the Electrical Resistance of Bismuth. 333 



also studied the effect of the composition of the alloys Bi — Sn, 

 Bi — Pb, upon their electrical conductivity. 



According to Matthiessen and Vogt, the electrical conduc- 

 tivity of the alloys of bismuth is modified by the first heating 

 and the first cooling. Jf X be the original value, and X 01 the 

 conductivity after cooling, we have the following results: — 



Pb-Bi (2-27 vol. Pb to 100 vol. Bi) . 8'101 7-633. 

 „ ( 18 „ „ „) . 4-558 4-565. 



These variations doubtless depend upon permanent changes 

 in the molecular structure. 



The conductivity of molten bismuth increases as the tem- 

 perature is lowered ; it diminishes rapidly when the metal 

 solidifies, according to the researches of Matteucci and 

 Matthiessen, and increases again as the solidified mass cools. 

 If small traces of tin or lead be added to the molten bismuth, 

 according to Matthiessen, the conductivity at first diminishes, 

 as in the case of solid metals, and afterwards increases. 



Fr. Weber has found for the specific electrical con- 

 ductivity of bismuth (C.G-.S.) 0-838 xl0~ 5 ; and L. Lorenz 

 has given for the same quantity the values 



0-929 x 10- 5 at 0° ; and 0-630 x 10~ 5 at 100°. 



M. Leduc* has observed that the electrical resistance of 

 wires made of an alloy of bismuth and lead increases when 

 the temperature is raised. He has also observed a difference 

 between the electrical properties of wires and of thin plates of 

 commercially pure bismuth, which he attributes to the method 

 of preparation and to the very different rates of cooling. 



More recently f the same physi6ist has found the following- 

 results with bismuth which had been run into a tube and then 

 slowly cooled. When the bismuth is heated for the first 

 time, say to 100°, it undergoes an annealing the effect of 

 which is to diminish its initial resistance about 30 per cent. 

 During this operation, between the temperatures 0° and 100°, 

 the following formula is obtained, which must be received with 

 caution : — 



r t = r Q (1 + 0-00344* + 0'0000077i 2 ), 



in which r Q and r t are the electrical resistances at the tempera- 

 tures 0° and t° respectively. This formula gives the value 

 + 0*00421 for the mean coefficient of variation of the re- 

 sistance between 0° and 100°. 



* Journal de Physique, [2] iii. (1884) p. 362. 



t Leduc, Thesis for doctor's degree presented in June 1888 to the 

 Faculty of Sciences of Paris. 



Phil Mag. S. 5. Vol. 28. No. 173. Oct, 1889. 2 B 



