330 SULPHUR. 



Gypsum, or hydrated sulphate of lime 2CaO,S 2 O 6 -f HO+3HO 

 Johnston's hydrated sulphate of lime 2CaO, S 2 O 6 + HO 



Glauberite (sulphate of soda and lime) a Q j + S 2 O 6 



Chromate of potash and soda -^ a Q j + Cr 2 O 



Uses. Sulphuric acid is employed to a large extent in elimi- 

 nating nitric acid from nitrate of potash, and in the preparation 

 of hydrochloric acid and chlorine, from chloride of sodium, and 

 also in the processes of bleaching. But the greatest consump- 

 tion of this acid is in the formation of sulphates, particularly of 

 sulphate of soda, by the decomposition of which salt, nearly all 

 the carbonate of soda of commerce is at present procured. 



HYPOSULPHUROUS ACID. 

 Eg. 602.34 ; S 2 O 2 or SO 2 -fS ; not isolable. 



The hyposulphites are better known than hyposulphurous 

 acid itself, which is a body of little stability, quickly undergoing 

 decomposition, when liberated by a stronger acid from a solu- 

 tion of any of its salts, and resolving itself into sulphurous acid, 

 sulphuretted hydrogen and sulphur. These salts, long con- 

 sidered as a species of double salts, and called sulphuretted 

 sulphites, were first supposed to contain a peculiar acid by Dr. 

 Thomson and by Gay-Lussac, a conjecture afterwards verified 

 by Sir John Herschell, whose early researches upon this acid 

 form the subject of a memoir of great interest.* 



Preparation. The sulphite of soda, prepared by saturating 

 a solution of carbonate of soda by sulphurous acid (page 319), 

 is converted into hyposulphite, by digesting it upon flowers of 

 sulphur at a high temperature, but without ebullition. The 

 sulphurous acid assumes an atom of sulphur, and remains in 

 combination with the soda ; or, in symbols 



NaO + SO 2 and S = NaO-{-SO 2 , S. 

 The solution may afterwards be evaporated, (ebullition being 



* Edinburgh Philosophical Journal, vol. 1, pp. 8 and 396t 



