MLA

Ford, Julia Ellsworth, 1859-1950. Granville-Barker, Harley. Box 1, folder 31. 1915 February 20. https://collections.library.yale.edu/catalog/17167828.

APA, 6th edition

Ford, Julia Ellsworth, 1859-1950. (["Box 1, folder 31"])(1915 February 20)[Granville-Barker, Harley]. https://collections.library.yale.edu/catalog/17167828.