SULPHUR. 107 



2. Silver nitrate and barium chloride produce white precipitates of 

 silver thiosulphate and barium thiosulphate. The silver salt becomes 

 dark on heating ; the barium salt is soluble in much water and is 

 decomposed by hydrochloric acid. 



Hydrogen sulphide, H 2 S = 34. (Hydrosulphuric acid, Sulphu- 

 retted hydrogen.) This compound has been mentioned as being liber- 

 ated by the decomposition of organic matter (putrefaction) and as a 

 constituent of some spring waters. It is formed also 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 SO 4 = FeSO 4 + H 2 S. 



Experiment 11. Use apparatus shown in Fig. 11, page 102. Place about 20 

 grammes of ferrous sulphide in the flask, cover the pieces with water, and add 

 sulphuric or hydrochloric acid. Pass a portion of the washed gas into water, 

 another portion into ammonia water. Use the solutions for the tests mentioned 

 below. Ignite the gas at the delivery tube and notice that sulphur is deposited 

 upon the surface of a cold plate held in the flame. Place the apparatus in the 

 fume chamber during the operation. How much ferrous sulphide is required 

 to liberate a quantity of hydrosulphuric acid sufficient to convert 1000 grammes 

 of 10 per cent, ammonia water into ammonium sulphide solution ? The reac- 

 tion taking place is this : 



2NH 3 + H 2 S = : (NH 4 ) 2 S. 



Hydrogen sulphide is a colorless gas, having an exceedingly offen- 

 sive 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 forming sulphur dioxide and 

 water. It is directly poisonous when inhaled, its action depending 

 chiefly on its power of reducing, and combining with, the blood- 

 coloring matter. Plenty of fresh air, or air containing a very little 

 chlorine, should be used as an antidote. 



Hydrogen sulphide gas and its solution in water are frequently 

 used as reagents in analytical chemistry for precipitating and recog- 

 nizing metals. This use depends on the property of the sulphur to 

 combine with many metals to form insoluble compounds, the color 

 of which frequently is very characteristic : 



CuS0 4 + H 2 S : : CuS + H 2 SO 4 . 

 The salts of hydrosulphuric acid are known as sulphides. 



