134.  Finishing polish

Put 2 drachms of shellac, and 2 drachms of gum benjamin, into 1/2 pint of the very best rectified spirits of wine, in a bottle closely corked; keep the bottle in a warm place, and shake it frequently till the gums are dissolved, when cold shake up with it 2 teaspoonsful of the best clear poppy oil, and it will be fit for use.  This polish may be applied with great advantage after any of those mentioned in the foregoing receipts have been used.  It removes the defects existing in them, increasing their lustre and durability, and gives the surface a most brilliant appearance.

135.  Composition used in 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 close 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; afterward being ground to a fine powder.  To use this composition, the steel to be welded is raised to a heat, which may be expressed by bright yellow, 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.

136.  Composition used in welding cast iron

Take good clear white course sand, 3 parts; refined solton, 1 part; fosterine, 1 part; rock salt 1 part; borax, 1 part; mix all together.  Take 2 pieces of cast iron, heat them in a moderate charcoal fire, occasionally taking them out while heating, and dipping them into the composition, until they are of a proper heat to weld, then at once lay them on the anvil, and gently hammer them together, and if done carefully by one who understands welding iron, you will have them nicely welded together.  One man prefers heating the metal, then cooling it in the water of common beans, and heating it again for welding.

137.  Cast iron cement

Take of clean borings or turning of cast iron, 16 parts; of sal-ammoniac, 2 parts; and flour of sulphur, 1 part; mix them well together on a mortar, and keep them dry.  When required for use, take 1 part of the mixture, and 20 parts of clean borings, mix thoroughly, and add a sufficient quantity of water.  Note.—­A little grindstone added improves the cement.

138.  Case hardening

This is the conversion of the surface of wrought iron into steel, for the purpose of adapting it to receive a polish, or to bear friction, &c.  The best method in the world of effecting this is by heating the iron to cherry red in a close vessel, in contact with carbonacious material, and then plunging it into cold water.  Bones, leather, hoofs, and horns of animals, are best for this purpose, after having been burnt or roasted, so that they can be pulverized.  Soot is very frequently used; it answers, but not so well.