V O L U M E 2 7 , NO. 9, S E P T E M B E R 1 9 5 5
1428
a filtering crucible sufficiently retentive to hold the nitrocellulose. .Ismall part of it is finely divided and may pass through most crucibles; this is the reason for refiltering the filtrate before saponifving the alkyd resin. Unless asbestos is used, glass crucibles will clog and filtration is difficult. It is apparent that the separation by adsorption of alkyd resins of low molecular weight from plasticizers of high molecular weight n-ill be increasingly difficult as these weights approach each other. It is possible that the procedure presented here may be unsuited for some separations; the technique could undoubtedly he modified for such special purposes. The eluates in these plasticizer separations also contain some oil and for this reason cannot be evaporated and weighed to measure the plasticizer separated. It has been noted that the oil separated varies with the oil length of the alkyd resin used and there are indications that a slight modification of this technique will permit measurement of uncombined oils in oil-modified alkyds.
I11 lacquers tested which contained diphenvl phthalate. as plasticizer, developed a bright red color when slcoholic alkali was added, probablv due to the presence of some phenolphthaleiri The phosphate plasticizers, tricresyl and triphenyl phosphate, give positive qualitative tests for phenol when a dried sample of lacquer is tested according to Method 514.1 of Federal Sperification TT-P-I4lb, paragraph 2 1.3 LITERATURE CITED
( 1 ) Shaefer, W. E., and Becker. 17. K.. A s . 4 ~ .CHEM.,25, 1220
(1953). (2) Shreve, 0. D., and Heether, 11. 1C.. Ibid., 23, 441 (195lj. (3) Swann. & H., I. Ibid., 21, 1448 (1949). (4) Swann, 31. H., and Esposito, 0. C . , Ihl'd., 26, 1054 (1954). R E C E I T EfDo r review .January 2 195:
tccepted 31ay 13, 1955
Determination of Fluorine in Catalysts Containing Alumina and Silica CHIA-CHEN CHU and 1. L. SCHAFER Petroleum and Chemical Research Laboratory, The
M. W. Kellogg Co.,
&lumina and silica interfere w i t h determination of fluorine. A one-precipitation method for removing aluminate and silicate has been developed using low temperature sodium peroxide fusion for decomposition of sample. Sodium peroxide fusion gives thorough decomposition of sample and yields a readily watersoluble melt. Aluminate and silicate are precipitated with zinc sulfate. One precipitation and filtration remove more than 99% of the silica present. Fluorine i b isolated by distillation as fluosilicic acid and titrated with thorium nitrate. The method is accurate to within 52.9% with 95970 confidence limit for samples containing as little as 0.197~of fluorine, and has a standard deFiation of 1.2%.
I
S RECEKT years the preseiict! of fluorine in catalysts containing alumina and silica has become a matter of intereFt i n the petroleum industry, and t,his in turn has stimulated interest in methods of determining the 'fluorine content of thew vatalysh. .4 simple and rapid method for determination of fluorine in presence of alumina and silira has been developed iri this laboratory. Both alumina and silica interfew with determinat,ion of Iluorine. Berzelius] gravimetric method (S) is tedious and not suitable for samples containing less than 10 mg. of fluorine. Steiger's peroxidized titanium procedure ( l o ) , as modified by l'arrish and others ( 6 ) , is rapid, but is not accurate for fluorinca (.ontents higher than 2%. Willard and Winter's method (11 i of volatilizing fluorine as hydrofluosilicic acid, followed by titrating with thorium nitrate, covers a wider concentration range than either Berzelius' or Steiger's method, but requires triple filtration for removing large amount of silica prior to distillation. .Isimple procedure for removal of alumina and silica has been (leveloped in which one precipitation with zinc sulfate a t pH 1 1.5 is sufficient to remove interfering amounts of alumina and silica; residual alumina and silica are too low to interfere with recovery of fluorine in the subsequent distillation step. Sodium peroxide is used rather than sodium carbonate in fusing the sample, since sodium peroxide is a more effective fusion agent. The fusion is performed a t 500" to 540" C., permitting use of platinum crucibles ( 7 ) . The constant-temperature steam-distil-
Jersey City,
N. J.
lation still designed by Huckabay and others ( 4 )is used nith slight modification. Hydrofluosilicic acid is distilled from sulfuric acid :it 145" C. Fluorine in t,he distillate is determined by the thorium iiit,rate titration method of Rowlz~.and Churchill (8). A halfiieutralized monochloroacetic acid buffer, prepared according to Kimball and Tufts (5), is used to maintain pH 3.0 during titration. .In artificial color standard of cobaltous nitrate and potaesium chromate] proposed hy Ebcrz and others ( I ) , is used for matching the end point. .Isuit'able amount of thorium fluoride i n the color standard helps in matching to a piecise end point ( 2 ) . This method apparently v a s developed concurrently with that of Shell and Craig (Q),the t,no methods being similar in broad outline but differing in n. number of details. The present method is believed to be more suitiihlc for accurate determination of low ronceritrations of fluorine and I ~ R Sseveral other advantages. Use of sodium peroxide fusion not only gives thorough derom[mition of sample but also yields a melt that is entirely and ieadily soluble in water. Furthermore, the completenesfi of ilissolution provides an indicatioir of the completeness of deromposition. In Shell and Craig's sodium carbonate-zinc oxide i'usion method, the melt cont,ains insohbk zinc salts which hinder the dissolution of soluble salts and the completeness of decomposition is assured only after a repetition of fusion and distillation. In the titration step, use of R buffer is much simpler than monitoring ryith a pH meter as required by Shell and Craig. Two milliliters of buffer was found to maintain the pH a t 3.0 to 3.2 for titrating fluorine concentrxtioiis up to 10 mg. of fluorine in 100 1111. of distillate] the largest umoniit of fluorine normally encountered. Use of a color standard is desirahle. as it enable8 an inexperienced worker t o detect the riitl point. nE.cEms
Sodiuin peroxide] reagent gradr. Zinc sulfate, 36 grams of zinr sulfate heptahydrate per 100 ml. of solution. Sodium sulfate, reagent grade, 170 aqueous solution. Sulfuric acid, concentrated, rcnpent grade, tested by didllation to be fluorine-free. Sodium hydroxide, reagent grade, 20% and 1% aqueous solution. Mixed indicator, 0.4 gram of 1,3,5-trinitrobenzene arid 0.4 gram of alkaline blue per 100 ml. of 95% ethyl alcohol. Soda-lime glass, finel>-ground, washed with sulfuric acid and m-ater.
1430
ANALYTICAL CHEMISTRY
Sodium alizarin sulfonate, 0.05% aqueous solution. Hydrochloric acid, reagent grade, diluted 1 to 250 with water. Buffer solution, pH 3.0, prepared according to Kimball and Tufts (5) by dissolving 9.4 prams of monochloroacetic acid in 30 ml. of water, diluting to 60 ml., neutralizing 38 ml. with 20% sodium hydroxide solution and mixing with remainder, and diluting to 100 ml. This solution decomposes within 2 weeks on standing at room temperature and then gives appreciable turbidity on addition of dilute silver nitrate solution and nitric acid. The buffer solution is stable for a few months if stored in a refrigerator.
I
t b201
until 100 ml. of distillate consumes no more than 0.04 ml. of 0.05N thorium nitrate solution, an amount required in a typical distillation blank. If distillation is carried out a t a faster rate, appreciable amount of sulfuric acid is carried over and results in a higher distillation blank. The volume of distillate to be collected varies with amount of fluorine present. Usually, collection of 200 ml. is sufficient for 1 to 5 mg. of fluorine, 500 ml. for 15 to 25 mg. of fluorine. Titration. The distillate is thoroughly mixed, and to a 100-ml. aliquot taken for titration, 0.80 ml. of 0.05% sodium alizarin sulfonate solution is added. Enough 1 % sodium hvdroxide solution is added to give a red color,-then-dilute hy&ochloric acid (1 to 250) is added dropwise until the red color fades. Two milliliters of buffer solution is added and the solution is titrated with thorium nitrate solution using a 5-mI. microburet. The end point is reached when color of the solution matches that of 100 ml. of color standard containing thorium fluoride, precipitated by adding 4 ml. of each of the standard solutions of thorium nitrate and sodium fluoride.
Table I.
mg. F added as NaF in 100 m/. Figure 1. Effect of fluorine concentration on titration equivalent of thorium nitrate solution
Sodium fluoride in 0.05h' solution, containing about 2.2 grami: of dry, pure, accurately weighed sodium fluoride per liter of solution. Thorium nitrate in 0.05,V solution, prepared by dissolving 7.3 grams of thorium nitrate tetrahydrate per liter of water. This solution is standardized against standard sodium fluoride solution that has been carried through the distillation step of the method. This is necessary because only 98.5y0 of fluorine is recovered. Color standard, containing 1.236 grams of cobaltous nitrate hexahydrate and, 0.0093 gram of potassium chromate per liter of water. Silver sulfate, reagent grade. 1,1,2,2-Tetrachloroethane, redistilled, for constant-temperature steam-distillation still.
Peroxide Compn.. Grams Fusion and Alumina Silica Separation NO 0.1 1.0 NO 0.02 0.2 NO 0.1 1.OQ N O 0.1 1.00 Yes 0.87 0.13 Yes 0.87 0.13 0.87 Yes 0.13 Yes 0.87 0.13 a Added as AlK(SOdz.lZHz0.
Fusion of Sample. A finely pulverized sample of not more than 2 grams, containing preferably 5 to 25 mg. of fluorine, is neighed into a pIatinum or nickel crucible. Eight to 10 times the sample weight of sodium peroxide is added and thoroughly mixed with the sample. The mixture is heated in a muffle furnace for 1 hour a t 500" to 540' C.,usually resulting in complete fusion. After cooling to room temperature, the melt is dissolved in 100 ml. of water with heating, and the solution simmered for about 1 hour to destroy any remaining peroxide. R a t e r should be added as required to keep volume up to 75 ml. Removal of Alumina and Silica. About 20 ml. of zinc sulfate solution per gram of sample is added slowly, with stirring, to the solution prepared in the previous step. One milliliter of mixed indicator solution is added and pH is adjusted to 11.5 by dropwise addition of sulfuric acid (1 to 3 ) until color of suspension changes from orange red to muddy violet. An extra drop of acid gives the suspension a definitely blue color; the pH may be readjusted by dropwise addition of 20% sodium hydroxide solution. The curdy precipitate of zinc aluminate and zinc silicate is digested on a steam bath until it becomes crystalline, usually requiring 1 hour. The hot solution is decanted through a mediumporosity sintered-glass filter funnel. The precipitate is then transferred into the filter funnel and washed thoroughly with hot 1% sodium sulfate solution. Filtrate and washings are combined and concentrated on a steam bath. This one-precipitation procedure removes more than 99% of the silica originally present in the sample. Distillation of Fluorine as Hydrofluosilicic Acid. The concentrated filtrates, together with 0.5 gram of soda-lime glass powder and a suitable amount of silver sulfate for binding any chloride present, are charged t o the constant-temperature steam-distillation still and followed by addition of 20 ml. of concentrated sulfuric acid. Distillate is collected in volumetric flasks a t a distillation rate of 2.5 to 5 ml. per minute Distillation is continued
Present,
Fluorine Found, ms.
27.18 21.74 54.35 10.87 18.70 17.04 4.925 1.970
27.22 21.62 ,54,32 10.92 18.31 16.61 4.938 1,999
ms.
Recovery % 100.1 99.4 99.9 100.3 98.0 97.6 100.2 131.5
Table 11. Analytical Results on Catalysts and Minerals Peroxide Fusion and Separation
Sample Alumina-rich catalyst . I Silica-rich catalyst B Lepidolite, Calif. Idocrase, Maine Zunyite, Utah
ANALYTICAL PROCEDURE
Analytical Results on Synthetic Samples
KO
No NO
Yes Yes Yes Yes Yes Yes YeS Ye3
Sample Size, Grams 0.23 0.21 1.07 1.02 1.03 0.22 0.21 0.21 1.09 0.42 0.32
%
Fluorine 7.14 7.22 1.42 1 , eo 1.60 7.56 7.50 2.10 2.06 4.73 4.79
Optimum concentration of fluorine for titration is 3.5 to 10 mg. per 100 ml. As shown in Figure 1, the amount of thorium nitrate needed per milligram of fluorine required for titrating undistilled sodium fluoride sohtioh remains constant for concentrations of fluorine ranging from 3.5 to 40 mg. per 100 ml. Below 3.5 mg. per 100 ml., thorium nitrate consumption increases steadily as fluorine concentration decreases. Therefore, for distillates containing less than 3.5 mg. of fluorine per 100 ml., a suitable amount of standard sodium fluoride solution is added to bring total fluorine up to 4 mg. DISCUSSION
Synthetics were prepared by adding sodium fluoride solution to mixture of alumina and silica gels, and evaporating to dryness; the alumina dissolved in sulfuric acid and the silica became gelatinous in sulfuric acid. .4nalytical results on these synthetics are summarized in Table I. Results on the first four synthetics show that quantities up to 1 gram of alumina gel and 0.1 gram of silica gel can be tolerated in distillation. Therefore, for catalysts rich in alumina and containing less than 10% of silica, the pulverized sample can be subjected to distillation without removal of alumina and silica, provided that sample size is 1gram or less. For silica-rich catalysts, separation is necessary before distillation; without separation, only about 90% of the fluorine is recovered. In Table 11, good agreement of duplicate fluorine determinations on various mineral samples shows that this method may prove useful in mineral analysis.
1431
V O L U M E 2 7 , N O . 9, S E P T E M B E R 1 9 5 5 Accuracy of this method has been tested with synthetics and found to be =k2.9% with 95% confidence limit for samples containing as little as 0.1% of fluorine. Duplicate determinations of catalysts and minerals showed a standard deviation of l.2yO.
(4) (5) (6)
ACKNOWLEDGMENT
The authors wish to express their appreciation to Ernest Solomon and J. hl. McCrea for their interest and generous hclp in preparation of this paper. LITERATURE CITED
(1) Ebers, W.F., Lamb, F. C.. and Lachele, C . F: , IND. ENG.CHEM., ASAL. ED. 10. 259 (1938). (2) Haslam, J , andkhettem, S.AI. A , J . A p p l . Chem. (London), 2, 399 (1952).
W.F.. Lundell. G. E. F.. Bright. H. .1..and Hoffman, J. I., “Applied Inorganic Analysis,” p. 939, Wiley, Sew York, 1953. Huckabay, W. B., U‘elrh, E. T., and Metler, A. V , A s 4 ~ . CHEM.,19, 154 (1947). Ximball, R. H., and Tufts, L. E., Ibid., 19, 150 (194i) Parrish, AT. C., Widmyer, J. H., Brunner, -4.J., and JIathon, F. R., Ibid., 19, 156 (1947). Rafter, T. A., Analyst, 75, 485 (1950). Rowley, R. J., and Churchill, H. V., IND.ENG.CHEM, -4r.4~.
(31 Hillebrand.
(7) (8)
ED.,9,551 (1937). (9) Shell, H. R., and Craig, R. L., ASAL. CHEM.,26, 996 (1054). (10) Steiger, G., J . Am. Chem. Soc., 30, 219 (1908). (11) Willard, H. H., and Winter, 0. B., IND.ENG.CHEX,A N ~ L ED., 5 , 7 (1933). RECEIVED for review February 17, 1955. Accepted M a y 12, 1955.
Determination of Oxygen in Calciwm Metal A. R. EBERLE, M. W. LERNER,
and
U. S. Atomic Energy Commission, N e w
G. J. PETRETIC
Brunswick Laboratory, N e w Brunswick,
A rapid procedure is presented for the determination of oxygen in calcium metal. The method consists of the reaction of calcium with anhydrous methanol and dissolution of the reahtion products by addition of an anhydrous salicylic acid-pyridine solution. The water formed by the reaction of the oxide with the salicylic acid is easily determined by titration with Karl Fischer reagent. A simple apparatus for the reaction and titration operations is described. Data are presented to show that pyridine effectively inhibits esterification between the salicylic acid and the methanol. Results are given on the determination of anhydrous calcium oxide equivalent to 2.5 to 13 mg. of oxygen with a precision of about 0.1 mg. Calcium metal containing 0.4 to 2% of oxygen was analyzed readily.
L
ITERATURE reviews have disclosed no recorded method for the determination of oxygen in calcium metal. Reccntly, White, Ross, and Rowan ( 7 ) have determined oxygen in sodium by the reaction between sodium and excess n-butyl bromide in hexane solution. The sodium monoxide which does not react with thc reagent was determined by titration, after addition of water. Pepkowitz and Judd (6) developed a method for olygen in sodium which essentially depends upon the extraction of sodium with mercury in an inert atmosphere and the separation of the residual sodium monoxide, which is insoluble in mercury. Williams and Miller (9) have reported a modification of the method of Pepkowitz and Judd. Xone of these methods was found to be adaptable to the determination of oxygen in calcium. The authors have developed a new method which is based upon the fact that methanol reacts with calcium to form calcium methylate, but does not react with calcium oxide. Following this rcaction, dissolution of the calcium methylate and calcium oxide by addition of a salicylic acid-pyridine solution yields soluble calcium snlicvlate, methanol. and water. The water which is liberated stoichiometrically from the oxide present i, determined by the Karl Fischer ( 6 ) method using the dead-stop end point technique of Foulk and Bowden ( I , 4 ) . 4PF4RATUS
The apparatus used for the reaction of calcium with methanol is shown in Figure 1.
N. J.
The borosilicate glass reaction and titrating flask of 250-ml. capacity has a T 24/40 center neck and a T 14/20 side neck which is fitted with a ground-glass stopper. The refluxing condenser is 300 mm. in length and connected to the center neck of the flask through a bushing type ada ter of T 24/40 outer g r o u n i zone and T 14/40 inner ground zone. A straight stopcock is sealed to the to of the condenser and is t i e n connected through a ball-andsocket joint to a Nesbitt absorption bulb containing a layer of Drierite covered with anhydrous magnesium perchlorate. Solutions are stirred with the aid of a magnetic s t i r r e r . T h e glass covered stirring bar is 35 mm. in length and 5 mm. in diameter. A Beckman Model K-F Aquameter is employed for carrying out the Karl Fischer titration. T h e s t a n d a r d 125-ml. titrating flask and duel platinum electrodes supplied with the Aquameter are used in determining the water (blank) content of an aliquot of the methanol drawn from the reaction flask prior to addition of the calcium. The smaller flask is also used for titrating the salicylic acidDvridine solution before addiFigure 1. Reaction and ;
