T - 1 



270 Dr. W. C. M C C. Lewis on the 



one obtains as before 



1 _ T 'dp * 

 BT ' 



Further, since 



we obtain 



where a x = the coefficient of expansion of the liquid with 

 temperature; 

 /3 =the coefficient of compressibility of the liquid at 

 constant temperature. 



Further, if p is the density of the liquid at the temperature 

 in question, the latent heat of vaporization L per gram may 

 be written 



L — PIT 



The quantities occurring in this expression are known at 

 least approximately for a number of liquids. In the following- 

 table are given the results obtained from data taken principally 

 from Landolt & BorDS.tein ? s Tabellen, Castell-Evans' Tables, 

 and "Winkelmann's Handbuch. 



Before giving the actual examples, however, it may be 

 well to point out that the introduction of Dupre's idea, in its 

 original as well as in its modified form, viz. that the internal 

 pressure of a liquid may be measured by the latent heat of 

 vaporization per unit volume of liquid, apparently leads to an 

 expression which is in disagreement with the well-known 

 Clapeyron expression 



BT v 2 — vi 



* It will be observed that this result, although deduced on the 

 assumption that K varies with temperature and is connected with I by 



the relation K — J=T -^, does not prove the validity of the latter 



relation. Thus if we assumed that K is independent of temperature and 



therefore %^ == 0, we should still obtain the same final result, viz. /= T ~~,. 



