Kennedy examined the edges of the hole carefully, and just the trace of a smile of satisfaction flitted over his face as he did so.  Without saying a word he took the glass stopper out of the larger bottle which he had brought and poured the contents on the top of the safe near the hole.  There it lay, a little mound of reddish powder.

Kennedy took a little powder of another kind from the other bottle and lighted it with a match.

“Stand back—­close to the wall,” he called as he dropped the burning mass on the red powder.  In two or three leaps he joined us at the far end of the room.

Almost instantly a dazzling, intense flame broke out, and sizzled and crackled.  With bated breath we watched.  It was almost incredible, but that glowing mass of powder seemed literally to be sinking, sinking right down into the cold steel.  In tense silence we waited.  On the ceiling we could still see the reflection of the molten mass in the cup which it had burned for itself in the top of the safe.

At last it fell through into the safe—­fell as the burning roof of a frame building would fall into the building.  No one spoke a word, but as we cautiously peered over the top of the safe we instinctively turned to Kennedy for an explanation.  The Central Office man, with eyes as big as half-dollars, acted almost as if he would have liked to clap the irons on Kennedy.  For there in the top of the safe was another hole, smaller but identical in nature with the first one.

“Thermit,” was all Kennedy said.

“Thermit?” echoed Andrews, shifting the cigar which he had allowed to go out in the excitement.

“Yes, an invention of a chemist named Goldschmidt, of Essen, Germany.  It is a compound of iron oxide, such as comes off a blacksmith’s anvil or the rolls of a rolling-mill, and powdered metallic aluminum.  You could thrust a red-hot bar into it without setting it off, but when you light a little magnesium powder and drop it on thermit, a combustion is started that quickly reaches fifty-four hundred degrees Fahrenheit.  It has the peculiar property of concentrating its heat to the immediate spot on which it is placed.  It is one of the most powerful oxidising agents known, and it doesn’t even melt the rest of the steel surface.  You see how it ate its way through the steel.  Either black or red thermit will do the trick equally well.”

No one said anything.  There was nothing to say.

“Someone uncommonly clever, or instructed by someone uncommonly clever, must have done that job,” added Craig.  “Well, there is nothing more to be done here,” he added, after a cursory look about the office.  “Mr. Andrews, may I have a word with you?  Come on, Jameson.  Good day, Mr. Kahan.  Good day, Officer.”

Outside we stopped for a moment at the door of Andrews’s car.

“I shall want to see Mr. Morowitch’s papers at home,” said Craig, “and also to call on Doctor Thornton.  Do you think I shall have any difficulty?”