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Report on the Geology & Gold Fields of Otago

Oil Shale

page 150

Oil Shale

Orepuki.

This mineral was forwarded from Orepuki through Mr. Daniel. It was reported on in December, 1873, as follows:—Laminated, very fissile, greyish black, shale flexible in thin layers, densely speckled with mica scales, cuts easily with the knife with unctuous, waxy, section; inflames readily over ignited lucifer match, and maintains after removal of the match a long somewhat smoky flame; the shale shows no trace of woody tissue.

Distilled at low and gradually increasing temperature it yields 42 gallons of crude tarry oil to the ton of shale. This oil possesses the characters of petroleum. It melts at 30°C (86° F.), and at 15°C. (59°F.), has a specific gravity of 0.897. This crude oil, after treatment with sulphuric acid and caustic soda and redistillation, yields from 1 ton of shale 15.2 gallons of purified oil of specific gravity, 0.798 to 0.860, suitable for burning in lamps; also 7 gallons of oil of specific gravity from 86 to 93, suitable for lubricating machinery. At higher temperatures the residue of the above distillation yields a still heavier oil, also suitable for lubricating purposes; finally a liquid tar is obtained, leaving charcoal in the retort. The products of the first distillation are:—
Water 25 per cent.
Earthy residue and charcoal 49.5 per cent.
Crude oil 16.8 per cent.

Dunedin.

This shale was forwarded by Dr. Burns from Burnside, near Blueskin. It is of the same mineral nature as the Orepuki shale, described above. It yields per ton of shale 38 gallons of crude oil. This, when purified by redistillation, after treatment with sulphuric acid and caustic soda in succession, yields per ton of shale about 14 gallons of oil, fit for burning in lamps, and 9 gallons of heavy unctuous oil suitable for lubricating purposes.

If we could produce our own sulphuric acid and soda cheaply, it might be profitable to extract burning and lubricating oils from these shales. As it is, the price of imported acids and alkalis is such as to deter the proprietors of these shales from importing the retorts and other appliances necessary for this purpose.