readily determined by Eggertz' method, which depends on the fact that, when iron or steel is dissolved in nitric acid, the intensity of the colour of the solution will be proportional to the amount of carbon originally present in the combined form. The graphite not being affected by nitric acid, will remain in the insoluble residue.

Grey pig-iron may be converted into white, by melting and sudden cooling, the iron being considerably hardened by this means. This principle is applied in chill-casting. Vice versa, white iron is changed to grey by melting and slow cooling. From the above remarks it will be observed that grey pig-iron is much softer than white, and the hardness of hardened steel may be due to the carbon passing into the combined form, while annealing restores it to the graphitic condition.

ALLOYS OF IRON.

Gold alloys with iron making it harder and more fusible. Platinum, when present in iron to the extent of 1 per cent., makes it fine grained, the alloy being tenacious, tough, and ductile. The presence of a little iron in brass and bronze increases their strength. Copper in iron is somewhat injurious making it hard, so that any notable quantity of copper in pig-iron renders it unfit for making the best classes of wrought iron. Zinc alloys with iron to the extent of 7 per cent., which is used for alloying with brass in the production of deltametal, Aich's metal, sterro-metal, etc. Zinc forms a surface alloy with iron in galvanising. A similar use is made of tin in the process of tinning iron plates, which coating is both ornamental, and protects the iron from oxidation. An alloy of 10 parts iron with 80 parts tin is said to be preferable to pure tin in tinning copper vessels. 7 parts of antimony to 1 part iron (termed martial regulus) is used for producing casts of medallions,

and similar objects. Antimony when present in iron to the extent of 2 per cent. makes it both hot- and coldshort. Nickel and cobalt alloy with iron without seriously affecting its malleability, as is shown by the workable nature of meteoric iron. Chromium makes iron white, hard, brittle, and less fusible. Oxide of tungsten, in the presence of iron and carbon at a high temperature, is reduced, the tungsten alloying with the iron and forming a very hard, fine-grained, white alloy. Titanium occurs in pig-iron smelted from titaniferous ores, but passes out in refining.

Manganese frequently occurs in iron ores, and is partially reduced along with the iron. When present to the extent of from 5 to 20 per cent., it causes the production of white pig-iron in a highly crystalline condition, containing a large amount of carbon wholly in chemical combination. This is termed "spiegel-eisen." When the manganese exceeds the above amount, the distinctive crystalline plates are no longer apparent. Alloys containing up to 87 per cent. of manganese are now manufactured for use in steel making, being distinguished by the name of "ferro-manganese.' These alloys are hard, crystalline and brittle.

QUESTIONS.

1. Describe the various kinds of iron ore that are used for iron smelting.

2. Enumerate the chief British iron ores, giving their chemical composition and the localities where they are found in quantity.

3. For what special purposes are any of these ores particuarly suitable or unsuitable, on account of their physical proerties or chemical composition?

4. If you wished to obtain a sample of pure iron, how would you proceed?

5. When iron is strongly heated in air it is oxidised. What is the difference in the change when iron is exposed to moist air without heating?

6. What is the action of nitric, hydrochloric, and sulphuric acids respectively on iron?

7. Name the three principal oxides of iron, and briefly explain how they differ from each other.

8. What is the effect of sulphur on iron? How do you suppose sulphur gets into iron during smelting?

9. What is the influence of phosphorus on iron? For what reason is phosphorus sometimes added to iron ?

10. Name any useful compound of iron and silicon, and state for what purpose it is used.

11. What do you understand by the terms "bull-dog” and "bull-dog slag"?

12. What are the chief peculiarities of cast-iron, wroughtiron, and steel?

13. What are the differences between white and grey pigiron, and what are the causes of these differences?

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14. What is "spiegel-eisen" and how does it differ from ferro-manganese"?

15. What is the effect of a prolonged heating of malleableiron to redness in contact with charcoal?

CHAPTER V.

MALLEABLE IRON. DIRECT METHODS OF EXTRACTION.

Properties of iron.-Malleable iron is of a greyishwhite colour, having a granular, crystalline, or fibrous fracture, according to the mode of treatment. When rolled or hammered hot the iron becomes fibrous, but continued cold hammering induces a crystalline or granular structure, making it hard and brittle. The nature of the fractured surface varies also with the manner in which the iron has been broken, for specimens broken by progressively increasing stresses are invariably fibrous, whilst the same specimen broken by a sudden blow will be crystalline. The presence of impurities generally tends

to impart a granular or crystalline fracture, and makes. the iron less malleable. When impurities, such as sulphur and arsenic, render the metal unworkable at a red-heat, it is said to be hot- or red-short. On the other hand, some substances, such as phosphorus, cause iron to crack when hammered cold, it is then termed cold-short. The specific gravity of iron is about 7.7, and when the metal is compressed at a high temperature, the density is increased; but in wire-drawing and cold-rolling the metal elongates more than its transverse section diminishes, and the density is diminished, but its tenacity is increased. Its fusing point is said to be about 2000° C.; but before melting it assumes a pasty state, when two pieces may be joined together by welding. To ensure a good weld the surfaces must be clean, and the metal at a white heat. In order to dissolve any scale the smith adds a little sand, which unites with the oxide and forms a fusible silicate. The presence of any foreign bodies, such as carbon, silicon, sulphur, phosphorus, copper, oxygen, etc., increases the difficulty of welding. Iron possesses considerable malleability, ductility, and tenacity. Its tensile strength ranges from 17 to 25 tons per square inch, but this, like all the other physical properties, is modified by the presence of impurities, which tend to make it harder, more fusible, and brittle. When iron is heated to dazzling whiteness, it burns, forming the black oxide Fe3O4, the iron becoming friable and brittle, and is then termed "burnt-iron." Iron may be magnetised by bringing it in contact with, or near to a magnet, but it loses its magnetism when the exciting magnet is withdrawn. Its specific heat is 1137, and its conductivity about 120, silver being taken as 1000. Its electric resistance is 5.8 times that of pure copper. When iron is exposed to moist air it readily rusts or oxidises, so that it is often coated with some substance to prevent this action, such as tinning, galvanising, and painting. Prof. Barff preserves iron from rusting by

exposing it at a red-heat to superheated steam, which imparts to it a coating of the black oxide Fe3O4

SCHEME FOR IRON AND STEEL PROCESSES.

Two distinct methods are employed for smelting iron ores, known respectively as the "direct" and "indirect methods: the former, which is the older and little used at the present time, having been superseded by the latter or more modern method. The various processes are represented in a general manner in the accompanying scheme Fig. 3.

In the direct method, the ore is reduced to iron or steel, in arrangements such as the Catalan-forge and Siemens'rotator, then hammered, re-heated, and finished with the hammer or rolls. In the indirect method, the ore is calcined, and afterwards reduced in a blast-furnace, the iron then being run into pig-moulds; the pig-iron so obtained is afterwards refined (or puddled direct), puddled, hammered, rolled, re-heated, and finished in the rolls for bar-iron. If steel is desired, the bars are heated with carbon in the cementation furnace, then melted in crucibles for cast steel.

In the old method, the finery and open-fire were used instead of the puddling and re-heating furnaces.

Pig-iron is treated in the Bessemer-converter for the production of Bessemer-steel; in the Siemens' furnace for Siemens-steel; and melted in the cupola for foundry purposes. The bloom of iron produced in the rotatoryfurnace may be made into steel by treating it in the Siemens' open-hearth furnace.

DIRECT METHODS OF MAKING MALLEABLE IRON.

When malleable iron is extracted from the ore in one operation the process is said to be "direct." Many