274 ^''- Hef^^y on Ferments and Fermentation, 



. important difcoveries of Black and Prieftley, 

 and of feveral other philofophical chemifts, who 

 have endeavoured to emulate their examples, have 

 happily explained many of the operations of 

 chemiftry, which were, before, wholly unin- 

 telligible : and the prefent time forms one of 

 the mofl: diftinguiflied ^ras in the hillory of' that 

 fcience. We now underfland the nature of lime 

 and of alkalis ; the difference between a metal 

 and its calx ; the caufe of the increafe of weight 

 in the latter, and of its decreafe when returned 

 to a metallic forhn. The conftitution of atmof- 

 pheric air has been demonflrated — Various gafes 

 refembling air, in many points, but differing 

 from it in others, have been difcovered > and, 

 among thefe, an setherial fluid, fuperior in its 

 properties to common air, and capable of fup- 

 porting life and combuftion more vigoroufly 

 and durably. Our acquaintance with this pure 

 fluid, which forms the vital part of common air, 

 feems to promife much enlargement to our che- 

 mical knowledge, in the invefligation of its va- 

 rious combinations J and we have already de- 

 rived much information, relative to the conftitu- 

 tion of the acids, and of water, from the re- 

 fearches of philofophers into the nature of pure 

 air. 



Of the gafes which have lb much engaged the 

 attention of the pneumatic chemifts, fixed air, 

 or, as it has more properly been denominated by 



Sir 



