on the Jpecifc Gravities , &c. of Saline Subfances. 197- 
three fubftantial reafons may be afiigned ; firft, the proportion* 
of fixed air in a given weight of crude calcareous earth, is 
much greater than that of phlogifton in any metal, as will 
hereafter be {hewn,, it being in the former one- third of the 
whole, and that of phlogifton in the latter for the mod: part 
not even one-fixtho Secondly, much of the phlogifton com- 
bines with the acid itfelf during the dilution, and expels part 
of its fpecihc quantity of fire, , as Dr. crawford has fhewn, . 
and as 1 have lince experienced ; and this fire lnuft occafion feu- 
ftble heat. Thirdly, much of the phlogifton, during folution, . 
unites to the furrounding atmofphere, expelling alio part of 
its fpecific fire, and this alfo muft occafion .feniible heat ; and : 
hence it is, that metallic folutions in vacuo are generally, at- - 
tended with lels heat, though with a more violent effervefcence 
than , in open air. The folution of metallic calces is not : 
attended with as much heat as that of their refpebtive metals, , 
not only becaufe neither the diflolving acids -nor the, furrouiid- 
ing air is much phlogifticated ; ■ but alfo becaufe they contain- 
an elaftic fluid in a concrete ftate, which abforbs-much of the- 
fire given out by the difiblving acids, as it acquires an aerial . 
ftate. 
The origin and formation of inflammable air being thus 
explained, I now proceed to fhew its identity and homoge- 
neity with phlogifton. . By phlogifton is generally underftood 
that principle in combuftible bodies on which their inflamma- 
bility principally depends ; that principle to which metals owe 
their malleability and fplendor ; that which combined with ; 
vitriolic acid forms fulphur ; that which diminifhes refpirable 
air. Now inflammable air is that very principle which alone 
is truly inflammable, as Mr. volta has elegantly fhewn. In < 
efFeft, combuftible fubftances are either animal or vegetable. 
