MLA
Poore, Benjamin Perley. Form Commissioning Benjamin Perley Poore a Captain in the Massachusetts Militia, Signed by George Nixon Briggs, Governor of Massachusetts - July 26, 1849. 1849. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 20, Folder 13. https://digital.library.emory.edu/purl/313zs7h59r-cor.
APA, 6th edition
Poore, B. P. (1849). Form commissioning Benjamin Perley Poore a captain in the Massachusetts militia, signed by George Nixon Briggs, Governor of Massachusetts - July 26, 1849 (Box 20, Folder 13) [Forms (documents)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/313zs7h59r-cor.
Chicago
Poore, Benjamin Perley. “Form Commissioning Benjamin Perley Poore a Captain in the Massachusetts Militia, Signed by George Nixon Briggs, Governor of Massachusetts - July 26, 1849.” Forms (documents). Civil War Collection, 1849. Box 20, Folder 13. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/313zs7h59r-cor.