PALLADIUM (Pd). A rare metal, chiefly occurring as an alloy with platinum and iridium, but sometimes in the pure state. For its natural history, see PLATLNUM, in NAT. HIST. Div. To isolate it, the platinum ore is dissolved in nitrohydroehlorie acid, chloride of ammo nium is added to precipitate the platinum, and the palladium is then thrown down as cyanide from the filtered solution by the addition of cyanide of mercury : the white flocculent cyanide of palladium is then heated with sulphur to expel cyanogen, and the sulphur finally got rid of by well roasting. Brazilian gold usually contains five or six per cent. of palladium, and is therefore another source of this metal.
Palladium is hard, white, ductile, and tenacious. It readily fuses before the oxhdydrogen blowpipe, and is volatile at the temperature of melted iridium. It is more oxidisable than silver, but is very slowly tarnished in the air. Its density is IPS. It dissolves in sine, but does not combine with that metal. It forms a crystalline alloy with tin, containing three equivalents of palladium to two of tin, and the resulting compound very much resembles the corresponding alloys of silver and copper with tin. Palladium is soluble in aqua or in hot nitric acid, but is not easily acted upon by the other acids. It is readily distinguished from platinum, which it somewhat re sembles in appearance, by being stained brown by a drop of solution of iodine.
The equivalent of palladium is Palladium and oxygen form two well-defined compounds, viz. :— I. Drotolide of palladium Pd0 2. Binoxide of palladium . . . . Pd°, According to Ran6 a suboxide (Pd. 0) is produced on heating the hydrated protoxide to incipient redness.
1. Protoxide of palladium is obtained as a black powder on heating nitrate of palladium to low redness. It has somewhat the appearance of black oxide of manganese, and loses its oxygen when heated to whiteness. It is precipitated as a dark brown hydrate (PdO, HO), on adding carbonate of potash or soda to a solution of a protosalt of palla dium. Tho hydrate is soluble in caustic potash, and loses its water when moderately heated.
2. Binoxide of palladium is obtained as a yellowish brown hydrate (Pd0„ HO) on adding solution of caustic potash, or carbonate of potash, to the solid double bichloride of potassium and palladium. It is reduced to the anhydrous state by mere boiling with water and is then black.
Carbide of palladium. Palladium is very apt to absorb carbon when heated in contact with that substance, and is thereby rendered exceed ingly brittle.
Sulphide of palladium (Pd 5). A blackish brown precipitate, formed on passing sulphurettecl hydrogen through a solution of a protosalt of palladium. The metal itself also when heated with sulphur combines
with incandescence, and forms a fusible gray lustrous mass.
Iodide of palladium (Pd I) is a black precipitate formed on adding iodide of potassium to a solution of a protosalt of palladium. It is insoluble in water, alcohol, or ether, but is decomposed on heating with caustic potash.
Bromide of palladium much resembles the iodide.
Palladium and chlorine form two chlorides : • Protochloride of palladium . . . . Pdel 2. Bichloride of palladium . . . . . PdCl, 1. Protochloride of palladium. The metal dissolves slowly in hydro chloric acid with production of protochloride, or quickly in aqua regia with production of biehloride. Ou evaporating the solution of bi chloride to dryness and gently heating, the protochloride remains. It is soluble in water, and may be obtained in brown hydrated crystals. With ammonia it forms a number of interesting bodies resembling those produced by acting upon protochloride of platinum with the same agent ; one of them is the chloride of palladamine CI) or chloride of ammonium, in which an equivalent of hydrogen is re placed by one of palladium. The oxide of palladamine is a powerful base.
2. Bicldoride of palladium is formed when the metal Is dissolved in aqua regia. On adding chloride of potassium a red crystalline precipi tate of chloropalludiute of potassium, or double chloride of pallarlhan and potassium is thrown down.
Cyanide of palladium (PdCy). Cyanogen has a greater affinity for palladium than for any other metal. White, or slightly yellow coloured sock. of cyanide of palladium are precipitated whenever a soluble cyanide is added to a palladium salt Cyanide of palladium is soluble in solution of cyanide of potassium, forming a double salt, which crystallises In prfions oontalning (Key, PsiCy, 3 AO.
Nitnsk of palladium Is formed by dissolving the metal in nitric acid. It is not very stable, hut by careful manipulation may be obtained In rhomboidal pilaus..
Ss/pane of palladiums (rao, SO,) may be produced by boiling the nitrate with sulphuric acid. It Is very deliquescent.
Alloys of palladium. Steel alloyed with one per cent of palladium Is well adapted for making cutting instrumento that require a per fectly smooth edge. Four part. copper and one palladium form a white ductile alloy. One part of palladium gives with six of gold an alloy that is near17 colourless.
Tessa for palladia:1c The colour of the iodide, and the production of the cyanide tinder the circumstances indicated, are the chief test; for 'albs:Hum Protochloride of tin throws down a black precipitate soluble in hydrochloric acid with production of an intensely green solution.