Faraday to William Phillips   10 September 1827¹

Royal Institution | Sep 10. 1827

My dear Sir

The specimen you sent me although consisting for the greater part still is intermingled with portions of a substance like that before analysed²: it also contains portions of copper nearly pure. Some of the purest and most uniform parts which I could select, when heated in a small green glass tube still gave out a little arsenious acid which sublimed & crystallized as in the former case; the quantity was however small, and the rest of the mineral fuzed at a red heat into a substance which, when cold, was brittle, gray, and by examination proved to consist of copper & arsenic in combination with a small quantity of sulphur & a trace of iron. I have no doubt that the gray metallic hard substance is an arseniuret of copper, but the difficulty of separating it perfectly or the specimens from the accompanying bodies will interfere with an accurate determination of its composition[.]

I am dear Sir | Truly Yours | M. Faraday

Mr. W. Phillips

Address: Mr. W. Phillips | George Yard | Lombard Street