TECHNICAL CHEMISTRY. 301 



retorts, as shown in Fig. 1, and yields a strongly fuming 

 liquid, to which the name of fuming sulphuric acid is given, 

 this, on addition of water, giving ordinary oil of vitriol. 



Sulphuric acid at the present day is made by a totally 

 different process. In order to understand the method as it 

 is now carried on, it will be necessary for us to inquire into 

 the chemical composition of the acid and the nature of the 



FIG. 1. 



reactions which take place when sulphur undergoes oxidation. 

 Sulphuric acid, like every other definite chemical compound, 

 possesses a constant composition, which we indicate by the 

 formula H 2 S0 4 , signifying that this body contains three 

 elements, hydrogen, sulphur, and oxygen, united together in 

 the proportion of two parts by weight of the first to thirty - 

 two of the second, and sixty-four of the last constituent. 

 When sulphur burns in the air, or in oxygen, it combines to 

 form the lower of its two oxides, termed sulphur dioxide, 

 and having the formula S0 2 . This body, belonging to the 

 class of acid-forming oxides, when brought into contact with 

 water, unites to form an acid 



