Volumes, and Chemical Characters of Liquids. 425 



bodies, when the absolute temperatures are proportional to 

 the absolute critical temperatures, the vapour-pressures are 

 (at any rate in the cases examined) not proportional to the 

 critical pressures. In the case of benzene and fluorbenzene, 

 for instance, between about 0° C. and the critical points the 

 ratios of the vapour-pressures at " corresponding " tempera- 

 tures, instead of being constant, vary from 1*340 to 1*073. 



I have, however, shown (Trans. Chem. Soc. 1889, lv. p. 514) 

 that at " corresponding " pressures the ratio of the molecular 

 volumes of benzene and fluorbenzene remain approximately 

 constant within wide limits ; and this is also the case, though 

 the deviations are greater, with the liquids (methyl, ethyl, 

 and propyl alcohol and ethyl ether) examined by Professor 

 Ramsay and myself, when compared either with fluorbenzene 

 or among themselves. It is therefore possible to obtain an 

 approximate value for the ratio of the molecular volumes of 

 such substances at " corresponding " pressures and to compare 

 these values with those given by the equation 



V 



rjy 



= Trrr X 



f 



The experimental data from 

 lated are given below : — 



'hich the ratios have been calcu- 



Substance. 



Formula. 



Absolute Critical 

 Temperature. 



Critical Pressure, 

 in millim. 



Fluorbenzene 



C 6 H 5 F 



CH 3 OH 

 C 2 H 5 OH 

 C 3 H 7 OH 



(C 2 H 5 ) 2 

 CC1 4 

 SnCl 4 



559-55 



561-5 



5130 



516-1 



536-7 



466-8 



556-15 



5930 



33190 



36390 

 59760 

 47850 

 38120 

 27060 

 34180 

 28230 



Benzene 



Methyl alcohol 



Ethyl alcohol 



Propyl alcohol 



Ethyl ether 



Carbon tetrachloride . . . 

 Tin tetrachloride 





y 



In the following Table the values of ^7, calculated from the 



above data, are compared with those obtained from the expe- 

 rimental results at corresponding pressures. The percentage- 

 differences between the values obtained by the two methods 

 are also given, and the Table is arranged in the order of these 

 differences. 



