164 s - HADA; HOW MERCUEOUS AND 



nitrate in the dark, even at 100°. But either at 150°, and then in a 

 few hours ; or, at the common temperature in strong daylight, slowly 

 in the course of days, though at a rate growing with the duration of 

 the experiment, a large fraction of the mercurous salt can become 

 mercuric, without separation of mercury. 



In analysing this change, it seems right to admit that nitrous 

 acid is essential to start the action, that traces of this acid are generated 

 by the heat or light, even in such weak nitric acid, and also that the 

 dissociation of the mercurous nitrate is caused by the same agency. 

 The ultimate change is represented by — 



(HgNO s ) 2 + 3HN0 3 =2Hg(N0 3 \ + HN0 2 +H 2 0; 

 but this includes those of 



(HgN0 3 ) 2 = Hg + Hg(N0 3 ) 2 ; 

 Hg + HN0 3 + HN0 2 =Hg(N0 2 ) 2 + H,0 ; 

 Hg(N0 2 ) 2 + 2HN0 3 = Hg(N0 3 ) 2 + 2HN0 2 ; 



the increase in nitrous acid being the cause of acceleration of rate of 

 change. 



Mercury nitrates. 



Conversion of mercuric nitrate to mercurous nitrate. — A solution of 

 mercuric nitrate shaken violently for a very short time with large 

 excess of mercury is fully converted into ona of mercurous nitrate. 

 This simple and perfect method of making a solution of mercurous 

 nitrate, free from nitrous acid, has been in use in this laboratory for 

 years. The solution of mercuric nitrate may be as weak as may be 

 desired, but it should not contain much more than 10 per cent, of 

 metal, for this becomes doubled in the process. The violent shaking 

 is conveniently carried out in a stoppered bottle. 



