J896.] P. C. Ray— On Mercurous Nitrite. $ 



Ifc is thus evident tliat in the clear solution we have both a m^.Tcu- 

 rnus and a inercuric salt as well as a vitrite. Urea does not give the 

 faintest opalesconoe to the lic^uid, showing the absence of mercuric 

 nitrate. 



Quantitative Analysis. 



A. Estimation of Mercury. 

 In determining the composition of the salt, the amount of mercury 

 in it will have the predominating voice, on account of its high atomic 

 weight; the nitrogen playing only a minor part. The estimation of 

 this metal will therefore be described somewhat in detail. 



It has already been shewn that when the salt is heated with a 

 large bulk of water, metallic mercury separates out, leaving in solution 

 both an ous and an ic salt. The mercury thus liberated sometimes 

 collects readily into a single globule ; sometimes it remains as a ^yqj 

 powder, the whole of which it is difficult to aggregate into globules, 

 even after continued heating with hydrochloric acid. For estimation, 

 the mercury is now transferred to a tared crucible and kept under a 

 dessicator. The mercury weighed in this form will be termed "free" 

 mercury all along. 



The solution decanted off the mercury with the rinsings of the 

 vessel is considerably diluted with water and an excess of hydrochloric 

 and phosphorous acids added to it. The mixture is now allowed to 

 stand overnight and the precipitate of mercurous chloride weighed in 

 the usual way. When, however, it is desired to estimate the ous and 

 the ic salts separately, treatment with sodium chloride is resorted to 

 previous to the addition of hydrochloric and phosphorous acids, and the 

 calomel then weighed in two instalments. Although this method yields 

 accurate results, it often proves a very tedious one. After removal of 

 the calomel by HCI + H3PO3, and further dilution of the filtrate with 

 water, a small quantity of precipitate, varying from a few centi- to 

 milligrams is generally obtained the succeeding day, and so on. Pro- 

 bably it was the nitrous acid necessarily present in the liquid which 

 caused this kind of retardation in the precipitation of calomel.* 



dn a few cases the mercury in the ic Sii.lt was estimated as the 

 sulphide. But this method is almost equally troublesome on account 

 of the large quantity of sulphur set free. The pores of the filter-paper 

 get choked up and the filtration, though carried on under reduced 

 pressure with the aid of Bnnsen's pump, proceeds very slowly. JNfore- 

 over the precipitate has to be digested with a strong solution of sodium 



* Jn the estimation of mercurous nitrate no such retarJation occurs. 



