MLA

Backus, Isaac, 1724-1806. Collected papers. Box 7, folder 27. 1751 October-December. https://collections.library.yale.edu/catalog/33554146.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 7, folder 27"])(1751 October-December)[Collected papers]. https://collections.library.yale.edu/catalog/33554146.