摘要:

204 OVENSTON AND REES : SPECTROPHOTOMETRIC DETERMIEATION OF SMALL [VOl. 75 The Spectrophotometric Determination of Small Amounts of Hydrogen Peroxide in Aqueous Solutions* BY T. C. J. OVENSTON AND W. T. REES S\-xoPsIs-An accurate and precise method for the determination of inicro- grani quantities of hydrogen peroxide in neutral aqueous solutions is described. The method depends on the liberation of iodine by the action of the hydrogen peroxide on potassium iodide, the reaction being catalysed by amnionium molybdate. The iodine liberated is determined by measurement of the absorption by the periodide ion at a wavelength of 353 mp. The comparative merits of the periodide and the starch-iodine methods for the absorptiometric determination o f liberated iodine are examined, and comparison is made with the peroxidised titanium method for the determina- tion of hydrogen peroxide.JVmx hydrogen peroxide is added to a solution containing an excess of iodide, iodine is set free according to the reaction The use of this reaction for the determination of hydrogen peroxide was proposed by Planes.1 The reaction is slow in neutral solution but the rate increases with fall of pH, although the presence of acid accelerates the photolysis of the unused iodide and leads to erratic results. Of the other absorptiometric methods which have been proposed, probably the most satisfactory is that based on the formation of the yellow complex when hydrogen peroxide is added to titanium sulphate in acid solution. This method has been adapted for abridged spectrophotometry by Allsopp2 and by Ei~enberg.~ Preliminary experiments suggested that the iodine method was very much more sensitive than the titanium method, and the iodine method was chosen for the present investigation when it was found that the reaction in neutral solution could be accelerated sufficiently by the addition of a small amount of ammonium molybdate.This catalyst has been employed in a titrimetric procedure using the same reaction.* The purpose of this paper is to assess the merits of the principal methods available for the measurement of the liberated iodine, and to present a rapid and accurate method for determining microgram quantities of hydrogen peroxide in aqueous solutions. In earlier work, the liberated iodine has been commonly determined by adding starch solution and comparing the blue colour of the starch - iodine complex with that of standards.This method has been studied very fully and it has been shown to possess some serious draw- backs. Starch itself is a material of variable composition, its two principal constituents being amyfose and amylopectin. Amylose gives with iodine (in the presence of iodide) a deep blue complex, and amylopectin gives a somewhat less intense violet colour. The colour obtained with different batches of starch is thus liable to vary. In addition, the colour intensity is dependent on the concentration of iodide and the temperature of the solution, and it also lacks stability. Nevertheless, a fair degree of precision is possible if conditions are carefully controlled.HaOa + 21‘ -+ 20H’ + I,. * After this paper had been written, another paper describing a spectrophotometric method for the determination of small concentrations of hydrogen peroxide was noted (Patrick, W. A., and Wagner, H. B., Anal. Chem., 1949, 21, 1279). The method is simi1a.r in principle to that described in the present paper, except that the liberation of iodine is carried out in an acid medium similar to that used in experiment D under the heading “Effect of acidity.” The present writers are of the opinion that the optimum conditions for accurate quantitative work are obtained only when using an approximately neutral medium. In further confirmation of this, ten tests were made by each method, using 8.6 pg. of hydrogen peroxide in each test. The results can be summarised in the following way- Blank reading Test reading Test corrected for blank r - Standard Standard Standard Method Mean E deviation Mean E deviation Mean E deviation Ovenston and Rees 0.0077 0.00067 0-7010 0.00245 0.8933 0.00275 0.00567 0-7354 0.00977 0-7072 0.01 268 Patrick and Wagner 0.0282April, 19501 AMOUNTS OF HYDROGEN PEROXIDE IN AQUEOUS SOLUTIONS 205 The adherents of the starch - iodine technique have possibly been influenced by the apparently high sensitivity of the method when the colour is examined visually.Even when using a photo-electric absorptiometer, Sendroy6 concluded that the relative colour intensity of the starch-iodine complex was about a hundred times that of the yellow colour of the periodide (I;) ion present in iodine - iodide solutions, which also is proportional to the iodine content.However, Sendroy had employed filter systems which were decidely favourable to the starch - iodine method. Despite this, he recognised that the measurement of the yellow periodide was more convenient and gave more accurate results, and later, with Alvings he found that the sensitivity could be increased at least fiftyfold by means of filters trans- mitting more in the ultra-violet. Further spectrophotometric studies of the starch - iodine method have been made, by Bairstow' and Pieters and Hanssen,s who have recommended it for the determination of the iodine liberated (in an adaptation of the Winkler method for oxygen in water), provided that suitable precautions are taken to ensure temperature control and standardisation of starch supply.Grossg has recommended spectrophotometric measurement of the absorption by the blue complex at a wavelength of 575mp. Another method of measuring the liberated iodine depends gn extraction with a solvent such as carbon disulphide, carbon tetrachloride or chloroform to give a violet solution. The efficiency of extraction of iodine from the aqueous phase depends very much on the concentra- tion and nature of the salts present, and methods relying on a single partition therefore tend to be unreliable. At the same time, if the iodine is removed completely by a series of extrac- tions, the total volume of the solvent so accumulated is so large that the sensitivity of the test is seriously reduced, concentration being impracticable owing to the volatility of the iodine. Very recently, spectrophotometric methods for the determination of liberated iodine by means of the periodide ion have been reported by Shahrokh and ChesbrolO and by Custer and Natelson,ll extinction measurements being made in each case with a Beckman quartz spectrophotometer.The latter authors published absorption spectra of iodine in water, potassium iodide solutions, benzene, toluene, alcohol and chloroform, but did not study the starch - iodine complex. Of these spectra, that for iodine in potassium iodide showed the strongest absorption bands. COMPARISON OF SENSITIVITIES OF METHODS FOR PHOTO-ELECTRIC SPECTROPHOTOMETRY Measurements were made with a Beckman quartz spectrophotometer (model DUV), using the tungsten-filament source at wavelengths above 320 mp.and the hydrogen-arc source at lower wavelengths. Absorption spectra of six solutions were plotted, the con- centration of free iodine being 4.5 pg. per ml. throughout. The solutions were- A. B. 0.002 I? )I 71 I, ?? 37 >I c. 0.01 YI ?I I9 Y? I 3 0 D. 0.1 3 , ?? I? II I, I 3 9 E. F. Pure chloroform. 0.0002 M potassium iodide solution containing 500 p g . of starch per ml. 0-1 M potassium iodide, without starch. The starch was typical material supplied by the British Drug Houses Ltd. The starch - iodine colours were all developed and measured at 20" C., and the spectra are shown in Fig. 1. The absorption due to the chloroform solution is so small in relation to the other solutions as to require no further consideration in the present work.For this concentration of iodine, at 20" C., it appears that the most intense absorption by the starch - iodine complex occurs in about 0.01 M potassium iodide solution. There is an indication of the formation of a different complex a t higher concentrations of potassium iodide. The largest specific extinction for the starch - iodine system at 20" C., as obtained from curve C (Fig. 1) at 605 mp., is 0-147 per cm. per p.p.m. of iodine. The corresponding values for the periodide ion in 0.1 M potassium iodide, as obtained from curve E (after correction for the absorption due to the presence of iodide), are 0.107 per cm. per p.p.m. of iodine at 353 mp. and 0.145 per cm. per p.p.m. of iodine at 289 mp. Using photo-electric receivers of adequate sensitivity for the various wavelengths concerned, the sensitivity of the periodide method is much greater than has generally been supposed, and is, in fact, about as sensitive as the starch - iodine method if measurements are made at 289 mp.Even if measurements are made at 353 mp., the periodide method still possesses three-quarters of the sensitivity of the starch-iodide method. In view of the many factors which render206 OVENSTON AND REES: SPECTROPHOTOMETRIC DETERMINATION OF SMALL [VOl. 75 the starch - iodide method liable to error, the best method for photo-electric measurement is clearly that using the absorption in the near ultra-violet part of the spectrum by the periodide ion. Fig. 1. Absorption spectra, based on an iodine concentration of 4.5 p g .per ml. Curves A, B, C, and D, starch - iodine complex developed with 0.0002 M , 0.002 M , 0.01 M and 0.1 M potassium iodide respectively. Curve E, I j complex developed with 0.1 M potassium iodide. Curve F, iodine in pure chloroform. CHOICE O F WAVELENGTH- Extinction - concentration graphs (not reproduced here) were plotted for various iodine concentrations in 0.1 M potassium iodide. In each case Beer’s law was obeyed, but the error for measurements made at 289 mp. was about four times as great as for those made a t 353 mp. There seems nothing to be gained by using the more intense peak, therefore, and all subsequent measurements of the periodide absorption were made at 353 mp. EFFECT OF POTASSIUM IODIDE CONCENTRATION-- The effect of potassium iodide concentration on the specific extinction at 353 mp.was briefly examined. Fig. 2 shows the relation between the concentration of the potassium iodide and extinction for an iodine concentration at 6-3 pg. per ml. The slope of the curve is very slight for 0.1 M potassium iodide, and this strength was used for the determination of hydrogen peroxide. 1 I 0.05 0.10 0.15 MOLARITY OF POTASSIUM IODIDE Fig. 2. Effect of concentration of potassium iodide on the development of the 1; complex (extinction measurements a t 353 mp) . H l a per 10 ml.. g. (MULTIPLY SCALE BY 20 FOR CURVE J) Fig. 3. Standard curves. Curve G, 1; method a t 353 mp. Curve H, 1; method adapted for Spekker absorptiometer. Curve J, Titanium method at 410 mp.April, 19501 AMOUNTS OF HYDROGEN PEROXIDE IN AQUEOUS SOLUTIONS 207 RECOMMENDED METHOD REAGENTS- If stored in the dark this will last a t least a week.An increase in the extinction of the reagent blank indicates that it requires renewal; this value was normally about 0.010 in the present investigation. This is used for preparation of the calibration graph, and may be prepared by volumetric dilution of 0.03 per cent. w/v hydrogen peroxide which has been standardised against permanganate after thousandfold dilution of purest 30 per cent. reagent. PROCEDURE- Take a volume of the neutral sample solution not exceeding 4 ml., containing not more than about 12 pg. of hydrogen peroxide, in a 10-ml. calibrated flask. Add 5 ml. of 0-2 M potassium iodide solution and 0.1 ml. of 0-5 per cent. w/v ammonium molybdate solution and dilute to the mark at 20” C.Allow to stand in the dark for 5 minutes and then measure the extinction of the solution at 353 mp. using a 1-cm. cell. Correct this reading for actual cell thickness and subtract the extinction reading of the reagent blank, prepared similarly and a t the same time, but with 4 ml. of water in place of the sample. Derive the hydrogen peroxide content of the sample by reference to a calibration graph prepared in the usual way by taking known amounts of 0*0003 per cent. w/v hydrogen peroxide covering the desired range, and plotting the weight against the extinction measurements after correction for the extinction of the reagent blank. ADAPTATIOK OF METHOD FOR USE WITH A SPEKKER PHOTO-ELECTRIC ABSORPTIOMETER Potassium iodide-4.2 M solution.A’mmonium molybdate--0.5 per cent. w/v solution. Hydrogen ~eroxide-0.0003 per cent. w/v solution. Although the best results are obtained with a prism spectrophotometer, it is possible to use a photo-electric filter absorptiometer with very little loss of sensitivity. Using a mercury-arc lamp as source, a suitable filter combination consists of Calorex heat absorbing filters together with Wood’s glass filters to isolate the 365-mp. mercury line. EFFECT OF ACIDITY In order to demonstrate the advantage of using an approximately neutral medium for the liberation of the iodine, a series of five experiments, A, B, C, D and E (Table I), were conducted in which various amounts of sulphuric acid were added, the determination% being otherwise as described in the recommended method.The same amount of hydrogen peroxide, 8.9pg., was present in each test, and a blank was run in the absence of peroxide in every experiment. The acid included in each experiment was sufficient to render the normality of the final 10 mi. of solution equal to the following values- Experiment Final normality of H,SO, A B C D E nil* 0.01 0.1 0.2 1.0 * No acid added. Extinction readings at 353 mp. were taken over a period of time, the solutions being kept in the dark, and the results obtained are given in Table I. I t is clear from these experiments that the rate of further liberation of iodine from the potassium iodide increases markedly with increase of acidity, and that even a small amount of acid causes a comparatively large increase in the magnitude of the “blank” reading.In experiment A (no acid) a decrease instead of an increase in the extinction reading of the test solution was eventually recorded. This decrease became noticeable after the solution had stood for half an hour, and is typical of other similar experiments carried out by the recom- mended method. DISCUSSIO~- This method has been developed mainly for the determination of very small concentrations of hydrogen peroxide in pure water and in neutral salt solutions. The presence of large amounts of fluoride, chloride and bromide ions were shown to have no measurable influence on the absorption of the periodide solution. The degree of accuracy that may be expected is shown by the position of the points from which the calibration graph was obtained; this graph is reproduced in Fig.3 as curve208 OVENSTON AND REES: DETERMINATION OF HYDROGEN PEROXIDE [Vol. 75 G. Curve H in the same figure is the corresponding graph obtained using a Spekker photo- electric absorptiometer with a mercury-arc source and the filters already mentioned. With monochromatic radiation of 353 mp., unit extinction per cm. is obtained with 12-4 pg. of hydrogen peroxide per 10ml. of final solution. The corresponding figure with the recom- mended filter system is 15.4 pg. As a matter of interest, and as it might possibly be of use at higher concentrations of hydrogen peroxide, the titanium method was given a trial. The conditions specified by Allsopp2 were followed, except that monochromatic radiation at 410 mp, (the absorption maximum of the peroxidised titanium system) was used. The calibration graph is shown as curve J in Fig.3, and the accuracy is again very good. However, it is well known that TABLIE I EXTINCTION READINGS AT 353 ~ p . Experiment A Time, min. . . 5 10 15 32 Ela. Test* . . 0.726 0.725 0.721 0.725 Blank . . 0.010 0.010 0.010 0.010 Experiment B Time, min. . . 3 5 18 48 Elcm. Test* . . 0.720 0.720 0.730 0.740 Blank . . 0.030 0.028 0.035 0.050 Experiment C Time, min. . . 3 5 12 32 Elcm. Test* . . 0-738 0.748 0.750 0.765 Blank . . 0.036 0.037 0-040 0-050 Experiment D Time, min. . . 4 5 19 49 Elcm, Test* . . 0.750 0-750 0.780 0.828 Blank . . 0.050 0.050 0.063 0.081 Experiment E Time, min. . . 3 6 18 48 Elcm. Test" . . 0.778 0.802 0.866 0.933 Blank . . 0.103 0.109 0.130 0.198 60 0.717 0.010 130 0.760 0.063 70 0.789 0,070 69 0.859 0.089 73 1-040 0-236 90 115 0.695 0.685 0.010 0.010 140 0.858 0-105 119 0.898 0.146 * The values of E recorded for the tests have not been corrected for their corresponding blanks.many anions, particularly fluorides, have a profound effect on the formation of the peroxidised titanium complex, and the authors consider it safer to use the more sensitive periodide method wherever practicable. The range of the periodide method may be extended by volumetric dilution of the sample. Conversely, its sensitivity may be increased to a limited extent by the use of cells of greater optical depth, provided that their working capacity does not exceed 10ml. This paper is published with the approval of the Lords Commissioners of the Admiralty, but the responsibility for any statements of fact or opinions expressed rests solely with the authors. REFERENCES 1. 2. 3. 4. 5. G . 7. 8. 9. 10. 11. Planes, P., J. Pharm. Chinz., 1904, 20, 538. Allsopp, C. B., Analyst, 1941, 66, 371. Eisenberg, G. M., Ind. Eng. Chem., Anal. Ed., 1943, 15, 327. Rothmund, V., and Burgstaller, A., Monatsch., 1913, 34, 693. Sendroy, J., J. Biol. Chem., 1939, 130, 605. Sendroy, J . , and Alving, A. S., Ibid., 1942, 142, 158. Bairstow, S., Francis, J . , and Wyatt, G. H., Analyst, 1947, 72, 340. Pieters, H. A. J., and Hanssen, W. J . , Anal. Chim. A d a , 1948, 2, 712. Gross, W. G., Wood, L. K., and McHargue, J . S., Anal. Chem., 1948, 20, 900. Shahrokh, B. K., and Chesbro, R. M., Ibid., 1949, 21, 1003. Custer, J . J., and Natelson, S., Ibid., 1949, 21, 1005. ADMIRALTY MATERIALS LABORATORY HOLTON HEATH POOLE, DORSET Jaunaj.y, 1950

ISSN:0003-2654    

DOI:10.1039/AN9507500204

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 19501 ETHRINGTOS, WAKREN AND MARSDEX 209 The Colorimetric Determination of Small Amounts of Hydrogen Sulphide in Effluent Gases by Means of the Spekker Absorptiometer BY C. G. ETHRINGTON, D. WARREN AND F. C . MARSDEN SYNoPsrs-The determination of small amounts of hydrogen sulphide in effluent gases can be carried out in the presence of excess sulphur dioxide and carbon disulphide, using a method based on the formation of an arsenious sulphide sol in the presence of a protective colloid. Interference from sulphur dioxide is axvoided by maintaining the PI-I at 6.0. IN the course of an investigation on the reaction between hydrogen sulphide and sulphur dioxide in effluent gases, it was necessary to carry out a large number of determinations of hydrogen sulphide in the mixed gases.A number of methods for the determination of hydrogen sulphide in air have been d e ~ i s e d , ~ ~ ~ , ~ ~ ~ , ~ , ~ but were regarded as unsuitable for one reason or another. For example, the commonly used lead acetate paper methodl was not suitable because (a) it was not sufficiently accurate, as it was designed to give a rapid indication of the relative safety of the atmosphere, and (b) it was demonstrated that the papers were affected by the sulphur dioxide present, the stains produced being less intense. Cadmium salts are widely used for the determination of small amounts of hydrogen ~ulphide,~ but in the presence of sulphur dioxide the method is not quantitative, and there is also the possibility of formation of caclmium sulphite, which interferes. Again, cadmium sulphide is sparingly soluble in sulphurous acid, and this may lead to low results.A colorimetric method4 has been suggested in which the hydrogen sulphide is absorbed in 6 per cent. solution of sodium hydroxide, but this method could not be used because of the presente in the gases of carbon disulphide, which forms thiocarbonates with the sodium hydroxide, and these in turn break down to give sodium sulphide. It is a well known fact that hydrogen sulphide and sulphur dioxide do not react in alkaline solution, and it was suggested that a weakly alkaline solution of ammonium arsenite should be used as the absorbing medium. Ammonium arsenite w s chosen because the thioarsenious acid, which is formed when the pH of the solution is lowered, breaks down to give arsenious sulphide and hydrogen sulphide.If the pH of the solution is kept above 4-5 there is no interference from sulphite, but trouble was experienced in the first instance due to flocculation of arsenious sulphide; this however was avoided by the addition of the protective colloid, gelatin. I t was found that by absorbing the mixed gases in ammonium arsenite solution at a pH between 8.0 and 8.5, and then reducing the pH to 5.0 in the presence of gelatin, the yellow arsenious sulphide sol which was produced could be used as a basis for the colorimetric determination of hydrogen sulphide. When the pH was reduced below 4.0, an opalescence caused by precipitated sulphur interfered with the determination. METHOD SOLUTIONS- 2H3AsS3 = As2S3 + 3H,S All reagents should be A.R.quality. Ammoniunz arseizite-Dissolve approximately 1.0 g. of arsenious oxide in the minimum amount of ammonium hydroxide (sp.gr. 0-880), and then remove the excess arrimonia by adding N hydrochloric acid, using phenolphthalein as indicator; make up to 1 litre. Sodium acetate - acetic acid-Buffer ~olution.~ Take 95 ml. of 0-2 N acetic acid and mix with 5 ml. of 0.2 N sodium acetate. The buffer should be checked by means of the pH meter before use. This solution must be freshly prepared. Gelatin-Dissolve pure gelatin in distilled water to make a 1 per cent. solution.210 ETHRINGTON, WARREX AND MAKSDEN COLORIMETRIC DETERMINATION OF [VOl. 75 PROCEDURE- Place 6 ml. of ammonium arsenite solution and 10 ml. of water in a suitable absorption tube, and aspirate a known volume of the mixed gases through the solution a t the rate of 500 ml.per minute. When aspiration is complete, transfer the contents of the tube quantita- tively to a 50-ml. graduated flask; add 5 ml. of gelatin solution, and enough acetate buffer to reduce the pH to 5.0. Care must be taken when adding the buffer to avoid local reduction of pH below this value, as it may cause the development of an opalescence. The solution is made up to the 50-ml. mark and allowed to stand for 15 minutes before matching. Prepare a blank by aspirating a similar volume of gas through an absorption tube containing the reagent, but do not develop the arsenious sulphide sol; use this in the subsequent determination on the Spekker. SPEKKER GRAPH- A series of standards is prepared by taking aliquots of a standard solution of sodium sulphide which should be checked immediately before and after use.The standards are prepared by taking known amounts of the sodium sulphide solution in increments of 100 pg., a suitable range being from 0 to 800 pg.; the standards are then treated as above and, after 16 minutes, the absorption is measured on the Spekker absorptiometer, using Ilford blue filters No. 602, with a zero setting and 4-cm. cells. Alternatively, Hilger O.B.l filters, which approximately double the sensitivity, can be used. A typical series of standards is as follows- H,S added, pg. . . 78 156 234 312 390 450 630 672 Drum reading . . 0.018 0.033 0,049 0.064 0-080 0.093 0.140 0.182 DISCUSSION- Spekker graphs were prepared from hydrogen sulphide water and sodium sulphide solution in the presence of 6000 pg.of sulphur dioxide and 2000 pg. of carbon disulphide, but no interference was observed so long as the pH was kept above 5.0; below 4.5 an opalescence developed which caused serious interference. It will be seen that the graph deviates from linearity when the solution contains more than 600 pg. of hydrogen sulphide, and the effective working range is 100 to 600 pg. of hydrogen sulphide. During the absorption of the gases, a second tube containing ammonium arsenite solution was placed in series, but no colour developed when the buffer solution was added. The volume of mixed gases aspirated through the ammonium arsenite should be such that about 400 pg. of hydrogen sulphide,are present in the solution, this volume being determined empirically.Finally, series of solutions were prepared. in which the hydrogen sulphide contents were unknown to the analyst, and the concentrations were determined by the above method. The results were.reproducible and the error did not, with one exception in series 3, exceed 5 per cent. over the range 100 to 600pg. SERIES 1 H2S added, pg. . . 45 90 156 270 :305 312 320 360 390 426 460 474 612 512 H,S found, pg. . . 48 88 158 260 304 306 325 358 381 610 442 478 500 520 SERIES 2 Containing WOO pg. of SO, H,S added, pg. . . 84 210 336 462 588 H,S found, pg. . . 100 208 344 470 588 SERIES 3 Containing 6000 pg. of SO, and 2000 pg. of CS, H,S added, pg. . . 63 274 405 41 1 544 548 686 H2S found, pg. . . 72 234 420 414 54 6 656 7 00 We wish to thank the directors of Messrs. Courtaulds Ltd. for permission to publish, Mr. R. S. Jones for the encouragement he has given and members of the laboratory staff at Preston for carrying out much of the experimental work.April, 19501 SMALL AMOVSTS OF HYDKOGEN SULPHIDE IS EFFLUENT GASES REFERENCES 21 1 1. 2. 3. 4. 5. 6. 7. Vogel, I. A., “A Textbook of Quantitative Inorganic Analysis,” Longmans Green & Co. “Methods for the Detection of Toxic Gases in Industry,” Leaflet No. 1, H.M.S.O., 1943. Sutton, F., “Volumetric Analysis,” Vol. 12, J. & A. Churchill, Ltd., London, p. 698. J . Chem. Soc., 1883, 43, 267. Feild, E., and Oldach, C. S., Ind. Eng. Chem., Asaal. Ed., 1946, 18, 665-7. Markova, L. N., and Gutman, S. M., Zavodskuya Lab., 1946, 12, 878-9. Hakewell, H., and Rueck, E. M., A.M. Gas Assoc. Proc., 1946, 28, 529. London, 1939, p. 808. COURTAULDS LTD. RED SCAR WORKS PRESTON J l m t , 1940

ISSN:0003-2654    

DOI:10.1039/AN9507500209

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 19501 SMALL AMOVSTS OF HYDKOGEN SULPHIDE IS EFFLUENT GASES 21 1 A Colorimetric Method for the Micro-De ter mina tion of Calcium in Plant Tissue Extracts BY A. J. IMcGREGOR SYNoPsIs-Calciuni is extracted from fresh or dried plant material by an acetate reagent and precipitated as oxalate. The washed and centrifuged precipitate is used to reduce the red colour of a standard ferric thiocyanate solution. The decrease in intensity of colour, measured absorptiometrically, is proportional to the calcium content of the extract. Magnesium does not interfere. A t very low concentrations the accuracy is of the order of 8 per cent., but over the range 24 to 60 parts of calcium per million the accuracy of repetition is within 2 per cent. Over a similar range of calcium concentra- tions the results are in close agreement with those obtained by permanganate titration.Added calcium is recovered to within about 2 per cent. WHAT is known as “lime deficiency” in soils is a common cause of partial failures of crops, The calcium status of the soil is reflected in that of the crop. A deficiency of calcium not great enough to produce visible signs of crop failure may injure quality, e g . , in peas, or lead to risk of calcium deficiency in animals consuming fodder crops. A prompt diagnosis of unsatisfactory nutrient levels in a crop may be important and can be most effectively ascertained by tests performed on the growing plants. The method described below is designed to determine colorirnetrically the calcium extractable by a reagent solution from fresh or dried plant material.As the method is rapid and simple it may be found useful for control in vegetable-processing factories as well as for agricultural advisory purposes. Essentially the method consists of precipitating the calcium as calcium oxalate, washing and centrifuging the precipitate and determining the amount of calcium by the reductionin colour of a standard ferric thiocyanate solution. The intensity of colour developed is measured in a Spekker absorptiometer. The method has proved satisfactory as a routine procedure and gives results that are ordinarily accurate to 2 per cent. The ability of oxalates to reduce ferric thiocyanate was utilised by Marriott and Howlandf in a method for the determination of calcium in blood. The method here described is a modification of this procedure and is applicable to plant extracts.The ferric thiocyanate reagent used is capable of estimating 0-05 to 0-6mg. of calcium in 10ml. METHOD REAGENTS- (I) Acetate reagent-30 ml. of glacial acetic acid (A.R.) are dissolved in 1 litre of a solution containing 100 g. of hydrated sodium acetate (A.R.). (2) Oxalate r e a g e n t 4 g. of ammonium oxalate (A.R.) are dissolved in 100 ml. of distilled water. (3) Wash soZ.ution-Prepared by mixing together 2 ml. of concentrated ammonia solution (spgr. 0.88), 98 ml. of distilled water, 100 ml. of redistilled ether and 100 ml. of redistilled ethyl alcohol.212 MCGREGOR : A COLORIMETRIC METHClD FOR THE MICRO-DETERMINATION [VOl. 75 (4) Diluted hydrochloric acid--50 ml. of concentrated hydrochloric acid (A.R.) are dissolved in distilled water and made up to 1 litre.(5) Ferric chZoride solution-8 g. of hydrated ferric chloride (A.R.) are dissolved in 500ml. of reagent (4), made up to 1 litre with that reagent and filtered through No. 42 M'hat man fil t er-paper . (6) Potassium thiocyanate-16 g. of potassium thiocyanate (A.R.) are dissolved in distilled water and made up to 1 litre. (7) Thiocyanate reagent-10ml. of ferric chloride reagent (5) and 10ml. of potassium thiocyanate reagent (6) are measured into a 200-ml. volumetric flask and made up to volume with distilled water. (8) Standard calcium solution--1.4984 g. of calcium carbonate (A.R.) (oven-dried) are dissolved in acetate reagent (1) and made up to' 1 litre with that reagent. The concentration of this solution is 600 parts of calcium per million.A 60-p.p.m. standard solution is prepared by suitable dilution with acetate reagent. PROCEDURE Preparation of the extract-Prepare the extract by treating 10 g. of finely chopped fresh plant tissue with 200 ml. of acetate reagent in a Waring blendor and decolorising with 1 g. of purified carbon (not bone charcoal). After 3 minutes, filter the extract through a No. 42 Whatman filter-paper. (Extracts of dry material can be prepared by shaking 1 g. of dry matter with 100 ml. acetate reagent (1) in a to-and-fro shaker for 1 hour, and then clarifying and filtering as above.) Place this volume in a 25-ml. centrifuge tube. (The volume of extract taken should contain between 0.05 mg. and 0.6 mg. of calcium.For samples containing greater amounts of calcium a suitable volume is diluted to 10 ml. with acetate reagent.) Precipitation of calcium-Heat the centrifuge tube containing the extract volume in a water-bath to a temperature of 80" to 90" C. Add 1 drop of methyl red indicator, followed by 2 ml. of warm oxalate reagent (2). Add diluted aqueous ammonia (1 in 4) drop by drop until the acidity is nearly neutralised and the solution is faintly acid. Mix the contents of the tube thoroughly by rotating it between the hands. Allow to stand for an hour before centrifuging. Washing the precipitate-Centrifuge the contents of tube at 3000 r.p.m. for 10 minutes. Suck off the supernatant liquid by means of a fine-bore glass tube connected to a water pump. Remove excess of oxalate and acetate reagents by two washings with the wash solution (3).Drying the precipitate-After washing the precipitate, place the tubes in an electric ovell at 90" C. till dry. DeveZoPment of colour-Add 1 ml. of the hydrochloric acid reagent (4), accurately measured, to each tube and dissolve the precipitate completely by shaking the tube. If the precipitate is difficult to dissolve the tube can be placed in a water-bath for 2 or 3 minutes. Add 10 ml. of the thiocyanate reagent (7) and mix thoroughly. Allow the colours to develop for 30 minutes. It is convenient to develop ccllours in 20 to 25 tubes at a time. Measurement of coZour intensity-Measure the intensity of the colour by means of a Spekker absorptiometer. Set the drum at 1-00 against distilled water.Calibration-Take 2, 4, 6, 8 and 10 ml. of the 60-p.p.m. calcium standard in centrifuge tubes, make up to 10 ml. with acetate reagent and treat as described above. Re-calibration is required when new potassium thiocyanate, ferric chloride or hydrochloric acid solutions are prepared. NOTES- Range of the method-When the concentration of calcium ions in the extract volume (10 ml.) is greater than 60 parts per million inaccurate results are obtained. If the concentra- tion is between 60 and 120 p.p.m., the colours may be adjusted by the addition of a further 1 ml. of reagent (4) and 10 ml. of reagent (7). I t may also be possible to measure higher concentrations of calcium by altering the strength of the thiocyanate reagent. This however has not been found necessary for most plant extracts.For extracts containing more than 60p.p.m., a suitable aliquot is diluted to the extract volume with acetate reagent. The method is therefore capable of measuring concentrations of calcium of from 10 to 600 p.p.m. The reagent is allowed to stand for half an hour before use. The extract volume-The standard extract volume is 10ml. Avoid over-heating. Use the 1-cm. cell, h.eat filters H503 and green filters No. 5.April, 19501 OF CALCIUM IN PLANT TISSUE EXTRACTS 213 Precipitation of caZcium-Under the conditions of precipitation calcium is precipitated quantitatively. In the presence of excess of ammonium oxalate, magnesium ions in the extract do not interfere. The method has been tested with concentrations of magnesium higher than are normally found in plant extracts but no error resulted in the determination of calcium (Table I).The precipitation is usually complete within half an hour (Table 11), but it is convenient to standardise the time at 1 hour. TABLE 1 THE EFFECT OF MAGNESIUM Concentration, p.p.rn. A I 1 Calcium Magnesium 12 - 12 6 12 20 12 160 36 - 36 80 Spekker reading (average of three determinations) 0.205 0.205 0.200 0-210 0-5 10 0.510 TABLE I1 THE EFFECT OF PRECIPITATION TIME Time between Concentration of precipitating and calcium, centrifuging Spekker reading p.p.m. 12 10 min. 0.185 60 10 9 ) 0.766 12 60 12 60 12 60 12 60 12 60 20 min. 20 3) 30 min. 30 9 ) 1 hour 1 )) 2 hours 2 9 ) 18 hours 18 9 ) 0.190 0.765 0.195 0.780 0.205 0.790 0.205 0-785 0-205 0-785 Washing the precipitate-Thorough washing of the precipitate is essential if accurate results are to be obtained.The wash solution recommended by Le Fevre and Nicholson2 was found to be satisfactory and much superior to washing with dilute ammonia, alcohol and ether. The latter technique required three washings and four centrifugings, which make it a long, tedious process. Inaccurate results were obtained owing to the difficulties of centrifuging the calcium oxalate precipitate from these liquids. Two washings with the “wash solution” (3) were found to be satisfactory. Furthermore, solution (3) gives a suspension which is easily centrifuged at 3000 r.p.m. The efect of acidity on intensity of colow-With increasing concentration of hydrochloric acid in the final solution, the sensitivity of the method is decreased (Table 111).Various concentrations of hydrochloric acid were tried for dissolving the calcium oxalate precipitate. Reagent (a), 5 per cent. v/v hydrochloric acid gave the most satisfactory range of colours. With concentrations below this, difficulty was experienced in dissolving the precipitate. The concentration of ferric thiocyanate was chosen to give a suitable range of Spekker readings under the conditions of the method. This was found to be 0-08 per cent. of potassium thiocyanate and 0.04 per cent. of ferric chloride, which gives a Spekker reading of about 0.04 in the absence of calcium and 0.75 with 60 p.p.m. of calcium in the extract volume. The graph of calcium concentration against the Spekker drum reading is linear up to approximately 0.7.With increasing calcium concentration above this point, the reduction214 MCGREGOR: A COLORIMETRIC METHOI) FOK THE MICRO-DETERMIXATIOS [VOl. 75 in colour becomes less rapid and the graph curves rapidly, owing to interference by the yellowish colour of reduced iron thiocyanate. The sensitivity of the method is increased by increasing the proportion of potassium thiocyanate to ferric chloride. A point is reached, however, at which further increases cause a serious reduction in the range of the method. The concentration of potassium thiocyanate TABLE I11 THE EFFECT OF HYDROCHLORIC ACID Concentration of Concentration of “concentrated’ ’ calcium in extract % p.p.m. hydrochloric acid (v/v), volume, Spekker reading Difference 5 12 0.205 0.5s5 60 0.790 10 15 20 12 60 12 60 12 60 0.255 0-745 0.315 0.730 0.360 0.715 0.490 0.415 0.365 and of ferric chloride prescribed for reagent (7) was found to give the maximum sensitivity for the range of calcium concentration required in this method. Development of colow-The development of the thiocyanate colour is almost instan- taneous, but it is advisable to allow the solutions to stand for several minutes in order to ensure that equilibrium has been reached.11: was found convenient to read the colours half an hour after development. The colours are stable up to 1Q hours after development. RESULTS The method was checked by determining the calcium contents of typical plant extracts; a known amount of calcium was then added to fresh samples of each extract and the calcium contents re-determined. The percentage recovery of calcium was calculated and was found to be satisfactory (Ta-ble IV).In addition some acetate extracts of plant tissue were made and the calcium concentration in each determined in 5 ml. and in 10 ml. of the extract. ‘igreement was good; the results for four samples are shown in Table V. TABLE: IV THE RECOVERY OF CALCIUM Calciuin in extract volume, mg. Originally amount added Calcium added, mg. A A 7 -- 7- 7 7- present plus Difference as yo of the Extract Determined (calculated) Re-determined Known Determined amount added 1 0.452 0.572 0.572 0.12 0.12 - 2 0.399 0.519 0-522 0.12 0.123 + 2.5 3 0.259 0-499 0.495 0-24 0.236 - 1.7 The accuracy of the method was also tested by comparison with the standard volumetric procedure of titrating the calcium oxalate with standard potassium permanganate solution TABLE V THE DETERMINATION OF CALCIUM IN 5 AND 1 0 M L . O F EXTRACT Results for four samples Concentration (p.p.m.) ,of calcium in extract volume (determind) r .1 Volume of A extract used 1 2 3 4 5ml. ,. .. 46.0 3!&6 36-2 41.2 10ml. . . .. 45.2 39.0 36.4 39.9 Difference, % . . 1.7 11.5 0.55 2.9April, 19501 OF CALCIUM IN PLANT TISSUE EXTRACTS 215 (Table VI). obtained by found to be Eleven typical plant extracts were used for this comparison. The values the two methods were in close agreement. The coefficient of correlation was +0.996. TABLE VI COMPARISON OF THE COLORIMETRIC METHOD AND VOLUMETRIC POTASSIUM PERMANGANATE METHOD Concentration of calcium, mg. per 100 ml. A I .l Sample Thiocy anate Permanganate 1 5.20 5.30 2 8.30 8.28 3 9.88 9.92 4 11.56 11.58 5 15.12 15.12 6 10.00 9.98 7 7.04 7-14 8 7.12 7.04 9 19-32 19.38 10 14.84 14.80 11 8.96 8.88 Mean 10-67 10.67 REFERENCES 1. 2. Marriott, W. M., and Howland, J., J . Biol. Chem., 1917, 32, 233. Le Fevre, M. L., and Nicholson, E., J . Dental Research, 1938, 17, 31; as quoted by Kochakian, C. D., and Fox, P. R., Iiad. Eng. Chenz., Anal. Ed., 1944, 16, 762. THE WEST OF SCOTLAND AGRICULTURAL COLLEGE 6, BLYTHSWOOD SQUARE, GLASGOW, C.2 May, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500211

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 19501 OF CALCIUM I N PLANT TISSUE EXTRACTS 215 A New Type of Polarographic Cell Suitable for Routine and Research BY G. S. SMITH SYNOPSIS-A flow-through type of polarographic cell, suitable for universal use, is described. It embodies an external anode with a simple liquid junction, provision for de-oxygenation of electrolytes in the absence of mercury, and means for determining the capillary characteristics. NEARLY all the various types of cells used in polarography fail to satisfy one or more of the following desirable requirements. (a) An external anode should be used to ensure that the anode potential is independent of the nature of the solution being analysed, and also, incidentally, to prevent wastage of pure mercury. (b) When an external anode is used, the junction should be simple to establish and maintain, the anode solution should not contaminate the electrolyte in the cell, or be contami- nated by it, and the resistance of the junction to electric current should be negligible.(c) Removal of dissolved oxygen by means of the passage of an inert gas should be capable of being carried out in the cell itself in the absence of mercury in order to avoid dissolution of traces of mercury. Afterwards the surface of the liquid should not be allowed to come into contact with oxygen of the air. (d) It should be possible to fill and empty the cell, and to wash it adequately, with a minimum of manipulation; thus, some form of flow-through cell is desirable. (e) Simple means of weighing the mercury drops forming in the actual solutions used should be available, so that from the rate of flow and the drop-time the characteristics of the216 SMITH: A NEW TYPE OF POLAROGRAPHIC CELL SUITABLE capillary may be calculated, and the results of diffusion-current measurements may be com- pared, when necessary, with those obtained with other capillaries. Pol.78 (f) The apparatus should be maintained at a constant temperature. With these objects plexity is only apparent out. Fig. 1. Cell for polarography. in view the apparatus described below was constructed. Its com- since all the operations with it are very simple and are rapidly carriedApril, 19501 FOR ROUTINE AND RESEARCH 217 DESCRIPTION OF THE APPARATUS The apparatus is shown diagrammatically in Fig. 1. The cell, A, is a Gooch crucible adaptor with a tap TI fused on to the stem.TI has a direct outlet and another outlet along the barrel. The stem of the cell passes through a split and re-sealed rubber bung held in the neck of a reagent bottle which has been cut off about half-way up the sides and inverted t o act as a water-bath, B. This bung carries two other tubes with taps: T, is for emptying the water-bath, and T3, which is normally left open, is an outflow for washings of the liquid- junction tube (see below). The top of the cell is fitted with a rubber bung with six holes through which pass tubes C and D for the inlet of nitrogen, a thermometer E, short tubes F and G for insertion of the capillary, I, and solution-delivery tube J, and finally the gas outlet tube, H. Tubes F and G are fitted with rubber sleeves, and I and J are slightly enlarged at suitable points so that they make air-tight seals with these rubber sleeves, but otherwise can be passed freely in or out of the outer tubes.The lower part of J is drawn off slightly. Normally, J and the parts connected to it do not require removal. The solution-delivery tube J, delivery funnel K with tap T4, liquid-junction tube L, tap T5, outlet tube M, connection tubes N to reservoir 0 (containing 3-5 M potassium chloride), through tap T,, and to calomel electrode P, are entirely glass with no intermediate rubber connections. Tube M is joined to the outlet tap T3 by rubber tubing. The gas inlet tubes C and D are connected to a three-way tap T,, the other side of the tap being connected through a safety bottle and washing bottles to a cylinder of nitrogen.Tube D terminates just below the rubber bung, but tube C continues to the bottom of the cell just above tap TI and it is drawn off to a point so that fine bubbles of gas can be passed through a solution in the cell when tap T, is suitably turned. The gas outlet tube H is connected to a tap T, which can be turned so as to allow gas to pass out through the barrel or through a bubbling tube Q, or, when necessary, to stop the outflow of gas altogether. The mercury capillary I is joined by means of plastic tubing to a capillary tube fitted with a fused-in platinum wire leading to mercury in the cup R for the cathode connection. The other end of the capillary tube is connected to a mercury reservoir. The calomel electrode is the anode ; it contains mercury covered by a layer of calomel and 3.5 M potassium chloride, and connection to the mercury is made through a platinum wire in the inner tube which is held by a bung at the top of tube P.Between the electrode and reservoir 0, and also in the connecting tube to tap T,, there is a continuous column of 3.5 M potassium chloride. OPERATION- Filling the cell-The solution to be examined is placed in the delivery funnel, K, and allowed to run into the cell through the tap T4. At the same time tap T, is turned momentarily so that some of the liquid passes through the tap and then out through tube M and tap T3. Tap T4 is then turned off so that a continuous column of liquid occupies the tubes J and L. Removal of oxygen-With a glass stopper, instead of the mercury capillary, inserted in the rubber sleeve of tube F, nitrogen gas is passed through C for several minutes, the gas escaping through tap T,.The capillary is then inserted, tap T, is turned so that no gas can escape, and tap T5 is turned so that the excess pressure in the cell drives some of the liquid up through J and out through T3, thus ensuring that de-oxygenated liquid is present in J. Nitrogen is then passed for a few minutes longer with tap T5 closed and tap T, open. Tap T, is then turned so that gas passes over the surface of the liquid in the cell and out through the barrel of tap T,. Establishment of liquid junction-With the stopper of 0 removed, tap T, is opened, and tap T, is gently turned so that a column of the dense potassium chloride solution rises slowly in tube L.Tap T, is then turned off, and the stopper of 0 is inserted. T5 is fully opened and left in this state until the polarogram has been obtained. A somewhat similar method of obtaining a liquid junction, but for another purpose, has been described by Coates.1 Emptying and washing the cell-Tap T5 is first turned off, taps TI and T4 are turned so that the liquid flows out of the cell, tap T, is then turned so that the liquid in tube L flows out through M and T,. and T, is turned so that the liauid in tube C is forced out. The cell and tubecare washegby pouiing water in the tap funhe1 K and allowing it to flow through L and J, taps T, and T3, and TI. Weighing ofmeycury drops-When it is desired to determine the drop weight or the rate of flow of mercury, 10 or 20 drops of mercury are allowed to collect at the bottom of the cell.The mercury, together with a small amount of the electrolyte, is then run out through218 SMITH: A NEW TYPE OF POLAROGRAPHIC CELL [Vol. 75 tap TI into a special tube as shown in Fig. 2. The mercury in the tube is washed several times with water and the washings are poured off through the side tube. It is then washed with alcohol, and finally with ether, and the globule, together with the small amount of Fig. 2. Washing tube for mercury drops. ether that cannot be removed by pouring, is tipped into a paper capsule obtained by cutting off the upper two-thirds of a Soxhlet thimble. The globule is swirled round inside the capsule once or twice to remove the ether by absorption and evaporation, then tipped on to a counter- poised watch-glass on a balance pan, and weighed immediately. GENERAL REMARKS- The dimensions of the cell, etc., may, of course, be chosen to suit the work of a particular laboratory.The capacity of the original cell was about 100 ml., and that of the delivery funnel was about 50ml. The connecting tubes consisted of ordinary &-inch diameter glass tubing. The reservoir for the potassium chloride solution was of 25-ml. capacity, and the level of liquid therein was kept below the level. of the horizontal part of tube L to avoid the risk of the solution flowing into the cell when taps T, and T5 were opened. The same cell may be used for the analysis of very small volumes, possibly single drops, if an internal anode is used.For this the mercury capillary is made long enough to reach into the stem of the cell and the side outlet of tap TI is connected to a small mercury reservoir with an anode connection. This tap is turned so that a small amount of mercury is allowed to run into the empty cell. Another turn of the tap allows the mercury to run out of the cell but leaves a column of mercury in the longitudinal bore of the tap, and another slight turn seals the cell without allowing any more inercury to run in. The liquid to be analysed is introduced into the stem of the cell through the opening G usually used for the delivery tube. Nitrogen is then passed through to remove oxygen, and tap TI is turned so that mercury rises in the stem and forces up the liquid until it comes in contact with the capillary. The apparatus is then ready for the taking of the polarogram. This paper is published by permission of the Ministry of Supply and the Controller of The apparatus described forms part of the subject-matter of H.M. Stationery Office. Provisional Patent Specification No. 5634/49, dated 1st March, 1949. RE FEliE N CE 1. Coates, G. E., J . Chem. SOL, 1945, 489. AERONAUTICAL INSPECTION DIRECTORATE HAREFIELD, MIDDLESEX MINISTRY OF SUPPLY First submitted, September, 1948 Amended, April, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500215

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 19501 NOTES 219 Notes A NOTE ON THE SEPARATION OF MIXTURES OF ADIPIC AND SEBACIC ACIDS THE separation of a mixture of acids into its component acids is a problem that frequently occurs in analytical chemistry. A method of separating such mixtures has been proposed by Brancker.1 The essential point of the method is that alkali is added to the stoichiometric end-point of the strongest acid in an aqueous solution in contact with a suitable solvent. The weaker acids are not neutralised by the alkali and so are in the un-ionised form which will be distributed between the solvent and the water. The strong acid, however, is almost completely neutralised and so remains mostly in the aqueous phase. By this “stoichiometric extraction” Brancker claims that a mixture can be resolved into its component acids.Brancker’s paper is theoretical and contains no practical proof of the method. Recently, however, Clasper and Haslam, separated a mixture of sebacic and adipic acids by a method similar to that suggested by Brancker using ether as the solvent. Analysts might conclude that the simple method proposed by Brancker is likely to be more useful in separating acids than more elaborate methods such as “dissociation extraction. ”8 It must be pointed out, however, that Brancker’s method is not efficient unless the acids in the mixture have widely different dissociation constants. He himself seems to be unaware of this fact, apparently owing to his use of “degree of dissociation’’ which makes the theory difficult to handle and to understand.I t will be shown below that the separation of adipic and sebacic acids achieved by Clasper and Haslam is much greater than can be explained by stoichiometric extraction, but that it is due t o preferential solvent extraction of the sebacic acid into the ether phase. The addition of alkali to the stoichiometric end-point of the adipic acid does not give the best separation. It will be convenient first to outline the theory in terms of dissociation constants using the same assumptions made by Brancker, namely that only the undissociated acid is distributed between the solvent and the water, that corrections for activity coefficients are negligible and that there is no association of acids in the solvent phase. If adipic and sebacic acids are represented by H,A and H,Sb respectively, we have the following equilibria- H,A + HA- + H+ K, = 3-8 x at 25OC. HA- f A-- + H+ 4, = 2.4 x 10-6 at 25°C.H,Sb s HSb- = H+ K, = 2-6 x at 25” C. HSb- + Sb-- + H+ 4, = 2.6 x at 100°C. The values quoted for the dissociation constants are taken from Heilbr~n.~ It will not seriously affect the argument if we put 4, = &. If Va is the volume of the aqueous phase, Vs is the volume of the solvent phase, D,, D, are the partition coefficients of the undissociated adipic and sebacic acids respectively. A, S are the total amounts of adipic and sebacic acids respectively, x is the hydrogen ion concentration, subscripts aq, s refer to the aqueous and solvent phases respectively, then we have that: A = Va[HzAjw + VaLHA-1 + Va[A--] + Vs[H,A], . , .. ..z.e., A = Va[H,A],( 1 + (1 + $) + 2 D,} . . .. .. A similar expression holds for sebacic acid, whence we get- where & = &( 1 + $) and similarly for p2. X220 NOTES Pol. 75 If we add b mols. of base BOH to the system, assuming that the salts formed are completely dissociated, we have- [B+] + [H+] = [HA-] + [A--] + [HSb-] + [Sb-'] + [OH-] D S K From equation (3) it follows that the maximum value of ~ [H2Sb18 is given by 2 2 V2Al s D,A * K2' If there is no solvent extraction effect, i.e., if D2 = D,, and if the mixture originally contained 50 per cent. sebacic acid, then the maximum proportion of the sebacic acid in the mixture can be calculated to be 60 per cent. This will be when ,d >* 1 + - D , i.e., at high pH values when the total amount of acid carried by the solvent is small.The fact that Clasper and Haslam achieved a. separation of the acids is due to the fact that D, > D, and not to any effect of stoichiometric extraction. The fact that D, > D, can be seen from Fig. 2 of Clasper and Haslam's paper, where the total amount of acid in the aqueous phase is plotted against the composition of the mixture of acids. When pure adipic acid was used, most of the acid was in the aqueous phase; on the contrary, most of the sebacic acid was in the solvent phase when pure sebacic acid was used. Indeed, the data of Clasper and Haslam can be used to calculate the partition coefficients of the acids. It can be shown that when the acids alone are shaken with water the pH is low enough for most of the acid to be in the undissociated form.When 0.500 g. of adipic acid was shaken with 50 ml. of water and 35 ml. of ether, the acid in the aqueous phase was equivalent to 2 x 24.12 ml. of 0.1 N sodium hydroxide solution, i.e., 0.354g. of adipic acid. ( T i ) The partition coefficient of adipic acid between ether and water is given by (0.500 - 0.354) 50 = o.g D, = :< - 35 0.354 The partition coefficient of sebacic acid between ether and water is given by a similar calculation as 50. These values of the partition coefficients .will be subject to correction due to the mutual solubility of the phases. The correction will be ignored, however, in the following calculations which will be insensitive to relatively small corrections in the partition coefficients. A', the total adipic acid in the aqueous phase can easily be shown to be given by A(1 + B) A' = ..* * ( 5 ) .. .. .. .. .. vs 1 + , d + - p l and the total adipic acid in the solvent phase is equal to (A - A'). sebacic acid. in the aqueous and solvent phases, for various values of B. these values of /I can be obtained by solving equation (4), putting P1 = F,. has been constructed for the case where A = S. Similar equations hold for the We can thus calculate the total acid and also the composition of the acids contained The values of b/A corresponding to In this way Table I Total acid in aqueous phase, b/A divided by A 0 0.5 1.0 1.5 2-0 0-73 0.9 1 1.14 1.55 2.00 TABL:E I Adipic acid in aqueous phase, %, 96 93 8 4 65 50 Total acid in Sebacic acid solvent phase, in solvent divided by A phase, % 1-27 1-09 0.86 0.45 0 77 90 95 99 100 From Table I it can be seen that a considerable separation of adipic and sebacic acids is theoretically predicted although, since we have assumed K, = K,, no stoichiometric extraction effect is possible for this calculated case. It can also be seen that as the total amount of alkali tends to the amount equivalent to the total acid present (Le., b/A tends to 2), the acid in the solventApril, 19501 NOTES 221 phase tends to be pure sebacic acid.The total amount of acid present in the solvent phase, how- ever, decreases as b/A increases. The best separation will therefore be achieved by extracting the mixture many times at a high pH value, so that at each extraction the ether phase removes nearly pure sebacic acid.This is the basis of the separation achieved by Clasper and Haslam in their continuous extraction apparatus. The effect is due to solvent extraction however and not to stoichiometric extraction. If D, were not much greater than D,, an elaborate technique would be required to separate the acids. In order to check these conclusions, an experiment was carried out for the case b/A = 1. 0.389 g. of adipic acid (equivalent weight 73-0) was neutralised by sodium hydroxide to the end- point of phenolphthalein and the volume made up to 50 ml. 0.531 g . of recrystallised sebacic acid (equivalent weight 102-0) was added, together with 35ml. of ether and the mixture was shaken at 20” C. for 30 miputes. The aqueous phase was removed and an aliquot titrated. Two experiments gave the result that the excess acidity in the aqueous layer was 23 and 24 per cent.of the total adipic acid present. From Table I when b/A = 1, the excess acidity is expected to be 14 per cent. This acidity can only be due to the sebacic acid so that the aqueous phase will not contain adipic acid purer than 82 per cent. Samples of acids obtained from the aqueous and the ether phases were examined qualitatively in the infra-red and it was found that the acid from the aqueous phase was mainly adipic acid contaminated by a considerable quantity of sebacic acid, and the acid from the ether phase was sebacic acid contaminated by adipic acid. In view of the assumptions made in the calculations for Table I the agreement between the experimental data and the calculated value can be regarded as satisfactory, clearly showing that it is not possible to separate completely a mixture of adipic and sebacic acids by a single extraction at b/A = 1.I am grateful to Mr. A. R. Philpotts for the infra-red analyses and to the Directors of the Distillers Company Limited for permission to publish this note. REFERENCES 1. 2. 3. 4. Brancker, A. V., J . SOC. Chem. Ind., 1947, 66, 453. Clasper, M., and Haslam, J., Analyst, 1949, 74, 224. Twigg, G. H., Nature, 1949, 163, 1006. Heilbron, “Dictionary of Organic Compounds,” Eyre & Spottiswoode, Ltd., London, 1937. THE DISTILLERS COMPANY LTD. GREAT BURGH, EPSOM RESEARCH AND DEVELOPMENT DEPARTMENT w. s. WISE September, 1949 THE COLORIMETRIC DETERMINATION OF ALDEHYDE IN DISTILLED LIQUORS THE procedures described in the A.0.A.C.l and in Scott2 for the colorimetric estimation of aldehyde in alcoholic beverages did not give satisfactory results when applied to the routine analysis of brandy.The agreement between duplicate samples was poor, the discrepancy often exceeding 10 per cent. The method was checked and it was found that the difference in behaviour of the standard solution compared with that of the sample with respect to colour development was an underlying cause for producing fluctuating results. In Fig. 1 the intensity of colour is plotted against the time allowed for colour development. The difference between the behaviour of the standard solution (10 parts of acetaldehyde per 100,000) and a brandy sample is clearly seen. The standard solution increases in intensity at a very high rate whereas, in comparison, the brandy sample undergoes very little darkening in colour.The A.O.A.C. and Scott recommend reading the colour 15 minutes after the addition of the fuchsin - sulphite reagent, but because of the great divergence between the curves every second that passes means that the sample is being compared with a standard of rapidly increasing intensity. This behaviour of the standard solution makes it virtually impossible to obtain good agreement between duplicate samples. It was felt that if the rate of increase of the intensity of the standard solution could be greatly reduced, the value of the method would be considerably enhanced. The standard solution, although made up in 50 per cent. v/v alcohol, differs from the brandy sample in that it does not contain small quantities of acetic acid, esters, furfural and fuse1 oil.Any one or a combination of these substances is probably responsible for preventing the increase in intensity of the colour of the222 NOTES [Vol. 75 sample. When acetic acid is incorporated in the standard aldehyde solution at a concentration of 16 parts per 100,000, which approximates to its level in a brandy, the rate of increase of colour intensity with time is reduced to about one-third of its former value. The curve is shown in Fig. 1. TIME (MINUTES) Fig. :L. The simple expedient of incorporating acetic acid in the standard solution is therefore recom- mended. Further improvement in the method is made possible by preparing a separate standard for each sample and suitably staggering the addition of the fuchsin - sulphite reagent to each pair of tubes.The authors wish to thank the management of the Castle Wine and Brandy Company for permission to publish this note. REFERENCES 1. 2. “A.O.A.C.,” 6th Ed., 1945, p. 194. Scott, W., W., “Standard Methods of Chemical CASTLE WINE AND BRANDY COMPANY LABORATORIES CAPE TOWN Analysis,” 6th Ed., 1939, Vol. 2, p. 2139. L. GORFINKEL G. S. SKELTON August, 1949 PRESSURE COOKING AS AN AID I N ’THE ISOLATION OF EXTRANEOUS MATTERS IN CEREAL PRODUCTS IT has been found that by using a pressure cooker the acid digestion stage in the method for the extraction of extraneous matters present in wheaten flour and biscuits’,’ is facilitated. A house- hold pressure cooker, fitted with a pressure gauge, large enough to hold at least two 800-ml.squat beakers is convenient, but any other closed heating vessel fitted with a pressure gauge, e.g., a steriliser or autoclave, should serve. Pressure cooking obviates the following disadvantages of the ordinary digestion : the varying time taken for the pasty admixture of acid and cereal product to come to boiling-point, the risk of local overheating and charring and the labour of manual stirring up to and during the boiling period. Its advantages are that two tests at least are digested simultaneously, so that tests on duplicate samples receive the same heat-treatment and the product subsequently shows much less “dross” at the interface of the petrol and aqueous layers. The method shouId be adaptable for the treatment of other cereal products.There has been no evidence that hairs or insect fragments are disintegrated by the use of a higher temperature. PROCEDURE Extract the fat from a quarter of a pound or 1.00 g. of the powdered biscuits or cereal product with light petroleum (b.p. 40” to 60” C.) and d v the residue. Wheaten flour does not require extraction. Place the dry material in a 800-ml. squat beaker and stir in boiling 0.5 N hydrochloric acid. Flour or biscuits of low fat content require 400ml. of acid, but for shortened biscuits 300 ml. are sufficient. Put 300 ml. of distilled water into the cooker and stand the beakers upon a metal platform. Close the lid of the cooker and raise the temperature of the water to boiling- point with the escape-valve open to allow of the free passage of air; it is important that no pressureApril, 19501 NOTES 223 builds up while air is being displaced.When all the air has been driven out by the steam, close the escape-valve and raise the pressure, slowly and steadily, to 20 lb. per square inch and maintain this pressure for 10 minutes. There is a risk of the contents of the beakers boiling over if the pressure is raised too rapidly. Allow the pressure to drop to zero by the gauge, which takes about 20 minutes, before un- clamping the lid of the cooker. Remove the beakers, wash down any solids on the sides with hot water and allow to cool. Tests on biscuits are now ready for adjustment to pH for the pancreatin digestion, but flour samples can be extracted for extraneous matters from the acid liquid without further treatment.For the routine examination of biscuits, a preliminary test has indicated that it may not be necessary to proceed with the pancreatin digestion before the separation of rodent hairs. REFERENCES 1. 2. Kent-Jones, D. W., Amos, A. J., Elias, P. S., Bradshaw, R. C. A., and Thackray, G. B., Analyst, Coppock, J. B. M., and Bradshaw, R. C. A., Journal of the Science of Food and Agriculture, 1960, 1948, 73, 128. 1, 57. MACFARLANE, LANG & Co., LTD. IMPERIAL BISCUIT WORKS OSTERLEY, MIDDLESEX D. M. FREELAND October, 1949 A CONSTANT TEMPERATURE BATH OPERATING BELOW ROOM TEMPERATURE A constant temperature bath has been designed to operate a t approximately 20" C. Room temperature is frequently above this, but tap water is almost always available at temperatures of from 8" to 20" C.The principle adopted was that of a continuous and uniform stream of tap water passing into the bath through a tubular electric heater, and then running to waste. The heater is controlled by a thermostat in the bath itself, and accordingly delivers cold and warmed tap water alternately, so maintaining the bath at a constant temperature. In the diagram (Fig. l), which is drawn to scale, tap water enters by the lower side-tube of the vertical tube A, and overflows by the upper tube. This forms a constant-level device, and from it the water flows down the fall tube and up through the heater B, the flow being regulated by a screw clip at the bottom of the heater. It then overflows by the side tube into the open tube E, which forms a convenient sight feed, past the thermometer F, and into the bath G through the tube H, near the front of the bath.The contact thermometer C can be an ordinary toluene thermo-regulator, but if the bath is to be used continuously, an enclosed-type contact thermometer is better, as the setting is not so likely to be upset by oxidation of the mercury. A contact thermometer of this type may operate at a fixed temperature, or it may be of the Beckmann or other adjustable type. The bath described here is fitted with a 20" C. fixed-contact thermometer, and the results obtained with it are given at the end of this note. The second contact thermometer D, inside the heater, need only be a very simple affair, with a bulb holding 2 to 3 ml.of mercury, and a stem of l-mm. bore manometer tubing. Its sole purpose is to prevent damage to the heater if the water supply fails. I t is set to operate at about 60" C., and is connected in parallel with C. The heater consists of about 5 feet of braided heating element, wound on a 2-foot length of 15-mm. glass tubing, and then overwound with several layers of asbestos string. It is designed to take 150 watts. The relay, R, is of the type that breaks the power circuit when the thermometer makes contact. The enclosed mercury type is recommended, as it will work for long periods without attention. The connections are not shown in detail, as they depend on the type of relay, and details are generally supplied by the makers. Any electrical equipment that satisfies the requirements can be used.The bath itself is a copper tank, 18 x 15 x 6 inches deep, holding 44 gallons of water when filled to the overflow. It is designed to take up to 24 samples of jelly in 100-ml. tall beakers, and is fitted with a perforated false bottom for this purpose. For continuous use, it is convenient to place the bath on a bench or shelf, and to have the glass parts and the relay mounted on a vertical board fixed to the wall. The contact thermometers It escapes through the overflow J, at the back.224 NOTES [Vol. 75 are best connected to the relay through plug and socket fittings, so that they can be disconnected and removed if required. To operate the apparatus, the tap water is regulated so that a slight overflow is maintained from A.The flow through the heater requires regulating according to the prevailing temperature of the tap water because, when the heater is on, the inlet thermometer F must indicate a temperature well above 20" C., e.g., 2 5 O or 30" Scale : Inchus 0 12 b. n F E A F1g. 1 In routine working, some 20 to 24 beakers of hot jelly are loaded into the bath at once. The temperature rises by about 1.5" or 2" C., but returns to normal after about 1Q hours. The insertion of odd single samples has no appreciable effect on the temperature. When equilibrium is reached, the temperature rises and falls rhythmically as the heater switches on and off. Table I shows the extremes of temperature observed in three widely separated positions in the bath, denoted A, B and C, while running under various conditions.April, 19501 REVIEWS 225 TABLE I Conditions TEMPERATURE VARIATIONS Temperature, C. A B C r A \ Bath empty Maximum . . . . . . 19.7 19.7 19-6 Minimum .. .. . . 19.4 19.4 19.3 Bath containing 12 beakers Maximum . . 19.8 19.7 19.7 Minimum . . 19-5 19.4 19-3 Bath containing 22 beakers Maximum . . 19.8 19.9 19.8 Minimum . . 19.4 19.6 19.3 The mean temperature is thus 19.6' C. and the extreme variation f0-3". If it is necessary to work exactly to a specified temperature, the use of an adjustable contact thermometer is advisable. This comparatively close regulation without mechanical stirring is probably attributable to the slow circulation caused by the flow of water, and to the shielding effect of the false bottom. THE LABORATORY JAMES KEILLER & SON LTD. TAY WHARF, SILVERTOWN, E.16 0. B. DARBISHIRE January, 1960

ISSN:0003-2654    

DOI:10.1039/AN9507500219

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 19501 REVIEWS 225 Reviews ANALYTICAL CHEMISTRY AND CHEMICAL ANALYSIS, 1948. Proceedings of the International New York: Elsevier Pub- The original of this book appeared as an issue of AnaZytica Chimica Acta (1948, Vol. 2, pp.‘419- 854) devoted to the International Congress on Analytical Chemistry, held at Utrecht, on June 1st to 3rd, 1948, under the auspices of the Netherlands Chemical Society. The Congress was divided into five sections, and the proceedings consisted of thirteen formal lectures, the presentation of forty-one original papers and four plenary sessions. The book prints in full all the lectures given and papers read in four of the five sections, and the ground covered is indicated by the following resum& Section 1 : General Methods and Standardisation-This section includes papers on standardisa- tion, statistical aspects of chemical analysis, the task of the analytical chemist in industry, recent developments in gas analysis, organic elementary analysis, the use of isotopes as tracers, and the mass spectrometer.Of interest to English readers is an account of the present situation in the field of standardisation in the Netherlands and the development there of an organisation dealing with the standardisation of analytical procedures ; rules for unification in the description of procedure are given and the necessity of standardising chemical glassware and commonly used apparatus is stressed. Also of considerable interest is a thesis on rationalising analysis; this is summarised in an assertion that the increasing demand for chemical analysis can be met by increasing the productivity per time unit of the scientific analyst, at the same time supplementing untrained people for routine analysis, but even then only with the aid of automatic apparatus. Section 2 : Electrical Methods-In this section, polarography is represented by papers on modern trends, and the application of polarography to the analysis of products of the metallurgy of zinc and some constituents of glass.The use of electrical methods in industrial problems is briefly discussed ; controlled potential electro-analysis is critically considered and a potentiostat and cells for different applications are described. Amperometric titrations and electrical methods for the analysis of water are reviewed. The paper on measurements of the salt content of river water has a considerable outside interest, as it tells of the danger of salt (sea) water rising up the River Maas above the intake for the Rotterdam public water supply, and the resulting necessity to know the movement of the “salt limit.” A full description of the self-recording conductivity meter installed for this purpose is given.Section 3: Emission Spectrography-The papers read in this section are not included, as they were to be published separately in Spectrochimica Acta. This decision would appear to be some- what unfortunate from our point of view, as the book under review is therefore not a complete record of the proceedings at Utrecht. Congress on Analytical Chemistry-Utrecht. lishing Company, Inc. London : Cleaver-Hume Press, Ltd.1948. Price 25s. Pp. vi + 436.226 REVIEWS [Vol. 75 Section 4 : Optical Measurements and Physical Methods of Separation-This section covers reviews and applications of chromatographic and adsorption technique, including analysis of hydrocarbon mixtures; a method for the analysis of hydrocarbon oils by thermal diffusion; a survey of colorimetric and photometric absorption analysis ; and applications of infra-red spectro- photometry with particular reference to powders and to vitamin D,. Two fundamental papers deal (a) with a research on the influence of reagent concentration in the colorimetric determination of copper, and (b) with a spectrophotometric development of Winkler’s method for determining oxygen in water, working on the iodine - starch complex, whereby as low a concentration as 0.005 mg.of oxygen per litre can be estimated. Section 5 : Microbiological Methods and Detection of Traces-The papers on microbiological work include a general review, estimation of copper, magnesium, molybdenum and lead in plant material and soil, determination of tryptophan, and practical experience in assays using lactic acid bacteria. A claim is made that, by the use of a newly isolated strain of AspergiZEus niger and an optimal culture solution, the deter- mination of potassium and phosphate in soil by a microbiological method equal in accuracy to chemical methods may be made in one quarter of the time; also that zinc can be determined by this method. A method is given for the determination of sugars in foods by reductiometric and biochemical methods in mixtures that may include fructose, glucose, saccharose, lactose, maltose and dextrins; the results are worked out by what appears to be a somewhat complicated mathe- matical procedure.New work on estimation of different forms of choline in biological substances concludes the papers in this section; and the book ends with a critical resumk of the work and conferences at the Congress. This book is valuable as an account of the proceedings of the Congress in Utrecht in 1948. These proceedings established a new status for analytical chemistry. Furthermore, they may well have influenced discussions at the meeting of the International Union of Pure and Applied Chemistry in Amsterdam in 1949, for at that meeting a division of Analytical Chemistry was pro- visionally arranged, and patronage was accorded to the next Congress of Analytical Chemistry to be held in England in 1952.Preliminary arrangements are now well in hand for this next Congress, and our Society is participating very actively in the preparations, both in respect of membership of Committees and financially. It is hoped that the centre for the meetings will be in Oxford-a pleasing prospect for many of us, and undoubtedly a great attraction for visitors from abroad. With this in mind, the record of the proceedings at Utrecht has an additional value as a background to and guide for the programme for the future event, and therefore may be reconsidered from this point of view. In the preface, Prof. C. J. Van Nieuwenburg, the President, and Dr.H. A. J. Pieters, the Secretary, present their impressions of the meeting in these words: “We have no doubt that this Congress has clearly shown the great changes analytical chemistry has undergone in recent years. Because of the demand for greater speed and accuracy and the need for handling small quantities of materials the classical methods based on gravimetric and volumetric procedures are rapidly being replaced or supplemented by physico-chemical and physical techniques. The status of analytical chemistry is being raised to a much higher level, and analytical chemistry is becoming a science for the specialist. Modern analysis, with its interests in optical, electrical and micro- biological methods, makes very high demands in the training of its practitioners, and it was stressed by speakers from several countries that the training of analytical chemists is a long way behind the requirements of modern industry.” These are impressions by officials recorded when the sense of the meeting was still fresh in mind and are to be accepted as such.But viewed in retrospect by the reader, with the next Congress in mind, other impressions are formed. There would appear to have been an over- emphasis on physical methods at the Utrecht meeting. New physical methods or significant developments of such accepted methods should be brought to the attention of analysts immediately or at the earliest possible moment. On the other hand, some physical methods are now fully accepted, and no particular advance in analysis is served by the reiteration of technique to such an extent as to overshadow or even eclipse the fundamental analytical work involved in the procedure.Many physical methods are not substitutes for, but aids to, fundamental chemical analysis. Thus, in one of the papers presented at Utrecht, the problem under attack was the determination of traces of oxygen in boiler water, and the experimental work was concerned with elaboration of Winkler’s method where the ox.ygen present is caused to oxidise a manganous salt and the extent of the oxidation is ultimately assayed by the liberation of an equivalent amount of iodine. A considerable amount of experimental work was undertaken in connection with the Trace elements in plants and animals come under review.April, 19501 REVIEWS 227 study of the iodine - starch complex and its colorimetric determination.The estimation of the colour is difficult visually, so either a Leifophotometer or a Spekker absorptiometer is used. The paper is entitled : “Spectrophotometric Determination of Traces of Oxygen in Water.” An alternative title might well have been : “Determination of Traces of Oxygen in Water by a Modified Winkler Method using the Spectrophotometric Technique for the Colour Estimation of the Starch Iodine Complex.” While possibly a cumbersome title it has the great advantage of giving a truer indication of the character of the paper. Another impression is that reviews occupied a very big proportion of the time of the meeting. Perhaps allowance must be made for the youth, as it were, of the Congress.Reviews serve a vital purpose when the workers in the industries in which analytical methods have application are met together for the first time. Subsequently, however, if such gatherings are resumed at fairly frequent intervals, the necessity for full reviews disappears, and brief summaries of develop- ment in the intervals should effectively serve such purposes. There is, however, a clearly defined place for lectures of a review nature by outstanding exponents of, or specialists in, some particular branch of the science. Finally, there is the question of how far methods should be divorced from the field of applica- tion. Yet it is often a technical problem which results, after due research, in a new or modified analytical procedure.An instance of this can be cited when the difficulty, arising during the manufacture of penicillin, of determining the moment a t which the mould growth should be stopped was resolved by an elegant modification of the paper partition chromatographic technique. To divorce this tale from the account of the relevant details of the manufacture of penicillin would deprive it of a very great interest and possibly of some useful incidental information. The Netherlands Chemical Society is to be heartily congratulated on sponsoring this momentous meeting. To all interested in the development of analytical chemistry, this book should be of the greatest interest, and constitute an indispensable reference work. Moreover, as out of the forty-eight addresses and presented papers included in its contents thirteen are in French and no less than thirty-five in English, it is easier for some of us to read than might have been anticipated.The Congress is based on methods of analysis. The account of the meeting is admirably presented in Analytica Chimica Acta. GEORGE TAYLOR MODERN PLASTICS. By H. BARRON, Ph.D., B.Sc., F.R.I.C., F.I.R.I., F.P.I. Second Edition. The purpose of this book is to enable the reader with a modest scientific or engineering know- ledge to obtain a general view of the plastics industry. The book is divided into six parts: introduction, thermosetting resins and their plastics, cellulose plastics, vinyl plastics, other leading plastics, Nylon, etc., and some important aspects of plastics, e.g., analytical and physical tests.The general method of treatment of individual resins is to describe the preparation of the raw materials and the resin itself, the chemistry underlying the production of the resin, and its various applications. Although the general field of plastic materials is covered fairly well, it is surprising, in a book of this size, to find no mention of such polymers as terylene and polytetra- A uorethylene. There is plenty of evidence throughout the book of careless proof-reading which should be remedied in future editions. Among the many errors in formulae may be mentioned: p . 132, /3-resin, p . 417, acetylene and vinyl acetylene, p . 418, polyvinyl acetal and polyvinyl butyral, p . 451, the SH radical, and on p . 214, monomethylol urea is described as monomethyl urea. There are many useful tables in the book giving information about the physical and electrical properties of various plastics and plastic materials.Usually these tables are not referred to at all in the text, and in any event, it would be much better if the original sources of the information were always given. There is a chapter of 28 pages on the analytical aspects of plastics which is of very doubtful value. Schemes for the examination of miscellaneous plastics are given in detail, but it is improbable that any of these schemes will find widespread use in industry. No mention whatsoever is made of one of the most useful practical schemes of this kind, i.e., that of Shaw (Ind. Eng. Chem., Anal. Ed., 1944, 16, 641). The analytical details are often quite erroneous, e.g., on p.704, it is not desirable to test for chlorine after a sodium fusion without taking precautions about the presence of nitrogen or nitrogen and sulphur in the plastic. On p. 710 details are given of the application of the bromide - bromate reaction to the determination of phenols in an aqueous extract without Pp. 779. London: Chapman & Hall, Ltd. 1949. Price 50s.228 REVIEWS [VOI. 76 any reference to the source of the aqueous extract. resin, we come across the statement- using the Kjeldahl method. N/10 acid neutralised = 0.003 gm. nitrogen.” On p. 712, dealing with urea - formaldehyde “The amount of urea present will be determined by straightforward nitrogen determination In this instance 1 C.C. of Presumably the factor refers to urea and not to nitrogen. On the same page it should be noted that it is bromine which is used up in oxidising the urea, and the equation given should make this plain.From the description of the method of determination of the nitrogen content of cellulose nitrate on p. 7 16, it is obvious that the author of this chapter is not very familiar with the chemistry of the nitrometer method; and the method given on p. 722 for the determination of free stearic acid in calcium stearate is really a method for total stearic acid. The book is well printed and illustrated and contains a large number of useful references. The price, SOs., is rather high, but despite its many errors and imperfections, this book contains a great deal of information about plastics which is bound to be useful, and particularly so to those chemists without prior knowledge of the subject.This has already been described. J. HASLAM THE TESTING OF BITUMINOUS MIXTURES. By D. C. BROOME, A.Inst.P., F.Inst.Pet. Second Edition. Pp. viii + 396. London: Edward Arnold & Co. 1949. Price 40s. net. The appearance of the second edition of this useful volume of the Roadmakers’ Library is very welcome, as many advances have been made in the testing of bituminous mixtures since it was first published fifteen years ago. Throughout the author wisely uses the word “bituminous” for coal-tar products as well as for petroleum bitumens. This agrees with international nomen- clature, although in some quarters in this country there is a desire to restrict the term, This material is rapidly gaining in popularity and is finding an ever-increasing field of usefulness.Information regarding the methods of test should be readily available. In the formula at the top of p. 6, the term within the brackets appears to have been inverted, as it wa.s in the first edition. The references to the bibliography numbered 23 and 24 on p. 115 have been transposed, and the whole of the bibliography for “Chapter XV” apparently refers to Chapter XIII. Actually there is no Chapter XV in the book. Near the bottom of p. 247 heat “impact” obviously means input. The methods of detecting the adulteration of asphalt rock that have been published since the original edition might well have been included, although it is true that they may be found in volume three of the Roadmakers’ Library. The book is well written and makes excellent reading. The analysis of bituminous materials requires a special technique, and no laboratory which has to deal with such samples can afford to be without a copy. Unfortunately the chapter on roofing felt has been omitted from the new edition. There are a few misprints. These are, however, all minor points. D. M. WILSON BIOLOGICAL METHODS GROUP THE next meeting of the Group will be a Symposium on the Assay of Vitamin B,,, to be held at 2 p.m. on Tuesday, May 23rd, 1950, at the Medical Society of London, 11, Chandos Street, Cavendish Square, London, W.l. The chair will be taken by Dr. S. K. Kon, and speakers will include Miss M. E. Coates, Dr. W. F. J. Cuthbertson, Mr. H. Pritchard, Mr. G. E. Shaw and Dr. C. C. Ungley. PHYSICAL METHODS GROUP THE 20th Ordinary Meeting of the Physical Methods Group will be held in the meeting rooms of the Iron and Steel Institute, 4, Grosvenor Gardens, London, S.W.l, on Tuesday, May 23rd, at 6.30 p.m. The following papers on Radiochemical Analysis will be read and discussed-“Radiometric assay in tracer research,’’ by F. P. W. Winteringham, A.R.I.C. ; “The determination of potash (in fertiliser) by measurement of its radioactivity,” by D. S. Lees, B.A., A.Inst.P., W. Broomfield and H. N. Wilson, F.R.I.C. ; “Radioactivation analysis-some glimpses of its scope,” by A. A. Smales, B.Sc.

ISSN:0003-2654    

DOI:10.1039/AN9507500225

出版商:RSC    

年代:1950

数据来源: RSC