|fj£ ANALYSIS OF BRITISH AND FOREIGN SALT. 



Agricultural Report of the county of Chester*. From his 

 account I shall extract, in order to render some parts of this 

 memoir more intelligible, a very brief statement of the cha- 

 racteristic differences of the several varieties of salt, which 

 are preparedjn North wich, and its neighbourhood, 

 ^separation of In making the sloved or lump salt, the brine is brought to 

 ^edwlump a k^Bng heat, which, in brine fuliy saturated, is 226° of 

 Fahrenheit. This temperature is continued during the 

 whole process ; and as the evaporation proceeds, small fiakey 

 crystals continue to form themselves, and to fall to the bot- 

 tom of the boiler. At the end of from eight to twelve 

 Iiours, the greatest part of the water of solution is found to 

 l>e evaporated; so much only being left, as barely to cover 

 the salt and the bottom of the pan. The salt is then re- 

 moved into conical wicker baskets, termed barrows; and, 

 after being well drained, is dried in stoves* where it sustains 

 a Toss of about one seventh, of its weight. 



Station of Q n tJie first application of heat to the brine, a quantity 

 as Maturities. rr . 



of carbonate of lime, and sometimes a little oxide of iron, 



both of which had been held in solution by an excess of 

 carbonic acid, are separated; and are either removed by 

 skimming, or are allowed to subside to the bottom of the 

 pan, along with the salt first formed, and with some sul- 

 phate of lime; and are afterward raked out. These two 

 operations are called clearing the pan. Some brines scarcely 

 require them at all, and others only occasionally. The whole 

 ©f the impurities, however, are not thus removed ; for a part, 

 subsiding to the bottom, forms a solid incrustation, termed 

 by the workmen pan-scale. The portion of this, which is 

 lowest, acquires so much induration and adhesion to the 

 pan, that it is necessary to remove it, once every three or 

 four weeks, by heavy blows with a pick-axe. These sedi- 

 ments are formed, also, in making the other varieties of 

 salt. 

 i. » s It. in preparing common salt, the brine is first raised to a 

 boiling heat, with the double view of bringing it as quickly 

 as possible to the point of saturation, and of clearing it from 

 its earthy contents. The fires are then slackened, and the' 



* PublibLcd hi iso8 t 



evaporation 



