A glossary of mining and metallurgical terms

50 A GLOSSARY OF MININTG AND METALLURGICAL TERMS.
or "mild" steels, which are more nearly wrought-iron fused and
cast) stands between them, having less carbon than cast-iron and
more than wronght-iron. Some of the carbon in cast-iron is usually
segregated during cooling in the form of graphite, and this deter-
mines the grade of the iron as No. 1 foundry (the most graphitic,
coarsely crystalline, soft and 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), and white (hard, brittle,
radially crystalline, containing its carbon mostly in alloy with the
iron, and 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 of silicon. Ingot
iron, see Steel. Anthracite, charcoal, and 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 band, argillaceous siderite). See
Fossil ore.
Iron-reduction process. See Precipitation process.
Ironstone. 1. Iron-ore. 2. See Irestone.
Jacket. A covering to prevent radiation of heat, as the jacket of
a steam boiler ;
also, a casing around a furnace hearth in which water
is allowed to stand or circulate to keep the walls cool.
JackJuad-pit. A small shaft sunk within a mine.
Jackhead-punip. A subordinate pumj^ in the bottom of 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 of carrying ore to the reduction-works in bags
on horses, mules, etc.
Jars. A part of percussion-di'iiling apparatus for deep holes,
which is placed between the bit and the rods or cable, anil which by
producing at each up-stroke a decided jar of 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 of a skip
and running round a post, to prevent its too rapid descent ou an
inclined plane.