Volume 6: December 8, 1919 to April 6, 1920
MLA
Butts, Mary, 1890-1937. Volume 6: December 8, 1919 to April 6, 1920. Box 2, folder 56. 1919-20. https://collections.library.yale.edu/catalog/16947654.
APA, 6th edition
Butts, Mary, 1890-1937. (["Box 2, folder 56"])(1919-20)[Volume 6: December 8, 1919 to April 6, 1920]. https://collections.library.yale.edu/catalog/16947654.