copper sulphate, or blue-stone crystals, is then dropped into the jar
to almost cover the copper. The zinc crowfoot is then hung in place,
occupying a position about 4 inches above the top of the copper. Clear
water is then poured in sufficient to fill the jar within about an
inch of the top.

If it is not required to use the cell at once, it may be placed on
short circuit for a time and allowed to form its own zinc sulphate.
The cell may, however, be made immediately available for use by
drawing about one-half pint of a solution of zinc sulphate from a
cell already in use and pouring it into the jar, or, when this is not
convenient, by putting into the liquid four or five ounces of
pulverized sulphate of zinc, or by adding about ten drops of sulphuric
acid. When the cell is in proper working condition, one-half inch in
thickness of heavy paraffin oil of good quality may be added.

If the blue line gets too low, and if there is in the bottom of the
cell a sufficient quantity of sulphate of copper, it may be raised by
drawing off a portion of the zinc sulphate with a battery syringe and
replacing this with water. If the blue line gets too high, it may be
lowered by short-circuiting the cell for a time, or by the addition of
more sulphate of zinc solution from another battery. If the copper
sulphate becomes exhausted, it should be replenished by dropping in
more crystals.

Care should be taken in cold weather to maintain the temperature of
the battery above 65° or 70° Fahrenheit. If below this temperature,
the internal resistance of a cell increases very rapidly, so much so
that even at 50° Fahrenheit the action becomes very much impaired.
This follows from the facts that the resistance of a liquid decreases