108 Anctlyis of several Varieties of 



of Fahrenheit. This temperature is continued during the 

 whole process; and as the evaporation proceeds, small 

 flaky crystals continue to form themselves, and to fall lo 

 the bottom of the boiler. At the end of from eight to 

 twelve hours, the greatest part of the water of solution is 

 found to he evaporated ; so much only being left, as barely 

 to cover the salt and the bottom of the pan. The salt is 

 then removed into conical wicker baskets, termed harrows ; 

 and, after being well drained, is dried in stoves, where it 

 sustains a loss of about one-seventh of its weight. 



On the first application of heat to the brine, a quantity 

 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 cither 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 oi lime ; and are afterwards raked out. These two 

 operations are called clearing the pan. Some brines scarcely 

 require them at all, and others only occasionally. The 

 whole of 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 sediments are formed, also, in making the other va- 

 rieties of salt. 



In preparing co?mnon salt, the brine is first raised to a 

 boding 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 evaporation is carried on for 24 hours, with the 

 brine heated to 160 or 170 J Fahrenheit. The salt, thus 

 formed, is in quadrangular pyramids or hoppers, which are 

 close and hard in their texture. The remainder of the 

 process is similar to that of making stoved salt, except that 

 after being drained it is carried immediately to the store- 

 house, and not afterwards exposed to heat, an operation 

 confined to the stoved salt. 



The large- grained flaky salt is made with an evapora- 

 tion conducted at the heat of 130 or 140 degrees. The 

 salt thus formed is somewhat harder than common salt, 

 and approaches more nearjy to' the cubic shape of the cry- 

 stals of muriate of soda. 



L;irge-gramed or fishery salt is prepared from brine 

 heated only to 100° or 110° Fahrenheit. No perceptible 



agitation, 



