672 Scientific Proceedings, Royal Dublin Society. 



The mean value of c calculated from the formula 



5L» = C^A 



M' B M b ' 



taking the molar percentages of benzene in the vapour calculated by liosanoff, 

 Bacon, and Schnlze (column 2 in above table) as correct, is 2 , 591, but the 

 individual values vary from 2'522 to 2-630. 



It may be noted that whilst benzene is a purely aromatic compound 

 toluene is partially aliphatic, so that the chemical relationship is not quite so 

 close as in the case of the other pairs of liquids examined by Miss Fortey 

 and ihe author. The volume and temperature changes which take place on 

 admixture of benzene and toluene, although slight, are noticeably greater than 

 in the other cases. It seems probable, therefore, that Brown's formula would 

 hold as well, if not better, for the other pairs of closely related liquids. 



Swmmary. 

 It is found that Brown's formula, 



m' a „ m a 

 — — = c — > 

 M' B M b 



is applicable without serious error to mixtures of benzene and toluene for 



which the formula P = mP a + (1 - m)P b gives results which are nearly, but 



certainly not quite, correct. 



It is also found that for benzene and toluene the best value of the 



p 

 constant c differs but slightly from the ratio ~. 



Pb 



