In the preparation
of carbon disulphide an electrical furnace is employed, such as
is represented in Fig. 45. The furnace is packed with carbon
C, and this is fed in through the hoppers B, as fast as
that which is present in the hearth of the furnace is used up.
Sulphur is introduced at A, and at the lower ends of the
tubes it is melted by the heat of the furnace and flows into
the hearth as a liquid. An electrical current is passed through
the carbon and melted sulphur from the electrodes E, heating
the charge. The vapors of carbon disulphide pass up through the
furnace and escape at D, from which they pass to a suitable
condensing apparatus.

~Comparison of sulphur and oxygen.~ A comparison of the formulas and the
chemical properties of corresponding compounds of oxygen and sulphur
brings to light many striking similarities. The conduct of
hydrosulphuric acid and water toward many substances has been seen to be
very similar; the oxides and sulphides of the metals have analogous
formulas and undergo many parallel reactions. Carbon dioxide and
disulphide are prepared in similar ways and undergo many analogous
reactions. It is clear, therefore, that these two elements are far more
closely related to each other than to any of the other elements so far
studied.

~Selenium and tellurium.~ These two very uncommon elements are still more
closely related to sulphur than is oxygen. They occur in comparatively
small quantities and are usually found associated with sulphur and
sulphides, either as the free elements or more commonly in combination
with metals. They form compounds with hydrogen of the formulas H_{2}Se
and H_{2}Te; these bodies are gases with properties very similar to
those of H_{2}S. They also form oxides and oxygen acids which resemble
the corresponding sulphur compounds. The elements even have allotropic
forms corresponding very closely to those of sulphur. Tellurium is
sometimes found in combination with gold and copper, and occasions some
difficulties in the refining of these metals. The elements have very few
practical applications.

~Crystallography.~ In order to understand the difference between the two
kinds of sulphur crystals, it is necessary to know something about
crystals in general and the forms which they may assume. An examination
of a large number of crystals has shown that although they may differ
much in geometric form, they can all be c