24 Dr. MacCulloch on certain products 



of fire, Is rendered probable, as much by these trials as by the geo- 

 logical observations above mentioned. The conversion of bitumi- 

 nized wood into true coal may possibly be the eifect of a consolida- 

 tion produced by the agency of fire, but I shall leave this argument 

 in the hands of those who have undertaken the defence of this 

 theory — having entered into this train of reasoning, not by design, 

 but from the unavoidable concatenation of experiments.* 



A circumstance occurred in the coaly residuum of the wood tar 

 which it is worth while to notice, although of an accidental nature, 

 and not essentially affecting the history of the vegetable bitumen or 

 pitch which I have described. It bore no resemblance to common 

 charcoal, but was more like black lead. It was as glossy, and 

 although not so soft, marked paper with a similar streak. It was 

 inflated, and therefore minutely scaly, and porous, and was attracted 

 by the magnet. Muriatic acid took up a portion of iron from it, 

 as it does from many varieties of plumbago, and the remainder 

 resembled plumbago after it had been submitted to the action of acids, 



* That I may not interrupt the text, I will add, in a note, a cursory account of th« 

 black matter which is deposited in bogs, and which seems to be the substance giving 

 the pitchy appearance to the more compact varieties of peat. I have not seen it in the 

 soft state in which it is first procured. 



When dry, it is black, sometimes dull, sometimes wiih the lustre of asphaltum. It is 

 heavier than water. It is not electric. It is brittle, and breaks with a fracture inter- 

 mediate between the splintery and conchoidal, resembling asphaltum generally in its 

 external characters. Exposed to a red heat it is incinerated, giving a smoke possessing 

 a modified smell of vegetable (pyroligneous) acid. It is not acted upon by boiling 

 alcohol, ether, or naphtha ; and in this latter circumstance, its difl'crence from asphal- 

 tum is marked. Neither is it soluble in boiling water. It is readily dissolved in lixivium 

 of potash, and by nitrous acid. It appears to be formed of the vegetable elements iti 

 the state of transition to bitumen, the carbon having been first held in solution, as it is 

 in the water of dunghills, by the other matters with which it was combined, and being 

 at length consolidated by the dissipation of a portion of them. The produce of its 

 combustion shows it is combined with both hydrogen and oxygen. 



