An American in Florence, a friend of the American Ambassador, Jonas Spaulding.

Quite possibly refers to William Waiters or his son Henry, the founders of the Walters Gallery in Baltimore, both of whom were in Florence during the 70’s, and whom Trollope may have met.

"..... a man of wealth and taste, who was resolved on having such a collection of pictures at his house in Baltimore, that no English private collection should in any way come near to it." - He Knew He Was Right