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I 11
24 MODERN MAGIC LANTERNS.
When on applying a glowing match to the open end
of the tube it is relit, showing that the air has been
driven out of the apparatus by the oxygen, connect
the pipe from the bag with the flask.
When gas has finally ceased to come off, close the
stopcock, disconnect the retort from the flask at once,
and then remove or extinguish the source of heat.
It is so unlikely that hydrogen gas will ever require to be
made, its place being supplied by alcohol or oxygen and
ether, that no apology is necessary for the omission here of
any details upon the subject. CHAPTER V.
Compre6eb Oaus.
MOST lanternists nowadays use the compressed oxygen,
and in some cases compressed coal gas also. The gas is
supplied in steel cylinders, such as shown in Fig. 18, into
which it is forced by powerful pumping machinery until it
reaches a pressure of 1,800 lb. per square inch, or 120
atmospheres. The extraordinary strength of these cylinders
can be best understood when it is pointed out that the
Fig. is. GAS CYLINDER.
weight of one to hold 10 cubic feet of gas is not more than
15 lb., and the outside dimensions for this capacity 4 inches
in diameter and 19 or 20 in length.
It might be supposed at first sight that such things must
be essentially of a dangerous nature, but when the large
number of cylinders in constant use all over the world is
taken into consideration, the almost entire immunity from
accident should beget confidence in reasonable minds
Still, as there is the potentiality of a great deal of mischief
in a charged cylinder, they should not be treated with
unnecessary violence.