MLA

Stieglitz, Alfred, 1864-1946. Laughlin, Clarence John. Box 30, folder 700. 1935 May 20. https://collections.library.yale.edu/catalog/17105640.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 30, folder 700"])(1935 May 20)[Laughlin, Clarence John]. https://collections.library.yale.edu/catalog/17105640.