310 The Variation in the Electrical Resistance of Bismuth. 



With the object of ascertaining this we have also tested 

 some very pure bismuth kindly sent to us by Mr. Edward 

 Matthey, and which was prepared by the reduction of the 

 oxy chloride. This being pressed into wire was found to give 

 a resistance-temperature curve very similar in general form to 

 that marked Griffin's Bismuth in Plate Y. The resistance 

 decreased down to about 0° C, and then increased again when 

 cooled to about — 160°, and finally decreased again. It is 

 clear, therefore, that the specimens of bismuth, viz. that pre- 

 pared for us by Mr. George Matthey from the oxide and that 

 prepared by Mr. Edward Matthey from the oxychloride, and 

 which are both very pure, behave quite differently at very 

 low temperatures with regard to their electrical conductivity. 

 We have also examined the variation of a sample of bismuth 

 prepared electrolytically, but the result of this examination we 

 reserve until the observations have been confirmed on other 

 samples of electrolytic bismuth. One fact of considerable 

 interest has presented itself in studying the action of a mag- 

 netic field on the electrical resistance of bismuth cooled to low 

 temperatures. It is well known that the electrical resistance 

 of bismuth is increased by being immersed in a magnetic field. 

 Taking a sample of the pure (Matthey) bismuth wire, we 

 measured its electrical resistance at 18° C. in the earth's field 

 and when placed transversely in the field of an electromagnet, 

 and found an increase of resistance due to the field in the 

 ratio of 1*361 to 1*434, or about 5 per cent. The same 

 sample was cooled in liquid oxygen, and measured again in 

 the same fields. The resistances were then in the ratio of 

 1*478 to 1*858. The increase in resistance in this last case is 

 nearly 25 per cent. Hence the cooling of the bismuth to 

 — 182° C. increased the effect of a given magnetic field in 

 altering its resistance about five times. 



Another experiment was made to ascertain whether in- 

 creased pressure on the surface of the bismuth affected its 

 resistance. When a sample of pure bismuth wire was sub- 

 jected to an external surface-pressure of 300 atmospheres, 

 a very slight but definite increase of resistance was found, 

 which disappeared instantly on removing the pressure. 



The above described observations show that there is a very 

 marked difference between different samples of bismuth as 

 regards electrical resistance when subjected to very low tem- 

 peratures, and that its behaviour at these temperatures in 

 magnetic fields is also abnormal. We propose to reserve 

 further remarks on this subject until we have completed the 



