MLA

Backus, Isaac, 1724-1806. Collected papers. box 9, folder 17. 1771 June–1771 July. https://collections.library.yale.edu/catalog/33573260.

APA, 6th edition

Backus, Isaac, 1724-1806. (["box 9, folder 17"])(1771 June–1771 July)[Collected papers]. https://collections.library.yale.edu/catalog/33573260.