1 44 The Prwcifi/es of Part III. 



or putrefied vegetables and animals, which 

 afford an abforbent earth, and likewife a 

 volatile fait. Almoft all earths have more 

 or lefs of abforbent particles in their com- 

 pofition. Thefe abforbent earths catch the 

 nitrous acid, as it paffes by them with the 

 air, or fix and collect it as it arifes from 

 the inner parts of the earth : for I am not 

 fure but it may be got likewife in that 

 way ; at leaft it does not feem to rife very 

 high from the ground. Mariot's experi- 

 ment is a proof of this. He expofed the 

 matrix of nitre for two years on a houfe- 

 top, and could get no nitre from it -, but 

 got it from the fame matrix kept in a 

 cellar. 



THE mixture of urine, and of putrefy- 

 ing vegetable and animal fubftances, will 

 be of confiderable ufe in carrying on an 

 inteftine motion in the mafs of earth, keep- 

 ing .it open, and allowing the influence of 

 the air to penetrate deeper into the body. 

 If there was no fuch putrefcent body mix- 

 ed 



