Volume IX:
MLA
Harkness, Mary Emma Stillman, 1874-1950. Volume IX:. Box 3, folder 9. 1730-1812. https://collections.library.yale.edu/catalog/2077106.
APA, 6th edition
Harkness, Mary Emma Stillman, 1874-1950. (["Box 3, folder 9"])(1730-1812)[Volume IX:]. https://collections.library.yale.edu/catalog/2077106.