MLA
Letter from W. W. Dunlap to John T. Champney - July 23, 1862. 1862. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 2, Folder 12. https://digital.library.emory.edu/purl/0687h44jzf-cor.
APA, 6th edition
Letter from W. W. Dunlap to John T. Champney - July 23, 1862 (Box 2, Folder 12). (1862). [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0687h44jzf-cor.
Chicago
“Letter from W. W. Dunlap to John T. Champney - July 23, 1862.” Letters (correspondence). Civil War Collection, 1862. Box 2, Folder 12. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0687h44jzf-cor.