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XXXVI. The Theory of Molecular Volumes. 

 By Gervaise Le Bas, B.Sc* 



Part I. 



The Existence of Additive Relations In 

 Molecular Volumes, 



MUCH of the recent work in Physical Chemistry is 

 connected with the correlation of the physical 

 properties of matter and the chemical constitution of the 

 molecules. The result is to show that the latter is reflected 

 in the physical properties in a remarkable way, just as we 

 may suppose that the nature of these is largely determined 

 by the nature and build of the chemical molecules* It is 

 usual to suppose that the physical properties of matter, 

 chemically considered,, are subject to at least three distinct 

 influences :— 



(a) An additive relation which is due to the subdivision of 

 the molecules into discrete portions called atoms. 



(6) A number of constitutive influences which are dependent 

 upon the mode of arrangement of these atoms, and 

 the particular distribution and force of residual 

 chemical affinity. 



{&) Certain effects dependent upon the play o£ interatomic 

 forces, or on the forces originating from the atomic 

 or electronic units. 



In molecular volumes we need concern ourselves only with 

 the first two. 



There has been a disposition during the last few years to 

 regard with suspicion any attempt to correlate the molecular 

 volumes of compounds and their chemical properties accord- 

 ing to the method just outlined^ owing to certain conceptions 

 regarding the intimate structure of liquid having become 

 current. This is certainly unnecessary, for it, is now 

 generally admitted that the co-volume, if it exist, is under 

 conditions of vapour pressure, low as compared with the 

 critical vapour pressure, proportional to the real molecular 

 volumes. It follows that the molecular volumes of com- 

 pounds at, say, the normal boiling-point, are also proportional 

 to the real molecular volumes. The method of discussing 

 these molecular volumes as originated by Kopp, and which 

 is followed in the present paper, is thus quite justified. 



* Communicated by Prof. W. J. Pope, F.Pt.S. 



