ANALYTICAL EDITION
318
Vol, 6 , No. 5
TABLE11. TITRATION OF COPPERSAMPLES W ~ I Q HOF T
SAMPLIU Gram
COPPBRPREBBNT
%
Gram
TOTAL KCNS
KIOs
USHlD
UBnD
KIO~/ KCNS
cc.
cc.
cc*
32.00 13.18 0.106qa 0.1064 23.60 18.77 64:96b 0.07003 0.1078 27.00 12.36 0.08916 0.1472 60.576 32.00 11.95 0,1105” 0.1105 30.00 15.40 0.0999a 0.0999 8.37 20.10 0.06879 64:96b 0.1059 17.88 26.10 0.08278 64.96b 0.1274 15.37 38.36 0.13616 60.578 0.2248 16.54 37.17 0.13023 0.2150 60.57b 47.20 15.55 0.17044 60.578 0.2814 a Nichols Copper Co apecial sample (99.993 per cent copper). b V. L. Logo, analysd,’ Falea Chemical Ca
...
3.800 3.800 3.800 4.010 4.010 4.010 4.010 4.010 4.010 4.010
mination. The titer obtained gives the potassium iodatepotassium thiocyanate ratio. Table I shows typical results for a standardization. STANDARDIZAT~ON OF POTASSIUM THIOCYANATE. The potassium thiocyanate need not be accurately weighed, but must be standardized by titration against a sample of known copper content, or against a sample of pure copper. For this standardization, the method should be carried out exactly as described above, and B. titer obtained of grams of copper per cubic centimeter of potassium thiocyanate. ANALYTICAL RESULTS. A number of samples of pure copper and German silver were analyzed by this method. Typical results are given in Table 11. SUMMARY A rapid potentiometric method for the determination of copper in certain alloys has been investigated and been found particularly suitabIe for German silver analysis, but is also
KCNS/Cu 0.003745 0.003745 0.003745 0.003823 0.003823 0.003823 0.003823 0.003939 0.003939 0.003939
COPPBR
EaLROR
FOUND Gram
Gram
0.1068 0.06988 0.08894 0.1109 0.1000 0.06885 0.08273 0.13601 0.13019 0.17064
$-0.0004 -0.00015 -0.00022 $0 .0004 $0. 0001 $0.00006 -0.00015 -0.00003 -0.00004 +0.00020
RISE
%
MV.
+0.37 -0.21 -0.24 $0.36 $0.10 +0.09 -0.04 -0.11 -0.03 $0.11
276 208 303 274 310 300 202 267 247 365
applicable to the analysis of other alloys if interfering elements are first removed. The effects of acid concentrations have been investigated. Pretreatment of the platinum electrodes may be necessary. It is not required that a titration curve be plotted, thus reducing the time of a complete analysis to approximately 30 minutes. ACKNOWLEDGMENT The authors wish to thank H. A. Fales and J. J. Beaver of Columbia University for helpful criticism of the manuscript. LITERATURE CITED (1) Biilmann, Ann. chim., [9] 15, 109 (1921). (2) Fenwick, F.,Dissertation, Univ. of Mich., p. 76 (1922). (3) Hostetter and Robertg, J. Am. Chem. SOC.,41, 1337 (1919). (4) Jamieson, Levy, and Wells, Ibid., 30, 760 (1908). (5) Kolthoff, I. M., and Furma;, N. H., “PotentiometricTitrations,” 2nd ed., p. 300, John Wiley & Sons, N. Y.,1931. R~~CBNVED May 7, 1934.
Combustion Method for the Determination of Iodine in Plant Material J. S. MCHARGUE, D. W. YOUNG,AND R. K. CALFEE,Kentucky Agricultural Experiment Station, Lexington, Ky.
R
ELIABLE information concerning the iodine content of forage crops and foods is important from the stand-
point of nutrition and good health. Iodine usually occurs in minute quantities in plant material grown under normal conditions in a fertile soil, and has an extremely important function in the metabolism of animals. The Kentucky Agricultural Experiment Station is now investigating the iodine content of forage crops and foods produced in the principal soil areas of the state. The authors have previously reported on the iodine content of soil and waters in Kentucky (6,6). New methods for the determination of iodine in various kinds of organic matter by combustion with pure oxygen gas in closed systems have been published in recent years (1-4). A study of these methods reveals some points to be desired in the way of less complicated apparatus and technic. The attainment most desired is complete combustion of rather large samples of plant material a t a uniform rate and a t a moderate temperature, together with as complete recovery of iodine as is possible. After a considerable number of check determinations (duplicate determinations being made on all samples) with the apparatus described in this paper, the authors feel that substantial progress has been attained in devising a method whereby considerable quantities of plant material can be completely burned in a closed system, without the customary white fumes mentioned by previous authors, and iodine and
other elements which occur in smaIl amounts determined quantitatively . The set-up of the apparatus as used in the authors’ laboratory is shown in Figure 1.
PROCEDURE A sample of 50 grams of finely ground, air-dry, plant material is weighed, transferred into a porcelain dish, and thoroughly mixed with 10 grams of finely pulverized calcium oxide and 10 grams of finely pulverized copper oxide. The sample is then distributed in 3 alundum boats which are put end t o end, in the large combustion tube. The right end of the large combustion tube is closed tight with a rubber stopper which carries a glass tube connecting with the wash bottle. The wash bottle on the left is connected to a suction pump. The current is connected to the electric furnace and when tube 3 attains a red heat air is drawn through the system and the first burner on the left of the gas furnace is lighted. After a short time the heat from this burner sets the plant material in the first boat on fire and a moderately ra id current of air drawn through the tubes and the turning on ofother burners of the gas furnace at the proper time kee s the sample burning at a slow and uniform rate, somewhat in t t e manner of a lighted cigar. Any unburned vapors from the sample are drawn over the red-hot platinized asbestos catalyst where they are completely burned and the iodine vapors are carried into the gas wash bottles and absorbed. After the combustion of the sample is completed the sources of heat are turned off and the apparatus is cooled by continuing t o draw the current of air through the system. The suction pump is turned off, the boats are careful1 removed and the ash is digested and leached with hot distilleiwater. ?he filtrate
September15,1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
319
from the ash is combined with t'he potassium carbonate solutions A number of duplicate determinations were made on several from the absorption flasks and evaporated to dryness* (The different plant materials, using different catalysts alone and authors have tried a solution of sodium bisulfite as suggested the iodine quanti- in combination. The results obtained are contained in by McClendon but were unable to tatively. Accordingly a solution of potassium carbonate has Table I. been used in these experiments.) Just enough distilled water is added to dissolve the residue and the solution is transferred DISCUSSION OF RESULTS to a separatory funnel of the proper size. Enough 95 per cent From Table I it is apparent that fairly consistent results ethyl alcohol is added to form two immiscible layers and the funnel is shaken vigorously for about 10 minutes. The aqueous for iodine in several different kinds of plant material can be portion of the solution is r u n i n t o a n o t h e r separatory funnel and the process of extraction re eated three times. The alcoholic extracts wlich contain the iodine are combined and evaporated slowly t o dryness so as to avoid s attering caused by too rapid boiling of the aycohol. The residue is dissolved in a few drops of water, filtered into a small separatory funnel, and made slightly a c i d w i t h sulfuric acid. About 3 cc. of a saturated solution of sulfurous acid are added and the funnel is stoppered and vigorously shaken for about 1 minute to reduce iodatje to iodide, after which 1 ml. of carbon disulfide, accurately measured, and about 2 ml. of a 10 per cent solution of sodium nitrite are added. The funnel is stoppered and vigorously FIGURE 1. DIAGRAM OF APPARATUS shaken for about 1minute and the carbon disul1. Absorption bottle containing 5 per cent potassium carbonate (2 bottles used) fide allowed t o settle. If it has a slight pink color, all the iodine has been absorbed. How3. silica 2. Rheostat catalyst tube ever, if the carbon disulfide has a deep pink 4. Platinized asbestos catalyst 5 . Electric tube furnace, maximum temperature 11000 C. color, it is run into a centrifuge tube, 1 ml. of 6. Asbestos cement seal sealing large combustion tube to smaller tube containing catalyst carbon disulfide added, and the extraction re7. Silica combustion tube peated until the last portion has only a f a i n t 8. Alundum boats containing sample 9, Gas ~ o d m t i o nfurnace color. The extracts are combined and centri10. Wash bottle containing 10 per cent potassium hydroxide fu alized, and a portion is in a microcoforimeter with an iodine standard prepared in a similar way. The results are reported in parts per million if obtained with the combustion apparatus described. The high, or parts per billion if low. principal advantages of the apparatus are moderate cost, simplicity, stability, and provision of a means, with the use of TABLEI. EXPERIMENTS TO TESTMETHOD the proper kind and amount of catalysts, for the complete IODINE RECOVERED Combustion combustion of plant material without smoke or other visible AMOUNT PLANT MATERIAL (AIR- IODINE CATALYST in quartz vapors passing out through the exit end of the system, in USED DRY) ADDED Usn~ Fusion tubes Gram about one-fourth of the time required for an iodine determinaGra?ns Gram Grams Sawdust (pine) 35 O.OOOO None O.OOOO Trace tion by fusion with potassium hydroxide. 25 0.000764 None 0.000760 25 o,oo190 (CaO) ,.. o,b,ji847 Several different catalytic agents which give up oxygen dur10 (CUO) ing the combustion have been tried and found satisfactory. When the finely ground plant material is wet with a 10 per Ni(NOs)l p . p , b , p. p , b. Persimmon leaves 50 3 160 180 cent solution of nickel nitrate and dried a t 100" C., very 50 ...... 3 '175 lS3 satisfactory combustion is obtained. However, a mixture of Forest leaves 50 ...... 3 127 120 powdered lime and finely pulverized copper oxide is as ef50 3 147 133 fective and more easily prepared and mixed with the plant Pine needles 50 ...... 3 material than the nickel nitrate. The copper oxide dust ad50 ...... 3 heres and forms a film around the particles of plant material Beet tops 50 ...... 3 540 590 Lespedeza 50 ...... 3 535 600 and furnishes oxygen for the combustion. The lime absorbs 50 ...... 3 521 'O0 carbon dioxide to form calcium carbonate and apparently Tobacco (dark) 50 3 1400 1520 assists in the combustion without furnishing any oxygen. Tobacco, Burley 50 3 1600 1680 Hay, soy bean C-608a 50 . . . . . . 3 ... 80 Some samples of plant material were found to contain conHay, timoth;, No, siderably more iodine than others, indicating either that 600 97956 50 ...... 3 ... Hay, red clover, No. different species of plants vary in their capacity to absorb 5oo 97972 50 ...... 3 ... Hay, orchard grass 50 . . . .. . 3 ... 1,200 iodine or that the soil in which they grew contained differHay, bluegrass, No. ent amounts of this element. 588 99494 50 ...... 3 ...
iTt
Mixed grain ration (,corn, wheat, oats linseed oil meal. aifalfa leaf meal) Hay, soy bean, C1172, 1933 crop
50
50 50 50
Hay (mixed) timothy re$ clover crab: grass, 2nd 'cutting, 1933 50 Corn grain yellow, c-io64,1833 50
Broom sedge
......
.. .. .. .. .. ..
LITERATURE CITED
3
...
356
5
...
390
8 [Ce(NO&] 10 (CuO) 10 (CaO)
20 (CuO) '
2;;
50
...,.. ... ... .... . .
5 [Ni(NOa)r] 10 (CaO) 20 (CUO)
50 50
...... ......
[Ni(NOs)z] 10 (CuO)
10 (CaO) 10 (CUO)
. ,. .. .. ..
... ., . . ,. .... ..
388
324 77 90 85
104
(1) Kams, G. M., IND. ENG.CHEM.,Anal. Ed., 4, 299 (1932). (2) Kolnitz, H.K., and Remington, R. E., Ibid., 5, 38 (1933). (3) McClendon, J. F., J . Am. Chem. SOC.,50, 1093-9 (1928). (4) McClendon, J. F., et al., Ibid., 52, 541 (1930). (5) McHargue, J. S., and Young, D. W., J . Am. Water Works Assoc., 25, 380-2 (1933). (6) McHargue, J. S., and Young, D. W., Soil Sci., 35, 425-35 (1933). R E C ~ I Y EMarch D 19, 1934. Presented before the Division of Agricultural and Food Chemistry a t the 86th Meeting of the American Chemical Society, Chicago, Ill., September 10 to 15, 1933. Published by permission of the Director, Kentucky Agricultural Experiment Station.
P a w
