MLA

Backus, Isaac, 1724-1806. Collected papers. Box 7, folder 25. 1751 January-May. https://collections.library.yale.edu/catalog/33555374.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 7, folder 25"])(1751 January-May)[Collected papers]. https://collections.library.yale.edu/catalog/33555374.