Chap. 12] MISCELLANEOUS GEOPHYSICAL METHODS 899 



of the work, the analytical procedures are similar if not actually alike. For 

 instance, for an analytical determination of methane and ethane, it makes 

 no difference whether the sample introduced into the apparatus is pumped 

 out of the ground or is obtained by boiling a soil sample with water and 

 solvents. While such analytical procedures in which the volatilizable frac- 

 tion is determined are therefore equivalent to gas-analj^ical methods (see 

 Table 82), there are other soil-analysis methods relying on the fractions 

 which are extractable by solvents (so-called liquid pseudo-hydrocarbons 

 and soil waxes). 



For an analysis of the volatilizable components — hydrogen, methane, 

 ethane (plus propane and butane if present) — soil samples are taken usually 

 by hand augers or light machine drills at depths varying from 5 to 15 feet. 

 Where practicable, they should be secured below the ground-water level 

 or below the surface-weathered layer. Contact with any oil- or grease- 

 contaminated soil, vicinity of pipe lines or roads, and the like, must, of 

 course, be avoided. Duplicate samples are usually taken at each location 

 and are shipped to the laboratory in mason jars. They are then freed of 

 moisture, and definite quantities are weighed out and transferred to a 

 degassing apparatus. Some companies liberate the occluded gases from 

 pulverized specimens at fairly high temperatures. (Others prefer to boil 

 them off from an aqueous solution to which, if necessary, certain solvents 

 may be added t.o accelerate the degassing process. 



After the gas has been driven out of the soil sample, it is passed to an 

 analytical apparatus consisting essentially of low-temperatiu'c condensa- 

 tion, combustion, and pressure-measuring components Descriptions and 

 illustrations of such apparatus or procedures, respectively, have been given 

 by V. A. Sokolov,"' L. Horvitz,*' E. E. Rosaire,'" and D. H. Stormont.'' 

 The diagram of Fig. 12-13 is a simplified scheme incorporating the more 

 important features of these descriptions. The pressure in the component 

 parts may be indicated by a compression manometer of the Arago-McLeod 

 type, as shown, or by some other low-pressure gauge. The vacuum is 

 generally produced by rotary Gaede or Cenco pumps working in conjunc- 

 tion with a mercury diffusion pump. More than the two condensers shown 

 in the scheme may be employed to increase the number of fractionation 

 components. 



To produce low temperatures, liquid oxygen (—183° C.) or liquid nitrogen 

 ( — 196° C.) is used. The lumiber of purification stages is subject to varia- 



" V. A. Sokolov, loc. cil. 

 "9 L. Horvitz, Geophysics, 4(3), 212 (1939). 



^o E. E. Rosaire, Handbook of Geochemical Prospecting, fig. 4, p. 20, Subterrex 

 (Houston, 1939). 



" D. H. Stormont, Oil and Gas J., 53 (Sept. 14, 1939). 



