摘要:

156 YARDLEY: THE ACCURATE DETERMINATION OF COBALT [Vol. 75 The Accurate Determination of Cobalt BY J. T. YARDLEY SYNopsIs-Methods for the accurate determination of cobalt have been surveyed, special attention being paid to the potentiometric titration of cobaltous salts with standard potassium ferricyanide. Working conditions and technique were adjusted to give the highest degree of repeatability and search was made for a reliable “reference” salt for use as a check on the accuracy of the method. A number of small batches of the salt were prepared and found on analysis to be identical within the known limits of repeatability of the methods applied. The conditions for the attainment of maximum accuracy in the potentiometric titration are given. Nickel in amounts similar to that of cobalt does not interfere, but the presence of similar quantities of iron under these conditions decreases accuracy, although no difficulties appear if the iron does not exceed one-twentieth of the cobalt.The results given by the potentiometric method are in excellent agreement with those of the gravimetric determination as anthranilate. This was found in potassium cobalticyanide. IN the course of routine work in these laboratories it became necessary to survey the methods available for the accurate determination of cobalt. The primary aim of the examination was to decide upon the method most suited to the assay of highly pure cobaltous salts, as a semi-routine undertaking. Earlier experiments had indicated that electro-deposition in ammoniacal solution gave low results, owing to incomplete deposition and the occasional formation of a slight anodic deposit in the absence of reducing agents.When reagents were added to inhibit anodic oxidation, results tended to become too high owing to contamination of the cathode plate. The gravimetric determination as cobalt anthranilate was found to be quite satisfactory and precipitation of the a-nitroso-/3-naphthol complex, followed by ignition in hydrogen, was found to give moderately successful results when the greatest possible care was exercised, but neither method was ideally suited to- the work. The precipitate obtained with phenylthiohydantoic acid, which like the nitroso-naphthol complex is extremely useful for separation purposes, was excessively bulky and defied accurate evaluation, except very indirectly via the anthranilic acid method.At an earlier date the potentiometric titration of cobaltous salts with standard potassium ferricyanide according to Tomicek and Freibergerl and Dickens and Maassen2 had received passing attention by the author, but without yielding wholly satisfactory results. Nevertheless, subsequent p a p e r ~ ~ , ~ , ~ dealing more particularly with the application of the method to the analysis of complex substances provided the incentive for a reconsideration of the method, and because of previous experiences the re-examination was conducted along slightly different lines. These fresh experiments at once gave very encouraging results, which were followed up despite doubts cast upon the completeness of the reaction by the recent work of Bagshawe and Hobson.5 The working conditions and technique were first adjusted until the highest degree of repeatability was achieved, and concurrent experiments to establish a reliable “reference salt” for use as a check on the accuracy of the method were carried out.The common hydrated cobaltous salts are not suitable as standards and electrolytic cobalt, in our experience, is invariably slightly impure. Ignition of the sulphate at temperatures between 400” and 550” C. always failed to produce a pure anhydrous salt, the product being either deficient in sulphate or containing traces of water. An attempt was made to prepare a pure metal by ignition of the oxalate in either hydrogen or carbon dioxide, but thisw as unsuccessful.The product obtained after the hydrogen treatment was so highly pyrophoric as to be unusable. Potassium ferricyanide was already being used as a standard in the cobalt titration (see below) and this raised the possibility of purifying the somewhat analogous cobalti- cyanide and sulphating weighed quantities o€ this anhydrous complex salt to provide standard cobaltous sulphate solutions. A number of small batches of this salt were prepared from AnalaR materials, as described below, and after repeated recrystallisations the separate batches gave analyses which were identical within the known limits of repeatability of theMarch, 19501 YARDLEY: THE ACCURATE DETERMINATION OF COBALT 187 methods applied. The potentiometric titration of standard potassium ferricyanide with approximately 0-05 M cobaltous solutions, derived from this purified cobalticyanide under the conditions to be described, was found to give results which were, with one exception, within f0.06 per cent.of the calculated values. The conditions which were found desirable for the attainment of maximum accuracy with the potentiometric titration were-(1) The cobaltous solution should be added to the ferricyanide solution in the presence of approximately those quantities of ammonia and ammonium citrate given in the experimental section (see below). (2) The cobaltous solution should be about 0.05M in strength. (3) The reactants should be covered with a layer of inert immiscible liquid in order to exclude air. This covering also serves to shield the operator and the equipment from the strongly ammoniacal vapours and to minimise the formation of encrustation on the burette tips.(4) It was essential to employ efficient mechanical stirring throughout the titration. EXPERIMENTAL Preparation of potassium cobalticyanide as re ference salt-A solution of 48 g. of CoCl,.GH,O (AnalaR) in 100ml. of hot water was added slowly to a nearly boiling solution of 80g. of potassium cyanide (AnalaR) in 100 ml. of hot water. When effervescence had ceased, 5 N hydrochloric acid was added until the mixture was acid to litmus and the whole was boiled for some minutes. Further small amounts of solid potassium cyanide were added until the slight precipitate redissolved. The solution was again made acid and the alternate addition of potassium cyanide and acid was continued until the faintly acid solution was almost clear and yellow-green in colour.A further 5 ml. of 5 N hydrochloric acid was added and the solution boiled until solid commenced to separate. The crude product was filtered, washed with alcohol and, after air-drying, recrystallised from the minimum amount of water, the hot solution being filtered through asbestos. This recrystallisation was repeated two, three and four times respectively with different batches and the purified material washed with alcohol and ether and dried in vacuo. Re ference-standard solutions of cobalt sulphate-These were prepared by careful decom- position of the cobalticyanide with concentrated sulphuric acid, in a Kjeldahl flask, using about 20ml. of acid for each 5 g .of the salt. After evaporation to dryness the residues were dissolved in water and diluted to suitable standard volumes at the temperature of st andardisation. Preparation of standard 0.10 N potassiwn ferricyanide solution--32.925 g. of potassium ferricyanide (AnalaR), previously recrystallised twice from water and dried at 80" C., was dissolved in water and diluted to 1 litre in a standard flask at the temperature of standardisa- tion. Check titrations were carried out iodometrically and the normality factors, referred to standard potassium iodate solutions (via Na,S,O,), were invariably identical with those calculated from the weights of ferricyanide taken. Apparatus-Titration assembly-Baird and Tatlock potentiometric titration apparatus. (Titration assembly only.) Electrodes-Saturated calomel and bright platinum, of the type supplied with the above apparatus.Potentiometer-Cambridge portable Cole potentiometer. PROCEDURE Dilute 25 ml. of 0.10 N K,Fe(CN), wit1 100 ml. of 5 N ammonia solution containing 5 g. of citric acid (AnalaR) . Cover the solution with a layer of about 25 ml. of light petroleum (b.p. 100" to 120OC.) and titrate, rather slowly, with the cobalt sulphate solution. (The potential falls slowly from an initial value of about 300 mV. (calomel -ve) .) When a reading of about 100mV. has been reached, further additions should be made in half drops and sufficient time should be allowed for the potential to become steady before proceeding to the next addition. Immediately after the end-point has been passed the solution becomes negative with respect to the calomel and if a complete titration curve is required it is necessary to reverse the galvanometer connections (calomel +ve).Under the conditions given, however, the end-point invariably occurs before this reversal of polarity and it is always possible to locate it by plotting dE/dV against V,, without proceeding beyond the point of equipotential. The inclusion of a reversing key in the circuit is therefore not essential, and in practice it is convenient to terminate titrations at this point.158 YARDLEY: THE ACCURATE DE-TERMINATION OF COBALT Pol. 75 RE s u LT s TABLE, I Expt. Co solution Co present, Co found, Remarks g. per 60 ml. g. per 50 ml. 1 A 0- 1804 0.1805 Solution A prepared from first batch of 2 n n 0.1805 K,Co(CN) after three recrystallisations 3 n n 0.1805 4 B 0.1777 0.1774 Solution B prepared from second batch of 7 ?> n 0.1776 8 Y9 99 0-1776 6 n n 0.1778 K,Co(CN) 6 after four recrystallisations 6 n Y Y 0.1777 9 10 11 12 C 0-1762 0-1763 Solution C prepared from third batch of n Y9 0.1762 K,Co(CN), after five recrystallisations n 99 0.17613 D 0.1762 0.1763 Solution D was derived from solution C +0.18 g.Ni by evaporating an aliquot, adding Ni(NO3),.6H2O and'then restoring original volume of aliquot The experiments in the above table were conducted at temperatures varying from 18.5" to 29.5;" C. TABLE I1 Cobalt (g. per 50 nil.) determined by r 7 ~ ~~ ~ Electro-deposition in Gravimetrically as Co Potentiometric titration ammoniacal solution anthranilate of K,Fe(CN), 0-2646 0.2630 0.2630 0.2645 0.2632 ' 0.2630 A typical complete titration curve is reproduced below.Cobalt sulphate solution ml. Temp. 25" C Fig. 1. A typical titration curve The lower portion of the curve (Co'"/Co'') invariably had the rather singular shape shown and during titrations it was always observed that there was a tendency for the recorded potential to drift slightly to more negative values in this region. In the absence of the covering layer this phenomenon was more pronounced and its occurrence is presumably connected with the higher concentration of oxidisable ions (ferrocyanide and Co") present in the solutioit after the end-point. A certain amount of potential drift was also encountered on the upper portion of the curve when no covering layer was added.March, 19501 YARDLEY: THE ACCURATE DETERMINATION OF COBALT 159 This curve and the relevant experimental results appear to be incompatible with the view of Bagshawe and Hobsons that the cobalt - ferricyanide reaction must always be a balanced one and cannot proceed to completion.Their low value of 4.2 x 103, for the equilibrium constant, was derived from potentials shown by the two systems, separately, oxygen being used to oxidise the cobalt. The predicted “overlap” of the two systems was not encountered under the changed conditions by the present author, possibly because of the considerable influence of ionic strength of the environment upon the redox systems involved. In order to satisfy the curve reproduced above, a value for the equilibrium constant of about 2 x lo6 would be required.Further ex$wiments-The addition of an amount of nickel equal to that of the cobalt in solution was not found to influence the titration (see Experiment 12), but the presence of similar amounts of iron reduced the accuracy of the determinations under these conditions. Smaller amounts of iron, up to 1/20 of the amount of cobalt present, produced no difficulties. In order to test the accuracy of the method when applied to cobalt nitrate, a solution of Co(N0,),.6H20 (AnalaR) was prepared and an aliquot was converted into the sulphate by repeated treatment with sulphuric acid. After restoring the original volume of the aliquot, precise agreement was obtained between titrations employing the two solutions. The potentiometric titration of a solution of cobalt bromide also gave a result in excellent agree- ment with that obtained by the gravimetric determination as anthranilate.SUMMARY- The cobalt - ferricyanide reaction has been re-examined and found to give accurate results under the conditions described. Potassium cobalticyanide has been used as a reference salt and concentrations of cobaltous solutions derived from this complex salt have been indirectly related to the concentrations of potassium iodate solutions. The conclusions of Bagshawe and Hobson6 concerning the incompleteness of the reaction are discussed and contrasted with the findings of this investigation. NOTE- After the completion of the above work an account of the potentiometric titration of cobalt in bright nickel-plating solutions was published by CarterI6 who, under somewhat different conditions, obtained results which were in good agreement with determinations by the a-nitrosb-/%naphthol method. Thanks are due to the Directors of Messrs. Baird & Tatlock (London) Ltd., and Messrs. Hopkin & Williams Ltd., for permission to publish this paper. The author also wishes to acknowledge the practical assistance rendered in the earlier stages of this investigation by Mr. D. R. Lind. REFERENCES 1. 2. 3. 4. 5. 6. Tomicek, O., and Freiberger, F., J . Amer. Chem. Soc., 1935, 57, 801. Dickens, P., and Maassen, G., Arch. Eisenhuttenw., 1935, 9, 487. Hall, A. J., and Young, R. S., Chem. and Ind., 1946, 44, 394. Chirnside, R. C., Cluley, H. J., and Proffit, P. M. C., Analyst, 1947, 72, 361. Bagshawe, B., and Hobson, J. D., Ibid., 1948, 73, 152. Carter, H. D., J . Electyodepositors Tech. SOC., 1949, 24, 27. HOPKIN & WILLIAMS LTD. 16-17, ST. CROSS STREET HAT’CON GARDEN, LONDON, E.C.l May, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500156

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

160 REES: THE DETERMINATION OF IRON, COPPER, LEAD AXD [Vol. 75 The Determination of Iron, Copper, Lead and Mercury in Fabricated Polyvinyl Chloride BY W. T. REES SYNoPsIs-Sensitive methods for the determination of microgram quantities of iron, copper, lead and mercury have been adapted to the determination of these metals in polyvinyl chloride plastics intended to be used in contact with pure hydrogen peroxide. The methods described are absorptiometric, requiring the use of a filter absorptiometer or a spectrophotometer. The development of an efficient wet oxidation procedure is described. In particular, attention is given to the preparation of the sample for the determination of mercury. A special distillation apparatus has been designed to avoid loss of this volatile metal during the digestion.The linear calibration graphs obtained for the four methods are charac- terised by the parts per million of the metal in the sample producing an extinction of 0.010. Typical results are also included for the recovery of the metals added to portions of the plastic. POLYVINYL chloride plastics frequently contain small traces of metals which can catalyse the decomposition of pure hydrogen peroxide in contact with the plastic. To investigate the desirable limits for the concentration of such metallic impurities, it has been necessary to develop suitable methods for the accurate determination of microgram quantities. The methods are absorptiometric, and require the use of a filter absorptiometer of the Spekker type or, preferably, a spectrophotorneter of the Beckman type.The stability of polyvinyl chloride to hydrogen peroxide suggests that it is not particularly amenable to wet oxidation. Nevertheless, a satisfactory procedure has been devised, using sulphuric and nitric acids. The destruction of the prganic matter by ashing was not considered, as it is well known that losses of metal may occur during the process. Even with a wet digestion procedure, mercury may be lost if a n open Kjeldahl flask is used. The special distillation apparatus which is described has been found to prevent loss of mercury during the wet destruction of the plastic. WET OXIDATION OF THE SAMPLE Samples were prepared for wet oxidation by cutting into small cubes of about $-inch sides. Boiling concentrated nitric acid alone merely bleached samples of the plastic, but concentrated sulphuric acid charred the material when the acid began to fume.Much frothing occurred, and careful control of heating was thus necessary to prevent loss of sample through the neck of the Kjeldahl flask. The carbonaceous matter was then oxidised by the addition of small portions of nitric acid to the fuming sulphuric acid digest. This method was adopted for the determination of mercury, since the volume of nitric acid used was kept to the minimum, an advantage in the subsequent procedure. Further investigation showed that preliminary digestion with a mixture of equal volumes of concentrated nitric and sulphuric acids accelerated the decomposition somewhat. When the sulphuric acid’began to fume, the oxidation was completed by the addition of further nitric acid, as previously described.This quicker method was used for the determination of iron, copper and lead. In both methods the nitric acid oxidation was continued until a clear, pale yellow solution was obtained, which remained clear and became colourless on cooling. Occasionally, although oxidation was apparently complete, white crystals formed or darkening occurred as the mixture cooled. (The crystals were probably a nitroderivative of a constituent of the plastic.) In such cases further digestion and treatment with nitric acid were necessary. The acids used for the wet oxidation were mainly responsible for the reagent blank, even though AnalaR quality acids were employed. Experience showed that 2 g. of polyvinyl chloride plastic, taken in a 50-ml.Kjeldahl flask, required at least 10ml. of sulphuric acid (or 20 ml. of mixed acids) for the digestion. The volume of nitric acid necessary to complete the oxidation was from 12 to 15ml. A reagent-blank experiment may therefore be runMarch, 19501 MERCURY I N FABRICATED POLYVINYL CHLORIDE 161 simultaneously with the test, by including 15 ml. of nitric acid while adding at least this volume to the test. Further nitric acid may be subsequently added to the blank if more than 15 ml. is used for the test. The blank is thus kept to a minimum. The reagent blanks and test results obtained by analysis of a typical sample of the plastic are shown in Table I. The high value of the reagent blank for the iron determination was traced to the strong acids used in the wet digestion.This blank could not be conveniently reduced, but was found to be strictly reproducible. TABLE I COMPARISON OF “BLANK” AND “TEST” RESULTS Reagent (a) Final extinction reading . . 0-20 0.02 0.02 <0.01 Metal content of the sample, p.p.m. . . .. 30 1 40 4 Iron Copper Lead Mercury blank { (b) Corresponding p.p.m. of inetal . . .. .. 20 1.5 4 1 The volatility of mercury compounds introduces difficulties in the preparation of organic samples for the determination of this metal. The presence of chloride in the plastic accelerates the loss of metal during the digestion process. Thus, mercury added to a portion of the plastic in an open Kjeldahl flask was completely lost. Kozelkal overcame such loss by using a closed flask with a side-arm leading to a condensing receiver.He distilled mercury quantita- tively by passing chlorine through the digest. The use of chlorine is inconvenient, but recovery of mercury, using apparatus similar to that described by Kozelka, was unsatisfactory, even though the Kjeldahl solution was treated with the distillate. A Friedrich condenser fitted to the Kjeldahl flask was inefficient in the present work, presumably because of the rapid evolution of vapour which occurred *when portions of nitric acid were added to the fuming sulphuric acid mixture. It was also necessary to remove water from the Kjeldahl flask to keep the sulphuric acid fuming. A modified apparatus was therefore designed which consisted of a 50-ml. Kjeldahl flask, closed with a standard-joint stopper carrying a tap funnel and fitted with a side-arm.The latter was connected to a receiving flask to collect the distillate, and this flask was also fitted with a reflux condenser (see Fig. 1). The flask served to buffer the effect of the sudden evolution of vapour from the Kjeldahl flask following the addition of nitric acid, and also to collect the water which distilled. Mercury added to a portion of the sample was not completely distilled from the Kjeldahl flask. Satisfactory recovery was obtained, however, by combining the solution from the Kjeldahl flask with the distillate before proceeding with the determination. THE DETERMINATION OF IRON AND COPPER A composite method was evolved for the determination of iron and copper, involving the wet oxidation of 2 g.of the sample. The Kjeldahl solution was transferred to a beaker, evaporated to a volume of approximately 1 ml., cooled, transferred to a 15-ml. calibrated flask, and diluted to the mark at 20” C. The acidity of this solution was determined on a convenient aliquot in order that approgriate adjustment could be made in the subsequent procedures. Iron was determined by taking a 5-ml. aliquot of this solution in a 10-ml. calibrated flask and applying the well-known thiocyanate reaction, following the recommendations of Ovenston and Parker.2 Thus, further sulphuric acid was added to render the final 10-ml. volume 1-5 N , and then 1 ml. of 0.5 per cent. w/v ammonium persulphate was added. After standing for a minute, 1 ml. of 20 per cent. w/v ammonium thiocyanate was added, the solution diluted to the mark and kept at 20” C.for 15 minutes. The extinction of this solution was measured in a 1-cm. cell at 475 mp. If a filter absorptiometer is employed, Ilford spectrum filters No. 603 or 604 are suitable; No. 604 allows greater precision, but with a sensitivity reduction of about 50 per cent. Copper was determined in a second 5-ml. aliquot of the same solution as that used for the iron determination. Dithizone was used to isolate the copper, the final determination being made with sodium diethyldithiocarbamate.162 [Vol. 76 Copper can be extracted from a 0.1 N mineral acid solution by a carbon tetrachloride solution of dithizone. Palladium, gold, silver, mercury and bismuth are co-extracted. The oxidation of some of the dithizone by any ferric iron present is of no consequence in an extraction process.Of these metals, therefore, only mercury and bismuth need be considered as sources of interference in the present work. Mercury will be absent owing to its volatility during the Kjeldahl digestion; and bismuth could be separated by extraction of a mixture of the dithizonates with 2 per cent. w/v potassium iodide in 0.01 N hydrochloric acid.s Bismuth was not dcwcted in the compositions examined; thus this extra step would not normally be necessary. The diethyldithiocarbamate extraction was made from an aqueous phase similar in composition to that used by Haddock and ever^,^ but carbon tetrachloride was chosen as the organic phase as recommended by SandelL5 REES: THE DETERMINATION OF IRON, COPPER, LEAD AND Fig.1. Modified Kjeldahl apparatus The 5-ml. aliquot was adjusted to 0.1 N acidity by appropriate dilution with water, and extracted with three 5-ml. portions of 0.01 per cent. w/v dithizone in carbon tetrachloride, the extracts being collected in a micro-Kjeldahl flask. The solvent was removed and the residue digested with 0.25 ml. of concentrated sulphuric acid and a few drops of concentrated nitric acid, to obtain a clear colourless solution. This solution was transferred to a separating funnel, and 2 ml. of copper-free citric acid solution (77 per cent. w/v of the monohydrate) were added, followed by 3.3 ml. of 14 N ammonium hydroxide and 1 ml. of sodium diethyl- dithiocarbamate solution (1 per cent. w/v in water). The mixture was diluted to about 15 ml., and extracted with a 2-ml.portion of carbon tetrachloride, which was then run off, through a small filter of glass wool previously wetted with the solvent, into a 10-ml. calibrated flask. The extraction was repeated with three further 2-ml. portions of carbon tetrachloride, running each into the 10-ml. flask. A further 1 ml. of solvent was then used to wash the filter and the stem of the funnel. The solution was adjusted to 20" C., and diluted to the mark. The extinction of this solution was then measured in a 1-cm. cell at 436mp. If a filter absorptiometer is employed, Ilford spectrum filters No. 601 are suitable.March, 19501 MERCURY I N FAUKICATED 1'OLYVIN YL CHLORIDE 163 THE DETERMINATION OF LEAD The method adopted for the determination of lead involves the wet oxidation of 2 g.of the sample, followed by a dithizone extraction, and finally absorptiometric application of the sodium sulphide method. The extraction of lead by dithizone has been studied by many workers, including Clifford and Wichmanno and Biefeld and Patrick.' Such extraction is possible from a slightly basic solution, using a chloroform or carbon tetrachloride solution of the reagent. Citrate is included to prevent precipitation of other metallic hydroxides, and the presence of cyanide precludes the co-extraction of all other metals except bismuth, stannous tin and thallium. Bismuth may be separated by the potassium iodide procedure previously described, and a special volatilisation procedure is available for the removal of tin.',8 Thallium is unlikely to occur in compositions of the type under consideration. The minimum pH necessary for extraction of lead from an ammonia - citrate - cyanide medium is 9.5.In view of the difficulties associated with dithizone colorimetry, the sulphide method was chosen as being sufficiently sensitive and reliable for the present purpose. A combination of the lead and mercury methods was undesirable, on account of the special apparatus used in the determination of mercury. The wet digestion product, of volume about 5 ml., was diluted with 10 ml. of water and cooled. A 1-ml. portion of 50 per cent. w/v citric acid (monohydrate) was added, and the mixture adjusted to the required pH by addition of ammonium hydroxide (sp.gr. 0.880) until the blue end-point of thymol blue indicator was reached.The solution was transferred to a separating funnel, 1 ml. of 10 per cent. w/v potassium cyanide was added, and the mixture was extracted successively with 7.5, 5 and 5 ml. of 0.1 per cent. w/v dithizone in chloroform. After washing the combined extracts with 10ml. of water to which 1 drop of ammonium hydroxide had been added, the organic solution was run into a 50-ml. Kjeldahl flask. The aqueous phase was extracted with 5 ml. of dithizone solution and the extract added to the Kjeldahl flask. The solvent was removed and the residue digested with 1 ml. of concentrated sulphuric acid, with the dropwise addition of 20 per cent. w/v hydrogen peroxide, until a clear colourless solution was obtained. One gram of solid ammonium persulphate was then added, and the mixture was heated strongly for 30 minutes.The cooled solution was trans- ferred to a 60-ml. calibrated flask, 4 ml. of 50 per cent. w/v ammonium acetate were added, followed by 2 ml. of 50 per cent. w/v citric acid (monohydrate), 5 ml. of ammonium hydroxide (sp.gr. 0.880) and 0.5 inl. of 10 per cent. w/v potassium cyanide. This mixture was diluted to the mark at 20" C., and the extinction measured with a filter absorptiometer in a 4-cm. cell, using Ilford spectrum filters KO. 601 in conjunction with Calorex heat filters. The extinction measurement was repeated after the addition of 2 drops of 10 per cent. w/v sodium sulphide solution. Thus correction was possible for any absorption shown by the solution before addition of the reagent.THE WTERMIXATIOX OF MERCURY Laug-and Nelson9 have described a. dithizone method for the determination of mercury. The metal is separated from lead, cadmium, zinc and nickel by extraction from N acid solution with dithizone in chloroform. Copper accompanies the mercury, but may be separated by shaking the mixture of the dithizonates with an acid bromide solution. Mercury enters the aqueous phase as the feebly dissociated HgBr," ion. If the pH of the separated aqueous phase is then adjusted to 6, mercury may be re-extracted by the dithizone reagent. This method was adopted for the present purpose. The final photometric measurements were made by the reversion procedure of Irving and co-workers,1° acid bromide being used as the reversion reagent.The whole method is given in detail below. SPECIAL SOLUTIONS REQUIRED (Sandel1,s p. 325)- (a) Hydroxylamine hydrochloride, 20 per cent. w/v-Extract a 20 per cent. w/v aqueous solution with portions of 0-01 per cent. w/v dithizone solution in chloroform until the chloroform layer remains pure green in colour. Then extract with three portions of pure chloroform to remove the last traces of dithizone. ( b ) Potassium bromide, 40 per cent. w/v-To 500 ml. of a 40 per cent. w/v aqueous solution add 1 drop of 6 AT sodium hydroxide solution, and extract with 0.01 per cent. w/v dithizone solution in chloroform until the chloroform layer remains pure green in colour.1 64 KEES: THE DETEKMISATIOY OF IKON, ('Ol'PEK, LEAD AKl) Make the aqueous phase just acid, extract the last traces of dithizone by means of pure chloroform, and then make just alkaline again.(c) BufleY solution-Dissolve 75 g. of disodium hydrogen phosphate (Na,HPO,) and 19 g. of anhydrous potassium carbonate in water and dilute to 500 ml. Extract with 0.01 per cent. w/v dithizone solution in chloroform until the chloroform layer remains pure green in colour. Then extract with generous portions of pure chloroform to remove the last traces of dithizone. (d) Dithizone, 0.1 per cent. w/v-Dissolve the weighed amount of dithizone (which should be good reagent quality, but need not be specially purified) in the appropriate volume of pure chloroform (chloroform o$ AnalaR or equivalent grade is recommended). (e) Dithizone, 0.01 per cent. W/ZJ and 0.001 per cent. w/v-Prepare by diluting the 0.1 per cent.w/v solution with chloroform as required. tf) Standard mercury sohtion-Dissolve mercuric chloride (AnalaR grade or equivalent) in N hydrochloric acid to give a solution containing 0.1 per cent. w/v of mercury metal. Dilute this stock solution as required with N hydrochloric acid to give a standard solution containing 0.0002 per cent. w/v of mercury metal: (One millilitre of this standard solution contains 2 pg. of Hg".) WET OXIDATION OF THE SAMPLE- Transfer 2g. of the comminuted sample to the Kjeldahl flask of the special apparatus previously described. Add 10 ml. of concentrated sulphuric acid (AnalaR) through the tap funnel, and heat the mixture to fuming over a small flame. Run in approximately 2-ml. portions of nitric acid (spgr.1-42) (AnalaR), during the digestion, and heat more strongly when frothing subsides. Continue the nitric acid oxidation until a clear and almost colourless solution is obtained; allow to cool. (When cool, the solution should remain clear and appear colourless if oxidation is complete.) Run in 10 ml. of water and simmer until fuming begins; allow to cool. DITHIZONE EXTRACTION- Dismantle the apparatus and wash the solution from the Kjeldahl flask into a 500-nd. calibrated flask. Add the solution from the round-bottomed flask and rinse out the apparatus thoroughIy, combining the rinsings with the solution in the calibrated flask. Dilute in this to the mark at 20" C. Pipette a 50-ml. aliquot of the solution into a 100-ml. conical flask and boil gently for 10 minutes on a hot-plate.Cool and pass a rapid stream of sulphur dioxide gas through the solution for 1 minute (as recommended by Kozelkal). Cool again if necessary, then add 0.26 ml. of 0.025 per cent. w/v methyl orange indicator solution and neutralise with strong ammonia solution, cooling as necessary during the neutralisation. Transfer the solution to a 100-ml. separating funnel and dilute to about 65 ml. with water. Add 5ml. of 13N sulphuric acid and 5 ml. of hydroxylamine hydrochloride reagent. (Occasionally the volume of the solution exceeds 65ml. after transference to the separating funnel. In such a case the volume of 13 N acid added should be proportionately increased.) Extract the aqueousmixture with four 10-ml. portions of 0.001 per cent. w/v dithizone reagent, running the extracts into a second 100-ml.separating funnel. Add 50 ml. of 0.25 N hydrochloric acid to the combined extracts, shake vigorously, and separate the chloroform solution into another 100-ml. separating funnel. Wash the hydrochloric acid solution with 5ml. of 0.001 per cent. w/v dithizone reagent, and add the separated chloroform phase to the previous extracts. Discard the aqueous phases. Add 50 ml. of 0-25 N hydrochloric acid and 5 ml. of potassium bromide reagent to the chloroform solution. Wash the aqueous phase with 10 ml. of chloroform and separate the chloroform as completely as possible. Add 10ml. of buffer solution to the aqueous solution, and mix, Pipette into the separating funnel 10.0 ml. of 0-001 per cent. w/v dithizone reagent.Run the chloroform phase through a small filter of glass wool into a suitable receiver. APPLICATION OF THE REVERSION PROCEDURE-- Using a photo-electric spectrophotometer, measure the extinction of the chloroform solution in a 1-cm. cell at 605 mp. (corresponding to a maximum in the absorption spectrum of dithizone in chloroform solution). If a filter absorptiometer is employed, Ilford spectrum [Vol. 35 Shake vigorously and discard the separated chloroform phase. Reject this chloroform washing. Shake carefully, with frequent release of pressure.March, 19501 MEIKUKY IX FABKICATED POLYVINYL CHLORIDE 165 filters No. 607 are appropriate with a tungsten-filament lamp. Conserve the solution as far as possible by using clean dry cells. Pour the solution from the cell into the receiver containing the remainder of the chloro- form extract, and transfer to a 100-ml.separating funnel containing 50 ml. of 0.25 N hydrochloric acid and 5 ml. of potassium bromide reagent. Shake vigorously, and run off the chloroform phase through a small filter of glass wool into a suitable receiver. (Avoid wastage of chloroform solution at each stage to permit complete fdling of cell and guard against evaporation.) Measure the extinction of this solution under exactly the same con- ditions as before. Subtract the first extinction reading from the second. Obtain a "reagent blank" by repeating the whole procedure described above, beginning with 10ml. of concentrated sulphuric acid in the Kjeldahl flask, and adding a volume of nitric acid equal to that required for the wet oxidation of the sample.Deduct the final difference reading so obtained from the corresponding reading for the test, and deduce the mercury content of the sample by reference to the calibration graph. CALIBRATION GRAPH- of Hg" in 100-ml. separating funnels. of N hydrochloric acid, and then dilute to 50 ml. with water. buffer reagent, and mix. funnel, and proceed from this stage as already described.for the test solution. mercury. Place quantities of the standard mercuric chloride solution covering the range 0 to 15 pg. Make up the volume in each case to 12.5 ml. by addition To each solution add 10 ml. of Pipette 10.0 ml. of 0.001 per cent. w/v dithizone reagent into each Subtract from the difference readings so obtained that corresponding to no addition of Plot the corrected difference readings against concentration of mercury.APPLICATION OF THE METHODS The absorptiometric procedures were applied directly to solutions of suitable salts of the metals, and linear calibration graphs were obtained. These graphs may be characterised by the parts per million of metal in the sample corresponding to an extinction reading of 0.010 in the final measurement when the methods described are applied. The figures thus relate to l-cm. cells, except in the case of lead, when a 4-cm. cell is employed. This value approaches the experimental error of the Spekker absorptiometer, and is well above that observed with the Beckman spectrophotometer. The data for the iron, copper, lead and mercury methods are shown in Table 11.TABLE I1 P.P.M. OF METAL I N SAMPLE GIVING E = 0.01 Iron Copper Lead Mercury 1.1 (b) Tungsten lamp.. 1.0 0.9 1.8 1.6 Beckman spectrophotometer . . .. . . 1.0 0-7 - Spekker absorptiometer (a) Mercury lamp . . 1.0 0-8 2.0 - the Standard metallic salt solutions were prepared, each 0.1 per cent. w/v with respect to metal, as follows- Iron-ferrous ammonium sulphate (AnalaR) in N sulphuric acid. Co$@r-copper sulphate (AnalaR) (avoiding crystals showing any efflorescence) in 0.1 N Lead-lead nitrate (AnalaR), dried for 2 hours at 105" C., in 1 per cent. v/v nitric acid. Mercurv-mercuric chloride (AnalaR) in N hvdrochloric acid. sulphuric acid. Immegately before use these' solutions were diluted to 0.002 per cent. w/v with respect to the metals. Known quantities of the metals, as aliquots of the dilute solutions, were added to 2-g.portions of a polyvinyl chloride plastic, and analysed by the prescribed procedures. The calibration graphs so obtained, after correction for the appropriate reagent blanks, were found to be parallel to those obtained directly on solutions of the metallic salts. The intercepts on the extinction axes corresponded to the metal content of the plastic used in these experiments. Examples of the recovery of metals added to the plastic and treated in this way, after due allowance for the metals present in the plastic itself, are given in Table 111. This The procedures described should be of general application to similar compositions.166 BLACK THE DETERMINATION OF ANTIMONY AND [Vol. 75 may be confirmed in any particular instance by checking recovery of the metals added as described above.The composition used in developing these met hods was reasonably homogeneous, but when this is not the case suitable control of sampling is obviously necessary. A sheet of polyvinyl chloride plastic which was “mottled” gave more than the normal variation in results TABLE I11 TYPICAL ANALYTICAL RESULTS Iron Added p.p.rn. . . .. .. 29 Recovered p.p.m. . . .. 29 Lead Added p.p.m. . . .. . . 23 Recovered p.p.rn. . . . . 23 Mercury A4dded p.p.m. . . .. . . 8 Recovered p.p.m. . . .. 7 Copper Added p.p.m. . . . . . . 15 Recovered p.p.m. . . .. 15 68 59 30 31 39 39 35 38 87 87 45 45 62 68 69 64 for the determination of iron. Determination of a calibration graph in the presence of the sample is helpful in such cases, the extinction intercept giving an average figure. The fact that such a graph should be parallel to that obtained directly on solutions of the metallic salts is of assistance in this respect. REFERENCES 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. Kozelka, F. L., Anal. Chew, 1947, 19, 494. Ovenston, T, C. J., and Parker, C. A., AnaE. Chim. Acta., 1949, 3, 277. Greenleaf, C. A,, J. Ass. OH. Agr. Chem., 1942, 25, 385. Haddock, L. A., and Evers, N., Analyst, 1932, 57, 495. Sandell, E. B., Colorimetric Determination of Traces of Metah, 1944. Clifford, P. A,, and Wichmann, H. J., J. Ass. Off. Agr. Chem., 1936, 19, 134. Biefeld, L. P., and Patrick, T. M., Ind. Eng. Chem., Anal. Ed., 1942, 14, 275. Ojiciai and Tentative Methods of Analysis of the A.O.A.C., 5th Edition, 1940, p. 400. Laug, E. P., and Nelson, K. W., J. Ass. O f . Agr. Chem., 1942, 25, 399. Irving, H., Andrew, G., and Risdon, E. J., Nature, 1948, 161, 4099, 805; J . Chem. SOC., 1949, 537. ROYAL NAVAL SCIENTIFIC SERVICE ADMIRALTY MATERIALS LAB o RAT ORY HOLTON HEATH, POOLE, DORSET July, 1949

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DOI:10.1039/AN9507500160

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年代:1950

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166 BLACK THE DETERMINATION OF ANTIMONY AND [Vol. 75 The Determination of Antimony and Tin in Cable Sheathing Alloys BY R. M. BLACK SYNoPsIs-The paper describes in detail the procedure employed for the determination of antimony and tin in cable-sheathing alloys, employing a mixture of hydrogen peroxide and acetic acid as reagent for the dissolution of the alloy. The antimony is deterrnined volumetrically with potassium bromate, and the tin by the method of R. S. Evans, both methods being slightly modified to ensure the complete decomposition of peroxide. THE analysis of alloys of lead with antimony and tin is of considerable importance in the cable industry, and has been the subject of much study, mainly directed to the development of a satisfactory and rapid method for bringing the metals into solution.Such analyses are often required quickly, as a verification of I-esults obtained by spectrographic methods, for example. Unfortunately, the usual methods for dissolution of the alloys are laborious and time-consuming. The treatment of the alloy with a mixture of concentrated hydrochloric acid and bromine requires subdivision of the sample, and the process of solution may take an hour or more. There is also the danger of loss of tin in the form of the halide, owing to the temperature being fairly high, in the region of the boiling-point of the acid mixture. The use of con- centrated sulphuric acid increases the rate of solution, but suffers from the disadvantage that the antimony is difficult to dissolve, and therefore heating at boiling-point for 16 minutesMarch, 19501 TIN I N CABLE SHEATHING ALLOYS 167 is required.Sulphur separates, and lead sulphate is precipitated on dilution. Evans’ has recommended the use of a mixture of phosphoric and perchloric acids; this procedure takes about 15 minutes and special precautions must be taken against loss of tin. Different solvents are recommended for the estimation of antimony, namely a mixture of hydrochloric and perchloric acids. The ideal solvent for the determination of antimony and tin would be hydrochloric acid, but this alone is not only slow in action but also liable to errors because of the volatility of the tin on boiling the concentrated acid. Lead appears to dissolve rapidly in only those materials which have readily available oxygen, and it was shown by Hamilton,2 after a number of experiments which included fusion with sodium peroxide, that 30 per cent.hydrogen peroxide attacked lead and sheathing alloys with great vigour. Accordingly, a mixture of hydrogen peroxide and acetic acid has been adopted in these laboratories as solvent for bringing the antimony and tin into solution. The reagent itself is based on one of the etching solutions commonly used to disclose lead structure. DISSOLUTION OF THE ALLOY- The following method is used for the dissolution of the alloy. Dissolve about 2.5 g. of the sample, which can be in the form of lumps, in a mixture of 10 ml. of 30 per cent. hydrogen peroxide, 10 ml. of distilled water and 5 ml. of glacial acetic acid. The best results are obtained when the reagent is mixed prior to addition to the weighed alloy.The addition of acetic acid, while not strictly necessary, hastens the decomposition of the alloy. The reaction commences immediately on the addition of the reagent, and in some cases the dissolution is so rapid that appreciable quantities of heat are evolved and cooling becomes necessary. The final disintegration of the alloy is easily observed after 2 to 15 minutes, depending on the composition and to some extent on the crystal size or grain structure of the lead, When antimony is absent, the resulting solution contains a white suspension which is thought to be lead hydroxide and basic lead acetate. The presence of antimony gives this suspension a grey coloration, due to metallic antimony which is insoluble in the reagent or gives a grey deposit in the absence of a suspension), and this forms a useful “spot” test or antimony.Complete solution cannot therefore be attained with acetic acid alone, and for the purposes of the determination the addition of 25 ml. of concentrated hydrochloric acid is made. This addition decomposes the greater part of the hydrogen peroxide, oxides of chlorine being evolved, dissolves the antimony and converts the other metals into chlorides. The antimony and tin may then be determined by the standard methods, providing that one or two modifica- tions are made in the procedure t o ensure the complete decomposition of the hydrogen peroxide. THE DETERMINATION OF ANTIMONY- The antimony in the hydrochloric acid solution is reduced with sulphur dioxide and determined by titration with standard potassium bromate solution.The method is the usual one, originally described by GyoryS and, with modifications by Siedler, by Nissensen and Rowell.4 The procedure used is further modified in the following manner. Warm the yellow solution produced on the addition of hydrochloric acid, as already described, on a hot-plate for a few minutes to encourage the decomposition of the peroxide, then remove from the hot-plate and add 25ml. of 20 per cent. sodium sulphite solution. Stand the flask (500-ml. conical, Quickfit B.24 neck) on a steam or boiling-water bath for 15 minutes. Boil off the excess sulphur dioxide, 15 minutes boiling on a low hot-plate usually being sufficient to remove the last trace, and then add 50 ml.of distilled water. Allow the flask to cool, and titrate the solution with 0.1 N (or weaker) potassium bromate from a micro-burette. Two-thirds of the way through the titration (this volume can be estimated if the approximate antimony content of the alloy is known), add a few drops of methyl red solution and continue the titration, adding the bromate a drop at a time, and shaking the flask after each addition. The end-point is indicated by the decoloration of the methyl red. 1 ml. of 0.1 N potassium bromate = 0.006088 g. of antimony. I THE DETERMINATION OF TIN- The method for the determination of tin is that due to EvansJ1s5 with slight modification. After the antimony determination as just described, insert a B.24 male joint into the top of the flask, and add 25 ml.of hydrochloric acid, 1 ml, of saturated mercuric chloride168 BLACK: CABLE SHEATHING ALLOYS [Vol. 75 solution and 2g. of sodium hypophosphite. Boil the solution for 15 minutes. During this period, boil 260 ml. of water containing 10 ml. of 4 per cent. potassium iodide in a separate flask, to remove dissolved air. After the lapse of 15 minutes, add the iodide solution to the tin solution, drop a small piece of solid carbon dioxide (Drikold) into the flask, and stand it in water to cool, adding further pieces of carbon dioxide from time to time to ensure the exclusion of oxygen from the flask. When the solution has reached room temperature, add a few drops of freshly prepared starch solution, and titrate the tin with 0.01 N iodine solution; the end-point being indicated by the usual grey or bluish tint of the solution.The addition of small pieces of carbon dioxide not only ensures the exclusion of oxygen, but also stirs the solution, and increases the rate of cooling; this reduces the time for a determination. 1 ml. of 0.01 N iodine solution = 0*0005935 g. of tin, NOTES ON THE DETERMINATION- It is important that, after dissolution of the alloy with the hydrogen peroxide reagent, all traces of hydrogen peroxide and other peroxides should be removed. This is particularly important for the determination of tin, and in the case of other alloying components when a polarographic method is to be employed. This is accomplished by the sulphite, but it was found that the addition of sulphite solution followed by the boiling off of the sulphur dioxide was insufficient to destroy all peroxide, and in consequence low results for antimony and a bad end-point for the tin determination were obtained. Heating for 15 minutes on a stearn-bath will, however, obviate these difficulties. A series of standardised alloys has been available, and the following analyses made by this method are given in Table I. TABLE I Percentage composition r 1 Standard methods Above methods -7 - h Alloy Sb Sn Sb Sn A B c D E I 1.98 0.86 - 1.03 I 0.46 - 0.4 1 - 0.2 0-4 0.2 1 0-39 0.15 -- 0.153 - The author’s acknowledgments are due to Dr. L. G. Brazier, Director of Research, British Insulated Callender’s Cables Limited, for permission to publish this paper, and to Mr. G. M. Hamilton, at whose suggestion the paper was written. REFERENCES 1. 2. 3. 4. 5. RESEARCH DEPARTMENT Evans, B. S., Analyst, 1932, 57, 554. Hamilton, G. M., Nature, 1946, 157, 875. Gyory, S., 2. anal. Chem., 1893, 32, 415. Rowell, W. H., J . SOC. Chem. Ind., 1907, 25, 1181. Evans, B. S., Analyst, 1931, 56, 171. BRITISH INSULATED CALLENDER’S CABLES, LTD. 38, WOOD LANE, LONDON, W.12 July, 1949

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DOI:10.1039/AN9507500166

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年代:1950

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March, 19501 NOTES I69 USE OF CHLOROPHYLL FOR BREAKING EMULSIONS IN ALKALOIDAL ASSAYS OF SOLANACEOUS DRUGS SINCE it was noticed, in the course of extracting alkaloids by the pharmacopoeia1 methods from alkaline solution with chloroform, that emulsification became worse with each successive extraction, it was thought that some constituent, which prevented emulsification, was being extracted along with the alkaloids. In order to test its preventive action, quantities ranging from a few drops to a few ml. of a 5 per cent. solution of chlorophyll in chloroform were added to the emulsions. Breaking began immediately on shaking, and was complete within a short time. This treatment was used with success on tinctures and extracts which contain chlorophyll. Commercial spirit-soluble chlorophyll (Wm.Ransom and Son Ltd.) was used, a blank determination showing it to have no effect on the final titre. Normally there is a slight tendency to emulsification in the subsequent acid extractions, and the added chlorophyll increases this somewhat; but no trouble is experienced if the acid layers are bulked together with any emulsion and shaken. One extra chloroform wash may be needed to remove all the chlorophyll. The preparations being assayed all contained chlorophyll. PHARMACEUTICAL LABORATORIES KEMPTHORNE PROSSER AND Co.’s NEW ZEALAND DRUG Co., LTD. DUNEDIN, NEW ZEALAND I. C. EDMUNDSON B. J. WILKINS Jdy, 1949 A COLOUR TEST FOR COCAINE JAMES and Roberts1 consider nitration of the benzene ring to be the fundamental reaction of the Vitali test for the solanaceous alkaloids, atropine, hyoscine and hyoscyamine.In the case of these alkaloids, nitric acid alone is sufficient for the nitration of the benzene ring; nitric acid alone has no action on cocaine, but a mixture of nitric and sulphuric acids easily brings about the nitration of the benzene ring in cocaine. The colour reaction of this nitro-compound with alkalis is the basis of the colour test for cocaine. To about 0.5mg. of the substance in a test tube add about 100mg. of potassium nitrate and 10 drops of concentrated sulphuric acid, and heat in a boiling water-bath for 10 minutes. Cool, dilute with water to about 30 ml., extract once with chloroform, and discard the chloroform. Make alkaline with ammonia and extract again with chloroform. Evaporate off the chloroform, dissolve the residue in about 2 ml.of acetone and add 1 to 2 drops of a 10 per cent. solution of sodium hydroxide. Cocaine hydrochloride (0.26 mg.) gave a strong purple colour; a light purple colour was obtained with 0.05 mg. Atropine, homatropine and a few cocaine substitutes were examined by this method. The colour reactions obtained with these using 0.25-mg. quantities are given below. Cocaine gives an intense purple colour. The colour appears to be specific for cocaine. Amylocaine hydrochloride . . . . No colour Procaine hydrochloride .. . . Light reddish-violet colour, changing quickly through brown to greenish- yellow Benzocaine . . .. . . . . No colour Hornatropine hydrobromide . . . . Light reddish colour Atropine sulphate . . .. .. Strong violet colour In the case of amylocaine, the acid - chloroform extract gave a purple colour similar to, but The purple colour with cocaine and the violet colour very much weaker than, that with cocaine. with atropine appear to remain unchanged for a long time. REFERENCE 1. James, W. 0. and Roberts, M., Quart. J . Pharm., 1945, 18, 29. GOVERNMENT ANALYST’S LABORATORY COLOMBO, CEYLON E. RATHENASINKAM J d y , 1949170 NOTES [Vol. 78 WATER-SOLUBLE MATTER IN VEGETABLE TANNED LEATHER THE International Society of Leather Trades’ Chemists describes an official methodl for the determination of the water-soluble matter in vegetable-tanned leather, and this has been reproduced by the British Standards Institution.2 In both of these publications it is stated that a Proctor extractor shall be used : a diagram is given in the first reference, but the second does not describe the extractor or the manner in which it should be used.In this laboratory it has been found to be more convenient to extract the leather in the apparatus shown in Fig. 1. This was made from Pyrex glass, and consists of a stoppered bottle with inlet and outlet tubes sealed into the side. The inlet tube A is drawn into a jet, and the outlet tube B has at its lower end a sintered glass disc of porosity No. 1 ; the sintered disc is about 5 mm. above the bottom of the bottle. To use the extractor, connect A with a reservoir of distilled water by a rubber sleeve fitted with a screw clip, and B with a siphon tube ending in a jet-the rubber connection carries another Screw clip.Place a layer of purified sand1 in the bottle, using sufficient to cover the filter disc; add the fat-free leather, and water, and continue as described in the references cited. ‘The outlet siphon H is easily filled by closing the bottle and blowing through the inlet tube A. This apparatus was designed to reproduce as closely as possible the action of the Proctor extractor, but with the number of separate components reduced to the minimum practicable. It is thought, however, that equally satisfactory results would be obtained if a finer porosity sintered disc were used and the sand eliminated. Siphon tube B Scale Cn Fig. 1 The author thanks the Railway Executive for permission to publish this note. REFERENCES 3. 2. Oscial Methods of Artalysis of the Intevnationa.2 Society of Leather Trades’ Chemists, A.Harvey, “Sampling and Analysis of Vegetable Tanned and Chrome Tanned Leathers,” B.S. 1309 : 1946. London, 1938. RAILWAY EXECUTIVE LONDON MIDLAND REGION SCIENTIFIC RESEARCH DEPARTMENT STONEBRIDGE PARK G. H. WYATT July, 1949 GENERATOR FOR AIR-FREE CARBON DIOXIDE (OR HYDROGEN) THE generator already described1Va has proved its usefulness, particularly as a source of air-free carbon dioxide in the micro-determination of nitrogen by the Dumas method, of methoxyl by the Zeisel method, and so on. Its use as an air-free hydrogen generator was handicapped, however, by the fact that since pure zinc (at least arsenic-free) had to be used, the liberation of hydrogen (on treatment with diluted hydrochloric acid) was inevitably slow, and once started continued for some time after the use of the apparatus had been discontinued.This drawback has now been completely eliminated by the use of the zinc - copper couple. In practice this is easily prepared by covering the zinc in situ with a 3 to 5 per cent. solution of copper sulphate; the zinc - copper couple is immediately formed, and by running in acid from the reservoir,‘spent liquor can be expelled as described formerly. In such a condition hydrochloric acid (1 vol. of concentrated hydrochloric acid/l vol. of water) acts immediately on the zinc: in fact, the evolution of hydrogen is nearly as rapid as that of carbon dioxide from the action of acid on marble and, furthermore, evolution of hydrogen ceases when the acid stream is turned off. This adaptation has rendered the generator invaluable as part of a permanent set-up in the apparatus used for the estimation of uns aturation by catalytic micro-hydrogenation and also to replace the usual hydrogen cylinder,March, 19501 REVIEWS 171 with its numerous disadvantages, in catalytic hydrogenation when dealing with quantities of 50 g. or less of material. Since the 5-litre container of the generator can hold 5 kg. of zinc, one charging lasts a long time. It has been-the practice to use with the generator a purification train2 consisting of solid potash, aqueous silver sulphate and alkaline potassium permanganate ; but latterly the silver sulphate has been replaced by mercuric chloride (to remove acetylenes inter aha). The hydrogen delivered is of a high degree of purity. REFERENCES 1. 2. - , Chew. and Ind., 1945, 270. THE UNIVERSITY, GLASGOW Tucker, S. H., Andyst, 1939, 64, 410; 1942, 67, 320. CHEMISTRY DEPARTMENT S. HORWOOD TUCKER Jzslae, 1948

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DOI:10.1039/AN9507500169

出版商:RSC    

年代:1950

数据来源: RSC

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March, 19501 REVIEWS 171 Reviews OUTLINES OF BIOCHEMISTRY. By Ross AIKEN GORTNER. Third Edition. Edited by R. A. London: Chapman & Hall, Ltd. The original preface says: “In most of the Universities of America the development of the field of biochemistry has been left very largely to the group interested in the medical aspects. Accordingly, in a very large measure the biochemistry of the American Universities is not biochemistry in its strictest sense. . . . The purpose of the present volume is that those students who are interested in biological phenomena may have an insight into the roles which organic chemistry and physical chemistry play in living processes.” A second edition came out in 1938 and this third edition is a co-operative effort; out of ten contributors, only one seems to be connected with a medical school.The book retains the original inspiration in that it is described as “a complete discussion of the fundamental organic and physico-chemical reactions of plant and animal organisms and the colloidal systems in which they take place.” The allocation of space to the more important sections is instructive: colloids 25 per cent., proteins 22 per cent., carbo- hydrates, etc. 22 per cent., lipids and essential oils 7 per cent., plant pigments 3-6 per cent., biochemical regulators 12 per cent. Whatever “biochemistry in its strictest sense” may be taken to mean in 1950, the subject needs to preserve strong links with general chemistry. There is a large overlap between this book and many treatises on both physical and organic chemistry; that is not necessarily a bad thing, although there is here a decided tendency to lay more stress on results than on the methods of reaching them.The subject index contains no reference to respiration, respiratory quotient, calories and nutrition, and the discussion of specific dynamic action is “in the air” when more elementary matters are omitted. The “hormones” of the thymus gland and the pineal body a‘re described perhaps uncritically since the latest references quoted are in the years 1935-38. There is little or nothing about biological assays, statistical methods or physiological mechanisms and “detoxication” processes are given only cursory treatment. The gesture of independence twenty-five years ago may well have been a salutary protest against too great a pre-occupation with medical biochemistry, but the new edition perhaps errs in the opposite sense.Its emphasis is on the fundamental chemistry, organic and physical, and on the corpus of biochemical knowledge viewed primarily through chemical spectacles. The student who has mastered a large part of his book will be well equipped to proceed to the study of other treatises which reflect more clearly the present position of biochemistry; that is as a discipline firmly resting on chemical foundations but reaching out in other directions and having debts to acknowledge as well as achievements to its credit. Perhaps, however, the only thing to cavil at in this excellent volume is its title, which now scarcely corresponds with its content. GORTNER jun.and W. A. GORTNER. 1949. Price 60s. Pp. xvi f 1078. The first edition of this well-known book was written about twenty-five years ago. The new edition is a large book of well over half a million words. As a conspectus of contemporary biochemistry the book must be judged defective. Nevertheless, this third edition has great merit and even at 60s. it is good value. R. A. MORTON172 REVIEWS [Vol. 76 TECHNIQUE OF ORGANIC CHEMISTRY. PHYSICAL METHODS OF ORGANIC CHEMISTRY. Part 11. Edited by A. WEISSBERGER. Second Edition. Pp. xi + 1023. New York and London : Interscience Publishers, Ltd. 1949. Price 100s. Volumes I and VII (organic solvents) are now in second editions, The first edition of Volume I came out in 1946 (see Analyst, 1946, 71, 451). This edition of Part I1 contains a new chapter on electrophoresis by D.H. Moore; there are new sections on nephelometry and turbidometry and the determination of light scattering ; the chapters on the determination of dipole moments, radio-activity and mass spectrometry have been entirely rewritten and other chapters have been revised. X-ray diffraction is covered by L. Fankuchen, electron diffraction by L. 0. Brockway; refractometry by N. Bauer and K. Fajans ; spectroscopy, spectrophotometry, colorimetry and fluorimetry by W. West; polarimetry by W. Heller ; dipole moments by C. P. Smyth ; potentiometry by L. Michaelis; polarography by 0. H. Miiller; magnetic susceptibility by L. Michaelis; radio- activity by .W. F. Balfe and J. F. Bonner jun.; and mass spectrometry by D.W, Stewart. There can be few persons competent to make a critical assessment of the whole book; the subjects with which the present reviewer is familiar are very well done. There is an interesting note on errors in spectrophotometry due to fluorescence (p. 1329) and the sections on light sources, infra-red spectroscopy and Raman spectroscopy are informative, but the treatment of ultra- violet absorption spectra is much too brief in relation to the space devoted to techniques. Several other sections are very sketchy in respect of examples of uses in organic chemistry. The chapter on refractometry is a very well finished piece of work, possibly because there is no great pressureof new work waiting to be assimilated; indeed, few of the references in this section are less than ten years old. The chapter on dipole moments, although now much expanded, is still reasonably brief but does not take too much for granted. T. Shedlovsky’s account of conductometry is very clearly written. The treatment of magnetic susceptibility illustrates the difficulty in a work of this kind of striking the right balance between experimental methods, pure theory and application to organic chemical problems. The accounts of radio-activity and mass spectrometry are practical and serviceable for chemists. Printing, paper, binding and illustrations are excellent, and even at ;tr5 this Part is not unreasonably priced. The absence of a section on chromatography will be noticed. This is probably because Volume V (by H. G. Cassidy) is entitled “Adsorption.” Many will still feel that (as was pointed out in the earlier review) a 1000-page volume on varied methods could with general advantage be subdivided into smaller volumes. Volume I. This work in seven volumes is planned on a large scale. Polarimetry is in much the same case. K. A. MORTON

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DOI:10.1039/AN9507500171

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年代:1950

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172 REVIEWS [Vol. 76 MICROCHEMISTRY GROUP INTERNATIONAL MICROCHEMICAL CONGRESS GRAZ, AUSTRIA, JULY %I> TO 5TH, 1950 MEMBERS who intend to take part in the above Congress and who wish to have their travelling arrangements simplified are advised to write to the Hon. Treasurer of the Group, Mr. G. Ingram, 39, All Saints Avenue, Maidenhead, Berks., who is in touch with Messrs. Thomas Cook regarding block bookings for travel, hotel and meal facilities, as well as currency, passports and military permits. It is possible if sufficient members desire to travel together under such an arrangement that the cost may be slightly less and that reserved compartments may be available. Mr. Ingram would therefore like to have names of all who are interested by May Zst, 1950. Messrs. Thomas Cook will then write to each individual separately.

ISSN:0003-2654    

DOI:10.1039/AN9507500172

出版商:RSC    

年代:1950

数据来源: RSC