as much propriety as that to which Dr. Black afid 
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 fhall 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 
alfo 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 demonflrated, 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 
