268 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



1133. But there are some disadvantag-es which I have not yet had time to over- 

 come, though I trust they will finally be conquered. One is the extreme difficulty of 

 making a wooden trough constantly water-tight under the alternations of wet and 

 dry to which the voltaic instrument is subject. To remedy this evil, Mr. Newman is 

 now engaged in obtaining porcelain troughs. The other disadvantage is a precipi- 

 tation of copper on the zinc plates. It appears to me to depend mainly on the cir- 

 cumstance 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 

 (1120.): 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 so be removed from every part of the trough when 

 the experiments in which it is used are completed. 



1134. 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 (1148.) ; — 

 and, next, on the superior quality of the rolled zinc above the cast zinc used in the 

 construction of the ordinary pile. It cannot be that insulation between the conti- 

 guous 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*, 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 obtained. 



1135. As, upon principle, there must be a discharge of part of the electricity 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 disadvantage. The plates need not be fastened in, but only set in their 

 places ; nor need they be in large single pieces. 



§ 17. Some practical results respecting the construction and use of the Voltaic 



Battery. 



1136. The electro-chemical philosopher is well acquainted with some practical re- 

 sults obtained from the voltaic battery by MM. Gay-Lussac and Thenard, and given 

 in the first forty-five pages of their 'Recherches Physico-Chimiques'. Although 

 the following results are generally of the same nature, yet the advancement made in 

 this branch of science of late years, the knowledge of the definite action of electricity, 



* A single paper thus prepared could insulate the electricity of a trough of forty pairs of plates. 



