ANALYTICAL EDITION
154
thiocyanate. Theindicator was found to have no effect. Ferrous chloride, however, will reduce the nitro compound to a slight extent, unless some ferric iron is present. The amount of ferric iron necessary to prevent reduction of the dinitrotoluene during the nitroglycerol determination does not appear to be critical, as is shown by the results given in Table 11,on two typical laboratory samples. TABLE11. EFFECTOF EXCESSOF FERROUS CHLORIDE ox DETERMINATION OF DINITROTOLUENE AND NITROGLYCEROL IN ADMIXTURE
FeCL ADDED Ce 15
.
NITROQLYCEROL DINITROTOLUENE
%
%
5.03 5 07
6.63 6.59
5
5.06
6.58
15
20.23
2.00
20
20.24
1 98
The results obtained on a sample of dinitrotoluene and on a known mixture of nitroglycerol and dinitrotoluene are given in Table 111. It was found that small amounts of diethyldiphenylurea or diphenylamine did not interfere in the determination of nitroglycerol and dinitrotoluene by the use of the foregoing method.
Vol. 5 , No. 3
TABLE111. DETERMINATION OF NITROGLYCEROL AND DINITROTOLUENE IN ADMIXTURE NITROQLYCEROL FOUND %
..... .....
99.87 99.90
DINITROTOLUENE FOUND % 39.28 99.22 99.36 99.26
ACKNOWLEDGMEKT The author is indebted to W. H. Fravel for certain of the analytical results used in this article.
LITERATURE CITED (1) Callan, T., and Henderson, J. A. R., J . SOC.Chem. Ind., 41, 157-61T (1922). (2) Dickson, W., and Easterbrook, W. C., Analyst, 47, 112-17 (1922). (3) English, F.L., J. IND. ENG.CIimf., 12, 994-97 (1920). (4) Huff, W. J., and Leitch, R. .D., J . Am. Chem. SOC.,44, 2643-45 (1922). (5) Knecht, E., and Hibbert, E., “New Reduction Methods in Volumetric Analysis,” 2nd ed., Longmans, 1925. (6) Muraour, H., Bull. SOC. chim., 45, 1189-92 (1929). (7) Silberaad, O., Phillips, H. A., and Merriman, H. J., J. SOC. Chem. I n d . , 25, 628-30 (1906). (8) Thornton, W. M., Jr., and Wood, A. E., IND. ENG.CHEY., 19, 150-52 (1927).
RECEIVED December 8, 1932.
Indicators for Determining Chromium and Vanadium in Alloy Steels Oxidized Diphenylamine Sulfonic Acid and Oxidized Diphenylamine HOBART H. WILLARD AND PHILENA YOUNG,University of Michigan, Ann Arbor, Mich.
D
grams of the barium salt (obIPHEXYLAMINE dThis paper describes an investigation of the fonic acid is an oxidaproperties of diphenylaminesulfonicacid as un t a i n a b l e from the Eastman Kodak Co., Rochester, N. Y.) in tion-reduction indicator indicatorfor chromium and vanadium in tungsten a liter of water, adding to this which may be used in the presence of tungstic acid, but its sfeels* Withapreliminaryoxidation Of solution a slight excess of sodium properties under such conditions amine sulfonic acid, the blank correction to be sulfate, and decanting or filtering the solution. have not been thoroughly tested applied when using this indicator is reduced to a PREPARAT1oNoFoXIDrZEDIN(4). It has been used in the very small value. It is suficiently constant with DICATOR. The volume of t h e Of chrome-vanadiumdefinite procedures to give very accurate results o.ol indicator solution specitungsten steels for vanadium (8). Though accurate results were for chromiumOr fied in a given experiment is obtained, the indicator blank A preliminary oxidation ‘of diphenylamine placed in a small beaker, 5 cc. of water, 3 or 4 drops of conwhich had to be applied, because completely eliminates a blank correction for this centrated sulfuric acid, and 3 of reduction of some v a n a d i c indicator used in vanadilim or chromium acid by the indicator, was unor 4 drous of 0.1 N potassium determinat ions. d i c h r o m a t e a r e added, and desirablv large. It was noted in then very dilute ferrous sulfate this pacer that an indicator with no blank correction could be prepared by a preliminary (0.01 to 0.02 N ) is added until the purple color, which appears oxidation, but this is only approximately true. on the addition of the first few drops of ferrous sulfate, just Since diphenylamine and diphenylbenzidine are of no turns to a bluish green. As this purple color begins to disvalue in the presence of tungstic acid (6),i t seemed important appear, the ferrous sulfate should be added in parts of a drop, to study the properties of an indicator not affected by this in order to have no excess present in the oxidized indicator substance. Methods for chromium or vanadium which do solution. This bluish green solution is added to the solution not involve the removal of tungstic acid and the determination to be titrated. I n the experiments described in this paper the of the small amount of vanadium which inevitably accom- oxidized indicator was prepared in separate samples for each panies the precipitate are obviously much more rapid and titration. simple. A stock solution of the oxidized indicator is often more convenient and may be prepared as follows: EXPERIMENTAL One hundred cubic centimeters of 0.01 iM diphenylaminesodium PREPARATION OF INDICATOR. A 0.01 M solution of di- sulfonate and 25 cc. of concentrated d f u r i c acid are diluted to phenylamine sodium sulfonate is prepared by dissolving 3.2 900 CC. in a liter volumetric flask. To this solution 25 CC. of
(5
May 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.1 N potassium dichromate are added slowly with frequent shaking, followed by 0.1 N ferrous sulfate with repeated shaking,
until one drop causes a visible change in color from bluish green to a clear deep green in the liquid when viewed through the neck of the flask. This will require approximately 6.5 cc. of ferrous sulfate.
Since the indicator will slowly settle out of this solution, it must be shaken before using. To avoid this as well as the necessity for adding an exact amount of ferrous sulfate, the precipitate may be washed free from acid and salts and then stirred up with water in which it remains as a colloidal solution. This is done as follows: One hundred cubic centimetersof 0.01 M diphenylamine sodium sulfonate and 5 cc. of concentrated sulfuric acid are diluted to about 300 cc. To this liquid 25 cc. of 0.1 N potassium dichromate are added slowly, followed by 8 cc. of 0.1 N ferrous sulfate. This green solution is allowed t o stand 3 or 4 days, until a portion of the supernatant liquid gives no color when added to 100 cc. of water containing 2 cc. of 0.1 N potassium dichromate and 5 cc. of concentrated sulfuric acid. Then the supernatant liquid should be siphoned off slowly, care being taken not to disturb the green precipitate which is the indicator. Three hundred cubic centimeters of water and 15 cc. of concentrated sulfuric acid are added to the precipitate, the latter is allowed to settle again, and the su ernatant liquid is siphoned off. More thorough and rapid wasgng can be obtained by centrifuging. The green precipitate is then shaken up with 100 cc. of water. In the absence of electrolyte the precipitate will not settle out appreciably; even when not centrifuged, it settles very slowly and requires only occasional shaking. One-half cubic centimeter of this mixture gives the same color intensity in a titration as 0.3 cc. of 0.01 M diphenylamine sulfonic acid, and therefore may be substituted for it.
155
(8), the strength of which had been determined against Bureau of Standards sodium oxalate (8). From the normality of the ferrous sulfate the volume of reducing agent equivalent to the dichromate present was calculated, and the difference between this value and the actual value obtained in the titration, using the indicator, was recorded as the apparent indicator blank. The results are given in Table I. Some of the values in the last column in this table involve more than the true indicator blank, as the volume of ferrous sulfate required to titrate a given amount of dichromate varies with the concentration of the latter (1, 5 ) and is reduced slightly by hydrofluoric acid if present in sufficient concentration (1).
TABLEI. TITRATION O F DICHROMATE
WITH SULFOXIC .4CID AS INDXCATOR
DIPHENYLAMINE BPPARENT
INDICATOR
HsPOa INDICATOR BLANKPOR KzCrzO? SP. GR. HF SP.GR. 0.01 M , INITIAL 0.025 N EXPT. 0.05N 1.5 48% 1.37 OXIDIZED VOLUME FeS04 cc. cc. Cc. cc. cc. cc. cc. .. 200 1 25 5 0.3 0.28 .. 0.3 2 5 100 0.31 25 &SO4
3 4 5 6
7 8 9 10 11 12
13
25 15 5 25 25 25 25 25 25 25 25
5 5 5 5 5 5 5 10 20 5 5
.. ,. .. ..
5 10 20 5 5 5 5
0.3 0.3 0.3 0.5 0.3 0.3 0.3
0.3
0.3 0.6 0.9
300
200 200
200 200 200 200 200 200 200 200
0.26 0.26 0.22 0.50 0.13 0.15 0.17 0.12 0.13 0.40 0.59
With the solutions containing hydrofluoric acid, there was a slight return of purple after the end point was apparently RELATIVEBLANKSFOR OXIDIZEDAND UNOXIDIZED INDI- reached, and an additional 0.04 to 0.08 CC. of 0.025 N ferrous CATOR. Twenty cubic centimeter portions of 0.05 N potassulfate was required to obtain a permanent end point. This sium dichromate solution were treated with 5 cc. of sulfuric latter volume of ferrous sulfate is the one recorded above. acid (specific gravity 1.5) and 5 cc. of phosphoric acid (specific From experiments 1 to 5 it is seen that variations in volume gravity, 1.37), and diluted with water to 200 cc. Three of and in concentration of dichromate cause only a very slight these samples were titrated with 0.025 N ferrous sulfate after change in the indicator blank and from 7 to 11that the blank adding 0.3, 0.6, and 0.9 cc. of 0.01 M unoxidized indicator, and in phosphoric acid solutions is consistently lower than in three more were titrated after adding these same volumes of hydrofluoric acid solutions. Experiments 7 to 11 also show 0.01 M indicator which had been oxidised. For the first that the blank is independent of acid concentration, while 6, three samples the blanks in 0.025 N ferrous sulfate were 0.30, 12, and 13 indicate that the blank is greatly influenced by 0.56, and 0.79 cc., respectively; for those containing the same the volume of indicator used, because the destruction of the volumes of indicator in oxidized form, the blanks were 0.15, latter is greater the greater the concentration. The end0.38, and 0.57 cc. point color change was less sensitive in 10 and 11, in which The theory has been advanced (4) that the first step in the considerable acid was present. oxidation of diphenylamine sulfonic acid is to diphenylbenzidine sulfonic acid, and the next to diphenylbenzidine sulfonic BLANKIN TITRATIONS OF VANADICACID IN acid violet, which in turn may form a meriquinoid compound, INDICATOR TUNGSTEN STEELS diphenylbenzidine sulfonic acid green, with unoxidized diphenylbenzidine sulfonic acid, or may form higher oxidation Since one of the most important uses of diphenylamine sulproducts if any excess of oxidizing agent is present. If this fonic acid is for titrations of vanadic acid in chrome-vanadiumexplanation is correct, the use of the oxidized indicator in ti- tungsten steels, the effect on the indicator blank of changes in trations of chromic or vanadic acid with ferrous sulfate should concentration of vanadium was studied. eliminate any blank correction due to the first step in the To 0.8-gram samples of ingot iron, potassium dichromate oxidation of the indicator, an irreversible reaction, and, since the next step in the oxidation represents a reversible reaction, equivalent to 0.035 gram of chromium, measured portions of an ammonium vanadate solution, and 5 cc. of sulfuric acid (specific should cause any blank correction to be due mainly to the irre- gravity, 1.83) were added. After the iron was dissolved, nitric versible reactions represented by the oxidation of diphenyl- acid (specific gravity, 1.42) was added, drop by drop, to the hot benzidine sulfonic acid violet, which means destruction of solution, about 5 cc. being used in all, and the solution was boiled 2 to 3 minutes to remove oxides of nitrogen. After diluting to the indicator, some loss of which is inevitable. 160-175 cc. and cooling to room temperature, 5 cc. of hydrofluoric To determine the indicator blanks with variations in con- acid (48 per cent) and sodium tungstate solution equivalent to centration of oxidizing agent, volume of solution, acidity, and 0.2 gram of tungsten were added. The permanganate-azide volume of oxidized indicator, measured portions of a standard method (7) was used to convert the vanadyl salt into vanadic solution of potassium dichromate prepared from material of acid. Then 3 cc. more of hydrofluoric acid (48 per cent) and 0.5 cc. of 0.01 M indicator, oxidized, were added, and the vanadic acid accurately determined oxidizing power were taken, treated titrated with 0.028 N ferrous sulfate standardized electrometriwith a definite volume of sulfuric, and of hydrofluoric or cally against standard ceric sulfate. phosphoric acid, and diluted to the volume specified in Table I. The results obtained are given in Table 11,each value in the The stated volume of 0.01 M indicator, oxidized, was added and the chromic acid titrated with 0.025 N ferrous sulfate second and third columns representing an average of three standardized electrometrically against standard ceric sulfate duplicate determinations.
ANALYTICAL EDITION
156
TABLE11. CHANGEIN VALWEOF INDICATOR BLANKWITH CHANGE IN VANADIVM PRESENT BLANKEXPREB8ED IN TERMS OB: Vanadium in I-gram FeSOa, 0.025 N sample of steel INDICATOR
VANADIUM PRESENT Cram
cc.
%
0.0048 0.0096 0.0144 0.0240 0.0336
0.02 0.12 0.22 0.18 0.18
0,002 0.015 0.027 0.023 0.023
For amounts of vanadium ranging from 0.96 to 3.36 per cent the error is small and sufficiently constant so that it may be eliminated by a proper correction. Experiments were also carried out with the quantity of vanadium kept constant to note the effect on the indicator blank of changes in volume of indicator used. For this purpose l-gram samples of Bureau of Standards steel 50 (a), containing 0.976 per cent of vanadium, were taken and the permanganate-azide method (7) was used. Before titrating the vanadic acid with ferrous sulfate, standardized against ceric sulfate, 3 cc. of hydrofluoric acid (48 per cent) and the indicated quantity of 0.01 M indicator, which had been oxidized, were added to the solution, approximately 200 cc. in volume. The results are given in Table 111. TABLE111. CHANGEIN VALUEOF INDICATOR BLANKFOR V ~ A D I U DETERMINATIONS M WITH CHANGEIN VOLW OF INDICATOR BLANK EXPRI88ED I N TERMSOF: VANADIUM.FOUND AFTER FeSOa, 0.025APPLYINQ BLANK OF 0.05 INDICATOR N,, per 0.1cc. cc. 0.025 N FeSOc PER 0.01 M , OXIDIZED FeSO4, 0.025N mdicator 0.1 c c . INDICATOR INDICATOR
cc.
cc.
cc,
%
0.3 0.6 0.9 1.2 1.5
0 01 0 12 0 07 0’29’0’31’0’26 0:4Q:0154: 0:47 0.54,0.64,0.59 0.84,0.82,0.82
0.023 0.047 0.055 0.047 0.056
0.994,0,980,0.986 0.997,0,975,0.982 0.971,0.964,0.973 0.984,0,984,0,977 0.966,0.967,0.967
With 0.6 to 1.5 cc. of indicator, the blank varies in direct proportion to the volume of indicator used, while with 0.3 cc. of indicator the blank is slightly smaller. The larger blank obtained with chromic acid is explained by the fact that vanadic acid is a weaker oxidizing agent and destroys less indicator. According to the data in Table I11 one would expect the second value in Table 11, column 2, to be approximately 0.24 cc. This discrepancy between synthetic samples and steels, though often observed, has not yet been satisfactorily explained. If the 0.025 N ferrous sulfate to be used for vanadium determinations in tungsten steels is standardized according to the procedure in experiment 7, 8, or 9 in Table I, using that quantity of dichromate which will require 35 to 40 cc. of the reducing agent, and if the vanadium is determined by the permanganate-azide method, it might be expected that no blank correction would be required with 0.3 cc. of 0.01 M indicator, oxidized, and that a correction of +0.10 cc. of 0.025 N ferrous sulfate would be necessary with 0.5 cc. of the same indicator when oxidized. This was tested by determinations of vanadium in Bureau of Standards steel 50 (a), containing 0.976 per cent of vanadium. With three samples, for each of which 0.3 cc. of 0.01 M indicator, oxidized, was used, a blank correction of +0.05 cc. of 0.025 N ferrous sulfate was applied, resulting in 0.980, 0.974, and 0.978 per cent of vanadium, while with three other samples for which 0.5 cc. of the same indicator was used, a blank correction of +O.lO cc. gave 0.978, 0.981, and 0.961 per cent of vanadium. From Tables I, 11, and I11 it might be assumed that when 0.3 cc. of the 0.01 M indicator in oxidized form is used in a vanadic acid titration in a 1-gram sample of steel, the blank correction should be -0.10 cc. if the vanadium is less than 0.85 per cent, +0.05 cc. for 0.85 to 1.2 per cent of vanadium, and +O.lO cc.
VOl. 3, No. 3
for 1.2-3.5 per cent of vanadium, .provided that the ferrous sulfate has been standardized against dichromate according to the procedure in experiment 7, Table I. Three analyses of Bureau of Standards steel 50, containing 0.756 per cent of vanadium, gave, after a blank correction of -0.10 cc. of 0.025 N ferrous sulfate, 0.756, 0.760, and 0.756 per cent of vanadium.
INDICATOR BLANKIN TITRATIONS OF CHROMIC PLUSVANADIC ACIDSIN TUNGSTEN STEELS To 0.8-gram samples of ingot iron, potassium dichromate solution equivalent to the quantities of chromium specified in Table IV and 5 cc. of sulfuric acid (specific gravity, 1.83), were added. After the iron was dissolved, hydrofluoric acid followed by nitric acid was added and the solution boiled to remove oxides of nitrogen. The chromium was oxidized by the usual persulfate method with silver ion as catalyst. (The details of this new procedure for chromium in tungsten steels are given in the following paper.) Before titration of the chromic acid with 0.05 N ferrous sulfate, a little hydrofluoric acid, sodium tungstate solution equivalent to 0.2 gram of tungsten, and 0.3 cc. of 0.01 M indicator, which had been oxidized, were added. The volume of solution a t this point was 300 cc. The ferrous sulfate solution was restandardized according to experiment 7, Table I, for each set of experiments listed in Table IV. An amount of dichromate approximately equivalent to that present in the samples was used for this purpose. It was found in this way that the normality of the ferrous sulfate was the same over the entire chromium range in Table IV. Therefore, in all later standardizations of ferrous sulfate against dichromate, using oxidized diphenylamine sulfonic acid as indicator, that amount of standard dichromate requiring 35 to 50 cc. of the ferrous sulfate was used, and the procedure of experiment 7, Table I, was followed. TABLEIv. TITRATION OF DICHROMATE AFTER OXIDATION
PERBULFATE
(Ferria iron and tungstic acid present, oxidized diphenylamine sulfonic acid as indicator) CHROMIUM PRESENT Gram 0.0131 0.0218 0.0305 0,0392 0.0479
CHROMIUM F o u N n AFTER CORRECTION O F
-0.15 cc.
OB
0.05 N FeSOl
Uram
0 0129 0 0130 0 0130 0’0218’0’0219’0’0218 0‘0304’0‘0304’0‘0304 0’0393’0’0393’0’0393 0:0478: 0:0479: 0:0478
When duplicate samples of a standard dichromate solution were titrated with 0.05 N ferrous sulfate, using the procedure of experiment 7, Table I, the ferrous sulfate was 0.05090 N . This same ferrous sulfate when standardized electrometrically against standard ceric sulfate was 0.05073 N . As this last method is known to be correct, a blank of -0.15 cc. of 0.05 N ferrous sulfate must be applied to volumes of this reagent used in chromic acid titrations if the reducing agent has been standardized against dichromate by the procedure above, using as indicator 0.3 cc. of 0.01 M diphenylamine sulfonic acid which has been oxidized. The data in Table IV to which this blank correction of -0.15 cc. has been applied show that this indicator method for chromium is quantitative over the range of chromium content usually encountered in tungsten steels. For some unexplained reason the color change a t the end point in the experiments in Table IV was never as sharp as in samples of steels. To study the effect on the indicator blank of changes in the volume of oxidized indicator used, 1-gram samples of Bureau of Standards steel 50 (a), containing 3.52 per cent of chromium, were taken, and the chromium and vanadium oxidized by the usual persulfate method with silver ion as cataIyst, hydrofluoric acid being present throughout the analysis to keep the tungstic acid in solution. Before the titration a
May 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
little more hydrofluoric acid and the indicated volume of 0.01 M indicator, oxidized, were added to the solution, approximately 300 cc. in volume. The results are given in Table V, each blank recorded being an average of three determinations. The values in the second column are the variations from the calculated volume of 0.05 N ferrous sulfate for the chromic acid, obtained from standardizing it against dichromate, using the procedure in experiment 7 , Table I. The values in the third column are the variations from the theoretical volume of 0.05 N ferrous sulfate required for the chromic acid when the ferrous sulfate is standardized electrometrically against standard ceric sulfate.
157
chromium, 3.611 and 3.607 per cent. The change in potential a t the end point was much smaller than for a similar solution without tungstic and hydrofluoric acids, so that the electrometric method for obtaining the end point here can not be recommended. In these titrations equilibrium was reached quite slowly in the region of the end point-an indication, possibly, that in a titration with the indicator slightly more than the theoretical quantity of ferrous sulfate is used before the color change takes place. Some oxidized indicator was added to another solution shortly before the end point was reached in an electrometric titration, to see whether the color change occurred a t the electrometric end point. The solution was still purple a t that end point and approximately TABLEV. CHANQE IN VALUE OF INDICATOR BLANKFOR CHRO- 0.07 cc. more of 0.05 N ferrous sulfate was required to produce MIUM DETERMINATIONS IN TUNGSTEN STEELSWITH CHANQE IN the change in color, This change was not sharp, however, VOLUME OF INDICATOR because of too high acid concentration, so that this experiment BLANK I N 0.05 N FeSO4 STAND- CHROMIUM FOUND while of use qualitatively in showing that the indicator end INDICATOR ARDIZED AQAINBT: AFTER APPLICATION OF 0.01 M , KrCrzOi, using Ce(SOa), elecINDICATOR BLANKI N point occurs after the electrometric, is not of value quantitaOXIDIZED indicator trometrioally SECOND COLUMN tively in determining the exact difference between these two CC. cc. cc. Yn end points. It seems probable that this slight error of 0.1 0.3 -0.36 -0.23 3.53,3:53,3.51 -0.07 3 52 3 51 3 53 0.6 -0.13 mg. of chromium is caused by a fairly slow reaction a t the fO .20 3'53' 3'52' 3'51 0.9 +0.07 1.2 +o. 10 +0.23 3:52: 3'51: 3:53 end point. The error appears always constant in value and is easily included in the blank correction and thus eliminated. The results in the last column show the close agreement beIN VALUEOF INDICATOR BLANK FOR CHROtween experiments in which the same volume of indicator is TABLEVI. CHANGE IN TUNGSTEN STEELSWITH CHANQE IN used. Obviously one would always expect larger positive MIUM DETERMINATIONS PERCEXTOF CHROMIUM PRESENT values in the third column than in the second, as the correct CHROMIUM PREBnormality of the ferrous sulfate by standardization electroENT AFTER BLANK CORRECmetrically against ceric sulfate is smaller than the normality TION OF CHROMIUM BLANKI N 0.05N -0.30 C C . OF against dichromate using the indicator. It is especially dif- SAMPLECHROMIUM PREBB~NT FOUND FeS04 0.05 N FeSOa ficult, however, to give a reason for any negative indicator Gram Gram Cc. Gram 1 blank in the third column. Whatever is responsible for the 0.02112 0.02117 -0.06 2 0.02112 0.02113 -0.01 -0.04 uniformly low blanks in this column must exert a like influence 0.02112 0.02827 0,02116 3 -0.05 0.02816 4 -0.13 in making the second column blanks of smaller positive value 0.02816 -0.26 -0.23 5 0.02839 0.02816 6 0.02841 than one would anticipate. -0.29 7 -0.35 0.03551 0.0352 Though this unexplained discrepancy in Table V, amount8 0,03560 0.0352 9 0.03548 0.0352 -0.29 ing to approximately 0.1 mg. of chromium or to 0.01 per cent -0.21 0.04412 0.04394 10 0.04412 0.04394 of chromium in a 1-gram sample, is very small, it seemed worth 11 0.05292 0.04427 0.04394 12 -0.38 while to investigate it further to see if it was constant with 0.06267 13 -0 29 0.05287 -0'301 -0.32 14 0.05293 steels of varying chromium content so that a correction could 0.05267 -0:38) 15 0.05300 be applied for it, and to try to explain the reason for it. Samples of Bureau of Standards steel 50 (a), containing OR DIPHENYLBENZIDINE IN DE3.52 per cent of chromium and 0.976 per cent of vanadium, were OXIDIZEDDIPHENYLAMINE TERMINATIONS OF CHROMIUM AND VANADIUM weighed out: samples 1 to 3 = 0.6 gram, 4 to 6 = 0.8 gram, Kolthoff and Sarver (8) consider the steps in the oxidation 7 to 9 = 1 gram, 10 to 12 = 1.0 gram to which 10 cc. of 0.05040 N potassium dichromate were added, and 13 to 15 = 1.0 of either of these indicators similar to the reactions suggested gram to which 20 cc. of the same dichromate solution were by them (4) for the oxidation of diphenylamine sulfonic added. These samples were prepared in the same way as acid. Consequently a preliminary oxidation of either indithose used in Table V. Three-tenths cubic centimeter of cator causes the value of any blank correction to become negli0.01 M indicator, oxidized, was added in every case before gible (S),as the blanks for these two indicators when not oxititration of the chromic and vanadic acids with 0.05 N ferrous dized are considerably smaller than the blank for unoxidized sulfate, standardized as directed for the experiments in Table diphenylamine sulfonic acid. One-tenth per cent solutions of diphenylamine and diV. The results of this series of experiments are given in phenylbenzidine were prepared by dissolving 0.1 gram of the Table VI. indicator in 10 cc. of sulfuric acid (specific gravity, 1.83) and The average indicator blank in experiments 4 to 15is -0.30 cc. and the data show that this value is quite independent of diluting this solution with 90 cc. of glacial acetic acid. The the quantity of chromium present. From previous state- method of preparing portions of oxidized indicator solution ments one would expect this blank to be -0.15 cc. rather than from these 0.1 per cent solutions was the same as used for di-0.30 cc. of 0.05 N ferrous sulfate. phenylamine sulfonic acid, except that 5 cc. of phosphoric Duplicate 1-gram samples of Bureau of Standards steels acid (specific gravity, 1.37) instead of water were added to a 50 and 50 (a) were prepared as for Table V. No indicator measured volume of the indicator in a very small beaker. No solution was added. Forty cubic centimeters of sulfuric sulfuric acid was added, but only 3 or 4 drops of dichromate, acid {specific gravity, 1.5) were added, the solutions cooled to followed by very dilute ferrous sulfate. The oxidized di5" to 6" C. and held a t this temperature during electrometric phenylamine solution was always clear, while with diphenyltitration with 0.05 N ferrous sulfate which had been standard- benzidine, probably because of its much smaller solubility, ized electrometrically against standard ceric sulfate. A silver the solution of the oxidized compound was not always clear chloride-platinum electrode system was used. For steel 50 nor was the color development of solutions to which it was (a), containing 3.52 per cent of chromium, 3.516 and 3.522 added always good. Since diphenylamine is less expensive per cent were obtained; for 50, containing 3.61 per cent of and more available, it was used in all further experiments.
I I
ANALYTICAL EDITION
15 8
Five-gram samples of ingot iron were treated with potassium dichromate solution equivalent to 35 mg. of chromium, ammonium vanadate solution equivalent to 10 mg. of vanadium, and 10 cc. of sulfuric acid (specific gravity, 1.83). The permanganate-azide method for vanadium in a chromevanadium steel was followed (7). To two of the samples 0.6 cc. of 0.1 per cent unoxidized diphenylbenzidine was added and after 5 minutes the solutions were titrated with 0.025 N ferrous sulfate. The volumes required were 7.97 and 7.93 cc., which, after the necessary indicator correction of 0.03 cc. of 0.025 N ferrous sulfate per 0.1 cc. of indicator used ( 8 ) , become 8.15 and 8.11 cc. Two more samples of vanadic acid were treated with 0.3 cc. of 0.1 per cent diphenylamine, which had been oxidized, and allowed to stand for 5 minutes. The volumes of ferrous sulfate required were 8.12 and 8.13 cc. Experiments in which measured portions of a solution of Dotassium dichromate were titrated with 0.025 N ferrous sulfate, after the addition of phosphoric acid, water, and cator, showed that the usual blank required for diphenylamine . . disappeared in these cases, as in vanadic acid titrations, when
voi. 5, No, 3
the oxidized indicator was used. Results for chromium and vanadium in chrome-vanadium steels, using oxidized diphenylamine as indicator, are given in the following paper. It was not found possible to make up a stable stock solution of oxidized diphenylamine, as was done with the sulfonic acid derivative. ACKNOWLEDGMENT The authors are indebted to G. Lindemulder for the method of preparing the oxidized indicator in quantity. LITERATURE CITED (1) (2) (3) (4) (5) (6) (7j ()'
Eppley and Vosburgh, J . Am. Chem. SOC.,44, 2148 (1922). Kolthoff and Sarver, Zbid., 52, 4179 (1930). Lang and Kurtz, 2. anal. Ckem., 86, 288 (1931). Sasver and Kolthoff, J . Am. Chem. SOC., 53, 2902 (1931). Willard and Gibson, IND. EXG.CHEY.,Anal. Ed., 3, 88 (1931). Willard and Young. IND. ENQ.CHEM..20. 764 11928). Willard and Young, Ibid., Anal. Ed., 4, 187 (1932). 1322 (1928). and YoungvJ . Am. 501
R ~ C E I Y EDecember D 21, 1932
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New Procedures for Chromium and Vanadium in Alloy Steels HOBART H. WILLARDAND PHILENA YOUNG,University of Michigan, Ann Arbor, Mich. I n chromium or aunadium determinations in be eliminated by the proper correction. The usual tungsten steels the tungsten is kept in solulion direct method for chromium with addition of exthroughout the analysis as a complex fluoride. cess standard ferrous sulfate and back-titration The excess of permanganate used in the oxidation with standard permanganale is applicable. These of vanadyl ion in vanadium determinations or procedures for aanadium and chromium in steels formed during a persulfate oxidation of vanadium containing tungsten are accurate and more rapid and chromium m a y be reduced either by sodium than those now in use. These same reducing agents have been applied azide, followed by boiling io remove hydrazoic acid, or by sodium nitrite at room temperature, to vanadium and chromium determinations in steels without tungsten, thereby shortening the profollowed by urea to destroy excess nitrite. I n such steels oxidized diphenylamine sulfonic cedures now used. I n these cases oxidized diacid is used as internal indicator in the titration phenylamine m a y be used as the internal indicator of vanadic or chromic acids with ferrous sulfate. f o r the titrations with ferrous sulfate. B y the use B y this preliminary oxidation of the indicator of this oxidized indicator both in the analysis and the blank is reduced to a aery small value, and is in the standardization of the ferrous sulfate, a n y suficiently constant with definite procedures to blank correction for the indicator is eliminated.
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HILE rapid and accurate indicator methods are available for chromium and vanadium in chromevanadiumsteels, there is a t present but one indicator method for either element in tungsten steels which does not involve the removal of the tungsten, and that is for vanadium (6). A separation of tungsten is undesirable, both because of the time required and also because the precipitated tungstic acid always contains traces of vanadium and sometimes of chromium which have to be determined separately. The chromium in the precipitated tungstic acid is much more easily determined than the vanadium, but good methods for the latter are of greater importance, since it is always present in the precipitate. In this method for vanadium the tungsten is kept in solution as a complex fluoride ( 5 ) ,and diphenylamine sulfonic acid is used as indicator. The blank required for the latter is undesirably large, but the authors, in a recent detailed study of
the behavior of this indicator in chromic and in vanadic acid solutions (6), have shown that the blank may be greatly reduced by a preliminary oxidation of the indicator, and they have worked out the values for blanks when definite procedures are followed. The permanganate-azide method for vanadium (6) makes use of sodium azide to destroy the excess of permanganate after the oxidation of the vanadyl salt, the excess of hydrazoic acid being destroyed by boiling. Lang and Kurtz (1) used sodium nitrite instead of azide for this purpose, followed by urea to destroy excess of nitrite, but they did not show the possible variation in conditions with this reducing 'agent. The authors have investigated this matter and have found that nitrite and urea may be used very satisfactorily under conditions requiring less time than those suggested by Lang and Kurtz. The substitution of nitrite and urea for sodium azide shortens the method for vanadium, as it is unnecessary
