620 PHILOSOPHICAL TRANSACTIONS. [aNNO I789. 



very offensive, though it might not be pronounced to be acid. I conjecture 

 however that this, and every other species of smell, is produced by some modi- 

 fication of the acid or alkaline principle. Some may be disposed to ascribe this 

 smell to the iron from which the inflammable air was produced ; but 'the smell 

 is the same, or nearly so, when the air is from tin, and would probably be the 

 same if it were from any other substance. Besides using atmospheric air, which 

 contains a greater proportion of phlogisticated air, I have sometimes used de- 

 phlogisticated air which was not very pure ; and in this case I have always ob- 

 served, that the' liquor I procured had less colour, and was less sensibly acid. 

 These observations might, I should think, satisfy any reasonable person, that 

 the acid liquor which I procured by the explosion of dephlogisticated and inflam- 

 mable air in close vessels did not come from the phlogisticated air which could 

 not be excluded, whether it was that which remained in the vessel after exhaust- 

 ing it by' the air-pump, or that with which the dephlogisticated air was more or 

 less contaminated. 



But besides these experiments, in which I procured the green acid liquor by 

 the explosion of dephlogisticated and inflammable air in close vessels, I made 

 another, to which I thought the same objection could not have been made, be- 

 cause no air-pump was used in it, and nothing but the purest dephlogisticated air 

 was employed, being separated in the process from precipitate per se in contact 

 with the purest inflammable air in a glass vessel which had been previously filled 

 with mercury. Accordingly, the only objection made to this*' experiment was, 

 that the preparation used might be impure, containing something which might 

 yield phlogisticated air. This appeared to me highly improbable, as the precipi- 

 tate had been made by M. Cadet, and for the purpose of philosophical experi- 

 ments. Besides, if the heat of a burning lens should dislodge phlogisticated air 

 from any unperceived impurity in this preparation, mere heat will not decom- 

 pose this air. Let any person try the effect of a lens on such air, or any sub- 

 stance containing it, and produce an acid if he can. 



M. Berthollet however, thinking that this might be the case, desired that I 

 would send him a specimen of my precipitate per se. Accordingly, I sent him 

 all that remained of it ; and in return he sent me a quantity on the goodness of 

 which I might depend. With this preparation I repeated my former experi- . 

 ment; and, by giving more attention to the process, found it to be far more de- 

 cisively conclusive in favour of my opinion than I had imagined. In the former 

 experiment I had attended only to the drop of water which was found in the 

 vessel in which the [)rocess was made ; and finding that it turned the juice of 

 turnsole red, I concluded that it contained nitrous acid : but I now examined 

 the air that remained in the vessel, and found that a considerable proportion of 

 it was fixed air -, so that I am now satisfied this was the acid with which it was 



