1890.] Determination of the Boiling Point of Sulphur, Sfc. 59 



The close agreement between the air thermometer experiments of 

 1887 and the present series, leads us to conclude that the number 

 above given is probably correct to a tenth of a degree, and that it may 

 be safely used for standardising platinum thermometers. 



The method which we recommend for standardising platinum ther- 

 mometers is briefly as follows : Observe the value B, of the resist- 

 ance in sulphur vapour in an apparatus such as we have described. 

 Calculate the value of pt s by the formula 



pt, = 100 (R,-R )/(R 100 -R ). 



Find the temperature t of the sulphur vapour, corresponding to the 

 corrected barometric pressure H , from the formula 



* = 444-53+0-082 (H -760). 



The appropriate value of 8 is then given by the equation 

 t-pt = 



Vfe have made use of this method to reduce the results given in a 

 previous communication, " On the Determination of some Boiling 

 and Freezing Points by means of the Platinum Thermometer,"* and 

 we find that the values of t deduced from the observations with 

 several thermometers of different patterns and with very different 

 coefficients, are in remarkably close agreement. The results found 

 with the three best thermometers are given in the following table : 



Table of Boiling a.nd Freezing Points reduced by Formula (d). 



The fixed points given in the above have not been so carefully de- 

 termined as the boiling point of sulphur. They rest entirely on the 



* See Griffiths, ' Phil. Trans.,' A, 1891. 



