The blast, after passing through the hot blast stoves, is conveyed in iron or steel conduits, lined with fire brick, to tuyeres, set in the walls of the crucible. These tuyeres are formed of an inner and outer shell with closed ends, water circulating between the two shells. The tuy eres are mostly made of bronze or copper and are set in larger tuyere blocks (also water cooled) of iron or bronze. Nozzles connect the lined air conduits to the tuyeres. The cooling water required by a modern blast furnace amounts to millions of gallons daily. A large furnace requires a boiler equipment of from 3,500 to 5,000 horse power for its blowing, pump ing and elevating machinery, electric plant, etc.
Blast furnaces are numerous in all manufac turing countries, but the United States leads in number and size. The Minnesota Steel Company has constructed two at Duluth, each of 280,000 tons annual capacity. In the Pittsburgh steel district are many large furnaces of over 500 tons daily capacity.
It is impossible to give the total number of blast furnaces in the United States, for the rea son that the number of those used for producing copper, silver, etc., are not collated, but lists of the furnaces employed in reducing iron ores are carefully reported b_y the American Iron and Steel Association. There were in 1909, in the United States, approximately 450 blast furnaces, whose aggregate reported capacity amounted to over 25,000,000 long tons of pig iron, but as all of these furnaces are not active at one time (25 per cent being often idle, and sometimes 40 per cent), the total annual output is the only practical gauge of the industry. In 1914, which
was a year of depression, 284 furnaces, belonging to 160 concerns, reported a pig iron production of 23,269,731 tons valued at $312,639,706; the other products of these establishments brought their total product up to a valuation of $317, 559,053. The year 1915 saw a recovery of pig iron production, which rose to 29,916,213 tons, or a gain of 16.6 per cent over 1909. About a third of the country's blast furnaces are in Pennsylvania, about one-fifth in Ohio, other States having an important share in the indus try being Alabama, Michigan, Illinois, New York, Virginia, Tennessee and Wisconsin. Of the pig iron produced 34 per cent is bessemer or low phosphorus, 40 per cent basic and 19 per cent foundry.
There are a little more than 200 plants in the United States manufacturing pig iron. In 1916 it is estimated that they gave employment to about 45,000 men, paying out wages of about $33,000,000, and adding almost $100,000,000 to the value of the ore and materials handled. See