386 Scientific Proceedings, Royal Dublin Society. 



A large number of additional experiments on this subject has since been 

 made by the same author, from time to time, during intervals of leisure from 

 professional and official work ; and the results have showed that the rate at 

 which water, when deprived of its usual air-content, dissolves and absorbs 

 the gases of the atmosphere, is a problem which involves so many variable 

 factors that its determination experimentally is by no means so simple a 

 matter as might at first appear. Amongst the factors referred to are — the 

 humidity of the air and the initial air-content, salinity, temperature, and 

 depth of the water. Some of these factors had, to some extent at least, 

 already been studied. 1 But before publishing the results obtained it was 

 thought desirable to make a careful experimental investigation of the question 

 of the rate of solution of atmospheric gases by the exposed surface-layer of a 

 quiescent body of de-aerated water, apart from that of the rate at which the 

 gases " stream " downwards through the lower layer of the water. 



Ic is proposed to describe in this communication the results of a research 

 which we have carried out with this object in view. 



Experiments were in the first instance directed towards carefully 

 studying the influence of the thickness of a layer of de-aerated water upon 

 the rate at which it becomes re- aerated, with a view to obtaining data by 

 means of which the factor of depth of water could be eliminated, when con- 

 sidering the question of the rate of solution by the surface-layer of the water. 



With a view to obtaining a sufficiently extended series of observations in 

 any one experiment, under constant conditions, or, in other words, within as 

 short a time as possible, it was intended to estimate the oxygen only in the 

 water under examination by a colorometric method. A number of preliminary 

 experiments was made with certain organic dyestuffs, including methylene 

 blue, indigo, and indigo carmine, after reduction with suitable re-agents, but 

 the results obtained were not encouraging. Alkaline pyrogallol was also 

 tried, but with like results. 



On the whole, it was concluded that no very simple method of estimating 

 oxygen in this way could be devised which could be relied upon to give results 

 of the accuracy required in the investigation. 



Letts' method of estimating oxygen with ferrous sulphate was then tried, 

 and gave good results, when the water examined was nearly saturated with 

 the gas ; but the exposure of the water to the air during manipulation 

 introduced errors, which could not be regarded as negligible, when the analyses 

 were made during the earlier stages of re-aeration. 



1 J. H. Coste has given a valuable notice and bibliography of the published work on 

 the Absorption of Atmospheric Gases by Water in his two communications on the subject to 

 the Journal of the Society of Chemical Industry, vol. xxxvi, p. 846, and vol. xxxvii, p. 170. 



