assium chloride is
added, and as the solution cools the sparingly soluble
potassium chlorate crystallizes out:

Ca(ClO_{3})_{2} + 2KCl = 2KClO_{3} + CaCl_{2}.

Electro-chemical processes are also used.

~Potassium nitrate~ (_saltpeter_) (KNO_{3}). This salt was formerly made
by allowing animal refuse to decompose in the open air in the presence
of wood ashes or earthy materials containing potassium. Under these
conditions the nitrogen in the organic matter is in part converted into
potassium nitrate, which was obtained by extracting the mass with water
and evaporating to crystallization. This crude and slow process is now
almost entirely replaced by a manufacturing process in which the
potassium salt is made from Chili saltpeter:

NaNO_{3} + KCl = NaCl + KNO_{3}.

This process has been made possible by the discovery of the Chili niter
beds and the potassium chloride of the Stassfurt deposits.

The reaction depends for its success upon the apparently
insignificant fact that sodium chloride is almost equally
soluble in cold and hot water. All four factors in the equation
are rather soluble in cold water, but in hot water sodium
chloride is far less soluble than the other three. When hot
saturated solutions of sodium nitrate and potassium chloride
are brought together, sodium chloride precipitates and can be
filtered off, leaving potassium nitrate in solution, together
with some sodium chloride. On cooling, potassium nitrate
crystallizes out, leaving small amounts of the other salts in
solution.

Potassium nitrate is a colorless salt which forms very large crystals.
It is stable in the air, and when heated is a good oxidizing agent,
giving up oxygen quite readily. Its chief use is in the manufacture of
gunpowder.

~Gunpowder.~ The object sought for in the preparation of
gunpowder is to secure a solid substance which will remain
unchanged under ordinary conditions, but which will explode
readily when ignited, evolving a large volume of gas. When a
mixture of carbon and potassium nitrate is ignited a great deal
of gas is formed, as will be seen from the equation

2KNO_{3} + 3C = CO_{2} + CO + N_{2} + K_{2}CO_{3}.

By adding sulphur to the mixture the volume of gas formed in
the explosion is considerably increased:

2KNO_{3} + 3C + S = 3CO_{2} + N_{2} + K_{2}S.

Gun