thermal conductivity of Indiarubber. 
191 
§ 2. The apparatus is arranged as in Fig. 1. Steam from 
the small boiler A flows through the tube of indiarubber P, P, 
which passes through three rings of wire fixed inside the copper 
calorimeter B, and finally escapes into the vessel G. The two 
screens S, S' prevent radiation from A or G from reaching B. The 
calorimeter contains water, which is kept in motion by a stirrer, 
and the temperature of the water is observed by a thermometer 
divided to fifths of a degree. Two marks E, F are made on the 
tube and the distance between them is measured while the tube 
is straight, before it is passed through the rings in the calorimeter. 
The length of tube immersed in the water can then be found by 
measuring the distances of E and F from the surface of the water 
when the tube is in place. 
The observations are made in the following manner : — 
The calorimeter is first dried and weighed and then the india- 
rubber tube is passed through the rings, care being taken that the 
tube does not touch the sides of the calorimeter. A beaker is now 
filled with water five or six degrees below the temperature of the 
room and is weighed, the weighing being repeated after a sufficient 
quantity of the water has been poured into the calorimeter ; the 
difference of mass gives the mass of water in the calorimeter. 
During these preliminary observations the water in the boiler 
has been caused to boil and when the water has been poured into 
the calorimeter the indiarubber tube is connected to the boiler. 
When the steam issues freely into the vessel G, the water in B is 
stirred continuously and the thermometer is read at intervals of 
one minute, the observations being continued till the temperature 
has risen four or five degrees above that of the room. 
A curve is then plotted showing how the temperature of the 
calorimeter depends upon the time. When its temperature is 
equal to that of the room the calorimeter neither loses heat to the 
room nor gains heat from it. Hence, if we neglect the radiation 
to the calorimeter from the parts of the indiarubber tube which 
are not immersed in the water, we may consider that the rate at 
which the calorimeter gains heat, when it is at the temperature of 
the room, is equal to the rate at which heat passes by conduction 
through the part of the tube immersed in the water. The rate of 
rise of temperature in degrees per second, when the calorimeter is 
at the temperature of the room, is easily found by drawing a 
tangent to the curve at the proper point. 
The ends of the tube, where it is attached to the pipe from the 
boiler and to the wastepipe, soon become permanently stretched, 
and hence a short portion should be cut from each end of the tube 
before the tube is used in the experiment. From measurements 
made on these portions the internal and external radii of the 
tube are deduced. 
