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Physics. — "On the hidden equilibria in the ij-x-diagram of a 

 Jiinary system in consequence of the appearance of solid 

 substances.'" By Dr. A. Smits. (Communicated by Prof. J. D. 

 VAX DER Waals). 



1. Some time ago Prof, van der Waals ^) showed that in a 

 binary mixture {A, B) one of the two ^;-J'-lines for the three phase 

 pressure, viz. that which runs from the eutectic point to the higher- 

 melting substance {E), can present some particularity. 



It proved, namely, that at the triplepoint this p-t-Yme must have 

 the direction of the melting line (of B). 



As for most substances vi > Vs, or in other words the substance 

 expands when melting, increase of pressure causes as a rule a rise 

 of the melting point. 



If in the ^>^projection, (Fig. 1), the triplepoint of the substance 

 B is denoted by d, then the melting line dg will in most cases 

 run from the triplepoint to the right, and as tlie three phase line 

 cd must have the directio]i of d g at d, this three phase pressure line 

 will have to present the particularity, that it does not only possess 

 a maximum of pressure, but also a maximum of temperature, as is 

 represented in Fig. J in an exaggerated manner. 



2. As has been shown before') and will be further discussed in 

 the second paper, in a dissociating composition the same course may 

 be found on a larger scale, and it is this part of the three phase 

 line, that is the most important in compositions. Therefore it seemed 

 desirable to me to examine the ^j-.r-diagrams from the ti-iplepoint to 

 higher temperatures for the simple case discussed just now, and to 

 treat the compositions afterwards. 



3. The ^>.i'-diagram at the triplepoint, and at a temperature 

 slightly higher are presented in Fig, 2. 



As appears from Fig. 1, we find a double section of the three 

 phase line for the first time at the triplepoint, when coming 

 from lower temperatures, and a consequence of this is, that 

 besides at the triplepoint pressure, three phases may also occur 

 at a much higher pressure. This case is more closely defined in 

 Fig. 2 by the j;-i'-diagram corresponding to the temperature t^. 

 The lowest three phase pressure or the triplepoint pressure is repre- 



1) These Proc. Vol. VI, p. 230. 



2) Bakhuis Roozeboom, Zeilsclir. f. pliy?.Chem. 4. 31. 

 Stortenbeker, „ „ „ , 3. 71. 



