767 



distinct discontinuity as was found cat 4°.19 K in Ihe electrical con- 

 ductivity, although the tliermal conductivity^' becomes much larger, 

 when the temperature decreases. As there do not exist direct deter- 

 minations for solid mercury, we only can make a rough estimation 

 with the aid of Wiedemann and Franz's law. 



At the melting point, the electrical conductivity of liquid mercury 

 amounts to J. 10. 10' cm. <2-iand of solid mercury to about five times 

 as much, thus to 5.50. 10' cm-i S2-K P'rom this we tind by comparison 

 e.g. with lead about 0.075 for the thermal conductivity. The values 

 here obtained in liquid helium are 3.5 and 5.5 times as large. 



Chemistry. ''Equilibria in ternary systems". XVII. By Prof. 



SCHREINEMAKERS. 



(Gomnumicated in the meeting of Oct. 31, 1914). 



Now we will consider the case, mentioned sub 3 (XVI), viz: 

 the solid substance is a binary compound of a volatile- and a 

 non-volatile component. A similar case occurs for instance in 

 the system Na^SO^ -\- water -\- alcohol, when the solid phase is 

 Na^SÓ,. JOH.O, or in the system FeCi, -f HCl + H,0, when the 

 solid phase is one of the hydrates of ferric chloride, for instance 

 Fe,Cl,.12H,0. 



For tixing ttie ideas we shall assume that of the three compo- 

 nents A, B, and C (fig. 1) only A and C are volatile» so that all 

 vapours consist either of .1 or of C or of ^ -j- C. 



In lig. 1 CAde represents a heterogeneous regioji L — G; ed is 

 the liquid curve, CA the corresponding straight vapour-line. The 

 liquid d, therefore, can be in equilibrium with the vapour A, the 

 liquid e with the vapour 6' and each liquid of curve ed with a 

 definite vapour of AC. 



Previously (XYI) we have seen that this heterogeneous region 

 L — G can arise in different ways on decrease of pi-essure, viz. either 

 in one of the angiepoints A and C or in a point of AC; also two 

 heterogeneous regions may occur, the one in A and the other in C, 

 which come together on further decrease of ])ressure somewhere in 

 a point of AC. 



In tig. i we may imagine that the region L — 6r has arisen in these 

 different ways; curve ed may of course also turn its convex side 

 towards AC. Besides this heterogeneous region L — G we also find 

 in tig. 1 the saturationcurve under constant pressure of the binary 



51 

 Proceedings Royal Acad. Amslerdain. Vol. XVII. 



