There are several kinds of so-called glass cement, said to be excellent for uniting broken glass, china, etc. (1) Pulverized glass, 10 parts; powdered fluorspar, 20; soluble silicate of soda, 60. Both glass and fluorspar must be in the finest possible condition, which is best done by shaking each, in fine powder, with water, allowing the coarser particles to deposit, and then to pour off the remainder, which holds the finest particles in suspension. The mixture must be made very rapidly, by quick stirring, and when thoroughly mixed must be at once applied. This is. said to yield an excellent cement. (2) Red lead, 3 parts; fine white sand, 2; crystallized boracic acid, 3. These ingredients are mixed and fused, and then reduced to a very fine powder, which may be made into a paste with a dilute solution of soluble glass, and applied as an ordinary cement, or it may be mixed with very weak gum water (just enough gum to make it adhesive); after it has been applied, the articles are exposed to a heat sufficient to melt the fusible glass, which is formed by the union of the three ingredients. (3) 2 parts of isinglass are soaked in distilled water until soft; the water is then poured off, and as much alcohol added as will cover the isinglass, and the whole heated until solution takes place; 1 part of mastic is then dissolved in 3 of alcohol, and the two solutions mixed; 1 part of gum ammoniac is then added, the whole well shaken and evaporated in the water-bath until a thick glue-like mass is produced, becoming a stiff jelly on cooling.

When required for use, the vessel containing the cement is placed in hot water or in an oven, and the cement applied by means of a brush. It hardens in 24 hours. - (Dingier's Polytech. J I.) (4) Melt 5 or 6 bits of gum mastia as large as peas in the smallest quantity of alcohol; mix with 2 oz. of a solution of isinglass (made by dissolving isinglass in boiling brandy to saturation), having previously mixed the isinglass solution with 2 or 3 bits of galbanum or gum ammoniac; keep in a well-corked bottle, and gently heat before using. (5) With a small camel-hair brush, rub the edges with a little carriage oil-varnish, and, if neatly put together, the fracture will hardly be perceptible, and, when thoroughly dry, will stand both fire and water. (6) Dissolve fine glue in strong acetic acid to form a thin paste. (7) Canada balsam or clear glue (gelatine), to which has been added a small quantity of bichromate of potash. The latter soon loses its yellow tint, and becomes unaffected by damp when exposed to daylight. (8) 2 parts of common black pitch and 1 part guttapercha, melted and worked together till mixed; or 2 parts shellac, 1 part Venice turpentine, melted together. These would want using warm.

They are both impervious to weather influences. (9) See Chrome.