. October 15, 1929
I N D U S T R I A L A N D ENGINEERING CHEMISTRY Literature Cited
(1) Barnard, J SOC..-1ulomolzue Eng., I?, 205 (1925). (2) Barnard, Myers, and Forrest, IXD.ENG.CHEM.,16, 347 (1924). (3) Bown, Oil Gas J., 26, 142 (1928). (4) Donaldson, J. SOC.Chem. I n d . , 46, 3241' (1927). ( 5 ) Gilson, IND. ENG.CHEM.,18, 467 (1926). ( 6 ) Langmuir, J. Am. Chem. Soc., 39, 1848 (1927). (7) Marley, Livingstone, and Gruse, Trans. SOC.Automotive Eng., 21, pt. 2, 150 (1926); a2, pt. 1, 69 (1927); IND. ENC. CHEM.,18, 502 (1926). (8) McKee, Trans. SOC.Automofive Eng., 21, pt. 2, 248 (1926).
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(9) Mougey, Oil Gas J., 26, No. 25 (1928). (10) Peterkin and Ferris, IND. ENG.CHEM.,17, 1248 (1925). (11) Walker, Lewis, and McAdams, "Principles of Chemical Engineering," p. 84, McGraw-Hill Book Co., 1927. (12) Wilkin, Oak, and Barnard, J . SOC.Aufomotive Eng., 22, 213 (1928). (13) Wilson and Barnard, J. IND.ENG.CHEM.,14, 682 (1922); J. SOC. Automotive Eng., 11, 143 (1922). (14) Wilson and Barnard, Proc. A m . SOC.Testing Maferials, 28, pt. 11. 677 (1928). (15) Wilson and Ries, Colloid Symposium Monograph, Vol. I, p. 145 (1923).
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Determination of True Sodium Content of Calcium Carbonate Intended for Use in J. Lawrence Smith Method for Alkalies' Earle R. Caley PRINCETON UNIVERSITY, PRINCETOY, N J
HE usual method of testing reagent-grade calcium carbonate for its alkali salt content is to boil 4 grams of the salt with 50 cc. of water, filter, evaporate the extract to dryness, and ignite and weigh the residue remaining ( 3 ) . It has long been recognized that this method is defective in principle, since it is generally impossible to extract small amounts of adsorbed alkali salts from insoluble precipitates by a simple washing process. Several experimenters have amply demonstrated this in the case of calcium carbonate in particular (A). Until recently, no suitable method of rapidly and accurately testing this chemical for alkali salts has been available. It appeared to the writer that the improved magnesium-uranyl acetate method for the direct determination of sodium (1) would provide a means for accurately determining the alkali content of this material, since by this method it is possible to determine small amounts of sodium in the presence of very large amounts of calcium, and the alkali content of reagent calcium carbonate consists almost wholly of sodium in some form, probably as the carbonate (2, 4). Experiments were therefore instituted which resulted in the formulation of a suitable procedure for the accurate determination of sodium in this reagent. Test analyses were made on several representative samples of ualcium carbonate from different sources by this new method, and the results were compared with those obtained by the extraction method as described in detail below,
T
in a large beaker containing water a t 20" C. and stir the solution with a motor stirrer for 30 to 45 minutes. Filter off the resulting precipitate into a weighed Gooch crucible and wash with four or five 5-cc. portions of special wash liquid. Finally dry the crucible and precipitate in an air oven a t 100-105° C. for 30 minutes. The weight of the precipitate multiplied by the factor 0.0153 gives the sodium content of the sample. PREPARATION OF REAGEII'T-The reagent is prepared in two parts, which are mixed to obtain the final working reagent. SOLUTION A Crystallized uranyl acetate.. ........................ 85 grams Glacial acetic acid.. . . . . . . . . . . . 60 grams Distilled water.. .............................. to 1000 cc. SOLUTION B Crystallized magnesium acetate. .................... 500 grams 60 grams Glacial acetic acid.. Distilled water. . . . . t o 1000 cc.
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Each solution is separately heated to about 70" C. until all the salts are in solution, and then the two solutions are mixed a t t>histemperature and allowed to cool to 20" C. The large vessel containing the mixed reagent is then placed in water a t 20" C. and held a t this temperature for an hour or two until the slight excess of salts has crystallized out. The reagent is finally filtered through a dry filter into a dry bottle. The reagent is permanent, although on long standing there may appear a slight precipitate due to the reaction with the sodium of the glass, in which case it is necessary to filter it Experimental Part before using it for an analysis. PREPARATION OF SPECIAL WASHLIQUID-Precipitate the The extraction method used in these experiments was that sodium from 1 to 2 cc. of dilute (1 to 2 per cent) sodium described by Murray (3). I n order t o insure the absence of chloride solution with 50 cc. of the special reagent by shaking weighable residues from sources other than the calcium car- the two solutions together and wash the resulting precipitate bonate, blanks were run on the distilled water used and the of sodium-uranyl-magnesium triacetate with successive porextractions and evaporations were conducted in platinum tions of 95 per cent alcohol. Suspend the washed precipitate vessels. in a large volume of 95 per cent alcohol and shake the mixture The magnesium-uranyl acetate method as modified for a t frequent intervals for an hour. Finally filter the solution this purpose was as follows. and use the filtrate for washing the sodium precipitates. PROCEDURE-weigh out 2.000 grams of the calcium car- The use of this special wash liquid is necessary in order to obbonate into a 150-cc. Erlenmeyer Pyrex flask. Dissolve the tain exact results in washing very small precipitates. For sample by cautious additions of dilute (1:1) hydrochloric acid technical control purposes sufficiently close results are obtainintroduced through a small funnel placed in the neck of the able if the precipitates are washed with ordinary 95 per cent flask. Evaporate the solution just to dryness on a hot plate alcohol. and dissolve the residue in 2 to 3 cc. of water. Then add GEXERAL REMARKS ON PROCEDURE-The excess of hydro25 cc. of magnesium-uranyl acetate reagent and mix the two chloric acid used in the solution of the sample must be nearly solutions thoroughly. Immerse the lower part of the flask all removed by evaporation, since precipitation is not complete in the presence of free hydrochloric acid. On the other 1 Received June 11. 1929.
ANALYTICAL EDITION
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hand, care must be taken not to bake the residue and thus decompose the calcium chloride, since in that case it will not be possible to obtain a clear solution in water. A safer procedure is to finish the evaporation over a water bath. For extensive manipulative notes on the remainder of the method the reader is referred t o the recent paper on the direct magnesium-uranyl acetate method for sodium ( I ) . No difficulties will be encountered, however, if the details as given above are followed. Results
Vol. 1, No. 4
T a b l e I-Comparative Results in Determination of S o d i u m in Samples of R e a g e n t Calcium C a r b o n a t e by Extraction M e t h o d a n d by Magnesium-Uranyl Acetate M e t h o d SODIUM ALKALI SODIUM ALKALI CONTENT CON- ACTUALLY CONTENT SODIUM C!AI.Cn. TENT PRESENT I N LABEL CONTENT TO EXTRAC-EXTRACSTATE- NEW CARBON- TION TION SAMPLE MENT METHOD ATE METHOD RE31DUEa
Per cent Per cen! Per cent Standard stock material None 0.13 0.30 Standard stock material . 0 . 0 5 0.12 0.28 Specially prepared lot Low 0.02 0.05 Standard stock material 0 . 0 1 0.008 0.018 Selected lot from standard stock material 0.053 0.006 0.014 a Expressed in percentage of sample taken.
Per cent
Pdr cent 0.002
0.02 0.02 0.04 0.01
0.003 0,001
