162 CARNEGIE INSTITUTION OF WASHINGTON. 



(12) An unusual sulfur crystal. F. Russell v. Bichowsky. J. Wash. Acad. Sci., 9, 126-131 



(1919). 



A description of an artificial crystal of sulphur showing unusual develop- 

 ment of the prism zone, two new faces f (211) and (3 (310) and the rare faces 

 X (210) ; 7} (130) ; K (120), as well as the more common faces c, b, a, e, m, v, s, y, 

 p, 7 , r, q. A list of the known faces of sulphur is given, and certain new zonal 

 relations pointed out. 



(13) The technique of optical glass melting. Clarence N. Fenner. J. Am. Ceram. See, 



2, 102-145 (1919). (Papers on Optical Glass, No. 7.) 



This article is based upon the experience acquired in the manufacture of 

 optical glass during the period of about 18 months in which the Labora- 

 tory was in cooperation with manufacturers of optical glass. The method 

 pursued in the article is to follow the course of melting operations from begin- 

 ning to end and describe the essential features of procedure. Details of 

 practice which are common to all forms of glass-making and are famihar to 

 glass-makers in general are either omitted or passed over with brief descrip- 

 tions, and attention is concentrated on those matters in which the making of 

 optical glass differs from that of other kinds. Because of the fact that the 

 purposes for which optical glass is to be used are in many respects radically 

 different from those of other glasses, and require that exact optical and other 

 physical properties be maintained and that certain defects be eliminated, it is 

 essential that manufacturing operations be controlled throughout by methods 

 of precision. The article describes the general course which must be fol- 

 lowed to accompHsh these results and the effects caused by departures from the 

 standard of procedure, and takes up in more detail the principal defects which 

 are likely to occur, and considers their causes and the methods of avoiding 

 them. Some of the subjects discussed are: the effects of different available 

 batch-materials upon melting operations and the range of choice in this 

 matter; the necessity of close temperature regulation and the results of inat- 

 tention to this; fining operations, especially with reference to the eUmination 

 of bubbles, and the causes and prevention of bubbles in general ; variations of 

 optical properties from requirements, and to what they are due; differences of 

 procedure required for the different types of glass; stirring operations, and 

 the manner in which they should be conducted to obtain glasses relatively 

 free from strise. 



(14) An improved method of optical glass manufacture. George W. Morey. J. Am. 



Ceram. Soc, 2, 146-150 (1919). (Papers on Optical Glass, No. 8.) 



Stirring is begun during the fill and is continued during the fining period. 

 Details are given of changes in procedure following this departure from 

 the usual schedule. The results show that with proper furnace control the 

 customary time of manufacture of a pot of glass can be reduced to 24 hours, 

 with improvement in color due to diminished pot corrosion, 



(15) Devitrification of glass. N. L. Bowen. J. Am. Ceram. Soc, 2, 261-278 (1919). 



(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 temperature where its 

 crystaHizing power is great. The various forms of devitrification in glass are 

 discussed from this point of view and suggestions are made as to the principle 

 that must be borne in mind in deciding upon modifications of procedure or 

 changes in composition that have as their object the avoidance of devitri- 



