72 Profs. J. Dewar and J. A. Fleming. On the Electrical 



to 



; ' On the Electrical Resistivity of Bismuth at the Tempera- 

 ture of Liquid Air." By JAMES DEWAR, LL.D., F.R.S., 

 Fullerian Professor of Chemistry in the Royal Institution, 

 and J. A. FLEMING, M.A., D.Sc.', F.R.S., Professor of Elec- 

 trical Engineering in University College, London. Re- 

 ceived May 19, Read June 4, 1896. 



In the course of last year we published some observations (see 

 ' Phil. Mag.,' September, 1895, p. 303)* on the electrical resistance 

 of bismuth at the temperatures of liquid and solid air, in which 

 the resistivity of certain samples of bismuth was measured at various 

 temperatures down to the temperature at which air solidifies. These 

 observations showed some anomalous results. In the case of two 

 samples of bismuth used by us, and prepared by different chemical 

 means, it was found that the resistivity reached a minimum value at 

 a temperature of about 80, and that after that point further cool- 

 ing increased the electrical resistivity of these samples of the metal. 

 In the case of another sample of commercial bismuth, the resistivity 

 curve was a curve of double curvature. These results, together 

 with the high absolute value of the resistivity of the samples, caused 

 us to feel a strong conviction that different results would be 

 obtained with bismuth prepared by an electrolytic method. Some 

 observers, particularly M. van Aubel, who have investigated the elec- 

 trical properties of bismuth, have expressed the opinion that bismuth 

 cannot be prepared in a state of perfect purity by any chemical means. 

 Finding the chemical methods of doubtful utility, we accordingly 

 solicited the assistance of Messrs. Hartmann and Braun, who have 

 devoted a large amount of attention to the preparation of pure electro- 

 lytic bismuth for the purposes of constructing spirals of bismuth for 

 measuring the strength of magnetic fields. They kindly prepared 

 for us at our request a considerable quantity of bismuth by an 

 electrolytic method, which examination showed to be exceedingly 

 pure, and this metal was pressed into a uniform wire with a diameter 

 of about half a millimetre. This electrolytic bismuth is very soft, 

 and in the form of wire can be bent without difficulty. Resist- 

 ance coils were accordingly constructed of this wire, of a form 

 suitable for use when measured in liquid air and at low temperatures. 

 In the case of one resistance coil, which may be denoted as electro- 

 lytic bismuth No. 1, the length of the wire employed was 8O85 cm. ; 

 the diameter of this wire was carefully measured with a microscopic 



* " The Variation in the Electrical Eesistance of Bismuth when cooled to the 

 Temperature of Solid Air," Dewar and Fleming, 'Phil. Mag.,' September, 1895, 

 p. 303. 



