Page:Scientific Memoirs, Vol. 1 (1837).djvu/531

Rh zinc is too fragile to be employed in too thin plates. In order to compare the effects, a plate of common zinc of the same size was combined with a plate of copper and plunged into the same acid. The deviation was at first 55½°, after 43′ it lowered to 12°, and on drying the pair of plates 13° was the highest to which it could be restored. On being subjected to the action of the acid for 1¾ʰ, the plate had disappeared, and its insoluble parts only remained.

I have also made experiments upon a liquid amalgam of zinc poured into a porcelain basin covering a surface of 48 square inches; instead of a plate I employed a copper wire of 1¼in. diameter, coiled into a flat spiral, in order to let the gas escape more easily. The effects of this combination were very extraordinary; for, without anything being touched, the needle had during fifteen hours' action only receded 11½° from 60°, and remained fixed at 49½°. After breaking the circuit, and exposing the spiral to the air for some time, the deviation was restored to 59°. This experiment was the more striking as the multiplier of the galvanometer consisted only of a single coil of copper wire 1¼ lin. in thickness; for it is known that the decrease of the needle is much more feeble on employing a very long and slender wire.

A plate of gilt copper and an amalgam of zinc, composed of one atom of zinc and one of mercury (Zn. Hg.), a composition which is solid enough to be used in plates, gave also very good effects, both as to the constancy of the deviation and to its restoration.

In order to try some other compositions, which, according to Ritter, are still more positive than the amalgam of zinc, I had some plates cast, of an equal size, of lead, tin and zinc, of different alloys of these metals, and of different amalgams. The alloys were composed of atom to atom, and moreover a plate of each composition was also amalgamated at its surface. The direction of the deviation of the needle of the galvanometer determined the place which each alloy ought to occupy. The liquid in which the plates were plunged was sulphuric acid diluted with four parts of water. I must remark, that the slightest change of the surface frequently affects the place of the metals the electrical relation of which does not differ much. It is chiefly in lead and its alloys that this phænomenon is most strikingly exhibited. Lead freshly polished is very positive in relation to lead exposed to the air for some minutes or steeped in any acid. The following is the result of two series of experiments, which I have made with the greatest care.