160 A. L. Day and R. B. Sosman— 



siderabie length in 1908.* The present paper extends the 

 observations to 1550°, and completes the work contemplated 

 under the original plan. 



No attempt will be made to offer an inclusive summary of 

 the whole investigation. It is a record of experimental 

 measurements covering an unusually wide range of details 

 which do not admit of brief classification. The errors which 

 have heretofore been present in measurements with the nitro- 

 gen thermometer have been reduced by the present investiga- 

 tion to about one-fourth their former magnitude and the 

 certainty of their evaluation is at least proportionately increased. 



The chief source of present uncertainty is the temperature 

 distribution over the surface of the bulb, in an air bath. No 

 indication of a limit to the temperature attainable with the 

 nitrogen thermometer or to its ultimate accuracy was discovered 

 during the present investigation. 



The magnitudes of the errors, and their effects on the tem- 

 perature, are summarized in Table IY, page 129. The deter- 

 minations of the expansion coefficient of the bulb material 

 (80 Pt, 20 Eh) are summarized on pp. 131-132. 



The melting temperatures of the metals and salts which 

 have been used as fixed points to establish the new scale 

 are brought together in the table below, together with 

 the conditions under which the determinations were made. 

 The generally accepted Reichsanstalt scale is printed beside it 

 for convenient comparison. The analyses of the metals are 

 summarized on p. 159. 



To this table has been added a new estimate of the melting 

 temperature of platinum, of which we could make no direct 

 determination. Its general acceptance and availability as a 

 fixed point of reference, and the wide disagreement between 

 the direct determinations heretofore made of it, form a suffi- 

 cient reason for its inclusion. The estimate is arrived at in this 

 way : There is a remarkably close agreement between inde- 

 pendent determinations of the temperature interval between 

 the melting points of palladium and platinum : 



Nernst and von Wartenbergf 204° 



Holborn and Valentiner (at the Reichsanstalt)J 207° 

 Waidner and Burgess (at the Bureau of 



Standards) § 207 ° 



If we therefore simply add 206° to our determination of the 

 palladium point, we obtain 1755° as the melting point of pure 

 platinum, with an absolute error of perhaps no more than 

 ± 5°. The table follows : 



* This Journal (4), xxvi, 405, 1908. 



f W. Nernst and H. von Wartenberg, Ber. d. Deutsch. phys. Ges., iv, pp. 

 48, 146, 1906. 



%~L. Holborn and S. Valentiner, Ann. d. Phys. (4), xzii, 1, 1907. 



§C. W. Waidner and G. K. Burgess, Bull. Bur. Standards, iii, p. 163, 1907. 



