THE GÖTTINGEN CHEMIST RICHARD ZSIGMONDY (1865-1929) WITH HIS SPANISH COLLEAGUE ANTONIO DE GREGORIO ROCASOLANO (1873-1941), working with the immersion ultramicroscope, developed by Zsigmondy and the Göttingen company Winkel,, circa 1920, Photograph (reproduction), Museum of Göttingen Chemistry, University of Göttingen