76 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



The present paper describes a series of experiments on the thermal 

 conductivities of different specimens of hard rubber, * or " vulcanite," 

 made by the method whicli we described at length last year. 



I had at my disposal fourteen different pieces of hard rubber thick 

 enough to be used conveniently in the apparatus, and much of this was 

 in sheets about 120 cm. by 50 cm. So much of it as was bought for the 

 purposes of this investigation came from three well known makers. 

 Besides this new rubber, however, there were a number of pieces from 



Figure 2. 



unknown sources, whicli had been lying in tlie laboratory for indefinite 

 periods. The specific gravities of the different specimens examined 

 differed slightly from each other, but by not nearly so much as one per 

 cent in the extreme cases. The specific gravity of the rubber used as a 

 standard is about 1.202, and its average specific heat between 25° C. and 

 100° C. is 0.339. The specific heat of sheet rubber usually increases 

 with the temperature, as may be inferred from the subjoined table, in 



* Stefan, Sitzungsbericlite der Wiener Akademie der Wissenschaften, 1876; 

 Lees, Pliifosophical Transactions, 1893. 



