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THE SPECTEUM OF THE EUBY— PAET III. 
By James Moir, M.A., D.Sc, F.C.S., F.E.S.S.Af. 
(Eead October 18, 1911.) 
1. In addition to the series of eight thin spectrum lines described in 
Part II., two additional faint bands have been discovered by employing a 
very deeply coloured artificial ruby and concentrated sunlight. Both lie 
in the extreme red beyond the transmission line, and their approximate 
wave-lengths are 7000 and 7150. 
2. By dissolving an artificial ruby in fused bisulphate, precipitating 
with ammonia, boiling till neutral, and fusing the precipitate (after wash- 
ing and drying) with soda and nitre, the author has succeeded in demon- 
strating the presence of chromium as the element causing the colour. 
The cause of the spectrum, however, still remains unsettled. 
3. The remarkable observation was made that the ruby, when heated 
to a temperature below a red heat, changes colour, through brown to 
green. Whilst hot the spectrum is that of ordinary chromium — w^ithout 
any of the special ruby lines. On cooling it slowly recovers its original 
colour and spectrum. This process was followed more closely by spectro- 
scoping a ruby immersed in a bath of hot spermaceti, and illuminated at 
the focus of a lens. Even at the low temperature of 250° 0. the red 
transmission band became faint and ill-defined. This and the two strong 
violet lines all disappeared at 290-300°, although faint signs of the two 
absorption bands bordering the red transmission could be seen up to 340°. 
In addition, the whole absorption of the stone shifts towards the red, the 
violet end shifting up to F as in the ordinary chromium spectrum. Even 
at 180° the stone is distinctly redder (less rose-coloured) than when cold. 
Plattner's book on the blowpipe describes a similar change of colour due 
to chromium in pyrope and spinel, which, however, have no definite 
spectrum, and are isotropic. 
4. By means of a specially improvised arrangement an examination of 
a corundum plate under the combined action of a red heat and of polarised 
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