1903.] Specific Heats, especially at Low Temperatures. 183 



Interval of 2 minutes, reading of platinum thermometer during the 



interval. 

 Period of 2J minutes, with readings of mercury thermometer at end 



of every half -minute. 

 Immersion of object in calorimeter (half a minute after the last 



reading). 

 Period of 7J minutes, with readings of mercury thermometer at end 



of every half-minute. 

 Interval of 2| minutes. 

 Period of 2| minutes, with readings of mercury thermometer at end 



of every half-minute. 



The first ten readings of the mercury thermometer gave the initial 

 rate of change of temperature and also the temperature at the moment 

 of immersion ; the last ten gave the final rate of change. The final 

 temperature was obtained as the mean of the later of the corrected 

 intermediate readings. It was found that equilibrium of temperature 

 was attained in about 3 minutes in the case of the copper cylinder 

 of Tables I and II. The weight of this cylinder was approximately 

 161J grammes; calorimeter D was used, and the fall of temperature 

 was approximately 4*6. 



The initial readings were always made with a falling temperature, 

 but this circumstance did not seem to introduce any important un- 

 certainty. During the final readings the temperature was sometimes 

 rising, sometimes falling. 



The copper used was obtained from Johnson, Matthey and Co., and 

 described as pure. 



Thallium. 



The original object of the investigation was to determine the specific 

 heat of this metal, but as the amount used was small, the experimental 

 error is here probably larger than in the case of the other metals. 

 The first specimen examined weighed about 30 grammes. After 

 forming the material into a single mass, approximately cubical, it gave 

 in two experiments 0*0299 (4) and 0-0298 (4) for the specific heat. A 

 second specimen, of nearly double the weight of the first and similarly 

 molten and compressed into a compact mass, gave 0'0298 (4) and 0'0301 

 (3). The two specimens together gave 0*0302 (4), 0*0300 (3), 0-0301 (3), 

 mean 0*0301. Calorimeter B was used, and the fall of temperature in 

 the last three experiments was approximately 2 -5. 



The first specimen was from Dr. Schuster, the second was bought as- 

 pure. An analysis of the second specimen by Mr. Joseph Race gave 

 thallium 99 per cent., oxygen (probably due to surface oxidation of 

 the fragments analysed) 1 per cent., traces of iron and zinc. 



