W.E.B. DuBois book https://books.google.com/books?id=04mJJlND1ccC&pg=PA118&lpg=PA118&dq=constitution+african+slaves+1818+%22released+from+bond%22&source=bl&ots=s4OfsqtLWD&sig=wRHgf1jgck1vhXEeTtSTH2m1ETQ&hl=en&sa=X&ved=0ahUKEwjkg9Oc2MjOAhVEPCYKHWGDAjkQ6AEIHjAA#v=onepage&q=constitution%20african%20slaves%201818%20%22released%20from%20bond%22&f=false