Comparison of soil particle density determined by a gas pycnometer using helium, nitrogen, and air

Abstract

Soil particle density (ρs) is often assumed as 2.65 g cm−3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρs in a gas pycnometer and relate measured ρs to soil particle size distributions. The ρs of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N2, and dry air. The ρs of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρs of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm−3, respectively. The ρs determined by air and N2 had much wider ranges with averages of 2.93 and 2.97 g cm−3, respectively. There was a near 1:1 relationship between ρs of all samples determined by air and N2 with a highly significant (p