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

6'2 SEA WATER DISTILLATION. hold. Particulars thereof may be obtained on applica- tion to the makers of the apparatus. 13. When it is necessary to produce distilled water in only very small quantities, and at intervals—e.g., for use in a large household for drinking water, or for electrical generating stations in connection with accumulators or storage batteries—gas affords a very handy means of supplying the heat needed to evaporate water that is too saline or otherwise impure for such uses. It can be turned on and off at pleasure, so that the initial cost of gas, as compared with coal, is very much diminished when this is taken into consideration. A coal fire would be too small for such a purpose, and would require keep- ing up, while oil, with its wick and constant cleaning of the lamp, is not so convenient as gas. The arrangement of a small distilling plant heated by gas will be described later on in Chapter x. 14. Town gas, as manufactured by the various gas companies, is supplied at a rate varying from 2s. 6d. to 3s. per 1,000 cubic feet. 15. The specific gravity of coal gas is 0’45 (air being 1), and the weight of 1,000 cubic feet of gas is, therefore, about 33 lbs. One thousand cubic feet of gas has a heat giving power of about 570,000 to 600,000 B.T.U., and 1,000 cubic feet of gas is produced by about 0-095 to 0’1 ton of average coal, or, put conversely, 1 ton of coal will yield about 9,500 to 10,000 cubic feet of gas. Much, of course, depends upon the kind of coal used. Composition of Gas. 16. Coal gas is obtained by the destructive distillation of coal, and its composition (by volume) is approximately as follows :—