4 BULLETIN 1226, IT. S. DEPARTMENT OF AGRICULTURE. 
where they can easily be tapped off separately through openings 
located at different levels, since the molten iron, because of its higher 
specific gravity, sinks to the bottom with the slag floating on its 
surface. 
The gaseous products of the reactions within the furnace rise 
through the descending column of ore, fuel, and flux, pass out through 
openings at the top, and are drawn through downcomers to be 
utilized in various ways. 
CLASSIFICATION AND SOURCES OF IRON ORES. 
The iron ores used in the blast-furnace industry of this country 
are the oxides, forming the three groups, the hematites, the brown 
ores, and the magnetites. An insignificent tonnage of iron-carbonate 
ore has been used in the past. There was no production of this ore 
during 1917 to 1919 and but 3,740 tons were mined in 1920. 
Iron ores are also divided into the two classes, Bessemer and non- 
Bessemer or basic, dependent upon the content of phosphorus. 
This classification arises from the fact that in the acid Bessemer 
method of making steel no phosphorus is removed during the process. 
The pig iron from which the steel is made must have no greater 
quantity of phosphorus than will maintain the Bessemer limit of 0.1 
per cent phosphorus in the steel. Since practically all the phos- 
phorus in the ore passes into the pig iron, a Bessemer ore must not 
contain over 0.001 per cent phosphorus for each per cent of iron in the 
ore. A Bessemer ore generally contains less than 0.05 per cent 
phosphorus. 
Ores containing more than 2 per cent manganese have been classed 
asmanganiferous and more than 18 per cent silica as siliceous. These 
are rather arbitrary classes, but are those adopted by the Lake 
Superior Iron Ore Association. 
Approximately 85 per cent of the iron ore mined in the United 
States is produced in the Lake Superior region which is divided into 
the Mesabi, Gogebic, Menominee, Marquette, Cuyuna, and Vermilion 
ranges. The most important of these ranges is the Mesabi, which 
produces over 64.7 per cent of the iron ore from the Lake Superior 
areas and nearly 55 per cent of the total production of the entire 
country. The other ranges produce, in the order mentioned, 12.5, 
10.0, 7.7, 2.6, and 2.5 per cent of the output of the Lake Superior 
region. The ores mined in this region are preponderantly hematites, 
though there is some brown ore and a little magnetite ore. 
In addition to the above-mentioned ranges, a small quantity of ore 
comes from the Baraboo and Mayville districts in south-central and 
southeastern Wisconsin and from the Michipicoten range and Moose 
Mountain district in Ontario, Canada, which is usually grouped with 
the ore of the Lake Superior region. 
Next in rank of production to the Lake Superior iron-ore region is 
the Birmingham district of Alabama. Alabama produces 9 per cent 
of the total production of iron ore of the United States. Of the ore 
mined in Alabama, 84.7 per cent is hematite, and the rest brown ore. 
New York State produces slightly less than 1.7 per cent of the 
country's total. Of this, 80 per cent is magnetite from the Adiron- 
dacks. The remaining 4.3 per cent of the iron ore mined in this 
