hton laboratory.

"Do you suppose vibration caused it?" I asked, remembering his watch
crystal test.

Craig shook his head. "The vibrations in a building can be shown by a
watch glass full of water. You saw the surface of the liquid with its
minute waves. There's vibration, all right, but that is not the cause of
such cracks as these."

He stood for a moment regarding the crack attentively. On the floor on
which we were was the Consolidated Bank itself. Beneath us were the
Consolidated Safety Deposit vaults.

"What did cause them, then?" I asked, mystified.

"Apparently escaping currents of electricity are causing electrolysis of
the Bank Building," he replied, his face wrinkled in thought.

"Electrolysis?" I repeated mechanically.

"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 sa