MERCURIC SALTS CHANGE INTO EACH OTHER. \Q^ 



sulphates, thiocyanates, oxalates, and iodides, and with all ammoniated 

 salts, or, again, when the mercurous compound is one which freely 

 changes, such as the oxide and the carbonate. 



Dissociation of mercurous salts into mercury and mercuric salts in 

 the presence of water is caused not only by an elevated temperature, 

 but by light also, even at the common temperature, and apparently in 

 all salts. 



The other proposition established in this paper is that some, anp 

 probably all, mercurous salts are oxiclisable by air, in presence of water, 

 when the temperature is much above 100° ; and that at and beîow that 

 temperature mercurous salts are not oxidisable in the air, or, if they 

 are, then so slowly that any effect of their oxidation is not recognisable 

 through being lost, by its smallness, in the effects of dissociation. 

 Mercurous oxide alone oxidises at the common temperature ; this fact 

 and that mercury itself does not, were established by Barfoed in 1883, 

 Berthelot's assumption that mercury is slightly oxidisable being, as 

 Barfoed shows, based on wrong apprehension of facts observed by him. 



Besides the two propositions substantiated by the present work 

 upon the interconvertibility of the two series of mercury salts, the fact 

 has been ascertained of there being another way in which mercurous 

 nitrate becomes a mercuric salt spontaneously, in presence of water, 

 which is that it is converted into mercuric nitrite and nitrate, both by 

 heat and by light. In so far as this is a case of the oxidising action 

 of nitric acid (namely, of that produced by the action of water on the 

 salt or else that added to prevent the formation of basic salts), its 

 occurrence is nothing new. But, under the circumstances, it is 

 remarkable and calls for consideration. One per cent, of nitric acid in 

 a ten per cent, solution of mercurous nitrate is amply sufficient to keep 

 away basic salts, even after much mercuric salt has been produced, and 

 a much stronger solution of the acid has no action upon mercurous 



