Two Fluids, and of Two Metals not in Contact. 547 



since, nevertheless, a specific distinction remains between the 

 effects of the two acids, the one, added to the water, developing 

 a shghter, and the other a greater electromotive force than the 

 iodide of potassium, we should be forced to admit that the qua- 

 lity of the chemical action produces a specific difference in the 

 excited electricity, and should thus again be brought back to 

 the position maintained by De la Rive, but hitherto not proved, 

 of the variety of electricities. I know not whether this is the 

 opinion of the English philosopher ; but the above-mentioned 

 position, and another in which he expresses as a conjecture, "The 

 same quantity of electricity may pass in the same time, in at 

 the same surface, into the same decomposing body in the same 

 state, and yet, differing in intensity, will decompose in one case, 

 and in the other not,'^* — would admit of such a construction. 



But be this as it may, so much is certain, that there is no 

 need of the hypothesis of an increase of the intensity of the 

 chemical action, in order to explain the experiment in question. 

 I have in fact convinced myself in the most positive manner 

 that the result of the addition of the nitric acid does decidedly 

 not arise from the chemical attack of this acid on the zinc, but 

 solely from an action of it on the platina. 



Instead of placing the zinc and platina in common in the 

 stronger mixture of acids mentioned at p. 545, I separated the 

 two acids by animal membrane (bladder), inserted the zinc 

 (amalgamated) in the sulphuric acid (1 vol. concentrated acid, 

 and 4 vol. water), and the platina in the nitric acid (1 vol. con- 

 cent, acid, and 6 vol. water), while the two other plates, zinc 

 and platina, stood in the solution of iodide of potassium. Now 

 although in this case the zinc underwent no other attack 

 in quantity and quality than in the experiment mentioned at 

 p. 543, in which the iodide of potassium had the ascendency 

 over the sulphuric acid, yet the direction of the current was the 

 reverse ; the iodide of potassium succumbed to the acid. The 

 cun'ent also possessed a very considerable intensity, and, if not 

 quite so powerful as in the case in which the zinc stood in the 

 acid mixture, this, evidently, merely arose from collateral cir- 

 cumstances, partly from the separated acids having perhaps a 

 weaker power of conduction than the mixed, partly, and with- 

 out doubt chiefly, from the metals in the present arrangement 

 being in a somewhat disadvantageous position, the communica- 

 tion between the two being made only by the membranous 



moderate degrees of concentration ; for it is at least in part decomposed, which 

 is indicated by the altered development of gas at the zinc, and more decidedly 

 evident from the ammonia, the existence of which in the solution of zinc may 

 be distinctly demonstrated by the addition of an excess of caustic potassa. 

 * Faraday, Experim. Res. § 988. 



