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Mr. J. J. Coleman on Liquid Diffusion. 5 



magnesic sulphate, the sections of liquid run off were esti- 

 mated by ordinary volumetric alkalimeter processes. 



A summary of the results may be conveniently added : — 



Comparative diffusion during twenty days ; temperature 

 12°-5 Cent. 

 One per cent, of the hydrochloric acid rose 250 millim. 

 „ „ nitric acid „ 225 



„ „ potassic hydrate „ 225 „ 



„ „ ammmonia „ 200 , 3 



„ „ sulphuric acid „ 175 



„ „ sodic hydrate „ 187 



sodic chloride „ 162 



magnesic sulphate „ 87 

 These results are put forward merely as preliminary expe- 

 riments with a method which is rapid in execution and sus- 

 ceptible of great accuracy, and which it is hoped will afford 

 or lead to the means of calculating the correct coefficient of 

 diffusion of a large number of substances, Sir W. Thomson 

 having kindly promised his assistance in any mathematical 

 calculations necessary. 



From the chemist's point of view, several interesting con- 

 siderations arise from a review of experiments already made, 

 particularly when taken in connection with Newland's and 

 Mendelejeff's periodic law, which was not put forward until 

 some time after the date of Graham's last paper. 



The periodic law classifies the elements into vertical groups 

 of the type R 2 0, HO, &c, and into series usually known as 

 horizontal series. Most of our recent textbooks quote the 

 3rd series as typical ; thus : — 



Na. Mg. Al. Si. P. S. CI. 



Atomic weight . 23 24 27*3 28 31 32 35*5 

 Atomic volume . 24 14 10 11 14*5 16 27 



It will be observed here that whilst there is a comparatively 

 small difference between the atomic weights commencing and 

 ending the horizontal series, the atomic volume commences 

 very high at the extreme left, gradually diminishes to less 

 than one half in the middle, and ends very high again at the 

 extreme right of the series. Diffusibility of the compounds 

 of these elements varies in the same way ; thus : — 



Na. Mg. Al. Si. P. S. CI. 



Na 2 S0 4 . MgS0 4 . A1 2 3S0 4 . Si 2 4 - PA- S A- OL,O r 

 Molec. vol. ...55 44 ? 45 55 82 ? 



Diffusibility, ..15 4 2*8 ? 9*79 18*48 25 



Coleman. Graham. Coleman. 



