330

PAINTING MATERIALS

fied conditions; the amount of iodine in
grams as iodine monochloride (Hiibl solu-
tion) or iodine trichloride (Wijs solution)
absorbed by 100 grams of the oil or fat;
the measure of unsaturation of an oil or fat.

Ion, an electrically charged atom, radical, or
molecule; a positively charged ion is a
cation; e.g., Na+; a negatively charged ion
is an anion; e.g., Cl~~.

Xonization, electrolytic dissociation; the break-
ing up of molecules into two or more op-
positely charged ions; a phenomenon that
happens when polar compounds like inor-
ganic acids, bases, and salts are dissolved
in water, as NaCl-> Na+ + Cl~.

Isomer, any compound having the same num-
ber and kinds of atoms as another but differ-
ing in molecular arrangement as well as in
chemical and physical properties; having
the same empirical but different structural
formula; <?.£., butane, CHsCHaCf^CHs,
and isomeric butane, CHsCHCCH^CHs.

Isotropic, having the same physical properties
in every direction (cf.y Anisotropic).

Laminated, made up in thin plates, scales,
layers, or plies, as mica or plywood.

Levigate, to reduce a substance to a powder
by grinding in water, followed by fractional
sedimentation in order to separate the
coarser from the finer particles.

Lignin, the cellulose-related material which
lines the vegetable cells of wood; it acts as
a cement for the cells and imparts rigidity
to woody substance. Ligno-Cellulose, any
of several closely related substances con-
stituting the essential part of woody tissue.

Lixiviate, to extract and separate a soluble
substance from its mixture with insoluble
matter; to leach.

Lumen, the bore or inside passage of a small
tube, vessel, or duct.

Lye, a solution of sodium or potassium hydrox-
ide or the alkaline solution (potassium
carbonate) obtained in leaching wood ashes.

Melting Point (m.p.), the temperature at
which a crystalline solid changes to a liquid.

Micelle, a unit structure built up from com-
plex molecules in colloids. It may have
crystalline properties and is capable of
increase or diminution in size without
change in chemical nature. The cellulose
micelle, for example, is a bundle of parallel
chains composed of polymeric molecules
derived from the simple unit, CeHioOg.

Micron, jti, or mti, a unit of length equal to one
millionth part of a meter or one thousandth
part of a millimeter.

Micro-organism, any minute animal or plant
visible only through a microscope, as a
bacterium.
Mildew, any whitish or spotted discoloration
caused by parasitic fungi like mold on cloth,
leather, or other vegetable matter (see
Mold).
Mineral, any inorganic or fossilized organic
substance found in nature. Minerals differ
from rocks in that they have definite chem-
ical composition and usually definite crystal
structure. Their composition can generally
be expressed by a chemical formula.
Mineral Acid, inorganic acid, as hydrochloric,
nitric, or sulphuric acids.
Miscibility, the property of certain liquids to
mix with each other in all proportions, as
alcohol and water.
Mold (mould), a variety of fungus growth,
usually filamentous, which grows on damp
vegetable material (see Fungus)*
Molecular Weight, the relative mass of a
molecule referred to the mass of the hydro-
gen atom. It is calculated by adding the
atomic weights of all the elements and their
multiples indicated in the chemical formula;
e.g.y molecular weight of water, H2O, is
18.016, which is the sum of the atomic
weights of two atoms of hydrogen (at. wt,
1.008) plus that of one atom of oxygen
(at. wt, 16).
Molecule, the chemical combination of two
or more like or unlike atoms. It is the small-
est quantity of matter that can exist in the
free state and retain all the properties of
the original substance.
Monomer, the simple unpolymerized form of
a compound, having low molecular weight
as distinguished from the dimer or polymer
(see Polymer).
Mutual Solvent, that which acts as a common
solvent or coupling agent; that which brings
about the miscibility of substances not
otherwise miscible with each other; t.g.9 the
action of acetone in producing a mixture of
certain oils with water (see Coupling Agent).
Neutralization, in chemistry, the process of
combining an acid with a base (hydroxide
or alkali) in proportions to form a salt and
water, leaving no excess of free acid (hy-
drogen ions, H*) or base (hydroxyl ions,
OH~); the opposite of hydrolysis. The end
point of neutralization is shown by indi-
cators like litmus or phenolphthalein or by
measurement of electrical conductivity.
Normal Salt, a salt in which all the hydrogen
atoms of the acid have been replaced by a