Phosphotungstic acid

Abstract: A simple technique has been developed for the study of the external form and structure of virus particles. High contrast with good preservation is obtained by mixing virus preparations with 1% phosphotungstic acid adjusted to pH 7.5 and spraying directly onto electron microscope supporting films made from evaporated carbon. The application of the technique to tobacco mosaic virus and turnip yellow mosaic virus is described. Structural details suggested by X-ray diffraction methods have been resolved.

Abstract: Phosphoric acid doped polybenzimidazole (PBI) and PBI composite membranes have been prepared in the present work. The PBI composites contain inorganic proton conductors including zirconium phosphate (ZrP), (Zr(HPO 4 ) 2 · n H 2 O), phosphotungstic acid (PWA), (H 3 PW 12 O 40 · n H 2 O) and silicotungstic acid (SiWA), (H 4 SiW 12 O 40 · n H 2 O). The conductivity of phosphoric acid doped PBI and PBI composite membranes was found to be dependent on the acid doping level, relative humidity (RH) and temperature. A conductivity of 6.8×10 −2 S cm −1 was observed for PBI membranes with a H 3 PO 4 doping level of 5.6 (mole number of H 3 PO 4 per repeat unit of PBI) at 200 °C and 5% RH. A higher conductivity of 9.6×10 −2 S cm −1 was obtained by composite of 15 wt.% of ZrP in a PBI membrane under the same conditions. Homogeneous membranes with good mechanical strength were prepared by introducing PWA (20–30 wt.%) and SiWA (20–30 wt.%) into PBI, and their conductivity were found to be higher than or comparable with that of the PBI membrane at temperatures up to 110 °C.

Abstract: THE structures and formulae of the heteropoly acids have long been a subject for speculation. In 1929, Pauling1, on theoretical grounds, proposed a structure for the molecules of the 12-heteropoly acids, which gave the formula of 12-phosphotungstic acid as H3[PO4.W12O18(OH)36]nH2O.

Abstract: This acid belongs to a large class of compounds known as the heteropolyacids, of which the structures and exact formulae have long been a subject for speculation. The heteropolyacids are compounds in which one atom of such elements as P, Si, As, B, Al, etc., is combined with a number of atoms of an element such as W or Mo, together with a relatively large number of atoms of oxygen. In addition to the elements mentioned, it has been shown that the oxides of a considerable number of other elements show a tendency to form heteropolyacids. All formulae proposed indicate a relatively large number of atoms in the molecule, and a complex structure. In spite of the complexity of the molecule, many of these acids are quite stable, and form stable salts with practically all metals, The best known compounds of this group are the silicotungstic, silicomolybdic, phosphotungstic and phosphomolybdic acids, in which one atom of silicon or phosphorus is combined with a number of atoms of tungsten or molybdenum. Mixed acids are also known in which a number of tungsten atoms are replaced by molybdenum atoms, or vice versa . The heteropolyacids are classified according to the ratio of the numbers of the two types of cations present. Throughout the whole class of heteropolyacids, those acids which have the same cation-cation ratio tend to be isomorphous and have similar properties.

Abstract: The fine structure of developing elastic fibers in bovine ligamentum nuchae and rat flexor digital tendon was examined. Elastic fibers were found to contain two distinct morphologic components in sections stained with uranyl acetate and lead. These components are 100 A fibrils and a central, almost amorphous nonstaining area. During development, the first identifiable elastic fibers are composed of aggregates of fine fibrils approximately 100 A in diameter. With advancing age, somewhat amorphous regions appear surrounded by these fibrils. These regions increase in prominence until in mature elastic fibers they are the predominant structure surrounded by a mantle of 100 A fibrils. Specific staining characteristics for each of the two components of the elastic fiber as well as for the collagen fibrils in these tissues can be demonstrated after staining with lead, uranyl acetate, or phosphotungstic acid. The 100 A fibrils stain with both uranyl acetate and lead, whereas the central regions of the elastic fibers stain only with phosphotungstic acid. Collagen fibrils stain with uranyl acetate or phosphotungstic acid, but not with lead. These staining reactions imply either a chemical or an organizational difference in these structures. The significance and possible nature of the two morphologic components of the elastic fiber remain to be elucidated.