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

THE EVAPORATOR. 89 47. Since the above types of heating surfaces have been introduced countless types, more or less like these already mentioned, have been placed in the market or advertised. Thus, coils are made in the form of a volute, either hori- zontally or vertically fitted to the casing (and it may here be noted that fitting the coil to the door is somewhat discountenanced), some coils are made zig-zag, or with various contortions, according to the fancy of the makers. 48. The type of heating surface or coil that is really best is the one that satisfies most completely all the re- quirements of practical working, and these requirements may be shortly summarised as follows :— 1st . The heating surface required should occupy the minimum of space. 2nd . The coil or tube surface should be capable of being easily freed from scale. 3rd . The coils should be light and easy to handle, remove, and replace. 4th . The joints must be tight and durable, and when the coils have to be removed, must be easily broken and re- made. 5th . All the coil joints should be exposed to view when tested either by water or by steam. 6th . The coils should allow the primary water to leave the inner coil surface easily, without lying there, as this deadens its heating power by preventing the access of steam to it. 55. The above points are perhaps the most important to keep in view when arranging for the heating surface of an evaporator, so as to give the greatest satisfaction in