837 



the neigliboiirhood of the boiling point. Calcnlating according to tlie 

 above formula the temperatures corresponding to these vaponr- 

 pressnres we do not find greater deviations than of 0.02 of a degree, 

 so that the temperature belonging to a given vapour- pressure is 

 pretty sure to be accurate to 0.02 of a degree. 



By means of the formula given above the vapour-pressure mea- 

 surements by Siemens may now be recalculated. Siemens gi\es the 

 resistance of his thermometer at an oxygen-pressure of 766.8 mm., 

 where according to the formula 7"= 90°, 21 K. According to the 

 table at this point the resistance-ratio for Pt ^ is 0.25211, whereas 

 for Siemens' thermometer it is 0.25923, so that u in Nehnst's linear 

 formula is equal to 0.00961; with tliit; constant the thermometer may 

 be reduced to Pt ^ and the temperatures may be calculated. 



It follows from the value of rf, in connection with what was found 

 above in the comparison between Pt\ and P^^ , that no greater 



