ISSN:0003-2654    

DOI:10.1039/AN95883FX009

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX011

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP033

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

...THE ANALYST XlllCLASSIFIED ADVERTISEMENTSThe rate for classifred adverlisments is 5s. a lane (or spaceeqitivalent of a line), with an extra charge of is. for theuse of of a Box ~\'icrnber. Semi-displayed clnssifredudverf iseinents ore 60s. per single-column inch.TI-IE BIRMINGHAM CHEMICAI. C'UMPrZXY I,IMITEI>"WII.TELL" WORKS, LICIiFIELD. STAFF>.(A member of The Sta\eley Coal and Iron Co. Ltd. Group)ADI)ITION;\L TECHNlCAL STAFFApplications are invited for the following positions:-(a) OK(;ASIC CHRMISI' for initiation and clevelopr~ientof processes for the manufacture of Aroniatic Cheinirakfor Flavouring and Ferfuinery. Experience in plantdesign an advantage. Candidates must be graduatesand/or o f full nieinbership statiis Royal Institute ofCheinis try.(6) DEVELOI'3IEST CHEMIST (lady or gentleiiian) forFlavour Conipounrling.Mnst have \vide kriowledgeand experience in this field and be well acquainted ttcithmodern developments.exprrience i n general food and beverage analysi5.Preferably with some experienre i r i ihe identificationand arialvsis of organic cheniicals iised in the FordIndustry.'Application to be made in writing to the Mailaging Director(c) AKA1,YTICAL C H ~ ~ ~ l l S I . Jluat haye Ill)-to-datestating age, experience and salary reqiiiretl.HERIISTS (13.S~. Honh,. or A.II.1.C. 5tdudard) 1 C w i t h a preference for orgaiiic analytiral work~ are required by the 1iese;irch Lalmratory of a' Conipariv concerned with the drvelopriient o f allbranchrs of electroplating and metal finishing.I Wiiile previous experience in this field is debir-iry preliiiiinarv training will IN:1 given. Thew \,arariries are for interestingpen>ioiial)le po3itions arid offer esrellent prospects. i balarv will he i n ,iccordanrc with (lualilications! and experience.Please reply i n rontidence to: The Secrtxtary,1 W. ~~anniiig k Co. I<td., Great Hanipton Street, j Biririin~h~i~ii.. . __--. -.INALYTIC.AL CHEMISTi n the. Analytiral L>i\-isioii of theion for Smith S. Septiew AabociatedCompanies I.td.. manufacturers of siirgiral dressings, adhesivebandages and pla\ters, plastic filrns, cosmetic, toilet aridethical phariiinceiitical preparations. The work. tvhich ISprogressivc iri character, is concerned with the investigationso f specifications and test riiethods relating tu the rawniaterials, 1nteriiiediate.i and tiiial products made bv rrienibersof the Group.The Iiiinimiini qualifications are a (JriiversipjDegree or the equivalent qualifications o f the lnstitiite ofChemistry. Soiiie industrial experience is desirable but notessential. Salary --ill he according to age and experience.Write to: The Technical Secretary, Sinith L% Sephew ResearchI.td.. Hunsdon Laboratorie>, Wxe, Harts.S'. IOhE ; _. XJ i WIKGTOS UOKOUGH COUSCII. inviteapplication5 for the appointment of part-time I'iil~licL4nalyst. Conditions of appointirient \vill tw in accordancewith the Public .%naly.;t Rrgulations, 1957. Fees payablein accordance with the Joint Segotiating Corriiiiittee forPublic Analvsts..Application fonris obtainable from theTown Clerk,' Town Hall, Stoke Ncwington Cliurch Street,Y.16, retiirriable by March Xlst, l!)h8.- -~T W O reliable .Iiialy>ts urgently required by well establishednew laboratories in Slough. Qualiticationsand experiertce of pharniaccuticd or finecheiuical industries prcferrrti. Good salaries and prospectsare offered and facilities \vill he given for part-time study.Box So. 39C2, 'The Analyst. I T Greshaiii Strcrt. I . o t i t l o n , I1.C.Y.NAL,YTIC,Al. CHEJI IST with considerablr esperieiicethe pharni. ' entical tielti requirerl by iiiani~facturerssituated in 3.M'. I . o i i c l o n . The successful applicant will berequired to control ruiitiiir analysis arid carry out researchon analytical method, for the standardi~ation of new productr..This appoiritiiicnt is a respc)nsihle one and carries a goodsalary.l'ensirm3 j('heuie. Applications will be treated a sstrictly confidential and shoiild iiiclude qii:ilitic~ations, ageand experience. Please write to Ros So. :;!K\, The Analyst,45 Gresham Street. L.onrlon, J-;.C',?.-- _. ._--I_ - .~~____HE I'ECHNICAL LIAISON DEPARTMENT of aTleading scientific instrument company has vacancies forgraduate scientists with zeal and enthusiasm to apply inthe rewarding field of instrumentation. The duties of theDepartment include analytical determinations in the corn-panv's Applications Laboratories, proving tests on newproducts, organisation of demonstrations and regular contactwith customers at home and ahroad.Siircessful applicantswill be encouraged to keep lip to date with developmentsthrough membership of appropriate societies and attendanceat meetings and conventions. Iieqtiired qualificationsinclude a degree in Physics and/or Chemistry (or equivalent),ability to premit the company's instrriinents to top-leveltechnical management and a readiness to accept responsibilityand riiake decisions. Every consideration will be given tonew graduates to ~liorri full training will be given. Attractivesalaries, fully consistent with age and experience will be paidand the prosprcts in this rapidly expanding field are excellent.Working conditions are good and a pension scheme is inoperation..Applications in writing, together with full details ofeducation and experiencc, to 'I'he Technical 1 .iaison Ofticer,linicairl Instruments Liniited, .\rt)ury Road, Carnbridge.H * M * l N E R OF PAPER AXD OFFICE REQUISITES.Five pvnsionahle posts (London -1, Chadderton, Lancs.I ) ;.lZ.:)i (exteiision for regularvice, and exceptional qriitli-ics and Chemistry to G.C.E.testing paper, photographiciiiatvrials and stationer's sundries &sirable. London salary(Mvn) C660- L1 ,050. Frornotioii prospects, r) clay wrelc.Write Civil Service Coriiinissioii, ti, 13urlingtori CaLoricion, W.I. for application form quoting KO. 205:Closing date 27th March, 195.Y.- _ _ _ _ _ _ _ _ _ - ~ - _ _ _ ~ - - . -STATIONERY OFFICE: ASSISTANT EXA31-~~IIADUA'I'E rcquircd in a t r w i i cmgagcd on the s o l ~ t i o ~ rday to clay works problems in the printing and alliedindustrics. Expcric~nct.in this field iiot t,ssential. SalaryLl;SV-LI, 100 accorcling to qualification5 and cxpt.riciicts.F.S.S.U. Five clay week. Application forms froiri l h ( ,Sccretary, Thc. Printing, Packaging & Allied Tradvs 12estwcliAssociation. Kandalls Road, I-rathrrhcad, Surrry.HEFFER'SOFpublish from time to timecatalogues and l i s t s of bookson various subjects, andan no u n ce m en t s of i n d i vi d ualnew books of special impor-tance. Let us add yourname to our mailing list.W. HEFFER 4% SONS, LIMITED3 & 4 PETTY CURY, CAMBRIDGXIV THE ANALYSTIllReprint ofTHE A N A L Y S TVOLUME I (1876) to VOLUME X (1885)Ready about March 31stEach Volume €6 6s.netBound in ClothThe early volumes o f this indispensable journal, out o f print soonafter publication and lacking from many library sets, have nowbeen made available again in response to repeated requests.We hope t o reprint all unavailable volumes, if the demandproves adequate.W. H E F F E R & SONS, LTD.C A M B R I D G E - E N G L A N DI ”C A R O T E N EI t s Determination in Biological Materialsby V. H. BOOTH18s. net“Few analysts have comparable experience in this field.” “ . . . this l i t t l ebook i s the work of an expert . . . Dr. Booth delights i n good manipulationand clearly desires that the reader, too, shall be an impeccable craftsman.”The Analyst.Heffer = CambridgTHE ANALYST xviiThrough a filter paper’s pores No .2The entire range of WhatmanFilter Papers is discussed inthe booklet ‘Buyers’ Guide.’Copies of this booklet, and ofchat containing the first seriesof monographs on Chromato-graphy, can be obtained fromthe address below.It would be of assistance ityou would quote the referenceFSz when replying to this adver-risement.cannot end more accurately than filtration begins.By presenting an unchanging face to the solventsand :reagents used, Whatman cotton celluloseFilter Papers reduce the risk of error.All Whatman papers are manufactured fromthe purest form of cellulose-that derived frombest quality, bleached cotton fibres.Unlike papersmade from cellulose of different origin, theycontain an absolute minimum of organic con-taminants. Organic estimations can thus be basedon Whatman papers with purity guaranteed fromthe start.Whatman paper is also freer from metallicsalts than many Analytical Grade reagents.Ittherefore ensures that a chemically clean precipi-tate will always be obtained when work is doneon inorganic substances.H. REEVE ANGEL & CO LTD * 9 BRIDEWELI, PLACE * LONDON * ECalso at 52 Duane Street New York 7(Manufacturers W. G. R. Balstori Ltd.xviii THE ANALYSTv B E E C R O F T &serviceFOR F I N E C H E M I C A L S ,LABORATORY GLASS WARE,L TECHNICAL E Q U I P M E N TOF ALL K I N D S .P A R T N E R SGeneral Medical CouncilBRITISH PHARMACOPEIA 1958This new edition of the Pharmacopia supersedes, as from September 1, 1958,the British Pharmacopia 1953 as amended by the Addendum 1955.The book hasbeen completely revised and greatly extended. It now contains 826 monographsof which 160 deal with substances and preparations new to the Pharmacopeia.The monographs provide standards and methods of test for a wide range of in-organic and organic compounds, synthetic chemicals, antibiotics and biologicalsubstances and also for preparations, including tablets, injections and ointments.There are 27 Appendices providing descriptions of chemical, physical and bio-logical assay procedures including:Quantitative tests for anenic and lead.Determination of melting-point, boiling-point, viscosity and light absorption.Determination of ash, alcohol content and total solids.Chemical analysis of fixed and volatile oils.The Appendix on biological assays and tests includes a section on the designand accuracy of biological assays and methods for antibiotics, serological andbacteriological products, hormones, etc.Publication Date: March 3, 1958 Oflcial from: September 1, 1958Published for theGeneral Medical CouncilbYTHE PHARMACEUTICAL PRESS, 17, Bloombury Square, London, W.C.lPages XXVI + 1012 Postage 2s.3d. (overseas 4s.) Price 63sxx THE ANALYSTIIIIIIIIIIIIIs m a l l w o n d e r . .The very wide rangeof motors include:A .C. 1 D.C. UNIVERSAL,SHUNT, SPLIT PHASE,3- PHASE, CAPACITOR,SYNCHRONOUS andSHADED POLE MOTORS:I1250 h.p. to 113 h.p., alsoGEARED UNITS 0.125io 600 r.p.nt. wiih TorqueIllus : Type 334C40 I Geared Motor, withA.C. and D.C inter-changeable frames.1-20 r.p.m. Torque:up io 850 Ibs./ins.- p i 20-10 Ibs ins.Our vast resources and many years of wide and practical * experience are available to you. Consult us first-andbe sure of success!FRACTIONAL H o P o MOTORS LTDRookery Way . Hendon . N.W.9 . Phone: COLindale 802214Birmingham . 6 Lansdowne Road . Erdington . Birmingham 24 . Phone: Erdington 0460DaF346Remarkable,.,how Eastman Organic Chemicals expandin numbers. There are now over 3,600of them. each of value to the researchchemist or the manufacturer.Thus,Cellulose Acctatc Phthalnte oppcalsto the pharmaceutical trade, having re-markable properties asan enteric coat ing.OxidisedCellulose,onother Eastman pro-duct, is of value to the endocrinologist.while Acridine Orange is a useful fluor-escent indicator in the pH range 8- 10.For information on these and otherEastman Organic Chemicals write to:-Kodak LrD.BINDINGHave your back numbersof The Analyst bound inthe standard binding caseSend the parts togetherwith a remittance for I2/6to :W. Heffer & Sons LtdHills Road Cambridg

ISSN:0003-2654    

DOI:10.1039/AN95883BP043

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

MARCH, 1958 Vol. 83, No. 984 THE ANALYST PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY NEW MEMBERS ORDINARY MEMBERS Derek Abson, B.Sc. (Birm.) ; Patrick Kieran Hanley, hl.Sc. (N.U.I.), H.Dip.Ed. ; Clive Holy- field; Charles Abell Horton, A.B. (Cornell), Ph.D. (Michigan) ; Maurice Jones; David Courtenay Newton, B.Sc. (Lond.) ; Patrick Noel O’Donoghue, B.Sc. (N.U.I.), A.R.I.C. ; Harold Kingsley Packer, M.A., B.Sc. (Oxon.), Dip.Chem.Eng. (Lond.) , A.M.I.Chem.E., A.R.I.C., A.M.1nst.F. ; Ronald James Starkey, A.R.I.C. ; Joseph Martin Stepanek, Dipl.Eng., Dr.T.Sc. (Prague) ; Leslie Norwood Stuffins, A.R.I.C. ; Hubert Morris Thompson, B.Sc., Ph.D. (Liv.), F.K.I.C. ; Keihei Ueno, Dr.Eng. (Kyushu) ; Gerrit Jan Van Kolmeschate, Dr.Phil.Nat. (Utrecht) ; Arthur Donald Walsh, M.A., Ph.D.(Cantab.), F.R.I.C. ; Patricia Olive Whitmore, B.Sc. (Lond.). JUNIOR MEMBERS James Frederick Marten, A.R.I.C. DEATHS WE record with regret the deaths of Julian Levett Baker Alfred Scholes William Henry Woodcock. NORTH OF ENGLAND SECTION THE thirty-third Annual General Meeting of the Section was held at 2.15 p.m. on Saturday, January 25th, 1958, at the Engineers’ Club, Albert Square, Manchester. The Chairman of the Section, Mr. A. N. Leather, B.Sc., F.R.I.C., presided. The following appointments were made for the ensuing year :-Chairman-Mr. A. N. Leather. Vice-Chairman-Dr. J. R. Edisbury. Hon. Secretary and Treasurer-Mr. A. C. Wiggins, J. Lyons & Co. Ltd., 5 Laurel Road, Liverpool, 7. Members of Committee-Messrs. A. A. D. Comrie, L. R. Flynn, C. J.House, B. Hulme, A. 0. Jones and R. Mallinder. Messrs. F. Dixon and T. W. Lovett were re-appoin t ed Hon. Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Section, at which a paper entitled “Micro-organisms in Analytical Chemistry’’ was given by S. A. Price, BSc., F.R.I.C. SCOTTISH SECTION THE twenty-third Annual General Meeting of the Section was held at 1.30 p.m. on Friday, January 24th, 1958, at the Rhul Restaurant, 123 Sauchiehall Street, Glasgow. The Chairman of the Section, Dr. Magnus Pyke, F.R.I.C., F.R.S.E., presided. The following office bearers were elected for the forthcoming year :-Chairman-Dr. Magnus Pyke. Vice-Chairman- Mr. A. N. Harrow. Hon. Secretary and Treasurer-Mr. J. A. Eggleston, Boots Pure Drug Co. Ltd., Airdrie Works, Airdrie, Lanarkshire.Members of Committee-Messrs. D. M. W. Anderson, R. A. Chalmers, R. Kerr, H. C. Moir, J. W. Murfin and A. D. Walsh. Messrs. J. Andrews and J. McL. Malcolm were re-appointed as Hon. Auditors. 121122 SUTCLIFFE AND PEAKE : THE SPECTROPHOTOMETRIC DETERMINATION [VOl. 83 The Annual General Meeting was followed ‘by an Ordinary Meeting of the Section, at which a paper entitled “Micro-organisms in Analytical Chemistry” was given by S. A. Price, B.Sc., F.R.I.C. WESTERN S‘ECTION THE third Annual General Meeting of the Section was held at 12 noon on Saturday, January l l t h , 1958, in the Davy House, College of Technology, Ashley Down Road, Bristol. The Chairman of the Section, Mr. P. J. C. Haywood, B.Sc., F.R.I.C., presided. The following appointments were made for the ensuing year :--Chairman-Mr. S. Dixon. Vice-Chairman -Dr. G. V. James. Hon. Secretary and Treasurer-Dr. T. G. Morris, Brockleigh, Clevedon Avenue, Sully, Glamorgan. Members of Committel~-Messrs. R. G. H. B. Boddy, R. C. Curtis, P. J. C, Haywood, C. H. Manley, J. A. Pickard and G. F. Price. Mr. R. E. Coulson and Dr. 2. Hybs were re-appointed as Hon. Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Section, which took the form of a discussion on “Perpetuation o:f Errors in Text Books.’’ MIDLANDS SECTION AN Ordinary Meeting of the Section was held at 6.30 p.m. on Thursday, Feburary 13th, 1958, in the Mason Theatre, The University, Edmund Street, Birmingham, 3. The Chair was taken by the Chairman of the Section, Dr. R. Belcher, F.R.I.C., F.1nst.F. The following paper was presented and discussed : “Nuclear Magnetic Resonance,” by I). H. Whiffen, D.Phi1.

ISSN:0003-2654    

DOI:10.1039/AN9588300121

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

122 SUTCLIFFE AND PEAKE : THE SPECTROPHOTOMETRIC DETERMINATION [Vol. 83 The Spectrophotometric Determination of Nickel in Copper - Nickel Alloys BY G. R. SUTCLIFFE A.ND D. M. PEAKE (Research Department, Imperial Chemical Industries Ltd., Metals Division, Kynoch Wovks, Witton, Birmingham) From a study of the absorptiometric characteristics of solutions of copper and nickel, a method has been developed for the direct determination of nickel in copper-base alloys. The optical density of the sample solution in a nitric acid - phosphoric acid medium is measured at 3950 A, where absorption is due almost entirely to nickel. A similar measurement is made on the same solution at 4 9 0 0 ~ . where neither copper nor nickel absorb,, and this permits a background correction to be made.The method has been satisfactorily applied to typical copper-base alloys with nickel contents ranging from about 1.5 to 30 per cent. and a single determination can be completed in about 30 minutes, as opposed to 3 hours by a reliable gravimetric procedure. DETERMINATION of alloying amounts of nickel is usually based on the use of dimethy1glyoxime.l This gravimetric procedure is relatively straightforward and can be applied in the presence of small amounts of copper, but becomes increasingly difficult to apply when a large amount of this metal is present. In such instances, copper in solution can be reduced to the cuprous state,2 but the most satisfactory way of overcoming this interference is to remove the metal by electro-deposition. A further disadvantage ass,ociated with the dimethylglyoxime method, particularly in control laboratories, is the relatively small sample that must be used for the examination of alloys containing 15 per cent.or more of nickel. EXPERIMENTAL A study of the absorption characteristics of simple solutions of metals was carried out with the idea of developing rapid photometric procedures for the determination of constituents that are commonly present in copper-base alloys containing up to about 30 per cent. of nickel. Absorption characteristics of copper as sulphate, nitrate and perchlorate in correspondingMarch, 19581 OF NICKEL I N COPPER - NICKEL ALLOYS 123 acid solutions were determined and were shown to be substantially independent of acid concentration (see Fig. 1, curve A). 2.01, Wavelength, A Wavelength, A Fig.1. Absorption spectra of solu- Fig. 2. Absorption spectrum of nickel nitrate, sulphate and perchlorate solutions containing 0-5 g of nickel per 100 ml tions containing 0-2 g of copper per 100 ml : curve A, copper nitrate, sulphate and per- chiorate; curve B, copper chloride in 5 per cent. v/v hydrochloric acid; curve C, copper chloride in 30 per cent. v/v hydrochloric acid Absorption by solutions containing copper chloride and free hydrochloric acid is very largely influenced by acidity ; this is attributed to complex-ion formation? An intense absorption by copper chloride solutions occurs at 4000 A (see Fig. 1, curve C) and the optical density is related to acid concentration. Examination of the absorption characteristics of solutions of copper in hydrochloric acid show that it is undesirable to use this acid in photo- metric determinations involving absorption at about 4000 A or between 6000 and 10,000 A.Absorption characteristics of nickel as sulphate, nitrate and perchlorate in corresponding acid solutions (see Fig. 2), are substantially independent of acidity. By comparing curve A, Fig. 1, with Fig. 2, it is interesting to observe that nickel solutions absorb strongly at 3950 A, whereas copper solutions have no absorption at this wavelength. Absorption characteristics of iron solutions show that they absorb to some extent at 3950 A, although nitrate solutions of the metal absorb considerably less at this wavelength than either the corresponding sulphate or perchlorate solutions.It was shown that phosphoric acid represses the absorption due to iron without affecting the absorption characteristics of either copper or nickel. Hence, the optical density due to 10mg of iron, i.e., 1 per cent. of iron in a 1-g sample, was only 0.001, and it appeared likely that a single optical- density determination at 3950 A of a simple solution containing both nickel and copper could form the basis of a rapid method for the direct absorptiometric determination of nickel. Copper and nickel alloys are readily soluble in nitric acid, and curve A, Fig. 1, and Fig. 2 show that this acid is permissible as a solvent. Further, the presence of phosphoric acid prevents precipitation of tin, which is present in some commercial alloys, and a mixed solvent of nitric and phosphoric acids was therefore used. Solutions containing known amounts of copper and nickel were prepared and these showed good proportionality between optical density and nickel content, although the reproducibility of optical-density measurements was not entirely satisfactory.This was attributed to haze and cell-surface variations, but the difficulty was resolved when it was found that neither copper nor nickel absorbs significantly at 4900 A. At this wavelength the optical density therefore gives an approximate assessment of the haze and cell blank, and, by measuring the optical124 SUTCLIFFE AND PEAKE : THE SPECTROPHOTOMETRIC DETERMINATION [VOl. $3 density of the solution at 3950 A and deducting the value of the optical density measured at 4900 A, good reproducibility and proportionality were found.When, however, attempts were made to apply this principle to the analysis of alloys containing a small amount of manganese, an unexpected oxidation to permanganate occurred when the sample solution was digested with the phosphoric acid - nitric acid mixture. This reaction is not quantitative and is probably due to oxidation by a perphosphoric acid. Addition of hydrogen peroxide, after dilution, is sufficient to reduce the permanganate and eliminate this interference, and excess of peroxide can be readily decomposed by boiling. A Unicam SP600 spectrophotometer was used for all optical-density measurements, and as the density scale is logarithmic, the lower end of the scale up to 0-25 was used, which permits accurate readings to be made to within &O.OOl.When 4-cm cells are used, this length of scale is equivalent to about 60 mg of nickel, ie., 6 per cent. of nickel in a l-g sample. For larger amounts of nickel, say up to 30 per ce:nt., the determination was made by difference, use being made of a reference liquid containing a solution of known nickel content These general principles were embodied in a provisional method that was applied to a series of commercial alloys. Nickel in these alloys was also determined by a gravimetric dimethylglyoxime procedure, after preliminary electro-deposition of copper. Two sets of results are shown in Table I. Hence, by dissolution of the sample in a nitric acid - phosphoric acid mixture, dilution to a standard volume and subsequent measurement of the optical densities at 3950 and 4 9 0 0 ~ against a solution containing either copper, or copper and a known concentration of nickel, a rapid and accurate determination of nickel can be made in about 30 minutes once the calibration graphs have been prepared, as opposed to 3 hours by a reliable gravimetric procedure.TABL:E I COMPARISON OF RESULTS :BY DIFFERENT METHODS Typical manganese content, % 0.25 1.2 0.1 0.2 0.1 0.15 1.4 Typical iron content, % 0.05 3.7 < 0.05 0.05 - (0.05 2.2 Nickel found by Nickel found by gravimetric method proposed method - \ . A . . 1 Analyst A, Analyst B, Analyst A, Y O % YO 1.69 4.29 { 4.62 5-02 7.27 9.39 18.51 24-98 30-34 30.26 30.37 30.05 1-75 1.70 1-84 1-95 2.18 2.17 4-37 4.43 - 4.66 - 5.01 - 7.32 - 6-92 - 6 7 3 - 6.64 9.46 9.38 9-74 9.7 1 10-03 9-99 - 18.40 - 25.03 - 30.22 - 30.25 - 30.32 - 30.03 Analyst B, 1.72 1.98 2.13 4.43 4.66 7-36 6-89 6.70 6.6 1 9.33 9.68 9-96 18.37 25-05 30.20 30.20 30.42 30- 13 Y O - METHOD APPARATUS- A Unicam SP600 spectrophotometev was used.Grade A caZibrated$asks must be used throughout, and, for work of the highest accuracy, The cells used for the preparation of the calibration graph must also be used in deter- the certified volumes must be used in the calculation of the nickel contents. mining nickel in the test solution. REAGENTS- Distilled water should be used for the preparation of all solutions. Nickel-Hilger H.P. quality was used.March, 19581 OF NICKEL I N COPPER-NICKEL ALLOYS 125 Cofifier-The metal nominally free from nickel was used, Nitric acid, diluted (1 + 1)-Dilute 1 volume of nitric acid, sp.gr.1.42, with 1 volume Phosphoric acid, sp.gr. 1-75. Hydrogen peroxide, 2-volume-Dilute 10 ml of 20-volume hydrogen peroxide with 90 ml of water. Standard nickel y e ference solutions-Reference solutions contain a combined weight of 1 g of nickel plus copper per 100 ml. The ratio of nickel to copper used for a particular solution is governed by the range of nickel contents to be determined, e g . , a reference solution for nickel in the range 5 to 11 per cent. should contain 0.0500 g of nickel plus 0.9500 g of copper per 100 ml. Transfer the calculated weight of nickel and copper to make 1 litre of solution to a large beaker. Dissolve it in 100 ml of diluted nitric acid (1 + 1) and add 300 ml of phosphoric acid.Evaporate to ensure removal of all nitrous fumes; it is not necessary to remove all the nitric acid by evaporation. Dilute to about 800 ml, add 20 ml of 2-volume hydrogen peroxide and boil for 5 minutes. Cool, transfer the solution to a l-litre calibrated flask, dilute almost to the mark and place in a thermostatically controlled water bath at 20" C for 1 hour. Dilute to the calibration mark and mix well. PROCEDURE FOR PREPARING A CALIBRATION GRAPH FOR BETWEEN 5 AND 11 PER CENT. OF Weigh accurately about 0.06, 0-07, 0.08, 0.09, 0.10 and 0.11-g portions of nickel and to each add copper to make a total sample weight of 1 g. Dissolve the samples in 10 ml of diluted nitric acid (1 + l ) , add 30 ml of phosphoric acid and evaporate to small volume to ensure removal of nitrous fumes.Cool, dilute to a volume of about 85 ml, add 2 ml of 2-volume hydrogen peroxide and boil gently for 5 minutes. Cool, transfer to a 100-ml calibrated flask and dilute to the mark at 20" C. Measure the optical density of each solution in a 4-cm cell at 3950 and at 4900 A with respect to the 5 per cent. reference solution, and record the difference in optical density. (For other ranges of nickel contents, the procedure is similar and measurements are made by using a reference solution appropriate to the range.) PROCEDURE FOR DETERMINING NICKEL- Weigh 1 g of sample and continue exactly as described for preparation of the calibration graph. Measure the optical density with respect to the appropriate reference solution and calculate the nickel content from the calibration graph. Acknowledgment is made to Mr. W. T. Elwell, Division Chief Analyst, Imperial Chemical Industries Limited, Metals Division, for his interest in this investigation and for assistance in the preparation of this paper. REFERENCES of water. NICKEL- 1. 2. 3. American Society for Testing Materials, "Methods of Analysis of Metals," 1956, p. 270. Bayley, W. J., unpublished work. Orgel, L. E., Quart. Rev. Chem. SOC., 1954, 8, 422. Received September 4th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9588300122

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

136 DESAI AND MURTHY : VOLUMETRIC DETERMINATION [Vol. 83 Volumetric Determination of Uranium in Presence of Iron BY M. W. DESAI AND T. K. S. MURTHY (Chemistry Division, Atomic Energy Establishment, Trombay, Bombay, India) A volumetric method is described for the determination of uranium in presence of iron. It is based on the oxidation of reduced uraniumIV with ferric sulphate and titration of the excess of ferric iron iodimetrically. Osmium tetroxide has been found to be a suitable catalyst for the reaction. EXTRACTION of uranium from its ores gives rise to the need for a rapid and fairly accurate method of determining it in solutions containing iron and sometimes also phosphate. A volumetric method that does not involve prior separation of uranium would obviously be rapid and suitable for the routine analysis of a large number of samples.The general volu- metric methods of determining uranium are discussed by Rodden and Warf,l but all are applicable only in the absence of iron. The potentiometric titration of uraniumIv with ferric sulphate as an oxidant has been studied by several w0rke1-s.~~~ This method has the advantage that it can be used in presence of iron, but the titration should be carried out at. about 90” C by a potentiometric or ampero- metric method, precautions being taken to exclude air from the titration assembly. This makes it rather unsuitable as a quick and routine method. I t has been observed that at room temperature uraniumIV can be readily oxidised by addition of an excess of ferric sulphate. The proposed method involves the addition of a known volume of a standard solution of ferric sulphate to the reduced uranium solution and then titration of the excess by the iodimetric method first proposed by M ~ h r , ~ which consists in the addition of potassium iodide and titration of the liberated iodine with sodium thiosulphate. IODIMETRIC DETERMINATION OF IRON- Although apparently simple, the accuracy of the iodimetric determination of ferric iron is influenced by several factors.After the original work of Mohr, several workers studied this method in detail,5ys 97 $8 and contradictory statements about the necessary conditions for accurate determination are not rare in the literature. Swift5 has given an excellent review of these methods. A difficulty in the titration i!; the reappearance of the blue starch - iodide colour despite its repeated discharge with sodium thiosulphate.This is often referred to as the “oxygen error.” It has been observed8 in actual titrations that the time required for the quantitative liberation of iodine and the maintenance of the potassium iodide concentration are to a large extent dependent on the concentration of iron[II and the acid present. It was therefore not possible to adapt, from published work, a set of conditions for carrying out the iodimetric determination of the excess of iron111 remaining after the oxidation of uraniumIV. An attempt was made to determine the necessary conditions for a successful determination under the experimental conditions. The samples contained 50 to 200mg of U,O, and various amounts of iron in sulphate solutions.After passage through a Jones’s reductor to reduce the uranium and washing the reductor, the volume of the solution was about 150 ml, and it was approximately 2 N in sulphuric acid. Excess of ferric sulphate was added to oxidise uraniumIV, the excess being 5 to 10mg of iron. It was found in a number of experiments that the amount of potassium iodide to be added to this final solution for the quantitative liberation of iodine in a reasonable time (say 5 minutes) was quite high (about 20 g), probably owing to the low concentration of ironIII. When the sample solution contained an appreciable amount of phosphate, even this amount of potassium iodide was insufficient, since the effective concentration of iron111 was further reduced by the formation of complexes.In such tests the titre was low and the end-point was not sharp. Similar trouble was :noticed when the samples contained a large amount of iron and the concentration of ferrous iron in the final solution was high. This was EXPERIMENTALMarch, 19581 OF URANIUM I N PRESENCE OF IRON 127 because of the reversible nature of the reaction. Whenever a long time was allowed for the liberation of iodine, it was found that the titres were not reproducible and tended to be high, because of the “oxygen error.” Studies were therefore undertaken to find a suitable catalyst that would increase the speed of the reaction considerably, thereby permitting the titration to be completed within a short time. This would also reduce the “oxygen error.” Cuprous iodideg has been recommended as a catalyst, but even its presence did not help appreciably. After a number of experiments, it was found that osmium tetroxide, in small concentration, was a good catalyst.It was possible to start the titration immediately after the addition of iodide, and the end-point was stable. However, a correction had to be applied to the titre, since osmium tetroxide oxidises iodide to liberate iodine. The correction factor was found by carrying out a blank determination. The method was first tested for the determination of ferric iron and then applied to the indirect determination of uranium in the presence of iron and phosphate. METHOD REAGESTS- All reagents should be of recognised analytical grade. Uranyl sulphate solution-Dissolve about 15 g of uranyl sulphate in distilled water and Standardise the solution by precipitating uranium with ammonium Ammonium ferric sulphate solution-Prepare an approximately 0.05 iV solution in 5 per Sodium thiosulphate solution-Prepare an approximately 0.05 N solution and standardise Osmium tetroxide solution-Dissolve 250 mg of osmium tetroxide in 100 ml of 5 per cent.dilute to 2 litres. hydroxide and igniting to the oxide, U,O,. cent. v/v sulphuric acid. iodimetrically against standard potassium dichromate.1° v/v sulphuric acid. PROCEDURE- Determination of iron-With a pipette place a known volume of ammonium ferric sulphate solution in a 400-ml conical flask and dilute to about 150 ml with 5 per cent. v/v sulphuric acid. Add about 1 g of sodium carbonate with stirring and then stopper the flask loosely.Allow the carbonate to dissolve and then add 10 g of solid potassium iodide and 2 drops of the osmium tetroxide solution, stopper the flask and swirl the contents to dissolve the iodide. Titrate the liberated iodine with sodium thiosulphate solution. using starch as the indicator. Standardise by titration with potassium dichromate. TABLE I IODIMETRIC DETERMINATION OF IRONIII Test No. 1 2 3 4 5 6 7 8 9 10 11 12 Concentration of ammonium ferric sulphate, N 0.0508 0.0508 0.0508 0.0508 0.0508 0.0508 0.0508 0-0508 0.038 1 0.038 1 0.038 1 0.038 1 Amount of ammonium ferric sulphate taken, ml 10 10 10 10 20 20 20 20 20 20 20 20 Amount of phosphate added, as P,O,, mg - - - - - - - - 100 250 500 500 Concentration Amount of sodium of sodium thiosulphate thiosulphate used, used, * N ml 0.055 1 9.26 0.0551 9.30 0-0551 9-25 0-055 1 9.23 0.0551 18.44 0.0488 20.82 0.0488 20.83 0.0488 20.85 0.05 14 14.85 0.0514 14-86 0.0514 14.82 0.0514 14-82 Calculated amount of sodium thiosulphate used, ml 9-22 9.22 9.22 9.22 18.44 20.82 20-82 20.82 14-82 14.82 14-82 14.82 * Corrected for a blank value of 0.15 rnl of 0.05 N sodium thiosulphate for each 2 drops of osmium tetroxide solution added.Determination of uranium-Add 2-5 ml of concentrated sulphuric acid to the solution of uranium sulphate containing about 100 mg of U,O, and dilute to 50 ml. Cool the solution and pass it through a Jones’s reductor and then rinse the reductor four times with 25-ml128 DESAI AND MURTHY 1 VOLUMETRIC DETERMINATION [Ivol.83 portions of 5 per cent. w/v sulphuric acid. Bubble clean air through the reduced solution for 5 minutes to oxidise any uranium111 formed. Add, from a burette, a known volume of ammonium ferric sulphate solution, set the solution aside for 5 minutes and then determine the excess of iron111 iodimetrically as before. From the amount of ferric iron consumed, calculate the uranium present on the basis of the following reaction- U I V + 2FeIII-+ IJvI + 2FeII. RESULTS Since phosphate was likely to be present in the sample solutions, its effect on the determination of ferric iron was investigated in tests 9 to 12 (see Table I). The results show that the addition of phosphate equivalent to up to 500 mg of phosphorus pentoxide has no effect on the titration.Some results for the determination of uranium by the proposed method are shown in Table 11. Results of the iodimetric determination of iron111 are shown in Table I. TABLE :[I DETERMINATION OF URANIUM BY T H E PROPOSED METHOD Uranium taken, mg 70.0 140.0 140.0 70.0 70.0 70.0 140.0 140.0 140.0 70.0 70-0 140.0 as U308, Phosphate added, Iron added, as P,O,, mg mg - - - 100 200 500 100 200 500 200 200 250 400 200 500 - - - - - Uranium found, as U308. mg 70.2 139.8 140.0 70.1 70.0 70.4 139.4 140.4 141.0 69.8 70-3 140.6 DISCUSSION The results shown in Table I1 indicate that the proposed method is applicable to the accurate determination of uranium in presence of iron and phosphate. The success of the method depends to a large extent upon the accuracy with which the iodimetric determination of ferric iron is carried out.The use of osmiurn tetroxide as a catalyst in this titration was found to give quite reliable results. Since it is a costly reagent, attempts were made to use some of the more readily available reagents, such as oxalic acid, sodium molybdate and cuprous iodide, but, under the conditions described, they were not satisfactory. Although the acid concentration of the solutions for titration was adjusted in all these experiments to about 2 N , it was found in many experiments that variation from 0.5 to 5 N had no appreciable effect on the titration, except when the samples contained phosphate; an acid concentration below 2 N would then cause precipitation of uranous phosphate and lead to erratic results. TABLE I EI DETERMINATION OF URANIUM I N PRESENCE OF NITRATE Uranium taken, as U308, mg 70.0 70-0 70.0 70.0 70.0 Sodium nitrate added, as NO3-, mg 0 60 100 200 600 Cranium found by titration with KIMnO,, as U,08, mg 70.3 - - 134.2 - Uranium found by proposed method, mg 69.8 69.9 70.3 69.7 70.2 as U308, Apart from permitting the determination of uranium in the presence of iron, the proposed method has another advantage.I n the other volumetric procedures for uranium, in which strong oxidising agents such as potassium permanganate, potassium dichromate and cericMarch, 19581 OF URANIUM I N PRESENCE OF IRON 129 sulphate are used, nitrate, if present, must be removed by repeatedly heating to fumes with sulphuric acid,ll otherwise the titres are higher than expected and the end-points are not sharp.Ferric sulphate, being a mild oxidising agent, does not react with the reduction products of nitrate formed during the reduction of a solution of uranium containing nitrate. Hence, by this method, the determination of uranium can be carried out even in the presence of appreciable amounts of nitrate. The results shown in Table I11 were found for pure solutions of uranium to which nitrate had been added in different amounts before passage through a Jones’s reductor. It is clear that the presence of nitrate does not interfere with this titration. We thank Dr. Jagdish Shankar, Chemist, Atomic Energy Establishment, for his keen interest in the progress of the work. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES Rodden, C. J., and Warf, J. C., in Rodden, C. J., Editor, “Analytical Chemistry of the Manhattan Blum, P., and Weiss, G., Bull. SOC. Chim. France, 1947, 735. Grimes, W. R., U.S. Atomic Energy Commission, declassified report AECD-2804, decl. Feb. 8, 1950. Mohr, C., Ann. Chem. Pharm., 1858, 53, 105. Swift, E. H., J . Amer. Chem. Soc., 1929, 51, 2682. Grey, E. C., J . Chem. SOC., 1929, 35. Wark, I. W., Ibid., 1922, 121, 358. Yamamoto, S., J . Chem. SOC. Japan, Pure Chem. Sect., 1952, 73, 668 and 677. Vogel, A. I., “Textbook of Quantitative Inorganic Analysis,’’ Second Edition, Longmans, Green Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” Second Edition, John Received June 27th, 1957 Project,” McGraw-Hill Book Co. Inc., New York, 1950, p. 51. & Co. Ltd., London, 1951, p. 356. Wiley & Sons Inc., New York, 1953, p. 111. -, oP. cit., p. 336.

ISSN:0003-2654    

DOI:10.1039/AN9588300126

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

March, 19581 OF URANIUM IN PRESENCE OF IRON 129 A Spectrochemical Solution Method for the Determination of Copper, Cobalt and Iron in Copper and Cobalt Concentrates BY G. L. MASON AND 2. DE BEER (Rhoanglo Mine Services Ltd., Research and Development Division, Kitwe, Northern Rhodesia) A solution method of spectrochemical analysis is described, whereby it is possible to determine copper, cobalt and iron in copper and cobalt concentrates over the range 5.0 to 40.0 per cent. for copper and iron, and 0-2 to 6-0 per cent. for cobalt. Excitation is by condensed spark and use is made of the Feldman porous-cup technique. Results show good agreement with chemical analyses, but reproducibility varies, according to the element and its concentration, from 1.25 to 8 per cent. of the amount determined.The time for one analysis is 1 hour, and twenty samples can be analysed in a working day. IN recent years, details have been published of several successful applications of the spectro- graphic technique to the determination of major constituents in minerals, ores, slags and ceramics, and ferrous and non-ferrous alloys. In view of these successes, it was felt that the application of such a technique to the determination of copper, cobalt and iron in copper and cobalt concentrates would be desirable. In the analysis of powdered samples, some workers1y2v3 have excited the powder directly without any pre-treatment except the addition of buffers such as ammonium chloride and lithium carbonate. The reproducibility of the results by these methods is rarely better than + 5 per cent.of the amount present, although errors can arise from the very small amount of sample used (usually (0.1 g). Experience has shown that the solution technique4s6 s 6 will provide a reproducibility better than $3 per cent. of the amount present. Further, by suitable chemical treatment, it is often possible to prepare a rather complex sample in the form of a relatively simple130 MASON AND DE BEER: DETERMINATION OF COPPER, COBALT AND [VOl. 83 solution. Such a transformation would be definitely advantageous when dealing with con- centrates containing approximately 20 per cent. of sulphur and silica. In view of these advantages, it was felt that the extra time involved by chemical preparation of the sample would be amply justified.EXPERIME:NTAL DECOMPOSITION OF CONCENTRATES- The object of the decomposition of the concentrates was to remove the silica and sulphur generally present in the sample. Here it was possible to draw on years of experience in chemical assaying of both copper and cobalt concent rates. Unfortunately, the accepted efficient method of decomposition-attack by a mixture of perchloric, nitric and sulphuric acids-could not be used, as the end-product is asulphate solution and the spectral emission from such a solution was too weak for further consideration. The methods tried, but which failed to extract all the copper, cobalt and iron, were as follows- (;) attack with aqua regia, (ii) attack with bromine and aqua regia, and (iii) attack with bromine and nitric, hydrochloric and perchloric acids. Method of decomposition JinalZy adopted-A.completely efficient and reasonably rapid extraction is achieved by decomposing a 0.5-g sample with bromine and nitric, hydrochloric, hydrofluoric and perchloric acids, the solution being evaporated to a paste, which is then dissolved in hydrochloric acid and diluted to the working volume with water. In this way the sulphur and silica are almost completely removed, the amount of residue being so small (<0.001 g) that filtration is eliminated by allowing the residue to settle before the required aliquot is removed by means of a pipette. A number of residues, after ignition, were excited spectrographically by using a 7-ampere d.c. arc. Examination of the resulting spectra revealed only a faint trace of copper and iron (<0.001 per cent.), and cobalt was not detected.SOLUTION FOR ANALYSIS- It was found that spectra of suitable density could be obtained from a solution prepared by adding 6 ml of the sample solution to 1 rnl of a standard solution of nickel containing 0.05 g of nickel per ml. Method of excitation-Previous experience with the Feldman porous cup7 had shown it to be a most satisfactory medium for reproducible excitation of solutions. For this work, 0.1 ml of solution was put into the porous cup by means of a small-bore pipette and excited by a high-voltage condensed spark. TRIAL CALIBRATION WITH CHEMICALLY ANALYSISD SAMPLES- A series of analysed samples was selected from our laboratory stock to provide a range of 3 to 35 per cent. of copper, 3 to 37 per cent.of iron and 0.5 to 7 per cent. of cobalt. Solutions of each of these standards, prepared as before, were excited under the following conditions- Lower electrode-A &inch diameter graphite rod pointed to an 80” blunt cone. Upper electrode-0.1 ml of sample solution in a Feldman porous cup. Spark gap-3 mm. Condensed spark-15 kV; 0.005 pF. E~pos~e-60 seconds on Kodak B10 plate (recorded in triplicate). Line pairs-Cu I1 2369.88 A - Ni I1 2356.41 A Fe 11 2359.10 A - Ni I1 2356.41 A. C O II 2353.42 A - Ni 11 2356.41 A The choice of line pairs was rather arbitrary in the absence of excitation potential tables. However, care was taken to select lines of the same order, Le., in this instance “spark” lines, and of suitable density. The initial choice proved to be most fortunate, as a test for homology made by photographing spectra at inductances of 0-015, 0.03 and 0-06 mH showed no marked change in log intensity ratio with change of inductance. In practice, the line pairs were found to be reliable and gave adequate accuracy.March, 19581 IRON I N COPPER AND COBALT CONCENTRATES 131 STANDARDISATION- Standard graphs for copper, cobalt and iron were plotted from the relevant photometric measurements of the selected line pairs, the points plotted being the mean values obtained from seven standard samples each exposed three times on each of two photographic plates.TRIAL ANALYSES OF COBALT CONCENTRATES- At this stage it seemed possible to carry out trial analyses by the proposed method, and six cobalt concentrates were selected at random from routine plant production.These were analysed by comparative chemical and spectrochemical methods; the results are given in Table I. TABLE I COMPARISON OF RESULTS BY CHEMICAL AND SPECTROCHEMICAL METHODS Copper found by- Iron found by- Cobalt found by- r chemical method, 14.28 13-78 14.14 14-10 14.06 14.12 % method, 14.30 14.05 14-30 14.30 13.90 14-40 % c chemical method, 16.90 16.20 16.60 16-75 16.80 16.80 % - spectrochemical method, % 17.15 16.60 17-20 16.70 17.05 17.15 7 chemical method, 4-88 4.59 4.74 4-82 4.96 4-88 % m % spectrochemical method, 5-40 4.85 5.15 5-25 5.10 5.30 It can be seen from the results in Table I that chemical and spectrochemical results for copper and iron show good agreement, but those for cobalt (with one exception) do not.The samples used for the spectrochemical analysis were then analysed chemically by an umpire method, while the spectrochemical solutions were again analysed, use being made of a calibration graph obtained from a series of pure solutions containing from 1 to 6 per cent. of cobalt. The results from both chemical and spectrochemical methods are shown in Table 11. TABLE I1 DETERMINATION OF COBALT BY DIFFERENT METHODS Cobalt found by chemical method, % Cobalt found by Cobalt found umpire’s chemical by spectrochemical method, method, % % 4.88 5.03 5-10 4-59 4-57 4.70 4-74 4.88 4.90 4.82 4-87 4.90 4.96 4-95 5.0 4-88 4.97 5-05 Cobalt found previously by spectrochemical method, 5.40 4.85 5-15 5.25 5-10 5.30 % I n view of the good agreement finally achieved, a further series of cobalt concentrates Comparative chemical was analysed, use still being made of the calibration graph for cobalt. and spectrochemical results on these samples are given in Table 111.TABLE I11 COMPARISON OF RESULTS BY CHEMICAL AND SPECTROCHEMICAL METHODS Copper found by- Iron found by- Cobalt found by- chemical spectrochemical chemical spectrochemical chemical spectrochemical method, method, method, method, method, method, 13.72 13.70 16.50 16.55 4.72 4.80 14.10 14-20 16.90 16.90 5-14 5.00 13.82 13-70 16-35 16-20 4.72 4.60 14-00 13.95 16.90 16.90 5.10 5.00 13.76 13.35 16.35 16-20 4-64 4.70 14.12 13-70 16-75 16.90 4.98 5-00 A A A r \ I \ f \ % % % % % %132 MASON AND DE BEER: DETERMINATION OF COPPER, COBALT AND [VOl. 83 Calibration by synthetic solution standards--In view of the success attained with the calibration graph for cobalt, it was felt that a complete calibration by synthetic solution standards for copper, iron and cobalt was desirable, since it would dispense completely with the need for accurately analysed standard samples. Initial trials with this form of calibration soon showed that solutions containing only the pure metals themselves were not sufficient--to these solutions must be added weighed amounts of lime, magnesia, alumina and sodium equivalent to the concentrations normally present in the concentrates.REPRODUCIBILITY OF RESULTS BY THE SPECTROCHEMICAL METHOD- After a calibration graph had been prepared :For copper, iron and cobalt from the synthetic solutions, a series of replicate analyses of a copper and a cobalt concentrate was carried out. These analyses were spread over a total of eight photographic plates exposed at intervals during a period of 1 month.From the results of the replicate analyses the reproducibility of the results by the spectrochemical method was calculated statistically, with the results shown in Table IV. Standard samples were not exposed on any of the plates. TABLE IV REPRODUCIBILITY OF RESULTS Cobalt concentrate Copper concentrate -. f \ Copper Iron Cobalt Copper Iron Cobalt" A Found by chemical analysis, % . . 12.68 18.45 4.96 37.34 14.40 0.23 Found by spectrochemical analysis (mean), yo . . .. . . 12.6 18.6 5.0 36.6 14.5 0-23 Standard deviation, yo . . . . tO.22 k0.27 +O.OS +O-93 k0.18 &O*OlS Standard deviation, yo of chemical content .. .. . . . . 1-74 1.46 1.61 2.5 1-25 7.83 Number of determinations . . 25 25 25 25 23 25 * The determination of low concentrations of cobalt requires the use of stronger sample solutions and a longer exposure time, see p. 133. METHOD REAGENTS- Bromine-Analytical-reagent grade. Nitric acid, concentrated. Hydrochloric acid, concentrated. Hydyojuoric acid, 40 per cent.-Analytical-reagent grade. Perchloric acid, 60 per cent.-Analytical-reagent grade. Standard nickeZ solation-Dissolve 5 g of Slpecpure nickel in 15 ml of nitric acid, cool and make up to 100 ml in a calibrated flask. 1 ml = 0.05 g of nickel. Standard cobalt solution-Dissolve 0.1 g of Specpure cobalt sponge in 10 ml of nitric acid, cool and make up to 100 ml in a calibrated flask, 1 ml = 0-001 g of cobalt.PROCEDURE FOR DECOMPOSING THE CONCENTRATES- Weigh 0.5 g of sample into a 400-ml Phillips conical beaker, moisten with a little distilled water, and add a few drops of bromine and 5 ml of concentrated nitric acid. Allow the sample to digest on a hot-plate at medium heat until all bromine and nitrous fumes are expelled. Add 5 ml of concentrated hydrochloric acid and proceed with digestion until further visible reaction ceases. Add 1 ml of hydrofluoric acid and 10 ml of perchloric acid, and continue heating until visible reaction ceases. Cool and add 5 ml of concentrated hydrochloric acid, washing down the sides of the beaker with a little distilled water. Heat until all salts are re-dissolved, cool and make up to 25 ml in a calibrated flask. These operations should take 30 to 35 minutes.By increasing the heat, evaporate the contents of the beaker to a paste.March, 19581 IRON I N COPPER AND COBALT CONCENTRATES 133 PROCEDURE FOR PREPARING THE SOLUTION FOR ANALYSIS- (;) Allow the sample solution to stand for 3 to 5 minutes to permit the small amount of residue to settle. (ii) For the determination of copper and iron in the range 3 to 40 per cent., and cobalt in the range 1 to 6 per cent., add by means of a pipette 5 ml of sample solution to a 50-ml flat-bottomed flask and then, by pipette, 1 ml of standard nickel solution. (iii) For the determination of low cobalt contents over the range 0.15 to 1.0 per cent., add by means of a pipette 10 ml of sample solution to a 50-ml flat-bottomed flask and then, by pipette, 1 ml of standard nickel solution.TABLE V COMPOSITION OF STANDARDS BASED ON l-g SAMPLE Standard number . . .. .. . . 1 2 3 4 5 6 Copper present, % . . . . .. . . 5.0 8.0 13-0 20.0 30.0 40.0 Weight of copper taken, g . . .. . . 0.05 0.08 0.13 0.20 0.30 0.40 Iron present, yo . . .. . . . . 5.0 8.0 13.0 20.0 30.0 40.0 Weight of iron taken, g . . .. . . 0.05 0.08 0.13 0.20 0-30 0.40 Cobalt present, yo . . .. .. . . 1.0 2.0 3-0 4-0 5.0 6.0 Weight of cobalt taken, g . . .. . . 0.01 0.02 0-03 0.04 0.05 0.06 Aluminium oxide present, yo Weight of aluminium oxide taken, g Magnesium oxide present, yo Weight of magnesium oxide taken, g Weight of calcium carbonate taken, g Weight of sodium chloride taken, g . . . . Calcium oxide present, yo .. Sodium present, yo . , .. .. .. . . . . . . . . . . .. . . .. 3% 0.03 2 0-001 3.0 0.03 If: 0*001 2.0 0.036 _+ 0.001 1.0 0.025 2 0.001 PROCEDURE FOR PREPARING SYNTHETIC SOLUTION STANDARDS- (a) For copper and iron between 5 and 40 per cent. and cobalt between 1 and 6 per cent.- Weigh into 400-ml Phillips conical beakers the respective amounts (based on a l-g sample) of Specpure copper, cobalt and iron and the oxides and salts of aluminium, magnesium, calcium and sodium as shown in Table V. Dissolve each standard mixture as described for the decomposition of the concentrates, finally adding 10 ml of concentrated hydrochloric acid and diluting to 50 ml in a calibrated flask. Add 5 ml of each standard solution to 1 ml of standard nickel solution as described previously.(b) For cobalt between 0.20 and 1-0 per cent.-Weigh into each of five 400-ml Phillips conical beakers the amounts of aluminium oxide, magnesium oxide, calcium carbonate and sodium chloride given in Table V, and 0-35 g of Specpure copper and 0.15 g of Specpure iron. To each mixture add, from a microburette, the volume of standard cobalt solution required to give, successively, 0.20, 0-40, 0.60, 0.80 and 1.0 per cent. of cobalt, ie., 2, 4, 6, 8 and 10m1, respectively. Dissolve each mixture as described for the decomposition of the concentrates, the final solution being made up to 50 ml with 20 per cent. v/v hydrochloric acid, Add, by pipette, 10 ml of each standard solution to 1 ml of the standard nickel solution. PROCEDURE FOR RECORDING THE SPECTROGRAMS- The spectrographic and photographic data used for recording the spectrograms are given in Table VI.Rate calibration-Routine plate calibration practice in this laboratory requires the individual calibration of each plate. Briefly, the procedure is similar in principle to that previously recommended by McK. Nobbs and Beale,8 the value of gamma for each plate being derived from an iron-spark spectrum recorded on that plate; the group of iron lines used, together with their relative intensity values, are given in Table VII. The particular deflection - relative intensity Table for that value of gamma is then selected from a series of such Tables compiled from a family of plate-response curves pre- pared to cover the range of gamma values experienced in normal practice.Kaiser - Seidel134 MASON AND DE BEER: DETERMINATION OF COPPER, COBALT AND [VOl. 83 transformationss (P values) are applied to straighten each of the plate-response curves, from which are drawn the Tables. TABLE VI SPECTROGRAPHIC AND PHOTOGRAPHIC DATA Spectrograph . . .. Slit width . . .. .. Slit length. . .. .. Source to slit distance . . Condensing lens . . .. Wavelength region . . Lower electrode . . .. Upper electrode . . .. Spark gap.. .. .. Capacitance . . .. Method of excitation . . Nominal secondary voltage Added inductance .. .. .. .. .. .. .. .. * . . . .. .. .. .. .. * . .. . . .. .. .. .. .. .. .. .. .. Exposure: (a) For the determination of Cu, Fe and Co in Co con- centrates, and Cu and Fe in Cu concentrates . . (b) For the determination of Co in Cu concentrates .. Photographic plate . . .. Plate processing . . .. .. Developer formula- Metol (Kodak) . . .. Hydroquinone . . .. Sodium sulphite, anhydrous Sodium carbonate, anhydrous Potassium bromide . . .. Distilled water to . . 1 . Densitometer . . .. .. Slit width . . .. .. .. Slit length .. .. .. Clear-glass deflection . . .. Line pairs (M.I.T. wavelengths)- Cu I1 2369.887 - Ni I1 2356.41 Fe I1 2359.104 - Ni I1 2356.41 Co I1 2353.42 - Ni I1 2356.41 . . .. .. .. .. . . .. . . .. .. .. .. .. .. .. Hilger large-quartz fully automatic 1.75 cnl 36 cm F. 1025 2230 to 2900 A &-inch diameter graphite rod (A.R.L. standard grade) pointed to 80" blunt cone Porous cup-a +-inch diameter hole drilled to within 1 mm of the end of a O.7-inch length of &inch diameter graphite rod.The base is first rendered porous by heating to dull redness in a blow-pipe flame. A 0.1-ml portion of the analysis solution is placed in the cup from a small-bore pipette 15 P 3 mm High-voltage condensed spark 15 kV, r.m.s. 0.005 pF Nil 60 seconds (triplicate exposures on each solution) 2 superimposed exposures of 75 seconds each (duplicate Kodak B.10 24 minutes' development a t 20" C followed by fixing in acid fixer for 1 minute, washing in running water for 3 minutes and drying in a current of warm air exposures on each solution) 1 g 2.2 g 9.0 g 13.0 g 0.3 g 1000 ml Hilger non-recording, optical magnification x 10 0.13 min 1-5 cm 50 cm (full-scale) Range Index value* .. .. 5 to 40% 11% .. .. 5 to 40% 14% , . " (4 1 to 6% 4.5 YO (b) 0.20 to 1% C C = beyond range of graph.* The index value is the concentration of the element being determined a t which the intensities of the analytical and internal standard lines are equal, i . e . , log intensity ratio = 0.0. TABLE VII IRON-SPARK CALIBRATION LINES M.I.T. wavelength, A Relative intensity 2793.888 2799.286 28 12-493 2819.333 2827.434 2828.634 1.40 1.00 0.16 0.19 0.45 1.06 Stnndardisation-The six standard solutions were each exposed three times on each of From the spectra of the standard solutions three plates spread over a period of 1 week.March, 19581 IRON IN COPPER AND COBALT CONCENTRATES 135 the densitometer deflection readings of the line pairs were obtained. These values were converted to log relative intensity values by reference to the relevant plate calibration data, and, from these intensity values, the log intensity ratios Ih/INi, I,,/I,, and IFe/IN, were found.The mean value for a line pair for each sample was then calculated and standard graphs for copper, cobalt and iron were constructed by plotting this mean log intensity ratio against log percentage concentration. These graphs have been found to be remark- ably constant and it has not been necessary to include spectra of standard samples on the same plate as unknown samples. Typical graphs are shown in Figs. 1 and 2. Log (amount of cobalt,%) Scale for curveA 0.2 0.4 0.6 Log (concentration of metal,%) Fig. 1. Standard curves for copper and iron in copper and cobalt concentrates: curve A, Cu 2369.8 - Ni 2356.4; curve B, Fe 2359.1 - Ni 2356.4 Log (amount of Fig.2. Scale for curve 6 Standard curves for cobalt in copper and cobalt concentrates with Co 2353.4 - Ni 2356-4 line pair: curve A, 1.0 to 6.0 per cent. of cobalt (cobalt concentrates) ; curve B, 0.20 to 1.0 per cent. of cobalt (copper concentrates) Evalztation-From the spectra of the concentrate solution the mean log intensity ratios of the line pairs were obtained in the manner described. These values were then referred to the corresponding standard graph and the concentrations of copper, cobalt or iron were read. SPEED OF ANALYSIS With practice, one operator can analyse a single sample in 1 hour, and a batch of 20 samples in a working day. We thank the Consulting Metallurgist, Anglo - American Corporation of South Africa Limited, for permission to publish this paper. We also express our appreciation for the collaborative chemical analyses carried out by colleagues of the analytical staff of the Research and Development Division. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. REFERENCES Rosza, J. T., Metal Progress, 1947, 593. Ahrens, I,. H., Spectrochim. A d a , 1951, 4, 302. Carlsson, C. G., Jernkont. Ann., 1951, 135, 607. Muir, S., and Ambrose, A. D., J . Iron 6% Steel Inst., 1954, 177, 400. Young, L. G., Berriman, J. M., and Spreadborough, B. E. J., Analyst, 1954, 79, 551. Scott, R. O., Chem. Age, 1953, 69, 1013. Feldman, C., Anal. Chem., 1949, 21, 1041. McK. Nobbs, J., and Beale, P. T., Spectrochim. Acta, 1955, 7, 165. Honerjager-Sohm, M., and Kaiser, H., Ibid., 1944, 2, 396. “Spectrographic Analysis of Low Alloy Steels,” Special Report No. 47, The Iron and Steel Institute, Received February 2nd, 1957 London, 1952.

ISSN:0003-2654    

DOI:10.1039/AN9588300129

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

136 HARVEY AND MURRAY: A SPECTROGRAPHIC METHOD FOR THE [Vol. 83 A Spectrographic Method for the Determination of Rarer Elements in Silicates BY C. 0. HARVEY AND K. L. H. MURRAY (Geological Survey and Museum, Exhibition Road, S. W.7 and Department of the Government Chemist, Clewent’s Inn Passage, Styand, W.C.2) A general method for the determination of rarer elements in silicate rocks and minerals is described. Calcium sulphate is used as the spectrographic buffer and internal standard, the source of energy being a d.c. carbon arc. MANY rarer elements are detectable by spectrographic methods in silicate rocks and minerals. The literature of the subject is extensive: inforrnation concerning their own work and the work of others has been summarised by Mitche1.P and by Ahrem2,3 In the development of the general method described later, the aim has been applicability to specimens that have widely different major constituents and a compromise between simple direct methods and the more accurate methods, in which a selected internal standard is added for the element to be determined. The features of the proposed method are as follows- (i) Its general suitability for silicate rock; and minerals.(ii) The provision for estimations by visua.1 inspection of the photographic plate and for photometric determinations of elements that are sometimes present in relatively large amounts, e.g., chromium, nickel and vanadium. (iii) Some measure of control is achieved by using an internal standard. In order to provide for (i) and (iii), the sample is buffered with calcium sulphate,* which, at the temperature of the arc, will rapidly decompose the minerals in the sample and, being relatively involatile, will persist in the arc gases until the “burn” is completed.This dilution with calcium sulphate helps to stabilise the excitation conditions and to reduce the effects of variations in the major constituents of the samples, and also provides an expedient whereby valid corrections for impurities in the carbon electrodes can be made: as is well known, the detection of impurities in electrodes is sometimes stimulated when the arc contains added mineral matter. To facilitate (ii), the spectra are stepped by using a rotating stepped sector, a device that also greatly widens the ranges of element concentrations determinable by a single exposure.PHOTOMETRIC DETERMINATIONS The calcium-atom line at 3140.78 A is used as the internal-standard control line, com- parison with the analysis lines being made at constant photographic density. At a suitable density, the linear separations of the curves for density against the log of the relative exposure for the calcium and analysis lines are measured and correlated with percentages by means of a working curve, e.g., Fig. 1 (a). A nomogram has been constructed to facilitate the calculation of Seidel densities. The requirements for an ideal internal-standard spectrographic technique include the use of pairs of lines known to respond similarly to changes in excitation conditions, of element pairs of similar volatility, of lines free from self-a.bsorption and of line pairs of similar wave- lengths.Ideal requirements cannot be satisfied in a general method, but the use of the calcium line at 3140.78 A provides some measure of control by internal standard, is practicable for a general method and is preferable to a direct method without an internal standard. Photographic processing conditions must be carefully st andardised in order to minimise the effects of variations of plate gamma with wavelength. * Since the work described in this paper was completed, Turekian, Gast and Kulp4 have shown that, for strontium determinations in silicates, the effects of varying matrix are reduced by adding calcium carbonate. Their figures for the strontium contents of two standard rock powders are similar to figures obtained by us for the same powders.March, 19583 DETERMINATION OF RARER ELEMENTS I N SILICATES 137 The presence of different amounts of calcium in the rock or mineral specimens will cause only slight variations in the density of the calcium line at 3140.78 A.For specimens con- taining up to 10 per cent. of CaO, errors arising from this source are small, and the provision of a series of working curves for a range of calcium contents is normally not necessary. L 0 I 1 I I I 1 1 I 0.001 I 0.003 1 0010 I 0.030 I 0.1 0 0402 6905 0.020 0.050 0.2 Chromium(Log, scale),% Fig. 1. Calibration curves for determin- ations of chromium by using the Cr 4254 line; (a) photometric method ; ( b ) step-counting method. With (0) synthetic base and (A) rock- powder base CORRECTION FOR BACKGROUND- Corrections for the background produced by continuous radiation are made by using the ratio of the galvanometer deflections for “background” and for “line plus background” to calculate the photographic density of the line freed from background. Although it is not strictly valid, this method of correction appears to serve quite well for a general spectrographic method when a buffer is used.VISUAL ESTIMATIONS Estimations are made by counting the number of steps in which an image of the element line is visible, with fractional estimations of the density of the weakest step, e.g., 3&, 3+, 32 or 4 steps for a line visible in the fourth step, but not in the fifth step. The visual comparison of stepped spectrograms has been used by earlier w o r k e r ~ .~ , ~ , ~ For any chosen element line, a count of the number of steps provides a relative inverse measure of the exposure necessary to produce a visible image, and is related to the intensity of emission. A rectilinear relationship between “number of steps” and “log, yo,” which should apply if reciprocity and intermittency effects are negligible, has been found to be valid for many of the calibratory plots actually obtained, e.g., Fig. 1 (b). The calcium line at 3140.78 A, used as the control line for photometric determinations, can also be used to correct observations made by the visual step-counting method. CORRECTION FOR BLANK DETERMINATIONS- A blank spectrum, obtained by striking an arc in a mixture of calcium sulphate and carbon, is recorded on every plate, so that corrections can be applied as necessary, notably for the small amounts of vanadium sometimes present in the carbon electrodes.The blank spectrum also helps with the avoidance of pitfalls, such as the confusion of a line of an (OH) band with the bismuth line at 3067.7 A. Dingles states that this band often appears in the spectrum of an arc in moist air. Correction for traces of an impurity in the carbon or calcium sulphate is difficult to apply in terms of weight or percentage when a similar correction must also be applied to138 HARVEY AND MURRAY: A SPECTROGRAPHIC METHOD FOR THE [Vol. 83 the standard spectra used for constructing the working curve, i.e., the amount of the impurity that produces the blank response is not easily determinable.For photometric determinations, which are usually made only when the element response is strong, correction for the small blank value should not be necessary. For estimations made by the visual step-counting method, we find that a sufficiently exact correction can be made by deducting the “intensity value” of the blank determination. We define the “intensity value” of the image of a stepped spectrum line visible in 1, 2, 3, 4, 5, 6 or 7 steps, as, respectively, 1, 2, 4, 8, 16, 32 or 64 for a stepped sector having an exposure ratio of 2 to 1. As an example, for an element line visible in, say, 34 steps, with a blank value of 1 step, the corrected “intensity value’’ is (6 - I), and the corrected number of steps is 3i. NOTES ON THE SPECTRUM LINES Carefully selected spectrum lines, suitable for determinations of the rarer elements in silicate rocks and minerals, are listed in Table 11, together with appropriate comments.Although many of the lines selected appear in Dingle’s* lists of sensitive multiplets, the most sensitive line for any particular element has not always been chosen, either because interference by (CN) bands or by emission from another element is likely, or because the most sensitive line is not located within the chosen wavelength range, i.e., 2750 to 4 6 7 0 ~ . Some elements have therefore been listed that will rarely be detected in silicate rocks, but the inclusion of these elements ensures that their presence in unexpectedly high amounts does not escape notice. The wavelengths quoted are based on those given by Harri~on.~ Many of the lines chosen, being atom lines, call for the use of an atom line as internal- standard control line.Noteworthy exceptions are the zirconium lines at 3392 and 3438~, the beryllium lines at 3130 and 3131 A and the niobium lines at 3163 and 3195 A, all of which are ion lines and none of which responds well to correction by the calcium-atom line at 3140.78 A. SEPARATION OF LINES- The variation of dispersion of a prism spectrograph with wavelength and the resolving power of the photographic emulsion are factors that affect the interference of one spectrum line with another of similar wavelength. TABLE :L SEPARATION OF SPECTKUM LINES Wavelength, 2780 3000 3200 3400 3500 3706 3906 4005 4227 4337 4427 4638 A Plate factors, A per mm 3.7 4.7 5.8 7.1 7.8 9.3 11.0 12.0 13.4 16.1 17.0 18.2 Wavelength differences necessary to eliminate interference by one line with a near line, 0.11 0.14 0-17 0-21 0.23 0.28 0.33 0.36 0.40 0.45 0.5 1 0.55 A TABLE 1 3 SELECTED SPECTRUM LINES Approximate minimum Wavelength Element detectable, of line used, * Comments % A Sb 0.06 2877.92 Ca line may produce slight blank value.Cr may sometimes As 0.1 2780.20 Separable frorn Mn line at 2 7 8 0 . 0 0 ~ interfere 2860-45 Ti line a t 2860.28 A should be separable if present * The lines used for the detection of the minimum percentages are given in italics.March, 19581 DETERMINATION OF RARER ELEMENTS IN SILICATES 139 Approximate minimum Wavelength Element detectable, of line used, * Ba Be Bi Cd Ce Cr C O cu % 0.00 1 0.001 0.01 0.02 0.2 ? 0~0005 0.002 0.0003 Ga 0.002 Ge 0.005 Tn 0.002 Pb Li Mn Mo 0.005 0.005 0.04 (0.02 if Fe absent) 0.0005 0.001 A 3071-59 4554.04 3130.42 3 13 1-07 3321.01 3321.09 3321.34 2897.98 3067-72 3261.06 3 194.83 3234-16 3272-25 2780-70 2843.25 302 1.56 4254.35 3449-17 3449.44 3453-51 2824.37 3247.54 3273.96 2943.64 2944.18 3039.06 3269.49 3039.36 3256.09 3258.56 3245.12 3337.49 2833.07 3232-61 4602.86 2799.84 2801.06 2914.60 2925-57 31 70.35 3193.97 TABLE II-continued Comments Ca line produces slight blank value An ion line.Both are ion lines. Inseparable Cr line will not normally interfere. Avoid confusion with V line a t 3130.27 A Carbon bandhead a t 4553.1 A and Ti line at 3130.80 A Weak Cr line a t 3321-19 A Inseparable weak Mn line should not often interfere Line of (OH) band may produce blank value.Weak Fe line a t 3067.94 A Very weak Ca line just separable. Very weak V line not separable Nb line at 3194.98 A will interfere unless very weak. Very weak Ca line may produce slight blank value Inseparable lines of Pr, Zr, etc., are normally unlikely to inter- fere. Weak Cr line a t 3234.06~. When strong, Ti and Fe lines interfere Inseparable lines of Zr, V, etc., are normally unlikely to interfere. Ti line a t 3272.08 A just separable, unless strong Weak Fe line not separable. Cr line only suitable for strong response An ion line Weak Ti line not separable, but unlikely to interfere. Weak Cr Inseparable Ag line will not normally interfere Mn line may interfere when Cu response is weak Ca line may produce slight blank value. Cu lines at 3247 and Avoid confusion with Co line a t 2943.48 A.Inseparable Fe line Avoid confusion with Ni line a t 2943.91 A and Fe line a t Very weak Ca line a t 3039.21 A Weak Fe line at 3269.24 A Inseparable Fe line should usually be very faint. Avoid con- Inseparable Mn line often interferes. Avoid confusion with Mn line at 3258.41 A : presence of this line indicates interference An ion line. Inseparable Ce line should not normally interfere An ion line. Inseparable Ce line should not normally interfere. lines a t 3453-33 and 3453.74 A 3273 A are usually detectable in a blank determination will not normally interfere 2944-40 A fusion with Co line a t 3039-57 A Fe line at 3255.89 A of Mn with In line a t 3256-09 A Fe line a t 3337.67 A is separable Sb line a t 3232.50 A will not normally interfere Usable only in absence of Fe Inseparable Zn line will not normally interfere Inseparable weak Fe line will not normally interfere Inseparable V line may sometimes interefere.Weak Fe line a t 3193.80 A * The lines used for the detection of the minimum percentages are given in italics.140 HARVEY AND MURRAY: A SPECTROGRAPHIC METHOD FOR THE TABLE II-continued Approximate minimum Wavelength Element detectable] of line used,* Ni 0-0007 2943-91 3012.00 3380.57 3446.26 3452.89 3163.40 3194.98 3269-90 4246.83 % A Nb sc 0-005 0.002 Sr Ta T1 Th Sn 0.00 1 0.2 0.01 0.03 0-005 W 0-02 U > 0.5 V 0.002 Y 0.00 1 3464-46 4607-33 3311.16 2767.87 2837.30 2870.41 2982.05 2839.99 2863.33 3175.02 2946.98 2882.74 4362.26 2914.93 2924.03 2924.64 3183.42 4379.24 3200.27 3327.88 4643.70 Zn > 0.3 3345.02 Zr 0.0007 3391.98 3438.23 [Vol.83 Comments Inseparable Cu line will not normally interfere Avoid confusion with Ti line a t 3380.28 A Avoid confusion with Co line a t 3446.09 A Weak Fe line at 3453.02 A may sometimes interfere Both are ion lines. Inseparable weak Fe line will not normally interfere An ion line. Inseparable Ce line should not normally interfere. Avoid confusion with Fe line at 4247.43 A. Heavy background An ion line. Yb line a t 3464.37 A will not normally interfere Possible interference by Fe and Mn lines is rarely appreciable. Carbon bandhead a t 4606.1 A Very weak Nb line a t 3311.34 A Inseparable Ce, W and V lines should not normally interfere Inseparable Ce and Zr lines should not normally interfere Inseparable u eak Cr line should not normally interfere.Avoid Fe line at 2981.88 A. Ce line at 2981-91 A Inseparable weak Mn and Cr lines should not normally interfere Sometimes not free from interference by Fe line a t 2863.44 A. Inseparable weak Fe and Ce lines should not normally interfere Avoid confusion with Co line a t 3174.91 A. Inseparable weak Ce and Fe lines should not normally interfere Inseparable Ta line should not normally interfere Avoid confusion with weak Mn line a t 2882.90 A confusion with V line at 2870.55 A An ion line. Inseparable weak Si and Fe lines will not normally interfere An ion line Inseparable Pr line will not normally interfere An ion line. Ti line at 3199.92 A and Fe line a t 3200.48 A inter- fere when strong.Weak Ni line at 3200.42 A will not normally interfere An ion line. Inseparable Ce and Sm lines will not normally interfere Useful only 1:o confirm higher percentages of Y . Avoid con- fusion with Co line a t 4644-32 A and with Eu line a t 4644.24 A. Inseparable from Er, Pr, and weak Fe lines Weak Cr and Ti lines will not normally interfere An ion line. Inseparable weak Fe line should not normally An ion line. Weak Fe line a t 3438.31 A will not normalIy interfere appreciably interfere a:ppreciably * The lines used for the detection of the minimum percentages are given in italics. Under the conditions prescribed later in this paper, and with the particular spectrograph used, visual or photometric work is possible if tlhe lines are not very strong and are not less than 0.03mm apart.Table I shows the wavelength differences necessary to eliminate interference by one line with a near line. REPRODUCIBILITY OF RESULTS The figures quoted below illustrate the degree of reproducibility attained when the method was applied to a series of silicate rocks, the figures enclosed in each pair of brackets being replicate photometric determinations made on the same sample. The replicate deter- minations are not sufficiently numerous to justify the calculation of coefficients of variation. For comparison, results of chemical determinations of mangancse, chromium and bariumMarch, 19581 DETERMINATION OF RARER ELEMENTS I N SILICATES 141 are printed in italics : the accurate chemical determinations of manganese indicate a fair degree of true accuracy for the spectrographic determinations.determinations of barium and chromium are only approximate. The chemical Manganese, %- Barium, "/d- - Chromium, ?;-- Nickel, yo-- - Strontium, Oh- - Vanadium, %,-- Yttrium, yi- Zirconium, yo- (0.072, 0.065, 0.066, 0*0G9)Q (0.018, 0.015, 0.016, 0.016) (0.072, 0.072. 0.072, 0*0S6)c (0.080, 0.090, 0.090, 0*07'O)d (0.014, 0.017, 0-013, 0.011)O (0.09, 0.10, 0.10, 0-08)d (0.030, 0.030, 0.030, 0.031)g (0.11, 0.12, 0.12, 0 ~ 1 2 ) ~ (0.11, 0.14, 0.12, 0 ~ 1 2 ) ~ (0.13, 0.17, 0.17, 0-17)d (0.014, 0.016, 0.014, 0*019)k (0.11, 0.10, 0.10, 0.08)' (0.060, 0-070, 0.070, 0 0 0 4 ) ~ (0.060, 0.072, 0.070, 0.05)" (0.062, 0.070, 0.073, 0 ~ 0 5 ) ~ (0.048, 0.057, 0.057, U-03)h (0-045, 0.049, 0.047, 0 ~ 0 4 ) ~ (0.020, 0.020, 0-020, 0-02)d (0.085, 0.095, 0.095, O*OG)k (0.020, 0-020, 0.020, 0-02)z (0.015, 0.015, 0.017, 0.01) (0.0069, 0.0074, 0-0067, 0*007)d (0.029, 0.029, 0.030, 0-03) Ir (0.030, 0.033, 0.030, 0.02) (0.032, 0.035, 0.035, 0.02) (0.0060, 0.0050, 0.0060) (0.0026, 0.0034, 0.0032) (0.0070, 0.0070, 0-0070, 0.0060) (0.014, 0.014, 0 ~ 0 1 5 ) ~ (0*0066, 0-0078, 0*0066)" (0.047, 0.048, 0*047)d (0.002, 0-002, 0.002)g (0.082, 0.090, 0.096)' (0.067, 0.072, 0.064)' (0.030, 0.034, 0.032)d (0.017, 0,018, 0 ~ 0 1 7 ) ~ (0-17, 0-19, 0.20)l (0.0058, 0.0033, 0.0050)" (0.0066, 0.0056, 0.0062)C (0.019, 0.018, 0-020)d (0.0070, 0.0080, 0*0070)d (0.0093, 0.0087, O-OIO)i (0.0087, 0*0080, 0-0087)m (0.017, 0.016, 0.015)" (0.021, 0-022, 0.021)' (0.030, 0.030, 0-030)d (0.035, 0.034, 0.033)' (0.0062, 0.0082, 0-0054)n (0.010, 0.011, 0.011, 0.013, 0.011)' (0-0031, 0.0043, 0.0050, 0-0058, 0.0055)c (0.013, 0.013, 0.014)d (0.0038, 0.0041, 0.0039)d Direct determinations, without internal standard.(0.10, 0.09, 0.11)" (0.022, 0.021, 0.022) (0.09, 0.12, 0.ll)C (0.027, 0.027, 0*026)d (0.025, 0.038, 0.023)5 (0.021, 0-020, 0-023)d (0.005, 0-007, 0-007)n (0.032, 0.037, 0~033)~ (0.012, 0-014, 0.012) (0.012, 0.010, O*OIS)m (0.009, 0.008, 0.008)P (0.020, 0.022, 0*021)h 40.016, 0-017, 0*016)i a = gneiss g = granite 1 = diorite b = felsite h = camptonite m = tonalite I: = hornfels i = lamprophyre n = pegmatite d = schist k = granulite o = porphyrite .Is indicated later in the description of the method, each plate carries a spectrum of a control mixture of known element contents..4lthough the original standard mixtures were made entirely from pure chemical compounds, the control mixtures were rock powders (a granite and a felsite) to which additions of compounds of rarer elements were made. The control determinations provide addi tiorial information about the reproducibility of the results: some figures obtained to date are listed below, the figures in italics being the amounts actually present. Manganese, ?(,--- Barium, %-- Chromium, ?A- Nickel, %-- Strontium, yo-- Vanadium, yo- Yttrium, yo- Zirconium, "/o-- 0.24, 0.20 0.13, 0.12, 0.12, 0.11, 0-12 0.044, 0.048, 0-046, 0.055, 0.045, 0.050 0.12, 0.14, 0.13, 0.13, 0.14 0.040, 0.044, 0.048, 0.043, 0.055, 0.057 The line used, Ba 4554.4, is an ion line 0.12, 0.10, 0.10, 0.11 0.038, 0.042, 0.044 0.060, 0.060, 0.052, 0.055 0.019, 0.020, 0.018 0.12, 0.10, 0.11, 0.11, 0.12 0.040, 0-034, 0.036, 0.047, 0.047 0.061, 0.051, 0.057, 0-060, 0.060, 0.051 0.030, 0-024, 0.025, 0-028 0.010, 0.006, 0.009, 0.010, 0.010 0.022, 0.020, 0.019, 0.019 0.010, 0.015, 0-011 Direct determinations, without internal standard 0.076, 0-072, 0.096, 0.10, 0.090, 0.10 0.039, 0-036, 0.037, 0.044 0.019, 0.027, 0.018, 0-018 LATITUDE- The use of only one calcium line for internal-standard control of all the other element lines is an empirical device that should eliminate gross errors when operating conditions are carefully standardised.To obtain information about the effects of deliberate departure from the standard operating conditions, some determinations have been made at increased142 HARVEY AND MURRAY: A SPECTROGRAPHIC METHOD FOR THE and decreased current (13 amperes and 8 amperes, respectively), and with a reduced amount of arcing mixture in the anode (35 mg instead of 512 mg).The figures quoted below show the minima and maxima found, the figures in italics being the amounts actually present. Manganese, yo- 0.13, 0.10 t o 0-12 Vanadium, yo- 0.030, 0.022 to 0.028 Nickel, %- 0.060, 0.040 to 0.065 Chromium,%- 0.12, 0.080 to 0.11 Barium, yo- 0.12, 0.070 to 0.17 Strontium, %- 0.12, 0-081 t o 0-15 Zirconium, yo- 0.039, 0.012 to 0.038 (not corrected by internal standard) These experiments demonstrate the effects of major changes in the operating conditions, and indicate that inadvertent fluctuations, which will be relatively minor, are not like&.to be a source of gross errors. METHOD OF RECORDING THE SPECTRA [Vol. $3 An outline of the method that was used for recording the spectra is as follows. Arcing wzixtures-one part by weight of the finely powdered sample is mixed with 3 parts of purified ignited calcium sulphate and 4 parts of powdered carbon. For the blank determinations, the same calcium sulphate and carbon powder are mixed in the ratio of 3 to 5 . The anode (bottom electrode) is drilled with a 3-mm diameter drill (a No. 32 carbon-steel drill was used) to a depth of & inch, and this cavity is completely filled with the arcing mixture (average weight about 50 mg), which is compacted by pressing with a steel rod during filling. The tips of both electrodes are flat, not tapered.(?$tics-A Hilger - Littrow spectrograph, F, 170 cm, with a quartz prism and lens is used. The wavelength range used is 2750 to 4670 A. An image of the arc is focused on a 4-cm horizontal mask attached to the collimating lens to exclude radiation from the electrode tips and to pass radiation from only the central $ of the arc. A six-step rotating sector, of step ratio 2 to 1, is used to produce the stepped spectra. The slit width used is 0.010 mm. PZates-Ilford Thin Film Half Tone ordinary plates (backed) are used and developed for 4$ minutes at 75” F in Ilford I.D.11 developer (M.Q. Borax), the temperature being con trolled thermostatically . Arcing technique-A d.c. arc with a 10-mm arc gap, the gap being maintained at 10mm during the entire arcing period, is used with no pre-arcing.The technique is as follows-- (a) The arc is struck at 3 to 4 amperes, the electrodes being separated gradually to reduce any tendency for mechanical loss during the destruction of minerals. (b) After 30 seconds, the current is increased to 6 to 7 amperes, this current being maintained for 15 seconds. (cj The current is now increased to 104 amperes and arcing is continued “to completion,” and thereafter for 10 seconds. “Completion” is indicated by a sudden change in the character of the arc accompanied by a fall in current of about 2 amperes. The total time of arcing is about 4 to 44 minutes. The current is controlled by means of a tapped resistance, sections of which are shorted by switches to effect the desired increases in current.The maximum current is adjusted before making the exposures by setting a variable resistance to pass a current of 8.6 amperes with a 10-mm arc between plain 5-mm carbon rods. Each plate carries spectra in triplicate of the sample, a spectrum of a control mixture of known element contents and a blank spectrum. Preparation of pur<fied calcium suZ$hate-The pure calcium sulphate normally obtainable often contains traces of strontium and barium. Calcium sulphate free from these metals has been prepared by the following method. Suspend 100 g of AnalaR calcium carbonate in about 500 ml of water and dissolve by adding 250 ml of concentrated hydrochloric acid. Dilute to about 1300 ml and precipitate about 90 per cent. of the calcium by adding to the boiling solution a hot aqueous solution containing 130 g of ammonium oxalate.After an interval of 15 minutes, add a little filter- paper pulp and filter through a large Buchner funnel, washing the precipitate once with hot water. Electrodes-Carbon rods of diameter 5 mm are used. Exposure, &.-The plate is exposed during the entire period of arcing.March, 19581 DETERMINATION OF RARER ELEMENTS IN SILICATES 143 Disperse the cake of calcium oxalate in about 500ml of hot water, heat the beaker on a steam-bath, and add concentrated hydrochloric acid gradually until dissolution is complete. Re-precipitate the calcium oxalate from the near-boiling solution by adding slowly, with constant stirring, a hot 9 N solution of ammonia. When the neutral point to methyl orange is reached, slightly acidify the solution by adding 20 drops of concentrated hydrochloric acid.Filter and wash the precipitate as before. Again re-precipitate in a similar manner. Convert the calcium oxalate to oxide and destroy organic matter by ignition at a tem- perature of about 900” C in a platinum basin, slake by the cautious addition of water, and convert to sulphate by adding a slight excess of diluted sulphuric acid (1 + 1 ) . Evaporate on a steam-bath and drive oft‘ the excess of sulphuric acid by heating at the fuming-point. Ignite the calcium sulphate at 900” C for about 1 hour and mix thoroughly. This calcium sulphate does not hydrate when exposed to a moist atmosphere.1° We thank Dr. G. 34. Bennett, C.K., F.R.S., the Government Chemist, and Sir William Pugh, O.B.E., F.R.S., Director of the Geological Survey and Museum, for permission to publish this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Mitchell, R. L., “The Spectrographic Analysis of Soils, Plants and Related Materials,” Tech. Ahrens, L. H., “Spectrochemical Analysis,” Addison - Wesley Press Inc., Cambridge, hlassachu- _- , “Quantitative Spectrochemical Analysis of Silicates,” Pergamon Press Ltd., London, 1954. Turekian, I<. K., Gast, P. W., and Kulp, J. L., Spectrochim. Acta, 1957, 9, 40. Breckpot, R., Spectrochirn. Acta, 1939, 1, 137; J . Inst. Metals, 1939, 64, 409. Strock, L. W., “Spectrum Analysis with the Carbon Arc Cathode Layer,” Adam Hilger, London, Eeckhout, J., Nature, 1945, 156, 175; Ver. Vlaan?. Acad. Wetem. Belg., 1045, 7, 5. Dingle, H., “Practical Applications of Spectrum Analysis,” Chapman & Hall Ltd., London, Harrison, G. R., “Massachusetts Institute of Technology Wavelength Tables,” John Wiley & Sons Harvey, C. O., “Notes on Spectrographic Analysis,” Bull. Geol. Szdrv. Gt. Britain No. 9, 1955, p. 52. Comm. Bur. Soil Sci. No. 44, 1948. setts, 1950. 1936, p. 43. 1950, p. 99. Inc., New York, 1939. Received June 7th. 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300136

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

March, 19581 DETERMINATION OF RARER ELEMENTS IN SILICATES Determination of Water in Granulated 143 Sugar BY S. HILL AND A. G. R. DOBBS (Tate & Lyle Research Laboratory, Westerham Road, Keston, Kent) Water in granulated sugar can be determined by grinding and drying the sample in a vacuum. Steel balls are used to grind the sample to a fineness of 3500 sq. cm per g and drying is carried out at 60" C for 15 hours. The water vapour evolved is collected and measured by observing the pressure exerted by it in a known volume. Tests have shown that the water in granulated sugar, usually about 0.04 per cent., can be determined with a coefficient of variation of less than 1 per cent. Comparisons have been made with other methods and the distri- bution of water between the surface and the interior of sugar crystals has been investigated.A METHOD for the accurate determination of the water content of granulated sugar (sucrose) is required for several reasons. Apart from the necessity of accurately analysing the output of granulated sugar from a sugar refinery, it is necessary to obtain a precise analysis of the sucrose that is used for the standardisation of saccharimeters, refractometers, etc. This analysis must include an estimate of the water content. Sucrose that is used for calibration purposes can be previously dried, but it may take up an unknown amount of water from the atmosphere during weighing and other operations before dissolution. A sounder method for purposes of standardisation is to allow the sucrose to come into equilibrium with the humidity in the atmosphere and to measure, and allow for, the amount of water in the sample.It can be safely stated that no satisfactory method of determining the water content of crystalline sicrose has previously been described. It is usually determined by measuring144 HILL AND DOBBS: DETERMINATION OF WATER IN GRANULATED SUGAR [VOl. 83 the loss of weight from a sample of about 20 g when it is heated at 105" C in air at atmospheric or reduced pressure.l It is generally recognised that, at this temperature, a certain amount of slow decomposition occurs, so a limit must be placed on the time of dehydration, As the total water content of a typical granulated sugar is of the order of 0.04 per cent., the amount of decomposition that can be tolerated is very small.An illustration of the uncertainty that exists on this subject is that different drying times of from 30 minutes to 3 hours have been recommended. Drying to constant weight is not sound, firstly on account of decom- position, and secondly because the regain of moj sture during weighing eventually cancels the loss during the intervening periods of dehydration. I t will be shown later that approximately half the water in granulated sugar is contained within the structure of the sugar crystals. A serious objection to the conventional method for determining water is the inaccessibility of this water, unless the crystals are finely ground. However, when the crystals are ground in air, there may be an unknown exchange of water between the newly created surfaces and the atmosphere before the sample can be weighed.Certain properties of granulated sugar depend primarily on the amount of the surface moisture. This can be caused by migration of water on account of temperature gradients. External moisture can be determined by the conventional method, but the limits of error are rather wide. The proposed method, although developed primarily for total water, can also be used, by omitting the grinding, to determine external moisture only, and it is much more accurate than the conventional method. The proposed method for determining water is not, in its present form, entirely suitable for routine analysis. It is intended mainly for use when a relatively elaborate procedure is justified and also as a standardising method, to which other more rapid procedures may be referred.One such property, for example, is caking of the sugar during storage. VACUUM DETERMINATION OF WATER About 15 g of the sugar under test are sealed in a thin glass ampoule, which is then enclosed in a flask that can be evacuated. After evacuation of the flask, the ampoule is broken, the sugar is finely ground in situ and the water is driven from the sample and con- densed in a second evacuated space of known volume. This space is then sealed and the condensed water is allowed to evaporate. The amount of water is indicated by the pressure exerted by the vapour in the known volume. This method for determining water has previously been used for certain other materials, e.g., paper,2 and a form of apparatus for this type of procedure is commercially available, but the adaptation of the method for use with granulated sugar required certain special features, which are described later.METHOD APPARATUS- About 15 g of sugar are sealed in the previously dried ampoule, P. Care must be exercised while sealing the ampoule to prevent any over-heating of the sugar. If any caramelisation occurs the sample must be rejected, otherwise cumulative decomposition will take place during the subsequent heating and the result will be incorrect. For this reason the ampoules are made from soft (soda or lead) glass. The ampoule is supported in the neck of the flask, A, by means of a glass rod, B, which is free to slide in a side axm of the flask. Inside the flask are four &inch diameter stainless-steel balls, which are latler used to break the ampoule and to grind the sugar.The flask is attached to the rest of the vacuum system by way of a conical joint, C, which is sealed with Picien wax, a tap, Ill, and a. spherical ground joint, E. A condensing tube, F, is sealed on at the level of tap D,. The known volume in which the water is collected is the section bounded by taps D, and D,, and by the Apiezon oil in the left-hand member of the manometer, M. This section includes a U-shaped cold trap, T, and a bulb, :K, which has been added to increase the volume to a convenient value for a 15-g sample, i.e., approximately 300ml. To the right of tap D, in the diagram are a NcLeod gauge and an oil diffusion pump. The gauge is con- venient rather than necessary.If :L good quality two-stage rotary pump is available, the diffusion pump is probably unnecessary also. The vacuum system is shown in Fig. 1, which is drawn approximately to scale.March, 19581 HILL AND DOBBS: DETERMINATION OF WATER~IN GRANULATED SUGAR controlled heater, L, in which the flask is heated, and a shaking machine. flasks can be attached simultaneously to the vacuum system. the practical maximum is probably about twelve. 145 Other items required are a vernier telescope for reading the ,manometer, a thermostatically A number of We have used four flasks; L D3 C ' . T Scale inches 4 O U U A = Flask F = Condensing tube C = Conical joint L = Thermostatically controlled heater D,, D, and D, = Taps E = Spherical joint T = U-shaped trap B = Glass rod K = Glass bulb M = Manometer P = Ampoule Fig.1. Apparatus for determining water in granulated sugar PROCEDURE- With taps D,, D, and D, open, flask A is heated at 120" C for 4 hour under vacuum to eliminate stray moisture and a flame is applied for a few seconds to the condensing tube. Taps D, and D, are closed and the flask is detached from the vacuum system at joint E. The polished steel balls, in a good vacuum, and making only single point contact with the wall of the flask, cool very slowly. A period of 9 hour must be allowed for coolingbefore the ampoule is broken by dropping it into the flask. The sugar is then ground by the steel balls for 1 hour by subjecting the flask to a circular motion in the shaking machine. The flask, which is mounted in the machine with its axis vertical, does not rotate.It performs a circular orbit 400 times per minute and its axis sweeps out a vertical cylinder of radius Q inch. These conditions are not critical, but the grinding procedure should produce in the sugar a specific surface of not less than 3500 sq. cm per g. After reconnecting the flask to the vacuum system, the space between taps D, and D, is evacuated, but tap D, remains closed. The condensing tube is cooled in a mixture of solid carbon dioxide and ethanol and the water is driven from the sugar by heating the flask at 60" C for 15 hours. Justification for the choice of 15 hours will be given later. Before discontinuing the heating, tap D, is closed and the refrigerant is transferred to the cold trap and tap D, is opened.By cooling the trap (at least 6 inches of which should be immersed) before opening tap D,, conden- sation is made to take place mainly in the left hand member of the trap in the neigh- bourhood of the "water line." Although ice has an appreciable vapour pressure at -72" C, the loss of water by diffusion through the trap is below the detectable limit. After the application of a flame to the condensing tube, tap D3 is opened for $ minute to eliminate the146 HILL AND DOBBS: DETERMINATION OF WATER IN GRANULATED SUGAR [VOl. 83 air that has been liberated from the ampoule. Enally, taps D,, D, and D, are closed and the refrigerant is removed. When equilibrium is reached, the vapour pressure of the water is read on the manometer. The volume occupied by the vapour must be large enough to keep the vapour pressure below the saturation value, i.e., 14.5 mm of mercury at 17" C.During the course of the early experiments, the grinding technique was such that the sugar was spread in a thin adhesive layer over the inner surface of the flask. When the sugar samples were heated, a white distillate acciimulated as a film in the part of the neck of the flask that was outside the heater. Also, hourly tests showed that the evolution of water settled down after a few hours to a relatively high constant rate, presumably owing to decomposition of the sugar. No distillate was formed unless the sugar was ground in situ. If the sugar was not ground, or if it was ground in a mortar and then put into the flask, the distillate did not appear.It seems that a reaction can occur between the sugar and the flask, which was originally made of Pyrex glass. The difficulty was eventually overcome by using flasks of Monax glass of the shape and size shown in Fig. 1, and by grinding as described, so that a thin layer of sugar is not formed. In view of the small difference between the chemical constitutions of Pyrex glass and Monax glass, the improvement was probably due to the change in the grinding technique. CALCULATION OF RESULTS- The percentage of water ($) in the sample is given by- 18-02 273 VhP 100 p = - 22.4 (273 + t ) 'i6 x 13.6 x' where V = the calibrated volume in litres, h = the manometer reading in cm, p = density of the oil in the manometer in g per ml, M = the mass of the sample in g, and t = the ambient temperature in "C.As V and p are instrumental constants- p=------- constant x h M (273 + t ) ' so that p can be read from a nomogram as a function of h, M and f. The following corrections must be applied to this result- (a) An allowance must be made for the increase in V caused by the fall in the level of oil in the left-hand member of the manometer. Alternatively, the design of the manometer can be such that the oil level in. the left-hand member can be restored to a fixed mark. 0 I-0 1.1 1.1 1.2 1.3 1.4 1.5; mass of sugar, g Ratio -- internal volume of ampoule, ml Fig. 2. Correction curve for water vapour in the air enclosed with the sample Time of heating. hours Fig. 3. Effect of time of heating on the evolution of water (b) The air enclosed with the sample in the ampoule contains water vapour, Fig.2 shows the correction to be applied if the enclosed air is assumed to have a relative humidityMarch, 19581 HILL AND DOBBS: DETERMINATION OF WATER I N GRANULATED SUGAR 147 of 50 per cent. at 20" C. As 'VIM need not exceed 1-25 ml per g, an error of 20 per cent. in the assumed relative humidity will introduce an error into the final result of less than &0.0002 per cent., ie., about 0.5 per cent. of the water to be expected in the sample. TESTS OF THE METHOD -1 number of observations have been made to test the validity of the method. Any leakage of moist air into the apparatus and any moisture on the ampoule or in Blank tests have shown that leakage is easily prevented -4fter the normal heating period in the vacuum apparatus, samples of sugar have been No further evolution of water BLANK TESTS- the flask will increase the result.rind that, after the preliminary heating, stray moisture is negligible. allowed to cool and observations have continued for 1 hour. vapour has occurred during the extra hour. CONTINUOUS OBSERVATION OF THE EVOLUTION OF WATER- from the condensing tube to the cold trap. is pumped away. evolution is less than 0.0001 per cent. per hour of the mass of sugar. have confirmed this result. At any stage the amount of water driven off can be measured by transferring the water After measurement each increment of water After 14 hours the rate of Many other tests Fig. 3 shows the result of such a procedure. EXAMINATION OF THE CONDENSATE- There is a high probability that the substance condensed in the cold trap is water, (a) Exposure of the vapour to phosphorus pentoxide reduced the vapour pressure to 0.005 of its original value.A sample of the condensate was allowed to evaporate into a suitable optical cell and its infra-red absorption spectrum was recorded. Apart from the well developed absorption bands due to water, the only feature of the spectrum was a small peak at 12.6 p. The height of this peak was not affected by exposure to phosphorus pentoxide. It follows that water vapour accounts for 99.5 per cent. of the total vapour pressure. (b) A gravimetric method of determining water, based on a reaction with cobaltous bromide, has been developed by Gardiner and Keyte of this l a b ~ r a t o r y . ~ Their method was applied to an amount of condensate that was estimated by the vacuum method to consist of 9.80 mg of water. The mass of water in 9.80 mg of sample was found by but confirmation is desirable. Accordingly, the following tests were carried out- 0.03C 8 e $ % 0.02c -6 9 0.025 - L U W f 3 0 E 4 0.0 I 5 0 1 I ' -A 1 I I # 0 10 20 30 40 50 Time of heating, hours Fig.4. Effect of prolonged heating on the evolution of water: curve A, at 90" C; curve 13, at 60" C148 HILL AND DOBBS: DETERMINATION OF WATER IN GRANULATED SUGAR [VOl. 83 the cobaltous bromide method to be 9.6 f. 0.5 mg. error. Agreement is within the experimental EFFECT OF PROLONGED HEATING- Although the rate of evolution of water decreases to a very low figure after 15 hours, it was considered necessary to investigate the effect of further heating.Curve B of Fig. 4 shows that the rate of evolution eventually becomes constant. This may reasonably be attributed to decomposition of the sugar. Extrapolation of the linear portion of the curve back to zero time will then give the true initial water content. To an accuracy that is at present sufficient, i.e., &O.OOl per cent., this is the result obtained after 15 hours of heating. Greater accuracy can, of course, be achieved by the extrapolation procedure. EFFECT OF TEMPERATURE OF DEHYDRATION- made between the results with similar samples at. 60" and 90" C. the result of prolonged dehydration at 90" C. 0.0281 and 0.0276 per cent. of water, respectively. sugar gave the following results- In order to establish whether all the water is eliminated at 60" C, comparisons have been Curve A of Fig.4 shows Biack extrapolation of curves A and B gives Another comparison with a different Sample No. . . .. .. . . .. 1 2 3 Temperature of dehydration, "C . . . . 90 90 60 Water, % . . .. .. .. . . 0.0524 0.0520 0.0516 ,The agreement shown is within the limits of the sampling errors. It will be observed that the rate of decomposition indicated by the asymptotic slope of curve A in Fig. 4 is greater than that shown by curve B. An estimate of decomposition can be obtained by deter- mining the final invert contents. The final inverts of the sample used to prepare curves A and B, determined by de Whalley's methylene blue test,4 were 0.029 and 0.022 per cent., respectively. The initial invert, similarly measured, was 0.007 per cent.STANDARD DEVIATION OF A MEASUREMENT- In order to find the reproducibility of the results by the method, determinations were made on a series of 10 samples of ordinary granulated sugar. These samples were drawn from a 2-lb batch that had been kept in a sealed container for several days so as to establish uniform distribution of moisture. Water, yo . . 0.04135 0.04129 0-04154 0.04138 0.04143 0.04135 0-04152 0.04088 0.04193 0.04146 The standard deviation of the results is &0*000260 per cent. with a coefficient of variation of 0.63 per cent. DIRECT CALIBRATION OF THE APPARATUS- the method. The results were as follows- Sample No. . . 1 2 3 4 5 6 7 8 9 10 To achieve this reproducibility very careful sampling is necessary.Small weighed amounts of water were sealed into ampoules and were determined by Sample No. 1 2 3 4 5 6 7 Total Water taken, mg . . 4-96 13.42 4-53 5.39 8-78 5.05 5.87 48-00 Water found, mg . . 5.01 13-44 4-93 5-21 8-75 5.07 5.88 48.29 The results were as follows- Except for sample No. 3, agreement is within the limits of accuracy of the weighing. To test the adequacy of the grinding procedure, four samples of granulated sugar were The water determinations were then completed, EFFECT OF GRINDING THE SUGAR- ground for periods of a, &, 1 and 2 hours. the results being as follows- Time of grinding, hours . . - - t ii 1 2 Specific surface, sq. cm per g . . 1150 2500 3570 4500 Water found, yo . . .. . . 0.0201 0.0249 0.0314 0.0312 It can be seen that grinding for 1 hour is adequate.The specific surfaces were measured by the air permeability method. WATER IN CRYSTALS OF GRANULATED SUGAR During the crystallisation of sucrose, some water is retained inside the structure of the crystal^.^,^ The magnitude of this effect has been shown by comparisons of the amountsMarch, 19581 HILL AND DOBBS: DETERMINATION OF WATER IN GRANULATED SUGAR 149 of water evolved when the determination was made as described and when the grinding procedure was omitted. Sugars of three different mean apertures were used (mean aperture = aperture of a square-mesh sieve through which 50 per cent. of the sugar will pass). Pure sucrose receives extra washing in the centrifugal machine before granulation, so that the surface impurities have been reduced to the minimum possible.This is the sugar that is used for standardisation purposes. The results are shown in Table I. In addition, a sample of pure sucrose was tested. TABLE I COMPARISON OF RESULTS ON GROUND AND UNGROUND SUGAR Water found in Water found in Sugar Mean aperture, ground sample, unground sample, inches Yo YO Liverpool No. 2 granulated . . 0.0360 0.037 1 0.0055 Tate and Lyle ordinary granulated 0.0253 0.0202 0-0108 Caster .. . . .. * . 0-0132 0.0299 0.0131 Pure sucrose .. .. .. 0-0188 0.0192 O.OQ99 It can be seen from the results in Table I that, as expected, the internal water constitutes The internal the greatest percentage of the total for the sugar of greatest mean aperture. water varies from 46 to 85 per cent. of the total. COMPARISON WITH THE STANDARD METHOD A recommendation of the International Commission for Uniform Methods of Sugar Analysis5 states that water in granulated sugar should be determined by measuring the loss in weight on heating at 105” C for 3 hours.At the laboratories of Tate & Lyle Ltd., the heating period is 1 hour. A comparison of the l-hour procedure with the proposed method, with and without grinding, was made. The average of ten determinations by the proposed method with grinding was 0.0414 per cent. of water, the average of two determinations by the proposed method without grinding was 0.0136 per cent. and the average of two deter- minations by the standard method was 0.012 per cent. Within the limits of error, the standard method gives a reasonably accurate figure for the external water. COMPARISON WITH THE METHOD OF GARDINER AND KEYTE The results of determinations on four types of sugar by the proposed method and by the method of Gardiner and Keyte,3 which is based on a reaction with cobaltous bromide, were as follows- Granulated Powdered Sucrose Refined sugar sucrose crystals sugar No. 3 Water found by cobaltous bromide method, yo 0.047 0.013 0.018 0.068 Water found by proposed method, yo . . 0.0414 0.0132 0.0195 0.0395 REFERENCES 1. 2 . 3. 4. 5. 6. Browne, C. A., and Zerban, F. W., “Sugar Analysis,” Third Edition, John Wley & Sons Inc., Vincent, R. S., Proc. Phys. SOC., 1940, 489. Gardiner, S. D., and Keyte, H. J., Analyst, 1958, 83, 150. de Whalley, H. C . S., Int. Sug. J., 1937, 39, 300. Proc. Int. Comm. Uniform Meth. Sugar Anal., Eleventh Session, 1954, p. 81. Powers, H. E. C., Nature, 1956, 178, 139. New- York, 1948, p. 24. Received August 12th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300143

出版商:RSC    

年代:1958

数据来源: RSC