CAPACITY FOR HEAT OF METALS AT DIFFERENT TEMPERATURES. 159 



r mjrcil 



[ms + MSJ 



1 CiHv fj 



n dt JR/ 







M = mass copper block -f case = 3392'37 

 ms = thermal capacity of oil, quartz, glass and solder = 4'898, 

 K = resistance of coil = 20'599, 

 E = E.M.F. standard cell at 15 (!. == 1 '01 848, 

 f=d (U)(d (Ft) at C. = 0'98480. 



Hence 



S = 0-09094. 



NOTE. / = 3 (#)/? (Pt). The values of 30/3 Pt at temperature fl are obtained from 



('IIAITIMS Mini HAKKKU'S tables, ' Phil. Trans.,' vol. l!)4, p. 114. Assuming S = T54. 



SECTION XI. 

 Experimental Re.mlts. Preliminary Experiments. 



A considerable number of preliminary experiments were performed with a view of 

 testing the apparatus employed and deciding on the most suitable conditions. Some 

 were carried out with a constantan heating coil of 10 ohms resistance, which was 

 replaced by a manganin coil of wider section and greater resistance. 



A large number of experiments were performed with silvered vacuum vessels 

 interposed between the metal blocks and the brass cases. The results obtained with 

 different rates of energy supply were discordant. The faster the rate of rise, the 

 lower the value found for the resulting specific heat. These differences were roughly 

 proportional to the duration of the heating ; the range being practically the same 

 in ail. 



The source of this error we traced to the effect of radiation, &c., on the inner walls 

 of the vacuum vessel. This surface received heat by radiation from the block and as 

 it parted with the heat but slowly, its temperature rose with that of the block to an 

 extent dependent on the rate of increase of temperature of the metal. 



After the removal of the vacuum vessels, the loss or gain by radiation was 

 dependent on 6 6 a only, as the surrounding walls were now those washed by the tank 

 water and remained at a constant temperature. Our anxiety to minimize loss or gain 

 of heat from external sources by the interposition of these flasks had led us, when 

 designing the apparatus, to regard the insertion of the non-conducting walls as 

 : this precaution, however, was a cause of much loss of time and labour. 



