INDUSTRIAL AND ENGINEERING CHEMISTRY
176
VOL. 9, NO. 4
for gold after removal of nitric acid. Tungsten interferes, because it precipitates as tungstic acid in acid solutions and must first be removed.
Summary A 1 per cent aqueous solution of hydroquinone precipitates gold rapidly and completely from 1.2 N acid solutions. Oc-
OF GOLDBY VARIOUSORGABIC TABLEI V . PRECIPITATION
clusion of platinum and palladium is negligible when they are present even in the proportion of 2 to 1 of gold. Hydroquinone will precipitate gold from cold acid solutions but about 2 hours’coniact is necessary for complete precipitation. Hydroquinone precipitates gold directly from acid solutions containing copper, nickel, and zinc and consequently offers a rapid method for the determination of gold in alloys containing these base metals. Palladium dimethylglyoxime can be precipitated directly from the filtrate of the gold precipitation. Platinum can be determined in the filtrate from t h e precipitation of gold after heating the evaporated residue t o destroy the organic matter and then digesting i t with a little aqua regia.
REDUCING REAGENTS
Reagent
Gold Added Mg. 33.83 Amidol (hydrochloride salt of 1,a-diamino4-hydroxybenzene) Rhodinal (p-aminophenol hydroohloride) 33.83 Res orcinol
33.83
Pyrogallol
33.83
Hydroxyhydroquinone
33,83
Phenylenediamine
33.83
Pyrocatechol
33.83
Photo1 (sulfate salt of p-N-methyl aminophenol) Phloroglucinol
33.83
o-Aminophenol
25.07
Phenol
33.83
25.07
Gold Recovered
MQ. 33.86 33.83 33.82 33.81 33.79 33.83 33.83 33.84 33.85 33.82 33.86 33.82 33.86 33.83 33.83 33.86 25.06 25.08 25.07 25.08 6.82
In view Of the fact that hydroquilloneprecipitates gold so efficiently, it seemed worth while to investigate the possible application of related organic compounds t o the estimation of gold. The procedure used for these determinations was identical to that described for hydroquinone. A few of the reagents tried are given in Table IV.
Acknowledgment The authors are indebted to E. C. Forbes of the Department of Chemistry for assistance in obtaining some of the results.
Literature Cited (1) Beamish, F. E,, and Russell, J. J., IND. ENQ.CHEM.,Anal. Ed., 8, 141 (1936). (2) Hillebrand and Lundell, “Applied Inorganic Analysis,” p. 288, New York, John Wiley & Sons, 1929. (3) Idenher* J * Am* soc‘l 359 547 (”13). RECEIVED November 24, 1936,
The Rapid Analysis of Zinc-Sodium Amalgams HERMAN A. LIEBHAFSKY, Research Laboratory, General Electric Company, Schenectady,
A
RECENT study of the reactivities of zinc amalgams (2) has shown t h a t t h e absolute rates a t which they are oxidized by various oxidizing agents-e. g., the oxygen of the air-increases only slightly with the concentrations of the amalgams. As a result, concentrated amalgams seem inert; dilute amalgams appear t o be extremely reactive. This peculiar behavior of zinc amalgams makes possible a satisfactory, rapid analytical method, which can probably be modified to suit other cases, for the determination of zinc and sodium in zinc-sodium amalgams, provided the zinc concentration exceeds 0.01 per cent. To a weighed sample of the amalgam in a dry Erlenmeyer flask, ap roximately twice the volume of standard acid equivalent to t l e sodium is slowly added from a pipet. The acid and amalgam are gently whirled about in the flask for 20 seconds, a t which time violent hydrogen evolution should have ceased. The excess of acid remaining is determined by titrating with standard base, phenolphthalein being used as indicator. The amalgam, which will now contain no sodium and will have lost no appreciable amount of zinc if the procedure has been properly carried out, is next transferred t o a cell-. g., of the H typewhere its electromotive force is measured against a concentrated known zinc amalgam as reference electrode with a 1 M zinc sulfate-0.05 M sulfuric acid solution serving as electrolyte. The unknown concentration of zinc is then calculated from the measured electromotive force by means of the Nernst equation, E = RT/NF In (Zn),/(Zn),. (It has long been known that zinc amalgams deviate systematically from the Nernst equation, 1. The accuracy of the analytical method described above is usually not great enough to warrant considering these deviations; their effect can be minimized by choosing as reference electrode an amalgam of nearly the same concentration as the unknown.) The results in Table I were obtained by the above method and
N. Y.
serve to test its reliability. For analysis 50- to 75-gram samples of known zinc-sodium amalgams were taken; 5 CC. of N sulfuric acid, 0.5 N sodium hydroxide, zinc amalgams of known concentration for reference electrodes, and the electrolyte solution were the reagents used. The zinc-sodium amalgams were prepared by dilution from more concentrated known zinc and sodium amalgams. The most concentrated (1 per cent) known zinc amalgam was prepared by dissolving a weighed amount of zinc in a weighed amount of mercury in a hydrogen atmosphere; the known sodium amalgam was obtained by dissolving sodium in mercury and determining the sodium content acidimetrically. TABLEI. ANALYTICAL RESULTSFOR ZINC-SODIUM AMALQAMS Naadded % Nafound,’% Zn added, % Zn found, %
1 0.082 0.084 0.87 0.88
2 0.063 0.062 0.098
0.107
3 0.077 0.076 0.059 0.059
4 0.082
0.080 0.0088
0.0080
5
0.040 0.038 0.0030 0.0024
6
0.063 0.062 1.7(10-4) Nil
The data in Table I and general experience in this laboratory indicate that the analytical method will usually give results accurate t o about 2 to 5 per cent, provided the zinc concentration exceeds 0.01 per cent. As the zinc amalgams become more and more dilute, t h e inertness of which this analytical method makes use tends increasingly t o disappear; and t h e results obtained are consequently low. Table I clearly illustrates this point; for amalgams more dilute than 0.001 per cent, the method is obviously of little value (No. 6).
Literature Cited (1) Liebhafsky, H. A., S.Am. Chem. Soc., 57,2657 (1935). (2)Ibid., 59,452-8 (1937). R ~ C E I V ENovember D 25, 1936.
