Guide to the Manuscript Collections of the Historical Society of Pennsylvania, 2nd ed. (1949).
Professor Otto E. Albrecht of the University of Pennsylvania reports that in various collections of the Society, particularly the Dreer and Pennypacker collections, there are such Russian-related holdings as correspondence of Michel Asantchevsky, Cesar Cui, Karl Iu. Davidov, Antoine de Kontski (3 letters), Alexis Lvov (2), Wassili Leps, and Sergei Rachmaninoff.