Young — On Brown s Formula for Distillation. 



671 



As the equation (I) of Rosanoff, Bacon, and Sehulze satisfactorily re- 

 produces the percentage composition of the vapour even when the substances 

 considered form mixtures of maximum or of minimum vapour-pressure, it 

 may be employed with great confidence in such a simple case as that of 

 benzene and toluene, more especially on account of the excellent agreement 

 between the observed vapour-pressures and those calculated from the 

 formula (II). 



We may, therefore, accept the calculated molar percentages of benzene in 

 the vapour without hesitation, although actual determinations have not been 

 made; and we may now make use of these data in order to find whether 

 Brown's formula is applicable without serious error to this pair of liquids. 

 We can also find whether the constant c in Brown's fm-mula agrees with the 

 ratio 



P A 748-7 

 P B 288-5 



2-5951 at 79-7°. 



Taking for the constant c 



P 



=3^ = 2-5951, the differences are considerably 



smaller than' those between the calculated (R., B., & S.) and observed 

 (Ziwidski) molar percentages of carbon tetrachloride in mixtures of that 

 substance with benzene, and, were it not for their regularity, they might 

 perhaps be regarded as within the limits of experimental error. 



The best agreement is obtained by making c = 2'589 — a value which differs 



but slightly from the ratio =p A • 



