96 



SALINES. 



[IV. 



The acid is then concentrated to 1.78, run off into deep, leaden 

 vessels, and gradually cooled to 32° F. After repose, the clear 

 portion is transvased into shallow pans and cooled down to 0°, 

 and* left until one-half of its volume has solidified, when the 

 congealed mass is to be separated and washed with pure acid. 

 These crystals are freed from adhering portions of sulphates 

 and arseniates of iron and lead, by fusion in glass vessels, 

 re-crystallization, and washing with pure acid. To obtain a 

 strong acid, the crystals must be melted and concentrated in 

 a platinum kettle. 



According to Wackenroder (Archiv. d. Pharm. (2) Iviii. 28), 

 the crystallized hydrate of sulphuric acid SO32HO, used by 

 Hayes as the source of his pure acid, may be readily obtained 

 by congealing sulphuric acid, rectified over sulphate of potassa 

 at 28.4° F. Very large rhombic crystals form and give, by 

 fusion at 71°, a liquid acid of 1.784 at 46°. The acid thus 

 prepared resolidifies at 39°. 



Bineau has constructed the following table of composition 

 of hydrated sulphuric acid, derived partly from his direct 



