Faraday needed this for his lecture of 12 April 1845 on "Gold - Platina - malleability, ductility" which was the first of his "Course of Eight Lectures on Certain Metals and Metallic Properties". For his notes for this course see RI MS F4 J5. For an account of this lecture see Lond.Med.Gaz., 1845, 1: 47-52. He acknowledged Pettigrew's loan on p.48. See also letter 1695.