Chap. 12] MISCELLANEOUS GEOPHYSICAL METHODS 901 



constituents, the difficulties of isolation increase because of isomerism. 

 Even for a mixture of normal homologues of one series, the calculation of 

 the constituents from the carbon dioxide and water formed in the com- 

 bustion is difficult if their number is greater than two.^^ 



The second group of soil-analysis methods (see Table 82) is concerned 

 with the determination of extractable liquids and organic and inorganic 

 solids. Since these occur in proportionately larger quantities than the 

 gaseous hydrocarbons, this determination is much easier and requires less 

 complicated apparatus. The so-called "liquid hydrocarbons" and "soil 

 waxes" are not members of the paraffin series, as has been stated in some 

 articles, but are probably more or less complex fatty acids. They may be 

 extracted by a variety of solvents, such as carbon tetrachloride, chloro- 

 form, ether, benzene, and so forth. Since these liquid organics and soil 

 waxes are found in their greatest concentration at the immediate surface, 

 the samples are taken (at undisturbed locations) with the grass roots and 

 are air dried. Definite quantities are weighed out and placed in an ex- 

 traction apparatus. The Soxhlet type or a modified form of the Bailey- 

 Walker apparatus, or some other form of extractor, preferably permitting 

 continuous operation, is suitable. 



The liquid containing the waxes, and the like, is then placed in a dis- 

 tillation apparatus; the solvent is distilled off through a condenser; and 

 the residue, in liquid or semisolid form, is determined by weighing. The 

 range encountered in soil analysis (from 0.01 to 1 per cent by weight) is 

 quite within the reach of ordinary accurate analytical procedure and there- 

 fore requires no special apparatus. An extraction method used in con- 

 junction with semiquantitative colorimetric analysis is briefly mentioned 

 by Rosaire.^ While the soil wax samples are taken at the immediate 

 surface (depth ^ inch), the specimens for colorimetric analysis are collected 

 at the depth of supposedly greatest bacterial action (about 6 inches). 

 Naturally, any topsoil samples must be taken . at locations undisturbed 

 by wind or water erosion, agriculture, and so on. 



Inorganic constituents, likewise determined by extraction, include 

 halides, sulfates, and carbonates ; more rarely there are bromides, iodides, 

 bicarbonates, and the like. Inasmuch as some of these constituents may 

 also be determined by their physical (for example, electrical resistivity) 

 expression, it is seen that a close relation must exist between results ob- 

 tainable by certain soil analysis and geophysical (resistivity, Eltran, and 

 similar) methods. 



** L. M. Dennis, Gas Analysis, Chapter XII (Macmillan, 1929). 

 " Op. ciL, p. 10. 



