They Change Places
This experiment is rather difficult to perform because its success depends on exact conditions; it is, nevertheless, well worth all the trouble you may expend on getting it accurate. Look first at the accompanying drawing. You will see two wine glasses, one inverted over the other. Naturally, this will call for two glasses of exactly similar dimensions. Note that when the glasses are inverted you will require them to hold water. Therefore, it is not sufficient for the lips just to rest in contact; they must adhere. This is only possible when the edges are ground flat and smeared with grease. To grind them, rub gently in a circular direction on a flat surface of emery paper. Mind it is level, or the glass will crack during the process.
To perform the experiment fill one glass with water and the other with claret, which will still be drinkable when we have done with it. Before charging them, the edges of the glasses should be touched with vaseline.
On the glass of water, rest a thin sheet of metal gauze that is perfectly flat and free from buckles. Flatten it down on to the greased lip to ensure suction; then put a piece of glass on top of the gauze. Invert the glass of water and rest it exactly over the glass of wine, so that the two are in perfect contact.
Slide away the sheet of glass and see that no water falls out or air rushes in. If you have performed this experiment properly and have manged to keep both the glasses quite full of liquid, a very curious thing happens. In less than a quarter of an hour the water and wine will have changed places. The water will now be underneath and the wine on top.
Why does this happen? Because the density of the claret is slightly less than that of the water. Accordingly, the water which you put on top had to find its way to the bottom glass.