92 BELL SYSTEM TECHNICAL JOURNAL 



these values. It was found that by drying the wire at very high speeds by 

 passing it rapidly through high temperatures, the natural shrinkage of the 

 pulp could be greatly reduced and that increased porosity could be obtained. 

 Results on capacitance from such wire were markedly better, and so high- 

 temperature radiant-heat drying was introduced into the process. In this 

 method a box type electric furnace with a heating chamber approximately 

 26 feet long, 3 feet wide and 8 inches high is used. The wire passes through 



Fig. 7 — Individual polisher 



this furnace horizontally. In the first third of the furnace 1500°F. is main- 

 tained, 1200°F. in the second third, and 800°F. in the last third. The water 

 is literally exploded out of the pulp in this process and leaves a soft porous 

 insulation which is easily stripped from the wire. Electrostatic capacitance 

 values of about .072 mf. per mi. on 24-gauge cables are obtained with this 

 method of drying and improved centering of the wire and roundness of 

 insulation. These values are practically the same as those obtained with 

 wrapped paper. At wire insulating speeds of 140 feet per minute the insu- 



