Jones wrote:
> This is the page that mentions the way that the
> characteristic greenish color of the light was
> obtained, with some other interesting stuff.
>
> http://www.chem.leeds.ac.uk/delights/texts/Demonstration_19.htm
>
> Apparently the greenish color occurs when the oxygen
> is cut-off or starved, which was apparently a likely
> occurrence back then, either planned or unplanned.
>
> Hydrogen was easily extracted from town gas but oxygen
> would have been comparatively expensive, one supposes.
>
> "Apart from thermoluminescence calcium oxide exhibits
> also so-called flame luminescence. When the oxygen of
> an oxy-hydrogen blast lamp used in the production of
> the limelight is turned off and the hydrogen flame is
> allowed to play over the surface of the slowly cooling
> lime cylinder, a greenish glow may sometimes be seen
> in the regions reached by the flame."
I have to admit I never tried starving the flame of oxygen, apparently the only
time the greenish glows appears. The fully oxygenated hydrogen flame on the
lime gives a really beautiful pure white light, much nicer than the carbon arc.
I've never found a historical reference to the characteristics of the limelight
spectrum, which is rather odd.
The article also mentions what I observed, which is that it must be a hydrogen
flame for the effect to occur. It makes me wonder what would happen if the lime
were exposed to the flame of a Langmuir torch. Would the lime be reduced to
metallic calcium and the lime cylinder melt away like a candle?
M.
