3.--The compressed-oxygen type.

[Illustration: PLATE XII.

Fig. 1.--Breathing and Rescue Apparatus.

Fig. 2.--Rescue Training Room.]

Apparatus of the first type, weighing 20 lb., supplies enough air to
last about 3 hours, and the products of breathing pass through a
check-valve directly into space. Apparatus of the second type supplies
oxygen obtained from oxygen-producing chemicals, and also provides means
of absorbing the carbonic acid gas produced in respiration. They contain
also the requisite tubes, valves, connections, etc., for the
transmission of the fresh air and the respired air so as to produce
sufficient oxygen while in use; to absorb and purify the products of
expiration; and to convey the fresh air to the mouth without
contamination by the atmosphere in which the apparatus is used. Three
oxygen-generating cartridges are provided, each supplying oxygen enough
for 1 hour, making the total capacity 3 hours. Changes of cylinders can
be made in a few seconds while breathing is suspended. This apparatus
weighs from 20 to 25 lb., according to the number of oxygen generators
carried. The cartridges for generating oxygen, provided with this
apparatus, are of no value after having been used for about an hour.

The third type of apparatus is equipped with strong cylinders charged
with oxygen under high pressure; two potash regenerative cans for
absorbing the carbon dioxide gas exhaled; a facial helmet; the necessary
valves, tubes, etc., for the control of the oxygen; and a finimeter