MLA
Ridenburgh, Wm. (William). Union patriotic envelopes dealing with secession - "Secession with her 'back up'. Gen. Scott will soon make her 'back down.'" Published by Wm. Ridenburgh. 1861. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/426m0cfzwk-cor.
APA, 6th edition
Ridenburgh, Wm. (William). (1861)[Union patriotic envelopes dealing with secession - "Secession with her 'back up'. Gen. Scott will soon make her 'back down.'" Published by Wm. Ridenburgh]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/426m0cfzwk-cor.
Chicago
Ridenburgh, Wm. (William), Union patriotic envelopes dealing with secession - "Secession with her 'back up'. Gen. Scott will soon make her 'back down.'" Published by Wm. Ridenburgh, 1861, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/426m0cfzwk-cor.