Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/14

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Dr. Mac Culloch on certain products

posing the fluids thus generated to a second heat, that so large a portion of the petroleum is distilled unchanged. By causing it to pass a second time in contact with heated iron, while in the state of vapour, it may be resolved completely into inflammable gas and charcoal, and the produce of gas be thus considerably increased. This circumstance explains also the contradictory accounts given by different persons of the relative products of distillation, as applied to the various compound inflammables. To instance the case of camphor, which according to the mode of managing the process, may be caused to yield essential oil or inflammable gas or a mixture of both in various proportions. I need scarcely point out the advantages so obviously to be derived from this consideration in the economical process of procuring light from pit-coal, an operation at present conducted with less skill than it demands.

I distilled a portion of this tar in such a way as to obtain inflammable air only, and took the gas in five portions. The first burnt very faintly, the second rather better, the third and fourth portions with a good white flame, and the fifth burnt feeble and blue. No portion of it was equal in brilliancy of inflammation to the gas from pit-coal. On examination, it was found to contain much carbonic oxide, by which its nature, as far as it differs from the gas of coal, is readily understood. The cause of this difference will be apparent when the other circumstances in the constitution of this substance have been detailed. I thought it superfluous to examine accurately the nature of these gasses, but they probably consist of different mixtures of carbonic oxide, with light and heavy hydrocarbonate and olefiant gasses, if indeed, (as I much doubt) there be any real boundary by which the composition of these three last gasses can be defined.

If the process of distillation which I have now described be