Miscellaneous Subsurface Methods 767 



stituents with respect to others in the sample and to compare their relative 

 quantities as well as certain ratios. 



Attempts to use the infrared absorption spectrometer for soil an- 

 alysis has not been too successful when applied to the soil samples proper. 

 Some success has been attained by analyzing qualitatively and quantita- 

 tively the solvent extracts and the gaseous components. 



The mass spectrometer has been used mostly for the analysis of the 

 soil gases for micro quantities of hydrocarbon constituents. 



The polarograph has been adapted to the qualitative and quantitative 

 determination of some of the metallic ions as well as organic constituents 

 in solutions taken from the samples. The techniques vary considerably 

 in the use of this instrument for these types of analyses. Its greatest use- 

 fuleness appears to be in the determination of the metallic trace-ions. 



In many instances, the biological effects caused by the presence of 

 minor or trace amounts of either hydrocarbons or inorganic substances 

 have been relied upon as a basis for the analytical technique. The pres- 

 ence of vanishingly small quantities of certain metallic ions in the soil 

 solution often inhibits or accelerates the growth of some indicator plants. 

 Very often these effects are magnified to such a point that they are easily 

 visible to even an untrained observer. In other instances, the eflfects are 

 much more subtle and changes in the metabolic rate or cell development of 

 certain tissues in specified plants can be observed only under a micro- 

 scope. In still other instances, a diagnostic ion may be concentrated in 

 the plant structure or in specified tissues of the plant in proportion to its 

 occurrence in the soil solution, but at much higher concentration values 

 than in the soil. 



Sometimes the content of a second element in the plant is caused to 

 vary over a fairly broad range when the primary element concentration 

 varies only a small amount in the nutrient solutions in the soil. Occasion- 

 ally the variation in the ratio of concentration of certain diagnostic sub- 

 stances is the most indicative. 



The macroorganisms are sometimes quite sensitive to changes in the 

 composition of their environment both with respect to metallic ions and 

 the presence of hydrocarbons in the soil gas. 



Several methods have been used with varying degrees of success for 

 determining the population of the microorganisms in the soil. One scheme 

 involves the determination of the total organic matter which is oxidized 

 by hydrogen peroxide. Modifications of this method are concerned with 

 the strength of the oxidant used in making the determination for organic 

 matter. The strength of the oxidant determines the class of organic matter 

 included in the reaction. 



In some areas it has been practical to determine the population density 

 of certain hydrocarbon-consuming bacteria such as bacillus methaniscus 

 and to compare their occurrence from point to point over the prospect. 

 The theory is that the number of colonies and the size of the colonies of a 



