348 PEAT. 



the bituminous lignites, as forming the intermediate 

 transition. It is true that the peculiar qualities of 

 peat have been attributed to bituminization ; but I shall 

 prove that there is a complete distinction : nor have I 

 ever seen a specimen containing bitumen, except under 

 a very high antiquity, or from casual impregnation. 

 The limit between peat and bituminized wood is in- 

 deed evanescent ; yet it is necessary to mark the boun- 

 dary wherever it is possible, that the latter maybe ranked 

 with the lignites. I must, however, here be brief; but 

 I have formerly treated this subject very fully in 

 the Geological Transactions and elsewhere. 



Chemistry does not yet possess any means of directly 

 analyzing the hydrocarbonaceous compounds ; and I 

 have therefore adopted the antient process of "destruc- 

 tive distillation," under some care and refinement. Ju 

 the usual rude manner of proceeding, the results were 

 worthless ; as the products consisted partly of new 

 compounds, and partly of the chemical elements pre- 

 sent : with more attention, the former alone are ob- 

 tained ; when, by repeating similar processes, the ele- 

 ments themselves can be procured, or inferred with 

 sufficient accuracy for the objects in view. Thus the 

 progress of the change can be traced, from the vege- 

 table, through peat to lignite, and finally to coal. 



If vegetable matter be thus treated, the volatile pro- 

 ducts are acetic acid, oil and tar ; charcoal remaining 

 behind ; but as the real nature of tar had never been 

 understood, I must remark that naval tar is a compound 

 of this substance and turpentine, as pitch is an analo- 

 gous one, combining bistre and resin. By further dis- 

 tillation, the vegetable tar becomes thick ; until acquir- 

 ing the consistence and aspect of asphaltum, it is the 

 bistre of artists. In this process, according to the heat, 

 more tar is procured, or else, more acid and volatile 



