Di-nickel Phosphide, Ni₂P

Nickel Subphosphide or Di-nickel Phosphide, Ni₂P, is obtained in the form of grey needles, of density 6.3, when nickel and phosphorus are heated together in an electric furnace, or when reduced nickel is exposed at dull red heat to vapours of phosphorus trichloride, tri-bromide, or tri-iodide. Small brilliant yellowish white crystals are obtained by this latter process. Nickel subphosphide also results on reducing the phosphate with hydrogen at high temperatures, and by pouring a suspension of nickel hydroxide into a boiling solution of caustic potash to which phosphorus has been added. A brown precipitate is first formed, but after a few minutes a black residue of Ni₂P or Ni₄P₂ is obtained, which dissolves but slowly in most dilute acids. Towards concentrated nitric acid it behaves like iron, but readily dissolves in dilute nitric acid.