946 



EXPLORATION GEOPHYSICS 



The gas extraction is carried out in an apparatus separate from that used 

 for analysis. Briefly, about 100 to 150 grams of sample are placed in a 500 

 cc. flask and the pressure is reduced to about 60 mm. If no reaction occurs 

 upon adding several cc. of acid, indicating that the carbonate content of 

 the sample is low, an additional 25 cc. portion of acid is added. If the 

 carbonate content of the sample is high, a vigorous reaction will occur 



Fig. 582. — Gas analysis units showing gas purifying train, special traps for separating hydro- 

 carbon fractions, combustion chambers, McLeod gauges used for measuring small quantities of 

 gases, and auxiliary equipment. (Courtesy of Horvitz Research Laboratories.) 



upon the addition of the first portion of acid. The carbon dioxide evolved 

 is rapidly removed by opening the flask to a chamber containing potassium 

 hydroxide solution and shaking the latter. The procedure is repeated until 

 the carbonates are decomposed. An excess of 25 cc. of acid is then added. 

 The flask containing the sample is now immersed in boiling water and 

 heated for 30 minutes. The gas sample is then displaced into the potassium 

 hydroxide flask where the volume of the sample is determined. It is next 

 displaced from there into a previously evacuated tube. 



