Bore a hole through a piece of coke, and suspend it by a string from a stick, placed across a hot solution of alum; it will float; but, as it becomes loaded with crystals, it will sink in the solution according to the length of the string. Gas-coke has mostly a smooth, shining, and almost metallic surface, which the crystals will avoid, while they will cling only to the most irregular and porous parts. If powdered tumeric be added to the hot solution of alum, the crystals will be of a bright yellow; litmus will cause them to be of a bright red; logwood will yield purple; and common writing ink, black; and the more muddy the solution, the finer will be the crystals. To keep coloured alumn crystals from breaking, or losing their colour, place them under a glass shade with a saucer of water; this will preserve the atmosphere moist, and prevent the crystals getting too dry. If crystals be formed on wire, they will be liable to break off, from the expansion and contraction of the wire by changes of temperature. TO CRYSTALLIZE CAMPHOR. Dissolve camphor in spirit of wine, moderately heated, until the spirit will not dissolve any more; pour some of the solution into a cold glass, and the camphor will instantly crystallize in beautiful tree-like forms, such as we see in the show-glasses of camphor in druggists’ windows. CRYSTALLIZED TIN. Mix half an ounce of nitric acid, six drams of muriatic acid, and two ounces of water; pour the mixture upon a piece of tin plate previously made hot, and, after washing it in the mixture, it will bear a beautiful crystalline surface, in feathery forms. This is the celebrated _moirée metallique_, and, when varnished, is made into ornamental boxes, &c. The figures will vary according to the degree of heat previously given to the metal. CRYSTALS IN HARD WATER. Hold in a wine-glass of hard water, a crystal of oxalic acid, and white threads will instantly descend through the liquid, suspended from the crystal. VARIETIES OF CRYSTALS. Make distinct solutions of common salt, nitre, and alum; set them in three saucers in any warm place, and let part of the water dry away or evaporate; then remove them to a warm room. The particles of the salts in each saucer will begin to attract each other, and form crystals, but not all of the same figure: the common salt will yield crystals with six square and equal faces, or sides; the nitre, six-sided crystals; and the alum, eight-sided crystals; and if these crystals be dissolved over and over again, they will always appear in the same forms. HEAT FROM CRYSTALLIZATION. Make a strong solution of Epsom salts in hot water, and while warm, bottle it, cork it closely, and it will remain liquid: draw out the cork, when the salts will immediately crystallize, and in the process, the remaining liquid and the bottle will become very warm. SPLENDID SUBLIMATION.