91 Prof. Adeney and Mr. Becker on the Hate of Solution 



These two factors, tending as they do to set up a slow 

 circulation from the surface to the bottom of a mass of 

 water, must be of much greater importance than diffusion, 

 which is such an extremely slow process that months are 

 required to detect its action even in the laboratory. This is 

 further indicated by the fact that, to examine the effects of 

 true diffusion experimentally, it would be necessary to take 

 great care to maintain an absolutely uniform temperature, 

 and to protect the column of water under observation from 

 .any external agency which might result in producing currents 

 in the water. 



The experiments so far discussed have been made with 

 very shallow depths of water not more than about 260 mm. 

 from the surface. It is, of course, necessary to extend them 

 in order to investigate the question as to what depths mixing 

 is appreciably induced by the conditions brought about by 

 the evaporation from the exposed surfaces of quiescent 

 waters, fresh or salt, under laboratory conditions. But such 

 experiments would require observations to be carried on for 

 very long periods of time, and very great care would be 

 necessary to ensure uniformity in the conditions affecting- 

 evaporation during their continuance. The authors have 

 not hitherto had time or opportunity of carrying out such 

 experiments, but it is hoped to commence some experiments 

 of this kind in this College next session. 



A number of preliminary experiments have been made by 

 one of the authors with columns of water of from 18 to 

 21 mm. cross-section *, and of such length to allow of 

 observations to be made to depths of about 1800 mm. The 

 results of these experiments prove that mixing induced by 

 evaporation from the exposed surfaces of columns of water 

 does take place down to depths of at least 1800 mm., and 

 that it occurs to a more decided extent in sea than in fresh 

 water. Each of these experiments, however, extended over 

 a considerable number of days, and no precautions were 

 made to keep the conditions of evaporation from the exposed 

 surfaces of the columns of water uniform. The results that 

 were obtained from different experiments were consequently 

 not sufficiently concurrent to determine whether they could 

 be brought within the simple law found for the more shallow 

 depths of water or not. 



The following experiment goes to show that the concen- 

 trated layers of salt solution, which result from evaporation 

 at the exposed surface of a de-aerated column of sea-water, 



* See '''Unrecognized Factors in the Transmission of Gases through 

 Water." By W. E. Adeney, Phil. Mag. March 1905. 



