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.