MLA

Downie, William, 1819-1893. Diary. Box 1, folder 2. 1860 Apr 18-22. https://collections.library.yale.edu/catalog/17440591.

APA, 6th edition

Downie, William, 1819-1893. (["Box 1, folder 2"])(1860 Apr 18-22)[Diary]. https://collections.library.yale.edu/catalog/17440591.