[ 2 3 8 ] 
per, or metal of any kind, this air was immediately 
produced in as great plenty as before ; fo that this 
remarkable kind of air is, in fadt, nothing more 
than the vapour, or fumes of fpirit of fait, which 
appear to be of fuch a nature, that they are not liable 
to be condenfed by cold, like the vapour of water, 
and other fluids. This vapour, however, feems to 
lofe its elafticity, in fome meafure, gradually, unlefs 
it fhould be thought to be affedted by the quick- 
filver, with which it is in contadl ; for it was always 
diminifhed, more or lefs, by ftanding. 
This elaftic acid vapour extinguifhes flame, and is 
much heavier than common air; but how much 
heavier, will not be eafy to afcertain. A cylindrical 
glafs veflel, about three fourths of an inch in dia- 
meter, and four inches deep, being filled with it, 
and turned upfide down, a lighted candle may be 
let down into it more than twenty times before it 
will burn at the bottom. It is pleafing to obferve 
the colour of the flame in this experiment ; for both 
before the candle goes out, and alfo when it is firft 
lighted again, it burns with a beautifully green, or 
rather light blue flame, fuch as is feen when com- 
mon fait is thrown into the fire. 
When this elaftic vapour is all expelled from any 
quantity of fpirit of fait, which is eafily perceived 
by the vapour being condenfed by cold, the re- 
mainder is a very weak acid, barely capable of dif- 
folving iron. 
Being now in the pofleflion of a new fubjedt of 
experiments, mz, an elaftic acid vapour, in the 
form of a permanent air, eafily procured, and 
effectually confined by glafs and quickfilver, with 
which 
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