92 
DR. T. E. THORPE AHD UR. J. W. RODGER ON THE RELATIONS 
anrl 90° tlie differences reach a niaximinn, l)ut never amount to more than 07 per 
cent. The conclusions based upon the coefficients r] given by the original sample 
remain, therefore, unaltered, and we do not think it necessary to deduce a new 
formula of the Slotte type to reproduce the values given by sample No. 2; 
because, when the temperature range is so extended as 130°, the average difference 
between calculated and observed values is as great as the above differences between 
the coefficients of the two samples. The formula already given for ethylbenzene, 
although derived from the values for sample No. 1, may still be taken to give values 
as near the truth as it is possible to obtain by means of a formula of the Slotte 
type from the coefficients given by sample No. 2. 
Graphical Representation of Results. 
The relative position of the viscosity-curves of different members of the series of 
esters and ethers is shown in the following figures. The ordinates are viscosity- 
coefficients multiplied by 10^, and the abscissie are temperatures. 
Esters (fig. ^). 
The esters investigated were the three lowest formates, the three lowest acetates, 
the three lowest propionates, methyl butyrate, and methyl isobutyrate. Fig. 1 
represents the curves obtained. The first noteworthy point in connection with the 
curves is, that in all cases their slope is comparatively small, and varies but little 
with the temperature. In this respect the esters differ to a most marked extent from 
the acids and alcohols from which they are derived, since one of the characteristic 
features of these two classes of compounds was the large effect exerted by temperature 
upon viscosity, and the large extent to which this effect altered as the temperature 
altered. The behaviour of the esters, therefore, is a further argument in support of 
our conclusion that the presence of the hydroxyl-group is the main cause of the 
exceptional course of the curves for the acids and alcohols, for it proves that when by 
the mutual interaction of an acid and alcohol the hydroxylic nature of both is 
destroyed, the resulting compound gives a curve in no way resembling those of the 
reacting substances. Indeed, the curves for the esters resemble in shape those of 
non-associated licpnds in general; they give no indication of the presence of molecular 
aggregates. This is, of course, in harmony with the mass of physical evidence, which 
goes to show that, with very few exceptions, hydroxy-liquids alone contain molecular 
aggregates. 
As regards the disposition of the curves, it has to be noted, in the first place, that 
according to the general rule obeyed in homologous series of simple liquids, they 
follow one another in the order of the molecular weiffiits of the esters. Passino- 
o o 
a.long the diagram from lielow upwards we have, first, the curve for methyl formate, 
