November 15,1934
IN D US T R I A L A N D E N G I N E E R I N G C H E M I ST R Y
out the solid reagents by volume from a spoon or spatula instead of by weight.
PRACTICAL APPLICATIONS While this test is capable of general qualitative use and even of incorporation in the usual qualitative scheme, it appears especially suited for the detection of calcium in nearly pure barium or strontium salts, where interference from magnesium is negligible, for purposes of analytical research or manufacturing control. Here it can be applied in a semiquantitative way, by testing a series of progressively smaller or larger samples until a negative or positive reaction is obtained, reference being made to previously established behavior of known concentrations of calcium in solutions whose concentration in respect to the particular barium or strontium
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salt is identical to that of the unknown test solution. I n making such comparisons the volumes of the solutions, the weights of reagents, and the time of observation must be the same. This scheme was found to be more practical than the usual method of comparison, since the nature of the test interferes with the convenient use of a series of turbidity standards. The feasibility of this procedure was tested on a representative specimen of c. P. strontium chloride. The test apparently possesses sufficient accuracy to determine whether or not the percentage of calcium present as an impurity is below or above a desired limit, and since it involves no preliminary separations it has the advantage of yielding rapid results. R ~ C B I VJuly ~ D7, 1934.
Pure Titanium Oxide as a Standard in the Volumetric Estimation of Titanium W. W. PLECHNER' AND J. M. JARMUS,Titanium P i g m e n t
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TTANIUM oxide in titanium pigments or other titanium-containing materials may be estimated by a volumetric method involving reduction of the titanium in solution and titration with a ferric salt (6, 7). A rapid and entirely satisfactory procedure for this estimation has been recently described (3). Standardized ferric ammonium sulfate solution is used in the titration of the reduced titanium solution, and is of such concentration that 1 ml. is equivalent to 0.005 gram of titanium dioxide. This solution is standardized by reduction and titration with 0.1 N potassium permanganate, which in turn has been standardized against sodium oxalate. [The ferric ammonium sulfate 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. The solution is finally diluted to 1 liter. I n standardizing, 50 ml. of the solution are made up to about 100 cc. in 5 per cent sulfuric acid, reduced in a Jones reductor (4) and titrated against standard 0.1 N potassium permanganate.] The authors have found it convenient to prepare pure titanium dioxide as a known sample to check the operation of their reductors and the standardization of the ferric ammonium sulfate solution. Since a zinc amalgam reductor loses its efficiency after considerable use, it is advisable occasionally to check its operation by running a known sample, and for this purpose pure titanium oxide is most suitable. I n laboratories which analyze for titanium as a matter of routine but have little other occasion to use a standardized potassium permanganate solution, pure titanium oxide might be an excellent means of standardizing ferric ammonium sulfate solution. About 0.2 gram of the pure oxide is weighed accurately into a 250-cc. beaker, 20 to 30 cc. of sulfuric acid and 10 grams of ammonium sulfate are added, and the mixture is carefully boiled until the titanium oxide is dissolved. After cooling, the contents are diluted to 125 to 150 cc., reduced in the usual manner in a Jones reductor, and titrated (ammonium thiocyanate indicator) with the ferric ammonium sulfate solution t o be standardized. In this way the preparation and standardization of a potassium permanganate solution, and any attendant errors are avoided.
-1
Present address, Southern Mineral Products C o w , Piney River, Va.
Company,
Inc., New York, N. Y.
Certain Bureau of Standards chemists (1) have shown that the results obtained for titanium dioxide in Titanox by following Barton's modification (7) of the Shimer method (6') are a little too low, owing, presumably, to the slight oxidation of the titanous sulfate a t the expense of atmospheric oxygen. This being the case, the proposed empirical standardization process will lead to more accurate values than can be obtained by working through a potassium permanganate solution whose titer has been otherwise set because a compensation of errors occurs.
PREPARATION OF PURETITANIUM OXIDE Pure titanium oxide is prepared by a modification of a previously published method (9): Crude titanium tetrachloride is distilled, collecting the 135" t o 138' C. fraction, in the presence of an excess of chlorine t o prevent the distillation of iron compounds with the titanium tetrachloride. The authors have found it advantageous to pack joints in the distillation apparatus with glass wool instead of using corks or stoppers. The distilled titanium tetrachloride is dissolved by pouring 500 cc. in small portions into 1500 cc. of distilled water with vigorous stirring. The mixing beaker should be immersed in a cold water bath and the operation carried out under a hood, using rubber gloves. (Titanium tetrachloride may be poured upon clean ice instead of into distilled water with much less attendant fuming, the weight of the ice in grams being equal to the volume of the water in cubic centimeters.) A clear solution containing about 15 per cent titanium oxide is obtained. This is reduced electrolytically or by means of stick zinc to about 0.5 gram per liter of reduced titanium oxide, and 100 cc. are further reduced t o about 3 grams per liter of reduced titanium oxide. The solution is reduced until distinctly colored by the resence of titanous ion; all the iron present must be in the Ferrous state to prevent hydrolysis and preci itation of ferric iron with the titanium. Dilute oxalic acid af)so prevents precipitation of any iron with the titanium. The highly reduced titanium tetrachloride solution is added drop by drop t o a boiling solution of 5 grams of oxalic acid in 3500 cc. of water contained in a round-bottomed flask. Then 400 CC. of the lightly reduced solution are added dropwise, over a period of 1 hour, and boiling is continued thereafter under reflux for half an hour. The precipitation yield will be about 99 per cent. The precipitate is transferred to a 4-liter beaker, allowed t o settle, decanted, repulped (brought back into suspension) with about 20 cc. of concentrated sulfuric acid er 4 liters, filtered, and washed with hot distilled water until tEe washings are free from chloride.
ANALYTICAL EDITION
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The hydrous titanium oxide so obtained is dehydrated to form pure titanium dioxide by igniting at about 900” C.
A spectroscopic analysis (by E. Posnjak, Geophysical Laboratory, Carnegie Institution, Washington, D. C.) of titanium oxide prepared as above showed the presence of 0.001 t o 0.01 per cent of sodium as the only impurity. This last is probably due to contamination during the handling of the calcined titanium dioxide, as no special care was observed in order to obtain a spectroscopically pure product. ACKNOWLEDQMENT Acknowledgment is due to J. L. Turner, Director of Research, Titanium Pigment Company, Inc., for the suggestion on which this paper is based.
Vol. 6 , No. 6
LITERATURE CITED (1) Hickson, E. F.,et al., PTOC.Am. SOC.Testing Materials, 24, I, 451 (1924). (2) Hixson, A. W., and Plechner, W. W., IND.ENG.CHEW.,25, 262 (1933). (3) Jarmus, J. M., and Willets, W. R., Paper Trade J., 98, 41-3 (1934). (4) Jones, C.,Trans. Am.Inst. Mining Engrs., 17, 414 (1889). (5) Scott, W. W.,“Standard Methods of Chemical Analysis,” 4th ed., Vol. 1, p. 5444, D.Van Nostrand Co., N. Y., 1925. and Shimer, E. B., Orig. Com. 8th Intern. Congr. (6) Shimer, P.W., Appl. Chem., I, 445 (1912). (7) Thornton, W.M., Jr., “Titanium,” Chemical Catalog Co., N. Y., 1927. RECEIVED June 12, 1934.
Inclusion of Rarer Metals in Elementary Qualitative Analysis 11. Inclusion of Titanium and Vanadium in Group I11 LYMANE. PORTER, University of Arkansas, Fayetteville, Ark.
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HE detection of tungsten and molybdenum in the presence of the common ions of groups I and I1 has been described in a previous paper (3). The detection of the only other two rarer metals to be considered in this series is outlined in the present paper. Solutions of titanium salts may be prepared by fusion of titanium dioxide with an excess of sodium bisulfate, followed by solution in water and acid. To remove the sulfate ion, the titanium is precipitated as the hydroxide by means of ammonium hydroxide, and the filtered and washed precipitate is dissolved in dilute hydrochloric or nitric acid and diluted to the desired volume. An alternative method is fusion of the oxide with sodium peroxide, followed by extraction with water and decomposition of the peroxide with acid and sodium sulfite. Vanadium may be conveniently used in the form of sodium vanadate which is readily soluble in water. Since vanadates recipitate in group I11 only in the presence of other members of e!lt group, it is essential that at least one such metal be present when testing for vanadate. The filtrate from group I1 is treated with hydrogen sulfide in the presence of ammonium chloride and ammonium hydroxide in the usual manner. A little more ammonium hydroxide should be added before filtration, in order to overcome the possible formation of soluble ammonium sulfovanadate. After filtering off the group I11 precipitate, the filtrate should be acidified with acetic acid and boiled to remove hydrogen sulfide. A brownish precipitate containing some of the vanadium may be formed at this point, and should be filtered off and added to the precipitate of group 111. The solution will contain groups IV and V. The entire precipitate of the group is suspended in 50 cc. of N hydrochloric acid, and the mixture is thoroughly stirred, allowed to stand from 3 to 5 minutes, and filtered. The residue may contain the sulfides of nickel and cobalt. The filtrate is evaporated to about half its original volume to remove hydrogen sulfide and part of the mineral acid. It is then made neutral with 5 N or 6 N sodium hydroxide, and 10 cc. of sodium hydroxide are added in excess, together with 10 cc. of 3 per cent hydrogen peroxide. Sodium peroxide may be substituted here if desired. The mixture is boiled for at least 5 minutes to decompose the excess of peroxide and insure the complete precipitation of the titanium. After being cooled, the mixture is filtered to separate the iron division from the aluminum division.
DETECTION OF TITANIUM IN THE IRON DIVISION The precipitate may contain ferric hydroxide, titanium hydroxide, and manganese dioxide. A common method for the separation of these with other metals includes the pre-
cipitation of the manganese by boiling with potassium chlorate and nitric acid, but this is not advisable in the hands of a large class because of the acid fumes that are evolved and because under these conditions much of the titanium may be precipitated with the manganese (2). Furthermore, ammonium hydroxide and ammonium chloride cannot be used to precipitate the iron and titanium from the manganese because some or all of the manganese will precipitate with the
titanium. The residue of these three metals is therefore dissolved in hot dilute nitric acid, with the addition of 1 or 2 drops of hydrogen peroxide. if necessary to effect solution. The excess hydrogen peroxide must be removed by boiling. The cooled solution is made neutral with ammonium hydroxide and a slight excess of dilute nitric acid is added to decompose any hydroxides that may be present. To this solution a suspension of barium carbonate in water is added until an excess remains undissolved. Upon standing for at least 3 minutes with occasional stirrin the excess of nitric acid is neutralized by dissolving some of tf;e barium carbonate, and the hydrogen-ion concentration in the resulting solution is such that all of the iron and titanium is completely precipitated as hydroxides while the manganese is left in solution. The use of a soluble base in place of the barium carbonate would result in the precipitation of part or all of the manganese. After filtration the lead dioxide test for manganese is made. The residue, including some excess barium carbonate along with the titanium and iron, is dissolved in dilute hydrochloric acid, and, after the addition of 1 gram of ammonium chloride, the titanium and iron are precipitated by an excess of ammonium hydroxide. The precipitate is filtered off to remove the soluble barium salts which would interfere with later tests. The residual hydroxides of titanium and iron may be dissolved in hydrochloric acid and the iron extracted with ether (2). Ether extraction may be avoided by making use of the fact that titanium phosphate will not be precipitated in the presence of an excess of hydrogen peroxide (1). The hydroxides of the two metals are dissolved in dilute sulfuric acid. To this are added 5 cc. of hydrogen peroxide, some sodium hydrogen hosphate, and an excess of sodium hydroxide. The residue of Ferric hydroxide and ferric phosphate is filtered off and the test for iron made in the usual manner. The filtrate is made slightly acid with dilute sulfuric acid, the formation of a yellow or orange solution a t this point indicating the presence of titanium, and is then treated with sodium sulfite and a little more phosphate and warmed. After the reduction of the peroxide, the formation of a white precipitate of TiOHP04 proves the presence of titanium. If the solution is too strongly acid for this precipitate to form, it should be neutralized with sodium hydroxide.
