•i 98 Continuation of the Experiments and Ohfervations 
as horns, hair, greafe, wood, &c. 5 from all of which Dr. 
HALES has extrafted inflammable air ; or charcoal, from which 
Mr. Fontana has extracted it, as did Dr. priestley from 
refins, fpirit of wine, and aether, in all which it is the only 
principle that is inflammable, and they are inflammable only 
.in proportion as they yield it ; or phofphorus, from whofe acid 
Dr. priestley has obtained this air by means of minium, for 
it was the acid, and not the minium, that contained it, as Dr. 
priestley rightly conjectured, the acid obtained by deliquel- 
cence being never thoroughly dephlogifticated until heated and 
vitrified, as Mr. margraaf has fhewn ; or they are mineral 
fubftances, as fulphur, from which inflammable air has been 
feparated by means of fixed alkalies, and, according to Dr, 
priestley, alfo by means of marine air, or bitumens or bitu- 
minous fubftances, all of which may be made to yield it ; or 
metallic fubftances, as zinc and regulus of arfenic, both of 
which are inflammable ; but neither of them is fo when de- 
prived of its inflammable air : this is, therefore, the true and 
only principle of inflammability in any fubflance. I acknowledge 
that the inflammable air, proceeding from almoft all thefe fab* 
fiances, is exceeding impure; that it contains from fome a 
mixture of aerial acid or of oil, and from all fome part of the 
fubftance which yields it or expels it, and hence its lmell is 
different, according to the clafs of the fubftances from which 
it is ext rafted ; but it is equally true, that none of thefe fub- 
ftances contribute to its inflammability ; on the contrary, it is 
fo much the lefs inflammable (that is, requires fo much more air 
to be mixed with it before it flames) as it contains more of thefe 
heterogeneous fubftances. Hence inflammable air of the mo- 
raft'cs is never totally confumed * ; and, on the contrary, 
* 
* 1 5 Roz. 146. 
in flam- 
