of Change of Condition on Vapour-pressure. 



65 



These numbers agree fairly well with Regnault's results at 

 and above 10°, Below that temperature his constants are 

 calculated from the vapour-pressures of the solid as well as of 

 the liquid, and of course are therefore incorrect. 



We give a Table of comparison of our calculated results, 

 with those calculated by Fischer, between 0° and 6°. 



Temp. 



Pressure. 



Temp. 



Pressure. 



F. 



R. and Y. 



F. 



R. and Y. 



o 







millim. 

 2640 



millim. 

 26-54 



o 

 4 



millim. 

 32-84 



millim. 

 32-99 



1 



27-87 



28-04 



5 



34-68 



34-80 



2 



29 43 



29-61 



6 



36-60 



36-69 



3 



31-10 



31-26 









It will be seen that the agreement is a very close one ; and 

 as our determinations were made by the dynamical method, 

 while Fischer's were obtained statically, there is a strong pre- 

 sumption that the substance in both cases was pure. 



In order to calculate the vapour-pressures of solid from 

 those of liquid benzene, the following formula was employed: — 



Vapour-pressure of solid at (Hl) = P r (F r F f .i) ( V ^ +F< " 4 



P = vapour-pressure of solid ; 

 P / = vapour-pressure of liquid ; 

 V =heat of vaporization of liquid ; 

 F =heat of fusion of solid ; 

 t = temperature of solid and liquid. 



It is therefore necessary to know the heat of vaporization 

 of liquid benzene at different temperatures, and the heat of 

 fusion of solid benzene ; and in order to calculate these, the 

 specific heats of liquid and of solid benzene. The following 

 determinations are available : — 



1. Heat of Vaporization of Liquid Benzene. — Regnault 

 (Memoires de Vlnstitut, xxvi. p. 881) has determined the total 

 heats of vaporization of benzene at different temperatures, 

 while Schiff (Annalen, ccxxxiv. p. 344) has made a single 

 determination at the boiling-point. Regnaultfs formula is 



~H.=za + bt + ct 2 , 



where a=109, 6 = 0'24429, and c= -0*0001315. Setoff's 

 Phil. Mag. S. 5. Vol. 23, No. 140, Jan. 1887. F 



