MLA

Amherst of Arracan, William Pitt Amherst, Earl, 1773-1857. Earl Amherst of Arracan letters to Sarah, Countess of Arracan, 1806-1822.. Box 1 | Folder 16. Undated. https://collections.library.yale.edu/catalog/11695522.

APA, 6th edition

Amherst of Arracan, William Pitt Amherst, Earl, 1773-1857. (["Box 1 | Folder 16"])(Undated)[Earl Amherst of Arracan letters to Sarah, Countess of Arracan, 1806-1822.]. https://collections.library.yale.edu/catalog/11695522.