OCTOBEK 8, 1886.J 



SCIEJSrCE. 



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them of large numbers of spherical bubbles, 

 rarely pear-shaped, sometimes containing stringy 

 portions showing how the bubbles had moved. 

 These bubbles all have rounded ends, and present 

 the same appearance as those seen in glass or other 

 fused mixtiu-es. They are nearly always in wavy 

 groups or cloudy masses. When| examined indi- 

 vidually, they always seem to be filled with gas or 

 air, and often form part of a cloud, the rest hav- 

 ing the waviness of a fused mixtvure. Some few 

 were observed enclosing inner bubbles, apparently 

 a double cavity, but empty. In natural rubies the 

 cavities are always angular or crystalline in out- 

 line, and are usually filled with some liquid, or, if 

 they form part of a ' feather,' as it is called by the 

 jewellers, they are often arranged with the lines 

 of growth. Hence the difference in appearance 

 between the cavities in the natural gem and those 

 in the fused gem is very great, and can readily be 

 detected by the pocket-lens. I have failed to find 

 in any of the artificial stones even a trace of any 

 thing like a crystalline or angular cavity. Another 

 distinguishing characteristic is that in many genu- 

 ine rubies we find a silky structure (called ' silk ' 

 by the jewellers), which, if examined under the 

 microscope or under a ^ to -^-^ inch objective, we 

 find to be a series of cuneiform or acicular crystals, 

 often iridescent, and arranged parallel with the hex- 

 agonal layers of the crystal. When in sufficient 

 number, these acicular and arrow-shaped crystals 

 produce the asteria or star effect, if the gem is cut 

 in en cabochon form, with the centre of the hex- 

 agonal prism on the top of the cabochon. I have 

 failed to find any of them in the stones under con- 

 sideration, or even any of the marking of the hex- 

 agonal crystal which can often be seen when a 

 gem is held in a good light, and the light allowed 

 to strike obliquely across the hexagonal prism. 

 Dr. Isaac Lea has suggested ' that these acicular 

 crystals are rutile, and. interesting facts and illus- 

 trations have been published by him. From my 

 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 corun- 

 dum 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, 8.8 or a trifle 

 less than 9, the only difference 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 



1 Proc. Philad. acad. sc, Feb. 16. 1869, and May. 1876. 



2 Paper on star garnets, N. Y. acad. sc, May, 1886. 



the case with a brittle^ material. After several 

 trials, I faintly scratched it with chrysoberyl, 

 which will also sHghtly 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 presence of 

 the included bubbles in the artificial stones, which 

 would slightly decrease the density. As a test, 

 this is too delicate for jewellers' use ; for if a true 

 ruby were not entirely clean, or a few of the bub- 

 bles that sometimes settle on gems in taking 

 specific gravities were allowed to remain undis- 

 turbed, it would have about the same specific 

 gravity as one of these artificial 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 polariscope, 

 what I believe to be annular rings were observed. 

 With the spectroscope, the red ruby line, some- 

 what similar to that in the true gem, is distinguish- 

 able, although perhaps a little nearer the dark end 

 of the spectrum. 



The color of all the stones examined was good, 

 but not one was so 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 

 appearance is evidently due in part to the bubbles. 

 The optical properties of these stones are such that 

 they are evidently individual or parts of individual 

 crystals, and not agglomerations of crystals or 

 groups fused by heating. 



In my opinion, these artificial rubies were pro- 

 duced by a process similar to that described by 

 Fremy and Fell {Comptes rendus, 1877, p. 1029), — 

 by fusing an aluminate of lead in connection with 

 silica in a siliceous crucible, the silica uniting with 

 the lead to form a lead glass, and liberating the 

 alumina, which crystallizes out in the form of 

 corundum in hexagonal plates, with a specific 

 gravity of 4.0 to 4.1, and the hardness and color of 

 the natural ruby, the latter being produced by the 

 addition of some chromium salt. By this method, 

 rubies were formed, that, like the true gem, were 

 decolorized temporarily by heating. 



It is not probable that these stones were formed 

 by Gaudin's method {Comptes rendus, xix. p.>1343), 



by exposing amorphous alumina to the flame of 



the oxyhydrogen blowpipe, and thus fusing it to a 

 limpid fluid, which, when cooled, had the hard- 

 ness of corundum, but only the specific gravity 

 3.45, much below that of these stones. Nor is it 

 at all likely that they were produced by fusing a 

 large number of natural rubies or corundum of 



