Did Cleo Melt Her Pearl?
There have been rumours flying about t'interweb that pearls melt in vinegar. Not having any pearls of our own, what we wanted to know was: can this be true? So we got chemistry boff, Simon Davies, on the case.
The first century historian, Pliny, tells a story about a wager between lovers Cleopatra and Mark Antony. The Egyptian queen bet Antony a large sum of money that she could host the most expensive banquet in history. Antony, a veteran of some pretty impressive parties, accepted.
When he arrived Antony found Cleopatra before a table, upon which was a single goblet. Thinking he had won the wager easily, he was surprised when she suddenly took off one of her pearl earrings and dropped it into the goblet. The pearl melted into the wine vinegar in the goblet and she proceeded to drink the contents. Cleopatra's pearls were the largest in the whole world and each one was reported to be worth the value of 15 kingdoms. Antony conceded defeat and paid up.
Could this have really happened? Do pearls really melt in vinegar? Could anyone drink a glass of vinegar without throwing up? The first thing we need to know is the composition of pearls. Pearls are formed in oyster shells when a foreign body like a grain of sand becomes stuck inside. As a kind of protection mechanism, layers of a substance called “nacre” build up around it and over several years this becomes a pearl. Nacre is made of the same chemical compound found in oyster shells, marble, limestone and antacid tablets: calcium carbonate.
Next we must think about vinegar. Wine vinegar is acidic. It is approximately a 5% solution of ethanoic (old name “acetic”) acid. Basic chemistry tells us that when a carbonate is placed into an acid a reaction occurs, which can be written in words like this.
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So if a pearl was put in a goblet of vinegar, it would fizz, giving off carbon dioxide, and leave behind a slightly bubbly solution of calcium ethanoate. This is not as foul tasting as vinegar and in fact was believed to be an aphrodisiac in the first century. Maybe that was why Mark Antony left his wife for Cleopatra.
We should say that it would be inaccurate to claim that pearls melt in vinegar. A better word to use would be 'dissolve'. This phenomenon, however, is probably not the most ideal way to test whether a pearl is real or not. Yes a pearl would only dissolve if it were real, but of course then you no longer have a real pearl, you simply have a solution of an alleged aphrodisiac. A better way to test the veracity of your pearls is to put a very small drop of vinegar on the pearl. If it fizzes, wipe it off immediately - you have a real pearl in your possession!Other pearls of wisdom from the Null:
- Interesting - Why we yawn
- Duh - Sweets can make you fat
- Podcast - Our thoughts on cyber trolleys
- How it works - Brain freeze
Image: Carol Kramberger
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