390 On the Scale of the Oxygen Thermometer. [June 26, 



IV. Ice Point. January 2, 1903. 



Pressure on gas 336'0 mm. 



Temperature of dead space 17*0 C. 



Pressure coefficient 0*0036692 



Constant 30*538 



Vapour Pressures of Liquid Oxygen. 



Pressure on gas in 



thermometer 109-3 mm. 109-4 mm. 109 '7 mm. 109-85 mm. 



Temperature of dead 

 space 16-8C. 16-7 C. 16-70. 16-7 C. 



Temperature of stem 116-0 116*0 121-0 121-0 



Vapour pressure of 



oxygen 591*8 mm. 591*8 mm. 614*1 mm. 618*5 mm. 



Temperature on oxy- 

 gen scale 87-04 87*14 87*40 87*50 



Deviation from he- 

 lium scale 0*82 0*72 0*78 0-78 



Discussion of the results. The mean values of the difference of the 

 temperatures corresponding to the vapour pressure of liquid oxygen on 

 the scales of the oxygen and helium thermometers, when plotted 

 against the initial pressures at which the oxygen thermometer was filled, 

 are found to lie nearly on a straight line. The smoothed results are 

 as follows : 



Initial pressure. A fouud. A smoothed. 

 1000 mm. 1-6 



731 1-18 1-18 



658 1-11 Ml 



484 0*85 0-89 



336 0-77 0-72 



o 0-4 



The values at 1000 mm. and at zero pressure are obtained by 

 extrapolation. 



According to Callendar,* the deviations of the constant volume 

 helium and hydrogen thermometers from the thermo-dynamic scale 

 should, at low temperatures , be equal and opposite in sign. According 

 to this, the deviation of the boiling point of oxygen measured on the 

 scale of an oxygen thermometer, filled at an initial pressure of 1000 mm., 

 is 1*4 below the true temperature, while the deviation in the case of 

 the boiling point of hydrogen on the scale of a hydrogen thermometer 

 is 0-1, the thermometers being filled at an initial pressure of 1000 mm. 



* Ltc. dt. 



