DENSITY OF SOIL SOLIDS AND THEIR GENETIC RELATIONS

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Abstract
A pycnometer method for the determination of soil densities has been given which, it is believed, is capable of producing highly accurate results. Insufficient removal of air is shown to be a source of error. Air is locked in soil pores by Jamin capillary forces and is not easily withdrawn. Adequate removal can be had and Jamin capillary forces overcome by subjecting the soil, when submerged in a liquid contained in a pycnometer, alternately to vacuum and atmospheric pressure until air is sufficiently removed. This constitutes the principal modification presented, of the ordinary pycnometer procedure for soils. Comparative studies of the densities obtained in water and in several organic liquids were made. The differences observed appear to be considerably smaller, in general, than those obtained by some other workers. The exceptions are surface horizons containing large amts. of organic matter. A method is given for determining the density of soil organic matter and of soil minerals. The organic matter is removed by chemical treatment, and its amt. detd. The density of the residue, or soil minerals, is ascertained. From the densities of the soil minerals and of the total soil solids, and from the amt. of organic matter removed, the density of the organic matter removed is found. The values obtained agree closely with those of lignin and cellulose. The densities of total solids, of soil [center dot] minerals, and of soil organic matter have been obtained for several complete profiles. The data show some simple genetic relationships and appear to warrant further study.

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