eupon, owing to the lower pressure in the
cylinder B, the liquid carbon dioxide expands and rises to the top of
the cylinder A and forces the liquid carbon dioxide into the cylinder B,
the same as the superior steam of a boiler forces the water of the
boiler out when the same is tapped below the surface of the liquid. Now
upon opening the tap H, this superior gas forces out the mixture of
water and liquid carbon dioxide, which suddenly expanding causes
portions of the globules of liquefied gas to be frozen, and these, being
protected by a rapidly evaporating portion of the liquefied gas, are
thrown on the fire in solid particles. At the same time the water is
blown into a spray, which is more or less frozen. The fire is thus
rapidly extinguished by the vaporization of the carbon dioxide and water
spray.

* * * * *

SMOKELESS GUNPOWDER.

BY HUDSON MAXIM.

During the last forty years leading chemists have continued to
experiment with a view to the production of a gunpowder which should be
smokeless. But not until the last few years has any considerable degree
of success been attained.

To be smokeless, a gunpowder must yield only gaseous products of
combustion. None of the so-called smokeless powders are entirely
smokeless, although some of them are very nearly so.

The smoke of common black gunpowder is largely due to minute particles
of solid matter which float in the air. About one-half of the total
products of combustion of black gunpowder of ordinary composition
consists of potassium carbonate in a finely divided condition and of
potassium sulphate, which is produced chiefly by the burning in the air
of potassium sulphide, another production of combustion, as on the
outrushing gases it is borne into the air in a fine state of division.

Another cause for the smoke of gunpowder is the formation of small
liquid vesicles which condense from some of the products of combustion
thrown into the air in a state of vapor, in the same manner as vesicles
of aqueous vapor form in the air on the escape of highly heated steam
from the whistle of a locomotive.

Broadly speaking, an explosive compound is one which contains, within
itself, all the elements necessary for its complete combustion, and
whose heated gaseous products occupy vastly more space than the original
compound. Such compound usually consists of oxygen, associated with
other elements, for which it has great affinity, a