Fluorescence and Luminescence A symposium w i t h dumonstrations, on fluorescence and luminescence, is to be held by the Divisions of Phsical and Inorganic Chemistry af the American Chemical Society at the North Jersey m e e t i n g in New York, September 11, 1944. The chairman of the symposium will be George S. Forbes, of Harvard University Papers will be given by Jacob Bigeisem, Columbia University, Henry Eyring, Princeton University H. W. Leverenz, R. C. A. Research Laboratories and Peter Pringsheim Ray Control Co. B e c a u s e of the importance of this little k n o w n , but i n t e r e s t i n g s u b j e c t , George S. Forbes has, prepared thea r t i c l ebelowtopoint out the historeical and timely aspects of this b r a n c h of chemistry. FROM earliest times mankindhaswondered at the light emitted by the firefly, marine organisms, or the will-o'-the-wisp. Boyle, Newton, Franklin, Priestley, Davy, von Humboldt, Faraday, and a host of later scientists have tried to penetrate its mysteries. E. Newton Harvey, of Prince ton, is everywhere known for bis studies of bioluminescence, culminating in "Liv ing Light" published in 1940 by the Prince ton University Press. Of late, his col league, Henry Eyring, best known perhaps through his theory for prediction of reac tion rates, or by his "Quantum Chemis try" (Wiley, 1944), has brought the re sources of his scholarship to bear upon the problem. Only a small part of his find ings has as yet appeared in print, but at the national meeting he will present addi tional data obtained by him and Frank H. Johnson, with special reference t o lumines cent bacteria. Λ piece of uranium glass or a flask of quinine sulfate solution exposed to the sun is filled with internal light. Some structural unit, by absorption of radiation, is excited to a more energetic state. This added energy is not all frittered away in setting up more violent molecular collisions with neighbors, as usually happens, but is re-radiated as visible light. Twenty-five years ago, Peter Pringsheim, of the Uni versity of Chicago (Dr. Pringsheim is now director of spectrographs research for the Ray Control Co., Pasadena, Calif.), pro duced one of the first truly scientific treatises on fluorescence and kindred topics which ever since has guided many others. At that time he felt that the subject was a matter of rather special scientific research, and did not hope that the book would arouse much interest out side of physical or chemical laboratories. His new book, "Luminescence of Liquids and Solids and Its Practical Applications" (Interscience Publishers, New York, 1943), calls attention to the vital roles of lumines cence in such diversified fields as vitamin analysis, television, blackout lighting, and petroleum prospecting. Chemists, physi ologists, criminologists, mineralogists, and industrial engineers allfindit a valuable VOLUME
S 2, N O . , 1 4
George S. Forbes Symposium Chairman
tool. Professor Pringsheim will unfold some recent developments, especially the measurement of incredibly small quanti ties of oxygen. Even the cave man obtained light from burning sofids, and the fact that we still depend u* s, incandescence for artificial illumination is perhaps the greatest of energetic tragedies. To be sure, we have improved matters by increasing the tem perature of the source, but possibilities in this direction are nearly exhausted. The human eye can fully utilize 0.07 per cent of the combustion energy of the candle and perhaps 3 per cent of the electrical energy expended in a pas-filled tungsten lamp. The sun has the ideal temperature from this standpoint, for its "luminous efficiency" is 14 per cent. The firefly holds the record—95 per cent approxi mately. The energy of oxidation of its secretion is converted not into heat ex clusively, but partly into yellow green light. We have not yet caught up with this insect's admirable efficiency, but we have outdistanced him as regards light intensity. The modern fluorescent lamp is essentially a gas discharge tube coated
» » » JULY
3 5, 1 9 4 4
inside with a highly specialized lumines cent solid. The ultraviolet light emitted by excited gas atoms energizes this solid, which theseupon gives out visible light. Great difficulties have been overcome in order to produce lamps at once inexpen sive, brilliant, and durable. The most superficial study of patent literature dis closes the outstanding qualifications of H. W. Leverenz, of the R. C. A. Labora tories at Princeton, N. J., to discuss this subject. He will speak also on cathodoluminescence, by which the energy of swift electrons falling upon a television screen is converted into visible light. In 1602 a Bolognese shoemaker, Vincencio Casciarola, saw a heavy stone (barium sulfate) which, he thought, might contain a precious metal. Heated with charcoal and left for some time in sunlight, it emit ted a reddish light even in the dark. The interest in "Bologna phosphor" was wide spread, and was in part responsible for the discovery of baryta by Scheele in 1774. Since those days, many other phosphors have been discovered, and many methods have been found to energize them. To day, the mere mention of thermodynamics, of chemical valence, or of heavy water brings to mind the name of Gilbert N. Lewis, of the University of California. In recent years he has brushed aside cer tain interpretations, and has pursued a fundamental investigation of phosphores cence, which behaves like a delayed fluorescence. He writes: I should have liked to take part because just in the past few months I think we have cleared up the meaning of phos phorescence and have found that the phos phorescent state is the lowest triplet state, the energy of which we have found for more than 100 substances. The theoreti cal interpretation is proving very inter esting indeed. In Jacob Bigeleisen, now of Columbia University, we have one of his recent and valued collaborators, who will interpret the California work on phosphorescence, and correlate it with his own researches upon photochemical reactions in rigid media including the polarization and ori• entation effects which accompany them. No single afternoon of papers and dis cussion could adequately cover a field so vast and diversified. Today the study of luminescence bas a growth rate and a vitality matched in few other scientific areas. It is of course hoped that popular interest will be aroused. Yet if even a few are in such a degree "excited" that they will "reradiate" in the years to come, the symposium will have attained even greater success. On page 1018 of CHBMICAL AND ENGI NEERING NEWS for June 25, 1944. it was in
correctly reported that C. R. Schohs of the Ciba Pharmaceutical Products would re port to the Division of Medicinal Chemistry on work he had done with the imidazole and imidazoline compounds. Dr. Scholz, how ever, is reporting this work not as his own but as that done in Ciba'a Laboratories, mostly in Basle, Switzerland. 1177
