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The blast furnaces were
built near small water-courses
(small rivers or streams), which,
however, only for a short time
during spring and summer
furnished sufficient water-power to
ran the bellows for the blast used
for the furnace. As in the blast
forge, the hearth of the blast
fnrnace was rectangular and the
balance of the furnace shaft of
a circular form.
At first only lake and bog
ores were used in the blast
furnaces but later also hard ores.
The old blast forges were,
how-erer, only gradually exchanged
for blast furnaces as both kinds
were simultaneously in use for nearly two centuries. As låte as at the end of
the 18th century blast forging was still carried on in the more remote forest
districts of Dalarne.
Technically the production of pig iron made very slow progress. Although
the height of the blast furnace was somewhat increased and timber walls substituted
by stone walls, the shape of the shaft and the material of which it was built,
the blowing-machinery, etc., remained about the same up to the year 1830.
The figure on the next page shows a Swedish blast furnace from this period. It
is only about 11 meters high which was then the usual height. At that period,
however, several important improvements were made. Hot blast came into nse,
the stack was built of fire bricks instead of stone, and the lower part, i. e. the
hearth, rammed with a material consisting of quartz and a little fire clay.
These rammed hearths were very durable, whereby the run of the blast
furnace was prolonged. But a more important improvement, however, was
introduced in roasting the ores. Previously this had been done in roastingstalls,
which now were exchanged for kilns fired with wood or gas from the blast furnace.
These kilns were more and more improved, until Mr. E. Westman, Director of
•Jernkontoret» (see p. 761), in 1850 introduced his well known type of roasting
kiln of a very perfect design, which has greatly contributed to the excellent quality
of the Swedish iron.
pig iron. 717
Old-fashioned Swedish blast forge (see p. 715).
Tablb 104. Imports, exports, and consumption of pig iron in Sweden.
Metric tons à 2,204 lbs.
Average for the
years
Mean
population.
[-Production.-]
{+Produc-
tion.+}
Tons.
Imports.
Tom.
Exports.
Ton».
Surplus
of
exports.
Tons.
Consumption.
Tons.
1861/65........... 3,993,000 204,826 5,533 14,212 8,679 196,147 49
1866/70......................4,166,000 267,854 4,530 24,280 19,750 248,104 60
1871/75......................4,274,000 332,456 13,436 54,320 40,884 291,572 68
1876/80......................4,500,000 357,224 15,900 35,973 20,073 337,151 75
1881/85......................4,605,000 429,377 20,050 53,093 33,043 396,334 86
1886/90......................4,742,000 446,578 25,515 59,205 33,690 412,888 87
1891/95....................4,832,000 471,147 28,027 66,766 38,739 432,408 89
1896 00......................5,032,000 517,796 47,233 82,781 35,548 482,248 96
In 1900 ..................5,117,000 526,868 50,932 84,477 33,545 493,323 96
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