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Page 40
[Illustration: FIG. 1.--SIMPLE BATTERY.]
Between the zinc plate and the wooden bar adjoining it is inserted a
strip of copper, c, for leading away the current from the zinc pole of
the battery, and between the carbon plates and the wooden bars is
inserted a doubled strip of copper, d, forming a connection between
the two carbon plates, and at the same time serving as a conductor for
conveying away the current from the carbon pole of the battery. This
element is to be plunged into a tumbler of sufficient depth to allow
the wooden bars to rest on the upper edge of the tumbler, while the
lower ends of the plates are one-half or three-quarters inch above the
tumbler bottom.
THE SOLUTION.
In the tumbler is placed a solution consisting of two-thirds of a
tumblerful of water, two ounces of bichromate of potash, and two
ounces of sulphuric acid. The bichromate of potash should be dissolved
first, then the acid should be slowly and carefully added. As the
solution heats, it is well to prepare it in an earthen vessel, which
is not liable to break. These materials should be used with great
caution, as they are poisonous, and the solution is very corrosive,
destroying almost everything with which it comes in contact. With
proper care, however, there is no danger in using the solution. It
gives off no poisonous vapors. Of course it is advisable to make the
solution in quantities of a gallon or so when convenient.
The battery compound known as the C and C battery compound, sold in
tin cans at most electric stores, is very convenient. It is only
necessary to place two or three ounces of it in the tumbler and add
the amount of water above mentioned, stirring the solution with a
glass or rubber rod until the crystals are dissolved.
A caution is necessary here. If only a portion of the contents of the
can are to be dissolved, it will be necessary to place the remainder
in a glass or earthen jar, as it will absorb moisture and rapidly eat
its way through the can.
The zinc plates should be amalgamated by plunging them into the
bichromate solution, then sprinkling on a minute quantity of mercury,
rubbing it about by means of a swab, until the entire exposed surface
is covered with mercury.
CONVENTIONAL SIGN FOR THE BATTERY AND GALVANOMETER.
In making electrical diagrams it is necessary to frequently represent
a battery. It requires too much time to make a sketch or drawing of a
battery. Besides this, the drawing of any particular kind of battery
might be misleading. A sign representing the galvanic battery has been
universally adopted. It consists of a long, thin mark or dash,
representing the carbon electrode, and a shorter, thick mark
representing the zinc electrode, thus: [Illustration] Where more cells
are required, this sign is repeated once for each cell, thus:
[Illustration] The galvanometer is represented thus: [Illustration]
By the use of the battery and a few articles such as may be found
anywhere, in addition to the pieces shown in Fig. 2, all the
experiments here described may be performed. As these pieces are shown
half size in the diagrams, Fig. 2, and about full size in the
perspective views, it will be unnecessary to give dimensions. The
bobbins, A A, are wound with No. 24 double cotton-covered magnet wire,
the terminals being soldered to eyes formed of pieces of spring wire
bent so as to form helical coils of two turns each, with the ends
inserted in holes drilled in heads of the spools. These coiled wires
answer a good purpose in making electrical connections. The magnet
frame, B, consisting of the cores and the yoke formed integrally of a
single soft gray iron casting, is adapted to receive the bobbins, A A,
to form an electro-magnet. The yoke of the magnet is provided with a
thumb-screw, e, for securing the magnet to the motor frame, C. The
latter is furnished with a base piece, f, a slotted standard for
receiving the clamping screw, e, of the magnet, and the standards, g,
in which is journaled the armature, h, on a wire extending through
both the standards and the armature.
The armature, h, consists of an oblong rectangular soft iron frame
having at one end a small pulley and at the other end an elliptical
boss, i, which is arranged obliquely to form in conjunction with the
spring, j, a circuit closer and opener, which closes the circuit twice
during each revolution of the armature, just as one of its side bars
is approaching the poles of the magnet and breaks it as the bar comes
opposite the poles of the magnet.
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