A N A. L Y T I C A L E D I T I O N
214
K
0.02 for brines containing CaC& = 25 to 50% of sodium chloride content = 0.01 for brines containing CaCly = 10 to 20% of sodium chloride content = 0.00 for brines containing CaCla = less than 10% of sodium chloride content =
To illustrate the application of this formula and method of calculation, the following examples, with data taken from Table VI, column 1, are given (slide rule used for all calculations) :
+
+
TS = R 0.577 X MgClz K X CaCl2 Total solids by ignition (750' (2.).. . . . . . . = R = 21.62 0.577 X 2.17.. ..................... 1.252 0.198 0.02 x 9.90........................ Total solids calculated. . . . . . . . . . . . . . . . 23.07 Total solids by summation of analytical data. ............................ 23.02
Vol. 4, No. 2
Error = 23.02 -23.07 0.21% 23.02 loo= Total solids at 150" C. (assuming no decomposition) = 23.24 = Error = 23.02 -23 24 0.95% 23.02 Total solids at 105" C. (assuming no decomposition) = 25.60 23.02 -25.60 = Error = 11.6% 23.02 LITERATURE CITED (1) E f r e m o v , J.Russian Phys.-Chem. SOC.,51,399-416 (1919). (2) Mellor, "A Comprehensive Treatise on Inorganic a n d Theoretical Chemistry," Vol. 111,p. 699, Longmans, 1923. (3) Mellor, Ibid., Vol. I V , p. 23. (4) Phalen, U. S. Geol. Survey, Bull. 669, 212 (1917). (5) Sweeney a n d Withrow, J. IND. ENG.CHEM.,9, 671 (1917).
RECEIVED March 23, 1931. Presented before the Division of Industrial and Engineering Chemistry a t the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931.
Determination of Iodine in Soils A New Method J. S. MCHARGUE, D. W. YOUNG,AND W. R. ROY,Kentucky Agricultural Experiment Station, Lexington, K y . during the burning. It can be demonstrated that most limestones contain iodine, as tests for its presence can be obtained by leaching 1000 grams of finely pulverized stone with distilled water, evaporating the filtrate to dryness, extracting the residue with alcohol, evaporating the alcoholic extract to dryness, and testing this residue for iodine by the carbon disulfide method. Apparently the iodine compound is volatilized when the stone is heated intensely, and should be recoverable from the gaseous products. Accordingly, an electric combustion-tube furnace was obtained for the purpose of burning as much as 100 grams of limestone or soil in a partially closed combustion tube and aspirating the volatile matter through a 5 per cent solution of potassium carbonate contained in a series of wash bottles. Figure 1shows the apparatus ready for use: 1 is an electric combustion-tube furnace having a 50-mm. hole through the center; 2, a quartz combustion tube, inside diameter 40 mm., EXPERIMENTAL PROCEDURE outside diameter 50 mm.; 3, a sillimanite combustion boat, Tests made on the water extract from 100 grams of burned 250 by 32 by 20 mm.; 4, a rheostat; and 5, gas wash bottles lime showed that no iodine was present. This fact led containing a 5 per cent solution of potasslum carbonate. to the inference that the limestone from which the lime was Three bottles are used. The combustion tube is inserted in burned either did not contain iodine or it had been volatilized the hole in the furnace. From 25 to 100 grams of soil or small pieces of rock are weighed into the combustion boat. The amount of material depends on whether the iodine content is high or low. Some limestone contains enough iodine to permit a determination to be m a d e on 25 g r a m s b y t h i s m e t h o d . ........................................................... Other rather pure limestone requires 100 grams, whereas sandstone rocks require 100 grams of material, and soils 25 to 50 grams. The small end of the quartz combustion tube is connected with three gas wash bottles. The large end of the tube is loosely stoppered by inserting an alundum crucible of the proper size. The wash bottles are connected by means of rubber tubing. A rubber stopper on the end of a bent glass tube connects the small end of the c o m b u s t i o n tube with the first wash FIGURE1. FURNACE READYFOR USE bottle. The last wash bottle is attached to a
S
INCE iodine occurs in very minute quantities in nature, an accurate method for its determination in rocks and soils is highly desirable because no iodine survey is complete without a fairly definite knowledge of the amount of iodine contained in the rocks and soils of the region studied. One of the principal difficulties encountered in an investigation to ascertain whether or not any region of country is adequately supplied with iodine has been the lack of a satisfactory method for the determination of the element in rocks and soils, which, after all, are the principal sources of iodine for plants and animals on land. The methods used heretofore for the determination of iodine in rocks and soils have consisted in fusing a relatively small quantity of either of these materials with potassium hydroxide or the extraction with dilute acids. The methods are tedious, cumbersome, and probably subject to considerable errors.
April 15, 1932
I N D,U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y TABLEI.
LABORATORY SOILNo. 98103-Mercer
Co., Ky.
98110-Mercer
Co., Ky.
98190-Mercer
Co., Ky.
98282-Nercer
Co., Ky.
98284-Mercer
Co., Ky.
98285-Xercer
Co., Ky.
98286-Mercer
Co., Ky.
RESULTS O F
DETERMINATION OF IODINE
VONFELLEN-Cow AXDREW'S BERQ'S BUSTIOX METHOD METHOD METHOD P.p. b. P.p . b. P.p . b. 3060 4020 3730 3800 3800 4050 4150 4000 4115 Av. 3620 4083 3765 5000 5700 5640 4819 5640 5800 4734 5580 5400 5613 Av. 4851 5640 3500 4200 4000 3500 4230 4000 3340 4120 4010 4146 Av. 3447 4040 3840 5500 5600 3630 6100 5400 3200 6000 5400 Av. 3556 5466 5866 3500 3320 3390 3545 2950 3590 4760 3522 3135 Av. 3913 8000 7100 8000 7300 8100 8150 7300 8120 7320 Av. 7255 8073 8076 5600 8350 8500 5750 8050 8000 5950 8550 6240 8560 6450 6360 Av. 6058 8377 8250
suction pump which draws air through the apparatus during the combustion. A rheostat controls the rate of heating the furnace. About 2 hours are required to bring the furnace to the maximum temperature of 1100" C., and the sample is heated for about 2 hours after the furnace reaches the maximum temperature. The current is then disconnected and the furnace allowed to cool. The solution in the wash bottles is rinsed into a porcelain dish and evaporated to dryness. The residue is dissolved in a few cubic centimeters of hot water and filtered into a small porcelain dish, evaporated to dryness again, and ignited gently to destroy the small amount of organic matter usually present. When cool, the residue is dissolved in a few drops of hot water, filtered into a separatory funnel, and pure 95 per cent ethyl alcohol is added until a layer stands on top of the aqueous solution. After being shaken vigorously for about 2 minutes, the two layers of solution are allowed to separate, the aqueous layer is run into an empty separatory funnel, and the extraction repeated twice. The residue from evaporating the alcoholic solution to dryness is dissolved in a few drops of water and transferred to a small separatory funnel, a few drops of sulfurous acid are added, and the funnel is stoppered and shaken. Then 1 cc. of carbon disulfide and approximately 1 cc. each of 1 to 1 sulfuric acid and 10 per cent sodium nitrite solution are added, and the funnel is shaken vigorously for about 2 minutes. If the carbon disulfide is colored pink it is allowed to stand awhile, after which a portion is compared in a rnicrocolorimeter with an iodine standard treated in the same way. The iodine content is calcula,ted to parts per billion, or milligrams per kilogram. To ascertain the accuracy of the combustion method in comparison with the methods of Andrew ( 1 ) and von Fellenberg @),a considerable number of duplicate determinations were made on several different soils by each of these methods. The results are contained in Table I. The Andrew method consists in heating gently in a nickel dish 1 gram of soil to which 1 cc. of a saturated solution of potassium carbonate has been added, until all of the water is expelled and the organic matter contained in the soil has
IN SOILS BY
THREEMETHODS
LABORATORY SOILNo. 98288-Mercer
Co., Ky.
98293-Mercer
Co., Ky.
98296-Mercer New Jersey
Co., Ky.
215
South Carolina Canada
VON FELLEN-COMANDREW'S BERQ'S BUSTION METHOD METHOD METHOD P. p . b. P. p. b. P. p. b. 4500 4530 5600 5600 5455 4500 5660 5295 4760 5750 Av. 4587 5610 5450 4560 5250 5300 4700 5355 5050 4750 5560 5400 Av. 4670 5388 5250 3500 3600 3480 7800 7000 6766 7000 7200 6823 6950 7160 7000 Av. 7250 7120 6863 2515 3200 3120 3000 3200 Av. 2757 3120 2240 2000 2700 2100 2300 2790 2700 2136 2895 2800 Av. 2079 2510 2795
J. Stoll's farm, Fayette County, KY.
0000 0000 0000
0000 Trace 0000
Blank 200 110 103
..
2610
2400
6060 4958 5190 5069
4820 4900 4700 4806
Av.
T. B. Beard, Farm No. 3, Breckenridge Co., Ky. Hardinsburg, No. 1,Breckenridge Co., Ky.
4100 4310 4015 Av. 4141
been destroyed. After cooling, the residue is digested in hot water, the solution is boiled and filtered, and the insoluble residue washed twice. The filtrate is evaporated to dryness and ignited gently, and the residue is cooled and extracted with 90 per cent alcohol. The alcoholic extract is evaporated to dryness, the residue taken up in a few drops of water, transferred to a separatory funnel, iodine is liberated in the usual way and absorbed in chloroform, and the color compared with an iodine standard treated in a like manner. The von Fellenberg method consists in adding 6 grams of potassium hydroxide and a little water to 2 grams of finely pulverized soil in an iron crucible and heating cautiously until the water has been expelled and the silicates are completely decomposed by fusion. The fused mass is slaked with enough water to form a sludge of the alkaline silicates. A small quantity of a saturated solution of sulfurous acid is added and the silicate sludge made acid by the addition of hydrochloric acid to decompose the alkaline silicates. The silicate sludge is then made distinctly alkaline by the addition of a saturated solution of potassium carbonate. The alkaline mass of silicates is evaporatedl to a pasty consistency and the iodide removed by repeated extractions with alcohol. The alcoholic extract is evaporated to dryness and iodine determined in the residue either colorimetrically or by titration with a standard solution of thiosulfate. DISCUSSION OF RESULTS The results for the iodine content of several different samples of soils by three different methods show that the von Fellenberg method gave slightly higher figures in most instances 1 A t this point the authors have found i t advantageous t o modify the von Fellenberg method as follows: After making the sludge alkaline by the addition of a saturated solution of potassium carbonate, the mass of silicate is transferred onto a folded filter and thoroughly washed with hot water. The filtrate is evaporated t o the point where soluble salts begin t o crystallize out. The solution is then transferred and rinsed into a separatory funnel. Pure 96 per cent ethyl alcohol is added, the mixture vigorously shaken, the aqueous solution separated, and the extraction repeated twice. The alcoholic extract is evaporated t o dryness and the iodine determined in the residue.
216
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
.(
