A good hardening compound for steel and wrought iron consists of the following parts, all pulverized and mixed intimately, viz.: One part each of saltpetre and calcined cow's hoofs and yellow prussiate of potash. 1-30 aloes, 1-30 gum-arabic and 1/2 common salt. The compound is to be scattered upon the wrought iron at a white heat, and steel at a red heat, and thoroughly burnt in.
To harden copper melt same with 1 to 6 per cent. of black oxide of manganese in a crucible. This is to be stirred thoroughly and the scum removed before it is poured out. The same method is to be used in preparing brass, a small quantity of zinc being added to the melted copper and oxide of manganese.
A hardening mixture for iron consists of;
1 lb. Yellow Prussiate of Potash, 1/2 pt. Hydro-chloric Acid.
2 oz. Charcoal, 2 1/2 lbs. Bonedust, 2 lbs. Rock Salt.
The red-hot iron is plunged into this mixture twice, being heated between the two times, and then, while yet hot, is quenched in cold water. These proportions may vary slightly, and at times it is well to add a little lime.
To harden soft iron wet it with water and scatter over its surface powdered yellow prussiate of potash. Then heat to a cherry red heat, which causes the potash to melt and coat the surface of the soft iron. Then immerse quickly in cold water and repeat the operation. A white heat must not be used, as this would not harden but oxidize the iron. Care must be used not to use red prussiate of potash instead of the yellow. It will not answer.
To harden steel piano-wire first heat it red-hot and then cool. Next plunge same in a bath composed of;
21 parts Tin,
26 parts Antimony.
12 parts Zinc,
1 part Bismuth, 40 parts Lead.
This bath should be heated above its melting point and the wire should stay in it until it has acquired the temperature of the bath. The time which this takes varies directly with the thickness of the wire.
To harden zinc bring into the melted metal from 1 76-100 to 3 52-100 ounces of sal-ammoniac per pound.
If brass has been joined with white solder the difference of color invites attention to the part where the junction has been effected. This may be obviated, it is said, by applying a saturated solution of sulphate of copper to the solder. If the place is then touched with a steel or iron wire it becomes coppered, and the coating of copper increases in thickness as the operation is repeated. To give the required yellow color, one part of saturated solution of sulphate of zinc is added to two parts of sulphate of copper. This mixture is applied to the coppered spot, and is rubbed in with a rod of zinc. The color can be further improved by using a gilding powder and by polishing.
To make red or carmine ink for bookkeeping purposes: Take 12 grains of carmine, add 3 ounces of aqua ammonia and heat gently, without boiling, for seven or eight minutes; then add 18 grains of gum arabic, stirring constantly. Keep well corked.