112 Analysis of Several Varieties of 



foreign salts, and of different varieties- of British salt with 

 caeh other, will best be made by an examination of the 

 following table, which comprehends the results of the 

 analysis of equal weights of each variety, 



1000 parts by weight consirt of 



-A. __ . ______ ______ 



I. The total amount of impurities, and the quantity of 

 real muriate of soda, contained in each variety of common 

 salt, may be learned by inspecting the two last columns of 

 the table. From these it appears, that the foreign bay salt 

 is purer, generally speaking, than salt whieh is prepared by 

 the rapid evaporation of sea water j but that it is contami- 

 nated with about three times the amount of impurities 

 discoverable in an equal weight of the Cheshire large- 

 grained salt, and with more than twice that of those that 

 are found in iht staved and common salt of the same district. 



II. The insoluble matter in the foreign salt, after the 

 action of boiling water, appears to be chiefly argillaceous 

 earth coloured by oxide of iron, and is probably derived in 

 part from the pits in which the sea water is submitted to 

 evaporation. We may, perhaps, assign the same origin to 

 the very minute portion of muriate of lime, which is not 

 found in the salt prepared by evaporating sea water in me- 

 tallic vessels, nor even in the mother liquor, or uncrystal- 

 lizable residue. In sea salt prepared by rapid evaporation, 

 the insoluble portion is a mixture of carbonate of lime 

 with carbonate of magnesia, and a fine siliceous sand ; and 

 in the salt prepared from Cheshire brine, it is almost en- 

 tirely carbonate of lime. The insoluble part of the less 

 pure pieces of rock salt is chiefly a marly earth, with some 

 sulphate of lime. The quantity of this impurity, as it is 

 stated in the table, is considerably below the average, which 

 m my experiments has varied from JO to 45 parts in 1000. 



Some 



