A remarkable Experiment, called Prince Rupert’s Drops.
Take up a small quantity of the melted matter of glass with a tube, and let a drop of it fall into a vessel of water. This drop will have a small tail, which, being broken, the whole substance of the drop will burst, with great violence, into a fine powder, and give a little pain to the hand, but do no hurt to it.
It is a remarkable circumstance in this experiment, that the bulb, or body, will bear the stroke of a hammer, without breaking; but when the tail is broken, the above-mentioned effect is produced. If the drop be cooled in the air, the same effect will not take place; and if it be ground away on a stone, nothing extraordinary appears; but if it be put into the receiver of an air-pump, and then broken, the effect will be so violent as to produce light.
How to make Sympathetic Inks of various Kinds.
By sympathetic inks, are meant those kinds of liquors, with which if any characters be written, they will remain invisible, till some method is used to give them a colour.
The first class of these inks consists of such as become visible by passing another liquor over them, or by exposing them to the vapour of that liquor.
The second, of those which do not appear so long as they are kept close, but soon become visible on being exposed to the air.
The third, of such as become apparent by strewing or sifting some very fine powder over them.
The fourth, of those which do not become visible till they are exposed to the fire, or heated.
The fifth, like the fourth, of such as appear by heat, but disappear again when the paper becomes cold, or has had a sufficient time to imbibe the moisture of the air.