357 



of 100 or 110 degrees. This process is so slow as to last seven or 

 eight days, instead of eight or ten hours, which is the shortest time 

 employed in the first mode of evaporating the same quantity of brine, 

 and accordingly the salt forms in large cubical crystals, proper to the 

 muriate of soda. 



Of these varieties, the stoved salt is that which is usually em- 

 ployed for domestic purposes. The common salt is consumed prin- 

 cipally in the salting of provisions that are not intended for sea- 

 voyages. But for this last purpose, the large-grained or fishery salt 

 is peculiarly fitted. 



With respect to the preparation of salt from sea- water, the author 

 takes notice of the process employed on the coasts of Scotland, both 

 east and west, where, from the cheapness of fuel, artificial heat alone 

 is used ; and of the salt-works at Lymington in Hampshire, where 

 advantage is taken of a milder climate for removing five sixths of 

 the water by spontaneous evaporation, previous to its admission into 

 the boilers. 



Since the evaporation in each of these works is conducted rapidly 

 during the formation of the salt, it generally resembles the stoved 

 salt of Cheshire ; but in consequence of the heat being slackened 

 during Sundays, a larger kind is then formed, and it is termed 

 Sunday salt. At Lymington, there are also formed, by drippings 

 from the salt during its drainage, large stalactical masses, termed 

 salt-cats, weighing sixty or eighty pounds each ; but these do not ex- 

 ceed T-ffu-th part of the salt prepared at Lymington. 



Of the several salts above described, the large-grained fishery salt 

 is that which most resembles the foreign bay-salt in appearance; 

 and in fact (says the author,) a large proportion of what is sold in 

 London as bay-salt, and esteemed as of foreign manufacture, is this 

 Cheshire salt. 



Dr. Henry next gives a table of the results of his chemical expe- 

 riments on eleven varieties of salt ; and in this it appears, that the 

 Lymington cat is that which contains the smallest quantity of impu- 

 rity, and the Lymington or Scotch common salt the largest quantity ; 

 the first amounting to only 12 parts in 1000, and that of the last 

 to 64. 



But it appears that all the kinds of Cheshire salt are nearly equal 

 to the Lymington cat in purity, and perhaps superior in respect to 

 the quality of the extraneous matter, which varies in different kinds 

 from 13^ to 17 in the thousand. The foreign bay-salts, on the 

 contrary, have as much as from 35 to 40 parts of impurity. Of these 

 about 10 parts are insoluble, and consist chiefly of argillaceous earth, 

 coloured by oxide of iron. The native rock salt of Cheshire also 

 contains as much or more of insoluble impurity, which is chiefly a 

 marly earth, with some sulphate of lime. The earthy muriates of 

 lime and magnesia abound most in salt which is prepared by rapid 

 evaporation of sea water. 



Since common salt contains extremely little water of crystalliza- 



