MERCURY. 177 



of mercury]. Mercurous chloride, like mercuric oxide, may be 

 made by two different processes, but the U. S. P. does not 

 state by which method calomel shall be made, though the pre- 

 cipitated salt is in a finer state of subdivision, and consequently 

 more energetic in its action than the sublimed article. 



The latter is made by thoroughly mixing with mercuric 

 sulphate a quantity of mercury equal to that contained in the 

 sulphate; by this operation mercurous sulphate is obtained, 

 which is mixed with sodium chloride, and sublimed from a 

 suitable apparatus into a large chamber, so that the sublimate 

 may fall in powder to the floor: 



HgS0 4 + Hg + 2NaCl = Na 2 SO 4 + Hg 2 01 2 . 



The second method for making calomel is the precipitation of 

 a soluble mecurous salt by any soluble chloride : 



Hg 2 2NO 3 + 2NaCl = 2NaNO 3 + Hg 2 Cl 2 . 



Mercurous chloride, made by either process, generally con- 

 tains traces of mercuric chloride, and should, therefore, be 

 washed with hot water until the washings are no longer acted 

 upon by ammonium sulphide or silver nitrate. 



Mercurous chloride is a white, impalpable, tasteless powder, 

 insoluble in water and alcohol; it volatilizes without fusing pre- 

 viously; when given internally, it should not be mixed either 

 with mineral acids, alkaline bromides, iodides, hydrates, or car- 

 bonates, all of which have a decomposing action upon this salt. 



Mercuric chloride, Hydrargyri chloridum corrosivum, HgCLj = 



270.5 (Corrosive chloride of mercury, Corrosive sublimate, Perchloride 

 or bichloride of mercury). Made by thoroughly mixing mercuric 

 sulphate with sodium chloride, and subliming the mixture, 

 when mercuric chloride is formed, and passes oft' in white fumes, 

 which are condensed in the cooler part of the apparatus, while 

 sodium sulphate is left: 



HgS0 4 + 2NaCl = Na 2 SO, + HgCl,. 



Mercuric chloride is a heavy, white powder, or occurs in 

 heavy, colorless, rhombic crystals or crystalline masses; it is 



