2oz Continuation of the Experiments and Obfervatmis 
fome an earth, and others refpirable air. To thefe hypotheses 
1 thall oppofe one general obfervation, which is, that fince in- 
flammable air, when pure, that is, when di fen gaged from all 
heterogeneous fubftances which no way contribute to its inflam- 
es 
inability, has always the fame properties ; it muft, if it con^ 
fills of phlogiflon combined with any other fubftance, be 
always united to the fame fpecific fubftance ; that is, if this be 
an acid, it muft be always the fame fpecies of acid, or if an earth, 
it muft be always the fame fpecies of earth ; for we find, that 
fubftances, which are only generic ally the fame, always produce, 
with any other given fubftance, compounds whofe properties 
are very different from each other. Thus we fee that the dif- 
ferent fpecies of alkalies, or earths, or metals, produce with 
one and the fame fpecies of acid compounds effentially dif- 
ferent. This is a rule which, as far as I know, admits of no 
exception : and if we apply it to the abovementioned fuppofi- 
tions it will intirely deftroy them ; for it is impoffible to think, 
that the phlogifton can in every fubftance, that produces inflam- 
mable air, meet either the fame acid, or earth, or any refpi- 
rable air. 
But to be more particular, the following reafons demonftrate 
that an acid of any fort cannot be the bafis of inflammable air. 
i ft. Inflammable air has been, by Dr. priestley, feparated 
from metals by mere heat. Now metals contain no acid, ex- 
cept perhaps their dephlogifticated calx, which thofe eminent 
chemifts, BERGMAN and scheele, fufpeft to be of an acid 
nature ; but thefe calces cannot enter into the compofition of 
inflammable air, otherwife the inflammable air of each different 
metal would have different properties, as already fhewn : nor 
indeed are thefe the acids that have been fuppofed to enter into 
the compofition of inflammable air ; but rather thofe acids by 
6 whofe 
