Sosman — Platinum- S hod lum Thermoelement. 5 



With these are included the results obtained by other 

 observers with similar ten per cent rhodiuiri alloys. Harker* 

 measured the e.m.f. at the melting point of tlie platinum wire 

 in a resistance furnace of refractory oxides. Waidner and 

 Burgessf made similar measurements in connection with their 

 optical determination of the melting point. Their figures, 

 being in terms of the United States legal volt (Clark at 15° = 

 1-434) have been corrected to the true volt (Clark at 15° = 

 1*4328). Other investigators (Holborn and Henning.;}: Nernst 

 and von Wartenberg,§ Holborn and Valentiner 1| ) have 

 measured the melting point of platinum in various ways, but 

 without recording the thermoelectric data. 



Table I. — Thermal E.M.F. at Melting Point of Platinum. 



Date 



No. of 



Per cent Eh in 



Silver 



Platinum 



Element 



alloy wire 



microvolts 



microvolts 



1910—19 Feb.... 



F 



10 



9103 



18619 



24 Feb.... 



F 



10 



9103 



18618 



25 Feb.... 



Y 



10 



9139 



18695 



25 Feb.... 



Z 



10 



9018 



18487 



8 Mar.... 



J 



10 



9106 



18603 



1 Mar.... 



I.J 



1 



1960 



3560 



15 Apr.... 



KJ 



5 



6495 



12444 



2 Mar 



I.sJ 



15 



10375 



22303 



4 Mar 



IisJ 



15 



10375 



22310 



1905— Harker... 



N. P. L. 3 



10 



(9084) 



18580 



(C ( ( 



T. 15 



10 



(9100) 



18693 



1907— W. and'B. 



P2 



10 



(9024) 



18369 



t( (( 



P3 



10 



(9040) 



18556 



U 11 



s, 



10 



(.8991) 



18250 



In general, the curves for all the different 10 per cent ele- 

 ments, both our own and those of other observers, are similar 

 in form, and the divergence of each from the mean increases 

 with increasing temperature. In this connection it should be 

 remarked that the e.m.f. at the palladium point (16140 micro- 

 volts) obtained by Holborn and Valentiner with an element 

 whose gold point was 10295, agrees almost exactly with a simi- 

 lar element from our series, with a gold point of 10295 and 

 palladium point of 16143. The disagreement between various 

 observers as to the melting points of these metals is, then, not 

 so much a matter of purity of metals or accuracy of thermo- 

 electric measurements, as it is of the evaluation of these in 

 terms of the nitrogen thermometer. 



It is of interest to find what value would be obtained for the 

 melting point of platinum by extrapolating the curves of our 



* J. A. Harker, Proc. Eoy. Soc, Ixxvi, A, 235-250, 1905. 

 ■I- C. W. Waidner and G. K. Burgess, Bull. Bur. Standaids, iii, 200, 1907. 

 JL. Holborn and F. Henning, Sitzb. Berl. Akad., xii, 311-317, 1905. 

 " W. Nernst and H. von Wartenberg, Ber. deut. Phys. Ges., iv, 48-58, 1906. 

 L. Holborn and S. Valentiner, Ann. Phys., xxii, 1-48, 1907. 



