November lo, 1893.] 



SCIENCE. 



25§ 



were employed to obtain this sensitized surface in a more 

 efficient and cheaper manner, such as dipping plates in 

 oxidizing acids so as to chemically prepare the surface, 

 scoring the plates, corrugating them, or giving them star- 

 like or other sections, so as to jDresent a larger surface for 

 the same weight, filling perforated cylinders or other hol- 

 low forms with finely divided lead. The greatest advance, 

 however, was made when it was discovered that by punch- 

 ing holes in the plates so as to give them the form of a 

 collander and filling them up with an acid paste of red 

 lead, or, better still, casting the plates in the form of a 

 grid or grate and tilling up the holes in the grid with an 

 acid mixture of red lead for the positive plate and lithage, 

 which is a lower oxide of lead, for the negative plate, 

 plates in this form required much less forming and a 

 much shorter time to charge, retained their charge for a 

 longer period and gave out their discharge with greater 

 regularity and in larger volume. This marked a distinct 

 advance in the storage of electricity, and in the various 

 forms of accumulators which are constructed in this man- 

 ner very reliable and efficient results have been produced. 



They have, however, one disadvantage: if they are 

 either charged or discharged too rapidly a disintegration 

 of the surface of the sensitised portions of the plate occurs. 

 It probably arises from this cause. The acid piaste of 

 lead oxide consists of a mechanical aggregation of mole- 

 cules of lead oxide, which are neither perfectly homo- 

 geneous in their structure nor perfectly regular in the 

 arrangement of the molecules. The interstices between 

 the molecules, from the very nature of the irregularity in 

 the mechanical structure, must also be irregular. When, 

 therefore, either in the charging or discharging, there is 

 an evolution of gas in the interstices of the sensitised por- 

 tion of the plate, especially at the surface, the increase in 

 volume by the change of the liquid portion of the electro- 

 lite into the gaseous form throws a pressure within the 

 interior of the molecular mass; and, in consequence of the 

 irregularity in the interstices, these gaseous streams con- 

 flict with each other, and hence portions of the surface of 

 the plate are disintegrated and fall down into the bottom 

 of the cells. When the current, either in charging or dis- 

 charging, is small in quantity, this disadvantage does not 

 appear in the same proportion as when the charge or dis- 

 charge is great. In actual use also it is generally desirable 

 to draw out the stored energy at a greater rate than to 

 charge it, so that the accumulator during the period of 

 charging is usually subjected to a much less strain than 

 during the period of discharge. When, therefore, the 

 charge requires to be drawn out very quickly, the plates 

 suffer rap)id deterioration, and this raj)id deterioration 

 very soon breaks up the sensitized portions of the plates, 

 and, by causing unequal expansion and contraction, causes 

 buckling and local action. 



This is one of the greatest disadvantages which this 

 form of accumulator possesses, and it is this fault which 

 has rendered them, not only in inexperienced hands, very 

 inefficacious, but also very costly to maintain. The most 

 modern form of accumulator to-day has now almost en- 

 tirely done away with this disadvantage. It is well known 

 that in a crystalline form the molecules of matter are 

 arranged in a different order from what they are in any 

 mechanical mixture. In the mechanical mixture the aggre- 

 gation of the atoms is strictly fortuitous, that is to say, it 

 is a mere question of chance how thej' are arranged, and 

 they have no cohesion amongst themselves beyond that 

 which is given to them by the cementing mixture which 

 holds them together. In the crystalline form, however, all 

 this is changed; the molecules of the body are arranged in 

 perfect symmetrical order, and they are held together by 

 molecular affinities which regulate the order of their dis- 

 tribution and secure the coherence of the mass. It is 



quite true that the material is denser unless some means 

 are emiDloyed to modify the density; but although this ia 

 the case, the molecular channels which exist in the inter- 

 stices of the crystal are arranged in as regular order as 

 the molecules of the crystals themselves. This property 

 has recentlj- been employed with very great success in 

 the formation of accumulators, and has enabled the plates 

 of which they are composed to have the greatest uniform- 

 ity in structure, caj)acity in storage, rajjidity in charging, 

 and regularity in discharging. While all these objects 

 have been obtained, it has been found, in addition, that 

 there is a greater durability in the life of the accumulator 

 and a greater power to retain the intensity of the voltage 

 almost to the end of the discharge. 



The active jjart of the plates is formed of chemically 

 pure lead, which is obtained in the following manner: 

 White chloride of lead, after being thoroughly washed 

 and dried, is mixed with a certain portion of chloride of 

 zinc. The proportion varies with the use to which the 

 accumulators are to be put, as upon this mixture depends 

 the degree of density or porosity of the reduced lead, and 

 this method of manufacture secures a most complete con- 

 trol over the structure of the p>lates. The mixture of lead 

 and zinc chlorides is then fused together into a molten 

 state, and cast in blocks like small tiles in suitable moulds. 

 The size and thickness of these tiles depend on the pur- 

 pose to which the accumulators are to be j)ut. The form 

 of the tile also varies with the particular form and size 

 of which the plates of the accumulator are to be made. 

 These chloride squares are then placed in a bath of 

 dilute hydrochloric acid, which removes all the chloride 

 of zinc. They are then dried and placed in suitable 

 moulds to receive the framework of lead into which they 

 are cast. The plates of lead enclosing the tiles of dried 

 lead chloride are then placed in a dilute solution of 

 chloride of zinc along with alternate plates of zinc, and, a 

 connection being made between these pilates, an electric 

 couple is obtained. The lead chloriie in the tiles is thus 

 reduced to a pure porous metallic lead. If a section is 

 made of one of these chloride tiles which has thus been 

 reduced to pure porous metallic lead, it is found that the 

 direction of the pores is always at right angles to the 

 surface of the plate, and this structure, therefore, enables 

 the electrolite with which the accumulator has been 

 formed to penetrate every portion of the porous lead, and 

 the structure also offers very little resistance to the dis- 

 engagement of the gas which is formed by the electrolitic 

 decomposition; and thus there is no tendency to disinte- 

 gration of the plate, because no pressure is thrown upon 

 the molecular structure. In the first formation of these 

 plates those which are intended for cathodes or negatives 

 and those which are intended for anodes or positives are 

 all treated alike; but it is found better to again treat 

 those plates which are intended for positives in a further 

 manner by placing them along with alternate ^slates of 

 lead in acidulated water and exposing them to the action 

 of a current of electricity which is sent into them from a 

 dynamo. By these means a reduction of the lead is more 

 completely jjerformed, and the greatest efficiency of the 

 accumulator secured. The formed plates can then be 

 built up alternately with the negative plates into any size 

 of accumulator which is required. 



The construction of this type of accumulator has solved 

 many of the difficulties hitherto experienced. It has pro- 

 duced an accumulator ynth every quality which is most 

 desirable, viz., a high rate of charge and discharge with- 

 out injury to the plate, a high capacity of storage, and the 

 maintenance of the voltage through a very large percent- 

 age of the capacity. Along with this there is also a very 

 greatly increased durability; and the fact that the same 

 number of ampere hours can be stored in half the weight 



