Originally jnihlislKMl in Z. phtj.s. Chciii. 89, 294 (1914) 



7. THE VELOCITY OF DISSOLUTION OF MOLECULAR 



LAYERS 



O. TIevesv and E. Rona 

 From the Clieniical Institvite of the Univeisity oi" Budapest 



The vf^ocity of dissolution ol' finite layers can be followed quantitatively 

 by considering the process of dissolution as being comprised of two 

 partial processes ; one of these consists in the formation of a layer ol" 

 saturated solution surrounding the solid surface and the other is a 

 process of diffusion from this boundary layer into the liquid^. 

 The velocity of dissolution is represented by the equation : 



dx/dt = DOF{r^ - c)ld 



where d denotes the thickness of the boundary layer, F a proportionality 

 factor, D the diffusion coefficient, the area, c^ the saturation con- 

 centration, and c the concentration of the solution. 



The dissolution will therefore proceed more rapidly the smaller Ihe 

 thickness of the boundary layer, i.e. the greater the speed of stirring, 

 the greater the diffusion velocity of the participating molecules and the 

 I'urther the solution is from the saturated state ; the formula also shows 

 a parallelism between solubility and velocity of dissolution. 



Nernst and Brunner^ have shown that these ideas are quite generally 

 applicable to heterogeneous reactions. 



The present communication discusses the course oi Ihe dissolution 

 process of molecular layers, which could be also described as infinitely 

 thin, and the extent to which the above simple equation is satisfied. 



THE PREPARATION OF INFINITELY THIN LAYERS 



It is well known that an infinitel}^ thin layer of radioactive metal or 

 its oxide, known as the so-called active deposit, can be obtained simply ; 

 by the decay of the gaseous emanations metallic products are formed, 

 which are isotopes of polonium, lead, ])ismuth and thallium and which 



1 NoYEs and Whitney, Z. phy.s. ('hem. 23, (i!S9 (1897). 



2 Nernst and Brunner, Z. phy.s. Chan. 47, o2, oO (1904). 



