The electrolytes are separated by a
porous pot. The cell gives an e.m.f. of
about 1.9 volts.
burette A graduated glass tube
with a tap at one end leading to a
Üne outlet tube, used for delivering
known volumes of a liquid (e.g. in
titration).buta-1,3-diene(butadiene)A
colourless gaseous hydrocarbon,
CH 2 :CHCH:CH 2 ; m.p. –109°C; b.p.
–4.5°C. It is made by catalytic dehy-
drogenation of butane (from petro-
leum or natural gas) and polymerized
in the production of synthetic rub-
bers. The compound is a conjugated
*diene in which the electrons in the
pi orbitals are partially delocalized
over the whole molecule. It can have
trans and cis forms, the latter taking
part in *Diels–Alder reactions.butanal(butyraldehyde)A colour-
lessÛammable liquid aldehyde,
C 3 H 7 CHO; r.d. 0.8; m.p. –99°C; b.p.
75.7°C.butaneA gaseous hydrocarbon,
C 4 H 10 ; d. 0.58 g cm–3; m.p. –138°C;
b.p. 0°C. Butane is obtained from
petroleum (from reÜnery gas or
by cracking higher hydrocarbons).
The fourth member of the *alkane
series, it has a straight chain of
carbon atoms and is isomeric with
2-methylpropane (CH 3 CH(CH 3 )CH 3 ,
formerly called isobutane). It can eas-
ily be liqueÜed under pressure and is
supplied in cylinders for use as a fuel
gas. It is also a raw material for mak-
ing buta-1,3-diene (for synthetic rub-
ber).butanedioic acid (succinic acid)A
colourless crystalline fatty acid,
(CH 2 ) 2 (COOH) 2 ; r.d. 1.6; m.p. 185°C;
b.p. 235°C. A weak carboxylic acid, it
is produced by fermentation of sugar
or ammonium tartrate and used as a
sequestrant and in making dyes. Itoccurs in living organisms as an in-
termediate in metabolism, especially
in the *Krebs cycle.burette 88b
CH 2C
H 2OOHOHOButanedioic acidbutanoic acid (butyric acid)A
colourless liquid water-soluble acid,
C 3 H 7 COOH; r.d. 0.96; b.p. 163°C. It is
a weak acid (Ka= 1.5 × 10 –5mol dm–3
at 25°C) with a rancid odour. Its es-
ters are present in butter and in
human perspiration. The acid is used
to make esters forÛavourings and
perfumery.butanolEither of two aliphatic
alcohols with the formula C 4 H 9 OH.
Butan-1-ol, CH 3 (CH 2 ) 3 OH, is a
primary alcohol; r.d. 0.81; m.p.
–89.5°C; b.p. 117.3°C. Butan-2-ol,
CH 3 CH(OH)C 2 H 5 , is a secondary al-
cohol; r.d. 0.81; m.p. –114.7°C; b.p.
100 °C. Both are colourless volatile
liquids obtained from butane and are
used as solvents.butanone(methyl ethyl ketone)A
colourlessÛammable water-soluble
liquid, CH 3 COC 2 H 5 ; r.d. 0.8; m.p.
–86.4°C; b.p. 79.6°C. It can be made
by the catalytic oxidation of butane
and is used as a solvent.butene(butylene)Either of two
isomers with the formula C 4 H 8 :
1-butene(CH 3 CH 2 CH:CH 2 ), which is
made by passing 1-butanol vapour
over heated alumina, and but-2-ene
(CH 3 CH:CHCH 3 ), which is made by
heating 2-butanol with sulphuric
acid. They are unpleasant-smelling
gases used in the manufacture of
polymers. The isomer 2-methyl-
propane ((CH 3 ) 2 C:CH 2 ) was formerly