MLA

Stieglitz, Alfred, 1864-1946. Andrew Droth. Box 135, folder 2569. [1939]. https://collections.library.yale.edu/catalog/2002708.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 135, folder 2569"])([1939])[Andrew Droth]. https://collections.library.yale.edu/catalog/2002708.