t 163 ] 



whereas tlie other pot produced only 15. The fame experiment 

 was made on ftock july-flowers and other plants with equal 

 fuccefs *. The manner in which fixed air a^ts in promoting 

 vegetation feems well explained by Mr. Senebier : he firft dif- 

 covered that frefh leaves expofed to the fun in fpring-water, 

 or water flightly impregnated with fixed air, always produce 

 pure air as long as this impregnation lafts ; but as foon as it is 

 exhaufted, or if the leaves be placed in water out of which this 

 air has been expelled by boiling, they no longer afford pure 

 airf; from whence he infers that fixed air is decompofed, its 

 carbonic principle retained by the plant, and its pure air expelled. 

 It appears to me alfo, by ading as a ftimulant, to help the 

 decompofition of water. Mr. Haffenfraz, indeed, denies its 

 decompofition, but his arguments do not appear to hie con- 

 clufive, for reafons too tedious and technical to mention here. 

 The vitriolic acid contained in various clays brought into multi- 

 plied contadl with calcareous earth by the agitation of foils in 

 agricultural operations, and the motion of the roots, gradually 

 fets loofe the fixed air contained in this laft mentioned earth ; 

 that portion alfo of this earth, which is by water introduced 

 into the plant, is decompofed, and its air fet loofe by the vegetable 

 acids of the plant. 



Of Saline Subjiances. .^ .^^^^^^g 



Saline fubftances (gypfum and phofphorated calx excepted) 

 feem to ferve vegetables as they do animals, rather as a condi- 



X - an^id b! mentum^ 



* 2d Chy. An. 1788, 399- t Sur I'influence de la Lumiere & 41 Rofier, 206. 



