008. It is clear that for such a purpose as this the acetylene must be
prepared from very pure carbide and at the lowest possible temperature in
the generator. Further investigations in this direction should be
welcome, because it is now fairly easy to obtain a carbide of standard
quality and to purify the gas until it is essentially pure acetylene from
a chemical point of view.
L. W. Hartmann has studied the flame of a mixture of acetylene with
hydrogen. He finds that the flame of the mixture is richer in light of
short wave-lengths than that of pure acetylene, but that the colour of
the light does not appear to vary with the proportion of hydrogen
present.
Numerous investigators have studied the optical or radiant efficiency of
artificial lights, _i.e._, the proportion of the total heat plus
light energy emitted by the flame which is produced in the form of
visible light. Some results are shown in the table on the previous page.
Figures showing the ratio of the visible light emitted by various
illuminants to the amount of energy expended in producing the light and
also the energy equivalent of each spherical Hefner unit evolved have
been published by H.
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