CONDUCTIVITIES OF IRON AND COPPER. 
579 
Table I. 4. 
Table showing values of k, the absolute thermal conductivity of iron,, at temperatures 
between 60° C. and 150° C. 
T. 
X. 
dOfdx 
(per centim.). 
N [Zo {deidt)l 
(per minute). 
e. 
M. 
h 
[C.G.S. units]. 
1 °C. 
centims. 
°C. 
60 
19-90 
9-0 
93-0 
41 
0-856 
[-147] 
1 80 
13-70 
14-2 
146-7 
51 
-862 
[-148] 
' 100 
9-20 
20-1 
206-6 
63 
-868 
-148 
; 110 
7-50 
23-4 
235-3 
68 
-871 
-146 
120 
5-90 
26-9 
267-0 
73 
-873 
-144 
1 130 
4-60 
30-6 
297-6 
79 
-877 
-141 
' 140 
3-45 
84-5 
325-7 
84 
-880 
•138 
150 
1 
2-50 
38-5 
352-7 
88 
-882 
•135 
From these values (between 100° C. and 150° C.), if we assume the conductivity at 
f C. to be given by 
kf = a — ht, 
we have, on reducing by method of least squares, 
ki = T75 — -OOO'iGf, 
or 
ki = -175 (I - -00150. 
Determination oj Specific Heat of Iron. 
Advantage was taken of the snowfall in January to use Bunsen’s calorimeter for 
^ this determination. The calorimeter was prepared for use by the inethod described 
by Bunsen in his paper given in the ‘Phil. Mag.,’ 1871, p. 161, and all the pre¬ 
cautions there detailed were observed. The tube used for determining the change of 
volume attendant on the melting of ice was of very fine l)ore, but was perfectly clean, 
so that there was no trouble with the sticking of the mercury thread. This tube 
was carefully calibrated, and a calibration curve drawn from which a length measured 
in any part of the tube could be converted into a length corresponding to the uniform 
bore taken as the basis of the calibration. 
The heater used was made specially for the work. It consisted of a hollow 
cylindrical oil bath shown in section at BB (fig. 2). This bath was heated up to a 
temperature of about 250° C., aiid then quickly placed in the woOden case shown in 
the figure and packed round on all sides with cotton wool. Thus packed, the bath 
took nearly a day to cool, and could, therefore, be used for a complete series of 
determinations at temperatures below 200° C. 
The piece of iron to be heated was suspended by a silk fibre in the cylindrical 
4 E 2 
