INDUSTRIAL ,AND ENGINEERING CHEMISTRY
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varnish, etc.) to add to a heavy batch of finished product to reduce it to the required weight per gallon, or specific gravity. This problem involves a rather complicated calculation or, if the batch is reduced by guesswork, nonuniform results; however, the use of the chart (which must be prepared for each type of product) greatly simplifies the p r ~ c e d u r e . ~As an illustration, assume that a batch of brushing lacquer has just been finished, which should weigh 9'/2 pounds per gallon. A gallon taken from the mixing tank weighs lo1/* pounds, and the clear lacquer that is to be added weighs 7'/2 pounds per gaIIon (the chart being constructed on this basis). Place a straightedge connecting the two points marked g1/2 (the desired weight) on the two scales. Then find the present weight (lo1/*) on the left-hand scale. Where this horizontal line meets the straightedge, read off (on the horizontal scale) the number of gallons of clear lacquer to be added for each 100 gallons of the heavy lacquer. Knowing the size of the batch, it is a simple matter to calculate the total amount to be added.
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30 40 50 60 70 80 SO id0 110 GALLONS LIGHTPRODUCT TO BE ADDED TO 100 GALLONS HEAVY PRODUCT T O OBTAIN DESIRED WEIGHT Figure 18-Alignment Chart for Calculating Q u a n t i t y of Liquid to Reduce Product to Required Specific Gravity 10
Vol. 20, No. 4
Acknowledgment
20
Figure 18 shows the type of alignment chart used to calculate the quantity of a standard liquid (solvent, clear lacquer,
The authors are indebted to E. A. Stoppel, of Valentine and Company, New York, for valuable suggestions and for permission to reproduce Figures 8 to 11, inclusive. 4 For method of constructing this chart, see Deming, J . Ind. Eng. Chem., 8, 264 (1816).
Titrometric Determination of Calcium and Magnesium Carbonates in Limestone' J. Stanton Pierce and W. C. Setzer, with A. M. Peter2 GEORGE~OWN COLLEGE,GBORGETOWN, KY.
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AGNESIUM is the most common metal associated the same indicator, determined magnesium, in the presence with calcium in limestone. In some industries, of calcium, by precipitating magnesium hydroxide in about particularly in cement manufacture, it is very im- 70 per cent alcohol solution. Still more recently Schoch,'a portant that the percentages of calcium and magnesium be with the same indicator, determined the magnesium in waters known accurately, and for plant control an easy, practical, containing calcium by titrating the hot solution with limerapid method of analysis of limestone for these elements is water. Kolthoff l 4 determined magnesium, in the presence of calcium, by precipitating the former with a slight excess very much needed. I n recent years g r a ~ i m e t r i c ,col~rimetric,~ ~ centrifugal,6 of alkali, filtering, and titrating the excess alkali. photometric,6 nephelometric,' conductivity,* electr~metric,~ Theoretical Considerations andvolumetric'Omethods have been studied for the determinaI n the method described in this paper, an alcoholic solution tion of calcium or magnesium in the presence of the other. A decade ago Moirl' used thymolphthalein as an indicator of trinitrobenzene is used to tell when the hydroxyl-ion confor the separation of magnesium from calcium alkalimetrically. centration becomes great enough to indicate that all the More recently, Willstatter and Waldschmidt-Leits12 using magnesium has been precipitated. Several indicators, including thymolphthalein, were tried, but trinitrobenzene 1 Received October 6,1927. was chosen because it was the only one which gave a distinct 9 Chief chemist, Kentucky Agricultural Experiment Station, Lexingcolor, at room temperature, in the absence of organic solvent, ton, Ky. 3 Congdon, Eddy, and Milligan, Chcm. News, 128,244 (1924). in saturated calcium hydroxide solution, and none in saturated 4 Gregoire, Carpiaux, Larose, and Sola, Bull. soc. chim. Belg., 32, magnesium hydroxide solution. 123 (1823). The method described herein may be used for the deter6 Arrhenius, J . A m . Chem. Soc., 44, 132 (1922); Arrhenius and Reim, mination of the calcium and magnesium present as carMedd. Vctcuskapsakad. Nobclinsf.,8, No. 14 (1928). 6 Hoskell, Concrete, 97, 101 (1925). bonates in limestone, dolomite, or magnesite, or part of the 7 Krisr, Biochrm. Z.,168,203 (1925); Ibid., 169, 359 (1925). procedure may be used to determine magnesium in the 8 Harned, J . A m . Chem. SOC.,89, 262 (1917). presence of soluble calcium compounds. 0 Wright and Morris, Proc. Iowa Acad. Sci., 81, 290 (1924); Pinkhof, The carbonate is dissolved in a measured portion of standPharm. Werkblad, 66, 794 (1919); Britton, J . Chem. Soc. (London), 197, 2110 (1925). ard acid, in excess, the carbon dioxide boiled out, and the Averitt, J . Ind. Eng. IOBucherer, 2. anal. Chem., 69, 287 (1920); excess acid determined by titrating back with standard Chcm., 14, 1139 (1922); Froboese, 2.anwg. Chcm., 8% 370 (1914). 11 J . Chem. Met. Mining SOC. S. Africa, 17, 129 (1917). 1 2 Brt.. 86, 488 (1923).
13 14
Ind. Eng. Chem., 19, 112 (1927). Rcc. trav. thim., 41, 787 (1922).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1928
alkali, bromothymol blue being used as an indicator for neutrality. The difference is the amount of acid required t o dissolve the carbonates. Magnesium hydroxide, being much less soluble than calcium hydroxide, is then precipitated from the reaction mixture, to which trinitrobenzene has been added. The precipitation is brought about by the addition of standard alkali, a dark brick-red color of trinitrobenzene indicating the end point. The solution need not be heated, nor is it necessary to add some organic solvent to decrease the solubility of magnesium hydroxide, as is the case when thymolphthalein is used. The excess alkali used, or that required to make the solution strongly enough alkaline to give the color with the indicator, is determined in each case by comparison with a blank test.
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Test of Method
It will be noted that in most cases the calcium oxide obtained by the titrometric method is lower than by standard procedure. This discrepancy is no doubt due to the fact that the titrometric method determines the calcium present as carbonate only. To check the accuracy of the method more carefully, mixtures were made of accurately measured solutions of calcium and magnesium salts, and the mixtures analyzed by titration, as above, with bromothymol blue and trinitrobenzene as indicators. The calcium was obtained from Iceland spar, for standardizing, and the magnesium from chemically pure magnesium oxide, free from calcium and interfering elements. The strength of the magnesium oxide was determined by dissolving it in excess of standard acid and titrating the excess. Procedure Definite amounts of the calcium carbonate and magnesium To the dry, finely pulverized sample (0.5 gram) in an oxide were weighed into volumetric flasks, measured quanti125-cc. Erlenmeyer flask or a small beaker, psipet 50 cc. ties of standard acid added to each, and when reaction was of 0.25 N hydrochloric acid. Cover the container with a complete the solutions were diluted to the mark with distilled watch glass to prevent loss from spattering. Allow to water. The solution of calcium contained 0.005 gram of stand till the reaction slows up somewhat and then place CaO per cc.; that of magnesium contained 0.002 gram of on a water bath at 70-80° C. till the reaction apparently has hlgO per cc. I n each solution, 1 cc. represents 0.2 cc. of N ceased. Then heat to boiling for 1 minute. Cool and wash hydrochloric acid. Definite amounts were used for each down the sides of the container with a little water. Add 1 test. cc. of 0.04 per cent alcoholic solution of bromothymol blue, The results are given in Table 11. and titrate with 0.25 N sodium hydroxide to the appearance T a b l e 11-Check D e t e r m i n a t i o n s of a blue color ( B I ) . Add 1 cc. of a saturated alcoholic CALCIUM OXIDE MAGNESIUM OXIDE solution of trinitrobenzene for every 10 cc. of solution, and Present Found Present Found titrate to a dark brick-red color (B2)with the sodium hydroxide Mg. Mg. Mg. Mg. 250 250.0 5 5.2 solution used above, stirring well when the end point is near. 250.8 9.8 250 10 249.5 250 19.3 20 T o another container of the same size add the same amount 250.8 29.4 250 30 of bromothymol blue and trinitrobenzene that was used in 250.3 250 39.5 40 150.6 150 49.3 50 the limestone solution and dilute with distilled water until 125 125.5 74.7 75 100 99.6 99.6 100 the volumes of the two solutions are equal. From another 75 97.9 100 75.8 buret add 0.25 N sodium hydroxide solution (B3) until the 51.2 50 98.0 100 25 27.3 200 196.4 same depth of color is obtained as in the limestone solution. As the brick-red color of the alkaline solution fades readily Acid-soluble ferric compounds do not interfere with this this test must be run immediately with every sample. test, for they are precipitated, either as an insoluble salt or Calculation of Results as ferric hydroxide, a t neutrality, and do not react with the excess alkali used to precipitate the magnesium hydroxide. The corrected volume of base (Bz - B3) represents the However, if a very large quantity of ferric compounds goes amount required to precipitate the magnesium hydroxide into solution, the precipitate should be filtered out a t neufrom a neutral solution, or trality, for the red color of the ferric hydroxide masks some(Bp - B3) X 0.25 X 0.02016 = grams MgO what the color of the trinitrobenzene. Acid-soluble aluThe acid (50 - B I ) required to dissolve the sample reacted minum compounds resemble the ferric compounds in being with both calcium and magnesium carbonates. Therefore, precipitated as an insoluble salt, or the hydroxide, a t neusince it takes the same number of equivalents of base to trality. However, if a qualitative test shows even a trace precipitate the magnesium hydroxide as it does of acid to of aluminum in solution, the precipitate must be filtered off dissolve the magnesium carbonate a t neutrality, for the aluminum hydroxide dissolves in the excess alkali required to precipitate the magnesium hydroxide. (50 - B I - B ~ Ba) X 0.26 X 0.02804 = grams CaO This method gives results which check satisfactorily with data obtained by recognized procedure,I5 as is shown by the analyses given in Table I. Calendar of Meetings
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Table I-Analyses b y Titrometric M e t h o d CALCIUM OXIDE MAGNESIUM OXIDE Found Gravimetric Found Per cent Per cent P e r cent
SAMPLEGravimetric Per cent
18 Samples 1, 3, 5, 6, 8, and 9 were analyzed by Dr. McHargue, of the Kentucky Agricultural Experiment Station; samples 4, 7, and 10 were sold by Diack and Smith as analyzed samples; sample 2 was given by the Bureau of Standards.
American Chemical Society-75th Meeting, St. Louis, Mo., April 16 to 20, 1928. Pacific.Northwest Regional Meeting-Reed College, Portland, Ore., April 6 and 7, 1928. 8th Midwest Regional Meeting-Minneapolis, Minn., June 7 to 9, 1928. Division of Colloid Chemistry4th National Colloid Symposium, Toronto, Canada, June 14 to 16, 1928. Institute of Chemistry-Northwestern University, Evanston, Ill., July 23 to August 18, 1928. American Electroche&cal Society-Hotel Stratfield, Bridgeport, Conn., April 26 to 28, 1928. American Oil Chemists Society-New Orleans, La., May 14 and 15, 1928. American Association of Cereal Chemists-Minneapolis, Minn.. June 4 to 9, 1928.
