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MODERN MAGIC LANTERNS.
the oxygen nozzle is withdrawn further into the jet, or, what
comes to the same thing practically, when a nozzle is fitted
to the jet, as shown in Fig. 31, the mixture of the gases is
effected very much better, and the light emitted from the
lime is proportionately increased, but a danger,
or rather an inconvenience, is experienced. If
in such a jet as Fig. 31 the oxygen be turned
completely off, the coal gas will to a certain
extent make its way into the oxygen tube, and
when that gas is turned on again the mixture
in that tube will cause a slight explosion or
Fig. 31.
" pop, " putting out the light and startling the
BLOW-THROUGH audience, although nothing more serious will
JET
WITH NOZZLE. result. Such an occurrence can be prevented
by turning the oxygen not quite but nearly off,
so that just a faint blue bead in the flame indicates that it
is still passing.
In this form of jet the coal gas or hydrogen is always in
large excess of the oxygen, and the area of lime heated is
much larger than with the mixed jet. On the other hand, a
light powerful enough for everything but the largest displays
can be obtained with a blow-through jet, together with an
almost complete guarantee against mishap.
To use the blow-through jet, the lime should be adjusted
about half an inch from the gas orifice, but not clamped
there, and the hydrogen lighted and turned full on. (We
might mention here that the hydrogen and oxygen pipes and
taps should be distinguished both by colour and by having
the words OXYGEN and HYDROGEN engraved on them, or,
better still, the handles of the taps should be different in
shape, telling the operator by the feel alone of which he has
hold.) The oxygen must now be slowly turned on until any
increase in its amount ceases to cause the light to increase.
When no more light can be obtained by adjustment either
of the hydrogen or oxygen, the lime should be moved slightly
nearer or further away from the jet until the position is
found where the light is most brilliant. When this is
ascertained, the holder should be clamped there once and
for all. To turn the jet out, the oxygen should first be
cut off, and then the hydrogen lowered.
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JETS.
As the jet plays upon the lime it gradually "pits "it, and
the lime must from time to time be turned. Large wings of
burning hydrogen should not be allowed to play each side of
the lime, as such a course is wasteful, and they may be
directed against the condenser and damage it ; they also
help to heat the lantern unnecessarily.
The mixed jet, which yields the most intense light of any,
is shown in Fig. 9. As its name implies, the gases are
'mixed before being burnt at the nipple, and to this end the
two tubes terminate in a chamber below the nipple itself.
The nature and form of this chamber have been the subject
of many and careful experiments by the Rev. Hardwich,
Mr. Lewis Wright, and others, and the outcome of their
work has resulted in the form shown in section in Fig. 32.
The chamber, which is here shown, is filled up with a series
of circular discs, each alternate disc having a central hole, and
the others a ring of smaller perforations, the discs being separated
by rings. These discs are shown by the side of the
chamber in the figure. Such a chamber ensures the gases
being most thoroughly mixed, and when burnt in this condition
the most intense heat and consequent light is produced.
As with the blowthrough
jet, the hydrogen
should first be
turned on and lit,
then the oxygen added
slowly until the
best light is obtained.
If the jet should roar,
the gas should be
regulated until it
ceases to do so ; with
some jets this cannot
be done. In this case
the roaring is a sign
that the gas passage
Fig. 32. MIXING CHAMBER.
in the nipple is not perfectly smooth, and this is best
remedied by the maker. To extinguish the jet, the oxygen
is first turned off and then the coal gas, the tubes on
no account being detached until the light is out. Should
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