532 THE POPULAR SCIENCE MONTHLY. 



posing the proportion was too slight to be appreciable. Count Mar- 

 sigli, who in the reign of Louis XIV tried to make sea-water artificially, 

 took great pains to mix bitumen with the salts he put in solution, in 

 order to make the reproduction perfect. The partisans of the theory- 

 cited the Dead Sea, which was near asphalt-beds, and the waters of 

 which were insupportably bitter. But Macquer, assisted by Lavoisier, 

 a hundred years ago, carefully distilled specimens of this water, and 

 found in it no more bitumen than had been found in Mediterranean 

 water — which was none at all. He attributed the bitter taste of this 

 water to the presence of salts of magnesia. 



It is not to-day that investigators have sought to make sea-water 

 potable by removing its nauseous taste. The problem w^as solved long 

 ago, and, as often happens, the usefulness of the invention once so 

 greatly desired has been much depreciated. AVhen fresh water for 

 the provisioning of vessels was stored in wooden casks, it was liable to 

 spoil in a short time. Now it ia carried in large iron tanks, in which, 

 instead of spoiling, it is improved by acquiring a ferruginous quality. 

 The ancients did not venture far from the shores, and were contented 

 with a simple coasting-trade ; nevertheless, this question interested 

 them, and Pliny describes two means of freshening the water of the 

 MediteiTanean, one of which is absurd and the other impracticable : 

 One was to plunge into the sea hollow balls of wax, which, the author 

 affirms, would be filled with pure water ; and the other was to expose 

 fleecy sheep-skins on the deck of the vessel, to collect the morning 

 dews. 



Whoever examines the series of memoirs published during the 

 seventeenth and eighteenth centuries, on the subject of freshening sea- 

 water by distillation, must be struck by the divergence of opinions and 

 the want of concordance in the results, some declaring that distilled 

 water is pure, healthy, and tasteless, others that it is unhealthy and 

 almost as detestable as before the operation. The differences between 

 them are easily explained. Marine salt is not the only substance dis- 

 solved in the water, but is accompanied by several other bodies, the 

 principal of which is chloride of magnesium. This salt when dry re- 

 sists the action of the most violent heat without changing ; but in boil- 

 ing water undergoes a double decomposition, in which the chlorine 

 leaves the magnesium to unite with the hydrogen of the water, while 

 the oxygen thereof unites with the magnesium. There is thereby pro- 

 duced magnesia, which remains in the vessel, and hydrochloric acid, 

 which is distilled over. Now, distilled water is made impotable and 

 unhealthy by any traces of that acid. The difiiculty may be obviated 

 by previously removing such salts as can be made to settle, or by add- 

 ing fresh sea-water. Water boils at a temperature several degrees 

 higher than usual when it is charged with salts. If it is sufficiently 

 diluted it will not disengage hydrochloric acid. Or the acid may be 

 absorbed b;f substances added to the water for that purpose, and which 



