ture. Connection tables are a useful
way of storing molecular data, both
from the point of view of graphics
programs and also for database
searches, in which it is possible to
use the table to look for substruc-
tures.
conservation The sensible use of
the earth’s natural resources in order
to avoid excessive degradation and
impoverishment of the environment.
It should include the search for alter-
native food and fuel supplies when
these are endangered (as by defor-
estation and overÜshing); an aware-
ness of the dangers of *pollution;
and the maintenance and preserva-
tion of natural habitats and the cre-
ation of new ones, e.g. nature
reserves, national parks, and sites of
special scientiÜc intrest (SSSIs).
conservation lawA law stating
that the total magnitude of a certain
physical property of a system, such
as its mass, energy, or charge, re-
main unchanged even though there
may be exchanges of that property
between components of the system.
For example, imagine a table with a
bottle of salt solution (NaCl), a bottle
of silver nitrate solution (AgNO 3 ), and
a beaker standing on it. The mass of
this table and its contents will not
change even when some of the con-
tents of the bottles are poured into
the beaker. As a result of the reaction
between the chemicals two new sub-
stances (silver chloride and sodium
nitrate) will appear in the beaker:
NaCl + AgNO 3 →AgCl + NaNO 3 ,but the total mass of the table and its
contents will not change. This con-
servation of mass is a law of wide
and general applicability, which is
true for the universe as a whole, pro-
vided that the universe can be con-
sidered a closed system (nothing
escaping from it, nothing being
added to it). According to Einstein’s
mass–energy relationship, every
quantity of energy (E) has a mass (m),
which is given by E/c^2 , where c is the
speed of light. Therefore if mass is
conserved, the law of conservation of
energymust be of equally wide appli-
cation.consolute temperature The tem-
perature at which two partially mis-
cible liquids become fully miscible as
the temperature is increased.constantanAn alloy having an
electrical resistance that varies only
very slightly with temperature (over
a limited range around normal room
temperatures). It consists of copper
(50–60%) and nickel (40–50%) and is
used in resistance wire, thermocou-
ples, etc.constant-boiling mixture See
azeotrope.
constant proportions See chemi-
cal combination.constitutional isomerismSee iso-
merism.contact insecticideAny insecti-
cide (see pesticide) that kills its target
insect by being absorbed through the
cuticle or by blocking the spiracles,
rather than by being ingested.contact process A process for
making sulphuric acid from sulphur
dioxide (SO 2 ), which is made by burn-
ing sulphur or by roasting sulphide
ores. A mixture of sulphur dioxide
and air is passed over a hot catalyst
2SO 2 + O 2 →2SO 3
The reaction is exothermic and the
conditions are controlled to keep the
temperature at an optimum 450°C.
Formerly, platinum catalysts were
used but vanadium–vanadium oxide
catalysts are now mainly employed
(although less efÜcient, they are less
susceptible to poisoning). The sul-141 contact process
c