MINERAL OILS.
Mineral oils include the folhiwing products :—Peat-oils, or the hydrocarbons which may be dis tilled from peat ; shale-oils, or similar bodies obtainable from bituminous shales; coal-tar-oils, or allied products of the distillation of the tar obtained in making illuminating-gas ; and, most im portant by far, the large series of petroleums or rock-oils found ready-formed in certain geological strata in many parts of the world.
Peat-oils.--Before the introduction of American petroleum, the distillation of oils from peat was a remunerative industry in this country ; but where petroleum, bituminous shale, or oil-coal can be had in abundance, the profitable utilization of peat-oil in this manner is impossible in the present state of our knowledge and appliances. Of the bog-peats formerly distilled by the Irish Peat Co., 100 ton, in close retorts, gave 2 ton 15 cwt. of tar, yielding 409 gal. of refined oils and paraffin ; by kiln treatment, 2 ton 8 owt. of tar, affording 304 gal. of oils and paraffin. Dense mountain peat from Antrim, in Dr. Hodge's experiments with 50 tons, produced at the rate of 4.44 per cent. of tar. The very dense bituminous peat cut by Sir James Matheson, in Lewis, one of the Hebrides, returns, from 100 tons, air-dried, by close retort, 2097 gal. of tar, equivalent to 1629 gal. of crude oil, 999 gal. of which may be secured in the refined state. This was highly profitable when the oil sold at 2s. a gal., but the production of oil has long been discontinued even here, and the tar is used in the ship-yards.
Shale-oils.--Beds of dark, coaly-looking mineral, known as " bituminous " or " bituminiferous shales, occur in this country in the Tertiary, Cretaceous, Oolitic, Triassic, and Carboniferous forma tions. These vary in quality and aspect, according to the proportion of mineralized organic matter present, ranging from a mere argillaceous mineral almost to coal. The beds vary in thickness and in character ; they are inte•stastified with sandstones, limestones, coals, &e.; and are mined much in the same way ss coal. Many of the Oolitic and Wealden shales, though valuable for some pur poses, are useless as sources of illuminating-oils, and it is those of the Carboniferous system that are ohiefly distilled for the production of paraffin and paraffin-oils. Bituminous shales occur in most
British coal-fields. Their production in 1880 was as follows :— The shales of the lower coal-measures of Linlithgow, Lanark, Ayr, Fife, and Midlothian are those most largely raised for distilling. Superior shales are recognized by their lightness and toughness, or " boardiness," in mining phraseology, and by their brown streak. Those in use yield a quantity of crude oil varying from 18 to 80 gal. a ton. This branch of manufacture is discussed at length in the article on Paraffin.
An earthy lignite occurring within a small portion of the Saxon Thuringian brown-coal forma tion, between Weissenfels and Zeitz, forms the material for a large mineral oil and paraffin industry, dealing with some 36,000 tons of tar annually, and producing about 12,500 tons of paraffin-oils, 6000 tons of gas- and lubricating-oils, 5000 tons of paraffin, and 3600 tons of accessory products. This lignite contains nests and branches of a fusible hydrocarbon (pyropissite), yielding as much as 66 per cent. of tar on distillation.
Coal-tar-oils.—The extraction and utilization of the oils contained in coal-tar will be found fully described and illustrated in the article on Coal-tar Products, pp. 641-684.
Petroleum, Rock-oil, Naphtha, or Mineral Tar (FR., Bitume liquids; GER., Erdal, Steintil).—These names are applied with little discrimination to a class of liquids occurring in various geological formations and geographical localities; possessing a more or less limpid, oily consistence, a strong bituminous odour, a usually dark yellowish-brown colour, a sp. gr. ranging from to 1.1; and composed of hydrocarbons varying in constitution and boiling-point in almost every case, as will be noticed further on. Very closely allied products are asphalte or native bitumen (see p. 341), and ozokerit or earth-wax (see Wax—Ozokerit).