CYANIDE OF MERCURY. 661 



gaseous bodies. Iodide of mercury is slightly soluble in water, 

 but requires more than 6000 times its weight of water to dissolve 

 it. It is much more soluble in alcohol and in acids, particularly 

 with the assistance of heat. Iodide of mercury is very soluble 

 in iodide of potassium ; it is also dissolved by a hot solution 

 of chloride of mercury. 



When treated with sulphuretted hydrogen water, iodide of 

 mercury forms the compound Hg I + 2Hg S, which is yellow. 

 Iodide of mercury absorbs a whole equivalent of dry ammo- 

 niacal gas, HgI-fNH 3 . The compound is white, but loses 

 ammonia in the air and becomes red. Iodide of mercury unites 

 with other iodides, and forms a class of salts as extensive as the 

 compounds of chloride of mercury. They have been studied 

 by M. P. Boullay.* Iodide of mercury also combines with 

 chlorides ; it is dissolved by a hot solution of chloride of mer- 

 cury, and two compounds have been obtained on the cooling of 

 the solution, a yellow powder, Hg I + Hg Cl, and white dendritic 

 crystals, Hg I + 2Hg Cl. 



Cyanide of mercury, Hg Cy, 1595.7 or 127.87- This salt is 

 most easily obtained by saturating hydrocyanic acid with red 

 oxide of mercury. To prepare the hydrocyanic acid required, 

 the process of Winkler may be followed. Fifteen parts of 

 ferrocyanide of potassium are distilled with 13 parts of oil 

 of vitriol diluted with 100 parts of water, and the distillation 

 continued by a moderate heat nearly to dryness. The vapour 

 should be made to pass through a Liebig's condensing tube, 

 and be afterwards received in a flask containing 30 parts of 

 water. A portion of the condensed hydrocyanic acid is put 

 aside, and the remainder mixed with 16 parts of oxide of mer- 

 cury in fine powder, and well agitated till the odour of hydro- 

 cyanic acid is no longer perceptible. The solution is drawn 

 off from the undissolved oxide of mercury, and the reserved 

 portion of hydrocyanic acid mixed with it. The last addition is 

 necessary to saturate a portion of oxide of mercury, which 

 cyanide of mercury dissolves in excess. This operation yields 

 12 parts of the salt in question. Cyanide of mercury crystal- 

 lizes in square prisms, which are anhydrous, and resembles 

 chloride of mercury in its solubility and poisonous qualities. 

 The red oxide of mercury, even when dry, absorbs hydrocyanic 



* An. de Chim- et de Phys , t. 34, p. 337. 



