Before Kościuszko left for France, he collected his back pay, wrote a will, and entrusted it to Jefferson as executor. Kościuszko and Jefferson had become firm friends by 1797 and thereafter corresponded for twenty years in a spirit of mutual admiration. Jefferson wrote that "He is as pure a son of liberty as I have ever known." In the will, Kościuszko left his American estate to be sold to buy the freedom of black slaves, including Jefferson's own, and to educate them for independent life and work.