328 SULPHUR. 



most advantage in the first mode, when concentrated, and in 

 the second when considerably diluted. 



The presence of sulphuric acid in a liquid may always be de- 

 tected by means of chloride of barium, which produces with 

 this acid a white precipitate of sulphate of barytes, insoluble 

 in both acids and alkalies. 



Sulphates. Of no class of salts do chemists possess a more 

 minute knowledge than of the sulphates. The sulphates of 

 zinc, magnesia and other members of the magnesian family 

 correspond closely with the hydrate of sulphuric acid. Thus 

 of the seven atoms of water which the crystallized sulphate of 

 magnesia possesses, it retains one at 400, and is then analogous 

 to the sulphate of water of sp. gr. 1.J8; the formula of these 

 two salts being, 



MgO, SO 3 + HO, 

 HO, SO 3 + HO. 



and the atom of water in both salts may be replaced by sulphate 

 of potash, when the sulphate of water forms the salt called the 

 bisulphate of potash, and the sulphate of magnesia forms the 

 double sulphate of magnesia and potash, of which the formulee 

 also correspond : 



HO, SO 3 + KO, SO 3 

 MgO, SO 3 + KO, SO 3 . 



In all these sulphates, there is one atom of acid to one of base. 

 But with potash, sulphuric acid forms a second salt, in which 

 two of acid are combined with one of base, and which has 

 lately been obtained in a crystallized state by M. Jacquelin.* 

 The sulphates are known to correspond with the chromates, and 

 this new salt corresponds with red chromate or bichromate of 

 potash. A third sulphate of potash is to be looked for, corres- 

 ponding with the terchromate of potash. The series of anhy- 

 drous sulphates of potash, admitting the latter, will therefore be 



I. II. III. 



Sulphate of potash KO + SO 3 KO + SO 3 K + SO 4 



Bisulphate of potash KO + 2SO 3 KO + S 2 O 6 K + S 2 O 7 



Tersulphate of potash KO + 3SO 3 KO + S 3 O 9 K + S 3 O 10 



* An. de Ch. et de Ph. t. 70, p. 311. 



