Chemistry Reference
In-Depth Information
reaction, chemical
See
chemical reaction
.
reaction, nuclear
See
nuclear reaction
.
recovery
The process of extracting valuable materials from
rocks
,
minerals
and
ores
.
recrystallization
(1) Repeated
crystallization
; (2) a
diagenetic
process that involves
the recrystallization of
minerals
after the dissolution by
groundwater
of
primary
or
secondary minerals
and the subsequent
precipitation
of new minerals.
reducing atmosphere
A smoke-laden
atmosphere
in which there is practically no
oxygen
.
reduction
A
chemical reaction
in which a
substance
loses
oxygen
and/or gains
hydro-
gen
or
electrons
.
redwood
See
camwood
.
refining
The removal of
impurities
from a
substance
.
reflected light
See
light reflection
.
refraction
The change in direction of a beam of
light
as it passes from one medium
(e.g., air or water) into another, such as
glass
.
refractive index
The numerical value of the extent to which a beam of
light
is
deflected from its original path when passing from a
vacuum
into a given
substance
.
refractory material
A solid
material
(i.e.,
pottery
or
brick
) that withstands high tem-
peratures without changes in shape or in chemical composition.
relative age
See
age
,
relative
.
relative date
See
date
,
relative
.
relative dating
See
dating
,
relative
.
remote sensing
A technology for acquiring information about distant objects or
phenomena, without physical contact with them; it is based on the use of
electro-
magnetic radiation
either reflected from or radiated by objects of interest.
replication
See
DNA replication
.
residual clay
See
primary clay
.
resin
A
solid
or semisolid
organic substance
, generally of high
molecular weight
, with
no definite
melting point
; until the twentieth century all resins were of natural
origin, most being exudations from plants.
respiration
The process by which living organisms use oxygen for their life
processes so as to make
substances
required for maintenance and growth, and give
off carbon dioxide.
retting
A bacterial process for softening and causing the
decay
of woody tissue asso-
ciated with vegetable
fibers
, such as
flax
and
hemp
.
rhyolite
A low-
density
volcanic
rock
, also known as
lava
, that contains a high
proportion of
silica
.
ribonucleic acid (RNA)
A
nucleic acid
in the
cell's cytoplasm
that transfers informa-
tion from
DNA
to the
proteinmaking
sites of the
cell
s; its
molecule
is very similar to
that of DNA, although it is single-stranded and consists of a chain of
ribonucleotides
instead of DNA's deoxyribonucleotides.
