233
V O L U M E 2 0 , NO. 3, M A R C H 1 9 4 8 generally resulted from saponification than from nonsaponification of samples. Differences in vitamin A content seemed t o be due primarily to the relative amounts of vitamin A alcohol and ester in the serum and to the effect of color inhibitors, Jvhich were removed by some methods but not by others. The Kimble method, the shortest of the four procedures, is suitable for the analysis of the blood serum of calves or of cows if interfering substances are of a relatively low concentration. This condition generally exists when carotenoids are less than 350 micrograms per 100 ml. of serum. Although a saponification procedure increases the time required for analysis, it should be used in the determination of vitamin A in the blood serum of dairy cattle especially when vitamin A ester and/or color inhibitors are likely to be present in significant quantities. Saponification removes the factors inhibiting the development of the blue color with antimony trichloride which results in low vitamin A values in certain samples of blood serum. At least part of these color inhibitors have been found sensitive to mild oxidation, which may serve as a basis for developing methods for overcoming the interference. ACKNOWLEDGMENT
The authors wish to thank Mrs. Helen Hamlin for valuable technical assistance in carrying out this study. LITERATURE CITED (1) Bessey, 0. A., Lowry, 0. H., Brock, J . Biol. Chem.,166, 177 (1946).
M.J., and Lopez,
J. A,,
Boyer, P . D., Phillips, P. H., and Smith, J. K., Zbid., 152, 445 (1944).
Boyer, P. D., Spitzer, R., Jensen, C., and Phillips, P. H., IND. ENG.CHEM.,ANAL.ED., 16, 101 (1944). Clausen, S. W.,and McCoord, A. B., J . Biol. Chem.. 113, 89 (1936).
., and Stewart, C. P., Biochem. J . , 39, 63 (1945). Emmerie, A , , Xature, 131, 364 (1933). Gallup, W.D., and Hoefer, J. d.,IBD.E S G . CHEM.,ABAL.ED., Drialoszynski, L. M., Mystkowski, E. &I
18,288 (1946).
Heilbron, I. M., Gillam, A. E., and Morton, R. A., Biochem. J., 25, 1352 (1931).
Hines, L. R., and AMattill,H. A., J . Biol. Chem., 149, 549 (1943). Hoch, H., Biochem. J . , 38, 304 (1944). Kimble, M.S., J . Lab. Clin. M e d . , 24, 1055 (1939). Koehn, C. J., and Sherman, W. C., J . Biol. Chem., 132, 527 (1940).
Latschar, C. E., Wise, G. H., Parrish, D. B., and Hughes, J. S., Kansas Agr. Expt. Station, unpublished data, 1946. Norris, E. R., and Church, A. E., J . Biol. Chem., 8 5 , 4 7 7 (192930).
Notevarp, O., and Weedon, H. W.,Biochem. J.,32, 1054, 1668 (1938).
Palmer, L. S.,”Carotenoids and Related Pigments,” A.C.8. Monograph 9, p. 23, New York, Chemical Catalog Co., 1922. Parrish, D. B., and Wise, G. H., Kansas Agr. Expt. Station, unoublished data, 1946. 1 W k ,G. H., Atkeson, F. W., Caldwell, M. J., Parrish, D. B., and Hughes, J. S.,J . Dairy Sci., 30, 279 (1947). (19) With, T. K., 2. Vitaminforsch.,11, 228 (1941). RECEIVED June 30, 1947. Presented before the 15th Midwest Regions1 CaEmcAL SOCIETY, Kansas City, hlo. ContrlbuMeeting of the AMERICAN tion 335, Department of Chemistry, and 169, Department of Dairy Husbandry.
Analysis of Thorium-C hro mium Mixtures RICHARD E. EWING AND CHARLES V. BAKKS I n s t i t u t e f o r A t o m i c Research, Iowa S t a t e College, A m e s , Iowa A method especially suitable for the analysis of thorium-chromium mixtures involves the perchloric acid oxidation of chromium in the presence of thorium, followed by titration with ferrous sulfate and tetrasulfatoceric acid. The thorium is precipitated as the oxalate and determined gravimhtrically after removal of the chromium as chromyl chloride.
A
SIMPLE and rapid method for analyzing thorium-chro-
mium mixtures was required in connection with a study of the metallurgical properties of thorium-chromium alloys. The literature revealed that very little work has been done on the analysis of such mixtures. Since thorium is unaffected by most of the common oxi8izing agents it seemed t h a t chromium might be conveniently determined titrimetrically by a modification of the iwersed Penny method (4). Chromic chromium has been oxidized in alkaline solution with hypobromite ( 1 , 2 ) hypochlorite ( I ) , and hydrogen peroxide (10). I n acid solution, ammonium peroxydisulfate Kith silver (j), lcxad peroxide ( 8 ) , perchloric acid (3, 6 , 12), potassium bromate ( 2 ) , potassium chlorate (11),and potassium permanganate ( 1 ) have been used. When the use of hydrogen peroxide and sodium peroxide was attempted in alkaline solution, the chromium was apparently oxidized; but though the solutions were boiltd several minutes t o destroy excess peroxide, the chromium was rvduced upon acidificatioa. This is due apparently to the fact that thorium forms a peroxide ( 7 ) which is not decomposed on boiling and liberates hydrogen peroxide upon acidification. Ahnmoniumperoxydisulfate could not be used because thorium sulfate is insoluble in hot aqueous solutions and thus interferes in the subsequent titration of the chromium. The other oxidizing
agents were less satisfactory than perchloric acid. Error in the perchloric acid method due to the loss of chromyl chloride (3, I d ) was eliminated by condensing the volatilized chromyl chloride and titrating it along with the bulk of the chromium. This method proved satisfactory and confirms the recent work of Schuldiner and Clardy (6). REAGENTS
Ferroin, Fe(C12H8N2)3S04. A 0.025 M ferroin solution was prepared by dissolving 14.8662 grams of GFS reagent grade 1,lO-phenanthroline monohydrate and 6.9505 grams of reagent grade ferrous sulfate heptahydrate in enough water to make 1 liter of solution. Ferrous Sulfate, FeS04. A 0.1 N ferrous sulfate solution was prepared by dissolving 39.5 grams of reagent grade Mohr’s salt and 10 ml. of concentrated reagent grade sulfuric acid in enough water to make 1 liter of solution. This solution was standardized each day against the standard tetrasulfatoceric acid solution using ferroin as the indicator. Fluosilicic Acid, HzSiFa. A 1 to 50 aqueous fluosilicic acid solution was prepared by adding 1 ml. of the concentrated (48%) reagent grade acid to 50 ml. of water. Hydrogen Chloride, prepared by dripping concentrated reagent grade hydrochloric acid into concentrated reagent grade sulfuric acid. Hydrogen Peroxide, Merck C.P. grade, 30% H?OA.
234
ANALYTICAL CHEMISTRY
Sitric Acid, reagent grade. Specific gravity: 1.42; 70% HNOa Nitrogen, commercial tank nitrogen. Oxalic Acid, H2C20a.2HZ0,reagent grade. Perchloric Acid, HCIO?, GFS reagent. Specific gravity: 1.54; 60% HClOa. Potassium Dichromatr, K2Cr207, reagent grade.
IOmm OotsideDio
Table 11. Determination of Thorium after Separation of Chromium as Chromyl Chloride Cr Present, Gram 0.077 0.077 0.154 0.154 0.261 0,261 0.261 0.522 0,522
Th Taken Gram’ 0.3194 0.3194 0.3194 0.3194 0.1785 0.1843 0,1868 0.2355 0.2296
Th Found, Gram 0.3194 0.3192 0.3193 0.3196 0.1783 0.1842 0.1868 0,2385 0,2295
Error, Th, Gram fO ,0000 -0,0002 -0.0001 +o ,0002 -0.0002 -0.0001 +o. 0000 10.0000
-0.0001
C P ( C ~ O ~ ) ~as- -well - as to react with the thorium, if quantitative precipitation of the thorium is t o be obtained. The last three determinations shown in Table I indicate t h a t thorium can be precipitated quantitatively in the presence of as much as 1 gram of chromium; but in every case sbectrographic analysis showed that the ignited thorium dioxide was contaminated with a small amount of chromium. I n some cases enough chromium was present t o be detected visuallj-,..
Table 111. Determination of Chromium in Presence of Thorium Th
Present, Gram 0,042 0.042 0.084 0.084 0.210
Figure 1. Apparatus Tetrasulfatoceric Acid, H4Ce(S04)4. A 0.1 N tetrasulfatoceric acid solution was prepared by dissolving anhydrous tetrasulfatoceric acid in dilute sulfuric acid, diluting to about 0.1 N with water, and filtering through glass wool. This solution was standardized against electrolytic iron, using ferroin as the indicator. Thorium nitrate, Th(SO3),.4HtO. Lindsay atomic weightgrade thorium nitrate was especially purified and finally recrystallized from reagent grade nitric acid. APPARATUS
The apparatus used is shown in Figure 1.
Precipitation of Thorium in Presence of Chromium
Tho2 Cr HzCzOc2HzO HzCzOc.2HzO ThOz Present, Taken, Present, Requireda, Found, Grama Gram Grams Gram Gram 4.0 0.1287 0.2706 1.00 7.5 4.0 0.2616 3.9 0.2706 0.50 4.0 0.2706 0,2706 0.25 2.1 0,2706 1.00 7.5 8.0 0.2707 5 0,2706 1.00 7.5 8.0 0,2704 a For both thorium and chromium.
Trial 1 2 3 4
Cr Found, Gram 0.06928 0,06842 0.06917 0.06920 0,07850
Error, Cr, Gram +O ,00017 -0,00003 -0.00001 so.00020 -0.000 10
In order t o eliminate this contamination and the necessity of adding large amounts of oxalic acid, the chromium was removed as chromyl chloride prior t o the precipitation of the thorium. It is not necessary to remove the chromium in this way if speed is more important than accuracy. Xeight burets were used in all the following experiments.
3OQml flask
Table I.
Cr Taken, Gram 0.06911 0,06845 0.06918 0,06900 0,07560
Error, ThOz, Gram -0.1419 -0.0090
10,0000
+0.0001 -0.0002
EXPERIMENTAL WORK
Determination of Thorium. The precipitation of thorium as the oxalate in the presence of chromium was studied by mixing known amounts of thorium and chromium solutions and then precipitating the thorium with oxalic acid. Results of these experiments (Table I) show that oxalic acid must be present in sufficient amounts to complex the chromium a b
Samples of the standard thorium nitrate solution, containing 200 to 300 mg. of thorium, were weighed into the round-bottomed reaction flask and mixed with varying amounts of a potassium dichromate solution. Three drops of hydrogen peroxide and 30 to 35 ml. of perchloric acid were added to each mixture. A 300inl. Erlenmeyer flask containing about 150 ml. of water was placed so that the tip of the condenser extended just below the water surface. Nitrogen was bubbled through the apparatus a t a rate of 1 to 2 bubbles per second, and the contents of the flask were heated. After oxidation of chromium had begun, hydrogen chloride gas was admitted to the reaction flask and the nitrogen flow was stopped. This procedure was continued until nearly all the chromium had been distilled over as chromyl chloride. The thorium solution in the round-bottomed reaction flask was then transferred to a beaker and evaporated to about 5 ml. to remove the excess perchloric acid. This sdlution was then diluted to about 300 ml. and heated to boiling temperature. Five milliliters of thick filter pulp and 5 grams of oxalic acid were added, and after digesting for 15 minutes the mixture was cooled and the thorium oxalate filtered, washed, and ignited to tjhe dioxide in platinum crucibles for weighing (9). The results of a series of determinations made according to the above procedure are shown in Table 11. Determination of Chromium. The possibility of determining chromium in the presence of thorium was investigated by using the following procedure. [After this work was completed Schuldiner and Clardy (6) published a similar method for determining chromium.] Samples of the standard potassium dichromate solution, containing 70 to 75 mg. of chromium, were weighed into Erlenmeyer reaction flasks and mixed with varying amounts of a thorium nitrate solution. Three drops of hydrogen peroxide and 20 to 25 ml. of perchloric acid were added to each mixture. A 200-ml. Erlenmeyer flask containing about 150 ml. of water was placed so that the tip of the condenser just extended into the water
.
V O L U M E 2 0 , NO. 3, M A R C H 1 9 4 8 The contents of the flasks were heated until the chromium was completely oxidized to the hexavalent state, after which the solutions were allowed t,o cool. I n analyzing each sample, the solution containing the volatilized chromium was combined with the main part of the chromium and the mixture boiled 20 minutes to expel any chlorine. After cooling, the chromium was determined by adding excess ferrous sulfate and back-titrating with tetrasulfatoceric acid, using 1 to 2 drops of ferroin as indicator. The results of a series of determinations by this method are shown in Table 111.
235 ACKNOWLEDGMENTS
The a u t h o p wish t o express their appreciation t o J. C . Warf and E. J. Fornefeld for valuable suggestions from time t o time during this investigation. LITERATURE CITED
Jarvinen, K. K., Z . anal. Chem., 75, 1-16 (1928). Kolthoff, I. M., and Sandell, E. B., IND. ENQ.CHEM.,ANAL.ED., 2, 140-5 (1930).
Lichtin, J. J.,Ibid.,2, 126-7 (1930). Penny, F., Chem. Gaz., 8,330 (1850). Schiffer, E., and Klinper, P., Arch. Eismhiittenw., 4, 7-15 (1930-
APPLICATIONS
The procedures described above have been used t o advantage i n the analysis of thorium-chromium alloys. Separate samples are used for the thorium and chromium determinations. Determination of Thorium. A sample, containing 200 to 300 rng. of thorium, is weighed into a beaker and dissolved in 10 to 15 ml. of concentrated nitric acid and 5 to 10 drops of the fluosilicic acid solution. The mixture is heated to effect complete solution and then transferred t o the round-bottomed reaction flask. Thirty t o 35 ml. of perchloric acid are added t o the solution and the analysis is completed as described above. Determination of Chromium. A sample, containing 70 t o 75 mg. of chromium, is weighed into a beaker and dissolved in 10 t o 15 ml. of concentrated nitric acid and 5 to 10 drops of the fluosilicic acid solution. The mixture is heated to effect complete solution and then transferred to the Erlenmeyer reaction flask. Twenty to 25 ml. of perchloric acid are added t o the solution and the analysis is completed as described above.
31).
Schuldiner, S., and Clardy, F. B., IND. ENG.CHEM.,ANAL.ED., 18,728-9 (1946).
Schwartz, R., and Giese, H., 2.nnorg. aZ2~em.Chem., 176, 20932 (1928).
Scott, W. W., "Standard Methods of Chemical Analysis," 5th ed., Vol. I , p. 296, New York, D. Van Nostrand Co., 1939 Ibid., p. 953. Sell, TV. J.. Chem. 'Vews, 54,299-300 (1886). Storey. F. H.. Proc. Am. Acad. Arts Sci., 4, 338-49 (1859). Willard, H. H., and Gibson. R. C., IND.ENG.C H E M ,ANAL. Ed., 3, 88-93 (1931). KLCEIVEO July 25, L947. Paper 18, lnstitute for Atomic Research. This document is based on work performed under Contract No. W-7405 eng-82 for the M a n h a t t a n Project a n d the information covered therein will appear in Division VI11 of t h e M a n h a t t a n Project Technical Series a s p a r t of t h e contribution of Iowa State College.
Determination of Carboxylic Acid Salts SIDNEY SIGGIA ILVD MADGE MAISCH General Aniline & F i l m Corporation, Easton, P a . The method for determining sodium acetate by igniting to the carbonate and titrating the carbonate has been extended to include other sodium salts as well as Dotassium, calcium, and barium carboxylic acid salts. The procedure is reproducible to * 0 . 5 ~ ~ .
THE
rnet,hod previously used to determine carbosylic acid salts was to liberate the acid by adding sulfuric or phosphoric acid ( I , 3 ) and distill the free acid into standard alkali. A method recently +vised by Palit ( 2 ) enables some salts to be titrated directly with acid. The method employs special solvents to accentuate the end point. However, Palit's method is not general for carboxylic acid salts, since usually only potassium and sodium salts are basic enough to be titrated, and some of these give poor end points. Salts of the alkaline earth metals ark generally insoluble in the solvent niistures used, and those which are soluble arp too weakly basic to give good end points. Ignition to sodium carbonate has been used (1, 3) for determining sodium acetate, but no other salts w r e tried, probably because of the difficulties involved in preparing pure samples. This method has now been extended and found to be applicable to a great variety of carbosylic salts, including salts of sodium, potassium, barium, and calcium. During the experimental work for t,his paper, no carbosylic salt was found xhich could not be determined by this method. Only potassium acetate gave difficulty. All indications point to the fact that potassium acet,ate can be deterniined by this method; however, it is so deliquescent that no representative sample can be obtained. This salt takes 011 water so rapidlv that accurate n-eighings cannot be made. PROCEDURE
A samplc containing about 0.010 equivalent of carbosylic acid salt is weighed into a platinum crucible and ignited to a red heat with a Rleker-type burner till no particles of carbon are visible. A muffle furnace a t 1200' to 1300" F . is more efficient than the burner; however, it is best to char the sample with a burner
before putting it in the furnace, since some samples sputter on heating, and others melt and creep badly. The contents of the crucible after ignition should be white or slightly gray. The crucible is allowed to cool and than dropped into a 250-ml. beaker containing 50 ml. of standard 0.5 1\' sulfuric acid. The beaker
Table I.
Determination of Carboxylic Acid Salts
Sodium acetate" Sodium benzoate" Sodium citrate5 Sodium succinateb Sodium caprylatec Sodium palmitatec Sodiumlaurate C Sodium caprate C Sodium potassium tartrate0 Potassium succinateb Potassium acid phthalate" Calcium acetaten Calcium gluconates Calcium citratea Calcium stearatea Barium acetate"
Experimental Mole 0,01285 0,00996 0,00995 0.01009 0.00367 0.00323 0.00638 0.00601 0.00449 0,00544 0,00486 0.00742 0.00994 0,00530 0.00988 0,00724 0.00385 0.00289 0.00179 0,00216 0.01038 0.00878 0.00713
Barium tartrated a Purchased C.P. chemical*. b Prenarrd bv precipitation from methanol.
Theoretical Mole 0.01286 0.00994 0,00993 0.01007 0.00365 0.00323 0.00642 0,00598 0,00449 0.00543 0.00491 0.00745 0.00993 0.00528 0,00987 0.00723 0.00383 0.00290 0.00180 0.00217 0,00879 0.01036 0.00716
Recovery
% 99.9 100.2 100.4 100.2 100.4 100.0 99.4 100.5 100.0 100.2 99.0 99.6 100.1 100.4 99.9 100.2 100.5 99.7 99.4 99.5 100.2 99.9 99.6
Alcoholic hydroxide added
?air
UTLBU.
de to aqueous solution of
tartaric acid.
__-
