Chap. 12] 



MISCELLANPJOUS GEOPHYSICAL METHODS 



89] 



took several years. Even a qualitative approach of this sort would not 

 be possible in soil analysis where hundreds of samples must be analyzed 

 in the course of one survey. This narrows most of the analytical work 

 down to the paraffin series whose first members, at least, can be isolated 

 satisfactorily. From butane upward, however, isolation by fractional dis- 

 tillation is difficult because the number of isomers of different boiling and 

 melting points increases considerably toward the end of the series. In one 

 phase of soil analysis (for liquid and solid "pseudo"-hydrocarbons) isola- 

 tion is not attempted, and these constituents are determined collectively 



Ttnptraturt 



Uolttuhr Wflfht 



60 



m 



Fig. 12-8. Melting points, boiling points, and molecular weights of some of the 



paraffin hydrocarbons. 



by extraction with certain solvents. In the "gas method," using the 

 hot-wire type of detector, no differentiation in the type of combustible 

 hydrocarbon molecule is made. 



Fig. 12-8 shows the variation of the" melting points, boiling pomts, and 

 molecular weights for the first members of the parafl&n series up to decane 

 and inclusive of hydrogen. The variation of the molecular weight is 

 linear; that of the boiling point, being a function of the molecular weight, 

 is regular but not linear; and that of the melting point is irregular, particu- 

 larly at the beginning of the series. At ordinary temperature and pressure, 

 methane, ethane, propane, and butane are gaseous. The differences in 



