process expels moisture, chemically
combined water, and volatile matter;
in the case of sulphides, the sulphur
is expelled as sulphur dioxide and
the ore is converted into an oxide.
Rochelle salt Potassium sodium
tartrate tetrahydrate, KNaC 4 H 4 O 6 .
4H 2 O. A colourless crystalline salt
used for its piezoelectric properties.
Rochon prism An optical device
consisting of two quartz prisms; the
Ürst, cut parallel to the optic axis, receives the light; the second, with the
optic axis at right angles, transmits
the ordinary ray without deviation
but the extraordinary ray is deÛected
and can be absorbed by a screen. The
device can be used to produce planepolarized light and it can also be
used with ultraviolet radiation.
rock An aggregate of mineral particles that makes up part of the earth’s
crust. It may be consolidated or unconsolidated (e.g. sand, gravel, mud,
shells, coral, and clay).
rock crystal See quartz.
rocking-chair cell See intercalation cell.
rock salt See halite.
rock salt structure (sodium chloride structure) A type of ionic crystal
structure in which the cations have a
face-centred cubic arrangement, with
anions occupying all the octahedral
holes. It can equally be described as a
fcc array of anions with cations in
the octahedral holes. Each type of
ion has a coordination number of 6.
Examples of compounds that have
the structure are NaCl, KBr, AgCl,
AgBr, HgO, CaO, FeO, NiO, and SnAs.
A
• An interactive version of the structure
roentgen The former unit of dose
equivalent (see radiation units). It is
named after the discoverer of X-rays,
W. K. Roentgen (1845–1923).
roentgenium Symbol Rg. A radioactive transactinide; a.n. 111. It was
made by fusion of
209 Bi with
64 Ni.
Only a few atoms have been detected.
A
• Information from the WebElements
site
Rohypnol See flunitrazepam.
root-mean-square value (RMS
value) 1. (in statistics) A typical value
of a number (n) of values of a quantity (x 1 ,x 2 ,x 3 …) equal to the square
root of the sum of the squares of the
values divided by n, i.e.
RMS value = √[(x 1
2 + x 2
2 + x 3
2 …)/n]
2. (in physics) A typical value of a
continuously varying quantity, such
as an alternating electric current, obtained similarly from many samples
taken at regular time intervals during a cycle. Theoretically this can be
shown to be the effective value, i.e.
the value of the equivalent direct current that would produce the same
power dissipation. For a sinusoidal
current this is equal to I m /√2, where
I m is the maximum value of the current.
ROSDAL A type of *line notation
used in databases. It is based on a
*connection table for the molecule
written in a single text line. ROSDAL
is an acronym for Representation of
Organic Structure Descriptions
Arranged Linearly.
Rose’s metal An alloy of low melting point (about 100°C) consisting of
50% bismuth, 25–28% lead, and
22–25% tin.
rosin A hard natural resin obtained
from pine tree oil and the wastes
from processing wood pulp. It may
be colourless, yellow, brown, or
465
rosin
r
www.AzShimi.ir www.AzShimi.com
combined water, and volatile matter;
in the case of sulphides, the sulphur
is expelled as sulphur dioxide and
the ore is converted into an oxide.
Rochelle salt Potassium sodium
tartrate tetrahydrate, KNaC 4 H 4 O 6 .
4H 2 O. A colourless crystalline salt
used for its piezoelectric properties.
Rochon prism An optical device
consisting of two quartz prisms; the
Ürst, cut parallel to the optic axis, receives the light; the second, with the
optic axis at right angles, transmits
the ordinary ray without deviation
but the extraordinary ray is deÛected
and can be absorbed by a screen. The
device can be used to produce planepolarized light and it can also be
used with ultraviolet radiation.
rock An aggregate of mineral particles that makes up part of the earth’s
crust. It may be consolidated or unconsolidated (e.g. sand, gravel, mud,
shells, coral, and clay).
rock crystal See quartz.
rocking-chair cell See intercalation cell.
rock salt See halite.
rock salt structure (sodium chloride structure) A type of ionic crystal
structure in which the cations have a
face-centred cubic arrangement, with
anions occupying all the octahedral
holes. It can equally be described as a
fcc array of anions with cations in
the octahedral holes. Each type of
ion has a coordination number of 6.
Examples of compounds that have
the structure are NaCl, KBr, AgCl,
AgBr, HgO, CaO, FeO, NiO, and SnAs.
A
• An interactive version of the structure
roentgen The former unit of dose
equivalent (see radiation units). It is
named after the discoverer of X-rays,
W. K. Roentgen (1845–1923).
roentgenium Symbol Rg. A radioactive transactinide; a.n. 111. It was
made by fusion of
209 Bi with
64 Ni.
Only a few atoms have been detected.
A
• Information from the WebElements
site
Rohypnol See flunitrazepam.
root-mean-square value (RMS
value) 1. (in statistics) A typical value
of a number (n) of values of a quantity (x 1 ,x 2 ,x 3 …) equal to the square
root of the sum of the squares of the
values divided by n, i.e.
RMS value = √[(x 1
2 + x 2
2 + x 3
2 …)/n]
2. (in physics) A typical value of a
continuously varying quantity, such
as an alternating electric current, obtained similarly from many samples
taken at regular time intervals during a cycle. Theoretically this can be
shown to be the effective value, i.e.
the value of the equivalent direct current that would produce the same
power dissipation. For a sinusoidal
current this is equal to I m /√2, where
I m is the maximum value of the current.
ROSDAL A type of *line notation
used in databases. It is based on a
*connection table for the molecule
written in a single text line. ROSDAL
is an acronym for Representation of
Organic Structure Descriptions
Arranged Linearly.
Rose’s metal An alloy of low melting point (about 100°C) consisting of
50% bismuth, 25–28% lead, and
22–25% tin.
rosin A hard natural resin obtained
from pine tree oil and the wastes
from processing wood pulp. It may
be colourless, yellow, brown, or
465
rosin
r
www.AzShimi.ir www.AzShimi.com