Eilhardt Mitscherlich. Coloured historical portrait of the German physical and organic chemist Eilhardt Mitscherlich (1794-1863). While studying in Berlin he discovered the phenomenon of crystal isomorphism. He observed that potassium phosphate and potassium arsenate form nearly identical crystals. He then worked in Stockholm with Berzelius for two years, continuing to measure crystal angles and forms. Where these were very similar in different compounds, he described them as isomorphous. This isomorphism is useful in deducing chemical formulae and thus atomic masses. In organic chemistry, he was the first person to synthesise benzene.