The Specific Heat of Non-conductors. 41 



out the experiments, though sold as "tin" foil, was found to 

 contain 80% of lead, and the determination of its specific 

 heat gave as a mean of several estimations '035, which 

 value has been used in the calculations. In all cases the 

 roll of rubber was completely encased in the foil, to prevent 

 it from sticking to the test tube in the heating chamber. 



About 20 grams of rubber as a rule were employed. 

 This was inter-rolled with the foil and heated for about 

 two hours in the chamber described, and then quickly 

 transferred to the calorimeter, the rubber being easily 

 slipped out of the glass tube. 



The readings of the temperature of the calorimeter 

 were noted at \ minute intervals, the calorimeter being 

 continuously stirred by hand. 



Method of Calculation. 

 The following formula was used : — 



_ W + K (0 + C)-^ Wa 

 ^ M ' T-(0H-C) M 

 where 



M = mass of rubber. 



M' = „ tinfoil. 



W = „ water in calorimeter. 



K = water equivalent of calorimeter, stirrer, and thermometer. 



T = temperature of the rubber. 



t = initial temperature of the water. 



6 = final temperature of the water. 



(7 = specific heat of the foil. 



x= „ rubber. 



The value of C, which represents the loss due to cooling, 

 may be obtained from one of the three following formulae : — 



Correction Formula. 



(i) Regnault-Pfaundler {Ann de Chim. et de PhysiquCy 

 4** Serie xi., p. 248, 1867.) 



