of more importance. Acetylene is readily and quickly produced from a raw
material--calcium carbide--which, relatively to the yield of light of the
gaseous product, is less bulky than the raw materials of other gases. In
comparison also with oils and candles, calcium carbide is capable of
yielding, through the acetylene obtainable from it, more light per unit
of space occupied by it. This higher light-yielding capacity of calcium
carbide, ready to be developed through acetylene, gives the latter gas a
great advantage over all other illuminants in respect of compactness for
transport or storage. Hence, where facilities for transport or storage
are bad or costly, acetylene may be the most convenient or cheapest
illuminant, notwithstanding its relatively high cost in many other cases.
For example, in a district to which coal and oil must be brought great
distances, the freight on them may be so heavy that--regarding the
question as simply one of obtaining light in the cheapest manner--it may
be more economical to bring calcium carbide an equal or even greater
distance and generate acetylene from it on the spot, than to use oil or
make coal-gas for lighting purposes, notwithstanding that acetylene may
not be able to compete on equal terms with oil--or coal-gas at the place
from which the carbide is brought. Likewise where storage accommodation
is limited, as in vehicles or in ships or lighthouses, calcium carbide
may be preferable to oil or other illuminants as a source of light.
Disregarding for the moment intrinsic advantages which the light
obtainable from acetylene has over other lights, there are many cases
where, owing to saving in cost of carriage, acetylene is the most
economical illuminant; and many other cases where, owing to limited space
for storage, acetylene far surpasses other illuminants in convenience,
and is practically indispensable.

The light of the acetylene flame has, however, some intrinsic advantages
over the light of other artificial illuminants. In the first place, the