1903.] On the Scale of the Oxyyen Thermometer. 387 



assumed to be a linear function of the initial pressure P , it may 

 be expressed by the formula 



a = 0-0036642 + 0-00000001 457P , 



where P is expressed in millimetres. 



In the equation employed to calculate the temperature on the gas 

 scale,* the reciprocal of the coefficient corresponding to the pressure 

 P replaces the corresponding values, 273*03 (or 273), for the ice point 

 on the helium or hydrogen scales. 



Apparatus and method of experiment. The apparatus employed in 

 these experiments was identical with that described by Travers, 

 Senter, and Jaquerod,f and employed by them in measuring the 

 vapour pressure of liquid oxygen and liquid hydrogen on the constant 

 volume hydrogen and helium scales. The volumes of the different 

 parts of the apparatus were as follows : 



Volume of the bulb at C 24*264 c.c. 



Volume of the stem 0*0625 



Volume of the dead space 0-473 



The method of experiment has already been fully described, i 

 As the thermometer was a new one, it was thought advisable to fill it 

 first of all with hydrogen, and to measure the vapour pressures of liquid 

 oxygen on the hydrogen scale. The results, which were perfectly 

 satisfactory, are as follows : 



Ice Point. 



Pressure on gas 959*6 mm. 



Temperature of dead space ... 16*8 C. 

 Constant 86*863 



The constant is the product of the pressure on the gas at the 

 melting point of ice and the volume which the whole of the gas in 

 the thermometer would occupy at that temperature, divided by the 

 value of the temperature of the melting ice on the gas scale. The 

 latter is the reciprocal of the pressure-coefficient for the gas corre- 

 sponding to that particular pressure. Since the constant involves the 

 three terms p, v, and T, in the simple gas equation, a knowledge of it 

 enables us to calculate temperatures, on the same scale, from observed 

 pressures, when the volume is constant. 



* ' Phil. Trans.,' A, vol. 200, p. 145. 

 t - Phil. Trans.,' A. vol. 200, p. 141. 

 + Loc. cit. 



2 E 2 



