SULPHUR. 91 



and as a constituent of some spring waters. It is also formed 

 during the destructive distillation of organic matter containing 

 sulphur. The best mode of obtaining it is the decomposition 

 of metallic sulphides by diluted sulphuric or hydrochloric acid. 

 Ferrous sulphide is usually selected for decomposition : 



FeS + H 2 S0 4 FeSO 4 + H 2 S. 



Hydrosulphuric acid is a colorless gas, having an exceedingly 

 offensive odor and a disgusting taste. Water absorbs about 

 three volumes of the gas, and this solution is feebly acid. It is 

 highly combustible in air, burning with a blue flame and form- 

 ing sulphur dioxide and water. It is directly poisonous when 

 inhaled, the sulphur entering into combination with the iron of 

 the blood. Plenty of fresh air, or air containing a very little 

 chlorine, should be used as antidotes. 



Hydrosulphuric acid gas and its solution in water are fre- 

 quently used as reagents in analytical chemistry for precipitating 

 and recognizing metals. This use depends on the property of 

 the sulphur to combine with many metals to form insoluble 

 compounds, the color of which is frequently very characteristic : 



CuSO 4 + H 2 S = CuS + H 2 S0 4 . 

 The salts of hydrosulphuric acid are known as sulphides. 



Tests for hydrosulphuric acid or sulphides. 



1. Hydrosulphuric acid or soluble sulphides when added to 

 soluble salts of lead, copper, mercury, etc., give black precipi- 

 tates of the sulphides of these metals. 



2. From insoluble sulphides, liberate the gas by sulphuric or 

 hydrochloric acid and test as above. 



Bisulphide of carbon, Carbonei bisulphidum, CS 2 = 76. This 

 compound is obtained by passing vapors of sulphur over heated 

 charcoal. It is a colorless, highly refractive, very volatile and 

 inflammable, neutral liquid, having a characteristic odor and a 

 sharp, aromatic taste. It boils at 46 ; it is insoluble in water, 

 soluble in alcohol, ether, chloroform, fixed and volatile oils ; 

 for the two latter it is an excellent solvent. 



