SELF-DIFFUSION OF RUBIDIUM AS INFLUENCED BY SOIL MOISTURE TENSION

A non steady-state method was used for the laboratory determination of the self-diffusion coefficient of rubidium in loam soil at soil moisture tensions of.16, 1.17, and 15 atmospheres. Soil volumes (half-cells) 1.0 centimeter long and 2.5 centimeters in diameter, containing rubidium labelled with Rb86, were placed in contact with similar but unlabelled half-cells. After varying time periods, the half-cells were separated and extracted with 1N NH4Ac, and the transfer of Rb86 determined.The diffusion followed the simple theory. The self-diffusion coefficients for rubidium at 25 °C. were as follows: 16 × 10−4 cm.2/hr. at 0.16 atm.; 4.9 × 10−4 cm.2/hr. at 1.17 atm.; 2.3 × 10−4 cm.2/hr. at 15 atm. In free solution, the self-diffusion coefficient is 7.2 × 10−2 cm.2/hr.