Diffusion of Liquid* 



321 



a b with the solution to be investigated. Distilled water is 

 then allowed to drop very slowly from a Mariotte's bottle into 

 the receiving-tube w. This water gradually displaces the 

 solution in the whole length of a r s t and flows out at b. In 

 i it stands at the level ef, though this is not independent of 

 certain other influences to be mentioned shortly. Diffusion 

 takes place between the solution below ef and the water above, 

 the diffused particles being carried away and discharged at b. 

 The concentration in i soon becomes less, and fresh portions 

 of salt then enter from below and around g h, at which level 

 the concentration changes, but very slowly, as above this is 

 the whole of the solution in the beaker-glass. This is equiva- 

 lent to saying that the diffusion takes place between a level of 

 constant concentration at g h and a level of concentration zero 

 at ef. 



As a matter of course, the first portions of water which flow 

 through the apparatus become nearly as saturated as the ori- 

 ginal solution ; and some time must elapse before this mecha- 

 nical mixing gives place to the real diffusion. The first expe- 

 riments tried were on this point. The glass was filled with 

 solution of JSTaCl at 8 h. 30 m. a.m. and the flow of the water 

 started. The portion carried over until 9 h. was thrown 

 away ; that flowing after this time was saved and titrated with 



4£ AgN0 3 solution*. The results for the first twenty-four 



hours were as follows, the velocity of the flowing water being 

 40 cubic centims. per hour : — 



Cub. cent. 



Time. 





|)W. 



9-10 



required 



80=0 



10-11 





22-0 



11-12 





11-0 



12-1 





8-1 



1-2 





6-4 



2-3 





6*1 



3-4 





5-9 



4-5 





5-7 



5-9 A.M. 





4*0 per hour 



9-10 





2-2 



4-5 





2-0 



And this rate continued for some length of time, as will be 

 shown further on. It is seen that, although the progress of 

 the diffusion is obscured at first by an excess of mechanically 



* Containing T \ equivalent in grams of silver in a litre. 



