ANALYTICAL EDITION
May 15, 1941
by means of Equation 3. After constructing the accumulation curve, the particle size distribution curve is obtained in the usual manner. There are many advantages of this apparatus in actual uae. Since a given height, h, of the liquid always corresponds to a definite position, I , of the pointer it is apparent that, knowing the bulk density of the material (determined with the liquid which is used as the suspending medium), the final position of the pointer, , ,Z can be calculated. This corresponds to complete settling. Since there is no flow of liquid from the side arm, disturbances which can be caused in this way in the manometer type of apparatus are eliminated. Because of the amplification of the pointer displacement, closer differentiation of particle sizes is possible.
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Experience has shown that this apparatus is more convenient in use than the usual type, and particle sizes of materials can be measured with it that are impossible to measure with the manometer type.
Literature Cited (1) Duncombe, C. S., and Withrow, J. R., J . Phys. Chem., 36, 31-51 (1932). (2) Kelly, W.J., IND.ESG. CHEM.,16, 928 (1924). (3) Knapp, R. T., Ibid., Anal. Ed., 6, 66 (1934). (4) Kraemer, E. O., and Stamm, A. J., J . Am. Chem. Soc., 46, 2709-18 (1924). (5) Ward, H. T., and Kammermeyer, K., IND. ENG. CHEM.,32, 622-6 (1940). PRESENTED before the Division of Industrial and Engineering Chemistry a t the 100th Meeting of t h e American Chemical Society, Detroit, IrIich.
Recovery of Mercuric Iodide and Iodine from
Nesslerized Solutions G. WEBER SCHIRIPFF AND RUSSELL E. POTTINGER Department of Biochemistry, Cook County Hospital, Chicago, Ill.
B
ECAUSE of the rising cost of mercury, it seemed advisable to investigate its recovery from the large quantities of nesslerized solutions prepared in the course of running hundreds of nonprotein nitrogen determinations according t o the Koch-;\lcMeekin method (2). Pullman (4)recovered the mercury and iodine by neutralizing the nesslerized solution with sulfuric acid and adding mercuric nitrate equivalent to the amount of mercury already present. He stated that all the mercury precipitated as mercuric iodide. this method ... ~ ~ . ~However. .. involved the use of a second mercury compound which required = H a rather large additional expenditure in order to recover the original mercuric iodide. Clifford ( 1 ) recovered mercuric iodide by neutralizing the nesslerized solution with sulfuric acid. Only a part of the mercuric iodide precipitated from the solution on standing.
In this investigation mercuric iodide and free iodine were precipitated by adding iulfuric acid and sodium dichromate to the nesslerized *elution. The free iodine was then separated from the mercuric iodide by a distillation procedure. The method is simple and inexpensive, and rewits in the almost, quantitative recovery of iodine and of mercriry as mercuric iodide.
Apparatus The apparatus consists of a &liter round-bottomed shortnecked flask, A , with standardtaper ground-glass joint 25/40, B , connected by a 50-cm. (20inch) length of 20-mm. (outside diameter) Pyrex tubing, C, to an opening in the bottom of a 1-
A
liter Erlenmeyer flask, D, which has a side arm, E, attached near the top. Through the mouth of the Erlenmeyer flask, F , there extends a cooling finger, G, which contains a running water inlet, H , and outlet, 1. G is fitted into F by means of a rubber washer which must be renewed occasionally-a glass connection would be preferable.
Procedure To 10 liters of the nesslerized solution contained in an earthenware crock are added, in the order given, 150 cc. of concentrated sulfuric acid and 75 cc. of 1.3 molar sodium dichromate solution. Upon addition of the sulfuric acid the mixture first becomes milky, then develops a pink color, Upon addition of the sodium dichromate solution, the color darkens considerably and a small amount of iodine vapor becomes noticeable. The mixture is covered and allowed to stand at room temperature in the hood for 12 hours, during which time the mercuric iodide and iodine are completely precipitated. The supernatant liquid is decanted and the residual mass transferred to flask A . (In case the nesslerized solution has been prepared in the course of urea determinations in which a direct nesslerization procedure has been used, it is advisable to free the precipitate from the supernatant liquid by suction filtration and to wash the residue with water prior to its transfer to the round-bottomed flask. This procedure removes the organic material which causes foaming during the heating process.) Enough water is introduced in transferring the precipitate to fill the flask one-fourth to onehalf full. (The water facilitates the rapid removal of free iodine from the mixture of mercuric iodide and iodine during the subsequent procedure.) The apparatus is assembled as shown. The mixture is boiled gently until A is free of iodine vapors. The apparatus is then disconnected and the free iodine, which has condensed on the cold finger, is scraped or washed into a beaker, collected in a Buchner funnel, and allowed to dry in the air. The mercuric iodide remaining in A is separated by suction filtration and washed well with distilled water and then with three 25-cc. portions of 95 per cent ethyl alcohol. It is heated in an oven a t 105" C. for 30 minutes in order to remove any moisture or free iodine that may still be present. The mercuric iodide is then ready for use in the preparation of Nessler-Fohn reagent.
Results From 54 batches of nesslerized solution, 10 liters each, a n average of 45 grams of iodine and 84 grams of mercuric iodide was recovered. The calculated amounts present in the 10 liters were 48.8 grams of iodine and 87.7 grams of
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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mercuric iodide. Percentage yield: iodine, 92.2.
mercuric iodide, 95.7;
PREP.4RATION O F NESSLER-FOLIN REAGEXT.The NesslerFolin reagent is prepared according to the method of Koch (5) except that 40.3 grams of the recovered mercuric iodide (instead of 30 grams of mercury and 22.5 grams of iodine) are added to 30 grams of potassium iodide in 30 cc. of water. The resulting solution is filtered, adjusted with a solution of iodine in potassium iodide, and diluted to 200 cc. This stock solution is then added to 975 cc. of 2.5 molar sodium hydroxide to give the
Vol. 13, No. 5
Nessler-Folin reagent. No difference has been observed in the behavior of the solutions prepared by the two methods. The recovered iodine has been used successfully in the preparation of Kessler-Folin reagent according to the method of Koch ( 3 ) .
Literature Cited (1) Clifford, W., J . Soe. Chem. Ind., 37, 179T (1918).
(2) Koch, F. C., “Practical Methods in Biocheniistry”. 2nd ed., pp. 119-21, Baltimore, Wm. Wood & Co., 1937. (3)Ibid., pp. 261-2. (4) Pullman, D.,Analyst, 44, 1 2 P 5 (1919).
Determination of Iodate Ion in the Presence of Cupric Ion P. L. KAPUR AND M. R. VERMA University Chemical Laboratories, Lahore, India
F
OR a number of routine determinations a method for estimating iodate ion in the presence of copper salts was required. Of the methods suggested for the estimation of iodates of alkali metals or iodic acid alone, the most important are: reducing iodates with oxalic acid and backtitrating the excess of oxalic acid ( I ) , reducing iodates with titanous chloride (S),and allowing the iodate and potassium iodide to react in the presence of a mineral acid and titrating the liberated iodine against standard sodium thiosulfate solution ( 5 ) . The last reaction is sufficiently rapid and accurate for all purposes. The velocity of the reaction 6H+
+ IOP + 51- +312 + 3Hz0
in acetic acid solution has been shown to be proportional to the square of the concentration of hydrogen and iodide ions and directly pFoportiona1 to the concentration of iodate ion (2). This rcaction has also been utilized for estimation of iodate ion in the presence of bromate and chlorate ions. If, however, estimation of iodate ion be attempted in the presence of copper ions, a complication is likely to arise on account of the liberation of iodine through the simultaneous reaction of cupric ions with potassium iodide according to the equation 2cu++
+ 21- *2 c u + I2
Kolthoff and Cremer (4, 7) showed that trivalent arsenic can be estimated volumetrically in the presence of copper ions by adding sodium pyrophosphate to a neutral solution of the mixture, when copper ions form a blue complex and no longer react with potassium iodide. It was found, however, that the complex of copper does not decompose in acidic solution up to pH 5.0, but decomposes a t greater acidity to react with potassium iodide, The authors made use of this fact for the estimation of iodate ion in the presence of copper salts. Mixtures containing known amounts of potassium iodate and copper sulfate were prepared, An excess of sodium pyrophosphate (free from reducing agent), acetic acid, and potassium iodide solution were added, in this order, to each of the solutions to be titrated. The iodine was liberated slowly and was titrated against standard sodium thiosulfate solution, using starch as indicator. After iodine had ceased to separate, the solution was set aside and kept for 24 hours in the dark. Under these conditions no more iodine was evolved, showing that the blue copper complex did not decompose to react with iodide.
In Table I are given typical results obtained in the course of this investigation. I n the fifth column are given the exact quantities of various solutions that were found to give the most consistent results. The results given in the last column show that the amount of iodate added to the solution in terms of its equivalent iodine can be estimated with accuracy even in the presence of very large amounts of copper salts. The only difficulty encountered in the present case was the extreme slowness with which the reaction proceeded, each titration taking several minutes, sometimes even half a n hour, for completion. A number of catalysts, including ammonium molybdate (6), which has been mentioned by Kolthoff as suitable for catalyzing the liberation of bromine from a mixture of bromide and bromate, were tried without success. The kinetics of the reaction are being studied and will be published shortly. TABLE I. TYPICAL RESULTS A. Sodium pyrophosphate solution 10%. B. Acetic acid solution, 10% C. Potassium iodide solution, 10%. Volume Volume of 0.1 N NazSzOa Volume Concenof of tration 0.2N TheoNo. KiOa N CuSO, Conditions retical Found cc. cc , cc. cc Cc . 1 25 0.1 5 B 25.0 25.0 10 c 2 25 0.1 .. 75 A 12 B 25.0 25.0 10 c 3 25 0.1 10 10 c 25.0 25.0 4 25 0.1 25 10 c 25.0 25.0 5 50 0.1 50 150 A 25 B 50.0 50.05 20 c Volume of 0.01 N NazSzOs 5.0 5.0 0.01 Sameasin4 6 5 10.0 sameasin4 10.0 0.01 7 10 25.05 25 Sameasin4 25.0 0.01 8 25
.
E
Literature Cited DQbourdeaux,L., Compt. rend., 138, 147 (1904). Dushman, S.,J . Phys. Chem., 8,453 (1904). Kikuchi, S.,J . Chem. Sac. Japan, 43,173 (1922). Kolthoff, I. M.,and Cremer, C. J., Pharm. Weekblad, 58, 1620-4 (1921). Kolthoff, I. M., and Furman, N. H., ”Volumetric Analysis”, Vol. 11, p. 385,New York, John U’iley & Sons, 1929. Ibid., p. 387. Ibid., p. 431.
