MEDIUMS AND ADHESIVES 5
also present in the cell contents of their tissues. Hydrocarbons do not seem to be
of so frequent occurrence as in the vegetable kingdom; among the alcohols there
are cholesterol and allied substances, which replace the phytosterols of the plants,
and higher aliphatic alcohols containing, as a rule, fewer carbon atoms than the
aliphatic plant alcohols. They have, in fact, the same carbon content (16, 18, 20)
as the most common fatty acids (Hilditch, p. 127).
Balsam (see also Resins). This general term has been used to designate the
resinous exudate from trees of the order Coniferae. It is also spoken of as oleo-
resin, turpentine, or gemme. The flow of balsam is quite profuse from shallow
incisions, except for larch balsam, and for that the heart of the tree is pierced.
The composition of balsams varies with the habitat of the tree. Those containing
the largest amount of essential oil come from trees growing in sandy soil near the
sea. Balsam is a soft, semi-liquid consisting of terpenes associated with bodies
of resinous character. By distillation, turpentine and the residue, colophony, are
obtained. The balsams most used in varnishes or as paint mediums are Venice
turpentine, Strasbourg turpentine, Canada balsam, and copaiba balsam. Bal-
sams flow easily on a surface and give a lustrous, pleasing quality when first
applied. Unless a harder resin is mixed with them, however, they deteriorate
easily.
Beeswax (see also Waxes) is produced by the common bee, Apis meUifica,
and also by some allied species. It is not collected by the bee, but is the
secretion of organs situated on the underside of the abdomen of the neuter or
working bees, and is used by them in forming the cells of the honeycomb. They
are said to consume about ten pounds of honey in order to secrete one pound of
wax. The wax may be obtained by melting the combs in hot water and by strain-
ing to free it from impurities, or by pressure extraction. A further yield may be
obtained by the use of volatile solvents. The industry is carried on in many parts
of the world and, naturally, the waxes from widely different localities vary con-
siderably in texture, color, and, to some extent, in chemical composition. The
color ranges from light yellow to dark, greenish brown. Those of light color are
used directly in many cases but the darker colored varieties are more frequently
bleached. This may be done by treatment with bleaching earths or charcoal, or
by chemical means such as simple exposure to light and air, or by treatment with
ozonized air or hydrogen peroxide; the use of oxidizing acids such as chromic
acid tends to cause deterioration. Beeswax is fairly brittle, but is plastic when
warm; bleached beeswax, * white wax/ is heavier, more brittle, and has a smoother
fracture. Like other waxes, beeswax is somewhat complex in composition and
contains about 10 per cent of hydrocarbons in addition to alcohols, acids, and
esters. It consists principally of melissyl (myricyl) palmitate (QsHsiCOOCaoHei)
and there are also present small proportions of a number of other alcohols and
acids, including ceryl and melissyl alcohols, palmitic, cerotic, melissic, and prob-
ably other higher fatty acids. Beeswax is very likely to be adulterated* In some
districts it is the custom to place artificial combs in the hives. These are fre-
quently composed of paraffin wax or stearic acid, or a mixture of the two, and