1621
V O L U M E 2 6 , NO. 10, O C T O B E R 1 9 5 4 a hot plate with constant swirling for one minute. This oxidizes a large proportion of the organic matter in the solution and prevents too vigorous a reaction when sulfuric acid is added. Add 1 ml of 31.1.7 sulfuric acid and place the flask in the hot box, until fumes of sulfuric acid are seen. Cool slightly, add 0.5 ml. of concentrated nitric acid, and heat until the nitric acid is evaporated Cool and wash down with 2 ml. of water, then add 2 drops of perchloric acid, and heat again ,just to fumes of sulfuric acid to ensure complete oxidation of all organic matter. To the flask add 2 85 ml. of supporting electrolyte consisting of 0 5W oxalic acid containing 0 1% volume hydrochloric acid and, 0.015% gelatin (and 0 001% uranium as uranyl sulfate-the spike-if a very low value is expected) and mix well. This addition may be made from an automatic buret calibrated to delivei 2.85 ml. The total volume of the sample is now 3 ml. The electrolyte must be prepared fresh each day, since decomposed gelatin n ill ruin the estimation. Transfer about 2 ml. of:olution t o the polarographic cell and place in a nater bath a t 20 rk 0.1’ C. An internal mercury pool anode is satiqfactory and convenient and gives better results than a silver nire anode -4ny type of cell may be used. The type employed in this work \\-a? a 65-mm. length of 15-mm. glass tubing with a sealed-in glass bubbler which did not quite touch the mercury surface Deaerate the solution by bubbling n i t h tank nitrogen, which should be first passed through alkaline pyrogallol solution and then through water also kept a t 25” =k 0.1” C. Record the polarogram from 0 to -0.5 volt. Results of satibfactory accuracy can be obtained on samples containing at least 24 y per ml. X ) by means of a single reading at -0.5 volt, which must be corrected for the electrolyte line. The method of standard addition gives the most accurate results, and is especially recommended for samples containing less than 20 y per ml. Hoxever, results are obtained more quickly by the use of a calihration curve and the precision is within &5%.
ACKNOW LEDGM E N 1
The author is indebted to Maxwell Lipworth and H. T. Tucker for their assistance in developing the uranium separation techniqueand in carrying out the polarographic v,-ork,respectively. Informat,ion regarding the behavior of locally important impurities, especially sulfate, in the cellulose column treatment was obtained from reports of the Sout,h African Government Metallurgical Laboratory. Acknowledgment is made to the consulting chemical and metallurgical engineer, F. L. Melvill, and to the board of Anglo-Transvaal Consolidated Investment Co., Ltd., for permission to publish this method. LITERATURE CITED
(1) Hurstall, F. H., and Wells, R. A,, Analyst, 76, 396 (1951).
(2) Crompton, C. E., Tichenor, R. L., and Young, H. A , , U. S. Atomic Energy Commission, CD-GS-35 (1945). (3) Harris, W. E., and Kolthoff, I. M.,J . Am. Chem. SOC..6 7 , 1484 (1945). (4) Ibid., p. 1488. (5) Kolthoff, I. AI., and Harris, W. E.. Ibid., 68, 1175 (1946). (6) Lewis, J. .I.,Ministry of Supply, Great Britain, Chemical Research Laboratory, Sci. R e p t . CRL/AE 56 (1950). (7) Lewis. J. -i., and Overton, K. C., Ibid.. CRL/AE 41 (1949). (8) Lingane, J. J., Chem. Revs.,29, 1 (1940). (9) Rodden, C. J., and Warf, J. C., “Analytical Chemistry of the Manhattan Project,” pp. 77-122, Kew York, NcGraw-Hill EookCo.. 1950. (10) Ibid.,pp. 122-35. (11) Ibid., pp. 596-610. (12) Strubl. R., Colleclion Czechosloz. Chrm. Conzmuna., 10, 466 (1938). R E C E I T Efor D reiieiv Augu4t 20, 1953. Accepted July 21, 1954,
Tu rbidimet ric Microdete rmination of Zi rconium GUY WILLIAM LEONARD, JR., DOUGLAS E. SELLERS, and LEROY E. SWIM Department o f Chemistry, Kansas State College, Manhattan, Kan.
The recent interest in the chemistry of zirconium and its compounds has necessitated the development of improved methods of analysis. As the reaction between zirconyl ion and phthalic acid gives a very finely divided precipitate which tends to stay in suspension, the possibility of using this reaction for a simple turbidimetric determination of zirconium was in%estigated. The zirconium phthalate suspension was found to be very stable and to follow Beer’s law up to 123 p.p.m. of zirconium. No critical control of the order of mixing, length of heating, period of cooling, or hydrogen ion concentration was necessary. The interference of the fluoride ion in a solution of known zirconium concentration can be used to estimate concentration of that ion. A simple, direct, and rapid turbidimetric method is described for the microdetermination of zirconium. This technique is useful for the determination of zirconium in the presence of high concentrations of various ions.
T
HE widespread interest in the study of zirconium and its compounds has necessitated the development of improved methods of analysis, especially in the micro range. An investigation of the reactions between organic reagents and zirconium salts in an acid solution showed that the precipitate formed by phthalic acid with zirconium ions was very finely divided and tended to stay in suspension. Because phthalic acid had been suggested as a selective reagent for the gravimetric determination
of zirconium ( I ) , the possibility of a turbidimetric method was investigated. REAGEYTS A \ D EQUIP\IE\T
Stoch solutions \yere prepared containing 7 grams of potassium hydrogen phthalate in 1 liter of 0 . 2 5 5 hydrochloric acid and also 20 grams of zirconyl chloride octohydrate in 1 liter of 0.25-V hydrochloric acid. All further solutions were made by dilutions of these stock solutions. The zirconium solution was standardized gravimetrically by mandelic acid. The Bausch and Lomb monochromatic colorimeter with a 430 mp filter was used as a photoelectric turbidimeter. PROCEDURE
The acidic solution of zirconyl ions was diluted to such a volume that the final concentration of zirconium was from 10 to 125 p.p.m. in approximately 0 . 2 5 5 hydrochloric acid. Five milliliters of this solution was transferred to a test tube and 10 ml. of the phthalic acid stock solution was added. The solution was mixed by inverting the tube. The tube was lightly corked and suspended in a beaker of briskly boiling water. The mixture was heated for about 1 minute and then the cork was pushed firmly into the test tube. Heating was continued for a total time of 10 minutes; then the test tube n a s placed in a beaker of cool water. After cooling, the solution was shaken vigorously for a few seconds. The test tube was set aside for 3 to 4 minutes to allow air bubbles to escape. The solution was then placed in a square cell of the Bausch and Lomb monochromatic colorimeter and the per cent transmittancy measured a t 430 mp. The concentration of zirconium was read from a calibration plot showing either per cent transmittancy or absorbancy versus concentration of zirconium. This calibration curve was obtained by similarly treating selected amounts of zirconium from the zirconyl chloride stock solution.
ANALYTICAL CHEMISTRY
1622 Table I.
Interference Study
(Effect of interfering ions on the turbidimetric determination of a 10 t o 125 p.p m. solution of zirconium) Concentration below Calculations Which No Interference Coinpound Based on Noted, P.P 31. Coed 1000 1000 1000
SaCl Sax08 SaBr KI BaClz IInClz cuc12 SlClZ ZnCh AI(N0a)a SnClz Th(N08)4 SaClOa rrri.
oon
1 ... .
1000 1000 1000 1000 1000
:!E? l"""
1000
500
2no
EXPERIMENTAL
Selection of Wave Length. Preliminary spectrophotometric investigation of the zirconium phthalate sol showed that the transmittancy decreases with decreasing wave length. Since in the ultraviolet region other ions such as nitrate or phthalic acid itself absorb, 430 mp was selected as the wave length a t which to make the transmittancy measurements. 100-
90-
heated solutions were cooled by placing in water kept at 20" and 30" C. There seemed to be no variation due to the length of cooling, as long as a reasonably cool solution resulted. Range, Accumcy, and Precision. The curve in Figure 2 was obtained by the suggested procedure. Concentrations above 190 p.p.m. result in relatively little change in transmittancy; therefore the recommended concentration range is from 10 to 125 p.p.m. A plot of absorbancy versus concentration gives a straight line up to 125 p.p.m. Analyses of ten separately prepared samples each for 125,57,and 10 p.p.m. of zirconium gave an average deviation of 1 p.p.m., a range of 4 p.p.m., and a standard deviation of 2 p.p.m. Interferences. Table I shows the permissible amourits of various ions that may be present without interfeiing with the determination of zirconium. Interference wap considered to occur when the average of four determinations of a sample containing a given amount of zirconium plus the interfering ion gave results that differed by more than 1 2 p,p.m, from the average of four control samples containing the same amount of zirconium. Each interference was determined on samples containing 10, 57,and 125 p.p.m. of zirconium. N o investigation was made of the influence of ions above 1000 p.p.m. Fluoride Study. Since 1 p.p.m. of fluoride ion interferes with the zirconium determinations, the degree of interference was investigated as a possible method of estimating fluoride concentration. The following method was developed. Ten milliliters of a zirconium stock solution (3 grams of zirconyl chloride octahj-drate per liter of 2.5'V hydrochloric acid) was transferred to a sample containing 10 to 70 p.p.ni. of fluoride and diluted to 100 ml. -4fter the sample was thoroughly miued, it as analyzed for the apparent zirconium concentration hy the suggested turbidinietric procedure.
80 -
706050 -
-
I
I
I
PPM. Z r
Effect of Heating. Figure 1 shows the increase in turbidity for a 57 p.p.m. zirconium solution with heating. Samples of zirconium ranging from 10 to 125 p.p.m. gave similar heating curves. Although the turbidity became constant after 6 or 7 minutes, 10 minutes was chosen as the boiling time to ensure a complete reaction. Stability of the Suspension. The turbid solution seemed stable. KOvariations in readings were noticed during a half-hour period after the cooled solutions had been shaken. Since some interfering ions may cause the suspension to settle out more rapidly, the transmittancy measurements were made a few minutes after the cooled solutions were shaken. When the solutions were allowed to stand overnight, the suspension settled. However, when the solutions were shaken again, the transniittancies were the same as the first measurements. Effect of Acid Concentration. The final hydrochloric acid concentration of a solution was varied from 0.18to 0.5N with only a slight change in the transmittancy. At lower acid concentrations the zirconyl ion will hydrolyze and a t higher acid Concentration the zirconium phthalate sol will not form. Order of Mixing and Cooling. KO variations in the results were observed on changing the order of mixing the reagents. Identical results were obtained for determinations in which the
Figure 2.
1
Concentration Range
40
I
I
10
I
I
I
50
30 PP.M. FLUORIDE
Figure 3.
Influence of Fluoride Ion
I
I
70
1623
V O L U M E 2 6 , NO. 10, O C T O B E R 1 9 5 4 Figure 3 shows that the turbidity of the 85 p.p.m. zirconium solution decreases 17 ith increasing concentration of fluoride ion. The limit of permitted concentration of other ions was found to be identical with that of Table I.
solution. KO critical conlrol is necessary of the length of heating, cooling, or hydrogen ion concentration. Thus the recommended turbidimetric procedure is a simple, direct, and rapid method for the microdetermination of zirconium. It can be modified to serve for the estimation of fluoride ion Concentration.
CONCLUSIONS
Zirconium in the prrsence of large amounts of various ions can be successfully determined by the suggested turbidimetric technique. This method makes use of readily available reagents and simple inexpensive equipment. illthough the Bausch and Lonib monochromatic colorimeter was selected for this investigation, any colorimeter or turbidimeter could be used. The suspension of zirconium phthalate is very stable and independent of the order of mixing the reagents, as the reaction takes place only above room temperature. Under these conditions the suspenqion is formed slowI?- from a homogeneous
ACKNOWLEDGMEYT
The authors wish to thank the Research Corp. for a grnnt in partial support of this work. LITERATURE CITED
(1) Purushottam, A , , and Rao, Bh. S. V. R., Analyst, 75, 654 (1950). RECEIVED for review January 18, 1954, hccepted June 29, 1954. Portion of a thesis submitted by Leroy E. Swim in partial fulfillment of the requirements for the degree of master of science, Kansas State College.
Simple Air-Permeability Method for Measuring Surface Areas of Fine Powders H.1. KAMACK Engineering Research Laboratory, Engineering Department,
Conventional techniques for measuring surface areas of powders cannot be applied to some materials either because, in the case of gas adsorption, some of the gas is taken up inside the material rather than on the surface of the particles or because, in the case of the airpermeability method, the powTder is so fine that the air flow rate is too low to measure conveniently. An experimental technique based on the air permeability method has been developed which is applicable to powders whose average size is below about 30 microns and which is especially useful for powders in the range from 5 to 0.2 microns. The method is simple and rapid. The method is useful for research work involving powders in the micron and submicron range, and also is useful as a rapid control test for such materials.
I
P; T H E
course of some grinding experiments in which ilmenite sand was used as a convenient test material, it became necessary to measure the surface area of the ilmenite during grinding. The two best-developed methods for measuring surface areas of powders are the nitrogen-adsorption method associated with the names of Brunauer, Emmett, and Teller, and the air-permeability method. The nitrogen-adsorption method depends on measuring the quantity of nitrogen needed to form a monomolecular layer on the surface of the porr-der. Besides being relatively expensive and time-consuming, this method was found to be inapplicable to ilmenite powder because nitrogen not only adsorbs on the surface of the particles of powder but also penetrates into the grains. Penetration was suspected when measurements by this method gave extremely high surface areas, and it was confirmed by testing the method on a sample of washed, unground ilmenite sand. These grains are in the range from 48 to 150 mesh and appear under the microscope as smooth, rounded, nonporous particles. The surface area calculated from the sieve analysis (which should be reliable, since the sand contained no dust) was 0.01 square meter per gram. Nevertheless, the apparent surface area obtained by the nitrogen-adsorption technique was 8 .square meters per gram. It is believed that the nitrogen may
E. 1.
du Pont d e Nemours
& Co., Wilmington,
Del.
have been held in tiny cracks between submicroscopic crystals of n hich the ilmenite is composed, and the width of these cracks is estimated to be less than 0.01 micron. Because of these limitations of the nitrogen-adsorption method. the author turned to the air-permeability method, which is based on measuring the flow rate of air through a compressed bed of the powder with a known pressure drop across the bed. This method measures only the external surface area of the particles, because air will not flow through the tiny cracks in the particles, even if they should happen to form continuous channels. However, the usual techniques of air-permeability measurement could not be applied to this special case, because some of the poffders to be measured were so fine that the air flow rate through the bed was too small to measure accurately. An attempt was made to increase the flow rate by using a relatively large area of sample bed and a large pressure drop across the bed, but this led to further difficulties in that the p o d e r bed tended to crack, which ruined the measurement. The method described beloFT is called, for convenience, the [‘manometer method.” It involves no new theoretical principles, being based on the permeability theory which has been developed and confirmed by previous investigators, but it involves an experimental technique that avoids the difficulties of measurement described above; in fact, the only limitation on the fineness of ponders that can be measured is imposed by the limits of applicability of the theory rather than any difficulty of measurement. The main reason for this is that the surface area is made to depend on a measurement of the time for a known quantity of air to flow through the powder, and this time becomes longer and therefore easier to measure accurately as the powder becomes finer. The method has been found to be practical, reliable, rapid, and simple, and i t has been used on several hundred powder samples ranging in fineness from 30 to 0.2 microns average particle diameter in specific surface. METHOD AND APPARATUS
The apparatus shown in Figure 1 is used, consisting of a manometer of about 1-cm. bore with one arm about half the length of the other, a sample tube of about 0.5-inch diameter, and a stopper and adapter for connecting the sample tube to the short arm of
