Tungstic acid, complexes

Polytungsta.tes, An important and characteristic feature of the tungstate ion is its abiUty to form condensed complex ions of isopolytungstates in acid solution (38). As the acidity increases, the molecular weight of the isopolyanions increases until tungstic acid precipitates. However, the extensive investigations on these systems have been hampered by lack of weU-defined soHd derivatives. 

Since columbite is a very complex mineral indeed, containing niobic, tantalic, titanic, and tungstic acids, zirconia, thoria, ceria, and yttria, Hatchett must have possessed great analytical ability in order to discover in it the new element, columbium. Although the greatest chem-... 

As with percarboxylic acids, hydrogen peroxide usually requires metal activation.151-154 Peroxo complexes of d° transition metals can often be used to cleave olefins. Tungstic acid cleaves olefins to the carboxylic acid using 35% m/m hydrogen peroxide.154 Sodium tungstate has also been reported to... 

Tungstates form complex acids with phosphoric, boric, and silicic acids tungstic acid cannot therefore be precipitated from these compounds by hydrochloric acid. The complexes may usually be decomposed by heating with concentrated sulphuric acid, tungstic acid being liberated. 

A white dihydrate, WO3.2H2O. With bases, both hydrates produce the same series of salts, and the first appears to be the true acid, tungstic acid, H2WO4, whilst the second is the hydrate, HjWOi.HaO. Both are insoluble in water, but colloidal forms of the acid e.xist. Several other hydrates have been described, but except in the case of the complex hydrate known as metatungstic acid (see p. 238) their existence has not been established. 

Various complex compounds of tungstic acid with organic acids, such as oxalic, tartaric, citric, malic, and lactic acids, have been described. ... 

Tungsten (W, at. mass 183.85) is an element similar to Mo and Cr. The basic properties of W(VI) are not so accentuated as those of Mo(VI). Tungstic acid is less soluble than molybdic acid in mineral acids. W(VI) gives tartrate, oxalate, fluoride, and chloride complexes, as well as heteropoly acids. Tungsten may occur also in the rather unstable V, IV, and III oxidation states. 

Complex tungstic acids arc numerous mid interesting. I hosplnirir, arsenic, antimonic, vanadic, and boric, acids condense with varying aiunuuis of tungstic acid. The ratio of the, otlner oxide, to W(), varies from 1 7 in 1 24 or more-... 

In general the heteropoly compounds of tungstic acid are more complexed and more resistant to hydrolysis than those of molybdic... 

Products Formed. — In the reactions involving pepsin it was seen that albumoses and peptones were produced as well as complex non-bimretic bodies not precipitated by phospho-tungstic acid but susceptible of crystallization. All these products of high molecular weight come from the partial hydrolysis of the albuminoid material. They also show the characteristics, more or less pronounced, of the substance from which they are derived. With trypsin, a much deeper effect is observed. Without doubt primary albumoses are still formed... 

Phosphoric acid and organic hydroxy acids (tartaric, citric, etc.), which form complex compounds with tungstic acid, hinder or prevent the precipitation of tungsten trioxide with mineral acids certain other organic acids also impair the reaction to some extent. 

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