|THE DEVELOPMENT OF AMERICAN INDUSTRIES SINCE COLUMBUS.|
IV. IRON-WORKING WITH MACHINE TOOLS.
WHILE the builders and operators of blast-furnaces were achieving such splendid results as have been described, the owners, managers, and engineers of rolling-mills were not idle. At the very beginning of rolling-mill construction in America the disposition to make improvements in known methods and to invent entirely new mechanisms and processes was promptly manifested. Even in the first mill of which we have any authentic account the rolls and heating furnaces w T ere decided improvements on previous practice; and from that day to the present time the best American rolling-mill practice has been characterized by originality of idea and perfection of construction. Fig. 41 is a longitudinal section
of a heating furnace in which coal was used as a fuel. The "fire-box" with its grate is seen at the left; to the right of this is the "bridge-wall" separating the "heating chamber" from the "fire-box." The bottom, a, of the "heating chamber" is made of silicious sand. On the extreme right of the furnace is seen the "cinder-tap," b, for the discharge of any liquid "cinder" made during the operation of heating the iron; near this "cinder-tap" is the lower part of the "chimney-flue." The iron to be heated was placed upon the sand bottom a, and the flame from the fuel in the fire-box passed over it, not only heating the metal directly but the roof and side walls and bottom of the heating chamber also, which, as was said when this form of furnace was first intro-