1 44 Scientific Proceedings^ Royal Dublin Society. 



for such an assumption in practice. Obviously if there be no mixing 

 of the water, the only process by which the air can penetrate into the 

 mass of the water is by diffusion of the dissolved gas molecules ; hence 

 the ordinary law for the diffusion of solutes would hold under these con- 

 ditions. But there is no experimental evidence to show that such conditions 

 ever occur under natural conditions ; and it is doubtful if they have ever 

 been produced artificially even in the laboratory. On the other hand, 

 there is evidence to show that it is not possible to expose a mass of water 

 to the air and still keep the exposed and unexposed portions of the 

 water unmixed. Thus, when Huefner was determining the velocity of 

 diffusion of dissolved gases in water, he found it necessary to expose the 

 columns of water to the gas at the lower surface through the medium of a 

 porous plate of hydrophaue, in order to avoid the mixing that he found to 

 occur when the upper surface of the columns of water was exposed to the 

 gas. A considerable number of experiments made by one of the authors 

 also points to the fact that the dissolved gases do not accumulate in the 

 upper layers of a column of water exposed to the air, as they would tend to 

 do if there were no mixing. Hence calculations based on the law of diffusion 

 cannot be of any practical value. 



The third set of conditions postulated, namely, solution at the surface 

 with slow mixing, seems to be that which would occur most frequently in 

 practice. Under these conditions the rate of solution will be dependent on 

 the rate of mixing. 



The formula applicable in this case might be expected to be of the same 

 form as that already derived from the experiments with thin films, where 

 the mixing was extremely rapid, but the constants will alter according to the 

 rate of mixing. It will be shown that the results of the experiments quoted 

 ■here can be approximately represented by an equation of the required form, 

 and that the constants vary with (1) the humidity of the air in contact with 

 the water, and (2) the salinity of the water. 



The method of experimenting consisted in filling a number of tubes of 

 about 30 cms. length and 4 cms. diameter with de-aerated tap-water, and 

 inserting rubber-stoppers in such a way as to exclude all trace of air. The 

 tubes were then placed in a thermostat until the water in them was at the 

 same temperature as that of the thermostat. The corks were then removed, 

 50 cc. water withdrawn, and the water remaining in the tubes exposed to the 

 air for periods of different length, and the air-content determined at the end 

 of the exposure. The initial air-content of the de-aerated water having been 

 previously determined, the data for calculating the rate of solution was then 

 8|,vailable, 



