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

MULTIPLE DISTILLATION. 201 ible (or gaseous) heat of the steam (at its particular pressure) inside the coils, and that of the sea water out- side the coils, which is continuously absorbing a sufficiency of latent heat to convert it into steam; whilst the steam inside the coils is being continuously converted into water, and more steam of same pressure (and, therefore, tem- perature) is being supplied inside the coils to meet the requirement outside the coils. Uniformity of Surface. 65. The evaporator surfaces should be the same in all the evaporators, to allow for the proportionate falling off of power as the pressure is gradually lowered at each successive distillation. This is required by the rule that as the steam pressure (and, therefore, heat) inside the coil is lowered, or counteracted by a pressure (and, there- fore, heat) outside the coil, so must the coil surface be proportionately increased, to do the same amount of work (see pp. 46, 47). Extent of Surface. 66. The exact amount of surface depends, as we have ' seen, upon the quantity of water to be evaporated in a given time, and the temperature and quantity of feed- water that is presented to be heated up to boiling point, also the pressure of steam inside of the coil. 2. Safety Valve. 67. As all the evaporators (except the final one, which discharges its steam into the distilling condenser, or rather, as will be seen, into the heaters) have to work at a pressure, more or less high, they should each have a