MLA
Magnus, Charles. Envelope with Confederate Generals on Them - "No. 12 Secesh Chain, Gen. R.S. Garnett", Published by Chas Magnus. Chas Magnus, 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 21, Folder 5. https://digital.library.emory.edu/purl/1741rn8qr6-cor.
APA, 6th edition
Magnus, C. (1861). Envelope with Confederate generals on them - "No. 12 Secesh Chain, Gen. R.S. Garnett", published by Chas Magnus (Box 21, Folder 5) [Envelopes]. Chas Magnus; Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/1741rn8qr6-cor.
Chicago
Magnus, Charles. “Envelope with Confederate Generals on Them - ‘No. 12 Secesh Chain, Gen. R.S. Garnett’, Published by Chas Magnus.” Envelopes. Civil War Collection. New York City, NY: Chas Magnus, 1861. Box 21, Folder 5. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/1741rn8qr6-cor.