Below are some reliable recipes for waterproof cements.

(1) Rub magnesia with a little concentrated solution of magnesium chloride; apply this cement at once. It is soluble in acids, but not appreciably so in water.

(2) Dissolve by the aid of heat loz. of gum sandarach and loz. of gum mastic in lpt. of alcohol, and add 1 pt. of turpentine and lqt. of strong vellum glue at boiling point.

(3) Canada balsam is a good transparent cement.

(4) Melt -I parts of glue with a small quantity of water and 1 part of Venice turpentine.

(5) Soak ti parts of glue in water, and, when soft, pour off the excess; the softened material is melted by heat, and 1 part of bichromate of potash, dissolved in the least quantity of water, is added. This cement should be kept in the dark till required, then melted down by heat and applied. On exposing the cemented parts to light the material becomes insoluble.

(6) Make astrong solution of gum arabic, and stir plaster-of-Paris in it, to make a thick paste. Apply v ith a brush. This takes longer to set than ordinary glue. The wood or other substance must be heated before applying.

(7) Boil lib. of common glue in 2 qt. of skimmed milk.

(8) Indiarubber solution is a good water proof cement. To make it, cutloz. of pure indiarubber into line threads with a sharp knife,place in a dry. wide-mouthed bottle, and add loz. To 6 OZ. of solvent; cork the bottle loosely and allow to stand in a warm place (away from any flame) until the rubber has entirely dissolved. If the material is too thick for use it may be diluted by adding a little more of the solvent and allowing to stand until it is absorbed. The solvent may be and of the following: Coal-tar naphtha, chloroform, oil of turpentine, eth:r, petroleum naphtha, bisulphide of enroon,and benzine.

(9) Pour 1 pt. of vinegar into 1 pf. of milk: clear it of lumps aud let it settle, then mix the whole well together. Sift in quicklime and stir ho thick paste.

(10) Make glue with linseed oil instead of with water, boiling well in t he ordinary way.

(11) Marine glue is quite waterproof and can be recommended. The true marine glue is a combination of shellac and a solution of caoutchouc in benzole. To make it, dissolve 1 part of indiarubber in 12 parts of solvent see above and add 20 parts of powdered sheila,-, heating mixture cautiously over the fire. Another recipe is: 1 part of caoutchouc or indiarubber is dissolved in 12 parts of benzine or naphtha with the aid of gentle heat. In from ten to fourteen days, when the solution is complete, 2 parts of asphalt are melted in an iron vessel, and the caoutchouc solution is poured in very slowly, in a fine stream and under continued heating, until the mass has become homogeneous and nearly all of the solvent lias been driven off. It is then poured out and cast into greased tin moulds to harden into dark brown or black cakes. This cement requires considerable heat to melt it, and to prevent it from being burned it is best to heat a piece of it in a water-bath until the cake softens and begins to be liquid. It is then carefully wiped dry and heated over a naked flame, under constant stirring, up to about 300Falir. The edges of the article to be mended should, if possible, be heated to at least 212' Fahr., so as to permit the cement to be applied at leisure and with care.

The thinner the cement is applied, the better it binds.

(12) A good waterproof cement, which is really a marine glue, is made by melting together llb. of guttapercha, 2oz. of linseed oil, 2oz. of pitch, loz. of shellac, and loz. of indiarubber. This cement should be used as hot as possible.