Three methods of firing the gas have been proposed. In one
the shock or contact with the water brings a small electric battery into
play which produces a spark between two terminals projecting across the
burner orifice; in the second, a cap at the head of the generator
contains a small quantity of metallic potassium, which decomposes water
with such energy that the hydrogen liberated catches fire; and in the
third a similar cap is filled with the necessary quantity of calcium
phosphide, or the "carbophosphide of calcium" mentioned in Chapter XI.,
which yields a flame by the immediate ignition of the liquid phosphine
produced on the attack of water. During the two or three seconds consumed
in the production of the spark or pilot flame, the water is penetrating
the main charge of calcium carbide in the interior of the apparatus,
until the whole is ready to give a bright light for a time limited only
by the capacity of the generator. It is obvious that such apparatus may
be of much service at sea: they may be thrown overboard to illuminate
separate lifebuoys in case of accident, or be attached to the lifebuoys
they are required to illuminate, or be used as lifebuoys themselves if
fitted with suitable chains or ropes; they may be shot ahead to
illuminate a difficult channel, or to render an enemy visible in time of
war.
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