phosphotungstic acid

A mixture of phosphoric and tungstic acids; a protein precipitant and reagent for arginine, lysine, histidine, and cystine; used with hematoxylin for nuclear and muscle staining; also used in electron microscopy as a stain for collagen and as a negative stain.

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phos·pho·tung·stic acid -.təŋ-stik- n any of several acids obtainable from solutions of phosphoric acid and tungstic acid and used chiefly as precipitants (as for alkaloids and for basic dyes for pigments) and in analytical reagents esp a greenish yellow crystalline acid H₃PW₁₂O₄₀·xH₂O used as a reagent and as a biological stain

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phos·pho·tung·stic ac·id (fos″fo-tungґstik) a strong acid and oxidizing agent used as a protein precipitant and color reagent; alkaloids, nitrogenous bases, and other substances reduce phosphotungstic acid to tungsten blue. It is also used in histology as a mordant for hematoxylin and other dyes.