L894.] The Viscosity of Liquids and their Chemical Nature. 140 



light or might not be taken as measures of a single physical magni- 



ide of the substance, i.e., its viscosity, the physical magnitude itself 



auld be measured, and the various influences which are found to 



feet its value could be allowed for. The physical constants thus 



jtained could then be treated from the point of view of the 



chemist, and the comparison would then be of the same kind as that 



iployed in connexion with other physical magnitudes. 



Full details of the conditions determining the dimensions of the 



apparatus and of the modes of estimating these dimensions, together 



rith the methods of conducting the observations, are given in the 



iper. 



The corrections to be applied to the direct results are then dis- 

 ssed. 



The question of the mathematical expression of the relation of 

 eosity of liquids to temperature is considered, and reasons are 

 fiven for preferring the formula of Slotte 



is here the coefficient of viscosity in dynes per square centimetre, 

 id c, &, and n are constants varying with the liquid. 

 With a view of testing the conclusions set out at length in the 

 ristorical section of the paper, and, in particular, of tracing the influ- 

 ice of homology, substitution, isomerism, and, generally speaking, of 

 changes in the composition and constitution of chemical compounds 

 upon viscosity, a scheme of work was arranged which involved the 

 stermination, in absolute measure, of the viscosity of some seventy 

 juids, at all temperatures between (except where the liquid 

 Nidified at that temperature) and their respective boiling points. 

 Part II of the memoir is concerned with the origin and modes of 

 iblishing the purity of the several liquids ; it contains the details 

 the measurements of the viscosity coefficients, together with the 

 ita required to express the relation of viscosity coefficients to tem- 

 srature by means of Slotte's formula, and tables are given showing 

 ic agreement between the observed and calculated values. 

 In Part III the results are discussed. In the outset the factors 

 son which the magnitude of the viscosity probably depends are 

 lealt with. The influence of possible molecular aggregations, as in- 

 dicated by observations of vapour densities, boiling points, and 

 critical densities, and, more especially, by measurements of surface 

 energy, made by Eotvos in 1886, and more recently by Ramsay and 

 lields. are taken note of. 



The deductions which may be made by considering the graphical 

 epresentation of the results, showing the variations of viscosity 

 efficients with temperature, are then set forth. 

 For liquids which probably contain simple molecules, or for which 



VOL. LV. M 



