2369. To Break a Glass Bottle or Jar Across its Circumference

2369.    To Break a Glass Bottle or Jar Across its Circumference. Place the bottle in a vessel of water, to the height where it is designed to break-it; also fill the bottle to the same level. Now pour coal oil inside and out on the water; cut a ring of paper, fitting the bottle. Saturate with alcohol or benzine, so that it touches the oil. Pour, also, some inside the bottle. Set on fire; the cold water prevents the glass from heating below its surface, while the expansion caused by the heat will break the vessel on the water line.

2370. Glass of Antimony

2370.    Glass of Antimony. Roast powdered antimony in a shallow vessel over a gentle fire, until it turns whitish gray, and ceases to emit fumes at a red heat; then heat it in a crucible until it fuses into a brownish red glass. If calcined too much, a little more antimony must be added to make it run well.

2371. Writing: on Glass

2371.    Writing: on Glass. This may be done with a piece of French chalk, or crayons prepared for the purpose; or even with a common pen held nearly perpendicular. India ink, or, when the article will be exposed to damp, shellac varnish, thickened with a little vermilion or lampblack, for red or black color, is best adapted for the purpose. Common ink is not sufficiently opaque.

2372. To Imitate Ground Glass

2372.    To Imitate Ground Glass. A ready way of imitating ground glass is to dissolve Epsom salts in beer, and apply with a brush. As it dries it crystallizes.

2373. To Make Prince Rupert's Drops

2373. To Make Prince Rupert's Drops. Prince Rupert's drops are made by letting drops of melted glass fall into cold water ; the drops assume by that means an oval form, with a tail or neck resembling a retort. They possess this singular property, that if a small portion of the tail is broken off, the whole bursts into powder, with an explosion, and a considerable shock is communicated to the hand that grasps it.

2374. To Etch on Glass

2374. To Etch on Glass. Etching with hydrofluoric acid on plate glass is practiced now to a very considerable extent, the French manufacturers especially producing splendid ornamental effects by this process. The drawings to be imitated or etched on the glass are first made on stone or plate and then printed on unsized paper with an ink consisting principally of a solution of asphaltum in oil of turpentine made with the aid of heat, to which some substance is added which shows a more or less crystalline structure on cooling, as stearic acid, spermaceti, naphthaline, par-afiine. This mixture is strained and rapidly cooled with constant stirring; it is the only kind of coating which thoroughly resists the action of the corrosive acid. The printed paper is laid flat with the blank side on water, to which from 10 to 25 per cent, of muriatic acid has been added, and as soon as the lines show signs of softening the negative printing is transferred to the glass by a slight pressure; when the paper is removed, the picture will adhere to the glass, and this is afterwards exposed to the fluoric vapors in leaden troughs.