Recognized HTML document

Metals.   339

the nozzle. These bellows require no valve, and are the simplest that can be made : they are in use throughout India. The nozzle or tube to convey the blast may be made of a plaster of clay or loam, mixed with grass, and moulded round a smooth pole.

Metals, to work.-Iron Ore is more easily reduced than the ore of any other metal : it is usually sufficient to throw the ore into a charcoal-fire and keep it there for a day or more, when the pure metal will begin to appear.

Welding Composition for iron or steel, is made of borax 10 parts, sat ammoniac 1 part; to be melted, run out on an iron plate, and, when cold, pounded for use.

Cast Steel.-9A mixture of 100 parts of soft iron, and two of lamp-soot, melts as easily as ordinary steel-more easily than iron. This is a ready way of making cast-steel where great heat cannot be obtained.

Case-hardening is the name given to a simple process, by which the outside of iron may be turned into steel. Small tools, fish-hooks, and keys, &c., are usually made of iron ; they are fashioned first, and case-hardened afterwards. There are good reasons for this : first, because it is the cheapest way of making them; and secondly, because while steel is hard, iron is tough; and anything made of iron and coated with steel, combines some of the advantages of both metals. The civilised method of case-hardening, is to brighten up the iron and to cover it with prussiate of potash, either powdered or made into a paste. The iron is then heated, until the prussiate of potash has burned away : this operation is repeated three or four times. Finally, the iron, now covered with a thin layer of steel, is hardened by quenching it in water. In default of prussiate of potash, animal or even vegetable charcoal may be used, but the latter is a very imperfect substitute. To make animal charcoal, take a scrap of leather, hide, hoof, horn, flesh, blood-anything, in fact, that has animal matter in it ; dry it into hard chips like charcoal, before a fire, and powder it. Put the iron that is to be case-hardened, with some of this charcoal round it, into the midst of a lump of loam. This is first placed near the fire to harden, and