In liquids, is the mutual molecular attraction of the particles of a liquid for one another. Since water is the most common liquid, the demonstrations that follow will be made with water unless there is a special reason for using some other liquid.
If a glass rod is dipped in water and then removed, a drop will form on the end of the rod and will grow larger and larger as the water runs down the side until the weight of the drop becomes great enough to break it away from the rod, when, as it falls, it takes the form of a sphere. In this experiment cohesion does two things: it keeps the water from falling as soon as it runs down the side of the rod; and it gives the drop the form of a sphere.
The spherical form of liquids can be studied by making a mixture of alcohol and water, using such proportions that the mixture will have the same density as olive oil. Introduce a small quantity of the oil below the surface of the mixture, by the use of a glass tube, and the oil will assume the globular form, as in Fig. 1.
Shot are formed by pouring molten lead through sieves at the top of a high tower; the lead is thus separated into small masses, each of which assumes the form of a sphere.
Demonstration. - Cover a smooth board with lycopodium powder or powdered lampblack. Drop a small quantity of water upon it from a height of 2 or 3 ft., and the water will scatter and take the form of spheres.
NOTE. - Lycopodium powder - which is made up of the spores from certain plants - can be obtained from any drug store. A few cents' worth will be found very useful for many experiments.
