KNOT TABLE.

The minutes and seconds of time in which a vessel passes over the measured knot being known, look for the corresponding number in this table, which will be the rate of the vessel in knots per hour.

CEMENTS

Shell-lac Cement, or Liquid Glue. -Fine orange shell-lac, bruised, 4 oz.; highly rectified spirit, 3 oz. Digest in a warm place, frequently shaking, till the shell-lac is dissolved. Rectified wood naphtha may be substituted for spirit of wine, where the smell is not objectionable. This is a most useful cement for joining almost any

material.

Shell-lac Cement, without Spirit.Boil 1 oz. of borax in 16 oz. water; add 2 oz. powdered shell-lac, and boil in a covered vessel till the lac is dissolved This is cheaper than the above, and for Both are useful in fixing paper many purposes, answers very well. labels to tin, and to glass when exposed to damp.

Keller's Armenian Cement, for Glass, China, &c.-Soak 2 dr. of cut isinglass in 2 oz. of water for 24 hours; boil to 1 oz.; add 1 oz. of spirit of wine, and strain through linen. Mix this, while hot, with a solution of 1 dr. of mastic in 1 oz. of rectified spirit, and triturate with dr. powdered gum ammoniac, till perfectly homogeneous.

6 oz. ;

Dr. Ure's Diamond Cement.-Isinglass, 1 oz.; distilled water, boil to 3 oz., and add 14 oz. of rectified spirit. Boil for a minute or two, strain, and add, while hot, first, oz. of a milky emulsion of ammoniac, and then 5 dr. of tincture of mastic.

Hoenle's Cement, for Glass or Earthenware.—Shell-lac, 2 parts; Venice turpentine, I part. Fuse together, and form into sticks.

Cheese Cement, for Earthenware, &c-Mix together white of egg, beaten to a froth, quick-lime, and grated cheese. Beat them to a paste, which forms an excellent cement.

Curd Cement.-Add pint of vinegar topint of skimmed milk. Mix the curd with the whites of 5 eggs well beaten, and sufficient powdered quick-lime to form a paste. It resists water, and a moderate degree of heat.

Cement for joining Spar and Marble Ornaments, &c.-Melt together 8 parts of resin, 1 of wax, and stir in 4 parts, or as much as may be required, of Paris plaster. The pieces to be made hot.

Hensler's Cement.-Grind 3 parts of litharge, 2 of recently burnt lime, and 1 of white bole, with linseed oil varnish. This is a very tenacious cement, but it takes considerable time to dry.

Singer's Cement, for Electrical Machines and Galvanic Troughs.— Melt together 5 lbs. of resin, and 1 lb. of beeswax, and stir in 1 lb of red ochre (highly dried, and still warm), and 4 oz. of Paris plaster, continuing the heat a little above 212°, and stirring constantly till all frothing ceases. Or (for troughs), resin, 6 lbs; dried red ochre, 1 lb.; calcined plaster of Paris, lb. ; linseed oil, 1 lb.

Composition for welding Cast Steel. Take of borax, 10 parts, sal ammoniac, 1 part; grind or pound them roughly together; then fuse them in a metal pot over a clear fire, taking care to continue the heat until all spume has disappeared from the surface. When the liquid appears clear, the composition is ready to be poured out to cool and concrete; afterwards, being ground to a fine powder, it is ready for use. To use this composition The steel to be welded is first raised to a "bright yellow" heat, it is then dipped among the welding powder, and again placed in the fire, until it attains the same degree of heat as before; it is then ready to be placed under the hammer.

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Cast-Iron Sement. Take of clean iron borings, or turnings, 1 cwt.; of sal-ammoniac 8 oz.; and 1 oz. of flour of sulphur. Mix them thoroughly, and add sufficient water. If the cement is not to be immediately used, care should be taken to keep the mixture soaked in water; if left dry, the cement will heat, and be spoiled.

Cement for Steam Pipe Joints, &c., with Faced Flanges —To 2 parts of white lead mixed, add 1 part of red lead dry, grind, or otherwise mix them, to a consistence of thin putty; apply interposed layers, with one or two thicknesses of canvas or gauze wire, as the necessity of the case may require.

Glues.-1. A very strong glue is formed by throwing a small quantity of powdered chalk into melted common glue.

2. To make a glue which will resist the action of water-boil one pound of common glue in two quarts of skimmed milk.

Botany Bay Cement.Take 1 part of Botany Bay gum, and melt and mix it with 1 part of brickdust.

Cap Cement. As Singer's; but 1 pound of dried Venetian red may be substituted for the red ochre and Paris plaster.

Bottle Cement.-Resin 15 parts; tallow 4 (or wax 3) parts; highly dried red ochre 5 parts. The common kinds of sealing-wax are also used.

Turner's Cement.-Beeswax 1 oz.; resin oz.; pitch oz. Melt, and stir in fine brickdust.

Coppersmith's Cement.-Powdered quick-lime, mixed with bullock's blood, and applied immediately.

Engineers' Cement.Equal weights of red and white lead, with drying oil, spread on tow or canvas. This is an admirable composition for uniting large stones in cisterns, &c.

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Iron Cement for Closing the Joints of Iron Pipes.-Take of iron borings, coarsely powdered, 5 lbs. of powdered sal-ammoniac 2 oz.; of sulphur 1 oz.; and water sufficient to moisten it. This composition hardens rapidly, but if time can be allowed it sets more firmly without the sulphur. It must be used as soon as mixed, and rammed tightly into the joints.