MLA
Johnston, S. R. Letter from S. R. Johnston (Cincinnati, Ohio) to James Longstreet - August 22, 1879 (typescript). August 22, 1879. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/361rfj6r6r-cor.
APA, 6th edition
Johnston, S. R. (August 22, 1879)[Letter from S. R. Johnston (Cincinnati, Ohio) to James Longstreet - August 22, 1879 (typescript)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/361rfj6r6r-cor.
Chicago
Johnston, S. R, Letter from S. R. Johnston (Cincinnati, Ohio) to James Longstreet - August 22, 1879 (typescript), August 22, 1879, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/361rfj6r6r-cor.