Thermal Hysteresis of Fused Silica. 723 



Randall's value at 1100° confirms Calendar's statement as 

 to the rapid increase in the expansion of silica at tempera- 

 tures above 1000°. The dotted portion of the curve beyond 

 1100° is qualitative only and is an expression o£ Callendar's 

 observations. 



Fiff. 1. 



700XICT 6 - 



•600- 



•500- 



B5 

 20 







_^_ 

















"4? 

 -4> 5 







> 



/ 









A 



s 





















-10° /t. 



y 



' -5 



1 



i 

 rEMPC 



0" 3 



0° 4- 



r s 



O'C. 



THERMAL EXPANSION OF FUSED SILICA 



R/lNDftLL,/9lO. 





• SCHEEL, /907 





<•> DORSEY, 1907 





4- Chappu/s, 1 90S 





B HOLBORN 



Henning. 1 90S 





® C/IUEND/W. /SO/ ' 





o" ^oo 



temperature it) 



800° 



1200V, 



The slope of the tangent to the curve at any point gives, 

 of course, a measure of the coefficient of expansion 



f _l dl\ 

 V-l'dt) 



at that temperature, and the curve shows that a is negative 

 below —80°, zero at —80°, slowly increases to a maximum 

 at about 500°, diminishes somewhat up to about 900°, and 

 afterwards rapidly increases. 



3B2 



