892 



MISCELLANEOUS GEOPHYSICAL METHODS 



[Chap. 12 



melting and boiling points of the earlier members in the paraffin series 

 are utilized for their isolation by low-temperature fractionation, as shown 

 below. 



C. Gas-Detection Methods 



Gas-detection methods are aimed at the measurement of the content of 

 combustible gases of the interstitial soil air near the surface. For this 

 purpose, portable detectors of the hot-filament type may be employed. 

 Samples of the soil are not taken. In these detectors no differentiation 



American Aakania Corp. 



Fig. 12-9. Original Laubmeyer gas apparatus. 



between ethane and methane is made; the effective amount of ethane 

 depends somewhat on the technique of evacuation of the drill hole (because 

 of the different densities and diffusion rates of ethane and methane). The 

 air is sampled from shallow holes. These are drilled to a depth of about 

 five feet, and are then sealed off with a lid provided with two concentric 

 cylinders of large radius and a piece of tubing ending in a stop cock. 



The hole is left alone for twelve to twenty-four hours before the air is 

 pumped into the combustion chamber, shown in Fig. 12-9. Because of their 

 natural agitation, the gas molecules in this chamber come into contact with 



« Illustration in G. Laubmeyer, Petroleum, 29(18), May 3, 1933. 



