I860.] on Acids and Salts. 235 



When two volumes- of chlorhydric acid, for instance, are acted upon 

 by a red hot iron-wire, the chlorine is absorbed by the iron, and one 

 volume of hydrogen gas liberated. The two volumes of chlorhydric 

 acid yield one volume of hydrogen, or the original bulk of gas is 

 reduced to one-half by the absorption of its chlorine. The above 

 four acids may be looked upon as substitution-representatives, one of 

 another. 



Chlorhydric acid yields the following series of oxides, convertible 

 into each other by mutual metamorphosis, 



IICl Chlorhydric acid. 

 HCIO Hypochlorous acid. 

 HCIO2 Chlorous acid. 

 HCIO3 Chloric acid. 

 HCIO4 Perchloric acid. 



When chlorhydric acid HCl, is oxidated by permanganic acid, hypo- 

 chlorous acid HCIO, is produced ; and, conversely, chlorhydric acid 

 may be reproduced by the deoxidation of hypochlorous acid. Hypo- 

 chlorous acid, when heated, breaks up into chloric acid HCIO3, and 

 other products. When chloric acid is deoxidated by nitrous acid, it 

 becomes chlorous acid HCIO2 ; and, when oxidated at the positive 

 pole of a galvanic battery, it becomes perchloric acid HCIO4. Here 

 then is a series of associated acids, expressed as unitary molecules, by 

 the simplest possible formulae, and arranged in a series, the successive 

 members of which differ from one another in composition by an incre- 

 ment of one atom, or volume, of oxygen. 



(^.) There are four other binary compounds of hydrogen, two 

 volumes of each of which, however, contain two volumes of hydrogen, 

 namely : 



HssO Water. 



HjS Sulphydric acid. 



HgSe Selenhydric acid. 



H^T Tellurhydric acid. 



A given volume of any one of these gases or vapours contains exactly 

 twice the quantity of hydrogen, that the same volume of any one of 

 the first class of gases contains. When two volumes of sulphydric 

 acid, for instance, are acted upon by a red hot iron-wire, the sulphur 

 is absorbed by the iron, and two volumes of hydrogen gas are liberated. 

 The two volumes of sulphydric acid yield two volumes of hydrogen, 

 or the abstraction of the sulphur produces no alteration in the bulk of 

 gas. The bihydric character of water, moreover, is well shown by the 

 experiment of its electrolytic decomposition, in which two volumes of 

 hydrogen are produced for every one volume of oxygen. 



In the sulphur series of oxygen acids we have two gaps, which, 

 however, can be filled up by the chloro-representatives of the missing 

 bodies, thus : 



