lphates. In smaller amounts it is found in a
great variety of minerals, and it is a constituent of many animal and
vegetable substances.

~Extraction of sulphur.~ Sulphur is prepared from the native substance,
the separation of crude sulphur from the rock and earthy materials with
which it is mixed being a very simple process. The ore from the mines is
merely heated until the sulphur melts and drains away from the earthy
impurities. The crude sulphur obtained in this way is distilled in a
retort-shaped vessel made of iron, the exit tube of which opens into a
cooling chamber of brickwork. When the sulphur vapor first enters the
cooling chamber it condenses as a fine crystalline powder called
_flowers of sulphur_. As the condensing chamber becomes warm, the
sulphur collects as a liquid in it, and is drawn off into cylindrical
molds, the product being called _roll sulphur_ or _brimstone_.

~Physical properties.~ Roll sulphur is a pale yellow, crystalline solid,
without marked taste and with but a faint odor. It is insoluble in
water, but is freely soluble in a few liquids, notably in carbon
disulphide. Roll sulphur melts at 114.8 deg.. Just above the melting point
it forms a rather thin, straw-colored liquid. As the temperature is
raised, this liquid turns darker in color and becomes thicker, until at
about 235 deg. it is almost black and is so thick that the vessel containing
it can be inverted without danger of the liquid running out. At higher
temperatures it becomes thin once more, and boils at 448 deg., forming a
yellowish vapor. On cooling the same changes take place in reverse
order.

~Varieties of sulphur.~ Sulphur is known in two general forms, crystalline
and amorphous. Each of these forms exists in definite modifications.

~Crystalline sulphur.~ Sulphur occurs in two crystalline forms, namely,
rhombic sulphur and monoclinic sulphur.

1. _Rhombic sulphur._ When sulphur crystallizes from its solution in
carbon disulphide it separates in crystals which have the same color and
melting point as roll sulphur, and are rhombic in shape. Roll sulphur is
made up of minute rhombic crystals.

2. _Monoclinic sulphur._ When melted sulphur is allowed to cool until a
part of the liquid has solidified, and the remaining liquid is then
poured off, it is found that the solid sulphur remaining in the vessel
has assumed the form of fine needle-shaped crystals. These differ much
in appearance from the rhombic crystals obtained