The purpose of this investigation was to evaluate the ease of obtaining and reproducing diffusion coefficients for carbon dioxide and oxygen in water at 25°C using a quiescent liquid absorption apparatus.

Absorption curves were obtained for carbon dioxide in water using both a zero initial concentration and specific initial concentration of carbon dioxide. The evacuation pressure, operating pressure, initial concentration, and pressure increment were varied.

The zero initial concentration tests gave values for the diffusion coefficient consistently lower than expected. In addition the values were not reproducible and could not be correlated to the variation of parameters for the system. The cause of this variation was considered to be a combination of the evacuation procedure and the condensation phenomena. The interrelation of these effects was not determined.

Tests made with specific initial concentrations gave good agreement for the value of the diffusion coefficient. A value of 1.95 ± 0.15 x 10⁻⁵ square centimeters per second was determined to represent the diffusion coefficient for carbon dioxide at 25°C. A slight trend toward lower values of the diffusion coefficient at higher pressure gradients was observed. The effect of the evacuation pressure and condensation were considered to be minimal in these tests.

In both zero and specific initial concentration tests, convection appeared between 4 and 6 minutes after the start of the absorption. test.

The absorption of oxygen in water at 25°C is nearly 15 times less than that of carbon dioxide. As a result, the absorption of oxygen was considered to be out of the applicable range for measurement of diffusion, coefficients with this apparatus.

The quiescent liquid system was considered to be a rapid and reasonably accurate method for measuring the absorption of very soluble gases, such as carbon dioxide, over a limited range. The adaptability of the apparatus to less soluble gases is rather limited. However, for repeated measurements for a few chosen gases the system would be ari inexpensive, competitive apparatus.