59* Olftrvaltpni of Gahanic Procejis. 



thy of the furfaces of the zine plates, whatever were their forms, gas Was always pro- 

 duced upon them : and both large and fniall furfaces in common water in a great 

 length of time became covered at fome of their points of conta£i: with that fluid 

 with a whitifli film. 



When finall oblong zinc plates were introduced into any part of the ferics inftead of the 

 larger plates, they appeared to oxidate rapidly, without giving out any gas. 



4. The fubftitution of oblong filver flips for many of tlie plates, did not apparently much 

 dhninifli the power of the ferics: I therefore conftrucled a feries of twxnty-feven glafles, 

 wholly compofed of zinc plates attached to thin filver wires. This combination with pump 

 water gave feeble fliocks, which were lefs vivid than thofe of the common feries of 

 eighteen. When, however, it was made analogous in all its parts, all the wires not deeply 

 iaferted in the water gave out gas, and the zinc plates flowly oxidated. In another ex- 

 periment, in which a feries of thirty glafles, containing wires and zinc plates, were ufed, 

 moft of the wires not only gave out gas, but after fome time became covered at their points 

 of conta£t with the furface of the water with a white film ; a few of them, not deeply 

 inferted, produced a flight white precipitation. 



5. Thefe fafts fcemed to ftiew that the quantity of hydrogen produced in a feries was in 

 fome meafure, and to a certain point, in the inverfe ratio of the quantity of the furface 

 of the filver plates. Speculating upon them, and comparing them with tlie experiments of 

 Mr. Cruicklhank, and thofe which I noticed in my laft paper on the figns of ammoniac 

 perceived during the aftion of a pile in common air, I could not but conjedure that 

 whilft oxygen was condenfcd on all the zinc excicors In the feries, hydrogen was produced 

 on all the fdver ones ; and in fmall furfaces chiefly liberated, whilft oni larger ones it wa* 

 almoft wholly condenfed by the nitrogen of atmofpheric air diflblved in the water, and this 

 conje£Vure was rendered more probable, when I confidered the white matter chiefly formed 

 round the filver at the furface of the water, and its folubility, without cloudinefs in acids, 



.as it might eafily have been produced by the decompofition of magnefian faks exifl;ing 

 in the pump water. 



To determine whether ammoniac was produced, I made many experiments on difi^erent 

 feries, conCfliing of from feventeen to thirty glafl*e6. In fome of thefe glafles wires were ufed, 

 and in fome of them plates. Sometimes dillillcd water was employed, and fometimes 

 pump water, both of which were occafionally tinged with red cabbage juice. 



Without being minute in the detail of thefe experiments, I fliall give tlieir general 

 refults. In the veflels containing red cabbage juice, that fluid, after many hours, became 

 tinged with grecn where it was in contaft with the filver, though at its points of contaft 

 with the zinc no change of colour could be obferved in it. In the pump water a white film 

 always formed on the furface of the water near its points of conta£l with the filver: 

 whilft in diftilled water fuch an appearance was hardly perceptible. The anomaly of its 

 being now and then perceptible I am inclined to refer to accidental impurities in the vefl^els. 



The 



