MERCUROUS COMPOUNDS. (>'53 



Sulphate of black oxide of mercury, Mercurous sulphate, HgO, 

 SO 3 ; 3132.8 or 251.04. It is obtained by digesting 1 part of 

 mercury in 1 i parts of sulphuric acid, avoiding a high tempera- 

 ture, and interrupting the process as soon as all the mercury is 

 converted into a white salt. It is also precipitated when sul- 

 phuric acid is added to a solution of the nitrate of the same 

 oxide. The salt may be washed with a little cold water. It 

 crystallizes in prisms, and requires 500 times its weight of cold 

 and 300 of hot water to dissolve it. With water of ammonia this 

 salt gives a dark grey powder, containing ammonia or its elements. 



Nitrates of black oxide of mercury, Mercurous nitrates. The 

 neutral nitrate is obtained, when mercury is dissolved in an 

 excess of cold nitric acid, and crystallizes readily in transparent 

 rhombs. It is soluble with heat in a small quantity of water, 

 but is decomposed by a large quantity of water, and an in- 

 soluble subsalt formed, unless nitric acid be added to the water. 

 The formula of this salt is Hg 2 O, NO 5 +2HO. A subnitrate 

 is formed when the black oxide is dissolved in a solution of 

 the preceding salt, or when an excess of mercury is digested 

 in diluted nitric acid at the usual temperature. It crystallizes 

 readily in white and opaque rhombic prisms, which contain, 

 according to both G. Mitscherlich and Kane, 2NO 5 , 3Hg 2 O 

 and 3HO. This salt was observed by the former chemist to 

 be dimorphous. When dissolved by dilute nitric acid, it gives 

 the neutral salt. The subnitrate is soluble in a little water, 

 but when treated with a large quantity, it leaves unclissolved, like 

 the neutral nitrate, a white powder, which as long as the super- 

 natant liquid is acid retains its colour, but if it be washed with 

 water becomes yellow. The yellow subnilrate of mercury was 

 found to contain NO 5 , 2Hg 2 O and HO (Kane). When very 

 dilute ammonia is added to the preceding soluble nitrates, 

 without neutralising the whole acid, a velvety black precipitate 

 falls, know as Hahnemanris soluble mercury. This salt contains, 

 according to the analysis of G. Mitscherlich, NO 5 , 3Hg 2 O and 

 NH 3 . But when pains were taken to avoid decomposition of 

 the salt in washing it, its composition was found by Dr. Kane 

 to be NO 5 , 2Hg 2 O and NH 3 . 



Acetate of black oxide of mercury, Hg 2 O, C 4 H 3 O 3 , falls, 

 when acetic acid or an acetate is added to the nitrate, in crystalline 

 scales of a pearly lustre. It is anhydrous, and sparingly soluble 

 in water. 



