154 £>'*• Priestley’s Experiments and Obfervations on 
of the fixed air carries off part of the water in the men- 
ftruum ; and that this part of the weight is about one-half of 
the whole. 
I muff obferve, that the fuppofition of water entering into 
the conftitution of all the kinds of air, and being, as it were, 
their proper bajis , that without which no aeriform fubftance 
can fubfift (which the preceding experiments render in a high 
degree probable) makes it unneceflary to fuppofe, as myfelf as 
well as others have done, that water confifts of dephlogifti- 
cated air and inflammable air, or that it has ever been either 
compofed or decompofed in any of our procefles. 
That water is decompofed when inflammable air is procured 
from iron by fleam, is not probable ; flnce the inflammable prin- 
ciple may very well be fuppofed to come from the iron, and the 
addition of weight acquired by the iron may be afcribed to the 
water which has difplaced it. Alfo when the fcale of iron , 
or finery cinder , is heated in inflammable air, it gives out what 
it had gained, viz. the water. 
The molt plaufible objection to this hypothefis is, that iron 
gains the fame addition of weight, and becomes the fame 
thing, whether it be heated in contact with fleam, or fur- 
rounded by dephlogifticated air. But from the preceding expe- 
riments it appears, that by far the greateft part of the weight 
of dephlogifticated air is water ; and the fmall quantity of 
acid that is in it may well be fuppofed to be employed in 
forming the fixed air y which is always found in this procefs : 
for that there is one common' principle of acidity, and that all 
the acids are convertible into one another (at leaft the nitrous 
acid into fixed air) is by no means an improbable fuppofition, 
though we are not yet in pofleflion of any procefs by which it 
may be done. It is pretty evident that, in this refpedt, nature 
a&ually does what we are not able to do. 
2 
111 
