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 scoriae 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.
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