Chemical elements
    Physical Properties
      Atomic Weight History
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    PDB 12ca-1ai0
    PDB 1aiy-1b6z
    PDB 1b71-1bs8
    PDB 1bsk-1cao
    PDB 1caq-1ctt
    PDB 1ctu-1de6
    PDB 1def-1dy0
    PDB 1dy1-1ed6
    PDB 1ed8-1exk
    PDB 1eyf-1fj9
    PDB 1fjg-1g0e
    PDB 1g0f-1gkq
    PDB 1gkr-1ha5
    PDB 1hbm-1hso
    PDB 1hsz-1i6v
    PDB 1i73-1im5
    PDB 1iml-1jcv
    PDB 1jcz-1jy8
    PDB 1jyb-1kh4
    PDB 1kh5-1kys
    PDB 1kzo-1llm
    PDB 1llu-1m7j
    PDB 1m9j-1mwo
    PDB 1mwq-1ndv
    PDB 1ndw-1nyq
    PDB 1nyr-1os4
    PDB 1os9-1p9w
    PDB 1paa-1pud
    PDB 1pv8-1q9l
    PDB 1q9m-1qv6
    PDB 1qv7-1r6o
    PDB 1r79-1ro9
    PDB 1ror-1sfo
    PDB 1sg0-1t3k
    PDB 1t4k-1tkh
    PDB 1tkj-1u0l
    PDB 1u10-1ums
    PDB 1umt-1v67
    PDB 1v6g-1vrq
    PDB 1vs0-1wew
    PDB 1wfe-1wwf
    PDB 1wwg-1xb1
    PDB 1xb8-1xpz
    PDB 1xq0-1y5w
    PDB 1y5x-1ylk
    PDB 1ylo-1z8r
    PDB 1z93-1zkx
    PDB 1zl6-258l
    PDB 2a03-2afo
    PDB 2afs-2atq
    PDB 2au3-2bfz
    PDB 2bg2-2c3a
    PDB 2c4r-2cij
    PDB 2cim-2czr
    PDB 2d0w-2djw
    PDB 2dkc-2e1b
    PDB 2e1s-2eer
    PDB 2eex-2em4
    PDB 2em5-2eoj
    PDB 2eok-2erq
    PDB 2esf-2fa7
    PDB 2fac-2fpx
    PDB 2fqp-2g84
    PDB 2g87-2gvf
    PDB 2gvi-2han
    PDB 2hap-2huc
    PDB 2hue-2imc
    PDB 2imr-2j65
    PDB 2j6a-2jq5
    PDB 2jr7-2kfn
    PDB 2kft-2l75
    PDB 2lgv-2nx9
    PDB 2nxa-2oc8
    PDB 2occ-2osm
    PDB 2oso-2p53
    PDB 2p57-2pow
    PDB 2ppb-2q8j
    PDB 2qa1-2qp6
    PDB 2qpj-2r71
    PDB 2r74-2sod
    PDB 2srt-2v86
    PDB 2v87-2vp7
    PDB 2vpb-2vyo
    PDB 2vz5-2wey
    PDB 2wfq-2wx0
    PDB 2wx1-2xam
    PDB 2xan-2xr9
    PDB 2xrg-2ytd
    PDB 2yte-2z30
    PDB 2z3g-2zet
    PDB 2zh0-3a32
    PDB 3a36-3aoi
    PDB 3at1-3bk1
    PDB 3bk2-3byr
    PDB 3byw-3cia
    PDB 3ciz-3d08
    PDB 3d09-3dbu
    PDB 3dc3-3dp6
    PDB 3dpe-3e1w
    PDB 3e1z-3ebh
    PDB 3ebi-3epk
    PDB 3epl-3f28
    PDB 3f2b-3fhe
    PDB 3fhp-3ful
    PDB 3fum-3g9y
    PDB 3ga3-3gpu
    PDB 3gpx-3h2w
    PDB 3h3e-3hfy
    PDB 3hgz-3hsn
    PDB 3hso-3i8v
    PDB 3i9b-3ij6
    PDB 3ijf-3ixe
    PDB 3iz0-3k34
    PDB 3k35-3kiy
    PDB 3kj1-3kvt
    PDB 3kwa-3lat
    PDB 3lcn-3lrr
    PDB 3ls1-3m1n
    PDB 3m1v-3mek
    PDB 3men-3mru
    PDB 3ms0-3n63
    PDB 3n64-3nin
    PDB 3nis-3ny2
    PDB 3ny3-3ohc
    PDB 3ohd-3oyl
    PDB 3oym-3pih
    PDB 3pki-3r0d
    PDB 3rj7-3t74
    PDB 3t87-3u9g
    PDB 3ua7-3v24
    PDB 3v25-4agl
    PDB 4agm-4dih
    PDB 4dii-4efs
    PDB 4eg2-4fc8
    PDB 4fgm-6tli
    PDB 6tmn-9nse

Electrodeposition of Zinc

It is difficult both to deposit zinc completely by electrolysis and to obtain good deposits. The frequent sponginess, looseness, or porosity of electrolytically deposited zinc has been ascribed to the presence of oxide or hydride. Occluded hydrogen may make the deposit brittle, and if the temperature rises to about 80° C. the zinc adheres badly to the cathode. Zinc is usually prepared electrolytically from sulphate solutions.

To obtain satisfactory deposits by electrolysis the current density at the cathode should be uniform and the acidity should be constant. High-current densities promote efficient deposition: investigation has steadily raised the suitable current density from about 1 amp. per sq. dcm. to about 20 amp., and up to 50. More positive metals than zinc should be absent. Copper and cadmium, if present in the electrolyte, are deposited with the zinc. The presence of iron is said to contaminate the zinc very little under efficient conditions for electrolysis, though Mcintosh mentions a low iron content in the electrolyte as one condition for good deposition. Mcintosh also says that colloids should not be present, but they increase the efficiency according to Hansen, and Pring and Tainton say that a little colloidal matter favours the electrolysis by producing bright, adherent deposits and permitting a higher current density which secures greater current efficiency. Neutral solutions, or solutions as neutral as possible, have been advocated, but acid solutions seem to be effective if the other conditions are good.

Zinc can be deposited from commercial solutions, according to Pring and Tainton, with an efficiency of 95 per cent, if the concentration of sulphuric acid is about 15 grm. per 100 c.c., the current density is 20-50 amp. per sq. dcm., and the P.D. is 5 volts between platinum electrodes or 3 volts between electrodes of zinc. According to Mcintosh, the zinc concentration should be high.

Palmer and Wejnarth have recently described an electrolytic method of extracting the zinc from solutions prepared from the ore by using a current density of 2-6 amp. per sq. dcm. at the cathode. The anode is lead and the cathode aluminium.

The American electrolytic methods, which are in extensive use, are similar to this method. Since high-current densities of upwards of 100 amp. per sq. foot are required for efficient deposition, they only attempt to deposit a portion of the zinc in the electrolyte, and the residual liquid is then again enriched from fresh ore. The electrolyte contains from 5-7.5 per cent, of zinc, a current density of about 25 amp. to the sq. foot is employed, and, though the optimum acidity is 25-30 grm. sulphuric acid per 100 c.c., the electrolyte is acidified with from 2-2.5 per cent. The temperature may be 30°-45° C., and a little glue is sometimes added, though the electrolyte must be otherwise very pure. The colloidal matter raises the over-voltage of hydrogen, and, by making the hydrogen bubbles more readily detachable, keeps the deposit smooth. The lead anodes and aluminium cathodes must also be very pure. Between 3 and 4 volts is a usual P.D.

Cyanide-plating solutions are the most effective, and zinc deposited from these provides a better rust-proof coating than the deposit from sulphate solutions. Good results are obtained with a current density of 2 amp. per sq. dcm., a temperature of 40° C., and moderate agitation of the electrolyte.

Rotating cathodes are not much used in the electrolytic preparation of zinc, but they are commonly used, to secure effectiveness, in its electrolytic estimation. Though zinc is a difficult metal to estimate by electrolytic methods, the estimation can be performed by using an electrolyte containing 2 grm. sodium sulphate and 1 grm. sodium acetate for every gram of zinc sulphate.

According to Engelenberg, zinc and cadmium can be separated quantitatively by electrolysis in hydrochloric acid solution containing hydroxylamine or hydrazine sulphate.

Accurate results can be secured by depositing the zinc on a weighed mercury cathode. The atomic weight of zinc has been determined by thus estimating the zinc in zinc chloride and zinc bromide.

Attempts have been made to estimate zinc by electrolysis in solutions containing (a) oxalate and free oxalic or tartaric acid; (b) acetate and free acetic acid; (c) caustic alkali or ammonia; (d) cyanide. But if the difficulty of depositing all the zinc is surmounted, the results then, according to Spear, tend to be too high through the inclusion of zinc oxide or hydroxide with the deposited metal. The difficulty of complete precipitation also increases, he adds, with the concentration of the hydroxyl ions.

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