MLA

Hansen, Bert, 1944-. "A Sardonic Soliloquy.. Box 6, folder 18. 1903 January 17. https://collections.library.yale.edu/catalog/32326778.

APA, 6th edition

Hansen, Bert, 1944-. (["Box 6, folder 18"])(1903 January 17)["A Sardonic Soliloquy.]. https://collections.library.yale.edu/catalog/32326778.