MLA
Bell, R. A. Letter from R. A. Bell (Camp Cleburne) to "Dear Sir." Bell Served in the Company E of the 10th Mississippi Infantry Regiment as a Captain - February 6, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 25. https://digital.library.emory.edu/purl/006sxksp11-cor.
APA, 6th edition
Bell, R. A. (1864). Letter from R. A. Bell (Camp Cleburne) to "Dear Sir." Bell served in the Company E of the 10th Mississippi Infantry Regiment as a captain - February 6, 1864 (Box 1, Folder 25) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/006sxksp11-cor.
Chicago
Bell, R. A. “Letter from R. A. Bell (Camp Cleburne) to ‘Dear Sir." Bell Served in the Company E of the 10th Mississippi Infantry Regiment as a Captain - February 6, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 1, Folder 25. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/006sxksp11-cor.