146 XV. Priestley’s 'Experiments on the 
If thefe refults be examined as that of the fir ft experiment, 
with common air, it will be found that, in all thefe proceffes, 
there was lefs phlogifticated air, or inflammable air, after the 
procefs than before; and this refult being thus uniform, I can- 
not help concluding, that this kind of air is in part decom- 
pofed, and purified by this means ; fo that by this emiffion of 
dephlogifticated air which the heat expels from the acid, fome- 
thing, and probably phlogifton, is at the fame time imbibed 
from it ; which proves that phlogifticated air is no Ample fub- 
ftance, but a compound, and that phlogifton is one conftituent 
part of it ; for this acid acquires the fame colour, and all the 
fame properties, by adding to it any thing that is fuppofed to 
contain phlogifton. 
As the fpirit of nitre can be rendered fmoking, or phlogifti- 
cated, by the mere expulfion of dephlogifticated air, it is evi- 
dent, that it contains two principles in clofe affinity with each 
other, and that nothing is neceffary to render either of them 
confpicuous befides the abfence of the other. 
It is alfo natural to fuppofe, that, for the fame reafon that the 
dephlogijlic citing principle (as it may be called) is expelled, the 
phlogijlicating principle fhould enter ; fo that the purification of 
the air in contact with the acid may be a neceflary confequence 
of the expulfion of the pure air contained in it, the whole 
tending, as it were, to an equilibrium in this refpeft. It is 
therefore by no means difficult to conceive, that phlogifton 
fhould be extracted from the contiguous air at the fame time 
that the dephlogifticated air not pure (that is, containing a mix- 
ture of phlogifticated air) is driven out of it ; for the acid 
always containing phlogiftion, whatever air is contained in it, 
and expelled from it, may neceflfarily contain phlogifton or phlo- 
gifticated air ; but the purer air may be emitted, and the 
lefs 
