342 
elastic combinations escape in the state of gas ; and 
thus the aeriform products of the distillation of ve- 
getable substances are mixtures of carbonic acid, 
carbonic oxide, olefiant, carburetted hydrogen, and 
simple hydrogen gases j or of two or more of these 
in various proportions V Until these sources of 
fallacy be duly attended to, and fairly estimated, it is 
in vain to place any great confidence in the attempts 
to ascertain the quantity of carbon in plants by the 
destructive mode of analysis that has now been 
stated. 
647. But M. de Saussure has attempted to shew, by 
arguments of a somewhat different kind, that grow- 
ing vegetables derive carbon from the atmosphere. 
M. Hassenfratz had before endeavoured to prove, 
that plants which grew in pure water, and were ex- 
posed to the atmosphere, contained less carbonic mat- 
ter than the seeds from which they sprang. M. de 
Saussure obtained a similar result when he caused 
plants to grow in places weakly illuminated ; and 
the absence of light, therefore, may, he supposes, ac- 
count for the results which M. Hassenfratz obtain- 
ed f. In other experiments, however, conducted 
under exposure to the sun, different results were af- 
forded. The roots of several plants of peppermint 
were plunged in phials of distilled water, and left to 
vegetate, in a free exposition to the sun and air, but 
protected from rain. After growing ten weeks, 10O 
parts by weight were increased to 216 parts. 
* Phil. Trans 1808, p. 283. 
t Recherches Chin?, p. 52. 
