MLA
Rogers, John. Letter from John Rogers (12th Alabama Infantry Camp near Orange, Virginia) to "Dear Sister." Rogers Served in Company E of the 12th Alabama Infantry Regiment - April 14, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 3. https://digital.library.emory.edu/purl/610wpzgnhq-cor.
APA, 6th edition
Rogers, J. (1864). Letter from John Rogers (12th Alabama Infantry camp near Orange, Virginia) to "Dear Sister." Rogers served in Company E of the 12th Alabama Infantry Regiment - April 14, 1864 (Box 6, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/610wpzgnhq-cor.
Chicago
Rogers, John. “Letter from John Rogers (12th Alabama Infantry Camp near Orange, Virginia) to ‘Dear Sister." Rogers Served in Company E of the 12th Alabama Infantry Regiment - April 14, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 6, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/610wpzgnhq-cor.