HISTORY OF SCIENCE. 



would be air that contained less phlogiston than the air of the atmo- 

 sphere ; but I had no idea that such a composition was possible. 



" Having procured a lens of 12 inches diameter and 20 inches focal 

 distance, I proceeded with great alacrity to examine by the help of it 

 What kind of air a great variety of substances, natural and factitious, 

 would yield, putting them into small phials made with round bottoms 

 and very thin, filled with mercury and inverted in a basin of the same. 

 With this apparatus, on the ist of August, 1774, I endeavoured to 

 extract air from merciirius calcinatus per se (red oxide of mercury} ; and 

 I presently found that by means of this lens air was expelled from it 

 very readily. Having got about three or four times as much as the 

 bulk of my materials, I admitted water to it and found that it was 

 not imbibed by it. But what surprised me more than I can well 

 express, was that a candle burned in this air with a remarkably vigorous 

 flame, very much like that enlarged flame with which a candle burns 

 in nitrous air, exposed to iron or liver of sulphur; but as I got nothing 

 like this remarkable appearance from any kind of air besides this 

 particular modification of nitrous air, and I know no nitric acid was 

 used in the preparation of merciirius calcinatus, I was utterly at a loss 

 to account for it. In this case, also, though I did not give sufficient 

 attention to this circumstance at the time, the flame of the candle, 

 besides being larger, burned with more splendour and heat than it 

 did in that species of nitrous air; and a piece of red-hot wood sparkled 

 in it exactly like paper dipped in -a solution of nitre, and it consumed 

 very fast : an experiment which I had never thought of trying with 

 dephlogisticated nitrous air (nitrous oxide gas]. 



" At the same time that I made the above-mentioned experiment, 

 I extracted a quantity of air, with the very same property, from the 

 common red precipitate (red oxide of mercury), which, being produced 

 by solution of mercury in spirit of nitre (nitric acid), made me con- 

 clude that this peculiar property, being similar to that of the modifi- 

 cation (nitrous oxide) of nitrous air (nitrous acid) above mentioned, 

 depended upon something being communicated to it by the nitrous 

 acid ; and since the mercurius calcinatus is produced by exposing 

 mercury to a certain degree of heat, where common air has access to 

 it, I likewise concluded that this substance had collected something 

 of nitre, in that state of heat, from the atmosphere. 



" This, however, appearing to me much more extraordinary than it 

 ought to have done, I entertained some suspicion that the mercurius 

 calcinatus on which I had made my experiments, being bought at a 

 common apothecary's, might in fact be more than red precipitate, 

 though, had I been anything of a practical chemist, I could not have 

 entertained any such suspicion. However, mentioning this suspicion 

 to Mr. Waltire, he furnished me with some which 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, 



