The province of Minas Geraes ocupies a vast extent in the empire
of Brazil, its superficies being about 900,000 square kilometers,
representing nearly a third of the total surface.
The population is relatively small and is disseminated throughout a much
broken country, where the means of communication are very few. So it is
necessary to succeed in producing what iron is needed by means that are
simple and that require but quickly erected works built of such material
as may be at hand. The iron ore is found in very great abundance in this
region and is very easily mined.
In the center of a mass of quartzites that seem lo constitute the upper
level of the eruptive grounds of the province, there are found strata of
an ore of iron designated as _itabirite_--a mixture of oxide of iron and
quartz. These strata are of great thickness, and have numerous outcrops
that permit of their being worked by quarrying.
These itabirites present themselves under two very distinct aspects and
offer a certain difference in their composition. Some are essentially
friable, and are called by the vulgar name of _jacutingaes_. It is
this variety (which is the one most easily mined) that is principally
consumed in the forges. The others, on the contrary, are compact.
Their exploitation is more difficult, and before putting them into the
furnaces it is necessary to submit them to breakage and screening; so
the use of them is more limited.
The first variety contains less iron and more gangue, but, _per contra_,
possesses much oxide of manganese. The second, on the contrary, is
formed almost wholly of oxide of iron with but little gangue and only
traces of oxide of manganese. The following are analyses of these two
varieties of ore:
_Friable Ore_.
Fe_{2}O_{2}.................................. 84.9
Oxide of manganese........................... 9.2
Water........................................ 1.9
Quartz....................................... 4.1
----
100.1
_Compact Ore_.
Fe_{2}O_{3} and traces of manganese.......... 99.6
Quartz....................................... 1.1
----
100.7
_Situation of the Forges_.--A forge is usually placed on the bank of
a brook, or rather of a torrent, which supplies the fall of water
necessary for the motive power by means of a flume about a hundred
meters in length. In most cases the forge is surrounded on all sides
with a forest which yields the wood necessary for the manufacture of the
charcoal, and is in the vicinity of the iron quarry, so as to reduce the
expense of hauling the ore as much as possible. The neighboring
rocks furnish the foundation stones and stones for the furnaces; the
decomposed schist gives the cement and refractory coating, and the
forest provides the wood necessary for the construction of the road,
sheds, etc. The head of the trip hammer, the anvils, and the tools are
the only objects that it is necessary to procure, and even these
the master of the forge often manufactures in part, after beginning
production with an incomplete set.
[Illustration: 7a FIG 1.--FOUR-CRUCIBLE FURNACE AND FORGE; (PLAN).]
_General Arrangement of a Forge_.--A forge usually consists of one or
two furnaces of three or four crucibles (the one shown in plan in Fig.
1 has only one four crucible furnace, A); 1 or 2 two fire reheating
furnaces, B; 1 trip hammer, C, actuated by a hydraulic wheel, D;
2 tromps which drive the wind, one of them, E, into the cadinhes
(crucibles), and the other, F, into the reheating furnace; 2 anvils,
G and H, placed near the furnace, for working delicate pieces; and
finally, the different tools that serve for maneuvering the bloom and
finishing the bars. The charcoal is preserved from rain under a shed, l.
The ore, which is brought in as needed, is dumped in a pile at M, in
the vicinity of the crucibles. The buildings are set back against the
mountain, and the water is led in by a double flume, L and N, made of
planks, and empties on one side into the wheel and into the tromp, F,
and on the other into the tromp, E, and then runs into a double waste
channel, P and Q, which carries it to the stream.
[Illustration: FIG 2.--FOUR-CRUCIBLE FURNACE; (PLAN).]
_Four Crucible Furnace_ (Fig. 2).--The arrangement of a furnace is very
simple. It consists of a cube of masonry containing several cylindrical
apertures with elliptic bases, whose large axis is paralleled with the
smaller side of the masonry. This form recalls that of a crucible;
and these cavities are, moreover, so named. In the front part of each
cadinhe there is a rectangular aperture that gives access to the bottom
of the crucible and facilitates the removal of the bloom therefrom. At
the back part there is a small aperture for the introduction of the
tuyere, and which permits, besides, of the nozzle of the latter being
easily got at so as to see whether the blast is working properly.
The sides of the crucibles are covered with a thin layer of refractory
clay, and their bottoms have a spherical concavity to hold the bloom.
The tuyere, which is fitted to a wooden conduit of square section
that runs along the back of the masonry, is placed in the axis of the
cadinhes and enters the masonry at a few centimeters from the bottom
in such away that its nozzle comes just flush with the surface of the
refractory lining. This arrangement prevents the tuyere from getting
befouled by scoriæ during the operation of the furnace and thus
interfering with the wind.
_Tromp_.--The tromp which furnishes the necessary wind to the cadinhes
consists of a hollow wooden conduit, a (Fig. 3), of square section,
which enters a chamber, b, along a length of 0.1 m. This conduit, which
is about 7 meters in height, receives the water from the flume through
the intermedium of an ajutage of pyramidal form, which serves to choke
the vein of liquid, and the extremity of which is at a few centimeters
from the conduit in order to facilitate the entrance of the air; the
latter being attracted by an ill defined action that is supposed to
be due to its being carried along by the water, and to a depression
produced by choking the flow of the liquid.
[Illustration: FIG. 3.--THE TROMP.]
Since the air that is sucked in during the operation has constantly same
pressure, there is no valve for regulating the entrance of the water
into the vertical conduit. Upon issuing from the latter, the mixture of
air and water strikes the surface of the water in the chamber, b,
and the violence of the shock upon the bottom is deadened by the
interposition of a stone. While the water is escaping through a lateral
aperture in the chamber, b, the air is reaching the tuyeres through a
wooden conduit of square section which is fitted to an aperture in the
upper part of the chamber. This sorry arrangement, which obliges the
mixture of air and water to penetrate the water at the bottom of the
upright conduit, a, retards the separation of the two fluids, and
results in damp air being forced into the crucibles.
_The Trip Hammer_.--Fig. 4 shows the general arrangement of the
apparatus that go to make up the forging mill. The hammer and cam shaft
have their axes parallel, and the latter is placed in the prolongation
of the axis of the wheel. The hammer consists of a roughly squared beam,
4 meters in length, and of 0.25 m. section. The head, A, consists of a
mass of iron weighing 150 kilos, including the weight of the straps
that surround the beam on every side of the piece of iron. The axis of
rotation is situated at the other extremity of the beam, B. The cam
shaft which serves to maneuver the trip hammer is provided with four
cams which lift the beam at a point near the hammer. The length of this
shaft (to the extremity of which is adapted the water wheel) is 4.75 m.,
and its diameter is 0.50 m. The wheel is an _overshot_ one, 3.25 m. in
diameter by 1 m. in width. The water, which is led to it by a flume,
acts upon it by its weight and impact, and is retained in the buckets
and kept from overshooting the mark by a jacket made of planks.
[Illustration: FIG. 4.--THE TRIP HAMMER.]
The anvil upon which the hammer strikes is surrounded by a bed of stones
(quartzites) derived from the neighboring rocks. It is a mass of iron,
75 kilogrammes in weight. In order to prevent vibrations in the trip
hammer when it is lifted, and increase the number of blows, there is
established a spring beam, which is formed of unsquared timber, which
is firmly fastened at one of its extremities, and which receives at the
other end the shock of the hammer head when the latter reaches the end
of its upward travel.
_Reheating Furnace_.--This is a double fire furnace, like those used in
our smithies, except that the wind, instead of being forced into it by
means of a bellows, is supplied by a tromp which receives water from the
same channel as the wheel. The two furnace tuyeres are arranged exactly
like those of the cadinhes, upon a wooden conduit which starts from the
wind chamber (Fig. 5). This furnace serves to prevent the cooling of
such blooms as are awaiting their turn to be shingled, and of such bars
of finished iron as are being made into tools.