ANALYTICAL CHEMISTRY
1832 Table IV.
Comparison with Bowen-Barthel Procedure
Column Technique Titration Gravimetric= Bowen-Barthel Procedure Nicotine Nornicotine Nicotine Nornicotine Nicotine Xornicotine
3.70 0.12 0.37 3.08 1.60 2.90
1.00 1.20 1.05 0.40 0.44 0.34
.. ..
3.80 0.15 0 38
, .
..
.. ..
3.20 1.50 3.09
0.35 0.35 0.30
Bowen-Barthel procedure is shown in Table IV, along with a comparison of results obtained by titration and gravimetric determination of the alkaloids in the solvent extracts. These are similar t o the results obtained by Jeffrey ( 4 ) in his study of various techniques for the determination of nicotine and nornicotine in tobacco.
0.85 1.10
LITERATURE CITED
0.8.5
..
.,
, .
..
..
(1)
Avens, A. W., and Pearce, G. IT'., IXD. ENG.C"af., .INAL. ED.,
11, 505 (1939). (2) Bowen, C. V., J. Assoc. Ofic.Agr. Chemists, 3 0 , 3 1 5 (1947).
Garner, W. W., Bacon, C. W., Bowling, J. D., and Brown, D. E., U.S. Dept. Agr., Tech. BulE. 414 (1934). (4) Jeffrey, R. N., J. Assoc. Ofic.Agr. Chemists, 3 4 , 8 4 3 (1951). (5) Willits, C. O., Swain, hI. L., Connelly, J. A., and Brice, B. A., A N ~ LCHEM., . 22, 430 (1950). (3)
Determined as silicotungstate.
0.02 N sodium hydroxide using 1drop of 0.1% methyl red as the indicator. The reproducibility of results by this technique is demonstrated in Table 111, and a comparison of results by the
RECEIVED for review June 7,19.52. .lccepted August 7,1952. Published by permission of the director of the Kentucky Agricultural Experiment Bttltion.
Determination of Titanium in Pigments and Ores Titrimetric M e t h o d
'
JOSEPH A. RAHR.1 Titanium Division, Sational Lead Co., S t . Louis, MO.
N T H E manufacture of composite pigments, precise deter-
mination of titanium a t several stages of the process is necessary. I n the past, a modified Jones reductor was used in a number of laboratories for the reduction of titanium to the titanous state, and the titanium was determined by titration with ferric ammonium sulfate. The Jones reductor suffers from several disadvantages both for routine work and for occasional analyses: Amalgamated zinc must be prepared; contaminants may spoil the column of zinc; determination of the condition of the reducing agent is difficult; and transfer of the sample to three different pieces of apparatus results in large volumes of solution a t the time of titration. In order to circumvent these disadvantages, a method of reducing titanium with aluminum was developed. The complete analysis is carried out in a 500-ml. Erlenmeyer flask and no special equipment is necessary. The method is admirably suitable for routine xork, and because it is not necessary to prepare a special reducing agent or use special apparatus, the procedure offers distinct advantages to those who run only an occasional analysis.
of titanium dioxide, or 0.0626 111. This solution is prepared by dissolving 16.9 grams of ferric chloride hexahydrate (FeCla.6HnO) in 800 ml. of distilled water containing 15 ml. of 18 ill sulfuric acid. This is diluted to 1 liter and standardized against a suitable sample of titanium dioxide such as the National Bureau of Standards Sample 154 which is a good primary standard for this purpose. The standard sample is brought into solution, reduced, and titrated as described under the procedure for routine analysis. PROCEDURE FOR ROUTINE 4NALYSIS OF PIGMENT
Transfer a 0.5000-gram sample of composite pigment, or a 0.1000- to 0.2000-gram sample of pure titanium dioxide, into a 500-ml. widemouthed Erlenmeyer flask. Add 25 ml. of 18 Jf eulfuric acid and 25 grams of ammonium sulfate.
APPARATUS
Figure 1 shows the apparatus used for the exclusion of :iir from an acid solution of reducted titanium. The apparatus consists of a 500-ml. widemouthed Erlenmeyer flask fitted with a delivery tube. The end of the delivery tube is maintained below the level of a saturated sodium bicarbonate solution contained in a 250-ml. glass beaker. Care should be taken to see that no undissolved sodium bicarbonate is in the bottle, since a slurry in this bottle can result in a blocked delivery tube with subsequent danger of explosion of the Erlenmeyer flask.
REAGENTS
Ferric chloride solution, 0.062G M Potassium thiocyanate solution, 45% by weight Hydrochloric acid, 12 M Sulfuric acid, 18 M Sulfuric acid, 20% solution by weight Ammonium sulfate Potassium bisulfate Sodium bicarbonate, 9% solution by weight Aluminum metal, 99.8%+ purity PREPARATION OF STANDARD FERRIC CHLORIDE SOLUTION
It is convenient to make up a standard solution of ferric chloride of such concentration that 1 ml. is equivalent to 0.005 gram
Figure 1 Place the flask over the flame of a AIeker burner and svirl the contents of the flask occasionally to assist the solution of the pigment. When the hot solution is a golden yellow and the last traces of pigment are in solution, remove the flask from the burner and allow the contents to cool to room temperature. Add 130 ml. of distilled water and 20 ml. of 12 M hydrochloric acid to the flask. Reheat the contents of the flask to boiling and remove the flask from the vicinity of any open flame. S ~ i r l the flask gently to release any superheated steam and then add 1 gram of aluminum metal. Insert the rubber stopper containing a delivery tube into the neck of the flask (as shown in Figure 1) and place the other end of the delivery tube below the level of the sodium bicarbonate solution. After all the aluminum has dissolved and no more hydrogen is evolved, place the flask in a cooling bath. When the reduced solution has cooled to less than 60" C., remove the delivery tube, add 2 ml. of potassium thiocyanate solution, and titrate with standard ferric chloride solution to the appearance of a light orange end point.
1833
V O L U M E 2 4 , N O . 11, N O V E M B E R 1 9 5 2 Table I.
Comparison of Precision of Two 3lethods Jones Reductor Method
h-0. of samples AverageX, % btandard deviation, 7
Aluminum Reduction Method
2001 29 97 0 22
784 30 02 0 13
ANALYSIS OF ORE AND RESIDUE
Transfer a 0.3000- to 0.5000-gram sample of minus 100-mesh ore or residue into a 500-ml. wide-mouthed Erlenmeyer flask containing 30 to 50 grams of potassium bisulfate. Place the flask on a wire triangle over the open flame of a bfeker burner and heat for 30 minutes.After all the ore is in solution, remove the flask from the burner and allow the melt to cool. TVhen the melt is cold. add 180 ml. of 20% sulfuric acid and 30 ml. of concentrated hyd~ochloricacid, and place the flask on a hot plate. Heat until all the melt has dissolved and the contents of the flask are boiling. Remove the flask from the vicinity of any open flame and gently swirl the contents to release any excess steam. Add 3 grams of aluminum metal. Insert the rubber stopper containing the delivery tube (as shown in Figure 1) and place the other end below the level of a saturated sodium bicarbonate solution. When all the aluminum has dissolved, cool the solution to less than GO” C., add 2 ml. of potassium thiocyanate solution, and titrate n i t h standard ferric chloride solution to the appearance of a light orange end point. DISCUSSIOY 4 Y D RESULTS
Typical Analysis of Ore, Pigment, and Residue. The major chemical constitutents of the samples that have been analyzed by this method are preqented below. The residue sample is the insoluble portion of a conimercial digestion reaction between ore and acid, and conskts primarily of undissolved ore, free titanium dioxide, silica, and silicates. 7
7
Titanium Dioxide Composite pigment Ore Residue Pure titanium dioxide pigment
28 t o 42 t o 20 t o 95 to
32 64 40 99
Ferrous% Calcium Silicon Oxide Sulfate Dioxide 25’;O’?O 10 to 20 ,
, ,
.
Ca. 70 .., , , . ... lj’tb’30 ... ...
Effect of Variables Influencing Accuracy. The rate of reaction and efficiency of reduction of titanium ion are dependent upon the initial acid concentration in solution. Increased acid concentration decreases the efficiency of the reduction of titanium ion, and increases the quantity of hydrogen gas. The use of larger acid concentration must be compensated by an increase in the quantity of reducing agent; otherwise low and erratic results \vi11 be obtained. IIore :Iluminum is required for reduction of an ore or residue sample than for a comparable quantity of pigment sample. Ore and residue samples contain an appreciable amount of iron ( l o to 40%) and this iron is oxidized to the ferric state during the initial fusion of the sample. The reduction reaction proceeds stepwise. All ferric iron is reduced to the ferrous state before the titanium can be reduced to the titanous form. The increased quantity of material to be reduced in ore and residue samples and the greater acid concentration require more reducing agent than do pigment samples. Decomposition of the thiocyanate indicator will occur a t temperatures exceeding 70” C. in the reduced solution. The odor of hydrogen sulfide can be detected and a fleeting end point obtained if the indicator solution is added to the hot reduced solution of titanium. If the solution is allowed to cool to GOo C. or loa-er before addition of the indicator, no interferences will occur. A blank titration ( 2 ) exists with almost all grades of nlu-
minum metal and a blank determination was made for all lots of aluminum used in this investigation. The blank is generally of the order of 0.05 t o 0.30 ml. of 0.06 M per gram of aluminum metal. For this reason, the same aluminum used in standardizing the ferric chloride solution should be used in analyzing samples. Aluminum metal foil of 99.8%+ purity used in the electrical and foil industry is an excellent reducing agent, and generally no blank titration is involved with this particular grade of metal. The presence of copper and antimony in a h minum is particularly objectionable because these metals are reduced to the metallic state during the reduction reaction, and subsequently interfere with the titration and obscure the end point. Tin and titanium are common impurities in aluminum metal and are the elements generally responsible for the small blank titration involved. PRECISION
Table I contains the data obtained for the aluminum reduction and Jones reductor methods. Standard samples of conipoaitr pigment were submitted to a control laboratory for the routine determination of titanium dioxide. Two thousand samples were submitted for analysis by the Jones reductor method over a 2-year period, and 784 samples were submitted for analysis by the aluminum reduction method over an 8-month period after the adoption of the method by the author’s laboratory. The data of Table I indicate that the precision of results is better for the aluminum reduction method, Calculation of the variance ratio ( 1 ) for the number of samples involved shows that the difference is significant. The variance ratio of 2.87 obtained indicates that there is less than 1 chance in 1000 of the precision of the t F o methods being the same.
Table 11. Precision of Ore and Residue Analyses Ore standard Ore and residue samples
No. of Samples 17 84
Standard Deviation, % 0.10 0.06
Table I1 contains the results of analysis of 42 ore sampler 42 residue samples, and 17 ore standards for titanium dioxide by the aluminum reduction method. Calculation of the precision of the method for this analysis is based upon the standard deviation of the differences ( 3 ) between duplicate samples. The data obtained for the ore standards were calculated separately and compared with the ore and residue results. Application of statistical principles to the data contained in Table I1 indicates that the precision of the method 99% of thP time n-ould be +0.30% for the standard sample and 50.18% for thr or? and residue samples. ACKNOWLEDGIlENT
The author is indebted to L. E. Olm~tedfor valuable suggestions and assistance, and to John Luethge for the drax-ing used in this report. LITERATURE CITED
(1) Davies, 0. L., “Statistical Methods in Research and Ploductlon,” London, Oliver & Boyd, 1949. (2) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” Blank Determinations, New Tork, Macmillan Co., 1943. (3) Simon, L. E., “Engineer’s hIanual of Statistical Methods, Measurement of Precision of Observation of a Variable,” Kew Tork, John Wiley & Sons, 1944. RECEIVED for review March 28,1952. Accepted August 14,1952
