1920
ANALYTICAL CHEMISTRY
-4 typical example has been solved using these equations. A buret 61 em. in length and 16 mm. in diameter is considered to be filled initially with dry air. The water available to saturate this air is a t 30" C. where the vapor pressure, Po,equals 31.8 mm. of mercury and the diffusion coefficient of water vapor into air, D, equals 0.2 sq. cm. per second. Figure 1 illustrates the case where the sides are not wetted and water is present only a t the base of the buret, and Figure 2 shows the other extreme where the sides of the buret are covered by a film of water. A time of 2 to 3 seconds suffices to saturate the air in the clean buret, whereas in the buret whose sides are not wetted, the air is not saturated even after 4 hours. Because most burets become dirty or nonwettable because of a layer of oil or grease on the glass, it is suggested that the water
used to saturate the gas contain a small amount of some neutral detergent. This procedure should keep burets cleaner and consequently decrease any analytical error from insufficient water vapor saturation. The calculations presented in this paper are valid only for the limiting cases where all water vapor is transported through the gas in the buret by molecular diffusion. I n any actual case, the gas entering the buret creates a large amount of turbulence which will aid in equalizing any water vapor pressure gradients. Thus the time required for saturation will be less than calculated; the amount less will depend on the actual case under consideration. RECEIVED for review June
24, 1953.
Accepted August 20. 1953.
Spectrophotometric Determination of Copper in Ores with 2,Z'-Bipyridine J . P. MEHLIG
AND P. L. KOEHRISTEDT1 Oregon S t a t e College, Corvallis, Ore.
the properties of 2,2'-bipyridine (2,2'B bipyridyl)described along with its method of preparation. Tartarini L.~U
(1)
(10) in discussing new color reactions involving cuprous salts reported that it forms a cupric complex which can be reduced with hydroxylamine in ammoniacal solution to give a highly colored cuprous complex. M o s s and llfellon (8)developed a colorimetric method for the determination of iron with 2,2'-bipyridine and Mehlig and Shepherd ( 7 ) applied 2,2'-bipyridine to the spectrophotometric determination of iron in ores. In a study of the 1,lO-phenanthroline-cuproussystem Moss and Mellon (9) stated that 2,2'-bipyridine, which contains the same cyclic -N-CC-Sgrouping, is not as sensitive as 1,lO-phenanthroline in the formation of a colored cuprous comple.;. but made no copper determinations with it. The purpose of the work described in this paper was to obtain further proof that macro constituents may be satisfactorily determined spectrophotometrically by application of 2,2'-bipyridine to the determination of copper in ores. APPARATUS AND SOLUTIONS
All spectrophotometric measurements were made n-ith a Beckman Model B spectrophotometer. 2,2'-Bipyridine. A solution made by dissolving 1 gram in 0.2M hydrochloric acid and diluting to 1000 ml. with distilled water. Hydroxylamine Hydrochloride. .4n aqueous solution containing 10 grams per 100 ml. Methyl Carbitol (Diethylene Glycol Monomethyl Ether). Commercial grade. Standard Copper Solution. One gram of electrolytically pure copper pellets was dissolved in 10 ml. of concentrated hydrochloric acid and 5 ml. of concentrated nitric acid and the solution x a s transferred to a 1000-ml. volumetric flask. The solution was neutralized with 6 X ammonium hydroxide until the first indication of the formation of the blue cupric ammonia complex, diluted to the mark a t 20' C. with distilled water, and thoroughly shaken. By means of a microburet 5 ml. of this solution were transferred to a 100-ml. volumetric flask, diluted to the mark at 20" C. with distilled water, and thoroughly shaken. Each milliliter of this solution contained 0.05 mg. of copper. THE COLOR REACTION
To produce the color system the volume of the standard copper solution required to give the desired concentration of copper was measured with a microburet into a 50-ml. volumetric flask. Then, in order, were added 2 ml. of 6.44 ammonium hydroxide to form the cupric-ammonia complex, 10 ml. of 2,2'-bipyridine solution, 1 ml. of hydroxylamine hydrochloride solution to reduce the copper to the cuprous state, and 20 ml. of methyl carbitol as a stabilizer. The mixture was diluted to the mark a t 20" C . with 1
Present address, Hanford Works. General Electric Co., Riohland, Wash.
distilled water and thoroughly shaken. The orange-brown color developed immediately. ill1 transmittance measurements were made with a 1-cm. Corex glass cell a t a wave length of 430 mw, the wave length of maximum absorption, after adjustment of the instrument so that the transmittance of the blank solvent containing the reagents was lOOyo. That Beer's law is obeyed bv the color system was proved by the straight line which resulted when the extinctions for six solutions containing 1, 2, 3, 4, 5, and 6 mg. of copper per liter were plotted against the respective concentrations. Above 6 mg. per liter the line began to curve.
Table I. Sample So.
1 2 3 4
5
6 7 8 9 10 11 12
Results Obtained with 2,2'-Bipyridine
Nature
Ore Ore
Ore OX Or?
OI? Oxide Oxide Oxide
Oxide Matte Matte
Copper by Copper by 2,2'-BiIodide pyridine Method, % Method, 70 10.43 11.16 12.04 20.33 19.40 18.63 15.02 14.00 13.23 22.31 21.61 14.09
10.48 11.16 12.00 20.37 19.31 18.61 15.05 14.03 13.22 22.30 21.63 14.02
Difference,
Error,
%
70
+0.05 0.00
+0.48 0.00 -0.33
-0.04 fO.04 -0.09 -0.02 f0.03 +0.03 -0.01 -0.01
+0.02 -0.07
+0.20 -0.46
-0.11 +0.20 70.21 -0.08 -0.05 +0.09 -0.50
DETERMINATION OF COPPER IN ORES
An accurately weighed sample of ore, varying from 0.1 to 0.2 gram depending upon the copper content, was heated with a mixture of 10 nil. of concentrated hydrochloric acid and 5 ml. of concentrated nitric acid until solution was complete or only a white siliceous residue remained. Iron was removed by double precipitation with 15M ammonium hydroxide. The filtrate in a 1000-ml. volumetric flask v a s acidified with 6M hydrochloric acid, then neutralized with 6 M ammonium hydroxide to the first appearance of the cupric ammonia complex, diluted to the mark a t 20" C. with distilled water, and thoroughly shaken. An aliquot of 4 ml. of this solution was measured with a microburet into a 50-ml. volumetric flask and the procedure from this point for the determination of the transniittancy at 430 mp was the same as that described ahove. The percentage of copper was calculated by use of the extinction coefficient, which had been determined by obtaining the transmittancy a t 430 mp of a series of solutions containing 1, 2, 3, 4,5, and 6 mg. of copper per liter. RESULTS
The method was applied to the determination of copper in six ores, four oxides, and two mattes. Duplicate determinations were made for each sample and at least two aliquots were analyzed for each duplicate. The results are shown in Table I along with the values obtained by the iodide titrimetric method (3).
V O L U M E 2 5 , NO. 12, D E C E M B E R 1 9 5 3 Table 11.
Ion Aluminuni Ammonium Bismuth Cadmium Chromic Cobaltous Ferric Lead Nickelons Potassium Sodium Zinc Chloride Cyanide Sitrate Oxalate Sulfate Thiosulfate
1921
Effect of Diverse Ions
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
