DECEMBER 1947
1039
Esperiments have shown that, depending on the nature of the compound, 15 to 50% of the fluorine present in the sample is collected as fluoride in the hanging drop. If the sample does not contain bromine or chlorine, the procedure can be simplified by onlit ting the hydrazine reduction.
ACKNOWLEDGMENT
Several of the tests used in the systematic scheme have been based upon tests described by Feigl ( 2 ) . The authors wish to express their appreciation of the assistance given by A. Briglio, D. Brown, G. Holzman, and T. Lee during the course of this work.
RESULTS OBTAINED WITH FLUORINE TEST
Onc-milligram samples of a number of fluorine-containing compounds were examined and the result of the test was recorded as: (A) equivalent to test obtained with 6 to 10 micrograms of fluoride ion, and (B) equivalent to test given by more than 10 micrograms of fluoride ion. The results are given in Table V. Segative tests were obtained with 1-mg. samples of 8-chloroethyl chlorosulfonate, 0-cbhloroethylisocyanide dichloride, and c~iinethylchloroarsirie. The system of qualitative analysis described above was used frequently during the war period for the rapid identification of tslt>inentsin organic compounds and no difficulty was experienced in obtaining unambiguous results. During the past year the system has been used with equal success in a laboratory course given for senior and first-year graduate students.
LITERATURE CITED
(1) Emich, F., and Schneider, F., “Microchemical Laboratory Manual,” New York, John Wiley & Sons, 1932. (2) Feigl, F., “Qualitative Analysis by Spot Tests,” Xew York, Elsevier-Nordemann Co.. 1939. (3) Johns, I. B., “Laboratory Manual of Microchemistry,” Minneapolis, Burgess Publishing Co., 1942. (4) Niederl, J. B., and Niedei-I, V., “Micromethods of Quantitative Organic Analysis,” New York, John Wiley & Sons, 1942. ( 5 ) Schneider, F., “Qualitative Organic Microanalysis,” New York, John Wiley & Sons, 1946. (6) Van Slyke, D. D., Dillon. R . T., -MacFadyen, D. A., and Haniil. 627 (1941). ton, P., J . Biol. C h ~ m .141, REmIvEo April 5, 1947. Based upon work done for the Office of Ycientific Research and Development under Contract OEhIsr-325 with t h e California Institute of Technology Contribution 1117 from Gates and Crellin Laboratories of Chemistry, California Institute of Technology.
Determination of Small Amounts of Sodium Bicarbonate in Sodium Carbonate ROBERT B. REGIER’, Wyandotte Chemicals Corp., Wyandotte, Mich.
HE procedure commonly employed determining sodium T bicarbonate in sodium carbonate is that of Winkler, in which the bicarbonate is neutralized with an excess of standard base, foi
barium chloride is added to pi ecipitate the carbonate ions quantitatively, and the excess of base is determined hy titration with standard acid in the presence of the barium carbonate ( 3 ) . For materials in which both carbonate and bicarbonate are present in appreciable quantities, this method is satisfactorr. But in soda ash, in which tlw sodium bicarbonate content seldom csxceeds 1wc and.is usually much less, application of Winkler’s met hod without suitable modification may result in errors as large as 100% of the true sodium bicarbonate content. The pi (%ripitationof barium carbonate appears to remove effectively somtt of the ewes- base fiom solution by occlusion in the barium cariionate. [Thc use of silver nitrate as an external indicator for the titration of sodium bicarbonate \I ith sodium hydroxide iri the presericr of rnuch sodium carbonate, a method also commonly in use ( I ) , is inaccurate. By this method the end point is i(vwhed uhen as much as 0.5(2 sodium hicarbonate is still not neutralized.] To correct for this effect when small quantities of sodium bicarbonate are being determined, it has been found necessary in this laboratory to make a blank determination on sodium carbonate that is free from bicarbonate. Such material may be prepared bv igniting reagent grade sodium carbonate at 140” C. for 3 hours or a t 160” C. for 1.5 hours ( 2 ) . The procedure employed i n this laboratory for determining small quantities of sodium bicarborlate in soda ash is as follows: =\pproximately 10 grams of sample, accurately weighed, are trail-ferred to a 250-ml. volumetric flask, dissolved in freshly boiled, cool distilled water, and diluted to the mark. A 50-ml. aliquot of the sample is treated with 5 ml. of 0.1 N sodium hydroxide, then with 50 ml. of 1.0 -V barium chloride that is neutral tp phenolphthalein. After thorough mixing the suspension 1s _ _ ~ 1
Present addrew, Phlllijis Petroleurn Co , Bartles\ille, Okla.
titrated potentiometrically with 0.1 N hydrochloric acid without undue delay, to prevent pickup of carbon dioxide from the atmosphere. The blank determination is performed in an identical manner. It is imperative that identical quantities of sodium hydroxide be used for both sample and blank, since the blank correction is related directly but not linearly to thp quantity of excess sodium hydroxide present when the barium carbonate is precipitated. The magnitude of the blank correction has been found to be approximately 0 . 2 9 sodium bicarbonate. For reabons not known, the correction varies sufficiently with different reagents, so that it should he measured for each determination unless its constancy has been established. The values cited in Table I were obtained over an interval of nearly two years, using different batches of sodium carbonate and different reagents. Table I shows results obtained from the analysis of two series of independently prepared synthetic samples. Without the blank correction systematic e i ~ o r sranging from 15 to over 10070 of the actual bicarbonate content are obtained, whereas deviations of the corrected results may hc attributed to experimental error. Table I. Piesent
Accuracy of Analysis of Sodium Bicarbonate Found
Trial I Corrected
Found
Trial I1 Corrected
72
%
70
72
%
0.20 0.40 0.60 0.80 1 .oo Blank
0.48 0.65 0.81 1.03 1.24 0.24
0.24 0.41 0.57 0.79 1.00
0.38 0.57 0.76 0.95 1.16 0.16
0.22 0.41 0.60 0.79 1.oo
..
..
LlTERATURE CITED (1) Am. SOC. Testing Materials, A.S.T.M. Standards, Part 111, D 5 0 1 4 3 , p. 978, 1944. (2) Carmody, W. R., IND. ENG.CHEM.,ANAL. ED.,17,577 (1945). (3) Winkler, C.,“Praktische Uebungen in der Maassanalyse,” p. 41, Freiberg, J. G. Engelhardt’sche Buchhandlung, 1888. RECEIVED February 20, 1947.
