y noting this time the time
average of the current, or if the current has been kept constant, the
current itself, can be deduced.

In employing the silver voltameter to measure currents of about 1
ampere, the following arrangements should be adopted. The kathode on
which the silver is to be deposited should take the form of a platinum
bowl not less than 10 cm. in diameter, and from 4 to 5 cm. in depth.

The anode should be a plate of pure silver some 30 square cm. in area
and 2 or 3 millimeters in thickness.

This is supported horizontally in the liquid near the top of the
solution by a platinum wire passed through holes in the plate at
opposite corners. To prevent the disintegrated silver which is formed
on the anode from falling on to the kathode, the anode should be
wrapped round with pure filter paper, secured at the back with sealing
wax.

The liquid should consist of a neutral solution of pure silver
nitrate, containing about 15 parts by weight of the nitrate to 85
parts of water.

The resistance of the voltameter changes somewhat as the current
passes. To prevent these changes having too great an effect on the
current, some resistance besides that of the voltameter should be
inserted in the circuit. The total metallic resistance of the circuit
should not be less than 10 ohms.

_Method of making a Measurement._--The platinum bowl is washed with
nitric acid and distilled water, dried by heat, and then left to cool
in a desiccator. When thoroughly dry, it is weighed carefully.

It is nearly filled with the solution, and connected to the rest of
the circuit by being placed on a clean copper support, to which a
binding screw is attached. This copper support must be insulated.

The anode is then immersed in the solution, so as to be well covered
by it, and supported in that position; the connections to the rest of
the circuit are made.

Contact is made at the key, noting the time of contact. The current is
allowed to pass for not less than half an hour, and the time at which
contact is broken is observed. Care must be taken that the clock used
is keeping correct time during this interval.

The solution is now removed from the bowl, and the deposit is washed
with distilled water and left to soak for at least six hours. It is
then rinsed successively with distilled water and absolute alcohol,
and dried in a hot-air bath at a temperature of about 160 deg. C. After
cooling in a desiccator, it is weighed again.