Liquid Drops and Globules, Their Formation and Movements / Three lectures delivered to popular audiences

by Charles R. Darling

Fig. 43.—Photograph of one globule absorbing another.

Analogies of Surface Tension Phenomena with Life.—When we watch the movements of globules on the surface of water, the resemblance to the antics of the lower forms of life immediately occurs to our [pg 76] minds. Now I do not intend here to intrude any opinion on the much-discussed subject of the Origin of Life, but merely to point out that certain phenomena, usually supposed to be associated only with living things, may result from the interplay of surface tensions. In our experiments we have witnessed expansive and contractile motion (aniline globules on water); movement of translation, of a very vigorous kind (xylidine and orthotoluidine globules); incorporation of external matter, or feeding (dimethyl-aniline absorbing orthotoluidine)—we are getting quite familiar with these long names now—, splitting up of masses, or division (skins of quinoline, etc., breaking up into branched portions, and sub-division of large globules); and formation of cellular structure (tar-oil on water). And the conclusion we may legitimately draw is this: that mechanical forces may account for many observed phenomena in connexion with life which formerly were attributed to the action of “vital” forces. Modern biological research all points in the same direction, and it seems probable that the operations of the animate and inanimate are controlled by the same forces. But the mystery of Life still remains.

Conclusion.—I have endeavoured in these lectures to bring to your notice some of the remarkable results which may be produced by the use of water and a few other liquids, and the scientific conclusions which may be drawn from them. It may be that the phenomena we have considered have little or no commercial application; but science has other uses in addition to its fruitful alliance with commerce. The study of the [pg 77] methods by which Nature achieves her ends stimulates the imagination and quickens the perceptions, and is therefore of the highest educational value. It is a great scientific achievement to run a railway to the summit of the Jungfrau, but we should not envy the mental condition of the individual to whom that glorious mountain appealed only through the railway dividends. And I trust that we shall never become so imbued with the industrial aspects of science, as to lessen our appreciation of the works of Nature, whether manifested in the snow-clad peak or the equally wonderful drop of water.

[pg 78]

APPENDIX

Apparatus and Materials required for Experiments on Drops and Globules.

Vessels.—For direct observation of liquid spheres, large drops, etc., beakers about 6 inches in height and 4 inches in diameter are suitable. It must be remembered, however, that a beaker containing water behaves like a cylindrical lens, and hence objects in the interior appear distorted in shape. In order to observe the true dimensions, flat-sided vessels must be used, in which the faces are of uniform thickness. Glass battery-vessels, which are made of a single piece of glass, have sides of irregular thickness, and are not to be recommended. A useful form of vessel is one in which the bottom and edges are made of copper, the sides being formed of windows of plate glass cemented to the copper framework. Water may be boiled in such a vessel without danger to the glass, starting with cold water; it is not advisable to pour hot water into the cold vessel, however, as the glass may crack. Suitable dimensions for a vessel of this kind are 6 inches high, and 4 inches in width and thickness. A beaker containing water, in which drops are formed may be placed in this square vessel, and surrounded by water, when distortion will be absent; and the whole of the contents may be kept hot—as required, for example, with the automatic aniline [pg 79] drop. It is best to conduct the experiments in beakers immersed as described, as the materials used may then be easily recovered without having to clean out the flat vessel.

For the formation of liquid columns, test-tubes, of diameter 1 to 2 inches, or small beakers, may be used. Test-tubes provided with a foot, which will stand upright, are most satisfactory; and the true shape may be seen by immersing the test-tube or beaker in water in a flat-sided vessel of the form described above. The effect of heat on the shape of the column may be observed by warming the water in the vessel. The centrifugoscope ([Fig. 7]) and the apparatus depicted in Figs. [8], [13], and [32], may be procured from the makers, Messrs. A. Gallenkamp & Co., Sun Street, E.C.

Experiments with skins and globules may be conducted in beakers of about 4 inches diameter, or in small porcelain photographic dishes. If intended for lantern projection shallow cells, with a bottom of plate glass, are necessary, and may be obtained from dealers in scientific apparatus.

Materials.—Sufficient quantities of the various liquids used may be procured from dealers in chemicals at a small cost. Aniline and orthotoluidine, which figure largely in the experiments, should be obtained in the “commercial” form, which is the cheapest and most suitable. The remaining liquids should be of the variety described as “pure” in the catalogues. When used for the formation of films, they should be kept in bottles in which the glass stopper is prolonged into a tapered rod, which dips into the liquid, and which, on removal, carries a convenient quantity of liquid to drop on to the water surface.