180 METALS AND THEIR COMBINATIONS. 



(a double compound of the sulphide of mercury in combination 

 with the mercuric salt), which soon turns black : 



HgCl 2 + H 2 S = 2HC1 + HgS. 



The black, amorphous, mercuric sulphide may be converted 

 into the red, crystallized variety, by sublimation, and is then 

 the officinal preparation known as red sulphide of mercury, Hydrar- 

 gyrum sulphidum rubrum, cinnabar, or vermilion. It forms brilliant, 

 dark red, crystalline masses, or a fine, bright, scarlet powder, 

 which is insoluble in water, hydrochloric or nitric acid, but 

 soluble in nitrohydrochloric acid. 



Mercuric and mercurous sulphides may also be made by tritu- 

 rating the elements mercury and sulphur in the proper pro- 

 portions, when they combine directly. 



Ammoniated mercury, Hydrargyrum ammoniatum, NH 2 HgCl = 

 251.1 ( White precipitate, Mercur ammonium chloride}. This com- 

 pound is made by pouring solution of mercuric chloride into 

 water of ammonia, when a white precipitate falls, which is 

 washed with highly diluted ammonia water and dried at a low 

 temperature : 



HgCl 2 + 2NH 4 HO = NH 2 HgCl + NH 4 C1 + 2H 2 O. 



As shown by the composition of this compound, it may be 

 regarded as ammonium chloride, NH 4 C1, in which two atoms of 

 hydrogen have been replaced by one atom of the bivalent mer- 

 cury. (There are many compounds known in which metallic 

 atoms replace hydrogen in salts of ammonium ; the ammonium 

 copper compounds belong to this group of substances.) 



Ammoniated mercury is a white, tasteless, insoluble powder. 



Antidotes. Albumen (white of egg), of which, however, not 

 too much should be given at one time, lest the precipitate 

 formed by the mercuric salt and albumen be redissolved. The 

 antidote should be followed by an emetic to remove the albu- 

 minous mercury compound. 



