TABLE 282. 

 RELATION BETWEEN THERMAL AND ELECTRICAL CONDUCTIVITIES. 



That there is a close relation 

 between the thermal and the 

 electrical conductivities of 

 metal was shown experimen- 

 tally by Wiedemann and Franz 

 in 1853, and had been referred 

 to by Forbes, with whom a 

 difficulty arose with regard to 

 the direction of the variation 

 with temperature. The ex- 

 periments of Tail and his stu- 

 dents have shown that this 

 difficulty was largely, if not 

 entirely, due to experimental 

 error. The same relation has 

 been shown to hold for alloys 

 by Chandler Roberts and by 

 Neumann, This relation was 



a. VALUKS IN ARBITKARY UNITS AT 15^ C. 



denied by H. F. Weber, and 

 has been again experimentally 

 investigated and apparently 

 established by the experiments 

 of Kirchhoff and Hansemann, 

 of L. Lorenz, of F. Kohl- 

 rausch, and of Berget. 



Putting /=: thermal conduc- 

 tivity, and k =r electrical con- 

 ductivity, Kirchhoff and 

 Hansemann find the values in 

 Table a. This table shows 

 iron to deviate considerably 

 from the other metals in the 

 relaiionship of the two con- 

 ductivities ; but this may possi- 

 bly be explained by its mag- 

 netic properties. 



Lorenz 's results* show that the ratio // k for the different metals, except iron, is nearly constant for values 

 at o and 100 C., but that the ratio is generally greater for poorly conducting substances. He shows that the 



ratio ^ -T- ~~ remains nearly constant for all metals examined, with the exception of iron, and has an aver- 

 age value, as shown by Table to, of about 1.37. He concludes that I / k constant X 7", where T is the abso- 

 lute temperature. 



In this table the values of / and k are given in c. g. s. units, and the metals are arranged in the order of 

 their heat conductivities. The same specimens were used for both the thermal and the electrical experiments. 



b. VALUES IN C. G. S. UNITS. 



Substances. 



k X io r> 



k loo X io 5 



Copper 

 Magnesium 

 Aluminium 

 Brass, red . 

 Cadmium . 

 Brass, yellow 

 Iron . 

 Tin . 

 Lead . 



German silver 

 Antimony . 

 Bismuth . 



0.7108 

 0.3760 



0-3435 

 0.2460 



O.22OO 

 0.2041 

 0.166; 

 0.1528 

 0.0836 

 0.0700 

 O.O442 

 0.0177 



0.7226 

 0.3760 

 0.3619 

 0.2827 

 0.2045 

 0.2540 

 0.1627 

 0.1423 

 0.0764 

 0.0887 

 0.0396 



0.016.1 



45-74 

 24.47 

 22.46 



15-75 

 14.41 

 12.62 



10-37 

 9-346 

 5.141 

 3.766 

 2.199 

 0.929 



33-82 

 17.50 



10.18 



I I.OO 



6.628 

 6.524 

 3.602 

 3-632 



1.522 



0.633 



1537 

 1529 

 1562 



!5 2 7 

 1617 

 1605 



1627 

 1858 



2OII 

 I9OO 



1-358 

 1.398 



1.367 

 1.360 



1.315 



1.428 

 1-530 



1-334 

 1.304 



i-3 J 4 

 1.294 



1-372 



C. BERGET'S EXPERIMENTS^ 



The same specimens were used for both experiments. It will be seen that the ratio is nearly constant, but not 



exactly so. 



Substance. 



k X io-- 



Substance. 



X-X 



Copper . . 



Zinc . . . 



Brass . . 



Iron . . . 



1.0405 

 0-303 

 0.2625 

 0.1587 



V 3 



18.00 



15-47 

 9.41 



1.6 



Tin . . . 

 Lead . . 

 Antimony 

 Mercury . 



0.151 

 0.08 1 o 

 0.042 



O.O2OI 



8-33 

 5.06 



2-47 

 i. 06 



1.8 

 1.6 

 i-7 

 1.8 



d. KOHLRAUSCH'S RESULTS. 



An interesting confirmation of the relationship of the two conductivities has been furnished by F. Kohl- 

 rausch, who has shown that tempering steel causes equal proportional changes in the thermal and electrical 

 conductivities of the metal, thus leaving the ratio l/k unchanged by the process.^ 



Tempered steel 

 Soft steel 



/= 0.062; 

 " = o.ni; 



= 3.3; l/k = 0.019 

 =5-5; " =0.020 



In the consideration of this subject it must be borne in mind that closely accurate values of thermal conduc- 

 tivity are very difficult to obtain, and hence fairly large variations are to be expected. 



* " \Vied. Ann." vol. 13, p. 5q8. 

 t " Compt. Rend." vol. no, p. 76. 



SMITHSONIAN TABLES. 



I is in c. g. s. units and k in terms of mercury. 



271 



