V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 a gieat deal more carbon black agglomeration and alignment. The same results were obtained when the samples were first cured and then aged.
1445
to thank -4. H. Nellen, JV. B. Ilunlap, Jr., and C. J. Glaser, Jr., Lee Rubber & Tire Co., for helpful advice throughout the work
SUMMARY
The autoradiograph technique making use of carbon 14 is useful in studying the carbon black distribution in rubber. I t is superior to the photomicrographic technique in studying carbon black dispersion in rubber. Autoradiographs of different carbon black-rubber mixes (tensile strengths varying from 300 to 3300 pounds per square inch) showed visible variations in the carbon black distribution which closely agree with the tensile strength data, whereas photomicrographs of the same mixes showed no differences among the various mixes. The autoradiographic technique is also useful in tracking down carbon black agglomeration in rubber.
LITERATURE CITED
(1) Axelrod, D. J., Atomic Energy Commission, Isotope Division,
Circ. A-4 (January 1948). ( 2 ) Boyd, G. A . , Atomic Energy Commission, MDDC-1226 (1947). (3) Calvin, -M., Heidelberger, C.,Reid, J. C., Tolbert, B. M.,a n d Yankwich, P. E., "Isotopic Carbon," S e w York, John Wiley &
Sons, 1949. (4) Grosse, -1. V., and Snyder, ,J., Science, 105, 241-2 (1947). ( 5 ) McClure, Tom, "Radioautography," T r o c ~ r l n h17, , 1-7 (March 1949). Available from Tracerlab, Inc., Boston, Mass. ( 6 ) Yagoda, H., "Radioactive Measurements with Suclear Emulsions," Chap. 10, New York, John Wiley & Sons. 1949.
ACKNOWLEDGMENT
The authors gratefully acknowledge the financial support of the Lee Rubber & Tire Co., Conshohocken, Pa. They also wish
RECEIVED March 2, 1961. Presented before the Division of Rubber Chem.%MERICAN C H E M I C A L SOCIETY, Washingcon, D. c., February 28, T o r l i sponsored by Lee Rubber and Tire C o . , Conshohocken, Pa.
istry, 1961.
Precipitation of Thallium(1) from Perchloric Acid Solutions OTTO L. FORCHHEIRlER AND ROBERT P. EI'PLE' Metcalf Research Laboratory, Brown L'nirersity, Procidence, R . I . A method of analysis for thallium(1) in the presence of thallium(II1) and iron(II1) in acidic solution has been devised by adapting the method of Moser and Brulcl to perchloric acid solutions. The proposed method involves the metathesis to the normal chromate of the complex dichromate precipitate formed in perchloric acid solutions. The precipitation is quantitative for weights of thalliunl(1) less than 50 mg., subject to the conditions described.
S
EVERAL methods for the determination of thallium( I j in the presence of thallium(II1) have been suggested.
Soyes, Pitzer, and Dunn (6) used a met,hod involving oxidation with bromate in acidic chloride or sulfate solutions. This method is based on the work of Kolthoff ( 3 ) and Zintl and Kienacker ( I 4 ) , and was used in oxidation potential studies by Stonehill (11). Swift and Garner (18) obtained good results by a titration with iodate in concentrated hydrochloric acid solution, using iodine monochloride as indicator. Singh and Singh (9) used chlorate and iodine monochloride in a potentiometric titration. Various gravimetric methods have also been used, Precipitation of thallium(1II) as the hydroxide in ammoniacal solution was used by Majer ( 4 ) and by Prestwood and Wahl ( 7 ) . The latter also precipitated the thallous ion as the bromide, chromate, and hexachloroplatinate. The chromate precipitation was extensively studied by Moser and Brukl (b'), who precipitated thallium chromate from ammoniacal solutions; they prevented the interference of a large variety of other cations by the use of complexing agents. Harbottle and Dodson ( 2 ) adapted the chromate precipitation in the presence of thallium(II1) (which would precipitate as the hydroxide in alkaline solution) by complexing it with cyanide. Prestwood and Wahl ('7) also used this method. I n these last two cases, the precipitation was made by adding a solution of ammonium hydroxide, sodium cyanide, and sodium chromate to the acidir solution containing the thallium(1) and (111) ions. The present authors used thallium perchlorates in perchloric acid. The method of analysis arose from the desire t o keep these solutions free from complesing agents during the Separation of thallium(1) from t,hallium(III) in the presence of iron. The 1
Present address, Tracerlab, Inc.. Boston, Mass.
separation of thalliuni(1) from an acidic solution would be a d a p t able to the separation from thallium(II1j occurring alone or in solutions containing iron(I1) or (111j, nickel, copper, aluminuni, manganese, and other elements that require complexing agents when t,he method of hIoser and Brukl is used. For example, when sulfosalicylic acid (prescribed by Moser and Brukl) was used to complex ferric iron, the thallium(II1 j present oxidized it and was reduced to thallium(1). When alkaline cyanide was used to complex the ferric iron, another equally serious difficulty occurred. Tests showed that although neutral or acidic solut,iona of ferricyanide have no effect on thallous ion, alkaline ferricyanide oxidizes the thallium to thallic hydroxide. This fact makes it impossible to use alkaline. cyanide for the separation when ferric iron is present. Therefore, attempts were made to precipitate thallous ion as the dichromate from acidic solutions; results were not reproducible. If the acid concentration Tvas 2F or more, high results were obtained, probably due to the formation of polychroniates. At lower concentrations of acid the results were low-probably owing to the formation of a mixed chromate-dichromate precipitate. At acid concentrations more than 1F the thallium(1) was incompletely precipitated; however, a t a perchloric acid concentration of 1F all the thallium(1) was precipitated when the solution was allowed to stand overnight and cooled to 0" C. before filtering. As the dichromate cannot be used as a weighable form, the precipitate must be converted to the chromate by alkali after other cations have been washed clear. This metathesis is carried out by the alkaline cyanide solution, and thus combines
1446
ANALYTICAL CHEMISTRY
Table I. Effect of Change Less than Quantitative Precipitation of Thallium(1) 1. Concentration of acid in original precipitating sohtion greater than 1F 2. Smaller concentration of CrOd-- used to precipitate thallium 3. Use of conversion solution containing no CrOd-4. Failure to cool to 0’ C. before filtering
in Conditions of Analysis Coprecipitation of Thallium(111) 1. Lower acid concentration in precipitating solution 2. Greater concentration of CrOl-- in conversion 8 0 1 ~ tion 3. Greater concentrations of both thallous and thallic ions in precipitating solution and larger weight of precipitate
The wash water was 0.5F in perchloric acid and 0.125F in sodium chromate. The washed precipitate was treated with a solution, the conversion solution, by pouring this solution into the crucible and letting the crucible stand for about 0.75 hour. The conversion solution was 1F in ammonia, and 1 F in sodium cyanide, and contained 2 rams of sodium chromate in I50 ml. The converted precipitate $now thallium chromate) was washed with a 50-50 solution of alcohol and water and dried for an hour a t 110” C. The process of conversion can be followed by watching the change in color of the precipitate from orange to yellow. The converted precipitates were examined under a microscope a t a magnification of 150, with illumination from above. The precipitate was homogeneous, yellow, and crystalline with no apparent flaws. So impurities could be detected in this manner. DISCUSSION
the advantages of the Harbottle and Dodson separation of thallium(1) from thallium(II1) with those of separation of thallium(1) from a variety of common elements-e.g., iron or nickel-whose chromates are soluble in acidic solutions and whose complex cyanides either are insoluble or form insoluble salts with thallium. When thallium(1) is being determined in the presence of severa1 of the common metals, it seems advantageous to separate it from an acidic solution, for then several other elements may be determined in the filtrate without complications caused by an alkaline cyanide solution. However, when thallium(1) is to be separated from thallium(II1) alone, the alkaline cyanide method of Harbottle and Dodson seems better becauee the conditions for using it are less stringent. REAGENTS
The reagents used in test solutions were prepared as follows. Thallous perchlorate was prepared by the method of Wagner (IS). Metallic thallium (c.P., Kahlbaum) was cleaned in cold 6F perchloric acid overnight and then dissolved in more of the same acid by gentle heating. The salt formed was recrystallized twice from water and dried a t 110’ C. It was tested for iron by means of potaasium thiocyanate and for chloride by means of silver nitrate, using spot tests as suggested by Feigl (1). Tho maximum amounts of the impurities turned out to be less than 25 p.p.m. of iron, and 10 p.p.m. of chlorine. Solutions containing thallic perchlorate were prepared by ozonizing perchloric acid solutions of the thallous salt made by the above method. The thallic perchlorate formed was sufficiently oxidized so that after the ozone had been swept out, the presence of thallous ion could not be detected with iodine monochloride in 4F hydrochloric acid. The thallic perchlorate solutions were stored in the dark, and a 0.01F solution in 2F perchloric acid showed no appreciable reduction over a %month period. Ferrous perchlorate was prepared by cleaning Baker and Adamson iron wire (“for standardization”) with crocus cloth and acetone and then dissolving it, while in contact with platinum foil, in 6 F perchloric acid. A Bunsen valve was used to provide a hydrogen atmosphere, and after solution was complete, it was diluted to the required volume. The ferrous perchlorate solutions were titrated against ceric sulfate that had been standardized against Bureau of Standards arsenious oxide. The chloride content of these solutions was accurately determined by titration with standard mercuric nitrate, using sodium nitroprusside as indicator; a t pica1 result for chloride was 37 f 1 p.p.m. The perchloric acicfused was G. F. Smith Chemical Cos’s72% vacuum distilled or 70% “purified” acid. The latter was found to have less iron (less than 5 X 10-6F) than the former. All stock solutions of thallium or iron salts were 2F in perchloric acid. The sodium chromate and sodium cyanide used were Baker and Adamson’s reagent grade, not further purified. PROCEDURE
The desired quantity of thallous perchlorate solution wm pipetted into a beaker and the thallic and ferrous perchlorates were added. Sufficient 0.5F sodium chromate was added to make the solution 0.125F in sodium chromate. The reaction between thallium(II1) and ferrous iron was sufficiently slow so that these reagents could be added together if the chromate was added immediately, thus oxidizing the iron present to the ferric state. The precipitate was allowed to stand overnight and was then cooled to 0’ C. and filtered, using Corning sintered-glass crucibles.
Two types of error can be introduced; the conditions under which they occur are listed in Table I. Table I1 contains the results obtained under the conditions described in the procedure. The conditions must be adjusted so that all the thallous chromate precipitates, with as little thallium(II1) as possible coprecipitating. Table I1 shows how good the method is within the limits of its applicability. The concentrations of thallium(1) and (111) should not exceed those given in Table 11, and the weight of the precipitate should not exceed 50 nig. The presence of iron a t no time caused difficulty. Table 111 shovs quantitatively some of the errors, the sources of which aere indicated in Table I. I n the first run the weight of the precipitate exceeds the u per limits of the method. The concentrations are the same as tiose of the fourth run in Table 11, but the conversion medium is not able to absorb all the thallium(IT1) in such a large quantity of precipitate. The second entry shows that, even with rather small amounts of thallium, appreciable negative errors caused by the solution of the precipitate occur only when the volume of the solution containing the precipitate is tripled. The weights of thallium used are the same as those in the last entry in Tahle 11, where the error in a volume of 100 ml. is negligible. The third entry in Table I11 demonstrates the loss of precipitate when no chromate is added to the conversion medium. Entries four and five show the effect of cooling to 0” C. before filtering. The samples in the fifth entry were cooled before filtering; those in the fourth were not. The weights in these two entries are greater than the stated maximum of 50 mg. The method can easily handle larger weights when no thallium(111) is present. As most of the unfavorable conditions listed in Table I were determined as the final method was being developed and this method is free of most of them, no further quantitative
Table 11. Results Fe(I1) or TliI) (111) Gram Gram 0.0340 None 0.0340 S o n e 0,0340 0.0490 0,0340 0.0245 0.0134 0.0122 0.0170 0.0122 0.0102 S o n e I n one sample
Calcd. Vol. Weight TI of of Actual Weight of T12CrOl (111) S o h . TllCrOi Obtained Gram M1. Gram Gram None 100 0.0436 0.0436,0.0431,0.0433,0.0430 0,0307 100 0,0436 0.0436,O. 0442,0,0435,0.0434 None 100 0,0436 0,0437,O. 0437 0.0307 100 0.0436 0.0433,0,0430 0.0184 100 0.0174 0.0173,0.0179 0.0284 100 0.0218 0 . 0 2 1 6 , 0 . 0 2 1 6 , 0 . 0 2 1 8 , 0 . 0 2 2 5 100 0.0131 0.0128.0.0128 0,0349gram Tl(II1) was present, in the other, none.
Table 111. Quantitative Results on Some Limitations of Method Calod. Vol. Weight TI of of Actual Weight of TltCrO, Obtained (111) Soln. T I ~ C ~ O ~ T~(I) MZ. Gram Gram Gram Gram Gram 0 0680 0 0735 0 Oh614 200 0 0872 0 0878,O 0882,O 0885,O 0890“ 0 0102 None 300 0 0131 0 0117,O 0119 0 0340 0 0270 0 0307 100 0 0436 0 0422,O 0422.0 0425,O 0431 0 1530 None None 100 0 1968 0 1934.0 1948 0 1530 None None 100 0 1968 0 1969,O 1960 a Four values chosen a s examples from eleven values actually obtained. All values had a similar error. b I n one sample 0.0349 gram Tl(II1) was present, in the other, none. Fe(I1)
GI)
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 results can be given on the limitations of the method. The statements made in Table I, however, apply equally t o the present method and to the analysis under slightly different conditions previously investigated. As can be seen from Table I, the larger the concentrations of chromate ion a t any time during the analysis, the greater the amount of coprecipitation. Furthermore, even after subjection to the alkaline conversion solution no thallic hydroxide can be seen on the precipitate, although thallium(II1) has coprecipitated. The authors feel that this indicates the formation of a complex between thallium( I), thallium(III), and chromate ion, not unlike the complexes formed by thallium with the halide ions (8). As the acid conc,entration in the precipitating solution has a large effect on the coprecipitation phenomenon, some partially hydrolyzed species of thallium(II1) may enter into such a complex. Other indications also seem to favor complex formation as an explanation rather than selective coprecipitation or the formation of a solid solution. If large quantities of thallium(II1) are present when the precipitation occurs, the precipitate is much larger in bulk than when thallium(1) is present alone. The dichromate precipitate, though usually orange in color, will be more yellow when large amounts of thallium(II1) have been coprr.cipitated. In an early experiment where extensive coprecipitation was indicated, the precipitate was first washed with the acidified chromate solution and then treated with the conversion solution containing alkaline cyanide. This solution was filtered, acidified with perchloric acid to drive off the cyanide, and then made alkaline with sodium hydroxide. Large quantities of black thallic hydroxide precipitated. This is strong corroborative evidence of the formation of a thallium(1)-(111) complex with chromate. All attempts to precipitate thallium(II1) alone as the dichromate failed, a t thallium concentrations as high as 0.OW.
1447 Using only thallium(I), the authors have been able to use the method to obtain thallium chromate precipitates n-eighing as much as 0.2624 gram, in good agreement with the calculated values. Hence they think that the positive errors occurring with precipitates of thallium chromate heavier than 50 mg. cannot be attributed to the failure of the conversion solution to reachall parts of the precipitate. Inasmuch as the cyanide complex of thallium(111)has been shown by Spencer and Abegg (10)to be very stable, the positive errors may be caused by the failure of the cyanide ions to reach the interior of the precipitate in sufficient concentration to pull the thallium(II1) ions from the precipitate and convert them to the cyanide complex. LITERATURE CITED
(1) Feigl, “Qualitative Analysis by Spot Tests,” pp. 97-98, 161, New York, Nordeman Publishing Co., 1939. (2) Harbottle and Dodson, J . A m . Chem. SOC.,70, 880 (1948);
Brookhaven National Laboratory, Chemical Conference No, 2 , 2 2 6 (1948). (3) Kolthoff, Rec. trav. chim., 41, 172 (1922). (4) Majer, Z. phys. Chem., 179A. 51 (1937). (5) hfoser and Brukl, Monutsh., 47, 709 (1926). (6) Noyes, Pitrer, and Dunn, J. A m . Chem. Soc., 57, 1229 (1935). (7) Prestwood and Wahl, Ibid., 70, 880 (1948); 71, 3137 (1949). (8) Sidgwick, “Chemical Elements and Their Compounds,” p. 486, S e w York, Oxford University Press, 1950. (9) Singh and Singh, J . Indian C h a . Soc., 16, 27 (1939). (10) Spencer and Abegg, Z . anorg. Chem., 44, 379 (1905). (11) Stonehill, Trans. Faraday Soc., 39, 72 (1943). (12) Swift and Garner, J . A m . Chem. Soc., 58, 113 (1936). (13) Tagner, J. H., thesis, Brown University, 1949. (14) Zintl and Rienacker, Z . anmg. allgem. Chem., 153, 278 (1926). RECEIVED October 18, 1950. Based on a portion of the thesis submitted by 0. L. Forohbeimer in partial fulfillment of the requirement for the degree of doctor of philosophy in the Graduate School of Brown University.
Radioactive Tracers in Paper Partition Chromatography of Inorganic Ions W. JOE FKIERSON‘ AND JOHN W. JONES2 Oak Ridge Institute of Nuclear Studies, Oak Ridge, Tenn. Paper partition chromatography has been successfully used in many separations of inorganic ions. A n effort has been made to develop techniques in the use of radioactive elements in order to enlarge the usefulness of this method of analysis. A device for scanning paper chromatograms is described. Radioactive tracers have been found useful for locating and identifying an element. The techniques for identification may be based on decay and growth,
energy of radiation, and type of radiation. They have been applied to the identification of radiochemical impurities, and they are useful in locating and identifying the elements on a paper chromatogram, especially when there is no satisfactory reagent for identifying small amounts of the ions on paper and the ions are not well separated. These methods should find important applications in nutrition and plant growth studies.
Ir
M
ANY separations of inorganic ions by paper partition chromatography have been reported in recent years. In genera], the procedures used for detecting the position of the various ions on the paper are based either on the addition of an inorganic or organic substance which will produce a characteristic color with the ion or on the fluorescent properties of the substance either alone or after the addition of a suitable reagent. Such methods have been found satisfactory for the separation and detection of very small amounts of inorganic substances. LaCourt ( 7 ) has reported the separation of aluminum, iron, and Present address, Agnes Scott College, Decatur, Ga. Present address, Department of Chemistry, Carnegie Institute of Technology Pittsburgh Pa. 1
titanium from a solution containing from 1 to 10 micrograms of the salt in 0.01 ml. of solution. This paper is an application of radioactive tracer techniques to inorganic paper chromatography. In particular, the following elements or combinations thereof have been studied: iron, cobalt, nickel, manganese, and zinc; lead, bismuth, and polonium; sodium and potassium; and titanium and scandium. Several papers have appeared on the use of P3* ( I ) , 1 1 3 1 (IO), C14 (3,4),and SJ* (11) activities in organic paper chromatography. To the authors’ knowledge no studies have been made with inorganic systems. The tracer use of activities is twofold in purpose: to locate a particular chemical on the paper, and to study the distribution of
