Postulate

3305

PotasSiiS

mail service is carried on between New York
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three-zone basis. Free Delivery was inaugu-
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was gradually extended until in 1887 it was
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more, or at any post office having a gross rev-
enue of $10,000. Rural free delivery was be-
gun on an experimental scale in 1896, and has
been extended continuously among the rural
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Second Class Matter embraces all newspa-
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cel Post.—Until Jan. i, 1913, merchandise was
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weight limit being 4 pounds. Since that
date it has been reorganized under parcel
post regulations. Fourth class matter, un-
der the 1925 regulations, embraces all mat-
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At the head of the U. S. Post Office Depart-
ment is the Postmaster-General. To his office
are attached the Chief Clerk, Superintendent
of Post Office Department Buildings, appoint-
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department, Purchasing Agent, and the di-
vision of post office inspectors under the Chief
Inspector. There are four assistant postmast-
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Office Department, though an officer of the
Treasury Department, is the Comptroller for
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postmasters are received and audited, and all
money order accounts are examined.

Postulate, a term brought into philosoph-
ical use by Kant, who used it to express as-
sumptions implied in morality, but not ca-
pable of theoretical demonstrations—viz., the
existence of free agents, the immortality of
the soul, and the existence of God as a moral
governor. By Kant himself these moral postu-
lates were, on the one hand, carefully dis-
tinguished from theoretical principles and hy-

potheses; and on the other, admitted only qg
the warrant of an objective moral necessity
We believe in free will, not merely because w<
wish to do so, but because as moral agents we
must. But the conception has come to be used,
especially by writers on the doctrine of prag-
matism, without any regard to these limita-
tions.

Potassium (K, 39.10), one of the alkaline
metals, first isolated by Sir Humphry Davy in
1807, and the first metal to be isolated from
an earth by the electric current. The impor-
tance to the world of the potassium supply
may be judged from an enumeration of the
wide uses to which its salts—commonly
known as potash—are put. Not only do the
potash salts form an essential ingredient of all
commercial fertilizers, but a large amount is
used in glass and soap making and in the
manufacture of numerous chemical products.
Potassium never occurs free in nature, al-
though it is present in fertile soils, from which
it is extracted by plants. In combination, usu-
ally as the chloride, sulphate, and carbonate, it
is found in sea water, in many minerals (micas
and feldspars), as an incrustation of the soil,
and in vegetable and animal substances. Be-
fore the beginning of the Great War (1914),
practically the world's entire supply of potash
salts came from the mines of Stassfurt in
Prussian Saxony.

In 1909-10 the German-American potash
war first awakened American interests to thfc
fact that they were dependent on Germany
for this most important product; and with the
complete cutting off of this main source of
supply by the war, the U. S. Geological Sur-
vey redoubled its efforts to discover new
sources in the United States. California is by
far the greatest producer, with Maryland sec-
ond, but far behind. The discovery of potash
in Western Texas in 1912 has led to the center-
ing of interest in that region as a probable
future commercial source of natural salts of
potash. The following are the chief compounds
of potassium: Potassium hydroxide, also
known as Caustic Potash, KOH, is formed by
the action of the metal on water and the elec-
trolysis of potassium salts, and prepared com-
mercially by boiling potassium carbonate with
milk of lime and evaporating the clear solu-
tion till it solidifies on cooling.

Potassium carbonate, or Potashes, KaCOa,
may be prepared as in the black ash process
for obtaining sodium carbonate, but is mainly
obtained from wood ashes and beet root resi-
due. Potassium nitrate, Nitre, or Salpetre,
KNOs, is chiefly obtained by the interaction of