MVA 



according to Krickmeyek's iiiveistigations '), only one of tlie two salts 



could be demonstrated in each of the coexisting solid phases at 25°. 



The real situation of the isotherms at the temperature of 25° has 



been given in B'ig. 4. According to this investigation the point Q lies at : 



8,20 mol. 7o NaCl 

 3,43 „ „ KCl 

 88,37 „ „ H,0 

 whereas van 't Hoff and Meijkrhoffer ^) found 



7,9 mol. 7„ NaCl 

 3,5 „ „ KCl 

 88,6 „ „ H,0. 

 The situation of the points P and R has not been determined 

 anew, but vvas derived from the literature ''). 



F denoting the solubility of Kr;i at 25°, lies at 7,96 mol 7„ KCl 



and 92,04 „ „ H,0 

 R denoting the solubility of NaCl at 25°, lies at 9,96 „ „ NaCl 



and 90,04 „ „ H/). 



4. What is remarkable about this is that these solubility-isotherms 

 PQ and RQ must be connected continuously by means of a ridge 

 with a partially metastable, partially unstable part, and that at the 

 temperature of the upper critical mixing point this continuity enters 

 the stable region. 



In this connection it may be pointed out that by this investigation 

 it has been proved for the first time that ?-lines exist for solid 

 mixtures, which must actually have a shape as is schematically 

 given in Fig. 5. This line points to an interrupted series of mixed 

 crystals, though the C-line is continuous. This contiimity, however, 

 lies here in the unstable region, and enters the stable region for 

 the first time at the upper critical mixing point. 



In Fig. 6 the 7^, T'-projection of the system KCl— NaCl is sche- 

 matically represented to show that here a plaitpoint curve for the 

 solid substance (*S, = >S,) must exist, which will probably run to 

 infinite pressure. 



In conclusion it may be stated that the phenomenon of the 

 appearance of an upper critical mixing point in the solid state 

 discussed here probably occurs for a number of other systems, as 



1) Z. f. phys. Ghem. 21, 53, (1896). 



2) Ber. Kgl. Pr. Akad. Wiss. Berlin 590 (1898). 



3) Andreae J. pr. Ghem. 29, 456 (1889). 



