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that was admitted to it ; but fo very great a quantity 

 of this air difappeared upon the admiffion of a very 

 finall 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 vanished . 

 upon the admiffion 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 

 Saturated with ii r 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 dhTolved iron very faft, and gene- 

 rated inflammable air. This lad obfervation, toge- 

 ther with another which immediately follows, led: 

 me to the difcovery 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 muft 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 diminished, till, inftead of being. one fourth 

 of the whole as I had firft obferved, it was not fo 

 much as one twentieth. Upon this, I concluded 

 that this fubtie air did not arife from the copper, 

 hut from the fpirit of fait; and prefently making 

 the experiment with the acid only, without any cop- 



4 P er * 



