Bisbee daily review., 1915-05-30
PHYSICAL WAYS ID DETERMINE
 RARE GEMS
Dr. Edgar T. Wherry, of U. S.
 National Museum, Works Up Method by Which Pre- cious Stones Can Be Told.

clous Stones Gan Be Told.
 WASHINGTON, May 29 The min eroloeist is frequently confronted with the problems of iudetifying and Naluing precious stones. for although an experienced dealer may be able to tell the gnuineness of gem at sight. scientific tests are frequently neces- sary to make certain
 When a large quantity of a mineral is available, various chemical tests my be applied, but when a single cut stone is presented for identification. chemicals may not be used Depend. ence is then placed on physical tests which do not affect the material in any way Two of these tests are. hardness or resistance to scratching. and specitc gravity or heaviuess with reference to water Even these. however, are sometimes not applica- ble, and the optical properties must be tested These include color. ef- feet on polarized light. and the index or reelection. One or another of these methods is applicable in pract. cally every case but it is rarely wise I to depend on a single test. the more ways in which a conclusion can be reached the more certain it is likely 10 be.
 Dr. Edgar T. Wherry, assistant cur ator in the Division of Mineraiogy and Petroiogy of the IT. S National ! Museum, has recently worked up method of Identification especially well adapted Co gems though not with out application to other miueralogical work. This system employs the mic rospectroscope. microscope-eye- piece containing a small prism for the purpose of splitting or dividing the light from the source into the spectrum or series of colors into which all light may be divided brilliant white light is used for this purpose, such as that given off by Welsbach burner As the eNamiua- ton must be carried on in as dark a place as possible, SO that the eye will be sensitive Co slight light effects the burner is surrounded by a dark chimney and only a marrow beam of light is allowed 10 escape. This beam Is focused on the side Of the spcci- men by means Of a lens or mirror, and its path in viewed through the mic roscope, using the microspectroscope eyepiece In examining colorless gems and crystals, like the diamond, only the containous spectrum is shown. with its colors ranging from red through orange, yellow, green and blue to violet but if the specimen is colored by the presence Of certain chemical elements or dyes. light of some color will be absorbed by it, and one or more bands will appear in the spectrum where the eliminated color would ordinarily be. The position and numbers of these bands are highly characteristic of certain substances, and therefore serve Co identify gems and minerals colored by these sub stances. The location of the bands is found by the use of a very finely divided scale within the instrument which reads in g,5OOOOOtbs of an inch
 The ruby owes it's color to the pres euce of small amount of an oxide of chromium, that element shows @ black band toward the extreme red of the spectrum separated from the invisible region beyond the red by a narrow bright line. When an un- known stone exhibits this type of spectrum in the microspectroscope it
 may be identified as genuine ruby
 with absolute certainty Snythetic
 ribies, which are identical with the
 natural ones in every respect, also show this type of spectrum, but the bits of red glass, which owe their color in copper or gold or Co the rare ' element selenium, SO often cut and ' sold as rubies do not show this type 1, of spectrum and can not at once be , detected.
 tauDmries car a'.o b" uos'tiNely I Identified by this same method only Y hcre the behavior Is reversed; true e sauul ries show 10 absorption bands, !, but a clear spectrum, while their blue q glass limitations have several strong t bands replacing the colors eliminated S from the spectrum. This method has r. also proved valuable in tho identfca .. ton of many transparent or fairly
 translucent precious stones, including IS the emerald, garnet tourmaline tur y quoise. beryl and topaz Considering !. the fact that it can be applied with
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