V O L U M E 19, NO. 2, F E B R U A R Y 1 9 4 7 Table I.
141
Dispersion Power Using the Dispersion Cylinder Determination
Sample
1
A B
0.018 0.020 0.038
C D E F
0.004
0,005 0.031
I
I1
1 2 1 Grams o f f e r r i c o x i d e per 100 ml. 0.018 0,021 0,020 0.019 0.021 0.021 0.021 0,020 0.038 0.041 0.040 0,040 0.004 0.005 0.004 0,004 0.006 0.007 0,007 0,006 0.030 0.031 0.030 0.029 2
I11 2 0.018 0.021 0.040 0,005
The method as described has been used in this laboratory as an indication of detergent ability for 3 years, during which time more than 400 determinations have been made on solutions of soaps, synthetic detergents, phosphates, and silicates. Regardless of the final method used for measuring the quantity of suspended matter, the use of the dispersion cylinder has increased the accuracy and reproducibility of this test.
0.006
0,030
Table 11. Dispersion Power by Method of Pipetting Determination Sample
RESULTS
I1
I
I11
Grams of ferric ozide p e r 100 ml.
I n Table I are listed the results of a series of tests made on six detergent compositions, using the method as described, Three separate dispersion tests were run, and two aliquots were analyzed for each sample. Table I1 indicates results obtained with identical techniques, but pipetting from a point 2 inches below the surface of the solution. The increased precision obtainable with the dispersion cylinder is especially well illustrated by samples C and F which contained large amounts of dispersed soil. Figure 1 is an actual photograph of samples E, D, and F, as they appeared after 24 hours of settling.
A B C D
E F
LITERATURE CITED (1) Sarin, J. L., and Uppal, M. Y., Ind. Eng. Chem., 33, 666 (1941). (2) Snell, F. D., Ibid., 24, 1052 (1932). (3) Ibid., 25, 163 (1933). (4) Vincent, J. Phys. Chem., 31, 1281 (1927).
Colorimetric Determination of Iron in Brass and Bronze WILLIAM GOODMAN c'. S. Xat-a1 Laboratory, Munhall, Pa.'
0% and co-workers (4, 5 ) obtained 1017 results for iron in yN.13.S. sample 37B (bronze) using both ferron and disodium1,2-dihydroxybenzene-3,5-disulfonateas the colorimetric reagents. They pointed out correctly that low results are due to the inadequacy of the method of separation of iron rather than to any inability of the colorimetric reagents to react quantitatively with the iron actually present. This posed the problem of obtaining the total iron present in a brass in solution, so that it could be determined colorimetrically without undergoing loss by coprecipitation. The method utilized is based on the procedures of McCay ( 2 ) and Ravner (3) for dissolving brass samples. Iron is determined with o-phenanthroline on a suitable aliquot of the sample. PREPARATION OF SAMPLE FOR ANALYSIS
of iron is obtained from the usual type of straight-line curve made
by plotting per cent transmittancy versus concentration on semilogarithmic paper. The calibration data for this curve can be obtained from iron standards carried through the procedure described above. In this manner any iron picked up from the reagents and glass is corrected for automatically, when the same lots of reagents are used in the analysis and the calibration runs. DISCUSSION
The accuracy obtained by this procedure was checked by means of National Bureau of Standards samples (Table I). I n each cme the average of several determinations is well within the range submitted by the cooperating analysts. Table I.
Transfer a 1.0000-gram sample to a 200-ml. Vycor beaker (ironfree). Add in order 15 ml. of distilled water, 0.5 to 1.0 ml. of hydrofluoric acid (48%),,and 10 ml. of nitric acid (sp. gr. 1.42). Cover with a platinum lid, allow to stand until solution is complete, and then boil to remove oxides of nitrogen. Rinse the lid with distilled water and dilute to 135 ml. Add 1 drop of 0.1 N hydrochloric acid and electrolyze a t 2 amperes. Complete the copper and lead determinations according to the directions of Ravner ( 3 ) . Reserve the electrolyte (freed from copper and lead) for the determination of iron. DETERMINATION OF IRON
Average Value Found
%
%
52B 52 37c 63 63A 62B
0.03 0.11 0.18 0.27 0.51 0.83
0,034 0.12 0.17 0.27 0.52 0.82
Iron Present
%
a
Present address, U. S. Bureau of Mines. Bruceton, Pa.
Sample NO.
Certificate Value
Average PH
4.1 4.1 4.1 4.1 4.1 4.1
Table 11. Effect of o-Phenanthroline concentration on Recovery of Iron in Presence of 3 Mg. of Zinc
Dilute the electrolyte to 150 ml. in a volumetric flask and transfer 1 ml. of pipet to a colorimetric tube. Add 18 ml. of hydroxylamine hydrochloride reducing solution (4 grams of hydroxylamine hydrochloride, 50 grams of ammonium acetate, and 35 mi. of concentrated hydrochloric acid diluted to 1 liter, adjusted with hydrochloric acid or ammonium acetate, so that a final pH of 4.3 is obtained). Then add 6 ml. of 0.15y0 o-phenanthroline solution, stopper, and shake well. The orange-red color develops immediately. Determine the per cent transmittancy with a Fisher electrophotometer, using the No. 425 darkblue filter, adjusted previously to 100% transmittancy with distilled water carried through the same procedure. The percentage 1
Determination of Iron in Bureau of Standards Brasses and Bronzes
0.30 0.30 0.30 0.60 0.60 0.60 0.82 0.82 0.82 1.10 1.10 1.10 0.5y0 solution.
Volume of oPhenanthrolinea Nl. 0.5 1 2 0.5 1 2 0.5 1
2 0.5 1 2
Iron Recovered 3 Mg.of a i m Dresent
T o zinc
present
%
70
0.30 0.30 0.31 0.60 0.61 0.61 0.82 0.83 0.84 1.11 1.12 1.12
0.19 0.31 0.31 0.38 0.60 0.61 0.54 0.82 0.84 0.74 1.01 1.12
142
A N A L Y T I C A L CHEMISTRY
Since fluoride ion does not interfere a t pH 4.1 (I), it was necessary to adjust to this acidity by buffering the hydroxylamine
hydrochloride solution. Of the elements commonly present in brass, zinc, which may be present up to 40%, causes the most serious interference by reducing the intensity of the iron color (1). This can be diminished almost entirely by adding an excess of o-phenanthroline (Table 11). Aluminum and manganese may be present in 250 times the amount of iron without interfering ( I ) . Nickel produces a change in hue but its interference is negligible below 1%. Most brasses and bronzes contain less than this amount. Tin does not interfere (4). Known amounts of iron were added to N.B.S. samples 124A and 6311 containing 4.8% and 9.7% of tin, respectively. The amounts of iron recovered were identical with the amoutlts added.
The proposed procedure is especially useful when applied to silicon bronze. If the sample is dissolved in the presence of hydrofluoric acid, a clear solution is obtained and an accurate value for copper, lead, and iron can be obtained. LITERATURE CITED
(1) Fortune, W. B., and Mellon, M. G., IND. ENQ.CHEM.,ANAL. ED., 10, 60 (1938). (2) McCay, L. W., J. Am. Chem. Soc., 31, 378-81 (1909). (3) Ravner, H., IND.ENQ.CHEM.,ANAL. ED., 17,41 (1945). (4) Yoe, J. H.,and Hall, R. T., J. Am. Chem. Soc., 59,872 (1937). (5) Y o e , J. H., and Jones, A. L., IND.ENG.CHEM.,ANAL. ED., 16,
115 (1944). THEopinions contained in this article are those of the author and are not t o be construed as official or reflecting the views of the Navy Department.
Adaptation of the Beckman Quartz Spectrophotometer for Measurement of Vitamin A by the Carr-Price Reaction G. IVOR JONES, F. BRUCE SANFORD, LYNNE G. McKEE, AND DAVID T. MIYAUCHI Fishery Technological Laboratory, U . S . Fish and Wildlife Service, Seattle, Wash.
HE quantitative determination of vitamin A by measurement the blue color developed when the vitamin is treated with antimony trichloride (Carr-Price reaction, 2 ) is difficult because of the corrosive nature of the reagent and the rapidity with which the color fades. Because of these undesirable features, ultraviolet absorption measurements for the determination of vitamin A have usually been favored. However, a recent paper by Oser et al. (3) presents data to show that the colorimetric assay for vitamin A gives results in essential agreement with the biological assay, even with materials for which the ultraviolet absorption method is unsatisfactory. While most vitamin A testing laboratories possess the Beckman quartz spectrophotometer for ultraviolet absorption measurements, this instrument has apparently not been widely used for the colorimetric assay. One reason for this might be that the absorption cells customarily used are small and their arrangement does not facilitate the rapid manipulations required in the antimony trichloride technique. Since many vitamin A laboratories ~
I
...........................................................
~.
do not have a separate instrument for measuring color, an adaptation of the Beckman spectrophotometer for this purpose would appear to be of value. This nrticle presents constructional details of a cuvet holder, by means of which the Beckman spectrophotometer more readily can be employed in vitamin A assays using the Carr-Price reaction. The cuvet holder was designed to accommodate square glass cuvets 0.5 inch in inside dimensions (more exactly 13 X 13 mm.) and 4.125 inches in length (procured from the Wilkens-Anderson Co., Chicago, Ill.). The outside dimensions of the cuvets were 20/32 X 21/32 inch. The cuvet chamber (Figure 1, E ) was constructed slightly larger than this to allow for small variations in the external dimensions of the cuvets. The entire adapter was constructed of semihard sheet brass. The sides of the cuvet chamber were cut from sheet brass 8/04 inch thick and then soldered together on the corners to form a tube 21/32 inch square inside and 4.625 inches in length. The cover plate, C, cuvet chamber cover, A , and casing, B , were made from 0.125-inch sheet brass and designed to fit cell compartment aswere 412/32 X 419/31 sembly No. 2510 ( I ) . The cover gibs, 19,
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TOP
Figure 1.
,
,
A
o .
c
"1
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c_i
-*
VIEW
__-
, _-IL
G
H
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Cuvet Adapter
SIDE
A , Cuvet chamber cover. B , Casing. C,Cover plates. D , Cover gibs.
F
E. C u v r t
oharnbsr.
VIEW
F , L i g h t openings.
G . Cuvet arrest.
H , Drain hole
