1003 



Messrs. Cohkn and Van Eyk ') found tliat when e. g. white tin 

 is left *in contact with a tin sohition at a temperature lying under 

 the ti'ansition point, the conversion of the inetastable white to the 

 stable grey tin is accelerated. Mr. Cohkn's explanation is this ^) that 

 when once a trace of grey tin is present, the tin from the solution 

 will deposit in the grey inodiiication on the grey tin, in consequence 

 of the dilFerence in "L()sungstension" of white tin and grey tin, the 

 white tin entering the solution. It is clear that all this refers to the 

 conversion of one niodilication to another or of one solid phase to 

 anotlier. 



My paper does not deal with the transformation which takes 

 place between two solid phases of an allotropic substance, but with 

 the chemical conrersion lokich can occur betuieen the different kinch of 

 molecules in each of the. .^olid phases according to the iheoi't/ of 

 allotropy. 



In the cited communication 1 namely pointed out that the just-men- 

 tioned theory states that a metal which presents the phenomenon of 

 allotropy, will contain different kinds of molecules. To simplify 

 the case as much as possible 1 assumed that double molecules 

 J/jj occur by the side of simple molecules M. If the metal is now 

 to behave as a substance of one component, so in a unary way, it 

 is necessary that the different kinds of molecules in each of the 

 phases of the metal are in equilibrium, and as we have to do here 

 with an equilibrium between the kinds of molecules of one and the 

 same substance, the word "internal equilibrium" is used here to 

 distinguish it from other equilibria. 



Up to now it has always been assumed that a metal emits only 

 one kind of ions into solution. In connection with the just-mentioned 

 internal equilibrium, in the homogeneous metal phase we come, 

 however, to the conclusion that the metal supposed here immersed 

 in an electrolyte will emit different ions, which, if the ion per 

 atom carries e.g. three positive charges, will be the ions M-- and 



i¥,:::. 



Just as the molecules M and M^ in the homogeneous metal phase 

 can be in equilibrium, this will also be the case for the ions M'" 

 and M^.:., and this equilibrium, too, may be called an interna] 

 equilibrium. 



Now 1 have among others pointed out that the metal can be in 

 unary electromotive equilibrium only when the different kinds of 



1) Zeitschr. f. phys. Ghera. 30, 601 (1899). 



2) „ „ „ „ 30, 623 (1899). ' 



65 

 Proceedings Royal Acad. Amsterdam. Vol. XVI. 



