1911.] NATURAL SCIENCES OF PHILADELPHIA. 109 



ception, hence this spectrum will serve to identify a red garnet with 

 practical certainty. Red spinels show no absorption bands in their 

 spectra. 



The ruby exhibits an interesting spectrum consisting of a very narrow 

 bright line between two absorption bands, at wave length .69 micron 

 in the extreme red. A careful search of the literature of the subject 

 has enabled me to find no evidence that this spectrum had been pre- 

 viously observed and recorded, but whether new or old, it is most 

 characteristic, not only of typical rubies, but of every variety of 

 corundum that contains a trace of red in its coloration, including the 

 various shades of pink and amethystine sapphires, even when so pale 

 as to appear colorless with artificial light, star rubies, Montana sap- 

 phires of pinkish cast and even corundum from North Carolina and 

 other localities, which has a pink tint. The remainder of the spectrum 

 may vary, all except the red being absorbed by deep colored oriental 

 rubies, or all the colors visible in light tinted varieties, but the narrow 

 bright band in the red remains the same. 



This spectrum is unquestionably due to chromium, the coloring 

 matter of the ruby, as it is likewise found in examining artificial 

 rubies which owe their color to the same element. It affords an infalli- 

 ble test for distinguishing a ruby from a garnet, spinel or tourmaline 

 of similar color, and is applicable to stones in deep mountings or even 

 if covered by a plate of glass. The artificial ruby is the only other 

 stone giving a similar spectrum, and it can readily be distinguished by 

 means of the microscope alone. 



A number of other precious stones exhibit fainter but nevertheless 

 characteristic spectra. Blue and violet spinels show two narrow and 

 fairly sharp lines in the yellow and green, and, as in the case of the 

 ruby, this spectrum is very persistent, the bands being scarcely less 

 visible when the stone is almost colorless than from one of deep color. 

 It is particularly available as a means for easily distinguishing pale 

 amethystine spinels from sapphires of identical color frequently 

 found mixed in same paper of Indian cut stones. 



Among green gems, the emerald exhibits a faint line in the red and 

 a broader shadowy band occluding the orange and yellow. Green 

 garnet or demantoid, often sold as " olivine," has two very faint bands 

 in the red, which coalesce into one when the stone is deep in color, 

 while the true olivine or peridot shows two bands in the blue and 

 violet, which, although rather broad and well-defined, are usually 

 extremely difficult to see, owing to the comparatively small amount 

 of light of the shorter wave lengths transmitted by this mineral. 



