es, or casings, which
receive the various instruments. For instance, the hook which carries
the telephone or the receiver, is hinged within the transmitter box. The
circuiting is all that it is intended to show.

[Illustration: _Fig. 88._ COMPLETE TELEPHONIC CIRCUIT]

The batteries of the two stations are connected up by a wire (A), unless
a ground circuit is used. The other side of each battery has a wire
connection (B, B') with one terminal of the transmitter, and the other
terminal of the transmitter has a wire (C, C') which goes to the
receiver. From the other terminal of the receiver is a wire (D, D')
which leads to the upper stop contact (E, E') of the telephone hook. A
wire (F, F') from the lower stop contact (G, G') of the hook goes to one
terminal of the bell, and from the other terminal of the bell is a wire
(H, H') which makes connection with the line wire (A). In order to make
a complete circuit between the two stations, a line wire (I) is run from
the pivot of the hook in station 1 to the pivot of the hook in station
2.

In the diagram, it is assumed that the receivers are on the hooks, and
that both hooks are, therefore, in circuit with the lower contacts (G,
G'), so that the transmitter and receiver are both out of circuit with
the batteries, and the bell in circuit; but the moment the receiver, for
instance, in station 1 is taken off the hook, the latter springs up so
that it contacts with the stop (E), thus establishing a circuit through
the line wire (I) to the hook of station 2, and from the hook through
line (F') to the bell. From the bell, the line (A) carries the current
back to the battery of station (A), thence through the wire (B) to the
transmitter wire (C) to receiver and wire (D) to the post (E), thereby
completing the circuit.

When, at station 2, the receiver is taken off the hook, and the latter
contacts with the post (E'), the transmitter and receiver of both
stations are in circuit with each other, but both bells are cut out.

CHAPTER XIII

ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING

DECOMPOSING LIQUIDS.--During the earlier experiments in the field of
electricity, after the battery or cell was discovered, it was noted that
when a current was formed in the cell, the electrolyte was charged and
gases evolved from it. A similar action takes place when a current of
electricity passes through a liquid, with the result that the liquid is
decomposed--that is, the liquid is