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

MULTIPLE DISTILLATION. 195 but taking its evaporative power at of the total out- put, then 4^ of 4,000 — 1,333 lbs. to be evaporated per hour. (5) For quintuple and sextuple distillation the primary or boiler pressure should be 150 lbs. per square inch or more. The size of the boiler would be ascertainable in the same way as before—i.e., by taking the proportion of boiler evaporation to the total output. Economy Involved. Note.—The economy one is able to obtain from a dis- tilling plant depends very much on the size and type of boiler selected. It should be borne in mind that a small boiler is less economical of fuel than a large boiler, and that a vertical boiler is less economical of fuel than a boiler of Cornish or Lancashire type. For a consumption of 1 lb. of coal a large Lancashire will evaporate 10 lbs. of water, whereas a small Cornish or a large vertical boiler will evaporate only about 7 to 8 lbs., and a small vertical boiler only 4 to 5 lbs. of water; in other words, large boilers are about 20 to 25 per cent, more economical than small boilers, and Cornish and Lancashire boilers about 20 to 25 per cent, more economical of fuel than boilers of vertical type. 50. In all these types it is well to remember that it is always best to work at the lowest boiler pressure possible, with the steam valve full open, and not at an excessive pressure with the valve partly open. 51. The above working pressures are perhaps not ap- plicable to every type or system of multiple distillation ; but with the system explained more in detail in these pages, the working for types of apparatus ranging from