reached. The effect is analogous to
the phenomenon of supercooling, i.e.
the cooling of a liquid below its
freezing point without freezing. See
also oscillating reaction.
bisulphateSee hydrogensulphate.bisulphiteSee hydrogensulphite;
aldehydes.
bite angleSee chelate.bittern The solution of salts re-
maining when sodium chloride is
crystallized from sea water.
bitumenSee petroleum.bituminous coalSee coal.bituminous sandSee oil sand.biuret test A biochemical test to
detect proteins in solution, named
after the substance biuret (H 2 NCON-
HCONH 2 ), which is formed when
urea is heated. Sodium hydroxide is
mixed with the test solution and
drops of 1% copper(II) sulphate solu-
tion are then added slowly. A positive
result is indicated by a violet ring,
caused by the reaction of *peptide
bonds in the proteins or peptides.
Such a result will not occur in the
presence of free amino acids.bivalent(divalent)Having a va-
lency of two.Black, Joseph(1728–99) British
chemist and physician, born in
France. He studied at Glasgow and
Edinburgh, where his thesis (1754)
contained theÜrst accurate descrip-
tion of the chemistry of carbon diox-
ide. In 1757 he discovered latent
heat, and was theÜrst to distinguish
between heat and temperature.blackdamp(choke damp)Air left
depleted in oxygen following the ex-
plosion ofÜredamp in a mine.black leadSee carbon.blancÜxe See barium sulphate.blast furnace A furnace for smelt-
ing iron ores, such as haematite
(Fe 2 O 3 ) or magnetite (Fe 3 O 4 ), to make
*pig iron. The furnace is a tall refrac-
tory-lined cylindrical structure that is
charged at the top with the dressed
ore (see beneficiation), coke, and a
Ûux, usually limestone. The conver-
sion of the iron oxides to metallic
iron is a reduction process in which
carbon monoxide and hydrogen are
the reducing agents. The overall reac-
tion can be summarized thus:
Fe 3 O 4 + 2CO + 2H 2 →3Fe + 2CO 2 +
2H 2 O
The CO is obtained within the fur-
nace by blasting the coke with hot
air from a ring of tuyeres about two-
thirds of the way down the furnace.
The reaction producing the CO is:
2C + O 2 →2CO
In most blast furnaces hydrocarbons
(oil, gas, tar, etc.) are added to the
blast to provide a source of hydrogen.
In the modern direct-reduction
process the CO and H 2 may be pro-
duced separately so that the reduc-
tion process can proceed at a lower
temperature. The pig iron produced
by a blast furnace contains about 4%
carbon and further reÜning is usually
required to produce steel or cast iron.blasting gelatinA high explosive
made from nitroglycerine and gun
cotton (cellulose nitrate).bleaching powderA white solid
regarded as a mixture of calcium
chlorate(I), calcium chloride, and cal-
cium hydroxide. It is prepared on a
large scale by passing chlorine gas
through a solution of calcium hy-
droxide. Bleaching powder is sold on
the basis of available chlorine, which
is liberated when it is treated with a
dilute acid. It is used for bleaching
paper pulps and fabrics and for steril-
izing water.bisulphate 74b