A Rapid Method for the Determination of Titanium HENRY B. HOPE, RAYMOND F. ,MORAN,
ARTHUR 0. PLOETZ, Cooper Union Institute of Technology, New York, N. Y.
AND
B
Reagents 0.1 N otassium permanganate. Coole$ freshly boiled, distilled water containing 1 per cent of sulfuric acid. Ferric ammonium sulfate solution (approximately 0.7 N ) . Liquid zinc amalgam. Tablets of sodium bicarbonate (approximately 5-grain) purchased a t any drug store. Potassium thiocyanate (saturated solution).
ECAUSE of the increased use of titanium pigments, a rapid and accu-
rate method for its quantitative estimation has become of considerable industrial importance. Gravimetric separations involving titanium are generally long and tedious because of the interference of many other common metals. The general commercial method now in use involves the reduction of the titanium by means of a Jones reductor and subsequent titration with an oxidizing agent. However, because of the extreme susceptibility of the titanous ion to oxidation, the complete reduction and protection of the reduced titanium by this method requires over-large apparatus, a long period of time for the reduction, and a device for the protection of the reduced solution with carbon dioxide. The method herein described gives quantitative results within 30 minutes and requires apparatus easily constructed from available laboratory glassware. I t s use results in a saving of a t least one-half of the normal time necessary for titanium determination by any of the standard methods now in use. It has been tested against samples of wide range of titanium content.
Procedure The ferric ammonium sulfate reagent is prepared by dissolving 30 grams of the salt in 300 cc. of distilled water acidified with 10 cc. of sulfuric acid. Potassium permanganate solution is added drop by drop, as long as the pink color disappears, and the solution is then diluted to 1 liter. This solution is standardized, after reduction with zinc amalgam in the special reductor, by titration with standard potassium permanganate. The zinc amalgam (1) is prepared as follows: Fifteen grams of fine-mesh iinc well washed with dilute sulfuric acid are heated for 1 hour on a water bath with 300 grams of mercury plus 5 cc. of dilute sulfuric acid (I to 4). After cooling, the amalgam is washed several times with dilute sulfuric acid. The liquid portion is separated from the solid by means of a separatory funnel. The solid is discarded. The liquid amalgam is preserved under dilute sulfuric acid. For the determination of titanium a sample equivalent to approximately 0.1 to 0.2 gram of titanium dioxide is digested with 20 cc. of concentrated sulfuric acid and 15 grams of powdered ammonium sulfate until it is entirely dissolved. Bulb D and the rubber tubing up through the stopcock are filled with the boiled water and both stopcocks are closed. Fifteen cubic centimeters of the zinc amalgam are added and the cooled sample is transferred to the funnel, using about 75 cc. of the distilled water. Two tablets of the sodium bicarbonate are now added and stopper C is inserted with cork A removed. When effervescence has ceased, two more tablets, broken into small pieces, are drop ed through tube B. When the gas evolution is completed, cor! A is immediately replaced and the entire apparatus vigorously shaken for 5 minutes. The two stopcocks are now opened and the amalgam is allowed to flow into D. This displacement is best accomplished by alternately squeezing and releasing tube E with the fingers. As soon as the last particle of amalgam has dropped from the funnel, both stopcocks are closed and bulb D is removed for convenience while titrating. Stopper A is removed and 5 cc. of the otassium thiocyanate solution are added by means of a pipet t&ough B. Stopper C is removed and both tube and stopper are washed into the funnel with distilled water. The solution is titrated in the funnel with the ferric ammonium sulfate. It is im ortant that the ferric ammonium sulfate be added very rapid& until the first appearance of a wine-red color. The upper stopcock is now opened and tube E squeezed several times to force its liquid into the funnel. This will cause the wine color to disappear. The titration is completed by adding the ferric ammonium sulfate drop by drop to the end point.
Discussion Nakazono (1) developed an apparatus for the reduction of various ions using liquid zinc amalgam as a reducing agent. The use of a liquid amalgam has the advantage of exposing a greater area of zinc than could be obtained by a Jones reductor and therefore gave complete reduction in a much shorter time. The disadvantage of the Japanese method, however, was in the use of special apparatus which was not readily available. The authors have modified their apparatus so that it may be easily constructed from common laboratory glassware (illustrated). The apparatus consisted of a 250-cc. globular separatory funnel, closed with a rubber stopper, C, carrying a piece of 0.63-cm. (0.25-inch) glass tubing, B , 5 em. (2 inches) long which was stoppered by a small cork, A . The outlet tube of the funnel was connected to a 20- to 30-cc. glass tube, D, by means of a length of rubber tubing, E , which was closed by means of a pinchcock, F. Tube D was an old 25-cc. volumetric flask, but any small bulb may be used in its place. After a number of experiments using both potassium permanganate and ferric ammonium sulfate as oxidizing agents for the titanous ion, i t was found that ferric ammonium sulfate gave much superior results, probably because of the elimination of any iron interference. I n general the method consisted of the reduction’of the titanium to the trivalent state by use of liquid zinc amalgam and its titration with ferric ammonium sulfate using potassium thiocyanate as an indicator. The end point was the appearance of the usual winecolored ferric thiocyanate complex.
Calcium sulfate, which is present in some commercial titanium pigments, does not interfere with the reduction because its precipitation is prevented by the high concentration of sulfuric acid. Barium sulfate should be removed by filtration before the reduction of the titanium.
Results The pure titanium dioxide used in samples 1 and 2 was prepared in the laboratory of the Titanium Pigment Co., Inc., 48
JANUARY 15, 1936
49
ANALYTICAL EDITIOK
TABLEI. RESULTSOF ANALYSES Weight of Titaniuma Di- Titanium DiSamDle SamDle oxide Preaent oxide Found Cram Cram Gram 0.2006 0,2000 0,2000 0.2000 0.2000 0.2000 0.2463 0.2500 0,2470 0.2470 0.2500 0.2470 0.1459 0.1468 0.5000 0.1470 0.1468 0.5000 0.1448 0.1459 0.5000 0,1452 0.1459 0.5000 0.5000 0.1458 0.1459 a .4nalyses by the Titanium Pigment Co., Inc.
Error
samples were analyzed in the aforementioned laboratories and the results were forwarded to the authors.
Gram
+ O , 0006 0.0000 -0.0007 0,0000 -0,0009 $0.0002 -0,001 1 -0,0007 -0.0001
Acknowledgment The authors wish to thank Joseph L. Turner, director of research of the Titanium Pigment Co., Inc., for the numerous analyzed samples contributed and for the private analytical methods of this corporation (3).
Literature Cited
by the method of Plechner and Jarmus ( 2 ) . Samples 3 and 4 were Titanox A, a technical titanium dioxide pigment. Samples j to 9, inclusive, were Titanox C, which contains a large percentage of calcium sulfate. All the commercial
(1) Nakazono, J . Chem. SOC.Japan, 42,526 (1921). ( 2 ) Plechner, W. w., and Jarmus, J. M., IND.ENG.CHEM.,Anal. Ed. 6, 447 (1934). (3) Titanium Pigment CO., InC., Private communication. RECEIVED October 7, 1935.
Determination of Organic Sulfur by the Liquid Ammonia-Sodium Method F. J. SOWA, V. G. ARCADI,
AND
J. A. NIEUWLAND, University of Notre Dame, Notre Dame, Ind.
C
HA4BLAY (1) and later Vaughn and Nieuwland (3)
showed that halogens were quantitatively removed as sodium halide from all types of organic compounds by the action of sodium in liquid ammonia. This reaction proved to be the basis of an excellent method for the quantitative determination of organic halogen. The observation that certain organic sulfur compounds were decomposed by the action of sodium in liquid ammonia, led to the belief that sulfur in organic compounds might be reduced to sodium sulfide or sulfite by this method of treatment. If so, the resulting inorganic sulfur could be oxidized to sodium sulfate with the subsequent determination of sulfur by precipitation as barium sulfate. Such proved to be the case. Kraus and White (2) studied the action of sodium in liquid ammonia on phenyl mustard oil, sodium benzene sulfonate, thiophenol, and diphenyl sulfide, and reported positive qualitative tests for sodium sulfite as a decomposition product of sodium benzene sulfonate. They also reported the formation of sodium sulfide in the decomposition of phenyl mustard oil and diphenyl sulfide. Williams and Gebauer-Fulnegg (4), however, have since shown that no sodium sulfide is formed in the case of organic sulfides, disulfides, and mercaptans. Inasmuch as the success of this method depends upon the formation of sodium sulfide or sulfite, it is apparent that not all types of sulfur compounds can be analyzed by this method. Diphenyl sulfide and related compounds might, however, be analyzed by this method if they are first oxidized to sulfones, sulfoxides, etc.
Procedure One-tenth gram of the material to be analyzed is placed in a 250-ml. beaker and approximately 175 ml. of liquid ammonia are added. If solution does not take place upon stirring, ether, monobutylamine, or other organic solvent inert towards sodium in liquid ammonia is slowly added until the sample is dissolved. Small pieces of freshly cut sodium are now added until a persistent blue solution of uniform depth is obtained. When the reaction is complete, the covered beaker is placed in a water bath at room temperature and the solution allowed to evaporate to approximately 25 ml. At this point 3 to 5 grams of ammonium chloride dissolved in a few milliliters of liquid ammonia are added t o
destroy the excess sodium not utilized in the reaction. Evaporation is then continued to dryness. The solids are dissolved in 75 ml. of hot water and 2 grams of sodium peroxide are added with stirring. The solution is heated to boiling, acidified with dilute hydrochloric acid, and heated vigorously for a few minutes to expel all traces of carbon dioxide and oxygen. A 5 per cent solution of barium chloride is then slowly added dropwise with constant stirring until the sulfate is com letely precipitated. The precipitate is digested on a steam bath, Ekered, washed, ignited, and weighed in the conventional manner. The beaker containing the sample should be cooled by placing in a shallow dish containing about 0.5 cm. of liquid ammonia before the solvent ammonia is added. This avoids the violent spattering caused by the rapid vaporization of the ammonia on contact with the bottom of the beaker. It has been found convenient at times to use a concentrated solution of sodium in liquid ammonia rather than finely cut pieces of metal. This modification is particularly useful when a large number of decompositions are being carried on at a single operation. The use of organic solvents reduces the time of reaction and minimizes the possibility of error through incomplete decomposition. Low results in analyses of compounds only slightly soluble in liquid ammonia or other solvents are partially remedied by the use of small samples and an excess of solvent. For example, by doubling the amount of solvent and reducing the size of the sample by one-half, the percentage of error in the determination of sulfur in thiourea was reduced from 1.3 to 0.26. Results of analyses of sulfur compounds are given in Table I. All percentages are the average of a t least two determinations. TABLEI. ANALYSESOF SULFUR COMPOUXDS Compound Thiourea Bensoyl sulfimide Acetone diethyl sulfone
Dinitrophenylthiocyanate
Diphenyl sulfone Benzenesulfonamide Benzenesulfonyl chloride n-Propyl-p-toluenesulfonate p-Toluenesulfonio acid 2-Naphthylamine-5,7-disulfonic acid
Sulfur Calcula+ed
Sulfur Found
%
%
42.12 17.48 28.09 14.24 14.68 20.41 18.16 14.97 16.86 16.81
42.01 17.35 27.89 13.49 14.13 20.51 18.07 14.83 16.45 16.27
Difference 0.11 0.13 0.20 0.75 0.55 0.10 0.09 0.14 0.41 0.54
