(1) One says, that after an experience of 15 years he has found nothing to equal the following: Common glue and isinglass, equal parts, soaked for 10 hours in just enough water to cover them. Bring gradually to a boiling heat, and add pure tannin until the whole becomes ropy, or appears like the white of eggs. Buff off the surfaces to be joined, apply this cement warm, and clamp firmly. (2) Mix 10 parts bisulphide of carbon with 1 of oil of turpentine, and then add enough guttapercha to make a tough thickly-flowing liquid. One essential pre-requisite to a thorough union of the parts consists in freedom of the surfaces to be joined from grease. This may be attained by laying a cloth upon them and applying a hot iron for a time. The cement is then applied to both pieces, the surfaces brought into contact, and pressure applied until the joint is dry. (3) Another leather cement is made of guttapercha dissolved in bisulphide of carbon, the mixture being about the thickness of syrup; the parts to be cemented must be well coated, so as to fill the pores of the leather; then heat the cement and join the ends, hammering the parts until the cement is cold. (4) To cement leather to metal: Wash the metal with hot gelatine; steep the leather in an infusion of nut galls (hot), and bring the two together. (5) 1 lb. guttapercha, 4 oz. indiarubber, 2 oz. pitch, 1 oz. shellac, 2 oz. linseed oil; melted together; it hardens by keeping, and needs remelting for use. (6) Leather to metal: (a) melt together equal parts asphalt and guttapercha, and apply hot under a press. (6) F. Sieburger recommends the following process by Fuchs. Digest 1 part crushed nutgalls with 8 distilled water for 6 hours, and strain; macerate glue with its own weight of water for 24 hours, and dissolve; spread the warm infusion of the galls on the leather, and the glue on the roughened metallic surface; apply the prepared surfaces together, and dry gently; the leather then adheres so firmly to the metal that it cannot be removed without tearing. (Polyt. No-tizblatt.) (7) Leather to Pasteboard. Strong glue, 50 parts, is dissolved with a little turpentine in a sufficiency of water, over a gentle fire; to the mixture is added a thick paste made with 100 parts of starch.

It is applied cold, and dries rapidly.

Marble Cement

(1) Keene's. Baked gypsum or plaster-of-Paris, steeped in a saturated solution of alum, and then recalcined and reduced to powder. For use it is mixed up with water as ordinary plaster-of-Paris. This preparation forms a stucco, rather than a cement. It takes a high polish, and when coloured is very beautiful, but does not unite pieces as strongly as: (2) An excellent cement for mending marble or any kind of stone, is made by mixing 20 parts of litharge and 1 of freshly burned lime in fine dry powder. This is made into a putty by linseed oil. It sets in a few hours, having the appearance of light stone. (3) Resin, 8 parts; wax, 1; plaster-of-Paris, 4; mix by fusion. The pieces to be joined must be made hot. (4) Lac coloured to imitate the marble; may be mixed with marble dust passed through a silken sieve. (5) W. F. Reid gives the following details for it. Begin with the raw gypsum in lumps of moderate size, burning them at the usual temperature (below red heat). The solution of alum should contain 1 part of this salt in 10 of water. There is no difficulty in dissolving this quantity if the water be previously heated and the alum coarsely pulverized.

By immersing the lumps of burnt gypsum in this solution while they are still warm, and leaving them in it for about 15 minutes, they will become thoroughly saturated with the liquid. They should then be allowed to drain and again burnt, but this time at a red heat. Gypsum which has been treated in this way forms, when pulverized, a slow-setting cement which ultimately attains great nardness, and has frequently been used for making paving tiles, especially in Italy. (6) Into a solution of chloride of zinc, sp. gr. 1.490 to 1.652, is introduced 3 per cent, of borax or sal ammoniac; when this is dissolved, oxide of zinc, which has been subjected to a red heat, is added,.till the mass attains the desired consistence. This cement becomes as hard as marble, and may be used for moulding. (7) 12 parts Portland cement, 6 slaked lime, 6 fine sand; 1 infusorial earth, and mix into a thick paste with silicate of soda. The object to be cemented need not be warmed. The cement sets in 24 hours, and the fracture can then hardly be detected.

The cemented portions are harder than the rest, and the fracture cannot by any chance be reopened. (Polytech. Centralblatt.)