V O L U M E 2 5 , NO. 12, D E C E M B E R 1 9 5 3 Effect of Diverse Ions
Table 11. Ion Aluminuni Ammonium Bismuth Cadmium Chromic Cobaltous Ferric Lead Nickelons Potassium Sodium Zinc Chloride Cyanide Sitrate Oxalate Sulfate Thiosulfate
1921
Added as
Concn., Mg./Liter 500 500 20 25 25 20 20 200 20 500 500 20 500 5
500 500 500
10
Effect Precipitate Negligible Precipitate Fading Change in hue Change in hue Change in hue Precipitate Change in hue Negligible Negligible Fading Kegligible Fading Negligible Fading Ne ligible Fa%ing
Approx. Limiting Concn., iVg./Liter 0
...
15 20 20 5 0 100 5
... ... 10 ... 0 ...
300
..
5
In no case was the difference between the two methods greater than =kO.O9% and the average difference was 0.03%. The percentage error ranged from -0.50 to +0.48% with an average of -0.03%. Results were duplicated on the same sample with a precision of &0.01 to * O . l l % . The results also checked closely with those of the ammonia (S), triethanolamine ( 5 ) , and 1 , l O phenanthroline (6) spectrophotometric methods, giving ample proof that the method can be applied to ores containing at least as much m 22% of copper. DISCUSSION
Order of Addition of Reagents. Just as in the determination of copper with 1,lO-phenanthroline (6, 9), it is very important that the reagents be added in the given order. The cupricammonia complex must first be formed and then be reduced in the presence of 2 2‘-bipyridine by the hydroxylamine hydrochloride. A4large excess of the bipyridine has no harmful effect. Adjustment of pH Value. The ammonia concentration is an important factor, easily controlled by adding 2 ml. of 6M ammonium hydroxide to the aliquot taken for analysis. An excess must be avoided, as it has been found (4, 11) that ammonia solutions show an appreciable absorption of light in the visible
region. KOparticular advantage is gained by buffering with ammonium acetate. Stability. The color system is stabilized for 30 minutes by the addition of methyl carbitol. Sensitivity. Although 2,2’-bipyridine is a more sensitive reagent toward copper than are ammonia and triethanolamine, it is less sensitive than 1,lO-phenanthroline. Effect of Diverse Ions. I n an interference study of 18 of the more common diverse ions, transmittancy measurements were made a t 430 mp on solutions containing 1 mg. of copper per liter and varying concentrations of the ion in question up to a maximum of 500 mg. per liter. Unless the added ion caused a variation of more than 0.1% in the transmittancy, it was assumed that there was no interference. The results which are listed in Table I1 are similar to those obtained by Moss and Mellon in their studies of the 1,lO-phenanthroline-coppersystem (9) and the 2,2‘-dipyridine-iron system (8). Cadmium, chromic, cobaltous, ferric, nickelous, and zinc ions interfere, apparently by complex formation with the reagent. Of the cations which precipitate in ammoniacal solution and are therefore removed in the course of the procedure, only iron is normally found in copper ores Cyanide and thiosulfate are the onlv common anions which interfere. LITERATURE CITED
(1) Blau, F., Monatsh., 19, 647 (1898). (2) Mahin, E. G., “Quantitative Analysis,” 4th ed., p. 257, S e w Tork, McGraw-Hill Book Co., 1932. (3) AIehlig, J. P., ISD. ENG.CHEST.,A N . ~ LED., . 7, 387 (1935). (4) Ibid., 13, 533 (1941). (5) Mehlig, J. P., and Durst, Dorothy, Chemist Andust, 37, 52 (1948). (6) Mehlig, J. P., and Gruzensky, P. AI., Ihid., 40, 5 2 (1951). (7) Mehlig, J. P., and Shepherd, M. J., Jr., Ibid., 36, 52 (1947). (8) Moss, M. L., and Mellon, 11. G., IND.ENG.CHEM.,ANAL.ED., 14, 862 (1942). (9) Ibid., 15, 116 (1943). (10) Tartarini, G., Gazz. chim. ital, 63, 597 (1933). (11) Yoe, J. H., and Barton, C. J., ISD. ENG.CHEM.,AXAL.ED., 12, 456 (1940).
RECEIVED for review April 9, 1952. Accepted September 9, 1953. Abstracted from a thesis submitted by P. L. Koehmstedt t o t h e Graduate School of Oregon State College in partial fulfillment of t h e requirements for t h e degree of master of science.
Europium Determination in Rare Earth Mixtures DAVID C. FOSTER AND HOWARD E. KREMERS Research Department, Lindsay Chemical Co., West Chicago, I l l . amounts of europium are present in all rare earth ores, S and partially separated rare earth mixtures will contain amounts of europium varying from traces to several per cent. xALL
Because of interference from other rare earth absorption bands, europium concentrates cannot be analyzed conveniently by spectrophotometric methods. McCoy (2) determined europium by passing a sample of europium chloride solution through a Jones reductor into an excess of standard iodine in a carbon dioxide atmosphere and titrated the excess iodine with standard sodium thiosulfate solution. This procedure is satisfactory for samples Containing fairly high europium concentrations, but it has not been found satisfactory in this laboratory for samples of low europium concentrations. This investigation has resulted in the development of a method which yields satisfactory results a t nearly any concentration of europium. making possible a rapid europium determination a t any stage of rare earth purification. The method consists of passing a rare earth chloride solution containing the europium through a Jones reductor into an excess of ferric chloride. An amount of ferric chloride equivalent to the amount of europous
chloride formed by reduction is reduced to ferrous chloride, and the latter is titrated with standard potassium dichromate solution. There is no interference from other rare earths such as samarium and ytterbium which can exist in the divalent state, as these rare earths are not reduced by zinc. REAGENTS
Standard potassium dichromate, 0.04N. Ferric chloride, ea. 0.04N, containing just enough hydrochloric acid to prevent hydrolysis. Hydrochloric acid, ea. 0.05N. Sodium diphenylamine-p-sulfonate, 0.3% aqueous solution. Amalgamated zinc is prepared by stirring 300 grams of reagent grade 20-mesh zinc with 300 ml. 20/, mercuric nitrate solution containing 2 ml. of concentrated nitric acid. The amalgamated zinc is washed well with water bv decantation, and is used to fill a Jones reductor 2 cm. in diameter and 23 cm. high. PROCEDURE
The sample size must be varied according to the concentration of europium in the rare earth mixture in order to obtain a suitable
1922
ANALYTICAL CHEMISTRY
titration for a microburet. Suitable amounts of europium are in the range 0.1 to 0.4 meq., which will require 2.5 to 10 ml. of 0.04N potassium dichromate. The rare earth sample must be purified to remove materials reducible by zinc. This is done by oxalate precipitation of the rare earths and ignition of the oxalate to oxide. Dissolve the sample of rare earth oxide in hydrochloric acid, evaporate to a sirup under an infrared lamp to remove excess acid, and dilute to about 20 ml. with distilled water. Flush the Jones reductor column with 150 ml. of 0.05N hydrochloric acid. ;\dd 20 ml. of 0.02N ferric chloride solution to a 500-ml. Erlenmeyer flask. Attach the flask to the Jones reductor with a threeholed rubber stopper fitted with a glass tube for introducing carbon dioxide gas below the liquid level in the flask. Bubble carbon dioxide through the solution in the flask for 7 minutes to remove air. iZdd the 20-ml. sample solution to the top of the reductor, and follow with 150 ml. of 0.05N hydrochloric acid wash solution; 10 minutes are required to pass the sample and wash solution through the reductor. Remove the flask, add 4 ml. of concentrated hydrochloric acid, 5 ml. of 85% phosphoric acid, and 3 drops of 0.3% sodium diphenylamine-psulfonate solution, and titrate with standard 0.04N potassium dirhromate solution. DISCUSSION
Kolthoff (1)states that if ferrous iron is titrated in the presence of hydrochloric acid with diphenylamine compounds as indicators, the end point is poor because the indicator is oxidized before the end point is reached. The addition of phosphoric acid lowers the oxidation potential of the ferric-ferrous iron system by forming a complex ferric phosphate ion, thereby avoiding premature oxidation of the indicator. By trial and error, the quantities of phosphoric acid and hydrochloric acid used were found to give a very sharp end point. The method is designed as a control method for europium purification techniques. The wide range of the method and its reliability are shown by the following typical experiment.
A sample of samarium acetate analyzed by the method was found to contain 2.21% Eu2O3in the rare earth oxide. A solution of 315 grams of the samarium acetate containing 159.7 grams of rare earth oxide was extracted nine times with liquid sodium amalgam to separate europium by the method of Marsh ( 4 ) . The rare earths from the extracts and residue were recovered by precipitation as oxalates, and analyzed for europium.
Table I.
Extract 1 2 3 4 5 6 7 8 9 Residue Total Rwowwd
Separation of Europium from Samarium Rare E a r t h Oxide, Grams In Sample for extract analysis 2.40 0.1419 1.90 0.1814 1.19 0.1778 5.27 0.4621 1.80 0.1872 3.56 0.2551 0.4609 30.65 0.1716 2.03 3.40 0.2719
0.0124.V KdhOT, All. 13.80 13.77 4.83 0.61 0.12 0.12 0.06 0.07 Si1
EuzOi in Rare Earth Oxide, 5% 72.55 56.62 20.30 0.98 0.48 0.35
Eui01 In
Extract, Grams 1.71 1.10
0.08
0.30 Nil
98.00
0.24 0.0.5 0,008 0.012 0.024
0.006 Si1
-~
150.26
3 18
X o t all of the rare earths taken n e i c recovered, because of
unavoidable incomplete precipitation of rare earth oxalate and mechanical losses in the eutractions. The data are given in Table I. The precision of the method is adequate. With rare earth ouide samples containing 2 to 3% EulOa, analyses can be duplicated to within 1% precision, and with essentially pure europium oxide the difference between duplicate samples is less than 0.5%. The method was checked against pure europium oxide prepared by McCoy (5) and results were consistently 3.3 to 3.5% low. Europium materials prepared in this laboratory known to contain a maximum of 0.2% impurities by spectroscopic tests also analyzed about 3% low. The cause of these low results could not be found, but this does not prevent the procedure from being a very useful tool for following a europium separation. It is possible to standardize the potassium dichromate solution empirically against pure europium compounds. LITERATURE CITED
(1) Kolthoff, J. A I , and Sandell, E. O., "Textbook of Quantitative Inoreanic Analvsis." u. G08. S e w York. Nacmillan Co.. 1935. (2) McCoy, H. N., A h . C h e m ' S o c . , 58, 1577-8 (1936). ' 13) I b i d , 59, 1131-2 (1937). (4) Marsh, J. K., J . Chem. Soc., 1943, 531-5.
RECEIVED for review March 9, 19%. Accepted August 13, 1953
Polarographic Analysis of lead Driers D. A. SKOOG AND ROBERT L. FOCH'I" Stanford University, Stanford, Calif. soaps are widely used in the paint industry as driers, and L numerous methods of determining the lead content of such EAD
materials have been reported. I n general, these methods require a preliminary separation of the metallic ion from the organic acid, followed by the determination of the lead by one of the standard procedures. I n the American Society for Testing Materials method ( I ) , the sample is wet oxidized with nitric and sulfuric acids, followed by determination of the lead as sulfate. Gracis ( 4 ) recommends separation of the lead by hydrolysis of the soaps with nitric acid. The lead is then determined in the aqueous solution by titration with molybdate. Castiglioni ( 2 ) hydrolyzed lead naphthenates in acetic acid and then removed the naphthenic acid by extraction with ether. The lead was then determined as the chromate. Gavarret (5) analyzed lead driers by dissolving in benzene or trichloroethylene and extracting the lead with nitric acid. The lead was determined in the extract by the ferrocyanide method. 1 Present address, International Minerals a n d ChemioaL Corp., San Jose, Calif.
411 of these procedures are time-consuming and tedious, and in the search for a simpler method the polarographic behavior of lead soaps dispersed in aqueous medium by means of a detergent was investigated, Preliminary experiments showed that most of the common lead driers could be readily suspended in aqueous dodecylamine acetate to give clear solutions. Such dispersions gave typical polarographic waves for lead, and it was found that the wave heights were directly related to the concentration of the lead in the driers. These experiments led to the development of a very simple and rapid procedure for the analysis of lead driers which does not require the preliminary isolation of the metallic ion from the organic substrate. This paper gives a detailed description of the method and the important variables affecting the results obtained by the procedure. MATERIALS Ah-D APPARATUS
Lead Soaps. Several lead driers were obtained from commercial sources. These included lead naphthenate, octoate, linoleate, and resinate from Frederic A. Stresen-Reuter, Inc., Chicago, I11 .; and lead naphthenate, octoate, and linoresinate from Advance
