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Chemistry. — '^ lliree-pliaseUnes in chloralalcokolate and aidluie- 

 hydroddoride". By Prof. H. W. Bakhuis Roozeboom. 



It is now 20 years since tlie study of the dissociation piieno- 

 niena of various solid compounds of water and gases enabled nie 

 to find experimentally the peculiar form of tliat three-phaseline which 

 shows the connection between temperature and pressure for binary 

 mixtures in which occurs a solid compound in presence of solution 

 and vapour, The general significance of that line was deduced, 

 thermodynamically, by van der Waals and the frequency of its 

 occurrence was proved afterwards by the study of immj other 

 systems. 



That this three-phaseline is so frequently noticed in practice in 

 the study of dissociable compounds is due to the circumstance that, 

 in the majority of the most commonly occurring cases, the volatility 

 of the two components or of one of them, is so small, that at the 

 least dissociation of the compound both liquid and vapour occur in 

 its presence. 



In the later investigations, which have led to a more complete 

 survey of the many equilibria which are possible between solid 

 liquid and gaseous phases, pressure measurements have been 

 somewhat discarded. When, however, the survey as to the connec- 

 tion of all these equilibria in binary mixtures got more and more 

 completed and could be shown in a representation in space on 

 three axes of concentration, temperature and pressure, the want was 

 felt to determine for some equilibria, theoretically and also experi- 

 mentally, the connection between temperature and pressure, in order 

 to fill up the existing voids. 



Of late, the course and the connection of several ^^, Mines, iiave 

 been again studied by van der Waals, Smits and myself either 

 qualitatively or qualitative-quantitatively. 



To the lines, which formerly had hardly been studied, belonged 

 the equilibria lines which are followed, when, with a constant 

 volume, the compound is exposed to change of temperature in presence 

 of vapour only. They can be readily determined experimentally only 

 when the volatility of the least volatile component is not too small. 

 Stortenbeker at one time made an attempt at this in his investigation 

 of the compounds of iodine with chlorine, but did not succeed in 

 obtaining satisfactory data. 



In the second place it was desirable to find some experimental 

 confirmation for the peculiar form of the three-phaseline of a 

 compound, recently deduced by Smits for the case in which a 



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