ANALYTICAL CHEMISTRY
1646 was cleaned by passing a chromic acid cleaning solution through the disk and then rinsing until no trace of chromate color remained. The regenerative method has been in use in the laboratory for 3 years, and the single use method has been used for the past year with excellent results. The procedures are sufficiently simple and convenient to be carried out by semiskilled technicians. LITER4TURE CITED
( 1 ) Am. Pub. Health Assoc., “ S t a n d a i d Methods for the Exami-
nation of Water a n d Sewage,” 9th ed., pp. 47-9 (Cu), 53 (Fe) 46 (SiOn), New York, 1946. (2) Kunin, Robert, ANAL.CHEY.,21, 87 (1949); 22, 64 (1950); 23,
45 (1951). (3) R O Y ,C. J., A ~ LJ .. S C ~ 243, . , 393-403 (1945). (4) Sussman, Sidney, “Ion Exchange-Theory and Application.” F. C. Nachod, ed., pp. 244-5, New York, Academic Press, 1949. (5) Sussman, Sidney, Nachod, F. C., a n d Wood, William, Ind. Eng. Chem., 37,618-24 (1945). RECEIVED for review February 27, 1952. Accepted July 14, 1952. Presented before the Meeting-in-Miniature of the Kew York Section, AMERICAN CHEMICAL SOCIETY, February 8, 1952.
Application of Absorption Spectrum of Ferric Acetate Complex to Determination of Iron WILHELJI REISS’, J. FRED HAZEL, AND WALLACE M. MCNABB Chemistry Department, University of Pennsylcania, Philadelphia, P a .
’HE purpose of the present work was to study the absorption characteristics of the ferric acetate complex in acetic acid. Absorption spectra were determined in both the visible and the ultraviolet region. It was found that the properties of the complex in 50% acetic acid in the ultraviolet region could he applied to the quantitative estimation of iron. S o reference was found in the literature to the determination of iron under thwe conditions. Riban (S) attempted to determine iron in neutral and weakly acid solutions by a ferric acetate color reaction, but wap unsuccessful because of the instability of the complex under thew conditions. Broda ( 1 )has determined acetic acid in an aqueous solution based upon a color reaction with ferric ions. rL
periods of months or which &-ereheated on a steam bath for several hours showed no significant change in the character or in the intensity of their absorption spectra. On the other hand, excess sulfuric acid, hydrochloric acid, and nitric acid were found to interfere with the formation of the ferric acetate romplw
m
-I
t/
.2
1
r
1.0
3.0
5.0
70
9.0
11.0
AcOH M/L Figure 2.
300
380
460
mu
540
620
Figure 1. Absorption Spectrum of Ferric Acetate Complex
The absorption spectrum of the ferric acetate complex in 50.0% acetic acid (8.7 iM)has been determined and is shown in Figure 1. Maxima occur a t 463 to 465 mp in the visible region and a t 337.5 mp in the ultraviolet region. It was found that the optical densities reached limiting values a t both these wave lengths when the acetic arid concentration corresponded to 50% (8.7 M). These facts are shown in Figures 2 and 3. The complex was found to be stable under these conditions. Solutions which were allowed to stand a t room temperature for 1
Pa.
Present address, Wyeth Institute of Applied Biochemistry, Philadelphia,
.4
Constant Volume Titration w i t h Acetic Acid
2.0
6.0 10.0 MOLES AcOH/L
14.0
Figure 3. Constant Volume Titration with Acetic Acid
Figure 4 shows that the optical density of the complex as determined a t 463 mp decreases linearly with the addition of increasing concentrations of nitric acid, This acid was used to evaluate the effect of hydrogen ion concentration because the nitrate ion has little, if any, tendency toward complex formation with the ferric ion. The effect of sulfate and chloride anions on the color reaction was obtained by determining Beer’s law curves a t 465 mw with standard solutions of ferric nitrate, ferric chloride, and ferric sulfate in 50.0% acetic acid. The slopes of these curves can be
V O L U M E 24, NO. 10, O C T O B E R 1 9 5 2
1647
taken as an indication of the complexing Table 11. Analyses of Iron Ores tendency of these anions. These slopes Aliquot were, in the order stated: 9.94 X 10-3, Ore Wt. Taken, Taken, I r o n Taken, Iron Found, 9 . i i X 10-8,and 9.46 X 10-3. Sample nlg./lOO MI. M1. Mg. Dss7.5 Mg. These preliminary experiments sugA 91.00 10.00 2.14 0,918 2.13 B 89.90 10.00 2.18 0,940 2.18 gested a procedure in which precipitated C 34.68 10.00 2.38 1.031 2.39 C 5.00 1.19 0.506 1.18 ferric hydroxide is washed and disC 5.00 1.19 0.512 1.19 solved in hot glacial acetic acid PIUS a value from three determinations. small, and minimum, amount of hydrochloric acid. The strong intensity- of thr absorption in the ultraviolet region permitted the use of dilute solutions. As a result, the interference of the chloride ion was reduced to negligible proportions.
Iron Found,
Iron Found by Titration
%
(8, %
23,40
23.55a
24.28
68.92 68.05 68.63
24.28a
68. 6Za
-
APPARATUS
Instrumentation. Measurements of optical density were made hy means of a Model DL7 Beckman spectrophotometer. Previously calibrated 1.000-cm. Corex and silica cells were used. The cells were cleaned with distilled water and spectroscopically pure methanol each time the solution was changed. The reference cell contained 50.0y0 acetic acid (by volume). 411 optical densities represent corrected values and are an average of a t least three individual readings. A standard Beer's law curve was constructed from optical density measurements a t 337.5 m,u on approximately 0.005 M solutions of ferric chloride, ferric nitrate, and a solution made by dissolving pure iron wire in hydrochloric acid. These solutions had a volume of 50 ml. and an acetic acid concentration of 50%. This standard curve, which hnd a slope of 0.4308, is shonn in Figure 5 . PROCEDURE
Heat the solution containing between 0.20 and 50.0 mg. of iron with a few drops of nitric acid. Add an excess of ammonium h>,-
1.0 Figure 5.
.OlO
.020
Beer's Law Curve
.----_ ____Medium Porosity Fritted Glass Funnel
.030
CONC" HNO, M/L
Figure 4. Effect of Concentration of Hydrogen Ion
Table I.
Analysis of Iron Solutions
Iron Taken,
nig.
0.15 0.15 0.18 0.23 0.25 0.51 0.82 1.53 1.53 1.74
Iron Found, D337.6
0.063
Mg. 0.15
Error,
%
0.12 -11 1 0.16 0.070 0 00 0.099 0.23 0 00 0.25 0.108 0.51 0 00 0.218 0.83 0.357 1 22 1.57 0.678 2 62 1.47 0.635 - 3 92 1.72 0,740 - 1 15 2.00 0.879 2.04 2 00 2.00 0.869 2.02 1 00 2.55 1.096 2.54 - 0 39 2.60 1.119 2.60 0 00 3.06 3 .OO 1.294 - 1 96 3.57 1,526 3.54 0 84 54.744 23.475a 54.49 - 0 46 30. OOa 12.95P 30.00 0 00 a The concentrated solution originally obtained was diluted 1 t o 25 with 50.070 acetic acid. 0.032
Figure 6. Apparatus
0 00 -20 0
++ + + -
droxide (1 to 1). Filter the precipitate by suction through a sintered glass filter funnel (diameter of disk, 15 mm.; capacity of funnel, 30 ml.) of medium porosity and supported in the apparntus as shown in Figure 6. TVash the precipitate throughly with water, release the vacuum and place a 50-ml. volumetric flask provided with a small funnel under the suction bell. Pour 1 ml. of hot water into the funnel containing the prrcipitate, followed by 0.2 to 0.5 ml. of hot 1 S hydrochloric acid, depending upon the amount of precipitate. Stir with a glass rod to aid in removing the precipitate from the dish (it dissolves in the hydrochloric acid, forming a clear, lemon-colored solution). Apply gentle suction and receive the solution into a 50.0-ml. volumetric flask. Pour 25 ml. of hot glacial acetic acid onto t h e filter disk and rinse the beaker, stirring rod, and funnel with hot water so as to transfer all the acetic acid to the volumetric flash.
1648
ANALYTICAL CHEMISTRY
Remove the flask and if the solution is a greenish-yellow color instead of the normal pink color then heat on the steam bath until the normal pale pink calor of the ferric acetate complex is obtained. Cool the solution to room temperature and dilute to the 50-ml. mark. Mix thoroughly and measure the optical density a t a wave length of 337.5 mp against a blank solution containing 0.2 ml. of hydrochloric acid in 50 ml. of 50% acetic acid by volume. The optical density reading multiplied by 2.321, the reciprocal of the slope of the standard Beer's law curve (Figure 5), gives the value in milligrams of iron per 50.0 ml.
Three samples of iron ore of the sefiquioxide type, designated A, B, C,were analyzed. The weighed samples were brought into solution by heating with concentrated hydrochloric acid. T h e respective solutions were filtercd quantitatively into 100.0-ml. volumetric flasks. Suitable aliquot portions of these solutions were analyzed according to t,he mocedure dexribed above. The results are given in Tahle 11. LlTERhTURl
As large as 3.00 mg. of iron can be determined directly by thifi procedure. Larger samples can be analyzed hy making an appropriate dilution with 50.0% acetic acid from the original solution oontained in the 50.0-ml. volumetric flask, Increased volumes of hot 1 N hydrochloric acid are needed to dissolve larger amounts of ferric hydroxide. Citlculations are made with the aid of the following exprossion: milligrams of iron in 50.0 ml. = optical density a t 337.5 mp X dilution factor X 2.321. Typical results are given in Table I.
(1) Broda, Z., Chem. Lisly. 37,2R9 (2) Cooke, W. D.. Hazel, J. P., and McNahh. W. At., 21, 643, 1011 (1949). (3) Riban, J., Bull. am. chim.. 6 , 3, 916-20 (1891).
ANAL.CHEM..
R E C E ~ V Ef oDr review J~nuary26, 1952. Aooepted June 20, 1952. Presented before the Meeting-in-Miniature of the Philadelphia Section. AYERICAN CHEMICAL SOCIETT, January 1911. Abstracted from s portion of B diasertation presented by Wilhelm Reisa to the Faculty of the Graduate School of the University of Pennsylvania in partial fulfillment of the requirements f o r the degree of doctor of philosophy
Preparing Crude Rubber Test Specimens for Oxygen-Absorption Measurements WILLIAM J. GOWANS
U. S. N a t u r a l Rubber Reswrc :hStation, Salinas, Cnlif. ECENT investigations (a, 5, 8) have shown the advantages of using a volumetric oxygen-absorption apparatus for accelerated aging tests on crude rubber. Current work in this laboratory has confirmed the advantages of this apparatus as a rapid means for determining the storage stability of a given crude rubber stock. Unfortunately, crude rubber test specimens cannot be placed in the oxygen-absorption apparatus in the same manner as can test specimens of vuloaniaates. The tendency of crude rubber t o flow, particularly during the more advanced stages of oxidation, m y cause errors in oxygen-absorption mea& urements by limiting the diffusion of oxygen into the test specimen. For this reason it was necessary t o devise a method of preparing rubber test specimens for oxygen-absorption measurements which is applicable t o crude rubber. Test specimens of crude ruhber suitable far oxygen-abmrption measurements can be readily prepared with the aid of an alumi num mold and a vulcanizing press. The method of pressing tbe crude ruhher into a sheet from which the specimens are taken is a slight modification of that used by McPherson and Cummings (3) in preparing samples far refractive-index measurements. Oxygen-absorption, data. were obtained in an apparatus similar to the one described by Shelton and Winn (6). The results indicate several important advantages of the present hoepress method of sample preparation as compared with the test tuhe-film method used by Glazer and coworkers ( 8 ) in preparing crude GR-S samples for oxy,. scuoies. ,,. gen-aosorpuan
.
EXPERIMENTAL
The mold used for pressing the crude rubber eonsisted of three pieces, each 12 inches square, cut from 20-gage sheet aluminum. One piece had a n %inch square opening which constituted the mold cavity when placed between the other two pieces. Approui-
necessary to ensure complete flow of the guayule and Hevea rubber samples used thus far. Antioxidants or other additives, which are to he investigated for their effects upon oxygen ahsorption, can be milled into the rubber on compounding rolls immediately before the pressing step. Milling guayule rubber for as long as 10 minutes had no apparent effect on the rate of oxygen absorption. Duplicate test specimens were cut from the pressed rubber sheet with the aid of a 1.25 X 3.25 inch template and weighed. Test specimens prepared by the ahove method w&gh between 2 and 3 grams and have a thickness of approximately 0.040 inch. Each specimen was enclosed in B 30-mesh stainless steel envelope, tied securely in place with stainless steel wire a6 shown in Figure 1, and placed in the oxygen-absorption unit. This means of supporting the sample prevents the rubber from flowing until late in the autocatalytic stage of oxidation. The screen is easily cleaned by boiling in nitric acid. It has been found that test specimens having a thickness in the range of 0.010 to 0.020 inoh may he more readily prepared without use of the press. The desired thickness in this range may be obtained by Eimply passing about 5 grams of the rubber sample twice through closely set rolls of a 4 X 9 inch laboratory mill
i \
A Figure 1. Method of S u p p o r t i n g Test Specimen in a Stainless Steel Screen Envelope
