Sect. II Agriculture and Vegetation. 137 



this fait - y nor are chymifts yet agreed about 

 its birth. Some alledge it is attra&ed, as 

 we fee it, from the air j others, that it is 

 produced from the animals and vegetables, 

 or their juices mixed with the nitrous earth, 

 and putrefying there: others, that it is 

 formed from the vitriolic acid, joining to 

 the phlogifton, or inflammable matter of 

 thefe lubftances : and others, that the acid 

 of nitre is a different acid from the former, 

 and attracted by thefe bodies, which are its 

 proper matrix. Let us examine thefe dif- 

 ferent opinions. 



SALTPETRE is an artificial body, as none 

 of it has ever yet been found in the bowels 

 of the earth. Some authors, on this ac- 

 count, thought that the nitre was altoge- 

 ther attracted from the air by the mate- 

 rials expofed to it. But this opinion is ap- 

 parently falfe, as no nitre can be got from 

 thofe materials before an alkaline fait is 

 added to them. The acid, indeed, does 

 in thefe materials, as I mail after- 

 wards 



