ELECTROLYTIC ACTION ON GIRDERS.
How They are Corroded by its Action.
(SPECIALLY WRITTEN FOR FIRE AND WATER ENGINEERING)
As this is a subject of wide importance, and one which, it is believed, will interest municipal authorities in many cities in this country, there is given below an instance of the corrosive effect of electrolysis on iron bridges. The accompanying cut shows this action as actually discovered.
The instance referred to is taken from a report upon “Electrolysis.” made by the writer for the city of Providence, R. I., during the past summer. The extract says:
“Upon removing some of the heavy planks which lay against the iron span, it was found there was a packing of black soil, composed principally of animal refuse, which had become lodged, through sweepings and wind, between the planks and iron of the span. This averaged about one quarter of an inch in thickness, and, of itself, would, no doubt, have caused corrosive action to some extent,” if there had not been a current passing through it. The action upon the iron, however, would be much more rapid, even if a very small current were leaving the iron and passing through this material, owing to the fact that its chemical composition made a much better electrolyte than is usually found in soils, and also from the additional fact that the material was continually being renewed.
“The trolley current was traced from the river to the iron piers of the bridge which support the shore spans. At the pier nearest the injured span a difference of potential of from 0.3 to 0.5 of a volt was found. Between the injured span and surrounding soil the reading was 0.04 to 0.05 of a volt showing that the current flow was from the span to soil, a condition favorable for electrolytic action. “The tracing of the current, therefore, being from the river to the piers which connect with the spans, and thence leaving the injured span for earth, the conclusion is reached that electrolytic action is clearly responsible for the greater part of the damage found at this span.
” rite photograph shows two small holes where it was eaten entirely through the metal. A third hole was discovered after the photograph was taken; other parts of the corroded surface were about the thickness of paper, the iron, when new, being threeeighths of an inch thick. This section of iron plate has since been removed and a new piece put in its place.”
There may be other bridges where the trolley current is getting in its work even more effectually than was here discovered, and this case may at least serve as a warning to those who have charge of such important properties.
The volunteer fire department of Wilktnsburg, Pa., having gone on strike, no one responded to an alarm of fire, the result being that the task of extinguishing a fire fell on a former chief of the department and some citizens. The volunteers assert that the councils have broken faith with them with respect to appointments in the paid fire department now being organised—politics, as usual, being at the bottom of the trouble. If, however, they had been in the neighborhood of the fire, they would have assisted as citizens in putting it out.