MLA

Backus, Isaac, 1724-1806. Collected papers. Box 7, folder 40. 1756 May-August. https://collections.library.yale.edu/catalog/33554313.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 7, folder 40"])(1756 May-August)[Collected papers]. https://collections.library.yale.edu/catalog/33554313.