>02 B. O. Peirce — Thermo-electric 



Art. XLIII. — On the Thermo-electric Properties of Platinoid 

 and Manganine ; by B. O. Peirce. 



During the last few years the attention of many physicists 

 has been occupied with the attempt to discover an alloy in every 

 respect suitable for making standards of electrical resistance. 

 Such an alloy, it is evident, must be non-magnetic, ductile, not 

 easily corroded and easily soldered to copper and brass. It 

 must have a high specific resistance independent of the tern 

 perature aud, when drawn into wire, its resistance must not be 

 subject to secular change. 



No one : substance is yet known to satisfy all these condi- 

 tions completely and, since there is still some doubt about the 

 permanency of artificially seasoned resistance coils made of 

 manganine wire, many makers of standards prefer to use plati- 

 noid in spite of its comparatively high temperature coefficient. 



I have been trying of late to reduce as much as possible the 

 disturbing effects of thermo-electric currents in a certain stand- 

 ard slide wire bridge and have had occasion to determine the 

 thermo-electric relations of copper to such ' 2 platinoid and 

 3 manganine as are to be obtained in the market. A few years 

 ago such determinations would have had very little practical 

 value, since different specimens of copper had very different 

 positions in the thermo-electric scale, but this last statement is 

 no longer true of copper bought in the American market. I 

 have tested against each other many specimens of copper wire 

 of different sizes, chosen at random from a rather large stock 

 bought at intervals during the last five years, and the highest 

 electromotive force that I have obtained was 0*06 microvolts 

 per centigrade degree, and this was very exceptionally large. 

 I believe that a thermal junction made of two specimens of 

 annealed copper wire bought of different reputable makers 

 would probably not yield more than one or two c. g. s. units 

 of electromotive force per centigrade degree even if one were 

 as large as no. 10 and the other as small as no. 36 on the Amer- 

 ican * Gauge. Professor E. H. Hall tells me that he has 



1 Feussner and Lindeck: — Zeitschrift fur Instriunentenkunde, 1889, pp. 233- 

 236. 



Nichols:— This Journal, 1890. pp. 471-477. 



Ahler, Haas and Angersiein: — Electrotechnische Zeitschrift, 1891, p. 250. 



Feussner: — Electrotechnische Zeitschrift, 1892, p. 66. 



Milthaler:— Wiedemann's Annalen, xliv, 1892, pp. 297-305. 



Lindeck: — Wiedemann's Annalen. xlvi, 1892, pp. 515-516. 



Weichert: — Wiedemann's Annalen, Hi, 1893, pp. 67-75. 



2 Bottomley and Tanakadate:— Phil. Mag., xxviii, 1889, pp. 163-169. 



s Englisch: — Wiedemann's Annalen, 1, 1893, pp. 88-110. 



*The diameter in inches of wire no. n in the American Gauge is approximately 

 n 

 (0-32) 2~6- 



