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

188 SEA WATER DISTILLATION. distilled water as is delivered for use outside the apparatus can be reckoned in the output. On the other hand, any extraneous heat used for obtaining steam for the pump annexed to the apparatus, or for heating the feed-water supplied to the apparatus, should be added to the coal account. These points are mentioned, as it is very easy to be misled. Note. In all cases where the economy of a distilling apparatus is specified as so many lbs. of water distilled by 1 lb. of coal, the specification should make it clear (1) that in the working of the apparatus heat from no other source is used, and (2) that the water counted is all available for use outside the apparatus. This is perhaps more im- portant than is at first sight apparent. Thus, to say 20 tons of water produced per ton of coal consumed may be strictly correct, yet if production is taken in the narrow sense of water distilled, the steam used by the pump may be ignored as not coming within the above wording, whilst the primary water, if returned to boiler and not available for use outside the apparatus, might still be held to come within the description of water pro- duced by distillation. Again, as will be seen presently, by starting a short trial with a high boiler pressure, and finishing off with a very much lower one, an extraordinary economy can be shown. In all these cases the true economy effected can only be ascertained after a long run with the apparatus, when the actual weight of coal used can be measured to a pound, and the actual quantity of distilled water actually delivered from the apparatus (foi extraneous use) counted to a gallon; then it will be seen to what extent the specified economy is real.