MLA

Kilpatrick, Jack Frederick (1915-1967). Wadi, Denili (Watt, Daniel). Unidentified letter. Box 7, folder 556. 1904 July 25. https://collections.library.yale.edu/catalog/15492781.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 7, folder 556"])(1904 July 25)[Wadi, Denili (Watt, Daniel). Unidentified letter]. https://collections.library.yale.edu/catalog/15492781.