C 19 ] 



No. 3. 



ON THE AERATION OF OUIESOENT COLUMNS OF DISTILLED 

 WATEll AND OF SOLUTIONS OF SODIUM CHLORIDE. 



Bv PIIOFESSOU W. E. ADENEY, ATlCScJ., D.Sc, F.I.C., 

 DII. A. G. G. LEONARD, F.E.C.SoJ., B.Sc, F.I.C, 



AND 



A. EICHARDSON, A.RC.Sc.I, A.I.C. 



[Read Ai-RiL 25. Printed June 23, 1922.] 



Introdiodory. 



In the course of his investigations on the downward transmission of atmospheric 

 gases through quiescent columns of water live feet in depth, one of the authors 

 showed that, as the oxygen and nitrogen are dissolved at the exposed surface of 

 the water, they do not remain concentrated in the surface layer, but are distri- 

 buted tlirough the lower layers with comparaLi\'e rapidity. 



From the fact tliat the distribution of the dissoh'ed gases, at various depths, 

 after a comparatively short time was almost uniform, it appeared impossible to 

 account for it on the assumption that it was entirely due to such an extremely 

 slow process as that of the diffusion of the dissolved gases from the saturated 

 surface layer. 



In addition to diffusion, it was suggested that a process of downward 

 " streaming " of the exposed layer of water occurs ; and that it results largely, 

 Lliougli possibly not wholly, from an increase in its density, whicli, in the case of 

 distilled water, is caused by the lowering of temperature attending evaporation, 

 and, in the case of salt solutions, by this factor and that of concentration. 



The downward streaming sets up a process of mixing of the constantly chanying 

 air-saturated surface layer with tlie lower layers of the water. When a slow 

 stream of dry air is continuously passed over the exposed layer of a column of 

 water, surface density ciianges are constantly occurring, and comparatively rapid 

 mixing ensues, with bhe result that, if the water be de-aerated at the commence- 

 ment of the experiment, it becomes re-aerated with comparative rapidity.' 



The experiments described in this investigation Jiave been carried out with 

 the object of investigating the process of the aeration of de-aerated columns of 

 water to a depth of ten feet. Columns of de-aerated distilled water and of solu- 

 tions of sodium chloride were exposed to a slow stream of dry air for periods of 

 from two to eight weeks, wlien samples at different depths were drawn off, and 

 the nitrogen content of each determined. 



Li general, it was found that re aeration proceeded more rapidly in salt solu- 

 tions than in pure water,^ and a further series of experiments was carried out 



' Uiireuo!;nised Factors in the Transniission of Gases througli Water." B3' W. K. Adeney, 

 Traiis^ li.D.S., p. 161, 1905; and Phil. Mag., 1905. 

 - See above references. 



SCIENT, PROC. R.D.S., VOL. XVII, NO. 3, F 



