glossary

327

common classes of paint materials. These
are listed with their symbols.
AI
Sb
As
Ba
Cd
c
Cr
Co
Cu
Au
H
Fe
Pb
Mn
Hg
Mo
N
0
P
K
Se
Si
Na
Sr
S
Sn
Ti
Zn
Aluminum
Antimony
Arsenic
Barium
Cadmium
Carbon
Chromium
Cobalt
Copper
Gold
Hydrogen
Iron
Lead
Manganese
Mercury
Molybdenum
Nitrogen
Oxygen
Phosphorus
Potassium
Selenium
Silicon
Sodium
Strontium
Sulphur
Tin
Titanium
Zinc
Chemically Pure (c.p.), of the highest grade
but not necessarily 100 per cent pure; some-
times applied to commercial pigments to
describe a grade free from extender or added
inert pigment; e.g., c.p. cadmium sulphide.
Chromophore, a structural arrangement of
atoms which endows dyes and other related
organic compounds with color; e.g._9 the
quinoid structure in dyes.
Colloid, a state of subdivision of matter which
consists either of single, large molecules
(proteins, organic polymers, etc.) or of ag-
gregates of smaller molecules (colloidal
gold, sulphur, etc.). There are eight recog-
nized classes of colloids: solid sols (solid in
solid) such as alloys; suspensions (solid in
liquid) such as paint; smokes (solid in gas)
such as carbon smoke and zinc oxide smoke;
gels (liquid in solid) such as glue gel and
fruit jelly; emulsions (liquid in liquid) such
as mUk;/0£$ (liquid in gas) such as clouds
or visible steam; solid foams (gas in solid)
such as sponge "rubber or pumice; foams
(gas in liquid) such as soap lather. The
colloidal particles are called the disperse

phase and the surrounding medium, the
continuous or external phase.
Compound (see Chemical Compound).
Conchoidal Fracture, the type of fracture in
which the broken edge of a material has
shell-shaped depressions and elevations.
This fracture is often shown in amorphous
or vitreous substances like glass, cold
asphalt, and resins.
Condensation) in organic chemistry, a process
in which molecules of the same or different
substances combine to form molecules of
greater molecular weight, accompanied
usually by the loss of water; e.g., phenol-
formaldehyde condensation to form bake-
lite; the transformation from gaseous to
liquid state, as steam to water.
Consistency, the viscosity or fluidity of a
liquid or paste; the resistance of a product
to deformation or flow.
Co-precipitate, an intimate combination of
substances which are precipitated simul-
taneously in one chemical reaction; e.g.,
ZnS (zinc sulphide)-}- BaSO^ (barium sul-
phate) to form lithopone.
Coupling Agent, a solvent which will cause
two immiscible liquids to mix; e.g., the
addition of butyl alcohol to effect the mix-
ing of petroleum spirit and ethyl alcohol.
Covering Power, the extent to which a certain
volume of paint will spread on a surface in
normal thickness, usually expressed in
square feet per gallon.
Cryptocrystalline, very finely crystalline,
microcrystalline.
Crystal, a form of matter in which atoms or
molecules regularly aggregate by forces of
molecular affinity; it is a solid with a definite
internal structure and an external form
enclosed by a number of symmetrically
arranged plane faces. The granular texture
of solids is caused by the irregular massing
of crystal aggregates. Crystals are usually
classified in six systems: isometric or cubic >
in which the crystal axes ara of equal length
and at right angles to each other (sodium
chloride, NaCl); tetragonal, in which the
three axes are at right angles to each other
but one is of unequal length (nickel sul-
phate, NiSOr6H20); rhombic or ortho-
rhombic, in which there are three unequal
axes all at right angles to each other (barium
sulphate, BaSQ_4); monoclinic, in which the
three axes are of unequal length, two at
right angles to each other and a third at
right angles to one but inclined with refer-
ence to the others (gypsum, CaSO^