TO THE MOVEMENT OF MACHINES. 519 
zamated 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 554°, 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 12", the plate had disap- 
peared, and its insoluble parts only remained. 
I have also made experiments upon a liquid amalgam of zine poured 
into a porcelain basin covering a surface of 48 square inches; instead 
of a plate I employed a copper wire of 14 lin. 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 113° 
from 60°, and remained fixed at 494°. After breaking the circuit, 
and exposing the spiral to the air for some time, the deviation was re- 
stored to 59°. This experiment was the more striking as the multiplier 
of the galvanometer consisted only of a single coil of copper wire 14 
lin. in thickness; for it is known that the decrease of the needle is 
much more feeble on employing avery long and slender wire. 
A plate of gilt copper and an amalgam of zinc, composed of one atom 
of zine 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 zine, 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 galvanome- 
ter 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 phe- 
nomenon 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. 
* In the alloys it is usual to combine the metals according to some relative 
proportion of weight. I united them by atoms, bearing in mind the general 
law of true chemical compositions. 
