SILVER MERCURY. 339 



or by thoroughly mixing with mercuric sulphate a quantity of mer- 

 cury equal to that contained in the sulphate ; by this operation mer- 

 curous 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 -f Hg + 2NaCl = Na 2 SO 4 + 2HgCl. 



Precipitated calomel, being in a finer state of subdivision, acts 

 more energetically when used medicinally. It is obtained by pre- 

 cipitation of a soluble mercurous salt by any soluble chloride: 



HgNO 3 + NaCl = NaNO 8 + HgCl. 



Mercurous chloride, made by either process, generally contains 

 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, in- 

 soluble in water and alcohol ; it volatilizes without fusing previously ; 

 when given internally, it should not be mixed with either mineral 

 acids, alkali bromides, iodides, hydroxides, or carbonates, except the 

 action of the decomposition products be desired. 



Mercuric chloride, Hydrargyri chloridum corrosivum, Hg-CL, 

 268.86 (Corrosive chloride of mercury, Corrosive sublimate, Perchlo- 

 ride or bichloride of mercury). Made by thoroughly mixing mercuric 

 sulphate with sodium chloride, and subliming the mixture, when 

 mercuric chloride is formed, and passes off in white fumes which are 

 condensed in the cooler part of the apparatus, while sodium sulphate 



is left : 



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



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

 colorless, rhombic crystals or crystalline masses; it is soluble in 16 

 parts of cold and 2 parts of boiling water, and in about 3 parts of 

 alcohol, in 4 parts of ether, and in about 14 parts of glycerin; when 

 heated, it fuses and is volatilized ; it has an acrid, metallic taste, an 

 acid reaction, and strongly poisonous and antiseptic properties. 



The halogen salts of mercury are very little ionized in solution. On this 

 account, mercuric chloride is much less hydrolyzed than mercuric nitrate, that 

 is, there is not so much tendency to precipitate a basic salt. Mercuric chloride 

 also has the tendency to form complex salts. Thus sodium chloride increases its 

 solubility in water and causes the solution to become neutral, because of the 

 formation of the salt, HgCl 2 .NaCl or NaHgCl 3 . Mercuric chloride tablets are 



