380 MISCELLANEOUS PKODUCTS USED IN AGRICULTURE. XVI. 



Mercuric Chloride, HgCl 2 , corrosive sublimate. This well- 

 known, poisonous substance is one of the best disinfectants. 



Since it is practically non-volatile at ordinary temperatures 

 it can only be applied in solution and must come into actual con- 

 tact with the infected material. A solution of 1 part in 10,000 

 is sufficient to kill many micro-organisms, though many spores, 

 e.g., those of anthrax, require a 1% solution. According to 

 Lingard," a solution of 1 part in 960 destroys the tubercular 

 bacillus in from four to eight hours. Mercuric chloride com- 

 bines with albuminoid substances to form insoluble compounds, 

 and this fact sometimes interferes with its success as a disin- 

 fectant of matter containing proteids. It is said that in such 

 cases the addition of a mineral acid, e.g., hydrochloric acid, or 

 even of tartaric acid, to the solution greatly increases its 

 effectiveness. Recent experiments! throw some doubt on this 

 point. Mercuric chloride is a heavy crystalline substance. 

 Its solubility in water is greatly affected by temperature. 

 100 parts of water dissolve 



5-73 parts of the salt at 



6-57 10 



7-39 ,, ,, 20 



53-96 100 



It is also soluble in alcohol, ether, and glycerine. The salt 

 melts at 288 and volatilises at 303; its vapour is very 

 poisonous. 



Mercuric chloride is largely employed in surgery as an 

 antiseptic, solutions containing from 1 in 1000 to 1 in 10,000 

 being used. 



Mercuric iodide, HgI 2 , and cyanide, Hg(CN) 2 , are also 

 employed as disinfectants. 



Mercury salts and mercury vapour are very poisonous to 

 plants, mercury even at the ordinary temperatures giving off 

 into the air sufficient vapour to kill many plants.] 



Plant Poisons. A great many substances act as plant 

 poisons. Some, however, w 7 hich when in solution are most 



* Quoted by Blyth, A Manual of Public Health, 1890. 

 t 'lark, Jour. Chein. Soc. 1901, abst. ii. 526. 

 J Dafert, Jour. Chem. Soc 1901, abst, ii. 269. 



