Constitution has been considered until recently to be of great importance in determining the fluidity of liquids. It is believed that association of liquid molecules also affects the fluidity so that it is surprising that in the earlier writings on fluidity, association as a cause of fluidity lowering was entirely overlooked. It appears that either chemical constitution or association might be effective but the problem of disentangling these effects is not easy. Gradually the so‐called constitutive factors have disappeared as the data and the methods of comparison have improved until there appeared to be but two left which were small or avoidable and might also be explained on the basis of association. Bingham and Darrall in their study of 23 octyl alcohols made the assumption that chemical constitution determines association and that association has a pronounced effect on fluidity, but that constitution itself is without effect on the fluidity. By this simplifying assumption they were able to calculate the association of those alcohols and to point out for the first time that a simple relation exists between chemical constitution and association, both among the octyl alcohols and also the lower members of the alcohol series. For example, it was found that in a normal aliphatic alcohol the association decreases regularly as the paraffin residue is increased. This conclusion was perhaps to be expected, but so far as known it had not been demonstrated before and it raised many questions. Would this conclusion be borne out with other classes of compounds? Does the association actually decrease in a linear manner or asymptotically? If linearly, is it possible to obtain compounds with a zero or even a negative association? A vast field for research seemed to open out. New data seemed the most urgent need but there was also need for newer points of view. Since constitution brings about the association, the effects upon the fluidity are due to the constitution anyhow. Constitution refers to the method in which given atoms are linked up but one cannot well give a number to the constitution of a certain octyl alcohol. One can, however, measure the association of that alcohol. Hence it may be said that association is a measure of resultant constitutional influences. When we are in a position to evaluate the resultant of the forces between the electric charges, the relation of constitution to association may be calculable.

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