900 



MISCELLANEOUS GEOPHYSICAL METHODS 



[Chap. 12 



tion. Additional purifiers of solid caustic potash and absorption tubes 

 with sulfuric acid may be added to take out unsaturates and aromatics. 

 In operation, the entire apparatus is evacuated, the Dewar flask containing 

 the liquid air or nitrogen is moved up to the condenser Ci , and the gas 

 sample is admitted at a. As the sample passes through Ci , ethane and 

 the heaviest hydrocarbons are retained and the remaining noncondensable 

 fraction (methane and hydrogen) are allowed to pass through d into the 

 combustion tube T. 



Upon isolation from the rest of the apparatus, hydrogen and methane 

 are burned with the oxygen of the air to carbon dioxide and water, which 

 are frozen out in condenser C2 . The remainder of the air is then pumped 

 out, the Dewar flask is withdrawn from d , and readings are taken on the 

 compression manometer, M, at various temperatures. This allows calcu- 



FiG. 12-13. Scheme of laboratory apparatus for gas and soil analysis (partly 

 after Sokolov). (a) Inlet from degassing apparatus; (F) vacuum; (C) condensers; 

 (M) manometfer; (D) Dewar flask; {T) combustion bulb. 



lation of the partial pressures and, therefore, of the relative amounts of 

 water vapor and carbon dioxide. Assuming that the volume of the CO2 

 formed upon combustion equals that of the methane, the content of the 

 latter in terms of volume or weight of the sample can be calculated. The 

 hydrogen content follows^^ (in approximation) from the excess of water 

 over that to be expected in accordance with eq. (12-6). After condenser 

 C2 , manometer M, and combustion tube T have been evacuated, they may 

 be used in the described manner for the determination of the heavy fraction 

 retained in Ci , which may be passed over into T upon warming of Ci ; 

 its combustion products may be condensed as before in C2 . In practice, 

 it may be necessary to deviate from this simple procedure to increase the 

 efl&ciency of combustion in this fraction and to narrow down the number 

 of hydrocarbons in one fraction by additional condensers and smaller steps 

 in the distillation temperatures. With increasing molecular weight of the 



« Horvitz, op. cit., p. 212. 



