Dictionary of Chemistry [6th Ed.]

bromomethane (methyl bromide)

A colourless volatile nonÛammable

liquid, CH 3 Br; r.d. 1.68; m.p. –93°C;

b.p. 3.56°C. It is a typical *halo-

alkane.

N-bromosuccinimide (NBS)A

crystalline solid, C 4 O 2 NBr, used ex-

tensively as a reagent for elec-

trophilic addition of bromine. It acts

by producing a small constant supply

of bromine in solution

C 4 O 2 NBr + H++ Br–→C 4 O 2 NH +

Br 2.

85 brusselator

b

N
O O

Br

N-bromosuccinimide

bromothymol blue An acid–base

*indicator that is yellow in acid solu-

tions and blue in alkaline solutions.

It changes colour over the pH range

6–8.

Brønsted, Johannes Nicolaus

(1879–1947) Danish physical chemist.

He worked on thermochemistry and

electrochemistry and is best known

for the Lowry–Brønsted theory of

*acids and bases, which he proposed

(independently of Lowry) in 1923.

Brønsted acid See acid.

Brønsted baseSee acid.

bronze Any of a group of alloys of

copper and tin, sometimes with lead

and zinc present. The amount of tin

varies from 1% to 30%. The alloy is

hard and easily cast and extensively

used in bearings, valves, and other

machine parts. Various improved

bronzes are produced by adding

other elements; for instance, phos-

phor bronzes contain up to 1% phos-

phorus. In addition certain alloys of

copper and metals other than tin are

called bronzes – aluminium bronze is

a mixture of copper and aluminium.

Other special bronzes include *bell

metal, *gun metal, and *beryllium

bronze.

Brownian movement The contin-

uous random movement of micro-

scopic solid particles (of about 1

micrometre in diameter) when sus-

pended in aÛuid medium. First ob-

served by the British botanist Robert

Brown (1773–1858) in 1827 when

studying pollen particles, it was origi-

nally thought to be the manifestation

of some vital force. It was later recog-

nized to be a consequence of bom-

bardment of the particles by the

continually moving molecules of the

liquid. The smaller the particles the

more extensive is the motion. The ef-

fect is also visible in particles of

smoke suspended in a still gas.

A

• Robert Brown’s original paper


• Jean Perrin’s paper
  brown-ring test A test for ionic ni-
  trates. The sample is dissolved and
  iron(II) sulphate solution added in a
  test tube. Concentrated sulphuric
  acid is then added slowly so that it
  forms a separate layer. A brown ring
  (of Fe(NO)SO 4 ) at the junction of the
  liquids indicates a positive result.

bruciteA mineral form of *magne-

sium hydroxide, Mg(OH) 2.

brusselatorA type of chemical re-

action mechanism that leads to an

*oscillating reaction. It involves the

conversion of reactants A and B into

products C and B by a series of four

steps:

A →X

2X + Y →3Y

B + X →Y + C

X →D