138 *Tbe Principles of Pgrt III. 



wards (hew 5 but the alkaline bafe rnuft be 

 given it by art, before any nitre will cryf- 

 tallife. Befides, nitre is not of itfelf a vola- 

 tile body ; and, therefore, cannot float in 

 the air. The aereaj nitre, which is got 

 flicking to old walls, is a very different fub- 

 flance from the nitre we are juft now 

 treating of. It has very different properties, 

 fuch as effervefcing with all acids, and a 

 urinous tafte, 



LEMERTy in a paper in the Mem. de 

 Tacad. des fciences pour fannee 1717, main-t 

 tains an opinion peculiar, I believe, to him- 

 felf, That the nitre which is generated, 

 arifes from the animal and vegetable fub- 

 flances which are ufed to colled it. The 

 arguments which he makes ufe of to fup- 

 port his opinion, are, indeed, few and 

 weak. I think his chief one is, that he has 

 extracted a nitrous fait from fome vege- 

 tables. It is true, that fome of them do 

 contain, in their natural flate, an inflam- 

 mable fait, which appears to have many of 



the 



