On the Extraction of Salts from Sea-Water. 103 



We may mention here a process which, although unknown in 

 France, is applied in Russia on the borders of the White Sea, and 

 may, perhaps, be advantageously employed on our own shores. It 

 consists in applying the cold of winter to the concentration of the 

 sea-water. At a low temperature a large quantity of ice separates 

 but all the saline matters rest in the liquid portions, so that by 

 separating the ice, a concentrated brine is obtained, which may 

 afterwards be evaporated by the summer's sun or by artificial heat. 



Treatment of the Bittern or Mother Liquors. — The waters which 

 have reached a density of 32° in the salting tables, have already 

 deposited the greater part of their common salt, and now contain 

 a large amount of sulphate and hydrochlorate of magnesia, together 

 with a portion of chlorid of potassium. The admirable researches 

 of Mr. Balard have taught us to extract from these mother liquors, 

 sulphate of soda, and salts of magnesia and potash, so that although 

 formerly rejected as worthless, these liquors are now almost as 

 valuable as the salt of which they are the residue. 



The production of sulphate of soda, which is directly employed 

 in the manufacture of glass, and as a manure, and still more large- 

 ly as a material for the fabrication of carbonate of soda, is the 

 most important object of the working of the mother liquors. Im- 

 mense quantities of sulphate of soda are now prepared in France 

 and England by decomposing sea-salt with sulphuric acid> 

 which is manufactured with sulphur obtained chiefly from 

 foreign sources. In view of this immense consumption of sulphur, 

 it becomes important, especially in time of war when this substance 

 is required for the fabrication of gunpowder, to find some source 

 of sulphate of soda other than the decomposition of sea-salt by 

 sulphuric acid. This process is besides objectionable from the 

 vast amount of hydrochloric acid disengaged, which in most local- 

 ities cannot be entirely consumed, and is very pernicious to both 

 animal and vegetable life in the vicinity. 



It had already been observed that under certain conditions the 

 reaction between sulphate of magnesia and chlorid of sodium 

 could give rise to sulphate of soda ; and Mr. Balard has shown that 

 by taking advantage of this decomposition, the sulphate of soda 

 can be advantageously prepared from the bittern of the salting 

 tables. 



When the liquors of 32° are evaporated by the summer's heat, 

 they deposit during the day a portion of common salt ; but the 

 coolness of the nights causes the separation of crystals of sulphate 



