Deactivation . The process of prior removal of the active corrosion 

 constituents, usually oxygen, from a corrosive liquid by controlled 

 corrosion of expendable metal or by other chemical means. 



Decomposition potential (or voltage) . The practical minimum potential 

 difference necessary to decompose the electrolyte of a cell at a 

 continuous rate. 



Depolarization . The reduction of counter e.m.f. by removing or 

 diminishing the causes of polarization. 



Deposit attack . Corrosion occurring under or around a discontinuous 

 deposit on a metallic surface. 



Dezincif ication . Corrosion of a zinc alloy, usually brass, involving 

 loss of zinc and a residue or deposit that remains in situ of one or 

 more less-active constituents, usually copper. 



Differential aeration cell . (See aeration cell. ) 



Drainage . Conduction of current (positive electricity) from an under- 

 ground metallic structure by means of a metallic conductor. 



a. Forced drainage . Drainage applied to underground metallic 

 structures by means of an applied e.m.f. or sacrificial 

 anode . 



b. Natural drainage . Drainage from an iinderground metallic 

 structure to a more negative structure, such as the 

 negative bus of a trolley substation. 



Driving force (driving potential ). The electromotive force generated in 

 a galvanic cell or the electromotive force applied to an electrolytic 

 cell. 



Electroendosmosis . (See electroosmosis . ) 



Electrolysis . The production of chemical changes in an electrolyte 

 resulting from the passage of electricity. 



Electrolyte . A chemical substance or mixture, usually liquid, containing 

 ions that migrate in an electric field. 



Electromotive force series (e.m.f. series) . A list of elements arranged 

 according to their standard electrode potentials, the sign being positive 

 for elements having potentials that are cathodic to hydrogen and negative 

 for those elements having potentials that are anodic to hydrogen. (This 

 convention of sign, historically and currently used in European litera- 

 ture, has been adopted by the Electrochemical Society and by the National 

 Bureau of Standards, and it is employed in this publication. The 

 opposite convention of G. N. Lewis has been adopted by the American 

 Chemical Society.) 



B-1+ 



