0.42 nig. Results of randomly submitted control standards simultaneously analyzed with routine samples b y a t r a i n d chemist are also shown in Table
111. Types of Samples Analyzed. A variety of samples containing such divt,ise ions as beryllium(II), alumin u m ( I I I ) , borate, nitrate, chloride, and jwrchlorate were analyzed by the over-all procedure. As shown in Table IT,n o interference is noted.
ACKNOWLEDGMENT
The authors appreciate evaluation aid given by John H. Sikes. LITERATURE
CITED
(1) Fritz, J . S., Oliver, R. T., Pieirzyk, Piei.rzyk, D.J., A X A L . CHEM.30,1111 (19%). ( 2 ) hleyer, R. J., Schulz, W., Z. anyew. Chem. 38, 203 (1925). (1925) (3) Powell, R. H., Menis, O., ANAL. 1549 (1958). CHEU.30, 154 ( 4 ) Simons, J. H., € "Fluorine Chemigtry,"
Vol. 2, pp. 83-9, Acade~nic Press, New York, 1954. (5) Warf, J. C., Cline, W.D., Tevebaugh, R. D.. ANAL.CHEM.26.342 11954). (6) Weaver, J. L., Purdy, \V: C., 'Anal. Chim. Acta 20,376 (1959). RECEIVEDfor review April 28, 1961. Accepted July 10, 1961. Fourth Conference on Analytical Chemistry in Nuclear Reactor Technology held October 12-14, 1960 at Gatlinburg, Tenn. The Idaho Chemical Processing Plant is operated by Phillips Petroleum Co. for the U. 9. Atomic Energy Commission under Contract X o . AT( 10-1)-205.
Analysis of Thallium Amalgams WILLIAM
T.
FOLEY and JUDITH M. OSYANY
Chemistry Departmenf, Sf. Francis Xavier University, Antigonish, Nova Scotia
b A sample of thallium amalgam is dissolved in nitric acid and, after removal of the mercury by precipitation with formic acid, the thallium is estimated either b y titration with iodate or by a coulometric titration with electrogenerated bromine. An electrolytic method of preparing pure thallium sulfate is described. Formic acid is proposed as a reducing agent for thallium(lll).
A
~ I M P L E precise
method of deterniining thallium in thallium amalgams nas needed in a current study of the diffusion coefficients of thallium in thnlliiun amalgams. The method of Richard. and Daniels ( 2 ) was not suitable. 111 preliminary experimcnts the prescwce of formic acid caused no interfvrence with the determination of macro amounts of thallium(1) by the iodate method ( 3 ) . I n another set of experiments microsamples of thallium(1) \I ere oxidized coulometrically with the use of electrogenerated bromine ( I ) and, after conversion to the sulfate, these samples were reduced with hot dilutc formic acid and again estimated with clectrogenerated bromine. The results showed t h a t formic arid was a good redwing agent for thallium(II1). REAGENTS
Thallium Sulfate. The thallium sulfate was purified by the folloiving procwliiie, which is less demanding on the time and attention of the 01)erator than the procedure of Richards and Daniels ( 2 ) . Thallium metal was dissolved in nitric acid, and the nitrate was conv c r t d to the sulfate, which was filtered off and dried. A sample of this salt was dissolved in water and the pOH of this solution was brought to 1 or
slightly less with sodium hydroxide. The thallium metal was electrolyzed into a mercury cathode b y means of a potentiostat a t a cathode potential of -0.51 volt us. thc hydrogen electrode. The reference electrode was mercurynierruric oxide. At this potential, lead remains in solution because Eo for the reduction of lead plumbite is -0.54 volt. From time to time more thallium sulfate was added to the electrolyte; hydrazine sulfate was used as a n anodic depolarizer. Enough salt was used to ensure a n amalgam concentration of about 20%. The amalgam was transferred t o filter paper in a funnel and, after i t was carefully washed with water, the amalgam mas transferred to a boiling flask. Slightly less than the stoichiometric amount of nitric acid, based on the reduction of the acid t o nitric oxide and on the oxidation of thallium, was added, and the mixture was heated under reflux. Enough water was added to dissolve the thallium nitrate and the mercury was filtered off. The solution now contained only thallium(1) and possibly trace amounts of salts of more noble metals. To free the thallium from any remaining impurities, the solution was adjusted t o pH 9.5 with ammonium hydroxide, and 4 grams of silver nitrate was added. The solution was electrolyzed at constant current. The current density was partially governed by the stirring and +he necessity of obtaining an adherent : h e r deposit at the cathode. With the conditions prevailing, the current density was 3 X l o + amperc per sq. cm. Thallium oxide appearrd as a very adherent deposit at the cathode. From time t o time more silver nitrate was added as needed, and the electrodes were removed occasionally to recover the products of electrolysis. The electrode containing the thallium oxide was immersed in a hot dilute solution of formic acid, which soon converted it to thallium(1) formate. The thallium formate was evaporated to dryness on the water bath and thcn, by
means of sulfuric acid, it was converted to thallium sulfate. The thallium sulfate was crystallized and dried. Mercury. RIercury was purified by drawing air through mercury which was covertd by a dilute solution of nitric acid. I t was then distilled to remove noblr metals. Thallium Metal and Thallium Amalgam. T h e method of Richards and Daniels (2) was used to prepare thallium metal from thallium sulfate, and the preparation of thallium amalgam was also according t o the procedure described by these authors. The amalgam was stored under hydrogen. The other chemicals used were analytical grade reagents. PROCEDURE
A weighed sample of amalgam was dissolved in 8111 nitric acid. Enough sulfuric acid mas added to ensure conversion of the nitrate to the sulfate, and the solution was evaporated on the water bath until the cover glass was dry. The salt rvas transferred to a 250-ml. round-bottomed flask. To remove a n y hydrolyzed mercury salt from the walls of the beaker, the latter was rinsed with 10 ml. of a 20% solution of formic acid, and the rinsings were added to the flask. A water-cooled condenser was attached t o the flask; the contents were heated to a gentle reflux, and this heating was continued until the mercury gathered in one or two globules. The reflux condenser was necessary t o prevent mercury from steam distilling from the reaction flask. The mercury was freed from the solution by filtration, and the beaker containing the filtrate was placed on the water bath until the volume was reduced to 15 to 20 ml. The procedure followed next was dependent on the sample size. If the sample was a macrosample, the solution was transferred to an iodine flask and sufficient concentrated hydrochloric acid was added to ensure a concentration of 3h' VOL. 33, NO. 12, NOVEMBER 1961
1657
at the conclusion of the titration. A few milliliters of carbon tetrachloride were added, and the solution WRS titrated with standard potassium iodate solution which had been prepared by direct weighing and dilution. The iodate was converted t o iodine monochloride, and the end point was marked by the disappearance of the iodine color in the carbon tetrachloride. The hydrochloric acid was maintained at 3N or greater to permit a rapid reaction. If the amalgam sample contained a micro amount of thallium, it was transferred to a 60-ml. beaker and titrated with electrogenerated bromine in the manner described by Buck, Farrington, and Swift ( I ) . EXPERIMENTAL RESULTS
An amalgam containing 14.71y0 thallium was prepared and analyzed ac-
lium was analyzed with the use of the coulometric modification of the procedure. The results obtained are given in Table I.
Table I. Analysis of Thallium Amalgams
0.2816Yc Thallium
14.71y0 Thallium
Sample
Sample
wt.. gram
Thallium.
70
0 6641 0.2818 0 7594 0.2815 0.8299 0.2807 0.5422 0.2820 0 5632 0.2809 0.7164 0 2816 0 8347 0 2806 0 6433 0.2822 Alean 0 28141
wt..
grams
Thalhum.
ACKNOWlEDGMENT
70
The financial assistance of the S a tional Research Council of Canada and of the Xova Scotia Research Foundation is gratefully acknovledged.
4.400 14 71 2.623 14.71 3.153 14.71 2.736 14.70 3.947 14.73 4.009 14.72 3.645 14.67 2.843 14.70 14.706
LITERATURE CITED
(1) Buck, R. P., Farrington, P. S., Swift, E. H., ANAL.CHEM.24, 1195 (1952). (2) Richards, T. W., Daniels, F., J . Am. Chem. SOC.41, 1732 (1919).
(3) Swift, E. H., Garner, C. S., Ibid., 58, 113 (1936).
cording to the above procedure with the use of 0.16005 K I 0 3 in the final step. A4namalgam containing 0.2816% thal-
RECEIVED for review June 5, 1061. Accepted A4ugust22, 1961.
Extraction and Determination of Gold with Tetraphenylarsonium Chloride J. W. MURPHY and H. E, AFFSPRUNG Departmenf of Chemistry, The University of Oklahoma, Norman, Okla.
b The gold chloride complex forms a precipitate with tetraphenylarsonium chloride which can b e extracted into chloroform. From 7 to 40 pap.m. of gold can b e determined spectrophotometrically b y measuring the absorbance a t 323 mp. Interference studies were made, and the optimum percentage of hydrochloric acid in the aqueous layer was evaluated. The iron interference can b e suppressed with fluoride, and none of the platinum metals seriously interfere with the determination when present in concentrations one tenth that of the gold.
S
very sensitive methods for the determination of gold are outlined by Sandell (7, 8), and an excellent study of the extraction of gold as the bromide complex has been made by McBryde and Yoe (4). Lenher and Kao (8) first reported the determination of gold by the extraction of the chloride complex. Mylius (6) had studied this extraction extensively, and i t was reported that the extraction was not quantitative when the concentration of gold was low. All of these methods have a number of interferences which require prior separation, and in the case of methods depending upon formation of a colloid, the interferences are severe. There are several methods for small traces of gold, but there is no EVERAL
1658
ANALYTICAL CHEMISTRY
really simple method for the determination of moderate amounts of gold which can be carried out rapidly and easily and which is relatively free from interferences. Colorimetric and spectrographic methods for the determination of gold have recently been reviewed by Beamish (2). Tetraphenylarsonium chloride forms a precipitate with the chloride complex of gold which is soluble in chloroform, and it appeared that this reaction and solubility could be used to estract and determine gold. For a colorimetric method chloroform, as an estraction solvent, has definite advantages over solvents which are less dense than nater. A great gain is made in ease of manipulation, and less danger of Ioss is present in the separation of immiscible solvent when repeated extractions are made. Also, the use of the chloride complex of gold is preferred over the bromide as the bromide ion is easy to oxidize, and bromine itself produces an interfering color. I n addition, i t is unnecessary to remove all traces of nitrates since they do not interfere in the extraction process. The gold is extracted into chloroform as the tetraphenylarsonium chloroaurate, and the concentration is determined spectrophotometrically. The method outlined here is designed to determine gold in solutions of gold chloride in concentrations too low for gravimetric methods
but large enough for the use of a direct extraction and colorimetric measurement. The method might he used after a concentration of gold in solutions containing metals common t o ores as very few metals interfere. EXPERIMENTAL
Apparatus and Materials. Beckman DU and DK-1 spectrophotometers were used for absorption measurements. Electrolytic gold, 24 carat (American Platinum Works) was used as a primary standard. Purity of the gold standard was confirmed by analysis of the metal using the hydroquinone reduction method. Gold standard solutions were prepared by dissolving 248.9 mg. of gold in aqua regia and evaporating nearly to dryness to remove oxides of nitrogen. The residue was dissolved with 2 ml. of concentrated hydrochloric acid and diluted to 250 ml. Aliquots were taken for subsequent analysis. Platinum and palladium solutions %-ere prepared from the pure metals (ilmerican Platinum Works). Tetraphenylarsonium chloride solutions 0.05M (K and K Laboratories). Absorption Spectra. A portion of the gold solution was pipetted into a 50-ml. volumetric flask, 1 to 2 ml. of concentrated hydrochloric acid were added, and the solution was diluted. An aliquot was introduced into a 60ml. separatory funnel and 20 drops
