(1) Plaster-of-Paris, baked and ground, acquires great hardness and solidity when left for twenty-four hours, in contact with a solution of alum, and when, after drying in the air, it is submitted to a second baking. (2) Still better results are obtained by employing an aqueous solution containing 1/20 of borate and 1/20 of cream of tartar; the plaster, baked and in fragments, is plunged into this solution until it is saturated; then it is calcined, and pulverized. (3) A mixture of silicate of potash, 100 parts; carbonate of potash, 27 parts; and water, 500 parts, may also be used.

Plumbers'

Black rosin, 1 part; brickdust, 2 parts. The brickdust should be finely powdered, thoroughly dried and added to the rosin when the latter is in a melted state.

Porcelain

(1) Add plaster-of-Paris to a strong solution of alum till the mixture is of the consistency of cream. It sets readily, and is said to unite glass, metal, porcelain, etc, quite firmly. It is probably suited for cases in which large rather than small surfaces are to be united. (2) Milk is coagulated by means of acetic acid, and the caseine thus formed is well washed in water, and then dissolved in a cold saturated solution of borax; a clear solution is thus obtained which is superior to gum arabic in adhesive power, and is colourless. For porcelain, this liquid is mixed with finely powdered quicklime, and the resulting cement is quickly brushed over the fractured surfaces, which are then bound together; the ware is then dried at a gentle heat. (Dingier's Poly tech. Jl.)

(3) To resist heat. It'is made of Stourbridge clay mixed with a little tow or asbestos to increase its coherence. It should be well beaten before application; the glass or china should be first rubbed over with a little of the cement mixed with water, taking care to press the two edges of the glass or china together. This cement will bear a very strong heat. (4) Take isinglass 1/2 oz., proof spirit sufficient to dissolve it; to every 2 dr. add finely powdered mastic and finely powdered gum ammoniacum - of each 10 gr. Stir till dissolved. In using, heat the edges to be joined, and let the cement get thoroughly dry before using the article. The gums should be added to solution of isinglass when hot. (5) Calcine oyster-shells; pound and sift them through a sieve, and grind them on a flat smooth stone with a muller, till reduced to the finest powder; then take white of egg, and form the whole into a paste. Join the pieces of glass or china and press together 6 or 7 minutes. This cement will stand both heat and water, and will never yield, if properly done. (6) Plaster-of-Paris and gum.

For very small articles this cement answers very well, but must not be too thick when well mixed.

Putty

(1) Good putty, for general purposes, is composed of raw linseed oil and whiting thoroughly incorporated, and can be made equally well by hand or machinery. The whiting should be dry. Linseed oil foots or "bottoms " is only used on the score of economy - that is, to use up a material that would be objectionable in paint. In the shop, putty is made by hand in winter for summer use, on the putty bench. Dry sifted whiting is mixed with as much oil as will enable it to be well beaten with a mallet, and well kneaded into lumps about the size of a 4 lb. loaf, which are then ranged on a shelf, and left for a week, by which time it will be found they have become very soft. More' whiting is now worked in, after which pack in casks, pressing it well down. This putty improves by keeping a few months - that is, gets tougher and more homogeneous. (2) A very strong putty is made of boiled oil and whiting for exposed situations, as sky-lights, but is not adapted for keeping - it gets too hard. (3) Putty for good inside work is improved by adding white lead. (4) Another putty which requires to be made as wanted (as it gets hard almost immediately) is composed of red lead in powder mixed with boiled oil and turpentine varnish, and is used for fronts of houses or any place requiring a hard putty. (5) Some manufacturers prepare an oil for the purpose by melting 20 lb. rosin and mixing it with 90 lb. linseed oil, the rosin being used for economy sake. (6) For some purposes a drying-oil may be used with the whiting: this is made by mixing 1 gal. linseed oil, 12 oz. litharge, 1 oz. sugar of lead, 1 oz. white vitriol, simmer for some time, allow to cool, and when settled draw it off. (7) French putty.

Ruban prepares this substance by boiling linseed oil (7 parts) with brown umber (4 parts) for two hours; 5 1/2 parts of chalk and 11 of white lead are then added, and the whole well mixed. This putty is very durable, and adheres well to wood, even though not previously painted.