on the fpecific Gravities, &c. of Sciljne SatfianceS-, 20 f 
with iron or bifmuth, or by diftilling tartar vitriolate with 
reguius of antimony. It is this alfo that diminiffies refpirablc 
air, as Dr. triestley has clearly (hewn in the 5th vol. of his 
Obfervations, p. 84. ; for though in its complete aerial Hate, 
after it has ablorbed that large quantity of fire requifite to its 
aerial form, it difficultly and (lowly unites to refpirable air in 
the heat of the atmofphere, their points of contact through 
their difference of denlity being very {mail, and there being 
no fubftance at hand to receive the large portion of elementary 
fire they both contain, and of which they muff lofe a large 
proportion before they can combine together ; yet while in- 
flammable air is (as Dr. Priestley elegantly exprefles it) in 
its nafcent Hate, before it acquires its whole quantity of fpe- 
cific fire, refpirable air eafily unites to it, and is diminiffied in 
proportion to its purity; but if to a mixture of' both, igneous 
particles of fufficient denfity to be vifible be introduced, a de- 
gree of heat is excited, which, as it rarifies the dephlogifficated 
part of refpirable air to a greater degree than it can inflammable 
air *, brings both into nearer contact, increafes their attra&ion 
to each other, and both uniting give out their fire, or in other 
words inflame , when in proper proportion to each other, with- 
out any decompofition of either, unlefs the lofs of a great 
part of their fpecific fire be called a decompofition, which lofs 
is not u finally called a decompofition ; for water is never faid 
to be decompofed when it becomes ice, nor metals when they 
become folid on cooling. 
In anfiwer to all this it will be faid, that inflammable air un- 
doubtedly contains phlogifton, which produces all the before- 
mentioned -effects ; but that the phlogifton it contains is united 
to fiome other fiubftance, which fome will have to be an acid, 
^ 5 PR IEST. 359. 
Vol. LXXIL D d fome 
1 
