The heating effect is all-important

It is usually expre ed in heat units, each unit being the amount of heat required to heat one kilogramme of water one degree Centrigrade. Thus the calorific value of pure carbon is 8,080 calories, which means that the heat evolved in the combustion of any given weight (as one kilogramme) of carbon would raise the temperature of 8,080 times that weight of water one degree Centigrade, or 8,080 x-14,544 kilos one degree Fahrenheit. The principal constituents of fuels are carbon, hydrogen, oxygen, water, and ash; only the first two are combustible, and only as much of the hydrogen as is not already combined with the oxygen present. The calorific power is determined experimentally by burning the finely-powdered fuel in compre ed oxygen gas in the "calorimetric bomb." which is immersed in water and the heat thus measured; or, practically, by finding out how much water the burning of a given weight of fuel will evaporate. Another simple method, giving reliable comparative results, is that of mixing the powdered fuel with litharge, heating to redne in a closed crucible, and comparing the weights of the lead buttons obtained, which vary directly as the calorific powers of the fuels. The following table gives the actual calorific powers as obtained in the calorimetric bomb, also the theoretical and the practical evaporative powers. The figures represent average values: IMG:content-0184.png:[ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small] The practical efficiency of liquid and gaseous fuels is nearer the theoretical efficiency than in the case of solid fuels, because they can be more perfectly consumed.