718 Mr. A. Holt on the 



The large glass bulb A had a capacity of 3948 c.c. at 

 15° C, and was connected by a ground-glass joint to the 

 bulb 1), which contained distilled water and a thermometer. 

 The platinum wire EF was heated by the current led in 

 through the mercury leads LM, but the resistance was only 

 determined for the distance GH in order to avoid the error 

 due to the cooling of the ends of the wire by the thick leads. 



A thermometer was hung inside the globe A to determine 

 the temperature of the vapour. 



Each experiment was carried out as follows : — The whole 

 apparatus being evacuated, the tap B was closed and the 

 bulb A allowed to fill with water vapour. The tap C was 

 left open until the water in D and the vapour in A had 

 assumed the same temperature, and this had been noted. 

 Then the tap C was closed and the wire heated to the 

 required temperature until equilibrium was reached. 



The wire was then allowed to cool, and the taps B and C 

 being opened, the gases in the bulb A were pumped out 

 through the condenser K surrounded by a freezing-mixture 

 in order to condense water vapour. 



The electrolytic gas was collected by a pump and analysed 

 by explosion. 



The platinum wire EF was about 7 cms. long and 05 mm. 

 diameter, and gave a value for 8 = 1-54. At the ends it was 

 welded to short pieces of thick platinum which communi- 

 cated with the mercury leads LM. Extremely fine platinum 

 wires, which would produce hardly any cooling effect, were 

 welded on to it about 2 mm. from each end at G and 

 H, and the resistance was determined between these two 

 points. 



The temperature of the wire up to 1300° was calculated 

 from the resistance by the Heyeock and Neville formula 



e= R '~ft° 100 



-ttioo - -tt-o 



5=8 {(l5o) -I5o}' 



where is the temperature on the platinum thermometer, 

 and t the temperature on the air thermometer. 



But for higher temperatures, since the temperature- 

 resistance curve becomes asymptotic to a straight line, the 

 formula proposed by Langmuir has been employed :--• 



T(abs.) = 344-4^-247. 



