366* CHLORINE. 



decomposes sulphurous acid and occasions, after standing some 

 time, a brown precipitate containing sulphur in combination 

 with tin (Girardin.) To purify hydrochloric acid, it should be 

 diluted till its sp. gr. is about I.I, for which the strongest acid 

 requires an equal volume of water ; and with the addition of a 

 portion of chloride of barium, the acid should then be redistilled. 

 As the acid brings over enough of water to condense it, Liebig's 

 condensing apparatus (page 60) can be used in this distillation. 

 The pure acid thus obtained is strong enough for almost every 

 purpose, and has the advantage of not fuming in the air. Hy- 

 drochloric acid, like chlorine and the soluble chlorides, gives 

 with nitrate of silver a white curdy precipitate, the chloride of 

 silver, soluble in ammonia, but not dissolved by hot or cold 

 nitric acid. 



Hydrochloric acid belongs to the class of hydrogen acids, or 

 hydracids, which do not exist in salts. On neutralizing this 

 acid with soda or any other basic oxide, no hydrochlorate of 

 soda is formed, but the hydrogen of the acid with the oxygen 

 of the soda forming water, the chlorine and sodium combine and 

 produce a metallic chloride. Zinc and the other metals which 

 dissolve in dilute sulphuric acid, with evolution of hydrogen, 

 dissolve with equal facility in this acid, with the same evolution 

 of hydrogen, and a chloride of the metal is formed. 



COMPOUNDS OF CHLORINE AND OXYGEN. 



Chlorine and oxygen gases exhibit no disposition to combine 

 with each other in any circumstances, but this is not incon- 

 sistent with their forming a series of compounds, as nitrogen 

 and oxygen, which exhibit a similar indifference to each other 

 also do. The oxides of chlorine are four in number, and all 

 bear acid appellations, namely : 



Hypochlorous acid. . . Cl O 



Chlorous acid Cl O 4 



Chloric acid Cl O 5 



Hyperchloric acid. . . Cl O 7 



Hypochlorous and chloric acids are always primarily formed 

 by a reaction occurring between chlorine and two different 

 classes of metallic oxides ; and the chlorous and hyperchloric 

 acids again are derived from the decomposition of chloric acid. 



