April 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
all mixtures analyzed, and checked each other within 0.1 per cent, which is as close as the volumes may be read. The total errors in analysis of each mixture are also shown in Table 11. The errors involved in preparing the mixtures and also the residual impurities in the nitrous oxide are included in this total error. It will be noted that the error involved in series B of Table I1 is much greater than the other determinations. This is to be expected, since the gaseous impurity was pure nitrogen, whereas the water was saturated with air instead of nitrogen. I n this case there is a tendency for the more soluble oxygen in the water to be replaced by less soluble nitrogen, with a greater residual volume. Accordingly, for greatest accuracy the water should be saturated with gas having approximately the same composition as the gaseous impurities of nitrous oxide. This makes air a satisfactory gas for saturating the water in the case of commercial nitrous oxide, since the impurities are largely nitrogen and a small amount of oxygen.
187
The calculated factors of Table I seem to be accurate within the limits of error of the apparatus, since equally good results were obtained on the 100 per cent samples of nitrous oxide whether air, nitrogen, or oxygen was used for saturating the water. The apparatus described may be used for determining nitrous oxide by Bennett’s method by using air-free water, without any additional modification. It is difficult, however, to determine the absorption rate of a small residual bubble, especially on samples containing more than 98 per cent nitrous oxide. This absorption rate is the essential feature of Bennett’s graphical calculation. The use of water saturated with air or nitrogen eliminates this difficulty and considerably shortens the time of analysis.
LITERATURE CITED (1) Bennett, J. Phys. Chem., 34, 1137-57 (1930). (2) International Critical Tables, Vol. 111,pp. 255-7 (1928). R ~ C E I V EAugust D 28, 1931.
Deterrnination of Vanadium in Special Alloy Steels HOBART H. WILLARDAND PHILENA YOUNG,University of Michigan, Ann Arbor, Mich.
I
T HAS been shown in an
speed and simplicity to some of Vanadium is determined in the presence of earlier paper ( I d ) that sothe selective oxidation methods chromium by selective oxidation in a cold soludium azide is an excellent now in use for vanadium, the tion with excess of potassium permanganate, the differential r e d u c i n g agent for more important of these being: excess being reduced by sodium azide. All ceric sulfate in the presence of (1) direct titration of a vanadyl azide is removed by boiling and the vanadic chromic acid. A large excess of salt with permanganate ( 3 ) ; (2) azide acting for a considerable oxidation with boiling nitric acid acid titrated with standard ferrous sulfate, ditime had no reducing action on (4) to v a n a d i c acid which is phenylbenzidine being used as internal indicator. the chromium. It was pointed titrated with ferrous sulfate elecI n steels containing tungsten, the tungsten is out in the same paper that an intrometrically, a process in which kept in solution as a complex fluoride, and in this the oxidation is not quite comternal indicator such as diphenylform causes no interference. In such steels dia m i n e or diphenylbenzidine plete; (3) oxidation by permancould not be used in the titration ganate, removal of excess perphenylamine sulfonic acid is used as internal of chromic acid with ferrous sulmanganate with hydrogen peroxindicator in the titration of vanadic acid with fate if even a small amount of ide in acetic acid solution (8),or ferrous sulfate. This method for vanadium in azide were present, as the azide by nitrite, followed by urea ( 6 ) , tungsten steels is more rapid than any of equal prevented any color development and titration of vanadic acid with accuracy in use at the present time. with the indicator. The possiferrous sulfate electrometrically bility of removing azide by boilor with diphenylamine as indicaA rapid method of oxidizing tungsten in steel ing the solution and of titrating tor ( 2 ) ; and (4) oxidation with to tungstic acid is also described. the chromic acid by an indicator bromate in a solution containing method was not studied a t that ammonium salts and a definite time. concentration of hydrochloric acid, removal of bromate by It is obvious that vanadic acid, which is a weaker oxidizing boiling, and titration of vanadic acid with ferrous sulfate elecagent than chromic acid, should not be reduced by sodium trometrically or with an indicator ( I O ) . A method has been azide. Therefore, if hydrazoic acid can be removed easily developed for the determination of vanadium in steels containfrom a solution by boiling, there arises the possibility of ing not only chromium but tungsten, which is based upon its determining vanadium in the presence of chromium by selective oxidation by permanganate in cold acid solution, and oxidizing the former a t room temperature with excess of removal of excess permanganate by sodium azide. permanganate and removing the excess of oxidizing agent with The determination of vanadium in steels containing tungsodium azide. After boiling off all hydrazoic acid, the vanadic sten offers special difficulties. In most methods the tungsten acid could be titrated with standard ferrous sulfate, using is removed in the form of tungstic acid, this precipitate always diphenylbenzidine as indicator ( I O ) . Such a method for carrying with it some vanadium as an impurity. A number of vanadium would be of special value in that it would obviate methods have been suggested for the estimation of this small the difficulty experienced by many in determining accurately amount of vanadium in the tungstic acid, none of them being the end point in the direct titration of a vanadyl salt with entirely satisfactory ( I O ) . There is one method for vanadium permanganate (3) when a considerable amount of chromic in which the tungsten is kept in solution throughout the salt is present, and also in that it should prove superior in analysis (IO),but the end point in the vanadic acid titration in
188
ANALYTICAL EDITION
that case has to be determined electrometrically because tungstic acid prevents any color development with the indicators diphenylamine or diphenylbenzidine. Since diphenylamine sulfonic acid is an indicator which may be used in the presence of tungstic acid (7), this makes i t possible to titrate vanadic acid visually with ferrous sulfate in the presence of tungstic acid. This method offers a procedure for vanadium in steels containing tungsten which is much more rapid than any in use a t the present time.
Vol. 4, No. 2
more cc. of azide are added, the solution should be boiled 10 minutes to remove all hydrazoic acid. The azide reacted with the permanganate in a slightly warm solution and all permanganate color disappeared when the solution was below the boiling temperature. The results indicate also that it is immaterial whether the phosphoric ,acid is added before the permanganate or later. The equations for the oxidation reaction and for the removal of excess permanganate are:
PRELIMINARY EXPERIMENTS Samples of a dichromate solution containing 0.026 gram of chromium were taken, treated with 5 CC. of sulfuric acid (sp. gr., 1.5), 2 grams of iron as ferric alum, varying amounts of 0.1 M sodium azide, 20 cc. of phosphoric acid (sp. gr., 1.37), a little acetate, and water to a volume of 300 cc. To this, 0.6 cc. of a 0.1 per cent solution of diphenylbenzidine was added and 5 minutes allowed for the blue color to develop. With 0.1 cc. of 0.1 M azide present, the color development was much more delicate than in the absence of azide, but with 0.25 cc. of the azide in solution it was very difficult to obtain an end point. Therefore, practically all of the azide must be removed before adding the indicator. Experiments with diphenylamine sulfonic acid (7) as indicator showed that a good end point could be obtained in solutions free from azide without buffering, but that the color development of this indicator in the presence of azide was as unsatisfactory as in the case of diphenylbenzidine. With 5 cc. of 0.2 M sodium azide in 300 cc. of a solution containing dichromate, ferric alum, and sulfuric acid boiling for 5 minutes sufficed to remove all hydrazoic acid, and with 10 to 20 cc. of azide present, 10 minutes' boiling was sufficient. Experiments in which the period of boiling was increased to 30 minutes were also satisfactory.
This oxidation method for vanadium was applied to alloy steels. I n Table I1 are given the results of a number of analyses. TABLEIT. VANADIUM IN CHROME-VANADIUM STEELSBY PERMANQANATE-AZIDE METHOD STEEL
B. S. 30(b) V = 0.215%; Cr = 1.03% B. 8. 30(c)
-
V = 0.2357. Cr 0.977% Chrome-vanad%rn V = 0.212%, peroxide method (8); Cr = 1.00% B. 9.73 V = 0.034%; Cr = 13.93% 1-gram samples used and 0.516% vanadium added B. S. ferrovanadium 81 V = 31.15%; Cr = 0.52%
VANADIUM
FOUND
% 0.215,0.215, 0,215 0.231, 0.230, 0.231, 0.232 0.216, 0.215, 0.211, 0.215 0.642, 0.629, 0.628, 0.533 31.02, 30.95,30.97
Five-gram samples of the first three steels were used and 0.2gram samples of the ferrovanadium. The end points in the last two steels had to be determined electrometrically, the deep green color caused by the large amount of chromium in No. 73 and the deep blue color caused by the large amount of reduced vanadium in No. 61 interfering with the clearness of VARYINGCONDITIONS IN PERMANGANATE-AZIDE METHOD the color change of the indicator. Table I1 indicates that Five-gram samples of a chrome-vanadium steel were dis- accurate determinations of vanadium may be made in steels of solved in sulfuric acid, the ferrous salt and carbonaceous widely varying composition. The method is simple and rapid. material oxidized with nitric acid in the usual way, and the STANDARDIZATION OB FERROUS SULFATE liquid boiled for a few minutes to remove oxides of nitrogen. The ferrous sulfate used in the analyses in Table I1 was The solution was cooled and diluted with water and phosphoric acid to 300 cc. Potassium permanganate was added slowly standardized electrometrically against standard ceric sulfate with stirring until an excess was present. After allowing the (11) whose strength had been determined electrometrically solution to stand for 2 to 5 minutes, the indicated quantity of against Bureau of Standards sodium oxalate (11). Since sodium azide was added and the hydrazoic acid removed by dichromate is the primary standard more commonly used in boiling for a definite period. After cooling to room tempera- this standardization and since its oxidizing power toward ture, 30 cc. of phosphoric acid (sp. gr., 1-37), if not already ferrous sulfate has been shown to vary considerably with present, enough crystallized sodium acetate to react with the dilution (1, 9), it seemed5mportant to determine the correct excess sulfuric acid in the solution and 0.6 cc. of 0.1 per cent conditions under which to standardize ferrous sulfate for diphenylbenzidine solution were added. After allowing 5 vanadic acid titrations. Samples of 50 cc. of 0.1 N ammonium vanadate, each with minutes for the blue color to develop, the solution was titrated with 0.025 N ferrous sulfate. Results of a number of experi- the same acidity, required, when titrated electrometrically in volumes of 100 and 600 cc., 53.59 and 53.58 cc. of a ferrous ments are given in Table I. sulfate solution. I n contrast to the titration of chromic acid TABLEI. RESULTS OF OXIDATION OF VANADYLSALT with ferrous sulfate, the result is not influenced by the volume (In presence of chromic salt with excess of ermanganate and removal of of the solution. A ferrous sulfate solution standardized excess of oxidizing agent witg sodium azide) TIMEOF electrometrically against standard ceric sulfate was found to &PO4 STANDINQ be 0.02757 N , and when standardized against very pure BEFORE BBFORE NaNs PERIOD OF OXIDA- KMnO4 ADDINQ dichromate by the following procedure was 0.02752 N . BeEXPT. TION 0.025 N' AZIDE 0.1 M BOILINQVANADIVM cause of this good agreement between the two methods, this cc. Cc. Min. Cc. Min. % 0.219 7 2 5 5 1 30 procedure is recommended: Weigh out samples of 0.05 to 0.06 6 5 0.221 2 30 12 2 gram of pure potassium dichromate, dissolve in a little water 5 6 0.221 3 30 7 5 12 5 5 5 0.221 4 30 containing 3 cc. of sulfuric acid (sp. gr., 1.83). Add sufficient 0.219 7 2 6 5 5 0 5 5 0.219 6 0 12 2 ferric sulfate or ferric alum solution, free from ferrous iron, to 7 2 20 10 0.220 7 30 be equivalent to 0.1 gram of iron, 10 cc. of phosphoric acid The 7 cc. of permanganate used in four of the experiments (sp. gr., 1.37), and dilute to 300 cc. Add 15 grams of crystalrepresent approximately 0.5 cc. excess. Experiments 2 and 4 lized sodium acetate, and, when dissolved, 0.6 cc. of 0.1 per show that an excess of 5.5 cc. caused no error. A large excess cent diphenylbenzidine. Allow 5 minutes for the brownish of azide, as shown in experiment 7, was not harmful. If 10 or color to develop and titrate with 0.025 N ferrous sulfate. An
April 15, 1932
INDUSTRIAL AND ENGINEERING
indicator correction of 0.03 cc. per 0.1 cc. of indicator used should be added to the volume of ferrous sulfate (IO).
CHEMISTRY
189
used in excess to oxidize the vanadium, azide added to destroy the excess of permanganate, and the solution boiled to remove all azide. After cooling the solution to room temperature, VANADIUM IN CHROME-VANADIUM STEELS sodium diphenylamine sulfonate is added as internal indicator A sample of 4 or 5 grams is convenient when the per cent of and the vanadic acid titrated with standard ferrous sulfate. vanadium is low (0.15 to 0.25 per cent). Place it in a 600-cc. It is not necessary to reduce the acidity to obtain a sharp color beaker, add 30 to 40 cc. of water, and run in a measured change a t the end point. Experiments in which phosphoric acid was used in place of volume of sulfuric acid (sp. gr., 1.83) from a buret. Each gram of iron requires 1.5 cc. of concentrated sulfuric acid for hydrofluoric acid to keep the tungstic acid in solution were not final conversion into ferric sulfate. If an excess of 2 to 2.5 cc. successful, as was to be expected from earlier work by the same authors (IO)in which it was shown that, in the presence of acid is allowed, the process of solution is rapid. After the steel has been completely decomposed, boil until a of phosphotungstic acid, vanadic acid forms a complex which considerable quantity of salts separates out, in order to assist is only partially reduced by ferrous sulfate. A few quantitative results were obtained using hydrochloric in decomposing carbides. Dilute with 20 cc. of water and heat until the salts have dissolved. Add nitric acid (sp. g., acid instead of hydrazoic acid as the reducing agent for the 1.42), drop by drop, to the hot liquid until the violent oxidation permanganate, but this method was not so satisfactory beof ferrous sulfate is over (3 to 3.5 cc. of acid are sufficient). cause of the closer control of conditions required. The Boil the solution to destroy oxides of nitrogen, cool to room presence of silver chloride was necessary (5) to obtain comtemperature, add 30 cc. of phosphoric acid (sp. gr., 1.37), and plete reduction. The amount of hydrofluoric acid (48 per cent) required to dilute to 300 cc. Add 0.1 N potassium permanganate from a buret until an excess is present. Then add three or four drops keep in solution throughout an analysis the tungstic acid from more and let the solution stand for 2 minutes to be sure that a 1-gram sample of steel containing 20 per cent of tungsten the color persists and all of the vanadium is oxidized. Add 5 was found to be 5 cc. Just before the addition of the indicc. of 0.1 M sodium azide1 and boil vigorously (in hood) for 5 cator and the titration with standard ferrous sulfate, 3 cc. minutes to remove all hydrazoic acid. If more than 5 cc. of more of the hydrofluoric acid were added. Otherwise the azide are used the solution must be boiled for 10 minutes. change in color of the indicator a t the end point was often Cool to room temperature and add 15 grams of crystallized unsatisfactory. With this additional hydrofluoric acid, the sodium acetate. (This should be the correct amount of color change was always very sharp. The action of the acetate to react with the 2 to 2.5 cc. excess of sulfuric acid hydrofluoric acid in the hot solution upon the glass beaker is used in dissolving the steel and with Ahe slight amount of very evident, but a beaker may be used for a great many nitric acid present. If too much acetate is added so that a determinations before becoming too thin for use. The indicator correction for diphenylamine sulfonic acid permanent precipitate forms, a drop or two of sulfuric acid is larger than for diphenylamine or diphenylbenzidine ( 7 ) . will cause the solution to clear.) As soon as the acetate has dissolved, add 0.6 cc. of 0.1 per For a given amount of indicator, however, the correction recent diphenylbenzidine solution, prepared by dissolving 0.1 mains constant if the titration is made immediately after the gram of the reagent in 10 cc. of concentrated sulfuric acid and addition of the indicator. The correction can be determined diluting this with 90 cc. of glacial acetic acid. Allow 5 for a supply of indicator solution by determiningvanadium in minutes for the color to develop, and titrate with 0.025 N a standard steel, or it can be eliminated by standardizing the ferrous sulfate. The correction to be applied for the indicator ferrous sulfate against sufficient standard dichromate to is added to the volume of ferrous sulfate and amounts to 0.03 require about the same volume of solution as used in the cc. of 0.025 I\i ferrous sulfate per 0.1 cc. of indicator. The end determination of vanadium, since Sarver and Kolthoff (7) have shown that the indicator correction for the dichromatepoint is very sharp. Diphenylamine sulfonic acid (7) may also be used, in which ferrous iron titration is approximately the same as for the case no acetate is necessary. The titration must be begun as vanadic acid-ferrous iron titration. Before titrating the soon as the indicator is added, because the color disappears on chromic acid, sulfuric acid, hydrofluoric acid, and ferric iron should be added as well as the indicator. The correction may standing. The blank is greater with this indicator. be eliminated by using indicator which has first been oxidized VANADIUM IN STEELSCONTAINING TUNGSTEN and then reduced by ferrous sulfate (6) as described later, or The permanganate-azide method is applicable to such steels. by electrometric titration. PREPARATION OF INDICATOR. A 0.005 M solution of A modification in procedure is necessary, however, to keep the tungsten in solution. Two different procedures have been diphenylamine sodium sulfonate is prepared by dissolving 3.2 tested. I n one, the tungsten, after oxidation to tungstic acid, grams of the barium salt (7) in a liter of water, adding to this is filtered off, dissolved in sodium hydroxide, and poured solution a slight excess of sodium sulfate, and decanting the back into the main solution to which hydrofluoric acid has clear liquid. A convenient amount to use in a titration is 0.3 been added. The tungstic acid forms with the hydrofluoric cc. of this solution. acid a soluble complex fluoride I n the other, the sulfuric RAPIDOXIDATION OF TUNGSTEN acid solution of the steel containing metallic tungsten in Special attention should be called to a procedure used in suspeqsion is treated with nitric acid in the presence of hydrofluoric acid. The ferrous iron and nearly all of the Method B (see later part of paper) for the oxidation of tungsten are oxidized in this way, the tungstic acid remaining tungsten by nitric acid by means of which the time for a in solution as a complex fluoride, the tungsten, however, tungsten determination in a steel may be greatly shortened. apparently not entirely in the sexivalent form. Persulfate is Add 10 cc. of water and 30 cc. of hydrochloric acid (sp. gr., used to oxidize the remainder of the tungsten. If this is not 1.18) to a 1-gram sample of the steel in a 400-cc. beaker. done, low results for vanadium are invariably obtained. The Warm gently until the steel is completely decomposed and the excess persulfate is removed by boiling and a little ferrous tungsten separates out as a black powder. Make sure by sulfate added finally to reduce any traces of persulfate which swirling the liquid in the beaker while tilting it that no might remain. In either procedure, permanganate is then particles of tungsten stick to the bottom. Add five or six drops of nitric acid to the boiling-hot liquid and mix thoroughly 1 Sodium azide and barium salt of diphenylamine sulfonic acid may be by tilting the beaker and giving the liquid a rotary motion. obtained from the Eastman Kodsk Company, Rochester, N. Y .
ANALYTICAL EDITION
190
Vol. 4, No. 2
Repeat this treatment, with a few drops of nitric acid and steady swirling of the liquid, two or three times, keeping the liquid boiling hot and giving plenty of time between the addition of each portion of nitric acid for all action t o be completed. I n this way all of the tungsten will usually go into solution just before any tungstic acid separates out. Thus there is no chance for particles of tungsten to become coated with tungstic acid, and the protracted period of boiling with nitric acid, often necessary to oxidize all of the tungsten, is reduced to 5 or 10 minutes. Add the remainder of the nitric acid (use 10 cc. in all) and boil down to 20 cc. From this point the usual procedure for a tungsten determination is followed.
hydrofluoric acid (48 per cent) and more nitric acid, using 5 cc. of nitric acid in all. Boil 2 minutes. A solution of clear greenish color is obtained. Occasionally some tungstic acid will precipitate a t this point, but adding the hydrofluoric acid sooner will usually prevent this. Dilute to approximately 100 cc., add 1 gram of ammonium persulfate, and boil 5 minutes. Add 5 cc. of 0.1 N ferrous sulfate, dilute to between 150 and 175 cc., and cool to room temperature. Add to this solution 0.1 N potassium permanganate from a buret until a distinct color persists for 2 minutes, to be sure all of the vanadium is oxidized. Add 5 cc. of 0.1 M sodium azide and boil vigorously (in hood) for 5 minutes to remove all the hydrazoic acid. Cool to room temperature, add 3 cc. of hydrofluoric acid (48 per cent), 0.3 VANADIUM IN CHROME-VANADIUM-TUNGSTEN STEELS cc. of a 0.005 M solution of diphenylamine sulfonate, and The results obtained for vanadium in a number of chrome- titrate within a minute with 0.025 N ferrous sulfate The vanadium-tungsten steels are given in Table 111. I n Method color change of the indicator a t the end point is from purple A, the tungsten was oxidized by nitric acid and persulfate in to green. The correction to be applied for the indicator must the presence of hydrofluoric acid, and was thus kept in solution be determined and added to the volume of ferrous sulfate used throughout the analysis. I n Method B, the tungstic acid was in the titration. Lang and Kurtz (6) used diphenylamine in the presence of filtered off, dissolved in sodium hydroxide, and returned to the main solution to which fluoride had been added. the complex tungsten fluoride. The color change is, however, not satisfactory when it is substituted in the above method. TABLE 111. VANADIUM IN CHROME-VANADIUM-TUNGSTEN Instead of using azide to reduce the excess of permanganate, STEELS good results were obtained by adding a slight excess of nitrite -VANADIUM FOUNDand removing the excess by the immediate addition of 5 STEEL Method A Method B grams of urea, as directed by Lang and Kurtz (6). The solu% % tion was allowed to stand 15 minutes before adding the inB. S. 50 0 758 0 753 0 746 0 763 V = 0.756%; Cr 3.61%; 0:766: 01756 0:744: 0:748 dicator. W = 17.56% B. S. 50(a) V = 0.976%: C r W = 18.25% No. 1 Cr = 3.11%; W No. 2 Cr = 4.10%; W No. 3 Cr = 4.03%; W
3.52%;
0 975 0 982 0.921, 0.940, 0.962 0:982: 0:974 0.974 0.983 1.32,’1.32, 1.32 1.28, 1.29, 1.28
VALUEOF INDICATOR CORRECTION FOR DIPHENYLAMINE SULFONIC ACID 1.90, 1.90, 1.90 1.84, 1.86 This value may be obtained from duplicate analyses of a 14.3% 1 88 1 85 3.56, 3.57, 3.57 3:53: 3:53 standard chrome-vanadium-tungsten steel, preferably a 17.1% 3.60, 3.53 Bureau of Standards steel, using the procedure given above These results show the close checks obtained in duplicate under Method A. If 0.3 cc. of 0.005 M diphenylamine sulanalyses by Method A. The values from this method are fonic acid is used for the standard steel, the difference between slightly higher always than those from Method B, possibly the theoretical volume of 0.025 N ferrous sulfate required for because of the more complete oxidation of the tungsten in the known quantity of vanadium present and the actual Method A. This method requires less time than Method B volume used for the vanadic acid will represent the indicator and appears more accurate. The indicator blank in these correction to be added to the volumes of 0.025 N ferrous sulanalyses amounted to 0.40 cc. of 0.025 N ferrous sulfate for the fate used in analysis of other steels. The ferrous sulfate solu0.3 cc. of indicator used. The indicator solution contained tion should be standardized against standard dichromate, using the procedure given in the first part of this paper. approximately 0.3 per cent of the sodium salt. To prepare an indicator with no blank correction take 0.3 Experiments using Method B were carried out in which 1 gram of persulfate was added to the filtrate from the tungstic cc. of the solution, 5 cc. of water, 3 or 4 drops of concentrated acid after the precipitate had been returned to the solution as sulfuric acid, 3 or 4 drops of 0.1 N dichromate, and add very a soluble complex fluoride. These solutions were boiled for 5 dilute ferrous sulfate until the purple color just turns to a minutes, then 5 cc. of 0.1 N ferrous sulfate were added to the bluish green. The purple color will appear when the first hot solutions to destroy any persulfate which might remain. few drops of ferrous sulfate are added. Add this bluish green After cooling, the solutions were treated with excess of solution t o the solution to be titrated. permanganate and the usual procedure followed from this LITERATURECITED point. The results with this modified procedure were the same as those given for Method B in Table 111. The cause (1) Eppley and Vosburgh, J. Am. Chem. Soc., 44, 2148 (1922). EXG.CHEM.,17, 314 (1925). (2) Furman, IND. of the slightly low results from this method were not investi(3) Kelley and Conant, Ibid., 8, 719 (1916). gated further, as obviously the more rapid procedure in (4) Kelley, Wiley, Bohn, and Wright, Ibid., 11, 632 (1919); 13, Method A is preferable. Lang and Kurtz (6) whose paper 939 (1921). appeared after this work was completed, obtained satisfactory ( 5 ) Lang, Ber., 60, 1389 (1927). (6) Lang and Kurtz, 2.anal. Chem., 86, 288 (1931). results by making a separate titration of the vanadium in the (7) Sarver and Kolthoff, J. Am. Chem. Soc., 53, 2902, 2906 (1931). tungstic acid, which had been dissolved as in Method B. (8) Willard and Fenwiok, I b i d . , 45, 84 (1923). METHOD A. Tungstic acid is kept in solution as a complex (9) Willard and Gibson, IXD. ENG. CHEX., Anal. Ed., 3, 88-93 fluoride throughout the analysis. Add .25 to 30 cc. of water (1931). and 4 cc. of sulfuric acid (sp. gr., 1.83) to a 1-gram sample of (10) Willard and Young, IND.ENG.CHEM.,20,764 (1928). (11) Willard and Young, J. Am. Chem. Soc., 50, 1322 (1928). the steel weighed into a 400-cc. beaker. Warm gently until (12) Willard and Young, Ibid., 51, 139 (1929). the steel is completely decomposed and the tungsten separates out as a black powder. Add five or six drops of nitric acid RECBIVED December 31, 1931. Presented before tne Division of Physioal (sp. gr., 1.42) to the boiling-hot solution and, while tilting and Inorganio Chemistry a t the 82nd Meeting of the Amerirnn Chemical So the beaker, swirl the liquid thoroughly. Then add 5 cc. of oiety, Buffalo, N. Y., Ailgust 31 to SeptPmbPr 4, 1931 19.1%
