Page:Scientific Memoirs, Vol. 1 (1837).djvu/530

518 this kind possesses a remarkable constancy, provided there are no secondary effects arising from the precipitation of the negative metal upon the positive plate. It may happen that some particle of the zinc may not be well amalgamated; in that case a direct action of the acid upon the zinc takes place, there is a development of hydrogen in that place, the negative metal accidentally dissolved in this liquid will be reduced in it by the gas, and there will be a partial pile, which will affect the principal action. These partial effects will be propagated by degrees over the whole surface, the positive state of which will then rapidly decrease. This will only take place when the negative metal is soluble in the acid.

I have made many experiments on this subject. A thin plate of zinc of seven inches square, and weighing 848 gr., was amalgamated, in order to form a voltaic pair with a plate of copper of the same size. The liquid was sulphuric acid, of a specific gravity of 1·105. There was no development of gas on the surface of the zinc: the bubbles of air which formed there by degrees rose so slowly, that they might with propriety have been disregarded, even if there had not been reason to believe that they were for the most part the atmospheric air contained in the water. After five hours of action the plate was again weighed, and had lost only 112 gr.; during this time the pair of plates had been twice withdrawn from the acid, and dried for five or six minutes near a stove.

The following is the table of the deviations of the needle which denote the decrease of the energy of the current.

The following day the experiments were repeated with the same pair of plates. The decrease of the deviation was not so rapid as before, and the original energy always restorable by drying the plates; once it even increased to 65°. At 10ʰ 50′ in the evening the deviation was still at 55°. The action must have continued through the night, but the next morning the plate was found broken in pieces.