MLA

Van Vechten, Carl, 1880-1964. Singer, Israel Joshua. Box 376, folder 5435. 1938 January 7. https://collections.library.yale.edu/catalog/10054064.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 376, folder 5435"])(1938 January 7)[Singer, Israel Joshua]. https://collections.library.yale.edu/catalog/10054064.