He was friends with Benjamin Franklin, originating probably from Franklin's visit to Scotland in 1759 and met him several times in London in 1764. A supporter of the American cause, he corresponded with George Washington and sent him a box made from the oak that hid William Wallace after the Battle of Falkirk. The box was designed by the Goldsmith Company of Edinburgh, and the earl requested that Washington, upon his death, pass it on to the man in his country who he believed should merit it best, and upon the same conditions that induced the earl to send it to Washington. In his will Washington thanked the earl for presenting the box to him along with sentiments which accompanied it; feeling incapable of making the choice asked of him he bequeathed the box back to the earl.