VOLTMETER 

 (SEE TEXT) 



TO PROTECTED 

 SUBSTRUCTURE 



CONTAINER OF INSULATING- 

 MATERIAL 



POROUS PLUG 



Wmm 





PURE COPPER ROD 

 INSULATING SEAL 



SATURATED SOLUTION 

 OF COPPER SULFATE 



SURPLUS CRYSTALS 

 OF COPPER SULFATE 



SOIL SURFACE 



CROSS SECTION 



SUBSURFACE 

 STRUCTURE 



VOLTMETER INDICATES FULLCELL 

 POTENTIAL BETWEEN ELECTRODE 

 AND STRUCTURE 



COPPER ROD- 

 IN ELECTRODE 



EARTH PATH 



HALF-CELL POTENTIAL HALF-CELL POTENTIAL ' 



BETWEEN STRUCTURE BETWEEN COPPER ROD 



AND EARTH (VARIABLE) AND EARTH (CONSTANT) 



EQUIVALENT CIRCUIT 



Figure 97. Copper sulfate electrode test circuit. 



354 



