2022 journal article
Comparison of soil particle density determined by a gas pycnometer using helium, nitrogen, and air
Soil Science Society of America Journal.
Abstract Soil particle density (ρ s ) 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 ρ s in a gas pycnometer and relate measured ρ s to soil particle size distributions. The ρ s 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, N 2 , and dry air. The ρ s of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρ s 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 ρ s determined by air and N 2 had much wider ranges with averages of 2.93 and 2.97 g cm −3 , respectively. There was a near 1:1 relationship between ρ s of all samples determined by air and N 2 with a highly significant ( p < .001) correlation coefficient ( r = .99). The average ratio of ρ s determined by He and water was 1.03, but the correlation coefficient for their relationship was only .416. Although the relationship between ρ s determined by He and either air or N 2 was relatively strong ( r < .61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρ s determined by N 2 or air but a weaker, yet statistically significant ( p < .05) relationship when using He.