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MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
The attempts made by Poiseuille to connect the magnitude of K with the nature of 
the liquid were practically restricted to an extension of the prior experiments of 
Girard on the influence of dissolved foreign substances in modifying the velocity of 
flow of w^ater. Poiseuille confirmed the fact that certain of these substances, like 
common salt, accelerate, wdiilst others, like nitre, retard the rate of flow’ of water, 
and that in general the action increases, within certain limits, with the amount of 
substance added. At first sight it may seem remarkable that Poiseuille should 
have sought to elucidate the problem by attacking its most complicaind side; that is, 
by studying the mutual action of heterogeneous molecules; but the circumstance is 
explained wdien we remember that his primary object was to establish the causes 
which determine the flow of blood in the capillaries, and to trace the influence of 
different alimentary substances and medicaments on its movement. Although no 
fundamental relations of the kind looked for were discovered, certain facts of a 
remarkably significant character were brought to light. Thus it wms found that in 
the case of mixtures of alcohol and water, there is a certain mixture for wdiich the 
time of flow measured at a definite temperature is a maximum, and that this 
maximum of transpiration-flow corresponds wdth the mixture which shows the 
maximum deo’ree of contraction, or in other wmrds is connected with the existence 
of an apparently definite hydrate, CoHgO.SHgO. Hence it was inferred that such 
observations might throw considerable light on the molecular constitution of liquids. 
The subject was next attacked from this point of view by Thomas Graham (‘ Phil. 
Trans.,’ 1861, p. 373). By a method of observation identical in principle with that of 
Poiseuille, he confirmed the fact that in the case of mixtures of alcohol and w^ater, the 
composition of the mixture which had the maximum transpiration-time corresponded 
with the hydrate C2Hg0.3H20 ; and he showed that similar relationships w’ere to be 
found in the case of mixtures of nitric, sulphuric, hydrochloric, acetic, butyric, valeric, 
and formic acids with water, although the connection of the phenomenon wdth definite 
degrees of hydration w’as not always so w^ell marked as it apparently is in the case of 
alcohol and water. Although we are not immediately concerned with this aspect of 
the subject, it may here be stated that subsequent investigation has shown that 
Graham’s main conclusion is not capable of the simple expression which he gave to 
it. WiJKANDER (‘ Lund, physiogr. Siillsk. Jubelskrift.,’ 1878, Abstr. in ‘ Wied. 
Beibliitter,’ vol. 3, 8, 1879) confirmed Graham’s observation that in the case of a 
mixture of acetic acid and water, the maximum transpiration-time occurs at 20° wdth 
the monohydrate C 2 H/) 2 .H 20 , but it was also found that at another temperature, 
the composition of the mixture having a maximum transpiration-time was not that of 
a definite hydrate, showing that the phenomenon is probably dependent on or 
modified by dissociative changes in the liquid. (Compare also J. Traltre, ‘ Cheni. 
Ber,,’ vol. 19, ]>. 871, 1886; Pagliani and E. Oddone, 'Atti 11. Acc. delle Sclenze di 
Torino,’ vol. 22, 314, 1887, Abstr. in ‘ Beibl.,’ 1887, p. 415; Arrhenius, ‘ Zeit. fiir 
physikal. Chem.,’ vol. 1, p. 285, 1887.) Further investigation is required to show 
