ISSN:0003-2654    

DOI:10.1039/AN94772FX025

出版商:RSC    

年代:1947

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN94772BX027

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

THE ANALYST10 cm....lii12.5cm.IIIIIIIIIIII3/104 I /-KAVALIER5/6~~60/-Filtering FunnelspCatalogue No. B 28-1351Sg.Supplies of these well-known funnels are now againavailable. They are equal to the pre-war standard ofquality. They have accurate 60" angles. They will with-stand hot liquids.DIAM.PRICEEachDoz.3.5 cm.1/10201-5.5 cm.214251-7-0 cm.218291-8.5 cm.3j I3 3/625 cm.26122851-Established as Scientific Instrument Makers in 1826LONDON MANCHESTER GLASGOW EDINBURGH7 Teviot Place, IBIRMINGHAM: STANDLEY BELCHER & MASON LTD., CHURCH ST., 3Kemble St., W.C.2. 19 Cheetham Hill Rd.. 4. 45 Redrew St., C.2vi THE ANALYSTCITY OF BIRMINGHAMASSISTANT ANALYSTAPPLICATIONS are invited for the post of AssistantAnalyst in the City Analyst’s Department.Applicants should possess a science degree and/or theAssociateship of the Royal Institute of Chemistry.The salary scale is A.P.T.Grade IV (E4204465) or Grade V(6460-6510), according to qualification, plus bonus (atpresent k59 19s. Od. per annum).The appointment is subject to the provisions of the LocalGovernment Superannuation Act, 1937, and the successfulcandidate will be required to pass a medical examination.Applications, stating age, qualifications and experience,accompanied by not more than three recent testimonials,should be received by the City Analyst, 152, Great CharlesStreet, Birmingham, 3, not later than 30th August, 1947.KENT COUNTY COUNCILApplications are invited for the appointment of ChiefAssistant to the County Analyst.Salary A.P.T.. GradeVIII (66254254700), plus war addition. Minimumqualifications F.R.I.C. (E) or equivalent with considerableexperience in foods and drugs (including spectroscopicmethods) fertilisers and feedin stuffs. Further particularsobtainabie from the County AnJyyst, County Hall, Maidstone,by whom applications should be received not later than 1stSeptember, 1947.W. L. PLATTS,Clerk of the County Council.CITY OF LEEDSPUBLIC HEALTH DEPARTMENTApplications are invited for post of DEPUTY to the CityAnalyst under the Leeds Corporation. Person appointedwill be required to devote the whole of his time to the workunder the direction of the City Analyst, and will not b iallowed to engage in private practice.Applicants must holdthe aqualification F.R.I.C. (Branch E). Salary 6700, risingsubject to satisfactory service, to a maximum of @OO. Acost of living bonus (at present amounting to 659 16s. perannum) is also payable. Subject to the approval of theMinistry of Health and the Ministry of Agriculture, personappointed will be called upon to act as Additional PublicAnalyst and Deputy Agricultural Analyst. He will berequired to pass a medical examination and to contribute tothe Superannuation Fund established under Local Govern-ment and Other Officers’ Superannuation Act, 1937. Appoint-ment will be subject to termination by three months’ noticeon either side.Applications, giving details of age, qualifications andexperience, with copies of three testimonials and endorsed,Deputy City Analyst, must be delivered at my office by 10 a.m.Monday September 8th.Canvassing in any form, eitherdirectly ’or indirectly, will be a disqualification.J. JOHNSTONE JERVIS,Medical Oflcer of Health.AQUALIFIED analytical chemist is required, preferablywith food experience, to improve and operate a qualitycontrol system in existing laboratory in a large factory en-gaged in the preservation of foods under proprietary brands.Experience in a public analyst’s laboratory. The position isopen to either male or female who will be directly responsibleto the Works Manager. The position is permanent andparticipates in a contributory pension scheme. Write,giving full particulars and salary required to Joseph Farrow& Co., Ltd., Peterborough.ASSISTANT ANALYTICAL CHEMIST (age preferably23-25) with B.Sc.Degree or equivalent required forcommercial firm in Colombo, Ceylon. Must have someexperience in general and, if possibe, agricultural analyticalwork. Practical agricultural experience would be anadvantage but not essentl’,““ Liberal salary and outfitallowance. Write Box B.B.”, c/o 95, Bishopsgate,London, E.C.2.TECHNOLOGIST with experience in Chemical Engineeringfor Winsford Bacon Factory Candidates will berequired to control technical proresses involving preservationof foods-especially meats (primarily pork). Some experiencein bacteriological technique will be an advantage but theabsence of such qualifications will not necessarily debarapplicants from consideration.Applications, stating age.qualifications and experience, to be addressed to the GroceryCommittee, C.W.S., Ltd., 1, Balloon Street, Msnchester, 4,endorsed “Chemical Technologist-Winsford.”ANALYST required with experience in drugs and pharma-ceuticals. London area. Write, giving full particulars,Box No. GA.256, 4-7, Salisbury Court, Fleet Street, E.C.4.PPLICATIONS are invited from Chemists (men andfor temporary appointments in the grades shownbelow in the Chemical Inspection Department, Ministry ofCandidates should be British subjects aged not less than19 years on 1st December, 1946, and should be qualified inone of the following categories:-For the Scientific Officer Class, an Honours Degree (1stor 2nd class) in chemistry or equivalent qualification withtwo or three years’ suitable experience, is required, whilefor the Experimental Officer class a minimum qualificationof Higher School Certificate, Higher National Certificate inChemistry, or equivalent qualiiication, is necessary.Certain of the appointments are for analytical work inconnection with Atomic Energy developments.For theseposts applicants for the Scientific Officer Class should have asound knowledge of physical chemistry with particularemphasis on its application to analytical chemistry. Know-ledge and experience of certain physico-chemical techniques(eg., chemical spectroscopy, polarography, chromatography,etc.) will be an advantage.For other Scientific Officer Class posts, a sound knowledgeof one of the following branches of chemical technology willbe expected: paint technology, rubbers, plastics, lubricants,petroleum products, metals (including physical metallurgy),textiles, explosives.Experimental Officers should have experience of analyticalprocedure, and experience of a specialised branch of chemicaltechnology will be an advantage in certain posts.Grading and salary at entry will be determined by agequalifications, and experience, and will be on the followi&inclusive ranges:-Senior Scientijic Oficer-Men: 6640 to ,$340 London) L610 to k810 (Provinces)Women: 6522 to ;E726 \London): &92 to L692 (Provinces)Men: E353 to6590 (London), 63333 toL560 (Provinces)Women: E338 to L502 (London), 6318 to L472 (Provinces)Men: L490 to E640 (London), L452 to E592 (Provinces)Women : 6392 to 6522 (London), 6354 to L492 (Provinces)Men: L205 to 6428 (London), El95 to L398 (Provinces)Women: L205 tof;343 (London), El95 to E323 (Provinces)Application forms may be obtained by post-card addressedto Ministry of Supply, Est.5.(B)2, Room 828, Adelphi,W.C.2, quoting No. Chem/65.GENATOSAN LTD. have vacancies in their AnalyticalLaboratories for the following:-AN~~~~T~: havingHonours Degree or A.R.I.C., and preferably with industrialexperience in the examination of fine chenlicals and medicinalsor in biochemical and microbiological methods of analysis.Commencing salary 6400-&450 per annum according toexperience.JUNIOR ANALYSTS: of Inter. B.Sc. Standard andkeenly interested in training for analytical posts offeringscope and variety. Applications to the Technical Director,Genatosan Limited, Loughborough, Leicestershire.Supply.Scientific Oficer-Experimental Omer-Assistant Experimental Oficer-ANALYST required for old-established Public Analysts’Prospect of partnership if services satis-factory. F.R.T.C. Branch E qualification State ageexperience and salary required. Write Box No. 3661, ThkAnalyst, 47, Gresham Street, London, E.C.2.Laboratory.ANTED-Works Chemist to contro electro-platingWsolutions, boiler, feed-water treatment and incomingferrous and non-ferrous materials. Write stating a eexperience and salary required to: The Secretary fhhdBifurcated & Tubular Rivet Co., Ltd., Aylesbury, Budks.ARTNERSHIP required in analytical and consultingPpractice by chemist, B.Sc., F.R.I.C. (Branch E) with 25years industrial experience in food manufacture, meatcanning, jams and preserves, pickles and sauces.Devonor Cornwall districts preferred. Ample capital available.Replies to Box No. 3660 THE ANALYST, 47, Gresham Street,London, E.C.2.SMALL lab. of experimental chemicals, Chemist BallanceApply Williams, 22,Brockswood Lane, Welwyn Garden City, Herts.URGENTLY required for binding, back numbers of TheAnalyst:-1934, January to May, October and December;1936 Januar * 1940 February and Index. 1941 January toJulyf 1942, &toberi 1944, January, Febiuary, ’April, July,September, December; 1945, February July August,October, November, December; 1946,’ July,’ P y u s t ,November, December. Write Box 904, “Willings, 133,Moorgate, London, E.C.2.(by Becker), various bottles, etc.ANTED Back volumes runs and sets of THE ANALYST-WJ.C.S.;*J.S.C.I.; Brit: Chew. Abs. A. and B.; Bio!chemical 3. ; Trans. Faraday Soc. ; Natwe; Annual Re#orts;and any chemical and Scientific Journals. Write BoxNo. 3659, THE ANALYST, 47, Gresham Street, London, E.C.P

ISSN:0003-2654    

DOI:10.1039/AN94772FP029

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

THE ANALYST viiweighing 0.1Pellets for generating hydro-gen are now made by B.D.H.under licence from the British$3 Non-ferrous Metals ResearchAssociation.Five of the pellets (eachg.) in dilute sodium chloride solution at roomS q itemperature yield about 200 C.C. of hydrogen in five minutes.The pellets are prepared from a formula developed fLAdmiralty purposes during the war and are already findingmany convenient applications in the laboratory.In free containers:250g. 5/3; xoog. IO/-THE BRITISH DRUG HOUSES LTD. B.D.H. LABORATORY CHEMICALS GROUP POOLE, DORSETTelegrams : Tetradome PooleHydllsTelephone : Poole 962UNIVERSITYOFMANCHESTERFaculty o f TechnologyParticulars of Degree Coursesin General Chemical Technology,Chemical Engineering, Metallurgyand Assaying, FermentationProcesses (including Brewing),Foodstuffs, Fuels, and ColouringMatters, and of the Post-Graduate Diploma Course inChemical Engineering , will besupplied on request by theRegistrar, College of Technology,Manchester, 1.pH determinationIndustrial Chemists and researchworkers should obtain particularsof the new test papers introducedby JOHNSONS OF HENDON.Thereare five books in the series.UNIVERSAL is a single papercovering completely the rangefrom 1 to 10 enabling pH valuesto be checked to within 0.5 pH.For inore exacting work thereare the COMPARATOR test papers,in four books, with which thepH value of any solution can beascertained to within 0.3 pH.D E S C R I P T I V E L E A F L E TS E N T O N A P P L I C A T I O NJOHNSON & SONS MFG.CHEMISTS LTD.HENDON, LONDON, N.W.4. ESTAB. 174viii THE ANALYSTIn the event of difficulty In obtainingsupplies, free samples, or copy of ourdescriptive booklet and price list, pleasewrite the Sole Sales Representatives:STOCKED B YLABORATORYFURNISHERSTHROUGHOUTT H E W O R L DI N SEALEDBOXESH. REEVE ANGEL & COMPANY, LTD.9, BRIDEWELL, PLACE, LONDON, E.C.4.Each grade isdistinctively labelledTHE WHATMANrange covers allrequirements ofthe chemist inevery branch dindustry and re-search.Made only byW. & R. BALSTON, Ltd.KENT - W e have made availablecertain Analytical Re-agents with ACTUALBATCH ANALYSIS con-firmed by INDEPEN-DENT Analysts of thehighest standing: par-ticulars of one exampleare given.* YOU ARE INVITEDTO COMPARE THEPURITY WITH THATGUARANTEED BY ANYCOMPETING MAKER.POTASSIUM CHLORIDE A.R.ACTUAL BATCH ANALYSISKCI. Mol. Wt. 74'55(Not merely maximum impurity values)Batch No. 18413Free Acid ................... .- ...Nitrate (NOa) .................... Sulphate (Sod) ..................Heavy Metals (Pb) .............. Iron (Fe) ......................Barium (Ba). .....................Calcium (Ca) .................... Magnesium (Mg) ................Ammonia (NH3). .................0.04 N/l%0.002%0.001 %0.0001%0.00005%0.002%0.002%0.002%0.00005%The above anrlysls Is based on the results, not of our own Control Laboratoriesalone, but also on the Confirmatory Analytical Certificate Issued by independentConsultants of International repute.The General Chemical & Pharmaceutical Co., Ltd.Chemical Manufacturers, Judex Works, Sudbury, Middlese

ISSN:0003-2654    

DOI:10.1039/AN94772BP033

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction JULY, 1947 THE ANALYST Vol. 72, No. 856 PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS AND OTHER ANALYTICAL CHEMISTS PHYSICAL METHODS GROUP THE Ninth Ordinary Meeting of the Physical Methods Group was held on Tuesday, February llth, 1947, in the rooms of the Chemical Society, Burlington House, London, W.1., with the Chairman of the Group, Mr.R. C. Chirnside, F.R.I.C., presiding. The subject of the meeting was Fluorimetric Analysis, and the following papers were presented and discussed: “Apparatus Design for Fluorescence Measurements,” by E. J. Bowen, M.A., F.R.S.; “Notes on Fluores- cence Quenching,” by the same author; “Some Applications of Fluorimetry in Vitamin Analysis,” by E. Kodicek, Ph.D., M.D.; “The Use of Fluorimetric Analysis in the Study of Pterins,” by Delia M. Simpson, M.A., Ph.D. The Tenth Ordinary Meeting of the Group was held on Friday, May 2nd, 1947, at King’s College, Newcastle-on-Tyne. Mr. Chirnside was again in the chair and about eighty members and visitors were present. The following papers on Physical Methods of Gas Analysis were presented and discussed: “Gas Analysis at Low Pressures,” by C. E.Ransley, M.Sc., Ph.D.; “The Analysis of Hydrocarbon Gases by Low-Temperature Distillation,” by J. H. D. Hooper, BSc., A.R.I.C.; “A New Apparatus for Gas Analysis by the Soap Film Method,” by W. J. Gooderham, B.Sc. , A.R.C.S., F.R.I.C., M.Inst .Gas E., who also demonstrated his apparatus. POLAROGRAPHIC DISCUSSION PANEL The first meeting of the panel was held, under the chairmanship of Dr. W. Cule Davies, in the Physical Chemical Lecture Theatre, Imperial College of Science and Technology, London, S.W.7, on Friday afternoon, April 25th, 1947. The attendance was 39 members and visitors and discussions followed contributions by Dr. G. Jessop on “Notes on Polaro- graphic Technique,” by Dr. W. Cule Davies on “Remarks on Polarographs” and by Dr.E. R. Roberts on “The Analysis of Brass Plating. ” Dr. Jessop dealt first with the instrumental aspects, in particular the measurement of current and potential and the various ways of determining wave height. He discussed such effects as arise from the ohmic resistance of the circuit and from variations in the anode potential, instancing the peculiar wave forms sometimes encountered when sodium sulphite is used in conjunction with a mercury pool anode. Dr. Cule Davies, discussing desirable features to be incorporated in a polarograph, considered that means should be provided for the accurate measurement of drop-rate, current and voltage, and that damping, if used, should alter neither the magnitude of the current nor the observed half-wave potential. Published accounts of polarographic work should give the characteristics of the dropping electrode, wave heights being expressed in units of current. Dr. Roberts pointed out that in the bonding of rubber to cast iron the latter must be brass-plated, and described polarographic methods of control of the plating, by means of which six bath samples could be analysed within half an hour, while plating could be stripped and examined similarly. De-oxygenation by sodium sulphite gave peculiar results for zinc, but sulphur dioxide was both rapid and effective. A simple cell incorporating an external reference electrode was developed for routine use and enabled results to be obtained by measuring the current at three predetermined potentials. 273

ISSN:0003-2654    

DOI:10.1039/AN9477200273

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction 274 ROBINSON : CHEMISTRY OF PENICILLIN [Vol. 72 Chemistry of Penicillin BY F. A. ROBINSON (Read at the meeting of the Society on May Wt, 1947) THE constitution of penicillin was elucidated as the result of collaborative research carried out in many laboratories in Great Britain and the U.S.A.during 1943-45.l In the course of this work, it was. discovered that several different penicillins exist. These vary according to the strain of Penicillium notatum or P . chrysogenum used and with the cultural conditions. Indeed, the proportion of certain penicillins in a mixture can be increased by addition to the medium of certain “precursors” which the mould is apparently able to assimilate and in- corporate into the penicillin molecule. All the penicillins have the common basic structure I NH.CO.R in which the group R varies from one penicillin to another. In the original penicillin produced by Sir Howard Florey and Dr. E. Chain and their colleagues at Oxford, R for the major con- stituent is a A2-pentenyl group.This species of penicillin was originally termed penicillin F, in order to identify it with the penicillin discovered by Fleming and to distinguish it from another antibiotic produced by P . notatum, which was originally called penicillin A and later notatin; it has a structure entirely different from that of the penicillins. The term penicillin F is still used in the U.S.A., but in this country this form is now generally known as penicillin I. Mild methods of reduction convert penicillin I into dihydro penicillin I, in which R is an amyl group, and the activity is apparently undiminished or even slightly increased by the hydrogenation. 1n.America the penicillin originally isolated was not penicillin F, but a different penicillin with approximately the same activity.It was considerably easier to isolate and more stable than penicillin F and was called penicillin G by the Americans; in this country it is known as penicillin 11. In this instance the group R is a benzyl group, and the presence of this form in the original American penicillin was associated with the use of a different strain of P . notatum and with addition to the medium of corn steep liquor, which contains benzyl derivatives that favour the production of penicillin I1 in preference to penicillin I. Since the adoption of corn steep liquor for routine production in this country, penicillin I1 is also the predominant form in British penicillin. Another form of penicillin produced by some strains of P. notatum and P.chrysogenum, especially in presence of the appropriate precursor, is penicillin I11 or penicillin X, in which R is a P-hydroxy benzyl group. Even under the best conditions, however, it is produced in limited amounts only, but, as it has rather unusual biological properties, interest in this form of penicillin may be expected to increase. In 1945 a new strain of P . chrysogenum, known as Q.176, was generally adopted for submerged culture, because it produced much larger quantities of total penicillin than the strain X.1612 previously employed. It was not immediately realised, however, that, in absence of precursors, the predominant form of penicillin so produced is not the therapeutically valuable penicillin I or penicillin 11, but another penicillin termed penicillin K, in which R is a n-heptyl group.This form of penicillin is rapidly inactivated in the animal or human organism and is therefore clinically less effective than penicillin I or 11. Even in presence of precursors, substantial amounts of penicillin K are produced. The relative effectiveness of the various forms of pencillin is still a matter of controversy, but the balance of evidence is in favour of reducing to a minimum the proportion of penicillin K in material to be used for clinical purposes. A substance isomeric with penicillin I and with similar biological properties is producedJuly, 19471 ROBINSON CHEMISTRY OF PENICILLIN 275 by AspergiZZusJEavus and has been given the names flavicin and flavicidin.2 In this substance R is a A3-pentenyl group.The discovery that different forms of penicillin do not have the same therapeutic value has made it imperative to find methods of estimating the individual penicillins in commercial penicillin, and this is proving to be an extremely difficult task. For a long time the only method of estimating the amount of total penicillins in a mixture was the bacteriological method of assay, and although this has been improved so that the errors of the method now in use are surprisingly small, such a method must always suffer from certain practical dis- advantages: for example, that the result can only be known several hours after submission of the sample for test, and that occasional highly erroneous results are obtained. Within recent months several chemical methods of estimating total penicillin have been described. S ~ u d i , ~ for example, published details of a colorimetric method and of a fluorimetric method of assay based on the fact that the p-lactam ring of all the penicillins is opened by organic bases to form substituted amides and, by using an amine containing a chromophoric group (N-( l-naphthyl-4-azobenzene)-ethylene diamine) or an amine containing a fluorophoric group (7-methoxy-2-chloro-5-~-aminoethylamino acridine) , products which are either coloured or fluorescent are produced and can be estimated by conventional procedures.These methods have very serious limitations, due mainly to the difficulty of completely removing excess of the reagent from the coloured product; moreover, they are tedious and the reagents are difficult to prepare.Reactions of this type can be represented as follows: (CH,), . -H. COOH (CH,),C-------CH. COOH 1 NH H,N. R1 I + S S ‘ N I \ C d ‘co I I CH.CO. NH , R1 NH.CO.R ‘ C k I NH.CO.R A similar reaction occurs with hydrazines and hydroxylamines and can likewise be utilised for the quantitative estimation of total penicillins. Such methods, however, cannot be used for the differentiation of individual penicillins, as these all behave in the same manner towards these reagents. A simpler method of estimating total penicillins is based on the fact that, on treatment with alkali or with a specific enzyme known as penicillinase, the p-lactam ring of penicillin is opened, with the formation of an additional carboxyl group, giving penicilloic acid; the amount of alkali required to neutralise the acidity thus produced is proportional to the penicillin content.These two methods are not very accurate, though the penicillinase modification is, as might be expected, highly specific. An improved procedure, which is likely to prove more useful than either of Scudi’s methods, is the iodimetric method of Alicino,* which is based on the observation that the difference in the amount of iodine con- sumed under standard conditions before and after inactivation by alkali is proportional to the amount of penicillin present. The alkali converts penicillin into penicilloic acid, which adds on six to nine equivalents of iodine, depending on the conditions used. The mechanism of the reaction is obscure but, provided the conditions are rigidly standardised, the amount of iodine reacting is always constant.The reaction undoubtedly depends on the fact that the thiazolidine ring in penicilloic acid is readily opened to form a free thiol group, whereas ring- cleavage does not occur with compounds, such as penicillin, in which the thiazolidine nitrogen atom is acylated. The free thiol group is then oxidised by the iodine, presumably to a sulphonic acid group, whilst an aldehyde group is probably liberated and then oxidised as in the scheme on p. 276. The bacteriological method of assay, in addition to its purely practical disadvantages, also suffers from a very serious theoretical objection, for not only do the ‘individual penicillins differ in therapeutic value, but they also differ in the extent to which they inhibit the growth of test-organisms.The degree of inhibition produced by a mixture of penicillins is therefore dependent on the proportions in which the constituents occur, and the biological assay may give an entirely different result from the chemical method of assay and probably neither will give a satisfactory estimate of the therapeutic efficacy. The proportion of two penicillins in a mixture can be determined from the ratio of the response of two different organisms, such as Staphylococcus aureus and BaciZZus subtilis, but the method is not very accurate276 ROBINSON : CHEMISTRY OF PENICILLIN [Vol. 72 and is invalid if a third penicillin is present; with commercial preparations, this is at present the rule rather than the exception. (CH,),.C--------CH.COOH (CH,),.C------CH.COOH I alkali or S ‘ NH I N I S ‘CH/ \co penicillinase ‘CH ’ I I CH.COOH NH.CO.R ‘Ck I NH.CO. R. (CH,), C-------CH.COOH I N I SH // CH CH.COOH I (CH,),. C L H .COOH I NH, I SO,H + COOH NH.CO.R I +.COO, NH.CO.R It is important, therefore, that satisfactory methods of estimating the individual penicillins should be made available as soon as possible. The only chemical method that has so far given satisfactory results is that of Sheehan et aL6 for the estimation of penicillin 11. This method depends on the observation that penicillin I1 forms with N-ethyl-piperidine a sparingly soluble salt which can be filtered off and weighed. The results are said to be quantita- tive with material containing not less than 50 per cent.of penicillin I1 and with a potency not less than 800 units per mg., but in our experience the results may not be reliable with material containing less than 90 per cent. of penicillin 11. The method has recently been improved in our laboratories by combining the method of Sheehan et al. with that of Alicino. A colorimetric method of estimating penicillin 11, actually a modification of the Kapeller- Adler method for the estimation of tyrosine, was described by Page and Robinson6 but is less specific than the method of Sheehan et al., since impurities containing aromatic rings also react, giving rise to coloured products and thus leading to high results. The same disadvantage applies to spectrophotometric methods of estimating penicillin I1 that depend on the absorption of the phenyl ring, although a method recently elaborated by Philpotts, Thain, and Twig7 has given valuable results with material of high potency.The only chemical method available for the estimation of penicillin K is one recommended by the Food and Drug Administration of the U.S.A., but it does not give reliable results. In this method the penicillin is distributed between a buffer solution of pH 6 and chloroform; most of the penicillin K goes into the chloroform phase, whilst most of the penicillin G remains in the aqueous phase. The amount of penicillin in the chloroform solution is estimated by iodimetric titration. Unfortunately the separation is not sharp and other penicillins present may be distributed more equally between the two phases and so increase the error of the method. The method to be described by Dr. Goodall and Dr. Levi is, like the foregoing, a distribu- tion method, but is of far greater value, since all the penicillins in a mixture can be estimated simultaneously. Morevoer, it is capable of indicating what penicillins are present, so that a qualitative and quantitative analysis of a mixture may be made at the same time. It is without doubt the most useful method yet described for the examination of mixturesof penicillins. REFERENCES 1. Nature 1945. 156 766. 2. 3. 4. 5. 6. 7. Bush, M. T., Goth, A., and Dickison, H.’L., J . PharmacoZ., 1945,84, 262; Fried, J., Koerber, W. L. Scudi, J. V., J . Biol. Chem., 1946, 164, 183; Scudi, J. V., and Jelinek, V. C., Ibid., 195. Alicino, J. F., Ind. Eng. Chem., Anal. Ed., 1946, 18, 619. Sheehan, J. C., Mader, W. J., and Cram, D. J., J . Amer. Chem. SOC., 1946, 68, 2407; Abst., this Page, J. E., and Robinson, F. A., Nature, 1946, 158, 910. Philpotts, A. R., Thain, W., and Twigg, G. H., Nature 1947, 159, 839. and Wintersteiner, O., J . Bid. Cham., 1946, 163, 341. vol. p. 313. THE DISTILLERS COMPANY LIMITED RESEARCH AND DEVELOPMENT DEPARTMENT GREAT BURGH, EPSOM

ISSN:0003-2654    

DOI:10.1039/AN9477200274

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

July, 19471 GOODALL AND LEVI : MICRO-CHROMATOGRAPHIC METHOD FOR PENICILLINS 277 A Micro-chromatographic Method for the Detection and Approximate Determination of the Different Penicillins in a Mixture BY R. R. GOODALL AND A. A. LEV1 (Read at the meeting of the Society on May 7th, 1947) INTRODUCTION-The following Table contains data (as available in February, 1947) on certain characteristics of the penicillins. TABLE I PENICILLINS : NOMENCLATURE AND TYPE OF SIDE-CHAINS O L N CH. COOH I I I R . C O . N H . H C L H - S - C . (CHJ, I NOTES- Name British American' I F I1 G I11 X K K IV - VI - VII - Activity per mg. r a, against b, against Side chain (R) B. subtilis S. aureus dB pentenyl 970 1550 benzyl 1667 1667 n-heptyl 700 2300 unknown unknown unknown A \ 9-hydroxy benzyl 800 900 Ratio a + b 0.63 1.0 0.89 0.30 - (a) Penicillin IV is not identical with penicillin K as stated by several authors.' (b) Penicillin K is probably identical with a penicillin originally called V (five) by ourselves, but this (c) The activities given are those currently available.* Differences due to strain variation may be (d) There is some uncertainty about the B.subtilis activity of penicillin I11 ( c f 8 ) . Commercial samples of penicillin may contain from at least three to seven individual types, the proportions of which may vary widely, depending on the strain of organism, method of culture and method of isolation. Although the penicillins hitherto isolated in a pure state (Table I, I to K) are not widely different in chemical structure, their therapeutic values are not identical, partly because of differences in chemical stability and partly because of possible differences in biological activity against different test organisms.Methods for determining certain of the penicillins in admixture with others have already been published. Schmidt, Ward and Coghill8 show how the composition of a two-component mixture can be deduced from the P. subtiZis/S. aweus assay ratio. The differential assay principle has recently been extended by Higuchi and Petersodl to mixtures of three com- ponents. Fischbach, Mundell and Elbe6 describe a macro-chromatographic method for determining penicillin K. Sheehan, Mader and Cram9 base a method for penicillin I1 on selective precipitation as the N-ethylpiperidine salt. Penicillin I11 and K contents can be determined by distribution between appropriate buffer solutions and chloroform.1° It is, however, desirable that an analytical method be available for determining directly the proportions of all the different penicillins in a given sample, and this is the aim of the present investigation.We have stated in a preliminary communication1 that the modified partition chromatogram2 obtained by using buffer salts in the stationary phase can be adapted to the micro scale, after the manner of Martin and co-wo~kers,~ who separated a mixture of amino acids and located the position of each component on the paper strip by colour reaction with ninhydrin. In our preliminary attempts to separate penicillin from impurities by the following method, we found that colour reactions were not readily applicable to the treated paper stripl and We therefore tried a biological technique similar in principle to the routine cannot now be confirmed.observed in practice. Values for penicillin K are based on unpublished data.278 GOODALL AND LEV1 : MICRO-CHROMATOGRAPHIC METHOD FOR THE [VOl. 72 "cup assay" for penicillin. This technique, which is very simple and highly sensitive, had potential quantitative applications, and it was found possible to establish a method for the approximate determination of the relative proportions of the various penicillins present in a given mixture. This method is described below. METHOD SPEC I AL RE AGENTS REQ u I RE D- 1. Stock potassium phosphate bufer solution-Dilute 500 ml. of phosphoric acid of sp.gr.1.75 with 1500 ml. of watei and add potassium hydroxide solution (containing 906 g. in 3 litres of solution) until 2ml. of the mixture, diluted to 60ml. with distilled water at room temperature, has pH 6.9 & 0.04 as measured by glass electrode, using, as standard, potassium hydrogen phthalate solution, PH 3.97, at room temperature. 2. Ether-Shake vigorously 2 litres of ether (anaesthetic quality) with 250 ml. of water for about 2 minutes. Remove the aqueous layer and store the wet ether in the cold room 3. Nutrient agar-Prepare twenty bottles of 285ml. of filtered sterile medium con- taining peptone log., Lemco 3 g., sodium chloride (A.R) 2g., and agar 25g. perlitre of aqueous solution. Adjust to pH 7-5 with 2 N sodium hydroxide before filtration.4. Bufered $Zter paper-Wet Whatman Filter Paper No. 4 with 30 per cent. buffer solution of pH 6.9 (Reagent 1). Remove the excess of buffer solution by pressing between sheets of clean blotting paper sandwiched between plate glass. Hang the damp treated paper vertically to dry in the air; it dries in about 2 hours. Cut the dry prepared paper into strips 1.8 by 30 cm. and mark each strip with a pencilled cross on the centre line 6 cm. from one end. The width should be as close to the above figure (1.8 cm.) as possible, and strips with ragged edges should be rejected. (0" to 5" C.). 5. Photographic material-Extra contrasty gaslight paper (16 by 16 inches), etc. SPECIAL APPARATUS REQUIRED- 1. Micro-pipettes--,4. Automatic pipettes for aqueous solutions-Draw out thick-walled capillary tubing approximately to the dimensions given in Fig.1. Cut the glass at point 0 so as to form two jets. Coat the inside of each jet with paraffin wax. Holding each tube vertic- ally, dip the tip into toluene or xylene. Remove the toluene by pressing the tip of the pipette on to filter paper. Repeat the toluene treatment four times and then dry the pipette by blowing air through it gently. Dip the tip of the pipette The solvent will rise to a definite height. 0ore 2 m j . t I 0.2rnm. approx. ~ ~ ~ - m ; c - . - . _ _ _ _ _ - -42mm. - - - - - - - - - - - 4 Fig 2. Approximate dimensions of capillary micro-pipette, type B. into distilled water and note that the liquid rises by capillarity to the boundary of the paraffin coating. Discharge the pipette by pressing gently on to filter paper. Cut down the jet of the pipette until the amount of water delivered in this way is constant at from 1 to 1.5 mg., and mark the position of the liquid meniscus. B.Capillary micro-pipettes for solvent extracts-Prepare a 1-microlitre glass pipette as shown in Fig. 2. 2. Apparatzcs for chromatograplaic developmefit-The apparatus is illustrated in Figs. 3A, 3 ~ , and 3c.July, 19471 DETECTION OF DIFFERENT PENICILLINS IN A MIXTURE 279 I 0 7- 65 i 0 Fig. 3 ~ . Section through 'A"A' of apparatus for development of 24 paper chromatograms. ' Chamber with lid and internal flange, IF., secured by 8 wing nuts on to a soft rubber gasket. C.C. Ring carrying 24 cups seating on a shoulder 3" from top of chamber. G. Stainless steel vent tube (f O.D.) attached to a short U trap containing mercury.D. Closed drum with 4 spacing pieces. Material of construction - body- welded stainless steel sheet 20 gauge, flange and lid )" stainless steel plate. B. Fig. 3 ~ . Plan of top of chamber F. Flange with 8 lugs for wing nuts. C.C. Ring, showing distance between centres of the cups. For true position of each cup, which is inclined inwards (at an angle of 16'). see Fig. 3 ~ . Each cup holds a glass reservoir (see Fig. 3c). with lid removed.280 GOODALL AND LEVI: MICRO-CHROMATOGRAPHIC METHOD FOR THE [Vol. 72 The vertical surface of the closed drum D (Fig. 3A) is tightly wound with one thickness of cotton bandage, 2 inches wide, and each end is stitched to the adjacent lap to prevent unwinding.Lengths of rustless spring curtain rod (about 23.5 inches long before expansion) are then clipped over the bandage, at 2-inch intervals, to form a set of eight horizontal rings. The bandage is moistened before the apparatus is to be used; the spring rings prevent the paper chromatographic strips from coming in contact with the wet cotton. Glass sleeve 3. Glass plates for agar medium-Construct these as detailed in Fig. 4 by cementing plate glass strips, 0.75 inch wide, to a square plate-glass base, 16 by 16 inches, with shellac dissolved in alcohol. Each plate will carry seven chromato- graphic strips, or six and a strip with standards. Provide a plate-glass lid, 16 by 16 inches, for each of the plates. A sheet of plate glass, 13.5 by 13-5 inches, just smaller than the space for the agar in the above plates, willalso be required. Clean and sterilise each plate before use (see below).4. Dilution pipette-In general, sufficient sample will be available to permit serial dilution by graduated pipettes. If, however, economy of sample is a prime consideration, the technique of the dilution pipette6 is readily applicable. These pipettes must not be used for organic solvent solutions. 5. Burettes for charging ether-Prepare two rough burettes holding 60 ml. and graduated at intervals of 8 ml. Control delivery of liquid by a spring clip on a rubber tube of 5 mm. bore. Paper strip inserted in glass reservoir Metal cup a Fig. 3c. Of glass etc., before assembly. 6. Vessel for humidifying strips- Obtain a large vessel (e.g., a large drum) with a lid.Provide means of keeping the atmosphere in this vessel damp (e.g., a damp cloth hanging round the mner circumference). Provide a stand on which the strips can be hung, well spaced out from each other, inside the vessel, so as to expose them freely to the atmosphere of the vessel. PROCEDURE- FIRST DAY Preparation of sample and stan- dards-Prepare a solution of the sample containing from 1 to 40 units per micro- litre. Dissolve the sample in half the calculated volume of water and make up to volume with 30 per cent. buffer solution of pH 6.9 (Reagent 1). Filter or centrifuge if necessary; 50 to 100 pl. of solution are ample. For standards make five serial dilu- tions of a solution of pure sodium penicillin I1 containing approximately 30 units per ml. in 30 per cent.#H 6-9 buffe; solution (Reaient l), eich g;, m I c '/i one-third the strength of the previous G9F solution, one volume of solution being diluted with two volumes of buffer at each stage. when actually required for use. After 14 days fresh solutions should be made up. Waxed pipettes must not be used for organic solvent extracts. 1 - €NO WEN- ' Fig. 4. Dimensions of plate glass for agar medium. All solutions and standards must be kept stoppered in the cold room (0" to 5" C.) except Solvent extracts and samples already in solution-These are used without further treatment.July, 19471 DETECTION OF DIFFERENT PENICILLINS IN A MIXTURE 281 " Spotting " solutions of sample, etc.-Fifteen minutes before beginning " spotting," place the required number of strips in the special apparatus 6 to humidify.After this treatment, apply to each strip a 1-pl. spot of the test solution at the marked point. Fix a wire paper- fastener to the bottom end of each strip (Le., the end remote from the marked point). Re- move the central drum from the special apparatus 2. The apparatus should be at room temperature during this operation. Place the top end of each spotted test strip in a glass reservoir supported in the frame of the apparatus and fur it in position by inserting the glass sleeve provided for each reservoir. Ensure that the top end of the strip just touches the bottom of the reservoir and that the "spot" is located about 1 cm. below the edge of the reservoir. Adjust the strips so that the clipped ends hang vertically, i.e., clear of each other and not touching any part of the apparatus.Remove the apparatus to the cold room. Wet the cloth apron round the central drum with water and carefully place the drum in the apparatus. Replace the lid. After 2 hours, and while the apparatus is still in the cold room, remove the lid. Deliver 8 ml. of ice-cold ether into each reservoir. Without delay, replace the lid on the apparatus and make gas-tight. This operation must be carried out as quickly as possible to avoid formation of ice on the strips. Put 50 ml. of ether in the bottom of the apparatus to form a pool. Allow development to proceed overnight. Cleaning and sterilisation of glass $lates-After removing used agar, rinse the plates thoroughly with water. Wipe the surface with dilute hydrochloric acid (0.4 per cent.).Allow the acid to remain on the plates for 2 to 3 minutes, rinse with water, wash with soap and water, and again rinse with water. Careful cleaning of the plates in this way is essential. Support the plates on top of an asbestos sheet, using cork spacers, and sterilise by heating at 120" to 130" C. for 3 hours. Store the required plates at 37" C. Spotting out standard solzction-Prepare one standard strip carrying undeveloped spots by delivering 1-pl. spots of each solution on to a pH 6.9 buffered strip at points 5 cm. apart along the strip. Store in the cold room until required. SECOND DAY Melt the agar medium and inoculate it with B. subtilis spores at a temperature not below 70" C.; shake and allow the froth to break at 70" C.Pour the medium on to an uncovered glass plate (special apparatus 3) just removed from storage at 37" C. and laid on a level glass surface. If necessary, flame the plate locally to assist covering by medium. Protect the medium with the plate lid, spaced 0.5 inch above the surface : allow to set and evolve moisture during 10 minutes. Then lower the lid on to two felt strips, placed on opposite sides of the plate, invert the plate and allow to cool during 15 minutes in an asbestos-lined box in a cold room (0" to 5" C.). Plating out the strips-Open the apparatus containing the developed chromatographic strips, remove the central drum carefully and transfer the strips to a clean glass container. If any reservoirs still contain ether, remove the strips from these first, otherwise ice will collect at the top of the strips owing to evaporation of ether.When the agar plates have been in the cold room for at least 15 minutes, begin plating out the strips in the following way. Support the 13-5 by 13-5 inch sheet of plate glass (special apparatus 3) on blocks so that it is raised off the bench about 2 inches and the edges are not obstructed in any way. Clean the surface with acetone. Arrange a set of strips evenly on the top of the glass. A card ruled at 1.9-inch intervals from the centre and attached to the under-side of the glass is a convenient guide. Lift the agar plate off the felt supports and lay it gently, face down, on top of the strips. When the strips have wetted out (this is easily observed) lift up the agar plate.The strips will adhere to the agar surface in their correct positions. Replace the agar plate on the felt supports on the lid and transfer with its lid, still with the agar face downwards, to the cold room. Incubation-After the plates carrying the strips have been in the box in the cold room for four hours, close the plates with the lids by removing the felt strips and place, face down- wards, in an incubator at 37°C. Allow incubation to proceed overnight.282 GOODALL AND LEVI: MICRO-CHROMATOGRAPHIC METHOD FOR THE pol. 72 THIRD DAY Reproducing the results-Remove the plates from the incubator and identify the strips with “Chinagraph” markings on the glass. Using the patterns on the plates as a negative, make contact prints on the gas-light paper. Measurement of zones-Measure the diameters of the circles given by the stationary (undeveloped) standards, estimating to 0-1 mm.Similarly measure the maximum width of each zone on each developed strip. CALCULATION OF RESULTS- Relative proportions of B. subtilis units-Let the diameters of the circles given by the standard spots be A, B, C, D, E, and F in descending order of magnitude. Then the slope b’ (compare conclusions following Table 11, p. 286) for the developed zones is given by the expression : b’ = 1.2 [5(A-F) + 3(B-E) + (C-D)]/35 log 3 = 0.0719 [5(A-F) + 3(B-E) + (C-D)] Divide the diameter (in mm.) of each developed zone by b’. The resulting value is the logarithm of the number of arbitrary units in the zone. Calculate the mean activity in arbitrary units for each zone, and from these obtain the percentage composition. The arbitrary B.subtilis units apply to the particular plate only. Conversion to relative proportions of S . aureus units- (i) Divide the per cent. activity in each zone (B. subtilis units) by the appropriate 100 (ii) Units against B. subtilis Units against S. aureus (iii) Proportionate activity (S. aureus units) in each zone Composition by weight- factor (Table I). = F - Sum of quotients from (i) = F x % activity in B. subtilis units. Per cent. activity in B. subtilis units Activity* (B. subtilis units) of the appro- (i) Per cent. of total activity in each zone = priate pure component. = P (ii) Per cent. of total sample weight in each zone = P x activity of the sample in B. subtilis units. Note-For penicillins of undetexmined activity the ratios B.subtilis/S aureus have been assumed to be unity, and the activity 1000 units per mg. Where these penicillins occur only as minor components of a mixture, as they have done in many samples we have examined, the error introduced into the over-all analysis by this approximation is probably not great. RESULTS AND DISCUSSION As a necessary preliminary, it was established, from the results of a series of experiments designed to detect a loss of 7 per cent. or more of the total activity, that no significant loss took place when the above method was applied to a blend of calcium penicillin (activity 300 units per mg.). Losses, however, occurred if the chromatograms were carried out at room temperature or if serious delay arose before completing the experiment.In these experiments the active zones were stripped from the paper with water and the activity of the resulting solution was compared with that of a freshly prepared solution of the same sample. QUALITATIVE SECTION The chromatographic identification of the zones (Fig. 5, A) obtained from an early sample, by reference to the results obtained from known penicillins developed simultaneously on adjacent strips, is illustrated in Fig. 5, A, B and C. The zone A I1 is attributed to penicillin I1 not only because it corresponds in situation to the zone C I1 obtained from pure penicillin 11, bat also because the increment in zone diameter (B 11-A 11) due to enrichment of the sample * See Table I.July, 19471 DETECTION OF DIFFERENT PENICILLINS IN A MIXTURE 283 with pure penicillin I1 is confined to the one appropriate zone and is of the expected order of magnitude, according to later deductions.Since the other major constituent of this sample was known to be penicillin I, by the macro-column technique, the identity of the substance producing the other zone in Fig. 5, A is in all probability penicillin I. The identity of penicillin I11 on the paper strip was established by similar comparative tests using a penicillin I11 fraction from a macro column. Resolution of penicillins I1 and I11 is shown in Fig. 5, D. The above three penicillins all occur in the same order as observed on macro columns. When the technique came to be applied to products from various sources, further zones of activity were resolved (e.g., Fig.5, E). Ideally, for the qualitative and quantitative develop- ment of the technique, the behaviour of mixtures of the pure individual penicillins should be studied, but only penicillin I1 was available in the pure state. However, there was little difficulty in identifying the various zones of activity, from the fixed order in which they occur after development. The behaviour is analogous to that of the amino acids reported by Martin and others3 Penicillin I1 was a convenient key zone, for it was usually known to be the major active constituent; if not, it was added as a “tracer,” in the manner of Fig. 5, B. The order from the point of application of the solution is: 111, VI, 11, I, IV, VII and K. The seven zones were detected on one strip (cf.reproduction in Fig. 5, E). The existence in Fig. 5, E and Fig. 6, C of the zone attributed to penicillin VII has been repeatedly confirmed. I t is also apparent in Fig. 6, C that there is a suggestion of further resolution at the front of the K zone. The existence of penicillin VI was clearly demonstrated in other experiments as shown in Fig. 6, A and B. Penicillins VE and VII have only been found in minor amounts, generally less than 5 per cent. of the activity of unfractionated material. Work on macro columns in these laboratories (to be published shortly) has confirmed that the zone usually attributed to penicillin I is due to a mixture of two penicillins, called I and IV (penicillin IV is not identical with penicillin K). This is also clearly shown by the present technique (see Fig.5, E). It is known that penicillin K is the fastest-moving penicillin.6 With further experience it has been found that the method of identification based on ratio of distances traversed by unknown and known “ spots ”l is less satisfactory than was at first thought. Following are comments on certain aspects of the technique. CONTROL OF DEVELOPMENT (1) Humidity-It cannot be stressed too strongly that the humidification treatment of the strip before and after spotting is of cardinal importance. For example, a prior treatment of the strip for one hour instead of 15 minutes will result in elongation of each zone, the K zone partly overshooting the end of the strip. The syrup obtained by evaporation of buffer solutions of the type used is very sensitive to the state of humidity of the atmosphere.The best method of controlling the moisture content of the strip was found to be to expose the treated paper to a fully humid atmosphere for a specified time. Even this is not entirely satisfactory. (2) Concentration of bzc$er-This also has very marked effects on distance of development. Strips were impregnated with phosphate buffer solutions ranging from 1 per cent. w/v up to 30 per cent. w/v (Reagent 1) and it was found that the use of the 30 per cent. w/v solution, which is about the maximum convenient concentration, led to zones of the most compact and most regular type; it also produced the farthest separation of the zones, in other words the greatest degree of resolution, obtained. (3) pH value-For the slower-moving zones, variations of f 0.1 unit in the pH of the applied buffer solution have little effect, but a closer control of pH is desirable in order to retain the fast-moving zones on the strip.The method outlined above lays down conditions adequate for separating the major constituents, I, 11, I11 and K. For the detection of traces of other penicillins ( e g . , VI) some variation in the conditions may be necessary. For example? the existence of the new penicillin VI was revealed between penicillins I11 and I1 when a chromatogram on a strip carrying buffer of pH 6.78 was repeated on a strip carrying buffer of pH 6.25 (cj. Fig. 6, A and B). (4) Width of strip-The width specified is a compromise between narrow strips (10 mm. wide) which are more productive of faults such as asymmetric zones (Fig.5, D 11), and wide strips (20 mm. wide), which obscure the appearance of the smaller zones and are an incon- venient size for fitting into the apparatus. Strips must be of uniform width and free from ragged edges. A mean change in strip width of 1 mm. caused a mean change in zone diameter of the order of 0.4 mm. The latter are liable to cause gross irregularities.284 GOODALL AND LEVI: MICRO-CHROMATOGRAPHIC METHOD FOR THE [VOl. 72 (5) Solvent-Of the available solvents, ether has been by far the most satisfactory. Adjustments of fiH will be necessary if other solvents are used. (6) Develofiment-The apparatus (Figs. 3~ and 3B) is designed to standardise as far as possible the degree of development, which is related to throughput of solvent and moisture I Typiic~ll Fault I Fig.6. x = Point at which penicillin solution was applied. The area where growth is inhibited is shaded. FIG. 6. content of the treated strip. In order to keep these two factors constant, the apparatus is made gas-tight, with individual reservoirs for each strip and with a large damp surface to keep the atmosphere humid. The junction at the flange and’lid is readily made gas-tight by means of a Neoprene sponge rubber gasket.July, 19471 DETECTION OF DIFFERENT PENICILLINS IN A MIXTURE 285 BIOLOGICAL PROCEDURE (1) Precautions regarding sterility-These were confined to the preparation and use of the biological plates, since no practical advantage was gained by sterilising the paper strips before use.Little infection was encountered under the specified conditions. (2) Medium-Inoculated agar sheets of uneven thickness are useless for quantitative work, owing to marked variation of zone diameter with depth of agar. Hence the molten medium must be poured under conditions that permit the agar to form a plane sheet before setting. (3) Difusion-Larger zones with clearer edges are obtained if a period is allowed for diffusion before incubation. Care must be taken that there is no temperature gradient across the plate. For example, from a plate containing only undeveloped zones kept cold in a domestic-type refrigerator, there was a significant variation in zone diameter across the plate from the side nearest to the cooling coils. QUANTITATIVE For the development of a quantitative technique, dimensions such as area or length of the inhibition zone were too highly dependent on degree of development and also were not precise when the zones overlapped.However, these objections did not apply to the maximum diameter of the zone, which in preliminary experiments appeared to be proportional to the logarithm of the units in the zone. The precise relationship defining the diameters of the inhibition zones obtainable both from developed and undeveloped spots was investigated in the following way. A set of solutions of penicillin I1 crystalline sodium salt (Table 11) was prepared by serial dilution. Using 1-pl. spots from each of these solutions a set of strips carrying 1-pl. developed spots were obtained after chromatographic development.These developed spots were arranged on a biological plate together with a set of 1-p1. undeveloped spots from the same set of solutions. The diameters of the resulting zones of inhibition are given in Table 11. The experiment was carried out under routine conditions without special supervision, and the figures are probably fairly representative. TABLE I1 COMPARISON OF INHIBITION ZONE DIAMETERS (MM.) OBTAINED FROM “ UNDEVELOPED ” (u) This is not, however, essential. AND “DEVELOPED” (D) SPOTS OF KNOWN ACTIVITY U D u D U D U D U D U D U D U D U D Sodium penicillin I1 solution; units@. (B. subtilis) : f A \ Mean Slope 10.47 3-49 1.163 0.388 0-129 0-043 (a and a’) (b and b’) 44-4 39.6 37.1 32.1 29-9 23-9 34.50 8.18 43-2 41.0 35.8 30-2 26-9 20-0 32.85 9.82 43.2 40-2 36.9 33.2 27.8 22-2 33.92 8.75 43-2 40.6 36.4 30.2 25.1 22.2 32.95 9-41 43-6 39.7 37.2 32.6 29.6 24.2 34-48 7.91 43.2 41.2 34.8 31.1 27.9 19.2 32-90 9- 80 42.9 41.4 37.3 33.6 28.5 24.8 34.75 7.96 44.0 40.5 36.8 31.6 27-2 21-5 33.60 9.44 44.9 40.8 38.1 33-0 31.0 24.8 36-43 7.66 45.4 42.0 36.2 32.5 28.2 22.1 34.40 9-77 46.5 43.0 39-8 35-1 31.1 25.0 36.75 8.86 44-0 43.8 37-8 33.1 30.0 20.8 34.93 9.69 43-9 40.7 37-2 32-8 29.3 24.8 34-7 8 7-66 45.1 41-1 36.5 31.9 26-4 23-7 34-1 1 8.86 38.3 36-7 33.1 26.8 26.1 21.7 30.45 7-25 40.0 36.9 32.3 28-5 23.8 19.1 30.11 8-87 39-1 36.5 33.0 28-8 25.2 21.2 30-63 7.64 39.5 36.7 32.7 29.1 23.0 18.9 29.99 8.86 b‘/b 1-20 1-08 1.24 1.19 1.20 1.10 1-16 1.22 1.16 Notes on Table II- a and a’ are ordinates, b and b’ are slopes for six results for undeveloped and developed spots respectively.Standard deviation of each zone diameter: U, 0.9; D, 1-24 mm.286 GOODALL AND LEVI: MICRO-CHROMATOGRAPHIC METHOD FOR THE [Vol. 72 The following conclusions were drawn from the data: (1) For both sets of spots the trend of the results is largely accounted for by an expression of the type diameter of zone = a + b log (units in zone) where a and b are constants for a particular biological plate. Both a and b may differ considerably between plates. (2) There is, however, a small but significant curvature, which is similar in magnitude for both sets, i.e., the relationship is only approximately rectilinear. A similar result has been observed in the ordinary cup assay when carried out with an extended range of concentrations. (3) The slopes for the undeveloped zones (b) were significantly lower than those for the developed zones (b’) .(4) The ratio of the slopes b’/b was sensibly constant, with a value of approximately 1.2; similar values were obtained on several other occasions. (5) The over-all standard error, including that due to the curvature, is of the order of =t 1 mm. This corresponds approximately, at 95 per cent. limits of error, to f 25 to 30 per cent. in the estimation of activity in any one zone. For a sample replicated on 6 strips the 95 per cent. limits of error are thus about f 15 per cent. In a further experiment in which solutions containing 30, 3, and 0.1 units were each developed with 1, 3, 5, 7, 9, and 11 ml. of ether, it was shown that zone diameters increased with distance of development for the strongest solution, while the reverse was true for the weakest solution.No effect was detectable at the intermediate strength. This phenomenon accounts for observation (3) above. OTHER POSSIBLE METHODS OF DETERMINING PLATE SLOPE- The method given above was adopted after considering three alternatives. (a) Comparison with the results from standard mixtures of the pure penicillins so arranged as to give series of developed inhibition areas appropriate to each penicillin. This is not possible in the absence of the pure components. (b) A planned distribution of the developed test spots and the undeveloped standard spots over several plates. This method is dependent on reasonable conformity of each plate to an average plate slope, but plate to plate variations of slope, even on a single day, were too great.(c) Serial dilution of the sample itself. As the minor zones soon disappeared in the results obtained from a set of serial dilutions, and as there is obviously an upper limit to the load (governed by the area available on the biological plate), this procedure did not permit adequate replication. Nevertheless if samples of suitable composition are available this method should provide useful information about the relative plate slopes of the different penicillins. In adopting the undeveloped spots as standards, the advantage that the results are, comparatively, of a high order of accuracy will counteract the errors due to the uncertainty of the empirical factor 1-2 used to calculate the slope for the developed spots.Small errors in the value of the slope are important only in connection with very small or very large zones, as, for example, in calculating the proportions of an impurity in a major component. It is probable that the slopes of the developed zones increase from pencillin I11 to penicillin K, but the evidence so far obtained is not conclusive. Since penicillin I1 is developed a moderate distance down the strip, the value of b’ for penicillin I1 is probably a reasonable value for the mean of slopes. Errors due to the use of this figure can be expected; thus differences between proportions of penicillin I11 in different samples will be minimised; differences between proportions of penicillin K will be exaggerated. TYPICAL NUMERICAL RESULTS- In the absence of samples of the pure components for making synthetic mixtures, checks on accuracy have had to be confined to such results as are shown below in Tables 111, IV TABLE I11 and V.Sample 1: REPLICATION OF ANALYSES BY ROUTINE OPERATOR Pencillins found : 111 I1 I IV VII K Six-strip assay . . . . 0.5 37.5 29-8 19.7 1.4 11-1 per cent. Repeat . . .. . . 1-1 39.6 28.5 17.7 trace 13.1 ,, ,I six-stripassay .. . . 1.9 15.6 18.8 16-4 - 47.0 per cent. Sample 2: 41*7 D D I D Repeat . . .. .. 1-8 15.9 22.5 17-8 -July, 19471 DETECTION OF DIFFERENT PENICILLINS IN A MIXTURE TABLE IV COMPARISON OF CALCULATED AND OBSERVED VALUES FOR DIFFERENTIAL ASSAYS 287 The figures below represent values of the ratio : units against B. subtilis + units against S.aureus, for a variety of samples containing from 3 to 7 component penicillins. Observed : 0.65 0.71 0.98 0.82 0.68 Calc. (see method): 0-69 0.71 0.98 0.88 0.56 Observed : 0-83 0.94 0.86 0.80 0.89 0.68 Calc. : 0.89 0-96 0.89 0.86 0.92 0.76 TABLE V MATERIAL BALANCE (MEGA-UNITS) ON PARTIAL FRACTIONATION OF A PENICILLIN SAMPLE Composition of each fraction, in mega-units calc.. from micro-chromatographic analysis and direct assay Total mega-units A \ Fraction No. (direct assay) I11 I1 I + IV K - - - 1 0.079 0-079* 2 0.218 0.002 0.175 0.038 0-003 3 0-507 - 0.446 0.060 0.002 4 0-07 1 - 0.008 0-062 0.001 6 0.632 - - 0-623 0.009 0.062 6 0.2 12 - - 0.160 7 0.477 - - 0.016 0.462 Total 2.096 0.081 0.629 0.868 0-629 Starting material 2.40 0.068 0.652 1-17 0.503 * Assumed to be penicillin 111, not analysed.Note-The recovery in a fractionation process of this kind is expected to be about 80 per cent. The data in Tables I11 to V are fairly representative of the results obtainable under routine conditions. The method described has proved to be very useful, particularly for the examina- tion of complex mixtures of the type shown in Table 111, which, for the first time, can now be directly analysed for every component. It is hardly likely that such a complete analytical picture could be obtained by other than chromatographic means. Bearing in mind that the procedure involves both a chromatographic stage and a biological assay, the reproducibility obtained is reasonably good. The application of the method to samples predominantly penicillin I1 has recently become of special interest, since clinical-quality salts containing from 90 to 100 per cent.of penicillin I1 are now being manufactured. In this connection it is pertinent to illustrate how the figure for the relative proportion of penicillin I1 is not greatly affected by comparatively large errors in the units found in each of the several penicillin zones. For example, let us assume that a sample of relatively pure penicillin I1 has the following composition in 23. subtilis units per cent. : Penicillins: III,l%; 11,94%; I, 2%; IV, 1% and K, 2%. Let us further assume that the error in the estimation of the penicillin I1 zone be f 15 per cent. (see p. 286), but that the errors in the minor (111, I, IV and K) zones be as much as f 50 per cent.Now although these deviations are large when considered as absolute errors on each individual unitage, it can be calculated that for mixtures of the above type, the extreme range for the relative proportions of the major constituent (pencillin 11) carries a much smaller error. In the case assumed the range is from 90.0 to 97.3 per cent., where the true figure is 94 per cent.; i.e., the extreme errors in the relative proportion are - 4.0 and + 3.3 per cent. It is shown below that the reproducibility in the proportions of penicillin I1 found in replicate analyses (6-strip assays) of this type is well within these limits: Pencillins present I11 I1 I I V K Sample 1: trace 98.2 1.0 0-6 0.4 per cent. Repeat : 0-4 98.0 0.7 0.3 Oe6 BB B D Sample 2: 0.7 93.0 3.3 0.9 2*o DD D B Repeat : 0-6 94.5 2.6 1.1 D # D B Hence the method serves to provide a reasonably accurate measure of the relative content of the major penicillin in this class of sainple.288 GOODALL AND LEVI : MICRO-CHROMATOGRAPHIC METHOD FOR THE SUMMARY [Vol.72 A method is described in which the various penicillins in a mixture are separated by a micro partition chromatographic technique, based on differences in distribution of the penicillins between ether (mobile phase) and phosphate buffer (stationary phase) supported on a strip of filter paper. The separated penicillins are invisible, but after incubation in con- tact with an agar sheet, pre-inoculated with B. subtilis spore suspension, elliptical zones free from bacterial growth are clearly visible in the neighbourhood of each active component.The technique is highly sensitive, 1 p1. of solution (1 to 30 international units) being adequate for a qualitative separation., The maximum diameter of each zone is proportional to the logarithm of the number of units in the zone. Quantitative data are given, indicating the order of reproducibility of the method. It is shown that the activity in crude products is mainly due to penicillins I, 11, 111, IV, and K. Small amounts of new penicillins (called VI and VII) have also been separated, but in the samples examined these have never represented more than 5 per cent. of the total activity. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Goodall, R. R., and Levi, A. A., Nature, 1946, 158, 675. Levi, A. A., and Terjesen, S.G., B.P. 569,844. Consden, R., Gordon, A. H., and Martin, A. J. P., Biochem. J., 1944. 38, 224. Fisher, J. W., and Woodruff, H. B., J,. Bact. 1944, 47, 43. Wright, A. E., and Colebrook, L., “ The Technique of the Teat and Capillary Glass Tube,” 1921, Fischbach, H., Mundell, M., and Elbe, T. E., Science, 1946. 104, 84. Editorial in The Lancet, 1946, 251, 387. Schmidt, W. H., Ward, G. E., and Coghill, R. D., J . Bat., 1945,49, 411. Sheehan, J. C., Mader, W. J., and Cram, D. J., J. Amer. Chem. Soc., 1946, 68, 2407; Abst., U.S. Federal Register, 1946, 11, 12134; 13905. Higuchi, K., and Peterson, W. H., Ind. Eng. Chem., Anal. Edn., 1947, 19, 68. Constable & Co. this vol. p. 313. IMPERIAL CHEMICAL INDUSTRIES, LIMITED RESEARCH AND ANALYTICAL LABORATORIES BLACKLEY, MANCHESTER, 9 February, 1947 DISCUSSION Mr.S. G. E. STEVENS congratulated the authors on a method which seemed to have great possibilities in evaluating penicillins and asked whether “halo” formation was observed and whether variations in the concentration of a penicillin introduced any undue vertical as well as horizontal diffusion. Dr. LEVI in reply said that the edges of the zones were quite sharp at all concentrations and halo effects had not been observed. Dr. E. LESTER SMITH said the authors were to be congratulated on this extremely elegant application of the chromatographic technique to a difficult and important problem. It seemed probable that chroma- tography, and in particular partition chromatography, would become of increasing importance to analysts.The speaker had obtained some experience with the procedure on the basis of the authors’ earlier brief report, and had rediscovered someof the snags, in particular the vital importance of humidity control. Another difficulty encountered had been a tendency for the zones, even on the standard strips, to merge into one another as though the paper was taking up too much moisture from the agar jelly and so permitting diffusion of penicillin along the strip. The paper strip chromatograms were remarkably effective in separating individual penicillins and appeared to give sharper separations than buffered silica gel columns. It was suggested that this might be correlated with the observation that penicillin K sodium salt behaves in aqueous solution as a colloidal electrolyte; its solutions froth badly and are capable of emulsifying organic solvents such as chloroform and solubilising certain dyes that are insoluble in water.Penicillin I1 sodium salt does not behave in this way in dilute aqueous solution but becomes colloidal in presence of strong buffers. The colloidal particles were likely to be adsorbed by the silica and this could account for the bad “tailing” of penicillin zones on these columns. The American system using various arbitrary letters was less tidy than the English numeral system, but the latter was rather spoiled because the number “Iv” had been allotted to different penicillins. It had to be conceded that I.C.I. workers were the first to claim this number for a new penicillin in a confidential report, whereas others, in ignorance of this report, had assigned the number to penicillin “K”; perhaps we should agree to use “V” for penicillin “K”? A zone on paper strip chromatograms probably corresponding with the 1.CI.penicillin IV was commonly found with submerged-culture penicillin. It seemed likely that this would be found identical with the dihydro-penicillin I recently claimed by American workers as a component of penicillin made by submerged culture. It was unfortunate that the nomenclature was so confused.July, 19471 DETECTION OF DIFFERENT PENICILLINS IN A MIXTURE 289 THE AUTHORS, in reply to Dr. Lester Smith, said they had observed the effects of merging of zones, and diflusion along the edges of the strip, to which he had referred. The main cause was irregularity of the strip edges, but there were undoubtedly other factors still unknown.The effects were certainly less frequent with strong buffer. Buffered columns on silica gel could give excellent separations, but care must be exercised in the correct choice of initial conditions, such as amount of charge relative to amount of adsorbent, initial con- centration, and so forth. Dr. Levi hoped to publish shortly a paper on the theory and practice of this type of chromatogram. Mr. F. A. ROBINSON said he had gained the impression that Dr. Levi, in studying the effect of various factors, had carried out factorial design experiments only on the chromatographic procedure : he asked whether similar experiments had been carried out to determine whether any of these factors interacted with factors involved in the bacteriological procedure.It was very difficult to obtain an agar jilm of uniform thickness, and an irregular film might well introduce errors, wrongly attributed to faults in the chromato- graphic technique. Dr. LEVI, in reply, said that such experiments had been carried out and that the method of pouring the plates was now very rigidly controlled; he did not believe that the variations in the thickness of the film at different points on the plate were sufficient to introduce serious errors, provided that the specified routine was strictly followed. Dr. GOODALL said it was important to use a refrigerator so designed as to minimise thermal gradients in the cold atmosphere enclosed. It had been noted that, when a domestic-type refrigerator was used, the diameters of a set of “standard” spots decreased in the proximity of the cooling coil.Dr. H. DRYERRE, enlarging on a point made by Mr. Stevens, thought that the thickness of the agar film was a factor which must not be neglected. The test was dependent upon the extent of diffusion of the penicillin lateral to the side of the paper strips. It was reasonable to assume that the penicillin diffused also downwards, and any increase in thickness of the agar layer would by diversion leave less penicillin to diffuse laterally. In reply, Dr. LEVI said there was no doubt that thickness of the agar film had a profound effect on zone diameter. The most important condition was that the agar should be above 70” C. when inoculated and poured.If the tem- perature were, say, 65” C., then visibly irregular films were liable to be obtained. Dr. A. J. P. MARTIN asked whether the use of a salt solution instead of water in the inner cylinder would not give a more uniform humidity in the chromatogram strips. Dr. LEVI said that potassium phosphate solutions of the type used, when evaporated, leave syrups that readily take up or evolve moisture according to the state of the atmosphere. There was, of course, no equilibrium vapour pressure. Salt mixtures had a vapour pressure less than saturation for the particular temperature and tended to dry the buffered paper strips. They were abandoned for this and other reasons. The best method so far found was to expose the strips to a fully humid atmosphere for a specified time.This was still unsatisfactory, as it was difficult to control the state of the strips before humidification was started. Thus strips in the centre of a pile might be more or less damp than those near the top, and so on. Mr. A. L. BACHARACH asked whether the iodination of penicillin and its hydrolytic product might not be affected by the nature of the side chain. He also enquired whether it was unnecessary, as he gathered, to sterilise the paper strips before attaching them to the agar plates. The problem of producing satisfactory strips of uniform width was surely one that should be referred back to the makers of the filter paper, par- ticularly if the test and its subsequent modifications were, as a result of the excellent work and description by the authors, to be widely used.He also emphasised the importance, even though the error of these tests should be steadily reduced, of so designing them and computing the results that not only the estimate of penicillin activity, but also its error, could be stated. Mr. ROBINSON said that the iodimetric method gave very satisfactory results, in the sense that these could readily be reproduced by different workers. He agreed with Mr. Bacharach that the individual penicillins might take up different amounts of iodine; this was especially likely to occur with the p-hydroxy benzyl group of penicillin 111, though he doubted whether the double bond in the side-chain of penicillin I would add on iodine under the conditions employed. Dr. GOODALL, in reply said that he had modified the iodimetric method of Alicino by increasing the nett titre and controlling the reaction temperature by thermostat.The reproducibility was thereby in- creased. He confirmed the experience of other speakers that it was necessary for each analyst to evaluate the iodine absorption of pure penicillin 11, as it varied according to conditions adopted. A manufacturer had not yet been found to produce strips, but further enquiries would be made in view of possible in- creased demand. Further details available in the paper when published would indicate that the error in estimating the activity in any zone was dependent on the type and proportion of penicillin referred to. Until results on known “synthetic” mixtures were available, it was estimated that for a mixture of several components present in similar proportions, the 95 per cent.limits of error were about f 15 per cent. for 6 replicates. It was mentioned that it was difficult to cut the strips exactly to size. Previous publication had been delayed by secrecy regulations. Conditions, however, had been worked out which give a reasonably uniform film. I t was not necessary to sterilise the paper strips before the chromatographic analysis.290 GOODALL AND LEVI: MICRO-CHROMATOGRAPHIC METHOD FOR PENICILLINS [VOl. 72 Where the sample had a 95 per cent. proportion of penicillin 11, the data to be published would show that the errors found were very much less (less than f4 per cent.) for the main component. Mr. STROUD asked if the quality of the ether used in the development of the strips was standard, and was the same quality always used? With respect to the iodimetric method of assay, the interference of unsaturated bonds is eliminated by the control blank experiment.Dr. LEVI said they always used anaesthetic ether, but he did not think the quality was critical. It was, of course, essential for the ether to be damp. Dr. E. C. WOOD considered that the necessary paper strips with clean-cut edges and precisely deter- mined width could be easily made by the manufacturer. The makers of the pressure-sensitive adhesive tapes, so widely employed nowadays for sealing purposes, used a machine that should be quite capable of dealing with filter-paper. He would like to ask Mr. Robinson if he would venture a definition of the word “penicillin.” The difficulty of defining the word “vitamin” was notorious, and it seemed that a similar difficulty was beginning to arise with the penicillins.If the definition were based on the chemical constitution, i t would be difficult to exclude certain substances that have little or no anti-biotic activity. If, on the other hand, a functional definition was attempted, very careful wording would be required if the definition was to be neither too wide nor too narrow. Mr. ROBINSON referred Dr. Wood to the Therapeutic Substances Amendment Regulations, 1946, in which a statutory definition of penicillin is given. Mr. S. S. RANDALL asked how many antibiotics the authors had discovered, With similar technique, but different solvents and buffers and with the aid of “differential” organisms, he had found evidence of fourteen.Dr. LEVI said they had found a t least nine. In reply to another question he said that so far they had encountered no differences in results attributable to differences between B. subtilis strains. Dr. HEATLEY asked if penicillin K was not still being called penicillin IV by some workers and if this error had ever been refuted in print. Dr. LEVI said that they discovered penicillin IV during the war and did work on it which, of course, could not then be published. In the meantime Americans had been working on penicillin K and it had been assumed that the two were identical. But there could now be no doubt that they are in fact quite distinct. Commenting on Dr. Heatley’s question, Mr. ROBINSON said that penicillin K was probably a mixture of several penicillins, with p K values of about 6, and penicillin IV was probably not identical with any of them. Craig, in America, had designed an apparatus capable of partitioning penicillin a large number of times between an aqueous phase and a solvent phase, and the results had indicated the existence of numerous penicillins not yet characterised. Mr. C. R. BOND, in congratulating the authors on the work they had done, said that the method had enabled a much clearer picture of the complex composition of penicillin as produced by the mould to be formed and was a valuable weapon in work on the purification of penicillin and the separation of individual penicillins. . He asked the authors whether they had applied the method to streptomycin, and, if so, whether this was likely to prove as complex as penicillin. He also enquired whether they could provide any infor- mation on the nature of the side chain in the newer penicillins such as IV, VI and VII. With reference to the confusion existing on the nomenclature of the penicillins, particularly penicillins K and IV, he said that the existence of more than one penicillin was first exclusively demonstrated in the I.C.I. laboratories in July, 1943, by the chromatographic separation of what were now known as penicillins I and 11. At that time the constitution of penicillin was not known and it was suggested that penicillins as they were discovered should be distinguished by the use of Roman numerals. Penicillin I11 was dis- covered in January, 1944, and shown to be a p-hydroxy derivative of penicillin 11. Penicillin IV was isolated shortly afterwards in the I.C.I. laboratories but sufficient was not obtained for a complete deter- mination of its constitution. It appeared, however, to be closely related to penicillin I ; it was certainly different from penicillin K, which was discovered later. He knew nothing of the chemical constitution of penicillins IV, VI or VII. There was confusion between penicillins IV and K in America and in this country. Mr. W. F. WILKINSON asked if differences in quality between different samples of agar had been found to have any effect on the readability and validity of results. In determinations of fungistatic and bacteriostatic values, considerable differences due to this cause had been encountered. Dr. LEVI thought that might well be, but he had not experienced difficulties in that direction, except with one particular batch of agar, which gave unusually small zones. Dr. LEVI said he would like to see streptomycin put on strips.

ISSN:0003-2654    

DOI:10.1039/AN9477200277

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years.The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion.The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on.Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp.15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C.Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner.He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years.The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions.After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on.Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175).Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408.London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent.and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks.,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C.AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks.,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years.The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d.net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion.The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on.Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp.15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction July, 19471 STOCK AMPEROMETRIC TITRATION 291 Polarography The following four papers were read at the Meeting of the Physical Methods Group on November 26th, 1946.Amperornetric Titration By J. T. STOCK POLAROGRAPHIC technique can be used not only for the direct determination of electro- reducible or electro-oxidisable substances in solution, but also for following the progress of a reaction such as the precipitation of one of the constituents of the solution. It is thus possible to employ polarometry for the location of the end-point in certain titrations. Since the process involves the measurement of current, Kolthoff and Pan1 proposed the name amperometric titratiort to replace the term polarometric titration suggested earlier by Majer.2 Though subject to some criti~ism,~ the newer term appears to have become firmly established.Titrations with the aid of the dropping mercury electrode were first performed in 1929 by Heyrovskjr and Berezicky? who studied the precipitation of barium, strontium and calcium as the sulphate, carbonate, etc. These workers added successive measured volumes of the reagent, e.g., potassium sulphate, to the solution to be titrated, e.g., barium chloride, polarographed the latter aft'er each addition and measured the height of the barium wave. The height decreased regularly as the reagent was added, owing to removal of electro-reducible barium ions from solution. After equivalence had been attained, further addition of the reagent caused the wave height'decrease to continue at a smaller rate, owing to the sup- pression of barium ions by the solubility-product effect.The change in the rate of decrease was taken to indicate the end-point, although the latter was actually found by comparing the wave height with that of an artificial equivalence solution. VOLUME OF TITRANT ADLED+ VOLUME OF TITRANT ADDED I / VOWME OF TITRANT AWED Fig. 1. Typical ampero- Fig. 2. Curve obtained when Fig. 3. Curve obtained when the reagent only is wave- metric titration curve obtained when only the substance ti- be determined are wave- forming, trated is wave-forming. forming. both reagent and substance to Considerable advances were made by Ma j er,2 who discussed the general characteristics of the method and pointed out the simplification, both in manipulation and in the necessary apparatus, which resulted from the use of a fixed applied e.m.f.instead of recording a series of polarograms. Several other Continental ~ o r k e r s ~ p ~ ~ ~ ~ ~ ~ ~ J ~ have also contributed to the development of the method. The systematic investigations by Kolthoff and his co-workers, the first results of which were published in 1939,l have shown that amperometric titration is capable of high accuracy, and have done much to extend the applications of the method. If a solution of an indifferent electrolyte, such as potassium nitrate, containing lead ions be placed in a polarographic cell and a potential of about -1-2 volt (all potentials are with respect to the saturated calomel electrode) be applied to the dropping mercury electrode, a diffusion current will be obtained, since lead ions are reduced well below this potential.(It is assumed that the usual precautions of oxygen-removal and of maximum-suppression have been observed.) Suppose small successive volumes of potassium oxalate solution are now added, the current being measured after each addition. Usually, a stream of hydrogen or nitrogen is bubbled through the solution for a few minutes to assist mixing; the gas stream292 STOCK : AMPEROMETRIC TITRATION [Vol. 72 is stopped before the current is read. The current flowing falls progressively as lead oxalate is precipitated, and becomes very small when equivalence is reached. Since oxalate is not reducible under the experimental conditions, its continued addition does not cause further change in the current. If the latter be plotted against the corresponding volume of oxalate solution added, a curve, shown diagrammatically in Fig.1, consisting of two straight lines intersecting in the form of a rough “L” is obtained. The end-point volume of the titration is indicated by the point of intersection of the two branches of the curve. In practice, introduction of the titrant unavoidably dilutes the test solution, causing deviation from linearity, as depicted by chain lines in Fig. 1. This effect may be minimised by using a titrant 10 to 20 times more concentrated than the test solution and in precise work may be allowed for by correcting the current readings by the relationship: where V is the initial volume of the test solution and v is the volume of reagent added.196 Owing to the solubility of the precipitate, a “rounding-off” in the region of the end-point, as shown by broken lines in Fig.1, is observed. Except when the solubility is appreciable, or when extremely dilute solutions have to be titrated, this curvature does not interfere; the end-point is located by producing the linear portions of the branches to intersect. In most cases, therefore, it is sufficient to plot three or four readings on each side of the end-point and not too close to the latter and to draw through the points a pair of straight lines to intersect - icorrected - t me and x (V + v)/v, at the end-point volume, A 1 POTEl Fig. 4. Anodic and cathodic curves. Fig. 5. Titration of an electro- oxidisable. substance with a re- ducible reagent. Suppose that the titration be repeated with potassium dichromate solution in place of the oxalate.As before, the current falls progressively until the end-point is reached. Since, however, dichromate forms a wave under the experimental conditions, continuance of the titration causes the current to rise progressively. The “V”-shaped titration curve (Fig. 2) obtained is characteristic of titrations in which both reagent and substance to be determined are electro-reducible. If the titration with dichromate be performed at zero potential and with the lead- containing solution rendered slightly acid, the current, initially small, does not alter appre- ciably until the end-point has been reached. It then increases progressively as addition of dichromate is continued, giving a titration curve of the “reversed L” type shown in Fig.3. Such curves are characteristic of titrations in which the reagent, but not the substance to be determined, is reducible. The titration curves so far discussed resemble those obtained in conductometric titration, although quite different principles are involved. In both conductometric and amperometric techniques the method of finding the end-point does not involve readings near this region. Accordingly, both techniques are applicable to the titration of very dilute solutions, or in other circumstances when methods based on the actual recognition of the end-point fail. However, foreign or indifferent salts, traces of which often have to be guarded against in conductometric work, may be present if the amperometric technique is employed, and are in fact normally added.The marked increase or cessation of flow of current that occurs in the end-point region of an amperometric titration is reminiscent of the effects observed in the “dead stop” methodJuly, 19471 STOCK : AMPEROMETRIC TITRATION 293 of titration.12 Both methods involve polarisation phenomena, although of different kinds. However, no actual measurement of the current is made when the “dead stop” method is used, hence the term “amperometric” is not strictly applicable to it. Alternative terminology has been proposed by Guzman and Rancano.13 Another type of titration curve is obtained when the substance to be determined forms an anodic wave (i.e., is oxidised at the dropping mercury electrode), whilst, under the same conditions, the titrant forms a cathodic wave.Such titrations were first studied by StrubL6 Thus in acidified tartrate solution tervalent titanium forms an anodic wave (Fig. 4a), the half wave potential of which is -0.44 volt. In the same medium tervalent iron gives a cathodic wave at a less negative potential, as depicted a t b in Fig. 4. Between the potential limits X and Y, either substance yields its diffusion current. If, therefore, an acid tartrate solution containing titanous ions be electrolysed at a potential lying between X and Y and titrated with ferric chloride solution, the anodic current initially obtained decreases to zero as the titanous ions are oxidised by the titrant. Beyond the end-point, however, the ferric iron now present gives rise to a cathodic current, the magnitude of which increases as further additions of titrant are made.Thus a reversal of the current occurs; the titration curve is shown dia- gramatically in Fig. 5. Generally, the slopes of the portions of the curve before and after the end-point are not identical. In the reverse titration, viz., when the titrant forms an Fig. 6. Titration cell for use with external reference electrode. Fig. 7. Kolthoff and Langer titration assembly. Fig. 8. Cell designed to promote efficient stirring. anodic wave and the substance to.be determined a cathodic wave, the titration curve slopes the opposite way. The work of Strubl was extended by SpalenkaJ7 who studied the deter- mination of chromate, ferricyanide, etc. , by the titration of titanous chloride solution. Other titrations involving substances that form anodic waves are of halides with soluble salts of ~ i l v e r l ~ , ~ ~ or mercury,16 of chromate with ferrous ammonium sulphatel’ and of stannous tin with copper sulphate.18 The last example is interesting in being based upon compensation of the anodic current of tin by the cathodic current of copper, no direct reaction between the ions occurring in the bulk of the solution.19 Although most examples of amperometric titration hitherto investigated have been perfurmed with the dropping mercury electrode, increasing interest is being shown in the possibilities of the rotating platinum micro-electrode.17~20~21~22~23~45 This is especially suitable for titrations that can be carried out in an open beaker.In its simplest form the rotating electrode consists merely of a short piece of platinum wire sealed through the wall near the lower closed end of a length of glass tubing, which is rotated at constant speed.294 STOCK : AMPEROMETRIC TITRATION [Vol.72 Various forms of titration cell have been described. That shown in Fig. 6 is used in conjunction with an external reference electrode (usually a large saturated calomel electrode) an agar - potassium salt plug allowing connection to be made with the solution to be titrated.14 Since the titrant may be stored and introduced into the cell in absence of air, the Kolthoff and Langer apparatus (Fig. 7) is suitable for routine work.24 In a cell designed by Spalenka,' the-gas stream enters through four tubes bent as shown at (a) in Fig. 8. Intensive stirring of the solution is thus caused.Owing to the danger of breaking fragile electrode capillaries, burette jets, and the like, on attempting removal from rubber stoppers, the writer prefers to use for beaker-type cells the bakelite clamp-on cap shown in Fig. 9. The electrode capillary or burette jet passes through a short glass tube cemented into the cap, a short sleeve of rubber tubing preventing ingress of air.25 A tall-form 100-ml. lipless Pyrex beaker A is used as the cell, and is retained by stirrup B. The thumbscrews CC enable the lip of the beaker to be lightly pressed into rubber joint D, thus forming a gas-tight seal. Fig. 9. Beaker-type cell Fig. 10. Micro-cell incor- Fig. 11. Circuit arrangement with clamp-on cap. porating calomel electrode. for amperometric titration.Langer has described both macro- and micro-scale cells.26 The latter is depicted in Fig. 10. It incorporates a saturated calomel reference electrode which surrounds the titration chamber, junction with the test solution being made through ground joint A. Other cells for the titration of small volumes of solution have also been de~cribed.~',~~ Since electricaI measurements are made,only as a means of end-point location, thermostatic control, which is at least desirable in normal polarography, is unnecessary. For the same reason the dropping mercury electrode capillary need not be calibrated, so replacement is simple if a breakage occurs. Amperometric titration is normally carried out with an applied e.m.f. that remains constant during the entire operation. Hence the electrical apparatus is comparatively simple.The potentiometer device shown in Fig. 11 may be used to select the desired applied e.m.f., the value of which is indicated by voltmeter V. To measure the current, a mirror galvano- meter G, or, if available, a sensitive microammeter, is used. Shunt S permits adjustment of the sensitivity. To damp the galvanometer oscillations, a large-capacity electrolytic condenser C may be incorporated in the c i r ~ u i t . 8 ~ 2 ~ ~ ~ A compact polarising unit that permits the degree of damping to be adjusted has been described by the author.28 Titra- tion of this metal with potassium dichromate yields very accurate results in solutions as dilute as 0.001 M . As indicated above, dichromate in 'acid solution is reduced at zero potential.The titration may therefore be performed without the aid of a battery or polarising Amperometric titrations involving lead have attracted considerable attention.product of lead chromate is much less than that of barium chromate. If the titration is performed at a potential of -1.0 volt, lead and chromate form waves, but barium does not. Hence as titration proceeds, the current at first falls pro- gressively until precipitation of lead is complete; it then remains a t almost zero until sufficient chromate has been added to precipitate the barium. causes a progressive rise in current. A titration curve of the type shown in Fig. 12, consisting of three linear portions, is thus obtained, permitting the simultaneous determination of lead and barium.Though the second point of intersection corre- T Further addition of reagent 9 ’ .296 STOCK AMPEROMETRIC TITRATION [Vol. 72 examined and the determination is completed by titrating back with standard copper solution. Reversal of titration or employment of back-titration is sometimes useful in reactions in which precipitation is sluggish. This is demonstrated by the curves shown in Fig. 13. Those at (a) were obtained by adding 4 ml. of 0.01 M copper sulphate to 40 ml. of an acetate buffer of pH 4-9 and titrating with 0.02 M quinaldinic acid solution. If 4 ml. of the latter are diluted with 40 ml. of the buffer and titrated with 0.01 M copper sulphate, titration curves as at (b) are obtained. These show that equilibrium is almost obtained within 3 minutes of mixing; when quinaldinic acid is added to the copper-containing solution , attainment of equilibrium takes several times as long.% For the titration of bismuth, 8-hydroxyquinoline has been used.“ According to ZankoJa this reagent may also be used to titrate zinc, copper and aluminium.1 . 1 1 1 I 1 2 3 4 5 6 7 WL. OF 0.02M. QOINAWW KID ADDED. ML. ,-> Fig. 13. (a) Titration of copper with quinaldinic acid. (b) Reverse titration. The amperometric titration of a-tocopherol with gold chloride solution is interesting as an example of the determination of an organic substance with an inorganic reagent.a In a similar manner, silver nitrate solution may be used for the titration of mercaptans.a,a A titration in which both reactants are organic in nature is that of picrolonic acid with methylene blue, which has been used as an indirect method of determining calcium.44 Since the principles involved are mainly as in polarography, amperometric titration possesses most of the advantages and disadvantages of the polarographic method.Inter- ference by metals or other substances that form waves at potentials below that at which the particular titration has to be performed is serious. Although use of a counter-current devi~e2~9~~ may minimise such interference , the presence of high concentrations of such substances renders titration impossible. By introduction of nitro, azo or other readily reducible groups it might be possible to modify existing specific organic precipitants by rendering them wave-forming and hence usable at low potentials The likelihood of inter- ference would then be diminished.REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 1 2. 13. 14. 16. Kolthoff, I. M., and Pan, Y . D., J . Amer. Chem. Soc., 1939,61, 3402. Majer, V., 2. Elektvochem., 1936, 42, 120, 122. Heyrovskq, J., “Polarographie, ” Springer-Verlag, Vienna, 1941, p. 424, footnote. Heyrovsky, J., and Berezicky, S., COX Czech. Chem. Commun., 1929, 1, 19. Abresch, K., Chem. Fabrik, 1935, 8, 380. Strubl, R., Coil. Czech. Chem. Commlan., 1938, 10, 4’76. Spalenka, M., Ibid., 1939, 11, 146. Neuberger, A., 2. anal. Chem., 1939, 116, 1. - , Arch. Eisenkuttenw., 1939, 13, 171. Thanheiser, J., and Willems, J., Ibid., p. 73. Kolthoff, I. M., and Pan, Y. D., J . Amev. Chem. SOC., 1940, 62, 3332. Foulk, C. W., and Bawden, A.T., Ibid., 1926,443, 2045. Guzman, J., and Rancano, A., Anales SOC. espan. 3s. quim, 1934, 32, 59.0. Kolthoff, I. M., and Lingane, J. J., Chem. Reviews, 1939,24, 1. Muller, 0. H., J . Chem. Ed., 1941, 18, 320. Also cited by Neuberger (see Ref. 8).July, 19471 STOCK : AMPEROMETRIC TITRATION 297 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32.. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. Kolthoff, I. M., and Miller, C. S., cited by Kolthoff, I. M., and Lingane, J. J., “Polarography,” Kolthoff, I. M., and May, D. R., Ind. Eng. Chem.. A n d . Ed., 1946, 18, 208. Lingane, J. J., J. Amer. Chem. Soc., 1943, 65, 866. Kolthoff, I. M., and Miller, C. S., Ibid., 1941, 63, 1013. Laitinen, H. A,, and Kolthoff, I. M., J.Phys. Chem., 1941,45, 1079. Kolthoff, I. M., and Harris, W. E., Ind. Eng. Chem., Anal. Ed., 1946, 18, 161. Laitinen, H. A., Jennings, W. P., and Parkes, T. D., Ibid., 355, 358. Gigurke, P. A., and Lauzier, L., Canad. J. Res., 1945, 2 3 ~ , 223. Kolthoff, I. M., and Langer, A., J. Amer. Chem. Soc., 1940, 62, 211. Furman, N. H., “Standard Methods of Chemical Analysis,” D. van Nostrand Co., Inc., New York. Langer, A., Ind. Eng. Chem., Anal. Ed., 1945, 17, 454. Fill, M. A., and Stock, J. T., ANALYST, 1944, 69, 178. Stock, J. T., Ibid., 1946, 71, 583, 585. Lingane, J. J., and Kerlinger, H., Ind. Eng. Chem., Anal. Ed., 1940, 12, 760. Fill, M. A., and Stock, J. T., Trans. Faraday Soc., 1944, 40, 602. Kolthoff, I. M., and Laitinen, H. A., Bec. trav. chim., 1940, 59, 922.Langer, A., and Stevenson, D. P., Ind. Eng. Chem., Anal. Ed., 1942, 14, 770. Davies, W. C., and Key, C., Indust. Chemist, 1943, 19, 167. Korshunov, I. A., and Gurevich, A. B., Zavod. Lab., 1945, 11, 648. Langer, A., Ind. Eng. Chem., Anal. Ed., 1940, 12, 411. Kolthoff, I. M., and Cohn, G., Ibid., 1942, 14, 412. Flagg, J. F., and McClure, F. T., J. Amer. Chem. Soc., 1943,65, 2346. Stock, J. T., Unpublished experiments. Langer, A., Ind. Eng. Chem., Anal. Ed., 1942, 14, 283. Kolthoff, I. M., and Langer, A., J . Amer. Chem. Soc., 1940, 62, 3172. Gillis, J., Eeckhout, J., and Standaert, G., Meded, Kon, Vlaamsche Acad. Wetensch., Letteren Zan’ko, A. M., Dopodivi Akad. Nauk. U.S.S.R., 1940, 27, 32. Smith, L. I., Spillane, L. J., and Kolthoff, I. M., J . Amer. Chem. SOC., 1942, 64, 646.Cohn, G., and Kolthoff, I. M., J. Biol. Chem., 1943, 148, 711. Kolthoff, I. M., May, D. R., Morgan, P., Laitinen, H. A., and O’Brien, A. S., Ind. Eng. Cbm., Hohn, H., Z . Elektrochem., 1936, 43, 127. Butenko, G. A., and Pindas, V. M., Zavod. Lab., 1940, 9, 634. Interscience Publishers, Inc., New York, 1941, p. 474. 1939, p. 2310. Schoone Kunsten Belgie, Klasse Wetensch., 1940, No. 7, 3; Chem. Zentv., 1942, 11, 202. Anal. Ed., 1946, 18, 442. CHEMISTRY DEPARTMENT L.C.C. NORWOOD TECHNICAL INSTITUTE LONDON, S.E.27 DISCUSSION Augetst, 1946 Mr. A. C. MASON asked whether, with precipitation reactions that take some minutes to reach com- pletion, the method would not require undue time for a determination requiring the plotting of several Dr. W. CULE DAVIES asked what were the advantages of amperometric titrations over other well Mr. J.HASLAM asked what order of accuracy should be expected when two points before and two Dr. W. STROSS asked how long an amperometric titration took to perform. Mr. K. GOLDSCHMIDT asked if the author had any information concerning the application of the method to very concentrated solutions. Was it a fact that trouble rather difficult to eliminate occurred ? Mr. F. C. J. POULTON asked if Mr. Stock had experience of amperometric titrations of copper a t very low concentrations, of the order of M/20,000, with a-benzoin oxime. Could he say if in such instances the amperometric method had any advantages over the orthodox polarographic method ? Mr.’ W. FURNESS asked if Mr. Stock would amplify his statement of the conditions that govern the choice of those points a t which tests should be made.If a very insoluble salt is produced it would seem best to choose points close to the point of discontinuity of the curve; but when the salt produced had ap- preciable solubility points well removed from the equivalence point would seem preferable. Mr. STOCK, replying to Mr. Mason, said that with the organic precipitants used 2 or 3 minutes for completion of precipitation could be allowed and sometimes less a t each point. The total time required for a titration was normally less than half an hour and often twenty minutes were sufficient. In reply to Dr. Cule Davies he said that another advantage of the method was that one did not have to ascertain the end-point directly. The method was comparatively new and other advantages might appear later.In reply to Mr. Haslam he considered that if the selected points were well chosen an accuracy rather better than 1 per cent. should be obtained, especially if a correction was made for dilution by the titrant. He had no information about application of the method to very concentrated solutions. In reply to Mr. Poulton the stock copper concentration he had titrated with a-benzoin oxime was M/1000; he had titrated 6 pg. in 500,000, but such titrations were difficult. In reply to Mr. Furness he said that normally he tested three points on either side of the end-point, to make sure that they lay on a straight line. With soluble precipitates the matter was more complicated, and several mathematical papers on the location of the end-point had been published, notably one by Langer and Stevenson.points. known methods of titration. points after the end-point were tested. Possibility of titrating very dilute solutions seemed to be one.298 MORRIS : THE ROTATING PLATINUM ELECTRODE [Vol. 72 The Rotating Platinum Electrode BY C. J. 0. R. MORRIS THE dropping mercury electrode has proved so satisfactory for most purposes in polarographic analysis that there has been little incentive to search for a substitute, at least so far as cathodic reactions are concerned. There are, however, two classes of reaction for which an alternative electrode system would be valuable. First, those cathodic reductions in which mercury interferes chemically with the electrode process, and secondly in the study of anodic oxida- tions.The latter class has not been of very much importance in inorganic polarography, but the increasing interest in the polarographic analysis of organic compounds has more recently caused greater attention to be given to such processes. There is, however, an important limitation in the study of anodic oxidations with the dropping mercury electrode. .While it is possible to carry out cathodic reductions at potentials up to about -2.7 v., on the anodic side oxidation of the mercury itself limits the range to about +0.4 v. The use of an inert electrode would extend the range up to about +1.1 v., at which point evolution of oxygen from the anode sets the upper limit of the process. Many workers have used solid metallic electrodes in the study of diffusion currents, both cathodic and anodic, but obstacles such as electrode polarisation (as distinct from concen- tration polarisation) made it very difficult to obtain reproducible results, and it was not until the introduction of the dropping mercury electrode by Heyrovskf that the measurement of diffusion currents became sufficiently reliable to be of value to the analyst. Nevertheless, under strictly controlled conditions, quantitative measurements can be made with solid metallic electrodes.Thus Glasstone and Reynolds1 studied the oxidation of ferrous ions at a platinum anode, and showed that the diffusion current was proportional to the ferrous ion concentration. The first thorough investigation of the platinum electrode from the standpoint of the analytical chemist was carried out by Laitinen and Kolthoff.2J They first examined the stationary platinum electrode and derived an equation for the diffusion current, viz., i = knDC, in which i is the diffusion current, n the number of electrons involved in the electrode reaction, D the diffusion coefficient, C the molar concentration of the diffusing substance, and k a constant.They confirmed this equation for silver, copper, thallous, lead, ferric and ferrous ions, and showed that analyses could be carried out with an accuracy of about 1 per cent. provided proper precautions were taken. In particular it was essential to prevent thermal convection near the electrode, and also to ensure absence of mechanical vibration.They found that the temperature coefficient of the diffusion current was about 4 per cent. per degree C., as compared with about 2 per cent. for the dropping mercury electrode. The stationary platinum electrode has, however, certain disadvantages. The greatest of these is the necessity of waiting for at least 2 minutes at each value of the applied potential for equilibrium to be reached. Thus a polarographic record in the usual sense is impossible. Other disadvantages are the rigorous temperature control necessary and the possibility of electrode polarisation. Laitinen and Kolthoff found that these difficulties could be largely overcome by rotating the platinum electrode at a constant rate. The zone of convection equilibrium attained with the stationary platinum electrode was then replaced by a zone of uniform stirring. Owing to the much greater rate of diffusion in this zone, the current density was much higher, and the observed diffusion currents were 10 to 20 times greater. In fact, under comparable conditions, the rotating platinum electrode gave larger diffusion currents than the dropping mercury electrode.The rotating electrode was less sensitive to external conditions than the stationary electrode, showed a temperature coefficient of diffusion current of about 2 per cent. per degree C. in the reactions studied, and was in general more similar in its behaviour to the dropping mercury electrode. It was found difficult, however, to get reproducible results from day to day, and this has also been our own experience with this electrode.Laitinen and Kolthoff suggested therefore that perhaps the greatest utility of the rotating platinum electrode was as an indicator electrode in amperometric titrations, where such reproducibility is not essential. Kolthoff and his collaborators have reported several such amperometricJuly, 29471 MORRIS THE ROTATING PLATINUM ELECTRODE 299 titrations, an interesting example being the titration of -SH groups with silver nitrate solution (Kolthoff and Harris5). The type of electrode used by Laitinen and Kolthoff is shown in Fig. 1. Kolthoff and Harris have suggested a modified form for use in suspensions (Fig. 2). This apparently functions by minimising disturbances of the diffusion layer by solid particles. A comparison of various electrodes for the continuous estimation of oxygen in sea- water was carried out by Giguere and Lauzier.7 They examined the dropping mercury electrode, the stationary platinum electrode and the rotating platinum electrode as cathodes, with the mercury pool, the saturated calomel electrode and various metallic electrodes as anodes.They made the important observation that when platinum electrodes were used for long periods with either the mercury pool or the saturated calomel electrode as anode, mercury was deposited electrolytically on the cathode and led to erratic results. They were able to overcome this difficulty by surrounding the anode with a fine-mesh platinum wire MERCU W€LL RY M S TAT I o N A RY I [ + REVOLVING Fig. 3 (Reproduced from Ind. Eng. Chem., Anal. Ed., 1946, 18, 162).Fig. 1. cage maintained at -0.2 v. with respect to the anode. Their apparatus is shown in Fig. 3. They found that the rotating platinum electrode gave considerably larger diffusion currents than either the stationary platinum electrode or the dropping mercury electrode, and obtained a linear relation between diffusion current and oxygen concentration over a wide range. The work of Giguere and Lauzier would appear to have wide application, especially in the measure- ament of oxygen uptake in biological systems, for theoretically the polarographic method should be more sensitive than the manometric methods generally used, and it offers the additional advantage of a continuous record. An interesting attempt to overcome one of the most serious disadvantages of solid electrodes, viz., electrode polarisation, has been described by S.D. Miillex-.* His apparatus is shown in Fig. 4. Two platinum electrodes are used with either a mercury pool or a solid metallic anode. When one electrode is cathodically polarised, the other is kept at anode potential. The states of polarisation and depolarisation are reversed at a constant frequency bv means of a commutator. Miiller used a metronome device to actuate the commutator and used polarisation times of 0.3 to 5-0 secs.; the best results were obtained at 1 to 2 secs. He examined the cathodic reduction of copper, lead, cadmium and zinc in sodium potassium tartrate solution and his published polarograms appear very similar to parallel runs with the dropping mercury electrode.We are constructing in our laboratory a similar arrangement300 MORRIS : THE ROTATING PLATINUM ELECTRODE [Vol. 72 with electronic control of the polarisation period. This is shown in Fig. 5. The frequency is controlled by the neon tube relaxation oscillator, which operates a uniselector switch acting as commutator. We are hoping to study various organic anodic oxidations with this apparatus. 1 I , A l B n + YLATIWUM VIM C Y I Fig. 3. B + O OA C I Fig. 4. O+ 8 0 Fig. 6 The various types of metallic electrode described do not replace the dropping mercury electrode, which is still the most reliable for general analytical purposes. They are, however, of value in special circumstances, and further study of such electrode systems will doubtless extend still further the range of polarographic analysis.REFERENCES 1. 2. 3. - and -, Ibid., 1079. 4. 5. 6. 7. 8. Glasstone, S., and Reynolds, G . D., Trans. Farad. SOL, 1933, 29, 399. Laitinen, H. A,, and Kolthoff, I. M., J . Phys. Chem., 1941, 45, 1061. Laitinen, H. A., Jennings, W. P., and Parkes, T. D., Ind. Eng. Chem., Anal. Ed., 1946, 18, 355, 358. Kolthoff, I. M., and Harris, W. E., Ibid., 161. Kolthoff, I. M., and May, D. R., Ibid., 208. Giguere, P. A., and Lauzier, P., Canad. J . Res., 1945,23~, 76, 223. Miiller, S. D., Trans. All-Union Con.. Anal. Chem., 1943, 2, 651. ENDOCRINE UNIT LONDON HOSPITAL, LONDON, E. 1July, 19471 RANDLES: THE APPLICATION OF THE CATHODE RAY OSCILLOGRAPH 301 DISCUSSION Mr. J. T. STOCK asked if, in the Miiller double electrode system there was a pronounced temperature coefficient, as might be expected from Dr.Morris’s remarks about stationary micro-electrodes in general, for in the fundamental equation for such electrodes the diffusion current appears as the &st power and not as the square root. Dr. J. E. PAGE asked if Dr. Morris had used the rotating platinum electrode to study the oxidation of organic substances, and if he knew whether its application to the measurement of oxygen concentrations had been used in respiration experiments (cf. R. J. Winzler, J. Cell. and Comp. Physiol., 1943,21, 229). Dr. J. E. B. RANDLES asked if any phenomena similar to those appearing with the ordinary direct mechanism had been noted. He had thought that Miiller used the ordinary galvanometer for his recording Dr.W. STROSS mentioned two arrangements described in a doctorate-thesis by W. Kaeppel (printed at Bonn in 1941) from v. Stackelberg’s laboratory; these were not accessible in ordinary publications but might be of interest. The first consisted of four stationary electrodes dipping in the test liquid which was separated by a diaphragm from a calomel reference electrode. A rotating contact connected one electrode a t a time in rapid succession (5 to 20 cycles per potential increase of 0.1 volt) as the cathode, whilst the other three were connected with a depolarising rail to which various potentials could be applied by means of a battery and a variable resistance. The second apparatus also consisted of four electrodes of which in t u r n one is dipped into the solution by an electromagnet every second, whilst the other three are kept above the liquid.The quinone - hydro- quinone system was regarded as reversible but when it was examined by Dr. Kaeppel’s technique oxidation of hydroquinone and reduction of benzoquinone occurred a t different potentials. Some of the statements in the thesis were unexpected and required confirmation. Dr. ZADE asked if it would be possible to use alternating current in amperometric titration with the rotating platinum electrode; if so, contact trouble could be overcome by capacitive coupling. Mr. G. S. SMITH asked if in order to avoid difficulty with contacts it would be possible either to cause the electrode to make a circular movement in the liquid without rotating or to make the liquid rotate round a stationary electrode.Dr. MORRIS, in reply to Mr. Stock, said he thought that the Miiller system might have a relatively high temperature coefficient, but he imagined trouble due to convection would be reduced. In reply to Dr. Page, he said he knew of no published work on the study of oxidation of organic compounds by means of the rotating platinum electrode; he and his colleagues were mainly interested to applying it to biological analysis. Replying to Dr. Randles, he said that contact trouble was the main difficulty with the rotating electrode, but it could be overcome; the kind of galvanometer used by Miiller was not clear from his re- ference to it. To Dr. Zade’s question as to the possibility of using alternating current he replied that this could be done.He thought Mr. Smith’s suggestions for avoiding contact difficulties were worth trying. Possibly, however, he had made too much of contact trouble; there were ways of overcoming it. Rotation of the liquid by means of a solenoid had been tried but was not a success. Both instruments were used for experiments on thiourea. Dr. PAGE said that Dr. Kaeppel’s thesis contained a number of interesting points. The Application of the Cathode Ray Oscillograph to Polarography : Underlying Principles BY J. E. B. RANDLES TIIE ordinary polarograph is applicable to the estimation of small quantities of many metals and electro-reducible or -oxidisable substances in general. Its use frequently gives results more accurate than are easily obtainable by purely chemical means and very often in a mere fraction of the time required for a chemical analysis.The most usual form of commercial instrument records the current - voltage curves photographically. This has some disadvan- tages in that an appreciable amount of time is spent in recording, developing and drying the polarograms before they can be measured. Furthermore, the actual form of the polaro- gram cannot be seen until the photograph is developed, so that any malformation is not perceived until the recording, or recordings, are completed. The photographic procedures are eliminated in pen recording instruments now made, and the polarogram can be seen as it is recorded, but the recording is still a comparatively slow process. Thus the idea of obtaining a current - voltage curve rapidly traced on the screen of a cathode ray tube has arisen.Work with this object in view has been carried out by Matheson and Nichols‘ and on less direct lines by Miiller, Garman, Droz and Petras2 and Heyrovskfr and ForejLs However, in no case has any near approach to a practicable precise analytical instrument been attained.302 RANDLES: THE APPLICATION OF THE CATHODE RAY OSCILLOGRAPH [VOl. 72 It is believed that the apparatus described below represents a considerable development in this direction. The basic principle of polarography is the measurement of the diffusion current passed by a micro-electrode in a state of concentration polarisation. It is usual to obtain, by one of two methods, a diffusion current, either steady or of steady average value, suitable for measurement by a galvanometer.The two methods are the use of the rotating platinum electrode and the use of the dropping mercury electrode. If, on the other hand, a cathode ray oscillograph is employed, rapidly changing currents may be followed without difficulty. This permits the measurement of diffusion currents under quite different conditions. To e-.)rplain this difference of principle a brief consideration of the elementary theory of diffusion currents is necessary. 2 P t a 5 : w V DISTANCE FROM ELECTRODE . 1 rnm. 2 mrn. Fig. 1. i ~ i ~ ~ - s e c o n d s I 5 10 20 30 60 POTENTIAL OF ELECTRODE Fig. 2. 1 If a micro-electrode is immersed in a solution containing an electro-reducible or -oxidisable substance (and an indifferent electrolyte), and a potential, sufficient to cause reaction of the substance, is applied suddenly to the electrode, a diffusion current is obtained which changes with time as shown in Fig.1 (b). The current starts at a high value and declines rapidly, being in its early stages proportional to t-lI2, t being the time measured from the application of the electrolysing potential. This decline is due to the widening of the diffusion layer as electrolysis proceeds, which is illustrated in Fig. 1 (a). Ordinates are concentrations of the reacting substance in the solution and abscissae the distances from the electrode surface. Successive curves refer to the values of t shown, but the numerical values in general are only intended to show approximate magnitude. Since the current passed by the electrode is proportional to the rate of v i v a 1 of reacting substance at its surface, which is proportional to the concentration gradient of the substance, close to this surface, the reason for the decline of the current is evident from Fig.1, (a). Although the decrease of the diffusion current to a stationary electrode becomes slower as time goes on, the current becomes unsteady owing to convection effects resulting from the concentration differences near the electrode. A stationary micro-electrode, cannot, therefore, be used in conjunction with a galvanometer for polarographic purposes. The difficulty of the widening diffusion layer is ordinarily overcome in two ways, as already mentioned. The thickness of the layer may be limited by controlled stirring, as with the rotating platinum electrode.Or the electrode and the solution undergoing electrolysis may be automatically renewed at frequent intervals, as is in fact done! when the dropping mercury electrode is used. The rotating electrode gives a steady current, and the dropping electrode a fluctuating current,July, 19471 TO POLAROGRAPHY : UNDERLYING PRINCIPLES 303 but of constant average value, for a given potential of the electrode. The rate at which the potential of such an electrode is changed in order to obtain a current - voltage curve (ie. the ordinary polarogram) must be slow (about 1.0 volt in 5 minutes) so that there shall not be significant lag in the attainment of the true current for each potential, and in the response of the galvanometer to the changes in current. Particularly the latter applies when the dropping electrode is employed, as the galvanometer must be sufficiently damped for it not to respond appreciably to the fluctuations of current with the growth and fall of each mercury drop. The form of current - voltage curve obtained with slow change of potential of the electrode,’and the condition of steady, or steady average, current for any given electrode potential, is that of the ordinary polarogram.The gradual increase of current is due to the gradual decrease of the concentration of the reacting substance at the electrode surface as the reaction becomes more complete with the change of the potential of the electrode. This is illustrated diagrammatically in Figs. 2 (a) and 2 (b) for the case of a diffusion layer of constant thickness as at the rotating platinum electrode.The concentration - distance curves in Fig. 2 (a) correspond to potentials of the electrode indicated by dotted lines in Fig. 2 (b). We may now turn to a consideration of diffusion currents varying with time as well as with the potential of the electrode. These arise,. as we have already seen, from the sudden application of a suitable potential to a micro-electrode in a solution containing an electro- reducible or -oxidisable substance ; or preferably, in practice, from the application to such an electrode of a rapid potential “sweep” covering say 1.0 volt in 1 to 2 seconds. Any electro-reduction or -oxidation having a polarographic “half-wave potential” within this range gives rise to a diffusion current which rises rapidly to a peak and then declines as the diffusion layer widens.Fig. 3, (a) is reproduced from a photograph of a cathode ray trace showing the current - voltage curve obtained with a platinum micro-electrode in this way. In practice successive potential “sweeps” are applied to the electrode, so that the trace is repeated, but with a stationary electrode there must normally be an interval of at least 10 seconds with the electrode a t its starting potential, between the “sweeps,” to allow time for the surrounding solution to regain its original uniformity. , - . - - . . 1 . 0.6 0.8 1.0 1.2 0.4 0.6 0.8 0.2 OI 0.6 0.8 1 9 (4 (b) (4 Fig. 3. Current voltage curves. 1/8 x 10-aM Cd” in M KC1. 1/16 x 10-sM Pb” , Cd” and Zn” in M KC1.Abcissae are voltages of the micro-electrode negative to a silver - silver chloride electrode. (a) ( b ) 1/4 x 10-SM Cd” in M KC1. Dropping mercury electrode. (c) Stationary platinum electrode. Dropping mercury. electrode. Although a stationary electrode has some advantages, in many cases a dropping mercury electrode is preferable. A potential “sweep” applied to a dropping electrode at a late stage of drop growth produces a current -voltage curve very similar to that obtained with a stationary electrode (see Fig. 3). The repetition of the “sweep” must be synchronised with drop formation in such a way that each sweep occurs at the same stage of drop growth, otherwise successive current - voltage curves would not be identical. The method of carrying this out will be explained shortly.Fig. 4 shows the simplest form of circuit for this purpose; it is very similar to one used by Matheson and Nichols. The starting potential of the “sweep” is controlled by potentiometer Q, and the rate of change of potential by rheostat R,. The potential differences between points A and B and between C and D, are amplified by direct-current amplifiers and applied to the deflector plates of the cathode ray tube giving horizontal and vertical deflection of the beam, respec- tively. Horizontal, deflection thus gives a measure of the potential difference across the The potential “sweep” is provided by the charging of a condenser.304 AIREY: THE APPLICATION OF THE CATHODE RAY OSCILLOGRAF’H [Vol. 72 polarographic cell and vertical deflection a measure of the current passing through it.The trace is therefore a current - voltage curve. The potential “sweep” is ended by short- circuiting the condenser by means of a relay-switch K. This relay is operated by an electronic circuit (“flip-flop” circuit) triggered by an impulse derived from the amplifier whose input is the potential difference across R,. The impulse arises from the sudden change in current when the mercury drop falls. After a certain delay (controlled by a rheostat in the %p- flop” circuit) to allow drop growth, the relay reopens and another Dotential sweep is Ll*+ Fig. 4 stahed, to be terminatedbhen the drop 'rails. In order that there shall be accurate proportionality between peak current and concentration of the reacting substance in the solution, not only is exact timing of the potential sweep required but also the rate of change of potential of the electrode must be constant and independent of the current passed.This cannot be achieved by the simple circuit of Fig. 4, for the rate of change of potential difference across the cell is inevitably affected by the sudden increase in Dotential &OD in R, when the current rises. To overcome this an electronic circuit was dehsed which aGplies tke potential difference to the cell in such a way that it is independent of the potential drop in R, and of the current. This, and the other circuits, will be described in detail elsewhere.4 REFERENCES 1. 2. 3. 4. Matheson, L. A.. and Nichols, N., Trans. Amer. Electrochem. Soc., 1938, 73, 93. Miiller, R. H., Garman, R.L., Droz, M. E., and Petras, J,, Ind. Eng. Chem., Anal. Ed., 1938,10, 339. Heyrovskj., J., and Forejt, J., Z . physzkal. Chem., 1943, 193, 77. Randles, J. E. B., Trans. Faraday SOC. (in press). CHEMISTRY DEPARTMENT BIRMINGHAM UNIVERSITY The Application of the Cathode Ray Oscillograph to Polarography: General Layout and Uses of the Cathode Ray Polarograph BY L. AIREY IN the present paper the apparatus of which the principles have been explained by Mr. Randles in the preceding paper is considered in more detail from the standpoint of instrumentation and uses. It is emphasised that a practical Cathode Ray Polarograph has been designed and built,* having uses both in analysis and in research. Details of construction and circuits will be published elsewhere but the general lay-out of the main parts is indicated in block diagram form in Fig.1 and further information on them is given in the folloiving Sections 1 to 4. 1. Cathode Ray Tube and Power Supply-The tube itself has a fluorescent screen showing long afterglow properties (about 10 secs.). As will be seen from the diagram, the units are separate, but they may commercially be combined in one box. 2. AmpliEers and Voltage Sweep Circuit, etc.-These units are mounted side by side on a common chassis and housed in one box. The lay-out of the circuits follows conventional electronic practice but emphasis must be laid on adequate electrical screening of the input leads, etc., and the provision of a satisfactory anti-vibration support for the two valves in the voltage sweep circuit.Other circuits included on the same chassis are (a) an electronic time delay circuit, (b) an auxiliary trigger amplifier and (c) an electromagnetic relay to control the cathode ray * The instrument was demonstrated a t the meeting.July, 19471 TO POLAROGRAPHY: GENERAL LAYOUT, ETC. 305 “spot” brightness during the quiescent condition. Circuit (a) is the conventional “flip-flop,” with provision for converting it to a multivibrator. As the former, it consists simply of a circuit having one stable and one metastable state into which it can be thrown on receipt of a suitable impulse (from the amplifier); the duration of its stay in the metastable condition can be altered at will by variation of resistance values in circuit. As the multivibrator, the circuit possesses two metastable states, and the frequency of change from one to the other may be precisely governed by variation of resistance values.VOLTAGE TRANSFORMER CELL UNIT El In order to utilise to full advantage the long afterglow screen of the cathode ray tube, it is necessary that full spot brilliancy be employed. However, if the beam at this intensity should rest on one portion of the screen for any length of time permanent damage is done to the screen. To obviate this, the circuit (c) is introduced whereby the intensity is diminished during the quiescent part of the cycle. 3. Power Sufifllies for AmpliJiers, etc.-Two independent power supplies for the am- plifiers and voltage sweep circuit respectively are required. Good stabilisation by means of gas discharge tubes is necessary, and for the supply for the voltage sweep circuit additional resistance capacity decoupling after the stabilisers is desirable.The precise location of the power pack chassis with respect to the amplifiers is not important but it is desirable to keep the connecting leads as short as possible and to avoid stray alternating magnetic fields. 4. Cell Assembly and Constant Voltage Transformer-The cell assembly can be of any design whatsoever; the mercury column is earthed and the leads to the amplifier are electro- statically screened. A point of some importance is to ensure that the cell assembly is com- pletely clear of stray magnetic fields from the apparatus. The constant voltage transformer is necessary only where main voltage fluctuations are greater than f 2 per cent.As an analytical tool the apparatus is essentially a comparison instrument and it resembles other types of polarographs in requiring calibration with known standards. It is therefore essential that the controls shall be precisely reproducible in setting. It will be convenient to consider the sequence of operations required for the production of a quantitative polarogram. (1) Adjustment of the drop time-With the capillary dropping in the test solution, the multivibrator circuit is set for a repetition frequency of 7 secs. (a convenient arbitrary time). With a constant known potential applied to the cell the drop break-away is apparent as a small “blip” in the cathode ray trace. By adjusting the head of mercury, the “blip” may be obtained at the same place on the trace in each successive cycle, and then the drop time is exactly that of the multivibrator.It is important, of course, that these measurements are made at a known potential, obtainable from a calibrated potentiometer included in the circuit.306 (2) Measurement of “Peak”-The voltage sweep rate is adjusted by means of the appropriate control. The multivibrator is switched over to “time delay’’ and the extent of the delay varied until a polarographic peak appears on the screen. Small variations in the fine control on the time delay circuit are then made until the horizontal projection of the “tail” of the peak is some convenient arbitrary length. A note is made of the initial starting voltage and of the “horizontal” amplifier gain setting.Finally the cell series resistor, R, is varied until the peak height is some definite figure (say 7-5 cm.). The value of R is recorded. The solution is then replaced by a standard, the peak length adjusted if necessary, and R varied to produce a peak height of 7.5 cm. The solution concentration being inversely proportional to the resistance, the unknown concentration is then easily evaluated. The description just given applies to the reduction of a single species of ion. When more than one is present in solution, the technique is modified slightly. By careful use of the controls governing the starting potential across the cell, together with those of the time delay circuit, it is possible to isolate and measure, as described above, peaks corresponding to each individual ion.The method is advantageous in the estimation of a small amount of, say, cadmium (-0-6 v. versus S.C.E.) in presence of a relatively large amount of lead (-0.4~. versus S.C.E.). By beginning at -06v., no peak is obtained for the lead ion, and it is possible to estimate cadmium in presence of 50 times as much lead and possibly more. AIREY: THE APPLICATION OF THE CATHODE RAY OSCILLOGRAPH [Vol. 72 USES OF THE INSTRUMENT- The instrument has so far been considered as an analytical tool, but it has other im- portant uses. Like other types of polarographs it may be used for certain fundamental physical measurements such as those of diffusion coefficient or the number of electrons in- volved in a reduction or oxidation process. It is particularly useful for rapidly checking the efficiency of electrolytic separations, and the relatively short time required for an observation (this can be reduced to about 4 secs.) makes it a valuable means for following the course of rapid reactions, e.g., tautomeric conversions.However a particular virtue lies in the fact that the shape of the reduction (or oxidation) peak is indicative of the nature of the reaction: Ions such as those of cadmium, thallium and lead are characterised by the fact that their reductions are thermodynamically reversible. Other ions such as those of stannic tin complexes, nickel in sulphate media, and a large number of reducible organic compounds do not show this ease of reduction but require an overvoltage to effect the change. The result is to introduce a rate-controlling process other than diffusion, and this manifests itself as a rounding and flattening of the polarographic peak.For truly reversible reactions the curves can be treated mathematically in a manner analogous to that used in deriving the Ilkovic equation, but so far little or no work has been done in attempting to treat irreversible reactions in this manner. Apart from the mathematical aspect of the matter, the appearance of the polarograms is a very useful criterion of the suitability of a reaction for analytical or electrochemical work. First, it has been shown that platinum micro-electrodes may be used in the region +1 to -0-3 volt (versus S.C.E.) with some success. Secondly, it has been shown that the dropping mercury electrode may be replaced by an amalgamate4 silver or preferably an amalgamated platinum micro- electrode.Providing that amalgamation is good, such electrodes may be used up to -2.1 volts without difficulties due to hydrogen evolution. The technique adopted with these “film electrodes,” as they may be described, is to execute a voltage sweep in the ordinary way and to observe the polarogram in a manner similar to that described above. The potential is then retuned to a point below the half-wave potential of the ion in question and maintained there for about lOseconds, during which period the deposited ion is redissolved and con- centration gradients are practically eliminated. As will be apparent, it is essential that the “film” be regenerated during the latter part of each cycle and in consequence the electrode can be used only for such metals as will dissolve easily from an amalgam.In the case of reduction (or oxidation) from one valency state to another the limitation does not of course Although much work remains to be done on this type of electrode it would appear that its main advantage lies in the great simplification in the circuit of the apparatus. The electrodes may be made of constant and accurately reproducible dimensions and appear to be reliable in operation. The use of a synchronising circuit is no longer necessary and hence a much simpler polarogram-measuring technique may be employed. Moreover it becomes It may be useful to consider briefly certain recent developments. apply.July, 19471 TO POLAROGRAPHY: GENERAL LAYOUT, ETC. 307 possible to enhance the sensitivity of the method by increasing the surface area of the electrode beyond that normally obtainable from a capillary tube. A point of theoretical interest which has not yet been investigated is that with both types of film electrodes some maximum suppressor appears to be necessary when dealing with certain iods. In conclusion a comparison of the three types of instrument-photographic, pen-recording (1) A ccwacy-There are no very significant differences. (2) Sensitivity and Robustness-It is considered that the cathode ray instrument is much superior to the other types owing to the lack of delicate moving parts. However, circuit characteristics would set a practical limit to an increased sensitivity at about one order greater than commercial equipment. (3) Adaptability-As an analytical tool the instrument has the merit of speed for routine work. As with the pen-recorder type, any malformation of the polarogram may be easily detected, but the lack of a permanent record may be a drawback. (4) Complexity and Size-On this score the apparatus is obviously inferior to the other types. Even with improved design it will require approximately twice the space required by a pen-recording instrument and some considerable knowledge of electronics may be required to trace and remedy any circuit faults that may develop. (5) Cost-A quite satisfactory apparatus can be built with limited workshop facilities, and it is thought that the cathode ray polarograph should be no more expensive than the other types. The authors wish to acknowledge valuable advice and criticism from Mr. S. H. Bales, Principal Scientific Officer and Mr. A. S. Nickelson, Principal Scientific Officer of the Chemical Inspection Department, Ministry of Supply. This Paper is published with the permission of the Chief Scientist, Ministry of Supply. and cathode ray tube polarographs-under various headings will be given. CHEMICAL INSPECTION DEPARTMENT, MINISTRY OF SUPPLY ROYAL ARSENAL, WOOLWICH DISCUSSION Mr. A. C. MASON asked if the apparatus described was more effective than the ordinary polarograph in separating waves whose half-wave potentials are close together. Dr. ZADE asked if dI/dE curves had been plotted on the cathode ray oscillograph, as in the method used by Heyrovsky recently, Dr. J. G. A. GRIFFITHS, referring to the use of “film electrodes” mentioned by Mr. Airey, asked if it was satisfactory to deposit a film of silver on a metal into which mercury does not diffuse. Mr. K. GOLDSCHMIDT said that Messrs. Randles and Airey had described a spectacular, but rather complicated instrument, and he was doubtful if it could be operated by an unqualified assistant. Had the authors had experience with simpler circuits in which the cathode ray oscillograph is employed as an in- dicator in conjunction with the usual polarographic measuring or recording equipment ? He had used a modification of a method first described by %eke and van Suchtelen (2. EZeRtrockem., 1939, 45, 753), in which a ‘small A.C. bias superimposed on the electrode potential permitted accurate detection of half-wave potential and of changes of curvature a t the beginning and end of a wave. From the latter the concen- tration could be derived by noting the difference between the corresponding deflections of a galvanometer, or alternatively by recording the desired part of a wave on a polarograph. Complete analysis of a solution could thus be carried out very rapidly, and in some instances continuously. The cathode-ray oscillograph may be of any commercial type, and the only other components necessary are a few radio-type resistors and capacitors. Interpretation of the pattern obtained on the cathode-ray tube is very simple, and the device can be used by an unqualsed investigator. Mr. AIREY, in reply to Mr. Mason, said the instrument was an improvement, but not a great one, on the ordinary polarograph in the separation of waves that were close together. Waves 0.15 volt apart could be separated but that was about the limit. H e had not yet attempted the plotting of dI/dE curves with the instrument. In reply to Dr. Griffiths he said that they had obtained satisfactory film electrodes by dipping red-hot platinum into mercury.

ISSN:0003-2654    

DOI:10.1039/AN9477200291

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction 308 NOTES [voi.72 Notes AIDS TO ACCURXCY IN QUANTITATIVE ESTIMATION FROM SIMPLE POLAROGRAMS IN quantitative polarographic estimations it is often a matter of some difKculty to decide the exact angle at which to draw the tangent to a diffusion current curve, as, for example, the choice between a and a’ in the accompanying diagram. In the “internal standard” method of estimation this difficulty can be overcome by making a second addition of a known amount of standard solution. The usual technique according to the “internal standard” procedure is to obtain a “waveJJ for the unknown, say C, to add a known amount of standard solution of the substance to be estimated, and obtain another “wave” as at B. Then concentration is proportional to wave height, and the latter is found by drawing parallel tangents to B and C and a tangent to the “foot” of the curve (D) the height being measured as the intercept on a vertical drawn at the half-wave potential.It will be obvious that the correct slope of the tangents is a matter of some importance in accurate work. If now a second addition is made, the ratios of the wave heights for the solutions (making an allowance for the approximate unknown concentration) are fixed, and tangents can be drawn to ensure these ratios. The common slope of all the diffusion current tangents is then completely determinate. In a case producing a, curve similar to that depicted, the intercepts could have been measured as follows: C = 11 to 14 mm.(unknown concentration) B = 17 J J 20 ,) (lOpg. per ml. addition) A = 24 J J 27 J J (20 J J J J S P ,, ). From the average values of C and B, the unknown concentration per ml. Thus, as a first approximation, the wave-height ratios were was about 21.25p.g. & 31.25 - - - - 1.32 and - = - - 1-47. hA 41.25 h, 31.25 12, 21.25 - -- The stipulation of both these ratios simultaneously narrows the possible intercept values (as may be seen by setting up the ratios on a slide rule) to: C = 12.4 to 13.6; B = 18.2 to 20.0; A = 24.0 to 26.4. Then taking C as 13.0 and drawing parallel tangents to all three curves, there is obtained: C = 13.0; B = 19.0; A = 26.0 whence the unknown concentration is 20%. per ml.July, 19471 MINISTRY OF FOOD: STATUTORY RULES AND ORDERS 309 For greater accuracy, successive approximations can be made for the unknown con- centration, which process is facilitated by a device for laying on the polarogram, comprising a sheet of transparent material on which a series of parallel lines (e.g., 1 nun.apart, with centimetres marked) is ruled, photographed, or otherwise applied. The “internal standard“ method of estimation is described in “Polarography,” by Kolthoff, I. M., and Lingane, J. J., Interscience Publishers, New York, 1941, p. 251, and an inspection of Fig. 91 on p. 252 will show the difficulty of measurement in some instances, particularly as the half-wave intercept method mentioned above is now generally used (cf., “Polarographic and Spectrographic Analysis of High P w i t y Zinc and Zinc Alloys for Die Casting,” H.M. Stationery Office, 1945, p. 26). It must be stressed that the method herein described involves a different principle from the known method of making successive additions, measuring wave heights and plotting back to the unknown concentration. At no point in that method is any wave-height accurately fixed, and systematic inaccuracies will be reflected in the final result. This paper is published by permission of the Director of the Chemical Research Laboratory. JOHN A. LEWIS DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH CHEMICAL RESEARCH LABORATORY TEDDINGTON, MIDDLESEX

ISSN:0003-2654    

DOI:10.1039/AN9477200308

出版商:RSC    

年代:1947

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction MINISTRY OF FOOD STATUTORY RULES AND ORDERS 309 Ministry of Food STATUTORY RULES AND ORDERS* 1947 876. The Pickles and Sauces Order, 1947. Dated May 7, 1947. Price 2d. I n this Order, which replaces the Pickles and Sauces Order, 1946 (S.R. & O., 1946, No. 2216)- “Pickles” means sweet pickles (whether mixed with any sauce or not) mixed pickles or piccalilli, or any pickled beetroot, cabbage, capers, cauliflowers, cucumbers, gherkins, mush- rooms, olives, onions, pimentos, tomatoes or walnuts, or any other pickled vegetables, fruit or fungi.“Sauce” means anchovy essence or sauce, caper sauce, chutney, fruit sauce of the type commonly used with meat or fish, mushroom ketchup, horseradish cream or sauce, mayonnaise, mint jelly or sauce, mushroom ketchup or sauce, mustard sauce, prepared mustard, salad cream or any other salad dressing, sandwich spread, tomato ketchup or sauce, walnut ketchup, Worcester sauce,. or any other similar products. No person shall sell any product under the description “tomato ketchup” or “tomato catsup” unless it contains no fruit or vegetable other than tomatoes (except onions, garlic and spices added for flavouring purposes). - 968. The Edible Gelatin (Control) (Amendment) Order, 1947. Dated May 16, 1947. Price Id. (a) $rooides that edible gelatin (see S.R. G. O., 1947, No. 161; ANALYST, 1947, 72, 66) may be manufactured by the blending together of two or more gelatins (not necessarily individually complying with the definition of “edible gelatin”); and adds jellied eels to the list of foods in the manufacture of which edible gelatin may be used. This amending Order (b) * Obtainable from H.M. Stationery Office. Italics signify changed wording.

ISSN:0003-2654    

DOI:10.1039/AN947720309b

出版商:RSC    

年代:1947

数据来源: RSC