506 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the equilibrium line that the change of volume VI-V was not sufficient 

 to raise the pressure to the equilibrium value VI-V. From D, pressure 

 was regularly reduced to E, the melting point of V. Beyond E, the 

 curve of increasing pressure was retraced. 



These remarks about the manner of appearance of V hold only for 

 temperatures above —25°. At lower temperatures, V may be made to 



U) 



oc 



bJ 



a. 



2 

 iij 



V- 



-10 



-20 







o 



3000 



4000 



5000 



6000 



PRESSURE, KGM/CM? 



Figure 24. The freezing curve V-L. 



separate from the solid phases III or II without the presence of glass. 

 In any event, V was the hardest of any of the solid forms to obtain, 

 the only certain way being via II, which demanded lowering the appa- 

 ratus to below —60°. 



The actual determination of the points on the V-L curve was made 

 with the apparatus for the middle temperature range, temperature 

 being kept constant as usual with a thermostat. The equilibrium 

 points are shown in Table XXII. and plotted in Figure 24. As is seen, 

 these points were obtained on a large number of occasions, with differ- 

 ent pressure measuring coils, and with nearly all possible combinations 

 of all the pieces of apparatus ever used with this general tyjDe of appa- 

 ratus, part after part being replaced as it was destroyed by explosion. 

 The lower part of the equilibrium line is a trifle high, still passing 

 through a number of points, but not through the mean of all the points. 

 This was demanded in order to obtain consistent values for the latent 

 heat at the triple point L-III-V, the slope of the upper end of the 

 III-L curve being extraordinarily sensitive to small changes, as already 

 explained. The curve as given does not differ by over 0.2° from the 

 best curve through the points for V-L alone. The curve as given ex- 



