in the Distillalion of Wood, &c. 217 



also readier means of imitating Nature in those operations in 

 which she has wrouglit with the same agent, it is worth our whili' 

 to consider, if hy it we can produce ■ from vegetables the bitu- 

 minous matters under review. It is not necessary to say how 

 jntim.atelv this question is connected with our speculations on 

 the origin of coal, since Sir James Hall's experinncuts were ex- 

 pressly intended to illustrate this view of the subject. In this, 

 it is related that " coal" was produced from "fir saw dust" by 

 the usual method employed in these experiments, and that pieces 

 of wood were changed " to a jet-black and inflammable sub- 

 stance, generally very porous," in some specimens of which " the 

 vegetable fibres were still visible." There is no reason to doubt 

 that the substance produced in these experiments was that black 

 matter which I have described in the first part of this ijaper, 

 'whicii, however resembling bitumen in colour and inflammability, 

 1 have proved to be a different substance, and that the igneous 

 theory of the origin of coal will receive no support from them, 

 as far at least as relates to the conversion of vegetable mattei 

 into bitumen. I need take no notice of the modifications de- 

 rived from a mixture of animal matter in these experiments, as 

 it is not my desire to enter into a discussion of the general ques- 

 tioti, but to state such chemical facts as arose in the experiments; 

 I undertook. And since it is certain that- vegetables alone are 

 competent to the production of bitumen, and that the geological 

 history of coal does not justify a supposition that animals have 

 been concejued in its production, it is perhaps unnecessary to 

 investigate that question further. 



To satisfy myself whether any essential chemical difference 

 would result from the experiments performed by simple heat, and 

 those perfonned by heat under pressure, 1 repeated these trials, 

 by heating wood in close gun barrels, introducing occasionally 

 lime, clay, or other matters, to absorb the acid generated, and 

 give the greater chance for the disoxvger.ation and bituminiza- 

 lion of the wood. But the produce only differed from that of the 

 experiments in open vessels, by the circumstance which is men- 

 tioned in Sir James Hall's paper, namely, the mixture of a porous 

 charcoal, or a half destroyed vegetable structure. In all cases 

 the bituminous-looking matter was vegetable tar, not bitumen. 



Thus far then perhaps we are justified in concluding that the 

 nction of water, and not that of fire, has converted the vegetable 

 .natters into bitumen. It is another question to deteimine how 

 that bituminous matter in its several forms of peat or Hgnitc 

 has been converted into coal, into a substance differing mechani- 

 -:ally rather than chemically from it, if, without misleading, I may 

 ii<-e the contrafct (jf these terms. 



[To be conuiiued.] 



XXXIX. On 



