A small phial may be charged by giving the sparks from the knobbed wire of the tube to that of the phial; but the phial will be charged negatively, whereas the tube is charged positively.
To fire the electrical Cannon by inflammable Air.
This instrument consists of a metallic barrel, made in the shape of a common cannon,—a glass tube is cemented into the top of the barrel, in the place of a touch-hole, and through this tube a wire passes, which is bent so as to come within an eighth of an inch of the inner surface of the cannon,—on the outer end of this wire, a ball is fixed, which serves to receive a spark from a charged jar, or from the prime-conductor.
The inflammable air with which this cannon is to be fired, may be prepared in a common porter bottle, by mixing a handful of iron filings with two wine-glassfuls of water, and an ounce of sulphuric acid, commonly called oil of vitriol. The air when thus made should be kept in a bottle closely stopped.
To use the instrument, have ready a cork, fitted to the mouth of the cannon,—uncork the bottle containing the air, and immediately apply the cannon to the mouth of the bottle; a sufficient quantity of the gas will rise into the cannon, in the course of a few seconds, when both the cannon and bottle must be corked. Now, if the knob of the wire passing through the tube be applied to the prime-conductor, so that a spark may pass through it to the inner surface of the cannon, the gas will be inflamed with a loud report, and the cork will be forced out with considerable violence.
Curious Figures made upon Glass, Paper, and other Substances, by means of Electricity.
Professor Lichtenburg first observed some curious figures made with pulverized rosin, on a large electrophorus; but since this original discovery, a variety of other methods have been contrived, for making them upon glass, paper, resinous substances and many others. The ingenious electrician may derive considerable information from these figures; their various appearances, in many instances, showing him the direction and quality of the electric fluid.
The principal method of making these impressions is to electrify a perfect or imperfect electric, and then to throw certain powders upon the electrified substance, which will be arranged in different forms. The most convenient method of projecting these powders is to put them into a small bottle of India-rubber, and then fasten a tube of glass or metal to the neck of the bottle; the orifice of this tube must be covered with a piece of flannel when used.
As to the nature of the powders, almost every substance which can be pulverized will do.—Thus chalk, rosin, sulphur, rose-pink, dragon’s blood, gum-arabic, lake, and evaporated decoctions of colouring woods, may be used with advantage, either singly or mixed.
Take a clean pane of glass, fourteen or fifteen inches square, and after drying it thoroughly, hold it by one corner, and pass over its surface the knob of a jar, moderately charged with positive electricity—then, keeping it suspended, project upon it, by means of the bottle above described, a mixed powder of dragon’s blood and gum-arabic, in equal parts. If you examine the glass, you will find that the two powders will be separated upon it, the red powder of dragon’s blood falling on certain places, and the white powder of gum-arabic falling upon certain other places, so as to form a track upon the parts which were touched with the charged jar, consisting of two colours disposed in a thousand different ways.