Salts or esters containing
the group –SCS(OR), where R is an or-
ganic group. Cellulose xanthate is an
intermediate in the manufacture of
rayon by the viscose process.
A member of a class of
which provide the characteristic yellow
and brown colours of autumn leaves.
Any substance foreign to
living systems. Xenobiotics include drugs,
pesticides, and carcinogens.
tion of such substances occurs mainly in
A piece of pre-existing rock
that occurs as an inclusion within an ig-
intrusion. Often it is a fragment
of the country rock surrounding the in-
clusion, although it may have been
ed to a hybrid rock by the intense
heat of the intruding magma.
Symbol Xe. A colourless odour-
less gas belonging to group 18 of the peri-
odic table (
); a.n. 54; r.a.m.
131.30; d. 5.887 g dm
; m.p. –111.9
C. It is present in the atmos-
phere (0.00087%) from which it is ex-
tracted by distillation of liquid air. There
are nine natural isotopes with mass num-
bers 124, 126, 128–132, 134, and 136.
Seven radioactive isotopes are also
known. The element is used in
cent lamps and bubble chambers. Liquid
xenon in a supercritical state at high tem-
peratures is used as a solvent for infrared
spectroscopy and for chemical reactions.
The compound Xe
noble-gas compound to be synthesized.
Several other compounds of xenon are
known, including XeF
, and XeO
. Recently, compounds
have been isolated that contain xenon–
carbon bonds, such as [C
which is stable under normal conditions.
The element was discovered in 1898 by
Ramsey and Travers.
Denoting conditions characterized
by an inadequate supply of water. Xeric
conditions exist in arid habitats, ex-
tremely cold habitats, and in salt
marshes. Certain plants are adapted to
live in such conditions.
Describing the structural
cations of certain plants (
phytes) that enable them to reduce water
loss, particularly from their leaves and
A plant that is adapted to
live in conditions in which there is either
a scarcity of water in the soil, or the at-
mosphere is dry enough to provoke ex-
cessive transpiration, or both. Xerophytes
have special structural (
cations, including swol-
len water-storing stems or leaves (
) and specialized leaves that may
be hairy, rolled, or reduced to spines or
have a thick cuticle to lower the rate of
transpiration. Examples of xerophytes are
desert cacti and many species that grow
on sand dunes and exposed moorlands.