By W. T. Elwell
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Extra resources for Analysis of Copper and its Alloys
M. of bismuth by increasing the sample weight. Alloying amounts of lead and tin also interfere, because these elements are precipitated in the procedure as lead sulphate and metastannic acid respectively, with consequential coprecipitation of bismuth. In a recently developed procedure, which is suitable for the simultaneous determination of 0Ό05 to 0-04 per cent of bismuth and [ 5 ]1 0-02 to 0-5 per cent of antimony in copper a l l o y s , interference by tin and lead is eliminated if tartaric acid and E D T A , respectively, are present.
And the complete scheme of analysis is as follows: After the precipitation (and filtration) of arsenic, selenium and tellurium with hypophosphorous acid, antimony and bismuth remaining in solution are deposited on to copper foil (Reinsch reaction), and are afterwards recovered by solution in sodium peroxide. Copper (from the foil) and bismuth are precipitated as sulphides, and antimony is determined colorimetrically as the pyridine/iodide complex. The precipitate of elemental arsenic, selenium and tellurium is dissolved, selenium is precipitated with hydriodic acid, recovered and oxidised to selenous acid; the trace of copper invariably present in solution is removed as the cobalticyanide, and the determination of selenium is completed iodometrically.
Calculate the arsenic content of the sample. NOTE. If the arsenic content of the sample exceeds about 0-25 per cent, titrate with potassium bromate solution (0Ό2Ν). It is an advantage to add the indicator just before the end-point is reached, but this can only be done if the arsenic content of the sample is known within certain limits. 2. 1. Special Procedure Reagents STANDARD ARSENIC SOLUTION. Dissolve Ο· 1320 g of arsenous oxide (dried at 105°C) in 5 ml of sodium hydroxide solution (5 per cent).