PROPERTIES AND COXSTITUTION OF SEA-WATER. 539 



When concentrated by any means, sea-water deposits, first, cai'- 

 bonate of lime, next gyi^sum, or sulphate of lime, and then salt ; and, 

 lastly, the salts of magnesia and the bromides. The phenomena are 

 not quite so simple in practice, and the deposits of salt-marshes are 

 rarely composed of a single substance ; but we have only intended to 

 indicate the general course of the operation. The salt of commerce 

 is rich in magnesia, or chloride of magnesium, in proportion to the 

 strength of the concentration. Some have even sought to ascribe the 

 enormous deposits of gypsum found in certain regions to ancient seas 

 which, in drying up, deposited that substance among the first. 



Potash and the bromides, substances that are relatively little abun- 

 dant, accumulate in the mother-waters till they become so condensed as 

 to make the industrial working-out of them remunerative. Bromine is 

 less abundant in the Mediterranean than in the waters of the Dead 

 Sea, which may some day become a source of production. Eighteen 

 centuries ago the Romans, according to Pliny, brought to Italy at 

 great expense the water of the Asphaltine Lake, the curative properties 

 of which were held in high esteem. The excess of bromine in this 

 water, however, corresponds exactly with its greater total saltness, so 

 that, except for a few qualifications to which we shall refer again, the 

 relative composition of the dry residue of the Dead Sea is the same 

 as of that from the ocean. In other words, any marine water evapo- 

 rated to the same degree of density as that of the Dead Sea would be as 

 deleterious to living beings. 



Marine ice was formerly regarded as formed of solidified pure wa- 

 ter retaining by mechanical adhesion traces of the saline liquid. These 

 traces could be expelled by energetic jDressure, when acids and bases 

 would be found in the residue of desiccation in invariable proportions 

 as in the sea. The question of chemical composition of the ice of the 

 Arctic Ocean is complicated in other ways, but it gains in interest 

 what it loses in simplicity. When salt-water is cooled artificially, a 

 small part escapes solidification. The uncongcaled residue is insup- 

 portably bitter to the taste, and analysis shows that nearly all the 

 magnesia is concentrated in it. The solid block, if it is homogeneous 

 and is not full of holes, and if previously drained, may furnish a pass- 

 able drink. The natural ices of the Northern Sea are frequently 

 moistened with a kind of bi'ine, which sometimes embodies crystals of 

 special character, easy to distinguish from the ice around them. Ac- 

 cording to Otto Petterssen, the relative proportions of chlorine and 

 magnesia are much stronger in these exudations than in the water at 

 the expense of which the ice is formed. The liquid can not then have 

 been mechanically absorbed. On the other hand, there is a deficiency 

 of sulphates ; and the conclusion that sea-water ice retains the sul- 

 phates more abundantly is confirmed by analysis. With congelation, a 

 sorting of matters takes place ; most of the sulphuric acid passes into 

 the part that solidifies, while magnesia and chlorine prevail in the part 



