( 536 ) 



long time. T ha\'e observed this in tlie investigation of the system 

 ethei'-anthraquinone, but only in the case that the liquid phase was 

 \ery viscous. 



When we have not to do with a viscous liquid phase, but as 

 here, with a solid solution, the said phenomenon of retardation will 

 be able to appear the sooner. 



It will, no doubt, not require any further elucidation now why 

 RoYSTON, when he did not heat up to 1030°, but to 720°, had to find 

 less cementite after cooling. It is possible that he did not reach the 

 line a's', then, but sf on the line ss' , so that tirst «-iron deposited. 



Further I think that it is clear why up to now the temperature 

 of the metastable mixed crystal eutectic point has, indeed, been 

 observed, but not once that of the stable mixed crystal eutectic point. 

 To enable us to pursue the stable equilibrium between martensite 

 mixed crystals and graphite to the point S a so slow cooling is 

 required, that a thermic determination is quite impossible. The only 

 method which may possibly yield a reliable result is the dilatometrical, 

 when an active catalyser shall have been found for the transformation 

 under consideration. 



These considerations do not seem devoid of interest to me because 

 they are of general application, and give a plausible explanation of 

 the mutual relation between the internal equilibrium in a homogeneous 

 phase, and the heterogeneous equilibrium that may arise from it. 

 Anorganic Chemical Laboratory of the Univer<iity. 



Amsterdam, Nov. 19, 1911. 



Chemistry. — "Determinations of vapour tensions of nitrogen 

 tetroxicUr By Dr. F. E. C. Scheffer and Mr. J. P. Treub. 

 (Communicated by Prof. A. F. Holleman). 



1. In 1884 Rams.\y and Young published a paper on vapour tension 

 determinations of ice and camphor ^). They demonstrated that statical 

 and dynamical methods yield concordant results, and that therefore, 

 just as the P-7'-line of liquids can be determined from boiling-point 

 determinatrons at varying pressure, also the P-T-line of the solid- 

 gas-equiUbriurti may be found by the observation of sublimation 

 temperatures at varying pressure. 



In a later investigation, however, it appeared that solid substances 

 which dissociate at their transition to vapour, in many cases according 

 to the dynamic method') furnish values for the vapour tension which 



^) Phil. Trans. 175. 37 (1884). - 



2) Phil. Trans. 177. 71 (1886). ■ i 



