MLA
Tucker, Nathaniel Beverly. Letter from Nathaniel Beverly Tucker (St. Catherine's, Ontario, Canada) to "Beloved Johnny." Written on Advertising Sheet of the Stephenson House of Which Tucker Was the Proprietor - June 5, 1869. 1869. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 9, Folder 38. https://digital.library.emory.edu/purl/453wstqkq9-cor.
APA, 6th edition
Tucker, N. B. (1869). Letter from Nathaniel Beverly Tucker (St. Catherine's, Ontario, Canada) to "Beloved Johnny." Written on advertising sheet of the Stephenson House of which Tucker was the proprietor - June 5, 1869 (Box 9, Folder 38) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/453wstqkq9-cor.
Chicago
Tucker, Nathaniel Beverly. “Letter from Nathaniel Beverly Tucker (St. Catherine's, Ontario, Canada) to ‘Beloved Johnny." Written on Advertising Sheet of the Stephenson House of Which Tucker Was the Proprietor - June 5, 1869.” Letters (correspondence). Civil War Collection, 1869. Box 9, Folder 38. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/453wstqkq9-cor.