Subsurface Laboratory Methods 321 



responds to the popular designation "glow"; that of phosphorescence to 

 "afterglow." 



Luminescent systems are of two kinds, both of which enter into the 

 theory and application of fluoroanalysis to petroleum detection and ex- 

 ploration. The homogeneous luminescent system consists of matter in 

 which all particles are identical, i.e., possessing no impurities and, in the 

 case of solids, ideal crystallographic and stoichiometric characteristics. In 

 the case of liquids, many highly purified organic compounds very nearly 

 conform to the requirements for a homogeneous luminescent system. The 

 heterogeneous luminescent system, in contrast to the homogeneous, con- 

 tains impurities and/or structural imperfections, and these may enter 

 into the luminescence. Solid heterogeneous luminescent systems are il- 

 lustrated by the light-emitting materials called "phosphors," which contain 

 a trace of activating substance, usually a metallic salt, in solid solution 

 in a bulk of relatively inert solvent. Liquid heterogeneous systems are 

 illustrated by crude oil, which contains many different organic substances, 

 one or more giving rise to the luminescent response to ultraviolet light 

 or other forms of exciting energy. Oil in a liquid solvent also comprises 

 a heterogeneous system. 



A number of monographs and treatises have been written on lum- 

 inescence and kindred subjects, and for a more thorough background of 

 fluorochemical methods of geophysical exploration it is recommended 

 that these be referred to.^ ^^ Likewise, extensive literature is available 

 on that branch of analytic science known as fluorochemical analysis, an 

 understanding of which is necessary in petroleum applications.^^ ^^ ^^ A re- 

 cent review has been given of fluorescent techniques in petroleum explora- 

 tion.14 



Petroleum Fluorochemistry 



The luminescence of petroleum has been recognized since the earliest 

 days of antiquity. This property has, in years gone by, been known from 

 the fact that crude oil may be of a clear color when taken from the 

 earth b"»^ is generally greenish in reflected light and claret-red in trans- 

 mitted light. 



TTltrqviolet light, filtered free of visible rays, evokes in crude oils a 

 fluorescence that is generally blue, blue-green, or greenish. There may 

 be considerable deviation from these colors, however, and oils from dif- 

 ferent localities may present typical fluorescent colors. 



The fluorescence of crude petroleum, which is excited by visible light, 

 is familiar as "bloom." Ultraviolet light of wave lengths down to 2,000 



° Pringsheim, P., and Vogel, M., Luminescence and Its Practical Applications, New York, Inter- 

 science Publishers, 1943. 



■'"' De Ment, Jack, Fluorochemistry (extensive bibliography). New York Chemical Publishing Co., 1945. 



" Radley, J., and Grant, J., Fluorescence Analysis in Uultra-Violet Light, 3d ed.. New York, D. Van 

 Nostrand Co., 1939. 



*- Danckwortt, P., Lumineszenz- Analyse im Filtrierten Ultra-violetten Licht, 4th. Au£f., Leipzeg, 

 Akad. Verlag., 1940. 



■" Haitinger, M., Die Fluoreszenzanalyse in der Mikrochemie, Vienna and Leipzig, Emil Haim, 1937. 



" De Ment, Jack, Geophysics, voL 12, pp. 72-98, 1947. 



