It would,
however, be a simple matter to erect an acetylene burner inside the
lantern in such a way that when needed an oil-lamp or candle could be
used instead. Artificial internal light of any kind is best avoided; the
only kind permissible being an electric glow-lamp. If this is employed,
it should be surrounded by a second bulb or gas-tight glass jacket, and
preferably by a wire cage as well; the wires leading to it must be
carefully insulated, and all switches or cut-outs (which may produce a
spark) must be out of doors. The well-known Davy safety or miner's lamp
is not a trustworthy instrument for use with acetylene because of
(_a_) the low igniting-point of acetylene; (_b_) the high
temperature of its flame; and (_c_) the enormous speed at which the
explosive wave travels through a mixture of acetylene and air. For these
reasons the metallic gauze of the Davy lamp is not so efficient a
protector of the flame as it is in cases of coal-gas, methane, &c.
Moreover, in practice, the Davy lamp gives a poor light, and unless in
constant use is liable to be found out of order when required. It should,
however, be added that modern forms of the safety lamp, in which the
light is surrounded by a stout glass chimney and only sufficient gauze is
used for the admission of fresh air and for the escape of the combustion
products, appear quite satisfactory when employed in an atmosphere
containing some free acetylene.
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