feet, the "head-race" taking its water from above the lock opposite the furnace, and the "tail-race" discharging into the lower level of the canal, below the lock. With one water-wheel the "make" of iron was only about twenty-five to thirty tons per week, but with the second wheel the production was increased to upward of forty tons, varying, of course, with the condition of the water-supply, and sometimes reaching sixty to seventy tons. In years afterward this furnace, with still more powerful blowing machinery, made one hundred and seventy-two tons of iron in a week. The furnace was filled by a water hoist, consisting of two "tubs" about six feet square, suspended to a chain passing over a large pulley at the top of the hoist tower; the tops of these tubs
Fig. 32.—A Charcoal Blast-Furnace.
were covered and formed platforms on which the barrows were raised. By letting the water out of the tub that chanced to be at the bottom of the tower, the weight of water in the tub at the top caused it to descend, thus raising the other tub with its load. In order to operate this hoist, it was necessary to have a water-supply at the top of the furnace to fill the tub that was at the top.
