MLA

Whitman, Walt, 1819-1892. George Routledge and Sons. Box 10, folder 208. 1868 Feb 19. https://collections.library.yale.edu/catalog/2053837.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 10, folder 208"])(1868 Feb 19)[George Routledge and Sons]. https://collections.library.yale.edu/catalog/2053837.