A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

FUELS. 55 Coal exists in many varieties. The most important are :— Anthracite class, which is almost pure carbon, and with this class may be included the hard Welsh steam coal. When burnt, the heat of this class of coal is very intense. Bituminous coal, which may be more or less hard, so as to be suitable to some extent for the same uses as the anthracite coal, or more or less soft, when it borders on a gas-making coal. Cannel coal, which is used almost exclusively for gas- making. 3. Coal varies considerably in its heating capacity— that is, its heat-giving power. The heat capacity is usually specified by the number of units of heat it is capable of emitting per lb. consumed—that is, the num- ber of units (B.T.U.) 1 lb. of coal is capable of imparting to water, so as to convert a proportionate weight (say in lbs.) of water into steam. 4. We know that to convert 1 lb. of water into steam at 212°, at atmospheric pressure, it requires 966 B.T.U. Therefore, if a certain quality of coal is capable of con- verting 10 lbs. of water (in ordinary working of a boiler), the calorific effect of such coal may be stated to be 9,660 (i.e., 966 x 10 = 9660). Of course, experiments with coal scientifically conducted may show a considerably higher efficiency, and the theoretical heating capacity may be, and in point of fact is, specified at about 30 to 50 per cent, more, but this cannot be realised in the ordinary working of a boiler, however economically the working in practice may be. By scientific experiments, made with something like 100 specimens of coal—English,