CHEMICAL METHODS 



945 



apparatus. The pressure in the sample jar is reduced, thereby eliminating 

 interstitial soil air, and the adsorbed constituents are liberated in gaseous 

 form by heating at 100° C. for about 45 minutes. Since the pressure within 

 the sample jar is less than atmospheric, the sample temperature never 

 reaches 100° C. Under these mild conditions, decomposition of organic 

 matter to produce methane is prevented. After freeing the liberated gases 

 of contaminating constituents normally present in the soil, they are sep- 

 arated into various fractions by employing refrigerants at different tem- 

 peratures. In this early work, the extracted hydrocarbons ranged from 

 methane throusrh butane. 



Fig. 581.— Bank of four extraction units for removing hydrocarbon gases from soil samples. 

 Sample flasks, potassium hydroxide chambers and gas collecting tubes may be observed. (Courtesy 

 of Horvitz Research Laboratories.) 



More recently, Horvitzf reported improved methods for extracting 

 and analyzing the hydrocarbons in soil. In some oil-bearing areas, the 

 quantities of hydrocarbons obtained when using the earlier technique were 

 too low for satisfactory correlation. It was found that heat alone was not 

 sufficient to remove the adsorbed and occluded gases. Investigation indi- 

 cated that heating the samples in the presence of an aqueous solution of 

 an acid, such as hydrochloric or phosphoric, increased considerably the 

 efficiency of extraction, yielding much larger quantities of significant con- 

 stituents. By this technique, the hydrocarbons are practically entirely 

 removed from the soil in one treatment without increasing the temperature. 



t Leo Horvitz, "Chemistry in Exploration for Petroleum," paper presented before the Petro- 

 leum Division, American Chemical Society, St. Louis meeting, April 7-11, 1941. 



