MLA
Barrow, George W. Letter from George W. Barrow to His Mother - August 16, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 22. https://digital.library.emory.edu/purl/402q573p68-cor.
APA, 6th edition
Barrow, G. W. (1864). Letter from George W. Barrow to his mother - August 16, 1864 (Box 1, Folder 22) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/402q573p68-cor.
Chicago
Barrow, George W. “Letter from George W. Barrow to His Mother - August 16, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 1, Folder 22. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/402q573p68-cor.