MERCURY 285 



the dose may be cautiously increased until toxic symptoms 

 appear, when the medicine should be suspended for a few 

 days, or if desirable, the injections may be continued in 

 diminishing doses until the degree of tolerance peculiar to 

 the patient has been ascertained. Then the optimum dose 

 may be given once a week for the remainder of the treatment. 

 Doses of arrhenal, horses, grs. viii. to grs. xxx. ; dogs, gr. | 

 to grs. ii. per day, given hypodermically in twenty parts of 

 boiled water. 



MERCURY AND ITS MEDICINAL COMPOUNDS 

 MERCURY. Hydrargyrum. Quicksilver. Hg. 



From its liquidity and volatility this metal is named 

 mercury ; to its silvery appearance it owes its synonym 

 hydrargyrum ; to its liquidity and metallic lustre such 

 appellations as aqua argentum, aqua metallica, and quick- 

 silver. Although occasionally found in metallic globules, its 

 most important source is the sulphide or cinnabar (HgS). 

 When the ore is roasted or heated with iron or lime, sulphur 

 is got rid of and mercury distils over. 



Mercury is easily distinguished by its liquidity and silver- 

 white lustre. It is tasteless and odourless ; freezes at 

 -40 Fahr., forming octahedral crystals ; slowly volatilises 

 at all temperatures, and boils at 662 Fahr., forming a dense, 

 colourless gas. Its specific gravity at 60 is 13*6, its atomic 

 weight 200. Triturated with fatty or saccharine substances, 

 as in the preparation of mercurial ointments, liniments, and 

 pills, the metal loses its fluidity and globular structure, is 

 reduced to the condition of a dark-grey powder, while a 

 small portion is oxidised. 



Mercury forms two series of salts the mercurous and 

 the mercuric. 



Mercurous salts in solution treated with hydrochloric 

 acid, produce a white precipitate of calomel (Hg 2 Cl 2 ) . Silver 

 and lead have similar white, insoluble chlorides ; and these 

 three are distinguished by their reaction with ammonia 

 solution, which blackens the mercurous chloride, dissolves 

 the silver chloride, but leaves the lead chloride unaltered. 



Mercuric salts treated with hydrochloric acid give negative 



