MLA

Kilpatrick, Jack Frederick (1915-1967). Letter. Box 6, folder 510. 1922 September 25. https://collections.library.yale.edu/catalog/15492650.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 6, folder 510"])(1922 September 25)[Letter]. https://collections.library.yale.edu/catalog/15492650.