34
THE BOOK OF THE LANTERN.
who some years ago was killed by such an explosion of an
oxygen retort.
Many old-fashioned operators use an iron mercury
bottle as a retort, and this, I believe, was the invariable
custom when oxygen was procured from manganese per¬
oxide alone. The heat required was so great that a thick
and lasting receptacle was necessary. But now-a-days,
when chlorate is used so universally, the gas comes off at a
much-reduced temperature, and a thin retort will last, with
care, for about fifty charges. My lantern assistant prefers
to use a kitchen digester, which he has had fitted with
a pipe and safety cap, and which he regards as a triumph
of art, which will not only last his own life-time, but will
be handed down to his descendants as an heir-loom. One
more word on the subject of retorts. Do not buy a copper
one ; it is very expensive, and quickly wears out, and has
no advantages whatever. In case a retort should be
wanted in a hurry, and cannot be obtained, a common
cast-iron kettle is a capital substitute for one. Put the
chlorate mixture in the kettle, and fasten on the lid with
a luting of white lead or clay ; cut a piece of firewood
to the correct size, to fit tightly between the lid and
the inside of the handle of the kettle, so that no pressure
will force it open. Use the spout as a delivery tube of the
gas.
The retort is charged with a mixture of chlorate of potash
and oxide of manganese, and the most usual proportions
are four parts by weight of the potash to one part of the
manganese.
This is the mixture as given in the various chemical text-