193 
thermal conductivity of Tndiarubber. 
§ 4. The following results, obtained in an actual experiment, 
will illustrate the working of the method : — 
Mass of copper calorimeter and stirrer = 1 62 *6 grms. 
Water in calorimeter =578 5 grms. 
Water equivalent of whole = 5780 + 162*6 x 0095 = 593"9 grms. 
Length of tube immersed = 1 5 "6 cm. 
Two external diameters at right angles were measured at each 
end of the two portions cut from the tube, and the observations 
were repeated for the internal diameters. The results were 
2 a ... 1-06, 1-07, 1-06, 107, 106, 107, 106, 108, 
2b ... 0-62, 0-62, 0-62, 0-61, 0-61, 0*61, 0*60, 0 62, 
giving the mean values a = 0 533 cm., b — 0‘307 cm. 
Hence log e (a/b) = 00517. 
While the steam was passing through the tube the following 
observations of the temperature of the water in the calorimeter 
were made : — 
Time 
Temperature 
Time 
Temperature 
Time 
Temperature 
min. 
min. 
min. 
32 
12-30 
37 
15-80 
42 
19-00 
33 
1300 
38 
16-45 
43 
19-55 
34 
13-75 
39 
1705 
44 
20-20 
35 
14-40 
40 
17-75 
45 
20-80 
36 
15-15 
41 
18-35 
46 
21-35 
The temperature of the room was 16°0 C. When the temperature 
was plotted against the time the slope of the curve at 16°5 
indicated that the temperature was rising at the rate of 0054 
degrees per min. Hence R — 0 0109 degrees per sec. 
Inserting the numerical values in (1) we have 
00109 x 5930 x 00517 
K ~ 2t r x~ 15-6 (100 - 160) 
— 0 000436 calories per square cm. per sec. per unit tempera- 
ture gradient. 
If we use the approximate formula (2) we obtain 
K = 
00109 x 593-9 x 0-226 
7 t x 150 (100 -160) x 0 840 
0000426. 
