SALT 



Solid contents in 100 parts of brine. 



743 



long by 24 wide, and elevated 4,000 feet above the level of the sea ; it is surrounded, 

 especially on the east and north, by some of the most remarkable surface-deposits of 

 rock-salt in the world, and through these salt streams are continually flowing into the 

 lake. The Russian brine pools are situated in the salt-impregnated steppe between 

 the rivers Ural and Wclga, and doubtless derive their saline constituents from thence. 

 The Great Salt Lake is a saturated solution of almost pure chloride of sodium, but 

 whence the salt is derived appears at present to be but a matter of conjecture. To 

 the second cause the origin of the Dead Sea is frequently attributed ; its surface is 

 about 1,300 feet below that of the Mediterranean, and it is thought to have lost a 

 column of water of that height by evaporation. The Crimean lakes also have pro- 

 bably originated thus. 



Bischof has shown that in proportion as chloride of magnesium increases in a 

 solution, it renders chloride of sodium and sulphate of lime more and more insoluble; 

 he is therefore of opinion that at the bottom of the Dead Sea, and similar lakes, an 

 impure rock-salt deposit, interstratified also with mud, is forming, similar to the 

 saliferous clays or clayey marls which are frequently met with on the Continent. 



Culinary salt is prepared from each of the four sources above mentioned. It but 

 rarely happens that rock-salt is sufficiently pure for immediate use, and when 

 employed, as in some places on the Continent, and formerly in Cheshire, it is dissolved 

 in water, the insoluble impurities allowed to subside, and the solution treated as a 

 concentrated brine. From its other sources, salt is obtained by evaporation, and this 

 is effected in two ways: 1. Entirely by the application of artificial heat; 2. By 

 natural evaporation preceding the application of artificial heat. 



The first method is employed invariably in this country, and also on the Continent 

 when the brines contain more than 1 6 or 20 per cent, of chloride of sodium, the cost 

 of fuel at different places of course regulating the application of this method. The 

 manufacture of salt at Droitwich in Worcestershire, is said to have existed in the 

 time of the Romans, and in Cheshire, the ' Wiches ' (Nantwich, &c.) were very pro- 

 ductive in the reign of Edward the Confessor. Some time elapsed before the method 

 of evaporation was devised, and the original mode of obtaining the salt was by pouring 

 the brine upon the burning branches of oak and hazel, from the ashes of which the 

 deposited salt was afterwards collected. The process of evaporation was first conducted 

 in small leaden vessels, which were afterwards exchanged for iron ones, having a sur- 

 face of about a square yard and a depth of six inches ; the size of these pans increased 

 but slowly, for only a century since the largest pans at Northwich were but 20 feet 

 long by 10 broad. The pans now in use in Cheshire, Worcestershire, and Staffordshire 

 have a length of 60 or 70 feet, with a width of from 20 to 25, and a depth of about 

 18 inches ; they are made of stout iron plates riveted together, are supported on 

 brickwork, and have from one to three furnaces placed at one end, the flues of which 

 are in immediate contact with the bottom of the pan. The brine is generally raised 

 by steam-power, and its supply appears inexhaustible. The shafts are lined with 

 wooden or iron casings to prevent the admixture of freshwater springs with* the brine ; 

 the depth of the borings is in Cheshire usually from 210 to 250 feet, but at Stoke, in 

 Worcestershire, a shaft of 225 feet was constructed, yet no satisfactory supply of brina 



