Prometheans consist of small rolls of waxed paper, in one end of which is a minute quantity of vitriol, in a glass bulb, sealed up, and surrounded with chlorate of potass: when the end thus prepared is pressed so as to break the bulb, the vitriol comes in contact with the composition, and produces light instantly.
For cigar-smokers, Prometheans are made with touch-paper; this ignites from the composition, and glows without flame, like a slow match; and as the wind will not extinguish it, a dry cigar may be readily lighted at it.
Lucifers and Prometheans must be used with caution, and should never be carelessly left about: by letting them fall upon a sanded floor, and being accidentally trod upon, they may take fire, and thus do great mischief.
TO COLOUR THE FLAME OF A CANDLE.
Take a piece of packthread, or cotton thread, boil it in clean water to free it from saline particles, and dry it; wet one end, and take upon it a little of either of the salts hereafter named, in fine powder, or strong solution. Then dip the wetted end of the thread into the cup of a burning wax candle, and apply it to the exterior of the flame, not quite touching the luminous part, but so as to be immersed in the cone of invisible but intensely heated air which envelopes it. Immediately, an irregular sputtering combustion of the wax on the thread will take place, and the invisible cone of heat will be rendered luminous, with a peculiarly coloured light, according to the salt employed.
Thus, common salt will give a bright yellow; muriate of potass will give a beautiful pale violet; muriate of lime will give a brick red; muriate of strontia will give a magnificent crimson; muriate of lithia will give a red; muriate of baryta will give a fine pale apple green; muriate of copper will give a beautiful bluish green; and green copperas will give a white light.
TO DIVIDE THE FLAME OF A CANDLE.
Provide about a foot square of brass or iron wire gauze, of the fineness of thirty meshes to the square inch: lower the gauze upon the flame of a wax candle, which will not rise through the meshes, but in its place will be the inflammable smoke of the flame; apply to this a piece of lighted paper, and it will be kindled, and the candle will burn with flame above and beneath the gauze. In this case, the gauze so cools the flame, as to extinguish it; and upon this principle is constructed the Davy Safety Lamp, in which the light is surrounded with wire-gauze.