25§ 



SCIENCE. 



[Vol. XXII. No. 562 



IMPROVEMENTS IN THE STORAGE OF ELEC- 

 TRICITY. 



DY r. H. BOWMAN, D. SC, F. K. S. EDIN., M. INST. E. E., AND ASSOC. 

 INSTS., C. E. AND M. E., ETC. BOWDON, ENGLAND. 



It is only within a comparatively recent period that 

 electricity has taken a foremost position for lighting, 

 motive power and general use in chemico-metallurgical 

 operations; still the very great advances which have been 

 made and which are continually in progress have rendered 

 it certain that electricity is the agent of the future, and 

 that the part which it will play in the industrial economy 

 of the world will ever be an increasingly useful and ad- 

 vantageous one. The discovery of the princijjles of the 

 dynamo by Faraday, and its working out into actual 

 practice by a long series of able inventors, have dispensed 

 with the old and cumbersome methods of the generation 

 of electricity by chemical means, and rendered its produc- 

 tion a simple and thoroughly reliabje process. 



Notwithstanding this, however, the energy is essentially 

 a dynamical one, and the continuance of the current is 

 entirely dependent on the continuous motion of the gen- 

 erating machinery; and hence, whenever the machine stops, 

 the current stops with it. More than this, any fluctuation 

 in the regularity of the power supplied to drive the 

 dynamo produces a more than corresponding fluctuation 

 in the quantity and intensity of the current; and hence it 

 it is necessary to have all the parts of the generating 

 machinery duplicated, which increases the expense of the 

 production of the current. Water power can be stored in 

 reservoirs so that the winter's rain may be made available 

 for summer's drought, and a constant flow of water thus 

 obtained. Gas, which is generated intermittently in 

 retorls, can be stored in suitable holders, and delivered 

 out in regulated quantities throughout any given number 

 of hours; and until it was j)ossible also to store electricity 

 the economical use of it was somewhat restricted, or per- 

 haps it would bo better to say that the possibility of its 

 application to a larger number of cases and with more 

 perfect regularity was secured by the method of electrical 

 slorage. 



It had been noticed in certain experiments with primary 

 chemical batteries that if a current from a battery was 

 sent into another cell, the two elements of which were 

 lead plates in an acid solution, a portion of this energy 

 could be stored up in the elements of this cell, so that 

 when the current was cut off from the charging battery 

 and a connection between the pilates of the charged bat- 

 tery completed, a current was obtainable, but flowing in 

 an opposite direction from that in which it had entered 

 the charged battery. This charged battery had its efficiency 

 very much increased by being continuously charged and 

 discharged when the currents sent into it were not so 

 strong as to destroy these efl^ects. The difference, there- 

 fore, between a primary battery and an accumulator may 

 be simply stated as follows: In the primary battery the 

 two plates are made of different materials, such as zinc 

 and copper or zinc and platinum, and a current is gener- 

 ated by chemical action upon one of these plates, the other 

 remaining unaffected; whereas in the accumulator both 

 plates are of the same material, namely, lead; and neither 

 of them wastes with the action of the current, the current 

 derived, when the connection is made, being entirely due 

 to the chemical action which has been set up in these 

 plates by the current which was sent into them. It was 

 soon found that, by a proper modification of the elements 

 of the accumulator, the capacity to store the energy could 

 be largely increased, and cou^ld also be retained for a con- 

 siderable period of time without loss. Since the days of 

 Ritter, Plante and Faure, to whom we owe the primary 



discoveries, very great improvements have been made in 

 these accumulators. The early accumulators, like the 

 early dynamos, were very ineffectual machines, very liable 

 to get out of order, and easily destroyed by local action, 

 and they were very irregular in their power to retain the 

 electric energy; but the improvements which have been 

 introduced into them have done away with many of these 

 difficulties, and the most modern accumulators have an 

 efficiency which but a tew years ago would have been con- 

 sidered absolutely impossible. 



The earliest form of jjractical accumulator was devised 

 by Plante, and consisted of two thin sheets of lead, which 

 were sejDarated from each other by a piece of flannel of 

 the same size as the plates. These plates were rolled 

 round in a cylindrical form so as to occupy the least pos- 

 sible space, and then placed in a jar or other suitable ves- 

 sel containing dilute sulphuric acid. The plates were 

 charged by connecting them respectively with the two 

 poles of a dynamo. The current from the dynamo decom- 

 piosed the acidulated water, and oxygen was accumulated 

 on one of the plates, and thus a store of chemical energy 

 was provided which could be expended in the generation 

 of an electric current when the charging was complete. 

 The oxygen attached itself to the plate by entering into 

 combination with the lead, thus forming a lead oxide, and 

 the action on the other plate was to remove any oxygen 

 which might be accumulated on the surface of that plate 

 in the form of oxide, and reduce it to a pure metallic 

 form. It will thus be seen that the electric current from 

 the dynamo had accomplished work by tearing asunder 

 the atoms of the acidulated water in which the plates of 

 the accumulator were immersed and storing up the oxy-' 

 gen in combination with the material of one of the plates. 

 A chemical strain is thus induced between the two plates, 

 which increases in intensity as long as the charging cur- 

 rent is sent into the acccumulator until a certain point is 

 reached, which point is that at which the whole of the 

 available surface of the oxidized plate has been com- 

 pletely changed into the lead oxide. After that the 

 oxygen is given off from the surface of the plate, and no 

 further storage takes place. When the charging current 

 is taken off and the two poles of the accumulator re- 

 connected, the strain tends to equalize itself, a portion of 

 the oxygen from the oxidized plate piassing by electrolitic 

 action to the unoxidized pilate until complete chemical 

 equilibrium is restored, when the action ceases. When 

 this ijrocess is continued for a length of time, which is 

 necessary, in order that an efficient accumulator may be 

 obtained, this alternate oxidizing and deoxidizing causes 

 the surface of the plates to become more porous, or 

 spongey, and thus it presents a larger surface to the 

 oxidizing agent than would otherwise be the case; and at 

 the same time, the surface of the lead being in a more 

 granular or finer state of division, the alternate oxidiza- 

 tion and deoxidization takes place with greater ease and 

 rapidity, and thus not only is the quantity of energy 

 which can be stored greater, but the time required for 

 charging and discharging becomes less. This is a most 

 important matter, because it not only enables a smaller 

 number of cells to be used for the storage of a given 

 quantity of electricity, but it also enables that which is 

 drawn out to be obtained at a more rapid rate, since it is 

 found that the power to receive the charging and to give 

 it out are almost p)roportional. 



The formation of this spongey surface on the plates of 

 the accumulator by the alternating action of an electric 

 current extends over a considerable period of time, and is 

 a most expensive process, because it requires a large 

 expenditure of electric energy to extend the spongey sur- 

 face to any depth in the plates. To get over this difficulty 

 in the more modern forms of the accumulator, devices 



