Whether a residue remains or not, an excess of ammonia is next added to the filtered solution in nitric acid: the formation of a permanent precipitate denotes the presence of _bismuth_. In this case, the fluid is filtered, and the alkaline filtrate further tested for copper and cadmium. For this purpose, cyanide of potassium is added, and sulphuretted hydrogen conducted through the filtrate: if _cadmium_ be present, a yellow precipitate is produced, copper not being thrown down in presence of an alkaline cyanide. The precipitate of sulphide of cadmium is separated from the solution by filtration, and the filtrate saturated with hydrochloric acid. _Copper_, if present, is now precipitated as sulphide: its separation is completed by conducting sulphuretted hydrogen through the fluid. The precipitate is collected, washed, dissolved in nitric acid, and its identity established as previously directed. If the metal be present in sufficient quantity, it should be obtained in a metallic state upon a plate of iron; it is then coherent, possesses its natural color, and can conveniently be exhibited to the Jury. TREATMENT OF SOLUTION _b_. This solution may contain: cobalt, nickel, iron, manganese, chromium, zinc and aluminium. Of these, only zinc and chromium are poisonous; the search for these two metals is therefore all that is necessary in criminal cases. The solution is treated with a slight excess of ammonia, sulphide of ammonium added, and the fluid, after being allowed to stand for several hours, filtered. The precipitate may consist of sulphide of zinc and hydrated oxide of chromium, as well as of traces of sulphide of iron and phosphate of lime. If the suspected materials contained a _chromate_, this salt, in presence of hydrochloric acid and sulphuretted hydrogen, would be converted into sesquichloride of chromium a compound which is precipitated by sulphide of ammonium as a hydrated oxide.