Potassium Platinicyanide, KPt(CN)₄

Potassium Platinicyanide, KPt(CN)₄, is obtained, combined with three molecules of platinocyanide, namely, as KPt(CN)₄.3K₂Pt(CN)₄. 6H₂O, by adding hydrogen peroxide (20-volume solution) to a concentrated solution of potassium platinocyanide, acidulated with sulphuric acid. Bronze, needle-shaped crystals are deposited, displaying a strong metallic reflection. They are readily soluble in water, yielding a colourless solution from which no precipitate is obtained with barium chloride. The solution bleaches cochineal, and liberates iodine from potassium iodide. Thus:

3K₂Pt(CN)₄.KPt(CN)₄ + KI = 4K₂Pt(CN)₄ + I.