886 Dr. E. van Aubel's Researches on 



In his Legons sur V EUctricite, Prof. Exner* mentions that 

 when bismuth is heated the resistance generally decreases, 

 and does not return to its original value on cooling, but 

 reaches a value which is higher as the cooling is more gradual. 



Ph. Lenard and J. L. Howard t have studied bismuth 

 wires obtained by means of a screw-press ; these wires were 

 rolled into a spiral immediately, while the metal was still hot. 

 They found that in the case of pure bismuth the electrical 

 resistance increased with the temperature between 0° and 36° 

 by 0*0052 for every degree Centigrade. 



Finally, in a preliminary communication, published last 

 yearf, I took up again the study of the question. Although 

 bought at the best manufactories in Germany, all the bismuth 

 that I used was very impure. 



I examined bismuth slowly cooled, hardened bismuth, and 

 finally compressed bismuth. The molecular structure exerts 

 a great influence upon the electrical properties of different 

 kinds of impure bismuth. All the alloys of bismuth and tin 

 which I studied gave an increase of electrical resistance when 

 the temperature was raised, although the bismuth specimens 

 which entered into the composition of these alloys produced 

 the opposite effect. I also proved, in these preliminary 

 experiments, the great influence of lead as an impurity 

 in bismuth. 



If my first results and those of the other physicists be com- 

 pared with the conclusions arrived at in my present treatise, 

 the wide differences which can be caused by impurities in the 

 pieces of metal under examination will be very striking. 



The modes of preparing and of suddenly cooling rods of 

 bismuth have been fully described in a preliminary commu- 

 nication §. 



Analysis of different Bismuths. 



We have measured the electrical resistances of several 

 different bismuths, which we will designate by 

 Latest Brommsdorff, 

 Classen I., 

 Classen II., 

 Classen III., 

 Classen IV., 

 and pure electrolyzed bismuth. 



The first is the metal as pure as it is possible to obtain it 



* Vorlesungen iiber Elektricitat, Wien (1888), p. 404. 

 f Elektrotechn. Zeitschrift, 1888, Bd. ix., July, Part xiv, 

 \ Bulletins de V Academie royale de Belgique, 1888, 3rd Series, xv. No. 1 

 (Preliminary communication). 



§ Phil. Mag. toI. xxv. p. 191 ; Proc. Phys. Soc. Lond. vol. ix. p. 124. 



