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 pre- 
sence of carbonaceous material; it was probably first ex- 
tracted 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 solu- 
bility 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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