The determination of sulphur in copper

Sulphur contents in unalloyed copper are usually below 50 Mg/g. alloys may contain a few 100 /jg/g. 

Analysis of Metals (1) proposes the combustion method combined with iodo-metric titration for the determination of sulphur concentrations above 50 Mg/g. The sample weight is 1 g. The combustion is carried out in a tube furnace at 1250 to 1300°C, using oxygen. The combustion gases are absorbed in 100 ml hydrochloric acid (3+200). The titration is performed using a potassium iodate-iodide solution (0.2225 g KIO /l) and starch as indicator, whereby in the course of the combustion so much iodate solution has to be continuously added that the light blue colour of the solution does not vanish. When the combustion is running lower it has to be titrated slowly. 

The reliability is reported to be 10 % (sulphur level 100 Mg/g). The method may also be applied to the analysis of copper alloys. The combustion of a standard sample of the same alloy type is used for calibration. 

Rooney and Scott (4) report that the recovery of sulphur dioxide varies from 61 to 83 % when the combustion temperature of a resistance type furnace is increased from 1200° to 1400°C and the oxygen flow rate from 1 to 2 liters per miqute. Radiochemical investigations show that when the sulphur present in the cast iron was evolved and titrated as sulphur dioxide, approximately 4 % was not trapped by the absorbent and 12 % remained behind in the boat or combustion tube. Fulton and Fryxell (5) studied the recovery of sulphur dioxide after combustion in an induction furnace and found a yield of 85 to 92 %, depending on the method of determination. 

Burke (3) concludes that unless many precautions are taken, a combustion procedure for the determination of sulphur will generally be empirical. 

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Based on the reaction between sulphides and hydrogen at higher temperatures, a method for the determination of sulphur in copper has been elaborated by Watson et al. (15). The sample is placed in a porcelain or alumina boat and introduced into a quartz tube, heated at 1100 to 1150°C by a resistance furnace and through which flows a stream of ultrapure hydrogen. Hydrogen sulphide released by the hot and/or molten metal is carried by the gas stream and absorbed by a sodium hydroxide solution. Fig. XI-4 shows the apparatus used. 

EXPERIMENTAL PROCEDURE FOR THE DETERMINATION OF SULPHUR IN COPPER AND NICKEL... 

Vandecasteele et al. (22) describe the determination of sulphur in copper and nickel. 

In addition to several empirical methods involving the evaluation of the a-cellulose content or the copper number of cellulose, there are methods such as the determination of furfural, mentioned in Chapter VI. Interest was also paid to the determination of sulphur in viscose rayon. 

The same problems exist thus with the determination of sulphur in nickel as with sulphur in copper. Also here, the dissolution methods are the more accurate ones. In any case, the combustion methods need reference materials with known sulphur contents to establish a reliable calibration. 

The Food and Agriculture Organization of the United Nations has recommended methods for the determination of mercury in pesticides. The method selected depends on the other constituents of the formulation and in the presence of copper the method of Brookes and Solomon (see p. 419) is most suitable. In the presence of most other constituents the selected method is one in which the sample is refluxed with concentrated sulphuric acid and potassium nitrate before determining the mercury volumetrically with thiocyanate. When large amounts of calcium carbonate or highly chlorinated compounds e,g, benzene hexachloride) are present, the mercury is isolated as a sulphide before conversion to the ionic form with strong acid. 

Atchinson and Beamer (14) describe the determination of phosphorus and sulphur in magnesium. Foster and Gaitanis (15) and Plumb (16) describe the determination of phosphorus in aluminium. The determination of phosphorus and sulphur in aluminium, magnesium, copper, iron and nickel was studied in considerable detail by Albert et al. (12)( 17)(18). 

This method allows the determination of sulphur concentrations as low as 5 /ig/g in copper. Since it is however subjected to interferences, it is not described in detail. 

According to Analysis of Metals (1) a method similar to that for copper can be used. Two g of chips are combusted at 1400 to lASO C in an oxygen stream in a tube furnace. The combustion boat is filled with the nickel chips, which are then covered by 2 g of copper chips. The determination of sulphur dioxide is carried out by iodometric titration. 

The Ag-DDTC method was used for determination of arsenic in waters [42,47,78-80], plant materials [41,48], food products [82], sewage and sediments [83], iron ores [44], cast iron and steel [45,84], copper and its salts [22,45], silver and gold [85], high purity reagents [21,46], germanium dioxide [86], hydrofluoric acid [87], phosphorus compounds [88], and sulphur 89]. 

The pararosaniline method has found numerous applications owing to its sensitivity and selectivity. It has been used in determinations of sulphur (or SO2) in air [22,97,98], plants [99,100], wine [101], soils [102], organic compounds [25], selenium [103], and copper [6,8]. This method has also been applied for continuous determination of SO2 in wine [ 104,105]. 

Dithizone is also used for the determination of metallic compounds such as copper (II) (Fig. 28). Because of the slight aqueous solubility of this compound, UV-visible spectra have been acquired in methanol/water (50/50) solution (Fig. 29). In strong acid medium (pH = 2.0), the maximum of absorption in the visible region is located at X = 588 nm (e = 13,700 Lmol-1 cm-1). A protonation may occur on the sulphur atom. The coloration of the solution is dark blue. In basic medium (pH = 12.0), the colour turns to orange X = 472 nm, e = 8100 Lmol-1 cm-1). Two isosbestic points, located at X = 425 nm and X = 517 nm, confirms this phenomenon. 

Chenevix obtained chlorine dioxide by the action of sulphuric acid on potassium chlorate, but he did not determine its composition. He analysed corundum and examined the chemical nature of the humours of the eye. Nicolas found phosphate of lime in them, but this was not found by Chenevix or by Berzelius. Chenevix analysed native cuprous oxide ( red octahedral copper ore ) from Cornwall, finding its composition more correctly than Proust (see p. 646), and several other minerals, and examined the magnetism of nickel and cobalt. He criticised the mineralogical systems of Werner and Haiiiy. ... 

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