─────────────────────────────────────────────────────────────────────── 1. Concentrate sample. Add 10 cc. NH_{4}Cl, a few drops NH_{4}OH and saturate with H_{2}S. Allow to stand, add more NH_{4}OH and H_{2}S. Boil, filter, and wash. ────────────────────────────────────────────────────────┬────────────── 2. Dissolve the precipitate in dilute HNO_{3}. Filter │3. Reject the and wash. Evaporate to 10 or 15 cc. Cool. Add 5 cc. │filtrate which concentrated H_{2}SO_{4}, and heat until white fumes are│contains the given off. Dilute slightly and treat with 150 cc. of 50 │coloring per cent alcohol. Allow to stand; filter, and wash with │matter. 50 per cent alcohol. │ ──────────────────────────┬─────────────────────────────┤ 4. The precipitate │5. The filtrate contains the │ contains the Pb. Dissolve │Zn and Cu. Concentrate to │ in NH_{4}C_{2}H_{3}O_{2} │expel alcohol. Add excess of │ solution. Filter into a 50│NH_{4}OH, filter and wash │ cc. Nessler tube and wash │precipitate. │ with water containing ├──────────────┬──────────────┴────────────── NH_{4}C_{2}H_{3}O_{2}. │6. Reject the │7. The filtrate contains the Divide filtrate in halves.│precipitate │Zn and Cu. Neutralize with Saturate one-half with │which contains│H_{2}SO_{4}. Add 10 cc. H_{2}S. Determine the Pb │the Fe. │concentrated H_{2}SO_{4} and in the other half by │ │1 g. urea. Electrolyze for adding HC_{2}H_{3}O_{2} │ │two hours with a current of and H_{2}S and comparing │ │0.5 ampere. Break circuit, with standards containing │ │empty dish and wash. known amounts of Pb. │ │ ──────────────────────────┼──────────────┴───────────────────────────── 8. The deposit is Cu. │9. The solution contains the Zn. Nearly Immerse the cathode in a │neutralize with NH_{4}OH. Concentrate to small amount of hot, │less than the capacity of the dish. Add 2 g. dilute HNO_{3}; wash off │K_{2}C_{2}O_{4} and 1.5 g. K_{2}SO_{4}. and evaporate to dryness. │Electrolyze for 3 hours with a current of Take up in water and wash │0.3 ampere. Siphon off solution, break into a Nessler tube. Make │circuit, wash with water, then alcohol, dry up to mark, and add 10 cc.│at 70° C., cool and weigh. of potassium sulfide ├──────────────────────────────────────────── solution. Compare with │10. The weighed residue is metallic Zn. standard. If large amount │ is present, dry and weigh │ as Cu. │ ──────────────────────────┴──────────────────────────────────────────── Table 11.—SCHEME FOR DETERMINATION OF COPPER ONLY.