( 131 ) 



/dg\ d*'i\> . 



points f — I =0, and also 4 times through the line — — = 0, in 

 \d.vj p *> 



which points ( — J = oc. Only for the loop-p-line the second minimum 

 \djsjp 



Fig. 23. 



coincides with the first maximum, but for lower p-lines it lies higher, 



as in the drawing. We have exactly the same shape for (/ as func- 

 tion of x, as in lig. 20 for p as function of v. Only one figure must 

 be turned over to cover the other, in accordance with the circum- 

 stance that (/ = — and p = . The combination c, (/ and e 



now yields a pair of coexisting phases, and the combination e, ƒ 



and g another pair. No other combinations are possible; and we 



should be justified in concluding that the binodal line has a simple 



course and remains limited to the stable region. But this conclusion 



would be perfectly valid only for all pressures not higher than those 



of the loop-p-line, though there are also coexisting phases with higher 



value of //. In this case it is certainly preferable to follow a gdine, 



and to construe p as function of v, which we have called preferable 



already above for other reasons. We know that then a highest 



pressure exists for the coexisting phases, viz. when .i\ = ,i\ ; this is 



dp 

 only possible if the chosen (/-line passes through the line — = 0, 



da: 



for only then this is the case for values of .<■ within certain limits. 



From this circumstance of the reciprocal case we conclude that in 



f/ 2 i|> dp 



the case under consideration, in which =: is cut by — = 0, 



dz> J dx 



