620 BELL SYSTEM TECHNICAL JOURNAL 



which was necessary to secure a fair penetration of the wood with creo- 

 sote. In so far as the creosote penetrated, the acid produced in heating 

 was neutralized to a great extent by the nitrogenous bases in the creo- 

 sote. Often, however, the total acid produced far exceeded the neutra- 

 lizing power of the creosote bases contained in the external shell of 

 creosoted wood. The sheath of many miles of cables underwent a par- 

 tial conversion into white lead via the classical Dutch process which, 

 though highly regarded by paint manufacturers, became anathema 

 to telephone engineers. The difficulty was met by fumigating the ducts 

 in service with a dilute ammonia-air mixture and by choosing a less acid 

 and more easily treatable wood for future construction. 



Underground corrosion of other metals, notably of iron and steel, is 

 also often serious. In the alkali soils of the southwest anchor rods for 

 telephone poles have sometimes corroded through in a few months. 

 Marshes represent another severe exposure for iron and steel, as, for 

 example, in the form of loading coil cases. A newly introduced form of 

 telephone cable for direct burial in the soil demands careful considera- 

 tion from this standpoint. A variety of protective finishes, chiefly of 

 asphaltic or pitchy nature, have been studied in this connection. Some 

 remarkable cases have been noted, in which a finish that proved to have 

 a superior protective effect in one highly corrosive soil was worse than 

 useless in another soil which had been regarded as less corrosive in the 

 general sense. 



The chemistry and physics of soils from many areas have required 

 attention with ^the control of corrosion as an object. Particle size, 

 saline content, and composition of subsoil atmospheres each has an 

 influence. 



In a like way the telephone chemist must concern himself with atmo- 

 spheric causes of corrosion in equipment above ground, especially in 

 central offices. Moisture and dust contribute to electrical leakage 

 from point to point through the complicated assemblies of electrical 

 equipment. Corrosion products of such leakage may build up at criti- 

 cal points and interfere with contacts, or essential though usually minute 

 portions of equipment may be etched away. Even faint tarnishes on 

 metallic contacts can so increase contact resistance as to imperil signal- 

 ing. In industrial areas soot and traces of sulfurous gases add materi- 

 ally to these hazards. 



Finishes 



It is partly to avoid such difficulties and partly for the equally utili- 

 tarian purpose of a good appearance that metal telephone apparatus 

 receives some special form of finish coating, whether paint, varnish, 

 lacquer, or electroplated surfacing. In the selection of such finishes 



