(By Maurie D. McInnis, author of “Slaves Waiting for Sale: Abolitionist Art and the American Slave Trade,” A professor of art history at the University of Virginia and the curator of “To Be Sold: Virginia and the American Slave Trade,” a show at the Library of Virginia on view until May 30.) We don’t know exactly when the last sale of enslaved persons occurred in Richmond, Va., known as “the great slave market of the South,” but it must have taken place before April 3, 1865. On the previous day, the order had come to evacuate in advance of the arrival ...