MAY 15, 1940
ANALYTICAL EDITION
boiling point determinations, quantitative elementary analysis, or the preparation of derivatives for further identification ( 3 ) . No changes in the cement were noticed after these investigations, as established b y photographic recording, but care should be taken that liquids with a marked solvent action do not remain in contact longer than absolutely necessary for the determination. Useful application of the microrefractometer may be made in the determination of refractive indices of solid compounds. After carrying out the Becke-line test with consideration of the details stressed b y Saylor ( I @ , frequently only 10 to 20 cu. mm. of immersion liquid remained, which were best measured in the microrefractometer. Satisfactory results are assured, since the accuracies of both methods (*0.001) are equivalent,
Literature Cited (1) (2) (3) (4) (5)
Alber, H . K., J . FTankZin Inst., 226, 813 (1938). Alher. H. K.. Mikrochemie, 18, 92 (1935). Ibid.. 25, 167 (1938). Alber, H. K., 2.anal. Chem., 90, 87 (1932). Alber, H. K., and von Rensenberg, M., Ibid., 86, 114 (1931).
307
Benedetti-Pichler, A. A., and Spikes, W.F., “Introduction to the Microtechnique of Inorganic Qualitative Analysis”, p. 41, Douglaston, N. Y., Microchemical Service, 1935. Chamot, 8. M., and Mason, C. W., “Handbook of Chemical Microscopy”, 2nd ed., Vol. I, 1). 358, New York, John Wiley & Sons, 1938. Edwards, A. E., and Otto, C. E., IXD.ENG.CHEM.,Anal. Ed., 10, 225 (1938). Emich, F., Monatsh., 50, 269 (1928); 53/54, 312 (1929). Jelley, E. E., J . Rou. Microscop. Soc., 54, 234 (1934): Abridged Sci. Pub. Kodak Research Lab., No. 537H, 17, 18 (1935). Kirk, P. L., and Gibson, C. S., IND.ENG.CHEM.,Anal. Ed., 11, 403 (1939). Kofler, L., Mikrochemie. 15, 242 (1934). Kofler, L., Ibid., 22, 241 (1937). Kofler, L., and Ruess, H . , Chem. Erde, 11, 590 (1938). Mayrhofer, A.. and co-workers, Pharm. Presse, Wiss.-prakt. Heft, 37, 130 (1932): Scientia Pharm., 5, 105 (1934); Phurm. Monatsh., 17, 41 (1936). Nichols, L., Natl. Paint Bull., 1, 12-13 (February), 14 (March, 1937); editorial, Ibid., 1, 5 (1937). Pregl, F., Fermenljorschung. 2, 63 (1917). Saylor, Ch. P., J . Research Natl. Bur. Standards, 15, 277 (1935). Schally, E., Monatsh, 58, 399 (1931). Wright, F. E., J . Wash. Acad. Sci., 4, 269 (1914). PRESENTED before the Division-of hlicrochemistry a t the 99th Meeting of the American Chemical Society, Cincinnati, Ohio.
Improvement of Formaldoxime Colorimetric Method for Manganese C. P. SIDERIS Pineapple Producers Cooperative Association, Honolulu, Hawaii
T
Reagents
HE author’s formaldoxime colorimetric method for
manganese (1) was found inadequate b y Wiese and Johnson ( 2 ) and in more recent studies also by the author in biological materials high in phosphates. However, the interference of phosphates can be eliminated by precipitation with P b + + in acetic acid solutions and the original method may be employed with very satisfactory results.
Method of Procedure -4n aliquot of 5 ml. of the acidified (hydrochloric acid) solution of the ashed biological materials is titrated with N sodium hydroxide using methyl red as indicator (and the volume of sodium hydroxide required is recorded). This aliquot is discarded, because the indicator (methyl red) will interfere with the accuracy of the results of the colorimetric determination. A new aliquot, preferably 10 ml., is placed in a graduated 50-ml. centrifuge tube or other container and a calculated volume of N sodium hydroxide is added, based on the titration value obtained with methyl red. The sample is then acidified with 2 ml. of a 20 per cent solution of acetic acid. The neutralization of hydrochloric acid xith sodium hydroxide favors the formation of ferric and manganic phosphate precipitates. However, the addition of acetic acid to the mixture dissolves the manganic phosphate precipitate but not that of ferric phosphate. Excess phosphate, with plant tissues of a high phosphorus content, is removed by the addition of 0.5 ml. of a 5 per cent solution of lead acetate. The mixture is agitated, allowed to stand for 10 minutes, and then treated, to remove excess lead, with 1 ml. of a 20 per cent solution of sodium sulfate. After 30 minutes the mixture is either centrifuged or filtered. .A 10-ml. aliquot of the centrifugate or filtrate is neutralized with 40 per cent sodium hydroxide, 3 t o 4 drops of the formaldoxime reagent are added, and then more of the 40 per cent sodium hydroxide solution until the pigment develops (1). The addition of sodium cyanide as stated in the original publication (1) is not necessary. Ferric chloride need not be added to the standard if the removal of iron from the unknoivn was complete. The final volume of the unknown and of the standard is made to either 1.5 or 20 ml. in a graduated test tube or in a volumetric flask.
A 5 per cent solution of lead acetate, Pb(CH,C00)2.3Hz0, and a 20 per cent solution of sodium sulfate, Na2SOa.10HZ0. TABLEI. MANGAXESE RECOVERED FROM SOLUTIONS CONT A I N I S G KNOWN AMOUSTS O F hIANGANEsE 4 S D PHOSPHATE RI n Present MQ . 0.01 0.01 0.01 0.01 0.01 0.01
0.01
0.01
0.005 0.005 0.01 0.01 0.01 0.01
0.01 0.005 0.005
-TreatmentPO1 Pb Mg. MZ. 0.100 0.5 0.100 0.5 0,050 0.5 0.050 0.5 0.025 0.5 0.025 0.5 0.010 0.5 0.010 0.5 0.050 0.5 0.050 0.5 0 0.5 0 0.5 0 0.5 0 0 0 0 0 0 0 0
SO1
RIn Found
Recovery
Ml.
Mg.
%
1.0
0,0096
96.0 98.0 100.0 98.0 100.0 96.0 96.0 100.0
1.0
1.0
1.0 1.0 1.0 1.0 1.0 1.0
1.0 1.0 1.0 1.0 0 0 0 0
0.0098 0.0100
0.0098 0.0100 0,0096 0,0096 0.0100 0.0050 0.0048 0.0100
0,0096 0,0096 0.0100 0.0100 0.0050 0.0050
100,0
96.0 100.0 9G.0 96.0 100.0 100.0 100.0 100.0
Difference
% -4
-2 0 -2 0 -4 -4 0 0 -4 0 -4 -4 0 0 0 0
T h e precision of the method may be evaluated from the data reported in Table I, which show that the method can be used very successfully Kith biological materials containing interfering amounts of PO4-- and F e + + + after both substances have been removed according to the above procedure. In a 10-ml. volume of sample containing from 0.005 to 0.01 mg. of manganese in the presence of 0.010 to 0.100 mg. of phosphate the average error was 2 per cent.
Literature Cited
c.
(1) %*is, P., I X D . ESG. C H E X . , Anal. Ed., 9, 445-6 (1937). (2) Tliese, 8 . C., and Johnson, B. C., J . B i d . Chem., 127, 203-9 (1939). PUBLISHED with the approval of the Director as Technical Paper No. 128 of the Pineapple Experiment Station, University of Hawaii.
