Closed Capillary Method for Tracer Diffusion Measurements in Liquids

Abstract

A continuous closed capillary method is described in which the lower half of the capillary is filled at the beginning of the experiment with radioactive solution and the upper half with inactive solution. Measurement of any change in the activity is based on the position dependent counting efficiency of the nuclear detector system. It has been shown that convection disturbances arising in the filling process present no difficulties to use of this method.

The tracer diffusion coefficient of 22NaCl has been determined in 0.1 and 1.44 mol dm–3 aqueous sodium chloride solutions at 298.15 K. The results agree with the corresponding open-ended capillary and diaphragm-cell values of other authors. An average precision of 0.4 % was attained in the measurements. The systematic errors of the open-ended capillary method, the ΔL-effect and the immersion effect, are eliminated in closed capillaries. Also, in contrast to the two other methods, no calibration is required.