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Particle Density of Volcanic Soils as Measured with a Gas Pycnometer

Bielders, C. L., De Backer, L. W., Delvaux, B.
Soil Science Society of America journal 1990 v.54 no.3 pp. 822-826
ethylene glycol, organic matter, soil sampling, surface area, volcanic soils, Martinique
In the absence of actual data, the particle density of soil is often assumed to be 2.65 Mg/m³. In this study, we will discuss whether this hypothesis applies with reasonable accuracy to various types of soils from Martinique. Thirty-nine samples taken from seven different subgroups of soils derived from volcanic materials were considered: Andeptic Troporthent, Typic Hydrandept, Typic Dystrandept, Andic Humitropept, Typic and Oxic Dystropept, and Entic Pellustert. Particle density was measured in triplicate on undisturbed, oven-dried samples by means of a gas pycnometer. The measurements were performed using air and He. Values found in He pycnometry ranged from 2.38 to 2.72 Mg/m³. The organic-matter content was a major factor in explaining low particle densities, but other soil constituents may be significantly involved also. Reproductibility of He pycnometry was found to be good. Air-pycnometry measurements revealed strongly distorted values for many soil materials when compared with He-pycnometry results. This was assigned to a gas adsorption phenomenon and found to be linearly related to the surface area of the soil samples as measured by ethylene glycol monoethyl ether.