ON THE SPECIFIC HEAT OF AQUEOUS SOLUTIONS. 
127 
9. The Method of Calculation.—hot 
U = watts developed in electrical heater, 
At = time of heating in minutes, 
AQ = joules absorbed from obturator, radiation, stirring and evaporation, 
A6 — rise of temperature, 
5 0 o 
- a , 
Then 
C,!‘ — mean capacity of calorimeter in joules between a° and b , 
S/ = mean specific heat of liquid in joules from a to b°, 
W = weight of liquid in grammes. 
Ux60 Af + AQ, = WS/A9 + QT AO. 
Hence we have 
WS/ + C/ = 60 U 
dd dQ 
dt^dd 
From this expression we get the mean specific heat for the interval when the 
capacity is known, or the capacity when the specific heat is known. It will be 
observed that we are really dealing with the total heat for each interval. Hence 
whenever specific heat is spoken of in this paper, what is really meant is the mean 
Cb 
specific heat for the interval under consideration, i.e ., s dd/(h—a). Thus for the 
J a 
interval 0 o, 5 C. to 13°'5 C. the mean temperature is 7 C., and the total heat for the 
interval divided by 13 is spoken of for brevity as the specific heat at 7 C. Also 
ddfdt is the average rise of temperature per minute during the interval and dQ/dd 
is the total heating from obturator, radiation, &c., during the interval divided 
by ( b—a ). 
10. The Specific Heat Observations. —The experiments necessary to determine the 
capacity of the calorimeter and the specific heat of the solutions were conducted in 
the same way. A three-litre flask was filled with water or with the solution, weighed 
and left all night in a refrigerator packed in ice. The calorimeter and the bath were 
cooled with ice, and the empty flask was weighed after pouring the contents into the 
cooled calorimeter. The electrical heating was divided into three periods which 
were approximately 0° C. to 13° C., 13° C. to 26 c C., and 26° C. to 39 C. In actual 
working the initial temperature was usually from about 0 '5 C. to 1 0. 1 he ends 
of the intervals were determined by stopping at the nearest exact half-minute, 
which gave about 13°'5 C., 26°'5 C., and 39°'5 C. + 0°*3 C. for the end temperatures of 
the intervals. The mean temperatures for the intervals were thus almost exactly 
7° C., 20° C. and 33° C. A specimen set of observations (Experiment No. 516) which 
is given in the Appendix will serve to make the course of an experiment clear. 
These observations were plotted as shown in fig. 1, in order to arrive at approximate 
straight-line intervals for the corrections. Table II. gives all the experimental data 
from Experiment 516, including the mean temperatures T B and T 0B of the bath and 
VOL. CCXVIII,-A, S 
