100 On the Extraction of Salts from Sea- Water, 



be formed, rendering the sea-salt impure. The mother liquor3 f 

 as they are called, are run off so soon as they have reached the 

 above density, and reserved for operations to be detailed further 

 on. When the salt has attained a sufficient thickness, it is broken 

 up and piled upon the sides of the basins in large pyramids, which 

 are covered with clay on the western coast of Fiance, but left 

 unprotected during the summer season, in the dry climate of the 

 south. In these heaps, the salt undergoes a process of purification ; 

 the moisture from the clay or from occasional rains penetrates 

 slowly through the mass, removing the more soluble foreign 

 matters, and leaving the salt much purer than before. In the 

 south, it is taken directly from these heaps and sent into the 

 market, but in the less favorable conditions presented on the 

 western coast, the thin layers of salt there collected are more or 

 less soiled with earthy matters, and for many uses require a process 

 of refining before they are brought into commerce. For this 

 purpose two methods are employed j the one consists in simply 

 washing the crude salt with a concentrated brine, which removes 

 the foreign salts, and a large portion of the earthy impurities The 

 other more perfect, but more costly process, consists in dissolving 

 the impure salt in water, and adding a little lime to precipitate the 

 salts of magnesia always present, after which the filtered brine is 

 rapidly boiled down, when a fine-grained salt separates, or is more 

 slowly evaporated to obtain the large-grained cubic salt which is 

 used in the salting of provisious. The masses of coarsely crystal- 

 line salt from the salines of the south have no need of these refining 

 processes. 



In practice, the evaporation of the brines for sea-salt at Berre 

 is carried as far as 32°, and the salt separated into three qualities, 

 Between 25° and 26° the brine deposits one-fourth of its salt, 

 which is kept apart on account of its great purity, and sold at a 

 higher price than the rest. In passing from a density of 26° ta 

 28°5, sixty per cent, more of salt of second quality are deposited, 

 and from this point to 32° the remaining fifteen per cent, are 

 obtained, somewhat impure and deliquescent from the magnesian 

 salts which it contains, but preferred for the salting of fish, on 

 account of its tendency to keep them moist. The average price of 

 the salt at the salines is one franc for 100 kilogrammes, (220 

 pounds avoirdupois,) while the impost upon it was until recently, 

 thirty times that sum, and is even now ten francs the 100 kilo- 

 grammes. 



