The Chemistry Student
I 1
WHERE CHEMICAL ANALYSES FAIL GUY BARTLEM, GENERAL ELECTRIC COMPANY. SCHENECTADY, NEWYORK
Only because Man in his laboratory has worked more carefully than has Nature in its workshop has it been possible in the past to distinguish between natural and synthetic sapphires, rubies, and other precious stones in the corundum family. Chemical analyses of natural and synthetic stones reveal the same constituents-aluminum oxide, A1103,with the slight trace of impurity that determines its color and therefore its classification as a precious stone. Chemically the two are alike, but Nature was somewhat slip-shod when it made its jewel-tiny particles of undissolved impurities, minute bubbles within the sparkling gem, or slight flaws between the atomic layers are revealed when a natural gem is examined under a highpowered magnifying glass; Man avoided such imperfections when be synthesized his jewel. In the past, then, the jeweler has depended on his expertness in detecting the minor flaws of Nature in ascertaining the worth of a gem. While the two typesnatural and syntheticmay be the same chemically, they differ in other respects. As gems, for instance, there is a decided difference in the value placed on Nature's and Ifan's rubies. Simply the fact that the one was dug from the ground makes it worth far more than the other, even though the unaided eye can perceive no difference and even though the expert has difticulty in distinguishing between them with a magnifying glass. In industry as well, the relative values of the two kinds of stones differ. The natural stone, with a better wearing surface, is preferred for jewel bearings. Even in the case of natural stones there is a difference in wearing quality, but it has been even more difficult for the expert to distinguish between natural stones from one country and those from another. Now, however, there has been devised a method for quickly and accurately distinguishingbetween synthetic and natural stones; between natural stones from different countries; and, in some cases, even between synthetic stones from diierent factories. The device which does this is the powerful cathode-ray tube developed by Dr. W. D. Coolidge of theGeneral Electric Research Laboratory three years ago.' The use of the tube in this work is its first commercial application. More than a million and a half sapphires, next below the diamond in the 1
"The Cathode-Ray Tub-A
New Chemical Agent" was described in Tnrs
J O U R 3,1369-79 N~, (Dec., 1926). 399
JOURNAL OP CHEMICAL EDUCATION
400
PLACING A
FEBRUARY, 1930
TRAYOF MIXEDNATURAL AND SYNTHETIC SAPPHIRES BEFORE CATHODE RAYTUBE
THE
scale of hardness, are used by the General Electric Company each year as jewels for bearings in meters and other delicate electrical instruments. If a tray of mixed stones is exposed, in a dark room, to the rays of the tube for a few seconds i t will be noticed that all of the stones are luminescent, glowing with different hues. When the rays are turned off, however, a decided difference is a t once apparent. The synthetic stones are phosphorescent, and continue to glow, while the natural stones cease to radiate
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402
J O U R N A L OF CHEMICAL E D U C A T I O N
FBBRUAUY, 1930
A CoLLECTloN OP NATURAL AND SYNTHETIC SAPPIURES TO BE IDENTIFIED CATHODE RAYTUBE
BY
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colors. And, by the color of the radiation and the duration of phosphorescence, it is possible to determine the source of the stone. "Should sapphires from Montana be mixed with stones which were supposed to come from Australia or Ceylon, for instance, we could determine the fact readily with cathode rays," says B. W. St. Clair of the standardizing laboratory of the company at Lynn, MassachusZtts, where the tests are conducted. "In the case of synthetic stones it is usually possible also to determine which factory made them by the different hues of the glow while the rays are on. We have one particular kind of natural sapphire which does not glow; in this case the absence of hue serves to reveal its origin.'' Some tests have been made with diamonds, and it has been found that imitation stones turn decidedly brown when placed in the rays, whereas there is no change in genuine stones. These tests have been meager, however, and definite conclusions have not been reached by the General Electric scientists.
