xo Dr. Priestley's Experiments 
acid vapour, together with the water with which it was com- 
bined, being drawn off uncondenfed in every procefs. I once 
made twenty fucceffive explofions of this kind, in a copper 
tube, out of which I found that I drew 37 ounce meafures of 
air by the adlion of the pump, and found not a Angle drop of 
liquid, though near an hour was employed in the whole pro- 
eefs, and the veffel was never made more than a little warmer 
than my hand. This was a degree of heat by no means fuf- 
ficient to keep the whole of any quantity of water in a ftate 
of vapour; and is a circumftance that of itfelf fufficiently 
proves, that the vapour did not confift of water only. 
Indeed, I think it impoffible for any one to fee this vapour 
in a tall glafs veffel, and efpecially to obferve how it falls from 
one end of it to the other, and the time that is required to its 
wholly difappearing, without being fatisfied that it confifts of 
fomething elfe than mere water, the vapour of which would be 
more equally diffufed. If the appearance to the eye (hould 
flail to convince any perfon of this* the fenfc of fmell would 
do it : for even in a glafs veffel it is very offenfive, though it 
might not be pronounced to be acid * I conjedture, how- 
ever, that this, and every other fpecies of fmell , is produced by 
fome modification of the acid or alkaline principle. Some may 
be difpofed to afcribe this fmell to the iron from which the 
inflammable air was produced; but the fmell is the fame, or 
nearly fo, when the air is from tin, and would probably be the 
fame if it were from any other fubftance. 
Befides ufing atmofpheric air, which contains a greater pro- 
portion of phlogiftieated air, I have fometimes ufed dephlogifti- 
cated air which was not very pure; and in this cafe I have 
always obferved, that the liquor I procured had lefs colouiy 
and was lefs fenfibly acid. 
