"378 Contributions to Experimental Chemistry. 



I have a few words to add, touching the nature of the gal- 

 vanic circle above described. It appears to me, that its effects 

 are as much depending upon the electromotive power of the 

 liquids, as on that of the metals : for if both cylinders are 

 filled with a solution of chloride of sodium or muriate of 

 ammonia, no hydrogen gas is evolved at the negative metal ^ ; 

 and the briskness with which the gas is disengaged, increases 

 with the greater difference in the electro-chemical nature of 

 the liquids employed. Thus, the interior of the cylinder being 

 filled with diluted muriatic acid, hydrogen gas will be more 

 rapidly disengaged, if the interior one be filled with a solution 

 of caustic alkali, in preference to a neutral salt. If, on the 

 contrary, the electro- negative metal be in contact with the 

 electro-positive liquid, scarcely any evolution of gas is visible — 

 and the less, the more the liquids differ in their electro-chemical 

 relation. 



On the Limits of the mutual Reaction of Iodide of Potassium 

 and Chloride of Platinum, 



Iodide of Potassium, with an additional quantity of diluted 

 sulphuric acid, renders a solution of the perchloride of platinum, 

 containing to,W^ ^^ ^^^ chloride, at the first moment, brown- 

 red, the liquid becomes afterwards dark green, and a black 

 precipitate is ultimately produced. If the solution of the 

 chloride of platinum is still more diluted, it turns red by the 

 reagent, and it is still very distinctly so when the chloride is 

 -T,ooi.oo-s of the weight of the liquid. The limit where iodide 

 of potash is still indicated by perchloride of platinum, and 

 some additional sulphuric acid, is at ■jooho'ff of the iodide. 

 Starch, with an addition of fuming nitric acid, indicates the 

 iodide very distinctly, if it amounts to t^o^o oo of the solution, 

 its colouring being limited at jo o!o o o of the salt present. The 

 reaction was not impeded when the solution contained at the 

 same time a quantity of chloride of potassium, equal to 10,000 

 times that of the iodide. 



•If both metals are at the same time in contact with a diluted acid, hydrogen gas 

 is evolved at the negative wire; but in this case, the instantaneous formation of a 

 metallic salt on the surface of the metal must be taken into account. In a paper 

 published in PoggendorfiF's Annalen derPhysik, 1825, I have treated more at largis 

 on the electromotive power of the binary combinations and their solutions. 



