Determination of arsenic in foodstuffs contaminated by arsenical war gases.

Date:
1941
Catalogue details

Licence: Public Domain Mark

Credit: Determination of arsenic in foodstuffs contaminated by arsenical war gases. Source: Wellcome Collection.

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    Prolonged heating at this stage is, however, to be avoided, since the solution may become re-oxidised. The solution is finally made up to 100 ml. with distilled water. Til. Gutzeir DETERMINATION. The procedure given in Appendix VIII of the British Pharmacopoeia, 1932, may be used for the determination of arsenic in the solution from Stage II, but the Sanger and Black “‘strip”’ modification described below has been found to be more satis- factory and to give more consistently reliable results. An aliquot portion of the solution from II containing between 0-005 and 0-045 mg. of arsenic is transferred to a Gutzeit vessel (of height about 11 cm. and capacity up to the shoulder about 100 ml.). To the solution are added 3-5 ml. of conc. hydro- chloric acid (AsT.) and 0-5 ml. of stannous chloride (AsT.) solution. The sulphuric acid content is then adjusted to 1 ml., allowance being made for the residual sulphuric acid from the oxidation, and the bottle is filled with water up to the 50 ml. mark. The outlet tube of the apparatus is then prepared. A piece of specially prepared fluted lead acetate paper is placed in the bottom of the tube and glass wool soaked in lead acetate solution in the top, to ensure that no hydrogen sulphide reaches the mercuric chloride paper. The end of the outlet tube is then fitted with a narrow-bore glass tube, 10 cm. long x 0-4 cm. diameter, in which is placed a strip of mercuric chloride paper. This paper is inserted until the lower end is about 4 cm. above the bottom of the tube. About 20 pellets (approx. + inch high) of AsT. zinc are then introduced into the Gutzeit vessel and the outlet tubes immediately placed in position. The vessel is placed in a water bath maintained at about 15° C., and the gas evolution is allowed to proceed for 1 hour. The stain on the mercuric chloride paper is then fixed by dipping in molten paraffin wax (white, m.p. 60-80° C.) and compared with stains similarly prepared from standard arsenite solutions. PREPARATION OF REAGENTS, PAPERS AND STAINS FOR THE GUTZEIT PROCEDURE. Mercuric Chloride Papers —Whatman filter paper (No. 1) is dipped in 1 per cent. mercuric chloride solution, drained of excess liquid and then dried, away from all hydrogen sulphide and other fumes. When dry, the outside 4 inch is trimmed off and discarded, as this contains uneven concentrations of the mercury salt. The paper is then cut into strips 4mm. x 8 cm. and kept in a stoppered bottle coated with black to exclude hght. It is essential that a good quality paper be used for this purpose. Uneven thicknesses produce variable stains. A paper with a high content of reducing substances should not be used and a paper packed with kaolin or similar filler produces poor stains. The humidity of the paper is also a factor, air-dried Whatman No. 1 being the most consistent in this respect. Stannous Chloride Solution.—80 g. of Stannous Chloride (AsT.) are dissolved in 100 ml. of water and 5 ml. of conc. hydrochloric acid are added. Lead Acetate Paper.—Filter paper is impregnated by immersion in saturated lead acetate solution and air-dried. It is then cut into pieces 7 cm. x 5 cm. and fluted before being placed in the Gutzeit outlet tube.
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