RICHARDS AND HEIMROD. 



THE IMPROVED VOLTAMETER. 



423 



pare the nitrite, we had recourse at first to a method used by Proust.* 

 He has found that on boiling an argentic nitrate solution with finely di- 

 vided silver, the nitrite is produced in quantity. In repeating this ex- 

 periment, powdered silver reduced from purest silver chloride by the 

 Stas method was boiled in a ten per cent argentic nitrate solution. 

 Nitrite was indeed formed, but a very fine film of crystallized metallic 

 silver was formed on the surface ; a complication which seemed to point 

 towards the existence of a reaction similar to the solution of copper in 

 cupric sulphate. But it was found that pure silver nitrite in neutral 

 silver nitrate solution likewise deposits a fine silver mirror on exposure 

 to the light; hence the silver in both cases must be supposed to result 

 simply from the decomposition of the nitrite. The solution boiled with 

 silver was filtered through a Gooch crucible, and after cooling was em- 

 ployed in a voltameter with a porous cup. The solution containing the 

 nitrite deposited 2.27945 grams of silver, while pure argentic nitrate in 

 another standard voltameter deposited 2.27944 grams, a difference of 

 only 0.01 milligram. (Exp. 15.) 



Evidently the nitrite present had no effect at the kathode ; and the 

 liquid in an ordinary voltameter could hardly contain more nitrite than 

 this solution which had been boiled with metallic silver. In order to 

 pursue the matter further, however, we prepared silver nitrite from pure 

 potassium nitrite and silver nitrate.f Pure potassic hydrate was neutral- 

 ized with nitric acid ; the nitrate was re-crystallized and fused in a silver 

 crucible, and the resulting mixture of nitrate aud nitrite was extracted 



TABLE IV. 

 Standard vs. Voltameter with Solution Saturated with AgN02. 



* .Journ. de Physique, March, 1806, 211 ; also Nicholson's Journal, 15 : 878. 



This reference has evidently been lost, since no text-book, including; Dam- 

 mer, gives it, although all mention Proust's observation. After a long search 

 through tlie journals published in Proust's days, the reference was rediscovered. 



t Victor Meyer, Liebig's Ann., 171, 23 (1874). 



