( 408 ) 



tilting the otlier //-atoms I )v feeble morphotropic groups such as .VO,. 

 In regard to this, lie recently informed me that both form a 

 dinitroderivative, l)ut with a ditferent melting point and that not 

 only tiie isomorphism is completely preserved, but that even the 

 typical twin formation in certain solvents takes place with both in 

 exactly the same manner, so that it looks as if one were dealing 

 with the same material. 



Chemistry. — "The mhliiri'ition lutes of btnm-// nu.('fure.s'\By PvcA'. 

 H. W. Bakhuis Roozeboom. 



(Communicated in the meeting of November 28, 1903). 



From the consideration of the j), t, ./--representation of the equi- 

 libria for solid, liquid and gaseous phases of binary mixtures given 

 by me a short time ago ^) it may be deduced in w^hat manner the 

 evaporation of the mixtures of two solid substances, or inversely 

 their condensation on cooling a mixture of vapours, takes place at 

 a constant pressure by a change of temperature. 



It is only necessary to take a f, ./'-section at constant pressure 

 through the figure at such a height, that ikj other equilibria occur 

 than those between solid and vajiour or between solid and solid. 

 This is possible as long as we keep below the pressure of the qua- 

 druple-point w^here solid .4, solid B, liquid and vapour coexist. 



The adjoined figure then indicates 

 the general character of the section, 

 in which the vertical axis represents 

 the temperature and the horizontal 

 axis the concentrations of the mixtures. 

 F is then the sublimation tempera- 

 ture of the pure substance A, (J, that 

 of pure B. These temperatures are 

 depressed along the lines F E and 

 G F until, below the point F, total 

 condensation of the vapour mixture to 

 solid A -\- solid B occurs. 



Conversely the sublimation com- 

 mences at the temperature given by 

 the line CE D and one of the two solid substances then disappears 

 according to the concentration, unless the composition corresponds 

 with F, in which case thev both sublime simultaneously. 



A 



coru 



B 



1) These Proc. V, p. 2711. 



