Sosman — Platinum -Rhodium Thermoelement. 15 



copper-cobalt, by Reichardt ; * copper-nickel, by Feussner and 

 Lindeck ; f and silver-zinc, by Puschin and Maxirnenko,:}: show 

 a similar relationship between the form of the curve and the 

 constitution of the alloy. 



The alloys of platinum and rhodium have not been studied 

 microscopically or thermally, but measurements in our carbon- 

 tube furnace showed that the melting points of the 1 per cent 

 and 5 per cent alloys are higher than 1755°. The melting 

 point of the 10 per cent alloy is given by von Wartenberg § as 

 1830°, and of pure rhodium as 1940°. It is very probable, 

 therefore, that platinum and rhodium form solid solutions at 

 least as far as 55 atomic per cent rhodium, with no compounds, 

 over the range of temperature covered by the data. 



6. Summary. 



1. In continuation of the recent work from the Geophysical 

 Laboratory on the nitrogen thermometer from zinc to palla- 

 dium the interpolation curve of the thermoelement Pt : (90 

 Pt lOPh) has been extended downward to 0° and upward to 

 the melting point of platinum, 1755°. The standard scale of 

 temperatures adopted is given on page 6. 



2. The value of the melting point of platinum obtained by 

 extrapolation of the curves of thermoelements with from 1 to 

 15 per cent rhodium confirms the value 1755° vpithin the esti- 

 mated limit of 5°. 



3. A simple method of interpolating temperatures with the 

 10 per cent thermoelement by means of a standard curve 

 (Table II, p. 9) and deviation curves (p. 7) is described. 



4. The variation of thermal e.m.f. with the temperature and 

 composition of the alloy wii'e is shown graphically in figs. 3 

 and 4, pages 13 and 14. The variation, both with temperature 

 and with composition, is, within the limits of error, continuous 

 over the entire range studied. 



5. The variation of thermoelectric power, -r-. with the tem- 

 perature and composition of alloys of platinum and rhodium, 

 is shown graphically in fig. 5, page 14. The data indicate 

 the formation of solid solutions, but no compounds, from 

 to 55 atomic per cent of rhodium. 



Geophysical Laboratory, 



Carnegie Institution of Washington, 

 Washington, D. C, April 30, 1910. 



* Ann. Phys. (4), vi, 833-55, 1901. 



t Wiss. Abh. Phys.-Teeh. Eeichsanst., ii, 1895. 



X Jour. Russ. Phys. Chem. Gas., xli, 500-524, 1909. 



gVerh. Deutseh. Phys. Ges., xii, 131-127, 1910. 



