s.
The current is then passed through the coil, and simultaneously the
water is started flowing through the heat-absorbing system and the whole
calorimeter is adjusted in temperature equilibrium as soon as possible.
When the temperature of the air and walls is constant and the
thermal-junction system in equilibrium, the exact time is noted and the
water-current deflected into the meter. At the end of one hour, the
usual length of a period, the water-current is deflected from the meter,
the meter is weighed, and the average temperature-difference of the
water obtained by averaging the results of all the temperature
differences noted during the hour. Usually during an experiment of this
nature, records of the water-temperatures are made every 4 minutes;
occasionally, when the fluctuations are somewhat greater than usual,
records are made every 2 minutes.

The calculation of the heat developed in the apparatus is made by means
of the formula C x E x _t_ x 0.2385 = calories, in which C equals the
current in amperes, E the electromotive force, and _t_ the time in
seconds. This gives the heat expressed in calories at 15 deg. C. This
procedure we have followed as a result of the recommendation of Dr. E.
B. Rosa, of the National Bureau of Standards. In order to convert the
values to 20 deg., the unit commonly employed in calorimetric work, it has
been necessary to multiply by the ratio of the specific heat of water at
15 deg. to that of water at 20 deg. Assuming the specific heat of water at
20 deg. to be 1, the specific heat at 15 deg. is 1.001.[16]

Of the many electrical check-tests made with this type of apparatus, but
one need be given here, pending a special treatment of the method of
control of the calorimeter in a forthcoming publication. An electrical
check-experiment with the chair calorimeter was made on January 4, 1909,
and continued 6 hours. The voltmeter and mil-ammeter were read every few
minutes, the water collected in the water-meter, carefully weighed, and
the temperature differences as measured on the two mercury thermometers
were recorded every 4 minutes.

The heat developed during the experiment may be calculated from the data
as follows: Average current = 1.293 amperes; average E. M. F. = 109.15
volts; time = 21,600 seconds; factor used to convert watt-seconds to
calories = 0.2385. (1.293 x 109.15 x 21600 x 0.2385) x 1.001 = 727.8
calories produced.

During the 6 hours 237.63 kilograms of water passed