I JOSEPH PRIESTLEY 19 



of the sun, by means of a large burning glass 

 which he had recently obtained, upon a substance 

 which was then called mercurius calcinatus per se, 

 and which is commonly known as red precipitate. 



" 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 lime of sulphur ; 

 but as I had got nothing like this remarkable appearance 

 from any kind of air besides this particular modification of 

 nitrous air, and I knew no nitrous acid was used in the 

 preparation of mercurius calcinatus, I was utterly at a loss 

 how to account for it. 



" In this case also, though I did not give sufficient atten- 

 tion to the circumstance at that time, the flame of the can- 

 dle, besides being larger, burned with more splendour and 

 heat than in that species of nitrous air; and a piece of red- 

 hot wood sparkled in it, exactly like paper dipped in a solu- 

 tion of nitre, and it consumed very fast — an experiment 

 which I had never thought of trying with nitrous air." * 



Priestley obtained the same sort of air from red 

 lead, but, as he says himself, he remained in 

 ignorance of the properties of this new kind of air 

 for seven months, or until March 1775, when he 

 found that the new air behaved with " nitrous 

 gas " in the same way as the dephlogisticated part 

 of common air does; f but that, instead of being 



* Expprimenfs and Ohservations on Different Kinds of 

 Air, vol. ii. pp. 34, 35, f Ihid. vol. 1. p. 40. 



