POTASH. 79 



soda, was procured in great abundance from a 

 plant called kali, by the Arabians. 



Alkalies have peculiar properties. They change 

 blue vegetable colours to green, and yellow to 

 reddish brown. They unite to oil and fat, forming 

 soap ; thus rendering them miscible with water. 

 They have an acrid and peculiar taste. They are 

 caustic, or act powerfully upon animal substances. 

 They combine with acids, forming with them a 

 peculiar class of salts in which the properties of 

 the acid and alkali disappear. 



Until lately, only three alkalies were known, 

 potash, soda, and ammonia. The two former 

 were called the jlxed, the latter the volatile alkali. 

 Their number is now increased by the addition of 

 lithia. 



POTASH. 



Potash had long been known by the name of 

 the vegetable alkali. 



It is procured from the ashes of burnt vegetables 

 in the following manner. Dried vegetables are 

 burned in heaps ; the ashes are collected and lix- 

 iviated with water. Thus the potash in the ashes 

 is dissolved, while the rest of the ashes is insoluble. 

 The solution is poured off from the sediment, and 

 evaporated : what remains*fe the potash of com- 

 merce, which is of a grayish colour, and contains 

 some impurities: these are separated by being 

 heated in a furnace. It is then white, and is 

 called pearlash. 



All wood ashes have in them more or less of this 

 alkali, and hence they are applied to the same 

 purposes as potash, or pearlash. 



