Eilhard Mitscherlich (January 7, 1794 - August 28, 1863) was a German chemist. In 1818 he went to Berlin and made analyses of phosphates and phosophites, arsenates and arsenites, confirming the conclusions of Berzelius as to their composition. His observation that corresponding phosphates and arsenates crystallize in the same form was the germ from which grew the theory of isomorphism which states that compounds crystallizing together probably have similar structures and compositions. In 1827 he showed that the salts of selenic acid are isomorphous with the sulphates and later he proved the same thing is true of the manganates, sulfates, permanganates and perchlorates. In 1833 Mitscherlich made a series of careful determinations of the vapor densities of a large number of volatile substances, confirming the law of Gay-Lussac. Mitscherlich was an honorary member of almost all the great scientific societies. In 1861 symptoms of heart disease made their appearance. He died at the age of 69.