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SPECTRUM-PHENOMENA IN THE CHEOMIUM COMPOUNDS. 
Being Part IY. of the Spectrum of the Euby and Emerald. 
By James Moir, M.A., D.Sc, F.I.C. 
In Parts I to III of my investigation of precious stones published 
between 1909 and 1912 (Trans. Eoy. Soc. S.A., I [2], p. 321, II [3], 
pp. 271 and 273, and II [4], p. 339), it was sliown that the almost unique 
spectra of ruby and emerald are due to chromium oxide which has been 
compelled to vibrate in an abnormal or constrained manner, leading to the 
production of narroiv absorption bands in the spectrum ; the constraining 
substance in the case of the ruby is crystalline alumina, and in the case of 
emerald it is beryllium silicate. It was found, in support of this conclu- 
sion, that quite a moderate degree of heating abolishes the characteristic 
spectrum, leaving unaffected the " ordinary " spectrum of chromium. In 
other words, a hot ruby has much the same spectrum as a solution of 
chromium sulphate or chloride. 
Further investigation has now been made to see if constrained vibration 
of ordinary chromiimi oxide could be induced by artificial means, so that 
the resulting mixture would show narrow absorption bands in the red in 
addition to the common broad band of unconstrained chromium (between 
the D and E lines in the case of violet salts and across D in the case of the 
green salts). 
The only previously known cases of these narrow bands are those 
mentioned in Part II of this work, viz. (1) a hazy band at A. 6960 seen in 
K.CrOx., and (2) a v^ery hazy band at X 6800 in chromium borax and 
" microcosmic " beads and in CrA3 solution. 
The first attempt to make a " constrained " chromium solution v/as 1_)y 
use of concentrated sulphuric acid. This was successful, the solution 
showing a red transmission band bounded by two narrow absorption ])ands 
just as in the case of the ruby, although the bands are not in the same 
place. The simplest method of making this solution is to add a few ]}er 
cent, of CrOo to concentrated sulphuric acid, heat, and gradually add small 
quantities of organic matter (e. g. starch) until the orange colour has 
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