MLA

Backus, Isaac, 1724-1806. volume 14. Box 1, folder 11. 1803 January 2–1806 March 16. https://collections.library.yale.edu/catalog/33297950.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 1, folder 11"])(1803 January 2–1806 March 16)[volume 14]. https://collections.library.yale.edu/catalog/33297950.