A dialogue concerning the slavery of the Africans [electronic resource] : shewing it to be the duty and interest of the American States to emancipate all their African slaves : with an address to the owners of such slaves : dedicated to the Honourable the Continental Congress : to which is prefixed, the institution of the society, in New-York, for promoting the manumission of slaves, and protecting such of them as have been, or may be, liberated.