80 Royal Institution : — 



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 : 



H a ,S Sulphydric acid. C1 3 S. 



H a SO Wanting. Cl a SO. 



H a SO a Wanting. Cl^SO 2 . 



H 2 S0 3 Sulphurous acid. 



H a S0 4 Sulphuric acid. 



The compounds Cl a SO and CI 2 SO 2 are obtainable from the chloro- 

 representative of sulphydric acid, CI 2 S, by successive oxidation. The 

 first product actually afforded by the oxidation of sulphydric acid is 

 sulphurous acid, H 2 S0 3 , which is produced by the combustion of 

 sulphydric acid in air or oxygen. Conversely, sulphydric acid may be 

 obtained by deoxidating sulphurous acid with nascent hydrogen. 

 Sulphuric acid, H 2 S0 4 , results from the oxidation of sulphurous 

 acid, and by deoxidation can reproduce that body, as in the ordinary 

 process for the preparation of sulphurous acid. Here then, includ- 

 ing the chloro-representatives, is a second series of acids associated 

 with one another by a common increment of composition, and by 

 mutual metamorphosis. 



Sulphuric acid, H 2 SO\ is the representative on the sulphur series, of 

 perchloric acid, HC10 4 , on the chlorine series. Each contains one 

 atom of the radical which gives the special character to the acid, in the 

 one case chlorine, in the other sulphur. Each contains also four 

 atoms, or volumes, of oxygen ; but whereas perchloric acid contains 

 only one atom, or volume, of hydrogen, sulphuric acid contains two 

 atoms, or two volumes. And this difference in composition leads to a 

 marked difference in the properties of the two acids. Perchloric 

 acid, HC10\ has only one atom of hydrogen that can be replaced. 

 Hence it forms only one description of salt, such, for instance, as 

 perchlorate of potassium, KC10 4 , and only one description of ether, 

 such, for instance, as perchloric ether, EtCIO 4 . But sulphuric acid has 

 two hydrogen atoms that can be replaced. Hence it can form acid 

 salts, neutral salts, double salts, acid ethers, neutral ethers, double 

 ethers, and saline ethers, as shown in the Table. 



H 2 S0 4 Sulphuric acid. 



KHSO 4 Acid sulphate of potassium. 



K 2 SO 4 Neutral sulphate of potassium. 



KNiSO 4 Potassio-sulphate of nickel. 



EtHSO 4 Ethylo-sulphuric acid. 



Et 2 S0 4 Neutral sulphate of ethyle. 



EtMeSO 4 Ethylo-sulphate of methyle. 



EtK SO 4 Ethylo-sulphate of potassium. 



This property of forming acid and double salts, and acid and 

 double ethers, &c, indicates a fundamental difference in character be- 

 tween sulphuric and perchloric acids, a difference that is satisfactorily 

 represented by the difference in their formulae as here written down, 



