Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/34

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Dr. Mac Culloch on certain products

of fire, is rendered probable, as much by these trials as by the geological observations above mentioned. The conversion of bituminized wood into true coal may possibly be the effect of a consolidation 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.[1]

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.

  1. That I may not interrupt the text, I will add, in a note, a cursory account of the 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 with the lustre of asphaltum. It is heavier than water. It is not electric. It is brittle, and breaks with a fracture intermediate 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 (pyroligueous) acid. It is not acted upon by boiling alcohol, ether, or naphtha; and in this latter circumstance, its difference from asphaltum 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 in 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.