MLA
Brady. Calhoun, Webster, and Clay, the Great Triumvirate Who Debated the Slavery Question a Quarter of a Century. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 74. https://digital.library.emory.edu/purl/573bzkh1c1-cor.
APA, 6th edition
B. Calhoun, Webster, and Clay, the great triumvirate who debated the slavery question a quarter of a century (Box 74) [Postcards]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/573bzkh1c1-cor.
Chicago
Brady. “Calhoun, Webster, and Clay, the Great Triumvirate Who Debated the Slavery Question a Quarter of a Century.” Postcards. Robert Langmuir African American Photograph Collection, n.d. Box 74. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/573bzkh1c1-cor.