MLA
Preston John Smithﾠ. Letter from John Smith Preston (Columbia, South Carolina) to [Unaddressed]. Preston Replies to Inquiry Regarding Requisition for Arms and Accoutrements - December 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 50. https://digital.library.emory.edu/purl/863fxpnwzn-cor.
APA, 6th edition
Preston John Smithﾠ. (1861). Letter from John Smith Preston (Columbia, South Carolina) to [unaddressed]. Preston replies to inquiry regarding requisition for arms and accoutrements - December 1861 (Box 5, Folder 50) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/863fxpnwzn-cor.
Chicago
Preston John Smithﾠ. “Letter from John Smith Preston (Columbia, South Carolina) to [Unaddressed]. Preston Replies to Inquiry Regarding Requisition for Arms and Accoutrements - December 1861.” Letters (correspondence). Civil War Collection, 1861. Box 5, Folder 50. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/863fxpnwzn-cor.