MLA
Williamson, J. W. Letter from J. W. Williamson (in Line of Battle near Atlanta) to "Miss Armittie Williams" - August 1, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 7, Folder 34. https://digital.library.emory.edu/purl/2085hqc0nx-cor.
APA, 6th edition
Williamson, J. W. (1864). Letter from J. W. Williamson (in line of battle near Atlanta) to "Miss Armittie Williams" - August 1, 1864 (Box 7, Folder 34) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/2085hqc0nx-cor.
Chicago
Williamson, J. W. “Letter from J. W. Williamson (in Line of Battle near Atlanta) to ‘Miss Armittie Williams’ - August 1, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 7, Folder 34. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/2085hqc0nx-cor.