144 



THE ROYAL SOCIETY OF CANADA 



resumed its original value as far as 1,400°C. When maintained at a 

 steady temperature in this region, the rod showed a continuous in- 

 crease in length, accompanied by a marked superficial devitrification," 

 etc. 



600- 



500- 



4-00- 



-300- 



200 



100- 



^3>k 



200° ^-*-"0° 200° 400° 



Temperature, (tj 



600° 



1200 C. 



Fig. 2. 



A second change point occurs near — 80°C. at which point 

 Scheel has noted a maximum density as well as a minimum length. 

 Dorsey 1 noticed a peculiar phenomenon within a range of about 60° on 

 either side of — 80°C. Above this point of minimum length, the 

 silica, when warmed, first contracts slightly , and then expands. For 

 temperatures below — 80°C. the converse is true. 



There is some evidence of a third change-point in fused silica 

 near 500°C. The expansion curve indicates a maximum value of 

 1 Loc cit. 



