Fig. 53
You may have noticed when I made the drops of oil in the mixture of alcohol and water, that when they were brought together they did not at once unite; they pressed against one another and pushed each other away if allowed, just as the water-drops did in the fountain of which I showed you a photograph. You also may have noticed that the drops of water in the paraffin mixture bounced against one another, or if filled with the paraffin, formed bubbles in which often other small drops, both of water and paraffin, remained floating.
In all these cases there was a thin film of something between the drops which they were unable to squeeze out, namely, water, paraffin, or air, as the case might be. Will two soap-bubbles also when knocked together be unable to squeeze out the air between them? This you can try at home just as well as I can here, but I will perform the experiment at once. I have blown a pair of bubbles, and now when I hit them together they remain distinct and separate (Fig. 54).
Fig. 54.
I shall next place a bubble on a ring, which it is just too large to get through. In my hand I hold a ring, on which I have a flat film, made by placing a bubble upon it and breaking it on one side. If I gently press the bubble with the flat film, I can push it through the ring to the other side (Fig. 55), and yet the two have not really touched one another at all. The bubble can be pushed backwards and forwards in this way many times.
Fig. 55.
I have now blown a bubble and hung it below a ring. To this bubble I can hang another ring of thin wire, which pulls it a little out of shape. Since the pressure inside is less than that corresponding to a complete sphere, and since it is greater than that outside, and this we can tell by looking at the caps, the curve is part of one of those represented by the dotted lines in C or E, Fig. 31. However, without considering the curve any more, I shall push the end of the pipe inside, and blow another bubble there, and let it go. It falls gently until it rests upon the outer bubble; not at the bottom, because the heavy ring keeps that part out of reach, but along a circular line higher up (Fig. 56). I can now drain away the heavy drops of liquid from below the bubbles with a pipe, and leave them clean and smooth all over. I can now pull the lower ring down, squeezing the inner bubble into a shape like an egg (Fig. 57), or swing it round and round, and then with a little care peel away the ring from off the bubble, and leave them both perfectly round every way (Fig. 58). I can draw out the air from the outer bubble till you can hardly see between them, and then blow in, and the harder I blow, the more is it evident that the two bubbles are not touching at all; the inner one is now spinning round and round in the very centre of the large bubble, and finally, on breaking the outer one the inner floats away, none the worse for its very unusual treatment.