摘要:

482 MACKERETH: A COLORIMETRIC METHOD FOR ROUTINE [Vol. 76 A Colorimetric Method for Routine Estimation of Calcium in Natural Waters BY F. J. H. MACKERETH A colorimetric method for determination of calcium in fresh water has been devised. The method is a colorimetric modification of the well known gravimetric technique making use of picrolonic acid, and is suitable for use on small samples (5 ml) of waters containing low concentrations of calcium. The sample should preferably contain 10 to 100 pg of calcium but as little as 1 pg in 2 ml may be estimated. An alternative, less sensitive, but more rapid procedure is also described. THE following colorimetric method for determination of calcium in fresh water is a modifica- tion of the well known gravimetric technique that makes use of picrolonic acid.192J It is suitable for small samples of waters containing low concentrations of calcium.METEIOI) The analysis is carried out in Pyrex centrifuge tubes of 10 ml capacity, the tips of which are drawn out to produce a thick-walled capillary base approximately 1.0 cm long and 1 mm bore. The sample containing 10 to 100 pg of calcium (as a rule 5 ml is sufficient in “soft” waters) is pipetted into the tube, and about 3 ml of saturated picrolonic acid solution added. This quantity of reagent represents a considerablle excess. In order to promote crystallisation, which would otherwise be very much delayed by the formation of super-saturated solutions, the sides of the tube are then rubbed down with a stainless steel rod tipped with a little rubber sleeve; the rod is washed into the tube with a drop of distilled water.The tube is then allowed to stand for about 3 hours at room temperature, stoppered with a washed cork to prevent evaporation. Calcium picrolonate is Fig. 1. (a) Centrifuge tube. (b) Centri- fuge tube in cup. The rubber tube, R, inserted in the centrifuge cup supports the tube clear of the base deposited as a very fine yellow powder, most of which gathers into the capillary tip of the tube. If the concentration of calcium in the sample is comparatively high, eg., 100 pg per ml, the calcium picrolonate is often precipitated froin cold solution as a yellow floc. If this happens, the contents of the tube must be warmed to redissolve the floc and precipitation carried out from the cooling solution; crystallisation will then occur.It is, however, still essential to rub down the sides of the tube when the liquid is cold to ensure complete precipita- tion. Precipitate that lodges on the side of the tube is loosened with the tipped rod with the usual precautions against loss; the tube is then centrifuged for about 5 minutes at approximately 2000 r.p.m. To protect their capilla-y tips, the centrifuge tubes are supported in the cups on short lengths of rubber tube. This treatment removes practically all the precipitate into the capillary tip, but any crystals remaining on the sides of the tube must be removed by means of the tipped rod and the tube re-centrifuged. When it is clear thatAugust, 195 11 ESTIMATION OF CALCIUM IN NATURAL WATERS 483 all the precipitate is in the capillary tip, the excess of reagent and sample is decanted off and the body of the tube washed once with distilled water.This is poured off without disturbing the precipitate. The tube is then half filled with saturated calcium picrolonate solution (at room temperature) and the precipitate gently blown into the body of the tube by means of a capillary jet from a wash bottle filled with saturated calcium picrolonate. The tube is again centrifuged so that the precipitate, now washed once, is returned to the capillary tip of the tube. The wash fluid is now decanted and allowed to drain, as much liquid being removed as possible by touching the meniscus in the capillary with a glass rod, care being taken that the precipitate is not disturbed.The washed calcium picrolonate (results are satisfactory without further washing of the precipitate) is now dissolved in 60 per cent. alcohol by blowing the precipitate into the tube with 5ml of the alcohol, delivered from a pipette drawn out at the tip so that it may be inserted into the base of the tube. To facilitate solution of the precipitate the tube should be warmed and the contents stirred with the tip of the pipette. The solution in the tube is now corked to prevent evaporation, and allowed to cool to room temperature. The yellow solution is compared with standards prepared from known amounts of calcium in the same way (a standard containing 1oOpg of calcium is usually suitable). For the comprtrison, an Ogal colorimeter has been used, which, with a 50-mm column, is well suited for dealing with 5-ml samples.The colour produced bears a linear relation to the calcium content over the range in- vestigated, i.e., 1 to 100p.g of calcium. I t is just possible to see the colour produced by 1 pg of calcium as picrolonate dissolved in 5 ml of 60 per cent. alcohol and this may be estimated by comparison with a 10-pg standard prepared in the same way. But comparison becomes difficult with amounts of calcium as small as 1 pg. The intensity of colour produced by a given quantity of calcium has been found to vary with the composition of the alcohol used for solution and with the temperature. It is important that the same concentration of alcohol is used for both standard and unknown. A concentration of 60 per cent. has been arbitrarily taken as a compromise between two factors, (1) diminishing colour intensity as the alcohol approaches purity, and (2) diminishing solubility as the alcohol is diluted.The colour variation is not great unless absolute alcohol is used, when a marked decrease in intensity occurs. As the colour is more intense at higher temperatures it is essential to have the standard and unknown at the same temperature for comparison. Room temperature is satisfactory. Standards are prepared as described above, or by weighing appropriate amounts of pure calcium picrolonate and dissolving in 60 per cent. alcohol as in usual volumetric technique (35.5 mg of calcium picrolonate dissolved in 100 ml of 60 per cent. alcohol is equivalent to 100 pg of calcium in 5 ml). Since no discrepancy has been observed between standards prepared by the two methods, solubility losses must be very small.This is confirmed by the observation that as little as 1 pg of calcium will produce a precipitate from an original 2 ml of solution to which 2 ml of reagent is added. The standard is stable for several months if protected from evaporation, but on longer keeping the hue alters slightly and the solution assumes a brownish discoloration. The method is applicable in the presence of 10 times as much magnesium as calcium, but interference is caused by copper, lead, barium and strontium. Since the completion of this work a previous paper(' has been brought to the notice of the author in which a substantially similar method of calcium determination is described, but this deals with somewhat larger quantities of calcium (from 600 to 2500pg).RESULTS Known quantities of calcium compared with standard obtained by weighing pure calcium picrolonate and diluting to a concentration of 100 pg of calcium in 5 ml of solution Calcium taken, pg . . 10 20 30 40 50 60 70 Calcium found, pg . . 10.2 21.0 30.2 40.8 51-0 60-0 70.0 Calcium taken, pg . . 80 90 100 110 120 130 140 Calcium found, pg . . 79.6 89.6 99.7 108.7 119.0 129-3 140.3 Analysis of 1 to 10p.g of calcium compared with 10% of standard prepared in the same way as the test samples Calcium taken, pg . . 1 2 3 4 6 6 7 8 9 Calcium found, pg . . 0.9 1-7 2.8 4.2 4.7 6.0 6-9 7-7 8.8 to 1.0484 MACKERETH [Vol. 76 Eight determinations of calcium in 5 ml of a natural water by the above method gave The following simpler but slightly less sensitive method is suitable for rapid determinations I t requires the same equipment and results varying between 14.2 and 14.8 parts per million.where large numbers of samples have to be ana'lysed. has been studied in this laboratory by Mr. R. J. Holt. SIMPLIFIED METHOD Measure 5 ml of the sample from a pipette into an ordinary 10-ml Pyrex centrifuge tube. One millilitre of saturated picrolonic acid solution is then added from a pipette. The tube is stoppered to keep out dust, heated t o 35" C, and then allowed to cool for 3 hours with fairly frequent rubbing down with the rubber-tipped steel rod. If convenient, standing overnight is found to give complete precipitation and is simpler as only one stirring before allowing to settle proved sufficient.When precipitation of crystalline calcium picrolonate is complete the precipitate is wiped from the sides of the tube and collected at the bottom by centrifuging. The clear solution of excess picrolonic acid is decanted carefully into one cup of the colorimeter and the colour compared with a standard made up by ti-eating 5 ml of water freshly distilled from a tin still in the same manner. As this graph is a straight line, three readings, using standard calcium solutions, are sufficient to define it for a given picrolonic acid reagent. The amount of calcium can be read from a graph, see Table I. TABLE: I Colour as per cent. of Calcium, standard tc6 200 36 176 42 160 50.8 125 59.2 100 64.4 Colour as per cent. of Calcium, standard PQ 75 77-8 50 88.2 25 93-0 10 98.8 (standard) (100) Interference in this method by other ions will be the same as for the former method. Table I1 shows the results obtained for calcium in the presence of magnesium. TABLE I1 Calcium, tcg 126 125 125 3 25 125 126 126 126 125 Magnesiu in, Pg 200 175 150 125 100 75 50 25 0 Colour as per cent. of standard 52 49.4 47.8 53-2 52.8 51.2 53.4 51.8 52.6 Table I shows that the range of this method is from 10 to about 200 pg of calcium in It would be possible to raise tht: upper limit by adding more picrolonic acid 5-ml samples. reagent but then the lower limit is also raised. REFERENCES 1. 2. 3. 4. FERRY HOUSE Kisser, J., Mikrochem., 1923, 1, 25. Dworzak, R., and Reich-Rohrwig, W., 2. a n d Cltem., 1931, 86, 98. Alten, F., Weiland, H., and Knippenberg, E., Biochem. Z., 1933, 265, 85. Klement, R., 2. anal. Chem., 1948, 128, 431. FRESHWATER BIOLOGICAL ASSOCIATION FAR SAWREY, AMBLESIDE November, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600482

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

August, 19511 GARDNER 485 The Photometric Determination of Small Amounts of Titanium with 8-Hydroxyquinoline BY K. GARDNER A method is described for the photometric determination of titanium. The procedure uses the colour obtained on extracting solutions of titanium containing hydrogen peroxide, with a 1 per cent. solution of 8-hydroxy- quinoline in chloroform. The method is more sensitive than that using the colour given by titanium solutions with hydrogen peroxide only, but the reaction is not very selective. The interference of several cations has been investigated. Small amounts of aluminium, iron or molybdenum can be tolerated, but zirconium and vanadium must be absent. The results of a brief investigation into the composition of the chloroform extract suggest the formation of a ‘ ‘peroxidised” titanium 8-hydroxyquinolinate.THE principal colorimetric reagents used for the determination of titanium are hydrogen peroxide and phenolic compounds. Hydrogen peroxide has the advantage of good selectivity, while the most useful of the phenolic compounds are probably thymo1,l chromotropic acid2 and di-sodium-l:2-dihydroxybenzene-3 :5-sulphonate. This last reagent has been fully investigated3 and is selective and very sensitive. This paper presents a procedure for the estimation of small amounts of titanium by means of an extraction with an 8-hydroxyquinoline solution. Previous papers have outlined procedures for the extraction of aluminium,4 p6 e6 cerium,b gallium6 s 9 and indium,s molybdenum, iron, tin, copper, nickel and manganese7 and thalliums by means of chloroform solutions of 8-hydroxyquinoline.Gentry and Sherrington use a 1 per cent. solution, which was shown to have wider application than the 0.01 per cent. solution used by Moeller.8 In the work described below a 1 per cent. solution of 8-hydroxyquinoline in chloroform was used for all extractions. During experiments using Gentry and Sherrington’s method4 for aluminium, it was confirmed that titanium interfered at the prescribed pH value of 5.0. An attempt to suppress this interference by adding hydrogen peroxide to the aqueous solution was found to result in an extract having a deeper yellow colour. This colour reaction was noted to be much more sensitive than that which hydrogen peroxide alone gives with titanium solutions. Measurements subsequently obtained are given in Table I, and show the drum-difference readings on the Spekker absorptiometer, with H503 and Ilford 601 filters, for various amounts of titanium by the hydrogen peroxide and 8-hydroxyquinoline methods. The final volume, for both methods, was 10 ml.A l-crn cell with a water - water setting at 1-00 was used. In the hydrogen peroxide method 2 N sulphuric acid was used. The relative sensitivities of the two methods are compared in Table I. TABLE I RELATIVE SENSITIVITY OF THE HYDROGEN PEROXIDE AND 8-HYDROXYQUINOLINE - HYDROGEN PEROXIDE METHODS. SHOWN AS DRUM-DIFFERENCE READINGS FOR VARIOUS CONCENTRATIONS OF TITANIUM Concentration of Ti, pg per 10 ml . . . . 10 30 50 Hydrogen peroxide method . . .. .. 0.01 0.03 0.05 8-Hydroxyquinoline - H,O, method .. . . 0.135 0.420 0.705 The effect of pH value on the extraction of the titanium colour was tested by means of buffer solutions containing 30pg of titanium in 50ml of solution. The solutions were extracted with 10-ml portions of 8-hydroxyquinoline solution. Fig. 1 shows that titanium is completely extracted between pH 2-5 and pH 5 ; the pH measurements being taken immediately after extraction. The effect of pH values above 5 was not investigated because of the instability of hydrogen peroxide in alkaline solutions. The possibility of using tartrate in order to obtain a colour blank reading was ihvestigated, and Table I1 gives typical results showing the effect of tartrate concentration. From this table it can be seen that 1 g of Rochelle salt is sufficient to suppress the extraction of titanium486 GARDNER: THE PHOTOMETRIC DETERMINATION OF SMALL AMOUNTS [VOl.76 in the absence of hydrogen peroxide, but that in the presence of hydrogen peroxide, 1 g of Rochelle salt only partially suppresses the extraction, TABLE I1 EFFECT OF TARTRATE AND HYDROGEN PEROXIDE ON EXTRACTION OF TITANIUM All solutions contained 30 pg of titanium H,O,, 2 ml H,O,, 2 ml Rochelle Rochelle Rochelle Rochelle H,O,, 2 ml salt, 0-1 g salt, 1 g salt, 0-1 g salt, 1 g Drum difference* . . . . 0-416 0-085 0.000 0.365 0.136 Percentage extraction . . .. 100 ti 0 88 33 In subsequent experiments a buffer solution of pH 3 was used, for which, in order to carry out a blank reading, it was found necessary to use sodium hydrogen tartrate as the masking agent.The use of this reagent avoids the precipitation of potassium hydrogen tartrate * The blank value was read from a solution containing 2 ml of H,O, only. PH Fig. 1. Effect of pH on extraction of titanium. Tungsten lamp used with 1-cm cell, H503 and Ilfords 601 filter and water - water setting of 1.00 on Spekker absorptiometer that occurs at pH 3 with Rochelle salt in strong solutions. found to be increased owing to transfer of 8-hydroxyquinoline to the aqueous layer. increase was of the order 0.1 to 0.2 pH unit (cf. reference No. 9). REAGENTS- The final pH of the solution was This METHOI) All the reagents used conformed to recognised analytical standards. Titanizlm solution-Prepare a solution from TiO, of more than 99.5 per cent. purity, by fusing the appropriate weight in potassium bisulphate and dissolving the melt in 5 per cent.v/v sulphuric acid. From this solution prepare a dilute titanium solution made up with 5 per cent. v/v sulphuric acid so that 1 ml contains 10 pg of titanium. 8-HydroxyquinoZine solution-A 1 per cent. w/v solution in chloroform. Sodium acetate soZution-A molar solution of salt. Hydrogen peroxide-A 20-vol. solution. Sodium hydrogen tartrate-A 6 5 g per litre solution, adjusted to pH 3.0. Sodifcm suZ$hate-Anhydrous. The sodium acetate and sodium hydrogen tartrate solutions were purified by extraction with 8-hydroxyquinoline solution. In this way the reagent blank was reduced to a low value. PROCEDURE- To the sulphuric acid solution containing titanium in a separating funnel add 2 ml of hydrogen peroxide.veutralise the solution by tlropwise addition of alkali and add 20mlAugust, 19511 O F TITANIUM WITH 8-HYDROXYQUINOLINE 487 of sodium acetate solution. Add immediately sufficient sulphuric acid to give the solution a pH of 3.0, and make up the volume to 50 ml with distilled water. Add exactly 10 ml of 8-hydroxyquinoline solution and shake for 5 minutes. Allow the organic layer to settle and transfer to a dry stoppered flask containing about a gram of sodium sulphate. Measure the absorption of the clear solution on the Spekker absorptiometer using the tungsten lamp with Ilford 601 and H503 filters, a 1-cm cell and a water - water setting of 1.00. The colour blank reading should be obtained by repeating the above procedure with the substitution of 10 ml of sodium hydrogen tartrate solution for 2 ml of hydrogen peroxide.The difference between the two absorptions gives the absorption due to titanium. The calibration graph was linear over the range 0 to 60pg of titanium. A sample containing 5Opg of titanium gave a drum-difference reading of 0.70. THE EFFECT OF OTHER METAL IONS In order to test the interference of certain other cations, appropriate solutions were made up and extractions carried out in the absence and presence of titanium. ALUMINIUM- The pH value of 3.0 was chosen for extraction because aluminium is only slightly extracted at this value.' Also by using a 601 filter with maximum transmission at 4300 A the effect of aluminium is lessened. Table I11 gives some typical results showing the effect of aluminium.TABLE I11 THE EFFECT OF ALUMINIUM ON TITANIUM ESTIMATION Aluminium present, pg . . .. 600 600 200 100 Titanium present, pg . . . . nil 30 30 30 Drum-difference reading* . . .. 0.04 0.03 0.01 0.005 * After deduction of absorption due to titanium, As tartrate prevents the extraction of aluminium, the quantity of aluminium allowable By is 100 pg, which gives an absorption value equivalent to less than 0.5 pg of titanium. using a spectrophotometer, larger amounts of aluminium could probably be tolerated. IRON- Ferric iron is extracted completely at pH 3.0 in the presence or absence of tartrate, and it is therefore included in the blank reading. It is possible to estimate titanium in the presence of 35 pg of ferric iron, but if the titanium content is considerably less than the iron content the blank reading becomes relatively too high for accurate estimation of the titanium. It was noticed that fe*c iron only was extracted at pH 3.0 in the presence of tartrate and that ferrous iron remained in the aqueous layer.This fact might form the basis of a method for the estimation of small amounts of ferric iron in the presence of ferrous iron. MOLYBDENUM- Molybdenum interferes because it is extracted at pH 3.0 in the presence of hydrogen peroxide but not in the presence of tartrate. With small amounts of molybdenum a correction graph could be applied or alternatively, it could be extracted at a lower pH value,' prior to titanium estimation. VANADIUM- completely in the presence of tartrate. Vanadium is partially extracted at pH 3.0 in the.presence of hydrogen peroxide and I t should therefore be absent. ZIRCONIUM- appears in the organic phase. should therefore be absent. In the presence of hydrogen peroxide, zirconium is partially extracted and a precipitate Zirconium Beryllium, calcium, magnesium and manganese do not interfere, No extraction occurs in the presence of tartrate.488 MILNER THE DETERMINA.TION OF INDIUM [Vol. 76 As a spectrophotometer was not available, a xough transmission curve was drawn using the Spekker absorptiometer with different sets of filters; this showed that the extracts obtained with and without hydrogen peroxide had different absorption spectra. The curve given by the extract from the solution containing hydrogen peroxide was displaced towards the blue end of the spectrum.A chloroform solution of titanium 8-hydroxyquinolinate, TiO(C,H,ON),, obtained by Berg’s method,lO had a much feebler absorption with the 601 filter than that of a solution obtained by extracting an identical amount of titanium in the presence of hydrogen peroxide. I t may be that this compound formed in the presence of hydrogen peroxide is a “per- oxidised” titanium 8-hydroxyquinolinate. DISCUSSION OF THE METHOD- This possibility seems to merit further study. The author is indebted to the Director of the Nelson Research Laboratories for permission to publish this work. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Lenher, V., and Crawford, W. G., J. Amer. Chent. SOC., 1913, 35, 141. Klinger, P., Stengel, E., and Wirtz, H., Metal1 tmd Erz, 1941, 38, 124. -Yoe, J. H., and Armstrong, A. R., Anal. Chem., 1947, 19, 100. Gentry, C. H. R., and Shemngton, L. G., Analyst, 1946, 71, 432. Westwood, W., and Mayer, A., Ibid., 1948, 73, 275. Lacroix, S., Anal. Chem. Ada, 1947, 1, 260. Gentry, C. H. R., and Sherrington, L. G., Analyst, 1950, 75, 17. Moeller, T., Ind. En4. Chem., Anal. Ed., 1943, 15, 346. Moeller, T., and Cohen, A. J., Anal. Chem., 1960, 22, 686. Welcher, F. J., “Organic Analytical Reagents,” D. Van Nostrand, Inc., N.Y., 1947, Vol. I, p. 295. THE ENGLISH ELECTRIC Co., LTD. XELSON RESEARCH LABORATORIES STAFPORD Kovembev, 1960

ISSN:0003-2654    

DOI:10.1039/AN9517600485

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

488 MILNER THE DETERMINA.TION OF INDIUM [Vol. 76 The Determination of Indium in Beryllium Compounds BY G. W. C . M:[LNER* A method is described for the determination of microgram quantities of indium occurring in beryllium compounlds. The indium is first separated from the beryllium and certain other constituents of these compounds by an extraction procedure using 8-hydroxyquirioline in chloroform. After con- centrating the extracts and decomposing organic matter, the indium is separated from iron and molybdenum by extraction with di-ethyl ether. The concentration of indium is determined polarographically by means of the well-defined step given by it from a base electrolyte consisting of hydrochloric acid, sodium formate and hydrazine hydrochloride. THE cbloro-indic complex ions are reduced from a 0.1 N potassium chloride base solution, in the presence of a small amount of gelatin, to give a well-defined and quantitative polaro- graphic step.1 During investigations on the polarographic determination of indium in refined tin samples2 this complex was also observed to give a suitable step from a base electrolyte consisting of 2 ml of 50 per cent.v/v hydrochloric acid, 1 ml of sodium formate solution, 68 g in 100 ml of water, 1 ml of 20 per cent. w/v hydrazine hydrochloride solution and 1 ml of 0.2 per cent. starch solution. The step has a half-wave potential value of a.pproximately -0.6 v. with respect to the mercury-pool anode. This paper describes the application of this reduction step to the determination of indium in beryllium compounds after separating the indium from interfering elements.* Present address : Chemistry Division, Atomic Energy Research Establishment, Harwell, Berks.August, 19511 I N BERYLLIUM COMPOUKDS EXPERIMENTAL SENSITIVITY- 489 The sensitivity of the indium step was investigated by adding 25, 50 and 100-pg amounts of indium, dissolved in hydrochloric acid, to three separate 30-ml tall-form beakers and evaporating each solution just to dryness. A 2-ml portion of 50 per cent. v/v hydrochloric acid was next added to each beaker and heat applied to ensure the complete solution of the salts. The l-ml additions of the sodium formate, hydrazine hydrochloride and starch solutions were then made and the resulting solutions heated just to boiling. After cooling the polarograms were recorded at a temperature of 25" C using a suitable sensitivity on a Tinslep pen-recording polarograph.The sensitivity and quantitative nature of the indium step is shown in Table I. TABLE I SEXSITIVITY AND QUANTITATIVE NATURE OF INDIUM STEP Step height a t a sensitivity Indium concentration, of 2 microamps. of 4 microamps. Step height at a sensitivity t% 25 8.75 divisions 4.5 divisions 50 19.0 " 9.26 9 ) 18.5 n 100 - EXTRACTION PROCEDURE FOR INDIUM- L41though the reduction of the beryllium ions at the dropping mercury electrode from the above base electrolyte does not interfere with the indium step, beryllium compounds may contain varying amounts of interfering elements; this makes the separation of the indium from as many of these elements as possible almost essential. Elements like iron, copper, bismuth, lead, thallium, tin, etc., reduce a t more positive potentials than indium, and cadmium shows a step that coincides with that of indium.Therefore, in applying this step to the determination of indium, cadmium must be completely absent from the final solution; and those elements reducing at more positive potentials must be present in not more than small concentrations, so as not to interfere with the evaluation of the indium step. TABLE I1 RECOVERY OF INDIUM Number Indium added to sample, Indium recovered, EG Pg 1 0 0 2 5 5 3 10 9.5 4 15 15 Indium is quantitatively extracted from aqueous solutions over the pH range 3.6 to 4-5 by a solution of 8-hydroxyquinoline in chloroform3 and so experiments were carried out to investigate the completeness of this extraction from solutions of beryllium salts adjusted to the correct pH range with the aid of screened methyl orange indicator.Sulphuric acid proved to be a suitable solvent for beryllium oxide and the best solution procedure consisted in dissolving 10 g of sample in 100 ml of 13 N sulphuric acid, followed by diluting the resulting solution to 200ml so as to obviate the danger of crystallisation of beryllium sulphate at room temperature. A 20 per cent. sodium hydroxide solution was used for adjusting the test solutions to the grey change-point of the indicator, slow additions being made in the neighbourhood of the change-point because of the slow re-solution of precipitated beryllium hydroxide. Dissolve four 10-g portions of a pure beryllium oxide sample in 100-ml portions of 13 N sulphuric acid, dilute each to approxi- mately 200ml and add various amounts of a standard indium solution to give samples containing 0, 5 , 10 and 15 micrograms of indium respectively.Add a 20 per cent. sodium hydroxide solution slowly from a burette to adjust each solution to the grey change-point of screened methyl orange indicator and then extract with three separate 15-ml portions of 0.5 per cent. 8-hydroxyquinoline in chloroform. Combine the total extracts of each solution into 50-ml Kjeldahl flasks and remove the chloroform by distillation. Add 4 ml of 20 N Details of these experiments were as follows.490 MILNER : THE DETERMINATION OF INDIUM [Vol. 76 sulphuric acid to each flask, destroy the organic matter by the dropwise addition of nitric acid, sp.gr.1-42, to the fuming sulphuric acid and then completely remove all acids by evaporation. Dissolve the salts in 2-ml portions of 50 per cent. v/v hydrochloric acid, add the 1-ml portions of the other reagents and record the indium polarogram. The results shown in Table I1 prove that the indium is completely extracted from the beryllium salts. Further investigations were conducted to determine the optimum amount of S-hydroxy- quinoline reagent to use and also the minimum number of extractions necessary to give complete separation of the indium. No improveiment could be effected in these conditions; so the procedure using three separate 15-ml portions of reagent was adhered to in all subsequent work.IMPROVEMENT OF SENSITIVITY- As indium generally occurs in beryllium compounds in very small amounts, it was desirable to apply all possible means for improving the sensitivity. Subsequent investiga- tions showed that it was possible to reduce the volumes of all the reagents constituting the base electrolyte by half, which doubled the sensitivity of the determination. Under these conditions the best defined reduction step was obtained by recording the polarograms with 2 volts applied across the main potentiometer instead of the usual 4 volts. INTERFERING ELEMENTS- The 8-hydroxyquinoline extraction procedure restricts the number of possible interfering elements to those that are extracted by it under the conditions of the method. Of these elements, those that have steps with half-wave potential values more negative than - 1.0 volt do not interfere with the indium step; the greatest interference comes from those elements that reduce a t the dropping mercury electrode at more positive potentials than -1.0 volt.Cadmium gives a step that coincides with the indium step, but fortunately it is not extracted by the oxine reagent. Iron is the most troubleslome element, for often 10 g of a beryllium compound contain approximately 1000 pg of iron. The iron is in the oxidised state after the .wet oxidation procedure for removing the organic matter and its interference could be eliminated by chemically reducing it to the ferrous condition, thereby causing the iron step to follow instead of precede the indium step. The acidity of the recommended base electrolyte was found to be too high to permit the complete reduction of the ferric iron by the hydrazine hydrochloride and so the ratio of the 50 per cent.hydrochloric acid to sodium formate was decreased in an effort to improve the reduction. The iron interference proved to be very much smaller in base solutions containing ratios of the above reagents of 1 :1, 1 :1.5 and 1 :2, but unfortunately under these conditions the definition of the indium step deteriorated by assuming an elongated form. These steps were found to be difficult to evaluate and completely unsuitable for this determina- tion. Therefore, the removal of iron from indium by an extraction procedure with isopropyl ether or di-ethyl ether was investigated. The results showed that the indium was completely retained in the acid layer free from iron.Moreover, the steps obtained for indium in these layers were well-defined and easy to evaluate. Molybdenum was observed to give an elongated step in the recommended base electrolyte, the top of which interfered with the indium step. As molybdenum is extracted with indium by 8-hydroxyquinoline, it became necessary to remove the molybdenum completely from the indium. Experiments with isopropyl ether and di-ethyl ether showed that although the former reagent does not extract the molybdenum, the latter does so satisfactorily and hence is suitable for the simultaneous extraction of iron and molybdenum from indium. Of the other elements which reduce at more positive potentials than indium, up to 100-pug quantities of copper, bismuth, thallium and tin do not interfere. The recommended method for the determination of small quantities of indium in beryllium compounds is as follows- REAGENTS- water.water. SuZphuric acid, 13 N-Add 2-5 litres of sulpliuric acid, 98 per cent. w/w, to 5 litres of SuZphuric acid, 20 N-Add 500 ml of sulphuric acid, 98 per cent. w/w, to 500 ml ofAugust, 19511 I N BERYLLIUM COMPOUNDS 491 Hydrochloric acid, sp.gr. 1.10-Dilute concentrated hydrochloric acid, sp.gr. 1.16, with water, using a hydrometer. Sodium hydroxide-Twenty per cent. w/v in distilled water. 8-Hydroxypuinoline-Dissolve 0-5 g of pure reagent in 100 ml of AnalaR chloroform. Sodium formate-Dissolve 68g of pure sodium formate in 100ml of water. Hydraxine hydrochloride-Twenty per cent.w/v in water. Starch solution-Mix 0.2 g of good quality soluble starch with a few ml of water to form Cool and dilute the solution to Screened methyl orange-Dissolve 0.2 g of methyl orange and 0.28 g of xylene cyanol FF a paste and then dissolve in a quantity of boiling water. 100 ml. in 100ml of 50 per cent. alcohol. SAMPLING AND SOLUTION OF BERYLLIUM COMPOUNDS- Add 100 ml of sulphuric acid, 13 N , and evaporate to low bulk. water and boil to take most of the oxide into solution. the diluted solution is clear and free from undissolved particles of oxide. approximately 200 ml. conical beaker and dissolve in 40 ml of sulphuric acid, 13 N . obtain complete solution. (a) Beryllizcm oxide-Weigh l o g of the oxide into a 600-ml lipped conical beaker.Add a small quantity of Boil and dilute repeatedly until Cool and dilute to (b) Beryllium suZ9hate-Weigh 70.4 g of the sulphate (BeS0,.4H20), place in a 600-ml Treat onwards as in (a) to Cool and dilute to approximately 200 ml. PROCEDURE- (a> Test solution-Add 5 drops of screened methyl orange to the sample solution and then sodium hydroxide, 20 per cent., dropwise from a burette. Carry out the sodium hydroxide additions with constant shaking. Just before the indicator change-point is reached, cool and carefully add further alkali until the indicator changes from magenta to grey. Transfer the solution to a 500-ml separating funnel with the minimum amount of distilled water for washing. Add 15 ml of 8-hydroxyquinoline solution, stopper the funnel and shake for 5 minutes. Allow the two phases to separate and run the bottom layer into a dry 50-ml Kjeldahl flask.Wash the aqueous layer left in the separating funnel with 8 ml of chloroform and transfer this also to the Kjeldahl flask. Carry out two further extractions with 15-ml portions of 8-hydroxyquinoline solution as before. Combine the extracts and washings in the Kjeldahl flask and remove the chloroform by distillation over a steam-bath (Note 1). Add 4 ml of sulphuric acid, 20 N , to the Kjeldahl flask and about 0.5 ml of nitric acid, sp.gr. 1.42. Heat gently at first and then strongly to fumes of sulphuric acid. Add further nitric acid dropwise to continue the oxidation of organic matter and finally complete it by the dropwise addition of perchloric acid, sp.gr.1.54. Cool, dilute with a few ml of water and heat to obtain complete solution of the salts. Transfer the solution to a 30-ml Pyrex tall-form beaker by means of three small washings with distilled water. Evaporate to fumes of sulphuric acid and continue heating to completely remove the acid. Dissolve the salts in a small quantity of hydrochloric acid, sp.gr. 1.16, and evaporate to dryness, Add 1 ml of hydrochloric acid, sp.gr. 1.10, and warm gently to obtain a clear solution. Transfer to a 25-ml separating funnel using a total of 3 ml of hydrochloric acid, sp.gr. 1-10, for washing. Cool the solution under a water tap, add 5 ml of diethyl ether and shake vigorously for about 30 seconds with cooling under water. Transfer the bottom layer to the original 30-ml beaker, remove the dissolved ether on a steam-bath and finally evaporate to dryness on a hot plate.Dissolve the salts in 1.0 ml of 50 per cent. hydrochloric acid, by applying very gentle heat, then add 0.5 ml of sodium formate solution, 0.5 ml of hydrazine hydrochloride solution and 0.5 ml of starch solution. Mix well, heat the solution just to boiling-point and cool. Transfer the solution to a polarographic cell, add a small quantity of mercury to form the anode and place in a thermostat for 5 minutes. With 2 volts applied across the main potentio- meter and a suitable galvanometer sensitivity setting (Note 2) record the polarogram. Measure the height of the indium step. (b) Reagent blank solution-For beryllium oxide samples dissolve 10 g of a spectro- graphically pure indium-free beryllium oxide sample in 100 ml of sulphuric acid, 13 N , and carry out the determination by the above procedure.492 NOTES [Vol.76 For beryllium sulphate samples dissolve 70-4 g of a pure indium-free beryllium sulphate sample in 40 ml of sulphuric acid, 13 N , and complete the determination by the above procedure. Obtain the difference between the step-height reading for the test solution and that for the corresponding reagent blank solution. Deduce the indium concentration by reference to a calibration graph prepared under the following conditions- Prepare a standard indium solution by dissolving 0.10 g of pure indium metal in 10 ml of hydrochloric acid, sp.gr. 1.16, dilute to 1 litrte with distilled water and mix thoroughly. Dilute 10 ml of solution to 200 ml with distilled water so that 1 ml of this solution contains 5 micrograms of indium.Then place 1, 2 and 3-ml aliquots of this solution in 30-ml tall- form beakers and evaporate to dryness. Dissolve the indium salts in l-ml portions of 50 per cent. hydrochloric acid, warm gently to ensure solution and then add 0.5-ml portions of the sodium formate, hydrazine hydrochloride and starch solutions. Mix thoroughly, heat just to boiling and then cool. Record the polarograms for each solution as described under (a) “Test Solution.” Measure the step heights and draw the calibration graph by plotting these values against the indium concentration. NOTES 1. It is necessary to commence the removal of the chloroform from the first extraction solution whilst the second extraction procedure is being carried out. If this technique is adopted throughout the extractions and washings there should always be sufficient space in the Kjeldahl flask for all the following extraction and washing solutions. 2. With a Tinsley pen-recording polarograph and a drop-time of 3 seconds, a suitable galvanometer sensitivity was attained when a current of 2 microamperes corresponded to a full-scale deflection of the pen. The Admiralty has granted permission for this paper to be published. REFERENCES 1 . 2. 3. Kolthoff, I. M., and Lingane, J. J., “Polarography,” Interscience Publishers, Inc., New York, Milner, G. W. C., unpublished work. Moeller, T., Ind. Eng. Chem., Anal. Ed., 1943, 15, 270. 1941, p. 276. BRAGG LABORATORY NAVAL ORDNANCE INSPECTION LABORATORY JANSON STREET, SHEPFIELD, 9 January, 1961

ISSN:0003-2654    

DOI:10.1039/AN9517600488

出版商:RSC    

年代:1951

数据来源: RSC

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492 NOTES [Vol. 76 A MODIFICATION OF MILTON’S METHOD FOR ESTIMATION OF TOTAL AVAILABLE CHLORINE IN WATER R. F. MILT ON^ has drawn attention to the fact that all the existing methods for the determination of available chlorine in water, such as the o-tolidine, benzidine blue, iodine replacement and modified paminodimethylaniline methods merely indicate oxidation potential. He proposed a method for the deternination of free chlorine in which the free chlorine reacts directly with cyanide to form cyanogen chloride, which is then allowed to react with pyridine (or a pyridine derivative) to form a quaternary compound that, on subsequent condensation with aromatic amines, produces intensely coloured di-anil derivatives. This method is stated to be specific for free chlorine (only free bromine reacting similarly), unlike the ‘methods dependent on oxidation-potential mechanisms, which may be affected by iron, nitrite and ammonia, etc.During a recent investigation of chlorination control of a swimming-bath, use was made of Milton’s method (in conjunction with o-tolidine and iodine-replacement methods) and certain defects became apparent. (1) The reagent concentrations were found to be unsuitable. In the original method, two reagents were employed: (a) potassium cyanide, 1 per cent., (b) benzidine hydrochloride, 2 per cent., in 25 per ce:nt. pyridine solution. The use of 5 ml of sample was recommended with the addition of 1 ml of potassium cyanide and 5 ml of the pyridine reagent.August, 19511 KOTES 493 It was found, however, that at room temperatures (about 65" F) addition of 6 ml of reagent (b) to water caused precipitation of a mass of finely divided crystals of benzidine or the hydrochloride, which was however soluble on the addition of further pyridine, and thus the ratio of pyridine to benzidine hydrochloride, on addition of reagent (6) to water, appears to control effective solution.I n the present study it was found that a 1 per cent. solution of benzidine hydrochloride in 25 per cent. pyridine was suitable and that it did not cause precipitation when added to the sample. (2) The method was found to be not specific for free chlorine, but measured total available chlorine concentration, Le., the concentration of free available chlorine and chlorine combined with nitrogenous compounds in the form of chloramines, etc.Because of crystallisation on addition of reagent (b) to the sample, recourse was made to the modified solution strength described in (1) above. Invariably the figures given by the original method, but using the modified reagents, were comparable with those given by o-tolidine and iodine-replacement methods for total available chlorine in water. Results for swimming-bath water are as shown in Table I, from which it is apparent that the original method measures the total available chlorine concentration and not the free chlorine concentration. TABLE I RESULTS OF TESTS ON SWIMMING-BATH WATER Total available Free chlorine (by Original method, chlorine by o-tolidine, o-tolidine arsenite), p.p.m. 0-30 0.63 0.94 p.p.m. 0.30 0.60 1.00 p.p.m.0.06 0.16 0.28 (3) The colours of chlorine solutions of increasing strengths were not of This change in colour was most pronounced; from 0.9 to 1.0 part per the colour changed from yellow to orange to a tan-red. At certain regions small difference in concentration of only some 0-03 parts per million gave the same tint. million of chlorine of concentration a markedly different colour tints; this makes estimation by comparison with standard chlorine solutions difficult and precludes preparation of satisfactory artificial standards, which are found to be very convenient in methods such as the o-tolidine method. Moreover, with the effects mentioned, the solution colours do not lend themselves to convenient measurement by normal photo-electric procedures. As a result of these observations, further work was undertaken to evolve a method free from these defects, but utilising the same reaction.It was found early in the study that, by adding larger quantities of cyanide and allowing this stage of the reaction to proceed for some 3 minutes before the addition of pyridine reagent, the red colour was completely prevented and yellow-brown solutions obtained. The intensities of colour of these solutions were linear with concentration. The colours produced were easily compared with those from standard chlorine solutions. It was also found that dilute solutions of iodine could be used as satisfactory colour standards. Separate solutions containing equivalent concentrations of free chlorine and chloramines gave the same colour intensity.Further evidence indicating the sensitivity of the method for the determination of total chlorine in the form of free and combined available chlorine is given in Table 11. TABLE 11 SENSIT~VITY OF THE METHODS EXAMINED Results in parts per million A B C I A -l Total available chlorine (by o-tolidine and by iodine replacement) . . . . . . . . 0.19 0-37 0.56 Free chlorine (o-tolidine arsenite) . . . . 0.15 0.30 0.45 Total available chlorine (method now proposed) 0.19 0.35 0.59 The figures given in Table I1 for the modification now proposed were obtained by comparing The modified method permits the determination of chlorine down to 0.05 part per million. Preparation of artificial colour standards can be readily achieved by the use of 0.0005 N iodine solution (freshly prepared from 0.1 fi) and the colours produced are the same as those given by the reaction, It has been found that 2.36 ml of 0.0005 N iodine solution gives a colour with standard chlorine solutions.494 NOTES [Vol.76 equivalent to each 0.10 part per million of chlorine. A series of chlorine solutions were prepared and the total available chlorine was determined by the o-tolidine method and by the proposed method against artificial colour standards. The results are shown in Table 111. TABLE III Solution 1 2 3 4 5 6 7 8 9 10 TOTAL AVAILABLE CHLORINE (Farts per million) 7 A > o-Tolidine method Modified Milton’s method 0.05 0.06 0.08 0.10 0.18 0.20 0.35 0.33 0.44 0.48 0.52 0.65 0.63 0.60 0.77 0-76 0.90 0.90 1.1 1 1-08 The figures obtained in this way indicate the true linearity of colour intensity with con- centration.MODIFIED METHOD REAGENTS- Potassium cyanide-A 1 per cent. solution. Benzidine hydrochlovide-A 1 per cent. in 25 per cent. pyridine solution. Iodine solution, 0.0005 N-Freshly prepared from standard 0.1 N solution. PROCEDURE- To 20 ml of sample contained in a 50-ml or 25-1111 Nessler tube, add 3 ml of potassium cyanide solution, mix immediately, and allow to stand for 3, minutes. Add 1 ml of the pyridine - benzidine reagent, nnix immediately, allow to stand for a further 3 minutes and compare the colour produced with standards prepared from 0.0005 N iodine solution. (2.36 ml of 0.0005 N iodine solution is equivalent to 0.10 parts per million of chlorine,) The artificial standards should be made up to a volume of approximately 24 ml, in the same way as the sample, to obtain the best comparison. The standard and sample solutions should be compared by viewing through the length of the Nessler tube, As an alternative the standard iodine is added to a Nessler tube until the colour produced matches that of the sample in the same volume of solution. The colour produced by the sample fades slowly on standing. We are indebted to the Government Analyst, Dunedin, for suggesting this work, and to the Director of the Dominion Laboratory for permission to publish this paper. REFERENCE 1. Milton, R. F., Nature, 1949, 164, 448. DOMINION LABORATORY NEW ZEALAND DUNEDIN H. A. L. MORRIS P. K. GRANT First submitted August, 1950 Amended February, 1951 ERRATUM: July (1951) issue, p. 433. The Note by Rudra and Choudhury should bear the date ‘ I Azcgust, 1950.”

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DOI:10.1039/AN9517600492

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年代:1951

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August, 19611 APPARATUS 495 Apparatus A MODIFIED APPARATUS FOR STEAM DISTILLATION AND EXTRACTION ON A SEMI-MICRO SCALE MINOR modifications of an appamtus originally described by the authors1 enable it to be used for steam distillation without the provision of an external steam generator, and also for extraction on a semi-micro scale. Steam distillation-To the bottom of the “cold finger” condenser is attached a modified cup A. This has a small orifice in the bottom and is provided with glass hooks that are longer than A Pyrex Insert Diom. 22 mrn Height U mrn 6 Complete Assembly for Extraction of a Solid Details of apparatus as modified for steam Fig. 1. distillation and extraction those in the origmal design. A small disc of filter-paper, 3.5 cm diameter, is folded to give a cone angle of approximately 40°, see Fig.1. The paper is inserted into the cup and wetted, a close fit around the upper edge being ensured. About 1 ml of the liquid to be steam distilled is placed in a 25 x 150 mm test tube, together with a few small pieces of porcelain. An equal volume of water is added, the “cold finger” unit attached and the liquid boiled gently. The distillate collects in the filter-paper and can be removed by a capillary pipette. The excess water drips back into the distillation tube and the amount of water admixed with the distillate is therefore kept to an absolute minimum. Some liquids to be steam distilled may already have sufficient water admixed with them. It is only necessary to keep the ratio of water to substance low for those whose solubility is appreciable, e.g., aniline.If the substance to be steam distilled is a solid, a portion of it may collect on the condenser, whence it may subsequently be removed. Extracfiout--The modified cup used for steam distillation may also be used for the extraction of solids. For this purpose the filter-paper cone may again be used or a small Soxhlet type thimble constructed to contain the solid. If it is desired to conserve the extract for crystallisation or weighing, as in a quantitative determination, a small insert B is used. This is made so that it is a reasonably close fit inside the distillation tube; a small glass hook attached to the side facilitates its withdrawal. The solvent is placed in B, which is then inserted into the distillation tube.The “cold finger” unit is attached, and the distillation tube is heated in a water or glycerol bath. When extraction496 APPARATUS [Vol. 76 is complete, B may be removed if crystallisation of the extract is to be carried out. Alternatively, if the solvent is to be evaporated, as in a quantitative determination, the extraction cup A is replaced by one of the normal type and the solvent distilled off. The modified cup and insert therefore serve to extend the range of the apparatus previously described. 1. REFERENIZE Connolly, J. M., and Oldham, G., Analyst. 1951, 76, 52. DEPARTMENT OF PURE AND APPLIED SCIENCE LOUGHBOROUGH COLLEGE LEICS. JOSEPH M. CONNOLLY GRAHAM OLDHAM March, 1961 A HIGH-PRESSURE HYDROGEN S'ULPHIDE GENERATOR FOR MICROCHEMICAL ANALYSIS THE customary use of capillary delivery tubes in micro-analysis requires a considerable pressure of hydrogen sulphide to overcome surface-tension effects.Commonly, the necessary pressure is obtained from a Kipp type generator in which the acid hea.d is increased to 50 cm or more.lJJ Alter- natively, the gas may be generated at or a little below atmospheric pressure and then pumped through the solution to be treated.4 A convenient pump type generator is shown in Fig. 1. By means of a grooved cork, the funnel solution takes-place with the minimum of gas and without spurting, (2) the rate of delivery is far below the maximum rate of gas-production, so that acid cannot be drawn up into the pump, (3) the reservoir effect of upper teat H becomes sufficient to allow continuous bubbling to be maintained by compressing G only about twice per minute.Except for highly precise work, the same delivery 0 2 4 6 8 10cm tube may be used repeatedly. With the gas still issuing, the contaminated tip is well rinsed and wiped with a scrap of filter-paper. The rate of diffusion of hydrogen sulphide through the fine jet is low, so that, if the generator is in fairly frequent use, gas is available at the first pressure on teat G. To avoid possible contamination of the bore of the delivery tube, it is never inserted into the solution to be treated until the gas is passing through it. 1 I b Fig. 1. High-pressure hydrogen sulphide generator tube A is supported in the mouth of an acid con- tainer B , a 500-ml conical flask or squat bottle, which is about two-thirds filled with diluted hydrochloric acid ( 1 + 1) to the level shown in Fig.1. The funnel tube, which contains broken iron sulphide stick and a glass wool spray-arrestor, is closed by a rubber stopper carrying the pump. The upper ends of portions C and D are constricted to about 1 mm bore and are ground square and flat. Valves E E are discs cut by a cork-borer from thin rubber sheet,6 and have a maximum lift of about 1.5mm. Glass studs F F lightly press the valves upon their seatings. G and EI are ordinary rubber teats. The generation of gas does not take place until acid is dlrawn into the funnel tube by gently squeezing and releasing the lower teat G. Further operation of this expels air and delivers hydrogen sulphide under pressure high enough to enable a delivery tube with an.orifice of about 0.1 mm to be used. This has the following advantages-( 1) extremely fine bubbles are produced, so that saturation of the FAugust, 19511 APPARATUS 497 REFERENCES 1. 2. 3. 4. 5. KNIGHT’S HILL Lidstone, A. G., Wilson, C. L., and Wilson, D. W., Metalluvgia, 1947, 35, 171. Stock, J. T., and Heath, P., Ibid., 1950, 41, 171. Stock, J. T., Heath, P., and Marshment, W. A. L., Ibid., 1960, 41, 346. Stock, J. T., and Fill, M.A., Ibid., 1948, 38, 118. -,- , Analyst, 1949, 74, 52. NORWOOD TECHNICAL COLLEGE LONDON, S.E.27 J. T. STOCK I?. HEATH March, 1961 A THERMOSTATICALLY-CONTROLLED HEATING BLOCK FOR SEALED-TUBE REACTIONS DESIGNED for small-scale organic preparative work, the device shown in Fig. 1 is otherwise useful, e.g., in preparing camphor solutions for molecular weight determination by the Rast meth0d.I Pockets for the thermometer and for three or four reaction tubes are old cork-borers, the lower ends of which are burred inwards and plugged with fine steel wool.Reaction tubes are placed in similarly-plugged cork-borers, The “heating block” proper is a tin can filled with small nails. G a F- !s- . . -? CM 0 . . $ . . . . 10 , _ _ _ _ Fig. 1 Thermnsta ticallv-cnntrnllerl heating block Fig. 2. E Detail of bv-Dass which slide easily into the pockets and have wire loops for lifting. This permits easy withdrawal of short reaction tubes. Temperature regulation is effected by the expansion or contraction of air trapped in bulb A , which has a capacity of about 20ml and is submerged in the filling of the “block.” Changes in volume are transmitted to a mercury cut-off which controls that portion of the gas supplj- passing to the burner through jet B.2 The height of mercury in the cut-off, and hence the temperature setting, is adjusted by screw clip C.498 MIKISTRY OF FOOD [Vol.76 Satisfactory regulation is obtained by passing only a portion of the gas through the jet, the remainder reaching the burner through variable by-pass D. The total gas supply may therefore be adjusted t o suit the operating temperature. The by-pass is shown enlarged in Fig. 2. The jet tube, within which gas supply tube E is a sliding fi.t, has a small hole F blown in the wall. Gas leaving E can reach the burner either through the jet or, after ascending the narrow annulus between the two tubes, through the hole.The length of the annulus, and hence the amount of gas by-passed, may be altered by sliding tube E in the soft rubber sleeve G. Suitable settings having been found by trial, a paper scale marked every 25" or so may be attached for future reference. To operate, the by-pass is appropriately set, the burner placed in position and the screw clip slackened. When the thermometer reading is a few degrees below the desired temperature, the screw clip is tightened until the mercury column jusi; closes the jet. After initial fluctuation the temperature should become stabilised, when final adjustments may be made. Normally, any predetermined temperature between 100" and 250" C can be held continuously to within +2". Slight re-adjustment may be needed if abnormal change in atmospheric or gas pressure occurs. To avoid possible striking-back, the air-regulating s:leeve on the burner may with advantage be replaced by a snugly fitting cylinder of fine copper gauze. REFERENCES 1 . 2. Milton, R., and Waters, W. .4., "Methods of Quantitative Micro-Analysis," Edward Arnold Csr. Co., Stock, J. T., and Fill, M. A., Metallurgia, 1944, 31, 104. London, 1949, p. 105. NORWOOD TECHNICAL COLLEGE KNIGHT'S HILL LONDON, S.E.27 J . T. STOCK 31. A. FILL March, 1951

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DOI:10.1039/AN9517600495

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年代:1951

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498 MIKISTRY OF FOOD [Vol. 76 Ministry of Food STATUTORY INSTRUMEXTS* 1951-No. 1009. The Condensed Milk Order, 1951. Price 3d. This Order, which came into operation on J u l y l s t , 1951, replaces the Condensed Milk (Control and Maximum Prices) Order, 1943 (S.R. & O., 1943, No. 1396; Analyst, 1943, 68, 332), as amended by S.R. G. O., 1945, No. 196 and S.I., 1949, .No. 1028. The principal change i s that vlzaximuni prices are prescribed for Special Full Cream Unsweetened Condensed Milk (Evaporated Milk) containing not less than 10 per cent. of butter fat. The following definition i s given in the Order- “Special full cream” in relation to condensed milk means full cream condensed milk (sweetened or unsweetened) which contains not less than 10 per cent. of butter fat and which is sold in a container bearing a label clearly specifying that the condensed milk in such container contains not less than 10 per cent.of butter fat. - No. 1029. The Meat Products and Canned1 Meat (Amendment No. 2) Order, 1951. This Order, which came into operation on June Ldth, 1951, (1) restricts the use of milk powder iiz sausages to “skim milk powder,” (2) permits whalemeat to be mixed with other meats provided that the product is labelled and sold as a whalemeat product and (3) frees meat pastz and $sh paste from control. I t amends 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, S.I., 1950, No, 1764 (Analyst, 1951, 76, 119) and S.I., 1951, No.314 (Analyst, 1951, 76, 320), as follows- (a) by deleting from Article 1 thereof the definitions of “Fish” and “Fish content”; (b) by substituting in Article 1 thereof for the definition “Milk powder” the following definition :- (c) by deleting from the proviso to the definition of “Meat product” in Article 1 thereof the word “Whalemeat” ; (d) by adding after the definition of “Tongue” in Article 1 thereof the following definition :- “‘Whalemeat product” means any product used or prepared for human con- sumption which is prepared from whalemeat whether with or without another ingredient, but does not include whale oil, whale liver oil, vitamin concentrates or pharmaceutical products.’ ; Price 2d. “‘Milk powder” means skim milk powder.’; * Obtainable from H.M.Stationery Office. Italics indicates changed wording.August, 19511 BRITISH’ STANDARDS INSTITUTION 499 by adding to the definition of “Excepted product” in Article 1 thereof the item “Meat paste” : by substituting in Article 1 thereof for the definition “Meat paste and Fish paste” the following definition :- ‘ “Meat paste” means any edible paste containing meat and usually known as “meat paste’’ but does not include any extract usually known as and called “meat extract.”’; by adding to Article 2 thereof the following paragraph:- any whalemeat product clearly labelled and sold as such”’; by deleting paragraph (3) of Article 4 thereof (which forbade the use of whalemeat in the preparation of any meat product); by inserting in Article 8 thereof after the words “specified food” the words “whale- meat product or meat paste” ; by deleting Article 10 thereof (which prescribed the meat and fish content of pastes) ; by deleting from Part I11 of the Second Schedule and Part I of the Third Schedule thereof the references to Meat paste; by deleting from Section B of Part I of the Fourth Schedule thereto the reference to Potted meat and Pate de foie.‘ “ ( c ) CURRENT STATUTORY INSTRUMENTS AND STATUTORY RULES AND ORDERS RELATING TO FOOD This Index of Current Statutory Instruments and Statutory Rules and Orders up to and including March 31st, 1961, includes- (a) Orders made by or under the authority of the Minister of Food. ( b ) Orders made by the Minister of Food jointly with another Minister or Secretary of State. (c) Charges Orders relating to food, made by the Lords Commissioners of H i s Majesty’s Treasury. (d) Orders made under the Merchandise Marks Act relating to food. (e) Orders and Charges Orders relating to matters which, although not food, are the responsibility of the Minister of Food. The Index, Sectional List No. 33, includes the prices of the individual Orders and may be obtained from H.M. Stationery Office at cost of postage.

ISSN:0003-2654    

DOI:10.1039/AN9517600498

出版商:RSC    

年代:1951

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August, 19511 BRITISH' STANDARDS INSTITUTION 499 British Standards Institution XEW SPECIFICATIONS* B.S. 1716 : 1951. Methods for the Analysis of Soaps. Price 5s. B.S. 1741 : 1961. B.S. 1742 : 1951. B.S. 1743 : 1951. Methods for the Chemical Analysis of Liquid Milk. Methods for the Chemical Analysis of Condensed Milk. Methods for the Chemical Analysis of Dried Milk. Price 2s. Price 2s. 6d. Price 2s. DRAFT SPECIFICATION A FEW copies of the following draft specification, issued for comment only, are available to interested members of the Society, and may be obtained on application to the Secretary, Miss D. V. Wilson, 7-8, Idol Lane, London, E.C.3. Draft Amendment prepared by Technical Committee FCC/&Solvents and Allied Products. CN(FCC) 2543-Draft -4mendment No. 2 to B.S. 573, Dibutyl Phthalate. * Obtainable from the British Standards Institution, Sales Department, 24, Victoria Street, London S.W.1.

ISSN:0003-2654    

DOI:10.1039/AN9517600499

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年代:1951

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500 BOOK REVIEW [Vol. 76 Book Review PRACTICAL SPECTROSCOPY. By GEORGE R. HARREON, Ph.D., Sc.D., RICHARD C. LORD, Ph.D., and JOHN R. LOOFBOUROW, Sc.D. Pp. xiv + 605. London: Blackie & Son Ltd. 1950, Price 36s. This admirable book was originally published in 1948 in America and is one of the F’rentice Hall Physics series, edited by Professor D. H. Menzel. It has now been issued in this country without modification. However, as it deals with the latest developments, it is not likely to become out of date rapidly except where industrial application has been made. The authors are masters of their subject, and well qualified to write with authority on all branches of spectroscopy. They have wisely included the Raman effect, the Vacuum Ultra-violet and Interferometric Spectroscopy, which have hitherto been regarded as of purely academic interest. This book is intended to “help the workers in any branch of science to evaluate the aid which the technique of spectroscopy might lend to the solution of his problems.” But the exposition is so clear and the advice so experienced that it vdl doubt!ess be of assistance to the worker in spectroscopy itself in the solution of his own problems.The book in fact achieves more than is claimed for it. After an introductory chapter, there follow three chapters describing the theory and design of instruments. The relative advantages of prism and diffraction grating instruments are also discussed. A well balanced review of available commercial instruments indicates how these advantages may be utilised. In the chapter dealing with grating spectrographs the classical types of mountings are discussed, including as an illustration the Paschen Runge mounting in the M.I.T.Spectroscopy Laboratory, which is built round a 10-metre concave grating. Five chapters are concerned with techniques .and practical advice in the use of instruments. One of these deals with the testing of optical components, the adjustment of both prism and grating spectrographs and the general care of such apparakus. In so far as this chapter imparts information that cannot be found either in manufacturers catalogues or in optics textbooks, it provides a useful background for the would-be operator. Twenty pages are devoted to the illurnination of the instrument, including an investigation into the optimum conditions for different types of work.The effects of slit widths on the purity of the spectrum and on the line shape are opposed in spectroscopy. There are normally two require- ments, namely, maximum sensitivity for qualitative work, when the arc or spark is focussed on the slit, and uniformity of illumination of the slit, when a lens close to the slit forms an image of the source of the collimating element. In the latter case the exposures are much longer, as the full aperture of the instrument is not employed. Although photo-electric detectors are finding comparatively small, but increasing, use in emission spectroscopy, photography is still by far the most common method of recording spectra. It is therefore most fitting that a complete chapter is devoted to this part of the procedure.Photo- graphic plates with special emulsions are produced for spectrographic use and great care must be taken in the correct choice of plate and of the blest methods for developing and processing. As this treatment is so important, one feels that a little more space might have been given to other methods of processing, such as have been tried in this country (see, for example, “Collected Papers on Metallurgical Analysis by the Spectrograph.” London : British Non-Ferrous Metals Research Association. 1945.) I t is doubtful whether the last word will ever be written about light sources in spectroscopy. Many types have been described, including some not mentioned here. What is gained in sensitivity may be lost in stability.It is certain, however, that this field will be of increasing importance when the over-all error of spectroscopic analysis is reduced by replacing the photographic emulsion by a photo-electric cell. The theory of emission and absorption is dealt with in some detail and it is certain that a full appreciation of these chapters would enable the reader to gauge the suitability of emission or absorption spectroscopy in different wavelength regions to any particular problem. The exposition of the basic principles of the subject is completed by two further chapters, one dealing with detectors for the measurement of spectral intensities and the other with principles and application of photographic photometry. Three separate chapters deal with absorption spectrophotometry, qualitative spectrographic analysis and quantitative spectrochemical analysis.Absorption spectrophotometry introduces a new range of terms about which in other works confusion has been caused by the use of different symbols for the same terms. The authors are, however, consistent in this respect and have providedAugust, 195 13 IXTERXATIONAL CONGRESS ON ANALYTICAL CHEMISTRY 501 a clear table defining the terms employed. Readers are warned, however, that they will find different names and symbols for the same terms in some other literature. These terms have been standardised by the list issued in this country (Analyst, 1942, 67, 164). These chapters include methods involving the use of photographic photo-electric and visual instruments, and the authors have not omitted a brief reference to abridged spectrophotometers or absorptiometers.A general survey of qualitative and quantitative methods of spectrochemical analysis is all that is required, as each worker naturally adapts the technique to his own particular problem. Plenty of useful information is given, however, to enable the usefulness of the method to be deduced. The subject is completed with chapters on Infra-red, Raman, Vacuum Ultra-violet and High Resolution Spectroscopy. Particular reference is made to the different types of apparatus required and the special techniques used in these fields. The text throughout is adequately supported by illustrations and specially drawn diagrams, particularly in the earlier chapters, so that the reader is more easily able,to follow the later chapters. The appendix includes wavelength tables showing the sensitive lines of elements arranged first according to elements and secondly according to wavelength. These tables are compiled from the M.I.T. wavelength tables of Harrison. There is little t o cnticise in this book, which is notable for its clarity and attention to detail. It is useful, both for reference and as a textbook, by all who either contemplate the employment of spectroscopy or by those already experienced in the use of this important analytical tool. R. A. C. ISBELL

ISSN:0003-2654    

DOI:10.1039/AN9517600500

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

August, 195 13 IXTERXATIONAL CONGRESS ON ANALYTICAL CHEMISTRY 501 INTERNATIONAL CONGRESS ON ANALYTICAL CHEMISTRY IN 1952 SOME further details are now available about the arrangements for the International Congress on Analytical Chemistry that is to be held in Great Britain next year. The Congress will meet at Oxford during the period September 4th to 9th and the scientific sessions will be held in the rooms of the Examination Schools. Three main Congress lectures by eminent chemists have been arranged. The programme for the scientific sessions is in the hands of a Programme Committee, under the chairmanship of Dr. G. M. Bennett, C.B.E., F.R.S., the Government Chemist, with Mr. L. W. Codd, M.A., of Imperial Chemical Industries Ltd., as Honorary Secretary. This Committee has appointed a number of “Advisers” who are expert in their particular fields, and the draft programme has been divided on a basis of broad techniques.Papers will be issued in pre-print form before the meeting and the contributors will give only a brief summary of their papers, most of the time being given over to discussion. Arrangements have been made to publish the whole of the proceedings in a special number, or numbers, of The Analyst, as soon as possible after the Congress. During the period of the Congress it is proposed to have in operation working demon- strations illustrating new techniques or special applications of older techniques in analytical chemistry. In addition to this, and quite separate from it, there will be a trade exhibition comprising apparatus and books. This exhibition will be under the management of Mr. W. Thompson, of Imperial College, London. Some visits have been planned and, at the week-end, a number of excursions to places of interest will be arranged. The arrangements at Oxford, for the time being, are in the hands of Dr. F. M. Brewer. Sir Wallace Akers, C.B.E., is Chairman of the Finance Committee; the Honorary Secretary of the Congress is Mr. R. C. Chirnside, F.R.I.C., Research Laboratories, The General Electric Company Ltd., Wembley, England.

ISSN:0003-2654    

DOI:10.1039/AN9517600501

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

502 PUBLICATIONS RECEIVED p o l . 76 Papers for Publication in THE ANALYST THE Editor welcomes Papers and Notes for insertion in The Analyst, whether from members of the Society or non-members. They are submitted to the Publication Committee, who decide on their suitability for insertion or otherwise. A copy of the current Notice to Authors, reprinted from The Analyst, 1951, 76, 386, can be obtained on application to the Editor, The Analyst, 7-8, Idol Lane, London, E.C.3. All Papers submitted will be expected to conform to the recommendations there laid down and any that do not may be returned for amendment.

ISSN:0003-2654    

DOI:10.1039/AN951760502b

出版商:RSC    

年代:1951

数据来源: RSC