XXVIII.—On a Method of Determining the Cohesion of Liquids

Abstract

While working at an investigation (about to be published), relating to the flow of liquid through capillary tubes, it was thought that the cohesion of a liquid might influence the rate of its flow, and a method was sought for, which would enable the cohesion of any liquid to be determined; the ordinary method of calculating the cohesion from observations of the flattening of a drop of the liquid resting upon a plane surface not being applicable to all liquids. The method which seemed most likely to yield results was that of observing the drops of a liquid so arranged that they fell from the end of a column of the same liquid, and accurately measuring the width of the neck of the drop at the instant of breaking, and the weight of the fluid which caused the rupture. It is easily seen that before this could be done a complete knowledge of the nature of drops would be required, and as the phenomenon of dropping has been made the subject of a long investigation by Professor Guthrie, an examination of his results was undertaken. They show that the drop increases in weight as the growth-time decreases, that is, the quicker the rate of flowing the larger the drop. Many experiments were made, which, agreeing with Professor Guthrie's numbers pretty closely, need not be quoted here. While, therefore, his experimental numbers may be taken as quite correct, they do not seem to prove the theory he has put forward in their explanation. The following is from his paper:—“The most prominent fact is that, on the whole, the drops undergo a continuous diminution in weight or size as G.t. increases. To such an extent is this the case, that the most rapidly falling drops of the above table are nearly twice as heavy as the most slowly falling ones. The cause of this is probably to be sought for in the circumstance that when the flowing to the solid is more slow, the latter is covered with a thinner film of liquid, so that, as the drop parts, the solid reclaims by adhesion more of the root of the drop than is the case when the adhesion of the solid to the liquid can satisfy itself from the thicker film which surrounds the drop in the case of a more rapid flow.”