Offprint (with additions of Chemisch Weekblad van 1 en 22 october 1927.77pp. 4 plates, (including two portraits), original softcover paper binding. Ernst Julius Cohen (7 March 1869 – 6 March 1944) was a Dutch Jewish chemist known for his work on the allotropy of metals. Cohen studied chemistry under Svante Arrhenius in Stockholm, Henri Moissan at Paris, and Jacobus van't Hoff at Amsterdam. In 1893 he became Van't Hoff's assistant and in 1902 he became professor of Physical Chemistry at the University of Utrecht, a position which he held until his retirement in 1939. Throughout his life, Cohen studied the allotropy of tin. Cohen's areas of research included polymorphism of both elements and compounds, photographic chemistry, electrochemistry, pizeochemistry, and the history of science. He published more than 400 papers and numerous books.