVERAL ELEMENTS. Thus far, each time that we have spoken of the polari- zation of the negative or conducting electrode of cells, we have implicitly supposed the cell to be alone, and that the current which produced the polarization was the current of the cell itself. In ordinary practice it is not thus ; several elements are generally joined in intensity, and the current which flows in each one is furnished by the entire battery. Let us place 10 cells, each having 10 units of resistance, in a circuit of 100 units (total resistance 200 units) ; it is clear that the current will be more intense than if 9 of the 10 cells were taken away ; consequently the current which produces the polarization in each cell will be more energetic than if there were only one cell. The result is that the weakening due to polarization is more marked in cells which are joined in intensity than when they are separate. In other words, when a current, passing through a cell, 'is more energetic than the current which the cell itself produces, the weakening of the current takes place under the following circumstances : At first hydrogen is given off upon the copper, and 48 SINGLE-LIQUID BATTERIES. produces that which we have termed polarization of the cell. But afterwards, when the greater part of the acid is converted into sulphate of zinc, the sulphate itself be- comes electrolyzed and reduced zinc deposits itself upon the copper. If at last this deposit covers the entire sur- face of the copper, it can be easily seen that the two electrodes will become identical, and consequently it is no longer a battery cell. We shall show instances where some of the cells of a battery not only cease to produce a current in the right direction, but actually produce a reverse current. CHAPTER IV. SULPHURIC-ACID BATTERIES. AT the point which we have now reached we are able to compare different batteries and to undertake their study. Up to this time we have only shown Yolta's battery and the modifications in its arrangement. We will now examine batteries which are analogous, but which differ more and more from the first model. This study will show how Yolta, in spite of his imper- fect means, happily chose the elements which have been used ever since ; it will be seen how advantageous and how imperative the use of. zinc is. We will first study those batteries in which the liquid is dilute sulphuric acid, but in which the electrodes differ from those in the voltaic battery. BATTEEIES WITH CARBON ELECTRODES. A battery differing from Yolta's only in the substitu- tion of carbon electrodes for those of copper is very often employed ; it was invented by Mr. Walker in 1849. In these cells the negative electrodes are made of gas carbon, which forms a shell upon the heated retorts in the preparation of gas. This substance has a very good conducting power, and it is very porous. On account of this porosity the electrode presents a considerable surface, and is very slowly polarized. 50 SINGLE-LIQUID BATTERIES. We have already explained, in speaking of Wollaston's battery, why it was advantageous to give the largest sur- face possible to the conducting electrode from which hydrogen is given off. The method that we have given to show the progress of polarization in a battery cell proves the superiority of a battery with carbon electrodes over that of Volta of equal dimensions. The zinc may be placed between two plates of carbon, or better still in the centre of a hollow cylinder of car- bon, always having in view the increase of the surface to be polarized and the checking of the polarization. MANUFACTURE OF CARBON ELECTRODES. When carbon electrodes have simple geometrical forms, or when they are simple plates more or less thick and wide, they may easily be cut from the residue in gas- retorts, and that is what is generally done. But if they are cylindrical, and especially hollow cylin- ders like that shown" in Fig. 18, the above process cannot be applied. The electrodes must be produced artificially in moulds, by pressing powdered carbon with proper cements. Bunsen suggests the following process to make carbon : A mixture of one part by weight of coal and two of coke is made (both having been reduced to an impalpable powder), which, placed in a sheet-iron mould, is heated to clear red until all gases have been given off. The carbon is then dipped in molasses and left to calcinate, protected from the air. John T. Sprague, of Birmingham, recommends the following process : "Plates or blocks may be built up from powdered SULPHURIC-ACID BATTERIES. 51 graphite mixed up with coal-tar or strong rice-paste into a stiff dough, which should be dried, heated, then packed in powdered carbon in a closed vessel and heated to clear red for some time. When cool they should be soaked in strong syrup of sugar, or treacle, again dried and treated as before ; this process must be repeated until the carbon is perfectly dense and strong." FIG. 18. USE OF CAEBOX ELECTKODES. The chief difficulty with carbon is in making the con- nection. The contact between the carbon and the me- tallic rheophore, by which it is connected with the adjoin- ing cell or with the circuit, must be perfect. This is commonly done by fixing a clamp on it to which the rheophores are attached. 52 SINGLE-LIQUID BATTERIES. A better plan is to deposit copper on the upper part and then solder the connection to it, as this gives continu- ous circuit. There is one drawback, however : the acid is soaked by capillary action into the pores of the sub- stance, reaches the surface of the carbon and the inner surface of the copper, which it attacks, thus destroying the connection. It is easy to avoid this action by im- mersing the upper part of the carbon in melted paraffin. The pores of the immersed part are thus filled by the paraffin,- which, when left to cool, becomes solid. All capillary action through the upper part of the carbon is thus prevented. The top of the carbon may also be immersed in melted zinc. But by capillarity the liquid can ascend and attack the zinc as it did the copper. The sulphate of zinc would present the same difficulties as the sulphate of cop- per, and it is also desirable in this case to dip the upper part of the carbon in paraffin. The experiment shows that paraffin does not affect the conductivity of the car- bon, and that the resistance of the battery is not increased by this addition. Lead may also be deposited upon the top of the carbon, but here the paraffin is indispensable, because the forma- tion of sulphate of lead is enough to diminish consider- ably the intensity by introducing in the current a matter almost without conductivity and nearly insoluble. In Switzerland the battery which we have above de- scribed is extensively used, especially in telegraph offices. The zinc should be well amalgamated before being placed in the centre of the carbon cylinder (Fig. 18), in order to diminish local actions while the battery is at rest; owing to this precaution the battery may be used a long time without any care being bestowed upon it. SULPHURIC-ACID BATTERIES. 53 We will see farther on how this battery has been inv proved upon by substituting a solution of sea-salt for the dilute sulphuric acid. ZINC-IKON BATTEKY. One of the first ideas, and the most natural, is to use iron on account of its cheapness. Iron may indeed be substituted for the copper, but a battery thus arranged is very inferior to that of Yolta. The substitution of iron for copper causes a notable diminution in the electro- motive force. It is important to note, however, that the copper may be effectively replaced by iron ; that it is still the zinc which is attacked ; and that the iron is preserved from the action of the sulphuric acid while the circuit is closed. IKON-COPPER BATTEKY. In Yolta's battery it is the zinc which is continuously dissolved ; it is therefore logical to search for something which may replace the zinc and which at the same time is less costly iron, for instance. This substitution of iron for zinc would be more advantageous than the sub- stitution of iron for copper ; but this battery (iron, cop- per, and sulphuric acid) is still inferior to the preceding one. OTHEK COMBINATIONS. If the question of economy be put aside, many other combinations might be usefully employed ; but, as we have said, the use of zinc is necessary, as no other metal practically acceptable can be advantageously substituted. 54 SINGLE-LIQUID BATTERIES. Even aluminium is less liable to be attacked, or, as it is said, is less electro-positive than the zinc. Only calcium, sodium, potassium, and analogous metals are more electro- positive. It is needless to say, however, that they cannot be used in batteries destined for practical purposes. For the negative or insoluble electrode there is, on the other hand, great choice : lead, silver, and platinum can be and are often employed. The electro-motive force of a zinc-platinum battery is rather superior to that of Yol- ta's (zinc-copper), and is about equal to the zinc-carbon battery. Following is a list of metals so arranged that if any two be taken to form the electrodes of a dilute sulphuric- acid battery, the one nearest the end of the list will be the positive electrode, or the negative pole of the cell thus arranged : 1. Silver. 2. Copper. 3. Antimony. 4. Bismuth. 5. Nickel. 6. Iron. 7. Lead. 8. Tin. 9. Cadmium. 10. Zinc. Too great an importance must not be attached to this list, for the order of the metala would be different if the liquid were other than dilute sulphuric acid. SMEE'S CELL. Many ways have been devised for reducing the polari- zation of the negative electrode of the batteries which we have described. In 1840 Smee indicated a very inge- nious way, which consists in using electrodes of platinum, upon whose surface he deposited, by means of electricity, platinum as a fine black powder. These electrodes of SULPHURIC-ACID BATTERIES. 55 platinized platinum tend to diminish considerably po- larization. The simple reason of this is that the bubbles of hydrogen free themselves much more easily than from the polished surface of a metal. For reasons of economy Smee placed the platinum plate between the two plates of zinc. It is in form a reversed Wollaston battery. Smee's battery is charged with a solution containing one part of acid to seven parts of water. Its work is much greater than could be expected from a single-liquid battery. Again, for economy, Smee replaced the platinized platinum by platinized silver. The following composition FIG. 19. had even been used, which produces a much cheaper cell: Upon a plate of copper is deposited a grainy layer of copper, then a layer of silver, and finally a layer of plati- num dust. The rough surface thus given to the silver facilitates the deposit of platinum, which is very difficult upon polished silver. 56 SINGLE-LIQUID BATTERIES. One of Smee's batteries would give very unsatisfactory results if the zinc were not amalgamated ; it is a precau- tion that should not be neglected. This battery is extensively used in England and the United States with many modifications, one of which is presented by Fig. 19. WALKER'S PLATINIZED CARBON BATTERY. We have stated above how, since 1849, Walker had used batteries with electrodes of carbon cut from the gas-retorts. In 1857 he resolved to platinize his carbons, and the battery thus constructed has been used by the South-Eastern Railway in England with great success ; nine thousand of these cells were in service in March, 1875. These cells are contained in an earthen jar, and the lower extremity of the zinc is immersed in a gutta-percha saucer filled with mercury ; the zinc is w r ell amalgamated, which reduces to its minimum the local action or loi chemical work; the top part of the carbon is copper- plated and tinned. The usual size of these cells is 4 inches by 2 inches ; their price (with the mercury and sulphuric acid), 42 cents. The cost of keeping them in order is calculated at 25 cents annually. This battery may be left twelve, fifteen, and sometimes seventeen months without needing any care whatever. It is a simple modification of Smee's battery, and with a liquid of one part of acid to eight parts of water there is an electro-motive force equal to that of Smee's (meas- urements made before any polarization). Polarization may reduce the electro-motive force one half. It will SULPHUEIC-ACID BATTERIES. 57 be seen from the tables at the end of this work that this force is equal to that which is taken as the unit ; namely, that of Darnell's battery. The internal resistance of Walker's battery is about 1 ohm, or 1 unit. It is certainly a very small resistance for a telegraph battery, a quality which we must point out. TYEE'S BATTERY. Tyer combined a modification of Smee's batteries, for the service of electric railroad signals, which presents many advantages. FIG. 20. In the bottom of the jar (Fig. 20) are placed a sufficient quantity of mercury and pieces of zinc ; this constitutes the generating electrode. A plate of platinized silver is held vertically in the jar 58 SINGLE-LIQUID BATTERIES. by means of a cross-piece of lead which rests on the rim of the jar, thus giving a good height and a certain firm ness to the conducting electrode. The top of the cross- piece of lead is furnished with a terminal, to which is fastened a copper wire covered with gutta-percha ; at the end of this wire is a ball of zinc which is wholly immersed in the mercury of the adjoining cell. The liquid is sulphuric acid diluted with twenty times its volume of water. This battery has the advantage of consiiming frag- ments of zinc and using them to their last particle. Those pieces which are wasted in the manufacture of other bat- teries can here be put to use. In this respect Tyer's is the best arrangement yet produced. The maintenance of this battery is reduced to a minimum, for in a well-closed box it can remain two or three years without examination. Great care should be taken, however, in the charging and cleaning of the bat- tery, in order to avoid any loss of mercury. BARON EBNER'S BATTERY. To the Austrian general, Baron Ebner, is due the fol- lowing arrangement of Smee's battery. The negative electrode is of platinized lead ; the generating electrode is, as in the preceding arrangement, composed of frag- ments of zinc in some mercury, which keeps them well amalgamated. A very large battery of this kind was used at the Paris Exposition of 1867 to run electric clocks ; which proved that the polarization was but slightly felt, as electric clocks do not work well unless a very constant current is provided. The electro-motive force of this battery is only about SULPHURIC-ACID BATTEEIES. 59 half that of Daniell's battery, of which we will speak farther on, and which is generally taken as a term of comparison. Its maintenance is very economical, for the same reasons given in the description of Tyer's battery. BATTEKIES ANALOGOUS TO THAT OF SMEE. Following Smee's example, Poggendorff deposited pul- verized copper upon a copper electrode and thus obtained a battery of Volta, or of Wollaston, notably improved, inasmuch as the polarization takes place less rapidly and with less intensity. Drivet, an Italian officer, carried out an analogous idea. He deposited upon the copper electrode of a voltaic cell a very thick layer ( of an inch) of spongy copper. The porosity of this metal gives it some of the qualities of carbon electrodes. The analogy with Smee's battery is more apparent than real, for the very thin layer of pul- verized platinum does not present the increase of surface which is the advantage in the use of carbon electrodes. We have ourselves tried a battery in which the nega- tive electrode is a plate of lead, upon whose surface a layer of spongy lead -fa of an inch thick is deposited. REMARKS UPON POLARIZATION IN THE PRECEDING BATTERIES. "We have seen in all batteries described thus far that polarization was the result of the freeing of gaseous bub- bles of hydrogen from the negative electrode. We have indicated several means, devised by different physicists, to diminish this effect, which is done either by increasing the surface of the electrode to be polarized (Wollaston's battery, carbon-electrode battery, and Dri- 60 SINGLE-LIQUID BATTERIES. vet's battery) or by modifying this surface in such a way as to facilitate the freeing of the gas (Smee's and similar batteries). The action of a battery is already vastly im- proved by giving a rough surface to the polarized elec- trode, instead of leaving it polished. We have also shown how the air acts favorably upon batteries, either by diminishing polarization while they are at work or by producing depolarization when the current has ceased to flow. Depolarization would un- doubtedly take place in the absence of the oxygen of the air, by the freeing of gas or by its dissolution in the liquid ; but the oxyen renders depolarization much more rapid, especially in the case of carbon electrodes, by com- bining with the hydrogen to form water. "We will indicate, as we proceed, much more effectual means for diminishing or suppressing polarization, which consist in the use of substances placed near the negative or conducting electrode, and by which the hydrogen is chemically absorbed. These are the only contrivances by which constant batteries can be produced ; that is, batteries whose electro-motive force is constant. We will describe in detail these constant batteries, which present a satisfactory solution of the problem of obtaining a continuous and regular electric current. They have taken the place of simple and inconstant batteries in all applications, and their study will be the crowning of the present work. But in order to proceed from the simple to the com- plex we ought to describe seve-ral other inconstant bat- teries, only a few of which have any practical interest. Their study is, however, necessary in order to under- stand the many varieties already tried and those which might be tried. CHAPTEE V. ACID BATTERIES ANALOGOUS TO THAT OF VOLTA. THUS far we have considered a series of batteries dif- fering very little from each other, all being composed of two different electrodes immersed in a single liquid, di- lute sulphuric acid. It is easily understood that by replacing the sulphuric acid by other acids, new batteries analogous to the first ones may be obtained. HYDEOCHLOEIC-ACID BATTEEIES. The cheapness of hydrochloric acid caused many per- sons to use it ; but none of the batteries thus constructed obtained any continued application, because hydrochloric acid, being gaseous and only soluble in water, escapes into the surrounding air, so that after a short time it is im- possible to remain in the room where it is placed. Besides, the hydrochloric acid liberates itself rapidly from the water in which it is dissolved, at least a good part of it, the liquid becoming immediately impoverish- ed ; and a new cause of the weakening of the current is added to those which we have already pointed out. OTTKIC-ACID BATTEEIES. Nitric-acid batteries could be very easily made, but they would have the same inconveniences as those with 62 SINGLE-LIQUID BATTEEIES. hydrochloric acid, and would not present the same eco- nomical advantage. It will be seen, however, that in cer- tain less rudimentary combinations nitric acid is put into use. YAEIOUS ACID BATTERIES. All acids employed by chemists maybe used in the composition of batteries, provided they be liquid or solu- ble in water and conductors of electricity. Acetic acid, found in all households, may be used in the absence of others. It has indeed been used by Pul- vermacher in his electro-medical battery. The electrodes were zinc and copper wires wound upon small pieces of wood. They were connected with each other, the posi- tive pole of each with the negative pole of the following one, and dipped in diluted vinegar. Twenty years ago this apparatus had great success, but to-day it is replaced by others more perfect. In all these voltaic combinations the chemical action is the same as in Yolta's battery. The zinc becomes oxy- dized at the expense of the water, and the oxide of zinc combines with the acid, forming a nitrate, an acetate of zinc, etc. The hydrogen of the water is given off upon the negative or conducting electrode. It can be seen without going any farther how many different batteries may be conceived by simply varying the nature of the electrodes and the liquid. But many of these combinations are far from possessing any interest, and our remark is only designed to call the attention of the reader to the number of solutions of the problem of constructing batteries. CHAPTER VI. BATTERIES WITHOUT ACIDS. IN addition to the acids there are numbers of liquids or solutions which may be used in batteries, a few of which are interesting. SEA-SALT BATTERIES. On account of the facility in obtaining chloride of so- dium, or sea-salt, or common salt, it is often made use of in batteries. The battery, whose electrodes are carbon and zinc, is almost exclusively used in Switzerland for tele- graph purposes, with dilute sulphuric acid, or more fre- quently with salted water. There are several dimensions of these. The smallest has flat electrodes 2f inches long ; the next size has elec- trodes 4 inches long and 1J inches wide. Both sizes have but a single piece of carbon in each cell. The first can work one month, the second three months, without care. These cells certainly cost very little, and there is scarce- ly any consumption of the zinc while the circuit is open, although the zinc is not amalgamated, which is a very satisfactory condition. The electrodes may be lifted out during the suspension of work, and this is facilitated by the electrodes being attached to a bar of wood. By lift- ing this bar the electrodes of ten cells may be raised at one time. Another model of this same battery is shown in Fig. 18. 64 SINGLE-LIQUID BATTEKIES. The carbon lias the form of a hollow cylinder, in tho centre of which is a plate of zinc, not amalgamated, as we have already stated ; these two electrodes are fastened to a strip of wood which rests upon the rim of the jar containing salted water. The comparatively large surface of the carbon is a very favorable condition (for single- liquid batteries), as we explained when speaking of Wol- laston's battery. In the model employed on Swiss lines the carbon is 5^ inches high, and has an exterior diame- ter of 3 inches. These batteries can do service from nine to twelve months without requiring attention. The friend to whom we are indebted for the preceding information uses salt-water batteries for domestic bells. He employs cells which have a height of 14 inches. Some batteries of this kind have been known to work from six to eight years without any care whatever. There is one which worked ten years ; the zinc had of course disappeared. Concerning the weakening of this battery, it has been found that it may be exhausted by causing a constant current of a short circuit to pass for ten or twelve hours, and that it only needs two or three hours of rest to regain its lost energy. In other words, depolarization takes place very rapidly. The sea-salt battery is not only used for the telegraph and electric bells, but for electric clocks. DUCHEMIN'S ELECTRIC BUOY. Duchemin placed elements of the preceding form directly in the sea by attaching them to scrme floating body. The constant agitation of water caused undoubt- edly an almost complete depolarization. Wh^rf "several BATTEEIES WITHOUT ACIDS. 65 cells are employed, however, they are in the same liquid ; there is therefore a small loss of electricity ; it cannot be of much consequence, because of the form of the carbon which surrounds the zinc. A perfect insulation of the wires connecting the cells is of great importance. The main object of these batteries was the preserva- tion of sheets of iron used in the construction of vessels, barges, buoys, etc. etc. It appears that the hull of a vessel undergoes a relatively less change during naviga- tion than when at anchor or in port ; it is in this case that the use of Duchemin's buoy is practicable. These buoys are used as follows : Seven cells about 4 inches in diameter, for instance, are joined in intensity. The positive pole of this battery is put into communication with the sheets of iron to be preserved ; the negative pole (that is, the zinc of the last cell) is in the sea, as indeed are the others. Under these circumstances it has been proved, by experiments made at Cherbourg by officers of the French navy appointed purposely by the Minister of Marine, that a surface of iron eighteen times larger than that of the zinc which forms the soluble electrodes of the battery may be pre- served from rust. It appears that the simple addition of a sheet of zinc is not sufficient to preserve the hull of an iron vessel from rust, but it can be done by means of one or seve- ral electric buoys ; that is the result, at least, of a pro- longed experiment on a small iron boat. These interesting experiments were unhappily discon- tinued during the war of 1870-71, and have not been re- sumed. Before leaving the subject, we will say that there is a possible superiority of sea-water over common salted 66 SINGLE-LIQUID BATTERIES. water ; for sea- water does not contain chloride of sodium alone. We have unfortunately no positive information upon this point. The salted-water or sea-water battery, although inferior to many others (especially to the sal-ammoniac battery, of which we will speak later), may be recommended, above all, in places near the sea, where the expense is compara- tively small. ZINC-COPPER-SEA-WATER BATTEEY. At the beginning of the present century the illustrious Sir Humphry Davy proposed to protect the copper hull of vessels by means of a sheet of zinc (or, indeed, of cast- iron) put into communication with the lining and im- mersed with it in the sea. A cell was thus constructed in which the zinc (or iron), by being attacked, protected the copper. The zinc had, of course, to be replaced at the end of a certain time ; but an extent of active zinc surface one hundred and fifty times larger than that of the copper was sufficient to protect the latter. This ingenious idea had to be abandoned in the practice for the following reason : The zinc-copper cell of which we have spoken gives off, indeed, hydrogen upon the surface of the copper ; but at the same time it decomposes certain salts con- tained in sea- water, and the bases (earthy oxides magne- sia and lime) deposit themselves upon the copper. To this crust sea-grasses and shell-fish attach themselves and slacken to a great extent the speed of the vessel. In the absence of the zinc the copper is slightly at- tacked by the sea-water, but the surface remains apparent- BATTERIES WITHOUT ACIDS. C7 ly clean. In the long-run the copper is used up ; but of two evils one must choose the less, and prefer to lose a little more on the resale of old linings than to increase the duration of voyages. ZINC-IRON-SEA-WATER BATTERY. "Within the last twenty or thirty years copper-lined vessels have gradually been abandoned and a great num- ber of iron ships have been constructed. Davy's idea is in this instance applicable. We do not know if many ex- periments have been made or not ; but the result of one experiment upon a French frigate showed that sheets of metal one metre square lost the following weights after remaining in sea-water one month : Grammes. Grammes. Steel 28.10 Iron 27.30 Copper 3.80 Lead only traces. Zinc.... 5.60 Galvanized iron. ... 1.80 Tin.. 1.50 These figures go to prove that iron is of all metals the most attacked by sea-water, and is therefore badly chosen, as far as preservation is concerned, for the construction of ships, buoys, etc. From a theoretical point of view there would be a great advantage in coppering or tanning iron. If the iron were thoroughly covered with a thin layer of cop- per or tin it would no longer be in contact with the water, and would consequently not be attacked. But a small accident, such as the scraping of the ship on a sand-bar, for instance, might be enough to chip off a little piece of 68 SINGLE-LIQUID BATTERIES. copper or tin, when the exposed iron would immediately be attacked. Thus would be established an iron-copper or iron-tin cell which would excite the action of the sea-water upon the iron. It might indeed go so far as to make a hole in the iron. It will be seen that the cell thus form- ed would possess peculiar conditions of activity, as the negative electrode is enormous when compared with the soluble electrode ; and besides, the constant agitation of the w r ater would tend to suppress all polarization. In the experiments above referred to the surface of the sheets of metal were, of course, well cleaned before each experiment. There is no doubt as to the zinc being the electro- positive element of the zinc-sea-water-iron battery, and consequently that the iron is electro-chemically protected by the zinc. It is possible that the feeble electro-motive force of this cell may be insufficient for a thorough protection. There may also be some accessory action which might make the action of .the cell worse than simply ineffectual, as in the case of the copper linings. This is, we think, a desirable question to elucidate. ACCIDENTAL REVERSING OF THE CURRENT. We have already shown how a voltaic cell may be rendered ineffective by electrolysis of the salt of zinc and the deposit of zinc upon the conducting electrode. We have said that in certain cases the current could be reversed ; this phenomenon was observed under the fol- lowing circumstances : BATTEEIES WITHOUT ACIDS. 69 Certain zinc-salt-water-carbon batteries that had been working two years were, by accident, short-circnited ; polarization was brought to its maximum, since there was no resistance in the external circuit, and consequently the intensity was the greatest it could be. Soon after the battery could supply almost no current whatever; and by close examination it was found that in one out of every four or five cells the poles were reversed ; that is, the zinc had become the positive pole, and the carbon the negative pole. There was present a polarization similar to that which would have taken place in a voltameter, or in a secondary battery placed in the circuit. This second- ary current neutralized, in a great measure, that of the other cells of the battery. In this singular instance the polarization of certain elements had become stronger than the element itself. It is easily understood that, if there had only been one cell in the circuit, this reversing of the poles would never have taken place ; for the current resulting from polari- zation is necessarily inferior in tension or electro-motive force to the polarizing current. One more remark before leaving this experiment. If the battery cells joined in intensity were and would re- main identical, the above phenomenon would not take place. If twenty cells were joined in intensity and in short circuit (that is, without any exterior resistance), the in- tensity is exactly the same as if there were but one cell in short circuit ; for in the first instance the electro-motive force is twenty times greater and the resistance of the circuit twenty times less than in the second instance, which establishes an exact compensation. If there be only one cell in the circuit, it cannot but 70 SINGLE-LIQUID BATTERIES. weaken, and no reversing of the poles can take place. Therefore in a battery whose cells are identical there can be no reversing. For the occurrence of this phenomenon the cells must necessarily be dissimilar, which is nearly always the case. Some are polarized from the beginning much more rapidly than others ; from that time they are no longer identical cells, and the poles of the weaker ones, which are the most polarized, may be reversed. If some of these cells should accidentally be closed while the others are open, they become rapidly polarized ; the cause of this may be the formation of climbing saltr or other causes. This remark shows the advantage of the careful cleaning of batteries, in order that they may work regularly and for a long time. We will return to this subject when speaking of the sulphate-of -mercury battery. CHEMICAL ACTION IN SEA-SALT BATTEEIES. No one, as far as we know, has analyzed the products formed in this battery ; it must be a very complex com- position, a mixture of chloride of sodium and oxide of zinc, or of soda and zinc chloride. There can only be conjectures upon this subject, as no analysis has been made. The only known fact is that hydrogen frees itself from the carbon. These analyses are probably very difficult, and the com- binations formed in batteries are in general very compli- cated ; the slowness of the actions favors the production of bodies more complicated than those of which mineral chemistry generally treats. Batteries may some day challenge the particular atten- tion of chemists, who will find, without doubt, that they BATTERIES WITHOUT ACIDS. 71 are as good as retorts and other apparatus used in labora- tories for the formation of composed bodies, of which a considerable number have not yet been studied. We are sure that chemistry will lose nothing, and it is certain that the science of electricity will be greatly benefited by this study. The difficulty of the chemical problem presented by the sea-salt battery, and indeed by nearly all batteries, is increased by the fact that the nature of the compositions formed is different when the current is closed, and when it is open. It is certain that if there were a change in electric conditions, the action of affinities would also change. Our attention will again be called to this subject, when we will give certain reasons supporting the above sugges- tion. MARINE BATTERIES. An old experiment shows that if a plate of zinc and a plate of copper be immersed in the sea at a considerable distance from each other and attached to a single con- ducting wire, there will be produced in this wire a cur- rent of considerable intensity. Whichever way it may be looked at, the internal resistance of this battery is very feeble ; either by considering the sea as the jar contain- ing the liquid and the two electrodes ; or, adopting recent views, by admitting that the electricity is lost in the earth (the common reservoir) at those two points where the line touches it. This combination is not susceptible of practical application, as it only furnishes one cell and not a multiple battery ; but from a theoretical point of view it deserves notice. 72 SINGLE-LIQUID BATTERIES. SAL-AMMONIAC BATTERIES. By substituting a solution of chloride of ammonium or sal ammoniac for the liquids previously mentioned, a new series of batteries, analogous to those already enumer- ated, may be realized. We will call the reader's atten- tion to but two of them, wliich possess particular interest. BAGRATION BATTERY. The electrodes of this battery are the zinc and the copper; they are immersed in a jar filled with earth sprinkled with sal ammoniac. " It produces a wonder- fully constant current which is the result either of the reduction of the hydrogen upon the copper by the com- position formed there by the sal ammoniac, or of the absorption of the hydrogen by the earth itself, which indeed acts as a diaphragm. It is best not to put the two plates of the cell too near to each other, and to im- merse the plate of copper, before putting it in the earth, in a solution of sal ammoniac, leaving it to dry until a greenish layer is formed upon its surface." * In spite of these precautions, this battery has been put aside ; but it is possible that it may again be taken up. CARBON-ELECTRODE BATTERY. This battery differs from the preceding one in the substitution of carbon for copper. We have already explained the advantages of carbon. To give to these batteries their maximun force, and to * De La Rive, Traite d'filectricite. BATTERIES WITHOUT ACIDS. 73 render polarization as slow as possible, they are arranged as follows : The carbon electrode is placed in a porous porcelain jar, which is then filled up with small pieces of carbon ; a considerable extent of surface is thus given to the nega- tive electrode. This porous jar is then placed in a glass or stoneware jar which contains the solution of sal am- moniac. The zinc is immersed in the liquid ; it has the form of a hollow cylinder, and a thickness of ^ of an inch is sufficient, as there is but little waste. This battery presents an important advantage, only found thus far in the Bagration battery and in the sea- salt battery. All batteries, indeed, in which the positive or soluble electrode is zinc in sal ammoniac have the same advan- tages. As long as the circuit is open there is no chemical work going on ; the action of the sal ammoniac upon the zinc does not commence until the circuit is closed, and ceases immediately upon the reopening of the circuit. In order to make this important point perfectly clear, the following experiment must be made : Place an ordi- nary piece of zinc in a solution of sal ammoniac and leave it there for some time, several weeks for instance, when it will be seen that the zinc is not attacked in the slightest degree. If now a fragment of metal, iron, or copper, or even a piece of carbon, be added in the jar, it is soon seen that the zinc is attacked and a white salt is formed. It is thus seen that for the attack of sal ammoniac upon the zinc the formation of a cell is necessary ; if the zinc does not touch the metal added, no attack takes place. We will not insist upon the many consequences of this 74 SINGLE-LIQUID BATTERIES. simple experiment, but the plain result is, that, in bat- teries formed with zinc immersed in a solution of sal ammoniac, there is no chemical action except when the battery is doing useful work. From a practical point of view this advantage of sal- ammoniac batteries is capital, for in most applications batteries only work at intervals. In the principal tele- graph offices, where the greatest number of telegrams are sent and received, only intermittent currents are used, but in such quantities that an almost constant demand for electric current is imposed upon the battery ; but in branch offices there are generally long intervals between telegrams, and there is most frequently no service at all during the night. In the application of domestic bells, the battery should always be ready for vrork night and day ; the current is consequently used, on an average, but a few minutes in the twenty-four hours. In applications of this kind it is seen that the period during which the batteries remain in- active is a hundred times, nay, tw r o hundred times, longer than that during which they work, and that the economy should therefore be made during the time in which no current is required. "We will add that, such as it is, it could be very well used for electric bells, and could, if necessary, serve in a branch telegraph office. The battery in question has indeed but one fault: it becomes polarized when fur- nishing a current. However, for such an intermittent ser- vice this inconvenience disappears; for during its short period of work, polarization is barely perceptible, and it has sufficient time to disappear completely during the long intervals of rest. To M. Leclanche is due the dis- covery of the advantages presented by the sal-ammoniac BATTERIES WITHOUT ACIDS. 75 battery. He first established the fact that a battery could be produced in which the waste did not exceed, in proportion, the electricity supplied. Another advantage of this battery is that if, at a cer- tain time, it is seen to weaken and there be no sal ammo- niac at hand, it can be charged for the time being with common salt. But this means should only be resorted to in an emergency, as the current obtained with common salt is less intense than that furnished by sal ammoniac. ACTION OF AIE UPON THE PRECEDING BATTERY. From various experiments made with carbon-electrode and sal-ammoniac batteries the following conclusions may be drawn : 1. The surface of the carbon should be as large as pos- sible compared to that of the zinc ; and by increasing the mass of carbon according to a given quantity of zinc, polarization may be suppressed. 2. A part of the carbon, should be exposed to the air; for it has been proved that when the carbon is totally immersed the intensity is diminished, but recovers as soon as some of the liquid has been taken out.- This is what a French physicist calls letting the carbon breathe. The use of porous jars which overreach the top of the glass jar is very important. 3. Preference should be given to gas-retort carbon, on account of its porosity, and, as we said in speaking of the chemical action in Yolta's battery, it must be used in fragments large enough to permit the access of air. The powdered cake, formerly used, should be discarded. These conclusions will be readily admitted by the 76 SINGLE-LIQUID BATTEEIE9. reader, who can understand that the presence of oxygen in the pores of the carbon contributes to the depolariza- tion of the battery. It is possible that the particular fac- ulty of the carbon for absorbing gases in large quantities here plays some part, and that the properties of the gases thus condensed in the pores of the carbon may be dif- ferent from what they are under ordinary circumstances. CHEMICAL ACTION IN SAL-AMMONIAC BATTEKIES. A French chemist, in analyzing crystals formed in sal- ammoniac batteries, found this formula for them : 3ZnCl, 4NH 3 , 4110. The gases given off from the element were found to be: J volume of hydrogen. J " nitrogen and carbonic acid. -J- " heavy carburet ted hydrogen. These results only confirm that which we have said above of the complicated composition of bodies formed in batteries. OTHER BATTERIES. ZINC-IEON-WATER BATTEKY. We have already spoken, several times, of batteries in which the electrodes were zinc and iron ; and we have seen that the zinc was always the generating electrode, and the iron the conducting electrode. OTHER BATTERIES. 77 Every one knows that to protect iron from rust it is covered with zinc, and is then generally known under the name of galvanized iron. If the galvanized iron be exposed to rain or humidity, the uncovered parts of the iron constitute a cell with the zinc, and the iron is protected by the zinc. This electro- chemical protection increases considerably the impor- tance of the process of galvanizing iron. It must be said that the oxide of zinc produced by the exposure of the zinc to the air is insoluble in water, and forms a protecting layer which hinders further oxidation ; that is the principal reason for the use of zinc in out-door works alone or with iron. IKON-TIN BATTEKY. It is interesting to examine, from the same stand-point, tinned iron. Tin is liable to but very little, alteration in water or when exposed to damp air. For many years it has been *the practice to tin iron, by which its dura- bility is greatly increased. It is important to note that if the iron be exposed at any point it is promptly attacked, because in the voltaic cell formed with water, or simply damp air, the iron is the generating electrode. Under these circumstances the rust is seen to advance step by step, and to lift up and undermine the protecting layer of tin. This metal pro- tects only the part it covers, but it renders the iron more liable to rapid rust than if it were not there. 78 SINGLE-LIQUID BATTEEIES. ALUM BATTEEY. Alum or potassio-aluminic sulphate (KA1 3 4SO 4 ) is employed in several branches of industry. A German physicist arranged a battery whose elec- trodes were ordinary zinc and carbon, and whose liquid was a solution of alum ; this battery undergoes polariza- tion, of course, but it is said to depolarize after the circuit has been open but a very short time. The chemical action must be very complicated in this battery. When the already complex nature of the alum is taken into consideration, the addition of the zinc can- not but lead one to believe that the composition thus pro- duced is extremely complicated. At Mulhouse they use for electric-clock purposes a battery whose liquid is a mixture of sea-salt (500 grammes) and pulverized alum (200 grammes) dissolved in water. This application deserves notice, as constant batteries are generally thought to be necessary for the service of elec- tric clocks. The cells of the above battery are very large : the hol- low carbon cylinder has an exterior diameter of 4J inches and an interior diameter of 3J inches ; the plate of zinc is 2f inches wide, and these two electrodes are immersed about 10 inches in the liquid. There are twenty clocks distributed in two distinct circuits ; there are two clos- ings of the circuit a minute, each lasting one second. There are sixteen cells, of which two are charged every week in order to always keep the battery the same ; each cell works, therefore, four months without any attention whatever. Another step in advance has been made in the ar- OTHER BATTERIES. 79 rangement of a battery which is only renewed once in every two years ; it is, however, only used in the fire- telegraph service, which demands but little work. These practical examples show once more that if the use of single-liquid batteries is well understood, they can be employed in many instances. KEMAEKS UPON SINGLE-LIQUID BAT- TEEIES. It might be generally said that by taking any two pieces of different metals, or a piece of metal and a piece of carbon, and immersing them in some liquid conductor of electricity, a battery could be made. The more lively the action of the liquid upon the posi- tive electrode (negative pole), the greater intensity the battery will possess ; there will be no action upon the other electrodes, at least not during the passage of the current ; that is, not while the exterior circuit is closed. The choice of this second electrode is, however, far from being a thing of indifference ; the less the electrode is capable of being attacked by the liquid, the greater will be the intensity of the battery. That is the reason why platinum and carbon should be preferred, at least with sulphuric acid, nitric acid, and the other liquids of which we have spoken. The electric action is the result, in reality, of the dif- ference of two chemical actions, one of which takes place while the other is prevented ; one of the electrodes is attacked, the other is preserved from the attack of the liquid (at least while the circuit is closed). The more energetic the action upon the positive elec- trode and the less this action upon the negative electrode, 80 SINGLE-LIQUID BATTERIES. the more developed will be the electric phenomenon. For instance, a zinc-acidulated water-iron battery has but little power ; the action of the liquid upon both electrodes is very lively as long as the circuit is open ; as soon as it is closed the action upon the iron is stopped ; but it reacts upon the attack of the zinc and diminishes it. If plati- num be substituted for iron, the zinc alone is acted upon and the platinum remains unattacked before the circuit is closed; when the circuit is closed and the current flows, the action upon the zinc is hardly diminished. Many persons have proposed compound liquids : mix- tures of sulphuric acid and sea-salt, mixtures of salted water and flower of sulphur, etc. Satisfactory results may possibly be obtained in this manner ; but this study has lost a great deal of interest on account of the invention of constant batteries, of which we will now speak. PAET II. TWO-LIQUID BATTERIES. rNTRODUCTIOK liave already said that in order to successfully oppose polarization of electrodes, chemical substances capable of absorbing the hydrogen as it is given off upon the negative electrode must be employed. A second liquid is most frequently used for this purpose ; nitric acid is eminently suitable for this office. Experiment. Let us take a zinc-sulphuric-acid-plati- num battery ; cause the current it furnishes to pass in a galvanometer. The deflection of the galvanometric needle is seen to decrease, and thus mark the progress of polarization. Let us now throw a few drops of nitric acid around the platinum, and the intensity of the current will be seen to increase immediately, thus making mani- fest a decrease in the polarization. It is easily understood that the nitric acid is decomposed by its contact with the hydrogen ; water and bioxide of nitrogen are formed, the freeing of which produces, at the contact with the air, nitric-tetroxide vapors, very sensible to the smell. In order to use nitric acid most advantageously, it should not be spread throughout the whole mass of the 82 TWO-LIQUID BATTERIES. liquid, but should be concentrated around the electrode to be polarized. To fulfil this condition porous jars have been adopted to separate the two liquids, one of which is designed to dissolve the zinc and the other to dissolve the hydrogen given off, or on the point of being given off, upon the negative electrode. The denomination " two-liquid battery" is badly chosen, because in many instances, which we will cite, solids are used as depolarizing agents instead of liquids ; it would have been more exact to say two-electrolyte battery, but as this appellation is not in use, we do not think best to adopi^ it. In most cases chemical depolarization is obtained by means of substances capable of furnishing oxygen, which, combining with the -oxygen, prevent the latter from free- ing itself and polarizing the negative electrode. In the experiment that we have described above, the nitric acid, being decomposed, produces oxygen, and hence the result. IS'itric acid NO 5 , being very rich ir. oxygen and easily decomposed, was naturally fixed upon ; it is one of the best batteries known. Other acids besides nitric acid could be used : chloric acid C1O 5 , chromic acid CrO 3 , permanganate acid Mn 2 O 7 are indicated ; but they are not generally used in this way. Salts (chlorate of potash, bichromate of potash, etc.) are generally substituted, which give off oxygen under the influence of the sulphuric acid. It may be said, in a general way, that all means of pro- ducing oxygen can be satisfactorily employed for the de- polarization of the negative electrode of a cell. Oxides from which oxygen is readily freed might be employed instead of acids ; oxygenized water would be INTRODUCTION. 83 excellent if the difficulty in preparing and preserving it did not render it practically impossible ; but the bioxide of manganese and the bioxide of lead may be used, as will be seen farther on. We have said how that acids rich in oxygen were not used alone ; they are generally in the shape of some salt from which they are freed by sulphuric acid, or, if need be, by some other. In the same manner, the combination of peroxides and sulphuric acid may be employed to give off oxygen. All the processes which we have just described con- sist in the use of oxidizing bodies or oxidizing mixtures ; there is one more kind to be indicated ; namely, the use of chlorine, which is also an oxidant in the presence of water, because it tends to combine with the hydrogen and to free the oxygen. All the means for producing chlorine may be used for depolarization. We have yet to speak of a chemical means of depo- larization very different from any that we have hitherto mentioned, and which according to many is the best. It consists in the use of salts, such as sulphate of copper, which decompose under the influence of the current, depositing their metal and checking the freeing of hydrogen. The result is that a metal is deposited upon the negative electrode instead of gaseous hydrogen ; if, at the start, the electrode was of copper, its surface would remain unchanged, and consequently there is no polariza- tion. We will examine in detail all these means of depolari- zation and indicate the most important applications that have been made, always following the same method that we employed in the study of single-liquid batteries. 84 TWO-LIQUID BATTERIES. The first idea upon the processes which we have just mentioned dates from the year 1829, and is found in a memoir of Becquerel. "It should be observed," says Becquerel, "that the battery carries in itself the cause of the continual diminu- tions in the intensity of the electric current ; for as soon as it begins to work, there take place decompositions and transportations which polarize the plates in such a man- ner as to produce currents contrary to the first one. The art consists, therefore, in dissolving these deposits, as they form, by means of properly placed liquids. . . . This is attained by means of the process that I have de- scribed. . . . By thus diminishing the intensity of the secondary current, sensibly constant effects may be obtained." It is this view, so plainly expressed fifty years ago, that has suggested the present work and which justifies the classification that we have adopted. The first indication of a battery depolarized by means of a salt of the metal which constitutes the conducting electrode is found in the following words taken from BecquereFs memoir : " Let us continue to use saturated solutions of metallic salts, which cause no decomposition of the .immersed metal. Let us then put with the copper a saturated solution of nitrate of copper, and with the zinc a satu- rated solution of sulphate of zinc. The deflection of the galvanometric needle will reach 88 and then undergo but a slow diminution. An addition of nitric acid to the solution of nitrate does not modify the intensity of the current. The result is the same when sulphuric acid is added in the solution of sulphate, the zinc having been well cleaned. Here is then a maximum effect." INTRODUCTION. 85 Finally, Becqnerel speaks of depolarization obtained by means of nitric acid ; he experiments upon a cell con- taining zinc, copper, and a porous partition, the common liquid, being a saturated solution of sulphate of zinc. He says : " According to the general rule the zinc ought to be more attacked than the copper, and such is the result ; the deflection is then 62, and if a few drops of nitric acid be added in the compartment containing the copper plate, where the chemical action is most feeble, the gal- vanometric needle will mark 86 and will remain station- ary for some time. . . . The same quantity of acid put with the zinc will sensibly diminish the intensity of the current." A little farther on he says : u I once suc- ceeded in obtaining a compensation, so that the needle's deflections remained constant during one hour, an advan- tage never found in ordinary batteries." The only thing that escaped Becquerel's notice is the part that the hydrogen plays in polarization ; he did not observe the nature of the chemical reactions whteh take place in those batteries now termed Danieli's battery and Grove's battery. He studied batteries from a purely physical stand-point and neglected the chemical problem. CHAPTER I. DANIELL'S BATTERY. IN a first series we will put all the batteries in which depolarization is effected by the use of salts. In order to facilitate our exposition, we ought to divide this series into several categories, that of sulphates, that of chlo- rides, etc. In fact, the two that we have just men- tioned are the only ones which possess any importance up to the present date. DESCKIPTIOK As we are not paying any attention to the chronologi- cal order of discoveries, we will not describe the battery FIG. 21 of Daniell under the form given to it by its inventor in 1836 ; the form which we give is that in present use. Fig. 21 represents three cells joined in intensity. In DANIELL'S BATTERY. 87 each are seen the outside glass jar, a thin hollow cylinder of zinc, z, a porcelain porous jar, and a strip of copper, c. The two liquids a saturated solution of sulphate of copper in the porous jar and dilute sulphuric acid in the outside jar are separated, but communicate with each other through the pores of the porcelain jar. The cop- per electrode is immersed in the sulphate, and the zinc in the acidulated water. The only difference between this battery and that of Yolta is the addition of sulphate of copper around the copper electrode. The zinc dissolves, oxidizing and form- ing sulphate of zinc. The hydrogen produced by this reaction, instead of being given off upon the negative electrode, takes the place in the sulphate of copper of an equivalent quantity of copper, which is deposited upon the electrode. This deposit not changing chemically the surface of the electrode, it is plain that there is nothing like polarization produced. In other words, the addition of sulphate of copper is sufficient to completely depolar- ize the negative or conducting electrode. Such is the simple combination due. to Darnell, the most perfect as yet invented. If the action of the battery continues for some time, all the sulphuric acid in the outside jar will be converted into sulphate of zinc ; the action, however, is not in the least checked by this, and the electro-motive force re- mains almost the same. The chemical action that then takes place consists in the substitution of zinc for the copper in the sulphate of copper, and the progressive transformation of sulphate of copper into sulphate of zinc. In general practice the battery is not charged with di- lute sulphuric acid ; neither is any sulphate of zinc put 88 TWO-LIQUID BATTEKIES. in the outside jar, but simply pure water. At first the action is more- feeble, and the internal resistance of the cell much greater; but the sulphate of copper, which traverses the porous partition, is transformed into sulphate of zinc by the action of the zinc, and the pure water is soon found to contain a certain proportion of salt, by which its conductivity is increased. This first period lasts a longer or shorter time, according to the circum- stances ; but a very effectual way of shortening it consists in closing the circuit with a very short conductor, which has no resistance ; the chemical action is thus made more lively, and at the end of an hour or two the battery may be said to have reached its normal state of work. Electro-motive Force. As this battery is not polarized, its electro-motive force ought to be invariable ; in fact, the two expressions are synonymous. The experiment shows that the electro-motive force of DanielPs battery is indeed very constant. In the prac- tice it may be taken as a unit, and others can be compared with it. The British Association has adopted a unit differing very little from this one, and has given to it the name of Yolt. The cell, in which the electro-motive force is ex- actly equal to the volt, differs but slightly from that of Daniell. It is a cell in which the copper is immersed in a solution of nitrate of copper, and the zinc amalgamated in sulphuric acid diluted with twelve times its weight of water. The electro-motive force of Daniell's cell is, we said, very constant, and it varies but slightly with the tempera- ture. It has been found that if it is 1000 at 18 centigrade, it will only reach 1015 at 100 centigrade. It changes DANIELL'S BATTERY. 89 very little with the acidity of the liquid. If it is 1079 with acid diluted with four times its weight of water, it only diminishes to 0.978 with acid diluted with twelve times its weight of water. The richness of a solution of sulphate of copper has but little influence upon it. M. Regnauld has given the following figures concern- ing a cell without sulphuric acid and charged with solu- tions of sulphate of zinc and sulphate of copper : Solution saturated with sulphate of copper 175 The same, diluted with twice its bulk of water 175 The same, diluted with ten times its bulk of water. 174 The same, diluted with fifty times its bulk of water 172 These numbers are not expressed in volts, but a unit was taken which is equal to the electro-motive force of a bismuth-copper thermo-electric cell whose solderings are and 100. The electro-motive force of a Daniell cell with sulphu- ric acid and a saturated solution of sulphate of copper is equal to 179 of the above units. It is therefore seen that the substitution of sulphate of zinc for dilute sul- phuric acid does not notably change the electro-motive force. We have said that it did not vary w T ith the richness of the solution of sulphate of zinc ; it has been shown that there is no perceptible change when the solution is at first concentrated and then diluted with one hundred times its bulk of water. The thickness or nature of the porous jar has no influence; porous partitions of many kinds have been tried, such as gold-beaters' skin, pipe-clay, under-baked porcelain, tubes of rosewood and of the pear-tree, of ebony and of boxwood. Resistance. It must, however, be acknowledged that 90 TWO-LIQUID BATTERIES. the condition and force of a battery are always variable ; for if at the start the solution is too weak, it becomes more and more concentrated, and its conductivity is con- stantly changing. The following figures show that it reaches a maximum and then decreases : Solution concentrated with sulphate of zinc (specific gravity 1.441) 5.77 The same, diluted with its bulk of water 7. 13 The same, diluted with three times its bulk of water 5.43* The conductivity of liquids varies also with the tem- perature ; that of a solution of sulphate of zinc reaches its maximum at 14 cent. If the nature of the liquid in the outside jar changes, that in the porous jar will also change. In fact, the solu- tion of sulphate of copper gradually weakens, and its con- ductivity changes with its state of concentration and the temperature. A few crystals of sulphate of copper may be added in the porous jar to keep up the solution. The more con- centrated the solution becomes the heavier it gets, and in order to keep it in a state of saturation up to the top of the jar, they used to suspend crystals to the upper part by means of a small diaphragm of copper soldered to the strip of copper ; but this precaution has been generally abandoned, and the crystals are now simply thrown in the bottom of the jar. This suppression causes no incon- veniences, because the battery loses none of its qualities w r hen the liquid ceases to be saturated ; it is indeed an advantage, for the consumption of sulphate is less active. A saturated solution of sulphate of copper has, how- * See table 3, end of volume. DANIELL'S BATTERY. 91 ever, a greater conductivity than when it is diluted with water, as the following table shows : Sulphate of copper. Saturated solution (specific gravity 1.171) 5.43 The same, diluted to half 3.47 The same, diluted to quarter 2.08 It should therefore be admitted that the use of a diluted solution increases the resistance of the battery ; but it is probable that the sulphate of zinc in mixing with the sulphate of copper increases the conductivity of the liquid. Endosmose causes the liquid in the porous jar to rise slightly above that in the outside jar ; finally, evapora- tion causes the two liquids to gradually descend and in- creases the richness of the solution. All these reasons, and others which we will soon give, go to prove that the resistance of Daniell's battery is constantly changing ; every time it is measured it is found to be different. The intensity of the current of Daniell's battery, as has been shown, varies considerably from one day or from one hour to another, and as the electro-motive force does not change, it is clear that it must be the resistance which varies. Figures relating to the resistance of battery cells would possess but little interest, as they can only be approxi- mate, and applicable only to jars and electrodes of deter- mined dimensions, and to certain heights of the liquids in the jars. SELECTION OF CELLS. In general, larger cells are used for local circuits, and smaller ones for telegraph lines, because the former are 92 TWO-LIQUID BATTERIES. less resistant than the latter ; this difference results from the fact that the immersed surface of the electrodes is greater in the large ones, whereas their distance is almost the same. Jf things were looked at from a physical point of view only, the use of large cells would always be advanta- geous ; but in the practice there are other things to be taken into consideration. The convenience, and above all the economy in buying and keeping them in order, must be thought of. Large cells are more cumbersome and more exposed to accidents ; besides, they are especi- ally dear, and the necessary supply of sulphate of copper and zinc plates tends to increase the expense. Conseqiiently the use of cells as small as possible is recommended. It is necessary to understand perfectly how in long circuits resisting batteries present but few inconveniences, and how the larger cells are preferable in short circuits. If in a very long circuit, of 3000 units of resistance, for instance, with a receiving instrument of 1000 units, a battery of 25 cells of 10 units each be employed, the total resistance of the battery will be 250 units, and that of the whole circuit 4250. The resistance of the battery is thus but a small fraction of that of the whole circuit ; consequently the substitution of smaller cells, even if their resistance were twice as great as that of the first ones, would not greatly increase the resistance of the circuit, nor, consequently, the intensity of the current. But if, on the other hand, we take a short circuit of 2 units with a receiving instrument of 3 units, and use a battery of 5 cells, each having 10 units of resistance, there will be in the battery 50 units and in the circuit 55 units of resistance. DANIELL'S BATTERY. 93 It is seen that the resistance of a battery is the most important element, and by diminishing it one half by the substitution of larger cells the resistance of the circuit will be reduced to 30 units, and consequently the inten- sity of the current will almost be doubled. Let us follow up this idea. The intensity of the current being much greater with the 5 new cells of 5 units of resistance each, their number might be reduced to 3, for instance ; the resist- ance of the battery would then be 15, that of the circuit 20, and finally the intensity of the current (^ or ) would be still greater than that we had at the beginning. Thus for a short circuit larger cells should be used, only less in number, by which a saving is obtained. POROUS JARS. The porous partitions which separate the liquids in constant batteries are generally made of porous porcelain ; but one can use wood, carbon, blad- ders, canvas, pipe-clay, paper pulp, and in general all substances not chemically acted upon by the liquids. In his first experiments Daniell used a piece of bladder inside of and having the shape of a copper tube pierced with holes, which served as the negative electrode of his cell ; this membrane partition presented great advantages, its cylindrical form was excellent, and it was very gener- ally adopted; it was very porous and electrically but little resistant. It was abandoned because it was too porous and too fragile. Finally porous jars, properly so called, were brought into use ; they are made of porous -porcelain. We will here only speak of this latter ; those made of parchment paper, canvas, etc., will be treated of in the description of those batteries in which they are used. We have explained how, in the regular and theoretical action of Daniell's cell, copper is deposited upon the cop- 94 TWO-LIQUID BATTERIES. per electrode. In the practice it is found that copper is also deposited upon the inside surface of the porous jar, and even in the pores, which are finally stopped up ; after a certain time the jar ceases to be porous enough and should be replaced. That is one of the inconveniences of this form of Daniell's cell, which, however, should not be exaggerated, as the porous jars are very cheap and may bo replaced at very little expense. In the telegraph service, a porous jar may sometimes serve six months or a year. Purchasers of old metals buy these porous jars, often very heavily charged with copper, and know how to use them to the greatest advan- tage. These deposits of copper in the interior of the po- rous jar frequently present a very interesting peculiarity : they show themselves upon the surfaces with a tree-like aspect ; it is a slow crystallization, which reminds one of the unfolding of a fern. It frequently happens that the deposit of copper accu- mulates upon certain points of the inside surface, and presents a crystalline structure, properly so called. Crys- tals are sometimes seen to attain the dimensions of -% or ^ of an inch. These deposits in the pores and upon the surface of the porous jar may easily be accounted for. They are the result of an electro-chemical action analogous to that shown in a previous experiment by De La Rive upon ordinary commercial zinc compared with chemically pure zinc. The porcelain contains various heterogeneous particles, which produce local actions and also the decomposition of the sulphate of copper. It is probable that this deposit takes place very slowly at first, but as the deposit accu- mulates the process becomes more and more rapid. DANIELL'S BATTEEY. 95 These deposits of copper in and upon the walls of the porous partition possess another quality which we should not forget ; namely, that of diminishing the internal re- sistance of the cell. This is a fact that oft-repeated ex- periments have proved. The explanation seems to us very clear. The porous partition presents a very great electric resistance, because the total section of the canals filled with liquid is extremely small. When a portion of this section is replaced by copper, a metal possessing great conductivity, the resistance should be reduced in proportion. It should be noted that, under these circumstances, the copper causes no polarization of the electrodes, otherwise the results would be entirely different. All this would lead to the belief that the choice of porous jars had great influence upon the intensity of the current, by changing the internal resistance of the cell. The results of several experiments show, however, that jars of different states of porosity can change but slightly the resistance of cells. The conclusion points to the preference of jars of little porosity in all batteries destined for continual and pro- longed work. They should be immersed in water before charging the battery ; or better, charge the battery sev- eral hours before using it, in order to allow the liquids to penetrate the pores and come into contact with each other. Yery porous jars have the disadvantage of allowing the liquids to mix too easily ; the result is a direct action of the zinc upon the sulphate of copper, and a deposit of the copper upon the zinc, which is a grave fault inherent in Daniell's battery, and upon which we will now enlarge. LOCAL ACTIONS ; WASTE. The sulphate of copper, 96 TWO-LIQUID BATTEKIES. which penetrates the porous partition, comes into contact with the zinc, and is decomposed by an electro-chemical local action. Copper is deposited upon the zinc in the shape of black mud, which cannot be put to any use. (This black powder is said by some to be oxide of copper, but this is an error, as can be easily shown by means of some feeble acid, as acetic acid.) This action does not co-operate in the production of the current ; it takes place especially, as can be easily un- derstood, with very porous jars ; but it exists in every ar- rangement of DanielPs cell, as will be seen as we advanc . . This inconvenience would be less if the current circu- lated continually ; but in almost all applications, batter- ies, and especially those of Daniell, are only used inter- mittently and at long intervals. Many of the telegraph batteries and those used for electric bells work but a few minutes daily, thus being nearly always in an open cir- cuit. Under these circumstances, the fault of which we speak is at its maximum. It is understood that if, on the contrary, the cells are very actively employed, as in an important telegraph office, this same fault is less grave ; the sulphate of cop- per and the zinc are consumed much more usefully. But even- in that exceptional case, where a Daniell cell fur- nishes a constant current, there is a certain quantity of sulphate of copper which, penetrating the porous jar, is decomposed by its contact with the zinc, and deposits upon the latter, copper in the shape of black mud. In short, we can say that an ordinary Daniell cell con- sumes almost as much zinc and sulphate of copper when its circuit is open, and when it does no useful work, as when its circuit is closed, and when it really acts as a pro- ducer of electricity. 97 This is about the only fault that can be found in the Daniell battery. Its gravity, however, has often led to the preference, in many instances, of other batteries, such as that of Leclanche, which, however, do not fully fill the conditions of a constant battery. This fault is present in the Daniell battery to a greater or less degree, according to the porosity of the jars. Among the improvements upon DanielFs battery, which we will soon describe, there are some which possess the advantage of greatly reducing the detrimental effect in question. The copper, by entering the pores, diminishes the po- rosity, thereby improving the battery, for a certain length of time at least. But it is plain that, if the porosity be too much reduced, the battery will no longer work, for if the pores of the partition are completely stopped up, it would no longer furnish any current. Finally, the pure loss in the consumption of sulphate of copper is less when the solution of sulphate is less con- centrated ; and, as the reduction of concentration does not diminish the electro-motive force, and does not nota- bly increase the resistance, there is a great advantage, as can be seen, in not using a saturated solution of sulphate of copper. It should be noticed that the deposit of copper upon the zinc does not change the electro-motive force of the cell, which confirms what we said of the constancy of this force in DanielFs cell. In some models, the zinc is sus- pended, so that it may not rest on the bottom of the jar and come in contact with any rubbish that might happen to accumulate there, which would result in local actions. It is an established fact that, in ordinary batteries, the lower part of the zinc is more consumed than that near 98 TWO-LIQUID BATTERIES. the top. The cause of this is due partly to the contact of this rubbish with the zinc, producing local actions. CLIMBING SALTS. The Daniell battery possesses one more little fault that should not be left unnoticed. When the liquid in the outside jar begins to become sat- urated with sulphate of zinc, climbing salts are formed, which ascend the walls of the outside jar, and even of the porous jar, running over the rim of the former and de- scending on the outside. All this can, however, be avoid- ed by proper care and attention. These salts establish permanent communication between the different elements of the cell, which communication contributes to the waste. The manner in which these salts are formed is very easy to understand. In the beginning, either by a slight movement or other- wise, some of the liquid is thrown upon the sides of the jar. Evaporation causes the disappearance of the water and leaves crystals. Immediately, capillary action sets in, either between the crystals and the side of the jar, or along the side of the crystals, and a small quantity of liquid thus rises above the general level. Evaporation again causes the formation of new crystals, which is facilitated by the thinness of the layer. This action continues step by step horizontally and vertically. As long as the formation of climbing salts does not run over the top of the glass jar, or establish any permanent communication between the elements, it is not unfavora- ble. It might indeed be considered as an advantage, as it reduces the concentration of the sulphate of zinc solution. "We have previously shown by figures that a saturated solution has less conductivity than when diluted to half. When the solution is saturated, it is incapable of dissolv- ing the salt formed by the action of the battery, and the 99 most unfavorable thing that can then happen is a deposit of crystallized sulphate of zinc upon the zinc or upon the immersed part of "the porous jar, for it stops the chemical action or the communication of the liquids. It is there- fore advisable to take the climbing salts completely away and not to put them back in the glass jar. To suppress the production of climbing salts, it has been proposed to spread a thin layer of oil upon the sur- face of the liquids, which would check all evaporation ; this has, however, received no application, on account of the uncleanliness it would inevitably cause. This layer of oil would also occasion rapid concentration, which, as we have stated, diminishes the conductivity. The climb- ing salts may be kept from running over the top of the glass jar by smearing the top with some greasy substance (paraffin, for instance). Climbing salts of sulphate of zinc are very easily de- tached from the glass, either with the fingers or with a rag ; but they hold much more firmly to the porous jar, and it is with difficulty that they may be detached from it by rubbing. Therefore, the top part of the porous jar which stands out of the liquid should be carefully glazed ; the salts may then be taken off as easily as from the glass. IMPROVED DANIELL CELL. We have sought to construct as satisfactory a Daniell element as possible. The following is the disposition that we have decided upon : The positive electrode is formed of a cylinder of zinc surrounding the porous jar, and is held at a small distance from the latter by means of small sticks of wood placed vertically between the two ; the zinc and the small sticks 100 TWO-LIQUID BATTERIES. are held in their place by being tightly bound together at the top and bottom with pieces of string. The connecting strap of the zinc is cut out of the same sheet of metal as the cylinder itself, which dispenses with any loss in the cutting, provided two cylinders with their connecting straps be cut out of the same piece, one in the reverse manner from the other. The copper electrode is cut in the same manner out of a sheet in the form of a cylinder, which is placed inside the porous jar ; small sticks of wood placed around the copper and bound to it with string keep it from coming into contact with the interior surface of the porous jar. ' At two thirds of the height of the copper is fixed, with- out solderings and simply fastened in the copper, a circular piece of copper pierced with holes, thus forming a parti- tion without impeding the movement of the liquid. Upon this partition are placed sulphate of copper crystals, which hold the solution at saturation. In the outer jar is put a solution of sulphate of zinc possessing its maximum conductibility ; that is, a solution at first saturated and then diluted with its bulk of water (specific weight about 1.10). This disposition is intended to reduce to a minimum the internal resistance of the ele- ment, and to render it as compact and solid as possible. For experiments of precision it is best to ascertain, at first starting, the density of the sulphate of zinc by means of an hydrometer, and to always keep it the same by add- ing, from time to time, some pure water, as the solution becomes concentrated either by evaporation or by the formation of sulphate of zinc in the battery. Undoubtedly the use of a saturated solution of sul- phate of copper greatly increases the expense of the bat- tery, but we are now supposed to be talking of an appara- DANIELL'S BATTERY. 101 tus designed for experiments of precision and in which the question of expense is secondary. , . \y From this point of view the precautions that we Jiave suggested appear to us to be indispensable How jri^ea' could the internal resistance of a cell be advantageously measured unless the respective distances between the elec- trodes were invariable and the composition of the liquids known and determined ? It is only with elements arranged in the above manner that it may be hoped to obtain concordant or even com- parable results. In truth, it is very probable that these precautions will not be sufficient, but they are necessary. BALLOON BATTEEY. Another arrangement of DanielFs battery, represented by Fig. 22, has been and is still used in some countries. It needs no attention for six months, or more, at a time. The flask, which surmounts the cell, contains two pounds of sulphate of copper crystals, and is filled with water. The flask is closed with a perforated cork fitted with a glass tube ; this tube descends as far as the liquid in the porous jar. The solution of sulphate of copper being more dense in proportion as it is more concentrated, it can be seen that the part of this solution which is in the po- rous jar is constantly held at saturation, for as it weakens it is supplied by the saturated solution which descends from the flask. The glass jar of the cell is closed with a wooden lid, which supports the flask. The result is that evaporation is reduced to almost nothing, and, consequently, there is a very slight or no formation at all of climbing salts, and the liquid is preserved. 102 TWO-LIQUID BATTERIES. This battery lias been known to work for more than a ye'ar without' ?eqmring any attention, during which time it .satisf aeterily met' all practical requirements. It has, however, been replaced by more economical batteries, such as Callaud's or Leclanche's. A EEYERSED FOBM OF DANTELL'S BATTEEY. For a long time Daniell's battery was arranged in a manner the reverse of that which we have already de- scribed. The zinc, in the shape of a solid cylinder, which served as soluble electrode, was placed inside of the porous jar, instead of outside. The copper was placed around the outside of the porous jar, serving at the same time as conducting electrode and as the jar containing DANIELL'S BATTERY. 103 the liquid. In addition to the exterior hollow copper cylinder, another was placed nearer the porous jar, in or- der to diminish the resistance of the cell. This interior cylinder of copper was pierced with holes, to facilitate the circulation of the liquid (solution of copper sulphate). Finally, crystals of copper sulphate were put between the two copper cylinders, in order to keep the solution in a state of saturation, in spite of the consumption of the battery. At first sight, this arrangement would appear to be much superior to that previously described. In this one the glass jar is suppressed, and -consequently the many accidents resulting from its brittleness are avoided. It has, however, been abandoned for the first arrangement on account of the following reasons : 1st. The battery with the copper jar costs a great deal more, because of the large quantity of copper required, and also on account of the quantity of copper sulphate with which the battery is charged at the beginning. 2d. The copper jar might become pierced, and the liquid would then leak out ; a few impurities in the metal would suffice to set up local electro-chemical actions, and thus bring about perforation. 3d. Cast zinc is used, which presents another disadvan- tage. For, during the process of casting, very often little cavities are formed in the zinc, into which the liquid pene- trates, thereby producing local actions and uselessly con- suming the zinc. 4th. The zinc nearly fills the porous jar, thus leaving but little room for the liquid, which is soon saturated with the sulphate of zinc and becomes incapable of dis- solving any more. This is a grave fault in the working of the battery. 104 TWO-LIQUID BATTERIES. "We must do Daniell the justice to say that he had foreseen this difficulty, and had proposed an accessory arrangement for the renewal of the water destined to dissolve the sulphate of zinc ; but this addition compli- cated the apparatus and increased the cost. The cell might be sensibly improved by the substitu- tion of a thin, hollow cylinder of zinc for the massive zinc used above ; the quantity of water in which" the zinc is immersed would thus be greatly increased. It is well to note, before leaving this subject, that the surface of the negative electrode is comparatively much larger than that of the soluble electrode. We said, in speaking of Wollaston's battery, that this condition was very favorable in single-liquid batteries, but it is not so in two-liquid batteries, or at least not in Daniell's battery. Since the depolarization of the negative electrode is com- plete, there is no advantage in increasing its surface. The considerations which prevail in the choice of elec- trodes have been clearly indicated in that which we have just said. TKOUGH BATTEKY. Still another arrangement of Daniell's battery is rep- resented by Fig. 23, and the above name given to it. A trough is made of teak and divided into ten cells by slate partitions ; each cell is then subdivided by a porous partition of unglazed porcelain. A zinc plate is placed in one of these divisions, and a thin copper plate in the next one, and so on, until the ten cells are occupied. The copper plate of one cell is permanently connected with the zinc of the next cell by a copper strap cast into the zinc and riveted to the copper, which is easily bent over the slate partition. DANIELL'S BATTERY. 105 The last copper and the last zinc plate are each con- nected to brass binding screws or terminals, which be- come respectively the positive and negative poles of the battery. A solution of sulphate of copper and a few crystals are placed in the copper divisions ; in the others, pure water or a very weak solution of sulphate of zinc. This arrangement presents great advantages; it dis- penses with glass jars, which sometimes break without any apparent cause. The trough is made water-tight by coating it internally with marine glue, and the liquids ought not to leak out. But it unfortunately happens, sometimes, that the marine glue chips off, and one cell FIG. 23. becomes leaky. When this occurs, the battery must be repaired. The trough is very solid, and is easily transported when not charged with liquid. The zinc and copper electrodes of each cell are at a well-regulated distance from each other, and do not touch the porous partition if the bat- tery is carefully charged. 106 TWO-LIQUID BATTEEIES. These last conditions are fulfilled with difficulty where cylindrical elements are used. The trough having a wooden lid, there is very little evaporation. Of all known forms, this is the least cumbersome. The dimensions of the electrodes are generally, for the zinc, 3 in. by 2 in., and for the copper, 3 in. square. The battery will work a month without the necessity of opening the trough. One of these batteries of ten cells costs $5.25, and the keeping it in order $2 per annum. CONVENTIONAL FIGURE. Batteries are generally represented by a conventional figure, which originally represented Daniell's trough bat- HttH- FIG. 24 tery, or the sand battery, of which we epoke in Part L Each cell is represented by two lines (Fig. 24), the short and thick one representing the zinc, and the long and narrow one the copper. Z and C mark respectively th? negative and positive poles of the battery. DANIELL'S BATTEEY. 107 MUIRHEAD'S BATTERY. There are a great many such in use in England The outside jar is made of white porcelain and is square. The porous jar, made of red earthenware, coir tains the negative electrode and the sulphate of copper, 108 TWO-LIQUID BATTEKIES. and is placed in the square porcelain jar, which contains the zinc electrode and the sulphate of zinc. The elec- trodes are the same as in the preceding battery. For economical reasons these cells are taken by twos ; that is, each outside porcelain jar contains two compart- ments and two complete cells. This arrangement pre- sents a very favorable condition, which is also met with ill the cylindrical cells described at the beginning ; viz., the compartment containing the sulphate of zinc is quite large. Fig. 25 represents several of these cells together. CAEEfi'S BATTEEY. Carre's battery differs from the ordinary Daniell bat- tery simply in the substitution of a vessel made of parchment paper for the ordinary porous jar. This porous partition offered very little resistance, which re- alized the object of its inventor. The whole battery indeed was arranged with a view to diminishing the re- sistance. The zinc cylinders were 22 in. high and 4-J in. in diameter. Sixty of these cells were used by M. Carre for electric- light purposes, which is, w r e think, worthy of mention, as it was the first time that DanielPs battery had been tried in that way. In fact, M. Carre's arrangement was only fit for elec- tric-light purposes ; that is, to furnish a continuous cur- rent of great intensity for several hours. The frailty of the porous partition rendered the battery useless for any work of long duration. We believe, however, that this battery, in spite of the disadvantage we have pointed out, should again be taken up by persons interested in the electric light, who could give it a fixed place and DANIELL'S BATTERY. 109 could take care of it. In the use of this battery, the dis- agreeable acid vapors, which are dangerous to inhale, would be avoided, and the expense would be compara- tively small. This battery has been known to work 200 successive hours without any sensible weakening, by carefully re- placing, every 2i hours, a part of the sulphate of zinc with pure water. SIEMENS AND HALSKE'S BATTERY. This battery is a Daniell battery with a porous jar, like those which precede, and is very extensively em- ployed in Europe. The copper, s|| ' d CD '-2 o '%. ^3 ' o' **!$$ *ff w t-i fcX) *^S ^^ 5 " O+i g NAMES OF METALS. ~S 9^ .0 3 ti CD-w'S O S) o g'-g'g *" : 3-2 * S' 23 s .S 0 0*0 "S cS O ^ Microhms. Ohms. Ohms. Ohms. Ohms. Silver annealed 1.521 0.01937 0.1544 9.151 .2214 Silver hard drawn 1.652 0.02103 OJ680 9! 936 2415 Copper annealed 1.616 0.02057 0.1440 9.718 .2064 Copper hard drawn l.(52 0.02104 1469 9 940 .2106 Gold annealed 2 081 02650 0^4080 12^52 .5849 Gold hard drawn 2.118 0.02697 0.4150 12.74 .5950 Aluminium, annealed 2.945 0.03751 0!0757 17^72 'l085 Zinc pressed 5 689 0.07244 0.4067 34.22 .5831 Platinum, annealed 9.158 0.1166 1^96 55 09 2 810 Iron annealed 9 825 0.1251 0.7654 59.10 1.097 Nickel annealed 12.60 0.1604 1.071 75.78 1 535 Tin pressed 13.36 0.1701 0^9738 80^36 l'396 Lead pressed 19.85 0.2526 2.257 119 39 3 236 Antimony, pressed 35.90 0.4571 816 3^456 Bismuth pressed 132.7 1.689 13^03 - 798 18 64 Mercury, liquid Platinum silver 99.74 24.66 1.2247 0.3140 13.06 2.959 578.6 148.35 18^72 4.243 German silver, hard or an- [ nealed \ 21.17 0.2635 1.85 127.32 2.652 Gold - silver alloy, hard or j annealed: two parts gold, V 10.99 0.1399 1.668 66.10 2.391 one part silver ) Resistance of one cu- bic centimetre be- tween opposed faces, expressed in microhms. Temperature, Centigrade. Graphite specimen, No. 1 " No. 2 " " No 3 2,390 3,7"80 41 800 22 22 22 Gas-retort carbon Carbon in Bunsen's battery 4,280 67200 25 26 2 Tellurium 212,500 19.6 Red phosphorus 132 ohms 20 TABLES. 255 III. CONDUCTIVITY OF LIQUIDS. (Ed. Becqucrel. Annales de Chimie et de Physique, June 1846.) SUBSTANCES. Specific Weight. Temperature, Centigrade. Conductibility. Coefficient of the increase of conductibility for 1 centigr. OBSERVA- TIONS. Silver 9.25 9.25 9.25 13.40 13.40 13.40 13.40 13.40 13.00 13.00 13.00 13.00 14.40 14.40 14.40 12.50 19.00 13.10 15.00 100,000,000.00 5.42 3.47 2.08 31.52 23.08 17.48 13.58 10.35 8.995 1C. 208 17.073 13.442 5.77 7.13 5.43 11.20 88.68 93.77 112.01 0.0286 0!0223 0.0263 Maximum. Maximum. Sulphate of copper, satu- rated 1.1707 1.1707 1.1707 1.1707 1.1707 1.1707 1.1707 1.1707 1.6008 Sulphate of copper, di- luted to half Sulphate of copper, di- luted to quarter Chloride ot sodium, satu- rated Chloride of sodium, di- luted to half Chloride of sodium, di- luted to third Chloride of sodium, di- luted to quarter Bichloride of copper, sat- urated and diluted with five times its bulk of water Nitrate of copper, satu- rated Nitrate of copper, diluted to i Nitrate of copper, diluted to half Nitrate of copper, diluted to quarter Sulphate of zinc, saturated Sulphate of zinc, diluted to half Sulphate of zinc, diluted to quarter 1.4410 1.4410 1.4410 1.4410 1.4410 1.4410 1.4410 Iodide of potassium, 30 gr. ; water, 250 gr Monohydrate sulphuric, 20 gr. ; water, 220 gr Nitric acid, commercial (sp w 1 31) Protochloride of antimo- ny. 30 gr. ; water, 120 gr. ; and hydrochloric acid, 100 gr This table shows the maximum conductibilities of the solutions of nitrate of copper and sulphate of zinc, but not that of chloride of sodium. The maxi- mum conductibility of this latter is found in a mixture of 24.4 parts of chloride for 100 of water. 256 TABLES. IV. LIQUID RESISTANCES. (Table taken from Fleeming Jenkin. Calculated by Becker.) SULPHATE OF COPPER. Percentage of salt in solu- tion. TEMPERATURE, CENTIGRADE. OBSERVATIONS. 14 16 18 20 24 28 30 8 12 16 20 24 28 45.7 36.3 31.2 28.5 26.9 24.7 43.7 34.9 30.0 27.5 25.9 23.4 41.9 33.5 28.9 26.5 24.8 22.1 40.2 32.2 27.9 25.6 23.9 21.0 37.1 29.9 26.1 24.1 22.2 18.8 34.2 27.9 24.6 22.7 20.7 16.9 32.9 27.0 24.0 22.2 20.0 16.0 Resistance of a cubic centimetre expressed in ohms. SULPHURIC ACID DILUTED. SPECIFIC GRAVITY. 40 8 12 16 20 24 28 1 10 1.37 1.17 1.04 .925 .845 .786 .737 .709 Resistance of one .20 1.33 1.11 .926 .792 .666 .567 .486 .411 cubic centi- .25 1.31 1.09 .896 .743 .624 .509 .434 .358 metre to con- .30 1.36 1.13 .94 .79 .662 .561 .472 .394 duction be- .40 .50 .60 1.69 2.74 4.82 1.47 2.41 4.16 1.30 2.13 3.62 1.16 1.89 3.11 1.05 1.72 2.75 .964 1.61 2.46 .896 1.52 2.21 .839 1.43 2.02 tween opposed faces expressed in ohms. .70 9.41 7.67 6.25 5.12 4.23 3.57 3.07 2.71 SULPHATE OF ZINC. 10 12 14 20.2 16 19.2 18 20 .. 22 16.3 24 15.6 96 grammes in 100 c.c. ) of solution f 22.7 21.4 au Resistance of one cubic centimetre. The same solution ) with an equal vol- V umeof water ) 10 12 14 18 21.120.319.518.818.1 17.3 Expressed in ohms. 2 1.94 4 8 1.65 12 16 20 24 28 Nitric acid (sp. w. ) 1 36) \ 1.83 1.50 1.39 1.30 1.22 1,18 Resistance of one, cubic centimetre in ohms. TABLES. 257 DILUTE SULPHURIC ACID. (Bineau's Table.) go I TEMPERATURE = CENTIG. TEMPERATURE = 15 CENTIG. PIJ 1 Monohydrate acid for 100 A n h y dride Monohydrate acid for 100 I acid for 100 Anhydride acid for IOC "S *s of the mix- of the mix- of the mix- of the mix- H & ture. ture. ture. ture. 0? 5.0 .060 5.1 4.2 5.4 4.5 10.0 .075 10.3 8.4 10.9 8.9 15.0 .116 15.5 12.7 16.3 13.3 20.0 . .161 21.2 17.3 22.4 18.3 25.0 .209 27.2 22.2 28.3 23.1 30.0 .262 33.6 27.4 34.8 28.4 33.0 .296 37.6 30.7 38.9 31.8 35.0 .320 40.4 33.0 41.6 34.0 36.0 .332 41.7 34.1 43.0 35.1 37.0 .345 43.1 35.2 44.3 39.2 38.0 .357 44.5 36.3 45.5 32.2 39.0 .370 45.9 37.5 46.0 38.3 40.0 .383 47.3 38.6 48.4 39.5 41.0 .397 48.7 39.7 49.9 40.7 42.0 .410 50.0 40.8 51.2 41.8 43.0 .424 51.4 41.9 52.5 42.9 44.0 .438 52.8 43.1 54.0 44.1 45.0 .453 54.3 44.3 55.4 45.2 46.0 .468 55.7 45.5 56.9 46.4 47.0 .483 57.1 46.6 58.2 47.5 48.0 .498 58.5 47.8 59.6 48.7 49.0 .514 60.0 49.0 61.1 50.0 50.0 .530 61.4 50.1 62.6 51.1 51.0 .546 62.9 51.3 63.9 52.2 52.0 .563 64.4 52.6 65.4 53.4 53.0 .580 65.9 53.8 66. S 54.6 54.0 .597 67.4 55.0 68.4 55.8 55.0 .615 68.9 56.2 70.0 57.1 56.0 .634 70.5 57.5 71.6 58.4 57.0 .652 72.1 58.8 73.2 59.7 58.0 .671 73.6 60.1 74.7 61.0 59.0 .691 75.2 61.4 76.3 62.3 60.0 .711 76.9 62.8 78.0 63.6 61.0 .732 78.6 64.2 79.8 65,.! 62.0 .753 80.4 65.7 81.7 66.7 63.0 .774 82.4 67.2 83.9 68.5 64.0 .796 84.6 69.0 86.3 70.4 65.0 .819 87.4 71.3 89.5 73.0 65.5 .830 89.1 71.2 91.8 749 65.8 .as? 90.4 73.8 94.5 77.1 66.0 1.842 91.3 74.5 100.0 81.6 66.2 1.846 92.5 75.5 .... 66.4 1.852 95.0 77.5 .... 66.6 1.85* 100.0 81.6 258 TABLES. VI. RESISTANCE OF DIFFERENT LIQUIDS. DILUTE SULPHURIC ACID after SA- WELJEV. CHLORIDE OP SODIUM. NITRATE OP POTASH. (Extract from WIEDEMANN.) | Ha* t- | 43 qj 11 *| 1 ||s 1 **{ it ||| if 1 Pi* s CO I iil ) T-< III 'is & fi H M PH s K~ 1.003 0.5 16.1 16.01 25.8758 0.59852 18.9167 0.83271 1.018 2.2 15.2 5.47 24.4033 0.57982 * 13.7647 1 . 10G26 1.053 7.9 13.7 1.884 20.9787 0.63840 10.4840 1.35099 1.080 12.0 12.8 1.368 17.0174 0.71109 6.6079 1.94955 1.147 20.8 13.6 0.960 10.4525 1.03934 3.3964 3.32633 1.190 26.4 13.0 0.871 6.0957 1.55599 1.5452 6.38318 1.215 29.6 12.3 0.830 3.6880 2.46492 1.225 30.9 13.6 0.862 1.7177 5.56571 1.252 34.3 13.5 0.874 1.277 87.3 0.930 * Minimum. 1.348 45.4 17.9 0.973 1.393 1.492 50.5 60.6 14.5 13.8 1.086 1.549 1.638 1.726 1.827 73.7 81.2 92.7 14.3 16.3 14.3 2.786 4.&37 5.320 The above figures are taken from a me- moir of Schmidt ; Annales de Poggen- dorff. See Wiedemann, vol. i. p. 324. It is seen that the maximum conducti- The above figures show the max- imum conductibility of the mix- ture to be that of 29 to 30 parts of the monohydrate acid for 100 of water ; a little different from that of the preceding table. bility or the minimum resistance of the sea-salt solution corresponds to 24.4 for 100 of water. The figures correspond to the Jacobi's standard of resistance, and must be mul- I tiplied by 598 X 10 7 to be brought to elec- I tro-magnetic absolute measurements. Experiments of Horsford, 1847. (See Wiedemann.) Chloride of potassium, 27. 6 grammes in 500 grammes of water 577,100 diluted to half 1,103,700 quarter 2,006,500 Chloride of sodium, 27.6 grammes in 500 grammes of water 577,100 diluted to half 1,488,200 Chloride of calcium, dissolved (sp. w., 1 . 04) 672,560 Chloride of magnesium 672,560 Chloride of zinc 1,092,500 Experiments of Wiedemann (lS56)from 18 to 20 Centigrade. SULPHATE-OF-COPPER SOLUTION. 31 . 17 grammes in one litre of water . 7,805,000 4,202,000 3,5i4,000 62.34 77.92 93.51 124.68 155.85 187.02 3,178,000 2,567,000 2.181,000 1,936,000 TABLES. 259 J rH 10 i-H >C ( S3 3S3I " o o o do o T-1 i oeooooooooooooeoo <-* ri ^ s^ssssssasfesseseeee s "^ ^J* T^ T-! T-) T i m r-t i i T-* r-i r-l vs 'O'O'OTJTJ^ sssflp la 58 mflliiUEHlJlE-igz SI i^ 03 ** -So 22SSllSSlSSl5l32l ll lllifi ! |l|P||I||l|Il||| 3t yiwviZ% 6cc ^MtgZ^MO^^O^ii^^faO^ ^^ : :fej> : Ilili o-g 2 %4%dOOlH 11++** 3=003 02 CC 02 02 O2 CO a : r> O ^ O r^ O If ^li^ljTiJ! ;Wr ' t. ^ ) 0) III 2" .S'C '' 11 IS . N < -< 260 TABLES. VIII. ELECTRO-MOTIVE FORCES. (Poggendorff, 1845. Extract from Wiedemann.) SINGLE-LIQUID BATTERIES. Zinc Daniell = Tin . . 1.000 409 Tin . ... Copper 410 Zinc 824 Iron Sulphuric acid (sp. w. 1 838) Copper 417 Zinc [ diluted with 49 times its weight -j Silver 1 053 Zinc of water 339 Cadmium. Iron .' . . 191 Amalgamated zinc.. Amalgamated zinc.. Iron Tin 0.537 531 Amalgamated zinc.. Amalgamated zinc.. Nitric acid (sp. w. = 1.22) diluted with 9 times its w'ght of water Copper Platinum .. 0.882 1.495 Amalgamated zinc.. Amalgamated zinc.. Copper Hydrochloric acid (sp. w. = 1 . 113), diluted with 9 times its weight of water Copper Platinum. . . Platinum. . . 0.788 1.537 0.771 Silver Zinc . Platinum. . . Iron 0.620 1 003 Zinc Potash in 6 times its weight of Silver 1 198 Zinc water Platinum 1 257 Zinc Antimony . . 541 Zinc Carbonate of potash Iron 832 Zinc ( Copper 909 Zinc [Carbonate of potash, concen- f trated Platinum. . . 1.078 Iron Zinc Choride of potassium ( Copper Iron 0.072 476 Zinc Copper 743 Zinc i Chloride of potassium, concen- trated " Platinum. . . 1.346 Iron . Copper 0.260 TWO-LIQUID BATTERIES. Iron. SO 3 HO-f49HO by weight 461 Iron. Zinc. Sulphuric acid Sulphuric acid 1, water 4 Nitric acid Nitric acid, fuming Platinum!."." Platinum 1.177 1 812 Zinc. Sulphuric acid 1, water 4 " (sp w 1 33) 1 678 Grove.. . - Zinc. Zinc. Zinc. Zinc. Zinc. Zinc. Sulphuric acid 1, water 12 Sulphuric acid 1, water 4 Sulphuric acid 1, water 12 Sulphate of zinc... Sea-salt, NaCl Sulphuric acid 1, water 4 " (sp.w.1.33) " (sp.w.1.19) " (sp.w.1.19) " (sp.w.1.33) ' (sp.w.1.33) Sulphate of cop- Platinum. . . Platinum. . . Platinum. . . Platinum. . . Platinum. . . Copper 1.603 1.558 1.512 1.550 1.765 1 000 Zinc. Sulphuric acid 1, water 12 per, concen--! trated Copper 906 Daniell. Zinc. Zinc. Zinc. Zinc. Sea-salt 1, water 4 . 1 Bichromate of j j potash 3. | Sulphuric acid j 4, water 18.... 1 Copper Copper Carbon .... Platinum. . . 'i'cis 1.574 0.977 TABLES. 261 8888 M > PS i PI <^ i e 1 S i ^ i SSlSS '5 'o '3 '3 c3 c3 eg c3 O O O O S S 3 S OOOO UCJOO O cccfl rtcec fi 'NNNN "STS'ST ^j^j^Jj _fc I'S'cS'eS "S'S'S'S "rt 'ass aasa a !