MLA
Mason, J. B. Letter from J. B. Mason to Susan A. Kenny. Mason Served in the 9th and Later the 58th Alabama Infantry Regiment - February 16, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 28. https://digital.library.emory.edu/purl/194hmgqpmd-cor.
APA, 6th edition
Mason, J. B. (1863). Letter from J. B. Mason to Susan A. Kenny. Mason served in the 9th and later the 58th Alabama Infantry Regiment - February 16, 1863 (Box 4, Folder 28) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/194hmgqpmd-cor.
Chicago
Mason, J. B. “Letter from J. B. Mason to Susan A. Kenny. Mason Served in the 9th and Later the 58th Alabama Infantry Regiment - February 16, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 4, Folder 28. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/194hmgqpmd-cor.