Conductivity of Copper fused with Mica. 



285 



temperature and causes the fall in resistance with temperature 

 to be much more rapid. 



While more brittle than copper, the copper-mica is not 

 as brittle as iron-mica compounds described below. The 

 hardness is almost the same as that of glass. X-ray photo- 

 graphs showed the composition to be quite homogeneous. 

 The mixture was black with a dull metallic lustre. 



(b) Iron and Mica. — Two mixtures were made as in the 

 case of the copper and mica, and the temperatures and 

 resistances were measured as before. In Case No. 1 (Graph 

 No. 5) the resistance fell from 1300 ohms to 100 ohms on 

 being heated from 25° C. to nearly 300° C. 





Graph 



No. 5. 





Temperature, 



Resistance 



Tempei-ature, 



Resista 



°0. 



(Ohms). 



°C. 



(Ohms 



26 



1,350 



303 



91 



42 



980 



308 



90 



47-5 



890 



165 



235 



52-5 



825 



138 



310 



54 



790 



116 



380 



104 



410 



97 



490 



134 



350 



75 



650 



138 



340 



83 



590 



178 



219 



64 



765 



195 



180 



55 



860 



209 



160 



51 



905 



218 



150 



45 



1,010 



165 



280 



40 



1,070 



214 



170 



38 



1.110 



263 



115 



33-5 



1,203 



282 



10:i 



31 



1,240 



294 



95 







In Case No. 2 (Graph No. 6) the resistance fell from 

 32,000 ohms on being heated from 160° O. to 380° C. 





Graph 



No. 6. 





perature, 



Resistance 



Temperature, 



Resistance 



°C. 



(Ohms). 



°C. 



(Ohms). 



250 



6,100 



294 



3,380 



228 



9,050 



282 



3.900 



280 



3.870 



255 



5,970 



318 



2,410 



242 



7,350 



335 



1,980 



231 



8,440 



344 



1,780 



222 



10,380 



360 



1.550 



214 



11,720 



377 



1,280 



204 



15,750 



360 



1.550 



197 



15,900 



336 



1,980 



187 



19,550 



322 



2.360 



175 



25,210 



309 



2,730 



164 



32,100 



