In shallow mines the hoisting shaft is usually large enough for ventilation. If there are several shafts connected with one another, the circulation of the air in the mine is facilitated. If there is an adit, it helps still further. Artificial circulation is secured by fans placed at the entrance of mines, or by the use of compressed air which is carried into the mine. Compressed air is often introduced for power, and as it escapes it serves for ventilation as well.
Transportation. When the material to be mined has been loosened from its natural position, it is carried to the main gangways in barrows, chutes or cars. In the main gangways are tramways. The cars are of iron or wood, with wheels so close together that the cars can be run on short curves. The motive power is furnished by men, mules, steam engines or electricity. In vertical shafts the material is hoisted in buckets or cages. In inclined shafts, the hoisting is done with skips. The skips are on wheels, the rear wheels being much larger than the front ones. When the skip reaches the horizontal dumping platform at the top, the forward pitch dumps the ore automatically. The hoisting power in large mines is steam or electricity.
Ore Dressing. In most instances the ore must be subjected to a preliminary treatment before it is fit for metallurgical processes. The method of treatment varies with the ore. In many cases the masses and lumps of ore are crushed, or even ground to powder, often by the pounding of huge hammers in a stamp mill. The valuable part of the ore is then separated from that which is without value, the process of separation being different in different cases. Where the ore is much heavier than the waste, the separation is brought about through differences in specific gravity. The final extraction of the metal, like the preliminary treatment of the ore, differs with the nature of the ore. Gold, for example, is passed over a copper plate coated with mercury. The mercury forms an amalgam with the gold, and is afterward separated from it by heating until the mercury is volatilized. At this stage the product passes from the hands of the miner to the hands of the metallurgist. Ores of other metals are treated by other processes. The concentration of the crude ore is milling. Under this term the extraction of the metal from the ore is also sometimes included. Properly speaking, the process of mining ceases when the ore is ready for the mill or for shipment.
Mink, a carnivorous animal valued for its fur. It is related to the weasel, but is stouter in the body and has a bushier tail. The European mink is a little smaller than the American mink, and is more northern in its range. The Siberian mink has fur of a clear, tawny-brown color. The American mink is 15 or 20 inches long, with a tail of eight or nine inches, is yellowish-brown or dark-brown in color with a white spot on the chin and sometimes on the chest. The darker the color, the more highly prized the fur. This little animal is still found in wooded lands in widely-scattered portions of North America. It lives along the banks of streams and hunts both in water and on land, either by night or day. It is a great nest-robber, being fond of birds; a famous mouser; eats frogs, fish, lizards, grubs etc.; in winter it chases rabbits over the snowy ground. It can almost equal a fish in swimming, and on land is wonderfully agile, well-able to take care of itself. Its body is long and supple, and, notwithstanding its short legs, it can elude almost any pursuer; taking advantage of every hiding place, disappearing as by magic; it can climb like a squirrel. The young begin life in a cozy home prepared in hollow log or stump, hidden in tall growth near a stream. Or the nest may be in a hole among rocks. Among its enemies the owl may be mentioned with the fox, wild-cat, dog and otter. When cornered, the mink is a foe to be reckoned with.
Min′neap′olis, the largest city of Minnesota, is situated on both sides of the Mississippi, about seven miles from St. Paul, though the interval between is so built up as to make them really one city. The name is from the Sioux word minne, meaning water, and the Greek word polis for city. The Falls of St. Anthony, with a descent of 50 feet, furnish the water-power which has built up the city. The Mississippi is crossed by 12 bridges. Minneapolis is one of the most enterprising and important of the younger cities of the United States. The population advanced from 46,887 in 1880 to 261,974 in 1905 and to 335,396 in 1914.
The basis of growth is found in the city's location with reference to the great wheat and lumber interests of the northwest. It is the greatest primary wheat-market of the world. The annual wheat product of Minnesota is more than 70,000,000 bushels. More than half of this is here manufactured into flour, while not only the product of Minnesota, but a large part of the yield of the great fields of the Dakotas finds a market here. A single one of the city's great flouring-mills has a capacity of 15,000 barrels per day, and the aggregate capacity of its 22 flouring mills is 84,000 barrels daily. The elevators have a storage capacity of about 40,000,000 bushels. The great timber industry of the upper Mississippi valley finds its chief market and manufacturing center in Minneapolis. All the great trunk-lines of railroads in the northwest run to or through Minneapolis and three
