current density
in this case was about 0.12 ampere per square inch and the watts
absorbed 30.5 per cubic inch. If it were not for the large amount of
water above both electrodes, it is doubtful if this current density
could have been maintained.

In test No. 5 a rectangular box, in which were placed two vertical
sheet iron plates, was filled with tap water. The distance between the
plates was 5/8 inch, and with a difference of potential of 414 at
start and 397 at end of the run, a current of 35 amperes was kept
flowing for 35 minutes. Cold tap water was kept running in between the
electrodes at the rate of 6.11 pounds per minute (about 1/10 cubic
foot) by means of a small rubber tube about 1/4 inch inside diameter.
This test is very interesting in comparison with the preceding. The
current carrying capacity, 0.3 ampere per square inch, was more than
double, and the energy absorbed 183 watts per cubic inch, more than
six times as great as in case where running water was not used.

The temperature in some places between the plates occasionally rose as
high as 205 deg. F., and it was necessary, in order to avoid too violent
ebullition, to keep the inflowing stream of water directed along the
water surface between the two plates. Less water would not have been
sufficient, and, of course, by using more water, the temperature
could have been kept lower, or with the same temperature the watts
absorbed could have been increased.

When a large current density is used, there is considerable
decomposition of the iron electrodes when either salt or pure water is
used, and in the case of horizontal electrodes, the under surface of
the top plate may become covered with bubbles of gas, making the
resistance between the plates quite variable. For large current
density a horizontal top plate is not advisable, unless a large number
of holes are drilled through it. A better form for the top electrode
would be a hollow cylinder long enough to give sufficient surface.
Washing soda is often a convenient substance to use instead of salt.

If, from experience, the size of a liquid rheostat for absorbing a
given amount of energy cannot be estimated, the dimensions may be
calculated approximately as follows:

Suppose, for instance, it is desired to absorb 60 amperes at 40 volts
difference of potential between the electrodes. Now, it is
inconvenient to obtain a saturated solution of salt, and to use tap
water would require too large a cross