=Coke.= About one-sixth of the bituminous coal mined in the United States is made into _coke_, that is, it is subjected to heat in ovens from which oxygen is excluded in order to drive off the volatile gases (chiefly hydrocarbons and water) which constitute about 40 per cent of the weight of the coal. The residual product, the coke, is a light, porous mass with a considerably higher percentage of fixed carbon than bituminous coal. In regard to composition, coking accomplishes artificially somewhat the same result reached by nature in its slow development of high-grade coals, but the texture of coke is far different from that of coal. Not all bituminous coals are suitable for coke manufacture; and such coals are frequently divided into two classes, known as _coking_ and _non-coking_ coals. Coke is used principally for smelting purposes. Because of its spongy, porous texture, it burns more rapidly and intensely than coal.
The gases eliminated in coking are wasted in the old-fashioned "beehive" ovens, but in modern "by-product" coke ovens these gases by proper treatment yield valuable coal tar products and ammonia. It is estimated that the sum of the value of the products thus recovered from a ton of coal multiplies the value of the ton of coal at the mine by at least thirteen times. The importance of this fact from the conservational standpoint cannot be too much emphasized. At present over half of the total coke produced in the United States comes from by-product ovens, and this proportion will doubtless increase in the future.
BALANCE SHEET SHOWING CONTRAST BETWEEN VALUE OF 1 TON OF BITUMINOUS COAL AT MINE AND VALUE OF PRODUCTS WHICH IT CONTAINS, BASED ON CONDITIONS PREVAILING IN 1915.[1]
_Value at _Value at point of mine 1915_ _Quantity_ production, 1915_ ------------------------------------------------------------------------- 1 ton (2,000 pounds) |(1,500 pounds smokeless fuel $5.00[2] bituminous coal |(10,000 cubic feet gas, at contains $1.13 | 90c. per 1,000 9.00[3] |(22 pounds ammonium sulphate at 2.8c. .61 |(2-1/2 gallons benzol, at 30c. .75[4] |(9 gallons tar, at 2.6c. .23[4] Total $1.13[5]| $15.59 ------------------------------------------------------------------------- 1: Gilbert, Chester G., and Pogue, Joseph E., The energy resources of the United States--A field for reconstruction: _Bull. 102, U. S. National Museum_, vol. 1, 1919, p. 11.