MLA
Letter [Fragment] from an Unknown Soldier (Ft. Pulaski, Georgia), to "My Dear Sister," Offering a Humorous Description of Their Camp - January 12, 1860. 1860. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 69. https://digital.library.emory.edu/purl/037hqbzm5n-cor.
APA, 6th edition
Letter [fragment] from an unknown soldier (Ft. Pulaski, Georgia), to "My dear sister," offering a humorous description of their camp - January 12, 1860 (Box 6, Folder 69). (1860). [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/037hqbzm5n-cor.
Chicago
“Letter [Fragment] from an Unknown Soldier (Ft. Pulaski, Georgia), to ‘My Dear Sister," Offering a Humorous Description of Their Camp - January 12, 1860.” Letters (correspondence). Civil War Collection, 1860. Box 6, Folder 69. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/037hqbzm5n-cor.