Dr. Odling on Acids and Salts. 79 



from which they Were derived. The doctrine of substitutions affords 

 great assistance to the doctrine of series ; for when, as frequently 

 happens, a gap exists in any series, that gap can almost always be 

 filled up by a substitution-representative of the missing body. 



(o.) There are four acid compounds of hydrogen, two volumes of 

 each of which contain one volume of hydrogen, namely : 

 HF Fluorhydric acid. 

 HC1 Chlorhydric acid. 

 HBr Bromhydric acid. 

 HI Iodhydric acid. 

 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 :— 



HC1 Chlorhydric acid. 



HCIO Hypochlorous acid. 



HCIO 2 Chlorous acid. 



HCIO 3 Chloric acid. 



HCIO 4 Perchloric acid. 

 When chlorhydric acid, HC1, 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, HCIO 3 , and 

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

 becomes chlorous acid, HCIO 2 ; and when oxidated at the positive 

 pole of a galvanic battery, it becomes perchloric acid, HCIO 4 . Here 

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

 the simplest possible formulas, 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. 



(/3.) There are four other binary compounds of hydrogen, two 

 volumes of each of which, however, contain two volumes of hydro- 

 gen, namely : — 



H 2 Water. 



H 2 S Sulphydric acid. 



H 2 Se Selenhydric acid. 



H 2 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 



