^5? ' 

 At another temperature. liowe\er, we get the following relations : 



• ■ (<3) ■'"'-=,/;^;'- ... (8) 



• • (7) ~=/>.-^ • . . (0) 



.Vs„ 1 s.. 



About the factors f we will only state here that they are in 

 connection with each other and t)ecoine at the same time = 1 at 

 the temperatnre of transition. 



These relations (6) and (9) are of (/eiicra/ raliditij, and of these 

 relations equation (6) is the most suitable to decide wiiich modification 

 is the stable one at a definite temperature. 



Let us suppose that /, ^1, i.e. liiat the case presents itself 

 indicated in fig. 1. The interna! c(|uilibriuni Z„ requires here 

 a greater concentration of A^ than prevails in the solution L. If 

 therefore at first we have (he saturate solution L in coexistence with 

 the two mixed crystal phases ^-1, and /i,, the transformation 



B -^ A 

 will take place in the solution, which renders the solution unsa- 

 turate with respect to i?-mixed crystals, and supersaturate with 

 respect to J-mixed crystals, with this consequence that /V-mixed 

 crystals dissolve, and yl-mixed crystals deposit. This process continues 

 till the 5-mixed crystals have entirely disappeared, and a solution 

 L„ is left, in which A and B ai'e in internal equilibrium, which 

 solution coexists with a mixed crystal phase A^, which is then also 

 in internal equilibrium. 



For the case ƒ <C i ^^e then get the reverse. 



It is now perfectly clear that by consideration of the relations 

 (7) or (8) and (9) we come to the same conclusion. 



These now are all self-evident relations, which, indeed, only allow 

 of a qualitative test, but which have this advantage, that as has 

 been said, they have (jeiieral validity. 



It will repeatedly happen that we do not know which of the two 

 forms of a substance is the stable modification at a definite tempe- 

 rature, and then equation (fi), as has been shown, indicates an exceed- 

 ingly simple way to decide this. 



At the said temperature we determine the concentrations of ^4 

 and B in the solution, inliich is saturate inith respect to the tioo solid 



jj/iases A^ and /?, (which will be mixed cry.stals). Thus we find -;:- . 



What is particular (d)oat this niethod is this that — does not refer 



24 

 Proceedings Royal Acad. Amsterdam. Vol. XVIIl. 



