l not "come up," that is, if its
voltage will not come up to 2.5-2.7 per cell on charge, and its
specific gravity will not come up to 1.280-1.300.

3. Whenever you charge a battery, at the end of the charge, when the
voltage and specific gravity no longer rise, make Cadmium tests to be
sure that both positives and negatives are fully charged.

4. When you put in a new group, charge the battery fully and make
Cadmium tests to be sure that both the new and old groups are fully
charged.

5. When a 20-minute high rate discharge test is made. See page 267.

That Cadmium Readings should be taken only while a battery is in
action; that is, while it is on discharge, or while it is on charge.

Cadmium Readings taken on a battery which is on open circuit are not
reliable.

When you are not using the Cadmium, it should be put in a vessel of
water and kept there. Never let the Cadmium become dry, as it will
then give unreliable readings.

Open Circuit Voltage Readings Worthless

Voltage readings of a battery taken while the battery is on open
circuit; that is, when no current is passing through the battery, are
not reliable. The voltage of a normal, fully charged cell on open
circuit is slightly over 2 volts. If this cell is given a full normal
discharge, so that the specific gravity of its electrolyte drops to
1.150, and is allowed to stand for several hours after the end of the
discharge, the open circuit voltage will still be 2 volts. Open
circuit voltage readings are therefore of little or no value, except
when a cell is "dead," as a dead cell will give an open circuit
voltage very much less than 2, and it may even give no voltage at all.

What the Cadmium Test Set Consists of

The Cadmium Tester consists of a voltmeter, Fig. 121, and two pointed
brass prods which are fastened in wooden handles, as shown in Fig.
122. A length of flexible wire having a terminal at one end is
soldered to each prod for attachment to the voltmeter. Fastened at
right angles to one of the brass prods is a rod of pure cadmium.

[Fig. 121 Special cadmium test voltmeter, & Fig. 122 Cadmium
test leads]

Cadmium tests may be made with any accurate voltmeter which gives
readings up to 2.5 volts in divisions of .05 volt.

The instructions given below apply especially to the special AMBU
voltmeter but these instructions may also be used in making cadmium
tests with any voltmeter that will give the correct reading.

The AMBU C