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26 IgODERN MAGIC LANTERNS. COMPRESSED GASES. 27
The amount of knocking about which a charged cylinder
can actually stand, if properly made and annealed, is surprising.
Mr. Murray, the engineer to the Brin Oxygen
Co., in his book on compressed gases, narrates how they
have for experimental purposes been dropped vertically from
a height of 35 feet two or three times in succession, crushed
with a 15-ton blow, and finally bent into a bow form ;
on testing them after this treatment they were found to
contain the full quantity of gas. To secure the degree of
safety indicated by this, the cylinders must not only be well
made of suitable steel, but inasmuch as the physical structure
of the steel becomes gradually altered, they must from
time to time be annealed, a process which restores them to
their original condition as far as strength is concerned. It
is therefore advisable, if baying a cylinder, or bottle as it is
sometimes called, to get a new one from a reliable maker,
and one which has been properly tested. The gas compressing
firms themselves let out cylinders on hire, which
can be relied upon, for those who do not wish to bay one
outright.
Inasmuch as the gas in these cylinders is at a very high
pressure, and the pressure required in the lantern is hardly
a hundredth part of this, means have to be taken to reduce
the pressure of the gas in its passage from the bottle to the
jet. The best method of doing this is by employing what
is known as a regulator, a little instrument which will
deliver the gas uniformly at any pressure desired until the
cylinder is empty, although the pressure in the bottle is
constantly decreasing as the gas is consumed. There are
several forms of regulator on the market ; the first to be
introduced, and one which is still extremely popular, is that
known as Beard's, after its inventor. Brier's and Clarkson's
are also well-known patterns. Broadly speaking, the
principle upon which these regulators are made is the same,
and can be understood best on reference to the Figs. 19
and 20, which illustrate the construction of the Beard
regulator. The cylinder has the regulator screwed into its
orifice, and the outlet P being closed, the gas is turned on
and passes into the bellows c, expanding them and tightening
up the spring s. As the top, D, of the bellows rises
with the pressure of the gas it gradually closes the valve f,
by mean of the system of levers seen at n, and so cuts off the
supply of gas. As the gas is used at the jet, the spring
forces D down again until the valve reopens and allows the
bellows once more to receive a supply from the cylinder, and
so on. The pressure at which the regulator delivers the
gas, as generally supplied, is about that of 12 inches of
water, but it can be varied by varying the strength of the
springs. Where both oxygen and hydrogen are used in
Fig. 19. BEARD'S REGULATOR Fig. 20. BEARD'S REGULATOR,
EXTERIOR. INTERIOR.
cylinders, separate regulators should be employed for each,
the hydrogen regulator never being attached to the oxygenbottle,
and vice versa. When using the regulator, the gas
can be adjusted by the jet taps, and if required they can be
turned completely off, which, if no regulator were employed,
would result in bursting or blowing off the tube.
In addition to a regulator, those who use cylinders habitually
will find a pressure gauge very useful, as showing at
a glance the amount of gas the cylinder contains. The