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Normal Bismuth Nitrate, Bi(NO3)3

Normal Bismuth Nitrate, Bi(NO3)3.5H2O, is obtained by dissolving powdered bismuth in nitric acid; on crystallising from solution, large, prismatic, triclinic crystals having the elements

a:b:c = 0.8053:1:0.6172; α = 90°4'; β = 104°26'; γ = 79°6'

are formed, being isomorphous with those of the corresponding but labile nitrates of the rare earth metals neodymium and praseodymium. Its density is 2.7 to 2.8. On exposure to dry air at the ordinary temperature the nitrate disintegrates and is gradually converted into a basic nitrate. It cannot be dehydrated completely by phosphorus pentoxide, as decomposition sets in. The action of heat on the normal salt is extremely complex, and the results obtained by different investigators are conflicting. Rutten observed that at 72° C. a little liquid is formed, but that maintaining the mass at that temperature does not produce more liquid. The remaining crystals, freed from liquid, melt at 75.5° C., giving basic salt and liquid. The trioxide results at 425° C. Earlier workers, however, stated that the anhydrous oxide was formed at as low a temperature as 260° C. The first product of decomposition appears to be the basic nitrate, 2BiONO3.H2O, but several other products have been reported.

Bismuth nitrate is soluble in water, but excess of water must be avoided; the solution, which is acid in consequence of hydrolysis, rapidly decomposes with the formation of oxynitrate, BiONO3. It is soluble in nitric acid, and the refractive power of the solution has been studied. It is insoluble in anhydrous hydrofluoric acid, but readily soluble in an aqueous solution of mannitol, forming a clear solution which probably contains complex compounds. This solution may be employed for the preparation of many bismuth salts.

The sesquihydrate, 2Bi(NO3)3.3H2O, is obtained by treating Bi2O3 or the normal pentahydrated salt with fuming nitric acid. It is very deliquescent. A dihydrate, Bi(NO3)3.2H2O, has also been prepared.

Many double nitrates have been obtained of the type 3M(NO3)2.2Bi(NO3)3.24H2O, in which M represents magnesium, zinc, nickel, cobalt or manganese. They are prepared by dissolving the simple nitrates in the smallest quantity of hot, fairly concentrated nitric acid, and allowing the solution to crystallise.. These double salts are isomorphous with the similar double nitrates obtained by substituting metals of the rare earths for bismuth. They are all decomposed by water. Magnesium bismuth nitrate, Mg3Bi2(NO3)12.24H2O, is colourless; its density is 2.32, and it melts with decomposition at 71° C. Zinc bismuth nitrate, Zn3Bi2(NO3)12.24H2O, is colourless; its density is 2.75, and it melts with decomposition at 67.5° C. Nickel bismuth nitrate, Ni3Bi2(NO3)12.24H2O, is green; its density is 2.51, and it melts without decomposition at 69° C. Cobalt bismuth nitrate, Co3Bi2(NO3)12.24H2O, is orange-red; its density is 2.48, and it melts without decomposition at 58° C. Manganese bismuth nitrate, Mn3Bi2(NO3)12.24H2O, is pale red; its density is 2.42, and it melts without decomposition at 43° to 44° C. In addition, mercury bismuth nitrate, Hg3Bi2(NO3)12.24H2O, has been obtained; it forms solid solutions with magnesium bismuth nitrate containing up to 25 per cent, of the mercury salt. Magnesium bismuth nitrate has been employed for the separation of the metals of the rare earths.

From an examination of the behaviour of normal bismuth nitrate, and of compounds of this salt with certain sugars and other organic substances, it has been suggested that the co-ordination formula should be

From a solution of bismuth nitrate in aqueous ammonium nitrate there is obtained by crystallisation a double compound which may be represented by

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