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SALT. 
In general usage the terms salt and common salt refer to the 
chemical salt, sodium chloride (NaCl). This occurs in nature 
in large quantities in aqueous solution, as the brine of the ocean, 
salt lakes and springs, and also in the solid form, known mineral- 
ogically as halite. When it occurs in massive deposits it is called 
rock salt. 
WINNING AND PREPARATION. 
The salt of commerce is obtained both from brines and 
from rock salt deposits. 
Rock salt. In some cases the deposits of salt lie at the sur 
face of the ground with little or no overburden and may be 
excavated by ordinary open-cut methods. Where the over 
burden of soil and rock is too great to warrant stripping, under 
ground methods may be used similar to those employed in coal 
mining, but if the overburden be very great, or if for other 
reasons it is advisable, the salt is won by dissolving it in situ 
and pumping the brine to the surface. The last method is 
the one employed in winning the salt in the Ontario salt dis 
trict. A drill hole is sunk through the deposit and cased with 
an iron pipe down as far as the upper limit of the salt. An inner 
pipe of considerably smaller diameter extends from the surface 
to the bottom of the deposit. Fresh water is forced down, 
between the inner and the outer pipes, to the deposit where it 
comes into contact with the salt. The salt is dissolved, forming 
a very strong brine, which is pumped to the surface through 
the small inner pipe. The salt is obtained from the brine by 
evaporating the water. 
In some cases the rock salt, mined by the first methods 
referred to above, contains impurities which render it unsuitable 
for many purposes. It must be purified to fit it for the market. 
This is done by dissolving it and then recrystallizing it by one of 
the methods given below. The brine produced in this process, 
as well as that resulting from the solution of rock salt in situ, re 
ferred to above, is called artificial brine in contrast to the natural 
brine of the ocean and salt springs.