The impurities mentioned below are originally derived either from the ore or fuel, and unless eliminated in subsequent processes, they will injure the respective metals produced in the manner stated.

Silicon is, next to carbon, the most common constituent of pig-iron. It is derived from the ore and from the fuel. A good deal of it is got rid of in the slag produced by smelting, and also during the refining and puddling processes.

In many respects silicon resembles carbon, and it affects cast iron in nearly the same way.

Wrought Iron is rendered by it hard and brittle. To obtain good wrought iron the silicon must be removed as far as possible by repeatedly heating and working the iron.

Steel

1/2000 Part makes it cool and solidify without bubbling and agitation; more makes it brittle. 5/10 per cent makes it unforgeable.

Phosphorus is very readily taken up by the iron during the smelting process, and is one of the worst impurities it can contain.

Cast Iron is hardened by it, but is made more readily fusible. Its tenacity is reduced.

Wrought Iron is injured by it in proportion to the quantity present.

1/10 per cent does not reduce the strength of wrought iron; and improves its capacity for welding.

3/10 per cent makes it harder, but not weaker.

5/10 per cent makes it "cold short " (see p. 275).

8/10 decidedly cold short.

1 per cent makes it very brittle, and unfit for any but special purposes.

Steel is injured by a very minute proportion.

1/20 per cent makes it unfit for the best cutlery.

1/10 per cent makes it cold short, and useless for tool-making of any kind.

Manganese nearly always exists in cast iron. It tends to produce the white variety, in which a large proportion is generally to be found.

In Wrought Iron and Steel it counteracts red shortness, probably by encouraging the departure of the sulphur and silicon (see p. 306).

Its presence is essential in the manufacture of Bessemer Steel, and in some other processes.

Sulphur is derived from the pyrites in the ore and coal.

In Cast Iron it tends to produce the mottled and white varieties.

In Wrought Iron 3/10, to 1/10 per cent produces red shortness.

In Steel more than 2/10 per cent unfits it for forging; but makes it more fluid, and better for casting. 1/10 per cent produces red shortness.

Copper has the following effects: -

In Cast Iron 2/10 per cent does no harm.

In Wrought Iron 3/100 per cent reduces tenacity, 5/10 per cent makes it red short

In Steel 5/10 per cent makes it red short. 2 per cent makes it brittle.

Arsenic is not a very frequent impurity in iron.

In Cast Iron a smaller proportion is said to be good for chilled castings.

In Wrought Iron it causes red shortness.

Among the impurities met with more rarely, or in smaller quantities, are

Tin, which makes wrought iron cold short.

Tungsten, which imparts hardness and elasticity to cast steel, and renders it more capable of retaining magnetism.

Antimony, which makes wrought iron both hot and cold short.

Titanium, which tends to produce mottled cast iron. The so-called "titanic steel " contains no traces of titanium. The good qualities attributed to it must arise from some indirect action 1

Classification, Of Pig-Iron

The different varieties of pig-iron are sometimes classed under three general heads.