142 Chemistry. [Lecture 29. 



Egypt, in pure crystals, also in Persia, where it 

 appears like hoar frost : we do not, however, meet 

 with it so in Europe. We sometimes, indeed, 

 find some particles of it pure in mineral springs, 

 also on the surface of new walls, in the form of 

 a damp or dewy efflorescence ; but here, as well 

 as in mineral springs, it is only found in small 

 quantities. In a compound state it is found in 

 abundance. Common salt is a combination of 

 it with muriatic acid ; and this is found in such 

 quantities in the bowels of the earth, that it 

 thence derived the name of fossil salt. The soda 

 which is used in the arts is prepared from the 

 ashes of sea plants; that which is in greatest 

 perfection comes from the Mediterranean. The 

 sea plant which yields it most plentifully is called 

 kali, and by the natives soda, hence its name. 

 Soda is used in the manufacture of soap, and of 

 glass, in bleaching, dyeing, &c. In commerce 

 it is often called by the name of barilla. 



Potassa, which is the other fixed alkali, agrees 

 in several circumstances with the former : it is 

 acrid when applied to the tongue ; requires as 

 great a degree of heat to melt ; and in a very 

 strong heat flies off totally in vapour. It differs 

 from soda in having a much stronger attraction 

 for water, dissolving more readily, and in less 

 quantities, in general not requiring more than 

 an equal weight of water. Its union is attended 

 with some heat, and this is thought a proof of 

 its strong attraction for water. It is deliquescent, 



