334 
4 
638. We have no grounds to believe that the cat- 
bon of vegetables, in combining with oxygen, passes 
off in a gaseous form ; for although, in the com- 
pounds of carbonic acid, and of carburetted hydro- 
gen and nitrogen, it exists in an elastic state, yet there 
is no evidence of its being able to maintain that state 3 
unless it be combined with some permanently elastic 
body ; and when, by decomposition, it is again sepa- 
rated from such combinations, it resumes a solid 
form. Thus Mr Tennant found charcoal to be pre- 
cipitated in the decomposition of carbonic acid by 
phosphorus (464.) ; and Mr Cruickshank and Dr 
Henry, on submitting pure carburetted hydrogen and 
defiant gases to electrization, observed the charcoal 
to be separated and deposited on the inner surface of 
the glass-tube, and the hydrogen then assumed a state 
of greater expansion,*. As, therefore, this substance 
does not seem capable of existing by itself in an 
elastic form, like some other inflammable bases, we 
have additional grounds for concluding that it really 
passes off from the seed in solution, or in combina- 
tion with water. 
639. But while we thus suppose that carbon is ra- 
ther given off by the seed or plant to unite with the 
surrounding gases, than that these gases are first at- 
tracted into the seed to combine with and carry off 
its carbon, we do not mean to deny that oxygen, and 
even other gases may not exert attractions towards 
the vegetable body, and, by their mechanical or 
* Phil. Trans; 1809, P- 448. 
