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Coral

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60
GEMS.
by the great number of such camei lately produced, and which, in consequence of competition and coarse work, were and are sold at very low prices. This made them common, and the upper classes of society considered them merely as ornaments for their in­feriors.
XXVI.
CORAL.
Coral is a marine production, the secretion of a par­ticular polyp, agglomerated according to certain laws, and disposed so as to resemble small trees without leaves.
In the sea it is covered with an almost cartilaginous net work of very delicate texture, covered with tubercles, in the centre of each of which is the polyp, of a milky-white colour, and provided with eight tentacles round the mouth. ' This net-work is called the bark of the polypi ; it is more delicate and soft than the centre, and is taken off in order to show the trunk, which, when out of the water, acquires the hardness of marble.
The substance of coral is composed of carbonate of lime, of organic elements in a great quantity, and of phosphate of lime.
Like all calcareous substances, it does not resist the file; it can also be cut, carved, engraved, and polished in the same manner as shells.
Alkalies do not corrode it, and in diluted acids it
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