Cork insulation; a complete illustrated textbook on cork insulation ...

REQUIREMENTS OF AN INSULATION 171
down and lose its original "dead-air" content ; and it must
not become saturated with moisture, since water is a rela-
tively good conveyor of heat. Suitable materials for the insu-
lation of warm or hot surfaces may possess the property of
absorbing water, for under normal conditions of service they
are rarely subjected to severe moisture conditions and are
almost constantly undergoing a drying out process; but cold
storage temperatures, on the other hand, involve moisture
conditions, through the precipitation of moisture from air in
contact with cold surfaces, and any material that is to retain
its original insulating efficiency in the almost continuous presence
of moisture and in the absence of appreciable heat, must
be impervious to moisture. In a word, a satisfactory insula-
tion for cold storage temperatures must be inherently free
from capillarity, as otherwise it will, in the presence of moist-
ure, become saturated and of no further value as an insulating
material.
At least as early as the reign of Augustus Caesar, cork was
used as stoppers for wine vessels, and has been used during
the intervening 2,000 years, practically unchallenged, as stop-
pers for liquid containers, thus amply demonstrating its inher-
ent imperviousness to moisture. And this important property
of cork—its entire freedom from capillarity— is in no way
impaired by the manufacturing process follow'ed in the pro-
duction of pure corkboard. On the contrary, the inherent or
natural ciualities of cork that makes it the basis for the best
cold storage <strong>insulation</strong> yet discovered or developed on a
commercial scale, are enhanced by the baking of the granules
of pure cork bark in metal molds under pressure at moderate
temperature ; for such manufacturing process brings out the
natural resin of the cork, which cements the particles firmly
together and makes the use of an artificial binder unnecessary,
and by coating the entire surface of each separate granule
with a thin film of the natural waterproof gum affords an
additional barrier against the possible entrance of moisture.
The "Navy Test" was designed by the United States Navy
Department some years ago to concentrate in a short period
of time those destructive forces to which all cold storage
<strong>insulation</strong> is subject during its term of actual service. The