The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part V. Mineral fuels

Collection:: Economics Books

264 ECONOMIC GEOLOGY Its age is generally Upper Pal®ozoic, and mainly Carboni- ferous; but it is found in the Bathonian rocks at Brora in Northern Scotland, and in still later rocks that have under- gone much disturbance. The two chief varieties of bitu- minous coal are the coking and non-coking. In coking coal some of the material becomes plastic and agglutinates the rest into firm cellular coke, from which the volatile con- stituents have been expelled as gas, pitch, coal-tar, and oil. Coke is a smokeless fuel, and is indispensable for blast furnaces as non-coking coals fall to pieces when burnt. The cause of coking has been long discussed, and is not yet fully understood. Many coals lose their coking quality on exposure to the atmosphere, and by gentle heating. The clue to this property was given by Anderson, who found that a coal which loses its coking property when heated in air retains it if heated in carbon dioxide. The loss of the pro- perty is due to the oxidation of some resinoid constituent, on the nature of which much light has been thrown by the researches of Prof. W. A. Bone (Proc. R. Soc., A, 1922, c, Pp. 582-08; cv, 1024, p. 625). The coking quality of coal is ex- pressed by the *‘ coking index,” which is the proportion of sand that is cemented by a given weight of the powdered coal when heated in a crucible. Coal with a coking index of less than 171 is useless for coke; that with an index of 12-15 can be mixed with better coking coal; the grades 16-19 include good, and 19-28 the best coking coals. Bituminous coal often consists of layers or patches of four different types of material. The dull black, often powdery charcoal-like material, known as mother-of-coal, or fusain, has been regarded as charcoal made by forest fires during the formation of the coal seam ; it appears to be derived from material which has undergone carbon enrichment by de- composition before burial in the seam. Dull hard layers in coal, which are opaque in thin sections and contain many spores, consist of durain; the glossy translucent variety is clarain ; and the jet-like structureless bands are vitrain. AnTtHRACITE—Anthracite is a hard black coal which does not stain the hand, burns slowly without smoke and with a slight blue flame, and gives off intense heat. It cannot be kindled with wood; but if ignited by bituminous coal or gas it burns steadily until entirely consumed. Anthracite

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