352
THE SEAS
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pearl essence usually
celluloid.
For the best
imitation pearls the pearl essence has to be chosen very
c’arefully because the effect produced depends on the size
of the guanin crystals.
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It is comparative'Iy easy to dlstinguiSh an imitation from
a real pearl.
The hollow glass imitation pearls can
be
detected by the sharp reection given by the glass surface
and by their lightness.
The solid variety are not so easy
to detect, but'the pearly coating can be cut off, is inam—
mable,_ and can be dissolved with amy]
or acetone,
while the coating does not extend evenly up to the edge
of the hole through which the string passes.
The genuine
pearl has a denite weight for its size and is somewhat
iridesœnt; it gives no sharp reection from its surface
and
string hole has clearly been_‘drilled.
Acetone and
amyl '
acetate have no effect upon its surface which is,
however, un1ike those of the imitation varieties‘, attacked
by acid, since the pearl is made of calcareous matter. ‘
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PREÇIOUS CORALS
‘
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The beautiful red coral of commerce (Comllz‘um nobile) is
quite. un1ike the “
stony
” corals which constitute the great
.
maSs. of coral reefs, being a . “ false ” cOral more nearly
a]Jièd to the
and sea fan so common in
_
outiOwnwbaters:
The red_coral substance_is not exposed
_
in life but formsthe centralsupp0rting framework» of the
_
colony; on the surface of which is a soft crust through which
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ramify the _canals [which connect the ower—like white
feedingpolÿpS with which the surface is dotted_ (Fig. 65).
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Red com-1 isfound especially in the Mediterranean, off
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the south of France, and around the coasts of COfsica,
Sardinia, and Sicyand alsoalong the north coast of AfriCa
.
from the Straitsof Gibraltar to Tunis (Plate
It spreads
into the Atlantic to“ some extent andds shed off the Cape