ISSN:0003-2654    

DOI:10.1039/AN95883FX037

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年代:1958

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No. 61 November, I958 THE SOCIETY FOR ANALYTICAL CHEMISTRY BULLETIN FORTHCOMING MEETINGS Joint Meeting of the Society with the Association of Public Analysts, December 3rd, 1958 A JOINT Meeting of the Society and the Association of Public Analysts will be held at 3 p.m. on Wednesday, December 3rd, 1958, in the Wellcome Building, Euston Road, London, N.W.1. The meeting will take the form of a Symposium on “Food Analysis.” Afternoon Session: 3 p.m. The following papers will be presented and discussed- “The Determination of Chemical Antioxidants in Fats after Separation by Partition Chromatography,” by K. G. Berger, M.A., N. D. Sylvester, MSc., F.R.I.C. and Miss D. M. Haines, B.Sc. “The Estimation of Egg in Certain Foods by Enzymic Hydrolysis of the Phospholipids,” by C. B.Casson, B.Sc., F.R.I.C. and F. J. Griffin, B.Sc., A.R.I.C. Evening Session: 5.15 p.m. To be opened by J. R. Nicholls, C.B.E., D.Sc., F.R.I.C. Under the general heading “The Identification of Coal Tar Colowing Matters in Food- stuffs,” two papers will be presented by P. s. Hall, B.Sc., F.R.I.C. and R. C. Spalding, M.A., A.R.I.C., and will be discussed. Joint Meeting of the North of England Section and the Northpancashire Section of the Royal Institute of Chemistry, December 4th, 1958 A JOINT Meeting of the North of England Section and the North Lancashire Section of the Royal Institute of Chemistry will be held at 7.30 p.m. on Thursday, December 4th, 1958, at the Storey Institute, Meeting House Lane, Lancaster. The following paper will be presented and discussed- “Recent Advances in Polarography and Some Other Electrical Methods,” by G.F. Reynolds, M.Sc., F.R.I.C. Joint Meeting of the Western Section with the Cardiff and District Section of the Royal Institute of Chemistry, December 19th, 1958 A JOINT Meeting of the Western Section with the Cardiff and District Section of the Royal Institute of Chemistry will be held on Friday, December 19th 1958, in Cardiff. The following paper will be presented and discussed- “New Techniques in Qualitative Analysis,” by D. W. Wilson, M.Sc., F.R.I.C. Ordinary Meeting of the Midlands Section, December 9th, 1958 AN Ordinary Meeting of the Section will be held at 7 p.m. on Tuesday, December 9th, 1958, in the Gas Showrooms, Nottingham. The following paper will be presented and discussed- “The Analysis of Tar Acids,” by H.G. Willcock. Ordinary Meeting of the Midlands Section, December 17th, 1958 AN Ordinary Meeting of the Section will be held at 6.30 p.m. on Wednesday, December 17th, 1958, in the Mason Theatre, The University, Edmund Street, Birmingham, 3. A discussion on “Flame Photometry” will be opened by L. Brealey, BSc.London Discussion Meeting) of the Microchemistry Group, December loth, 1958 THE seventeenth London Discussion Meeting of the Group will be held at 6.30 p.m. on Wednesday, December loth, 1968, in the restaurant room of “The Feathers.” Tudor Street, off Bouverie Street, Fleet Street, London, E.C.4. Annual General Meeting of the Biological Methods Group, December 9th, 1958 THE Annual General Meeting of the Group will be held at 6.30 p.m.on Tuesday, December 9th, 1958, in the restaurant room of ?The Feathers,’’ Tudor Street, off Bouverie Street, Fleet Street, London, E.C.4. The Annual,General Meeting will be followed by a Discussion Meeting of the Group, at which a discussion on “Methodological Reminiscences” will be opened by S. K. Kon, Ph.D., D.Sc., F.R.I.C. SUMMER SCHOOL IN ANALYTICAL CHEMISTRY August 30th to September 5th, 1959 ARRANGEMENTS have been made for a Summer School in Analytical Chemistry to be held at The School of Pharmacy, Brunswick Square, London, W.C.l, from August 30th to September 5th, 1959. There will be three separate, but concurrent, courses covering instrumental organic analysis, modern inorganic analysis and gas chromatography. Attendance at the School will be open to Fellows, Associates and Graduate Members of the Royal Institute of Chemistry and Members of the Society for Analytical Chemistry.Full particulars and application forms will be distributed with the January issue of The Analyst. LIBRARY OF THE CHEMICAL SOCIETY Christmas Closing, 1958 THE Chemical Society has announced that the Library will close at 1 p.m. on Tuesday, December 23rd, 1968, and will reopen at 9.30 a.m. on Monday, December 30th, 1958. COMMUNICATIONS ACCEPTED FOR PUBLICATION IN THE ANALYST THE following communications have been accepted for publication in The A d y s t , and are expected to appear in the near future. “A Simple Spectrophotometric Method for Determining Magnesium, Calcium, Strontium, Barium, Cadmium and Zinc with Ethylenediaminetetra-acetic Acid,” by J. R. Dunstone and E. Payne. “The Determination of Bismuth in Lead and Lead Cable-sheathing Alloys,” by J. H. Thompson and B. W. Peters. “Zone Electrophoresis: Some Basic Considerations in Design,” by N. H. Martin. “Determination of Small Amounts of Triisooctylamine in Aqueous Solution,” by A. W. Ashbrook. “Direct Titration of Hydroxyl Groups with Lithium Aluminium Di-n-Butyl Amide,” by L. A. Small. “A Rapid Micro-method for Carbon Tetrachloride in Blood,” by A. C. Kondos and “The Determination of a-(PChloro-2-methylphenoxy)propionic Acid in Commercial Acid “The Awlysis of Synthetic Detergents. A Review,’’ by W. B. Smith, G. L. McClymont. of This Name,” by L. A. Haddock and L. G. Phillips. -~ ~ PRlNTED BY W. HEFFER & SONS LTD.. CAMBRIDGE. ENGLAND

ISSN:0003-2654    

DOI:10.1039/AN958830X039

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX041

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP169

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BP179

出版商:RSC    

年代:1958

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OCTOBER, I958 Vol. 83, No. 991 Obituary JAMES RAWSON WALMSLEY JAMES RAWSON WALMSLEY died in hospital in Manchester on June 4th, 1958. He began his scientific career as an apprentice in retail pharmacy, qualifying as a pharmaceutical chemist in 1912. He held a number of positions in retail pharmacy, but after the 191618 war entered the wholesale trade with Joseph Brooks & Co. Ltd. In 1921, he was appointed Works Analyst to James Woolley, Sons & Co. Ltd., of Manchester, a position he held until prolonged ill-health compelled him to retire in 1953. After a period of rest, however, his active spirit rebelled against enforced idleness and he spent much time during his last years assisting in the Pharmacy Department of a local hospital. When he died, he had served pharmacy diligently and enthusiastically for over 50 years.In 1922, he qualified for the Fellowship of the Institute of Chemistry in Branch E, being one of the first to do so under the new regulations instituted a year or two previously, 545 He was 69. Walmsley was a native of Manchester and spent most of his working life there.546 ROONEY: THE DETERMINATION OF TRACE AMOUNTS OF [Vol. 83 For some years he was a part-time lecturer at the Manchester College of Technology. He was a competent and resourceful analyst. He had an expert knowledge of crude drugs and was a skilful botanist and a keen gardener. Part of his garden at Wilmslow was devoted to the cultivation of medicinal plants. He played an active part in Manchester pharmaceutical circles, serving in 194647 as President of the Manchester Pharmaceutical Association and in 1955-56 as Chairman of the Manchester, Salford and District Branch of the Pharmaceutical Society. He was a regular visitor to the Annual Meetings of the British Pharmaceutical Conference and occasionally presented papers to its Science Sessions.He joined the North of England Section of the Society for Analytical Chemistry in 1924 and did much to foster and encourage its growth. He attended its scientific meetings with unfailing regularity and served on the Committee for several years. He was Honorary Auditor of the Section for a long period prior to 1953, Vice Chairman in 1953-55 and Chairman in 1955-57. The historical aspects of a subject always appealed to him. He had an especial love of his native city and a considerable and detailed knowledge of its history back to Roman times.For many years he was a member of the Manchester Literary and Philosophical Society and the Manchester Microscopical Society. He loved the open air and the English and Scottish countryside where his knowledge of botany and natural history provided added interest to his excursions. A quiet unassuming man, with a quiet sense of humour, a loyal colleague and a “guide, philosopher and friend” to those less experienced than himself, Walmsley pursued his profes- sion and his many interests with a lively zest. He was a sociable and companionable man, never happier than in the society of his fellow analysts, and he leaves behind him in our Society and in pharmacy a wide circle of friends who will long remember him with affection and think of his passing with regret. Walmsley took a keen interest in all aspects of pharmaceutical life. Walmsley was a studious man whose reading embraced a wide field. Mrs. Walmsley predeceased him by some years, and he left no family. G. J. W. FERREY

ISSN:0003-2654    

DOI:10.1039/AN958830545b

出版商:RSC    

年代:1958

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546 ROONEY: THE DETERMINATION OF TRACE AMOUNTS OF The Determination of Trace Amounts [Vol. 83 of Aluminium in Cast Iron BY R. C. ROONEY (The British Cast Iron Research Association, Bordesley Hall, Alvechurch, Birmingham) A method is described for determining trace amounts of aluminium in cast iron. After preliminary separation of the major constituents by extrac- tion as their diethyldithiocarbamate complexes into chloroform, the aluminium is selectively extracted as cupferrate at pH 4.5. The final determination is made by the polarographic procedure of Willard and Dean. The determination of the acid-insoluble aluminium fraction is described, and the purity of reagents is discussed. The method is also applicable to steel. RECENT work at the British Cast Iron Research Association and elsewhere has shown that small amounts of aluminium can have marked effects on the properties of cast iron, particu- larly with regard to pinholing1 inoculation2 and annealabilit~.~ ,4J5 In order to investigate these effects, it has become necessary to develop analytical methods for determining aluminium at concentrations well below 0.01 per cent.It was also considered desirable t o develop a method to cover the range 0.01 to 0.2 per cent.; this latter figure represents the useful lower limit of the fluoride volumetric method previously developed in these laboratories.6 Colorimetric procedures for iron and steel, in which lake-forming reagents, such as Eriochrome cyanine and aluminon, are used have been reported,',* s9 but these reagents have disadvantages. Close control of conditions is necessary if reproducible results are to be obtained, and the reagents are subject to interferences, especially from iron. Measurement of the colour of aluminium 8-hydroxyquinolat e in chloroform has been used,l0+ but this reagent is again subject to interference by iron and many other constituentsOct., 19581 ALUMINIUM IN CAST IRON 547 of cast iron. Other methods suggested include turbidimetric measurements with cupferron as reagent12J3 and fluorimetric measurements with reagents such as Pontachrome blue- black R.14 The polarographic method of Willard and Dean15 is very successful for steels containing more aluminium than titanium and vanadium, but in cast iron these elements are usually present in far greater amounts than the aluminium. The mercury-cathode separation used by these workers does not separate aluminium from titanium and vanadium, and, when microgram amounts of aluminium are involved, there is interference from the residual amounts of nickel, chromium, lead, etc.in the electrolyte. The chromatographic separation used by Bishop16 suffers from the same defects, as separation from titanium, vanadium, lead, cerium, zirconium, chromium, nickel, cobalt and several other possible micro and semi-micro constituents of cast iron is either not effected by this procedure or only partly effected. The small-scale mercury-cathode electrolysis recommended by Bishop after elution of the aluminium is effective for removing some of these elements, but not all. It is obvious that, in order to determine aluminium satisfactorily by any of the colori- metric procedures at the microgram level, it must be completely separated from all traces of the other constituents of the cast iron.In practice, it was found to be impossible to obtain the aluminium completely free from other metals, especially in a laboratory in which other analysis was being carried out. It was found that air-borne contamination of the solutions with microgram amounts of iron was particularly difficult to prevent, and led to the presence of iron in the final solutions, although it could be shown that, at the intermediate stages, the solutions were completely iron-free. The polarographic procedure is more tolerant to many metals in small amounts, and, if a polarograph with good resolution is used, interfering elements, such as iron, titanium and nickel, can be tolerated so long as their concentration can be reduced below that of the aluminium.Because of this, the polarographic method of determination was used; a cathode- ray polarograph gave the necessary sensitivity and resolution. POLAROGRAPHY- The polarographic determination of aluminium with Solochrome violet RS was investi- gated by using the conditions recommended by Willard and Dean. When 20.0 ml of a 0.05 per cent. aqueous solution of Solochrome violet RS and a final volume of 50 ml were used, a straight-line graph was obtained over the range 50 to 200pg of aluminium. At 40pg, measurement of the aluminium peak became somewhat difficult, owing to the previous reduction of the dye-stuff.A second graph was plotted, for which 5.0 ml of dye solution were used, and it satisfactorily covered the range 10 to 60 p g ; a third graph, for which 1.0 ml of reagent was used, covered the range 1 to 15 pg. The blank value of the cell reagents was originally 4 pg, but, after a considerable amount of work (see “Purity of Reagents,” p. 548) this was reduced to 1 p g ; work below this level was deferred until better reagents are available. These graphs had different slopes, the factors being 1 pA = 24, 14 and 12 pg, respectively. This effect is ascribed to increases in the viscosity leading to lower diffusion coefficients in the solutions containing large amounts of dye-stuff. The range of aluminium that could be determined was further extended by using one-fifth of the volume of all reagents in a final volume of 10 ml.These conditions were used in conjunction with the graph covering the range 1 to 15 pg to give a range of 0-2 to 3.0 pg. Because of the difficulties that were encountered with regard to blank values, this range was rarely used. The effect of various elements under the conditions used for the polarographic deter- mination was next examined. By using 100 pg of each element and 20 ml of dye solution, most of the elements likely to be present with the aluminium were examined. Interference was found to be caused by ferric and ferrous iron, titanium, vanadium, nickel, cobalt, zir- conium and chromium. This agrees with the work of Perkins and Reynolds,l’ who also found interferences from large amounts of cadmium, molybdenum, thorium, antimony, lead, copper and tin.As many of these elements are likely to be present in cast iron at concentra- tions equal to or greater than that of the aluminium, any separation procedure must remove them. SEPARATION OF ALUMINIUM- most likely to be useful was one in which the smallest amounts of reagents were used. EXPERIMENTAL It became obvious duringTthe early part of this work that the separation procedure Great648 ROONEY: THE DETERMINATION OF TRACE AMOUNTS OF [Vol. 83 difficulty was encounteredwith aluminium in thereagents, aluminium in filter-paper, aluminium leached from the glassware and many other sources of contamination. Rosotte’s methodla was used as a starting point for the work, as she had already reported the interference of residual iron after separation at a mercury cathode, together with that of titanium and vanadium, and had overcome this.No mention was made, however, of residual amounts of elements, such as manganese and chromium, which are difficult to deposit completely in mercury. Rosotte removed the residual iron, together with titanium and vanadium, by extraction of the cupferrates at pH 0.3, and, after destroying the excess of cupferron, adjusted the pH to 3.9 and added more cupferron. The turbidity caused by the finely divided aluminium cupferrate was used to determine its concentration, but it seemed preferable to extract this aluminium cupferrate in order to use the more satisfactory method of determination. First, the pH conditions for extraction were examined by using 250 pg of aluminium and 1.0 ml of a 1 per cent.solution of cupferron. The results, corrected for the blank value, were as follows- pH .. .. . . 0.5 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Aluminium found, pg .. Nil 0.35 155 196 240 246 228 209 10.7 From these results it is apparent that a preliminary extraction with cupferron would be satisfactory, provided that the pH is kept below 1.0, and that, for efficient extraction of the aluminium, the pH must lie between 4 and 5. This is readily achieved by the use of an acetate - acid buffer system. Under these conditions, extractions were made over a range of aluminium concentrations (the extractions of 0.1 and 1.0 pg were made at a later stage with lower blank values). The results, corrected for the blank values, were as follows- Extraction, yo .. .. Nil 0.14 62 79 98 99 91 84 4 Aluminium added, pg . . . . 0.1 0.1 1.0 1.0 10.0 50 100 200 Aluminium found, pg . . . . 0.1 0.1 1.2 0.96 9.8 61 96 205 Recovery, % . . .. .. 100 100 120 96 98 102 98 103 The recoveries were considered to be satisfactory. Extraction of 10 pg of aluminium was also successfully accomplished in the presence of 10 mg of phosphorus pentoxide; phosphate in solutions of high-phosphorus irons will therefore not interfere. As 1 pg of aluminium can be determined readily, it was considered likely that aluminium contents of 0.001 to 0-2 per cent. could be determined easily by using a 0-1-g sample of iron: this corresponds to the range of the graphs, 1.0 to 200 pg. For cast irons containing very little nickel, chromium or cobalt, no preliminary separation of these elements should be necessary, so that a direct cupferron separation of iron, titanium, vanadium, etc., could be made, followed by adjustment of pH and extraction of the aluminium.This procedure was used and a blank value of 14 pg was obtained, equivalent to 0.014 per cent. The procedure was applied to a further series of samples after a preliminary separation at a mercury cathode; a blank value of 11 pg was obtained. It became apparent that an investigation of the purity of the reagents was necessary. PURITY OF REAGENTS- The reagents used in the experimental work were examined by various concentration and extraction procedures in order to determine their aluminium contents; some alternative reagents were also examined.The results are shown in Table I. It was found that ashless filter-papers could contribute 2 to 3 pg of aluminium; silica and graphite residues were therefore removed by centrifugation in all the subsequent work. Samples of lead-free perchloric acid, which had been redistilled, were obtained from the British Drug Houses Limited and from Hopkin and Williams Limited. The aluminium contents were found to be of the order of 0.05 to 0.1 p.p.m., which indicates the difficulty associated with the further purification of reagents. It was decided to use lead-free acids when possible and to attempt to purify the cupferron and sodium acetate. Many methods for both reagents were used, including selective solvent extraction with a number of reagents and solvents, ion exchange under various conditions with both anion and cation-exchange resins, recrystallisation and synthesis of the reagents under closely controlled conditions. However, the aluminium content of the reagents wasOct., 19581 ALUMINIUM I N CAST IRON 549 never significantly decreased, and it is suggested that this is probably due to the aluminium in these neutral reagents being present as aged aluminium hydroxide, which would be comparatively unreactive.TABLE I ALUMINIUM CONTENT OF REAGENTS Reagent Grade Perchloric acid . . . . Sulphuric acid . . . . Hydrochloric acid . . .. Nitric acid . . .. .. Hydrogen peroxide, 100-volume Sodium acetate . . . . Cupferron .. .. Sodium diethyldithiocarbamate . . Chloroform . . .. .. a . . . .. .. .. .. Aluminium content, p.p.m. 3.0 1.0 0.65 0.83 0.032 0*088 4.4 <0.001 <0*001 0.25 ..“Lead free, for foodstuffs ana1vsis”t 0.007 Perchloric acid . , Hydrochloric acid . . Nitric acid . . .. * . - ‘ 1 0.034 * Samples of reagents of similar grade were examined and found to have similar aluminium contents. t When aged in glass bottles, the aluminium content rises appreciably. In view of the high aluminium content of cupferron, it was decided to use sodium diethyl- dithiocarbamate for the preliminary separation of iron. This would also remove copper, nickel, cobalt, manganese and vanadium,lS and recent work in our laboratory has shown that the bulk of the titanium is also extracted.lS Any residual titanium will be detected and can be separated. No more attempts were made to purify sodium acetate further; each batch used was tested for aluminium and any very impure batches were rejected.APPARATUS- Oelschlager20 reported that microgram amounts of aluminium could be leached from glassware by a variety of reagents. This work was confirmed, and it was found that a blank value of 6 pg when glass apparatus was used could be reduced to 1.8 pg if silica or polythene apparatus was substituted whenever possible. Silica and polythene apparatus was there- fore used when possible in the subsequent work. APPLICATION OF THE METHOD TO CAST IRON ACID-SOLUBLE ALUMINIUM- Methods were devised for determining aluminium in cast iron and were checked by investigating the recovery of aluminium added to samples of pure iron. The results are shown in Table 11.An outline of the procedures used, which are described fully under “Method,” p. 550, is as follows- Procedure A-Iron extracted as diethyldithiocarbamate from a 0.1-g sample. Blank value = 2.1 pg = 0.0021 per cent. of aluminium. Procedure B-Iron extracted with isobutyl acetate from a 5-g sample. Blank value = 22 pg E 0.00044 per cent. of aluminium. Procedure C-Electrolysis - dissolution procedure on a 5-g sample. Blank value = 1.2 pg = 0.000024 per cent. of aluminium, I t is apparent that the useful lower limit of the method is set by the blank value. In our laboratory, for a figure to be regarded as reliable, it must not be lower after correction than the blank value alone, i.e., the “signal-to-noise” ratio must not be less than 1 to 1. In order to obtain the lowest possible blank value for the lowest aluminium contents, the sample must be dissolved in a very small amount of acid and the bulk of the iron separated by using a minimum of reagents. This problem was solved in an elegant manner by Chirnside, Cluley and Proffit21 in their method for the determination of boron in nickel strip.The solid sample is used as anode in a mercury-cathode electrolysis cell, a small amount of acid is added and dissolution and deposition proceed simultaneously. By using a high current density and feeding the sample into the electrolyte as it dissolves, 5 g of iron can be dissolved550 ROONEY: THE DETERMINATION OF TRACE AMOUNTS OF [Vol. 83 in about 2 hours in only 1-0 ml of perchloric acid. The extraction of the elements remaining in solution (mainly titanium and vanadium) also requires small amounts of reagents.TABLE 11 RECOVERY OF ALUMINIUM ADDED TO SAMPLES OF PURE IRON Aluminium PLg Nil 10 Procedure Basis material added, -[ 1:: A Commercially pure iron . . 200 50 ‘.{ ;:: B Spectrographically pure iron r- 1.0 5.0 C Spectrographically pure iron “i 10 50 Aluminium found (corrected for blank value), Recovery, Pg % 0.9’ - 9.8 OR 52 1 105 1 199 49 98 101 200 101 100 0.98 98 5.0 100 9.9 99 50 100 * This figure is lower than the blank value and should be neglected. If solid samples or the electrolysis apparatus are not available, the lower limit can be extended below 0.002 to about 0.0004 per cent. by using a 5-g sample and extracting the iron with isobutyl acetate. The 11 per cent. loss of aluminium reported by Werz and Neu- berger,22 who extracted the iron with diethyl ether, is not confirmed, and it is suggested that this discrepancy is caused by the relatively high solubility of diethyl ether in hydrochloric acid compared with the almost complete insolubility of isobutyl acetate.For large numbers of samples with aluminium contents greater than 0.0004 per cent., procedure B is often more convenient than procedure C. The interfering elements left in solution in all procedures are most likely to be titanium, cerium, zirconium, etc., if present, and chromium. Of these, titanium, cerium, etc., will be extracted quantitatively with the aluminium as cupferrates, and, if the pH is greater than 4.2 to 4.3, some chromium may also be extracted. The presence of most of these elements with the aluminium will be obvious, however, and they can be removed fairly simply.ACID-INSOLUBLE ALUMINIUM- Because the aluminium present can be partly extracted from filter-papers by acid solutions, it was decided to determine the acid-insoluble fraction on a different sample. This would allow the use of a large sample weight, as the aluminium in the acid used to dissolve the sample would pass through the filter-paper and be discarded; the large sample weight would minimise the effect of the blank values contributed by reagents such as sodium carbon- ate and hydrofluoric and sulphuric acids, which are difficult to purify. It has been found with several samples that the results for acid-insoluble aluminium are erratic; one particularly bad example gave results ranging from 0.00016 to 0.00052 per cent.As other samples gave reproducible results, it is thought possible that there is a tendency to marked heterogeneity in the distribution of the insoluble aluminium throughout some samples. The methods have been applied to a number of samples; representative results are shown in Table 111. I t is considered that these results, with the exception of the insoluble fractions in the samples of grey iron and iron containing 4 per cent. of chromium, show satisfactory reproducibility. METHOD APPARATUS- Normal volumetric glassware is satisfactory, but solutions should not be allowed to remain in contact with it for longer than necessary; pipettes should not be left standing in bottles of reagents. Polythene storage bottles should be filled with concentrated hydrochloric acid and set aside for 48 hours; they should then be washed well with water before use.All beakers should be of silica, with silica or polythene covers.551 Oct., 19581 ALUMINIUM I N CAST IRON TABLE 111 DETERMINATION OF ACID-SOLUBLE AND ACID-INSOLUBLE ALUMINIUM I N SAMPLES OF IRON Acid-soluble aluminium Acid-insoluble aluminium Sample Procedure found, yo found, yo 0.010, 0*011, 0*010 0.0022, 0.0022 0.0022, 0.0022, 0.0020 0*00076, 0.00078 0.0075, 0*0080, 0.0082 0.0013, 0.0012 0.00092, 0*00096, 0.00095 0.00016, 0.00032, 0.00018, 0.00052, 0.00040 Pig iron , . .. .. A Grey iron . . * . * . B Iron containing 4 per cent. of Spectrographically pure iron C 0*00003, 0.00004, 0.00003 Not determined chromium .. .. c 0.00038, 0.00040, 0.00038 0.00045, 0.00072, 040058 For polarography, a cathode-ray polarograph was used to attain maximum sensitivity. The utility of the method will be limited by the instrument available. For procedure C, a 50-ml tall platinum crucible is recommended for the electrolysis, but satisfactory results can be obtained by using pure nickel or stainless-steel crucibles, provided that they do not give rise to high blank values. REAGENTS- Perchloric acid, 5 N-Dilute 500 ml of perchloric acid, sp.gr. 1.54, to 1 litre with distilled water (see “Water” below). For aluminium contents greater than about 0.01 per cent., AnalaR or equivalent grade perchloric acid should be satisfactory; for below 0.01 per cent. of aluminium, redistilled or “lead free for foodstuffs analysis” perchloric acid should be used.It is advisable to dilute the lead-free acid as soon as received and to store it in a polythene bottle. Hydrochloric acid, sp.gr. 1.18-For aluminium contents greater than about 0.01 per cent., AnalaR or equivalent grade is satisfactory. For lower aluminium contents, the “lead free for foodstuffs analysis” acid should be used, preferably stored in polythene. Nitric acid, sp.gr. 1-42.-Use the grades of reagent as described for hydrochloric acid, but do not store in polythene. Chloro form-AnalaR or equivalent grade is satisfactory. Acetic acid, glacial-AnalaR or equivalent grade is usually satisfactory. For very low aluminium contents, it may be necessary to redistil the acid. Sodium acetate solution, 2 M-Dissolve 272 g of the purest hydrated sodium acetate available in water and dilute to 1 litre.Sodium diethyldithiocarbamate solution, 20 per cent.-Dissolve 20 g of AnalaR or equivalent grade sodium diethyldithiocarbamate in water and dilute to 100 ml. This solution must be freshly prepared. Cupferron solution, 1 per cent.-Dissolve 1 g of the purest available cupferron in 100 ml of water and spin in a centrifuge at 10-cm radius and 2000 r.p.m. for 3 minutes. Use the supernatant liquid. This solution must be freshly prepared. isoButyl acetate-Analytical-reagent grade is usually satisfactory. If high blank values are obtained, the reagent can be purified by shaking it for about 10 minutes with half its own volume of 5 N hydrochloric acid. Solochrome violet RS solution, 0.05 per cent.-Dissolve 0.5 g of the pure dye-stuff in 1 litre of distilled water and store in a polythene bottle.Water-For the earlier stages of the method, distilled or de-ionised water is satisfactory, but the solutions used in the base electrolyte must be made up with distilled water. De- ionised water can give rise to spurious polarographic waves and false figures.= Standard aluminium solution A-Dissolve exactly 2.5 g of high-purity aluminium in hydrochloric acid, add 50 ml of perchloric acid and evaporate to the appearance of fumes. Cool, and dilute to 500 ml. This solution is stable indefinitely. 1 ml = 0.005 g of aluminium. Distilled water must be used for this solution. Standard aluminium solution B-Dilute 2.0 ml of solution A to 1 litre with redistilled water.This solution should be freshly prepared as required. 1 ml = 10 pg of aluminium.552 ROONEY: THE DETERMINATION OF TRACE AMOUNTS OF [Vol. 83 This solution should be freshly prepared as required. PREPARATION OF CALIBRATION GRAPHS- Graph for 40 to 200 pg of aluminizcm-In a series of 50-ml calibrated flasks place 0, 4, 8, 12, 16 and 20-ml portions of standard aluminium solution B, and add 1 drop of methyl red indicator solution. Make just alkaline by adding N sodium hydroxide, and then add 1.0 ml of 5 N perchloric acid. Add 5.0 ml of 2 M sodium acetate solution, 20 ml of 0.05 per cent. Solochrome violet RS solution and dilute to the mark. Immerse the flasks in a water bath at 55" to 70" C for 5 minutes, and then cool a.nd record polarograms between -0.50 and -0.85 volt against the internal pool anode; the aluminium peak occurs at about -0.72 volt.Plot a graph of microamperes against micrograms of aluminium per 50 ml, subtracting the blank value from all readings in order to make the line pass through the origin. Graph for 10 to 60% of aluminium-Proceed as for the preparation of the graph for 40 to 200 pg of aluminium, but use 0, 1, 2, 3, 4, 5 and 6-ml portions of standard aluminium solution B and 5.0 ml of Solochrome violet RS solution. Immediately after diluting to the mark, transfer the solutions to 50-ml stoppered polythene bottles for the period of heating. Graph for 1 to 15 pg of aluminium-Proceed as for the preparation of the graph for 10 to 60 pg of aluminium, but use 0,1,3,5,7,10,12 and 15-ml portions of standard aluminium solution C and 1.0 ml of Solochrome violet RS solution.These solutions will need to be de-oxygenated very thoroughly. PROCEDURE FOR DETERMINING ACID-SOLUBLE ALUMINIUM- A . Aluminium contents from 0.002 to 0.2 per cent.-Weigh 1.0 g of sample into a 150-ml squat beaker and dissolve without heating in 20 ml of diluted hydrochloric acid (1 + 1). When dissolved, cool, and dilute to the mark in a 100-ml calibrated flask. Transfer im- mediately to a polythene centrifuge tube and spin in a centrifuge at 10-cm radius and 2000 r.p.m. for 2 to 3 minutes. By pipette, place 10 ml of the supernatant liquid (= 0.10 g of sample) in a 150-ml conical separating funnel and add 5.0ml of acetic acid, 10ml of sodium acetate solution and 20 ml of sodium diethyldithiocarbamate solution.Shake the separating funnel for 10 to 20 seconds, add 30ml of chloroform, and shake vigorously for 30 seconds. Allow the two layers to separate, rinse the stopper and neck of the funnel with chloroform from a polythene wash-bottle in order to remove particles of precipitate adhering to them, and run off the chloroform layer. Add a further 10 ml of chloroform, shake again, and allow the layers to separate. Add a few drops of sodium diethyldithio- carbamate solution to test for completeness of precipitation; there should be a white pre- cipitate. If the precipitate is coloured, add 5 ml of sodium diethyldithiocarbamate solution, and shake to extract the precipitate in the chloroform layer. Again test for completeness of precipitation; repeat until a white precipitate is obtained when sodium diethyldithiocar- bamate solution is added.Shake, allow the two layers to separate, and then run off the chloroform layer. Extract the aqueous layer with 10-ml portions of chloroform, washing the neck and stopper of the funnel with chloroform after each extraction until the chloroform layer is perfectly colourless (25 ml of sodium diethyldithiocarbamate solution and 50 to 60 ml of chloroform should be sufficient). Discard the chloroform extracts and wash the stem of the funnel with chloroform, removing any stubborn particles with a "spill" of filter-paper. To the aqueous solution in the separating funnel, add 1.0 ml of cupferron solution and set aside for 1 to 2 minutes. Add 15 ml of chloroform, shake vigorously for 30 seconds, and allow the two layers to separate. Note whether the chloroform extract is perfectly colourless or coloured.Run the chloroform layer into a 50-ml beaker, and repeat the extraction with 10 and then 5ml of chloroform, adding these extracts to the 50-ml beaker. Evaporate the chloroform extracts to dryness and add 1.0 ml of nitric acid and 2.0 ml of 5 N perchloric acid. Keep the beaker covered with a well fitting lid in order to minimise loss of perchloric acid, and evaporate to fumes of perchloric acid; continue heating until all organic matter has been destroyed. If the chloroform extract is green owing to the co- extraction of a small amount of chromium from high-chromium irons, the residue in the beaker will probably be orange at this stage, owing to the oxidation of chromium.If chromium is present, add a further 2.0 ml of 5 N perchloric acid, evaporate to the appearance of fumes, and remove the lid. Add 0.5 to 1.0ml of hydrochloric acid to volatilise the Standard aluminium solution C-Dilute 20 ml of solution B to 200 ml with water. 1 ml = 1 pg of aluminium.Oct., 19581 ALUMINIUM I N CAST IRON 553 chromium as chromyl chloride, replace the lid, and again evaporate to the appearance of fumes. If sufficient chromium is left to colour the residue, add a further 0.5 ml of hydro- chloric acid. Continue this procedure, adding more perchloric acid if necessary to maintain the volume, until no orange colour is obtained on further heating to fumes. One addition of hydrochloric acid is usually sufficient. When all organic matter and chromium have been removed, remove the lid and evaporate to dryness.If the chloroform extract is colourless or pale green, proceed as follows. Dissolve the residue in 1.0 ml of 5 N perchloric acid and transfer the solution to a 50-ml calibrated flask. Add 5.0 ml of 2 M sodium acetate and 1.0, 5-0 or 20.0 ml of Solo- chrome violet RS solution, according to the amount of aluminium present. Dilute to the mark with distilled water, and, if 1.0 or 5.0ml of dye solution were used, transfer the solution to a screw-top polythene bottle. Complete the determination as for the preparation of the calibration graphs and read the aluminium contents corresponding to the step or peak heights from the appropriate curve. If the chloroform extract is yellow or brown, owing to the presence of titanium or iron, proceed as follows. Dissolve the residue in 1.0 ml of 5 N perchloric acid and transfer the solution to a 150-ml conical separating funnel.Adjust the volume to 50 to 60 ml and add 1.0 ml of cupferron solution. Add 10ml of chloroform, shake for 30 seconds, and then allow the two layers to separate. Run off the chloroform layer, and wash the aqueous layer with a further 10 ml of chloroform. Continue to shake with 10-ml portions of chloroform until the extract is colourless; two 10-ml portions are usually sufficient. Add 10 ml of 2 M sodium acetate solution, shake, and add 1.0ml of cupferron solution. Extract the aluminium as before, and complete the determination as described. A blank determination must be carried out by treating the reagents alone in the manner described for the sample. If a batch of samples is processed, one blank determination is sufficient, but all samples must then be processed similarly, even though some may contain no chromium or titanium.Unless these samples are processed identically with any that do contain chromium or titanium, and with the blank determination, the correction applied for the blank value will no longer be accurate. B. Aluminium contents from 0.0004 to 0.004 per cent. in plain cast irons only-Weigh 5 g of sample into a 400-ml beaker and dissolve it in 40 ml of hydrochloric acid and 10 ml of nitric acid without heating. When dissolved, cool, and transfer the solution to a centrifuge tube, washing with concentrated hydrochloric acid from a polythene wash-bottle.Spin in a centrifuge at 10-cm radius and 2000 r.p.m. for 3 minutes, and then transfer the super- natant liquid to a 250-ml conical separating funnel. Add 150 ml of isobutyl acetate, and shake for 30 seconds. Allow the two layers to separate and run the lower (acid) layer into a 150-ml beaker. Evaporate to dryness, add 5.0 ml of nitric acid and 4.0 ml of 5 N perchloric acid, and then evaporate to fumes of perchloric acid. When all organic matter has been destroyed, cool, and transfer the solution to a 150-ml separating funnel. Add 15 ml of 2 M sodium acetate and 20 ml of 20 per cent. sodium diethyldithiocarbamate solution. Extract the interfering elements and then the aluminium, and complete the determination as for procedure A .C. Aluminium contents less than 0.0004 per cent. in plain cast irons or less than 0.005 per cent. in alloy cast iron-Solid samples must be used for this determination and they should be pencil shaped. Weigh the sample and calculate the approximate length that will corre- spond to the desired weight of sample. Set up a cell as described by Chirnside, Cluley and Proffit,21 with a 50-ml platinum crucible containing a 20-ml pool of mercury. The crucible is connected to the cathode lead, and 20 ml of water and 2.0 ml of 5 N perchloric acid are added. Connect the sample to the anode lead by means of a crocodile clip, and electrolyse at 3 to 5 amperes. Lower the sample into the solution as it dissolves, and maintain the volume of electrolyte at about 20ml by the addition of water.It is advantageous to cool the crucible in running water if possible and to stir the mercury pool with a bone spatula from time to time. When the calculated length of sample has dissolved, remove, wash and dry the sample, and re-weigh it in order to obtain the weight dissolved. With a flat spiral of platinum wire as anode, continue to electrolyse until the electrolyte gives no test for iron. Disconnect the leads and decant the solution from the mercury into a polythene centrifuge tube, washing with water. If this operation is carried out quickly, the amount of iron that will re-dissolve is very small. Spin in a centrifuge at 10-cm radius and 2000 r.p.m. for 2554 ROONEY [Vol. 83 minutes in order to remove any insoluble residue of silica, graphite, etc., and transfer the supernatant liquid to a 150-ml squat beaker.Add 2 or 3 drops of 100-volume hydrogen peroxide, and boil for a few minutes to destroy excess of peroxide. Cool, and transfer to a 150-ml conical separating funnel. Add 1.0 ml of 1 per cent. cupferron solution, shake, and extract the precipitate in 10 ml of chloroform. Add a further 1.0 ml of cupferron solution, and, if a coloured precipitate forms, shake once more to extract it in the chloroform layer. Continue until the precipitate obtained is white; this should not require more than 3 or 4 ml. Shake for 30 seconds, allow the two layers to separate, and run off the chloroform layer. Extract the aqueous layer with further 10-ml portions of chloroform until the chloroform layer is colourless; add 20 ml of 2 M sodium acetate and then 1 ml of 1 per cent.cupferron solution. Extract the aluminium and complete the determination as for procedure A . PROCEDURE FOR DETERMINING ACID-INSOLUBLE ALUMINIUM- Weigh a 10-g sample into a 400-ml beaker and dissolve it in 100 ml of diluted hydrochloric acid (1 + 1). Boil, and filter through a No. 541 filter-paper of the smallest convenient size, washing well with hot dilute hydrochloric acid (1 + 19). Dry and ignite in a platinum crucible at 700" to 800" C until all carbonaceous matter has been destroyed. Treat the residue with 2 or 3 ml of hydrofuoric acid and 10 drops of dilute sulphuric acid (1 + 4), and then heat on a radiation bath until all the silica has been volatilised and white fumes of sulphur trioxide appear.Add a further 10 drops of dilute sulphuric acid (1 + 4) and again evaporate to dryness. Add 5 ml of hydrochloric acid, 1 or 2 drops of nitric acid and evaporate just to dryness. Dissolve the residue in 1.0 ml of hydrochloric acid, and transfer the solution to a 150-ml separating funnel. Add 5.0 ml of acetic acid and 10 ml of 2 M sodium acetate, shake, and then add 10 ml of sodium diethyldithiocarbamate solution. Complete the determination as for pro- cedure A (see Note). A blank determination must be carried out on the reagents, including the filter-paper and the hydrochloric acid used to dissolve the sample. NOTE-If the acid-insoluble aluminium content is in excess of 0.002 per cent., 1.0 ml of cupferron solution may be insufficient for precipitation.This will be shown by the formation of a coagulated precipitate of aluminium cupferrate rather than a milky suspension; the most satisfactory procedure then is to extract the aluminium in the chloroform layer and add a further 1.0 ml of cupferron solution, If a precipitate forms, extract this in the chloroform and continue until no further precipitate forms. The determination should then be carried out on an aliquot of the final solution containing less than 200 pg of aluminium; the size of aliquot to be taken can be approximately determined from the relationship between cupferron and aluminium, i.e., 1 ml of 1 per cent. cupferron solution is approximately equivalent to 500 p g of aluminium. I thank the Director and Council of the British Cast Iron Research Association for Evaporate to dryness, but do not bake. Fuse the residue with 1.0 g of sodium carbonate and leach the melt with hot water. permission to publish this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 11. 18. 19. 20. 21. 22. 23. REFERENCES Dawson, J. V., and Smith, L. W. L., B.C.I.R.A. J. Res. and Dev., 1956, 6, 226. Dawson, J. V., Ibid., 1957, 7 , 2. Khoroshev, I. I., Dokl. Akad. Nauk SSSR, 1954, 94, 221. Palmer, S. W., Proc. Inst. Brit. Foundrym., 1946/1947, 40, 64~. Taub, A,, Foundry, 1955, 83, 131. Clarke, W. E., and Rooney, R. C., B.C.I.R.A. J . Res. and Dev., 1957, 6, 666. Wacykiewicz, K.. Prace Inst. Minist. Hutn., 1955, 7, 35. Short, H. G., Analyst, 1950, 75, 420. Jean, M., Anal. Chim. Acta, 1954, 10, 526. Wiberley, S. E., and Bassett, L. G., Anal. Cham., 1949, 21, 609. Kassner, J. L., and Ozier, M. A., Ibid., 1951, 23, 1453. Rocquet, P., Rev. Mdtall., 1943, 40, 276. Rosotte, R., Chim. Anal., 1956, 38, 250. Weissler, A., and White, C. E., Ind. Eng. Chem., Anal. Ed., 1946, 18, 530. Willard, H. H., and Dean, J . A., Anal. Chem., 1950, 22, 1264. Bishop, J. R., Analyst, 1956, 81, 291. Perkins, M., and Reynolds, G. F., Anal. Chim. Acta, 1958, 18, 616. Bode, H., 2. anal. Chem., 1955, 144, 165. Rooney, R. C., Anal. Chim. Acta, in the press. Oelschlager, W., Z . anal. Chem., 1957, 154, 329. Chirnside, R. C., Cluley, H. J., and Proffit, P. M. C., Analyst, 1957, 82, 18. Werz, W., and Neuberger, A., Arch. Eisenhicttenw., 1955, 26, 205. Ferrett, D. J., Milner, G. W. C., and Smales, A. A., Analyst, 1954, 79, 731. Received December 13th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300546

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Oct., 19581 BLUNDY 555 The Determination of Chromium by a Solven t-extraction Met hod BY P. D. BLUNDY (Chemical Engineering Division, A.E.R.E., Harwell, nr. Didcot, BerRs.) A method is described for the determination of small amounts of chromium in the presence of similar amounts of iron and nickel in solutions 0.04 M in uranium and 0.005 M in copper. The chromium is oxidised to chromate with ammonium hexanitratocerate in hot acid solution. The chromate is ex- tracted with isobutyl methyl ketone from a solution M with respect t o hydro- chloric acid at a temperature of < 10" C. The chromate is then extracted from the isobutyl methyl ketone by two successive water washes and is determined colorimetrically xith diphenylcarbazide. In the presence of 100 pg each of nickel and iron, chromium was determined in the range 10 t o 100 pg with a mean recovery of 100.3 per cent.and a standard deviation of 10.8 per cent. A METHOD was required for determining 1 to 100 pg of chromium in solutions 0.04 M in uranium, 0.005 M in copper and containing 1 to 100 pg each of iron and nickel. Chromium, iron and nickel arise from corrosion of a stainless-steel containing vessel at high temperature and pressure. The colorimetric determination of chromium with diphenylcarbazide after oxidation to chromate is the most sensitive method known. The critical stage in this procedure is the oxidation of chromium to chromate. Several methods have been described for this oxidation and they are summarised in Table I. Some were tried in this laboratory, but, at the low concentrations of chromium involved, complete oxidation was evidently not achieved, the results being neither reproducible nor in agreement with those for pure dichromate solutions.TABLE I METHODS FOR THE OXIDATION OF TERVALENT CHROMIUM Oxidant Method for destroying Medium excess of oxidant Results Sulphuric acid Boiling Not reproducible Sulphuric acid and a Boiling Not reproducible Orthophosphoric acid Boiling Thorium phosphate trace of silver nitrate precipitated azide or hydrochloric acid hydrochloric acid are evolved Acid solution Decomposition with Not attempted Potassium bromate Perchloric acid - Evaporation until fumes Not attempted Ceric sulphate or ammonium Hot acid solution Addition of sodium Complete oxidation Ammonium persulphate Potassium permanganate Sulphuric acid, 0.5 N Addition of sodium Sot reproducible hexanitratocerate azide or sodium and good reproduci- Willard and Young1 describe a volumetric method for chromium in which ceric sulphate in acid solution at a temperature of 100" C is used as oxidant.Excess of ceric ions may be destroyed with sodium azide or sodium nitrite, the former being preferred. The literature contains conflicting reports about the elements that interfere in the chromate - diphenylcarbazide reaction. A variety of solvent systems are suggested for preparing diphenylcarbazide reagent solution. Urone2 studied this problem and found that acetone and ethyl acetate give the most stable reagent solutions. Bryan and Dean3 describe the use of isobutyl methyl ketone (hexone) as a selective solvent for chromate from M hydrochloric acid before a flame-photometric determination of chromium.The selective action of hexone for chromate is fully described by Weinhardt and H i ~ s o n . ~ nitrite bility556 BLUNDY: THE DETERMINATION OF CHROMIUM BY [Vol. 83 It was decided, therefore, to utilise the hexone extraction of chromium, after oxidation to chromate by ceric solutions, for the separation from interfering elements before a colorimetric determination with diphenylcarbazide. EXPERIMENTAL CERIC OXIDATION- Aliquots of chromium potassium sulphate solution containing 10 to 100 pg of chromium111 were placed in 40-0-ml centrifuge tubes. Two millilitres of 4 N sulphuric acid and 2.0 ml of approximately 0.02 N ammonium hexanitrat,ocerate were added.These solutions were diluted to about 15.0ml and the tubes were immersed in boiling water for 25 minutes. They were then removed and cooled to <lo" C. Sodium azide solution (2.0 per cent.) was added dropwise with swirling to destroy the excess of ceric ions. The solutions were then transferred to 100-ml calibrated flasks containing 3.0 ml of 4 N sulphuric acid and diluted to approximately 90 ml. Two millilitres of a 1.0 per cent. solution of diphenylcarbazide in acetone were added to each flask and the solutions were made up to the mark. After they had been set aside for 5 minutes, the optical density of each solution was measured in 2-cm cells with a Spekker absorptiometer, Ilford No. 605 filters being used, The procedure was then repeated with aliquots of potassium dichromate solution over the range 10 to 1OOpg of chromium.The results agreed with those for the chromium potassium sulphate solutions and also with those found for potassium dichromate solutions in which the ceric oxidation had been omitted. SOLVENT EXTRACTION- Aliquots of potassium dichromate solution containing between 10 and 100 pg of chromiumv1 were taken and the ceric oxidation procedure was repeated as far as the cooling stage, and then 8.0 ml of 4 M hydrochloric acid were added while the solutions were cooling. Each solution was then transferred to a 100-ml graduated separating funnel and was diluted to 32 ml with water, which made each solution M with respect to hydrochloric acid. Twenty millilitres of hexone saturated with M hydrochloric acid were then added to each.After they had been shaken for 1 minute, the layers were allowed to separate and the aqueous layers were run off and discarded. The hexone layers were then washed twice with 20.0-ml portions of water and the washings were run into 100-ml calibrated flasks containing 5.0 ml of 4 N sulphuric acid. The diphenylcarbazide colours were developed and the optical densities were measured in the same way as before. The procedure was repeated with a solution of chromium potassium sulphate; the results were in good agreement with those for the potassium dichromate solution. About 97 per cent. of the chromium is recovered by the extraction, but the loss can be compensated for by incorporating the extraction in the calibration procedure. The mean temperature of the solutions during oxidation was 93" C and before extraction it was <lo" C.EFFECT OF INTERFERING IONS- Cations-Suitable amounts of elements that might interfere in the determination were added, singly and together, to solutions containing 50 pg of chrorniumv1. Colours were developed with diphenylcarbazide and the optical densities were measured with a Spekker absorptiometer. It was found that, when the solutions contained copper or iron, the colour faded rapidly, but, in the other solutions, the colour was stable for at least 2 hours. The results in Table I1 show that uranium, thorium and nickel do not interfere, but iron and copper cause low results. Identical results were obtained from solutions of tervalent chromium, which were oxidised to the sexavalent state by ceric oxidation, the excess of ceric ions being removed with sodium azide.Table I1 also shows results obtained when ceric oxidation was followed by solvent extraction. Interference from iron and copper was greatly reduced, and a twenty-fold excess of these elements produced individual errors of 2 per cent. or less. The combined interference of solution A was apparently slightly greater, but much less than without the solvent-extraction stage. As the chromium to be determined . in these solutions arose from the corrosion of stainless steel, the ratio of iron to chromium was unlikely to exceed 20. It was only necessary to take a 1.0-ml aliquot for the deter- mination of 10 pg of chromium, and hence the copper present was not likely to exceed 0.3 mg.To test the accuracy and precision of the method, forty-four replicate determinations were carried out at 10 to 90-pg levels of chromium in the presence of 11.4 mg of uranium, 0.305 mgOct., 19581 A SOLVENT-EXTRACTION METHOD 667 of copper, 0.106 mg of nickel and 0.105 mg of iron. The mean recovery was 100.3 per cent. and the standard deviation was & 0.8 per cent. TABLE I1 Each solution contained 50 pg of chromium EFFECTS OF INTERFERING ELEMENTS AND OF SOLVENT EXTRACTION Colour develo$ed from chromiumv1 solution without solvent extraction- Amount of uranium added, mg 0.0 5.0 10.0 20.0 50.0 Amount of chromium found, pg 50.0 50.0 49.8 50.0 49.8 Amount of thorium added, mg 0-0 100 200 300 400 Amount of chromium found, pg 50.0 50.1 50.0 50.2 50.0 Amount of nickel added, mg 0.0 0.20 0053 1.06 5.28 Amount of chromium found, pg 50.0 50.0 49.9 49.8 60.0 Amount of copper added, mg 0.0 0,193 0-386 0,579 0.772 0.963 2.0 5.0 Amount of chromium found, pg 50.0 46.3 45.9 45.7 45.7 45.4 43.2 42.6 Amount of iron added, mg 0.0 0.255 0.510 0.765 1.02 1-25 2.60 6.25 Amount of chromium found, pg 50.0 47.7 46.5 45.7 45.7 43.5 43.5 44-0 Amount of chromium found, pg 50.0 44.0 42.7 40.7 Amount of copper added, mg 0.0 0.2 0.4 0.6 0.8 1.0 1.93 4.8 Amount of chromium found, pg 50.0 49.7 49.7 49.7 49.4 49.2 48.9 47.0 Amount of iron added, mg 0.0 0.255 0,510 0.765 1.02 1.25 2.50 6.25 Amount of chromium found, pg 50.0 49-7 49.8 49.2 49.0 48.2 47.2 46.5 Amount of solution A added, ml* 0.0 0.5 1.0 2.0 Amount of chromium found, pg 50.0 49.5 49.1 49.8 Amount of solution A added, ml* 0.0 0-5 1.0 2.0 Colour developed after ceric oxidation and solvent extraction of chromium111 solution- * Solution A contained, per millilitre, 11.4 mg of uranium, 0.305 mg of copper, 0,1056 mg of nickel Anions-Oxidations were carried out in the presence of 400 mg of nitrate ion and trace and 0.1251 mg of iron.' amounts of chloride, perchlorate and fluoride ; no interference was observed. REAGENTS- Ammonium hexanitratocerate, 0.02 N-Dissolve 10,965 g of analytical-reagent grade am- monium ceric nitrate, (NH,),Ce(NO,),, in water. Make the solution N with respect to sulphuric acid when diluted to 1 litre. Sulphuric acid, 4 N. Hydrochloric acid, 4 M. Hexone saturated with M hydrochloric acid-Shake 500 ml of isobutyl methyl ketone with 500 ml of M hydrochloric acid, and allow the layers to separate. Run off the aqueous layer and pass the solvent layer through a Whatman No.1 filter-paper into a clean dry bottle. Diphenylcarbazide solution, 1 per cent. w/v-Dissolve 0.5 g of diphenylcarbazide in acetone and dilute to 50.0 ml with acetone. Standard chromium potassium sulphate solutiort, 1.00 mg per ml-Dissolve 4.8031 g of analytical-reagent grade chromium potassium sulphate, CrK(SO4)J2H,O, in water, add a few millilitres of 4 N sulphuric acid and dilute to 1 litre. For calibration purposes, dilute 10.0ml of this solution to 1 litre. PROCEDURE- Place an aliquot containing 10 to 90 pg of chromium in a 40-ml centrifuge tube. Neutralise any excess of free acid with ammonium hydroxide, and then make slightly acid with sulphuric acid.If ferrous iron is known to be present, oxidise it to the ferric state with 0.02 N am- monium hexanitratocerate. Add 2.0 ml of 4 N sulphuric acid and 2.0 ml of 0.02 N ammonium hexanitratocerate, dilute to about 15 ml, and immerse in boiling water for 25 minutes. Remove, and cool to <lo" C. Add 8.0 ml of 4 M hydrochloric acid while the solution is cooling. Transfer to a 100-ml calibrated separating funnel, and dilute to 32 ml with water. Add 20.0 ml of hexone saturated with M hydrochloric acid. Shake for 1 minute, allow the layers to separate, and then run off and discard the aqueous layer. Add 20.0 ml of water to the separating funnel, and shake for 1 minute. When the layers have separated, run the METHOD' Prepare this solution freshly each day.558 BLC'KDY AXD SIMPSON: THE DETERMIXATION OF [Vol.83 aqueous layer into a 100-ml calibrated flask containing 5.0 ml of 4 A' sulphuric ticid. Repeat the washing with a further 20.0 ml of water, and add it to the previous washings. Dilute to about 90 ml, and add 2-0 ml of 1 per cent. diphenylcarbazide solution. Dilute to the mark and set aside for 5 minutes. Measure the optical density against water in 2-cm cells with a Spekker absorptiometer, llford No. 605 filters and a mercury-vapour lamp being used. Prepare a blank solution in the same manner and measure its optical density against water. Prepare a calibration graph from aliquots of chromium potassium sulphate solution in the range 10 t o 9Opg of chromium, to which interfering elements in the concentrations expected in the samples have been added. CONCL~SIOSS Compared with other published methods, the proposed method has been found tobe rapid and reliable. The interference from iron is not likcly to exceed 2 per cent. in the worst conditions envisaged. The method has been extended t o solutions obtained from the erosion and corrosion of stainless steel by thoria slurries. 1 thank Mr. W. H. Hardwick and Mr. K. Todd for helpful discussions during this work, and hlr. M. P. Sirnpson, who carried out some of the earlier experimental work. REFERENCES 1. 2. 3. 4. Willard, H. H., and Young, P., J. Amer. Chena. SOC., 1929, 51, 139. Crone, Y. F., Anal. Chem., 1955, 27, 1354. Bryan, 11, A, and Dean, J. X., Ibid., 1957, 29, 1289. Weinhardt, A. E., and Hixson, A. N., Ind. EnR. Clietn., 1951, 43, 1676. Received Februmy 26fh, I958

ISSN:0003-2654    

DOI:10.1039/AN9588300555

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

558 BLC'KDY AXD SIMPSON: THE DETERMISATION OF The Determination of Nickel [Vol. 83 a Solvent-extraction Method BY P. D. BLUNDY AND 11, P. SIMPSON (Chemical Engineering Division, A .E. R.E., Harwell, 921. Didcot, Bevks.) A method is described for the rapid determination of nickel in solutions containing uranium, thorium, copper, iron and chromium. The aqueous insoluble 4-methylcyclohexane- 1 : 2-dionedioxime complex of nickel is ex- tracted with toluene, and the optical density of this phase is measured with a Spekker absorptiometer, a Hilger H556 filter being used. Interference by copper is suppressed with thioglycollic acid, and tartaric acid is used to prevent formation of iron thioglycollate. Tartrate also prevents the hydrolysis of thorium. A RAPID method for determining small amounts of nickel in solutions containing uranium, thorium, copper, iron and chromium was required.Methods in which ion-exchange tech- niques are used have been developed' for radioactive solutions containing these elements, but the procedures are extremely exacting and time-consuming. Many analogues of dimethylglyoxime have been suggested for colorimetric and gravi- metric determinations of nickel. The nickel complexcs can be extracted with organic solvents, e.g.) nickel has been determined absorptiometrically after extraction of its x-furildioxime complex with chloroform.2 This method was tried in our laboratories, but the results werc not reproducible, and further, the range of 0 to 20 pg was too limited for our requirements. Banks and Hooker3 described a reagent 4-methylcyclohexane-1 : 2-dionedioxime (Q-methyl- nioxime), for the gravimetric determination of nickel in the pH range 3 to 7.They studied the interference of some twenty-nine elements. rind tlicir results suggested that the reagent would he suitable for our purpose. I.: x PE KIM E ST AL Approximately SO pg of nickel were precipitated with a 0.1 per cent. aqueous solution of 4-methylnioxime from a solution buffered at pH 5 to 5.5 with ammonium acetate. The red precipitat e first appeared as a. colloid, which rapidly coagulntcd under thcsc conditions.Oct., 19581 NICKEI. BY A SOLVENT-EXTRACTION METHOD 559 Attempts were made to extract the precipitate with a variety of organic solvents; the results are shown in Table I. loluene was found to be the best solvent, extraction being rapid and complete in one stage.The organic phase was yellow, and, when measured with a Unicam spectrophotometer, showed a broad absorption band with a maximum a t 340 mp. (The molar extinction coefficient at 365 mp is 3340.) The colour WAS stable for at least 2 hours, and Beer's law was obeyed over a concentration range of 5 to 200 pg of nickel per 2.5 ml of toluene. TABLE 1 SOLUBILITY OF NICKEL - 4-METHYLNIOXIME COMPLEX I N VARIOUS ORGANIC SOLVENTS Extractions were carried out from solutions containing 100 pg of nickel and 1.0 ml of 10 per cent. w/v sodium acetate solution Solvcnt Solutility Colour of solvcnt phase isoUiityl nicthyl kctonc (industrial) . . Slightly soluble Faint ycllow ('hloroform . . .. .. . . . . Slightly soluble Pale yellow ('arlmn tctrachloride .. . . . . Slightly soluble Pale ycllow i.w.imyl alcohol . . .. .. . . Slightly solublc Red str.-Butyl alcohol . . . . .. . . Sliglitlv soluhle Red Di-n-btityl ether . . . . . . . . Insoluble - iaolhtyl methyl ketone (purc) . . .. Insoluble - rycloHcxane . . .. . . .. . . Insoluble - 7r-fIcxane . . .. .. .. .. Insoluble - Ethyl acetate . . .. . . .. Insoluble - Rcnzene . . . . . . .. . . Rcadily soluble Yellow 'Toluene . . .. .. . . . . IIighly soluble Yellow EFFECT OF ISTERFERINC IONS- Cations-For each of the ions expected to accompany nickel in sample solutions, the following procedure was used to determine individual and collective interference. .4 solution containing a suitable concentration of the interfering element or elements was buffered at pH 4 with ammonium acetate.One millilitre of 0.1 per cent. 4-methylnioxime solution was added and the solution was extracted with toluene. Precipitation was not apparent in any solution. Tartaric acid was added to the solution containing thorium to prevent hydrolysis. l'he absorption spectra of the tolueiie phases were examined; those derived from solutions containing uranium, thorium, iron and chromium showed no absorption in the region of 365 mp, the wavelength transmitted by a Hilger I-1556 filter. In this region, however, copper caused an absorption band similar to that of nickel. Various methods of masking were tried, e.g., ethylenediaminetetra-acetic acid, ammonia, citrate, tartrate, cyanide and ammonium tliiocyanate after reduction of copper to the cuprous form with sulphur dioxide, but none was satisfactory.Pellowe and Hardy4 described the use of thioglycollic acid for masking copper in the analysis of aluminium. I t was found that 1.0 ml of 10 per cent. thioglycollic acid solution prevented formation of the copper - 4-methylnioxime complex. I t was then necessary to add tartaric acid and to use sodium hydroxide instead of ammonium hydroxide for neutralising free acid to prevent interference from iron thioglycollate. In the presence of tartaric acid the optimum pH was 5 to 5.5. A12ions--.Extractioris were carried out in solutions containing a hundred-fold excess of sulphate, chloride and nitrate without interference. In the presence of citrate, precipitation was retarded and recoveries were low.METHOD KEAGESTS- Sodium Iydroxide, 2 X. Thioglycollic acid solution, 10 per cenf. ;~/v--Dissolve 10.0 ml of analytical-reagent grade thioglycollic acid in water and dilute to 100 ml. The solution is stable for about 1 month. Sodium acztate solution, 10 per cent. w/u. Tartaric acid solution, 20 per cent. wlv. Chfethylnioxime solution, 0.1 per cent. w/r!--l)issolve 0.1 g of 4-methylcyclohexane-1 : 2- Standard nickel solution-Dissolve approximately 24 g of nickel sulphate, NiS0,.7H20, dionedioxime in water and dilute to 100 ml. in water and dilute to 1 litre. The solution is stable indefinitely. Standardise the solution gravimetrically.560 BLUNDY AND SIMPSON: THE DETERMINATION OF [Vol. 83 Place an aliquot containing 5 to 100 pg of nickel in a 50-ml beaker, and add sufficient 20 per cent.w/v tartaric acid solution to prevent hydrolysis of thorium. Add 1.0 ml of 10 per cent. w/v sodium acetate solution, and adjust the pH to between 5 and 5.5 with 2 N sodium hydroxide. Transfer the solution to a 100-ml separating funnel, add 1.0 ml of 0.1 per cent. 4-methylnioxime solution, and dilute to 30 ml with distilled water. Add exactly 25 ml of sulphur-free toluene, and shake for 2 minutes. Allow the layers to separate and run off the aqueous layer. Pass the solvent layer through a Whatman No. 1 filter-paper, to remove the last traces of water, into a clean dry 2-cm absorptiometer cell, and cover the cell to prevent evaporation. Measure the optical density with a Spekker absorptiometer fitted with H556 PROCEDURE I N PRESENCE O F THORIUM, IRON AND CHROMIUM- 0.6 6 to Wavelength, IT u Fig.1. Absorption spectrum of the nickel - 4-methyl- nioxime complex in toluene: the complex was prepared from 105 pg of nickel and 1.0 ml of 0.1 per cent. 4-methylnioxime solution in 25 ml of toluene, and the optical densities were measured in a 1-cm cell TABLE I1 EFFECT OF OTHER ELEMENTS ON THE DETERMINATION OF NICKEL All solutions contained 1.0 ml of 10 per cent. w/v sodium acetate solution, 1-0 ml of 20 per cent. w/v tartaric acid solution and 1.0 ml of 10 per cent. v/v thioglycollic acid solution Uranium Thorium Copper Iron Chromium Nickel Nickel Solution present, present, present, present, present, added, found, mg mg mg mg mg mg mg 11.0 - 0.0 0.0 - 0.0 <0*001 1 2* - 46.0 0.0 0.0 3 - - 0.963 - 1.02 - 0.0 <0.001 4 - - 0.236 0.0 <0.001 5 - 0.132 0.132 6 - 0,0528 0.053 7 11.0 - 0.482 0.102 0,250 0,132 0.132 9 11.0 - 0.482 0.255 0.250 0.132 0.131 8 10 11.0 - 0.482 0.510 0.250 0.132 0.130 11 11.0 - 0.241 0.102 0.250 0.132 0.129 12 11.0 - 0.241 0.255 0.250 0.132 0.130 13 11.0 - 0.241 0.510 0.250 0.132 0.130 - - 0.250 0,132 0.130 14 11.0 - 15 11.0 - 0.241 0.102 0.025 0,0528 0.053 16* - 37.5 - 1.38 0.221 0.132 0.132 5.38 104.5 0.150 0.051 0.047 0.0504 0.050 5.38 104.5 0.150 0.051 0,047 0.1032 0.1035 17t 5.38 104.5 0.150 0.051 0.047 0,156 0.155 1st - - - - - - - - - - - - - - - - - - - 19t * Solution contained no thioglycollic acid.t Solution contained 2 ml of 20 per cent. w/v tartaric acid solution.Oct., 19581 NICKEL BY A SOLVENT-EXTRACTION METHOD 561 filters and a mercury-vapour lamp.Use a blank solution, prepared in a similar manner, in the comparison cell. PROCEDURE IN PRESENCE OF URANIUM, COPPER, IRON AND CHROMIUM- Place an aliquot containing 5 to 200 pg of nickel in a 50-ml beaker, and add 1.0 ml of 20 per cent. w/v tartaric acid solution. Add 1-0 ml of 10 per cent. v/v thioglycollic acid solution and 1.0 ml of 10 per cent. w/v sodium acetate solution. Adjust the pH to between 5 and 5.5 against a pH meter with 2 N sodium hydroxide, and continue as described under “Procedure in Presence of Thorium, Iron and Chromium.” PREPARATION OF CALIBRATION GRAPH- use the procedures described. Take aliquots of standard nickel solution to cover the range 5 to 200 pg of nickel and RESULTS AND CONCLUSIONS Fig. 1 shows the absorption spectrum of the nickel - 4-methylnioxime complex. Table I1 shows the effect of cations on the nickel determination. Eighteen replicate deter- minations were carried out at 50, 100 and 150-pg levels of nickel in the presence of 6 mg of uranium, 0.15 mg of copper, 104 mg of thorium, 0.05 mg of iron and 0.05 mg of chromium; the mean recovery was 99-8 per cent. and the standard deviation was k1.2 per cent. The proposed method is rapid, simple and accurate; it has been used constantly in our laboratories for the last 6 months. We thank Mr. R. Todd and Mr. W. H. Hardwick for helpful discussions during this work. REFERENCES 1. 2. 3. 4. Horton, A. D., Thomason, P. F., and Kelley, M. T., Anal. Chem., 1957, 29, 388. Taylor, C. G., Analyst, 1956, 81, 369. Banks, C. V., and Hooker, D. T., Anal. Chem., 1956, 28, 79. Pellowe, E. F., and Hardy, F. R. F., Analyst, 1954, 79, 226. Received February 26tk, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300558

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Oct., 19581 The NICKEL BY A SOLVENT-EXTRACTION METHOD Determination of Direct Magnesium Photometry in 561 Solution BY R. 0. SCOTT AND A. M. URE (The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen, Scotland) The spectrochemical determination of magnesium in solution by the porous-cup - spark method has been greatly facilitated by the direct photo- meter described. The magnesium line at 2802 A is used with the strontium line at 4077 A as internal standard. Solutions containing from 0.3 to 24 p.p.m. of magnesium are analysed directly with a coefficient of variation of about &2-0 per cent. at a rate of forty determinations per hour. Inter- ferences are found to be negligible for most types of agricultural samples, such as extracts of soils and plant materials. IN agricultural laboratories, many thousands of samples have to be analysed each year for potassium, sodium, calcium and magnesium.Of these elements, the first three can be determined conveniently by flame photometry, especially when a multi-channel instrument is avai1able.l The determination of magnesium in this manner is unsatisfactory. In the first place, magnesium is not very sensitive in the flame and solutions generally have to be concentrated before adequate sensitivity is achieved. Secondly, the most sensitive flame line at 2851 A lies in an (OH)-band system, and, at the low concentrations required, some form of background correction is necessary. For the past few years, a spectrographic technique in which the porous-cup - spark method of excitation2 is used has been employed at the Macaulay Institute for determining magnesium in soil and plant extracts.The sensitivity is such that magnesium, in the range 0.3 to 24 p.p.m. in solution, can be determined without further concentration in the aceticSCOTT AND URE: THE DETERMINATION OF [Vol. 83 562 acid soil extract used for the flame-photometric determination of readily soluble potassium, sodium and calcium in soils. This spectrographic method proved to be so satisfactory that a direct-reading attachment for a Hilger small-quartz spectrograph has been constructed specifically for determining magnesium by the porous-cup method. DESCRIPTION OF APPARATUS DIRECT-READING ATTACHMENT- The plate-holder mounting of an E484 Hilger small-quartz spectrograph has been removed, and, in its place, the direct-reading attachment is fitted to the spectrograph casting.Two optical channels are provided, one for the magnesium line at 2 8 0 2 ~ and the other for a strontium internal-standard line at 4077 A. Fig. 1 shows schematic diagrams of the attachment and Fig. 2 shows a view of the interior. A steel backplate, A, slotted for the light beam, is bolted to the spectrograph casting. This plate bears guide rails, B, which carry two slides, C. These slides provide a coarse adjustment parallel to the focal plane and can be clamped by the guide rails. The magnesium slide is slotted to pass the magnesium line and carries a small 90" quartz prism, D, which reflects the magnesium line to an exit slit, as shown in Fig. 1 (c). The slides carry shelves, E, hung from brackets, F, by beryllium - copper springs, G.On these shelves are mounted the slit units and holders for the photomultiplier tubes. An independent movement of each shelf along the focal plane is provided by micrometer screws, H and J, which act against the appropriate double-spring assembly. A Scale inches 0 1 2 3 Magnesium shelf Strontium shelf (c) Fig. 1. Schematic diagram of the direct-reading attachment for a Hilger small- quartz spectrograph: A, steel backplate; B, guide rails; C, slides; D, quartz prism; E. shelves; F, shelf brackets; G, beryllium - copper springs; H and J, micrometer screws; K, exit slits; L, slit-focusing screws ; M, pivots ; N, photomultiplier tubes Fig. 1 (a). Elevation Fig. I@). Side view Fig. l(c). Plan The slits, K, Fig.1 (c), are supported on pivots, M, mounted on the shelves, E. The slits are fitted to brass discs that can be rotated to align them parallel to the entrance slit. The slits can be moved approximately 1 2 mm along the axis of the emergent light beamsSCOTT AND URE: THE DETERMINATION OF [Vol. 83 562 acid soil extract used for the flame-photometric determination of readily soluble potassium, sodium and calcium in soils. This spectrographic method proved to be so satisfactory that a direct-reading attachment for a Hilger small-quartz spectrograph has been constructed specifically for determining magnesium by the porous-cup method. DESCRIPTION OF APPARATUS DIRECT-READING ATTACHMENT- The plate-holder mounting of an E484 Hilger small-quartz spectrograph has been removed, and, in its place, the direct-reading attachment is fitted to the spectrograph casting. Two optical channels are provided, one for the magnesium line at 2 8 0 2 ~ and the other for a strontium internal-standard line at 4077 A.Fig. 1 shows schematic diagrams of the attachment and Fig. 2 shows a view of the interior. A steel backplate, A, slotted for the light beam, is bolted to the spectrograph casting. This plate bears guide rails, B, which carry two slides, C. These slides provide a coarse adjustment parallel to the focal plane and can be clamped by the guide rails. The magnesium slide is slotted to pass the magnesium line and carries a small 90" quartz prism, D, which reflects the magnesium line to an exit slit, as shown in Fig. 1 (c).The slides carry shelves, E, hung from brackets, F, by beryllium - copper springs, G. On these shelves are mounted the slit units and holders for the photomultiplier tubes. An independent movement of each shelf along the focal plane is provided by micrometer screws, H and J, which act against the appropriate double-spring assembly. A Scale inches 0 1 2 3 Magnesium shelf Strontium shelf (c) Fig. 1. Schematic diagram of the direct-reading attachment for a Hilger small- quartz spectrograph: A, steel backplate; B, guide rails; C, slides; D, quartz prism; E. shelves; F, shelf brackets; G, beryllium - copper springs; H and J, micrometer screws; K, exit slits; L, slit-focusing screws ; M, pivots ; N, photomultiplier tubes Fig. 1 (a). Elevation Fig. I@). Side view Fig. l(c).Plan The slits, K, Fig. 1 (c), are supported on pivots, M, mounted on the shelves, E. The slits are fitted to brass discs that can be rotated to align them parallel to the entrance slit. The slits can be moved approximately 1 2 mm along the axis of the emergent light beamsSCOTT AND URE: THE DETERMINATION OF [Vol. 83 562 acid soil extract used for the flame-photometric determination of readily soluble potassium, sodium and calcium in soils. This spectrographic method proved to be so satisfactory that a direct-reading attachment for a Hilger small-quartz spectrograph has been constructed specifically for determining magnesium by the porous-cup method. DESCRIPTION OF APPARATUS DIRECT-READING ATTACHMENT- The plate-holder mounting of an E484 Hilger small-quartz spectrograph has been removed, and, in its place, the direct-reading attachment is fitted to the spectrograph casting.Two optical channels are provided, one for the magnesium line at 2 8 0 2 ~ and the other for a strontium internal-standard line at 4077 A. Fig. 1 shows schematic diagrams of the attachment and Fig. 2 shows a view of the interior. A steel backplate, A, slotted for the light beam, is bolted to the spectrograph casting. This plate bears guide rails, B, which carry two slides, C. These slides provide a coarse adjustment parallel to the focal plane and can be clamped by the guide rails. The magnesium slide is slotted to pass the magnesium line and carries a small 90" quartz prism, D, which reflects the magnesium line to an exit slit, as shown in Fig.1 (c). The slides carry shelves, E, hung from brackets, F, by beryllium - copper springs, G. On these shelves are mounted the slit units and holders for the photomultiplier tubes. An independent movement of each shelf along the focal plane is provided by micrometer screws, H and J, which act against the appropriate double-spring assembly. A Scale inches 0 1 2 3 Magnesium shelf Strontium shelf (c) Fig. 1. Schematic diagram of the direct-reading attachment for a Hilger small- quartz spectrograph: A, steel backplate; B, guide rails; C, slides; D, quartz prism; E. shelves; F, shelf brackets; G, beryllium - copper springs; H and J, micrometer screws; K, exit slits; L, slit-focusing screws ; M, pivots ; N, photomultiplier tubes Fig. 1 (a). Elevation Fig. I@). Side view Fig.l(c). Plan The slits, K, Fig. 1 (c), are supported on pivots, M, mounted on the shelves, E. The slits are fitted to brass discs that can be rotated to align them parallel to the entrance slit. The slits can be moved approximately 1 2 mm along the axis of the emergent light beamsOct., 19581 MAGNESIUM IN SOLUTION BY DIRECT PHOTOMETRY 563 by means of screws, L, which act through pivots M, and by a similar amount across the axis of the beam. On account of the curvature of the spectral lines, the width of each exit slit was made greater than that of the entrance slit. A 3-mm x 0.02-mm entrance slit is used, with fixed-width exit slits of 10 mm x 0.05 mm for magnesium and 10 mm x 0.1 mm for strontium. A piece of suitably exposed and developed photographic plate, which serves as a neutral filter, is mounted behind the strontium exit slit to reduce the light intensity on the strontium photomultiplier tube. To facilitate the initial setting up, a piece of photographic film was held against the face of the slit and the image of the line was recorded on it.Without being moved, the film was then exposed to light through the slit from the'back. The film thus recorded the position 'of the spectral line image relative to the slit. A convenient accessory for this operation is an iron film-holder held against the face of the slit by a button magnet (Eclipse type A) placed against the back of the slit. A miniature lamp mounted inside the magnet serves to record the slit image. For the final more accurate setting, provision is made in the electronic circuitry for profiling either line by using the instantaneous voltage developed in a resistor by the photomultiplier current.After removal of the bases, each photomultiplier tube, N, with its resistance chain was fitted into a 40-mm diameter brass tube so as to project about 45 mm above the rim of the tube. These brass tubes were then filled with Di-jell 171 wax (obtained from Astor Boisselier and Lawrence Ltd.), and opaque plastic covers, with windows opposite the photocathodes, were fitted over the photomultiplier tubes. The RCA 1P28 photomultiplier tube used for magnesium had, at 950 volts, a dark current of 5 x lo-" ampere, compared with 8 x ampere before removal of its base. The brass tube carrying the photomultiplier and resistance chain is a sliding fit in a second brass tube, which is mounted on shelf E.The photomultiplier can therefore be rotated and moved vertically into its correct position before it is clamped. A cross-movement of the whole photomultiplier mount of about +2 mm is provided. The direct-reading attach- ment is light-proof, and has slides at the top and back. Parts inside the box are blackened, and the entire attachment is electrically earthed. INTEGRATING PHOTOMETRIC EQUIPMENT- The instrument has an integrating circuit in which the photomultiplier output current charges a condenser. The voltage developed in the condenser is a measure of the total light energy received and is measured by a null-reading electrometer - bridge circuit. The method used is basically that of Naish and Ram~den.~ A 1P28 photomultiplier tube, V,,, is used for the magnesium line and a 931A photomultiplier tube, VI2, for the internal-standard strontium line.V,, is operated at about 950 volts, but V,, has its voltage reduced to about 700 volts by resistor R16. Both voltages are supplied from a stabilised power pack, as shown in Fig. 3 (a). In addition, the 50-cycle mains voltage supply to the laboratory is controlled by a Ferranti voltage regulator, with a voltage stability of k0.5 per cent. The complete apparatus is shown in Fig. 4. When a determination is made, the integrating condenser for magnesium, C,, is con- nected in by S, and that for strontium, C, or C,, is selected by s,. With the measuring potentiometer, R,,, at zero and switches S, and S, at position 1, the integration is started by setting S, to position 2.The photomultiplier currents then charge their respective condensers until, a t the end of the exposure, S, is switched to position 3 and the two con- densers are isolated preparatory to measuring their voltages. To measure the voltage of the magnesium condenser, S, is switched to position 2 and the measuring potentiometer, R,,, is turned until an equal and opposite voltage is applied to the electrometer grid to balance the condenser voltage, as shown by a zero reading on galvanometer M,. To measure the voltage of the internal-standard (strontium) condenser, R,, is returned to zero, S, is switched to position 3 and the required angular rotation of R,, is read as before. The cycle of operations is completed and the instrument is re-set for further determinations by returning R,, to zero and S, and S, to position 1.R,, is a linear-law potentiometer, and thus the ratio of the magnesium and strontium angular rotations is proportional to the ratio of the magnesium and strontium condenser voltages and hence to the ratio of the relative intensities of the magnesium and strontium The circuit is shown in Fig. 3.564 SCOTT AND URE : THE DETERMINATION OF [Vol. 83 spectral lines. as the scale for Rl,. A 5-inch diameter 360" plastic protractor, illuminated from below, is used q x x x ' z 8 Either line can be profiled by using the instantaneous voltage developed by the photo- To profile the magnesium line, for example, multiplier current in a resistor (R, or R2,).S, is set at position 3, S, at position 1 or 2, S, at position 1 and S, at position 2. EXCITATION AND OPERATING CONDITIONS The porous-cup electrodes used for the determination of magnesium are made from 56mm diameter carbon rods, obtained from C. H. Champion & Co. Ltd. (less-pure grade). The cups are approximately 16 mm long and have a bore of 3.2 mm (4 inch), a drill with an included angle of 135" being used. The base thickness is 0.60 0.01 mm and no pre-heating or pre-sparking of the empty electrode is necessary. The counter-electrode has a sharpOct., 19581 MAGNESIUM I N SOLUTION BY DIRECT PHOTOMETRY 565 point of 70" included angle. The spark gap is 2mm and is not adjusted during the exposure. The source is an uncontrolled Hilger-type spark of 15,000 volts with 0.02-mH inductance, 0.001-pF capacitance and no added resistance.With these parameters, a relatively weak undamped spark is produced. Strontium has proved to be a suitable internal standard and is present in only small amounts in the materials being examined, so that a constant standard addition can be made, provided it is large enough. The magnesium to strontium ratio for a solution is determined by filling the porous cup with solution and sparking for 56 seconds. The direct reader is set to the integrating position, with the slit open, immediately before the spark is made, and sparking is stopped by a time switch after the discharge has continued for 56 seconds. During this period, about 0.11 ml of solution is consumed. All solutions to be analysed contain 600 p.p.m.of strontium and 2.0 t o 2.25 per cent. of acetic acid. The voltage ratio is calculated from the angular rotations of R,,, as described previously. The voltage of the magnesium con- denser, which can be measured by R,,, is limited by B, (see Fig. 3) to about 8 volts. If the solution tested gives too high a voltage with the 0.05-pF magnesium condenser, C,, the series combination of the nominal O.1-pF condenser, C,, and resistor R,, is switched in in parallel with C,, the charge of which is then distributed over a total capacity of about 0.15pF. The voltage is thus lowered to a readable value without the necessity for a second exposure. Resistor R,, is included to limit excessive current surges at this switching action. Should even higher magnesium contents have to be determined, provision could be made to in- corporate further condensers in parallel with C, and C,.The porous cup is placed 20 cm from the entrance slit with no condensing lens. With the nominal 0.05-pF condenser used for the magnesium line at 2802 A and the 1P28 photo- multiplier tube operated at about 950 volts, 6 p.p.m. of magnesium produce a condenser voltage of about 5.6 volts, 0.3 p.p.m. of magnesium about 0.72 volt and a blank solution (containing only strontium and acetic acid) about 0.24 volt. The dark current produces a condenser voltage of about 0.05 volt. A reduced voltage of about 700 volts to the 931A photomultiplier tube and a neutral filter behind the exit slit are required to lower the condenser voltage to a readable value.Other available strontium lines are not suitable, those at 4161 and 4215 A are in a band system, that at 4305 A is interfered with by calcium and that at 4607 A, which is almost as strong as the line at 4077 A, is an arc line. It is undesirable to reduce the added amount of strontium to less than 500 p.p.m. because a few parts per million may be present in the original solution. EFFECT OF VARIATION IN ELECTRODE PARAMETERS- Base thickness of the porous cup-Table I shows the effect of change in the base thickness of the porous cup on the relative intensities and intensity ratios of the magnesium and strontium lines. There is apparently a depression of the observed magnesium to strontium ratio with increase in base thickness, the relative intensity of strontium increasing more rapidly than that of magnesium.Such changes in base thickness as occur during preparation of the cups should introduce only very small errors. TABLE I Each determination was carried out in presence of 3 p.p.m. of magnesium A 0-1-pF condenser is used for the strontium line a t 4077 A. Each result is an average of seven replicate determinations. EFFECT OF CHANGE IN BASE THICKNESS OF THE POROUS CUP Base Relative Relative Intensity Error in thickness, intensity of intensity of ratio magnesium mm magnesium strontium (Mg to Sr) content, yo 0.40 125.0 148.8 0.839 + 5.7 0.60 129.3 161.1 0.802 0.0 0.80 131.9 168-8 0.782 - 2.4 Counter-electrode shape-Table I1 shows the effect of different shapes of counter-electrode. Each result is an average of six replicate determinations and the apparent magnesium contents were read from a standard curve prepared by using counter-electrodes with 70" points.It can be seen that, when rods with flat tops were used as counter-electrodes, both the relative566 SCOTT AND URE: THE DETERMINATION OF [vo~. 83 intensities and the intensity ratio increased with the diameter, the relative intensity of magnesium increasing more rapidly than that of strontium. When pointed rods were used, both the relative intensities and the intensity ratio increased with the included angle of the point, but much more slowly than with increase in rod diameter. Little change in the intensity ratio is found for points with included angles between 70" and 90". TABLE I1 EFFECT OF COUNTER-ELECTRODE SHAPE Each determination was carried out in presence of 1.2 p.p.m.of magnesium Rod Relative Relative Intensity Error in diameter, Included intensity of intensity of ratio magnesium mm angle magnesium strontium (Mg to Sr) content, % 2.0 - 43.9 113.2 0.388 +8 58.8 136.3 0.431 + 23 2.5 71.7 152.5 0.468 + 37 3.0 4.0 - 96.7 174.3 0.556 + 73 5.5 - 158.9 237.3 0.669 + 110 - 50" 43.1 129.2 0.334 - 8.4 - 60" 44.9 133.6 0.337 - 6.7 - 70' 46.7 130.3 0,358 0.0 - 80" 52.0 147.3 0.353 - 1.8 - goo 53.9 148.3 0.364 + 2.7 - 110" 62.7 156.1 0.395 + 14.1 - 125' 74.3 167.1 0.443 + 30.8 Flat-top#ed counter-elecirode- - - Pointed counier-electrode- Length of spark gap-The effect of change in the length of spark gap on the intensity ratio is shown in Table 111. Increase in the gap length produces only a slight increase in intensity ratio and apparent magnesium content, although the individual relative intensities increase considerably.In practice, an optical projection system is used to position the electrodes and the gap is set to within 10.05 mm of 2.0 mm. No error should result from such slight changes in the gap length. TABLE I11 EFFECT OF THE LENGTH OF SPARK GAP Each determination was carried out in presence of 1.2 p.p.m. of magnesium Relative Relative Intensity Error in magnesium mm magnesium strontium (Mg to Sr) content, yo 1.5 42.1 130.5 0.323 - 0.5 2.0 53.1 163.5 0.325 0.0 2.5 58.7 174.5 0.336 + 4.0 3.0 72.1 209.9 0.343 + 6.9 Gap length, intensity of intensity of ratio TABLE IV EFFECT OF VARIATION IN POSITION OF ELECTRODES ACROSS THE OPTICAL AXIS Each determination was carried out in presence of 1.8 p.p.m.of magnesium Distance moved Relative Relative Intensity Error in across optical axis,* intensity of intensity of ratio magnesium mm magnesium strontium (Mg to Sr) content, Yo + 2.8 55.1 124-0 0.444 + 7.7 +2*1 52.2 125.6 0,416 - 0.4 + 1.4 56.6 133.3 0.423 + 1.4 + 0.7 59.4 142.7 0.416 - 0.4 0 58.5 139.7 0.418 0.0 -0.7 57.6 128.9 0.446 + 8.4 - 1.4 59.2 130.8 0,453 + 10.5 -2.1 57.7 119.1 0,485 + 20.3 - 2.8 61.0 111.3 0,547 $40.4 * Distance measured from an arbitrary zero position.Oct., 19581 MAGNESIUM IN SOLUTION BY DIRECT PHOTOMETRY 567 Position of electrodes on optical axis-Instantaneous current readings, by means of the profiling circuits, were taken while the discharge was moved horizontally across the optical axis. A constant current was obtained for magnesium over about f 3 mm and for strontium over about f 1.5 mm.Similarly, on the vertical axis, constant currents were found for magnesium over f 8 mm and for strontium over f 5 mm. The vertical position of the electrodes does not appear to be critical. The effect of moving the spark across the axis is shown in Table IV, an arbitrary zero position being taken within the constant current region. It can be seen that, over a range of 2.1 mm (from +2.1 mm to the zero position) the magnesium to strontium ratio is constant. With the working position set at +1.0 mm, small changes in the horizontal position of the electrodes should not affect the results. Discharge conditions-Several sparking procedures that gave good reproducibility are compared in Table V.The results are from twenty replicate determinations by each pro- cedure. It can be seen that procedure C is better than A or B and is also the simplest. In procedures A, B and C the electrodes were taken consecutively from storage racks of two hundred cups and points, as would be done in practice. Procedure D is the same as C except that the electrodes were taken at random from a stock of six hundred cups and points. Procedure C is now used with an expected coefficient of variation of +146 per cent. for a single determination. TABLE V STATISTICAL ANALYSIS OF DETERMINATION OF 1.8 p.p.m. OF MAGNESIUM In all instances the exposure was 56 seconds and a counter-electrode with a 70" sharp point was used. Each result is the average of twenty replicate determinations, and was obtained from a standard curve prepared by using procedure A BY DIFFERENT PROCEDURES Time Mean Amount of pre- amount of Coefficient Maximum Maximum of solution sparking, magnesium Standard of negative positive Procedure used seconds found, deviation, variation, error, error, p.p.m.p.p.m. % % % Full cup 15 1.942 0.0549 & 2.85 4.8 7.5 A * 0.11 ml 15 1.793 0,0496 & 2.76 4.8 6.1 Full cup Nil 1.648 0.0306 & 1-86 3.5 2.9 Bf D§ Full cup Nil 1.660 0.0401 12.41 3.5 4.6 c: * Spark gap was re-set to 2.0 mm after pre-sparking with cup empty. f Spark gap was not re-set after pre-sparking with cup empty. $ Spark gap was set to 2.0 mm and not altered during exposure. J As for procedure C, but cups and counter-electrodes were selected a t random from stock of 600 of each.EFFECT OF OTHER VARIABLES- No change in the magnesium to strontium ratio was observed when the input voltage t o the photomultiplier power pack was varied from 240 to 210 volts. Similarly, no change was produced by altering the current from the standard battery, B, (see Fig. 3), in the measuring circuit from 458 to 470 mA. Change in room temperature from 14.5" to 24" C has not caused curve drift, and it would appear that the exit slits are sufficiently wide to take care of any normal temperature change in the surroundings. Long-term curve drift has occurred at intervals of about 3 months, when it has been necessary to re-set the exit slits by means of micrometer screws H and J (see Figs. 1 and 2).As the exit slits require to be re-set in opposite directions, this is probably the result of the beryllium - copper springs, G (see Figs. 1 and 2), being twisted by the side pressure of the micrometers. The design, in fact, should be modified, so that the micrometers act along the central axes of the springs. To carry out a routine check of exit-slit positions by profiling, freshly prepared hemispherical MG5 aluminium-alloy electrodes are used for magnesium, and, for strontium, a porous cup in which is placed a solution containing 1000 p.p.m. of the element is used. Short-term curve drift was observed in the early stages of setting up the instrument, when a sphero-cylindrical quartz lens was used to focus the spark on the entrance slit. A slow decrease in intensity ratio was caused by the gradual fogging of this lens, which then568 SCOTT AND URE: THE DETERMINATION OF [Vol.83 absorbed more of the ultra-violet (magnesium) light than of the visible (strontium) light. No condensing lens is now used between spark and entrance slit. EFFECT OF EXTRANEOUS ELEMENTS- The amounts of calcium, aluminium, potassium and phosphorus liable to be present in soils and plants and in the extracts used for determining magnesium are shown in Table VI. The effects of the presence of different amounts of these elements on the apparent magnesium content are shown in Table VII. Aluminium, potassium and phosphorus have practically no effect on the apparent magnesium content, most of the errors being within the experimental error of the method.In practice, variation of these elements in soil extracts and plant materials should not produce significant errors. Increase of the calcium present appears to enhance the magnesium content, possibly because the specially purified calcium carbonate used in the preparation of the solutions contained about 50 p.p.m. of magnesium. (The purest commercially available calcium carbonate contained considerably more magnesium.) Extracts of Scottish soils normally contain 50 to 70 p.p.m. of calcium and seldom more than 200 p.p.m. At this level, the effect of variation in the calcium content can be ignored. TABLE VI AMOUNTS OF VARIOUS ELEMENTS NORMALLY PRESENT IN SOIL AND PLANT MATERIAL Acetic acid extract of soil A Amount of element present per 100 g of soil, mg Element Calcium .. . . 80to400 Aluminium . . 80 to 240 Potassium . . 2.4 to 80 Phosphorus . . 0.4 to 140 Amount of element present in final solution, p.p.m. 20 to 100 20 to 60 0.6 to 20 0.1 to 35 Plant material Amount of Amount of element present element present in dry material, in final solution, 0.05 to 6.0 0.4 to 48 0.001 to 1.0 0.008 to 8.0 1.2 to 64 0.15 to 8.0 0.05 to 1.0 0.4 to 8.0 I A > % p.p.m. TABLE VII ERRORS I N APPARENT MAGNESIUM CONTENT IN PRESENCE OF EXTRANEOUS ELEMENTS Calcium Aluminium Potassium Phosphorus and potassium &- A > Amount Error in Amount Error in Amount Error in Amount of Amount of Error in of element magnesium of element magnesium of element magnesium phosphorus potassium magnesium present, content, present, content, present, content, present, p.p.m.% p.p.m. % p.p.m. % p.p.m. Each determination carried out in presence of 0.6 $.P.m. of magnesium- 0 0.0 0 0.0 0 0.0 0 100 0.0 6 + 1.0 10 + 1.0 10 500 + 5.3 12 - 1.0 50 f 1.0 50 1000 + 8.5 32 0.0 100 - 1.0 100 - - 64 -4.1 _- - - 0 0.0 0 0.0 0 0.0 0 100 +0*2 6 +0*2 10 - 0.6 10 500 + 1.8 12 -0.8 50 -0.8 50 1000 +2.0 32 -0.8 100 -0.8 100 APPLICATION TO AGRICULTURAL MATERIALS Each determination carried out in presence of 3.0 $.p.m. of magnesium- - - - - 64 0.0 - ACETIC ACID EXTRACTS OF SOILS- present, p.p.m. 0 13 63 126 - 0 13 63 126 - content, % 0.0 + 1.9 + 1.0 + 1.0 - 0.0 + 0.6 - 0.4 + 0.2 - Ten grams of soil are shaken for 2 hours with 400 ml of 2.5 per cent. acetic acid, and the suspension is filtered. Part of the extract is used directly for determining sodium, potassium and calcium by flame photometry.For magnesium, 5 ml of strontium chloride solution (containing 5-0 g of strontium per litre) are diluted to 50 ml with the acetic acid extract. The standard solutions are prepared by diluting 5 ml of strontium chloride solution to 50 mE with stock solutions containing from 0.3 to 24 p.p.m. of magnesium in 2.5 per cent. acetic acid. These solutions are sparked in porous cups as described under “Excitation and Operating Conditions,” and the magnesium to strontium intensity ratios are calculated.Oct., 19581 MAGNESIUM IN SOLUTION BY DIRECT PHOTOMETRY 569 Two standard curves are plotted of the magnesium to strontium intensity ratio for the standard solutions against magnesium concentration (in milligrams of magnesium per 100 g of soil).One curve is plotted from 0.3 to 6 p.p.m., the 0.05-pF condenser being used, and another from 6 to 24 p.p.m., the 0.05-pF condenser again being used for the integration, but with the O a l - p F condenser connected in parallel before measurement of the voltage ratio. Samples with magnesium contents above 24 p.p.m. are diluted with a solution containing 500 p.p.m. of strontium in 2.25 per cent. acetic acid. AMMONIUM ACETATE EXTRACTS OF SOILS- Twenty grams of soil are mixed with 100ml of a N solution of neutral ammonium acetate, the suspension is set aside overnight, filtered, and then leached with ammonium acetate solution to a volume of 1 litre. Five millilitres of strontium chloride solution and 1 ml of glacial acetic acid are diluted to 50 ml with the extract.Acetic acid is necessary to ensure percolation through the porous base of the cup. Standard solutions containing from 0.3 to 24 p.p.m. of magnesium and 500 p.p.m. of strontium are prepared in a base solution of N ammonium acetate and 2 per cent. acetic acid. Standard curves are plotted as before for the ranges 0.3 to 6 p.p.m. and 6 to 24 p.p.m. of magnesium. PLANT MATERIAL- Ten grams of dry plant material are ashed at 450" C overnight and the ash is twice evaporated to dryness with 2.5 ml of concentrated hydrochloric acid to precipitate silica. The residue is extracted with 25 ml of dilute hydrochloric acid (1 + 4 v/v), filtered, and diluted to 500 ml with distilled water. An aliquot of this solution, generally 2 ml, is placed by pipette in a 50-ml calibrated flask, 5 ml of strontium chloride solution are added, and the solution is diluted to the mark with 2.5 per cent.acetic acid. Standard curves are plotted as before, standard solutions in acetic acid incorporating potassium dihydrogen phosphate, potassium sulphate, calcium carbonate and sodium chloride in proportions corresponding to an average plant ash being used. Twenty samples of turnips were analysed in duplicate by the proposed method and by a colorimetric procedure with Titan yellow? The mean values for magnesium were, respec- tively, 0.0687 and 0.0685 per cent. (standard deviations j0-00168 and -t0.00384 per cent.), but the coefficient of variation was better by the proposed method (k2-4 per cent.) than by the colorimetric procedure (k5.6 per cent.).From other statistical comparisons, it would appear, as might be expected, that with the proposed method the coefficient of variation is constant at both high and low magnesium contents, although the standard deviation is constant for the colorimetric procedure. OTHER MATERIALS- Because of the high sensitivity of the method and the small effect of extraneous elements, magnesium can be determined in solutions derived from practically any material of agricul- tural interest. At the dilution required for determining magnesium in most limestones, for example, there are no more than 150 to 200 p.p.m. of calcium present in the final solution, an amount that, as shown previously, has little effect on the results. Similarly, with other materials, after the required dilution the effect of extraneous elements is generally negligible.Materials that have been analysed include woods, limestones, sands and minerals. The instrument has now been in use for over 2 years and has proved to be thoroughly reliable, three to four hundred magnesium determinations per week being carried out. Some forty determinations per hour are possible. The life of the batteries is at least 1 year under these conditions. APPENDIX LIST OF COMPONENTS USED IN THE CONSTRUCTION OF THE POWER PACK AND STABILISER FOR PHOTOMULTIPLIER TUBES AND THE INTEGRATING AND MEASURING CIRCUITS (Fig. 3) = 1-megohm &watt resistor (five 200,000-ohm 1-watt carbon resistors in series). = 100-ohm #-watt carbon resistor. = 200,000-ohm 5-watt resistor (five 1-megohm 1-watt carbon resistors in parallel).570 SCOTT AND URE [Vol.83 R,, R,, R,, R7 = 1.5-megohm f-watt carbon resistor. = 25,000-ohm 15-watt resistor (five 5000-ohm 3-watt wire-wound resistors in = 15,000-ohm 3-watt wire-wound resistor. = 80,000-ohm 12-watt resistor (four 20,000-ohm 3-watt wire-wound resistors in = 35,000-ohm 3-watt wire-wound variable resistor. = 10,000-ohm 5-watt wire-wound resistor. Rl, = 20,000-ohm 3-watt wire-wound variable resistor. R14? R13 = 100,000-ohm 3-watt wire-wound variable resistor. R16 = 400,000-ohm 2-watt resistor (four 100,000-ohm )-watt high-stability carbon = 20,000-ohm 10 per cent. 10-watt wire-wound linear-law potentiometer = 5000-ohm 3-watt wire-wound resistor. = 4000-ohm 3-watt wire-wound variable resistor.= 5000-ohm 3-watt wire-wound variable resistor. = 50-megohm f-watt high-stability carbon resistor. = 500-ohm 3-watt wire-wound variable resistor. = 1000-ohm f-watt carbon resistor. = 0.5-pF condenser, 3.5-kV working. = 0.05-pF TCC Plastapack polystyrene dielectric condenser, 350-volt working. = 0.1-pF TCC Plastapack polystyrene dielectric condenser, 350-volt working. = ET.38 valve. series). series). R, Rs RlO Rll Rl, resistors in series). (Painton CV25). Rl, Rl,, R,,, R,, Rl, RZa, R24 R26 R2O R,, Cl, c,, c, ‘4, ‘8 V. c,, c7 - - - - -. -. Vi, V,, V,, V,, V, = CV1070 (7475) valve. V, = EF36 valve. = 250-volt 15-watt indicator lamp. = CVllll (R11, V1907) valve. = &volt 0-3-ampere indicator lamp. = RCA 1P28 photomultiplier tube. = RCA 93lA photomultiplier tube. = 9-volt grid bias. = 4.5-volt section of 9-volt grid bias. = 6-volt section of 9-volt grid bias. = 15-volt Ever Ready Batrymax B121. = Voltage dividers (ten 100,000-ohm )-watt high-stability carbon resistors in = Low-frequency choke. = 0-2000-volt electrostatic voltmeter. = 0-500-pA moving-coil microammeter. = 450-ohm Cambridge spot galvanometer, 180 mm per pA. = Single-pole ON - OFF switch. = 2-section 3-postion shorting switch, with silicone-treated ceramic insulation and non-shorting moving contacts. = 3-section 3-position switch, with silicone-treated ceramic insulation and non- shorting moving contacts. = Double-pole ON - OFF switch. = Mains transformer : primary windings, 0-210-230-250 volts : secondary windings, (a) 0-1800-2000 volts, 20 mA, (b) 4 volts, 2 amperes, 2-kV working. = Mains transformer: primary windings, 0-210-230-250 volts; secondary windings, two of 6.3 volts, 1.5 amperes, 2-kV working. = Mains transformer: primary windings, 0-230-250 volts: secondary winding, 6.3 volts, 1.5 amperes. = Mains transformer : primary windings, 0-200-230-250 volts : secondary winding, 0-30 volts, 2 amperes, multi-tappings, 0-8-volt tapping used. v, v, Vl, Vll Vl, VlS = 28D7 (Sylvania) valve. B,, B, B, B, Dl, D, Ll Ml M, Ma Sl, s,, s7 ss B6 series). s,, s,, s, s, TI T* T, T4 We acknowledge the assistance of Mr. A. M. Fraser in the design and construction of the adaptor fitted to the small-quartz spectrograph. REFERENCES 1. 2. 3. 4. Mitchell, R. L., Spectrochim. Acta, 1950, 4, 62. Mitchell, R. L., and Scott, R. O., Appl. Spectroscopy, 1957, 11, 6. Naish, J. M., and Ramsden, W., Spectrochim. Acta, 1952, 5, 295. Hunter, J. G., Analyst, 1950, 75, 91. Received February 28th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300561

出版商:RSC    

年代:1958

数据来源: RSC