On the Extraction of Salts from Sea-Water. 107 



already covered with a layer of sea-salt, are very advantageously 

 employed for the evaporation of the mother liquors, from the ease 

 with which the potash and magnesia salts may be collected from 

 it in a state of purity. 



The amount of salt produced in France in 184*7 was about 570, 

 000 tons, of which 263,000 were from the salt-marshes of the Me- 

 diterranean, 231,000 from those of the western coast, and 76,000 

 from salt-springs and a mine of rock-salt ; there were employed 

 in these 16,650 workmen. If we estimate the produce of the salt 

 marshes in round numbers at 500,000 tons, the amount of chlorid 

 of potassium to be obtained from the mother liquors, at one per 

 cent., will be 5000 tons, and that of the sulphate of soda at seven 

 per cent, will be 35,000 tons. The amount of sulphate of soda 

 annually manufactured in France is 65,000 tons, requiring for 

 this purpose 54,000 tons of sea-salt, and nearly 14,000 tons of 

 sulphur, which is completely lost in the manufacture of carbonate 

 of soda.* If now the mother liquors from an area twice as great 

 as is now occupied by all the salines in France, were wrought 

 with the same results as atBaynas, they would yield besides 70, 

 000 tons of sulphate of soda, or more than is required for the 

 wants of the country, 10,000 tons of chlorid of potassium, equal 

 to 9,250 tons of pure carbonate of potash, a quantity far greater 

 than is consumed in France, and would enable her to export poi- 

 ash salts. According to Mr. Balard the consumption of potash 

 in France amounted in 1848 to 5,000 tons, of which 3,000 were 

 imported, and 1,000 tons extracted from the refuse of the beet- 

 root employed in the manufacture of sugar. 



The production of the two alkalies, potash and soda, offers some 

 very interesting relations. Previous to the year 1792, soda was 

 obtained only by the incineration of sea-weed and maritime plants, 

 but it was at that epoch, when France was at war with the whole 

 of Europe that her necessities led to the discovery of a mode of ex- 



* The soda manufactory of Chaunay, established in connection with 

 the glass works of St. Gobain, consumes above 5,000 tons of sulphur 

 yearly, and the immense establishment of Tennant, at St. Rollox, near 

 Glasgow, employs annually 17,000 tons of salt, 5,550 of sulphur, and 

 4,500 tons of oxyd of manganese. It produced in 1854, 12,000 tons of so- 

 da-ash, 7,000 of crystallized carbonate of soda, besides 7,000 tons of 

 chlorid of lime, prepared with the chlorine obtained by decomposing the 

 waste hydrochloric acid from the soda process by the oxyd of manganese. 

 The cost of sulphur in England in 1854 was about twenty-five dol- 

 lars the ton. 



