vidual photographic plates over a period of several weeks. Table I1 summarizes the data obtained for the graphite electrode procedure. Relative standard deviation is reported on the basis of oxygen concentration. The platinum bath procedure yielded similar data. ACKNOWLEDGMENT
The authors are grateful to the Fanstcel Metallurgical Gorp. and to E. I. du Pont de Nemours & Go., Inc., for supplying several niobium samples used in this investigation. LITERATURE CITED
(1) ANAL.CHEM.33, 480 (1961).
(2) Fassel, V. A., Altpeter, L. L., Spedtocham. Acta 16,443 (1960).
(3) Fasscl, V. A., Gordon, W. A., ANAL. CHEM.30, 179 (1958). (4) Fassel V. A., Gordon, W. A. Jasinski, R. J., “hoc. 2nd Intern. Conference on Peaceful Uses of Atomic Energy,” Vol. 28 p. 583-92, 1958. (5) Fwse V. A., Gordon, W. A., Jminski, R. J., Evens, F. M., Rea. unw. nines 15, 278 (1959). (6) FasscI, V. A. Gordon, W. A., Taheling, It. W., A S T M Spec. Publ. 222, 41-60 (1958). (7) Faasel, V. A., Tabeling, R. W., Speclrochin. Acta 8, 201 (1956). (8) Hansen, W.R., Mallet, M. W., ANAL. CHEM.29, 1868 (1957). (9).Harris, W. F., “Technology of Columbium (Niobium),” p. 57-9, Electrochemical Society, %ley, New York, 1958. (10) Laboratory Equi ment Cor St. Jose h, Mich., “Con&ctimetric &ygen Annkaer for Ferrous and Nonferrous . _. Met&and Alloys,” 1959. (11) McIntosh, A. B., J . Zml. Metals 85, 367 (1957).
’P,
(12) Niobium Task Force, Oxygrn Srth Group, Division M, Committee E-3, ASTM, “Recommended Method for the Determination of Oxygen in Com-
mercial Grade Niobium, Vaciium, Fusion Platinum Bath Technique,” 1960. (13) Parker, A., “Determination of Case3 in Metals,” pp. 64-74 Iron and Steel Institute, Percy Lund, Humphries & Co. London, 1960. (14) Qmiley,W. G.,ANAL.CHEM.27,1098 (1955). (15) Tottle, C. It.,J. Inst. Metals 85,375 (1957). (16) Walter. D. I., ANAL. CHEM.22. 297 ’ (i950). ’ (17) Wilkens, D. H., Fleischer, J. F., Anal. Chim. Acfa 15,334 (1956). RECEIVEDfor review January 3, 1961. Accepted March 29, 1961. Contribution No. 977. Work performed in the AmLaboratory of the U. 5. Atomic Energy Commission.
A Critical Review of Colorimetric and Spectrographic Methods for Gold F. E. BEAMISH Departmenf o f Chemistry, University of Toronto, Toronto 5, Ontario, Canada
b This review deals with the colorimetric and spectrographic methods for gold recorded up to August 1960. In view of the wide industrial and scientific uses for gold and its alloys one must hope for the development of a more useful choice of well defined instrumental methods. Among those currently available the author ‘recommends the bromaurate, tin(ll), and rhodanine spectrophotometric methods, and internal standard methods for spectrographic determinations of solutions. For the direct analysis of gold alloys no spectrographic procedure was found which gave adequate attention to homogeneity.
I
T IS evident that the most acceptable spectrographic methods are of Europcan origin, which situntion may be due to the reluctance of the industrial organizations and consulting institutes which possess modern spectrographic equipment, t o make their methods of analysis generally available. This secrecy is regrettable, particularly since these organizations are privileged to use the benefits of a century of scientific literature. Furthcrmore, from a long range point of view, one may doubt that the economic advantagcs of a policy of secrecy would equal the benefits derived from a free interchange of analytical information. I n the case of spectrophotometric methods for noble metals,
i t is unlikely that private organizations retain any significant amount of analytical knowledge unavailable to the analyst. The history of the development of colorimetric and related methods for gold emphasizes the general approach of the researcher to the development of new analytical procedures. Long established color reagents are forced into the role of quantitative adaptations and relatively little effort is made to tap the great volume of organic compounds, from which source one can cxpect sensitive and specific reagents. While investigations directed toward the establishment of structure-reagent relationships and the subsequent syntheses of suitable compounds have provided few new analytical procedures, one cannot thus dismiss the responsibility of the researcher to produce a choice of more effcctivc spectrophotometric methods for metals such as gold, whose applications are a concern of so many fields of scicntific activity. An empirical approach, however distasteful to the inflexible mind, will permit the examination, in a relatively short time, of large numbers of reagents and conditions of application. With a little ingenuity in the construction of suitable equipment one may obtain a volume of data which could provide many new analytical reagents as well as encourage more fruitful generalizations concerning structure-reagent relationships.
While it is generally accepted that very dilute solutions of gold salts rapidly decrease in gold content, there has been little recognition of the action of light on these solutions. Svedberg (63.4)has discussed the finding that alkaline gold solutions yield both more numerous and smaller particles if exposed to ultraviolet light prior to the addition of a reductant. Since many of the proposed colorimetric methods require a very low acid or a basic medium, one may expect that, prior to the addition of the reduct8ant,lengthy exposure to light would be detrimental to precision and accuracy for both colloidally dispersed and dissolved colored constituents. An examination of this characteristic could be of considerable value. The instability of dilute solutions of gold and other dissolved constituents was also discussed by Leutwein (90A), who ascribed the loss of strength to base exchange reactions with the glass container and to adsorption. Solutions containing 0.001% of gold showed 0.1 to 0.3% of the original strength after storage of 230 days in Jena glass, whereas in quartz flasks the loss was very slight. With one exception ( S A , @ A ) , the colorimetric methods for gold involve absorptivity measurements on colloidal gold solutions, on the colored oxidized product of the organic precipitant, or on an organic extract of the colloidal suspension. No colored goldVOL. 33, NO. 8, JULY 1961
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organic complex, soluble in aqueous media, has yet been applied to colorimetric determinations. COLORED CONSTITUENTS IN AQUEOUS MEDIA
o-Tolidine or 3,3’-dimethylbenzidine &asperhaps thti first reagent for gold to be applied effcctivcly in a colorimetrir detcrmination. Pollard (@?A) in 1919 usrd a hydrochloric acid solution of o-tolidinc to detect 1 pg. of gold in 20 nil. of solution a t a dcpth of 10 cm. The yellow color resulted from oxidation by gold(II1) salts, chlorine, iron(III), or nitrous acid. Subscqucnt to the separation by fire assay Geilmann and Mcyer-Hoissen ( H A ) rccommcnded the tolidine method for thc determination of gold in glasses. An arcuracy to 5% could be expectrd. In 1946, Clabaugh (Ian) recordd a morr detailed description of the tolidine method and used it to detrrminc the thickness of electrodeposited gold coatings. Because of persistent impurity the tolidine was purified from sulfuric acid solution, in which solution the reagent was satisfactorily stablr. The instability of dilute gold solutions was recognized and stability was Achieved by the addition of large amounts of both hydrochloric and nitric acids to solutions containing 1 mg. of gold per liter of solution. For the preparation of samples Clabaugh removed nitrous acid, etc., by impinging on the surface of the gold solution a jet of air purified by passing it through concentrated sulfuric acid, Ascarite, and a fritted-glass filter. The usual evaporations with hydrochloric acid wcrc rejected because of the reduction to gold or gold(1) salts. This claim is invalid when sufficient care is exercised during the evaporations. The intensity of the color developmrnt reached a maximum in 1 to 3 minutes and remained stable for 10 to 30 minutes. Twenty-five milliliters of solution in cylindrical cells 5 cm. in length werc used a t a wave length of 437 mr and 1 to 4 pg. of gold could be determined with an avcrage deviation of 4%. Prior to use all glassware was cleaned with aqua regia. From this and earlier publications it would appear that there were no intcrferences from silver, copper, nickel, zinc, iridium, lead, mercury, platinum, rhodium, tin(IV), and many other metal cations. There was interference from iron and ruthenium. Ne11 (%A) used o-tolidine in hydrochloric acid solution to determine gold in plating solutions. The color was developed for 10 to 20 minutes and the absorbance was measured with a 4250 to 4400-A. filter. The o-tolidine method was examined in considerable detail by Schreiner, Brantner, and Hecht (48A), who were apparcntly unaware of the report by 1060
ANALYTICAL CHEMISTRY
Clabaugh ( I d A ) published six years earlier. Contrary to the latter’s procedure, no effort was made to purify the tolidine. Hydrochloric acid solutions a t pH 1 were used and the method permitted the determination of 10 pg. of gold in 100 ml. of solution with a layer thickness of 34 mm. A mercury light source and a mercury blue filter werc used. In general the data concerning interferences reported earlier were confirmed. The interference from iron was rcmoved by phosphoric acid. The authors’ reference to the “yellow gold complex compound” is unacceptablc. No evidence is offered in any pertinent publication to suggest that gold is a constituent of the source of the ycllow color. In the present author’s opinion the color arises from the oxidation of the tolidinc and not improbably is due to a pitraquinoid structurc. Sincc this colorimctric method is widely used and has a high Sensitivity (0.004 pg. per sq. cm.) Sandell’s expression of sensitivity [ ( p g . / cm.9 for an absorbance of 0.001 (&A)], one must hope that the charactrr of this reaction will receive somc attention. In particular, it would be of interest to learn thc cffccts of low :tridity and salt content on the stability of the’yellow constituent. o-Dianisidine, like o-tolidinc, was used by Pollard (4dA) as an indicator in B volumctric method for gold. Block and Buahanan ( 7 A , 8.4) modified Pollard’s (42.4) method for the determination of gold in urine, blood plasma, etc. Thc colorimetric method involved a development of the red color by the reaction between thc slightly acid o-dianisidine reagent and gold(II1) salt in the presence of the buffer and the iron ion inhibitor, potassium fluoride or the bifluoride in thc case of blood plasma. The maximum color dcvclopment occurred within 3 to 10 minutes and followed Beer’s law. Excess acid and oxidizing impurities such as aqua regia and nitrosyl chloride interfered. The method was applied to urine containing 5 to 300 pg, of gold and to blood plasma containing 5 to 30 pg. of gold. The data obtained from the salted samplcs scarcely support the authors’ claim of accuracy and, most assuredly, methods such as this cannot be described as specific. Furthermore, the preliminary destruction of organic matter by sulfuric acid, all of which must subsequently be removed, could surely be replaced by a more suitable procedure. Researchers inhestcd in colorimetric reagents of the dianisidine type should give some attention to the discussion of new indicators for the microvolumetric determination of gold by Belchcr and Nutten (JA). Similarly applying the oxidation potential of gold(II1) salts, Kul’bcrg (%?A) used the lcueo compound of
malachite green, which thus produccd a change from colorless to blue-green, The reacting salt solution, containing sodium fluoride to decolorize iron(III), was buffered by acetate to a pH of 3.6 and heated for a few minutes, and the color was compared visually with standard solutions using a yellow filter, Three micrograms of gold in 10 ml. of solution could thus be obtaincd. For sniallrr proportions of gold thc green constituent was vxtractcd with ehloroform, by which technique the author was able to determine 3 X gold in a copper alloy. While one would expect interference from associated noble metals and from the oxidizing substances associated with the dissolution of gold, methods such as these are often very sensitive and easily devised. The compound, Brilliant Green, in which the methyl groups of malachite grccn are replaced by ethyl groups, was recommended by Lapim and Grin (d39A) for the colorimctric dcterrnination of gold subsequent to extraction by toluene. Iodine, bromine, and iron intrrfercd. The authors provided no data and no detailed procedure and from an analytical point of view the report is of little value. COLORED COLLOIDAL CONSTITUENTS
A useful spectrophotometric method involving extinction measurements at 380 mp of the orange bromoaurate ion was described by McBryde and Yoe ( S S A ) . The gold chloride solution was treated with hydrobromic acid to produce a salt content such that the bromide concentration was at least one third that of the chloride content, in which case the color formation was immediate and permanent with a pH of less than 2. By visual comparisons 0.5 p.p.m. could be detected. Quantitativcly, a t 380 mp the sensitivity was about 0.04 pg. per sq. cm. and Beer’s law applied. The platinum and associated base metals interfered, but with the exception of osmium these could be isolated by solvent extraction with isopropyl ether from 211f hydrobromic acid solutions. Prior to measurement of color the gold was transferred to an aqueous medium and the aqueous extract was treated with hydrobromic acid and heated to restore the full color of the aurobromatc ion. The method waa applird to a gold ore subsequent to an aqua regia treatment of the roasted ore. From the small amount of data provided one cannot recommend this application. In gencral, this spectrophotometric method is rccommrndcd as moderately sensitive and accrptably accurate. Good selcctivity is achieved by solvent extraction with isopropyl ether, which must be frce of alcohols and peroxides. The anions AuBr4- and AuC14- wcre also used by Vydra and Celikovsky
(64.1) for the spectrophotometric determination of gold in the ultraviolet region, the absorption maximum being 254 mp for the former anion and 311.5 mp for the lattrr. Standard solutions of gold free from nitric oxides contained 0.2 to 4 pg. of gold per ml. in the form of AuHr4- and 2 to 35 pg prr ml. in the case of AuC14- With the latter anion, in 0.1N HCI media and over the optimum concrntrntion range of 4 to 30 pg. Ff gold per ml., the maximum denation was +3y0 and the maximum error was f1 .07y0. Sodium chloride conrentrations of 0.1M werc acceptable, but a t pH’s higher than 2.5 the absorption dccreased rapidly. With the anion AuBr,- traces of bromine in the 0.1N HBr interfered with the absorption band, but this was avoidcd with 0.1M KBr. There was interference from higher values of the bromide salt. As indicated hy hlcl3ryde and Yoe ( M A ) , the chloride anion was readily converted to AuHr,-. Ovcr the optimum concentration range of 0.5 to 4 pg. per ml. the maximum deviation was The h 7 2 and error was *3.3%. method was applied only to anhydrous chloroform extractions of gold. The application of dithizone to the detection and colorimetric determination of gold and many other metals was discussed by Fischer and Weyl (20A). The many colored insoluble complexes were selectively extracted by carbon tetrachloride from an aqueous media. Bleyer, Nagel, and Schwaibold ( 6 A ) and Beaumont ( 2 A ) used dithizone for the quantitative estimation of gold and many other metal cations. The first explanation for the reaction between dithizone and gold was recorded by Erdey and Rady (18A) who ascribed the yellow-brown of the rarbon tetrachloride extract to the compound Au(HD& which was formed in a 0.5 to 0.1N acid solution. Interference from palladium was eliminated by thiocyanate; silver was removed as the bromide, and iron was complexed with phosphoric acid. Quadrivalent platinum did not interfere. In the presence of copper the proposed mrthod required two filters, one of which was used for the sum of the copper and gold content and the serond for thr copper contrnt alone. Becausr this dithizone mrthod is one of the few procedures which involvrs formation of n colored gold complex and because the elimination of intrrfrrence from copper should not be a difficult problem, onc may hope that the method will receive further attrntion. Dime th ylaminobrnzylidenrrhodanine is one of the morr accvptable reagents for the colorimrtric determination of gold. Mercjkovsky (3bA) used this reagent for the microdetermination of gold in organic tissucs. However, Block and Ruchanan ( 8 A ) were unable
to apply the method to biological tissues because of “the large blank from the reagent itself and the inadequate direct,ions.” Polucktov ( 4 J A ) used the reagent in a solution containing ethyl alcohol, chloroform, and benzene, added to a solution of gold Containing a few drops of nitric acid. The pink-violet organic layer permitted thc visual detection of 0.1 to 0.2 pg. in 5 ml. of solution. To isolate gold the author coprecipitated with mercuric salt and tin(I1) chloride. Sandell (44A) used dicthylaminobenzylidenerhodanine in a useful colorimetric method for gold following its isolation by tellurium precipitated by tin(I1) chloride. In contrast to such collectors as mercury salts, tellurium provided no interference in subsequent operations and as little as 0.2 mg. in 50 to 100 ml. of solution served to isolate 0.2 to 0.3 pg. of gold in the presence of 0.5 gram of iron, copper, and lead. Tin(I1) chloride was found superior to sulfur dioxide when iron and other reductants were present. In weakly acid solutions the rhodanine reagent produced an insoluble red-violet product, which by analogy with known salts contained the rhodanine complex of univalent gold. While strong oxidizing substances reacted with the rhodanine reagent to produce a violet-red product, the latter, in contrast t o the gold complex, was soluble in carbon tetrachloride. The colloidal red-violet aurous complex was formed in 0.12M and 0.075M hydrochloric acid solutions; with the former concentration there was greater precision but at the lower acidity as little as 0.5 pg. of gold could be determined in a final volume of 4 or 5 mi. with a 1-cm. cell. The full color intensity of the suspensions was attained in 1 or 2 minutes a t the lower acidity and more rapidly a t the higher acidity. With the latter the average error was 3% in the range of 1 to 8 pg. of gold. The interference from palladium present in small amounts could be avoided by the addition of dimethylglyoxinie. Traces of iron were complexed with sodium fluoride. Quadrivalent platinum did not interfere, but divalent platinum in amounts of the order of 1 p.p.m. or more may interfere, particularly on standing. The procedure involved d i s ~ ~ l u t i o n of the tjcllurium-gold precipitate in aqua regia, removal of oxidizing substances, and addition of sodium fluoride and an alcoholic solution of the rhodanine. For amounts of gold in excrw of about 0.4 p g . visiial comparisons can be made; for lesser amounts a photometric mcasurcmrnt with a green filter (500 mp) is rreommrndrd. Tho time of color development must bc measured exactly and the preparation of standards need not, include a trllurium collection. Beer’s law was obcycd up to a t least
2 p.p.m. and the sensitivity was 0.01 pg. per sq. cm. at 500 mp. The procedure was applied successfully to the determination of gold in the ash of certain plant materials. The method is designed for, small amounts of gold only and is acceptably free of interference, provided the initial isolation with tcllurium or othrr suitable reductants and collectors is usrd. As onc would expect with colloidal dispersions, the presence of electrolytes affects the color distribution; the method is particularly scnsitive to the time of color development and to the acidity of the reaction medium. Natelson and Zuckerman (%A) applied the method to the estimation of gold in biological materials. These authors introduced a modification of Sandell’s ashing technique and applied the centrifuge to avoid filtration. The claim for a simplification of procedure lacks sufficient support and furthermore the claim for an increase in sensitivity by a factor of 6 is incorrect. No data were presented to indicate any increase in sensitivity. However, the authors found Beer’s law to apply only to gold concentrations below 1 pg. per ml. rather than the 2 p.p.m. reported by Sandell (44.1). Hars (.MA) used pdimethylaminobenzylidenerhodanine for 0.03 to 0.3 p.p.m. of gold. The red color reached maximum intensity after 5 minutes and was stable for 30 minutes. A filter of 562 mp was used. The interference from iron was removed by sodium metaphosphate. Cotton and Woolf ( I 7 A ) recorded a modified rhodanine method for the determination of gold in thin films. These authors rejected the o-tolidine method because of poor sensitivity, the dithizone method as lacking in precision, and the rhodanine method because of inaccuracy. The p-dimethylaminobenzylidenerhodanine procedure recorded by Sandell (44A) failed to provide the necessary precision. The proposed method involved a solvent extraction by isoamyl acetate. To attain the desired accuracy a minimum excess of reagent was required and toward this end the authors used a dilute solution of isoamyl alcohol. Since the color failed to develop a t acidities greater than 1N and faded with time, the pH, the periods of extraction, and color development required careful control. The procedure involvad dissolution of gold in aqua regia, removal of acid by an air current, dissolution, addition of hydrochloric acid and reagent t o an aliquot containing 4 to 10 pg. of gold, e,xtraction with isoamyl acetate, filtration, and measurement of absorption a t 515 mp. Experimental data indicated a gold-rhodanine reagent ratio of 1 to 1. The authors regarded as unlikely the presence of univalent gold and suggested the presVOL. 33, NO. 8, JULY 1961
* 1061
ence of trivalent gold in a complcx anion. Compared to the aqueous method (44A) the procedure provided much greater precision and equal sensitivity. In the prcscnt author’s opinion it is one of the most reliable methods for the determination of small amounts of gold and its integration with some form of gold coprecipitation would be a contribution, Rhodaminc l3 has been used for the colorimetric detcrmination of gold. Goto ( M A ) used this and other rcagcnts for fluorescent detection of gold. This approach is worthy of further examination. A colorimetric application was reported by McNulty and Woollard (31A) to be suitable for 0 to 30 pg. of gold. The method could bc applied subscquent to the removal of platinum by coprecipitation with manganese dioxide and the isolation of gold with tellurium as the carrier. For maximum sensitivity the concentration of hydrochloric acid must be controlled and maintained a t a low levcl--e.g., 0.5Mand the chloride concentration kept below 2111. The gold-rhodamine constitucnt was extracted by purified isopropyl ether and the absorbance was measured using Ilford 605 filters. No data were included to support the authors’ claim for a scnsitivity double that provided by the pdimethylaminobenzilidenerhodanine reagent. The method requires precise techniques and high purity reagents. 1-Naphthylamine hydrochloride was used by Paul’snn and Pevzner (98A) for the colorimetric detcrmination of gold. The intensity of the violet color increased during the first few minutes and remained constant for 1 to 2 hours. Beer’s law was obeyed and an accuracy to *2% was attained. Small amounts of copper, zinc, lead, and iron did not interfere. Strong acids, basic solutions, excess of sodium chloride, and palladium interfered with the color development. The reagent was also used by West and McCoy (66A) for the detection of gold in nonaqueous media. An intcnse violet color was developed in n-butyl alcohol solutions of gold chloride. One may hope that these researches will be integrated with suitable separations and extended to provide a useful spectrophotometric method for gold in alloys and natural products. Tin(I1) chloride has a long history of application for the detection of gold. From time to time techniques were recorded which allowed the purple of Cassius test to be applied semiquantitatively. Bette1 in 1911 (6A) made visual comparisons with standards subsequent to isolation of gold from cyanide solutions by precipitation with a ainc-copper couple. Excess cyanide waa added to emure dissolution of ferrocyanides and sinc cyanide. To compensate for the impurities usually present in the zinc,
1062
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ANALYTlCAL CHEMISTRY
the latter was measured accurately. Ten minutes were required for a determination and for more accurate results the author used a modified procedure which required 17 to 20 minutes and which was “as perfect as any colorimetric process of its class can be.” Brodigan ( 9 A ) also used the tin(I1) mcthod for barren cyanide solutions, from which the gold WRS removed by reduction with zinc in the prescnce of excess cyanide and lead nitrate. Depending upon the quantity of gold, the color varied from yellow to purple. Seven minutes were required for a determination and since no standards were used the accuracy was surprisingly high. With suitable reductants and more precise techniques this method for cyanide solutions would provide increased accuracy and applications. Stanbury (61A) applied the purple of Cassius method to certain excretions from patients subjected to gold salt treatments. The various factors affecting the accuracy and precision of the tin(I1) method were first recorded by Fink and Putnam (19A). It was found that the tint of color was related to the acid concentration and solutions below 0.05N produced only yellow to light brown colors irrespective of the gold content. At 0.64N the purple color appeared. The time of color development was also dependent upon the acid strength, proceeding more rapidly with the weaker acid solutions; with the latter the color intensity was not a function of the reagent strength. The yellow colloidal form was acceptably stable, whereas the purple form precipitated rapidly in strong acid media. As would be expected, the salt content of the solution must be kept a t a minimum. The authors provided a procedure for the colorimetric determination of gold in cyanide solutions. It was stated that “when less than 0.04 mg. of gold is to be determined, the low acid stannous chloride test is believed to be superior to the gravimetric assay procedure with respect to accuracy and speed.” I t is disappointing that no data were provided to substantiate this dubious claim. However, one cannot doubt that colorimetric methods competitive with the classical assay are within the realm of probability, It is surprising that no one has yet recorded data to prove that any colorimetric, volumetric, or spectrographic method for gold or any noble metal offers the speed, accuracy, and precision of the classical assay when applied to ores. Sandell (46A) recorded the sensitivity of the tin(I1) method as 0.05 pg. per ml. of solution. A procedure was provided for solutions containing 10 to 100 pg. of gold per 20 ml. or less. An acidity of 0.05N waa preferable, although acceptable results could be ob-
tained a t 1N acidity. Although a filter was not necessary, slightly lon.er transmittancies could be obtained with a green light. There was interference from platinum, palladium, ruthenium, tellurium, selenium, silver, mercury, etc, An interesting application of the tin(I1)-gold reaction was described by Cole (19A), who used textile fibers previously immersed in a solution containing pyrogallol and tin(I1) chloride to produce a range of colors when in contact with gold solutions. The method offers potential applications for chromatographic separations as well as for semiquantitative determinations. Nider (SYA), without sufficient justification, rejected the tin(I1) method in favor of the application of K2HgId and potassium iodide to an alkaline gold solution. The sensitivity was approximately 1 pg. per ml. Certain derivatives of phenols, amines, and aminophenols have been used for gravimetric, volumetric, and colorimetric determinations of gold. The colorimetric procedures may involve direct absorbance measurements of the resulting colloidal system or a measurement of the color of the oxidized reductants, which method is used in the oLtolidene method described above. Gallic acid was used by Heredia and Cuezao (d4A) to determine gold in minerals containing copper. The gold, precipitated in the acetate medium (.26A),was removed and the absorption of the oxidized product in the filtrate was measured. Shnaiderman (49A)examined the colorimetric application of phenol, pyrocatechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, 1naphthol, and 2-naphthol. The sensitivity reached 0.5 to 10 fig. in 5 ml. of solution. The dependence of the color intensity of the colloidal dispersion stabilized by starch, on acidity, time of reaction, presence of electrolytes, excess of reagent, and gold concentration, was examined. The precipitating medium was adjusted by a pH 3 to 6 buffer and the gold content was determined from a calibration curve. Amino acids in an alkaline solution of formaldehyde were used by It0 (26.4) to produce a reddish violet colloidal solution which obeyed Beer’s law. The method was sensitive to 1 pg. per ml. o-hinobeneenearsonic acid was used by Chen and Yeh (11A) to produce, a t a pH of 4, a red colloidal solution which could be stabilized by gelatin, and obeyed Beer’s law up to about 7 pg. per ml. A filter of 500 mp was used. There were no interferences from silver, lead, nickel, and a large number of foreign elements. The interference from iron was controlled by ethylenediamine; copper interference was removed by dissolution with potassium cyanide of the precipitate formed with
the reagent; and platinum was also removed by precipitation by the reagent. Palladium interfered. A procedure was described for application to gold contents of a few micrograms per milliliter and a limit of identification was set a t about 0.1 pg. per ml. 13enzidine has also been used as a colorimetric reagent. Tananazv and Vasil’cva (63.4) matched the color of a gold solution sddcd to benzidine paper with a series of standards. The error ranged from *2% for 100 pg. to *20% for 60 pg. Plank (41A) used a hydrochloric acid solution of benzidine and an 5-50 color filter and measured the intensity of the red color by a photometer. Beer’s law was not obeyed and working graphs were required. None of the above derivatives of phenol or amino reductants offer significant advantages over the established tin(I1) reduction method. Compared to the Latter one may expect in some instances a greater degree of freedom from interference in the presence of certain associated metals. In general, one is well advised to isolate the gold prior to a colorimetric determination. Formaldehyde in a basic medium has been used to produce a blue colloidal solution. Muller and Foix (34.4) and Serio and Indovina (47A) have a p plied this color development; the former thus determined the gold content of rocks and the latter the gold content of drugs. Neither of these methods is as applicable as the tin(I1) reduction. This is true also of the hydrogen peroxide reduction in a basic mrdium described by Chechnevn (IOA), who used the method subsequent to the separation of gold from platinum by adsorption on mercurous sulfidc. An inkresting method for the separation and semiquantitative deternunation of gold involved the reduction and adsorption of the latter by finely powdered mercurous chloride (%A) ; 0.1 gram of the latter, addcd to solutions whose gold content varied between 0.05 and 200 pg., produced variations of color from a faint pink to a dark purple. Thc author claimed a recovery of one part of gold from 10* parts of sea wakr. Furthermore, pure gold could be recovercd by sublimation of the niprcury salt. Standard controls prepared under precisely the same conditions were required. Strong oxidizing constitucnts must be absent as well as large proportions of associated base and noble metals. Colored solutions introduced no difficulty. The mcthod was applied to cyanide solutions subsequent to the removal of gold by zinc and dissolution to produe 200 fig. per 100 ml. of solution (66A). Plaksii and Suvorovskaya (40A) discussed the fact that colorimetric determinations by formaldehyde, benzidine, 1-naphthylamine, tin(I1) chlo-
ride, and mercury(1) chloride were each particularly sensitive to the presence of salts of both alkali and heavy metals. This criticism applies also to the methods of determination by 88corbic acid (6OA), thionalide (4A), and nitrosobenzene with potassium hexacyanoferrate (d7A). Shnalderman stated that ascorbic acid produced a stable suspension of gold a t p H 3 to 6 in the presence of starch. Rather large proportions of iron, nickel, copper, lead, etc., could be tolerated. Beer’s law was not obeyed. Thionalide (2mercapto-N-Znephthylacetamide) was used by Berg and coworkers (4A) for the colorimetric determination of gold in sulfuric acid solutions and Kraljic (27A) used nitrosobenzene and potassium hexacyanoferrate in gold solutions at p H 5 and measured the extinction using a green filter of 528 mp. None of the above three methods provides the advantages of the tin(I1) chloride reagent. Phenyl a-pyridyl ketoxime was used by Sen (46A) for the spectrophotometric determination of gold, subsequent to the extraction of the orangeyellow gold chelate from a solution adjusted to a pH between 3 and 6. Beer’s law applied over the range of 2 to 16 p,p.m. The sensitivity was about 1 pg. per ml. and the chloroform extract showed a sharp absorption peak at 450 mp with a second absorption band in the ultraviolet region. The color development was instantaneous, stable, and unaffected by the usual variations of time, temperature, and preparation of reagcnts. The method compares favorably with several of the better colloidal methods but it is subject to the usual sensitivity to salt content. The statement that “therc was no interference by thc ions with which gold is ususlly associated” is incorrect. Palladium, cyanide, and iodide interfered and in the presence of copper, cobalt, and nickel the addition of EDTA was required, which reagent caused a slight decrease in absorbance. The remaining platinum metals, silver, iron, lead, etc., did not interfere. Chromatographic Determinations. A variety of semiquantitative methods involve the development of colored gold salts on a filter paper medium. Costeanu passed purified carbon monoxide (16A) or phosphine (16A) over strips of filter paper moistened with solutions of both known and unknown gold content. Filter paper impregnated with zinc chloride or tannin could also be uscd ( l 4 A ) . Zvyagintsev and coworkers applied this technique to papers, impregnated with mercury(1) salts, to cyanide solutions previously oxidized with nitric acid and potassium chlorate (67A). For application to ores the gold was first extracted with iodine and amalgamated with mercury. The
sensitivity was given as 5 mg. per ton (69A). A modified method was used for field determination (68A). An interesting photometric determination of gold in native and commercial alloys and bullion without dissolution of the sample was described by Al’Bov ( 1 A ) . The procedure involved the photometric measurement of the reflection coefficients in both red and blue light. The ratio of the coefficients was experimentally relatcd to the compositions of the alloys. The method was applied to both binary and ternary alloys. A description of the physical equipment was included. SPECTROGRAPHIC METHODS
The most effective spectrographic and spectrophotometric methods recorded for gold, each applied under optimum conditions, provide approximately similar sensitivity, precision, accuracy, and speed. Furthermore, considering the variety of materials of which gold is a constituent, the applicable spectrographic procedures are too few in number, These techniques have been applied to the determination of gold in alloys, ores, rocks, solutions, and organic tissues. For gold alloys various effective procedures for spectrographic determinations have been recorded. From the point of view of speed the spectrographic determination of traces of gold in alloys is in general superior to all other methods and the method can be made comparable in accuracy and precision to spectrophotometric methods. A satisfactory experimental evaluation of the relative accuracy of spcctrographic and classical methods for the determination of gold in rocks, ores, and concentrates would be a useful contribution. Considering the simplicity of the two techniques, it is surprising that none of the reports which deal with this problem contains sufficient data to evaluate properly the relative success of spectrographic methods. Preferably, these data should include a comparison of the speed and accuracy of gold dctcrminrttions on a variety of ores by fusion, cupellation, and parting, and by spectrographic procedures applied directly t o the ore and indirectly through selective dissolution with single acids and complete dissolution with aqua regia. For thc determination of traces of gold in solution the author prefers spectrophotometric methods, although a variety of acceptable spectrographic methods have bcen recorded. For organic tissues, where ignition is applicable, the spectrographic determination of gold is in general comparable in efficiency to any chemical method. Furthermore, spectrographic VOL. 33, NO. 8, JULY 1961
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methods for thc direct examination of gold in tissues have been recorded. It is surprising that fluorescent methods for determining gold in situ have not been examined. More effective liaison between chemical and medical researches would rncourage this development. For the drtermination of gold in minerals and orrs Toisi (27B) described spectrographic methods designed to allow a more complete vaporization of the gold than could be ohtained by the more conventional addition of ore or mineral to the cavity of an electrode. The equipment provided for a continual, uniform addition of finely powdered ore delivered by a conveyor belt to a glass tube, whose inside diameter was similar to the width of the electrode gap, and whose lower end was protected from thc heat of the arc by a graphite crucible which contained an aperture simibr in diameter to the glass tube. The sharpened carbon electrodes were inclined from the horizontal position. The recommended initial current of 10 amperes provided an operating current of 12 to 13 amperes. The 10-second exposure involved a consumption of 0.35 ml. of the powder. A quartz spectrograph was used and measurrments were made with the ultimate gold line, 2676 A., which prohded a dctcctable limit of 6 X lod6gram per gram of sample. Presumably the precision was satisfactory, but the accuracy was not acceptable. The former was explained on the assumption that thc position of the particles within the arc area allowed romplrte distillation of the admixed gold and the lack of accuracy on the assumption that the gold-containing partieles were not always uniformly distributed. Furthermore, the constnnt addition of the particles encouraged wide variations in the current density. The second method was designed to provide increased accuracy and sensitivity and involved an addition to the former system of a magnetic firld of about 2 gauss to blow the flame horizontally into an inner and outer flame. Addition of the sample to a single portion of the flame only, permitted detection of local changes in excitation. The author found that the gold line was emitted most eff,qctively a t about 5 mm. distant from the electrodes. The maximum intensity-concentration relationship oceurrrd with gold contents between 21 X lo-’ and 60 X gram per gram of sample. The author stated that, while the method did not provide high accuracy, the order of magnitude of the gold content was readily obtained. Since the applicable concentrations involve ores whose values arc approximately 0.030 troy ounce per short ton and since the surccss of the method assumes a uniform distribution of this gold, one cannot, 1064
ANALYTICAL CHEMISTRY
with half-gram samples, even rely upon the order of magnitude without some prior knowledge of the character of the gold deposit. I t is unfortunate that the author included no data from a fire assay collection, which could readily have been achieved with a few assay tons, and subsequent scorification and cupellation. This addition would a t least support the method for samples of exceptional homogeneity. Iwamura (fOB)attempted the preparation of rleetrodes with 25-gram samples of gold ore. Onc method involved the usc of zinc oxide as a binder and a second involved silica, carbon, and molasses. The conccntration-density relationships or thc gold line 2676 A. used and the srnsitivities with tho two types of electrodes varied between 4X and 3 X %. Lead-Gold Alloys. While, with the techniques available, one can doubt the usefulness of spectrographic methods for the direct determination of gold in ores, these techniques may provide an excellent approach to both qualitative and quantitative determination of gold in the synthetic alloys required for the extraction from ores and concentrates. This id particularly true when these alloys contain other noble metals or when the gold content is of the order of micrograms. For milligram amounts of gold, in the absence of other noble metals, the cupellation and acid dissolution of silver beads will provide greater accuracy and perhaps comparable speed. The accuracy of the spectrographic determination of gold in lend alloys, such as an assay regulus, will, of course, depend upon a variety of factors, of which homogeneity is of primary importance. Unfortunakly, the few publications dealing with thc dekrmination of gold in lead havc given this important condition too little attention. Jolibois and Bossuet (11B) used the ultimate spark lines 2676.1 to determine gold in 10 mg. of lead ~ l l o ywith a sensitivity of 2 x lo-‘%. With an assay ton of ore and the usual 30-gram button this method would, of course, not compcte in accuracy with the cupellation and subsequent arid treatment of the silver h a d . To determine gold In lead alloys Guenther (9B) adjusted the electrical conditions to ensure rqual intensity of the lead arc line 2567 and Rpark line 2562. Subsequently pairs of lead and gold lines of equal intensity were identified for fixed proportions of each metal. From these tables the proportion of gold in the unknown acid could be obtained. The range of application was stated as 10 to The method can be useful if high sensitivity and accuracy are not required. Nedler and coworkers (16B, IYB,3OB) selectively extracted gold from ores
by aqua regia or by a fire rxtmction to produce a lead button, rrmoving lend with nitric acid and treating the impure gold residue with aqua rrgia. Platinum was used as an internal standard and the solution was added to a graphite olcrtrode and subjected to a high-trnbion flame arc. With the line pair of 2665 for gold and 2428 for platinum the sensitivity was 1 0 - 4 ~ 0and thc avrrage error was 5 to 6%. A scwxid pulhvition (17B) reported us(’ of thr gold line 2676 and the platinum lint. 2658 and rceordcd the accuracy as f4Y0. Nedler (16B) also rccordrd n procc duw for the determination of noblv nictals in whieh a silver rlcctrodc was usrd. To determine gold in soap Chub, Hegemann, and Rost (6B) extracbd with bromine and ether, evaporated an aliquot of the extract, aqd fuwd the residue with lead aretatc to produce a lead button. The latter was partcd with acid and bromine a a t r r and used directly in thr arc. Silver-Gold Alloys. Some effort has been made to apply spectrographic methods to determine gold in silver alloys, particularly silver assay beads. With the latter, free from other noble metals, the spectrographic method % o d d offer few, if any, advantages ovcr thr parting procrdure. On thr othcr hand standard wrt procedures applied to complrx beads are difficult and time-consuming. This problem has received some attention in a previous review (4B). KO effort is made here to deal with methods drsigned to determine the total noble mctal content in silver beads nor to deal with base metal impurities in gold alloys. Mankin (13B) attempted the spectrographic analysis of silver-gold beads by relating concentrations to the inknsity of three sets of silvcr-gold lines (19B). Various technical difficulties were suggested for the author’s failure to achieve quantitative results, some of which were valid and most of which could have been readily corrected. Jolibois and Bossuct (11B)in 1925 used the ultimate gold lines 2676 and 2428 to determine gold in cupelled beads and claimed a sensitivity of 2 X mg. on a 10-mg. silver bead. For an assay ton of ore this would permit the detection of about 0.02 troy ounce per ton of ore. However, the author’s data include no reference to the degree of homogeneity in the silver bead. Pardo (%?OB, 81B) recorded in good detail directions for the spectrographic determination of gold subsequent to a collection by cupellation to a silver bead, The procedure avoided the necessity of the usual assay furnaces and accessories and involved only standard equipment. The silver-gold bead was placed in the crater of a carbon electrode and covered with a few grams of borax glass, to which was added, as an
intcrn:il st:intlnrd, an tiqrieous solution of nmmonium molybdate. Arc rxritation :it 220 volts was applied. Line intrrisify comp:irisons wcre made from synthrtie st:indards containing gold to 3 X IO-’ wrying from 4 X grnin. Thc gold line 2428.0 was usrd Iirtnwn 3 x 1 0 - h and gram and the, linr 3029.2 hrtncon 10+ and 4 X 10 gr:im ‘flrc, mcthod \vas applied to n v:tric+y of s:tn~plcq,some of which h:id hrrn s i i I ~ ] ( v ~ tto ~ d thv clnssiral fir(. n w r y . ‘I’hc tlclctrrious cffccts of nonhoniogcwity wcrr nvoidcrl by comp k t r hiirning. Thc author’s claim of 30% prrriiion 19 siipj)ortrd by a few data hut, allowing for some dcgrcc of misunderstanding due to inaccurntr translation, one cannot ~ ~ x c u sthe c failiirr to den1 Kith thr prohlrm of proprr mi\ing and sampling of thc orrs Unclout>tetlly the author was denline; nith thr difficult distrihiition of nativr gold, hut to accopt an error of 500% incroly through n lark of homogrneity is scarrely reassuring The author corrcctly pointrrl out the valur of thc combined application of classical and spcctrogr:iphic methods to brads containing gold and plntiniim metals, but from the tcrhniquc nnd data providrd one can do no more than acrrpt the potentiality. An intrgratrd rlcctrolytic and spectrographic method for the determination of gold was also described, but unfortunatdy no conclusion was reached conrcrning the rficiency of this interesting and potentially useful separation. Thc proccrlurc involved the trmtmrnt of the ore sample with aqua regia and zinr to produce R residue from which the gold was removed by rcpcatrd extractions with a dilute potassium cyanidr solution. The 1:lttt.r was suhjectcd to clcctrolysis with the gold collrctrd hy mr’rcury plaerd in thr cavity of a cnrhon clcctrode The latter ma? subsequently usrd RS an clrctrode for spcctrogrnphir drtrrmination. A condensed report of the above rescarchcs was also rrcordcd by Azrona and Pardo
(sm.
Base Metal-Gold Alloys. Considerable effort has been made to determine gold in copper alloys by spectrographic methods. Rreckpot and Mevis (6R) thus drtrrmincd some ninr mrtals, including gold, in conccntrations betwrrn 1 and The characteristic lines of each metal n err compared to ndjacrnt copprr lirirs Nedlcr (16B) iiscd spcctrographic mcthods for the analysis of single gold particlrs cxtractrd mechanically from ores. He uscd clectrodrs of cadmium, into one of which the gold particle was pinched and then subjcctcd to a high voltage spark. Standard alloys were prepared by fusion with lead and subsequrnt cupellation. Here again the data included no spcrial
effort to achirvc homogrneity, although the author made no claim for high accuracy. A somewhat similar approach was used by Pastorr and Occhialini (22B) to determine gold, plat,inum, and silvrr in coppcr, the length of linrs bring compared to those of the principal metal. Ostmhrvskaya (IRB, f9B) comp:srvd t,hr logarithmic srctor and micropliot,omrt,ric mrtliotls for th(: drt,rrmination of gold, :tnt.imony, and bismuth in coppcr and concluded that comp:iral)lc rcwlts corild hc: c>xpcctcd. A pn.rtiriilarIy siiitnhle pair of lines was 2427.9 for gold and 2442.6 for copprr. The optimum conditJions wrrc 10 to 20 an~pm-cs3.5 to 25 volts, and cxposiircs from 30 sccmids to 3 niinutm. I t was possihlr to dctcrminc gdrl in coppcr t>o1.7 X Gold Solutions. T o obtain traces of gold in solution *Joliboih and Bossurt ( I I B ) usrrl mrrcurir or bismuth sulfidc RS a carrirr and pln.ced the mixed prccipitntrs in thc cnvity of a carbon elcctrodc. The arc sprctrum allowed the detection of 1 pg. of gold. These authors drscril)cd an o.ltern:ttive mrthod which involvpd tJhc clrctmlytic deposition of gold at, boiling tmnprratures on a ring or wire rlcctrode. Baylc and Amy (33) usc>d this techniqur and applird a highly cohrlcnscd spark attaining a srnsitivity of 1 pg, TJrbain (2RB) acknowlrdgcd the sensitivity of thc above. methods (JR, 11B) but found thc accuracy unacccptable. To avoid the difficult,irs incident to the mcasuremcnt of the intensity of ultimate lines, thr authors uscd silvcr as an internal standard. Directions for the electrolysis of thc cyanidr solution of gold and silvrr includcd t,hc use of a carbon cathode and a platinum wire anode. An accuracy to about 10% was obtained. TJrbain (2.9B) nlso applied an electrolytic method to collect 1 to 5 pg. of gold from solutrions of biological products containing silvcr and potassium cyanide; 0.001 smpcre WRS used with a ca.rhon cathodc and a platinum wirr anode. The total deposit was volntilizrd by x spark and the gold contrnt was ohtained from the previously rlctrrmincd rrlat,ionship between gold content and the intensity ratio of the thrcr scts of gold-silver doublets, 267G-2660; 2428-2438; 31233281. The mrthod provided a precision of about 6% nnd by sclrctivc elrctrolysis intcrfcrcnccs were largcly avoided. Price and Telford (2SB) discussed briefly thc dc4xrrnination of gold in “ores m d other matcrials.” The recommendcd procrdurc includcd a precipitation of uranium and subsequently a separation of gold by coprccipitation with tcllurium. The mixed precipitate was dried and a 15-mg. portion was mixed with graphite and completely burned on a graphitc rlcctrode by a d.c. arc. The intensities of the 2675.95
and 2748.26 gold lines Nere coinparrd with n set of standards or alternativrly with the 2967.2 tellurium line as an internal standard. A second method involved the solvcnt extraction of gold dithizonatc and addition of the evaporated extract to a coppcr clcctrode. Comparisonq acre madr ttith the 2675.95 gold line in sample and standartls. The sensitivity of the goldtcllurium method was rrcordcd n9 0.3 p.p m. One must not concludc that cithrr of t h t above mrthods uill hc applirahlr to gold ores in genrr:il or to all other mrttcrials containing traces of gold. In a 1)ricf communication T m i s and S u i n ( I d B ) discussrd thr cxtrartion of 4 to 50 p g . of gold from solutions containing 0.2 to 10 pg. prr ml. The mcthod involved adsorption of gold on a miktiirr of rthylrrllulose and cellulose pmdcr. The pad was ignited at 600’ C., thr ignited rrsidue was diwolvd in aqua regia and, subsequent t o a rrdriction in volume, the solution was adsorbd on alumina. The latter m s ground with a mivture of alumina, silvcr chloridc, and tin oxide. The accuracy of this carrirr distillation method was improved by a two-linepair mrthod of evaluation which reduced the photographic error caused by the deviation from unity of the deflection ratios. The technique, discussed in earlier papers ( I B , 26B) consisted of utilizing two line pairs for each determination. the ratio of one being grretcr than unity and the second less than unity. The author used the gold line 2428.0 and the tin linrs 2421.7 and 2428 5. This method is worthy of furthrr rvamination; an improved mixing trchnique and additional data concerning the rrlat,ionship of pH and adsorption and/or reduction could improve the accuracy and precision. A useful technique for the adaptation of a spectrographic method t o gold solutions was recorded by Rohner (24B). ‘I’hc 0.1-ml. sample containing a measurrd amount of cobalt as a reference rlcmrnt was adsorbed In a disk of gelatin, which was insrrted in a high frequency spark. From standard solutions and 19 homologous pairs together with photometric deflection ratios and their corresponding gold values the gold content could be obtained by Interpolation. Applied to two samplrs tho method proved accurate to within .5 to 10%. However, it is rinfortunatc that this accuracy was not chrckcd by a method more a p propriate than a gravimetric procedure which. of course, is not applicable t o the small amounts of gold used by the author. Rohner (26B)also discussed a method of spectral analysis, which involved the sirnultancous extraction of the dithizonatcs of gold and a suitable inVOL. 33, NO. 8, JULY 1961
* 1065
ternal standard by carbon tetrachloride and the continued addition of the latter extract to a copper electrode. The intensity ratios of lines from a condensed spark were plotted against the concentration of gold, etc. No data were provided for gold determinetione, but the favorably selective removal, from acid solutions of ores, of the dithizonates of gold, palladium, mercury, and copper offers potentially useful applications. Organic Tissues. Spectrographic methods applied to organic tissues were described by Morel and Policard (I@). One technique required the dissolution of the ash of the sample in acids and the application of a spark from a platinum wire to the solution in a platinum cup which constituted the second electrode. The lines for gold were 2676 and 2428. The second technique provided improvements over Gerlach’s methods (7B, 8B) for the direct examination of histological specimena. Sections of these were placed on a platinum sheet grounded by a lead to the mctal stage. The objective, moved from its position, allowed the manipula,tion of a platinum wire electrode which could be adjusted to any desired area of the organic section and by means of a high frequency discharge, associated with a suitable spectrograph, the metal contcnt and the various areas of gold conrrntration could be determined. With some modifications the method could be applied to a variety of materials, including mixcd mineral specimens. LITERATURE CITED
Colorimetric (1A) Al’Bov, M. N., Zapiski Vsessoyuz Mineralog. Obshchestoa (Mem. SOC. russe mineral.) 82,285-91 (1953). (2A) Beaumont, F. T., Metullurgia 29,
217-20 (1944). (3A) Belcher, R., Nutten, A. J., J. Chem. SOC.1951, 550-1. (4A) Berg, R., Fahrenkamp, E. S., Roebling, W., Mikrochem.ie, Festschr. von Hans Molisch, 1936,42-51. (5A) Bette], W., Mining Eng. World 35, 987-8 (1912). (6A) Bleyer, B., Nagel, G., Schwaibold, J . . Sci. Pharm. 10. 121-4 (1939). (7Aj Block, W. D., Buchanan, 0. H., J . Biol. Chem. 136, 379-85 (1940). (8A) Block, W. D., Buchanan, 0. H., J . Lab. Clin. Med. 28,118-20 (1942). (9A) Brodigan, C. B.. Met. Chem. Ena. 12,460 (igi4). ‘ (10A) Chechneva, A. N., Trudy Ural. Politekh. Znst.. Sbornik 1956. No. 57. 178-82; Refirat. Zhur., Met. 1957; Abstr. No. 920310. (11A) Chen, T.-C., Yeh, S.-K., Hua Hsueh Hsueh Pao 23, 474-9 (1957). (12A) Clabaugh, W. S., J . Research Null. Bur. Standards 36, 119-27 (1946); Research Paper R.P.1694. (13A) Cole, H. I., Philippine J . Sci. 21, 361-4 (1923). (14A) Costeanu, N. D., Bul. chim. soc. romdne chim. 37, 63-5 (1935). (15A) Costeanu, N. D., Bull. soc. chim. 3, 1527-30 (1936).
.---
1066
-
\
-
I
ANALYTICAL CHEMISTRY
(MA) Costeanu, R. N., Z . anal. Chem. 102,336-8 (1935). (17A) Cotton, T. M., Woolf, A. A., Anal. Chim. Acta 22, 1 9 2 4 (1960). (18A) Erdey, Ladislaus, Rady, George, Z . anal. Chem. 135, 1-10 (1952). (19A) Fink, C. G., Putnam, G. L., IND. ENB. CIIEM., ANAL. ED. 14, 468-70 (1942). (20A) Fischer, H., We 1, W., Wiss. VeroffentlichSiemens-drken 14, No. 2, 41-53 (1935). (21A) Geilmann, W., Meyer-Hoissen, O., Glastech. Ber. 13, 86-9 (1935). (22A) Goto, H., Sci. Repts. Tohoku Imp. Univ., First Ser. 29, 204~18(1940). (23A) Hara, Shigeo, Bunaeki Kagaku 7 , 147-51 (1958). (24A) Heredia, P. A., Cuezzo, J. C., Arch. farm. bioqutm. Tucumun 5 , 57-01 (1950). (25A) Heredia, P. A., Cuezao, J. C., Mon. farm. y terap. (Madrid) 57, 361-2 (1951).
(28A). Ito, T., J . Chem. Soc., Japan
58,288-91 (1937). (27A) Kraljic, I., Bull. sci., Conseil acad. RPF Yougoslavia 3,103-4 (:1957). (28A) Kul’berg, L. M., Zat)odskaya Lab. 5,170-5 (1936). (29A) Lapim, L. N., Gein, V. O., Trud Komissii Anal. Khim., Akad. Nau! S.S.S.R.. Znst. Geokhim. i . Anal. Khim.
7,217-22 (1956). (30A) Leutwein, Friedrich, Zenlr. Mineral., Geol. 1940A, 129-33 (1940). (31A) McNulty, B. J., Woollard, L. D., Anal. Chim. Acta 13,154-8 (1955). (32A) Merejkovsky, B. K., Bull. soc. chim. biol. 15, 1336-8 (1933). (33A) McBryde, W. A. E.,. Yoe, J . H., ANAL.CHEM.20, 1094-9 (1948). (34A) Muller, J. A., Foix, A., Bull. SOC. chim. 33, 717-20 (1922). (35A) Natclson, S., Zuckerman, J. L., ANAL.CHEM.23,653 (1951). (36A) Nell, Karl, Plating 35, 345-50 (1948). (37A) Nider, D., Kolloid-Z. 44, 139-40 (1928). (38A) Paul’ren, I. A., Pevzner, S. M., J . Appl. Chem. (U.8.S.R.) 2, 697-700 (1938). (39A) Pierson, G . C., INn. ENG.CHEM., ANAL.ED.6,437-9 (1934). (40A) Plaksin, I. N., Suvorovskaya, N. A., Zavodskaya Lab. 7, 1202-3 (1938). (41A) Plank, J., Magyar Chem. Folyoiral 47,8540 (1941). (42A) Pollard, W. B., Anal?/st 44, 94-5 (1919). (43A) Poluc~htov,N. S., Trudy Vsesoyuz Konferents??. Anal. Khim. 2 , 393-8 ( 1943).
(44.4) Sandell. E. B., ANAL.CHEM.20, ’ 253-6 ( 1948j. (45A) Sandell, E. B., “Colorimetric Metal Analysis,” 3rd ed., Interscience, New Ynrk. 1959.
(46A) &i-,-Buddhadev, Anal. Chim. Acta 21,35-40 (1050). (47A) Serio, F., Indovina, R., Biochim. Z . 262,308-20 (1933). (48A) Schreiner, H., Brantner, H., Hecht, F., Adikrochemie uer Mikrochim. Actu
36/37, 1056-74 (1951). (40A) Shnalderman, S. Ya., Izvest. Kiev. Politekh. Znst. 17, 204-13 (1956); Referat. Zhur., Zihim., 1957, Abstr. No. 8433. (50A) ShnaIderman, S.Ya., Ukrain Khim. Zhur. 21, 261-4 (1955). (51A) Stanbury, W. S., Tubercle 13, 396-9 (1932). (52A) Svedberg, T., 2.Chem. Znd. Kolloide 6. 23840 (1910). (53A) Tananaev,”. A., Vasil’eva, E. V., Ukrain. Khem. Zhur. 7, Wiss. Ted. 50-4 (1932).
(54A) Vydra, F., Celikovsky, J., Chem. listy 51, 768-70 (1957). (%A) Wenaer. P. E.. Monnier. D.. Rusconi,-Y:, Helv. ‘Chim. Aclh 30; 1636-8 (1947). (56A) West, Philip W., McCoy, T. C., ANAL.CHEM.27, 1820-1 (1955). (57A) Zvyagintsev, 0. E., Zolotaya Prom., No. 3, 36 (1939). (58A) Zvya intsev, 0. E., Shabarin, d. K., Voro%’eva, V. A,, Bochkareva, A. P., Trudy Vsesoylr. Konferentsii Anal. Khim. Akad. Nauk S.S.S.R. 1, 375-83 (1939); Khim. Referat Zhur. 1940, No. 2, 6 3 4 . (59A) Zvyagintsev, 0. E., Vorob’eva, V. A., Shabarin, S. K., Zavodskaya Lab. 8,909-10 (1939). Spectrographic (IB) Argyle, A., Price, W. J., J . SOC. Chem. Ind. (London) 67, 187-90 (1948). (2B) Azcona, J. M., Perdo, P., Spectrochim. Acta 2, 185-201 (1942). (3B) Bayle, E., Amy, L., Compt. rend. 185,268-70 (1927). (4B) Beamish, F. E., Talanta 2, 244-65 (1959). (5B) Breckpot, H. R., Mevis, A., Ann. S O C . S C ~ Bruxelles . BW.99-119 (1934). (6B) CIaus, C., Hegemann, Fr., Rost, Fr., 2.angew. Mineral 1, 60-82 (1938). (7B) Gerlach, W., Arch. exptl. Pathol. Pharmakol. 179, 286-95 (1935); Arch. Gewerbepathol. 2 , 7 (1931). (8B) Gerlach, W., Ruthardt, K., Prusener, L.. Beitr. vath. Anat. 91. 617-42 (1933). (9B)’ Guenther, A , , Z . ’ anorg. hllgem. Chem. 200,409-18 (1931). (lOB) Iwamura, A., Mem. Coll. Sci. Kvoto I m n Univ., Ser. A. 15, 359-64 (1332). . (1lR) Jolibois, P., Bossuet, R., Bull. SOC. chim. 37, 1297-304 (1925). (1273) Lewis, J. A,, Serin, P. A., Analyst 78,385 (1953). (13B) Rfankin, Winifred, J. Proc. Roy. SOC.N. S . Wales 70, 95-9 (1936). (14B) Morel, A., Policard, A., &ll. S O C . chim. 51, 1125-31 (1932). (15B) Kedler, V. V., J . Tech. Phvs. (U.S.S.R.) 6, 1138-43 (1936). (l6B) Ncdler, V. V., Trudy Vsesoyuz. Kon,ferentsii Anal, Khim. Akad. Nauk S.S.S.R. 1, 385-91 (1939); Khim. Referat Zhur. 1940, No. 2, 63.
(17B) Nedler, V. V., Efendiev, F. hl., Zavodskaya Lab. 10, 164-7 (1941); Chem. Zentr. 1943,II, 1213. (18B) Ostashevskaya, A. L., Bull. acad. sci. U.R.S.S. Ser. Phys. 4, 9-15 (1940). (19B) Ostashevskaya, A. L., Zavodskaya Lab. 7,958-63 (1938). (20B) Pardo, P., Ajlnidad 18, 257-79 ( 1 941 ). \ - - - - I .
(21R) Pardo, P., Anales f i s . y quim. 37, 321-3 (1941). (22B) Pastore, Salvatore, Occhialini, Emilio,, Ricerca sci. 9, 11, 619-22 (1938). (233) Price, T. D., Telford, R. E., Nall. Nuclear Energy Set., Diu. VIIZ,
1. Anal. Chem.. Manhattan Proiect. . . 1950: (24B) Rohner, F., Helv. Chim. Acta 21, 23-32 (1938). (25B) Ibid., 20, 1054-9 (1937). (2613) Sander?, C., J. Soc. Chem. Ind. 67, 185-7 (1948). (2713) Toisi, Kenao, Sci. Papers Inst. Ph!js. Chem. Research (Tokyo) 38, 87-99 ( 1940). (28B) Urbain, M. P., Bull. SOC.chim. France 47, 1183 (1930). (29B) Urbain, M. P., Compt. rend. 190, 940-2 (1930). (30B) Zakhovskil, N. K., Nedler, V. V., Tsvetnaya Metal. 16, NO. 6-7, 61 (1941); Chem. Zentr. I, 1802-3 (1943). RECEIVED for review January 13, 1961. Accepted March 24, 1961. pp. 404-14,
