jx PAINTING MATERIALS
on the twigs and leaves of which the wax is deposited. Wax is removed first by
scraping, and finally by skimming water in which the scraped leaves and branches
are boiled. Insect wax is pale-colored and resembles spermaceti but has a more
fibrous structure and is more opaque. Chemically, it consists largely of ceryl
cerotate (C^HsiCOOC-zeBUs) together with other wax- esters and a small propor-
tion of hydrocarbons. It contains very little free fatty acid. It is employed in the
East for much the same purpose as beeswax, but it is not largely exported.
Chinese Wood Oil (see Tung Oil).
Collagen (see also Gelatin and Glue) is the organic material which largely
comprises the bones, the tendons, the cartilage, and the skin of animals. There
is no tissue which consists exclusively of collagen and it is invariably associated
with other protein material such as keratin, elastin, mucin, chondrin, etc., in
addition to other non-protein organic material and inorganic salts. When collagen
is heated in water to 80° or 90° C, it is slowly converted into the protein, gelatin.
Collodion (see also Cellulose Nitrate). It is said (Wilson, p. 140) that pharma-
ceutical collodion still consists of 8 ounces of pyroxylin dissolved in 3 parts ether
and I part alcohol. Proprietary substitutes are made up in amyl and butyl acetate
solutions and give a better product. As a plasticizer for flexible collodion, 3
ounces of camphor and 2 ounces of castor oil are used.
Colophony (see also Balsam and Resins), or rosin, is the residue which remains
after spirits of turpentine has been distilled off from the balsam or crude tur-
pentine produced by various species of pine. A large amount of colophony comes
from the long-leaf pine of the southern United States, and, in France, from the
Pinus maritima. The proportion of colophony to turpentine seems to be related
to the condition of the trees' habitat. The usual ratio is about three to one* There
is a larger amount of essential oil in the balsam from trees near the coast. After
distillation, the residue, which is rather dark, must be purified. Colophony has
a low melting point (100° to 130° C.) and is very soluble. It facilitates the running
of harder resins, and is supposed to improve the flowing qualities of a varnish.
In industry it is often used as a clarifier for dammar and other natural resin
varnishes (see Dammar). Its acid value is between 165 and 175, which corre-
sponds to about 89 to 97 per cent of abietic acid. Being so strongly acidic, it
probably acts by combining with basic substances which would otherwise be
precipitated*
As a varnish resin, colophony has many defects. The pale color and brilliant
gloss evident when it is freshly applied disappear rapidly on exposure. The film
becomes permanently whitened by the action of water and is easily destroyed
by abrasion. The introduction of Chinese wood oil to rosin varnish has materially
raised its value for industrial use. Colophony retards the gelation of the oil, and
the rapid drying and hard film of the oil reduce the weakness of the resin. A
synthetic resin called * ester gum,* made by esterifying colophony with glycerine,
is now widely used in the varnish industry. From ancient recipes for oil varnishes