95 
of British and Foreign Salt . 
for some hours in the pans, which are used in summer to pre- 
pare common salt ; and the impurities, which rise to the 
surface, are removed by skimming. During the evaporation, 
a portion of common salt separates ; and this, as it is too im- 
pure for use, is reserved for the purpose of concentrating the 
brine in summer. The evaporated bitter liquor is then re- 
moved into wooden coolers 8 feet long, 5 feet wide, and 1 
foot deep. In these it remains twenty four hours, during 
which time, if the weather prove clear and cold, the sulphate 
of magnesia, or Epsom salt crystallizes at the bottom of the 
coolers, in quantity equal to about one eighth of the boiled 
liquor. The uncrystallizable fluid is then let off through plug- 
holes at the bottom of the coolers ; and the Epsom salt, after 
being drained in baskets, is deposited in the store-house. This 
is termed single Epsom salts, and after solution and a second 
crystallization, it acquires the name of double Epsom salts. 
Four or five tons of sulphate of magnesia are produced from 
a quantity of brine, which has yielded 100 tons of common, 
and 1 ton of cat salt. 
On the banks of the Mersey, near its junction with the Irish 
Channel, the water of that river before evaporation is brought 
to the state of a saturated brine, by the addition of rock salt. 
The advantage of this method of proceeding, will be obvious 
when it is stated, that 100 tons of this brine yield at least 23 
tons of common salt, whereas from the same quantity of sea 
tion of the mode of making Epsom salt, because no correct statement of the process 
has, I believe, been hitherto published. The analysis of sea water, indeed, by a justly 
distinguished chemist (Bergman), excludes, erroneously, the sulphate of magnesia 
from its composition ; and his results have led to the opinion, that to manufacture this 
salt on the large scale, requires the addition either of sulphuric acid, or of seme sul- 
phate to the bitter liquor . (See Aikin’s Chemical Dictionary, II. 388.) 
