J.L. Bell at Boston1775 writes on Cambridge (MA) Dr. Samuel Danforth's flirtations with alchemy during the 1770s, making note of Danforth's 1773 letter to Benjamin Franklin announcing that he'd discovered the Philosopher's Stone (Franklin's response is, naturally, priceless).
It would be fascinating to see a full study of alchemical thinking in colonial New England; I remember being quite surprised and intrigued to discover that among the Winthrop Library books at MHS are John Dee's Monas Hieroglyphica, as well as Five Treatises of the Philosopher's Stone, Michael Maier's Jocus Severus, and Agnello's A Revelation of the Secret Spirit (there are probably more such with the majority of the Winthrop books at the New York Society Library).
Bell's post got me doing a little digging and I've discovered a few interesting articles on John Winthrop Jr.'s alchemical predilections, including several of those in the footnotes to this piece.