January 15, 1929 -
INDUSTRIAL A N D ENGINEERING CHEMISTRY
25 -
Determination of Iron and Aluminum Oxides, Magnesium Oxide, and Calcium Oxide in Portland Cement' Rapid Method J. Stanton Pierce and W. C. Setzer GEORGETOWN COLLEGE, GEORGETOWN, KENTUCKY
OSTROL analysis in the annual production of over le0 million barrels of Portland cement in the United States is no small task, for GovernmentZ and other standard specifications are very rigorous. The standard method of analysis of cement3 is rather tedious and this as well as many of the more rapid methods for the determination of magnesium4 in mixtures containing calcium require the reiiioval of the latter before the magnesium can be determined. This is a distinct disadvantage, for quite frequently it is necessary t o determine the magnesium and not the calcium. I n a recent paper from this laboratoryJ5the procedure for the titroinetric determination of calcium aqd magnesium in limestone was given. In this work bromothymol blue was used t o indicate neutrality, a t which point iron and aluminum were completely precipitated as the hydroxides, and t'rinitrobenzene was used to indicate the precipitation of magnesium hydroxide, calcium remaining in solution. The method mentioned above, however, is not' applicable to cement analysis but by using the same indicators and modifying the procedure somewhat, iron and aluminum oxides, magnesium oxide, aiid calcium oxide are determined satisfactorily. (Work is now in progress in this laborat'ory for t'he determination of inagnesium in various mixtures.) Theoretical Considerations
C
Ferric hydroxide is insoluble in neutral or alkaline solution, and aluminum hydroxide is insoluble in neutral solut,ioii but appreciably soluble in slightly alkaline6 solution. Therefore, in order t o remove the iron and aluminum quantitatively from the solution of cement, the pH must be near 7. Broinot,hymol blue is used to indicate this point. The precipitated hydroxides of iron and aluminum are filt'ered ~ f fmashed, , dissolved, reprecipitated, and ignited to the oxides by standard procedure. Trinitrobenzene gives a dark brick-red color in saturated calcium hydroxide solution but does not in saturated magnesium hydroxide solution. Therefore, magnesium hydroxide is precipitated by the addition of trinitrobenzene and carbonate-free alkali to the filtrate from iron and aluminum hydroxides until a dark brick-red color is obtained. The precipitate of magnesium hydroxide is filtered off, washed, dissolved in excess standard acid, and the excess acid titrated with sta,iidard alkali, dimethylaminoazobenzene being used as indicator. 1 2
Received June 29, 1928. Federal Specification Board Specification KO.la, Bur. Standards,
Circ. 55. S A . S.
T. M., C9-21.
Arrhenius, J . A m . Chem. S a . , 44, 132 (1922); Bruckmiller, Ibid., 59, 610 (1917); Hahn and Meyer, Be?., 60B, 975 (1927); Klingenfuss, Z. anorg. allgem. Chem., 158, 195 (1924); Bucherer, 2 . anal. Chem., 59, 297 (1920); Gregoire and Sola, Bull. SOC. shim. Belg., 82, 131 (1923); Bruckmiller, Chemist-AnalySt, 28, 7 (1919); Springer, Z. angew. Chenl., 82, 192 (1919); Canals, Bull. soc. chim., [41 25, 656 (1919). 5 Pierce and Setzer, with Peter, IXD,EKG.CHEM., 20, 436 (1928). 6 Blum, J . Am. Chem. Soc., 38, 1282 (1916); Jander and Ruperti, Z. anovg. nllgem. Chem., 155, 253 (1926). 4
T o the filtrate from magnesium hydroxide, sodium carbonate is added in excess, the precipitated calcium carbonate filtered off, dissolved in excess standard acid, and the excess titrated, with dimethylaminoazobenzene as indicator.
Experimental Procedure Five-tenths of a gram of cement is weighed to the nearest milligram into a 400-cc. beaker. Standard procedure3 is used for its solution, evaporation, dehydration of silica, solution of other substances present, and removal of silica by filtration. Since there is nothing new about the procedure through the removal of silica, it was not determined, but was discarded. The filtrate from silica is treated with 1 cc. of 0.04 per cent alcohol solution of bromothymol blue and 0.25 AT sodium hydroxide is added until a slight blue color is obtained. The precipitate of iron and aluminum hydroxides is filtered off and washed thoroughly with hot water, the washings being caught in the same beaker as the original filtrate. The precipitate is dissolved in dilute nitric acid, reprecipitated with ammonium hydroxide, filtered, washed thoroughly with hot water, and ignited t o the oxides of iron and aluminum by standard procedure. The number of centigrams of ignited precipitate, multiplied by 2, gives the per cent of R203 in the sample. The slightly blue filtrate froin iron and aluminum hydroxides is acidified with hydrochloric acid, boiled for a few minutes to expel carbon dioxide, and cooled. One cubic centimeter of a saturated alcoholic solution of trinitrobenzene is added for every 10 cc. of solution and carbonate-free sodium hydroxide is added slowly t o the stirred solution until a deep red color is obtained, the solution being kept covered with a watch glass as much as possible to prevent the absorption of carbon dioxide from the air. The precipitated magnesium hydroxide is filtered off and washed, the funnel being kept covered with a watch glass except when the solution is being poured in it. After the wash water has drained completely out of the funnel, the precipitate of magnesium hydroxide and filter paper are transferred t o the beaker in which ' hydrochloric acid precipitation took place, 10 cc. of 0.25 h are pipetted into the beaker, about 50 cc. of water and 4 drops (or more if the color fades) of 0.1 per cent alcoholic solution of dimethylaminoazobenzene are added, and the excess acid is titrated with 0.25 N sodium hydroxide, a very slight pink being taken as the end point. The number of cubic centimeters of acid required to dissolve the precipitate of magnesium hydroxide is the per cent of MgO in the sample. The filtrate from magnesium hydroxide is heated to boiling, excess N sodium carbonate is added slowly, with stirring, and the solution is boiled gently for a few minutes. The solution is filtered hot, the precipitate is washed and, with the filter paper, transferred to the beaker in which precipitation took place. The beaker is covered with a watch glass aiid 50 cc. of 0.25 N hydrochloric acid are added from a pipet. After reaction has ceased, the sides of the beaker
ANALYTICAL EDITION
26
and the cover are washed, 4 drops of 0.1 per cent alcohol solution of dimethylaminobenzene are added, and the solution is titrated with 0.25 N sodium hydroxide to a slight pink color of the indicator. The number of cubic centimeters of 'acid required to dissolve the precipitate of calcium carbonate multiplied by 1.4 gives the per cent of CaO in the sample. Table I-Representative RZOS SAMPLEPresent Found Per cent Per cent 9.4 1 9.3
2 3 4
Present Per cent
Found Per cent
CALCIUM OXIDE Present Found Per cent Per cent
5.0 61.8 62.0 64.0 64.5 1.1 61.7 61.9 3.3 1.5 62.5 82.7 Acknowledgment is made to the Bureau of Standards, from whom the 8.9 10.5 9.2
a
Analyses of Cementa
MAGNESIUM OXIDE
8.9 10.4 9.3
4.9 1.1 3.1 1.5
analyzed samples were obtained.
Discussion of Method I n the calculation of results, for strict accuracy, the number of cubic centimeters of acid required to dissolve the magnesium hydroxide should be multiplied by 1.008 instead of 1, and the number of cubic centimeters of acid required to dissolve the calcium carbonate should be multiplied by 1.4018 instead of 1.4. However, since this method will be of use only for control work, where the highest accuracy is not required, the approximations given will be satisfactory. The fact that the results by this method are as near correct as shown in the above representative set of analyses is due to a balancing of errors. The loss of magnesium hydroxide in the filtrate is offset by the precipitate of calcium carbonate, due to the slight amount of carbon dioxide absorbed from the air, and to the presence of a small amount of sodium hydroxide not washed out of the precipitated magnesium hydroxide. After magnesium was determined, the solutions were filtered and the calcium determined by precipitation of the oxalate and titration with potassium permanganate. The results, expressed in terms of MgO, were 0.3, 0.3, 0.4, and 0.2 per cent, respectively, for samples 1, 2, 3, and 4. The slightly high results for calcium, in spite of this loss, must be due to the sodium carbonate remaining after three washings. I n order to cut carbonation oi the calcium to a minimum, the precipitate of magnesium hydroxide should be filtered in a room in which there are few burners, and the beaker and funnel containing the precipitate should be kept covered as much as possible. To see what would be the effect of filtering in the presence of an abundance of carbon dioxide, the following experiment was carried out: In two solutions, each containing 10 cc. of magnesium chloride solution (1 cc. = 2 mg. Mg) and calcium chloride equivalent to
Vol. 1, No. 1
300 mg. of CaO, the magnesium was precipitated as the hydroxide and the precipitates were filtered off with lighted Bunsen burners at full height on each side 10 cm. from the funnels.
In one case the beaker and funnel containing the magnesium hydroxide were left uncovered and the beaker was allowed to stand by one burner. In the other case both beaker and funnel were kept covered except while the funnel was being filled. The magnesium was determined as described above and the calcium present with the magnesium hydroxide precipitate was determined as the oxalate. The values obtained are given below: UNCOVERED
SAMPLE 1Mg.
Magnesium Magnesium equivalent of calcium
22 8 33
COVERED SAMPLE
Mg. 21.3 2.1
It is quite evident from these results that precautions should be taken to prevent carbonation. However, if due precautions are taken, no great error should be introduced, for even with the excellent chance for carbonation in the covered sample, the magnesium found was only 1.3 mg. higher than the amount present. I n a 0.5-gram sample of cement, this corresponds to a little over 0.4 per cent of MgO. The determination of iron and aluminum oxides by this method takes a little longer than by two precipitations with ammonium hydroxide, for when this method is used the first washing must be thorough enough to insure practically complete removal of calcium and magnesium. This is because the filtrate from the second precipitation contains ammonium hydroxide, which, if mixed with the original filtrate, will interfere with subsequent tests. The accuracy of the two methods should be about the same. This method for the determination of calcium and magnesium is much more rapid than the customary procedure of precipitating the calcium as the oxalate and the magnesium as magnesium-ammonium phosphate, particularly if a double precipitation of magnesium is carried out. I n this procedure no evaporation is necessary, and both calcium and magnesium are determined volumetrically with one set of standard solutions. However, it is not quite so accurate as the customary procedure, for calcium oxalate can be washed more thoroughly than can calcium carbonate, without danger of loss, and in spite of balancing errors, the results for magnesium are not so accurate as those obtained by the more tedious gravimetric method. This procedure should be of especial advantage for control work, where magnesium alone is determined. When extreme accuracy is not required, it should find a field of usefulness, also, when Rz03and calcium are to be determined.
X-Ray Quantitative Analysis of Tetraethyl Lead in Gasoline' R. .H. Aborn and R. H. Brown DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE
-RAY methods have been applied successfullyto quantitative analysis in but very few instances and these have been confined largely to spectral absorption methods. The possibility that a mass absorption method might serve as a means of determining the amount of tetraethyl lead in gasoline was suggested to the writers by George Calingaert of the Ethyl Gasoline Corporation. The concentration range of tetraethyl lead in commercial
X 1
Received August 20, 1928.
OF
TECHNOLOGY, CAMBRIDGE, MASS.
gasolinesvaries from under 0.5 to 3 cc. per gallon (3.7854 liters), and an error in analysis under 0.1 cc. per gallon is desirable. With the experimental arrangement described below the method is capable of an accuracy of 0.1 cc. per gallon. With further refinements it is believed the precision can be increased to the accuracy required in commercial analysis. 0.1 cc. per gallon is equivalent to 1 part in 14,000 parts by weight. Such high sensitivity is possible only when the constituents (in this case solvent and solute) differ very widely
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