A very large deposit of the almost pure salt has been found in
Wyoming. Its name was given to it because of its abundant occurrence in
the waters of the Epsom springs in England.

Magnesium sulphate has many uses in the industries. It is used to a
small extent in the preparation of sodium and potassium sulphates, as a
coating for cotton cloth, in the dye industry, in tanning, and in the
manufacture of paints and laundry soaps. To some extent it is used in
medicine.

~Magnesium silicates.~ Many silicates containing magnesium are known and
some of them are important substances. Serpentine, asbestos, talc, and
meerschaum are examples of such substances.

ZINC

~Occurrence.~ Zinc never occurs free in nature. Its compounds have been
found in many different countries, but it is not a constituent of common
rocks and minerals, and its occurrence is rather local and confined to
definite deposits or pockets. It occurs chiefly in the following ores:

Sphalerite (zinc blende) ZnS.
Zincite ZnO.
Smithsonite ZnCO_{3}.
Willemite Zn_{2}SiO_{4}.
Franklinite ZnO.Fe_{2}O_{3}.

One fourth of the world's output of zinc comes from the United States,
Missouri being the largest producer.

~Metallurgy.~ The ores employed in the preparation of zinc are chiefly the
sulphide, oxide, and carbonate. They are first roasted in the air, by
which process they are changed into oxide:

ZnCO_{3} = ZnO + CO_{2},
ZnS + 3O = ZnO + SO_{2}.

The oxide is then mixed with coal dust, and the mixture is heated in
earthenware muffles or retorts, natural gas being used as fuel in many
cases. The oxide is reduced by this means to the metallic state, and the
zinc, being volatile at the high temperature reached, distills and is
collected in suitable receivers. At first the zinc collects in the form
of fine powder, called zinc dust or flowers of zinc, recalling the
formation under similar conditions of flowers of sulphur. Later, when
the whole apparatus has become warm, the zinc condenses to a liquid in
the receiver, from which it is drawn off into molds. Commercial zinc
often contains a number of impurities, especially carbon, arsenic, and
iron.

~Physical properties.~ Pure zinc is a rather heavy bluish-white metal with
a high luster. It melts at about 420 deg., and if heated much above this
temperature in the air takes fire and burns with a very bright bluish
flame. It boils at about 950 deg. and can therefore be purified by