摘要:

90 HERINGTON SOME QUALITATIVE AYD QUANTITATIVE COLOUR [Vol. 76 Some Qualitative and Quantitative Colour Reactions for the Lower Homologues of the Pyridine Series BY E. F. G. HERINGTON Attention is drawn to the lack of specific colour reactions for bases of the pyridine series and to the desirability of developing methods for the detection and estimation of certain hornologues. New qualitative tests based on the use of a phenol- chloroform- sodium ethoxide mixture are described. The colours obtained with this type of reagent when the phenol is phenol itself, p-chlorophenol or thiophenol are recorded. The presence of as little as 0.1 per cent. of y-picoline in fLpicoline or 2:6-lutidine can be detected with the phenol reagent, while 0.0005 ml of y-picoline produces a detectable colour if other bases are absent.The reagent containing thiophenol yields particularly brilliant and characteristic colours suitable for the identifica- tion of single bases. A reagent containing 1-chloro-2 :4-dinitrobenzene, acetamide and 2 :6-lutidine is described; this is suitable for the quantitative estimation of p- and y-picoline in admixture with 2 :&lutidine. THE formation of coloured compounds from bases of the pyridine series has been known for a long time but, although certain of these substanws (e.g., the cyanine dyes) have found widespread application in photography, few colour reactions specific for individual bases have been described. Recently, several bases of this series have become available commercially and it is likely that they will give rise to new and useful products with a variety of applications.Moreover, interest continues in the synthesis of pyridine bases (cf. Janz et aZ.1929394), so that the development of simple methods for the identification and estimation of these compounds appeared to be of interest. Simple fractional distillation by modern distillation technique will readily separate a-picoline and pyridine from a mixture, but the homologues p-picoline, y-picoline and 2 : 6- lutidine boil at so nearly the same temperature that other methods have to be used in their separation (see Coulson and Jones5). For this reason special attention is paid in this paper to the analysis of these close-boiling mixtures. A large number of different types of reagent, for example, afl-ethynyl ketone (JohnsonG), were examined in preliminary experiments, but noine appeared to be as suitable for analytical applications as those whose detailed use is now described. PURITY OF BASE SAMPLES EMPLOYED- To establish unambiguously the colours developed by any reagent it is necessary to use specimens of the pyridine bases of high and preferably known purity.The preparation of samples of these bases was undertaken for other purposes and will be described elsewhere, but the type of material used in the present investigation is indicated by the mole per cent. purity that was established by the freezing-point technique of Herington and Handley,' as follows : pyridine, 99.85 0.07 ; a-picoline, 99.87 & 0.06 ; P-picoline, 99-97 & 0-02 ; y-picoline, 99.75 & 0.13; 2:6-lutidine, 99.93 & 0.04.QUALITATIVE COLOUR REACTIONS OF PYRIDINE BASES WITH A PHENOL - CHLOROFORM - Certain phenols give strongly coloured products when allowed to react with chloroform and a pyridine base in the presence of sodium ethoxide. A number of phenolic substances have been tried in such mixtures; they include a- arid /%naphthol, catechol, o-, m- and 9-cresol, 9-phenylphenol, 1 : 3 : 5-xylenol, tribromophenol, trichlorophenol, o-chlorophenol and o- hydroxyl diphenyl, but the strongest and most characteristic colours were obtained when phenol itself, P-chlorophenol or thiophenol were used. The behaviour of the reagents con- taining each of these three phenols is described because the reagent containing phenol provides a sensitive test for y-picoline, that containing $-chlorophenol gives a characteristic colour with /3-picoline and that containing thiophenol gives brilliant and characteristic colours SODIUM ETHOXIDE MIXTURE-Feb., 19511 REACTIONS FOR LOWER HOMOLOGUES OF THE PYRIDINE SERIES 91 with the different bases.The colours produced by these reagents are modified by the addition of water and chloroform, and because these colour changes are in some instances characteristic of the base, the colours of the chloroform layers after the addition of water are recorded. The colour observed when a mixture of bases reacts with one of these reagents is not the sum of the colours given by the constituent bases when they react singly, and as a result these reagents are not suitable for quantitative work.Nevertheless, the reagent containing phenol itself can be used to detect the presence of traces of y-picoline in j3-picoline and 2: 6-lutidine, and its use for this purpose is described. COLOURS PRODUCED BY SINGLE BASES PHENOLIC REAGENT- of the base and then 1 ml of sodium ethoxide (5 g of sodium in 1 litre of alcohol). the mixture in an open test tube to 80” C for 10 minutes and then cool. the colours shown in Table I, column 3. listed in Table I, column 4. Take 1 ml of a solution of phenol in chloroform (25 g of phenol per litre), add 0.05 ml Heat The bases give Add 1 ml of chloroform and 10 ml of water and shake. The colours so obtained are p-CHLOROPHENOL REAGENT- above, but use a concentration of 20 g of 9-chlorophenol per litre of chloroform. obtained are recorded in Table I, columns 3 and 4.Use the same experimental conditions 3s described under the heading “phenolic reagent” The colours THIOPHENOL REAGENT- Take 1 ml of thiophenol solution (2 ml of thiophenol plus 10 ml of chloroform), add 0.1 ml of the base and then 1 ml of sodium ethoxide solution (50g of sodium in 1 litre of alcohol). Allow the mixture to stand for 1 hour. Good colours can be obtained only if care is taken with the concentration of the reactants, and the solution must not be heated, otherwise certain colours, e.g., that from /?-picoline, will be destroyed. The colours observed are listed in Table I, as are also the colours after the addition of chloroform and water. TABLE I COLOURS OBSERVED WITH THE PHENOL - CHLOROFORM - SODIUM ETHOXIDE REAGENT Phenolic constituent Phenol .... p-Chlorophenol . . Thiophenol . . Base pyridine a-picoline p-picoline y-picoline 2 : 6-lutidine reagent alone pyridine a-picoline PP.* icoline y-picoline 2 : 6-lutidine reagent alone p yridine a-picoline /I-picoline y-picoline 2 : 6-lutidine reagent alone Colour of chloroform layer after addition Colour of water pale reddish orange yellow pale reddish orange colourless slightly orange colourless purple bright blue pale yellow colourless pale yellow colourless pink pale yellow pale brown colourless red colourless blu e-vioIe t, grey-purple yellow pale yellow pale yellow pale yellow turning grey red red reddish brown red brilliant red orange brilliant blue-green strong green pale orange yellow pale orange colourless SENSITIVITY OF PHENOLIC REAGENT FOR THE DETECTION OF y-PICOLINE ALONE- The phenol - chloroform - sodium ethoxide reagent, under the conditions described above, gives a colour with 0.0005 ml of y-picoline that is distinguishable from that exhibited by the reagent alone.92 HERINGTON : SOME QUALITATIVE AND QUANTITATIVE COLOUR [Vol.76 DETECTION OF y-PICOLINE IN fl-I'ICOLINE OR 2 : 6-LUTIDINE One-tenth of 1 per cent. of y-picoline can be detected in /3-picoline or 2:6-lutidine by means of the phenol - chloroform - sodium ethoxide reagent provided that the colours can be compared with those formed by pure samples of p-picoline or 2:6-lutidine. For the application of this test for the presence of y-picoline in samples that consist chiefly of /I- picoline or 2:6-lutidine, it was found to be advantageous to use more concentrated reagent solutions than those already described, and the following conditions are recommended. Take 1 ml of a solution of phenol in chloroform (280 g of phenol per litre), add 0.5 ml of the base and then 1 ml of a sodium ethoxide soliition (50 g of sodium per litre of alcohol).Heat the mixture to 80" C for 10 minutes. The single bases give the colours shown in Table 11, column 2. Add 1 ml of chloroform and 10 ml of water and shake. Under these conditions 0.1 per cent. v/v of y-picoline in 2 : 6-lutidine gives a purplish colour, but the same strength of 7-picoline in fl-picoline yields a more scarlet shade than does fl-picoline alone, and a brownish colour after adding chloroform ,and water. The colours obtained with a single base under these conditions are given in Table 11, columns 2 and 3.TABLE I1 COLOURS OBSERVED WITH THE MORE CONCENTRATED PHENOL - CHLOROFORM - SODIUM ETHOXIDE: REAGENT Rase Coloiir Colour of chloroform layer after addition of water Pyridine . . . . .. orange-red yellow or-Picoline . . .. brown brown /3-Picoline . . .. red pale yellow y-Picoline . . .. deep purple purple-blue 2 : 6-Lutidine . . . . reddish orange pale yellow Reagent alone . . .. pale yellow pale yellow QUANTITATIVE ESTIMATION OF y-PICOLINE Hamer and Rathbone* report that 1-chloro-2 : 4-dinitrobenzene does not combine with a-picoline or 2 : 6-lutidine to give a pyridinium salt. The behaviour of mixtures of this com- pound with each of the five bases was studied and a:; a result a method for estimating y-picoline was devised.All five bases were found to give a. purple colour when 0.001 ml of the base was heated to 100" C for 1 hour with 5 ml of a solution made by dissolving 50 g of l-chloro- 2:kdinitrobenzene in 1 litre of alcohol; the colclur produced by y-picoline was the most intense. y-Picoline was the only base that gave a purple colour under similar conditions if 40 g of acetamide were added to 1 litre of the reagent. The colours yielded by the other bases were pale and were as follows : pyridine, yellow-brown ; a-picoline, brown-red ; p-picoline, yellow ; 2 : 6-lutidine, reddish brown. The behavioiir of the 1-chloro-2 : 4-dinitrobenzene - acetamide reagent when two bases, one of which was y-picoline, were simultaneously present was observed by adding 0.050 ml of the other base to 0.001 ml of y-picoline.The product from the mixtures containing pyridine or /3-picoline as the additional base gave pale brown solutions, while the presence of a-picoline or 2:6-lutidine greatly enhanced the colour due to the y-picoline, although these bases alone at the same concentration did not give a purple colour. The addition of this fifty-fold excess of a-picoline to y-picoline gave a colour of twice the intensity of that produced by the y-picoline alone, while the same quantity of 2 : 6-lutidine increased the intensity approximately eight-fold. Clearly it is impossible to use this simple 1-chloro-2 : 4- dinitrobenzene - acetamide reagent for the estimation of y-picoline when unknown amounts of a-picoline and 2 : 6-lutidine are present in the mixture under analysis because of the enhance- ment of colour produced by these two a-substituted bases.However, this difficulty can be overcome by deliberately adding a large excess of pure 2 : 6-lutidine to the reagent so that any additional enhancement of the colour resulting from the presence of a-picoline or 2 : 6- lutidine in the sample under analysis is negligible. The following conditions were found to be satisfactory for the estimation of y-picoline in mixtures.Feb., 19511 REACTIOKS FOR LOWER HOMOLOGUES OF THE PYRIDINE SERIES METHOD FOR ESTIMATION OF ~-PICOLINE IN MIXTURES REAGENT- 93 Dissolve 50 g of l-chloro-2 : 4-dinitrobenzene, 40 g of acetamide and 10 ml of pure 2: 6-lutidine in 1 litre of industrial methylated spirit.PROCEDURE- Dilute 0.1 ml of the sample under investigation to 100 ml with alcohol and treat 0.1 ml of pure y-picoline similarly. Run 5 ml of the reagent into each of three dry boiling tubes. Add 1 ml of the dilute solution of the unknown to one tube, add I ml of the dilute y-picoline solution to the second and add 1 ml of alcohol to the third. Immerse the uncorked tubes simultaneously in boiling water and leave for 1 hour. Shake the tubes gently from time to time and ensure that water does not condense inside the tubes by placing them in a beaker of boiling water in such a way that the open ends protrude. At the end of the hour, cool the tubes in ice and dilute the product from each to 50 ml with alcohol. Measure the absorp- tion immediately, because the colours have a tendency to fade.The Spekker absorptiometer is set with a full scale reading of 1-30 drum units with Ilford filter No. 606 and the blank solution containing 1 ml of alcohol in a l-cm absorption cell. Measure the absorption of the other two solutions using the same cell. Calculate a first approximation to the volume percentage of y-picoline in the unknown from the expression lOO(1.30 - a)/(l.30 - b), where a and b are the drum readings for the unknown and the y-picoline standard solutions respec- tively. The first approximate value of the y-picoline content is used to calculate a fresh dilution of the unknown base mixture so that the new solution contains 0.1 ml of y-picoline in 100 ml of alcohol, and the experiment is repeated using this fresh dilution.If this second experiment is correctly carried out the readings a and b should be nearly equal. The percentage of y-picoline in the unknown is calculated in the same manner as described above, but taking cognisance of the new dilution factor. The mean of the first and second estimation is taken to be the y-picoline content. Typical results of analysis of synthetic mixtures expressed as volume percentages are shown in Table 111. Pyridine, a-picoline and 2:6-lutidine do not interfere with this determination. The dilutions recorded here may not be suitable for all absorption spectrophotometers, but the dilution should be chosen such that the reading (1.30 - b) may be made with a suitable accuracy, while the unknown should be diluted similarly. The rate of decay of the purple colour was found to be a function of the concentration of the coloured compound; for this reason a second determination is recommended, a dilution calculated on the results of the first experiment being used.In general, the results of the first approximation tend to be low (see Table 111, column 4) and that of the second tend to be high (column 5 ) ) while the means of these values (column 6) are nearer the true figures than the individual determina- tions. TABLE I11 DETERMINATION OF y-PICOLINE y-Picoline found Synthetic mixture I A 3 ,S-Picoline, 2 : 6-Lutidine, y-Picoline, approximation, approximation, Mean, A I 7 First Second % % % % 04 % 90 - 10 7.0 - 90 10 8.0 45 45 10 7.0 33.3 33.3 33.3 36.9 - 50 -_ 50 26 25 50 50 50 48.4 55.7 45.1 10.5 8.8 10.9 9.5 11.5 9.3 31.4 34.2 56.0 53.3 57.3 52.2 54.5 51.2 QUANTITATIVE ESTIMATION OF p-PICOLINE The method recommended for the colorimetric estimation of /3-picoline is based on the observation that if sodium ethoxide is added to the product obtained by heating the base with l-chloro-2 : 4-dinitrobenzene - acetamide - 2 : 6-lutidine reagent, both 16- and y-picoline yield a purple coloured product but that produced by y-picoline fades more rapidly.The94 HERINGTON : SOME QUALITATIVE AND QUANTITATIVE COLOUR [Vol. 76 jSrpicoline yields a red-brown solution after 1 hour, while the colour of the y-picoline solution differs little from that of the reagent. Under the conditions finally chosen, y-picoline produces a colour whose intensity is approximately one-tenth of that generated by the same volume of /3-picoline, and for this reason it is recommend.ed that the blank and reference P-picoline solutions employed should be at approximately the same y-picoline concentration as the unknown.METHOD FOR ESTIMATION OF /J-PICOLINE IN MIXTURES REAGENTS- of acetamide and 10ml of pure 2:6-lutidine in 11 litre of industrial methylated spirit. l-Chloro-2 : 4-dinitrobenzene reagent-Dissolve 50 g of l-chloro-2 : 4-dinitrobenzene, 40 g Acetamide solation-Dissolve 40 g of acetamide in 100 ml of water. Sodium ethoxide solution-Allow 50 g of clean sodium to react with 1 litre of industrial methylated spirit. PROCEDURE- Dilute 0.1 ml of the solution under investigation to 100 ml with alcohol, and treat 0.1 ml of pure /3-picoline and 0.1 ml of pure y-picoline similarly.Run 5 ml of the l-chloro-2:4- dinitrobenzene reagent into each of three dry boiling tubes. Add 1 ml of the dilute solution of the unknown to one tube, and to the second add x m l of the dilute y-picoline solution ( x is the volume fraction of y-picoline in the unknown as measured by the method described above). Sufficient accuracy will be obtained if this value of x is adjusted to the nearest 0.05m1, e.g., if the volume percentage of y-picoline had been found to be 34.1 per cent., then x = 0.35 ml. Add to the third tube x ml of the dilute y-picoline solution and (1 - x) ml of the dilute P-picoline solution. Heat the three tubes for 1 hour in boiling water and take care that water does not condense inside the tubes. Shake the tubes gently from time to time.Dissolve the product from each tube in 10 ml of alcohol and cool the solutions to room temperature (i-e., to between 10" and 20" C). Add 5 ml of the aqueous acetamide solution and then 1 ml of the sodium ethoxide solution. Shake the tubes and allow them to stand in a beaker of water at room temperature for 1 hour. Dilute the product from each tube to 100ml with alcohol. The following precautions must be observed: (i) the solutions must be cooled to room temperature before the sodium ethoxide solution is added, otherwise the reagent alone will give an intensely coloured solution ; (ii) the specified concentration of sodium ethoxide must be adhered to, because it will be found that a smaller quantity than that recommended will fail to destroy the colour produced by y-picoline, while a higher concentration will give a highly coloured solution with the reagent alone; (iii) the three solutions must be treated similarly in every way and the colours must be compared 1 hour after adding thesodium ethoxide, because if left too long the /3-picoline solution also will lose its red colour.The Spekker absorptiometer is set with a full scale reading of 1.30 drum units with Ilford filter No. 605 and with the solution made from the x ml of y-picoline solution in the cell. The drum readings for the unknown, a, and for the synthetic mixture containing (1 - x) ml of P-picoline solution, b, are recorded and the percentage of 13-picoline in the unknown is calculated by the relationship lOO(1 - x)(1.30 - a)/(l.30 - b).Typical results obtained in this way are shown in Table IV, column 4. Prepare this solution just before use. TABLE 1:V DETERMINATION OY #I-PICOLINE Synthetic mixture Percentage 6-picoline found p-Picoline, 2 : 6-Lutidine, y-Picoliiie, 90 - 10 - 90 10 45 45 10 33.3 33.3 33.31 50 - 50 - 50 50 25 35 50 % % % Exact value, 91.2 0 46.0 33.6 50 0 26-1 % 1 Rough value, 88.0 3.0 45.5 38.4 56.2 6.1 32.3 %Feb., 19511 REACTIONS FOR LOWER HOMOLOGUES OF THE PYRIDINE SERIES 95 Rough values of the P-picoline content can, however, be found without first determining the y-picoline concentration by employing 1 ml of alcohol in the blank and 0.5 ml of ,&picoline as standard. Such values tend to be too high by approximately one-tenth of the y-picoline concentration.a-Picoline and 2 : 6-lutidine do not interfere, but pyridine produces a colour having approxi- mately 45 per cent. of the intensity of that given by an equal volume of p-picoline. Thus, if pyridine is present in a sample, the /I-picoline concentration found will be too high by approximately +y per cent. where the pyridine concentration is y per cent. For example, a concentration of 28-1 per cent. of /3-picoline was found for a synthetic mixture containing 25 per cent. of P-picoline, 10 per cent. of pyridine, 50 per cent. of y-picoline and 15 per cent. of 2:6-lutidine. In another example, 36.7 per cent. of /3-picoline was found in a synthetic sample containing 25 per cent. of /?-picoline, 25 per cent. of pyridine and 50 per cent. of y-picoline. Clearly, if a considerable quantity of pyridine is present in a sample under analysis, the pyridine should either be removed before the analysis for /3-picoline is undertaken or allowance should be made for its presence by determining the pyridine content by some independent method.The pyridine can readily be removed by fractional distillation with an efficient fractionating column (pyridine, b.p. 115.3" C; /3-picoline, b.p. 144" C; y-picoline, b.p. 145" C; 2:6-lutidine, b.p. 144" C). Pyridine can be estimated colorirnetrically by the method due to Ploquin9 or by the clearing point method described by Hamer, Pomfret and S t ubbings. lo The values shown in Table IV, column 5, were obtained in this way. I wish to thank Dr. E. A. Coulsen, J. B. Ditcham, E. C. Holt and A. Sleven for supplying the pure base samples used, and R. Handley and A. J. Cook for the estimations of the purity of the bases. The work described has been carried out as part of the research programme of the Chemical Research Laboratory and this paper is published by permission of the Director, Chemical Research Laboratory, Teddington. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Janz, G. J., Ascah, R. G., and Keenan, A. G., Canad. J . Res., 1947, 25B, 272. Janz, G. J., and Keenan, A. G., Ibid., 1947, 25B, 283. Harkins, P. J., and Janz, G. J., J . Chern. SOC., 1949, 1479. _ _ - , Ibid., 1949, 1485. Coulkm, E. A., and Jones, J. Idris, J . S O ~ . Chew. I n d . , 1946, 65, 169. Johnson, A. W., J . Chern. SOL, 1947, 1626. Herington, E. F. G., and Handley, R., Ibid., 1950, 199. Hamer, F. M., and Rathbone, R. J., Ibid., 1947, 960. Ploquin, M. J., Bull. Soc. Chirn. France, 1947, 700. Hamer, A., Pomfret, R., and Stubbings, W. V., Analyst, 1946, 71, 419. CHEMICAL RESEARCH LABORATORY TEDDINGTON May, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600090

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

96 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR [Vol. 76 The Arsenic Electrode as a Indicator BY A. A. MlDUSA* The preparation of arsenic electrodes by the deposition of sublimed arsenic on rotating platinum bases is described. An investigation has shown that these electrodes may be used for electrometric recording of pH during acid-base titrations with a number of monobasic, dibasic and tribasic acids, and in particular with acids such as arsenious, arsenic and hydrocyanic that incapacitate the hydrogen and quinhydrone electrodes. The pk,’ values obtained with the arsenic electrode agree closely with hitherto accepted values. The arsenic electrode is shown to be applicable also to the measurement of pH in precipitation reactions, and the results of such experiments with magnesium, zinc, cadmium, lead and aluminium are recorded.THE behaviour of both massive arsenic and massive antimony electrodes in aqueous solutions at different pH values, as explained in the light of the theory of lattice defects, has recently been reported.l,2 It was shown that these electrodes could legitimately be regarded as metal - metal oxide - oxygen electrodes; this necessarily implies a particular significance to the role played by oxygen. From several studies in this connection it was judged that the freshly deposited arsenic electrode could with advantage be used to replace the antimony electrode for pH measurements. This judgment was based chiefly on: (a) the readiness with which oxygen molecules accommodate themselves at fixed positions on the electrode surface, a fact that is reflected in the instantaneous establishment of steady potentials and also in the establishment of potential - pH relationships covering almost the whole pH range; and (b) the fact that the oxygen overvoltage effect at the electrode surface decays but slowly and that arsenious oxide, unlike antimoriious oxide, dissociates in a simple manner,ss4 so that marked deviations from a strictly rectilinear relationship, especially in the course of prolonged pH measurements, are not to be expected.Before recording the experiments carried 0u.t to test the validity of using the arsenic electrode in pH measurements, it is of value to state the following facts to serve as a general guide when making measurements with that eleckrode. (i) The electrode should be freshly deposited; aged electrodes or electrode systems involving the metal powder cannot be used.(ii) Addition of arsenious oxide to the test solution must be avoided; a pre-immersion adsorbed oxide film with its oxygen doublets will do this with advantage. (iii) Since the electrode process is subject to an oxygen overvoltage mechanism, the effect of temperature should not be overlooked. (iv) The rate of the cathodic process, 0, -j- 2H,O + 4e -+ 40H’, that occurs at the electrode surface varies with the partial pressure of oxygen ; measurements should, therefore, be made in the presence of a non-reacting gas such as nitrogen or hydrogen. (v) As the electrode is a self-polarised one, the formal equation E = E‘, - (RT,/F) pH, derived on grounds of complete reversibility, should not be expected to hold.It is therefore essential to construct calibration graphs of the type E = K - S.pH, in which K stands for the term E’, subject to the influence of the above-mentioned factors, and S for the slope of the potential - pH curves obtained experimentally. EXPERIMENTAL PREPARATION OF ELECTRODES- As in the previous investigation^,^ s 4 freshly deposited arsenic electrodes were made by subliming and depositing the pure metal on platinum bases sealed into glass tubes; these, when furnished with a mercury contact, served as electrodes in the usual way. In the present investigation, however, it was found convenient t o carry out the process of deposition while the electrode was rotating at a moderate speed; in this manner a compact homogeneous coating adhering firmly to the platinum base and the adjacent portion of the glass tube was always obtained.The apparatus used for this purpose is shown diagrammatically in Fig. 1. * Present address : Department of Physical Chemistry, Free School Lane, Cambridge.Feb., 19511 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR 97 Crystals of arsenic metal were first placed in the sublimation vessel, V, made of Pyrex glass, and the electrode was then fitted in through the cup, C, of a mercury seal with the tip of the platinum base about half a centimetre above the crystals. A fine stream of oxygen-free nitrogen was allowed to circulate in the vessel, and the sublimation of the metal was carried out by heating with an ordinary bunsen burner while the electrode was rotated. The sub- limation was continued for about 5 minutes, after which the electrode was left to cool in the circulating gas.Any oxide or unstable modification of arsenic metal that might have been deposited on the remote portions of the glass tube was carefully rubbed off with emery paper before the electrode was used. d Arsenic Crystals 6 Fig. 1. Apparatus for deposition of arsenic on rotating electrode TEST SOLUTIONS AND CALIBRATION GRAPH- As the first object was to obtain a calibration graph on the basis of which the observed potentials might be converted to pH values, a modified form of the Prideaux - Ward universal buffer5 was used. For this purpose, 0.12 M stock solutions of phosphoric, acetic and boric acids were prepared and standardised.A 100-ml mixture of the three acids was accurately diluted to 200ml with redistilled water, then neutralised by gradual addition of exactly 0-20M sodium hydroxide, which was prepared and kept out of contact with atmospheric carbon dioxide. The neutralisation was performed inside an air-bath, specially designed for the titrations, whose temperature was kept constant to within &0.05" C. For the measure- ments carried out at temperatures above that of the laboratory, which varied from 18" to 20" C, the temperature of the mixture after each addition of alkali could be restored readily by means of a heating element supported by the titration vessel. The pH value of the mixture at each stage of neutralisation was determined electrometrically with a hydrogen electrode of the Hildebrand type used in conjunction with a saturated calomel electrode as a half-cell.Three sets of measurements carried out at 20", 25" and 30" C are shown in Table I. Similar acid mixtures were then neutralised with a stationary freshly deposited arsenic electrode as the indicator. This neutralisation was performed in the presence of oxygen-free98 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR [Vol. 76 nitrogen, which was allowed to bubble through the solution. The electrode subjected in this way to varying pH was sensitive to variation in pot'ential, and the instantaneous establishment of steady values was remarkable. In Table I areshown the potential values EHas referred to the normal hydrogen electrode; these were recorded within 2 to 4 minutes after each addition of alkali.TABLE I: RELATIONSHIP BETWEEN pH AND POTENTIAL vus. NORMAL HYDROGEN ELECTRODE AT VARIOUS TEMPERATURES Alkali added, ml nil 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 7 PH 2-24 2.42 3-11 4-40 5.44 6.73 7.52 8.81 9-76 11.16 11.59 20" c --h---7 EH + 0.207 + 0.202 $0.180 +@*I07 + 0.050 - 0.024 - 0.070 - 0.144 - 0.198 - 0.281 - 0.306 7 PH 2.22 2.40 3-08 4.37 5.30 6.66 7.42 8.77 9.64 11.02 11-37 f!5" c -- EH $0.190 +0*184 +0*168 -b 0.096 + 0.04 1 - 0.039 - 0.083 - 0.164 - 0-222 - 0.300 -0.317 30" C PH 2-25 2.39 3.06 4.29 5.29 6.51 7.38 8-63 9.56 10.87 11.24 + 0-1 80 $0.176 +0.152 + 0.090 + 0.028 - 0.048 - 0.100 -0.172 - 0.234 -0.310 - 0.328 Except for acid solutions up to a pH of about 3, the potential - pH curves were almost straight lines that, when extrapolated to pH = O,, gave average values of K of 0.368, 0.355 and 0.344 volt at 20", 25" and 30" C respectively.The corresponding average values for the term S (AElApH), as calculated from each pair of successive readings within the region of linearity, amounted to 0.0590, 0.0597 and 0.0602 respectively. Calibration graphs for the arsenic electrode may therefore be represented by the following equations- E H (observed) = 0.368 - 0.0590 pH at 20" C E H (observed) = 0-355 - 0.0597 pH at 25" C E H (observed) = 0-344 - 0.0606 pH at 30" C where the observed potentials are referred to the normal hydrogen electrode. If the observed potentials are referred to the saturated calomel electrode the values of K in the above equations become 0.121, 0.112 and 0.104 volt respectively.THE VALIDITY OF USING THE ARSENIC ELECTRODE IN ACID - BASE TITRATIONS- A number of monobasic acids, including acetiic, boric, arsenious and hydrocyanic acids, some dibasic acids, including tartaric, oxalic, malonic, maleic and succinic acids, and some tribasic acids, including citric, arsenic and phosphoric acids, were each titrated against the arsenic electrode, to ascertain the extent to which it could be used in the determination of the titration end-points, and the dissociation constants were calculated from the neutralisation curves. In performing these titrations the experimental procedure described above was followed and the temperature of the bath was kept constant at 20" C. Fig. 2 shows repre- sentative curves obtained by plotting the Esat.values at the different stages of neutralisation against the amount of titrant added ; the concentrations of the solutions examined are recorded below each diagram. An inspection of the curves reveals that the inflexions marking the end-points are well defined and in good agreement with the theoretical. amounts; further, that the most flattened portions of the curves possess slopes proportionad in magnitude to the buffering capacity of each acid with its sodium salt-. The arsenic electrode therefore provides a suitable and readily attainable method for the titration of those acids such as arsenious, arsenic and hydrocyank, in particular, that incapacitate the hydrogen and the quinhydrone electrodes. The fifth column of Table I1 contains the mean pk,' values for some of the acids; these were calculated on the basis of the familiar Henderson - Hasselbalch equation in the form pH = pk,' + log b/(a - b), where a represents the original concentration of acid, b the concentration of added base and a - b the concentration of unneutralised acid.The pH values used in the above equation were computed, for at least three different neutralisation stages in each example, from the relation ESat. (observed) = 0.121 - 0.0590 pH. The pk,'Feb., 19511 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR 99 -O0[ -500. - 4 0 0 m c, & 3 -300. & . A E 2 u -200- -too I m- !- 10.00 20.00 30.00 40.00 0.079 N sodium hydroxide, ml I 10.0 ml of 0.050 M succinic acid I1 10.0ml of 0-050M tartaric acid I11 10.0 ml of 0.100 M citric acid - - B -ro.oo 30.00 50.00 0.039 N sodium hydroxide, ml I 25.0 ml of 0.040 M acetic acid I1 10.0 ml of 0.040 Ma phosphoric acid Fig.2 I 0.079 N sodium hydroxide, ml I 10.0 ml of 0.100 M oxalic acid I1 10.0 ml of 0.100 M malonic acid I11 10.0 ml of 0.050 M maleic acid -'0° t 1 2 ' . , . 8 I 8 00 1600 24.00 I 0.200 N sodium hydroxide II- 0028 N hydrochloric acid I 25*0ml of 0.072M As,O, solution I' 50-0 ml of 0.022 M As,O, solution I1 50.0ml of 0.100M potassium hydroxide100 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR [Vol. 76 II -to.oo ' 30.00 50.00 70.0 0 0.079 N sodium hydroxide, ml I 20.0 ml of 0.050 M boric acid I1 10.0 ml of 0.112 M arsenic acid Fig. 2-continued values obtained agree closely with the hitherto accepted values that have been obtained by different methods, and, as may be inferred frorn the data in columns 3 and 4, the fidelity of the arsenic electrode in responding to minute changes in pH is noteworthy.THE VALIDITY OF USING THE ARSENIC ELECTRODE IN PRECIPITATION REACTIONS GOVERNED BY pH- The importance of pH as a governing factor in some precipitation reactions has been further emphasised recently in connection with the behaviour of metal electrodes in aqueous solutions, where the separation of the metal hydroxide (or a basic salt) is often to be expected; hence the introduction of a new type of electrode The separation of metal hydroxides from their salt solutions by the gradual addition of alkali was originally investi- gated by Hildebrands and extended later by Britton9 and Britton and Robinson.10 According to the last-named authors, the precipitation pH value of a particular cation is essentially the same whether the phase separated is the pun: hydroxide, which very seldom occurs, or a basic salt, and in general is but slightly affected by the concentration of the cation and the nature of anion combining with it.Nevertheless, it has been observed that in some instances, e.g., the separation of zinc cations, the reported precipitation pH values are inconsistent among themselves, and that in some other instances, e.g., the separation of lead cations, the nature of the phase separated as well as the course of its separation are not critically established. Therefore, it appeared necessary to test the validity of using the arsenic electrode in tracing pH during such separations, searching at the same time for any advantage of the electrode over those previously used and to which the anomaly observed has often been ascribed.The first column of Table I11 shows particulars of the solutions examined. The separation of cations was effected through the gradual addition of exactly 0.111 N sodium hydroxide with a freshly deposited arsenic electrode serving as an indicator electrode. The curves in Fig. 3 show the different steps in the course of separation of each cation and were obtained by plotting the Esat. values against the amount of alkali added. By reasonable normalisationFeb., 19511 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR 101 of the curves, the number of equivalents of alkali corresponding to every step could be deter- mined with fair accuracy; these are given in the second column of the table.Since it was TABLE I1 pk,’ VALUES CALCULATED FROM pH VALUES AS MEASURED BY THE ARSENIC ELECTRODE Acid Boric . . .. Hydrocyanic . . Arsenious Sol. 1 . . Sol. 1’ . . Maleic . . .. Malonic (2nd step) Oxalic (2nd step) . . Arsenic (2nd step) (3rd step) . . Amount of acid neutralised. .. .. .. .. .. .. .. .. .. % 40.0 55.5 71.4 41.7 50.0 64.2 50.0 (31.1 72.2 45-45 54.5 63.6 43.0 60.1 75.2 41.7 49.6 57.5 41.7 49.6 57.5 41.1 48.0 54.9 32.4 46.5 60.7 &at. -0.413 - 0.43 2 - 0.451 - 0.468 - 0.463 - 0.462 - 0.450 - 0.462 - 0.474 - 0.446 - 0.456 - 0.466 - 0.222 - 0.239 - 0.257 - 0.187 - 0.193 - 0.201 - 0.1 13 -0.117 - 0.123 - 0.273 - 0.281 - 0.289 - 0.558 - 0.570 - 0.583 PH 9.06 9.38 9.69 9.98 9.90 9.88 9.68 9-88 10.09 9.61 9.78 9.95 5-80 6.10 6.4 1 5-22 5.32 5.46 3.97 4.03 4.13 6.68 6-81 6.95 11-51 11.71 11.93 pka’ 9.24 9.28 9.29 9-83 9.90 9.81 9.68 9.68 9.68 9.69 9.70 9.7 I 5.92 5-92 5.93 5.37 5.33 5-33 4.12 4.04 4.00 6.84 6-84 6.86 11-83 11.77 11-74 Mean Published* pka’ pka’ 9-27 9.85 9.69 8-92 6.50 8-34 6-40 4.06 3.90 6-85 6.77 11-78 11-33 * From H.T. S. Britton, “Hydrogen Ion Concentration,” Volume I, Chapman and Hall, Ltd., London, 1942. practically impossible to detect visually the initial formation of precipitates, it was considered justifiable to define the pH range within which precipitation occurs rather than to ascertain a particular pH value for incipient precipitation as has often been done.In the third column of the table are shown the pH ranges within which the different phases are precipitated (or otherwise); the values were computed from the relation Esat. = 0.121 - 0.0590 pH, since the measurements were performed at 20” C and the potentials were referred to the saturated calomel electrode. Except for lead cations, the pH values that might be considered to indicate incipient precipitation (points a on the curves) are in dose agreement with those previously reported from hydrogen, oxygen or glass electrode measurements. For zinc, the value obtained in this investigation, 6.88, supports the values previously reported by Kolthoffll and Prytz12 and is approximately one pH unit higher than that obtained by Britton and Robinson.10 For lead cations, the value obtained cannot be compared with those previously reported as the course of their separation is found to be materially different, as shown below.As is inferred by the data in the second column of Table 111, the phase separated from all the solutions examined is almost invariably a basic salt and not a true hydroxide. In agreement with the previous observations, the salt separated from each of the magnesium, zinc and cadmium solutions possesses the composition MX,.SM(OH),. [xH,Oj, where X stands for a102 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR TABLE 111 [Vol. 76 USE OF THE ARSENIC ELECTRODE TO MEASURE pH IN PRECIPITATION REACTIONS Solution (diluted to 200 ml) 10.00 ml of 0.100 M MgC1, + 2-50 ml of 0.200 N HC1 10.00 ml of 0.103 M ZnSO, + 10.00 ml of 0.114 N H,S04 10.00 ml of 0.096 M CdC1, + 5.00 ml of 0.200 N HC1 10.00 ml of 0.119 M Pb(NO,), 10.00 ml of 0.106 N HNO, 10.00 ml of 0.101 M Al,(SO,), { g::zzp Equivalents of NaOH 1.66 1.56 1.49 .. 0-98 ..0-45 . . 4.57 . . 1-99 pH range 10.53 to 10.86 6.88 t o 7.47 6-80 to 7.31 5.51 to 5.92 7-47 to 8.66 4-00 to 4.32 9.44 to 10.36 monovalent acid radical, since three-quarters only of the stoicheiometric amount of the alkali was consumed in every case. The curve for aluminium shows that within the range ab a basic salt is formed, and that further addition of alkali causes its decomposition as indicated by the gradual slope of the inflexion bc. The point c corresponds to exactly six equivalents 4 0 4 I2 ’ 20 2 8 36 44 52 tr 10 30 50 70 90 For Aluminium ‘4 0.1 I I N sodium hydroxide, mi Fig.3. Steps in the separation of each cation. Curve (l), magnesium chloride : curve (2), zinc chloride ; curve (3), cadmium chloride; curve (a), lead nitrate; curve (5), aluminium sulphateFeb., 19511 MOUSA: THE ARSENIC ELECTRODE AS A pH INDICATOR 103 of sodium hydroxide; the composition of the phase at that point corresponds therefore to A1,0,.[xH20]. The portion cd on the curve corresponds to about two equivalents and indicates the dissolution of the phase to form aluminate. For the separation of lead cations, the curves that have been reported by previous investigators (Britton and Robinsonlo from oxygen electrode measurements, and Dorling13 from glass electrode measurements) showed only one inflexion, which indicated the complete separation of a basic salt having the same composition as that separated from magnesium, zinc or cadmium solutions.For incipient separation of the salt, the former authors reported the pH value of 6.0. The curve obtained in this investigation, however, is peculiar as it shows two inflexions. The portion ab corresponds approximately to one equivalent of sodium hydroxide and so indicates the separation of a phase somewhat less basic than would correspond to M(X),.M(OH), within the pH range 5.51 to 5.92. The portion cd corresponds to half an equivalent of sodium hydroxide and indicates the separation of the basic salt M(X),.3M(OH), within the pH range 7.47 to 8.66. The separation of these two basic salts has recently been reported by Geloso and Faucherre14; the former phase within the pH range 5 to 7, and the latter phase within the range 7 to 8. The above results show clearly that the freshly deposited arsenic electrode serves satis- factorily for tracing pH during the separation of metal cations; the limitation imposed, however, is to be anticipated from the position of arsenic metal in the electromotive series since the electrode cannot be used for solutions of nobler cations. REFERENCES 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. Tourky, A. R., and Mousa, A. A., J . Chem. SOC., 1949, 1297. t , Ibid., 1948, 752. > , Ibid., 1948, 759. -- -- -- , Ibid., 1949, 1305. Prid&aux, E. B. R., and Ward, A. T., Ibid., 1924, 125, 278. Tourky, A. R., and El Wakkad, S. E. S., Ibid., 1948, 740. Mousa, A. A., J . Chem. SOC., 1950, 403. Hildebrand, J. H., J . Amev. Chem. SOC., 1913, 35, 847. Britton, H. T. S., J . Chem. SOC., 1925, 127, 2110. Britton, H. T. S., and Robinson, R. A., Trans. Farad. SOC., 1932, 28, 531. Kolthoff, I.'M., and Kameda, T., J . Amer. Chem. SOC., 1931, 53, 832. Prytz, M., 2. anorg. Chem., 1931, 200, 133. Dorling, M., Ph.D. Thesis, London, 1936, p. 87. Geloso, M., and Faucherre, J., Comptes Rend., 1948, 227, 1243. FOU.4D 1 UNIVERSITY FACULTY OF SCIENCE ABBASSIA, CAIRO, EGYPT January, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600096

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

104 DWYER AND GIBSON : THE MICRO-ESTIMATION OF [Vol. 76 The Micro-Estimation of Osmium in its Organic Compounds BY F. P. DWYER AND N. A. GIBSON A method is described for the colorimetric estimation of micro quantities of osmium in organic compounds. Fusion with sodium peroxide and sodium carbonate of an amount of substance equjivalent to 4 mg of osmium metal is recommended. The sodium osmate resulting from the fusion is then con- verted to hydrogen hexabromosmate by means of concentrated hydro- bromic acid and estimated colorimetricalliy with thiourea by a modification of Sandell's method. The over-all accuracy of the method is of the order of 1 per cent., and the reproducibility of the colorimetric part of the analysis is of the order of 0.3 per cent. THE estimation of osmium in its organic compounds is usually difficult owing to the ease of formation and the volatility of its oxide, OsO,.This prevents the use of normal methods of oxidation of the organic matter by fuming in sulphuric acid and an oxidising agent in an open vessel and also direct ignition to the metal 01' its oxide. Up to the present, the methods used have all involved oxidation under wet conditions with simultaneous distillation of the tetroxide into a suitable reducing medi~m.l,~,~,*J The osmium can then be estimated by several methods. These include the colorimetric estimation with t h i ~ u r e a , ~ titration with thiosulphate of the iodine released from potassium iodide,l$g precipitation and weighing as osmium dioxide' or titration with potassium per~nanganate.' Despite claims that have been made for the completeness of the distillation of the osmium tetroxide, it has been the experience of the authors and also of otherss that the recovery of osmium is often of the order of but 90 to 95 per cent.and hence it can scarcely be claimed that this method is sufficiently accurate for quantitative work. METHOD I n the method used in the present work, the organic matter was destroyed under alkaline conditions by the gentle heating of an intimate mixture of the compound to be analysed with about forty times its weight of sodium peroxide. By this treatment the osmium was converted into s?dium osmateV1, which was then dissolved in water, acidified with con- centrated hydrobromic acid and was thereby converted to hydrogen hexabromosmatelV, which was estimated colorimetrically with thiourea.The results obtained rarely varied from the theoretically expected result by more than 2 per cent. and were usually of the order of 1 per cent. or better. The method has the advantage of simplicity of technique and apparatus; no special apparatus other than the colorimeter is required. The colorimetric estimation of osmium with thiourea has already been described by Gilchrist,3 and by SandelLs The method used by Sandell was followed in general, with small modifications made necessary by the presence i n the solution of a large concentration of hydrobromic acid as well as some free bromine. The most important modification was the use of a larger amount of stannous chloride to remove the bromine, which otherwise oxidised the thiourea with the formation of colloidal sulphur.In each determination, colorimetric comparison was made on three aliquot portions o€ the solution obtained after fusion. These did not differ from each other, on the average, by more than 0.3 per cent. REAGENTS- Thiourea soZutiout-Dissolve pure B.D.H. thiourea in cold distilled water to form a 10 per cent. solution, filter through two thicknesses of Whatman No. 42 filter-paper. Prepare stannous chloride solution by dissolving C.P. stannous chloride in 2.5 N hydrochloric acid (A.R.) with warming to form a 10 per cent. solution, cool and filter through two thicknesses of Whatman No. 42 filter-paper. PROCEDURE- Weigh sufficient of the compound to contain about 4 mg of osmium into a small silica crucible, mix thoroughly with about 0.8 g of sodium peroxide and cover with a layer of sodiumFeb., 19511 OSMIUM I N ITS ORGANIC COMPOUNDS TABLE I Compound (PhNH,),OsRr, . .. . . . . . . . (PhMe,As),OsBr, . . . . . . . . Os(dipy),Br2.3H,0 . . . . . . . . Os(dipy),I2.20s(dipy),(SbOTart.),. 12H,O . . 0 s (phenan), (C10,) ,. H20 (d form) Compound Os(dipy),C1,.6H20 . . .. Os(dipy),12.3H20 . . .. Os(dipy),(C10,),.H20 . . .. Os(dipy),(Tart.).3H20 . . .. Os(dipy),(SbOTart.),.2H20 . . Os(dipy),(ClO,),.H,O (racemate) Os( dipy), (ClO,),. H20 ( I form) [Os(NH,),Br](C10,),.H20 . . (NH,),OsBr, . . .. . . Os(phenan),C1,.8H20 . . .. Os(phenan),'I,.SH,O . . .. .. .. .. .. .. .. .. .. .. .. . . .. Os(phenan),(SbOTart.),.3H20 (d form) .. Osmium 7--- Calc., Found, 22.17 22.08 22.61 22.37 21-62 21-73 22-20 22.25 21-72 22.02 21.80 21.97 19.48 19.48 19.86 19.72 19.80 19-80 19.93 21.80 21-60 21.69 21.60 21.46 21.46 21.36 15.86 15-80 15-88 15.92 15.76 15.94 15-76 20.07 20.05 20.05 20.05 20.09 20.14 20.23 % % TABLE I1 ... . .. .. .. . . . . .. .. .. .. .. Osmium - Calc . , Found, % % 22.70 22.33 22-40 19-68 19.54 21.72 21-35 21.36 21.78 15.02 15.26 14-69 19-51 19-13 19.5 1 19.63 26-99* 27.05 27-25 33.24 33.64 32.90 20.11 19.98 20.17 18-32 17-97 17-93 14.03 13-92 13.93 22.09 21-49 * Denotes gravimetric estimation by ignition to 0 s metal in ammonia. Tart. = tartrate; dipy = dipyridyl; phenan = o-phenanthroline. Mean, 22.35 % 21-68 22.23 21.88 19-69 19.84 21.63 21-43 15.87 15-82 20.05 20.15 Average deviation from mean, 0.1 0.0 1.2 0.6 0.3 0.4 0.6 0-6 0.5 0.3 0.3 0.2 0.2 0.2 0.3 0.4 0.0 0.3 0.0 0.1 0.5 % 106 Percentage deviation from calc.+ 0.8 - 2.2 + 0.3 - 1.3 + 1.1 +1-8 - 0.8 - 1.7 -0.1 - 0.3 - 0.2 + 0.4 Percentage deviation from calc. -2.1 - 1.3 - 0.7 - 1.7 - 1.7 - 2.7 - 1.4 + 1.9 - 1.9 - 1-9 + 0.6 +0-2 + 1.0 + 1.2 - 1.0 - 0.6 + 0.3 - 1.9 -2.1 - 0.8 - 0.7106 DWYER AND GIBSON [Vol. 76 carbonate about one-tenth of an inch thick. Cover the crucible with a lid, place in a larger covered crucible and heat with a small flame for approximately one hour. Usually, after being heated for several minutes, the mixture emits a loud crackling sound and sometimes flashes of light are seen. The violent reaction with perchlorate compounds is moderated by mixing 25 to 30 per cent. of sodium carbonate with the sodium peroxide.When the fusion is complete, allow the small crucible and its contents to cool and transfer it to a wide- necked flask fitted with a ground-in reflux condenser. Add 20 ml of water down the condenser and dissolve the contents of the crucible by boiling under reflux. Cool the flask and contents to room temperature, and add 20 ml of 50 per cent. hydrobromic acid down the condenser, with swirling to produce complete mixing. During the addition of the hydrobromic acid, the solution usually loses its light brown colour, becomes almost colourless and then changes to a deep red-brown. In some determina- tions a little flocculent silicic acid separates at this stage owing to attack on the crucible by the fusion mixture. This precipitate is removed by centrifugation before the colorimetric samples are withdrawn.Allow to stand for a short time and transfer the acidified solution to a 100-ml graduated flask, washing in with normal hydrochloric acid. In the presence of a metal such as antimony, whose salts are liable to form a basic precipitate by hydrolysis, 2.5 N hydrochloric acid is used for the washing. Filter the solution through a sintered-glass filter of porosity 2, to remove traces of suspended impurities. Measure three 10-ml portions, by means of a pipette, into tubes that are ground to fit reflux condensers, add 1 ml of 10 per cent. thiourea solution and 1 ml of 10 per cent. stannous chloride in 2.5 N hydrochloric acid. Fit the tubes to reflux condensers and heat the mixture in boiling water for 15 minutes to develop the colour.Cool and make up each portion to 25 ml in a standard flask with either distilled water or, in presence of metals that form basic salts, with 2.5 N hydrochloric acid. CALIBRATION GRAPH- Prepare a calibration graph by treating measured quantities of a standard osmium solution, made from ammonium bromosmate and containing 0.1 mg of osmium per ml, with thiourea, stannous chloride and hydrobromic acid as described in the procedure above. Measure the optical density by means of a photo-electric absorptiometer; with the Spekker absorptiometer use Ilford protective filters H503, blue-green spectrum filters No. 603 and 10-mm cells. RESULTS Test analyses were carried out on a wide variety of compounds in which the osmium was present in anionic, cationic and neutral coimplexes and also on compounds in which arsenic and antimony were present with organic matter. The results of representative analyses are given in full in Table I, and others in an abridged form in Table 11. REFERENCES 1. 2. 3. 4. 6. 6. 7. 8. Criegee, R., Annalen, 1936, 522, 75. Sandell, E. B., Ind. Eng. Chem., Anal. Ed., 1944, 16, 342. Gilchrist, R., J . Res. Bur. Stand., 1931, 6, 421. Hoffman, J. I., and Lundell, G. E. F., Ibid., 1939, 22, 465. Wolbling, H., Ber., 1934, 67B, 773. Klobbie, E. A., Cenfrbl., 1898, 11, 69, 65. Ruff, O., and Bornemann, F., 2. anorg. Chem., 1910, 65, 429. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Interscience Publishers, Inc., New York, 1944, p. 346. DEPARTMENT O F CHEMISTRY UNIVERSITY OF SYDNEY N.S.W., AUSTRALIA May, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600104

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Feb., 19511 VENKATARAMANIAH AND RAGHAVA RAO 107 Estimation and Separation of Zirconium by Use of Fumaric Acid BY M. VENKATARAMANIAH AND BH. S. V. RAGHAVA RAO Fumaric acid precipitates zirconium completely from solutions up to 0.35 N in hydrochloric acid. The precipitate, which has the approximate composition O=Zr=X (where X stands for the fumarate radical), is gelatinous; i t is ignited to give the oxide. From solutions 0.25 N in hydrochloric acid the reagent separates zirconium from aluminium, beryllium, uranium, nickel, barium, calcium, iron, manganese, thorium and the ceria earths in a single precipitation; vanadium, chromium, titanium, and tin are completely removed in a double precipitation. Zirconium has also been estimated in zircon. FUMARIC acid was recommended by Metzgerl for the separation of thorium from rare earths in 40 per cent.ethanol solution, but in aqueous solution the precipitation of thorium is incomplete. Zirconium, however, is completely precipitated as a white gelatinous substance from solutions 0.30 to 0.40 N in hydrochloric acid. Under the same conditions many other elements including thorium are held in solution. The reagent thus has valuable properties for use in the analysis of zirconium minerals. ESTIMATION OF ZIRCONIUM- Twenty millilitres of a stock solution of zirconyl chloride in 0.10 N hydrochloric acid were used for the determination of zirconium by precipitation with mandelic acid2 and ignition to the oxide: the weight of ZrO, found was 0.0923 g. By precipitation with fumaric acid by the procedure detailed below, the weight of 21-0, found was 0*0924g, a value in excellent agreement with that found by the mandelic acid precipitation.Experiments with smaller quantities of zirconyl chloride solution indicated that as little as 0.0115 g of 21-0, could be accurately estimated. Smaller quantities may be determined by employing micro methods; work in this direction is in progress. EFFECT OF ACID CONCENTRATION- Since thorium and other elements are partly precipitated at lower acid concentrations, their removal from zirconium depends on the control of acidity. The solubility of zirconium fumarate in hydrochloric acid was studied by determining the degree of precipitation in dilute acid of different concentrations. EXPERIMENTAL The results are shown in Table I.TABLE I EFFECT OF HYDROCHLORIC ACID Concentration o acid in the final liquid, N 0.10 0.15 0.20 0.20 0.25 0.30 0-35 0.35 0.35 0-40 0.45 0.50 If ZrO, taken, g 0-0924 0.0924 0.0924 0.0693 0.0693 0.0693 0.0462 0,0231 0.0215 0-0462 0.0462 0.0462 ZrO, found, g 0.0924 0.0923 0.0924 0.0694 0.0692 0.0693 0.0462 0.0230 0.0114 0.0460 0.0458 0.0452 Difference, mg nil -0.1 nil + 0.1 -0.1 nil nil -0-1 - 0.1 - 0.2 - 0.4 - 1.0 COMPOSITION OF THE PRECIPITATE- The precipitate obtained in 0-30 N hydrochloric acid was washed and dried to constant weight at 105" C. Ignition tests showed this residue to contain 41 per cent. of zirconium.108 VENKATARAMANIAH AND RAGHAVA RAO: ESTIMATION AND [Vol. 76 This points to the empirical formula 0 = Zr = I( (where X represents the funiarate radical) but the composition of the precipitate is subject to slight variation, so direct weighing of the dried precipitate is not possible.PROCEDURE- To the solution containing not more than @log of ZrO, add 5 g of solid ammonium nitrate and the calculated volume of 2.0 N hydrochloric acid to give a concentration of 0-25 N free acid in 200 ml. To the boiling solution add slowly and with continuous stirring 100 ml of a boiling 2 per cent. solution of fumaric acid. Continue to boil for 5 minutes and then set aside to cool. Filter the cold solution through an ll-cm Whatman No. 42 filter-paper. Wash first with a hot 0.20 per cent. solution of the reagent in 0-25 N hydrochloric acid and then with water. Ignite and weigh the residue as ZrO,. To reprecipitate-Dissolve the washed precipitate in hot diluted hydrochloric acid (1 + l), collecting the filtrate in the original beaker.Add dilute ammonia until the concentration of free acid is reduced to 0.20 to 0-30 N, and then repeat the precipitation with fumaric acid as described above. Results by both single and double precipitation are shown in Table 11. All impurities, added as chloride or nitrate, are calculated to oxide. INTERFERENCES- Aluminum, beryllium, uranium, nickel, barium, calcium, manganese and the ceria earths are not precipitated by the reagent, even from neutral solutions. Thorium and iron are partly precipitated in :neutral solution, but in 0.10 N hydrochloric acid no precipitation occurs. Vanadium and chromium when present alone are not precipitated in neutral solution, but in the presence of zirconium small quantities axe carried down even in 0.35 N hydrochloric acid. TABLE I1 Concentration of free acid = 0.25 N SEPARATION OF ZIRCONIUM FROM OTHER ELEMENTS Dilute to 100 ml and boil.SEPARATION OF ZIRCONIUM FROM OTHER ELEMENTS ZrO, taken = 0.0462 g. Impurity added, -7 ZrO, found, Difference, g g mg u30, 0-51 10 0.0462 nil Fe*O, 0-4332 0-0462 nil MnO 0.1894 0.0463 +0*1 CaO 0.2548 0.0463 +0*1 BaO 0.4100 0.0462 nil 0.4300 0.0461 - 0.1 Be0 0.4330 0.0464 + 0.2 NiO 0.8220 0.0463 +0*1 Tho, 0.1250 0.0464 + 0.2 Tho, 0.1875 0.0463 +0.1 .r (a) 0-0466f + 0.4 (b) 0.0461 -0.1 S O . 1 (a) 0-0480 + 1.8 (b) 0.0462 nil (a) 0.0482 + 2.0 ‘ [ ( b ) 0.0463 +0*1 R2°3* Tho, 0.0625 0.0462 nil Cr203 0.2173 v,o* 0.21 10 {[;I ;:;t;;t + 1.2 0.0462 nil ‘1 SnO 0-2380 Ti02 0.1143 0.4210 (a) Single precipitation ; (b) Double :precipitation.* Ceria earths; t The residue was slightly coloured. Titanium and tin, which are not precipitated in 0.10 N hydrochloric acid, are, however, precipitated with zirconium even in 0.35 N hydrochloric acid. Titanium, tin, vanadium and chromium are completely removed by a second precipitation. The fact that large quantities of nickel cause no interference is of importance in the analysis of zirconium minerals, since these are most easily decomposed by sodium peroxide fusion in a nickel crucible.Feb., 19512 SEPARATION OF ZIRCONIUM BY USE OF FUMARIC ACID ANALYSIS OF ZIRCON Zircon from Travancore, India, was fused with borax3 and, after removal of silica, the zirconium was determined by double precipitation in 0.25 N hydrochloric acid with fumaric acid. Qualitative analysis of the ore showed that it contained only titania and small amounts of ferric oxide in addition to silica. Zirconium was also determined for comparison by the standard cupferron method.* The results are shown in Table 111. 109 TABLE I11 ANALYSIS OF ZIRCON Cupferron method Fumaric acid method A 7 7 r I A Weight of sample, ZrO, found, Weight of sample, ZrO, found, g 74 g % 0.1034 65-03 0.1249 65.06 0-1 145 65.11 0.1048 65.1 2 - - 0.0964 65.04 65-07 - Mean . . - - 65-06 Mean . . - REFERENCES 1. 2. 3. 4. Metzger, F. J., J. Awzer. Cheun. Soc., 1902, 24, 901. Kumins, C. A., I n d . Eng. Chem., Anal. Ed., 1947, 19, 376. Lundell, G. E. F., and Knowles, H. B., J. Amer. Chew. Soc., 1920, 42, 1439. Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” John Wiley and Sons, Inc., New York, 1929, p. 448. CHEMICAL LABORATORIES ANDHRA UNIVERSITY TVALTAIR, s. INDIA May, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600107

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Feb., 19512 The SEPARATION OF ZIRCONIUM BY USE O F FUMARIC ACID Absorp tiometric Estimation of Acenaph th ylene 109 BY M. KAUFMAN* AND A. FOWLER WILLIAMS An absorptiometric method has been devised for the determination of acenaphthylene in pure material and works products. Satisfactory results were obtained from dilute toluene solutions of standards and test solutions by means of a mercury vapour lamp and an Ilford Spectrum Violet filter No. 601. In presence of acenaphthene the results are accurate to within 1 per cent. but the effect of all possible impurities, such as naphthalene and a-methyl naphthalene has not been investigated. THE unsaturated hydrocarbon acenaphthylene has not yet been produced on a commercial scale, and as far as the writers are aware, details of a reliable method of estimation have not hitherto been reported.The trial manufacturing process consists of catalytic vapour- phase dehydrogenation of the hydrocarbon acenaphthene, which makes up about 1 per cent. of typical coke-oven tar. The loss of two hydrogen atoms converts the colourless acenaphthene (m.p. 95" C) to the yellow acenaphthylene (m.p. 92" to 93" C), but the reaction can also yield mono- and di-methyl naphthalenes as well as naphthalene. In addition, the product is usually contaminated with small amounts of highly condensed compounds of the chalcacene type. The possibilities inherent in the dehydrogenation reaction are illustrated in Fig. 1. The relative amounts of these contaminants depend on the conditions of the conversion; the method described was designed to estimate the purity of a particular crude product that was to be used as the monomer in a process for producing high polymers from acenaphthylene. There were several possible methods of estimating acenaphthylene, for example, measure- ment of the degree of unsaturation by the addition of hydrogen or halogens to the double Present address : The British Oxygen Co.Ltd., Research and Development Department, Morden Factory Estate, Morden Road, London, S.W.19.110 KAUFMAN AND WILLIAMS : 'THE ABSORPTIOMETRIC [Vol. 76 bond, or use of the fact that acenaphthylene is an intensely coloured product amongst generally uncoloured impurities. Modifications of Wij's :method were tried, but it was found that neither with iodine nor with bromine could consistent quantitative results be obtained.The values obtained were rather high, and it was concluded that, under the test conditions, a variable amount of substitution in, as well as addition to, the acenaphthylene molecule was taking place. A colorimetric method making use of the Spekker photo-electric absorptiometer was then tried. Initially a tungsten filament lamp wits used in conjunction with an Ilford No. 602 filter as the source of light, but with this white light it was not possible to obtain a straight line calibration curve as required by Beer's law, nor were the results obtained consistent. It appeared that the tungsten lamp and filter provided too wide a waveband (4400 to 5000 A) and too many possible absorptions. A mercury vapour lamp was therefore meld in conjunction with an Ilford Spectrum Violet filter, the principal wavelengths so provided being 2007.8, 4046.6, 4339-2 and 4358.4 A.This selectivity in wavelengths allowed a satisfactory method to be devised for the estimation of acenaphthylene in the crude products. H,C CH, r52 --H2 , 1 : %DIMETHYLNAPHTHALENE H& ACENAPHTHENE ACENAPHTHYLENE \ in the Dresence I I CHALCACENE Fig. 1. Possible dehydrogenation CONSTRUCTION OF THE CALIBRATION CURVE- of hydrdgen and // steam --+ 1 YJ \/ ALPHA MONO METHYLNAPHTHALENE NAPHTHALENE reactions of acenaphthene To establish the calibration curve, Fig. 2, pure acenaphthylene was prepared from the crude product in the following manner. The crude material (m.p. 87" to 88" C) was twice recrystallised from 2 parts by weight of alcohol and then treated in benzene solution with picric acid to form the hydrocarbon picrate.This was twice recrystallised from benzene to a final melting-point of 201" C, and the acenaphthylene was regenerated from the final picrate by treatment with dilute ammonia solution. The product was washed free from ammonia and picric acid with copious quantities of warm water and finally recrystallised from alcohol. A solution of this purified material in light petroleum, boiling range 40" to 60" C, was poured on to a column of activated alumina measuring 40 cm x 4 cm, which was eluted to colourless washings with the same solvent. After removal of the light petroleum by evapora- tion, the acenaphthylene had a final melting-point of 92.5" C. From the sample used by the authors, two strongly adsorbed bands were left at the top of the column; one of these was yellow and was located above a colourless band that fluoresced blue in ultra-violet light.For calibration and testing a mercury vapoixr lamp was used with an Ilford Spectrum Violet filter 601. It was necessary to ensure that the lamp was fixed in the correct position; none of the books on absorptiometric technique that were consulted mention this, but difficulties were encountered until this source of trouble was found. With redistilled toluene (b.p. 110.5" C) as the solvent, the Spekker was found to be reasonably sensitive and it was possible to use solution concentrations of up to 0.25 per cent. with a "toluene setting" of 1.5 on the drum. The solutions were irradiated in glass cells 1 cm in width.Feb., 19511 ESTIMATION OF ACENAPHTHYLENE 111 The curve (Fig.2) is linear up to concentrations of about 160 mg per 100 ml and there is very close similarity with a curve drawn for “picrated” but unchromatographed acenaphthylene. Purification of standard acenaphthylene beyond the “picration” stage therefore seems to be unnecessary. Fig. 2. Calibration curve for acenaphthylene, using the Hilger Spekker photo-electric absorptiometer. M.p. of acenaphthylene : 92” to 92.5” C (corr). Toluene setting: 1.500. Mercury lamp + Ilford Spectrum Violet filter 601. l-cm glass cells. 0 = Unchromatographed, “picrate pure” sample; X = Chromatographed, “picrate pure” sample The calibration curve was then tested in a number of ways. First the crude product was estimated in various concentrations and Table I shows the good agreement between results.TABLE I ESTIMATION OF CRUDE PRODUCT IN KNOWN CONCENTRATIONS Acenaphthylene added, per 100 ml Spekker reading . . . . . . 0.840 0.625 0.422 0.234 Acenaphthylene found, yo . . . . 92.2 92.0 92.2 92.0 of toluene . . . . . . . . 0.1132 0.1454 0.1864 0.2187 Synthetic mixtures of pure acenaphthylene and pure acenaphthene were then prepared and tested, and these results are shown in Table 11. TABLE I1 ESTIMATION OF ACENAPHTHYLENE IN ARTIFICIAL MIXTURES WITH ACENAPHTHENE Acenaphthylene added, per 100 ml Acenaphthene added, per 100 ml Acenaphthylene found by Error, % . . .. .. . . 4.0 0.75 1.0 0.8 1.3 1.5 of toluene . . . . . . 0.0403 0.1064 0.1259 0.1419 0.1560 0.1862 of toluene .. . . . . 0-1653 0.0907 0.0851 0.0559 0.0485 0.0172 Spekker, g . . .. . . 0-0418 0.1172 0.1240 0.1408 0.1540 0.1835 In the first experiment with artificial mixtures (Table 11, column l), although the percentage error appears large, the difference in weight between the acenaphthylene present and that determined experimentally is only 1.5mg. The last two experiments (Table 11, columns 5 and 6) gave readings that are off the linear portion of the calibration curve and hence may be neglected. These and many other determinations have shown that the error can be kept within 1 per cent.112 KAUFMAN AND WILLIAMS [Vol. 76 With the Spekker absorptiometer, it is necessary to check the original calibration curve periodically, particularly when there is a lapse of a few months between determinations.METHOD- The method may obviously be applied when acenaphthylene is the only significant constituent of the test mixture that absorbs the relevant wavelengths. When the presence of impurities whose absorptions would interfere is suspected, they must first be removed chemically or by differential absorption on a column of alumina or silica gel. The crude product of the particular dehydrogenation reaction under examination is coloured bright orange to deep red. Examination of the highly coloured impurities that were removed by adsorption on a column of alumina from light petroleum solution indicated that they were a mixture of rhodacene and chalcacene. However, quantitative estimation under the prescribed conditions of these compounds in the crude product, calculated as their acenaphthylene equivalents, gave a value of about 0.3 per cent.of a typical sample. Since this figure lies within the limits of experimental error, its contribution to the authentic acenaphthylene content was considered unimportant. Thus, for the material examined by the authors, preliminary chromatographic puri:hcation of the crude sample for analysis proved unnecessary, although it is conceivable that for acenaphthylene prepared under different conditions purification would be required. The procedure to be adopted for routine analysis is very similar to that already described for the construction and testing of the calibration curve. Three solutions of the sample in toluene, of various concentrations up to 0.15 per cent., are prepared. A mercury lamp in conjunction with an Ilford Spectrum Violet filter 601 is used as the source of light, and measure- ments made on each solution contained in l-cm glass cells. Table I11 shows results obtained by the examination of the products from successive crystallisations of crude acenaphthylene from a pilot plant. The agreement between the individual determinations for the second and third crops is somewhat better than is the general rule. TABLE I11 EXAMINATION OF SUCCESSIVE CRYSTALLISATI ONS OF CRUDE ACENAPHTHYLENE Acenaphthylene in Acenaphth ylene Sample 100 ml of toluene, Drum reading determined, i:::} 98.4 0 ’ g / O 1st crop . . .. . . 0.1293 0.702 0-1342 0.675 0.1096 0.820 98.0 2nd crop . . .. . . 3rd crop . . .. 0.1238 0.1312 0.1360 0.1234 0.1329 0.1200 0.752 ‘35.3 0.712 0.690 95-2 0.758 0.705 0.792 92.8 92.8 The authors wish to acknowledge the assistance of Mr. F. V. Bethell in the experimental work and to thank the Directors of the Company for permission to publish, POWELL DUFFRYN RESEARCH LABORATORIES 140, BATTERSEA PARK ROAD LONDON, S.W.ll First submitted, March, 1950 Amended, October, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600109

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Feb., 19511 NORWITZ 113 The Electrolytic Determination of Large Amounts of Lead as Lead Dioxide BY GEORGE NORWITZ An electrolytic method is described for the determination of lead, in which the well-known tendency for the formation of non-adherent anodic deposits is overcome by using an electrolyte containing perchloric acid. With the apparatus described, deposits of dioxide from as much as one gram of lead can be handled with ease. The conversion factor for lead dioxide to lead is determined empirically. PRESENT methods for the electrolytic determination of lead as lead dioxide are not satisfactory for the determination of more than 0.10 to 0-12 g of lead1y2s3s4 because of the difficulty of obtaining adherent deposits. A method has been devised by the author for determining up to 1 g of lead as lead dioxide.A perchloric - nitric acid medium is used. The perchloric acid has the effect of making the deposit adhere firmly to the electrode. It has been stated by Willard and Furmans that the addition of a few drops of sulphuric acid will make lead dioxide more adherent; but the danger of precipitating lead as lead sulphate limits the use of sulphuric acid to the deposition of small amounts of lead dioxide. The temperature used by the author to dry the lead dioxide was 120" C. This temperature is recommended by Kolthoff and SandellJ3 Willard and F ~ r m a n , ~ and the American Society for Testing Materia1s.l The factor used by the author to convert the lead dioxide to lead was the empirical factor 0.8611. This was the average factor obtained when several samples of very pure sheet lead, scraped clean of oxide, were carried through the determination.It is advisable for each laboratory to determine its own factor. The method can be used for the determination of lead in high grade pig lead for which the specification requires a minimum of 99.90 per cent. of lead. The amount of tin, bismuth, arsenic and antimony that might be found in this type of material does not interfere with the method. The addition of some copper nitrate before the electrolysis is recommended in order to prevent the deposition of metallic lead on the cathode. EXPERIMENTAL Accurately weighed portions of pure lead, contained in 300-ml electrolytic beakers, were dissolved in a mixture of 25 ml of perchloric acid, 25 ml of nitric acid and 25 ml of water TABLE I Lead present, g 0.2000 0*2000 0~2000 0.5000 0.5000 0.5000 1*0000 1~0000 1~0000 Lead found, g 0.1996 0.2001 0.1998 0.4999 0.5003 0.4999 1*0001 0.9995 0.9996 by heating on the hot plate.The solutions were diluted to 190 ml and 1 ml of a copper nitrate solution, prepared by dissolving 21.5 g of Cu(N0J2.5H,0 in 1 litre of water, was added. This amount of the copper nitrate solution is equivalent to 0.005 g of copper. The solutions were heated to about 70" C and electrolysed, with stirring, at 2 amperes for 1 hour. Large platinum gauze cylinders (50mm high and 45mm in diameter) were used as anodes and platinum spirals as cathodes. At the end of the electrolysis, the beaker containing the114 NOTES [Vol. 76 electrolyte was quickly lowered and quickly replaced by a beaker containing water.The beaker containing the water was moved up and down a few times in order to wash the deposit thoroughly. The anodes were dipped in alcohol, dried at 120” C for 30 minutes, cooled and weighed. The deposits were stripped in nitric acid (1 + 1) containing a little hydrogen peroxide. The anodes were washed with water, dipped in alcohol, dried at 120” C for a few minutes, cooled and weighed again. The differlence in weight was PbO,. The factor for converting PbO, to Pb was 0.8611. The results obtained for lead are shown in Table I. REFERENCES 1. 2. 3. 4. 5. “A.S.T.M. Methods of Chemical Analysis of Metals,” American Society for Testing Materials, Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” John Wiley and Sons, Kolthoff, I. M., and Sandell, E. B., “Applied Inorganic Analysis,” Macmillan Co., New York, Furman, N. H., “Scott’s Standard Methods of Chemical Analysis,” Fifth Edition, Vol. I, D. Van Willard, H. H., and Furman, N. H., “Elementatry Quantitative Analysis,” D. Van Wostrand Co., Philadelphia, 1946, p. 200. Inc., New York, 1929, p. 182. 1946, pp. 700-01. Nostrand Co., New York, 1939, p. 508. New York, 1935, p. 390. 3353, RIDGE AVENUE PHILADELPHIA 32, PA. J d y , 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600113

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

114 NOTES [Vol. 76 THE DETERMINATION OF ZINC. OXIDE IN ZINC POWDER ZINC powder always contains a small proportion of zinc oxide; several methods for the determina- tion of the amount of this impurity are mentioned in the literature, but these are mostly based on the reducing power of the zinc. This may be measured by several reactions, e.g., potassium bichromate, iodate, ferric sulphate and iodine. Fresenius proposed dissolving the zinc dust in dilute sulphuric acid and, after drying the gas, passing the resultant dry hydrogen over heated copper oxide in a combustion tube, absorbing the water formed in a calcium chloride tube. None of these methods is really satisfactory in that the results obtained by these different methods are not concordant and are not reproducible by the same method.The method most widely used in specialised laboratories is that based on the volurne of hydrogen evolved when a sample of zinc dust is dissolved in dilute sulphuric acid; here again the zinc is measured, but the apparatus and technique is very complicatedl and not suitable for the chemist who has only an occasional sample to examine. Another method has recently been described in America,2 but again the apparatus and technique required are beyond the reach of any but the specialist. Confronted by this problem, we have devised a simple but accurate method based on experi- mental evidence that showed that zinc oxide is soluble in ammonium acetate solution whilst zinc metal is not, and it may well prove of use to the chemist who has only an occasional determination to make.Procedure-Take 2 g of the powder in a 250-ml beaker and add 100 ml of water containing 30 g of ammonium acetate. Filter on a sintered glass of No. 4 porosity with suction, and wash with cold water. If washed with absolute alcohol or sodium-dried ether, the zinc can be weighed after drying by suction and placing in a vacuum desiccator for 15 minutes. If a chemical finish is desired, dissolve the residue in hot dilute sulphuric acid, cool, add an excess of caustic soda and electrolyse the zinc, a copper-coated cathode being used. Alternatively, the zinc may be precipitated as the sulphide, and converted to the oxide in the well-known manner. This result gives the amount of zinc metal present. Stir well for 10 minutes, and then allow to stand for 2 hours.Feb., 19511 NOTES 115 The zinc oxide that has been dissolved out by the ammonium acetate can be determined by precipitation with hydrogen sulphide after addition of 10 ml of ammonia.When all the sulphide has precipitated, boil with a little paper pulp to help coagulation. Filter on sintered glass of No. 2 porosity with a paper-pulp pad and suction. Dissolve the residue in 6 N sulphuric acid and boil. Filter on sintered glass and wash well with hot water. Add an excess of caustic soda and, after cooling, electrolyse the solution on a copper-coated cathode in the usual manner. Calculate to ZnO. The author thanks the Directors of the British Drug Houses Limited for permission to publish this note. REFERENCES 1. 2. Furman, N. H., “Scott’s Standard Methods of Chemical Analysis,” Fifth Edition, Volume I, Balis, E.W., Bronk, L. B., and Liebhafsky, H. A., Anal. Chein., 1949, 21, 1373. D. Van Nostrand Co., New York, 1939, p. 1069. ANALYTICAL DEPARTMENT THE BRITISH DRUG HOUSES LIMITED POOLE, DORSET LABORATORY CHEMICALS GROUP G. H. OSBORN July, 1950 1-NITRO-2-NAPHTHOL AS A REAGENT FOR ESTIMATING COBALT ~-NITRO-~-NAPHTHOL is described in some modern textbooks1-2 as a precipitant for cobalt that is superior to the more usual l-nitroso-2-naphthol. We find that pure 1-nitro-2-naphthol does not give a precipitate with cobalt. This is in agreement with Mayr and Prodinge? who reported that the reagent used previously by Herfeld and Gerngross,4 and by Mayr,s which actually pre- cipitated cobalt, must have contained l-nitroso-2-naphthol.l-Nitro-2-naphthol is prepared by oxidising 1-nitroso-%naphthol with nitric acid,1 and the above-mentioned erroneous observations appear to be due to a difficulty in separating the nitro- compound from the nitroso-compound. We have found that l-nitro-2-naphthol can be separated from the crude oxidation product by steam distillation and finally purified by crystallisation from alcohol. The steam distilled l-nitro-2-naphthol melted at 101’ to 103” C; after one crystallisation from alcohol the melting-point was 103” C, in agreement with the figure recorded in the literature.6 Acknowledginent is made to the Chief Scientist, Ministry of Supply, foi- permission to publish this note. 1. 2. 3. 4. 5. 6. REFERENCES Vogel, A. I., “Textbook of Quantitative Inorganic Analysis,” Longmans, Green and Co., London, 1948, pp. 164, 548. Yoe, J. H., and Sarver, L. A., “Organic Analytical Reagents,” John Wiley and Sons Inc., New York, 1941, pp. 129, 245. Mayr, C., and Prodinger, W., 2. anal. Chew., 1939, 117, 334. Herfeld, H., and Gerngross, O., Ibid., 1933, 94, 7. Mahr, C., Ibid., 1934, 98, 402. Heilbron, I., and Bunbury, H. M., “Dictionary of Organic Compounds,’’ Eyre and Spottiswoode, Londm, 1946. MINISTRY OF SUPPLY, EXPLOSIVES RESEARCH AND DEVELOPMENT ESTABLISHMENT WALTHAM ABBEY ESSEX N. J. BLAY L. A. WARREN -July, 1950 A COLOUR TEST FOR AMPHETAMINE IN the test for cocaine previously described by the author,l amphetamine gives a purple colour similar to that of cocaine; the colour, however, changes in about 7 minutes to a beautiful violet colour. The test will detect 0.025 mg of amphetamine. A strong reaction is given by 0.1 mg of amphetamine. REFERENCE 1. Rathenasinkam, E., Analyst, 1950, 75, 169. GOVERNMENT ANALYST’S LABORATORY COLOMBO E. RATHENASINKAM CEYLON July, 1950

ISSN:0003-2654    

DOI:10.1039/AN951760114b

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

116 APPARATUS [Vol. 76 Appara.tus A MODIFIED APPARATUS FOR THE DETERMINATION OF ALCOHOL I N BLOOD AND URINE THIS laboratory, like others engaged in forensic work, is experiencing an increasing demand for the determination of alcohol in urine or blood. Our practice, which we believe is common, was to use the modified form of the Southgate apparatus described by Evans and Jones.' This apparatus has proved reliable as regards accuracy ; it is, however, cumbersome and bulky. This becomes a noticeable disadvantage when series of estimations have to be made involving, as they do, duplicates and blanks that should be run concurrently. It is clear that the excessive bulk is due to an unnecessarily large evaporation chamber. With this in mind, we investigated the factors essential to accurate and.reproducible results. From the experience gained, we designed the apparatus illustrated in the diagram, Fig. 1; its over-all dimensions are approximately half of those of the modified Sout hgate apparatus. The evaporation chamber is an enlargement, of approximately 2~5ml capacity, of the inner U-tube, The apparatus as illustrated was made to our specification by Messirs. Quickfit and Quartz Ltd. I I +- t3.6 cm+ Fig. 1. Diagram of apparatus Procedure-For urine, place 2 ml in the evaporation chamber by means of a pipette; for blood, weigh a comparable quantity into the chamber. Put 25 ml of 0.1 N potassium dichromate in 66 per cent. v/v sulphuric acid in the outer or absorption tube. Place the whole apparatus in a water-bath at 80" C. After completion of the test, the inside of the bubbler tube can be washed out easily with a wash bottle fitted with a n A7 cone in place of the ordinary jet, Identity of conditions between the duplicates and blanks is obtained by coupling in parallel to the same air dryer and purifier.Over a period of 18 months this arrangement has given concurrent and accurate results. We use the apparatus for simultaneous duplicate and blank analyses. REFERENCE 1. Evans, J., and Jones, A. O., Analyst, 1929, 54., 134. SOUTH-WESTERN FORENSIC SCIENCE LABORATORY 55, BROADMEAD BRISTOL, 1 E. B. PARKES June, 1950Feb., 19511 -70 - -60 - - 50 - -40 - - 30 - - 20 - -10 - L O cm APPARATUS 117 AN ALL-PURPOSE EXTRACTOR IT is frequently necessary in a biochemical laboratory to perform one or other of the following operations upon large quantities of material: (a) continuous extraction of a solid with a volatile solvent (percolation or Soxhlet extraction) , (b) extraction of a liquid with a less dense immiscible liquid, or (c) extraction of a liquid with a more dense immiscible liquid.Special types of apparatus have been designed for each of these operations (see, e.g., Herzogl), but there is an advantage in the ability to adapt a single apparatus to any task required. The apparatus described in this paper has been in use for some years in this laboratory. It is versatile, easily constructed, compact and robust, and it will operate automatically in all circumstances. The relative dimensions given below have been selected as the result of experience. CONSTRUCTION- The apparatus, Fig.1, which is of Pyrex glass, consists of a main tubular body, E, of 5 crn diameter and 95 cm total length, with a tap, A, at the lower end and, at the upper end, a B34 socket to take a water-cooled condenser, F. The vapour tube, D, 22 mm in diameter, has a B24 cone at its lower end, and the upper end enters the body, E, 15 cm below the top. The solvent t Fig. 1. A Extractor return tube, G, 7 mm in diameter, leaves E just above its lower constriction and, after rising vertically alongside E, bends downwards 44 cm above its exit from E; after passing through the tap, B, it enters the vapour tube, D, just above the B24 cone. I t is advantageous to have tap B sloping downwards away from G, since it is not then continually charged with solvent during operation.C is a round-bottomed flask with a B24 socket in which the solvent may be boiled, H is an extension tube, 32 mm in diameter and 30 cm long, with B34 joints, and J is a conducting118 OFFICIAL APPOINTMENTS [Vol. 76 funnel for light solvents, made of 7-mm tubing, 112 cm long and widened to 25 mm diameter at the top, this being the maximum diameter that allows it to pass through the B34 cones on H and F. It carries a coarse sintered plate, 20mm in diameter (gas distribution tube, porosity No. 1) at the bottom. The whole apparatus is conveniently mounted on a wooden back-board or metal frame. 0 PER ATI ON- As percolator-The column is packed with solid. material, covered with solvent, and the rate of percolation regulated by tap A. Continuous percolation may be achieved by boiling the solvent in the flask, C (tap A closed) , and allowing a suitable rate of return to C by regulating tap B.The vapour tube, D, acts as a safety overflow and prevents the overfilling of the column. A s a liquid - liquid extractor using a less dense extracting soluent-The extension tube, H, is fitted between the condenser, F, and the main tube, E, and the funnel, J, is inserted in the apparatus to rest on the bottom of E and arranged so that the solvent dropping from condenser, F, falls into its open end, Taps A and B are closed and the solvent is boiled in flask C, in which the extracted material collects. At the end of the experiment the extracted solution is run off through tap A and separated from the supernatant layer of lighter solvent. A s a liquid - liquid extractor using a more dense extracting solvent-The solvent is boiled in flask C as before, but no extension or conducting funnel is required. Tap A is closed and some solvent is poured into the main tube, E, before adding the less dense solution for extraction. This prevents fouling the solvent return tube, G, with the less dense solution. Tap B is opened to allow the heavy liquid to return to the boiling flask, C . With an apparatus of the dimensions described, it is possible to extract 1 litre of aqueous solution, of density approximately 1, with chloroform or ether. I wish to thank Professor C. Rimington for hi:: interest and for suggestions relating to the publication of this note. REFERENCE 1. Herzog, J., in Houben, J., “Die Methoden der organischen Chemie,” Volume I, Thieme, Leipzig, 1925. DEPARTMENT OF CHEMICAL PATHOLOGY UNIVERSITY COLLEGE HOSPITAL MEDICAL SCHOOL LONDON, W.C. 1 A. w. HEblMINGS June, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600116

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

118 OFFICIAL APPOINTMENTS [Vol. 76 Official Appointments PUBLIC ANALYST APPOINTMENTS NOTIFICATION of the following appointments has been received from the Ministry of Food since the last record in The Analyst (1951, 76, 54). Public Analyst Appointments GREEVES, William Francis (Deputy) . . . . County Borough of Ipswich. LYNE, Francis Arthur . . .. .. . . County Borough of Oxford. MCLACHLAN, Thomas (Additional) . . . . County Borough of Oxford. KYMER, Thomas Edward (Deputy) . . . . Eiorough of Kingston-upon-Thames. OFFICIAL AGRICULTURAL ANALYST APPOINTMENTS NOTIFICATION of the following appointments has been received from the Ministry of Agriculture and Fisheries since the last record in The Analyst (1951, 76, 54). Agricultuval Analyst A fipointments GREEVES, William Francis (Deputy) . . . . County Borough of Ipswich. JONES, William Elwyn (Deputy) . . . . County of Worcestershire.

ISSN:0003-2654    

DOI:10.1039/AN9517600118

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Feb., 19511 MINISTRY OF FOOD 119 Ministry of Food STATUTORY INSTRUMENTS* 1950-No. 1764. The Meat Products and Canned Meat (Amendment) Order, 1950. Price Id. This Order, which came into operation on November 5th, 1950, provides that the Meat Products and Canned Meat (Control and Maximum Prices) Order, 1948 (S.I., 1948, No. 1509; Analyst, 1948, 73, 341), as amended by S.I., 1949, Nos. 782, 1303 and 2045, shall be further amended as follows- (a) by substituting for Article 3 thereof the following Article :- A person shall not by way of trade prepare or manufacture or sell or have in his possession for sale any description of specified food mentioned in column 1 of the First Schedule to this Order the meat content of which is less than the minimum meat content prescribed as respects that description in column 2 of the said Schedule: provided that in any proceedings in which a person is charged with an infringement of this Article the Court may disregard any variation in the prescribed minimum meat content of beef sausages, beef sausage meat and beef slicing sausage if the meat content thereof is not less than 473 per cent.or in the case of pork sausages, pork sausage meat and pork slicing sausage if the meat content is not less than 624 per cent.: provided also that any fat of vegetable origin used in the manufacture of beef sausages, beef sausage meat, or beef slicing sausage shall be deemed to be meat for the purpose of assessing the meat content of any of those products, if the total quantity of such fat so used does not exceed 25 per cent.of the prescribed minimum meat content of the product”; by substituting for the First Schedule thereto the First Schedule to this Order; by substituting for Part I11 of the Second Schedule thereto the Second Schedule to this Order. “3. (b) (c) THE FIRST SCHEDULE (To be substituted for the First Schedule to the Meat Products and Canned Meat (Control and Maximum Prices) Order, 1948) MINIMUM MEAT CONTENT OF SPECIFIED FOODS (NOT CANNED) Description of Specified Food Column 1 Column 2 Minimum Meat Content 65 per cent., of which a t least 80 per cent. shall consist of pork. Pork sausages, pork sausage meat, pork slicing sausage . . Beef sausages, beef sausage meat, beef slicing sausage Cooked sausages of the following descriptions :- Luncheon sausage, breakfast sausage and polony .. . . 50 per cent. . . ) 30 per cent. Liver sausage . . . . .. . . .. .. . . 45 per cent. 7 Meat roll or galantine . . . . . . .. ,. . . J (The Second Schedule i s a list of ma’ximum prices.) - No. 1871. The Food Standards (Preserves) (Amendment) (Commencement) Order, 1950. Price Id. This Order, which came into force on November 29th, 1950, provides that the Food Standards (P?<eserves) (Amendment) Ordev, 1950 (S.I., 1950, No. 1056; Analyst, 1950, 75, 503), shall come into force in respect of wholesale sales on January 25th, 1951, and in respect of retail sales on Mary 25th, 1951. The Order came into force on September 25th, 1950, in respect of sales by manufacturers. This Order, which came into operation o n December 17th, 1950, replaces the Feeding Stuffs (Manu- The principal - No.1988. The Feeding Stuffs (Manufacture) Order, 1950. Price 6d. facture) Order, 1949, as amended (S.I., 1949, No. 1067 and S.I., 1950, No. 1540). changes are- (i) (ii) (iii) (iv) (v) ( v i ) The definition of “Animal protein rich substance” does not exclude dried blood. The Order does not apply to food for any birds except pigeons, poultry and game-birds. Formulae are prescribed for National Cattle Food N o . 4 and National Poultry Food No. 3 8 , both of which may now be manufactured by any licensed compounder. The proportions of the ingredients of some compounds have been changed, and the permitted use of certain ingredients in additional compounds has been extended. The method of expressing calcium in the analysis of National compounds has been chavlged; i t i s now expressed as CaO.The permitted substitutes for cod-liver oil are added to. * Obtainable from H.M. Stationery Office. Italics indicate changed wording.120 MINISTRY O:F FOOD [Vol. 76 1951-No. 13. The Food Standards (Ice-Cream) Order, 1951. Price 2d. This Order, which comes into operation on March lst, 1951, should be read with the Food Standards (General Provisions) Order, 1944, as amended (S.R. & O., 1944, Nos. 42 and 654; Analyst, 1944, 69, 49 and 247). STANDARD FOR ICE-CREAM I t prescribes standards for ice-cream, as follows- 1. cent. milk solids other than fat: The standard for ice-cream shall be as follows:- Ice-cream shall contain not less than 5 per cent. fat, 10 per cent. sugar and 7 4 per Provided that- (i) ice-cream containing any fruit, fruit pulp or fruit puree shall either conform to the standard set forth above or, alternatively, the total content of fat, sugar and milk solids other than fat shall be not less than 25 per cent.of the ice-cream, including the fruit, fruit pulp or fruit puree, as the case may be, and such total conteat of fat, sugar and milk solids other than fat shall include not less than 79 per cent. fat, 10 per cent. sugar and 2 per cent. milk solids other than fat; (ii) “Parev” (kosher) ice sold, offered or exposed for sale under that description shall contain not less than 10 per cent. fat and not less than 14 per cent. sugar, and the standard for ice-cream set forth above shall not apply to this product. For the purpose of the standards prescribed above “sugar” means sucrose, invert sugar or the solids of any sweetening material derived from starch so however that no ice- cream shall contain less than 7& per cent. sucrose.Each reference in this Schedule to any proportion or percentage means that proportion or percentage by weight. 2. 3. CIRCULAR P6F 1/51 This circular (price l d . ) , dated January 5th, 1951, received with S.I., 1951, No. 13 (above), refers to it It is intended that the standard shall apply to any products (including those supplied in catering establishments) which are sold as “ice-cream” or “ices,” including products where either of these descriptions is qualified by the mention of a flavour, fjuch as “coffee ice.” The standard is not intended to apply to water ices sold as such, or to “ice lollies.” and points out inter alia that- CIRCULAR lrdF 2/51 This circular (price 2d.), dated January lath, 1951, directs attention to the Defence Regulations (No.8) Order, 1950, which came into operation on December loth, 1950, and which revokes certain Regulations of the Defence (General) Regulations, 1938. Particular attentio9z i s directed to Article 4 of the Order which revokes the provisions af/ecting the use o f borax as a preservative jor imported bacon. Under Regulation 60 C A A of the Defence (General) li’egulations, 1939, certain departures from the Public Health (Preservatives, etc., in Food) Regulations weye permitted, among them being the use of borax as a preserving agent in imported bacon. The effect of the present revocation i s to restore the position as it was prior to the operation of Regulation 60 C A A , i.e., the matter is again governed by the provisions of the Public Health (Preservatives, etc., in Food) Regulations. NOTICES THE Ministry of Food have informed us of the following- FOOD STANDARDS COMMITTEE The Minister of Food has appointed Mr.Robert Norman Wright, B.Sc., A.R.C.S., to be a member of the Food Standards Committee in succession to Sir. Harry Hague, M.P.S., who has resigned. The Minister has also appointed Dr. E. L. Sturdee, O.B.E., M.R.C.S., L.R.C.P., to be an additional member of the Food Standards Committee. Mr. Wright, who was nominated by the Food Manufacturers’ Federation is a Director of Crosse and Blackwell Limited; Dr. Sturdee is a Principal Medical Officer of the Ministry of Health. REPORT OF THE MANUFACTURED MEAT PRODUCTS WORKING PARTY The Minister of Food, in consultation with the Minister of Health and the Secretary of State for Scotland, has approved the publication of the Report of the Manufactured Meat Products Working Party. The Report, published on November 22nd, 1950, deals with the hygienic manufacture and with the whole- someness of meat products. Copies may be obtained from H.M. Stationery Office or through any bookseller, price 1s. 3d.

ISSN:0003-2654    

DOI:10.1039/AN9517600119

出版商:RSC    

年代:1951

数据来源: RSC