MLA

Backus, Isaac, 1724-1806. Collected papers. box 8, folder 43. 1770 February–1770 March. https://collections.library.yale.edu/catalog/33566995.

APA, 6th edition

Backus, Isaac, 1724-1806. (["box 8, folder 43"])(1770 February–1770 March)[Collected papers]. https://collections.library.yale.edu/catalog/33566995.