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Basic Bismuth Nitrate

The earliest investigators were well aware that bismuth nitrate is decomposed by water; indeed a cosmetic known as "Spanish White" was prepared in this way. Many substances have been described as resulting from the hydrolysis of bismuth nitrate, but there can be little doubt that many of these are mixtures. The composition of the product obtained depends upon a number of factors, such as the quantity and temperature of the water employed, the time that the precipitated substance stands in contact with the liquid, the process of washing, etc.

The system Bi2O3-N2O5-H2O has been systematically investigated, and the various compounds produced by hydrolysis have been examined by analysis and by titrimetric measurements, and from the results co-ordination formulae have been given. The first product obtained by the action of cold water, or very dilute nitric acid, upon normal hydrated bismuth nitrate is the compound Bi2O3.N2O5.2H2O, or BiONO3.H2O, which forms very thin crystalline plates showing double refraction. When this body is treated with a little warm water, or when it is allowed to stand in contact with liquid containing not more than six per cent, of nitrogen pentoxide, monoclinic crystals of the basic salt Bi2O3.N2O5.H2O or [BiO(NO3).Bi(OH)2]NO3 are formed. This compound may also be obtained in the form of thin hexagonal prisms by the action of heat upon the hydrated normal nitrate, which decomposes at about 72° C. Its solubility in water falls with rise of temperature. When the compound BiONO3.H2O is allowed to stand in contact with very dilute solution, or when the normal nitrate is decomposed by a large excess of water, rhombic crystals of a complex compound 6Bi2O3.5N2O5.9(8)H2O or are obtained. The same compound is obtained in the form of hexagonal plates when the basic compound Bi2O3.N2O5.H2O is acted upon by excess of warm water. The final product obtained by hydrolysis, using boiling water, is 2Bi2O3.N2O5.H2O or BiO(NO3).BiO(OH), which forms hexagonal crystals.

Solubility of Bismuth Nitrate in Nitric Acid
Solubility of Bismuth Nitrate in Various Concentrations of Nitric Acid.
By precipitation from solutions of bismuth nitrate with ammonium hydroxide, the basic nitrate (Bi2O3)2.N2O5.H2O is obtained. Similarly the basic nitrates Bi2O3.N2O5 and 2Bi2O3.N2O5 are obtained by the action of sodium acetate upon solutions of bismuth nitrate.

From measurements of electrical conductivity it has been shown that hydrolysis of bismuth nitrate occurs even in the presence of excess of nitric acid; from these measurements it is also deduced that the compound Bi2O3.N2O5.2H2O is not produced directly, but that an intermediate compound, which may perhaps be BiOH(NO3)2, is formed first. This compound does not appear to have been isolated.

Basic bismuth nitrate combines with certain sugars to form compounds in which the NO3 group is not ionised.

In addition to the above-mentioned substances, two other basic compounds have been obtained, Bi2O3.2N2O5.2H2O and 10Bi2O3.9N2O5.7H2O. Other basic salts mentioned in the literature would appear to be mixtures.

In the following tables are given the solubilities of the basic and normal nitrates of bismuth at different temperatures in various concentrations of nitric acid. The solubilities are expressed as grams of Bi2O3 and N2O5 respectively per 100 grams of solution.

The results contained in this second table are shown diagrammatically in fig.

Solubilities of Bismuth nitrate sesquihydrate, 2Bi(NO3)3.3H2O

At 20° C.Bi2O38.58 grams4.05 grams
N2O568.28 grams74.90 grams
Bi2O34.59 grams
N2O577.90 grams

The quadruple points corresponding to the coexistence in equilibrium of the phases Bi2O3.N2O5.H2O-Bi(NO3)3.5H2O-Solution- Vapour, at various temperatures, are as follows:

Basic Quadruple Points

Point in FigTemp., °C.Bi2O3. GramsN2O5 grams

These points appear to be fairly well established, some of them having been obtained by extrapolation from a considerable number of solubility data.

The following quadruple points are given by Rutten and correspond to the coexistence in equilibrium of the following phases: Bi(NO3)3. 5H2O-2Bi(NO3)3.3H2O-Solution-Vapour. These points are open to criticism in that the data from which they were derived appear somewhat scanty. For this reason the curves connecting Rutten's data in these regions are shown as broken lines in fig.

Acid Quadruple Points

Point in Fig. Temp., °C.Bi2O3. GramsN2O5. Grams.

The conditions of equilibria above 65° C. are very uncertain, for the dihydrate, Bi(NO3)3.2H2O, appears, and the experimental difficulties are considerable.

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