703 



solubilities of the salts at different temperatures. For we have already 

 fonnerlj drawn atteiition ') to tiie fact, tliat below and above the 

 transition-temperature, the melastable forms must liave, as in all 

 sucii cases, the greater solubility; aiul this was exactly one of the 

 arguments used by us to reject Wkhnkk's conclusions about the 

 occurrence of a spontaneous fission in the case of (he potasaium- 

 rhodiuni-o.miate. 



Indeed, our experiments fidly contirmed this view: we were 

 able to demonstrate, that below 14° C. the solubility of the inactive 

 form is really smaller than that of (he optically-active antipodes, 

 whereas above 14° (J. the reverse was the case. Thus 100 grammes 

 of water at 0° C e.g. appeared to dissolve 34 50 grammes of the 

 racemic salt, at 14° C 36, 8J grammes; etc. On the other hand, 

 100 grammes of water at 20° C. dissolved 37.40 grammes of the 

 laevogyratory salt, at 22° C. 37,6 grammes; etc. The fig. 4 shows, 

 that the transitionpoint (o be determined, without appreciable error, 

 may be fixed as 13,2° C. ; this temperature, at which the reaction: 



2 rac. [ lQCo{C\OM + 3^/^,0] ^'^^ \d~-K,\Co{C^)X\ + 



-h \HJ)] -f [/- K,\Co{C^)X\ + 1 ///>] -f 5/y,0, 



takes place, is therefore a /?^/?i/?/??/7??-temperature for the existence 

 of the optically-active salts. 



The dilatometrical experiments were rather difficnlt, because of 

 the tendency of the compound to decompose, when its solution is 

 kept at somewhat higher temperatures for a long time, and 

 because of the inevitable retaidation-pheuomena. Notwithstanding 

 this, we were able to prove a sharp discontinuity of the volume- 

 temperatnre-cuj've, at a temperature between 12° and 16° C. That 

 such retardation-phenomena really occur, cannot be doubted ; even 

 in solution, the active sail is transformed just below the transition- 

 temperature into the racemic one, with considerable slowness. 

 Thus we found, that at 12° C, the dilute solution of the laevogy- 

 ratory antipode lost in one day about half, in two days two thirds, 

 in three days almost five sixths, and in four days about nine tenths 

 of its original optical activity, while at the said temperature the 

 optical antipodes beyond all doubt are already metastable with lespect 

 to the racemic salt. 



Crystallisation-experiments made in a thermostate at 22° C gave 

 results in full agreement with our conclusions : the solutions deposited 



1) A. Webnkr, Ber. d. d. Chem. Cies. 47. 1954 (1914). 



