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

THE EVAPORATOR. IOI yield by large evaporators for the same time ; therefore, a minimum should be adopted before the proportion is worked out. To facilitate the understanding of this subject, suppose the diameters of two evaporators have to be deter- mined, one for generating steam at the hourly rate of 1,000 lbs., the other of 20 lbs. Assume that the area at the brine level is 400 square inches, which would make the diameter of the shell 22| inches. By the rule of pro- portion 1,000 : 20 :: 400 : 8. The diameter of a shell with an area of 8 square inches would be barely 3| inches, an absurd dimension for an evaporator. A minimum diameter should be fixed, so that the ratio would cause the small evaporator to be of a suitable diameter. (6) Material of Casing. 74. Undoubtedly the best material is gun-metal—that is, an alloy of copper and tin—the proportion of tin being between 10 and 12 per cent., and that of zinc 2 per cent, or less. This is Admiralty quality, and evaporator casings, especially the lower part containing the sea water, should be made of it. The steam-room is some- times made of iron or steel galvanised, as also are the base and cover, but it is best for the entire evaporator to be made of gun-metal, as the. corrosion is very great. When iron or steel is used it must be extra thick, in order to allow for the wear that sets in very quickly. Under these circumstances steel or iron casings become heavy and expensive, and are, then, not nearly so reliable as gun-metal. The upper part or steam-room may be made of copper, if preferred. It may be mentioned that quite small evaporators may be made of galvanised cast iron.