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16 MODERN MAGIC LANTERNS.
kinds may be considered as most suitable for different forms
of jet. The soft limes incandesce at a lower temperature, but
are not so lasting as the harder ones ; for this reason they
should be used for the oxy-alcohol and blow-through types
of jet ; while the harder limes, of which the Nottingham
is an example, are used to best advantage in the intense heat
of the mixed jet. Messrs. Newton and Co. have lately
introduced a new lime known as the "Newtonian," which
possesses certain advantages over the above-mentioned, in
that it is turned and bored with great accuracy and is far
less affected by exposure to the air.
All limes, except at the time of using, must be carefully
protected from moisture, and consequently from the
atmosphere. They are generally supplied, packed in powdered
lime, in hermetically sealed tins or bottles, and under
such conditions will keep for a considerable time. When
once the case has been opened, however, they begin to
deteriorate unless special care is taken to protect them. Mr.
Hepworth recommends that each lime should be dipped in
melted paraffin wax or beeswax, half-way, and then allowed
to cool. When the wax is firm, the lime should be held by
the waxed portion, and its other half immersed ; and when
the waxen coating is solid, the limes wrapped up separately
in paper and stored away until required. This is said to
protect them perfectly from the action of air, and
the coating is peeled off very readily when the lime
is wanted for use, provided that the wax in which they were
dipped was only just above its melting point and no hotter.
Most dealers in lantern requisites supply tubular cases of
brass with a screw lid, which are capable of holding six limes,
one on the top of another, and these are handy for storing
purposes, the contents of a tin being transferred to them
as soon as it is first opened. The Newtonian limes just
mentioned are sold separately, wrapped in thin paper, and
packed in a tin tube with sliding lid : a means of storing
which is satisfactory with this particular make of lime,
but one which we should not recommend for others. It
must be remembered that limes are really quicklime, and
that with exposure to the air they slake-that is, they
absorb moisture, swell, and fall to pieces ; and that a lime
THE LIMELIGHT. 17
is not used to the best advantage after its surface has lost
its initial hardness.
If a lime is taken from its case, put into the lantern, and
the jet turned full on it at once, the probabilities are
that it will crack and be rendered useless. This is only
what might be expected when it is borne in mind how
unevenly it is heated, one side being- exposed to one of the
fiercest flames known, the other to the cold air rushing to
supply that flame. For this reason limes before use should
be heated by being put in an oven, on the hob, or exposed to
the coal gas or hydrogen flame in the lantern, and turned
round occasionally, for an hour or two before they are
wanted.
When a lime is required for use, the hole through it will
most likely be found to be filled with the powdered lime in
which it was packed. This should be got out by tapping the
lime gently on a hard surface, and no attempt must be made
to force it on the lime pin while the hole is clogged up, as
by so doing the powder is only rammed more tightly together
and the lime for the time being made useless.
Mr. E. G. Wood some years ago introduced what he called
a lime shield--a little cylindrical piece of thin metal which
surrounded the lime, with an opening where the jet was
directed against it ; this serves the useful purposes both of
protecting the lime from draughts, keeping it warm, and of
protecting the condenser from an accidental reflection of
the flame upon it from a pitted or otherwise uneven lime.
It can be seen in Fig. 7 surrounding the lime and connected
with the fixed portion of the jet, the lime being free to
revolve within it.
From time to time substitutes for lime have been proposed,
but as none of them have ever come into anything like
general usea fact accounted for by all of them possessing
one or more disadvantages rendering them inferior to lime
itselfanything more than an allusion to them is out of
place here.