SECT, V. ELABORATION OF CARBONIC ACID. J'15 



placed under a glass vessel filled with common air 

 for the space of one night only, had so affected its 

 atmosphere by next morning that a candle would 

 not burn in it, and yet the leaf showed no symp- 

 toms of putrefaction.* This fact he did not at the 

 time attempt to account for ; so that it was not yet 

 known whether the change produced in the atmos- 

 phere of the leaf was occasioned by the abstraction 

 of any constituent part, or by the addition of any 

 extraneous substance. The true cause was after- 

 wards ascertained by Saussure : into a receiver con- 

 taining only atmospheric air, Saussure introduced 

 some plants of Vitia Faba, and placed the appa- 

 ratus in the shade ; but at the end of six days 

 when the experiment was stopped, the atmosphere 

 of the receiver was found by the application of 

 lime water to contain ^y^ of carbonic acid* Into 

 another receiver containing also atmospheric air he 

 introduced at the same time several other plants of 

 the same species, together with a small quantity of 

 lime, and placed the receiver over lime water, 

 leaving the apparatus in the shade. At the end of 

 the six days of experiment the atmosphere of the 

 feceiver contained --f-y- of carbonic acid, though a 

 great deal must have been abstracted also by the 

 lime ; but in both these experiments the excess of 

 Carbonic acid gas found in the atmosphere of the 

 plants, could have been derived only from the 

 plants themselves. Plants, then, vegetating in coii- 



* Priestley on Air, vol. i. p. 51. 

 VOL, II. 



