MLA

Backus, Isaac, 1724-1806. Account of journeys. Box 2, folder 2. 1749 November 9–1753 May 24. https://collections.library.yale.edu/catalog/33600280.

APA, 6th edition

Backus, Isaac, 1724-1806. (["Box 2, folder 2"])(1749 November 9–1753 May 24)[Account of journeys]. https://collections.library.yale.edu/catalog/33600280.