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

MULTIPLE DISTILLATION. 175 heating medium to the evaporator, but on a land ap- paratus, where boiler water does not acquire a greasy taint, the whole of the water, whether produced by the boiler or by the evaporators, can be mixed together, and counted as the production obtained by the coal or other fuel consumed. In land apparatus, therefore, the primary- water is included with the gained water. 12. In some types of land distilling machinery the prim- ary water is still returned to the boiler, and only the water distilled from the steam generated by the evaporators is counted. By this means the boiler is fed with fresh water instead of sea water, but the difference in the economy of working (i.e., the amount of drinking water produced against the amount of coal consumed, weight for weight, is necessarily very much less than when the boiler is fed with sea water), and all the distilled water (including boiler evaporation) is counted against the amount of coal consumed (weight for weight, as before). Not only is the economy a good deal less (how much less will be shown presently), but the apparatus will have to be considerably larger, and consequently more expensive for the daily amount of water required, if the boiler dis- tillation is retained, and not included in the general output per day. 13. Therefore, for the present purpose of explaining the principles of multiple distillation, it is proposed to assume that the boiler, like the evaporators, is fed with the same class of sea water, and that the water distilled from the boiler and evaporators, and the condensed steam or vapour from evaporation are mixed, and the total output counted against the coal that has been consumed to obtain it.