Lady Fi's Onions and a bit on gold, for good measure.

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Lady Fi asks: Have you read my post about onions?
Why not tell us more about the tearful reactions they can trigger in lots of us?

Also - what's the deal about alchemy turning stuff into gold? How did it start? Why did people try? And is it really impossible?

Onions make you cry because, when you cut them, you release Propanethial S-oxide, a volaile compound that reacts with the moist surface of your eye to form sulphuric acid. Your eyes then water in response to this irritation.

Interestingly, onions do not contain propanethial S-oxide and it is thought that onions produce this tear inducing compound to protect the plant from herbivores. It is the product of a series of chemical reactions that occur once the onion has been damaged. Cells are broken open as the onion is cut and this releases the enzyme alliinase and water, which react with S-1-propenyl-L-cysteine sulfoxide forming a mixture of products including propanethial S-oxide.

Various suggestions are about to stop this process - cutting onions under water, chilling onions to reduce the volatility of the compound, heating the onion to kill the enzymes that create the compound, or what I sometimes do if the stove is free, cutting the onions under the exhaust fan on the stove.

And gold?

The alchemists have dreamed of turning lead into gold but, alas, had to fall back on other retirement schemes. Modern day nuclear physics has successfully transmuted lead into gold, but the expense far exceeds any gain. Ironically, it transpired that, under true nuclear transmutation, it is far easier to turn gold into lead than the reverse reaction, which was the one the alchemists had ardently pursued.


Reference:
http://www.chm.bris.ac.uk/motm/pso/psoc.htm
http://en.wikipedia.org/wiki/Nuclear_transmutation