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JOURNAL OF CHEMICAL EDUCATION
We know that the color of indigo can be changed from blue to colorless by a very slight change in its molecu1e, for example, the addition of two atoms of hydrogen. The blue color can be restored by a mild oxidation which removes the two hydrogen atoms. Thus, we may think of the absorption of visible light which occurs in gems as a resonance effect among the valence electrons of the atoms of the coloring impurities. and conclude that the energies, or frequencies, of the outer electron level of the eight elements which have~ been mentioned as causing the colors, are in tune with the energies. or frequencies, of some part of visible light. Part of the light is transformed-perhaps into heat-and part succeeds in penetrating into the atomic maze, the resu1ting color depending on the element involved. In the case of colorless minerals, none of the light energy is removed' by vibrating "sym pathetically" within the mineral. All the energy in the visible spectrum comes out equally well, and white light is not absorbed by the material. If a stone contains more than a small amount of a coloring agent, it appears black. The coloring agent must be in a condition corresponding to dilute solution in order to pick up the specific energy and transmit the rest of the light. OUf theory, then, is that color in gems is due to
selective absorption of parts of the visible frequencies of light by a resonance effect among the valence electron levels of particular atoms. These atoms, most often found in the transition series, are present only in small amount, i. e., in low concentration in the space lattices of the crystals. Probably effects similar to what we call color occur when electromagnetic energy of frequencies unrecognizable to the human eye passes through layers of other elements, thus being sympathetically absorbed or passed on, according to resonance effects. There are many optical effects involved. in rationalizing the many interesting behaviors of gems. Dichroism, the differential absorption in different directions in some crystalline materials, is accompanied by plane polarization of light. Fluorescence, with its accompanying change of frequency, usually but not always toward lower frequency, must be accounted. for; also phosphorescence, a slow dying-out of the disturbed condition after the source of provoking energy has been cut off. Refraction and reflection still must be accounted for on a modern basis. It is the author's hope that this attempt to rationalize color effects in gems may lead some better-prepared scientists to apply their physics and mathematics successfully to this interesting problem.
Fih:ns Available THE following films are available for loan provided the borrower is responsible and pays transportation charges: Meat and Romance.-16 mm., sound. Quentin L. Lambert, Department of Information, National Live Stock and Meat Board, 407 South Dearborn Street, Chicago, Illinois. Fight That Fire.-16 mm., sound, color, also black and white. 11 minutes. Instructor's manual available. Pyrene Manufacturing Company, 560 Belmont Avenue, Newark, New Jersey; also 242 Spring Street, Atlanta, Georgia; 444 N. La!;e Shore Drive, Chicago, Illinois; 977 Mission Street, San Francisco, California. Forty-seven assorted subjects. Send for G M Film Catalog, Fifth Edition, 1943-1944, 1775 Broadway, New York 19, New York. Six titles dealing with aluminum and its fabrication -sound, 16 or 35 mm. Aluminum Company of America, Pittsburgh, Pennsylvania.
Nine titles related to fertilizers and soils, some with limited distribution. American Potash Institute, Inc., 1155 Sixteenth Street, Washington, D. C. Six subjects, including structure of matter. Ask for Teaching Aids from Westinghouse School Senna. Westinghouse Electric and Manufacturing Company, 306 Fourth Avenue, P. O. Box 1017, Pittsburgh 30, Pennsylvania. Call local telephone business office to inquire about films related to telephone business.
Rayon-A New Frontie,. of Progress-16 mm., 37 minutes. Betty Lou Larson, Manager, Educational Division, American Viscose Corporation, 350 Fifth Avenue, Tew York, New York. A list of Supplementary EducatiomU Material includes films dealing with woods, plywood, and forests. American Forest Products Industries, Inc., 1319 Eighteenth Street. N. W., Washington 6, D. C.
The zinc~coated steel penny, coined in 1943,"saves 4f)(}O tons oj copper. A new cop.. per penny, being coined this year, is madeJrom_discarded cartridge shells.
