INDUSTRIAL AND ENGINEERING CHEMISTRY
598
Table 111. Determination of Magnesium in Plant Materials Sample No. Weight of Sample MgO Found MgO Reported" Gram % % Tobacco 0.2020 1.16 1.24 0.1987 1.17 ... 0.1969 1.45 1.54 0.2045 1.39 ... 0.2318 L58 1.59 0.1898 1.70 1.70 0.1956 1.70 ... Pine Seedling Cuttings 0.Sa60 0.14 0.3437 0.14 O.'lZb 0.12 0.3709 ... 0 MgO determined by gravimetric separation and determination of Mg as pyro hosghats b B)peotroscopic value. Sample CaIa (7).
The solution decomposes slightly with time and a blank has t o be run each time it is used. The decomposition can be followed
Vol. 16, No. 9
polarographically, but a t the present time the decomposition products are not known. The precipitation has t o be carried out a t room temperature because ammonium 8-hydroxyquinolate is too volatile even a t 60" C. Ammonium tartrate has no effect on either I , or Id, and hence the calibration data are good for solutions containing small amounts of tartrate. LITERATURE CITED (1) Am. Public Health Assoc., "Standard Methods for Examination of Water and Sewage", 1940. (2) Carruthers, C., IND. ENQ.CHEM.,ANAL.ED., 15, 412 (1943). (3) Furman, N. H.. Bricker, G. E.. and Whitesell. E. B.. Ibid.. 14, 333 (1942). (4) Kolthoff, I. M., Chem. Weekblad, 24,254 (1927). (6) Lundell, G. E. F., and Hoffman, J. I., "Outlines of Methods of Chemical Analysis'', New York, John Wiley & Sons, 1938. (6) Melaven, A. D., IND. EXQ.CHEM.,ANAL.ED., 2, 180 (1930). (7) Routien, J. B., and Dawson, R. F., Am. J . Bot., 30, 440 (1943).
NOTE ON ANALYTICAL PROCEDURE Use of a Color Indicator in the Tannin M e t h o d for Determination of Beryllium and Aluminum GEO. W. SEARS AND HELEN GUNG Department of Chemistry, University of Nevada, Reno, Nevada
T
H E accuracy of the tannin method, as modified by Nichols and Schempf ( d ) , for the separation and determination of beryllium and aluminum depends on a n accurate control of the p H during precipitation of the aluminum. The only means now available for obtaining this control is the pH meter, a n instrument very difficult to obtain a t the present time. Because of the strategic importance of these metals a search for a suitable color indicator seemed advisable.
I n order to determine the value of this mixed indicator in the analysis, a series of determinations was made on a solution mixture of aluminum and beryllium sulfates of known concentration, the results of which are shown in Table I. Although in each analysis the Beakman pH reading was taken, no further adjustment of the acidity was made. The accuracy obtained eompares favorably with that of Nichols and Schempf. LITERATURE CITED
Table
1.
(A1108 taken,
Beckman No.
1 2 3 4
6
-
Re%n~
4.60 4.68 4.68 4.69 4.62
(1) Lange's Handbook of Chemistry, 4th ed.,p. 943, Sandueky, Ohio, Handbook Publbhers, 1941. (2) Nichols, M. L., m d Schempf, J. M., IND. ENG.C H ~ MANAL. ., ED., 11, 278 (1939).
Use of Color In#utor in Analysis 0.0743 gram; B e 0 taken, 0.0753 gram) Ala01 Obtained Gram 0.0747 0.0747 0,0748 0.0745 0.0743
Error
ME. 4-0.4 +0.4 4-0.5 4-0.2 tO.0
Be0 Obtained Gram 0,0750 0,0762 0,0748 0.0768 0.0760
Error ME. -0.3 -0.1 -0.6 4-0.6 -0.2
Of the numerous indicators tried, a mixture of 1 drop of methyl
red to 6 d r o p of bromocresol green (0.1% solutions) per 500 ml. of the buffer solution prescribed by Nichols and Schempf, was found satisfactory if the color change is approached from the basic side as described below. To the solution, diluted to 500 ml. and containing the buffer and indicators, ammonia (1 to 1) is added until the solution asmmes a blue-green color, indicating a pH well above 6. Dilute (6 N ) sulfuric acid is then added slowly and with constant stirring. The following color changes are noted: blue-green, blue, purple, reddish purple, red. The first appearance of the reddish purple waa found to coincide very closely with a p H of 4.6, the pH necessary for the complete separation of the two metals. The color change is definite and easily distinguished. If desired, however, i t may be checked against the Clark and Lubs buffer mixture ( 1 ) having a p H of 4.6.
Fifteen-Year Collective Index for Analytical Edition A fifteen-year collective index of the ANALYTICAL EDITION of INDUBTRIAL AND ENGINEERING CH~MISTBY, complete through 1943, is being prep& by Charles L. Bernier, associate editor of Chemical Abslrads. with the expectation of being able to issue it early in 1945, as @ pamphlet of the Same page size aa regular h u e s of the ANALYTICAL EDITION, if suf6cient paper for printing can be obtained. Both subject and author indexes are to be included, following in general the practice of Chemical Abatraets, but with certain variations suggested by the special nature of this analytical index. Present plans contemplate furnishing copies of the index at a nominal price to any subscriber to the ANALYTICAL EDITION who places his order before publication, and selling copies after that time a t a somewhat higher price. At present no definite price can be quoted, aa it w i l l depend somewhat upon the number of copies printed. It will be very helpful if those wishing to reoeive the index will notify Walter J. Murphy, Editor, 1155 Sixteenth St., N. W.. Washington 6, D. C., preferably prior to October 1.
