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

58 SEA WATER DISTILLATION. ably less powerful than coal in giving heat, whilst pet- roleum is a good deal more so. 8. Wood fuel entirely depends on its dryness, and its closeness or density, for its power of giving heat, as the composition does not vary. In India, larch or Casuarina plantations are cultivated to supply wood fuel. The heating power of wood is about half to a third that of the same weight of coal. Note.—The heating power of wood may be taken as follows :—One lb. of perfectly dry wood contains 0'51 of carbon, whilst the residue, 0’47, consists of hydrogen, 0'053, and oxygen, 0'417. In the process of combustion this 0‘47 of hydrogen and oxygen must be ignored, as they combine so as to form water. Thus we have— B.T.U. Carbon,_____________________051 x 12,906 = 6,582 Hydrogen, . 0'053 Less, . 0’052 used with oxygen to form water (0-417 4- 8 = 0-052). 0'001 surplus x 62,535 . (say) = 62 B.T.U. obtainable from 1 lb. of dry wood . . = 6,644 The prolonged experiments of Péclet in wood com- bustion in a practical way show that from about 3,500 to 5,500 B.T.U. is the heat obtainable per lb. of wood of ordinary dryness. 3,500 B.T.U. seem rather low, whilst 5,500 B.T.U. seem rather high in practice. The effect of moisture in wood can be demonstrated as follows by- dealing with 1 lb. of wood having, say, 20 per cent, of moisture, which is ordinary dryness.