662 Prof. J. Patterson on the Electrical 



the bismuth films in a similar manner their resistance would 

 also be decreased. A number of films were heated in dif- 

 ferent oils and to temperatures from 40° C. to 70° 0. The 

 oil ^as carefully dried before the films were put in, but in 

 every case th» y were destroyed. 



A bismuth film was put into a glass tube having the elec- 

 trodes sealed through the glass. The tube was exhausted as 

 far as possible, dried, and then heated. The resistance of film 

 before heating was 398*70 ohms. It was then heated for 

 twenty-four hours to 70° C. and allowed to cool, the resistance 

 was then 41P8. After heating for seven hours more to 

 110° C. its resistance was 439'7 ohms, and heating for four 

 hours to 120° C. did not change its resistance, which was 

 then 4398 ohms. Its resistance was also measured while it 

 was cooling, and the result indicated a negative temperature- 

 coefficient. This was measured accurately and found to be 

 -0 002. 



This same film was kept sealed up in the tube and its 

 resistance ten months alterwards was 438*4 ohms at the 

 temperature of the room. 



These results indicate that the gradual increase of the re- 

 sistance of the films was due to the action of the air on them, 

 and that when they were kept in vacuo, the resistance did 

 not decrease with time or on being heated, but remained 

 fairly constant. 



Resistance of Platinum Films. 



The cathode from which the films were deposited consisted 

 of platinum foil fixed on a mica disk 5 cm. in diameter. 



The resistances of the films w r ere measured shortly after 

 they were made. Longden* found that heating the films 

 reduced their resistance, and if the heating was continued 

 the resistance finally became constant. To test this two films 

 were heated in a hot-air bath for several hours and their re- 

 sistance measured before and after heating. This operation 

 was repeated until the resistance became constant. The 

 effect of heating on the resistances of the films is shown in 

 Table IV. 



From Table IV. it will be seen that the greatest fall 

 in resistance occurs during the first heating, and that sub- 

 sequent heatings have a comparatively small effect on the 

 resistance of the films. 



* Physical Review, vol. xi. p. 40 (1900). 



