MLA

Backus, Isaac, 1724-1806. Collected papers. Box 7, folder 38. 1756 January-March, n.d.. https://collections.library.yale.edu/catalog/33554305.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 7, folder 38"])(1756 January-March, n.d.)[Collected papers]. https://collections.library.yale.edu/catalog/33554305.