420 Prof. Masson on the Boiling-points, Molecular 



I may perhaps be allowed to briefly recapitulate bis chief 

 results, in so far as they affect this question. 



(1) The critical pressures of C 6 H 5 F, C 6 H 5 C1, C 6 H 5 Br, 

 and C 6 H 5 I are equal, or very nearly so. Equal pressures are 

 therefore corresponding pressures. But C 6 H 6 has a different 

 critical pressure. 



(2) Compared at equal pressures, from 5 millim. up to the 

 critical point, the absolute boiling-temperatures of the four 

 halogen derivatives (but not of benzene) bear constant ratios to 

 one another. 



(3) At all equal pressures the molecular volumes at boiling- 

 points of the four halogen derivatives also bear constant ratios 

 to one another. 



Young gives the values of V T and T for each compound at 

 various pressures, and also the constant ratio numbers appli- 

 cable to any pressure for comparison of the fluoride with the 

 chloride &c. in respect to each of these variables. 



In Table V. the second column gives Young's boiling- 

 temperature ratios, the third gives his molecular volume-ratios, 



and in the last are the values of the ratios-^ which I have cal- 

 culated from them. They are good for any equal pressure. 



Table V. 



Compound. 



Comparative Values of 



T. 



v T . 



V T 

 T 



CXF 



1-0000 



1-1308 

 1-1974 



1-2884 



1-0000 

 11244 

 1-1800 

 1-2772 



1-0000 

 09943 

 0-9854 

 09913 



C 6 H-C1 



CJLBr 



C 6 H 5 I 



The figures in the last column prove (1) that the approxi- 



mate equality of the ratio -^- exhibited by these four compounds 



at a pressure of 760 millim. holds good at other pressures ; 

 (2) that the deviations from perfect equality, such as they 

 are, characterize all pressures alike, at all events up to the 

 limits actually reached in Young's experiments. 



