Preparation of Hydrogen Sulphide

These two gases can readily be prepared by the action of acids on selenides and tellurides respectively, the reactions being analogous to that for the preparation of hydrogen sulphide. 

Preparation of Hydrogen Sulphide from Its Elements. Perform the experiment in the presence of your instructor ) Assemble an apparatus as shown in Fig. 65 and check... 

Discussion As was pointed out in Experiment 53, hydrochloric acid, or as it may be called hydrogen chloride, was formed by the double decomposition between a chloride and an acid, under such conditions that the hydrogen chloride could escape. In a similar way hydrogen sulphide may be prepared by double decomposition between a sulphide and an acid. Since hydrogen sulphide is only slightly soluble in water, the reaction may take place in dilute solution, so that a solution of hydrochloric acid may be used as the necessary acid. The sulphides of many metals are so insoluble that this double decomposition takes place chiefly in the reverse direction and so these sulphides can not be used for the preparation of hydrogen sulphide. 

Sulphur. Moisten the centre of a filter paper with sodium plumbite solution. Add about 10 ml. of dilute hydrochloric acid to the residue in the dish and immediately cover it with the prepared filter paper. If zinc sulphide is present in the residue, a dark brown stain, visible on the upper surface of the paper, will be obtained frequently the presence of hydrogen sulphide can also be detected by its odour. 

Hydrogen sulphide is used in the preparation of metal sulphides, oil additives ete., in the purifieation and separation of metals, as an analytieal reagent and as raw material in organie synthesis. It burns in air with a blue flame ... 

Consequently, the ammonia (sp. gr. 0 88) must be diluted with at least four times its volume of water in order that the hydrogen sulphide and ammonia may unite in equal volumes. The quantity of hydrogen sulphide taken up by one mol. of ammonia does not vary continuously with the cone., but remains constant, NH3 H2S=1 1 for wide limits when the dilution exceeds 1 4. It follows from the fifth of the above experiments that the most cone. soln. contains less than 19 per cent, of ammonium hydrosulphide, NH4HS, and that corresponding with the 1 4 dilution contains 16 per cent. NH4HS consequently, the most cone. aq. soln. of ammonium hydrosulphide which can be prepared by this process contains between 16 and 19 per cent, of that salt. 

Preparation of Crystalline Cadmium Sulphide. Dissolve 3 g of cadmium sulphate in 80 ml of water, add 20 ml of a 1 N sulphuric acid solution to the reaction vessel, and pass a stream of hydrogen sulphide through it up to complete precipitation of cadmium sulphide. Filter off the cadmium sulphide precipitate, wash it several times with water saturated with hydrogen sulphide, remove it from the filter, and dry it in a drying... 

Preparation of Cadmium Pigments. Place two thin layers (from 0.5 to 1 g) of cadmium carbonate spaced 6 cm apart into the middle part of a refractory glass tube 40 cm long and 5 cm in diameter and pass a stream of hydrogen sulphide through the tube. When the colour of the first layer changes, heat the place of the reac-... 

Selenic Acid, HaSe04.—This acid was first prepared by Mitscher-lich in 1827, who suspended lead selenate in water and precipitated the lead by means of hydrogen sulphide. By the oxidation of aqueous solutions of selenious acid with suitable reagents, e.g. chlorine or bromine, selenic acid may also be obtained.6 When chlorine is used, any hydrogen chloride must be removed as soon as it is formed, for selenic acid is reduced by hot hydrogen chloride to selenious acid, with liberation of chlorine the process is best carried out6 by passing a... 

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... 

---