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Physics. — "On the measurement of very loio temperatures". XXVI. 

 The vapour- pressuren of oxygen and nitrogen according to the 

 pressure-measurements by v. Siemens ami the temperature- 

 determinations by Kamerlingh Onnes c. s. By Dr. G. Holst. 

 (Communications from tlie Physical Laboratory at Leiden. J48a). 

 (Communicated by Prof. H. Kamerlingh Onnes). 

 (Communicated in the meeting of Sept. 25. 1915.) 



§. 1. hitroduction. The main object of this communication is a 

 correction of the calculation of the results contained in a paper by 

 H. VON Siemens, Annalen der Physik Vol. 42, p. 871, 1913. Siemens 

 determined the vapour-pressure as a function of the temperature for 

 a number of substances using a piatinum-resistance-thermometer. 

 This thermometer had been reduced to the Leiden- standard-platinum- 

 thermometer Pt^ by means of Nernst's linear reduction-formula. 

 For a handy calculation of the temperatui-es Siemens used an 

 interpolation-table in which the resistance is given divided by the 

 resistance at ()°C. below 80°K. for every two degrees and for 

 temperatures between 80'K. and 290°K. for every five degrees. For 

 this purpose he used the data of the Leiden-calibration of 1905 — 1906. 

 It has appeared, however, afterwards that this calibration does not 

 agree so well with subsequent ones as these among themselves and 

 that, particularly in the oxygen-region, considerable deviations occur 

 which must therefore also affect the results obtained by Siemens. 

 We will therefore begin by a detailed evamination of these deviations. 



• ^ 2. The calibration of Pt^. 



The first comparison of this resistance-thermometer with the 

 hydrogen-thermometer was carried out in 1905 — 1906 by Kamerlingh 

 Onnes, Braak and Clay. The results are contained in the table on 

 p. 44 of Comm. 95f. Subsequently Pt^ broke and waf^. then once more 

 wound. The repaired thermometer was called Pt\. It was again 

 compared with the hydrogen-thermometer in 1907. On page 5 

 of Comm. 101^^ its resistance at nine different temperatures is given. 

 Small differences showed themselves at the time up to 0,04 of a 

 degree. In the end of 1907 and the beginning of 1908 another 

 calibration was |)erformed at six different points : the results were 

 published in Comm. 107r/ page 6. 



In 1913 a new series of measui-ements was made by Kamerlingh 

 Onnes and Holst, the results being contained in Table 1 Comm. 141« 

 page 7.') 



') An interpolation-formula representing these observations between 15° K. and 

 230°K. was given by Zernike. (These Proceedings Kon. Ale. v. Wet. XXIII, p. 742, 1914). 



