METALLIC MATERIALS IN THE TELEPHONE SYSTEM 143 



and for the preparation of new cable sheath alloys. With this equip- 

 ment commercial extrusion conditions can be investigated or, when 

 desired, extrusion conditions can be varied to determine the effect on 

 the properties of the alloy. 



The general layout of the metallurgical microscopic laboratory is 

 shown in Fig. 4. In the foreground is a metallurgical microscope and 

 camera equipped with facilities for examination with polarized light 

 and dark field illumination. The preparation of specimens and photo- 

 graphic processing are done in conveniently arranged adjoining rooms. 

 The microscopic equipment is complemented with X-ray diffraction 

 apparatus shown in Fig. 5. This equipment consists of a demountable 

 X-ray tube so arranged that targets can be readily interchanged. 

 Cameras are provided for structure identification, precision determina- 

 tion of lattice constants, and texture and orientation studies. 



Microscopic and X-ray diffraction equipment are both extremely 

 valuable in a great diversity of metal problems. Some examples are 

 given here of the utilization of microscopic equipment in cable sheath 

 development studies. The possibilities of prolonging the life of cable 

 sheath which has developed a weakened structure in service have been 

 established through microscopic examination after a heat treatment 

 consistent with the alloy structure. Again, the results of thermal 

 treatment incident to the soldering and repair operations on cable in 

 the field can be observed and used as a guide to the value of certain 

 procedures. An interesting example is concerned with the opening 

 of splices in installed cable sheathed with lead-antimony alloy, a pro- 

 cedure frequently necessary. During aging in service the antimony- 

 rich particles coalesce into relatively large lumps. When material in 

 this condition is heated by pouring hot solder over the joint, pools of 

 liquid are formed around each lump of antimony, and if an attempt is 

 made to pry the sleeve of the splice open at once, the sleeve crumbles. 

 If heating is prolonged a few minutes, however, the tiny antimony- 

 rich liquid pools diffuse into the surrounding solid material; at this 

 time the sleeve can be opened without injury. 



A few years ago, a new lead alloy containing from three to four 

 hundredths per cent of calcium was produced and is being extensively 

 studied now for cable sheathing and other applications. Laboratory 

 tests indicate that under some conditions this material excels lead- 

 antimony in resistance to fatigue failure. To illustrate the careful 

 consideration given materials before making changes which might 

 vitally affect telephone service, about one hundred miles of cables 

 sheathed with a lead-calcium alloy have been installed for a commercial 

 field test. In addition, thirty-six thousand feet of experimental 



