the reduction in luminous intensity
of light passing through a material to
the length of the light’s path through
the material: i.e.
log(I/I 0 ) = –ε[J]l,
where ε is the molar *absorption
coefÜcient, I is the intensity after
passing through a sample of length l,
I 0 is the incident intensity, and [J] is
the molar concentration of species J.
The Beer–Lambert law was formed
empirically; however, it can be derived on the basis that the loss in intensity dI is proportional to the
thickness dl of the sample, the concentration [J], and the intensity I
(since the rate of absorption is proportional to the intensity). The
Beer–Lambert law means that the intensity of light (or any other form of
electromagnetic radiation) passing
through a sample diminishes exponentially with the concentration and
the thickness of the sample (for a
given wave number).
beet sugar See sucrose.
Beilstein’s test A test for the presence of a halogen (chlorine, bromine,
or iodine) in an organic compound. A
piece of copper wire or gauze is preheated strongly in the oxidizing
Ûame of a Bunsen burner (until the
Ûame is no longer green) and the test
substance placed on the wire or
gauze, which is re-heated. A green
Ûame indicates the presence of a
halogen.
bell metal A type of *bronze used
in casting bells. It consists of 60–85%
copper alloyed with tin, often with
some zinc and lead included.
Belousov–Zhabotinskii reaction
See b–z reaction.
Bénard cell A structure associated
with a layer of liquid that is conÜned
by two horizontal parallel plates, in
which the lateral dimensions are
much larger than the width of the
layer. Before heating the liquid is homogeneous. However, if after heating
from below the temperatures of the
plates are T 1 and T 2 , at a critical value
of the temperature gradient ∆T = T 1 –
T 2 the liquid abruptly starts to convect. The liquid spontaneously organizes itself into a set of convection
rolls, i.e. the liquid goes round in a
series of ‘cells’, called Bénard cells.
Benedict’s test A biochemical test
to detect reducing sugars in solution,
devised by the US chemist S. R. Benedict (1884–1936). Benedict’s reagent –
a mixture of copper(II) sulphate and a
Ültered mixture of hydrated sodium
citrate and hydrated sodium carbonate – is added to the test solution and
boiled. A high concentration of reducing sugars induces the formation
of a red precipitate; a lower concentration produces a yellow precipitate.
Benedict’s test is a more sensitive alternative to *Fehling’s test.
beneÜciation (ore dressing) The
separation of an ore into the valuable
components and the waste material
(gangue). This may be achieved by a
number of processes, including
crushing, grinding, magnetic separation, froth Ûotation, etc. The dressed
ore, consisting of a high proportion
of valuable components, is then
ready for smelting or some other
reÜning process.
bent sandwich See sandwich compound.
benzaldehyde See benzenecarbaldehyde.
benzene A colourless liquid hydrocarbon, C 6 H 6 ; r.d. 0.88; m.p. 5.5°C;
b.p. 80.1°C. It is now made from
gasoline from petroleum by catalytic
reforming (formerly obtained from
coal tar). Benzene is the archetypal
*aromatic compound. It has an un61
benzene
b
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of light passing through a material to
the length of the light’s path through
the material: i.e.
log(I/I 0 ) = –ε[J]l,
where ε is the molar *absorption
coefÜcient, I is the intensity after
passing through a sample of length l,
I 0 is the incident intensity, and [J] is
the molar concentration of species J.
The Beer–Lambert law was formed
empirically; however, it can be derived on the basis that the loss in intensity dI is proportional to the
thickness dl of the sample, the concentration [J], and the intensity I
(since the rate of absorption is proportional to the intensity). The
Beer–Lambert law means that the intensity of light (or any other form of
electromagnetic radiation) passing
through a sample diminishes exponentially with the concentration and
the thickness of the sample (for a
given wave number).
beet sugar See sucrose.
Beilstein’s test A test for the presence of a halogen (chlorine, bromine,
or iodine) in an organic compound. A
piece of copper wire or gauze is preheated strongly in the oxidizing
Ûame of a Bunsen burner (until the
Ûame is no longer green) and the test
substance placed on the wire or
gauze, which is re-heated. A green
Ûame indicates the presence of a
halogen.
bell metal A type of *bronze used
in casting bells. It consists of 60–85%
copper alloyed with tin, often with
some zinc and lead included.
Belousov–Zhabotinskii reaction
See b–z reaction.
Bénard cell A structure associated
with a layer of liquid that is conÜned
by two horizontal parallel plates, in
which the lateral dimensions are
much larger than the width of the
layer. Before heating the liquid is homogeneous. However, if after heating
from below the temperatures of the
plates are T 1 and T 2 , at a critical value
of the temperature gradient ∆T = T 1 –
T 2 the liquid abruptly starts to convect. The liquid spontaneously organizes itself into a set of convection
rolls, i.e. the liquid goes round in a
series of ‘cells’, called Bénard cells.
Benedict’s test A biochemical test
to detect reducing sugars in solution,
devised by the US chemist S. R. Benedict (1884–1936). Benedict’s reagent –
a mixture of copper(II) sulphate and a
Ültered mixture of hydrated sodium
citrate and hydrated sodium carbonate – is added to the test solution and
boiled. A high concentration of reducing sugars induces the formation
of a red precipitate; a lower concentration produces a yellow precipitate.
Benedict’s test is a more sensitive alternative to *Fehling’s test.
beneÜciation (ore dressing) The
separation of an ore into the valuable
components and the waste material
(gangue). This may be achieved by a
number of processes, including
crushing, grinding, magnetic separation, froth Ûotation, etc. The dressed
ore, consisting of a high proportion
of valuable components, is then
ready for smelting or some other
reÜning process.
bent sandwich See sandwich compound.
benzaldehyde See benzenecarbaldehyde.
benzene A colourless liquid hydrocarbon, C 6 H 6 ; r.d. 0.88; m.p. 5.5°C;
b.p. 80.1°C. It is now made from
gasoline from petroleum by catalytic
reforming (formerly obtained from
coal tar). Benzene is the archetypal
*aromatic compound. It has an un61
benzene
b
www.AzShimi.ir www.AzShimi.com