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

90 SEA WATER DISTILLATION. working ; these points may be supplemented by the following observations :— (1) The volute-shaped coil would appear to be the best for cracking off the scale as it accumulates. (2) The original vertical straight tube would appear to be the best for allowing the primary water to get away from the inside of the heating surface. (3) Most makers prefer the primary steam to enter at the top of the coil, and the primary water to drain away at the bottom, so as to be helped by gravitation. This is not, however, obligatory, as the primary water will always be blown forward by the primary steam, whether the coil (in volute shape) is placed vertically or horizon- tally. (4) The coil in volute, when lying horizontally, accom- modates itself better to the cylindrical casing. (5) Again, it is better for the coils to be similar and distributed in sets of eight or ten each than to be grouped in one sheaf or nest. Lightness and ease of cleaning are at once obtained by having the coils separate. (7) The coils should be interchangeable. 50. The foregoing description of various types of heating surface is not, as already stated, intended to be exhaustive, there being a great number of designs of heating surface, more or less alike in their description, and more or less favoured. The object was to show the gradual improve- ments made in evaporative surfaces on the original straight and vertical sheaf of tubes shown in Fig. 5. First, there came the horizontal U-shaped tubes grouped together in one sheaf or nest; then the circular or volute- shaped coils, also grouped together and fitted to the inside of the cleaning door ; then the same class of coils, but not