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ANALYTICAL EDITION
than the combustion method, but the differences are not material. Only three of the fifteen samples gave a higher result by the Andrew method than by the combustion method, and in only two of the samples slightly higher figures were obtained by the Andrew method than by the method of von Fellenberg. From the procedure described in the Andrew method, we would not expect total iodine to be obtained because all of the silicates would not be decomposed by the low heat applied in the fusion procedure. Andrew states that in no case was he able to recover more than 60 to 70 per cent of the total iodine present, and attributes this to losses from overheating. It is possible, however, that the low results obtained by the Andrew method are due in part, at least, to incomplete decomposition of the soil silicates. Andrew further states that as a result of his experimental work it was concluded that there are no practical means of improving the extraction of iodine, but that, if the amount of iodine obtained is increased by onehalf, this quantity is a true indication of the iodine content of the soil. From the results which have been obtained by the three methods the authors do not concur in this opinion. It is true that serious losses may occur from overheating and possibly other unrecognized causes as well in both the Andrew and von Fellenberg methods, but the authors are of the opinion that as much as 95 per cent recovery of the total iodine content of soils is possible by either the von Fellenberg or the combustion method. The principal advantage of the combustion method is that the tedious manipulations of extracting a small quantity of iodine from a relatively large mass of silicate material is obviated. It requires about 2 hours to make a combustion after the furnace has attained the maximum temperature. By having several combustion boats, it is possible to run samples continuously by removing the ignited sample and inserting a fresh portion without allowing the furnace to cool. In this way it is possible to make three combustions per day with a single-tube furnace. Since electric furnaces carrying as many as four tubes are on the market, it is possible to increase the number of determinations per day accordingly.
Vol. 4 , No. 2
To ascertain if iodine was retained by the soil after ignition in the electric furnace, 5-gram portions were finely ground and fused in an iron crucible with potassium hydroxide according to the method of von Fellenberg (d), but no iodine was found, These tests convinced the authors that iodine can be completely volatilized a t 1100” C. from residual soils such as occur in Kentucky. To ascertain if the iodine volatilized was uncombined, a solution of water-soluble starch was placed in the gas wash bottles and a distillation made in the usual way. The starch solution was not colored blue. However, the sensitivity of this test is probably less than the small quantity of iodine which can be determined colorimetrically by the carbon disulfide method. After several trials the authors have discarded the titrimetric method of determining small quantities of iodine and concur in the statement made by Andrew-namely, “One is adding very many times the quantity of the substance for which one is looking and there is always a risk of decomposition of the K I and the liberation of an excess of iodine.” For these reasons results have been obtained by absorbing the iodine in carbon disulfide, centrifuging any occasional turbid solution until clear, and making the comparisons with a freshly prepared iodine standard in a microcobrimeter. With these precautions and by a considerable number of duplications, these determinations represent at least 95 per cent recovery of the total iodine present. The amount of current used in making a determination was about 6 kw-hr. This makes the cost for current in this laboratory about 20 cents a determination.
LITERATURE CITED (1) Andrew, R. L., Analyst, 55 (647), 269 (1930). (2) Fellenberg, von, T.,Biochem. Z.,152, 116 (1924).
RECEIVED April 15, 1931. Presented before the Division of Agricultural and Food Chemistry a t the 80th Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931. Published by permission of the Director, Kentucky Agricultural Experiment Station.
Effect of Temperature on Sulfuric Acid Method for Lignin C. J. PETERSON, A. W. WALDE,AND R. M. HIXON,Iowa State College, Ames, Iowa N A preceding paper ( I ) it was pointed out that the sulfuric acid method for the determination of lignin gave values considerably higher for the cornstalk than did the Willstiitter method. A similar discrepancy for flax and hemp has been reported by Schwalbe and Becker (3). As analytical data for the cornstalk accumulated over a three-year period, it was observed that the lignin values obtained in the summer were consistently higher than the values obtained in the winter. Since this variation was observed in the results of independent workers in spite of every effort at uniformity in the method, it was concluded to be caused by the seasonal variation in temperature. Direct experiment not only proved that the values obtained for lignin by the 72 per cent sulfuric acid method depend upon the temperature a t which the analysis is made, but also revealed the fact that the difficulty of filtration frequently encountered in this analysis is also due to the higher temperatures.
ANALYTICALPROCEDURE The lignocellulose materials were prepared for these analyses by grinding in a Wiley mill fitted with a 60-mesh screen. After the grinding, the wood samples were dried in a vacuum oven at 60’ C. and then extracted with alcoholbenzene mixture to remove the resins and waxes. The alcohol-benzene extraction was omitted in the case of the cornstalk materials and pulps, since these materials contain very little extractable matter. Two-gram samples were taken for analysis. The determination was carried out as reported by Schorger (d), except that instead of standing a t room temperatures the samples were placed in compartments a t controlled temperatures. The sulfuric acid was 72.6 per cent by analysis. The samples were weighed out and placed in 150-cc. beakers within a desiccator placed in the compartment a t the desired temperature. When the samples and the acid had come to the proper temperature, 30 cc. of the acid were slowly poured
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April 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
into the beakers containing the samples and the contents stirred until uniform. The samples were t,hen left, with occasional stirring, at the constant temperature for 18 hours. At the expiration of 18 hours, the samples were removed from the constant-temperature apparatus, made up to 1200 cc. with water, and gently boiled for 2 hours. After the flocculent precipitate had settled, the material was filtered through a prepared Gooch crucible, washed with hot water until free of sulfates, dried at 106" C., cooled, and weighed. The carbonaceous matter was burned in a muffle furnace, and the crucibles cooled and weighed again. The loss in weight was taken as lignin.
Temperature, *C.
FIGURE1. EFFECTOF TEMPERATURE ON PER CENT OF LIGNINAS DETERMINED BY SULFURIC ACIDMETHOD The lignin in several lignocelluloses was determined by this procedure a t temperatures of 30", 15" C., and at an "ice box temperature" which was practically constant a t 4" C. The lignin values were also obtained by the Willstatter hydrochloric acid method in order to have values representative of different methods of lignin determination. The results are reported in Table I and shown graphically in Figure 1. All results are reported on the dry basis.
2 17
ture for the hydrolysis of the carbohydrate material should be kept at least below 15" and preferably at about 4" C., or the temperature obtainable in an ordinary ice box. The effect of temperature upon the character of the lignin residue is indicated by the fact that at 4" and 15" C. a residue is obtained which is comparatively easy to filter and is of a light brown color. The residue obtained at 30" C. is black in color and of such fine semi-colloidal nature that filtration is very difficult. A possible explanation for the increase in lignin value with increase in temperature is the increased carbonization of the hydrolyzed carbohydrates at the higher temperatures. If this were the case, the variation in lignin values of those materials low in lignin should be more pronounced than the variation in those lignocelluloses high in lignin, as there would be a larger percentage of carbohydrate material hydrolyzed in comparison to the amount of lignin present. An examination of the data shows this to be the case. With the cornstalk pulp containing very little lignin, the increase is some 1280 per cent, whereas with a cornstalk pulp of high lignin value, the increase is 100 per cent, and with the original lignocelluloses the increase is from 44.5 with aspen wood to 30.0 per cent with cornstalks. This conclusion is also supported by the data in Table I1 showing the increased percentage of carbon found in the lignin obtained by treating the cornstalk at 30" C. as compared to similar lignin prepared a t 4" C. It should be noted that there was no appreciable difference in the percentage of sulfur in the lignin, a fact which eliminates the possibility of the difference being due to sulfonation of the lignin. TABLE11. CARBON, HYDROGEN, AND SULFUR ANALYSISON LIGNIN (Obtained from cornstalk at various temperatures by 72% sulfuric acid method) T ~ M POF. LIQNIN PREPARATION CARBON HYDROQEN SULFUR
c. 30 30 4 4
%
%
%
62.2 62.1 61.4 61.3
4.94 6.33 5.82 5.77
0.31 0.78 0.04 Trace
Laboratory temperatures will vary from 18" to 40" C. in this vicinity according to season. The data presented clearly show that the 7 2 per cent sulfuric acid method for TABLEI. COMPARISON OF LIQNINVALUESOBTAINEDBY 72 lignin would have little significance if carried out a t such PER CENTSULFURIC ACID METHODAT VARIOUSTEMPERA- varied "room temperatures." In standardizing a temTURES AND BY WILLSTATTER HCl METHOD perature for the determination, one conveniently attained MOIS- 72% SULFURIC ACIDMETHODWILLST~TTER MATERIAL TURE At 30° C. At 15' C. At 4O C. HC1 METHOD in any laboratory should be selected, although the data Spruce wood 2.5 31.40 28.35 28.05 27.70 indicate little change in results between 4" and 15" C. The Aspen wood 5.2 29.55 21.50 20.45 20.00 temperature of the ice box suggests itself as the most conTotal cornstalk 7.9 30.80 24.00 23.70 22.80 Cornstalk pulp; NaOH venient practical solution of the problem. The procedures process 15.70 7.60 7.70 7.50 Cornstalk pulp: NaOH as described in the literature (2) would need no change, except proress 8.30 0.60 that the sample and reagent should be cooled to these temCornstalk. outer shell 7.6 33.50" 25.20 25.40 Cornstalk, vascular peratures before mixing and then kept at this temperature bundles 8.0 35.20a 22.50 22.00 Cornstalk pith 8.3 32.00a 16.50 15.90 in a closed container for the prescribed 18 hours for hydrolysis Cornstalk pith meof the carbohydrates. chanically separated 8.4 28.01a 19.72 19.60
5 Made at room temperatures during summer months before significance of temperature was noted. Although no record of laboratory temperature is available, it may be stated as between 30° and 37O C.
DISCUSSION OF RESULTS The data in Table I indicate that the temperature has a very great effect upon the values obtained for lignin in lignocelluloses when determined by the 7 2 per cent sulfuric acid method. I n the case of cornstalks, the variation is from 23.7 per cent a t 4" C. to 30.8 per cent at 30" C. The variahion in the case of the spruce wood is not so great, but with aspen there is a variation from 20.45 to 29.55 per cent. This would indicate that in the use of the 72 per cent sulfuric acid method for the determination of lignin, the tempera-
LITERATURE CITED (1) Peterson and Hixon, IND. ENQ.CHEM., Anal. Ed., 1, 65 (1929). (2) Schorger, "Chemistry of Cellulose and Wood," p. 524, McGrawHill, 1926. (3) Schwalbe and Becker, 2. angew. Chem., 32, 126 (1919). RECEIVBD November 9, 1931.
To INCREASE ALCOHOLCONSUMPTION, the Italian Government has decreed that importers of gasoline securelocally 428 liters of waterfree spirits for each hundred uintals (3170 gallons), and mix these so that a certain portion of %e finished product will comprise 20 per cent alcohol and 80 per cent benzine.
