Plaster-of-Paris Cements. — There is a class of cements of which plaster of Paris or gypsum is the basis, in which the hardening is due to the union of the plaster with water, but they require the addition of various other ingredients to give them ad hesive properties. For the use of gum arabic with plaster of Paris, see above under " Gum Arabic." Or mix into a paste plaster of Paris and white of egg. Used for mending broken glass or china.
Or substitute oyster shells burnt in a stove or open fire and pulverized to powder.
Or melt 2 ounces of rosin and stir in 1 ounce of plaster of Paris.
Or melt 1 ounce each of rosin and beeswax, and stir in 1 ounce of plas ter of Paris.
Or melt 8 ounces of rosin and 1 ounce of beeswax, and stir in 4 ounces of plaster of Paris. Apply these cements to alabaster, broken plaster casts, marble, porphyry, and similar materials.
Or mix equal quantities of pulver ized alum and plaster of Paris, and add sufficient water to make a thin paste.
Or mix plaster of Paris with a saturated solution of alum, and bake in an iron vessel in an oven until dry. Pulverize this mixture to a fine pow der, and when wanted mix to the con sistency of paste with a solution of 1 ounce of alum in 12 ounces of water. This cement is suitable for attaching glass to metal.
Or boil 3 ounces of rosin, 1 ounce of caustic soda, and 5 ounces of water. Stir in 4 ounces of plaster of Paris. This cement is especially recommend ed for fitting the brass work to kero sene-oil lamps, as it is not affected by petroleum products. It is a poor con ductor of heat.
Or melt alum and use for the same purpose while melted. Kerosene does not penetrate this.
Or mix 1 pint each (dry measure) of litharge, plaster of Paris, and fine, dry white sand, and pint of finely powdered rosin. Make into et stiff paste with boiled linseed oil and ap ply within 19 hours after mixing. This cement hardens under water and may be used for tanks, aquaria, water tanks for animals, and all similar pur poses, as it contains nothing which is injurious to animals. Allow this cement to set 3 or 4 hours before wetting it.
Ironware Cements.—Mix 5 parts of powdered fire clay and 1 part of fine iron filings with enough boiled linseed oil to make a paste. This is not suit able for iron exposed to red heat, as a stove.
Or mix equal quantities of sifted wood ashes, powdered fire clay, and common salt. Moisten to a paste with
water and fill cracks in stoves and other ironware.
Or use equal quantities of sifted wood ashes and common salt mixed to a paste with water, but without the clay. Let the mixture set before heat ing.
Or melt 2 ounces of sulphur in an iron pan, and stir in 1 ounce of fine black lead. Pour on 0, stone or an iron plate to cool. When cold, break in small pieces. An iron pot can be mended by soldering with this sub stance, using a hot soldering iron.
Or, to mend a small hole, insert a copper rivet or one of the brass brads used to fasten documents together, hammer smoothly on both sides, and cover with this cement.
Or melt 5 ounces of brimstone, and stir in 2 ounces of black lead and 2 ounces of cast-iron filings. Apply to leaks in cast-iron tanks, cisterns, etc., by drying the leak, heating it by means of red-hot iron, and pouring the melted cement from a ladle over the leak.
Or mix 4 ounces of barytes and 4 ounces of fine fire clay to a paste with soluble glass or a saturated solution of borax.
Or mix equal quantities of clay and powdered glass with soluble glass or a saturated solution of borax, and apply with a brush to cracks in iron stoves or furnaces.
Or mix 2 pounds of cast-iron filings with 1 ounce of sal ammoniac and I ounce of flowers of sulphur. Stir in enough water to form a paste. Mix this preparation in an iron vessel, as it becomes very hot from chemical ac tion. Prepare when wanted and ap ply immediately, as it soon sets very hard.
Or mix 8 ounces of steel filings, 11 ounces of sal ammoniac, and 1 ounce of flowers of sulphur. Preserve this mixture in dry form until wanted. When required, add 1 ounce of it to 15 ounces of iron filings, and mix with water acidulated with sulphuric acid to form a paste. Apply this cement to the joints of iron pipe and for similar purposes. Clean surfaces to be cemented with nitric or strong sul phuric acid. Use this cement for all iron and steel work.
Or mix 10 ounces of powdered fire clay, 4 ounces of fresh iron filings free from rust, 2 ounces of peroxide of manganese, 1 ounce of sea salt, and 1 ounce of borax. Powder finely, mix to a paste with water, and apply im mediately. Gradually bring the parts to a, white heat. This cement is both fireproof and waterproof.