MLA
Thornton, Hiram H. Letter Form Hiram H. Thornton (Camp near Richmond, Virginia) to His Wife. Hiram Served in Company C of the 53rd Georgia Infantry Regiment - August 17, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 53. https://digital.library.emory.edu/purl/805fbg7b33-cor.
APA, 6th edition
Thornton, H. H. (1862). Letter form Hiram H. Thornton (Camp near Richmond, Virginia) to his wife. Hiram served in Company C of the 53rd Georgia Infantry Regiment - August 17, 1862 (Box 6, Folder 53) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/805fbg7b33-cor.
Chicago
Thornton, Hiram H. “Letter Form Hiram H. Thornton (Camp near Richmond, Virginia) to His Wife. Hiram Served in Company C of the 53rd Georgia Infantry Regiment - August 17, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 6, Folder 53. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/805fbg7b33-cor.