ANALYTICAL EDITION
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(10) Lockemann, G., Chem.-Ztg.,50,701-2 (1926). (11) Noyes, A. A., and Bray, W. C., “Qualitative Analysis of the Rarer Elements,” p. 285, Macmillan Co., N. Y., 1927. (12) Remington, R. E., J . Am. Chem. SOC.,49, 1410 (1927). (13) Sanger, C. F., and Black, 0. F., J. SOC.Chem. Ind., 26, 153-67 (1907). (14) Ibid., 26, 1118-23 (1907). (15) Snnger, C. F., and Black, 0. F., Proc. Am. Acad. Arts Sci., 43, 327-40 (1907); J. SOC.Chem. Ind., 26, 1123-7 (1907).
(16) (17) (18)
Vol. 6, No. 5
Satterlee, H. S., “The Arsenical Content of City Dust, with Some Observations on the Biological Significance of Arsenic,” not yet published. Thorpe, T. E., J. Chem. Soc., Proc., 19, 183 (1903). U. S. Pharmacopeia X, p. 428 (1925).
RECEIVED January 31, 1934. The expense8 of thiB research have been in part defrayed by a private grant “In memory of G. P. C.,” for which grateful acknowledgment is hereby made. ’
Sulfur Determination in Sulfite Waste Liquor and Organic Compounds Potassium Perma.nganate Method R. N. POLLOCK, Rainier Paper and Pulp Company, Shelton, Wash.,
AND
A. M. PARTANSKY, University
of Washington, Seattle, Wash.
T
HE usual determination of total sulfur in a sample re-
solves itself into two parts: oxidation of sulfur to sulfate, and determination of the sulfate. For the second part there are a standard method of precipitation with barium chloride and several volumetric methods, but the first step has always presented difficulties to the analytical chemist. Benson and Benson‘ used five different methods (Schreiber’s, Schorger’s, fuming nitric acid and potassium chlorate, bromine, and the U. S. Forest Products Laboratory method) for determination of total sulfur content of sulfite liquor, but report considerable difficulty in obtaining check results. The authors had a similar experience with the above methods as well as with the Eschka method and obtained consistently good results only with Parr’s sodium peroxide bomb method. Since the bomb is not always available, the following method, which can be used in any modestly equipped laboratory, was developed. METHOD A sample containing enough sulfur to give a barium sulfate precipitate of about 0.15 gram is placed in a porcelain crucible of 25-ml. ca acity or larger, 0.5 ml. of concentrated sodium hydroxide sorution and 5 ml. of saturated potassium permanganate solution (about 1 gram of potassium permanganate) are added, and the contents of the crucible thoroughly mixed with a little stirring rod. The rod is then removed, care being taken to wash off the adhering mixture into the crucible. After evaporation to dryness on a water bath or in a drying oven the crucible is ignited for half an hour in a muffle furnace or on a Meeker burner a t approximately 500’ C. A thorough ignition is essential; otherwise low results were invariably obtained. The cooled melt is moistened with a little dilute permanganate solution to oxidize any sulfides which may have formed, and hydrochloric acid is then carefully added, care being taken t o prevent loss by effervescence. After evolution of the carbon dioxide has ceased, more hydrochloric acid (total of about 5 ml. of 12 N acid or an equivalent amount of dilute acid) is added and the crucible warmed over a steam bath until all manganese dioxide has been converted into soluble manganous chloride. Hot water is then added and the contents of the crucible are filtered through a rapid filter into the precipitating beaker. (Alkali permanganate attacks porcelain crucibles; the amount of silica extracted increases with use of the crucible. On the average, porcelain crucibles can be used only six to eight times, after which results become irregular.) Washing the crucible and the filter is continued until from 200 to 300 ml. of hot water have been used. From this point on analysis proceeds in the usual way: dilution to 400 ml., adjusting the acidity,.precipitation with barium chloride, digestion, filtration, ignition, and weighing. 1 Benson, H. K., and Benson, W. R., IND. ENG. CHEM.,Anal. Ed., 4, 220 (1932).
The permanganate method here described has been successfully used by the authors in determination of total sulfur in sulfite waste liquor for a considerable length of time, checks within 0.1 per cent being common, but, as shown by Table 11, the method can be used for determination of sulfur in other organic compounds, regardless of its state of oxidation or chemical bonds. TABLEI. SULFUR CONTENT OF SULFITE WASTELIQUOR SULFITELIQUOR SAMPLE 1
2 3
BY PERMANGANATE BY PARR’S METHOD BOMBMETHOD Mg./ml. Mg./ml. 8.67 8.57 8.83 8.80 8.77 .. 8.45 8.27 8.47 8.32 8.60 8.37 8.22
..
..
TABLE11. DETERMINATION OF SULFURIN PURE ORGANIC COMPOUNDS BY PERMANOANATE BY PARR’SBOMB THEORETICAL METHOD METHOD PERCENTAQE Weight of Weight of COMPOUND OF SULFUR sample Sulfur sample Sulfur Gram % Gram % ,... ... Sulfanilic 18.52 0.1849 18.36 acid 0.19013 18.48 .... 0.2300 18.45 .... Trional 26.47 0,0809 26.35 0.0855 26:25 0.0995 20.30 0.0898 26.24 0.1702 26.20 Thiourea 42.13 0.0616 4i:i)2 0.0740 41.94 ... 0.0700 42.13 ...
...
....
.... ....
...
....
TABLE111. EFFECTOF PRESENCE OF MANGANOUS CHLORIDE ON BARIUM SULFATEPRECIPITATE Manganous chloride present (KMn04 equivalent)
None Gram
1 gram Gram
2 grams Gram
DI~CUSSION Table I gives a typical set of checks obtained in sulfur determination of three samples of sulfite waste liquor by the alkali permangante method and a comparison of one set with results obtained by Parr’s method. In the determination by the permanganate method, 2-ml. samples of the liquor were used, while in the determination by bomb method 25 ml. of the liquor were neutralized and evaporated to dryness,
September 15,1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
and the weight of the solids was determined. The solids were then ground and samples weighed out, the sulfur content was determined, and the results obtained were recalculated on the volume basis. The slight difference in the results may be due to the difference in methods of taking samples. Table I1gives results of sulfur determination on pure sulfurcontaining substances. The values obtained are in sufficiently close agreement with the theoretical. Table I11 gives results of precipitating sulfates from 10 ml. of known sodium sulfate solution in the presence of various amounts of manganous chloride. It shows that an amount equivalent to 1 gram of potassium permanganate (the amount used in the authors’ procedure) has no effect, and twice that amount gives a variation of only 6 parts in 2000. The chief advantages of the permanganate method are: It is simple; no special apparatus is required; there is nothing to regulate or watch; and only small quantities of very common inexpensive reagents are used. The method can be used for oxidation of sulfur compounds in water solutions (like sulfite waste liquor) without preliminary evaporation to dryness. The oxidation is rapid and complete in cases tried and the re-
331
sults agree closely with either those obtained by the peroxide bomb or with the theoretical percentages as shown by Tables I and 11. Compounds which will float on the surface of the alkaline permanganate solution cannot be completely oxidized, owing to loss by evaporation or sublimation. The two filtrations in the procedure are time-consuming. However, if crucibles were made of a material which is resistant to both alkali permanganate and hydrochloric acid, such as acid-resistant alloys, the first filtration would be eliminated and the time necessary for the determination cut to two-thirds of that required a t present. The authors did not have such crucibles a t hand. ACKNOWLEDGMENT The authors wish to express their appreciation to H. K . Benson of the University of Washington for his encouragement and advice in the development of this method, as well as in the preparation of this manuscript. Acknowledgment is also made to the National Research Council for its Grantin-Aid whereby this study was made possible. RECEIVSID Maroh 13. 1934.
Colorimetric Determination of Iodine by the Starch-Iodine Reaction HELENQUINCYWOODARD, Huntington Fund for Cancer Research, Memorial Hospital, New York, N. Y. HE use of the starch-iodine reaction for the quantita-
T
tive determination of iodine has been considered by von Fellenberg (S), Remington et al. (79, and others to be unsatisfactory, and the method has seldom been used, although Turner (IO) employs it over a limited concentration range. Examination of the literature of starch-iodihe suggests a number of possible sources of error in the use of its formation for the determination of iodine. While Dhar (2) considers that a true but unstable compound between starch and iodine is formed, most authors agree that the union of starch and iodine is by adsorption. Gorbatscheff and Winogradowa (6) claim that molecular iodine is adsorbed. Angelescu and Mirescu ( I ) , Firth and Watson ( d ) , and others consider that the blue color is due to the adsorption of potassium triiodide by starch, while Gramenitski (6) and Staiger (8) present evidence to show that hydriodic acid is the substance adsorbed. It was early pointed out by Treadwell (9) that the starch-iodine compound is readily dissociated a t low concentrations. The present investigation was undertaken in order to develop a rapid method of determining iodine in the presence of 10 per cent of potassium iodide. A study was made of the influence of potassium iodide, acids, and salts on the intensity of the starch-iodine color, and the degree of dissociation of the compound was estimated under a number of different conditions.
‘
METBOD. The method has been described in detail in a previous publication (11). A stock solution of approximately 0.025 per cent iodine in approximately 0.2 per cent potassium iodide was prepared and standardized by titration against sodium thiosulfate. Portions of this were then diluted with starch and potassium iodide solution in 10- or 25-cc. volumetric flasks as required, and read in the colorimeter. For art of the work a solution of iodine in 25 per cent ethyl alcohofinstead of 0.2 per cent potassium iodide was used. The stock starch solution was prepared by making a paste of 2 grams of soluble starch with 30 cc. of cold water, adding this slowly t o 70 cc. of boilin water, and boiling for 5 minutes. The solution was made f r e k every
3 or 4 days. The colorimeter used was a Klett instrument having cups and plungers with black walls, and substage illumination through blue glass.
RESULTS The effect of potassium iodide on the intensity of the starchiodine color was studied by adding small quantities of potassium iodide to solutions containing 2.5 per cent alcohol, 0.5 per cent starch, and 1.8 and 5.0 mg. of iodine per 100 cc. It was found that the intensity of color increased rapidly with increasing potassium iodide concentration until the normality ratio of potassium iodide to iodine reached 0.35. This ratio must therefore be equaled or exceeded whenever iodine is to be determined by the starch-iodine reaction. Further additions of potassium iodide caused a slight increase in color intensity until a t 1 per cent concentration it became purplish. The color became progressively redder and fainter with increasing concentration of potassium iodide beyond this point. I n general it was found that differences in concentration insufficient to change the tint of the starch-iodine color caused no significant change in the intensity of the color, and could be disregarded in analytical work. It is probable that addition of small quantities of potassium iodide to the alcoholic starchiodine solution increases the intensity of color through the formation of potassium triiodide, which gives the characteristic deep blue compound with starch. Further additions of potassium iodide after all the iodine has been converted to potassium triiodide may then change the tint and intensity of the color by changing the colloidal state of the compound. Starch-iodine solutions containing sufficient potassium iodide to be definitely reddish do not obey Beer’s law with some types of illumination. The deviation is small when the blue filter a t present provided with the Klett biocolorimeter is used. In the preparation of the correction curves (Figure 1) the colorimeter plunger was set always a t the same depth in the standard solution. The same standard setting was then used for making readings on unknown solutions which were
