[ 2 37 3 
that was admitted to it; but fo very great a quantity 
of this air difappeared upon the admifiion of a very 
fmall quantity of water, that I could not help con- 
cluding that appearances favoured the former hy- 
pothefis. I found, however* that when I admitted 
a- much fmaller quantity of water, confined in a 
narrow glafs tube, a part only of the air difappeared, 
and that very flowly, and that more of it vanifhed 
upon the admifiion of more water. This obfer- 
vation put it beyond a doubt, that this air was pro- 
perly imbibed by the water, which, being once fully 
faturated with it, was not capable of receiving any 
more. The water thus impregnated tailed very 
acid, even when it was much diluted with other 
water, through which the tube containing it was 
drawn. It even difiblved iron very fail, and gene- 
rated inflammable air. This lail obfervation; toge- 
ther with another which immediately follows, led 
me to the difeovery of the true nature of this re- 
markable kind of air, as it had hitherto been called. 
Happening, at one time, to ufe a good deal of 
copper and.a fmall quantity of fpirit of fait, in the ge- 
neration of this kind of air, I was furprized to find that 
air was produced long after, I could not but think that 
the acid muil have been faturated with the metal; 
and I alfo found that the proportion of inflammable 
air to that which was abforbed by the water con- 
tinually diminilhed, till, inftead of being one fourth 
of the whole as I had firfi: obferved, it was not fa 
much' as one twentieth. Upon this, I concluded 
that this fubtle air did not arife from the copper, 
but from the fpirit of fait; and prefently making 
the, experiment with the acid only, without any cop- 
4 " per. 
