MLA
Philips, T. A. Letter from T. A. Philips to Confederate General Albert Sydney Johnston - October 4, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 57. https://digital.library.emory.edu/purl/699n2z35jb-cor.
APA, 6th edition
Philips, T. A. (1861). Letter from T. A. Philips to Confederate General Albert Sydney Johnston - October 4, 1861 (Box 6, Folder 57) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/699n2z35jb-cor.
Chicago
Philips, T. A. “Letter from T. A. Philips to Confederate General Albert Sydney Johnston - October 4, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 6, Folder 57. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/699n2z35jb-cor.