Collecting Train for Recovering Traces of Iodine from Ashed Samples GEORGE M. KARNS,Mellon Institute of Industrial Research, University of Pittsburgh, Pittsburgh, Pa. N CARRYIKG out determinations of iodine in minute amounts in large samples of organic material, in ashing apparatus of the McClendon or Pfeiffer type (7,9-13), it is necessary that the iodine in the gaseous combustion products be collected in some kind of train. The type of train usually used has contributed t o the difficulty of the analysis in a number of ways. Its interference with the egress of combustion products from the apparatus complicates the burning process. The elimination of the liquid and solid reagents contained in the train, as must be done before the final determination is made, adds to an already cumbersome procedure. The use of large amounts of reagent in a few recommended types of train, some of which is difficult to render iodine-free, offers the possibility of introducing a considerable correction for the blank determination. The collecting train described herein was devised to collect iodine with a minimal interference with the gas stream and without the use of large amounts of liquid or solid reagent. It may be employed with any type of ashing device in which the streani of evolved gas is sufficiently slow, such as the wet ashing method of Pfeiffer or the ashing bulb previously described by the writer (3). Figure 1, showing the assembled apparatus with such a bulb, and Figure 2, illustrating individual parts of the apparatus, make a detailed description unnecessary. The function of each part, however, will be discussed briefly.
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the sample. The coils are present to facilitate heat exchange between the tube and the gas. For this purpose, other materials than nichrome would undoubtedly serve better, but the particular coils described are satisfactory for reasons hereinafter indicated, and at the same time are low in cost. Rubber connections and rubber stoppers are used throughout the entire train, with the usual precautions to expose as little rubber as possible to the gas stream, The first tube serves to condense most of the moisture of combustion. With it is caught considerable solid smoke. The packing of glass wool assists in bringing smoke and moisture into contact. In this first tube from 32 to 37 per cent of the iodine is collected from representative samples. The second freezing tube removes most of the remainder of the moisture. This step is necessary in order that the gas stream will not be saturated with water when it reaches the first Cottrell precipitator. It is also essential to avoid the freezing-shut of the third collecting tube. The precipitator as illustrated, under the conditions herein described, is adequate for collecting the solid material which has passed through the glass wool in the first condensing tube from most types of sample. I n some samples, however, in which the mineral content is quite high, this precipitator is rendered ineffective by the deposited material in the latter part of runs on 60-gram samples, In such cases it is well to have available a second precipitator connected into the system in parallel, by means of a three-way stopcock and T-tube. The amount of iodine caught in the OPERATIONOF APPARATUS precipitator is governed largely by the form in which it A normal operation of the apparatus is without the de- occurs and by the mineral constituents present with it. velopment of any back pressure, The manometer, there- The amount usually runs from 3 to 8 per cent of the total. fore, is inserted into the system to serve as a warning device Whether or not the precipitators may be eliminated from the only. The activating mechanism for the Cottrell precipita- system, as has been done by some investigators, depends on tors is similar to that described by other authors on iodine the nature of the samples and the familiarity of the operator analysis (8). The coils in the last three collecting tubes are with them. It is the author’s experience that the precipitator made from No. 20 nichrome wire by wrapping it about a rod illustrated is more easily cleaned than a tower containing of such size that the finished coil will fit tightly between the beads or glass wool that may be substituted for it. The third collecting input tube and the tube i m m e r s e d i n wall of the collecting acetone and solid cartube. They are b on dioxide collects stretched till there are 38 to 50 per cent of the about ten turns to the total iodine, and the inch before being second similar tube 3 w r a p p e d about the i n n e r tube a n d into 8 per cent. When s a m p l e s containing serted i n their proper considerable nitrogen place. T h e s e coils are burned, nitrogen u n d e r g o very little dioxide is frozen out corrosion except when in these last two colnitrogenous materials are burned. The salts lecting tubes. Care r e s u l t i n g from this must be t a k e n t o neutralize t h i s con c o r r o s i o n cause no densed material bedifficulty in the final determination when fore the t u b e h a s the a l c s h o l - p o t a s warmed completely, s i u m carbonate exlest elemental iodine be swept out with the traction m e t h o d is used in concentrating FIGURE 1. ASHINGAPPARATUSAND COLLECTING TRAIN expanding vapors. 375
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The final precipitator is appended as a precautionary measure and in a normal run collects very little material. The train a t the end of the run contains nothing but precipitated solid ash and the condensable products of the combustion. These combustion products are washed from the train with water containing sufficient potassium carbonate to assure distinct alkalinity in order that the iodine will be retained during concentration and subsequent treat-
Vol. 4, No. 4
LIMITATIONS OF APPARATUS
A collecting train of this type has certain inherent limitations which it is well to point out. Under ideal operating conditions, the limit of recovery in any train is set by the vapor pressure of the pure products in the train, the partial pressure of the products in solution, and the volume and approach to saturation of the emerging gas. I n those types of train using reagents, the desired products are converted to compounds which have negligible vapor pressure at room t m.m CAPILL.ARY temperature. In the train described, the collected materials are modified only as the products of combustion act as reagents, the effectiveness of collection depending on the fact that the vapor pressure of the products is negligible a t the temperatures attained in the collecting tubes. We emrn. ID. are dealing with a number of possible iodine compounds as products, whose actual nature is dependent largely on the original state of combination and the nature of the other material in the sample. At the temperature of combustion we would expect that, in the absence of basic metals, most of the iodine would be released as the free element, both hydrogen iodide and oxides of iodine being unstable a t elevated temperatures. Most of the metallic iodide salts would probably be decomposed as well. The basic products capable of being volatilized on assuming the form of dust beyond the elevated temperature zone might recombine with iodine to give iodides and oxy-salts of iodine. These products would condense and settle in the system, dissolve in the water of condensation, or be thrown out in the precipitators. The dissolved salts with acid products of combustion would tend to form acids, the most volatile of which, hydriodic acid, in the dilution formed with the water of condensation from most samples, would have a negligible partial pressure (1, 6) even 2orn.m. in the first collecting tube. If samples giving no water were FIRST COLL€CTLNQ Lmm. CAPlLLARv TUBE being burned, it would be well to add a few cubic centimeters to the first collecting tube. FIGURE2. PRECIPITATOR If we assume that the possible organic combinations of iodine are unstable under the conditions of combustion, ment. The entire washings from the train and from the bulb type of ashing apparatus previously described usually amount it is evident that iodine itself is the next most probable source of loss under ideal operating conditions. to about 300 cc. Of that part of the free iodine that is not held by basic The efficiency of collection in this type of train is dependent materials after recombination, some will remain in solution to a considerable extent on the speed of the gas stream. The latter, in turn, is dependent on the initial oxygen-input in the condensed water vapor. Its slight solubility, however, rate, the completeness of oxygen utilization, the amount of will not allow us to depend on this factor for recovery, condensable combustion products, and the cross section of especially since the products of combustion of nitrogenous the gas stream in the selective portions of the apparatus. materials will insure the absence of iodides in solution. The recovery of approximately 90 per cent, using an oxygen Aside from solution in water, we may expect iodine to be input of 1.4 liters per minute, although no higher than that held as the condensed pure solid or more probably as a solid reported using other types of train, iF considerably more mixture with ice and other condensable combustion products. consistent than that obtained with other types in the author's Concerning the state of these mixtures we know little except experience. The recoveries made with the train are consist- that the vapor pressure of iodine from them will likely be ently higher on samples of food materials and animal tissues less than that of the pure solid. Occurring alone in the than determinations made by the open-dish ashing method collecting tube (as it would seldom do with samples usually using controlled temperatures. This observation is interest- dealt with), iodine would be in its most fugitive condition. ing in view of the fact that the open-dish ashing technic Of the behavior of pure elemental iodine we may speculate. The approximate calculated vapor pressure ( 2 , 6 )of iodine used gave good recoveries of potassium iodide. in the temperature of the collecting tubes is of the order of 10-lo atmospheres. The loss in saturated emerging gas TABLEI. RECOVERY DETERMINATIONS OF IODINE , would be 0.1 or 0.2 y of iodine per hundred liters. I n a ACCOMPANYINQ IODINHl C O N T A I N E D I O D I N E IODINE IODINE system utilizing its oxygen efficiently, this would mean a MATERIAL IN PULP ADDED FOUNDRECOVERED RECOVERY loss of less than 5 per cent on samples containing 100 parts Grams y/kg. y "I Y r % of iodine per billion. The presence of almost any conceivable 280 1.8 6.5 106 98.2 96.4 90;9 280 95.5 90.0 1.7 106 6.2 97.2 accompanying products of combustion would tend to de750 13.5 20 18.0 31.8 18.3 91.5 crease this loss. NOTE. Determinations were made by the titrimetric method after
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oxidation with iodine-free (4)bromine. The Greek letter y is used for 1 miorogram (I
0.001 mg.).
Examples of recovery determinations of iodine added as potassium iodide to samples of paper pulp made with the collecting train described are shown in Table I.
LITERATURE CITED (1) (2) (3) (4)
Bates and Kirchman, J. Am. C h m . Soc., 41, 1991 (1919) International Critical Tables, 5, 88 (1929). Anal. Ed., 4, 299 (1932). Karns, IND.ENQ.CHEM., Karns and Donaldson, J. Am Chem. SOC.,54, 442 (1932).
October 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
(5) Lewis and Randall, “Thermodynamics,” p. 526, McGraw-Hill, 1923. (6) Lewis and Randall, Ibid., p. 522. (7) McClendon, J. Bzol. Chem., 60, 289 (1924). (8) McClendon, J. Am. Chem. Soc., 50, 1093 (1928). (9) McClendon and Remington, Ibid., 51, 394 (1929). (10) McClendon, Remington, von Kolnits, and Rufe, Zbid., 52, 541 (1930). (11) Pfeiffer, Biochem. Z., 215, 126-36 (1929).
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(12) Remington, McClendon, von Kolnite, and Culp, J. Am. Chem SOC.,52, 980 (1930). (13) Remington, McClendon and von Kolnite, Ibid.,53, 1245 (1931).
RECEIVED April 4, 1932. Presented before the Division of Agricultural and Food Chemistry a t the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 t o September 4, 1931. A contribution from Mellon Institute’s Industrial Fellowship on Iodine, which is sustained by the Iodine Educational Bureau, New York, N Y
Determination of Copper Number of Paper J. D. PIPERAND C. H. FELLOWS, The Detroit Edison Co., Detroit, Mich.
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N INVESTIGATION into the service deterioration of the oil-impregnated paper insulation of 24,000-volt underground cable led to the use of the copper number test for following the changes which occurred in the paper. I n a series of experiments in which oil and paper were subjected in vacuo to electric discharge (which had been shown to be one of the chief causes of service deterioration), it was found that an increase in the time or intensity of bombardment was accompanied by an increase in the copper number of the paper (12). The copper number was therefore used as an indication of the amount of deterioration. Early tests in 1928 soon demonstrated the necessity of experimental work to modify one of the existing test methods for the determination of this factor so as to obtain a reliable test procedure for the requirements. The method finally adopted (7) has proved exceedingly satisfactory, and although essentially a standard method, the modifications are thought worthy of description as of general interest. A copper number test, to be satisfactory for the purpose mentioned, must be rapid, sensitive, and capable of yielding results which are reproducible within reasonable limits on a sample not larger than 1.5 grams. In addition the apparatus required must not be expensive. Early determinations were made by means of Schwalbe’s method (IS) and some of its modifications, but the results were unsatisfactory. The values obtained were erratic because of the instability of the Fehling solution during the boiling period, and because of the error due to adsorption by the paper of bivalent copper. Differences in paper samples subjected to different deteriorating treatments were not always brought out, probably because of the effect of caustic alkali in modifying the reducing properties of the cellulose (4). I n later work the method described by Braidy (2) and others (9), in which the Fehling solution is replaced by a sodium carbonate-bicarbonate solution, was used with more satisfactory results. As Clibbens and Geake point out (4,the method gives a low and constant blank, is sensitive to slight modifications of the cellulose, and is reproducible within reasonable limits. Finally, the improved Braidy method as worked out by the Bureau of Standards and later published ( 3 ) was found, aft>er minor modifications had been introduced, to satisfy the requirements completely. The Bureau of Standards specified a method of thoroughly disintegrating the paper without heating the fibers in order to obtain more accurate results. The Gault-Mukerji molybdophosphoric acid method (6) of determining the cuprous oxide was adopted. The size of the sample was reduced to 1.5 grams.
MODIFICATIONS OF OLD METHOD The modifications of the Bureau of Standards method are as follows: 1. The shredder recommended by the Bureau of Standards was too large and costly for the type of work being carried out in these laboratories. A Hamilton-Beach malted milk mixer modified in the manner described by the Okonite Callender Cable Company (11) was found to meet the requirements. The shredder is shown in Figure 1. The stirring motor was mounted on a telescoping shaft, A , so that it, together with t h e stirrer, could be raised or lowered to any desired h e i g h t . A variable rheostat, B, was included to control the rate of stirring. A hotplate, C, was i n s t a l l e d for heating the l i q u i d d u r i n g the shredding process. The original stirring shaft was replaced by a brass shaft, D, on which were mounted two shredd i n g wheels 1.5 inches in diameter made from ‘/arinch sheet brass. Each wheel consisted of eight blades whose cutting edges were FIGURE1. PAPERSHREDDER sharDened. The two ;heels w e r e mounted so that the liquid was thrown upwards by the lower wheel and downwards by the upper wheel. The brass fingers, E, are important since they help to throw the fibers constantly into the shredding wheels. When used a t high speed with a hot solution, the disintegration of the paper is complete after one minute. The short time involved eliminates the irregularities attendant upon long continued beating (8, IO).
