ustic soda, has a
brackish, salty taste, and is, in fact, a solution of salt. This can
be demonstrated by evaporating the neutral liquid to dryness and
examining the residue of solid matter, which proves to be common salt.

When an acid is mixed with a base, the result is a substance more or
less similar in its properties to common salt; for this reason all
compounds formed by the neutralization of an acid with a base are
called salts. If, instead of hydrochloric acid (HCl), we use an acid
solution of potassium tartrate, and if instead of caustic soda we use
bicarbonate of soda (baking soda), the result is a brackish liquid as
before, but the salt in the liquid is not common salt, but Rochelle
salt. Different combinations of acids and bases produce different
salts. Of all the vast group of salts, the most abundant as well as
the most important is common salt, known technically as sodium
chloride because of its two constituents, sodium and chlorine.

We are not dependent upon neutralization for the enormous quantities
of salt used in the home and in commerce. It is from the active,
restless seas of the present, and from the dead seas of the
prehistoric past that our vast stores of salt come. The waters of the
Mediterranean and of our own Great Salt Lake are led into shallow
basins, where, after evaporation by the heat of the sun, they leave a
residue of salt. By far the largest quantity of salt, however, comes
from the seas which no longer exist, but which in far remote ages
dried up and left behind them their burden of salt. Deposits of salt
formed in this way are found scattered throughout the world, and in
our own country are found in greatest abundance in New York. The
largest salt deposit known has a depth of one mile and exists in
Germany.

Salt is indispensable on our table and in our kitchen, but the amount
of salt used in this way is far too small to account for a yearly
consumption of 4,000,000 tons in the United States alone. The
manufacture of soap, glass, bleaching powders, baking powders, washing
soda, and other chemicals depends on salt, and it is for these that
the salt beds are mined.

210. Baking Soda. Salt is by all odds the most important sodium
compound. Next to it come the so-called carbonates: first, sodium
carbonate, which is already familiar to us as washing soda; and
second, sodium bicarbonate, which is an ingredient of baking powders.
These are both obtained from sodium chloride by relativ