SULPHURIC ACID. 91 



taining less oxygen, called nitrous acid, a substance 

 which is decomposed by sulphurous acid, when water 

 is present ; giving up a portion of its oxygen to the 

 sulphurous acid, and converting it into the sulphuric. 

 In fact, when sulphur is thus burnt, and the fumes 

 produced by its combustion are condensed in cold 

 water, a very acid liquid is formed, which is called 

 oil of vitriol, or sulphuric acid. 



180. It is a heavy, very corrosive, poisonous fluid, 

 although its elements are only oxygen and sulphur, 

 the one being that part of the air necessary to sup- 

 port life, and the other a tasteless, yellow, solid sub- 

 stance. Sulphuric acid in its free state is chiefly re- 

 markable as being one of the strongest acids we know, 

 destroying vegetable and animal substances: that is 

 to say, abstracting and combining with some of their 

 elements, and causing the others to enter into new 

 combinations ; and having a strong afiinity for bases, 

 with which it forms a class of compounds called sul- 

 phates : some of these are of very great importance, 

 and must be considered hereafter (159, 213, 224, 237.) 



181. Sulphuric acid is a most valuable substance 

 to the chemist ; being one of the strongest known 

 acids, it enables him to expel or drive out most other 

 acids from their combinations, and thus through its 

 agency many other acids are obtained pure and sepa- 

 rate, from their compounds with bases (167, 188, 195). 



182. Under certain conditions sulphur combines 

 with hydrogen to form sulphuretted hydrogen — a 

 transparent colorless gas, remarkable for the exceed- 



