Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/16

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Dr. Mac Culloch on certain products

softest specimens of the pitch are nearly as soluble, leaving only a small residuum, which is infusible and powdery. The harder specimens become in proportion less soluble, and leave a larger residuum; and those which have been the longest exposed to heat scarcely give a stain to the alcohol, resembling in this respect the driest specimens of asphaltum. The analogy is here very apparent, for asphaltum may approach more or less to petroleum, and the various specimens of it are found to exhibit various degrees of solubility in alcohol. That which is least fusible in the fire, is, in both cases, the least soluble in alcohol. And by this consideration, the jarring accounts which have been given of the solubility of asphaltum in alcohol may be reconciled, and it will be seen in the sequel, that the history of this substance illustrates, in every respect, the true nature of the several varieties of the bitumens, substances whose mutual relations, and the causes of whose chemical diversity have hitherto not been understood.

If a perfectly soluble specimen be dissolved in alcohol, it is obtained unchanged by evaporating the spirit. In any other case, the matter which the alcohol has taken up is precisely similar to the pitch in its first state, and the residuum resembles that which is the result of fusion when it refuses longer to melt. Alcohol therefore separates the pure pitch from that, which by a process of decomposition has been nearly carbonized. Ether acts upon this substance as readily and in the same manner as alcohol does. In lixivium of pure potash it is more completely soluble than in alcohol, and forms with it an intensely brown solution which is diffusible in water without change, and which, on the addition of an acid, deposits the matter in a powdery form and apparently unchanged. It is also soluble in water of ammonia with similar appearances. It is scarcely soluble in the pale oil of turpentine, but more readily