118 JOSEPH PRIESTLEY. 



mon air, and consequently support combustion better 

 than common air does? 



Now, Priestley says that, in 1774, the possibility of 

 obtaining air less phlogisticated than common air had not 

 occurred to him.* But in pursuing his experiments 

 on the evolution of air from various bodies by means 

 of heat, it happened that, on the 1st of August 1774, 

 he threw the heat of the sun, by means of a large burn- 

 ing glass which, he had recently obtained, upon a sub- 

 stance which was then called mercurius calcinatus per 

 se y 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 mercuriu* calcinatut, 

 I was utterly at a loss how to account for it. 



" In this case also, though I did not give sufficient attention to 

 the circumstance at that time, the flame of the candle, 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 solution of nitre, and it consumed 

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

 nitrous air.' 1 f 



Priestley obtained the same sort of air from red 

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



* " Experimenis and Observations on Different Kinds of Air," vol. ii, 

 p. 31. f Ibid. pp. 34, 35. 



