112 



DIVEES AND HAGA. 



c;ise of the normal mercury dipotassium salt we know that nitric acid 

 of itself should act as represented by this equation — 



Hg(OHgOS02)2NHgN(S03Na)j+2HN03 = 



-Hg(OHgOS02)2NH + HN(S03Na)2 + Hg(N03)2 



— replacing the imidic mercury by hydrogen, but not touching the 

 oxy mercuric group, in conformity with its inability in other cases 

 (sulphites and sulphates) to do so when the group is joined to sulphu- 

 ryl. In the .absence of mercuric nitrate this reaction is slowly followed 

 by hydrolysis of the disodium hydrogen salt through the unavoidable 

 excess of nitric acid, but in presence of mercuric nitrate hydrolysis does 

 not take place. The mercuric nitrate ünishes the formation, just 

 formulated, of the oxymercuric hydrogen salt, in the way shown l)y 

 the equation — 

 HN(S03Na)2+3Hg(N03)2+'20H2 = HN(S020HgO),Hg + 2NaN03 + 4HN03. 



— from which equation it will also be sufficiently clear how the whole 

 chmo-e can be effected by mercuric nitrate without any addition of 

 nitric acid. 



From the constitution given to this salt may be seen why it can, 

 so remarkably, be left for days in a nitric-acid solution of mercuric 

 nitrate without hydrolysing. For hydrolysis can only occur when 

 some of the sulphonic group becomes acid, or SO3H, and here tlie 

 nitric acid, especially in pre-sence of much mercuric nitrate, is power- 

 less to displace the oxymercuric group by hydrogen. 



There remains now only to tabulate the three merciu'ic salts, 

 the constitution of which has been discussed, in order to bring out 

 their relations quite clearly, and particularly the intermediate relation 

 of the oxymercuric s<.dium salt. 



