MLA

Backus, Isaac, 1724-1806. Collected papers. Box 7, folder 42. 1757 January-July. https://collections.library.yale.edu/catalog/33554374.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 7, folder 42"])(1757 January-July)[Collected papers]. https://collections.library.yale.edu/catalog/33554374.