Sulphide, definition

Sulphides.—Definite sulphides of niobium have not been prepared. Solutions of alkali niobates do not yield precipitates with hydrogen... 

Sulphur. Moisten the centre of a filter-paper with lead acetate solution. Then add about 10 ml. of dilute hydrochloric acid to the residue in the evaporating-basin, and at once cover the latter with the paper. If zinc sulphide is present in the residue, the hydrogen sulphide evolved will give a definite daA brown coloration with the lead acetate paper. The presence of hydrogen sulphide can often be confirmed by its odour. 

Evans, D.T.W. Kean, B.F. 2002. The Victoria Lake Supergroup, central Newfoundland - its definition, setting and volcanogenic massive sulphide mineralization. Open File NFLD/2790, 80 p. 

The precipitate on analysis gave the ratio Ba 90AsaS8. The constancy of the ratio however depends entirely on the size and charge of the arsenious sulphide particles, since the reaction proceeds to the isoelectric point, i.e. electrical neutrality, and is therefore independent of any definite stoichiometric ratio of reactants. 

In the tables for both Cu-S and Cu-Se (Tables 6.4 and 6.5), the column denoting conductivity type has been deleted (these semiconductors are always p-type), and, in its place, the phase (and/or composition) has been given. In some cases, particularly for the sulphides, where no XRD pattern was seen (except for CuS), no phase (or composition) was proven and therefore no entry is given in the table. This was not a problem for Cu-Se, since XRD spectra were always clear and definitive. 

A mixture of ammonia and hydrogen sulphide does not unite if the press, is less than a certain critical value, which depends on the temp. If the press, is at or above this value crystals of ammonium hydrosulphide are formed if the press, be increased,more crystals will form and if the press, be reduced, crystals will decompose. When the two gases are present in eq. amounts this press, is called the dissociation pressure of the solid. In the present case, if the vapour phase has the same composition as the solid with which it is in equilibrium, the system is univariant, and there is a definite dissociation press, for each temp. F. Isambert found the dissociation press, of ammonium hydrosulphide, in mm. of mercury, increases rapidly with a rise of tomp. ... 

It is probable that the inconstancy of the results obtained by various investigators for the specific gravity and other characteristics of y-sulphur is due to contamination of the substance examined with other forms of sulphur or with foreign substances. Such a probability is increased by the description of a hydrated form of amorphous sulphur the composition of which points to its being a definite hydrate, S8.H20 this compound is stated to be obtainable by the interaction of hydrogen sulphide and sulphurous acid in aqueous solution.5... 

Other forms of amorphous sulphur, which have been described at various tunes in chemical literature, are the so-called blue sulphur and black sulphur our present state of knowledge of these is far from satisfactory, and their existence as definite modifications of pure sulphur is questionable, especially in the case of the latter variety, the colour of which appears to be due to small quantities of carbon or of metallic sulphides.1... 

Of these, the first reaction is the one usually recorded, and in the majority of cases it is the one that occurs to the largest extent. The presence of alkali pushes the equilibrium well to the left, so that in alkaline solution the thiosulphate is stable. This explains the formation of thiosulphates on boiling alkaline sulphite solutions with sulphur. The laws of chemical equilibria, however, demand the presence of perfectly definite although perhaps very small quantities of sulphite and free sulphur in solution, and if alkaline thiosulphate solutions containing alkali sulphide are boiled in the absence of air, they become deep yellow, owing to polysulphide formation, the extra sulphur for which is obtained from the thiosulphate. Assuming the sodium derivatives to be used, the equation may be written... 

On the other hand, much stronger evidence is available in favour of the earlier formula,4 which accords well with the relationship between the acid and the polythionic acids.5 The formation of sodium thiosulphate by Spring s synthesis from sodium sulphide and sodium sulphite (p. 194) is definitely favourable to this constitution, as also especially is the fact that an alkali thiosulphate will react with only an equimoleeular proportion of an organic (alkyl) halide,6 the product... 

Hydrogen sulphide reduces selenious acid solution with formation of a mixture of selenium and sulphur.13 The proportion of the two elements in the precipitate varies with the conditions. At one time this precipitate was regarded as a definite sulphide of selenium, but the sulphur can be entirely extracted by a mixture of benzene and carbon disulphide. The so-called sulphur selenide obtained by fusing together sulphur and selenium probably is also not a true compound, but only mixed crystals of the elements.14... 

Certain unstable thiotellurites have been prepared by the action of hydrogen sulphide on solutions of alkali tellurites, the most definite being the potassium salt, K2TeS3.5... 

Vanadium Oxysulphides.—No vanadium oxysulphides of definite composition have been prepared. By the action of acids on solutions of vanadium pentoxide in ammonium sulphide, or on solutions of alkali vanadates which have been saturated with hydrogen sulphide, brown precipitates are obtained which consist of oxysulphides of variable composition.1... 

Borodowski1 failed to obtain evidence of the formation of this sulphide in his study of the freezing point curves (see p. 237) because, with mixtures containing 20 to 60 molar per cent, of arsenic, the products are viscous and do not give definite freezing points. 

These colours, termed also bronze pigments, generally consist of finely powdered metals or metallic alloys, sometimes partially oxidised or sulphided to obtain definite colours. The principal metals used for this pur-A.c, 11, 26... 

Orange-red diamagnetic complexes of Pd and Pt with mercaptoacetic acid and 3-mercaptopropionic acid have been reported (see p. 390)48 Simple bis-complexes of N-pyrrolidyl monothiocarbamate with Pd and Pt are not formed,50 but i.r. studies indicate that the tetrakis-complexes are bonded through both O and S, although no definite structure has been proposed. Extraction of the metals Pd, Pt, Ag, and Au from aqueous solution by a large number of alkyl and alkene disulphides and sulphides has been reported (see p. 390).51,52... 

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