324 Subsurface Geologic Methods 



biochemical applications, and through their sensitivity fractions of a 

 microgram of certain fluorescent substances may be detected. 



Optical photometers have been adapted to fluorometry, such as the 

 Duboscq type.-^ 



Fluorography 



The appraisal of fluorescent light by photography is called "fluor- 

 ography." Both black-and-white and color methods can be used. Weak 

 luminescence is often advantageously detected and measured by the long 

 exposures possible with photographic emulsions. An ordinary camera, 

 the lense of which is covered with a filter transparent to visible light but 

 opaque to ultraviolet light, can be employed. In a fluorograph, only the 

 emitted light is recorded and portions of an object that absorb ultraviolet 

 light but do not luminesce appear dark, as is true of ultraviolet reflecting 

 areas, the light from which is intercepted by filter. Through densitometry 

 of the photograph the intensity of the fluorescence may be measured. 



The fluorographic method of fluorometry has been adapated to petro- 

 leum detection in soil samples ^^ and is described in more detail below. 



Fluoroadsorption Analysis 



The adsorption of fluorescent materials upon an inert, nonfluorescent 

 substance serves both to enhance emission and enable detection of separ- 

 ated substances from oft-complex mixtures. 



The fluoroadsorption methods of analysis are either two-dimensional, 

 i.e., involving paper, or, three-dimensional, i.e., involving solid columns, 

 depending upon the adsorbent. In both cases the aim is to isolate oil 

 traces from a large bulk of other material, e.g., soil, rock, or solvent, 

 depending upon the method used. 



The sorption phenomenon lays the basis for an extremely delicate 

 physicochemical method of analysis, and the sensitivity is greatly en- 

 hanced by examination under ultraviolet light. Molecules that ordinarily 

 do not fluoresce in the condensed phase, as in liquid or solid states, may 

 often emit brightly when dispersed by adsorption. 



While the pioneer work on ordinary capillary analysis was done in 

 1829 by Shonbein, it remained for one of his students, Goppelroeder, 

 just prior to 1901, to apply fluorochemical methods to the technique. 

 Important contributions have been made by numerous investigators;^^ one 

 of the best recent reviews is that of Germann.-^ 



When a solid column of adsorbent is used, the solution is drawn 

 therethrough, the method being known as "chromatographic analysis," 

 although erroneously termed "ultrachromatography" when an ultraviolet- 

 light examination is relied upon for an appraisal of the results. Various 

 crude oils in fractions can be separated upon a column of alumina, fol- 



2* Koch, W., Nature (London), vol. 154, p. 239, 1944. 



=5 Ferguson, W. B., U.S. Patent 2,356,454, Aug. 22, 1944. 



^^ Neugebauer, H., Die KapillaT-Lumineszenzanalyse, Leipzig, Schwabe, 1933. 



" Germann, F., Colorado Univ. Studies, vol. D, pp. 1-14, 1940. 



