This material, used either as a liquid spray or as a moist dressing, has
been said to prove a useful garden insecticide and weed-killer.
There are also numerous applications of the acetylene light, each of much
value, but involving no new principle which need be noticed. The light is
so actinic, or rich in rays acting upon silver salts, that it is
peculiarly useful to the photographer, either for portraiture or for his
various positive printing operations. Acetylene is very convenient for
optical lantern work on the small scale, or where the oxy-hydrogen or
oxy-coal-gas light cannot be used. Its intensity and small size make its
self-luminous flame preferable on optical grounds to the oil-lamp or the
coal-gas mantle; but the illuminating surface is nevertheless too large
to give the best results behind such condensers as have been carefully
worked to suit a source of light scarcely exceeding the dimensions of a
point. For lantern displays on very large screens, or for the projection
of a powerful beam of light to great distances in one direction (as in
night signalling, &c.), the acetylene blowpipe fed with pure oxygen, or
with air containing more than its normal proportion of oxygen, which is
discussed in Chapter IX.
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