Sect. II. Agriculture and Vegetation. 149 



cannot join to the marine acid, becaufe that 

 has already got an alkaline bafe. 



IF thefe abforbent earths attract the acid 

 of nitre from the air, in the manufacture 

 of nitre, furely they will do the fame when 

 laid on the earth, and be converted to the 

 fame fait, confiding of the nitrous acid and 

 an abforbent bafe. It is not, therefore, a 

 real nitre, as was thought, which is the 

 caufe of vegetation, but an imperfect ni- 

 trous fait. This reafoning admits yet of 

 ilronger proof, when we confider, that this 

 very fait exifting in hard waters, has al- 

 ready, by experiment, appeared to be a 

 great affiftant of vegetation j and that an 

 artificial one, of much the fame nature, 

 compofed of lime and fpirit of nitre, when 

 joined with a proper quantity of an oily 

 fubftance, rendered a poor foil remarkably 

 fertile. 



IF this reafoning is juft, the effects of 



different manures on the ground mould be 



L 3 vifible, 



