258 BELL SYSTEM TECHNICAL JOURNAL 



change. The resultant compositions are illustrated by the following 



batch which was developed and used for clear amber glass; and the 



functions of the various raw materials in this composition are given 



below : 



Glass Sand 45 



Red Lead 30 



Sodium Nitrate 10 



Sodium Carbonate 10 



Manganese Dioxide 3 



Ferric Oxide 2 



100 

 Scrap Glass — 50 parts approximately. 



As is common practice, glass sand was used as the most economical 

 means of obtaining the desired silica content. The sodium content was 

 introduced by the use of sodium nitrate and sodium carbonate. The 

 oxidizing action of the nitrate and manganese dioxide assisted in (1) 

 the prevention of lead reduction; (2) the oxidation of any organic 

 materials present; and (3) the maintenance of the iron in ferric form. 

 The liberation of gas during the decomposition of the sodium nitrate 

 and carbonate tended to stir the glass during melting and in addition 

 the escape of large gas bubbles during this decomposition assisted in 

 the removal of small bubbles of occluded gas. Some of the sodium 

 was introduced as sodium carbonate because it was cheaper than the 

 nitrate. Red lead was used as an economical means of obtaining 

 the desired lead oxide content and to lessen the possibility of any 

 difficulties from unoxidized lead particles. A percentage of glass 

 scrap from the punching and drawing operations was used in each 

 batch as a means of reclaiming the scrap, facilitating melting and 

 improving the working characteristics of the glass when drawn into 

 rods. The amber color obtained in this glass was of course dependent 

 on the predominance of the brown color of ferric iron. If sufficiently 

 oxidizing conditions were not maintained during melting and working, 

 the iron would be reduced to the ferrous state resulting in a greenish 

 color. The color intensity obtained was very sensitive to changes in 

 the amount of heating and to atmospheric conditions in the furnace. 

 This complicated the problem of maintaining the glass within close 

 limits for color and translucency. 



After satisfactory glasses with twice the impact strength of the 

 previously imported glasses were developed, open pot manufacture 

 of clear glasses was started on a limited basis.^ It was then found 

 desirable in order to obtain better signaling characteristics to obtain 



i-H. T. Bellamy Patent 1,271,652, "Method of Making Colored Glass," July 9, 

 1918. • 



