MERCURIC SALTS CHANGE INTO EACH OTHER. \Q^ 



(Literat ure). — What has long been known and recorded of the 

 possibility of combining mercuric nitrate with mercury is this. 

 Bucholz (1810), for the preparation of mercurous nitrate, directs 

 (according to Gmelin's Handbook) that the mixture of basic mer- 

 curous and mercuric nitrates, obtained by dissolving mercury in 

 strong nitric acid and evaporating to dryness, shall be triturated 

 with mercury and a little water, and the product be dissolved 

 in hot water and a little nitric acid. Lefort (1845 ; Annalen, 

 56) says that it is true that mercuric nitrate, occurring along 

 with mercurous nitrate, may be converted into mercurous salt by 

 boiling the dilute solution with mercury, but that the boiling 

 must be long continued. In a paper on mercurous oxide (' The be- 

 haviour of mercurous salts with soda' ; in Danish, 1883 ; /. pht. Cli. 

 1888) Barfoed mentioned the fact that mercuric nitrate solution 

 dissolves finely divided mercury. But so little has this fact been 

 generally known that, for instance, Bruns and von der Pfordten in 

 1888 (Berichte) showed themselves to be unaware of it. Nowhere 

 does it appear to be known that, in a few minutes, mercuric nitrate can 

 be fully converted into mercurous nitrate by violently shaking its cold 

 solution with excess of liquid mercury. 



The stability of mercurous nitrate. — Before treating of the ways in 

 which mercurous nitrate passes into mercuric nitrate, something has to 

 be said as to its stability. It must be a matter of common observation 

 that, as Gmelin-Kraut-Jörgensen's Handbuch states, mercurous nitrate 

 kept for some time becomes yellow through partial oxidation. But 

 this, I have found, is not true of the carefully prepared salt. As 

 Marignac pointed out (1849), its crystals usually enclose mother-liquor, 

 and this is strongly acid. By selecting small clear crystals, or crush- 

 ing large ones, and thoroughly pressing in filter paper, the salt is 

 obtained in a stable condition. If it is to be kept, as usual, in a bottle, 



