1894.] The Viscosity of Liquids and their Chemical Nature. 153 



viscosity. Values were also assigned to the effects of the iso-gronping 

 of atoms, the double linkage of carbon atoms, and the ring grouping. 

 The values thus obtained are given in the following table : 



fundamental Viscosity Constants (molecular viscosity at the boiling 

 point, in dynes X 10*) . 



As regards the meaning to be attached to fundamental viscosity 

 instants in general, the following points may be noted. Viscosity 

 ay be taken as a measure of the attractive forces in play be- 

 reen molecules, i.e., of intermolecular attraction. From the fact 

 lat an increment of CH 2 in chemical composition, or the substitu- 

 ion of an atom of chlorine, bromine, or iodine for an atom of 

 rdrogen, brings about a definite change in the viscosity, it is evi- 

 ent that intermolecular attraction is really a property of the atoms 

 jrming molecules. Bat, besides change in molecular weight, 

 ige in the mode of grouping of the same atoms also affects the 

 jnitude of the viscosity. The observations show that iso-com- 

 junds have values differing from those of isomeric normal com- 

 pounds ; ring compounds have not the values which, by the study of 

 straight chain compounds, they might be expected to have. Com- 

 )unds containing hydroxyl oxygen give values of the viscosity 

 liffering widely from those of compounds containing carbonyl 

 tygen. The same atoms must, therefore, exert different effects 

 ?hen differently linked together. That the effects of all the atoms 

 the molecule are not altered by change in the mode of linkage is 

 )ved by the fact that the effect of CH 2 , of iodine, of bromine, <fec., 

 the same in normal and in iso-compounds. 



In the present state of the question it is impossible to say what 

 fticular atoms are affected by change in the mode of linkage, 

 tence the method adopted in deducing fundamental constants is to 

 sume that certain atoms retain the same values under all conditions, 



