Procure a quantity of old boots, burn these until they become charred, beat off the black and charred portion with a hammer, until sufficient powdered carbon is obtained; then place this powder with the articles to be operated upon in a sheet-iron box or a piece of wrought-iron gas-pipe sufficiently large, taking care that the articles are well covered and in the centre of the mass; lute the ends or top of the box with clay, and place the whole in a fire made of coke, keeping them there for an hour or more, taking care that the heat shall be equal (between dark-red and red); now plunge the contents into water. Should the articles require to be blue, such as the barrels or chambers of pistols, repolish them on an emery wheel, and put them into a sand bath or powdered charcoal, until the blue colour is attained, taking them out immediately this change takes place. The following are mixtures that will do instead of the burnt leather: - 3 parts of prussiate of potash to 1 sal ammoniac; or 2 parts sal ammoniac, 2 bone-dust, 1 prussiate of potash. Bones, urine, and night-soil, are also used for this purpose.
A simple method of case-hardening iron is to sprinkle powdered prussiate of potash over it at a red heat and plunge into water; bichromate of potash,' with the pith of rams' horns, may be used with good results, instead of the prussiate.
The following colours and temperatures are required: - Pale straw, 430° F., for lancets, &c; dark yellow, 470° F., for razors, etc.; dark straw, 480° F., for penknives; clay yellow, 490° F., for chisels and. shears; brown yellow, 500° F., for adzes and plane irons; very pale purple 520° F., for table-knives; light purple, 530° F., for swords and watch-springs; dark purple, 550° F., for softer swords and watch-springs; dark blue, 570° F., for small fine saws; blue, 590° F., for large saws; pale blue, 610° F., for saws, the teeth of which are set with pliers; greenish blue, 630° F., for very soft temper. To obtain the proper temper lay the metal on a lump of iron heated to a sufficiently strong heat in the forge or other fire. The desired temper may be thus secured with the greatest facility and exactitude, as the clean bright metal shows the degrees of oxidation from the blue upwards most distinctly, which oxidation can be arrested at will. Cleanliness, or rather brightness of surface, is essential.
2 oz. fluoric acid, 1 oz. nitric acid, 1 oz. saltpetre, to 10 lb. of metal. When the metal is melted, add the solution. It can be made in a crucible in a brass furnace. When you have cast off patterns, the castings want keeping at red heat for three or four days in. iron boxes in a furnace.
(a) Heat the metal to a bright red, cool quickly in water, reheat, and then anneal by cooling slowly in ashes. .
(6) Heat the metal to a red heat, let it lie a few minutes until nearly black, and then throw it into soapsuds.
(c) Place the castings, surrounded by saw-dust, in an iron box, close it up with clay to exclude the air, and subject it to a red heat for several hours. The castings must be cold before they are withdrawn.
(6) Put them in a moderately hot oven for half an hour if large files; but if small the first plan is the best.
Dissolve a small quantity of sal ammoniac . in water, make the metal red, drop it into the mixture for a second or two, and take it out, leaving enough heat in the metal to draw it back a bit. If left till cold, the steel will be a great deal too hard.
(a) Heat the bill to a blood-red heat, and then hammer it till nearly cold; again heat it to a blood-red, and quench as quick as possible in 3 gallons of water, in which is dissolved 2 oz. of oil of vitriol, 2 oz. of soda, and 1/2 oz. of saltpetre; or, 2 oz. of sal ammoniac, 2 oz. spirit of nitre, 1 oz. oil of vitriol. The bill to remain in the liquor until it is cold.
(6) 1 oz. white arsenic, 1 oz. spirits of salts, 1 oz. sal ammoniac, dissolved in 4 gallons of spring water, and kept in a tube or iron phial for use. Heat the tool to a blood-red heat, then quench it in this mixture, draw it gently over the clean fire till the spittle flashes off it, then let it cool.
(c) To 3 gallons of water add 3 oz. o spirit of nitre, 3 oz. of spirits of hartshorn, 3 oz. of white vitriol, 3 oz. of sal ammoniac, 3 oz. of alum, 6 oz. of salt, with a double handful of hoof parings; the steel to be heated a dark cherry-red. Used to temper chisels for cutting French burr stones.
Get a piece of spring steel about the size of spring wanted; when forged and filed to tilt, make it warm-red, immerse in spring water (a little cow-dung improves it, mixed well with the water before using it). Dry the spring, then tie a piece of wire fast to the spring in any form, so as to hold it. Dip in clean tallow or oil, put it on the fire till all the grease is burnt off, and swing round and round as swift as you can till cold.