PAPERS ON CHEMISTRY AND PHYSICS 299 



pressure and the heats of vaporization, of sublimation 

 and of fusion, in accordance with the principles dis- 

 cussed in a later section of this paper. The latent heat 

 of fusion of tungsten is not known, but it may be shown 

 that for most metals the molecular latent heat of fusion, 

 expressed in small calories, is about 2.6 times the abso- 

 lute melting temperature. The values used for making 

 the calculations for these two substances are, 



M. Pt. Ht. of Ht. of Ht. of 



(Abs.) sublimation fusion vaporization 



Tungsten 3540 210,400 9200 201.200 



Platinum 2028 123,500 5300 118,200 



Under column 3, Table I, are recorded the slopes of the 

 log P vs 1/T cuiwes which have been deteiToined from 

 the experimental curves plotted on large scale coordinate 

 paper, Xow it is very evident that there is a gradual 

 change in the slopes of the log P vs. 1 T curves as one 

 passes from the substances having low normal boiling 

 points to those having higher boiling points. This 

 change is observed readily when the experimental slopes 

 are plotted against the normal boiling points for these 

 substances. The points on this plot lie very close to a 

 line which may be represented by the equation: 



2 



S = — 68 + 4.877 Tb + 0005 T— (3) 



b 



In this equation S is the calculated slope and Tb the ab- 

 solute boiling point of the substance under normal pres- 

 sure. 



Under (i), Table 1, are given the slopes of the log 

 P vs. 1/T curves calculated from equation (3), and in 

 column 5 the differences between the observed and cal- 

 culated slopes are recorded. It is quite evident, except 

 at the very lowest temperatures where negative results 

 are obtained, that this equation expresses the slope with 

 a high degi-ee of precision. Applied to the high boiling 

 metals, the equation expresses the true slope with re- 

 markable accuracy, the variations being both positive and 

 negative. Indeed it may be said, that at all temperatures 

 above 20" Abs., equation (3) expresses the true slope of 



