[EVANS] SPECIFIC HEAT OF WATER OF CRYSTALLIZATION 123 
The calorimeter is inclosed in two metal jackets and immersed in 
a large thermostat. At present the determinations are being made at 
room temperature, though later on it is intended to make them at a 
series of different temperatures. 
The method of determining the specific heat of a solid as at 
present carried out with this apparatus, is as follows: 100 gr. benzol 
is introduced into the little calorimeter which is then stood in cold 
water till its temperature has fallen considerably below that of the 
thermostat. It is then wiped dry, placed in its jackets in the 
thermostat, and its temperature brought to nearly four degrees below 
that of the thermostat by passing the current through the heating 
spiral; then the whole is allowed to stand for at least fifteen minutes 
with the stirrer running. With a little practice the temperature de- 
sired (namely, four degrees below that of the thermostat) can be thus 
obtained to within a tenth of a degree. During the time that no cur- 
rent has been running through the heating spiral, it has been running 
through the auxiliary resistance. When the necessary time has elapsed, 
the temperature is accurately read, the current is quickly switched 
from the resistance to the spiral, and the time taken by starting a 
stop-watch. The readings of the two meters are ‘then recorded each 
minute during the time of heating. With the apparatus employed, a 
current of about 0-840 amperes is used, the potential difference between 
the terminals of the spiral is about 5-00 volts, and the time required to 
raise the temperature of the 'system eight degrees is approximately 
seven minutes. When the temperature has risen to about four degrees 
above that of the thermostat the current is switched off and the watch 
stopped; the maximum thermometer reading is then accurately noted. 
The means of the readings of the ammeter and voltmeter are calcu- 
lated, and the quantity of heat in calories introduced into the calori- 
meter is determined from the equation: 
U = CVt — 41838 
where U represents the calories, C the current in amperes, V the drop 
in potential in volts between the terminals of the heating spiral, and 
t the time in seconds during which the current is passing. By dividing 
the number of calories thus obtained by the number of degrees through 
which the system has been raised (about eight in the experiments now 
being carried on) the number of calories required per degree is ob- 
tained. 
The determination can be repeated as often as desired by remov- 
ing the calorimeter from its jackets, cooling it, and again going through 
the above process. 
