MLA
Seddon, James A. (James Alexander), 1815-1880. Letter from Confederate Secretary of War James A. Seddon (Richmond, Virginia) to William H. Hidell (Richmond, Virginia), stating that the complaint Hidell had registered as to the appointment of officers would be investigated - December 30, 1862. December 30, 1862. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/2322bvq8s8-cor.
APA, 6th edition
Seddon, James A. (James Alexander), 1815-1880. (December 30, 1862)[Letter from Confederate Secretary of War James A. Seddon (Richmond, Virginia) to William H. Hidell (Richmond, Virginia), stating that the complaint Hidell had registered as to the appointment of officers would be investigated - December 30, 1862]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/2322bvq8s8-cor.
Chicago
Seddon, James A. (James Alexander), 1815-1880, Letter from Confederate Secretary of War James A. Seddon (Richmond, Virginia) to William H. Hidell (Richmond, Virginia), stating that the complaint Hidell had registered as to the appointment of officers would be investigated - December 30, 1862, December 30, 1862, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/2322bvq8s8-cor.