Chap. 2 .] [ 5 ] 



CHAP. II. 



ALKALIS. 



Mineral fixed Alkali ; where found, Vegetable fixej Alkali; ho*.? 

 obtained, Ufe cf the fixed Alkalis in the Arts.-r-Ufe of Alkalis in 

 making Glafs. Procefs of making Soap, Volatile Alkali; bo-inj 

 obtained; a compound Body, Alkaline Air. 



MINERAL fixed alkali, foda or natron, is the 

 fait which is found recorded in antient hiftory 

 under the name of nitre. It is faid to be found in 

 Egypt in tolerably pure cryftals, and alfo in Perfia, 

 where it appears in a form refembling that of hoar, 

 froft. Even in Europe jc is found in fmall quantities 

 in mineral fprings, and alfo on the furface of new walls, 

 in the form of a damp and dewy efflorefcence. In a 

 compound ftate it is found in abundance; ic makes, 

 half the weight of common fait, and is alfo occafionally 

 found naturally combined with other acids. The mi- 

 neral alkali cannot be obtained from the native falts 

 containing it, without great labour and expence : what 

 is uled in the arts is procured by the burning of 

 certain -plants growing near the fea-fide. The crude 

 mineral alkali in commerce is called foda or barilla. 



Alkalis are either mild or cauftic: the latter is their 

 mod fimple ftate, as when mild they are united with 

 the carbonic acid, with which they form a kind of neu- 

 tral fait. Though the carbonic acid has lefs affinity 

 with the alkalis than any other acid, yet it is difficult 

 to feparate it entirely. The ufual method of accom- 

 plifhing it is to diflblve the mild alkali in water, to add 

 to this iolution fome quick-lime, and then to filtrate 

 the liquor, and evaporate it in clofed veflels , the fa- 

 B 3 line 



