A method of advancing power-operated supports on a longwall face.
Double-acting hydraulic jacks are used in conjunction with supports that
slide forward on the floor and provide their own abutments for both their
forward movement and that of the conveyor. Nelson
A wave that advances by alternate compression and rarefaction of a medium,
causing a particle in its path to move forward and backward along the
direction of the wave's advance. In connection with waves in the Earth,
also known as primary wave, compressional wave, longitudinal wave, or
P-wave. Leet, 1
See:P wave
To haul by hand. Mason
A process of decomposition of organic substances that occurs in the
presence of water and with the complete exclusion of air. It is a kind of
slow distillation whereby chiefly methane (CH4 ) and smaller
quantities of other gaseous products, such as hydrogen (H2 ),
ammonia (NH3 ), and hydrogen sulfide (H2 S), are formed.
CF:disintegration
There are two main types of belts: (1) solid woven carcass impregnated and
covered with polyvinyl chloride; and (2) normal multiple construction,
which has polyvinyl chloride interlayers and covers. PVC belts are now
used widely in coal mines, being not only fire resistant but equal, if not
better, in quality than normal rubber belting. See also:conveyor
Nelson
A seismic wave that propagates by alternating compressions and
rarefactions in an elastic medium; the motion is in the direction of
propagation. It is the type that carries sound. Syn:compressional wave;
dilatational wave; irrotational wave; longitudinal wave; pressure wave;
push wave. AGI
A variety of topaz occurring in massive columnar aggregates. Also spelled
pychite.
A steep vertical gradient of density. Hy
a. A device for weighing and thus determining the specific gravity of
small quantities of oil or other liquids. Also spelled pyknometer.
Hess
b. A small bottle for determining the specific gravity of grains or small
fragments.
See:pyribole
A garnet composition between pyrope and almandine. See also:pyrope
The pyrope, almandine, spessartine subgroup of the garnet group.
See also:pyrope
An open crystal form consisting of nonparallel faces that intersect the c
crystallographic axis and consist of three (trigonal), four (tetragonal),
six (ditrigonal, hexagonal), or eight (ditetragonal) faces meeting at a
point. CF:bipyramid; hemipyramid; dome.
Descriptive of a crystal habit dominated by pyramids or bipyramids.
Same as idocrase; a variety of vesuvianite. Fay
a. In tunnel driving or shaft sinking, a pattern of shotholes drilled so
that the middle holes converge and outline a pyramid-shaped volume of
rock. These holes are fired first, and thus create a free face or
relieving cut. Pryor, 3
b. This cut has received its name from the shape of the initial opening.
The three or four holes are so directed that they meet at a point farthest
in. The pyramid cut is mainly employed in raises and for shaft sinking but
is not recommended for horizontal tunnels where a machine setup for a
definite direction of the four holes cannot easily be obtained.
Syn:German cut
c. This type of cut usually consists of four holes drilled to meet at a
common apex in the center of the face. This arrangement permits a high
concentration of explosive to be used, and the pyramid cut is therefore
particularly suitable for breaking hard ground. In very hard ground the
number of holes forming the cut may be increased to six. The main
disadvantage of this type of cut is the difficulty in drilling the holes
at the correct angles so that they will meet at the back of the cut. As in
the case of the wedge cut, therefore, a hole director should be used. Also
called diamond cut. McAdam, 2
d. In underground blasting, a type of cut employed in which the three cut
holes in the center may be drilled to form a pyramid. Also applied to four
holes meeting in a point. The simultaneous firing of these holes is
somewhat equivalent to using a very heavy charge of explosive and makes a
powerful blast. Lewis
e. A cut in which four central holes are drilled towards a focal point,
and when fired break out a tetrahedral section of strata. BS, 12
A bit crown, the face of which is covered with a series of stubby
pyramids, each apex of which is set with a diamond. Long
In crystallography, that of a crystal in which three or more inclined
faces cut the three crystal axes. Pryor, 3
A trigonal mineral, Ag3 SbS3 ; dimorphous with
pyrostilpnite; rhombohedral cleavage; soft; deep red; in late-primary or
secondary-enrichment veins, and an important source of silver.
Syn:antimonial red silver; dark red silver ore; dark ruby silver.
A tetracyclic hydrocarbon obtained from the coal-tar fraction boiling
above 360 degrees C; C16 H10 ; soluble in carbon disulfide,
toluene, and ligroin. CTD; Handbook of Chemistry and Physics, 2