1887.] NEW-YORK MICROSCOPICAL SOCIETY. 57 



own observations on many specimens, I believe there is little 

 doubt of the truth of this hypothesis/ My explanation is, that 

 they were deposited from a solution, either heated or cold, while 

 the corundum was crystallizing, and I doubt very much whether 

 they will ever be found in any substance formed by fusion. 



The hardness of these stones I found to be about the same as 

 that of the true ruby, 8.S, or a little less than 9, the only differ- 

 ence being that the artificial stones were a trifle more brittle. 

 The testing point used was a Siamese green sapphire, and the 

 scratch made by it was a little broader but no deeper than on a 

 true ruby, as is usually the case with a brittle material. After 

 several trials I faintly scratched it with a chrysoberyl, which will 

 also slightly mark the true ruby. 



The specific gravity of these stones I found to be 3.93 and 

 3.95. The true ruby ranging from 3.98 to 4.01, it will be seen 

 that the difference is very slight, and due doubtless to the pres- 

 ence of the included bubbles in the artificial stones, which 

 would slightly decrease the density. As a test, this is too deli- 

 cate for jewelers' use ; for if a true ruby were not entirely clean 

 or a few of the bubbles of air that sometimes settle on gems in 

 taking specific gravities were allowed to remain undisturbed, it 

 would have about the same specific gravity as one of these arti- 

 ficial stones. 



I found, on examination by the dichroscope, that the ordinary 

 image was cardinal red, and the extraordinary image a salmon 

 red, as in the true ruby of the same color. Under the polari- 

 scope, what I believe to be annular rings were observed. With 

 the spectroscope, the red ruby line, somewhat similar to that in 

 the true gem, is distinguishable, although perhaps a little nearer 

 the dark end of the spectrum. 



The color of all the stones examined was good, but not one 

 was as brilliant as a very fine ruby. The cabochons were all 

 duller than fine true stones, though better than poor ones. 

 They did not differ much in color, however, and were evidently 

 made by one exact process or at one time. Their dull appear- 

 ance is evidently due in part to the bubbles. The optical prop- 

 erties of these stones are such that they are evidently individual 

 or parts of individual crystals, and not agglomerations of crys- 

 tals or groups fused by heating. 



* Paper on star garnets, N. Y. Acad. Sc, May, 1886. 



