MLA

Koch, Frederick R. (Frederick Robinson). Mugnone, Leopoldo. Box 50, folder 1049. 1897 Feb 17. https://collections.library.yale.edu/catalog/16101622.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 50, folder 1049"])(1897 Feb 17)[Mugnone, Leopoldo]. https://collections.library.yale.edu/catalog/16101622.