There once lived in the Middle Ages in the German town of Hamburg a merchant by the name of Hennig Brand. We do not know how inventive he was in his trade operations, but can assert confidently that he had only a very crude idea of chemistry.

   But even he could not resist the temptation to try and become a rich man all at once. This seemed easy: all he had to do was to find the notorious "philosopher's stone" which, the alchemists claimed, could change even a cobble­stone to gold.

   Years passed. Brand's name was mentioned less and less frequently in conversations between merchants, and when it was, heads were wagged sadly. Meanwhile he dissolved , mixed, sieved, and calcined various minerals and concoctions, and his hands were covered with unhealing acid and alkali burns.

   One fine evening the former merchant had a streak of luck. A substance, white as snow, settled at the bottom of his retort. It burned quickly, forming thick asphyxiating fumes. And the strangest thing was that it glowed in the dark. The cold light it gave off was so bright that Brand could read his ancient alchemical treatises by it (for him these treatises had now taken the place of business letters and receipts).

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