VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. SIQ 



greater proportion of phlogisticated air, it might be expected that, if the acid I 

 got before came from the small quantity of phlogisticated air which I could not 

 possibly exclude, I should certainly get more acid when, instead of endeavouring 

 to exclude it, I purposely introduced a greater quantity. But the consequence 

 was the production of much less acid than before, the liquor I procured being 

 sometimes not to be distinguished from pure water, except by the greatest at- 

 tention possible : for though the decomposition was made in the same copper 

 vessel which I used in the former experiments, there was now no sensible tinge 

 of green colour in it. 



When I repeated this experiment in a glass vessel, I perceived, as I imagined, 

 the reason of the small produce of acid in these new circumstances : for the 

 vessel was filled with a vapour which was not soon condensed, and being diffused 

 'through the phlogisticated air, (which is not affected by the process) is drawn 

 away along with it, when the exhausting of the tube is repeated ; whereas, 

 when there is little or no air in the vessel besides the 2 kinds that unite with 

 each other, and are decomposed, the acid vapour, having nothing to attach 

 itself to and support it (by being entangled with it) much sooner attacks the 

 copper, making the deep green liquor which I have described. Sometimes 

 however I have procured a liquor which was sensibly green by the decomposition 

 of atmospheric and inflammable air, but by no means of so deep a colour, or 

 so sensibly acid, as when the dephlogisticated air is used. 



The extreme volatility of the acid thus formed (and which accounts for the 

 escape of some part of it in all these processes) is apparent from this circum- 

 stance, that if the explosions be made in quick succession (the tube being ex- 

 hausted immediately after each of them, and filled again as soon as possible) no 

 liquor at all will be collected, the whole of the acid vapour, together with the 

 water with which it was combined, being drawn off uncondensed in every 

 process. I once made 20 successive explosions of this kind, in a copper tube, 

 out of which I found that I drew 37 oz. measures of air by the action of the 

 pump, and found not a single drop of liquid, though near an hour was em- 

 ployed in the whole process, and the vessel was never made more than a little 

 warmer than my hand. This was a degree of heat by no mean sufficient to keep 

 the whole of any quantity of water in a state of vapour ; and is a circumstance 

 which of itself sufficiently proves, that the vapour did not consist of water only. 

 Indeed, I think it impossible for any one to see this vapour in a tall glass 

 vessel, and especially to observe how it falls from one end of it to the other, and 

 the time that is required to its wholly disappearing, without being satisfied that 

 it consists of something else than mere water, the vapour of which would be 

 more equally diffused. If the appearance to the eye should fail to convince any 

 person of this, the sense of smell would do it : for even in a glass vessel it is 



