Modern Gasworks Practice

360 MODERN GASWORKS PRACTICE time a knowledge of the percentage of oxygen is of decided valne to the gas engineer, in that it conveys a useful idea as to the proportion of volatile matter. The latter is accounted for by both humus and resin constituents (in addition to the hydrocarbon bases), in both of which oxygen is present. Lewes has emphasized the importance ■of oxygen and has laid down the following axioms :— (1) The higher the oxygen in the coal, the higher the volatile matter. (2) The higher the oxygen, the. lower the coke yield. (3) The higher the oxygen, the greater the amount of CO and CO2. (4) Oxygen above 10 per cent, or below 4 per cent, means inferior coke or indicates a non-coking coal. As an illustration of the last statement the figures for the types of non-caking coals (about 13 per cent, of oxygen) and for anthracites (0-25 per cent.) may be recalled. Stopes and Wheeler,1 while agreeing that the classification suggested by Lewes deserves careful consideration, point to the faet that it is purely hypothetical, and there is considerable doubt whether “ carbon residuum ” and “ hydrocarbons ” exist at all in a normal coal. They state that his assumptions, therefore, are possibly quite incorrect, and that anthracite coals, for example, are not compounded ■of resin compounds and carbon, and that coking coals do not contain 30 per cent, of free hydrocarbons. It would seem that, as our knowledge of the subject stands at present, the suggestion made by Wheeler is the most helpful. This authority assumes that most coals contain— (a) A degradation product of cellulose (insoluble in pyridene). (&) A “ cellulosic ” constituent (soluble in pyridene, but insoluble in Chloroform). (1) A resinous constituent-, probably derived from the resinous portions of the original vegetable matter which produced the coal (soluble both in pyridene and in. Chloroform). Bone 2 states that among the parent substances in the organic débris from ■which. coals have originated, the following are chiefly of concern :— (2) Celluloses, i.e. ligno-celluloses. essentially carbohydrates n (C12H18O9) of a cyclic type. (6) Eesinic, i.e. gums, resins, and waxes, compounded of carbon, hydrogen, and oxygen. (c) Nitrogenens, i.e. proteid bodies, or compounds of carbon, hydrogen, ■oxygen, nitrogen, and sulphur. This worker states further that there is some evidence that small quantities of hydrocarbons are present in coals, whether associated with the resinic constituents or independently of them is not quite certain, but they are neitlier so prominent nor invariable as the three principal constituents mentioned above. 1 Monograph on the Constitution of Coal, 1918, p. 46. 2 Coal and its Scientific Uses, p. 73.