171 



be taken through it, a slight explosion follows, with 

 a production of carbonic acid and water *. 



135. To these facts, tending to prove the emis- 

 sion of carbon from seeds, it may perhaps be ob- 

 jected, that this substance exists in so fixed a state, 

 that it cannot pass off in the attenuated form, which, 

 in these cases, is required ; but this objection ap- 

 plies equally to every case where carbonic acid is 

 spontaneously formed. Those who suppose the 

 oxygen gas to enter into the seed, and, by the power 

 of chemical affinity, to abstract its carbon, must 

 likewise admit, that this carbon is raised into a ga- 

 seous out of a fixed state, or no carbonic acid could 

 be formed. This power of assuming the gaseous 

 form, differs not only according to the circumstan- 

 ces in which the carbon may be placed, but also ac- 

 cording to the state of combination in which it ex- 

 ists. Thus, in its pure state of diamond, a very in- 

 tense heat is required to effect the union of carbon 

 with oxygen gas : in the example of plumbago, a 

 lower heat will suffice ; and in that of charcoal, a 

 much lower still. Not only, however, by these high 

 degrees of heat, but at the ordinary temperature of 

 the atmosphere, may this carbon be separated from 

 its combination with various substances. Mr Cruick- 

 shank observed, that the gas which arises from the 

 slow decomposition of humid vegetable matter, is si- 

 milar to that obtained by the decomposition of cam- 

 phor or aether by heat t *. and many examples have 



* Murray's System of Chemistry, vol. ii. p. 385, 

 f Ibid. vol. ii. p. 384, 



