CHEMISTRY IN THE TELEPHONE INDUSTRY 



613 



bon — namely, graphite and diamond. The so-called amorphous car- 

 bons, according to this view, are complex hydrocarbons in which the 

 carbon greatly predominates over the hydrogen and in which, especially 

 if the carbon has been roasted at a high temperature, the carbon atoms 

 are in part arranged in a graphite lattice. 



Vacuum-Tube Filaments 



The filaments of vacuum tubes represent a very special form of con- 

 ductor, the primary function of which is, of course, the emission of 

 electrons. Vacuum tubes are used in repeater sets in all long-distance 

 telephone lines. The filaments in these vacuum tubes consist of plati- 

 num alloys coated with the oxides of barium and strontium. It is im- 

 portant that these filaments should be constant in their electrical char- 

 acteristics and have as long a life as possible. The manufacture of 

 platinum alloys and the methods of coating them have been subjects of 

 study by our metallurgists and chemists for several years, and as a 



Fig. 3 — A corner of the electroplating laboratory. 



result many improvements in the manufacture of the filaments have 

 been made. Probably the most outstanding improvement has con- 

 sisted in the substitution of platinum-nickel and platinum-cobalt 

 alloys for the platinum-iridium-rhodium alloy formerly used as a fila- 

 ment core. This substitution resulted in increasing the life of repeater 

 tubes from a few months to several years. 



