MLA
Atkins, Thomas M. Letter from Thomas M. Atkins (Mobile, Alabama), to "Mrs. Holmes" - May 24, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 12. https://digital.library.emory.edu/purl/757np5hrdd-cor.
APA, 6th edition
Atkins, T. M. (1864). Letter from Thomas M. Atkins (Mobile, Alabama), to "Mrs. Holmes" - May 24, 1864 (Box 1, Folder 12) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/757np5hrdd-cor.
Chicago
Atkins, Thomas M. “Letter from Thomas M. Atkins (Mobile, Alabama), to ‘Mrs. Holmes’ - May 24, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 1, Folder 12. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/757np5hrdd-cor.