u8 POPULAR SCIENCE MONTHLY. 



have entertained any such suspicion. However, mentioning this sus- 

 picion to Mr. Warltire, he furnished me with some that he had kept for 

 a specimen of the preparation, and which, he told me, he could warrant 

 to be genuine. This being treated in the same manner as the former, 

 only by a longer continuance of heat, I extracted much more air from 

 it than from the other. 



This experiment might have satisfied any moderate sceptic; but, 

 however, being at Paris in the October following, and knowing that 

 there were several very eminent chymists in that place, I did not omit 

 the opportunity, by means of my friend, Mr. Magellan, to get an ounce 

 of mercurius calcinatus prepared by Mr. Cadet, of the genuineness of 

 which there could not possibly be any suspicion; and at the same time, 

 I frequently mentioned my surprise at the kind of air which I had got 

 from this preparation to Mr. Lavoisier, Mr. le Eoy and several other 

 philosophers, who honored me with their notice in that city; and who, I 

 dare say, cannot fail to recollect the circumstance. 



At the same time I had no suspicion that the air which I had got 

 from the mercurius calcinatus was even wholesome, so far was I from 

 knowing what it was that I had really found; taking it for granted that 

 it was nothing more than such kind of air as I had brought nitrous air to 

 be by the processes above mentioned; and in this air I have observed that 

 a candle would burn sometimes quite naturally, and sometimes with a 

 beautiful, enlarged flame, and yet remain perfectly noxious. 



At the same time that I had got the air above mentioned from mer- 

 curius calcinatus and the red precipitate, I had got the same kind from 

 red lead or minium. In this process that part of the minium on which 

 the focus of the lens had fallen turned yellow. One third of the air in 

 this experiment was readily absorbed by water; but, in the remainder, a 

 candle burned very strongly and with a crackling noise. 



That fixed air is contained in red lead I had observed before, for I 

 had expelled it by the heat of a candle, and had found it to be very 

 pure. (Vol. I., p. 192.) I imagine it requires more heat than I then 

 used to expel any of the other kinds of air. 



This experiment with red lead confirmed me more in my suspicion 

 that the mercurius calcinatus must get the property of yielding this 

 kind of air from the atmosphere, the process by which that preparation 

 and this of red lead is made being similar. As I never make the least 

 secret of anything that I observe, I mentioned this experiment also, as 

 well as those with the mercurius calcinatus and the red precipitate, to all 

 my philosophical acquaintances at Paris and elsewhere, having no idea 

 at that time to what these remarkable facts would lead. 



Presently, after my return from abroad, I went to work upon the 

 mercurius calcinatus which I had procured from Mr. Cadet, and, with a 

 very moderate degree of heat, I got from about one fourth of an ounce 



