SALT.
It may seem curious to the reader that we should care to discuss a
subject seemingly so simple as common salt. But it is a very usual thing
for us to live and move in the presence of things that are very common
to our everyday experience, and yet know scarcely anything about them,
beyond the fact that they in some way serve our purpose.
Salt is one of the commonest articles used in the preparation of our
food. It has been questioned by some people whether salt was a real
necessity as an animal food, or whether the taste for it is merely an
acquired one. All peoples in all ages seem to have used salt, and
reference to it is made in the earliest histories. Travelers tell us
that savage tribes, wherever they exist, are as much addicted to the use
of salt as civilized people. One of the early African travelers, Mungo
Park, tells us that the children of central Africa will suck a piece of
rock salt with the same avidity and seeming satisfaction as the
ordinary civilized child will a lump of sugar.
All animals seem to require salt, and it is claimed by those who have
tried the experiment that after one has refrained from the use of salt
for a certain length of time the craving for it becomes exceedingly
painful. It is most likely that the taste for salt is a natural craving.
In any event, whether it is a natural or an artificial taste, it has
become an article of the greatest importance in the preparation of food,
as well as on account of its use in the arts. Salt is a compound of
chlorine and sodium. In chemical language it is called sodium chloride.
The symbol is NaCl, which means that a molecule of salt is composed of
one atom of sodium and one of chlorine. Chlorine is an exceedingly
poisonous gas.
Formerly the chemist when he wished to obtain sodium extracted it from
common salt and discharged the chlorine gas into the air. It was found
that in establishments where the manufacture of sodium was conducted on
a large scale the destructive properties of the chlorine discharged into
the air was such that all vegetation was killed for some distance around
the manufactory. This came to be such a nuisance that the manufacturers
were either compelled to stop business or in some way take care of the
chlorine. This is done at the present day by uniting the chlorine gas
with common lime, forming a chloride of lime, which is used for
bleaching and purifying purposes.
Salt is found in great quantities as a natural product under the name of
rock salt. It is found in some parts of the world in great veins over
100 feet in thickness. In some cases the rock salt is mined, when it has
to be purified for commercial purposes. The common mode of obtaining
salt, however, is by pumping the solution from these great beds where it
is mingled with water--salt water; the water is then evaporated, and
when it reaches a certain stage of evaporation the salt crystallizes and
falls to the bottom.
Different substances crystallize in different forms. The crystallization
of water when it freezes, as we shall see hereafter, arranges its
molecules in such a form as to make a lump of ice of given dimensions
lighter than the same dimensions of water would be. Salt in
crystallizing does not follow the same law; the salt crystal is in the
shape of a cube and is denser in its crystalline form than in solution,
hence it is heavier and falls to the bottom.
It is said that there is a deposit of rock salt in Galicia, Austria,
covering an area of 10,000 square miles. There are also very large
deposits in England, the mining of which has become a great industry.
There are also great beds of salt in various parts of the United
States, notably near Syracuse, N. Y., where large salt deposits were
exposed in an old river bed formed in preglacial times. The common mode
of preparing salt for domestic purposes is by the process of evaporation
from brine that has been pumped from salt wells. The quality of the salt
is determined largely by the temperature at the time of evaporating the
water from it. Ordinary coarse salt, such as is used for preserving meat
or fish, is made at a temperature of about 110 degrees; what is known as
common salt is made at a temperature of about 175 degrees; while common
fine or table salt is made at a temperature of 220 degrees. Thus it will
be seen that the process of granulation with reference to its fineness
is determined by the rapidity of evaporation. Salt is one of the
principal agents in preserving all kinds of meats against putrefaction.
It will also preserve wood against dry rot. Vessel builders make use of
this fact to preserve the timbers used in the construction of the
vessels.
Salt at the present day is very cheap, but at the beginning of the
present century it was worth from $60 to $70 per ton. The methods of
decomposing salt to obtain its constituents, which are used in various
other compounds, are very simple to-day as compared with the processes
that prevailed in the days before the advent of electricity in large
volume, such as is produced by the power of Niagara Falls. It is curious
to note that a substance so useful and so harmless as common salt should
be made out of two such refractory and dangerous elements as chlorine
and sodium. Both of these elements, standing by themselves, seem to be
out of harmony with nature, but when combined there are few substances
that serve a better purpose.
These great salt beds that are found to exist in England and America and
other parts of the world were undoubtedly deposited from the water of
the ocean at some stage in the formation of the earth's crust. It is
well known that sea water is exceedingly saline; 300 gallons of sea
water will produce a bushel of salt. Undoubtedly beds of salt are also
formed by inland lakes, such as the Great Salt Lake in Utah. Only about
2.7 per cent. of ocean water is salt, while the water of the Great Salt
Lake of Utah contains about 17 per cent. When there is so much salt in
water that it is called a saturated solution, salt crystals will form
and drop to the bottom, which process will in time build up under a
large body of salt water a great bed of rock salt.
The water in all rivers and springs contains salt to a certain degree,
and where it runs into a basin like that of a lake with no outlet,
through the process of evaporation pure water is being constantly
carried off, leaving the salt behind. It is easy to see that if this
process is kept up long enough the water will become in time a saturated
solution, when crystallization sets in and precipitation follows,
accounting for the deposits of rock salt.
AIR.