Dictionary of Chemistry [6th Ed.]

potassium hydroxide. The reaction
on discharge is

2NiOOH.H 2 O + Fe →2Ni(OH) 2 +

Fe(OH) 2 ,

the reverse occurring during charg-
ing. Each cell gives an e.m.f. of about
1.2 volts and produces about 100 kJ
per kilogram during each discharge.
The nickel–cadmium cell is a similar
device with a negative cadmium elec-
trode. It is often used as a *dry cell.
Compare lead–acid accumulator.

nickelous compounds Com-
pounds of nickel in its +2 oxidation
state; e.g. nickelous oxide is nickel(II)
oxide (NiO).

nickel(II) oxide A green powder,
NiO; r.d. 6.6. It can be made by heat-
ing nickel(II) nitrate or carbonate
with air excluded.

nickel(III) oxide (nickel peroxide;
nickel sesquioxide)A black or grey
powder, Ni 2 O 3 ; r.d. 4.8. It is made by
heating nickel(II) oxide in air and
used in *nickel–iron accumulators.

nickel silverSee german silver.

Nicol prismA device for producing
plane-polarized light (see polarizer).
It consists of two pieces of calcite cut
with a 68°angle and stuck together
with Canada balsam. The extraordi-
nary ray (see double refraction)
passes through the prism while the
ordinary ray suffers total internal
reÛection at the interface between
the two crystals, as the refractive
index of the calcite is 1.66 for the or-
dinary ray and that of the Canada
balsam is 1.53. ModiÜcations of the
prism using different shapes and ce-
ments are used for special purposes.
It was devised in 1828 by William
Nicol (1768–1851).

nicotinamideSee nicotinic acid.

nicotinamide adenine dinu-
cleotide See nad.

nicotinamide adenine dinu-

cleotide phosphate (NADP)See

nad.

nicotineA colourless poisonous

*alkaloid present in tobacco. It is

used as an insecticide.

nicotinic acid (niacin)A vitamin of

the *vitamin B complex. It can be

manufactured by plants and animals

from the amino acid tryptophan. The

amide derivative, nicotinamide, is a

component of the coenzymes *NAD

and NADP. These take part in many

metabolic reactions as hydrogen ac-

ceptors. DeÜciency of nicotinic acid

causes the disease pellagra in hu-

mans. Good sources are liver and

groundnut and sunÛower meals.

nido-structure See borane.

nielsbohriumSee transactinide

elements.

NIFE cellSee nickel–iron accumu-

lator.

ninhydrinA brown crystalline sub-

stance, C 9 H 4 O 3 .H 2 O (see formula). It

reacts with amino acids to give a blue

colour. Ninhydrin is commonly used

in chromatography to analyse the

amino-acid content of proteins. It is

371 ninhydrin

n

N

O

OH

Nicotinic acid

O

O

OH

OH

Ninhydrin