640 abstracts: ceramic chemistry 



("degeneration") as to lead to extinction. If we possessed a knowledge 

 of the whole evolution of the Aculeate group, we should probably find 

 that the total number of parasitic species which it produced during the 

 ages was very great, but that the vast majority of them, after reach- 

 ing the Anergates or a similarly specialized, or degenerate stage, lingered 

 on precariously for a time and then disappeared." 



The paper is completed with a list of the literature examined. 



S. A. ROHWER. 



CERAMIC CHEMISTRY.— Devitrification of glass. N. L. Bowen. 



Journ. Amer. Ceram. Soc. 2: 261-278. April, 1919. (Geophysical 



Lab. Papers on Optical Glass, No. 9.) 

 Devitrification of glass is the result of the tendency of the glass to 

 reach the stable crystalline condition and takes place whenever the glass 

 is held for a sufficiently long period of time within the range of tem- 

 perature where its crystallizing power is great. The various forms of 

 devitrification in glass are discussed from this point of view and sug- 

 gestions are made as to the principles that must be borne in mind in 

 deciding upon modifications of procedure or changes in composition 

 that have as their object the avoidance of devitrification. Specific 

 examples of the devitrification of optical glasses are given, together with 

 identification of the crystalline phases separating. N. L. B. 



CERAMIC CHEMISTRY.— r/z^ volatilization of iron from optical 

 glass pots by chlorine at high temperatures. J. C. HosTETTER, 

 H. S. Roberts and J. B. Ferguson. Journ. Amer. Ceram. 

 Soc. 2: 356-372. May, 1919. (Geophysical Lab. Papers on 

 Optical Glass, No. 12.) 



Of all the ordinary impurities found in optical glass, iron exerts the 

 greatest influence on transmission. The iron-content of the glass arises 

 from pots used as containers during melting as well as from the raw 

 materials. Tlie content of iron in the glass and, therefore, its trans- 

 mission, would be considerably improved if the iron could be removed 

 from the pot- walls before use. Chlorine appeared to be a suitable 

 agent for this purpose, and experiments demonstrated the fact that 

 approximately 80 per cent of the iron could be extracted from the in- 

 terior of the clay pots and volatilized by the action of chlorine at tem- 

 peratures easily secured in a pot-arch or glass-melting furnace. I^arge- 

 scale experiments were carried out and conditions developed for remov- 

 ing more iron from the bottom of the pot, where the most corrosion 



