ON SWEETENING SEA-WATER. 3GQ 



9. water, which contains so little saline matter as scarcely to be dis- 

 tinguished from fresh water I>y the taste, or indeed by chemical 

 tests. It is evident, however, that this method can only be resorted 

 to in certain latitudes or at certain seasons of the year. 



The otlier method, therefore, viz. that of distillation, is greatly 

 to be preferred, being feasible (with a proper apparatus) at all times 

 and in all situations, and, when properly conducted, yielding a water 

 as pure and as sweet as that procured by congelation. It was for- 

 merly supposed that in order to obtain fresh water from sea-water 

 it was necessary to add to this last, before the distillation, calcareous 

 earth, potash, or certain other substances, for the purpose of ab- 

 sorbing and retaining a bituminous matter, which all sea-water was 

 supposed to contain in greater or less quantity, and to which was 

 ascribed the unpleasant empyreumatic taste of the water distilled 

 from it, especially if too strong a fire is employed, or the distillation 

 is pushed too far. Dr. James Lind, however, has proved that such 

 additions are useless, since pure rain water contracts in like manner 

 a burnt taste by distillation ; which shows that it is derived from 

 the action of the elementary water on the heated metallic vessels. 

 This disagreeable flavour, however, goes off, for the most part, on 

 exposing the distilled water to the air. Nothing more is requisite, 

 then, for obtaining fresh water from salt water, than to be provided 

 with a common still j or with still-head covers made to fit the cop- 

 pers used for boiling provisions on bo^rd of ship ; and a worm. tub 

 or cooler for condensing the steam. (See Dr. Lind's Essay on pre-, 

 serving the health of Seamen. Also, the Appendix to his Essay on 

 Diseases incidental to Europeans in Hot Climates.) Some years after 

 this discovery was made known by Dr. Lind, [It would appear how- 

 ever that the simple distillation of sea-water, for the purpose of 

 procuring fresh water, was practised by Sir Richard Hawkins, in the 

 reign of Queen Elizabeth. See the Bishop of Llandaff's (Dr. Wat- 

 son's) Chemical Essays, vol. ii.] an improvement was suggested by 

 Dr. Irving, in the mode of distillation; wherein he substituted for 

 the condensation of the steam, a large open pipe kept constantly wet 

 with mops, in place of the small slender pipe passed through a tub 

 of cold water, in the usual way. This, ffomlbeUig applied to larger 

 coppers than the common method ever had been in the distillation 

 of sea-water, yielded in a given time, and with the same quantity of 

 i'nel, a larger quantity of fresh water. 



VOL. III. 2 B 



