INDUSTRIAL AND ENGINEERING CHEMISTRY
48
Vol. 13, No. 1
Loss of precipitate due to solubility was prevented by using a decanted portion of the mother liquor in transferring the precipitate to the Gooch crucible and by washing with minimum amounts of petroleum ether containing 3 parts of the fractionated pyridine per 100 ml. of petroleum ether (boiling point 30" to 60" C.). Heating the precipitate in an air oven to constant weight a t 110" C. drove off all the pyridine. The nitrogen content of the heated residue showed it to be dianilinogossypol (6).
and 33.0 X 81.3 X 20.3 cm. (13 X 32 X 8 inches), respectively. The bath was lined with 28.35-gram (16-ounce) soft sheet copper and was surrounded with a layer of plywood (Celotex) made from 24.1 X 19.1 cm. (9.5 X 0.75 inch) boards. Two heating units made from No. 25 Chromel A wire were drawn through two 2.54-cm. (1-inch) copper pipes lined with asbestos paper except at the top surface. They were placed 1.27 cm. (0.5 inch) from the bottom of the bath, running lengthwise through it. The Chromel A wire was 43.7 and 38.1 cm. (17.2 and 15 feet) long, having 25.3 and 30.5 ohms resistance, giving 3.16 and 3.65 amperes with a wattage of 347 and 402, respectively.
Need for Constant Temperature and Agitation Considerable difficulty was encountered in obtaining complete precipitation of the last 1 to 3 mg. of gossypol. In order to expedite and complete the precipitation, constant agitation with increased temperature was found necessary. The production of fair-sized crystals and the most complete precipitation of gossypol occurred with moderate shaking a t 43" to 46" C. The crystals of precipitated gossypol should be large enough so that they will not pass through the Gooch crucible or clog i t while filtering. Too quick precipitation of the gossypol compound results in small crystals, and too vigorous shaking causes a fine precipitate to form rapidly. If the solution is not sufficiently agitated, the gossypol precipitation may not be complete in 72 hours. When shaken 48 hours, 97 to 98 per cent of the gossypol was recovered. An additional 24 hours of shaking was necessary for a more complete precipitation. Precipitation also requires proper control of the temperature. Agitation was accomplished in a constant-temperature water bath suspended by 20.3-cm. (8-inch) arms from center to center from a wood frame by bearings. The bath holding 10 Erlenmeyer flasks is moved back and forth with a stroke of 1.27 cm. (0.5 inch), approximately 120 revolutions per minute, by means of an electric motor with the proper reducing gears (Eimer and Amend, ball mill, No. 21,481/1) and with an offset of 0.64 cm. (0.25 inch) off center for the connecting arm on the reducing gear to the water bath. The water bath had the following outside and inside dimensions: 40.6 X 87.7 X 24.1 cm. (16 X 34.5 X 9.5 inches)
Summary A comparatively rapid method for the estimation of gossypol in crude cottonseed oil is presented. The gossypol was precipitated in a good crystalline condition a t 43" C. by constant agitation for 72 hours. Precipitation was in part expedited by the addition of gossypol in an ether-extracted oil made from cottonseed meats. The crystalline precipitate was readily washed and filtered. The gossypol compound was prevented from adhering to the glass container in which p r e cipitation occurred by the elimination of practically all water. Loss in washing the precipitate was also largely prevented. A rather high recovery of gossypol was obtained with good reproducibility of results. Acknowledgment The authors are indebted to the Buckeye Cotton Oil Company, subsidiary of the Procter & Gamble Company, for the cottonseed oil and the cottonseed meats used in this investigation. Literature Cited (1) Lishkevitch, M., Maslobolno Zhirovoe DeZo, No. 27, 6-8 (1939). (2) Royce, H. D., Oil & Soup, 10, 183-5 (1933). (3) Royce, H. D., and Kibler, M. C., Zbid., 11, 116, 118, 119 (1934). (4) Smith, F. H., IND.ENQ.CHEM.,Anal. Ed., 8, 400 (1936). (5) Smith, F. H., and Halverson, J. O., Ibid., 11, 475 (1939). PUBLISHED with the approval of the Acting Director of the North Carolina Agricultural Experiment Station as No. 116 of the Journal Series.
Rapid Method for Determination of Manganese in Feeds I
J. W. COOK', Agricultural Experiment Station, Pullman, Wash.
M
ETHODS for the determination of manganese have received much attention in the past due to the importance of manganese in both the steel industry and agriculture. Much more interest has been shown in the determination of manganese in biological materials since Wilgus, et al. (10) showed that this element is important in the prevention of perosis in chicks. Most methods that are used for the preparation of a sample previous to the determination of manganese in biological materials involve a lengthy dry-ash procedure which requires a number of steps of manipulation. Also, i t was shown by Bolin ( 2 ) , Davidson (S), and others that the acid-insoluble portion of ash contained appreciable quantities of manganese, but that it could be recovered by a sodium carbonate fusion or by volatilization of silica with hydrofluoric acid. Hundreds of fiamples of feeding materials have been wetashed in this laboratory by the procedure outlined by Gerritz (4, using a nitric acid oxidation followed by a perchloric acid 1 Present addresa, U. S. Department of Agriculture, Food and Drug Administration, Seattle, Wash.
oxidation previous to the determination of calcium and phosphorus. This procedure is rapid and lends itself well to the analysis of feed ingredients and plant materials. It seemed desirable to adapt it to the determination of manganese. Experimental The common methods for the final determination of manganese in minute quantities, as it is found in plant material, involve the oxidation of bivalent manganese to heptavalent manganese by some oxidizing agent stronger than the permanganic ion, such as periodic acid, with a subsequent colorimetric comparison of the permanganic ion. Chlorides interfere with this reaction and are commonly present in rather high concentration, especially in mixed feeds, but the use of perchloric acid readily eliminates this difficulty. The products of decomposition of perchloric acid (8) are chlorine and oxygen. Chlorides are volatilized either as hydrogen chloride or as chlorine after oxidation. Remaining small traces must be eliminated by boiling in the presence of sodium periodate before the color of permanganic acid will develop.
ANALYTICAL EDITION
January 15, 1941
49
good recovery of added manganese, ranging from 90 to 98 per cent when organic matter was present, and 100 per cent recovery when no organic matter was present. Table I1 gives the results of another recovery study and a comparison of the perchloric acid method and the method of the Association of Official Agricultural Chemists (1) The recovery of added manganese was very satisfactory. The average of group 1 0.158 mg. per 4 grams, plus the average of group 3, 0.110 mg. per 4 grams, equals 0.268, which is essentially the same as the average of group 2,0.271. A comparison of groups 3 and 4 shows again that in the absence of organic matter there was no loss of manganese during digestion. A comparison of groups 1 and 5 shows that the A. 0. A. C. method gives materially lower values than the perchloric acid method. This is in line with the report of Bolin (2) and T.~BLEI. RECOVERY O F M.4XGANESE FOLLOWING DIGESTIOX Davidson (3) that in the case of dry-ashing procedure a sodium carbonate fusion or silica volatilization is necessary to WITH PERCHLORIC ACID Weight Standard Manganese recover all the manganese. Smith (9) stated that the A. 0. of Manganese Digestion per 100 h11. A. C. method included all acid-soluble forms of manganese in Samplea Solution Period of Solution Recovery the ash of feeds and that it seemed unlikely that compounds Grams m. Man. Mg. % 0.225 4.000 Sone 15 excluded by this treatment are of nutritional value. However, 0.218 0.225 he presented no data and the question needs investigation. Av. 0 . 2 2 4 It would also be desirable to have data comparing the recovery of manganese using the perchloric acid digestion and a sodium carbonate fusion and a silica volatilization. A\-. 0.4362 90.2 Serious explosions have been known to occur from the use 4.000 25.00 43 0.455 of perchloric acid In the oxidation of organic matter, but the 0.455 0.455 author has experienced no accidents in many hundred perhv. 0.4550 98.3 chloric acid digestions However, great care should be ex4.000 25.00 80 0.455 ercised in varying the procedure materially, especially the 0.450 Av. 0.4525 97.2 use of larger samples without greater nitric acid oxidation and None 25.00 15 0.235 possibly more perchloric acid. If i t is desirable to use much 0.235 Av. 0.2350 100.0 larger samples than indicated, i t probably would be better to None 25.00 Xone 0.235 use a nitric-sulfuric-perchloric oxidation, but this is more 0.236 Av. 0.2360 time-consuming and needs closer attention throughout the a Sample used ior this study was a mixed poultry feed. digestion period. During the digestion with nitric acid alone the solution should be boiled slowly so that it requires 30 to 40 minutes Procedure to evaporate the 40 ml. of nitric acid. I t is possible otherWeigh a suitable quantity of plant or feed material, usually 3 wise to evaporate the nitric acid and not oxidize the material t o 4 grams, and transfer it to a 500-ml. Xjeldahl flask. Add 40 ml. of concentrated nitric acid and boil gently over a gas flame. Avoid heating the flask above the surface of the liquid by placing OF PERCHLORIC ACID METHODWITH TABLE11. COMPAISON it on an asbestos board with a hole approximately 4 cm. in diA. 0. A. C. METHOD FOR MANGANESE ameter. When the sample is nearly dry (avoid burning the samManganese in ple) remove the flask from the heat, add 13 ml. of 60 per cent 4-Gram Group Sample NO. Description perchloric acid, and again boil gently. When the remaining nitric acid and water are driven off there is a vigorous evolution of gas, MU. 1 4 grams of standard feed samplea (digested with 0.152 the solution boils rapidly, and white fumes appear. Just preHNOs iollowed by HClOa) 0.165 vious to the ap earance of white fumes turn down the gas flame 0 160 as low as pos&le, so that it is barely touching the flask, and 0.158 continue the digestion for 10 to 15 minutes; boiling need not be 0,155 0.158 rapid. Remove from the flame, allow to cool for 5 to 10 minutes, AV. 0 . 158 add a few milliliters of water, and filter on an asbestos pad (the as2 0.255 4 grama of standard feed sample + 10 ml. of MnS04 bestos must be digested with potassium permanganate and acid0.246 solution containing approximately 0.1 mg. of manwashed) or on a sintered-glass funnel into a 150-ml. beaker. 0.255 ganese (digested as in group 1) 0.280 Wash with about 50 ml. of water, add 0.3 gram of sodium perio0.275 date, boil for about 2 t o 5 minutes with stirring to avoid bump0.300 ing, and place on a steam bath for about 0.5 hour. Transfer to a 0,288 100-ml. volumetric flask, make up to volume with boiled disAv. 0 . 2 7 1 tilled water, and compare in a colorimeter against a standard 0 110 3 10 ml. of hlnS04 solution + 10 ml. of HClO4 (di0.105 gested as in group 1) solution of potassium permanganate of approximately equal con0.105 centration. A blue filter aids in this color comparison. 0.104 Richards (7’) has shown that when a small amount of manganese is to be determined there should be from 5 to 6 per cent of sulfuric acid in the solution previous to adding periodate to develop permanganic acid color. When this same percentage of perchloric acid was present, however, a t the time of development of color there was considerable fading and sometimes precipitation of manganese dioxide. T o determine the optimum quantity of perchloric acid required, equal amounts of a standard manganese solution were added to 0, 1, 5, 10, and 15 per cent perchloric acid solutions. On adding sodium periodate and heating there was a rapid precipitation of manganese dioxide in the 0 and 1 per cent solutions, some fading in the 5 per cent, but none in the 10 or 15 per cent solutions.
~
Discussion Kahane (6) showed that a wet combustion using a nitricsulfuric-perchloric acid digestion of organic matter gave a loss of chromium and manganese by entrainment in the vapors from the digest. In order to determine whether such a loss was significant in studying animal feeds an experiment was set up, the outline and results of which are shown in Table I. The colorimetric readings in this experiment were made with a photoelectric colorimeter that had been standardized with standard potassium permanganate solutions. There was
4
10 ml. of >Ins04 solution (no digestion with HC104)
5
4 grams of standard feed sample. Manganese determined by A. 0. A. C. method
~~~
0.118 0.118 Av. 0.110 0.115 0.118 0.116 Av. 0.116 0.140
0.138
0.140
0.145 0.138 0.125 Av. 0.137 (1
Mixed poultry feed.
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Vol. 13, No. 1
INDUSTRIAL A N D ENGINEERING CHEMISTRY
sufficiently. If copious nitrogen peroxide fumes are still visible in the flask when the sample is nearly to dryness, as will often be the case when fish meals or oily substances are present, another 15 ml. of nitric acid should be added and the slow digestion continued. Care should be taken to avoid burning or charring the sample. All the perchloric acid should be added at one time. Precautions of Kahane (5) are: (1) Oxidize as much as possible with nitric acid before adding the perchloric acid because it is the easily oxidized material that reacts vigorously with perchloric acid, and (2) always add a n excess of perchloric acid and never boil the solutions too rapidly.
Acknowledgment The author wishes to thank James Maddox, student, for his technical assistance.
Literature Cited (1) Assoc. Official Agr. Chem., J . Assoc. Oficial Agr. Chem., 22, 78-80 (1939). (2) Bolin, D. W., J . A ~ TResearch, . 48, 657-63 (1934). (3) Davidson. Jehiel, J . Assoc. Official AQT.Chem.. 14, 551 (1931). Gerritz, H. W., IND.ENQ.CHEM.,Anal. Ed., 7, 167-8 (1935). (5) Kahane, E., 2.anal. Chen., 111, 14-17 (1937). (6) Kahane, E., and Brand, D., Bull. SOC. china. biol., 16, 710-19 (1934). (7) Richards, M. B., Analyst, 55, 554-60 (1930). (8) Smith, G. F., “Perchloric Acid”, G. F. Smith Chemical Co., 1931.
(4
(9) Smith, J. B., and Dessyck, E. J., J. Assoc. Oficial A g r . Chem., 22, 673 (1939). (10) Wilgus, H. S., Jr., Norris, L. C., and Heuser, G. F., Science, 84, 252-3 (1936). SCIENTIFIC PAPBR474, College of Agriculture and Agricultural Experiment Station, State College of Washington.
Boron Determination in Volatile Organic Compounds Using the Parr Oxygen Bomb WINTHROP M. BURKE, Standard Oil Company of California, Richmond, Calif.
A
REVIEW of the literature regarding the methods for the
determination of boron in organic compounds reveals the fact that some of the methods are either lacking in accuracy or are long and cumbersome. I n foods and fertilizers boron is usually present as boric acid or borax, which are less volatile than the aliphatic boron compounds, and the organic matter may be destroyed by ashing in the presence of a n alkaline substance. This method (2) obviously cannot be applied to organic compounds which volatilize before decomposing or oxidizing. Several attempts have been made to analyze for boron when fluorine is present. Bowlus and Nieuwland (S) analyzed boron fluoride for boron with an average error of about 6 per cent, using the Carius method of decomposition. Pflaum and Wenzke (6)used the Parr fusion bomb with a n oxidizing mixture of sodium peroxide, sugar, and potassium chlorate. The high concentration of alkali caused difficulties in the determination of fluorine, which were overcome by adding ammonium chloride. Then in preparation for the boron determination, more strong sodium hydroxide was used to remove the ammonium ion. Snider, Kuck, and Johnson (6) used the Parr fusion bomb for the determination of boron in boronic acids. They obtained good results, but the fusion bomb has the limitations of a maximum sample of about 0.3 gram and the introduction of larger amounts of reagents; these limitations are not necessary in decomposing aliphatic boron compounds by the oxygen bomb method described below. The digestion with hydrogen peroxide and the subsequent evaporation and fusion with sodium hydroxide are timeconsuming, and still involve the use of large amounts of rea gents.
Improved Oxygen Bomb Method An accurately weighed sample of approximately 1 gram is used in the Parr oxygen bomb according to A. S. T. M. Method D-129-39 ( I ) , with the addition of about 1 gram of sodium carbonate to the water in the bomb. Volatile substances should be weighed in a gelatin capsule. After the oxidation, the alkaline solution containing the boron in the form of sodium borate is evaporated t o about 25-ml. volume, transferred t o a 500-ml. Erlenmeyer flask, and then acidified with 3 N hydrochloric acid
using methyl red indicator and 3- to 5-ml. excess of acid. The solution is boiled for about 20 minutes under R reflux condenser to liberate carbon dioxide, cooled, and brought t o neutrality with carbonate-free sodium hydroxide. Then 0.1 N hydrochloric acid is added until the sample is just pink t o methyl red, and the solution is finally titrated with 0.1 N sodium hydroxide in the presence of mannitol, using phenolphthalein as an indicator. Results are calculated thus: ml. of 0.1 N NaOH required X 0.001082 X 100 % boron = weight of sample According to Hillebrand and Lundell (4) the boric oxide titer of sodium hydroxide is not accurate when calculated directly from the sodium hydroxide content; hence the 0.1 N sodium hydroxide was standardized using pure dry boric oxide. A blank test was run on the reagents used, determining the differences between the methyl red and phenolphthalein TABLE
Weight of Sample
Titration
Gram6
M1.
1.0270 1.0861 1.1719 1.0280
38.04 40.69 43.49 38.29
I. RESULTS OF ANALYSIS
Blank Net Titration Boron M1. Ml. % Amyl Borate (B. P. 122-123O C., 3 Mm. Hg Pressure). NaOH (0.1001 N ) , 1 M1. = 0.001083 Gram of Boron 1.09 1.09 1.09 1.09
3.90 3.91 3.95 3.92 3.92 3.97
36.95 39.60 42.40 37.20
Average Theoretical Amyl Borate (Eastman Practical). NaOH (0,1020N ) , M1 1. Gram of Boron 1.0060 1.0221 1.0230
36.90 37.50 37.40
1.09 0.80 0.80
35.81 36.70 36.60
Average Theoretical
=
0.001103 3.93 3.96 3.95 3.95 3.97
n-Butyl Borate (Eastman White Label). NaOH (0.0994 N ) , 1 M1. = 0.001076 Gram of Boron 52.30 4.65 53.33 1.05 1.2103 1.0321 1.0214 1.0815
45.90 45.38 48.20
1.05 1.05 1.05
44.85 44.33 47.15
Average Theoretical
4.68 4.67 4.69 4.67 4.70
