Variation of Thermal Conductivity of Metals, 543 



abruptly decreases by about 13 per cent, during the melting 

 (jitl3°C). The same experiments on Na 2 HP0 4 + 12H 2 0, 

 Paratoluidine, Naphthylamine, and CaCl 2 + 6fl 2 were also 



made by 0. H. Lees'" ; but there was no apparent break 

 in the regularity o£ the change of thermal conductivity at 

 the melting-point in the case of the first three substances, 

 and a decrease of about 20 per cent, in the case of 

 (JaCl 2 + 6H 2 0. A. W. Porter and F. Simeon f made a 

 similar experiment with mercury and sodium, and showed 

 that the abrupt change in the thermal conductivity during 

 melting is of the same order of magnitude as the corre- 

 sponding change in the electrical conductivity — that is, the 

 ratio of the thermal conductivity for the solid state to that 

 for the liquid is 3'91 for mercury and 1*31 for sodium. 

 The only experiment at high temperatures was that of 

 E. F. Northrup and F. II. Pratt % for two typical metals — 

 tin and bismuth, for each of which the conductivity changes 

 in the opposite direction during melting, but their result 

 is rather of a qualitative nature. They concluded that the 

 characteristic change of thermal conductivity for tin and 

 bismuth during melting is substantially the same as the 

 corresponding change for the electrical conductivity, and 

 that Wiedemann-Franz's law holds good, at least qualita- 

 tively, through the change of state of these metals. 



So far, the literature regarding the abrupt change of 

 the conductivity during melting has been very meagre. 

 Hence, to determine as accurately as possible the thermal 

 conductivity of different metals at temperatures both below 

 and above their melting-points Avas a very important work, 

 and, therefore, I began — as a preliminary experiment — with 

 some fusible metals. The following pages contain the 

 method and the result of the present experiment. 



§ 2. Description of the Apparatus. 



The method used in the present experiment is to measure 

 the conductivity of metals at different high temperatures 

 relative to the values at room-temperature. A vertical 

 section of the main part of the apparatus is shown in fig. 1. 

 A, B, D are short cylindrical pieces made of a very low 

 carbon steel, and (J is the specimen to be tested. The iron 

 cylinders A and B are each 2*5 cm. in height and 2*2 cm. 

 in diameter; between these two pieces there i^ a flat 



* Phil. Trans. Roy. Soc. A. exci. p. 399 (1898). 

 t Proc. Phys. Soc. xxvii. p. 307 (1915). 

 X Jour. Frank. Inst, clxxxiv. p. 676 (1917). 



