action is easier to perform than the
Sandmeyer reaction and takes place
at lower temperature, but generally
gives lower yields. It was discovered
in 1890 by the German chemist Ludwig Gattermann (1860–1920). See also
gattermann–koch reaction.
gauche See conformation; torsion angle.
Gay-Lussac, Joseph (1778–1850)
French chemist and physicist whose
discovery of the laws of chemical
combination in gases helped to establish the atomic theory. It also led to
*Avogadro’s law. See also charles’
law.
Gay Lussac’s law 1. When gases
combine chemically the volumes of
the reactants and the volume of the
product, if it is gaseous, bear simple
relationships to each other when
measured under the same conditions
of temperature and pressure. The law
was Ürst stated in 1808 by J. L. GayLussac and led to *Avogadro’s law.
2. See charles’ law.
gaylussite A mineral consisting
of a hydrated mixed carbonate of
sodium and calcium, Na 2 CO 3 .
CaCO 3 .5H 2 O.
GC-IR See gas chromatography infrared.
GCMS See gas chromatography.
Geiger counter (Geiger–Müller
counter) A device used to detect and
measure ionizing radiation. It consists of a tube containing a lowpressure gas (usually argon or neon
with methane) and a cylindrical hollow cathode through the centre of
which runs a Üne-wire anode. A potential difference of about 1000 volts
is maintained between the electrodes. An ionizing particle or photon passing through a window into
the tube will cause an ion to be produced and the high p.d. will accelerate it towards its appropriate electrode, causing an avalanche of further ionizations by collision. The
consequent current pulses can be
counted in electronic circuits or simply ampliÜed to work a small loudspeaker in the instrument. It was
Ürst devised in 1908 by the German
physicist Hans Geiger (1882–1945).
Geiger and W. Müller produced an
improved design in 1928.
gel A lyophilic *colloid that has coagulated to a rigid or jelly-like solid.
In a gel, the disperse medium has
formed a loosely-held network of
linked molecules through the dispersion medium. Examples of gels are
silica gel and gelatin.
gelatin(e) A colourless or pale yellow water-soluble protein obtained
by boiling collagen with water and
evaporating the solution. It swells
when water is added and dissolves in
hot water to form a solution that sets
to a gel on cooling. It is used in photographic emulsions and adhesives,
and in jellies and other foodstuffs.
gel electrophoresis See electrophoresis.
gel Ültration A type of column
*chromatography in which a mixture of liquids is passed down a column containing a gel. Small
molecules in the mixture can enter
pores in the gel and move slowly
down the column; large molecules,
which cannot enter the pores, move
more quickly. Thus, mixtures of molecules can be separated on the basis
of their size. The technique is used
particularly for separating proteins
but it can also be applied to other
polymers and to cell nuclei, viruses,
etc.
gelignite A high explosive made
from nitroglycerin, cellulose nitrate,
sodium nitrate, and wood pulp.
gauche
244
g
www.AzShimi.ir www.AzShimi.com
Sandmeyer reaction and takes place
at lower temperature, but generally
gives lower yields. It was discovered
in 1890 by the German chemist Ludwig Gattermann (1860–1920). See also
gattermann–koch reaction.
gauche See conformation; torsion angle.
Gay-Lussac, Joseph (1778–1850)
French chemist and physicist whose
discovery of the laws of chemical
combination in gases helped to establish the atomic theory. It also led to
*Avogadro’s law. See also charles’
law.
Gay Lussac’s law 1. When gases
combine chemically the volumes of
the reactants and the volume of the
product, if it is gaseous, bear simple
relationships to each other when
measured under the same conditions
of temperature and pressure. The law
was Ürst stated in 1808 by J. L. GayLussac and led to *Avogadro’s law.
2. See charles’ law.
gaylussite A mineral consisting
of a hydrated mixed carbonate of
sodium and calcium, Na 2 CO 3 .
CaCO 3 .5H 2 O.
GC-IR See gas chromatography infrared.
GCMS See gas chromatography.
Geiger counter (Geiger–Müller
counter) A device used to detect and
measure ionizing radiation. It consists of a tube containing a lowpressure gas (usually argon or neon
with methane) and a cylindrical hollow cathode through the centre of
which runs a Üne-wire anode. A potential difference of about 1000 volts
is maintained between the electrodes. An ionizing particle or photon passing through a window into
the tube will cause an ion to be produced and the high p.d. will accelerate it towards its appropriate electrode, causing an avalanche of further ionizations by collision. The
consequent current pulses can be
counted in electronic circuits or simply ampliÜed to work a small loudspeaker in the instrument. It was
Ürst devised in 1908 by the German
physicist Hans Geiger (1882–1945).
Geiger and W. Müller produced an
improved design in 1928.
gel A lyophilic *colloid that has coagulated to a rigid or jelly-like solid.
In a gel, the disperse medium has
formed a loosely-held network of
linked molecules through the dispersion medium. Examples of gels are
silica gel and gelatin.
gelatin(e) A colourless or pale yellow water-soluble protein obtained
by boiling collagen with water and
evaporating the solution. It swells
when water is added and dissolves in
hot water to form a solution that sets
to a gel on cooling. It is used in photographic emulsions and adhesives,
and in jellies and other foodstuffs.
gel electrophoresis See electrophoresis.
gel Ültration A type of column
*chromatography in which a mixture of liquids is passed down a column containing a gel. Small
molecules in the mixture can enter
pores in the gel and move slowly
down the column; large molecules,
which cannot enter the pores, move
more quickly. Thus, mixtures of molecules can be separated on the basis
of their size. The technique is used
particularly for separating proteins
but it can also be applied to other
polymers and to cell nuclei, viruses,
etc.
gelignite A high explosive made
from nitroglycerin, cellulose nitrate,
sodium nitrate, and wood pulp.
gauche
244
g
www.AzShimi.ir www.AzShimi.com