662 MERCURY. 



acid, with the formation of water and evolution of heat. The 

 affinity of mercury for cyanogen appears to be particularly 

 intense ; oxide of mercury decomposing all the cyanides, even 

 cyanide of potassium and liberating potash. Cyanide of mer- 

 cury is consequently not precipitated by potash. Nor is it 

 decomposed by any acid, with the exception of hydrochloric, 

 hydriodic and sulphuretted hydrogen. By a heat approaching 

 to redness, cyanide of mercury is decomposed, and resolved into 

 mercury and cyanogen gas. When hydrocyanic acid is (digested 

 upon mercurous oxide, the mercuric cyanide dissolves, and 

 metallic mercury is liberated. 



Oxicyanide of mercury, Hg Cy-f Hg O, appears when hydro- 

 cyanic acid of considerable strength (10 or 20 per cent) is 

 agitated with red oxide of mercury in large excess, as a white 

 powder intermixed with the red oxide. It is sparingly soluble 

 in cold water, but may be dissolved out by hot water, and 

 crystallizes on cooling in transparent four sided acicular prisms. 

 When heated gently, it blackens slightly, and then explodes. 

 (Mr. Johnston, Phil. Trans. 1839, p. 113). 



Cyanide of mercury, when digested upon red oxide of mercury, 

 dissolves a large quantity of it, and forms, according to M. Kuhn, 

 a tribasic cyanide of mercury \ Hg Cy + 3HgO, which is more 

 soluble in water than the neutral cyanide, and crystallizes with 

 more difficulty in small acicular crystals. 



Cyanide of mercury and potassium, KyCy + HgCy, is formed 

 on dissolving cyanide of mercury in a solution of cyanide of 

 potassium, and crystallizes in regular octohedrons. Cyanide of 

 mercury forms also crystallizable double salts with other 

 cyanides, such as the cyanides of sodium, barium, calcium, 

 magnesium, &c. It also combines with chlorides, bromides, 

 iodides, and also with several oxi-salts, such as chrpmate and 

 formiate of potash, 2(KO, Cr O 3 ) + Hg Cy and KO, F + Hg Cy. 



Sulphate of mercury, Mercuric sulphate, HgO, SO 3 ; 1867 or 

 149.6 It is formed by boiling 5 parts of sulphuric acid upon 

 4 parts of mercury, till the metal is converted into a dry saline 

 mass. Sulphate of mercury is a white crystalline salt, neutral 

 in composition, but which, like most of the neutral salts of 

 mercury, cannot exist in solution. It gives a dense yellow 

 powder when decomposed by water, and sulphuric acid is 

 dissolved. This subsulphate is known as turbith mineral, a 

 name applied to it by the old chemists, because it was supposed 



