GLOSSARY

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metal, or all the hydroxyl radicals of a base
have been replaced by an acid radical; e.g.,
sodium carbonate, NaaCOs, normal salt,
and sodium bicarbonate, NaHCOa, acid
salt.

Occlusion, the adhesion of a finely dispersed
substance to larger solid particles or their
retention inside a solid mass.

Organic Acid, a compound containing one or
more carboxyl radicals, — COOH. A mono-
basic acid contains a single carboxyl group;
e.g., acetic acid CH3COOH; a dibasic acid
contains two carboxyl groups; e.g., oxalic
acid, (COOH)2, etc.

Oxidation, the act of combining with oxygen
or any electronegative element or radical,
as the addition of oxygen, chlorine, or
sulphur; increasing the positive valence of
an atom or ion by loss of electrons; e.g.,
Fe++ - i electron -* Fe+++.

Oxycellulose, oxidized cellulose, a degradation
product of cellulose formed by natural
oxidation or by bleaching processes.

Paint Film, a thin, continuous layer of medium
and pigment combined.

Particle Size, the average diameter of par-
ticles, as those of pigments or of colloids,
usually expressed in microns (ju).

Paste, in general, a,glutinous or other tena-
cious substance used as an adhesive; in paint
technology, a thick, putty-like mixture of
medium (usually oil) and pigment.

pH, a measure of acidity, neutrality, or
alkalinity in aqueous solutions; the symbol
for the logarithm of the reciprocal of the hy-
drogen ion concentration; pH «= log i/Cn+.
Solutions with pH 1-6 are acid, pH 7 are
perfectly neutral, and pH 8-14 are alkaline.
pH is measured electrometrically or colori-
metrically with the use of indicators.

Phase, any homogeneous substance, either
solid, liquid, or gaseous, that exists as a
distinct and mechanically separate portion
in a heterogeneous system, as in an emul-
sion; any homogeneous parts of a system
that are separated from one another by
definite physical boundaries.

Pleochroism, a change in color exhibited by
certain optically biaxial colored crystals
when rotated in polarized transmitted
light. If only two extremes of hue are ob-
served, the substance is said to be dichroic;
if three, trichroic.

Polarized Light is that in which the light
waves vibrate unilaterally, parallel to each
other in the same plane, elipse or circle,
whereas in non-polarized light the waves

vibrate in a number of planes. Light may be
plane polarized by reflection or refraction
at non-metallic surfaces or by transmission
through crystals showing double refraction.
Polyhydric Alcohol, an alcohol that contains
more than one hydroxyl group, as glycerol,
(CH2OH)2CHOHL
Polymer, in organic chemistry, a compound
formed by the combination of two or more
molecules of the same substance to produce
a new compound with the same empirical
formula but with higher molecular weight.
The polymerization process is usually ac-
companied by a change in state (as liquid
to solid) and a transfer of energy. A poly-
merized substance is often named with the
prefix, poly-; e.g., polyvinyl acetate.
Precipitate, the deposit of an insoluble sub-
stance in a solution after the addition of a
chemical or precipitating agent or on
evaporation, cooling, or electrolysis. Pre-
cipitation takes place in a solution when
conditions are such that the solution con-
tains more of the component than is re-
quired for saturation and there is an excess
of the component to be thrown out of the
solution.
Priming, in painting construction, a thin,
continuous layer between the ground and
the paint film, sometimes confused with
c ground.' A priming layer may consist of
pigment in medium but is usually medium
alone.
Protein, one of a group of nitrogenous organic
compounds of high molecular weight that
occurs in vegetable and animal matter.
Examples of protein-containing substances
are animal glue and egg albumen.
Pyrogenetic, produced of or by heat; made by
a furnace process.
Radiography, photography with x-rays.
Rectification, the redistillation of a liquid for
the purpose of purification.
Reduction, the act of depriving of oxygen or
any electronegative element or radical; in-
creasing the negative valence of an atom or
ion by addition of electrons; e.g., Fe*"1"4" -f- I
electron —»• Fe++; opposite of oxidation but
both reactions take place concurrently.
Refraction, the bending or deflection of light
rays when passing from one transparent
medium to another of different density.
Refractive Index, the ratio of the velocity of
light in a certain medium compared with
its velocity in air under the same conditions;
it is expressed as the ratio of the sine of the
incident angle of light to the sine of the