PEAR. Syn. Pyrus, L. The fruit of Pyrus communis (Linn.), one of the rosaceæ. Its general qualities resemble those of the apple.
Composition of the Pear.
| Soluble matter— | |
| Sugar | 7·000 |
| Free acid (reduced to equivalent in malic acid) | 0·074 |
| Albuminous substances | 0·260 |
| Pectous substances, &c. | 3·281 |
| Ash | 0·285 |
| Insoluble matter— | |
| Seeds | 0·390 |
| Skins | 3·420 |
| Pectose | 1·340 |
| [Ash from insoluble matter included in weights given] | 0·050] |
| Water | 83·950 |
| ———— | |
| 100·000 | |
| (Fresenius.) |
PEARL. Syn. Margarita, Margaritum Perla, Unio, L. The most beautiful and costly pearls are obtained exclusively from the pearl oyster (Meleagrina margaritifera) of the Indian Seas. The principal fisheries are on the coast of Ceylon, and at Olmutz, in the Persian Gulf. An inferior description of pearl is procured from a fresh-water shell-fish (Unio margaritifera) in the neighbourhood of Omagh, county of Tyrone. A similar quality is also procured from the river Ythan, Aberdeenshire. It is probable that pearls from this source collected by the ancient Britons may have given rise to the statement by Tacitus, in his ‘Life of Agricola,’ of pearls “not very orient, but pale and wan,” being among the indigenous products of Great Britain.
Pearls are composed of membrane and carbonate of calcium; or, in other words, of substances similar to bladder and chalk, in alternate layers.
The cause of the production of pearls is highly curious and interesting. When any foreign body gains a permanent lodgment within the shells of any of the mollusca which are lined with pearly matter, or nacre, the pearly secretion of the animal, instead of being spread in layers on the inside of its habitation, is accumulated around the offending particles in concentric films of extreme tenuity, and more or less spherical, forming a pearl.
Pearls were formerly used in medicine as absorbents or antacids; and among the ancients they were occasionally taken, dissolved in acid, both as a remedy and for the purpose of displaying the careless opulence and luxury of their possessors. A perfect pearl, large, truly spherical, highly iridescent, and reflecting and decomposing the rays of light with vivacity, claims to rank with the most costly of the gems, and in some parts of the East is, with justice, more highly prized than even the diamond. In Europe, however, the present estimation of their value is somewhat different, “A handsome necklace of Ceylon pearls, smaller than a large pea, costs from £170 to £300; but one of pearls about the size of peppercorns may be had for £15. The pearls in the former sell at a guinea each, and those in the latter at about 1s. 6d.” (Milburn.) Seed pearls are of little value, however beautiful.
Pearl, Artificial. These are hollow spheres or beads of glass, perforated with two holes at opposite sides to permit of their being strung
into necklaces. A small portion of essence d’orient is introduced into each, by suction, and is then spread over the inner surface of the glass. When this has become dry and hard, the globe is filled up with white wax, spermaceti, or gum Arabic. The glass of which the beads are formed is slightly bluish and opalescent, and very thin. The latest improvement consists in removing the glassy appearance of the surface of the prepared bead by exposure to the fumes of hydrofluoric acid, highly diluted.
Pearl, Mother of. Syn. Unionum conchæ, L.; Nacre de perle, Fr. This is the internal or nacreous layer of those shells which produce the pearls for ornamenting the person; hence the term ‘mother of pearl’ is by no means inappropriate. It is also derived from several other species known in trade as ear-shells, green snail-shells, Bombay-shells, &c.