SALTS SULPHATES. 323 



c&mpound of sulphate and sulphite of potassa. The finest neutral 

 crystals of this salt are obtained when acid predominates in the mix- 

 ture. 



Not found among mineral bodies, but exists in some animal fluids, 

 and in the ashes and juices of some vegetables, as tobacco.* 



BI-SULPHATE OF POTASSA. 



1 . PREPARATION. By heating together three parts of sulphate of 

 potassa, and one of sulphuric acid ; discovered by Rouelle senior ; 

 may be obtained in needle formed crystals, and even in six sided 

 prisms. 



2. PROPERTIES. 



(a.) Soluble in 2 parts of water, at 60, and in less at 212. 



(b.) Melts readily, with the appearance of oil, but becomes of an 

 opake white on cooling ; heated for a long time, its superfluous acid 

 is dissipated, and it becomes sulphate of potassa. 



!c.) Taste acrid ; reddens the blue test colors. 

 d.) The bi-sulphate is usually obtained in the process for nitric 

 acid. 



(e.) With ice, it generates cold.f Of little use, except to form the 

 sulphate, which is done by neutralizing the excess of acid by chalk ; 

 it may be used in crystallizing alum, and is sometimes employed as 

 a flux. 



After the process for nitric acid, if the salt, while still fluid, is pour- 

 ed into a pan, it effloresces most beautifully in the course of a few 

 months, presenting a delicate downy coating of crystalline filaments, 

 which make their way over and down the sides of the vessel ; if it 

 is glazed, the glazing will peal off and leave the naked biscuit. 



It contains two proportions of sulphuric acid, and one of potassa, 

 40X2=80 acid, -f 48 potassa = 128 for its equivalent. 



SULPHATE OF SODA. 



1. NAMES. Named Glauber's salt, after a German chemist, who 

 discovered it in the residuum of the process for muriatic acid. 



2. NATURAL HISTORY. 



(a.) Found in sea water, and in the ashes of marine vegetables, 

 and in kelp. 



(b.) In the earth, near ASTRACHAN.{ 



(c.) In salt and mineral springs. 



(d.) Often effloresces at the surface of the ground, upon the walls 

 of subterraneous edifices and other buildings. 



* Four. III. 33. t Four. Ill, 39. t Kirw. Mfti 



