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Result search of : J
Title Description
 Jargon   

A colorless, yellow, or smoky gem variety of zircon.  
 Joy Microdyne   

A wet-type dust collector for use at the return end of tunnels or hard headings. It may be either 6,000 ft3 /min or 12,000 ft3 /min (2.8 m3 /s or 5.7 m3 /s) in capacity. It wets and traps dust as it passes through the appliance, and releases it in the form of a slurry, which is removed by a pump. The microdyne is bolted to the outby end of the exhaust pipe, and the auxiliary fan is bolted to the outby end of the dust collector. 
 Jack Hole   

Eng. In coal mining, a bolthole.  
 Jig Bed   

The agent used in a jig that consists of the heavy fractions in the coal that behave in some respects like a dense fluid. The pulsation of the water or the motion of the screen keeps the bed open or in suspension during part of the cycle so that heavy minerals entering the jig can settle into the bed. Lighter materials cannot penetrate the jig bed and therefore are forced to remain in the upper part of the jig and eventually discharge over the top. Other agents in use are lead shot, iron punchings, iron shot, pyrite, and magnetite. 
 Jurassic   

The second period of the Mesozoic Era (after the Triassic and before the Cretaceous), thought to have covered the span of time between 190 million years and 135 million years ago; also, the corresponding system of rocks. It is named after the Jura Mountains between France and Switzerland, in which rocks of this age were first studied. 
 Jugglers   

Timbers set obliquely against pillars of coal to carry a plank partition, making a triangular air passage or manway.  
 Jet Rock   A coallike shale containing jet.  
 Jenkin   A drivage at right angles to the main cleat. Mason b. Eng. A road driven bordways in a pillar of coal. A jud driven bordways along a pillar of coal with goaf or an old bord on one side is called a "loose end jenkin." 
 Jack   A name for zinc ore; blackjack. See: sphaleriteb. Cannel coal interstratified with shale. c. Coaly shale, commonly canneloid. d. To drill a rock by hand, using a 4-lb (1.8-kg) hammer in one hand and a steel drill in the other ("single jacking"). "Double jacking" is to use a two-handed (sledge) hammer with the steel drill held by another worker. e. A portable device used for exerting great pressure or for lifting a heavy body through a small distance. Syn: anchor jack 
 Jar Mill   A small batch mill of ceramic material used in ore-testing laboratories in investigation of grinding problems.  
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