Bismuth Thiosulphates

Bismuth thiosulphate itself has not yet been prepared. Addition of a thiosulphate to a bismuth solution results in the precipitation of bismuth trisulphide, a reaction which has been recommended for the separation and detection of bismuth.1 Several complex compounds containing bismuth and alkali or alkaline earth thiosulphates have been described, however; solutions of these are in general acid, and do not respond to the usual reactions for thiosulphates unless they are made neutral; it is suggested that they contain an unstable anion Bi(S₂O₃)₃^-3.

Sodium Bismuth Thiosulphate, Na₃Bi(S₂O₃)₃, is obtained in the form of orange-yellow crystals when bismuth nitrate is rubbed with excess of sodium thiosulphate. The mixture is extracted with aqueous alcohol, and the compound precipitated as a yellow oil by addition of more alcohol, crystals being obtained by drying over sulphuric acid. A solution of this salt has been suggested as a reagent for the detection and estimation of potassium, but has been found unsatisfactory for the purpose, as the potassium salt precipitated is always contaminated with the sodium salt. A crystalline precipitate of sodium bismuth thiosulphate has also been obtained by the action of aniline and alcohol on a solution containing bismuth oxynitrate, acetic acid and sodium thiosulphate. By the interaction of a solution of bismuth nitrate in mannitol and sodium thiosulphate in the presence of manganese chloride a compound, more stable than that described by Hauser, has been obtained in the form of small octahedra to which the formula Na₃Bi(S₂O₃)₃ has been ascribed.

Potassium Bismuth Thiosulphate, K₃Bi(S₂O₃)₃, is obtained by precipitation from a solution of the sodium salt on adding a potassium salt and alcohol, or by the addition of solutions of potassium chloride and sodium thiosulphate to one of bismuth trioxide in hydrochloric acid. It may be obtained in the anhydrous and hydrated forms. The corresponding salts of rubidium and caesium, Rb₃Bi(S₂O₃)₃ and Cs₃Bi(S₂O₃)₃, both of which are yellow, crystalline powders, ammonium, (NH₄)₃ Bi(S₂O₃)₃, strontium, Sr₃[Bi(S₂O₃)₃]₂, barium, Ba₃[Bi(S₂O₃)₃]₂, silver and copper have been prepared in a similar manner. The barium and strontium salts are readily hydrolysed by water, the silver salt decomposes in a few seconds with the formation of a black compound, while the copper salt is precipitated only on the addition of alcohol.

By the interaction of the double thiosulphate of sodium and thallium with bismuth trichloride, a thallium bismuth thiosulphate, Tl₃Bi(S₂O₃)₃, is obtained. It may also be prepared by the interaction of a thallous salt with potassium bismuthothiosulphate, but it is soluble in excess of the latter. It is a sparingly soluble, microcrystalline yellow powder. Although moderately stable in neutral solutions, it is readily decomposed by acids with evolution of sulphur dioxide and precipitation of bismuth trisulphide, the latter being quantitative.

Attempts to obtain bismuth dithionate and bismuth trithionate have proved unsuccessful.