Endless Amusement / A Collection of Nearly 400 Entertaining Experiments in Various Branches of Science; Including Acoustics, Electricity, Magnetism, Arithmetic, Hydraulics, Mechanics, Chemistry, Hydrostatics, Optics; Wonders of the Air-Pump; All the Popular Tricks and Changes of the Cards, &c., &c. to Which is Added, a Complete System of Pyrotechny; Or, the Art of Making Fire-works.

by Unknown

Dissolve zaffre, in powder, in aqua regia, for twenty-four hours. Pour the liquor off, and the same quantity of common water, and keep it in a bottle well corked.

This ink will not be visible till exposed to the fire or the sun; and will again be invisible when it becomes cold.

Invisible Violet Ink.

Express the juice of lemons, and keep it in a bottle well corked. Use the violet infusion to make the writing visible.

Invisible Grey Ink.

Mix alum with lemon-juice. The letters written with this ink will be invisible till dipped in water.

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We now present our readers with a variety of amusing experiments, which may be performed by the foregoing inks; and they will, probably, suggest others equally amusing and useful.

A Secret Correspondence by means of Invisible Ink.

A person wishing to carry on a correspondence with another, and who is fearful of having his letter opened, or intercepted, can adopt the following plan: