Sodium Nitroprusside

SODIUM NITROPRUSSIDE, Na₂Fe(CN)₅NO·2H₂O, dark red rhombic crystals, readily soluble in water and alcohol. It is obtained by the action of nitric acid on yellow blood salt K₄Fe(CN)₆. When acted upon by caustic soda, it decomposes into iron hydroxide, sodium nitrite, and yellow blood salt. It gives precipitates with many heavy metals. With solutions of alkaline sulfides, it gives a red-violet coloring that disappears upon the addition of acid. With sulfite ion, it gives a reddish coloring that disappears upon the addition of acid, intensifies upon the addition of a saturated solution of sulfate (or nitrate) of zinc; subsequent addition of yellow blood salt gives a red precipitate; acid decolorizes the solution. Thiosulfates do not give colorations. Primary amines give with N. a red-violet coloring, some secondary and tertiary amines a red-orange coloring, and aliphatic amines in the presence of pyruvic acid a violet color that turns blue upon the addition of acetic acid. Sodium nitroprusside is used as a reagent for acetone, creatinine, indole, and skatole.