( 699 ) 



undertaken that of tlie Helium-stars and miglit perhaps afterwards 

 try the same method for the stars of Pickering's 5''» Type. 



In concluding it is only just to say that, whatever be the merit 

 of the present investigation, it belongs mainly to Dr MöiNnichmeyer. 

 As compared with his careful and elaborate labour, that spent on 

 the derivation of the present result is quite insignificant. 



Chemistry. — "On the course of melting-point curves for compounds 

 ic/iicli are pariialli/ dissociated in the liquid phase, the proportion 

 of the jyroclucts of di'^sociation being arbitrary" , by J. J. van 

 Laar. (Communicated by Prof. H. W. Bakhuis Roozeboom"). 



1. It is well known, that a liquid mi.xture of e. g. two comiio- 

 nents \A and B, which can form a compound J,, Bj.^, reaches its 

 maximum point of solidification, when the ratio of the molecular 

 quantities of the two components is as r, : r,, in other words when 

 there is no excess of one of the products of dissociation of the com- 

 pound A-j^ B,„. 



Expressed differently: when we determine the points of solidification 

 of a series of liquid mixtures of A, B and the compound with 

 increasing excess x of one of the products of dissociation of the 



compound under consideration, then — =0 for tlie curve of soli- 



ya-^' y Ü 



dification or melting-point line thus formed. 



Hence the melting-point curve of a compound, with increasing 

 addition x of one of the products of dissociation, will have an 

 horizontal direction at x = 0, as soon as there is but the 

 slightest dissociation of the compound in the liquid phase. If there 

 is no dissociation at all, the admixture may be considered as an 

 alien, indiflerent substance, and the initial direction of the melting- 

 point curve will show all at once the no)'mal descending course at 

 x = 0. 



As will also appear from the following computation, the initial 



horizontal course \^i\\ of course pass the sooner into a descending 



course, the slighter the dissociation of the compound is. 



/dT\ 

 The peculiaritv mentioned of -— becoming zero with the slight- 



\dx Jo 



est trace of dissociatioji of the compound, was already proved by 



Prof. LoRENTZ in 1892, on the occasion of an investigation of 



Stortenbeker on chlorine-iodides '). Pi'of. van der Waals too i:as 



1) Z. f. Ph. Gh. 10, bl. J 94 et seq. 



49 



Proceedings Royal Acad. Amsterdam. Vol. VIII. 



