MERCURIC SALTS CHANGE INTO EACH OTHER. \QQ 



flasks. The products were : — where carbon dioxide was used, metallic 

 mercury, 0.1191 gram, mercuric radical, 0.1213 gram ; where air was 

 passed and no nitric acid added, metallic mercury, 0.1195 gram, mer- 

 curic radical, 0.1202 gram ; where air was passed and nitric acid 

 added, metallic mercury, 0.1104 gram, mercuric radical, 0.1066 gram. 

 That in the last case the very little nitric acid added played no part as 

 an oxidising agent was further shown by titrating for free acid after 

 the sodium chloride had been added, and finding the acidity closely 

 equivalent to that of the nitric acid which had been added. 



Thus, in eight hours at or near 100°, one third of the mer- 

 curous nitrate had decomposed into mercuric nitrate and metal in 

 the two experiments made without addition of nitric acid, and not 

 much less in the third experiment where this acid was present. 

 Further, in eio-ht hours at 100° in a current of air no sensible oxidation 

 of mercurous nitrate by air or nitric acid had taken place. 



Literature and criticism. — Gmelin tells us that " The solution of 

 this salt [mercurous nitrate in presence of a little nitric acid], when 

 exposed to the air takes up oxygen and is converted into mercuric 

 nitrate ; the same change is produced by continued boiling, mercury 

 being then given off together with the water (Proust). This is very 

 confusing. From it, however, may be seen that Proust (1816) knew 

 that mercurous nitrate exposed to the air in solution was partly con- 

 verted to mercuric nitrate, and that on boiling its solution mercury 

 itself volatilised with the steam. But, as is shown in this paper, the 

 mercuric nitrate is not produced by oxidation, at least, not to any 

 sensible extent. Proust seems, further, not to have put the natural 

 interpretation upon the facts which he had observed, namely, that 

 mercurous nitrate decomposes (dissociates) into mercuric nitrate and 

 mercury, and, after having been once recorded in Gmelin's Handbook, 

 the facts pointing to this decomposition ceased to be mentioned or re- 



