82 CHEMISTRY FOR AGRICULTURAL STUDENTS 



The chloride of silver is an insoluble salt of characteristic 

 appearance. Unlike other insoluble silver salts, it is not 

 acted upon by acids, but combines with ammonia, forming 

 a soluble compound. The solution of a chloride may there- 

 fore be distinguished by its giving a white precipitate with a 

 solution of nitrate of silver, insoluble in nitric acid, but soluble 

 in solution of ammonia. Test (i) distilled water, (2) tap 

 water, and (3) brine, for chlorides. 



XX. CHLORINE 



How can the element chlorine be obtained? If it were 

 possible to oxidise the hydrogen of hydrochloric acid to water 

 by means of the oxygen of the air, or an oxide which easily 

 loses a portion of its oxygen, such as red lead, chlorine might 

 be set free. Compare the action of Htharge and red lead on 

 hot concentrated hydrochloric acid. Note that in each case a 

 salt — the chloride of lead — crystallises out when the liquid 

 cools, but that with red lead a new gas of characteristic odour 

 is given off. The reactions, though they no doubt take place 

 simultaneously, may be expressed in three stages as follows : — 



Red lead = litharge + oxygen. 



Litharge -h hydrochloric acid = chloride of lead + water. 



Oxygen -f hydrochloric acid = chlorine + water. 



Express these equations by chemical formulae. The composi- 

 tion of chloride of lead has not yet been referred to, but if lead 

 combines with oxygen, oxygen with hydrogen, and hydrogen 

 with chlorine in the proportions represented by the formulae 

 PbO, OH2, and HCl (Fig. 36), the probable formula can be 

 deduced. 



