Positive earth corrosion

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Sir,

As selling organisation for “Bodyguard” sacrificial anodes, we were interested in your correspondent’s remarks regarding positive-earth corrosion.

It is an established fact that the positive or anodic side of a D.C. circuit is sacrificial to the negative or cathodic side.

When subjected to electrolytic conditions, i.e. ranging from complete saturation to slightly damp air on a car body which is wired positive to earth, the areas which sacrifice themselves to the cathode in terms of rust are where water can collect and remain (thereby serving as the electrolite) until naturally drying out.

Inside the bottoms of doors are particularly prone to corrosion, the areas adjacent to negative connections, for instance the rear lamp back plates which seem to trap water are prone to corrosion.

It is of the greatest importance that the sacrificial anodes are of a high degree of purity; ordinary commercial quality is not of much use. As far as we know the reason for the change from negative earth to positive earth was to improve the efficiency of the car’s electrical system. Whether car manufacturers were aware that body corrosion would occur with positive to earth installations we do not know, but in our opinion it was a genuine effort on their part to improve the efficiency of the electrical system. Until it is possible to dispense with car batteries which provide for the lighting and starting equipment, we are of the opinion that the fitting of sacrificial anodes are the only satisfactory way of dealing with the problem.

Berkhamsted.
A. J. Reid.
Step Industrial Equipment Ltd.
[We have received a great many erudite letters on this subject which is now closed.—ED.]