CHEMISTRY OF THE EIGHTEENTH CENTURY. 359 



only by a longer continuance of heat, I extracted mucii.more any from 

 it than from the other. ^ 'A ^ / 



"This experiment might have satisfied any moderate sceptic; but/V * 

 however, being at Paris in the October following, and/Jmowirrg^that > 

 there were several very eminent chemists in that place, I dijd not omit 

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

 of mercurius calcinatus prepared by M. Callet, 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 M. Lavoisier, M. le Roy, and several 

 other philosophers who honoured me with their notice in that city. 

 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 really was that I had found, taking it for granted that 

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

 air (nitrous acid) to be by the processes above mentioned (/.<?., exposure 

 to deoxidizing agents) ; and in this air I have observed that a candle 

 would burn sometimes quite brightly and sometimes with a beautiful 

 enlarged flame, and yet [the gas would] remain perfectly noxious. 



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

 mercurius 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. 

 This experiment with red lead confirmed me more in my suspicion 

 that the mercurius calcinatus must have got the property of yielding 

 this kind of air from the atmosphere, the process by which that pre- 

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

 the least secret of anything that I observe, I mentioned this also, as 

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

 all my philosophical acquaintance in 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 M. Callet, and with 

 a very moderate degree of heat I got from some of it an ounce 

 measure of air, which I observed to be not readily imbibed, either by 

 the substance itself from which it had been expelled (for I suffered 

 them to continue for a long time together before I transferred the air 

 to another place), or by water over which I suffered this air to stand 

 a considerable time before I made my experiment upon it. 



" In this air, as I had expected, a candle burned with a vivid flame ; 

 but what I observed new at this time (iQth of November, 1774), and 

 which surprised me no less than the fact I had discovered before, 

 was that, whereas a few moments' agitation in water will deprive the 

 modified nitrous air (nitrous oxide) of its property of admitting a 



