MLA

Backus, Isaac, 1724-1806. volume 7. Box 1, folder 5. 1767 October 13–1771 October 23. https://collections.library.yale.edu/catalog/33297939.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 1, folder 5"])(1767 October 13–1771 October 23)[volume 7]. https://collections.library.yale.edu/catalog/33297939.