the Elementary Law of Hydro diffusion. 52$ 



From equation (5), however, an extremely convenient 

 method for the investigation of the course of diffusion is obtained 

 in the following manner : — 



When the constant galvanic current has traversed the salt- 

 solution during a suitable long time, say during the time T, 

 the current is to be interrupted. The differences of concen- 

 tration produced in the different layers by the simultaneous 

 action of the current and the diffusion will from that instant 

 gradually be equalized by the diffusion proceeding alone. 

 This gradual equalization can be followed with extraordinary 

 accuracy, and, on that account, can serve as one of the finest 

 means of testing the correctness of Fick's elementary law of 

 diffusion. 



The law according to which this equalization proceeds can 

 easily be ascertained. In every place x> and <L, and" 

 at any time, the following differential equation is to be 

 satisfied : — 



Wt =k W (,) 



For all moments of time t the limiting equations 



(s)„.-° < 8 » 



and 



©-- » 



subsist. As the initial point of time we will take the instant 

 at which the current was interrupted. Let the value of the 

 concentration which is present at that point of time in any 

 layer at the depth .'/; below the upper electrode be z*. The 

 initial state of the diffusion-process is then determined by the 

 equation, For i — 0, 



# h ( L\ 4 I/i f (it \ 1 /3tt \ 



+ —B 5 eo8(-£x y j+... }, . (10) 

 in which it is supposed that 



B x = e l 2 , B 3 = e l 2 ,... 



The discovery of the general solution for z, which satisfies 

 all the conditions, presents no difficulty. As giving the cal- 

 culation would only be a repetition of what has alreadv been 



