MLA
Collins, N. M. Postal Card Note by N. M. Collins to Captain J. W. Anderson. 1885. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 49. https://digital.library.emory.edu/purl/740ksn03x5-cor.
APA, 6th edition
Collins, N. M. (1885). Postal Card Note by N. M. Collins to Captain J. W. Anderson. (Box 3, Folder 49) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/740ksn03x5-cor.
Chicago
Collins, N. M. “Postal Card Note by N. M. Collins to Captain J. W. Anderson.” Letters (correspondence). Civil War Collection, 1885. Box 3, Folder 49. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/740ksn03x5-cor.