MLA

Koch, Frederick R. (Frederick Robinson). Music/Sonata, piano. Box 321, folder 1730. 1863 Apr 6. https://collections.library.yale.edu/catalog/10593442.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 321, folder 1730"])(1863 Apr 6)[Music/Sonata, piano]. https://collections.library.yale.edu/catalog/10593442.