Notes on the Devitrification of Old Glass. — By H. Ritchie 

 Chipman, M. a,, Ph. D., F. C. I. C, and Douglas Mc- 

 Intosh, M. a., D. Sc.,Dalhousie,University, Halifax, N. S. 



(Read 14 December, 1925) 



It has been generally supposed that the devitrification of 

 glass is a phenomenon similar to that studied by Tammann 

 (Zeitm. Electrochem. 10- 532, 1904), Guertler, (Zeit. Anorg. 

 Chem. 40268, 1904) and others, which depends on the form 

 ation of crystal nuclei from which crystallization proceeds. 



The devitrification of glass as a surface phenomenon has 

 been explained by Albert Germann (J. A. C. S. 43:11, 1921) as 

 follows. There is always a film of moisture on glass in equili- 

 brium with the atmosphere. The silicates of the glass are in 

 equilibrium with this film and must be more or less hydrolyzed 

 depending on the condition of the glass, so that we may assume 

 the presence of silicic acid, calcium hydroxide, and sodium hy- 

 droxide. The bases, however, absorb carbon dioxide and are 

 converted to the acid carbonates. When the glass is 

 heated the absorbed moisture is driven off, the silicic acid be- 

 comes dehydrated and roughens the surface. The separated 

 silica forms an infusible coating over the surface of the glass 

 which may under certain conditions dissolve in the underlying 

 silica and the surface clear up, or under other conditions yield 

 difficultly fusible calcium silicate in which case well defined 

 crystal surfaces appear. 



Germann took some old glass which showed a tendency 

 to devitrify when heated and removed the surface layer by 

 washing with hydrofluoric acid. If the devitrification was en- 

 tirely due to the conditions of the surface its removal should 

 destroy the tendency towards devitrification. Germann found 

 this to be the case and suggests that old glass may be easily 

 worked in the blast lamp flame if it is previously washed with 

 hydrofluoric acid. 



All of this work had been done with old glass which had 

 been worked in the blast lamp flame and no mention has been 

 made of glass devitrifying at lower temperatures. One of the 



