4 Mayow 



the nitre is volatilised, the fixed salt being left in the 

 retort. And there is no ground for saying that the 

 nitre of the air is of a more volatile nature than ordi- 

 nary nitre. For if earth from which all the nitrous 

 salt has been lixiviated is exposed to the air, sal 

 niiriim^ not volatile, I say, but fixed and of the ordi- 

 nary sort, will after some lapse of time be produced. 

 Consequently, if that nitre were wholly derived from 

 the air, then nitre of the more fixed sort, that is, 

 common nitre, must reside in the air, but that such 

 should fly about in the very rare air is not to be sup- 

 posed. But you may say that the same nitre which 

 is volatile when flying about in the air, becomes fixed 

 in the earth. But I would ask how that can take 

 place, unless something fixed from the earth be added 

 to the volatile nitre of the air ? And what else is 

 this, but saying that the volatile part of the nitre is 

 derived from the air, while its more fixed part is deriv^ed 

 from the earth ? 



To this we further add that if nitre, such as is 

 extracted from the earth, resided in the air, then as 

 the aerial nitre, whatever it be, mixes with kindled 

 fires (for the aerial nitre becomes food for the fire), it 

 would necessarily follow that every flame, even the 

 mild flame of a lamp, would constantly detonate on 

 account of the nitrous particles mixed with it ; yet 

 this does not take place. 



From these considerations it seems to be established 

 that sal 7iitrum is derived partly from the air and 

 partly from the earth, and this will appear still clearer 

 from what follows. 



Let us consider then, in the next place, what part 

 of the nitre is contributed by the earth, and, also, 

 what is contributed by the air. With regard to this, 

 it is our opinion that the fixed salt of which nitre in 



