CHAPTER II
FLUIDITY AND THE CHEMICAL COMPOSITION
AND CONSTITUTION OF PURE LIQUIDS
Attention was first strongly drawn to the desirability of study-
ing the viscosity of homogeneous liquids in relation to their other
properties by Graham in 1861. He himself measured the
viscosity of several organic liquids at the uniform temperature of
20° and noted that the times of flow increase with the boiling-
point, from which he inferred that there is a connection between
viscosity and chemical composition similar to that which exists
between the boiling-point and the chemical composition. By
comparing the times of flow of " equivalent amounts/' obtained
by multiplying the times of flow of equal volume by the molecu-
lar weights and dividing by the density (rjM/p}, Rellstab (1868)
sought to gain a more intimate knowledge of this relation. He
measured the viscosity over a range of temperatures from 10 to
50° and then compared the substances at temperatures at which
their vapor-pressures are equal, as well as at a given temperature.
No simple quantitative relationship was found between his times
of flow and the molecular weight or vapor-pressure, but he stated
several qualitative relationships. Thus he noted that the time
of flow always decreases as the temperature rises, that an incre-
ment of CH2 in a homologous series is in general accompanied
by an increase in the time of flow, but that metameric substances
may have very different efflux-times. Without attempting a
complete summary of his observations, the above suffice to show
that he regarded temperature, chemical composition and con-
stitution as all important in determining the rate of flow.
Pribram and Handl (1878-1881) studied a large number of
pure liquids over a range of temperatures from 10 to 60° express-
ing their results in "specific viscosities7' taking water at 0° as 100.
Their researches marked a great step in advance but only to the
extent of confirming and extending the qualitative observations
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