Conductivity of Copper fused with .)fica. 289 



III. Results. 



When examined under the microscope different specimens 

 were found to exhibit different appearances. Most samples 

 appeared to he quite uniform in structure, while in some 

 many little globules could be seen, which from their lustre 

 appeared to be pure copper. 



Specimens which possessed a high temperature coefficient 

 were found both under high and low power magnification to 

 show no change in structure, either by normal or oblique 

 illumination, when heated to temperatures as high ;is 400° C. 



PI. VII. fig. 1 shows the appearance of a specimen at room 

 temperatures with a magnification of 46. The resistance of 

 this sample, which was 3200 ohms at 21° (J., fell to IG00 

 when at 95° C. The structure of the specimen appeared 

 very uniform, and no copper could be discerned in it judging 

 by metallic lustre. 



PL VII. fig. 2 shows the appearance of this specimen when 

 etched with ammonia solution for an hour. As pure copper 

 was found to require approximately about seven hours' 

 exposure to ammonia to bring out its crystalline structure, 

 the markings on the plate may be taken to indicate the 

 boundaries between copper and mica or the constituents of 

 the latter. The regularity of the markings would indicate 

 that the copper and mica fused into an intimate and homo- 

 geneous mass. 



A specimen, whose resistance at 100° C. was found to be 

 95,000 ohms and only 3000 ohms at 400° C, was polished 

 and examined previous to etching it with ammonia, both 

 with high-power and low-power magnification, and with 

 oblique and direct illumination. 



PI. VII. fig. 3 shows its appearance when illuminated 

 obliquely under a magnification of 46. 



PI. VII. fio-s. 4 & 5 show the same region when illuminated 

 by normally reflected light under magnifications 46 and 205 

 respectively. The structure in this case, as will be seen, is 

 quite different from that shown in PL VII. fig. 1. 



With the sample illustrated by figs. 3, 4, and 5 there 

 appeared to be a great many streaks of light and dark, 

 bounded by straight lines running in all directions, while 

 in other specimens there appeared to be nothing uniform 

 in the shapes of the patches. The portions of the surface 

 which are dark in PL VII. fig. 3 it will be seen are light 

 in Pl.VII. fig. 4. In this specimen much detail was brought 

 out with the low-power objective. It was therefore used 

 among others with low magnification to study the effect of 

 any increase in temperatures. A water-cell provided with 



