502 PURIFICATION OF AIR 



philosopher has not been equally successful. 

 He is recorded as the discoverer of the expi- 

 ration of plants, but it appears from his 

 work that he merely observed the bubbles 

 of air which cling to leaves, dead as well as 

 living, and indeed to any other body, when 

 immersed in water and exposed to the light 

 of the sun. He found these bubbles disap- 

 peared in the evening, and returned again 

 when the sun shone, and he faithfully reports 

 that by their attachment to the surfaces of 

 leaves, the latter were rendered more buoyant, 

 and rose in the water ; a sure proof that the 

 air had not previously existed, in the same 

 volume at least, in the substance of those 

 leaves. Accordingly, Bonnet concluded that 

 the latter, in imbibing the surrounding water, 

 left the air which had been contained in the 

 water, and that this liberated air became 

 visible from being warmed and rarefied by 

 the sun. This was as near the truth as Bon- 

 net could come, it not being then known 

 that light has a power of separating air of a 

 peculiar kind, carbonic acid gas, from water. 

 I find no indications in his work of his having 

 had any idea of leaves absorbing air and 



