( 270 ) 



gives llie point l^ and the transition surface meets of each of the 

 melting-point surfaces the line for the soHd phase, and tlius we tind 

 the points S^ and S^. 



So we get a second stable three-phase equilibrium, but now be- 

 tween rhombic and monoclinic mixed cr^'Slals and a liquid; the tem- 

 perature of this three phase e(piilibrium we might call the transition 

 temperature lowered by S^j.. 



With withdrawal of heat the transformation aS^ -^ S^ -\- 4 takes 

 place, i. e. the monoclinic mixed crystals disappear, and the two- 

 phase equilibrium between rhombic mixed crystals and liquid, which 

 was metastable before, now becomes stable. 



Though the pseudo-components *S'/^ and Sm will not always be 

 in internal equilibrium under all circumstances, and Sy. never 

 behaves as a true component, it will appear later that the view of 

 this case, discussed here may be of some use. 



Remark. The reader will perhaps have seen already, that the 

 new theory of allotropy for the first time gives a rational explana- 

 tion of the rule, found by Ostwald, that with the appearance of a 

 new phase the metastable state occurs first. I hope to treat this 

 question in a separate communication later on. 



Anorganic Chemical Laboratory 

 of the University. 

 Amsterdam, September 1911. 



Physics. — ''On the plienomena of condensation for niLviures of 

 carbonic acid and nitrobenzene in connection with double retro- 

 grade condensation" . By Prof. Ph. Kohnstamm and J. Chii. 

 Reedeks". Van der Vf am.?,- fonds researches. N°. 3. (Connnu- 

 nicated by Prof. J. D. van der Waals;. 



In These proceedings April 23, 1909, (Vol. XI p. 913) we 

 demonstrated by means of some experiments how great the influence 

 is which slight quantities of urethane exert on the phenomena of 

 condensation of carbonic acid ; we further showed that at our smal- 

 lest concentration of 3-///qo we were still very far from that con- 

 centration for which double retrograde coudensation will be found. 

 We shall proceed to give some similar observations on the system 

 carbonic acid and nitro-benzene. These observations were undertaken 

 in the hope that we might succeed in proving the existence of double 

 retrograde condensation for this system.. This hope has proved vain; 



