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THE POPULAR SCIENCE MONTHLY. 



feet, the " head-race " taking its water from above the lock oppo- 

 site 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-sup- 

 ply at the top of the furnace to fill the tub that was at the top. 



