MLA

Purdy, James, 1914-2009. Burkhardt, Rudolf. Box 1, folder 14. 1956-58. https://collections.library.yale.edu/catalog/32210110.

APA, 6th edition

Purdy, James, 1914-2009. (["Box 1, folder 14"])(1956-58)[Burkhardt, Rudolf]. https://collections.library.yale.edu/catalog/32210110.