6 Diftingut/hing Marks of Alkalis. [Book VL 



line fubftance left after evaporation is an alkali almoft 

 entirely deprived of carbonic acid. This procels is 

 founded oh the greater attraction which the carbonic 

 acid has for quick-lime than for the alkalis. 



The VEGETABLE fixed alkali, pot-afh or kali, 

 agrees in feveral circumftances with die former. It 

 is acrid when applied to the tongae, requires as great 

 a degree of heat to melt it ; and in a very ftrong heat 

 flies off totally in vapour. It differs from the fofiil 

 alkali in having a much ftronger attraction for water. 

 This alkali may be cryftallized, but not fo eafily as the 

 foffil. Little of the vegetable alkali has been found 

 in a ftate of nature, and that only as entering into the 

 compofidon of nitre. It is obtained in coniiderable 

 quantities from the afhes of almoft all land vegetables, 

 by infufing them in water; the liquid, when (trained 

 from the dregs, v<iil then contain the lalt in a ftate of 

 folution, and by evaporation we obtain the alkali in a 

 folid form. It is alfo eafily obtained from a fubftance 

 called tartar, which is depofit; d by wine. The pro- 

 perties and ufes of the vegetable- alkali are very limilar 

 to thofe of the mineral. 



The fixed alkalis are employed in feveral of the arts, 

 and particularly in that of making glafs; for though 

 many fubftances will fufe the vitrifiable earths, and 

 reduce them to a kind of glafs, the alkalis are found 

 the moft effectual and convenient. 



In the foap manufactory alfo the alkalis are a prin- 

 cipal and eflential ingredient. Common foap is in- 

 deed a combination of fixed alkali in a cauftic ftate 

 with fat and oily matters. A very fine fpecies of foap 

 is formed by the union of mineral alkali with olive- 

 oil, or oil of fweet almonds. In the making of this 

 fubftance, the alkali is firft rendered cauftic by boiling 

 it with half its weight of quick-lime, which abftracts 

 3 its 



