This substance known as "thermit" is in current use for repairing,
heating or soldering large pieces of metal and consists of a mixture
of aluminum and oxide of iron, the latter being replaced, according to
the requirement, by oxide of lead, peroxide of sodium or peroxide of
barium. This composition is thoroughly mixed together, or is used in
the form of cartridges or tablets, which ignite by means of a piece of
magnesium fixed in the substance like a wick. The heat developed is
more than sufficient to cause the hardest steel to melt.
Although this process is rapid and silent and really marvelous from
the point of view of the result obtained, it is not without much
danger to those using it, for at the high temperature produced by it
an inexperienced operator runs the risk of being seriously burned.
In consequence the prudent and careful burglar uses accessories
which render him secure against such accidents. He protects his eyes
by means of heavy dark glasses, wears shields of aluminum over his
hands and applies the mixture through a small hole in the bottom of a
crucible. When the reaction takes place it lasts long enough to allow
the operator to charge the crucible again and again in proportion as
the melting of the metal plate is effected, thus making an opening of
the desired size in the safe. It is a simple enough operation for a
skilled burglar, but a very dangerous one for an amateur.