(1) Glue to which bichromate of potash has been added, and which has afterwards been exposed to strong sunlight, becomes insoluble. The proportions are not very well ascertained, but about 1 part of the bichromate, dissolved in water, and added to a solution of 6 parts of solid glue, answers very well. (2) The following is a valuable cement which, if properly applied, will be insoluble even in boiling water: Gelatine, 5 parts; soluble acid chromate of lime, 1. Cover the broken edges with this, press lightly together, and expose to the sunlight; the effect of the latter being to render the compound insoluble. (3) It is said by the British Journal of Photography, that the following recipe gives excellent re-, suits: Take alcohol, 1 pint; sandaraty 1 oz.; mastic, 1 oz.; common white turpentine, 1 oz.; glue and isinglass, sufficient; water, sufficient. Dissolve the two resins - sandarac and mastic - in the spirit, and then add the turpentine to the solution. Make some very strong glue, and add to it a good pinch of isinglass. Now heat the alcoholic varnish until the liquid begins to boil, then very slowly stir in the warm glue.

The amount of the liquid glue to be added is determined by noting the point at which, after thorough mixture, a magma or thin paste is formed, capable of being easily strained through cloth. When required for use, the strained mixture is to be warmed, and applied like ordinary glue to the articles to be united. A strong junction is effected, which is not destroyed by cold water, and only after a comparatively considerable time by hot water or ordinary saline solutions. (4) Glue, 1 part; skimmed milk, 8. Melt and evaporate in a water-bath to the consistence of strong glue. This cement cannot be called waterproof, but it resists the action of water better than common glue. (5) Melt common glue with as little water as possible, add \ of boiled linseed oil, dropping it gently into the glue, which is to be stirred all the time. (6) From the account published by C. Puscher,in Kunst und Gewerbe, of the many experiments which he has made to render cement and lime plaster proof against the effects of the weather, it appears that a cold solution of 1 part green copperas in 3 of water is extremely effective. Cement manufactures are put into the solution for 24 hours, and then, coloured greenish black by the oxidulated iron hydrate which has been formed, dried in the air.

The absorbed solution of copperas has been decomposed in the cement, and the combination of hydrated peroxide of iron formed is stated not only to render the cement denser and harder, but also, as it is not affected by the weather, to impart to it greater resistance. The weight of the cement 4s increased by 10 per cent., without any change in form. Cement plaster is protected against the effects of the weather by repeated applications of the copperas solution. If, after the 4 th application, the cement does not turn a dark greenish-black, it is a sign that the surface has become saturated with the iron combination. After drying, a coating is formed on the cement of an ochre-like colour, which cannot be washed off with water, and which will take water-colours. If cement plaster thus prepared is to be permanently painted with oil colours - which, as is well known, peel off ordinary cement - two applications of 5 per cent, soap water are sufficient to render it waterproof, and, after drying and rubbing with a cloth, as shiny as oil colour, so that one coating of the latter may be saved.

In order to protect cement manufactures prepared with copperas against acids, alkalies, and the influence of the weather, a layer of a heated mixture of equal parts of ordinary paraffin and paraffin oil, or petroleum, is sufficient, which is obtained by immersing the heated cement articles in it for a few minutes. This cheap copperas solution may also be used for old or new lime plaster; old lime plaster must, however, first be freed from loose particles of colour by washing off. It is not advisable to mix the cement and sand at once with the copperas solution, as cement thus prepared cracks after drying. (Builder.) (7) Tar, 1 part; callow, 1; fine brickdust, 1; the latter is warmed over a very gentle fire; the tallow is added, then the brickdust, and the whole is thoroughly mixed. It must be applied while hot. (8) Good grey clay, 4 parts; black oxide of manganese, 6; limestone, reduced to powder by sprinkling it with water, 90; mixed, calcined, and powdered. (9) Manganese iron ore, 15 parts; lime, 85; calcined and powdered. Both (8) and (9) require to be mixed with a little sand for use; thrown into water, they harden rapidly. (10) Fine, clean sand, 1 cwt.; powdered quicklime, 28 lb., bone ash, 14 lb.

Beaten up with water for use. (ll) Quicklime, 5 parts; fresh cheese,6; water, 1. The lime is slaked by sprinkling with the water; thereupon it is' passed through a sieve, and the fresh cheese is added. The latter is prepared by curdling milk with a little vinegar, and removing the whey. The cement thus formed is very strong; but it requires to be applied immediately, as it sets very quickly. (12) Fresh curd, as before, 1 part; quicklime, 1; Roman cement, 3. Used for joining stone, metals, wood, etc. (13) A paste composed of hydraulic lime and soluble glass. (14) 1 glue, 1 black rosin, 1/4 red ochre, mixed with least possible quantity of water. (15) 4 glue, 1 boiled oil by weight, 1 oxide of iron. (16) Mix a handful of quicklime with 4 oz. linseed oil, thoroughly lixiviate the mixture, boil it to a good thickness, and spread it on tin plates in the shade. It will become very hard, but it can be dissolved over a fire, like common glue, and is then fit for use.