290 Electrical Conductivity of Copper fused with Mica. 



running water was placed between the specimen and the 

 microscope objective, in order to cut off the heat from the 

 objective, and the specimen was heated up to 400° 0. No 

 change could be discerned in the appearance of the etching. 



PI. VII. fig. 6 shows the appearance of a portion of the 

 surface at a temperature of 350° C. 



The specimen was then etched with the ammonia solution. 

 Here, again, the surface was found to be marked by fine lines 

 after an attack of about an hour, but no copper could be 

 detected. It was heated again to 400° 0. after etching, but 

 no change in structure could be observed due to the rise in 

 temperature. 



IV. Resistance-temperature coefficient of Glass. 



In studying these specimens one gained the impression 

 that they possessed a number of the characteristics of glass. 

 In most cases the specimens were very hard, and one could 

 easily produce scratches on a glass plate with many of them. 

 It is known, too, that many glasses when strongly heated 

 become electrically conducting, and with a view of making a 

 comparison between the behaviour of these specimens and 

 that of a sample of glass, some measurements were made on 

 the resistance of a rod of glass when its temperature was 

 gradually raised. 



In these experiments a rod of " Schmeltzglas " about 

 8'0cm. long and 5*0 mm. in diameter was used. Short 

 platinum wires were attached. These were then joined in 

 circuit with the mains of the 110 volt D.c. circuit, and the 

 glass portion was placed within an electric furnace. As the 

 temperature rose observations were made on the current 

 which passed and on the fall of potential between the ends 

 of the glass rod, contact being made with the circuit at the 

 platinum junctions. 



In these observations practically no current was found to 

 pass through the glass until a temperature of about 300° C. was 

 reached. Even then the current was only of the order of 

 10 -7 ampere, which showed that the resistance of the glass rod 

 at this temperature was very high, practically about 10 9 ohms. 



From this result it would appear that the high resistance 

 temperature coefficient possessed by the fused copper-mica 

 mixtures is something specific, and it does not appear that the 

 remarkable property they exhibit finds a direct parallel in 

 the behaviour of glass. 



The Physical Laboratory, 

 University of Toronto, 

 May 15th, 1920. 



