CHAPTER IX
ORES OF IRON

[RoON—HiIsTORY AND QUALITIES

Iron (Fe; at. wt. 56: sp. gr., 7-5 to 7-8; melting-point,
2900° F) is the most indispensable of all metals. It is
fortunately plentiful, for it is the most abundant constituent
of the earth, varying in rocks from less than I per cent. in
ordinary granite up to 30 per cent.; the barysphere may
contain 80 per cent. Native iron is rare, but is found in
meteorites, and where iron oxide has been heated in the presence
 of carbonaceous material; it was probably first extracted
 from its ore by the same reaction when grains of iron
oxide in.sand were accidentally reduced by hot charcoal.
This process was apparently first used by negroes in tropical
Africa. Iron was used in Egypt in 7000-6000 B.c., according
to Flinders Petrie (F. Iron and St. Instit., 1912, i, pp. 182-3),
but did not come into general use there until 500 B.C., when
It had long been the common domestic metal in China. Its
Introduction to Northern and Central Europe is assigned to
about 600 5.c. According to most archeologists man worked
bronze earlier than iron ; but metallurgists insist that some
use of iron preceded that of bronze (St. J. V. Day, Prehistoric
Use of Iron, 1877, p. 3, etc.; J. Percy, Metallurgy. Iron
and Steel, 1864, pp. 873-4; L. Beck, Geschichte Eisens, 1,
1884, pp. 78, 82-4).
The widespread distribution of iron and its conspicuousness
as the chief colouring matter in rocks are aided by the solubility
 of its salts and the readiness with which iron is oxidized
Into rust. The latter quality, though the greatest industrial
defect of iron, has rendered it available as a cheap metal
Owing to its concentration into high-grade ores. The mobility
of iron is aided by its two oxides (ferric, Fe,0, with 70 per
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