58G 
MESSiiS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
coefficients than normal butyl alcohol. These results are no doubt to be ascribed to 
differences in the mode in which the complexity alters in the two series. 
The preceding discussion serves to show that the effect which temperature exercises 
on the viscosity of a liquid substance is related to its chemical nature and physical 
constitution. 
Conclusions concerning the Effect of TempercUure on Viscosity. 
1. Slotte’s formula gives the best results in the case of observed viscosity curves 
in which the slope varies but little with the temperature. 
Where the variation of the slope is considerable, as in the case of the alcohols, 
several formulae of this type have to be employed in order to represent the effect of 
temperature upon viscosity with sufficient accuracy. 
2. As regards the relations between the chemical nature of the substances, and the 
magnitudes of their tem23erature coefficients, it is evident that ;— 
(a) From the mode in which the constants n and h, in Slotte’s formula, are 
derived, their individual values cannot be expected to be simply related to 
chemical nature ; 
{h) For the majority of the liquids, the formula, 
7^ = C/ (1 + + yf), 
olitained from Slotte’s formula by neglecting terms in the denominator 
involving higher powers of t than t^, closely expresses the effect of tempera¬ 
ture on viscosity, and, in this formula, the magnitudes of the coefficients 
^ and y are definitely related to the molecular weight and the constitution 
of the substances ; 
(c) The substances, to which this modified formula does not apply, are charac¬ 
terized by large temperature coefficients, and these substances are in general 
those which, like water, the acids, and the alcohols, contain molecular 
aggregates. 
Comparisons of Viscosity Magnitudes at Comparable Temperatures. 
Convparahle I'einpcratures. 
The examination of the curves for families of related substances gives, of course, a 
general idea of how the viscosity varies from member to member. In order, however, 
to obtain quantitative relationships between viscosity and chemical nature, and to 
compare one group of substances with another, it rvas necessary to fix upon particular 
temperatures, and to obtain and compare the values corresponding with those 
temperatures. 
The first point to decide was at what temperature viscosities should be compared. 
