( 21 ) 



« 



by . Iheon iis rcpre«eiited in Ki^-. 2. Tlie dotted 

 vertical lines are the four coniponeiils of the qiia- 

 druplei. 



Ill ('oniparinu' tiie figures 1 and 2 one must take 

 into consideration, tjiat in Fi<>,-. 2 is represented the 

 shape of tiie fringes, which arise from a single 

 horizontal l)aiid. In Kig. 1 in the central |»arl of 

 the field als(> occnr parts, originating tVoin fringes 

 lying above and under the middle. The vertical 

 medium line of Fig. 1 corresponds to th(^ almost 

 ever present absorption line due to the arc light and is tliu^ in no 

 way connected with the phenomenon which occupies us. 



The agreement in the region between the two interior com|)onents 

 of the ([uadrni)let is undoubtedly of great importance. The whole 

 form of the double curved line ma}' certainly be regarded as a con- 

 firmation of theory. How far the darker parts between the exterior 

 components in the middle of Fig. 1 correspond to the tj-sha])ed parts 

 of Fig. 2 is at i)resent not yet to be decided. 



Fiö'. 2. 



Chemistry. — ''The codr.se of the ineltiny- point-line of aUoys.'' 

 (Third communication). By J. J. van Laar. (Communicated 

 by Prof. H. W. Bakhuis Roozeboom). 



I. I have shown in two papers (these proceedings Jan. 31 and 

 March 28, 1903) that the expression (see the second jiaper) : 



1 + 



(1 + r.tf 



T=T„ ^— ^ '— , (1) 



very accuratel}' represents the solidification temperatures of tin- 

 amalgams. This equation maj' be derived from the general expressions 

 for the molecular thermodynamic potentials of one of the two com- 

 ponents in solid condition and in the fluid alloy. 



1 also pointed out (in the first i)aper), that already the simple 

 formula 



T— '- (2) 



qualitatively represents tlie course of the melting-point-line» |)ei-fectly. 

 This is simply done by not omitting the logai'ilhmic function A^// (1 — .v). 

 Though it is a matter of course, that — loij (1 — .v) can only be 

 replaced by .v., or .r-{- \ .v^-\- etc. iji the case that .r is very small, it 



