74 
is, by that process, converted into carbonic acid, such 
conversion must have occurred while these plants 
were kept in the shade ; consequently, although no 
carbonic acid was found in the vessels after they had 
been exposed to the sun, its non-appearance is not to 
be received as proof against its formation in the shade, 
but only of its reconversion into oxygen gas under 
exposure to the sun. 
3(;8. This inference is completely borne out by the 
results of experiments related by M. de Saussure. 
He confined plants in vessels of atmospheric air, from 
the top of which he had previously suspended a por- 
tion of lime ; and then placed them to vegetate in 
sunshine. On the second day, the atmosphere was 
diminished in volume ; and on the fifth day, the air 
was examined and found to be much depraved : it 
contained only -& of oxygen gas, and no sensible 
quantity of carbonic acid. This experiment he re- 
peated many times with different plants, and always 
with similar results. We see, by these experiments, 
says M. de Saussure, that there had been an attrac- 
tion, and consequently a formation, of carbonic acid ; 
and we observe also another remarkable fact, name- 
ly, that plants, even in sunshine, produce, with the 
oxygen of the atmosphere, pure carbonic acid. It is, 
therefore, only because they decompose it, after ha- 
ving formed it, that they do not, like animals, vitiate 
the atmospheric air in which they are made to grow*. 
Hence then we learn, that, in sunshine as well as in 
the shade, plants, by their growth, naturaHy convert 
the oxygen gas of the air into carbonic acid. 
* Annales de Chimie, torn, xxiv. p. 145 
