60 BELL SYSTEM TECHNICAL JOURNAL 



and, as in the case of the change of capacity with frequency, is more 

 pronounced in condensers with low- voltage films. In Fig. 14 the 

 effect of temperature on the electrical characteristics, at 1,000 cycles 

 for 24-volt and 48-volt condensers, is shown. Here the change in 

 resistance is due to the negative temperature coefficient of the electro- 

 lyte which, with increasing temperature, causes a reduction in that 

 component of the total condenser resistance representing the resistance 

 of the electrolyte. 



In the normal adaptations of these condensers in low-pass electric 

 wave-filters, the inherent changes in capacity and resistance with 

 frequency and temperature cause no serious engineering difficulties. 

 The limitations imposed by these variations are more than offset by 

 the advantages of the corrugated structure in the matter of com- 

 pactness and simplicity of design. 



Corrosion of the Condenser Anodes 



Notwithstanding the care taken in the manufacture and installation 

 of condensers, there remains some possibility that the positive electrode 

 will be attacked by corrosion. This corrosion may make its appear- 

 ance as a gray growth or pitting on the surface of the anodes, or on 

 the anode supports where they extend through the electrolyte. It is 

 usually accompanied by the deposit of a granular or finely divided 

 gray substance, probably aluminum oxide, which collects in the bottom 

 of the condenser jar. Corrosion may occur shortly after a condenser 

 is put in service or months can elapse before it appears. 



In cases where corrosion has occurred, provided proper materials 

 were used in the manufacture of the condenser, it has been noticed 

 that the electrical properties of the cells were not seriously impaired. 

 Such units have often continued to perform satisfactorily from a 

 circuit standpoint for a number of years after the electrodes were 

 attacked, even though the mechanical structure of the electrodes was 

 damaged and weakened. 



The long life that can be obtained from a corroded condenser 

 under these circumstances is due in part to the tendency for areas 

 affected to heal and restore the condenser to normal conditions. 

 This indicates that the influence responsible for corrosion dissipates 

 itself or it may be carried away from the corroded area by some of 

 the products of the action to lie inert in the bottom of the cell. A 

 number of spots on aluminum anodes have been observed, where 

 the attack on the metal has ceased and a film has formed over the 

 affected surface. 



The leakage current of a condenser increases substantially when 



