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.

[pg 80]

Accessories such as glass rods, plates, tubing of various diameters, thin copper wire, and an aluminium plate for the spheroidal state, can be obtained from any dealer in apparatus; and the same applies to clamp-stands for holding funnels, etc.

Water.—Ordinary tap-water suffices for all the experiments described, and for work with films and globules is superior to distilled water, which often possesses a surface so greasy as to retard or even entirely prevent the desired result. All experiments conducted on the surface of water should be performed in a clean vessel which has been rinsed out several times with tap-water before filling.

Lantern Projection.—In demonstrating the phenomena to an audience, a lantern may be used to advantage. It should be of the type now procurable, which is arranged for the projection of experiments conducted either in a horizontal or vertical position, by the use of the electric arc or other suitable source of light. Flat-sided vessels are essential for the successful projection of views of objects in a vertical position; and for showing globules, etc., on the surface of water, better definition is secured if cells with plate-glass bottoms are used instead of vessels made of a single piece of glass. The author has generally used a “Kershaw” lantern for lecture purposes, with quite satisfactory results. This lantern may also be adapted for projecting solid objects by reflected light—as, for example, a hot plate on which a spheroid of water is floating (Fig. 34). The contrivance known as the “Mirrorscope” may also be used, with slight modification, for producing a magnified image of solid objects on the screen.

[pg 81]