as much propriety as that to which Dr. Black arid 

 others have given that denomination, fince it is ori- 

 ginally part of fome folid fubftance, and exifts in an 

 unelaftic flate, and therefore may be alfo called fac- 

 titious. The term mephitic is equally applicable to 

 what is called fixed air, to that which is inflammable, 

 and to many other kinds; fince they are equally 

 noxious, when breathed by animals. Rather, how- 

 ever, than to introduce new terms, or change the 

 fignification of old ones, I {hall ufe the term fixed 

 air, in the fenfe in which it is now commonly ufed, 

 and diftinguifh the other kinds by their properties, or 

 fome other periphrafis. I {hall be under a neceflity, 

 however, of giving a name to one fpecies of air, to 

 which no name was given before. 



Of FIXED AIR. 



Fixed air is that which is expelled by heat from 

 lime, and other calcareous fubftances, and, when 

 deprived of which, they become quick-lime. It is 

 alio contained in alkaline falts, and is generated in 

 great quantities from fermenting vegetables ; and 

 being united with water, gives it the principal pro- 

 perties of Pyrmont- water. This kind of air is alfo 

 well known to be fatal to animals; and Dr. Mac- 

 bride has demonftrated, that it checks or prevents 

 putrefaction. 



Living for fome time in the neighbourhood of a 

 public brewery, I was induced to make a few expe- 

 riments on this kind of air, there being always a 

 large body of it, ready formed, upon the furface of 

 the fermenting liquor, generally about nine inches 



or 



