MLA
Anderson, David L. Letter from David L. Anderson to His Sister. David L. Anderson Served in the 8th Alabama Infantry Regiment - January 26, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 4. https://digital.library.emory.edu/purl/392g79cpq3-cor.
APA, 6th edition
Anderson, D. L. (1862). Letter from David L. Anderson to his sister. David L. Anderson served in the 8th Alabama Infantry Regiment - January 26, 1862 (Box 1, Folder 4) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/392g79cpq3-cor.
Chicago
Anderson, David L. “Letter from David L. Anderson to His Sister. David L. Anderson Served in the 8th Alabama Infantry Regiment - January 26, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 1, Folder 4. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/392g79cpq3-cor.