1782Purple powder of Cassius [see sense B. 4]. 1823 A. Ure (ed. 2) 492/2 A plate of tin, immersed in a solution of gold, affords a purple powder, called the purple powder of Cassius.
1848 20 May 548/1 The oxide, or rather deutoxide, of gold,—the purple powder of Cassius, is the next form.