摘要:

Jan., 19511 SMALL AMOUNTS OF HYDROQUINONE 49 The Determination of Gold, Palladium and Platinum by Dithizone BY R. S. YOUNG ,4 volumetric method has been devised for the determination of small amounts of gold, palladium and platinum by the dithizone extraction method. The procedure is rapid in operation and applicable to the beads obtained in the assay of precious metals. IN the base metal industry the analysis of silver, gold and the platinum metals is usually carried out by separating these elements by means of a fire assay,, or a combination of wet methods and fire assay, to give a bead containing all the silver, gold, and the platinum group metals in the sample. From this point the procedures generally r e ~ o m m e n d e d ~ , ~ ~ ~ for the determination of the individual metals, gold, platinum, palladium, etc., are lengthy and often unsuitable for the very small quantities of these elements that may be present.For some years diphenylthiocarbazone, generally abbreviated to dithizone, has been used in certain instances for the determination of small quantities of about a dozen metals and the procedures and literature have been reviewed in recent b0oks.~1~ The method outlined below is an extractive titrimetric procedure employing dithizone, which should prove useful to many base metal laboratories that have occasion to carry out regularly a small number of precious metal determinations. Gold, palladium and platinum form dithizonates when shaken with dithizone' in dilute mineral acid solution. The end-point of the reaction is indicated by colour changes and the quantity of dithizone used gives an accurate measure of the metal present.Palladium can be separated from the other metals by extraction of its dimethylglyoxime complex with chloroform. Gold can then be extracted with dithizvne from dilute hydrochloric acid solution, extraction of any silver present being prevented by addition of sodium bromide. Platinic chloride does not react with dithizone, and therefore platinum does not interfere in the gold titration provided that the solution is free from reducing agents. In dilute acid platinous chloride reacts quantitatively with dithizone and platinum can therefore be extracted with this reagent, after removal of the gold, by reducing the platinic to platinous chloride with stannous chloride.50 YOUNG: THE DETERMINATION OF GOLD, [Vol.76 REAGENTS- Stir thoroughly 45 mg of dithizone powder with 200 ml of carbon tetrachloride, and filter into a 250-ml separatory funnel. Cover with 30 to 40ml of sulphurous acid solution. Dilute the stock dithizone solution ten times with carbon tetrachloride and standardise against weighed (quantities of gold, palladium and platinum by the procedures described below. T'ne solutions can conveniently contain 0.01 to 0-02 mg of gold, palladium or platinum per ml, and the v,alue of the dilute standard dithizone solution will be approximately 1 ml = 0.01 mg of gold or platinum and 0.05 mg of palladium. The standard solutions can be made by dissolving the metals in aqua regia, evaporating to dryness, taking up in hydrochloric acid and diluting to appropriate volumes so that the hydrochloric acid concentration is about 1 per cent.Stannous chloride-Dissolve 80 g of SnC1,.2H20 in 180 ml of warm hydrochloric acid and dilute with 300ml of water. Place a stick of tin in the bottle to keep the solution in the reduced state. PALLADI u M- The starting material for this determination is the silver - gold bead, containing small quantities of the platinum group metals, obtained from a direct fire assay of an ore, or from a combination wet and dry assay of a concentrate, matte, blister copper, lead bullion, refinery slime, or similar product. After weighing the bead on the assay balance, place it in a 50-ml beaker, add 5 ml of 1 + 1 sulphuric acid, and fume strongly on a hot plate.The silver and palladium dissolve, but gold, platinum and the rest of the platinum metals remain unattacked as a black residue. Cool, carefully dilute with water, and separa-te the soluble silver and palladium from the Temaining metals by decanting the solution into a 100-ml separatory funnel and wash the insoluble residue with water by decantation. If the gold and insoluble platinum metals are so finely divided that it is impossible to separatle and wash by decantation, filter through a small Whatman No. 40 paper with pulp, wash, dry and ignite the paper and residue in a small porcelain crucible. To the solution containing the silver and palladium, in a volume of about 50 ml in the separatory funnel, add 2 ml of a 1 per cent. aqueous solution of dimethylglyoxime sodium salt.Allow to stand for 10 minutes, shaking the separatory funnel occasionally to speed the reaction. Extract the palladium glyoxime by shaking twice with 4 to 5-ml portions of chloroform and drawing off the lower layer into a 50-ml beaker. Evaporate the chloroform on the edge of a hot plate, add 3 to 4 ml of hydrochloric acid and 2 to 3 ml of nitric acid and evaporate to dryness. Dissolve the palladium in 5 ml of hydrochloric acid with gentle heating, cool and transfer the solution to a 50-ml separatory funnel. Rinse the beaker with 15 ml of water so that the final concentration of hydrochloric acid is 25 per cent. Add 0.2 ml of stannous chloride solution and run in the standard dithizone solution from a 10-ml burette in small portions, shaking vigorously between additions and withdrawing the lower layer from the separatory funnel.When all the palladium has been extracted by dithizone the carbon tetrachloride layer in the funnel changes from the dull olive-green of palladium dithizonate to the un- mistakably brilliant emerald green of dithizone in carbon tetrachloride. If the palladium titration shows a colour change from olive-green to yellow near the end- point, it is probable that the reducing action of stannous chloride has been exhausted and the yellow oxidation product of dithizone is appearing. The addition of a drop or two of stannous chloride will restore the true green colour of unchanged dithizone, or the grey-green of palladium dit hizonat e. The number of millilitres of standard dithizone used to extract the palladium is a measure of the quantity of the latter present.The dithizone is standardised against known quantities of palladium by the procedure used for the sample. The usual precautions regarding clean- liness of glassware and reagent blanks, which apply to all dithizone procedures, must be observed. By a simple modification of the above procedure, palladium may be determined not only in the presence of silver, but also of gold and platinum. This is of importance, for instance, where the method used to decompose the sample or to part the assay bead leaves Dithizone solzttions-(a) Concentrated stock solution. ( b ) Dilute standard solution. PROCEDUREJan., 19511 PALLADIUM AND PLATINUM BY DITHIZONE 51 gold, platinum and most of the palladium unattacked.Dissolve the mixed metals in dilute aqua regia and to the resulting solution containing silver, gold, platinum, palladium, etc., and about 0-2 ml of hydrochloric acid and 0.1 ml of nitric acid in a volume of 10 ml, add 2ml of dimethylglyoxime solution and proceed as described above. The presence of the small quantity of nitric acid prevents precipitation of gold and co-precipitation of platinum with the palladium glyoxime. Retain the upper layer in the separatory funnel, after the with- drawal of the two chloroform extractions, for determination of the gold and platinum as described below. GOLD- Dissolve the residue of gold and platinum, obtained in parting the assay bead, in aqua regia, and evaporate the solution to dryness and take up the chlorides in a minimum quantity of hydrochloric acid.Dilute this solution or the solution of gold and platinum from which palladium has been removed by extraction with dimethylglyoxime and chloroform as described above, to 10 to 15 ml in a 50-ml separatory funnel, add 0.2 ml of hydrochloric acid and 0.1 ml of a 10 per cent. solution of sodium bromide and titrate with standard dithizone as in the palladium analysis, adding 0-2-ml portions at a time, shaking vigorously until the lower TABLE I Synthetic solutions Cupellation heads & & Taken, Found, Taken, Found, mg mg mg mg Gold .. .. .. . . 0.017 0.016 0.025 0.023 0.022 0.021 0,030 0.032 0.016 0.015 0-02 1 0.023 0.018 0.017 0.029 0.027 Palladium . . .. .. . . 0.011 0.012 0.013 0.015 Platinum . . .. .. * . 0.012 0.013 0.02 1 0.020 layer shows the yellow colour of gold dithizonate, and withdrawing.Combine the additions, shaking and drawing off until the dithizone layer remains green, which indicates that all the gold has been extracted. The addition of sodium bromide prevents the interference of silver, which if present, would also give a yellow dithizonate. Excessively long shaking may cause a slight fading of the dithizone colour at the end-point in the gold titration, since reducing agents must be absent to keep any platinum present in the platinic state. The dithizone is standardised against a known gold solution under the same conditions. PLATINUM- After removing gold, as described above, and drawing off any excess of dithizone from the separatory funnel, add sufficient hydrochloric acid to bring the acidity to 25 per cent.of concentrated acid, and then add 0.2 to 0.3ml of stannous chloride solution, shake and allow to stand several minutes. Now titrate the platinum with standard dithizone as described above, until the carbon tetrachloride layer no longer acquires the light yellow colour of platinous dithizonate. The titration value of the dithizone solution is determined against a known platinum solution under the same conditions. RESULTS In material like assay beads, silver is usually determined by difference from the initial weight of the bead. The other platinum metals, osmium, rhodium, iridium and ruthenium, do not react with dithizone under the conditions described above. They will, therefore, be counted as silver in any difference calculation unless the gold and platinum metal residues are weighed after parting the bead. Some typical results on synthetic solutions containing known quantities of gold, platinum and palladium are shown in Table I. In all the beads the quantity of silver present was equivalent to ten times the weight of the combined precious metals, but no other metals were present in more than traces. This condition is similar to that found in an assay bead.52 APPARATUS [Vol. 76 Cupellation beads of known composition were also analysed by this procedure with the results shown in the table. REFERENCES 1. 2. 3. 4. 6. Bugbee, E. E., “A Textbook of Fire Assaying,” J. Wiley & Sons, New York, 1933. Schoeller, W. R., and Powell, A. R., “The Analysis of Minerals and Ores of the Rarer Elements,” Smith, E. A., “The Sampling and Assay of the Precious Metals,” Charles Griffin & Co., London, Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Interscience Publishers Jnc., Welcher, F. J., “Organic Analytical Reagents,” Vol. 3, D. Van Nostrand Co., New York, 1947. Charles Griffin & Co., London, 1940. 1947. New York, 1944. RHODESIA COPPER REFINERIES LIMITED NKANA, NORTHERN RHODESIA December, 1 949

ISSN:0003-2654    

DOI:10.1039/AN9517600049

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

52 APPARATUS [Vol. 76 Apparatus APPARATUS FOR DISTILLATION ON A SEMI-MICRO SCALE THIS apparatus, Fig. 1, is designed to carry out semi-micro operations involving distillation, fractionation and distillation under reduced pressure. One of the difficulties encountered in preparing or purifying small (0.5 to 1.5 ml) amounts of liquid is the loss of material inherent in the experimental method. This loss is due to the liquid that wets the comparatively large surface of the distillation apparatus and collecting vessel, tmogether with the vapour that fills the distilling flask. Quantities of 1 ml or less may be distilled, the only loss being the volume of liquid that when volatilised would fill the apparatus to the top of the collecting cup. The apparatus described considerably reduces this loss.DESCRIPTION AND USE OF APPARATUS SIMPLE DISTILLATION- The apparatus for simple distillation consists of a “cold finger” water condenser, A, to the bottom of which is fastened a detachable cup, B. The cup is provided with two glass hooks, C, which engage with two glass projections, D, on the bottom of A. The cup and condenser unit is fixed by means of a cork into the distillation tube, IE, which is fitted with a thermometer pocket, F. A groove is cut in the cork in order to avoid any pressure rise during distillation. The liquid to be distilled is placed in E and gently boiled by means of a semi-micro burner, the condensate from the cold finger dripping into the collecting cup. Condensate from the outside of B is prevented from dripping on the thermometer bulb either by suitable positioning of the thermometer pocket or by providing the cup with a projection as shown.The condensate in B is cooled by the end of A, the water inlet tube of which is drawn out and extended to the bottom. The length of the thermometer pocket, F, is such that vapours condense before reaching the rubber sleeve holding the thermometer. In practice, since the diameter of the thermometer is only slightly less than the internal diameter of the side arm, the small amount of condensate trapped therein forms an effective vapour block. Aerial oxidation of the distillate is prevented by the vapour which jackets it. Thus aromatic amines such as rn-toluidine can be distilled with very little, if any, aerial oxidation. For high-boiling liquids, adequate cooling of the condenser is obtained by half filling it with cold water and aspirating air through.it by suction at G, by means of a filter pump or other suitable device. The apparatus in this form may be used for organic preparations involving simple distillation, e.g., preparation of the volatile acid chloride of an aliphatic acid by distillation of a mixture of the acid and a small excess of benzoyl ch1oride.l No drying tube is required, the acid chloride in the collecting cup being unaffected by atmospheric moisture during the short time required for the operation. Certain inorganic preparations involving distillation, such as the preparation of chromyl chloride, may also be conveniently carried out on a small scale with this apparatus. Removal of the collecting cup converts the apparatus into the conventional semi-micro reflux apparatus. VACUUM DISTILLATION- The distillation tube of the apparatus can be modified for vacuum distillation by the provision of an air leak tube, H, and a tube, J , which can be connected to the vacuum pump via a manometer.The cup and condenser unit must be fitted to the distillation tube by means of a rubber stopper, and the thermometer pocket can be omitted if the distillation temperature is not required. It may also be used for semi-micro sublimation.Jan., 19511 APPARATUS 53 Omission of the air leak tube and collecting cup allows the apparatus to be used for semi-micro vacuum sublimation. FRACTIONAL DISTILLATION- This is fitted with a small fractionating column, K, containing glass helices or other suitable packing.The liquid to be distilled is placed in the distillation tube, very gently boiled, and fractions distilling at the desired temperature are collected in the cup. The apparatus described is an improvement on existing semi-micro distillation apparatus of a more conventional type. Small quantities of liquid can be distilled with little loss, and as the For fractional distillation, a modified distillation tube is used. t Pyrex Tube 5 mm.x 150 mm. S C Pyrex Height 20 mm. r Condensing Unit and Receiver I Pyrex Tube 25 mm.x 150 mm. DISTILLATION TUBES Simple Vacuum Frattionat ion Fig. 1. Details of apparatus I Complete Assembly for Simple Distiltation distillate and vapour do not come into contact with the stopper, the apparatus is equivalent to one of all-glass construction. It may therefore be used to distil liquids which attack cork and rubber stoppers. Such liquids would normally require distillation apparatus of all-glass construc- tion. The apparatus is inexpensive and may readily be made by any worker possessing moderate skill in glass blowing. REFERENCE 1. Brown, H. C., J . Amer. Chem. SOL, 1938, 60, 1326. DEPARTMENT OF PURE AND APPLIED SCIENCE LOUGHBOROUGH COLLEGE, LEICS. JOSEPH M. CONOLLY GRAHAM OLDHAM June, 1960

ISSN:0003-2654    

DOI:10.1039/AN9517600052

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

54 BRITISH STANDARDS INSTITUTION pol. 76 British Standards Institution NEW SPECIFICATIONS* B.S. 1428 : 1950. Microchemical Apparatus. Price 2s. each part. Part Al-Carbon and Hydrogen combustion train (Pregl type). Part D2-Washout pipettes. Part D3-Micro-nitrometer (Pregl type). Group A of the series comprises combustion trains foy the determination of elements. Group D of the series includes volumetric microchemical apparatus; part D1 was published in 1938 as B.S. 846, Part 3: Burettes with pressure filling device and automatic zero. B.S. 1672: 1950. Methods of testing rubber latex, Price 2s. * Obtainable from the British Standards Institution, Sales Department, 24, Victoria Street, London, S.W. 1.Jan., 19511 BOOK REVIEWS 55 DRAFT SPECIFICATIONS A FEW copies of the following draft specifications, issued for comment only, are available to interested members of the Society, and may be obtained on application to the Secretary, Miss D. V. Wilson, 7-8, Idol Lane, London, E.C.3. Draft Specifications prepared by Technical Committee PVC/1-Pigments, Sub-Committee PVC/l/lO- Miscellaneous Pigments. CM(PVC) 6656-Draft Revision of B.S. 314, Ultramarine Blue and Violet for Paints. CM(PVC) 6657-Draft Revision of B.S. 318, Green Oxide of Chromium for Paints. Draft Specification prepared by Technical Committee NFE/ 13-Raw Copper, Sub-Committee NFE/13/2--Sampling and Analysis of Raw Copper. CM(NFE) 6783-Draft B.S. Methods for the Analysis of Raw Copper-Silver and Tin. Draft Specification prepared by Technical Committee ISE/lS-Sampling and Analysis of Iron and CM(1SE) 6903-Draft B.S.-Method for the Determination of Tin in Ferro-Tungsten and Steel. Tungsten Metal.

ISSN:0003-2654    

DOI:10.1039/AN951760054b

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Jan., 19511 BOOK REVIEWS 55 Book Reviews CELLULOSE ACETATE PLASTICS. By VIVIAN STANNETT, Ph.D., F.R.I.C. Pp. xxiv + 325. In the preface to this book it is claimed to be the first on its subject, yet cellulose acetate is the most versatile of plastics and is produced in tremendous quantities. Moreover, this material is by no means a recent introduction, although its use has markedly increased during the last twenty years or so. The author felt, therefore, that the time had come for a book on all aspects of cellulose acetate technology. The early history of this substance is controversial, but the author describes clearly the developments during the latter half of the nineteenth century and the industrial applications that followed. The book is designed to appeal to the average reader and small user, while stimulating the specialist; the writing is interesting and the author’s objects should be achieved.This addition to the numerous publications on plastics follows a common pattern. An account of the status of the industry, and of the raw materials upon which it is dependent, serves as an introduction to a description of the technology of cellulose acetate. The last-mentioned section forms the major part of the book and is accompanied by many illustrations of the specialised plant that is used. After the concluding chapter, entitled “Applications,” there are three appendixes, viz. , “Table of Properties,” “Chemical Tests” and “Trade Names.” The analyticaI section does not give details of the methods included, but it will doubtless serve adequately the readers for whom the book is intended.In brief, this book gives a very good account of the plastic and its technology: the reviewer has no hesitation in recommending it. London: Temple Press Ltd. Price 30s. G. H. WYATT ORGANIC SYNTHESES. Vol. 29. Edited by C. S. HAMILTON. Pp. 93 + index. New York: With nearly a thousand items to its credit, this well-established annual series of checked preparative methods might well be expected to have left for present treatment only some of the more obscure organic chemicals. On the contrary, we have here such relatively simple compounds as p-nitrobenzonitrile, protocatechuic and homophthalic acids, tertbutylamine (by an alternative method to that in Vol. 27), methacrylamide, un-methoxybenzaldehyde, 2 : 6-dichlorophenol and 3-chloropropyl acetate.In any event, the starting materials are always available, either as commercial chemicals (at least, in America) or described elsewhere in the series. There are pre- parations for all tastes. The young dye-chemist can try 1-methylaminoanthraquinone and its 4-bromo- derivative; the acetylene worker 1-ethynylcyclohexanol; the ring-breaker 1 : 2 : 5- pentanetriol and 4-chlorobutyl benzoate ; the heterocyclist indazole, 3-aminophthalhydrazide (luminol) , trimethylene oxide, the cyclic sulphone of isoprene and 4-hydroxy-2-methylquinoline, while for the less ambitious there is oleyl alcohol by sodium reduction. In all, 34 preparations are described, some with intermediate stages ; a few, e.g., m-aminobenzaldehyde dimethylacetal and phthaltertbutylimide are new compounds.In addition, some further varieties of Raney nickel, particularly effective for low-pressure hydrogenations, are described. Finally, a warning is issued against crystallising benzoyl peroxide from hot chloroform, as had been formerly recom- mended. The cumulative subject index covers volumes 20 to 29 inclusive. Volumes 27, edited by R. L. Shriner, and 28, edited by H. Snyder, are also to hand and follow the general pattern. The analyst, as such, may be interested in 2 : 4 : 7-trinitrofluorenone John Wiley & Sons Inc. London: Chapman & Hall, Ltd. 1949. Price 20s.56 PUBLICATIONS RECEIVED [Vol. 76 (Vol. 28) which forms stable complex compounds with a wide variety of aromatic compounds ( J . Arner. Chew.SOL, 1946, 1727; 1947, 1225), though less useful than picric acid or trinitrobenzene for naphthalene derivatives of low molecular weight. B. A. ELLIS THE PHARMACEUTICAL INDUSTRY IN GERMANY DURING THE PERIOD 1939-45. British Intelligence Objectives Sub-committee Surveys Report No. 24. Edited by J. B. M. COPPOCK. Pp. 120. London: H.M. Stationery Office. 1950. Price 3s. 6d. net. This review of the German pharmaceutical industry, edited by Dr. J. B. M. Coppock, is the collaborative study of 28 main subjects covering the whole field of pharmaceutical research and manufacture and reported upon by specialist contributors. These surveys have been prepared from published reports in the B.I.O.S. series and include references to appropriate unpublished documents. A considerable portion of the report is devoted. to research into production of synthetic fine chemicals and isolates of medicinal value, but insecticides, rodenticides, antiseptics and disinfectants, amino-acids, protein hydrolysates and pharmaceutical preparations are also reviewed. Some diagrams and plates of tablet processing are given and eleven pages of references are included.Although the subject-matter in each section is reported similarly, contributors have used their own individual styles and given their personal opinions on the value of the German work in their particular field; some full syntheses are given where interesting features are present. The writers are to be congratulated on transforming a documentary report into a readable descrip- tion of the state of German pharmaceutical research during the war years. The book gives little information of interest in the analytical field and throughout it is evident that scientific control was inadequate as judged by British standards. Further, the investigators found that little is to be learned of value in connection with pharmaceutical processing; in fact, apparently few new achievements have been effected compared with the state of knowledge before the war and technique appears to have been inferior to the methods used in this country. However, much of the information given may still be of value to industry and it is presented in a convenient form for consultation. D. C. GARRATT

ISSN:0003-2654    

DOI:10.1039/AN9517600055

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

56 PUBLICATIONS RECEIVED [Vol. 76 Publications Received HETEROCYCLIC COMPOUNDS. VOLUME 1. THREE-, FOUR-, FIVE- AND SIX-MEMBERED MONOCYCLIC COMPOUNDS CONTAINING ONE 0, N AND S ATOM. Pp. ix + 703. New York: John Wiley & Sons, Inc. London: Messrs. Chapman & Hall. 1950. Price 88s. SYSTEMATIC ORGANIC CHEMISTRY. MODERN METHODS OF PREPARATION AND ESTIMATION. Fourth Edition. By W. M. CUMMING, O.B.E., D.Sc., F.R.I.C., M.I.Chem.E., F.R.S.E., I. VANCE HOPPER, Ph.D., A.R.C.Sc.I., F.R.I.C., and T. SHERLOCK WHEELER, D.Sc., F.R.C.Sc.I., F.R.I.C. Pp. xxviii + 556. London: Constable & Co., Ltd. 1950. Price 37s. 6d. INORGANIC MICRO-ANALYSIS. By H. V. A. BRISCOE, D.Sc., A.R.C.S., F.R.I.C., and P. F. HOLT, B.Sc., Ph.D., D.I.C., F.R.I.C. London: Messrs. Edward Arnold & Co. 1950.Price 12s. 6d. THE CONDENSED CHEMICAL DICTIONARY. Fourth Edition. Editorial Director : FRANCIS M. TURNER. Pp. xxix + 726. New York: Reinhold Publishing Corporation. London: Messrs. Chapman & Hall. 1950. Price 80s. HANDBUCH DER ANALYTISCHEN CHEMIE. ELEMENTE DER SIEBENTEN HAUPTGRUPPE. TEIL 111, BAND VII AX. By W. FRESENIUS and G. JANDER. Pp. xiii + 245. Berlin: Springer- Verlag. 1950. Price DM 38, CHEMICAL ANALYSIS. VOLUME 3. COLORIMETRIC DE:TERMINATION OF TRACES OF METALS. Second Edition. By E. B. SANDELL, Ph.D. Pp. xix + 673. New York and London: Interscience Publishers Inc. 1950. Price 72s. Edited by R. C. ELDERFIELD. Pp. vii + 1’71. Reports of the Analytical Methods Committee THE Report of the Carotene Panel of the Sub--Committee on Vitamin Estimation, “The Determination of Carotene in Green Leaf Material: Part I, Fresh Grass,” reprinted from The Analyst, November, 1950, 75, 568-576, is now available from the Editor; price to members 1s. 6d. and to non-members 2s. 6d.

ISSN:0003-2654    

DOI:10.1039/AN9517600056

出版商:RSC    

年代:1951

数据来源: RSC