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