MERCURIC SALTS CHANGE INTO EACH OTHER. \Jl 



solution must not be poured off and replaced by water, but the loss of 

 water by evaporation be made good from time to time. 



Another instance of ill-defined and, therefore, unavailable in- 

 formation concerning the behaviour of mercury nitrates on boiling: 

 them in water is to be found in Poyg. Ann., 66 where Brooks, who 

 prepared a mercurous-mercuric nitrate, is made to say that in the air 

 mercurosic nitrate boiled with water becomes mercurous nitrate in 

 solution, and mercuric oxide and mercury metal separated ; while 

 with exclusion of air mercuric nitrate goes into solution, along with 

 traces of mercurous nitrate, leaving a residue of both oxides. 



Dissociation of mercurous nitrate by light. — Although dissociation of 

 mercurous nitrate in cold solution may be assumed to be caused by 

 the action of light, its occurrence has not been experimentally esta- 

 blished, because of the interference of the effects of light upon the 

 nitric acid. It may, however, be mentioned that strong daylight 

 soon darkens basic mercurous nitrate as it lies under its mother-liquor, 

 and such an effect in the case of some mercurous salts is certainly one 

 of dissociation. 



Oxidation of mercurous nitrate Inj oxygen at 160°. — A gram of 

 mercurous nitrate was heated at 150° for six hours with water lOcc, 

 in a sealed tube, the air in which had been displaced by oxygen, to 

 represent condensed air in the small space available. Much of the oxy- 

 gen was absorbed and 6.5 per cent, of the mercurous nitrate converted 

 to mercuric salt, partly in solution, partly in form of brilliant yellow 

 crystals of basic salt (both mercurous and mercuric). 



Another gram was heated in oxygen for five hours, but this time 

 all in solution in lOcc. of one per cent, nitric acid. In this experiment 

 more than 28 per cent, of the mercurous salt became mercuric nitrate. 

 Much oxygen had been absorbed and no nitric acid had been 

 reduced. 



