resembles the metallic elements, many of which
produce sulphides under similar conditions. The sulphides of arsenic,
both those produced artificially and those found in nature, are used as
yellow pigments.

ANTIMONY

~Occurrence.~ Antimony occurs in nature chiefly as the sulphide
(Sb_{2}S_{3}), called stibnite, though it is also found as oxide and as
a constituent of many complex minerals.

~Preparation.~ Antimony is prepared from the sulphide in a very simple
manner. The sulphide is melted with scrap iron in a furnace, when the
iron combines with the sulphur to form a slag, or liquid layer of melted
iron sulphide, while the heavier liquid, antimony, settles to the bottom
and is drawn off from time to time. The reaction involved is represented
by the equation

Sb_{2}S_{3} + 3Fe = 2Sb + 3FeS.

~Physical properties.~ Antimony is a bluish-white, metallic-looking
substance whose density is 6.7. It is highly crystalline, hard, and very
brittle. It has a rather low melting point (432 deg.) and expands very
noticeably on solidifying.

~Chemical properties.~ In chemical properties antimony resembles arsenic
in many particulars. It forms the oxides Sb_{2}O_{3} and Sb_{2}O_{5},
and in addition Sb_{2}O_{4}. It combines with the halogen elements with
great energy, burning brilliantly in chlorine to form antimony
trichloride (SbCl_{3}). When heated on charcoal with the blowpipe it is
oxidized and forms a coating of antimony oxide on the charcoal which has
a characteristic bluish-white color.

~Stibine~ (SbH_{3}). The gas stibine (SbH_{3}) is formed under conditions
which are very similar to those which produce arsine, and it closely
resembles the latter compound, though it is still less stable. It is
very poisonous.

~Acids of antimony.~ The oxides Sb_{2}O_{3} and Sb_{2}O_{5} are
weak acid anhydrides and are capable of forming two series of
acids corresponding in formulas to the acids of phosphorus and
arsenic. They are much weaker, however, and are of little
practical importance.

~Sulphides of antimony.~ Antimony resembles arsenic in that
hydrogen sulphide precipitates it as a sulphide when conducted
into an acidified solution containing an antimony compound:

2SbCl_{3} + 3H_{2}S = Sb_{2}S_{3} + 6HCl,

2SbCl_{5} + 5H_{2}S = Sb_{2}S_{5} + 10HCl.

The two sulphides of antimony are called the trisulphide and
the pentasulphide respectively. When pr