Sulphite precipitation

Jumau s process (ut supra) for the electrolytic extraction of copper from its ores is also applicable to the production of pure copper from solutions of its compounds.8 The cupric sulphite or cupro-cupric sulphite precipitated from the copper solution by the action of sulphurous acid or a sulphide is decomposed by sulphuric acid into cupric sulphate and metallic copper. The metal thus liberated is pressed into a form suitable for an anode, and refined electrolytically. 

Addition of barium chloride precipitates white barium sulphite ... 

Alternatively, the iodide is precipitated as copper(I) iodide by addition of copper(II) sulphate, in presence of sulphite, thus ... 

Copperil) oxide, CujO, occurs naturally as the red cuprite. It is obtained as an orange-yellow precipitate by the reduction of a copper(II) salt in alkaline solution by a mild reducing agent, for example glucose, hydroxylamine or sodium sulphite ... 

Oxidation to acids. Varm together in a small conical flask on a water-bath for lo minutes a mixture of 0 5 ml. of benzaldehyde or salicylaldehyde, 15 ml. of saturated KMn04 solution, and 0-5 g. of NajCOj. Then acidify with cone. HCl, and add 25% sodium sulphite solution until the precipitated manganese dioxide has redissolved. On cooling, benzoic or salicylic acid crystallises out. 

Cuprous bromide. The solid salt may be prepared by dissolving 150 g. of copper sulphate crystals and 87 5 g. of sodium bromide dihydrate in 500 ml. of warm water, and then adding 38 g. of powdered sodium sulphite over a period of 5-10 minutes to the stirred solution. If the blue colour is not completely discharged, a little more sodium sulphite should be added. The mixture is then cooled, the precipitate is collected in a Buchner funnel, washed twice with water containing a little dissolved sulphurous acid, pressed with a glass stopper to remove most of the liquid, and then dried in an evaporating dish or in an air oven at 100 120°. The yield is about 80 g. 

Another method for the hydroxylation of the etliylenic linkage consists in treatment of the alkene with osmium tetroxide in an inert solvent (ether or dioxan) at room temperature for several days an osmic ester is formed which either precipitates from the reaction mixture or may be isolated by evaporation of the solvent. Hydrolysis of the osmic ester in a reducing medium (in the presence of alkaline formaldehyde or of aqueous-alcoholic sodium sulphite) gives the 1 2-glycol and osmium. The glycol has the cis structure it is probably derived from the cyclic osmic ester ... 

The soluiiou of silver nitrate is acidified with dilute uitric scid, boiled so 49 to decompose an v ailvov sulphite that might have been formed, aud the precipitate filtered, washed, etc. 

Determination of sulphite by oxidation to sulphate and precipitation as barium sulphate Discussion. Sulphites may be readily converted into sulphates by boiling with excess of bromine water, sodium hypochlorite, sodium hypobromite, or ammoniacal hydrogen peroxide (equal volumes of 20-volume hydrogen peroxide and 1 1 ammonia solution). The excess of the reagent is decomposed by boiling, the solution acidified with hydrochloric acid, precipitated with barium chloride solution, and the barium sulphate collected and weighed in the usual manner (Section 11.72). 

Mssolve 10 g. of p-nitroaniline (Section IV,51) in a mixture of 21 ml. of concentrated hydrochloric acid and an equal volume of water, and cool rapidly to 0° in order to obtain the hydrochloride of the base in a fine state of division. Diazotise in the usual way (see Section IV,68) by the gradual addition of a solution of 6 0 g. of sodium nitrite in 12 ml. of water. Continue the stirring for a few minutes, filter the solution rapidly, and add it from a separatory funnel to an ice-cold solution of 41 g. of sodium sulphite (90 per cent. Na2S03,7H20) in 100 ml. of water containing 4 g. of sodium hydroxide (1) stir the mixture during the addition which requires about 5 minutes. (If the diazonium solution is added too rapidly, an orange-red precipitate of sodium p-nitrodiazobenzene sulphonate is produced, and is apt to form a resin.) AUow the solution to stand for... 

The alkaline sodium sulphite solution may be replaced by saturated amtnonlum sulphite solution prepared as follows. Pass sulphur dioxide into a mixture of 1 part of concentrated ammonia solution (sp. gr. 0-88) and two parts of crushed ice in a freezing mixture imtil the liquid smells strongly of sulphur dioxide, and then neutralise with ammonia solution. This solution slowly deposits ammonium sulphite crystals and contains about 0-25 g. of SOj per ml. Use 60 ml. of this ice-cold ammonium sulphite solution to which 8 ml. of concentrated ammonia solution are added. After the addition of the solution of p-nitrophenyldiazonium chloride, allow the mixture to stand for 1 hour in a freezing mixture, filter oft the yellow precipitate of ammonium p-nitrophenyUiydrazine disulphonate, heat it on a water bath with 20 ml. of concentrated hydrochloric acid at 70-80° for 7 minutes, cool the blood-red solution, and dissolve the resulting precipitate of p-nitrophenylhydr-azine hydrochloride and ammonium salts in water, and isolate the base as above. 

In the other study [155], ammonia-complexed Hg(N03)2 was mixed with the selenosulphate solution. As for the corresponding HgS deposition, a white precipitate formed on addition of ammonia to the HgCNOs) [Eq. (4.9)]. This precipitate dissolved partly in the excess ammonia used, due to formation of various am-mine complexes, and completely when the selenosulphate solution was added, due to additional formation of selenosulphate (and maybe sulphite from the excess sulphite in the selenosulphite solution) complexes. It is likely that mixed ammine-selenosulphate/sulphite complexes were formed. The deposition was carried out on polyester substrates (the transparencies used in overhead projectors) at 10°C. Deposition occurred over several hours to a terminal thickness of ca. 250 nm. Bulk precipitation occurred in parallel with the deposition, suggesting that the cluster mechanism was dominant. 

When solutions of sulphites are mixed with solutions of srgentio nitrate, a white precipitate of argentic sulphite is formed "... 

In 1862, E. C. C. Stanford proposed the carbonization of the drift-weed in closed retorts so as to recover tar and ammoniacal liquor in suitable condensers. This modification did not flourish because of the subsequent difficulties in extracting soluble iodides from the charcoal. V. Vincent (1916) claims that soln. containing aluminium sulphate extract the alkali iodides from seaweed leaving behind the organic matter which prevents the direct precipitation of iodine or iodides. The alkali iodide soln. is treated with copper sulphate for cuprous iodide, or by soln. of sulphites for iodine. M. Paraf and J. A. Wanklyn proposed to heat the drift-weed first with alkali hydroxide so as to form oxalic and acetic acids, which could be crystallized from the lixivium. The economical treatment of seaweed for iodine has been discussed by A. Puge. 

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