FILE No.20Unsolved
During a check of a museum’s security system, a crimson jewel was stolen from a display case.
The jewel was cut round, and an iron ring held it by gripping its rim. No glue or clasp was used, yet at room temperature it could not be pulled out by hand. The jewel is a material that magnets do not attract.
The display case could be opened with a key by anyone on the inspection staff.
After the theft, only the iron ring was left in the case. The ring had no cuts or pry marks, and part of its outer side had a sooty black deposit.
Which of the following is the most likely way the jewel was removed without damaging the jewel or the ring?
If you get stuck, open the hints one at a time, in order.
What does the sooty black deposit on the ring suggest was there?
What happens to the size of a metal when it is heated?
If you cool it, does the ring loosen?
Which of the following is the most likely way the jewel was removed without damaging the jewel or the ring?
Choose the answer closest to the truth.
The iron ring was heated to widen its inner diameter
The answer is “The iron ring was heated to widen its inner diameter.”
When an iron ring is heated, the metal expands and the diameter of the hole grows too. The thief used this property: once the ring’s grip loosened, the jewel could be drawn out. The sooty deposit is also a clue that a flame may have been used.
No glue was used, and the jewel is not attracted to magnets. And if only the ring were cooled, its hole would shrink and the grip would get tighter.
* In this puzzle, assume the fit is only very slightly tight, so the ring could be taken off by heating the ring before the whole jewel warmed up.
You assume a ring like that can never move.
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