30 THE ELEMENTS.
starting the electrolysis maintain a sufficient flame to supplement
the heating effect of the current in keeping the mass just liquid.
For the anode, use a rod, 0.8 cm. in diameter, of arc-lamp car-
bon which is not attacked by the liberated chlorine; and for the
cathode use an iron rod 0.3 cm. thick. Insert the cathode through
a cork in the upper end of a glass tube, of 2 cm. diameter, and
place the whole in the fused electrolyte so that the glass tube dips
1 cm. below the surface and the iron rod 0.3 cm. deeper (Fig. 9).
The metallic lithium collects in the space between the iron wire
and the glass tube, and the glass mantle protects it from being
disseminated throughout the electrolyte. When all is ready close
the circuit, noting the time, and regulate the resistance so that a
current of between 6 and 10 amperes passes. In order to obtain
this current, the voltage of the storage battery, since it has the
resistance of the electrolyte to overcome, must not be too small;
it should be between 7 and 12 volts (3 to 6 accumulator cells
connected in series). During the electrolysis note frequently the
time and amperage, and from these readings compute the number
of ampere-seconds by multiplying the average reading of the
ammeter by the number of seconds which have elapsed.When the reaction is progressing with moderate strength, but
without being disturbed by too vigorous an evolution of chlorine,
metallic lithium can be observed collecting at the cathode in the
space between the iron rod and the glass tube. From time to
time flashes of light occur at the anode which are probably due
to an insulating envelope of chlorine gas which is formed about
the carbon and causes a marked lessening of the current; this
difficulty is easily remedied by occasionally breaking the circuit
for a moment. At the end of twenty minutes a considerable
amount of lithium should have collected. Raise the cathode
from the fused salt, holding an iron spoon to prevent any lithium
from falling out of the glass tube, and dip the whole under petro-
leum. After cooling remove the lithium from the tube with a
knife and weigh it under petroleum. The current yield, i.e., the
yield reckoned on the amount which the current should theoretic-
ally produce, is about 70%.
The lithium thus prepared is contaminated with a little potas-
sium. Determine the density by means of a pycnometer, using
petroleum of known density. For this purpose weigh the pyc-