PEAT. 351 



water on the vegetable compound are similar: in the 

 case of the two bistres, from water and from fire, they 

 are identical : and whatever other differences there are, 

 they are explained by the imperfection of the process 

 in peat, and its perfection in the case of fire ; since, 

 by the latter, the whole process is completed in an 

 instant, as, in the other it may occupy centuries. Thus, 

 except in the case of solution, the hydrocarbonaceons 

 compound forming peat could not be identical with 

 the produce of fire from the vegetable substance : but 

 all that is essential to the present question remains. 

 This is all that I can afford on this subject ; but here 

 ajl comparison between these two agents ceases. Fire 

 has never yet produced that further change, either on 

 vegetable matter or peat, which follows the prolonged 

 action of water, namely, bituminization. This is the 

 generation of the woody lignites, as the preliminary to 

 the formation of coal : and I must now therefore pro- 

 ceed to the subject of chief interest under this question. 

 The first needful enquiry, here as before, consists 

 in the chemical differences between the bitumens and 

 " these results of vegetable decomposition ; as the as- 

 signment of a test for the commencement of bitumi- 

 nization is also necessary. And the distinctions in 

 question will be rendered most apparent by comparing 

 the several substances where they most resemble each 

 other. 



The decided varieties of Bitumen are, asphaltum, 

 petroleum, and naphtha ; the others being mixtures 

 or modifications of these : and they are severally ana- 

 logons to the bistre, the tar, and the volatile oil of 

 wood or peat, while they all undergo similar changes 

 from the action of air and from heat.. Thus the as- 

 phaltum and the bistre produce petroleum and tar, by 

 distillation ; as, by the same process, petroleum is se- 



