Dictionary of Chemistry [6th Ed.]

contaminants for use in chemical

analyses.

analyserA device, used in the *po-

larization of light, that is placed in

the eyepiece of a *polarimeter to ob-

serve plane-polarized light. The

analyser, which may be a *Nicol

prism or *Polaroid, can be oriented

in different directions to investigate

in which plane an incoming wave is

polarized or if the light is plane po-

larized. If there is one direction from

which light does not emerge from

the analyser when it is rotated, the

incoming wave is plane polarized. If

the analyser is horizontal when ex-

tinction of light takes place, the po-

larization of light must have been in

the vertical plane. The intensity of a

beam of light transmitted through an

analyser is proportional to cos^2 θ,

where θis the angle between the

plane of polarization and the plane

of the analyser. Extinction is said to

be produced by ‘crossing’ the *polar-

izer and analyser.

analysisThe determination of the

components in a chemical sample.

Qualitative analysis involves deter-

mining the nature of a pure un-

known compound or the compounds

present in a mixture. Various chemi-

cal tests exist for different elements

or types of compound, and system-

atic analytical procedures can be

used for mixtures. Quantitative

analysisinvolves measuring the pro-

portions of known components in a

mixture. Chemical techniques for

this fall into two main classes: *volu-

metric analysis and *gravimetric

analysis. In addition, there are numer-

ous physical methods of qualitative

and quantitative analysis, including

spectroscopic techniques, mass spec-

trometry, polarography, chromatog-

raphy, activation analysis, etc.

analyser 36

a

anchimeric assistanceSee neigh-

bouring-group participation.

Andrews titration A titration

used to estimate amounts of reduc-

ing agents. The reducing agent being

estimated is dissolved in concen-

trated hydrochloric acid and titrated

with a solution of potassium iodate.

A drop of tetrachloromethane is

added to the solution. The end point

of the titration is reached when the

iodine colour disappears from this

layer. This is due to the reducing

agent being oxidized and the iodate

being reduced to ICl. This reaction in-

volves a four-electron change.

ANFOAmmonium nitrate–fuel oil.

A mixture used extensively as a blast-

ing agent in mining and quarrying.

The proportions are approximately

94% ammonium nitrate and 6% fuel

oil. ANFO has been used in terrorist

attacks (e.g. an attack on the Murrah

Federal Building, Oklahoma City, in

1995).

angle-resolved photoelectron

spectroscopy (ARPES)A technique

for studying the composition and

structure of surfaces by measuring

both the kinetic energy and angular

distribution of photoelectrons

ejected from a surface by electromag-

netic radiation. See also photoelec-

tron spectroscopy.

anglesiteA mineral form of

*lead(II) sulphate, PbSO 4.

angle strainThe departure of a

bond angle from its normal value.

The effects of angle strain are often

apparent in aliphatic ring com-

pounds. For example, in cyclopen-

tane, C 5 H 10 , the angles between the

bonds of the ring differ from the nor-

mal tetrahedral angle (109° 28 ′),

which is found in cyclohexane. This

ring form of angle strain is often

called Baeyer strain.