ClIAP. 10] 



ELECTRICAL METHODS 



679 



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Kundehmgu conglomerate. It was possible to determine the boundary 

 of the area occupied by the conglomerate and to locate the uplifted por- 

 tions of the beds in the mine series. The extreme right of Fig. 10-29 

 shows plainly the rela- 

 tion between the loca- 

 tion of a mine and the 

 maxima in the self- 

 potential anomaly. 



The problem of pipe 

 line corrosion is one of 

 great commercial impor- 

 tance. Extensive studies 

 have been made in recent 

 years to determine its 

 cause and to devise reme- 

 dies. Various electrical 

 prospecting methods and 

 modifications thereof 

 have been instrumental 

 in making possible a 

 better understanding of 

 the phenomena involved. 



When a metal is im- 

 mersed in a conductive 

 liquid it emits positive 

 ions and takes on a nega- 

 tive charge. Under nor- 

 mal conditions an equili- 

 brium is established, 

 since the positive ions 

 are held near the metal 

 by the negative charge. 

 Two agents will disturb 

 this equilibrium : 



1. Acid solutions (rich 

 in oxygen, sulfate, and 

 chloride ions). These 

 have a tendency to elimi- 

 nate the metallic ions as soon as they appear, and the metal will there- 

 fore be strongly attacked. Destruction will occur at the points of lowest 

 potential, that is, in the anodic zones or zones of positive potential. 



2. Stray currents. Metallic conductors attract currents in certain zones 



dronite 



\ / 



dneiss 



Fig. 10-28. Potential gradients, potential profile, 

 and geologic section uncovered on the basis of the 

 survey (after Hunkel). 



