"Yes. I suppose you know how stray or vagrant currents affect steel and concrete?"
I shook my head in the negative.
"Well," he explained as we stood there, "I believe that in one government test at least it was shown that when an electric current of high voltage passes from steel to concrete, the latter is cracked and broken. Often a mechanical pressure as great as four or five thousand pounds a square inch is exerted and there is rapid destruction due to the heating effect of the current."
I expressed my surprise at what he had discovered. "The danger is easily overestimated," he hastened to add. "But in this case I think it is real, though probably it is a special and extreme condition. Still it is special and extreme conditions which we are in the habit of encountering in our cases, Walter. That is what we must be looking out for. In this instance the destruction due to electrolysis is most likely caused by the oxidation of the iron anode. The oxides which are formed are twice as great in volume as the iron was originally and the resulting pressure is what causes the concrete to break. I think we shall find that this condition will bear strict watching."
For a moment Kennedy stopped at the little office of the superintendent of the building, in the rear.
"I was just wondering whether you had noticed those cracks in the walls down the corridor," remarked Kennedy after a brief introduction.
The superintendent looked at him suspiciously. Evidently he feared we had some ulterior motive, perhaps represented some rival building and might try to scare away his tenants.
"Oh, that's nothing," he said confidently. "Just the building settling a bit—easily fixed."
"The safety vault company haven't complained?" persisted Kennedy, determined to get something out of the agent.
"No indeed," he returned confidently. "I guess they've got troubles of their own—real ones."