426 Boiling-points and Molecular Volumes of Liquids. 



Substances compared. 



T >' 



Approximate ratio of 



molecular volumes at 



" corresponding" 



pressures. 



Percentage- 

 difference. 



C 3 H 7 OH/C 2 H 5 OH ... 



1-305 



1-30 



0-4 



(C 2 H 5 ) 2 0/0 6 H 5 F 



1-045 



1-04 



0-5 



aH ft /C fl H-F 



•935 



•945 



11 



CCl 4 /SnCl 4 



'775 



•795* 



2-8 



C 2 H g OH/0 6 H 5 F 



•640 



•61 



4-7 



C 3 H 7 OH/C 6 H 5 F 



•853 



•80 



6-2 



SnCL/CLH-F 



1-246 



1-34* 



7-5 



CCL/C fi H-F 



•965 



1-07* 



109 



C 2 H 5 OH/CH 3 OH ... 



1-256 



1-44 



14-7 



C 3 H 7 OH/CH 3 OH ... 



1-640 



1-89 



15-2 



CH 3 OH/C 6 H 5 F 



•509 



•42 



17-5 



The number of comparisons is hardly great enough to allow 

 of very certain generalizations ; but it may be pointed out 

 that in three out of the four cases where there is the closest 

 concordance between the values calculated by the two methods, 

 we have to do with bodies which, as far as constitution is 

 concerned, are closely related. Of the seven remaining com- 

 parisons only two are between compounds which are so related, 

 and in both cases methyl alcohol is one of the compounds. 

 The want of concordance exhibited by methyl alcohol when 

 compared with the other alcohols of the same series, both in 

 this case and in many of its properties, may perhaps be due to 

 the preponderating influence of the hydroxy 1 as against the 

 alkyl group. 



The following conclusions may perhaps be tentatively drawn 

 from the foregoing data : — 



1. When the critical pressures of two closely related sub- 

 stances are equal, the ratio of their molecular volumes in the 

 liquid state (and probably also in that of saturated vapour) at 

 their boiling-points under any equal pressures is equal to the 

 ratio of their boiling-points measured on the absolute scale of 

 temperature, and therefore also to the ratio of their absolute 

 critical temperatures. 



2. When the critical pressures of two nearly related sub- 

 stances are unequal, their molecular volumes at their boiling- 

 points under u corresponding " pressures are (approximately) 



* Calculated from single readings of volume, taking that of SnCl 4 at the . 

 boiling-point under 760 millim. pressure and the others at " corresponding" 

 pressures. 



