172 



been given, in which carbonic acid and carburetted 

 hydrogen gases were formed by moistened seeds, at 

 the ordinary temperature of the atmosphere. Nor 

 is even the decomposition of the seed necessary to 

 extricate its carbon ; for M. Vauquelin found, that 

 moistened seeds, which had yielded carbonic acid in 

 hydrogen gas, would afterwards grow when placed 

 in the open air *. From these facts it follows, that 

 the carbon of vegetable bodies may be made to 

 unite with oxygen gas at a low temperature, as well 

 as at a high one ; and that this matter may be given 

 out by seeds antecedent to their decomposition, as 

 well as under that process. 



136. It is more difficult to ascertain the form 

 which carbon assumes, and the means by which, in 

 these various examples, it is brought into that form 

 in which it exists at the momerit of its union with 

 oxygen gas. In the processes where heat is employ, 

 ed, its particles are perhaps so changed or attenua- 

 ted by the operation of that subtile fluid, as to be 

 rendered capable of combining with the oxygen gas 

 presented to them ; but no such operation of heat 

 can be going on where the carbon is made to unite 

 with that gas at the ordinary temperature of the at- 

 mosphere. Some other means, therefore, must be 

 sought, which shall be sufficient to reduce the car- 

 bon to the state required for such a combination. 

 Now, we have seen, that the carbon of the seed 

 does not combine with the oxygen gas of the air, so 

 long as the seed continues in a dry state ; but when 



* Phil. Mag. vol. xxv. p. 223. 



