Jewellers'.—(a) Gum mastic, five or six pieces as large as peas, is dissolved in as much spirits of wine as will suffice to render it liquid ; ih a separate vessel, is dissolved, in rum or other spirit, as much isinglass, previously softened in water and strained dry, as will fill a 2-oz. phial with very strong glue, adding a little gum galbanum or ammoniacum, which must be rubbed or ground till it is dissolved. The whole is then mixed, under the influence of sufficient heat. It is kept in a closely stoppered bottle, which is placed in hot water when the cement is to be withdrawn for use. It will effectually unite most substances, even glass to polished steel, and is principally used for joining broken pieces of china and glass. (b) The following is another mode of preparing the same ingredients :—Isinglass, 1 oz., in distilled water, 6 oz., boiled down together to 3 oz.; to this is added strong spirits of wine, oz. ; the mixture is boiled for a minute or two, and strained ; while still hot, it receives, first, milky emulsion of gum ammonia.cum, 4- oz. ; then, alcoholic solution of resin mastic, 5 drachms. (c) Shellac, melted and run into sticks as large as quills. Used for joining glass, earthenware, &c. ; the edges are heated sufficiently to melt the cement, which is then applied, and the joint is made while the heat lasts. (d) Tears of gum mastic employed in the same way. (c) Shellac, 2 parts, Venice turpentine, 1 part ; fused together and formed into sticks. Used as the preceding.
Labels, for.—Gelatine, 25 grammes; sugar-candy, 50 grammes ; gum arable, 12 grammes; water, 100 grammes. After having macerated the gelatine in water, overnight, it is mixed with the sugar and gum arable in a porcelain vessel, and heated over a spirit lamp, with constant agitation. Ebullition must be continued till the mass becomes quite fluid. The labels are coated with the liquid, and left to dry ; on moistening the coated surface, they will adhere strongly to glass and wood.
Lapidaries'.—(a) Rosin, 1 lb., is melted, and to it is added dry plaster of Paris, 4 oz. Makes a very strong cement for rough purposes. (b) Rosin, tempered with beeswax and a little tallow, and hardeacd with whiting and red ochre, or Spanish brown.
Leather, for.—(a) Guttaperoha dissolved in bisnlphide of carbon, to form a mass of treacly con sistence. This forms a good cement for splicing leather. The parts to be joined must be thinned down ; a small quantity of the cement is then poured on each end, and spread so as to thoroughly fill all the pores of the leather ; the parts are warmed over a fire for a few moments, applied quickly, and hammered wall together. To preserve this cement, it should be tightly corked in a bottle, and kept in a 000l place. (b) Gnttapercha, 1 lb. ; indiarubber, 4 oz. ; pitch, 2 oz. ; shellac, 1 oz. ; linseed oil, 2 oz.; melted together. It hardens by keeping, and needs remeltiog before application.
Leather and Metal, for.—A cement for joining leather and metal may be made by melting together equal parts of asphalt and guttapercha, and applying the mass hot under a press.
Marble, for.—The following curious composition is recommended for cementing pieces of marble, porcelain, or glass. About 100 snails are caught, and kept fasting for two months or less, taking care to clean them occasionally. They are then sprinkled with a little water to make them quit
their shells, the excess of water being decanted as soon as they have come out. Thereupon is added a pinch of culinary salt, then the juice of four or five lemons, and a drop of vinegar, and the whole is beaten up together. The snails give off their mucus, which iB collected, and intimately mixed, in a mortar, with 8 grammes of gum tragacanth, then 40 or 50 grammes of garlic juice, and 200 grammes of alcohol. The cement keeps quite opaque, and may be coloured to suit the materials to be joined. It is applied cold ; but the joint must subsequently be exposed to the sun or a fire.
" Marine Glue."—(a) Finely shredded indiarubber, 1 part ; coal-tar (or mineral) naphtha, 12 parts ; digested in a covered vessel with heat and agitation ; when the solution is complete, 20 parts of powdered shellac are added ; the heating and stirring is continued till perfect lique faction has taken place ; the fused mass, while still hot, is poured out on slabs of polished metal or stone, so as to form thin sheets. For use, it is heated to its melting-point, 120° to 121° (248° to 250° F.), in an iron vessel, and applied, in a liquid state, with a brush. It is used by shipbuilders and others. (b) Indiarubber, 15 to 20 grains ; chloroform, 2 1 oz. ; dissolved ; powdered mastic, / oz., is added. The cement must be kept well corked, and in a cool place, to prevent loss by evaporation. (c) Finely divided indiarubber, 1 part, is dissolved in naphtha oil, or crude naphtha, 40 parts. The solution is not completed in less than ten or twelve days, and, in order to facilitate it, the mixture should be repeatedly agitated. To it, is then added gum lac, in the proportion of 2 parts by weight of lac to 1 part of solution. The compound is then placed in an iron vessel over a Ere, and constantly thinned till it becomes homogeneous. It is then poured on a cold surface, such as a slab of marble or a flag-stone, and left till cool, when it is broken up and put by for use. The indiarubber is somethnes omitted, in which case, the proportions will be 1 part of naphtha and 2 parts of lac. When required for use, the cement is heated at a temperature not exceeding 100° to 110° (212° to 230° F.), in a thick vessel of copper or cast iron, and is brushed in thin and even layers on the surface to be joined ; these are then brought into close contact, and strongly pressed. If the surfaces are so wide that the cement becomes cool before the operation is finished, it is well to pass a hot iron—say at about 60° (140° F.)—over it. It is valuable, not only for repairing broken wood, brit also for cementing the moulds used in foundries, for caulking ships, for joining blocks of marble or granite, and for uniting wood and iron. It can be made as hard as desired, by increasing the proportion of lac. With the addition of bichloride of mercury dissolved in wood spirit, this cement might, with economy, replace the copper sheathing of ships. Wood, iron, plaster, and brick, to which it is applied, assume a varnished appearance ; timber is rendered free from the attacks of insects and from liability to rot, and iron is preserved from rust.