Floating Pins and Needles
Fig. 13.—The floating pin.
If a drop of water is placed on glass it will at once spread, but if the same thing is done with a drop of mercury, the liquid will not spread, but remain in the form of a bead.
These two different results are due to the fact, that whilst the water wets the glass the mercury does not.
Now take a pin which has been well dried; it is a body which water will moisten, but owing to its very smooth surface, not so easily as in the case of glass.
Suppose, then, that by some means or other you can place the pin so gently on the surface of the liquid that the water does not make it wet, you will notice that the water takes on either side of the pin a convex shape, and in this way a sufficient volume of water is displaced to allow the pin to float as if it were a match.
The experiment may, of course, be as easily performed with a needle; nor must it be thought it is confined to pins and needles which are thin, for, with care, you may even succeed with big darning-needles.
It has not yet been shown, however, how to place the pin on the water in such a manner that it is not made even wet.
There are several ways of doing this, some requiring considerable practice.
The following is the simplest.
Float on the surface of the water a cigarette paper; place the pin upon it; leave the paper to sink to the bottom when it has become soaked, and the pin will float without any difficulty, for on either side of the pin the water takes the convex shape before mentioned, thus displacing sufficient water to allow the pin to float.
In order to hide from the spectators the stratagem you have employed, gently remove the paper before showing them the floating pin.