TJu Specific Heat of Non-conductors. 39 



time of the mixture attaining its maximum temperature 

 will be prolonged, and the correction for cooling large and 

 its calculation uncertain. We find, however, by applying 

 the correction formulae, that the error from this source 

 becomes unimportant, and certainly less than the errors 

 incident to the variation in the composition of the sub- 

 stance, or to the difficulty of ascertaining its exact tempera- 

 ture when heated. 



Description of Apparatus. 



Calorimeter, 

 This was made of thin hard-rolled brass 62*^"* diam. and 

 152*""^ long. It was enclosed within an outer zinc can 

 120'"'" diam. and 188"*"* in depth, separated by corks. This 

 zinc can was soldered to an outer can filled with water 

 200™™ diam. and 25 5""™ deep. Finally, the whole was 

 enclosed within a box packed with wool. 



The outer can was provided with an annular stirrer, 

 while the calorimeter had a smaller stirrer with a glass 

 handle. A baize curtain divided the calorimeter from the 

 heating apparatus. 



Three different kinds of stirrers were used : — 

 (i) Perforated bucket of very thin sheet with a 

 wooden handle. The roll of rubber was 

 dropped into this. 



(2) A glass handle was fixed to a zig-zag piece of 



brass which was fixed in the rubber. 



(3) A thermometer was fixed in the centre of the 



roll of rubber. 

 In the latter two cases the stirrer was also in the 

 heating vessel. 



Heating Apparatus. 



In the earlier experiments a steam oven, having a 

 constant temperature of 98° C, was employed. The rubber 



