ANALYTICAL CHEMISTRY
1632 The results obtained by the carbon dioxide, titration, and carbazole methods agree fairly well. The anhydrouronic acid values calculated from the calcium analysis of the Carr6Haynes calcium pectate yielded results that were about 10% higher (except for the sample of tomato pectin) than the results from the carbon dioxide or carbazole method. This may be explained by the possibility that all of the calcium fails to associate only with carboxyl groups of pectate. Calcium pectates obtained by the Carr6Haynes procedure from different plant sources are not of constant composition and the calcium analyses of the calcium pectates cannot be used to calculate reliable anhydrouronic acid contents. Therefore, this method has little to recommend it for the quantitative determination of pectic substances The carbazole method was standardized n.ith galacturonic arid hydrate vihose purity was determined by titration. The results of the analyses of pectin are slightly lower than those obtained by the titration method. The presence of acidic constituents, salts, or acetyl groups in pectic substances lead to high anhydrouronic acid values by titration. The precision of the colorimetric carbazole method is about 2%; however, the results in Table IV are ahout 4% higher than those with the carbon dioxide method.
ACKNOWLEDGMENT
The authors wish to express their appreciation to L. R. Leinbach for the carbon dioxide analyses and to Stanley Friedlander for determining the absorption spectra of the uronic acid-sulfuric acid-carbazole mixtures. LITERATURE CITED
(1) Assoc. Official Agr. Chemists, “Official and Tentative Methods of Analysis,” 6th ed., 1945. (2) C a d , M. H., and Haynes, Dorothy, Biochem. J., 16, 80 (1922). (3) Dische, Z., J . BioZ. Chen~.,167, 189 (1947). (4) Ibid., 183, 489 (1950). (5) Hinton, C. L., “Fruit Pectins, Their Chemical Behavior and
Jelling Properties,” New York, Chemical Publishing Co., 1940. (6) Holsman, G., RIacAllister, R. V., and Niemann, Carl, J . Bid. Chem., 171,27 (1947). (7) BIcCready, R. M , , Shepherd, ,4.D., Swenson, H. A , Erlandsen, R. F., and Maclay, IT. D., ANAL.CHEX., 23, 975 (1951). (8) RIcCready, R. hl., Swenson, H. A , and Maclay, K . D., IND ENG.C H E M . , A N A L . ED., 18, 290 (1946). (9) Stark, S. hi., Jr., A s . 4 ~ CHEM., . 22, 1158 (1950). RECEIVED for review March 11, 1952. Accepted June 27, 1962. hleution of products by specific manufacturers does not Imply t h a t they are endorsed or recommended by the Department of Agriculilire over others of a similar nature not mentioned.
Determination of Titanium in Titanium Metal J . M.THOMPSOX Pigments Department, Chemical Dicision, E. I . du Pont de ,Vemours & Co., Inc., Newport, Del. is described for the determination of titanium in A METHOD high-purity titanium metal. This test was developed by the
Pigments Department, Chemical Division Laboratories of E . I. du Pont de Nemours & Co., Inc., and has been used extensively over the past 6 years. The method is based on the work of Knecht and Hibbert ( 2 ) , who employed a standard solution of ferric salt for titrimetric estimation of titanium. Modification included the use of thiocyanate added directly to the test solution instead of employment as an outside indicator (3, 4 ) . The method was modified and adapted to the determination of titanium in titanium pigments by J. W. Stillman of the Du Pont Chemical Department and C. R. Wicker of this laboratory. Further changes utilizing a twostage reduction were made and applied t o the determination of titanium in ores and pigments by E. N. Kramer and E. D. Lewis of this laboratory. In the instant method for determination of titanium in commercially pure metal, interfering elements are not normally present. Chromium, molybdenum, tungsten, and vanadium may be present in some alloys and must be removed. A method for removal is outlined. Table I indicates the reproducibility of the method. The results listed were obtained by two laboratories on unknown samples of commercial sponge. Each value listed is the average of two determinations. Inspection of the data shows that a difference greater than 0.2% between laboratories occurred on only one sample of the 24 and this maximum deviation was 0.23%. The difficulty in obtaining representative samples of ductile titanium sponge is recognized. Closer agreement will result when improved methods of sample preparation become available. APPARATUS AND REAGENTS FOR DETERMINATION OF TITANIUM
Erlenmeyer flasks, 300-ml., borosilicate glass Tuttle covers Potassium bisulfate, fused, pure Sulfuric acid, concentrated Meker burners
Hydrochloric acid, 50% by volume Florence flask, 1000 ml. Cylinder of carbon dioxide with regulating valve Amalgamated zinc shot Amalgamated 20-mesh zinc Modified Jones reductor Flow meter for measuring carbon dioxide Glass wool Flask tongs Hydrochloric acid, 10% by volume Standard 0.1 N ferric alum solution Potassium thiocyanate or sodium thiocyanate solution, 400 grams per liter PROCEDURE FOR DETERMISATION OF TITANIUM
1. Accurately weigh about 0.2 gram of the sample and transfer to a 300-ml. borosilicate glass flask which contains 15 to 25 grams of potassium bisulfate and 10 drops of concentrated sulfuric acid. 2. Place a Tuttle cover in the neck of the flask and heat over a Meker burner, gently a t first, and then over the full flame unqil the bisulfate has fused and no undecomposed sample remains. This operation will require about 30 minutes. During the fusion, pick up the flask frequently with a pair of tongs and whirl to mix the contents. 3. Remove the flask from the flame with the tongs and by means of a rotary motion cause the melt to solidify in a uniform layer on the side and bottom of the flask. 4. When the contents of the flask have cooled, add 100 ml. of 50y0 (by volume) hydrochloric acid and dissolve the fusion by cafeful heating. Avoid violent boiling. D. Add 60 to 80 grams of amalgamated zinc shot. 6. Place on a hot plate and bring to a boil. Boil gently for 10 minutes. 7 . For the initial sample in a series, prepare the reductor assembly by first drawing the liquid level in the reductor reservoir to about 0.25 to 0.5 inch above the top of the zinc column. Set the 1-liter Florence flask in place in the reductor assembly. Connect the carbon dioxide supply, turn it on, regulate the flow to 1 or 2 liters per minute, and allow it to run for 2 minutes to flush all the air out of the flask before it is used. 8. Drain the acid remaining in the reductor down to the level of the top of the zinc column. 9. Pour the reduced solution from the Erlenmeyer flask into the reductor. Give the zinc shot a preliminary rinse by shaking
V O L U M E 2 4 , NO. 10, O C T O B E R 1 9 5 2
1633
with not more than 15 ml. of lOy0 hydrochloric acid and pour it into reductor. 10. Open the stopcock and allow the solution to oass through the reductor into the receiving flask. 11. When the liquid level in the reductor has dropped almost to the top of the zinc column, close the stopcock, rinse the sides of the reductor reservoir and stirring rod with a few milliliters of 10% hydrochloric acid from a wash bottle, and drain the rinsings to the top of the zinc column. 12. Rinse the zinc shot in the flask with not less than three successive 75- to 100-ml. portions of loyohydrochloric acid and pass them through the reductor, permitting each rinse to be drawn down nearly to the top of the zinc column before adding the succeeding rinse. 13. Rinse the sides of the reductor reservoir and the stirring rod again as in Step 11. 14. Finally rinse the reductor with an additional portion of 1070 hydrochloric acid. Allow this to drain down to about 0.25 to 0.5 inch above the top of the zinc column. The total volume of the reduced solution in the receiving flask should now be 500 to 750 ml. 15. Remove the receiving flask from the reductor. If another sample is to follow immediately, place another Florence flask in the reductor ass-nibly in order to allow the carbon dioxide to displace the air in preparation for the next sample. If another sample is not to follow a t once, turn off the carbon dioxide and fill the reductor reservoir with 10% hydrochloric acid. (See Discussion of Method which follows after Step 18 regarding care of the reductor. ) 16. Quickly add 20 ml. of sodium thiocyanate or potassium thiocyanate solution (400 grams per liter) to the flask containing the reduced solution. Do not shake the flask to hasten mixing- of the indicator solution. 17. Place the flask under a buret filled with standard 0.1 N ferric alum solution and proceed immediately with the titration, allowing about 90% of the estimated requirement of ferric alum to enter the flask. Then shake the flask gently until the solution is decolorized. Continue the titration, shaking only enough to decolorize the solution until the permanent straw-colored end point is reached, a t which time the violence of the shaking may be increased t o ensure that the end point is permanent. Before making the final buret reading, wash down the neck of the flask with a little distilled water from a wash bottle to ensure coniplete reaction between the reduced titanium and ferric alum. 18. Calculation:
-
essentially all of the ferric alum a i t h little or no shaking before adding the thiocyanate indicator. This is permissible. It is recommended that the Jones reductor, when idle, should be left with 10% acid covering the zinc. This is preferable to replacement of the acid mith aater, even for periods of a week or more. As an aid to precision ivork, it is recommended that a standard sample of known titanium content (standard titanium dioyide sample No. 154 may be obtained from the National Bureau of Standards) be carried through the procedure, parallel with each sample or series of samples. REMOVAL O F IMPURITIES
Chromium, Molybdenum, Tungsten, and Vanadium ( I , 5). After solution of the sample in Step 4, add 5 ml. of 1% ferric chloride solution, nearly neutralize with sodium hydroxide solution, and pour, while stirring, into 200 ml. of a boiling 5y0solution of sodium hydroxide. Cool, add 5 ml. of 30y0 hydrogen peroxide solution, and boil for 30 minutes to decompose soluble pertitanate. Filter and wash with a hot dilute solution of sodium hydroxide containing sodium sulfate. Repeat the precipitation if the above elements are present in appreciable proportion. Decompose paper and precipitate by treatment with nitric and sulfuric acids. Nitric acid must be completely removed by fuming with sulfuric acid, diluting with 5 m!. of water, and fuming again. Dilute to 100 ml. with 1 to 1 hydrochloric acid and proceed with the reduction as in Step 5. FURTHER DETAILED RECOMMENDATIOIS
M I . of ferric alum X factor X 100 = 70titanium IVt. of sample taken Factor in this case is grams of titanium equivalent to 1.0 nil. of standard ferric alum. Or, if preferred:
MI. of ferric alum X S X 0.0479 X 100 Wt. of sample taken
3c
-
- % titanium
DISCUSSION O F METHOD
The time required for the acid solution from the flask t o pass through the reductor should be between 3 and 5 minutes. This rate may increase considerably in the succeeding washing operation. I t is also important that solutions flow through the reductor by gravity and are not forced through by means of vacuum or pressure. Furthrrmore, the solution after flask digestion and after the small preliminary rinse mentioned in Step 11 should never be diluted with water or weak acid in order to make it flow faster through the reductor. It is imperative that the zinc column in the reductor is not exposed to air at any time. The level of the liquid must never be drawn below the top of the column. The mechanics of carrying out the titration have been outlined in considerable detail in Step 17, as an aid to uniformity and precision. Vnnecessary shaking must be avoided in order to prevent loss of carbon dioxide from the flask. In routine work the approyimate titration will be known; therefore, most of the ferric alum may be added before any shaking is done. In the case of unknowns, it is preferable to carry out duplicate titrations, the first to be run as a pilot and the second to be done more carefully. The result of the second n-ill be used for reporting. Some analysts \ d l prefer to carry out the titration by adding
Figure 1. Detail of Modified Jones Reductor
Preparation of 0.1 N Ferric Alum Solution. APPARATUS A K D REAGENTS. Ferric ammonium sulfate (ferric alum) Fea(SO& (NH,)zS04.24H,O C.P. Sulfuric acid, concentrated, C.P. Potassium permanganate dilute solution Standard titanium dioxide sample Jones reductor and other equipment for determination of titanium PROCEDURE. Since the 0.1 S ferric alum solution is usually prepared in LL volume of 18 liters (5 gallons), the quantities given below are for a final volume of 18 liters of the solution. Dissolve 870 to 875 grams of C.P. ferric ammonium sulfate (ferric alum) in 2 to 3 liters of distilled water with agitation. Add 500 ml. of C.P.concentrated sulfuricacid and mix thoroughly. Filter through a No. 5 Whatman filter paper. Transfer to the final container and dilute to volume with distilled water which is a t room temperature. Add dilute potassium permanganate solution drop by drop and with mixing, until a permanent faint pink coloration is discernible in the solution. Mix completely by roll-
ANALYTICAL CHEMISTRY
1634 ing for 1hour or by bubbling clean (filtered) air through the solution for about 16 hours (usually overnight). Allow the solution to stand relatively undisturbed for a t least 24 hours before using, to allow for temperature equilibrium and for air bubbles to escape. Standardization Procedure for 0.1 N Ferric Alum Solution. Dry a portion of the standard titanium dioxide in a weighing bottle in an oven a t 140’ C. for not less than 1 hour. Cover the weighing bottle, remove from the oven, place in a desiccator, and permit it to cool. Retain the dried portion of the sample in the desiccator, except when weighing out portions, until it is depleted. The drying may be repeated a t intervals as necessary. Accurately weigh approximately 0.30-gram portions of thc dried standard titanium dioxide. Proceed according to Steps 1 through 17 of preceding method for determination of titanium. CALCULATION. Wt. _-of standard sample X % titanium of sample = factor M1. of ferric alum X 100 Titanium factor as usedin Step 18 of method for determination of titanium. Amalgamation of Zinc Shot for Flask Reduction. APPARATUS A N D REAGENTS.Zinc shot (reagent grade) Hydrochloric acid, concentrated, C.P. Mercuric chloride TVooden paddle PROCEDURE. Weigh 1000 grams of zinc shot into a 1- or 2liter beaker or jar. Wash the zinc twice with tap water, and then cover with n a t r r to 0.5 inch above the top of the zinc. Prepare an amalgam solution by weighing 24 grams of mercuric chloride into a 400-ml. beaker and dissolving completely with 220 ml. of concentrated, C.P. hydrochloric acid. Add the amalgam solution to the zinc with vigorous agitation with a wooden paddle. Continue the agitation for 1 to 2 minutes. Pour off the amalgam solution and wash the zinc by decantation with tap water no less than 12 times, or, if preferred, transfer the zinc to a funnel and allow tap water to flow over it for 0.5 hour. Finally wash the zinc twice with distilled water, and store it in a covered beaker or jar, and keep the zinc covered with diitilleti water until used.
Table I.
Reproducibility Titanium, %
Sample No. 1 2 3 4 5
6 7 8 9 10 11 12 13 14 15
16 17 18 19 20 21 22 23 24
Laboratory A 99.61 99.74 99.51 99.58 99,70 99.60 99.85 99.63 99.65 99.50 99.62 99.67 99.77 99.72 99.77 99.77 99.84 99,50 99.70 99.74 99.84 99.49 99.67 99.76
Laboratory B 99.63 99.67 99.53 99.48 99.57 99.60 99.82 99.72 99.54 99.66 99.50 99,84 99.73 99.66 99.75 99.82 99.74 88.47 99.50 99.69 99.84 99.60 99.57 99.53
Difference 0.02 0.07 0.02 0.10 0 13 0.00 0.03 0.09 0.11 0.16 0.12 0.17 0.04 0.06 0.02 0.05 0.10 0.03 0.20 0.05
0.00 0.11 0.10 0.23
Amalgamation of 20-Mesh Zinc, and Method of Charging Jones Reductor. APPARATUSA N D REAGENTS.20-mesh zinc (reagent grade) Concentrated, c.P., hydrochloric acid Mercuric chloride Modified Jones reductor PROCEDURE. Refer to Figure8 1 and 2. Weigh 300 grams of 20-mesh zinc into a 1-liter Florence flask. Wash the zinc twice with tap water, and then cover with water to 0.5 inch above top of zinc. Pre are amalgam solution by weighing 14 grams of mercuric chlorize into a 400-ml. beaker and dissolving completely with 122 ml. of concentrated, C.P. hydrochloric acid. Add the amalgam solution to the zinc in six portions with a
vigorous 15-seconds up-and-down shaking after each addition. After the last addition, continue the shaking for 1.5 minutes. Pour off the amalgam solution and wash with tap water no less than 12 times, 0.5 minute being sufficient for each wash with fresh urater. To the reductor, which has been previously prepared with a mat of glass wool and filled with water, immediately add the washed zinc and let it settle down into position in the reductor column (see Notes on Procedure in following section).
AMALQAMATED 20 MESH ZINC
QLASS WOOL
Figure 2. Assembly for “Flask-Reductor” Filtration Allow the charged reductor to stand undisturbed for a t least 2 hours (preferably longer) before being used. This allows the zinc to “set” in position and lengthens the useful life of the reductor. Just before using the reductor, wash it with three 300-ml. portions of hot 15% hydrochloric acid. When finished with a reductor, leave it standing with the zinc covered with 10% hydrochloric acid. A reductor must never be allowed to dry. NOTESOX PROCEDURE. This quantity of amalgamated zinc is about right t o give a zinc column of 13 cm. with reductors of the dimensions shonn in Figure 1. Since the internal diameter of the reductors varies slightly from time to time, it is necessary t o vary the quantity of amalgamated zinc to ensure the 13-cm. column. After continued use, the rate of flow through the reductor will decrease considerably. When this occurs, the zinc column should be discarded and the reductor should be recharged. If the reductor is used infrequently, it is well to include a standard sample in any series of determinations. If deviation from the standard value is appreciable, the zinc column should be discarded and the reductor should be recharged. During the amalgamation, heat is evolved. Appropriate safety precautions should be taken. LITERATURE CITED
Hillebrand, W. F., and Lundell, G. E. F.. “Applied Inorganic Analysis,” Xew York, John Wiley & Sons, 1929. Kneoht, E., and Hibbert, E., Ber., 36, 1549 (1903). (3) Knecht, E., and Hibbert, E., “New Reduction Methods in Volumetric Analysis,” pp. 11, 51, London, Longmans, Green and Co., 1918. (4) Ibid.,pp. 10, 70, 1925. (5) Thornton, Wm., Jr., “Titanium,” A.M.CHEM.SOC. Series, No. 33, Kew York, Chemical Catalog Co., 1927.
RECEIVED for review March 5 , 1952. .4ccepted July 10,1952.
