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

MULTIPLE DISTILLATION. 183 less. Thus, although in double distillation the total pro- duction is more than in single distillation, yet the second- ary water is less than the primary water, and in treble distillation, although the total production is more than in double distillation, yet the tertiary water is less in quantity than the secondary water, and so on. Fourthly.—That although at each successive distillation the production is less in degree (though more in total), the evaporators all have the same amount of heating surface. Thus, in quadruple distillation, although the 3rd evaporator affords only a gain of 5'2 tons, as against 8 tons by the 1st evaporator, both evaporators have the same evaporative surface. Fifthly.—That the combined or joint production (in point of time) of all the evaporators in multiple distil- lation is about the same as the production would be if only one of the evaporators were used and worked with the same pressures (initial and final) as the multiple distilling apparatus. Uniform evaporators are understood. Note.—To make this point clear—say that in treble distillation the primary water is 10 tons in a fixed time, and that the gained water (secondary and tertiary) in the same time is 14’4, making a total mixed production of 24'4 tons in the given time, and that the initial pressure (boiler steam) is 75 lbs. per square inch, and the final pressure in the 2nd evaporator casing is { lb. If, instead of the evaporators being coupled together, the boiler steam at 75 lbs. pressure went into the 1st evaporator, and the pressure in that evaporator casing is reduced to lb., while the 2nd evaporator is cut out altogether, then the existing surface of the 1st evaporator, with 75 lbs. steam pressure inside the coil, would be capable of producing