E

EACEmergency action code. See
hazchem code.

Earnshaw’s theorem The princi-
ple that a system of particles interact-
ing via an inverse square law, such as
Coulomb’s law of electrostatics, can-
not exist in a state of static equilib-
rium. The Reverend Samuel
Earnshaw (1805–88) proved this re-
sult in 1842. The theorem is of funda-
mental importance in chemistry
since it shows that it is not possible
to construct a correct model of atoms
and molecules if the electrons are
taken to be stationary.

earthThe planet that orbits the sun
between the planets Venus and Mars.
The earth consists of three layers: the
gaseous atmosphere (see earth’s at-
mosphere), the liquid hydrosphere,
and the solid lithosphere. The solid
part of the earth also consists of
three layers: the crustwith a mean
thickness of about 32 km under the
land and 10 km under the seas; the
mantle, which extends some
2900 km below the crust; and the
core, part of which is believed to be
liquid. The composition of the crust
is: oxygen 47%, silicon 28%, alu-
minium 8%, iron 4.5%, calcium 3.5%,
sodium and potassium 2.5% each,
and magnesium 2.2%. Hydrogen,
carbon, phosphorus, and sulphur are
all present to an extent of less than
1%.

earth’s atmosphere The gas that
surrounds the earth. The composi-
tion of dry air at sea level is: nitrogen
78.08%, oxygen 20.95%, argon 0.93%,
carbon dioxide 0.03%, neon 0.0018%,
helium 0.0005%, krypton 0.0001%,

and xenon 0.00001%. In addition to

water vapour, air in some localities

contains sulphur compounds, hydro-

gen peroxide, hydrocarbons, and

dust particles.

eboniteSee vulcanite.

ebullioscopic constantSee eleva-

tion of boiling point.

ebullioscopyThe use of *elevation

of boiling point to determine relative

molecular masses.

echelon A form of interferometer

consisting of a stack of glass plates

arranged stepwise with a constant

offset. It gives a high resolution and

is used in spectroscopy to study

hyperÜne line structure.

eclipsedSee conformation.

eclipsed conformationSee con-

formation.

eclipsingSee conformation.

ecstasy(methylenedioxymetham-

phetamine; MDMA)A designer drug

based on methamphetamine (see am-

phetamines). Originally intended as

an appetite suppressant, it produces

a feeling of euphoria and is widely

used as a club drug. It is a class A

drug in the UK.

O

O

C

H 2

N

H

CH 3

CH 3

Ecstasy

Edison cellSee nickel–iron accu-

mulator.