

Thermo-electric Powers of Metals and Alloys. 101 



The platinum temperature pt (measured from melting- 

 point of ice) is obtained from E, the resistance at pt°, by the 

 equation 



pt = 9M2R- 283-0. 



The platinum temperature of solid carbonic acid melting in 

 ether at 760 mm. is — 81'9 platinum degrees by this thermo- 

 meter ; and the platinum temperature of liquid oxygen 

 boiling at 760 mm. is — 196*7 platinum degrees by this 

 thermometer. 



The constants of our working thermometer P 2 are: — 



E =resistance at 0° C. = 7*303 ohms. 

 Rioo = resistance at 100° C. = 10' 140 ohms. 

 a =mean temperature-coefficient between 0° C. and 

 100° C. = -003885. 



--=-257°-42. 



a 



The absolute zero of this wire is — 283 o, in terms of its own 

 platinum temperature. 



Platinum temperature as measured by this thermometer 

 is given by the equation 



pt= 35-25R-257-42, 



where R is the resistance of the wire at pt°. 



The platinum temperature of solid carbonic acid in ether at 

 760 mm. is — 81°"3 platinum degrees by this thermometer ; 

 and the platinum temperature of liquid oxygen boiling under 

 760 millim. is — 193 0, 3 platinum degrees by this thermometer. 



We find that the number representing the platinum tem- 

 perature of liquid oxygen boiling under 760 mm. when taken 

 by the working platinum thermometer P 2 is not quite identical 

 with that given by the standard platinum thermometer P x . 

 Into the cause of this we will not now stop to enquire, because 

 it did not interfere at all with our use of the working thermo- 

 meter P 2 . Having determined the resistance of the working- 

 platinum thermometer and of the standard platinum thermo- 

 meter when immersed together in boiling liquid oxygen, solid 

 carbonic acid and ether, melting ice (0° 0.), and boiling water 

 (100° C), we were able to construct a curve which gave us the 

 true platinum temperature in terms of our standard platinum 

 thermometer Pj of the working platinum thermometer P 2 

 when immersed in any medium which gave it a definite 

 resistance, and hence a definite point of balance on the slide- 

 wire of the bridge. Jn order to shorten the labour of 

 correcting the observations, a scale was constructed which 

 enabled us to infer by inspection at once from the actual 



