PHYSICAL AND LITERARY. 215 



that it is compofed of an alkali and of a par- 

 ticular faline fubftance called the fedativs 

 fait, which adheres to the alkali in the fame 

 manner as an acid, but can be feparated by 

 the addition of any acid whatever, the added 

 acid joining itfelf to the alkaji in the place 

 of the fedative fait. As this conjunftion of 

 an acid with the alkali of borax happens 

 without the leaft effervefcence, our principles 

 lay Us under a neceffity of allowing that alkali 

 •to be perfectly free of air, which muft proceed 

 from its being incapable of union with fixed 

 air and with the fedative fait at the fame time: 

 .whence it follows, that, were we to mix. the 

 fedative fait with an alkali faturated with airj 

 the air would immediately be expelled, or the 

 two falts in joining would produce an effer* 

 vefcence. This I found to be really the cafe 

 upon making the trial, by mixing a fmall 

 quantity of the fedative fait with an equal 

 quantity of each of the three alkalis, rubbing 

 the mixtures well in a mortar, and adding a 

 little water. It is however proper in this 

 place to obferve^./that, if the experiments be 

 made in a different manner, they are attend- 

 ed with a Angular circumftance. If a fmall 

 quantity of the fedative fait be thrown into a 



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