powder is simply a mechanical mixture of these three
substances in the proportion required for the above reaction.
While the equation represents the principal reaction, other
reactions also take place. The gases formed in the explosion,
when measured under standard conditions, occupy about two
hundred and eighty times the volume of the original powder.
Potassium sulphide (K_{2}S) is a solid substance, and it is
largely due to it that gunpowder gives off smoke and soot when
it explodes. Smokeless powder consists of organic substances
which, on explosion, give only colorless gases, and hence
produce no smoke. Sodium nitrate is cheaper than potassium
nitrate, but it is not adapted to the manufacture of the best
grades of powder, since it is somewhat deliquescent and does
not give up its oxygen so readily as does potassium nitrate. It
is used, however, in the cheaper grades of powder, such as are
employed for blasting.

~Potassium cyanide~ (KCN). When animal matter containing nitrogen is
heated with iron and potassium carbonate, complicated changes occur
which result in the formation of a substance commonly called yellow
prussiate of potash, which has the formula K_{4}FeC_{6}N_{6}. When this
substance is heated with potassium, potassium cyanide is formed:

K_{4}FeC_{6}N_{6} + 2 K = 6KCN + Fe.

Since sodium is much cheaper than potassium it is often used in place of
it:

K_{4}FeC_{6}N_{6} + 2Na = 4KCN + 2NaCN + Fe.

The mixture of cyanides so resulting serves most of the purposes of the
pure salt. It is used very extensively in several metallurgical
processes, particularly in the extraction of gold. Potassium cyanide is
a white solid characterized by its poisonous properties, and must be
used with extreme caution.

~Potassium carbonate~ (_potash_) (K_{2}CO_{3}). This compound occurs in
wood ashes in small quantities. It cannot be prepared by the Solvay
process, since the acid carbonate is quite soluble in water, but is made
by the Le Blanc process. Its chief use is in the manufacture of other
potassium salts.

~Other salts of potassium.~ Among the other salts of potassium frequently
met with are the sulphate (K_{2}SO_{4}), the acid carbonate (KHCO_{3}),
the acid sulphate (KHSO_{4}), and the acid sulphite (KHSO_{3}). These
are all white solids.

LITHIUM, RUBIDIUM, CAESIUM

Of the three remaining elements of the family--lithium, ru