SECT. V. ELABORATION OF CARBONIC ACID. 149 



assimilated in the state in which it is inhaled ? or 

 is it previously decomposed ? It had been observed 

 by Ingenhoutz that the leaves of plants, if placed 

 in water and exposed to the action of the sun's rays, 

 will evolve a quantity of oxygene gas. It was af- 

 terwards ascertained by Senebier that this process 

 takes place only when the leaves are fresh and the 

 water impregnated with carbonic acid. For when 

 the water was deprived of its carbonic acid by 

 boiling, or in the course of experiment, there was 

 no more oxygene evolved. But when the water 

 was again impregnated with carbonic acid, the 

 extrication of oxygene recommenced as before ; the 

 conclusion, therefore, is obvious and the pheno- 

 menon satisfactorily accounted for. The carbonic 

 acid gas contained in the water is abstracted and 

 inhaled by the leaf, and immediately decomposed ; 

 the carbon being assimilated to the substance of the 

 plant, and the oxygene evolved. 



Such was the important discovery of Senebier, 

 affording an undoubted proof of the decomposition 

 of carbonic acid. But the effects of that decompo- 

 sition had not yet been analysed ; nor was it yet 

 ascertained whether the quantity of oxygene evolved 

 was more or less than the quantity contained in 

 the composition of the carbonic acid, or equal to it. 

 The solution of the question was reserved for Saus- 

 sure, who after a variety of experiments obtained 

 the most satisfactory results. 



In an artificial atmosphere composed of common 



