| SYMBOL | ATOMIC WEIGHT | DENSITY | APPROXIMATE MELTING POINT | OXIDES | |
| Iron | Fe | 55.9 | 7.93 | 1800° | FeO, Fe2O3 |
| Cobalt | Co | 59.0 | 8.55 | 1800° | CoO, Co2O3 |
| Nickel | Ni | 58.7 | 8.9 | 1600° | NiO, Ni2O3 |
The family. The elements iron, cobalt, and nickel form a group in the eighth column of the periodic table. The atomic weights of the three are very close together, and there is not the same gradual gradation in the properties of the three elements that is noticed in the families in which the atomic weights differ considerably in magnitude. The elements are very similar in properties, the similarity being so great in the case of nickel and cobalt that it is difficult to separate them by chemical analysis.
The elements occur in nature chiefly as oxides and sulphides, though they have been found in very small quantities in the native state, usually in meteorites. Their sulphides, carbonates, and phosphates are insoluble in water, the other common salts being soluble. Their salts are usually highly colored, those of iron being yellow or light green as a rule, those of nickel darker green, while cobalt salts are usually rose colored. The metals are obtained by reducing the oxides with carbon.
IRON
Occurrence. The element iron has long been known, since its ores are very abundant and it is not difficult to prepare the metal from them in fairly pure condition. It occurs in nature in many forms of combination,—in large deposits as oxides, sulphides, and carbonates, and in smaller quantities in a great variety of minerals. Indeed, very few rocks or soils are free from small amounts of iron, and it is assimilated by plants and animals playing an important part in life processes.
Metallurgy. It will be convenient to treat of the metallurgy of iron under two heads,—Materials Used and Process.
Materials used. Four distinct materials are used in the metallurgy of iron:
1. Iron ore. The ores most frequently used in the metallurgy of iron are the following:
| Hematite | Fe2O3. |
| Magnetite | Fe3O4. |
| Siderite | FeCO3. |
| Limonite | 2Fe2O2·3H2O. |
These ores always contain impurities, such as silica, sulphides, and earthy materials. All ores, with the exception of the oxides, are first roasted to expel any water and carbon dioxide present and to convert any sulphide into oxide.