50 A GLOSSARY OF MININTG AND METALLURGICAL TERMS. or "mild" steels, which are more nearly wrought-iron fused <strong>and</strong> cast) st<strong>and</strong>s between them, having less carbon than cast-iron <strong>and</strong> more than wronght-iron. Some <strong>of</strong> the carbon in cast-iron is usually segregated during cooling in the form <strong>of</strong> graphite, <strong>and</strong> this deter- mines the grade <strong>of</strong> the iron as No. 1 foundry (the most graphitic, coarsely crystalline, s<strong>of</strong>t <strong>and</strong> black), No. 2 foundry (less open in grain), gray forge or mill-iron (still closer in grain, suitable for puddling), mottled (spotted with white iron), <strong>and</strong> white (hard, brittle, radially crystalline, containing its carbon mostly in alloy with the iron, <strong>and</strong> showing no visible graphite). These grades are also called simply No. 1, 2, 3, etc. So-called silver-gray, glazy, or carbonized iron is usually an iron rendered brittle by excess <strong>of</strong> silicon. Ingot iron, see Steel. Anthracite, charcoal, <strong>and</strong> coke iron are names given to pig-iron according to the fuel with which it is made. Iron hat. See Gossan. Iron-ores: 3Iagnetic {magnetite, iwotoperoxide), specular (hematite proper, red hematite, anhydrous peroxide), brown iron ore {hematite, broion hematite, limonite, etc., hydrated peroxides), spathic {siderite, carbonate), clay-ironstone (black b<strong>and</strong>, argillaceous siderite). See Fossil ore. Iron-reduction process. See Precipitation process. Ironstone. 1. Iron-ore. 2. See Irestone. Jacket. A covering to prevent radiation <strong>of</strong> heat, as the jacket <strong>of</strong> a steam boiler ; also, a casing around a furnace hearth in which water is allowed to st<strong>and</strong> or circulate to keep the walls cool. JackJuad-pit. A small shaft sunk within a mine. Jackhead-punip. A subordinate pumj^ in the bottom <strong>of</strong> a shaft, worked by an attachment to the main i)ump-rod. Jack-rull, Newc. See Wiiidla.ss. Jadding or Judding. See Holing. Jagging. A mode <strong>of</strong> carrying ore to the reduction-works in bags on horses, mules, etc. Jars. A part <strong>of</strong> percussion-di'iiling apparatus for deep holes, which is placed between the bit <strong>and</strong> the rods or cable, anil which by producing at each up-stroke a decided jar <strong>of</strong> the bit jerks it up, though it may be tightly wedged in the hole. Jig-brow. See Jinny-road. Jig-chain. S. Stafp'. A chain hooked to the back <strong>of</strong> a skip <strong>and</strong> running round a post, to prevent its too rapid descent ou an inclined plane.
A GLOSSARY OF MINING AND METALLURGICAL TERMS, 51 Jigging, Corn. Separatinjy ores acoordino- to specific o;ravity witli a sieve agitated up <strong>and</strong> down in water. The apparatus is called a _//
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