Platinum

3754

Plato

ing minerals, is found principally in the Ural
mountains, in Colombia, and in the United
States, where the principal deposits arc lo-
cated in Alaska, in Butte, Humboldt, Plumas,
Sacramento and Yuba counties, California,
in Southwestern Oregon, and along the Gila
River in Arizona. Native or crude platinum
occurs usualh7 in small glistening granules of
a steel-gray color, which always contain,
along with some gold, copper, iron, and sand,
an admixture, in varying proportions, of sev-
eral metals—iridium, rhodium, palladium, os-
mium, ruthenium—most of which arc rarely
found except in association with platinum.
Sometimes, however, it is found in masses of
the size of a pigeon's egg, and pieces weighing
10 or even 20 pounds have occasionally been
known. Crude platinum is obtained by two
methods—hand sluicing and dredging.

Platinum is a tin-white metal of metallic
lustre, tenacious, malleable, and ductile. It
melts at the high temperature of 177° c., has
a specific gravity of 21.5, and is about as
hard as copper. It is a poor conductor of elec-
tricity, is easily welded at red heat, and is
particularly valuable in having a coefficient
of linear expansion (.0000907 at 50° K) ap-
proximately equal to that of glass, thus al-
lowing wires to be sealed into glass vessels
without the latter cracking on cooling—a
feature of especial importance in the manu-
facture of electrical apparatus. Platinum, par-
ticularly when in a spongy form prepared
by heating some of its compounds, has the
remarkable property of bringing about the
union of oxygen and hydrogen. In a similar
way it brings about the union of sulphur
dioxide and oxygen to form sulphur trioxide,
a process employed commercially in the man-
ufacture of sulphuric acid by the contact
process.

Platinum is used chiefly for making and
covering various apparatus and utensils for
use in the chemical laboratory, as crucibles,
spoons, blowpipe points, boilers, and tongs,
tt is employed also in the manufacture of
concentrated sulphuric acid, essential in the
production of explosives, and for incande-
scent lamps. The metal is used extensively in
photography, and in the manufacture of
jewelry, especially as a setting for precious
stones. The known supply of platinum is
small, and is rapidly diminishing with the
exhaustion of the mines in the Ural Moun-
tains. Formerly a minor producer of plati-
num, the U. S. since 1938 has been filling a
large proportion of its platinum needs from
deposits within its own borders.

Plato, the central figure in Greek philoso-
phy, was born in 427 K.C., of an aristocratic
Athenian family, tie was a pupil of Socrates
from whom he acquired that moral convic-
tion of the value of knowledge for life, and
of the vital connection between knowledge
and life, which continued to miirk his think-
ing. Thu condemnation and death of Socrates
in 399 B.C. broke up the circle of his disciples,
and Plato among others seems to have fled to
Megara. During the next ton or twelve years
he is said to have traveled widely, visiting,
among other places, Egypt, Gyrene, the
Greek colonies in Italy, and finally Syra-
cuse, then governed by the tyrant Dionysius.
On his return to Athens about 388 B.C. he
founded the school afterwards famous as the
Academy, and settled clown to the study and
teaching of philosophy.

The writings of Plato have come down to
us in a much more complete and finished
state than those of most of UK other great
thinkers of antiquity. Yet Plato apparently
attached much less importance to his writings
than to his oral teaching. In the Phcvdrus, a
dialogue which has been regarded by some as
a sort of inaugural discourse, written at the
time of the foundation of the Academy, writ-
ing is contrasted to its disadvantage with the
patient husbandry of the Socratic method of
discussion. And his writings themselves take
the form of dialogue, which is evidently a
literary reproduction of the Socratic conver-
sation. In most of them Socrates himself is
represented as the chief interlocutor, though,
of course, as Plato's philosophy develops, the
thought goes far beyond the scope of actual
Socratic teaching.

The early group includes (i.) a sub-group
of three 'Socratic' dialogues, so called because
they appear to go but little beyond the mas-
ter's teaching, tho Laches, Charwides, and
Lysis, the last of which is concerned with
friendship, while the two former work out
for the virtues of courage and temperance
the Socratic thesis that Virtue is knowledge.'
(2.) There may also be placed in the early
group the Apology, which is not a dialogue,
but appears to give the defence of Socrates
at his trial; and the two dialogues, the Bulky-
pkro, wherein Socrates, who was charged
with impiety, is made to show how little the
popular mind has grasped the nature of the
piety it extols; and the Critot in which So-
crates is shown, after his condemnation, as
nobly accepting the decision of the law, and
refusing to avail himself of his friends' offers
to aid him to escape. The remaining dialogue