Galvanic Batteries. 173 



tight under the alternations of wet and dry to which the voltaic in- 

 strument is subject. To remedy this evil, Mr. Newman is now enga- 

 ged in obtaining porcelain troughs. The other disadvantage is a pre- 

 cipitation of copper on the zinc plates. It appears to me to depend 

 mainly on the circumstance that the papers between the coppers retain 

 acid when the trough is emptied ; and that this acid slowly acting on 

 the copper, forms a salt, which gradually mingles with the next charge, 

 and is reduced on the zinc plate by the local action : the power of the 

 whole battery is then reduced. I expect that by using slips of glass 

 to separate the coppers at their edges, their contact can be sufficiently 

 prevented, and the space between them be left so open that the acid 

 of a charge can be poured and washed out, and be so removed from ev- 

 ery part of the trough when the experiments in which it is used are 

 completed.* 



" The actual superiority of the troughs which I have constructed 

 on this plan, I believe to depend, first and principally, on the closer 

 approximation of the zinc and copper surfaces ; — in my troughs they 

 are only one tenth of an inch apart ; — and, next, on the superior quali- 

 ty of the rolled zinc above the cast zinc used in the construction of 

 the ordinary pile. It cannot be that insulation between the contiguous 

 coppers is a disadvantage, but I do not find that it is any advantage ; 

 for when, with both the forty pairs of three-inch plates and the twenty 

 pairs of four-inch plates, I used papers well imbibed with wax,t these 

 being so large that when folded at the edges they wrapped over each 

 other, so as to make cells as insulating as those of the porcelain 

 troughs, still no sensible advantage in the chemical action was ob- 

 tained. 



" As, upon principle, there must be a discharge of part of the elec- 

 tricity from the edges of the zinc and copper plates at the sides of the 

 trough, I should prefer, and intend having, troughs constructed with a 

 plate or plates of crown glass at the sides of the trough : the bottom 

 will need none, though to glaze that and the ends would be no disad- 

 vantage. The plates need not be fastened in, but only set in their 

 places ; nor need they be in large single pieces."! 



* Dr. Hare has obviated these difficulties by making one trough to go into an- 

 other, the whole being cemented while heated by a flambeau of alcohol, so as not 

 only to keep the cement liquid, but also to expel the moisture and air from the 

 pores, which in refrigerating absorb the cement. The cement was made by melt- 

 ing together one part of suet and seven of rosin. 



t A single paper thus prepared could insulate the electricity of a trough of forty 

 pairs of plates. 



t Dr. Hare mentioned in his account of his deflagrator made with copper cases, 

 that he had found a series in which the side edges were exposed deficient of power. 

 He objected to having the cases like those employed by Faraday, open at the sides. 

 His cases were plosed at the side.s, and open above and below. 



