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isovol
isovol n.
Brit. 
/ˈʌɪsə(ʊ)vɒl/
, /ˈʌɪsə(ʊ)vɒl/U.S. /ˈaɪsəˌvɑl/
[vol- (in volatile n. and adj.)] a line (either imaginary or on a map) joining places at which the coal has the same ratio of fixed to volatile carbon./ˈaɪsəˌvɑl/ΘΚΠ
the world > the earth > earth sciences > geography > map-making > map > [noun] > line on map > geological features or phenomena
isoseismal1883
isobase1892
isopachyte1912
isovol1915
isopach1918
isograd1924
isochron1968
1915 D. White in Jrnl. Washington Acad. Sci. 5 198 Lines were then drawn through the points of equal fixed carbon (or volatile matter). Such lines,..which I have termed ‘isovols’, are drawn to mark each 5 per cent increase in the fixed carbon in the pure coal.
1923 Glasgow Herald 11 June 7 The isovols for the Hutton seam take the form of a number of rings with a common centre to the north-west of Durham.
1928 E. R. Lilley Geol. Petroleum & Nat. Gas v. 113 The greater part of the oil of Pennsylvania is produced from pools lying between the isovols..of 55 and 60%.
1968 D. Murchison & T. S. Westoll Coal xv. 370 Fig. 15 shows lines of equal magnetic vertical intensity and the isovols of the Wealden coals.
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