146 NOTES ON THE DEVITRIFICATION OF OLD GLASS 



A bulb was carefully broken into small pieces which 

 were placed in a pyrex bulb and fastened to the pump. The 

 system was exhausted and the bulb heated to 450°C, the pres- 

 sure rising considerably. The gases were pumped off and were 

 found to be about 50% carbon dioxide. On examination of the 

 pieces after heating it was found that they were frosted on their 

 outside surfaces only. 



Some substances when heated will allow the passage of 

 certain gases. It was observed that the devitrified bulbs did 

 not permit the diffusion of any of the gases of the atmosphere 

 when heated to 450°C. The fact that no diflFusion took place 

 when the glass was devitrified may be offered as additional 

 evidence that the devitrification had only taken place on the 

 surface, as it would have been expected to occur had the glass 

 been crystalline throughout. 



Germann states that the absorption of water from the at- 

 mosphere causes a tendency towards devitrification and that 

 certain gases in the air of the laboratory may act catalytically. 

 Apparently something like this has occurred in the case of the 

 bulbs which has caused them to be so "weathered" that they will 

 devitrify at 100°C. The results of these experiments are 

 evidence that the devitrification of these bulbs is a surface 

 phenomenon. 



