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

i82 SEA WATER DISTILLATION. Economy and Time Productions. 25. It cannot be too often repeated that the economical working of an apparatus is a totally different thing from its productive power in point of time. The yield of a fixed quantity in a fixed time may be the same for any type of distiller, but the economy varies with each evap- orator added, and is dependent, therefore, wholly on the type of apparatus at work. Generally, the same appar- atus will show the same economy whether its time production is large or small. The larger the apparatus (or, to put it strictly, the larger the boiler) the more economically will the whole apparatus work. Summary of Types. 26. The following points may be summarised in com- paring the various types of distilling apparatus as the multiple effect is gradually increased :— First.—That as every evaporator is added, in order to get more distilled water for the same weight of primary steam—that is, indirectly, the same coal consumption— the primary pressure must be gradually increased, or the final pressure must be reduced. Secondly.—That the lower the pressure is (from first to last) the more must be the evaporator heating surface. Thus if, in treble distillation, the initial pressure is 75 lbs. and the final zero, the heating surface must be greater if such initial pressure is, say, only 50 lbs. per square inch. Thirdly.—That at each successive distillation, although the total production is more, each distillation produces