(42) 
ed with the fact, that vegetation is always vigorous 
in the neighborhood of dead animal matter, led to 
the opinion, that azote contributed largely to the 
growth of plants; but experiments, more exactly 
made and often repeated, disprove this opinion, and 
shew that in any quantity it is unnecessary, and that 
in a certain proportion it is fatal to vegetation. 
In hydrogen gas, plants are found to be variously 
affected, according to their local situation; if in- 
habitants of mountains, they soon perish—if of 
plains, they shew a constant debility—but if of mar- 
shy grounds, their growth is not impeded. 
Carbonic acid is formed and given out during the 
process of fermentation, putrefaction, respiration, 
&c. and makes 28 parts out of 100 of atmospheric 
air. It is composed (according to Davy.) of oxigen 
and carbon, in the proportion of 34 of the former 
to 13 of the latter. It combines freely with many 
different bodies ; animals and vegetables are almost 
entirely composed of it; for the coal which they 
give, oncombustion, is but carbon united toa little 
oxigen, &c. Priestly was the first to discover that 
plants absorbed carbonic acid; and Ingenhouse, 
Sennebier and De Saussure have proved, that it is 
their principal aliment. Indeed the great consump- 
tion made of it, cannot be explained by any natu- 
ral process, excepting that of vegetation. On this 
head we cannot do better than digest the, experi- 
ments of the last of these chemists into a few dis- 
tinct proportions :(1) 
(1) Recherches chymiques sur la vegetation, chap. ii, 
