1898.] on Some Becent Besults of Physico-Chemical Inquiry. 657 



method indicated by Van der Waals ; or, lastly, we may compare the 

 viscosity values at the temperatures of equal slope, or at temperatures 

 at which drj / dt is the same for the different liquids — that is, points 

 at which temperature is exercising the same effect on viscosity. 



Now, no matter which of these modes of comparison be instituted, 

 definite general relations are apparent. Thus, if we compare the 

 viscosity coefficients at the boiling points, it is found that as a 

 homologous series is ascended the coefficients, as a rule, diminish. 

 Of corresponding compounds, the one having the highest theoretical 

 molecular has the highest coefficient. Normal propyl compounds 

 have higher values than allyl compounds, and an iso-compound has a 

 larger coefficient than a normal compound. In the case of other 

 metameric substances, branching of the atomic chain and the sym- 

 metry of the molecule influence the magnitudes of the coefficients, 

 the ortho-position in the case of aromatic compounds having a more 

 marked effect than either the meta- or para-positions. There are, 

 however, certain significant exceptions to the universality of these 

 rules, but these are in all probability dependent upon differences in 

 molecular complexity, as there is independent reason for believing 

 that the anomalous liquids contain molecular aggregates. Very similar, 

 although less definite, relationships are obtained at corresponding 

 temperatures obtained by the method of Van der Waals, and these are 

 still more obvious when the comparisons are made at temperatures of 

 equal slope. 



The attempt has been to ascertain if molecular viscosity can be 

 expressed as the sum of partial effects which may be ascribed to the 

 atoms and to the modes of atom linkage which occur in the molecule, 

 and it has been found possible to obtain values for particular ele- 

 ments and groups, and to trace the special influence of the iso- 

 grouping, of ring grouping, and of double linkage, upon the viscosity 

 of a liquid in such manner as to obtain a very fair agreement between 

 the observed and calculated value. Fundamental viscosity constants 

 have thus been obtained for the various elements, and it fs possible 

 to assign a quantitative value to specific differences in molecular 

 arrangement. Thus the fundamental viscosity constants at tempera- 

 tures of equal slope may, for a particular slope, be expressed as 

 follows : — 



Fundamental Viscosity Constants. 



Hydrogen 



Carbon 



Hydroxyl-oxygen C — O — H 



Ether-oxygen .. .. -.. .. C— O— C 

 Carbonyl-oxygen C = 



H 



C 



o 



o< 



II 



o 



44-5 



31 

 166 



58 

 198 



