704 
MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
benzene, and propylene dibromide, giving viscosity curves which are abnormal when 
compared with those of their homologues. 
2, The temperature relationships may also be regarded as general, and thus 
independent of the value of the slope, except in the case of the alcohols, which, in this 
respect, as in that of viscosity at equal slojDe, are anomalous. 
General Conclusions regarding Physico-chemical Comparisons. 
It is evident from the foregoing tables tliat the liquids showing irregularity in the 
magnitudes of their temperatures of equal slope are the dihalogen comjiounds, the 
acids, benzene, ortho-xylene, the alcohols, &c,, and these are the liquids which were 
shown both by the graphical and algebraical treatment of our results to possess 
viscosity-curves having courses which were peculiar as compared with those of the 
majority of other related substances. Although at equal slope the viscosity-magni¬ 
tudes of many of these compounds, the acids included, exhibit more or less different 
relationships, yet when we consider the magnitudes of the temperatures at equal 
slope, the peculiarities of the substances stand out as clearly as before. This points 
to the conclusion that, if the disposition of the curve of a substance is peculiar as 
conqiared with those of related substances, then no matter how we choose the con¬ 
ditions of comparison the original peculiarity expressed by the curve must still exist 
and may be discovered by regarding the results from different points of vdew. 
Since the magnitude of the boiling-point of a substance is more or less definitely 
related to its chemical nature, if we choose the boiling-point as the condition of 
comparison, we insure that the temperatures of the substances will exhibit more or 
less definite physico-chemical relationships; and hence the viscosity-magnitudes of 
those liquids which give peculiar viscosity-curves will not be definitely related at the 
boiling-point. This we have seen to be the case. Similar considerations apply in the 
case of other physical properties. 
At equal slope, on the other hand, we have found that the viscosity-magnitudes of 
many of the peculiar substances accord with the regular behaviour of those of most 
of the other liquids, but, as has just been shown, the peculiarities, although they 
no longer exist in magnitudes of the viscosities, are clearly indicated by the magnitudes 
of the temperatures. 
This argument does not necessarily prove that for the purposes of physico-chemical 
comparisons the boiling-point has as much to recommend it as a temperature of equal 
slope ; indeed, the latter, both by the results obtained and from general considerations, 
seems to be by far the more preferable. The real conclusion indicated is that to use a 
system of temperatures of comparison merely for the sake of obtaining and discussing 
the magnitudes of physical properties at those temperatures, is but a partial method of 
arriving at a true estimate of the behaviour of the substances, for that behaviour is 
expressed, not only in the magnitude of the physical property, but also in the 
