Kekulé's views on the linking of atoms and on the valency of such chains of atoms, the foundation on which our modern system of constitutional chemistry rests. In 1865 Kekulé put forward his well-known benzene theory—pronounced by Professor Japp the crowning achievement, in his hands, of the doctrine of the linking of atoms, and the most brilliant piece of scientific prediction to be found in the whole range of organic chemistry. The conception of closed chains, or cycloids, which he thus introduced, has shown itself to be capable of boundless expansion.
Kekulé's students all speak admiringly of his qualities as a teacher. The memorialist of the German Chemical Society said: "All of us who have attended his lectures or heard him in other places will ever remember what a teacher Kekulé was. With incomparable lucidity and sometimes with the happiest humor, he could go playfully through the theme he was considering, masterfully presenting it in new and often surprising aspects. The charm of his personality affected all who came in contact with him; it was the geniality which shone out of his whole being, and involuntarily commanded admiration. Numerous pupils flocked to him, and many of those who to-day fill chairs of chemistry in Germany and other countries have made his name highly honored."
Professor Thorpe, of London, who spent a little time in Kekulé's laboratory, describes him as having been one of the very best expositors, with the single possible exception of Kirchhoff, to whom it had been his lot to listen. As a laboratory teacher he was excellent. He was a most severe judge of work, striving to exact the same high manipulative finish, the same neatness and order, which he invariably bestowed on everything he did, and he was absolutely intolerant of anything slovenly or "sloppy." "But it was as a lecturer that he was seen at his best. He was singularly luminous as a thinker, a close and accurate reasoner, with a remarkable power of concentrated expression. . . . His language was apt and well chosen, and his delivery easy and natural"; and his whole address showed that every detail had been carefully considered.
At a distance of thirty years, Professor Dewar said, at the London memorial meeting, that to look back and call to mind the presence and personality of the great chemist as he knew him was indeed a pleasure. He was a man of noble mien, handsome, dignified, and yet of a homely and kindly disposition. He was a severe critic, having a haughty contempt for the accidental and bizarre in scientific work. His originality and suggestiveness seemed endless, so that he had no need to commit trespass or to follow just in the wake of other people's ideas. "Everything that passed through the Kekulé alembic was indeed transmuted into pure gold. His precision of