E 238 ] 



per, of metal of any kind, this air was immediately 

 produced in as great plenty as before ; fo that this 

 remarkable kind of air is, in fact, 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 affected by the quick- 

 filver, with which it is in contact ; for it was always 

 diminished, more or lefs, by Handing. 



This elaftic acid vapour extinguifhes flame, and is 

 much heavier than common air 5 but how much 

 heavier, will not be eafy to afcertain. A cylindrical 

 glafs vefTel, 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 leen 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 pofTefTion of a new fubject of 

 experiments, viz. an elaftic acid vapour, in the 

 form of a permanent air, eafily procured, and 

 effectually confined by glafs and quickfilver, with 



which 



