( 522 ) 



to iiiid the values of ,v and T at the ^'critical" point. We iind as 

 above : 



'Vc = {óa) 



r 



The temperature /c of tliis critical point is found from—- = 0, 



ux 



that is to say from 



a;c{l—Xc)_ Tc 



We consequently Iind : 



1 .I'c 



or, as 1 + rx,: = 3 : 



2—Xc 



1 2« xA2—XcY 



' 27 " {l—XcY ^ ^ 



At this, or at lower tem|»eratnres, ^— being tiien |)ositive. we find 



ox 



ourselves therefore in the plait. 



In the case of tin and mercury we find for .v,, the value 0,863 



(see above), if r = — 0,74. For Tc we find : 



504,8 0,0906 



T, = ^ X X 67.G0 = 289^2. 



27 ^ 0,396 



The "critical" i>oint is therefore situated at 16^ C, that is to say 

 fully 37° lower than the point of the meltingpoint-line, belonging to 

 ,(; = 0,863 (13,7 atom-percent tin), namely 83°,2 C. 



There are of course cases, where that distance is smaller, and 

 where consequently a trifling supercooling already carries us within 

 the region of the plait, which then — in the absence of the solid 

 phase — causes a separation into two layers. 



I may observe, that the \alue .Vc does not correspond as a rule 

 with a point of. inflection (with oblique tangent) on the meltingpoint- 

 line, when the ci'itical point is not situated 07i the meltingpoint-line. 



For -^ =3 0, —^ = do not lead to = 0. Avhen these differen- 



d.v ö.r^ dx^ 



tial-coeffients do not become on the meltingpoint-line. 



5. The value of q, the heat of fusions of tin in the liquid amal- 

 gam, is evidently: 



/ ax^ 



