Arsenal, Woolwich. A list of those sanctioned is published by the Home
Office. They are mostly distinguished by special trade names, and are
mainly of two classes--those containing ammonium nitrate and
nitrobenzene or nitronaphthalene, and those containing nitroglycerin and
nitrocellulose, which are essentially weak dynamites. The safety
property attributed to them is due to the depression of the temperature
of the flame or products of explosion to a point below that necessary to
ignite fire-damp or coal dust in air from a blown-out shot. New
explosives that are found to be satisfactory when tested are added to
the list from time to time, the composition being stated in all cases.

Aerophores.

Methods for enabling miners to penetrate into workings where the
atmosphere is totally irrespirable have come into use for saving life
after explosions and for repairing shafts and pit-work under water. The
aerophore of A. Galibert was in its earlier form a bag of about 12 cub.
ft. capacity containing air at a little above atmospheric pressure; it
was carried on the back like a knapsack and supplied the means of
respiration. The air was continually returned and circulated until it
was too much contaminated with carbonic acid to be further used, a
condition which limited the use of the apparatus to a very short period.
A more extended application of the same principle was made in the
apparatus of L. Denayrouze by which the air, contained in cylinders at a
pressure of 300 to 350 lb per sq. in., was supplied for respiration
through a reducing valve which brought it down nearly to atmospheric
pressure. This apparatus was, however, very heavy and became
unmanageable when more than an hour's supply was required. The newer
forms are based upon the principle, first enunciated by Professor
Theodor Schwann in 1854, of carrying compressed oxygen instead of air,
and returning the products of respiration through a regenerator
containing absorptive media for carbonic acid and water, the purified
current being returned to the mouth with an addition of fresh oxygen.
The best-known apparatus of this class is that developed by G. A. Meyer
at the Shamrock colliery in Westphalia, where a body of men are kept in
systematic training for its use at a special rescue station. This corps
rendered invaluable service at the exploring and rescue operations after
the explosion at Courrieres in March 1906, the most disastrous mining
accident on record, wh