352 PEAT. 



parated into asphaltum and naphtha, and tar into bistre 

 and the oil of wood ; both the solid compounds equally 

 terminating in charcoal, and each oil becoming a hy- 

 drocarburetted gas. And, under exposure to air, the 

 transitions, in both sets, are similarly uninterrupted, if 

 under differences of rapidity in the changes. 



With this general analogy, however, there are im- 

 portant differences, most striking in the fluid varieties. 

 To pass over the other chemical relations, the oil of 

 wood does not unite with naphtha : and hence the 

 vegetable tar and the bistre are not soluble in it, just 

 as asphaltum and petroleum will not dissolve in the 

 oil of wood. Thus does naphtha offer a convenient 

 test of the progress of bituminization, for geological 

 purposes. Where that is but commenced, as in some 

 antient peats, the products of distillation will not indi- 

 cate the change, though they may suffice in the lig- 

 nites ; while, by means of naphtha, the mixed produce, 

 in oil or tar, can be sufficiently analyzed for all the 

 ends of geology. The smell, indeed, is so different in 

 the two oils, as to be test enough for general use : 

 while their mixture, as produced from a peat in the 

 incipient stage of bituminization, explains the peculiar 

 odour of certain peats when burning. 



Thus is it easy to trace the progress of this, from 

 recent peat, in which it has not yet commenced, 

 through the more antient submerged woods, brown 

 coal, and surturbrand, down to jet ; the most perfectly 

 bituminized of the organic vegetable substances, still 

 however showing those traces of the tar or oil of 

 wood which disappear only in coal. Of antient peat 

 in which bituminization has commenced, the papyri 

 of Herculaneum offer an interesting example, since 

 they contain matter soluble in naphtha : while they, 

 who, as chemists, ought to have known better, have 



