ISSN:0003-2654    

DOI:10.1039/AN95075FX013

出版商:RSC    

年代:1950

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95075BX015

出版商:RSC    

年代:1950

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95075FP025

出版商:RSC    

年代:1950

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95075BP029

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

APRIL 1950 Vol. 75, No. 889 Method for the Estimation of Small Amounts of Carbon in Steel BY K. GARDNER, W. J. ROWLAND AND H. THOMAS SYNOPSIS-A brief survey is given of the methods available for the determina- tion of small amounts of carbon (less than 0-03 per cent.) in steel. The method described utilises a combustion procedure in which the carbon dioxide produced is absorbed in baryta solution. The decrease in electrical conductivity of this solution is related to the carbon content. The difficulties which arise are discussed and necessary precautions are described. A device for the introduction of the sample into the combustion zone, without ingress of air, is shown. Adsorption of carbon dioxide by the pre-ignited boats is avoided by storing over soda-asbestos. A high efficiency of absorption in the baryta solution is attained by the use of a cell having a long absorption path and by addition of a non-ionic wetting agent, Lissapol N, to the absorbing solution.For steels containing less than 0.03 per cent. of carbon, the average deviation from the mean value does not exceed f0.0005 per cent. The determination occupies 40 minutes, half the time needed for similar methods previously published. The apparatus can be constructed from laboratory equipment, and is robust and comparatively inexpensive. The method has been in satisfactory operation for over two years, and the results compare favourably with those obtained by the standard low-pressure method. IN the course of an investigation in these laboratories, it was necessary to develop a method for the accurate determination of the carbon content of steel containing less than 0.03 per cent.of carbon. Three types of method were considered. (a) Classical microgravimetric procedures-These have the disadvantages that a skilled operator is required and that the time for an estimation is long. ( b ) Low-pressure combustion method-This method may be considered the standard procedure at the present time for the determination of carbon in low-carbon steels. The basic principles were devised by Yensenl in 1920. A system is evacuated and the sample of 173174 GARDNER, ROWLAND AND THOMAS: METHOD FOR THE ESTIMATION v o l . 76 steel then heated and ignited in purified oxygen. The carbon dioxide formed is collected in a liquid air trap and subsequently determined by expanding the gas into a known evacuated volume and observing the pressure. Improvements in the technique were made in the methods of Wooten and Guldner,Z Murray and Ashley3 and Murray and Niedrach.4 In the method of Stanley and Yensen: it is claimed that the average time for an estimation is 20 minutes and that an accuracy of f0.0005 per cent.is obtained. Nesbitt and Hendersons use a modification of this method in which the steel is burned in a stream of purified oxygen and the evolved carbon dioxide collected in a special absorber containing caustic soda. The solution is then acidified and the volume of gas evolved is measured at low pressure. All these methods have the disadvantage that the apparatus required is complicated and relatively expensive.Attention was, therefore, focussed on the third type of method. (c) Combustion of the sample in 0xyge.n followed by absorption of the carbon dioxide in barium hydroxide solution-The reduction in concentration of the barium hydroxide can then be measured, either by titrating the residual base with standard acid, as in Kalina and Joseph’s method,’ or by measuring the decrease in conductance of the solution. Cain and Maxwells used the conductimetric method for the rapid determination of carbon with an accuracy of _tO.OI per cent. Bolliger and Treadwellg used a conductimetric method for the estimation of carbon in aluminium, the carbon dioxide being absorbed in caustic soda solution. After much work had been carried out by the authors on this method, their attention was drawn to a reference in “Reports on the Progress of Applied Chemistry’’ to the work of Ericcson.lo Using an absorption cell similar in design to that of Kalina and Joseph, he was able to determine carbon contents with a n accuracy of f0.0005 per cent.The average time for each analysis, however, was greater than 1 hour. APPARATUS Oxygen is admitted from a cylinder, through the flow gauge A and thence is passed through sodium hydroxide B and sulphuric acid C. Carbon monoxide and hydrocarbons are converted to carbon dioxide and water by catalytic combustion of the gas in furnace D, which is packed with palladised asbestos and operated at 400” C. Any water and carbon dioxide formed are absorbed in U-tubes E and F, which contain anhydrous calcium chloride and soda-asbestos respectively. These are followed by a Pregl type bubble-counter G, containing sulphuric acid, which serves to indicate any leakage in the train.It is followed by a glass wool filter H and a 2-litre aspirator bottle J, which is connected to the combustion furnace by tap K. The aspirator provides a reservoir of oxygen for use during combustion of a sample. All joints between the purification furnace D and the combustion furnace are glass to glass, the .rubber tubing merely acting as a seal. A mullite combustion tube, L (type triangle H6/T3411), is used, and after combustion the gases pass through a manganese dioxide tube M, which absorbs any sulphur dioxide formed. This tube is connected through rubber tubing and clip N to the absorption vessel P.Morgan 28 combustion boats are used. The entrance to the combustion tube is illustrated in Fig. 2. This part of the apparatus provides a gas-tight joint from the train to the furnace and at the same time minimises the volume of air introduced into the tube on insertion of the sample of steel. The steel cone R is fixed to the end of the tube by means of a ring of large-diameter heavy-section rubber tubing U. The steel cone is fitted to a B40 standard cone end-cap S, which is sealed at the extremity by glass tube V with rubber tubing. Extending to the narrow end of this end-cap is a steel tube T, which slides into the side-arm of the furnace tube. The sample boat W may be inserted into the position shown in the diagram, by removing the glass cone. Oxygen can then be passed through tube T until any atmospheric carbon dioxide is completely removed.The glass tube V can then be quickly removed and the boat pushed into the hot zone of the furnace tube with a steel rod, while oxygen passing out through T prevents admission of any air. The tube V is replaced and the combustion of the sample carried out. The absorption vessel, details of which are shown in Fig. 3, was prepared by modifying a Friederich type absorption vessel (Pyrex catalogue type S31). The gas passes through the central spiral which contains the conductivity electrodes (A, A) and bubbles into the absorbent through a sintered-glass bubbler €3. The bubbler was prepared by the method of Stone and Weissll using 40 to 60 mesh Pyrex glass. The small gas bubbles produced follow a 26-inch path round the spiral and out through C.In order to measure the conductance, air is forced through a soda-asbestos tube into C by means of a rubber bulb, forcing the A diagram of the apparatus is shown in Fig. 1.April, 19501 OF SMALL AMOUNTS OF CARBON IN STEEL 7 t U m d 176176 GARDNER, ROWLAND AND THOMAS: METHOD FOR THE ESTIMATION [VOl. 75 liquid back through the sinter into the measuring cell. Bubbles of purified air rising through the sinter serve to stir the liquid completely. The clip N is closed and the conductance measured with a Cambridge conductivity bridge. The cell is maintained at 20.0 f 0.1" C. by means of a water-bath. REAGENTS In order to obtain a suitable range on the conductivity bridge, for steels containing about 0.03 per cent.of carbon, it is desirable to use a concentration of 1 g. of hydrated baryta, Ba(OH),.$H,O, per litre. In addition, to ensure complete absorption, the absorbent contains 10ml. of 2 per cent. v/v Lissapol N* solution per litre. The exact concentration of the baryta is not important. To facilitate delivery of a standard volume into the absorption vessel, the absorbent is stored in an aspirator bottle connected to an autornatic pipette. The bottle is protected by a guard tube containing soda-asbestos. PROCEDURE A suitable volume of reagent in the absorption vessel is 50ml. Place 2 g. of the sample in a combustion boat and insert into the cool end of the com- Empty and dry the outer surfaces bustion tube. Close the tube by means of the glass cone.\ R U w \ Fig. 2. Details of entrance to combustion tube of the absorption vessel and blow purified air through the sinter to remove any liquid from the inside of the cell. Connect the cell to the apparatus and pass oxygen through at: a rate of 2.7 to 3-0 litres per hour. Adjust the temperature of the water-bath to 20 f 0.1" C. and measure the conductivity at 5-minute intervals until the bridge reading is constant. Isolate the absorption vessel by means of clip N. Remove the stopper V from the end of the glass cone and push the boat into the hot zone of the furnace with a clean steel rod. The temperature of the furnace should be 1200" to 1250" C. Close the end of the cone and increase the oxygen flow to prevent the pressure in the apparatus falling unduly. If the sample consists of drillings, combustion will start almost immediately; with sheet samples there is a lag of about 1 minute.In both cases the time for burning a 2-g. sample is 2 .to 3 minutes. During combustion the rate of oxygen flow increases to 7 to 10 litres per hour. When combustion is complete, as shown by a decrease in oxygen flow, open the clip which isolates the absorption cell and reduce the oxygen flow to 2.7 to 3.0 litres per hour. Determine the conductivity of the baryta solution after 15 minutes and thereafter at 5-minute intervals until the bridge reading is constant. With carbon contents of less than 0.01 per cent., a constant reading will be obtained in 20 minutes. The method of correlating the difference in bridge reading with carbon content is given below.Barium carbonate may be removed, when necessary, from the sintered glass bubbler by means of dilute hydrochloric acid, followed by washing with water. Run in 50 ml. of baryta solution from the pipette. With higher carbon contents 30 minutes is usually required. Lissapol N is an ethylene oxide condensation product prepared by Imperial Chemical Industries Ltd.April, 19503 OF SMALL AMOUNTS OF CARBON IN STEEL 177 EXPERIMENTAL The efficiency of the absorption was first checked with a known quantity of calcium carbonate as a carbon standard. This method proved successful for carbon contents greater than 0.02 per cent. For lower carbon contents it was difficult to weigh out the small amounts of calcium carbonate required and, therefore, sucrose was used. A standard solution of sucrose was made such that 1 ml.was equivalent to 0.4mg. of carbon. Known volumes of this solution were delivered from a micro-burette either on to a porous boat lid or into a non-porous boat and these were placed inside an ordinary combus- tion boat. Water was removed, either by desiccating over phosphorus pentoxide or drying in an oven at approximately 90” C. These samples were then ignited as for a steel. The first experiments were carried out with an absorbent containing 1 g. of hydrated barium hydroxide per litre with no wetting agent. With gas flows below 2.5 litres per hour, the time for sweeping out carbon dioxide from the combustion tube was excessive. When the flow was increased to 2.7 to 3.0 litres per hour, absorption was incomplete as shown in Fig.4 (A) in which the difference in conductivity for this absorbent is plotted against carbon content. A theoretical curve for complete absorption is also shown, Fig. 4 (C). This theoretical curve was constructed from data relating conductance and concentration obtained from Gmelin’s Handbook12 and the “Handbook of Chemistry and Physics.”13 These data were checked by measuring the con- ductance of baryta solutions of known concentra- tions, the cell constant being determined by measurement of standard potassium chloride solutions. The absorption was increased by the introduc- tion of butyl alcohol into the absorption reagent, and by doubling the concentration of barium hydroxide, but was still incomplete. Finally, a non-ionic surface-active agent, Lissapol N, was incorporated in the reagent.The relation between conductivity difference for this solution and percentage carbon is shown in Fig. 4 (B). I t is seen that for carbon contents below 0.03 per cent., the difference between this curve and the theoretical curve does not exceed 0.0005 per cent. of carbon. It was considered that curve B, Fig. 4, was sufficiently close to the theoretical curve to warrant its use as a calibration curve for the met hod. Fig. 5 shows the percentage absorption of the two reagents as a function of carbon concentration. With carbon contents greater than 0.03 per cent., the absorption falls off rapidly. Fig. 3. Details of absorption vessel Owing to the small amount of carbon estimated, care had to be taken in the preparation of the samples of steel, e.g., all surface grease had to be carefully excluded and samples were never touched by hand after preliminary cleaning by abrasion.It was found that if the combustion furnace was switched off and allowed access to the air, a considerable period (2 to 3 hours) was required, on re-heating, to attain a steady reading on the conductivity bridge. This was probably due to carbon dioxide adsorption on the walls178 GARDNER, ROWLAND AND THOMAS: METHOD FOR THE ESTIMATION [vd. 75 CARBON CONTENT (PERCENTAGE ON 2 g.) Fig. 4. Relationship between carbon content Fig. 5. Effect of carbon content on absorption. and conductivity difference. Curve A, Lower curve, solution containing 1 g. of solution containing lg. of Ba(OH),.SH,O Ba(OH),.8H20 per litre.Upper curve, per litre. Curve B, solution containing solution containing lg. of Ba(OH),.8H20 lg. of Ba(OH),.8H20 plus 0.2 ml. of plus 0.2 ml. of Lissapol N per litre Lissapol N per litre. Curve C, theoretical relationship DETERMINATION OF CARBON CONTENT OF B.C.S. CARBON STEELS B.C.S. Steel No. Weight of sample, No wetting agent 218 0.1 200 0.2087 0-2377 156 0-2147 0.2620 213 0-2264 158 0.2289 5- Carbon expressed on basis of assumed 2-g. sample Calculated, Found, A I 7 % Yo 0*0092 0.0090 0.0161 0.0155 0.0183 0.0185 0.0245 0-0245 0.0300 0.0292 0.0414 0.0412 0.0531 0.0635 0-02 per cent. of Lissapol N present 0.2010 0.0155 0.0 160 218 0.2045 0.0234 0.0230 156 0.2062 0.0377 0.0380 213 158 0.2010 0.0467 0.0470April, 19501 OF SMALL AMOUNTS OF CARBON I N STEEL 179 of the combustion tube.During routine analysis, this difficulty was avoided by maintaining the combustion furnace overnight at a temperature of 700" to 800" C., while passing a very slow trickle of oxygen through the apparatus. The combustion boats had to be ignited in oxygen before use and stored in a desiccator over soda-asbestos. It was found that, if the boats were exposed to the air for an appreciable time after ignition, a blank of 0.01 mg. of carbon (0-0005 per cent. on a 2-g. sample) was obtained. Because of the difficulty in obtaining low-carbon standard steels, a number of determina- tions were carried out on small weights of B.C.S. carbon steels. The results are shown in Table I. Table I1 shows the results of ten analyses on a sample of commercial low-carbon steel.These results show the expected deviation caused by heterogeneity of the steel. The average deviation from the mean is very close to the value obtained by Stanley and Yenson,6 who analysed a similar steel by the low-pressure combustion method. TABLE I1 CARBON CONTENT OF A COMMERCIAL LOW-CARBON STEEL Carbon, % . . 0.0067 0.0070 0.0080 0.0072 0.0070 0.0067 0,0075 0.0075 0.0077 0.0080 Mean 0.0073 & 0*0004(1)% Duplicate determinations were carried out on a standardised sample of low-carbon The results were steel which had been analysed by the low-pressure combustion method. as follows- Carbon, yo Low-pressure method . . . . .. . . 0.0060 f 0-0005 Conductimetric method .. .. .. 0.0065 0.0062 SUMMARY With this conductimetric method for the determination of carbon in low-carbon steels, containing less than 0.03 per cent.of carbon, the average deviation from the mean value does not exceed ~t0-0005 per cent. The determination occupies about 40 minutes, about half the time needed for similar methods previously published. The apparatus can be constructed from laboratory equipment and is robust and comparatively inexpensive. This method has been in satisfactory operation in these laboratories for over two years. The authors are indebted to the Director of the Nelson Research Laboratories for permission to publish this work. REFERENCES 1. Yensen, T. D., Trans. Amer. Electrochem. Soc., 1920, 37, 227. 2. Wooten, I. A., and Guldner, W. G., Ind. Eng. Chem., Anal. Ed., 1942, 14, 835. 3. Murray, W. M., and Ashley, S. E. Q., Ibid., 1944, 16, 242. 4. Murray, W. M., and Niedrach, L. W., Ibid., 1944, 16, 634. 5. Stanley, J. K., and Yensen, T. D., Ibid., 1945, 17, 699. 6. Nesbitt, C. E., and Henderson, J . , Ibid., 1947, 19, 401. 7. Kalina, M. H., and Joseph, T. L., Blast Furnace Steel Plant, 1939, 27, 347. 8. Cain, J . R., and Maxwell, L. C., Ind. Eng. Chem., 1919, 11, 852. 9. Bolliger, H. R., and Treadwell, W. D., Helv. Chim. Acla. 1948, 31, 1247. 10. Ericsson, G., Jernkontor. Ann., 1944, 128, 579. 11. Stone, H. W., and Weiss, L. C., Ind. Eng. Chem., Anal. Ed., 1939, 11, 220. 12. Gmelin, Handbuch anorg. chem., 8 Aufl. System No. 30: Barium, 1932, p. 123. 13. Hodgman, C . D., "Handbook of Chemistry and Physics," 31st Edition, Chemical Rubber 14. Naughton, J . J., and Uhlig, H. H., Anal. Chem., 1948, 20, 477. Publishing Co., Cleveland, Ohio, 1949, p. 1995. ENGLISH ELECTRIC COMPANY NELSON RESEARCH LABORATORIES STAFFORD September, 1949

ISSN:0003-2654    

DOI:10.1039/AN950750173b

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

1 80 HOUGHTON : THE DETERMINATION OF [Vol. 75 The Determination of Residual Chlorine in Water BY G. U. HOUGHTON (Read at the meeting of the Society on Wednesday, November 2nd, 1949) SuNoPsis-The introduction of break-point chlorination created a need for tests which would distinguish between free and combined residual chlorine. A satisfactory method for the determination of residual chlorine must be highly sensitive, tolerably free from interference from traces of other oxidants and able to give sharp differentiation between free chlorine and chloramines . A review is given of the methods a,vailable, including several methods, both colorimetric and amperometric, based on the original acid tolidine method of Ellms and Hauser, and methods using P-amino-dimethylaniline, methyl orange or neutral o-tolidine, and an iodimetric method for higher chlorine con tents.THE large-scale chlorination of water has now been practised for over 40 years, so that the measurement of small amounts (under 1 p.p.m.) of residual chlorine has long been a matter of considerable technical importance. It is therefore rather remarkable that prior to the second world war very few methods of measuring residual chlorine had been put forward and, indeed, the well-known o-tolidine method has, until quite recently, been unchallenged. However, in 1939 the whole subject received considerable impetus from the discovery, or rather the re-discovery, of the break-point effect in the chlorination process.* The recognition of the importance of this effect by Faber3 and a little later by Griffin4 and Calvert5 created a need for simple control tests which would distinguish between free and combined residual chlorine.It also directed attention to the reactions which take place between hypochlorite and ammonia at high dilution. By this time too, it had become widely appreciated that chloramines are far less potent germicides than free hypochlorous acid. The ideal require- ment nowadays is therefore a method which is at once sensitive, free from interference by traces of other oxidants and able to give sharp differentiation between free chlorine and chloramine; it should also preferably be sufficiently simple to serve as a waterworks control test. The more important of the tests that have been used for residual chlorine and some of the recent advances that have been made in the methods for its determination are as follows. THE O-TOLIDINE COLORIMETRIC METHOD- This method was devised by Ellms and Hauser6 as far back as 1913 and has the great merit of simplicity combined with high sensitivity : unfortunately, however, other oxidants interfere, notably ferric iron, nitrite and oxidised manganese.Owing to the difficulty of preparing reliable standards from chlorine water or hypochlorite it has always been the custom to match the o-tolidine-chlorine colours against permanent standards prepared from dichromate or against colour-glasses. The standards employed have been those originally given by Ellms and Hauser, but it has long been realised that they are not entirely satisfactory, the main difficulty being that they are only strictly applicable at a cell depth of 300mm.The Ellms and Hauser method has been studied exhaustively in the past and various procedures have been proposed whereby the effect of interfering oxidants may be overcome. Nevertheless, in view of the great importance of the o-tolidine method it has recently been reviewed by the Control of Chlorination Committee of the American Waterworks Association, whose recommendations were incorporated in the 1946 edition of “Standard Methods for the Examination of Water and Sewage” (p. 92). The method recommended by the American Committee was based mainly on the thorough studies of the o-tolidine method made earlier by Chamberlain and Glass.’ The method put * The Dutch workers, Holwerda in 1928’ and I?ays as early as 1914a had demonstrated the phenomenon, but i t is fair to say that it was the intensive studies of the American workers in 1939 and 1940 that opened up a new chapter in chlorination practice.April, 19501 RESIDUAL CHLORINE IN WATER 181 forward by these workers, which was subsequently adopted, differs from the earlier American standard method in the following important particulars- (1) The use of a greater proportion of tolidine in the final colour mixture.(2) The use of a more acid reagent, so that the final pH of the solution lies between 0.3 and 1.3 and there is consequently less interference from iron and nitrite and also more rapid colour-formation. (3) The addition of the sample to the reagent instead of vice versa. (4) The permanent standards proposed are a modification of those worked out by Scott and are buffered chromate solutions, without any.addition of copper sulphate. They have the great merit that for chlorine contents up to 1.0 p.p.m. the cell depth employed is immaterial. In addition to the advantages mentioned above, Chamberlain and Glass state that the procedure gives increased stability of colour and that Beer’s law is obeyed up to 1.5 p.p.m. of chlorine and deviations therefrom are at a uniform rate between 1-5 and 10p.p.m. Manganese, however, still interferes. It must also be noted that with the more strongly acid reagent and quicker colour development, the “flash” and “arsenite - tolidine” methods, vide infya, become far more difficult to apply. THE 0-TOLIDINE “FLASH” TEST- It has long been known that chloramines produce colour with acid o-tolidine reagent much more slowly than does free chlorine.In 1940, Laux8 used this fact as the basis of a qualitative test for free chlorine. The sample is rapidly mixed with o-tolidine reagent and the rate of colour development observed. Any delay in colour development is taken to indicate the presence of chloramine. The test is very rough, but on account of its simplicity has been much used, particularly in swimming-bath control, and it is accepted as standard in the United States. Oxidised manganese interferes by giving a “flash” colour with tolidine and the rate of colour development is dependent on temperature. 0-TOLIDINE - ARSENITE METHOD- This rather ingenious method, which was first put forward by Hallinan9 in 1944, is a means of distinguishing between free and combined residual chlorine, but it also permits a correction to be made for interfering substances.Use is made of the fact that under the prescribed experimental conditions arsenite can reduce both chlorine and chloramines but not nitrite or oxidised iron or manganese. Free chlorine is therefore measured by adding arsenite immediately after the tolidine, so as to reduce any chloramine before it has time to produce colour. Simultaneously, colorimetric evaluations are made for total residual chlorine and interfering oxidants (viz., without arsenite) and for interfering oxidants only (viz., by adding arsenite before tolidine). The amount of total, free and combined chlorine can then be ascertained by difference.Although this method does not give very clear-cut differentiation of the free chlorine and has certain pitfalls, it has proved very useful. It is seriously affected by temperature, and traces of bromide cause difficulty by accelerating the production of colour by the chloramine. AMPEROMETRIC TITRATION METHOD- This review would not be complete without brief reference to the amperometric method of determining residual chlorine first described by Marks and Glasslo in 1942. As far as is known this method has not been used in this country except for research purposes, but it is of great promise. The procedure consists in titrating the chlorine with sodium arsenite in neutral solution, the end-point being observed amperometrically using a gold or platinum cathode and a silver anode in 2 M potassium chloride. Under these conditions the iron, manganese and nitrite do not oxidise the arsenite and do not interfere.A first titration is made which gives the free chlorine: potassium iodide is then added to “activate” the chloramine which may then be determined by a second titration. The outstanding merits of this method are its freedom from interference by manganic compounds and high precision: it was claimed by Marks and Glass that amounts of chlorine up to 10 p.p.m. could be deter- mined to within 0.01 p.p.m. $-AMINO-DIMETHYLANILINE (P.A.D.A.) METHOD- for available chlorine, with which it gives a red coloration. . A number of workersr1J2J3J4 have investigated the use of this substance as a reagent Moore16 found that at pH 6.0182 HOUGHTON : THE DISTERMINATION OF [Vol. 75 the reaction was obtained with free chlorine only and that it was necessary to lower the pH to 4.0 to obtain a coloration with chloramines: on this fact he based a qualitative and semi- quantitative method.Palin16 placed the reactions on a more rigidly quantitative basis by matching the red colour against that produced by running a standard iodine solution into a control tube containing buffer and reagent ; reaction of the chloramine was obtained by subsequent addition of potassium iodide. Manganese interferes somewhat in the amino-dimethylaniline method but, as when using o-tolidine, the interfering colour may be allowed for by its measurement after reduction of the chlorine with arsenite. Copper also interferes but may be inhibited by using hexa- metaphosphate in the buffer solution.A comparator fitted with colour standards from 0.1 to 2.0 p.p.m. of chlorine has now been developed for use with this reagent in the control of swimming-pool chlorination. METHYL ORANGE METHOD FOR FREE CHLORINE- In hydrochloric acid solution (pH 3), free chlorine bleaches methyl orange but chloramine is without immediate effect. This was the basis of a volumetric method for the determination of free chlorine advanced by Holwerdal in 1928, Quite recently Taras has again investigated this method and has put forward a colorimetric17 and a micro-titrationl* procedure using methyl orange. These methods are of considerable interest and appear to be worthy of further study and trial. NEUTRAL 0-TOLIDINE METHOD- If in the o-tolidine test the reagent is of low acid concentration (q., 5 ml.of 20 per cent. v/v hydrochloric acid per litre) only free chlorine will produce a colour, the pH of the test solution being too high to effect hydrolysis of the chloramines. The “neutral” tolidine test, which depended on this fact, was proposed by Laux and Nickelfg in 1942. In their test the colour produced was blue with samples of pH below about 7.9 but yellow or orange at higher pH values. This colour difference was a serious drawback, as also was the fact that the colour was somewhat affected by the o-tolidinelchlorine ratio, besides fading rapidly. Palin20 has recently re-examined the neutral o-tolidine test and used the reagent in a novel method of chlorine determination.In this new method the tolidine is used at pH 5 to 6, in the presence of metaphosphate and wxth an o-tolidinelchlorine ratio of 6/1. Under these conditions free chlorine produces a pure, stable, blue colour which, provided the residuum does not exceed 4 p.p.m., can be matched against standard glasses; the higher residual chlorine may be titrated with ferrous ammonium sulphate. Further, after addition of potassium iodide, monochloramine may be made to give a blue colour with the reagent and likewise be titrated or matched. Chlorine testing kits (one of them photo-electric) which make use of the Palin neutral o-tolidine method are on the market. In studies using this method, Palin observed that with certain chlorinated waters the results obtained for total residual chlorine were decidedly lower than the corresponding iodimetric figures. Moreover, it appeared that in these waters a chloramine was present which could not react with iodide to give the colour reaction unless the solution was first acidified and then brought back to neutrality with bicarbonate.This discovery was in line with an observation made many years previously by Harold21 that unless acid was present in the iodimetric titration, all the chloramine would not react with iodide. This phenomenon was attributed by Harold to the presence of dichloramine. From detailed investigations, Palin has likewise concluded that in his neutral tolidine method the first fraction of the chloramine, activated by iodide, is monochloramine, while the second, which is not so activated unless previously hydrolysed, is dichloramine.Nitrogen trichloride may also be produced during break-point chlorination and by a further extension of the Pdlin method, it too may be determined. For this purpose the solution is tested again after prior extraction with carbon tetrachloride, the nitrogen trichloride present being calculated from the difference between the “free chlorine” values before and after extraction. It is thus possible to draw up a balance sheet showing the proportions of free chlorine and mono-, di- and tri-chloramines in the total residual content. Unfortunately, any oxidised manganese present interferes, even under the practically neutral conditions, but may be allowed for by its measurement after adding arsenite to reduce the chlorine. Iron and nitrite are without effect.It would seem that these studies by Palin are most important. Not only are they valuable from the point of view of analytical control but, applied in this way, the neutralApril, 19501 RESIDUAL CHLORINE IN WATER 183 o-tolidine method should be useful for research purposes, e.g., for the study of possible differences in the germicidal efficiency of the three chloramines. Incidentally, they also show that it is not safe to regard as chloramine only that part of the chlorine residuum which reacts after the so-called “activation” by iodide. Such an assumption was made by Marks and Glass and, indeed, by Palin himself in his earlier work using amino-dimethylaniline. The mechanism by which iodide induces the reaction of monochloramine with tolidine is uncertain; it may depend on intermediate liberation of iodine and this is a point which might repay investigation.In an analogous way bromide promotes the reaction of tolidine and chloramine in acid solution. In the Palin (neutral tolidine) method any nitrogen trichloride reacts as free chlorine. The formation of this compound during break-point chlorination has been recognised by several workers (e.g., Holwerdal and Marks and Glasslo), but there is apparently little informa- tion as to its germicidal value. A feature of Palin’s results is that they give a simple method of measuring the content of trichloride and they show that surprisingly large amounts may be present. The possibility that nitrogen trichloride would react as free chlorine in the amino- dimethylaniline and arsenite - tolidine tests must also be borne in mind. IODIMETRIC METHOD- In general, this method is useful for chlorine residua over 1 p.p.m., provided nitrite and manganese are absent and ferric iron does not exceed 2p.p.m.The thiosulphate used is conveniently 0.0025 N and a 500-ml. or 1000-ml. sample may be used, but in the past the advisability of standardising the t hiosulphate under similar conditions has usually been ignored. The iodimetric method suggested by the Joint British Water Analysis Committee therefore requires the thiosulphate to be standardised against iodine liberated from iodate a t high dilution. I t should also be stressed that since, as mentioned earlier, dichloramine does not appear to react with iodide in neutral solution, the sample should always be acidified with sulphuric acid before iodimetric titration.L4PPROVED BRITISH METHODS FOR THE DETERMINATION OF RESIDUAL CHLORINE- The British Committee that has been considering methods of water analysis soon found that the prescription of an approved method for residual chlorine would be one of its most difficult tasks, The shortcomings of the Ellms and Hauser o-tolidine method were realised, but the Committee had to bear in mind the effect of any changes on the validity of the residual chlorine testing kits which are in use at waterworks and swimming-baths throughout the country. I t was recognised that any change should only be undertaken after full discussion with all parties concerned.It accordingly recommended that the existing Ellms and Hauser method and standards be approved pro tern. but that a new and wider Committee should be convened to go into the whole question. The position was complicated by the fact that while the Committee was sitting, the new (1946) American standard methods for residual chlorine were laid down. Much time and trouble have obviously been devoted to the new American methods, but it was agreed that further study was necessary before they could be recommended forthwith as the basis on which British testing kits could be manufactured. The Committee were also impressed by the fact that the whole subject of residual chlorine determination was in a somewhat fluid condition and that new and apparently improved methods were still being introduced.Dr. A. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. In the preparation of this survey I have received a number of useful suggestions from T. Palin, and to him my grateful acknowledgment is due. REFERENCES Holwerda, K., Medeelingen van den Dienst der Volksgezondheid in Nederlandsch-Indae, 1928, 17, Ruys, J. D., “Drinkwaterreiniging met Hypochlorieten,” 1914 (vide Lea, C., and Mills, A. J., Faber, H. A., Water Works and Sewage, 1939, 86, 337. Griffin, A. E., J . Amer. Water Works Assoc., 1939, 31, 2121. Calvert, C. K., Water Works a d Sewage, 1940, 87, 299. Ellms, J. W., and Hauser, S. J., Ind. Eng. Chem., 1913, 5 , 916, 1030. Chamberlain, N. S., and Glass, J. R., J . Amer. Water Works Assoc., 1943, 35, 1066, 1206. Laux, P. C., Ibid., 1940, 32, 1027.Hallinan, F. J., Ibid., 1944, 36, 296. Marks, H. C., and Glass, J. R., Ibid., 1942, 34, 1227. 251 (Part 1 ) ; 1930, 19, 325 (Part 2). Annual Conference of the National Association of Bath Superintendents, 1949).184 HOUGHTON : RESIDUAL CHLORINE IN WATER [Vol. 75 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Kolthoff, I. M., Chem. Weekblad, 1926, 23, 203. Alfthan, K., and Jarvis, A. C., J . Amer. Water Works Assoc., 1928, 20, 407. Haase, L. W., and Gad, G., 2. anal. Chem., 1936, 107, 1. Byers, D. H., and Mellon, M. G., Ind. Eng. Chem., Anal. Ed., 1939, 11, 202. Moore, W. A., J . Amer. Water Works Assoc., 1.943, 35, 427. Palin, A. T., Analyst, 1945, 70, 203. Taras, M., J . Amer. Water Works Assoc., 1946, 38, 1146. -, Ind. Eng. Chem., Anal. Ed., 1947, 19, 342. Laux, P.C., and Nickel, J. B., J . Amer. Watev Works Assoc., 1942, 34, 1785. Palin, A. T., J. Inst. Water Eng., 1949, 2, 100. Harold, C. H. H., 29th Ann. Rept. of Director of Water Exam. Met. Water Bd., 1934. SOUTH ESSEX WATERWORKS Co. LANGHAM, COLCHESTER LANGHAM VALLEY WORKS DISCUSSION MR. R. F. MILTON drew attention to a completely new method for the estimation of residual chlorine. He said that this was the first time that a direct method for the determination of chlorine had been put forward, all the existing methods being based on oxidation potential and not directly on the presence of chlorine, A short description of this method had been published’; briefly, it depended on the fact that when free chlorine was brought into contact with the cyanide ion, cyanogen chloride was produced quantitatively.The cyanogen chloride was then allowed to react with pyridine to form a quarternary derivative which, when coupled with a.n aromatic amhe, produced an intense colour which could be made the basis of a quantitative estimation. This method would also detect free bromine, but otherwise was entirely specific for free chlorine. Mr. Milton felt that the method was worth further investigation. The high concentration of pyridine, 6 per cent., was a disadvantage, but it might be possible to use other organic compounds such as nicotinic acid. DR. HOUGHTON replied that he had made a few tria.ls of the method described by Mr. Milton, working on 6-ml. quantities of water. He could confirm the high sensitivity of the method, but he had found difficulty with the benzidine precipitating. He thought the method showed promise, however, and was of considerable interest. DR, H. LIEBMANN said that he had tried Mr. Milton’s recently published method, and could also confirm its high sensitivity. However, this sensitivity appeared to vary in accordance with the concentration of the residual free chlorine, decreasing very markedly a t higher concentrations as determined in distilled water by amperometric titration. Above about 4 p.p.m. of free chlorine, further increase produced only a very slight increase in colour density. He had also obtained some evidence that a t least a part of the chloramine is estimated in addition to free, available chlorine by Milton’s method. These experiments, however, had been carried out on highly polluted water, with which all methods for the determination of free chlorine became rather uncertain. For this reason they were not specific. REFERENCE TO :DISCUSSION 1. Milton, R. F., Natuvs, 1949, 164, 440.

ISSN:0003-2654    

DOI:10.1039/AN9507500180

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 1950; BLACK AND SCHWARTZ 185 The Estimation of Chitin and Chitin Nitrogen in Crawfish Waste and Derived Products BY Miss M. M. BLACK AND H. M. SCHWARTZ SvNorsrs-The determination of chitin and chitin nitrogen in crawfish waste and derived products has been subjected to a critical study. In the proposed method, chitin is isolated and either weighed as such or, in the case of the determination of chitin nitrogen, its nitrogen content is determined by one of the standard methods. When applied to crude chitin samples, the precision of the proposed method is of the order of 0.5 per cent. of the mean. I t is somewhat lower ( &3 per cent. of the mean) in the case of crawfish meals. The method is similar to the A.O.A.C. method for the determination of crude fibre. A comparison of the results obtained on a number of crawfish meals by the two methods shows close agreement.The chitin, chitin nitrogen and total nitrogen content of a number of crawfish meals are reported, and the importance of making a correction for chitin'nitrogen when calculating the protein content of such meals is stressed. APPROXIMATELY 90oO tons of waste are available annually from the production of canned and frozen crawfish tails on the west coast of the Union of South Africa and South-West Africa. At present only a limited proportion of the waste is converted into crawfish meal, which is used for poultry feed. An investigation into the possibility of producing chitin on a commercial scale from crawfish waste was undertaken by the authors. The results of this work will be published elsewhere.As part of this investigation the determination of chitin in crawfish waste and products derived from it was studied. The estimation of chitin nitrogen in crawfish meals used for feeding purposes was also studied. This is of interest because it is customary to sell the meal on the basis of its protein content, which is calculated from the total nitrogen content. Since chitin contains 6.90 per cent. of nitrogen, and since it is very doubtful whether this is available to animals, with the possible exception of ruminants, it is desirable to subtract the chitin nitrogen from the total nitrogen when calculating the protein content of crawfish meal. A survey of the literature revealed that the methods most commonly used for the estima- tion of chitin in plant and animal tissues are based on the isolation of chitin.lp2g3 Crustacean shells are usually tre9ted first with excess of hydrochloric acid to dissolve out the mineral matter.The sample is then subjected to repeated treatments with 4 to 10 per cent. aqueous sodium or potassium hydroxide. The residue is finally decolorised with dilute potassium permanganate and extracted with alcohol and ether. No attempt appears to have been made to determine the number of alkali treatments necessary to remove completely all non-chitinous material, or the extent to which repeated alkali digestions cause de-acetylation and subsequent loss of chitin. Chitin has also been determined by conversion to de-acetylated chitin (chitosan) by the action of very concentrated potassium hydroxide at 120" to 150" C., and then weighed as such.4 This method is unsatisfactory, however, since the amount of chitosan obtained varies inversely with the duration of the alkali treatment.3 EXPERIMENTAL In the present method, chitin is extracted and weighed as such. The following procedure was finally adopted. Estimation of chitin-Weigh 0.2 to 0.4g. of crude chitin or 2 g. of crawfish waste or meal into a 250-ml. beaker, add 50 ml. of N hydrochloric acid and heat on a boiling water- bath for 1 hour. At the end of this period, filter the contents of the beaker through a sintered glass crucible (porosity G1) or a piece of linen. Wash the beaker and the filter with boiling water until the washings are no longer acid. Then wash the residue on the filter back into the beaker with 100 ml.of 5 per cent. w/v sodium hydroxide solution, and digest on a steam- bath for 1 hour. The residue at this stage should consist of chitin together with any silica186 present in the sample. Filter it through an alunldum crucible or through a Gooch crucible prepared with ignited asbestosJ5 wash thoroughly with boiling water and finally wash twice with about 15 ml. of acetone. Dry the crucible and contents at 110" C. to constant weight. Incinerate the contents of the crucible in an electric muffle-furnace or over a Meker burner at a dull red heat until all carbonaceous matter is consumed. Cool the crucible and re-weigh. Report the loss in weight as chitin. Estimation of chitin nitrogen-Carry out the acid and alkali digestions as described above. Filter the residue left after the alkali digestion through a sintered-glass crucible or through a piece of linen, and wash thoroughly with hot water.Transfer the chitin to a 250-ml. Kjeldahl flask, using the least possible amount of water. Evaporate the water to less than 5 ml., taking care to avoid bumping. Add 25 ml. of concentrated sulphuric acid and 10 g. of potassium sulphate (0.25g. of copper selenite or any other catalyst may also be added if desired) and complete the nitrogen determination in the usual way.6 RESULT s BLACK .4XD SCHWARTZ: THE ESTIMATIOS OF CHITIN AND CHITIN [Vol. 75 NUMBER OF ALKALI TREATMENTS REQUIRED- Previous workers have used at least three alkali treatments to purify their chitin in the estimation of chitin in both animal and plant r n a t e r i a l ~ .~ ~ ~ ~ ~ The number of alkali treatments necessary to ensure the removal of all non-chitinous organic matter was investigated. The isolation of chitin from crawfish meal samples was carried out by the recommended procedure. The residue after the first alkali digestion was dried and weighed and then subjected to a TABLE I EFFECT OF SUCCESSIVE TREATMENTS WITH 100ML. OF 5 PER CENT. NaOH ON THE WEIGHT OF THE RESIDUE: BEFORE IGNITION Weight of residue after 1st treatment, 2nd treatment, 3rd treatment, €5 g. g. 0.2749 0.2701 0.2660 0.2410 0.2369 0.2 3 2'7 0.2554 0-2508 0.24513 0.2074 0.2054 0.2030 0.2543 0.2507 0.250 1 0.2992 0.2946 0.2916 0.2542 0.2499 0.2488 A I 7 Loss in weight* ind treatment, 3rd treatmen;, 1.8 3.2 1-7 3.5 1-8 3.7 1.0 2.1 1.4 1.7 1.4 2.4 1.7 2.1 A % % * As percentage of weight of residue after 1st alkali treatmen!. TABLE I1 DE-ACETYLATION OF CHITIN UXDER CONDITIONS OF ESTIMATION No.of alkali treatments Weight of chitin isolated, g. 0.1821 0.1843 0.2532 0.2660 0.2660 0.2327 0.2459 Weight after acetic acid treatment, g. 0.1817 0.1834 0-2522 0.2639 0-2651 0.2313 0.2451 De-acetylated chitin, 0.2 0-5 0.4 0.8 0-3 0.6 0.3 % second and finally a third treatment with 100 ml. of 5 per cent. sodium hydroxide solution, The results are summarised in Table I. It will be seen that the second and third alkali treatments cause small losses in the weight of the residue obtained after the first treatment, These losses, however, are only of the order of 2 to 4 per cent.of the weight of the chitin in the sample. This is of the order of experimental error of the method, and consequently one treatment with alkali is deemed sufficient in the estimation of chitin in crawfish meals andApril, 19501 NITROGEN IN CRAWFISH WASTE AND DERIVED PRODUCTS 187 derived products. That one alkali treatment suffices to remove all but a trace of non- chitinous organic matter was further demonstrated by the fact that fish meals, which were known not to have been admixed with crawfish meal, gave less than 0-2 per cent. of residue when treated according to the proposed method (Table I11 ( a ) ) . The de-acetylation of chitin even after three treatments with 5 per cent. sodium hydroxide solution under the conditions employed in the determination is negligible.This was demon- strated by heating samples of chitin isolated by the proposed method with 3 per cent. v/v acetic acid on a steam-bath for 1 hour. Under these conditions de-acetylated chitin dissolves readily. The loss in weight of the chitin preparations, however, was less than 1 per cent. (Table 11) , The chitin isolated from crawfish wastes by the proposed method was pure white in colour. Most of the colour was removed by the alkali treatment and what remained was taken out by washing with acetone. Further decolorisation with dilute potassium perman- ganate as employed by other workers is thus unnecessary for products derived from crawfish waste. PRECISION OF METHOD- Pure chitin was prepared from crawfish shells by treatment with hydrochloric acid, followed by repeated treatment with 5 per cent.sodium hydroxide. Any de-acetylated chitin produced in the process was removed by treatment with 3 per cent. acetic acid. The purified chitin was added to samples of pilchard meal which had been shown to contain less than 0-2 per cent. of chitin. Determination of the chitin content of the mixtures by the proposed method gave recoveries of 98.2 to 100.1 per cent. (Table 111). The recovery of chitin added to fish ineals was studied. rrA4BLE 111 RECOVERY OF PURIFIED CHlTIN ADDED TO FISH MEALS (a) BLANK DETERMINATIONS ON PILCHARD MEALS Weight of meal Sample taken, isolated, Weight of chitin g. g . 1 2.0402 o*oooo 2.0690 0~0001 2- 1369 1,9300 (L) RECOVERY OF ADDED CHITIN Weight of Pilchard pilchard meal meal used taken, g - 1 2.2344 1-9917 2 2.7097 2.0703 8.7022 2.2167 Chitin in pilchard meal, g.nil nil 0.0032 0.0024 0.0032 0.0027 0.0023 0.0026 Purified chitin added, g. 0.2015 0.2081 0.3354 0.43 16 0.1969 0.2634 % nil nil 0.1 1 0.13 Chitin found, Recovery, g- % 0.2018 1 oo. 1 0.2070 99.5 0.3330 98.4 0-4270 98.3 0.1964 98.2 0.2639 98-7 Determination of the chitin content of thirteen samples of crude chitin, containing 60 per cent. or more of chitin, was carried out in duplicate by the method described. The difference between duplicate deterininations ranged from 0-2 to 1.6 per cent. of the mean. The average deviation from the mean was 0.4 per cent. When the method was applied to crawfish meals, the agreement between replicate determinations was not so close. Duplicate, and in some cases quadruplicate, determinations were carried out on thirteen samples of crawfish meal from various sources.The deviation of a single determination from the mean for the sample ranged from 0.2 to 10.7 per cent. The average deviation from the mean was 3.0 per cent. One reason for the lower precision of the method when applied to crawfish meals appears to be the difficulty of sampling the meal properly, even after it has been finely ground. This was particularly noticeable when the meal contained a high proportion of sand.188 BLACK AND SCHFVARTZ: THE ESTIMATION OF CHITIN AND CHITIX [VOl. 75 The precision of the method for the determination of chitin nitrogen in meals is of the same order as that for the determination of chitin, The determination of the chitin nitrogen content of nine crawfish meals was carried out in duplicate.The difference between duplicates ranged from 1.4 to 9-1 per cent. of the mean. The average deviation from the mean was 1-8 per cent. COMPARISON OF THE METHOD WITH THE A.O.A.C. METHOD FOR THE DETERMINATION OF CRUDE The method described here for the determination of chitin is very similar in principle to the A.O.A.C. method for the determination of crude fibre.5 A comparison of the values obtained by the two methods for a number of crawfish meals is given in Table IV. The results in each case refer to the dry, fat-free meal. The values obtained by the two methods FIBRE- TABLE I V COMPARISON of; VALUES Meal sample FOR CHITIN AN11 CRUDE IY CRAWFISH MEALS Chitin, 11.4 9.4 11.2 10.5 13.1 11.5 13.8 % FIBRE (A.o.A.c.METHOD) Crude fibre, 11.7 10.5 11.6 10.2 13.1 11-8 15.4 % are in very close agreement, except in two cases (samples 4 and 9), and here the differences are within the limits of the experimental errors clf the methods. The A.O.A.C. method for crude fibre determination may therefore be used to determine chitin in crawfish products. The method described here is preferred, however, since it requires less rigid adherence to specified conditions. THE CHITIN AND CHITIN NITROGES COXTENT OF CRAWFISH MEALS- The chitin, chitin nitrogen and total nitrogen content of nine crawfish meals are recorded in Table V. The chitin nitrogen content as determined by the proposed method is generally TABLE V CHITIN, CHITIN NITROGEX AND TOTAL NITROGES COXTEXT OF CRAWFISH MEALS Chitin nitrogen, % r - y Chitin nitrogen/ Chitin, (Calc.) (Found) Total nitrogen, total nitrogen, Ye O/ % / O 13.1 12.1 11.4 11.2 10.5 13.1 11-5 13.8 13-6 0.91 0.84 0.79 0.77 0-73 0.90 0-79 0-96 0.94 0.75 0.86 0.73 0.68 0-82 0-81 0.76 0.94 0.94 7.06 6.29 7.70 9.79 9-20 7-37 9-12 8.16 7.91 10-7 13.6 9.5 7.0 8.9 11.1 8.3 11.6 11.9 slightly lower than that calculated from the chitin content of the meal, using the theoretical value of 6.90 per cent.for the nitrogen content of chitin. This is to be expected, since even carefully purified chitin samples generally contain less than the theoretical amount of nitr0gen.l In the meals examined, the chitin nitrogen ranged from 7.0 to 13.6 per cent. of the total nitrogen in the meal. The importance of making a. correction for chitin nitrogen in calculating the protein content of crawfish meals is therefore apparent. We are indebted to the South African Council for Scientific and Industrial Research UJe are also indebted to the Fishing Industries Research for permission to publish this work. Institute, Cape Town, for supplying a number of crawfish meals used in this work.April, 19501 NITROGEN IN CRAWFISH WASTE AND DERIVED PRODUCTS 189 REFERENCES 1. 2. 3. 4. 5. 6. Ibid., p. 26. Pringsheim, H., and Kriiger, D., “Handbuch der Pflanzenanalyse,” Vol. 3/1, p. 77, Vienna, Julius Bergmann, W., Ann. Entomol. SOC. Am., 1938, 31, 315. Lafon, M., Compt. Rend., 1941, 212, 456. Tauber, 0. E., J . Morphol., 1934, 56, 61. “Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists,” Springer, 1932. 6th Edition, 1945, p. 408. 17hTS AND PROTEINS UNIT OF THE NATIONAL CHEMICAL RESEARCH LABORATORY UNIVERSITY OF CAPE TOWN RONDEBOSCH, SOUTH AFRICA Sepember, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500185

出版商:RSC    

年代:1950

数据来源: RSC

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April, 19501 NITROGEN IN CRAWFISH WASTE AND DERIVED PRODUCTS 189 The Analysis of p-Nitrophenyl Diethyl Thiophosphate, E605, Parathion BY J. C. GAGE SYNoPsrs-The high toxicity of the insecticidal compound generally known as parathion or E605 has necessitated a sensitive method for its determination in the atmosphere or in edible crops. A method is described in which the compound in toluene solution is reduced to the corresponding amino compound, which is extracted into acid, diazotised and coupled with N-sulphatoetliyl- m-toluidine. The coefficient of variation of a solution containing 5 pg. per ml. is of the order of 2 per cent.; the lower limit of sensitivity for the analysis of plant tissues depends upon the blank value for the material. THE historical development and chemical synthesis of the organic phosphorus insecticides have been discussed at a recent symposium of the Association of Applied Bio1ogists.l One of these compounds, 9-nitrophenyl diethyl thiophosphate (I), has been shown to be highly effective against a wide range of insect pests; it was synthesised in Germany and given the code reference E605, and in America the U.S.Department of Agriculture has used the official name “parathion.” I t is being manufactured in this country and both names are in current use; more recently the tendency, which will be followed in this communication, is to use the term parathion. / \ S OC,H, */ b C , H , (1) (11) (111) Analytical methods for determining parathion are not only necessary to control the strength of the crude commercial product, and of insecticidal dusts and solutions made therefrom, but also, on account of the high mammalian toxicity of the compound, to determine the concentration in the atmosphere during its manufacture and use.Moreover, if edible crops have been treated with such an insecticide, it may be desirable to know the residual a.mount of parathion present in the crop after harvesting. It is possible to base a colorimetric method on the hydrolysis of parathion to nitrophenol, which takes place readily in alkaline solution. Such a method is not, however, sufficiently sensitive for the determination of parathion in the atmosphere or in plant tissues. Averell and Norris2 have described a sensitive method which has been used to estimate the residual amount in a variety of plant materials; the tissues are extracted with benzene, which is then evaporated to dryness after treatment with an adsorbent to remove pigments.The residue is dissolved in aqueous alcohol and after reduction of the nitro group to an amino group with zinc dust and hydrochloric acid, an azo dye is developed by diazotisation and coupling with N-( 1-naphthylethylenediamine) after removal of excess of nitrite with ammonium190 GAGE: THE ANALYSIS OF p-NITROPHENYL DIETHYL [Vol. 75 sulphamate. In the method described in this paper, reduction is effected by heating a toluene solution, which may be a plant tissue extract or the absorbing liquid from a suitable air sampler, with zinc dust and acetic acid under refluxing conditions; the reduced parathion is then extracted from the toluene with dilute hydrochloric acid.The advantage of this procedure is that evaporation of the solvent is avoided and, as plant pigments are not extracted from the organic liquid into the aqueous phase, there may be no necessity for their removal. In the development of the azo dye it has been found advantageous to couple with.N-/3- sulphatoethyl-m-tol~idine,~ which is more readily available and more stable than the reagent used by Averell and Norris,2 and does not require the addition of ammonium sulphamate; it is, however, necessary to neutralise the hydrochloric acid and part of the extracted acetic acid to facilitate coupling, and the addition of alcohol gives greater stability to the colour. METHOD The following procedure was designed for th.e estimation of atmospheric contamination If or of residual parathion in plant material, in which only a few micrograms are present.larger amounts can be taken for analysis, suitable modifications may be made if desired. REAGENTS- ToZuene-Ten parts of commercial redistilled toluene shaken with 1 part of concentrated sulphuric acid for 2 hours and washed free from acid.* GZaciaZ acetic acid-Analytical reagent quality. Zinc dust4ommercial zinc metal dust. Hydrochloric acid, 0.5 N . Concentrated hydrochloric acid-Analytical reagent quality. Sodium hydroxide solution, 10 per cent.-Ten grams of sodium hydroxide of analytical N-~-suZphatoethyZ-m-toZuidine, 1 per cent .----he gram of the pure commercial product It should be stored in an amber Sodiztm nitrite solution, 0.25 per cent.-Freshly prepared each week from a 6 per cent.Ethanol-95 per cent. reagent quality dissolved and made up to 100 ml. with distilled water. dissolved and made up to 100ml. with distilled water. bottle and discarded when the solution turns pink. stock solution of sodium nitrite (analytical reagent quality) kept in a refrigerator. REDUCTION OF THE NITRO GROUP- Approximately 15 ml. of the toluene solution, containing not more than 7 pg. per ml. of parathion, is introduced into a 6 x 1 inch test tube fitted with a 30-cm. air condenser by means of a ground glass joint. To this is added 0.25 ml. of glacial acetic acid and 0.25 g. of zinc dust. The tube is then placed in an oil-bath at 130" to 140" C. and the contents heated under reflux for 15 minutes.After cooling, the zinc is allowed to settle and 10 ml. of the clear solution are transferred to a stoppered 6 x Q inch test tube, and shaken for 3 minutes with 2.5 ml. of 0 . 5 N hydrochloric acid. After separation of the layers, 2 ml. of the aqueous layer are removed by a pipette to a. tube graduated at 5 ml. DEVELOPMENT OF THE AZO COLOUR- Add 0.2 ml. of 0.25 per cent. sodium nitrite solution, mix and allow to stand for 15 minutes. Add 0.4 ml. of 1 per cent. N-sulphatoethyl-m-tcduidine followed by 0.6 ml. of 10 per cent. sodium hydroxide solution; mix and allow to stand for 15 minutes. Add 3 drops of concen- trated hydrochloric acid and 1 ml. of 95 per cent. ethanol and make up to 5 ml. with distilled water. COLOUR MEASUREMENT- diameter tubes and the azo colour read at 510mp.Ilford filter No. 604 is suitable. volume and is stable for several hours. For this investigation the Unicam D.G. spectrophotometer has been used with O-5-iiich With the Spekker absorptiometer, The colour ma.y be read immediately after making up to * Some supplies of toluene were not amenable to this treatment. It has since been found that the B.D.H. sulphur-free grade is satisfactory without acid treatment.April, 19501 THIOPHOSPHATE, E605, PARATHION 191 A standard curve relating optical density to concentration is constructed from toluene solutions containing known amounts of parathion and submitted to the above procedure, the colours being read against a blank from toluene similarly treated. For all determinations a toluene blank is employed; when plant material is investigated the toluene is first shaken with similar material that has not been treated with parathion. DISCUSSION- The method is specific for compounds that can be reduced to an amino compound capable of forming an azo dye.Amines may be excluded by acidifying the initial aqueous solution or washing the toluene solution with acid. $-Nitrophenol, which occurs in small quantity in commercial parathion, does not interfere, but bis-$-nitrophenyl ethyl thiophosphate (11), which is present as up to 10 per cent. of the crude product, does give a colour. Some difficulty has been experienced in obtaining a pure sample of parathion as a reference; many of the so-called pure samples obtained by distillation are grossly contaminated by an isomer (111), which is produced if parathion is heated above 140" C.4 Methods of analysis for these impurities are being elaborated and will be the subject of a later communication.Twelve determinations on a toluene solution containing 5 pg. per ml. gave a mean optical density 0690 with a standard deviation of 0.010 and a coefficient of variation of less than 2 per cent. In the analysis of plant tissues the lower limit of sensitivity is largely controlled by the blank value, the apparent parathion content of the untreated material; the optical density obtained with this blank may be of the order of 0.05. The method has been used satisfactorily to analyse the atmosphere during the manufacture of parathion insecticides, a sample of air being passed through toluene in a gas bubbler. An investigation of the residual parathion in a variety of plant materials is a t present in progress; the results will be reported in detail later. REFERENCES 1. 2. 3. 4. INDUSTRIAL HYGIENE RESEARCH LABORATORY Ann. Appl. Biol., 1949, 36, 153. Averell, P. R., and Norris, M. V., Anal. Chem., 1948, 20, 753. Rose, F. L., and Bevan, H. G. L., Hiochem. J., 1944, 38, 116. British Intelligence Objectives Sub-committee Report No. 1808, p. 9. IMPERIAL CHEMICAL INDUSTRIES LIMITED WELWYN, HERTS. Septembsr, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500189

出版商:RSC    

年代:1950

数据来源: RSC

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April, 19501 THIOPHOSPHATE, E605, PARATHION 191 Spot-tests for the Identification of Alloying Elements in Copper-Base Alloys* BY B. S. EVANS AND D. G. HIGGS SYNoPSIS-’rhe tests described in this paper constitute a complete qualitative scheme for the non-destructive examination of copper and its alloys. The elements that can be detected are: manganese, zinc, tin, iron, lead, silicon, nickel, aluminium, beryllium, arsenic, cadmium, cobalt, chromium and phosphorus. The tests consist of addition of drops of reagent to the cleaned metal surface, followed by further reagent to produce a coloured precipitate characteristic of the metal sought, or removal of the drop of solution from the metal surface on to a filter-paper or spot-plate, for production of a specific reaction. The aim has been to reduce to a minimum the number of operations and the manipulative skill required so that the tests can be applied with satisfactory results by persons of limited chemical knowledge.THE tests to be described in this paper constitute the last of a series of researches dealing with the detection of alloying elements in various types of alloys. Papers already published for the spot-testing of alloys include, “Steels,”l “Aluminium and Magnesium-base Alloys,”Z “Zinc-base alloy^,"^ “Lead-base Alloys”4 and “Tin-base Alloys. J ’ s As far as possible these tests have been employed in the present series. * Communication from the Armament Research Establishment (formerly Research Department, Woolwich),192 EVANS AND HIGGS: SPOT-TESTS FOR THE IDENTIFICATION OF Apparatus-It has not been found necessary to introduce any new apparatus and, since adequate description has already been given in previous papers, no further words need be added here.[Vol. 75 THE TESTS- Copper offers a very wide range of alloying elements, and tests have been evolved for the following elements : manganese, zinc, tin, iron, lead, silicon, nickel, aluminium, beryllium, arsenic, cadmium, cobalt, chromium and phosphorus. The usual alloying quantities of selenium, tellurium and silver are so small that no definite tests have been forthcoming; hence these elements are not included in the present work. The test to be described for silicon is based on dye-absorption by the hydrated silica; the preliminary results were so perplexing that an investigation was carried out, ‘by one of us, to determine the exact condition under which absorption occurred.The findings of this investigation have been adapted to the test for silicon, but a more detailed account will be published at some future date by the author concerned. It has been found possible to test for aluminium and beryllium at the same time in such a way that both elements can be detected by their distinctive markings. After a single-wash treatment, to bleach the aluminium completely, the beryllium can be plainly seen. Compositions of the trial alloys are given in the Appendix, pp. 199-200, and the numbers at the end of each test refer to that Appendix. It is very important to the success of the tests that the surface of the specimen should be thoroughly cleaned with a fine emery paper, Grade IG or similar, immediately before the reagents are applied. (I) MANGANESE Reagents-(a) Diluted nitric acid (sp.gr.1.20). Method-Place 3 drops of (a) on the cleaned surface and leave for 5 minutes, add a further 2 drops and transfer, with the aid of a capillary tube, to the well of a white spot-plate. Drop into the solution a little of (b), stir and leave for the full development of colour. In presence of more than 15 per cent. of manganese, rapid decomposition into the hydrated oxide occurs; between 0.4 per cent. and 15 per cent. of manganese is indicated by varying intensities of purple permanganic acid, and 0.1 per cent. is visible as a light purplish coloration of the drop. Tried on: Samples Nos. 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12*-Manganese present; all results Nos, 13, 14, 15, 16, 17, M, 19, 20, 21, 22-Manganese absent and all Our aim, as before, has been to make every test specific and unambiguous. (b) Sodium bismuthate (solid).In absence of manganese the drop remains blue. positive. results negative. (11) ZINC Reagents-(a) Concentrated nitric acid (sp.gr. 1-42). (bj Distilled water. (c) Sodium hydroxide solution (20 per cent.). (d) Diphenylcarbazone (1 -5 per cent. solution in alcohol). (e) Ammonium nitrate solution (20 per cent.). Method-Place 1 drop of (a) on the cleaned surface and leave until the vigorous attack has subsided, then wash off with a fine jet of distilled water on to a clean watch-glass. Add 3 drops of (c) and stir thoroughly; the mixture should now react alkaline to litmus paper.Filter off the cupric hydroxide precipitate through a glass-tube filter, collecting the filtrate on a 12.5-cm. Whatman No. 541 filter-paper, supported on the open mouth of a beaker. Wash the watch-glass with 3 drops of (b) and pour through the filter-tube. Remove the tube, place the filter-paper on a clean tile and cover with a second filter-paper thoroughly soaked with (e); ensure complete contact at all points by rolling with a glass rod. After 20 to 30 seconds, strip off the ammonium nitrate paper, replace t.he test paper on its beaker and leave exposed to air for 5 to 10 minutes. At the end of this period the filter-paper ought to be free from all “fixed” alkali and substantially free from ammonia. Add 4 drops of (a), followed when * First discovered by spot-tests and subsequently confirmed by chemical analysis.April, 19501 ALLOYING ELEMENTS I N COPPER-BASE ALLOYS 193 spreading is complete by a further 4 drops.Again transfer to the tile and re-treat with a filter-paper well soaked in (e); this time manipulate the glass rod from the outer edges of the coloured spot to prevent undue spreading of the colours and to ensure an ample excess of ammonium nitrate all over the coloured patch. Remove the upper paper and suspend the test-paper to dry. When more than 3 per cent. of zinc is present, the first addition of reagent (d) to the slightly ammoiiiacal test-paper results in a deep violet patch, whilst 1 per cent. of zinc gives a violet ring just inside the outer edge of the reagent patch, the remainder being orange-red in colour.In absence of zinc, or where the zinc content is low, the coloured ring is usually reddish-brown. Final treatment with (e) tends to accentuate the zinc colour whilst changing the reagent - ammonium nitrate colour from reddish-brown to brown. When dry, all papers not containing zinc show a peach-colouredcentre with a brownish outer ring; 0.5 to 2.0 per cent. of zinc gives a peach centre more or less completely flecked with violet and a rather broad violet ring, or band, at the outer edge. Above 3 per cent. of zinc gives a deep violet colour to the whole reagent patch. If the zinc content is less than 1 per cent., the above test should be replaced by the following. Treat a 12.5-cm. Whatman No. 541 filter-paper with 2 or 3 ml.of an equal mixture of (d) and (e) and leave to dry; the paper should then appear very pale mauve with a yellow outer band. Filter the alkaline mixture, obtained as described above, on to this pre-treated paper. Remove the tube, wash the paper, from the centre, with 2 drops and then with 3 drops of (e), and finally treat with a disc of filter-paper moistened with (e) and hang up to dry. The zinc should now appear as a broadish irregular purple-violet band about 2 to 3 inches in diameter. Tried on: Samples Nos. 17, 23, 24, 25, 26, 27, 21, 28, 16, 22, 1, 29, 30, 31, 32, 33, 34, Nos. 13, 14, 4, 37, 40, 41, 19, 45, 12, 15, 5, 42, 43-Zinc absent and 35, 36-Zinc present ; all results positive. all results negative. (111) TIN Reagents-(a) Concentrated nitric acid (sp.gr.1-42}, 1 vol. ; tartaric acid solution (50 per cent.), 1 vol. (b) Potassium iodide solution (20 per cent.). (c) Concentrated hydrochloric acid (sp.gr. 1*16), 1 vol. ; potassium cobalti- cyanide solution (10 per cent.), 5 vols. (d) Toluene-3 : 4-dithiol* solution in acetone (0.5 per cent.), 2 vols.; thio- glycollic acid solution in acetone (0.5 per cent.), 1 vol. Method-Attack the surface of the cleaned specimen with 1 drop of (a) and leave to react for 5 minutes. Add 2 drops Bf (b), stir well, spread out the drop and leave until the iodine colour has disappeared. Add 6 drops of (c) , stir thoroughly, then remove about half the volume of the liquid, by means of a capillary tube, and drop on the centre of a 12.5-cm. filter-paper. When the liquid has finished spreading, add 4 drops of (d) to the centre of the cobalticyanide precipitate.In presence of tin, a yellowish band moves outwards until spreading ceases, then transformation occurs and the yellow ring turns red from the outer edge; for tin contents above 1 per cent., the whole of the area bounded by the ring also appears red. Notes on Method-The transferred precipitate should be light buff or greenish-blue in colour. The transformation, or development time, varies somewhat for different percentages of tin, e.g., more than 0.3 per cent. of tin gives a colour almost immediately, 0.3 to 0.1 per cent. takes about 1 minute to give a colour and less than 0.1 per cent. may take 3 or 4 minutes; full development of the colour takes place within 5 minutes of addition of the “dithiol’ ’ reagent.Tried on: Samples Nos. 44, 22, 21, 46, 47, 48, 49, 50, 51, 52,” 53,* 1*-Tin present; Nos. 6, 40, 19, 4, 37, 16, 15, 54, 55, 14, 13, 56, 11, 42, 36, 34, 35, In absence of tin the paper remains white. all results positive. 57-Tin less than 0.06 per cent. and all results negative. * First discovered by spot-tests and subsequently confirmed by chemical analysis.[Vol. 75 194 EVANS AND HIGGS: SPOT-TESTS FOR THE IDESTIFICATIOS OF (IV) IRON Reagents-(a) Diluted nitric acid (spgr. 1.20). (b) Potassium cyanide solution (20 per cent.), 2 vols.; sodium hydroxide solution (20 per cent.), 1 vol. (c) Ammonium nitrate solution (5 per cent.). (d) Ammonium thiocyanate solution (10 per cent .) , 2 vols ; hydrochloric acid (sp.gr. 1-16), 1 vol. Method-Add 2 drops of (a) to the cleaned surface and allow to react for 3 or 4 minutes. Transfer the drops of acid t o the well of a glazed p(orce1ain spot-plate, add 6 drops of mixture ( b ) , stir well until all the blue copper hydroxide has been converted to double cyanide, and add more reagent ( b ) if necessary to complete the solution of hydroxide.Specimens con- taining neither iron nor manganese give a water-white solution, nickel in Large amounts imparts a yellow colour, and high tin contents result in formation of a white precipitate. Iron gives a brown precipitate of ferric hydroxide, often no more than a brown coloration for contents below about 0.1 per cent.; however, coagulation occurs on standing, and a slight precipitate may be seen. Manganese, when present, gives a dark brownish-black precipitate, completely masking any iron that may be present; hence further treatment is necessary to distinguish the iron.Transfer the dark brownish manganese precipitate to the centre of a No. 541 filter-paper (or any filter-paper that does not give an iron reaction with thiocyanate), and wash 3 or 4 times with 1-drop washings of (c). To the washed precipitate add 2 drops of ( d ) ; a red coloration develops in presence of iron, but if manganese alone is present, it merely dissolves in the acid leaving the paper white. Tried on: Samples Nos. 15, 11, 1, 6, 58, 59, 49, 21, 32, 51, 50, 48, lo,* 35,* 5,* 27," Nos. 40,25,28,37,22,42,45,44-1ron absent and all results negative. Reagents-(a) Concentrated nitric acid (sp.gr. 1.42), 1 vol.; tartaric acid solution (50 per cent.), 1 vol. ( b ) Distilled water. (c) Sodium chromate solution (5 per cent. in water). 4*-1ron present ; all results positive. (V) LEAD Method-To the surface of the cleaned specimen add 2 drops of (a), leave until the reaction appears to be completed, then add 3 drops of (b) followed by 2 drops of (c), stir well and leave for a few seconds. Transfer the drop and precipitate, if any, by means of a capillary tube, to the centre of a close-grained filter-paper in such a manner that each drop is allowed to spread completely before the next drop is added; finally, wash tvyice with 3 drops of ( b ) . In presence of lead, a yellow patch is visible at the centre of the paper; when wet, the paper usually has an outer yellow band of excess reagent, but this is completely reduced to tervalent chromium during the drying process.In absence of lead, or for lead contents below about 0.15 per cent., the paper is exactly as described above but without a central yellow patch. Tried on: Samples Nos. 21, 48, 51, 49-Lead present ; all results positive. NOS. 50, 22, 11, 17, 20, 1!3, 15, 6, 45, 44, 14, 13, 16, 1, 52, 42, 40- Lead less than 0.16 per cent. and all results negative. Reagewds-(a) Concentrated nitric acid (sp.gr. 1.42), 1 vol. ; syrupy phosphoric acid (sp.gr. 1-75), 1 vol. (VI) SILICON ( b ) Distilled water. (c) Ammonium chloride solution (saturated). (d) Rhodamine B solution7 (0.05 per cent. in water). (e) Ammonium chloride solution (5 per cent.), 1 vol.; hydrochloric acid solution (5 per cent.), 1 vol.Method-Add 2 drops of (a) to the cleaned surface and leave to react for at least 5 minutes, add 3 drops of ( b ) , stir, then tilt the specimen and allow the drops to fall on to a clean watch- glass, scraping the surface of the specimen to remove any adhering particles. Add 4 drops of (c), stir, and follow with 4 drops of (d), stir again thoroughly and leave for 5 minutes for * Iron first found by spot-tests and subsequently confirmed by chemical analysis.April, 1950' ALLOYING ELEMENTS I N COPPER-BASE ALLOYS 195 precipitation and absorption to be completed. Transfer the reaction solution, by means of a capillary tube, dropwise on to the centre of a filter-paper, supported on the open mouth of a beaker. Wash by dropping 2 drops of (c) on to the centre from near the surface of the paper; repeat twice with 2-drop washings and finally with 3 or 4 1-drop washings of ( e ) ; the last washing treatment clears out any precipitated reagent leaving the centre quite clear in the absence of silicon.The presence of silicon is indicated by the formation of a deep magenta- coloured absorption precipitate, which dries to a light magenta spot against a pale pink back- ground, I t has been found that when cobalt is present, as well as silicon, there is a tendency towards formation of a black matrix, which is quite insoluble in all acid mixtures except those containing hydrofluoric acid. Our reluctance to employ such a dangerous acid compels us, for once, to accept a test which is not quite specific, but which has never been known to fail in absence of cobalt.In presence of cobalt, a black precipitate without other indications of silicon would suggest that silicon may be a constituent of the alloy. Tried on: Samples Nos. 60, 35, 61, 62, 63, 64, 65, 66,* 67,* 75,* 76,* 77," 78, 79- Nos. 40, 49, 6, 19, 51, 11, 22, 50, 68-Silicon less than 0.1 per cent. The papers when dried can be kept indefinitely. Silicon present ; all results positive. and all results negative. (VII) NICKEL Reqents--(a) Brominated hydrochloric acid (sp.gr. 1-20). (b) Diluted ammonia solution (1 + I ) , 3 vols.; ammonium phosphate solution (10 per cent.), 1 vol. (c) Alcoholic dimethylglyoxime solution (saturated). (d) Diluted ammonia solution (1 + 9). Method-Attack the cleaned surface with 1 drop of ( a ) and leave until the bromine colour has been dispelled. Add 2 drops of ( b ) , or sufficient to make the drop alkaline (test with a fragment of litmus paper), stir, then follow with 4 or 5 drops of (c) and stir again.The nickel glyoxime precipitate can be plainly seen from as little as 0.5 per cent. of nickel; however, it is better, as a matter of routine, to transfer the drops to the centre of a filter-disc and to wash three or four times with (d); by this procedure a slight dirty pink precipitate can be obtained from nickel contents down to 0.08 per cent, The background colour of the paper is a light greenish-yellow with an outer emerald-green edge. In absence of nickel, the centre of the paper is free from coloured precipitate. Tried on: Samples Nos. 56, 42, 43, 69, 70, 71, 59, 11, 54, 72, 57, 58, 74, 19, 73, 39, 34, Kos. 33, 15, 16, 1, 36, 22, 13, 14, 51, 52-Nickel absent and all 21, 48-Nickel present ; all results positive.results negative. (VIII) L4LUMINIUM AND BERYLLIUM Keageitts-(a) Brominated hydrochloric acid (sp.gr. 1-16>. (b) Sodium hydroxide solution (20 per cent.), 1 vol.; potassium cyanide solution (10 per cent .), 2 vols. (c) Sodium hydroxide solution (5 per cent.). (d) Ammonium chloride solution (20 per cent.). (e) Ammonium chloride solution (20 per cent.), 1 vol.; ammonium citrate solution (50 per cent.), 1 vol. (f) Ammonium aurine tricarboxylate solution (0.1 per cent. in alcohol). (g) Ammonium citrate solution (50 per cent.). PyeParalioth of veagent paper-Pipette 1 ml. of reagent (f) on to a 12.5-cm.filter-paper (preferably No. 541), causing the liquid to spread as evenly as possible whilst attempting to concentrate the reagent into a wet patch approximately 8 to 9 cm. in diameter; dry over a source of hot air. Method-Place 1 drop of (a) on the cleaned surface and leave to react for 5 minutes. Add 4 to 5 drops of (b), stir well until the original white precipitate has dissolved; the solution should now be alkaline and quite clear, except in presence of iron when a brownish-black * Only black cobalt-silicide ( ?) was visible.196 precipitate will be observed. prepared reagent paper supported on the open mouth of a beaker. ALUMINIUM- Transfer the filter-paper to a white glazed tile, moisten a 9-cm. filter-disc with reagent (d), place flat on the wet patch of the reagent paper and ensure thorough contact by rolling a glass rod over the papers.Remove the upper ammonium chloride paper, discard, replace the reagent paper on its beaker and leave for 1 minute. In absence of both aluminium and beryllium the paper becomes perfectly white. Aluminium is indicated by a broad band of scarlet, approximately 1-5 to 2-6 inches in diameter, the inner edge being slightly irregular and slightly paler in colour. Beryllium, when present with aluminium, is indicated by a narrow irregular ring, always just inside the inner edge of the aluminium band and of a more intense scarlet colour; the remainder of the paper is white. BERYLLIUM- To confirm the presence of beryllium, repeat the test but, after the transferred liquid has finished spreading, treat with 2 drops of (c), which causes the beryllium ring to become twisted into a scalloped pattern.Transfer to a glazed tile, soak a 9-cm. filter-disc with mixture (e), place over the reagent paper and ensure thorough contact at all points by rolling with a glass rod; leave for 1 minute, remove the chloride - citrate paper and discard. Place the reagent paper on its beaker and wash once with (g) by allowing the liquid to flow readily from a capillary tube whilst describing a circle, just inside the coloured area. The broad band due to aluminium is completely bleached by this treatment and, after about 5 minutes, the paper is completely white in absence of beryllium. Beryllium is indicated by a narrow irregular reddish-scarlet ring, the colour of which seems to be enhanced by the ammonium citrate treatment; the aluminium colour remains bleached even when the paper is dry.Tried on: Samples Nos. 11, 36, 34, 6, 54, 80, 81, 73, 59, 68, 82, 83, &Q, 56-Aluminium Nos. 1, 19, 45, 16, 17, 22, 15, 12, 14, 13, 10-Aluminium absent Nos. 38,55, 66,68, 85, 86, 87,88, 89,90,91,92,93,94,95-Beryllium Nos. 11, 36, 34, 6, 54, 80, 81, 73, 59, 58, 82, 83, 84, 56-Beryllium Note-In all instances of aluminium and beryllium being present together, both reactions EVANS AND HIGGS: SPOT-TESTS FOR THE IDENTIFICATION OF [Vol. 75 Transfer the alkaline solution dropwise to the centre of a present ; all results positive. and all results negative. present ; all results positive. absent and all results negative. were clearly visible. (IX) ARSEKIC Reagents-(a) Diluted nitric acid (sp.gr.1.20), 1 vol. ; potassium ferricyanide solution (10 per cent.), 1 vol. ( b ) Diluted sulphuric acid (1 + 3). (c) Mercuric chloride solution (saturated). (d) Zinc metal (arsenic-free and previously treated as detailed below). (i) Preparation of reagent pa$er-Soak a filter-paper in reagent ( c ) , hang up to drain off excess of the reagent, and allow to dry; brush off loose crystals of mercuric chloride and cut the paper into small strips of approximateky 1.5 x 0.25 inches. (ii) Preparation of metallic zinc-Boil small lumps of granulated zinc in a 1 per cent. solution of cadmium sulphate for a few minutes, remove and wash the zinc, and store under distilled water until required for the test. Method-Place 4 drops of (a) on the cleaned surface, the liquid being spread out immediateZy, as far as possible, with a pointed glass rod.Leave to react for a few seconds until it turns semi-solid, and then immediately scrape off on to a watch-glass, rinsing the specimen with a few drops of distilled water, which is rubbed vigorously on the surface to remove as much as possible of any film there may be. In absence of arsenic, etc., the mass detaches easily, leaving the copper clean; but if a.rsenic is present, it deposits rapidly on the metal and is then extremely difficult to remove; this in itself is a very good preliminary test for arsenic. Stir the liquid in the watch-glass and transfer, by means of a capillary tube, to a wide test tube, rinse in with a little water followed by an amount of (b) equal in volume to the aqueous solution already present.Close the mouth of the test tube with a rubberApril, 19501 ALLOYING ELEMENTS IN COPPER-BASE ALLOYS 197 stopper carrying a short length (about 2.5 inches) of glass tubing, closed at both ends by cotton-wool plugs, and holding between the plugs a strip of reagent paper. Insert a few small lumps of prepared reagent (d) into the test tube, replace the rubber stopper and leave for half an hour; if required, add more solid zinc, but without removing the stopper for longer than necessary. The presence of arsenic is indicated by an orange stain at the bottom end of the strip, tailing off into yellow. In absence of arsenic the paper remains white. Tried on: Samples Nos. 14, 96, 97, 98, 99-Arsenic present ; all results positive.Nos. 1, 35, 13, 33, 19, 90, 69, 22, 82-Arsenic absent and all results negative. (X) CADMIUM Reagents-(a) Diluted nitric acid (sp.gr. 1-20), (b) Sodium hydroxide solution (20 per cent.). (c) Potassium cyanide solution (20 per cent.). ( d ) Dinitrodiphenylcarbazide8 solution (saturated alcoholic solution). (e) Formalin solution (37 to 41 per cent.). Meth,od-Place 2 drops of (a) on the cleaned surface of the specimen and leave to react for 3 minutes. Shake the drop into the well of a white glazed spot-plate, add 2 drops of ( b ) , which should render the drops alkaline to litmus, follow with 5 or 6 drops of (c), or sufficient only to dissolve the blue cupric hydroxide completely; the majority of any iron or manganese present will remain as light brown and dark brown precipitates respectively.Add 1 drop of (d) followed by 4 or 5 drops of (e) and stir well until the reddish-brown colour has been dispelled. Cadmium gives a deep green or greenish-blue coloration, developing quickly into a greenish-yellow solution and a blue precipitate. In absence of cadmium, the liquid assumes a greyish-brown colour, slowly developing into a light dirty-brown precipitate and a greyish- brown solution. Tried on: Samples Nos. 41, 13, 7, 100, 101-Cadmium present; all results positive. Nos. 40, 35, 54, 21, 22, 11, 1, 43, 37, 16, 19, 15, 45, 38, 60-Cadmium absent and all results negative. (XI) COBALT lieagenfs-(a) Broniinated hydrochloric acid (sp.g. 1 *IS). (b) Sodium hypophosphite (solid). (c) Ammonium thiocyanate (solid).(a) Ethyl alcohol. (e) isoPropy1 alcohol. Method-Place 1 drop of (a) on the cleaned surface of the specimen, stirring continuously with a pointed glass rod until the drop has become practically white (or fawn). Transfer the drop to a watch-glass, rinse in with 3 or 4 drops of distilled water and add a further drop or two of (a) until the liquid is clear. Add approximately 0.1 g. of (b), and stir until dissolved, follow with about the same quantity of (c) and again stir well. Drop the mixture on to the centre of a filter-disc, supported on the open mouth of a beaker, keeping the solid confined as closely as possible to the centre of the wet patch. Wash four times with 2 or 3-drop quantities of (d). Any notable amount of cobalt, q., about 2 per cent., is manifested at this stage by the formation of light blue rings passing outwards from the centre; the fourth wash concentrates the cobalt as a band close to the outer edge of the wetted patch.No indication is obtained at this stage from 0.2 per cent. of cobalt. The colour with ethyl alcohol is transient and rapidly disappears. When dry, treat the edge of the paper with a few drops of (e), then tilt the paper so as to let the liquid run towards the centre of the paper; where the isopropyl alcohol cuts the cobalt ring the blue colour is at once reformed. This colour, though transient, is somewhat more permanent than that with ethyl alcohol; it is most vivid as the alcohol dries. The lower limit of 0-2 per cent. is revealed, by careful examination, as a faint blue ring on the outside edge of the paper.In absence of cobalt, or when cobalt is present in quantities less than that stated above, no blue colour is at any stage produced. Tried on : Samples Nos. 66, 67, 68, 75, 76, 77, 78, 79-Cobalt present ; all results positive. Nos. 1, 17, 22, 15, 48, 52, 54, 42, 55, 14, 13, 16-Cobalt absent and Hang up the paper to dry. all results negative.198 EVANS AND HIGGS: SPOT-TESTS FOR THE IDENTIFICATION OF (XII) CHROMIUM [Vol. 76 Reagents-(a) Diluted nitric acid (sp.gr. 1.20). (b) Diluted sulphuric acid (1 + ,3). (c) Bromine water. (a) Sodium hydroxide solution (20 per cent.). (e) Diphenylcarbazide solution (1 per cent. in glycerol), 1 vol.; diluted sulphuric acid (1 + 3), 1 vol. Method-Attack the cleaned sample with 2 drops of (a) and leave until the attack is complete.Gently remove the liquid by means of capillary tube and add 2 drops of (b) to the deposit on the copper surface; after about 1 to 2 minutes, crystals of copper sulphate separate out of solution. Stir the liquid to detach the crystals, etc., and transfer to a clean watch- glass. Add 2 or 3 drops of (c), or until present in excess, then follow with 3 or 4 drops of (d), which should make the mixture alkaline; if not, more alkali is added until a blue reaction is obtained with litmus paper. Place a 126-cin. filter-disc, previously soaked in bromine water and dried, on the open mouth of a beaker and treat the centre with 3 drops of ( e ) . Prepare a filter-tube, consisting of a short length of glass tubing, approximately 0.75 x O-Sinch, into the end of which is pressed some filter-paper pulp; place this tube over the wet reagent patch and filter through it the alkaline liquid obtained above, wash once with 3 drops of water, remove the tube and discard it. Add 6 to 8 drops of (e) equidistant from the centre of the wet patch and just inside the wet area.Chromium is indicated by an immediate formation of purple crescents at the interface between the alkali chromate and the acid diphenyl- carbazide. The coloured pattern of the paper takes the following design: at the centre of the paper is a small colourless area surrounded by a light pinkish band (probably the alkaline reagent colour), which is more pronounced in a.bsence of chromium. Immediately outside the pink band appears the purple colour of chromium, if present; and further out still is the yellow glycerol - reagent colour.The alkaline solution does not spread out uniformly, but tends to break through the periphery at certain points to form a series of inlets, All papers tend to develop a purplish colour after standing for some time, but as little as 0.2 per cent. of chromium should show clearly by the time filtration has ceased. In absence of chromium, the paper appears as described above but without the purple bands just outside the alkaline pink area. Tried on: Samples Nos. 16, 37, 102, 103, 104, 105-Chromium present; all results Nos. 43, 41, 4, 14, 11, 25, 45, 19, 49, 6, 21, 60, 22, 40-Chromium positive. absent and all resuits negative. (XIII) PHOSPHORUS Reagents-(a) Ammonium persulphate (solid). (b) Diluted ammonia (1 + 3).(c) Potassium cyanide solution (10 per cent.). ( d ) Diluted nitric acid (sp.gr. 1.:20). ( e ) Ammonium molybdate solution (10 per cent.). (f) Diluted, boiled out, nitric acid solution (5 per cent.). (g) Stannous chloride solution (5 per cent. in 10 per cent. hydrochloric acid). Method-Place a little of the solid (a) on the surface of the cleaned specimen and dissolve in 2 drops of (b), stir, and leave to stand for 3 to 5 minutes. Add 4 or 5 single drops of (c), stir well after each addition; if any blue or green precipitate remains unattacked, a further addition of cyanide should be made; leave for 5 minutes with occasional stirring. Transfer the liquid to a watch-glass, acidify with 2 drops of (d), stir, then follow with a small quantity of (a), stir again, and leave for a few minutes.As a rule this results in a clear solution, but if there is a precipitate still unattacked, add a little more persulphate and a third drop of (d). Regardless of whether there is still any precipitate, the process is proceeded with. One drop of (e) is added and thoroughly stirred, and allowed to stand with occasional stirring for a t least 10 minutes. Transfer the liquid, slowly in a dropwise manner, to the centre of a filter-paper, to localise the precipitate to a small. spot, wash with four 1 or 2-drop ,quantities of (f). When the spreading of the wash-liquor has ceased, add 2 or 3 drops of (g) , whereupon phosphorus is indicated by a blue spot approximately 1 inch in diameter. High siliconApril, 19501 ALLOYING ELEMENTS IN COPPER-BASE ALLOYS 199 contents may also result in the formation of zi blue spot, but this spot is washed out into a large, faintly blue area by continued treatment with (g).Arsenic, if not completely removed by re-deposition on the sample, shows up as a blue ring at the outer edge of the paper upon drying. In absence of phosphorus there is no blue spot at the centr'e of the paper. The presence of iron, manganese or nickel may result in a brown spot at the centre of the paper, but this should not obscure any reaction due to phosphorus. Tried on: Samples Nos. 20, 22-Phosphorus present ; both results positive. or less than 0.05 per cent. and all results negative. Nos. 21, 14, 11, 43, 1, 82, 63, 13, 15, 40, 45, 9-Phosphorus absent SUMMARY Tests have been described for the alloying elements in copper-base alloys.The elements so detected are manganese, zinc, tin, iron, lead, silicon , nickel, aluminium, beryllium, arsenic, cadmium, cobalt , chromium and phosphorus. With the alloys at our disposal all the tests have proved specific and unambiguous, with the exception of silicon which cannot be detected directly in presence of large amounts of cobalt, but the presence of a black insoluble precipitate, when cobalt is known to be present, would indicate silicon. A new separation of aluminium and beryllium has been described which may provide a useful analytical procedure for the estimation of beryllium in presence of aluminium. Thanks are due to the Chief Scientist, Ministry of Supply, for permission to publish this paper, and also to Johnson Matthey & Co., Ltd., for the supply of Mallory alloys, 73,84 and 100.APPENDIX SPECIMENS OF ALLOYS USED IN THE TESTS No. Sample 1 Mn4 2 M n 3 3 Mn2 4 RLN 5 RLQ 6 TAHU 7 880 8 h h 5 9 MNP 10 "7" 11 TAHG 12 Cu/Ni 13 RLP 14 RLO 16 SFP 16 SDQ 17 RLH 18 RBP 19 CuSb 20 P 6 21 D F L l 22 DRF 23 SEC 24 RLK 25 SEB 26 SEA 27 SDT 28 SDZ 29 S 898 30 S897 31 S896 32 L11 33 IC 34 RBS 35 RBT 36 RBP Mn Zn Sn 28.8 15 6 4.75 2-3 2-17 1 1.0 0.4 0.10 0.15 - 1-72 0.08 ? ? ? ? - - - - 31.3 0.06 0.03 - ? ? ? ? 40 - - - - - 4.7 - 30.7 - - - - - - - 5-10 5.65 - 2-08 9-71 - 14-6 2.1 17.9 - - 12.5 - 8-81 - 2.26 5.12 - 4.82 - 0.59 - - 0.62 - 0.19 - 0.04 0.30 - 0.01 0.26 - - (0.10 - 1.15 <0*10 - - - - - - Constituents, per cent.No. Sample 37 SDP 38 S876 39 RBR 40 Copper 41 S 883 42 GM 43 RRG 44 Speculum 45 CuSn 46 RLR 47 RLK 48 RYB 49 CMC 50 TNR 51 COB 62 S 2 3 53 OZN 54 SDU 55 Cu/Be 66 DDU 57 SDW 58 SDX 59 SDY 60 SDK 61 RLM 62 S 15 63 S 12 64 RLL 65 S 11 66 MA 100 67 MA 84 68 MA73 69 RRJ 70 RRH 51 SDM 72 SDO 73 RBQ 74 SDN 75 922 76 923 77 924 78 925 79 926 80 5 81 4 82 3 83 2 84 1 85 865 86 866 87 867 88 868 89 869 90 870 91 871 92 872 93 873 95 875 96 884 97 885 98 886 99 887 100 881 101 882 102 RLD 103 RLE 104 RLF 105 RLG 94 a74 EVANS AND HIGGS: SPOT-TESTS FOR THE IDENTIFICATION OF APPENDIx--continued Mn Zn Sn Fe Pb - - - - I - - - - - - I _ _ - - - - 50.0 - - - 15.0 - - - 5.2 - - 2-10 - ' - 0.50 >0*10 2.05 0.22 1.50 0.06 0.16 0.12 1.84 0.73 - 0.04 - - - - - - - _ . - 0.45 - 0.21 - - I - - ? - ? - ? - - - - - - - - - - -- - - - - - - - - - - - - - - - - I - - - - - - - - - - - - - 1.66 - 4.13 - 2.48 - 1.17 - 1.68 - 1.16 - 1-10 - 0.70 - 0.31 - 1.44 -- 2.43 - 0.38 - 0.22 - 0.19 - 0.49 - ? - ? - - - - - - - - - I-Vol. 75 0.22 -April, 19501 ALLO\-ING ELEMENTS I N COPPER-BASE ALLOYS 201 1. 2. 3. 4. 5 . 6. 7. 8. REFERENCES Evans, B. S., and Higgs, I). G., Analyst, 1945, 70, 75-82. , , Ibid., 1946, 71, 464-474. , Ibid., 1947, 72, 101-105. , Ibid., 1947, 72, 105-109. Ibid., 1947, 72, 439-443. -- I I -- -- -- , Clark, R. E. D., Ibid., 1936, 61, 242. Eegriwe, E.. 2. anal. Chenz., 1927, 70, 400. Feigl, F., “Qualitative Analysis by Spot Tests,” 2nd English Edition, Nordniarin Publishing Co., Febvzrary, 1950 Inc., New York, 1939, p. 49.

ISSN:0003-2654    

DOI:10.1039/AN9507500191

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

April, 19501 ALLO\-ING ELEMENTS I N COPPER-BASE ALLOYS 201 The Micro-Estima tion of Cadmium BY F. P. DWYEK AXD N. A. GIBSON SYNOPSIS-A new reagent, triphenylmethylarsonium iodide, is recommended for the nephelometric and gravimetric estimation of cadmium in the presence of zinc. The nephelometric procedure is suitable in the range 1 to 100 pg. of cadmium per ml., with an accuracy of approximately 5 per cent., and the gravimetric procedure for the estimation of quantities of the order of 10 mg., with an accuracy of 1. per cent. The accuracy of the nephelometric method, however, decreases markedly when the comparative standard and the unknown solution are far apart in concentration. THE usual method for the quantitative estimation of cadmium depends upon the formation of sparingly soluble salts of the type R,CdX, (X = I or CNS), in which an organic base of high molecular weight is used as the cation.Many reagents based on this principle, however, fail to separate cadmium from zinc, whilst others are unsatisfactory because of the tendency of excess of reagent to be occluded, lack of definite composition, or unsuitable physical properties of the precipitate. The most valuable reagent appears to be trimethylphenyl ammonium iodide,l but the solubility of the salt (Me,PhN),CdI, limits its applicability for much less than 1 mg. of the metal. The colorimetric method using dithizone, developed by Fischer and Leopoldi,2 is claimed to be suitable in the range 1 to 100 pg. of cadmium, but as this reagent forms coloured complexes with many metals, considerable care must be exercised in its use.Micro-quantities of the metal can be estimated by spectrographic and polarogfaphic methods, and it is claimed by Hammond3 that these are the only completely satisfactory procedures, since a specific quantitative reagent for cadmium has not yet been found. The quaternary arsonium salts of the tetraiodocadmate ion (CdI,)” have been described in a previous paper,4 in which it was shown that with several of the arsonium iodides, cadmium could be detected at concentrations below 1 pg. per ml. The salts (R,As),CdI, had very high molecular weights, and separated usually as almost colloidal suspensions, which appeared to be suitable for the nephelometric estimation of cadmium in the presence of zinc. This observation has now been confirmed, and the reagent triphenylmethylarsonium iodide is put forward as suitable for the nephelometric estimation of cadmium in the concentration range of 1 to 100 pg.per ml., and for the gravimetric estimation of 1 to 100 mg. THE NEPHELOMETRIC ESTIMATIOK OF CADMIUM REAGEKTS AND APPARATUS-Pure recrystallised triphenylmethylarsonium iodide4 was dissolved in 0-5 per cent. potassium iodide solution so as to obtain a 0.5 per cent. solution. This solution was almost saturated with respect to the arsonium salt. The protective colloid solution, a 1 per cent. solution of gelatin, was prepared freshly each week. The standard cadmium salt solution (1000 pg. of cadmium per ml.) was prepared by dissolving A.R. cadmium oxide in a slight excess of dilute sulphuric acid, and diluted as required.The opacity of the solutions was determined with a Spekker photo-absorptiometer, with neutral filters H508. The cells were 10 mm. thick (capacity, 9 ml.) for solutions containing from 1 to 10 pg. of cadmium per ml., and 2-5mm. thick (capacity, 2ml.) for solutions containing from 10 to 1OOpg. of cadmium per ml.202 DWYER AND GIBSON THE MICRO-ESTIMATION OF CADMIUM [Vol. 75 PRocEDuRE-(a) Solutions containing 1 to 8 pg. of cadmium per m1.-Reference solution : 10 pg./ml. The test and the reference solutions (10 ml.) in separate test tubes were each treated with gelatin solution (2 drops) and mixed thoroughly. To both, simultaneously, the reagent solution (5 ml.) was then added, and after stirring, each was transferred at once t o the absorptiometer tubes. (b) Solutions containing 10 to 100 pg.of cadmium per m1.-Reference solution: 100 pg./ml. In this concentration range, 2 ml. each of the reference and test solutions were used, with 2 drops of gelatin solution as before, and 1 ml. of the reagent. The reference solution increased in optical density for 10 to 15 minutes after the addition of the reagent, remained steady at this maximum for a further 10 to 15 minutes, after which the white precipitate of the complex salt began to separate. It was usually an hour before the separation was visible. The reading for the test solution was the mean of the readings taken while the reference solution gave a steady reading, one reading being taken each minute for 6 minutes. A greater volume of the gelatin solution unnecessarily prolonged the time required for the estimation, without improving the reproducibility of the readings.The effect of raising the temperature was to decrease the time required to reach the maximum optical density, which was itself reduced, but in the range 15" to 25" C. these effects were not significant. The acidity of the solutions was not critical, and usually lay between 0.01 and 0401 N . Calibration curves were constructed for each range of concentrations, using the mean value of six determinations for each point on the curve. The results obtained by the use of these curves are shown in Tables I and 11. TABLE I REFEREXCE SOLUTION COXTAINING 10 ~G./ML. SAMPLES CONTAINING 1 TO 8 p G . OF CADMIUM PER ML. COMPARED WITH Found Cd used, -2 Max.Pi5 /ml. 1 1.25 0.85 2 2.40 1.55 4 4-36 3.60 6 6.70 5.55 8 8.35 7.80 Mean Mean deviation, deviation, 0.15 15 0-35 18 0.35 9 0.40 7 0.20 3 Clg./ml. % TABLE I1 SAMPLES CONTAINING 10 TO 8 0 ~ ~ . OF CADMIUM PER ML. COMPARED WITH REFEREKCE SOLUTIOS CONTAINING 100 ~G./ML. r Cd used, Max. 10 12-0 20 21.0 40 41.6 60 62.6 80 81.5 Pg./ml* Found --7 Mean 31 in. deviation, CLg./ml. 7.5 1.0 18.5 1.0 3'3.0 0.5 68.5 1.0 78.5 1.0 Mean deviation, 10 5 1.3 1.7 1.3 % TABLE I11 CADMIUM IN PRESENCE OF A HUNDREDFOLD QUAKTITY OF ZINC Reference solution : 10 pg./ml. or 100 pg./ml. as appropriate Mean Cd Cd used, additional KI) deviation, 1.0 1.2 20 8.0 6.9 14 10.0 7.0 30 80.0 72.5 9 found (without Mean Pg*/ml. 94 Mean Cd found (with Mean additional KI) deviation, % 1.35 36 7.9 1.3 11-3 13 81.2 1.5April, 19501 203 In order to test the suitability of the reagent in presence of large amounts of zinc, solutions were prepared containing 100 times as much of this metal as cadmium.Employing the procedures above, only part of the complex cadmium salt was obtained, owing to the reduction in iodide ion concentration by the formation of the ZnI," ion. This difficulty was overcome by addition of 1 or 2 drops of 10 per cent. potassium iodide solution. The results of a series of tests are shown in Table 111. DWYER AXD GIBSON : THE MICRO-ESTIMATION OF CADMIUM THE MICRO-GRAVIMETRIC ESTIMATION OF CADMIUM A solution of cadmium sulphate (50 ml.), containing 10 mg. of cadmium, was heated t o boiling-point, and the triphenylmethylarsonium iodide reagent (50 ml., three equivalents), was added slowly, with stirring.The mixture was allowed to stand for 1 hour to cool, and then cooled in running water for a further half-hour. The precipitate was collected in a sintered-glass filter (porosity 4), washed with 0.5 per cent. potassium iodide solution, and dried at 105" to 110" C. The compound (Ph,MeAs),CdI, contains 8.903 per cent. of cadmium. The results of typical determinations are shown in Table IV. TABLE I V Cd used, mg. 10 10 10 10 11* 11* 12* 12* Cd found, Percentage error mg- 9-94 - 0.6 9.99 - 0.1 10.04 + 0.4 10.05 + 0-5 11-06 + 0-6 11.19 + 1.7 11-78 - 1.8 12.19 + 1.6 * Determinations made by students. In the presence of zinc acetate (3.36 g., equivalent to 1 g. of zinc, or 100 times the amount of cadmium) it was necessary to add 10 ml. of 10 per cent. potassium iodide solution in order to precipitate the cadmium quantitatively, but as shown in Table V, the reagent is equally satisfactory in such large concentrations of zinc. TABLE V Cd used, Cd found, Percentage error mg. mg- 10.00 10-06 0.6 10.00 10.06 0.6 10.00 10.09 0.9 In both the nephelometric and gravimetric methods using this reagent, interference is caused by silver, lead, mercury, copper, bismuth, antimony and arsenic, which either form insoluble iodides or similar complex compounds. As has already been shown by Pass and Ward,' these elements are easily eliminated by boiling the acid solution with iron wire and filtering before addition of the reagent. REFERENCES 1. 2. 3. 4. Pass, A., and Ward, A. M., Analyst, 1933, 58, 667. Fischer, H., and Leopoldi, G., Micvochim. Acta, 1937, 1, 30. Hammond, W. H., Trans. Electrochem. Soc., 1945, 88, 393. Dwyer, F. P., Gibson, N. A., and Nyholm, R. S., J . BOG. Roy. Soc., N.S.W., 1944, 78, 226. DEPARTMENT OF CHEMISTRY UNIVERSITY OF SYDNEY N.S.W., AUSTRALIA J d y , 1049

ISSN:0003-2654    

DOI:10.1039/AN9507500201

出版商:RSC    

年代:1950

数据来源: RSC