INDCSTRIAL i l S D ESGISEERISG CHEJIISTRY
836
Vol. 18. No. 8
Iodometric Determination of the Halogens’ By P. L. Hibbard DIVISION OF
PLANT
NUTRITION, UNIVaRSITY
OF CAI,IFORNIA,
BERKELEY,C A L I F .
METHOD for determination of bromine only in plant oxide is present and there is much iodate, some iodine will sap has already been described.2 A somewhat be set free, but this is quickly reduced by addition of more similar procedure is here given for determining io- sulfur d i ~ x i d e . ~After the sodium hydrogen sulfite, dilute dine, bromine, and chlorine. The method is applicable to sulfuric acid is added to slight permanent acidity, indicated small amounts of these elements. All three may be deter- by methyl orange, and the solution is boiled to remove the mined in a single small portion of the original substance, with excess sulfur dioxide. After the sulfur dioxide is removed, little expense of time, apparatus, and materials. No pub- but while the solution is still dilute, 30 to 50 cc., a slight excess lished method for accomplishing such a result so conveniently of sodium hydroxide (free of chlorine) is added to make is known to the writer. slightly alkaline in order to avoid possible loss of halogens The method is applicable to mixtures containing from 0.1 while evaporating the acid solution. Concentrate to 5 to to 10 mg. of iodine, chlorine, or bromine. The results may 10 cc. and transfer to the aeration tube for determination of be expected to be accurate to 1 5 per cent or less of the actual iodine. amount present, if this is more than 1 mg. Small amounts of free iodine, set free by acidifying an ioB e f o r e b e g i n n i n g the date, may be reduced by analysis, the halogens must careful addition of dilute be brought into solution by sodium thiosulfate till the This process of estimating iodine, bromine, or chlorine some method which removes iodine color disappears, inconsists in oxidizing them one at a time, in the order organic matter, commonly stead of by the treatment given, absorbing the element thus set free in gaseous by ignition a t low temperawith sulfur dioxide. form in potassium iodide and titrating the equivalent ture with sodium peroxide. liberated iodine with sodium thiosulfate. First the Estimation of Iodine The procedure is essentially iodine is set free by boiling the solution with ferric sulthe same for estimation of T h e s a m e apparatus is fate. Chlorides and bromides are not thus oxidized. used as for determination of iodine whether or not broThe bromine is liberated by chromic anhydride, which bromine. To the properly mine or chlorine is present. in the cold does not set free much chlorine. The It is not necessary to remove prepared solution, 5 to 10 chlorine is then set free by distilling with potassium cc. in volume, contained in iodine in order to determine permanganate and free sulfuric acid. bromine, but both iodine the aeration tube, add 2 to 3 cc. 5 N sulfuric acid, 0.2 to and bromine must be removed before proceeding with the determination of chlorine. 0.4 gram ferric sulfate, and enough 1 N nitric acid to make The manner of preparing the solution for analysis, the the whole mixture about 0.1 N of nitric acid. Connect a t apparatus, reagents, and procedure employed in estimating once with the absorption tube and aerate with a moderate bromine have been described in the previous article.2 Mod- stream of air. Heat the aerator to gentle boiling by means ifications used in determination of iodine and chlorine will of a microburner, but avoid much heat after boiling starts, in order to prevent heating the absorber, which would render be mentioned hereafter. the end reaction less delicate. Reduction of Oxidized Halogens after Ignition The liberated iodine is titrated as it comes over with the -4ny iodide in the original material becomes iodate during sodium thiosulfate, as described in the previous article. ignition with sodium peroxide for removal of organic matter. Most of the iodine will come over in a few minutes, usually When the solution of the fusion is acidified, iodine is a t once all within 10 minutes. When no more appears after 1 to 2 set free. If the solution containing a soluble bromide in the minutes, the determination is regarded as completed. The presence of iodate is heated with acid, the bromine is set number of cubic centimeters of 0.01 N thiosulfate used times free, being oxidized by the iodate, under the conditions given 1.27 is the number of milligrams of iodine found. The solufor determination of the iodine. I n this case some bromine tion remaining in the aerator is now free of iodine and suitable for determination of bromine. If it is not desired to would be included in the iodine determination. Bromate does not seem to be formed by ignition of a bro- estimate iodine, its presence may be neglected in the determide with sodium peroxide, but if any bromate should be mination of bromine. Iodide seems to become iodate a t present it may be reduced by the same method used to reduce once in the chromate mixture used for determination of broiodate. Bromate alone does not decompose in cold solution mine, so that no iodine is liberated during the bromine deof chromium trioxide as used for the bromine determination. termination, even if iodide were originally present. A more accurate method for determining small amounts of But if chloride is present, as it usually is, it is oxidized by the iodine is given by Kendall,4 but in his method bromine or bromate so that both bromine and chlorine are obtained chlorine cannot be determined in the same portion of the in the bromine determination. I n order to secure correct results, the higher oxides of the substance. halogens which may have been formed during ignition with Bromine Determination sodium peroxide must be reduced before beginning the After removal of the iodine, the solution in the aerator separation. This is accomplished by adding 0.1 to 0.2 gram sodium hydrogen sulfite to the alkaline solution before adding must be cooled in preparation for estimation of the bromine. acid. Then, when acid is added, the free sulfur dioxide I n case i t is not desired to determine iodine, or none is supformed reduces them. If only a small amount of sulfur di- posed to be present, the solution is prepared for determina-
A
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1 2
Received April 7, 1926. Hibbard, THISJOURNAL, 18, 57 (1926).
3
4
Hendrixson, J . A m . Chem. Soc.. 47, 1323 (1925). Kendall, J . Bioi. Ckem., 43, 149 (1920).
August, 1926
I S D r S T R I A L -4-1'0EAVGINEERISGCHEIllISTRY
tion of bromine in the same manner as described for iodine, except that no ferric sulfate and no nitric acid are added, but it is acidified with 2 to 3 cc. 5 N sulfuric acid. The volume should be kept as small as possible, 10 to 15 cc. It must not be warm. When the absorber is ready, add to the solution in the aerator powdered chromic anhydride in the proportion of 1 gram for every 1 cc. of liquid present. If the solution contains little chlorine, the result for bromine is more nearly correct if about 5 mg. chlorine are added as sodium chloride. But if i t is desirable to determine chlorine also in the solution, none should be added in this wag'. If much chlorine is present, it is important that the concentration of chromic anhydride be about 50 per cent. If stronger, more chlorine is carried over with the bromine. If weaker, some bromine may not be liberated. Connect a t once with the absorber and execute the-determination as previously described. When much more than 5 mg. of chlorine are present, it is advisable to make a double separation of the bromine and chlorine as described in the previous article. Chlorine Determination
The solution having been freed of iodine and bromine, as already described, is suitable for determination of chlorine. For this, a small amount of organic matter, a few milligrams, if it should be present, will do no harm as it is oxidized under the conditions of the procedure to be described. Much organic matter is liable to cause very low results. The apparatus (see illustration) for chlorine is somewhat different from that used for iodine and bromine, though the same in principle. For the aerator, a 100-cc. round-bottom flask with a neck of 2.5 cm. diameter is used instead of the large test tube. The inlet tube to the aerator should be about 3 mm. inside diameter a t the lower end in order to avoid clogging by the chromic anhydride toward the end of the operation. Instead of the W trap a t the top, as used for iodine and bromine, a good bulb trap, such as is used for Kjeldahl work in determination of nitrogen, is necessary to prevent carrying over sulfuric and chromic acids from the aerator to the absorber. This trap connects by a rubber tube, glass to glass, with a glass tube about 4 mm. in diameter. This tube extends up to the top of a Liebig condenser jacket, in vertical position, then down through the jacket, so that steam is condensed, and connects with the tube passing to the bottom of the absorber. For the absorber there is used, instead of a 2.5 X 30-cm. tube, a similar tube having a bulb of about 200 cc. capacity fused to the top of the tube. On top of the bulb is a neck to permit connections with the absorber by means of a rubber stopper. This bulb is desirable in order to accommodate the water distilled over during the operation. (This same apparatus may be used for determination of iodine and bromine as well as chlorine, except that it is larger and more cumbrous than desirable for the former two.) When the absorber is in position properly charqed and the air current is passing through a t the rate of 200 to 300 cc. per minute, wash the liquid from the bromine determination into the 100-cc. aerator flask, add 2 to 3 cc. of a saturated solution of potassium permanganate, and a t once connect with the absorber. One cubic centimeter of saturated solution of potassium permanganate can liberate about 50 mg. chlorine. Dry powdered potassium permanganate may be used. but if it is used it should all be dissolved in the liquid before heating is begun. Excess potassium permanganate does no harm, except to give a higher blank. The chloride may not be added to the hot solution of potassium permanganate. This is liable to cause formation of oxides of chlorine which are not decomposed under the conditions here given.
837
Proper dilution with mater is important in order to obtain a correct determination of the chlorine. If the solution is too concentrated, some chlorine is not easily set free. Probably it becomes oxidized to C103- or Clod- instead of Clz. Except nThen the amount of chlorine present is less than 1 mg., the volume of the mixture should be not less than 25 cc. If more than 5 mg. chlorine are present, dilute to 30 cc. o r more. Experiments indicate that it is best to have no more free sulfuric acid present in the chlorine determination than is added for the bromine determination. When more sulfuric acid is present, it seems more difficult to remove the last of t h e chloride. Chlorates and iodates are but little, if at all, decomposed by this treatment; therefore they should be previously reduced. But bromate is decomposed with liberation of bromine, which is, therefore, included with the chlorine. If the solution has been properly reduced at first before the determination of iodine, no bromate will remain after t h e bromine determination. Conduct the determination of chlorine about as described for iodine, heating gently a t first. If much chlorine is present, it begins to come over a t once w i t h o u t heating, but in order to obtain all of it the solution in the aerator must be evaporated to dryness. For this reason, a bath of Woods' fusible alloy is desirable for heating the aerator in order to prev e n t b r e a k a g e . The temperature of this bath should be 150'to 180" C. At, the end of the analysis, the b a t h m u s t b e lowered away from the flask a t once when the f l a s k b e c o m e s dry in order to prevent carrying over into the absorber fumes of sulfuric acid and chromic anhydride. Shortly before the end of the analysis, t h e i n l e t tube to the aerator is liable to be clogged by solidification of chromic acid. This difficulty is o v e r c o m e b y adding, through the funnel tube, a f e w d r o p s of water A--Aerator E-Condenser when necessary. B- Absorber F-Vent in Kjeidahd C-Outlet t o suction trap Titration of the liber- D-Buret G-Rubber connections ated iodine is performed Apparatus for Determination of as described u n d e r ioChlorine dine. exceDt that on account of the large volume of sodium thiosulfate sometimes required a 50-cc. buret is preferable. During the chlorine determination, considerable water is distilled over into the potassium iodide solution, so that i t becomes dilute. I n this condition it does not absorb the chlorine so well, so that lower results are obtained. Consequently, whenever the potassium iodide becomes diluted to more than three times its original volume-i. e., till it contains only about 0.3 per cent potassium iodide-it should be replaced by fresh potassium iodide-phosphate mixture.
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I.VD USTRIAL A N D E,VGINEERIA-G CHEMISTRY
838
On account of impurities in reagents and errors inherent in the procedure, it is usually desirable to make a correction in the amount of sodium thiosulfate used. The magnitude of this correction is found by running a determination with a known amount of chlorine similar to the amount found in the unknown. A table of such corrections may be made up once for all by making determinations with amounts of chlorine of 0.1 to 10 mg. as here indicated. Chlorine present Mg. 0.1
1.0 2.0 5.0 10.0
0.01 K NazSz03 to be subtracted cc.
0.25 0.35 0.50 0.65 1.20
After subtracting the correction, the number of cubic centimeters of 0.01 N sodium thiosulfate used times 0.355 is the number of milligrams chlorine found. The result is liable to be in error to the extent of *O.l mg. for quantities of 1 mg. found. For larger amounts of chlorine, as 5 to 10 mg., the error may be *0.2 to 0.3 mg. Somewhat higher precision may perhaps be obtained by using the Volhard silver titration method where it is applicable; but this cannot be used
Vol. 18, No. 8
on the solutions which contain chromate after the bromine determination. Analytical Results
The accompanying table shows a few of the results of analyses of mixtures containing the three halogens by the method described. During the past year this procedure has been followed many times with very satisfactory results in the analysis of the sap of the alga Nitella, and of the culture solution in which the plant was grown. Analytical Results (Amounts in milligrams) 7 IODINE -BROMINE-CHLORINE 7 Taken Found Error Taken Found Error Taken Found Error From Pure Salts 5 4.80 -0.20 5 4.93 -0.07 5 5.04 +0.04 5 5.01 4-0.01 5 4.97 -0.03 5 5.04 4-0.04 1 0.99 -0.01 1 0.95 -0.05 5 5.04 +0.04 1 1.00 0.0 1 0.98 -0.02 1 1.06 +0.06 From 1 Gram Dried Seaweed 0.84 0.82 (This material contained 0.82 0.83 about 20 per cent chlo0.86 0.89 rine, but the amount was not accurately determined)
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The Coking Constituents of Mesa Verda and Pittsburgh Coals’.‘ By Joseph D. Davis and D. A. Reynolds BUREAU OF MINES,PITTSBURGH EXPERIMENT STATION, PITTSBURGH, PA.
I
N T H E course of an investigation carried on by
Coking constituents of Mesa Verda and Pittsburgh coals were investigated by the method of Fischer, which consists in extraction of the coal bitumens by benzene under pressure, separation into solid and oily bitumens by petroleum ether, and testing them separately by the volatile matter coking test. Contrary to the findings of Fischer, the solid bitumen possessed stronger agglomerating power than the oily bitumen and neither produced appreciable swelling of the coke. Pressure extraction with benzene does not remove all the agglutinating constituents from coal. Adequacy of the volatile-matter test for estimating the coking Power of coal constituents is questioned.
the Bureau of Mines on the low-temperature carbonization of Some Western nonc o k i n g coals, a study was made of the coking constitcoal in uents of Mesa comparison with Pittsburgh coal as a standard coking coal. The conclusions apply o n l y t o t h e two coalsin question-namely, Utah coal from the King No. l mine, Mesa Verda bed, and coal from the Pittsburgh bed, near Bruceton, Allegheny County, Pa. The Mesa Verda coal is noncoking, whereas the Pittsburgh coal is coking, in the generally accepted meaning of the term. Nature of Coals Tested
Table I gives proximate and ultimate analyses of the coals examined. The Pittsburgh coal comes from the high-volatile portion of the bed. It is rich in agglutinating constituents and is often mixed with a lower volatile coal for coking in a byproduct oven, although it will produce a satisfactory coke when coked unmixed. The coal contains less than 10 per cent oxygen on the moisture and ash-free basis, which is usually considered the upper limit of oxygen content for coals suitable for by-product coking. The Mesa Verda coal con1 Received March 27, 1926. Presented under the title “The Coking Constituents of Castlegate and Pittsburgh Coals” before the Division of Gas and Fuel Chemistry at the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, 1926. 1 Published with approval of the Director, U. S. Bureau of Mines.
tains 13.3 per cent oxygen; it is not adapted to by-product coking, because when heat is applied it does not melt and form a homogeneous mass before decomposition begins, Experimental Method Used
The method adopted for isolation and test of the coking constituents was based mainly on that recently described by Fischer.3 This method consists of extracting the coal bitumens with benzene a t 285” C. under a pressure of 55 atmospheres, evaporating the benzene extract to a sirup, and separating this into a “solid” and “oily” bitumen by means of petroleum ether. The sirup is poured into a large excess of Detroleum ether, whereupon the solid precipitates of Mesa Verda and Pittsburgh Coals (Per cent) --MESA VERDA-PITTSBURGHMoisture and Moisture and As received ash free As received ash free Proximate 3.4 ... 2.2 ... 42.9 48.1 38.8 41.9 46.2 51.9 53.8 58.1 7.5 5.2 Ultimate 2.4 2.6 0.9 0.8 5.9 5.2 5.4 5.6 78.3 75.2 81.2 69.9 1.6 1.7 1.6 1.4 13.3 10.4 9.1 14.8 13,650 14,740 14,350 12,790
Table I-Analyses
Moisture Volatile matter Fixed carbon Ash Sulfur Hydrogen Carbon Nitrogen Oxygen B. t. u. 8
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THIS JOURNAL, 17. 707 (1925).
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