into bars by means of grooved-rolls. superseded almost all the older methods.

This gradually

In 1828 James Neilson recommended the use of the hot-blast, in direct opposition to the views of the most eminent metallurgists of the day. Four years after its introduction at the Clyde works, their weekly output was doubled without the consumption of extra fuel, the air being heated to 300° C.

In 1855 a total revolution occurred in the iron trade by the valuable invention of the Bessemer process, an invention, which, as Sir L. Bell says, "will probably for some time, if not permanently, remain as a culminating point in the progress of the manufacture of iron.” For some

time the invention seemed likely to fail, until Mr. R. F. Mushet proposed to add a manganese compound at the completion of the blow, thus bringing about complete

success.

Subsequently, Messrs. Siemens conceived the notion of constructing a furnace in which an intense temperature could be produced, with the aid of heat from the combustion of gaseous fuel. These renowned metallurgists have given to the world an invention, invaluable as a means of producing temperatures hitherto undreamt of, which ranks equal in importance with that of Bessemer. In fact Siemens and Bessemer may truly be said to have inaugurated a new era, termed the "Age of Steel."

The next great advance, made by the collection and utilisation of the waste gases of the blast-furnace, by a Frenchman at Ebbw Vale in South Wales, was so successful, that in a few years it was almost universally adopted, with a saving of a million and a half tons of coal per annum. This utilisation of the waste gases led Mr. Cowper to adopt the regenerative principle of Siemens in stoves for heating the blast, thus placing at the disposal of ironmasters much higher temperatures than before.

Lastly, of quite recent date, Messrs. Thomas & Gilchrist

have adopted the principle of a basic lining for the Bessemer converter, whereby common pig-iron-containing a considerable quantity of phosphorus-may be employed for making good steel. The success of the process has led many experimenters to test the suitability of basic linings for the Siemens furnace, and excellent results have been obtained, so that the dephosphorisation of pig-iron, both in the Bessemer-vessel and in the open-hearth, must now be recognised as an accomplished fact.

CHAPTER II.

DEFINITION OF METALLURGICAL TERMS. REFRACTORY MATERIALS. FUEL.

Ore. An ore is a naturally occurring substance containing a metal, chiefly in the forms of oxide, sulphide, and carbonate. These compounds are generally associated with earthy matter, termed gangue, which may often be separated by mechanical means, such as crushing, washing, and sorting. Some metals are found in nature in the metallic state, when they are said to occur "native."

Calcination and roasting. When an ore or other substance is subjected to a temperature, insufficient to melt it, but sufficient to expel volatile matter, and render the body more porous and more fit for the subsequent smelting, it is said to be "calcined." When the main object of the process is to oxidise the substance, the operation is termed "roasting."

Slag. The fusible compound formed by the union of metallic oxides with silica is termed a "C silicate," in which other bodies are often dissolved. When such a "silicate" is a waste product of an operation it is termed a "slag." It may be glassy, crystalline, or stony. Rapid cooling tends to produce a glassy slag, while slow

cooling induces the crystalline form. The presence of much lime and other earths renders a slag stone-like in character.

Flux. A flux is a substance added to ores, or other metalliferous substances, for the purpose of uniting with the foreign matter and forming a fusible slag. The kind of flux added will vary with the nature of the bodies to be removed; thus, a siliceous gangue requires a basic flux, and a basic gangue a siliceous one. Smelting. This term in its broadest sense is applied to the whole of the processes by which a metal is extracted from its ores with the aid of heat.

Welding. When two pieces of metal are joined together by pressure to form one compact mass, they are said to be welded. This union is effected at different temperatures, according to the character of the metal, thus-iron requires a white-heat, but steel must be welded at a lower temperature. It is necessary that the metals should be in a soft condition, with clean surfaces, and that the metal should possess considerable malleability and tenacity; for this reason cast-iron cannot be welded.

Occlusion. Metals, when melted in contact with air or other gases, absorb them more or less, and retain a portion after solidification; the portion thus retained is said to be occluded.

Cementation. When a metal is heated in contact with a powder, which modifies its nature and composition, without melting, the process is termed cementation, and the powder employed is termed the cement. Iron is heated in this way with carbon to form steel; this is a 'carburising" cementation. When cast-iron is heated with oxide of iron, the oxygen of the latter so modifies the character of the iron that it becomes malleable; this is an "oxidising" cementation.

Fining and refining.-The term "fining" is applied to the operation of purifying pig-iron, either in the

puddling-furnace or in the old charcoal-finery.

66

The

term refining" is applied to a preliminary process originally used to partially purify pig-iron, and convert it into white iron, before fining it.

Hot-short and cold-short.-When a metal cannot be hammered or rolled at or above a low red-heat, without cracking, it is termed "red-short." On the other hand, a metal, which cannot similarly be worked below a low red-heat, is said to be "cold-short."

Metal. This term is applied to a certain number of the chemical elements which have well defined characters in common, such as metallic lustre, conductivity, and high specific gravity. The influence of heat upon metals is very varied; some melt at a low temperature, others require a red-heat, a strong-red, or a white-heat respectively, to melt them. The following table by Pouillet will explain the temperatures corresponding to different colours

Incipient red-heat corresponds to
Dull-red

525° C. 977° F.

700

1292

Metals expand when heated and contract on cooling, and within certain limits, the expansion is proportional to the range of temperature. Certain anomalies however exist, thus-molten pig-iron expands at the moment of becoming solid, and solidified bismuth occupies a larger space than bismuth in the liquid state. One of the most distinctive features of a metal is an internal mobility, in virtue of which, its shape may be altered by pressure with

out disruption of the mass. This property is possessed by metals in various degrees, so that the "malleability" or power of being extended by pressure without cracking, and ductility," or the capability of being permanently elongated by a tensile stress combined with lateral pressure, are by no means equal in extent; nor is the order of their malleability the same as of their ductility, for the former depends on the softness and tenacity, while the latter is much more dependent on tenacity. By "tenacity" or tensile strength is understood the resistance a body offers to an attempt to pull its particles asunder when a stretching force is applied. The tenacity is generally diminished by a rise in temperature, while the reverse is often the case with regard to malleability and ductility. Some metals have a feeble tenacity, and are then said to be brittle. When a body resists rupture by a bending or twisting force, it is said to be "tough." Elasticity is a property of bodies, in virtue of which they tend to recover their size and shape after being subjected to a disturbing force. There is a limit in every solid body, beyond which, it will not return to its original form on the withdrawal of the force; this is termed the limit of perfect elasticity. "Hardness, ," which is measured by resistance to a compressive force, like all the other physical properties of a metal, is modified by the presence of impurities, so that in many cases softness is a test of purity. All malleable metals become hardened by pressure, and often require annealing during the process of manufacture. The fractured surface of metals is often characteristic, being spoken of as fibrous, crystalline, granular, columnar, and con choidal, thus-wrought-iron is fibrous, zinc is crystalline, steel is granular, tin is columnar, and hard steel is conchoidal. Crystalline structure is often accompanied by brittleness, and fibrous structure by high tenacity. Most metals are much heavier than water, and the ratio which expresses the number of times a body is heavier than an