THE MOLECULAR VOLUMES OF LIQUIDS 195 



branching of the hydrocarbon chain, self-affinity between 

 side-chains, cross-linking, and double bonds, ring systems, etc. 

 All the experimental data hitherto obtained bearing upon 

 these questions have been summarised and discussed in Mr. 

 Le Bas's monograph, to which the reader who desires the 

 information must be referred. There is the less need for 

 dwelling on certain of these points in an article of this character 

 for the reason that the evidence is as yet very meagre. Far 

 more work is needed in several directions before conclusions 

 of sufficiently well-proved generality can be drawn. 



What, however, has been stated will suffice to show the 

 character of information which the study of the relations 

 between chemical nature and molecular volume is calculated 

 to afford. In the space which remains we will briefly touch 

 upon the facts yielded by the study of the other groups of 

 substances above referred to and incidentally state what 

 appear to be the more interesting points in the present condi- 

 tion of knowledge on the question. 



The values for the halogens in a state of combination, as 

 calculated by Kopp, are not very dissimilar from the average 

 volumes obtained from a discussion of much subsequent work, 

 both on organic and inorganic compounds ; and these values 

 are not very different from their volumes in the free state. 

 Few observations on fluorine compounds are, however, avail- 

 able on account of the difficulty of preparing these substances 

 and their instability, especially in contact with atmospheric 

 moisture whereby glass vessels are liable to be attacked. In 

 the family of the halogens the atomic volumes increase with 

 the atomic weights, but not proportionally. Their values 

 appear to be affected, but only to a relatively slight effect, 

 by constitutive influences, and they have practically the same 

 value in aromatic as in aliphatic compounds. There is, how- 

 ever, some evidence to show that in the chlorobenzenes the 

 position of the chlorine atom in the molecule is not witheut 

 influence upon its volume. Far more work, however, is needed 

 before the precise effect of this and other constitutive influ- 

 ences can be said to be satisfactorily made out. 



The study of the molecular volumes of substances con- 

 taining oxygen presents features of special interest. It was 

 recognised by Kopp that the value of the oxygen atom was 

 not uniform, but was influenced by the particular method of 



