MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 463 



is shown in Fig. 21. Numerous other loaded cables have been laid 

 since 1924; the total mileage of loaded submarine telegraph cables is 

 now upwards of 16,000 nautical miles. 



Another purpose for which permalloy is now used extensively is 

 for loading coils for telephone transmission circuits. Before the 

 introduction of permalloy, finely powdered, insulated and compressed 

 iron dust was used for the cores of these coils. Permalloy has now 

 replaced iron for loading coil cores, and upwards of a million cores 

 per year are used by the Bell System.^ For these cores the permalloy 

 is used in the form of compressed insulated powder. Some of the 

 advantages in using permalloy result from its lower hysteresis losses 

 and higher permeability. Taking advantage of these qualities in the 

 design of the coils, it has been possible to reduce materially their 



Fig. 22 — Compressed powdered core loading coils: left, electrolytic iron core; 

 right, permalloy core. 



sizes. This is illustrated in Fig. 22 where two standard loading coils 

 for use in the same circuits are shown. One of these has a permalloy 

 core and the other a core of iron. The former is approximately one- 

 third of the size of the latter. 



When these coils are used in service usually a large number are 

 placed in containers which are placed at difTerent points in vaults or 

 on poles along the telephone circuits. In Fig. 23 two such iron cases 

 with their cable connecting stubs are shown; each contains 200 coils. 

 The small case contains the permalloy coils, and the large case the 

 iron core coils. The use of permalloy has reduced the combined 

 weight of the coils and the cases from approximately 1,700 lbs. to 

 about 700 lbs.« 



' The use of permalloy core loading coils is increasing very rapidly. Recent 

 figures show that approximately 2,000,000 of these coils will be required by the Bell 

 System per year during the next few years. 



* The decreased size of the coils and containers has resulted in a very substantial 

 saving in the cost of loading. 



