564
ANALYTICAL CHEMISTRY
trations of reacting species, and different pretreatment of the copper electrode, it was impossible to prevent a drift in the measured e.m.f. It is suspected that the copper metal which in the presence of Versene reduces hydrogen ion as the drift was substantially repressed by vigorous stirring. Under these conditions it is possible to compute standard e.m.f.’s for Reactions 7 and 8, and the stability constant. Values obtained are in general agreement with previous values but exhibit a definite trend over the course of the titration and are not regarded as significant. Determination of Copper in the Presence of Iron. Since the reduction of +3 iron normally precedes that of copper, it is desirable to have available a simple method of preventing the prior reduction of iron in determinations involving unfavorable ratios of iron to copper. Faucherre and Souchay (S) claimed that this can be accomplished by the addition of fluoride. This was verified in this study, provided that the high concentration of flouride stated by the earlier authors, 14 M , is used. At lower concentrations of fluoride, ca. 1 M, an interesting situation prevails. Consider the following stability constants ( 2 , 6): Fe(II1) Y - , 1026; Fe(I1) Y’, Fe(II1) F2+, and Fe(I1) F+, < 30. Of the Fe(II1) complexes, the Versenate is the more stable. Yet the ferric-Versenate complex iF far more easily reduced than the ferric-fluoride complex (the half-wave potential is about 1 volt less negative) because of the existence of a stable ferrous-Versenate complex and a very weak ferrous-fluoride com-
plex. The stability constants quoted indicate this qualitative behavior. Therefore] in order to form the ferric-fluoride complex and prevent the prior reduction of iron in mixtures of copper. iron, Versene, and fluoride, it is necessary to use a fluoride concentration of the order of 50 times that of the Versene concentration. LITERATURE CITED
Alrose Chemical Co., Providence, R. I., Technical Bulletins, May and October, 1951. (2) Dodgen, H. W.,and Rollefson, G K., J . Am. Chem. Soc., 7 1 , (1)
2600 (1949). (3)
Faucherre, J., and Souchay, P I Bull.
soc. chtm. Fmnce, 1949,
722. (4)
Furness, W., Crawshaw, P., and Davies, W. C., Analyst, 74, 629 (1949).
(5) Kolthoff, I. M.,andiluerbach, C., J . Am. Chem. Soc., 74, 1462 (1962).
(6) Kolthoff, I. M., and Lingane, J. J., “Polarography,” p. 92, Xew York, Interscience Publishers, 1952. (7) Ibid., p. 213. ( 8 ) Ibid., p. 228. ( 9 ) Ibid., p. 234. (10) Pecsok, R. L., J . Chem. Educ., 29, 597 (1952). (11) Schwarsenbach. G.. and -4ckermann. H., Helu. Chim. Acta. 30, 1798 (1947). (12)
Schwarzenbaoh, G., and Freitag, E., Ibid., 34, 1492 (1951).
RECEIVED for review August 4, 1952. Accepted December 29, 1952. Presented before the Division of Analytical Chemistry at the 132nd 3Ieeting of the . 4 v E R I c a m CHEMICAL SOCIETY, Atlantic City, N. J.
Determination of Aluminum in Zirconium Based on Separation by Ion Exchange HARRY FREUND AND FREND JOHN MIRiER Oregon State College, Corz;allis, Ore. No entirely satisfactory method for the determination of small amounts of aluminum in zirconium has been available, owing to the lack of a suitable separation method. This paper describes an ion exchange separation whereby the zirconium in a solution 0.06 M in hydrochloric acid and 0.8 M in hydrofluoricacid is exchanged on a column of Dowex1, while the aluminum passes through the column. The aluminum may be determined in the eluate by conventional gravimetric or colorimetric procedures. Synthetic samples containing amounts of aluminum varying from 0.001 to 3.8% have been analyzed, As a consequence, a satisfactory method is now available for the separation and determination of small amounts of aluminum in zirconium.
N
0 E S T I R E L Y satisfactory method is knolm for the deter-
mination of small amounts of aluminum in zirconium. Employment of a caustic solution to precipitate the zirconium is not feasible, as small amounts of aluminum will inevitably be coprecipitated with the gelatinous zirconium hydrous oxide. Separations based on the precipitation of zirconium from acid solution with cupferron ( 8 ) ,arsonic acids ( d ) , mandelic acid and its derivatives (S, 6), phthalic acid ( I I ) , and m-nitrobenzoic acid ( I O ) have been suggested. I n each case, although aluminum is not precipitated by the reagent, the precipitation of the major constituent creates other serious problems. The direct precipitation of aluminum is thus far not feasible for the lack of a reagent that will precipitate aluminum but not zirconium. Ion exchange offers a superior technique for the separation of
these metals. Under suitable conditions the negatively changed zirconium fluoride complex is exchanged while the aluminum complex passes through the resin column. The fluoride complexes are obtained when the metal is dissolved in hydrofluoric acid according t o the customary solution procedures. EQUILIBRIUM EXPERIMENTS
Iiraus and Xoore ( 5 ) have reported exchange characteristics for the zirconium fluoride complex. A somewhat more extensive study of the zirconium complex and the hafnium complex and a comparable investigation of the aluminum complex are required to determine suitable conditions for the analytical separation. The partition of the metal fluoride complex between the solution and the resin is determined by equilibrating a weighed quantity of the resin with a solution containing a known total concentration of the metal. The distribution coefficient is defined as the ratio of the concentration of the metal in the resin phase to the concentration of the metal in the solution. At constant weight of resin and volume of solution a modified coefficient may be computed equal to the ratio of the millimoles of metal in the resin to the millimoles of metal in the solution. I t has been shown that the greater the separation between the distribution coefficientsof two ions, the more easily they may be separated (9). Reagents. Dowex-1. The resin used was 200- to 400-mesh. It is available from hlicrochemical Specialties Co., Berkeley, Calif. Zirconium metal. Metal turnings of production-run zirconium were furnished by the Bureau of Mines, Blbany, Ore. Hafnium metal. Metal turnings were furnished by the Bureau of Mines, Albany, Ore. Aluminum metal. Reagent grade metal foil was used.
565
V O L U M E 25, NO. 4, A P R I L 1 9 5 3 8-Quinolinol (Oxine, 8-Hydroxyquinoline) Reagent. The solution was prepared by dissolving 5 grams of Eastman's White Label oxine in 10 ml. of glacial acid, filtering, and diluting to 100 ml. with boiling dist i l l e d water. The solution was stored out of direct sunlight. All other chemicals used were of reagent grade. DOWEX-I, 3 0 GRAMS Procedure for Equilibrium Experi.. ments. Two grams of oven-dried resin is placed in a 250-ml. polyethylene bottle. Aluminum or zirconium metal is dissolved in predeterCOTTON PLUGmined quantities of PARAFFINED TYGON TUBE COR?,% 3/8 hydrochloric and hydrofluoric acids and the resulting solution is diluted to 100 ml. and added to t h e POLY E THY LENE BOTTLE bottle. T h e bottle is shaken mechanically until exchange equiF I S H E R FILTRATOR librium is attained, Figure 1. Construction of usually 2 to 3 hours. Exchange Column After shaking, the solution is filtered to remove the resin, 2 or 3 ml. of concentrated sulfuric acid is added, and the solution is evaporated in platinum dishes on a steam bath. The sulfuric acid solution is fumed and concentrated nitric acid is added dropwise to oxidize any organic matter present. Gravimetric Determination of Aluminum. The aluminum is determined gravimetrically by oxine precipitation (4). Despite strong fuming with sulfuric acid, a trace of fluoride may remain and interfere with the precipitation. The addition of 8 to 10 grams of boric acid in a precipitation volume of 150 nil. coniplexes any fluoride and eliminates the interference. Gravimetric Determination of Zirconium. The zirconium determinations were made by precipitating with ammonium hydroxide and igniting to zirconium oxide for weighing.
Furthermore, varying the hydrofluoric acid concentration does not materially change the magnitude of the coefficient. The lowest practical limit of hydrochloric acid is determined by the concentration that will prevent hydrolysis from occurring. The system selected for further study was 0.06 iZI in hydrochloric acid and 0.8 JI in hydrofluoric acid. A mixed acid elutriant of this composition was prepared and used in subsequent column experiment 8 . COLUMN EXPERIMERTS
The distribution coefficients differed by almost enough to use a batch process, in which the resin was merely equilibrated with the solution by stirring and then separated by filtration. -4s somewhat erratic results were obtained, i t was decided to utilize a column separation.
i
-2%
Column Construction. The exchange column is constructed as shown in Figure 1. All parts of the column that come in contact with solution must be plastic. Treatment of Resin. Dowex-1 is used for all the column separations. The resin, as received, is washed thoroughly with 3 N hydrochloric acid on a Buchner funnel to convert it to the chloride form. It is then washed with distilled water until only a slight opalescence is produced with a silver nitrate solution. The resin is dried between 80" and 90" C. for 1 hour. Reclamation of Resin. After the exchange reaction. the resin is washed with 3 -Yhydrochloric acid to remove the zirconium and the washing is continued until no further precipitation of zirconium results on neutralization of test portions of the wash solution. After renioval of the zirconium, the resin is nashed n i t h distilled water until the excess hydrochloric acid is removed, as shown by the silver nitrate test. Procedure for Column Run. A slurry made of resin and elutriant solution is poured into the column and suction is applied. The solution containing the sample is introduced into the column. T h e n the liquid level has fallen to the top of the resin bed, the polyethylene bottle in the Filtrator is replaced with an empty polyethylene bottle and the suction is adjusted to obtain the desired flon rate. Elutriant solution is added to the column just as the last of the solution containing the sample enters the resin. I t is run through the column until the desired volume of liauid has been collected. The solution is analyzed, as previously dkscribed, for aluminum or zirconium.
The anticipated aluminum content of the zirconium metal was such that a 1-gram sample should provide adequate aluminum for the colorimetric aluminon-thiogl) colic acid method. On the basis of the equilibrium data, which indicated that essentially complete exchange of 100 mg of zirconium rould be achieved The data in Table I indicate thr appreciable difference in the with 2 grams of resin, 30 grams of resin was selected for the magnitudes of the distribution coefficients of zirconium and hafcolumn experiments. With a flow rate of 5 1111. per minute, it nium as compared to aluminum and that this difference is acwas established that 1 gram of zirconium in 100 nil. of solution. centuated by decreasing concentrations of hydrochloric acid. 0.06 J4 in hydrochloric arid and 0.8 JI in h\ drofluoric acid, was completely excahanged. R'aPhTable I. Distribution Coefficients ing with up to 500 ml. of Hafnium, Millimoles 4cld Concn , Zirconium, Millimoles bluminum, hlillimole elutriant did not produce break.If Metal Metal Dist. hIetal hIetal Dist. Metal hletal Dist. -___ through. taken remaining coef, HF HC1 taken remaining coef. taken remaining coef. Varying amounts of alumi1 0 0 5 1.01 0.798 0.560 1.02 2.81 1 0 0 2 num in 100 ml. of a solution 0,269 1 0 01 1.01 6.78 0.130 0.06 JI in hydrochloric acid 0.716 0.0137 0 5 1 0 .... 0,726 0.678 0.0146 1:63 0.553 0.688 0 5 0 5 0: 663 and 0.8 in hydrofluoric 0.678 0,0357 2.71 0 5 0 2 1.02 0.700 0.276 0.678 0.0369 1.03 0 5 0 1 0.704 0.134 acid were passed through 6.68 0.663 0,0136 01 3 0 0.672 the column. U n d e r t h e s e 1:01 0 1 05 0.718 0.0079 0.723 0 : 663 0.503 ,... 01 0 2 1.01 0.463 1.19 conditions practically no alu01 01 .... 0 : 707 0.0420 .... 0:iis ,... 0 8 1 0 1:06 0.166 .... minum was exchanged and 0.828 0 0.997 0.763 0.308 1.04 0.752 0 8 0 5 0:775 0.808 0.596 2-50 m l . of t h e e l u t r i a n t 1.012 0.320 2.16 3.58 0 0.744 0 8 0 2 1.06 0.211 0.742 0.0457 0.973 12.5 0,0717 1.02 0.626 0 8 005 18.4 0.656 0.053 washed the aluminum free 0.111 19.1 0 8 002 0.980 0.0487 1.08 0.718 0.0 .... 0,808 1.09 0.125 0.688 0 8 001 of the column. The recovery 0.786 0.0 0.209 0.533 0 8' 0 005 1.07 .... 0.674 0.0 data are l i s t e d i n T a b l e 0.216 0.645 0 8 0 0 .. 0,822 ... ....
11.
566
ANALYTICAL CHEMISTRY
DETERMINATION OF ALUMINUM IN SYNTHETIC ZIRCONIUMALUMlNUM SAMPLES
Reagents. .4LUMINON-'FHIOGLYCOLIC ACID REAGENTS (7, 19). Standard Aluminum Solution. Dissolve 0.1 gram of metallic aluminum in 50 ml. of concentrated hydrochloric acid and dilute to 1 liter. Dilute 10 ml. of this solution to 100 m]. and use as a standard aluminum solution containing 10 y of aluminum per ml. Cupferron Solution. Dissolve 1 gram of cupferron in 100 ml. of distilled water. Prepare a fresh solution each day. Chloroform. Redistill the commercial product. Thioglycolic Acid Solution. Dilute 10 ml. of thioglycolic acid to 250 ml. with distilled water. Prepare a new solution each week. Ammonium Aurintricarboxylate, 0.10%. Dissolve 0.10 gram of the salt in water, add 10 ml. of 10% .. benzoic acid in methanol, and dilute to 100 ml. Gelatin, 1%. Dissolve 1 gram of gelatin in hot water, cool, add 10 ml. of 10% benzoic acid in methanol, and dilute t o 100 ml. Buffer Solution. Mix 470 ml. of 15 M ammonium hydroxide and 430 ml. of glacial acetic acid, and cool to room temperature. Dilute t o 1 liter. Composite Reagent Solution. Mix equal volumes of the ammonium aurintricarboxylate, gelatin, and buffer solutions. Allow to stand a t least overnight and preferably for several days.
Table 11.
Recovery of Aluminum Passed through Column
R u n No.
A1 Taken, Mg.
1 2 3 4 5
41.8 41.0 7.0 8.7 8.4
AI Recovered, Mg. 41.7 40.0 6.8 7.5 8.3
Y
Y
6 7 8
20 40
14' 42 60 58 Runs 1 through 5,A1 determined raTimetrically with oxine. R u n s 6 through 8, AI determinef colorimetrically by aluminon-thioglycolic acid method.
Synthetic zirconium-aluminum samples were prepared, using metallic aluminum or a standard aluminum solution and either metallic zirconium or the salt, zirconium oxychlpride. One gram of the metallic zirconium was found to contain several hundred micrograms of aluminum. Consequently the metal was used only with large amounts of aluminum. Essentially aluminum-free zirconium was prepared by recrystallizing the oxychloride and this zirconium was used with microgram samples of aluminum. An estimated aluminum content of 8 p.p.m. was obtained by both spectrographic and colorimetric analysis of the salt. When the oxychloride was used as the source of zirconium, a few milligrams of zirconium came through the column. ' Presumably not all of the zirconium was converted to the anionic fluoride species that was exchanged completely. The small amount of zirconium passing through the resin was removed either by precipitation with sodium hydroxide, when milligram quantities of aluminum were employed, or by a cupferron-chloroform extraction when microgram quantities were to be measured. As later interference studies indicate, the removal of iron(II1) was required and this also was achieved by the cupferron precipitation and extraction. Preparation of Sample for Column Run. A gram of metallic zirconium, or its equivalent of zirconium oxychloride, is placed in a platinum dish and covered with 15 to 20 ml. of water. Three milliliters of concentrated hydrofluoric acid (48y0)is added slowly. Care must be taken that the reaction does not become too violent or splattering will occur. When all of the sample has dissolved, 2 ml. of 3 N hydrochloric acid is added and the resulting solution is made up to 100 ml. This solution is then ready to pass through the exchange column. The procedure for the column run is the same as described previously. Colorimetric Analysis of Aluminum. The mixed hydrochlorichydrofluoric acid solution from the ion exchange separation is
transferred to platinum dishes, 5 ml. of concentrated perchloric acid is added, and the solution is evaporated to fumes. As the volume decreases, the solutions are combined until the entire sample is in a single platinum dish. The side of the vessel is rinsed with distilled water and the solution refumed. The solution is diluted with 50 m]. of water, warmed, transferred to a separatory funnel, and cooled under running tap water to room temperature or slightly below. Four milliliters of a 1% cupferron solution is added t o the separatory funnel and the solution is swirled to ensure mixing. Fifteen milliliters of redistilled chloroform is added and the system is shaken for 1 minute (not too vigorously). The layers are separated and the lower chloroform layer is discarded. ' Then 2 ml. of cupferron is added and the solution is extracted with 15 ml. of chloroform. Usually the extraction of iron, etc., will be complete and a further extraction with 5 ml. of chloroform nil1 remove most of the cupferron from the aqueous phase. The aqueous layer is filtered through a No. 40 Whatman paper into a 250-ml. Vycor beaker, which is then placed on the hot plate. When most of the solvent has evaporated, 2 ml. of concentrated nitric acid is added and the solution is taken to fumes. Immediately before fuming, a further addition of 2 ml. of concentrated nitric acid is made. After fuming vigorously, a mixture of 3 ml. of concentrated nitric acid, 2 ml. of concentrated hydrochloric acid, and 3 ml. of concentrated perchloric acid (if appreciable perchloric acid has been lost owing to previous fuming) is added and the solution refumed, making certain the perchloric acid is heated to boiling. The solution is then cooled somea hat, 50 ml. of water added, and the solution again heated to boiling to drive off any chlorine. The solution is cooled and transferred to a 100-ml. volumetric flask and a 50.00-ml. aliquot which should contain no more than 40 y of aluminum is then transferred to a 250-ml. Vycor beaker. If the aluminum content is too high, a smaller aliquot may be taken later together with a similar aliquot from the blank. Into this is pipetted 2 ml. of the thioglycolic acid solution and, using a glass electrode, the PH is adjusted to 5.0 zt 0.1 with a saturated solution of ammonium carbonate in concentrated ammonia. The solution is then transferred to a 100-rnl. volumetric flask, 18.00 ml. of composite reagent is added, and the flask is placed in a vigorously boiling water bath for 10 minutes. After cooling on the bench for 10 minutes, the flask is immersed in running, cold tap water for 2 minutes, filled to the mark with distilled water, and again permitted to stand. The absorbancy is determined a t 525 mp 30 minutes after the sample has been placed in the hot water bath. A series of solutions containing 0, 20,40,60, and 80 micrograms of aluminum may be carried through the entire process described above. -4plot of absorbancy us. concentration of aluminum in the color solution (0, 0.10, 0.20, 0.30, and 0.40 y of aluminum per ml.) is then made. The blank solution will have an absorbancy due to the excess dye and to the aluminum picked up from the reagents. Whenaliquotsof different size are used, the absorbancy due to aluminum pickup will change proportionally while the contribution of the dye remains the same. Results accurate to within the reproducibility of the method also have been obtained from a standardization curve prepared directly from the aluminum standard solution without carrying the samples through the separation procedurea.
Table 111. -4nalysis of Synthetic Aluminum-Zirconium Samples R u n No. 1
a
3 4 5
(1 gram of Zr, as Zr', taken) A1 Taken, Mg. 41 Recovered, ME. 36.8 37.8 38.9 38.6 0.97 1.0 0.5 0.62 0.48 0.5 Y
in
7 8 9 10 11
Source of Zr.
20 30 40
50
7'
21 27 51 59
67
Runs 1 a n d 2 metal Runs 3 through 11 ZrOCli Runs 1 through 5 , A1 determined iravirnetrically with oxine. Runs, 6 through 11, A1 determined colorimetrically by aluminon-thioglycolic acid method.
567
V O L U M E 25, NO. 4, A P R I L 1 9 5 3 Table IV. Element Fe V Sn Ti Nb Hf Zr
M0 Ta
Interference Studies Distribution Coe5cient Ca. 0 1.2 2.4 9.1 10.5 11 18.4 Ca. 20 22
Results of the analysis of the synthetic samples are given in Table 111. INTERFERENCE STUDIES
In the procedure developed, interference may occur during the Reparation steps or during the final aluminum measurement. .4ny metallic ions not forming anionic complexes will pass through the column and are potential interferences, depending upon their behavior with cupferron and the reagent used for the final determination of aluminum. When 8-quinolinol (15) or aluminon ( 7 ) is used, the interference picture is well known, as is the behavior of many metals with cupferron (I). The interference studies 1% ere confined, therefore, to those elements forming stable fluoride complexes and likely to be exchanged on the resin to an indeterminate extent. .is with zirconium, distribution coefficients were determined by equilibrating with Dowex-1 a 0.06 M hydrochloric acid and 0.8 M hydrofluoric acid solution containing the interfering metals. From the data tabulated in Table IV the relative behavior of various metals may be compared. The most serious interference is iron(III), which passes through the column and thus accompanies aluminum. A subsequent cupferron separation is therefore necessary. To a lesser extent tin(1V) and vanadium(V) would also come through and require further separation. Otherwise the metals tested would be exchanged on the column.
Sulfate was studied as a possible source of interference, because potassium bisulfate is csften used to fuse zirconium containing samples not soluble in acid. Two or 3 grams of the sulfate did not affect the determination of milligram quantities of aluminurn. The effect of the sulfate on the analysis of microgram quantities of aluminum was not determined. ACKNOWLEDGMENT
The authors wish to thank the Northwest Electrodevelopment Laboratory, U.S. Bureau of Mines, for its generous cooperation in supplying certain facilities and materials that aided in this research. LITERATURE CITED
(1) Furman, X. H., Mason, W.B., and Pekola, J. S.,h i L . CHEM., 21,1325-30 (1949). (2) Geist, H. H., and Chandlee, G. C., IND.ESG. CHEM.,As.iL. ED., 9,169-70 (1937). (3) Hahn, R. B., ANAL.CHEM.,21, 1579-80 (1949). (4) Kolthoff, I. AI., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” 3rd ed., p. 321, Kew York, Blacmillan Co., 1952. (5) Kraus, K. A,, and Moore, G. E., J . A m . Chem. Soc., 73, 9-13 (1951). . , (6) Kumins, C. 1., ANAL.CHEY.,19,376-7 (1947). (7) Luke, C. L., I b i d . , 24, 1122-6 (1952). ( 8 ) Lundell, G. E. F., and Knodes, H. B., J . Ani. Chem. SOC.,42. 1439-48 (1920). (9) RZicrochemical Specialties Co., Berkeley. Calif., “Ion Ex-
change Resins.- Laboratory Procedures.” (10) Osborn, G. H., Analpst, 73, 381-4 (1948). (11) Purushottam, A , , and Rao, R. S.V., I b i d . , 75, 684-6 (1950). (12) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., p. 175, Sew York, Interscience Publishers, 1950. (13) Killard, H. H., and Diehl, H., “ildvanced Quantitative .Inalysis,” pp. 74-81, Sew York, D. Tan Nostrand Co., 1943.
RECEIVED for review October 23, 1952. Accepted December 29, 1952. Presented in part a t the Pacific Sorthnest Regional Meeting, AMERICAN CHEMICAL SOCIETY,Corvallis, Ore., J u n e 1952. Published with the approval of the Oregon State College Monographs Committee. Research Paper No. 218, Department of Chemistry, School of Science.
Spectrophotometric Investigation of Reaction of Titanium with Chromotropic Acid WARREN W. BRANDT AND ALVIN E. PREISER Department of Chemistry, Purdue University, West Lafayette, Znd.
T
HE color formed by the reaction of quadrivalent titanium with chromotropic acid (4, 5-dihydroxy-2, 7-naphthalene disulfonic acid) was first observed by Geissow in 1902 ( 5 ) . The early applications of the reaction as a qualitative and quantitative method for the determination of titanium set the pattern for its subsequent usage. Hall and Smith ( 7 )and Lenher and Crawford ( 9 ) worked R-ith dilute sulfuric acid medium while Levy (10) used concentrated acid. Later investigations (3,4,8,18,19) have followed these two lines of approach, and individual investigators i n general list no specific reason for utilizing the particular solvent they choose. Endredy and Brugger ( 2 ) made the first investigation which concerned itself with the understanding of the reaction between quadrivalent titanium and chromotropic acid. They determined formulas and stability constants for the complexes formed by means of equilibrium measurements. Their results indicated the existence of a 1 t o 1 complex in concentrated sulfuric acid and a 2 to 1 chromotropic acid-titanium complex in 2% sulfuric acid. They proposed a correlation b e k e e n the two specie8 present in
the different media. In their work they demonstrated the application of the color reaction to the quantitative determination of titanium using a Pulfrich photometer. The present investigation was concerned with furthering the study of the nature of the reactions of quadrivalent titanium with chromotropic acid. It included the possibility of the extension of the quantitative scheme of Endredy and Brugger ( 2 ) in concentrated sulfuric acid to more complex mixtures of ions than previously reported. A spectrophotometric investigation of the variables functioning in the dilute acid solution was carried out to determine the relative advantage of the two methods. Detailed studies and applications of the dilute acid system have been published since the completion of this work (If, 16). APPARATUS AND REAGENTS
All spectrophotometric curves were obtained with a General Electric automatic recording spectrophotometer having a 10-mp band width. The Beckman Model B spectrophotometer was used for measuring absorbance a t a particular wave length. One-
