MLA
Sandlin, Alfred W. Letter from Alfred W. Sandlin (Johnson's Island, Ohio) to His Children. Alfred W. Sandlin Served in the 1st Mississippi Infantry Regiment and Was Captured at Port Hudson, Louisiana on July 7, 1863 - August 9, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 11. https://digital.library.emory.edu/purl/767wm37qk5-cor.
APA, 6th edition
Sandlin, A. W. (1864). Letter from Alfred W. Sandlin (Johnson's Island, Ohio) to his children. Alfred W. Sandlin served in the 1st Mississippi Infantry Regiment and was captured at Port Hudson, Louisiana on July 7, 1863 - August 9, 1864 (Box 6, Folder 11) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/767wm37qk5-cor.
Chicago
Sandlin, Alfred W. “Letter from Alfred W. Sandlin (Johnson's Island, Ohio) to His Children. Alfred W. Sandlin Served in the 1st Mississippi Infantry Regiment and Was Captured at Port Hudson, Louisiana on July 7, 1863 - August 9, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 6, Folder 11. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/767wm37qk5-cor.