Spectrophotometric Determination of Molybdenum with


P. W. West. Analytical Chemistry 1952 24 (1), 76-85 ... William H. Dresher , Milton E. Wadsworth , W. Martin Fassell. JOM 1956 8 (6), 794-800. Article...
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ANALYTICAL CHEMISTRY

304 does not require as complete a separation from these elements as is necessary for gravimetric determination. The spectrophotometric method offers an especially advantageous means for determining platinum in the presence of the more base metals of the acid hydrogen sulfide group; determination of platinum through the sulfide ( 3 , p. 289) requires absence of all other elements that are precipitated with hydrogen sulfide in acid solution. Wohler and Spengel ( 1 6 ) suggested that the color produced in the reaction of platinum(1V) with tin(I1) chloride was due to colloidal platinum. This suggestion is probably erroneous, in view of the fact that the colored material readily passes through semipermeable membranes such as collodion. Further evidence that the colored species is not the colloidal metal is shown by the rapid and complete extraction into organic solvents. The color has been attributed also to platinum(I1) (6). However, the authors found that when the platinum(1V) chloride solution (dilute chloroplatinic acid) was evaporated to fumes with sulfuric acid to expel hydrochloric acid, and the sulfuric acid solution was treated with tin(I1) sulfate, no color developed. Simple reduction to platinum(II), therefore, cannot account for the color reaction. Furthermore, addition of hydrochloric acid to the colorless platinum and tin sulfate solution immediately produced ax1 intense yellow color. I t appears, therefore, that chloride ion ia one of the requisites for color formation. The color is not due to chloroplatinous acid, as has been claimed (12, I d ) . h solution containing 10 p.p.m. of platinum as chloroplatinous acid (potassium chloroplatinite in 10% hydrochloric acid solution, prepared so as to prevent any possible atmospheric oxidation) was essentially colorless. Upon the addition of tin(I1) chloride to this solution, an immediate yellow color developed, comparable in intensity with that produced from 10 p.p.m. of platinum(1V). A solution containing 1000 p.p.m. of platinum as chloroplatinous acid had a color intensity comparable to that produced by 10 p.p.m. of platinum(1V) in the tin(I1) reaction. The spectral curve (transmittancy versus wave length) of the 1000 p,p.m. solution of chloroplatinous acid was of the same general shape, below 420 mp, as the curve for the solutions from the platinum(1V)-tin(I1) chloride reaction (Figure l), except that the maximum occurred a t 360 m r (instead of 353 mp), and the minimum occurred at 390 mp (instead of 403 mp); in addi-

tion, the chloroplatinous acid had another minimum a t 475 q. It is obvious, therefore, that the color is not due simply to chloroplatinous acid, but in some way involves the tin. A further study of the chemistry of the reaction process is under way in this laboratory, and will be made the subject of a later report. ACKNOW LEDGMEYT

Much of the work reported in this paper was made possible by a grant from the University of Texas Research Institute to Gilbert H. .\yes; this assistance is gratefully acknowledged. LITERATURE CITED

(1) Ayres, G. H.,ANAL. CHEM.,21, 652 (1949). (2) Figurovskii, N. A . , Ann. secteur platine, Inst. chim. yen. (U.S.S.R.), KO.15,129(1938). (3) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” New York, John Wiley & Sons, 1929. (4) Hiskey, C. F., ANAL.CHEM.,21, 1440 (1949). (5) Hopkins, B.S., “Chapters in the Chemistry of the Less Familiar Elements,” Chap. 21, p. 39, Champaign, Ill., Stipes Publishing Co., 1940. ( 6 ) Hunter, D., Milton, R., and Perry, K. 11. A., Brit. J . I n d . .Wed., 2,92 (1945). (7) Karpov, B. G., and Savchenko, G. S., Ann. secteur platine.I m t . chim. gen. (U.S.S.R.), No. 15, 125 (1938). (8) Langstein, E.,and Prasunitz, P. H., Chem.-Ztg., 38,802 (1914). (9) Leutwein, F., Zentr. Mineral. Geol., 1940A,129. (10) Poluektov, N. S., and Spivak, F. G., Zavodskaya Lab., 11, 398 (1945). (11) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” pp. 358-60, New York, Interscience Publishers, 1944. (12) Scott’s “Standard Methods of Chemical Analysis.” S . H. Furman, ed., 5th ed., Vol. I, p. i13, New York. D. Van Nostrand Co., 1939. (13) Thompson, S. O.,Beamish, F. E., and Scott, M., INO.ENG. CHEX.,ANAL.ED.,9,420(1937). (14) Treadwell, F. P., and Hall, W. T., “Analytical Chemistry,” 6th English ed., Vol. I, p. 284, New York. John Wiley & Sons, 1921. (16) Wohler, L.,Chem.-Ztg., 31,938 (1907). (16) Wobler, L.,and Spengel, A . . Z. Chem. I d . Kolloide. 7 243 (1909). (17) Wolbling, H., Ber., 67B,773 (1934). RECEIVED June 5.1950.

Spectrophotometric Determination of Molybdenum with Phenylhydrazine Hydrochloride GILBERT H. AYRES A N I BARTHOLOMEW L. TUFFLY T h e Unizersity of Texas, Austin, Tex.

T

H E most widely used photometric method for the deterniination of molybdenum is based upon the amber to orange color produced by treatment with thiocyanate and a reducing agent, usually tin(I1) chloride; ordinarily, the colored complex is extracted into butyl acetate for the color measurement (IO). The color intensity is dependent upon a number of variables ( 6 ) ; one of the serious disadvantages of the method is fading of the color, and the rather rigid control necessary t o minimize this effect. By using water-acetone solutions and tin(I1) chloride reduction, Grimaldi and Wells ( 4 ) eliminated the extraction procedure, and found the acetone to exert a stabilizing effect on the color. Recently, Ellis and Olson ( 2 ) used acetone as the reducing agent, and found that this increased both the color stability and the sensitivity; extraction into organic solvents was not recommended. Among the several other color reactions of molybdenum that have been observed, i t appeared that the reaction with phenylhy-

drazine might prove useful for photometric analysis. Spiegel and Maass (9) observed that molybdates in acid solution reacted with phenylhydrazine to produce a blood-red color or a red precipitate. The reaction was later studied by Montignie (S), and reported t o be specific for molybdenum; color formation was said to involve the Oxidation, by molybdate, of the phenylhydrazine to a diazonium salt, which then coupled with the excess phenylhydrazine and molybdate. The method has been used as a spot test for molybdenum ( S ) , but appears not t o h a w been studied for application t o quantitative spectrophotometric analysis. I t was the purpose of this investigation to study the molybdenum-phenylhydrazine reaction to establish the best con ditions for color development, to evaluate the optimum range and the accuracy of the photometric process, to determine the nature and extent of interference from diverse ions, and to test the applicability of the method to the spectrophotometric determination of molybdenum in steel.

V O L U M E 23, NO. 2, F E B R U A R Y 1 9 5 1 This investigation was undertaken to study the red color system produced when acid solutions of molybdenum(V1) are treated with phenylhydrazine hydrochloride, with a view to its application to the spectrophotometric determination of molybdenum in steel. The red color is produced by treating molybdenum(V1) with an excess of phenylhydrazine hydrochloride, in 50% acetic acid solution. The color develops rapidly in hot solution, and is reproducible and stable. The optimum concentration range is from 2 to 10 p.p.m. Iron(II1) may be

REAGENTS

Ammonium heptamolybdate tetrahydrate, (NHr)&LlorO?a.4H20, was used for the preparation of standard molybdenum solution. Computed on the assay of 80,5’% molybdenum trioxide (theoretical, 81.4% MOO,), 9.315 grams of ammoniuni heptamolybdate tetrahydrate were dissolved in water containing 10 ml. of concentrated ammonium hydroxide and diluted t o 500.0 ml.; the solution contained exactly 10 grams of molybdenum per liter. Working standards were prepared by quantitative dilution of the stock solution. Eastman’s phenylhydrazine hydrochloride was used in the final procedure; phenylhydrazine acetate and also the phenylhydrazine base were used in some of the preliminary testing. Glacial acetic acid, and the salts used in the study of inteiferences, were analytical reagent grade. National Bureau of Standards steels No. 153, 8.39% molybdenum, and No. 139, 0.178% molybdenum, were used in testing the application of the method. APPARATUS

Transmittancy measurements were made with a Beckniaii Model DU spectrophotometer, using matched. 1.000-cm. cell!. The instrument waa operated a t constant sensitivity, using sht widths corresponding to band widths of about 2 to 4 millimicrone. Calibrated weights and calibrated volumetric ware were used throughout.

305 tolerated up to a 20 to 1 weight ratio to molybdenum; for higher ratios, iron interference is eliminated by selective reduction. The usual alloying elements do not interfere. The method has been tested by analyzing Bureau of Standards steels, one of high aud one of low molybdenum content. The method is simple, rapid, and accurate; it is applicable in steel analysis without change in usual dissolution procedures. I t has the advantage over thiocyanate method that no extraction into organic solvents is involved and color is not subject to fading.

precision. Satisfactory results were obtained with phenylhydrazine hydrochloride; hence this reagent was adopted for use. For work of high accuracy, it is advisable to use blanks prepared concurrently with samples; for routine work, blanks should be not more than 8 hours old. Figure 2 shows the influence of varying amounts of pht%iiylhydrazine hydrochloride (same amount in both sample and hlank) on the transmittancy of solutions containing 5 p.p.ni. of molybdenuin; with 10 p.p.m., minimum transmittancy was reached also with 1 gram of reagent. I n order to provide an adequate amount of reagent to ensure full development of amounts of molybdenum in the high portion of the working range, the use of 1 . 5 grams of phenylhydrazine hydrochloride per 100 ml. of final solution wits adopted for the standard procedure. When 1.5 granis of phenylhydrazine hydrochloride were used for color devclopnieut, the amount of the reagent in the blank could be varied \vithin the limits of 1 t o 2 grams without influencing the measured transmit tancy.

EXPERIMENTAL

Spectral Characteristics. Solutions of several concentrations of molybdenum were color-developed with phenylhydrazine hydrochloride in acid solution a t elevated temperature, and the transmittancy was measured a t frequent wave-length intervals over the range 375 to 700 mp. The curves of transmittancy versus wave length had a minimum a t 505 mp. This wave length was used for making transmittancy measurements in studying the influence of various factors on the color; a moderate wavelength re ion on either side of 505 mp was scanned to detect any possible Aift in the position of minimum transmittanry. Figure 1 shows the spectral curves for solutions containing from 1 t o 10 p.p.m. of molybdenum, developed by the standardized procedure described below. I n the concentration range studied, the system conforms t o Beer’s law. A concentration of 5 p.p.m. of molybdenum is about in the middle of the optimum concentration range; a constant amount of molybdenum, 5 p.p.m., was therefore used in testing the influence of various factors on the color intensity. Molybdenum Oxidation State Required. Molybdate solutions which were reduced with tin(I1) chloride gave no color when treated with the phenylhydrazine reagent. Oxidation state +6 (molybdate) is required for the color reaction. Phenylhydrazine Reagent. Use of the phenylhydrazine base uas not satisfactory on account of the ease with which the liquid oxidized to give yellow to brown colored oxidation products : photometric results were not precise when the free base was used. The same difficulty was experienced with a sample of phenylhydrazine acetate which contained some free base; the product recrystallized from ether gave a considerable improvement of

0

I

400

I

450 WAVE

I

1

500 LENGTH,

5 50

6 0

mp

Figure 1. Spectral Curves for Molybdenum with Phenylhydrazine Hydrochloride Effect of Acids. Reproducible results were not obtained with hydrochloric acid or sulfuric acid, and the effect of increasing the acid concentration was a decrease of color intensity. When acetic acid was used, it was found that increasing the acid concentration increased the color intensity-Le., decreased the transniittancy-up to 50% acid (by volume), above which the

ANALYTICAL CHEMISTRY

306 Table I.

Rate of Color Development

( 5 p.p.m. of molybdenum. 1.5 grama of phenylhydrazine hydrochloride per 100 ml. of 50% 'acetic acid; transmittanciea at 505 mp)

A t Room Temperature % tram-

Time, min. 0 10 20 30 60 100 150 200 250 300 350

390

450

At Boiling Temperature

70trans-

mittancy

Time, min.

mittancy

99.8 78.0 61.3 55.3 47.7 45.2 42.3 39.2 37.5 36.7 35.2 35.0 36.0

0 1 2 3 4 5 10 16

99.8 36.8 35.5 35.0 35.0 35.0 34.9 35.0

color intensity remained constant (Figure 3). Replicate samples gave good reproducibility. Rate of Color Formation. The characteristic red color developed very slowly a t room temperature, but formed very rapidly a t the boiling point, as shonm in Table I. Stability of Color. Color-developed samples gave constant transmittancies over a period of 2 to 3 weeks, if compared with a blank of the same age. On longer standing, a dark scum separated in both blank and sample. Temperature Coefficient of Transmittancy. Over the teniperature range of 20" to 30" C. the transmittancy was constant; from 30" to 40" C. the transmittancy increased at an averagc' rate of 0.08% (absolute) per 1" C.

within the limits 34.8 and 35.3%. The average deviation wns 0.12%, and the standard deviation was 0.17% absolute transmittancy. Effect of Diverse Ions. For application of the method to the analysis of molybdenum in steel, the possible interference froni a number of metals must be considered. The other elements most commonly met in such samples are iron, chromium, manganese, nickel, cobalt, vanadium, and tungsten. For studying interference effects, these elements were used in the osidatioii state that would be present in the solution after various dissolution procedures-namely, iron(III), chromium(II1 or \-I), manganese(II), nickel(II), cobalt(II), vanadium(V), and tungsten(V1). By the use of phenylhydrazine hydrochloride as the color-developing reagent, some of the elements of high oxidation state are rcduced-.g. , chromium(V1) to chromium(II1).

5 P.P.M. OF M O L Y B D E N U M

H Y D R O C H L O R I D E P E R 100 ML.

44 0

OF MOLYBDENUM

IN 5 0 % A C E T I C

-

z 4

+ 42-

c

z5 40-

(r

c

3s-

36 5 P.P.M.

34

I

0

ACID

+

1.5 G. OF P H E N Y L H Y D R A Z I N E

I IO

I 20

I 30

I 40

I 50

I 60

I 70

I 80

90

% A C E T I C A C I D BY VOLUME

Figure 3.

: I

it

a

30

a

\

I

I

I

I

I

0

I 2 3 G R A M S P H E N Y L H Y D R A Z I N E HYDROCHLORIDE P E R 100 M L .

Figure 2. Effect of Phenylhydrazine Hydrochloride Concentration on Transmittancy at 505 m u Standardized Procedure. An aliquot of the working standard solution, or sample for analysis, to give the desired final concentration of molybdenum (optimum range, 2 to 10 p.p.m.) wa5 added to 50 ml. of 50% acetic acid solution. After 1.5 grams of phenylhydrazine hydrochloride had been added, the mixture was boiled for 5 minutes. The cooled solution was transferred to a 100-ml. volumetric flask, 25 ml. of glacial acetic acid were added, and the solution was diluted to volume with water. Blank solutions prepared by the same method were usable for a period of about 8 hours. The transmittancy a t 505 mp was measured a t room temperature (about 25" (3.). Reproducibility. I n 24 replicate determinations, made over a period of several weeks, the transmittancy of solutions containing 5 p.p.m. of molybdenum averagrd 35.07,, all results lwing

Effect of Acetic Acid Concentration on Transmittancy at 505 mp

In order to establish the tolerance of the molybdenum system for another element, solutions containing 5 p.p.m. of molybdenum and added increments of the foreign element were developed and measured in the usual nay. The tolerance was taken as the largest amount of foreign element that would give a transmittancy within 0.4% of that of the molybdenum alone. The toleranrw are given in Table 11. Removal of Iron(II1) Interference. Interference of iron(I1II deserves special mention, because the principal application of the method would be the determination of molybdenum in steel. B s shown in Table 11, iron(II1) does not interfere when the ratio of iron to molybdenum is less than 20 to 1; hence, for steels containing more than 5 % molybdenum, removal of iron( 111) is unnecessary. For low-molybdenum steels, however, removal of at least a considerable part of the iron(II1) would bc required. Because iron(I1) can be tolerated in very largr amounts, the obvious procedure is to reduce iron(II1) to iron(I1) However, the spectrophotometric determination requires molybdenum in the oxidation state +6. The problem, therefore, is to reducr the iron( 111) without also reducing the molybdenum( VI). On the basis of the standard redox potentials of the systems involved (?), it would appear that the reduction of iron(II1) to iron(I1) with a Jones reductor, for example, would be difficult to accomplish without simultaneous reduction of molybdenum(\Y) to molybdenum(II1). On the other hand, if the reduction of iron(II1) is very rapid in comparison with the rate of reduction of molybdenum(VI), it might still be possible to reduce moderate to largp amounts of iron(II1) without reducing small [email protected] molybdenum(VI), by using a Jonea reductor and a high flow rate [.Although reduction of molybdenum(V1) to molybdenuni(II1)

307

V O L U M E 23, NO. 2, F E B R U A R Y 1 9 5 1 with a Jones reductor is a standard procedure for the titrimetric determination of molybdenum (IO), the operating directions for this method do not specify any conditions of flow rate.] For testing this procedure, a Jones reductor was prepared in a SO-ml. buret, using a 30-cm. column of amalgamated 20-mesh zinc. Samples of the molybdenum standard containing 0.5 mg. of niolybdenuni(V1) ( t o give a final concentration of 5 p.p.m. for spectrophotonietric measurement) in 1 ,If hydrochloric acid were passed through the reduct'or a t various flow rates, and the effluent qolution was treated for color development by the standardized procedure. I n a second series of experiments, the solutions contained 0.5 mg. of molybdenuni(\T) arid 250 mg. of iron(II1) in I M hydrochloric acid ( 5 p.p.m. of molybdenum and 2500 p.p.111. nf iron in the final solution for color measurement). After passing through the reductor, the molybdenum color was developed and measured. In a third series of tests, using molybdenum only, the solution from the reductor was delivered under ferric :ilum solution, and the iron(I1) equivalent to t,he reduced niolybclmum was titrat,ed with 0.00250 S potassium permangannte x)lut,iori.

reduced even by very slow passage through the reductor, it 1s clearly shown that a t least with small amounts of molybdenum the amount of reduction is markedly influenced by the rate of flm-of the solution through the reductor.

ACETIC

ACID

'rhe results of the reduction tests, summarized in Table 111, .diow that when the flow rate is a t least 0.5 ml. per second, interr'tarence from iron( 111) can be eliminated in the spectrophotometric determination of molybdenum. The third experiment ( fcbrric slum method) shored that a t the high flow rates about 4% (0.02 mg.) of the molybdenum was reduced; because only t'he iiiolybdenum(V1) develops the red color on treatment with phenylhydrazine hydrochloride, a reduct,ion of 4% of the molybdenum prcwnt should be detectable in the spectrophotonietric method :tn an absolute difference of about 1.5% transmittancy (see Discussion). The failure of the spectrophotometric measurement to show any reduction in these cases, and much less reduction at the slower flow rates, is due to the ease with which the reduced molybdenum is rcosidized a t the boiling temperature during the color development procedure. This explanation was confirmed by using the effluent solutions from low flow rates, either molybdenum alone or molybdenum-iron niixturrs, arid subjecting them to a longer boiling period, and in some cases also aeration with a stream of compressed air. The color int,ensity increased, the transmittancy approaching 35.0%, the value for a fully developed sample of 5 p.p.m. of molybdenum. In interpreting the results of the ferric alum titrimetric method, it should be noted that the sample contained only 0.5 mg. of molybdenum; although only about 50% of the molybdenum was

Table 11. Effect of Foreign Elements (All solutions, 5 p.p.m. of molybdenum) Element Added Tolerance. P.P.11 100 >3

>5 >5

x x

100

x

100 4 20

103

Table 111. Effect of Flow Rate through Jones Reductor (All solutions, 0.5 nig. of niolybdenum)

0.01 0.05 0.1 0.2 0.25 0 33 0.5 1.0

...

...

...

37.2 36.6 35.5

6.0 4.3 1.4

34.9 35.0

0'

37,o 36.5 35.7 35.5 35.0 35.0

... ...

...

'

0

... ...

5.4 4.0 L9 1.4 0 0

Iron(II1) interference can be eliminated also by reduction with sulfur dioxide in acid solution; after excess sulfur dioxide haB been boiled out, the color is developed in the usual way. I n the authors' experience, this procedure is somewhat longer than the Jones reductor method. Removal of iron(II1) by multiple precipitation of the hydrous oxide vias too tedious to be practiral, and the molybdenum found was alnays too low. Assay of Molybdenum(VI) Oxide. An accurately neighed iample of reagent grade molybdenum(V1) oxide was dissolved in ammonium hydroxide and made to known volume. Several aliquots of the solution were developed by the standardized procedure, the transmittancy was measured, and the molybdenum concentration was read from the calibration curve. The molybdenum, calculated as Mooa, \$as found t o be 100%. The :issav given by the manufacturer was 99.95% MoO3. Determination of Molybdenum in Steel. The Sational Bureau of Standards steels used, and the certified a n a l y w for alloying metals, are show1 in Table IV. Table 1V.

Tungsten produced an increase in transiiiittancy; all others gave a decrease in transmittancy.

Plow Kate, 111 /Sec

2 3 4 5 6 8 C O N C E N T R A T I O N O F Mo, p.p.rn.

Figure 1. Calibration Curve

103 103

a

Lxpeiinient 2 , Experiment 1, 250 LIg of Iron(II1) Molybdenum On11 Added _ _ ~ 70trans- 5% .\lo '2trans- % hlo mittancy reduced mittanrv reduced

I

hlolybdenuni Chromium Nickel Cobalt Tungsten Vanadium Manganese Copper

Steels Teated

Sample 139, Cr-Si-No Steel (N.E. 8637), %

Sample 153, Co-hlo-W Steel, %

0.179 0.549 0.563

8.39 4.14 0.107 8.45 1.58 2.04 0.219 0,099

...

0 : 002 0.8137 0.089

3,

'fo$:21e,"udii,nqni~ Method. 70 hlo Reduced 51 50 30

...

19

...

3.8 3.6

The steel samples were dissolved in aqua regia, and repeatedly evaporated wit,h hydrochloric acid to remove nitric acid. In the analysis of the low-molybdenum steel, sample 139, the solution lyas passed rapidly through Jones reductor to reduce iron( 111), and the color was developed in the usual way. From the measured transmittancy, the molybdenum content was determined by reference to the calibration curve. The results are shown in Table V. .inalysis of the high-molybdenum steel, sample 153, did not require the removal of iron(II1). After dissolving and making up to volume, two aliquots of each sample, of

ANALYTICAL CHEMISTRY

308 such volume as would give a final concentration in the optimum range, were developed and measured in the usual way. Table VI gives the results of ten determinations, each involving measurement of two aliquots of the sample solution.

Table VI. Detn. No. 1

DISCUSSION

-

Table

Sample Wt., G. 0.1052 0.1Y04

2

The calibration curve for the proposed method is shown in Figure 4, in which per cent absorptancy (100 % transmittancy) is plotted against log concentration. The maximum attainable photometric accuracy, evaluated from the slope of thr curve, is 2.9% relative error per 1% ’ absolute photometric error, conforming closely t o derivations from Beer’s law ( 1 ) ; for an absolute photometric error of 0.2%, the relative analysis error is therefore 0.6%. Maximum accuracy occurs a t about 5 p.p.m. of molybdenum, although the accuracy is essentially as good in the range of 2 t o 10 p.p.m. The range can be extended t o higher concentrations, with an increase in accuracy, by measuring transmittancy ratios ( 1 , 5 ) .

Detn. No.

Analysis of Standard Steel 153

3

0 1081

4

0 2193

5

0.1231

6

0.1149

7

0 2000

8

0.1051

9

0.1123

10

0.1637

AV.

Av. deviation Certified analysis by N.B.S. Range of results. N.B.S. analysts Av. deviation, N.B.S. analysts

Mo Found, % 8.37 8.35 8.33 8.33 8.35 8.36 8.22 8.23 8.33 8.33 8.29 8.29 8.36 8.38 8.26 8.26 8.52 8.61 8.38 8.37 8.34 0.05 = 0.65% 8.39 8.35-8.45 0.4 = 0.48%

V. Analysis of Standard Steel 139 Sample Wt., G. 0.2971 0 3229 0 3G3H 0.2980 0 3388 1 000

Av. Av. deviation Certified analysis by N.B.S. Range of results, N.B.S. analysts Av. deviation, N.B.S. analysts a S o t included in average

Mo Found, 72 0.169 0.174 0,208“ 0.156 0.167 0.168 0.167 0.005 = 3 . 0 % 0 178 0 172-0 180 0 002 = 1 l c c

In comparison with the widely used method with tin(I1) cliloride and thiocyanate, the proposed method has the advantage of greater color stability, and requires no extraction procedure. The sensitivity is comparable t o the tin( 11) chloride method and t o thr method of Grimaldi and Wells ( 4 ) , although not quite as high as that of the method of Ellis and Olson ( 2 ) . I n the analysis of molybdenum in steels, no interference from iron( 111) is encountered unless the ratio of iron to molybdenum exceeds about 20 to 1; the proposed method is therefore especially useful for the analysis of high-molybdenum steels. The usual alloying cle-

ments (except vanadium if present in amounts nearly equal to the amount of molybdenum) are without interference. Phosphate, up t o a t least 1000 p.p.m. as phosphoric acid, did not interfere. LITERATURE CITED

(1) Ayres, G. H., ANAL.CHEM.,21, 652 (1949). (2) Ellis, Roscoe, Jr., and Olson, R. V., Ibid., 22, 328 (1950). (3) Feigl, F., “Qualitative Analysis by Spot Testa,” 3rd English ed.. p. 94, New York, Elsevier Publishing Co., 1946. (4) Grimaldi, F. S., and Wells, R. C., IND.ENG.CHEM..ANAL. ED., 15,315 (1943). ( 5 ) Hiskey, C. F., ANAL.CHEM.,21, 1440 (1949). (6) Hurd, L. C., and Allen, H. O., IND. ENG.CHEM.,ANAL. ED.,7, 396 (1935). (7) Lundell, G. E. F., and Hoffman, J. I., “Outlines of Methods of Chemical Analysia,” PP. 137-9, New York, John Wley & Sons, 1938. (8) Bfontignie, E., Bull. SOC. chim., [4] 47, 128 (1930). (9) Spiegel, L., and Maass, T. A., Ber., 36, 512 (1903). (IO) U.S.Steel Corp., ”Sampling and Analysis of Carbon and .Alloy Steels.” pp, 172-8, New York, Reinhold Publishing Corp., 1938. RECEIVED June 13, 1950. Condensed from a thesis submitted by Bartholome% L. Tuffly t o the Graduate School of the University of Texas in partial fulfillment of the requirements for the degree of master of arts, 1930.

Spectrophotometric Studies on Refined Sugars in Solution F. W. ZERBAN, LOUIS SATTLER, AND JAMES MARTIN New York Sugar Trade Laboratory, S e w Y o r k , S. Y .

P

ETERS and I’helps, of the National Bureau of Standards, were the first to devise a method for the determination of the color of sugars and sugar products, based on strictly scientific principles. The results of these investigations, which were CHEMICAL SOCIETY presented at eight, meetings of’ the AMERICAN between 1921 and 1925, have not been published in estenso, but Peters and Phelps (9) did present the detailed description of a n improved method of preparation and clarification of solutions for color determinations and a discussion of spectrophotomctric data, including ratios of absorbancy indexes under various conditions. They concluded from their results that the negative logarithm of the transmittancy for 1-cni. thickness and a concentration of 1 gram of dry substance in 1 ml. of solution (“absorbancy index,” a ) measured a t wave length 560 mp, is equivalent, colorimetrically, to the integral absorption over the visible spectrum under the same conditions of thickness and

concentration, and that therefore the measurement of the absorbancy at that wave length is sufficient for determining the color concentration of the sample without going through the entire spectrum between 400 and 700 mp, If desired, the various types of coloring matters may be grouped and differentiated by means of the absorption (Q)ratios for selected wave lengths. In a later publication, Peters and Phelps (8) showed that by interpolation between-log t for the wave lengths 546 mp and 578 mp. the --log t for 560 mp may be calculated with sufficient precision for all ordinary purposes. Brewster and Phelps ( 2 ) continued the earlier studies and revised the existing methods of preparing the solutions and certain other details of the manipulation. In addition, Brewster ( 1 ) described a simplified apparatus for technical use. Since that time important advances have been made in the determination of the color of many types of materials, and color is now defined as follom ( 7 ) : “Color consists of the characteristics