ISSN:0003-2654    

DOI:10.1039/AN95176FX013

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176BX015

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176FP031

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176BP037

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

APRIL, 1951 Vol. 76, No. 901 THE ANALYST PROCEEDINGS OF THE AND OTHER SOCIETY OF PUBLIC ANALYSTS ANALYTICAL CHEMISTS “iN Ordinary Meeting of the Society was held at 7 p.m. on Wednesday, February 7th, 1951, in the Meeting Room of the Chemical Society, Burlington House, London, W.l. The Chair was taken by the President, Mr. George Taylor, O.B.E., F.R.I.C. The following papers were presented and discussed : “Inorganic Chromatography on Cellulose, Part I V : Determination of Inorganic Compounds by Paper Strip Separation and Polarography,” by J. A. Lewis, A.R.I.C., and Mrs. J. M. Griffiths; “Inorganic Chromatography on CelluIose, Part V: The Use of Columns of Cellulose in Combination with Organic Solvent Extraction for the Separation of Uranium from Other Metals,” by F. H. Burstall, M.Sc., F.R.I.C., and R.A. Wells, B.Sc., A.R.I.C. ; “Microphotometric Determination of Carboxy- haemoglobin in Blood,” by H. B. Salt, MSc., F.R.I.C. A JOINT Meeting of the Society with the Newcastle-upon-Tyne Section of the Society of Chemical Industry was held a t 6.30 p.m. on Wednesday, February 21st, 1951, in the Lecture Theatre, New Chemistry Department, King’s College, Newcastle-upon-Tyne. The Chair was taken by the Chairman of the Newcastle-upon-Tyne Section, Mr. E. W. Muddiman, B.Sc., F.R.I.C. The following paper was presented and discussed : “Analytical Control and Investigation in the Food Industry,’’ by E. B. Hughes, D.Sc., F.R.I.C. NEW MEMBERS ELECTED FEBRUARY 7TH, 1951 Sidney Charles Barnes, A.M.C.T., A.II.1.C.; Malcolm McRae Burns, M.Sc. (N.Z.), Ph.D (Aber.), F.N.Z.I.C.; George Herbert Butler, M.S.A.Chem.Inst., A.M.Inst.S.P., F.R.I.C.; Albert Ross Crawford; Ezra Gwyn Harry, B.Pharm.(Wales), Ph.C.; Arthur Harvey, F.R.I.C.; Clive Jackson, A.R.I.C. ; Philip Francis Kane, BSc. (Lond.), A.R.I.C. ; James Vernon Mitchell, Ph.C. ; Bernard David Owen, B.Sc. (Manc.) ; David Child Soul, B.Sc. (Lond.), A.R.C.S., A. R.1 .C. DEATHS WE regret to record the deaths of Eric Morgan Hall Joseph Henry Lane (Editor of the Analyst) Alexander Henry Mitchell Muter. NORTH OF ENGLAND SECTION THE Twenty-sixth Annual General Meeting of the Section was held at Manchester on Saturday, January 27th, 1951. The Chairman, Mr. J. G. Sherratt, presided over an attendance of 36. The Hon. Secretary presented the Report and Financial Statement, which were adopted.Appointments for the forthcoming year were made as follows:--€hairman-Mr. A. A. D. Comrie. Vice-Chairman-Mr. T. W. Lovett. Hon. Secretary a d Treasurer-Mr. Arnold Lees, 87, Marshide Road, Southport, Lancs. Elected Committee Members-Messrs. A. Alcock, 187188 OBITUARY [Vol. 76 W. Gordon Carey, J. R. Edisbury, N. Heron, A. 0. Jones and F. Morris. Hon. Auddo~s- Messrs. C. J. House and J. R. Walmsley. The Annual General Meeting was followed by an Ordinary Meeting at which the following paper was read and discussed : “Some Applications of the Mass Spectrometer in Analytical Chemistry,” by Dr. J. G. A. Griffiths, B.A., F.R.I.C. PHYSICAL METHODS GROUP THE Twenty-ninth Ordinary Meeting of the Group was held at 6.30 p.m. on Tuesday, February 6th, 1951, at the Iron and Steel Institute, 4, Grosvenor Gardens, London, S.W.1. Mr. B. S. Cooper was in the Chair and about 401 members and visitors were present. The following papers on “X-ray Analysis’’ were read and discussed : “Some Examples of X-ray Analysis in Atomic Energy Research,” by J. Thewlis, D.Sc.; “X-ray Diffraction Study of Interfacial Compounds formed in Radio Valve Cathodes,” by Miss Y. Budge, B.Sc. ; “Some Analytical Uses of X-rays,” by H. J. Dothie, B.Sc., A.R.I.C.

ISSN:0003-2654    

DOI:10.1039/AN9517600187

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

188 OBITUARY [Vol. 76 Obituary BERNARD SCOTT EVANS BERNARD SCOTT EVANS died on December loth, 1950, in his 70th year. He received his early education a t the Grammar School, Faversham, Kent, afterwards entering the laboratory of L. Taylor, F.I.C., the Public Analyst for Hackney, London, as pupil and later as assistant, where he remained four years. He then joined Messrs. Briant & Harman, Consultants, as assistant, retaining this post for thirteen years. The first World War now claimed him and he became a first lieutenant and had a distinguished career in the Army. He was awarded the M.C. for gallantry and was severely wounded in the Battle of Arras, 1917. He was invalided out of the Army and worked in the Ministry of Munitions, Chemical Warfare Department, carrying out research work on arsenic compounds, for which he was awarded the M.B.E.In 1919 he was appointed assistant iin the writer’s laboratory (Analytical Section, Metallurgical Branch, Armament Research Dept ., Woolwich), where he remained till his retirement owing to ill-health in November, 1948. He obtained the B.Sc. degree, London University, in 1904; the Ph.D. degree in 1923, and the D.Sc. degree in 1932. He passed the A.I.C. examination of the Royal Institute of Chemistry in 1909 and was elected to the Fellowship in 1915. He joined the Society of Public Analysts in 1917 and remained a member until his death. He supported the Society with whole-hearted enthusiasm and served as Vice-president from 1937 to 1939. He has been on many committees for the Society, and in particular, served on the Publication Committee from 1929 till his death in 1950. He also served on committees of the Institute of Chemistry, London University and the Iron and Steel Institute, and on Government committees dealing with methods of analysis.In his work in the writer’s laboratory he showed grea.t aptitude for analytical research in dealing with the many problems which arose. This work was published in The Analyst in the form of a continuous flow of papers, no less than 61 in all, of which 44 were entirely his own and the remainder in collaboration with colleagues. He also wrote many reviews for The Analyst. These reviews made interesting reading, and his suggestions and criticisms were evidence of careful perusal. One severe comment on a book was the subject of a protest by the authors; however, another review, by a well-known analyst, that appeared almost simultaneously, was, to Evans’s satisfaction, equally critical. Of his early work the most outstanding was his research into the Reinsch reaction, which resulted in the method for estimation of antimony in copper and copper alloys, now a standard procedure.This work was the subject of his thesis for the D.Sc. degree. Of his later work may be mentioned the use of sodium hydrosulphite in analytical chemistry, impurities in lead and its alloys, direct estimation of zinc in alloys, complex cyanides in separations-the complete list is too numerous to give here, and in fact Evans covered a very wide range indeed in the field 0.f inorganic analysis. He was awarded the Beilby medal in 193’7 for his great work in analytical chemistry.He showed immense patience and pertinacity in solving his problems and seldom gave up any particular line of approach until a vast amount of work had been done. He was an extremely pleasant colleague to work with, quiet and rather reserved, of even temperament and scarcely ever ruffled whatever the provocation. His work was hisApril, 19511 OBITUARY 189 main occupation and he was not ambitious in a financial sense. He was not disturbed unduly by the usual indifference shown towards chemical analysis, particularly in a metal- lurgical branch where analysis is looked upon as an unavoidable necessity. He was happy so long as he was left in peace and got what he wanted in the way of materials and apparatus.The scientific staff of the laboratory frequently consulted him with regard to their own problems and he was always willing to help them and generally had useful suggestions to make. It is regrettable that he did not live longer; for I feel sure that he had a great deal more to say on his subject of inorganic analysis. He leaves a widow and one son. A. T. ETHER~DGE BERNARD SCOTT EVANS-AN APPRECIATION I will not try to add to the tribute that has been paid to Dr. Evans’s professional life. He was a chemist of much ability and resourcefulness, who kept up with scientific advances on a wide front, but who saw nothing to apologise for in devoting his career to the science and craft of analysis. He indeed preferred to describe himself as an analyst, and anyone who was bold enough to talk about “mere analysts” in his hearing was likely to bring on himself a memorable rebuke.Evans was, what not all good scientists necessarily are, a philosopher, both in his attitude to the implications of science and to life as a whole. His chief outside study was history, particularly of the Middle Ages, which he much preferred to later times, and he probably knew as much history as a non-professional can now hope to. His views on current events, views which were often only too sombrely accurate, had a firm foundation independent of the mood of the time. He was a great and wide reader, including in his range large numbers of modern novels, and his criticisms were always unpredictable and often pungent. He was deeply steeped in poetry and had a particularly high regard for Tennyson.He would, incidentally, have fitted in very well a t the Tennysonian Round Table. From time to time, for his own amusement or to clear his mind, he wrote articles ranging from metaphysical essays to light sketches on horse riding; but he never published them. He was partly of Welsh origin and although he never lived in Wales until his work took him there in 1939, regarded himself as a Welshman, and was a strong Welsh patriot and a deep student of Welsh history and culture. He fought with distinction in the 1914 war, getting a severe head wound which probably contributed to his death. He was always an out-of-door man. Rock climbing he had always enjoyed; in his fifties he became an enthusiastic horseman and later still took up ski-ing.He was an amateur artist and was particularly keen on metal working. Beauty was perhaps what meant more to him than anything else, although nobody was less like the typical aesthete. Everything that he did take up, he did with gusto. Many of the things that enthuse most people--“vicarious sport” as he termed it, for instance, moved him not a t all, and he abhorred anything involving the killing of animals. He rather enjoyed his active war service, but he also thoroughly enjoyed the good things of life when they came his way. He was an individual if there ever was one, but “individualist” would have been the last word for one who was so uninterested in “getting on,” or who gave so freely of himself to such unpaid activities as his work on the Publication Committee of The Analyst.Above and behind all these characteristics, Evans had the massive simplicity of a big man; he was “all of a piece.” His sincerity, and the almost physical though impersonal, dislike that went with it, of wanglers, go-getters, busybodies and humbugs, did not seem like a virtue which he had mastered, but part of the essential shape of the man. “Gravitas” he had in full Roman measure-in fact there was something of the Roman about him-but it was quite unmixed with solemnity or egoism, and he was warmly human as only a good man can be. He disliked gregariousness and “slap- on-the-back” fellowship, and could sometimes wear a quite unmeant bleakness of demeanour, which could be forbidding but for his complete lack of pompousness or conceit.Even then, an infectious smile or a loud laugh were never far below the protective surface. He had a rich humour that could be at the same time subtle and uproarious, this made him great company on a walk or at a picnic or in the home, and made his letters a delight. I suppose that what will go to posterity from Evans’s life will be an imposing collection of papers in The Analyst. But there may be one or two who knew him well who would say of him, as was said of Socrates, that he was “the wisest and the noblest of men I have known.” Evans not only had an all-round mind; he was an all-round man. In casual contacts he was reserved and somewhat shy. H. R. AMBLER190 OBITUARY [Vol. 76 FREDERICK WILLIAM RICHARDSON FREDERICK WILLIAM RICHARDSON died in his 91st year at his home in Bournemouth on December 17th, 1950, after a month’s illness.Born on March 23rd, 1860, Richardson was the youngest of the four sons of George Richardson of Sandhouse, near Bridlington, and attended Hull Grammar School, which he left at the age of 18 to become pupil - assistant to Rimmington, the Bradford City Analyst. In due course he set up in private practice, acting, amongst other things, as consultant to local woollen manufacturers. As the result of the problems investigated, he published in the Journal of the Society of Chemical Indzcstry many papers dealing with wool grease, textile oils, water and sewage. It was during this time, too, that (in 1888) he joined our Society, of which he was a member for no less than 62 years.In 1897 he was elected a Fellow of the Institute of Chemistry and was appointed Bradford City Analyst, the senior appointment of West Riding County Analyst following in 1905. Consequent upon the arsenic-in-beer scare of 1900, Richardson, in common with other public analysts in the North of England, found himself frequently called upon to examine the various substances used in the brewing industry. One outcome of this was his paper (published in 1902 in the Journal of the Society of Chemical Intdustry) on the estimation of arsenic in malt liquors. A paper of quite a different nature, concerning the polarimetric determination of tartrates in baking powder, followed in 1903. In the meantime, not only was the practice of Richardson and Jaff6 in Hustlergate growing, but, Richardson himself was rapidly acquiring a reputation as an expert witness of no mean ability.In later years he took particular pleasure in recounting some of his causes cel2bres to the resultant entertainment of his listeners. He related, for instance, how on one occasion he was giving evidence in respect of a particularly badly watered milk, the vendor of which was represented by a well known Leeds solicitor. The latter, faced with the hopeless predicament of his client, suddenly interjected in the course of cross-examination, “I suppose, Mr. Richardson, that you will receive your fee for this?”, to which immediately came the stinging reply, “And I am perfectly certain that you will have already received yours!” Between 1912 and 1914 he was the author (or joint author) of four papers published in The Analyst, these concerning the polarhnetric determination of natural and synthetic camphor in camphorated oil (1908) (with Walton) ; extraneous mineral matter in rice (1910) ; and the determination of boric acid and fat in cream (two papers: 1913) (with Walton).Besides his Bradford and West Riding appointments, Richardson held several others in Yorkshire, and following the death of B. A. Bui-nell, in 1927, was called upon to carry out the duties of Leeds City Analyst until the appsintment of a full-time successor had been effected. It was under these circumstances that the present writer and his wife first made the acquaintance of Mr. and Mrs. Richardson, who extended the hand of friendship and hospitality to them from the outset. Richardson was a generous host, whether entertaining his friends in the city or in his own home.In addition to his Fellowships of the Chemical and Royal Microscopical Societies, he was a member of the Bradford Athenaeum Club, and a foundation member of the Yorkshire Analysts’ Association, which functioned actively until 1931, the year in which Richardson tendered resignation of his Bradford and West Riding appointments, but was prevailed upon to continue in office for awhile owing to the onset of the national financial crisis in September of that year. He lost his partner, Adolf Jaffk, through death in 1943, but from 1940 onwards had as deputy to share the responsibility of his public appointments, his nephew, F. W. M. Jaffk, the present head of the practice. He himself continued to work in his private laboratory at Bournemouth, whither he had meantime retired, and to devote himself to nutritional and biochemical problems. Apart from his mother, who died at the age of 72, he came of a short-lived stock, and attributed his longevity to the fact that he was a life-long teetotaller and non-smoker. He was deeply interested in theological matters and was also well known in his time as a lecturer and debater. Until his final illness he continued to take comparatively long walks. Those of us who knew him intimately had fully expecteld to see him attain in due course the century mark. Consequently, the news of his death, following that of his wife in 1946, came as some- what of a shock. He had no family, his nearest surviving relation, apart from his nephew, being his cousin, William Lowson, formerly senior lecturer in Analytical Chemistry at Leeds University. He will be greatly missed by those members of the profession who were privileged to know him. C. H. MANLEY

ISSN:0003-2654    

DOI:10.1039/AN9517600188

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

April, 19511 WESTWOOD AND PRESSER 191 Chemical Determination of Magnesium in Cast Iron BY W. WESTWOOD AND R. PRESSER (Presented at the meeting of the Society on Wednesday, November lst, 1950) A method is described for the chemical determination of magnesium in cast iron. It is based on dissolution in hydrochloric acid, extraction of most of the iron with isopropyl ether, removal of manganese and some of the remaining elements by electrolysis with a sodium amalgam cathode, forma- tion of complex ions with citric acid of any remaining interfering elements and double precipitation of magnesium as phosphate. Zirconium interferes with the method as described. A METHOD of producing nodular graphite structures in cast iron1 has been developed, and this necessitated the accurate determination of its magnesium content.For routine control work a spectrographic method2 has been developed and was entirely satisfactory, but for standardisation of the spectrograph and for laboratories not possessing this instrument, a chemical method was required. Methods previously published3s4 include the following procedures: (a) removal of most of the iron by ether extraction or mercury cathode electrolysis ; (b) precipitation of the remaining manganese ; (c) removal of small amounts of iron and other elements by hydrogen sulphide precipitati61-1, or by mercury cathode electrolysis, if this has not been used previously; (a) precipitation of calcium as oxalate; (e) precipitation of magnesium ammonium phosphate and ignition to pyrophosphate. In these extensive preliminary separations there are many possibilities of losing magnesium, and we have found by spectrographic examination of the precipitates that some loss of magnesium invariably occurs even if reprecipitation of the interfering elements is carried out.This is supported by the evidence of La Rochelle and Fournier,3 who found that 8 per cent. of the added magnesium was lost when mercury cathode separation was employed to remove the remaining traces of interfering elements, and more than 8 per cEnt. if mercury cathode electrolysis was omitted and the interfering elements were precipitated with ammonia and ammonium persulphate. It appears likely that the extent of the loss depends on the amount of interfering elements present and the experimental conditions employed, particularly as regards reprecipitation.Also, we invariably found that the final precipitate of magnesium pyrophosphate was contaminated to some extent with other elements, particularly manganese ; this indicated that the preliminary separations of interfering elements were not completely satisfactory. The experimental evidence suggested that it would be desirable to develop a method that involved no preliminary separations by precipitation. The work was carried out in three stages: (i) removal of the large amount of iron; (ii) removal of manganese and small amounts of other elements ; (iii) precipitation of magnesium as phosphate and prevention of interference by small amounts of other elements, not hitherto removed, by formation of complex ions. REMOVAL OF IRON The amounts of magnesium to be determined varied between 0.01 and 0.25 per cent., so that to obtain a satisfactory precipitate of magnesium pyrophosphate a 5-g sample of iron was required.The two most convenient methods available for removing this quantity of iron were mercury cathode electrolysis and ether extraction. It was found possible to remove 5 g of iron into the mercury cathode in a reasonable time and, in addition, the mercury cathode has the advantage that many other elements can be removed at the same time, for example, copper, nickel, chromium and some of the manganese, and a more complete removal of iron can be achieved than with ether extraction. The main disadvantages are the large volume of mercury required when a number of determinations are to be carried out and the necessity for a mercury distillation apparatus to recover the mercury after use.isoPropyl ether has some advantages over ethyl ether for the extraction of iron from aqueous hydrochloric acid solution, as it gives a more efficient extraction over a wider range of acid concentrations. Also, a more complete extraction of the iron can be achieved by a single extraction with isopropyl ether than with ethyl ether, The optimum acidity is said to be192 WESTWOOD AND PRESSER: CHEMICAL DETERMINATION OF [Vol. 76 7-75 to 8.00N hydrochloric acids and a satisfactory separation of iron from copper, cobalt, manganese, nickel, aluminium, chromium, zinc , vanadium and titanium can be attained. The ether used in this extraction can be readily recovered, as described later. In view of the short time required for the ether separation and the ease of recovery of the ether, this separation was used to remove the bulk of the iron. ETHER EXTRACTION- Preliminary experiments indicated that 5 g of iron dissolved in hydrochloric acid, diluted to 50 ml and adjusted to 8 N , could be extracted very quickly and fairly completely by shaking for about half a minute with 100 ml of isopropyl ether at about 10" C.Various amounts of magnesium were then added to the iron - hydrochloric acid solution before extraction with isopropyl ether. The ether layers were evaporated to dryness and each residue was examined spectrographically for magnesium; none could be detected. When the solution was more acid than 8 N , extraction of iron was imore complete, but occasionally three layers formed on shaking the isopropyl ether with the liydrochloric acid.The third layer could be eliminated by reducing the normality slightly by addition of a little water, but this made the extraction less efficient. When three layers formed, small amounts of magnesium were lost into the ether layer. It was therefore decided to use 8 N acid for extraction and washing. If the silica present in the iron was not removed by a double baking procedure with hydrochloric acid, a gelatinous precipitate was sometimes formed in the ether layer. Because of the danger of loss of magnesium on this gelatinous precipitate, it was necessary to carry out a double evaporation and baking proceduire prior to the ether extraction.Provided that this was done, the procedure proved satisfactory for the removal of the bulk of the iron without loss of magnesium. A second extraction with isopropyl ether was considered unnecessary, as the subsequent electrolysis would remove any iron left after the first extraction. In order to avoid precipitation in alkaline media, with the danger of losing magnesium by adsorption or co-precipitation, the remaining iron and many of the other elements were removed by electrolysis with a mercury cathode in sulphuric acid solution. ELECTROLYSIS WITH A MERCURY CATHODE By electrolysis with a mercury cathode in 'dilute sulphuric acid solution, elements such as iron, chromium, nickel, cobalt, copper, tin and molybdenum are deposited in the cathode, while elements such as aluminium, titanium, zirconium and vanadium remain in the solution.From work that we had carried out on the precipitation of magnesium as phosphate we were aware that the majority of the elements remaining after mercury cathode electrolysis (with the exception of zirconium) could be formed into complex ions and prevented from interfering in the precipitation. Manganese, however, presented a major difficulty. During electrolysis, part of the manganese was deposited on the anode as manganese dioxide after most of the iron had been removed, and part deposited as metal in the cathode. It was impossible to obtain complete removal of manganese from the solution under normal conditions, even by prolonged electrolysis. REMOVAL OF MANGANESE- A solution of manganese sulphate was prepared to contain 0.10 g of manganese per 100 ml.This solution, on electrolysis in the usual way, deposited manganese dioxide immediately on the anode, but it was not possible to remove all the manganese in a period of 2 hours. In an attempt to avoid precipitation on the anode and deposit all the manganese in the cathode, additions of reducing agents such as hydroxylamine were made to the solution. Manganese then did not deposit on the anode, but after 2 hours, 0.004 g of manganese remained in the solution. Similar results were obtained with other reducing agents such as sulphur dioxide, sodium sulphite and sodium dithionite (Na$,O,), which also evolved hydrogen sulphide and precipitated sulphur in the solution. In presence of nitric acid a heavier deposit was obtained on the anode, and at high concentrations of sulphuric acid permanganic acid was formed, but in neither instance was removal of manganese from the solution complete.I t was also noticed that whenever manganese was deposited as dioxide on the anode some of the deposit was redissolved by acid spray during removal of the anode from the electrolyte. Other methods of removing manganese that did not involve precipitation were investigated. The method of Abrahamczik6 in which extraction with acetyl acetone inApril, 19511 MAGNESIUM IN CAST IRON 193 carbon tetrachloride was used completely removed manganese only when it was in the manganic state. Attempts to extract manganese with 8-hydroxyquinoline in carbon tetra- chloride or in chloroform were likewise only successful when the manganese was in the manganic state. This could be attained most readily by converting the manganese to permanganate and then shaking with the reagent that reduced and extracted the manganese. The introduction of reagents to oxidise the manganese to permanganate (e.g., bismuthate or silver nitrate and persulphate) rendered this method unsuitable. Stepwise extraction of the 8-hydroxyquinoline compounds at various pH values showed that magnesium could be separated from iron, aluminium, titanium, etc., but that there was insufficient difference between the pH values requited for the separation of the manganese and magnesium com- pounds.I t was also found that precipitation of manganese as phosphate could not be prevented completely by complex ion formation with citrate when more than 0.001 g of manganese was present.During a series of experiments on electro-deposition from manganese sulphate solution containing citric acid it was noticed that, if the solution was adjusted to be slightly alkaline by means of sodium hydroxide added during the electrolysis, on subsequent acidification with citric acid the manganese was removed rapidly and completely into the mercury cathode. Separate tests with acid solutions containing sodium ions and citrate ions indicated that the mere presence of these ions was not sufficient to account for the phenomenon. I t was also noticed that when the mercury cathode was in contact with acid solutions a considerable amount of hydrogen was evolved, even when electrolysis was not taking place.It was thought likely, therefore, that the removal of manganese was due to the formation in the cathode of sodium amalgam, which greatly enhanced the reducing condition at the cathode during electrolysis, This was verified by forming the sodium amalgam separately as described in Note 2, p. 198, and using this amalgam as the cathode in the electrolytic cell. As long as some sodium amalgam remained in the mercury cathode it was possible to remove iron and manganese completely from the solution; in fact, the sodium amalgam alone without electrolysis would remove these ions, but under these conditions the solution soon became alkaline. If this was prevented by the addition of acid, the iron and manganese were effectively removed in a fairly short time without electrolysis, but a large quantity of sodium salts was introduced into the solution.It was found advisable to carry out the electrolysis in a solution just acid with citric acid as mineral acids caused too rapid a decomposition of the amalgam. In the presence of citric acid it was found that, whatever the pH of the electrolyte before electrolysis, it adjusted itself to a value between 4 and 5 within 5 to 10 minutes of beginning the electrolysis. This pH proved to be ideal for the removal of iron and manganese and, as the amalgam did not decompose rapidly, it did not result in too much contamination of the solution with sodium ions. An appreciable amount of the sodium remained in the amalgam at the end of the electrolysis. The interference of mineral acids, which not only brought about rapid decomposition of the amalgam but also tended to cause the manganese to precipitate as dioxide on the anode, could be overcome by neutralising the free acid with sodium hydroxide in the presence of citric acid to form the iron and manganese into complex ions, and then re-acidifying with citric acid.The experimental conditions used during the tests mentioned above were as follows. The electrolyte had a volume of 100 ml and contained 0.1 g of manganese as MnS0,.4H20, equivalent to 2.0 per cent. of manganese in a 5-g sample. The cell was made from a 400-ml Pyrex beaker with a recessed base and double-bore tap. The volume of the mercury cathode was approximately 25ml and its surface area about 40 sq. cm. The stirrer, which just touched the mercury surface, was rotated a t 300 to 400 r.p.m.The anode was a piece of platinum wire bent into a circle of 3 cm radius; it was held 2.5 cm from the cathode surface. Tests for the presence of manganese after electrolysis were carried out with silver nitrate and ammonium persulphate after destroying organic matter, and also by a formaldoxime test, which is described later. To investigate whether magnesium was removed into the sodium amalgam cathode under the above conditions the following tests were carried out. Solutions containing 0.0050 g of magnesium (10 ml of a solution of 0.5 g of magnesium dissolved in citric acid and diluted to 1 litre), 3 ml of 20 per cent. sulphuric acid and 10 ml of 20 per cent. citric acid were neutralised with sodium hydroxide and then adjusted to the pH values shown in Table I by means of citric acid or sodium hydroxide before electrolysis.The results are shown in Table I. The electrolytic current was 6 amp.194 WESTM’OOD AND PRESSER : CHEMICAL DETERMINATION OF [Vol. 76 Under the normal conditions of electrolysis magnesium was not deposited in the cathode. If the pH value before electrolysis was outside the normal range of 4 to 5, it quickly adjusted itself to the correct value and good recovery of .magnesium in the electrolyte was obtained. When the pH value was maintained a t approximately 8 by additions of sodium hydroxide the magnesium recovery was erratic, but these are conditions that would not be obtained in practice under the conditions specified.TABLE I EFFECT OF pH OF SOLUTION ON ELECTROLYTIC REMOVAL OF MAGNESIUM pH of solution before electrolysis 4 3 10 10 8 8 8 pH after electrolysis for 10 minutes 4-5 4-5 4-5 4-5 Maintained at 8 by additions of sodium hydroxide Total time of electrolysis, minutes 30 30 60 60 30 30 30 Magnesium added, g 0.0050 0.0050 0.0050 0.0050 0.0060 0~0060 0.0050 Magnesium found in electrolyte, g 0-0049 0.0052 0-0051 0-005 1 0~0000 0-0013 0-0054 Calcium, which may be present and would interfere in the magnesium determination, was removed during the electrolysis. This was established by electrolysing solutions of calcium sulphate containing 0.05g of calcium per 1 O O m l and having pH values between 4 and 5. The results are shown in Table 11, which shows that under the conditions used for removing iron and manganese, the calcium also is deposited in the amalgam.TABLE I1 REMOVAL OF CALCIUM BY ELECTROLYSIS pH of solution before pH after electrolysis Total time of Calcium Calcium found in electrolysis for 10 to 15 minutes e1ectro:ly sis, added, electrolyte, 4-6 475 30 0.0025 0~0001 10 about 5 30 0-0025 0~0001 3 4-5 30 0.0025 0~0000 minutes g R Maintained at 3 by, 3 continuous additions of citric acid Maintained at approximately 9 by additions of sodium hydroxide 9 0.0025 0.0003 0.0025 0-0004 A simple test7 was devised to indicate when the iron and manganese were removed satisfactorily. By means of a capillary pipette,, 0.2 ml of electrolyte was transferred to a test tube. Three drops of formaldoxime hydrochloride solution (5 per cent.solution in water) were added and the solution made just alkaline with ammonia. The presence of iron or manganese was shown by the development of a pink colour; the absence of a pink colour showed satisfactory removal. Quantities of iron down to 0.01 mg and manganese down to 0.003 mg could be detected by the production of a pink colour in this test. Small amounts of nickel, about 0.005 mg, gave a yellow colour, the blank being colourless. PRECIPITATION OF MAGNESIUM AS PHOSPHATE A standard magnesium solution was prepared by dissolving 0.5 g of magnesium in the minimum quantity of hydrochloric acid and diluting to 1 litre with water. To prove that the amounts of magnesium likely to be present in nodular iron can be precipitated quantita- tively, the usual technique for precipitating magnesium as phosphate was carried out on solutions containing known amounts of magnesium, as follows.To 80ml of solution con- taining the magnesium, 0 - 5 g of ammonium chloride and 10ml of 5 per cent. ammonium phosphate solution were added and the solution was made alkaline to phenolphthalein withApril, 19511 MAGNESIUM I N CAST JROW 195 ammonium hydroxide. Ten millilitres of ammonium hydroxide were added, the solution was stirred, allowed to stand overnight and the precipitate was filtered, washed with a solution containing 2 per cent. of ammonium nitrate and 5 per cent. of ammonium hydroxide, ignited and weighed as magnesium pyrophosphate. The results, which showed that satisfactory precipitation of magnesium was obtained, were as follows- Magnesium added, g .. . . nil 0~0010 0.0020 0.0030 0.0040 Magnesium recovered, g . . 0.0002 0.001 1 0.00 19 0.0029 0.0039 Preliminary tests had indicated that the presence of citric acid introduced during the electrolysis would prevent interference from small amounts of most of the elements that might remain after extraction with ether and electrolysis with the sodium amalgam cathode. The effect of citric acid on the precipitation of magnesium as phosphate was examined and the following effects were noted. Citric acid tended to prevent complete precipitation of magnesium under normal conditions, although this could be overcome by vigorous mechanical stirring. The precipitates formed in the presence of citrate with or without mechanical stirring were different in appearance from those obtained without citrate in that the crystals were somewhat larger and transparent, but no difference in chemical composition could be found by analysis.The crystal forms are shown in Figs, 1 and 2. Theoretical recovery of magnesium was obtained with up to 5 g of citric acid present in the solution. In the presence of citrate no interference in the magnesium determination was detected from the following elements in the amounts indicated, expressed as percentage on 5-g sample: aluminium, 2 per cent.; manganese, 0.02 per cent.; nickel, 5 per cent.; silicon, 2 per cent.; titanium, 0-5 per cent.; vanadium, 2 per cent.; zinc, 1 per cent. In addition to the individual tests on these elements, the possibility of interference from other elements that might be present in nodular cast iron was investigated by adding the following elements to samples of cast iron and carrying out separation with isopropyl ether and electrolysis with the sodium amalgam cathode before the magnesium precipitation. The test solutions contained 4.5 g of iron, 0402g of arsenic, 0.025 g of aluminium, 0.1 g of copper, 0.1 g of chromium, 0.08 g of manganese, 0.05 g of molybdenum, 0.055 g of phosphorus, 0.25 g of nickel, 0.144 g of silicon, 0-002 g of sulphur, 0.005 g of tin, 0.025 g of titanium, 0.025 g of vandium, and various amounts of magnesium.The results by the method described later were as follows- Magnesium added, g .. . * 0~0010 0~0010 0.0052 0.0104 Magnesium found, g . . .. . . 0.0011 0.00 12 0.0054 0.0102 These results indicate that the interference from all these elements is overcome a t some stage of the procedure, i.e., during dissolution, separation with isopropyl ether, electrolysis with the sodium amalgam cathode, or by formation of complex ions with citric acid.Zirconium was found to interfere in the determination by being precipitated with the magnesium. In some earlier work on the development of a synthetic mixed oxide method for the stacdardisation of the spectrograph, it was established that there was a great danger of contamination of precipitates by magnesium picked up from reagents and from glassware. Throughout this investigation, therefore, silica beakers were used where possible and blank determinations were invariably carried oilt. Distilled water and pure reagents were used throughout. The procedure for the determination of magnesium that resulted from these investigations is given below.APPARATUS- METHOD Silica bedew-These should be of 250-ml capacity, marked at 30 ml. Electrolysis apparatus. Separation funnels-These should be pear-shaped, of 5Wml capacity and marked at 50 and 150ml. REAGENTS- soh tion. Hydrochloric acid-Concentrated, a 70 per cent. v/v solution Nitric acid-Concentrated and a 50 per cent. v/v solution. isoPropyl ether-Dry. Hydrojuoric acid. and a 50 per cent. v/v196 WESTWOOD AND PRESSER: CHEMICAL DETERMINATION OF [Vol. 76 Sulphuric acid-A 60 per cent. v/v solution and a 20 per cent. v/v solution. Sodium carbonate. Citric acid-A 20 per cent. solution, freshly prepared before use. Sodium hydroxide-A 20 per cent.solution, freshly prepared. Formaldoxime hydrochloride-A 5 per cent. solution in water. Ammonium phusphate-A freshly-prepared 5 per cent. solution. PhenophthaZein indicator-A 0.5 per cent. solution in 50 per cent. alcohol. Ammonia-Sp.gr. 0.880. Wash soZutiuw--A solution of 2 per cent. of ainrnonium nitrate in 5 per cent. ammonium Distilled water should be used for all reagents. Pulp pads should be made from ashless hydroxide. filter-paper or ashless clippings. PROCEDURE- Transfer a 5-g sample to a 250-ml silica beaker and add 50 ml of 50 per cent. hydrochloric acid; when the vigorous reaction has subsided heat gently and finally boil. When the solution has boiled down to about 25 ml, add concentrated nitric acid dropwise until oxidation is complete, evaporate to dryness and bake on a hot-plate at a temperature of about 250" C for 15 minutes.Dissolve the salts in 30 ml of 50 per cent. hydrochloric acid, boil the solution and filter off silica and graphite on a pad, washing alternately with hot 50 per cent. hydro- chloric acid and hot water until the washings a.re colourless (about five washings will be required) and then three times with hot water. After removing the water from the stem of the funnel, transfer the entire residue and pad. to a platinum crucible, ignite and reserve this residue. Evaporate the filtrate to dryness, bake, dissolve, filter and wash as before. Add this residue to the one previously obtained and reserved, ignite, remove silica with hydrofluoric acid and sulphuric acid in the usual manner, re-ignite, fuse with 2 g of sodium carbonate and retain the fusion cake.Rinse the 500-ml pear-shaped separating funnel with concentrated hydrochloric: acid and transfer the evaporated filtrate to it; wash the beaker with concentrated hydrochloric acid to make the volume in the separating funnel up to 50ml. Retain this beaker (Note 1). Well cool the separating funnel under running water, add isopropyl ether carefully down the sides of the funnel without mixing until the level reaches the 150-ml mark. Cool to below room temperature, then shake vigorously until the solution appears green (only about half a minute is required). Cool well, shake a@in and cool. Rinse the outside of the funnel with distilled water, taking care not to let any water enter the funnel, and.allow the layers to separate. Withdraw the lower layer into the beaker previously used, pour 5 ml of 70 per cent. hydrochloric acid into the funnel, cool, shake, allow to separate and run the lower layer into the one withdrawn before. Repeat this washing twice more, adding the washiiigs to the beaker, and then boil the contents to expel dissolved ether. Now dissolve the sodium carbonate fusion cake in this solution, boil it down to about 10 mi, add 6 ml of 50 per cent. sulphuric acid and evaporate; rotate the beaker from time to time. Evaporate as much of the sulphuric acid as possible. Cool, add 50 ml of water and 10 ml of 20 per cent. citric acid solution, heat to dissolve the salts and transfer the hot solution to the electrolytic cell containing the sodium amalgam previously prepared (see Note 2). Pass a current of 6 amp., stir at 600 r.p.m.and use the anode as described in Note 2. Neutralise the electrolyte with 20 per cent. sodium hydroxide solution, litmus paper being used as indicator; acidify with 20 per cent, citric acid solution and add 2 ml of that acid in excess. Electrolyse for half an hour to an hour, according to the amount of alloying elements present ; the electrolyte should remain acid during this electrolysis. Withdraw 0.2 ml of the electrolyte by means of a capillary pipette, place in a test tube and add 3 Crops of 5 per cent. fonnaldoxime hydrochloride and a slight excess of ammonia; a red colour indicates the presence of iron or manganese or both, and a yellow colour indicates the presence of traces of nickel, the blank being colourless.Continue the electrolysis until all iron and manganese are removed. After withdrawing the electrolyte into a 250-ml silica beaker and washing the cell, evaporate to 50 ml and filter through a pulp pad into a glass beaker and wash with hot water. Cool to below 20°C, add 10ml of 5 per cent. ammonium phosphate solution, make alkaline to phenolphthalein with ammoniu:m hydroxide and add 10 ml of ammonium Evaporate the filtrate to 30ml in a silica. beaker. Dilute the electrolyte to 100 ml.Fig. 1. Crystals of magnesium ammonium phosphate precipitatetl in presence of ammonium citrate. Transmitted light [ x 800 Fig. 2. Crystals of magnesium ammonium phosphate precipitated uncler the usual conditions. Transmitted light x 800April, 19511 MAGNESIUM IN CAST IRON 197 hydroxide in excess.The total volume should be 100 ml. Stir mechanically for 10 minutes at 600 r.p.m. and allow to stand overnight. Filter on a 9-cm Whatman No. 540 filter-paper. Wash three or four times with the ammonium nitrate wash solution and then dissolve the precipitate through the filter-paper back into the beaker in which precipitation was carried LOG % Mg Fig. 3. Calibration graph for Mg 2802.7 A/Fe 2799-3 A. Curve A, Mg unfiltered/Fe unfiltered; curve B, Mg filtered/Fe unfiltered out, by means of hot 50 per cent. nitric acid and hot water; 10 washings should be sufficient. Add 10 ml of 20 per cent. citric acid, cool, add 10 ml of 5 per cent. ammonium phosphate and neutralise to phenolphthalein with ammonium hydroxide, the solution being kept cool all the time.Add 10ml of ammonium hydroxide in excess; the total volume should beWESTWOOD AND PRESSER : CHEMICAL DETERMINATION OF [Vol. 76 198 1 0 m l . Filter on the same type of paper as before; wash the precipitate free from phosphate with ammonium nitrate wash solution (about 8 washings are sufficient) and transfer the entire precipitate and paper to a prepared platinum crucible (see Note, 3). Burn off at about 600" C and finally ignite at 1000" C for 20 minutes. Cool in a desiccator and weigh as Mg,P,O,, which contains 21.85 per cent. of magnesium. Stir as before and allow to stand overnight. Range: 0.01 to 0.30 per cent. of magnesium. Reproducibility: &0*003 per cent. of magnesium. NOTES- (1) If a little of the solution remains in this beaker it can be left there, as the beaker is used again after the isopropyl ether separation.(2) The sodium amalgam can be prepared readily by the following procedure. Electrolyse 100 ml of 10 per cent. sodium hydroxide solution, with stirring a t 600 r.p.m., over 25 ml of mercury (surface area 40 sq. cm.), with a platinum wire anode bent into a horizontal circle of 6 cm diameter, a t a distance of 2-5 cm from the mercury surface. The current should be 8 amp., i.e., a current density of 0-20 amp. per sq. cm. at the cathode, and the time 10 minutes. Under these conditions approximately 1.1 g of sodium is deposited in the cathode. By electrolysing for longer periods more sodium can be deposited. With quantities of sodium up to 5 g in the cathode the pH of the electrolyte during the determination still adjusts itself to a value between 4 and 5 during electrolysis.(3) As ignition is carried out in a platinum crucible it is very important to remove carbon by igniting first at a low temperature to ;%void attack on the platinum. (4) The isopropyl ether can be purified readily by shaking it with three 100-ml portions of dilute hydrochloric acid, and then with two portions of water. After drawing off the last washing, allow the ether to stand in a dark, stoppered bottle in order to allow any remaining water to settle out, and then decant into a similar but dry bottle containing anhydrous sodium sulphate. Shake the ether and allow it to settle. It was found that ether so purified contained only 0-2 mg of residue per 50 ml on evaporation to dryness; it can therefore be used without distillation.(5) Titanium, if present in the sample, may be reduced during electrolysis and will not pass into the amalgam cathode. It is removed by the filtration preceding the magnesium precipitation. Separate the amalgam from the sodium hydroxide electrolyte. TABLE 111 RESULTS ON SYNTHETIC SAMPLES Magnesium added, percentage on 5-g sample 0.005 0.010 0-052 0.104 0.156 0.20s 0,260 Magnesium found, percentage on 5-g sample 0.007 0.007 0-053 0.106 0.156 0.212 0-262 The filtrations carried out before the final magnesium phosphate precipitation do not result in loss of magnesium. The residue remaining after volatilisation of the silica is fused and added to the solution.The residues from the other two filtrations have been examined spectrographically for magnesium in many experiments. Magnesium has always been either absent or present only as a very faint trace. Typical results with samples of iron to which known amounts of magnesium have been added are shown in Table I11 and typical results for a sample of nodular graphite iron in Table IV. Spectrographic standardisation determinations have also been carried out and give excellent calibration graphs between 0.01 and 0.15 per cent. of magnesium, as shown in Fig. 3. Spectrographic results obtained from these graphs have been of considerable meta'llurgical value. Composition of iron to which magnesium was added: total carbon, 2.S9y0 ; silicon, 2.84% ; manganese, 0.64y0 ; sulphur, o.038y0 ; phosphorus, 1.10% ; nickel, 2.0%April, 19511 MAGNESIUM I N CAST IRON 199 Colorimetric methods for determining magnesium in cast iron by means of titan yellow, quinalizarin and diphenylcarbazone had previously been found unsatisfactory because of the interfering elements, which could not be removed satisfactorily by the conventional separation methods.These reagents have not been tried after the separation procedures described in this paper. TABLE IV MAGNESIUM IN SAMPLES OF NODULAR GRAPHITE IRON Magnesium, % Sample I A 3 1 0.005 0.005 0.006 0.007 2 0.021 0.018 3 0.022 0.027 4 0.037 0.038 0.041 5 0.077 0.079 0.081 0.083 6 0.143 0.145 0.147 0-149 7 0-27 1 0.274 It is possible that electrolysis with a sodium amalgam cathode as described for removing manganese may have other applications, particularly for separating calcium and magnesium, for slag and refractories analysis and for the determination of trace elements.Further work on these lines is contemplated. The authors wish to thank the Director and Council of the British Cast Iron Research Association for permission to publish. REFERENCES 1. Morrogh, H., B.C.I.R.A. J . of Res. and Dev., 1950, 3, 251. 2. Argyle, A., and Price, W. J., Ibid., 1950, 3, 521. 3. LaRochelle, E. A., and Fournier, J. A., Amer. Foundryman, 1950, 17, 65. 4. Kennedy, W. R., Foundry, October, 1949, p. 80. 5. Dodson, R. W., Forney, G. J., and Swift, E. H., J . Amer. Chem. Soc., 1936, 58, 2573. 6. Abrahamczick, E., Mikvochem. mikrochim. Ada, 1947, 33, 209. 7. “The B.D.H. Book of Organic Reagents,” 9th Edition, The British Drug HousesLtd., London, 1946, p.83. BRITISH CAST IRON RESEARCH ASSOCIATION ALVECHURCH, BIRMINGHAM DISCUSSION THE PRESIDENT said that the author’s method of determining magnesium was very interesting. There was one point of technique he wished to raise. In his laboratory they had had to determine magnesium by use of magnesium ammonium phosphate. Their work had been on much larger quantities than the authors had described, and it had been their experience that a solubility factor was involved in the presence of citric acid. MR. WESTWOOD replied that, in the work described, the amounts of alloying elements remaining after the separations were so small that only very small amounts of citric acid had been required to complex them during the magnesium precipitation.They had found that under the conditions used there was no evidence of solubility of the magnesium ammonium phosphate. In this connection the mechanical stirring was very important, and with small amounts of magnesium complete precipitation did not occur without this stirring. MR. G. H. OSBORN asked whether the authors could confirm that magnesium was in fact extracted from Pyrex or other normal laboratory glassware, so compelling the use of silica beakers. It was difficult to believe that so much magnesium could be present. MR. WESTWOOD replied that he had no information on the extent to which magnesium might be extracted from glassware, but spectrographic evidence suggested that i t was sufficient to interfere. He mentioned that the glass used was not all Pyrex.DR. J. H. HAMENCE asked if the author could say whether extraction with isopropyl cther would also remove lead besides iron. He pointed out that he had always been very interested in the separation of iron and lead by the use of solvents, and quite clearly if lead was insoluble in isopropyl ether, then this would provide a very efficient method for the removal of iron. He also asked whether it was really necessary to remove the whole of the manganese before precipitating the magnesium. He had always held the view that ammonium citrate was capable of holding in solution quite substantial quantities of manganese, and he would like to know the authors’ experiences in this matter. MR. WESTWOOD replied that he had no information as to how much lead was removed in the isopropyl ether, but he thought it would be very little.I t seemed desirable to investigate this further.200 [VOl. 76 They had to take care to keep the amount of citric acid as small as possible to avoid interference in the magnesium precipitation. Under their conditiorts they were only able to tolerate the presence of a small amount of manganese during the phosphate precipitation. MISS PRESSER said that the amount of manganese that could be removed by complexing was not sufficient for this purpose. MR, WESTWOOD said that if manganese was not completely removed a t the amalgam cathode electrolysis it could be found in the magnesium phosphate precipitate. MR. E. F. WATERHOUSE asked the authors whether i,hey had had any experience in the separation of nickel and cobalt from iron by means of isopropyl alcohol. He also asked whether the pH readings were made by means of a meter or by use of indicators. Finally, he asked whether the authors had found inter- ference in the separation as described from the addition of tantalum or niobium. MR. WESTWOOD replied that nickel and cobalt remained in the aqueous layer, but he could give no figures; it was safe to say that a large proportion of these elements remained in the aqueous layer. MISS PRESSER said that there was no need to measure the pH with a meter before electrolysis, as it adjusted itself, but during the research into the method a pH meter had been used, MR. WESTWOOD said that i t was not necessary to measure the pH with a high degree of accuracy and indicator paper was satisfactory. He had had no experience in respect of interference of tantalum and niobium. MR. F. L. OKELL enquired whether the authors, during the course of their very careful research work on the determination of magnesium by way of magnesium ammonium phosphate, had found any evidence of errors caused by solubility of the precipitate in the test solution, or by inconstancy in the composition of the pyrophosphates as weighed. Much had been written on this subject, but very little in confirmation of his own unpublished experiments, which showed that by the usual analytical methods the results could be relied on to within the accuracy of an ordinary analytical balance. They had found that under the conditions used, Mg,P,O, was obtained after ignition.* X-ray diffraction examination would be very helpful in ascertaining the composition of precipitates obtained under various conditions. MR. WESTWOOD said that as far as he could tell, there was no solubility of magnesium ammonium phosphate under the conditions used in the procedure. McCAMLEY, SCOTT AND SMART: THE :DETERMINATION OF SODIUM IE; They had checked the values occasionally with a pH meter. MISS PRESSER confirmed the information about inconsistency in the literature.

ISSN:0003-2654    

DOI:10.1039/AN9517600191

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

200 McCAMLEY, SCOTT AND SMART: THE :DETERMINATION OF SODIUM IE; [vol. 76 The Determination of Sodium in Aluminium and its Alloys by Vacuum Distillation BY W. McCAMLEY, T. E. L. SCOTT AND R. SMART (Presented at the meeting of the Society o;sz Wednesday, November Ist, 1950) A quantitative separation of sodium from aluminium and many alloying constituents is attained by distilling th,e metal in V ~ C U O at 900" C. The sodium in the distillate may be rapidly and accurately determined by the zinc uranyl acetate method. The method has been successfully applied to all commercial grades of aluminium and to many aluminium alloys. In the upper ranges of sodium content (i.e., above 0.005 per cent.) there was good agreement with existing methods and the precision was considerably higher.The range of the new method extends far below that of any previous method, and is limited mainly by the quantity of sample it is convenient to use. Under the conditions described, 0*0001 to 0.001 per cent. of sodium was determined with a standard error of &0.00014 per cent. RECENT methods for the determination of sodium in aluminium and its alloys have been described both by Osborn and Smart. Osbornl has adapted the "fusion-leach'' method for pure aluminium ( Scheuer2 and Bridges and Lee3) to aluminium alloys containing magnesium, by the use of fine millings in place of a solid metal sample. Smart4 has adapted the zinc uranyl acetate method for the determination of sodium (Barber and Kolthoff5) to solutions of the alloy from which the bulk of the aluminium had been separated by (a) precipitation as aluminium chloride by saturation of the solution with hydrogen chloride (Gooch and HavensJs Schiirmann and Schob') or ( b ) precipitation as aluminium hydroxide from an amyl * This has since been confirmed by X-ray diffraction examination carried out for the authors by the \Yestinghouse Brake and Signal Company.April, 19511 ALUMIXIUM AND ITS ALLOYS BY VACUUM DISTILLATIOX 201 alcohol solution of the aluminium (Koide8). Smart also found that the Scheuer method for pure aluminium could be made more sensitive by employing the zinc uranyl acetate finish.All the above methods are satisfactory for sodium contents above 0.005 per cent., and give reasonable agreement with each other. Below this value, however, accurate discrimina- tion becomes difficult owing to (a) limited precision of the “solution” methods and (b) in- complete extraction of the sodium by the “fusion-leach” method and its modifications.The precision of “solution” methods is limited mainly by the presence of relatively large quantities of sodium in the reagents, and also by contamination from apparatus, which may result in the blank becoming considerably higher than the sodium contribution from the sample itself. A very thorough test of Osborn’s methodl for samples of the duralumin type containing 0.002 per cent. of sodium showed that three sintering and extraction processes were required to ensure a reasonably complete extraction of the sodium; this made the method too lengthy. Similarly, the Scheuer method2 applied to pure aluminium containing 0.005 per cent.of sodium was found to give little more than 50 per cent. recovery in two heating and leaching processes, including rinsing of the tube. (In carrying out these tests, the more accurate zinc uranyl acetate procedure was used for the determination of the sodium, in place of the original volumetric procedure). However, the sodium content of aluminium and its alloys is normally considerably less than 0*005 per cent., and in some metallurgical investigations “fourth place’.’ accuracy is desirable in the determination. It was found possible to attain this order of accuracy by separating the sodium from the aluminium by vacuum distillation. LOW VACUUM METHOD Preliminary experiments were carried out in a comparatively low vacuum of 0.1 mm of mercury or better, such as could easily be attained by a rotary oil pump.A transparent quartz tube, sealed at one end and closed at the other by a ground-on cap and having a side arm for the attachment of the vacuum connection, was used for the distillation. A sample of metal, weighing 5 to 40g, in a clean graphite boat, was inserted as far as possible into the quartz tube, which was capped and evacuated. The end of the tube containing the sample was heated in a tube furnace at 900” C and the other end was cooled by a jet of cold water. At the conclusion of the distillation the tube was allowed to cool, the vacuum broken, and the boat and regulus carefully withdrawn. The deposit of sodium and other metals that had collected in the cooled part of the tube was dissolved in hydrochloric acid and the sodium estimated gravimetrically by the zinc uranyl acetate method.Good results were obtained by this simple procedure on aluminium alloys of the duralumin type containing about 1 per cent. of magnesium. In Table I the method is compared with the amyl alcohol method* and aluminium chloride precipitation method* on samples of TABLE I COMPARISON OF VACUUM DISTILLATION METHOD WITH AMYL ALCOHOL METHOD AND ALUMINIUM CHLORIDE PRECIPITATION METHOD Sodium found by AICI, Amy1 alcohol precipitation Sample method, method, 1 0.11 0.10 2 0.13 0.12 3 0.08 0.07 4 0.07 0-07 5 0.09 0.07 O/O % Vacuum distillation method, 0.1 1 0.12 0.07 0.08 0.08 % duralumin alloy of high sodium content. With samples of low sodium content, it was found necessary to redistil the regulus from the first distillation to obtain complete recovery of the sodium. A sample containing about 0.002 per cent.of sodium yielded 90 per cent. of the total in the first distillation, and the remaining 10 per cent. in the second; no further sodium was yielded by a third distillation. About two days were required to complete a test including two distillations. The standard error of a determination was calculated to be &0-0002 per cent. on samples covering a range of 0.0004 to 0.0025 per cent. of sodium.202 [VOl. 76 The above method therefore appeared to be satisfactory for aluminium alloys containing appreciable quantities of magnesium; but attempts to apply it to pure aluminium failed; for three distillations were insufficient to free the regulus entirely from sodium.The addition of magnesium to the metal before fusion (0-2g placed in the graphite boat below the aluminium) was successful in clearing the sodium from the aluminium in two distillations, and the results so obtained were in good agreement with those later obtained by the high vacuum method. The low vacuum procedures described above are, therefore, satisfactory methods for the determination of sodium in aluminium and its alloys both with and without magnesium, which, however, must be added if not already present in the metal. The high vacuum method described below does not require the presence of magnesium to help volatilise the sodium, and all the sodium can be separated in a single distillation.For these reasons, the low vacuum method was abandoned in favour of the high vacuum method. McCAMLEY, SCOTT AND SMART: THE DETERMINATION OF SODIUM IN HIGH VACUUM METHOD The procedure used was the same as for the low vacuum method, except that a vacuum of 10-4 to 10-6 mm of mercury was maintained in the quartz tube throughout the distillation ; this was easily achieved by the use of a three-stage mercury vapour diffusion pump. A sudden rise of pressure, due to release of gas, was found to occur during the test when the metal melted, but the pressure rapidly returned to its former value of less than 10-4mm and the deposition of the metallic mirror then commenced in the cold portion of the tube. It was found that practically all the sodium could be recovered in a single distillation at 900" C provided sufficient time was allowed. Table I1 shows the results of tests on a sample of pure aluminium for various times of (distillation a t 900" C.These and further TABLE I1 EFFECT OF TIME OF DISTILLATION ON RECOVERY OF SODIUM Sodium, yo /l I \ First Second Duration of each each distillation distillation distillation Total 75 min. 0-0065 0*0002 0.0067 60 min. 0.0064 0.0004 0.0068 45 min. 0.0051 0*0010 0.0061 30 min. 0.0042 0.0025 0.0067 tests showed that not more than 0.0001 to 0.0002 per cent. of sodium would remain undistilled by a single distillation of 75 minutes, and this was adopted as the standard time. To obtain reliable results with a single distillation, however, it was found essential to maintain a vacuum of less than 10"mm of mercury during the deposition of the metal.On one occasion when, owing to a leak, the pressure rose to mm of mercury, a low value was obtained in the first distillation, and a redistillation of the metal regulus yielded 0.0009 per cent. of sodium. In routine operation, the pressure is checked periodically during the distillation by a McLeod gauge reading to 10-6m:rn of mercury. Normally it is satisfactory to finish the determination gravimetrically as described by the original authors. Alternatively, the yellow sodium zinc uranyl acetate precipitate may be redissolved (after filtering and washing) in warm water, diluted and determined absorptio- metrically. An interesting volumetric procedure for determining the sodium zinc uranyl acetate was found useful in one of our laboratories where large numbers of samples of low sodium content (<0.005 per cent.) were being tested and is given below in full.Excellent agreement between the gravimetric, photometrk and volumetric finishes was obtained. The complete method as finally adopted is given below. EXPERIMENTAL METHOD APPARATUS- The silica distillation tube, 14 x 13 in., is provided with a ground-on cap in silica or Pyrex glass, and has a short side-arm, 1Q x +in., situated 1& inches from the open end. The side-arm The arrangement of the distillation tube and heating furnace is shown in Fig. 1.April, 19511 ALUMINIUM AND ITS ALLOYS BY VACUUM DISTILLATION 203 terminates in a flat, ground surface that forms, with a similar surface, the joint to the high vacuum line.The silica tube is loosely held in a co-axial cooling jacket provided with a water spray and a drain tube. The cooling jacket is held in position by the drain tube, which passes through a rubber bung fixed in a hole in the steel base plate. The source of high vacuum is a three-stage mercury diffusion pump, backed by a rotary oil pump. A large cylindrical glass bulb (about 1 litre capacity) may be inserted in the vacuum line between the diffusion pump and the backing pump, so that the latter can be switched off as soon as a high vacuum is obtained in the apparatus: the glass bulb should be fitted with a mercury manometer sealed into the top and a glass tap, connected to the backing pump, at the bottom. The high vacuum side of the diffusion pump is connected to the flat ground joint by wide-bore glass tubing, which carries a T-joint connecting to a McLeod gauge capable of reading to 10-5mm of mercury.The large tap above the flat ground joint enables the vacuum in the distillation tube to be broken independently of the rest of the apparatus, so that there is the minimum delay in changing the distillation tube and commencing the next distillation. A liquid-air trap may be inserted in the vacuum line above the large tap to obviate the possibility of mercury vapour passing from the diffusion pump into the distillation tube. The distillation tube is heated by a tube furnace consisting of a quartz tube 6f inches long by 18 inches bore wound with wire to give a tube temperature of 900" C, corresponding with a furnace temperature of about 1000" C, contained in a rectangular box packed with thermal insulating material. The temperature of the furnace is registered by a thermo- couple inserted through a fireclay plug in the outer end of the tube, and is controlled by a resistance in series with the furnace winding.The furnace as a whole can slide on runners fixed to the base plate that carries the cooling jacket and tube, giving a convenient means of moving the tube furnace over or away from the distillation tube as required. The graphite boats used for holding the samples are constructed from graphite rod 23 mm in diameter and about 60 mm long. A hole 17 mm in diameter is drilled along the axis of the rod to about 5 mm from the end. A graphite plug about 5mm long is made to fit the open end of the hollow cylinder.About half of the portion of the hollow cylinder between the plugged and closed ends is cut away, to form a boat about 50 mm long, 17 mm wide and 10 mm deep. Each new boat is cleaned before use by repeatedly distilling in it a piece of scrap aluminium until the blank value becomes negligible. The silica distillation tube is cleaned after each test with chromic - sulphuric acid mixture, and dried with methylated spirits and ether, finishing with a gentle stream of dry air. New tubes are cleaned by distillation as for new graphite boats. REAGENTS- (a) Fm gravimetric procedure- Acetic acid-A diluted (1 + 1) solution. Zinc uranyl ncetnte Ye~gent-sOLUTION A-Dissolve 77 g of uranyl acetate, U02~C2H302),.2H20, in 410 ml of water containing 13.3 ml of glacial acetic acid SOLUTION B -Dissolve 231 g of zinc acetate, Zn(C,H,02),.3H,0, in 262 ml of water containing 6.6 ml of glacial acetic acid.Heat solutions A and B to 70" C, mix, and stir the combined solution until clear. Allow the solution to stand at least 24 hours, and filter immediately before use. . Alcoholic wash solutio-This is 95 per cent. alcohol saturated with sodium zinc uranyl acetate, NaZn(UO,),. (C2H302)9.6H20. Prepare sodium zinc uranyl acetate by precipitating 0.1 g of sodium chloride, dissolved in 5 ml of water, with 50 ml of zinc uranyl acetate reagent as described below for the test. Filter the precipitate on a small sintered-glass crucible (porosity 3) and wash thoroughly with 95 per cent. ethyl alcohol. Transfer the precipitate to a bottle containing 1 litre of 95 per cent.ethyl alcohol, shake well, and allow to stand at least 24 hours. The zinc uranyl acetate reagent and alcoholic wash solution are stored at about 20" C. (b) For volumetric procedure- The following reagents are required in addition to those for the gravimetric procedure. Ammonium fluoride-A 2 per cent. solution. Potassium thiocyanate-A 10 per cent. solution. Filter the solution just before use.zQ4 [Vol. 76 This solution is usually prepared in bulk, and stored and used under an atmosphere of hydrogen. Suitable storage apparatus is described and illustrated in publication No. 405 of the British Aluminium Company Ltd.s and in many standard works on chemical analysis. Prepare the reagent by adding 200ml of 15 per cent.titanous chloride solution to 200ml of hydrochloric acid (sp.gr. 1.16) in a large beaker. Boil the mixture for 2 minutes and rapidly dilute to 5 litres by pouring into cold water. Mix the solution and immediately transfer to the reservoir of the storage apparatus and connect to the hydrogen generator. Allow the solution to stand overnight before use. Dissolve 0.500 g of standard steel (99.7 per cent. of iron) in 20 ml of sulphuric acid (1 + 1) and osidise by boiling with an excess of bromine water. Boil off the excess of bromine, cool the solution and dilute to 500.0 ml. 1.0 ml of N/56 iron solution = 0.00006845 g of sodium. PROCEDURE- Cut a sample of metal weighing 5 to 20 g (depending on the sodium content) and of suitable dimensions to fit the graphite boat, from the cast metal.Care should be taken not to include any surface skin. Clean the sample by heating it in dilute hydrochloric acid (1 + 9) for a few minutes, wash well with distilled water and dry. The sample should not be touched with the fingers after washing. Weigh the sample, transfer it to a clean graphite boat, and insert as far as possible in the distillation tube. Place the latter in position in the cooling jacket, and place the cap on the tube, a soft vacuum grease being used to lubricate the joint. Connect the tube to the vacuum line, a hard vacuum grease being used for the flat joints. Start the backing pump, and when the pressure in the apparatus has fallen below 1 cm of mercury, start the mercury vapour diffusion pump. As soon as the pressure in the apparatus, as indicated by the McLeod gauge, has fallen below 10-4mm of mercury, move the furnace, which has been allowed to heat up to 900" C, over the end of the distillation tube, and start the cooling spray.Heat the sample at 900" C for la hours, during which time the reading on the vacuum gauge must be checked periodically. Then withdraw the furnace from the distillation tube, and cool the tu'be to room temperature with an air blast. Disconnect the distillation tube from the vacuum line, remove the cap of the tube and carefully clean off the grease on the ground joints with benzene. Remove the graphite boat from the tube, taking care not to rub off any of the distilled film of metal. Remove the film of metal by adding 5 ml of hydrochloric acid dropwise from a pipette and rinse the tube with about 40ml of water. Boil the contents of the tube gently for a few minutes, and transfer to a 150-ml silica beaker or basin.Repeat the extraction procedure and transfer the liquor to a second 150-ml beaker to serve as a blank. Cover the beakers with silica covers and evaporate the contents to dryness. Extract the residues with 1-0 ml of water and 5 drops of diluted acetic acid (1 + 1); warm the beakers to assist solution. Cool the solutions to 20 & 1" C, and add 10 ml of zinc uranyl acetate solution with vigorous stirring. If the original sample contained more than 0.4g of magnesium, 3.0ml of water and 15 drops of acetic acid should be used for the extraction and 30 ml of zinc uranyl acetate for the precipitation. Allow the precipitating solution to stand for 30 minutes at 20" C, with occasional stirring.Collect the precipitate on a small sintered glass crucible (porosity 3 or a), and rinse the beaker with five 2-ml portions of the zinc uranyl acetate reagent, so that all the precipitate is transferred to the crucible. Then wash the crucible with five 1-ml portions of alcoholic wash solution and finally with 5ml of dry ether. (a) GravimetricJinish-Dry the crucible in an oven at 100" C for 30 minutes (no more), cool and weigh. Extract the precipitate on the ci-ucible under suction with hot water until the yellow precipitate is completely dissolved. Again wash the crucible with alcoholic wash solution and ether, dry as before, and reweigh. 'The difference between the two weighings gives the weight of sodium zinc uranyl acetate, from which the blank is subtracted.MCCAMLEY, SCOTT AND SMART: THE DETERMINATION OF SODIUM IN Titanous cMoride-An approximately N/28 scllution. Standard iron-A N/56 solution. Factor 0.01495. (b) Photometric $nis&Extract the precipitate on the crucible under suction with small additions of hot water and collect the extracts in a small tube inside the suction flask. Cool the solution and dilute to a known volume, depending on the intensity of colour, in a graduated flask. Measure the extinction of the solution in a Spekker absorptiometer, using a l.O-cmFig. 1. General view of tube furnace assemblyInternal Furnace Silica Support - Copper Copper- Fig. 2 --L n -A -B 7 Dlc n Fig. 3 Fig. 2. Distillation apparatus for sodium determinations Fig.3. Details of construction of internal furnace -4, sample: B, loose graphite crucible; C , graphite crucible with platinum immersion heater (0.5-mm. platinum wire with alumina tube insulation) : 11, alumina block: E, spacing wiresApril, 19511 ALUMINIUM AND ITS ALLOYS BY VACUUM DISTILLATION 205 cell, and Ilford No. 601 (violet) filters. The corresponding sodium content is read from a graph prepared by subjecting measured quantities of standard sodium chloride solution to the precipitation and ensuing procedures described above. (c) Volumetric finish-Extract the precipitate on the crucible under suction with hdt water into a 350-ml filtration flask. Cool the solution in the flask and add 10 ml of hydro- chloric acid.Titrate the contents of the flask with a slight excess of titanous chloride solution (N/28) to a faint pink colour. Allow the solution to stand for 5 minutes, and add 20 to 25 ml of ammonium fluoride to form a complex with the uranous salt. Shake the mixture and add 10 ml of 10 per cent. potassium thiocyanate solution. Titrate back the excess titanous chloride with standard iron solution (N/56) until a pink colour persists. Treat the blank in the same way as the sample. Standardisatiozz of the titanous chloride solution-Measure 20.0 ml of standard iron solution (N/56) into a conical flask, add 10 ml of sulpliuric acid (1 + 2) and 10ml of 10 per cent. potassium thiocyanate solution and titrate the mixture with the titanous chloride solution. Calculate the titre of the titanous chloride solution in accordance with the equations- (1) (UO,)Cl, + 2TiC1, + 4HC1 + UC1, + 2TiC1, + 2H,O (2) TiC1, + FeC1, = TiC1, + FeCl, whence NaZn(U0,),!C2H,02),.6H20 = 6TiC1, = 6FeCl,, i.e., 1.0 ml of N/56 iron solution = 0.0685 mg of sodium.TESTS WITH MODIFIED APPARATUS The lack of alternative methods of analysis, and the difficulty of preparing standards containing fixed amounts of sodium, has made it difficult to check the absolute accuracy of the vacuum distillation method below 0-005 per cent. of sodium. It appeared possible that some of the sodium vapour evolved from the sample during distillation might react with the hot silica tube, and possibly penetrate into it, so that all the sodium would not be recovered in the subsequent washing with acid.Although the high reproducibility of the method suggested that this was unlikely, an attempt was made to check the possibility. A modification of the apparatus was therefore designed, in which the sodium was con- densed immediately on a cold surface without having had the opportunity of coming into contact with hot silica. The sample in the form of a short cylinder was contained in a graphite crucible 8 inch in outside diameter and 18 inches long with a wall thickness of 1/16 inch and a slight taper to the bottom to allow the regulus to be removed after the experiment. This crucible fitted closely into another graphite crucible, which had vertical holes drilled in the wall to accommodate a heating element consisting of platinum wire 0-5 mm in diameter.The wire was insulated from the graphite by means of thin, highly-fired alumina tubing. To cut down radiation losses, the heated crucible was enclosed in two concentric cylindrical screens made from bright nickel sheet. The inner screen was spaced from the graphite by three vertical nickel wires of 1 mm diameter, and the outer screen was spaced from the inner one in the same way. The whole graphite assembly was supported on a small block of alumina placed on the bottom of the inner nickel pot. With this arrangement, the metal charge could be raised to the operational temperature of about 900" to 950" C with only 100 watts input to the heater, and the main radiation loss was from the open top of the crucible. An air blast on the top of the glass bulb was sufficient to keep it cool, and the sodium vapour was found to condense satisfactorily on the upper walls of the bulb.A three-stage diffusion pump was used for evacuation of the apparatus. Owing to the use of a glass bulb for condensation of the sodium, the blank on the apparatus was rather high; a quartz bulb would have eliminated this trouble. The blank was reduced considerably by (a) rinsing the bulb with hydrochloric acid (1 + 1) just before the test and (b) placing a small piece of zinc (about 10 mg) on the sample. The zinc volatilised at 400" to 500" C and formed a protective layer on the glass bulb. Attempts were made to check the recovery of sodium by the apparatus with sodium carbonate and sodium azide. A small hole was drilled in the sodium-free regulus from a previous distillation, a small weighed quantity of the sodium salt was introduced, and the "salted" metal was then distilled by the usual method.Although sodium carbonate gave Details of the modified apparatus are shown in Figs. 2 and 3.206 McCAMLEY, SCOTT AND SMART: THE DETERMINATION OF SODIUM I N [VOl. 76 low results, possibly owing to the difficulty of reducing this salt a t 900” C, quantitative recovery was obtained from sodium azide additions equivalent to 0.050 per cent. of sodium in the metal. These tests indicated that the apparatus was working satisfactorily and that all the sodium volatilised was condensed on the glass bulb. A comparison was then made between the first apparatus and the modified apparatus on a number of samples of aluminium of ordinary purity.The results of these tests are shown below- Sodium, yo n 7 ___- Apparatus c------- Silica tube . . .. .. 0.0067 0.0002 0*0101 0.0122 Glass bulb . . . . .. 0.0068 0.0007 0*0110 0.01 19 The agreement between the two methods is reasonably good and affords convincing proof that there is no appreciable loss of sodium when distillation is carried out in a quartz tube. However, a s the quartz tube apparatus is more convenient for general use, it was adopted in the standard procedure and the following comments refer to the use of this apparatus. SCOPE AND ACCURACY OF THE HIGH VACUUM DISTILLATION METHOD The vacuum distillation method as described above has been satisfactorily used for the determination of sodium in aluminium of commercial and high purity grades, and for many alloys covering a wide range of sodium content.Elements such as magnesium and zinc, mhich distil together with the sodium do not interfere with the final determination as sodium zinc uranyl acetate unless present in large excess. When more than 0.4g of magnesium was present in the original sample, it was found necessary to increase from 1 to 3 ml the amount of water used for dissolving the salts prior to the addition of zinc uranyl acetate reagent, and to increase the corresponding amount of zinc uranyl acetate reagent from 10 to 30 ml, to avoid precipitation of magnesium chloride. As stated above, the method was devised for trace quantities and so far it has been used satisfactorily in the range O-OOOl to 0.06 per cent., which covers more than the com- mercial range.Although the sample weight can be adjusted to suit various sodium contents without any consequent changes in the analytical conditions, it is obvious that for much greater amounts of sodium the sample weight would become so small as to reduce the precision of the method. Furthermore, some additional special samples examined, which contained over 0.1 per cent. of sodium, had to be heated extremely cautiously in order to minimise spattering during the distillation. Such samples normally contain much gas, and some improvement was noted by heating them very dowly through the melting range. The precision of the method was found to compare very favourably with that of existing methods. The standard error obtained during research on the method was calculated to be -+040027 per cent.from 83 results on 27 samples containing from 0.0002 to 0-012 per cent. of sodium. Under routine operation the following standard deviations were obtained- +0.00014 per cent. for 0.0001 to 0.001 per cent. of sodium &0-00022 per cent. for 0.001 per cent. of sodium *0.0011 per cent. for over 0.01 per cent. of sodium to 0.01 The standard errors obtained for the amyl alcohol method, the aluminium chloride precipita- tion method and the Scheuer method were as follows*- Range AlCl, (sodium Amy1 alcohol precipitation Scheuer Metal content), method, method, method, % % % % Duralumin . . .. . . 0.05 -0.15 f0-007 *0.009 - Duralumin . . .. . . 0*001-0*005 f0.0007 - Pure aluminium . . . . 0.05 -0-20 f0.010 -&0.010 & O .O l l Pure aluminium . . . . 0*001-0*005 fo~oolo - The precision of the vacuum distillation method appears to be 3 to 10 times as great as that of existing methods for sodium contents greater than 0.001 per cent. A factor contributing greatly to the success of the vacuum distillation method is the extremely low blank, which is practically negIigible in the fourth decimal place for ordinary sample weights, and is independent of the amount of sample taken. The precision of the method could thereIore De increased still further by distilling a larger sample. blank by the vacuum distillation method is an important point in its favour; for all r‘solution” - - TheApril, 19511 ALUMINIUM AND ITS ALLOYS BY VACUUM DISTILLATION 207 methods are handicapped by the considerable blank introduced by impurities in the reagents ; for accurate work this places a lower limit of about 0.005 per cent.of sodium on all these met hods. The authors are indebted to The British Aluminium Co., Ltd., for permission to publish this work. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. Osborn, G. H., J . SOC. Chem. I n d . , 1943, 62, 216. Scheuer, E., 2. &letallkunde, 1933, 25, 139, 157. Bridges, R. W., and Lee, M. F., Ind. Eng. Chem., Anal. Ed., 1932, 4, 264. Smart, R., J . SOC. Chem. I n d . , 1943, 62, 213. Barber, H. H., and Kolthoff, I. M., J . Amer. Chem. SOC., 1928, 50, 1625. Gooch, F. A., and Havens, F. S., Awzev. J . Scz., 1896, (iv) 2, 416. Schurmann and Schob, Chem-Ztg., 1924, 48, 97. Koide, M., J . SOC. Chem. Ind. Japan, 1940, 43, 3 5 1 ~ .“Analysis of Aluminium and Its Alloys,” Publication No. 405, British Aluminium Company Ltd., pp. 85-86. THE BRITISH ALUMINIUM COMPANY LTD. KINLOCHLEVEN, ARGYLL RESEARCH LABORATORIES DISCUSSION MR. R. F. MILTON asked whether the method gave a value for total sodium or only for metallic sodium, i.e., whether sodium salts, for example, the fluoride, were reduced to the metallic state in the distillation process. When the sodium had been separated, would it be possible to dissolve it in water and carry out a micro-titration against standard acid? If the sodium was precipitated as the triple uranyl salt, was it not preferable to estimate it colorimetrically after formation of uranium ferrocyanide ? MR. C. E. BARRS asked whether the author had tested aluminium alloy L33 by his method, and whether nickel could be used in the construction of the apparatus.MR. V C r ~ ~ ~ ~ ~ ~ ~ asked if any practical difficulties due to leaks had been encountered in using the apparatus, and if any special precautions were taken in connection with the purity of the graphite used for boats. MR. G. H. OSBORN asked if the authors had tried the estimation of sodium in aluminium alloys by the flame photometer with a monochromator. Would the authors give their opinion on such a method as compared with vacuum distillation. MR. SMART, replying to Mr. Milton, said that, as far as he knew, sodium salts were not normally present in aluminium and its alloys. However, if present, they would probably be a t least partly reduced by the aluminium. This had been found in practice by his colleague, Mr.J. H. G. Thomson, who experimented with small quantities of cryolite in the presence of aluminium. Once the sodium had been separated by vacuum distillation, a number of methods could be used for its determination. The micro-titration with standard acid suggested by Mr. Milton could be used in the absence of interfering elements, but the zinc uranyl acetate method was much more generally applicable. The methods described for the estimation of the triple uranyl salt had been found to give an ample degree of accuracy. Replying to Mr. Barrs, Mr. Smart said that the method had been applied to a number of alloys, including L33, and had given satisfactory results. ?So attempt had been made to use anything but quartz for the vacuum tube. In reply to Mr. Westwood, Mr. Smart said that all the connections in the high vacuum line were sealed glass, the only joint being the flat ground-glass joint between the high-vacuum line and the quartz vacuum tube. The only possibility of leakage was a t this joint and the ground-on cap of the vacuum tube, and both of these were held tight by the vacuum itself. In practice, no trouble had been experienced from leaks. The graphite used for the boats was not of special purity, and i t was always necessary to subject the boat to repeated distillations with a piece of scrap aluminium until no further sodium was evolved. Replying to Mr. Osborn, hlr. Smart said that a simple type of flame photometer had been tried but had been found useless over the lower ranges of sodium content owing to interference by aluminium. MR. J. H. G. THOMSON said that he had not had the opportunity of using a flame photometer equipped with a monochromator. In the simple type of instrument used, a hydrochloric acid solution of the sample was atomised in a coal-gas flame and the sodium line isolated by an Ilford Spectrum filter. I t was found that in the presence of aluminium the sensitivity of the process was very much reduced. Although a direct procedure based on a photometer with monochromator would be simpler, there seemed some doubt whether the accuracy would be as good for the very low sodium contents. The great advantage of the separation by vacuum distillation was that the concentration of sodium in solution could be increased to any desired extent.

ISSN:0003-2654    

DOI:10.1039/AN9517600200

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

208 BLACK: THE DETERMINATION OF LEAD OXIDE [Vol. 76 The Determination of Lead Oxide in the Presence of Lead BY R. M. BLACK (Presented at the meeting of the Society on Wednesday, November l s t , 1950) A method has been devised for the estimation of lead and lead oside in lead dross; it makes use of the reaction between lead monoxide and an ammonium salt to give ammonia and the corresponding lead salt. The ammonia is removed from the solution by steam distillation, absorbed in an excess of boric acid, and the ammonium borate so formed titrated with standard acid in the usual manner. The :method gives reasonable accuracv with quantities of lead oxide as small as 101 mg, but requires further develop- ment before it becomes applicable to small oxide inclusions in lead sheathing alloys.IN the cable industry it is occasionally necessary to determine the composition of the dross formed upon the surface of the melting pots for cable sheathing alloys and to calculate the lead - oxygen ratio; this, for example, enables the efficiency of a fluxing agent to be assessed. The grey dross formed upon the surface of the melt is chiefly a mixture of lead and lead monoxide or litharge; the usual method for the analysis of such a mixture involves treatment with acetic acid, removal of the lead by filtration and gravimetric estimation as sulphate or chromate of the lead remaining in solution. It is known,l however, that on trituration with lead oxide, ammonium chloride decom- poses with the evolution of ammonia and the formation of lead chloride, the reaction being- PbO + 2NH4C1+ PbCl, + H,O + 2NH, A similar reaction takes place if the lead oxide is trea.ted with an aqueous solution of ammonium chloride, or any other ammonium salt.The work described here was carried out with the object of utilising this reaction, not only for the estimation of lead oxide in lead dross, for which it would appear eminently suitable, but also, by the use of a semi-micro scale apparatus, for the detenriination of lead oxide inclusions in sheathing alloys. The problem resolved itself into two major sections; the first, that of the estimation of the evolved ammonia, was overcome by making use of a technique similar to that applied in the estimation of nitrogen by a micro (or semi-micro) Kjeldahl method.2 The ammonia, separated by steam distillation, was absorbed in an excess of boric acid and the ammonium borate so formed titrated with 0.1 N or 0.01 N hydrochloric acid, a mixture of bromocresol green and methyl red being used as indicator.The second section of the problem, of partictilar importance in the estimation of small quantities of lead oxide, arose from the blank reading produced by the dissociation of ammonium salt solutions on steaming them. With 5 N ammonium chloride steamed for 15 minutes a quantity of ammonia, equivalent t o about 5ml of 0.01 iV acid, was carried over. NH,' ", NH, + H' and as steaming progressed the pH of the solution fell from 4.5 to below 2-0 owing to the production of hydrochloric acid. The amount of ammonia produced is dependent on the initial concentration of the ammonium chloride solution and on the time of steaming.Experiments to examine this dissociation were canied out by steaming a known volume of 5 N ammonium chloride solution at a constant rate (10 ml of water condensed per minute) and changing the absorbing solution, an excess of boric acid, at 5-minute intervals. The results indicated that the rate of evolution of ammonia decreased with time, reaching zero aiter about 1 hour (Fig. 1). The reactions of various other ammonium salts were examined both as to their action with lead oxide and their rate of dissociation on steaming in aqueous solution. I t was found that of the ammonium salts examined, nitrate, phosphate, acetate and chloride, the nitrate The production of ammonia resulted from the disturbance of the equilibrium-April, 19511 IN THE PRESENCE OF LEAD 209 dissociated more rapidly than the chloride and gave the lowest blank, but it was not so rapid in its action on the lead oxide; other salts of weaker acids were, of course, more unstable and hence unsuitable for our purpose.The problem of dissociation of the ammonium salt solution made imperative the standardisation of steaming conditions and times in order to get a reproducible blank reading. A suitable steaming time was found to be 15 minutes and this was confirmed by treating known quantities of lead oxide with ammonium nitrate solution and changing the absorption flask at 2.5-minute intervals. 8 -E7 9 6 2 5 - 8 4 :3 Y - 2 5. 10 IS 20 25 30 Time of Steaming. Minutes Time of Steaming. Minutes 1;ig.I . Decomposition of ammonium chloride Fig. 2. Removal of ammonia by steaming from an oxide determination with ammonium nitrate solution (5 &'V) by steaming Fig. 2 shows the relationship obtained and indicates that the greater part of the ammonia was removed from the solution during the first 15 minutes, the residual slope of the curve indicating only the dissociation of the ammonium nitrate solution. For the purpose of estimating lead oxide in dross, particularly when its metallic lead content was high, disintegration of the dross by amalgamation with mercury was found TABLE I DETERMINATIOX OF LEAD OXIDE ADDED TO 1 G OF PURE LEAD Lead oxide Error A -7 r- I -I A Taken, Found, Difference Per cent. E: 0-0009 0.004 1 0-0048 0.0099 0.0100 0.0135 0-0246 0.0255 0.0340 0.0427 0.0598 0.1099 0.1693 g 0.0022 0.0057 0.0038 0.0096 0*0097 0.0141 0.0246 0.0250 0.0350 0.0439 0.0581 0.1125 0.1683 +0.0013 +0*0016 - 0~0010 - 0.0003 - 0.0003 + 0*0006 0.0000 - 0.0005 + O ~ O O l O +0-0012 -0.0017 + 0.0026 - 0~0010 + 142.0 + 41.0 - 21.0 - 3.3 - 3.0 + 4.4 0.0 - 2.0 + 2.9 + 2-8 - 2.8 + 4-0 - 0.6 efiective, the oxide forming a scum upon the surface.Amalgamation was accomplished in either of two ways-by heating with a small quantity of mercury in a vacuum, or in a current of oxygen-free nitrogen. METHOD REAGEXTS- Ammonium chloride solzttion-Dissolve 270g of the salt in 1 litre of water. Boric acid solzction-Dissolve 40 g of boric acid, A.R., in water, add 10 ml of bromocresol green solution and 2 ml of methyl red solution (a 0.1 per cent.solution in 95 per cent. alcohol) and make up with water to 2 litres.210 BLACK: THE DETERMINATION OF LEAD OXIDE [Vol. 76 PROCEDURE- Dissolve about 1 g of the dross in 5 ml of mercury in a 50-ml round-bottomed flask by heating it gently in a bunsen flame. Cool, add 20 ml of ammonium chloride solution to the flask, heat the solution to boiling and steam distil into 25 ml of 2-0 per cent. boric acid solution for 15 minutes. 1 ml of 0.1 N hydrochloric acid = 0.01116 g of PbO. Then titrate the ammonium borate with 0.1 N hydrochloric acid. The use of a mixture of bromocresol green and methyl red as indicator gave a sharp end-point reproducible to within 0.05 ml of 0.01 N acid. To assess the accuracy of the method, determinations were made on 1 g of pure lead to which weighed amounts of lead oxide had been added. From the results shown in Table I it appears that quantities of oxide greater than about 10 mg can be determined within reasonable limits of accuracy, and the method is, therefore, eminently suitable for the analysis of small samples of lead dross.The accuracy is not sufficient, however, for the method to be applicable to the determination of small oxide inclusions that may occur in sheathing alloys, and improvement in the accuracy of the method is required before its usefulness can be fully evaluated. The author’s acknowledgments are due to Dr. L. G. Brazier, Director of Research and Engineering of British Insulated Callender’s Cables Limited, for permission to publish this paper, and to Mr. G. M. Hamilton at whose suggestion this work was carried out.REFERENC:ES 1. 2. Isambert, F., Compt. rend., 1885, 100, 857. Ma, T. S., and Zuazaga, G., Ind. Eng. Chenz., Awal. Ed., 1942, 14, 280. 38, WOOD LANE BRITISH INSULATED CALLENDER’S CABLES LTD. SHEPHERDS BUSH, LONDON, W.12 DISCUSSION T H E PRESIDENT thanked Mr. Black for his paper. He said that there was a significant blank on steam distilling the ammonium salt, and asked if there was any significance in the different ammonium salts, for instance, in the effect of nitrate or chloride ion in the blank. MR. BLACK replied that ammonium nitrate gave the lowest blanks, but that ammonium chloride was used in the experiments described. Because of the lower blank, he suggested that ammonium nitrate should be used when the quantity of lead oxide to be determined was very small.DR. W. STROSS enquired whether the author had tried a technique frequently used in biological work for driving over the ammonia, particularly when there was a risk of ammonia originating from other sources through the application of heat. This technique consists in sucking or blowing a stream of air (purified by passing it first through dilute sulphuric acid) at rooin temperature through the test liquid and the absorbent, This technique might reduce the high blank and the necessity for the rigorous standardisation of the conditions of distillation. MR. BLACK replied that he had not tried this technique. Purified hydrogen or nitrogen would have to be used instead of air owing to the facility of oxidation of the lead amalgam.MR. G. H. OSBORN asked the author if i t were a fair assumption that only PbO was present. If not, and PbO, or Pb,O, were also present, he would like to know whether they would react in the same way, or whether the method could be used to differentiate between the different oxides of lead. MR. BLACK said that the dross, as far as he knew and could ascertain by a study of the literature, was composed entirely of a mixture of lead oxide (PbO) and metallic lead. Any Pb,O, present would be converted into PbO a t the temperature of the molten lead. PbO, and Pb,O, react with ammonia salts under the conditions described above to evolve ammonia, although the reaction is slower than with PbO. The reaction follows a similar type of equation to that formulated for the reaction with PbO. It would not appear possible, therefore, that the oxides can be separated by this method. MR. W. E. GREEN enquired whether Mr. Black had considered the effect of dissolved oxygen in the ammonium salt solutions. It had been found that dissolked oxygen would attack metallic lead to produce lead hydroxide i n amounts of several milligrams of PbiOH), per 100ml. A number of variations of the technical details had been published.1~2~3~416April, 19511 IN THE PRESENCE OF LEAD 211 MR. BLACK replied that the reagents for this method were prepared from fresh distilled water. It was possible, however, that some oxygen might be present. Nevertheless, if an appreciable quantity of oxygen had been present, it would have been apparent in the standardisation. Air had been excluded. REFERENCES TO DISCUSSION 1. 2. 3. 4. 5. Folin, O., et al., Z . Physiol. Chem., 1902, 37, 161. - , J . Biol. Chem., 1912, 11, 524; 493; 527. Myers, V. C., “Practical Chemical Analysis of Blood,” Mosby Co., St. Louis, and H. Kimpton, Marshall, E. K., J. Biol. Chem., 1913, 15, 487. Van Slyke, D. D., and Cullen, G. E., Ibid., 1914, 19, 211. London, 1924.

ISSN:0003-2654    

DOI:10.1039/AN9517600208

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

April, 19511 I N THE PRESENCE OF LEAD 211 The Estimation of Mercury on the Peel of Apples BY W. ARTHINGTON AND A. C. HULME Existing methods for the estimation of traces of mercury in biological materials are discussed. A technique is described for the estimation of mercury (as spray residues) on the skins of apples; after freeze-drying the tissues, which are digested with a nitric - sulphuric acid mixture, the mercury is extracted and estimated by means of dithizone, the reversion technique of Irving, Andrew and Risdon being used. By the application of this technique results are consistent and recoveries are generally satisfactory. NUMEROUS experiments have been carried out on the control of fungal rotting of fruit by the use of sprays containing mercurial compounds,1y2 and a t this laboratory recent storage trials with skin-coated apples3 have included samples treated with emulsions incorporating a fungicide in the form of phenyl mercuric chloride.Efforts were therefore made to determine the amount of mercury left on the skin of the fruit after treatment. At the concentrations used it was clear that the mercury would be present only in micro- gram quantities, in contrast to the extremely large amounts of organic matter in the sample. A study of the literature on the estimation of traces of mercury in biological materia14~s~6~7~8 revealed a variety of methods. In general, these depended upon a digestion of the organic matter followed by a colorimetric technique based on the formation of a coloured complex between mercury and diphenylthiocarbazone (dithizone) .The number and variety of the published methods showed that the accurate determina- tion of small quantities of mercury was not easy. The following methods were examined. METHOD OF THE ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS, 1945 The A.O.A.C. method4 is based on a digestion with nitric acid and potassium perman- ganate followed by an extraction with dithizone in carbon tetrachloride. Interfering metals are removed by an aqueous thiosulphate transfer and the mercury is then re-extracted with dithizone in chloroform. Results by this method were disappointing, possibly because of a high blank; trouble also appeared to centre round the use of the pennanganate. Typical results are shown in Table I. THE METHOD OF MILTON AKD HOSKINS AND BUCKNELL et aE.Milton and Hoskins5 and Bucknell et aLs estimated mercury in urine and used a technique of co-precipitation by hydrogen sulphide of mercury and added arsenic from a sulphuric acid and potassium permanganate digest. The mercury sulphide was selectively extracted from copper and similar metals with aqua regia, and the mercury was then extracted from the acid solution with dithizone after destruction of nitric acid by hydroxylamine. This method when applied to apple peel gave fairly high recoveries, but the results. were not always reproducible, partly because of incomplete precipitation of the mercury sulphide and partly because of the difficulty of separating the combined sulphides from the[Vol. 76 digest even by means of high-speed centrifugation.Examples of the results obtained are given in Table 11. 212 ARTHINGTON AND HULME: THE ESTIMATION OF MERCURY TABLE I: TYPICAL RECOVERIES OF MERCURY BY THE A.O.A.C. METHOD 25 g of peel, Mercury found, Recovery, 100.0 86.0 86 50.0 43.8 88 60.0 40.0 80 25.0 16.0 64 Mercury added to Pg Pg Y O TABLE I1 TYPICAI, RECOVERIES OF MERCURY BY THE METHOD OF MILTON AND HOSKINS' AND BUCKNELI, et aL6 Mercury added to 26 g of peel, Clg 160.0 100.0 70.0 70.0 60-0 40.0 Mercury found, Recovery, Pt3 Y O 82.0 55 73.0 73 71.0 101 63.0 76 48.0 96 24.0 60 THE METHOD OF LAUG AND NELSON The salient feature of the method of Laug a:nd Nelson' (see Sandells) is the separation of mercury from copper by shaking the chloroform solution of the dithizonates with an acid solution of potassium bromide.The mercury is transferred to the aqueous phase and allowed to react with an excess of dithizone in chloroform at pH 6.0. The mercury is then determined in the chloroform layer by the mixed colour method (i.e., the excess of dithizone is not removed). The sample is given a preliminary digestion with a 1 + 1 mixture of concentrated sulphuric acid and nitric acid. Although this method of digestion proved excellent when the nitric acid was increased to the ratio of 3 to 5, as suggested by Dr. H. Irving (private communication) , the recoveries of added mercury estimated by the Laug and Nelson method as a whole were so low that the method was abandoned. PAPER PARTITION CHROMATOGRAPHY In view of the results obtained by Arden et aL9 on the separation of inorganic ions on paper chromatograms, the separation of mercury was attempted by this method.Good resolution was obtained but the mercury dithizonate spots were too irregular in shape to give satisfactory quantitative results. The chromatographic technique was, however, used successfully to test the efficacy of the procedure for removal of interfering metals by thiosulphate in the A.O.A.C. method. This survey of the available methods suggested that the difficulties of estimating mercury in biological material are mainly caused by- (a) Loss of mercury by evaporation during digestion owing to the relatively high volatility of the metal and its compounds. (b) The sensitivity of the dithizone reagent to oxidation, which necessitates complete removal of the oxidising agents used in the digestion.(c) The non-specificity of dithizone for mercury. RECOMMENDED METHOD With the above points in mind the following technique was developed and, as will be seen by the results shown in Table 111, it proved satisfactory for the estimation of mercury residues on apple peel. It is based on the digestion method of Laug and Nelson' followed by the determination of mercury in the digest by the reversion technique of Irving, Andrew and Ridon.'*April, 19511 ON THE PEEL OF APPLES 21 3 REAGENTS- Sul9huric acid-Concentrated A.R. Nitric acid-As.T. of the British Pharmacopoeia. Reversion mixture-A solution of 10.2 g of potassium hydrogen phthalate, A.R., and 30 g of potassium iodide, A.R., made up to 600 ml. Pithizone-Purified as directed by A.0.A.C4 Methyl alcohol-A.R.Chloro form-A.R. Hydroxylamine sulphate. All reagents, except the dithizone, were used as supplied by the manufacturers. The solutions were made up with glass-distilled water and the glassware used was cleaned with nitric acid, washed with distilled water and finally rinsed with glass-distilled water. 08 0.7 I I I I I I - Fig. 1. Calibration curve for converting rever- sion values to pg of mercury flask was fitted a condenser of the type known as a “cold finger,’’ reaching well down into the centre of the flask. This condenser was fed with tap water passed through a large copper coil surrounded by ice and proved most successful in preventing loss of mercury by volatilisa- tion during the digestion process. Before inserting the cold finger, 50 ml of a mixture of sulphuric and nitric acids in the proportion of 3 to 5, which had been chilled at -10” C overnight, were added, the condenser was replaced and very gentle heating was applied to the flask.A copious evolution of brown fumes of oxides of nitrogen took place and the heating was increased very slowly, since it was essential to prevent excessive foaming and spluttering. After a short time (about half an hour) the solution cleared and heating was increased cautiousIy until the liquid simmered gently, with the neck of the flask barely warm to the touch. Digestion was continued for 4 to 6 hours until a pale-yellow. clear liquid was obtained. During digestion a wax-iike compound collected on the cold finger. Therefore, from time to time the flask was cooled and the condenser washed down with glass-distilled water.When digestion was complete the solution was cooled, the “wax” that settled out on the surface of the liquid was removed by filtration on a Buchner funnel with a Whatman2 14 ARTHINGTON AND HULME: THE ESTIMATIOS OF MERCURY No. 60 paper, and the filtrate was made up to 260 ml. A 50-ml portion of this solution was added to 15 g of hydroxylamine sulphate (to reduce any excess of nitric acid) and made up to 1OOml. Duplicate portions of this solution (which was about 2.0 to 2.2 N in acid) were then used for the estimation of mercury, [Vol. 7 6 ESTIMATION OF MERCURY- Twenty-millilitre portions of the digest, free from nitric acid and prepared as described above, were shaken with dithizone (66mg per 1OOOml of chloroform).The reversion values were then determined by the procedure described by Irving, Andrew and Risdon,*o except that the densities were measured on a Zeiss Pulfrich Photometer with the red filter (approximately 610 mp). The amounts of mercury corresponding to the reversion values were read from the calibration curve shown in Fig. 1. In constructing this calibration curve mercuric acetate was dissolved in sulphuric acid and reversion values, R, were found for different concentrations of mercury. The line of “best fit” was calculated by the method of least squares. The reliability of the method for recovering mercury from plant tissues was determined by adding various amounts of phenyl mercuric chloride (75 to 750 pg of mercury per 25 g of peel) to untreated apple peel and carrying out the digestion and reversion as outlined above.In addition, added mercury was determined in the presence of 10 to 30 times its weight of added copper. The results are given in Table 111. TABLE III RECOVERY OF MERCURY ADDED ALONE OR WITH COPPER TO APPLE PEEL Apple sample + added nierc?.rry--- T1 + 455.0 pg of mercury = 18.20 pg/20 ml T1 + 682.5 pg of mercury F- 27.3 pg/20 ml T1 + 227.5 pg of incrcury = 9-1 pg/20ml T1 + 75.83 pg of mercury = 3.03 pg/20 ml With added coppev- 27.3 pg of mercury per 276.9 pg of copper { 20 ml 18.2 pg of mercury per 276.9 pg of copper { 20 ml 9.1 pg of mercury per 2764 pg of copper { 20 ml En, * (2) 0.323 (ii) 0.335 (Zii) 0.342 (i) 0.194 (2%) 0.193 (iii) 0.193 ( 2 ) 0-443 (25) 0-455 (iii) 0.435 (0 0.632 (27) 0.650 (iii) 0.644 (2) 0.223 (Zi) 0.216 (t) 0.372 (22) 0.348 (2) 0.506 (22) 0.493 (Zii) 0.489 Ey* 0.623 0.617 0.628 0.025 0.628 0.633 0.619 0.621 0.61 2 0.694 0.708 0,696 0.654 0.644 0.658 0.637 0.644 0.655 0.630 1< 0.300 0.282 0.286 0.43 1 0.435 0-436 0.176 0.166 0,177 0.062 0.058 0.052 0.43 1 0.428 0.286 0.289 0.139 0.157 0.150 Mercury, pg/20 ml 19.43 18-30 18.55 27-67 27.92 27.99 11-64 11-00 11.70 4-47 4-2 1 3-90 27.67 27.49 18.55 18-74 9.31 10.44 10.00 Minus blank 18.14 17.01 17.26 26.38 26.63 26.70 10.35 9.7 1 10.42 3-18 2.92 2.61 26.38 26.20 17-26 17.45 8.02 9.15 8.71 Kecovery, iMean, % % 99.7 93.5 } 96.0 94.8 97.8 113.7 114.6 104.9 96.4 } 95.8 86.1 * Optical densities calculated for a l-cm cell.It will be seen that results were consistent and. that recoveries were in general satisfactory.The mercury on the peel of apples from storage trials carried out in 1947, 1948 and 1949 was estimated by this method and the results will be reported elsewhere. The work described in this paper was carriedt out as partof the programme of the Food Investigation Organisation of the Department o:F Scientific and Industrial Research.April, 1951) ON THE PEEL OF APPLES 215 REFERENCES 1. Shaw, H., and Moore, M. H., Ann. Re+ort of East Malling Res. Star., 194.1, p. 128. 2. Marsh, R. W., J. Pornology, 1947, 23, 185. 3. “The Storage of Apples,” D.S.I.R. Food Investigation Technical Paper No. 1, Department of 4. “Official and Tentative Methods of Analysis,” Association of Official Agricultural Chemists, 5. Milton, R. F., and Hoskins, J., Analyst, 1947, 72, 6. 6. Bucknell, M., Hunter, D., Milton, K. F., and Perry, K., Brit. J . Indust. Med., 1946, 3, 65. 7. b u g , E. P., and Nelson, K. W., J. Ass. 08. Agric. Chem., 1942, 25, 399. 8. Sandell, H. B., “Colorimetric Determination of Traces of Metals,” Interscience Publishers Inc., 9. Arden, T. U., Burstall, F. H., Davies, G. R., Lewis, J. A., and Linstead, R. P., Nutwe, 1948, 10. Irving, H., Andrew, G., and Risdon, E. J., J. Chem. SOC., 1949, 541. Scientific and Industrial Research, 1949. Washington, 1945, p. 470. New York, 1944, p. 384. 162, 691. DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH DITTON LABORATORY EAST MALLING MAIDSTONE, KENT September, 1960

ISSN:0003-2654    

DOI:10.1039/AN9517600211

出版商:RSC    

年代:1951

数据来源: RSC