osite end.

[Illustration: FIG. 241.--Diagram of a simple telephone circuit.]

324. Cost of Electric Power. The water power of a stream depends
upon the quantity of water and the force with which it flows. The
electric power of a current depends upon the quantity of electricity
and the force under which it flows. The unit of electric power is
called the watt; it is the power furnished by a current of one ampere
with a voltage of one volt.

One watt represents a very small amount of electric power, and for
practical purposes a unit 1000 times as large is used, namely, the
kilowatt. By experiment it has been found that one kilowatt is
equivalent to about 1-1/3 horse power. Electric current is charged for
by the watt hour. A current of one ampere, having a voltage of one
volt, will furnish in the course of one hour one watt hour of energy.
Energy for electric lighting is sold at the rate of about ten cents
per kilowatt hour. For other purposes it is less expensive. The meters
commonly used measure the amperes, volts, and time automatically, and
register the electric power supplied in watt hours.

INDEX

Absorption, of heat by lampblack, 143-144.
of gases by charcoal, 57.
of light waves, 135-138.

Accommodation of the eye, 123.

Acetanilid, 259.

Acetylene, as illuminant, 152-153.
manufacture of, 152-153.
properties of, 220.

Acid, boric, 253.
carbolic, 152, 251, 252.
hydrochloric, 55, 80, 227, 238, 241.
lactic, 230.
oxalic, 247, 248.
salicylic, 253.
sulphuric, 55, 80, 240, 241, 307.
sulphurous, 242.

Acids, action on litmus, 220.

Adenoids, 51.

Adulterants, detection of, 16.

Air, characteristics of, 81-83, 86, 189.
compressibility of, 91.
expansion of, 10-11.
humidity, 38, 39.
pumps, 201-205.
transmits sound, 269.
weight of, 86.
_See_ Atmosphere.

Alcohol, 234.
in patent medicines, 260.

Alizarin, 248.

Alkali, 222.

Alternating current, 351.

Alum, 247.
in baking powder, 230.

Ammeter, 341, 343.

Ammonia, 152.
a base, 221-222.
in bath, 226.
in manufacture of ice, 98.
neutralizing chlorine, 240.

Ampere, 342.

Anemia, 259.

Angle, of incidence, 110.
of reflection, 110.
of refraction, 114.

Aniline, 152, 245.

Animal charco