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You can stop puzzling over what to do with those unwanted recordable CDs.
Researchers at the University of São Paulo in Brazil have developed a way
to make electrodes out of the pre-polished gold that lines them. Using nitric
acid, they removed the CD’s plastic layers to reveal the gold layer, which is
about 50 to 100 nanometres thick. The gold is the perfect thickness for use in
many types of electrolytic cells—particularly those used to measure levels
of mercury and copper in drinking water.