422 Ferguson and Mertvin — Melting Points of 



Temperature Sample Quenched 

 (corrected). after: Eesults. 



1653° 30 min. A little more glass, some having 



higher refraction and some lower 

 than cristobalite. 

 1691° 30 min. 2-3% glass all having lower re- 



fraction than cristobalite. 



3. Single clear crystal of quartz. 

 Temperature Sample Quenched 



(corrected). after: Results. 



1691° 60 min. Quartz with layer of glass, and 



then outside a homogeneous 

 layer of cristobalite. 



4. Clear quartz crystals that had been heated all night at 

 1550°. Material was entirely crystallized to cristobalite. 

 Temperature Sample Quenched 



(corrected). after: Results. 



1698° 30 min. No glass, the crystals perhaps a 



little larger. 

 1737° 30 min. All glass. 



1718° 30 min. Trace of crystals, and rest glass. 



1708° 32 min. Main part of charge all crystals, 



but a few grains were mostly 



glass. 



5. Silica glass made by heating some of the cristobalite 

 obtained from clear quartz as in (3) to 1737°. 

 Temperature Sample Quenched 



(corrected). 



after : 



Results. 



1646° 



45 min. 



Not all crystallized, but where 

 crystallized at all the whole mass 

 is cristobalite. 



1679° 



30 min. 



All crystals, not a trace of glass. 



6. Baker and Adamson specially purified quartz finely ground ; 

 contains many minute inclusions which are not determinable but 

 are mostly of much lower refractive index ; after heating for two 

 hours at 1550° has all changed to cristobalite with the exception 

 of some minute specks too small to identify. 

 Temperature Sample Quenched 



(corrected). 



after : 



Results. 



1646° 



45 min. 



Unchanged. 



1679° 



30 min. 



Trace of material with refrac- 

 tion higher than cristobalite ; 

 probably glass. 



1693° 



38 min. 



Charge seems similar to that 

 at 1679°. 



