JOURNAL OF THE COLLEGE OF SCIENCE, IMPERIAL UNIVERSITY, 

 TOKYO, JAPAN. 



VOL. XIX., ARTICLE 8. 



On the Diffusion of Liquids. 

 By 



S. NAKAMURA. Rigakushi, 

 Assistant Professor of Physics, Tokyo Imperial I niversity. 



§1. The lirst thorough experimental study of the free diffusion of 

 liquids was made by Graham } in 1850 — 1861, and soon after Fick (2) 

 developed a theory of the free diffusion of an aqueous solution of salt 

 under the supposition that it obeys a law analogous to the conduction 

 of heat. When the concentration u depends simply on time t and a 

 coordinate x, then Fick assumed that the quantity of salt dS which 

 passes through a cross section having an area equal to q and perpen- 

 dicular to the axis of x during the time At is proportional to q.dt and 



, r , . "bit 



trie "radient oi the concentration — — : or 



° Zx ' 



dS = kq.dt.^- 0) 



where /,; is a constant depending on the nature of the solution 

 and is called the constant of diffusion. It is easy to deduce from (1) 

 the following differential equation satisfied by w, 

 "hu "à- u 



A.' 



U 7>x- (2) 



Several experiments were conducted To test Kick's equation and 



(1) Graham, Phil. Mag. [4] 3. 18Ü2. 



(2) Fick, Pogg. Ann. 9t. 1855. 



