232 SCIENCE PROGRESS. 



boiling-point. As regards the effect of temperature on 

 viscosity, it varies to a remarkable extent with the nature of 

 the liquid, and is most marked in the case of hydroxy 

 compounds, particularly the alcohols ; indeed, both as. 

 regards their large viscosities at low temperatures, and 

 their large temperature coefficients, the higher fatty alco- 

 hols foreshadow the well-known behaviour of the glycols, 

 glycerin, and other polyhydric alcohols. The most gene- 

 rally useful formula for connecting viscosity and temperature- 

 is that of Slotte, v= c (i + bl)'\ where 17 is the viscosity co- 

 efficient and c, b, and 11 are constants varying w T ith the liquid.. 

 In attempting to correlate viscosity and chemical nature 

 the authors determine, at different series of comparable 

 temperatures, values of the molecular viscosity, and mole- 

 cular viscosity-work. The former is the product of the 

 viscosity coefficient and the molecular area, and is the 

 viscosity referred to a surface upon which there lies in the 

 case of different liquids the same number of molecules. 

 The latter is the product of the viscosity coefficient and the 

 molecular volume. The comparable temperatures used are 

 the boiling-point, the corresponding temperature of van der 

 Waals, and the temperature of equal slope. The last is the 

 temperature, varying with the liquid, at which temperature 

 is in each case exerting" the same effect upon the viscosity. 

 The most definite stoichiometric relationships are obtained 

 at this new system of comparable temperatures. By giving 

 definite values to the different atoms and modes of atom- 

 linkage, such as iso-linkage, double-linkage, and the ring- 

 grouping of atoms, it is possible to calculate values of the 

 molecular viscosity and molecular viscosity-work, which 

 closely agree with those actually observed. Chemical con- 

 stitution has a marked effect ; for example, on keeping the 

 values of carbon and hydrogen the same, widely different 

 values have to be ascribed to carbonyl-, ether-, and hydroxyl- 

 oxygen. The values for hydroxy compounds differ greatly 

 from those of other oxy-compounds, and together with 

 irregularities which they exhibit amongst themselves, give 

 evidence of molecular complexity. One important point is 

 that the relationships obtained between the viscosity con- 



