THE MOLECULAR VOLUMES OF LIQUIDS 



By SIR EDWARD THORPE, C.B., F.R.S. 



As soon as it was clearly recognised that homogeneous chemical 

 compounds had fixed and definite compositions, capable of 

 being expressed quantitatively and in terms of the atomic 

 hypothesis, and that the weights of their unit volumes under 

 standard conditions were equally fixed and definite, it was 

 inevitable that, as the number of such compounds increased, 

 attempts should be made to ascertain what relation, if any, 

 existed between the two physical quantities. Moreover, as 

 with the increase in the number and complexity of such com- 

 pounds it became possible to classify them into groups, of 

 which the members exhibited relations among themselves 

 more or less well defined, depending upon chemical nature, it 

 became of additional interest to trace the possible connection 

 between chemical nature, as such, and the weight of the unit 

 volume ; and the inquiry became still further widened when 

 precise conceptions concerning chemical constitution, struc- 

 ture, molecular arrangement, and the. various problems of 

 spatial chemistry became part of the current doctrine of the 

 science. Stated broadly, then, the object was to discover the 

 connection between the molecular weights of substances and 

 the weights of their unit volumes under comparable condi- 

 tions, or, in other words, their molecular volumes, and their 

 other characteristics, depending upon chemical nature, con- 

 stitution, symmetry, homology, etc. 



For obvious reasons the inquiry soon became more par- 

 ticularly restricted to the case of liquid substances. In the 

 first case, the material was sufficiently abundant to afford 

 the promise of comprehensive generalisations ; in fact, many 

 of the questions raised by the inquiry could only be solved 

 by the consideration of facts deduced from the study of liquids. 

 And in the second place, it was easier in their case than in 

 that of solids to establish what might presumably be properly 

 regarded as valid conditions of comparison. The systematic 

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