boats (_zeugma_); the Til-Barsip of the Assyrian inscriptions, now
Birejik (q.v.).

4. The earlier Myrlea of Bithynia, now Mudania (q.v.), the port of
Brusa. The name was given it by Prusias I., who rebuilt it.

5. A city mentioned by Stephanus and Pliny as situated near the Tigris,
the identification of which is still uncertain.

6. A Greek city in Parthia, near Rhagae.

APARRI, a town of the province of Cagayan, Luzon, Philippine Islands, on
the Grande de Cagayan river near, its mouth, about 55 m. N. of
Tuguegarao, the capital. Pop. (1903) 18,252. The valley is one of the
largest tobacco-producing sections in the Philippines; and the town has
a considerable coastwise trade. Here, too, is a meteorological station.

APATITE, a widely distributed mineral, which, when found in large
masses, is of considerable economic value as a phosphate. As a mineral
species it was first recognized by A.G. Werner in 1786 and named by him
from the Greek [Greek: apatan], to deceive, because it had previously
been mistaken for other minerals, such as beryl, tourmaline, chrysolite,
amethyst, &c. Although long known to consist mainly of calcium
phosphate, it was not until 1827 that G. Rose found that fluorine or
chlorine is an essential constituent. Two chemical varieties of apatite
are to be distinguished, namely a fluor-apatite, (CaF)Ca4P3O12, and a
chlor-apatite, (CaCl)Ca4P3O12: the former, which is much the commoner,
contains 42.3% of phosphorus pentoxide (P2O5) and 3.8% fluorine, and the
latter 4.10 P2O5 and 6.8% chlorine. Fluorine and chlorine replace each
other in indefinite proportions, and they may also be in part replaced
by hydroxyl, so that the general formula becomes [Ca (F, Cl, OH)]
Ca4P3O12, in which the univalent group Ca(F, Cl, OH) takes the place of
one hydrogen atom in orthophosphoric acid H3PO4. The formula is
sometimes written in the form 3Ca3(PO4)2 + CaF2. Mangan-apatite is a
variety in which calcium is largely replaced by manganese (up to 10%
MnO). Cerium, didymium, yttrium, &c., oxides may also sometimes be
present, in amounts up to 5%.

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

Apatite frequently occurs as beautifully developed crystals, sometimes a
foot or more in length, belonging to that division of the hexagonal
system in which there is pyramidal hemi-hedrism. In this type of
symmetry, of which apatite is the best example, there is only one plane
of symmetry, which is perpendicular