306 Profs. Dewar and Fleming on the Variation 

 Pure Bismuth (B) (Matthey's). 



Volume Specific 



Temperature 



Volume Specific 



Temperature 



Resistance 



in Platinum 



Resistance 



in Platinum 



in O.G-.S. units. 



degrees. 



in C.G.S. units 



degrees. 



175100 



+49-2 



150600 



- 8°7-9 



174850 



4-48-0 



151300 



-100-5 



165100 



4-18-8 



151300 



-103-9 



163050 



+ 11-3 



152000 



-114-8 



161550 



4- 3-6 



152850 



-118-8 



161250 



+ 1-3 



154950 



-132-2 



158400 



-11-5 



155900 



- 136-1 



157900 



-18-3 



159450 



-148-1 



153750 



-365 



161200 



-152-2 



153300 



-400 



166300 



-168-0 



152350 



-51-6 



169850 



- 174-9 



152050 



-55-3 



179550 



-193-4 



151000 



-66-8 



181000 



-196-2 



150850 



-710 



181000 



-196-8 



150500 



-83-3 







The ahove numerical results are set out in the form of three 

 curves (see Plate V.). It will be seen that the specific electrical 

 resistance of all the bismuth specimens taken from 100° C. 

 downwards gradually diminishes to a point which, in the case 

 of the specimen of pure bismuth " A " was about 50° P x , and 

 in the case of the specimen a B " about —83° P x . After these 

 temperatures had been reached, further cooling increased instead 

 of diminishing the electrical resistance of the A and B bismuth, 

 until, at the lowest temperature reached by the employment 

 of large quantities of solid air, the electrical resistance of the 

 specimen " A " had become increased by nearly 80 per cent, 

 of its minimum resistance, and at the same time the mean 

 temperature coefficient had become very large, and of course 

 negative. It may be noted that the melting-point of solid air, 

 as determined by our standard platinum thermometer, is 

 — 232°*2 P 1? liquefaction taking place under a pressure of 

 14 millim. of mercury. The boiling-point of liquid air under 

 a pressure of 746 millim. is —209°* 75 P v The same general 

 facts were observed in the case of the specimen of pure 

 bismuth " B," only in this instance the temperature was not 

 taken below about —200° P 1# As regards the commercial 

 bismuth (Griffin's) the curves show that after reaching a 

 minimum point, which for that specimen appears to occur 

 at about 0° C, there is another point of inflexion in the 

 resistance-curve in the neighbourhood of —200° P 1? after 

 which the resistance again diminishes. In the case of each 



