1904.] 



On High Temperature Standards. 



217 



" On the High Temperature Standards of the National Physical 

 Laboratory : an Account of a Comparison of Platinum 

 Thermometers and Thermo-junctions with the Gas Thermo- 

 meter." By J. A. Harker, D.Sc, Fellow of Owens College, 

 Manchester, Assistant at the National Physical Laboratory. 

 Communicated by E. T. Glazebrook, F.E.S. Eeceived 

 January 20,— Eead February 11, 1904. 



This paper contains an account of a continuation of the work of 

 Dr. P. Chappuis and the author,* on a comparison of the scale of the 

 gas thermometer with that of certain specially-constructed platinum 

 thermometers, from temperatures below zero up to the boiling point of 

 sulphur, and in one case to a point close to 600° C. 



The results of this work substantially confirm the experiments of 

 Callendar and Griffiths, and show that the indications of the platinum 

 thermometer may be reduced to the normal scale by the aid of 

 Callendar 's difference formula : 



where pt is the platinum temperature, T the temperature on the normal 

 scale, and 8 a constant which, for pure platinum, does not differ much 

 from the value 1*5. 



The temperatures chosen for the determination of 8 are 0° C, 100° C, 

 and the boiling point of sulphur. 



In the present paper the work is extended to a temperature of 

 1000° C. Moreover, a number of standard thermo-junctions of 

 platinum — platinum -rhodium were included in the comparisons. 



The gas-thermometer employed for this work was presented to the 

 laboratory by Sir Andrew Noble ; it was obtained, along with 

 materials for the electric furnaces and thermo-junctions, through the 

 kindness of Dr. Holborn, of the Eeichsanstalt. The bulbs used were 

 of porcelain, glazed inside and out, and the gas used was pure dry 

 nitrogen. The thermo-junctions, which were carefully compared by 

 Dr. Holborn with the standards of the Eeichsanstalt, at a number of 

 fixed points up to 960° C, were again tested and compared together 

 before use, with concordant results. A special potentiometer designed 

 and made in the laboratory enabled the thermo- junction readings to be 

 taken with great accuracy. 



(From the National Physical Laboratory.) 

 (Abstract.) 



VOL. LXXIII. 



* ' Phil. Trans.,' A, 1900. 



R 



