466 COMPOUND PRODUCTS. CHAP. I. 



dients of which they are composed. These may 

 be reduced to three, alkalies, earths, and metals, 

 which must therefore be considered as ingredients 

 in the composition of the vegetable. But vegetable 

 ashes contain also a variety of other principles, oc- 

 curring, however, in such small proportions as gene- 

 rally to escape observation. Perhaps they contain 

 all substances not capable of being volatilized by 

 the action of fire. 



SECTION XXVI. 



Alkalies. 



Whence THE alkalies are a peculiar class of substances, 

 ' distinguished by a caustic taste and the property of 

 changing vegetable blues to green. They are gene- 

 rally regarded as being three in number, potass, 

 soda, and ammonia, of which the two former only 

 are found in the ashes of vegetables. Ammonia is, 

 indeed, often obtained from vegetable substances by 

 means of distillation, but then it is always formed 

 during the process. 



Potass. If the ashes of vegetables burnt in the open ai 

 are repeatedly washed in water, and the water filtered 

 and evaporated to dryness, potass is left behind 

 The potass of commerce is manufactured in this 

 manner, though it is not quite pure. But it may 

 be purified by dissolving it in spirits of wine, and 

 evaporating the solution to dryness in a silver vessel. 



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