ON THE SPECIFIC HEAT OF AQUEOUS SOLUTIONS. 
123 
necessary notes made by two observers, although the subsequent application of the 
corrections is more troublesome. 
3. Calibration of the Mercury Thermometer Resistance .—The heater used for the 
observations for the former paper was broken and had to be mended and re-calibrated. 
The resistance measured was that of the actual heater, designated by M 2 , together with 
the resistance of the primary circuit of the watt balance, other than the heater M 2 , 
denoted by p. The necessary experimental data in bridge ohms are given in Table I. 
together with the differences on the values calculated from the formula 
c5 
M 2 + p = 7*8039 + 0’0280m + 0’0002054m 2 , 
where m is the reading of the thermometer resistance graduated in centimetres. 
Table I.—Calibration of Thermometer Kesistance. 
Experiment 390. 
Temperature. 
m. 
Mo + p 
observed. 
Difference from 
calculated values. 
1 • 005 
2-12 
7-8640 
+ 0-0002 
13-87 
5-16 
7■9537 
+ 0-0001 
26 • 37 
8-11 
8-0448 
-0-0003 
39-05 
11-05 
8-1383 
+ 0-0001 
To reduce to international ohms the constant 7'8039 must be multiplied by the 
bridge factor which gives the final value of the constant as 
7'8020. 
The bridge factor in measuring with the 10,000/10 ratio is given by 
f = 0’9995+f (0—8) x 10- 4 . 
The bridge factor corrects for errors in coils as well as in the ratio arms. 
The value of p was 0'0770. 
4. The Watt Balance .—-The Kelvin watt balance used was of an ordinary type. 
The use of this balance showed certain small defects which may be noted for future 
improvement. 
{a) Accuracy depends on knowing the exact value of the shunt resistance (approxi¬ 
mately 500 ohms). With the balance employed the temperature could only be 
ascertained by a thermometer inserted among the coils. Designing the resistance so 
that it could be placed in a well stirred oil-bath would remove this source of uncertainty. 
(6) The oil in the dash-pot appears to creep over the edge of the pot so that the 
level of the oil is gradually lowered. This affects the flotation of the dash-pot piston 
