GLOSSARY

329

parts, as liquids of a certain boiling point or
boiling range, by distillation.

Fungicide, an agent which destroys fungi; as
mercuric chloride or Bordeaux mixture,

Fungus, a cryptogamous plant, destitute of
chlorophyll, deriving nourishment wholly or
chiefly from organic compounds; included
are bacteria, molds, rusts, smuts, and
mushrooms.

Gel, a jelly; same as jell; the colloidal suspen-
sion of a liquid in a solid; the solid phase of
a colloidal system as opposed to the sol, or
liquid, phase; a colloidal system in which
matter is dispersed in a solid dispersion
medium and in which the particles of the
disperse phase are at a standstill in contra-
distinction to those in a sol (see Sol) where
they are in motion.

Glyceride, an ester derived from the tribasic
alcohol, glycerol. The animal and vegetable
fats and oils are mainly triglycerides of the
higher fatty acids, as linolein.

Grain is the longitudinal arrangement of
fibres or particles in wood, stone, leather or
a fabricated substance; it may be the plane
of cleavage along which a material can be
split into two or more parts. In substances
that have grain, physical properties such
as moisture absorption, heat conduction,
and thermal expansion are likely to be
different with the grain than they are across
it. Tensile strength, flexure breaking
strength, and compressibility may also be
affected by the direction of the grain. Ma-
terials with grain may be said to be hetero-
geneous in physical properties.

Ground, the film or stratum in a painting
which lies between the support and the
paint or design proper. The materials in
the ground, paint, and surface layers have
many points of identity, but can be con-
sidered separately because they represent
different structural units in a picture. All
contain, except in true fresco and in some
gypsum grounds, a film material, or ad-
hesive, or binding medium. This occurs
alone in a surface film and often in a prim-
ing and acts as a vehicle or carrier of inert
pigment particles in the paint film and
usually in the ground. The ground is a
mechanical preparation on which the design
of the picture is executed. The surface film
is likewise mechanical and often is not
applied by the artist himself. Differences in
the function and in the treatment of these
three parts of a painting make it expedient

Hiding Power, the capacity of a paint to ob-
scure or hide the surface on which it is
applied; the degree of opacity in a paint or
pigment.
Homologous Series, a series of compounds,
the members of which differ in composition
by a constant amount and in which physical
constants change uniformly; e.g., the
paraffin series of hydrocarbons, the mem-
bers of which differ regularly by the addi-
tion of (—CH2) but have each the general
formula, CnH2n+2.
Hydrocarbon, any compound consisting of
hydrogen and carbon, as benzene, C6Hc.
Hydrolysis, (i) a decomposition reaction in-
volving water; (2) the partial reversal of a
neutralization or condensation reaction.
Hydrolyze, to cause hydrolysis.
Hydrophobic, said of a substance which does
not absorb or is not wetted by water.
Hydrophyllic, said of a substance which ab-
sorbs or is wetted by water.
Hydrous, containing water, as opposed to
anhydrous. Hydrous Salt, a salt contain-
ing water of crystallization, as gypsum,
Ca$O4*2H2O.
Hygroscopic, said of a substance which ab-
sorbs moisture from the atmosphere, as
calcium chloride or sodium hydroxide,
Inclusion, a foreign body, gaseous, liquid, or
solid, usually of minute size, enclosed in a
mineral or other body.
Infra-Red, the invisible part of the spectrum
between radio waves and the red portion of
the visible spectrum, consisting chiefly of
thermal rays; the wave-length region be-
tween 0.03 centimeter and 8000 A units.
Inorganic, not organic; pertaining to chem-
icals or substances which do not contain the
element, carbon; designating or composed
of matter other than animal or vegetable.
Inorganic acid, same as mineral acid; a
compound of hydrogen with a non-metal
other than carbon, or an acid radical con-
taining no carbon; ^., HC1 (hydrochloric
acid), HNOS (nitric acid), and H2SO4
(sulphuric acid).
Interface, the boundary between two phases;
e.g., the boundary between the dispersed
phase and the continuous phase in an
emulsion of immiscible liquids.
Interfacial Tension, the forces that orient
molecules and keep them together at the
boundary of a phase; the surface tension of
a liquid/liquid boundary surface.
Iodine Number or Value, the amount of
iodine absorbed by a fat or oil under speci-