"(Germ.) Berlin. Portrait. 11 x 14. Painted thirty years ago, when Knaus was a pupil in the Dusseldorf Academy."
A Catalogue of Paintings in the Gallery of D.W. Powers, Rochester, N.Y. with Explanations and Sketches of Painters by C.C. Merriman. Rochester, N.Y.: E.R. Andrews, Book and Job Printer, Aqueduct Street, 1877.