(Tungstophosphoric acid). H3PO4.12WO3xH2O M.W. 2880.17 Pb(NO3)2 M.W. 331.20 Purity > 99% Positive and negative stain Metal stain for ultra thin sections. Holt, J.Ultrastruct. Res., 68, 58 (1979) J. Histochem., Cytochem., 11, 2, ( 1963) J.Ultrastruct Res., 45, 183 (1973) Sato, T., J. Electron Micro., 16, 733 ( 1976) Farragiana, T. and Marinozzi, V. J. Cell Biol., 50, 550