8 BELL SYSTEM TECHNICAL JOURNAL 



that occur along the faces, while the glass wrapping round the edges 

 of the ribbon is called upon to withstand much greater tensile stresses 

 and gives way. If the edges of the ribbon are sharpened as shown in 

 Fig. 2 (b), a tight seal results, the reason being that the forces of 



a 



Fig. 2 



adhesion between the glass and copper acting along the flat contact 

 faces are sufficient to stretch the thin copper at the edge and prevent 

 its drawing away when cooled. There is a definite relation between 

 the elastic properties of the metal and glass and the angle of edge 

 that can be used for a successful seal. 



By proper shaping of the metal ribbon, seals have been successfully 

 made up to very large sizes. Some of these are shown in Fig. 3, the 

 the largest in the photograph being about 1 in width, and capable 

 of successfully conducting a current of 150 to 200 amperes. 



The principles involved in the making of the disc seal are the same 

 as those involved in making the ribbon seal. If a metal disc is sealed 

 wholly into glass the edges must be sharpened or the glass and copper 

 break away from each other as in the case of the ribbon seal. 



In the general use to which these seals are put there is no necessity 

 for having the glass surround the circumference of the copper disc 



