( 839 ) 

 when we pul : 



As minimum value for which this is the case, we should then have : 



Ida 8 



a da 'S 



In all such eases, in which the critical circumstances of a mixture 



</> 

 taken as homogeneous, tall in the region in which — <[ 0, these 



circumstances are not to be realised. Nor are they to be realised when 



d' 2 ty 



— — ]> 0, but then the spiuodal curve passes at least at a small 



distance round this point, and the plaitpoint circumstances are not 



very different from these which would be the critical circumstances 



d' 2 \p 



with an homogeneous substance. If <[ 0, a considerable difference 



d.v 2 



may be expected. 



Ihe spinodal curve and the plaitpoints when - IS POSITIVE. 



da 



Let us now again proceed to the discussion of the course of the spinodal 



curve and the plaitpoints; but now in the case that with increasing 



value of 1) the quantity T/- rises. Let 7\, be much higher than 7\ , 



a. «, d 2 ty 

 and "> - . Now two cases are possible. Ihe value of niav be 



/>. 2 1> X </,r- 



positive or negative in the critical points of even arbitrary mixture. 



For ,v = 0, and in general for very small value of ,r, where 



as(l — x) 



d*ti) 



is very large, is certainly positive, however large the value ot 



d*a 



—■■: a may be, and also for values of,/; differing liltle from 1. 



d*a 



d.v 2 d*\l> 



If — is small, - - is positive in the critical points of all mixtures. 



a </y- 



d"a 

 But for large values of — : a there are two values ot x, between 



dx 1 



value of b not clcpeiuling on v. Hence in this equation we get the factor - : , for 



5 



which, as we have already repeatedly observed, we should really substitute — . 



