I JOSEPH PRIESTLEY 19 



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 cal- 

 cinatus, 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 



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 ; 2 but that, instead of being 

 diminished to four-fifths, it almost completely 

 vanished, and, therefore, showed itself to be " be- 

 tween five and six times as good as the best 



1 Experiments and Observations on Different Kinds of Air. 

 vol. ii. pp. 34, 35. 



2 Ibid. vol. i. p. 40. 



C 2 



