Salt is one of the most widely spread and plentiful minerals which
the earth gives for the use of man; all the water of the ocean
derives its saline taste from salt; many springs are completely
saturated and are hence called “brine springs,” and it also exists
crystallized in beds within the earth of immense thickness and
extending for miles each way. The salt mines of Cheshire are the
finest and most extensive in England, and in some places the stratum
or layer of salt is more than one hundred feet thick, perfectly white
and crystallized. Salt is not a simple body, but is composed of two
simple bodies or elements, chlorine and sodium, hence it is called
by chemists the chloride of sodium, it can be formed by putting
carbonate of soda into hydro-chloric acid (sometimes called muriatic
acid,) until no more effervescence takes place, the result will taste
salt and yield pure salt on evaporation. The waters of the sea are
in some places evaporated by the heat of the sun in shallow hollows
dug out in the beach, this is called “bay salt” and is very impure;
but the chief part of the salt of commerce is procured by evaporating
the waters of brine springs; this water is pumped up into large iron
cisterns placed beneath slight sheds to keep the rain off, and having
flues running beneath them, the first impurities are thrown away,
and as evaporation goes on, the salt crystallizes and falls to the
bottom of the cistern in a fine white powder; this is taken out with
wooden shovels and placed in conical vessels with a hole in their
lower part to drain off all the moisture; it is then dried by stoves
and is fit for use; when no more salt falls down, the impure liquor,
called “bittern,” is drawn off and used to procure Epsom salts from,
by mixing it with sulphuric acid. The bittern contains chloride
of magnesium, and the sulphuric acid changes it into sulphate
of magnesia, which, when purified, forms the Epsom salts sold by
druggists.
About half a million tons of salt are made in England every year.
Salt, besides its general use as a condiment, and in preserving
food for storing ships, &c., is also used for several manufacturing
purposes. By adding sulphuric acid and heating it, the acid called
“hydrochloric” is given off, which is largely used for many purposes;
but the chief use made of salt by the manufacturing chemist is to
prepare soda for cleansing and soap making.