Barium Acetate Sulphide

Crucibles fitted with permanent porous plates are cleaned by shaking out as much of the solid as possible, and then dissolving out the remainder of the solid with a suitable solvent. A hot 0.1 M solution of the tetrasodium salt of the ethylenediaminetetra-acetic acid is an excellent solvent for many of the precipitates [except metallic sulphides and hexacyanoferrates(III)] encountered in analysis. These include barium sulphate, calcium oxalate, calcium phosphate, calcium oxide, lead carbonate, lead iodate, lead oxalate, and ammonium magnesium phosphate. The crucible may either be completely immersed in the hot reagent or the latter may be drawn by suction through the crucible. 

Another volumetric process which has been recommended consists in reducing the sulphuric acid or sulphate (excepting barium sulphate) by heating with a mixture of hydriodic acid, phosphorus and phosphoric acid, absorbing the resulting hydrogen sulphide in a solution of zinc acetate, and estimating the precipitated zinc sulphide iodo-metrically.2... 

Sulphides.—The 1 20 aqueous solution of barium hydroxide, when acidulated with hydrochloric acid, should not have an odor of hydrogen sulphide, nor should it acquire a dark color on adding lead acetate solution. 

Qualitative Examination.—A few grams of the substance are treated repeatedly with boiling water and filtered the solution may contain lead acetate and calcium sulphate (if both are present, however, soluble calcium acetate and insoluble lead sulphate are formed). In the solution lead is tested for with hydrogen sulphide, calcium (after elimination of the lead) with ammonia and ammonium oxalate, and sulphuric add with barium chloride. Acetic add may be detected in a separate portion of the substance by moistening it with sulphuric add and a few drops of alcohol and heating gently in presence of acetates, the odour of ethyl acetate is observed. 

The residue insoluble in water or a new portion of the substance is treated with dilute acetic acid, in which the zinc oxide should dissolve easily without evolution of gas. Effervescence indicates carbonates (white lead, chalk) if hydrogen sulphide is evolved, zinc sulphide (lithopone) may be present. Any residue insoluble in acetic acid may contain lead, barium or calcium sulphate or day, these being recognised as in white lead (q.v., paragraph i). Lastly, the acetic acid solution, when treated with caustic soda, should give a white precipitate quite soluble in excess of alkali and the alkaline solution should give a white precipitate with ammonium sulphide. 

The acid filtrate is treated with excess of ammonium chloride and with ammonia to precipitate the ferric oxide and any alumina, the precipitate being tested for the latter in the usual way. The filtrate is divided into three parts one is acidified with acetic acid and tested for copper with ferrocyanide in another the manganese (if present) is precipitated with ammonium sulphide, lime and magnesia being then tested for in the third sulphates are tested for with barium chloride. Manganese is best sought in a separate portion of the substance by the well-known dry reaction. 

The test is usually carried out by adding the reagent to the solution acidified with dilute hydrochloric acid carbonates, sulphites, and phosphates are not precipitated under these conditions. Concentrated hydrochloric acid or concentrated nitric acid should not be used, as a precipitate of barium chloride or of barium nitrate may form these dissolve, however, upon dilution with water. The barium sulphate precipitate may be filtered from the hot solution and fused on charcoal with sodium carbonate, when sodium sulphide will be formed. The latter may be extracted with water, and the extract filtered into a freshly prepared solution of sodium nitroprusside, when a transient, purple colouration is obtained (see under Sulphides, Section IV.6, reaction 5). An alternative method is to add a few drops of very dilute hydrochloric acid to the fused mass, and to cover the latter with lead acetate paper a black stain of lead sulphide is produced on the paper. The so-called Hepar reaction, which is less sensitive than the above two tests, consists of placing the fusion product on a silver coin and moistening with a little water a brownish-black stain of silver sulphide results. 

Sulphurj in the unoxidized condition, is tested for by heating the compound with metallic sodium or with sodium carbonate, by which treatment the sulphur is converted into sodium sulphide. If the fused product is placed on a silver coin and moistened, a spot of siVoer sulphide will be produced. The fused mass may also be dissolved in water, neutralized with nitric acid, and a little lead acetate solution added. The formation of a black precipitate of lead sulphide proves the presence of sulphur. These tests are applicable only in case the sulphur is in an unoxidized form. To test for sulphur in either the oxidized or unoxidized form a little of the compound is boiled with strong nitric acid or is heated with sodium peroxide. This treatment converts the sulphur into the form of sulphuric acid or a sulphate, either of which will yield a white precipitate of barium sulphate when tested with barium nitrate in the presence of nitric acid. 

Characters and Tests.—Thin, translucent, and colourless crystalline plates, of a pearly lustre, with a sharp unpleasant taste evolving acetic acid (recognisable by the characteristic odour of its vapour) when decomposed by sulphuric acid soluble in water, forming a solution which gives a white precipitate (zinc sulphide) with sulphuretted hydrogen. A dilute aqueous solution should not be aflected by barium chloride (showing the absence of sulphates), or by... 

The use of water in place of organic solvents as a paint thinner has obvious attractions. The first important commercial product of this type was the oil-bound water paint, the vehicle being an emulsion of oil or varnish in an aqueous solution of gelatine. The preferred white pigment was lithopone (zinc sulphide/ barium sulphate), and a high ratio of pigment to binder was used. This product was eventually replaced by the emulsion paint (known as latex paint in USA and dispersion paint on the continent of Europe). It used a synthetic vinyl polymer as a binder, mainly a co-polymer of vinyl acetate with either vinyl versatate or butyl acrylate, with titanium dioxide as the white pigment. Attempts to use an alkyd emulsion based on oil as the vehicle were commercially unsuccessful. The droplet size of the dispersion at emulsion is normally about 0.2-1 //m. 

Make a standard zinc solution by dissolving 7-70 g of zinc in about 75 ml of dilute hydrochloric acid, adding excess of ammonia solution and diluting to 1 litre. Make an alkaline lead solution by dissolving 1 g of lead acetate in about 20 ml of hot 5 per cent potassium hydroxide solution and diluting to 100 ml. Heat to boiling about 1 g of barium sulphide in about 50 ml of water and titrate with the standard zinc solution until no black or brown colour is obtained by adding a drop of the filtered barium solution to a drop of the lead indicator, spotted on a porcelain tile. 1 ml zinc solution = 0 0201 g BaS. 

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