Chemical Absorption of Gases. 363 



strength of the absorbing agent influenced the rate of absorp- 

 tion of a gas, carbonic dioxide in an atmosphere of dry air 

 being selected as most easily and satisfactorily purified. The 

 solution of potash was reduced in strength by dilution with 

 distilled water by 5 per cent, without producing any percep- 

 tible effect; then by 10, 15, and 30 per cent., but no variation 

 in the rate of absorption was visible ; then the strength was 

 reduced to one half, still the rate was practically the same as 

 when the strong potash was employed : and finally it was 

 reduced to only one fourth of its original strength. With this 

 comparatively great alteration in the potash solution the varia- 

 tion in the rate of absorption was not great, and was chiefly 

 observable at the start of the experiment by a retardation : 

 after the first minute the rise of the water in the manometer 

 was about the same as when the strong potash was used. 

 This result may be accounted for by the fact that the dilute 

 solution, when introduced into the absorption-vessel containing 

 a thoroughly dry atmosphere, would evolve aqueous vapour 

 and so depress the gauge, at the same time as the gas wag 

 being absorbed; and for this reason solutions of a less strength 

 were not employed. The results of these experiments are 

 illustrated by the following three tables (p. 364), marked a, @ y 

 and 7, which show the numbers obtained when the potash 

 solution had a strength of 1, \, and \ respectively. 



No systematic series of experiments of a similar nature were 

 made with the other gases ; but as two complete sets of expe- 

 riments with the different gases in hydrogen and in air were 

 made in which the strengths of the potash differed by 30 per 

 cent., and the results obtained in the two cases showed no 

 greater differences than individual experiments of either set, 

 there is no doubt that what the above results show to be true 

 for C0 2 , viz. that the rate of absorption practically does not 

 vary with the strength of the absorbing agent, holds good for 

 the other absorbable gases. If it be assumed that, by mea- 

 suring the rate of absorption of a gas, an estimate is obtained 

 of its rate of interdiffusion through another gas, the above 

 result is what might be expected ; for the mere strength of 

 the absorbing agent cannot influence the number of impacts 

 of the molecules on its surface. This number will be the same 

 whether a strong or a weak solution be employed ; and if all 

 the impinging molecules of the gas be absorbed, the rate of 

 absorption would remain invariable with a variation in the 

 strength of the absorbing agent. 



In every case it is seen that the hypothesis that the rate of 

 absorption is proportional to the pressure breaks down ; this is 

 especially noticeable in those cases in which the gas is absorbed 



2B2 



