Copper Drip Pipe after Seventeen Days’ Exposure in Salt Water to the Action of Electricity. Half size.
To produce electrolytic disintegration of pipes, etc., on a scale grand enough to cause apprehension, a bountiful source of electricity is essential. Unfortunately, this condition is not lacking to-day in any town in which the usual overhead trolley electric railway is in operation. This system of electric propulsion is based upon the use of a “ground return”—that is to say, the electricity passes out from the power house to the bare trolley wire, thence to the pole on the roof of the car, thence through the motors to the wheels, whence it is expected to return to the power house, via the rails.
As a matter of fact, however, the released electricity by no means confines itself to the rails and the copper return feeders—legitimate paths provided for it. It avails itself, on the other hand, of what may be termed, for brevity’s sake, the illegitimate return—comprising all underground electrical conductors except the rails and return feeders, and including subterranean water-courses, sewers, and metallic earth veins.
Wrought-Iron Service Pipe for Water after One Year’s Burial beneath a Trolley Track.
The fibrous appearance of the surface is characteristic of wrought iron and steel.
In the light of our experience of the last eight years, it is easy to identify as electrolysis the effects shown in the accompanying cuts of buried metals that have been actually subjected to a flow of electricity. It is not to be inferred that the destructive action here depicted is universal throughout our towns, but, rather, that the damage occurs in spots, its rate of progress being dependent upon the amount of current and the duration of the flow. Dry, sandy soils tend to keep down the flow of current by interposing a high resistance, so that in such localities electrolytic effects are not as pronounced as in wet, loamy soils. In the same way, the character of the pipe surface—or coating, if there be any—acts as a partial barrier to check the passage of electricity.
Until recently it was generally supposed that cast iron was not attacked—at least not rapidly enough to cause alarm. In Brooklyn the water mains, of very hard, dense, even-grained cast iron, containing alloyed rather than combined carbon, have not been appreciably corroded. At Dayton, Ohio, on the other hand, seventy-seven thousand dollars’ worth of damage has already resulted. One peculiarity of electrolyzed cast iron is that the original shape is usually retained, the iron being eaten away and leaving a punky formation of pure or nearly pure graphite. In such a case a superficial examination detects nothing wrong, and it requires a mechanical scraping to show that the strength is not there. For this reason good photographs of cast-iron electrolysis are somewhat hard to obtain.
