ANALYTICAL EDITION
December, 1946
methanes, and higher polymers, much less mixtures of thew compounds. However, knowing which compounds bron-m’ a t t : normally, and which brominate abnormally, and ho\v variow bromination conditions affect the results, i t should be possible t u determine accurately a large number of compounds by modilying the procedure where necessary. Further research is needed hPfore bromination can be used for the quantitative analysis of tlx. complex mixtures which result from the rraction of phmols x i ; h formaldehydc. LITERATURE CITED
(1) “Allen’s Commercial Organic Analysis”, 4th ed., Vol. 111, pp. 480-2, Philadelphia, P. Blakiston’s Son & Co., 1910. (2) .luwers, K., B e T . , 40, 2524 (1907). (3) Callan and Henderson, J . SOC.(‘hem. Ind., 41, 161 (1922).
759
(4) Day and Taggart, ISD. ENG.CHEJI..20, 545 (1928). (5) Fox and Barker, J . SOC.Chem. Ind., 37, 268 (1918). (6) Ibid., 39, 169 (1920). ( i )Francis, A. W., J . Am. Chem. Soc., 48, 1631 (1926). (8) Francis and Hill, ISD. EKG.CHEY.,.%SAL. ED.,13, 357 (1941). (9) Francis and Hill, J . d m .Chem. SOC.,46, 2498 (1924). (10) Koebner, M., Brit.Plastics, 14, 95 (1942). (11) Koppeschaar, IT. F., Z . anal. Chem., 15, 233 (1876). (12) Lapworth and Schoesmith, J . Chem. Soc., 121, 1391 (192%). (13) %leer, S. van der, Rec. trap. chim.. 63, 147 (1944). (14) Niederl, J. B., ISD.ESG. CHEX.,30, 1269 (1938). (15) Redman, Weith, and Brock, J. ISD. ESG.CHEM.,5,389 (1913) (16) Ruderman, I. IT., J . SOC.Chem. I d . , 64, 204 (1945). (17) Sprung, M. hZ., IKD.EKG.CHEM., .$NAL. ED., 13, 35 (1941). (18) Strating and Backer, Rec. trav. chim.. 62, 57 (1943). (19) Ullmann and Brittner, Ber., 42, 2539 (1909). (20) Zinke. Hanus. and Ziegler, 6.prnkt. Chem., 152, 126 (1939).
Determination of Calcium in Magnesite and Fused Magnesia WALLACE M. HAZEL’ AND WARREN
K. EGLOF, Department of
A method for the determination of calcium oxide in materials containing a high magnesium oxide content is proposed, whereby a separation of the magnesium from the lime is first effected. This procedure is the reverse of the usual technique employed. M a n n i t e i s used to pr:vint precipitation of the calcium during precipitation of the magnesium as hydroxide. The method i s direct, requiring fewer preliminary separations than the existing methods. Quantitative recovery of the lime is assured. Spectrographic examination of a number of the precipitates of lime showed them to b e of analytical purity, free from contamination b y other impurities in the samples.
E
X T R E M E L Y small amounts of calcium, especially in the presence of much magnesium, as in magnesites and fused magnesia, cannot he determined satisfactorily by direct precipitation a3 oxalate ( 3 ) . In material of this type, the usual procedure is t o precipitate the calcium first as sulfate, then as oxalate, and to treat the residual sulfates so that’ a saturated solution of magnesium sulfate is formed. To this are added mixtures oi ethyl alcohol, methyl alcohol, and sulfuric acid, in which the magnesium sulfate is appreciably soluhle, while the insoluhle calcium sulfate is removed hy filtration. While the calcium sulfate i.: purported to be Tvholly insoluhle, careful study shorn that results obtained by these procedure are usually somewhat low. The precipitation as sulfate is successful only in the absence of alkali metals, the sulfates of which are for the most part difficultly soluble in alcohol. This, of course,’makeh this method of separation entirely unsuitable for substances whit-h must be first attacked by an alkali fusion-e.g., some fuyed and high-temperature fired periclase in which recrystallization has occurred. In other methods for the separation of small aniount,s of lime from large amounts of magnesium, such as may occur in magnesium alloys ( 2 , 6),a sugar solution is used to dissolve the calcium hydroxide, leaving the magnesium hydroxide almost completely precipitated in strong alkali solution, from which the calcium may be separated by filtration. The alloys, however, are relatively free of the impurities usually found in appreciable amounts in magnesite. During work in this laboratory involving many thousands of boron analyses, solutions containing a polyhydric alcohol, in this particular case mannite, \yere titrated to an approximate p H of 11. Although in many cases rather large quantities of calcium were present as the chloride, no calcium hydroxide was precipitated. If, hoj\-ever, these solutions contained magnesium chloride, an precipitate Of magnesium hydroxide Occurred, render1
Present address, S o r t o n Co., Chippawa. Ontario.
Chemistry, Niagara University, Niagara University,
N. Y.
ing the boron analysei uGeless and making removal of the magnesium ion obligatory. These phenomena suggested a possible new means of separating calcium from appreciable magnesium, providing conditions could be found which would yield a quantitative separation of the calcium from either all or a major portion of the magnesium. EXPERIMENTAL
Samples of very high-grade, specially prepared magnesiuni oxide obtained from the high-temperature calcination of magnesium hydroxide were used in the preliminary study. This material was supplied by the J. T. Baker Chemical Company. Both chemical and spectrographic analysis showed that various shipments of this material contained from 0.04 to 0.0S7c calcium oxide. Two-gram samples of this magnesium oxide were dissolved in hydrochloric acid and various amounts of reagent grade mannite from the Hercules Powder Company were added to the acid solution contained in 500-ml. volumetric flasks. The solution was then made alkaline with carbonate-free sodium hydroxide, diluted t o 500 ml., mixed, and allowed to stand overnight. Examination of the clear supernatant liquid showed that from 95 to 99% of the magnesium had been removed. The next step consisted of adding various amounts of a chloride solution prepared from calcium oxide purified by triple precipitat’ion as oxalate after preliminary separation of the interfering elements. The additions of calcium ranged from 2 t o 20 mg., calculated as oxide per 100 ml. of solution contained in the volumetric flask. iZlter treatment of this solution n-ith mannite and sodium hydroxide, as described in thc general procedure, the calcium was separated from the clear supernatant liquid as oxalate by double precipitation. The recoveries obtained were excellent (Table I ) . Follon-ing these t e h , the iarnple of calcined magnesite S o . 101 insued by the Sational Bureau of Standards, and a series of magnesite samples from various sources were analyzed by the method deacrihed. The r e d t . i n Tahle I indicate excellent recoveries of the lime with accuracy equal to, or better than, some of the present generally accepted methods. G E N E R A L PROCEDURE
FTeigh out samples of the or fused magnesia into 100-cc. porcelain casseroles, add 35 to 40 cc. of 1 to 1 hydrochloric acid, and n-arm until solution is efiected. I n the event that the material is not entirely soluble in the dilute hydrochloric acid, place the in a 20-cc. platinum crucihle and intimately mix with it about 3 to 5 grams of sodium carbonate. piace the crucible in a muffle furnace. or Over a Fisher burner. sinter for about 30 minutes a t 900” to 1000” C., cool, and dis: solve in the casserole with 50 to 60 CC. of 1 to 1 hydrochloric acid. After solution has been brought about by either method, evaporate the solution to dryness on a bath and bake the residue in a drying oven for one hour at, 120”C. Add 5 cc. of concentrnted
INDUSTRIAL AND ENGINEERING CHEMISTRY
760 Table
I.
Gravimetric Determination of Calcium in the Presence of Large Amounts of Magnesium CaO Found by CaO Usual Found by CaO Alcohol Error, Proposed Error, Substance Present Nethod CaO Method CaO 'UO Mo . l gi Mg. .ug . hIgO CaOa 4 0 3 7 -0 3 3 9 -0 1 8 n 7. ..8 -n z R 1 +o 1 12.5 -0.1 12.1 -0 4 lZ.4 0.0 15.6 -0 4 16.0 16.0 20.0 -0.2 19.8 19.8 -0 2 25.0 0.0 24.5 -0.5 25.0 31.1 +o. 1 31.1 31.0 +o 1 35.8 -0.2 35.5 36.0 -0 5 40.1 $0.1 39.4 40.0 -0 6 40.1 -0 5 +0.1 39.5 40.0 India magnesite 8.5b -0 8 +0.4 8.9 7.7 9 2 9.lb +0.1 8.4 -0 7 10.0 -0 3 +0.3 9.4 9.7b 0.0 9.9 9.5 9.96 -0 4 Magnesite 104< 27.4 +0.6 26.8 26.2 -0 6 27.2 +0.4 26.8 26.6 1; 27.4 +0.6 26.8 26.1 26 9 26.8 26.1 -0 7 +0.1 27.3 26 8 26.2 +0.5 -0 6 26.4 26.8 -0.4 -0 4 26.4 26.2 -0 3 -0.6 26.8 26.5 26 9 26.8 -0 8 +O.l 26.0 27.0 26.8 +0.2 -0 8 26.0 27.1 26.8 26.1 +0.3 -0 7 Sea-water magnesite 18.Ob 17 5 -0 5 17.9 -0 1 a Pure calcium oxide additions to magnesium oxide. b Averaged values reported b y chemical laboratory of Xorton Co., Chip-
+
.
;
--
nawa -
U. 8. Sational Bureau of Standards burned magnesite sample 104
hydrochloric acid to the baked residue and then about 50 to 75 cc. of hot water, and digest until salts are in solution. Filter off the silica, nashing the precipitate 4 to 5 times with hot 1 to 4 hydrochloric acid wash and finally n i t h hot water. The silica content of the sample may be determined by the usual ignition and treatment of the precipitate with hydrofluoric acid, although very accurate determinations require tTyo dehydrations. If the precipitated silica has been properly mashed, no calcium will be found in the residue after hydrofluoric acid treatment. To the cooled filtrate contained in a 500-cc. volumetric flask add 15 to 25 grams of mannite. When solution of the mannite has been effected, add 6 drops of phenolphthalein indicator and a solution of 9.0. S carbonate-free sodium hydroxide dropxise until the pink color of the indicator appears. The sodium hydroxide used must be carbonate-free because of the possibility of forming calcium carbonate, which is insoluble in the polyhydric alcohol solution and would lead to low lime results. S o w add an excess of 5 cc. of the sodium hydroxide solution by dropwise additions while the solution in the flask is agitated to ensure prompt mixing of the two solutions, Cool the flasks t o room temperature, dilute to 500 cc. with distilled viater, shake the flask well, and allon to stand for 6 to 8 hours, or overnight. Pour the solution through a loose, dry, filter paper until a 200-cc. aliquot can be obtained. The aliquot may be removed by means of a pipet from the clear supernatant liquid in the flask, although in many cases this method is not satisfactory. To the aliquobs contained in 400-cc. beakers add 5 drops of ?ethyl red indicator and acidify with hydrochloric acid, adding o cc. in excess. An addition of 5 grams of ammonium chloride a t this point is desirable should, for some reason, an undue amount of magnesium remain in the solution. T o the boiling solution add 0.5 gram of ammonium oxalate and, when dissolved, add ammonium hydroxide until the solution is neutral. Digest on a steam bath until the calcium oxalate precipitat'e is well formed. Remove, add 2 cc. of ammonium hydroxide dropwise, and allon- precipitate to stand for 4 hours. Filter the solution through a S o . 40 Khatman paper and wash Jyith a cold 1 5 solution of ammonium oxalate, Dissolve the washed precipitate through the paper with 50 cc. of hot 1 t'o 2 hydrochloric acid and reprecipitate, filter, and wash the calcium exactly as described for the initial precipitation; Convert the calcium oxalate to the oxide by ignition a t 1100 to 1200" C. in tared platinum crucibles to constant n-eight', observing all of the usual precautions necessary for the veighing of this hygroscopic precipitate (4). The 200-cc. aliquot taken for this analysis represents an 0.8gram sample. The percentage of calcium oxide in the sample may be calculated as follows: Keight of precipitate X 100 .= 0.8
cc CaO
Vol. 18, No. 12
The authors prefer weighing the lime as oxide as described, but there is no objection to using the volumetric oxalate-permanganate titration to obtain the lime values. The described procedure is less subject t o errors than the volumetric method. DISCUSSION OF RESULTS
I n this investigation, samples of magnesium oxide with various additions of pure calcium oxide in amounts equivalent t o samples containing from 0.5 to 5.0% were analyzed by the above procedure. I n addition, ten separate and individual analyses of the sample of calcined magnesite S o . 104, issued by the Bureau of Standards, four samples of India magnesite, and one sample of magnesite from sea water were analyzed by the same method. These latter samples were then analyzed by precipitation of the calcium as sulfate and then as oxalate after solution of the sulfate by the mixed alcohols. The results of these investigations, which are shown in Table I, indicate that the values obtained by this new procedure are accurate and reliable. I n general, as expected, the results are slightly higher than those found by the so-called alcohol method, probably because of the slight solubility of the calcium sulfate in the alcohol mixture. The number of milligrams of calcium oxide present in the Bureau of Standards burned magnesite sample 104 is taken from the averaged certificate value of 3.35% calcium oxide (1). Four of the eight cooperating analysts reported higher values for lime than the averaged value. If the value obtained by the Bureau of Standards analyst Lvere substituted for the value shown in the table, the calcium oxide present would be 27.0 mg. instead of 26.8 mg. Substitution of this value would show greater devistions for the analyses obtained by the alcohol, while the results obtained by the procedure proposed herein would show better agreement in eight of the ten analyses. While there is no justification for assuming that this value is better than the average reported value, the results obtained by the proposed method are in very close agreement with those reported by excellent analysts using the existing procedures. The aluminum oxide content of standard sample 104 is given in the certificate as 0.8470. One might expect the aluminum t o be a possible source of error in this method. Because of the solubility of the aluminum hydroxide in the sodium hydroxide solution, it might later be expected to coprecipitate partially or completely with the calcium. S o trouble from this source waa encountered. A number of the calcium oxide precipitates obtained by the use of the proposed method were examined spectrographically for purity. I n these examinations the spectra obtained using a large Bausch & Lomb Littrow type prism spectrograph viere inspected critically. Only the usual spectrographic traces of impurities which are always detectable in the most precise chemical separstions were present. The precipitates of calcium oxide obtained were judged, therefore, to be free from any coprecipitated constituents of the sample. LITERATURE CITED
(1) Bureau of Standards Certificate of Analyses of Standard Sample 104, Burned Magnesite, Washington, D. C., 1933. (2) Donmetal Laboratory Methods, Bull DM-41-a(1943). (3) Hillebrand, IT. F., and Lundell, G E. F.. "Applied Inorganio .Inalvsis", p. 487, Xew York. John ITiley 8; bons. 1929. (4) Scott, W.TI-., ' Standaid Xerhods of Chemical Analysis", 5th ed., p. 211, S e w York, D. Van S o s t r a n d Co., 1939. (5) Ibid., p . 551. A DISSERTATION submitted in partial fulfillment of the requirements for the degree of master of science to the faculty of the Graduate School of Xiagars University ,
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