MERCURY SULPHITES AND OXYGENOUS SALTS. 105 



the touch of a hot wire at any point of a mass of it, or a rise of tempera- 

 ture to about 73° C. , or percussion. Another of the properties of 

 the sulphite, calling for notice, is its indifference to sufficiently dilute 

 nitric acid, although it is a basic or oxysalt. Another is that, when 

 dissolved by stronger acid, it rapidly changes- into the metameric 

 substance, mercurous sulphate. The same change takes place in the 

 oxysulphite, under any circumstances, upon keeping it for a day. The 

 metamerism shown by mercurous sulphate and mercuric oxysulphite, 

 is of very rare occurrence in inorganic chemistry, though so common 

 in organic chemistr3\ Treated with potassim hydroxide, three-fourths 

 only of its mercury are left as oxide, the rest dissolving as double sul- 

 phite. Sodium chloride leaves half the mercury as oxide, and dissolves 

 the other as double salts. 



Mercury hydrogen sulphite, Hrj (SOJI\. This salt we can get 

 only in dilute solution, by cautiously adding precipitated mercuric 

 oxide suspended in water to excess of sulphurous acid. Mercuric 

 oxide rashly added precipitates the sulphite next described. So, too, 

 strange to state, does a little sulphuric or nitric acid added to the sul- 

 phurous solution of the mercuric oxide. The solution is unstable, 

 slowly decomposing into metallic mercury and sulphuric acid. Potas- 

 sium hydroxide does not precipitate the mercury. 



Mercurosic sulphite^ Hg (SOgJ-^ Hg\, 4:Ho,0, can be prepared in two 

 sets of ways, either by hydrolysis of mercuric hydrogen sulphite, or by 

 some form of double decomposition. When sulphurous acid is treated 

 with precipitated mercuric oxide, mercuric hydrogen sulphite is first 

 formed, as already described, but the attempt to make much of it in 

 the same solution is at once followed by the precipitation of mercurosic 

 sulphite, and the generation of sulphuric acid, thus : — 



3 Hg {SO, H). + 0H^= Hg, {S0,).^+ SO, H^+ 3 SO, H^ 

 Mercuric oxide, in a thin paste with water, is treated with a stream of 



