TO THE MOVEMENT OF MACHINES. 519 



gamated 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 

 de^aation was at first 55^°, 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 l^^, the plate had disap- 

 peared, and its insoluble parts only remained. 



I have also made experiments upon a liquid amalgam of zinc poured 

 into a jjorcelain basin covering a surface of 48 square inches ; instead 

 of a plate I employed a copper wire of 1^ 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 11^° 

 from 60°, and remained fixed at 49^°. After breaking the circuit, 

 and exposing the spiral to the air for some time, the deviation was re- 

 stored to 59°. This exjjerimeut was the more striking as the multiplier 

 of the galvanometer consisted only of a single coil of copper wire 1 ^ 

 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. Jiff.), 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 galvanome- 

 ter determined the place which each alloy ought to occupy. The liquid 

 in whicli 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 whicli 

 does not differ much. It is chiefly in lead and its alloys that this phae- 

 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 imited them by atoms, bearing in mind the general 

 law of true clieniical compositions. 



