ANALYTICAL CHEMISTRY
1208 formed is stable and p H of the solutions need not be regulated closely. The color is a function of the total iron present, both ferric and ferrous ion reacting, and its formation occurs in acid solution. The sensitivity of this method is as good as that of the o-phenanthroline or a,&-bipyridine method. Isonitrosodimedon can be easily prepared, as the starting material, dimedon, an important reagent for aldehydes is available in any laboratorj-. ACKIVOW LEDGMENT
The author wishes to express his sincere thanks to Sir J. C. Ghosh, director, Indian Institute of Science, for the opportunitieq
afforded to him for carrying out this investigation and to S. C’ Bhattacharyya for valuable suggestions and assistance during the c o u r v of thiq work. LITERATURE CITED
(1) Griffing, XI., and Mellon, >I. G., ANAL.CHEX.,19, 1014 (1947). (2) Guha-Sircar, S. S., and Bhattacharjee, S. C., J . Indian Chem. Soc., 18, 155 (1941). (3) Haas, Paul, J . Chem. Soc., 91, 1436 (1907). (4) Shome, S.C., Currertt Sei., 15, 107 (1946). (5) Sideris, P., ISD.ESG. C H E x , -&SAL. ED., 14, 756 (1942). (6) Whitley, & A, I.J . Chem. Soc., 83, 44 (1903). R E C E I V E>la> D 13, 1948.
c.
Spectrophotometric Determination of Iron and Titanium in Cathode Nickel G . YICTOR POTTER AND CLARENCE E. ARMSTRONG, Sylcania Electric Products, Inc., Towanda, Pa.
A rapid and reproducible spectrophotometric method of determining small amounts of iron and titanium in cathode nickel tubing is described. The method depends upon the formation of iron and titanium complexes of disodium 1,2-dihydroxybenzene-3,5-disulfonate,recently discussed by Yoe and co-workers. T H E object of this study was to develop a rapid and sensitive 1 method for the determination of iron and titanium in cathode nickel tubing. As it was felt that the determination of iron would present no serious difficulties, because numerous reagents were available for selection and study, attention was placed on titanium. The peroxide method proved insensitive for the quantities of titanium present in cathode nickel. The reagent disodium 1,2-dihydroxybenzene-3,8-disulfonate(Tiron) described by Yoe et al. (4,5) was found well adapted to the determination of both iron and titanium in cathode nickel. After preliminary separations, the absorption of the Tiron complex of iron is measured a t 560 mp, the color of the iron is bleached with sodium dithionite, and the titanium is measured a t 399 mp. The conditions used in the final determination are those worked out by Yoe and Armstrong (4). APPARATUS AND SOLUTIONS
Instruments. Beckman spectrophotometer, Alodel DU. Beckman pH meter. Reagents. Tiron Solution. Dissolve 4 grams of disodium1,2-dihydroxybenzene-3,5-disulfonatein 100 ml. of water. The water-clear solution becomes pale yellow on standing several weeks and should then be discarded. Buffer Solution. Mix equal volumes of molar sodium acetate and molar acetic acid. The pH of the solution is 4.7. Sulfuric acid, 6 S. Nitric acid, concentrated. Ammonium hydroxide, concentrated. Sodium hydrosulfite, Na2S20a. Standards. The titanium standard ( 2 ) was made by fusing exactly 0.1668 gram of titanium dioxide with 2 grams of potassium bisulfate in a platinum crucible. The fusion was taken up in 50 ml. of concentrated sulfuric acid and diluted to 1000 ml. This gives a convenient concentration of 0.1 mg. of titanium per ml. The iron standard ( 1 ) was made by dissolving exactly 0.8638 gram of ferric ammonium sulfate, FeNHa(SOa)2.12H20, in 10 ml. of 10% sulfuric acid and diluting to 1000 ml. This gives a concentration of 0.1mg. of iron per ml.
Allow the solution to stand for about an hour or until the precipitate coagulates. Filter and wash thoroughly a i t h nater made slightly ammoniacal, making sure that all coloration is removed from the filter paper. Then dissolve the precipitate into the original beaker with 6 S sulfuric acid, keepiag the volume to a maximum of about 10 ml. At this point add 8 ml. of Tiron reagent and adjust the pH to 4.7 (*0.1) IYith concentrated ammonium hydroxide. [If the pH is not controlled a-ithin the given limits (+0.1) differences in the color intensities give erroneous results. Yoe and -4rmstrong believe that sodium dithionite is unstable and decomposes at low p H values, precipitating colloidal sulfur and that when sodium dithionite is used a reading should be tahen within 20 minutes, as sulfur may precipitate on long standing. Below a p H of 4.3 the color intensity of the titanium complex is not fully developed.] Transfer to a 50-ml. volumetric flask. Wash beaker with 5 ml. of buffer solution and enough water to bring the solution up to the mark. Mix well and observe the per cent transmittance of the solution a t 560 mp, using the ultraviolet sensitive phototube on the spectrophotometer. Then bleach the color of the iron complex with a very few crystals of sodium dithionite and with as little agitation as possible. (Vigorous shaking may precipitate colloidal sulfur, as sodium dithionite, S a & 0 4 , is very unsta-
FE, MG./50ML. S O L U T I O N
70
-
80-
PROCEDURE
Dissolve 0.1 gram of the nickel sample in a minimum amount of Concentrated nitric acid using a 100-ml. beaker. After complete solution, dilute with 5 ml. of water, warm gently, and make ammoniacal to a deep blue color to precipitate iron and titanium. Avoid excessive heat here, as difficultly soluble metatitanic acid is precipitated a t high temperatures. [Because metatitanic acid is formed in hot alkaline solutions (S),it is advisable to warm gently in order to avoid any possibility of its precipitation.]
40
1
1
.01
.a2
I .03
I
I
.04
.Ob
TI, MW50 ML. SOLUTION
Figure 1. Calibration Curves
I
.oe
1209
V O L U M E 20, N O . 1 2 , D E C E M B E R 1 9 4 8 Table I . Determination of Iron and Titanium Melt
_-1
% Iron
% Titanium 3
2
2
1 0.030
-
3
0.054 0.055 0.030 0.029 0 05i 0.060 0.032 0.032 0.028 0.086 0.082 0 084 0.022 0.023 0.022 0.058 0.029 0.028 0.055 0.058 0.028 0.158 0.152 0,160 0,022 0,024 0,024 0.174 0.180 0.180 0.025 0,020 0.024 I n cases similar t o melts 73 and 74 where the iron differs in order of magiiitude f r o m the titanium, separate aliquots must be taken for the iron deterxiination. 63 66 il 72 73a 74’
0 053
0.060
8
Table 1 1 .
.icruracy of Determinations % Titanium
‘;C I r o n
reagent are present, as confirmed experimentally. The ultraviolet sensitive phototube is still used here along with the stray radiant energy filter. Calculate results using calibration curves, such as those of Figure 1, which are based on standards. The results given in Table I were obtained using: the above procedure. Good accuracy was obhined, as is indicated by Table 11. According to Yoe and Armstrong, solutions containing as much as 4 p.p.ni. of titanium and 10 p.p.m. of iron can he determined spectrophotometrically on the same sample. Above these concentrations the inteiisity of the color does not increase proportionately 13-ith the concentration and thus does not. conform to Beer’s lay.
-
LITERATURE CITED
~
Other laboratoriea Uelt ti6 H-1400 .A.S.T.>I.
0.05Y 0.036
0.053
So. of analystr
Tiron pro?. 0.0%
0.033 0.047
Other laboratones 0.027 0.033 0.032
So. of analysts
Tiron
5
0.027 0,031 0.030
3
proc.
(2j
(3)
tile., Then observe the per cent transmittance of the titanium complex at 399 nip. Below about 390 m,u sodium dithionite absorbs light, although the absorption is slight a t longer wave lengths, and may be disregarded if very small quantities of the
Joseph, “Reagent Chemicals and Standards.” second printing, p. 6, New York, D. Van Nostrand Co., 1943. Snell, F. D., and Snell, C. T.. “Colorimetric Methods of rltialysis,” fourth printing, Vol. I, p. 363, New York, D. Van No>trand Co., 1943. Treadwell, F. P., and Hall, IT. T., “Analytical Chemistry,” 9th ed., Yo]. I, p. 548, New York, John Wiley & Sons, 1937. Yoe, J. H., and Armstrong, A. R., AXAL.CHEM.,19, 100 (1947). Yoe, J. H., and Jones, L. A., IKD. EX. CHEM., ANAL.ED.,16, 111
(1) Ilo,siii.
(4) (5)
(1944). RECEIVEDApril 30, 1948.
Colorimetric Determination of Rhenium A . D. 3IELiYEN
AND
K. B. WHETSEL, Cniversity of Tennessee, I- for qualitarive work, and with further refirir~tiientit might have quantitative :tpplicat ion. Hurd and Hiskey (81,in a method for determiniiig rhenium ill pyrolusite, used a combination ether extraction and steam tlidllation from sulfuric acid. .Ilthough this method is satisfactory for pyrolusite, which contains little or no molybdenum, i t is not entirely satisfactory for the determination of rhenium i i i niolybdenites because some molybdenum is carried over either inechanically or by distillation. FIoffinan and Lundell ( 5 ) used differential reduction with niercury to qeparate rhenium and mol)-bdenum. Under proper I
cunditions, only niolybdenum ia rtduced and this may he extracted with ether after treatment vith a thiocyanate. This method is satisfactory, except that it is long and detailed. These authors also separated rhenium from molybdenum by distilling the rhenium from a solution cont,aining hydrogen bromide, phosphoric acid, and perchloric acid (6). Hiskey and Meloche (4) used a modified steam distillation from sulfuric acid to effect separation. These authors report that any color formed by the molybdenum carried over during distillation will fade upon standing 20 to 00 minute,. APPARATUS AND REAGENTS
Spectrophotometer. .Z Coleman Electric Company Model 11 photoelectric spectrophotometer was used in this work. The 1.00-cm. rectangular cuvettes which accompanied the instrument were used. .\I1 readings of per cent transmittance were obtained by the direct reading met,hod. Volumetric Flasks. The volumetric flasks were calibrated to contain the desired volume a t 27” C. Pipets. The pipets were calibrated to deliver the desired volume a t 27” C. The same pipet was used throughout the work to measure the standard potassium perrhenate solution. Potassium Perrhenate. The potassium perrhenate was prepared in this laboratory and found to be 100.07, pure when a,nalyzed by the method of Willard and Smith (IO). -A standard solution containing 1.00 mg. of rhenium in 1.00 ml. was prepared by placing 0.3884 gram of potassium perrhenate in a 250-ml. calibrated volumetric flask, followed by enough distilled water to fill to the mark. The salt was dried at 110” C. and cooled in a desiccator before weighing.
