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 (1120.):  the power of the whole battery is then reduced.  I expect that by using slips of glass or wood 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 the latter 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 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-soaked in wax[A], 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.

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

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.

S 17. Some practical results respecting the construction and use of the Voltaic Battery (1034. &c.).

1136.  The electro-chemical philosopher is well acquainted with some practical results 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, and the more accurate and philosophical mode of estimating the results by the equivalents of zinc consumed, will be their sufficient justification.