Laboratory manual for the detection of poisons and powerful drugsAuthorized translation of the completely rev4th German ed. . hydrogen from 15-20 grams of zinc, treated with dilutearsenic-free sulphuric acid, through the strongly heated ignition tube C of theMarsh apparatus should not give a trace of arsenic after i hour. The metal isthen pure enough for use. Bertha spelter from the New Jersey Zinc Companywill meet such a test. ^ Add I volume of pure arsenic-free concentrated sulphuric acid to 5 volumes ofdistilled water. This diluted acid when cold is suitable for use in the M arsh test. META
Laboratory manual for the detection of poisons and powerful drugsAuthorized translation of the completely rev4th German ed. . hydrogen from 15-20 grams of zinc, treated with dilutearsenic-free sulphuric acid, through the strongly heated ignition tube C of theMarsh apparatus should not give a trace of arsenic after i hour. The metal isthen pure enough for use. Bertha spelter from the New Jersey Zinc Companywill meet such a test. ^ Add I volume of pure arsenic-free concentrated sulphuric acid to 5 volumes ofdistilled water. This diluted acid when cold is suitable for use in the M arsh test. METALLIC POISONS 151 generating hydrogen slowly. Otherwise, there is danger ofpartial reduction of sulphuric acid to sulphur dioxide and thento hydrogen sulphide which interferes more or less with thedetection of arsenic. Place the reduction flask A in a dish ofcold water, if the acid becomes too warm. Certain precautions are necessary in using the Marsh ap-paratus. 1. Have the apparatus absolutely tight. 2. Expel air completely before igniting hydrogen. To tellwhen this point is reached, collect hydrogen in a dry test-tube. Fig. 14.—Marsh Apparatus, (a) Hydrogen-generator; (6) Chloride of cal-cium drying-tube; (c) Hard glass tube; {d) Arsenic mirror. until it ignites without detonation when carried to a flame. Ifthe hydrogen stands this test, ignite the gas at the end of igni-tion tube C. There is no danger of an explosion within theapparatus. If the apparatus is tight and the evolution ofhydrogen is not too rapid, it requires about 8 minutes to expelthe air. 3. Test the hydrogen to insure its entire freedom from the arsenic mirror nor spot appears. If the hydrogen is arsenic-free, graduall}^ introduce theperfectly cold sulphuric acid solution, containing arsenic asarsenic acid (page 150), in small portions into reduction flask the same time heat ignition tube C to redness Just back of 152 DETECTION OF POISONS the capillary tube. If the solution contains ars
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