A distinct variety of pig-iron made from haematite ores for conversion by the Bessemer process (see p. 304). It should be as free as possible from sulphur, phosphorus, or copper; but a small percentage of manganese and of silicon improves it for the purpose.

Foundry Pig, including all pigs having a fracture of a grey colour, containing a considerable proportion of free carbon, and being therefore adapted for the use of the ironfounder.

This iron is produced when the furnace is at a high temperature and properly provided with fuel.

Forge Pig, consisting of those pigs which are almost free from uncombined or graphitic carbon, and are therefore unfit for superior castings, being useful only for conversion into wrought iron.

This description of iron occurs when the temperature is low, or the fuel insufficient, also when there is much sulphur in the ore or fuel.

Forge iron is generally run from the blast furnace into iron moulds (instead of sand), by which it is kept free from the impurities of the sand, and also chilled, and thus rendered brittle and easy to break up for further treatment.

The pig-iron of commerce is more carefully divided into six or sometimes eight varieties.

The exact classification varies at different works. The following is condensed from one given in Wilkie's Manufacture of Iron in Great Britain, and quoted by Mr. Matheson in his Works in Iron : -

No. 1. - The fracture of this quality of pig is of a dark-grey colour, with high metallic lustre; the crystals are large, many of them shining like particles of freshly cut lead.

This iron is of the best description, and the highest in price. The amount of carbon it contains is from 3 to 5 per cent, which makes it fusible and specially fitted for foundry work.

No. 2 is intermediate in quality between Nos. 1 and 3.

No. 3 contains much less carbon than No. 1. The crvstals shown in a fracture of this iron are smaller and closer than in No. 1, but are larger and brighter in the centre than nearer the edges of the fracture.

1 Bauerman's Metallurgy.

The colour is a lighter grey than that of No. 1, with less lustre.

No. 4 or Bright. - This iron has a light-grey fracture, and but little lustre, with very minute crystals of even size over the whole fracture. It is not fusible enough for foundry purposes, but it is used in the manufacture of wrought iron.

It is the cheapest of the grey irons.

When inferior in quality, and nearly passing into the variety called mottled, there is usually a thin coat or "list" of white iron round the exterior edges of the fracture.

No. 5, Mottled is intermediate between No. 4 and white iron, the fracture being a dull dirty white, with pale greyish specks, and with a white "list" at the edges. It is fit only for the manufacture of wrought iron.

No. 6, White. - This is the worst, most crude, hard, and brittle of the pig-irons, the fracture being metallic white, with but little lustre, not granulated, but having a radiating crystalline appearance. This iron is largely used in the manufacture of inferior bar iron.

Cinder Iron is an inferior material obtained from the slag of the puddling furnace, technically called "cinder."

This cinder contains a large proportion of iron; but also the phosphorus and sulphur which have been extracted in making the better iron.

Such iron can only be extracted by the hot blast, and has done a great deal to discredit the material produced by that process.

It is, however, very fusible, and therefore valuable to mix with other irons, and is useful in itself for castings which do not require much strength.

Mine Iron is a name given to iron smelted from the ore only, without admixture of slag.

When iron is specified as "hot-blast - all-mine," it means that no cinder-iron or slag has been used in its production.