into sulphureted hydrogen. The other constituents of coal-gas--methane,
carbon monoxide, olefines, etc.--are not affected by passing through
boiling sulphur, and for ordinary laboratory work their removal is quite
unnecessary, as they do not in any way interfere with the precipitation
of metallic sulphides.

[Illustration: PREPARATION OF HYDROGEN SULPHIDE FROM COAL-GAS.]

A convenient apparatus for the preparation of hydrogen sulphide from
coal-gas, such as we have at present in use in the Christ College
laboratory, consists of a retort, R, in which sulphur is placed.
Through the tubulure of the retort there passes a bent glass-tube, T E,
perforated near the closed end, F, with a number of small holes. (The
perforations are easily made by piercing the partially softened glass
with a white-hot steel needle; an ordinary crotchet needle, the hook
having been removed and the end sharpened, answers the purpose very
well.) The end, T, of the glass tube is connected by caoutchouc tubing
with the coal-gas supply, the perforated end dipping into the sulphur.
The neck of the retort, inclined slightly upward to allow the condensed
sulpur, as it remelts, to flow back, is connected with awash bottle, B,
to which is attached the flask, F, containing the solution through which
it is required to pass the hydrogen sulphide; F is connected with an
aspirator, A.

About one pound of sulphur having been introduced into the retort and
heated to the boiling-point, the tap of the aspirator is turned on and
a current of coal-gas drawn through the boiling sulphur; the hydrogen
sulphide formed is washed by the water contained in B, passes on into
F, and finally into the aspirator. The speed of the current may be
regulated by the tap, and as the aspirator itself acts as a receptacle