IRON-ORE DRESSING MACHINERY.—III this country much money, labor, and thought have been devoted to the enrichment of iron ores by roasting to drive off sulphur and carbonic acid, or make the ore more friable, and by washing and screening to remove the clay and sand from earthy ores. Iron ores being so different in character from lead, zinc, and copper ores, their value per ton being so much less, and many varieties being magnetic, a property which is made available in the separation of the mineral from the gangue, iron-ore dressing works, and the machinery used in them, is quite different from that employed for other ores. Earthy, clayey ores are cleaned in many districts by crude machines of large capacity, such as log-washers, which snffice to make a fairly good separation of the mineral and gangue, the difference in specific gravity being so great. Rough jigs are used in many places, and in some localities elaborately equipped dressing works have been erected. For many years the magnetites of the Adirondack region have been roasted, and jigged on screens in water. Laterally crushers and rolls have been introduced for comminuting toe ore, and plunger and rotary jigs have taken the place of the cruder jigs formerly in use. At the large dressing works of the Chatcaugay Ore and Iron Co., at Lyon Mountain, N. Y., the cost of dressing 137.551 tons of ore, from September 26, 1886, to January 1, 1888, was 30 7 cents per ton, which was divided as follows : Fuel, 61 cents ; labor, 15', cents ; oil, waste, etc., cents ;
supplies, renewals, and repairs, cents. The ore was crushed from 15 in. size to!, in. size by Blake rock breakers and multiple crushers, and was washed on Conkling jigs. Recently much attention has been given to the magnetic concentration of iron ores, and several plants, which have already made large outputs, have been erected. The most extensive and systematic work with this process has probably been done at Witherbee, Sherman & Co.'s mines at Port Henry, N. Y., and at the Croton mines, at Brewster, N. Y. At the latter place, Mr. W. H. Hoffman states that 88 per cent. ore is concentrated at a cost of $1.95 per gross ton of concentrates. This expense is divided as follows : Mining and delivering to roasters, 81.13 : roasting, 23 cents ; handling at roasters, 3 cents ; preparation and screening, 22 cents ; supplies and repairs, 5:3- cents ; separating, including labor and power, 7 cents; delivering concentrates to railway, 4 cents ; office and laboratory expenses, 4i- cents ; insur ance, interest, and taxes. 13 cents. This is equivalent to a cost of less than 16 cents per ton of crude ore for dressing, and is very remarkable, and, at the present time, exceptional practice.