MLA
Hammond, J. F. Letter from J. F. Hammond (West Point, New York) to LeRoy Pope Walker, Confederate Secretary of War (Montgomery, Alabama), Offering His Service as Surgeon to the Confederate Army - February 28, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 47. https://digital.library.emory.edu/purl/0580k6dkh4-cor.
APA, 6th edition
Hammond, J. F. (1861). Letter from J. F. Hammond (West Point, New York) to LeRoy Pope Walker, Confederate Secretary of War (Montgomery, Alabama), offering his service as Surgeon to the Confederate Army - February 28, 1861 (Box 3, Folder 47) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0580k6dkh4-cor.
Chicago
Hammond, J. F. “Letter from J. F. Hammond (West Point, New York) to LeRoy Pope Walker, Confederate Secretary of War (Montgomery, Alabama), Offering His Service as Surgeon to the Confederate Army - February 28, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 3, Folder 47. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0580k6dkh4-cor.