at even at 50 deg. Fahrenheit the action becomes very much impaired.
This follows from the facts that the resistance of a liquid decreases
as its temperature rises, and that chemical action is much slower at
lower temperatures.

The gravity cell has a practically constant voltage of 1.08 volts. Its
internal resistance is comparatively high, seldom falling below 1 ohm
and often rising to 6 ohms. At best, therefore, it is only capable of
producing about 1 ampere. The gravity cell is perhaps the most common
type of cell wherein depolarization is affected by electro-chemical
means.

Fuller Cell:--A form of cell that is adapted to very heavy
open-circuit work and also closed-circuit work where heavier currents
are required than can be supplied by the gravity battery is the
Fuller. In this the electrodes are of zinc and carbon, respectively,
the zinc usually being in the form of a heavy cone and placed within a
porous cup. The electrolyte of the Fuller cell is known as
_electropoion fluid_, and consists of a mixture of sodium or potassium
bichromate, sulphuric acid, and water.

The various parts of the standard Fuller cell, as once largely
employed by the various Bell operating companies, are shown in Fig.
65. In this the jar was made of flint glass, cylindrical in form, six
inches in diameter and eight inches deep. It is important that a good
grade of glass be used for the jar in this cell, because, on account
of the nature of the electrolyte, breakage is disastrous in the
effects it may produce on adjacent property. The carbon plate is
rectangular in form, about four inches wide, eight and three-quarters
inches long, and one-quarter inch thick. The metal terminal at the top
of the carbon block is of bronze, both it and the lock nuts and bolts
being nickel-plated to minimize corrosion. The upper end of the carbon
block is soaked in paraffin so hot as to drive all of the moisture out
of the paraffin and out of the pores of the block itself.

The zinc, as is noted from the cut, is in the form of a truncated
cone. It is about two and one-eighth inches in diameter at the base
and two and one-half inches high. Cast into the zinc is a soft copper
wire about No. 12 B. & S. gauge. This wire extends above the top of
the jar so as to form a convenient terminal for the cell.

The porous cup is cylindrical in form, about three inches in diameter
and seven inches deep. The wooden cover is of kiln-dried white wood
thoroughly coated