German chemist Friedrich Stromeyer discovered cadmium (atomic number 48) in 1817. It was discovered as an impurity in zinc oxide. Stromeyer was also an inspector of apothecaries, and in this capacity, he inspected various pharmacies. Zinc oxides were used to treat skin diseases during that time but many pharmacies used zinc carbonate instead of zinc oxide.
Stromeyer began heating these samples of zinc carbonate in his laboratory and observed that they were becoming discolored at high temperatures. Knowing that pure zinc carbonate does not discolor, Stromeyer reasoned that some impurity must have caused the reaction. He created an experimental procedure to identify the impurity and was able to isolate cadmium, a silver-blue metal.
Cadmium was also discovered by German Chemist Karl Hermann in 1818 independently.
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