uch
condensing power upon the oxygen of the air, as to bring both within
the combining distance, thus enabling the oxygen to attack and destroy
the vapours in the pores of the charcoal. In this way, effluvia of
all kinds may be virtually burnt up; and this is the principle of the
excellent charcoal respirators invented by Dr. Stenhouse. Armed with
one of these, you may go into the foulest-smelling places without
having your nose offended.

But, while powerful to arrest vapours, the charcoal respirator is
ineffectual as regards smoke. The smoke-particles get freely through
the respirator. With a number of such respirators, tested in a proper
room, from half a minute to a minute was the limit of endurance. This
might be exceeded by Faraday's simple method of emptying the lungs
completely, and then filling them before going into a smoky
atmosphere. In fact, each solid smoke particle is itself a bit of
charcoal, and carries on it, and in it, its little load of irritating
vapour. It is this, far more than the particles of carbon themselves,
that produces the irritation. Hence two causes of offence are to be
removed: the carbon particles which convey the irritant by adhesion
and condensation, and the free vapour which accompanies the particles.
The cotton-wool moistened with glycerine I knew would arrest the
first; fragments of charcoal I hoped would stop the second. In the
first fireman's respirator, Mr. Carrick's arrangement of two valves,
the one for inhalation, the other for exhalation, was preserved. But
the portion of the respirator which holds the filtering and absorbent
substances, was prolonged to a depth of four or five inches (see fig.
5). Under the partition of wire-gauze q r at the bottom of the space
which fronts the mouth was placed a layer of cotton-wool, c, moistened
with glycerine; then a thin layer of dry wool, c'; then a layer of
charcoal fragments; and finally a second thin layer of dry
cotton-wool. The succession of the layers may be changed without
prejudice to the action. A wire-gauze cover, shown in plan under fig.
5, keeps the substances from falling out of the respirator. A layer
of caustic lime may be added for the absorption of carbonic acid; but
in the densest smoke that we have hitherto employed, it has not been
found necessary, nor is it shown in the figure. In a flaming
building, indeed, the mixture of air with the smoke never permits the
carbonic acid to become so dense as to