Dr. Mac Culloch on the Ligidtes, 225 



to lignite, it will be convenient to give a slight sketch of the 

 chemical circumstances in which peat itself differs from recent 

 vegetable matter. 



If recent vegetables be decomposed by the ordinary process of 

 destructive distillation, they are resolved into carbon and hydrogen 

 principally, together with certain inferior proportions of oxygen 

 and azote ; the earthy and saline matters which they may contain 

 being here 'neglected, as not entering into the present consider- 

 ation. These elements are not, however, obtained in a simple 

 state by one process. Various compounds are first procured, 

 which may, by a repetition of similar methods, or by other well 

 known means, be at length resolved into their simple elements. 

 Thus the hydrogen and carbon are found in the state of car- 

 buretted hydrogen of various composition, and also in a solid 

 form ; producing compounds of various kinds, into which oxygen 

 also occasionally enters, so as to produce a substance analogous 

 to the resins, and which I have described in the Transactions of 

 the Geological Society by the name of Bistre. Acetic acid and 

 ammonia are, in a similar manner, obtained ; and, from the pro- 

 portions of these different products, it is easy either to estimate, 

 or else from their analogies to discover, the relative proportions 

 of the several ingredients ; within limits, at least, sufficient for 

 the present objects. 



Now, in examining peat, and in comparing the relative pro- 

 portions of these different ingredients, it is discovered that those 

 of the oxygen, and of the azote, which is always in very small 

 quantity, are diminished, and that a new compound, which is the 

 basis of peat, has been formed of the hydrogen and carbon, con- 

 taining also a small proportion of oxygen. In tracing also the 

 varieties of peat, from the first change which the vegetable has 

 undergone to the most perfect specimens of this nature, it is dis- 

 covered that the proportion of oxygen experiences a progressive 

 diminution, but is never entirely absent. The same reasoning 

 applies to the submerged wood of peat, which is here distinguished 

 from the lignites. 



It is sufficient to have thus briefly stated these circumstances 



