MLA
Letter [Fragment] from an Unknown Soldier (Fredericksburg, Virginia) to "Dear Mother" - May 16, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 70. https://digital.library.emory.edu/purl/525k98sfxg-cor.
APA, 6th edition
Letter [fragment] from an unknown soldier (Fredericksburg, Virginia) to "Dear Mother" - May 16, 1862 (Box 6, Folder 70). (1862). [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/525k98sfxg-cor.
Chicago
“Letter [Fragment] from an Unknown Soldier (Fredericksburg, Virginia) to ‘Dear Mother’ - May 16, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 6, Folder 70. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/525k98sfxg-cor.