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

38 SEA WATER DISTILLATION. In the second case it is— 239 - 60 = 179 units of sensible heat] 10 lbs. (net) 946 units of latent heat J pressure. 1,125 units (total) heat. 8. From a study of Table E it will be seen that as the pressures rise the sensible heat increases, whilst the latent heat cZecreases, so that the total heat is consequently not very much affected. It will thus be observed that, for practical purposes, the total heat required (or the fuel consumed) to generate steam will not vary greatly what- ever may be the pressure at which such steam is generated, because the pressure obtained can be kept up with very- little augmentation of heat expense. Note.—This state of things lias a most important bear- ing in the distillation of sea water, especially when the distilling apparatus is of the multiple or compound type. 9. To illustrate this, for the purpose of understanding what takes place in distillation, Fig. 2 shows a vessel (E) with a Bunsen gas burner (G) under it. Let us suppose that 1 lb. of water is put in the vessel (open at top), and its temperature is, say, 60°, as indicated by a thermometer placed in the water. On lighting the gas the temperature of the water will gradually rise, and will continue to do so till the temperature of 212° is reached. Then the water will boil, and will continue to do so, but the ther- mometer will record no more heat, whether its bulb is put in the water or in the steam rising therefrom, because it can only record the sensible heat. 10. The water keeps on boiling, whilst the gas is still burning, and steam keeps on being given off at the open